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Sample records for temperature creep deformation

  1. Tantalum alloys resist creep deformation at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Buckman, R. W., Jr.

    1966-01-01

    Dispersion-strengthened tantalum-base alloys possess high strength and good resistance to creep deformation at elevated temperatures in high vacuum environments. They also have ease of fabrication, good weldability, and corrosion resistance to molten alkali metals.

  2. Features of the low-temperature creep of a Nb-Ti alloy after large plastic deformations at 77 K

    NASA Astrophysics Data System (ADS)

    Aksenov, V. K.; Volchok, O. I.; Karaseva, E. V.; Starodubov, Ya. D.

    2004-04-01

    The low-temperature (77 K) creep and the corresponding changes in the resistivity of a niobium-titanium alloy subjected to plastic deformation by drawing at 77 K are investigated. It is shown that after large plastic deformations (ɛ>99%) one observes anomalies of the low-temperature creep which do not appear in tests of samples subjected to low and medium deformations. The creep rate in the transient stage is significantly higher than would follow from the classical ideas about the mechanisms of low-temperature creep (logarithmic law), and the time dependence of the creep deformations is described by a power law, which corresponds to recovery creep. In the creep process oscillations appear on the resistivity curves; these are especially pronounced after drawing in liquid nitrogen. Possible causes of the observed effects are discussed.

  3. Time-, stress-, and temperature-dependent deformation in nanostructured copper: Creep tests and simulations

    NASA Astrophysics Data System (ADS)

    Yang, Xu-Sheng; Wang, Yun-Jiang; Zhai, Hui-Ru; Wang, Guo-Yong; Su, Yan-Jing; Dai, L. H.; Ogata, Shigenobu; Zhang, Tong-Yi

    2016-09-01

    In the present work, we performed experiments, atomistic simulations, and high-resolution electron microscopy (HREM) to study the creep behaviors of the nanotwinned (nt) and nanograined (ng) copper at temperatures of 22 °C (RT), 40 °C, 50 °C, 60 °C, and 70 °C. The experimental data at various temperatures and different sustained stress levels provide sufficient information, which allows one to extract the deformation parameters reliably. The determined activation parameters and microscopic observations indicate transition of creep mechanisms with variation in stress level in the nt-Cu, i.e., from the Coble creep to the twin boundary (TB) migration and eventually to the perfect dislocation nucleation and activities. The experimental and simulation results imply that nanotwinning could be an effective approach to enhance the creep resistance of twin-free ng-Cu. The experimental creep results further verify the newly developed formula (Yang et al., 2016) that describes the time-, stress-, and temperature-dependent plastic deformation in polycrystalline copper.

  4. Microstructures of beta silicon carbide after irradiation creep deformation at elevated temperatures

    SciTech Connect

    Katoh, Yutai; Kondo, Sosuke; Snead, Lance Lewis

    2008-01-01

    Microstructures of silicon carbide were examined by transmission electron microscopy (TEM) after creep deformation under neutron irradiation. Thin strip specimens of polycrystalline and monocrystalline, chemically vapor-deposited, beta-phase silicon carbide were irradiated in the high flux isotope reactor to 0.7-4.2 dpa at nominal temperatures of 640-1080 C in an elastically pre-strained bend stress relaxation configuration with the initial stress of {approx}100 MPa. Irradiation creep caused permanent strains of 0.6 to 2.3 x 10{sup -4}. Tensile-loaded near-surface portions of the crept specimens were examined by TEM. The main microstructural features observed were dislocation loops in all samples, and appeared similar to those observed in samples irradiated in non-stressed conditions. Slight but statistically significant anisotropy in dislocation loop microstructure was observed in one irradiation condition, and accounted for at least a fraction of the creep strain derived from the stress relaxation. The estimated total volume of loops accounted for 10-45% of the estimated total swelling. The results imply that the early irradiation creep deformation of SiC observed in this work was driven by anisotropic evolutions of extrinsic dislocation loops and matrix defects with undetectable sizes.

  5. Creep Deformation of Allvac 718Plus

    DOE PAGESBeta

    Hayes, Robert W.; Unocic, Raymond R.; Nasrollahzadeh, Maryam

    2014-11-11

    The creep deformation behavior of Allvac 718Plus was studied over the temperature range 650° to 732°C at initial applied stress levels ranging from 517 to 655 MPa. Over the entire experimental temperature stress regime this alloy exhibits Class M type creep behavior with all creep curves exhibiting a decelerating strain rate with strain or time throughout primary creep. However, unlike pure metals or simple solid solution alloys this gamma prime strengthened superalloy does not exhibit steady state creep. Rather, primary creep is instantly followed by a long duration of accelerating strain rate with strain or time. These creep characteristics aremore » common amongst the gamma prime strengthened superalloys. Allvac 718Plus also exhibits a very high temperature dependence of creep rate. Detailed TEM examination of the deformation structures of selected creep samples reveals dislocation mechanisms similar to those found in high volume fraction gamma prime strengthened superalloys. Strong evidence of microtwinning is found in several of the deformation structures. The presence of microtwinning may account for the strong temperature dependence of creep rate observed in this alloy. In addition, due to the presence of Nb and thus, grain boundary delta phase, matrix dislocation activity which is not present in non Nb bearing superalloys occurs in this alloy. The creep characteristics and dislocation mechanisms are presented and discussed in detail.« less

  6. Creep Deformation of Allvac 718Plus

    SciTech Connect

    Hayes, Robert W.; Unocic, Raymond R.; Nasrollahzadeh, Maryam

    2014-11-11

    The creep deformation behavior of Allvac 718Plus was studied over the temperature range 650° to 732°C at initial applied stress levels ranging from 517 to 655 MPa. Over the entire experimental temperature stress regime this alloy exhibits Class M type creep behavior with all creep curves exhibiting a decelerating strain rate with strain or time throughout primary creep. However, unlike pure metals or simple solid solution alloys this gamma prime strengthened superalloy does not exhibit steady state creep. Rather, primary creep is instantly followed by a long duration of accelerating strain rate with strain or time. These creep characteristics are common amongst the gamma prime strengthened superalloys. Allvac 718Plus also exhibits a very high temperature dependence of creep rate. Detailed TEM examination of the deformation structures of selected creep samples reveals dislocation mechanisms similar to those found in high volume fraction gamma prime strengthened superalloys. Strong evidence of microtwinning is found in several of the deformation structures. The presence of microtwinning may account for the strong temperature dependence of creep rate observed in this alloy. In addition, due to the presence of Nb and thus, grain boundary delta phase, matrix dislocation activity which is not present in non Nb bearing superalloys occurs in this alloy. The creep characteristics and dislocation mechanisms are presented and discussed in detail.

  7. Creep Deformation of Allvac 718Plus

    NASA Astrophysics Data System (ADS)

    Hayes, Robert W.; Unocic, Raymond R.; Nasrollahzadeh, Maryam

    2015-01-01

    The creep deformation behavior of Allvac 718Plus was studied over the temperature range of 923 K to 1005 K (650 °C to 732 °C) at initial applied stress levels ranging from 517 to 655 MPa. Over the entire experimental temperature-stress regime this alloy exhibits Class M-type creep behavior with all creep curves exhibiting a decelerating strain rate with strain or time throughout primary creep. However, unlike pure metals or simple solid solution alloys, this gamma prime strengthened superalloy does not exhibit steady-state creep. Rather, primary creep is instantly followed by a long duration of accelerating strain rate with strain or time. These creep characteristics are common among the gamma prime strengthened superalloys. Allvac 718Plus also exhibits a very high temperature dependence of creep rate. Detailed TEM examination of the deformation structures of selected creep samples reveals dislocation mechanisms similar to those found in high volume fraction gamma prime strengthened superalloys. Strong evidence of microtwinning is found in several of the deformation structures. The presence of microtwinning may account for the strong temperature dependence of creep rate observed in this alloy. In addition, due to the presence of Nb and thus, grain boundary delta phase, matrix dislocation activity which is not present in non-Nb-bearing superalloys occurs in this alloy. The creep characteristics and dislocation mechanisms are presented and discussed in detail.

  8. Creep Deformation of B2 Alumindes

    NASA Technical Reports Server (NTRS)

    Nathal, M. V.

    1991-01-01

    The creep resistance and elevated temperature deformation mechanisms in CoAl, FeAl, and NiAl are reviewed. The stress and temperature dependencies of the steady state creep rate, the primary creep behavior, the dislocation substructure, and the response during transient tests are used as the main indicators of the deformation processes. In single phase intermetallics, the influence of grain size, stoichiometry, and solid solution hardening have been examined. In addition, the effect of adding dispersoids, precipitates, and other types of reinforcements to improve creep strength are compared.

  9. Dislocation creep accommodated Grain Boundary Sliding: A high strain rate/low temperature deformation mechanism in calcite ultramylonites

    NASA Astrophysics Data System (ADS)

    Rogowitz, Anna; Grasemann, Bernhard

    2014-05-01

    Grain boundary sliding (GBS) is an important grain size sensitive deformation mechanism that is often associated with extreme strain localization and superplasticity. Another mechanism has to operate simultaneously to GBS in order to prevent overlaps and voids between sliding grains. One of the most common accommodating mechanisms is diffusional creep but, recently, dislocation creep has been reported to operate simultaneous to GBS. Due to the formation of a flanking structure in nearly pure calcite marble on Syros (Cyclades, Greece) at lower greenschist facies conditions, an extremely fine grained ultramylonite developed. The microstructure of the layer is characterized by (1) calcite grains with an average grain size of 3.6 µm (developed by low temperature/high strain rate grain boundary migration recrystallization, BLG), (2) grain boundary triple junctions with nearly 120° angles and (3) small cavities preferentially located at triple junctions and at grain boundaries in extension. These features suggest that the dominant deformation mechanism was GBS. In order to get more information on the accommodation mechanism detailed microstructural and textural analyses have been performed on a FEI Quanta 3D FEG instrument equipped with an EDAX Digiview IV EBSD camera. The misorientation distribution curves for correlated and uncorrelated grains follow almost perfect the calculated theoretical curve for a random distribution, which is typical for polycrystalline material deformed by GBS. However, the crystallographic preferred orientation indicates that dislocation creep might have operated simultaneously. We also report Zener-Stroh cracks resulting from dislocation pile up, indicating that dislocation movement was active. We, therefore, conclude that the dominant deformation mechanism was dislocation creep accommodated grain boundary sliding. This is consistent with the observed grain size range that plots at the field boundary between grain size insensitive and grain

  10. Elevated Temperature Creep Deformation in Solid Solution <001> NiAL-3.6Ti Single Crystals

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel; Noebe, Ronald D.; Darolia, Ram

    2003-01-01

    The 1100 to 1500 K slow plastic strain rate compressive properties of <001> oriented NiAl-3.6Ti single crystals have been measured, and the results suggests that two deformation processes exist. While the intermediate temperature/faster strain rate mechanism is uncertain, plastic flow at elevated temperature/slower strain rates in NiAl-3.6Ti appears to be controlled by solute drag as described by the Cottrell-Jaswon solute drag model for gliding b = a(sub 0)<101> dislocations. While the calculated activation energy of deformation is much higher (approximately 480 kJ/mol) than the activation energy for diffusion (approximately 290 kJ/mol) used in the Cottrell-Jaswon creep model, a forced temperature compensated - power law fit using the activation energy for diffusion was able to adequately (greater than 90%) predict the observed creep properties. Thus we conclude that the rejection of a diffusion controlled mechanism can not be simply based on a large numerical difference between the activation energies for deformation and diffusion.

  11. High-temperature measurements of lattice parameters and internal stresses of a creep-deformed monocrystalline nickel-base superalloy

    NASA Astrophysics Data System (ADS)

    Biermann, Horst; Strehler, Marcus; Mughrabi, Haël

    1996-04-01

    High-temperature X-ray line profile measurements were performed to maximal temperatures of 1050 °C on samples of the nickel-base superalloy SRR 99. The samples with rod axes near the [001] direction were investigated in the initially undeformed state and after creep deformation at different temperatures and stresses. For the measurements of the (002) and (020) line profiles, a special X-ray double crystal diffractometer with negligible line broadening was used which was equipped with a high-temperature vacuum chamber. The line profiles were evaluated for the lattice parameters of the matrix phase γ and the precipitated γ' phase and for values of the lattice mismatch parallel and perpendicular to the stress axis, respectively, which were found to be different. Elastic, tetragonal distortions of the phases γ and γ' could be determined between room temperature and about 900 °C. These distortions are thermally induced due to the different thermal expansion coefficients of the two phases and deformation induced due to interfacial dislocation networks which were built up during deformation. At the high temperatures of the X-ray measurements, at least partial recovery of the deformation-induced internal stresses occurred, depending on the temperature of the X-ray measurements. The results are discussed and compared with data obtained by complementary techniques.

  12. On The Creep Behavior and Deformation Mechanisms Found in an Advanced Polycrystalline Nickel-Base Superalloy at High Temperatures

    NASA Astrophysics Data System (ADS)

    Deutchman, Hallee Zox

    Polycrystalline Ni-base superalloys are used as turbine disks in the hot section in jet engines, placing them in a high temperature and stress environment. As operating temperatures increase in search of better fuel efficiency, it becomes important to understand how these higher temperatures are affecting mechanical behavior and active deformation mechanisms in the substructure. Not only are operating temperatures increasing, but there is a drive to design next generation alloys in shorter time periods using predictive modeling capabilities. This dissertation focuses on mechanical behavior and active deformation mechanisms found in two different advanced polycrystalline alloy systems, information which will then be used to build advanced predictive models to design the next generation of alloys. The first part of this dissertation discusses the creep behavior and identifying active deformation mechanisms in an advanced polycrystalline Ni-based superalloy (ME3) that is currently in operation, but at higher temperatures and stresses than are experienced in current engines. Monotonic creep tests were run at 700°C and between 655-793MPa at 34MPa increments, on two microstructures (called M1 and M2) produced by different heat treatments. All tests were crept to 0.5% plastic strain. Transient temperature and transient stress tests were used determine activation energy and stress exponents of the M1 microstructure. Constant strain rate tests (at 10-4s-1) were performed on both microstructures as well. Following creep testing, both M1 and M2 microstructures were fully characterized using Scanning Electron Microscopy (SEM) for basic microstructure information, and Scanning Transmission Electron Microscopy (STEM) to determine active deformation mechanism. It was found that in the M1 microstructure, reorder mediated activity (such as discontinuous faulting and microtwinning) is dominant at low stresses (655-724 MPa). Dislocations in the gamma matrix, and overall planar

  13. The high temperature creep deformation of Si3N4-6Y2O3-2Al2O3

    NASA Technical Reports Server (NTRS)

    Todd, J. A.; Xu, Zhi-Yue

    1988-01-01

    The creep properties of silicon nitride containing 6 wt percent yttria and 2 wt percent alumina have been determined in the temperature range 1573 to 1673 K. The stress exponent, n, in the equation epsilon dot varies as sigma sup n, was determined to be 2.00 + or - 0.15 and the true activation energy was found to be 692 + or - 25 kJ/mol. Transmission electron microscopy studies showed that deformation occurred in the grain boundary glassy phase accompanied by microcrack formation and cavitation. The steady state creep results are consistent with a diffusion controlled creep mechanism involving nitrogen diffusion through the grain boundary glassy phase.

  14. Room temperature creep in metals and alloys

    SciTech Connect

    Deibler, Lisa Anne

    2014-09-01

    Time dependent deformation in the form of creep and stress relaxation is not often considered a factor when designing structural alloy parts for use at room temperature. However, creep and stress relaxation do occur at room temperature (0.09-0.21 Tm for alloys in this report) in structural alloys. This report will summarize the available literature on room temperature creep, present creep data collected on various structural alloys, and finally compare the acquired data to equations used in the literature to model creep behavior. Based on evidence from the literature and fitting of various equations, the mechanism which causes room temperature creep is found to include dislocation generation as well as exhaustion.

  15. Creep deformation mechanisms in modified 9Cr-1Mo steel

    NASA Astrophysics Data System (ADS)

    Shrestha, Triratna; Basirat, Mehdi; Charit, Indrajit; Potirniche, Gabriel P.; Rink, Karl K.; Sahaym, Uttara

    2012-04-01

    Modified 9Cr-1Mo (Grade 91) steel is currently considered as a candidate material for reactor pressure vessels (RPVs) and reactor internals for the Very High Temperature Reactor (VHTR). The tensile creep behavior of modified 9Cr-1Mo steel (Grade 91) was studied in the temperature range of 873-1023 K and stresses between 35 MPa and 350 MPa. Analysis of creep results yielded stress exponents of ∼9-11 in the higher stress regime and ∼1 in the lower stress regime. The high stress exponent in the power-law creep regime was rationalized by invoking the concept of threshold stress, which represents the lattice diffusion controlled dislocation climb process. Without threshold stress compensation, the activation energy was 510 ± 51 kJ/mol, while after correcting for the threshold stress, the activation energy decreased to 225 ± 24 kJ/mol. This value is close to the activation energy for lattice self-diffusion in α-Fe. Threshold stress calculations were performed for the high stress regime at all test temperatures. The calculated threshold stress showed a strong dependence on temperature. The creep behavior of Grade 91 steel was described by the modified Bird-Mukherjee-Dorn relation. The rate controlling creep deformation mechanism in the high stress regime was identified as the edge dislocation climb with a stress exponent of n = 5. On the other hand, the deformation mechanism in the Newtonian viscous creep regime (n = 1) was identified as the Nabarro-Herring creep.

  16. Spatial fluctuations in transient creep deformation

    NASA Astrophysics Data System (ADS)

    Laurson, Lasse; Rosti, Jari; Koivisto, Juha; Miksic, Amandine; Alava, Mikko J.

    2011-07-01

    We study the spatial fluctuations of transient creep deformation of materials as a function of time, both by digital image correlation (DIC) measurements of paper samples and by numerical simulations of a crystal plasticity or discrete dislocation dynamics model. This model has a jamming or yielding phase transition, around which power law or Andrade creep is found. During primary creep, the relative strength of the strain rate fluctuations increases with time in both cases—the spatially averaged creep rate obeys the Andrade law epsilont ~ t - 0.7, while the time dependence of the spatial fluctuations of the local creep rates is given by Δepsilont ~ t - 0.5. A similar scaling for the fluctuations is found in the logarithmic creep regime that is typically observed for lower applied stresses. We review briefly some classical theories of Andrade creep from the point of view of such spatial fluctuations. We consider these phenomenological, time-dependent creep laws in terms of a description based on a non-equilibrium phase transition separating evolving and frozen states of the system when the externally applied load is varied. Such an interpretation is discussed further by the data collapse of the local deformations in the spirit of absorbing state/depinning phase transitions, as well as deformation-deformation correlations and the width of the cumulative strain distributions. The results are also compared with the order parameter fluctuations observed close to the depinning transition of the 2d linear interface model or the quenched Edwards-Wilkinson equation.

  17. Homogenized Creep Behavior of CFRP Laminates at High Temperature

    NASA Astrophysics Data System (ADS)

    Fukuta, Y.; Matsuda, T.; Kawai, M.

    In this study, creep behavior of a CFRP laminate subjected to a constant stress is analyzed based on the time-dependent homogenization theory developed by the present authors. The laminate is a unidirectional carbon fiber/epoxy laminate T800H/#3631 manufactured by Toray Industries, Inc. Two kinds of creep analyses are performed. First, 45° off-axis creep deformation of the laminate at high temperature (100°C) is analyzed with three kinds of creep stress levels, respectively. It is shown that the present theory accurately predicts macroscopic creep behavior of the unidirectional CFRP laminate observed in experiments. Then, high temperature creep deformations at a constant creep stress are simulated with seven kinds of off-axis angles, i.e., θ = 0°, 10°, 30°, 45°, 60°, 75°, 90°. It is shown that the laminate has marked in-plane anisotropy with respect to the creep behavior.

  18. Fluctuations and Scaling in Creep Deformation

    NASA Astrophysics Data System (ADS)

    Rosti, Jari; Koivisto, Juha; Laurson, Lasse; Alava, Mikko J.

    2010-09-01

    The spatial fluctuations of deformation are studied in the creep in Andrade’s power law and the logarithmic phases, using paper samples. Measurements by the digital image correlation technique show that the relative strength of the strain rate fluctuations increases with time, in both creep regimes. In the Andrade creep phase characterized by a power-law decay of the strain rate γt˜t-θ, with θ≈0.7, the fluctuations obey Δγt˜t-γ, with γ≈0.5. The local deformation follows a data collapse appropriate for a phase transition. Similar behavior is found in a crystal plasticity model, with a jamming or yielding transition.

  19. Deformation Microstructures and Creep Mechanisms in Advanced ZR-Based Cladding Under Biazal Loading

    SciTech Connect

    K. Linga Murty

    2008-08-11

    Investigate creep behavior of Zr-based cladding tubes with attention to basic creep mechanisms and transitions in them at low stresses and/or temperatures and study the dislocation microstructures of deformed samples for correlation with the underlying micromechanism of creep

  20. Mapping microscale strain heterogeneity during creep deformation

    NASA Astrophysics Data System (ADS)

    Quintanilla Terminel, A.; Evans, J.

    2013-12-01

    We use a new technique combining microfabrication technology and compression tests to map the strain field at a micrometric scale in polycrystalline materials. This technique allows us to map local strain while measuring macroscopic strain and rheological properties, and provides insight into the relative contribution of various plasticity mechanisms under varying creep conditions. The micro-strain mapping technique was applied to Carrara Marble under different deformation regimes, at 300 MPa and temperatures ranging from 200 to 700 °C. At 600 °C, strain of 10%, and strain rate of 3e-5s-1, the local strain at twin and grain boundaries is up to 5 times greater than the average sample strain. At these conditions, strains averaged across a particular grain may vary by as much as 100%, but the strain field becomes more homogeneous with increasing strain. For example, for the analyzed experiments, the average wavelength of the strain heterogeneity is 70 micrometers at 10% strain, but increases to 110 micrometers at 20%. For a strain of 10%, heterogeneity is increased at slower strain rate (at 1e-5s-1). This increase seems to be associated with a more important role of twin boundary and grain boundary migration. As expected, twin densities are markedly greater at the lower temperature, though it is still unclear whether the relative twin volume is greater. However, twin strains are still important at 600 °C and accommodate an average of 14 % of the total strain at 10% deformation and a strain rate of 3e-5s-1.

  1. Creep deformation of an unirradiated zircaloy nuclear fuel cladding tube under dry storage conditions

    NASA Astrophysics Data System (ADS)

    Mayuzumi, Masami; Onchi, Takeo

    1990-05-01

    Measurements of creep deformation were made on an internally gas pressurized tubular Zircaloy-4 specimen with plugs welded to its ends. Creep tests were conducted at temperatures between 577 and 693 K for holding times of up to 26640 ks, to formulate the creep equation needed for predicting creep strain during dry storage of spent fuel. Discussion was also given to the difference of creep behaviour between irradiated and unirradiated fuel cladding, indicating that the equation derived is applicable for predicting creep strain of spent fuel cladding during dry storage.

  2. Temperature, Thermal Stress, And Creep In A Structure

    NASA Technical Reports Server (NTRS)

    Jenkins, Jerald M.

    1991-01-01

    Report presents comparison of predicted and measured temperatures, thermal stresses, and residual creep stresses in heated and loaded titanium structure. Study part of continuing effort to develop design capability to predict and reduce deleterious effects of creep, which include excessive deformations, residual stresses, and failure.

  3. Analysis of Slip Activity and Deformation Modes in Tension and Tension-Creep Tests of Cast Mg-10Gd-3Y-0.5Zr (Wt Pct) at Elevated Temperatures Using In Situ SEM Experiments

    NASA Astrophysics Data System (ADS)

    Wang, Huan; Boehlert, Carl J.; Wang, Qudong; Yin, Dongdi; Ding, Wenjiang

    2016-05-01

    The tension and tension-creep deformation behavior at elevated temperatures of a cast Mg-10Gd-3Y-0.5Zr (wt pct, GW103) alloy was investigated using in situ scanning electron microscopy. The tests were performed at temperatures ranging from 473 K to 598 K (200 °C to 325 °C). The active slip systems were identified using an EBSD-based slip trace analysis methodology. The results showed that for all of the tests, basal slip was the most likely system to be activated, and non-basal slip was activated to some extent depending on the temperature. No twinning was observed. For the tension tests, non-basal slip consisted of ~35 pct of the deformation modes at low temperatures (473 K and 523 K (200 °C and 250 °C)), while non-basal slip accounted for 12 and 7 pct of the deformation modes at high temperatures (573 K and 598 K (300 °C and 325 °C)), respectively. For the tension-creep tests, non-basal slip accounted for 31 pct of the total slip systems at low temperatures, while this value decreased to 10 to 16 pct at high temperatures. For a given temperature, the relative activity for prismatic slip in the tension-creep tests was slightly greater than that for the tension tests, while the activity for pyramidal slip was lower. Slip-transfer in neighboring grains was observed for the low-temperature tests. Intergranular cracking was the main cracking mode, while some intragranular cracks were observed for the tension-creep tests at high temperature and low stress. Grain boundary ledges were prevalently observed for both the tension and tension-creep tests at high temperatures, which suggests that besides dislocation slip, grain boundary sliding also contributed to the deformation.

  4. Creep deformation behavior in eutectic Sn-Ag solder joints using a novel mapping technique

    SciTech Connect

    Lucas, J.P.; Guo, F.; McDougall, J.; Bieler, T.R.; Subramanian, K.N.; Park, J.K.

    1999-11-01

    Creep deformation behavior was measured for 60--100 {micro}m thick solder joints. The solder joints investigated consisted of: (1) non-composite solder joints made with eutectic Sn-Ag solder, and (2) composite solder joints with eutectic Sn-Ag solder containing 20 vol.%, 5 {micro}m diameter in-situ Cu{sub 6}Sn{sub 5} intermetallic reinforcements. All creep testing in this study was carried out at room temperature. Qualitative and quantitative assessment of creep deformation was characterized on the solder joints. Creep deformation was analyzed using a novel mapping technique where a geometrical-regular line pattern was etched over the entire solder joint using excimer laser ablation. During creep, the laser-ablation (LA) pattern becomes distorted due to deformation in the solder joint. By imaging the distortion of laser-ablation patterns using the SEM, actual deformation mapping for the entire solder joint is revealed. The technique involves sequential optical/digital imaging of the deformation versus time history during creep. By tracing and recording the deformation of the LA patterns on the solder over intervals of time, local creep data are obtained in many locations in the joint. This analysis enables global and localized creep shear strains and strain rate to be determined.

  5. A TEM Study of Creep Deformation Mechanisms in Allvac 718Plus

    SciTech Connect

    Unocic, Raymond R; Unocic, Kinga A; Hayes, Robert; Daehn, Glenn; Mills, Michael J.

    2010-01-01

    A preliminary study on the evolution of creep deformation substructure in Ni-base superalloy Allvac 718Plus has been performed. Specimens crept at 620 MPa and at temperatures ranging from 690-732 C were examined utilizing diffraction contrast TEM characterization techniques. Creep was interrupted at 1-2.5% strain in order to study the deformation substructure following a limited amount of deformation. The dominant deformation modes at each of the test temperatures were highly planar in nature and involved shearing of the matrix and precipitates on {111} glide planes. In addition, paired a/2<110> dislocations were evident which suggest an antiphase boundary shearing mechanism. Creep induced microtwinning was also observed at the highest creep temperature which was created by identical a/6<112> Shockley partial dislocations that shear the matrix and precipitates on consecutive close packed {111} glide planes.

  6. On the creep deformation mechanisms of an advanced disk nickel-base superalloy

    NASA Astrophysics Data System (ADS)

    Unocic, Raymond R.

    The main objective of this research was aimed at investigating the fundamental relationship between microstructure and creep deformation mechanisms using a variety of electron microscopy characterization techniques. The alloy used in this research, Rene 104, is a newer generation powder metallurgy Ni-base superalloy that was developed specifically for aircraft gas turbine disk applications with extended service durability at temperatures exceeding 650°C. The influence of stress and temperature was studied first and it was found that during creep deformation at temperatures between 677--815°C and stresses between 345--724MPa a variety of distinctly different creep deformation mechanisms were operative. In addition to identifying the creep deformation mechanisms an attempt was made to determine the creep rate limiting process so that an improved understanding of the fundamental processes that control deformation can be better understood. Microtwinning was found to the dominant deformation mechanism following creep at 677°C/690MPa and 704°C/724MPa. Microtwins form by the motion of paired a/6<112> Shockley partial dislocations that shear both the gamma matrix and gamma' precipitates. The rate limiting process in this mechanism is diffusion mediated atomic reordering that occurs in the wake of the shearing, twinning partial dislocations in order to maintain the ordered L12 structure of the gamma' precipitates. This reordering process helps to fundamentally explain the temperature and rate dependence of microtwinning under creep conditions within this temperature and stress regime. At a slightly higher temperature but lower stress (760°C and 345MPa), a stacking fault related shearing mechanism, which typically spanned only a few micrometers in length, was the principle deformation mode. The faults left behind in the gamma' precipitates determined to be extrinsic in nature. During creep at the highest temperature and lowest stress (815°C and 345MPa) a thermally

  7. Creep deformation of a soft magnetic iron-cobalt alloy

    NASA Astrophysics Data System (ADS)

    Fingers, R. T.; Coate, J. E.; Dowling, N. E.

    1999-04-01

    The U.S. Air Force is in the process of developing magnetic bearings, as well as an aircraft integrated power unit and an internal starter/generator for main propulsion engines. These developments are the driving force for the new emphasis on the development of high saturation, low loss magnets capable of maintaining structural integrity in high stress and high temperature environments. It is this combination of desired material characteristics that is the motivation of this effort to measure, model, and predict the creep behavior of such advanced magnetic materials. Hiperco® Alloy 50HS, manufactured by Carpenter Technology Corporation, is one of the leading candidates for these applications. Material specimens were subjected to a battery of mechanical tests in order to study and characterize their behaviors. Tensile tests provided stress versus strain behaviors that clearly indicated: a yield point, a heterogeneous deformation described as Lüders elongation, the Portevin-LeChatelier effect at elevated temperatures, and most often a section of homogeneous deformation that concluded with necking and fracture. Creep testing indicated three distinct types of behavior. Two types resembled a traditional response with primary, secondary, and tertiary stages; while the third type can be characterized by an abrupt increase in strain rate that acts as a transition from one steady-state behavior to another. The relationships between the tensile and creep responses are discussed. Analyses of the mechanical behavior include double linear regression of empirically modeled data, and constant strain rate testing to bridge the tensile and creep test parameters.

  8. Finite Element Analysis of Plastic Deformation During Impression Creep

    NASA Astrophysics Data System (ADS)

    Naveena; Ganesh Kumar, J.; Mathew, M. D.

    2015-04-01

    Finite element (FE) analysis of plastic deformation associated with impression creep deformation of 316LN stainless steel was carried out. An axisymmetric FE model of 10 × 10 × 10 mm specimen with 1-mm-diameter rigid cylindrical flat punch was developed. FE simulation of impression creep deformation was performed by assuming elastic-plastic-power-law creep deformation behavior. Evolution of the stress with time under the punch during elastic, plastic, and creep processes was analyzed. The onset of plastic deformation was found to occur at a nominal stress about 1.12 times the yield stress of the material. The size of the developed plastic zone was predicted to be about three times the radius of the punch. The material flow behavior and the pile-up on specimen surface have been modeled.

  9. A New Creep Constitutive Model for 7075 Aluminum Alloy Under Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Lin, Y. C.; Jiang, Yu-Qiang; Zhou, Hua-Min; Liu, Guan

    2014-12-01

    Exposure of aluminum alloy to an elastic loading, during "creep-aging forming" or other manufacturing processes at relatively high temperature, may lead to the lasting creep deformation. The creep behaviors of 7075 aluminum alloy are investigated by uniaxial tensile creep experiments over wide ranges of temperature and external stress. The results show that the creep behaviors of the studied aluminum alloy strongly depend on the creep temperature, external stress, and creep time. With the increase of creep temperature and external stress, the creep strain increases quickly. In order to overcome the shortcomings of the Bailey-Norton law and θ projection method, a new constitutive model is proposed to describe the variations of creep strain with time for the studied aluminum alloy. In the proposed model, the dependences of creep strain on the creep temperature, external stress, and creep time are well taken into account. A good agreement between the predicted and measured creep strains shows that the established creep constitutive model can give an accurate description of the creep behaviors of 7075 aluminum alloy. Meanwhile, the obtained stress exponent indicates that the creep process is controlled by the dislocation glide, which is verified by the microstructural observations.

  10. Experimental investigation of creep crack tip deformation using moire interferometry

    NASA Astrophysics Data System (ADS)

    Kang, B. S.-J.; Zhuang, Y.-N.

    High temperature moire interferometry was applied to obtain full-field creep crack tip displacements of a three-point bend Al 2024-T4 specimen under constant temperature of 200 C up to 720 hr. C* was evaluated by the moire data obtained at discrete time intervals. Test results indicated that under steady-state creep condition, the creep crack tip v-displacement rate agreed with the asymptotic solution based on C*-integral, however, no creeping behavior was observed for the crack tip u-displacement field after t = 276 hr. This discrepancy may be due to the initial large creep crack tip blunting and cavitation damage which alter the creep crack tip singular field such that the C*-integral is no longer applicable to characterize steady-state creep crack tip field. It is suggested that the size and shape of material grain boundaries may play an important role on the creeping behavior of the material.

  11. High-temperature creep of polycrystalline chromium

    NASA Technical Reports Server (NTRS)

    Stephens, J. R.; Klopp, W. D.

    1972-01-01

    The creep properties of high-purity, polycrystalline chromium were determined over the temperature range 0.51 to 0.78 T sub m, where T sub m is the melting temperature. Creep rates determined from step-load creep tests can be represented by the general creep equation; epsilon/D = k((sigma/E) to the nth power) where epsilon is the minimum creep rate, D is the diffusivity, k is the creep rate constant, sigma is the applied stress, E is the modulus, and n is the stress exponent, equal to 4.3 for chromium. This correlation and metallographic observations suggest a dislocation climb mechanism is operative in the creep of chromium over the temperature range investigated.

  12. Effect of Tungsten on Primary Creep Deformation and Minimum Creep Rate of Reduced Activation Ferritic-Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Vanaja, J.; Laha, Kinkar; Mathew, M. D.

    2014-10-01

    Effect of tungsten on transient creep deformation and minimum creep rate of reduced activation ferritic-martensitic (RAFM) steel has been assessed. Tungsten content in the 9Cr-RAFM steel has been varied between 1 and 2 wt pct, and creep tests were carried out over the stress range of 180 and 260 MPa at 823 K (550 °C). The tempered martensitic steel exhibited primary creep followed by tertiary stage of creep deformation with a minimum in creep deformation rate. The primary creep behavior has been assessed based on the Garofalo relationship, , considering minimum creep rate instead of steady-state creep rate . The relationships between (i) rate of exhaustion of transient creep r' with minimum creep rate, (ii) rate of exhaustion of transient creep r' with time to reach minimum creep rate, and (iii) initial creep rate with minimum creep rate revealed that the first-order reaction-rate theory has prevailed throughout the transient region of the RAFM steel having different tungsten contents. The rate of exhaustion of transient creep r' and minimum creep rate decreased, whereas the transient strain ɛ T increased with increase in tungsten content. A master transient creep curve of the steels has been developed considering the variation of with . The effect of tungsten on the variation of minimum creep rate with applied stress has been rationalized by invoking the back-stress concept.

  13. Creep deformation characteristics of ductile discontinuous fiber reinforced composites

    SciTech Connect

    Biner, S.B.

    1993-10-01

    Role of material parameters and geometric parameters of ductile reinforcing phase on the creep deformation behavior of 20% discontinuously reinforced composite was numerically investigated including debonding and pull-out mechanisms. Results indicate that for rigidly bonded interfaces, the creep rate of the composite is not significantly influenced by the material properties and geometric parameters of the ductile reinforcing phase due to development of large hydrostatic stress and constrained deformation in the reinforcement. For debonding interfaces, the geometric parameters of the reinforcing phase are important; however, event with very weak interfacial behavior low composite creep rates can be achieved by suitable selection of the geometric parameters of the ductile reinforcing phase.

  14. Low Temperature Creep of Hot-Extruded Near-Stoichiometric NiTi Shape Memory Alloy. Part I; Isothermal Creep

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Noebe, R. D.

    2013-01-01

    This two-part paper is the first published report on the long term, low temperature creep of hot-extruded near-stoichiometric NiTi. Constant load tensile creep tests were conducted on hot-extruded near-stoichiometric NiTi at 300, 373 and 473 K under initial applied stresses varying between 200 and 350 MPa as long as 15 months. These temperatures corresponded to the martensitic, two-phase and austenitic phase regions, respectively. Normal primary creep lasting several months was observed under all conditions indicating dislocation activity. Although steady-state creep was not observed under these conditions, the estimated creep rates varied between 10(exp -10) and 10(exp -9)/s. The creep behavior of the two phases showed significant differences. The martensitic phase exhibited a large strain on loading followed by a primary creep region accumulating a small amount of strain over a period of several months. The loading strain was attributed to the detwinning of the martensitic phase whereas the subsequent strain accumulation was attributed to dislocation glide-controlled creep. An "incubation period" was observed before the occurrence of detwinning. In contrast, the austenitic phase exhibited a relatively smaller loading strain followed by a primary creep region, where the creep strain continued to increase over several months. It is concluded that the creep of the austenitic phase occurs by a dislocation glide-controlled creep mechanism as well as by the nucleation and growth of deformation twins.

  15. Threshold Stress Creep Behavior of Alloy 617 at Intermediate Temperatures

    SciTech Connect

    J.K. Benz; L.J. Carroll; J.K. Wright; R.N. Wright; T. Lillo

    2014-06-01

    Creep of Alloy 617, a solid solution Ni-Cr-Mo alloy, was studied in the temperature range of 1023 K to 1273 K (750 °C to 1000 °C). Typical power-law creep behavior with a stress exponent of approximately 5 is observed at temperatures from 1073 K to 1273 K (800 °C to 1000 °C). Creep at 1023 K (750 °C), however, exhibits threshold stress behavior coinciding with the temperature at which a low volume fraction of ordered coherent y' precipitates forms. The threshold stress is determined experimentally to be around 70 MPa at 1023 K (750 °C) and is verified to be near zero at 1173 K (900 °C)—temperatures directly correlating to the formation and dissolution of y' precipitates, respectively. The y' precipitates provide an obstacle to continued dislocation motion and result in the presence of a threshold stress. TEM analysis of specimens crept at 1023 K (750 °C) to various strains, and modeling of stresses necessary for y' precipitate dislocation bypass, suggests that the climb of dislocations around the y' precipitates is the controlling factor for continued deformation at the end of primary creep and into the tertiary creep regime. As creep deformation proceeds at an applied stress of 121 MPa and the precipitates coarsen, the stress required for Orowan bowing is reached and this mechanism becomes active. At the minimum creep rate at an applied stress of 145 MPa, the finer precipitate size results in higher Orowan bowing stresses and the creep deformation is dominated by the climb of dislocations around the y' precipitates.

  16. Features controlling the early stages of creep deformation of Waspaloy

    NASA Technical Reports Server (NTRS)

    Ferrari, A.; Wilson, D. J.

    1974-01-01

    A model has been presented for describing primary and second stage creep. General equations were derived for the amount and time of primary creep. It was shown how the model can be used to extrapolate creep data. Applicability of the model was demonstrated for Waspaloy with gamma prime particle sizes from 75 - 1000 A creep tested in the temperature range 1000 - 1400 F (538 - 760 C). Equations were developed showing the dependence of creep parameters on dislocation mechanism, gamma prime volume fraction and size.

  17. Stress versus temperature dependence of activation energies for creep

    NASA Technical Reports Server (NTRS)

    Freed, A. D.; Raj, S. V.; Walker, K. P.

    1992-01-01

    The activation energy for creep at low stresses and elevated temperatures is associated with lattice diffusion, where the rate controlling mechanism for deformation is dislocation climb. At higher stresses and intermediate temperatures, the rate controlling mechanism changes from dislocation climb to obstacle-controlled dislocation glide. Along with this change in deformation mechanism occurs a change in the activation energy. When the rate controlling mechanism for deformation is obstacle-controlled dislocation glide, it is shown that a temperature-dependent Gibbs free energy does better than a stress-dependent Gibbs free energy in correlating steady-state creep data for both copper and LiF-22mol percent CaF2 hypereutectic salt.

  18. Creep Behavior, Deformation Mechanisms, and Creep Life of Mod.9Cr-1Mo Steel

    NASA Astrophysics Data System (ADS)

    ABE, Fujio

    2015-12-01

    The creep behavior, deformation mechanisms, and the correlation between creep deformation parameters and creep life have been investigated for Mod.9Cr-1Mo steel (Gr.91, 9Cr-1Mo-VNb) by analyzing creep strain data at 723 K to 998 K (450 °C to 725 °C), 40 to 450 MPa, and t r = 11.4 to 68,755 hours in NIMS Creep Data Sheet. The time to rupture t r is reasonably correlated with the minimum creep rate {dot{\\varepsilon }}_{ min } and the acceleration of creep rate by strain in the acceleration region dln {dot{\\varepsilon }} /d ɛ, as t r = 1.5/[ {dot{\\varepsilon }}_{ min } ( dln {dot{\\varepsilon }} /d ɛ)], where {dot{\\varepsilon }}_{ min } and dln {dot{\\varepsilon }} /d ɛ reflect the creep behavior in the transient and acceleration regions, respectively. The {dot{\\varepsilon }}_{ min } is inversely proportional to the time to minimum creep rate t m, while it is proportional to the strain to minimum creep rate ɛ m, as {dot{\\varepsilon }}_{ min } = 0.54 ( ɛ m/ t m). The ɛ m decreases with decreasing stress, suggesting that the creep deformation in the transient region becomes localized in the vicinity of prior austenite grain boundaries with decreasing stress. The duration of acceleration region is proportional to the duration of transient region, while the dln {dot{\\varepsilon }} /d ɛ is inversely proportional to the ɛ m. The t r is also correlated with the t m, as t r = g t m, where g is a constant. The present creep life equations reasonably predict the degradation in creep rupture strength at long times. The downward deviation takes place in the t r vs {dot{\\varepsilon }}_{ min } curves (Monkman-Grant plot). At the same {dot{\\varepsilon }}_{ min } , both the ɛ m and t m change upon the condition of t m ∝ ɛ m. The decrease in ɛ m with decreasing stress, corresponding to decreasing {dot{\\varepsilon }}_{ min } , causes a decrease in t m, indicating the downward deviation of the t r vs {dot{\\varepsilon }}_{ min } curves.

  19. Creep resistant high temperature martensitic steel

    SciTech Connect

    Hawk, Jeffrey A.; Jablonski, Paul D.; Cowen, Christopher J.

    2015-11-13

    The disclosure provides a creep resistant alloy having an overall composition comprised of iron, chromium, molybdenum, carbon, manganese, silicon, nickel, vanadium, niobium, nitrogen, tungsten, cobalt, tantalum, boron, and potentially additional elements. In an embodiment, the creep resistant alloy has a molybdenum equivalent Mo(eq) from 1.475 to 1.700 wt. % and a quantity (C+N) from 0.145 to 0.205. The overall composition ameliorates sources of microstructural instability such as coarsening of M.sub.23C.sub.6 carbides and MX precipitates, and mitigates or eliminates Laves and Z-phase formation. A creep resistant martensitic steel may be fabricated by preparing a melt comprised of the overall composition followed by at least austenizing and tempering. The creep resistant alloy exhibits improved high-temperature creep strength in the temperature environment of around 650.degree. C.

  20. Vertebroplasty reduces progressive ׳creep' deformity of fractured vertebrae.

    PubMed

    Luo, J; Pollintine, P; Annesley-Williams, D J; Dolan, P; Adams, M A

    2016-04-11

    Elderly vertebrae frequently develop an "anterior wedge" deformity as a result of fracture and creep mechanisms. Injecting cement into a damaged vertebral body (vertebroplasty) is known to help restore its shape and stiffness. We now hypothesise that vertebroplasty is also effective in reducing subsequent creep deformations. Twenty-eight spine specimens, comprising three complete vertebrae and the intervening discs, were obtained from cadavers aged 67-92 years. Each specimen was subjected to increasingly-severe compressive loading until one of its vertebrae was fractured, and the damaged vertebral body was then treated by vertebroplasty. Before and after fracture, and again after vertebroplasty, each specimen was subjected to a static compressive force of 1kN for 1h while elastic and creep deformations were measured in the anterior, middle and posterior regions of each adjacent vertebral body cortex, using a 2D MacReflex optical tracking system. After fracture, creep in the anterior and central regions of the vertebral body cortex increased from an average 4513 and 885 microstrains, respectively, to 54,107 and 34,378 microstrains (both increases: P<0.001). Elastic strains increased by a comparable amount. Vertebroplasty reduced creep in the anterior and central cortex by 61% (P=0.006) and 66% (P=0.017) respectively. Elastic strains were reduced by less than half this amount. Results suggest that the beneficial effects of vertebroplasty on the vertebral body continue long after the post-operative radiographs. Injected cement not only helps to restore vertebral shape and elastic properties, but also reduces subsequent creep deformation of the damaged vertebra. PMID:26459490

  1. In Situ Observation of High Temperature Creep Behavior During Annealing of Steel

    NASA Astrophysics Data System (ADS)

    Zhang, X. F.; Terasaki, H.; Komizo, Y.; Murakami, Y.; Yasuda, K.

    2012-12-01

    Previous studies on creep suggested a close relationship between polycrystal grain size, substructure, and creep rate. At present, however, our understanding of the influence of polycrystal grain size, substructure, and thermal stress on creep deformation behavior seems rather insufficient, especially as there is a general lack of in situ data on structural changes during creep. In this study, the effects of thermal stress, austenite grain size, and cooling rate on slip deformations in C-Mn-Al steel during annealing were investigated systematically on the basis of in situ observations using high temperature laser scanning confocal microscopy. Finally, a kinetics model based on thermal expansion anisotropy and temperature difference was developed to explain these interesting experimental results. The in situ investigation of slip deformation during annealing greatly contributes to the understanding of high temperature creep behavior.

  2. Deformation and crack growth response under cyclic creep conditions

    SciTech Connect

    Brust, F.W. Jr.

    1995-12-31

    To increase energy efficiency, new plants must operate at higher and higher temperatures. Moreover, power generation equipment continues to age and is being used far beyond its intended original design life. Some recent failures which unfortunately occurred with serious consequences have clearly illustrated that current methods for insuring safety and reliability of high temperature equipment is inadequate. Because of these concerns, an understanding of the high-temperature crack growth process is very important and has led to the following studies of the high temperature failure process. This effort summarizes the results of some recent studies which investigate the phenomenon of high temperature creep fatigue crack growth. Experimental results which detail the process of creep fatigue, analytical studies which investigate why current methods are ineffective, and finally, a new approach which is based on the T{sup *}-integral and its ability to characterize the creep-fatigue crack growth process are discussed. The potential validity of this new predictive methodology is illustrated.

  3. Elevated temperature deformation of TD-nickel base alloys

    NASA Technical Reports Server (NTRS)

    Petrovic, J. J.; Kane, R. D.; Ebert, L. J.

    1972-01-01

    Sensitivity of the elevated temperature deformation of TD-nickel to grain size and shape was examined in both tension and creep. Elevated temperature strength increased with increasing grain diameter and increasing L/D ratio. Measured activation enthalpies in tension and creep were not the same. In tension, the internal stress was not proportional to the shear modulus. Creep activation enthalpies increased with increasing L/D ratio and increasing grain diameter, to high values compared with that of the self diffusion enthalpy. It has been postulated that two concurrent processes contribute to the elevated temperature deformation of polycrystalline TD-nickel: (1) diffusion controlled grain boundary sliding, and (2) dislocation motion.

  4. Elevated temperature creep-rupture behavior of the single crystal nickel-base superalloy NASAIR 100

    NASA Technical Reports Server (NTRS)

    Nathal, M. V.; Ebert, L. J.

    1985-01-01

    The creep and rupture behavior of 001-line-oriented single crystals of the nickel-base superalloy NASAIR 100 was investigated at temperatures of 925 and 1000 C. In the stress and temperature ranges studied, the steady state creep rate, time to failure, time to the onset of secondary creep, and the time to the onset of tertiary creep all exhibited power law dependencies on the applied stress. The creep rate exponents for this alloy were between seven and eight, and the modulus-corrected activation energy for creep was approximately 350 kjoule/mole, which was comparable to the measured activation energy for Ostwald ripening of the gamma-prime precipitates. Oriented gamma-prime coarsening to form lamellae perpendicular to the applied stress was very prominent during creep. At 1000 C, the formation of a continuous gamma-gamma-prime lamellar structure was completed during the primary creep stage. Shear through the gamma-gamma-prime interface is considerd to be the rate limiting step in the deformation process. Gradual thickening of the lamellae appeared to be the cause of the onset of tertiary creep. At 925 C, the fully developed lamellar structure was not achieved until the secondary or tertiary creep stages. At this temperature, the gamma-gamma-prime lamellar structure did not appear to be as beneficial for creep resistance as at the higher temperature.

  5. A True-Stress Creep Model Based on Deformation Mechanisms for Polycrystalline Materials

    NASA Astrophysics Data System (ADS)

    Wu, Xijia; Williams, Steve; Gong, Diguang

    2012-11-01

    A true-stress creep model has been developed based on well-recognized deformation mechanisms, i.e., dislocation glide, dislocation climb, and grain boundary sliding. The model provides a physics-based description of the entire creep deformation process with regards to the strain-time history (primary, secondary, and tertiary creep), rupture strain and lifetime, which finds good agreement with experimental observations for Waspaloy. A deformation-mechanism map is constructed for Waspaloy, and a creep failure criterion is defined by the dominant deformation mechanisms leading to intergranular/transgranular fracture. Thus, the model is a self-consistent tool for creep life prediction.

  6. Creep Properties and Deformation Mechanisms of a FGH95 Ni-based Superalloy

    NASA Astrophysics Data System (ADS)

    Xie, Jun; Tian, Su-gui; Zhou, Xiao-ming

    2013-07-01

    By means of full heat treatment, microstructure observation, lattice parameters determination, and the measurement of creep curves, an investigation has been conducted into the microstructure and creep mechanisms of FGH95 Ni-based superalloy. Results show that after the alloy is hot isostatically pressed, coarse γ' phase discontinuously distributes along the previous particle boundaries. After solution treatment at high temperature and aging, the grain size has no obvious change, and the amount of coarse γ' phase decreases, and a high volume fraction of fine γ' phase dispersedly precipitates in the γ matrix. Moreover, the granular carbides are found to be precipitated along grain boundaries, which can hinder the grain boundaries' sliding and enhance the creep resistance of the alloy. By x-ray diffraction analysis, it is indicated that the lattice misfit between the γ and γ' phases decreases in the alloy after full heat treatment. In the ranges of experimental temperatures and applied stresses, the creep activation energy of the alloy is measured to be 630.4 kJ/mol. During creep, the deformation mechanisms of the alloy are that dislocations slip in the γ matrix or shear into the γ' phase. Thereinto, the creep dislocations move over the γ' phase by the Orowan mechanism, and the < { 1 10 } rangle super-dislocation shearing into the γ' phase can be decomposed to form the configuration of (1/3) < { 1 12 } rangle super-Shockleys' partials and the stacking fault.

  7. Primary creep of Ni{sub 3}(Al, Ta) single crystals at room temperature

    SciTech Connect

    Uchic, M.D.; Nix, W.D.

    1997-12-31

    This study examines the time-dependent deformation of Ni{sub 3}(Al, Ta) at room temperature. Tension creep experiments have been performed on single crystals with one [111]<101> slip system active at the start of the test, where the applied stress ranged from 66.4 MPa (the measured 0.01% flow stress) to 143 MPa (which produced approximately 9% plastic strain). All creep curves displayed primary creep leading to eventual exhaustion, where the measured creep strain declined at a rate faster than predicted for logarithmic creep. However, no correlation between the applied stress and the form of the declining creep rate can be made at this time. Many creep curves can be obtained from one sample, as the creep curves from both virgin samples and samples with prior deformation history (at the same test stress) were indistinguishable. At the beginning of an incremental creep test, where the stress is increased by a small amount to reinitiate plastic flow in an exhausted sample, a significant retardation of the plastic response of the sample occurred when the stress increment was below 4 MPa. Preliminary TEM studies of a sample strained to 6% suggest that room temperature creep tests may not be ideal for examining the flow of Anti-Phase-Boundary (APB) dissociated dislocations.

  8. Stress versus temperature dependent activation energies in creep

    NASA Technical Reports Server (NTRS)

    Freed, A. D.; Raj, S. V.; Walker, K. P.

    1990-01-01

    The activation energy for creep at low stresses and elevated temperatures is lattice diffusion, where the rate controlling mechanism for deformation is dislocation climb. At higher stresses and intermediate temperatures, the rate controlling mechanism changes from that of dislocation climb to one of obstacle-controlled dislocation glide. Along with this change, there occurs a change in the activation energy. It is shown that a temperature-dependent Gibbs free energy does a good job of correlating steady-state creep data, while a stress-dependent Gibbs free energy does a less desirable job of correlating the same data. Applications are made to copper and a LiF-22 mol. percent CaF2 hypereutectic salt.

  9. High temperature creep behavior of single crystal gamma prime and gamma alloys

    NASA Technical Reports Server (NTRS)

    Nathal, M. V.; Diaz, J. O.; Miner, R. V.

    1989-01-01

    The creep behavior of single crystals of gamma-prime and gamma alloys were investigated and compared to the response of two-phase superalloys tested previously. High temperature deformation in the gamma alloys was characteristic of a climb-controlled mechanism, whereas the gamma-prime based materials exhibited glide-controlled creep behavior. The superalloys were much more creep resistant than their constituent phases, which indicates the importance of the gamma/gamma-prime interface as a barrier for dislocation motion during creep.

  10. Assessment of Tungsten Content on Tertiary Creep Deformation Behavior of Reduced Activation Ferritic-Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Vanaja, J.; Laha, Kinkar

    2015-10-01

    Tertiary creep deformation behavior of reduced activation ferritic-martensitic (RAFM) steels having different tungsten contents has been assessed. Creep tests were carried out at 823 K (550 °C) over a stress range of 180 to 260 MPa on three heats of the RAFM steel (9Cr-W-0.06Ta-0.22V) with tungsten content of 1, 1.4, and 2.0 wt pct. With creep exposure, the steels exhibited minimum in creep rate followed by progressive increase in creep rate until fracture. The minimum creep rate decreased, rupture life increased, and the onset of tertiary stage of creep deformation delayed with the increase in tungsten content. The tertiary creep behavior has been assessed based on the relationship, , considering minimum creep rate () instead of steady-state creep rate. The increase in tungsten content was found to decrease the rate of acceleration of tertiary parameter ` p.' The relationships between (1) tertiary parameter `p' with minimum creep rate and time spent in tertiary creep deformation and (2) the final creep rate with minimum creep rate revealed that the same first-order reaction rate theory prevailed in the minimum creep rate as well as throughout the tertiary creep deformation behavior of the steel. A master tertiary creep curve of the steels has been developed. Scanning electron microscopic investigation revealed enhanced coarsening resistance of carbides in the steel on creep exposure with increase in tungsten content. The decrease in tertiary parameter ` p' with tungsten content with the consequent decrease in minimum creep rate and increase in rupture life has been attributed to the enhanced microstructural stability of the steel.

  11. The creep deformation and elevated temperature microstructural stability of a two-phase TiAl/Ti{sub 3}Al lamellar alloy

    SciTech Connect

    Bartholomeusz, M.F.; Wert, J.A.

    1995-08-01

    Enhanced work hardening of the phases in the lamellar microstructure has been cited as an explanation for the lower minimum creep rates of a two-phase TiAl/Ti{sub 3}Al lamellar alloy compared with the minimum creep rates of the individual TiAl and Ti{sub 3}Al single-phase alloys tested between 980 K and 1,130 K. This proposition is confirmed by TEM observations. Thermal and thermomechanical exposure result in the microstructural evolution, which increases the minimum creep rate ({dot {var_epsilon}}{sub min}) of the lamellar alloy. The effect of microstructural evolution on {dot {var_epsilon}}{sub min} will be discussed in the present paper.

  12. Temperature-dependent transient creep and dynamics of cratonic lithosphere

    NASA Astrophysics Data System (ADS)

    Birger, Boris I.

    2013-11-01

    Large-scale mantle convection forms the upper boundary layer (lithosphere) where the vertical temperature drop is about 1300 K. Theoretical rheology and laboratory experiments with rock samples show that transient creep occurs while creep strains are sufficiently small. The transient creep is described by the temperature-dependent Andrade rheological model. Since plate tectonics allows only small deformations in lithospheric plates, creep of the lithosphere plates is transient whereas steady-state creep, described by non-Newtonian power-law rheological model, takes place in the underlying mantle. The solution of stability problem shows that the lithosphere is stable but small-scale convective oscillations are attenuated very weakly in regions of thickened lithosphere beneath continental cratons (subcratonic roots) where the thickness of the lithosphere is about 200 km. These oscillations create small-scale convective cells (the horizontal dimensions of the cells are of the order of the subcratonic lithosphere thickness). Direction of motion within the cells periodically changes (the period of convective oscillations is of the order of 3 × 108 yr). In this study, the oscillations of cratonic lithosphere caused by initial relief perturbation are considered. This relief perturbation is assumed to be created by overthrusting in orogenic belts surrounding cratons. The perturbation of the Earth's surface relief leads to a fast isothermal process of isostatic recovery. In the presence of vertical temperature gradient, vertical displacements, associated with the recovery process in the lithosphere interior, instantly produce the initial temperature perturbations exciting thermoconvective oscillations in the cratonic lithosphere. These small-amplitude convective oscillations cause oscillatory crustal movements which form sedimentary basins on cratons.

  13. A microstructural study of creep and thermal fatigue deformation in 60Sn-40Pb solder joints

    SciTech Connect

    Tribula, D.

    1990-06-02

    Thermal fatigue failures of solder joints in electronic devices often arise from cyclic shear strains imposed by the mismatched thermal expansion coefficients of the materials that bind the joint as temperature changes are encountered. Increased solder joint reliability demands a fundamental understanding of the metallurigical mechanisms that control the fatigue to design accurate accelerated probative tests and new, more fatigue resistant solder alloys. The high temperatures and slow strain rates that pertain to thermal fatigue imply that creep is an important deformation mode in the thermal fatigue cycle. In this work, the creep behaviour of a solder joint is studied to determine the solder's microstructural response to this type of deformation and to relate this to the more complex problem of thermal fatigue. It is shown that creep failures arise from the inherent inhomogeneity and instability of the solder microstructure and suggest that small compositional changes of the binary near-eutectic Pn-Sn alloy may defeat the observed failure mechanisms. This work presents creep and thermal fatigue data for several near-eutectic Pb-Sn solder compositions and concludes that a 58Sn-40Pb-2In and a 58Sn-40Pb-2Cd alloy show significantly enhanced fatigue resistance over that of the simple binary material. 80 refs., 33 figs., 1 tab.

  14. Motion of a Deformed Sphere with Slip in Creeping Flows

    NASA Astrophysics Data System (ADS)

    Benard, Andre; Jia, Liping; Petty, Charles

    2004-11-01

    An analytical solution for the motion of a slightly deformed sphere in creeping flows with the assumption of slip on the particle surface is presented. Explicit expressions are obtained for the hydrodynamic force and torque exerted by the fluid on the deformed sphere. A perturbation method, based on previous work done by Brenner [1964] and Lamb[1945], is used to solve for the motion of a fluid influenced by the presence of a deformed sphere. Slip is assumed at the surface of the particle. Hydrodynamic force and torque exerted by the fluid on the deformed sphere are expressed explicitly for a translational and rotational deformed sphere. The equation governing the motion and orientation of a spheroid induced by homogenous flows is also presented. This evolution equation for the orientation of the spheroid is similar to the equation derived by Jeffery [1922]. Solutions of this equation show that the period of rotation of the particle with slip is longer than for the same particle without slip. Furthermore, when the slip coefficient is sufficiently low, the particle rotates to a fixed angle that corresponds to a quasi-steady state in the flow. REFERENCES Brenner, H. 1964 The Stokes resistance of a slightly deformed sphere. Chemical Engineering Science 19, 519-539 Jeffery, G.B.1922 The motion of ellipsoidal particles immersed in a viscous fluid. Proc. Soc. Lond. Math., 102, 161-179 Lamb, H. 1945 Hydrodynamics, sixth version, Dover, New York, U.S.A

  15. Creep deformation modeling of a tool steel with a tempered martensitic structure used for extrusion dies

    NASA Astrophysics Data System (ADS)

    Reggiani, Barbara; Donati, Lorenzo; Tomesani, Luca

    2011-05-01

    Aim of an extrusion die is to allow the production of the profile with the required dimension tolerances and quality level. One of the main impediment to achieve this aim could be an excessive die deformation due to the high cyclic loads and temperatures acting on the die during the extrusion process. In order to investigate the mechanisms that influence the die deformation, a physical experiment reproducing the thermo-mechanical conditions of a die was performed on a martensitic tool steel used for extrusion tools (AISI H11). The design of experiment consisted of 4 levels of temperature, 3 levels of stress and 3 types of load, i.e. pure creep, pure fatigue and creep-fatigue. In all cases, the same pattern of the mandrel displacement-time curve was found consisting of 3 stages as those typical of the strain evolution in a standard creep test with a marked primary phase. Thus, with the aim to define an easy-applicable equation to estimate the die deformation, the time hardening creep law was chosen. In order to obtain the temperature gradient within the specimen coupled thermo-electric simulations were previously performed. The nodal temperature have been then imported within the structural model and the mechanical properties assigned to the each element as a function of these values. Coefficients of the time-hardening law were optimized, for each testing condition, on the basis of experimental data starting from values for similar alloys found in literature. The values found were validated against additional experimental data performed with different specimen geometries. A good average agreement was found between experimental and numerical results.

  16. Improved Creep Measurements for Ultra-High Temperature Materials

    NASA Technical Reports Server (NTRS)

    Hyers, Robert W.; Ye, X.; Rogers, Jan R.

    2010-01-01

    Our team has developed a novel approach to measuring creep at extremely high temperatures using electrostatic levitation (ESL). This method has been demonstrated on niobium up to 2300 C, while ESL has melted tungsten (3400 C). This method has been extended to lower temperatures and higher stresses and applied to new materials, including a niobium-based superalloy, MASC. High-precision machined spheres of the sample are levitated in the NASA MSFC ESL, a national user facility and heated with a laser. The samples are rotated with an induction motor at up to 30,000 revolutions per second. The rapid rotation loads the sample through centripetal acceleration, producing a shear stress of about 60 MPa at the center, causing the sample to deform. The deformation of the sample is captured on high-speed video, which is analyzed by machine-vision software from the University of Massachusetts. The deformations are compared to finite element models to determine the constitutive constants in the creep relation. Furthermore, the non-contact method exploits stress gradients within the sample to determine the stress exponent in a single test.

  17. Analyses of Transient and Tertiary Small Punch Creep Deformation of 316LN Stainless Steel

    NASA Astrophysics Data System (ADS)

    Ganesh Kumar, J.; Ganesan, V.; Laha, K.

    2016-07-01

    Creep deformation behavior of 316LN stainless steel (SS) under small punch creep (SPC) and uniaxial creep test has been assessed and compared at 923 K (650 °C). The transient and tertiary creep deformation behaviors have been analyzed according to the equation proposed for SPC deflection, δ = δ0 + δ_{T} \\cdot (1 - {e}^{ - κ \\cdot t} ) + dot{δ }_{s} t + δ3 {e}^{{[ {φ ( {t - t_{r} } )} ]}} on the basis of Dobes and Cadek equation for uniaxial creep strain. Trends in the variations of (i) rate of exhaustion of transient creep (κ) with steady-state deflection rate ( dot{δ }_{s} ) (ii) `κ' with time to attain steady-state deflection rate, and (iii) initial creep deflection rate with steady-state deflection rate implied that transient SPC deformation obeyed first-order reaction rate theory. The rate of exhaustion of transient creep (r') values that were determined from uniaxial creep tests were correlated with those obtained from SPC tests. Master curves representing transient creep deformation in both SPC and uniaxial creep tests have been derived and their near coincidence brings unique equivalence between both the test techniques. The relationships between (i) rate of acceleration of tertiary creep (φ) and steady-state deflection rate, (ii) `φ' and time spent in tertiary stage, and (iii) final creep deflection rate and steady-state deflection rate revealed that first-order reaction rate theory governed SPC deformation throughout the tertiary region also. Interrelationship between the transient, secondary, and tertiary creep parameters indicated that the same mechanism prevailed throughout the SPC deformation.

  18. Analyses of Transient and Tertiary Small Punch Creep Deformation of 316LN Stainless Steel

    NASA Astrophysics Data System (ADS)

    Ganesh Kumar, J.; Ganesan, V.; Laha, K.

    2016-09-01

    Creep deformation behavior of 316LN stainless steel (SS) under small punch creep (SPC) and uniaxial creep test has been assessed and compared at 923 K (650 °C). The transient and tertiary creep deformation behaviors have been analyzed according to the equation proposed for SPC deflection, δ = δ0 + δ_{{T}} \\cdot (1 - {{e}}^{ - κ \\cdot t} ) + dot{δ }_{{s}} t + δ3 {{e}}^{{[ {φ ( {t - t_{{r}} } )} ]}} on the basis of Dobes and Cadek equation for uniaxial creep strain. Trends in the variations of (i) rate of exhaustion of transient creep ( κ) with steady-state deflection rate ( dot{δ }_{{s}} ) (ii) ` κ' with time to attain steady-state deflection rate, and (iii) initial creep deflection rate with steady-state deflection rate implied that transient SPC deformation obeyed first-order reaction rate theory. The rate of exhaustion of transient creep ( r') values that were determined from uniaxial creep tests were correlated with those obtained from SPC tests. Master curves representing transient creep deformation in both SPC and uniaxial creep tests have been derived and their near coincidence brings unique equivalence between both the test techniques. The relationships between (i) rate of acceleration of tertiary creep ( φ) and steady-state deflection rate, (ii) ` φ' and time spent in tertiary stage, and (iii) final creep deflection rate and steady-state deflection rate revealed that first-order reaction rate theory governed SPC deformation throughout the tertiary region also. Interrelationship between the transient, secondary, and tertiary creep parameters indicated that the same mechanism prevailed throughout the SPC deformation.

  19. Creep and precipitation behaviors of AL6XN austenitic steel at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Meng, L. J.; Sun, J.; Xing, H.

    2012-08-01

    Creep behaviors of the solution-treated AL6XN austenitic stainless steel have been investigated at 873-1023 K and 120-260 MPa. The results showed that the creep stress exponent and activation energy of the AL6XN steel are 5 and 395.4 kJ/mol, respectively in the power-law breakdown regime. TEM observations revealed that dislocations distributed homogenously in grains. The creep deformation mechanism is mainly attributed to viscous dislocation glide. Precipitates in the steel after creep deformation were additionally analyzed by TEM, and the results showed that there are four different types of precipitates, such as M23C6, M6C, σ phase and Laves phase. The M23C6 carbides were observed at grain boundaries in the steel after creep at 873 K. The M6C, σ phase and Laves phase precipitates were found when the creep temperature increases to 923-1023 K. Although the AL6XN steel exhibited low steady state creep rates, a high volume fraction of brittle precipitates of σ and Laves phases reduced the creep lifetime of the steel at elevated temperatures.

  20. Creep deformation and rupture behavior of CLAM steel at 823 K and 873 K

    NASA Astrophysics Data System (ADS)

    Zhong, Boyu; Huang, Bo; Li, Chunjing; Liu, Shaojun; Xu, Gang; Zhao, Yanyun; Huang, Qunying

    2014-12-01

    China Low Activation Martensitic (CLAM) steel is selected as the candidate structural material in Fusion Design Study (FDS) series fusion reactor conceptual designs. The creep property of CLAM steel has been studied in this paper. Creep tests have been carried out at 823 K and 873 K over a stress range of 150-230 MPa. The creep curves showed three creep regimes, primary creep, steady-state creep and tertiary creep. The relationship between minimum creep rate (ε˙min) and the applied stress (σ) could be described by Norton power law, and the stress exponent n was decreased with the increase of the creep temperature. The creep mechanism was analyzed with the fractographes of the rupture specimens which were examined by scanning electron microscopy (SEM). The coarsening of precipitates observed with transmission electron microscope (TEM) indicated the microstructural degradation after creep test.

  1. Compressive creep behavior of an electric brush-plated nanocrystalline Cu at room temperature

    NASA Astrophysics Data System (ADS)

    Wang, Guoyong; Lian, Jianshe; Jiang, Zhonghao; Qin, Liyuan; Jiang, Qing

    2009-10-01

    Creep tests were conducted on a nanocrystalline Cu at room temperature. The results at very low strain rates (<4×10-8 s-1) are consistent with Coble creep. An overall view of stress-strain rate behavior of this nanocrystalline Cu indicates that as the strain rate decreases, the deformation mechanism transition from predominantly dislocation activity to diffusion Coble creep, as evidenced by the strain rate sensitivity on stress trending to m =1 and activation volume trending to υ =1.5b3. The typical strain rate sensitivity of m =0.5 for surperplasticity can hardly be obtained at such low homogenous temperature.

  2. Non-contact Creep Resistance Measurement for Ultra-High Temperature Materials

    NASA Technical Reports Server (NTRS)

    Lee, J.; Bradshaw, C.; Rogers, J. R.; Rathz, T. J.; Wall, J. J.; Choo, H.; Liaw, P. K.; Hyers, R. W.

    2005-01-01

    Conventional techniques for measuring creep are limited to about 1700 C, so a new technique is required for higher temperatures. This technique is based on electrostatic levitation (ESL) of a spherical sample, which is rotated quickly enough to cause creep deformation by centrifugal acceleration. Creep of samples has been demonstrated at up to 2300 C in the ESL facility at NASA MSFC, while ESL itself has been applied at over 3000 C, and has no theoretical maximum temperature. The preliminary results and future directions of this NASA-funded research collaboration will be presented.

  3. Room Temperature Creep Of SiC/SiC Composites

    NASA Technical Reports Server (NTRS)

    Morscher, Gregory N.; Gyekenyesi, Andrew; Levine, Stanley (Technical Monitor)

    2001-01-01

    During a recent experimental study, time dependent deformation was observed for a damaged Hi-Nicalon reinforced, BN interphase, chemically vapor infiltrated SiC matrix composites subjected to static loading at room temperature. The static load curves resembled primary creep curves. In addition, acoustic emission was monitored during the test and significant AE activity was recorded while maintaining a constant load, which suggested matrix cracking or interfacial sliding. For similar composites with carbon interphases, little or no time dependent deformation was observed. Evidently, exposure of the BN interphase to the ambient environment resulted in a reduction in the interfacial mechanical properties, i.e. interfacial shear strength and/or debond energy. These results were in qualitative agreement with observations made by Eldridge of a reduction in interfacial shear stress with time at room temperature as measured by fiber push-in experiments.

  4. Micro-scale strain mapping technique: a tool to quantify strain partitioning during creep deformation

    NASA Astrophysics Data System (ADS)

    Quintanilla-Terminel, Alejandra; Zimmerman, Mark; Evans, Brian; Kohlstedt, David

    2016-04-01

    Several deformation mechanisms interact to accommodate plastic deformation. Quantifying the contribution of each to the total strain is necessary for establishing a better link between observed microstructures and mechanical data, as well as to allow more confident extrapolation from laboratory to natural conditions. In this contribution, we present the experimental and computational technique involved in micro-scale strain mapping (MSSM). The MSSM technique relies on analyzing the relative displacement of initially regularly spaced markers after deformation. We present several microfabrication techniques that permit us to pattern various rocks with micrometric and nanometric metal markers, as well as the challenges faced in working at high temperatures and pressures. A Hough transform algorithm was used to detect the markers and automate as much as possible the strain analysis. The von Mises strain is calculated for a set of n-points and their relative displacements, which allow us to map the strain at different length scales. We applied the MSSM technique to study strain partitioning during deformation creep of Carrara marble and San Carlos olivine at a confining pressure, Pc, of 300 MPa and homologous temperatures of 0.3 to 0.6. We measured the local strain and strain heterogeneity produced during creep deformation of split cylinders of Carrara marble under conventional triaxial loading to inelastic strains of 11 to 36% at a strain rate of 3x10‑5s‑1, Pc = 300 MPa and 400o < T <700oC. We conclude that the evolution of deformation structures in marble takes place over a substantial interval in strain and that the duration of this interval depends on strain rate, temperature, and pressure. Our first results on strain mapping of olivine deformed at T = 1150oC and Pc = 300 MPa demonstrate promise for characterizing intragranular strain and better defining the contribution of grain boundary sliding to the total strain.

  5. Non-contact Creep Resistance Measurement for Ultra-high temperature Materials

    NASA Technical Reports Server (NTRS)

    Hyers, Robert W.; Lee, Jonghuyn; Bradshaw, Richard C.; Rogers, Jan; Rathz, Thomas J.; Wall, James J.; Choo, Hahn; Liaw, Peter K.

    2005-01-01

    Continuing pressures for higher performance and efficiency in propulsion are driving ever more demanding needs for high-temperature materials. Some immediate applications in spaceflight include combustion chambers for advanced chemical rockets and turbomachinery for jet engines and power conversion in nuclear-electric propulsion. In the case of rockets, the combination of high stresses and high temperatures make the characterization of creep properties very important. Creep is even more important in the turbomachinery, where a long service life is an additional constraint. Some very high-temperature materials are being developed, including platinum group metals, carbides, borides, and silicides. But the measurement of creep properties at very high temperatures is itself problematic, because the testing instrument must operate at such high temperatures. Conventional techniques are limited to about 1700 C. A new, containerless technique for measuring creep deformation has been developed. This technique is based on electrostatic levitation (ESL) of a spherical sample, which is heated to the measurement temperature and rotated at a rate such that the centrifugal acceleration causes creep deformation. Creep of samples has been demonstrated at up to 2300 C in the ESL facility at NASA MSFC, while ESL itself has been applied at over 3000 C, and has no theoretical maximum temperature. The preliminary results and future directions of this NASA-funded research collaboration will be presented.

  6. Improved high temperature creep resistant austenitic alloy

    DOEpatents

    Maziasz, P.J.; Swindeman, R.W.; Goodwin, G.M.

    1988-05-13

    An improved austenitic alloy having in wt% 19-21 Cr, 30-35 Ni, 1.5-2.5 Mn, 2-3 Mo, 0.1-0.4 Si, 0.3-0.5 Ti, 0.1-0.3 Nb, 0.1-0.5 V, 0.001-0.005 P, 0.08-0.12 C, 0.01-0.03 N, 0.005-0.01 B and the balance iron that is further improved by annealing for up to 1 hour at 1150-1200/degree/C and then cold deforming 5-15%. The alloy exhibits dramatically improved creep rupture resistance and ductility at 700/degree/C. 2 figs.

  7. High temperature creep resistant austenitic alloy

    DOEpatents

    Maziasz, Philip J.; Swindeman, Robert W.; Goodwin, Gene M.

    1989-01-01

    An improved austenitic alloy having in wt % 19-21 Cr, 30-35 Ni, 1.5-2.5 Mn, 2-3 Mo, 0.1-0.4 Si, 0.3-0.5 Ti, 0.1-0.3 Nb, 0.1-0.5 V, 0.001-0.005 P, 0.08-0.12 C, 0.01-0.03 N, 0.005-0.01 B and the balance iron that is further improved by annealing for up to 1 hour at 1150.degree.-1200.degree. C. and then cold deforming 5-15 %. The alloy exhibits dramatically improved creep rupture resistance and ductility at 700.degree. C.

  8. Fatigue and Creep-Fatigue Deformation of an Ultra-Fine Precipitate Strengthened Advanced Austenitic Alloy

    SciTech Connect

    M.C. Carroll; L.J. Carroll

    2012-10-01

    An advanced austenitic alloy, HT-UPS (high-temperature ultrafine-precipitation-strengthened), has been identified as an ideal candidate material for the structural components of fast reactors and energy-conversion systems. HT-UPS alloys demonstrate improved creep resistance relative to 316 stainless steel (SS) through additions of Ti and Nb, which precipitate to form a widespread dispersion of stable nanoscale metallic carbide (MC) particles in the austenitic matrix. The low-cycle fatigue and creep-fatigue behavior of an HT-UPS alloy have been investigated at 650 °C and a 1.0% total strain, with an R-ratio of -1 and hold times at peak tensile strain as long as 150 min. The cyclic deformation response of HT-UPS is directly compared to that of standard 316 SS. The measured values for total cycles to failure are similar, despite differences in peak stress profiles and in qualitative observations of the deformed microstructures. Crack propagation is primarily transgranular in fatigue and creep-fatigue of both alloys at the investigated conditions. Internal grain boundary damage in the form of fine cracks resulting from the tensile hold is present for hold times of 60 min and longer, and substantially more internal cracks are quantifiable in 316 SS than in HT-UPS. The dislocation substructures observed in the deformed material differ significantly; an equiaxed cellular structure is observed in 316 SS, whereas in HT-UPS the microstructure takes the form of widespread and relatively homogenous tangles of dislocations pinned by the nanoscale MC precipitates. The significant effect of the fine distribution of precipitates on observed fatigue and creep-fatigue response is described in three distinct behavioral regions as it evolves with continued cycling.

  9. Long-term performance of ceramic matrix composites at elevated temperatures: Modelling of creep and creep rupture

    SciTech Connect

    Curtin, W.A.; Fabeny, B.; Ibnabdeljalil, M.; Iyengar, N.; Reifsnider, K.L.

    1996-07-31

    The models developed, contain explicit dependences on constituent material properties and their changes with time, so that composite performance can be predicted. Three critical processes in ceramic composites at elevated temperatures have been modeled: (1) creep deformation of composite vs stress and time-dependent creep of fibers and matrix, and failure of these components; (2) creep deformation of ``interface`` around broken fibers; and (3) lifetime of the composite under conditions of fiber strength loss over time at temperature. In (1), general evolution formulas are derived for relaxation time of matrix stresses and steady-state creep rate of composite; the model is tested against recent data on Ti-MMCs. Calculations on a composite of Hi-Nicalon fibers in a melt-infiltrated SiC matrix are presented. In (2), numerical simulations of composite failure were made to map out time-to-failure vs applied load for several sets of material parameters. In (3), simple approximate relations are obtained between fiber life and composite life that should be useful for fiber developers and testers. Strength degradation data on Hi-Nicalon fibers is used to assess composite lifetime vs fiber lifetime for Hi-Nicalon fiber composites.

  10. Elevated temperature creep properties of the 54Fe-29Ni-17Co "Kovar" alloy.

    SciTech Connect

    Stephens, John Joseph, Jr.; Rejent, Jerome Andrew; Schmale, David T.

    2009-01-22

    The outline of this presentation is: (1) Applications of Kovar Alloy in metal/ceramic brazing; (2) Diffusion bonding of precision-photoetched Kovar parts; (3) Sample composition and annealing conditions; (4) Intermediate temperature creep properties (350-650 C); (5) Power law creep correlations--with and without modulus correction; (6) Compressive stress-strain properties (23-900 C); (7) Effect of creep deformation on grain growth; and (8) Application of the power law creep correlation to the diffusion bonding application. The summary and conclusions are: Elevated temperature creep properties of Kovar from 750-900 C obey a power law creep equation with a stress exponent equal to 4.9, modulus compensated activation energy of 47.96 kcal/mole. Grain growth in Kovar creep samples tested at 750 and 800 C is quite sluggish. Significant grain growth occurs at 850 C and above, this is consistent with isothermal grain growth studies performed on Kovar alloy wires. Finite element analysis of the diffusion bonding of Kovar predict that stresses of 30 MPa and higher are needed for good bonding at 850 C, we believe that 'sintering' effects must be accounted for to allow FEA to be predictive of actual processing conditions. Additional creep tests are planned at 250-650 C.

  11. Experimental and computational simulation studies on creep deformation mechanisms of a novel nanostructured Cu and Cu-10%Sn Alloy

    NASA Astrophysics Data System (ADS)

    Abo-Elsoud, Mohamed A.

