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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. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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 700C 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 dislocation activity were also present. At higher stresses (758-793MPa), there is still planar activity present, but now non-planar "wavy" slip appears. Wavy slip was also present in the constant strain rate sample of the M1 microstructure. M2 showed much of the same activity as M1, but wavy slip was not present in either the high stress creep conditions or the constant strain rate conditions. The second part of this dissertation focused on Alloy X, which is a next generation alloy system. Three variants were examined (decreased levels of Cr and Co, decreased levels of Cr and Co with added Hf, and decreased levels of Cr and Co with added Hf and a faster cooling rate). The variants were all tested at 700C/690MPa, 760C/490MPa, and 815C/345MPa, to various strains. In Alloy X, the dominant mechanisms that appear throughout all strains, stresses, and temperatures are unpaired dislocations and discontinuous stacking faults. In the Hf bearing variants, , unpaired dislocations appear to start at grain boundaries and move in to the grains with increasing strain and temperature. Through 3D stereo imaging using STEM images, it appears that the dislocations are able to climb over precipitates at larger strains. It is postulated that the decreasing levels of Cr and Co have changed the stacking fault energy so it is unfavorable to form microtwins anymore. This was discussed in terms of the Dislocation Activity Diagram (DAD).

  8. Deformation twinning in a creep-deformed nanolaminate structure

    NASA Astrophysics Data System (ADS)

    Hsiung, Luke L.

    2010-10-01

    The underlying mechanism of deformation twinning occurring in a TiAl-(?)/Ti3Al-(?2) nanolaminate creep deformed at elevated temperatures has been studied. Since the multiplication and propagation of lattice dislocations in both ? and ?2 thin lamellae are very limited, the total flow of lattice dislocations becomes insufficient to accommodate the accumulated creep strains. Consequently, the movement of interfacial dislocations along the laminate interfaces, i.e., interface sliding, becomes an alternative deformation mode of the nanolaminate structure. Pile-ups of interfacial dislocations occur when interfacial ledges and impinged lattice dislocations act as obstacles to impede the movement of interfacial dislocations. Deformation twinning can accordingly take place to relieve a stress concentration resulting from the pile-up of interfacial dislocations. An interface-controlled twinning mechanism driven by the pile-up and dissociation of interfacial dislocations is accordingly proposed.

  9. Deformation twinning in a creep-deformed nanolaminate structure.

    PubMed

    Hsiung, Luke L

    2010-10-01

    The underlying mechanism of deformation twinning occurring in a TiAl-(?)/Ti(3)Al-(?(2)) nanolaminate creep deformed at elevated temperatures has been studied. Since the multiplication and propagation of lattice dislocations in both ? and ?(2) thin lamellae are very limited, the total flow of lattice dislocations becomes insufficient to accommodate the accumulated creep strains. Consequently, the movement of interfacial dislocations along the laminate interfaces, i.e., interface sliding, becomes an alternative deformation mode of the nanolaminate structure. Pile-ups of interfacial dislocations occur when interfacial ledges and impinged lattice dislocations act as obstacles to impede the movement of interfacial dislocations. Deformation twinning can accordingly take place to relieve a stress concentration resulting from the pile-up of interfacial dislocations. An interface-controlled twinning mechanism driven by the pile-up and dissociation of interfacial dislocations is accordingly proposed. PMID:21403216

  10. Influence of the second phase on the room-temperature tensile and creep deformation mechanisms of ?-? titanium alloys: Part I. Tensile deformation

    NASA Astrophysics Data System (ADS)

    Jaworski, A.; Ankem, S.

    2006-09-01

    The effects of ? and ? phase interactions on the room-temperature tensile and creep deformation behavior of ? + ? titanium alloys with Widmansttten microstructures were studied using Ti-6.0 wt pct Mn and Ti-8.1 wt pct V as the model two-phase alloy systems. This article, Part I, deals with tensile deformation. It was found that when the ? phase is present as thin (<10-m) plates in the ? + ? alloys, significant twinning occurs. No significant twinning was observed in single-phase alloys with the same chemistry and similar grain size. Additionally, the ? phase of Ti-8.1 V deforms by stress-induced hexagonal martensite (?'), while only twinning occurs in the single-phase ? alloy with the same chemistry. Twinning in the ? phase in association with stress-induced martensite (SIM) in the ? phase was observed for the first time in a two-phase titanium alloy. This behavior is explained in terms of a number of factors including elastic interaction stresses between the ? and ? phases, coherency between the ? phase and hexagonal martensite, and ? phase stability.

  11. Creep fracture during solute-drag creep and superplastic deformation

    SciTech Connect

    Taleff, E.M.; Lesuer, D.R.; Syn, C.K.; Henshall, G.A.

    1996-10-01

    Creep fracture behavior has been studied in Al-Mg and Al-Mg-Mn alloys undergoing solute-drag creep and in microduplex stainless steel undergoing both solute-drag creep and superplastic deformation. Failure in these materials is found to be controlled by two mechanisms, neck formation and cavitation. The mechanism of creep fracture during solute-drag creep in Al-Mg is found to change from necking-controlled fracture to cavitation-controlled fracture as Mn content is increased. Binary Al-Mg material fails by neck formation during solute-drag creep, and cavities are formed primarily in the neck region due to high hydrostatic stresses. Ternary alloys of Al-Mg- Mn containing 0.25 and 0.50 wt % Mn exhibit more uniform cavitation, with the 0.50 Mn alloy clearly failing by cavity interlinkage. Failure in the microduplex stainless steel is dominated by neck formation during solute-drag creep deformation but is controlled by cavity growth and interlinkage during superplastic deformation. Cavitation was measured at several strains, and found to increase as an exponential function of strain. An important aspect of cavity growth in the stainless steel is the long latency time before significant cavitation occurs. For a short latency period, cavitation acts to significantly reduce ductility below that allowed by neck growth alone. This effect is most pronounced in materials with a high strain-rate sensitivity, for which neck growth occurs very slowly.

  12. 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

  13. High-temperature creep of Nb-Al-V alloys

    SciTech Connect

    Rong, T.S.; Aindow, M.

    1999-07-01

    Nb-15Al-20V alloys with about 45% by volume of an A15 phase in a B2 matrix have been subjected to creep deformation at temperatures between 1,000 C and 1,200 C and stresses from 80 MPa to 240 MPa in vacuum. The creep curves show a rapid transition from primary to steady-state creep with a well-defined activation energy. Microstructural observations show that the creep deformation occurs mainly in the B2 matrix and is controlled by dislocation mechanisms. Samples which had been cold-rolled and annealed to reduce the size of A15 precipitates and increase the yield strength were found to have lower creep resistance than those with unrefined microstructures. The significance of these observations for the creep mechanisms is discussed.

  14. 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 Lders 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.

  15. 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.

  16. Temperature-dependent creep buckling of plates

    NASA Technical Reports Server (NTRS)

    Ross, D. A.; Berke, L.

    1981-01-01

    Time-dependent lateral deflection of flat rectangular plates is predicted by the Norton-Bailey (Norton 1929, Bailey 1935) power law for material creep. The plates have a through-thickness steady-state temperature distribution, and the effects are considered by using Maxwell's law to modify the power creep law. Equations are derived for creep exponents of 3 and 5, using the sandwich plate element to predict creep buckling of plates. Predictions of creep buckling with a temperature variation between the inner and outer plate surfaces are found to be somewhat dependent on the creep buckling relationship assumed. When significant scatter justifies a variation in the creep constants up to an order of magnitude, discrepancies in predictions using the two exponents are reasonable, and for one engineering material, the predictions have the same degree of agreement with experimental data as have the respective creep laws.

  17. 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 650C. The influence of stress and temperature was studied first and it was found that during creep deformation at temperatures between 677--815C 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 677C/690MPa and 704C/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 (760C 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 (815C and 345MPa) a thermally activated climb/bypass mechanism of a/2<110> dislocations were found to be the dominant deformation mechanism. In this mechanism, the gamma' precipitates were not sheared but instead were bypassed by a/2<110> matrix dislocations. In addition to the identification of creep deformation mechanisms as a function of stress and temperature, characterization of the post creep gamma' precipitate microstructure revealed that microstructural evolution of the gamma' precipitates has occurred during creep at the higher test temperatures where the secondary gamma' precipitates have coarsened and the tertiary gamma' precipitates have dissolved. In combination with creep at low stress and high temperature, the microstructural evolution may have contributed to the transition from one deformation mode to another. In an attempt to link the influence of microstructure (gamma' precipitate size scale, distribution, volume fraction, and gamma channel width spacing) on creep deformation behavior and creep deformation mechanisms, specimens with different size scaled microstructural features were crept at the same temperature and stress (677C and 724MPa) in order to provide a direct comparison between differences in microstructure. It was found that a microstructure consisting of a bimodal distribution of gamma' precipitates with coarse secondary gamma' precipitates, a high volume fraction of tertiary gamma' precipitates and a wide gamma channel width spacing results in a less creep resistance microstructure that deformed primary by a/2<110> dislocation activity in the gamma matrix at small strain and secondary gamma' shearing via superlattice intrinsic stacking faults at higher strains. The more creep resistant microstructure consisted of a bimodal distribution of gamma' precipitates with a finer secondary gamma' precipitate size, low volume fraction of gamma' and narrow gamma channel width spacing. The combination of these microstructural features promoted a/2<110> dislocation dissociation and decorrelation of a/6<112> Shockley partial di

  18. Viscoelastic creep of high-temperature concrete

    SciTech Connect

    Pfeiffer, P.A.; Marchertas, A.H.; Bazant, Z.P.

    1985-01-01

    Presented in this report is the analytical model for analysis of high temperature creep response of concrete. The creep law used is linear (viscoelastic), the temperature and moisture effects on the creep rate and also aging are included. Both constant and transient temperature as well as constant and transient moisture conditions are considered. Examples are presented to correlate experimental data with parameters of the analytical model by the use of a finite element scheme.

  19. 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.

  20. 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.

  1. 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 ? 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.

  2. 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.

  3. 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.

  4. Creep resistant high temperature martensitic steel

    DOEpatents

    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.

  5. 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 ?, as t r = 1.5/[ {dot{\\varepsilon }}_{ min } ( dln {dot{\\varepsilon }} /d ?)], where {dot{\\varepsilon }}_{ min } and dln {dot{\\varepsilon }} /d ? 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 ? m, as {dot{\\varepsilon }}_{ min } = 0.54 ( ? m/ t m). The ? 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 ? is inversely proportional to the ? 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 ? m and t m change upon the condition of t m ? ? m. The decrease in ? 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.

  6. 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.

  7. 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 ?' 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 ?' phase decreases, and a high volume fraction of fine ?' phase dispersedly precipitates in the ? 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 ? and ?' 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 ? matrix or shear into the ?' phase. Thereinto, the creep dislocations move over the ?' phase by the Orowan mechanism, and the < { 1 10 } rangle super-dislocation shearing into the ?' phase can be decomposed to form the configuration of (1/3) < { 1 12 } rangle super-Shockleys' partials and the stacking fault.

  8. 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.

  9. Sharp interface model of creep deformation in crystalline solids

    NASA Astrophysics Data System (ADS)

    Mishin, Y.; McFadden, G. B.; Sekerka, R. F.; Boettinger, W. J.

    2015-08-01

    We present a rigorous irreversible thermodynamics treatment of creep deformation of solid materials with interfaces described as geometric surfaces capable of vacancy generation and absorption and moving under the influence of local thermodynamic forces. The free energy dissipation rate derived in this work permits clear identification of thermodynamic driving forces for all stages of the creep process and formulation of kinetic equations of creep deformation and microstructure evolution. The theory incorporates capillary effects and reveals the different roles played by the interface free energy and interface stress. To describe the interaction of grain boundaries with stresses, we classify grain boundaries into coherent, incoherent and semicoherent, depending on their mechanical response to the stress. To prepare for future applications, we specialize the general equations to a particular case of a linear-elastic solid with a small concentration of vacancies. The proposed theory creates a thermodynamic framework for addressing more complex cases, such as creep in multicomponent alloys and cross-effects among vacancy generation/absorption and grain boundary motion and sliding.

  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. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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 (??min) and the applied stress (?) 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Creep mechanisms and interface-enhanced deformation twinning in a two-phase lamellar TiAl alloy

    SciTech Connect

    Hsiung, L.M., LLNL

    1997-03-01

    Deformation mechanisms and the role of interfaces in deformation twinning of a two-phase [TiAl({gamma})/Ti{sub 3}Al({alpha}{sub 2})] lamellar alloy creep deformed at elevated temperatures have been investigated. Since the multiplication of lattice dislocations within both {gamma} and {alpha}{sub 2} lamellae is very limited at a low stress level due to a refined lamellar microstructure, the glide of interfacial dislocations on both {gamma}/{alpha}{sub 2} and {gamma}/{gamma} interfaces (i.e interface sliding) becomes an important deformation mode. Obstacles such as impinged lattice dislocations can impede the movement of interfacial dislocations, which glide in a cooperative fashion along the lamellar interfaces. The impediment of dislocation motion subsequently causes a dislocation pile-up in front of obstacles as creep strain accumulates. When the crystals deform at high stress level, deformation twinning becomes a predominant deformation mode. Deformation twins are found to nucleate from the interfaces as a result of a local stress concentration generated from dislocation pile-ups. It is suggested that the deformation twinning in lamellar TiAl/Ti{sub 3}Al crystals can be vieived as a stress relaxation process for the concentration of stress at the head of each dislocation pile-up. An interface-assisted twinning mechanism is accordingly proposed and discussed.

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

    NASA Astrophysics Data System (ADS)

    Wen, Xingshuo

    The Very High Temperature Reactor (VHTR) is one of the leading concepts of the Generation IV nuclear reactor development, which is the core component of Next Generation Nuclear Plant (NGNP). The major challenge in the research and development of NGNP is the performance and reliability of structure materials at high temperature. Alloy 617, with an exceptional combination of high temperature strength and oxidation resistance, has been selected as a primary candidate material for structural use, particularly in Intermediate Heat Exchanger (IHX) which has an outlet temperature in the range of 850 to 950C and an inner pressure from 5 to 20MPa. In order to qualify the material to be used at the operation condition for a designed service life of 60 years, a comprehensive scientific understanding of creep behavior at high temperature and low stress regime is necessary. In addition, the creep mechanism and the impact factors such as precipitates, grain size, and grain boundary characters need to be evaluated for the purpose of alloy design and development. In this study, thermomechanically processed specimens of alloy 617 with different grain sizes were fabricated, and creep tests with a systematic test matrix covering the temperatures of 850 to 1050C and stress levels from 5 to 100MPa were conducted. Creep data was analyzed, and the creep curves were found to be unconventional without a well-defined steady-state creep. Very good linear relationships were determined for minimum creep rate versus stress levels with the stress exponents determined around 3-5 depending on the grain size and test condition. Activation energies were also calculated for different stress levels, and the values are close to 400kJ/mol, which is higher than that for self-diffusion in nickel. Power law dislocation climb-glide mechanism was proposed as the dominant creep mechanism in the test condition regime. Dynamic recrystallization happening at high strain range enhanced dislocation climb and 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.

  6. 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.

  7. 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.

  8. 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.

  9. High temperature creep of refractory bricks. Final report

    SciTech Connect

    McGee, T.D.

    1991-05-15

    The uniaxial compressive creep of the 13 high chromia-commercial refractories that are candidate materials for lining coal gasification vessels was studied using stresses from 50 to 1500 psi (0.34 MPa to 10.3 MPa) and temperature from 1900{degrees}F to 2600{degrees}F (1038{degrees} to 1427{degrees}C). The regimes to stress and temperature in which creep was active varied widely, depending on impurities and microstructure, not chromia content, and was active at lower stresses and temperatures than would be expected from hot strength data. The creep was always primary, going through steady state to failure as a transient phase. One specimen with a liquid phase at temperature gave a longer steady-state region. The primary creep time exponent varied from 0.4 to nearly one. It was smaller at low stresses and temperatures, but was often a linear function of stress. Activation enthalpies were less for refractories containing a significant liquid phase at temperature, and were in the range expected for cation diffusion. Current theoretical models to not fit these systems. Two models are suggested to explain the primary creep regime. More research to correlate primary creep with microstructure is needed.

  10. Postseismic deformation due to the Mw 6.0 2004 Parkfield earthquake: Stress-driven creep on a fault

    E-print Network

    Fialko, Yuri

    Postseismic deformation due to the Mw 6.0 2004 Parkfield earthquake: Stress-driven creep on a fault investigate the coseismic and postseismic deformation due to the Mw 6.0 2004 Parkfield, California, earthquake deformation due to the Mw 6.0 2004 Parkfield earthquake: Stress- driven creep on a fault with spatially

  11. 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.

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

    SciTech Connect

    Jones, L.E.; Tressler, R.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{degree}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{sup {minus}7} to 10 {sup {minus}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{degree}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.

  13. 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.

  14. 2 Transient creep, aseismic damage and slow failure in Carrara marble 3 deformed across the brittle-ductile transition

    E-print Network

    Fortin, Jrme

    2 Transient creep, aseismic damage and slow failure in Carrara marble 3 deformed across the brittle triaxial compression experiments were performed 8 on Carrara marble at high confining pressure, in creep 9 in Carrara marble deformed across the brittle-ductile transition, 31 Geophys. Res. Lett., 33, LXXXXX, doi:10

  15. High-Temperature Creep Degradation of the AM1/NiAlPt/EBPVD YSZ System

    NASA Astrophysics Data System (ADS)

    Riallant, Fanny; Cormier, Jonathan; Longuet, Arnaud; Milhet, Xavier; Mendez, Jos

    2014-01-01

    The failure mechanisms of a NiAlPt/electron beam physical vapor deposition yttria-stabilized-zirconia thermal barrier coating system deposited on the AM1 single crystalline substrate have been investigated under pure creep conditions in the temperature range from 1273 K to 1373 K (1000 C to 1100 C) and for durations up to 1000 hours. Doubly tapered specimens were used allowing for the analysis of different stress states and different accumulated viscoplastic strains for a given creep condition. Under such experiments, two kinds of damage mechanisms were observed. Under low applied stress conditions ( i.e., long creep tests), microcracking is localized in the vicinity of the thermally grown oxide (TGO). Under high applied stress conditions, an unconventional failure mechanism at the substrate/bond coat interface is observed because of large creep strains and fast creep deformation, hence leading to a limited TGO growth. This unconventional failure mechanism is observed although the interfacial bond coat/top coat TGO thickening is accelerated by the mechanical applied stress beyond a given stress threshold.

  16. 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.

  17. 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.

  18. 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.

  19. 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 ? 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 ? > 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 and inclusions.

  20. 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.

  1. 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 1000C 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 1200-1300C, 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 samples deformed at 450MPa, the thin ortho- and clino-pyroxene lamellae are bound by partial c dislocations in (100) planes, suggesting extensive gliding of partial c dislocations on (100) in samples deformed in the orthoenstatite field. Our high-stress mechanical data for protoenstatite is in perfect agreement with the extrapolation of the flow law for dislocation creep on (100)[001], obtained for single crystals deformed in the protoenstatite stability field (Mackwell, 1991). This confirms that the deformation in our samples is likely controlled by slip on (100)[001], arguably the weakest slip system in enstatite. Comparison of our results with dislocation creep flow laws for olivine indicates that enstatite is almost half an order of magnitude stronger than olivine at our experimental conditions. However, as enstatite has a slightly higher activation energy than olivine, the difference in strength is not likely to be as high in the upper mantle.

  2. 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 1360C to 1240C by furnace attached to the machine. Prior to the applying the load to the samples the grain size was saturated at 1360C 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 1300C 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 energy to lattice diffusion of Si and lower activation energy to apparent values where deformation mechanism transits from volume diffusion to grain boundary diffusion at lower temperature condition.

  3. 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 n?, and temperature exponent nt of the established constitutive models were determined through experimental data via numerical optimization techniques. The relationship of k, n?, and nt was evaluated, and a new coefficient model of k-T, n?-T, nt-T, and nt-n? was formulated through the parameters of the isothermal creep equation. Moreover, the isothermal creep equation for this material at every temperature point from 450C to 1000C 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.

  4. 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.

  5. 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 given dome. Characteristics defined by the transient analysis are related quantitatively to the volume loss creep rate of the SPR caverns. This increase in understanding of the domal material creep response already has pointed to the possibility y of delineating the existence of material spines within a specific dome. Further definition of the domal geology and structure seems possible only through expansion of the creep databases for domal salts.

  6. Solution Creep as a Deformation and Softening Mechanism in the Mid- and Lower- Crust

    NASA Astrophysics Data System (ADS)

    Wintsch, R. P.; Stokes, M. R.; McWilliams, C.; Attenoukon, M.

    2008-12-01

    Chemical zoning preserved in grains of micas, feldspars, and amphiboles especially in foliated and lineated rocks implicates chemical processes in the development of these fabrics. Detailed electron microprobe analyses reveals monotonic and bell- or U-shaped patterns with the strongest chemical gradients present along the length of grains parallel to foliation and to lineation where present. Phyllosilicates preserve zoning in greenschist and lower amphibolite facies rocks in grains as small as 50 m. Zoning in plagioclase of greater than 30% An content is preserved up to upper amphibolite facies. Core to rim zoning in amphiboles can range from 6.0 to 7.8 Si atoms p.f.u. We interpret these zoning patterns as growth zoning because pairs of parallel muscovite and chlorite, or muscovite and biotite flakes, and pairs of elongate amphibole and plagioclase grains are sympathetically zoned. Moreover, temperatures calculated using the amphibole- plagioclase thermometer correlate positively with Ti concentration in amphibole to 700C, confirming both prograde and retrograde growth. These relationships strongly suggest that an instantaneous equilibrium existed between these pairs of minerals that crystallized simultaneously, but in an environment in which intensive variables were evolving during growth. Grains that are most strongly zoned along the length of the grain occur in rocks that are most strongly foliated; minimal zoning is found across the short dimensions of the grains. We interpret this to indicate that crystallization of these grains was syntectonic, parallel to the extension direction. Evidence of dissolution on the grain boundaries facing the shortening direction is less common, but present in the form of truncated grains and truncated zoning patterns within grains. Amphibole-plagioclase thermometry in amphibolites from Vermont and North Carolina suggests that solution creep is important to at least 730C in rocks where amphibole interfaces were load bearing. However, in orthogneisses from Connecticut where networks of feldspar grains were load bearing, plagioclase is pervasively zoned, while relic magmatic amphibole grains show no evidence of recrystallization. We interpret that the development of a preferred orientation of amphiboles enhances deformation by solution creep in the direction of the c-axes of grains. Micas in phyllites and schists from New England show similar patterns, where crenulations tend to concentrate phyllosilicates into quartz- and feldspar-free layers, and in the limit, into cm or longer folia. These observations converge to suggest that solution creep is the dominant deformation mechanism. Thus foliations in both amphibole- and phyllosilicate-rich rocks are produced by a syntectonic incongruent dissolution-precipitation process (a type of metamorphic reaction) that tends to produce monomineralic folia. These in turn weaken the rock, lowering its viscosity. These reactions localize strain, and contribute to defining the base of the seismic zone at lower amphibolites facies conditions.

  7. 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.

  8. Room-temperature transverse compressive creep of thick Kevlar fabric/ epoxy laminates

    SciTech Connect

    Ericksen, R.H.; Guess, T.R.

    1980-01-01

    Creep and recovery of thick Kevlar 49/epoxy composites were investigated in transverse compressive loading at room temperature. Cylindrical samples with void contents of 4 and 14 percent were tested along with those of unreinforced resin. The composites exhibited logarithmic creep. Creep rates were 2 times higher over the entire stress range for the high porosity composites. At a stress of 87 MPa the resin creep curve was similar to that of the composites. At higher stresses, the resin crept faster and exhibited more strain. It is proposed that axial compressive creep of the cylindrical composite specimens is governed by Poisson induced strains leading to tensile loading of the reinforcing fibers. Axial initial strain and creep rate data for the composite were converted to radial data using measured values of Poisson ratio. These values of composite specimen radial creep rate were in good agreement with tensile creep data of Kevlar 49 fibers.

  9. 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-boundary diffusion and precipitation on pore walls. As a first step to better describe creep in sands and sandstones, we have derived a simple model for intergranular pressure solution (IPS) within an ordered pack of spherical grains, employing existing IPS rate models, such as those derived by Renard et al. (1999) and Spiers et al. (2004). This universal model is able to predict the conditions under which each of the respective pressure solution serial processes, i.e. diffusion, precipitation or dissolution, is dominant. In essence, this creates generic deformation mechanism maps for any granular material. We have used our model to predict the amount and rate of compaction for sandstone reservoirs, and compared our predictions to known subsidence rates for reservoirs around the world. This gives a first order-comparison to verify whether or not IPS is an important mechanism in controlling reservoir compaction.

  10. 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.

  11. 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 CARES/Creep program.

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

    SciTech Connect

    Wu, Rui; Pettersson, Niklas; Martinsson, sa; Sandstrm, 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.

  14. Introduction Creep is a time-dependent deformation that happens when metals or other materials are

    E-print Network

    Cambridge, University of

    and slows with time. The region CD stands as secondary or steady state creep, which has a relatively uniform of categories primary creep, tertiary creep, and steady state creep [7] 1.2.1 Primary Creep During primary creep, the strain rate decreases with time until a constant rate is reached. And this tends to occur over a short

  15. 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.

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. 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.

  3. A constitutive law for low-temperature creep of water-saturated sandstones

    E-print Network

    , Scotland, UK Brian R. Crawford ExxonMobil Upstream Research Company, Houston, Texas, USA Brian G. D. SmartA constitutive law for low-temperature creep of water-saturated sandstones Bryne T. Ngwenya, Ian G we present results of room temperature creep experiments on a suite of water-saturated sandstones

  4. Modelling and analysis of creep deformation and fracture in a 1 Cr 1/2 Mo ferritic steel

    NASA Astrophysics Data System (ADS)

    Dyson, B. F.; Osgerby, D.

    A quantitative model, based upon a proposed new mechanism of creep deformation in particle-hardened alloys, has been validated by analysis of creep data from a 13CrMo 4 4 (1Cr 1/2 Mo) material tested under a range of stresses and temperatures. The methodology that has been used to extract the model parameters quantifies, as a first approximation, only the main degradation (damage) processes - in the case of the 1CR 1/2 Mo steel, these are considered to be the parallel operation of particle-coarsening and a progressively increasing stress due to a constant-load boundary condition. These 'global' model parameters can then be modified (only slightly) as required to obtain a detailed description and 'fit' to the rupture lifetime and strain/time trajectory of any individual test. The global model parameter approach may be thought of as predicting average behavior and the detailed fits as taking account of uncertainties (scatter) due to variability in the material. Using the global parameter dataset, predictions have also been made of behavior under biaxial stressing; constant straining rate; constant total strain (stress relaxation) and the likely success or otherwise of metallographic and mechanical remanent lifetime procedures.

  5. 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 deformation modes, so as to design and develop higher performance Ti alloys.

  6. Temperature Dependence of Creep and Hardness of Sn-Ag-Cu Lead-Free Solder

    NASA Astrophysics Data System (ADS)

    Han, Y. D.; Jing, H. Y.; Nai, S. M. L.; Xu, L. Y.; Tan, C. M.; Wei, J.

    2010-02-01

    The creep behavior and hardness of Sn-3.5Ag-0.7Cu solder were studied using Berkovich depth-sensing indentation at temperatures of 25C to 125C. Assuming a power-law relationship between the creep strain rate and stress, an activation energy of 40 kJ/mol and stress exponents of 7.4, 5.5, and 3.7 at 25C, 75C, and 125C, respectively, were obtained. The results revealed that, with increasing temperature, the creep penetration and steady-state creep strain rate increased whereas the stress exponent decreased. The stress exponent and activation energy results also suggested that the creep mechanism is dislocation climb, assisted by diffusion through dislocation cores in Sn. Furthermore, the hardness results exhibited a decreasing trend with increasing temperature, which is attributed to softening at high temperature.

  7. Local TimeTemperature-dependent Deformation of a Woven Composite

    E-print Network

    Sottos, Nancy R.

    temperature- dependent response, Moir interferometry, creep and stress relaxation, multilayer circuit boards, textile composites Introduction Multilayer printed circuit boards (PCBs) are used exten- sively in electronic

  8. 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.

  9. Neutron Diffraction Study of Strain/Stress States and Subgrain Defects in a Creep-Deformed, Single-Crystal Superalloy

    NASA Astrophysics Data System (ADS)

    Wu, Erdong; Sun, Guangai; Chen, BO; Zhang, Jian; Ji, Vincent; Klosek, Vincent; Mathon, Marie-Helene

    2014-01-01

    A single crystal superalloy with initial sample axis 10 deg deviated from [001] was creep deformed at 1273 K (1000 C) 235 MPa and its triaxial strain/stress state and subgrain defects were studied by neutron diffraction. Normal internal stresses with their directions close to the loading axis and their scales smaller than those perpendicular to the axis were observed and attributed to a lattice rotation toward [001] pole. The internal stress at a level approaching to the loading stress and mostly in the state of interphase stress was induced during the first stage of creep prior to rafting and associated to lattice rotation, microstrain relaxation and line-up of misoriented ?'-precipitates. The internal stress was diminished and released at final stage of creep associated with a reduction in unit-cell volume and a transition of strain/stress state between the two phases. The observation was explained by development of dislocations and raft structure during creep.

  10. Effect of titanium on the creep deformation behaviour of 14Cr-15Ni-Ti stainless steel

    NASA Astrophysics Data System (ADS)

    Latha, S.; Mathew, M. D.; Parameswaran, P.; Nandagopal, M.; Mannan, S. L.

    2011-02-01

    14Cr-15Ni-Ti modified stainless steel alloyed with additions of phosphorus and silicon is a potential candidate material for the future cores of Prototype Fast Breeder Reactor. In order to optimise the titanium content in this steel, creep tests have been conducted on the heats with different titanium contents of 0.18, 0.23, 0.25 and 0.36 wt.% at 973 K at various stress levels. The stress exponents indicated that the rate controlling deformation mechanism was dislocation creep. A peak in the variation of rupture life with titanium content was observed around 0.23 wt.% titanium and the peak was more pronounced at lower stresses. The variation in creep strength with titanium content was correlated with transmission electron microscopic investigations. The peak in creep strength exhibited by the material with 0.23 wt.% titanium is attributed to the higher volume fraction of fine secondary titanium carbide (TiC) precipitates.

  11. 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 cuttings tested by others. We also considered weakening by diffusion-accommodated grain boundary sliding. There are two main trends in the microstructural data that provide a basis for explaining the creep rate and seismic activity: 1. Clay content of the gouge including serpentinite and talc increases toward the 1-3m wide borehole casing deformation zones, which are expected to be deforming at above the average creep rate 2. Evidence of pressure solution creep and fracture sealing is more abundant in the siltstone cataclasites than in the shale. Such rocks could act as rigid inclusions that are repeatedly loaded to seismic failure by creep of the surrounding clay gouge. Regular cycles of fracture and restrengthening by fracture sealing in and around the inclusions are thus expected. The inclusions may be viewed as asperity patches (or cluster of patches) that predominantly deform by pressure solution at below the average creep rate.

  12. Interseismic deformation and creep along the central section of the North Anatolian Fault (Turkey): InSAR observations

    E-print Network

    Fialko, Yuri

    Interseismic deformation and creep along the central section of the North Anatolian Fault (Turkey the central section of the North Anatolian Fault (NAF) in Turkey using interferometric synthetic aperture along the central section of the North Anatolian Fault (Turkey): InSAR observations and implications

  13. Interseismic deformation and creep along the central section of the North Anatolian Fault (Turkey): InSAR observations

    E-print Network

    Sandwell, David T.

    Interseismic deformation and creep along the central section of the North Anatolian Fault (Turkey Anatolian Fault (NAF) in Turkey using interferometric synthetic aperture radar data from the Advanced Land Anatolian Fault (Turkey): InSAR observations and implications for rate-and-state friction properties, J

  14. 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 550C with the stress 424.5 MPa and for Ferritic Low Carbon Steel (2.25Cr-1Mo) in 570C 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 ?=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 addition, it was also developed a new method for predicting the remaining life using quantification of microstructure and using expansion of parameter Larson Miller from Taylor series for critical component in high temperature in industry. It was found that the proposed method was easier to be applied in field with the results more accurate then Larson Miller Method.

  15. 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.

  16. PHILOSOPHICAL MAGAZINE, 2003, VOL. 83, NO. 3, 401414 Effects of pressure on high-temperature dislocation creep

    E-print Network

    Jung, Haemyeong

    -temperature dislocation creep in olivine Shun-ichiro Karatoy and Haemyeong Jungz Department of Geology and Geophysics form 14 August 2001] Abstract Effects of pressure on high-temperature, dislocation creep in olivine using a newly developed high-resolution dislocation density measurement technique to estimate the creep

  17. 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.

  18. The fate of fluid inclusions during high-temperature experimental deformation of olivine aggregates

    NASA Astrophysics Data System (ADS)

    Carter, Matthew J.; Zimmerman, Mark E.; Teyssier, Christian

    2015-05-01

    Torsion experiments on initially wet and dry olivine aggregates at equivalent deformation conditions investigated the fate of fluid inclusions (FIs) during high-temperature deformation. Wet samples were produced by adding water to San Carlos olivine powders before hot pressing; those hot pressed without water are considered dry. After hot pressing, wet and dry aggregates have comparable grain sizes, but wet aggregates have more abundant primary FIs. Talc jackets were fitted around some wet and dry samples prior to deformation to hydrate samples during deformation via talc dehydration at elevated temperature, whereas other samples were deformed without talc. At similar strain rates (~1.0 10-4 s-1), the peak shear stress for the dry sample (no talc) was 190-220 MPa, whereas all other samples reached 180 MPa; the strengths of wet ( talc) and dry (+ talc) specimens appear similar. Deformed samples reveal abundant FIs, reduced grain size, shape preferred orientation of olivine, and a pervasive low-angle fabric (C') to the shear plane defined by aligned FIs. Samples deformed with talc have FI-rich and FI-depleted domains; where FIs are abundant, the C' fabric is better developed and grain size is smaller. Electron backscatter diffraction pole figures suggest that olivine deformed in the dislocation creep regime via the (010)[100] slip system. Results of these experiments suggest that FIs are redistributed during dislocation creep, leading to the development of grain-scale, high-diffusivity pathways.

  19. 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 are consistent with the values of the respective stress exponents and activation energies that were obtained and provide confirmatory evidence for the operation of diffusional (former alloy) or dislocation (latter alloy) creep mechanisms. In contrast, the intermetallic phases contained very few dislocations, but many cracks. The relative contributions of the {alpha}-Mo and the intermetallic particles to the overall deformation process, including their individual and collective dependence on temperature and strain rate are discussed in light of the present results and those from previous reports.

  20. 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 the CARES/Creep program.

  1. 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 600C to 750C 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 evolution of heat treated steel was correlated with the differential scanning calorimetric study. The combination of microstructural studies with optical microscopy, scanning and transmission electron microscopy, microhardness profiles, and calorimetric plots helped in the understanding of the evolution of microstructure and precipitates in Grade 91 steel. The residual stresses were determined at the mid-thickness of the plate, 4.35 mm and 2.35 mm below the surface of the as-welded and post-weld heat treated plate. The residual stresses of the as-welded plate were compared with the post-weld heat treated plate. The post-weld heat treatment significantly reduced the residual stress in the base metal, heat affected zone, and the weld zone. Vickers microhardness profiles of the as-welded, and post-weld heat treated specimens were also determined and correlated with the observed residual stress profile and microstructure.

  2. 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.

  3. 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.

  4. 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 cracking due to the imposed deformation. By measuring the AE generated during deformation we are then able to apply fracture forecast models to predict, retrospectively, the time of failure. We find that higher temperatures increase the strain rate during creep for the same %Ss, and that the accuracy of the forecast does not change with increasing temperature.

  5. Standard test method for flexure-creep of sandwich constructions

    SciTech Connect

    Not Available

    1980-01-01

    This method covers the determination of the creep characteristics and creep rate of sandwich constructions loaded in flexure, at any desired temperature. The determination of the creep rate provides information on the behavior of sandwich constructions under constant load. Creep is defined as deflection under constant load over a period of time beyond the initial deformation due to the application of the load. Deflection data obtained from this method can be plotted against time, and a creep rate determined. By using standard specimen constructions and constant loading, the method may also be used to evaluate creep behavior of adhesives for use in sandwich panels.

  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. 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.

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. High-temperature creep behavior of second-phase particle-strengthened tungsten-rhenium alloys

    SciTech Connect

    Chen, Borliang.

    1990-01-01

    The creep behavior of W{sup {minus}4}Re{sup {minus}0}.26HfC, W{sup {minus}3}.6Re{sup {minus}1}ThO{sub 2}, W{sup {minus}11}Re{sup {minus}1}ThO{sub 2}, and W{sup {minus}26}Re{sup {minus}1}ThO{sub 2} alloys were evaluated at elevated temperatures (between 1955 and 2500 K) in a custom-built high vacuum creep testing facility. These alloys are promising emitter materials for the Thermionic Energy Converter. The effects of stress and temperature on the creep rate of these alloys were determined and the stress exponents and creep activation energies of these alloys were measured. Results showed that HfC particles have a very high strengthening effect on the W{sup {minus}4}Re matrix up to 2200 K. At temperatures higher than 2200 K the coarsening rate of HfC is so high that they lose their strengthening effect rapidly. Comparing the creep strength of the arc-melted W{sup {minus}4}Re{sup {minus}0}.26HfC with that of the P/M W-Re{sup {minus}1}ThO{sub 2} alloys, it was found that at temperatures less than or equal to 2200 K, W{sup {minus}4}Re{sup {minus}0}.26HfC has the highest creep.

  14. 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.

  15. 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.

  16. Deformation of contour and Hawking temperature

    E-print Network

    Chikun Ding; Jiliang Jing

    2010-01-19

    It was found that, in an isotropic coordinate system, the tunneling approach brings a factor of 1/2 for the Hawking temperature of a Schwarzschild black hole. In this paper, we address this kind of problem by studying the relation between the Hawking temperature and the deformation of integral contour for the scalar and Dirac particles tunneling. We find that correct Hawking temperature can be obtained exactly as long as the integral contour deformed corresponding to the radial coordinate transform if the transformation is a non-regular or zero function at the event horizon.

  17. 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.

  18. Apparent activation volume for creep of copper and alpha brass at intermediate temperatures

    NASA Technical Reports Server (NTRS)

    Raj, S. V.

    1989-01-01

    Experimental measurements of the apparent activation volume for creep, V-asterisk, of Cu and Cu-30 pct Zn conducted at intermediate temperatures showed two types of strain dependencies. At the lower temperatures and higher stresses, V-asterisk decreased with increasing creep strain, while at higher temperatures and lower stresses, V-asterisk was essentially independent of strain. The low temperature-high stress behavior for Cu and Cu-30 pct Zn was found to be consistent with the dominance of a dislocation intersection mechanism. The high temperature-low stress data for the pure metals suggest that the rate-controlling process involves the nonconservative motion of jogs on screw dislocations. For the latter conditions, an additional contribution from solute drag-limited dislocation glide also appears to be important in governing the creep behavior of the alloy.

  19. 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 accumulation of displacement reaches about 1m, which is significantly-distinguishable by photogrammetric method. We measure profiles across the fault on 1978 and 2007 air-photograph by photogrammetric system respectively. The comparing result is shown that there are regional differences in deformation in relatively narrow region. About this result, we think two possibility; one is the creeping is not uniformity along the fault, second is the photogrammetry is not enough quality. We should actually check the creeping or not. We made thee new leveling survey lines in last year. In this August , we carried out second leveling survey in three area. We can show the variation of the deformation pattern and uplift rate across the LVF in this presentation.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Room-Temperature Nanoindentation Creep of Thermally Cycled Ultrasonically Bonded Heavy Aluminum Wires

    NASA Astrophysics Data System (ADS)

    Agyakwa, P. A.; Marques, V. M. F.; Corfield, M. R.; Li, J. F.; Yang, L.; Johnson, C. M.

    2013-03-01

    Recent findings suggest that creep occurs during thermal cycling of ultrasonically bonded wires, the extent of which is influenced by the nature of the temperature cycle, particularly its peak temperature. In this work, this hypothesis is investigated through a study of the power-law creep behavior of bonded 375- ?m aluminum wires that have been thermally cycled. Data from a study of two wire purity levels (99.999% and 99.99%) and two different cycling profiles (-55C to 125C and -60C to 170C) are presented. Room-temperature creep stress exponents are derived for the wire bonds from constant-load nanoindentation tests and compared with their respective microstructures.

  8. JOURNAL OF MATERIALS SCIENCE 37 (2002) 2899 2907 Creep deformation and monotonic stress-strain

    E-print Network

    Fatemi, Ali

    2002-01-01

    of Mechanical, Industrial and Manufacturing Engineering, The University of Toledo, Toledo, Ohio, USA E of a typical creep curve. turbine blade in a military aircraft engine (tR = 100 hrs) [1]. In such short life hardening, softening, and damage processes, resulting in a nearly constant creep rate. The tertiary stage

  9. 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.

  10. Strain localization and grain size reduction during high-stress low-temperature plasticity and subsequent creep below the seismogenic zone

    NASA Astrophysics Data System (ADS)

    Trepmann, Claudia

    2014-05-01

    A sequence of high-stress crystal-plasticity with accompanying microcracking and subsequent creep at low stresses in the plastosphere can be triggered by the rupture of a fault in a major earthquake within the overlying seismogenic zone. In this study, microfabrics are analyzed by polarized light microscopy and electron microscopic techniques (SEM/EBSD, FIB, TEM) in rocks (vein quartz, peridotite) experimentally deformed at conditions that correspond to those prevailing in the upper plastosphere following a major earthquake. The experiments are carried out in a Griggs-type solid medium apparatus with a deformation stage at low temperature (300 to 600 C) and high stress ("kick") followed by a stage at higher temperature (900 to 1000 C) and isostatic ("cook") or low stress ("creep"). The resulting microfabrics show amazing resemblance to those observed in rocks from natural deep continuations of seismically active fault zones (i.e., shear zones). Localized zones of small new grains (a few m in diameter) without systematic crystallographic preferred orientation within deformed host grains occur. The new grains develop by grain-boundary migration driven by the reduction in surface and strain energies at low stresses from highly damaged zones formed by initial low-temperature plasticity with associated cataclasis at high-stress deformation. A high variability in grain size is observed with the smallest grain size in the center of the highly damaged zones. The grain size reduction is controlled by strain during the initial high-stress deformation and growth is occurring only during the low-stress stage - rendering conventional grain size piezometers inappropriate. In large remnant host grains, short-wavelength undulatory extinction is reflecting low-stress modification (recovery) outside the highly damaged zones but in areas of original high dislocation densities formed at high-stress low-temperature plasticity. Extrapolation to natural conditions suggests that the observed characteristic microstructures may develop within as little as tens of years and less than ten thousands of years. The characteristic deformation and recrystallization microstructures can be expected to be stable over geological time scales, since driving forces for further modification are not sufficient to erase the characteristic heterogeneities. Thus, they are diagnostic for a past sequence of high-stress deformation (a combination of brittle failure and low-temperature plasticity) followed by creep at low stresses (recovery and recrystallization) in shear zones as deep continuations of seismically active fault zones. Such a sequence can explain initial grain size reduction localized along highly damaged zones during high-stress crystal-plasticity further leading to localized recrystallization during subsequent low-stress creep.

  11. Elevated Temperature Deformation of Cr3Si Alloyed with Mo

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Whittenberger, J. Daniel; Zeumer, B.; Sauthoff, G.

    1998-01-01

    Four-point bend, constant load compressive creep and constant engineering strain rate tests were conducted on arc-melted and powder-metallurgy (PM) processed Cr40Mo30Si30 specimens in the temperature range 1400 and 1700 K. This is a two phase alloy consisting of (CrMo)3Si and (Cr,Mo)5Si3 phases. The PM specimens, which were substantially weaker than the arc-melted materials, exhibited a stress exponent n, of about 2 and an apparent activation energy for creep, Q(sub 3), of 485 kJ/mol. The mechanism in these specimens appeared to be controlled by creep of a glassy phase. In the case of arc-melted specimens for which nis approximately 3 and Q(sub 3) is approximately 430 kJ/mol, the rate-controlling creep mechanism appeared to be that dominant in the (Cr,Mo)5Si3 phase. In this case, it is suggested that the Nabarro creep mechanism, where dislocation climb is controlled by Bardeen-Herring vacancy sources, is the dominant creep mechanism. Finally, an analysis of the present and literature data on Cr3Si alloyed with Mo appeared to suggest that the creep rate decreases sharply with an increase in the Mo/Si ratio.

  12. 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.

  13. 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.

  14. 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.

  15. Thermal-mechanical effects of low-temperature plasticity (the Peierls mechanism) on the deformation of a viscoelastic shear zone

    NASA Astrophysics Data System (ADS)

    Kameyama, Masanori; Yuen, David A.; Karato, Shun-Ichiro

    1999-04-01

    We studied for the first time the effects of low-temperature plasticity on the formation of shear zones. A thermal-mechanical model has been developed for describing the shear deformation of Maxwell viscoelastic material with a rheology close to dry olivine. We employed a one-dimensional model with a half-width of L deforming under a constant velocity U at the boundary, and the spatially-averaged strain rate U/L was set to O(10-14) s-1. In addition to diffusion and power-law creep, we included deformation by low-temperature plasticity, called the Peierls mechanism, which is significant at low temperatures and has a strong exponential dependence on the stress. When a sufficient magnitude of heat is generated by the rapid conversion from elastically-stored energy into viscous dissipation, thermal instability takes place and the deformation localizes in a narrow region. By comparing the condition for thermal instability, we found that the low-temperature plasticity inhibits the development of thermal instability in shear zones in case of constant strain rate. The Peierls mechanism enhances deformation at a significantly lower stress compared to the rheology with solely diffusion creep and power-law creep. The enhanced deformation by low-temperature plasticity produces lower amount of dissipative heating, and thus stabilizes the shear zone. Comparing the stability between constant strain-rate and constant stress boundary conditions, we found that the Peierls mechanism exerts an opposite destabilizing effect in the case of constant stress. For dry olivine rheology and realistic magnitude of the strain rate, the effect of low-temperature plasticity is significant for temperatures between around 800 K and 1000 K. This finding suggests that the low-temperature plasticity may be crucial in determining the thermal-mechanical stability in the shallow portion of slabs.

  16. 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-8 Cr-4 Nb alloy. The Rocketdyne Division of Rockwell International is conducting independent testing to analyze the properties for their projected needs in advanced rocket engine applications. Metallamics, a company based in Traverse City, Michigan, is entering into a Space Act Agreement to evaluate and test Cu-Cr-Nb alloys as materials for welding electrodes that are used in robotic welding operations. Creep rate is one of the alloy properties that determines the degree to which a welding electrode will mushroom or expand at the tip. A material with a low creep rate will resist mushrooming and give the electrode a longer life, minimizing downtime. This application holds the potential for large-scale usage of the alloy in the automotive and other industries. Success here would dramatically decrease the cost of the alloy and increase availability for aerospace applications.

  17. 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.

  18. 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.

  19. 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 a corresponding development of a back stress due to a significant increase in the dislocation density during thermal cycling.

  20. 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 950C, 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 950C. 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.

  1. 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 ?-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 ?-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 ?-TiAl, whereas the former can be rationalized by the instability of the microstructure containing metastable phases.

  2. 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.

  3. 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.

  4. Deformation Induced Dissolution-Creep in the Ductile Lishan Fault Zone, Taiwan

    NASA Astrophysics Data System (ADS)

    Stokes, M.; Wintsch, R. P.; Kunk, M. J.; Bish, D. L.

    2011-12-01

    Slates of similar low metamorphic grade on either side of the Lishan fault zone, central Taiwan display a single pervasive cleavage defined by muscovite (mu)and chlorite (chl) folia whereas interbedded quartzites are commonly fractured. CL imaging of quartz in the slates reveals three distinct populations, namely detrital quartz of mixed provenance, authigenic overgrowths, and metamorphic overgrowths and ribbons. Textures show that metamorphic quartz with overgrowths is widespread and that boundaries of these complex grains are sharply truncated by cleavage forming mu+chl folia. Electron petrography of the phyllosilicates shows three texturally distinct generations of muscovite: detrital, pre-deformation mu-chl stacks, and metamorphic mu+chl folia. Both detrital grains and mu-chl stacks are truncated and dissolved by the younger mu+chl cleavage-forming fabric. Detrital plagioclase grains are also truncated by mica folia and are commonly overgrown by quartz pressure shadows. These observed textures qualitatively demonstrate the active role of dissolution and precipitation in the slaty cleavage development. To further assess the dissolution-precipitation process, we have applied whole-rock 40Ar/39Ar analysis, and X-ray diffraction (XRD) to bulk samples. Widely ranging Cenozoic whole-rock 40Ar/39Ar total gas ages from the slates reflect the isotopic contributions from the three muscovite age populations, and demonstrate that the slates never exceeded the Ar retention temperature for muscovite. XRD data show significant range of broadening of muscovite peaks (modeled using a strain parameter in the Rietveld refinement). We attribute to the peak broadening (high value of strain parameter) to the presence of multiple muscovite populations of varied chemical composition; this was confirmed by energy-dispersive X-ray analyses. The total gas ages decrease with the narrowing of the muscovite peaks and drop in the muscovite strain parameter. This can be explained by the disappearance of older muscovite populations (> ~15 Ma) via dissolution with the concomitant precipitation of young (< ~5 Ma) fabric-forming muscovite. The ratio of metamorphic quartz to total quartz (quantified from CL transects) correlates positively with total gas ages. However, the relative proportion of metamorphic quartz correlates inversely with the relative amount of cleavage forming muscovite as inferred from the strain parameter. These correlations suggest that quartz recrystallization induced by deformation was active, but independent of the degree of muscovite recrystallization. However, both mineral populations were actively participating in the development of the fabric. Thus the deformation-induced dissolution of detrital and authigenic minerals and precipitation of fabric-forming minerals dominated the development of slaty cleavage during lower greenschist facies deformation.