    2015-04-01

    This work presents experimental and computational simulation studies on creep deformation mechanisms of a novel nanostructured Cu and Cu-10%Sn alloy that prepared by mechanical alloying (MA) copper with elemental Tin. Mechanical Newtonian creep model is employed for computational simulation of creep deformation mechanism under low stress-high temperature and to justify the experimental findings. The observed behaviors are discussed and compared with the predications of the Nabarro-Herring (N-H) theory of directional diffusion. A simple theory based on the climb controlled generation of dislocations from a fixed density of sources is developed to explain the observed behavior. TEM and SEM investigations are convenient and powerful techniques for characterization of phases and a novel nano-grain structured of the resulting materials. The reduction of grain size to the nanometer scale improves their mechanical properties.

  12. High-Temperature Creep of Fine-Grained Anorthite Aggregate

    NASA Astrophysics Data System (ADS)

    Yabe, K.; Koizumi, S.; Hiraga, T.

    2014-12-01

    Rheology of the lower crust has often been compared to the creep properties of polycrystalline anorthite. Samples that have been used in previous studies (Dimanov et al., 1999; Rybacki and Dresen, 2000) were prepared through crystallization of anorthite glass which can remain in the experiment and also contain some impurities such as absorbed water, TiO2, MgO and Fe2O3. In this study, we synthesized genuinely pure polycrystalline anorthite using the technique that does not allow the contamination of water and glass phase. Also, we prepared anorthite aggregates with glass phase and/or a small amount (1wt%) of MgO to investigate the creep properties of pure and impure anorthite aggregates. Pure anorthite powders were prepared through high temperature reaction of highly pure and nano-sized powders of CaCO3, Al2O3 and SiO2 and then they were vacuum sintered (Koizumi et al., 2010). For MgO doping, we added Mg(OH)2powders at the synthesis of anorthite powders. Glass phase was introduced to the samples by sintering above melting temperature and subsequent quenching. Constant load tests under 1 atmosphere were performed at temperatures ranging from 1150 to 1380˚C and stresses of 10 to 120 MPa. We measured Arithmetic mean grain size of specimens by microstructural observations using scanning electron microscopy (SEM) before and after creep tests. Grain sizes of all the specimens were around 1 μm before and after the creep test. Log stress versus log strain rate showed a linear relationship where its slope gave a stress exponent, n of 1, indicating that all the samples were deformed under diffusion creep. Anorthite containing MgO and glass phase were more than two and one orders of magnitude weaker than genuinely pure anorthite aggregates, respectively. Further, our pure aggregate exhibited three orders of magnitude lager strength compared to the "pure" aggregate used in previous studies. These results indicate that a small amount of glass and/or impurities including water

  13. Elevated temperature creep properties for selected active metal braze alloys

    SciTech Connect

    Stephens, J.J.

    1997-02-01

    Active metal braze alloys reduce the number of processes required for the joining of metal to ceramic components by eliminating the need for metallization and/or Ni plating of the ceramic surfaces. Titanium (Ti), V, and Zr are examples of active element additions which have been used successfully in such braze alloys. Since the braze alloy is expected to accommodate thermal expansion mismatch strains between the metal and ceramic materials, a knowledge of its elevated temperature mechanical properties is important. In particular, the issue of whether or not the creep strength of an active metal braze alloy is increased or decreased relative to its non-activated counterpart is important when designing new brazing processes and alloy systems. This paper presents a survey of high temperature mechanical properties for two pairs of conventional braze alloys and their active metal counterparts: (a) the conventional 72Ag-28Cu (Cusil) alloy, and the active braze alloy 62.2Ag- 36.2Cu-1.6Ti (Cusil ABA), and (b) the 82Au-18Ni (Nioro) alloy and the active braze alloy Mu-15.5M-0.75Mo-1.75V (Nioro ABA). For the case of the Cusil/Cusil ABA pair, the active metal addition contributes to solid solution strengthening of the braze alloy, resulting in a higher creep strength as compared to the non-active alloy. In the case of the Nioro/Nioro ABA pair, the Mo and V additions cause the active braze alloy to have a two-phase microstructure, which results in a reduced creep strength than the conventional braze alloy. The Garofalo sinh equation has been used to quantitatively describe the stress and temperature dependence of the deformation behavior. It will be observed that the effective stress exponent in the Garofalo sinh equation is a function of the instantaneous value of the stress argument.

  14. Creep-strengthening of steel at high temperatures using nano-sized carbonitride dispersions.

    PubMed

    Taneike, Masaki; Abe, Fujio; Sawada, Kota

    2003-07-17

    Creep is a time-dependent mechanism of plastic deformation, which takes place in a range of materials under low stress-that is, under stresses lower than the yield stress. Metals and alloys can be designed to withstand creep at high temperatures, usually by a process called dispersion strengthening, in which fine particles are evenly distributed throughout the matrix. For example, high-temperature creep-resistant ferritic steels achieve optimal creep strength (at 923 K) through the dispersion of yttrium oxide nanoparticles. However, the oxide particles are introduced by complicated mechanical alloying techniques and, as a result, the production of large-scale industrial components is economically unfeasible. Here we report the production of a 9 per cent Cr martensitic steel dispersed with nanometre-scale carbonitride particles using conventional processing techniques. At 923 K, our dispersion-strengthened material exhibits a time-to-rupture that is increased by two orders of magnitude relative to the current strongest creep-resistant steels. This improvement in creep resistance is attributed to a mechanism of boundary pinning by the thermally stable carbonitride precipitates. The material also demonstrates enough fracture toughness. Our results should lead to improved grades of creep-resistant steels and to the economical manufacture of large-scale steel components for high-temperature applications. PMID:12867976

  15. Creep behaviour of Cu-30 percent Zn at intermediate temperatures

    NASA Technical Reports Server (NTRS)

    Raj, S. V.

    1991-01-01

    The present, intermediate-temperature (573-823 K) range investigation of creep properties for single-phase Cu-30 percent Zn alpha-brass observed inverse, linear, and sigmoidal primary-creep transients above 573 K under stresses that yield minimum creep rates in the 10 to the -7th to 2 x 10 to the -4th range; normal primary creep occurred in all other conditions. In conjunction with a review of the pertinent literature, a detailed analysis of these data suggests that no clearly defined, classes M-to-A-to-M transition exists in this alloy notwithstanding the presence of both classes' characteristics under nominally similar stresses and temperatures.

  16. Dislocation decorrelation and relationship to deformation microtwins during creep of a y' precipitate strengthened Ni-based superalloy

    SciTech Connect

    Unocic, R. R.; Zhou, N.; Kovarik, Libor; Shen, C.; Wang, Y.; Mills, M. J.

    2011-11-01

    The evolution of microtwins during high temperature creep deformation in a strengthened Ni-base superalloy has been investigated through a combination of creep testing, TEM characterization, theoretical modeling and computer simulation. Experimentally, microtwin nucleation sources were identified and their evolution was tracked by characterizing the deformation substructure at different stages of the creep deformation. Initially, deformation is highly localized around stress concentrators such as carbides, borides and serrated grain boundaries, which act as sources of a/2<110> matrix type dislocations. Due to microstructural effects such as fine channels between particles and low matrix stacking fault energies, the a/2<110> matrix dislocations dissociate into a/6<112> Shockley partials, which were commonly observed to be decorrelated from one another, creating extended intrinsic stacking faults in the matrix. As deformation progress further, microtwins form via partial dislocations cooperatively shearing both and phases on adjacent {111} glide planes. The TEM observations lead directly to an analysis of dislocation-precipitate interactions. Through phase field simulations and theoretical analysis based on Orowan looping, the important processes of dislocation dissociation and decorrelation are modeled in detail, providing comprehensive insight into the microstructural features and applied stress conditions that favor the microtwinning deformation mode in strengthened Ni-based superalloys.

  17. Creep in solid 4He at temperatures below 1 K

    NASA Astrophysics Data System (ADS)

    Zhuchkov, V. A.; Lisunov, A. A.; Maidanov, V. A.; Neoneta, A. S.; Rubanskyi, V. Yu.; Rubets, S. P.; Rudavskii, E. Ya.; Smirnov, S. N.

    2015-03-01

    Creep in solid 4He at temperatures of ˜100-1000 mK is studied experimentally by detecting the flow of helium through a frozen porous membrane under a constant external force. Creep curves are measured for different temperatures and mechanical stresses. This method has made it possible to detect low creep rates in helium down to the lowest temperatures in these experiments. It is found that throughout this temperature range, creep is thermally activated and the activation energy decreases with falling temperature and increasing mechanical stress. An analysis shows that for temperatures above ≈500 mK, Nabarro-Herring diffusive creep takes place in solid helium with mass transfer by self diffusion of atoms and a counterflow of vacancies. The experimental data have been used to obtain the self-diffusion coefficient as a function of temperature for different stresses. At temperatures below ≈500 mK creep takes place at a very low flow rate (˜10-13 cm/s) and a very low activation energy (˜0.5-0.7 K), while the creep mechanism remains unclear.

  18. Dislocation decorrelation and relationship to deformation microtwins during creep of a precipitate strengthened Ni-based superalloy

    SciTech Connect

    Unocic, Raymond R; Zhou, Ning; Kovarik, Libor; Shen, Chen; Wang, Yunzhi; Mills, Michael J.

    2011-01-01

    The evolution of microtwins during high temperature creep deformation in a strengthened Ni-base superalloy has been investigated through a combination of creep testing, transmission electron microscopy (TEM), theoretical modeling, and computer simulation. Experimentally, microtwin nucleation sources were identified and their evolution was tracked by characterizing the deformation substructure at different stages of creep deformation. Deformation is highly localized around stress concentrators such as carbides, borides and serrated grain boundaries, which act as sources of a/2<110> matrix-type dislocations. Due to fine channels between particles, coupled with the low matrix stacking fault energy, the a/2<110> matrix dislocations dissociate into a/6<112> Shockley partials, which were commonly observed to be decorrelated from one another, creating extended intrinsic stacking faults in the matrix. Microtwins are common and form via Shockley partial dislocations cooperatively shearing both and phases on adjacent {111} glide planes. The TEM observations lead directly to an analysis of dislocation-precipitate interactions. Through phase field simulations and theoretical analyses based on Orowan looping, the important processes of dislocation dissociation and decorrelation are modeled in detail, providing comprehensive insight into the microstructural features and applied stress conditions that favor the microtwinning deformation mode in strengthened Ni-based superalloys.

  19. CREEP-2: Long-term time-dependent rock deformation in a deep-sea observatory.

    NASA Astrophysics Data System (ADS)

    Boon, Steve; Meredith, Philip; Heap, Michael; Berenzoli, Laura; Favali, Paolo

    2010-05-01

    Earthquake rupture and volcanic eruptions are the most spectacular manifestations of dynamic failure of a critically stressed crust. But these are actually rather rare events, and most of the crust spends most of its time in a highly-stressed but sub-critical state. Below a few hundred metres, the crust is saturated, and water-rock chemical reactions lead to time-dependent deformation that allows rocks to fail over extended periods of time at stresses far below their short-term strength by the mechanism of stress corrosion crack growth. This process is highly non-linear and a change in applied stress of around 5% can lead to a change in the time-to-failure of more than an order of magnitude. Theoretical calculations based on reaction rate theory suggest that such cracking may occur down to stresses as low as 20% of the rock strength, implying that time-dependent cracking will be an important deformation mechanism over geological time and at typical tectonic strain rates. A number of theoretical models have been proposed to explain this behaviour. However, it is currently not possible to discriminate between these competing models due to the relatively narrow bandwidth of strain rates that are practicably achievable in conventional laboratory experiments. Ultra-long-term experiments at very low strain rates are clearly essential to address this problem. We have therefore used the stability of the deep-sea environment to conduct ultra-long-term experiments. At depth, the temperature remains constant throughout the year and water pressure also remains essentially constant, especially in the Ionian Sea where the tidal range is minimal. We have successfully conducted a pilot experiment (CREEP-1) in which we used the constant sea-water pressure at depth to provide both a constant confining pressure and a constant deforming stress for our rock samples. Building on that success, we are now building a multi-sample deformation observatory (CREEP-2) to be deployed at

  20. Creep Behavior of High Temperature Alloys for Generation IV Nuclear Energy Systems

    NASA Astrophysics Data System (ADS)

    Wen, Xingshuo

    are believed to be responsible for the monotonically increasing creep rates. Apart from dislocation creep, diffusional creep in existence at low stress level in fine-grained (ASTM 8) material also contributed partly to the creep rates. A reasonable prediction on the long term performance of alloy 617 was also made by extrapolation method using optimized parameters based on creep test data. Furthermore, microstructure characterization was performed utilizing Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Electron Backscattered Diffraction (EBSD), Transmission Electron Microscopy (TEM) and related analytical techniques on samples from both before and after creep, with special attention given to grain size effects, grain boundary type, and dislocation substructures. Evidences for dislocation climb and dislocation glide were found through detailed dislocation analysis by TEM, proving the dislocation climb-glide mechanism. The formation of subgrain boundary, the changes in boundary characters and grain sizes was confirmed by EBSD analysis for dynamic recrystallization. The effects of initial grain size and grain boundary character distribution on the creep behavior and mechanism were also evaluated. Through the results obtained from this experimental study, new insights were provided into how changes in microstructure take place during high temperature creep of alloy 617, creep mechanism at different conditions was identified, and the creep deformation model was discussed. The results will also serve to technological and code case development and design of materials for NGNP.

  1. Circular Functions Based Comprehensive Analysis of Plastic Creep Deformations in the Fiber Reinforced Composites

    NASA Astrophysics Data System (ADS)

    Monfared, Vahid

    2016-06-01

    Analytically based model is presented for behavioral analysis of the plastic deformations in the reinforced materials using the circular (trigonometric) functions. The analytical method is proposed to predict creep behavior of the fibrous composites based on basic and constitutive equations under a tensile axial stress. New insight of the work is to predict some important behaviors of the creeping matrix. In the present model, the prediction of the behaviors is simpler than the available methods. Principal creep strain rate behaviors are very noteworthy for designing the fibrous composites in the creeping composites. Analysis of the mentioned parameter behavior in the reinforced materials is necessary to analyze failure, fracture, and fatigue studies in the creep of the short fiber composites. Shuttles, spaceships, turbine blades and discs, and nozzle guide vanes are commonly subjected to the creep effects. Also, predicting the creep behavior is significant to design the optoelectronic and photonic advanced composites with optical fibers. As a result, the uniform behavior with constant gradient is seen in the principal creep strain rate behavior, and also creep rupture may happen at the fiber end. Finally, good agreements are found through comparing the obtained analytical and FEM results.

  2. Brittle, creep and melt damage mechanics of the lithosphere: is slow creep deformation a key to intraplate volcanic provinces?

    NASA Astrophysics Data System (ADS)

    Liu, J.; Regenauer-Lieb, K.; Karrech, A.; Rosenbaum, G.; Lyakhovsky, V.

    2014-12-01

    We investigate the problem of intraplate melt generation with the aim of understanding spatial and temporal relationships between magmatism and extremely slow intraplate deformation. We present numerical models that consider feedback between melt generation and lithospheric deformation and incorporate three different damage mechanisms: brittle damage, creep damage, and melt damage. Melt conditions are calculated with a Gibbs energy minimization method, and the energy equation solved self-consistently for latent heat and shear heating effects. We use an extremely slowly lithosphere extension model (1-1.5 mm/y) to investigate the mechanics leading to intraplate volcanism in a cold lithosphere (~50mW/m2) such as the Harrat Ash-Shaam volcanic field in NW Arabia. We find that the extremely slow extension is a key to a very potent melt transfer mechanism through the lithosphere. The mechanism relies on multiple feedback mechanisms active in the accommodation of strain in the presence of fluids. These are capable of generating melts in the lithosphere/asthenosphere even in regions of relatively low heat flux. Once low degrees of partial melts are generated, the triple feedback between brittle-creep and melt damage leads to high porosity lithospheric-scale shear zones capable of transferring melts and fluids to the surface. Efficient localization in the weaker ductile domains implies that the final pattern of strain distribution is controlled by slow creep from below rather than by brittle deformation from above. Our model provides an explanation for intraplate volcanic provinces, which appear to rely on slowly deforming lithospheres. A significant finding is that slow extension, rather than fast extension, can localize melt damage more effectively in the deeper creeping section of the lithosphere. This finding may have profound implications to the fundamental dynamic control on intraplate volcanism.

  3. Creep and Environmental Effects on High Temperature Creep-Fatigue Behavior of Alloy 617

    SciTech Connect

    L. J. Carroll; C. Cabet; R. Madland; R. Wright

    2011-06-01

    Alloy 617 is the leading candidate material for Intermediate Heat Exchanger (IHX) of a Very High Temperature Reactor (VHTR), expected to have an outlet temperature as high as 950 C. System start-ups and shut-downs as well as power transients will produce low cycle fatigue (LCF) loadings of components. Acceptance of Alloy 617 in Section III of the ASME Code for nuclear construction requires a detailed understanding of the creep-fatigue behavior in both air and impure helium, representative of the VHTR primary coolant. Strain controlled LCF tests including hold times at maximum tensile strain were conducted at total strain range of 0.3% in air at 950 C. Creep-fatigue testing was also performed in a simulated VHTR impure helium coolant for selected experimental conditions. The fatigue resistance decreased when a hold time was added at peak tensile stress, consistent with the observed change in fracture mode from transgranular to intergranular with introduction of a tensile hold. Increases in the tensile hold time, beyond 180 sec, was not detrimental to the creep-fatigue resistance. Grain boundary damage in the form of grain boundary cracking was present in the bulk of the creep-fatigue specimens. This bulk cracking was quantified and found to be similar for hold times of up to 1800 sec consistent with the saturation in failure lives and rapid stress relaxation observed during the creep portion of the creep-fatigue cycle.

  4. High temperature creep of SiC densified using a transient liquid phase

    SciTech Connect

    Jou, Z.C.; Virkar, A.V. ); Cutler, R.A. )

    1991-09-01

    Silicon carbide-based ceramics can be rapidly densified above approximately 1850 {degree}C due to a transient liquid phase resulting from the reaction between alumina and aluminum oxycarbides. The resulting ceramics are fine-grained, dense, and exhibit high strength at room temperature. SiC hot pressed at 1875 {degree}C for 10 min in Ar was subjected to creep deformation in bending at elevated temperatures between 1500 and 1650 {degree}C in Ar. Creep was thermally activated with an activation energy of 743 kJ/mol. Creep rates at 1575 {degree}C were between 10{sup {minus}9}/s and 10{sup {minus}7}/s at an applied stress between 38 and 200 MPa, respectively, resulting in a stress exponent of {approx}1.7.

  5. Orientation dependence of high temperature creep strength and internal stress in Ni{sub 3}Al alloy single crystals

    SciTech Connect

    Miura, Seiji; Peng, Z.L.; Mishima, Yoshinao

    1997-12-31

    High temperature creep behavior of a nickel-rich Ni{sub 3}(Al,Ta) with the L1{sub 2} structure is investigated in order to clarify the influence of crystallographic orientation with respect to the stress axis. The single crystals with four different orientations are deformed in compressive creep at temperatures ranging from 1,123 to 1,273 K under a constant load, initial shear stress being 35 to 120 MPa for (111)[{bar 1}01] slip system. The results show a distinct orientation dependence of creep strength, although shape of creep curves, stress exponent and the activation energy seem to be independent of the orientation. It is shown, however, the internal stress, being measured by strain transient dip tests, is found to be orientation dependent and the creep behavior is independent on orientation if it is interpreted using the effective stress instead of the applied shear stress.

  6. Phenomenological and microstructural analysis of room temperature creep in titanium alloys

    SciTech Connect

    Neeraj, T.; Hou, D.H.; Daehn, G.S.; Mills, M.J.

    2000-04-03

    Primary creep is the dominant mode of deformation during creep of titanium alloys at room temperature. Based on a study of both Ti-6Al and Ti-6Al-2Sn-4Zr-2Mo, it is shown that the transient creep behavior can be described by a power law of the form {var_epsilon} = At{sup a}, while the strain-rate-sensitive Hollomon law, {sigma} = K{var_epsilon}{sup n}{dot {var_epsilon}}{sup m}, represents the constant strain rate behavior of titanium alloys reasonably well. A simple analytical result is derived to relate these two expressions. Using this solution, the long time creep response has been predicted reasonably well from the constant strain rate results for the two alloys studied. Relative to other metals, it is shown that titanium alloys exhibit exceptionally low values of strain hardening. Optical microscope observations of slip line evolution have been used to relate the deformation mechanisms to the macroscopic behavior. Operative slip systems, as well as dislocation distributions and morphologies, are also presented for the first time following creep of a single-phase {alpha} microstructure in Ti-6Al.

  7. The constitutive representation of high-temperature creep damage

    NASA Technical Reports Server (NTRS)

    Chan, K. S.

    1988-01-01

    The elastic-viscoplastic constitutive equations of Bodner-Partom were applied to modeling creep damage in a high temperature Ni-alloy, B1900 + Hf. Both tertiary creep in bulk materials and creep crack growth in flawed materials were considered. In the latter case, the energy rate line integral was used for characterizing the crack driving force, and the rate of crack extension was computed using a local damage formulation that assumed fracture was controlled by cavitation occurring within the crack-tip process zone. The results of this investigation were used to assess the evolution equation for isotropic damage utilized in the Bodner-Partom constitutive equations.

  8. A model for high temperature creep of single crystal superalloys based on nonlocal damage and viscoplastic material behavior

    NASA Astrophysics Data System (ADS)

    Trinh, B. T.; Hackl, K.

    2014-07-01

    A model for high temperature creep of single crystal superalloys is developed, which includes constitutive laws for nonlocal damage and viscoplasticity. It is based on a variational formulation, employing potentials for free energy, and dissipation originating from plasticity and damage. Evolution equations for plastic strain and damage variables are derived from the well-established minimum principle for the dissipation potential. The model is capable of describing the different stages of creep in a unified way. Plastic deformation in superalloys incorporates the evolution of dislocation densities of the different phases present. It results in a time dependence of the creep rate in primary and secondary creep. Tertiary creep is taken into account by introducing local and nonlocal damage. Herein, the nonlocal one is included in order to model strain localization as well as to remove mesh dependence of finite element calculations. Numerical results and comparisons with experimental data of the single crystal superalloy LEK94 are shown.

  9. The high temperature creep behavior of oxides and oxide fibers

    NASA Technical Reports Server (NTRS)

    Jones, Linda E.; Tressler, Richard E.

    1991-01-01

    A thorough review of the literature was conducted on the high-temperature creep behavior of single and polycrystalline oxides which potentially could serve as fiber reinforcements in ceramics or metal matrix applications. Sapphire when oriented with the basal plane perpendicular to the fiber axis (c-axis oriented) is highly creep resistant at temperatures in excess of 1600 C and applied loads of 100 MPa and higher. Pyramidal slip is preferentially activated in sapphire under these conditions and steady-state creep rates in the range of 10(exp -7) to 10 (exp -8)/s were reported. Data on the creep resistance of polycrystalline beryllia suggest that C-axiz oriented single crystal beryllia may be a viable candidate as a fiber reinforcement material; however, the issure of fabricability and moisture sensitivity must be addressed for this material. Yttrium aluminum garnet (YAG) also appears to be a fiber candidate material having a high resistance to creep which is due to it's complex crystal structure and high Peierl resistance. The high creep resistance of garnet suggests that there may be other complex ternary oxides such as single crystal mullite which may also be candidate materials for fiber reinforcements. Finally, CVD and single crystal SiC, although not oxides, do possess a high resistance to creep in the temperature range between 1550 and 1850 C and under stresses of 110 to 220 MPa. From a review of the literature, it appears that for high creep resistant applications sapphire, silicon carbide, yttrium aluminum garnet, mullite, and beryllia are desirable candidate materials which require further investigation.

  10. Elevated temperature deformation of thoria dispersed nickel-chromium

    NASA Technical Reports Server (NTRS)

    Kane, R. D.; Ebert, L. J.

    1974-01-01

    The deformation behavior of thoria nickel-chromium (TD-NiCr) was examined over the temperature range 593 C (1100 F) to 1260 C (2300 F) in tension and compression and at 1093 C (2000 F) in creep. Major emphasis was placed on: (1) the effects of the material and test related variables (grain size, temperature, stress and strain rate) on the deformation process; and (2) the evaluation of single crystal TD-NiCr material produced by a directional recrystallization process. Elevated temperature yield strength levels and creep activation enthalpies were found to increase with increasing grain size reaching maximum values for the single crystal TD-NiCr. Stress exponent of the steady state creep rate was also significantly higher for the single crystal TD-NiCr as compared to that determined for the polycrystalline materials. The elevated temperature deformation of TD-NiCr was analyzed in terms of two concurrent, parallel processes: diffusion controlled grain boundary sliding, and dislocation motion.

  11. Plastic Deformation of Aluminum Single Crystals at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Johnson, R D; Young, A P; Schwope, A D

    1956-01-01

    This report describes the results of a comprehensive study of plastic deformation of aluminum single crystals over a wide range of temperatures. The results of constant-stress creep tests have been reported for the temperature range from 400 degrees to 900 degrees F. For these tests, a new capacitance-type extensometer was designed. This unit has a range of 0.30 inch over which the sensitivity is very nearly linear and can be varied from as low a sensitivity as is desired to a maximum of 20 microinches per millivolt with good stability. Experiments were carried out to investigate the effect of small amounts of prestraining, by two different methods, on the creep and tensile properties of these aluminum single crystals. From observations it has been concluded that plastic deformation takes place predominantly by slip which is accompanied by the mechanisms of kinking and polygonization.

  12. Fatigue and creep-fatigue deformation of several nickel-base superalloys at 650 C

    NASA Technical Reports Server (NTRS)

    Miner, R. V.; Gayda, J.; Maier, R. D.

    1982-01-01

    Transmission electron microscopy has been used to study the bulk deformation characteristics of seven nickel-base superalloys tested in fatigue and creep-fatigue at 650 C. The alloys were Waspalloy, HIP Astroloy, H plus F Astroloy, H plus F Rene 95, IN 100, MERL 76, and NASA IIB-7. The amount of bulk deformation observed in all the alloys was low. In tests with inelastic strain amplitudes less than about 0.003, only some grains exhibited yielding and the majority of those had the 110 line near the tensile axis. Deformation occurred on octahedral systems for all of the alloys except MERL 76 which also showed abundant primary cube slip. Creep-fatigue cycling occasionally produced extended faults between partial dislocations, but otherwise deformation was much the same as for fatigue cycling.

  13. High-Temperature Deformation of Enstatite Aggregates

    NASA Astrophysics Data System (ADS)

    Bystricky, M.; Lawlis, J.; Mackwell, S. J.; Heidelbach, F.; Raterron, P. C.

    2011-12-01

    Although enstatite is a significant component of the upper mantle, its rheology is still poorly understood. We have performed an experimental investigation of the mechanical properties of enstatite at high pressure and temperature in the proto- and ortho-enstatite stability fields. Synthetic enstatite powders were produced by reacting San Carlos olivine powders with lab-grade quartz. Powders were hot-pressed at high PT, and were then baked at 1000°C under controlled oxygen fugacity conditions to remove all hydrous defect species. The polycrystalline enstatite samples were deformed in a Paterson gas-medium apparatus at temperatures of 1200-1300°C, an oxygen fugacity buffered at Ni/NiO, and confining pressures of 300 or 450 MPa. Under these conditions, samples were in the orthoenstatite field at 450 MPa and likely mainly in the protoenstatite field at 300 MPa. At both confining pressures, the mechanical data display a progressive increase of the stress exponent n from 1 to 3 as a function of differential stress, suggesting a transition from diffusional to dislocation creep. Non-linear least-square fits to the high-stress data yielded flow laws with n=3 and activation energies of 600 and 720 kJ/mol for ortho- and proto-enstatite, respectively. The measured strengths are significantly higher than those derived from Raleigh et al. (1971) and Ross and Nielsen (1978), due to the influence of water on the mechanical behavior of their samples. Deformed samples were analysed using optical microscopy, SEM and TEM. Because enstatite reverts to clinoenstatite during quenching, the microstructures present highly twinned grains composed of thin alternating domains of clino- and ortho-pyroxene. Nevertheless, the microstructures show evidence of dislocation processes in the form of undulatory extinction and kink bands. Crystallographic preferred orientations measured by EBSD are axisymmetric and indicate preferential slip on (100)[001]. High resolution TEM indicates that for

  14. Deformation mechanisms responsible for the creep resistance of Ti-Al alloys

    SciTech Connect

    Morris, M.A.; Lipe, T.

    1997-12-31

    Two {gamma}-based Ti-Al alloys with similar grain sizes and, respectively, lamellar and duplex microstructures have been creep tested at 700 C and constant stresses ranging between 280 and 430 MPa. TEM observations have confirmed that the duplex alloy deforms by extensive mechanical twinning whose density increases with applied stress and increasing strain. The new twin interfaces subdivide the {gamma} grains throughout the primary stage of creep. At the onset of the minimum creep rate, the twin interfaces in the duplex alloy behave in the same way as the {gamma}/{gamma} or the {alpha}{sub 2}/{gamma} interfaces in the lamellar alloy. However, single dislocations were also present and it appears that in both alloys the deformation process is controlled by the accumulation and emission of dislocations from the different interfaces.

  15. Analysis of slip activity and heterogeneous deformation in tension and tension-creep of Ti-5Al-2.5Sn (wt %) using in-situ SEM experiments

    NASA Astrophysics Data System (ADS)

    Li, H.; Boehlert, C. J.; Bieler, T. R.; Crimp, M. A.

    2012-08-01

    The deformation behavior of a Ti-5Al-2.5Sn (wt %) near-α alloy was investigated during in-situ deformation inside a scanning electron microscope. Tensile experiments were performed at 296 K and 728 K (≈0.4 T m), while tensile-creep experiments were performed at 728 K and 763 K. Active deformation systems were identified using electron backscattered diffraction-based slip trace analysis. Both basal and prismatic slip systems were active during the tensile experiments. Basal slip was observed for grains clustered around high Schmid factor orientations, while prismatic slip exhibited less dependence on the crystallographic orientation. The tension-creep experiments revealed less slip but more development of grain boundary ledges than in the higher strain rate tensile experiments. Some of the grain boundary ledges evolved into grain boundary cracks, and grain boundaries oriented nearly perpendicular to the tensile axis formed ledges earlier in the deformation process. Grain boundaries with high misorientations also tended to form ledges earlier than those with lower misorientations. Most of the grain boundary cracks formed in association with grains displaying hard orientations, where the c-axis was nearly perpendicular to the tensile direction. For the tension-creep experiments, pronounced basal slip was observed in the lower-stress creep regime and the activity of prismatic slip increased with increasing creep stress and temperature.

  16. Phase boundary mobility in naturally deformed, high-grade quartzofeldspathic rocks: evidence for diffusional creep

    NASA Astrophysics Data System (ADS)

    Gower, Robert J. W.; Simpson, Carol

    1992-03-01

    Grain shape fabrics and optical microstructures of some quartzofeldspathic rocks deformed under upper amphibolite facies conditions in the southwestern Grenville Province, Ontario, Canada, suggest that quartz and feldspar have accommodated intracrystalline plastic strains by both diffusional and dislocation creep. In these rocks, quartz and feldspar form polycrystalline domains separated by gently curved and locally cuspate phase boundaries whose morphology is similar in certain respects to the phase boundary morphology of rocks annealed experimentally under hydrostatic stress conditions. In the naturally deformed rocks, however, phase boundary cusps consistently point along the foliation and parallel to the mineral fibre lineation (i.e. in directions of inferred finite extension) which implies that phase boundary motion and cusp formation occurred during deformation. Optical microstructures in feldspar and crystallographic preferred orientations in quartz are consistent with the accommodation of some intracrystalline plastic strains by dislocation creep. However, the morphology of quartz-feldspar phase boundaries cannot be explained by either dislocation creep or static annealing alone. We propose that phase boundary motion resulted from a diffusion-assisted process involving dissolution at foliation-parallel quartz-feldspar phase boundaries, mass transfer over length scales of the order of feldspar domain size (≈200 μm or greater) and precipitation at quartz-feldspar phase boundary cusps. This study extends the range of natural deformation conditions under which diffusional creep has been identified in quartzofeldspathic rocks. It also has important implications for the natural rheological behavior of the mid- and lower-continental crust.

  17. Correlation of creep rate with microstructural changes during high temperature creep

    NASA Technical Reports Server (NTRS)

    Young, C. T.; Sommers, B. R.; Lytton, J. L.

    1977-01-01

    Creep tests were conducted on Haynes 188 cobalt-base alloy and alpha titanium. The tests on Haynes 188 were conducted at 1600 F and 1800 F for stresses from 3 to 20 ksi, and the as-received, mill-annealed results were compared to specimens given 5%, 10%, and 15% room temperature prestrains and then annealed one hour at 1800 F. The tests on alpha titanium were performed at 7,250 and 10,000 psi at 500 C. One creep test was done at 527 C and 10,000 psi to provide information on kinetics. Results for annealed titanium were compared to specimens given 10% and 20% room temperature prestrains followed by 100 hours recovery at 550 C. Electron microscopy was used to relate dislocation and precipitate structure to the creep behavior of the two materials. The results on Haynes 188 alloy reveal that the time to reach 0.5% creep strain at 1600 F increases with increasing prestrain for exposure times less than 1,000 hours, the increase at 15% prestrain being more than a factor of ten.

  18. Examination of the distribution of the tensile deformation systems in tension and tension-creep of Ti-6Al-4V (wt.%) at 296 K and 728 K

    NASA Astrophysics Data System (ADS)

    Li, H.; Boehlert, C. J.; Bieler, T. R.; Crimp, M. A.

    2015-03-01

    The deformation behaviour of an α + β Ti-6Al-4V (wt.%) alloy was investigated during in situ deformation inside a scanning electron microscopy (SEM). Tensile experiments were performed at 296 and 728 K (~0.4Tm), while a tensile-creep experiment was performed at 728 K and 310 MPa (σ/σys = 0.74). The active deformation systems were identified using electron backscattered diffraction-based slip-trace analysis and SEM images of the specimen surface. The distribution of the active deformation systems varied as a function of temperature. Basal slip deformation played a major role in the tensile deformation behaviour, and the relative activity of basal slip increased with increasing temperature. For the 296 K tension deformation, basal slip was less active than prismatic slip, whereas this was reversed at 728 K. Twinning was observed in both the 296 and 728 K tension experiments; however, no more than 4% of the total deformation systems observed was twins. The tension-creep experiment revealed no slip traces, however grain boundary ledge formation was observed, suggesting that grain boundary sliding was an active deformation mechanism. The results of this work were compared with those from previous studies on commercially pure Ti, Ti-5Al-2.5Sn (wt.%) and Ti-8Al-1Mo-1V (wt.%), and the effects of alloying on the deformation behaviour are discussed. The relative amount of basal slip activity increased with increasing Al content.

  19. Effect of HIP Temperature on Microstructure and Creep Property of FGH95 Alloy

    NASA Astrophysics Data System (ADS)

    Xie, Jun; Tian, Su-Gui; Zhou, Xiao-Ming

    2012-02-01

    By means of hot isostatic pressing (HIP) treatment, microstructure observation and creep properties measurement, the effects of the HIP temperatures on the microstructure and creep properties of FGH95 nickel-base superalloy are investigated. The results show that, when the HIP temperature is lower than solubility of γ' phase, the coarser γ' phase is precipitated in the previous particle boundary (PPB) regions, and the quantity and size of the coarser γ' phase which is distributed in the regions decrease as the HIP temperature increases. No feature of the grain growing up is detected after the alloy is solution treated at 1140 °C. Moreover, there are a few of carbide particles distributing along the grain boundary and in the grain. After HIP treated at 1180 °C and fully heat treated, coarser γ' phase is dissolved in the alloy, and the depleted zone of the fine γ' phase has disappeared. In addition, the grains grow up obviously in the alloy, and the γ' phase and fine carbide particles are dispersedly precipitated in the grains and along boundaries, which can enhance the creep resistance of the alloy. The deformation mechanisms of the alloy are that the dislocations slip in the matrix or shear into γ' phase during creep.

  20. High temperature tensile creep, creep damage and failure under superimposed compressional stress

    NASA Astrophysics Data System (ADS)

    Boček, M.

    1985-04-01

    The paper presents a theoretical examination of the influence of compressional stresses upon the characteristics of high temperature tensile creep. The calculations are based on a phenomenological creep cavitation model, which is adapted for superimposed pressure loading. Therefrom a power law strain rate/stress equation is obtained in which the hydrostatic pressure P enters in the stress function σ1n = ( σ - P) n. However, impeding cavity growth, P has an additional influence upon the strain rate through a variable structure parameter described by the damage function A< σ1>. From A< σ1> the stress rupture lines tf< σ1> for superimposed creep are obtained. The calculations are compared to experimental results from literature. By means of the life fraction rule the lifetime is calculated for load cycling in which tensional and compressional loading phases alternate. The lifetime depends sensitively upon the ratio of the minimum to maximum stress amplitude ( r) and upon a stress factor η characterizing the influence of the stress state upon cavitation damage. The lifetime computations are compared with experimental results obtained on the stainless steel AISI 304. The calculations show that the Monkman-Grant relationship should also be obeyed for superimposed creep.

  1. Creep deformation of a fully lamellar gamma based titanium aluminide alloy

    SciTech Connect

    Herrouin, F.; Bowen, P.; Jones, I.P.

    1997-12-31

    A complex two phase {gamma}-TiAl alloy, Ti-47Al-1Cr-1Mn-2Ta-0.2Si (at.%) in a fully lamellar condition, has been creep tested at a stress of 200 MPa and a temperature of 700 C. This simulates the in-service operating conditions for several potential gas turbine aero engine applications where creep resistance is a design limiting material property. The results indicate that reduction in lamellae thickness and avoidance of feathery type microstructures contribute to improved creep resistance.

  2. Strain localization during high temperature creep of marble: The effect of inclusions

    NASA Astrophysics Data System (ADS)

    Rybacki, E.; Morales, L. F. G.; Naumann, M.; Dresen, G.

    2014-11-01

    The deformation of rocks in the Earth's middle and lower crust is often localized in ductile shear zones. To better understand the initiation and propagation of high-temperature shear zones induced by the presence of structural and material heterogeneities, we performed deformation experiments in the dislocation creep regime on Carrara marble samples containing weak (limestone) or strong (novaculite) second phase inclusions. The samples were mostly deformed in torsion at a bulk shear strain rate of ≈ 1.9 × 10- 4 s- 1 to bulk shear strains γ between 0.02 and 2.9 using a Paterson-type gas deformation apparatus at 900 °C temperature and 400 MPa confining pressure. At low strain, twisted specimens with weak inclusions show minor strain hardening that is replaced by strain weakening at γ > 0.1-0.2. Peak shear stress at the imposed conditions is about 20 MPa, which is ≈ 8% lower than the strength of intact samples. Strain progressively localized within the matrix with increasing bulk strain, but decayed rapidly with increasing distance from the inclusion tip. Microstructural analysis shows twinning and recrystallization within this process zone, with a strong crystallographic preferred orientation, dominated by {r} and (c) slip in < a >. Recrystallization-induced weakening starts at local shear strain of about 1 in the process zone, corresponding to a bulk shear strain of about 0.1. In contrast, torsion of a sample containing strong inclusions deformed at similar stress as inclusion-free samples, but do not show localization. The experiments demonstrate that the presence of weak heterogeneities initiates localized creep at local stress concentrations around the inclusion tips. Recrystallization-induced grain size reduction may only locally promote grain boundary diffusion creep. Accordingly, the bulk strength of the twisted aggregate is close to or slightly below the lower (isostress) strength bound, determined from the flow strength and volume fraction of matrix

  3. Characterization of micro-scale creep deformation of an electro-active paper actuator

    NASA Astrophysics Data System (ADS)

    Lee, Sangwoo; Kim, Joo-Hyung; Kang, Kwangseon; Kim, Jaehwan; Kim, Heung Soo; Yang, Chulho

    2009-09-01

    The creep deformation process of an electro-active paper (EAPap) actuator was investigated by adapting stepwise dead-weight loading. To understand the deformation mechanism of the EAPap film, including morphological and structural changes, various loading conditions below yield strength were applied to cellophane EAPap. From the structural observation, micro-dimples and micro-cracks were detected at applied load lower than 10% of yield strength, while they were not found in higher load conditions. It is hypothesized that only short and random fibers in the amorphous region may respond to the applied stress at the low loading condition, not the fibers in the crystalline area. As a result, deformation energy at the localized spot accumulated and created micro-defects at the surface. Meanwhile, fibers in the crystalline region may sustain most of the loads as creep load increases to a high level. Molecular chains in the fiber may rotate and elongate with high load. Elongated fibers were observed only at a high level of load. From the structural change as a function of applied load, a peak shift of crystal orientation was observed only in high load conditions by wide angle x-ray measurement. This may confirm that creep deformation could give rise to structure changes in EAPap.

  4. Submarine creeping landslide deformation controlled by the presence of gas hydrates: The Tuaheni Landslide Complex, New Zealand

    NASA Astrophysics Data System (ADS)

    Gross, Felix; Mountjoy, Joshu; Crutchle, Garethy; Koch, Stephanie; Bialas, Jörg; Pecher, Ingo; Woelz, Susi; Dannowski, Anke; Carey, Jon; Micallef, Aaron; Böttner, Christoph; Huhn, Katrin; Krastel, Sebastian

    2016-04-01

    Methane hydrate occurrence is bound to a finite pressure/temperature window on continental slopes, known as the gas hydrate stability zone (GHSZ). Hydrates within sediment pore spaces and fractures are recognized to act like a cement, increasing shear strength and stabilizing slopes. However, recent studies show that over longer strain periods methane hydrates can undergo ductile deformation. This combination of short term strengthening and longer term ductile behavior is implicated in the development of slow creeping submarine landforms within the GHSZ. In order to study this phenomenon, a new high-resolution seismic 3D volume was acquired at the Tuaheni Landslide Complex (TLC) at the Hikurangi margin offshore the North Island of New Zealand. Parts of TLC have been interpreted as a slow moving landslide controlled by the gas hydrate system. Two hypotheses for its slow deformation related to the presence of methane hydrates have been proposed: i) Hydrofracturing, driven by gas pressure at the base of the GHSZ, allows pressurized fluids to ascend toward the seafloor, thereby weakening the shallow debris and promoting failure. ii) The mixture of methane hydrates and sediment results in a rheology that behaves in a ductile way under sustained loading, resulting in slow deformation comparable to that of terrestrial and extra-terrestrial rock glaciers. The 3D dataset reveals the distribution of gas and the extend of gas hydrate stability within the deformed debris, as well as deformation fabrics like tectonic-style faulting and a prominent basal décollement, known to be a critical element of terrestrial earth-flows and rock glaciers. Observations from 3D data indicate that the TLC represents the type example of a new submarine landform - an active creeping submarine landslide - which is influenced by the presence of gas hydrates. The morphology, internal structure and deformation of the landslide are comparable with terrestrial- and extra-terrestrial earth flows and

  5. Measurement of Creep Properties of Ultra-High-Temperature Materials by a Novel Non-Contact Technique

    NASA Technical Reports Server (NTRS)

    Hyers, Robert W.; Lee, Jonghyun; Rogers, Jan R.; Liaw, Peter K.

    2007-01-01

    A non-contact technique for measuring the creep properties of materials has been developed and validated as part of a collaboration among the University of Massachusetts, NASA Marshall Space Flight Center Electrostatic Levitation Facility (ESL), and the University of Tennessee. This novel method has several advantages over conventional creep testing. The sample is deformed by the centripetal acceleration from the rapid rotation, and the deformed shapes are analyzed to determine the strain. Since there is no contact with grips, there is no theoretical maximum temperature and no concern about chemical compatibility. Materials may be tested at the service temperature even for extreme environments such as rocket nozzles, or above the service temperature for accelerated testing of materials for applications such as jet engines or turbopumps for liquid-fueled engines. The creep measurements have been demonstrated to 2400 C with niobium, while the test facility, the NASA MSFC ESL, has processed materials up to 3400 C. Furthermore, the ESL creep method employs a distribution of stress to determine the stress exponent from a single test, versus the many tests required by conventional methods. Determination of the stress exponent from the ESL creep tests requires very precise measurement of the surface shape of the deformed sample for comparison to deformations predicted by finite element models for different stress exponents. An error analysis shows that the stress exponent can be determined to about 1% accuracy with the current methods and apparatus. The creep properties of single-crystal niobium at 1985 C showed excellent agreement with conventional tests performed according to ASTM Standard E-139. Tests on other metals, ceramics, and composites relevant to rocket propulsion and turbine engines are underway.

  6. Microstructural behavior of 8Cr-ODS martensitic steels during creep deformation

    NASA Astrophysics Data System (ADS)

    Shinozuka, K.; Esaka, H.; Tamura, M.; Tanigawa, H.

    2011-10-01

    Oxide dispersion strengthened (ODS) steels show a high anisotropy in their creep behavior because of the δ-ferrite grain elongated in the hot-rolled direction and the characteristic formation of creep cavities. In this work, the relationship between the δ-ferrite grain and the growth of creep cavities in 8Cr-ODS steels was investigated. The samples of two ODS steels with different δ-ferrite volume fractions were machined parallel and perpendicular to the hot-rolled direction. Creep rupture tests and interrupted tests were performed at 700 °C and about 197 MPa. Cavities formed in the martensite along δ-ferrite grains during creep deformation. The area fraction of the cavities of all specimens increased in proportion to the cube root of test time. When the volume fraction of δ-ferrite was high and δ-ferrite grains elongated parallel to the load direction, δ-ferrite then obstructed the propagation of cracks. However, when the volume fraction of δ-ferrite was low and δ-ferrite grains elongated perpendicular to the load direction, δ-ferrite grains had little effect on crack propagation.

  7. High-temperature deformation and diffusion in oxides

    SciTech Connect

    Routbort, J.L.

    1992-06-01

    High-temperature, steady-state deformation is usually controlled by diffusion of the slowest moving ion along its fastest diffusion path. Therefore, measurements of steady-state deformation can, in principle, be used to obtain information concerning diffusion. This paper will briefly review the assumptions that relate creep, defect chemistry, and diffusion. Steady-state deformation of the NaCI-structured oxides, Co{sub 1-x}O and Mn{sub l-x}O, and the perovskite-structured high-temperature superconductors YBa{sub 2}Cu{sub 3}0{sub x} and Bi{sub 2}Sr{sub 2}CaCu{sub 2}0{sub x} will be discussed, emphasizing diffusion of the minority defects.

  8. Elevated temperature creep behavior of Inconel alloy 625

    SciTech Connect

    Purohit, A.; Burke, W.F.

    1984-07-01

    Inconel 625 in the solution-annealed condition has been selected as the clad material for the fuel and control rod housing assemblies of the Upgraded Transient Reactor Test Facility (TREAT Upgrade or TU). The clad is expected to be subjected to temperatures up to about 1100/sup 0/C. Creep behavior for the temperature range of 800/sup 0/C to 1100/sup 0/C of Inconel alloy 625, in four distinct heat treated conditions, was experimentally evaluated.

  9. Creep Deformation and Rupture Behavior of Single- and Dual-Pass 316LN Stainless-Steel-Activated TIG Weld Joints

    NASA Astrophysics Data System (ADS)

    Vijayanand, V. D.; Vasudevan, M.; Ganesan, V.; Parameswaran, P.; Laha, K.; Bhaduri, A. K.

    2016-03-01

    Creep deformation and rupture behavior of single-pass and dual-pass 316LN stainless steel (SS) weld joints fabricated by an autogenous activated tungsten inert gas welding process have been assessed by performing metallography, hardness, and conventional and impression creep tests. The fusion zone of the single-pass joint consisted of columnar zones adjacent to base metals with a central equiaxed zone, which have been modified extensively by the thermal cycle of the second pass in the dual-pass joint. The equiaxed zone in the single-pass joint, as well as in the second pass of the dual-pass joint, displayed the lowest hardness in the joints. In the dual-pass joint, the equiaxed zone of the first pass had hardness comparable to the columnar zone. The hardness variations in the joints influenced the creep deformation. The equiaxed and columnar zone in the first pass of the dual-pass joint was more creep resistant than that of the second pass. Both joints possessed lower creep rupture life than the base metal. However, the creep rupture life of the dual-pass joint was about twofolds more than that of the single-pass joint. Creep failure in the single-pass joint occurred in the central equiaxed fusion zone, whereas creep cavitation that originated in the second pass was blocked at the weld pass interface. The additional interface and strength variation between two passes in the dual-pass joint provides more restraint to creep deformation and crack propagation in the fusion zone, resulting in an increase in the creep rupture life of the dual-pass joint over the single-pass joint. Furthermore, the differences in content, morphology, and distribution of delta ferrite in the fusion zone of the joints favors more creep cavitation resistance in the dual-pass joint over the single-pass joint with the enhancement of creep rupture life.

  10. Creep Deformation and Rupture Behavior of Single- and Dual-Pass 316LN Stainless-Steel-Activated TIG Weld Joints

    NASA Astrophysics Data System (ADS)

    Vijayanand, V. D.; Vasudevan, M.; Ganesan, V.; Parameswaran, P.; Laha, K.; Bhaduri, A. K.

    2016-06-01

    Creep deformation and rupture behavior of single-pass and dual-pass 316LN stainless steel (SS) weld joints fabricated by an autogenous activated tungsten inert gas welding process have been assessed by performing metallography, hardness, and conventional and impression creep tests. The fusion zone of the single-pass joint consisted of columnar zones adjacent to base metals with a central equiaxed zone, which have been modified extensively by the thermal cycle of the second pass in the dual-pass joint. The equiaxed zone in the single-pass joint, as well as in the second pass of the dual-pass joint, displayed the lowest hardness in the joints. In the dual-pass joint, the equiaxed zone of the first pass had hardness comparable to the columnar zone. The hardness variations in the joints influenced the creep deformation. The equiaxed and columnar zone in the first pass of the dual-pass joint was more creep resistant than that of the second pass. Both joints possessed lower creep rupture life than the base metal. However, the creep rupture life of the dual-pass joint was about twofolds more than that of the single-pass joint. Creep failure in the single-pass joint occurred in the central equiaxed fusion zone, whereas creep cavitation that originated in the second pass was blocked at the weld pass interface. The additional interface and strength variation between two passes in the dual-pass joint provides more restraint to creep deformation and crack propagation in the fusion zone, resulting in an increase in the creep rupture life of the dual-pass joint over the single-pass joint. Furthermore, the differences in content, morphology, and distribution of delta ferrite in the fusion zone of the joints favors more creep cavitation resistance in the dual-pass joint over the single-pass joint with the enhancement of creep rupture life.

  11. Multimechanism-Deformation Parameters of Domal Salts Using Transient Creep Analysis

    SciTech Connect

    MUNSON, DARRELL E

    1999-09-01

    Use of Gulf Coast salt domes for construction of very large storage caverns by solution mining has grown significantly in the last several decades. In fact, among the largest developers of storage caverns along the Gulf Coast is the Strategic Petroleum Reserve (SPR) which has purchased or constructed 62 crude oil storage caverns in four storage sites (domes). Although SPR and commercial caverns have been operated economically for many years, the caverns still exhibit some relatively poorly understood behaviors, especially involving creep closure volume loss and hanging string damage from salt falls. Since it is possible to postulate that some of these behaviors stem from geomechanical or reformational aspects of the salt, a method of correlating the cavern response to mechanical creep behavior as determined in the laboratory could be of considerable value. Recently, detailed study of the creep response of domal salts has cast some insight into the influence of different salt origins on cavern behavior. The study used a simple graphical analysis of limited non-steady state data to establish an approach or bound to steady state, as an estimate of the steady state behavior of a given salt. This permitted analysis of sparse creep databases for domal salts. It appears that a shortcoming of this steady state analysis method is that it obscures some critical differences of the salt material behavior. In an attempt to overcome the steady state analysis shortcomings, a method was developed based on integration of the Multimechanism-Deformation (M-D) creep constitutive model to obtain fits to the transient response. This integration process permits definition of all the material sensitive parameters of the model, while those parameters that are constants or material insensitive parameters are fixed independently. The transient analysis method has proven more sensitive to differences in the creep characteristics and has provided a way of defining different behaviors within a

  12. Influence of flowing sodium on creep deformation and rupture behaviour of 316L(N) austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Ravi, S.; Laha, K.; Mathew, M. D.; Vijayaraghavan, S.; Shanmugavel, M.; Rajan, K. K.; Jayakumar, T.

    2012-08-01

    The influence of flowing sodium on creep deformation and rupture behaviour of AISI 316L(N) austenitic stainless steel has been investigated at 873 K over a stress range of 235-305 MPa. The results were compared with those obtained from testing in air environment. The steady state creep rates of the material were not influenced appreciably by the testing environments. The time to onset of tertiary stage of creep deformation was delayed in sodium environment. The creep-rupture lives of the material increased in sodium environment, which became more pronounced at lower applied stresses. The increase in rupture life of the material in flowing sodium was accompanied by an increase in rupture ductility. The creep damage on specimen surface as well as inside the specimen was less in specimen tested in sodium. SEM fractographic investigation revealed predominantly transgranular dimple failure for the specimen tested in sodium, whereas predominantly intergranular creep failure was observed in the air tested specimens. Almost no oxidation was observed in the specimens creep tested in the sodium environment. Absence of oxidation and less creep damage cavitation extended the secondary state in liquid sodium tests and lead to increase in creep rupture life and ductility of the material as compared to in air.

  13. Probabilistic material degradation under high temperature, fatigue, and creep

    NASA Technical Reports Server (NTRS)

    Boyce, L.

    1993-01-01

    A methodology has been developed and embodied in two computer codes for quantitatively characterizing the material strength degradation of aerospace propulsion system structural components that are subjected to various random effects over the course of their service lives. The codes, PROMISS and PROMISC, constitute a material-resistance model that is used in the NESSUS aerospace structural-reliability program. NESSUS addresses the service life-reducing effects of high temperature, mechanical fatigue, and creep.

  14. High-Temperature Deformation of Dry Diabase with Application to Tectonics on Venus

    NASA Technical Reports Server (NTRS)

    Mackwell, S. J.; Zimmerman, M. E.; Kohlstedt, D. L.

    1998-01-01

    We have performed an experimental study to quantify the high-temperature creep behavior of natural diabase rocks under dry deformation conditions. Samples of both Maryland diabase and Columbia diabase were investigated to measure the effects of temperature, oxygen fugacity, and plagioclase-to-pyroxene ratio on creep strength. Flow laws determined for creep of these diabases were characterized by an activation energy of Q = 485 +/- 30 kJ/mol and a stress exponent of n = 4.7 +/- 0.6, indicative of deformation dominated by dislocation creep processes. Although n and Q are the same for the two rocks within experimental error, the Maryland diabase, which has the lower plagioclase content, is significantly stronger than the Columbia diabase. Thus the modal abundance of the various minerals plays an important role in defining rock strength. Within the s ample-to-sample variation, no clear influence of oxygen fugacity on creep strength could be discerned for either rock. The dry creep strengths of both rocks are significantly greater than values previously measured on diabase under "as-received" or wet conditions. Application of these results to the present conditions in the lithosphere on Venus predicts a high viscosity crust with strong dynamic coupling between mantle convection and crustal deformation, consistent with measurements of topography and gravity for that planet.

  15. Understanding creep in sandstone reservoirs - theoretical deformation mechanism maps for pressure solution in granular materials

    NASA Astrophysics Data System (ADS)

    Hangx, Suzanne; Spiers, Christopher

    2014-05-01

    Subsurface exploitation of the Earth's natural resources removes the natural system from its chemical and physical equilibrium. As such, groundwater extraction and hydrocarbon production from subsurface reservoirs frequently causes surface subsidence and induces (micro)seismicity. These effects are not only a problem in onshore (e.g. Groningen, the Netherlands) and offshore hydrocarbon fields (e.g. Ekofisk, Norway), but also in urban areas with extensive groundwater pumping (e.g. Venice, Italy). It is known that fluid extraction inevitably leads to (poro)elastic compaction of reservoirs, hence subsidence and occasional fault reactivation, and causes significant technical, economic and ecological impact. However, such effects often exceed what is expected from purely elastic reservoir behaviour and may continue long after exploitation has ceased. This is most likely due to time-dependent compaction, or 'creep deformation', of such reservoirs, driven by the reduction in pore fluid pressure compared with the rock overburden. Given the societal and ecological impact of surface subsidence, as well as the current interest in developing geothermal energy and unconventional gas resources in densely populated areas, there is much need for obtaining better quantitative understanding of creep in sediments to improve the predictability of the impact of geo-energy and groundwater production. The key problem in developing a reliable, quantitative description of the creep behaviour of sediments, such as sands and sandstones, is that the operative deformation mechanisms are poorly known and poorly quantified. While grain-scale brittle fracturing plus intergranular sliding play an important role in the early stages of compaction, these time-independent, brittle-frictional processes give way to compaction creep on longer time-scales. Thermally-activated mass transfer processes, like pressure solution, can cause creep via dissolution of material at stressed grain contacts, grain

  16. Intragranular deformation heterogeneities during the creep of ice polycrystals: experimental measurements vs. modeling

    NASA Astrophysics Data System (ADS)

    Grennerat, F.; Montagnat, M.; Castelnau, O.; Vacher, P.; Suquet, P.; Moulinec, H.; Duval, P.

    2011-12-01

    Similarly as minerals from the Earth mantle, ice exhibits a strongly anisotropic rheology resulting from the small number of independent slip systems for dislocations. Therefore, a significant heterogeneity of stress and strain distributions is expected at the inter- and intra-granular scale during polycrystal deformation, owing to the mechanical interaction between adjacent grains. A Digital Image Correlation (DIC) technique has been adapted to polycrystalline ice specimens in order to characterize the development of strain heterogeneities at an intragranular scale during transient creep deformation. Specimens exhibit a columnar microstructure so that plastic deformation is essentially 2-D with no in-depth gradients, and therefore surface DIC analyses are representative for the whole specimen volume. Local misorientations at the intragranular scale were also extracted from microstructure analyses carried out with an automatic texture analyzer before and after deformation. Highly localized strain patterns are evidenced by the DIC technique. Local equivalent strain can reach values as high as one order of magnitude larger than the macroscopic average. The structure of the strain pattern does not evolve with strain in the transient creep regime. Almost no correlation between the measured local strain and the Schmid factor of the slip plane of the underlying grain is observed, highlighting the importance of the mechanical interactions between neighboring grains resulting from the very large viscoplastic anisotropy of ice crystals. Finally, the experimental microstructure was introduced in a full-field FFT polycrystal model; simulated strain fields are in good match with experimental ones.

  17. High Precision Measurements of Temperature Dependence of Creep Rate of Polycrystalline Forsterite

    NASA Astrophysics Data System (ADS)

    Nakakoji, T.; Hiraga, T.

    2014-12-01

    Obtaining temperature dependence of creep rate, that is, activation energy for the creep is critical in geophysics, since its value can indicate deformation mechanism and also allows to extrapolate the creep rate measured in the room experiments to geological conditions when the creep mechanism is identical in both cases. Although numerous experimental results have been obtained so far, the obtained activation energy often contains error range of >50 kJ/mol, which often causes large uncertainties in strain rate at applied geological conditions. To minimize this error, it is important to collect strain rates at many different temperatures with high accuracy. We conducted high temperature compression experiments on synthetic forsterite (90%vol) and enstatite (10vol %) aggregates under increasing and decreasing temperatures. We applied a constant load of ~20 MPa using uniaxial testing machine (Shimadzu AG-X 50kN). The temperature was changed from 1360°C to 1240°C by furnace attached to the machine. Prior to the applying the load to the samples the grain size was saturated at 1360°C for 24 hours to minimize grain growth during the test. Decreasing-rate of temperature was 0.11min/°C and 0.02min/°C at temperature ranges of 1360 to 1300 and 1300 to 1240 respectively. The increasing-rate of the temperature was the same as the decreasing-rate. Strain rates from every 1 degree were obtained successfully. After the experiment, we analyzed the microstructure of the sample with scanning electron microscopy to measure the grain diameter. Arrhenius plots of strain rate demonstrate very linear distribution at > 1300 °C giving an activation energy of 649 ± 14 kJ/mol, whereas weak transition to lower activation energy 550 ± 23 kJ/mol below 1300°C was observed. Tasaka et al. (2013) obtained the activation energy of 370 ± 50 kJ/mol from similar temperature ranges used in our study but finer-grained samples. Combining these results, we interpret our results of high activation

  18. Cell structure in cold worked and creep deformed phosphorus alloyed copper

    SciTech Connect

    Wu, Rui; Pettersson, Niklas; Martinsson, Åsa; Sandström, Rolf

    2014-04-01

    Transmission electron microscopy (TEM) examinations on as-received, cold worked, as well as cold worked and creep tested phosphorus-alloyed oxygen-free copper (Cu-OFP) have been carried out to study the role of the cell structure. The cell size decreased linearly with increasing plastic deformation in tension. The flow stress in the tests could also be correlated to the cell size. The observed relation between the flow stress and the cell size was in excellent agreement with previously published results. The dense dislocation walls that appeared after cold work in tension is likely to be the main reason for the dramatic increase in creep strength. The dense dislocation walls act as barriers against dislocation motion and their presence also reduces the recovery rate due to an unbalanced dislocation content.

  19. Developing Dislocation Subgrain Structures and Cyclic Softening During High-Temperature Creep-Fatigue of a Nickel Alloy

    NASA Astrophysics Data System (ADS)

    Carroll, M. C.; Carroll, L. J.

    2013-08-01

    The complex cyclic deformation response of Alloy 617 under creep-fatigue conditions is of practical interest both in terms of the observed detriment in failure life and the considerable cyclic softening that occurs. At the low strain ranges investigated, the inelastic strain is the sole predictor of the failure life without taking into consideration a potentially significant environmental influence. The tensile-hold creep-fatigue peak stress response can be directly correlated to the evolving dislocation substructure, which consists of a relatively homogenous distribution of subgrains. Progressive high-temperature cycling with a static hold allows for the rearrangement of loose tangles of dislocations into well-ordered hexagonal dislocation networks. The cyclic softening during tensile-hold creep-fatigue deformation is attributable to two factors: the rearrangement of dislocation substructures into lower-energy configurations, which includes a decreasing dislocation density in subgrain interiors through integration into the subgrain boundaries, and the formation of surface grain boundary cracks and cavity formation or separation at interior grain boundaries, which occurs perpendicular to the stress axis. Effects attributable to the tensile character of the hold cycle are further analyzed through variations in the creep-fatigue waveform and illuminate the effects of the hold-time character on the overall creep-fatigue behavior and evolution of the dislocation substructure.

  20. High-precision Non-Contact Measurement of Creep of Ultra-High Temperature Materials for Aerospace

    NASA Technical Reports Server (NTRS)

    Rogers, Jan R.; Hyers, Robert

    2008-01-01

    For high-temperature applications (greater than 2,000 C) such as solid rocket motors, hypersonic aircraft, nuclear electric/thermal propulsion for spacecraft, and more efficient jet engines, creep becomes one of the most important design factors to be considered. Conventional creep-testing methods, where the specimen and test apparatus are in contact with each other, are limited to temperatures approximately 1,700 C. Development of alloys for higher-temperature applications is limited by the availability of testing methods at temperatures above 2000 C. Development of alloys for applications requiring a long service life at temperatures as low as 1500 C, such as the next generation of jet turbine superalloys, is limited by the difficulty of accelerated testing at temperatures above 1700 C. For these reasons, a new, non-contact creep-measurement technique is needed for higher temperature applications. A new non-contact method for creep measurements of ultra-high-temperature metals and ceramics has been developed and validated. Using the electrostatic levitation (ESL) facility at NASA Marshall Space Flight Center, a spherical sample is rotated quickly enough to cause creep deformation due to centrifugal acceleration. Very accurate measurement of the deformed shape through digital image analysis allows the stress exponent n to be determined very precisely from a single test, rather than from numerous conventional tests. Validation tests on single-crystal niobium spheres showed excellent agreement with conventional tests at 1985 C; however the non-contact method provides much greater precision while using only about 40 milligrams of material. This method is being applied to materials including metals and ceramics for non-eroding throats in solid rockets and next-generation superalloys for turbine engines. Recent advances in the method and the current state of these new measurements will be presented.

  1. Modeling of high homologous temperature deformation behavior for stress and life-time analyses

    SciTech Connect

    Krempl, E.

    1997-12-31

    Stress and lifetime analyses need realistic and accurate constitutive models for the inelastic deformation behavior of engineering alloys at low and high temperatures. Conventional creep and plasticity models have fundamental difficulties in reproducing high homologous temperature behavior. To improve the modeling capabilities {open_quotes}unified{close_quotes} state variable theories were conceived. They consider all inelastic deformation rate-dependent and do not have separate repositories for creep and plasticity. The viscoplasticity theory based on overstress (VBO), one of the unified theories, is introduced and its properties are delineated. At high homologous temperature where secondary and tertiary creep are observed modeling is primarily accomplished by a static recovery term and a softening isotropic stress. At low temperatures creep is merely a manifestation of rate dependence. The primary creep modeled at low homologous temperature is due to the rate dependence of the flow law. The model is unaltered in the transition from low to high temperature except that the softening of the isotropic stress and the influence of the static recovery term increase with an increase of the temperature.

  2. Dissolution and Replacement Creep:A Significant Deformation Mechanism in Mid-crustal Rocks

    NASA Astrophysics Data System (ADS)

    Wintsch, R. P.

    2001-12-01

    Zoning patterns and zoning truncations in metamorphic minerals in a granodioritic orthogneiss from the Bronson Hill terrane, New England indicate that strain and S-C fabrics in these rocks were produced by dissolution, precipitation, and replacement processes, even at epidote-amphibolite facies metamorphic conditions. The metamorphic fabric is defined by alternating layers and folia dominated by quartz, feldspars, and biotite + epidote. Zoning patterns in most metamorphic plagioclase, orthoclase, epidote, and sphene are truncated at boundaries normal to the shortening direction, suggesting dissolution. Interfaces of relict igneous orthoclase phenocrysts that face the shortening direction are embayed and replaced by biotite, epidote and myrmekitic intergrowths of plagioclase and quartz. Metamorphic plagioclase grains are also replaced by epidote. We interpret these microstructures to reflect strain-enhanced dissolution. The cores of many grains show asymmetric overgrowths with at least two generations of beards, all oriented on the ends of grains that face the extension direction. We interpret these textures to reflect precipitation of components dissolved by deformation enhanced dissolution. While biotite and quartz probably deformed by dislocation creep, the overall deformation was accommodated by dissolution perpendicular to the shortening direction, and precipitation parallel to it. These chemical processes must have been activated at lower stresses than the dislocation creep predicted from extrapolations of data from experiments in dry rocks. Thus wet crust is likely to be weaker than calculated from these experimental studies. Where such processes dominate, stress may not be high enough to reach brittle failure.

  3. Dissolution and replacement creep: a significant deformation mechanism in mid-crustal rocks

    NASA Astrophysics Data System (ADS)

    Wintsch, R. P.; Yi, Keewook

    2002-07-01

    Zoning patterns and zoning truncations in metamorphic minerals in a granodioritic orthogneiss indicate that strain and S- C fabrics in these rocks were produced by dissolution, precipitation, and replacement processes, even at epidote-amphibolite facies metamorphic conditions. The metamorphic fabric is defined by alternating layers and folia dominated by quartz, feldspars, and biotite+epidote. Zoning patterns in most metamorphic plagioclase, orthoclase, epidote, and sphene are truncated at boundaries normal to the shortening direction, suggesting dissolution. Interfaces of relict igneous orthoclase phenocrysts that face the shortening direction are embayed and replaced by biotite, epidote, and myrmekitic intergrowths of plagioclase and quartz. Metamorphic plagioclase grains are also replaced by epidote. We interpret these microstructures to reflect strain-enhanced dissolution. The cores of many grains show asymmetric overgrowths with at least two generations of beards, all oriented on the ends of grains that face the extension direction. We interpret these textures to reflect precipitation of components dissolved by deformation-enhanced dissolution. While biotite and quartz probably deformed by dislocation creep, the overall deformation was accommodated by dissolution perpendicular to the shortening direction, and precipitation parallel to it. These chemical processes must have been activated at lower stresses than the dislocation creep predicted from extrapolations of data from experiments in dry rocks. Thus wet crust is likely to be weaker than calculated from these experimental studies.

  4. An experimental study of uniaxial creep, cyclic creep and relaxation of aisi type 304 stainless steel at room temperature

    NASA Astrophysics Data System (ADS)

    Kujawski, D.; Kallianpur, V.; Krempl, E.

    1980-04-01

    FOLLOWING previous work ( KREMPL, 1979), a servocontrolled testing machine and strain measurement at the gage length were used to study the uniaxial rate(time)-dependent behavior of AISI Type 304 stainless steel at room temperature. The test results show that the creep strain accumulated in a given period of time depends strongly on the stress-rate preceding the creep test. In constant stress-rate zero-to-tension loading the creep strain accumulated in a fixed time-period at a given stress level is always higher during loading than during unloading. Continued cycling causes an exhaustion of creep ratchetting which depends on the stress-rate. Periods of creep and relaxation introduced during completely reversed plastic cycling show that the curved portions of the hysteresis loop exhibit most of the inelasticity. In the straight portions, creep and relaxation are small and there exists a region commencing after unloading where the behavior is similar to that at the origin for virgin materials. This region does not extend to zero stress. The results are at variance with creep theory and with viscoplasticity theories which assume that the yield surface expands with the stress. They support the theory of viscoplasticity based on total strain and overstress.

  5. Ambient-temperature creep failure of silver-aided diffusion bonds between steel

    SciTech Connect

    Henshall, G.A.; Kassner, M.E.; Rosen, R.S.

    1990-01-15

    It has long been known that thin (e.g., 1 {mu}m {minus} 1 mm) interlayer bonds between higher strength base materials may have high ultimate tensile or rupture strengths despite the relatively low strength of the filler metal. The high strength of the joint is due to the mechanical constraint provided by the stronger base metals which restricts transverse contraction of the interlayer. The constraint produces a triaxial state or stress and reduces the effective stress, thus reducing the tendency for the interlayer to plastically deform. Plasticity of the base metal reduces the constraint and decreases the strength of the bond. The purpose of this work was twofold. First, the validity of the base-metal- accelerated'' delayed-failure theory for bonds utilizing plastic base metals was checked. Creep-rupture tests were performed on diffusion-bonded specimens using silver interlayers deposited by planar-magnetron sputtering (PMS), a physical vapor-deposition process. The PMS process was preferred because of the superior quality and strength of the bond and because this modern low-temperature joining process is increasingly utilized for joining ceramic and composite materials. The role of plastic base metals in the fracture process was further investigated by conducting tensile-rupture tests of diffusion bonds made with stainless steel base metals of different yield strengths, and therefore different creep rates. The second purpose was to determine whether delayed failure occurs in interlayer bonds between elastic base metals, which do not creep over the range of applied stresses. This question is particularly relevant since many alloys, ceramics and composites fall within this category. Again, ambient and near-ambient temperature creep-rupture tests were performed at a variety of stresses below the UTS of the bond. 25 refs., 7 figs.

  6. Elevated temperature creep properties of NiAl cryomilled with and without Y2O3

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel; Luton, Michael J.

    1995-01-01

    The creep properties of lots of NiAl cryomilled with and without Y2O3 have been determined in compression and tension. Although identical cryomilling procedures were used, differences in composition were found between the lot ground with 0.5 vol% yttria and the lot ground without Y2O3. Compression testing between 1000 and 1300 K yielded similar creep strengths for both materials, while tensile creep rupture testing indicated that the yttria-containing alloy was slightly stronger than the Y2O3-free version. Both compression and tensile testing showed two deformation regimes; whereas the stress state did not affect the high stress exponent (n approximately equals 10) mechanism, the low stress exponent regime n was approximately 6 in tension and approximately 2 in compression. The strengths in tension were somewhat less than those measured in compression, but the estimated activation energies (Q) of approximately 600 kJ/mol for tensile testing were closer to the previously measured values (approximately 700 kJ/mol) for NiAl-AlN and very different from the Q's of 400 and 200 kJ/mol for compression tests in the high and low stress exponent regimes, respectively. A Larson-Miller comparison indicated that cryomilling can produce an alloy with long-term, high-temperature strength at least equal to conventional superalloys.

  7. High temperature tensile deformation behavior of Grade 92 steel

    NASA Astrophysics Data System (ADS)

    Alsagabi, Sultan; Shrestha, Triratna; Charit, Indrajit

    2014-10-01

    Candidate structural materials for advanced reactors need to have superior high temperature strength and creep-rupture properties among other characteristics. The ferritic-martensitic Grade 92 steel (Fe-9Cr-2W-0.5Mo, wt.%) is considered such a candidate structural material. Tensile tests were performed at temperatures of 600, 650 and 700 °C in the strain rate range of 10-5-10-3 s-1. After analyzing the tensile results using the Bird-Mukherjee-Dorn (BMD) equation, a stress exponent of about 9.5 and an activation energy of about 646 kJ/mol were obtained. In the light of high values of the stress exponent and activation energy, the threshold stress concept was used to elucidate the operating high temperature deformation mechanism. As a result of this modification, the true activation energy and stress exponent of the high temperature deformation in Grade 92 steel were found to be about 245 kJ/mol and 5, respectively. Thus, the dominant high temperature deformation mechanism was identified as the high temperature climb of edge dislocations and the appropriate constitutive equation was developed.

  8. Monotonic and transient creep experiments for single phase gamma TiAl at intermediate temperatures

    SciTech Connect

    Lu, M.; Hemker, K.J.

    1997-12-31

    Monotonic creep experiments (constant stress and constant temperature) of a single phase {gamma} Ti{sub 47}Al{sub 51}Mn{sub 2} were conducted within a temperature region where the yield stress anomaly is observed (500 C--600 C). The creep strength was found to have a normal temperature dependence. In addition to the monotonic creep experiments, temperature change experiments were performed. The creep activation energy obtained by the transient experiments was found to be significantly lower than that obtained from the monotonic experiments. TEM observations indicate that the microstructure evolves throughout creep, and no evidence of the formation of subgrains was observed. Instead, the mobility and the multiplication of ordinary dislocations were found to play a dominant role in intermediate temperature creep of single phase {gamma}TiAl.

  9. Creep deformation and fracture behaviour of a nitrogen-bearing type 316 stainless steel weld metal

    NASA Astrophysics Data System (ADS)

    Sasikala, G.; Mathew, M. D.; Bhanu Sankara Rao, K.; Mannan, S. L.

    1999-08-01

    Creep properties of a nuclear grade type 316 stainless steel (SS) weld metal containing ˜0.08 wt% of nitrogen were studied at 873 and 923 K. These properties were compared with those of a type 316 SS weld metal without nitrogen. In general, the nitrogen-bearing weld metal exhibited better creep and rupture properties. The rupture strengths of the nitrogen-containing weld metal was ˜40% higher than that for the type 316 SS weld metal at both the temperatures. The steady-state (minimum) creep rates were up to two orders of magnitude lower for the nitrogen-containing weld metal compared to 316 SS weld metal. Rupture ductility of nitrogen-containing weld metal was lower at all the test conditions; the long-term ductility at 923 K was below 5%. The differences in creep behaviour of the two weld metals are discussed with respect to the influence of nitrogen on microstructural evolution in the two weld metals.

  10. Transient creep, aseismic damage and slow failure in Carrara marble deformed across the brittle-ductile transition

    NASA Astrophysics Data System (ADS)

    Schubnel, A.; Walker, E.; Thompson, B. D.; Fortin, J.; Guéguen, Y.; Young, R. P.

    2006-09-01

    Two triaxial compression experiments were performed on Carrara marble at high confining pressure, in creep conditions across the brittle-ductile transition. During cataclastic deformation, elastic wave velocity decrease demonstrated damage accumulation (microcracks). Keeping differential stress constant and reducing normal stress induced transient creep events (i.e., fast accelerations in strain) due to the sudden increase of microcrack growth. Tertiary creep and brittle failure followed as damage came close to criticality. Coalescence and rupture propagation were slow (60-200 seconds with ~150 MPa stress drops and millimetric slips) and radiated little energy in the experimental frequency range (0.1-1 MHz). Microstructural analysis pointed out strong interactions between intra-crystalline plastic deformation (twinning and dislocation glide) and brittle deformation (microcracking) at the macroscopic level. Our observations highlight the dependence of acoustic efficiency on the material's rheology, at least in the ultrasonic frequency range, and the role played by pore fluid diffusion as an incubation process for delayed failure triggering.

  11. Creep of 304 LN and 316 L stainless steels at cryogenic temperatures

    SciTech Connect

    Roth, L.D.; Manhardt, A.E.; Dalder, E.N.C.; Kershaw, R.P. Jr.

    1985-08-07

    Creep behavior of Type 304 LN plate and 316 L shielded-metal-arc (SMA)-deposited stainless weld metal was investigated at 4/sup 0/K. Testing was performed at constant load in a creep machine with a cryostat designed for long-term stability. Both transient and steady-state creep were observed during tests lasting over 2000 hours. Steady-state creep rates were much greater than expected from extrapolations of 300-K creep data. Creep rates on the order of 10/sup -10/ s/sup -1/ were observed at stresses around the yield stress for both materials. The stress exponent under these conditions if approx.2.3. Possible creep mechanisms at this temperature and the impact of these results on the design of engineering structures for long-term structural stability at cryogenic temperatures are discussed.

  12. Analytical, Numerical, and Experimental Investigation on a Non-Contact Method for the Measurements of Creep Properties of Ultra-High-Temperature Materials

    NASA Technical Reports Server (NTRS)

    Lee, Jonghyun; Hyers, Robert W.; Rogers, Jan R.; Rathz, Thomas J.; Choo, Hahn; Liaw, Peter

    2006-01-01

    Responsive access to space requires re-use of components such as rocket nozzles that operate at extremely high temperatures. For such applications, new ultra-hightemperature materials that can operate over 2,000 C are required. At the temperatures higher than the fifty percent of the melting temperature, the characterization of creep properties is indispensable. Since conventional methods for the measurement of creep is limited below 1,700 C, a new technique that can be applied at higher temperatures is strongly demanded. This research develops a non-contact method for the measurement of creep at the temperatures over 2,300 C. Using the electrostatic levitator in NASA MSFC, a spherical sample was rotated to cause creep deformation by centrifugal acceleration. The deforming sample was captured with a digital camera and analyzed to measure creep deformation. Numerical and analytical analyses have also been conducted to compare the experimental results. Analytical, numerical, and experimental results showed a good agreement with one another.

  13. Deterministic Multiaxial Creep and Creep Rupture Enhancements for CARES/Creep Integrated Design Code

    NASA Technical Reports Server (NTRS)

    Jadaan, Osama M.

    1998-01-01

    High temperature and long duration applications of monolithic ceramics can place their failure mode in the creep rupture regime. A previous model advanced by the authors described a methodology by which the creep rupture life of a loaded component can be predicted. That model was based on the life fraction damage accumulation rule in association with the modified Monkman-Grant creep rupture criterion. However, that model did not take into account the deteriorating state of the material due to creep damage (e.g., cavitation) as time elapsed. In addition, the material creep parameters used in that life prediction methodology, were based on uniaxial creep curves displaying primary and secondary creep behavior, with no tertiary regime. The objective of this paper is to present a creep life prediction methodology based on a modified form of the Kachanov-Rabotnov continuum damage mechanics (CDM) theory. In this theory, the uniaxial creep rate is described in terms of sum, temperature, time, and the current state of material damage. This scalar damage state parameter is basically an abstract measure of the current state of material damage due to creep deformation. The damage rate is assumed to vary with stress, temperature, time, and the current state of damage itself. Multiaxial creep and creep rupture formulations of the CDM approach are presented in this paper. Parameter estimation methodologies based on nonlinear regression analysis are also described for both, isothermal constant stress states and anisothermal variable stress conditions This creep life prediction methodology was preliminarily added to the integrated design code CARES/Creep (Ceramics Analysis and Reliability Evaluation of Structures/Creep), which is a postprocessor program to commercially available finite element analysis (FEA) packages. Two examples, showing comparisons between experimental and predicted creep lives of ceramic specimens, are used to demonstrate the viability of Ns methodology and the

  14. Modeling creep deformation of a two-phase TiAl/Ti[sub 3]Al alloy with a lamellar microstructure

    SciTech Connect

    Bartholomeusz, M.F. ); Wert, J.A. . Dept. of Materials Science and Engineering)

    1994-10-01

    A two-phase TiAl/Ti[sub 3]Al alloy with a lamellar microstructure has been previously shown to exhibit a lower minimum creep rate than the minimum creep rates of the constituent TiAl and Ti[sub 3]Al single-phase alloys. Fiducial-line experiments described in the present article demonstrate that the creep rates of the constituent phases within the two-phase TiAl/Ti[sub 3]Al lamellar alloy tested in compression are more than an order of magnitude lower than the creep rates of single-phase TiAl and Ti[sub 3]Al alloys tested in compression at the same stress and temperature. Additionally, the fiducial-line experiments show that no interfacial sliding of the phases in the TiAl/Ti[sub 3]Al lamellar alloy occurs during creep. The lower creep rate of the lamellar alloy is attributed to enhanced hardening of the constituent phases within the lamellar microstructure. A composite-strength model has been formulated to predict the creep rate of the lamellar alloy, taking into account the lower creep rates of the constituent phases within the lamellar microstructure. Application of the model yields a very good correlation between the predicted an experimentally observed minimum creep rates over moderate stress and temperature ranges.