  5. 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.

  6. Effect of Nb and Cu on the high temperature creep properties of a high MnN 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 MnN austenitic stainless steel was investigated at 600 and 650 C. In the original high MnN 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.

  7. Microstructural Evolution of an Extensional Shear Zone: the Transition from Dislocation Creep to Grain Boundary Sliding in Naturally Deformed Plagioclase

    NASA Astrophysics Data System (ADS)

    Miranda, E.; Hirth, G.; John, B. E.

    2014-12-01

    We present microstructural, LPO, and misorientation data from EBSD analyses to interpret the deformation mechanisms of naturally deformed plagioclase in an amphibolite-facies extensional shear zone within oceanic crust. Textural data and mineral chemistry data for thermometry were acquired on samples of gabbro mylonite collected from the footwall of the Atlantis Bank oceanic core complex; we focus on a monophase plagioclase layer with a high ratio of recrystallized matrix grains to porphyroclasts. Sample microstructures are subdivided into three regions: seven porphyroclasts, recrystallized grains immediately adjacent to those porphyroclasts, and the population of recrystallized matrix grains. All porphyroclasts exhibit subgrain development and show clustering of low-angle (3-10) misorientation axes within the {010} plane, consistent with slip on {010}. However, only one porphyroclast is oriented for operation of the {010}<001> easy slip system. The small recrystallized grains immediately adjacent to the porphyroclasts do not show a host control relationship with their respective porphyroclasts, and these grains are also smaller than the subgrains of the porphyroclasts. Recrystallized matrix grains are fine-grained (mean grain size 8 ?m) and slightly elongate parallel to foliation, with local misorientations concentrated along grain boundaries and junctions. They exhibit a weak, nonrandom LPO suggesting the activity of the {111}<110> slip system, and their neighbor-pair misorientations are shifted towards higher angles. We interpret the distinctive relationships between the three regions as evidence of a transition from dislocation creep to dislocation-accommodated grain boundary sliding (DisGBS). Porphyroclast subgrains and misorientation axes suggest the operation of dislocation creep, but the lack of host control in the adjacent recrystallized grains precludes grain size reduction through subgrain rotation recrystallization alone. High driving force bulge nucleation likely contributed to the grain size reduction and recrystallization of matrix grains, triggering the onset of grain size sensitive DisGBS. We suggest that the transition between deformation mechanisms is an effective weakening mechanism that contributed to development of the shear zone.

  8. 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 Industrial Materials program is sponsoring work to conduct creep testing and analysis on refractories of interest to the glass industry. An earlier stage of the project involved identifying which refractories to test and this is described elsewhere. Conventional silica was one such identified refractory category, and the present report describes the creep behavior of this class of refractories. To portray a more complete understanding of how these refractories perform at service temperatures, their fundamental corrosion resistances, dimensional stabilities, and microstructure were characterized as well.

  9. High-temperature fracturing and subsequent grain-size-sensitive creep in lower crustal gabbros: Evidence for coseismic loading followed by creep during decaying stress in the lower crust?

    NASA Astrophysics Data System (ADS)

    Okudaira, Takamoto; Je?bek, Petr; Stnitz, Holger; Fusseis, Florian

    2015-05-01

    The mechanism of shear zone formation in lower crustal, relatively "dry" rocks is still poorly understood. We have studied the high-temperature deformation of the Hasvik gabbro (northern Norway) which commences by fracturing. The 10-20 m wide fractures show little displacement. The fine-grained plagioclase and orthopyroxene in the fractures lack a crystallographic preferred orientation (CPO) or a systematic crystallographic orientation with respect to the host grains. Fractures grade into narrow shear zones, which are composed of fine (10-20 m), equant grains of recrystallized plagioclase, amphibole, and pyroxene. Recrystallized plagioclase and pyroxene have compositions different from the magmatic grains, suggesting that they have formed by nucleation and growth. Based on conventional plagioclase-amphibole thermobarometry, the shear zones have formed at temperatures and pressures of 700-750C and 0.5-0.6 GPa. The observed primary minerals cut by fractures suggest high-temperature fracturing in the absence of high pore pressures, which implies a high strength of the lower crustal gabbros and high stresses at fracturing. The shear zones are characterized by the lack of CPO and a small grain size, suggesting that the mechanism of deformation of the fine-grained plagioclase and orthopyroxene has been grain boundary sliding accommodated by diffusive mass transfer. The amphibole grains have strong CPOs, which most likely result from oriented growth and/or rigid body rotations during deformation. The process that initiated the fracturing and subsequent viscous creep in the Hasvik gabbro may have resulted from a process of coseismic loading followed by creep during decaying stress in the lower crust.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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

  16. 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

  17. 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.

  18. 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.

  19. Effect of nitrogen high temperature plasma based ion implantation on the creep behavior of Ti-6Al-4V alloy

    NASA Astrophysics Data System (ADS)

    Oliveira, A. C.; Oliveira, R. M.; Reis, D. A. P.; Carreri, F. C.

    2014-08-01

    Nitrogen high temperature plasma based ion implantation (HTPBII) performed on Ti-6Al-4V significantly improved the creep behavior of the alloy. Treatments were performed for 1 h at a working pressure of 4 mbar and negative high voltage pulses of 7.5 kV, 30 ?s and 500 Hz were applied on the specimens heated at 800 C and 900 C, respectively. Microstructural characterization of the treated samples revealed the formation of nitrided layers, with simultaneous formation of TiN and Ti2N. The most intense peaks of these compounds were obtained at higher treatment temperature, probably due to the diffusion of nitrogen into titanium. The presence of nitrides caused surface hardening up to three times higher in comparison with untreated alloy. Constant load creep tests were conducted on a standard creep machine in air atmosphere, at stress level of 319 MPa at 600 C. Significant reductions of the steady-state creep rates (?) were measured for martensitic Ti-6Al-4V treated by nitrogen HTPBII, reaching minimum creep rates of 0.0318 h-1 in comparison with 0.1938 h-1 for untreated sample. The improvement of the creep resistance seems to be associated with the formation of a thick nitrided layer, which acts as a barrier to oxygen diffusion into the material. In addition, the increase of the grain size generated by the heating of the substrate during the treatment can affect some creep mechanisms, leading to a significant reduction of ?.

  20. Influence of phosphorus on the creep ductility of copper

    NASA Astrophysics Data System (ADS)

    Sandstrm, Rolf; Wu, Rui

    2013-10-01

    Around 1990 it was discovered that pure copper could have extra low creep ductility in the temperature interval 180-250 C. The material was intended for use in canisters for nuclear waste disposal. Although extra low creep ductility was not observed much below 180 C and the temperature in the canister will never exceed 100 C, it was feared that the creep ductility could reach low values at lower temperatures after long term exposure. If 50 ppm phosphorus was added to the copper the low creep ductility disappeared. A creep cavitation model is presented that can quantitatively describe the cavitation behaviour in uniaxial and multiaxial creep tests as well as the observed creep ductility for copper with and without phosphorus. A so-called double ledge model has been introduced that demonstrates why the nucleation rate of creep cavities is often proportional to the creep rate. The phosphorus agglomerates at the grain boundaries and limits their local deformation and thereby reduces the formation and growth of cavities. This explains why extra low creep ductility does not occur in phosphorus alloyed copper.

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

    SciTech Connect

    Stoica, Grigoreta M; Stoica, Alexandru Dan; Miller, Michael K; Ma, Dong

    2014-01-01

    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.

  2. Role of coupled cataclasis-pressure solution deformation in microearthquake activity along the creeping segment of the SAF: Inferences from studies of the SAFOD core samples

    NASA Astrophysics Data System (ADS)

    Hadizadeh, J.; Gratier, J.; Renard, F.; Mittempregher, S.; di Toro, G.

    2009-12-01

    Rocks encountered in the SAFOD drill hole represent deformation in the southern-most extent of the creeping segment of the SAF north of the Parkfield. At the site and toward the northwest the SAF is characterized by aseismic creep as well as strain release through repeating microearthquakes M<3. The activity is shown to be mostly distributed as clusters aligned in the slip direction, and occurring at depths of between 3 to 5 kilometers. It has been suggested that the events are due to frequent moment release from high strength asperities constituting only about 1% or less of the total fault surface area within an otherwise weak fault gouge. We studied samples selected from the SAFOD phase 3 cores (3142m -3296m MD) using high resolution scanning electron microscopy, cathodoluminescence imaging, X-ray fluorescence mapping, and energy dispersive X-ray spectroscopy. The observed microstructural deformation that is apparently relevant to the seismological data includes clear evidence of cyclic deformation events, cataclastic flow, and pressure solution creep with attendant vein sealing and fracture healing fabrics. Friction testing of drill cuttings and modeling by others suggest that the overall creep behavior in shale-siltstone gouge may be due to low bulk friction coefficient of 0.2-0.4 for the fault rock. Furthermore, the low resistivity zone extending to about 5km beneath the SAFOD-Middle Mountain area is believed to consist of a pod of fluid-filled fractured and porous rocks. Our microstructural data indicate that the foliated shale-siltstone cataclasites are, in a highly heterogeneous way, more porous and permeable than the host rock and therefore provide for structurally controlled enhanced fluid-rock interactions. This is consistent with the observed pressure solution deformation and the microstructural indications of transiently high fluid pressures. We hypothesize that while the friction laws defining stable sliding are prevalent in bulk deformation of the creeping segment, there exist the possibility of steady conditions for repetitive healing, dilation, and rupture of populations of stress-oriented patches due to operation of pressure solution creep along the fault zone. The limitation on the total area of the locked patches at any given time would be controlled primarily by the imposed tectonic and near field rates of slip and fluid flux within the local permeability structure. The available geophysical data for the creeping section of the SAF including hypocenter cluster distribution, moment release rate, seismic rupture area (? healed patch size), stress drop and return time characteristics point to a highly heterogeneous internal structure at the SAFOD site, and could be used to test the proposed coupled cataclasis-pressure solution microstructural model.

  3. 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 ?m) 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 ~3.510-6 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.

  4. 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.

  5. Strain heterogeneity during creep of Carrara marble

    E-print Network

    Quintanilla Terminel, Alejandra

    2014-01-01

    Creep processes in calcite have been extensively studied, leading to the establishment of deformation mechanism maps. However, flow laws assuming a steady-state and homogeneous creep deformation cannot describe the strain ...

  6. Analysis of the Deformation Behavior in Tension and Tension-Creep of Ti-3Al-2.5V (wt pct) at 296 K and 728 K (23 C and 455 C) Using In Situ SEM Experiments

    NASA Astrophysics Data System (ADS)

    Li, Hongmei; Boehlert, Carl J.; Bieler, Thomas R.; Crimp, Martin A.

    2014-12-01

    The deformation behavior of a Ti-3Al-2.5V (wt pct) near-? alloy was investigated during in situ deformation 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-creep experiment was performed at 728 K (455 C) and 180 MPa ( ?/ ? ys = 0.72). The active deformation systems were identified in the ? phase using electron backscattered diffraction based slip-trace analysis and SEM images of the surface. Prismatic slip deformation 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 deformation mode at both 296 K and 728 K (23 C and 455 C), but the extent of twinning activity decreased with increased temperature. 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-creep 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 deformation 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).

  7. Room-temperature deformation in a Laves phase

    SciTech Connect

    Livingston, J.D.; Hall, E.L. )

    1990-01-01

    Transmission electron microscopy of two-phase V-Hf-Nb and V-Hf-Nb-Ti alloys plastically deformed at room temperature shows that {l brace}111{r brace}{l angle}112{r angle} twinning is a major deformation mode for the HfV{sub 2}-based Laves phase. Bands of concentrated shear are also observed. Possible approaches to enhance low-temperature deformability in other Laves phases are discussed.

  8. 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 ? phases (W6Fe7 type) cover the boundary. The formation of ? 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 ? 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.

  9. Microstructural influence on high temperature creep flow of Zr-1%NbO alloy in near- ?, ( ? + ?), and ? temperature ranges in a high vacuum environment

    NASA Astrophysics Data System (ADS)

    Kaddour, Djilali; Gourgues-Lorenzon, Anne-Franoise; Brachet, Jean-Christophe; Portier, Laurence; Pineau, Andr

    2011-01-01

    Uniaxial tensile creep tests were carried out at 650-1100 C in a high vacuum environment on Zr-1%NbO tubes with various microstructures. The effect of microstructure on creep flow in the ( ? + ?) temperature range is significant (the creep rate being modified by up to three orders of magnitude) under stresses lower than 10 MPa, that is, for stress values of one order of magnitude lower than those characteristic of prototypical Loss-of-coolant-accident (LOCA) conditions. Under stresses higher than about 20 MPa, this effect is much smaller. No transformation-induced plasticity was detected from anisothermal creep tests, once the creep strain was thoroughly taken into account to process experimental strain vs. time data.

  10. A unified creep-plasticity model suitable for thermo-mechanical loading

    NASA Technical Reports Server (NTRS)

    Slavik, D.; Sehitoglu, H.

    1988-01-01

    An experimentally based unified creep-plasticity constitutive model was implemented for 1070 steel. Accurate rate and temperature effects were obtained for isothermal and thermo-mechanical loading by incorporating deformation mechanisms into the constitutive equations in a simple way.

  11. 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. Progress report

    SciTech Connect

    Not Available

    1991-12-31

    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.

  12. Elevated temperature compressive steady state deformation and failure in the oxide dispersion strengthened alloy MA 6000E

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.

    1984-01-01

    The compressive flow strength-strain rate behavior of the oxide-dispersion-strengthened alloy MA 6000E has been studied in the temperature range 1144-1366 K, with strain rates ranging from 2.1 x 10 to the -5th to 2.1 x 10 to the -7th per s. It is found that the inherent strength of the alloy is essentially the same in all test directions and that the low strength observed in tensile tests results from the inability of grain boundaries to support high tensile stresses. The failure of MA 6000E under high-temperature, slow plastic flow conditions is shown to be the result of concentrated slip. Slow plastic deformation in MA 6000E can be described by a threshold stress model of creep where threshold stresses are calculated from relatively fast testing procedures and the effective stress exponent for creep is assumed to be 3.5.

  13. Stress relaxation and creep of high-temperature gas-cooled reactor core support ceramic materials: a literature search

    SciTech Connect

    Selle, J.E.; Tennery, V.J.

    1980-05-01

    Creep and stress relaxation in structural ceramics are important properties to the high-temperature design and safety analysis of the core support structure of the HTGR. The ability of the support structure to function for the lifetime of the reactor is directly related to the allowable creep strain and the ability of the structure to withstand thermal transients. The thermal-mechanical response of the core support pads to steady-state stresses and potential thermal transients depends on variables, including the ability of the ceramics to undergo some stress relaxation in relatively short times. Creep and stress relaxation phenomena in structural ceramics of interest were examined. Of the materials considered (fused silica, alumina, silicon nitride, and silicon carbide), alumina has been more extensively investigated in creep. Activation energies reported varied between 482 and 837 kJ/mole, and consequently, variations in the assigned mechanisms were noted. Nabarro-Herring creep is considered as the primary creep mechanism and no definite grain size dependence has been identified. Results for silicon nitride are in better agreement with reported activation energies. No creep data were found for fused silica or silicon carbide and no stress relaxation data were found for any of the candidate materials. While creep and stress relaxation are similar and it is theoretically possible to derive the value of one property when the other is known, no explicit demonstrated relationship exists between the two. For a given structural ceramic material, both properties must be experimentally determined to obtain the information necessary for use in high-temperature design and safety analyses.

  14. New constraints on upper mantle creep mechanism inferred from silicon grain-boundary diffusion rates

    NASA Astrophysics Data System (ADS)

    Fei, Hongzhan; Koizumi, Sanae; Sakamoto, Naoya; Hashiguchi, Minako; Yurimoto, Hisayoshi; Marquardt, Katharina; Miyajima, Nobuyoshi; Yamazaki, Daisuke; Katsura, Tomoo

    2016-01-01

    The creep in the Earth's interior is dominated either by diffusion creep which causes Newtonian mantle flow, or by dislocation creep which results in non-Newtonian mantle flow. Although previous deformation studies on olivine claimed a transition from dislocation creep to diffusion creep with depth in the upper mantle, they might misunderstand the creep rates due to experimental difficulties. Since creep 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 temperature, pressure, and water content, showing activation energy, activation volume, and water content exponent of 220 30kJ /mol, 4.0 0.7cm3 /mol, and 0.26 0.07, respectively. Our results based on Si diffusion in forsterite predict that diffusion creep dominates at low pressures and low temperatures, whereas dislocation creep dominates under high pressure and high temperature conditions. Water has negligible effects on both diffusion and dislocation creep. There is a transition from diffusion creep in the shallow upper mantle to dislocation creep in deeper regions. This explains the seismic anisotropy increases at the Gutenberg discontinuity beneath oceans and at the mid-lithosphere discontinuity beneath continents.

  15. 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 1073K and 1173K 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 10-9s-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 1173K and lower strain rate less than 10-4s-1. The grain boundary sliding couldn't be rate-controlling process at 1073K for the as-cold rolled TD specimen, where a dynamic recovery of the dislocation produced by cold-rolling is related to the deformation process.

  16. 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 Fe10Ni6.5Al10Cr3.4Mo 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.

  17. Steady, dynamic, creep/recovery, and textural properties of yoghurt/molasses blends: Temperature sweep tests and applicability of Cox-Merz rule.

    PubMed

    Eroglu, Ali; Bayramba?, Kadir; Eroglu, Zeynep; Toker, Omer S; Yilmaz, Mustafa T; Karaman, Safa; Dogan, Mahmut

    2016-01-01

    In this study, physicochemical, rheological (steady, dynamic, and creep/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. Temperature 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 deformation stability and internal viscosity (?1) decreased with concentration. Creep 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 deformation decreased with increase in molasses concentration. PMID:25614154

  18. High-temperature elastic-plastic and creep properties for SA533 Grade B Class I and SA508 materials

    SciTech Connect

    Reddy, G.B.; Ayres, D.J.

    1982-12-01

    High temperature elastic-plastic and creep properties are presented for SA533 Grade B Class I and SA508 Class II materials. These properties are derived from tests conducted at Combustion Engineering Material and Metallurgical Laboratories and cover the temperature range of 70/sup 0/F to 1200/sup 0/F.

  19. 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 main event. Using the distribution of the AE events the position of the fault in the source area was successfully delineated. The rupture area, elastic properties of the rock, the state of stress before the event occurred and frictional parameters of the rupture were used as input parameters to both numerical and analytical tools to reproduce the expected tilt. The calculated values were compared with the real values as recorded by the installed tiltmeters. A good correlation between the calculated and monitored amount of tilt was found. The tilt changes associated with this event showed a well pronounced after-tilt. The distribution of the AE events following the main shock was related to after tilt in order to quantify post slip behavior of the source. There was no evidence found for coseismic expansion of the source after the main slip. Therefore the hypothesis of the post-seismic creep behaviour of the source was proposed to explain the large amount of tilt following the main shock.

  20. 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 expressed as earthquakes large enough to model. Because the ratio of the rate of creep relative to the total slip rate is often used to infer the average depth of creep, the ?depth? of creep can be calculated and used to reduce the surface area of a fault that generates earthquakes in our model. This reduction of surface area of rupture is described by an ?aseismicity factor,? assigned to each creeping fault in Appendix A. An aseismicity factor of less than 1 is only assigned to faults that are inferred to creep during the entire interseismic period. A single aseismicity factor was chosen for each section of the fault that creeps by expert opinion from the observations documented here. Uncertainties were not determined for the aseismicity factor, and thus it represents an unmodeled (and difficult to model) source of error. This Appendix simply provides the documentation of known creep, the type and precision of its measurement, and attempts to characterize the creep as interseismic, afterslip, transient or triggered. Parts 2 and 3 of this Appendix compare the WG-07 deformation model and the seismic source model it generates to the strain generated by the Pacific - North American plate motion. The concept is that plate motion generates essentially all of the elastic strain in the vicinity of the plate boundary that can be released as earthquakes. Adding up the slip rates on faults and all others sources of deformation (such as C-zones and distributed ?background? seismicity) should approximately yield the plate motion. This addition is usually accomplished by one of four approaches: 1) line integrals that sum deformation along discrete paths through the deforming zone between the two plates, 2) seismic moment tensors that add up seismic moment of a representative set of earthquakes generated by a crustal volume spanning the plate boundary, 3) strain tensors generated by adding up the strain associated with all of the faults in a crustal volume spanning the plate

  1. Experiment and Modeling of Simultaneous Creep, Plasticity and Transformation of High Temperature Shape Memory Alloys During Cyclic Actuation

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

    The present work is focused on studying the cycling actuation behavior of HTSMAs undergoing simultaneous creep and transformation. For the thermomechanical testing, a high temperature test setup was assembled on a MTS frame with the capability to test up to temperatures of 600 C. Constant stress thermal cycling tests were conducted to establish the actuation characteristics and the phase diagram for the chosen HTSMA. Additionally, creep tests were conducted at constant stress levels at different test temperatures to characterize the creep 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 creep effects. The model calibration is based on the test results. The creep 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.

  2. Creep properties of catalyst coated membranes for polymer electrolyte fuel cells

    NASA Astrophysics Data System (ADS)

    Sadeghi Alavijeh, Alireza; Khorasany, Ramin M. H.; Habisch, Aronne; Wang, G. Gary; Kjeang, Erik

    2015-07-01

    Creep as a time-dependent mechanical damage acting either independently or in conjunction with other degradation mechanisms is known to reduce the membrane durability of polymer electrolyte fuel cells (PEFCs). Due to the important ionomer coupling of membrane and catalyst layers in PEFCs, the present work evaluates membrane creep when constrained within a catalyst coated membrane (CCM). Three key factors dominating creep life in commonly used perfluorosulfonic acid (PFSA) ionomer membranes, including creep stress, temperature, and relative humidity, were investigated by applying ex-situ creep loading and unloading experiments under controlled temperature and humidity conditions. The creep strain and recovery of the CCM were found to be highly dependent on the environmental conditions and applied stress levels, where the temperature effect on creep strain was the most significant. Repetitive creep - recovery cycles revealed that significant creep damage can accumulate in the material over time. This accumulated creep damage was found to be independent of the loading frequency while both peak strain and permanent deformation increased with the stress duration. Based on the present findings, it is recommended to reduce the operating temperature and ensure adequate membrane hydration in order to mitigate harmful creep effects in PEFCs.

  3. Tensile creep behavior and cyclic fatigue/creep interaction of hot- isostatically pressed Si sub 3 N sub 4

    SciTech Connect

    Liu, K.C.; Pih, H.; Stevens, C.O.; Brinkman, C.R.

    1991-01-01

    Tensile creep 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 temperatures ranging from 1200 to 1370{degree}C. Creep strain was measured with an optical strain extensometer until creep rupture occurred, in some cases for periods in excess of 2000 h. To study the effects of various preloading material histories on creep 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 creep behavior and enhance the resistance to creep deformation and hence the creep-rupture lifetime. However, the influence of the preloading histories on creep rate was diminished by high temperature 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 creep-rupture lifetime was observed for a precycled specimen tested at 1300{degree}C. Steady-state creep was absent in some cases under certain conditions of temperature, stress, and heat treatment. Little or no tertiary creep was usually detected before specimen fracture occurred. The steady-state creep rate of this material was found to be a function of applied stress, temperature, and possibly the level of crystallinity in the intergranular phase. 9 refs., 15 figs.

  4. Creep property and microstructure evolution of a nickel-base single crystal superalloy in [011] orientation

    SciTech Connect

    Han, G.M. Yu, J.J.; Hu, Z.Q.; Sun, X.F.

    2013-12-15

    The creep property and microstructure evolution of a single crystal superalloy with [011] orientation were investigated at the temperatures of 700 C, 900 C and 1040 C. It is shown that there exist stages of primary, steady-state, and tertiary creep under the lower temperature 700 C. As the temperature increases to high temperatures of 900 C and 1040 C, steady-state creep stage is reduced or disappears and the shape of creep curves is dominated by an extensive tertiary stage. The minimum creep 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 ?? phase almost keep original shape at the lower temperature 700 C and high applied stress. With the increasing creep temperature, ?? 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 ?? precipitates by stacking faults or bending dislocation pairs are the main deformation mechanism at the lower temperature of 700 C. At the high temperatures of 900 C and 1040 C, dislocation networks are formed at ?/?? interfaces and the ?? rafts are sheared by dislocation pairs. - Highlights: Creep properties of < 011 >-oriented single crystal superalloys were investigated. ?? phases become rafting at an angle of 45 inclined to the applied stress. Creep deformation mechanisms depend on temperature and stress.

  5. Flaw assessment guide for high-temperature reactor components subject to creep-fatigue loading

    SciTech Connect

    Ainsworth, R.A. . Berkeley Nuclear Labs.); Ruggles, M.B. ); Takahashi, Y. . Komae Research Lab.)

    1990-10-01

    A high-temperature 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 creep-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 creep 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.

  6. 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 intracrystalline deformation microstructures in naturally deformed vein quartz show particular geometrical relationships, in our opinion a to date underexposed aspect of these microstructures. Several of these geometrical relationships will be presented and their potential implications with respect to deformation mechanisms and conditions will be discussed. The geometrical relationships observed may suggest a similar formation mechanism for the different microstructures, a weakening effect for successive microstructure formation and a strong dependency on the crystallographic orientation.

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

    PubMed

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

    2014-01-01

    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-temperature creep, 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 temperature-dependent elastic anisotropy that leads to elastic softening and instability of the ferrite. We also demonstrate, from anisotropy-induced intergranular strains, that a deformation crossover exists from low-temperature lattice hardening to high-temperature lattice softening in response to extensive plastic deformation. PMID:25300893

  8. Unified creep-plasticity model for halite

    SciTech Connect

    Krieg, R. D.

    1980-11-01

    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 deformations and stresses must be predictable for these applications. At 300K, the nominal initial temperature for both applications, the salt is at 0.28 of the melting temperature and exhibits a significant time dependent behavior. A constitutive model has been developed which describes the behavior observed in an extensive set of triaxial creep tests. Analysis of these tests showed that a single deformation mechanism seems to be operative over the stress and temperature range of interest so that the secondary creep data can be represented by a power of the stress over the entire test range. This simple behavior allowed a new unified creep-plasticity model to be applied with some confidence. The resulting model recognizes no inherent difference between plastic and creep strains yet models the total inelastic strain reasonably well including primary and secondary creep 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.

  9. Impression creep behavior of atmospheric plasma sprayed and hot pressed MoSi{sub 2}/Si{sub 3}N{sub 4}

    SciTech Connect

    Hollis, K.J.; Butt, D.P.; Castro, R.G.

    1997-09-01

    The use of MoSi{sub 2} as a high temperature oxidation resistant structural material is hindered by its poor elevated temperature creep resistance. The addition of second phase Si{sub 3}N{sub 4} holds promise for improving the creep properties of MoSi{sub 2} without decreasing oxidation resistance. The high temperature impression creep behavior of atmospheric plasma sprayed (APS) and hot pressed (HP) MoSi{sub 2}/Si{sub 3}N{sub 4} composites was investigated. Values for steady state creep rates, creep activation energies, and creep stress exponents were measured. Grain boundary sliding and splat sliding were found to be the dominant creep mechanisms for the APS samples while grain boundary sliding and plastic deformation were found to be the dominant creep mechanisms for the HP samples.

  10. Time and space evolution of an active creeping zone: competition between brittle and ductile deformations, new insights from microstructure studies of SAFOD (San Andreas Fault Observatory at Depth) samples.

    NASA Astrophysics Data System (ADS)

    Richard, Julie; Gratier, Jean-Pierre; Doan, Mai-Linh; Boullier, Anne-Marie; Renard, Franois

    2013-04-01

    Creep processes can relax an important part of the tectonic stresses in active faults, either by permanent steady-state creep or by episodic post-seismic creep. 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 creeping zone: the Central Deforming Zone at 3296,6-3299,1m depth (relative to Phase 3 Core). 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 creep is an active deformation process in the SAF. We propose a model of microstructural evolution to characterize in which conditions pressure solution creep 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 creep 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 creep. However, the progressive healing of the fracture annihilates this effect. Meanwhile, growth of phyllosilicate minerals, associated with postseismic fluid flow may also activate the creep rate. - During much longer geological periods (hundred thousands to millions of years), the composition of gouge material deformed by pressure solution evolves by the passive concentration of phyllosilicates due to the dissolution of soluble minerals. If their content is large enough, phyllosilicates could control the creep mechanism and accommodate the deformation by friction on clay layers. The steady state creeping zone of the SAF illustrates both effects thanks to very fine grains resulting from successive fracturing processes, very few amount of healing, possible growth of metamorphic clays and a general passive concentration of phyllosilicates with volume decrease. Conversely, in the nearby damaged zone, healing reduces the efficiency of pressure solution. Microseismicity, resulting from the fracturing of healed zones, may maintain a dynamic equilibrium between fracturing and healing. The southern part of the permanent creeping zones, which shows 20-30 years "Parkfield"-like earthquake cycles with postseismic creep, may illustrate the competition between healing/strengthening and creep processes that occur during interseismic periods.

  11. Modeling the Role of Dislocation Substructure During Class M and Exponential Creep. Revised

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Iskovitz, Ilana Seiden; Freed, A. D.

    1995-01-01

    The different substructures that form in the power-law and exponential creep regimes for single phase crystalline materials under various conditions of stress, temperature and strain are reviewed. The microstructure is correlated both qualitatively and quantitatively with power-law and exponential creep as well as with steady state and non-steady state deformation behavior. These observations suggest that creep is influenced by a complex interaction between several elements of the microstructure, such as dislocations, cells and subgrains. The stability of the creep substructure is examined in both of these creep regimes during stress and temperature change experiments. These observations are rationalized on the basis of a phenomenological model, where normal primary creep is interpreted as a series of constant structure exponential creep 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 creep behavior of a single phase material using quantitative microstructural data. In this technique the thermally activated deformation mechanisms proposed by dislocation physics are interlinked with a previously developed multiphase, three-dimensional. dislocation substructure creep model. This procedure leads to several coupled differential equations interrelating macroscopic creep plasticity with microstructural evolution.

  12. Bend stress relaxation and tensile primary creep of a polycrystalline alpha-SiC fiber

    NASA Technical Reports Server (NTRS)

    Hee Man, Yun; Goldsby, Jon C.; Morscher, Gregory N.

    1995-01-01

    Understanding the thermomechanical behavior (creep 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 temperature applications. It is important to understand and model the total creep of fibers at low strain levels where creep 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 creep 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 creep conditions. The temperature, time, and stress dependences will be discussed for the stress relaxation and creep results. In addition, some creep and relaxation recovery experiments were performed in order to understand the complete viscoelastic behavior, i.e. both recoverable and nonrecoverable creep components of these materials. The data will be presented in order to model the deformation behavior and compare relaxation and/or creep behavior for relatively low deformation strain conditions of practical concern. Where applicable, the tensile creep results will be compared to bend stress relaxation data.

  13. Temperature Dependence of the Anisotropy and Creep in a Single-Crystal Nickel Superalloy

    NASA Astrophysics Data System (ADS)

    Pandey, Amit; Hemker, Kevin J.

    2015-07-01

    The thermomechanical response of the second-generation single-crystal nickel superalloy (SC180) was obtained for wide range of temperatures (25-1000C). Uniaxial tension and stress relaxation experiments were performed to study the influence of [100] and [110] crystallographic orientation on stress anisotropy and creep 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.

  14. Determination of Static Strength and Creep Buckling of Unstiffened Circular Cylinders Subjected to Bending at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Mathauser, Eldon E.; Berkovits, Avraham

    1959-01-01

    A method based on a semiempirical procedure is presented for predicting static strength and creep buckling of unstiffened circular cylinders subjected to pure bending at elevated temperatures. The method is applicable to cylinders that are loaded into the inelastic stress range prior to buckling and fail in a local mode. The predicted bending moments associated with static strength and creep buckling are compared with experimental data (taken from NACA RM 57El7) obtained from tests at 500 F on 5052-0 aluminum-alloy cylinders with radius- thickness ratios ranging from 125 to 250.

  15. Creep of carbon-yarn and carbon-carbon composites at high temperatures and high stresses. Technical report

    SciTech Connect

    Sines, G.; Yang, Z.; Vickers, B.D.

    1988-05-01

    To better understand the creep-behavior of carbon yarn and carbon-carbon composites, creep experiments were developed that permitted testing at high temperatures (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 creep, 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 creep 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 creep resistance.

  16. High temperature deformation of hot-pressed polycrystalline orthoenstatite. Ph.D. Thesis

    NASA Technical Reports Server (NTRS)

    Dehghan-Banadaki, A.

    1983-01-01

    Artificial hot pressed polycrystalline samples were prepared from purified powder of Bamble, Norway, orthoenstatite, (Mg0.86Fe0.14)SiO3. The uniaxial creep behavior of the polycrystalline orthoenstatite was studied over stress ranges of 10-180 MPa and temperatures 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 creep deformation 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.

  17. Influence of the High-Temperature Creep on the Phase Composition and Morphology of the ?' Phase of a Nickel Alloy

    NASA Astrophysics Data System (ADS)

    Nikonenko, E. L.; Popova, N. A.; Koneva, N. A.; Nikonenko, A. V.; Kozlov, . V.

    2015-07-01

    of electron microscopic study of Ni-Cr-Al based superalloy are presented. The superalloy prepared by the method of directed crystallization is investigated in the initial state and after creep for 10 h at C = 1100C and ? = 100 MPa. It is established that the alloy in both states is formed by ? and ?' phases based on the FCC crystal lattice; the ?' phase has ordered arrangement of atoms (the L12 superstructure) and is the main phase in all states. The phase composition and morphology are studied. The change in the phase composition and particle sizes of phases as a result of creep is analyzed. The influence of the high-temperature creep on the superalloy structure is established.

  18. Application of neutron diffraction in characterization of texture evolution during high-temperature creep in magnesium alloys

    SciTech Connect

    Vogel, Sven C; Sediako, Dimitry; Shook, S; Sediako, A

    2010-01-01

    A good combination of room-temperature and elevated temperature 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 temperature applications. Extrudability and high temperature 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 creep testing and studies of in-creep texture evolution for several wrought magnesium alloys developed for use in elevated-temperature 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.

  19. Creep Laboratory manual

    NASA Astrophysics Data System (ADS)

    Osgerby, S.; Loveday, M. S.

    1992-06-01

    A manual for the NPL Creep Laboratory, a collective name given to two testing laboratories, the Uniaxial Creep Laboratory and the Advanced High Temperature Mechanical Testing Laboratory, is presented. The first laboratory is devoted to uniaxial creep testing and houses approximately 50 high sensitivity creep machines including 10 constant stress cam lever machines. The second laboratory houses a low cycle fatigue testing machine of 100 kN capacity driven by a servo-electric actuator, five machines for uniaxial tensile creep testing of engineering ceramics at temperatures up to 1600C, and an electronic creep machine. Details of the operational procedures for carrying out uniaxial creep testing are given. Calibration procedures to be followed in order to comply with the specifications laid down by British standards, and to provide traceability back to the primary standards are described.

  20. Correlation of Creep Behavior of Domal Salts

    SciTech Connect

    Munson, D.E.

    1999-02-16

    The experimentally determined creep responses of a number of domal salts have been reported in, the literature. Some of these creep results were obtained using standard (conventional) creep tests. However, more typically, the creep data have come from multistage creep tests, where the number of specimens available for testing was small. An incremental test uses abrupt changes in stress and temperature to produce several time increments (stages) of different creep 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-Deformation (M-D) constitutive model. This model utilizes considerable general knowledge of material creep deformation to supplement specific knowledge of the material response of salt. Because the creep 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. Creep 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 assumptions permit the set to be completed. From the analysis, two distinct response groups were evident, with the salts of one group measurably more creep resistant than the other group. Interestingly, these groups correspond well with the indirectly determined creep closure of the SPR storage caverns, a correlation that probably should be expected. Certainly, the results suggest a simple laboratory determination of the creep characteristics of a salt material from a dome site can indicate the relative behavior of any potential cavern placed within that dome.

  1. Development of constitutive models for cyclic plasticity and creep behavior of super alloys at high temperature

    NASA Technical Reports Server (NTRS)

    Haisler, W. E.

    1983-01-01

    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 temperature below which the total strain consists essentially of elastic and rate insensitive inelastic strains only. Above this temperature, the rate dependent inelastic strain (creep) 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 temperature-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 temperature 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.

  2. Creep deformation and fracture of a Cr/Mo/V bolting steel containing selected trace-element additions

    NASA Astrophysics Data System (ADS)

    Larouk, Z.; Pilkington, R.

    1999-08-01

    The article reports the creep 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 creep strength or creep crack-growth resistance at 565 C. The fine-grained material shows low creep strength but notch strengthening, while the coarse-grained material shows higher creep strength and exhibits notch weakening for test times up to 2750 hours. From creep crack-growth tests, it appears that the C* parameter is not appropriate for correlating the creep crack-growth rate under the present test conditions. The parameters K I or ? 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.

  3. Comparison of measured temperatures, thermal stresses and creep residues with predictions on a built-up titanium structure

    NASA Technical Reports Server (NTRS)

    Jenkins, Jerald M.

    1987-01-01

    Temperature, thermal stresses, and residual creep 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 temperature 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 temperatures from measured values result in far more than proportional increases in thermal stress values. Measured residual stresses due to creep 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 creep law. Computational methodology advances in predicting residual stresses due to creep require significantly more viscoelastic material characterization.

  4. High temperature deformation behavior, thermal stability and irradiation performance in Grade 92 steel

    NASA Astrophysics Data System (ADS)

    Alsagabi, Sultan

    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 temperature strength and creep-rupture properties are required. The high temperature deformation mechanism was investigated through a set of tensile testing at elevated temperatures. Hence, the threshold stress concept was applied to elucidate the operating high temperature deformation mechanism. It was identified as the high temperature 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 temperatures 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 760C 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 temperature (i.e. 720C). The influence of the tempering temperature 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 500C. Overall, the irradiated samples showed some irradiation-induced hardening which was more noticeable at 30C. Additionally, irradiation-induced defect clusters and dislocation loops were observed and the irradiated samples did not show any bubble or void.

  5. Low-temperature creep of SnPb and SnAgCu solder alloys and reliability prediction in electronic packaging modules

    E-print Network

    Dao, Ming

    Low-temperature creep of SnPb and SnAgCu solder alloys and reliability prediction in electronic solder alloys. Experimental results showed that both solder alloys creep significantly within for the lead-free solder alloy Sn3Ag0.5Cu. 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights

  6. Temperature dependent deformation mechanisms in pure amorphous silicon

    SciTech Connect

    Kiran, M. S. R. N. Haberl, B.; Williams, J. S.; Bradby, J. E.

    2014-03-21

    High temperature nanoindentation has been performed on pure ion-implanted amorphous silicon (unrelaxed a-Si) and structurally relaxed a-Si to investigate the temperature dependence of mechanical deformation, 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 deformation under the indenter. While unrelaxed a-Si deforms entirely via plastic flow up to 200?C, a clear transition in the mode of deformation is observed in relaxed a-Si with increasing temperature. 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 temperature, plastic flow rather than phase transformation is the dominant mode of deformation. It is believed that the elevated temperature 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.

  7. Creep of Uncoated and Cu-Cr Coated NARloy-Z

    NASA Technical Reports Server (NTRS)

    Walter, R. J.; Chiang, K. T.

    1998-01-01

    Stress rupture creep 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 creep 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 creep. 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 temperatures, by formation of a continuous chromium oxide scale. As the result of reducing oxygen ingress, the coating prevented SAGBO initiated early creep failure, extended creep deformation and increased the creep rupture life of NARloy-Z over the entire 482 C to 704 C test temperature range.

  8. Modeling the creep properties of olivine by 2.5-dimensional dislocation dynamics simulations

    NASA Astrophysics Data System (ADS)

    Boioli, Francesca; Carrez, Philippe; Cordier, Patrick; Devincre, Benoit; Marquille, Matthieu

    2015-07-01

    In this work we performed 2.5-dimensional (2.5D) dislocation dynamics simulations coupling climb with the glide dislocation motion to model the creep 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 creep strain rate in a material with high lattice resistance, such as olivine. We show that by including the climb mechanism we reach steady state creep conditions. Moreover, we find that a creep 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 creep strain rates in the high temperature and low stress regime. The model presented is relevant to describe the plastic flow of olivine in the Earth's mantle deformation conditions and can be useful to derive the high temperature creep behavior of other materials.

  9. Overview of strategies for high-temperature creep and oxidation resistance of alumina-forming austenitic stainless steels

    SciTech Connect

    Yamamoto, Yukinori; Brady, Michael P; Santella, Michael L; Bei, Hongbin; Maziasz, Philip J; Pint, Bruce A

    2011-01-01

    A family of creep-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 creep-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) temperature 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-temperature creep 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. Creep, tensile, and oxidation properties of the AFA alloys are discussed relative to compositional and microstructural factors.

  10. Temperature dependence of the anisotropic deformation of Zr-2.5%Nb pressure tube material during micro-indentation

    NASA Astrophysics Data System (ADS)

    Bose, B.; Klassen, R. J.

    2011-12-01

    The effect of temperature on the anisotropic plastic deformation 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 temperature 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 creep increases, from 0.72 to 1.33 eV, with increasing temperature from 25 to 300 C and is independent of indentation direction. At temperature between 300 C and 400 C the measured activation energy is considerably reduced for indentation creep in the transverse direction relative to that of either the axial or radial directions. We conclude that, over this temperature 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 temperature dependence of the yield stress and creep rate, particularly in the radial direction, of Zr-2.5%Nb pressure tubes and shed new light on the effect of temperature 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.

  11. Creep of Rocks Under Small Mechanical Loading

    NASA Astrophysics Data System (ADS)

    Berest, P.; Charpentier, J. P.; Vales, F.

    Study of rocks under small (typically s = 0.1 MPa) mechanical loading is of great importance both for a better understanding of geological deformation features and for the analysis of rock mass behavior at large distance from underground openings. A very small amount of experimental data is available. Very long-term tests are required, as the creep rates induced by such small mechanical loading are exceedingly small (10 13 to 10-12s-1). Accurate displacement measurements and a thorough control of both hygrometry and temperature must be used. We used high resolution displacements sensors, whose resolution is 10-9m, designed for purpose by P.A.Blum from IPG Paris. The creep test system were set in a 20-m deep gallery where hygrometry is close to 100%PHs suburbs ; and in a 200-m deep salt mine where hygrometry is 54+/-2% RH . In both sites daily temperature fluctuations are smaller than a few hundredth of a Celsius degree, allowing for quite constant ambient conditions during several month long tests, the observed displacement-versus-time curves can be corrected from the thermoelastic effects. Creep of salt samples was measured in the 200-m deep mine ; transient creep, steady-state creep and the effcts of stress drop were observed during a 18-month long test. The measured steady-state creep rates (10-12s-1) are much faster than the values extrapolated from standard tests performed under larger mechanical loading. Argillite creep was measured in the 20-m deep gallery. High hygrometry conditions result in relatively fast clay swelling. In this context, argillite creep rate, which is slower than swelling rate by one order of magnitude, is difficult to identify

  12. Cast heat-resistant austenitic steel with improved temperature creep properties and balanced alloying element additions and methodology for development of the same

    DOEpatents

    Pankiw, Roman I; Muralidharan, Govindrarajan; Sikka, Vinod Kumar; Maziasz, Philip J

    2012-11-27

    The present invention addresses the need for new austenitic steel compositions with higher creep strength and higher upper temperatures. The new austenitic steel compositions retain desirable phases, such as austenite, M.sub.23C.sub.6, and MC in its microstructure to higher temperatures. The present invention also discloses a methodology for the development of new austenitic steel compositions with higher creep strength and higher upper temperatures.

  13. Creep Strain and Strain Rate Response of 2219 Al Alloy at High Stress Levels

    NASA Technical Reports Server (NTRS)

    Taminger, Karen M. B.; Wagner, John A.; Lisagor, W. Barry

    1998-01-01

    As a result of high localized plastic deformation experienced during proof testing in an International Space Station connecting module, a study was undertaken to determine the deformation response of a 2219-T851 roll forging. After prestraining 2219-T851 Al specimens to simulate strains observed during the proof testing, creep tests were conducted in the temperature range from ambient temperature 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 creep. Select specimens were subjected to incremental step loading and exhibited initial creep rates of similar magnitude for each load step. Although the creep rates decreased quickly at all loads, the creep rates dropped faster and reached lower strain rate levels for lower applied loads. The initial creep rate and creep rate decay associated with primary creep were similar for specimens with and without prestrain; however, prestraining (strain hardening) the specimens, as in the aforementioned proof test, resulted in significantly longer creep life.

  14. High-temperature flexural creep of ZrB2-SiC ceramics in argon atmosphere

    SciTech Connect

    Guo, Wei-Ming; Zhang, Guo-Jun; Lin, Hua-Tay

    2012-01-01

    Four-point flexure creep deformation 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 creep 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 creep resistance at 1500 C in argon atmosphere.

  15. Effect of interconnect creep on long-term performance of SOFC of one cell stacks

    SciTech Connect

    Liu, Wenning N.; Sun, Xin; Khaleel, Mohammad A.

    2008-02-01

    Creep deformation becomes relevant for a material when the operating temperature is near or exceeds half of its melting temperature (in degrees of Kelvin). The operating temperatures for most of the solid oxide fuel cells (SOFC) under development in the SECA program are around 1073oK. High temperature ferritic alloys are potential candidates as interconnect (IC) materials and spacers due to their low cost and CTE compatibility with other SOFC components. Since the melting temperature of most stainless steel is around 1800oK, possible creep deformation of IC under the typical cell operating temperature should not be neglected. In this paper, the effects of interconnect creep behavior on stack geometry change and stress redistribution of different cell components are predicted and summarized. The goal of the study is to investigate the performance of the fuel cell stack by obtaining the fuel and air channel geometry changes due to creep of the ferritic stainless steel interconnect, therefore indicating possible SOFC performance change under long term operations. IC creep models were incorporated into SOFC-MP and Mentat FC, and finite element analyses were performed to quantify the deformed configuration of the SOFC stack under the long term steady state operating temperature. It is found that creep behavior of the ferritic stainless steel IC contributes to narrowing of both the fuel and the air flow channels. In addition, stress re-distribution of the cell components suggests the need for a compliant sealing material that also relaxes at operating temperature.

  16. Mechanisms of high-temperature, solid-state flow in minerals and ceramics and their bearing on the creep behavior of the mantle

    USGS Publications Warehouse

    Kirby, S.H.; Raleigh, C.B.

    1973-01-01

    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-temperature flow mechanisms in ceramics and their relation to empirical flow laws. The intimate association of solid-state diffusion and high-temperature creep 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 creep rates compare remarkably well. This comparison is paralleled by the near universal occurrence of similar creep-induced structures, and it is thought that the derived empirical flow laws can be associated with dislocation creep. Creep 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 creep primarily by a quasi-viscous grain-boundary sliding mechanism which is unlikely to predominate in the earth's deep interior. Creep predictions for the mantle reveal that under most conditions the empirical dislocation creep 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.

  17. CREEP AND CREEP-FATIGUE OF ALLOY 617 WELDMENTS

    SciTech Connect

    Wright, Jill; Carroll, Laura; Wright, Richard

    2014-08-01

    The Very High Temperature Reactor (VHTR) Intermediate Heat Exchanger (IHX) may be joined to piping or other components by welding. Creep-fatigue deformation 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 temperature deformation. These periods of elevated temperature deformation are greatly influenced by a materials creep 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 temperature failures occur at the weldments or in the heat-affected zone. Reliably guarding against this type of failure is particularly challenging at high temperatures 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 creep-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 deformation 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 the cycles to failure and whether a saturation in reduced cycle life with increased hold times is observed, the microstructural stability over long cycle times, and finally, the location of the generated weldment data on a creep-fatigue damage diagram (D-diagram).

  18. Microstructural development and mechanical behavior of eutectic bismuth-tin and eutectic indium-tin in response to high temperature deformation

    SciTech Connect

    Goldstein, J.L.F.

    1993-11-01

    The mechanical behavior and microstructure of eutectic Bi-Sn and In-Sn solders were studied in parallel in order to better understand high temperature deformation 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 deform non-uniformly, with deformation concentrating in a band along the length of the sample for Bi-Sn and In-Sn on Cu, though the deformation is more diffuse in In-Sn than in Bi-Sn. Deformation of In-Sn on Ni spreads throughout the width of the joint. The different deformation 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 creep behavior of In-Sn also depends on the substrate, with the creep deformation 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 creep behavior changes to resemble that of In-Sn on Cu. The creep behavior of Bi-Sn changes with temperature. Two independent mechanisms operate at lower temperatures, but there is still some question as to whether one or both of these, or a third mechanism, operates at higher temperatures.