  15. Modeling creep deformation of a two-phase TiAI/Ti3Al alloy with a lamellar microstructure

    NASA Astrophysics Data System (ADS)

    Bartholomeusz, Michael F.; Wert, John A.

    1994-10-01

    A two-phase TiAl/Ti3Al alloy with a lamellar microstructure has been previously shown to exhibit a lower minimum creep rate than the minimum creep rates of the constituent TiAl and Ti3Al single-phase alloys. Fiducial-line experiments described in the present article demonstrate that the creep rates of the constituent phases within the two-phase TiAl/Ti3Al lamellar alloy tested in compression are more than an order of magnitude lower than the creep rates of single-phase TiAl and Ti3Al alloys tested in compression at the same stress and temperature. Additionally, the fiducial-line experiments show that no interfacial sliding of the phases in the TiAl/Ti3Al lamellar alloy occurs during creep. The lower creep rate of the lamellar alloy is attributed to enhanced hardening of the constituent phases within the lamellar microstructure. A composite-strength model has been formulated to predict the creep rate of the lamellar alloy, taking into account the lower creep rates of the constituent phases within the lamellar micro-structure. Application of the model yields a very good correlation between predicted and experimentally observed minimum creep rates over moderate stress and temperature ranges.

  16. Creep-fatigue interaction at high temperature; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991

    SciTech Connect

    Haritos, G.K.; Ochoa, O.O.

    1991-01-01

    Various papers on creep-fatigue interaction at high temperature are presented. Individual topics addressed include: analysis of elevated temperature fatigue crack growth mechanisms in Alloy 718, physically based microcrack propagation laws for creep-fatigue-environment interaction, in situ SEM observation of short fatigue crack growth in Waspaloy at 700 C under cyclic and dwell conditions, evolution of creep-fatigue life prediction models, TMF design considerations in turbine airfoils of advanced turbine engines. Also discussed are: high temperature fatigue life prediction computer code based on the total strain version of strainrange partitioning, atomic theory of thermodynamics of internal variables, geometrically nonlinear analysis of interlaminar stresses in unsymmetrically laminated plates subjected to uniform thermal loading, experimental investigation of creep crack tip deformation using moire interferometry.

  17. Creep-fatigue interaction at high temperature; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991

    NASA Astrophysics Data System (ADS)

    Haritos, George K.; Ochoa, O. O.

    Various papers on creep-fatigue interaction at high temperature are presented. Individual topics addressed include: analysis of elevated temperature fatigue crack growth mechanisms in Alloy 718, physically based microcrack propagation laws for creep-fatigue-environment interaction, in situ SEM observation of short fatigue crack growth in Waspaloy at 700 C under cyclic and dwell conditions, evolution of creep-fatigue life prediction models, TMF design considerations in turbine airfoils of advanced turbine engines. Also discussed are: high temperature fatigue life prediction computer code based on the total strain version of strainrange partitioning, atomic theory of thermodynamics of internal variables, geometrically nonlinear analysis of interlaminar stresses in unsymmetrically laminated plates subjected to uniform thermal loading, experimental investigation of creep crack tip deformation using moire interferometry. (For individual items see A93-31336 to A93-31344)

  18. Constitutive Modeling of High Temperature Uniaxial Creep-Fatigue and Creep-Ratcheting Responses of Alloy 617

    SciTech Connect

    P.G. Pritchard; L.J. Carroll; T. Hassan

    2013-07-01

    Inconel Alloy 617 is a high temperature creep and corrosion resistant alloy and is a leading candidate for use in Intermediate Heat Exchangers (IHX) of the Next Generation Nuclear Plants (NGNP). The IHX of the NGNP is expected to experience operating temperatures in the range of 800 degrees - 950 degrees C, which is in the creep regime of Alloy 617. A broad set of uniaxial, low-cycle fatigue, fatigue-creep, ratcheting, and ratcheting-creep experiments are conducted in order to study the fatigue and ratcheting responses, and their interactions with the creep response at high temperatures. A unified constitutive model developed at North Carolina State University is used to simulate these experimental responses. The model is developed based on the Chaboche viscoplastic model framework. It includes cyclic hardening/softening, strain rate dependence, strain range dependence, static and dynamic recovery modeling features. For simulation of the alloy 617 responses, new techniques of model parameter determination are developed for optimized simulations. This paper compares the experimental responses and model simulations for demonstrating the strengths and shortcomings of the model.

  19. Experimental characterization of crack tip deformation fields in Alloy 718 at high temperatures

    SciTech Connect

    Liu, J.; Lyons, J.; Sutton, M.; Reynolds, A.

    1998-01-01

    A series of fracture mechanics tests were conducted at temperatures of 650 C and 704 C in air, using Inconel 719. A noncontacting measurement technique, based on computer vision and digital image correlation, was applied to directly measure surface displacements and strains prior to and during creep crack growth. For the first time, quantitative comparisons at elevated temperatures are presented between experimentally measured near-crack-tip deformation fields and theoretical linear elastic and viscoelastic fracture mechanics solutions. The results establish that linear elastic conditions dominate the near-crack-tip displacements and strains at 650 C during crack growth, and confirm that K{sub 1} is a viable continuum-based fracture parameter for creep crack growth characterization. Postmortem fractographic analyses indicate that grain boundary embrittlement leads to crack extension before a significant amount of creep occurs at this temperature. At higher temperatures, however, no crack growth was observed due to crack tip blunting and concurrent stress reduction after load application.

  20. Elevated-temperature flow strength, creep resistance and diffusion welding characteristics of Ti-gAl-2Nb-1Ta-0.8Mo

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.; Moore, T. J.

    1977-01-01

    A study of the flow strength, creep resistance and diffusion welding characteristics of the titanium alloy Ti-6Al-2Nb-1Ta-0.8Mo was conducted. Two mill-processed forms of this alloy were examined. The forged material was essentially processed above the beta transus while the rolled form was subjected to considerable work below the beta transus. Between 1150 and 1250 K, the forged material was stronger and more creep resistant than the rolled alloy. Both forms exhibit superplastic characteristics in this temperature range. Strain measurements during diffusion welding experiments at 1200 K reveal that weld interfaces have no measurable effect on the overall creep deformation. Significant deformation appears to be necessary to produce a quality diffusion weld between superplastic materials. A 'soft' interlayer inserted between faying surfaces would seemingly allow manufacture of quality diffusion welds with little overall deformation.

  1. Elevated temperature flow strength, creep resistance and diffusion welding characteristics of Ti-6Al-2Nb-1Ta-0.8Mo

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.; Moore, T. J.

    1979-01-01

    A study of the flow strength, creep resistance and diffusion welding characteristics of the titanium alloy Ti-6Al-2Nb-1Ta-0.8Mo has been conducted. Two mill-processed forms of this alloy were examined. The forged material had been processed above the beta transus (approximately 1275 K) while the rolled form had been subjected to work below the beta transus. Between 1150 and 1250 K, the forged material was stronger and more creep resistant than the rolled alloy. Both forms exhibit superplastic characteristics in this temperature range. Strain measurements during diffusion welding experiments at 1200 K reveal that weld interfaces have no measurable effect on the overall creep deformation. Significant deformation appears to be necessary to produce a quality diffusion weld between superplastic materials. A 'soft' interlayer inserted between faying surfaces would seemingly allow manufacture of quality diffusion welds with little overall deformation.

  2. In-situ scanning electron microscopy (sem) observations of the tensile and tensile-creep deformation of Titanium-8Aluminum-1mo-1v (wt.%) alloy

    NASA Astrophysics Data System (ADS)

    Ghosh Dastidar, Indraroop

    Titanium (Ti) and titanium alloys (Ti alloys) are attractive for structural applications, such as in the aerospace and automotive industries due to their high specific strength, excellent corrosion resistance and good ability to withstand elevated temperatures. To develop Ti alloys with better mechanical properties, it is necessary to comprehend the deformation behavior of available Ti alloys. Previous studies performed by another graduate student, Dr. Hongmei Li, involved investigation of the deformation behavior of commercially pure (CP) Ti, Ti-5Al-2.5Sn (wt.%), Ti-3Al-2.5V (wt.%) and Ti-6Al-4V (wt.%) alloys. The current thesis focused on investigating the deformation behavior of Ti-8Al-1Mo-1V (wt.%). In-situ tensile and tensile-creep experiments were performed at temperatures ranging from room temperature (RT) to 650OC inside a scanning electron microscope (SEM), which allowed for the observation of the surface deformation evolution. Electron Back Scattered Diffraction (EBSD) was used to identify the distribution of the active deformation systems. In this thesis efforts were made to characterize the various deformation modes of the Ti-8Al-1Mo-1V (wt.%) alloy as a function of the testing conditions (stress and temperature). It was observed that prismatic slip made up the majority of the observed slip systems during the RT tensile deformation, while basal and prismatic slip were almost equally active during the 455OC tensile deformation. Grain boundary ledges were observed during the elevated temperature tensile-creep deformation and from this observation it was suggested that grain boundary sliding was an active deformation mode. This work also involved estimating the Critical Resolved Shear Stress (CRSS) ratios of the alpha-phase deformation modes. The CRSS ratios were compared with the CRSS ratios of CP Ti and other Ti alloys. Overall, this work was intended to add more data to the scientific literature of Ti alloys in order to better comprehend their

  3. Correlation of creep rate with microstructural changes during high temperature creep

    NASA Technical Reports Server (NTRS)

    Young, C. T.; Hochella, W. A.; Lytton, J. L.

    1973-01-01

    The techniques of electron microscopy were used to examine the microstructural changes which occur during primary creep for two important types of engineering alloys: (1) alloys strengthened by solid-solution additions, and (2) dispersion-strengthened alloys. The metals chosen for study are unalloyed titanium, Ti-6Al-4V, and the cobalt-base alloy, Haynes 188. Results to date on NGR 47-004-108 show that development of prior dislocation substructure in Haynes 188 by 10% prestrain and annealing for one hour at 1800 F increases the time to reach 0.5% creep strain at 1600 F by more than an order of magnitude for creep stresses from 3 to 20 ksi. For creep at 1800 F, similar results were obtaind for stresses above 7 ksi, but the prior substructure decreases creep resistance below 7 ksi. This effect appears to be related to instability of grain structure at 1800 F in prestrained material.

  4. Effect of inclusions on strain localization during high temperature creep of marble

    NASA Astrophysics Data System (ADS)

    Rybacki, E.; Morales, L. G.; Naumann, M.; Dresen, G. H.

    2013-12-01

    The deformation of rocks in the Earth's lower crust is often localized in ductile shear zones. Strain localization in rocks deforming at high temperature and pressures may be induced by various physical, chemical, or structurally-related mechanisms. Here, we studied the initiation and propagation of localized deformation in the ductile deformation regime by high temperature deformation experiments on marble with weak or strong inclusions. As starting material we used samples of coarse-grained Carrara marble containing one or two thin artificially prepared sheets of fine-grained Solnhofen limestone or Arkansas novaculite, which act under the applied experimental conditions as soft or strong material heterogeneities, respectively. Samples were deformed in the dislocation creep regime using a Paterson-type gas deformation apparatus at 900°C temperature and confining pressures of 300-400 MPa. Torsion experiments were performed on hollow cylinder samples at a bulk shear strain rate of ≈1.9 x 10-4 s-1 to shear strains γ between 0.02 and 2.9. At low strain, twisted specimens with weak inclusions show minor strain hardening that is replaced by strain weakening at shear strains in excess of ≈0.1- 0.2. Peak shear stress at the imposed condition is about 20MPa, which is ≈8% lower than the strength of inclusion-free samples. Strain progressively localized within the weak inclusions with increasing bulk strain, approaching at γ ≈ 1 a strain ratio of ≈24 with respect to the adjacent matrix strain. This ratio is about half of the strain ratio that is expected from the creep strength contrast between pure marble and limestone at the measured bulk stress. The localization of strain extended into narrow bands in front of the inclusions, where the degree of localization decays exponentially with increasing distance from the tip of the inclusion. Microstructural analysis shows twinning, recrystallization and the development of a strong crystallographic preferred

  5. The role of interfacial dislocation networks in high temperature creep of superalloys

    NASA Technical Reports Server (NTRS)

    Gabb, T. P.; Draper, S. L.; Hull, D. R.; Mackay, R. A.; Nathal, M. V.

    1989-01-01

    The dislocation networks generated during high-temperature creep of several single-crystal nickel-based superalloys are analyzed. The networks continually evolve during creep at relatively low temperatures or eventually reach a more stable configuration at high temperatures. Specifically, the role of these networks in directional coarsening processes are studied, along with their formation kinetics, characteristics, and stability during creep. The results of this study combined with previous findings suggest that the directional coarsening process is strongly influenced by elastic strain energy. The dislocation networks formed during primary creep are found to be stable during all subsequent creep stages. Aspects of these dislocation networks are determined to be a product of both the applied creep stress and coherency strains.

  6. Generation of long time creep data on refractory alloys at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Sheffler, K. D.; Ebert, R. R.

    1971-01-01

    Ultrahigh vacuum creep tests were conducted on tantalum, tungsten, and molybdenum alloys to develop creep data and to evaluate the influence of liquid lithium exposure on the creep behavior of the tantalum alloy T-111. Test conditions were generally selected to provide 1% creep in 1000 to 10,000 hours, with test temperatures ranging from 1600 to 2912 F (1144 to 1873 K). Tests on T-111 specimens exposed to vacuum and to liquid lithium for various times and temperatures showed large reductions in creep strength for exposures in the 1800 to 1900 F (1255 to 1310 K) range. Tests on the ASTAR 811c showed a significant influence of grain size on the creep strength of this material, with larger grain size specimens being significantly stronger above the equicohesive temperature of 2000 F (1366 K).

  7. Generation of long time creep data on refractory alloys at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Sheffler, K. D.

    1971-01-01

    Ultrahigh vacuum creep tests were performed on tungsten, molybdenum, and tantalum alloys to develop design creep data and to evaluate the influence of liquid lithium exposure on the creep resistance of a tantalum alloy. Test conditions were generally selected to provide 1% creep in 1000 to 10,000 hours, with the test temperatures ranging between 1600 and 2900 F (1144 K and 1866 K). One percent creep life data from a tantalum-base T-111 alloy (Ta-8%W-2%Hf) were analyzed using a station function method to provide an improved parametric representation of the T-111 data. In addition, the minimum creep rate data from an ASTAR 811C alloy (Ta-8%W-1%Re-0.7%Hf0.025%C) were analyzed to determine the stress and temperature dependence of creep rate. Results of this analysis indicated that the activation energy for creep decreased from about 150 Kcal/mole (5130 J/mole) above 2400 F (1589 K) to about 110 Kcal/mole (3760 J/mole) below 2000 F (1361 K). This temperature range corresponds to the range where the creep mechanism changes from grain boundary sliding to intragranular creep.

  8. Application of an Uncoupled Elastic-plastic-creep Constitutive Model to Metals at High Temperature

    NASA Technical Reports Server (NTRS)

    Haisler, W. E.

    1983-01-01

    A uniaxial, uncoupled constitutive model to predict the response of thermal and rate dependent elastic-plastic material behavior is presented. The model is based on an incremental classicial plasticity theory extended to account for thermal, creep, and transient temperature conditions. Revisions to he combined hardening rule of the theory allow for better representation of cyclic phenomenon including the high rate of strain hardening upon cyclic reyield and cyclic saturation. An alternative approach is taken to model the rate dependent inelastic deformation which utilizes hysteresis loops and stress relaxation test data at various temperatures. The model is evaluated and compared to experiments which involve various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy-X.

  9. Mechanisms of High Temperature/Low Stress Creep of Ni-Based Superalloy Single Crystals

    SciTech Connect

    Michael J. Mills

    2009-03-05

    Cast nickel-based superalloys are used for blades in land-based, energy conversion and powerplant applications, as well as in aircraft gas turbines operating at temperatures up to 1100 C, where creep is one of the life-limiting factors. Creep of superalloy single crystals has been extensively studied over the last several decades. Surprisingly, only recently has work focused specifically on the dislocation mechanisms that govern high temperature and low stress creep. Nevertheless, the perpetual goal of better engine efficiency demands that the creep mechanisms operative in this regime be fully understood in order to develop alloys and microstructures with improved high temperature capability. At present, the micro-mechanisms controlling creep before and after rafting (the microstructure evolution typical of high temperature creep) has occurred have yet to be identified and modeled, particularly for [001] oriented single crystals. This crystal orientation is most interesting technologically since it exhibits the highest creep strength. The major goal of the program entitled ''Mechanisms of High Temperature/Low Stress Creep of Ni-Based Superalloy Single Crystals'' (DOE Grant DE-FG02-04ER46137) has been to elucidate these creep mechanisms in cast nickel-based superalloys. We have utilized a combination of detailed microstructure and dislocation substructure analysis combined with the development of a novel phase-field model for microstructure evolution.

  10. Implications of Microstructural Studies of the SAFOD Gouge for the Strength and Deformation Mechanisms in the Creeping Segment of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Hadizadeh, J.; Gratier, J. L.; Mittempergher, S.; Renard, F.; Richard, J.; di Toro, G.; Babaie, H. A.

    2010-12-01

    The San Andreas Fault zone (SAF) in the vicinity of the San Andreas Fault Observatory at Depth (SAFOD)in central California is characterized by an average 21 mm/year aseismic creep and strain release through repeating M<3 earthquakes. Seismic inversion studies indicate that the ruptures occur on clusters of stationary patches making up 1% or less of the total fault surface area. The existence of these so-called asperity patches, although not critical in determining the fault strength, suggests interaction of different deformation mechanisms. What are the deformation mechanisms, and how do the mechanisms couple and factor into the current strength models for the SAF? The SAFOD provides core samples and geophysical data including cores from two shear zones where the main borehole casing is deforming. The studies so far show a weak fault zone with about 200m of low-permeability damage zone without anomalous temperature or high fluid pressure (Zoback et al. EOS 2010). To answer the above questions, we studied core samples and thin sections ranging in measured depths (MD) from 3059m to 3991m including gouge from borehole casing deformation zones. The methods of study included high resolution scanning and transmission electron microscopy, cathodoluminescence imaging, X-ray fluorescence mapping, and energy dispersive X-ray spectroscopy. The microstructural and analytical data suggest that deformation is by a coupling of cataclastic flow and pressure solution accompanied by widespread alteration of feldspar to clay minerals and other neomineralizations. The clay contents of the gouge and streaks of serpentinite are not uniformly distributed, but weakness of the creeping segment is likely to be due to intrinsically low frictional strength of the fault material. This conclusion, which is based on the overall ratio of clay/non-clay constituents and the presence of talc in the actively deforming zones, is consistent with the 0.3-0.45 coefficient of friction for the drill

  11. Creep of CMSX-4 superalloy single crystals: Effects of rafting at high temperature

    SciTech Connect

    Reed, R.C.; Matan, N.; Cox, D.C.; Rist, M.A.; Rae, C.M.F.

    1999-09-29

    The creep performance of (001)-orientated CMSX-4 superalloy single crystals at temperatures beyond 1000 C is analyzed. Rafting of the {gamma}{prime} structure occurs rapidly, e.g., for the 1150 C/100 MPa tests rafting is completed within the first 10 h. At this stage and for a considerable time thereafter the creep strain rate decreases with increasing strain, implying a creep hardening effect which is absent at lower temperatures when the kinetics of rafting is less rapid. Once a critical strain {epsilon}* of (0.7 {+-} 0.3)% is reached, the creep strain increases dramatically and failure occurs within a few tens of hours. It is demonstrated that methods of interpretation which, assume a proportionality between the creep strain rate and creep strain, are unable to account for creep hardening which occurs as a consequence of rafting. A modification is proposed which accounts for the blocking of the glide/climb of {l{underscore}brace}111{r{underscore}brace}{l{underscore}angle}1{bar 1}0{r{underscore}angle} creep dislocations which occurs as the number of vertical {gamma} channels is reduced and cellular dislocation networks become stabilized. Consequently, failure must be taken to be associated with creep cavitation, which occurs predominantly around casting porosity. It is emphasized that more work is required to quantify the interaction between the various creep damage mechanisms.

  12. Nonlinear deformation and localized failure of bacterial streamers in creeping flows

    PubMed Central

    Biswas, Ishita; Ghosh, Ranajay; Sadrzadeh, Mohtada; Kumar, Aloke

    2016-01-01

    We investigate the failure of bacterial floc mediated streamers in a microfluidic device in a creeping flow regime using both experimental observations and analytical modeling. The quantification of streamer deformation and failure behavior is possible due to the use of 200 nm fluorescent polystyrene beads which firmly embed in the extracellular polymeric substance (EPS) and act as tracers. The streamers, which form soon after the commencement of flow begin to deviate from an apparently quiescent fully formed state in spite of steady background flow and limited mass accretion indicating significant mechanical nonlinearity. This nonlinear behavior shows distinct phases of deformation with mutually different characteristic times and comes to an end with a distinct localized failure of the streamer far from the walls. We investigate this deformation and failure behavior for two separate bacterial strains and develop a simplified but nonlinear analytical model describing the experimentally observed instability phenomena assuming a necking route to instability. Our model leads to a power law relation between the critical strain at failure and the fluid velocity scale exhibiting excellent qualitative and quantitative agreeing with the experimental rupture behavior. PMID:27558511

  13. Nonlinear deformation and localized failure of bacterial streamers in creeping flows.

    PubMed

    Biswas, Ishita; Ghosh, Ranajay; Sadrzadeh, Mohtada; Kumar, Aloke

    2016-01-01

    We investigate the failure of bacterial floc mediated streamers in a microfluidic device in a creeping flow regime using both experimental observations and analytical modeling. The quantification of streamer deformation and failure behavior is possible due to the use of 200 nm fluorescent polystyrene beads which firmly embed in the extracellular polymeric substance (EPS) and act as tracers. The streamers, which form soon after the commencement of flow begin to deviate from an apparently quiescent fully formed state in spite of steady background flow and limited mass accretion indicating significant mechanical nonlinearity. This nonlinear behavior shows distinct phases of deformation with mutually different characteristic times and comes to an end with a distinct localized failure of the streamer far from the walls. We investigate this deformation and failure behavior for two separate bacterial strains and develop a simplified but nonlinear analytical model describing the experimentally observed instability phenomena assuming a necking route to instability. Our model leads to a power law relation between the critical strain at failure and the fluid velocity scale exhibiting excellent qualitative and quantitative agreeing with the experimental rupture behavior. PMID:27558511

  14. Creep deformation and mechanisms in Haynes 230 at 800 °C and 900 °C

    NASA Astrophysics Data System (ADS)

    Pataky, Garrett J.; Sehitoglu, Huseyin; Maier, Hans J.

    2013-11-01

    Creep was studied in Haynes 230, a material candidate for the very high temperature reactor's intermediate heat exchanger, at 800 °C and 900 °C. This study focused on the differences between the behavior at the two elevated temperature, and using the microstructure, grain boundary serrations and triple junction strain concentrations were quantitatively identified. There was significant damage in the 900 °C samples and the creep was almost entirely tertiary. In contrast, the 800 °C sample exhibited secondary creep. Using an Arrhenius equation, the minimum creep rate exponents were found to be n ≈ 3 and n ≈ 5 for 900 °C and 800 °C, respectively. The creep mechanisms were identified as solute drag for n ≈ 3 and dislocation climb for n ≈ 5. Strain concentrations were identified at triple junctions and grain boundary serrations using high resolution digital image correlation overlaid on the microstructure. The grain boundary serrations restrict grain boundary sliding which may reduce the creep damage at triple junctions and extend the creep life of Haynes 230 at elevated temperatures.

  15. Quantitative analysis of microstructure deformation in creep fenomena of ferritic SA-213 T22 and austenitic SA-213 TP304H material

    NASA Astrophysics Data System (ADS)

    Mulyana, Cukup; Taufik, Ahmad; Gunawan, Agus Yodi; Siregar, Rustam Efendi

    2013-09-01

    The failure of critical component of fossil fired power plant that operated in creep range (high stress, high temperature and in the long term) depends on its microstructure characteristics. Ferritic low carbon steel (2.25Cr-1Mo) and Austenitic stainless alloy (18Cr-8Ni) are used as a boiler tube in the secondary superheater outlet header to deliver steam before entering the turbin. The tube failure is occurred in a form of rupture, resulting trip that disrupts the continuity of the electrical generation. The research in quantification of the microstructure deformation has been done in predicting the remaining life of the tube through interrupted accelerated creep test. For Austenitic Stainless Alloy (18Cr-8Ni), creep test was done in 550°C with the stress 424.5 MPa and for Ferritic Low Carbon Steel (2.25Cr-1Mo) in 570°C with the stress 189 MPa. The interrupted accelerated creep test was done by stopping the observation in condition 60%, 70%, 80% and 90% of remaining life, the creep test fracture was done before. Then the micro hardness test, photo micro, SEM and EDS were obtained from those samples. Refer to ASTM E122, microstructure parameters were calculated. The results indicated that there are a consistency of decreasing their grain diameters, increasing their grain size numbers, micro hardness, and the length of crack or void number per unit area with the decreasing of remaining life. While morphology of grain (stated in parameter α=LV/LH) relatively constant for austenitic. However, for ferritic the change of morphology revealed significantly. Fracture mode propagation of ferritic material is growth with voids transgranular and intergranular crack, and for austenitic material the fracture growth with intergranular creep fracture void and wedge crack. In this research, it was proposed a formulation of mathematical model for creep behavior corresponding their curve fitting resulted for the primary, secondary and tertiary in accelerated creep test. In

  16. Creep rupture analysis of a beam resting on high temperature foundation

    NASA Technical Reports Server (NTRS)

    Gu, Randy J.; Cozzarelli, Francis A.

    1988-01-01

    A simplified uniaxial strain controlled creep damage law is deduced with the use of experimental observation from a more complex strain dependent law. This creep damage law correlates the creep damage, which is interpreted as the density variation in the material, directly with the accumulated creep strain. Based on the deduced uniaxial strain controlled creep damage law, a continuum mechanical creep rupture analysis is carried out for a beam resting on a high temperature elastic (Winkler) foundation. The analysis includes the determination of the nondimensional time for initial rupture, the propagation of the rupture front with the associated thinning of the beam, and the influence of creep damage on the deflection of the beam. Creep damage starts accumulating in the beam as soon as the load is applied, and a creep rupture front develops at and propagates from the point at which the creep damage first reaches its critical value. By introducing a series of fundamental assumptions within the framework of technical Euler-Bernoulli type beam theory, a governing set of integro-differential equations is derived in terms of the nondimensional bending moment and the deflection. These governing equations are subjected to a set of interface conditions at the propagating rupture front. A numerical technique is developed to solve the governing equations together with the interface equations, and the computed results are presented and discussed in detail.

  17. Creep deformation behavior of Sn-3.5Ag solder/Cu couple at small length scales

    SciTech Connect

    Kerr, M.; Chawla, N

    2004-09-06

    In order to adequately characterize the behavior of solder balls in electronic devices, the mechanical behavior of solder joints needs to be studied at small length scales. The creep behavior of single solder ball Sn-Ag/Cu solder joints was studied in shear, at 25, 60, 95, and 130 deg. C, using a microforce testing system. A change in the creep stress exponent with increasing stress was observed and explained in terms of a threshold stress for bypass of Ag{sub 3}Sn particles by dislocations. The stress exponent was also temperature dependent, exhibiting an increase in exponent of two from lower to higher temperature. The activation energy for creep was found to be temperature dependant, correlating with self-diffusion of pure Sn at high temperatures, and dislocation core diffusion of pure Sn at lower temperatures. Normalizing the creep rate for activation energy and the temperature-dependence of shear modulus allowed for unification of the creep data. Microstructure characterization, including preliminary TEM analysis, and fractographic analysis were conducted in order to fully describe the creep behavior of the material.

  18. Creep and creep-rupture behavior of Alloy 718

    SciTech Connect

    Brinkman, C.R.; Booker, M.K.; Ding, J.L.

    1991-01-01

    Data obtained from creep and creep-rupture tests conducted on 18 heats of Alloy 718 were used to formulate models for predicting high temperature time dependent behavior of this alloy. Creep tests were conducted on specimens taken from a number of commercial product forms including plate, bar, and forgoing material that had been procured and heat treated in accordance with ASTM specifications B-670 or B-637. Data were obtained over the temperature range of 427 to 760{degree}C ad at test times to about 87,000 h. Comparisons are given between experimental data and the analytical models. The analytical models for creep-rupture included one based on lot-centering regression analysis and two based on the Minimum Commitment Method. A master'' curve approach was used to develop and equation for estimating creep deformation up to the onset of tertiary creep. 11 refs., 13 figs.

  19. High temperature deformation mechanisms of L12-containing Co-based superalloys

    NASA Astrophysics Data System (ADS)

    Titus, Michael Shaw

    Ni-based superalloys have been used as the structural material of choice for high temperature applications in gas turbine engines since the 1940s, but their operating temperature is becoming limited by their melting temperature (Tm =1300degrees C). Despite decades of research, no viable alternatives to Ni-based superalloys have been discovered and developed. However, in 2006, a ternary gamma' phase was discovered in the Co-Al-W system that enabled a new class of Co-based superalloys to be developed. These new Co-based superalloys possess a gamma-gamma' microstructure that is nearly identical to Ni-based superalloys, which enables these superalloys to achieve extraordinary high temperature mechanical properties. Furthermore, Co-based alloys possess the added benefit of exhibiting a melting temperature of at least 100degrees C higher than commercial Ni-based superalloys. Superalloys used as the structural materials in high pressure turbine blades must withstand large thermomechanical stresses imparted from the rotating disk and hot, corrosive gases present. These stresses induce time-dependent plastic deformation, which is commonly known as creep, and new superalloys must possess adequate creep resistance over a broad range of temperature in order to be used as the structural materials for high pressure turbine blades. For these reasons, this research focuses on quantifying high temperature creep properties of new gamma'-containing Co-based superalloys and identifying the high temperature creep deformation mechanisms. The high temperature creep properties of new Co- and CoNi-based alloys were found to be comparable to Ni-based superalloys with respect to minimum creep rates and creep-rupture lives at 900degrees C up to the solvus temperature of the gamma' phase. Co-based alloys exhibited a propensity for extended superlattice stacking fault formation in the gamma' precipitates resulting from dislocation shearing events. When Ni was added to the Co-based compositions

  20. Mechanisms Governing the Creep Behavior of High Temperature Alloys for Generation IV Nuclear Energy Systems

    SciTech Connect

    Vasudevan, Vijay; Carroll, Laura; Sham, Sam

    2015-04-06

    This research project, which includes collaborators from INL and ORNL, focuses on the study of alloy 617 and alloy 800H that are candidates for applications as intermediate heat exchangers in GEN IV nuclear reactors, with an emphasis on the effects of grain size, grain boundaries and second phases on the creep properties; the mechanisms of dislocation creep, diffusional creep and cavitation; the onset of tertiary creep; and theoretical modeling for long-term predictions of materials behavior and for high temperature alloy design.

  1. Time-dependent deformation at elevated temperatures in basalt from El Hierro, Stromboli and Teide volcanoes

    NASA Astrophysics Data System (ADS)

    Benson, P. M.; Fahrner, D.; Harnett, C. E.; Fazio, M.

    2014-12-01

    Time dependent deformation describes the process whereby brittle materials deform at a stress level below their short-term material strength (Ss), but over an extended time frame. Although generally well understood in engineering (where it is known as static fatigue or "creep"), knowledge of how rocks creep and fail has wide ramifications in areas as diverse as mine tunnel supports and the long term stability of critically loaded rock slopes. A particular hazard relates to the instability of volcano flanks. A large number of flank collapses are known such as Stromboli (Aeolian islands), Teide, and El Hierro (Canary Islands). Collapses on volcanic islands are especially complex as they necessarily involve the combination of active tectonics, heat, and fluids. Not only does the volcanic system generate stresses that reach close to the failure strength of the rocks involved, but when combined with active pore fluid the process of stress corrosion allows the rock mass to deform and creep at stresses far lower than Ss. Despite the obvious geological hazard that edifice failure poses, the phenomenon of creep in volcanic rocks at elevated temperatures has yet to be thoroughly investigated in a well controlled laboratory setting. We present new data using rocks taken from Stromboli, El Heirro and Teide volcanoes in order to better understand the interplay between the fundamental rock mechanics of these basalts and the effects of elevated temperature fluids (activating stress corrosion mechanisms). Experiments were conducted over short (30-60 minute) and long (8-10 hour) time scales. For this, we use the method of Heap et al., (2011) to impose a constant stress (creep) domain deformation monitored via non-contact axial displacement transducers. This is achieved via a conventional triaxial cell to impose shallow conditions of pressure (<25 MPa) and temperature (<200 °C), and equipped with a 3D laboratory seismicity array (known as acoustic emission, AE) to monitor the micro

  2. High-Temperature Creep Behavior Of Fiber-Reinforced Niobium

    NASA Technical Reports Server (NTRS)

    Petrasek, Donald W.; Titran, Robert H.

    1990-01-01

    Study conducted to determine feasibility of using composite materials in advanced space power systems, described in 22-page report. Tungsten fibers reduce creep and mass in advanced power systems. Reinforcing niobium alloys with tungsten fibers increases their resistances to creep by factors of as much as 10.

  3. Creep Deformation, Rupture Analysis, Heat Treatment and Residual Stress Measurement of Monolithic and Welded Grade 91 Steel for Power Plant Components

    NASA Astrophysics Data System (ADS)

    Shrestha, Triratna

    Modified 9Cr-1 Mo (Grade 91) steel is currently considered as a candidate material for reactor pressure vessels (RPVs) and reactor internals for the Very High Temperature Reactor (VHTR), and in fossil-fuel fired power plants at higher temperatures and stresses. The tensile creep behavior of Grade 91 steel was studied in the temperature range of 600°C to 750°C and stresses between 35 MPa and 350 MPa. Heat treatment of Grade 91 steel was studied by normalizing and tempering the steel at various temperatures and times. Moreover, Thermo-Ca1c(TM) calculation was used to predict the precipitate stability and their evolution, and construct carbon isopleths of Grade 91 steel. Residual stress distribution across gas tungsten arc welds (GTAW) in Grade 91 steel was measured by the time-of-flight neutron diffraction using the Spectrometer for Materials Research at Temperature and Stress (SMARTS) diffractometer at Lujan Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, NM, USA. Analysis of creep results yielded stress exponents of ˜9-11 in the higher stress regime and ˜1 in the lower stress regime. The creep behavior of Grade 91 steel was described by the modified Bird-Mukherjee-Dorn relation. The rate-controlling creep deformation mechanism in the high stress regime was identified as the edge dislocation climb with a stress exponent of n = 5. On the other hand, the deformation mechanism in the Newtonian viscous creep regime (n = 1) was identified as the Nabarro-Herring creep. Creep rupture data were analyzed in terms of Monkman-Grant relation and Larson-Miller parameter. Creep damage tolerance factor and stress exponent were used to identify the cause of creep damage. The fracture surface morphology of the ruptured specimens was studied by scanning electron microscopy to elucidate the failure mechanisms. Fracture mechanism map for Grade 91 steel was developed based on the available material parameters and experimental observations. The microstructural

  4. ACCEPT: a three-dimensional finite element program for large deformation elastic-plastic-creep analysis of pressurized tubes (LWBR/AWBA Development Program)

    SciTech Connect

    Hutula, D.N.; Wiancko, B.E.

    1980-03-01

    ACCEPT is a three-dimensional finite element computer program for analysis of large-deformation elastic-plastic-creep response of Zircaloy tubes subjected to temperature, surface pressures, and axial force. A twenty-mode, tri-quadratic, isoparametric element is used along with a Zircaloy materials model. A linear time-incremental procedure with residual force correction is used to solve for the time-dependent response. The program features an algorithm which automatically chooses the time step sizes to control the accuracy and numerical stability of the solution. A contact-separation capability allows modeling of interaction of reactor fuel rod cladding with fuel pellets or external supports.

  5. Fatigue and creep-fatigue deformation of several nickel-base superalloys at 650 °c

    NASA Astrophysics Data System (ADS)

    Miner, R. V.; Gayda, J.; Maier, R. D.

    1982-10-01

    Specimens of seven nickel-base superalloys for gas turbine disk application that had been failed in fatigue and creep-fatigue at 650 °C were examined by transmission electron microscopy to observe the effects of composition and microstructure on the deformation characteristics of the alloys. The alloys were Waspaloy, HIP Astroloy, H+F Astroloy, H+F René 95, IN 100, MERL 76, and NASA IIB-7. The amount of bulk deformation observed in all the alloys was low. At inelastic strain amplitudes less than about 10-3 only favorably oriented grains exhibited yielding, and the majority of those had <110> near the tensile axis. Deformation occurred on octahedral systems for all the alloys except MERL 76, which also exhibited primary cube slip. The difference in slip behavior between MERL 76 and its parent composition, IN 100, was attributed to the addition of Nb. Deformation occurred in well-defined slip bands in the alloys that contained only fine aging γ', 0.01 to 0.06 μm in size. Alloys which also contained a population of larger aging γ' particles, 0.1 to 0.3 μm, exhibited more homogeneous deformation. Deformation in the creep-fatigue cycle, which employed a 15 minute dwell at the maximum tensile strain of the cycle, was not greatly different from fatigue deformation except that a few extended faults were formed.

  6. Creep deformation of grain boundary in a highly crystalline SiC fibre.

    PubMed

    Shibayama, Tamaki; Yoshida, Yutaka; Yano, Yasuhide; Takahashi, Heishichiro

    2003-01-01

    Silicon carbide (SiC) matrix composites reinforced by SiC fibres (SiC/SiC composites) are currently being considered as alternative materials in high Ni alloys for high-temperature applications, such as aerospace components, gas-turbine energy-conversion systems and nuclear fusion reactors, because of their high specific strength and fracture toughness at elevated temperatures compared with monolithic SiC ceramics. It is important to evaluate the creep properties of SiC fibres under tensile loading in order to determine their usefulness as structural components. However, it would be hard to evaluate creep properties by monoaxial tensile properties when we have little knowledge on the microstructure of crept specimens, especially at the grain boundary. Recently, a simple fibre bend stress relaxation (BSR) test was introduced by Morscher and DiCarlo to address this problem. Interpretation of the fracture mechanism at the grain boundary is also essential to allow improvement of the mechanical properties. In this paper, effects of stress applied by BSR test on microstructural evolution in advanced SiC fibres, such as Tyranno-SA including small amounts of Al, are described and discussed along with the results of microstructure analysis on an atomic scale by using advanced microscopy. PMID:12741492

  7. High temperature inelastic deformation under uniaxial loading - Theory and experiment

    NASA Technical Reports Server (NTRS)

    Chan, K. S.; Lindholm, U. S.; Bodner, S. R.; Walker, K. P.

    1989-01-01

    The elevated-temperature uniaxial inelastic deformation behavior of an Ni-base alloy, B1900 + Hf, is investigated by performing isothermal tensile, creep, cyclic, stress relaxation, and thermomechanical fatigue tests. The range of strain rates examined is from 10 to the -7th to 100 per sec, while the test temperatures range from 25 to 1093 C. This extensive constitutive data base has been used for evaluating the unified constitutive models of Bodner and Partom (1972) and of Walker (1972) which apply for the small-strain regime. Comparison of test results with independent model predictions indicates good agreement over a broad range of loading conditions, demonstrating the applicability of the unified-constitutive-equation approach for describing the strongly nonlinear and temperature-dependent response of meals under a wide range of deformation and thermal histories. Thus the results give confidence that the unified approach is an effective and efficient approach in which complex history-dependent thermoviscoplastic flow can be represented within a single inelastic strain-rate term.

  8. Influence of deformation behavior, oxydation, and temperature on the long time cyclic stress behavior of high temperature steels

    NASA Technical Reports Server (NTRS)

    Maile, K.

    1982-01-01

    The influence of different parameters on the creep-fatigue behavior of several steel alloys was investigated. The higher the temperature the lower the crack initiation value. Pauses during the cycle reduce the damage. Oxidation reduces and protective gas increases the lifetime. Prior loading and prior deformation reduce the lifetime. Short annealing slightly affects the cycle stress behavior. The test results do not satisfactorily agree with methods of extrapolation and damage accumulation.

  9. Tensile and creep rupture properties of (16) uncoated and (2) coated engineering alloys at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Fritz, L. J.; Koster, W. P.

    1977-01-01

    Sixteen test materials were supplied by NASA-Lewis Research Center as wrought bar or cast remelt stock. The cast remelt stock was cast into test blanks with two such materials being also evaluated after Jocoat coating was applied. Mechanical properties evaluated included tensile, modulus of elasticity, Poisson's Ratio, creep properties and creep rupture strength. Tests were conducted at temperatures applicable to the service temperature of the various alloys. This range extended from room temperature to 1000 C.

  10. Parameter correlation of high-temperature creep constitutive equation for RPV metallic materials

    NASA Astrophysics Data System (ADS)

    Xie, Lin-Jun; Ren, Xin; Shen, Ming-Xue; Tu, Li-Qun

    2015-10-01

    Constant-temperature and constant-load creep tests of SA-508 stainless steel were performed at six temperatures, and the creep behavior and properties of this material were determined. Constitutive models were established based on an isothermal creep method to describe the high-temperature creep behavior of SA-508. Material parameter k, stress exponent nσ, and temperature exponent nt of the established constitutive models were determined through experimental data via numerical optimization techniques. The relationship of k, nσ, and nt was evaluated, and a new coefficient model of k-T, nσ-T, nt-T, and nt-nσ was formulated through the parameters of the isothermal creep equation. Moreover, the isothermal creep equation for this material at every temperature point from 450 °C to 1000 °C was obtained from the models. This method can serve as a reference for isothermal creep analysis and provide a way for the safety assessment of components of reactor pressure vessels.

  11. Processing, Microstructure and Creep Behavior of Mo-Si-B-Based Intermetallic Alloys for Very High Temperature Structural Applications

    SciTech Connect

    Vijay Vasudevan

    2008-03-31

    This research project is concerned with developing a fundamental understanding of the effects of processing and microstructure on the creep behavior of refractory intermetallic alloys based on the Mo-Si-B system. In the first part of this project, the compression creep behavior of a Mo-8.9Si-7.71B (in at.%) alloy, at 1100 and 1200 C was studied, whereas in the second part of the project, the constant strain rate compression behavior at 1200, 1300 and 1400 C of a nominally Mo-20Si-10B (in at.%) alloy, processed such as to yield five different {alpha}-Mo volume fractions ranging from 5 to 46%, was studied. In order to determine the deformation and damage mechanisms and rationalize the creep/high temperature deformation data and parameters, the microstructure of both undeformed and deformed samples was characterized in detail using x-ray diffraction, scanning electron microscopy (SEM) with back scattered electron imaging (BSE) and energy dispersive x-ray spectroscopy (EDS), electron back scattered diffraction (EBSD)/orientation electron microscopy in the SEM and transmission electron microscopy (TEM). The microstructure of both alloys was three-phase, being composed of {alpha}-Mo, Mo{sub 3}Si and T2-Mo{sub 5}SiB{sub 2} phases. The values of stress exponents and activation energies, and their dependence on microstructure were determined. The data suggested the operation of both dislocation as well as diffusional mechanisms, depending on alloy, test temperature, stress level and microstructure. Microstructural observations of post-crept/deformed samples indicated the presence of many voids in the {alpha}-Mo grains and few cracks in the intermetallic particles and along their interfaces with the {alpha}-Mo matrix. TEM observations revealed the presence of recrystallized {alpha}-Mo grains and sub-grain boundaries composed of dislocation arrays within the grains (in Mo-8.9Si-7.71B) or fine sub-grains with a high density of b = 1/2<111> dislocations (in Mo-20Si-10B), which

  12. Generation of long time creep data on refractory alloys at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Sheffler, K. D.; Ebert, R. R.

    1973-01-01

    Four separate studies of various aspects of the vacuum creep behavior of two tantalum alloys (T-111 and ASTAR 811C) and of pure CVD tungsten are reported. The first part of the program involved a study of the influence of high temperature pre-exposure to vacuum or to liquid lithium on the subsequent creep behavior T-111 alloy. Results of this study revealed significant effects of pre-exposure on the 1% creep life of T-111, with life reductions of about 3 orders of magnitude being observed in extreme cases. The second part of this study involved an investigation of the creep behavior of T-111 under conditions of continuously increasing stress and decreasing temperature which simulated the conditions anticipated in radioisotope capsule service. Results of this study showed that such test conditions produced a creep curve having a very unusual shape, and led to the identification of a new creep design parameter for this type of service. The third area of investigation was a study of the influence of heat treatment on the microstructure and creep behavior of ASTAR 811C. The fourth part of the program was directed toward a preliminary characterization of the 1% creep life of CVD tungsten as obtained from two different sources.

  13. Creep deformation and fracture behavior of types 316 and 316L(N) stainless steels and their weld metals

    SciTech Connect

    Sasikala, G.; Mathew, M.D.; Bhanu Sankara Rao, K.; Mannan, S.L.

    2000-04-01

    The creep properties of a nuclear-grade type 316(L) stainless steel (SS) alloyed with nitrogen (316L(N)SS) and its weld metal were studied at 873 and 923 K in the range of applied stresses from 100 to 335 MPa. The results were compared with those obtained on a nuclear-grade type 316 SS, which is lean in nitrogen. The creep rupture lives of the weld metals were found to be lower than those of the respective base metals by a factor of 5 to 10. Both the base and weld metals of 314L(N)SS exhibited better resistance to creep deformation compared to their 316SS counterparts at identical test conditions. A power-law relationship between the minimum creep rate and applied stress was found to be obeyed for both the base and weld metals. Both the weld metals generally exhibited lower rupture elongation than the respective base metals; however, at 873 K, the 316 SS base and weld metals had similar rupture elongation at identical applied stresses. Comparison of the rupture lives of the two steels to the ASME curves for the expected minimum stress to rupture for 316 Ss base and weld metals showed that, for 316L(N) SS, the specifications for maximum allowable stresses based on data for 316 SS could prove overconservative. The influence of nitrogen on the creep deformation and fracture behavior, especially in terms of its modifying the precipitation kinetics, is discussed in light of the microstructural observations. In welds containing {delta} ferrite, the kinetics of its transformation and the nature of the transformation products control the deformation and fracture behavior. The influence of nitrogen on the {delta} ferrite transformation behavior and coarsening kinetics is also discussed, on the basis of extensive characterization by metallographic techniques.

  14. Creep deformation and fracture behavior of types 316 and 316L(N) stainless steels and their weld metals

    NASA Astrophysics Data System (ADS)

    Sasikala, G.; Mannan, S. L.; Mathew, M. D.; Rao, K. Bhanu

    2000-04-01

    The creep properties of a nuclear-grade type 316(L) stainless steel (SS) alloyed with nitrogen (316L(N) SS) and its weld metal were studied at 873 and 923 K in the range of applied stresses from 100 to 335 MPa. The results were compared with those obtained on a nuclear-grade type 316 SS, which is lean in nitrogen. The creep rupture lives of the weld metals were found to be lower than those of the respective base metals by a factor of 5 to 10. Both the base and weld metals of 316L(N) SS exhibited better resistance to creep deformation compared to their 316 SS counterparts at identical test conditions. A power-law relationship between the minimum creep rate and applied stress was found to be obeyed for both the base and weld metals. Both the weld metals generally exhibited lower rupture elongation than the respective base metals; however, at 873 K, the 316 SS base and weld metals had similar rupture elongation at identical applied stresses. Comparison of the rupture lives of the two steels to the ASME curves for the expected minimum stress to rupture for 316 SS base and weld metals showed that, for 316L(N) SS, the specifications for maximum allowable stresses based on data for 316 SS could prove overconservative. The influence of nitrogen on the creep deformation and fracture behavior, especially in terms of its modifying the precipitation kinetics, is discussed in light of the microstructural observations. In welds containing δ ferrite, the kinetics of its transformation and the nature of the transformation products control the deformation and fracture behavior. The influence of nitrogen on the δ ferrite transformation behavior and coarsening kinetics is also discussed, on the basis of extensive characterization by metallographic techniques.

  15. An investigation of the deformation mechanism in grain size-sensitive Newtonian creep

    SciTech Connect

    Wang, J.N.

    2000-04-19

    Creep of polycrystalline materials at low stresses often shows a linear relationship between strain rate and stress, and an inverse dependence on grain size squared or cubed. Attribution of this behavior to diffusional creep or grain boundary sliding (GBS) has evoked much confusion and controversy in the literature. A model is proposed to unify these two creep mechanisms. The model predicts a change in dominant mechanism from diffusional creep to GBS accommodated mainly by diffusion or by GBS itself as the amount of matter moved by diffusion decreases. Corresponding to this change, the model also predicts a spectrum of creep rate with the absolute value being dependent upon the extent of diffusion accommodation. Although experimental data exhibit scattering, most of them are in very good agreement with the prediction of the GBS model. Therefore, it is suggested that the Newtonian creep behavior with grain size dependence be induced by GBS rather than by conventional diffusion creep as believed before.

  16. Theory of collective flux creep. [in high temperature superconductors

    NASA Technical Reports Server (NTRS)

    Feigel'man, M. V.; Geshkenbein, V. B.; Larkin, A. I.; Vinokur, V. M.

    1989-01-01

    The nature of flux-creep phenomena in the case of collective pinning by weak disorder is discussed. The Anderson concept of flux bundle is explored and developed. The dependence of the bundle activation barrier U on current j is studied and is shown to be of power-law type: U(j) is proportional to j exp -alpha. The values of exponent alpha for the different regimes of collective creep are found.

  17. Temperature dependence of creep compliance of highly cross-linked epoxy: A molecular simulation study

    SciTech Connect

    Khabaz, Fardin Khare, Ketan S. Khare, Rajesh

    2014-05-15

    We have used molecular dynamics (MD) simulations to study the effect of temperature on the creep compliance of neat cross-linked epoxy. Experimental studies of mechanical behavior of cross-linked epoxy in literature commonly report creep compliance values, whereas molecular simulations of these systems have primarily focused on the Young’s modulus. In this work, in order to obtain a more direct comparison between experiments and simulations, atomistically detailed models of the cross-linked epoxy are used to study their creep compliance as a function of temperature using MD simulations. The creep tests are performed by applying a constant tensile stress and monitoring the resulting strain in the system. Our results show that simulated values of creep compliance increase with an increase in both time and temperature. We believe that such calculations of the creep compliance, along with the use of time temperature superposition, hold great promise in connecting the molecular insight obtained from molecular simulation at small length- and time-scales with the experimental behavior of such materials. To the best of our knowledge, this work is the first reported effort that investigates the creep compliance behavior of cross-linked epoxy using MD simulations.

  18. High temperature tensile and creep behaviour of low pressure plasma-sprayed Ni-Co-Cr-Al-Y coating alloy

    NASA Technical Reports Server (NTRS)

    Hebsur, M. G.; Miner, R. V.

    1986-01-01

    The high temperature tensile and creep behavior of low pressure plasma-sprayed plates of a typical Ni-Co-Cr-Al-Y alloy has been studied. From room temperature to 800 K, the Ni-Co-Cr-Al-Y alloy studied has nearly a constant low ductility and a high strength. At higher temperatures, it becomes weak and highly ductile. At and above 1123 K, the behavior is highly dependent on strain rate and exhibits classic superplastic characteristics with a high ductility at intermediate strain rates and a strain rate sensitivity of about 0.5. At either higher or lower strain rates, the ductility decreases and the strain rate sensitivities are about 0.2. In the superplastic deformation range, the activation energy for creep is 120 + or - 20 kJ/mol, suggesting a diffusion-aided grain boundary sliding mechanism. Outside the superplastic range, the activation energy for creep is calculated to be 290 + or - 20 kJ/mol.

  19. Creep deformation and buttressing capacity of damaged ice shelves: theory and application to Larsen C ice shelf

    NASA Astrophysics Data System (ADS)

    Borstad, C. P.; Rignot, E.; Mouginot, J.; Schodlok, M. P.

    2013-12-01

    Around the perimeter of Antarctica, much of the ice sheet discharges to the ocean through floating ice shelves. The buttressing provided by ice shelves is critical for modulating the flux of ice into the ocean, and the presently observed thinning of ice shelves is believed to be reducing their buttressing capacity and contributing to the acceleration and thinning of the grounded ice sheet. However, relatively little attention has been paid to the role that fractures play in the ability of ice shelves to sustain and transmit buttressing stresses. Here, we present a new framework for quantifying the role that fractures play in the creep deformation and buttressing capacity of ice shelves. We apply principles of continuum damage mechanics to derive a new analytical relation for the creep of an ice shelf that accounts for the softening influence of fractures on longitudinal deformation using a state damage variable. We use this new analytical relation, combined with a temperature calculation for the ice, to partition an inverse method solution for ice shelf rigidity into independent solutions for softening damage and stabilizing backstress. Using this new approach, field and remote sensing data can be utilized to monitor the structural integrity of ice shelves, their ability to buttress the flow of ice at the grounding line, and thus their indirect contribution to ice sheet mass balance and global sea level. We apply this technique to the Larsen C ice shelf using remote sensing and Operation IceBridge data, finding damage in areas with known crevasses and rifts. Backstress is highest near the grounding line and upstream of ice rises, in agreement with patterns observed on other ice shelves. The ice in contact with the Bawden ice rise is weakened by fractures, and additional damage or thinning in this area could diminish the backstress transmitted upstream. We model the consequences for the ice shelf if it loses contact with this small ice rise, finding that flow speeds

  20. Creep deformation and buttressing capacity of damaged ice shelves: theory and application to Larsen C ice shelf

    NASA Astrophysics Data System (ADS)

    Borstad, C. P.; Rignot, E.; Mouginot, J.; Schodlok, M. P.

    2013-07-01

    Around the perimeter of Antarctica, much of the ice sheet discharges to the ocean through floating ice shelves. The buttressing provided by ice shelves is critical for modulating the flux of ice into the ocean, and the presently observed thinning of ice shelves is believed to be reducing their buttressing capacity and contributing to the acceleration and thinning of the grounded ice sheet. However, relatively little attention has been paid to the role that fractures play in the flow and stability of ice shelves and their capacity to buttress the flow of grounded ice. Here, we develop an analytical framework for describing the role that fractures play in the creep deformation and buttressing capacity of ice shelves. We apply principles of continuum damage mechanics to derive a new analytical relation for the creep of an ice shelf as a function of ice thickness, temperature, material properties, resistive backstress and damage. By combining this analytical theory with an inverse method solution for the spatial rheology of an ice shelf, both backstress and damage can be calculated. We demonstrate the applicability of this new theory using satellite remote sensing and Operation IceBridge data for the Larsen C ice shelf, finding damage associated with known crevasses and rifts. We find that increasing thickness of mélange between rift flanks correlates with decreasing damage, with some rifts deforming coherently with the ice shelf as if completely healed. We quantify the stabilizing backstress caused by ice rises and lateral confinement, finding high backstress associated with two ice rises that likely stabilize the ice front in its current configuration. Though overall the ice shelf appears stable at present, the ice in contact with the Bawden ice rise is weakened by fractures, and additional damage or thinning in this area could portend significant change for the shelf. Using this new approach, field and remote sensing data can be utilized to monitor the structural

  1. Generation of long time creep data on refractory alloys at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Sheffler, K. D.

    1970-01-01

    Creep tests were conducted on two tantalum alloys (ASTAR 811C and T-111 alloy), on a molybdenum alloy (TZM), and on CVD tungsten. The T-111 alloy 1% creep life data have been subjected to Manson's station function analysis, and the progress on this analysis is described. In another test program, the behavior of T-111 alloy with continuously varying temperatures and stresses has been studied. The results indicated that the previously described analysis predicts the observed creep behavior with reasonable accuracy. In addition to the T-111 test program, conventional 1% creep life data have been obtained for ASTAR 811C alloy. Previously observed effects of heat treatment on the creep strength of this material have been discussed and a model involving carbide strengthening primarily at the grain boundaries, rather than in a classical dispersion hardening mechanism, has been proposed to explain the observed results.

  2. Deterministic and Probabilistic Creep and Creep Rupture Enhancement to CARES/Creep: Multiaxial Creep Life Prediction of Ceramic Structures Using Continuum Damage Mechanics and the Finite Element Method

    NASA Technical Reports Server (NTRS)

    Jadaan, Osama M.; Powers, Lynn M.; Gyekenyesi, John P.

    1998-01-01

    High temperature and long duration applications of monolithic ceramics can place their failure mode in the creep rupture regime. A previous model advanced by the authors described a methodology by which the creep rupture life of a loaded component can be predicted. That model was based on the life fraction damage accumulation rule in association with the modified Monkman-Grant creep ripture criterion However, that model did not take into account the deteriorating state of the material due to creep damage (e.g., cavitation) as time elapsed. In addition, the material creep parameters used in that life prediction methodology, were based on uniaxial creep curves displaying primary and secondary creep behavior, with no tertiary regime. The objective of this paper is to present a creep life prediction methodology based on a modified form of the Kachanov-Rabotnov continuum damage mechanics (CDM) theory. In this theory, the uniaxial creep rate is described in terms of stress, temperature, time, and the current state of material damage. This scalar damage state parameter is basically an abstract measure of the current state of material damage due to creep deformation. The damage rate is assumed to vary with stress, temperature, time, and the current state of damage itself. Multiaxial creep and creep rupture formulations of the CDM approach are presented in this paper. Parameter estimation methodologies based on nonlinear regression analysis are also described for both, isothermal constant stress states and anisothermal variable stress conditions This creep life prediction methodology was preliminarily added to the integrated design code CARES/Creep (Ceramics Analysis and Reliability Evaluation of Structures/Creep), which is a postprocessor program to commercially available finite element analysis (FEA) packages. Two examples, showing comparisons between experimental and predicted creep lives of ceramic specimens, are used to demonstrate the viability of this methodology and

  3. Assessment of the deformation of the Bateman bipolar hip prosthesis inner bearing due to moisture absorption and creep.

    PubMed

    Lockie, K; Binns, M; Fisher, J; Jobbins, B

    1992-01-01

    The mechanism of inner bearing stiffness of bipolar hip prostheses has been investigated. The Ultra-high Molecular Weight Polyethylene (UHMWPE) component of the Bateman bipolar hip prosthesis has been subjected to a series of static and dynamic tests to assess water absorption and creep. Although deformation of the UHMWPE occurred, this did not produce an increased resistance to movement in the inner bearing. PMID:1572706

  4. Investigation of the rate-controlling mechanism(s) for high temperature creep and the relationship between creep and melting by use of high pressure as a variable

    SciTech Connect

    Not Available

    1991-01-01

    Using high pressure as a variable, the rate-controlling mechanism for high temperature creep and the relationship between creep and melting is investigated for silicon and nickel. An apparatus is used in which the samples are heated to melting point and subjected to 1 to 3 GigaPascal pressure. The stress behavior of the materials are then studied.

  5. Creeping Deformation by the Precise Leveling Survey at the central part of the Longitudinal valley fault, Southeast Taiwan

    NASA Astrophysics Data System (ADS)

    Matta, N.; Murase, M.; Ishiguro, S.; Ozawa, K.; Lin, J.; Chen, W.; Lin, C.

    2011-12-01

    We would like to know the distributed asperity for seismic hazard and forecast. It is closely related to slip distribution on the fault in interseismic. We focused on the accumulating process of the stress at the boundary between the creeping and the locking zone, to clear the behavior on the fault. The Longitudinal Valley Fault (LVF), 150 km long and NNE-SSW striking, passes through the eastern Taiwan, and represents the obvious surface expression of the collision boundary between the Philippine Sea plate and the Eurasian continental plate. Owing to such a high deformation rate, many earthquakes have occurred along the LVF. The 1951 earthquake sequence represents a good example. The southern of LVF segment is observed to be high speed creeping based on the creep meter and leveling survey etc. The northern of LVF segment is not observed to be creeping and are found huge earthquakes evidence by paleo-seismology study in the trench. Yuili fault is one of the active segments of the longitudinal valley faults, is located around the boundary between creeping and locking area. It is reverse fault with east dip. We established about 30km leveling route from Yuli to Changbin to detect the vertical deformation in detail. Murase et al. (2009, 2010, and 2011) established about 30 km densely leveling route from Yuli to Changbin to detect the vertical deformation across the LVF for two years. As a result, the vertical displacement is 1.7 cm in 200 m across the LVF and 2.7 cm in 1000 m, referred to the west end of our route. In addition, a synclinal deformation is detected on the hanging wall side of the fault. This result is caused by the geometry of and the slipping distribution on the fault. The deformation detected in the period from 2009 to 2010 denotes the same tendency and rate of that from 2008 to 2009. We compared to the airphotographs which are taken by Taiwanese government at different age (1978 and 2007). If the creeping on the fault has continued for 30 years, the

  6. Creep behavior of uranium carbide-based alloys

    NASA Technical Reports Server (NTRS)

    Seltzer, M. S.; Wright, T. R.; Moak, D. P.

    1975-01-01

    The present work gives the results of experiments on the influence of zirconium carbide and tungsten on the creep properties of uranium carbide. The creep behavior of high-density UC samples follows the classical time-dependence pattern of (1) an instantaneous deformation, (2) a primary creep region, and (3) a period of steady-state creep. Creep rates for unalloyed UC-1.01 and UC-1.05 are several orders of magnitude greater than those measured for carbide alloys containing a Zr-C and/or W dispersoid. The difference in creep strength between alloyed and unalloyed materials varies with temperature and applied stress.

  7. Effect of creep in titanium alloy Ti-6Al-4V at elevated temperature on aircraft design and flight test

    NASA Technical Reports Server (NTRS)

    Jenkins, J. M.

    1984-01-01

    Short-term compressive creep tests were conducted on three titanium alloy Ti-6Al-4V coupons at three different stress levels at a temperature of 714 K (825 F). The test data were compared to several creep laws developed from tensile creep tests of available literature. The short-term creep test data did not correlate well with any of the creep laws obtained from available literature. The creep laws themselves did not correlate well with each other. Short-term creep does not appear to be very predictable for titanium alloy Ti-6Al-4V. Aircraft events that result in extreme, but short-term temperature and stress excursions for this alloy should be approached cautiously. Extrapolations of test data and creep laws suggest a convergence toward predictability in the longer-term situation.

  8. Phase Transformation and Creep Behavior in Ti50Pd30Ni20 High Temperature Shape Memory Alloy in Compression

    NASA Technical Reports Server (NTRS)

    Kumar, Parikshith K.; Desai, Uri; Monroe, James; Lagoudas, Dimitris C.; Karaman, Ibrahim; Noebe, Ron; Bigelow, Glenn

    2010-01-01

    The creep behavior and the phase transformation of Ti50Pd30Ni20 High Temperature Shape Memory Alloy (HTSMA) is investigated by standard creep tests and thermomechanical tests. Ingots of the alloy are induction melted, extruded at high temperature, from which cylindrical specimens are cut and surface polished. A custom high temperature test setup is assembled to conduct the thermomechanical tests. Following preliminary monotonic tests, standard creep tests and thermally induced phase transformation tests are conducted on the specimen. The creep test results suggest that over the operating temperatures and stresses of this alloy, the microstructural mechanisms responsible for creep change. At lower stresses and temperatures, the primary creep mechanism is a mixture of dislocation glide and dislocation creep. As the stress and temperature increase, the mechanism shifts to predominantly dislocation creep. If the operational stress or temperature is raised even further, the mechanism shifts to diffusion creep. The thermally induced phase transformation tests show that actuator performance can be affected by rate independent irrecoverable strain (transformation induced plasticity + retained martensite) as well as creep. The rate of heating and cooling can adversely impact the actuators performance. While the rate independent irrecoverable strain is readily apparent early in the actuators life, viscoplastic strain continues to accumulate over the lifespan of the HTSMA. Thus, in order to get full actuation out of the HTSMA, the heating and cooling rates must be sufficiently high enough to avoid creep.

  9. 1/2 CREEP FRACTURE IN CERAMIC POLYCRYSTALS I. CREEP CAVITATION EFFECTS IN POLYCRYSTALLINE ALUMINA

    SciTech Connect

    Porter, J. R.; Blumenthal, W.; Evans, A. G.

    1980-09-01

    Fine grained polycrystalline alumina has been deformed in creep at high temperatures, to examine the evolution of cavities at grain boundaries. Cavities with equilibrium and crack-like morphologies have been observed, distributed non-uniformly throughout the material. The role of cavities during creep has been described. A transition from equilibrium to crack-like morphology has been observed and correlated with a model based on the influence of the surface to boundary diffusivity ratio and the local tensile stress. The contribution of cavitation to the creep rate and total creep strain has been analyzed and excluded as the principal cause of the observed non-linear creep rate,

  10. The effect of environment on the creep deformation of ultra-high purity nickel-chromium-iron alloys at 360 degrees Celcius

    NASA Astrophysics Data System (ADS)

    Paraventi, Denise Jean

    2000-10-01

    Steam generators in pressurized water nuclear power plants have experienced significant problems with intergranular stress corrosion cracking (IGSCC) on the inner diameter of steam generator tubing for over 25 years. In the course of research to understand IGSCC, it has been shown that creep deformation may play a significant role in the cracking of commercial Alloy 600 (Ni-16Cr-9Fe-0.03C). The primary water environment can cause decreases in creep resistance (i.e., faster creep rates, shorter time to failure, and higher creep strains). During corrosion under the conditions of interest, both hydrogen reduction and metal dissolution occur. One or both may contribute to the enhancement of creep. The purpose of this work was to isolate the mechanism by which the water environment causes the creep deformation to increase. Activation area and activation enthalpy for glide were measured in argon and primary water on high purity Ni-16Cr-9Fe alloys. The results indicated that the activation area was reduced by primary water, consistent with a hydrogen enhanced plasticity mechanism for enhanced creep. The stress dependence of creep was also examined in argon and primary water. The results indicated that the internal stress of the alloy is reduced by the primary water environment. Lower internal stress is consistent with both a hydrogen model as well as a vacancy-aided climb model for enhanced creep. To isolate the effect of hydrogen on the creep of the alloy, experiments were conducted in a dissociated hydrogen environment. The results indicated that hydrogen would only increase the steady state creep rate if present before loading of the samples. However, if the sample was already in steady state creep and hydrogen introduced, a transient in the creep strain was observed. The creep rate returned to the original steady state rate in a short time. The results indicate that while hydrogen does affect the steady state creep to an extent, hydrogen cannot completely account for

  11. Creep strength and microstructure of F82H steels near tempering temperature

    NASA Astrophysics Data System (ADS)

    Shinozuka, K.; Esaka, H.; Sakasegawa, H.; Tanigawa, H.

    2015-09-01

    Creep rupture tests near the tempering temperature were performed, and the creep behavior at high temperatures and the structures of fracture specimens were investigated. Three kinds of F82H test specimens were used: IEA-heat, mod.3, and BA07. The time-to-rupture of the BA07 specimens was the longest under all the test conditions. This was because the minimum creep rates of BA07 were smallest, and a large quantity of fine precipitates of MX from the ESR treatment were considered to be effective in providing creep resistance. Although mod.3 specimens showed a high creep resistance under high stress, the time-to-rupture of mod.3 and IEA-heat were almost the same at low stress. This was because the fine tempered martensitic structure was weakened by being subjected to a high temperature for a long period. Therefore, it is considered that a large quantity of fine MX precipitates are effective for creep resistance near the tempering temperature.

  12. Low Temperature Creep of a Titanium Alloy Ti-6Al-2Cb-1Ta-0.8Mo

    NASA Technical Reports Server (NTRS)

    Chu, H. P.

    1997-01-01

    This paper presents a methodology for the analysis of low temperature creep of titanium alloys in order to establish design limitations due to the effect of creep. The creep data on a titanium Ti-6Al-2Cb-1Ta-0.8Mo are used in the analysis. A creep equation is formulated to determine the allowable stresses so that creep at ambient temperatures can be kept within an acceptable limit during the service life of engineering structures or instruments. Microcreep which is important to design of precision instruments is included in the discussion also.

  13. Effects of cold rolling deformation on microstructure, hardness, and creep behavior of high nitrogen austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Sun, Shi-Cheng; Sun, Gui-Xun; Jiang, Zhong-Hao; Ji, Chang-Tao; Liu, Jia-An; Lian, Jian-She

    2014-02-01

    Effects of cold rolling deformation on the microstructure, hardness, and creep behavior of high nitrogen austenitic stainless steel (HNASS) are investigated. Microstructure characterization shows that 70% cold rolling deformation results in significant refinement of the microstructure of this steel, with its average twin thickness reducing from 6.4 μm to 14 nm. Nanoindentation tests at different strain rates demonstrate that the hardness of the steel with nano-scale twins (nt-HNASS) is about 2 times as high as that of steel with micro-scale twins (mt-HNASS). The hardness of nt-HNASS exhibits a pronounced strain rate dependence with a strain rate sensitivity (m value) of 0.0319, which is far higher than that of mt-HNASS (m = 0.0029). nt-HNASS shows more significant load plateaus and a higher creep rate than mt-HNASS. Analysis reveals that higher hardness and larger m value of nt-HNASS arise from stronger strain hardening role, which is caused by the higher storage rate of dislocations and the interactions between dislocations and high density twins. The more significant load plateaus and higher creep rates of nt-HNASS are due to the rapid relaxation of the dislocation structures generated during loading.

  14. Creep of dry clinopyroxene aggregates

    NASA Astrophysics Data System (ADS)

    Bystricky, Misha; Mackwell, Stephen

    2001-01-01

    We have determined diffusional and dislocation creep rheologies for clinopyroxenite Ca1.0Mg0.8Fe0.2Si2O6 under dry conditions by deforming natural and hot-pressed samples at confining pressures of 300-430 MPa and temperatures of 1100°-1250°C with the oxygen fugacity buffered by either nickel-nickel oxide or iron-wüstite powders. The coarse-grained natural Sleaford Bay clinopyroxenite yielded a stress exponent of n = 4.7 ± 0.2 and an activation energy for creep of Q = 760 ± 40 kJ mol-1, consistent with deformation in the dislocation creep regime. The strength of the natural clinopyroxenite is consistent with previous high-temperature measurements of dislocation creep behavior of Sleaford Bay clinopyroxenite by Kirby and Kronenberg [1984] and Boland and Tullis [1986]. Fine-grained clinopyroxenite was prepared from ground powders of the natural clinopyroxenite. Hot-pressed samples were deformed under similar conditions to the natural samples. Mixed-mode deformation behavior was observed, with diffusional creep (n = 1) at lower differential stresses and dislocation creep (with n and Q similar to those of the natural samples) at higher differential stresses. Within the dislocation creep field the predried hot-pressed samples generally yielded creep rates that were about an order of magnitude faster than the natural samples. Thus, even at the highest differential stresses, a component of strain accommodation by grain boundary diffusion was present in the hot-pressed samples. Optical and electron microscope investigations of the deformation microstructures of the natural and hot-pressed samples show evidence for mechanical twinning and activation of dislocation slip systems. When extrapolated to geological conditions expected in the deep crust and upper mantle on Earth and other terrestrial planets, the strength of dry single-phase clinopyroxene aggregates is very high, exceeding that of dry olivine-rich rocks.

  15. Creep-fatigue interaction in aircraft gas turbine components by simulation and testing at scaled temperatures

    NASA Astrophysics Data System (ADS)

    Sabour, Mohammad Hossein

    Advanced gas turbine engines, which use hot section airfoil cooling, present a wide range of design problems. The frequencies of applied loads and the natural frequencies of the blade also are important since they have significant effects on failure of the component due to fatigue phenomenon. Due to high temperature environment the thermal creep and fatigue are quite severe. One-dimensional creep model, using ANSYS has been formulated in order to predict the creep life of a gas turbine engine blade. Innovative mathematical models for the prediction of the operating life of aircraft components, specifically gas turbine blades, which are subjected to creep-fatigue at high temperatures, are proposed. The components are modeled by FEM, mathematically, and using similitude principles. Three models have been suggested and evaluated numerically and experimentally. Using FEM method for natural frequencies causes phenomena such as curve veering which is studied in more detail. The simulation studies on the life-limiting modes of failure, as well as estimating the expected lifetime of the blade, using the proposed models have been carried out. Although the scale model approach has been used for quite some time, the thermal scaling has been used in this study for the first time. The only thermal studies in literature using scaling for structures is by NASA in which materials of both the prototype and the model are the same, but in the present study materials also are different. The finite element method is employed to model the structure. Because of stress redistribution due to the creep process, it is necessary to include a full inelastic creep step in the finite element formulation. Otherwise over-conservative creep life predictions will be estimated if only the initial elastic stresses are considered. The experimental investigations are carried out in order to validate the models. The main contributions in the thesis are: (1) Using similitude theory for life prediction of

  16. Static tensile and tensile creep testing of four boron nitride coated ceramic fibers at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Coguill, Scott L.; Adams, Donald F.; Zimmerman, Richard S.

    1989-01-01

    Six types of uncoated ceramic fibers were static tensile and tensile creep tested at various elevated temperatures. Three types of boron nitride coated fibers were also tested. Room temperature static tensile tests were initially performed on all fibers, at gage lengths of 1, 2, and 4 inches, to determine the magnitude of end effects from the gripping system used. Tests at one elevated temperature, at gage lengths of 8 and 10 inches, were also conducted, to determine end effects at elevated temperatures. Fiber cross sectional shapes and areas were determined using scanning electron microscopy. Creep testing was typically performed for 4 hours, in an air atmosphere.

  17. Static tensile and tensile creep testing of five ceramic fibers at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Zimmerman, Richard S.; Adams, Donald F.

    1989-01-01

    Static tensile and tensile creep testing of five ceramic fibers at elevated temperature was performed. J.P. Stevens, Co., Astroquartz 9288 glass fiber; Nippon Carbon, Ltd., (Dow Corning) nicalon NLM-102 silicon carbide fiber; and 3M Company Nextel 312, 380, and 480 alumina/silica/boria fibers were supplied in unsized tows. Single fibers were separated from the tows and tested in static tension and tensile creep. Elevated test temperatures ranged from 400 C to 1300 C and varied for each fiber. Room temperature static tension was also performed. Computer software was written to reduce all single fiber test data into engineering constants using ASTM Standard Test Method D3379-75 as a reference. A high temperature furnace was designed and built to perform the single fiber elevated temperature testing up to 1300 C. A computerized single fiber creep apparatus was designed and constructed to perform four fiber creep tests simultaneously at temperatures up to 1300 C. Computer software was written to acquire and reduce all creep data.

  18. Static tensile and tensile creep testing of five ceramic fibers at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Zimmerman, Richard S.; Adams, Donald F.

    1988-01-01

    Static tensile and tensile creep testing of five ceramic fibers at elevated temperature was performed. J.P. Stevens, Co., Astroquartz 9288 glass fiber, Nippon Carbon, Ltd., (Dow Corning) Nicalon NLM-102 silicon carbide fiber, and 3M Company Nextel 312, 380, and 480 alumina/silica/boria fibers were supplied in unsized tows. Single fibers were separated from the tows and tested in static tension and tensile creep. Elevated test temperatures ranged from 400 to 1300 C and varied for each fiber. Room temperature static tension was also performed. Computer software was written to reduce all single fiber test data into engineering constants using ASTM Standard Test Method D3379-75 as a reference. A high temperature furnace was designed and built to perform the single fiber elevated temperature testing up to 1300 C. A computerized single fiber creep apparatus was designed and constructed to perform four fiber creep tests simultaneously at temperatures up to 1300 C. Computer software was written to acquire and reduce all creep data.

  19. Creep Mechanisms of a Ni-Co-Based-Wrought Superalloy with Low Stacking Fault Energy

    NASA Astrophysics Data System (ADS)

    Tian, Chenggang; Xu, Ling; Cui, Chuanyong; Sun, Xiaofeng

    2015-10-01

    In order to study the influences of stress and temperature on the creep deformation mechanisms of a newly developed Ni-Co-based superalloy with low stacking fault energy, creep experiments were carried out under a stress range of 345 to 840 MPa and a temperature range of 923 K to 1088 K (650 °C to 815 °C). The mechanisms operated under the various creep conditions were identified and the reasons for their transformation were well discussed. A deformation mechanism map under different creep conditions was summarized, which provides a qualitative representation of the operative creep mechanisms as a function of stress and temperature.

  20. Irradiation creep in structural materials at ITER operating conditions

    SciTech Connect

    Grossbeck, M.L.

    1994-09-01

    Irradiation creep is plastic deformation of a material under the influence of irradiation and stress. Below the regime of thermal creep, there remains a deformation mechanism under irradiation that is weakly temperature dependent and clearly different from thermal creep. This is irradiation creep. Both stress and irradiation are required for irradiation creep. Irradiation creep studies for applications in the past focused mostly on liquid metal fast breeder reactors where temperatures are usually above 400{degrees}C. Fusion reactors, especially nearterm devices such as the ITER will have components operating at temperatures as low as 100{degrees}C exposed to high neutron fluxes. Theories of irradiation creep based on steady-state point defect concentrations do not predict significant irradiation creep deformation at these temperatures; however, data from research reactors show that irradiation creep strains at 60{degrees}C are as high or higher than at temperatures above 300{degrees}C for austenitic stainless steels. Irradiation creep of nickel has also been observed at cryogenic temperatures.

  1. Elevated-temperature tensile and creep properties of several ferritic stainless steels

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.

    1977-01-01

    The elevated-temperature mechanical properties of several ferritic stainless steels were determined. The alloys evaluated included Armco 18SR, GE 1541, and NASA-18T-A. Tensile and creep strength properties at 1073 and 1273 K and residual room temperature tensile properties after creep testing were measured. In addition, 1273 K tensile and creep tests and residual property testing were conducted with Armco 18SR and GE 1541 which were exposed for 200 hours to a severe oxidizing environment in automotive thermal reactors. Aside from the residual tensile properties for Armco 18SR, prior exposure did not affect the mechanical properties of either alloy. The 1273 K creep strength parallel to the sheet-rolling direction was similar for all three alloys. At 1073 K, NASA-18T-A had better creep strength than either Armco 18SR or GE 1541. NASA-18T-A possesses better residual properties after creep testing than either Armco 18SR or Ge 1541.

  2. High temperature deformation behavior of Inconel 718 at temperatures reaching into the mushy zone

    NASA Astrophysics Data System (ADS)

    Lewandowski, Michael Stanley

    2000-10-01

    The mechanical response of Inconel 718 with various microstructures (cast directionally-solidified, cast random dendritic, and equiaxed non-dendritic) in the solid and semi-solid state has been characterized. The activation energy for plastic flow in the solid phase was in good agreement with the activation energies for self diffusion and creep in pure nickel and pure iron. When the dendrites were aligned along the compression axis, the directionally solidified materials exhibited a similar activation energy for plastic flow, even at temperatures within the mushy zone. However, in samples containing either the random dendritic or equiaxed non-dendritic microstructures in the semi-solid state, the deformation exhibited a greater dependence on temperature. A simple analysis indicates that this greater temperature dependence is simply a consequence of the transition from plastic flow in the solid to viscous flow in the liquid as the fraction liquid increases (i.e., lubricated flow of the grains due to intergranular liquid in the mushy zone). The deformation behavior is compared against a number of investigations from the literature and a general constitutive equation relating peak now stress versus temperature compensated strain rate is presented. The temperature compensated strain rate is often termed the Zener-Holloman parameter, Z=ėexp (QRT) , where ė is the strain rate, T is the temperature, R is the gas constant, and Q is the activation energy for plastic flow. The results obtained in this investigation for solid state deformation were in good agreement with published literature values and extended the experimental range to higher temperatures and lower strain rates.