  19. Improved microstructure for creep strength in high-temperature austenitic alloys for energy conversion applications

    NASA Astrophysics Data System (ADS)

    Rayner, Garrett

    The current dominant role of fossil fuels for use in energy conversion applications is unlikely to change in the foreseeable future. In order to ensure the continued availability of these limited resources, it is critically important that remaining fossil fuel reserves are utilized as efficiently as possible. Increasing operating temperature in power plants is the most straightforward method of increasing plant efficiency, but over long life cycles in the harsh operating conditions of modern supercritical coal-fired power plants, current-generation materials are cannot be used above 620C due to corrosion and/or creep-strength limitations. One possible class of materials for higher-temperature use are dispersion-strengthened alumina-forming austenitic stainless steels: in this work, Fe-20Cr-(20-30)Ni-2Nb-5Al at. % strengthened by a fine Fe2Nb C14 Laves phase dispersion. While the Laves phase has not been successfully used as a strengthener before, some prior research has indicated that the Laves phase could act as a stable high-temperature strengthener, if it could be more finely dispersed. This work attempted to refine the Laves phase by first solutionizing the alloy, then cold-working to introduce a dense dislocation structure, and finally aging in order to allow the Laves phase to nucleate on these dislocations. Transmission electron microscopy and scanning electron microscopy were used to analyze the material after thermomechanical processing. Final results showed that the size, scale, homogeneity of dispersion, and volume fraction of precipitated Laves phase particles were all altered by prestraining, and at high levels of prestrain (90% reduction in thickness), a significantly finer Laves phase dispersion was obtained when compared with the non-prestrained aged material.

  20. Two-temperature continuum thermomechanics of deforming amorphous solids

    NASA Astrophysics Data System (ADS)

    Kamrin, Ken; Bouchbinder, Eran

    2014-12-01

    There is an ever-growing need for predictive models for the elasto-viscoplastic deformation of solids. Our goal in this paper is to incorporate recently developed out-of-equilibrium statistical concepts into a thermodynamically consistent, finite-deformation, continuum framework for deforming 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 temperature 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 temperatures. 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 deformation. 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 deformation phenomenology. Directions for future investigation are briefly discussed.

  1. Oscillatory rheology and creep behavior of barley ?-D-glucan concentrate dough: effect of particle size, temperature, and water content.

    PubMed

    Ahmed, Jasim; Thomas, Linu; Al-Attar, Hasan

    2015-01-01

    Small amplitude oscillatory rheology and creep behavior of ?-glucan concentrate (BGC) dough were studied as function of particle size (74, 105, 149, 297, and 595 ?m), BGC particle-to-water ratio (1:4, 1:5, and 1:6), and temperature (25, 40, 55, 70, and 85 C). The color intensity and protein content increased with decreasing particle size by creating more surface areas. The water holding capacity (WHC) and sediment volume fraction increased with increasing particle size from 74 to 595 ?m, which directly influences the mechanical rigidity and viscoelasticity of the dough. The dough exhibited predominating solid-like behavior (elastic modulus, G' > viscous modulus, G?). A discrete retardation spectrum is employed to the creep data to obtain retardation time and compliance parameters, which varied significantly with particle size and the process temperature. Creep tests exhibited more pronounced effect on dough behavior compared to oscillatory measurement. The protein denaturation temperature was insignificantly increased with particle fractions from 107 to 110 C. All those information could be helpful to identify the particle size range and WHC of BGC that could be useful to produce a ?-d-glucan enriched designed food. PMID:25603841

  2. Probabilistic Material Strength Degradation Model for Inconel 718 Components Subjected to High Temperature, Mechanical Fatigue, Creep and Thermal Fatigue Effects

    NASA Technical Reports Server (NTRS)

    Bast, Callie Corinne Scheidt

    1994-01-01

    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 temperature, mechanical fatigue, creep, 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 temperature, mechanical fatigue, creep, 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, creep, 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 temperature 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.

  3. Low temperature deformation kinetics of ruthenium aluminide alloys

    SciTech Connect

    Lu, D.C.; Pollock, T.M.

    1999-07-01

    The kinetics of low temperature deformation were investigated in several different polycrystalline RuAl alloys with the use of strain rate change experiments at 77 K and 298 K. Compositions investigated include RuAl, RuAl+0.5%B, Ru{sub 51.5}Al{sub 48.5}, Ru{sub 52}Al{sub 48}, Ru{sub 53}Al{sub 47}+0.5%B. Ru{sub 54.5}Al{sub 45.5}, and Ru{sub 52}Al{sub 43}Sc{sub 5}. Flow stresses did not vary substantially with temperature between 77 K and 298 K. Rate sensitivities were low compared to other B2 compounds and similar in all compositions investigated. Analyses of dislocation substructures after low strain deformation were conducted. The deformation kinetics and substructural observations suggest a higher intrinsic deformability for RuAl alloys with respect to the other high temperature B2 aluminides.

  4. Experimental investigations of creep in gold RF-MEMS microstructures

    NASA Astrophysics Data System (ADS)

    Som, Aurelio; De Pasquale, Giorgio; Saleem, Muhammad Mubasher

    2015-05-01

    Lifetime prediction and reliability evaluation of micro-electro-mechanical systems (MEMS) are influenced by permanent deformations caused by plastic strain induced by creep. Creep in microstructures becomes critical in those applications where permanent loads persist for long times and thermal heating induces temperature increasing respect to the ambient. Main goal of this paper is to investigate the creep mechanism in RF-MEMS microstructures by means of experiments. This is done firstly through the detection of permanent deformation 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 creep. 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 temperature. Results demonstrated the presence of plastic deformation due to creep, combined with a component of reversible strain linked to the viscoelastic behavior of the material.

  5. Improved High-Temperature Microstructural Stability and Creep Property of Novel Co-Base Single-Crystal Alloys Containing Ta and Ti

    NASA Astrophysics Data System (ADS)

    Xue, F.; Zhou, H. J.; Feng, Q.

    2014-12-01

    The influence of Ta and Ti additions on microstructural stability and creep behavior in novel Co-Al-W base single-crystal alloys has been investigated. Compared to the ternary alloy, the ?' solvus temperature and ?' 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 ?- ?' two-phase microstructure and more than 60% ?' volume fraction existed in the quinary alloy after prolonged aging treatment at 1050C for 1000 h. The creep behavior at 900C revealed lower creep rates and longer rupture lives in the quaternary alloys compared to the ternary alloy, whereas the quinary alloy exhibited even better creep resistance. When the creep temperature was elevated to about 1000C, the creep resistance of the quinary alloy exceeded the previously reported Co-Al-W-base alloys and first-generation Ni-base single-crystal superalloys. The improved creep resistance at approximately 1000C was considered to be associated with high ?' volume fraction, ?' directional coarsening, and dislocation substructure, which included ?- ?' interfacial dislocation networks and the sheared ?' precipitates containing stacking faults and anti-phase boundaries.

  6. High temperature creep behavior and substructure in KCl-KBr solid solution alloys

    SciTech Connect

    Duong, H.; Wolfenstine, J. . Dept. of Mechanical and Aerospace Engineering); Beeman, M. )

    1994-03-01

    The creep behavior and dislocation substructure of pure KCl, pure KBr and two KCl-KBr solid solution alloys was investigated at 700 C. The reduced primary stage compared to that for the pure materials, stress exponent close to 3, nature of the creep transient after a stress reduction for the KCl-KBr alloys is in good agreement with creep behavior observed in class 1 metallic, KCl-NaCl and KCl-RbCl solid solution alloys, where the creep rate is controlled by a viscous dislocation glide process. The creep behavior of the KCl-KBr solid solution alloys is in agreement with the prediction of the glide-climb criterion for solid solution alloys developed by Mohamed and Langdon. The dislocation substructure of KCl-KBr solid solution alloys consisted of well-developed subgrains whose size was larger than that for the pure materials at an equivalent value of normalized stress and varied inversely with applied stress. 66 refs., 10 figs.

  7. Deformation mechanisms of NiAl cyclicly deformed near the brittle-to-ductile transformation temperature

    NASA Technical Reports Server (NTRS)

    Antolovich, Stephen D.; Saxena, Ashok; Cullers, Cheryl

    1992-01-01

    One of the ongoing challenges of the aerospace industry is to develop more efficient turbine engines. Greater efficiency entails reduced specific strength and larger temperature gradients, the latter of which means higher operating temperatures 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 temperature engines. Ceramic, intermetallic, and various composite systems are being explored in an effort to exploit the much higher melting temperatures of these systems. NiAl is considered a potential alternative to conventional superalloys due to its excellent oxidation resistance, low density, and high melting temperature. 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 temperature 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-temperature strength and low-temperature ductility. On-going research in alloy design continues to make improvements in the high-temperature strength of NiAl. The factors controlling low temperature ductility have been identified in the last few years. Small, but reproducible ductility can now be achieved at room temperature 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 deformation 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, probing the deformation mechanisms operating in fatigue will lead to a better understanding of NiAl's unique characteristics. Low cycle fatigue properties have been reported on binary NiAl in the past year, yet those studies were limited to two temperature ranges: room temperature and near 1000 K. Eventually, fatigue property data will be needed for a wide range of temperatures and compositions. The intermediate temperature range near the brittle-to-ductile transition was chosen for this study to ascertain whether the sharp change occurring in monotonic behavior also occurs under cyclic conditions. An effort was made to characterize the dislocation structures which evolved during fatigue testing and comment on their role in the deformation process.

  8. Temperature Dependent Cyclic Deformation Mechanisms in Haynes 188 Superalloy

    NASA Technical Reports Server (NTRS)

    Rao, K. Bhanu Sankara; Castelli, Michael G.; Allen, Gorden P.; Ellis, John R.

    1995-01-01

    The cyclic deformation behavior of a wrought cobalt-base superalloy, Haynes 188, has been investigated over a range of temperatures 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 deformation behavior and microstructural substructure was made through detailed transmission electron microscopy. Although DSA was found to occur over a wide temperature range between approximately 300 and 750 C the microstructural characteristics and the deformation mechanisms responsible for DSA varied considerably and were dependent upon temperature. 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 temperature in the TMF cycle.

  9. Mechanisms of elevated-temperature deformation in the B2 aluminides NiAl and CoAl

    NASA Technical Reports Server (NTRS)

    Yaney, D. L.; Nix, W. D.

    1988-01-01

    A strain rate change technique, developed previously for distinguishing between pure-metal and alloy-type creep behavior, was used to study the elevated-temperature deformation behavior of the intermetallic compounds NiAl and CoAl. Tests on NiAl were conducted at temperatures between 1100 and 1300 K while tests on CoAl were performed at temperatures ranging from 1200 to 1400 K. NiAl exhibits pure-metal type behavior over the entire temperature range studied. CoAl, however, undergoes a transition from pure-metal to alloy-type deformation behavior as the temperature 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 temperatures may, therefore, be related to a greater lattice friction strengthening effect in CoAl than in NiAl.

  10. Clash of Porphyroblasts - Mechanical and chemical interaction of strong objects in a weak deforming matrix and the acceleration of dissolution precipitation creep

    NASA Astrophysics Data System (ADS)

    Bender, Hagen; Huet, Benjamin; Grasemann, Bernhard; Schuster, Ralf

    2015-04-01

    The presence of porphyroblasts in metamorphic rocks has a strong influence on the microstructures that develop during deformation. Valuable as gauges for the sense of shear, single isolated porphyroblasts and -clasts have attracted enormous attention and vigorous discussion in the geological community. Naturally, however, porphyroblasts often occur in populations. Therefore, the understanding of multi-porphyroblast interaction is of great significance. We use amphibolite-facies garnet mica schists from the Upper Austroalpine Wlz Complex for a case study. The microstructure of mm-cm sized, densely distributed garnet porphyroblasts indicates interference of the blasts. Blasts are subjected to convergence parallel to the instantaneous shortening axis, causing (i) accumulation and deformation of strain caps, (ii) fracturing of the garnets and (iii) dissolution of garnet at collision sites. Parallel to the instantaneous stretching axis, (i) cone-shaped strain shadows are linked between neighbouring garnets and (ii) separation of garnet clusters occurs preferably. Dissolution precipitation creep accommodates the major part of deformation. Consequently, the matrix separates due to the dense population of porphyroblasts. The matrix differentiates to dissolution sites and precipitation sites in the respective quadrants of stretching and shortening around the blasts. Quantitative chemical analysis and thermodynamic modelling are utilised to examine compositional variations in minerals within the stretching and shortening domains. The results show that the present-day assemblage in these rocks records no deviations from lithostatic pressure.

  11. Observations of orientation dependent creep of Ni{sub 3}Al

    SciTech Connect

    Knobloch, C.; Glock, K.; Glatzel, U.

    1999-07-01

    The influence of crystal orientation on the high temperature creep behavior of Ni{sub 3}(Al Ti Ta) was investigated by tensile creep testing under a constant load at a temperature of 1,123K. The single crystals were oriented close to [001], [011], [111], [557] and [012]. The results show an increasing stationary creep rate from [111] over [011] to [001]. The evolution of the microstructure during creep deformation was studied, using transmission electron microscopy (TEM). Only few systems are active in the primary regime, whereas several slip systems operate in the secondary stage. habit planes of dislocation pairs separated by an antiphase boundary were examined and compared with anisotropic elastic calculations, explaining the good creep response of [111] oriented using crystals.

  12. Transient and steady-state creep in a tin-silver-copper lead-free solder alloy: Experiments and modeling

    NASA Astrophysics Data System (ADS)

    Shirley, Dwayne R.

    It has been conventional to simplify the thermo-mechanical modeling of solder joints by omitting the primary (transient) contributions to total creep deformation, assuming that secondary (steady-state) creep strain is dominant and primary creep is negligible. The error associated with this assumption has been difficult to assess because it depends on the properties of the solder joint and the temperature-time profile. This research examines the relative contributions of primary and secondary creep in Sn3.8Ag0.7Cu solder using the constant load creep and stress relaxation measurements for bulk tensile specimens and the finite element analysis of a chip resistor (trilayer) solder joint structure that was thermally cycled under multiple temperature ranges and ramp rates. It was found that neglect of primary creep can result in errors in the predicted stress and strain of the solder joint. In turn, these discrepancies can lead to errors in the estimation of the solder thermal fatigue life due to the changing proportion of primary creep strain to total inelastic strain under different thermal profiles. The constant-load creep and stress relaxation data for Sn3.8Ag0.7Cu span a range of strain rates 10-8s-1 < 3? < 10-4 s-1, and temperatures 25C, 75C and 100C. Creep and stress relaxation measurements show that transient creep caused faster strain rates during stress relaxation for a given stress compared to the corresponding minimum creep rate from constant-load creep tests. The extent of strain hardening during primary creep was a function of temperature and strain rate. A constitutive creep model was presented for Sn3.8Ag0.7Cu that incorporates both transient and steady-state creep to provide agreement for both creep and stress relaxation data with a single set of eight coefficients. The model utilizes both temperature compensated time and strain rate to normalize minimum strain rate and saturated transient creep strain, thereby establishing equivalence between decreased temperature and increased strain rate. The apparent activation energy of steady-state creep was indicative of both dislocation core and bulk lattice diffusion was the most sensitive model parameter. A saturation threshold was defined that distinguishes whether primary or secondary creep is dominant under either static or variable loading.

  13. Evaluation of Magnesium Die-Casting Alloys for Elevated Temperature Applications: Microstructure, Tensile Properties, and Creep Resistance

    NASA Astrophysics Data System (ADS)

    Zhu, Suming; Easton, Mark A.; Abbott, Trevor B.; Nie, Jian-Feng; Dargusch, Matthew S.; Hort, Norbert; Gibson, Mark A.

    2015-08-01

    Several families of magnesium die-casting alloys have been developed to operate at the elevated temperatures experienced in automotive powertrain applications. Most alloys are based on the Mg-Al system with alloying additions such as silicon, strontium, calcium, and rare earth elements (RE), although alloys with RE as the primary alloying constituent are also considered. This work presents an evaluation of the tensile properties and creep resistance of the most common magnesium die-casting alloys, in conjunction with the analysis of microstructure. The alloys investigated include AS31 (Mg-3Al-1Si), AJ52 (Mg-5Al-2Sr), MRI153A (Mg-9Al-1Ca-0.1Sr), MRI153M (Mg-8Al-1Ca-0.3Sr), MRI230D (Mg-6.5Al-2Ca-1Sn-0.3Sr), AXJ530 (Mg-5Al-3Ca-0.2Sr), AE42 (Mg-4Al-2RE), AE44 (Mg-4Al-4RE), and AM-HP2+ (Mg-3.5RE-0.4Zn). It is shown that, among the various alloys evaluated, MRI230D, AXJ530, and AM-HP2+ have higher yield strength than the Al alloy A380, but the ductility is relatively low at room temperature for these alloys. In contrast, AS31 and the AE series alloys have very good room temperature ductility, but their yield strength is lower than that of A380. In terms of creep resistance, MRI230D, AXJ530, AE44, and AM-HP2+ are all comparable to the Al alloy counterpart at 423 K and 448 K (150 C and 175 C). Microstructural factors that are most important to the strength and creep resistance of the Mg die-casting alloys are discussed.

  14. Relation between creep compliance and elastic modulus in organic-rich shales observed through laboratory experiments.

    NASA Astrophysics Data System (ADS)

    Sone, Hiroki; Zoback, Mark

    2013-04-01

    We studied the ductile creep 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 creep on other rock properties. Laboratory experiments conducted at room-temperature conditions show that creep deformation observed at in-situ differential stress conditions is approximately linear with the applied differential pressure. The creep behavior is also anisotropic such that creep occurs more in the bedding-perpendicular direction than in the bedding-parallel direction. The reduction in sample volume during creep suggests that the creep 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 creep (creep compliance) is generally observed to increases with clay and kerogen volume. However, the strongest correlation is found between creep compliance and Young's modulus. A strong negative correlation between creep 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 creep and elastic stiffness depend on somewhat different physical attributes. We attempt to quantitatively explain the correlation between creep 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 creep behavior is linear against the applied stress, we forward calculate the creep compliance of the whole rock. Results show that when creep is linear against stress, a unique relation between creep compliance and elastic modulus can be established for rocks with similar mineral assemblages, consistent with our laboratory results. Thus, our results provide insights into how creep behaviors of poly-mineralic rocks can be re-constructed from the creep properties of the individual phases composing the rock.

  15. A deformation-mechanism material model for NIKE 3-D

    SciTech Connect

    Raboin, P.J.

    1993-01-04

    The structural, finite element code, NIKE2D has a, new material model called the Deformation-Mechanism Model (DMM). This model uses kinetic equations to predict deformation rates for specific deformation-mechanisms. These mechanisms depend on temperature, applied stress, a strength parameter and grain size. Five kinetic equations are available, and they model Obstacle Controlled Plasticity, Power Law Creep, Power Law Breakdown, Diffusion Controlled Deformation and Slip Creep. A strength parameter models isotropic strain hardening and dynamic recovery. Grain size changes are modeled with a dynamic grain growth equation which depends on temperature, current grain size and the deformation rate. These kinetic equations and their evolutionary parameters are capable of predicting rate-dependent deformation behavior for many metals. In addition, multiple deformation-mechanisms can be combined in this material model to predict the rate dependent behavior of a material across several regimes of deformation behavior.

  16. Deformation characteristics and time-dependent notch sensitivity of Udimet 700 at intermediate temperatures

    NASA Technical Reports Server (NTRS)

    Wilson, D. J.

    1974-01-01

    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 creep deformation was localized. For each alloy and notched specimen geometry, a stress-average particle size zone can be defined that characterizes the notch sensitive behavior.

  17. Creep in Topopah Spring Member welded tuff. Yucca Mountain Site Characterization Project

    SciTech Connect

    Martin, R.J. III; Boyd, P.J.; Noel, J.S.; Price, R.H.

    1995-06-01

    A laboratory investigation has been carried out to determine the effects of elevated temperature and stress on the creep deformation 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 creep at a confining pressure of 5.0 MPa, a pore pressure of 4.5 MPa, and temperatures 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 temperature 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 creep deformation 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 deformation 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 temperature, stress, creep deformation to failure, and total failure time at a fixed creep stress.

  18. Autonomous Repair Mechanism of Creep Damage in Fe-Au and Fe-Au-B-N Alloys

    NASA Astrophysics Data System (ADS)

    Zhang, S.; Kwakernaak, C.; Tichelaar, F. D.; Sloof, W. G.; Kuzmina, M.; Herbig, M.; Raabe, D.; Brck, E.; van der Zwaag, S.; van Dijk, N. H.

    2015-12-01

    The autonomous repair mechanism of creep cavitation during high-temperature deformation has been investigated in Fe-Au and Fe-Au-B-N alloys. Combined electron-microscopy techniques and atom probe tomography reveal how the improved creep properties result from Au precipitation within the creep cavities, preferentially formed on grain boundaries oriented perpendicular to the applied stress. The selective precipitation of Au atoms at the free creep cavity surface results in pore filling, and thereby, autonomous repair of the creep 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 creep cavities. The mechanism responsible for the self-healing can be characterized by a simple model for cavity growth and cavity filling.

  19. Kinetics of low-temperature discontinuous deformation of metals

    NASA Astrophysics Data System (ADS)

    Vorob'ev, E. V.; Anpilogova, T. V.

    2015-06-01

    Kinetic characteristics of discontinuous yielding at a temperature of 4 K as functions of a number of factors are obtained using numerical simulation and experimental data for austenitic steel and aluminum alloy. During the development of a strain jump, the deformation rate and acceleration are 19 s-1 and 5000 s-2, respectively, for steel specimens and are much lower for aluminum alloy. The jump duration is mainly determined by the characteristics of the loading system. An equation relating the strain jump and the critical stress for low-temperature ductile materials is derived. The energy balance and the mechanism of low-temperature discontinuous yielding of metals are discussed. Its dynamic and thermally activated components are estimated taking into account the strain hardening of the material.

  20. Laser-Interferometric Creep Rate Spectroscopy of Polymers

    NASA Astrophysics Data System (ADS)

    Bershtein, Vladimir A.; Yakushev, Pavel N.

    Laser-interferometric creep rate meter (LICRM) and creep rate spectroscopy (CRS), as an original high-resolution method for discrete relaxation spectrometry and thermal analysis, were developed in the authors' Materials Dynamics Laboratory at Ioffe Physical-Technical Institute of the Russian Academy of Sciences (Saint-Petersburg). In the last few decades they have been successfully applied to solving various problems of polymer physics and materials science, especially being combined with DSC, structural, and other techniques. CRS involves measuring ultra-precisely a creep rate at small tensile or compressive stress, typically much lower than the yield stress, as a function of temperature, over the range from 100 to 800 K. LICRM setup allows one to register precisely creep rates on the basis of deformation increment of 150-300 nm. The survey describes this method and summarizes the results of numerous studies performed with the LICRM setup and CRS technique for different bulk polymeric materials, films, or thin fibers. This approach provided new experimental possibilities superior in resolution and sensitivity compared to the conventional relaxation spectrometry techniques. Among such possibilities are discrete analysis of dynamics; creep on submicro-, micro- and meso-scales; revealing relations between stepwise microplasticity and morphology; kinetic information on creep at any temperature and deformation; polymer dynamics at interfaces; analysis of microplasticity, relaxations, and phase transitions in brittle materials; using creep rate spectra for non-destructive prediction of temperature anomalies in mechanical behavior of materials, etc. Considerable attention has been paid to combined CRS/DSC analysis of the peculiarities of segmental dynamics, nanoscale dynamic, and compositional heterogeneity in different kinds of complex polymer systems and nanocomposites.

  1. Effects of NaCl, pH, and Potential on the Static Creep Behavior of AA1100

    NASA Astrophysics Data System (ADS)

    Wan, Quanhe; Quesnel, David J.

    2013-03-01

    The creep 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 creep behavior, producing creep rates comparable to those measured in lab air at room temperature. 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. Creep strain produces a continuous deformation 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 deformation 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 creep strain rates are discussed relating to the anodic dissolution of the free surface and hydrogen influences on deformation mechanisms. Consistencies of pH dependence between corrosion creep and SCC at low pH prove a creep-involved SCC mechanism, while the discrepancies between corrosion creep behavior and previous SCC results at high pH indicate a rate-limit step change in the crack propagation of the SCC process.

  2. Irradiation Creep of Chemically Vapor Deposited Silicon Carbide as Estimated by Bend Stress Relaxation Method

    SciTech Connect

    Katoh, Yutai; Snead, Lance Lewis; Hinoki, Tatsuya; Kondo, Sosuke; Kohyama, Akira

    2007-01-01

    The bend stress relaxation technique was applied for an irradiation creep 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 temperatures in the range {approx}400 to {approx}1080 C. Irradiation creep strain at <0.7 dpa exhibited only a weak dependence on irradiation temperature. However, the creep strain dependence on fluence was non-linear due to the early domination of the initial transient creep, and a transition in creep behavior was found between 950 and 1080 C. Steady-state irradiation creep 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 creep compliances of 1-2 x 10{sup -6} (MPa dpa){sup -1} were obtained for doses of 0.6-0.7 dpa at all temperatures. Monocrystalline 3C SiC samples exhibited significantly smaller transient creep strain and greater subsequent deformation when loaded along <0 1 1> direction.

  3. Numerical simulation of the experiment on the measurement of salt creep

    NASA Astrophysics Data System (ADS)

    Li, Shiyuan; Abe, Steffen; Urai, Janos L.