  3. Preliminary study of creep thresholds and thermomechanical response in Haynes 188 at temperatures in the range 649 to 871 C

    NASA Technical Reports Server (NTRS)

    Ellis, J. R.; Bartolotta, P. A.; Mladsi, S. W.

    1987-01-01

    The following conclusions were drawn from this study of creep thresholds and thermomechanical response: (1) creep threshold can be determined using the latest electrohydraulic test equipment, providing that test durations are short and relatively large accumulations of creep strain are used in defining the threshold; (2) significant creep strains were measured under monotonic loading as stress levels as low as 4 ksi at temperatures predicted for solar receiver service; and (3) the material exhibited creep ratchetting during simulated service cycles, a result not predicted by analysis using current constitutive models for Haynes 188.

  4. The Creep of Single Crystals of Aluminum

    NASA Technical Reports Server (NTRS)

    Johnson, R D; Shober, F R; Schwope, A D

    1953-01-01

    The creep of single crystals of high-purity aluminum was investigated in the range of temperatures from room temperature to 400 F and at resolved-shear-stress levels of 200, 300, and 400 psi. The tests were designed in an attempt to produce data regarding the relation between the rate of strain and the mechanism of deformation. The creep data are analyzed in terms of shear strain rate and the results are discussed with regard to existing creep theories. Stress-strain curves were determined for the crystals in tinsel and constant-load-rate tests in the same temperature range to supplement the study of plastic deformation by creep with information regarding the part played by crystal orientation, differences in strain markings, and other variables in plastic deformation.

  5. Temperature effects on the strainrange partitioning approach for creep-fatigue analysis.

    NASA Technical Reports Server (NTRS)

    Halford, G. R.; Hirschberg, M. H.; Manson, S. S.

    1972-01-01

    Examination is made of the influence of temperature on the strain-range partitioning approach to creep-fatigue. Results for 2.5Cr-1Mo steel and Type 316 stainless steel show the four partitioned strain range-life relationships to be temperature insensitive to within a factor of two on cyclic life. Monotonic creep and tensile ductilities were also found to be temperature insensitive to within a factor of two. The approach provides bounds on cyclic life that can be readily established for any type of inelastic strain cycle.

  6. The influence of cavitation damage upon high temperature creep under stationary and non-stationary loading conditions. Part III: Creep at steady increasing load and true stress

    NASA Astrophysics Data System (ADS)

    Boček, M.; Hoffmann, M.

    1984-11-01

    In this paper for ideally plastic materials the influence of high temperature cavitation damage upon creep at steady increasing loads is investigated. The damage function A(t) enters a constitutive equation for plastíc flow through an effective stress σ e. For given loading conditions the latter is derived from the solution of Hart's tensile test equation. In the present paper the case of time linear increase in load ( F = constant) and in true stress ( /.s = constant) is investigated. The creep equations for cavitating as well as for non-cavitating materials are derived and the volume change during creep at /.F = constant are calculated.

  7. Investigation of the Compressive Strength and Creep Lifetime of 2024-T3 Aluminum-Alloy Plates at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Mathauser, Eldon E; Deveikis, William D

    1957-01-01

    The results of elevated-temperature compressive strength and creep tests of 2024-t3 (formerly 24s-t3) aluminum alloy plates supported in v-grooves are presented. The strength-test results indicate that a relation previously developed for predicting plate compressive strength for plates of all materials at room temperature is also satisfactory for determining elevated-temperature strength. Creep-lifetime results are presented for plates in the form of master creep-lifetime curves by using a time-temperature parameter that is convenient for summarizing tensile creep-rupture data. A comparison is made between tensile and compressive creep lifetime for the plates and a method that made use of isochronous stress-strain curves for predicting plate-creep failure stresses is investigated.

  8. Fiber creep rate and high-temperature properties of SiC/SiC composites

    SciTech Connect

    Lewinsohn, C.A.; Jones, R.H.; Youngblood, G.E.; Henager, C.H. Jr.

    1998-03-01

    Results of studies aimed at relating the fiber creep rate to the subcritical crack growth rate and fracture properties of SiC/SiC composites have demonstrated that the crack growth rate in a bulk composite is controlled by the fiber creep rate. This result was demonstrated for Nicalon-CG and Hi-Nicalon fiber reinforced material where a 50--75 c shift in the creep strength of the fiber resulted in a similar shift in the crack growth rate of the composite. Irradiation enhanced creep of SiC fibers and matrix must also be considered in the performance assessment of SiC/SiC composites. The shape of the displacement versus time curve for composites containing Hi-Nicalon fibers were similar to those of the previously tested materials, containing Ceramic-grade fibers, that exhibited subcritical crack growth controlled by time-dependent relaxation of the fiber-bridging stresses due to fiber creep. The crack velocity in the CG-C composites at 1100 C in argon was very close to that of the Hi-C materials at 1150--1175 C, this roughly corresponds to the temperature differential shown by DiCarlo et al. to obtain the same relaxation in 1 hour bend stress relaxation (BSR) tests in the two fibers. This supports the hypothesis that subcritical crack growth in SiC/SiC composites is controlled by fiber creep.

  9. Damage Susceptibility of Grain Boundaries in HT9 Steel Subjected to High-Temperature Creep

    NASA Astrophysics Data System (ADS)

    Leng, Zhe; Field, David P.

    2012-10-01

    HT9 steel is an attractive ferritic/martensitic steel that is used in components of nuclear and fossil power plants because of its high strength and good swelling resistance. Specific phenomena (such as segregation, voiding, cracking, etc.) are prevalent along grain boundaries since these interfaces act as efficient sources for vacancies. The accumulation of vacancies in grain boundaries may result in intergranular fracture. In this study, HT9 steel was subjected to creep tests at elevated temperature (about 0.5 T m) and two different creep conditions (where creep lifetimes were about 100 and about 1000 hours, respectively). The grain boundaries in HT9 steel after creep tests were studied by the use of scanning electron microscopy in order to establish the relationship between the grain boundary structure and creep damage. Images and data obtained using electron backscatter diffraction reveal a high susceptibility of high-angle boundaries to creep cavitation, as expected. In addition, the Σ3 boundaries are also susceptible to damage under these conditions at a similar or even higher rate as compared with random high-angle boundaries.

  10. Effect of unloading time on interrupted creep in copper

    SciTech Connect

    Chandler, H.D. . School of Mechanical Engineering)

    1994-06-01

    The effect of unloading time on the interrupted creep behavior of polycrystalline copper specimens was investigated over the temperature range 298--773 K. Up to 553 K, cyclic creep acceleration could be explained in terms of deformation and hardening using a dislocation glide model with recovery during unloading being due to dislocation climb. At higher temperatures, recrystallization effects probably influence behavior.

  11. Irradiation creep of nano-powder sintered silicon carbide at low neutron fluences

    SciTech Connect

    Koyanagi, Takaaki; Shimoda, Kazuya; Kondo, Sosuke; Hinoki, Tatsuya; Ozawa, Kazumi; Katoh, Yutai

    2014-12-01

    The irradiation creep behavior of nano-powder sintered silicon carbide was investigated using the bend stress relaxation method under neutron irradiation up to 1.9 dpa. The creep deformation was observed at all temperatures ranging from 380 to 1180 °C mainly from the irradiation creep but with the increasing contributions from the thermal creep at higher temperatures. Microstructural observation and data analysis were performed.

  12. Low Cycle Fatigue and Creep-Fatigue Behavior of Alloy 617 at High Temperature

    SciTech Connect

    Cabet, Celine; Carroll, Laura; Wright, Richard

    2013-10-01

    Alloy 617 is the leading candidate material for an intermediate heat exchanger (IHX) application of the Very High Temperature Nuclear Reactor (VHTR), expected to have an outlet temperature as high as 950 degrees C. Acceptance of Alloy 617 in Section III of the ASME Code for nuclear construction requires a detailed understanding of the creep-fatigue behavior. Initial creep-fatigue work on Alloy 617 suggests a more dominant role of environment with increasing temperature and/or hold times evidenced through changes in creep-fatigue crack growth mechanism/s and failure life. Continuous cycle fatigue and creep-fatigue testing of Alloy 617 was conducted at 950 degrees C and 0.3% and 0.6% total strain in air to simulate damage modes expected in a VHTR application. Continuous cycle specimens exhibited transgranular cracking. Intergranular cracking was observed in the creep-fatigue specimens, although evidence of grain boundary cavitation was not observed. Despite the absence of grain boundary cavitation to accelerate crack propagation, the addition of a hold time at peak tensile strain was detrimental to cycle life. This suggests that creepfatigue interaction may occur by a different mechanism or that the environment may be partially responsible for accelerating failure.

  13. High temperature deformation behavior of a fine-grained tetragonal zirconia

    SciTech Connect

    Morita, K.; Hiraga, K.

    1999-12-31

    The stress exponent, n, defined in the following creep equation has often been regarded as a primary parameter to characterize superplastic deformation in fine-grained tetragonal zirconia containing 2.5 {approximately} 4 mol% yttria (Y-TZP): {var_epsilon} = A{sigma}{sup n}/d{sup p} where {var_epsilon} is the strain rate, {sigma} is the stress, d is the grain size, n is the stress exponent, p is the grain size exponent and A is a material constant. Recent studies have noted that the stress exponents of high-purity Y-TZP can be divided into two categories: n {approximately} 3 at low stresses and n {approximately} 2 at high stresses, where the stress dividing the deformation regions depends on both temperature and grain size. To argue the origins of such regions and relating mechanisms, however, some additional examination seems to be necessary for confirming that the regions characterized with n {approximately} 2 and {approximately} 3 are the genuine ones. This is because experimental limitations have tended to prevent the examination of deformation behavior by Eq. (1) in a strict sense. For example, the n-values have been derived from the overall strain rates that may indispensably include the effects of deformation around the grips of tensile specimens or those of constrained deformation near both sides of compression specimens. Furthermore, the data were obtained under an assumption that the effects of grain growth on the strain rate is negligible in Y-TZP. There seems to be rather little assurance, however, that these situations did not affect the evaluation of the stress exponent. From this point of view, the present study was conducted (1) to examine the effects of grain growth and some other experimental factors on creep behavior and (2) to evaluate the stress exponent from creep strain-rate curves corrected for both instantaneous stress and strain in a high purity Y-TZP.

  14. Temperature dependence of optically induced cell deformations

    NASA Astrophysics Data System (ADS)

    Fritsch, Anatol; Kiessling, Tobias R.; Stange, Roland; Kaes, Josef A.

    2012-02-01

    The mechanical properties of any material change with temperature, hence this must be true for cellular material. In biology many functions are known to undergo modulations with temperature, like myosin motor activity, mechanical properties of actin filament solutions, CO2 uptake of cultured cells or sex determination of several species. As mechanical properties of living cells are considered to play an important role in many cell functions it is surprising that only little is known on how the rheology of single cells is affected by temperature. We report the systematic temperature dependence of single cell deformations in Optical Stretcher (OS) measurements. The temperature is changed on a scale of about 20 minutes up to hours and compared to defined temperature shocks in the range of milliseconds. Thereby, a strong temperature dependence of the mechanics of single suspended cells is revealed. We conclude that the observable differences arise rather from viscosity changes of the cytosol than from structural changes of the cytoskeleton. These findings have implications for the interpretation of many rheological measurements, especially for laser based approaches in biological studies.

  15. Optimization of High Temperature Hoop Creep Response in ODS-Fe3Al Tubes

    SciTech Connect

    Kad, B.K.; Heatherington, J.H.; McKamey, C.; Wright, I.; Sikka, V.; Judkins, R.

    2003-04-22

    Oxide dispersion strengthened (ODS) Fe3Al alloys are currently being developed for heat-exchanger tubes for eventual use at operating temperatures of up to 1100 C in the power generation industry. The development challenges include (a) efforts to produce thin walled ODS-Fe3Al tubes, employing powder extrusion methodologies, with (b) adequate increased strength for service at operating temperatures to (c) mitigate creep failures by enhancing the as-processed grain size. A detailed and comprehensive research and development methodology is prescribed to produce ODS-Fe3Al thin walled tubes. Current single step extrusion consolidation methodologies typically yield 8ft. lengths of 1-3/8 inch diameter, 1/8 inch wall thickness ODS-Fe3Al tubes. The process parameters for such consolidation methodologies have been prescribed and evaluated as being routinely reproducible. Recrystallization treatments at 1200 C produce elongated grains (with their long axis parallel to the extrusion axis), typically 200-2000 {micro}m in diameter, and several millimeters long. The dispersion distribution is unaltered on a micro scale by recrystallization, but the high aspect ratio grain shape typically obtained limits grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloys requires an understanding and manipulating the factors that control grain alignment and recrystallization behavior. Current efforts are focused on examining the processing dependent longitudinal vs. transverse creep anisotropy, and exploring post-extrusion methods to improve hoop creep response in ODS-Fe3Al alloy tubes. In this report we examine the mechanisms of hoop creep failure and describe our efforts to improve creep performance via variations in thermal-mechanical treatments.

  16. Low-temperature irradiation creep of fusion reactor structural materials*1

    NASA Astrophysics Data System (ADS)

    Grossbeck, M. L.; Mansur, L. K.

    1991-03-01

    Irradiation creep has been investigated in the Oak Ridge Research Reactor in an assembly spectrally tailored to achieve a He : dpa ratio of 12-14:1 appm/dpa in austenitic stainless steels. Temperatures of 60-400°C were investigated to address the requirements of near term fusion devices. It was found that austenitic alloys, especially PCA, have higher creep rates at 60°C than at 330 and 400°C. Since this phenomenon could not be explained by existing theoretical models, a new mechanism was proposed and a corresponding theoretical model was developed. Since vacancy migration times can be a few orders of magnitude longer than the irradiation times in this temperature regime, the immobile vacancies do not cancel climb produced by mobile interstitials absorbed at dislocations. The result is a high climb rate independent of stress-induced preferred absorption (SIPA) mechanisms. Preliminary calculations indicate that this mechanism coupled with preferred-absorption-driven glide at higher temperatures predicts a high creep rate at low temperatures and a weak temperature dependence of irradiation creep over the entire temperature range investigated.

  17. Experimental Deformation of Olivine Single Crystals at Mantle Pressures and Temperatures

    SciTech Connect

    Raterron, P.; Amiguet, E; Chen, J; Li, L; Cordier, P

    2008-01-01

    Deformation experiments were carried out in a deformation-DIA high-pressure apparatus (D-DIA) on oriented San Carlos olivine single crystals, at pressure (P) ranging from 3.5 to 8.5 GPa, temperature (T) from 1373 to 1673 K, and in poor water condition. Oxygen fugacity (fO2) was maintained within the olivine stability field and contact with enstatite powder ensured an orthopyroxene activity aopx = 1. Two compression directions were tested, promoting either [1 0 0] slip alone or [0 0 1] slip alone in (0 1 0) crystallographic plane, here called, respectively, a-slip and c-slip. Constant applied stress (s) and specimen strain rates ({bar {var_epsilon}}) were monitored in situ using time-resolved X-ray synchrotron diffraction and radiography, respectively. Transmission electron microscopy (TEM) investigation of run products revealed that dislocation creep was responsible for sample deformation. Comparison of the obtained high-P deformation data with the data obtained at room-P by Bai et al. [Bai, Q., Mackwell, S.L., Kohlstedt D.L., 1991, High-temperature creep of olivine single crystals. 1. Mechanical results for buffered samples, Journal of Geophysical Research, 96, 2441-2463] - on identical materials deformed at comparable T-sefO2-aopx conditions - allowed quantifying the P effect on a-slip and c-slip rheological laws. A slip transition with increasing pressure, from dominant a-slip to dominant c-slip, is documented. a-slip appears sensitive to pressure, which translates into the high activation volume V*{sub a} = 12 {+-} 4 cm{sup 3}/mol in the corresponding rheological law, while pressure has little effect on c-slip with V*{sub c} = 3 {+-} 4 cm{sup 3}/mol. These results may explain the discrepancy between olivine low-P and high-P deformation data which has been debated in the literature for more than a decade.

  18. Nanogranular origin of concrete creep

    PubMed Central

    Vandamme, Matthieu; Ulm, Franz-Josef

    2009-01-01

    Concrete, the solid that forms at room temperature from mixing Portland cement with water, sand, and aggregates, suffers from time-dependent deformation under load. This creep occurs at a rate that deteriorates the durability and truncates the lifespan of concrete structures. However, despite decades of research, the origin of concrete creep remains unknown. Here, we measure the in situ creep behavior of calcium–silicate–hydrates (C–S–H), the nano-meter sized particles that form the fundamental building block of Portland cement concrete. We show that C–S–H exhibits a logarithmic creep that depends only on the packing of 3 structurally distinct but compositionally similar C–S–H forms: low density, high density, ultra-high density. We demonstrate that the creep rate (≈1/t) is likely due to the rearrangement of nanoscale particles around limit packing densities following the free-volume dynamics theory of granular physics. These findings could lead to a new basis for nanoengineering concrete materials and structures with minimal creep rates monitored by packing density distributions of nanoscale particles, and predicted by nanoscale creep measurements in some minute time, which are as exact as macroscopic creep tests carried out over years. PMID:19541652

  19. Nanogranular origin of concrete creep.

    PubMed

    Vandamme, Matthieu; Ulm, Franz-Josef

    2009-06-30

    Concrete, the solid that forms at room temperature from mixing Portland cement with water, sand, and aggregates, suffers from time-dependent deformation under load. This creep occurs at a rate that deteriorates the durability and truncates the lifespan of concrete structures. However, despite decades of research, the origin of concrete creep remains unknown. Here, we measure the in situ creep behavior of calcium-silicate-hydrates (C-S-H), the nano-meter sized particles that form the fundamental building block of Portland cement concrete. We show that C-S-H exhibits a logarithmic creep that depends only on the packing of 3 structurally distinct but compositionally similar C-S-H forms: low density, high density, ultra-high density. We demonstrate that the creep rate ( approximately 1/t) is likely due to the rearrangement of nanoscale particles around limit packing densities following the free-volume dynamics theory of granular physics. These findings could lead to a new basis for nanoengineering concrete materials and structures with minimal creep rates monitored by packing density distributions of nanoscale particles, and predicted by nanoscale creep measurements in some minute time, which are as exact as macroscopic creep tests carried out over years. PMID:19541652

  20. Copper modified austenitic stainless steel alloys with improved high temperature creep resistance

    DOEpatents

    Swindeman, R.W.; Maziasz, P.J.

    1987-04-28

    An improved austenitic stainless steel that incorporates copper into a base Fe-Ni-Cr alloy having minor alloying substituents of Mo, Mn, Si, T, Nb, V, C, N, P, B which exhibits significant improvement in high temperature creep resistance over previous steels. 3 figs.

  1. Creep testing of foil-gage metals at elevated temperature using an automated data acquisition system

    NASA Technical Reports Server (NTRS)

    Blackburn, L. B.

    1983-01-01

    A method is being developed to obtain creep data on foil gage metals at elevated temperatures using an automated data acquisition system in conjunction with a mechanically counter balanced extensometer. The automated system components include the Hewlett-Packard (HP) 9845A desktop computer, the HP 3455A digital voltmeter and the HP 3495A scanner. Software for test monitoring and data collection was developed; data manipulation, including curve plotting was done with a HP regression analysis software package. Initial creep tests were conducted on .003 in. thick foil specimens of Ti-6A1-4V at temperatures of 800 F and 1000 F and at stress levels of 25 ksi and 45 ksi. For comparison, duplicate tests were run on .049 in. thick specimens sheet of the same alloy. During testing, the furnace and specimen temperature, bridge voltage, strain and load output were automatically monitored and recorded at predetermined intervals. Using the HP regression analysis program, recorded strain output was plotted as a function of time. These resultant creep curves indicate that, under similar conditions of temperature and stress, foil gage specimens exhibit a higher creep rate than sheet specimens.

  2. Effect of temperature on tensile and creep characteristics of PRD49 fiber/epoxy composites

    NASA Technical Reports Server (NTRS)

    Hanson, M. P.

    1972-01-01

    Tensile and creep data of PRD49-1 and 3 fiber/epoxy-resin composites are presented. Tensile data were obtained from 20 to 477 K (-423 to 400 F). Tensile strengths and moduli were determined at selected temperatures. Creep data are presented for fiber composites at 297, 422 and 450 K (75, 300, and 350 F) for as long as 1000 hours at stress levels of approximately 50 and 80 percent of the ultimate tensile strength at 297 K (75 F). Details of tensile specimens and test procedures used in the investigation are presented.

  3. Effect of temperature on the formation of creep substructure in sodium chloride single crystals

    NASA Technical Reports Server (NTRS)

    Raj, Sai V.; Pharr, George M.

    1992-01-01

    The effect of temperature on the substructure morphology and the cell and subgrain size was investigated experimentally in NaCl single crystals under creep in the temperature range 573-873 K. It is found that the effect of temperature on the cell and subgrain sizes is weak in comparison with the effect of stress. However, there was a qualitative change in the substructure morphology with temperature, with the cells and subgrains better defined at higher temperatures. The volume fraction of the cell boundaries decreased with increasing temperature, thereby indicating a refinement of the microstructure at higher temperatures.

  4. Creep Testing of High-Temperature Cu-8 Cr-4 Nb Alloy Completed

    NASA Technical Reports Server (NTRS)

    1995-01-01

    A Cu-8 at.% Cr-4 at.% Nb (Cu-8 Cr-4 Nb) alloy is under development for high-temperature, high heatflux applications, such as actively cooled, hypersonic vehicle heat exchangers and rocket engine combustion chambers. Cu-8 Cr-4 Nb offers a superior combination of strength and conductivity. It has also shown exceptional low-cycle fatigue properties. Following preliminary testing to determine the best processing route, a more detailed testing program was initiated to determine the creep lives and creep rates of Cu-8 Cr-4 Nb alloy specimens produced by extrusion. Testing was conducted at the NASA Lewis Research Center with constant-load vacuum creep units. Considering expected operating temperatures and mission lives, we developed a test matrix to accurately determine the creep properties of Cu-8 Cr-4 Nb between 500 and 800 C. Six bars of Cu-8 Cr-4 Nb were extruded. From these bars, 54 creep samples were machined and tested. The figure on the left shows the steady-state, or second-stage, creep rates for the samples. Comparison data for NARloy-Z (Cu-3 wt % Ag-0.5 wt % Zr), the alloy currently used in combustion chamber liners, were not unavailable. Therefore the steady-state creep rates for Cu at similar temperatures are presented. As expected, in comparison to pure Cu, the creep rates for Cu-8 Cr-4 Nb are much lower. The lives of the samples are presented in the figure on the right. As shown, Cu-8 Cr-4 Nb at 800 C is comparable to NARloy-Z at 648 C. At equivalent temperatures, Cu-8 Cr-4 Nb enjoys a 20 to 50 percent advantage in stress for a given life and 1 to 3 orders of magnitude greater life at a given stress. The improved properties allow for design tradeoffs and improvements in new and existing heat exchangers such as the next generation of combustion chamber liners. Average creep rates for Cu-8 Cr-4 Nb and pure Cu are shown. Average creep lives for Cu-8 Cr- 4 Nb and NARloy-Z are also shown. Currently, two companies are interested in the commercial usage of the Cu

  5. Deformation behavior of a Ni-30Al-20Fe-0.05Zr intermetallic alloy in the temperature range 300 to 1300 K

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Locci, I. E.; Noebe, R. D.

    1992-01-01

    The deformation properties of an extruded Ni-30Al-20Fe-0.05Zr (at. pct) alloy in the temperature range 300-1300 K were investigated under initial tensile strain rates that varied between 10 exp -6 and 10 exp -3/sec and in constant load compression creep between 1073 and 1300 K. Three deformation regimes were observed: region I, occurring between 400 and 673 K, which consisted of an athermal regime of less than 0.3 percent tensile ductility; region II, between 673 and 1073, where exponential creep was dominant; and region III, between 1073 and 1300 K, where a significant improvement in tensile ductility was observed.

  6. Temperature effects on the strainrange partitioning approach for creep-fatigue analysis

    NASA Technical Reports Server (NTRS)

    Halford, G. R.; Hirschberg, M. H.; Manson, S. S.

    1972-01-01

    Examination is made of the influence of temperature on the strainrange partitioning approach to creep-fatigue. Results for Cr-Mo steel and Type 316 stainless steel show the four partitioned strainrange-life relationships to be temperature insensitive to within a factor of two on cyclic life. Monotonic creep and tensile ductilities were also found to be temperature insensitive to within a factor of two. The approach provides bounds on cyclic life that can be readily established for any type of inelastic strain cycle. Continuous strain cycling results obtained over a broad range of high temperatures and frequencies are in excellent agreement with bounds provided by the approach. The observed transition from one bound to the other is also in good agreement with the approach.

  7. The effects of physical aging at elevated temperatures on the viscoelastic creep on IM7/K3B

    NASA Technical Reports Server (NTRS)

    Gates, Thomas S.; Feldman, Mark

    1994-01-01

    Physical aging at elevated temperature of the advanced composite IM7/K3B was investigated through the use of creep compliance tests. Testing consisted of short term isothermal, creep/recovery with the creep segments performed at constant load. The matrix dominated transverse tensile and in-plane shear behavior were measured at temperatures ranging from 200 to 230 C. Through the use of time based shifting procedures, the aging shift factors, shift rates and momentary master curve parameters were found at each temperature. These material parameters were used as input to a predictive methodology, which was based upon effective time theory and linear viscoelasticity combined with classical lamination theory. Long term creep compliance test data was compared to predictions to verify the method. The model was then used to predict the long term creep behavior for several general laminates.

  8. Steady-state creep of bent reinforced metal-composite plates with consideration of their reduced resistance to transverse shear. 1. Deformation model

    NASA Astrophysics Data System (ADS)

    Yankovskii, A. P.

    2014-05-01

    The problem of deformation of reinforced metal-composite plates is formulated in rectangular Cartesian coordinates using the second version of Timoshenko theory and taking into account the reduced transverse shear resistance of the plates under steady-state creep conditions. A similar model problem of axisymmetric bending of reinforced plates is considered in polar coordinates.

  9. In-situ Creep Testing Capability Development for Advanced Test Reactor

    SciTech Connect

    B. G. Kim; J. L. Rempe; D. L. Knudson; K. G. Condie; B. H. Sencer

    2010-08-01

    Creep is the slow, time-dependent strain that occurs in a material under a constant strees (or load) at high temperature. High temperature is a relative term, dependent on the materials being evaluated. A typical creep curve is shown in Figure 1-1. In a creep test, a constant load is applied to a tensile specimen maintained at a constant temperature. Strain is then measured over a period of time. The slope of the curve, identified in the figure below, is the strain rate of the test during Stage II or the creep rate of the material. Primary creep, Stage I, is a period of decreasing creep rate due to work hardening of the material. Primary creep is a period of primarily transient creep. During this period, deformation takes place and the resistance to creep increases until Stage II, Secondary creep. Stage II creep is a period with a roughly constant creep rate. Stage II is referred to as steady-state creep because a balance is achieved between the work hardening and annealing (thermal softening) processes. Tertiary creep, Stage III, occurs when there is a reduction in cross sectional area due to necking or effective reduction in area due to internal void formation; that is, the creep rate increases due to necking of the specimen and the associated increase in local stress.

  10. Plastic Deformation of Micromachined Silicon Diaphragms with a Sealed Cavity at High Temperatures

    PubMed Central

    Ren, Juan; Ward, Michael; Kinnell, Peter; Craddock, Russell; Wei, Xueyong

    2016-01-01

    Single crystal silicon (SCS) diaphragms are widely used as pressure sensitive elements in micromachined pressure sensors. However, for harsh environments applications, pure silicon diaphragms are hardly used because of the deterioration of SCS in both electrical and mechanical properties. To survive at the elevated temperature, the silicon structures must work in combination with other advanced materials, such as silicon carbide (SiC) or silicon on insulator (SOI), for improved performance and reduced cost. Hence, in order to extend the operating temperatures of existing SCS microstructures, this work investigates the mechanical behavior of pressurized SCS diaphragms at high temperatures. A model was developed to predict the plastic deformation of SCS diaphragms and was verified by the experiments. The evolution of the deformation was obtained by studying the surface profiles at different anneal stages. The slow continuous deformation was considered as creep for the diaphragms with a radius of 2.5 mm at 600 °C. The occurrence of plastic deformation was successfully predicted by the model and was observed at the operating temperature of 800 °C and 900 °C, respectively. PMID:26861332

  11. Plastic Deformation of Micromachined Silicon Diaphragms with a Sealed Cavity at High Temperatures.

    PubMed

    Ren, Juan; Ward, Michael; Kinnell, Peter; Craddock, Russell; Wei, Xueyong

    2016-01-01

    Single crystal silicon (SCS) diaphragms are widely used as pressure sensitive elements in micromachined pressure sensors. However, for harsh environments applications, pure silicon diaphragms are hardly used because of the deterioration of SCS in both electrical and mechanical properties. To survive at the elevated temperature, the silicon structures must work in combination with other advanced materials, such as silicon carbide (SiC) or silicon on insulator (SOI), for improved performance and reduced cost. Hence, in order to extend the operating temperatures of existing SCS microstructures, this work investigates the mechanical behavior of pressurized SCS diaphragms at high temperatures. A model was developed to predict the plastic deformation of SCS diaphragms and was verified by the experiments. The evolution of the deformation was obtained by studying the surface profiles at different anneal stages. The slow continuous deformation was considered as creep for the diaphragms with a radius of 2.5 mm at 600 °C. The occurrence of plastic deformation was successfully predicted by the model and was observed at the operating temperature of 800 °C and 900 °C, respectively. PMID:26861332

  12. Evaluation of Permanent Deformation of CRM-Reinforced SMA and Its Correlation with Dynamic Stiffness and Dynamic Creep

    PubMed Central

    Mashaan, Nuha Salim; Karim, Mohamed Rehan

    2013-01-01

    Today, rapid economic and industrial growth generates increasing amounts of waste materials such as waste tyre rubber. Attempts to inspire a green technology which is more environmentally friendly that can produce economic value are a major consideration in the utilization of waste materials. The aim of this study is to evaluate the effect of waste tyre rubber (crumb rubber modifier (CRM)), in stone mastic asphalt (SMA 20) performance. The virgin bitumen (80/100) penetration grade was used, modified with crumb rubber at four different modification levels, namely, 6%, 12%, 16%, and 20% by weight of the bitumen. The testing undertaken on the asphalt mix comprises the indirect tensile (dynamic stiffness), dynamic creep, and wheel tracking tests. By the experimentation, the appropriate amount of CRM was found to be 16% by weight of bitumen. The results show that the addition of CRM into the mixture has an obvious significant effect on the performance properties of SMA which could improve the mixture's resistance against permanent deformation. Further, higher correlation coefficient was obtained between the rut depth and permanent strain as compared to resilient modulus; thus dynamic creep test might be a more reliable test in evaluating the rut resistance of asphalt mixture. PMID:24302883

  13. Evaluation of permanent deformation of CRM-reinforced SMA and its correlation with dynamic stiffness and dynamic creep.

    PubMed

    Mashaan, Nuha Salim; Karim, Mohamed Rehan

    2013-01-01

    Today, rapid economic and industrial growth generates increasing amounts of waste materials such as waste tyre rubber. Attempts to inspire a green technology which is more environmentally friendly that can produce economic value are a major consideration in the utilization of waste materials. The aim of this study is to evaluate the effect of waste tyre rubber (crumb rubber modifier (CRM)), in stone mastic asphalt (SMA 20) performance. The virgin bitumen (80/100) penetration grade was used, modified with crumb rubber at four different modification levels, namely, 6%, 12%, 16%, and 20% by weight of the bitumen. The testing undertaken on the asphalt mix comprises the indirect tensile (dynamic stiffness), dynamic creep, and wheel tracking tests. By the experimentation, the appropriate amount of CRM was found to be 16% by weight of bitumen. The results show that the addition of CRM into the mixture has an obvious significant effect on the performance properties of SMA which could improve the mixture's resistance against permanent deformation. Further, higher correlation coefficient was obtained between the rut depth and permanent strain as compared to resilient modulus; thus dynamic creep test might be a more reliable test in evaluating the rut resistance of asphalt mixture. PMID:24302883

  14. Creep-fatigue of High Temperature Materials for VHTR: Effect of Cyclic Loading and Environment

    SciTech Connect

    Celine Cabet; L. Carroll; R. Wright; R. Madland

    2011-05-01

    Alloy 617 is the one of the leading candidate materials for Intermediate Heat eXchangers (IHX) of a Very High Temperature Reactor (VHTR). System start-ups and shut-downs as well as power transients will produce low cycle fatigue (LCF) loadings of components. Furthermore, the anticipated IHX operating temperature, up to 950°C, is in the range of creep so that creep-fatigue interaction, which can significantly increase the fatigue crack growth, may be one of the primary IHX damage modes. To address the needs for Alloy 617 codification and licensing, a significant creep-fatigue testing program is underway at Idaho National Laboratory. Strain controlled LCF tests including hold times up to 1800s at maximum tensile strain were conducted at total strain range of 0.3% and 0.6% in air at 950°C. Creep-fatigue testing was also performed in a simulated VHTR impure helium coolant for selected experimental conditions. The creep-fatigue tests resulted in failure times up to 1000 hrs. Fatigue resistance was significantly decreased when a hold time was added at peak stress and when the total strain was increased. The fracture mode also changed from transgranular to intergranular with introduction of a tensile hold. Changes in the microstructure were methodically characterized. A combined effect of temperature, cyclic and static loading and environment was evidenced in the targeted operating conditions of the IHX. This paper This paper reviews the data previously published by Carroll and co-workers in references 10 and 11 focusing on the role of inelastic strain accumulation and of oxidation in the initiation and propagation of surface fatigue cracks.

  15. High temperature creep behaviour of Al-rich Ti-Al alloys

    NASA Astrophysics Data System (ADS)

    Sturm, D.; Heilmaier, M.; Saage, H.; Aguilar, J.; Schmitz, G. J.; Drevermann, A.; Palm, M.; Stein, F.; Engberding, N.; Kelm, K.; Irsen, S.

    2010-07-01

    Compared to Ti-rich γ-TiAl-based alloys Al-rich Ti-Al alloys offer an additional reduction of in density and a better oxidation resistance which are both due to the increased Al content. Polycrystalline material was manufactured by centrifugal casting. Microstructural characterization was carried out employing light-optical, scanning and transmission electron microscopy and XRD analyses. The high temperature creep of two binary alloys, namely Al60Ti40 and Al62Ti38 was comparatively assessed with compression tests at constant true stress in a temperature range between 1173 and 1323 K in air. The alloys were tested in the cast condition (containing various amounts of the metastable phases Al5Ti3 and h-Al2Ti) and after annealing at 1223 K for 200 h which produced (thermodynamically stable) lamellar γ-TiAl + r-Al2Ti microstructures. In general, already the as-cast alloys exhibit a reasonable creep resistance at 1173 K. Compared with Al60Ti40, both, the as-cast and the annealed Al62Ti38 alloy exhibit better creep resistance up to 1323 K which can be rationalized by the reduced lamella spacing. The assessment of creep tests conducted at identical stress levels and varying temperatures yielded apparent activation energies for creep of Q = 430 kJ/mol for the annealed Al60Ti40 alloy and of Q = 383 kJ/mol for the annealed Al62Ti38 material. The latter coincides well with that of Al diffusion in γ-TiAl, whereas the former can be rationalized by the instability of the microstructure containing metastable phases.

  16. Low Temperature Creep of Hot-Extruded Near-Stoichiometric NiTi Shape Memory Alloy. Part 2; Effect of Thermal Cycling

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Noebe, R. D.

    2013-01-01

    This paper is the first report on the effect prior low temperature creep on the thermal cycling behavior of NiTi. The isothermal low temperature creep behavior of near-stoichiometric NiTi between 300 and 473 K was discussed in Part I. The effect of temperature cycling on its creep behavior is reported in the present paper (Part II). Temperature cycling tests were conducted between either 300 or 373 K and 473 K under a constant applied stress of either 250 or 350 MPa with hold times lasting at each temperature varying between 300 and 700 h. Each specimen was pre-crept either at 300 or at 473 K for several months under an identical applied stress as that used in the subsequent thermal cycling tests. Irrespective of the initial pre-crept microstructures, the specimens exhibited a considerable increase in strain with each thermal cycle so that the total strain continued to build-up to 15 to 20 percent after only 5 cycles. Creep strains were immeasurably small during the hold periods. It is demonstrated that the strains in the austenite and martensite are linearly correlated. Interestingly, the differential irrecoverable strain, in the material measured in either phase decreases with increasing number of cycles, similar to the well-known Manson-Coffin relation in low cycle fatigue. Both phases are shown to undergo strain hardening due to the development of residual stresses. Plots of true creep rate against absolute temperature showed distinct peaks and valleys during the cool-down and heat-up portions of the thermal cycles, respectively. Transformation temperatures determined from the creep data revealed that the austenitic start and finish temperatures were more sensitive to the pre-crept martensitic phase than to the pre-crept austenitic phase. The results are discussed in terms of a phenomenological model, where it is suggested that thermal cycling between the austenitic and martensitic phase temperatures or vice versa results in the deformation of the austenite and

  17. Deformation of granite at elevated temperature and pressure. Final report, 1 March 1984-28 February 1985

    SciTech Connect

    Carter, N.L.

    1985-03-15

    The purpose was to determine the evolution of substructure and mechanical behavior of westerly granite, deformed under both wet and dry conditions, from the initial stages of transient creep well into the steady-state. Following calibration of the 10 kb gas apparatus at elevated temperature and pressure, the main pressure vessel burst. As a consequence, other studies were pursued. These include: (1) analysis of olivine fabrics of ophiolites; (2) upper mantle deformation in collision zones; (3) flow properties of continental lithosphere; and (4) mechanical behavior of oceanic layer 2 basalts. (ACR)

  18. Compressive Creep Performance and High Temperature Dimensional Stability of Conventional Silica Refractories

    SciTech Connect

    Karakus, M.; Kirkland, T.P.; Liu, K.C.; Moore, R.E.; Pint, B.A.; Wereszczak, A.A.

    1999-03-01

    Furnace designers and refractory engineers recognize that optimized furnace superstructure design and refractory selection are needed as glass production furnaces are continually striving toward greater output and efficiencies. Harsher operating conditions test refractories to the limit, while changing production technology (such as the conversion to oxy-fuel from traditional air-fuel firing) can alter the way the materials perform. Refractories for both oxy- and air-fuel fired furnace superstructures are subjected to high temperatures during service that may cause them to excessively creep or subside if the refractory material is not creep resistant, or if it is subjected to high stress, or both. Furnace designers can ensure that superstructure structural integrity is maintained if the creep behavior of the refractory material is well understood and well represented by appropriate engineering creep models. Several issues limit the abilities of furnace designers to (1) choose the optimum refractory for their applications, (2) optimize the engineering design, or (3) predict the service mechanical integrity of their furnace superstructures. Published engineering creep data are essentially non-existent for almost all commercially available refractories used for glass furnace superstructures. The limited data that do exist are supplied by the various refractory suppliers. Unfortunately, these suppliers generally have different ways of conducting their mechanical testing and they also interpret and report their data differently; this makes it hard for furnace designers to draw fair comparisons between competing grades of candidate refractories. Furthermore, the refractory supplier's data are often not available in a form that can be readily used for furnace design and for the prediction and design of long-term structural integrity of furnace superstructures. With the aim of providing such comparable data, the US DOE's Office of Industrial Technology and its Advanced

  19. Creep-rupture in powder metallurgical nickel-base superalloys at intermediate temperatures

    NASA Astrophysics Data System (ADS)

    Law, C. C.; Blackburn, M. J.

    1980-03-01

    To gain insight into the factors which control the creep-rupture properties of powder metallurgical nickel-base superalloys at intermediate temperatures (650 to 775°C), a comparative study was conducted on the alloys AF115, modified MAR-M432 (B6) and modified IN100 (MERL76). Creep-rupture properties in these alloys were characterized in terms of the stress and temperature dependence of the secondary creep rate, ɛS, andrupture time, t R . Within the limited stress ranges used, the stress dependence of both ɛS and t R at 704°C can be represented by power laws ɛS and C n and t R = Mσ -p ; where C, M, n, and p are constants. The stress exponents n and p are approximately equal for both AF115 and B6 with values of 16 and 7, respectively. In the case of MERL76, n and p are different, with values of 15 and 5, respectively. The apparent activation energies, Q, are 700, 370 and 520 KJ mol-1 for AF115, B6 and MERL76, respectively. For these alloys, long creep-rupture lives are associated with large values of n and Q. The sig-nificant differences in n and Q values between AF115 and B6 were related to creep re-covery processes for which the lattice misfit between the gamma and the gamma prime was identified to be an important parameter. However, the unequal n and p values in MERL76 compared with those in AF115 and B6, were traced to differences in fracture mode. Failures in AF115 and B6 were initiated at carbide particles at grain boundaries. In contrast, fracture in MERL76 was initiated at grain boundary triple junctions. The rupture lives of AF115 and B6 can be modeled reasonably well by the growth of cavities during secondary creep and propagation of a surface-nucleated crack during the tertiary creep.

  20. PROCESSING, MICROSTRUCTURE AND CREEP BEHAVIOR OF Mo-Si-B-BASED INTERMETALLIC ALLOYS FOR VERY HIGH TEMPERATURE STRUCTURAL APPLICATIONS

    SciTech Connect

    Vijay K. Vasudevan

    2005-12-21

    This research project is concerned with developing a fundamental understanding of the effects of processing and microstructure on the creep behavior of refractory intermetallic alloys based on the Mo-Si-B system. During this year, the compressive creep behavior of a Mo-3Si-1B (in wt.%) alloy at 1100 and 1200 C were studied and related to the deformation mechanisms through electron microscopy observations of microstructural changes and deformation structures. The microstructure of this alloy was three-phase, being composed of {alpha}-Mo, Mo{sub 3}Si and T2-Mo{sub 5}SiB{sub 2} phases. Results of compressive creep tests at 1200 and 1100 C showed that the creep rates were quite high at stress levels between 250 and 500 MPa, Two minima in the creep strain rate versus strain data were noted, one at small strain values and the second at much larger strains. A stress exponent of 4.26 was obtained upon plotting the strain rate corresponding to the first minima versus stress, which suggests that dislocation climb and glide dominate the creep process in the early stages. On the other hand, the large strain, minimum creep rate versus stress data gave a stress exponent of {approx}1.18, which indicates diffusional mechanisms and recrystallization dominate the later stages of the creep process. At 1100 C, a stress exponent of 2.26 was obtained, which suggests that both diffusional and dislocation mechanisms contribute to the creep strain. Based on the minimum creep rate data at 1100 C and 1200 C, the activation energy for creep was determined to be 525 kJ/mole, which is somewhat higher than that reported for self diffusion in {alpha}-Mo. Microstructural observations of post-crept samples indicated the presence of many voids in the {alpha}-Mo grains and few cracks in the intermetallic particles and along their interfaces with the {alpha}-Mo matrix. In addition, TEM observations revealed the presence of recrystallized grains and sub-grain boundaries composed of dislocation arrays

  1. The solid-solution alloying effects of Ti on the high-temperature deformation behavior of NiAl single crystals

    SciTech Connect

    Kitabjian, P.H.; Nix, W.D.; Garg, A.; Noebe, R.

    1997-12-31

    The authors have investigated the high-temperature deformation behavior of the solid-solution strengthened alloy Ni-47.5Al-2.5Ti. Single crystals were deformed in compression in the hard <001> and soft <111> orientations, at temperatures between 900 C and 1,200 C. The results show that Ti has a very powerful solute strengthening effect in NiAl. The creep rates for the solid-solution alloy were observed to be three to four orders of magnitude lower than for the stoichiometric material. They discuss the efforts to understand this solid-solution strengthening effect. They have studied high-temperature deformation transients in an effort to determine whether solute drag effects contribute to the creep resistance of this solid solution. In addition, they have examined the solute size effect of Ti as it replaces Al on the Al sub-lattice. They discuss the probable mechanism of creep of this alloy in light of TEM observations of the dislocation structures in creep-deformed crystals.

  2. Temperature-dependent elastic anisotropy and mesoscale deformation in a nanostructured ferritic alloy

    SciTech Connect

    Stoica, G. M.; Stoica, A. D.; Miller, M. K.; Ma, D.

    2014-10-10

    Nanostructured ferritic alloys (NFA) are a new class of ultrafine-grained oxide dispersion-strengthened steels, promising for service in extreme environments of high temperature and high irradiation in the next-generation of nuclear reactors. This is owing to the remarkable stability of their complex microstructures containing a high density of Y-Ti-O nanoclusters within grains and along the grain boundaries. While nanoclusters have been recognized to be the primary contributor to the exceptional resistance to irradiation and high-temperature creep, very little is known about the mechanical roles of the polycrystalline grains that constitute the bulk ferritic matrix. Here we report the mesoscale characterization of anisotropic responses of the ultrafine NFA grains to tensile stresses at various temperatures using the state-of-the-art in situ neutron diffraction. We show the first experimental determination of temperature-dependent single-crystal elastic constants for the NFA, and reveal a strong temperature-dependent elastic anisotropy due to a sharp decrease in the shear stiffness constant [c'=(c_11-c_12)/2] when a critical temperature ( T_c ) is approached, indicative of elastic softening and instability of the ferritic matrix. We also show, from anisotropy-induced intergranular strain/stress accumulations, that a common dislocation slip mechanism operates at the onset of yielding for low temperatures, while there is a deformation crossover from low-temperature lattice hardening to high temperature lattice softening in response to extensive plastic deformation.

  3. Temperature-dependent elastic anisotropy and mesoscale deformation in a nanostructured ferritic alloy

    DOE PAGESBeta

    Stoica, G. M.; Stoica, A. D.; Miller, M. K.; Ma, D.

    2014-10-10

    Nanostructured ferritic alloys (NFA) are a new class of ultrafine-grained oxide dispersion-strengthened steels, promising for service in extreme environments of high temperature and high irradiation in the next-generation of nuclear reactors. This is owing to the remarkable stability of their complex microstructures containing a high density of Y-Ti-O nanoclusters within grains and along the grain boundaries. While nanoclusters have been recognized to be the primary contributor to the exceptional resistance to irradiation and high-temperature creep, very little is known about the mechanical roles of the polycrystalline grains that constitute the bulk ferritic matrix. Here we report the mesoscale characterization ofmore » anisotropic responses of the ultrafine NFA grains to tensile stresses at various temperatures using the state-of-the-art in situ neutron diffraction. We show the first experimental determination of temperature-dependent single-crystal elastic constants for the NFA, and reveal a strong temperature-dependent elastic anisotropy due to a sharp decrease in the shear stiffness constant [c'=(c_11-c_12)/2] when a critical temperature ( T_c ) is approached, indicative of elastic softening and instability of the ferritic matrix. We also show, from anisotropy-induced intergranular strain/stress accumulations, that a common dislocation slip mechanism operates at the onset of yielding for low temperatures, while there is a deformation crossover from low-temperature lattice hardening to high temperature lattice softening in response to extensive plastic deformation.« less

  4. Quantification of uncertainties in coupled material degradation processes - High temperature, fatigue and creep

    NASA Technical Reports Server (NTRS)

    Boyce, L.; Chamis, C. C.

    1991-01-01

    This paper describes the development of methodology that provides for quantification of uncertainties in lifetime strength of aerospace materials subjected to a number of diverse effects. A probabilistic material degradation model, in the form of a randomized multifactor interaction equation, has been postulated for lifetime strength degradation of structural components of aerospace propulsion systems. The model includes effects that typically reduce lifetime strength and may include temperature, mechanical fatigue, creep and others. The paper also includes the analysis of experimental data from the open literature for Inconel 718. These data are used to provide an initial check for model validity, as well as for calibration of the model's empirical material constants. The model validity check and calibration is carried out for three effects, namely, high temperature, mechanical fatigue and creep.

  5. In situ proton irradiation-induced creep at very high temperature

    NASA Astrophysics Data System (ADS)

    Campbell, Anne A.; Was, Gary S.

    2013-02-01

    This objective of this work was to develop an experimental facility that can perform in situ high temperature proton irradiation-induced creep experiments on a range of materials. This was achieved by designing an irradiation chamber and stage that allows for load application and removal, provides a method for controlling and monitoring temperature and proton flux, and a means to make in situ measurement of dimensional change of the samples during the experiment. Initial experiments on POCO Graphite Inc. ZXF-5Q grade ultra-fine grain samples irradiated at 1000 °C at a damage rate of 1.15 × 10-6 dpa/s exhibited a linear dependence of measured creep rate on applied stress over a range of stresses from 10 MPa to 40 MPa.

  6. Effect of carbide precipitation on the creep behavior of alloy 800HT in the temperature range 700 C to 900 C

    SciTech Connect

    El-Magd, E.; Nicolini, G.; Farag, M.

    1996-03-01

    The creep behavior of alloy 800HT was studied at 700 C, 800 C, and 900 C under stresses ranging from 30 to 170 MPa. Samples that were tested in the as-quenched condition after solution treatment exhibited longer creep life than those that were over aged before testing. This difference in creep life was found to increase at lower creep stresses at a given temperature. This phenomenon is attributed to the precipitation of M{sub 23}C{sub 6} carbides during the early stages of creep, which strengthen the material by exerting threshold stresses on moving dislocations and thereby reducing the creep rate. A model is developed to describe the influence of carbide precipitation during creep on the behavior of the material under different creep temperatures and stresses. Comparison with the experimental results shows that the model gives accurate predictions of the creep behavior of the material in the range of stresses and temperatures used in the present study. In addition to its predictive value, the model is useful in understanding the factors that affect the creep behavior of materials when precipitation of hard phases is taking place during creep. The strengthening effect of particle precipitation during creep, as represented by the value of the threshold stress, is shown to be a complex function of the supersaturation of the matrix, the applied creep stress, and the test temperature.

  7. Effect of carbide precipitation on the creep behavior of Alloy 800HT in the Temperature Range 700 ° to 900 °

    NASA Astrophysics Data System (ADS)

    El-Magd, E.; Nicolini, G.; Farag, M.

    1996-03-01

    The creep behavior of alloy 800HT was studied at 700 °, 800 °, and 900 ° under stresses ranging from 30 to 170 MPa. Samples that were tested in the as-quenched condition after solution treatment exhibited longer creep life than those that were overaged before testing. This difference in creep life was found to increase at lower creep stresses at a given temperature. This phenomenon is attributed to the precipitation of M23C6carbides during the early stages of creep, which strengthen the material by exerting threshold stresses on moving dislocations and thereby reducing the creep rate. A model is developed to describe the influence of carbide precipitation during creep on the behavior of the material under different creep temperatures and stresses. Comparison with the experimental results shows that the model gives accurate predictions of the creep behavior of the material in the range of stresses and temperatures used in the present study. In addition to its predictive value, the model is useful in understanding the factors that affect the creep behavior of materials when precipitation of hard phases is taking place during creep. The strengthening effect of particle precipitation during creep, as represented by the value of the threshold stress, is shown to be a complex function of the supersaturation of the matrix, the applied creep stress, and the test temperature.

  8. Creep deformation and rupture behavior of 2.25Cr-1Mo steel weldments and its constituents (base metal, weld metal and simulated heat affected zones)

    SciTech Connect

    Laha, K.; Chandravathi, K.S.; Rao, K.B.S.; Mannan, S.L.

    1995-12-31

    Microstructure across a weldment base metal through transformed heat-affected zone (HAZ) to cast weld metal. HAZ of 2.25Cr-1Mo weldment consists of coarse-grain bainite, fine-grain bainite and intercritical region. These HAZ microstructures were simulated by isothermal heat-treatments. Creep tests were carried out on base metal, weld metal, weldment and the simulated HAZ structures. Creep deformation and fracture behavior of 2.25Cr-1Mo weldments has been assessed based on the properties of its constituents. Coarse-grain bainite with low ductility and intercritical structure with low strength are the critical components of HAZ determining performance of the weldments.

  9. Thermocouples with improved high-temperature creep property by oxide dispersion strengthening

    NASA Astrophysics Data System (ADS)

    Hamada, T.; Yamasaki, H.; Kodama, T.

    2013-09-01

    Platinum-based thermocouples, especially type R and S, whose negative branch is made of pure platinum, often rupture during high-temperature operation. The phenomenon occurs because high-temperature creep strength of pure platinum is very low. In order to avoid this rupture, oxide dispersion strengthened (O.D.S.) platinum was applied to construct high-temperature thermometers for the first time. The W(Ga) value of the O.D.S. platinum was found to be 1.11790, which is not high enough for use as standard platinum resistance thermometer. On the other hand, its purity was found sufficiently high for constituting the negative branch of type R and S thermocouples. Type R thermocouple was prepared with the O.D.S. platinum and was calibrated at the fixed points of tin, zinc, aluminum, silver, gold and palladium and the measured E.M.F. satisfied the IEC class 1 tolerance. The production process for the thermocouple material is similar to that of our original O.D.S. alloy, modified to avoid the contamination from the production process. The observed cross-section microstructure of the developed material was highly elongated, which is typical for O.D.S. platinum and creep rupture strength was almost similar to our original O.D.S. platinum, i.e. the initial stress of the creep rupture was several times higher than that of normal pure platinum when comparing with same rupture time.

  10. Effect of prior creep at 1365 K on the room temperature tensile properties of several oxide dispersion strengthened alloys

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.

    1977-01-01

    An experimental study was conducted to determine whether oxide dispersion-strengthened (ODS) Ni-base alloys in wrought bar form are subject to creep degradation effects similar to those found in thin-gage sheet. The bar products evaluated included ODS-Ni, ODS-NiCr, and advanced ODS-NiCrAl types; the alloys included microstructures ranging from an essentially perfect single crystal to a structure consisting of very small elongated grains. Tensile test specimens were exposed to creep at various stress levels at 1365 K and then tensile tested at room temperature. Low residual tensile properties, change in fracture mode, appearance of dispersoid free bands, grain boundary cavitation, and/or internal oxidation are interpreted as creep degradation effects. The amount of degradation depends on creep strain, and degradation appears to be due to diffusional creep which produces dispersoid free bands around grain boundaries acting as vacancy sources.

  11. Accelerator-Based Irradiation Creep of Pyrolytic Carbon Used in TRISO Fuel Particles for the (VHTR) Very Hight Temperature Reactors

    SciTech Connect

    Lumin Wang; Gary Was

    2010-07-30

    Pyrolytic carbon (PyC) is one of the important structural materials in the TRISO fuel particles which will be used in the next generation of gas-cooled very-high-temperature reactors (VHTR). When the TRISO particles are under irradiation at high temperatures, creep of the PyC layers may cause radial cracking leading to catastrophic particle failure. Therefore, a fundamental understanding of the creep behavior of PyC during irradiation is required to predict the overall fuel performance.

  12. Creep of plasma sprayed zirconia

    NASA Technical Reports Server (NTRS)

    Firestone, R. F.; Logan, W. R.; Adams, J. W.

    1982-01-01

    Specimens of plasma-sprayed zirconia thermal barrier coatings with three different porosities and different initial particle sizes were deformed in compression at initial loads of 1000, 2000, and 3500 psi and temperatures of 1100 C, 1250 C, and 1400 C. The coatings were stabilized with lime, magnesia, and two different concentrations of yttria. Creep began as soon as the load was applied and continued at a constantly decreasing rate until the load was removed. Temperature and stabilization had a pronounced effect on creep rate. The creep rate for 20% Y2O3-80% ZrO2 was 1/3 to 1/2 that of 8% Y2O3-92% ZrO2. Both magnesia and calcia stabilized ZrO2 crept at a rate 5 to 10 times that of the 20% Y2O3 material. A near proportionality between creep rate and applied stress was observed. The rate controlling process appeared to be thermally activated, with an activation energy of approximately 100 cal/gm mole K. Creep deformation was due to cracking and particle sliding.

  13. Modeling creep behavior in a directionally solidified nickel base superalloy

    NASA Astrophysics Data System (ADS)

    Ibanez, Alejandro R.

    Directionally solidified (DS) nickel-base superalloys provide significant improvements relative to the limitations inherent to equiaxed materials in the areas of creep resistance, oxidation, and low and high cycle fatigue resistance. Since these materials are being pushed to the limits of their capability in gas turbine applications, accurate mathematical models are needed to predict the service lives of the hot-section components to prevent unscheduled outages due to sudden mechanical failures. The objectives of this study are to perform critical experiments and investigate the high temperature tensile, fracture toughness, creep deformation, creep rupture and creep crack growth behavior of DS GTD111 as well as to apply creep deformation, rupture and crack growth models that will enable the accurate representation of the life times of the DS GTD111 superalloy gas turbine components that are exposed to high temperatures under sustained tensile stresses. The applied models will be capable of accurately representing the creep deformation, rupture and crack growth behavior as a function of stress, time and temperature. The yield strength and fracture toughness behavior with temperature is governed by the gamma particles. The longitudinal direction showed higher ductility and strength than the transverse direction. The TL direction exhibited higher fracture toughness than the LT orientation because the crack follows a more tortuous path. The longitudinal direction showed higher creep ductility, lower minimum strain rates and longer creep rupture times than the transverse direction. The results in the transverse direction were similar to the ones for the equiaxed version of this superalloy. Two models for creep deformation have been evaluated. The power-law model includes a secondary and a tertiary creep term with the primary creep represented by a constant. A theta-projection model has also been evaluated and it appears to provide a more accurate representation of creep

  14. Preliminary investigation of the compressive strength and creep lifetime of 2024-T3 (formerly 24S-T3) aluminum-alloy plates at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Mathauser, Eldon E; Deveikis, William D

    1955-01-01

    The results of elevated-temperature compressive strength and creep tests of 2024-T3 (formerly 23S-T3) aluminum-alloy plates supported in V-grooves are presented. For determining elevated-temperature strength, where creep effects are negligible, a relation previously developed for predicting plate compressive strength at room temperature was satisfactory. Creep-lifetime results are presented for the plates in the form of master creep-lifetime curves by using a time-temperature parameter that is convenient for summarizing tensile creep-rupture data. A comparison is made between tensile and compressive creep lifetime for the plates, and the magnitude by which the design stress is decreased because of material creep and loss of strength due to exposure at elevated temperatures is indicated.

  15. Elevated temperature tension, compression and creep-rupture behavior of (001)-oriented single crystal superalloy PWA 1480

    NASA Technical Reports Server (NTRS)

    Hebsur, Mohan G.; Miner, Robert V.

    1987-01-01

    Tensile and compressive flow behavior at various temperatures and strain rates, and tensile creep rupture behavior at 850 and 1050 C and various stresses were studied for (001)-oriented single crystals of the Ni-base superalloy PWA 1480. At temperatures up to 760 C, the flow stress is insensitive to strain rate and of greater magnitude in tension than in compression. At temperatures of 800 C and above, the flow stress decreases continuously with decreasing strain rate and the tension/compression anisotropy diminishes. The second stage creep rate and rupture time exhibited power law relationships with the applied stress for both 850 and 1050 C, however with different stress dependencies. The stress exponent for the steady state creep rate was about 7 at 1050 C, but much higher at 850 C, about 12. Directional coarsening of the gamma' phase occurred during creep at 1050 C, but not at 850 C.

  16. Effect of Phosphorous Inoculation on Creep Behavior of a Hypereutectic Al-Si Alloy

    NASA Astrophysics Data System (ADS)

    Faraji, Masoumeh; Khalilpour, Hamid

    2014-10-01

    Creep behavior of Al-Si hypereutectic alloys inoculated with phosphorus was investigated using the impression creep testing. The results showed that at stress regimes of up to 400-450 MPa and temperatures up to 300 °C, no significant creep deformation occurred in both uninoculated and inoculated specimens; however, at temperatures above 300 °C, the inoculated alloys presented better creep properties. Creep data were used to calculate the stress exponent of steady-state creep rate, n, and creep activation energy, Q, for different additive conditions where n was found varied between 5 and 8. Owing to the fact that most alloys have lower values for n (4, 5), threshold stress was estimated for studied conditions. The creep governing mechanisms for different conditions are discussed here, with a particular attention to the effect of phosphorous addition on the microstructural features, including number of primary silicon particles, mean primary silicon spacing, and morphology and distribution of eutectic silicon.

  17. Precipitation Behavior in the Heat-Affected Zone of Boron-Added 9Cr-3W-3Co Steel During Post-Weld Heat Treatment and Creep Deformation

    NASA Astrophysics Data System (ADS)

    Liu, Yuan; Tsukamoto, Susumu; Sawada, Kota; Tabuchi, Masaaki; Abe, Fujio

    2015-05-01

    In the previous paper, we demonstrated that the addition of boron was effective in preventing type IV failure due to suppression of grain refinement in the heat-affected zone at the peak temperature of around AC3 (AC3 HAZ). However, some fine prior austenite grains (PAGs) still remained around the coarse PAG boundaries, and these fine PAGs may affect the creep property of the welded joint. In the present study, the effect of these fine PAGs on the creep property of the boron-added 9Cr-3Co-3W steel (B steel) Ac3 HAZ is investigated. Different heat treatments are carried out on B steel base metal to form different Ac3 HAZ-simulated microstructures of coarse PAG with and without fine PAGs. Ac3 HAZ microstructure shows that a lot of M23C6 carbides are formed at the block boundary in the interior of coarse PAG. On the other hand, few M23C6 carbides are formed at the fine PAG boundaries, but a number of μ phases (W6Fe7 type) cover the boundary. The formation of μ phase retards the recovery of dislocation at the fine PAG boundary and contributes to stabilizing the microstructure in the primary and transient creep regions. The μ phase transforms to the Laves phase during creep. As the growth rate of Laves phase is higher than that of M23C6 carbides during creep, the creep strength of fine PAG boundary, which is strengthened only by Laves phase, becomes a little bit lower than the other boundaries strengthened by M23C6 carbides after long-term creep. The mismatch of creep strength between the fine PAG boundary and the matrix should be taken into account to attain an excellent long-term creep property of the B steel welded joint.

  18. Contribution to irradiation creep arising from gas-driven bubbles

    SciTech Connect

    Woo, C.H.; Garner, F.A.

    1998-03-01

    In a previous paper the relationship was defined between void swelling and irradiation creep arising from the interaction of the SIPA and SIG creep-driven deformation and swelling-driven deformation was highly interactive in nature, and that the two contributions could not be independently calculated and then considered as directly additive. This model could be used to explain the recent experimental observation that the creep-swelling coupling coefficient was not a constant as previously assumed, but declined continuously as the swelling rate increased. Such a model thereby explained the creep-disappearance and creep-damping anomalies observed in conditions where significant void swelling occurred before substantial creep deformation developed. At lower irradiation temperatures and high helium/hydrogen generation rates, such as found in light water cooled reactors and some fusion concepts, gas-filled cavities that have not yet exceeded the critical radius for bubble-void conversion should also exert an influence on irradiation creep. In this paper the original concept is adapted to include such conditions, and its predictions then compared with available data. It is shown that a measurable increase in the creep rate is expected compared to the rate found in low gas-generating environments. The creep rate is directly related to the gas generation rate and thereby to the neutron flux and spectrum.

  19. How stress and temperature conditions affect rock-fluid chemistry and mechanical deformation

    NASA Astrophysics Data System (ADS)

    Nermoen, Anders; Korsnes, Reidar; Aursjø, Olav; Madland, Merete; Kjørslevik, Trygve Alexander; Østensen, Geir

    2016-02-01

    We report the results from a series of chalk flow-through-compaction experiments performed at three effective stresses (0.5 MPa, 3.5 MPa and 12.3 MPa) and two temperatures (92° and and 130°). The results show that both stress and temperature are important to both chemical alteration and mechanical deformation. The experiments were conducted on cores drilled from the same block of outcrop chalks from the Obourg quarry within the Saint Vast formation (Mons, Belgium). The pore pressure was kept at 0.7 MPa for all experiments with a continuous flow of 0.219 M MgCl2 brine at a constant flow rate; 1 original pore volume (PV) per day. The experiments have been performed in tri-axial cells with independent control of the external stress (hydraulic pressure in the confining oil), pore pressure, temperature, and the injected flow rate. Each experiment consists of two phases; a loading phase where stress-strain dependencies are investigated (approx. 2 days), and a creep phase that lasts for more than 150-160 days. During creep, the axial deformation was logged, and the effluent samples were collected for ion chromatography analyses. Any difference between the injected and produced water chemistry gives insight into the rock-fluid interactions that occur during flow through of the core. The observed effluent concentration shows a reduction in Mg2+, while the Ca2+ concentration is increased. This, together with SEM-EDS analysis, indicates that magnesium-bearing mineral phases are precipitated leading to dissolution of calcite, an observation . This is in-line with other flow-through experiments reported earlier. The observed dissolution and precipitation are sensitive to the effective stress and test temperature. Typically. H, higher stress and temperature lead to increased concentration differences of Mg2+ and Ca2+ concentration changes.. The observed strain can be partitioned additively into a mechanical and chemical driven component.

  20. Creep of chemically vapor deposited SiC fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1984-01-01

    The creep, thermal expansion, and elastic modulus properties for chemically vapor deposited SiC fibers were measured between 1000 and 1500 C. Creep strain was observed to increase logarithmically with time, monotonically with temperature, and linearly with tensile stress up to 600 MPa. The controlling activation energy was 480 + or - 20 kJ/mole. Thermal pretreatments near 1200 and 1450 C were found to significantly reduce fiber creep. These results coupled with creep recovery observations indicate that below 1400 C fiber creep is anelastic with neglible plastic component. This allowed a simple predictive method to be developed for describing fiber total deformation as a function of time, temperature, and stress. Mechanistic analysis of the property data suggests that fiber creep is the result of beta-SiC grain boundary sliding controlled by a small percent of free silicon in the grain boundaries.

  1. High temperature deformation mechanism of 15CrODS ferritic steels at cold-rolled and recrystallized conditions

    NASA Astrophysics Data System (ADS)

    Sugino, Yoshito; Ukai, Shigeharu; Oono, Naoko; Hayashi, Shigenari; Kaito, Takeji; Ohtsuka, Satoshi; Masuda, Hiroshi; Taniguchi, Satoshi; Sato, Eiichi

    2015-11-01

    The ODS ferritic steels realize potentially higher operating temperature due to structural stability by the dispersed nano-size oxide particles. The deformation process and mechanism of 15CrODS ferritic steels were investigated at 1073 K and 1173 K for the cold-rolled and recrystallized conditions. Tensile and creep tests were conducted at the stress in parallel (LD) and perpendicular (TD) directions to the grain boundaries. Strain rate varied from 10-1 to 10-9 s-1. For the LD specimens, deformation in the cold rolled and recrystallized conditions is reinforced by finely dispersed oxide particles. The dominant deformation process for the recrystallized TD specimen is controlled through the grain boundary sliding and stress accommodation via diffusional creep at temperature of 1173 K and lower strain rate less than 10-4 s-1. The grain boundary sliding couldn't be rate-controlling process at 1073 K for the as-cold rolled TD specimen, where a dynamic recovery of the dislocation produced by cold-rolling is related to the deformation process.

  2. Significance of geometrical relationships between low-temperature intracrystalline deformation microstructures in naturally deformed quartz

    NASA Astrophysics Data System (ADS)

    Derez, T.; Pennock, G.; Drury, M. R.; Sintubin, M.

    2013-12-01

    Although quartz is one of the most studied minerals in the Earth's crust when it comes to its rheology, the interpretation of intracrystalline deformation microstructures with respect to deformation conditions and mechanisms, remains highly contentious. Moreover, inconsistent use of terminology for both deformation microstructures and mechanisms makes a correct assessment of observations and interpretations in published material very difficult. With respect to low-temperature intracrystalline deformation microstructures in quartz, different conflicting genetic models have been proposed. Most probably, the lack of consensus means that there is no unique interpretation for these microstructures, primarily because their initiation and development depend on many ambient conditions. We extensively studied these intracrystalline deformation microstructures by means of optical microscopy, Hot-Cathodoluminescence, SEM-Cathodoluminescence and Electron Backscatter Diffraction Orientation Imaging, in vein quartz of the High-Ardenne slate belt (Belgium, France, Luxemburg, Germany), (de)formed in a low-temperature regime. Firstly, we propose a new, purely descriptive terminology for the low-temperature intracrystalline deformation microstructures in naturally deformed quartz: fine extinction bands (FEB), wide extinction bands (WEB) and strings. The strings can be further subdivided into blocky (BS), straight (SS) and recrystallised (RS) morphological types. FEBs have consistently been called deformation lamellae in quartz and planar slip bands in metals. WEBs have been called deformation bands, prismatic kink bands or type II kink bands. Strings have formerly been called shear bands, deformation bands or type I kink bands. No distinction between blocky and straight morphological string types had ever been made. Secondly, a survey of the pre-recrystallisation stages in the history of the intracrystalline deformation microstructures reveals that the different types of low-temperature

  3. Deformation mechanisms in a precipitation-strengthened ferritic superalloy revealed by in situ neutron diffraction studies at elevated temperatures

    DOE PAGESBeta

    Huang, Shenyan; Gao, Yanfei; An, Ke; Zheng, Lili; Wu, Wei; Teng, Zhenke; Liaw, Peter K

    2014-10-22

    In this study, the ferritic superalloy Fe–10Ni–6.5Al–10Cr–3.4Mo strengthened by ordered (Ni,Fe)Al B2-type precipitates is a candidate material for ultra-supercritical steam turbine applications above 923 K. Despite earlier success in improving its room-temperature ductility, the creep resistance of this material at high temperatures needs to be further improved, which requires a fundamental understanding of the high-temperature deformation mechanisms at the scales of individual phases and grains. In situ neutron diffraction has been utilized to investigate the lattice strain evolution and the microscopic load-sharing mechanisms during tensile deformation of this ferritic superalloy at elevated temperatures. Finite-element simulations based on the crystal plasticitymore » theory are employed and compared with the experimental results, both qualitatively and quantitatively. Based on these interphase and intergranular load-partitioning studies, it is found that the deformation mechanisms change from dislocation slip to those related to dislocation climb, diffusional flow and possibly grain boundary sliding, below and above 873 K, respectively. Insights into microstructural design for enhancing creep resistance are also discussed.« less

  4. Deformation mechanisms in a precipitation-strengthened ferritic super alloy revealed by in situ neutron dffraction studies at elevated temperatures

    SciTech Connect

    Huang, Shenyan; Gao, Yanfei; An, Ke; Zheng, Lili; Teng, Zhenke; Wu, Wei; Liaw, Peter K.

    2015-01-01

    The ferritic superalloy Fe–10Ni–6.5Al–10Cr–3.4Mo strengthened by ordered (Ni,Fe)AlB2-type precipitates is a candidate material for ultra-supercritical steam turbine applications above 923 K. Despite earlier success in improving its room-temperature ductility, the creep resistance of this material at high temperatures needs to be further improved, which requires a fundamental understanding of the high-temperature deformation mechanisms at the scales of individual phases and grains. In situ neutron diffraction has been utilized to investigate the lattice strain evolution and the microscopic load-sharing mechanisms during tensile deformation of this ferritic superalloy at elevated temperatures. Finite-element simulations based on the crystal plasticity theory are employed and compared with the experimental results, both qualitatively and quantitatively. Based on these interphase and intergranular load-partitioning studies, it is found that the deformation mechanisms change from dislocation slip to those related to dislocation climb, diffusional flow and possibly grain boundary sliding, below and above 873 K, respectively. Insights into microstructural design for enhancing creep resistance are also discussed.

  5. Deformation mechanisms in a precipitation-strengthened ferritic superalloy revealed by in situ neutron diffraction studies at elevated temperatures

    SciTech Connect

    Huang, Shenyan; Gao, Yanfei; An, Ke; Zheng, Lili; Wu, Wei; Teng, Zhenke; Liaw, Peter K

    2014-10-22

    In this study, the ferritic superalloy Fe–10Ni–6.5Al–10Cr–3.4Mo strengthened by ordered (Ni,Fe)Al B2-type precipitates is a candidate material for ultra-supercritical steam turbine applications above 923 K. Despite earlier success in improving its room-temperature ductility, the creep resistance of this material at high temperatures needs to be further improved, which requires a fundamental understanding of the high-temperature deformation mechanisms at the scales of individual phases and grains. In situ neutron diffraction has been utilized to investigate the lattice strain evolution and the microscopic load-sharing mechanisms during tensile deformation of this ferritic superalloy at elevated temperatures. Finite-element simulations based on the crystal plasticity theory are employed and compared with the experimental results, both qualitatively and quantitatively. Based on these interphase and intergranular load-partitioning studies, it is found that the deformation mechanisms change from dislocation slip to those related to dislocation climb, diffusional flow and possibly grain boundary sliding, below and above 873 K, respectively. Insights into microstructural design for enhancing creep resistance are also discussed.

  6. Lifetimes statistics for single Kevlar 49 aramid filaments in creep-rupture at elevated temperatures

    SciTech Connect

    Wu, H.F.

    1987-01-01

    Kevlar 49 fibrous composites are routinely fabricated to have strengths above 1.5 GPa(200 ksi), but in many applications one would like to sustain such stresses for long time periods, sometimes at elevated temperatures. Thus the temperature dependence of the creep-rupture process in the fibers is of interest. Experimental data are presented for the lifetime of single Kevlar 49 filaments under constant stress at elevated temperatures. The goal of this research was to fully characterize the statistical strength and lifetime behavior of single filaments in order to separate fiber effects from fiber/matrix interactions in the creep-rupture lifetime of Kevlar 49/epoxy composites as described for example in Phoenix and Wu (1983). First we conducted experiments to determine distributions for the strength of filaments from the two distinct spools as a function of temperature. As expected, the data could generally be fitted by a two-parameter Weibull distribution. Lifetime experiments at 80 and 130/sup 0/C were conducted at several stress levels chosen as suitable fractions of the Weibull scale parameter for short-term strength for that temperature. The lifetime data were well modelled by a two-parameter Weibull distribution with large variability.

  7. Dislocation creep of fine-grained olivine

    NASA Astrophysics Data System (ADS)

    Faul, U. H.; Fitz Gerald, J. D.; Farla, R. J. M.; Ahlefeldt, R.; Jackson, I.

    2011-01-01

    Deformation experiments conducted in a gas medium apparatus at temperatures from 1200 to 1350°C with a fine-grained, solution-gelation derived Fe-bearing olivine show a stress dependence of the strain rate at stresses above ˜150 MPa, which is much stronger than previously reported for polycrystalline samples. The data can be fit by a power law with ??σn with n ˜ 7-8, or equally well by a Peierls creep law with exponential stress dependence. Due to the observed strong stress dependence the samples deform at significantly higher strain rates at a given stress than single crystals or coarse-grained polycrystals with n ˜ 3.5. TEM observations indicate the presence of dislocations with at least two different Burgers vectors, with free dislocations predominantly of screw character. Subgrain walls are present but are only weakly developed and have small misorientation angles. Both the rheology and dislocation structures are consistent with creep rate-limited by dislocation glide or cross slip for aggregates with grain sizes smaller than or approaching the recrystallized grain size. Deformation mechanism maps extrapolated to lithospheric temperatures using the melt-free diffusion creep rheology of Faul and Jackson (2007), the dislocation creep rheology of Hirth and Kohlstedt (2003), and the results described here indicate that deformation conditions of ultramylonitic shear zones fall near the triple point of Peierls, dislocation, and diffusion creep.

  8. Evidence of post-seismic creep type deformations derived by tilt and acoustic emission monitoring of mining induced seismic events

    NASA Astrophysics Data System (ADS)

    Milev, Alexander; Share, Pieter-Ewald; Naoi, Makoto; Durrheim, Raymond; Yabe, Yasuo; Ogasawara, Hiroshi; Nakatani, Masao

    2015-04-01

    In this study we try to understand pre- and post-failure rock behavior associated with mining induced seismic events. This involves underground installation of various high precision instruments, including geophones, acoustic emission sensors, tilt- and strain-meters at a number of sites in deep level South African gold mines. The rate of tilt, strain and the seismic ground motion were analysed in order to understand the coseismic and aseismic deformation of the rocks. A good correspondence between the coseismic and the aseismic deformations was found. The rate of coseismic and aseismic tilt, as well as seismicity recorded by the mine seismic network, are approximately constant until the daily blasting time, which takes place from about 19:30 until shortly before 21:00. During the blasting time and the subsequent seismic events, the coseismic tilt and strain shows a rapid increase. Much of the aseismic deformation, however, occurs independently of the seismic events and blasting. In an attempt to distinguish between the different mechanisms of tilting two types of events were recognized. The "fast" seismic events characterized with sharp increase of the tilt during the seismic rupture and "slow" seismic events characterized by creep type post seismic deformations. Tilt behaviour before and after a seismic event was also analysed. The fact that no recognizable aftertilt was observed for more of the "fast" seismic events means that there is no gradual release of stress and an associated continuous strain rate change afterwards. It can therefore be concluded that a large seismic event causes a rapid change in the state of stress rather than a gradual change in the strain rate During the monitoring period a seismic event with MW 2.2 occurred in the vicinity of the instrumented site. This event was recorded by both the CSIR integrated monitoring system and JAGUARS acoustic emission network. More than 21,000 AE aftershocks were located in the first 150 hours after the

  9. Diffusion creep of enstatite at high pressures

    NASA Astrophysics Data System (ADS)

    Zhang, G.; Mei, S.; Kohlstedt, D. L.

    2014-12-01

    Deformation behavior of fine-grained enstatite (g.s. ~ 8 μm) was investigated with triaxial compressive creep experiments at high pressures (4.2 - 6.9 GPa) and high temperatures (1373 - 1573 K) using a deformation-DIA apparatus. Experiments were carried out under anhydrous conditions. In each experiment, a sample column composed of a sample and alumina pistons was assembled with a boron nitride sleeve and graphite resistance heater into a 6.2-mm edge length cubic pressure medium. Experiments were carried out at the National Synchrotron Light Source at Brookhaven National Laboratory. In a run, differential stress and sample displacement were monitored in-situ using synchrotron x-ray diffraction and radiography, respectively. Based on results from this study, the deformation behavior of enstatite under anhydrous conditions has been quantitatively presented in the form of a flow law that describes the dependence of deformation rate on stress, temperature, and pressure. Specifically, data fitting yields the dependence of creep rate on stress with an exponent of n ≈ 1; indicating samples were deformed in the regime of diffusion creep. Experimental results also yield the dependences of creep rate on temperature and pressure with an activation energy of ~250 kJ/mol and activation volume of ~3.5×10-6 m3/mol, respectively. The flow laws for enstatite, one important constituent component for the upper mantle, quantified from this study provides a necessary constraint for modeling the dynamic activities occurring within Earth's interior.

  10. Compilation of Surface Creep on California Faults and Comparison of WGCEP 2007 Deformation Model to Pacific-North American Plate Motion

    USGS Publications Warehouse

    Wisely, Beth A.; Schmidt, David A.; Weldon, Ray J., II

    2008-01-01

    This Appendix contains 3 sections that 1) documents published observations of surface creep on California faults, 2) constructs line integrals across the WG-07 deformation model to compare to the Pacific ? North America plate motion, and 3) constructs strain tensors of volumes across the WG-07 deformation model to compare to the Pacific ? North America plate motion. Observation of creep on faults is a critical part of our earthquake rupture model because if a fault is observed to creep the moment released as earthquakes is reduced from what would be inferred directly from the fault?s slip rate. There is considerable debate about how representative creep measured at the surface during a short time period is of the whole fault surface through the entire seismic cycle (e.g. Hudnut and Clark, 1989). Observationally, it is clear that the amount of creep varies spatially and temporally on a fault. However, from a practical point of view a single creep rate is associated with a fault section and the reduction in seismic moment generated by the fault is accommodated in seismic hazard models by reducing the surface area that generates earthquakes or by reducing the slip rate that is converted into seismic energy. WG-07 decided to follow the practice of past Working Groups and the National Seismic Hazard Map and used creep rate (where it was judged to be interseismic, see Table P1) to reduce the area of the fault surface that generates seismic events. In addition to following past practice, this decision allowed the Working Group to use a reduction of slip rate as a separate factor to accommodate aftershocks, post seismic slip, possible aseismic permanent deformation along fault zones and other processes that are inferred to affect the entire surface area of a fault, and thus are better modeled as a reduction in slip rate. C-zones are also handled by a reduction in slip rate, because they are inferred to include regions of widely distributed shear that is not completely

  11. Development of a constitutive model for creep and life prediction of advanced silicon nitride ceramics

    SciTech Connect

    Ding, J.L.; Liu, K.C.; Brinkman, C.R.