    2010-05-01

    In this research, we collect data on salt creep and establish a database for creep of evaporite rocks at temperature up to 250C, and compare different published creep laws based on solution-precipitation creep, and dislocation creep. The largest differences stem from lithological variations, with bischofite and epsomite being the weakest, carnalite intermediate, halite, sylvite and anhydrite being the strongest ductile evaporite. Under the same conditions, different halites can creep at two orders of magnitude different rates at a given differential stress, in agreement with observations of small scale folding in salt mines. We support this work by finite element simulations of the uniaxial compression of a cylindrical sample with variable rheologies and comparison of the computed stress-strain response with measurements, for different values of friction at the pistons. We use the commercial finite element package ABAQUS(tm), and model salt as a power-law creep material including elasticity. We find that friction at the piston produces different barreling profile for different power law exponents of the creep law, and a small but significant effect on the stress-strain response as compared to frictionless piston with homogeneous deformation. We discuss different methods to compensate for this effect and to extract the optimum creep law from such measurements.

  4. Effect of prior cold work on creep properties of a titanium modified austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Vijayanand, V. D.; Parameswaran, P.; Nandagopal, M.; Panneer Selvi, S.; Laha, K.; Mathew, M. D.

    2013-07-01

    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 creep strength and resistance to void swelling. In this study, the influence of PCW in the range of 16-24% on creep 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 creep deformation rate of the steel at both the test temperatures; creep 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 creep testing conditions. A well-defined dislocation substructure was observed on creep testing at 923 K; a well-annealed microstructure with evidences of recrystallization was observed on creep testing at 973 K. Creep 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. Creep 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).

  5. The instantaneous rate dependence in low temperature laboratory rock friction and rock deformation experiments

    USGS Publications Warehouse

    Beeler, N.M.; Tullis, T.E.; Kronenberg, A.K.; Reinen, L.A.

    2007-01-01

    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 deformation rate, and determines the duration of precursory slip. Although an instantaneous rate dependence is observed for fracture, friction, crack growth, and low temperature 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 temperature dislocation glide experiments. The same normalization scheme is used to compare rate dependence in friction to rock fracture and to low-temperature 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 creep 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.

  6. A model of compaction creep in carbonates

    NASA Astrophysics Data System (ADS)

    Keszthelyi, Daniel; Jamtveit, Bjrn; Dysthe, Dag Kristian

    2015-04-01

    Rocks in compressional stress conditions are subject to long-term creep deformations. We created a simple conceptual micomechanical model of creep 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, temperature 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 creep experiments were used to verify the model which was able to predict the magnitude of the resulting strain in largely different effective stress, temperature 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 creep of rocks in compressional settings.

  7. Very slow creep tests on salt samples

    NASA Astrophysics Data System (ADS)

    Brest, P.; Braud, J. F.; Brouard, B.; Blum, P. A.; Charpentier, J. P.; de Greef, V.; Gharbi, H.; Vals, F.

    2010-06-01

    Long-term creep tests have been performed on rock-salt and argillite samples under very small uniaxial loadings (? = 0.02 to 0.1 MPa) . To minimize the effects of temperature variations, testing devices were set in a mine where temperature fluctuations are of the order of one-hundredth of a degree Celsius. The mechanical loading was provided by dead weights. The deformations were measured through special displacement sensors with a resolution of ?? = 10-8. Strain rates as small as ? = 7 10-13s-1 were measured. These tests allow rock-sample creep to be investigated at very small strain rates. The tests also prove that extrapolation of constitutive laws at very small rates is often incorrect.

  8. Plastic Deformation of Wadsleyite and Olivine at High-Pressure and High-Temperature using a Rotational Drickamer Apparatus (RDA)

    SciTech Connect

    Nishihara, Y.; Tiner, D; Kawazoe, T; Xu, Y; Jing, Z; Matsukage, K; Karato, S

    2008-01-01

    Large-strain plastic deformation experiments of wadsleyite and olivine were conducted using a rotational Drickamer apparatus (RDA) up to pressure and temperature conditions corresponding to the Earth's mantle transition zone. Sintered ring-shaped (Mg,Fe)2SiO4 wadsleyite and olivine samples were deformed at P not, vert, similar 16 GPa and T = 1600 and 1800 K, and P not, vert, similar 11 GPa and T = 1800 K, respectively, with equivalent strain rate of View the MathML source. In situ observations of deforming samples were carried out using the synchrotron radiation facility at Brookhaven National Laboratory, NSLS, X17B2. Stress was measured by X-ray diffraction at six different angles with respect to the compression axis. The stress estimated by X-ray diffraction was in good agreement with the stress estimated from dislocation density (for olivine). Strain was determined using X-ray radiographs of a strain marker (Re or Mo foil). Deformation of samples with a RDA involves both uniaxial compression and simple shear. A new formulation is developed to analyze both components to determine the rheological properties of a sample. Stress-strain curves show strain-hardening up to the equivalent strain of var epsilonE not, vert, similar 0.2 followed by the quasi-steady state deformation. Wadsleyite is found to be stronger than olivine compared at similar conditions and the creep strength of olivine at P not, vert, similar 11 GPa is much higher than those at lower pressures.

  9. Creep deformation of a two-phase TiAl/Ti[sub 3]Al lamellar alloy and the individual TiAl and Ti[sub 3]Al constituent phases

    SciTech Connect

    Bartholomeusz, M.F.; Wert, J.A. ); Qibin Yang )

    1993-08-01

    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-temperature fracture toughness, tensile strength and fatigue resistance. However, information about the high-temperature creep 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 creep rates of the lamellar alloy would be between the creep rates of TiAl and Ti[sub 3]Al. In contrast to composite model predictions of strength, Polvani and coworkers found that the minimum creep rates of two duplex alloys, a [gamma]/[gamma][prime] nickel-base superalloy and NiAl/Ni[sub 2]AlTi, were significantly lower than the minimum creep 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 creep 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 creep rates that the individual constituent phases. The objective of the present study is to evaluate the creep 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.

  10. Extended-time-scale creep measurement on Maraging cantilever blade springs

    NASA Astrophysics Data System (ADS)

    Virdone, Nicole; Agresti, Juri; Bertolini, Alessandro; DeSalvo, Riccardo; Stellacci, Rosalia; Kamp, Justin; Mantovani, Maddalena; Sannibale, Virginio; Tarallo, Marco; Kaltenegger, Lisa

    2008-08-01

    Two controlled temperature facilities were built to induce an accelerated creep rate in a Maraging steel GAS spring and to measure the material's creep 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 creep for six more years before measuring the permanent deformation integrated over time. The data from this first experiment was polluted by a defect in the data acquisition software, but yielded overall creep limits and an evaluation of the Arrhenius acceleration of creep speed with temperature (1.280.13 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 creep. The result of both experiments also produced a simple procedure capable of eliminating all practical effects of creep from the Advanced LIGO seismic isolation and suspensions. Measurements of creep 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.

  11. The evolution of the grain boundary ensemble of polycrystalline nickel under creep at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Naydenkin, E. V.; Ivanov, K. V.

    2013-03-01

    The evolution of the grain boundary ensemble of polycrystalline nickel under creep at 823 K (~0.5 ?m) has been investigated by the electron backscattered diffraction technique. At low strains, delamination of twin grain boundaries ?3 is found to take place, giving rise to coincidence site lattice grain boundaries ?9 and ?27. Low-angle misorientations in the material are shown to increase considerably with increase in the degree of strain, which causes a decrease in the fraction of the coincidence site lattice grain boundaries due to interaction with lattice dislocations.

  12. Review of deformation behavior of tungsten at temperature less than 0.2 absolute melting temperature

    NASA Technical Reports Server (NTRS)

    Stephens, J. R.

    1972-01-01

    The deformation behavior of tungsten at temperatures 0.2 T sub m is reviewed, with primary emphasis on the temperature dependence of the yield stress and the ductile-brittle transition temperature. It appears that a model based on the high Peierls stress of tungsten best accounts for the observed mechanical behavior at low temperatures. 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.

  13. Mechanisms of time-dependent deformation in porous limestone

    NASA Astrophysics Data System (ADS)

    Brantut, Nicolas; Heap, Michael J.; Baud, Patrick; Meredith, Philip G.

    2014-07-01

    We performed triaxial deformation experiments on a water-saturated porous limestone under constant strain rate and constant stress (creep) conditions. The tests were conducted at room temperature and at low effective pressures Peff=10 and Peff=20 MPa, in a regime where the rock is nominally brittle when tested at a constant strain rate of 10-5 s-1. Under these conditions and at constant stress, the phenomenon of brittle creep occurs. At Peff=10 MPa, brittle creep follows similar trends as those observed in other rock types (e.g., sandstones and granites): only small strains are accumulated before failure, and damage accumulation with increasing strain (as monitored by P wave speeds measurements during the tests) is not strongly dependent on the applied stresses. At Peff=20 MPa, brittle creep is also macroscopically observed, but when the creep strain rate is lower than ?10-7 s-1, we observe that (1) much larger strains are accumulated, (2) less damage is accumulated with increasing strain, and (3) the deformation tends to be more compactant. These observations can be understood by considering that another deformation mechanism, different from crack growth, is active at low strain rates. We explore this possibility by constructing a deformation mechanism map that includes both subcritical crack growth and pressure solution creep processes; the increasing contribution of pressure solution creep at low strain rates is consistent with our observations.

  14. Brittle creep and subcritical crack propagation in glass submitted to triaxial conditions

    NASA Astrophysics Data System (ADS)

    Mallet, Cline; Fortin, Jrme; Guguen, Yves; Bouyer, Frdric

    2015-02-01

    An experimental work is presented that aimed at improving our understanding of the mechanical evolution of cracks under brittle creep conditions. Brittle creep may be an important slow deformation process in the Earth's crust. Synthetic glass samples have been used to observe and document brittle creep due to slow crack-propagation. A crack density of 0.05 was introduced in intact synthetic glass samples by thermal shock. Creep 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 creep. The effect of temperature on creep was investigated from ambient temperature to 70C. The activation energy for crack growth was found to be 32 kJ/mol. In secondary creep, 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 creep, failure in tertiary creep 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 creep phase and also to give an analytical expression for the time to rupture. Comparison between glass and crystalline rock indicates that the brittle creep behavior is probably controlled by the same process even if stress sensitivity for glass is lower than for rocks.

  15. Elevated Temperature Creep Properties of Conventional 50Au-50Cu and 47Au 50Cu-3Ni Braze Alloys

    SciTech Connect

    STEPHENS JR.,JOHN J.; SCHMALE,DAVID T.

    2000-12-18

    The elevated temperature creep properties of the 50Au-50Cu wt% and 47Au-50Cu-3Ni braze alloys have been evaluated over the temperature range 250-850 C. At elevated temperatures, i.e., 450-850 C, both alloys were tested in the annealed condition (2 hrs. 750 C/water quenched). The minimum strain rate properties over this temperature range are well fit by the Garofalo sinh equation. At lower temperatures (250 and 350 C), power law equations were found to characterize the data for both alloys. For samples held long periods of time at 375 C (96 hrs.) and slowly cooled to room temperature, an ordering reaction was observed. For the case of the 50Au-50Cu braze alloy, the stress necessary to reach the same, strain rate increased by about 15% above the baseline data. The limited data for ordered 47Au-50Cu-3Ni alloy reflected a,smaller strength increase. However, the sluggishness of this ordering reaction in both alloys does not appear to pose a problem for braze joints cooled at reasonable rates following brazing.

  16. Back stress in dislocation creep. Part 1: Basic concepts and measuring techniques

    NASA Technical Reports Server (NTRS)

    Cadek, J.

    1984-01-01

    A theory is proposed whereby the plastic deformation 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 deformation. The back stress is usually equivalent to the internal stress or the friction stress and depends on the magnitude of the applied stress and temperature. The concept of back stress is applied to the case of the dislocation creep of precipitation-hardened or dispersion-strengthened metal materials. An additivity rule is formulated which can be useful in interpreting the creep behavior of such materials.

  17. Brief summary of the evolution of high-temperature creep-fatigue life prediction models for crack initiation

    NASA Astrophysics Data System (ADS)

    Halford, Gary R.

    1993-10-01

    The evolution of high-temperature, creep-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-temperature fatigue life prediction methods by providing a background from which choices can be made. The need for high-temperature, 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-temperature, high-pressure boilers and steam turbines, nuclear reactors, high-temperature 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 analyses, advanced constitutive stress-strain-temperature-time relations, and creep-fatigue-environmental models for crack initiation and propagation. The high-temperature durability methods that have evolved for calculating high-temperature fatigue crack initiation lives of structural engineering materials are addressed. Only a few of the methods were refined to the point of being directly useable in design.

  18. Brief summary of the evolution of high-temperature creep-fatigue life prediction models for crack initiation

    NASA Technical Reports Server (NTRS)

    Halford, Gary R.

    1993-01-01

    The evolution of high-temperature, creep-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-temperature fatigue life prediction methods by providing a background from which choices can be made. The need for high-temperature, 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-temperature, high-pressure boilers and steam turbines, nuclear reactors, high-temperature 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 analyses, advanced constitutive stress-strain-temperature-time relations, and creep-fatigue-environmental models for crack initiation and propagation. The high-temperature durability methods that have evolved for calculating high-temperature fatigue crack initiation lives of structural engineering materials are addressed. Only a few of the methods were refined to the point of being directly useable in design. Recently, two of the methods were transcribed into computer software for use with personal computers.

  19. Creep Behavior of Glass/Ceramic Sealant Used in Solid Oxide Fuel Cells

    SciTech Connect

    Liu, Wenning N.; Sun, Xin; Koeppel, Brian J.; Khaleel, Mohammad A.

    2010-01-02

    High operating temperature of solid oxide fuel cells require that sealant must function at high temperature between 600o and 900oC and in the oxidizing and reducing environments of fuel and air. It should be noted that creep deformation becomes relevant for a material when the operating temperature is near or exceeds half of its melting temperature (in degrees of Kelvin). The operating temperatures for most of the solid oxide fuel cells (SOFC) under development in the SECA program are around 800oC, which exceeds the glass transition temperature Tg for most glass ceramic materials. The goal of the study is to develop a creep model to capture the creep behavior of glass ceramic materials at high temperature and to investigate the effect of creep of glass ceramic sealant materials on stresses in glass seal and on the various interfaces of glass seal with other layers. The self-consistent creep models were incorporated into SOFC-MP and Mentat FC, and finite element analyses were performed to quantify the stresses in various parts. The stress in glass seals were released due to its creep behavior during the operating environments.

  20. Low oxygen fugacity dependency for the deformation of partially molten lherzolite

    NASA Astrophysics Data System (ADS)

    Wang, Yongfeng; Zhang, Junfeng; Jin, Zhenmin; Kohlstedt, David L.

    2012-12-01

    We present the results of an experimental investigation of the influence of oxygen fugacity on the deformation of a partially molten spinel lherzolite using a 0.1 MPa gas-media creep rig under temperatures of 1160-1190 C, stresses of 4-74 MPa and well-controlled oxygen fugacities of 10- 7 to 10- 11 MPa. The partially molten spinel lherzolite was deformed by a dislocation-mediated creep process such as dislocation creep or dislocation-accommodated grain boundary sliding (DGBS) (n = 3.5 0.3) as well as in the diffusion creep regime (n = 1.2 0.2). The average oxygen fugacity exponent of lherzolite is 0.04 0.02, which is significantly smaller than the values measured for olivine single crystals (0.10-0.36) and dunite rocks (0.20) deformed by dislocation creep. We attribute the low oxygen fugacity exponent of partially molten lherzolite samples either to the operation of grain boundary sliding, if DGBS dominates the deformation, or to the presence of pyroxenes whose deformation has a weak or no dependency on oxygen fugacity, if dislocation creep dominates the deformation. In the latter case, the oxygen fugacity exponent decreases rapidly with decreasing volume fraction of olivine. The low oxygen fugacity exponent for our partially molten lherzolite samples implies that dislocation creep or DGBS of mantle peridotite will most likely be insensitive to variations of oxygen fugacity in the upper mantle.

  1. Non-Contact Measurements of Creep Properties of Refractory Materials

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

    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-temperature (>2000 C) materials. At such high temperatures, creep rises as one of the most important design factors to be considered. Since conventional measurement techniques for creep resistance are limited to about 17OO0C, a new technique is in demand for higher temperatures. 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 creep deformation by centrifugal acceleration. The deformation of the samples was captured with a high speed camera and then the images were analyzed to estimate creep 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.

  2. Low-temperature direct copper-to-copper bonding enabled by creep on (111) surfaces of nanotwinned Cu.

    PubMed

    Liu, Chien-Min; Lin, Han-Wen; Huang, Yi-Sa; Chu, Yi-Cheng; Chen, Chih; Lyu, Dian-Rong; Chen, Kuan-Neng; Tu, King-Ning

    2015-01-01

    Direct Cu-to-Cu bonding was achieved at temperatures 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 creep is presented; and the calculated and measured time of bonding is in reasonable agreement. PMID:25962757

  3. Concentration profiles and the rafting mechanism of Ni base superalloys in the initial stage of high temperature creep tests

    SciTech Connect

    Saito, Masakazu; Aoyama, Takashi; Hidaka, Kishio; Tamaki, Hideki; Ohashi, Tetsuya; Nakamura, Shigeyoshi; Suzuki, Takaya

    1996-04-15

    The rafting mechanism is one of the most important and interesting phenomena which appears in Ni base superalloys during high temperature creep tests. The precipitated {gamma}{prime} particles, which are arrayed periodically in the {gamma} matrix, coalesce and form rafting structures in the direction perpendicular to tensile stresses. To understand this phenomenon, element profiles and diffusion process have been investigated in the vicinity of the {gamma}/{gamma}{prime} interfaces. In this paper, the authors analyzed accurate element profiles, especially Al and Cr which are main alloying elements, in the most vicinity of {gamma}/{gamma}{prime} interface regions. The rafting mechanism is correlated with the diffusion process on the basis of Al concentration profiles in a few nano meter distance from the {gamma}/{gamma}{prime} interfaces.

  4. Low-temperature direct copper-to-copper bonding enabled by creep on (111) surfaces of nanotwinned Cu

    NASA Astrophysics Data System (ADS)

    Liu, Chien-Min; Lin, Han-Wen; Huang, Yi-Sa; Chu, Yi-Cheng; Chen, Chih; Lyu, Dian-Rong; Chen, Kuan-Neng; Tu, King-Ning

    2015-05-01

    Direct Cu-to-Cu bonding was achieved at temperatures 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 creep is presented; and the calculated and measured time of bonding is in reasonable agreement.

  5. Low-temperature direct copper-to-copper bonding enabled by creep on (111) surfaces of nanotwinned Cu

    PubMed Central

    Liu, Chien-Min; Lin, Han-Wen; Huang, Yi-Sa; Chu, Yi-Cheng; Chen, Chih; Lyu, Dian-Rong; Chen, Kuan-Neng; Tu, King-Ning

    2015-01-01

    Direct Cu-to-Cu bonding was achieved at temperatures of 150250?C using a compressive stress of 100?psi (0.69?MPa) held for 1060?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 creep is presented; and the calculated and measured time of bonding is in reasonable agreement. PMID:25962757

  6. Experimental Deformation, Partial Melting, and Compositional Changes in Perthitic K-feldspar at High Pressure and Temperature

    NASA Astrophysics Data System (ADS)

    Negrini, M.; Stunitz, H.; Menegon, L.; Nasipuri, P.

    2011-12-01

    In order to study the relationship between partial melting, cracking and transition to diffusion creep processes, we have performed (i) axial compression experiments on natural perthitic K-feldspar single crystals (compression normal to the {010} plane), (ii) shear experiments (on 10-20 ?m grain size powder obtained from the same perthitic K-feldspar) and (iii) hydrostatic experiments (on powder and single crystals) with a solid medium Griggs-type deformation apparatus at T=900C, Pc varying from 0.75-1.5 GPa and axial shortening ranging from 3 to 40% at a constant strain rate of 10-6 s-1. Samples were deformed as-is and with added H2O (up to 0.2 wt %). Deformation in the single crystal samples at 900C is largely accommodated by shear fractures. The mechanical data, however, show an inverse normal stress dependence (flow stress at 1.5 GPa is 330 MPa, at 1.0 GPa it is 450-500MPa, and at 0.75GPa it is 680 MPa) and peak stresses below the Goetze criterion, indicating that along the cracks deformation is not dominantly friction controlled. Melt (less than 7%vol.) is distributed along cracks and shear zones are oriented at 40 to ?1 . EPMA analysis reveals inhomogenous melt compositions, suggesting that the melt pockets along cracks are not interconnected. Hydrostatic experiments performed at the same P, T conditions for the same amount of time as the deformation experiments do not contain any melt, indicating that melt kinetics are - at least in part - controlled by the cracking process (solidus T=725C). Chemical homogenization is evident in the fine-grained fragments of the fault gouges, which have variable intermediate chemical compositions between the K-feldspar (Ab8 An0 Or92) and the albite lamellae (Ab98 An1 Or1) of the starting material. In powder shear experiments the melt fraction is higher than in single crystals. Melt is distributed along shear bands and around single grains, which are completely homogenized (Ab21 An0 Or79). The strength of the material is as high (100-150 MPa) as the strength of pure labradorite deformed in shear, where no melt was detected. These observations suggest that the deformation of single feldspar crystals at high pressure and temperature is controlled by a simultaneous formation of micro-cracks and melt. The formation of wet melt is accelerated by cracking as demonstrated by the absence of melt in hydrostatic experiments. Melt formation occurs faster at higher confining pressure, and weakens the sample as demonstrated by the inverse dependence of peak-strength with confining pressure. The melt along the cracks accommodates the deformation by viscous processes, but it does not dramatically weaken the samples because the melt pockets are not interconnected at the low melt fraction of 7%. The coalescence of the initial micro-cracks generates conjugate cracks in which the fine grained fragments of the gouge undergoes chemical homogenization. The deformation mechanism in the gouge is likely to be melt-enhanced diffusion creep, which is likely to also assist the chemical homogenization process.

  7. Segregation At Stacking Faults Within The ?' Phase Of Two Ni-base Superalloys Following Intermediate Temperature Creep

    SciTech Connect

    Viswanathan, G. B.; Shi, R.; Genc, Arda; Vorontsov, V. A.; Kovarik, Libor; Rae, C.M. F.; Mills, M. J.

    2015-01-01

    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 ?' precipitates following intermediate temperature deformation 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 deformation of the alloys.

  8. Effect of high temperature creep and oxidation on residual room temperature properties for several thin sheet superalloys

    NASA Technical Reports Server (NTRS)

    Royster, D. M.; Lisagor, W. B.

    1972-01-01

    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, creep, and residual properties of thin-gage sheet material.

  9. Tensile, Fatigue, and Creep Properties of Aluminum Heat Exchanger Tube Alloys for Temperatures from 293 K to 573 K (20 C to 300 C)

    NASA Astrophysics Data System (ADS)

    Kahl, Sren; Ekstrm, Hans-Erik; Mendoza, Jesus

    2014-02-01

    Since automotive heat exchangers are operated at varying temperatures and under varying pressures, both static and dynamic mechanical properties should be known at different temperatures. Tubes are the most critical part of the most heat exchangers made from aluminum brazing sheet. We present tensile test, stress amplitude-fatigue life, and creep-rupture data of six AA3XXX series tube alloys after simulated brazing for temperatures ranging from 293 K to 573 K (20 C to 300 C). While correlations between several mechanical properties are strong, ranking of alloys according to one property cannot be safely deduced from the known ranking according to another property. The relative reduction in creep strength with increasing temperature is very similar for all six alloys, but the general trends are also strong with respect to tensile and fatigue properties; an exception is one alloy that exhibits strong Mg-Si precipitation activity during fatigue testing at elevated temperatures. Interrupted fatigue tests indicated that the crack growth time is negligible compared to the crack initiation time. Fatigue lifetimes are reduced by creep processes for temperatures above approximately 423 K (150 C). When mechanical properties were measured at several temperatures, interpolation to other temperatures within the same temperature range was possible in most cases, using simple and well-established equations.

  10. Models for coupled diffusive/strain controlled growth of creep cavities

    SciTech Connect

    Lu, H.M.; Delph, T.J. )

    1993-08-01

    The importance of intergranular creep cavitation to high-temperature failure processes in metals and ceramics has been well-recognized for some time now. In general, creep cavity growth at elevated temperature is thought to occur by one of two processes. The first of these is diffusive growth, whereby matter is transported from the cavity surface and is deposited on the grain boundary. The second is strain-controlled growth, in which the cavity grows entirely as a consequence of creep deformation of the surrounding material under the action of an applied stress. Several models of cavity growth have been proposed in which these processes are coupled to each other and occur simultaneously. These models have attained some currency and have been used in several studies involving the growth of creep cavitation. The purpose of the present note is to investigate in some detail one particular class of these models.

  11. Non-Classical Creep Behavior of Fusion-Cast Alumina Refractories

    SciTech Connect

    Hemrick, James Gordon; Wereszczak, Andrew A

    2009-01-01

    The compressive creep behavior of a typical 50% ?-/50% ?-alumina fusion-cast refractory block was examined as a function of temperature. Test temperatures (1450-1650oC) were chosen to correspond to those typical of service conditions, while relatively high compressive test stresses (0.6 and 1.0 MPa compared to 0.2-0.4 MPa which is typical of service) were chosen to promote exaggerated deformation and to more accurately measure the resulting creep strain. It was found that the measured creep strain responses in this alumina were a sum of (contracting) compressive creep strain and expansion strain due to time and temperature dependent microcracking. Long term, isothtermal expansion tests were also conducted, and their results allowed for the deconvolution of the compressive creep and expansion strains present in the measured creep strain test data. The analysis shows that despite complications associated with conflicting expansion and contraction effects, classical creep analysis may be used with this alumina refractory after the strains associated with the non-steady-state mechanism are considered and accounted for.

  12. Changes in borehole temperatures, ice content and creep velocities - results from 10 years of monitoring mountain permafrost in Switzerland

    NASA Astrophysics Data System (ADS)

    Noetzli, Jeannette; Vonder Muehll, Daniel

    2010-05-01

    The network for permafrost monitoring in Switzerland (PERMOS) has been built up since the early 1990s aiming to document the state and changes of mountain permafrost on a long-term basis. Following a 6 year pilot-phase starting in 2000, the PERMOS network is now funded and integrated into the national and international monitoring structures. The observations are based on three elements: (1) ground temperatures measured in boreholes and at the surface near to the drill site, (2) changes in subsurface ice and water content at the drill sites by geo-electrical surveys, and (3) velocities of permafrost creep determined by geodetic surveys and/or photogrammetry. In addition, standardized documentation of fast mass movements from permafrost areas (e.g., rock fall) is being established. In this contribution, we present measurement results of all observation parameters and their joint interpretation, along with a short overview on PERMOS and its monitoring strategy. The connection between air temperatures and permafrost temperatures is not straightforward. Effects of winter snow conditions, surface cover (cooling effects by coarse blocks), subsurface ice content (effects of latent heat), and steep topography mask changes in atmospheric conditions when they propagate into the subsurface. The signal is additionally delayed by the high thermal inertia of the system. This can explain why temperature time series from 24 boreholes of up to 20 years length do not (or not yet) reflect a clear warming signal. Seasonal variations in air temperatures and snow conditions, however, are well visible in active layer thicknesses in most boreholes, with the intensity of the signal depending on site characteristics. The information gained from borehole temperatures is complemented by geo-electrical surveys. Results can be linked to changes in frozen and unfrozen water content, indicate substantial degradation of ground ice, and show the potential of a combined approach compared to thermal monitoring alone. Kinematics results show an increase of creep velocities or even a destabilization of rock glaciers in the past years or decades. In view of the borehole measurements, this acceleration may be related to changes in water content or availability. The inventory of rock falls comprises more than 150 events from permafrost regions, with an increase of events in the past two decades. This is likely a result of a combination of factors: growing human activities in high mountain regions, raised public and scientific awareness to this phenomena, and an increase of such events.

  13. Deformation of Lawsonite at High Pressure and High Temperature - Implications for Low Velocity Layers in Subduction Zones

    NASA Astrophysics Data System (ADS)

    Amiguet, E.; Hilairet, N.; Wang, Y.; Gillet, P.

    2014-12-01

    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 deformation, lawsonite plasticity and crystal preferred orientation (CPOs) may strongly influence the dynamic of subduction zones and the seismic properties. We present a deformation study at high presssure and high temperature on lawsonite. Six samples were deformed 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% deformation 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 temperature and strain rate. Texture analysis coupled with transmission electron microscopy showed that dislocation creep is the dominant deformation mechanism under our deformation 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 Science Letters, 163, 361-379,1998 [5] Wang et al, Review for Scientific Instruments, 74(6), 3002-3011, 2003 [6] Chantel et al., Earth and Planetary Science Letters, 349-350, 116-125, 2012

  14. Influence of high pressure hydrogen environment on creep deformation of Mo-Re, Haynes 188, and NARloy-Z alloys

    NASA Technical Reports Server (NTRS)

    Sastry, S. M. L.; Yang, Charles C.; Ouyang, Shewang; Jerina, K. L.; Schwartz, D. S.

    1994-01-01

    The present study focuses on the investigation of the influence of hydrogen on the mechanical properties of three types of alloys at elevated temperatures. 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 temperature and should have good strength in hydrogen atmosphere at elevated temperature. The paucity of information concerning the mechanical performance in hydrogen atmosphere at elevated temperature has been a limiting factor in the selection and design of structural components for operation in hydrogen environment.

  15. A Method to Identify Steady Creep Strain from Indentation Creep Using a New Reference Area of Indentation

    NASA Astrophysics Data System (ADS)

    Takita, Atsuko; Sasaki, Katsuhiko; Ohguchi, Ken-ichi

    2014-07-01

    For the design of high-density electronic packages, finite element method (FEM) analyses to evaluate strength reliabilities of solder joints should be conducted by employing the material parameters which can precisely reflect the creep properties of solder joints in actual electronic equipment. To obtain accurate results of the structural analyses of the solder joints, a method to evaluate the steady-state creep deformation in situ must be developed. The indentation creep test is an effective method to evaluate the creep properties of the solder joints in situ; however, the creep properties obtained by this method do not give the same results as those obtained by tensile creep tests using bulk specimens. In this paper, the indentation creep test at 1 N loading for 9,000 s duration was experimentally conducted to confirm that the steady-state creep deformation obtained by the indentation creep test did not coincide with that by the tensile creep tests using bulk specimens. To identify the reason, the indentation creep simulation was conducted by FEM analysis. As a result, it was found that the reference area used to obtain the creep strain from the indentation creep test should be modified. A method to obtain the new reference area is proposed from comparisons of experiments with simulations. Finally, this paper shows that the creep properties obtained by the indentation creep test using the new reference area coincided with those obtained by tensile creep tests using bulk specimens.

  16. Creep of plasma-sprayed-ZrO2 thermal-barrier coatings

    NASA Technical Reports Server (NTRS)

    Firestone, R. F.; Logan, W. R.; Adams, J. W.; Bill, R. C., Jr.

    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 6900, 13,800, and 24,100 kPa (1000, 2000, and 3500 psi) and temperatures of 1100, 1250, and 1400 C. The coatings were stabilized with lime, MgO, and two different concentrations of Y2O3. 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 while the stress, particle size, and porosity had a lesser effect. Creep deformation was due to cracking and particle sliding.

  17. Life Estimation and Creep Damage Quantification of Service Exposed Reformer Tube

    NASA Astrophysics Data System (ADS)

    Raj, A.; Roy, N.; Roy, B. N.; Ray, A. K.

    2015-11-01

    This paper deals with evaluation of creep 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 creep deformation under identical test conditions, optical microscopy and fractography. Accumulation of damage due to creep has been quantified through microstructural studies. The as received tubes did not reveal any degradation in the material like creep cavitation or voids, but there was indeed loss of tensile strength from room temperature to 870C for the bottom portion of the tube due to ageing and overheating. Scatter in creep deformation 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 creep damage in the tertiary region as well. A remnant life of >10 years is estimated at the operating stress-temperature conditions of the top as well as bottom portion of the tube.

  18. Low-cycle fatigue of a VZh175 high-temperature alloy under elastoplastic deformation conditions

    NASA Astrophysics Data System (ADS)

    Belyaev, M. S.; Terent'ev, V. F.; Bakradze, M. M.; Gorbovets, M. A.; Gol'dberg, M. A.

    2015-04-01

    The low-cycle fatigue of a VZh175 nickel superalloy is studied under conditions of complete deformation per loading cycle at an initial cycle asymmetry R = 0, a deformation amplitude ?a = 0.4-0.6%, and a temperature of 20 and 650C. 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 deformation amplitude and the test temperature.

  19. Deformation twinning in nanocrystalline copper at room temperature and low strain rate

    E-print Network

    Zhu, Yuntian T.

    processed by ball milling at liquid nitrogen temperature9 and in nc Al film produced by physical vapor for deformation twinning in the ball-milled Al powder.9,10 In fact, both high strain rate and low temperature Federation Received 23 September 2003; accepted 28 November 2003 The grain-size effect on deformation

  20. Creep Resistant Zinc Alloy

    SciTech Connect

    Frank E. Goodwin

    2002-12-31

    This report covers the development of Hot Chamber Die Castable Zinc Alloys with High Creep 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 creep 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 creep resistant zinc die-casting alloy were identified as follows: (1) temperature capability of 1470 C; (2) creep stress of 31 MPa (4500 psi); (3) exposure time of 1000 hours; and (4) maximum creep 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--Creep 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.

  1. Creep Measurement Video Extensometer

    NASA Technical Reports Server (NTRS)

    Jaster, Mark; Vickerman, Mary; Padula, Santo, II; Juhas, John

    2011-01-01

    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 creep 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 deformation, while maintaining adequate resolution to capture the true deformation response of the material. The measurement system comprises a high-resolution digital camera, computer, and software that work collectively to interpret the image.

  2. Time-dependent cracking and brittle creep in crustal rocks: A review

    NASA Astrophysics Data System (ADS)

    Brantut, N.; Heap, M. J.; Meredith, P. G.; Baud, P.

    2013-07-01

    Rock fracture under upper crustal conditions is driven not only by applied stresses, but also by time-dependent, chemically activated subcritical cracking processes. These subcritical processes are of great importance for the understanding of the mechanical behaviour of rocks over geological timescales. A macroscopic manifestation of time-dependency in the brittle field is the observation that rocks can deform and fail at constant applied stresses, a phenomenon known as brittle creep. Here, we review the available experimental evidence for brittle creep in crustal rocks, and the various models developed to explain the observations. Laboratory experiments have shown that brittle creep occurs in all major rock types, and that creep strain rates are extremely sensitive to the environmental conditions: differential stress, confining pressure, temperature and pore fluid composition. Even small changes in any of these parameters produce order of magnitude changes in creep strain rates (and times-to-failure). Three main classes of brittle creep model have been proposed to explain these observations: phenomenological, statistical, and micromechanical. Statistical and micromechanical models explain qualitatively how the increasing influence of microcrack interactions and/or the increasing accumulated damage produces the observed evolution of macroscopic deformation during brittle creep. However, no current model can predict quantitatively all of the observed features of brittle creep. Experimental data are limited by the timescale over which experiments are realistically feasible. Clearly, an extension of the range of available laboratory data to lower strain rates, and the development of new modelling approaches are needed to further improve our current understanding of time-dependent brittle deformation in rocks.

  3. Thermal deformation of concentrators in an axisymmetric temperature field

    NASA Technical Reports Server (NTRS)

    Bairamov, R.; Machuev, Y. I.; Nazarov, A.; Sokolov, Y. V.; Solodovnikova, L. A.; Fokin, V. G.

    1985-01-01

    Axisymmetric thermal deformations of paraboloid mirrors, due to heating, are examined for a mirror with a optical axis oriented toward the Sun. A governing differential equation is derived using Mushtari-Donnel-Vlasov simplifications, and a solution is presented which makes it possible to determine the principal deformation characteristics.

  4. Investigation of the structure of two heat-temperature nickel-based alloys after high-temperature deformation

    NASA Astrophysics Data System (ADS)

    Davydov, D. I.; Vinogradova, N. I.; Kazantseva, N. V.; Stepanova, N. N.

    2015-02-01

    The structural tests of turbine blades made from two commercial high-temperature nickel-based alloys were carried out after their test operation at elevated temperature and stresses. Both alloys contain 40% of a hardening intermetallic phase and the upper operating temperature of both alloys is limited to 900C, but they have a different resistance to high-temperature deformation.

  5. Present-day deformation along the El Pilar Fault in eastern Venezuela: Evidence of creep along a major transform boundary

    NASA Astrophysics Data System (ADS)

    Jouanne, Franois; Audemard, Franck A.; Beck, Christian; Van Welden, Aurlien; Ollarves, Reinaldo; Reinoza, Carlos

    2011-05-01

    The right-lateral strike-slip El Pilar Fault is one of the major structures that accommodate the relative displacement between the Caribbean and South-America Plates. This fault, which trends East-West along the northeastern Venezuela margin, is a seismogenic source, and shows numerous evidence for active tectonics, including deformation of the Quaternary sediments filling the Cariaco Gulf. Because the main El Pilar Fault strand belongs to a set of strike-slip faults and thrusts between the stable Guyana shield (South) and the Caribbean oceanic floor (North), a GPS network was designed and installed to measure the relative motion of the El Pilar Fault and other faults. The results obtained from the comparison of 2003 and 2005 surveys indicate: (i) a lack of significant displacement (especially shortening) in the Serrania del Interior (Neogene cordillera overthrusted above the Guyana craton), (ii) an eastward displacement (relative to fixed south America plate) up to 22 mm/year of benchmarks located north of the El Pilar Fault. Velocities simulations using dislocations in an elastic half-space show: (1) the concentration along the El Pilar Fault of the whole Caribbean-South America relative displacement, (2) the existence of an important component of aseismic displacement along the upper part of the El Pilar Fault. Between 12 km depth and the surface, only 40% of displacement is locked for the western segment and 50% for the eastern segment. This last phenomenon may be related to the existence of serpentinite lenses along the fault zone as observed for segments of San Andreas and North Anatolian faults.

  6. Creep Properties of Solid Oxide Fuel Cell Glass-Ceramic Seal G18

    SciTech Connect

    Milhans, Jacqueline; Khaleel, Mohammad A.; Sun, Xin; Tehrani, Mehran; Al-Haik, Marwan; Garmestani, Hamid

    2010-11-01

    This study utilizes nanoindentation to investigate and measure creep 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 temperatures to investigate the strain rate sensitivity during inelastic deformation. The temperature dependent behavior is important since SOFCs operate at high temperatures (800-1000C). Results show that the samples with higher crystallinity were more resistant to creep, and the creep compliance tended to decrease with increasing temperature, especially with further aged samples.

  7. Sessile dislocations by reactions in NiAl severely deformed at room temperature

    SciTech Connect

    Geist, D.; Gammer, C.; Rentenberger, C.; Karnthaler, H. P.

    2015-02-05

    B2 ordered NiAl is known for its poor room temperature (RT) ductility; failure occurs in a brittle like manner even in ductile single crystals deforming by single slip. In the present study NiAl was severely deformed at RT using the method of high pressure torsion (HPT) enabling the hitherto impossible investigation of multiple slip deformation. Methods of transmission electron microscopy were used to analyze the dislocations formed by the plastic deformation showing that as expected dislocations with Burgers vector a(100) carry the plasticity during HPT deformation 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 deformation-induced embrittlement. In spite of the severe deformation, the chemical order remains unchanged.

  8. Sessile dislocations by reactions in NiAl severely deformed at room temperature

    PubMed Central

    Geist, D.; Gammer, C.; Rentenberger, C.; Karnthaler, H.P.

    2015-01-01

    B2 ordered NiAl is known for its poor room temperature (RT) ductility; failure occurs in a brittle like manner even in ductile single crystals deforming by single slip. In the present study NiAl was severely deformed at RT using the method of high pressure torsion (HPT) enabling the hitherto impossible investigation of multiple slip deformation. Methods of transmission electron microscopy were used to analyze the dislocations formed by the plastic deformation showing that as expected dislocations with Burgers vector a?100? carry the plasticity during HPT deformation 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 deformation-induced embrittlement. In spite of the severe deformation, the chemical order remains unchanged. PMID:25663749

  9. Creep behavior of Fe-bearing olivine under hydrous conditions

    NASA Astrophysics Data System (ADS)

    Tasaka, Miki; Zimmerman, Mark E.; Kohlstedt, David L.

    2015-09-01

    To understand the effect of iron content on the creep behavior of olivine, (MgxFe(1 - x))2SiO4, under hydrous conditions, we have conducted tri-axial compressive creep experiments on samples of polycrystalline olivine with Mg contents of x = 0.53, 0.77, 0.90, and 1. Samples were deformed at stresses of 25 to 320 MPa, temperatures of 1050 to 1200C, 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 creep regime: ??=??0.90((1-x/0.1))1/2exp[2261030.9-x/RT]. In this equation, the strain rate of San Carlos olivine, ??0.90, is a function of T, ?, and fH2O. As previously shown for anhydrous conditions, an increase in iron content directly increases creep rate. In addition, an increase in iron content increases hydrogen solubility and therefore indirectly increases creep 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.

  10. High-temperature deformation of uniaxially aligned lamellar TiAl/Ti{sub 3}Al

    SciTech Connect

    Heinrich, H.; Abaecherli, V.; Wilkins, D.J.; Kostorz, G.

    1999-07-01

    Uniaxially aligned polysynthetically twinned two-phase TiAl/Ti{sub 3}Al material is produced by induction zone melting and deformed in uniaxial compression. Above 1,000 K the strain rate sensitivity is independent of the lamellar orientation and increases strongly with increasing deformation temperature. Results for the strain rate sensitivity parameters are somewhat lower than those obtained for {gamma}-TiAl single- and polycrystals. If the lamellae are oriented parallel or perpendicular to the deformation axis, the flow stress decreases with increasing strain. After plastic deformation the dislocation density in the lamellae is remarkably low indicating recovery processes. At the lamellar interfaces misfit dislocations and periodic arrangements of dislocations with Burgers vectors inclined to the lamellar boundaries are found. In contrast to deformation at lower temperatures, deformation twinning is rare.

  11. Creep-Fatigue Interaction Testing

    NASA Technical Reports Server (NTRS)

    Halford, Gary R.

    2001-01-01

    Fatigue fives in metals are nominally time independent below 0.5 T(sub Melt). At higher temperatures, fatigue lives are altered due to time-dependent, thermally activated creep. Conversely, creep rates are altered by super. imposed fatigue loading. Creep and fatigue generally interact synergistically to reduce material lifetime. Their interaction, therefore, is of importance to structural durability of high-temperature 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 creep-fatigue began in the era following World War II. In this article experimental and life prediction approaches are reviewed for assessing creep-fatigue interactions of metallic materials. Mechanistic models are also discussed briefly.

  12. Thermal creep model for CWSR zircaloy-4 cladding taking into account the annealing of the irradiation hardening

    SciTech Connect

    Cappelaere, Chantal; Limon, Roger; Duguay, Chrstelle; Pinte, Gerard; Le Breton, Michel; Bouffioux, Pol; Chabretou, Valerie; Miquet, Alain

    2012-02-15

    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 creep deformation under the hoop stress induced by the internal pressure of the fuel rod. The thermal creep is a potential mechanism that might lead to cladding failure. A new creep model was developed, based on a database of creep tests on as-received and irradiated cold-worked stress-relieved Zircaloy-4 cladding in a wide range of temperatures (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 creep and the steady-state creep, but also the early creep acceleration observed on irradiated samples tested in severe conditions, which was not taken into account in the previous models. The extrapolation of the creep model in the conditions of very long-term creep tests is reassuring, proving the robustness of the chosen formalism. The creep model has been assessed in progressively decreasing stress conditions, more representative of a transport. Set up to predict the cladding creep behavior under variable temperature 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)

  13. Microstructural Characterization of Dislocation Networks During Harper-Dorn Creep of fcc, bcc, and hcp Metals and Alloys

    SciTech Connect

    Przystupa, Marek A.

    2007-12-13

    Harper-Dorn (H-D) creep is observed in metals and geological materials exposed to very low stresses at temperatures close to the melting point. It is one of several types of creep processes wherein the steady-state strain rate is proportional to the applied stress, Nabarro-Herring creep and Coble creep being two other important processes. H-D creep can be somewhat insidious because the creep rates are much larger than those expected for Nabarro-Herring or Coble creep. Since the working conditions of structural components of power plants and propulsion systems, as well as the motion of the earths mantle all involve very low stresses, an understanding of the factors controlling H-D creep is critical in preventing failures associated with those higher-than-expected creep rates. The purpose of this investigation was to obtain missing microstructural information on the evolution of the dislocation structures during static annealing of materials with fcc, bcc and hcp structure and use obtained results to test predictive capabilities of the dislocation network theory of H-D creep. In our view the evolutionary processes during static annealing and during Harper-Dorn creep are intimately related. The materials used in this study were fcc aluminum, hcp zinc and bcc tin. All characterizations of dislocation structures, densities and dislocation link length distributions were carried out using the etch pit method. To obtain quantitative information on the evolution of the dislocation networks during annealing the pure fcc aluminum samples were pre-deformed by creep at 913 and 620 K and then annealed. The higher deformation temperature was selected to generate starting dislocation networks similar to those forming during Harper-Dorn creep and the lower, to obtain higher dislocation densities suitable for reliable estimates of the parameters of the network growth law. The measured experimental link length distribution were, after scaling, (1) the same for all annealing temperatures, (2) time invariant and (3) identical to the distributions obtained previously for Harper-Dorn creep. This has never been shown before and confirms our theoretical expectations that evolution of the dislocation networks during annealing and H-D creep is governed by the same growth law. Obtained results were also used to predict H-D steady creep rates from annealing kinetics data using equations of the dislocation network theory. For the three considered stresses the theory predicts systematically smaller creep rates by the average factor of 4.5. Considering that the creep rates have been predicted from the annealing data alone and without any adjustable parameters, this results shout be considered as outstanding. In case of hcp zinc the samples were pre-deformed in compression at constant stress of 4 MPa at temperature of 573 K and subsequently annealed at the same temperature. During annealing samples readily recrystallized, but it was possible to obtain information on the link length distributions from several unrecrystallized grains. The results showed that the scaled link length distributions were time invariant and similar to those of the aluminum. The annealing studies on bcc tin were also curtailed by the concurrent recrystallization. It was only possible to obtain link length distribution for samples deformed in compression at constant load of 2 MPa at 423 K after unloading. The link length distribution was also in this case similar to that of the aluminum and zinc. These results suggest that the scaled link length distribution is universal and the same for the three considered crystal structures. This supports theoretical findings of these studies that appropriately scaled dislocation link length distribution should both universal and time invariant. We have also investigated the possibility of using alternative methods of estimating local dislocation densities from etch pits which could give more precise estimates of the dislocation link-lengths. The two most promising method are based on the use of Voronoi diagrams and uniform 3-connected nets

  14. Invited review paper: Fault creep caused by subduction of rough seafloor relief

    NASA Astrophysics Data System (ADS)

    Wang, Kelin; Bilek, Susan L.

    2014-01-01

    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/creeping state, we find that creeping 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 creeping state is not yet constrained by geodetic observations, but the very rugged subducting seafloor and lack of large earthquakes also suggest aseismic creep. 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 creep 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 creeps because of distributed deformation of fractured rocks, and the creep 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 creep with very rugged subducting seafloor calls for further investigation. Seafloor near-trench geodetic monitoring, high-resolution imaging of subduction fault structure, studies of exhumed ancient subduction zones, and laboratory studies of low-temperature creep will greatly improve our understanding of the seismogenic and creep processes and their hazard implications.

  15. High temperature deformation mechanisms and strain heterogeneities in calcite rocks

    E-print Network

    Xu, Lili, Sh. D. Massachusetts Institute of Technology

    2008-01-01

    In nature, carbonates often accumulate large amounts of strain in localized shear zones. Such marble sequences play a key role in crustal deformation processes. Despite extensive field and laboratory investigation, many ...

  16. Microstructure and Creep Behavior of a Directional Solidification Nickel-based Superalloy

    NASA Astrophysics Data System (ADS)

    Tian, Ning; Tian, Sugui; Yu, Huichen; Li, Ying; Meng, Xianlin

    2015-07-01

    By means of creep property measurement and microstructure observation, an investigation has been made into microstructure and creep behavior of a directional solidification Ni-based superalloy at high temperatures. Results show that after full heat treatment, small cuboidal ?' precipitates distribute in the dendrite regions, while coarser ones distribute in the inter-dendrite regions. In the primary stage of creep, the ?' phase in alloy is transformed into the rafted structure along the direction vertical to stress axis, and then the creep of alloy enters the steady state stage. And dislocations slipping in the g matrix and climbing over the rafted ?' phase are thought to be the deformation mechanism of the alloy during steady creep stage. At the latter stage of creep, the alternate slipping of dislocations may shear and twist the rafted ?'/? phases, which promotes the initiation and propagation of the micro-cracks along the boundaries near the coarser rafted ?' phase. And the bigger probability of the creep damage occurs in the grain boundaries along 45 angles relative to the stress axis due to them bearing relatively bigger shearing stress.

  17. Corrosion and Creep of Candidate Alloys in High Temperature Helium and Steam Environments for the NGNP

    SciTech Connect

    Was, Gary; Jones, J. W.

    2013-06-21

    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 temperature, 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 temperature range 500-600 degree C; and examining the application of static and cyclic stresses in combination with impure He environments in the temperature rang 750-850 degree C; and examining the application of static and cyclic stresses in combination with impure He environments in the temperature 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.

  18. Computational simulation of probabilistic lifetime strength for aerospace materials subjected to high temperature, mechanical fatigue, creep, and thermal fatigue

    NASA Technical Reports Server (NTRS)

    Boyce, Lola; Bast, Callie C.; Trimble, Greg A.