    1992-12-31

    A constitutive model capable of describing deformation and predicting rupture life was developed for high temperature ceramic materials under general thermal-mechanical loading conditions. The model was developed based on the deformation and fracture behavior observed from a systematic experimental study on an advanced silicon nitride (Si{sub 3}N{sub 4}) ceramic material. Validity of the model was evaluated with reference to creep and creep rupture data obtained under constant and stepwise-varied loading conditions, including the effects of annealing on creep and creep rupture behavior.

  12. Creep induced substructures in titanium aluminide

    NASA Astrophysics Data System (ADS)

    Cerreta, Ellen Kathleen

    Many investigations have examined the creep properties of titanium aluminides. Attempts to classify observed behaviors with existing models for high temperature deformation have been met with limited success. Several researchers have shown that an understanding of substructural evolution in the early stages of the creep curve may offer insight into the mechanisms, which control the rate of deformation. Creep deformation has been shown to include twinning, recrystallization, grain boundary sliding, ordinary and super dislocation activity, and faulting depending on the microstructure of the alloy and testing conditions. However, the environments that these alloys are likely to be exposed to are not similar to the test conditions in the literature. Furthermore the emphasis of much of the research into this group of alloys has been on the effects of microstructure particularly, the volume fraction of lamellar phase and ternary elemental additions. With all of these studies little information is available on the deformation behavior of the gamma phase. The alloys in these studies are mostly composed of the gamma phase and yet its creep behavior is not well understood. For this reason single phase binary gamma titanium aluminides were investigated in this study. To understand the effects of aluminum, interstitial oxygen content, and stress on creep, five alloys of varying Al concentrations and interstitial oxygen contents were deformed at temperatures ranging from 700--800°C and at stresses of 150, 200, and 250MPa. Full creep curves were developed under these conditions and phenomenological parameters for creep were calculated from these data. Additional tests were interrupted during primary and secondary creep at 760°C. Specimens from the interrupted tests as well as from the as-processed materials were examined optically and by TEM. Creep data and the microscopy were analyzed in concert to determine rate-controlling mechanisms for creep. Evolution of the substructure

  13. Tensile behavior and cyclic creep of continuous fiber-reinforced glass matrix composites at room and elevated temperatures

    NASA Astrophysics Data System (ADS)

    Boccaccini, A. R.; West, G.; Janczak, J.; Lewis, M. H.; Kern, H.

    1997-06-01

    In this study we investigated the stress-strain behavior at room and elevated temperatures and the tensile creep and cyclic creep response of a unidirectional SiC fiber-reinforced aluminosilicate glass matrix composite. The interfacial condition of the as-received material was measured by a push-out indentation technique. The stress-strain behavior was that expected for this kind of composite, i.e. “pseudoductile” behavior with extensive fiber “pull-out” at room temperature and brittle failure at intermediate temperatures (750 °C) due to oxidation embrittlement. The stiffness of the composite at 750°C was analyzed for different loading rates, highlighing the influence of the loading rate on apparent composite stiffness, due to matrix softening. The creep studies were conducted at temperatures above and below the softening temperature of the glass (T g, 745 °C) in air. The cyclic creep experiments showed the existence of extensive viscous strain recovery during the unloading period. The creep strain recovery was quantified using strain recovery ratios. These ratios showed a slight dependence on the temperatures investigated (700 and 750 °C). The crept composites retained their “graceful” fracture behavior only partially after testing, indicating that oxidation of the fiber/matrix interface due to oxygen diffusion through the matrix occurred in the peripheral area of the samples.

  14. Effect of Nb and Cu on the high temperature creep properties of a high Mn–N austenitic stainless steel

    SciTech Connect

    Lee, Kyu-Ho; Suh, Jin-Yoo; Huh, Joo-Youl; Park, Dae-Bum; Hong, Sung-Min; Shim, Jae-Hyeok; Jung, Woo-Sang

    2013-09-15

    The effect of Nb and Cu addition on the creep properties of a high Mn–N austenitic stainless steel was investigated at 600 and 650 °C. In the original high Mn–N steel, which was initially precipitate-free, the precipitation of M{sub 23}C{sub 6} (M = Cr, Fe) and Cr{sub 2}N took place mostly on grain boudaries during creep deformation. On the other hand, the minor addition of Nb resulted in high number density of Z-phases (CrNbN) and MX (M = Nb; X = C, N) carbonitrides inside grains by combining with a high content of N, while suppressing the formation of Cr{sub 2}N. The addition of Cu gave rise to the independent precipitation of nanometer-sized metallic Cu particles. The combination of the different precipitate-forming mechanisms associated with Z-phase, MX and Cu-rich precipitates turned out to improve the creep-resistance significantly. The thermodynamics and kinetics of the precipitation were discussed using thermo-kinetic simulations. - Highlights: • The creep rupture life was improved by Nb and Cu addition. • The creep resistance of the steel A2 in this study was comparable to that of TP347HFG. • The size of Z-phase and MX carbonitride did not change significantly after creep test. • The nanometer sized Cu-rich precipitate was observed after creep. • The predicted size of precipitates by MatCalc agreed well with measured size.

  15. Interseismic deformation and creep along the central section of the North Anatolian Fault (Turkey): InSAR observations and implications for rate-and-state friction properties

    NASA Astrophysics Data System (ADS)

    Kaneko, Y.; Fialko, Y.; Sandwell, D. T.; Tong, X.; Furuya, M.

    2013-01-01

    AbstractWe present high-resolution measurements of interseismic <span class="hlt">deformation</span> along the central section of the North Anatolian Fault (NAF) in Turkey using interferometric synthetic aperture radar data from the Advanced Land Observing Satellite and Envisat missions. We generated maps of satellite line-of-sight velocity using five ascending Advanced Land Observing Satellite tracks and one descending Envisat track covering the NAF between 31.2°E and 34.3°E. The line-of-sight velocity reveals discontinuities of up to ˜5 mm/yr across the Ismetpasa segment of the NAF, implying surface <span class="hlt">creep</span> at a rate of ˜9 mm/yr; this is a large fraction of the inferred slip rate of the NAF (21-25 mm/yr). The lateral extent of significant surface <span class="hlt">creep</span> is about 75 km. We model the inferred surface velocity and shallow fault <span class="hlt">creep</span> using numerical simulations of spontaneous earthquake sequences that incorporate laboratory-derived rate and state friction. Our results indicate that frictional behavior in the Ismetpasa segment is velocity strengthening at shallow depths and transitions to velocity weakening at a depth of 3-6 km. The inferred depth extent of shallow fault <span class="hlt">creep</span> is 5.5-7 km, suggesting that the deeper locked portion of the partially <span class="hlt">creeping</span> segment is characterized by a higher stressing rate, smaller events, and shorter recurrence interval. We also reproduce surface velocity in a locked segment of the NAF by fault models with velocity-weakening conditions at shallow depth. Our results imply that frictional behavior in a shallow portion of major active faults with little or no shallow <span class="hlt">creep</span> is mostly velocity weakening.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006JSG....28..902W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006JSG....28..902W"><span id="translatedtitle">Quartz veins <span class="hlt">deformed</span> by diffusion <span class="hlt">creep</span>-accommodated grain boundary sliding during a transient, high strain-rate event in the Southern Alps, New Zealand</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wightman, Ruth H.; Prior, David J.; Little, Timothy A.</p> <p>2006-05-01</p> <p>The crystallographic preferred orientations (CPOs) and microstructures of <span class="hlt">deformed</span> quartz veins were measured for four samples in the hanging-wall of the Alpine Fault in the Southern Alps, New Zealand. Their <span class="hlt">deformation</span> and exhumation has occurred since 4 Ma. The quartz veins have been ductilely sheared to finite shear-strains of 5-15 in late Cenozoic shear zones at 450±50 °C, 310±90 MPa and strain-rates between 2×10 -11 and 2×10 -9 s -1. The sheared veins have a polygonal microstructure with few subgrains and an average grain-size of ˜100 μm. The CPO of the veins is random to very weak within the shear zones. We suggest that dislocation <span class="hlt">creep</span> accommodated initial shear <span class="hlt">deformation</span>, at high stresses and strain-rates. The <span class="hlt">deformation</span> must have created a strong CPO and concomitant dynamic recrystallization reduced the grain-size significantly. Dissipation of stresses during initial <span class="hlt">deformation</span> lead to a stress and strain-rate drop required for a switch to diffusion <span class="hlt">creep</span>-accommodated grain boundary sliding (GBS). Continued shearing accommodated by GBS destroyed the CPO. Post-<span class="hlt">deformational</span> grain growth gave rise to a final polygonal microstructure with a similar grain size in veins and in the wall rocks. Analysis of existing experimental data suggest that this sequence of events is possible in the time available. Rates of all processes may have been enhanced by the presence of a water-rich fluid within the shear zones. These observations of naturally <span class="hlt">deformed</span> rocks provide a model for the processes that may occur during short-lived <span class="hlt">deformation</span> at transiently-high stresses at mid-crustal depths or deeper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10135702','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10135702"><span id="translatedtitle">Investigation of the rate-controlling mechanism(s) for high <span class="hlt">temperature</span> <span class="hlt">creep</span> and the relationship between <span class="hlt">creep</span> and melting by use of high pressure as a variable. Progress report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Not Available</p> <p>1991-12-31</p> <p>Using high pressure as a variable, the rate-controlling mechanism for high <span class="hlt">temperature</span> <span class="hlt">creep</span> and the relationship between <span class="hlt">creep</span> and melting is investigated for silicon and nickel. An apparatus is used in which the samples are heated to melting point and subjected to 1 to 3 GigaPascal pressure. The stress behavior of the materials are then studied.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25300893','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/25300893"><span id="translatedtitle"><span class="hlt">Temperature</span>-dependent elastic anisotropy and mesoscale <span class="hlt">deformation</span> in a nanostructured ferritic alloy.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Stoica, G M; Stoica, A D; Miller, M K; Ma, D</p> <p>2014-01-01</p> <p>Nanostructured ferritic alloys are a new class of ultrafine-grained oxide dispersion-strengthened steels that have promising properties for service in extreme environments in future nuclear reactors. This is due to the remarkable stability of their complex microstructures containing numerous Y-Ti-O nanoclusters within grains and along grain boundaries. Although nanoclusters account primarily for the exceptional resistance to irradiation damage and high-<span class="hlt">temperature</span> <span class="hlt">creep</span>, little is known about the mechanical roles of the polycrystalline grains that constitute the ferritic matrix. Here we report an in situ mesoscale characterization of anisotropic responses of ultrafine ferrite grains to stresses using state-of-the-art neutron diffraction. We show the experimental determination of single-crystal elastic constants for a 14YWT alloy, and reveal a strong <span class="hlt">temperature</span>-dependent elastic anisotropy that leads to elastic softening and instability of the ferrite. We also demonstrate, from anisotropy-induced intergranular strains, that a <span class="hlt">deformation</span> crossover exists from low-<span class="hlt">temperature</span> lattice hardening to high-<span class="hlt">temperature</span> lattice softening in response to extensive plastic <span class="hlt">deformation</span>. PMID:25300893</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014NatCo...5E5178S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014NatCo...5E5178S"><span id="translatedtitle"><span class="hlt">Temperature</span>-dependent elastic anisotropy and mesoscale <span class="hlt">deformation</span> in a nanostructured ferritic alloy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Stoica, G. M.; Stoica, A. D.; Miller, M. K.; Ma, D.</p> <p>2014-10-01</p> <p>Nanostructured ferritic alloys are a new class of ultrafine-grained oxide dispersion-strengthened steels that have promising properties for service in extreme environments in future nuclear reactors. This is due to the remarkable stability of their complex microstructures containing numerous Y-Ti-O nanoclusters within grains and along grain boundaries. Although nanoclusters account primarily for the exceptional resistance to irradiation damage and high-<span class="hlt">temperature</span> <span class="hlt">creep</span>, little is known about the mechanical roles of the polycrystalline grains that constitute the ferritic matrix. Here we report an in situ mesoscale characterization of anisotropic responses of ultrafine ferrite grains to stresses using state-of-the-art neutron diffraction. We show the experimental determination of single-crystal elastic constants for a 14YWT alloy, and reveal a strong <span class="hlt">temperature</span>-dependent elastic anisotropy that leads to elastic softening and instability of the ferrite. We also demonstrate, from anisotropy-induced intergranular strains, that a <span class="hlt">deformation</span> crossover exists from low-<span class="hlt">temperature</span> lattice hardening to high-<span class="hlt">temperature</span> lattice softening in response to extensive plastic <span class="hlt">deformation</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22476098','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22476098"><span id="translatedtitle">Effect of minor carbon additions on the high-<span class="hlt">temperature</span> <span class="hlt">creep</span> behavior of a single-crystal nickel-based superalloy</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Wang, L. Wang, D.; Liu, T.; Li, X.W.; Jiang, W.G.; Zhang, G.; Lou, L.H.</p> <p>2015-06-15</p> <p>Different amounts of carbon were added to a single-crystal nickel-based superalloy. The microstructural evolution of these alloys before and after high-<span class="hlt">temperature</span> <span class="hlt">creep</span> tests was investigated by employing scanning electron microscopy and transmission electron microscopy. Upon increasing the carbon contents, the volume fraction and diameter of the carbides increased gradually: however, the <span class="hlt">creep</span> lives of the alloys increased slightly at first and subsequently decreased. The formation of second-phase particles, such as the nano-sized M{sub 23}C{sub 6}, blocky and needle-shaped μ phase, was observed in the <span class="hlt">creep</span> samples, which was closely related to the high-<span class="hlt">temperature</span> <span class="hlt">creep</span> behaviors. - Highlights: • <span class="hlt">Creep</span> behaviors of alloys with different amounts of carbon were investigated. • The <span class="hlt">creep</span> rupture lives increased and later decreased with more carbon. • Second-phase particles were responsible for the different <span class="hlt">creep</span> behaviors.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li class="active"><span>14</span></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_14 --> <div id="page_15" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="281"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880012134','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880012134"><span id="translatedtitle">A unified <span class="hlt">creep</span>-plasticity model suitable for thermo-mechanical loading</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Slavik, D.; Sehitoglu, H.</p> <p>1988-01-01</p> <p>An experimentally based unified <span class="hlt">creep</span>-plasticity constitutive model was implemented for 1070 steel. Accurate rate and <span class="hlt">temperature</span> effects were obtained for isothermal and thermo-mechanical loading by incorporating <span class="hlt">deformation</span> mechanisms into the constitutive equations in a simple way.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JNuM..429..257M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JNuM..429..257M"><span id="translatedtitle">Microstructural examination of high <span class="hlt">temperature</span> <span class="hlt">creep</span> failure of Zircaloy-2 cladding in irradiated PHWR fuel pins</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mishra, Prerna; Sah, D. N.; Kumar, Sunil; Anantharaman, S.</p> <p>2012-10-01</p> <p>Cladding samples taken from the ballooned region of the irradiated Zircaloy-2 cladded PHWR fuel pins which failed during isothermal heating tests carried out at 800-900 °C were examined using optical and scanning electron microscopy. The examination of samples from the fuel pin tested at 900 °C showed an intergranular mode of failure in the cladding due to formation of cracks, cavities and zirconium hydride precipitates on the grain boundaries in the cladding material. A thin hard α-Zr(O) layer was observed on outer surface due to dissolution of the oxide layer formed during reactor operation. Grain boundary sliding was identified to be the main mode of <span class="hlt">creep</span> <span class="hlt">deformation</span> of Zircaloy-2 at 900 °C. Examination of the cladding tested at 800 °C showed absence of cracks or cavities in the <span class="hlt">deformed</span> material and no localisation of hydrides was observed at the grain boundaries. The failure of the cladding occurred after necking followed by extensive wall thinning of the cladding tube.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25614154','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/25614154"><span id="translatedtitle">Steady, dynamic, <span class="hlt">creep</span>/recovery, and textural properties of yoghurt/molasses blends: <span class="hlt">Temperature</span> sweep tests and applicability of Cox-Merz rule.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Eroglu, Ali; Bayrambaş, Kadir; Eroglu, Zeynep; Toker, Omer S; Yilmaz, Mustafa T; Karaman, Safa; Dogan, Mahmut</p> <p>2016-01-01</p> <p>In this study, physicochemical, rheological (steady, dynamic, and <span class="hlt">creep</span>/recovery), and textural properties of yoghurt/molasses blends (0, 5, 10, and 15% molasses) were investigated. The blends showed shear thinning behavior, as described by Ostwald de Waele model (R(2) ( )≥ 0.955). Consistency coefficient value (K) of the blends decreased with increasing molasses concentration in the sample. Storage modulus (G') of blends was higher than loss modulus (G″), exhibiting weak gel-like behavior. Molasses addition decreased G' and G″ values. <span class="hlt">Temperature</span> sweep tests indicated that blends followed Arrhenius relationship. A modified Cox-Merz rule was applicable using shift factors. Compliance values (J(t)) increased as molasses concentration increased, revealing that <span class="hlt">deformation</span> stability and internal viscosity (η1) decreased with concentration. <span class="hlt">Creep</span> behavior was characterized using Burger model. Obtained J data as a function of time could be satisfactorily fitted to Burger model (R(2) ( )≥ 0.994). The final percentage recovery of blends remarkably decreased with the increase of molasses concentration. Firmness, consistency, cohesiveness, and viscosity index values decreased with molasses addition. According to the results of the current study, molasses amount to be added to the yoghurt should be determined regarding rheological properties since resistance of the sample to <span class="hlt">deformation</span> decreased with increase in molasses concentration. PMID:25614154</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/16243708','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/16243708"><span id="translatedtitle">High-<span class="hlt">temperature</span> <span class="hlt">creep</span> rupture of low alloy ferritic steel butt-welded pipes subjected to combined internal pressure and end loadings.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Vakili-Tahami, F; Hayhurst, D R; Wong, M T</p> <p>2005-11-15</p> <p>Constitutive equations are reviewed and presented for low alloy ferritic steels which undergo <span class="hlt">creep</span> <span class="hlt">deformation</span> and damage at high <span class="hlt">temperatures</span>; and, a thermodynamic framework is provided for the <span class="hlt">deformation</span> rate potentials used in the equations. Finite element continuum damage mechanics studies have been carried out using these constitutive equations on butt-welded low alloy ferritic steel pipes subjected to combined internal pressure and axial loads at 590 and 620 degrees C. Two dominant modes of failure have been identified: firstly, fusion boundary failure at high stresses; and, secondly, Type IV failure at low stresses. The stress level at which the switch in failure mechanism takes place has been found to be associated with the relative <span class="hlt">creep</span> resistance and lifetimes, over a wide range of uniaxial stresses, for parent, heat affected zone, Type IV and weld materials. The equi-biaxial stress loading condition (mean diameter stress equal to the axial stress) has been confirmed to be the worst loading condition. For this condition, simple design formulae are proposed for both 590 and 620 degrees C. PMID:16243708</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22476003','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22476003"><span id="translatedtitle">Tensile and compressive <span class="hlt">creep</span> behavior of extruded Mg–10Gd–3Y–0.5Zr (wt.%) alloy</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Wang, H.; Wang, Q.D.; Boehlert, C.J.; Yin, D.D.; Yuan, J.</p> <p>2015-01-15</p> <p>The tensile and compressive <span class="hlt">creep</span> behavior of an extruded Mg–10Gd–3Y–0.5Zr (wt.%) alloy was investigated at <span class="hlt">temperatures</span> ranging from 200 °C to 300 °C and under stresses ranging from 30 MPa to 120 MPa. There existed an asymmetry in the tensile and compressive <span class="hlt">creep</span> properties. The minimum <span class="hlt">creep</span> rate of the alloy was slightly greater in tension than in compression. The measured values of the transient strain and initial <span class="hlt">creep</span> rate in compression were greater than those in tension. The <span class="hlt">creep</span> stress exponent was approximately 2.5 at low <span class="hlt">temperatures</span> (T < 250 °C) and 3.4 at higher <span class="hlt">temperatures</span> both in tension and in compression. The compression <span class="hlt">creep</span> activation energy at low <span class="hlt">temperatures</span> and high <span class="hlt">temperatures</span> was 83.4 and 184.3 kJ/mol respectively, while one activation energy (184 kJ/mol) represented the tensile–<span class="hlt">creep</span> behavior over the <span class="hlt">temperature</span> range examined. Dislocation <span class="hlt">creep</span> was suggested to be the main mechanism in tensile <span class="hlt">creep</span> and in the high-<span class="hlt">temperature</span> regime in compressive <span class="hlt">creep</span>, while grain boundary sliding was suggested to dominate in the low-<span class="hlt">temperature</span> regime in compressive <span class="hlt">creep</span>. Precipitate free zones were observed near grain boundaries perpendicular to the loading direction in tension and parallel to the loading direction in compression. Electron backscattered diffraction analysis revealed that the texture changed slightly during <span class="hlt">creep</span>. Non-basal slip was suggested to contribute to the <span class="hlt">deformation</span> after basal slip was introduced. In the tensile–<span class="hlt">creep</span> ruptured specimens, intergranular cracks were mainly observed at general high-angle boundaries. - Highlights: • <span class="hlt">Creep</span> behavior of an extruded Mg–RE alloy was characterized by EBSD. • T5 aging treatment enhanced the tension–compression <span class="hlt">creep</span> asymmetry. • The grains grew slightly during tensile <span class="hlt">creep</span>, but not for compressive <span class="hlt">creep</span>. • Precipitate free zones (PFZs) were observed at specific grain boundaries. • Intergranular fracture was dominant and cracks mainly originated at</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFMMR51A..01S&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFMMR51A..01S&link_type=ABSTRACT"><span id="translatedtitle"><span class="hlt">Creep</span> Behavior of Organic-Rich Shales - Evidences of Microscale Strain Partitioning</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sone, H.; Morales, L. F. G.; Dresen, G. H.</p> <p>2015-12-01</p> <p>Laboratory <span class="hlt">creep</span> experiments conducted using organic-rich shales show that these rocks exhibit some ductility under sustained loading conditions although they may appear to be elastic and brittle (Young's modulus 15-80 GPa) at shorter time scales. At room-<span class="hlt">temperature</span> and in-situ pressure conditions, <span class="hlt">creep</span> strain observed after 3 hours of sustained loading reach strains on the order of 10-5per megapascal of applied differential stress. The <span class="hlt">creep</span> behavior is highly anisotropic such that <span class="hlt">creep</span> occurs more in the direction perpendicular to the bedding plane than in the direction parallel to the bedding plane. In general, we find that the <span class="hlt">creep</span> behavior is largely controlled by the amount of clay mineral and organic content. This is also supported by evidences of elastic stiffening and sample volume reduction during <span class="hlt">creep</span> which imply that the <span class="hlt">creep</span> is accommodated by localized compaction occurring within clay-aggregates and/or organic materials, the relatively porous members in the rock. We also find that the tendency to <span class="hlt">creep</span> has a unique relation with the Young's modulus regardless of the loading direction or the mineral composition. Sone and Zoback (2013) explained this correlation by appealing to the stress partitioning behavior that occurs between the relatively stiff and soft components of the rock, and also by assuming that <span class="hlt">creep</span> only occurs within the soft components, namely the clay and organic contents, with a specific local 3-hour <span class="hlt">creep</span> compliance value of 10-4 MPa-1. In order to confirm that such strain-partitioning occurs during <span class="hlt">creep</span> <span class="hlt">deformation</span>, we also performed <span class="hlt">creep</span> experiments under a scanning electron microscope using a <span class="hlt">deformation</span> stage setup. Such experiments allow us to directly observe the <span class="hlt">deformation</span> and quantify the strain-partitioning occurring between the different mineral constituents with the aid of digital image correlation analysis. Results suggest that strain-partitioning do occur during <span class="hlt">creep</span> <span class="hlt">deformation</span> and inferred <span class="hlt">creep</span> properties of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996MMTA...27..127W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996MMTA...27..127W"><span id="translatedtitle">Effect of <span class="hlt">creep</span> strain on microstructural stability and <span class="hlt">creep</span> resistance of a TiAi/Ti3ai lamellar alloy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wert, J. A.; Bartholomeusz, M. F.</p> <p>1996-01-01</p> <p><span class="hlt">Creep</span> of a TiAl/Ti3Al alloy with a lamellar microstructure causes progressive spheroidization of the lamellar microstructure. Microstructural observations reveal that <span class="hlt">deformation</span>-induced spheroidization (DIS) occurs by <span class="hlt">deformation</span> and fragmentation of lamellae in localized shear zones at interpacket boundaries and within lamellar packets. <span class="hlt">Deformation</span>-induced spheroidization substantially increases the interphase interfacial area per unit volume, demonstrating that DIS is not a coarsening process driven by reduction of interfacial energy per unit volume. <span class="hlt">Creep</span> experiments reveal that DIS increases the minimum <span class="hlt">creep</span> rate (ɛmin) during <span class="hlt">creep</span> at constant stress and <span class="hlt">temperature</span>; the activation energy ( Q c ) and stress exponent ( n) for <span class="hlt">creep</span> are both reduced as a result of DIS. Values of n and Q c for the lamellar microstructure are typical of a dislocation <span class="hlt">creep</span> mechanism, while estimated values of n and Q c for the completely spheroidized microstructure are characteristic of a diffusional <span class="hlt">creep</span> mechanism. The increase in (ɛmin) associated with DIS is thus attributed primarily to a change of <span class="hlt">creep</span> mechanism resulting from microstructural refinement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012PhDT.........6R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012PhDT.........6R"><span id="translatedtitle">The effect of elevated <span class="hlt">temperature</span> on the inelastic <span class="hlt">deformation</span> behavior of PMR-15 solid polymer</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ryther, Chad E. C.</p> <p></p> <p>The inelastic <span class="hlt">deformation</span> behavior of PMR-15 neat resin, a high-<span class="hlt">temperature</span> thermoset polymer, was investigated at <span class="hlt">temperatures</span> in the 274--316 °C range. The experimental program was developed to explore the influence of <span class="hlt">temperature</span> on strain-controlled tensile loading, relaxation and <span class="hlt">creep</span> behaviors. The experimental results clearly demonstrate that the mechanical behavior of PMR-15 polymer exhibits a strong dependence on <span class="hlt">temperature</span>. During strain-controlled tensile loading, the slope of the stress-strain curve in the quasi-elastic region decreases and the slope of the stress-strain curve in the flow stress region increases with increasing <span class="hlt">temperature</span>. At a given strain rate, the flow stress level decreases with increasing <span class="hlt">temperature</span>. Furthermore, the transition from quasi-elastic behavior to inelastic flow becomes less pronounced with increasing <span class="hlt">temperature</span>. During relaxation, the amount of the stress drop for a given prior strain rate decreases with increasing <span class="hlt">temperature</span>. At a given prior strain rate and <span class="hlt">creep</span> stress level, increasing <span class="hlt">temperature</span> results in increased <span class="hlt">creep</span> strain accumulation. Based on the experimental results the Viscoplasticity Based on Overstress for Polymers (VBOP) theory was augmented to account for the effects of elevated <span class="hlt">temperature</span>. Several model parameters were determined to depend on <span class="hlt">temperature</span>. Those parameters were developed into functions of <span class="hlt">temperature</span>. The augmented VBOP was then employed to predict the response of the PMR-15 polymer under various test histories at <span class="hlt">temperatures</span> in the 274--316 °C range. An enhanced procedure for determining VBOP model parameters that utilizes a McLean type dip test to assess the equilibrium stress was developed. Model predictions were considerably improved by employing an enhanced model characterization procedure. Additionally, the effects of prior isothermal aging at various <span class="hlt">temperatures</span> in the 260--316 °C range on the inelastic <span class="hlt">deformation</span> behavior of PMR-15 at 288 °C were evaluated. For</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850003553','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850003553"><span id="translatedtitle">High <span class="hlt">temperature</span> <span class="hlt">deformation</span> of hot-pressed polycrystalline orthoenstatite. Ph.D. Thesis</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dehghan-Banadaki, A.</p> <p>1983-01-01</p> <p>Artificial hot pressed polycrystalline samples were prepared from purified powder of Bamble, Norway, orthoenstatite, (Mg0.86Fe0.14)SiO3. The uniaxial <span class="hlt">creep</span> behavior of the polycrystalline orthoenstatite was studied over stress ranges of 10-180 MPa and <span class="hlt">temperatures</span> of 1500-1700 K (0.82-0.93 T sub m) under two different oxygen fugacities, namely equilibrium (Mo-MoO2 buffer) and a reducing (graphite heating element) atmosphere, respectively. An intergranular glassy phase of different compositions with a cavitational <span class="hlt">creep</span> <span class="hlt">deformation</span> were observed. In the Mo-MoO2 buffer atmosphere with PO2 approx. 10 to the minus 11 power - 10 to the minus 13 power atmospheres, the results of an analytical electron microscopy analysis indicate that the glassy phases are richer in Ca and Al due to the residual impurities after hot pressing. In the reducing atmosphere with an oxygen fugacity of PO2 approx. 10 to the minus 3 power - 10 to the minus 25 power atmospheres, the results of analytical electron microscopy analysis indicate that the glassy phase is almost pure silica with the presence of free iron precipitate on grain facets and at triple junctions due to the reduction of bulk materials.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009PhDT.......107P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009PhDT.......107P"><span id="translatedtitle">Electromagnetic detection and monitoring of <span class="hlt">creep</span> induced damage in high <span class="hlt">temperature</span> resistant steels</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Polar, Alberto</p> <p></p> <p>Monitoring and remaining life assessment of ferritic-martensitic alloys exposed to <span class="hlt">creep</span> was addressed using electromagnetic evaluation. In order to determine the correlation between the <span class="hlt">creep</span> damage and the change in magnetic properties, two steels were exposed to different extent of <span class="hlt">creep</span> and magnetic properties were evaluated for each sample. A close evaluation of the <span class="hlt">creep</span> damage was performed in each sample using optical microscopy, as well as SEM and TEM techniques. It was found that the microstructural changes occurring during the <span class="hlt">creep</span> progress have a correlation with variations in the magnetic response at the different levels of <span class="hlt">creep</span> damage. Saturation decreases as <span class="hlt">creep</span> damage progress due to the increases of demagnetized sites. Remanence shows the characteristic behavior of isotropic materials and coercivity changes as a function of the progress of the <span class="hlt">creep</span> damage. Even though this established correlation may be used to directly monitoring the <span class="hlt">creep</span> damage evolution, a magnetically determined damage factor was defined using the relationship of the hysteretic Jiles-Atherton factors with the extent pf <span class="hlt">creep</span> damage. On the base of existing Continuous Damage Mechanics (CDM) models for <span class="hlt">creep</span>, a model has been proposed for the monitoring and assessment of <span class="hlt">creep</span> damage using the described magnetic damage factor.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22271185','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22271185"><span id="translatedtitle"><span class="hlt">Temperature</span> dependent <span class="hlt">deformation</span> mechanisms in pure amorphous silicon</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kiran, M. S. R. N. Haberl, B.; Williams, J. S.; Bradby, J. E.</p> <p>2014-03-21</p> <p>High <span class="hlt">temperature</span> nanoindentation has been performed on pure ion-implanted amorphous silicon (unrelaxed a-Si) and structurally relaxed a-Si to investigate the <span class="hlt">temperature</span> dependence of mechanical <span class="hlt">deformation</span>, including pressure-induced phase transformations. Along with the indentation load-depth curves, ex situ measurements such as Raman micro-spectroscopy and cross-sectional transmission electron microscopy analysis on the residual indents reveal the mode of <span class="hlt">deformation</span> under the indenter. While unrelaxed a-Si <span class="hlt">deforms</span> entirely via plastic flow up to 200 °C, a clear transition in the mode of <span class="hlt">deformation</span> is observed in relaxed a-Si with increasing <span class="hlt">temperature</span>. Up to 100 °C, pressure-induced phase transformation and the observation of either crystalline (r8/bc8) end phases or pressure-induced a-Si occurs in relaxed a-Si. However, with further increase of <span class="hlt">temperature</span>, plastic flow rather than phase transformation is the dominant mode of <span class="hlt">deformation</span>. It is believed that the elevated <span class="hlt">temperature</span> and pressure together induce bond softening and “defect” formation in structurally relaxed a-Si, leading to the inhibition of phase transformation due to pressure-releasing plastic flow under the indenter.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016E%26PSL.433..350F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016E%26PSL.433..350F"><span id="translatedtitle">New constraints on upper mantle <span class="hlt">creep</span> mechanism inferred from silicon grain-boundary diffusion rates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fei, Hongzhan; Koizumi, Sanae; Sakamoto, Naoya; Hashiguchi, Minako; Yurimoto, Hisayoshi; Marquardt, Katharina; Miyajima, Nobuyoshi; Yamazaki, Daisuke; Katsura, Tomoo</p> <p>2016-01-01</p> <p>The <span class="hlt">creep</span> in the Earth's interior is dominated either by diffusion <span class="hlt">creep</span> which causes Newtonian mantle flow, or by dislocation <span class="hlt">creep</span> which results in non-Newtonian mantle flow. Although previous <span class="hlt">deformation</span> studies on olivine claimed a transition from dislocation <span class="hlt">creep</span> to diffusion <span class="hlt">creep</span> with depth in the upper mantle, they might misunderstand the <span class="hlt">creep</span> rates due to experimental difficulties. Since <span class="hlt">creep</span> in olivine is controlled by silicon diffusion, we measured the silicon grain-boundary diffusion coefficient in well-sintered iron-free olivine aggregates as a function of <span class="hlt">temperature</span>, pressure, and water content, showing activation energy, activation volume, and water content exponent of 220 ± 30 kJ /mol, 4.0 ± 0.7 cm3 /mol, and 0.26 ± 0.07, respectively. Our results based on Si diffusion in forsterite predict that diffusion <span class="hlt">creep</span> dominates at low pressures and low <span class="hlt">temperatures</span>, whereas dislocation <span class="hlt">creep</span> dominates under high pressure and high <span class="hlt">temperature</span> conditions. Water has negligible effects on both diffusion and dislocation <span class="hlt">creep</span>. There is a transition from diffusion <span class="hlt">creep</span> in the shallow upper mantle to dislocation <span class="hlt">creep</span> in deeper regions. This explains the seismic anisotropy increases at the Gutenberg discontinuity beneath oceans and at the mid-lithosphere discontinuity beneath continents.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFM.T31C2607R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFM.T31C2607R"><span id="translatedtitle">Time and space evolution of an active <span class="hlt">creeping</span> zone: competition between brittle and ductile <span class="hlt">deformations</span>, new insights from microstructure studies of SAFOD (San Andreas Fault Observatory at Depth) samples</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Richard, J.; Gratier, J.; Doan, M.; Renard, F.; Boullier, A.</p> <p>2012-12-01</p> <p><span class="hlt">Creep</span> processes can relax an important part of the tectonic stresses in active faults, either by permanent steady-state <span class="hlt">creep</span> or by episodic post-seismic <span class="hlt">creep</span>. Here, our goal is to better constrain the micro-physical parameters that control this transition between seismic and aseismic behavior, both in time and in space. We present new results from microstructural studies on natural samples collected from the SAFOD (San Andreas Fault Observatory at Depth) drilling project, located on the Parkfield segment of the San Andreas Fault (SAF). Seven samples were collected from the main active <span class="hlt">creeping</span> zone: the Central <span class="hlt">Deforming</span> Zone at 3301-3303m depth. We performed chemical and mineralogical analyses and microscope observations on twenty thin sections cut from those samples. In a previous study (Gratier et al., Geology, 2011), we have already shown that pressure solution <span class="hlt">creep</span> is an active <span class="hlt">deformation</span> process in the SAF. We propose a model of microstructural evolution to characterize in which conditions pressure solution <span class="hlt">creep</span> is efficient enough to relax stress and to prevent the nucleation of moderate to large earthquakes. We show that two crucial parameters may accelerate pressure solution: the presence of phyllosilicates and the degree of rock fracturing. The initial structure and composition of the rocks may explain why pressure solution <span class="hlt">creep</span> is efficient or not. Moreover, both the content of phyllosilicates and the degree of fracture may evolve with time at various scales during the seismic cycle: - During interseismic periods (years to millennia): fracturing activates postseismic <span class="hlt">creep</span>. However, the progressive healing of the fracture annihilates this effect. Meanwhile, growth of phyllosilicate minerals, associated with postseismic fluid flow may also activate the <span class="hlt">creep</span> rate. - During much longer geological periods (hundred thousands to millions of years), the composition of gouge material <span class="hlt">deformed</span> by pressure solution evolves by the passive concentration of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T33D..02C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T33D..02C"><span id="translatedtitle">New Insights on the Rheology of Olivine <span class="hlt">Deformed</span> under Lithospheric <span class="hlt">Temperature</span> Conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cordier, P.; Demouchy, S. A.; Mussi, A.; Tommasi, A.</p> <p>2014-12-01</p> <p>Rheology of mantle rocks at lithospheric <span class="hlt">temperatures</span> remains poorly constrained, since most experimental studies on <span class="hlt">creep</span> mechanisms of olivine single crystals ((MgFe)2SiO4, Pbnm) and polycrystalline olivine aggregates were performed at high-<span class="hlt">temperatures</span> (T >> 1200oC). In this study, we report results from <span class="hlt">deformation</span> experiments on oriented single crystals of San Carlos olivine and polycrystalline olivine aggregate at <span class="hlt">temperatures</span> relevant of the uppermost mantle (ranging from 800o to 1090oC) in tri-axial compression. The experiments were carried out at a confining pressure of 300 MPa in a high-resolution gas-medium mechanical testing apparatus at various constant strain rates (from 7 x 10-6 s-1 to 1 x 10-4 s-1). Mechanical tests show that mantle lithosphere is actually weaker than previously inferred from the extrapolation of high-<span class="hlt">temperature</span> experiments. In this study, we present characterization of dislocation microstructures based on transmission electron microscopy and electron tomography. It is shown that below 1000°C, dislocation activity is restricted to [001] glide with a strong predominance of {110} as glide planes. We observe recovery mechanisms which suggest that the mechanical properties observed in laboratory experiments represent an upper bound for the actual behavior of olivine under lithospheric mantle conditions. Moreover, the drastic reduction in slip system activity observed questions the ability of <span class="hlt">deforming</span> olivine aggregates in the ductile regime at such <span class="hlt">temperatures</span>. We show that ductility is preserved thanks to the activation of alternative <span class="hlt">deformation</span> mechanisms in grain boundaries involving disclinations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1242420','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1242420"><span id="translatedtitle">Designing Nanoscale Precipitates in Novel Cobalt-based Superalloys to Improve <span class="hlt">Creep</span> Resistance and Operating <span class="hlt">Temperature</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Dunand, David C.; Seidman, David N.; Wolverton, Christopher; Saal, James E.; Bocchini, Peter J.; Sauza, Daniel J.</p> <p>2014-10-01</p> <p>High-<span class="hlt">temperature</span> structural alloys for aerospace and energy applications have long been dominated by Ni-base superalloys, whose strength and <span class="hlt">creep</span> resistance can be attributed to microstructures consisting of a large volume fraction of ordered (L1<sub>2</sub>) γ'-precipitates embedded in a disordered’(f.c.c.) γ-matrix. These alloys exhibit excellent mechanical behavior and thermal stability, but after decades of incremental improvement are nearing the theoretical limit of their operating <span class="hlt">temperatures</span>. Conventional Co-base superalloys are solid-solution or carbide strengthened; although they see industrial use, these alloys are restricted to lower-stress applications because the absence of an ordered intermetallic phase places an upper limit on their mechanical performance. In 2006, a γ+γ' microstructure with ordered precipitates analogous to (L1<sub>2</sub>) Ni<sub>3</sub>Al was first identified in the Co-Al-W ternary system, allowing, for the first time, the development of Co-base alloys with the potential to meet or even exceed the elevated-<span class="hlt">temperature</span> performance of their Ni-base counterparts. The potential design space for these alloys is complex: the most advanced Ni-base superalloys may contain as many as 8-10 minor alloying additions, each with a specified purpose such as raising the γ' solvus <span class="hlt">temperature</span> or improving <span class="hlt">creep</span> strength. Our work has focused on assessing the effects of alloying additions on microstructure and mechanical behavior of γ'-strengthened Co-base alloys in an effort to lay the foundations for understanding this emerging alloy system. Investigation of the size, morphology, and composition of γ' and other relevant phases is investigated utilizing scanning electron microscopy (SEM) and 3-D picosecond ultraviolet local electrode atom probe tomography (APT). Microhardness, compressive yield stress at ambient and elevated <span class="hlt">temperatures</span>, and compressive high-<span class="hlt">temperature</span> <span class="hlt">creep</span> measurements are employed to extract mechanical behavior</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013MMTA..tmp..473S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013MMTA..tmp..473S"><span id="translatedtitle">High-<span class="hlt">Temperature</span> <span class="hlt">Creep</span> and Oxidation Behavior of Mo-Si-B Alloys with High Ti Contents</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schliephake, Daniel; Azim, Maria; von Klinski-Wetzel, Katharina; Gorr, Bronislava; Christ, Hans-Jürgen; Bei, Hongbin; George, Easo P.; Heilmaier, Martin</p> <p>2013-08-01</p> <p>Multiphase alloys in the Mo-Si-B system are potential high-<span class="hlt">temperature</span> structural materials due to their good oxidation and <span class="hlt">creep</span> resistance. Since they suffer from relatively high densities, the current study focuses on the influence of density-reducing Ti additions on <span class="hlt">creep</span> and oxidation behavior at <span class="hlt">temperatures</span> above 1273 K (1000 °C). Two alloys with compositions of Mo-12.5Si-8.5B-27.5Ti and Mo-9Si-8B-29Ti (in at. pct) were synthesized by arc melting and then homogenized by annealing in vacuum for 150 hours at 1873 K (1600 °C). Both alloys show similar <span class="hlt">creep</span> behavior at stresses of 100 to 300 MPa and <span class="hlt">temperatures</span> of 1473 K and 1573 K (1200 °C and 1300 °C), although they possess different intermetallic volume fractions. They exhibit superior <span class="hlt">creep</span> resistance and lower density than a state-of-the-art Ni-base superalloy (single-crystalline CMSX-4) as well as other Mo-Si-B alloys. Solid solution strengthening due to Ti was confirmed by Vickers hardness measurements and is believed to be the reason for the significant increase in <span class="hlt">creep</span> resistance compared to Mo-Si-B alloys without Ti, but with comparable microstructural length scales. The addition of Ti degrades oxidation resistance relative to a Mo-9Si-8B reference alloy due to the formation of a relatively porous duplex layer with titania matrix enabling easy inward diffusion of oxygen.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=20110014514&hterms=desai&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3D%2528c%2Bdesai%2529','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=20110014514&hterms=desai&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3D%2528c%2Bdesai%2529"><span id="translatedtitle">Experiment and Modeling of Simultaneous <span class="hlt">Creep</span>, Plasticity and Transformation of High <span class="hlt">Temperature</span> Shape Memory Alloys During Cyclic Actuation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Kumar, Parikshith K.; Desai, Uri; Chatzigeorgiou, George; Lagoudas, Dimitris C.; Monroe, James; Karaman, Ibrahim; Noebe, Ron; Bigelow, Glen</p> <p>2010-01-01</p> <p>The present work is focused on studying the cycling actuation behavior of HTSMAs undergoing simultaneous <span class="hlt">creep</span> and transformation. For the thermomechanical testing, a high <span class="hlt">temperature</span> test setup was assembled on a MTS frame with the capability to test up to <span class="hlt">temperatures</span> of 600 C. Constant stress thermal cycling tests were conducted to establish the actuation characteristics and the phase diagram for the chosen HTSMA. Additionally, <span class="hlt">creep</span> tests were conducted at constant stress levels at different test <span class="hlt">temperatures</span> to characterize the <span class="hlt">creep</span> behavior of the alloy over the operational range. A thermodynamic constitutive model is developed and extended to take into account a) the effect of multiple thermal cycling on the generation of plastic strains due to transformation (TRIP strains) and b) both primary and secondary <span class="hlt">creep</span> effects. The model calibration is based on the test results. The <span class="hlt">creep</span> tests and the uniaxial tests are used to identify the viscoplastic behavior of the material. The parameters for the SMA properties, regarding the transformation and transformation induced plastic strain evolutions, are obtained from the material phase diagram and the thermomechanical tests. The model is validated by predicting the material behavior at different thermomechanical test conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/192402','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/192402"><span id="translatedtitle">Development of a steady state <span class="hlt">creep</span> behavior model of polycrystalline tungsten for bimodal space reactor application</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Purohit, A.; Hanan, N.A.; Bhattacharyya, S.K.; Gruber, E.E.</p> <p>1995-02-01</p> <p>The fuel element for one of the many reactor concepts being currently evaluated for bimodal applications in space consists of spherical fuel particles clad with tungsten or alloys of tungsten. The fuel itself consists of stabilized UO{sub 2}. One of the life limiting phenomena for the fuel element is failure of the cladding because of <span class="hlt">creep</span> <span class="hlt">deformation</span>. This report summarizes the information available in literature regarding the <span class="hlt">creep</span> <span class="hlt">deformation</span> of tungsten and its alloys and proposes a relation to be used for calculating the <span class="hlt">creep</span> strains for elevated <span class="hlt">temperatures</span> in the low stress region ({sigma} {le} 20 MPa). Also, results of the application of this <span class="hlt">creep</span> relation to one of the reactor design concepts (NEBA-3) are discussed. Based on the traditional definition of <span class="hlt">creep</span> <span class="hlt">deformation</span>, the <span class="hlt">temperatures</span> of 1500 K to 2900 K for tungsten and its alloys are considered to be in the {open_quotes}high{close_quotes} <span class="hlt">temperature</span> range. In this <span class="hlt">temperature</span> range, the rate controlling mechanisms for <span class="hlt">creep</span> <span class="hlt">deformation</span> are believed to be non-conservative motion of screw dislocations and short circuit diffusional paths. Extensive theoretical work on <span class="hlt">creep</span> and in particular for <span class="hlt">creep</span> of tungsten and its alloys have been reported in the literature. These theoretical efforts have produced complex mathematical models that require detailed materials properties. These relations, however, are not presently suitable for the <span class="hlt">creep</span> analysis because of lack of consistent material properties required for their use. Variations in material chemistry and thermomechanical pre-treatment of tungsten have significant effects on <span class="hlt">creep</span> and the mechanical properties. Analysis of the theoretical models and limited data indicates that the following empirical relation originally proposed by M. Jacox of INEL and the Air Force Phillips Laboratory, for calculating <span class="hlt">creep</span> <span class="hlt">deformation</span> of tungsten cladding, can be used for the downselection of preliminary bimodal reactor design concepts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850023221','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850023221"><span id="translatedtitle">Micromechanics of high <span class="hlt">temperature</span> <span class="hlt">deformation</span> and failure</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nasser, S. N.; Weertman, J. R.</p> <p>1985-01-01</p> <p>The micromechanics of the constitutive behavior of elastoplastic materials at high <span class="hlt">temperatures</span> was examined. The experimental work focused on the development of microscopic defects in superalloys (Waspaloy), especially the formation of voids at grain boundary carbides, and slip induced surface cracks within grains upon cyclic loading at high <span class="hlt">temperatures</span>. The influence of these defects on the life expectancy of the material was examined. The theoretical work consists of two parts: (1) analytical description of the mechanisms that lead to defects observed experimentally; and (2) development of macroscopic elastoplastic nonlinear constitutive relations based on mechanical modeling.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999MMTA...30.2049L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999MMTA...30.2049L"><span id="translatedtitle"><span class="hlt">Creep</span> <span class="hlt">deformation</span> and fracture of a Cr/Mo/V bolting steel containing selected trace-element additions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Larouk, Z.; Pilkington, R.</p> <p>1999-08-01</p> <p>The article reports the <span class="hlt">creep</span> behavior, at 565 °C, of 1Cr1Mo0.75V (Ti, B) (Durehete D1055) steel, in each of two grain sizes and doped with individual trace elements such as P, As, and Sn, in comparison to a reference cast of the base material containing 0.08 wt pct Ti. The addition of the trace elements P, As, or Sn (each <0.045 wt pct) appears to produce no significant effect on <span class="hlt">creep</span> strength or <span class="hlt">creep</span> crack-growth resistance at 565 °C. The fine-grained material shows low <span class="hlt">creep</span> strength but notch strengthening, while the coarse-grained material shows higher <span class="hlt">creep</span> strength and exhibits notch weakening for test times up to 2750 hours. From <span class="hlt">creep</span> crack-growth tests, it appears that the C* parameter is not appropriate for correlating the <span class="hlt">creep</span> crack-growth rate under the present test conditions. The parameters K I or σ net are found to correlate better, but, from the present data, it is not possible to judge which of these parameters is more appropriate for general use. It is suggested that the presence of Ti in CrMoV steels has an inhibiting effect on trace-element embrittlement.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li class="active"><span>15</span></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_15 --> <div id="page_16" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="301"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/6286841','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6286841"><span id="translatedtitle">Flaw assessment guide for high-<span class="hlt">temperature</span> reactor components subject to <span class="hlt">creep</span>-fatigue loading</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ainsworth, R.A. . Berkeley Nuclear Labs.); Ruggles, M.B. ); Takahashi, Y. . Komae Research Lab.)</p> <p>1990-10-01</p> <p>A high-<span class="hlt">temperature</span> flaw assessment procedure is described. This procedure is a result of a collaborative effort between Electric Power Research Institute in the United States, Central Research Institute of Electric Power Industry in Japan, and Nuclear Electric plc in the United Kingdom. The procedure addresses preexisting defects subject to <span class="hlt">creep</span>-fatigue loading conditions. Laws employed to calculate the crack growth per cycle are defined in terms of fracture mechanics parameters and constants related to the component material. The crack-growth laws can be integrated to calculate the remaining life of a component or to predict the amount of crack extension in a given period. Fatigue and <span class="hlt">creep</span> crack growth per cycle are calculated separately, and the total crack extension is taken as the simple sum of the two contributions. An interaction between the two propagation modes is accounted for in the material properties in the separate calculations. In producing the procedure, limitations of the approach have been identified. 25 refs., 1 fig.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013MTDM...17..427C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013MTDM...17..427C"><span id="translatedtitle">Application of time-<span class="hlt">temperature</span>-stress superposition on <span class="hlt">creep</span> of wood-plastic composites</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chang, Feng-Cheng; Lam, Frank; Kadla, John F.</p> <p>2013-08-01</p> <p>Time-<span class="hlt">temperature</span>-stress superposition principle (TTSSP) was widely applied in studies of viscoelastic properties of materials. It involves shifting curves at various conditions to construct master curves. To extend the application of this principle, a <span class="hlt">temperature</span>-stress hybrid shift factor and a modified Williams-Landel-Ferry (WLF) equation that incorporated variables of stress and <span class="hlt">temperature</span> for the shift factor fitting were studied. A wood-plastic composite (WPC) was selected as the test subject to conduct a series of short-term <span class="hlt">creep</span> tests. The results indicate that the WPC were rheologically simple materials and merely a horizontal shift was needed for the time-<span class="hlt">temperature</span> superposition, whereas vertical shifting would be needed for time-stress superposition. The shift factor was independent of the stress for horizontal shifts in time-<span class="hlt">temperature</span> superposition. In addition, the <span class="hlt">temperature</span>- and stress-shift factors used to construct master curves were well fitted with the WLF equation. Furthermore, the parameters of the modified WLF equation were also successfully calibrated. The application of this method and equation can be extended to curve shifting that involves the effects of both <span class="hlt">temperature</span> and stress simultaneously.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JGRB..120..827F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JGRB..120..827F"><span id="translatedtitle">Micromechanisms of <span class="hlt">creep</span> in clay-rich gouge from the Central <span class="hlt">Deforming</span> Zone of the San Andreas Fault</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>French, M. E.; Chester, F. M.; Chester, J. S.</p> <p>2015-02-01</p> <p>We report the strength and constitutive behavior of gouge sampled from the Central <span class="hlt">Deforming</span> Zone (CDZ) of the San Andreas Fault. Layers of flaked CDZ gouge were sheared in the triaxial saw cut configuration using the stress relaxation technique to measure the gouge strength over 4 orders of magnitude in shear strain rate and at rates as low as 5 × 10-10s-1 and within an order of magnitude of in situ rates. <span class="hlt">Deformation</span> conditions correspond to the in situ effective normal stress (100 MPa) and <span class="hlt">temperature</span> (65 to 120°C) at the sampling depth of 2.7 km. Gouge was sheared dry and with brine pore fluid at 25 MPa pore pressure. Dry gouge is stronger and more rate strengthening than brine-saturated gouge. Brine-saturated CDZ gouge strengthens with increasing strain rate and decreasing <span class="hlt">temperature</span>, and the dependencies of strength on strain rate and <span class="hlt">temperature</span> increase at rates below ˜5 × 10-9s-1. At strain rates greater than ˜5 × 10-9s-1, the rate dependence is consistent with previous studies on the CDZ gouge conducted at even higher rates. The increase in rate dependence below ˜5 × 10-9s-1 indicates a change in the rate-controlling <span class="hlt">deformation</span> mechanism. The magnitude of the friction rate dependence parameter, a, and the <span class="hlt">temperature</span> sensitivity of a are consistent with crystal plasticity of the phyllosilicates. We hypothesize a micromechanical model for the CDZ gouge whereby a transition from fracture and delamination-accommodated frictional flow to crystal plasticity-accommodated frictional flow occurs with decreasing strain rate.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5643366','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5643366"><span id="translatedtitle">Tensile <span class="hlt">creep</span> behavior and cyclic fatigue/<span class="hlt">creep</span> interaction of hot- isostatically pressed Si sub 3 N sub 4</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Liu, K.C.; Pih, H.; Stevens, C.O.; Brinkman, C.R.</p> <p>1991-01-01</p> <p>Tensile <span class="hlt">creep</span> data are reported for a high-performance grade of hot isostatically pressed Si{sub 3}N{sub 4} that is currently being investigated as a candidate material for advanced heat engine applications. Specimens were tested in pure uniaxial tension at <span class="hlt">temperatures</span> ranging from 1200 to 1370{degree}C. <span class="hlt">Creep</span> strain was measured with an optical strain extensometer until <span class="hlt">creep</span> rupture occurred, in some cases for periods in excess of 2000 h. To study the effects of various preloading material histories on <span class="hlt">creep</span> behavior, specimens were prepared and tested in several conditions, i.e., unannealed, annealed, or precycled. Test results show that either treatment by thermal annealing or by precycling at 1370{degree}C can dramatically modify the initial transient <span class="hlt">creep</span> behavior and enhance the resistance to <span class="hlt">creep</span> <span class="hlt">deformation</span> and hence the <span class="hlt">creep</span>-rupture lifetime. However, the influence of the preloading histories on <span class="hlt">creep</span> rate was diminished by high <span class="hlt">temperature</span> exposure after about 500 h of testing. The rupture lifetime of the precycled specimen at 1370{degree}C was significantly higher than those of the unannealed and annealed specimens. In contrast, no significant extension of the <span class="hlt">creep</span>-rupture lifetime was observed for a precycled specimen tested at 1300{degree}C. Steady-state <span class="hlt">creep</span> was absent in some cases under certain conditions of <span class="hlt">temperature</span>, stress, and heat treatment. Little or no tertiary <span class="hlt">creep</span> was usually detected before specimen fracture occurred. The steady-state <span class="hlt">creep</span> rate of this material was found to be a function of applied stress, <span class="hlt">temperature</span>, and possibly the level of crystallinity in the intergranular phase. 9 refs., 15 figs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JNuM..444...14K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JNuM..444...14K"><span id="translatedtitle">In situ monitored in-pile <span class="hlt">creep</span> testing of zirconium alloys</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kozar, R. W.; Jaworski, A. W.; Webb, T. W.; Smith, R. W.</p> <p>2014-01-01</p> <p>The experiments described herein were designed to investigate the detailed irradiation <span class="hlt">creep</span> behavior of zirconium based alloys in the HALDEN Reactor spectrum. The HALDEN Test Reactor has the unique capability to control both applied stress and <span class="hlt">temperature</span> independently and externally for each specimen while the specimen is in-reactor and under fast neutron flux. The ability to monitor in situ the <span class="hlt">creep</span> rates following a stress and <span class="hlt">temperature</span> change made possible the characterization of <span class="hlt">creep</span> behavior over a wide stress-strain-rate-<span class="hlt">temperature</span> design space for two model experimental heats, Zircaloy-2 and Zircaloy-2 + 1 wt%Nb, with only 12 test specimens in a 100-day in-pile <span class="hlt">creep</span> test program. Zircaloy-2 specimens with and without 1 wt% Nb additions were tested at irradiation <span class="hlt">temperatures</span> of 561 K and 616 K and stresses ranging from 69 MPa to 455 MPa. Various steady state <span class="hlt">creep</span> models were evaluated against the experimental results. The irradiation <span class="hlt">creep</span> model proposed by Nichols that separates <span class="hlt">creep</span> behavior into low, intermediate, and high stress regimes was the best model for predicting steady-state <span class="hlt">creep</span> rates. Dislocation-based primary <span class="hlt">creep</span>, rather than diffusion-based transient irradiation <span class="hlt">creep</span>, was identified as the mechanism controlling <span class="hlt">deformation</span> during the transitional period of evolving <span class="hlt">creep</span> rate following a step change to different test conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19990008062&hterms=B12&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DB12','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19990008062&hterms=B12&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DB12"><span id="translatedtitle">Transient <span class="hlt">Creep</span> of a Composite Lower Crust. 2; A Polymineralic Basis for Rapidly Evolving Postseismic <span class="hlt">Deformation</span> Modes</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Ivins, Erik R.</p> <p>1996-01-01</p> <p>Postseismic horizontal strain and displacement following the June 28, 1992, Landers, California, earthquake (M(sub W) 7.3) is broad scale and cannot be explained solely by delayed afterslip located at the rupturing fault trace. Both the observed strain at Pifion Flat Observatory (PFO) and observed Global Positioning System receiver velocities evolve rapidly after the Landers-Big Bear earthquake sequence. The observed exponential decay of these motions, with timescales of 4-34 days, may reflect a soft <span class="hlt">creep</span> rheology in the lower crust and brittle-ductile transition zone or even within the seismogenic crust itself. Here a simple model of a two-dimensional screw dislocation in a layered Maxwell viscoelastic Earth is employed in conjunction with a composite rheology to demonstrate that the short timescale transient response modes (approx. = 4-34 days) are consistent with the behavior of a biviscous lower crust. The lowest viscosity of this system is derivable from laboratory experimental data on the long-term <span class="hlt">creep</span> of natural quarztites, and the highest viscosity is consistent with isostasy-related lower crustal flow in a continental extensional tectonic environment. The model predicts significant stress relaxation at the base of the seismogenic crust. Near the base of the seismogenic zone, and about 4 km away from the mainshock, the rate of predicted relaxation is of the order of 0.01 MPa/ d during the first 20 days of postseismic flow. Oblate spheroidal inclusions at 5% concentration levels that are both aligned and fairly flat in shape and that have a viscosity of 3-4 x 10(exp 15) Pa s are consistent with both the amplitude and decay time of horizontal crustal strain observed at PFO after the Landers mainshock. It is speculated that the structures exposed in cross sections and in seismic reflection profiles of the lower crust that have mylonitic associations are, in part, the cause of such rapid postseismic evolution in southeastern California. Unmylonitized quartz</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994AIAAJ..32..190X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994AIAAJ..32..190X"><span id="translatedtitle">Treatment of material <span class="hlt">creep</span> and nonlinearities in flexible mulitbody dynamics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xie, M.; Amirouche, F. M. L.</p> <p>1994-01-01</p> <p>This paper addresses the modeling of the generalized active forces resulting from <span class="hlt">deformable</span> bodies when subjected to high <span class="hlt">temperature</span> conditions, elastic-plastic <span class="hlt">deformations</span>, <span class="hlt">creep</span> effects, and material nonlinearities. The effects of elastic-plastic <span class="hlt">deformations</span> are studied making use of the nonlinear stress-strain relationship and the geometrical stiffness concepts. <span class="hlt">Creep</span> conditions resulting from high <span class="hlt">temperature</span> are studied through several proposed models. Materials nonlinearities for isotropic and composites are accounted for by their tangential elasticity matrix. A general procedure used in the study of multibody systems dynamics with elastic-plastic bodies depicting the characteristics mentioned is developed. This includes an explicit formulation of the equations of motion using Kane's equations, finite element method, continuum mechanics, and modal coordinate reduction techniques. A numerical simulation of a flexible robotic arm with a prescribed angular velocity subject to high <span class="hlt">temperature</span> conditions is analyzed. The effects of <span class="hlt">creep</span> are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhDT........15I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhDT........15I"><span id="translatedtitle">Probabilistic models for <span class="hlt">creep</span>-fatigue in a steel alloy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ibisoglu, Fatmagul</p> <p></p> <p>In high <span class="hlt">temperature</span> components subjected to long term cyclic operation, simultaneous <span class="hlt">creep</span> and fatigue damage occur. A new methodology for <span class="hlt">creep</span>-fatigue life assessment has been adopted without the need to separate <span class="hlt">creep</span> and fatigue damage or expended life. Probabilistic models, described by hold times in tension and total strain range at <span class="hlt">temperature</span>, have been derived based on the <span class="hlt">creep</span> rupture behavior of a steel alloy. These models have been validated with the observed <span class="hlt">creep</span>-fatigue life of the material with a scatter band close to a factor of 2. Uncertainties of the <span class="hlt">creep</span>-fatigue model parameters have been estimated with WinBUGS which is an open source Bayesian analysis software tool that uses Markov Chain Monte Carlo method to fit statistical models. Secondly, <span class="hlt">creep</span> <span class="hlt">deformation</span> in stress relaxation data has been analyzed. Well performing <span class="hlt">creep</span> equations have been validated with the observed data. The <span class="hlt">creep</span> model with the highest goodness of fit among the validated models has been used to estimate probability of exceedance at 0.6% strain level for the steel alloy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010EGUGA..1213462S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010EGUGA..1213462S"><span id="translatedtitle">High pressure and <span class="hlt">temperature</span> <span class="hlt">deformation</span> experiments on San Carlos olivine and implications for upper mantle anisotropy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shekhar, Sushant; Frost, Daniel J.; Walte, Nicolas; Miyajima, Nobuyoshi; Heidelbach, Florian</p> <p>2010-05-01</p> <p>Crystallographic preferred orientation developed in olivine due to shearing in the mantle is thought to be the prominent reason behind seismic anisotropy in the upper mantle. Seismic anisotropy in upper mantle can be observed up to a depth of 350 km with a marked drop in the strength of anisotropy seen around 250 km. Studies on natural rock samples from the mantle and <span class="hlt">deformation</span> experiments performed on olivine have revealed that olivine <span class="hlt">deforms</span> mainly through dislocation <span class="hlt">creep</span> with Burgers vectors parallel to the [100] crystallographic axis under low pressure conditions (up to 3 GPa). Under similar pressures, evidence of [001] slip has been reported due to the presence of water. In order to understand the <span class="hlt">deformation</span> mechanism in olivine at pressures greater than 3 GPa, we have performed experiments using the <span class="hlt">deformation</span> DIA multi-anvil apparatus. The DIA consist of 6 square faceted anvils that compress a cubic high-pressure assembly. The <span class="hlt">deformation</span> DIA possesses two vertically acting opposing inner rams, which can be operated independently of the main compressive force to <span class="hlt">deform</span> the sample assembly. The experimental setup consists of a hot-pressed sample of polycrystalline dry San Carlos olivine 0.2 mm cut from a 1.2 mm diameter core at 45° . This slice is sandwiched between alumina pistons also cut at 45° in simple shear geometry. Experiments have been performed at 3, 5 and 8 GPa at a <span class="hlt">deformation</span> anvil strain rate of 1.0x10-4 s-1and <span class="hlt">temperatures</span> between 1200-1400° C. <span class="hlt">Deformed</span> samples were cut normal to the shear plane and parallel to the shear direction. Then the sample was polished and analyzed using electron back scattered diffraction (EBSD) to identify the crystallographic preferred orientation (CPO). The fabric that developed in olivine <span class="hlt">deformed</span> at 3 GPa mainly resulted from the [100] slip on the (010) plane. Samples <span class="hlt">deformed</span> at 5 GPa showed both [100] and [001] slip. On the other hand, samples <span class="hlt">deformed</span> at 8 GPa and 1200° C, show <span class="hlt">deformation</span> mainly</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/7055246','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/7055246"><span id="translatedtitle">Unified <span class="hlt">creep</span>-plasticity model for halite</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Krieg, R. D.</p> <p>1980-11-01</p> <p>There are two national energy programs which are considering caverns in geological salt (NaCl) as a storage repository. One is the disposal of nuclear wastes and the other is the storage of oil. Both short-time and long-time structural <span class="hlt">deformations</span> and stresses must be predictable for these applications. At 300K, the nominal initial <span class="hlt">temperature</span> for both applications, the salt is at 0.28 of the melting <span class="hlt">temperature</span> and exhibits a significant time dependent behavior. A constitutive model has been developed which describes the behavior observed in an extensive set of triaxial <span class="hlt">creep</span> tests. Analysis of these tests showed that a single <span class="hlt">deformation</span> mechanism seems to be operative over the stress and <span class="hlt">temperature</span> range of interest so that the secondary <span class="hlt">creep</span> data can be represented by a power of the stress over the entire test range. This simple behavior allowed a new unified <span class="hlt">creep</span>-plasticity model to be applied with some confidence. The resulting model recognizes no inherent difference between plastic and <span class="hlt">creep</span> strains yet models the total inelastic strain reasonably well including primary and secondary <span class="hlt">creep</span> and reverse loadings. A multiaxial formulation is applied with a back stress. A Bauschinger effect is exhibited as a consequence and is present regardless of the time scale over which the loading is applied. The model would be interpreted as kinematic hardening in the sense of classical plasticity. Comparisons are made between test data and model behavior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992RSPSA.437..567D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992RSPSA.437..567D"><span id="translatedtitle">Modeling of combined high-<span class="hlt">temperature</span> <span class="hlt">creep</span> and cyclic plasticity in components using continuum damage mechanics</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dunne, F. P. E.; Hayhurst, D. R.</p> <p>1992-06-01</p> <p>A computer-based finite-element viscoplastic damage solver is presented to analyze structural components subject to combined cyclic thermal and mechanical loading. The solver is capable of predicting the combined evolution of <span class="hlt">creep</span> and cyclic plasticity damage by solution of the combined boundary-initial value problem. The solver has been used to predict the high-<span class="hlt">temperature</span> behavior of a slag tap component subjected to cyclic thermal loading generated by infrared heaters and water cooling ducts. It is found that the initiation of damage and microcracking occur early in the lifetime at about 3000 cycles adjacent to the cooling duct. The propagation of failure zones stabilizes at 60,000 cycles after which no further damage evolution occurs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JOM....67g1617P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JOM....67g1617P"><span id="translatedtitle"><span class="hlt">Temperature</span> Dependence of the Anisotropy and <span class="hlt">Creep</span> in a Single-Crystal Nickel Superalloy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Pandey, Amit; Hemker, Kevin J.</p> <p>2015-07-01</p> <p>The thermomechanical response of the second-generation single-crystal nickel superalloy (SC180) was obtained for wide range of <span class="hlt">temperatures</span> (25-1000°C). Uniaxial tension and stress relaxation experiments were performed to study the influence of [100] and [110] crystallographic orientation on stress anisotropy and <span class="hlt">creep</span> responses. Experiments were conducted using micromechanical testing systems and strains were measured using two-dimensional digital image correlation technique. Results were reported on coefficient of thermal expansion, Young's modulus ( E), yield strength, work hardening ( n), and activation energies ( Q). The stress relaxation experiments were used to calculate activation energy in [100] and [110] crystallographic directions and found to be 300 kJ/mol and 350 kJ/mol, respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/881356','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/881356"><span id="translatedtitle">An Evaluation for <span class="hlt">Creep</span> of 3013 Inner Can Lids</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>DAUGHERTY, W. L.; GIBBS, K. M.; LOUTHAN JR., M. R.; DUNN, K. A.</p> <p>2005-09-01</p> <p>The deflection of Type 304L austenitic stainless steel can lids on inner 3013 containers is monitored to identify any buildup of pressure within the container. This paper provides the technical basis to conclude that <span class="hlt">creep</span>-induced <span class="hlt">deformation</span> of these lids will be insignificant unless the <span class="hlt">temperature</span> of storage exceeds 400 C. This conclusion is based on experimental literature data for Types 304 and 316 stainless steel and on a phenomenological evaluation of potential <span class="hlt">creep</span> processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19880031657&hterms=prime&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dprime','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19880031657&hterms=prime&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dprime"><span id="translatedtitle">Effect of initial gamma prime size on the elevated <span class="hlt">temperature</span> <span class="hlt">creep</span> properties of single crystal nickel base superalloys</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nathal, M. V.</p> <p>1987-01-01</p> <p>The influence of initial gamma-prime size and shape on the high-<span class="hlt">temperature</span> <span class="hlt">creep</span> properties of two single-crystal Ni-base superalloys was investigated. The two alloys were chosen to represent different magnitudes of gamma/gamma-prime lattice mismatch. A range of initial microstructures was produced by various quenching and aging treatments. <span class="hlt">Creep</span>-rupture testing at 1000 C was performed under stresses where gamma-prime directionally coarsens to form gamma/gamma-prime lamellae in the early portion of the <span class="hlt">creep</span> life. Both alloys exhibited a peak in <span class="hlt">creep</span> resistance as a function of initial gamma-prime size. The peak corresponded to an initial microstructure consisting of cuboidal precipitates aligned along 001 line directions. These aligned cuboidal gamma-prime particles directionally coarsened into a relatively perfect lamellar gamma/gamma-prime structure in the early stages of <span class="hlt">creep</span>, whereas the more irregularly shaped and distributed gamma-prime particles in both under- and overaged material formed more irregular lamellae with more imperfections. The alloy with a lower magnitude of mismatch was less sensitive to initial gamma-prime size and shape.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/6810038','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/6810038"><span id="translatedtitle"><span class="hlt">Creep</span> of carbon-yarn and carbon-carbon composites at high <span class="hlt">temperatures</span> and high stresses. Technical report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Sines, G.; Yang, Z.; Vickers, B.D.</p> <p>1988-05-01</p> <p>To better understand the <span class="hlt">creep</span>-behavior of carbon yarn and carbon-carbon composites, <span class="hlt">creep</span> experiments were developed that permitted testing at high <span class="hlt">temperatures</span> (up to 2500 C) and at high stresses (up to 850 MPa) on specially prepared, uniaxial specimens that had a known gage length. Using a Dorn-type power-law relation to model steady-state <span class="hlt">creep</span>, the apparent activation energy for the carbon-yarn and carbon-composite specimens was determined to be 1082 kj/mol. This value represents a single thermally activated process, vacancy diffusion, that compares favorably with the various types of graphitizable carbon. The value determined for the stress exponent was 7.5. It too was found to be independent of the carbon-matrix's presence and independent of the specimens' loading history. Values of the pre-exponential constant for the carbon yarn and carbon composites were also calculated. The carbon matrix greatly improves the <span class="hlt">creep</span> resistance of the carbon composite. This improvement was attributed to the matrix's microstructure. It distributes applied loads more evenly and it may also impose a triaxial stress state in the yarns's filaments. It is proposed that such a stress state may inhibit the flux of vacancies, thus accounting in part for this increase in <span class="hlt">creep</span> resistance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JMPSo..73..269K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JMPSo..73..269K"><span id="translatedtitle">Two-<span class="hlt">temperature</span> continuum thermomechanics of <span class="hlt">deforming</span> amorphous solids</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kamrin, Ken; Bouchbinder, Eran</p> <p>2014-12-01</p> <p>There is an ever-growing need for predictive models for the elasto-viscoplastic <span class="hlt">deformation</span> of solids. Our goal in this paper is to incorporate recently developed out-of-equilibrium statistical concepts into a thermodynamically consistent, finite-<span class="hlt">deformation</span>, continuum framework for <span class="hlt">deforming</span> amorphous solids. The basic premise is that the configurational degrees of freedom of the material - the part of the internal energy/entropy that corresponds to mechanically stable microscopic configurations - are characterized by a configurational <span class="hlt">temperature</span> that might differ from that of the vibrational degrees of freedom, which equilibrate rapidly with an external heat bath. This results in an approximate internal energy decomposition into weakly interacting configurational and vibrational subsystems, which exchange energy following a Fourier-like law, leading to a thermomechanical framework permitting two well-defined <span class="hlt">temperatures</span>. In this framework, internal variables, that carry information about the state of the material equilibrate with the configurational subsystem, are explicitly associated with energy and entropy of their own, and couple to a viscoplastic flow rule. The coefficients that determine the rate of flow of entropy and heat between different internal systems are proposed to explicitly depend on the rate of irreversible <span class="hlt">deformation</span>. As an application of this framework, we discuss two constitutive models for the response of glassy materials, a simple phenomenological model and a model related to the concept of Shear-Transformation-Zones as the basis for internal variables. The models account for several salient features of glassy <span class="hlt">deformation</span> phenomenology. Directions for future investigation are briefly discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011JNuM..419..235B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011JNuM..419..235B"><span id="translatedtitle"><span class="hlt">Temperature</span> dependence of the anisotropic <span class="hlt">deformation</span> of Zr-2.5%Nb pressure tube material during micro-indentation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bose, B.; Klassen, R. J.</p> <p>2011-12-01</p> <p>The effect of <span class="hlt">temperature</span> on the anisotropic plastic <span class="hlt">deformation</span> of textured Zr-2.5%Nb pressure tube material was studied using micro-indentation tests performed in the axial, radial, and transverse directions of the tube over the <span class="hlt">temperature</span> range from 25 to 400 °C. The ratio of the indentation stress in the transverse direction relative to that in the radial and axial directions was 1.29:1 and 1.26:1 at 25 °C but decreased to 1.22:1 and 1.05:1 at 400 °C. The average activation energy of the obstacles that limit the rate of indentation <span class="hlt">creep</span> increases, from 0.72 to 1.33 eV, with increasing <span class="hlt">temperature</span> from 25 to 300 °C and is independent of indentation direction. At <span class="hlt">temperature</span> between 300 °C and 400 °C the measured activation energy is considerably reduced for indentation <span class="hlt">creep</span> in the transverse direction relative to that of either the axial or radial directions. We conclude that, over this <span class="hlt">temperature</span> range, the strength of the obstacles that limit the time-dependent dislocation glide on the pyramidal slip system changes relative to that on the prismatic slip system. These findings provide new data on the <span class="hlt">temperature</span> dependence of the yield stress and <span class="hlt">creep</span> rate, particularly in the radial direction, of Zr-2.5%Nb pressure tubes and shed new light on the effect of <span class="hlt">temperature</span> on the operation of dislocation glide on the prismatic and pyramidal slip systems which ultimately determines the degree of mechanical anisotropy in the highly textured Zr-2.5Nb pressure tube material used in CANDU nuclear reactors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JNuM..455..402L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JNuM..455..402L"><span id="translatedtitle">Improving high <span class="hlt">temperature</span> <span class="hlt">creep</span> resistance of reduced activation steels by addition of nitrogen and intermediate heat treatment</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, W. B.; Zhang, C.; Xia, Z. X.; Yang, Z. G.</p> <p>2014-12-01</p> <p>In the present study, we report an enhanced high-<span class="hlt">temperature</span> <span class="hlt">creep</span> resistance in reduced activation ferrite/martensite (RAFM) steels, by introducing nitrogen (0.035 wt%, M3 steel) and employing a novel intermediate heat treatment I-Q-T (intermediate treatment, quenching and tempering). In comparison with all the control groups, the uniaxial tests of the I-Q-T treated M3 steel showed significant increase in rupture time and decrease in elongation. The microstructures of the samples were further characterized to elucidate the origin of the enhanced <span class="hlt">creep</span> resistance. It is found that, by introducing nitrogen, the primary TaC particles were refined; by employing the I-Q-T heat treatment, the dispersed fine secondary MX precipitates, as well as the lath subgrains containing high-density dislocations, were increased: all are responsible for the improved <span class="hlt">creep</span> resistance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19960038406','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19960038406"><span id="translatedtitle">Bend stress relaxation and tensile primary <span class="hlt">creep</span> of a polycrystalline alpha-SiC fiber</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hee Man, Yun; Goldsby, Jon C.; Morscher, Gregory N.</p> <p>1995-01-01</p> <p>Understanding the thermomechanical behavior (<span class="hlt">creep</span> and stress relaxation) of ceramic fibers is of both practical and basic interest. On the practical level, ceramic fibers are the reinforcement for ceramic matrix composites which are being developed for use in high <span class="hlt">temperature</span> applications. It is important to understand and model the total <span class="hlt">creep</span> of fibers at low strain levels where <span class="hlt">creep</span> is predominantly in the primary stage. In addition, there are many applications where the component will only be subjected to thermal strains. Therefore, the stress relaxation of composite consituents in such circumstances will be an important factor in composite design and performance. The objective of this paper is to compare and analyze bend stress relaxation and tensile <span class="hlt">creep</span> data for alpha-SiC fibers produced by the Carborundum Co. (Niagara Falls, NY). This fiber is of current technical interest and is similar in composition to bulk alpha-SiC which has been studied under compressive <span class="hlt">creep</span> conditions. The <span class="hlt">temperature</span>, time, and stress dependences will be discussed for the stress relaxation and <span class="hlt">creep</span> results. In addition, some <span class="hlt">creep</span> and relaxation recovery experiments were performed in order to understand the complete viscoelastic behavior, i.e. both recoverable and nonrecoverable <span class="hlt">creep</span> components of these materials. The data will be presented in order to model the <span class="hlt">deformation</span> behavior and compare relaxation and/or <span class="hlt">creep</span> behavior for relatively low <span class="hlt">deformation</span> strain conditions of practical concern. Where applicable, the tensile <span class="hlt">creep</span> results will be compared to bend stress relaxation data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20000003020','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20000003020"><span id="translatedtitle">Modeling the Role of Dislocation Substructure During Class M and Exponential <span class="hlt">Creep</span>. Revised</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Raj, S. V.; Iskovitz, Ilana Seiden; Freed, A. D.</p> <p>1995-01-01</p> <p>The different substructures that form in the power-law and exponential <span class="hlt">creep</span> regimes for single phase crystalline materials under various conditions of stress, <span class="hlt">temperature</span> and strain are reviewed. The microstructure is correlated both qualitatively and quantitatively with power-law and exponential <span class="hlt">creep</span> as well as with steady state and non-steady state <span class="hlt">deformation</span> behavior. These observations suggest that <span class="hlt">creep</span> is influenced by a complex interaction between several elements of the microstructure, such as dislocations, cells and subgrains. The stability of the <span class="hlt">creep</span> substructure is examined in both of these <span class="hlt">creep</span> regimes during stress and <span class="hlt">temperature</span> change experiments. These observations are rationalized on the basis of a phenomenological model, where normal primary <span class="hlt">creep</span> is interpreted as a series of constant structure exponential <span class="hlt">creep</span> rate-stress relationships. The implications of this viewpoint on the magnitude of the stress exponent and steady state behavior are discussed. A theory is developed to predict the macroscopic <span class="hlt">creep</span> behavior of a single phase material using quantitative microstructural data. In this technique the thermally activated <span class="hlt">deformation</span> mechanisms proposed by dislocation physics are interlinked with a previously developed multiphase, three-dimensional. dislocation substructure <span class="hlt">creep</span> model. This procedure leads to several coupled differential equations interrelating macroscopic <span class="hlt">creep</span> plasticity with microstructural evolution.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_14");'>14</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li class="active"><span>16</span></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_16 --> <div id="page_17" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="321"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/986888','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/986888"><span id="translatedtitle">Application of neutron diffraction in characterization of texture evolution during high-<span class="hlt">temperature</span> <span class="hlt">creep</span> in magnesium alloys</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Vogel, Sven C; Sediako, Dimitry; Shook, S; Sediako, A</p> <p>2010-01-01</p> <p>A good combination of room-<span class="hlt">temperature</span> and elevated <span class="hlt">temperature</span> strength and ductility, good salt-spray corrosion resistance and exceUent diecastability are frequently among the main considerations in development of a new alloy. Unfortunately, there has been much lesser effort in development of wrought-stock alloys for high <span class="hlt">temperature</span> applications. Extrudability and high <span class="hlt">temperature</span> performance of wrought material becomes an important factor in an effort to develop new wrought alloys and processing technologies. This paper shows some results received in <span class="hlt">creep</span> testing and studies of in-<span class="hlt">creep</span> texture evolution for several wrought magnesium alloys developed for use in elevated-<span class="hlt">temperature</span> applications. These studies were performed using E3 neutron spectrometer of the Canadian Neutron Beam Centre in Chalk River, ON, and HIPPO time-of-flight (TOF) spectrometer at Los Alamos Neutron Science Center, NM.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19860004886','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19860004886"><span id="translatedtitle">Development of constitutive models for cyclic plasticity and <span class="hlt">creep</span> behavior of super alloys at high <span class="hlt">temperature</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Haisler, W. E.</p> <p>1983-01-01</p> <p>An uncoupled constitutive model for predicting the transient response of thermal and rate dependent, inelastic material behavior was developed. The uncoupled model assumes that there is a <span class="hlt">temperature</span> below which the total strain consists essentially of elastic and rate insensitive inelastic strains only. Above this <span class="hlt">temperature</span>, the rate dependent inelastic strain (<span class="hlt">creep</span>) dominates. The rate insensitive inelastic strain component is modelled in an incremental form with a yield function, blow rule and hardening law. Revisions to the hardening rule permit the model to predict <span class="hlt">temperature</span>-dependent kinematic-isotropic hardening behavior, cyclic saturation, asymmetric stress-strain response upon stress reversal, and variable Bauschinger effect. The rate dependent inelastic strain component is modelled using a rate equation in terms of back stress, drag stress and exponent n as functions of <span class="hlt">temperature</span> and strain. A sequence of hysteresis loops and relaxation tests are utilized to define the rate dependent inelastic strain rate. Evaluation of the model has been performed by comparison with experiments involving various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy X.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/43782','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/43782"><span id="translatedtitle"><span class="hlt">Creep</span> analysis of fuel plates for the Advanced Neutron Source</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Swinson, W.F.; Yahr, G.T.</p> <p>1994-11-01</p> <p>The reactor for the planned Advanced Neutron Source will use closely spaced arrays of fuel plates. The plates are thin and will have a core containing enriched uranium silicide fuel clad in aluminum. The heat load caused by the nuclear reactions within the fuel plates will be removed by flowing high-velocity heavy water through narrow channels between the plates. However, the plates will still be at elevated <span class="hlt">temperatures</span> while in service, and the potential for excessive plate <span class="hlt">deformation</span> because of <span class="hlt">creep</span> must be considered. An analysis to include <span class="hlt">creep</span> for <span class="hlt">deformation</span> and stresses because of <span class="hlt">temperature</span> over a given time span has been performed and is reported herein.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MTDM...20..245M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MTDM...20..245M"><span id="translatedtitle">Effect of fiber-matrix adhesion on the <span class="hlt">creep</span> behavior of CF/PPS composites: <span class="hlt">temperature</span> and physical aging characterization</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Motta Dias, M. H.; Jansen, K. M. B.; Luinge, J. W.; Bersee, H. E. N.; Benedictus, R.</p> <p>2016-06-01</p> <p>The influence of fiber-matrix adhesion on the linear viscoelastic <span class="hlt">creep</span> behavior of `as received' and `surface modified' carbon fibers (AR-CF and SM-CF, respectively) reinforced polyphenylene sulfide (PPS) composite materials was investigated. Short-term tensile <span class="hlt">creep</span> tests were performed on ±45° specimens under six different isothermal conditions, 40, 50, 60, 65, 70 and 75 °C. Physical aging effects were evaluated on both systems using the short-term test method established by Struik. The results showed that the shapes of the curves were affected neither by physical aging nor by the test <span class="hlt">temperature</span>, allowing then superposition to be made. A unified model was proposed with a single physical aging and <span class="hlt">temperature</span>-dependent shift factor, a_{T,te}. It was suggested that the surface treatment carried out in SM-CF/PPS had two major effects on the <span class="hlt">creep</span> response of CF/PPS composites at a reference <span class="hlt">temperature</span> of 40 °C: a lowering of the initial compliance of about 25 % and a slowing down of the <span class="hlt">creep</span> response of about 1.1 decade.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MTDM..tmp....6M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MTDM..tmp....6M"><span id="translatedtitle">Effect of fiber-matrix adhesion on the <span class="hlt">creep</span> behavior of CF/PPS composites: <span class="hlt">temperature</span> and physical aging characterization</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Motta Dias, M. H.; Jansen, K. M. B.; Luinge, J. W.; Bersee, H. E. N.; Benedictus, R.</p> <p>2016-02-01</p> <p>The influence of fiber-matrix adhesion on the linear viscoelastic <span class="hlt">creep</span> behavior of `as received' and `surface modified' carbon fibers (AR-CF and SM-CF, respectively) reinforced polyphenylene sulfide (PPS) composite materials was investigated. Short-term tensile <span class="hlt">creep</span> tests were performed on ±45° specimens under six different isothermal conditions, 40, 50, 60, 65, 70 and 75 °C. Physical aging effects were evaluated on both systems using the short-term test method established by Struik. The results showed that the shapes of the curves were affected neither by physical aging nor by the test <span class="hlt">temperature</span>, allowing then superposition to be made. A unified model was proposed with a single physical aging and <span class="hlt">temperature</span>-dependent shift factor, a_{T,te}. It was suggested that the surface treatment carried out in SM-CF/PPS had two major effects on the <span class="hlt">creep</span> response of CF/PPS composites at a reference <span class="hlt">temperature</span> of 40 °C: a lowering of the initial compliance of about 25 % and a slowing down of the <span class="hlt">creep</span> response of about 1.1 decade.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19880002743','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19880002743"><span id="translatedtitle">Comparison of measured <span class="hlt">temperatures</span>, thermal stresses and <span class="hlt">creep</span> residues with predictions on a built-up titanium structure</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jenkins, Jerald M.</p> <p>1987-01-01</p> <p><span class="hlt">Temperature</span>, thermal stresses, and residual <span class="hlt">creep</span> stresses were studied by comparing laboratory values measured on a built-up titanium structure with values calculated from finite-element models. Several such models were used to examine the relationship between computational thermal stresses and thermal stresses measured on a built-up structure. Element suitability, element density, and computational <span class="hlt">temperature</span> discrepancies were studied to determine their impact on measured and calculated thermal stress. The optimum number of elements is established from a balance between element density and suitable safety margins, such that the answer is acceptably safe yet is economical from a computational viewpoint. It is noted that situations exist where relatively small excursions of calculated <span class="hlt">temperatures</span> from measured values result in far more than proportional increases in thermal stress values. Measured residual stresses due to <span class="hlt">creep</span> significantly exceeded the values computed by the piecewise linear elastic strain analogy approach. The most important element in the computation is the correct definition of the <span class="hlt">creep</span> law. Computational methodology advances in predicting residual stresses due to <span class="hlt">creep</span> require significantly more viscoelastic material characterization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JGRB..118..943H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JGRB..118..943H"><span id="translatedtitle">High-<span class="hlt">temperature</span> <span class="hlt">deformation</span> and recrystallization: A variational analysis and its application to olivine aggregates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hackl, Klaus; Renner, JöRg</p> <p>2013-03-01</p> <p>We develop a framework for a variational analysis of microstructural evolution during inelastic high-<span class="hlt">temperature</span> <span class="hlt">deformation</span> accommodated by dislocation mechanisms and diffusive mass transport. A polycrystalline aggregate is represented by a distribution function characterizing the state of individual grains by three variables, dislocation density, grain size, and elastic strain. The aggregate's free energy comprises elastic energy and energies of lattice distortions due to dislocations and grain boundaries. The work performed by the external loading is consumed by changes in the number of defects and their migration leading to inelastic <span class="hlt">deformation</span>. The variational approach minimizes the rate of change of free energy with the evolution of the state variables under constraints on the aggregate volume, on a relation between changes in plastic strain and dislocation density, and on the form of the dissipation functionals for defect processes. The constrained minimization results in four basic evolution equations, one each for the evolution in grain size and dislocation density and flow laws for dislocation and diffusion <span class="hlt">creep</span>. Analytical steady state scaling relations between stress and dislocation density and grain size (piezometers) are derived for quasi-homogeneous materials characterized by a unique relation between grain size and dislocation density. Our model matches all currently available experimental observations regarding high-<span class="hlt">temperature</span> <span class="hlt">deformation</span> of olivine aggregates with plausible values for the involved micromechanical model parameters. The relation between strain rate and stress for olivine aggregates maintaining a steady state microstructure is distinctly nonlinear in stark contrast to the majority of geodynamical modeling relying on linear relations, i.e., Newtonian behavior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/3651','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/3651"><span id="translatedtitle">Correlation of <span class="hlt">Creep</span> Behavior of Domal Salts</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Munson, D.E.</p> <p>1999-02-16</p> <p>The experimentally determined <span class="hlt">creep</span> responses of a number of domal salts have been reported in, the literature. Some of these <span class="hlt">creep</span> results were obtained using standard (conventional) <span class="hlt">creep</span> tests. However, more typically, the <span class="hlt">creep</span> data have come from multistage <span class="hlt">creep</span> tests, where the number of specimens available for testing was small. An incremental test uses abrupt changes in stress and <span class="hlt">temperature</span> to produce several time increments (stages) of different <span class="hlt">creep</span> conditions. Clearly, the ability to analyze these limited data and to correlate them with each other could be of considerable potential value in establishing the mechanical characteristics of salt domes, both generally and specifically. In any analysis, it is necessary to have a framework of rules to provide consistency. The basis for the framework is the Multimechanism-<span class="hlt">Deformation</span> (M-D) constitutive model. This model utilizes considerable general knowledge of material <span class="hlt">creep</span> <span class="hlt">deformation</span> to supplement specific knowledge of the material response of salt. Because the <span class="hlt">creep</span> of salt is controlled by just a few micromechanical mechanisms, regardless of the origin of the salt, certain of the material parameters are values that can be considered universal to salt. Actual data analysis utilizes the methodology developed for the Waste Isolation Pilot Plant (WIPP) program, and the response of a bedded pure WIPP salt as the baseline for comparison of the domal salts. <span class="hlt">Creep</span> data from Weeks Island, Bryan Mound, West Hackberry, Bayou Choctaw, and Big Hill salt domes, which are all sites of Strategic Petroleum Reserve (SPR) storage caverns, were analyzed, as were data from the Avery Island, Moss Bluff, and Jennings salt domes. The analysis permits the parameter value sets for the domal salts to be determined in terms of the M-D model with various degrees of completeness. In turn this permits detailed numerical calculations simulating cavern response. Where the set is incomplete because of the sparse database, reasonable</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003AGUFM.S22A0425M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003AGUFM.S22A0425M"><span id="translatedtitle"><span class="hlt">Creep</span>: Long-term Time-Dependent Rock <span class="hlt">Deformation</span> in a Deep-sea Laboratory in the Ionian sea: a Pilot Study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Meredith, P. G.; Boon, S.; Vinciguerra, S.; Bowles, J.; NEMO Group,.</p> <p>2003-12-01</p> <p>Time-dependent brittle rock <span class="hlt">deformation</span> is of first-order importance for understanding the long-term behavior of water saturated rocks in the Earth's upper crust. Interpretation of results from traditional laboratory brittle <span class="hlt">creep</span> experiments have generally been in terms of three individual <span class="hlt">creep</span> phases; primary (decelerating), secondary (constant strain rate or quasi-steady-state) and tertiary (accelerating or unstable). The <span class="hlt">deformation</span> may be distributed during the first two, but localizes onto a fault plane during phase three. More recently, models have been proposed that explain the trimodal shape of <span class="hlt">creep</span> curves in terms of the competition between a weakening mechanism and a strengthening mechanism, with the weakening mechanism eventually dominating and leading to localized failure. However, a major problem is that it is difficult to distinguish between these competing mechanisms and models given the lower limit of strain rates achievable in laboratory experiments over practicable time scales. This study aims to address that problem directly by extending significantly the range of achievable strain rates through much longer-term experiments conducted in a deep-sea laboratory in the Ionian sea. The project takes advantage of a collaboration with the NEMO Group-INFN, a consortium that is developing a large volume (1 km3) deep-sea detector for high-energy (>1019 eV) cosmic neutrinos. A suitable test site has been identified, some 20km north-east of Catania in Sicily, at a depth of 2100m. Within the <span class="hlt">CREEP</span> <span class="hlt">deformation</span> apparatus, confining pressure is provided by the ambient water pressure (>22MPa), and the constant axial stress is provided by an actuator that amplifies this pressure. Measurement transducers and a data acquisition system are sealed internally, with power provided for up to 6 months by an internal battery pack. The great advantage of operating in the deep sea in this way is that the system is essentially passive, has few moving parts, and requires no</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1984JMPSo..32..373T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1984JMPSo..32..373T"><span id="translatedtitle">On the <span class="hlt">creep</span> constrained diffusive cavitation of grain boundary facets</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tvergaard, Viggo</p> <p></p> <p><span class="hlt">CREEP</span> rupture in a polycrystalline metal at a high <span class="hlt">temperature</span>, by cavity growth on a number of grain boundary facets, is studied numerically. An axisymmetric model problem is analysed, in which a cavitating facet is represented as disk-shaped, and the model dimensions are taken to represent spacings between neighbouring cavitating facets. For the grains both power law <span class="hlt">creep</span> and elastic <span class="hlt">deformations</span> are taken into account, and the description of cavity growth is based on an approximate expression that incorporates the coupled influence of grain boundary diffusion and power law <span class="hlt">creep</span>. The cases considered include <span class="hlt">creep</span>-constrained cavity growth at low stresses, where the voids link up to form grain boundary cracks at relatively small overall strains, as well as the power law <span class="hlt">creep</span> dominated behaviour at higher stress levels, where rupture occurs at large overall strains. The numerical results are compared with results based on various simplified analyses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930006641','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930006641"><span id="translatedtitle"><span class="hlt">Deformation</span> mechanisms of NiAl cyclicly <span class="hlt">deformed</span> near the brittle-to-ductile transformation <span class="hlt">temperature</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Antolovich, Stephen D.; Saxena, Ashok; Cullers, Cheryl</p> <p>1992-01-01</p> <p>One of the ongoing challenges of the aerospace industry is to develop more efficient turbine engines. Greater efficiency entails reduced specific strength and larger <span class="hlt">temperature</span> gradients, the latter of which means higher operating <span class="hlt">temperatures</span> and increased thermal conductivity. Continued development of nickel-based superalloys has provided steady increases in engine efficiency and the limits of superalloys have probably not been realized. However, other material systems are under intense investigation for possible use in high <span class="hlt">temperature</span> engines. Ceramic, intermetallic, and various composite systems are being explored in an effort to exploit the much higher melting <span class="hlt">temperatures</span> of these systems. NiAl is considered a potential alternative to conventional superalloys due to its excellent oxidation resistance, low density, and high melting <span class="hlt">temperature</span>. The fact that NiAl is the most common coating for current superalloy turbine blades is a tribute to its oxidation resistance. Its density is one-third that of typical superalloys and in most <span class="hlt">temperature</span> ranges its thermal conductivity is twice that of common superalloys. Despite these many advantages, NiAl requires more investigation before it is ready to be used in engines. Binary NiAl in general has poor high-<span class="hlt">temperature</span> strength and low-<span class="hlt">temperature</span> ductility. On-going research in alloy design continues to make improvements in the high-<span class="hlt">temperature</span> strength of NiAl. The factors controlling low <span class="hlt">temperature</span> ductility have been identified in the last few years. Small, but reproducible ductility can now be achieved at room <span class="hlt">temperature</span> through careful control of chemical purity and processing. But the mechanisms controlling the transition from brittle to ductile behavior are not fully understood. Research in the area of fatigue <span class="hlt">deformation</span> can aid the development of the NiAl system in two ways. Fatigue properties must be documented and optimized before NiAl can be applied to engineering systems. More importantly though</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1988MTA....19..855N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1988MTA....19..855N"><span id="translatedtitle">Elevated <span class="hlt">temperature</span> <span class="hlt">creep</span>-fatigue crack propagation in nickel-base alloys and 1 Cr-Mo-V steel</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nazmy, M.; Hoffelner, W.; Wüthrich, C.</p> <p>1988-04-01</p> <p>The crack growth behavior of several high <span class="hlt">temperature</span> nickel-base alloys, under cyclic and static loading, is studied and reviewed. In the oxide dispersion strengthened (ODS) MA 6000 and MA 754 alloys, the high <span class="hlt">temperature</span> crack propagation exhibited orientation dependence under cyclic as well as under static loading. The <span class="hlt">creep</span> crack growth (CCG) behavior of cast nickel-base IN-738 and IN-939* superalloys at 850 °C could be characterized by the stress intensity factor, K 1. In the case of the alloy IN-901 at 500 °C and 600 °C, K 1 was found to be the relevant parameter to characterize the <span class="hlt">creep</span> crack growth behavior. The energy rate line integral, C*, may be the appropriate loading parameter to describe the <span class="hlt">creep</span> crack growth behavior of the nickel-iron base IN-800H alloy at 800 °C. The <span class="hlt">creep</span> crack growth data of 1 Cr-Mo-V steel, with bainitic microstructure, at 550 °C could be correlated better by C * than by K 1.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/442158','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/442158"><span id="translatedtitle">Irradiation <span class="hlt">creep</span> at <span class="hlt">temperatures</span> of 400 {degrees}C and below for application to near-term fusion devices</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Grossbeck, M.L.; Gibson, L.T.; Mansur, L.K.</p> <p>1996-12-31</p> <p>To study irradiation <span class="hlt">creep</span> at 400{degrees}C and below, a series of six austenitic stainless steels and two ferritic alloys was irradiated sequentially in two research reactors where the neutron spectrum was tailored to produce a He production rate typical of a fusion device. Irradiation began in the Oak Ridge Research Reactor; and, after an atomic displacement level of 7.4 dpa, the specimens were moved to the High Flux Isotope Reactor for the remainder of the 19 dpa accumulated. Irradiation <span class="hlt">temperatures</span> of 60, 200, 330, and 400{degrees}C were studied with internally pressurized tubes of type 316 stainless steel, PCA, HT 9, and a series of four laboratory heats of: Fe-13.5Cr-15Ni, Fe-13.5Cr-35Ni, Fe-1 3.5Cr-1 W-0.18Ti, and Fe-16Cr. At 330{degrees}C, irradiation <span class="hlt">creep</span> was shown to be linear in fluence and stress. There was little or no effect of cold-work on <span class="hlt">creep</span> under these conditions at all <span class="hlt">temperatures</span> investigated. The HT9 demonstrated a large deviation from linearity at high stress levels, and a minimum in irradiation <span class="hlt">creep</span> with increasing stress was observed in the Fe-Cr-Ni ternary alloys.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/1018576','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/1018576"><span id="translatedtitle">Overview of strategies for high-<span class="hlt">temperature</span> <span class="hlt">creep</span> and oxidation resistance of alumina-forming austenitic stainless steels</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Yamamoto, Yukinori; Brady, Michael P; Santella, Michael L; Bei, Hongbin; Maziasz, Philip J; Pint, Bruce A</p> <p>2011-01-01</p> <p>A family of <span class="hlt">creep</span>-resistant, alumina-forming austenitic (AFA) stainless steel alloys is under development for structural use in fossil energy conversion and combustion system applications. The AFA alloys developed to date exhibit comparable <span class="hlt">creep</span>-rupture lives to state-of-the-art advanced austenitic alloys, and superior oxidation resistance in the {approx}923 K to 1173 K (650 C to 900 C) <span class="hlt">temperature</span> range due to the formation of a protective Al{sub 2}O{sub 3} scale rather than the Cr{sub 2}O{sub 3} scales that form on conventional stainless steel alloys. This article overviews the alloy design approaches used to obtain high-<span class="hlt">temperature</span> <span class="hlt">creep</span> strength in AFA alloys via considerations of phase equilibrium from thermodynamic calculations as well as microstructure characterization. Strengthening precipitates under evaluation include MC-type carbides or intermetallic phases such as NiAl-B2, Fe{sub 2}(Mo,Nb)-Laves, Ni{sub 3}Al-L1{sub 2}, etc. in the austenitic single-phase matrix. <span class="hlt">Creep</span>, tensile, and oxidation properties of the AFA alloys are discussed relative to compositional and microstructural factors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013FrME....8..181M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013FrME....8..181M"><span id="translatedtitle">A model for <span class="hlt">creep</span> life prediction of thin tube using strain energy density as a function of stress triaxiality under quasistatic loading employing elastic-<span class="hlt">creep</span> & elastic-plastic-<span class="hlt">creep</span> <span class="hlt">deformation</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mahmood, Tahir; Kanapathipillai, Sangarapillai; Chowdhury, Mahiuddin</p> <p>2013-06-01</p> <p>This paper demonstrates the application of a new multiaxial <span class="hlt">creep</span> damage model developed by authors using stress traixiality to predict the failure time of a component made of 0.5%Cr-0.5%Mo-0.25%V low alloy steel. The model employs strain energy density and assumes that the uniaxial strain energy density of a component can be easily calculated and can be converted to multi-axial strain energy density by multiplying it to a function of stress trixiality which is a ratio of mean stress to equivalent stress. For comparison, an elastic-<span class="hlt">creep</span> and elastic-plastic-<span class="hlt">creep</span> finite element analysis (FEA) is performed to get multi-axial strain energy density of the component which is compared with the calculated strain energy density for both cases. The verification and application of the model are demonstrated by applying it to thin tube for which the experimental data are available. The predicted failure times by the model are compared with the experimental results. The results show that the proposed model is capable of predicting failure times of the component made of the above-mentioned material with an accuracy of 4.0%.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/624244','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/624244"><span id="translatedtitle"><span class="hlt">Creep</span> crack growth behavior of aluminum alloy 2519. Part 1: Experimental analysis</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hamilton, B.C.; Saxena, A.; McDowell, D.L.; Hall, D.E.</p> <p>1997-12-31</p> <p>The discipline of time-dependent fracture mechanics has traditionally focused on the <span class="hlt">creep</span> crack growth behavior of high-<span class="hlt">temperature</span> materials that display <span class="hlt">creep</span>-ductile behavior, such as stainless steels and chromium-molybdenum steels. Elevated <span class="hlt">temperature</span> aluminum alloys, however, have been developed that exhibit <span class="hlt">creep</span>-brittle behavior; in this case, the <span class="hlt">creep</span> crack growth rate correlates with the stress intensity factor, K. The fracture characteristics of aluminum alloy 2519-T87 were studied at 135 C, and the <span class="hlt">creep</span> and <span class="hlt">creep</span> crack growth behavior were characterized utilizing experimental and numerical methods. The strain to failure for <span class="hlt">creep</span> <span class="hlt">deformation</span> specimens was limited to only 1.2 to 2.0%. <span class="hlt">Creep</span> crack growth tests revealed a unique correlation between the <span class="hlt">creep</span> crack growth rate and K, a result consistent with <span class="hlt">creep</span>-brittle behavior. No experimental correlation was found between the <span class="hlt">creep</span> crack growth rate and the C{sub t} parameter. Microscopy of fracture surfaces revealed distinct regions of intergranular and transgranular fracture, and the transition between the fracture regions was found to occur at a critical K-level. Experimental results also appeared to show that initiation of crack growth (incubation) is controlled by the accumulation of a critical amount of damage ahead of the crack tip and that a correlation exists between the incubation time and K. Total time to failure is viewed as a summation of the incubation period and the crack growth period, and the design importance of incubation time is discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19960007619','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19960007619"><span id="translatedtitle"><span class="hlt">Temperature</span> Dependent Cyclic <span class="hlt">Deformation</span> Mechanisms in Haynes 188 Superalloy</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Rao, K. Bhanu Sankara; Castelli, Michael G.; Allen, Gorden P.; Ellis, John R.</p> <p>1995-01-01</p> <p>The cyclic <span class="hlt">deformation</span> behavior of a wrought cobalt-base superalloy, Haynes 188, has been investigated over a range of <span class="hlt">temperatures</span> between 25 and 1000 C under isothermal and in-phase thermomechanical fatigue (TMF) conditions. Constant mechanical strain rates (epsilon-dot) of 10(exp -3)/s and 10(exp -4)/s were examined with a fully reversed strain range of 0.8%. Particular attention was given to the effects of dynamic strain aging (DSA) on the stress-strain response and low cycle fatigue life. A correlation between cyclic <span class="hlt">deformation</span> behavior and microstructural substructure was made through detailed transmission electron microscopy. Although DSA was found to occur over a wide <span class="hlt">temperature</span> range between approximately 300 and 750 C the microstructural characteristics and the <span class="hlt">deformation</span> mechanisms responsible for DSA varied considerably and were dependent upon <span class="hlt">temperature</span>. In general, the operation of DSA processes led to a maximum of the cyclic stress amplitude at 650 C and was accompanied by pronounced planar slip, relatively high dislocation density, and the generation of stacking faults. DSA was evidenced through a combination of phenomena, including serrated yielding, an inverse dependence of the maximum cyclic hardening with epsilon-dot, and an instantaneous inverse epsilon-dot sensitivity verified by specialized epsilon-dot -change tests. The TMF cyclic hardening behavior of the alloy appeared to be dictated by the substructural changes occuring at the maximum <span class="hlt">temperature</span> in the TMF cycle.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10115053','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10115053"><span id="translatedtitle">Microstructural development and mechanical behavior of eutectic bismuth-tin and eutectic indium-tin in response to high <span class="hlt">temperature</span> <span class="hlt">deformation</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Goldstein, J.L.F. |</p> <p>1993-11-01</p> <p>The mechanical behavior and microstructure of eutectic Bi-Sn and In-Sn solders were studied in parallel in order to better understand high <span class="hlt">temperature</span> <span class="hlt">deformation</span> of these alloys. Bi-Sn solder joints were made with Cu substrates, and In-Sn joints were made with either Cu or Ni substrates. The as-cast microstructure of Bi-Sn is complex regular, with the two eutectic phases interconnected in complicated patterns. The as-cast microstructure of In-Sn depends on the substrate. In-Sn on Cu has a non-uniform microstructure caused by diffusion of Cu into the solder during sample preparation, with regions of the Sn-rich {gamma} phase imbedded in a matrix of the In-rich {beta} phase. The microstructure of In-Sn on Ni is uniform and lamellar and the two phases are strongly coupled. The solders <span class="hlt">deform</span> non-uniformly, with <span class="hlt">deformation</span> concentrating in a band along the length of the sample for Bi-Sn and In-Sn on Cu, though the <span class="hlt">deformation</span> is more diffuse in In-Sn than in Bi-Sn. <span class="hlt">Deformation</span> of In-Sn on Ni spreads throughout the width of the joint. The different <span class="hlt">deformation</span> patterns affect the shape of the stress-strain curves. Stress-strain curves for Bi-Sn and In-Sn on Cu exhibit sharp decays in the engineering stress after reaching a peak. Most of this stress decay is removed for In-Sn on Ni. The <span class="hlt">creep</span> behavior of In-Sn also depends on the substrate, with the <span class="hlt">creep</span> <span class="hlt">deformation</span> controlled by the soft P phase of the eutectic for In-Sn on Cu and controlled by the harder {gamma} phase for In-Sn on Ni. When In-Sn on Ni samples are aged, the microstructure coarsens and changes to an array of {gamma} phase regions in a matrix of the {beta} phase, and the <span class="hlt">creep</span> behavior changes to resemble that of In-Sn on Cu. The <span class="hlt">creep</span> behavior of Bi-Sn changes with <span class="hlt">temperature</span>. Two independent mechanisms operate at lower <span class="hlt">temperatures</span>, but there is still some question as to whether one or both of these, or a third mechanism, operates at higher <span class="hlt">temperatures</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19910038567&hterms=ageing&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dageing','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19910038567&hterms=ageing&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dageing"><span id="translatedtitle">A <span class="hlt">creep</span> apparatus to explore the quenching and ageing phenomena of PVC films</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lee, H. H. D.; Mcgarry, F. J.</p> <p>1991-01-01</p> <p>A <span class="hlt">creep</span> apparatus has been constructed for an in situ determination of length and length change. Using this apparatus, the <span class="hlt">creep</span> behavior of PVC thin films associated with quenching and aging was studied. The more severe the quench through the glass transition <span class="hlt">temperature</span>, the greater is the instantaneous elastic <span class="hlt">deformation</span> and the subsequent <span class="hlt">creep</span> behavior. As aging proceeds, the quenched films gradually lose the ductility incurred by quenching. These results agree well with the well-known phenomena of physical aging. Thus, the changes reflecting molecular mobilities due to quenching and aging can be properly monitored by such a <span class="hlt">creep</span> apparatus.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19980201213','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19980201213"><span id="translatedtitle"><span class="hlt">Creep</span> of Uncoated and Cu-Cr Coated NARloy-Z</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Walter, R. J.; Chiang, K. T.</p> <p>1998-01-01</p> <p>Stress rupture <span class="hlt">creep</span> tests were performed on uncoated and Cu-30vol%Cr coated NARloy-Z copper alloy specimens exposed to air at 482 C to 704 C. The results showed that <span class="hlt">creep</span> failure in air of unprotected NARloy-Z was precipitated by brittle intergranular surface cracking produced by strain assisted grain boundary oxidation (SAGBO) which in turn caused early onset of tertiary <span class="hlt">creep</span>. For the protected specimens, the Cu-Cr coating remained adherent throughout the tests and was effective in slowing down the rate of oxygen absorption, particularly at the higher <span class="hlt">temperatures</span>, by formation of a continuous chromium oxide scale. As the result of reducing oxygen ingress, the coating prevented SAGBO initiated early <span class="hlt">creep</span> failure, extended <span class="hlt">creep</span> <span class="hlt">deformation</span> and increased the <span class="hlt">creep</span> rupture life of NARloy-Z over the entire 482 C to 704 C test <span class="hlt">temperature</span> range.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhRvB..92a4115B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhRvB..92a4115B"><span id="translatedtitle">Modeling the <span class="hlt">creep</span> properties of olivine by 2.5-dimensional dislocation dynamics simulations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Boioli, Francesca; Carrez, Philippe; Cordier, Patrick; Devincre, Benoit; Marquille, Matthieu</p> <p>2015-07-01</p> <p>In this work we performed 2.5-dimensional (2.5D) dislocation dynamics simulations coupling climb with the glide dislocation motion to model the <span class="hlt">creep</span> behavior of olivine, one of the main component of the Earth's upper mantle. In particular, we present an application of this method to determine the <span class="hlt">creep</span> strain rate in a material with high lattice resistance, such as olivine. We show that by including the climb mechanism we reach steady state <span class="hlt">creep</span> conditions. Moreover, we find that a <span class="hlt">creep</span> power law with a stress exponent close to 3 can be extracted from our simulations and we provide a model based on Orowan's law to predict the <span class="hlt">creep</span> strain rates in the high <span class="hlt">temperature</span> and low stress regime. The model presented is relevant to describe the plastic flow of olivine in the Earth's mantle <span class="hlt">deformation</span> conditions and can be useful to derive the high <span class="hlt">temperature</span> <span class="hlt">creep</span> behavior of other materials.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SMaS...25a5020Q','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SMaS...25a5020Q"><span id="translatedtitle"><span class="hlt">Creep</span> and recovery behaviors of magnetorheological elastomer based on polyurethane/epoxy resin IPNs matrix</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Qi, S.; Yu, M.; Fu, J.; Li, P. D.; Zhu, M.</p> <p>2016-01-01</p> <p>This paper mainly investigated the <span class="hlt">creep</span> and recovery behaviors of magnetorheological elastomers (MRE) based on polyurethane/epoxy resin (EP) graft interpenetrating polymer networks (IPNs). The influences of constant stress level, content of EP, particle distribution, magnetic field and <span class="hlt">temperature</span> on the <span class="hlt">creep</span> and recovery behaviors were systematically investigated. As expected, results suggested that the presence of IPNs leads to a significant improvement of <span class="hlt">creep</span> resistance of MRE, and <span class="hlt">creep</span> and recovery behaviors of MRE were highly dependent on magnetic field and <span class="hlt">temperature</span>. To further understand its <span class="hlt">deformation</span> mechanism, several models (i.e., Findley’s power law model, Burgers model, and Weibull distribution equation) were used to fit the measured <span class="hlt">creep</span> and recovery data. Results showed that the modeling of <span class="hlt">creep</span> and recovery of samples was satisfactorily conducted by using these models. The influences of content of EP and magnetic field on fitting parameters were discussed, and relevant physical mechanism was proposed to explain it qualitatively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/1042839','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/1042839"><span id="translatedtitle">High-<span class="hlt">temperature</span> flexural <span class="hlt">creep</span> of ZrB2-SiC ceramics in argon atmosphere</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Guo, Wei-Ming; Zhang, Guo-Jun; Lin, Hua-Tay</p> <p>2012-01-01</p> <p>Four-point flexure <span class="hlt">creep</span> <span class="hlt">deformation</span> of ZrB2-30 vol% SiC ceramics in argon atmosphere under a static load of 19 MPa for 0-100 h at 1500 and 1600 C was investigated. The strain rate at 1600 oC was 3.7 times higher than that at 1500 oC. Microstructural evolution during <span class="hlt">creep</span> consisted of nucleation and growth of triple-point cavitations which were always associated with SiC particles. Due to the low stress, only isolated cavitations were nucleated, and no microcracks were formed. For up to 100 h at 1500 and 1600 C, the grains maintained their size and shape. The cavitations in both size and number showed no obvious difference from 26 to 100 h at 1500 C, whereas that showed a significant increase from 26 to 100 h at 1600 C. Present study suggested that ZrB2-30 vol% SiC exhibited relatively good microstructural stability and <span class="hlt">creep</span> resistance at 1500 C in argon atmosphere.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1080301','DOE-PATENT-XML'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1080301"><span id="translatedtitle">Cast heat-resistant austenitic steel with improved <span class="hlt">temperature</span> <span class="hlt">creep</span> properties and balanced alloying element additions and methodology for development of the same</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Pankiw, Roman I; Muralidharan, Govindrarajan; Sikka, Vinod Kumar; Maziasz, Philip J</p> <p>2012-11-27</p> <p>The present invention addresses the need for new austenitic steel compositions with higher <span class="hlt">creep</span> strength and higher upper <span class="hlt">temperatures</span>. The new austenitic steel compositions retain desirable phases, such as austenite, M.sub.23C.sub.6, and MC in its microstructure to higher <span class="hlt">temperatures</span>. The present invention also discloses a methodology for the development of new austenitic steel compositions with higher <span class="hlt">creep</span> strength and higher upper <span class="hlt">temperatures</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JSG....71....3D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JSG....71....3D"><span id="translatedtitle">Low-<span class="hlt">temperature</span> intracrystalline <span class="hlt">deformation</span> microstructures in quartz</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Derez, Tine; Pennock, Gill; Drury, Martyn; Sintubin, Manuel</p> <p>2015-02-01</p> <p>A review of numerous genetic interpretations of the individual low-<span class="hlt">temperature</span> intracrystalline <span class="hlt">deformation</span> microstructures in quartz shows that there is no consensus concerning their formation mechanisms. Therefore, we introduce a new, purely descriptive terminology for the three categories of intracrystalline <span class="hlt">deformation</span> microstructures formed in the low-quartz stability field: fine extinction bands (FEB), wide extinction bands (WEB) and localised extinction bands (LEB). The localised extinction bands are further subdivided into blocky (bLEB), straight (sLEB) and granular (gLEB) morphological types. A detailed polarised light microscopy study of vein-quartz from the low-grade metamorphic High-Ardenne slate belt (Belgium) further reveals a series of particular geometric relationships between these newly defined intracrystalline <span class="hlt">deformation</span> microstructures. These geometric relationships are largely unrecognised or underemphasised in the literature and need to be taken into account in any future genetic interpretation. Based on our observations and a critical assessment of the current genetic models, we argue that the interpretation of the pertinent microstructures in terms of ambient conditions and <span class="hlt">deformation</span> history should be made with care, as long as the genesis of these microstructures is not better confined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/1019263','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/1019263"><span id="translatedtitle">Low <span class="hlt">temperature</span> <span class="hlt">deformation</span> detwinning - a reverse mode of twinning.</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Wang, Y. D.; Liu, W.; Lu, L.; Ren, Y.; Nie, Z. H.; Almer, J.; Cheng, S.; Shen, Y. F.; Zuo, L.; Liaw, P. K.; Lu, K.</p> <p>2010-01-01</p> <p>The origin of the plasticity in bulk nanocrystalline metals have, to date, been attributed to the grain-boundary-mediated process, stress-induced grain coalescence, dislocation plasticity, and/or twinning. Here we report a different mechanism - detwinning, which operates at low <span class="hlt">temperatures</span> during the tensile <span class="hlt">deformation</span> of an electrodeposited Cu with a high density of nanosized growth twins. Both three-dimensional XRD microscopy using the Laue method with a submicron-sized polychromatic beam and high-energy XRD technique with a monochromatic beam provide the direct experimental evidences for low <span class="hlt">temperature</span> detwinning of nanoscale twins.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/203524','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/203524"><span id="translatedtitle">Effect of <span class="hlt">creep</span> strain on microstructural stability and <span class="hlt">creep</span> resistance of a TiAl/Ti{sub 3}Al lamellar alloy</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Wert, J.A.; Bartholomeusz, M.F.</p> <p>1996-01-01</p> <p><span class="hlt">Creep</span> of a TiAl/Ti{sub 3}Al alloy with a lamellar microstructure causes progressive spheroidization of the lamellar microstructure. Microstructural observations reveal that <span class="hlt">deformation</span>-induced spheroidization (DIS) occurs by <span class="hlt">deformation</span> and fragmentation of lamellae in localized shear zones at interpacket boundaries and within lamellar packets. <span class="hlt">Deformation</span>-induced spheroidization substantially increases the interphase interfacial area per unit volume, demonstrating that DIS is not a coarsening process driven by reduction of interfacial energy per unit volume. <span class="hlt">Creep</span> experiments reveal that DIS increases the minimum <span class="hlt">creep</span> rate ({dot {var_epsilon}}{sub min}) during <span class="hlt">creep</span> at constant stress and <span class="hlt">temperature</span>; the activation energy (Q{sub c}) and stress exponent (n) for <span class="hlt">creep</span> are both reduced as a result of DIS. Values of n and Q{sub c} for the lamellar microstructure are typical of a dislocation <span class="hlt">creep</span> mechanism, while estimated values of n and Q{sub c} for the completely spheroidized microstructure are characteristic of a diffusional <span class="hlt">creep</span> mechanism. The increase in {dot {var_epsilon}}{sub min} associated with DIS is thus attributed primarily to a change of <span class="hlt">creep</span> mechanism resulting from microstructural refinement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFM.T41C2916T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFM.T41C2916T"><span id="translatedtitle">Experimental <span class="hlt">Deformation</span> of Magnetite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Till, J. L.; Rybacki, E.; Morales, L. F. G.</p> <p>2015-12-01</p> <p>Magnetite is an important iron ore mineral and the most prominent Fe-oxide phase in the Earth's crust. The systematic occurrence of magnetite in zones of intense <span class="hlt">deformation</span> in oceanic core complexes suggests that it may play a role in strain localization in some silicate rocks. We performed a series of high-<span class="hlt">temperature</span> <span class="hlt">deformation</span> experiments on synthetic magnetite aggregates and natural single crystals to characterize the rheological behavior of magnetite. As starting material, we used fine-grained magnetite powder that was hot isostatically pressed at 1100°C for several hours, resulting in polycrystalline material with a mean grain size of around 40 μm and containing 3-5% porosity. Samples were <span class="hlt">deformed</span> to 15-20% axial strain under constant load (approximating constant stress) conditions in a Paterson-type gas apparatus for triaxial <span class="hlt">deformation</span> at <span class="hlt">temperatures</span> between 900 and 1100°C and 300 MPa confining pressure. The aggregates exhibit typical power-law <span class="hlt">creep</span> behavior. At high stresses, samples <span class="hlt">deformed</span> by dislocation <span class="hlt">creep</span> exhibit stress exponents close to 3, revealing a transition to near-Newtonian <span class="hlt">creep</span> with stress exponents around 1.3 at lower stresses. Natural magnetite single crystals <span class="hlt">deformed</span> at 1 atm pressure and <span class="hlt">temperatures</span> between 950°C and 1150 °C also exhibit stress exponents close to 3, but with lower flow stresses and a lower apparent activation energy than the aggregates. Such behavior may result from the different oxygen fugacity buffers used. Crystallographic-preferred orientations in all polycrystalline samples are very weak and corroborate numerical models of CPO development, suggesting that texture development in magnetite may be inherently slow compared with lower symmetry phases. Comparison of our results with experimental <span class="hlt">deformation</span> data for various silicate minerals suggests that magnetite should be weaker than most silicates during ductile <span class="hlt">creep</span> in dry igneous rocks.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004JSG....26..793I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004JSG....26..793I"><span id="translatedtitle">Development of shape- and lattice-preferred orientations of amphibole grains during initial cataclastic <span class="hlt">deformation</span> and subsequent <span class="hlt">deformation</span> by dissolution-precipitation <span class="hlt">creep</span> in amphibolites from the Ryoke metamorphic belt, SW Japan [review article</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Imon, Reiko; Okudaira, Takamoto; Kanagawa, Kyuichi</p> <p>2004-05-01</p> <p>Amphibolites from the Ryoke metamorphic belt, SW Japan were <span class="hlt">deformed</span> initially by cataclasis and subsequently by dissolution-precipitation <span class="hlt">creep</span>. Initial cataclastic <span class="hlt">deformation</span> produced a rather weak shape-preferred orientation (SPO) of brown amphibole grains with small aspect ratios as well as a poorly developed amphibole lattice-preferred orientation (LPO) with n α (≈ a[100]) axes scattered subnormal to the foliation and n γ or c[001] axes scattered around the lineation. During later <span class="hlt">deformation</span> by dissolution-precipitation <span class="hlt">creep</span>, preferential dissolution at grain boundaries subparallel to the foliation and simultaneous compaction normal to the foliation have likely produced a distinct SPO of elongate brown amphibole grains subparallel to the foliation as well as their LPO such that their n γ or c axes are scattered around the lineation, while n α (≈ a) and n β (= b[010]) are spread along a girdle normal to the lineation. Also during this <span class="hlt">deformation</span> green amphibole precipitated as isolated grains or in pressure shadow regions around brown amphibole grains. Nucleation and anisotropic growth of isolated green amphibole grains according to the orientations of the principal stress directions produced an LPO of these grains such that their n α (≈ a) are oriented normal to foliation, n β (= b) within the foliation normal to the lineation and n γ (or c) axes are parallel to the lineation. In addition, there is an associated SPO. Growth of green amphibole in pressure shadow regions around brown amphibole grains occurs either syntaxially or anisotropically according to the orientations of the principal stress directions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70010096','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70010096"><span id="translatedtitle">Mechanisms of high-<span class="hlt">temperature</span>, solid-state flow in minerals and ceramics and their bearing on the <span class="hlt">creep</span> behavior of the mantle</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Kirby, S.H.; Raleigh, C.B.</p> <p>1973-01-01</p> <p>The problem of applying laboratory silicate-flow data to the mantle, where conditions can be vastly different, is approached through a critical review of high-<span class="hlt">temperature</span> flow mechanisms in ceramics and their relation to empirical flow laws. The intimate association of solid-state diffusion and high-<span class="hlt">temperature</span> <span class="hlt">creep</span> in pure metals is found to apply to ceramics as well. It is shown that in ceramics of moderate grain size, compared on the basis of self-diffusivity and elastic modulus, normalized <span class="hlt">creep</span> rates compare remarkably well. This comparison is paralleled by the near universal occurrence of similar <span class="hlt">creep</span>-induced structures, and it is thought that the derived empirical flow laws can be associated with dislocation <span class="hlt">creep</span>. <span class="hlt">Creep</span> data in fine-grained ceramics, on the other hand, are found to compare poorly with theories involving the stress-directed diffusion of point defects and have not been successfully correlated by self-diffusion rates. We conclude that these fine-grained materials <span class="hlt">creep</span> primarily by a quasi-viscous grain-boundary sliding mechanism which is unlikely to predominate in the earth's deep interior. <span class="hlt">Creep</span> predictions for the mantle reveal that under most conditions the empirical dislocation <span class="hlt">creep</span> behavior predominates over the mechanisms involving the stress-directed diffusion of point defects. The probable role of polymorphic transformations in the transition zone is also discussed. ?? 1973.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015RMRE...48.2603G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015RMRE...48.2603G"><span id="translatedtitle">Steady-State <span class="hlt">Creep</span> of Rock Salt: Improved Approaches for Lab Determination and Modelling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Günther, R.-M.; Salzer, K.; Popp, T.; Lüdeling, C.</p> <p>2015-11-01</p> <p>Actual problems in geotechnical design, e.g., of underground openings for radioactive waste repositories or high-pressure gas storages, require sophisticated constitutive models and consistent parameters for rock salt that facilitate reliable prognosis of stress-dependent <span class="hlt">deformation</span> and associated damage. Predictions have to comprise the active mining phase with open excavations as well as the long-term development of the backfilled mine or repository. While convergence-induced damage occurs mostly in the vicinity of openings, the long-term behaviour of the backfilled system is dominated by the damage-free steady-state <span class="hlt">creep</span>. However, because in experiments the time necessary to reach truly stationary <span class="hlt">creep</span> rates can range from few days to years, depending mainly on <span class="hlt">temperature</span> and stress, an innovative but simple <span class="hlt">creep</span> testing approach is suggested to obtain more reliable results: A series of multi-step tests with loading and unloading cycles allows a more reliable estimate of stationary <span class="hlt">creep</span> rate in a reasonable time. For modelling, we use the advanced strain-hardening approach of Günther-Salzer, which comprehensively describes all relevant <span class="hlt">deformation</span> properties of rock salt such as <span class="hlt">creep</span> and damage-induced rock failure within the scope of an unified <span class="hlt">creep</span> ansatz. The capability of the combination of improved <span class="hlt">creep</span> testing procedures and accompanied modelling is demonstrated by recalculating multi-step <span class="hlt">creep</span> tests at different loading and <span class="hlt">temperature</span> conditions. Thus reliable extrapolations relevant to in-situ <span class="hlt">creep</span> rates (10^{-9} to 10^{-13} s^{-1}) become possible.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20040086471','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20040086471"><span id="translatedtitle"><span class="hlt">Creep</span> Strain and Strain Rate Response of 2219 Al Alloy at High Stress Levels</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Taminger, Karen M. B.; Wagner, John A.; Lisagor, W. Barry</p> <p>1998-01-01</p> <p>As a result of high localized plastic <span class="hlt">deformation</span> experienced during proof testing in an International Space Station connecting module, a study was undertaken to determine the <span class="hlt">deformation</span> response of a 2219-T851 roll forging. After prestraining 2219-T851 Al specimens to simulate strains observed during the proof testing, <span class="hlt">creep</span> tests were conducted in the <span class="hlt">temperature</span> range from ambient <span class="hlt">temperature</span> to 107 C (225 F) at stress levels approaching the ultimate tensile strength of 2219-T851 Al. Strain-time histories and strain rate responses were examined. The strain rate response was extremely high initially, but decayed rapidly, spanning as much as five orders of magnitude during primary <span class="hlt">creep</span>. Select specimens were subjected to incremental step loading and exhibited initial <span class="hlt">creep</span> rates of similar magnitude for each load step. Although the <span class="hlt">creep</span> rates decreased quickly at all loads, the <span class="hlt">creep</span> rates dropped faster and reached lower strain rate levels for lower applied loads. The initial <span class="hlt">creep</span> rate and <span class="hlt">creep</span> rate decay associated with primary <span class="hlt">creep</span> were similar for specimens with and without prestrain; however, prestraining (strain hardening) the specimens, as in the aforementioned proof test, resulted in significantly longer <span class="hlt">creep</span> life.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19890030007&hterms=coal&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dcoal','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19890030007&hterms=coal&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dcoal"><span id="translatedtitle">Mechanisms of elevated-<span class="hlt">temperature</span> <span class="hlt">deformation</span> in the B2 aluminides NiAl and CoAl</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Yaney, D. L.; Nix, W. D.</p> <p>1988-01-01</p> <p>A strain rate change technique, developed previously for distinguishing between pure-metal and alloy-type <span class="hlt">creep</span> behavior, was used to study the elevated-<span class="hlt">temperature</span> <span class="hlt">deformation</span> behavior of the intermetallic compounds NiAl and CoAl. Tests on NiAl were conducted at <span class="hlt">temperatures</span> between 1100 and 1300 K while tests on CoAl were performed at <span class="hlt">temperatures</span> ranging from 1200 to 1400 K. NiAl exhibits pure-metal type behavior over the entire <span class="hlt">temperature</span> range studied. CoAl, however, undergoes a transition from pure-metal to alloy-type <span class="hlt">deformation</span> behavior as the <span class="hlt">temperature</span> is decreased from 1400 to 1200 K. Slip appears to be inherently more difficult in CoAl than in NiAl, with lattice friction effects limiting the mobility of dislocations at a much higher tmeperature in CoAl than in NiAl. The superior strength of CoAl at elevated <span class="hlt">temperatures</span> may, therefore, be related to a greater lattice friction strengthening effect in CoAl than in NiAl.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003EAEJA.....4338M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003EAEJA.....4338M"><span id="translatedtitle"><span class="hlt">Creep</span>: long-term time-dependent rock <span class="hlt">deformation</span> in a deep-sea laboratory in the ionian sea: a pilot study</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Meredith, P.; Boon, S.; Vinciguerra, S.; Bowles, J.; Hughes, N.; Migneco, E.; Musumeci, M.; Piattelli, P.; Riccobene, G.; Vinciguerra, D.</p> <p>2003-04-01</p> <p>Time-dependent brittle rock <span class="hlt">deformation</span> is of first-order importance for understanding the long-term behaviour of water saturated rocks in the Earth's upper crust. The traditional way of investigating this has been to carry out laboratory "brittle <span class="hlt">creep</span>" experiments. Results have been interpreted involving three individual <span class="hlt">creep</span> phases; primary (decelerating), secondary (constant strain rate or steady state) and tertiary (accelerating or unstable). The <span class="hlt">deformation</span> may be distributed during the first two, but localizes onto a fault plane during phase three. However, it is difficult to distinguish between competing mechanisms and models given the lower limit of strain rates practicably achievable in the laboratory. The study reported here aims to address this problem directly by extending significantly the range of achievable strain rates through much longer-term experiments conducted in a deep-sea laboratory in the Ionian sea. The project takes advantage of a collaboration with the Laboratori Nazionali del Sud (LNS) of the Italian National Institute of Nuclear Physics (INFN), that is developing a deep-sea laboratory for a very large volume (1 km3) deep-sea detector of high-energy (>1019 eV) cosmic neutrinos (NEMO). A suitable deep-sea site has been identified, some 20km south-west of Catania in Sicily, with flat bathymetry at a depth of 2100m. The <span class="hlt">CREEP</span> <span class="hlt">deformation</span> apparatus is driven by an actuator that amplifies the ambient water pressure, while the confining pressure around the rock sample is provided by the ambient water pressure (>20MPa). Measurement transducers and a low-energy data acquisition system are sealed internally, with power provided for up to 6 months by an internal battery pack. The great advantage of operating in the deep sea in this way is that the system is simple; it is "passive", has few moving parts, and requires no maintenance. The apparatus is fixed approximately 10m above the seabed; held in place by a disposable concrete anchor and</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1168621','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1168621"><span id="translatedtitle"><span class="hlt">CREEP</span> AND <span class="hlt">CREEP</span>-FATIGUE OF ALLOY 617 WELDMENTS</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Wright, Jill; Carroll, Laura; Wright, Richard</p> <p>2014-08-01</p> <p>The Very High <span class="hlt">Temperature</span> Reactor (VHTR) Intermediate Heat Exchanger (IHX) may be joined to piping or other components by welding. <span class="hlt">Creep</span>-fatigue <span class="hlt">deformation</span> is expected to be a predominant failure mechanism of the IHX1 and thus weldments used in its fabrication will experience varying cyclic stresses interrupted by periods of elevated <span class="hlt">temperature</span> <span class="hlt">deformation</span>. These periods of elevated <span class="hlt">temperature</span> <span class="hlt">deformation</span> are greatly influenced by a materials’ <span class="hlt">creep</span> behavior. The nickel-base solid solution strengthened alloy, Alloy 617, is the primary material candidate for a VHTR-type IHX, and it is expected that Alloy 617 filler metal will be used for welds. Alloy 617 is not yet been integrated into Section III of the Boiler and Pressure Vessel Code, however, nuclear component design with Alloy 617 requires ASME (American Society of Mechanical Engineers) Code qualification. The Code will dictate design for welded construction through significant performance reductions. Despite the similar compositions of the weldment and base material, significantly different microstructures and mechanical properties are inevitable. Experience of nickel alloy welds in structural applications suggests that most high <span class="hlt">temperature</span> failures occur at the weldments or in the heat-affected zone. Reliably guarding against this type of failure is particularly challenging at high <span class="hlt">temperatures</span> due to the variations in the inelastic response of the constituent parts of the weldment (i.e., weld metal, heat-affected zone, and base metal) [ref]. This work focuses on the <span class="hlt">creep</span>-fatigue behavior of nickel-based weldments, a need noted during the development of the draft Alloy 617 ASME Code Case. An understanding of Alloy 617 weldments when subjected to this important <span class="hlt">deformation</span> mode will enable determination of the appropriate design parameters associated with their use. Specifically, the three main areas emphasized are the performance reduction due to a weld discontinuity in terms of the reduced number of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JNuM..447...28T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JNuM..447...28T"><span id="translatedtitle">Biaxial thermal <span class="hlt">creep</span> of Inconel 617 and Haynes 230 at 850 and 950 °C</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tung, Hsiao-Ming; Mo, Kun; Stubbins, James F.</p> <p>2014-04-01</p> <p>The biaxial thermal <span class="hlt">creep</span> behavior of Inconel 617 and Haynes 230 at 850 and 950 °C was investigated. Biaxial stresses were generated using the pressurized tube technique. The detailed <span class="hlt">creep</span> <span class="hlt">deformation</span> and fracture mechanism have been studied. <span class="hlt">Creep</span> curves for both alloys showed that tertiary <span class="hlt">creep</span> accounts for a greater portion of the materials' life, while secondary <span class="hlt">creep</span> only accounts for a small portion. Fractographic examinations of the two alloys indicated that nucleation, growth, and coalescence of <span class="hlt">creep</span> voids are the dominant micro-mechanisms for <span class="hlt">creep</span> fracture. At 850 °C, alloy 230 has better <span class="hlt">creep</span> resistance than alloy 617. When subjected to the biaxial stress state, the <span class="hlt">creep</span> rupture life of the two alloys was considerably reduced when compared to the results obtained by uniaxial tensile <span class="hlt">creep</span> tests. The Monkman-Grant relation proves to be a promising method for estimating the long-term <span class="hlt">creep</span> life for alloy 617, whereas alloy 230 does not follow the relation. This might be associated with the significant changes in the microstructure of alloy 230 at high <span class="hlt">temperatures</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004PSSAR.201.2001L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004PSSAR.201.2001L"><span id="translatedtitle">Defects in silicon plastically <span class="hlt">deformed</span> at room <span class="hlt">temperature</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Leipner, H. S.; Wang, Z.; Gu, H.; Mikhnovich, V. V., Jr.; Bondarenko, V.; Krause-Rehberg, R.; Demenet, J.-L.; Rabier, J.</p> <p>2004-07-01</p> <p>The article [1] describes specific features of positron trapping in silicon plastically <span class="hlt">deformed</span> at room <span class="hlt">temperature</span>. The results are related to the dislocation core structure and the inhomogeneous <span class="hlt">deformation</span>. The picture shows the probability density function of a positron localized in a vacancy in silicon. The calculation was performed with the superimposed-atom model. The degree of localization and consequently the defect-related positron lifetime vary for different open-volume defects, such as vacancies, voids, and dislocations.The first author, Hartmut S. Leipner, is CEO of the Center of Materials Science of the University Halle-Wittenberg. His research activities are focused on the characterization of extended defects in semiconductors.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014PhDT........50A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014PhDT........50A"><span id="translatedtitle">High <span class="hlt">temperature</span> <span class="hlt">deformation</span> behavior, thermal stability and irradiation performance in Grade 92 steel</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Alsagabi, Sultan</p> <p></p> <p>The 9Cr-2W ferritic-martensitic steel (i.e. Grade 92 steel) possesses excellent mechanical and thermophysical properties; therefore, it has been considered to suit more challenging applications where high <span class="hlt">temperature</span> strength and <span class="hlt">creep</span>-rupture properties are required. The high <span class="hlt">temperature</span> <span class="hlt">deformation</span> mechanism was investigated through a set of tensile testing at elevated <span class="hlt">temperatures</span>. Hence, the threshold stress concept was applied to elucidate the operating high <span class="hlt">temperature</span> <span class="hlt">deformation</span> mechanism. It was identified as the high <span class="hlt">temperature</span> climb of edge dislocations due to the particle-dislocation interactions and the appropriate constitutive equation was developed. In addition, the microstructural evolution at room and elevated <span class="hlt">temperatures</span> was investigated. For instance, the microstructural evolution under loading was more pronounced and carbide precipitation showed more coarsening tendency. The growth of these carbide precipitates, by removing W and Mo from matrix, significantly deteriorates the solid solution strengthening. The MX type carbonitrides exhibited better coarsening resistance. To better understand the thermal microstructural stability, long tempering schedules up to 1000 hours was conducted at 560, 660 and 760°C after normalizing the steel. Still, the coarsening rate of M23C 6 carbides was higher than the MX-type particles. Moreover, the Laves phase particles were detected after tempering the steel for long periods before they dissolve back into the matrix at high <span class="hlt">temperature</span> (i.e. 720°C). The influence of the tempering <span class="hlt">temperature</span> and time was studied for Grade 92 steel via Hollomon-Jaffe parameter. Finally, the irradiation performance of Grade 92 steel was evaluated to examine the feasibility of its eventual reactor use. To that end, Grade 92 steel was irradiated with iron (Fe2+) ions to 10, 50 and 100 dpa at 30 and 500°C. Overall, the irradiated samples showed some irradiation-induced hardening which was more noticeable at 30°C. Additionally</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940024337','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940024337"><span id="translatedtitle">Probabilistic Material Strength Degradation Model for Inconel 718 Components Subjected to High <span class="hlt">Temperature</span>, Mechanical Fatigue, <span class="hlt">Creep</span> and Thermal Fatigue Effects</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bast, Callie Corinne Scheidt</p> <p>1994-01-01</p> <p>This thesis presents the on-going development of methodology for a probabilistic material strength degradation model. The probabilistic model, in the form of a postulated randomized multifactor equation, provides for quantification of uncertainty in the lifetime material strength of aerospace propulsion system components subjected to a number of diverse random effects. This model is embodied in the computer program entitled PROMISS, which can include up to eighteen different effects. Presently, the model includes four effects that typically reduce lifetime strength: high <span class="hlt">temperature</span>, mechanical fatigue, <span class="hlt">creep</span>, and thermal fatigue. Statistical analysis was conducted on experimental Inconel 718 data obtained from the open literature. This analysis provided regression parameters for use as the model's empirical material constants, thus calibrating the model specifically for Inconel 718. Model calibration was carried out for four variables, namely, high <span class="hlt">temperature</span>, mechanical fatigue, <span class="hlt">creep</span>, and thermal fatigue. Methodology to estimate standard deviations of these material constants for input into the probabilistic material strength model was developed. Using the current version of PROMISS, entitled PROMISS93, a sensitivity study for the combined effects of mechanical fatigue, <span class="hlt">creep</span>, and thermal fatigue was performed. Results, in the form of cumulative distribution functions, illustrated the sensitivity of lifetime strength to any current value of an effect. In addition, verification studies comparing a combination of mechanical fatigue and high <span class="hlt">temperature</span> effects by model to the combination by experiment were conducted. Thus, for Inconel 718, the basic model assumption of independence between effects was evaluated. Results from this limited verification study strongly supported this assumption.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2006JEMat..35.1050R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2006JEMat..35.1050R"><span id="translatedtitle"><span class="hlt">Creep</span>-constitutive behavior of Sn-3.8Ag-0.7Cu solder using an internal stress approach</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rist, Martin A.; Plumbridge, W. J.; Cooper, S.</p> <p>2006-05-01</p> <p>The experimental tensile <span class="hlt">creep</span> <span class="hlt">deformation</span> of bulk Sn-3.8Ag-0.7Cu solder at <span class="hlt">temperatures</span> between 263 K and 398 K, covering lifetimes up to 3,500 h, has been rationalized using constitutive equations that incorporate structure-related internal state variables. Primary <span class="hlt">creep</span> is accounted for using an evolving internal back stress, due to the interaction between the soft matrix phase and a more <span class="hlt">creep</span>-resistant particle phase. Steady-state <span class="hlt">creep</span> is incorporated using a conventional power law, modified to include the steady-state value of internal stress. It is demonstrated that the observed behavior is well-fitted using <span class="hlt">creep</span> constants for pure tin in the modified <span class="hlt">creep</span> power law. A preliminary analysis of damage-induced tertiary <span class="hlt">creep</span> is also presented.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008MTDM...12..275S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008MTDM...12..275S"><span id="translatedtitle">Mechanisms for tertiary <span class="hlt">creep</span> of single crystal superalloy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Staroselsky, Alexander; Cassenti, Brice</p> <p>2008-12-01</p> <p>During the thermal-mechanical loading of high <span class="hlt">temperature</span> single crystal turbine components, all three creep—stages: primary, secondary and tertiary, manifest themselves and, hence, none of them can be neglected. The development of a <span class="hlt">creep</span> law that includes all three stages is especially important in the case of non-homogeneous thermal loading of the component where significant stress redistribution and relaxation will result. Thus, local <span class="hlt">creep</span> analysis is crucial for proper design of damage tolerant airfoils. We have developed a crystallographic-based constitutive model and fully coupled it with damage kinetics. The model extends existing approaches for cyclic and thermal-cyclic loading of anisotropic elasto-viscoplastic <span class="hlt">deformation</span> behavior and damage kinetics of single-crystal materials, allowing prediction of tertiary <span class="hlt">creep</span> and failure initiation of high <span class="hlt">temperature</span> components. Our damage model bridges the gap between dislocation dynamics and the continuum mechanics scales and can be used to represent tertiary as well as primary and secondary <span class="hlt">creep</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1999PhDT........56V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1999PhDT........56V"><span id="translatedtitle">Hot <span class="hlt">deformation</span> behaviour of alloys for applications at elevated <span class="hlt">temperatures</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Voyzelle, Benoit</p> <p></p> <p>The present study investigated the <span class="hlt">deformation</span> behaviour, microstructure evolution and fracture behaviour under hot working conditions of alloys designed for elevated-<span class="hlt">temperature</span> applications. For this purpose, iron-aluminum and titanium-aluminum alloys were selected and their compositions are: Fe-8.5wt%Al-5.5Cr-2.0Mo-0.2Zr-0.03C, Fe-16.5Al-5.5Cr-1.0Nb-0.05C and Ti-33.3Al-2.8Mn-4.8Nb. These alloys were tested in the as-cast condition and in the form of hot-rolled + annealed plate for the iron-aluminum alloys and in the HIP'ed condition for the titanium-aluminum alloy. Isothermal compression tests were carried out with a Gleeble 2000 over a range of <span class="hlt">temperatures</span> from 800 to 1250°C and constant strain rates from 10-3 to 10 s-1. In general, the flow curves are marked by a peak stress and softening which decline as <span class="hlt">temperature</span> rises, and a flow stress which diminishes with rise in <span class="hlt">temperature</span> and decrease in strain rate. The flow behaviour at peak stress (sigmap) and 0.5 true strain of these materials was described well by the Zener-Hollomon parameter Z=3˙exp /RTQHW , where Z=K3sinha sn . A numerical curve-fitting method was used to yield values of the following parameters: (i) stress exponent, n and (ii) activation energy, QHW . The dynamic material modeling approach was performed to extract from hot compression data: (i) the strain rate sensitivity parameter, m, (ii) the efficiency of power dissipation, eta, and (iii) the instability parameter, xi. The microstructure evolution and fracture behaviour were assessed using optical and electron microscopy. The <span class="hlt">deformation</span> processes occuring were determined by correlation of the sigma-epsilon curves, m and microstructural observations. The resulting <span class="hlt">deformation</span> map indicates that at lower <span class="hlt">temperatures</span> and higher strain rates, the dominant restoration occurs by dynamic recovery, while at lower strain rates and higher <span class="hlt">temperatures</span> dynamic recrystallization is the operative mode. At the highest <span class="hlt">temperatures</span>, dynamic</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JSG....37...89Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JSG....37...89Z"><span id="translatedtitle">Extreme ductile <span class="hlt">deformation</span> of fine-grained salt by coupled solution-precipitation <span class="hlt">creep</span> and microcracking: Microstructural evidence from perennial Zechstein sequence (Neuhof salt mine, Germany)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Závada, Prokop; Desbois, Guillaume; Schwedt, Alexander; Lexa, Ondrej; Urai, Janos L.</p> <p>2012-04-01</p> <p>Microstructural study revealed that the ductile flow of intensely folded fine-grained salt exposed in an underground mine (Zechstein-Werra salt sequence, Neuhof mine, Germany) was accommodated by coupled activity of solution-precipitation (SP) <span class="hlt">creep</span> and microcracking of the halite grains. The grain cores of the halite aggregates contain remnants of sedimentary microstructures with straight and chevron shaped fluid inclusion trails (FITs) and are surrounded by two concentric mantles reflecting different events of salt precipitation. Numerous intra-granular or transgranular microcracks originate at the tips of FITs and propagate preferentially along the interface between sedimentary cores and the surrounding mantle of reprecipitated halite. These microcracks are interpreted as tensional Griffith cracks. Microcracks starting at grain boundary triple junctions or grain boundary ledges form due to stress concentrations generated by grain boundary sliding (GBS). Solid or fluid inclusions frequently alter the course of the propagating microcracks or the cracks terminate at these inclusions. Because the inner mantle containing the microcracks is corroded and is surrounded by microcrack-free outer mantle, microcracking is interpreted to reflect transient failure of the aggregate. Microcracking is argued to play a fundamental role in the continuation and enhancement of the SP-GBS <span class="hlt">creep</span> during halokinesis of the Werra salt, because the transgranular cracks (1) provide the ingress of additional fluid in the grain boundary network when cross-cutting the FITs and (2) decrease grain size by splitting the grains. More over, the ingress of additional fluids into grain boundaries is also provided by non-conservative grain boundary migration that advanced into FITs bearing cores of grains. Described readjustments of the microstructure and mechanical and chemical feedbacks for the grain boundary diffusion flow in halite-brine system are proposed to be comparable to other rock-fluid or</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19740022222','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19740022222"><span id="translatedtitle"><span class="hlt">Deformation</span> characteristics and time-dependent notch sensitivity of Udimet 700 at intermediate <span class="hlt">temperatures</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wilson, D. J.</p> <p>1974-01-01</p> <p>Time dependent notch sensitivity was observed in Udimet 700 sheet, bar, and investment castings between 1000 and 1400 F (538 -760 C), but not at 1600 F (871 C). As was the case for modified Waspaloy, Waspaloy and Inconel 718, it occurred in notched specimens loaded below the yield strength when the <span class="hlt">creep</span> <span class="hlt">deformation</span> was localized. For each alloy and notched specimen geometry, a stress-average particle size zone can be defined that characterizes the notch sensitive behavior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009MMTA...40..539E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009MMTA...40..539E"><span id="translatedtitle">Microstructural Evolution during <span class="hlt">Creep</span> of Alloy 800HT in the <span class="hlt">Temperature</span> Range 600 °C to 1000 °C</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Erneman, J.; Nilsson, J.-O.; Andrén, H.-O.; Tobjörk, D.</p> <p>2009-03-01</p> <p>The microstructure of SANICRO 31HT (alloy 800HT) <span class="hlt">creep</span> tested to a maximum of 85,388 hours in the <span class="hlt">temperature</span> range of 600 °C to 1000 °C was investigated. Coarse Ti(C, N) precipitates were found to form in the melt and remained stable after solution annealing and aging at all <span class="hlt">temperatures</span> investigated. M23C6 precipitating in the range of 600 °C to 700 °C was found in two different distributions: as intergranular precipitates and as small intragranular particles. The γ' precipitation sequence was followed at 600 °C, 650 °C, and 700 °C, and the volume fraction and precipitate diameter was assessed using energy-filtered transmission electron microscopy (EFTEM). The γ' precipitates grew and coarsened slowly at 600 °C (10 to 30 nm) but somewhat faster at 650 °C (25 to 50 nm). The volume fraction was largest at 600 °C. The γ' precipitates formed at 700 °C were not homogeneously distributed in the matrix. Instead, γ' was observed in the immediate vicinity of M23C6 and Ti(C, N) precipitates. Atom probe field ion microscope analysis of γ'-precipitate showed that it contained slightly more Ti than Al and that its Fe content was a few atomic percent. Nitrogen uptake was very pronounced in <span class="hlt">creep-deformed</span> material aged at 1000 °C, and AlN formed as grain boundary needles and in the interior of grains.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JMEP...25.2084K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JMEP...25.2084K"><span id="translatedtitle">Room-<span class="hlt">Temperature</span> Indentation <span class="hlt">Creep</span> and the Mechanical Properties of Rapidly Solidified Sn-Sb-Pb-Cu Alloys</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kamal, Mustafa; El-Bediwi, A.; Lashin, A. R.; El-Zarka, A. H.</p> <p>2016-05-01</p> <p>In this paper, we study the room-<span class="hlt">temperature</span> indentation <span class="hlt">creep</span> and the mechanical properties of Sn-Sb-Pb-Cu alloys. Rapid solidification from melt using the melt-spinning technique is applied to prepare all the alloys. The experimental results show that the magnitude of the <span class="hlt">creep</span> displacement increases with the increase in both time and applied load, and the stress exponent increases with the increase in the copper content in the alloys which happens primarily due to the existence of the intermetallic compounds SbSn and Cu6Sn5. The calculated values of the stress exponent are in the range of 2.82 to 5.16, which are in good agreement with the values reported for the Sn-Sb-Pb-Cu alloys. We have also studied and analyzed the structure, elastic modulus, and internal friction of the Sn-Sb-Pb-Cu alloys.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/228503','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/228503"><span id="translatedtitle">A technique to achieve uniform stress distribution in compressive <span class="hlt">creep</span> testing of advanced ceramics at high <span class="hlt">temperatures</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Liu, K.C.; Stevens, C.O.; Brinkman, C.R.; Holshauser, N.E.</p> <p>1996-05-01</p> <p>A technique to achieve stable and uniform uniaxial compression is offered for <span class="hlt">creep</span> testing of advanced ceramic materials at elevated <span class="hlt">temperatures</span>, using an innovative self-aligning load-train assembly. Excellent load-train alignment is attributed to the inherent ability of a unique hydraulic universal coupler to maintain self-aligning. Details of key elements, design concept, and pricniples of operation of the self-aligning coupler are described. A method of alignment verification using a strain-gaged specimen is then discussed. Results of verification tests indicate that bending below 1.5% is routinely achievable usin the load-train system. A successful compression <span class="hlt">creep</span> test is demonstrated using a dumbbell-shpaed Si nitride specimen tested at 1300 C for over 4000 h.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4942832','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4942832"><span id="translatedtitle">Coarsening behaviour of M23C6 carbides in <span class="hlt">creep</span>-resistant steel exposed to high <span class="hlt">temperatures</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Godec, M.; Skobir Balantič, D. A.</p> <p>2016-01-01</p> <p>High operating <span class="hlt">temperatures</span> can have very deleterious effects on the long-term performance of high-Cr, <span class="hlt">creep</span>-resistant steels used, for example, in the structural components of power plants. For the popular <span class="hlt">creep</span>-resistant steel X20CrMoV12.1 we analysed the processes of carbide growth using a variety of analytical techniques: transmission electron microscopy (TEM) and diffraction (TED), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). The evolution of the microstructure after different aging times was the basis for a much better understanding of the boundary-migration processes and the growth of the carbides. We present an explanation as to why some locations are preferential for this growth, and using EBSD we were able to define the proper orientational relationship between the carbides and the matrix. PMID:27406340</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016NatSR...629734G&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016NatSR...629734G&link_type=ABSTRACT"><span id="translatedtitle">Coarsening behaviour of M23C6 carbides in <span class="hlt">creep</span>-resistant steel exposed to high <span class="hlt">temperatures</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Godec, M.; Skobir Balantič, D. A.</p> <p>2016-07-01</p> <p>High operating <span class="hlt">temperatures</span> can have very deleterious effects on the long-term performance of high-Cr, <span class="hlt">creep</span>-resistant steels used, for example, in the structural components of power plants. For the popular <span class="hlt">creep</span>-resistant steel X20CrMoV12.1 we analysed the processes of carbide growth using a variety of analytical techniques: transmission electron microscopy (TEM) and diffraction (TED), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD). The evolution of the microstructure after different aging times was the basis for a much better understanding of the boundary-migration processes and the growth of the carbides. We present an explanation as to why some locations are preferential for this growth, and using EBSD we were able to define the proper orientational relationship between the carbides and the matrix.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/755861','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/755861"><span id="translatedtitle"><span class="hlt">Creep</span> in electronic ceramics</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Routbort, J. L.; Goretta, K. C.; Arellano-Lopez, A. R.</p> <p>2000-04-27</p> <p>High-<span class="hlt">temperature</span> <span class="hlt">creep</span> measurements combined with microstructural investigations can be used to elucidate <span class="hlt">deformation</span> mechanisms that can be related to the diffusion kinetics and defect chemistry of the minority species. This paper will review the theoretical basis for this correlation and illustrate it with examples from some important electronic ceramics having a perovskite structure. Recent results on BaTiO{sub 3}, (La{sub 1{minus}x}Sr){sub 1{minus}y}MnO{sub 3+{delta}}, YBa{sub 2}Cu{sub 3}O{sub x}, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x}, (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} and Sr(Fe,Co){sub 1.5}O{sub x} will be presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JNuM..433..188W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JNuM..433..188W"><span id="translatedtitle">A mechanism-based framework for the numerical analysis of <span class="hlt">creep</span> in zircaloy-4</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, H.; Hu, Z.; Lu, W.; Thouless, M. D.</p> <p>2013-02-01</p> <p>A <span class="hlt">deformation</span>-mechanism map has been developed for unirradiated zircaloy-4 based on the <span class="hlt">creep</span> data available from the literature of the last 35 years. These data have been analyzed to identify different <span class="hlt">creep</span> mechanisms, based on the forms of the relationships between stress, <span class="hlt">temperature</span> and strain rate. This identification allowed the activation energies and other associated <span class="hlt">creep</span> parameters to be derived for each mechanism. The <span class="hlt">creep</span> parameters were used to construct a <span class="hlt">deformation</span>-mechanism map for zircaloy-4 that shows the conditions under which different mechanisms are dominant. This information provides an important tool for assessing the effects of stress and <span class="hlt">temperature</span> in design, especially when extrapolating to different regimes. As an example of how this information might be used in a numerical analysis for design purposes, a novel mechanism-based <span class="hlt">creep</span> framework was implemented within a finite-element code. Although the framework was developed specifically for zircaloy-4, it provides a general example of how mechanism-based <span class="hlt">creep</span> laws can be implemented into finite-element analyses. This approach allows the <span class="hlt">creep</span> of complex geometries to be analyzed rigorously, with the dominant <span class="hlt">deformation</span> mechanisms being identified and evolving automatically in response to the local <span class="hlt">temperatures</span> and stresses.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1811121S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1811121S"><span id="translatedtitle">The role of fluid pressure in fault <span class="hlt">creep</span> vs. frictional instability: insights from rock <span class="hlt">deformation</span> experiments on carbonates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Scuderi, Marco M.; Collettini, Cristiano</p> <p>2016-04-01</p> <p>Fluid overpressure is one of the primary mechanisms for tectonic fault slip. This mechanism is appealing as fluids lubricate the fault and fluid pressure, Pf, reduces the effective normal stress that holds the fault in place. However, current models of earthquake nucleation imply that stable sliding is favored by the increase of pore fluid pressure. Despite this opposite effects, currently, there are only a few studies on the role of fluid pressure under controlled, laboratory conditions. Here, we use laboratory experiments, conducted on a biaxial apparatus within a pressure vessel on limestone fault gouge, to: 1) evaluate the rate- and state- friction parameters as the pore fluid pressure is increased from hydrostatic to near lithostatic values and 2) fault <span class="hlt">creep</span> evolution as a function of a step increase in fluid pressure. In this second suite of experiments we reached 85% of the maximum shear strength and than in load control we induced fault slip by increasing fluid pressure. Our data show that the friction rate parameter (a-b) evolves from slightly velocity strengthening to velocity neutral behaviour and the critical slip distance, Dc, decreases from about 100 to 20 μm as the pore fluid pressure is increased. Fault <span class="hlt">creep</span> is slow (i.e 0.001μm/s) away from the maximum shear strength and for small increases in fluid pressure and it accelerates near the maximum shear strength and for larger fluid pressure build-ups, where we observe episodic accelerations/decelerations that in some cases evolve to small dynamic events. Our data suggest that fluid overpressure can increase aseismic <span class="hlt">creep</span> with the development of frictional instability. Since fault rheology and fault stability parameters change with fluid pressure, we suggest that a comprehensive characterization of these parameters is fundamental for better assessing the role of fluid pressure in natural and human induced earthquakes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70012540','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70012540"><span id="translatedtitle">Transient <span class="hlt">creep</span> and semibrittle behavior of crystalline rocks</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Carter, N.L.; Kirby, S.H.</p> <p>1978-01-01</p> <p>We review transient <span class="hlt">creep</span> and semibrittle behavior of crystalline solids. The results are expected to be pertinent to crystalline rocks undergoing <span class="hlt">deformation</span> in the depth range 5 to 20 km, corresponding to depths of focus of many major earthquakes. Transient <span class="hlt">creep</span> data for crystalline rocks at elevated <span class="hlt">temperatures</span> are analyzed but are poorly understood because of lack of information on the <span class="hlt">deformation</span> processes which, at low to moderate pressure, are likely to be semibrittle in nature. Activation energies for transient <span class="hlt">creep</span> at high effective confining pressure are much higher than those found for atmospheric pressure tests in which thermally-activated microfracturing probably dominates the <span class="hlt">creep</span> rate. Empirical transient <span class="hlt">creep</span> equations are extrapolated at 200?? to 600??C, stresses from 0.1 to 1.0 kbar, to times ranging from 3.17??102 to 3.17??108 years. At the higher <span class="hlt">temperatures</span>, appreciable transient <span class="hlt">creep</span> strains may take place but the physical significance of the results is in question because the flow mechanisms have not been determined. The purpose of this paper is to stimulate careful research on this important topic. ?? 1978 Birkha??user Verlag.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016JGRB..121.3348K&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016JGRB..121.3348K&link_type=ABSTRACT"><span id="translatedtitle">First principles model of carbonate compaction <span class="hlt">creep</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Keszthelyi, Daniel; Dysthe, Dag Kristian; Jamtveit, Bjørn</p> <p>2016-05-01</p> <p>Rocks under compressional stress conditions are subject to long-term <span class="hlt">creep</span> <span class="hlt">deformation</span>. From first principles we develop a simple micromechanical model of <span class="hlt">creep</span> in rocks under compressional stress that combines microscopic fracturing and pressure solution. This model was then upscaled by a statistical mechanical approach to predict strain rate at core and reservoir scale. The model uses no fitting parameter and has few input parameters: effective stress, <span class="hlt">temperature</span>, water saturation porosity, and material parameters. Material parameters are porosity, pore size distribution, Young's modulus, interfacial energy of wet calcite, the dissolution, and precipitation rates of calcite, and the diffusion rate of calcium carbonate, all of which are independently measurable without performing any type of <span class="hlt">deformation</span> or <span class="hlt">creep</span> test. Existing long-term <span class="hlt">creep</span> experiments were used to test the model which successfully predicts the magnitude of the resulting strain rate under very different effective stress, <span class="hlt">temperature</span>, and water saturation conditions. The model was used to predict the observed compaction of a producing chalk reservoir.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009CoMP..157..339X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009CoMP..157..339X"><span id="translatedtitle">The effect of dissolved magnesium on <span class="hlt">creep</span> of calcite II: transition from diffusion <span class="hlt">creep</span> to dislocation <span class="hlt">creep</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xu, Lili; Renner, Jörg; Herwegh, Marco; Evans, Brian</p> <p>2009-03-01</p> <p>We extended a previous study on the influence of Mg solute impurity on diffusion <span class="hlt">creep</span> in calcite to include <span class="hlt">deformation</span> under a broader range of stress conditions and over a wider range of Mg contents. Synthetic marbles were produced by hot isostatic pressing (HIP) mixtures of calcite and dolomite powders for different intervals (2-30 h) at 850°C and 300 MPa confining pressure. The HIP treatment resulted in high-magnesian calcite aggregates with Mg content ranging from 0.5 to 17 mol%. Both back-scattered electron images and chemical analysis suggested that the dolomite phase was completely dissolved, and that Mg distribution was homogeneous throughout the samples at the scale of about two micrometers. The grain size after HIP varied from 8 to 31 μm, increased with time at <span class="hlt">temperature</span>, and decreased with increasing Mg content (>3.0 mol%). Grain size and time were consistent with a normal grain growth equation, with exponents from 2.4 to 4.7, for samples containing 0.5-17.0 mol% Mg, respectively. We <span class="hlt">deformed</span> samples after HIP at the same confining pressure with differential stresses between 20 and 200 MPa using either constant strain rate or stepping intervals of loading at constant stresses in a Paterson gas-medium <span class="hlt">deformation</span> apparatus. The <span class="hlt">deformation</span> tests took place at between 700 and 800°C and at strain rates between 10-6 and 10-3 s-1. After <span class="hlt">deformation</span> to strains of about 25%, a bimodal distribution of large protoblasts and small recrystallized neoblasts coexisted in some samples loaded at higher stresses. The <span class="hlt">deformation</span> data indicated a transition in mechanism from diffusion <span class="hlt">creep</span> to dislocation <span class="hlt">creep</span>. At stresses below 40 MPa, the strength was directly proportional to grain size and decreased with increasing Mg content due to the reductions in grain size. At about 40 MPa, the sensitivity of log strain rate to log stress, ( n), became greater than 1 and eventually exceeded 3 for stresses above 80 MPa. At a given strain rate and <span class="hlt">temperature</span>, the stress at</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JOM....66l2486X','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JOM....66l2486X"><span id="translatedtitle">Improved High-<span class="hlt">Temperature</span> Microstructural Stability and <span class="hlt">Creep</span> Property of Novel Co-Base Single-Crystal Alloys Containing Ta and Ti</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Xue, F.; Zhou, H. J.; Feng, Q.</p> <p>2014-12-01</p> <p>The influence of Ta and Ti additions on microstructural stability and <span class="hlt">creep</span> behavior in novel Co-Al-W base single-crystal alloys has been investigated. Compared to the ternary alloy, the γ' solvus <span class="hlt">temperature</span> and γ' volume fraction were raised by individual additions of Ta and Ti, and increased further in the quinary alloy containing both alloying additions. In contrast to ternary and quaternary alloys, an improved microstructural stability with the stable γ- γ' two-phase microstructure and more than 60% γ' volume fraction existed in the quinary alloy after prolonged aging treatment at 1050°C for 1000 h. The <span class="hlt">creep</span> behavior at 900°C revealed lower <span class="hlt">creep</span> rates and longer rupture lives in the quaternary alloys compared to the ternary alloy, whereas the quinary alloy exhibited even better <span class="hlt">creep</span> resistance. When the <span class="hlt">creep</span> <span class="hlt">temperature</span> was elevated to about 1000°C, the <span class="hlt">creep</span> resistance of the quinary alloy exceeded the previously reported Co-Al-W-base alloys and first-generation Ni-base single-crystal superalloys. The improved <span class="hlt">creep</span> resistance at approximately 1000°C was considered to be associated with high γ' volume fraction, γ' directional coarsening, and dislocation substructure, which included γ- γ' interfacial dislocation networks and the sheared γ' precipitates containing stacking faults and anti-phase boundaries.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/1237954','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/1237954"><span id="translatedtitle">Finite Element Based Stress Analysis of Graphite Component in High <span class="hlt">Temperature</span> Gas Cooled Reactor Core Using Linear and Nonlinear Irradiation <span class="hlt">Creep</span> Models</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mohanty, Subhasish; Majumdar, Saurindranath</p> <p>2015-01-01</p> <p>Irradiation <span class="hlt">creep</span> plays a major role in the structural integrity of the graphite components in high <span class="hlt">temperature</span> gas cooled reactors. Finite element procedures combined with a suitable irradiation <span class="hlt">creep</span> model can be used to simulate the time-integrated structural integrity of complex shapes, such as the reactor core graphite reflector and fuel bricks. In the present work a comparative study was undertaken to understand the effect of linear and nonlinear irradiation <span class="hlt">creep</span> on results of finite element based stress analysis. Numerical results were generated through finite element simulations of a typical graphite reflector.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SPIE.9517E..0HS','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SPIE.9517E..0HS"><span id="translatedtitle">Experimental investigations of <span class="hlt">creep</span> in gold RF-MEMS microstructures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Somà, Aurelio; De Pasquale, Giorgio; Saleem, Muhammad Mubasher</p> <p>2015-05-01</p> <p>Lifetime prediction and reliability evaluation of micro-electro-mechanical systems (MEMS) are influenced by permanent <span class="hlt">deformations</span> caused by plastic strain induced by <span class="hlt">creep</span>. <span class="hlt">Creep</span> in microstructures becomes critical in those applications where permanent loads persist for long times and thermal heating induces <span class="hlt">temperature</span> increasing respect to the ambient. Main goal of this paper is to investigate the <span class="hlt">creep</span> mechanism in RF-MEMS microstructures by means of experiments. This is done firstly through the detection of permanent <span class="hlt">deformation</span> of specimens and, then, by measuring the variation of electro-mechanical parameters (resonance frequency, pull-in voltage) that provide indirect evaluation of mechanical stiffness alteration from <span class="hlt">creep</span>. To prevent the errors caused be cumulative heating of samples and dimensional tolerances, three specimens with the same nominal geometry have been tested per each combination of actuation voltage and <span class="hlt">temperature</span>. Results demonstrated the presence of plastic <span class="hlt">deformation</span> due to <span class="hlt">creep</span>, combined with a component of reversible strain linked to the viscoelastic behavior of the material.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016MMTA...47.2560K&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016MMTA...47.2560K&link_type=ABSTRACT"><span id="translatedtitle">Observation of Etch-Pits and LAGB Configurations During Ambient <span class="hlt">Creep</span> of Ti-6Al-4V Alloy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kumar, Jalaj; Singh, A. K.; Raman, S. Ganesh Sundara; Kumar, Vikas</p> <p>2016-06-01</p> <p>The present work describes the microstructural features of alloy Ti-6Al-4V during constant stress <span class="hlt">creep</span> at ambient <span class="hlt">temperature</span>. Samples tested at 800 and 900 MPa stress levels exhibit the presence of etch-pits and/or voids. The ambient <span class="hlt">creep</span> strain increases with an increase in applied stress due to higher strain rate sensitivity at higher stresses. A high density of low-angle grain boundaries is noticed in and around etch-pits in the <span class="hlt">creep</span>-tested specimens due to occurrence of slip. The inverse pole figure obtained by EBSD indicates prismatic texture as the main <span class="hlt">deformation</span> component in the <span class="hlt">creep</span>-tested specimens.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MMTA..tmp..181K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MMTA..tmp..181K"><span id="translatedtitle">Observation of Etch-Pits and LAGB Configurations During Ambient <span class="hlt">Creep</span> of Ti-6Al-4V Alloy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kumar, Jalaj; Singh, A. K.; Raman, S. Ganesh Sundara; Kumar, Vikas</p> <p>2016-03-01</p> <p>The present work describes the microstructural features of alloy Ti-6Al-4V during constant stress <span class="hlt">creep</span> at ambient <span class="hlt">temperature</span>. Samples tested at 800 and 900 MPa stress levels exhibit the presence of etch-pits and/or voids. The ambient <span class="hlt">creep</span> strain increases with an increase in applied stress due to higher strain rate sensitivity at higher stresses. A high density of low-angle grain boundaries is noticed in and around etch-pits in the <span class="hlt">creep</span>-tested specimens due to occurrence of slip. The inverse pole figure obtained by EBSD indicates prismatic texture as the main <span class="hlt">deformation</span> component in the <span class="hlt">creep</span>-tested specimens.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011JMEP...20.1310L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011JMEP...20.1310L"><span id="translatedtitle"><span class="hlt">Creep</span> Constitutive Model and Component Lifetime Estimation: The Case of Niobium-Modified 9Cr-1Mo Steel Weldments</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lewis, Gladius; Shaw, Kevin M.</p> <p>2011-10-01</p> <p>The θ-projection parametric method was used to analyze the <span class="hlt">creep</span> strain versus time data, obtained in uniaxial tension, from weldments fabricated using a niobium-modified 9Cr-1Mo steel as the weld metal (Ellis, Private communication, 1991, provided the data). We used these data to illustrate a methodology whereby the θ-projection method may be used to obtain estimates of component design <span class="hlt">creep</span> lifetimes, for specified sets of design stress, <span class="hlt">temperature</span>, and strains. Furthermore, it is suggested that the <span class="hlt">creep</span> strain results may be consistent with dislocation climb being the <span class="hlt">creep</span> <span class="hlt">deformation</span> mechanism in the alloy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70030748','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70030748"><span id="translatedtitle">The instantaneous rate dependence in low <span class="hlt">temperature</span> laboratory rock friction and rock <span class="hlt">deformation</span> experiments</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Beeler, N.M.; Tullis, T.E.; Kronenberg, A.K.; Reinen, L.A.</p> <p>2007-01-01</p> <p>Earthquake occurrence probabilities that account for stress transfer and time-dependent failure depend on the product of the effective normal stress and a lab-derived dimensionless coefficient a. This coefficient describes the instantaneous dependence of fault strength on <span class="hlt">deformation</span> rate, and determines the duration of precursory slip. Although an instantaneous rate dependence is observed for fracture, friction, crack growth, and low <span class="hlt">temperature</span> plasticity in laboratory experiments, the physical origin of this effect during earthquake faulting is obscure. We examine this rate dependence in laboratory experiments on different rock types using a normalization scheme modified from one proposed by Tullis and Weeks [1987]. We compare the instantaneous rate dependence in rock friction with rate dependence measurements from higher <span class="hlt">temperature</span> dislocation glide experiments. The same normalization scheme is used to compare rate dependence in friction to rock fracture and to low-<span class="hlt">temperature</span> crack growth tests. For particular weak phyllosilicate minerals, the instantaneous friction rate dependence is consistent with dislocation glide. In intact rock failure tests, for each rock type considered, the instantaneous rate dependence is the same size as for friction, suggesting a common physical origin. During subcritical crack growth in strong quartzofeldspathic and carbonate rock where glide is not possible, the instantaneous rate dependence measured during failure or <span class="hlt">creep</span> tests at high stress has long been thought to be due to crack growth; however, direct comparison between crack growth and friction tests shows poor agreement. The crack growth rate dependence appears to be higher than the rate dependence of friction and fracture by a factor of two to three for all rock types considered. Copyright 2007 by the American Geophysical Union.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016HTMP...35..128W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016HTMP...35..128W"><span id="translatedtitle">Microstructural Changes of a <span class="hlt">Creep</span>-Damaged Nickel-Based K002 Superalloy Containing Hf Element under Different HIP <span class="hlt">Temperatures</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Xiaomeng; Zhou, Yu; Dong, Jian; Wang, Tianyou; Zhao, Zihua; Zhang, Zheng</p> <p>2016-02-01</p> <p>Effects of hot isostatic pressing (HIP) <span class="hlt">temperature</span> on the microstructural evolution of a nickel-based K002 superalloy containing Hf element after long-term service were investigated using three different soaking <span class="hlt">temperatures</span> during HIP. The degraded γ' precipitates represented coarse and irregular morphology after long-term service. These γ' precipitates still were of coarse and irregular shape, but the size and volume fraction of γ' precipitates were markedly reduced under HIP condition of 1,190°C/200 MPa/4 h, indicating that the γ' precipitates were experiencing a dissolution process. Meanwhile, the concentrically oriented N-type γ' rafting structure around the cavities was formed. With HIP <span class="hlt">temperature</span> increase to 1,220°C and 1,250°C, the small-sized, cubic and regular γ' precipitates were re-precipitated, and the concentrically oriented γ' structure vanished. The unstable morphology induced by the nucleation and growth of γ matrix was found near the <span class="hlt">creep</span> cavities, indicating that the solute atoms diffused inward the <span class="hlt">creep</span>-induced cavities during HIP. However, at HIP <span class="hlt">temperature</span> of 1,220°C and 1,250°C, a large number of blocky MC(2)-type carbides containing amounts of Hf elements were precipitated, demonstrating that HIP treatment at higher <span class="hlt">temperatures</span> can result in the formation of a large number of blocky MC(2)-type carbides.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/250705','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/250705"><span id="translatedtitle">High <span class="hlt">temperature</span> <span class="hlt">deformation</span> behavior of a nanocrystalline titanium aluminide</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Mishra, R.S.; Mukherjee, A.K.; Mukhopadhyay, D.K.; Suryanarayana, C.; Froes, F.H.</p> <p>1996-06-01</p> <p>Gamma titanium intermetallic alloys are potentially attractive for elevated <span class="hlt">temperature</span> applications. The room <span class="hlt">temperature</span> ductility and fracture toughness have been improved considerably by the addition of ternary and quaternary elements. The synthesis of nanocrystalline materials has provided further avenues for possible improvement in the mechanical properties. The exciting prospect of low <span class="hlt">temperature</span> superplasticity in nanocrystalline materials has been discussed. Recently, nanocrystalline {gamma}-TiAl alloys have been synthesized by hot isostatic pressing (HIP) of mechanically alloyed (MA) Ti-47.5 Al-3 Cr (at.%) powders. The purpose of this study was to evaluate the possibility of observing low <span class="hlt">temperature</span> superplasticity in this nanocrystalline alloy. By determining the stress exponent for flow, it should be possible to comment on the micromechanism of <span class="hlt">deformation</span> in a nanocrystalline intermetallic alloy. A number of studies have shown that superplasticity is possible in {gamma}-TiAl alloys and it is important to establish whether the scaling law extends to nanocrystalline {gamma}-TiAl regime or the flow behavior changes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JMEP...25.2000G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JMEP...25.2000G"><span id="translatedtitle">High-<span class="hlt">temperature</span> Tensile Properties and <span class="hlt">Creep</span> Life Assessment of 25Cr35NiNb Micro-alloyed Steel</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ghatak, Amitava; Robi, P. S.</p> <p>2016-05-01</p> <p>Reformer tubes in petrochemical industries are exposed to high <span class="hlt">temperatures</span> and gas pressure for prolonged period. Exposure of these tubes at severe operating conditions results in change in the microstructure and degradation of mechanical properties which may lead to premature failure. The present work highlights the high-<span class="hlt">temperature</span> tensile properties and remaining <span class="hlt">creep</span> life prediction using Larson-Miller parametric technique of service exposed 25Cr35NiNb micro-alloyed reformer tube. Young's modulus, yield strength, and ultimate tensile strength of the steel are lower than the virgin material and decreases with the increase in <span class="hlt">temperature</span>. Ductility continuously increases with the increase in <span class="hlt">temperature</span> up to 1000 °C. Strain hardening exponent increases up to 600 °C, beyond which it starts decreasing. The tensile properties are discussed with reference to microstructure and fractographs. Based on Larson-Miller technique, a <span class="hlt">creep</span> life of at least 8.3 years is predicted for the service exposed material at 800 °C and 5 MPa.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19720006900','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19720006900"><span id="translatedtitle">Review of <span class="hlt">deformation</span> behavior of tungsten at <span class="hlt">temperature</span> less than 0.2 absolute melting <span class="hlt">temperature</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Stephens, J. R.</p> <p>1972-01-01</p> <p>The <span class="hlt">deformation</span> behavior of tungsten at <span class="hlt">temperatures</span> 0.2 T sub m is reviewed, with primary emphasis on the <span class="hlt">temperature</span> dependence of the yield stress and the ductile-brittle transition <span class="hlt">temperature</span>. It appears that a model based on the high Peierls stress of tungsten best accounts for the observed mechanical behavior at low <span class="hlt">temperatures</span>. Recent research is discussed which suggests an important role of electron concentration and bonding on the mechanical behavior of tungsten. It is concluded that future research on tungsten should include studies to define more clearly the correlation between electron concentration and mechanical behavior of tungsten alloys and other transition metal alloys.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2014MMTA...45.6053L&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2014MMTA...45.6053L&link_type=ABSTRACT"><span id="translatedtitle">Analysis of the <span class="hlt">Deformation</span> Behavior in Tension and Tension-<span class="hlt">Creep</span> of Ti-3Al-2.5V (wt pct) at 296 K and 728 K (23 °C and 455 °C) Using In Situ SEM Experiments</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Hongmei; Boehlert, Carl J.; Bieler, Thomas R.; Crimp, Martin A.</p> <p>2014-12-01</p> <p>The <span class="hlt">deformation</span> behavior of a Ti-3Al-2.5V (wt pct) near-α alloy was investigated during in situ <span class="hlt">deformation</span> inside a scanning electron microscopy (SEM). Two plates with distinct textures were examined. Tensile experiments were performed at 296 K and 728 K (455 °C) (~0.4 T m), while a tensile-<span class="hlt">creep</span> experiment was performed at 728 K (455 °C) and 180 MPa ( σ/ σ ys = 0.72). The active <span class="hlt">deformation</span> systems were identified in the α phase using electron backscattered diffraction based slip-trace analysis and SEM images of the surface. Prismatic slip <span class="hlt">deformation</span> was the dominant slip mode observed for all the experiments in both plates, which was supported by a critical resolved shear stress (CRSS) ratio analysis. However, due to the texture of plate 1, which strongly favored the activation of prismatic slip, the percentages of prismatic slip activity for specimens from plate 1 tested at 296 K and 728 K (23 °C and 455 °C) were higher than the specimens from plate 2 under the same testing conditions. T1 twinning was an active <span class="hlt">deformation</span> mode at both 296 K and 728 K (23 °C and 455 °C), but the extent of twinning activity decreased with increased <span class="hlt">temperature</span>. T1 twinning was more frequently observed in specimens from plate 2, which exhibited a higher fraction of twinning systems favoring activation at both 296 K and 728 K (23 °C and 455 °C). The tension-<span class="hlt">creep</span> experiment revealed less slip and more grain boundary sliding than in the higher strain rate tensile experiments. Using a previously demonstrated bootstrapping statistical analysis methodology, the relative CRSS ratios of prismatic, pyramidal < a>, pyramidal < c+ a>, and T1 twinning <span class="hlt">deformation</span> systems compared with basal slip were calculated and discussed in light of similar measurements made on CP Ti and Ti-5Al-2.5Sn (wt pct).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5713724','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5713724"><span id="translatedtitle"><span class="hlt">Deformation</span> and thermal fatigue in high <span class="hlt">temperature</span> austenitic alloys</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ferro, P.D.; Yost, B.; Swindeman, R.W.; Li, Che-Yu . Dept. of Materials Science and Engineering)</p> <p>1991-03-01</p> <p>The flow properties of modified austenitic alloys are reviewed. The important strengthening mechanisms discussed include precipitation hardening produced by a combination of cold work and aging and by <span class="hlt">creep</span> aging. Grain boundary sliding enhanced by reduced grain size is shown to reduce the flow strength of these alloys. 5 refs., 11 figs., 2 tabs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMMR13A2220N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMMR13A2220N"><span id="translatedtitle">Mechanical behavior of low porosity carbonate rock: from brittle <span class="hlt">creep</span> to ductile <span class="hlt">creep</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nicolas, A.; Fortin, J.; Gueguen, Y.</p> <p>2013-12-01</p> <p>Mechanical compaction and associated porosity reduction play an important role in the diagenesis of porous rocks. They may also affect reservoir rocks during hydrocarbon production, as the pore pressure field is modified. This inelastic compaction can lead to subsidence, cause casing failure, trigger earthquake, or change the fluid transport properties. In addition, inelastic <span class="hlt">deformation</span> can be time - dependent. In particular, brittle <span class="hlt">creep</span> phenomena have been deeply investigated since the 90s, especially in sandstones. However knowledge of carbonates behavior is still insufficient. In this experimental study, we focus on the mechanical behavior of a low porosity (9%) white Tavel (France) carbonate rock (>98% calcite) at P-Q conditions beyond the elastic domain. It has been shown that in sandstones composed of quartz, cracks are developing under these conditions. However, in carbonates, calcite minerals can meanwhile also exhibit microplasticity. The samples were <span class="hlt">deformed</span> in the triaxial cell of the Ecole Normale Superieure de Paris at effective confining pressures ranging from 35 MPa to 85 MPa and room <span class="hlt">temperature</span>. Experiments were carried on dry and water saturated samples to explore the role played by the pore fluids. Time dependency was investigated by a <span class="hlt">creep</span> steps methodology: at each step, differential stress was increased rapidly and kept constant for at least 24h. During these steps elastic wave velocities (P and S) and permeability were measured continuously. Our results show two different <span class="hlt">creep</span> behaviors: (1) brittle <span class="hlt">creep</span> is observed at low confining pressures, whereas (2) ductile <span class="hlt">creep</span> is observed at higher confining pressures. These two <span class="hlt">creep</span> behaviors have a different signature in term of elastic wave velocities and permeability changes. Indeed, in the brittle domain, the primary <span class="hlt">creep</span> is associated with a decrease of elastic wave velocities and an increase of permeability, and no secondary <span class="hlt">creep</span> is observed. In the ductile domain, the primary <span class="hlt">creep</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002CzJPS..52A.125J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002CzJPS..52A.125J"><span id="translatedtitle">Spectral analysis of <span class="hlt">creep</span> recovery process in finemet type amorphous alloy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Juríková, A.; Csach, K.; Ocelík, V.; Miškuf, J.; Bengus, V. Z.</p> <p>2002-01-01</p> <p>The <span class="hlt">creep</span> recovery process in Finemet type amorphous alloy has been analyzed using the method for calculating the relaxation time spectra. The influence of structural relaxation and <span class="hlt">temperature</span> on the spectra shape has been studied. The <span class="hlt">creep</span> recovery spectrum of the anelastic <span class="hlt">deformation</span> of the multicomponent Fe-Nb-Cu-Si-B amorphous alloy seems to be more complex in comparison with standard amorphous alloys.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1980RScI...51.1352C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1980RScI...51.1352C"><span id="translatedtitle">High-<span class="hlt">temperature</span>, multi-atmosphere, constant stress compression <span class="hlt">creep</span> apparatus</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Carter, C. H., Jr.; Stone, C. A.; Davis, R. F.; Schaub, D. R.</p> <p>1980-10-01</p> <p>A <span class="hlt">creep</span> apparatus is presented in which uniaxial compressive stresses, constant to within 1% for strains up to 10%, can be applied to the sample and strains can be read with an accuracy of 5 x 10 to the -7th m. Loads as great as 440 kg can be applied, and the furnace can be operated in vacuum or inert gas to 2573 K or used with a muffle tube. Data acquisition, manipulation, and plotting is computer controlled.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013EGUGA..1513115S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013EGUGA..1513115S"><span id="translatedtitle">Relation between <span class="hlt">creep</span> compliance and elastic modulus in organic-rich shales observed through laboratory experiments.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sone, Hiroki; Zoback, Mark</p> <p>2013-04-01</p> <p>We studied the ductile <span class="hlt">creep</span> behavior of organic-rich shales from shale gas reservoirs in North America through laboratory triaxial experiments to better understand controls on the physical behavior of these rocks over time and the effect of <span class="hlt">creep</span> on other rock properties. Laboratory experiments conducted at room-<span class="hlt">temperature</span> conditions show that <span class="hlt">creep</span> <span class="hlt">deformation</span> observed at in-situ differential stress conditions is approximately linear with the applied differential pressure. The <span class="hlt">creep</span> behavior is also anisotropic such that <span class="hlt">creep</span> occurs more in the bedding-perpendicular direction than in the bedding-parallel direction. The reduction in sample volume during <span class="hlt">creep</span> suggests that the <span class="hlt">creep</span> is accommodated by a small amount of pore compaction occurring in the clay-aggregates and/or the relatively porous kerogen in the rock. Thus, the tendency to <span class="hlt">creep</span> (<span class="hlt">creep</span> compliance) is generally observed to increases with clay and kerogen volume. However, the strongest correlation is found between <span class="hlt">creep</span> compliance and Young's modulus. A strong negative correlation between <span class="hlt">creep</span> compliance and elastic Young's modulus exists regardless of the sample orientation and despite the wide range of sample mineralogy (5-50% clay, 5-60% quartz-feldspar-pyrite, 0-80% carbonates). This correlation is quite interesting as inelastic <span class="hlt">creep</span> and elastic stiffness depend on somewhat different physical attributes. We attempt to quantitatively explain the correlation between <span class="hlt">creep</span> behavior and elastic stiffness by appealing to a stress-partitioning that occurs between the soft components (clay and kerogen) and stiff components (quartz, feldspar, pyrite, carbonates) of the shale rock. First, the stress-partitioning occurring within the soft and stiff components is quantified based on the rock composition, elastic properties of the individual components, and the overall average Young's modulus of the rock. By combining the stress-partitioning behavior with knowledge that the <span class="hlt">creep</span> behavior is linear</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/6136555','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/6136555"><span id="translatedtitle"><span class="hlt">Creep</span> <span class="hlt">deformation</span> of a two-phase TiAl/Ti[sub 3]Al lamellar alloy and the individual TiAl and Ti[sub 3]Al constituent phases</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Bartholomeusz, M.F.; Wert, J.A. ); Qibin Yang )</p> <p>1993-08-01</p> <p>Two-phase TiAl/Ti[sub 3]Al alloys in which the constituent phases form a lamellar microstructure are reported to possess good combinations of low-<span class="hlt">temperature</span> fracture toughness, tensile strength and fatigue resistance. However, information about the high-<span class="hlt">temperature</span> <span class="hlt">creep</span> properties of the two-phase TiAl/Ti[sub 3]Al alloys with lamellar microstructures (referred to as lamellar alloys in the remainder of the paper) is limited. Based on a simple rule of mixtures model of strength, it would be expected that the <span class="hlt">creep</span> rates of the lamellar alloy would be between the <span class="hlt">creep</span> rates of TiAl and Ti[sub 3]Al. In contrast to composite model predictions of strength, Polvani and coworkers found that the minimum <span class="hlt">creep</span> rates of two duplex alloys, a [gamma]/[gamma][prime] nickel-base superalloy and NiAl/Ni[sub 2]AlTi, were significantly lower than the minimum <span class="hlt">creep</span> rates of either of the constituent phases. They also reported that most dislocations in the two-phase NiAl/Ni[sub 2]AlTi alloy were contained within the semi-coherent interfacial dislocation networks between the two phases. Based on this observation they proposed that the <span class="hlt">creep</span> rate is controlled by the rate at which dislocations moving through both phases are emitted and absorbed by the interphase dislocation networks. The greater strain hardening rate of the lamellar TiAl/Ti[sub 3]Al alloy suggests that it may exhibit lower steady-state <span class="hlt">creep</span> rates that the individual constituent phases. The objective of the present study is to evaluate the <span class="hlt">creep</span> properties of a TiAl/ Ti[sub 3]Al lamellar alloy and of the individual constituent phases. In this paper, the results of this investigation will be presented and compared with previously published results for this alloy system.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009MMTA...40..116K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009MMTA...40..116K"><span id="translatedtitle">Impression <span class="hlt">Creep</span> Behavior of a Cast AZ91 Magnesium Alloy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kabirian, F.; Mahmudi, R.</p> <p>2009-01-01</p> <p>The <span class="hlt">creep</span> behavior of the cast AZ91 magnesium alloy was investigated by impression testing. The tests were carried out under constant punching stress in the range 100 to 650 MPa, corresponding to 0.007 ≤ σ imp/ G ≤ 0.044, at <span class="hlt">temperatures</span> in the range 425 to 570 K. Assuming a power-law relationship between the impression velocity and stress, depending on the testing <span class="hlt">temperature</span>, stress exponents of 4.2 to 6.0 were obtained. When the experimental <span class="hlt">creep</span> rates were normalized to the grain size and effective diffusion coefficient, a stress exponent of approximately 5 was obtained, which is in complete agreement with stress exponents determined by the conventional <span class="hlt">creep</span> testing of the same material reported in the literature. Calculation of the activation energy showed a slight decrease in the activation energy with increasing stress such that the <span class="hlt">creep</span>-activation energy of 122.9 kJ/mol at σ imp/ G = 0.020 decreases to 94.0 kJ/mol at σ imp/ G = 0.040. Based on the obtained stress exponents and activation energy data, it is proposed that dislocation climb is the controlling <span class="hlt">creep</span> mechanism. However, due to the decreasing trend of <span class="hlt">creep</span>-activation energy with stress, it is suggested that two parallel mechanisms of lattice and pipe-diffusion-controlled dislocation climb are competing. To elucidate the contribution of each mechanism to the overall <span class="hlt">creep</span> <span class="hlt">deformation</span>, the <span class="hlt">creep</span> rates were calculated based on the effective activation energy. This yielded a criterion that showed that, in the high-stress regimes, the experimental activation energies fall in the range in which the operative <span class="hlt">creep</span> mechanism is dislocation climb controlled by dislocation pipe diffusion. In the low-stress regime, however, the lattice-diffusion dislocation climb is dominant.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhDT.......120K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhDT.......120K"><span id="translatedtitle">EBSD characterization of low <span class="hlt">temperature</span> <span class="hlt">deformation</span> mechanisms in modern alloys</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kozmel, Thomas S., II</p> <p></p> <p>For structural applications, grain refinement has been shown to enhance mechanical properties such as strength, fatigue resistance, and fracture toughness. Through control of the thermos-mechanical processing parameters, dynamic recrystallization mechanisms were used to produce microstructures consisting of sub-micron grains in 9310 steel, 4140 steel, and Ti-6Al-4V. In both 9310 and 4140 steel, the distribution of carbides throughout the microstructure affected the ability of the material to dynamically recrystallize and determined the size of the dynamically recrystallized grains. Processing the materials at lower <span class="hlt">temperatures</span> and higher strain rates resulted in finer dynamically recrystallized grains. Microstructural process models that can be used to estimate the resulting microstructure based on the processing parameters were developed for both 9310 and 4140 steel. Heat treatment studies performed on 9310 steel showed that the sub-micron grain size obtained during <span class="hlt">deformation</span> could not be retained due to the low equilibrium volume fraction of carbides. Commercially available aluminum alloys were investigated to explain their high strain rate <span class="hlt">deformation</span> behavior. Alloys such as 2139, 2519, 5083, and 7039 exhibit strain softening after an ultimate strength is reached, followed by a rapid degradation of mechanical properties after a critical strain level has been reached. Microstructural analysis showed that the formation of shear bands typically preceded this rapid degradation in properties. Shear band boundary misorientations increased as a function of equivalent strain in all cases. Precipitation behavior was found to greatly influence the microstructural response of the alloys. Additionally, precipitation strengthened alloys were found to exhibit similar flow stress behavior, whereas solid solution strengthened alloys exhibited lower flow stresses but higher ductility during dynamic loading. Schmid factor maps demonstrated that shear band formation behavior</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/250691','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/250691"><span id="translatedtitle">Recrystallization at ambient <span class="hlt">temperature</span> of heavily <span class="hlt">deformed</span> ETP copper wire</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Schamp, J.; Verlinden, B.; Van Humbeeck, J.</p> <p>1996-06-01</p> <p>Recrystallization of electrolytic tough pitch (ETP) copper wire at room <span class="hlt">temperature</span> has been reported by several authors. The phenomenon changes the mechanical properties of the wire which can cause a loss of process control, but remains largely unpredictable. The aim of this study is to get a better understanding of the conditions under which partial recrystallization can be expected. It is observed that the recrystallization pattern is non-homogeneous across the cross-section of the wire. Recrystallization starts in a cylindrical zone with diameter 0.5 to 0.8 times the wire diameter. The core and the surface of the wire recrystallize at a later stage. It is proposed that this is due to different modes of <span class="hlt">deformation</span> along the wire diameter. The progress of recrystallization at room <span class="hlt">temperature</span> depends on a large extent on the chemical composition of the material. It is well known that all impurity elements slow down recrystallization, but some elements, such as Se, Te, Bi, S and Pb are more deleterious than others. It is shown that a few tenths of ppm`s of these impurities determine whether the wire is stable in time or not.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/82462','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/82462"><span id="translatedtitle"><span class="hlt">Creep</span> in Topopah Spring Member welded tuff. Yucca Mountain Site Characterization Project</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Martin, R.J. III; Boyd, P.J.; Noel, J.S.; Price, R.H.</p> <p>1995-06-01</p> <p>A laboratory investigation has been carried out to determine the effects of elevated <span class="hlt">temperature</span> and stress on the <span class="hlt">creep</span> <span class="hlt">deformation</span> of welded tuffs recovered from Busted Butte in the vicinity of Yucca Mountain, Nevada. Water saturated specimens of tuff from thermal/mechanical unit TSw2 were tested in <span class="hlt">creep</span> at a confining pressure of 5.0 MPa, a pore pressure of 4.5 MPa, and <span class="hlt">temperatures</span> of 25 and 250 C. At each stress level the load was held constant for a minimum of 2.5 {times} 10{sup 5} seconds and for as long as 1.8 {times} 10{sup 6} seconds. One specimen was tested at a single stress of 80 MPa and a <span class="hlt">temperature</span> of 250 C. The sample failed after a short time. Subsequent experiments were initiated with an initial differential stress of 50 or 60 MPa; the stress was then increased in 10 MPa increments until failure. The data showed that <span class="hlt">creep</span> <span class="hlt">deformation</span> occurred in the form of time-dependent axial and radial strains, particularly beyond 90% of the unconfined, quasi-static fracture strength. There was little dilatancy associated with the <span class="hlt">deformation</span> of the welded tuff at stresses below 90% of the fracture strength. Insufficient data have been collected in this preliminary study to determine the relationship between <span class="hlt">temperature</span>, stress, <span class="hlt">creep</span> <span class="hlt">deformation</span> to failure, and total failure time at a fixed <span class="hlt">creep</span> stress.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015MMTA...46.5656Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015MMTA...46.5656Z"><span id="translatedtitle">Autonomous Repair Mechanism of <span class="hlt">Creep</span> Damage in Fe-Au and Fe-Au-B-N Alloys</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, S.; Kwakernaak, C.; Tichelaar, F. D.; Sloof, W. G.; Kuzmina, M.; Herbig, M.; Raabe, D.; Brück, E.; van der Zwaag, S.; van Dijk, N. H.</p> <p>2015-12-01</p> <p>The autonomous repair mechanism of <span class="hlt">creep</span> cavitation during high-<span class="hlt">temperature</span> <span class="hlt">deformation</span> has been investigated in Fe-Au and Fe-Au-B-N alloys. Combined electron-microscopy techniques and atom probe tomography reveal how the improved <span class="hlt">creep</span> properties result from Au precipitation within the <span class="hlt">creep</span> cavities, preferentially formed on grain boundaries oriented perpendicular to the applied stress. The selective precipitation of Au atoms at the free <span class="hlt">creep</span> cavity surface results in pore filling, and thereby, autonomous repair of the <span class="hlt">creep</span> damage. The large difference in atomic size between the Au and Fe strongly hampers the nucleation of precipitates in the matrix. As a result, the matrix acts as a reservoir for the supersaturated solute until damage occurs. Grain boundaries and dislocations are found to act as fast transport routes for solute gold from the matrix to the <span class="hlt">creep</span> cavities. The mechanism responsible for the self-healing can be characterized by a simple model for cavity growth and cavity filling.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.T43D..07F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.T43D..07F"><span id="translatedtitle">Can Competition Between Frictional Sliding and Viscous <span class="hlt">Creep</span> Determine Megathrust Fault Slip Style?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fagereng, A.</p> <p>2014-12-01</p> <p>In exhumed megathrust analogues, <span class="hlt">deformation</span> is partitioned between continuous and discontinuous <span class="hlt">deformation</span> structures, commonly reflecting partitioning between concurrent frictional and viscous shear. This partitioning is a function of material properties, strain rate, and fluid pressure distribution. Mineral strength and preferred <span class="hlt">deformation</span> mechanism vary down-dip as a function of <span class="hlt">temperature</span> and pressure; however, incoming sediment composition, roughness of the sea floor, and the relative proportions of competent and incompetent material, all affect bulk rheology, and may vary both with depth and along strike. Fluid pressure varies with depth, but also along strike if fluid sources and/or permeability vary along the margin. At the locations of major dehydration reactions, localized peaks in fluid pressure occur if permeability is low. These zones of low effective stress may allow for frictional sliding in rocks normally <span class="hlt">deforming</span> by viscous shearing flow, and could relate to zones of tremor and slow slip. Frictional sliding and possible associated tensile fractures would, however, allow fluid escape, resulting in fluid pressure fluctuations and a time-dependent interplay between continuous and discontinuous <span class="hlt">deformation</span>. Locally elevated effective stress increases frictional strength, promoting failure by viscous mechanisms. If this is true, and representative of large-scale megathrust behavior, then decreased fluid pressure may promote <span class="hlt">creep</span>. In a fluid-saturated, tabular fault zone with small grain size, this <span class="hlt">creep</span> can take place by pressure solution <span class="hlt">creep</span> at subgreenschist conditions. If pressure solution is the active mineral <span class="hlt">deformation</span> mechanism, and shear is distributed though a tabular zone, viscous shearing flow at plate boundary rates is possible at <span class="hlt">temperatures</span> significantly less than required for the onset of dislocation <span class="hlt">creep</span> in quartzofeldspathic rocks. In a wide shear zone, such viscous flow may occur at low differential stress. A hypothesis to</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MS%26E..118a2030F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MS%26E..118a2030F"><span id="translatedtitle">Influence of thermally activated processes on the <span class="hlt">deformation</span> behavior during low <span class="hlt">temperature</span> ECAP</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fritsch, S.; Scholze, M.; F-X Wagner, M.</p> <p>2016-03-01</p> <p>High strength aluminum alloys are generally hard to <span class="hlt">deform</span>. Therefore, the application of conventional severe plastic <span class="hlt">deformation</span> methods to generate ultrafine-grained microstructures and to further increase strength is considerably limited. In this study, we consider low <span class="hlt">temperature</span> <span class="hlt">deformation</span> in a custom-built, cooled equal channel angular pressing (ECAP) tool (internal angle 90°) as an alternative approach to severely plastically <span class="hlt">deform</span> a 7075 aluminum alloy. To document the maximum improvement of mechanical properties, these alloys are initially <span class="hlt">deformed</span> from a solid solution heat-treated condition. We characterize the mechanical behavior and the microstructure of the coarse grained initial material at different low <span class="hlt">temperatures</span>, and we analyze how a tendency for the PLC effect and the strain-hardening rate affect the formability during subsequent severe plastic <span class="hlt">deformation</span> at low <span class="hlt">temperatures</span>. We then discuss how the <span class="hlt">deformation</span> <span class="hlt">temperature</span> and velocity influence the occurrence of PLC effects and the homogeneity of the <span class="hlt">deformed</span> ECAP billets. Besides the mechanical properties and these microstructural changes, we discuss technologically relevant processing parameters (such as pressing forces) and practical limitations, as well as changes in fracture behavior of the low <span class="hlt">temperature</span> <span class="hlt">deformed</span> materials as a function of <span class="hlt">deformation</span> <span class="hlt">temperature</span>.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013MMTA...44.1311W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013MMTA...44.1311W"><span id="translatedtitle">Effects of NaCl, pH, and Potential on the Static <span class="hlt">Creep</span> Behavior of AA1100</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wan, Quanhe; Quesnel, David J.</p> <p>2013-03-01</p> <p>The <span class="hlt">creep</span> rates of AA1100 are measured during exposure to a variety of aggressive environments. NaCl solutions of various concentrations have no influence on the steady-state <span class="hlt">creep</span> behavior, producing <span class="hlt">creep</span> rates comparable to those measured in lab air at room <span class="hlt">temperature</span>. However, after an initial incubation period of steady strain rate, a dramatic increase of strain rate is observed on exposure to HCl solutions and NaOH solutions, as well as during cathodic polarization of specimens in NaCl solutions. <span class="hlt">Creep</span> strain produces a continuous <span class="hlt">deformation</span> and elongation of the sample surface that is comparable to slow strain rates at crack tips thought to control the kinetics of crack growth during stress corrosion cracking (SCC). In this experiment, we separate the strain and surface <span class="hlt">deformation</span> from the complex geometry of the crack tip to better understand the processes at work. Based on this concept, two possible explanations for the environmental influences on <span class="hlt">creep</span> strain rates are discussed relating to the anodic dissolution of the free surface and hydrogen influences on <span class="hlt">deformation</span> mechanisms. Consistencies of pH dependence between corrosion <span class="hlt">creep</span> and SCC at low pH prove a <span class="hlt">creep</span>-involved SCC mechanism, while the discrepancies between corrosion <span class="hlt">creep</span> behavior and previous SCC results at high pH indicate a rate-limit step change in the crack propagation of the SCC process.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MMTA..tmp..247W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MMTA..tmp..247W"><span id="translatedtitle">Rationalization of <span class="hlt">Creep</span> Data of <span class="hlt">Creep</span>-Resistant Steels on the Basis of the New Power Law <span class="hlt">Creep</span> Equation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Q.; Yang, M.; Song, X. L.; Jia, J.; Xiang, Z. D.</p> <p>2016-05-01</p> <p>The conventional power law <span class="hlt">creep</span> equation (Norton equation) relating the minimum <span class="hlt">creep</span> rate to <span class="hlt">creep</span> stress and <span class="hlt">temperature</span> cannot be used to predict the long-term <span class="hlt">creep</span> strengths of <span class="hlt">creep</span>-resistant steels if its parameters are determined only from short-term measurements. This is because the stress exponent and activation energy of <span class="hlt">creep</span> determined on the basis of this equation depend on <span class="hlt">creep</span> <span class="hlt">temperature</span> and stress and these dependences cannot be predicted using this equation. In this work, it is shown that these problems associated with the conventional power law <span class="hlt">creep</span> equation can be resolved if the new power law equation is used to rationalize the <span class="hlt">creep</span> data. The new power law <span class="hlt">creep</span> equation takes a form similar to the conventional power law <span class="hlt">creep</span> equation but has a radically different capability not only in rationalizing <span class="hlt">creep</span> data but also in predicting the long-term <span class="hlt">creep</span> strengths from short-term test data. These capabilities of the new power law <span class="hlt">creep</span> equation are demonstrated using the tensile strength and <span class="hlt">creep</span> test data measured for both pipe and tube grades of the <span class="hlt">creep</span>-resistant steel 9Cr-1.8W-0.5Mo-V-Nb-B (P92 and T92).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016MMTA...47.3479W&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016MMTA...47.3479W&link_type=ABSTRACT"><span id="translatedtitle">Rationalization of <span class="hlt">Creep</span> Data of <span class="hlt">Creep</span>-Resistant Steels on the Basis of the New Power Law <span class="hlt">Creep</span> Equation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Q.; Yang, M.; Song, X. L.; Jia, J.; Xiang, Z. D.</p> <p>2016-07-01</p> <p>The conventional power law <span class="hlt">creep</span> equation (Norton equation) relating the minimum <span class="hlt">creep</span> rate to <span class="hlt">creep</span> stress and <span class="hlt">temperature</span> cannot be used to predict the long-term <span class="hlt">creep</span> strengths of <span class="hlt">creep</span>-resistant steels if its parameters are determined only from short-term measurements. This is because the stress exponent and activation energy of <span class="hlt">creep</span> determined on the basis of this equation depend on <span class="hlt">creep</span> <span class="hlt">temperature</span> and stress and these dependences cannot be predicted using this equation. In this work, it is shown that these problems associated with the conventional power law <span class="hlt">creep</span> equation can be resolved if the new power law equation is used to rationalize the <span class="hlt">creep</span> data. The new power law <span class="hlt">creep</span> equation takes a form similar to the conventional power law <span class="hlt">creep</span> equation but has a radically different capability not only in rationalizing <span class="hlt">creep</span> data but also in predicting the long-term <span class="hlt">creep</span> strengths from short-term test data. These capabilities of the new power law <span class="hlt">creep</span> equation are demonstrated using the tensile strength and <span class="hlt">creep</span> test data measured for both pipe and tube grades of the <span class="hlt">creep</span>-resistant steel 9Cr-1.8W-0.5Mo-V-Nb-B (P92 and T92).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/978263','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/978263"><span id="translatedtitle">Irradiation <span class="hlt">Creep</span> of Chemically Vapor Deposited Silicon Carbide as Estimated by Bend Stress Relaxation Method</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Katoh, Yutai; Snead, Lance Lewis; Hinoki, Tatsuya; Kondo, Sosuke; Kohyama, Akira</p> <p>2007-01-01</p> <p>The bend stress relaxation technique was applied for an irradiation <span class="hlt">creep</span> study of high purity, chemically vapor-deposited beta-phase silicon carbide (CVD SiC) ceramic. A constant bend strain was applied to thin strip samples during neutron irradiation to fluences 0.2-4.2 dpa at various <span class="hlt">temperatures</span> in the range {approx}400 to {approx}1080 C. Irradiation <span class="hlt">creep</span> strain at <0.7 dpa exhibited only a weak dependence on irradiation <span class="hlt">temperature</span>. However, the <span class="hlt">creep</span> strain dependence on fluence was non-linear due to the early domination of the initial transient <span class="hlt">creep</span>, and a transition in <span class="hlt">creep</span> behavior was found between 950 and 1080 C. Steady-state irradiation <span class="hlt">creep</span> compliances of polycrystalline CVD SiC at doses >0.7 dpa were estimated to be 2.7({+-}2.6) x 10{sup -7} and 1.5({+-}0.8) x 10{sup -6} (MPa dpa){sup -1} at {approx}600 to {approx}950 C and {approx}1080 C, respectively, whereas linear-averaged <span class="hlt">creep</span> compliances of 1-2 x 10{sup -6} (MPa dpa){sup -1} were obtained for doses of 0.6-0.7 dpa at all <span class="hlt">temperatures</span>. Monocrystalline 3C SiC samples exhibited significantly smaller transient <span class="hlt">creep</span> strain and greater subsequent <span class="hlt">deformation</span> when loaded along <0 1 1> direction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22288700','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22288700"><span id="translatedtitle"><span class="hlt">Creep</span> property and microstructure evolution of a nickel-base single crystal superalloy in [011] orientation</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Han, G.M. Yu, J.J.; Hu, Z.Q.; Sun, X.F.</p> <p>2013-12-15</p> <p>The <span class="hlt">creep</span> property and microstructure evolution of a single crystal superalloy with [011] orientation were investigated at the <span class="hlt">temperatures</span> of 700 °C, 900 °C and 1040 °C. It is shown that there exist stages of primary, steady-state, and tertiary <span class="hlt">creep</span> under the lower <span class="hlt">temperature</span> 700 °C. As the <span class="hlt">temperature</span> increases to high <span class="hlt">temperatures</span> of 900 °C and 1040 °C, steady-state <span class="hlt">creep</span> stage is reduced or disappears and the shape of <span class="hlt">creep</span> curves is dominated by an extensive tertiary stage. The minimum <span class="hlt">creep</span> strain rate exhibits power law dependence on the applied stress; the stress exponents at 700 °C, 900 °C and 1040 °C are 28, 13 and 6.5, respectively. Microstructure observation shows that the morphologies of γ′ phase almost keep original shape at the lower <span class="hlt">temperature</span> 700 °C and high applied stress. With the increasing <span class="hlt">creep</span> <span class="hlt">temperature</span>, γ′ precipitates tend to link together and form lamellar structure at an angle of 45° inclined to the applied stress. Transmission electron microscopy (TEM) investigations reveal that multiple < 110 > (111) slip systems gliding in the matrix channels and shearing γ′ precipitates by stacking faults or bending dislocation pairs are the main <span class="hlt">deformation</span> mechanism at the lower <span class="hlt">temperature</span> of 700 °C. At the high <span class="hlt">temperatures</span> of 900 °C and 1040 °C, dislocation networks are formed at γ/γ′ interfaces and the γ′ rafts are sheared by dislocation pairs. - Highlights: • <span class="hlt">Creep</span> properties of < 011 >-oriented single crystal superalloys were investigated. • γ′ phases become rafting at an angle of 45° inclined to the applied stress. • <span class="hlt">Creep</span> <span class="hlt">deformation</span> mechanisms depend on <span class="hlt">temperature</span> and stress.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19900013338','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19900013338"><span id="translatedtitle">Elevated <span class="hlt">temperature</span> crack growth in aluminum alloys: Tensile <span class="hlt">deformation</span> of 2618 and FVS0812 aluminum alloys</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Leng, Yang; Gangloff, Richard P.</p> <p>1990-01-01</p> <p>Understanding the damage tolerance of aluminum alloys at elevated <span class="hlt">temperatures</span> is essential for safe applications of advanced materials. The objective of this project is to investigate the time dependent subcritical cracking behavior of powder metallurgy FVS0812 and ingot metallurgy 2618 aluminum alloys at elevated <span class="hlt">temperatures</span>. The fracture mechanics approach was applied. Sidegrooved compact tension specimens were tested at 175, 250, and 316 C under constant load. Subcritical crack growth occurred in each alloy at applied stress intensity levels (K) of between about 14 and 25 MPa/m, well below K (sub IC). Measured load, crack opening displacement and displacement rate, and crack length and growth rate (da/dt) were analyzed with several continuum fracture parameters including, the C-integral, C (sub t), and K. Elevated <span class="hlt">temperature</span> growth rate data suggest that K is a controlling parameter during time dependent cracking. For FVS0812, da/dt is highest at 175 C when rates are expressed as a function of K. While crack growth rate is not controlled by C (sub t) at 175 C, da/dt appears to better correlate with C (sub t) at higher <span class="hlt">temperatures</span>. <span class="hlt">Creep</span> brittle cracking at intermediate <span class="hlt">temperatures</span>, and perhaps related to strain aging, is augmented by time dependent transient <span class="hlt">creep</span> plasticity at higher <span class="hlt">temperatures</span>. The C (sub t) analysis is, however, complicated by the necessity to measure small differences in the elastic crack growth and <span class="hlt">creep</span> contributions to the crack opening displacement rate. A microstructural study indicates that 2618 and FVS0812 are likely to be <span class="hlt">creep</span> brittle materials, consistent with the results obtained from the fracture mechanics study. Time dependent crack growth of 2618 at 175 C is characterized by mixed transgranular and intergranular fracture. Delamination along the ribbon powder particle boundaries occurs in FVS0812 at all <span class="hlt">temperatures</span>. The fracture mode of FVS0812 changes with <span class="hlt">temperature</span>. At 175 C, it is characterized as dimpled rupture</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JNuM..438...51V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JNuM..438...51V"><span id="translatedtitle">Effect of prior cold work on <span class="hlt">creep</span> properties of a titanium modified austenitic stainless steel</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vijayanand, V. D.; Parameswaran, P.; Nandagopal, M.; Panneer Selvi, S.; Laha, K.; Mathew, M. D.</p> <p>2013-07-01</p> <p>Prior cold worked (PCW) titanium-modified 14Cr-15Ni austenitic stainless steel (SS) is used as a core-structural material in fast breeder reactor because of its superior <span class="hlt">creep</span> strength and resistance to void swelling. In this study, the influence of PCW in the range of 16-24% on <span class="hlt">creep</span> properties of IFAC-1 SS, a titanium modified 14Cr-15Ni austenitic SS, at 923 K and 973 K has been investigated. It was found that PCW has no appreciable effect on the <span class="hlt">creep</span> <span class="hlt">deformation</span> rate of the steel at both the test <span class="hlt">temperatures</span>; <span class="hlt">creep</span> rupture life increased with PCW at 923 K and remained rather unaffected at 973 K. The dislocation structure along with precipitation in the PCW steel was found to change appreciably depending on <span class="hlt">creep</span> testing conditions. A well-defined dislocation substructure was observed on <span class="hlt">creep</span> testing at 923 K; a well-annealed microstructure with evidences of recrystallization was observed on <span class="hlt">creep</span> testing at 973 K. <span class="hlt">Creep</span> rupture life of the steel increased with the increase in PCW at 923 K. This has been attributed to the partial retention of prior cold work induced dislocations which facilitated the extensive precipitation of secondary Ti(C,N) particles on the stable dislocation substructure. <span class="hlt">Creep</span> rupture life of the steel did not vary with PCW at 973 K due to softening by recrystallization and absence of secondary Ti(C,N).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/474149','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/474149"><span id="translatedtitle">Redistribution of a grain-boundary glass phase during <span class="hlt">creep</span> of silicon nitride ceramics</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Jin, Q.; Ning, X.G.; Wilkinson, D.S.; Weatherly, G.C.</p> <p>1997-03-01</p> <p>The compressive <span class="hlt">creep</span> behavior of a high-purity silicon nitride ceramic with and without the addition of Ba was studied at 1,400 C. Two distinct <span class="hlt">creep</span> stages were observed during high-<span class="hlt">temperature</span> <span class="hlt">deformation</span> of both materials. Transmission electron microscopy (TEM) has been used to characterize the intergranular glass film thickness. Statistical analysis of a number of grain-boundary films indicates that the film thickness is confined to a narrow range in the as-sintered materials. However, the mean thickness is greater in the Ba-doped ceramic than in the undoped material. The standard deviation of the film thickness of a given material is considerably larger after <span class="hlt">creep</span> than before. The authors conclude that the grain-boundary glass phase is redistributed during <span class="hlt">creep</span>, suggesting that viscous flow of the glass phase is responsible for the first stage of the <span class="hlt">creep</span> process.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JMEP..tmp..364S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JMEP..tmp..364S"><span id="translatedtitle">Effects of Microstructure and Processing Methods on <span class="hlt">Creep</span> Behavior of AZ91 Magnesium Alloy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shahbeigi Roodposhti, Peiman; Sarkar, Apu; Murty, Korukonda L.; Scattergood, Ronald O.</p> <p>2016-07-01</p> <p>This review sheds light on the <span class="hlt">creep</span> properties of AZ91 magnesium alloys with a major emphasis on the influence of microstructure on the <span class="hlt">creep</span> resistance and underlying <span class="hlt">creep</span> <span class="hlt">deformation</span> mechanism based on stress exponent and activation energy. Effects of processing routes such as steel mold casting, die casting, and thixoforming are considered. Roles of a wide range of additional alloying elements such as Si, Sb, Bi, Ca, Sn, REs, and combined addition of them on the microstructure modification were investigated. The reaction between these elements and the Mg or Al in the matrix develops some thermally stable intermetallic phases which improves the <span class="hlt">creep</span> resistance at elevated <span class="hlt">temperatures</span>, however does not influence the <span class="hlt">creep</span> mechanism.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19750054660&hterms=waspaloy&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dwaspaloy','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19750054660&hterms=waspaloy&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dwaspaloy"><span id="translatedtitle"><span class="hlt">Deformation</span> characteristics and time-dependent notch sensitivity of Udimet 700 at intermediate <span class="hlt">temperatures</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wilson, D. J.</p> <p>1975-01-01</p> <p>Time-dependent notch sensitivity of Udimet 700 sheet, bar, and investment castings was observed between 1000 and 1400 F (538-760 C) but not at 1600 F (871 C). As was the case for Modified Waspaloy, Waspaloy, Rene 41, Inconel 718, and TD-NiCr, it occurred when notched specimens were loaded below the yield strength and when <span class="hlt">creep</span> <span class="hlt">deformation</span> was localized. For each gamma-prime strengthened alloy and notched specimen geometry, a stress-average particle size zone can be defined to characterize the notch-sensitive behavior.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.7107K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.7107K"><span id="translatedtitle">A model of compaction <span class="hlt">creep</span> in carbonates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Keszthelyi, Daniel; Jamtveit, Bjørn; Dysthe, Dag Kristian</p> <p>2015-04-01</p> <p>Rocks in compressional stress conditions are subject to long-term <span class="hlt">creep</span> <span class="hlt">deformations</span>. We created a simple conceptual micomechanical model of <span class="hlt">creep</span> in rocks combining microscopic fracturing and pressure solution. This was then scaled up to macroscopic scale by a statistical mechanical approach to predict strain rate at core scale. The model uses no fitting parameter and have a few input parameters: effective stress, porosity, pore size distribution, <span class="hlt">temperature</span> and water saturation. Internal parameters are Young's modulus, interfacial energy of wet calcite and dissolution rates of calcite, all of which are measurable independently. Existing long-term <span class="hlt">creep</span> experiments were used to verify the model which was able to predict the magnitude of the resulting strain in largely different effective stress, <span class="hlt">temperature</span> and water saturation conditions. The model was also able to predict the compaction of a producing chalk reservoir with a good agreement. Further generalization of the model might function as a general theory of long-term <span class="hlt">creep</span> of rocks in compressional settings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013GeoRL..40..697T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013GeoRL..40..697T"><span id="translatedtitle">Magnetite <span class="hlt">deformation</span> mechanism maps for better prediction of strain partitioning</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Till, J. L.; Moskowitz, Bruce</p> <p>2013-02-01</p> <p><title type="main">Abstract A meta-analysis of existing experimental <span class="hlt">deformation</span> data for magnetite and other spinel-structured ferrites reveals that previously published flow laws are inadequate to describe the general <span class="hlt">deformation</span> behavior of magnetite. Using updated rate equations for oxygen diffusion in magnetite, we present new flow laws that closely predict <span class="hlt">creep</span> rates similar to those found in <span class="hlt">deformation</span> experiments and that can be used to predict strain partitioning between cubic Fe oxides and other phases in the Earth's crust. New <span class="hlt">deformation</span> mechanism maps for magnetite have been constructed as functions of <span class="hlt">temperature</span> and grain size. Using the revised <span class="hlt">creep</span> parameters, estimates of strain partitioning between magnetite, ilmenite, and plagioclase indicate that concentrated zones of Fe-Ti oxides in oceanic crust near slow-spreading ridges could accommodate significant amounts of strain at moderate <span class="hlt">temperatures</span> and may contribute to aseismic <span class="hlt">creep</span> along spreading-segment faults.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950011631','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950011631"><span id="translatedtitle">Influence of high pressure hydrogen environment on <span class="hlt">creep</span> <span class="hlt">deformation</span> of Mo-Re, Haynes 188, and NARloy-Z alloys</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sastry, S. M. L.; Yang, Charles C.; Ouyang, Shewang; Jerina, K. L.; Schwartz, D. S.</p> <p>1994-01-01</p> <p>The present study focuses on the investigation of the influence of hydrogen on the mechanical properties of three types of alloys at elevated <span class="hlt">temperatures</span>. The reasons for the consideration of hydrogen effects are the potential use of hydrogen as a coolant in gas-cooled reactors and fuel in advanced hypersonic vehicles. The materials used in hydrogen atmosphere must not be embrittled by hydrogen at ambient <span class="hlt">temperature</span> and should have good strength in hydrogen atmosphere at elevated <span class="hlt">temperature</span>. The paucity of information concerning the mechanical performance in hydrogen atmosphere at elevated <span class="hlt">temperature</span> has been a limiting factor in the selection and design of structural components for operation in hydrogen environment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFMDI21B..02A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFMDI21B..02A"><span id="translatedtitle"><span class="hlt">Deformation</span> of Lawsonite at High Pressure and High <span class="hlt">Temperature</span> - Implications for Low Velocity Layers in Subduction Zones</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Amiguet, E.; Hilairet, N.; Wang, Y.; Gillet, P.</p> <p>2014-12-01</p> <p>During subduction, the hydrated oceanic crust undergoes a series of metamorphic reactions and transform gradually to blueschists and eclogite at depths of 20-50 km. Detailed seismic observations of subduction zones suggest a complex layered structure with the presence of a Low Velocity Layer (LVL) related to the oceanic crust [1] persisting to considerable depths (100- 250 km).While the transformation from blueschist to eclogite [2] and the presence of glaucophane up to 90-100 km [3] could explain some of these observations, the presence of LVL at greater depths could be related to the presence of the hydrous mineral lawsonite (CaAl2(Si2O7)(OH)2 H2O). Its stability field extends to 8.5 GPa and 1100K corresponding to depths up to 250 km in cold hydrous part of subducting slabs [4]. Because these regions undergo large and heterogeneous <span class="hlt">deformation</span>, lawsonite plasticity and crystal preferred orientation (CPOs) may strongly influence the dynamic of subduction zones and the seismic properties. We present a <span class="hlt">deformation</span> study at high presssure and high <span class="hlt">temperature</span> on lawsonite. Six samples were <span class="hlt">deformed</span> at 4-10 GPa and 600K to 1000K using a D-DIA apparatus [5] at 13-BMD at GSECARS beamline, APS, in axial compression up to 30% <span class="hlt">deformation</span> with strain rates of 3.10-4s-1 to 6.10-6s-1. We measured in-situ lattice strains (a proxy for macroscopic stress), texture and strain using synchrotron radiations and calculated the macroscopic stress using lawsonite elastic properties [6]. Results from lattice strain analysis show a dependence of flow stress with <span class="hlt">temperature</span> and strain rate. Texture analysis coupled with transmission electron microscopy showed that dislocation <span class="hlt">creep</span> is the dominant <span class="hlt">deformation</span> mechanism under our <span class="hlt">deformation</span> conditions. [1] Abers, Earth and Planetary Science Letters, 176, 323-330, 2000 [2] Helffrich et al., Journal of Geophysical Research, 94, 753-763, 1989 [3] Bezacier et al., Tectonophysics, 494, 201-210, 2010 [4] Schmidt & Poli, Earth and Planetary</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/17738997','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/17738997"><span id="translatedtitle">Activation volume for <span class="hlt">creep</span> in the upper mantle.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ross, J V; Ave'lallemant, H G; Carter, N L</p> <p>1979-01-19</p> <p>The activation volume for <span class="hlt">creep</span>, V*, of olivine-rich rocks has been determined in pressure-differential <span class="hlt">creep</span> experiments on dunite at <span class="hlt">temperatures</span> from 1100 degrees to 1350 degrees C and confining pressures from 5 to 15 kilobars. Values of V* range from 10.6 to 15.4 cubic centimeters per mole with a mean value of 13.4 cubic centimeters per mole, near that expected for oxygen ion self-diffusion. The quantity V* is incorporated into existing flow equations; in combination with observations on naturally <span class="hlt">deformed</span> mantle xenoliths, estimates are given of the variation with depth of stress, strain rate, and viscosity. PMID:17738997</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/437788','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/437788"><span id="translatedtitle"><span class="hlt">Temperature</span> dependence of the <span class="hlt">deformation</span> behavior of type 316 stainless steel after low <span class="hlt">temperature</span> neutron irradiation</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Robertson, J.P.; Rowcliffe, A.F.; Grossbeck, M.L.; Ioka, Ikuo; Jitsukawa, Shiro</p> <p>1996-12-31</p> <p>A single heat of solution annealed 316 ss was irradiated to 7 and 18 dpa at 60, 200, 330, and 400 C. Tensile properties were studied vs dose and <span class="hlt">temperature</span>. Large changes in yield strength, <span class="hlt">deformation</span> mode, strain to necking (STN), and strain hardening capacity were seen. Magnitude of the changes are dependent on both irradiation <span class="hlt">temperature</span> and neutron dose. Irradiation can more than triple the yield strength and decrease STN to <0.5% under certain conditions. A maximum increase in yield strength and a minimum in STN occur after irradiation at 330 C but failure mode remains ductile.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009MMTA...40.2971N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009MMTA...40.2971N"><span id="translatedtitle"><span class="hlt">Creep</span> Behavior and Damage of Ni-Base Superalloys PM 1000 and PM 3030</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nganbe, M.; Heilmaier, M.</p> <p>2009-12-01</p> <p>Two oxide dispersion strengthening (ODS) nickel-base superalloys, a solely dispersion-strengthened alloy (PM 1000) and an additionally γ'-strengthened alloy (PM 3030) are investigated regarding <span class="hlt">creep</span> resistance at <span class="hlt">temperatures</span> between 600 °C and 1000 °C. The <span class="hlt">creep</span> strength advantage of PM 3030 over PM 1000 decreases as the <span class="hlt">temperature</span> increases due to the thermal instability of the γ' phase. The particle strengthening contribution in both alloys increases linearly with load. However, solid solution softening leads to an apparent drop in particle strengthening in PM 1000. <span class="hlt">Deformation</span> concentration in slip bands is more accentuated in PM 3030-R34 due to additional γ' strengthening combined with strongly textured coarse and elongated grain structure. Finer, equiaxed grains reduce <span class="hlt">creep</span> strength at higher <span class="hlt">temperatures</span> due to grain boundary <span class="hlt">deformation</span> processes and premature pore formation, but have only minor impact at low and intermediate <span class="hlt">temperatures</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007APS..MARD22009D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007APS..MARD22009D"><span id="translatedtitle">Statistical properties of microcracking in polyurethane foams under tensile and <span class="hlt">creep</span> tests: influence of <span class="hlt">temperature</span> and density.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Deschanel, Stephanie; Vigier, Gerard; Godin, Nathalie; Vanel, Loic; Ciliberto, Sergio</p> <p>2007-03-01</p> <p>For some heterogeneous materials fracture can be described as a clustering of microcracks: global rupture being not controlled by a single event. We focus on polyurethane foams whose heterogeneities (pores) constitute the termination points where microcracks can stop. We record both the spatial and time distributions of acoustic emission emitted by a sample during mechanical tests: each microcrack nucleation corresponds to a burst of energy that can be localized on the widest face of the specimen. The probability distributions of the energy released is power-law distributed, independently of the material density, the loading mode or the mechanical behavior. On the other hand, the agreement of a power law for the time intervals between two damaging events seems to require a quasi constant stress during damaging. Moreover, we notice a behavior difference of the cumulative number of events and the cumulative energy of the localized events with <span class="hlt">temperature</span> in the case of tensile tests and not any more for <span class="hlt">creep</span> tests. The occurrence of a unique behavior and a power law in a restricted time interval for the cumulative number of events and the cumulative energy in <span class="hlt">creep</span> allow us to apprehend interesting later studies of materials' lifetime prediction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5633656','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5633656"><span id="translatedtitle">Resistance to <span class="hlt">deformation</span> of structural steels exposed to current pulses and cryogenic <span class="hlt">temperatures</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Strizhalo, V.A.; Novogrudskii, L.S.; Znachkovskii, O.Y.</p> <p>1986-01-01</p> <p>This paper studies the resistance to <span class="hlt">deformation</span> of structural materials acted upon by electric current at cryogenic <span class="hlt">temperatures</span> in dependence on the magnitude of residual <span class="hlt">deformation</span>, the degree of preliminary <span class="hlt">deformation</span>, and other factors. The authors used an installation UTN-10 at <span class="hlt">temperatures</span> of 293, 77, and 4.2 degrees K with fivefold specimens of chromenickel steel and chrome-manganese steel. The dependence of the change of resistance to <span class="hlt">deformation</span> of steels on the residual <span class="hlt">deformation</span> at which a current pulse was applied is shown. Lowering the <span class="hlt">temperature</span> to 77 degrees K or less strengthens the role of the interaction between electrons and dislocations in reducing the resistance to <span class="hlt">deformation</span> of steels 12Kh18N10T and 03Kh13AG19 at the instant when an electric-current pulse acts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2014JNuM..455...73K&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2014JNuM..455...73K&link_type=ABSTRACT"><span id="translatedtitle">Irradiation <span class="hlt">creep</span> of nano-powder sintered silicon carbide at low neutron fluences</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koyanagi, T.; Shimoda, K.; Kondo, S.; Hinoki, T.; Ozawa, K.; Katoh, Y.</p> <p>2014-12-01</p> <p>The irradiation <span class="hlt">creep</span> behavior of nano-powder sintered silicon carbide was investigated using the bend stress relaxation method under neutron irradiation up to 1.9 dpa. The <span class="hlt">creep</span> <span class="hlt">deformation</span> was observed at all <span class="hlt">temperatures</span> ranging from 380 to 1180 °C mainly from the irradiation <span class="hlt">creep</span> but with the increasing contributions from the thermal <span class="hlt">creep</span> at higher <span class="hlt">temperatures</span>. The apparent stress exponent of the irradiation <span class="hlt">creep</span> slightly exceeded unity, and instantaneous <span class="hlt">creep</span> coefficient at 380-790 °C was estimated to be ∼1 × 10-5 [MPa-1 dpa-1] at ∼0.1 dpa and 1 × 10-7 to 1 × 10-6 [MPa-1 dpa-1] at ∼1 dpa. The irradiation <span class="hlt">creep</span> strain appeared greater than that for the high purity SiC. Microstructural observation and data analysis indicated that the grain-boundary sliding associated with the secondary phases contributes to the irradiation <span class="hlt">creep</span> at 380-790 °C to 0.01-0.11 dpa.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/10188601','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/10188601"><span id="translatedtitle"><span class="hlt">Creep</span> behavior in SiC whisker-reinforced alumina composite</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Lin, H.T.; Becher, P.F.</p> <p>1994-10-01</p> <p>Grain boundary sliding (often accompanied by cavitation) is a major contributor to compressive and tensile <span class="hlt">creep</span> <span class="hlt">deformation</span> in fine-grained aluminas, both with and without whisker-reinforcement. Studies indicate that the <span class="hlt">creep</span> response of alumina composites reinforced with SiC whiskers can be tailored by controlling the composite microstructure and composition. The addition of SiC whiskers (< 30 vol%) significantly increases the <span class="hlt">creep</span> resistance of fine-grained (1--2 {mu}m) alumina in air at <span class="hlt">temperatures</span> of 1,200 and 1,300 C. However, at higher whisker contents (30 and 50 vol%), the <span class="hlt">creep</span> resistance is degraded due to enhanced surface oxidation reactions accompanied by extensive <span class="hlt">creep</span> cavitation. Densification aids (i.e., Y{sub 2}O{sub 3}), which facilitate silica glass formation and thus liquid phase densification of the composites, can also result in degradation of <span class="hlt">creep</span> resistance. On the other hand, increasing the matrix grain size or decreasing the whisker aspect ratio (increased whisker number density) results in raising the <span class="hlt">creep</span> resistance of the composites. These observations not only explain the variability in the <span class="hlt">creep</span> response of various SiC whisker-reinforced alumina composites but also indicate factors that can be used to enhance the elevated <span class="hlt">temperature</span> performance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008NIMPA.593..597V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008NIMPA.593..597V"><span id="translatedtitle">Extended-time-scale <span class="hlt">creep</span> measurement on Maraging cantilever blade springs</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Virdone, Nicole; Agresti, Juri; Bertolini, Alessandro; DeSalvo, Riccardo; Stellacci, Rosalia; Kamp, Justin; Mantovani, Maddalena; Sannibale, Virginio; Tarallo, Marco; Kaltenegger, Lisa</p> <p>2008-08-01</p> <p>Two controlled <span class="hlt">temperature</span> facilities were built to induce an accelerated <span class="hlt">creep</span> rate in a Maraging steel GAS spring and to measure the material's <span class="hlt">creep</span> over an artificially extended period of time. The data acquisition of the first experiment lasted for almost a year, but then the blades were allowed to <span class="hlt">creep</span> for six more years before measuring the permanent <span class="hlt">deformation</span> integrated over time. The data from this first experiment was polluted by a defect in the data acquisition software, but yielded overall <span class="hlt">creep</span> limits and an evaluation of the Arrhenius acceleration of <span class="hlt">creep</span> speed with <span class="hlt">temperature</span> (1.28±0.13 °C -1). The duration of the second experiment was only 1 year but more free of systematic errors. The effective test period of this second experiment (normalized with the Arrhenius acceleration measured in the first experiment) extends in billions of years showing no sign of anomalous <span class="hlt">creep</span>. The result of both experiments also produced a simple procedure capable of eliminating all practical effects of <span class="hlt">creep</span> from the Advanced LIGO seismic isolation and suspensions. Measurements of <span class="hlt">creep</span> under various stress levels, and of the thermal variations of Young's modulus (2.023 (±0.013)×10 -4 °C -1) are reported as well.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011JNuM..414..440G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011JNuM..414..440G"><span id="translatedtitle">The effect of <span class="hlt">deformation</span> <span class="hlt">temperature</span> on the microstructure evolution of Inconel 625 superalloy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guo, Qingmiao; Li, Defu; Guo, Shengli; Peng, Haijian; Hu, Jie</p> <p>2011-07-01</p> <p>Hot compression tests of Inconel 625 superalloy were conducted using a Gleeble-1500 simulator between 900 °C and 1200 °C with different true strains and a strain rate of 0.1 s -1. Scanning electron microscope (SEM) and electron backscatter diffraction technique (EBSD) were employed to investigate the effect of <span class="hlt">deformation</span> <span class="hlt">temperature</span> on the microstructure evolution and nucleation mechanisms of dynamic recrystallization (DRX). It is found that the relationship between the DRX grain size and the peak stress can be expressed by a power law function. Significant influence of <span class="hlt">deformation</span> <span class="hlt">temperatures</span> on the nucleation mechanisms of DRX are observed at different <span class="hlt">deformation</span> stages. At lower <span class="hlt">deformation</span> <span class="hlt">temperatures</span>, continuous dynamic recrystallization (CDRX) characterized by progressive subgrain rotation is considered as the main mechanism of DRX at the early <span class="hlt">deformation</span> stage. However, discontinuous dynamic recrystallization (DDRX) with bulging of the original grain boundaries becomes the operating mechanism of DRX at the later <span class="hlt">deformation</span> stage. At higher <span class="hlt">deformation</span> <span class="hlt">temperatures</span>, DDRX is the primary mechanism of DRX, while CDRX can only be considered as an assistant mechanism at the early <span class="hlt">deformation</span> stage. Nucleation of DRX can also be activated by the twinning formation. With increasing the <span class="hlt">deformation</span> <span class="hlt">temperature</span>, the effect of DDRX accompanied with twinning formation grows stronger, while the effect of CDRX grows weaker. Meanwhile, the position of subgrain formation shifts gradually from the interior of original grains to the vicinity of the original boundaries.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940018140','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940018140"><span id="translatedtitle">Brief summary of the evolution of high-<span class="hlt">temperature</span> <span class="hlt">creep</span>-fatigue life prediction models for crack initiation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Halford, Gary R.</p> <p>1993-01-01</p> <p>The evolution of high-<span class="hlt">temperature</span>, <span class="hlt">creep</span>-fatigue, life-prediction methods used for cyclic crack initiation is traced from inception in the late 1940's. The methods reviewed are material models as opposed to structural life prediction models. Material life models are used by both structural durability analysts and by material scientists. The latter use micromechanistic models as guidance to improve a material's crack initiation resistance. Nearly one hundred approaches and their variations have been proposed to date. This proliferation poses a problem in deciding which method is most appropriate for a given application. Approaches were identified as being combinations of thirteen different classifications. This review is intended to aid both developers and users of high-<span class="hlt">temperature</span> fatigue life prediction methods by providing a background from which choices can be made. The need for high-<span class="hlt">temperature</span>, fatigue-life prediction methods followed immediately on the heels of the development of large, costly, high-technology industrial and aerospace equipment immediately following the second world war. Major advances were made in the design and manufacture of high-<span class="hlt">temperature</span>, high-pressure boilers and steam turbines, nuclear reactors, high-<span class="hlt">temperature</span> forming dies, high-performance poppet valves, aeronautical gas turbine engines, reusable rocket engines, etc. These advances could no longer be accomplished simply by trial and error using the 'build-em and bust-em' approach. Development lead times were too great and costs too prohibitive to retain such an approach. Analytic assessments of anticipated performance, cost, and durability were introduced to cut costs and shorten lead times. The analytic tools were quite primitive at first and out of necessity evolved in parallel with hardware development. After forty years more descriptive, more accurate, and more efficient analytic tools are being developed. These include thermal-structural finite element and boundary element</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1993cmfa.nasa..121H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1993cmfa.nasa..121H"><span id="translatedtitle">Brief summary of the evolution of high-<span class="hlt">temperature</span> <span class="hlt">creep</span>-fatigue life prediction models for crack initiation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Halford, Gary R.</p> <p>1993-10-01</p> <p>The evolution of high-<span class="hlt">temperature</span>, <span class="hlt">creep</span>-fatigue, life-prediction methods used for cyclic crack initiation is traced from inception in the late 1940's. The methods reviewed are material models as opposed to structural life prediction models. Material life models are used by both structural durability analysts and by material scientists. The latter use micromechanistic models as guidance to improve a material's crack initiation resistance. Nearly one hundred approaches and their variations have been proposed to date. This proliferation poses a problem in deciding which method is most appropriate for a given application. Approaches were identified as being combinations of thirteen different classifications. This review is intended to aid both developers and users of high-<span class="hlt">temperature</span> fatigue life prediction methods by providing a background from which choices can be made. The need for high-<span class="hlt">temperature</span>, fatigue-life prediction methods followed immediately on the heels of the development of large, costly, high-technology industrial and aerospace equipment immediately following the second world war. Major advances were made in the design and manufacture of high-<span class="hlt">temperature</span>, high-pressure boilers and steam turbines, nuclear reactors, high-<span class="hlt">temperature</span> forming dies, high-performance poppet valves, aeronautical gas turbine engines, reusable rocket engines, etc. These advances could no longer be accomplished simply by trial and error using the 'build-em and bust-em' approach. Development lead times were too great and costs too prohibitive to retain such an approach. Analytic assessments of anticipated performance, cost, and durability were introduced to cut costs and shorten lead times. The analytic tools were quite primitive at first and out of necessity evolved in parallel with hardware development. After forty years more descriptive, more accurate, and more efficient analytic tools are being developed. These include thermal-structural finite element and boundary element</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1990mmms.proc...39M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1990mmms.proc...39M"><span id="translatedtitle">Thermally activated flux <span class="hlt">creep</span> and critical current densities in high <span class="hlt">temperature</span> superconductors</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Matsushita, Teruo</p> <p></p> <p>The effect of flux <span class="hlt">creep</span> is discussed for projected strongly pinned oxide superconductors. It is determined, that if a superconducting wire with a critical current density higher than 10-billion A/sq m at 77 K and 5 T can be produced, the wire will be able to be applied to equipment at high fields; nonzero critical density will be obtained even at 77 K and high fields. The decay of persistent current is expected to be noticeable even in such strongly pinned superconductors, when those are used at 77 K. Although this will be managed in power equipment by lowering the operating current; variation in the magnetic field due to the variation in the current distribution inside superconducting wires appears to be unavoidable. It is suggested that an effort should be made to reduce the variation by reducing the diameter of the superconducting filaments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19720025884','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19720025884"><span id="translatedtitle">Effect of high <span class="hlt">temperature</span> <span class="hlt">creep</span> and oxidation on residual room <span class="hlt">temperature</span> properties for several thin sheet superalloys</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Royster, D. M.; Lisagor, W. B.</p> <p>1972-01-01</p> <p>Superalloys are being considered for the primary heat shields and supports in the thermal protection system of both hypersonic transport and space shuttle vehicles. Since conservative design philosophy dictates designs based on residual material properties at the end of the service life, material characterization after exposure to the environmental conditions imposed by the flight requirements of these two classes of vehicles is needed on the candidate alloys. An investigation was conducted to provide some of the necessary data, with emphasis placed on oxidation, <span class="hlt">creep</span>, and residual properties of thin-gage sheet material.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/1166817','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/1166817"><span id="translatedtitle">Segregation at stacking faults within the γ′ phase of two Ni-base superalloys following intermediate <span class="hlt">temperature</span> <span class="hlt">creep</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Viswanathan, G. B.; Shi, R.; Genc, A.; Vorontsov, V. A.; Kovarik, L.; Rae, C. M. F.; Mills, M. J.</p> <p>2015-01-01</p> <p>Using state-of-the-art energy dispersive spectroscopy, it has been established for the first time that there exists significant compositional variation (enrichment of Co and Cr and deficiency of Ni and Al) associated with superlattice intrinsic stacking faults created in the ordered γ' precipitates following intermediate <span class="hlt">temperature</span> <span class="hlt">deformation</span> of two commercial superalloys. The results indicate that long range diffusion of these elements is intimately involved in the precipitate shearing process and is therefore closely linked to the time-dependent <span class="hlt">deformation</span> of the alloys.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015NatSR...5E9734L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015NatSR...5E9734L"><span id="translatedtitle">Low-<span class="hlt">temperature</span> direct copper-to-copper bonding enabled by <span class="hlt">creep</span> on (111) surfaces of nanotwinned Cu</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liu, Chien-Min; Lin, Han-Wen; Huang, Yi-Sa; Chu, Yi-Cheng; Chen, Chih; Lyu, Dian-Rong; Chen, Kuan-Neng; Tu, King-Ning</p> <p>2015-05-01</p> <p>Direct Cu-to-Cu bonding was achieved at <span class="hlt">temperatures</span> of 150-250 °C using a compressive stress of 100 psi (0.69 MPa) held for 10-60 min at 10-3 torr. The key controlling parameter for direct bonding is rapid surface diffusion on (111) surface of Cu. Instead of using (111) oriented single crystal of Cu, oriented (111) texture of extremely high degree, exceeding 90%, was fabricated using the oriented nano-twin Cu. The bonded interface between two (111) surfaces forms a twist-type grain boundary. If the grain boundary has a low angle, it has a hexagonal network of screw dislocations. Such network image was obtained by plan-view transmission electron microscopy. A simple kinetic model of surface <span class="hlt">creep</span> is presented; and the calculated and measured time of bonding is in reasonable agreement.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4649891','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4649891"><span id="translatedtitle">Low-<span class="hlt">temperature</span> direct copper-to-copper bonding enabled by <span class="hlt">creep</span> on (111) surfaces of nanotwinned Cu</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Liu, Chien-Min; Lin, Han-Wen; Huang, Yi-Sa; Chu, Yi-Cheng; Chen, Chih; Lyu, Dian-Rong; Chen, Kuan-Neng; Tu, King-Ning</p> <p>2015-01-01</p> <p>Direct Cu-to-Cu bonding was achieved at <span class="hlt">temperatures</span> of 150–250 °C using a compressive stress of 100 psi (0.69 MPa) held for 10–60 min at 10−3 torr. The key controlling parameter for direct bonding is rapid surface diffusion on (111) surface of Cu. Instead of using (111) oriented single crystal of Cu, oriented (111) texture of extremely high degree, exceeding 90%, was fabricated using the oriented nano-twin Cu. The bonded interface between two (111) surfaces forms a twist-type grain boundary. If the grain boundary has a low angle, it has a hexagonal network of screw dislocations. Such network image was obtained by plan-view transmission electron microscopy. A simple kinetic model of surface <span class="hlt">creep</span> is presented; and the calculated and measured time of bonding is in reasonable agreement. PMID:25962757</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015JGRB..120..879M&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015JGRB..120..879M&link_type=ABSTRACT"><span id="translatedtitle">Brittle <span class="hlt">creep</span> and subcritical crack propagation in glass submitted to triaxial conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mallet, Céline; Fortin, Jérôme; Guéguen, Yves; Bouyer, Frédéric</p> <p>2015-02-01</p> <p>An experimental work is presented that aimed at improving our understanding of the mechanical evolution of cracks under brittle <span class="hlt">creep</span> conditions. Brittle <span class="hlt">creep</span> may be an important slow <span class="hlt">deformation</span> process in the Earth's crust. Synthetic glass samples have been used to observe and document brittle <span class="hlt">creep</span> due to slow crack-propagation. A crack density of 0.05 was introduced in intact synthetic glass samples by thermal shock. <span class="hlt">Creep</span> tests were performed at constant confining pressure (15 MPa) for water saturated conditions. Data were obtained by maintaining the differential-stress constant in steps of 24 h duration. A set of sensors allowed us to record strains and acoustic emissions during <span class="hlt">creep</span>. The effect of <span class="hlt">temperature</span> on <span class="hlt">creep</span> was investigated from ambient <span class="hlt">temperature</span> to 70°C. The activation energy for crack growth was found to be 32 kJ/mol. In secondary <span class="hlt">creep</span>, a large dilatancy was observed that did not occur in constant strain rate tests. This is correlated to acoustic emission activity associated with crack growth. As a consequence, slow crack growth has been evidenced in glass. Beyond secondary <span class="hlt">creep</span>, failure in tertiary <span class="hlt">creep</span> was found to be a progressive process. The data are interpreted through a previously developed micromechanical damage model that describes crack propagation. This model allows one to predict the secondary brittle <span class="hlt">creep</span> phase and also to give an analytical expression for the time to rupture. Comparison between glass and crystalline rock indicates that the brittle <span class="hlt">creep</span> behavior is probably controlled by the same process even if stress sensitivity for glass is lower than for rocks.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/414880','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/414880"><span id="translatedtitle"><span class="hlt">Temperature</span> dependence of the <span class="hlt">deformation</span> behavior of 316 stainless steel after low <span class="hlt">temperature</span> neutron irradiation</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Pawel-Robertson, J.E.; Rowcliffe, A.F.; Grossbeck, M.L.</p> <p>1996-10-01</p> <p>The effects of low <span class="hlt">temperature</span> neutron irradiation on the tensile behavior of 316 stainless steel have been investigated. A single heat of solution annealed 316 was irradiated to 7 and 18 dpa at 60, 200, 330, and 400{degrees}C. The tensile properties as a function of dose and as a function of <span class="hlt">temperature</span> were examined. Large changes in yield strength, <span class="hlt">deformation</span> mode, strain to necking, and strain hardening capacity were seen in this irradiation experiment. The magnitudes of the changes are dependent on both irradiation <span class="hlt">temperature</span> and neutron dose. Irradiation can more than triple the yield strength over the unirradiated value and decrease the strain to necking (STN) to less than 0.5% under certain conditions. A maximum increase in yield strength and a minimum in the STN occur after irradiation at 330{degrees}C but the failure mode remains ductile.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011MSMSE..19a5005M&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011MSMSE..19a5005M&link_type=ABSTRACT"><span id="translatedtitle">A <span class="hlt">creep</span> model for austenitic stainless steels incorporating cavitation and wedge cracking</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mahesh, S.; Alur, K. C.; Mathew, M. D.</p> <p>2011-01-01</p> <p>A model of damage evolution in austenitic stainless steels under <span class="hlt">creep</span> loading at elevated <span class="hlt">temperatures</span> is proposed. The initial microstructure is idealized as a space-tiling aggregate of identical rhombic dodecahedral grains, which undergo power-law <span class="hlt">creep</span> <span class="hlt">deformation</span>. Damage evolution in the form of cavitation and wedge cracking on grain-boundary facets is considered. Both diffusion- and <span class="hlt">deformation</span>-driven grain-boundary cavity growth are treated. Cavity and wedge-crack length evolution are derived from an energy balance argument that combines and extends the models of Cottrell (1961 Trans. AIME 212 191-203), Williams (1967 Phil. Mag. 15 1289-91) and Evans (1971 Phil Mag. 23 1101-12). The time to rupture predicted by the model is in good agreement with published experimental data for a type 316 austenitic stainless steel under uniaxial <span class="hlt">creep</span> loading. <span class="hlt">Deformation</span> and damage evolution at the microscale predicted by the present model are also discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JNuM..444..283B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JNuM..444..283B"><span id="translatedtitle">Characterization of a 14Cr ODS steel by means of small punch and uniaxial testing with regard to <span class="hlt">creep</span> and fatigue at elevated <span class="hlt">temperatures</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bruchhausen, M.; Turba, K.; de Haan, F.; Hähner, P.; Austin, T.; de Carlan, Y.</p> <p>2014-01-01</p> <p>A 14Cr ODS steel was characterized at elevated <span class="hlt">temperatures</span> with regard to its behavior in small punch and uniaxial <span class="hlt">creep</span> tests and in low cycle fatigue tests. A comparison of small punch and uniaxial <span class="hlt">creep</span> tests at 650 °C revealed a strong anisotropy of the material when strained parallel and perpendicular to the extrusion direction with rupture times being several orders of magnitude lower for the perpendicular direction. The stress-rupture and Larson-Miller plots show a very large scatter of the <span class="hlt">creep</span> data. This scatter is strongly reduced when rupture time is plotted against minimum deflection rate or minimum <span class="hlt">creep</span> rate (Monkman-Grant plot). Fatigue tests have been carried out at 650 °C and 750 °C. The alloy is cyclically very stable with practically no hardening/softening. Results from the tests at both <span class="hlt">temperatures</span> can be described by a common power law. An increase in the test <span class="hlt">temperature</span> has little influence on the fatigue ductility exponent. For a given total strain level, the fatigue life of the alloy is reduced with increasing <span class="hlt">temperature</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1208056','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1208056"><span id="translatedtitle">Sessile dislocations by reactions in NiAl severely <span class="hlt">deformed</span> at room <span class="hlt">temperature</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Geist, D.; Gammer, C.; Rentenberger, C.; Karnthaler, H. P.</p> <p>2015-02-05</p> <p>B2 ordered NiAl is known for its poor room <span class="hlt">temperature</span> (RT) ductility; failure occurs in a brittle like manner even in ductile single crystals <span class="hlt">deforming</span> by single slip. In the present study NiAl was severely <span class="hlt">deformed</span> at RT using the method of high pressure torsion (HPT) enabling the hitherto impossible investigation of multiple slip <span class="hlt">deformation</span>. Methods of transmission electron microscopy were used to analyze the dislocations formed by the plastic <span class="hlt">deformation</span> showing that as expected dislocations with Burgers vector a(100) carry the plasticity during HPT <span class="hlt">deformation</span> at RT. In addition, we observe that they often form a(110) dislocations by dislocation reactions; the a(110) dislocations are considered to be sessile based on calculations found in the literature. It is therefore concluded that the frequently encountered 3D dislocation networks containing sessile a(110) dislocations are pinned and lead to <span class="hlt">deformation</span>-induced embrittlement. In spite of the severe <span class="hlt">deformation</span>, the chemical order remains unchanged.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19850007897','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19850007897"><span id="translatedtitle">Back stress in dislocation <span class="hlt">creep</span>. Part 1: Basic concepts and measuring techniques</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cadek, J.</p> <p>1984-01-01</p> <p>A theory is proposed whereby the plastic <span class="hlt">deformation</span> of metal materials is determined by the difference between the applied stress and the back stress which characterizes the resistance of the material to plastic <span class="hlt">deformation</span>. The back stress is usually equivalent to the internal stress or the friction stress and depends on the magnitude of the applied stress and <span class="hlt">temperature</span>. The concept of back stress is applied to the case of the dislocation <span class="hlt">creep</span> of precipitation-hardened or dispersion-strengthened metal materials. An additivity rule is formulated which can be useful in interpreting the <span class="hlt">creep</span> behavior of such materials.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMMR33C..02K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMMR33C..02K"><span id="translatedtitle">In Situ <span class="hlt">Creep</span> Strength Measurements on Ringwoodite at 18 GPa and 1700K Using a <span class="hlt">Deformation</span>-DIA Apparatus Combined with Synchrotron Radiation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kawazoe, T.; Nishihara, Y.; Ohuchi, T.; Maruyama, G.; Higo, Y.; Funakoshi, K.; Irifune, T.</p> <p>2013-12-01</p> <p>In order to study rheology of deep Earth materials at pressure-<span class="hlt">temperature</span> conditions of the lower mantle transition zone, technical improvements in <span class="hlt">deformation</span> experiments with a <span class="hlt">deformation</span>-DIA (D-DIA) apparatus have been made. We optimized dimensions of anvil truncation, a pressure medium and gasket to achieve the <span class="hlt">deformation</span> experiments at 18 GPa at relatively low press load (0.5 MN) to minimize damage of X-ray transparent second-stage anvils. Stress and strain of a sample were determined quantitatively by means of in situ X-ray radial diffraction and radiography, respectively, in conjunction with synchrotron radiation at BL04B1 beamline, SPring-8. We adopted low X-ray absorption materials (e.g. cubic BN anvils, graphite window in a LaCrO3 heater) along an X-ray path to enable the in situ stress-strain measurements. Based on the developed technique, the <span class="hlt">deformation</span> experiments on ringwoodite were carried out in uniaxial geometry at pressures of 17-18 GPa and <span class="hlt">temperatures</span> of 1500-1700 K with strain rates of 3.38-5.56 × 10-5 s-1 and strains up to 26.0 %. In the present study, the pressure condition of the in situ stress-strain measurements in the D-DIA apparatus was successfully expanded from 14.5 GPa to 18 GPa at <span class="hlt">temperatures</span> of 1500-1700 K. The present technical improvements in the in situ stress-strain measurements with the D-DIA apparatus should greatly contribute to studies on rheology of the deep Earth materials.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MMTA...47...49M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MMTA...47...49M"><span id="translatedtitle"><span class="hlt">Deformation</span> Mechanisms in Austenitic TRIP/TWIP Steel as a Function of <span class="hlt">Temperature</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Martin, Stefan; Wolf, Steffen; Martin, Ulrich; Krüger, Lutz; Rafaja, David</p> <p>2016-01-01</p> <p>A high-alloy austenitic CrMnNi steel was <span class="hlt">deformed</span> at <span class="hlt">temperatures</span> between 213 K and 473 K (-60 °C and 200 °C) and the resulting microstructures were investigated. At low <span class="hlt">temperatures</span>, the <span class="hlt">deformation</span> was mainly accompanied by the direct martensitic transformation of γ-austenite to α'-martensite (fcc → bcc), whereas at ambient <span class="hlt">temperatures</span>, the transformation via ɛ-martensite (fcc → hcp → bcc) was observed in <span class="hlt">deformation</span> bands. <span class="hlt">Deformation</span> twinning of the austenite became the dominant <span class="hlt">deformation</span> mechanism at 373 K (100 °C), whereas the conventional dislocation glide represented the prevailing <span class="hlt">deformation</span> mode at 473 K (200 °C). The change of the <span class="hlt">deformation</span> mechanisms was attributed to the <span class="hlt">temperature</span> dependence of both the driving force of the martensitic γ → α' transformation and the stacking fault energy of the austenite. The continuous transition between the ɛ-martensite formation and the twinning could be explained by different stacking fault arrangements on every second and on each successive {111} austenite lattice plane, respectively, when the stacking fault energy increased. A continuous transition between the transformation-induced plasticity effect and the twinning-induced plasticity effect was observed with increasing <span class="hlt">deformation</span> <span class="hlt">temperature</span>. Whereas the formation of α'-martensite was mainly responsible for increased work hardening, the stacking fault configurations forming ɛ-martensite and twins induced additional elongation during tensile testing.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=20060016347&hterms=contact&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dcontact','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=20060016347&hterms=contact&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dcontact"><span id="translatedtitle">Non-Contact Measurements of <span class="hlt">Creep</span> Properties of Refractory Materials</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lee, Jonghyun; Bradshaw, Richard C.; Hyers, Robert W.; Rogers, Jan R.; Rathz, Thomas J.; Wall, James J.; Choo, Hahn; Liaw, Peter</p> <p>2006-01-01</p> <p>State-of-the-art technologies for hypersonic aircraft, nuclear electric/thermal propulsion for spacecraft, and more efficient jet engines are driving ever more demanding needs for high-<span class="hlt">temperature</span> (>2000 C) materials. At such high <span class="hlt">temperatures</span>, <span class="hlt">creep</span> rises as one of the most important design factors to be considered. Since conventional measurement techniques for <span class="hlt">creep</span> resistance are limited to about 17OO0C, a new technique is in demand for higher <span class="hlt">temperatures</span>. This paper presents a non-contact method using electrostatic levitation (ESL) which is applicable to both metallic and non-metallic materials. The samples were rotated quickly enough to cause <span class="hlt">creep</span> <span class="hlt">deformation</span> by centrifugal acceleration. The <span class="hlt">deformation</span> of the samples was captured with a high speed camera and then the images were analyzed to estimate <span class="hlt">creep</span> resistance. Finite element analyses were performed and compared to the experiments to verify the new method. Results are presented for niobium and tungsten, representative refractory materials at 2300 C and 2700 C respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5048342','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5048342"><span id="translatedtitle">Analysis of elevated-<span class="hlt">temperature</span> tensile and <span class="hlt">creep</span> properties of normalized and tempered 2-1/4 Cr-1 Mo steel</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Booker, M.K.; Booker, B.L.P.; Swindeman, R.W.</p> <p>1982-01-01</p> <p>The ferritic 2-1/4 Cr-1 Mo steel is an important construction material for elevated-<span class="hlt">temperature</span> applications worldwide. It is of particular interest for coal conversion pressure vessels. Tensile and <span class="hlt">creep</span> data are presented for normalized and tempered 2-1/4 Cr-1 Mo steel from American, Japanese, British, French, and German sources. These include <span class="hlt">creep</span> data obtained at <span class="hlt">temperatures</span> from 427 to 600/sup 0/C (800 to 1112/sup 0/F) and tensile data from room <span class="hlt">temperature</span> to 550/sup 0/C (1022/sup 0/F). Properties examined included yield strength, ultimate tensile strength, 10/sup 5/-h <span class="hlt">creep</span>-rupture strength, and 10/sup -5/%/h <span class="hlt">creep</span> strength. These are the properties used in setting allowable stresses for Secton VIII, Division 1, of the ASME Boiler and Pressure Vessel Code. The data were analyzed by using lot-centered regression approaches that yielded expressions for the variations in the above properties with loading condition, as well as accounting for lot-to-lot variations in properties.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015RuMet2015..778A&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015RuMet2015..778A&link_type=ABSTRACT"><span id="translatedtitle">Irreversible <span class="hlt">deformation</span> and the superplasticity of a TN-1 alloy during thermal cycling through the martensitic transformations ranges under loading</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Andronov, I. N.; Ryabkov, Yu. I.; Bogdanov, N. P.; Severova, N. A.; Danilov, A. N.; Churilina, I. V.</p> <p>2015-10-01</p> <p>The influence of the thermal cycling conditions on the thermal-cycling <span class="hlt">creep</span> of a TN-1 alloy and the related irreversible <span class="hlt">deformations</span> is studied. The conditions under which an anomalous increase in the irreversible <span class="hlt">deformations</span> begins are determined. The structural mechanism of the irreversible <span class="hlt">deformations</span> of an equiatomic alloy is shown to be analogous to the structural mechanism of metal <span class="hlt">creep</span> at high <span class="hlt">temperatures</span>: it predominantly has a dislocation character. It is proposed to use the effect of anomalous increase in the <span class="hlt">deformation</span> of materials with reversible martensitic transformations for forming parts made of these materials at low <span class="hlt">temperatures</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JNuM..453..253C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JNuM..453..253C"><span id="translatedtitle">Helium effects on <span class="hlt">creep</span> properties of Fe-14CrWTi ODS steel at 650 °C</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, J.; Jung, P.; Rebac, T.; Duval, F.; Sauvage, T.; de Carlan, Y.; Barthe, M. F.</p> <p>2014-10-01</p> <p>In the present paper, the effects of helium on <span class="hlt">creep</span> properties of Fe-14CrWTi ODS steel were studied by in-beam and post He-implantation <span class="hlt">creep</span> tests. In-situ <span class="hlt">creep</span> was performed in an in-beam <span class="hlt">creep</span> device under uniaxial tensile stresses from 350 to 370 MPa during homogeneous helium implantation. Helium ions of energies varying from 0 to 25 MeV were implanted at a rate of 6 × 10-3 appm/s (corresponding to a displacement dose rate of 1.5 × 10-6 dpa/s). The average <span class="hlt">temperature</span> was controlled to 650 °C within ±2 °C. In addition, post He-implantation <span class="hlt">creep</span> tests were conducted at 650 °C as well. Subsequently, fracture surfaces and helium bubble evolution were studied in detail by SEM and TEM observations, respectively. Preliminary <span class="hlt">creep</span> results show that helium slightly shortens the <span class="hlt">creep</span> life time of ODS steel at 650 °C. Fracture surfaces of reference as well as implanted specimens, show areas with various grades of <span class="hlt">deformation</span>. Areas of highest <span class="hlt">deformation</span> can be interpreted as necking, while areas of low <span class="hlt">deformation</span> show in helium implanted specimens a more granular structure. The results are discussed in terms of possible embrittlement of ODS steels by helium.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFM.T33H..06F&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015AGUFM.T33H..06F&link_type=ABSTRACT"><span id="translatedtitle"><span class="hlt">Creep</span> of quartz by dislocation and grain boundary processes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fukuda, J. I.; Holyoke, C. W., III; Kronenberg, A. K.</p> <p>2015-12-01</p> <p>Wet polycrystalline quartz aggregates <span class="hlt">deformed</span> at <span class="hlt">temperatures</span> T of 600°-900°C and strain rates of 10-4-10-6 s-1 at a confining pressure Pc of 1.5 GPa exhibit plasticity at low T, governed by dislocation glide and limited recovery, and grain size-sensitive <span class="hlt">creep</span> at high T, governed by diffusion and sliding at grain boundaries. Quartz aggregates were HIP-synthesized, subjecting natural milky quartz powder to T=900°C and Pc=1.5 GPa, and grain sizes (2 to 25 mm) were varied by annealing at these conditions for up to 10 days. Infrared absorption spectra exhibit a broad OH band at 3400 cm-1 due to molecular water inclusions with a calculated OH content (~4000 ppm, H/106Si) that is unchanged by <span class="hlt">deformation</span>. Rate-stepping experiments reveal different stress-strain rate functions at different <span class="hlt">temperatures</span> and grain sizes, which correspond to differing stress-<span class="hlt">temperature</span> sensitivities. At 600-700°C and grain sizes of 5-10 mm, flow law parameters compare favorably with those for basal <a> plasticity and dislocation <span class="hlt">creep</span> of wet quartzites (effective stress exponents n of 3 to 6 and activation enthalpy H* ~150 kJ/mol). <span class="hlt">Deformed</span> samples show undulatory extinction, limited recrystallization, and c-axis maxima parallel to the shortening direction. Similarly fine-grained samples <span class="hlt">deformed</span> at 800°-900°C exhibit flow parameters n=1.3-2.0 and H*=135-200 kJ/mol corresponding to grain size-sensitive Newtonian <span class="hlt">creep</span>. <span class="hlt">Deformed</span> samples show some undulatory extinction and grain sizes change by recrystallization; however, grain boundary <span class="hlt">deformation</span> processes are indicated by the low value of n. Our experimental results for grain size-sensitive <span class="hlt">creep</span> can be compared with models of grain boundary diffusion and grain boundary sliding using measured rates of silicon grain boundary diffusion. While many quartz mylonites show microstructural and textural evidence for dislocation <span class="hlt">creep</span>, results for grain size-sensitive <span class="hlt">creep</span> may apply to very fine-grained (<10 mm) quartz mylonites.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014APS..MARS20004M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014APS..MARS20004M"><span id="translatedtitle">Challenges in predicting non-linear <span class="hlt">creep</span> and recovery in glassy polymers</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Medvedev, Grigori; Caruthers, James</p> <p>2014-03-01</p> <p>The phenomenon of non-linear <span class="hlt">creep</span> of amorphous polymeric glasses is difficult to predict using the traditional viscoelastic and viscoplastic constitutive frameworks, where two features present a particular challenge: (i) the tertiary stage of the <span class="hlt">creep</span> and (ii) the recovery from large <span class="hlt">creep</span> upon removal of the load. Representative examples of these two nonlinear responses will be shown for lightly cross-linked PMMA and an epoxy material, where the <span class="hlt">creep</span> and recovery behavior has been studied as a function of <span class="hlt">temperature</span> and aging time. The acceleration of <span class="hlt">creep</span> during the tertiary stage is not caused by damage since the original dimensions of a cross-linked sample are fully recoverable by annealing above Tg. The assumption that the relaxation time is a function of strain runs into qualitative problems when predicting multi-step constant strain rate loading experiments. Recovery from <span class="hlt">creep</span> as predicted by the constitutive models where the relaxation time depends on the <span class="hlt">deformation</span> history is too abrupt compared to the experiment - this known as the ``accelerated aging'' problem. A recently developed Stochastic Constitutive Model that acknowledges dynamic heterogeneity in the glass state naturally predicts both the tertiary <span class="hlt">creep</span> and the smooth recovery from <span class="hlt">creep</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013MMTA...44..136W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013MMTA...44..136W"><span id="translatedtitle">Advanced Procedures for Long-Term <span class="hlt">Creep</span> Data Prediction for 2.25 Chromium Steels</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Whittaker, Mark T.; Wilshire, Brian</p> <p>2013-01-01</p> <p>A critical review of recent <span class="hlt">creep</span> studies concluded that traditional approaches such as steady-state behavior, power law equations, and the view that diffusional <span class="hlt">creep</span> mechanisms are dominant at low stresses should be seriously reconsidered. Specifically, <span class="hlt">creep</span> strain rate against time curves show that a decaying primary rate leads into an accelerating tertiary stage, giving a minimum rather than a secondary period. Conventional steady-state mechanisms should therefore be abandoned in favor of an understanding of the processes governing strain accumulation and the damage phenomena causing tertiary <span class="hlt">creep</span> and fracture. Similarly, <span class="hlt">creep</span> always takes place by dislocation processes, with no change to diffusional <span class="hlt">creep</span> mechanisms with decreasing stress, negating the concept of <span class="hlt">deformation</span> mechanism maps. Alternative descriptions are then provided by normalizing the applied stress through the ultimate tensile stress and yield stress at the <span class="hlt">creep</span> <span class="hlt">temperature</span>. In this way, the resulting Wilshire equations allow accurate prediction of 100,00 hours of <span class="hlt">creep</span> data using only property values from tests lasting 5000 hours for a series of 2.25 chromium steels, namely grades 22, 23, and 24.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1321909','DOE-PATENT-XML'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1321909"><span id="translatedtitle"><span class="hlt">Creep</span>-resistant, cobalt-free alloys for high <span class="hlt">temperature</span>, liquid-salt heat exchanger systems</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Holcomb, David E; Muralidharan, Govindarajan; Wilson, Dane F.</p> <p>2016-09-06</p> <p>An essentially Fe- and Co-free alloy is composed essentially of, in terms of weight percent: 6.0 to 7.5 Cr, 0 to 0.15 Al, 0.5 to 0.85 Mn, 11 to 19.5 Mo, 0.03 to 4.5 Ta, 0.01 to 9 W, 0.03 to 0.08 C, 0 to 1 Re, 0 to 1 Ru, 0 to 0.001 B, 0.0005 to 0.005 N, balance Ni, the alloy being characterized by, at 850.degree. C., a yield strength of at least 25 Ksi, a tensile strength of at least 38 Ksi, a <span class="hlt">creep</span> rupture life at 12 Ksi of at least 25 hours, and a corrosion rate, expressed in weight loss [g/(cm.sup.2 sec)]10.sup.-11 during a 1000 hour immersion in liquid FLiNaK at 850.degree. C., in the range of 3 to 10.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/1239557','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/1239557"><span id="translatedtitle"><span class="hlt">Creep</span> cavitation bands control porosity and fluid flow in lower crustal shear zones</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Menegon, Luca; Fusseis, Florian; Stunitz, Holger; Xiao, Xianghui</p> <p>2015-03-01</p> <p>Shear zones channelize fluid flow in Earth’s crust. However, little is known about deep crustal fluid migration and how fluids are channelized and distributed in a <span class="hlt">deforming</span> lower crustal shear zone. This study investigates the <span class="hlt">deformation</span> mechanisms, fluid-rock interaction, and development of porosity in a monzonite ultramylonite from Lofoten, northern Norway. The rock was <span class="hlt">deformed</span> and transformed into an ultramylonite under lower crustal conditions (<span class="hlt">temperature</span> = 700–730 °C, pressure = 0.65–0.8 GPa). The ultramylonite consists of feldspathic layers and domains of amphibole + quartz + calcite, which result from hydration reactions of magmatic clinopyroxene. The average grain size in both domains is <25 mm. Microstructural observations and electron backscatter diffraction analysis are consistent with diffusion <span class="hlt">creep</span> as the dominant <span class="hlt">deformation</span> mechanism in both domains. Festoons of isolated quartz grains define C'-type bands in feldspathic layers. These quartz grains do not show a crystallographic preferred orientation. The alignment of quartz grains is parallel to the preferred elongation of pores in the ultramylonites, as evidenced from synchrotron X-ray microtomography. Such C'-type bands are interpreted as <span class="hlt">creep</span> cavitation bands resulting from diffusion <span class="hlt">creep</span> <span class="hlt">deformation</span> associated with grain boundary sliding. Mass-balance calculation indicates a 2% volume increase during the protolith-ultramylonite transformation, which is consistent with synkinematic formation of <span class="hlt">creep</span> cavities producing dilatancy. Thus, this study presents evidence that <span class="hlt">creep</span> cavitation bands may control deep crustal porosity and fluid flow. Nucleation of new phases in <span class="hlt">creep</span> cavitation bands inhibits grain growth and enhances the activity of grain size–sensitive <span class="hlt">creep</span>, thereby stabilizing strain localization in the polymineralic ultramylonites.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013ApPhL.103d3118Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013ApPhL.103d3118Y"><span id="translatedtitle">Compressive-tensile <span class="hlt">deformation</span> of nanocrystalline nickel at high pressure and <span class="hlt">temperature</span> conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yu, Xiaohui; Wang, Yuejian; Zhang, Jianzhong; Xu, Hongwu; Zhao, Yusheng</p> <p>2013-07-01</p> <p>We conducted uniaxial compressive and tensile <span class="hlt">deformation</span> on nanocrystalline Ni at a confining pressure of 6 GPa and <span class="hlt">temperatures</span> up to 900 °C. The determined compressive yield strength is 0.8 GPa, identical to the tensile yield strength obtained in the same <span class="hlt">deformation</span> experiment, indicating that the Bauschinger effect is absent in nanocrystalline Ni. The yield strength obtained at 6 GPa is also comparable to that at ambient pressure, suggesting that the dislocation-mediated mechanisms are no longer activated during plastic <span class="hlt">deformation</span>. Based on peak intensity and peak width analyses, grain rotation and grain growth are main factors underlying the plastic <span class="hlt">deformation</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19830041055&hterms=limites&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dlimites','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19830041055&hterms=limites&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dlimites"><span id="translatedtitle"><span class="hlt">Creep</span> of plasma-sprayed-ZrO2 thermal-barrier coatings</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Firestone, R. F.; Logan, W. R.; Adams, J. W.; Bill, R. C., Jr.</p> <p>1982-01-01</p> <p>Specimens of plasma-sprayed-zirconia thermal-barrier coatings with three different porosities and different initial particle sizes were <span class="hlt">deformed</span> in compression at initial loads of 6900, 13,800, and 24,100 kPa (1000, 2000, and 3500 psi) and <span class="hlt">temperatures</span> of 1100, 1250, and 1400 C. The coatings were stabilized with lime, MgO, and two different concentrations of Y2O3. <span class="hlt">Creep</span> began as soon as the load was applied and continued at a constantly decreasing rate until the load was removed. <span class="hlt">Temperature</span> and stabilization had a pronounced effect on <span class="hlt">creep</span> rate while the stress, particle size, and porosity had a lesser effect. <span class="hlt">Creep</span> <span class="hlt">deformation</span> was due to cracking and particle sliding.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013JMEP...22.2019Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013JMEP...22.2019Z"><span id="translatedtitle">The Effect of <span class="hlt">Temperature</span> Condition on Material <span class="hlt">Deformation</span> and Die Wear</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhi, Jia; Jie, Zhou; Jin-jin, Ji; Liang, Huang; Hai, Yang</p> <p>2013-07-01</p> <p>The characteristics of <span class="hlt">temperature</span> change on die and billet are very complex during the <span class="hlt">deformation</span> process because of the interaction between them and some unstable external factors. In this paper, the numerical simulation model for the crank shaft die forging was established by means of the rigid-plastic FEM method. The model was validated by optical non-contact 3D measurement—ATOS. Based on available research results, this paper explored the effect of <span class="hlt">temperature</span> conditions on material <span class="hlt">deformation</span> and die wear. Three parameters, press velocity and initial <span class="hlt">temperature</span> of billet and die, were chosen to illustrate the effects. From the experimental results, the effect of process parameters on <span class="hlt">deformation</span> ability of the material is simple, while the effect on die wear is relatively complicated. The press velocity plays an important role on die wear when the initial <span class="hlt">temperature</span> of the billet has larger influence on material <span class="hlt">deformation</span>. A conclusion can be drawn that when the initial <span class="hlt">temperature</span> of the billet is 1100 °C, the initial <span class="hlt">temperature</span> of the die is 250 °C, and the velocity is kept in the range of 200-300 mm/s, the optimum solution for <span class="hlt">deformation</span> ability of the material and die wear can be obtained. It is possible for the conclusion to be extended further for the control of <span class="hlt">temperature</span> condition to optimize die life and material <span class="hlt">deformation</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5154547','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5154547"><span id="translatedtitle">Analysis of elevated-<span class="hlt">temperature</span> tensile and <span class="hlt">creep</span> properties of normalized and tempered 2 1/4 Cr-1 Mo steel</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Booker, M.K.; Booker, B.L.P.; Swindeman, R.W.</p> <p>1982-01-01</p> <p>Tensile and <span class="hlt">creep</span> data were collected for normalized and tempered 2 1/4 Cr-1 Mo steel from American, Japanese, British, French, and German sources. These included <span class="hlt">creep</span> data obtained at <span class="hlt">temperatures</span> from 427 to 600/sup 0/C (800 to 1112/sup 0/F) and tensile data from room <span class="hlt">temperature</span> to 550/sup 0/C (1022/sup 0/F). Properties examined included yield strength, ultimate tensile strength, 10/sup 5/-h <span class="hlt">creep</span>-rupture strength, and 10/sup -5/%/h <span class="hlt">creep</span> strength. These are the properties used in setting allowable stresses for Section VIII, Division 1, of the ASME Boiler and Pressure Vessel Code. The data were analyzed by using lot-centered regression approaches that yielded expressions for the variations in the above properties with loading condition, as well as accounting for lot-to-lot variations in properties. No indications were found of systematic differences in any of the properties examined for data from the different countries. However, the estimated allowable stresses from this investigation fell up to 10% below those currently given for this material in the ASME Code. Several possible reasons were cited for the differences, and we concluded that our results are not overly conservative. On the other hand, there is no direct evidence that the current code allowable stresses are insufficiently conservative, since those stresses rely on factors (such as service experience) other than experimental data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015HTMP...34..111R&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2015HTMP...34..111R&link_type=ABSTRACT"><span id="translatedtitle">Life Estimation and <span class="hlt">Creep</span> Damage Quantification of Service Exposed Reformer Tube</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Raj, A.; Roy, N.; Roy, B. N.; Ray, A. K.</p> <p>2015-11-01</p> <p>This paper deals with evaluation of <span class="hlt">creep</span> damage of ~11 years service exposed primary hydrogen reformer tube made of HP-40 grade of steel in a petrochemical industry, which has been carried out in terms of Kachanav's continuum damage mechanics (CDM) model (K-model) and Bogdanoff model (B-model) based on Markov process. Residual life of the tubes was estimated based on hot tensile, conventional <span class="hlt">creep</span> <span class="hlt">deformation</span> under identical test conditions, optical microscopy and fractography. Accumulation of damage due to <span class="hlt">creep</span> has been quantified through microstructural studies. The as received tubes did not reveal any degradation in the material like <span class="hlt">creep</span> cavitation or voids, but there was indeed loss of tensile strength from room <span class="hlt">temperature</span> to 870°C for the bottom portion of the tube due to ageing and overheating. Scatter in <span class="hlt">creep</span> <span class="hlt">deformation</span> behaviour of the material is probably due to variation in mode of fracture and scatter in voids. From statistical point of view, Weibull distribution pattern for analysing probability of rupture due to void area shifts with increase in true strain towards the higher population of void. The estimation of mean time to reach a specific damage state from K- model and B-model is in close agreement with that of experimental data and can describe the sudden changes of the <span class="hlt">creep</span> damage in the tertiary region as well. A remnant life of >10 years is estimated at the operating stress-<span class="hlt">temperature</span> conditions of the top as well as bottom portion of the tube.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/939198','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/939198"><span id="translatedtitle">MOLECULAR DYNAMICS STUDY OF DIFFUSIONAL <span class="hlt">CREEP</span> IN NANOCRYSTALLINE UO2</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Tapan G. Desai; Paul C. Millett; Dieter Wolf</p> <p>2008-09-01</p> <p>We present the results of molecular dynamics (MD) simulations to study hightemperature <span class="hlt">deformation</span> of nanocrystalline UO2. In qualitative agreement with experimental observations, the oxygen sub-lattice undergoes a structural transition at a <span class="hlt">temperature</span> of about 2200 K (i.e., well below the melting point of 3450 K of our model system), whereas the uranium sub-lattice remains unchanged all the way up to melting. At <span class="hlt">temperatures</span> well above this structural transition, columnar nanocrystalline model microstructures with a uniform grain size and grain shape were subjected to constantstress loading at levels low enough to avoid microcracking and dislocation nucleation from the GBs. Our simulations reveal that in the absence of grain growth, the material <span class="hlt">deforms</span> via GB diffusion <span class="hlt">creep</span> (also known as Coble <span class="hlt">creep</span>). Analysis of the underlying self-diffusion behavior in undeformed nanocrystalline UO2 reveals that, on our MD time scale, the uranium ions diffuse only via the grain boundaries (GBs) whereas the much faster moving oxygen ions diffuse through both the lattice and the GBs. As expected for the Coble-<span class="hlt">creep</span> mechanism, the <span class="hlt">creep</span> activation energy agrees well with that for GB diffusion of the slowest moving species, i.e., of the uranium ions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20110011967','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20110011967"><span id="translatedtitle"><span class="hlt">Creep</span> Measurement Video Extensometer</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Jaster, Mark; Vickerman, Mary; Padula, Santo, II; Juhas, John</p> <p>2011-01-01</p> <p>Understanding material behavior under load is critical to the efficient and accurate design of advanced aircraft and spacecraft. Technologies such as the one disclosed here allow accurate <span class="hlt">creep</span> measurements to be taken automatically, reducing error. The goal was to develop a non-contact, automated system capable of capturing images that could subsequently be processed to obtain the strain characteristics of these materials during <span class="hlt">deformation</span>, while maintaining adequate resolution to capture the true <span class="hlt">deformation</span> response of the material. The measurement system comprises a high-resolution digital camera, computer, and software that work collectively to interpret the image.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/809087','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/809087"><span id="translatedtitle"><span class="hlt">Creep</span> Resistant Zinc Alloy</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Frank E. Goodwin</p> <p>2002-12-31</p> <p>This report covers the development of Hot Chamber Die Castable Zinc Alloys with High <span class="hlt">Creep</span> Strengths. This project commenced in 2000, with the primary objective of developing a hot chamber zinc die-casting alloy, capable of satisfactory service at 140 C. The core objectives of the development program were to: (1) fill in missing alloy data areas and develop a more complete empirical model of the influence of alloy composition on <span class="hlt">creep</span> strength and other selected properties, and (2) based on the results from this model, examine promising alloy composition areas, for further development and for meeting the property combination targets, with the view to designing an optimized alloy composition. The target properties identified by ILZRO for an improved <span class="hlt">creep</span> resistant zinc die-casting alloy were identified as follows: (1) <span class="hlt">temperature</span> capability of 1470 C; (2) <span class="hlt">creep</span> stress of 31 MPa (4500 psi); (3) exposure time of 1000 hours; and (4) maximum <span class="hlt">creep</span> elongation under these conditions of 1%. The project was broadly divided into three tasks: (1) Task 1--General and Modeling, covering Experimental design of a first batch of alloys, alloy preparation and characterization. (2) Task 2--Refinement and Optimization, covering Experimental design of a second batch of alloys. (3) Task 3--<span class="hlt">Creep</span> Testing and Technology transfer, covering the finalization of testing and the transfer of technology to the Zinc industry should have at least one improved alloy result from this work.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/885787','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/885787"><span id="translatedtitle">Development of Advanced Corrosion-Resistant Fe-Cr-Ni Austenitic Stainless Steel Alloy with Improved High <span class="hlt">Temperature</span> Strenth and <span class="hlt">Creep</span>-Resistance</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Maziasz, PJ</p> <p>2004-09-30</p> <p>In February of 1999, a Cooperative Research and Development Agreement (CRADA) was undertaken between Oak Ridge National Laboratory (ORNL) and Special Metals Corporation-Huntington Alloys (formerly INCO Alloys International, Inc.) to develop a modified wrought austenitic stainless alloy with considerably more strength and corrosion resistance than alloy 800H or 800HT, but with otherwise similar engineering and application characteristics. Alloy 800H and related alloys have extensive use in coal flue gas environments, as well as for tubing or structural components in chemical and petrochemical applications. The main concept of the project was make small, deliberate elemental microalloying additions to this Fe-based alloy to produce, with proper processing, fine stable carbide dispersions for enhanced high <span class="hlt">temperature</span> <span class="hlt">creep</span>-strength and rupture resistance, with similar or better oxidation/corrosion resistance. The project began with alloy 803, a Fe-25Cr-35NiTi,Nb alloy recently developed by INCO, as the base alloy for modification. Smaller commercial developmental alloy heats were produced by Special Metals. At the end of the project, three rounds of alloy development had produced a modified 803 alloy with significantly better <span class="hlt">creep</span> resistance above 815EC (1500EC) than standard alloy 803 in the solution-annealed (SA) condition. The new upgraded 803 alloy also had the potential for a processing boost in that <span class="hlt">creep</span> resistance for certain kinds of manufactured components that was not found in the standard alloy. The upgraded 803 alloy showed similar or slightly better oxidation and corrosion resistance relative to standard 803. <span class="hlt">Creep</span> strength and oxidation/corrosion resistance of the upgraded 803 alloy were significantly better than found in alloy 800H, as originally intended. The CRADA was terminated in February 2003. A contributing factor was Special Metals Corporation being in Chapter 11 Bankruptcy. Additional testing, further commercial scale-up, and any potential</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JMEP...23.1954J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JMEP...23.1954J"><span id="translatedtitle">Effect of High-<span class="hlt">Temperature</span> Severe Plastic <span class="hlt">Deformation</span> on Microstructure and Mechanical Properties of IF Steel</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jindal, Vikas; Rupa, P. K. P.; Mandal, G. K.; Srivastava, V. C.</p> <p>2014-06-01</p> <p>Extensive research work has been carried out on interstitial-free steel to understand its response to <span class="hlt">deformation</span>; particularly, the behavior during severe plastic <span class="hlt">deformation</span> (SPD). However, most of these studies were mainly undertaken in the ferritic regime. The present investigation reports the initial results of our attempt to employ accumulative roll bonding (ARB), one of the variants of SPD, at a high <span class="hlt">temperature</span> (950 °C). A considerable grain refinement has been observed, which may be attributed to the severity of <span class="hlt">deformation</span> and recrystallisation at high <span class="hlt">temperatures</span>. Nanoindentation tests have been performed at various stages of ARB process to understand the evolution of mechanical properties.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015RuMet2015..317B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015RuMet2015..317B"><span id="translatedtitle">Low-cycle fatigue of a VZh175 high-<span class="hlt">temperature</span> alloy under elastoplastic <span class="hlt">deformation</span> conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Belyaev, M. S.; Terent'ev, V. F.; Bakradze, M. M.; Gorbovets, M. A.; Gol'dberg, M. A.</p> <p>2015-04-01</p> <p>The low-cycle fatigue of a VZh175 nickel superalloy is studied under conditions of complete <span class="hlt">deformation</span> per loading cycle at an initial cycle asymmetry R = 0, a <span class="hlt">deformation</span> amplitude ɛa = 0.4-0.6%, and a <span class="hlt">temperature</span> of 20 and 650°C. The specific features of cyclic hardening/softening of the alloy under these conditions are detected. The mechanisms of fatigue crack nucleation and growth are analyzed as functions of the <span class="hlt">deformation</span> amplitude and the test <span class="hlt">temperature</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4614441','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4614441"><span id="translatedtitle">On rate-dependent polycrystal <span class="hlt">deformation</span>: the <span class="hlt">temperature</span> sensitivity of cold dwell fatigue</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Zhang, Zhen; Cuddihy, M. A.; Dunne, F. P. E.</p> <p>2015-01-01</p> <p>A <span class="hlt">temperature</span> and rate-dependent crystal plasticity framework has been used to examine the <span class="hlt">temperature</span> sensitivity of stress relaxation, <span class="hlt">creep</span> and load shedding in model Ti-6Al polycrystal behaviour under dwell fatigue conditions. A <span class="hlt">temperature</span> close to 120°C is found to lead to the strongest stress redistribution and load shedding, resulting from the coupling between crystallographic slip rate and slip system dislocation hardening. For <span class="hlt">temperatures</span> in excess of about 230°C, grain-level load shedding from soft to hard grains diminishes because of the more rapid stress relaxation, leading ultimately to the diminution of the load shedding and hence, it is argued, the elimination of the dwell debit. Under conditions of cyclic stress dwell, at <span class="hlt">temperatures</span> between 20°C and 230°C for which load shedding occurs, the rate-dependent accumulation of local slip by ratcheting is shown to lead to the progressive cycle-by-cycle redistribution of stress from soft to hard grains. This phenomenon is termed cyclic load shedding since it also depends on the material's <span class="hlt">creep</span> response, but develops over and above the well-known dwell load shedding, thus providing an additional rationale for the incubation of facet nucleation. PMID:26528078</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003PhRvB..67n4101G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003PhRvB..67n4101G"><span id="translatedtitle">Model of high-<span class="hlt">temperature</span> plastic <span class="hlt">deformation</span> of nanocrystalline materials: Application to yttria tetragonal zirconia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gómez-García, D.; Lorenzo-Martín, C.; Muñoz-Bernabé, A.; Domínguez-Rodríguez, A.</p> <p>2003-04-01</p> <p>The possibility of the influence of segregation-induced local electric fields in the bulk diffusion of the species controlling the plastic <span class="hlt">deformation</span> of nanocrystalline materials has been pointed out. Until now, there is only a model applicable to the case of a monodimensional system. In spite of its simplicity, it predicts a significative influence of a local electric field in <span class="hlt">creep</span>. Our work develops a different model applicable to three-dimensional systems. It takes as a starting point the diffusional model, and it can be generalized to those systems in which the grain-boundary sliding model accommodated by diffusional processes accurately describes plasticity in the submicron range of grain size. The range of validity, as well as the different behavior of nanocrystalline materials from the submicron ones is discussed. Preliminary results are in good agreement with the published data for yttria tetragonal zirconia (YTZP) nanocrystalline ceramics.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/971584','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/971584"><span id="translatedtitle">Analysis of Tensile <span class="hlt">Deformation</span> and Failure in Austenitic Stainless Steels: Part I- <span class="hlt">Temperature</span> Dependence</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kim, Jin Weon; Byun, Thak Sang</p> <p>2010-01-01</p> <p>This paper describes the <span class="hlt">temperature</span> dependence of <span class="hlt">deformation</span> and failure behaviors in the austenitic stainless steels (annealed 304, 316, 316LN, and 20% cold-worked 316LN) in terms of equivalent true stress-true strain curves. The true stress-true strain curves up to the final fracture were calculated from the tensile test data obtained at -150 ~ 450oC using an iterative technique of finite element simulation. Analysis was largely focused on the necking <span class="hlt">deformation</span> and fracture: Key parameters such as the strain hardening rate, equivalent fracture stress, fracture strain, and tensile fracture energy were evaluated, and their <span class="hlt">temperature</span> dependencies were investigated. It was shown that a significantly high strain hardening rate was still retained during unstable <span class="hlt">deformation</span> although overall strain hardening rate beyond the onset of necking was lower than that of the uniform <span class="hlt">deformation</span>. The values of the parameters except for fracture strain decreased with <span class="hlt">temperature</span> up to 200oC and were saturated as the <span class="hlt">temperature</span> came close to the maximum test <span class="hlt">temperature</span> 450oC. The fracture strain increased and had a maximum at -50oC to 20oC before decreasing with <span class="hlt">temperature</span>. It was explained that these <span class="hlt">temperature</span> dependencies of fracture properties were associated with a change in the dominant strain hardening mechanism with test <span class="hlt">temperature</span>. Also, it was seen that the pre-straining of material has little effect on the strain hardening rate during necking <span class="hlt">deformation</span> and on fracture properties.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/6782953','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/6782953"><span id="translatedtitle">Model for transient <span class="hlt">creep</span> of southeastern New Mexico rock salt</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Herrmann, W; Wawersik, W R; Lauson, H S</p> <p>1980-11-01</p> <p>In a previous analysis, existing experimental data pertaining to <span class="hlt">creep</span> tests on rock salt from the Salado formation of S.E. New Mexico were fitted to an exponential transient <span class="hlt">creep</span> law. While very early time portions of <span class="hlt">creep</span> strain histories were not fitted very well for tests at low <span class="hlt">temperatures</span> and stresses, initial <span class="hlt">creep</span> rates in particular generally being underestimated, the exponential <span class="hlt">creep</span> law has the property that the transient <span class="hlt">creep</span> strain approaches a finite limit with time, and is therefore desirable from a <span class="hlt">creep</span> modelling point of view. In this report, an analysis of transient <span class="hlt">creep</span> is made. It is found that exponential transient <span class="hlt">creep</span> can be related to steady-state <span class="hlt">creep</span> through a universal <span class="hlt">creep</span> curve. The resultant description is convenient for <span class="hlt">creep</span> analyses where very early time behavior is not important.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/874043','DOE-PATENT-XML'); return false;" href="http://www.osti.gov/scitech/servlets/purl/874043"><span id="translatedtitle">Cryogenic <span class="hlt">deformation</span> of high <span class="hlt">temperature</span> superconductive composite structures</span></a></p> <p><a target="_blank" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p>Roberts, Peter R.; Michels, William; Bingert, John F.</p> <p>2001-01-01</p> <p>An improvement in a process of preparing a composite high <span class="hlt">temperature</span> oxide superconductive wire is provided and involves conducting at least one cross-sectional reduction step in the processing preparation of the wire at sub-ambient <span class="hlt">temperatures</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19900019424','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19900019424"><span id="translatedtitle">High-<span class="hlt">temperature</span> <span class="hlt">deformation</span> and microstructural analysis for Si3N4-Sc2O3</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cheong, Deock-Soo; Sanders, William A.</p> <p>1990-01-01</p> <p>It was indicated that Si3N4 doped with Sc2O3 may exhibit high <span class="hlt">temperature</span> mechanical properties superior to Si3N4 systems with various other oxide sintered additives. High <span class="hlt">temperature</span> <span class="hlt">deformation</span> of samples was studied by characterizing the microstructures before and after <span class="hlt">deformation</span>. It was found that elements of the additive, such as Sc and O, exist in small amounts at very thin grain boundary layers and most of them stay in secondary phases at triple and multiple grain boundary junctions. These secondary phases are devitrified as crystalline Sc2Si2O7. <span class="hlt">Deformation</span> of the samples was dominated by cavitational processes rather than movements of dislocations. Thus the excellent <span class="hlt">deformation</span> resistance of the samples at high <span class="hlt">temperature</span> can be attributed to the very small thickness of the grain boundary layers and the crystalline secondary phase.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22476156','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22476156"><span id="translatedtitle">Evaluation of microstructure anisotropy on room and medium <span class="hlt">temperature</span> ECAP <span class="hlt">deformed</span> F138 steel</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>De Vincentis, N.S.; Kliauga, A.; Ferrante, M.; Avalos, M.; Brokmeier, H.-G.; Bolmaro, R.E.</p> <p>2015-09-15</p> <p>The microstructure developed during severe plastic <span class="hlt">deformation</span> results in improved mechanical properties because of the decrease in domain sizes and accumulation of defects, mainly dislocation arrays. The characteristic <span class="hlt">deformation</span> stages observed in low stacking fault energy (SFE) face centered cubic (FCC) materials are highly influenced by the development of the primary and secondary twinning that compete with dislocation glide. In this paper, a low SFE F138 stainless steel is <span class="hlt">deformed</span> by equal channel angular pressing (ECAP) up to 4 passes at room <span class="hlt">temperature</span> (RT) and at 300 °C to compare the grain refinement and twin boundary development with increasing <span class="hlt">deformation</span>. Tensile tests were performed to determine the <span class="hlt">deformation</span> stages reached by the material before and after ECAP <span class="hlt">deformation</span>, and the resulting microstructure was observed by TEM. X-ray diffraction and EBSD, average technique the first and local the second one, were used to quantify the microstructural changes, allowing the determination of diffraction domain sizes, dislocation and stacking fault densities and misorientation indices, which lead to a complete analysis of the <span class="hlt">deformation</span> introduced in the material, with comparative correlations between various microstructural parameters. - Highlights: • The microstructure of ECAP pressed F138 steel was studied using TEM, EBSD and XRD. • Increasing <span class="hlt">deformation</span> reduced domain sizes and increased dislocation densities. • Dislocation array compactness and misorientation increased with higher <span class="hlt">deformation</span>. • Largest dislocation densities, mostly screw, match with simultaneous activation of twins. • Several correlations among microstructural features and parameters have been disclosed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2002LTP....28..864B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2002LTP....28..864B"><span id="translatedtitle">Low-<span class="hlt">temperature</span> <span class="hlt">deformation</span> and fracture of bulk nanostructural titanium obtained by intense plastic <span class="hlt">deformation</span> using equal channel angular pressing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bengus, V. Z.; Tabachnikova, E. D.; Natsik, V. D.; Mishkuf, Ä.¬.; Chakh, K.; Stolyarov, V. V.; Valiev, R. Z.</p> <p>2002-11-01</p> <p>The low-<span class="hlt">temperature</span> plasticity and fracture of polycrystals of coarse-grained (CG) and nanostructural (NS) technical-grade titanium of two structural modifications with grain size 0.3 and 0.1 μm, which were prepared by equal channel angular pressing (ECAP) with additional thermomechanical treatment are studied. The measurements are performed at <span class="hlt">temperatures</span> 300, 77, and 4.2 K with uniaxial compression at <span class="hlt">deformation</span> rate 4×10-4 s-1. The "stress-plastic <span class="hlt">deformation</span>" hardening curves are obtained, the macroscopic yield stress, and the ultimate plasticity are measured for samples with compression axis orientations parallel and transverse to the ECAP axis. It is found that the yield stress for NS titanium is 1.5-2 times higher than for CG titanium and the yield stress on cooling from 300 to 4.2 K. Plasticity anisotropy is also observed in NS titanium—the yield stress is 1.2-1.5 times greater when the compression axis is oriented perpendicular to the ESAP axis than for parallel orientation. The ultimate plasticity with such changes in the structure of samples and under the experimental conditions systematically decreases, but the <span class="hlt">deformation</span> to fracture remains above 4%. Nanostructural titanium does not show cold-brittleness right down to liquid-helium <span class="hlt">temperatures</span>, but at 4.2 K plastic flow becomes jumplike, just as in CG titanium. It is established that for low-<span class="hlt">temperature</span> uniaxial compression NS titanium fractures as a result of unstable plastic shear accompanied by local adiabatic heating of the material. This phenomenon is not characteristic of CG titanium. A study of the morphology of the shear-fracture surfaces using a scanning electron microsope shows a characteristic "vein" pattern, attesting to local heating at <span class="hlt">temperatures</span> ⩾800 °C. It is established that plastic <span class="hlt">deformation</span> in NS titanium is thermally activated at low <span class="hlt">temperatures</span>. It is shown that microstructural internal stresses due to thermal anisotropy and possible microtwinning affect the yield</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1087118','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1087118"><span id="translatedtitle">Corrosion and <span class="hlt">Creep</span> of Candidate Alloys in High <span class="hlt">Temperature</span> Helium and Steam Environments for the NGNP</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Was, Gary; Jones, J. W.</p> <p>2013-06-21</p> <p>This project aims to understand the processes by which candidate materials degrade in He and supercritical water/steam environments characteristic of the current NGNP design. We will focus on understanding the roles of <span class="hlt">temperature</span>, and carbon and oxygen potential in the 750-850 degree C range on both uniform oxidation and selective internal oxidation along grain boundaries in alloys 617 and 800H in supercritical water in the <span class="hlt">temperature</span> range 500-600 degree C; and examining the application of static and cyclic stresses in combination with impure He environments in the <span class="hlt">temperature</span> rang 750-850 degree C; and examining the application of static and cyclic stresses in combination with impure He environments in the <span class="hlt">temperature</span> range 750-850 degree C over a range of oxygen and carbon potentials in helium. Combined, these studies wil elucidate the potential high damage rate processes in environments and alloys relevant to the NGNP.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhDT........40K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhDT........40K"><span id="translatedtitle"><span class="hlt">Creep</span>, fatigue and <span class="hlt">creep</span>-fatigue interactions in modified 9% Chromium - 1% Molybdenum (P91) steels</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kalyanasundaram, Valliappa</p> <p></p> <p>Grade P91 steel, from the class of advanced high-chrome ferritic steels, is one of the preferred materials for many elevated <span class="hlt">temperature</span> structural components. <span class="hlt">Creep</span>-fatigue (C-F) interactions, along with oxidation, can accelerate the kinetics of damage accumulation and consequently reduce such components' life. Hence, reliable C-F test data is required for meticulous consideration of C-F interactions and oxidation, which in turn is vital for sound design practices. It is also imperative to develop analytical constitutive models that can simulate and predict material response under various long-term in-service conditions using experimental data from short-term laboratory experiments. Consequently, the major objectives of the proposed research are to characterize the <span class="hlt">creep</span>, fatigue and C-F behavior of grade P91 steels at 625 C and develop robust constitutive models for simulating/predicting their microstructural response under different loading conditions. This work will utilize experimental data from 16 laboratories worldwide that conducted tests (<span class="hlt">creep</span>, fatigue and C-F) on grade P91 steel at 625°C in a round-robin (RR) program. Along with 7 <span class="hlt">creep</span> <span class="hlt">deformation</span> and rupture tests, 32 pure fatigue and 46 C-F tests from the RR are considered in this work. A phenomenological constitutive model formulated in this work needs just five fitting parameters to simulate/predict the monotonic, pure fatigue and C-F behavior of grade P91 at 625 C. A modified version of an existing constitutive model is also presented for particularly simulating its isothermal <span class="hlt">creep</span> <span class="hlt">deformation</span> and rupture behavior. Experimental results indicate that specimen C-F lives, as measured by the 2% load drop criterion, seem to decrease with increasing strain ranges and increasing hold times at 625°C. Metallographic assessment of the tested specimens shows that the damage mode in both pure fatigue and 600 seconds hold time cyclic tests is predominantly transgranular fatigue with some presence of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1980pca..rept.....G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1980pca..rept.....G"><span id="translatedtitle">Long-term <span class="hlt">creep</span> of Hanford concrete at 250 deg F and 350 deg F</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gillen, M.</p> <p>1980-10-01</p> <p>Test results described cover the <span class="hlt">creep</span> behavior of Hanford concretes at elevated <span class="hlt">temperatures</span>. Two each of 6 by 12 in. concrete cylinders were subjected to static compressive loads of 500 psi at 350 F and 1500 psi at 250 F and 350 F. Test cylinders were cast with materials and mix designs similar to those used in Hanford concrete structures. Effects of load and <span class="hlt">temperature</span> on <span class="hlt">deformation</span> of Hanford concrete are discussed. Increased static load reduced the amount of thermal strain when cylinders were heated above ambient. At 350 F, the magnitude of <span class="hlt">creep</span> strain of cylinders increased with increased static load. At a test load of 1500 psi, magnitude of <span class="hlt">creep</span> strain increased with increased <span class="hlt">temperature</span>. <span class="hlt">Creep</span> data were satisfactorily modeled with an expression of the form <span class="hlt">creep</span> strain = A log10 (t) + B, where <span class="hlt">creep</span> strain is in millionths, and t is time at test <span class="hlt">temperature</span>, in days. Values for the coefficient, A, varied from 255.6 to 286.9. Magnitude of the constant B, ranged from 182.1 to 718.6.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1997JEMat..26..839M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1997JEMat..26..839M"><span id="translatedtitle">Tensile, <span class="hlt">creep</span>, and ABI tests on sn5%sb solder for mechanical property evaluation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Murty, K. Linga; Haggag, Fahmy M.; Mahidhara, Rao K.</p> <p>1997-07-01</p> <p>Sn5%Sb is one of the materials considered for replacing lead containing alloys for soldering in electronic packaging. We evaluated the tensile properties of the bulk material at varied strain-rates and <span class="hlt">temperatures</span> (to 473K) to determine the underlying <span class="hlt">deformation</span> mechanisms. Stress exponents of about three and seven were observed at low and high stresses, respectively, and very low activation energies for <span class="hlt">creep</span> (about 16.7 and 37.7 kJ/mole) were noted. A maximum ductility of about 350% was noted at ambient <span class="hlt">temperature</span>. <span class="hlt">Creep</span> tests performed in the same <span class="hlt">temperature</span> regime also showed two distinct regions, albeit with slightly different exponents (three and five) and activation energy (about 54.4 kJ/mole). Ball indentation tests were performed on the shoulder portions of the <span class="hlt">creep</span> samples (prior to <span class="hlt">creep</span> tests) using a Stress-Strain Microprobe@ (Advanced Technology Corporation) at varied indentation rates (strain-rates). The automated ball indentation (ABI) data were at relatively high strain-rates; however, they were in excellent agreement with <span class="hlt">creep</span> data, while both these results deviated from the tensile test data. Work is planned to perform <span class="hlt">creep</span> at high stresses at ambient and extend ABI tests to elevated <span class="hlt">temperatures</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920024899','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920024899"><span id="translatedtitle">Computational simulation of probabilistic lifetime strength for aerospace materials subjected to high <span class="hlt">temperature</span>, mechanical fatigue, <span class="hlt">creep</span>, and thermal fatigue</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Boyce, Lola; Bast, Callie C.; Trimble, Greg A.</p> <p>1992-01-01</p> <p>The results of a fourth year effort of a research program conducted for NASA-LeRC by The University of Texas at San Antonio (UTSA) are presented. The research included on-going development of methodology that provides probabilistic lifetime strength of aerospace materials via computational simulation. A probabilistic material strength degradation model, in the form of a randomized multifactor interaction equation, is postulated for strength degradation of structural components of aerospace propulsion systems subjected to a number of effects or primitive variables. These primitive variables may include high <span class="hlt">temperature</span>, fatigue, or <span class="hlt">creep</span>. In most cases, strength is reduced as a result of the action of a variable. This multifactor interaction strength degradation equation was randomized and is included in the computer program, PROMISC. Also included in the research is the development of methodology to calibrate the above-described constitutive equation using actual experimental materials data together with regression analysis of that data, thereby predicting values for the empirical material constants for each effect or primitive variable. This regression methodology is included in the computer program, PROMISC. Actual experimental materials data were obtained from industry and the open literature for materials typically for applications in aerospace propulsion system components. Material data for Inconel 718 was analyzed using the developed methodology.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930004102','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930004102"><span id="translatedtitle">Computational simulation of probabilistic lifetime strength for aerospace materials subjected to high <span class="hlt">temperature</span>, mechanical fatigue, <span class="hlt">creep</span> and thermal fatigue</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Boyce, Lola; Bast, Callie C.; Trimble, Greg A.</p> <p>1992-01-01</p> <p>This report presents the results of a fourth year effort of a research program, conducted for NASA-LeRC by the University of Texas at San Antonio (UTSA). The research included on-going development of methodology that provides probabilistic lifetime strength of aerospace materials via computational simulation. A probabilistic material strength degradation model, in the form of a randomized multifactor interaction equation, is postulated for strength degradation of structural components of aerospace propulsion systems subject to a number of effects or primitive variables. These primitive variables may include high <span class="hlt">temperature</span>, fatigue or <span class="hlt">creep</span>. In most cases, strength is reduced as a result of the action of a variable. This multifactor interaction strength degradation equation has been randomized and is included in the computer program, PROMISS. Also included in the research is the development of methodology to calibrate the above-described constitutive equation using actual experimental materials data together with regression analysis of that data, thereby predicting values for the empirical material constants for each effect or primitive variable. This regression methodology is included in the computer program, PROMISC. Actual experimental materials data were obtained from industry and the open literature for materials typically for applications in aerospace propulsion system components. Material data for Inconel 718 has been analyzed using the developed methodology.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20010064392','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20010064392"><span id="translatedtitle"><span class="hlt">Creep</span>-Fatigue Interaction Testing</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Halford, Gary R.</p> <p>2001-01-01</p> <p>Fatigue fives in metals are nominally time independent below 0.5 T(sub Melt). At higher <span class="hlt">temperatures</span>, fatigue lives are altered due to time-dependent, thermally activated <span class="hlt">creep</span>. Conversely, <span class="hlt">creep</span> rates are altered by super. imposed fatigue loading. <span class="hlt">Creep</span> and fatigue generally interact synergistically to reduce material lifetime. Their interaction, therefore, is of importance to structural durability of high-<span class="hlt">temperature</span> structures such as nuclear reactors, reusable rocket engines, gas turbine engines, terrestrial steam turbines, pressure vessel and piping components, casting dies, molds for plastics, and pollution control devices. Safety and lifecycle costs force designers to quantify these interactions. Analytical and experimental approaches to <span class="hlt">creep</span>-fatigue began in the era following World War II. In this article experimental and life prediction approaches are reviewed for assessing <span class="hlt">creep</span>-fatigue interactions of metallic materials. Mechanistic models are also discussed briefly.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JGRB..120.6039T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JGRB..120.6039T"><span id="translatedtitle"><span class="hlt">Creep</span> behavior of Fe-bearing olivine under hydrous conditions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tasaka, Miki; Zimmerman, Mark E.; Kohlstedt, David L.</p> <p>2015-09-01</p> <p>To understand the effect of iron content on the <span class="hlt">creep</span> behavior of olivine, (MgxFe(1 - x))2SiO4, under hydrous conditions, we have conducted tri-axial compressive <span class="hlt">creep</span> experiments on samples of polycrystalline olivine with Mg contents of x = 0.53, 0.77, 0.90, and 1. Samples were <span class="hlt">deformed</span> at stresses of 25 to 320 MPa, <span class="hlt">temperatures</span> of 1050° to 1200°C, a confining pressure of 300 MPa, and a water fugacity of 300 MPa using a gas-medium high-pressure apparatus. Under hydrous conditions, our results yield the following expression for strain rate as a function of iron content for 0.53 ≤ x ≤ 0.90 in the dislocation <span class="hlt">creep</span> regime: ɛ˙=ɛ˙0.90((1-x/0.1))1/2exp[226×1030.9-x/RT]. In this equation, the strain rate of San Carlos olivine, ɛ˙0.90, is a function of T, σ, and fH2O. As previously shown for anhydrous conditions, an increase in iron content directly increases <span class="hlt">creep</span> rate. In addition, an increase in iron content increases hydrogen solubility and therefore indirectly increases <span class="hlt">creep</span> rate. This flow law allows us to extrapolate our results to a wide range of mantle conditions, not only for Earth's mantle but also for the mantle of Mars.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012SPIE.8563E..0HL','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012SPIE.8563E..0HL"><span id="translatedtitle">Continuous turbine blade <span class="hlt">creep</span> measurement based on Moiré</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Liao, Yi; Tait, Robert; Harding, Kevin; Nieters, Edward J.; Hasz, Wayne C.; Piche, Nicole</p> <p>2012-11-01</p> <p>Moiré imaging has been used to measure <span class="hlt">creep</span> in the airfoil section of gas turbine blades. The ability to accurately assess <span class="hlt">creep</span> and other failure modes has become an important engineering challenge, because gas turbine manufacturers are putting in place condition-based maintenance programs. In such maintenance programs, the condition of individual components is assessed to determine their remaining lives. Using pad-print technology, a grating pattern was printed directly on a turbine blade for localized <span class="hlt">creep</span> detection using the spacing change of moiré pattern fringes. A <span class="hlt">creep</span> measurement prototype was assembled for this application which contained a lens, reference grating, camera and lighting module. This prototype comprised a bench-top camera system that can read moiré patterns from the turbine blade sensor at shutdown to determine <span class="hlt">creep</span> level in individual parts by analyzing the moiré fringes. Sensitivity analyses and noise factor studies were performed to evaluate the system. Analysis software was also developed. A correlation study with strain gages was performed and the measurement results from the moiré system align well with the strain gage readings. A mechanical specimen subjected to a one cycle tensile test at high <span class="hlt">temperature</span> to induce plastic <span class="hlt">deformation</span> in the gage was used to evaluate the system and the result of this test exhibited good correlation to extensometer readings.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015MSMSE..23e5006V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015MSMSE..23e5006V"><span id="translatedtitle">Field theory and diffusion <span class="hlt">creep</span> predictions in polycrystalline aggregates</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Villani, A.; Busso, E. P.; Forest, S.</p> <p>2015-07-01</p> <p>In polycrystals, stress-driven vacancy diffusion at high homologous <span class="hlt">temperatures</span> leads to inelastic <span class="hlt">deformation</span>. In this work, a novel continuum mechanics framework is proposed to describe the strain fields resulting from such a diffusion-driven process in a polycrystalline aggregate where grains and grain boundaries are explicitly considered. The choice of an anisotropic eigenstrain in the grain boundary region provides the driving force for the diffusive <span class="hlt">creep</span> processes. The corresponding inelastic strain rate is shown to be related to the gradient of the vacancy flux. Dislocation driven <span class="hlt">deformation</span> is then introduced as an additional mechanism, through standard crystal plasticity constitutive equations. The fully coupled diffusion-mechanical model is implemented into the finite element method and then used to describe the biaxial <span class="hlt">creep</span> behaviour of FCC polycrystalline aggregates. The corresponding results revealed for the first time that such a coupled diffusion-stress approach, involving the gradient of the vacancy flux, can accurately predict the well-known macroscopic strain rate dependency on stress and grain size in the diffusion <span class="hlt">creep</span> regime. They also predict strongly heterogeneous viscoplastic strain fields, especially close to grain boundaries triple junctions. Finally, a smooth transition from Herring and Coble to dislocation <span class="hlt">creep</span> behaviour is predicted and compared to experimental results for copper.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/1001116','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/1001116"><span id="translatedtitle"><span class="hlt">Creep</span> Properties of Solid Oxide Fuel Cell Glass-Ceramic Seal G18</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Milhans, Jacqueline; Khaleel, Mohammad A.; Sun, Xin; Tehrani, Mehran; Al-Haik, Marwan; Garmestani, Hamid</p> <p>2010-11-01</p> <p>This study utilizes nanoindentation to investigate and measure <span class="hlt">creep</span> properties of a barium calcium aluminosilicate glass-ceramic used for solid oxide fuel cell seals (SOFCs). Samples of the glassceramic seal material were aged for 5h, 50h, and 100h to obtain different degrees of crystallinity. Instrumented nanoindentation was performed on the samples with different aging times at different <span class="hlt">temperatures</span> to investigate the strain rate sensitivity during inelastic <span class="hlt">deformation</span>. The <span class="hlt">temperature</span> dependent behavior is important since SOFCs operate at high <span class="hlt">temperatures</span> (800-1000°C). Results show that the samples with higher crystallinity were more resistant to <span class="hlt">creep</span>, and the <span class="hlt">creep</span> compliance tended to decrease with increasing <span class="hlt">temperature</span>, especially with further aged samples.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930017046','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930017046"><span id="translatedtitle"><span class="hlt">Deformation</span> mechanisms of NiAl cyclicly <span class="hlt">deformed</span> near the brittle-to-ductile transition <span class="hlt">temperature</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cullers, Cheryl L.; Antolovich, Stephen D.</p> <p>1993-01-01</p> <p>The intermetallic compound NiAl is one of many advanced materials which is being scrutinized for possible use in high <span class="hlt">temperature</span>, structural applications. Stoichiometric NiAl has a high melting <span class="hlt">temperature</span>, excellent oxidation resistance, and good thermal conductivity. Past research has concentrated on improving monotonic properties. The encouraging results obtained on binary and micro-alloyed NiAl over the past ten years have led to the broadening of NiAl experimental programs. The purpose of this research project was to determine the low cycle fatigue properties and dislocation mechanisms of stoichiometric NiAl at <span class="hlt">temperatures</span> near the monotonic brittle-to-ductile transition. The fatigue properties were found to change only slightly in the <span class="hlt">temperature</span> range of 600 to 700 K; a <span class="hlt">temperature</span> range over which monotonic ductility and fracture strength increase markedly. The shape of the cyclic hardening curves coincided with the changes observed in the dislocation structures. The evolution of dislocation structures did not appear to change with <span class="hlt">temperature</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/989120','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/989120"><span id="translatedtitle">Plastic Instability in Amorphous Selenium near its Glass Transition <span class="hlt">Temperature</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Su, Caijun; Lamanna Jr, James; Gao, Yanfei; Oliver, Warren C.; Pharr, George M</p> <p>2010-01-01</p> <p><span class="hlt">Deformation</span> behavior of amorphous selenium near its glass transition <span class="hlt">temperature</span> (31 C) has been investigated by uniaxial compression and nanoindentation <span class="hlt">creep</span> tests. Cylindrical specimens compressed at high <span class="hlt">temperatures</span> and low strain rates <span class="hlt">deform</span> into drum-like shape, while tests at low <span class="hlt">temperatures</span> and high strain rates lead to fragmentation. These results agree nicely with the stress exponent and kinetic activation parameters extracted from the nanoindentation <span class="hlt">creep</span> tests by using a similarity analysis. The dependence of <span class="hlt">deformation</span> modes on <span class="hlt">temperature</span> and strain rate is understood as a consequence of material instability and strain localization in the rate-dependent solids.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1185851','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1185851"><span id="translatedtitle">Universal mechanism of thermo-mechanical <span class="hlt">deformation</span> in metallic glasses</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Dmowski, W.; Tong, Y.; Iwashita, T.; Egami, Takeshi; Yokoyama, Y.</p> <p>2015-02-11</p> <p>Here we investigated the atomistic structure of metallic glasses subjected to thermo-mechanical <span class="hlt">creep</span> <span class="hlt">deformation</span> using high energy x-ray diffraction and molecular dynamics simulation. The experiments were performed in-situ, at high <span class="hlt">temperatures</span> as a time dependent <span class="hlt">deformation</span> in the elastic regime, and ex-situ on samples quenched under stress. We show that all the anisotropic structure functions of the samples undergone thermo-mechanical <span class="hlt">creep</span> can be scaled into a single curve, regardless of the magnitude of anelastic strain, stress level and the sign of the stress, demonstrating universal behavior and pointing to unique atomistic unit of anelastic <span class="hlt">deformation</span>. The structural changes due to <span class="hlt">creep</span> are strongly localized within the second nearest neighbors, involving only a small group of atoms.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_24 --> <div id="page_25" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="481"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/pages/biblio/1185851-universal-mechanism-thermo-mechanical-deformation-metallic-glasses','SCIGOV-DOEP'); return false;" href="http://www.osti.gov/pages/biblio/1185851-universal-mechanism-thermo-mechanical-deformation-metallic-glasses"><span id="translatedtitle">Universal mechanism of thermo-mechanical <span class="hlt">deformation</span> in metallic glasses</span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGESBeta</a></p> <p>Dmowski, W.; Tong, Y.; Iwashita, T.; Egami, Takeshi; Yokoyama, Y.</p> <p>2015-02-11</p> <p>Here we investigated the atomistic structure of metallic glasses subjected to thermo-mechanical <span class="hlt">creep</span> <span class="hlt">deformation</span> using high energy x-ray diffraction and molecular dynamics simulation. The experiments were performed in-situ, at high <span class="hlt">temperatures</span> as a time dependent <span class="hlt">deformation</span> in the elastic regime, and ex-situ on samples quenched under stress. We show that all the anisotropic structure functions of the samples undergone thermo-mechanical <span class="hlt">creep</span> can be scaled into a single curve, regardless of the magnitude of anelastic strain, stress level and the sign of the stress, demonstrating universal behavior and pointing to unique atomistic unit of anelastic <span class="hlt">deformation</span>. The structural changes due tomore » <span class="hlt">creep</span> are strongly localized within the second nearest neighbors, involving only a small group of atoms.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22274005','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22274005"><span id="translatedtitle">Thermal <span class="hlt">creep</span> model for CWSR zircaloy-4 cladding taking into account the annealing of the irradiation hardening</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Cappelaere, Chantal; Limon, Roger; Duguay, Chrstelle; Pinte, Gerard; Le Breton, Michel; Bouffioux, Pol; Chabretou, Valerie; Miquet, Alain</p> <p>2012-02-15</p> <p>After irradiation and cooling in a pool, spent nuclear fuel assemblies are either transported for wet storage to a devoted site or loaded in casks for dry storage. During dry transportation or at the beginning of dry storage, the cladding is expected to be submitted to <span class="hlt">creep</span> <span class="hlt">deformation</span> under the hoop stress induced by the internal pressure of the fuel rod. The thermal <span class="hlt">creep</span> is a potential mechanism that might lead to cladding failure. A new <span class="hlt">creep</span> model was developed, based on a database of <span class="hlt">creep</span> tests on as-received and irradiated cold-worked stress-relieved Zircaloy-4 cladding in a wide range of <span class="hlt">temperatures</span> (310 degrees C to 470 degrees C) and hoop stress (80 to 260 MPa). Based on three laws-a flow law, a strain-hardening recovery law, and an annealing of irradiation hardening law this model allows the simulation of not only the transient <span class="hlt">creep</span> and the steady-state <span class="hlt">creep</span>, but also the early <span class="hlt">creep</span> acceleration observed on irradiated samples tested in severe conditions, which was not taken into account in the previous models. The extrapolation of the <span class="hlt">creep</span> model in the conditions of very long-term <span class="hlt">creep</span> tests is reassuring, proving the robustness of the chosen formalism. The <span class="hlt">creep</span> model has been assessed in progressively decreasing stress conditions, more representative of a transport. Set up to predict the cladding <span class="hlt">creep</span> behavior under variable <span class="hlt">temperature</span> and stress conditions, this model can easily be implemented into codes in order to simulate the thermomechanical behavior of spent fuel rods in various scenarios of postirradiation phases. (authors)</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Tectp.610....1W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Tectp.610....1W"><span id="translatedtitle">Invited review paper: Fault <span class="hlt">creep</span> caused by subduction of rough seafloor relief</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Kelin; Bilek, Susan L.</p> <p>2014-01-01</p> <p>Among the wide range of thermal, petrologic, hydrological, and structural factors that potentially affect subduction earthquakes, the roughness of the subducting seafloor is among the most important. By reviewing seismic and geodetic studies of megathrust locking/<span class="hlt">creeping</span> state, we find that <span class="hlt">creeping</span> is the predominant mode of subduction in areas of extremely rugged subducting seafloor such as the Kyushu margin, Manila Trench, northern Hikurangi, and southeastern Costa Rica. In Java and Mariana, megathrust <span class="hlt">creeping</span> state is not yet constrained by geodetic observations, but the very rugged subducting seafloor and lack of large earthquakes also suggest aseismic <span class="hlt">creep</span>. Large topographic features on otherwise relatively smooth subducting seafloor such as the Nazca Ridge off Peru, the Investigator Fracture Zone off Sumatra, and the Joban seamount chain in southern Japan Trench also cause <span class="hlt">creep</span> and often stop the propagation of large ruptures. Similar to all other known giant earthquakes, the Tohoku earthquake of March 2011 occurred in an area of relatively smooth subducting seafloor. The Tohoku event also offers an example of subducting seamounts stopping rupture propagation. Very rugged subducting seafloor not only retards the process of shear localization, but also gives rise to heterogeneous stresses. In this situation, the fault zone <span class="hlt">creeps</span> because of distributed <span class="hlt">deformation</span> of fractured rocks, and the <span class="hlt">creep</span> may take place as transient events of various spatial and temporal scales accompanied with small and medium-size earthquakes. This process cannot be described as stable or unstable friction along a single contact surface. The association of large earthquakes with relatively smooth subducting seafloor and <span class="hlt"