    1992-01-01

    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 temperature, fatigue, or creep. 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.

  19. Computational simulation of probabilistic lifetime strength for aerospace materials subjected to high temperature, mechanical fatigue, creep and thermal fatigue

    NASA Technical Reports Server (NTRS)

    Boyce, Lola; Bast, Callie C.; Trimble, Greg A.

    1992-01-01

    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 temperature, fatigue or creep. 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.

  20. Computational simulation of probabilistic lifetime strength for aerospace materials subjected to high temperature, mechanical fatigue, creep, and thermal fatigue

    NASA Astrophysics Data System (ADS)

    Boyce, Lola; Bast, Callie C.; Trimble, Greg A.

    1992-08-01

    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 temperature, fatigue, or creep. 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.

  1. Computational simulation of probabilistic lifetime strength for aerospace materials subjected to high temperature, mechanical fatigue, creep and thermal fatigue

    NASA Astrophysics Data System (ADS)

    Boyce, Lola; Bast, Callie C.; Trimble, Greg A.

    1992-11-01

    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 temperature, fatigue or creep. 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.

  2. Tensile creep behavior of polycrystalline alumina fibers

    NASA Technical Reports Server (NTRS)

    Yun, H. M.; Goldsby, J. C.

    1993-01-01

    Tensile creep studies were conducted on polycrystalline Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Test conditions were temperatures from 800 to 1050 C and stresses from 60 to 1000 MPa. For both fibers, only a small primary creep portion occurred followed by steady-state creep. The stress exponents for steady-state creep of Nextel 610 and Fiber FP were found to be about 3 and 1, respectively. At lower temperatures, below 1000 C, the finer grained Nextel 610 had a much higher 0.2 percent creep strength for 100 hr than the Fiber FP; while at higher temperatures, Nextel 610 had a comparable creep strength to the Fiber FP. The stress and grain size dependencies suggest Nextel 610 and Fiber FP creep rates are due to grain boundary sliding controlled by interface reaction and Nabarro-Herring mechanisms, respectively.

  3. Transient Creep and Strain Energy Dissipation: An Experimental Perspective

    NASA Astrophysics Data System (ADS)

    Faul, Ulrich; Jackson, Ian

    2015-05-01

    Energy dissipation due to intrinsic attenuation occurs at elevated temperatures in rocks as a result of a range of processes. Examples where small-strain, transient deformation occurs are seismic waves, tidal deformation, and at longer timescales post-glacial rebound and far-field post-seismic deformation. Experiments at mantle temperatures and seismic frequencies show that grain boundary sliding is a key process that results in a broad absorption band, as indicated by seismic observations. Models of grain boundary sliding predict a smooth transition from elastic behavior through an anelastic regime toward viscous (Maxwell) behavior, consistent with experimental observations. Other mechanisms that may contribute to dissipation in Earth, at least locally, are dislocations and melt. Extrapolation of the laboratory data shows that first-order observations of planetary behavior and structure can be explained by the effects of temperature and pressure on transient creep properties, but that locally, additional mechanisms are required.

  4. Electrochemical control of creep in nanoporous gold

    SciTech Connect

    Ye, Xing-Long; Jin, Hai-Jun

    2013-11-11

    We have investigated the mechanical stability of nanoporous gold (npg) in an electrochemical environment, using in situ dilatometry and compression experiments. It is demonstrated that the gold nano-ligaments creep under the action of surface stress which leads to spontaneous volume contractions in macroscopic npg samples. The creep of npg, under or without external forces, can be controlled electrochemically. The creep rate increases with increasing potential in double-layer potential region, and deceases to almost zero when the gold surface is adsorbed with oxygen. Surprisingly, we also noticed a correlation between creep and surface diffusivity, which links the deformation of nanocrystals to mobility of surface atoms.

  5. Anisotropic deformation of Zr-2.5Nb pressure tube material at high temperatures

    NASA Astrophysics Data System (ADS)

    Fong, R. W. L.

    2013-09-01

    Zr-2.5Nb alloy is used for the pressure tubes in CANDU reactor fuel channels. In reactor, the pressure tube normally operates at 300 C and experiences a primary coolant fluid internal pressure of approximately 10 MPa. Manufacturing and processing procedures generate an anisotropic state in the pressure tube which makes the tube stronger in the hoop (transverse) direction than in the axial (longitudinal) direction. This anisotropy condition is present for temperatures less than 500 C. During postulated accident conditions where the material temperature could reach 1000 C, it might be assumed that the high temperature and subsequent phase change would reduce the inherent anisotropy, and thus affect the deformation behaviour (ballooning) of the pressure tube. From constant-load, rapid-temperature-ramp, uniaxial deformation tests, the deformation rate in the longitudinal direction of the tube behaves differently than the deformation rate in the transverse direction of the tube. This anisotropic mechanical behaviour appears to persist at temperatures up to 1000 C. This paper presents the results of high-temperature deformation tests using longitudinal and transverse specimens taken from as-received Zr-2.5Nb pressure tubes. It is shown that the anisotropic deformation behaviour observed at high temperatures is largely due to the stable crystallographic texture of the ?-Zr phase constituent in the material that was previously observed by neutron diffraction measurements during heating at temperatures up to 1050 C. The deformation behaviour is also influenced by the phase transformation occurring at high temperatures during heating. The effects of texture and phase transformation on the anisotropic deformation of as-received Zr-2.5Nb pressure tube material are discussed in the context of the tube ballooning behaviour. Because of the high temperatures in postulated accident scenarios, any irradiation damage will be annealed from the pressure tube material and thus the unirradiated material results presented in this paper are also applicable to irradiated pressure tubes.

  6. Low cycle fatigue and creep-fatigue behavior of Ni-based alloy 230 at 850 C

    SciTech Connect

    Chen, Xiang; Yang, Zhiqing; Sokolov, Mikhail A; ERDMAN III, DONALD L; Mo, Kun; Stubbins, James

    2013-01-01

    Strain-controlled low cycle fatigue (LCF) and creep-fatigue testing of Ni-based alloy 230 were carried out at 850 C. The material creep-fatigue life decreased compared with its low cycle fatigue life at the same total strain range. Longer hold time at peak tensile strain further reduced the material creep-fatigue life. Based on the electron backscatter diffraction, a novel material deformation characterization method was applied, which revealed that in low cycle fatigue testing as the total strain range increased, the deformation was segregated to grain boundaries since the test temperature was higher than the material equicohesive temperature and grain boundaries became weaker regions compared with grains. Creep-fatigue tests enhanced the localized deformation, resulting in material interior intergranular cracking, and accelerated material damage. Precipitation in alloy 230 helped slip dispersion, favorable for fatigue property, but grain boundary cellular precipitates formed after material exposure to the elevated temperature had a deleterious effect on the material low cycle fatigue and creep-fatigue property.

  7. Influence of the Temperature of Gases on the Deformation Characteristics of Moving Water Droplets

    NASA Astrophysics Data System (ADS)

    Antonov, D. V.; Volkov, R. S.; Zhdanova, A. O.; Kuznetsov, G. V.; Strizhak, P. A.

    2015-07-01

    An experimental analysis of the influence of the temperature of gases on the deformation characteristics of water droplets moving through them is carried out. High-speed (up to 105 frames per second) photography with video cameras and cross-correlation complexes, as well as panoramic optical methods of recording the motion parameters of gaseous and liquid flows, were used. The laws governing the movement of water droplets through gases with a temperature of about 1100 K and in air at relatively low (to 280 K) and moderate (about 300 K) temperatures have been studied. The principal characteristics of the deformation of water droplets (duration, extension, and amplitudes of "deformation cycles") have been established. The differences in the characteristic shapes of droplets during their motion in gaseous media (at different temperatures of the latter) have been determined. The times during which droplets retain a certain shape in the deformation process have been calculated.

  8. Effect of Creep of Ferritic Interconnect on Long-Term Performance of Solid Oxide Fuel Cell Stacks

    SciTech Connect

    Liu, Wenning N.; Sun, Xin; Khaleel, Mohammad A.

    2010-08-01

    High-temperature ferritic alloys are potential candidates as interconnect (IC) materials and spacers due to their low cost and coefficient of thermal expansion (CTE) compatibility with other components for most of the solid oxide fuel cells (SOFCs) . However, creep deformation becomes relevant for a material when the operating temperature exceeds or even is less than half of its melting temperature (in degrees of Kelvin). The operating temperatures for most of the SOFCs under development are around 1,073 K. With around 1,800 K of the melting temperature for most stainless steel, possible creep deformation of ferritic IC under the typical cell operating temperature should not be neglected. In this paper, the effects of IC creep behavior on stack geometry change and the stress redistribution of different cell components are predicted and summarized. The goal of the study is to investigate the performance of the fuel cell stack by obtaining the changes in fuel- and air-channel geometry due to creep of the ferritic stainless steel IC, therefore indicating possible changes in SOFC performance under long-term operations. The ferritic IC creep model was incorporated into software SOFC-MP and Mentat-FC, and finite element analyses were performed to quantify the deformed configuration of the SOFC stack under the long-term steady-state operating temperature. It was found that the creep behavior of the ferritic stainless steel IC contributes to narrowing of both the fuel- and the air-flow channels. In addition, stress re-distribution of the cell components suggests the need for a compliant sealing material that also relaxes at operating temperature.

  9. Microplastic deformation of submicrocrystalline and coarse-grained titanium at room and elevated temperatures

    NASA Astrophysics Data System (ADS)

    Dudarev, E. F.; Pochivalova, G. P.; Kolobov, Yu. R.; Bakach, G. P.; Skosyrskii, A. B.; Zhorovkov, M. F.

    2012-12-01

    Results obtained from a comparison study on the deformation behavior of submicrocrystalline and coarsegrained titanium in the temperature interval 295-773 K are presented. The microplastic strain mechanisms underlying a change in the deformation behavior of submicrocrystalline titanium in the melting temperature interval 0.35-0.40 ? m and a reduction in the strain hardening effect due to formation of submicrocrystalline structure of the material are examined. A multiscale model for development of microplastic deformation in submicrocrystalline metals and alloys is offered.

  10. Effect of High-Temperature Severe Plastic Deformation on Microstructure and Mechanical Properties of IF Steel

    NASA Astrophysics Data System (ADS)

    Jindal, Vikas; Rupa, P. K. P.; Mandal, G. K.; Srivastava, V. C.

    2014-06-01

    Extensive research work has been carried out on interstitial-free steel to understand its response to deformation; particularly, the behavior during severe plastic deformation (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 temperature (950 C). A considerable grain refinement has been observed, which may be attributed to the severity of deformation and recrystallisation at high temperatures. Nanoindentation tests have been performed at various stages of ARB process to understand the evolution of mechanical properties.

  11. On rate-dependent polycrystal deformation: the temperature sensitivity of cold dwell fatigue

    PubMed Central

    Zhang, Zhen; Cuddihy, M. A.; Dunne, F. P. E.

    2015-01-01

    A temperature and rate-dependent crystal plasticity framework has been used to examine the temperature sensitivity of stress relaxation, creep and load shedding in model Ti-6Al polycrystal behaviour under dwell fatigue conditions. A temperature close to 120C 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 temperatures in excess of about 230C, 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 temperatures between 20C and 230C 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 creep 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

  12. Creep of CoO single crystals.

    NASA Technical Reports Server (NTRS)

    Clauer, A. H.; Seltzer, M. S.; Wilcox, B. A.

    1971-01-01

    The crystals were creep tested in compression over ranges of temperature, stress, and oxygen pressure. The creep curves were S-shaped, and only the inflection creep rate was analyzed. A formula is presented for the inflection creep rate in the range from 1000 to 1200 C, 850 to 1700 psi, and 0.001 to 1 atm oxygen. Slip was found to occur on two orthogonal slip systems. The presence of subboundaries was observed by optical and transmission electron microscopy. It is suggested that the creep rate is controlled by oxygen diffusion.

  13. The Role of Eta Phase Formation on the Creep Strength and Ductility of INCONEL Alloy 740 t 1023 k (750 Degrees C)

    SciTech Connect

    Shingledecker, John P; Pharr, George Mathews

    2012-01-01

    INCONEL alloy 740 is an age-hardenable nickel-based superalloy proposed for advanced ultrasupercritical steam boiler applications operating at high stress and long times above 973 K (700 C), where creep will be the dominate deformation mode. During high-temperature exposure, the alloy can form eta phase platelets that many have suggested may be detrimental to creep strength and ductility. In this study, creep-rupture tests were conducted on smooth and notched bars of INCONEL alloy 740 at 1023 K (750 C) for times up to 20,000 hours. Examination of the creep-rupture life, creep ductility, failure modes, and microstructure by quantitative electron microscopy shows that a small amount of eta phase does not diminish the creep performance. Applied stress appears to have a minor effect on the precipitation of the eta phase but not its growth rate. Based on the observation that the microstructure after 20,000 hours of creep exposure has reached equilibrium in comparison to thermodynamic calculations, it is concluded that 20,000 hour creep tests are adequate for prediction of long-term creep performance.

  14. Analysis of Tensile Deformation and Failure in Austenitic Stainless Steels: Part I- Temperature Dependence

    SciTech Connect

    Kim, Jin Weon; Byun, Thak Sang

    2010-01-01

    This paper describes the temperature dependence of deformation 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 deformation and fracture: Key parameters such as the strain hardening rate, equivalent fracture stress, fracture strain, and tensile fracture energy were evaluated, and their temperature dependencies were investigated. It was shown that a significantly high strain hardening rate was still retained during unstable deformation although overall strain hardening rate beyond the onset of necking was lower than that of the uniform deformation. The values of the parameters except for fracture strain decreased with temperature up to 200oC and were saturated as the temperature came close to the maximum test temperature 450oC. The fracture strain increased and had a maximum at -50oC to 20oC before decreasing with temperature. It was explained that these temperature dependencies of fracture properties were associated with a change in the dominant strain hardening mechanism with test temperature. Also, it was seen that the pre-straining of material has little effect on the strain hardening rate during necking deformation and on fracture properties.

  15. Study on the high temperature deformation measurement using the mark shearing technique

    NASA Astrophysics Data System (ADS)

    Wang, Huaixi; Xie, Huimin; Dai, Xianglu; Wu, Lifu

    2015-09-01

    The mark shearing technique has been successfully utilized for room-temperature strain measurement in solid mechanics research. However, when the method is applied to deformation measurement at high temperature, some new issues will occur. From our experience, we have found that an inevitable thermal radiation will emit from the oven in the measurement and may lead to a distortion of the measuring system. As a result, an undesired measurement error will arise; furthermore, the oxidation resistance marker is crucial to obtain an ideal result. In order to solve the abovementioned issues, the mark shearing techniques for high-temperature deformation measurement are studied in this work, and a novel method for fabricating the marker pattern is proposed, which can be utilized to fabricate a deformation carrier for high temperature on a different specimen surface. In combination with this marker with our self-developed mark shearing system, the high-temperature (1000?C) mechanical properties of the high-temperature nickel alloy (GH4037) was measured. In order to characterize the thermal deformation caused by the oven during the high temperature experiment, the surface temperature distribution of the mark shearing system is measured by an infrared camera. On the basis of this result, the corresponding thermal deformation is analyzed by the finite element analysis (FEM) method. From the analysis result, we can conclude that the virtual strain of the system incurred by thermal radiation cannot be ignored for a long-time measurement.

  16. Creep fatigue life prediction for engine hot section materials (isotropic)

    NASA Technical Reports Server (NTRS)

    Moreno, Vito; Nissley, David; Lin, Li-Sen Jim

    1985-01-01

    The first two years of a two-phase program aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components are discussed. In Phase 1 (baseline) effort, low cycle fatigue (LCF) models, using a data base generated for a cast nickel base gas turbine hot section alloy (B1900+Hf), were evaluated for their ability to predict the crack initiation life for relevant creep-fatigue loading conditions and to define data required for determination of model constants. The variables included strain range and rate, mean strain, strain hold times and temperature. None of the models predicted all of the life trends within reasonable data requirements. A Cycle Damage Accumulation (CDA) was therefore developed which follows an exhaustion of material ductility approach. Material ductility is estimated based on observed similarities of deformation structure between fatigue, tensile and creep tests. The cycle damage function is based on total strain range, maximum stress and stress amplitude and includes both time independent and time dependent components. The CDA model accurately predicts all of the trends in creep-fatigue life with loading conditions. In addition, all of the CDA model constants are determinable from rapid cycle, fully reversed fatigue tests and monotonic tensile and/or creep data.

  17. Observation of Grain Rotations to Elucidate the Development of Crystal Preferred Orientation during Diffusion Creep

    NASA Astrophysics Data System (ADS)

    Maruyama, G.; Hiraga, T.

    2014-12-01

    The seismic anisotropy in Earth's upper mantle is explained by the crystallographic preferred orientation (CPO) of rock-forming minerals, which have anisotropic elasticity. Our team showed that the CPO of forsterite is produced even during diffusion creep (Miyazaki et al. 2013). The purpose of this study is to understand the mechanism of the development of CPO of forsterite by observations of samples surface after the sample deformation where the fine-scale strain markers were imposed.We deformed cylindrical polycrystalline samples of synthesized forsterite plus 20 vol. % diopside at its diffusion creep regime. We polished the lateral side of the sample where we imposed grooves parallel to the compression axis of the sample using a focused ion beam. These marker lines allow us to observe grain rotation due to a plastic deformation of the sample. After the high temperature compression creep experiment under atmosphere, we observed the marker lines under scanning electron microscope.We succeeded to observe the marker lines after the deformation. Strain of bulk sample and of the marker line exhibit the similar value indicating the similar deformation proceeded both at bulk and surface regions of the samples. Grain rotation, which is identified by misfits of the markers at grain boundaries and rotation of intra-granular markers, were observed in all the samples. No distortion of the markers within the grains was found indicating the absence of intragranular deformation process such as a glide of dislocations; however, in the samples deformed at high stress (~300 MPa), curved intra-granular markers were observed, which is consistent with dislocation activity at high stress condition. Our results show the significant grain rotation, which is necessary process for the development of CPO, during diffusion creep as well as the ability of identification of the deformation mechanism of the bulk sample by the observation of the sample surface.

  18. High-temperature deformation and microstructural analysis for silicon nitride-scandium(III) oxide

    NASA Technical Reports Server (NTRS)

    Cheong, Deock-Soo; Sanders, William A.

    1992-01-01

    It was indicated that Si3N4 doped with Sc2O3 may exhibit high temperature mechanical properties superior to Si3N4 systems with various other oxide sintered additives. High temperature deformation of samples was studied by characterizing the microstructures before and after deformation. 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 tripple and multiple grain boundary junctions. These secondary phases are devitrified as crystalline Sc2Si2O7. Deformation of the samples was dominated by cavitational processes rather than movements of dislocations. Thus the excellent deformation resistance of the samples at high temperature can be attributed to the very small thickness of the grain boundary layers and the crystalline secondary phase.

  19. High-temperature deformation and microstructural analysis for Si3N4-Sc2O3

    NASA Technical Reports Server (NTRS)

    Cheong, Deock-Soo; Sanders, William A.

    1990-01-01

    It was indicated that Si3N4 doped with Sc2O3 may exhibit high temperature mechanical properties superior to Si3N4 systems with various other oxide sintered additives. High temperature deformation of samples was studied by characterizing the microstructures before and after deformation. 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. Deformation of the samples was dominated by cavitational processes rather than movements of dislocations. Thus the excellent deformation resistance of the samples at high temperature can be attributed to the very small thickness of the grain boundary layers and the crystalline secondary phase.

  20. Deformation of a Step Composite Beam in a Temperature Field

    NASA Astrophysics Data System (ADS)

    Starovoitov, . I.; Pleskachevskii, Yu. M.; Leonenko, D. V.; Tarlakovskii, D. V.

    2015-07-01

    Consideration is given to thermal force deformation of an elastic three-layer beam with a stepwise thickness of one supporting layer. To describe the kinematics of a rod that is asymmetric across the bundle, the hypotheses of a broken normal are adopted. A system of equilibrium equations is derived and its general analytical solution in displacements is obtained. A numerical parametric analysis of the stressed-strained state of a metal-polymer threelayer beam is carried out.

  1. Materials Science and Technology, Volume 6, Plastic Deformation and Fracture of Materials

    NASA Astrophysics Data System (ADS)

    Mughrabi, Hael

    1996-12-01

    This self-contained handbook focuses on the mechanisms of plastic deformation and fracture affecting a wide variety of materials. From the Contents: Mughrabi: Introduction. Gil Sevillano: Flow Stress and Work Hardening. Leffers/Van Houtte/Aernoudt: Deformation and Textures of Metals at Large Strain. Kubin: Dislocation Patterning. Neuhuser/Schwink: Solid Solution Strengthening. Umakoshi: Deformation of Intermettalic Compounds. Reppich: Particle Strengthening. Blum: High Temperature Deformation and Creep of Crystalline Solids. Mukherjee: Superplasticity in Metals, Ceramics and Intermetallics. Argon: Inelastic Deformation and Fracture of Glassy Solids. Suresh: Cyclic Deformation and Fatigue. Riedel: Frature Mechanisms. Kato: Friction and Wear.

  2. ATOMISTIC SIMULATIONS OF DIFFUSIONAL CREEP IN A NANOCRYSTALLINE BODY-CENTERED CUBIC MATERIAL

    SciTech Connect

    Paul C. Millett; Tapan Desai; Vesselin Yamakov; Dieter Wolf

    2008-08-01

    Molecular dynamics (MD) simulations are used to study diffusion-accommodated creep deformation in nanocrystalline molybdenum, a body-centered cubic metal. In our simulations, the microstructures are subjected to constant-stress loading at levels below the dislocation nucleation threshold and at high temperatures (i.e., T > 0.75Tmelt), thereby ensuring that the overall deformation is indeed attributable to atomic self-diffusion. The initial microstructures were designed to consist of hexagonally shaped columnar grains bounded by high-energy asymmetric tilt grain boundaries (GBs). Remarkably the creep rates, which exhibit a double-exponential dependence on temperature and a double power-law dependence on grain size, indicate that both GB diffusion in the form of Coble creep and lattice diffusion in the form of NabarroHerring creep contribute to the overall deformation. For the first time in an MD simulation, we observe the formation and emission of vacancies from high-angle GBs into the grain interiors, thus enabling bulk diffusion.

  3. Cryogenic deformation of high temperature superconductive composite structures

    DOEpatents

    Roberts, Peter R. (Groton, MA); Michels, William (Brookline, MA); Bingert, John F. (Jemez Springs, NM)

    2001-01-01

    An improvement in a process of preparing a composite high temperature 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 temperatures.

  4. Creep-fatigue as a possible cause of dental amalgam margin failure.

    PubMed

    Williams, P T; Hedge, G L

    1985-03-01

    Fracture of the margins is the most common cause of failure of dental amalgam restorations. Both corrosion and creep have been identified as possible contributors to this type of failure. The stresses that induce creep may arise from the continued setting expansion of the amalgam, the formation of corrosion products, mastication, or from the thermal expansion of the amalgam during ingestion of hot foods. The latter two are low-frequency cyclic stresses. The amalgams used in dentistry have fusion temperatures only about 40 degrees C above mouth temperature, and they experience grain boundary sliding during creep deformation. Since grain boundary sliding, low-frequency cyclic stresses, and a temperature near the fusion temperature of the alloy are prerequisites for so-called "creep-fatigue fracture", this type of fracture may contribute to amalgam margin failure. Amalgam made from seven different alloys was condensed into stainless steel dies. After being allowed to set for seven days, the specimens were thermally cycled between 4 degrees C and 50 degrees C for 500 and 1000 cycles. Amalgam margin integrity was evaluated by scanning electron microscopy both before and after each cycling period. The amount of margin fracture was calculated after 1000 cycles. Thermal cycling of amalgam restorations placed in stainless steel dies resulted in predominantly intergranular fracturing of the amalgam margins, indicating that creep-fatigue failure may be a significant contributor to in vivo margin fracturing. PMID:3855901

  5. Matrix cracking and creep behavior of monolithic zircon and zircon silicon carbide fiber composites

    NASA Astrophysics Data System (ADS)

    Anandakumar, Umashankar

    In this study, the first matrix cracking behavior and creep behavior of zircon matrix silicon carbide fiber composites were studied, together with the fracture and creep behavior of the monolithic zircon. These behaviors are of engineering and scientific importance, and the study was aimed at understanding the deformation mechanisms at elevated temperatures. The first matrix cracking behavior of zircon matrix uniaxially reinforced with silicon carbide fiber (SCS-6) composites and failure behavior of monolithic zircon were studied as a function of temperature (25C, 500C, and 1200C) and crack length in three point bending mode. A modified vicker's indentation technique was used to vary the initial crack length in monolithic and composite samples. The interfacial shear strength was measured at these temperatures from matrix crack saturation spacing. The composites exhibited steady state and non steady state behaviors at the three different temperatures as predicted by theoretical models, while the failure stress of zircon decreased with increasing stress. The intrinsic properties of the composites were used to numerically determine the results predicted by three different matrix cracking models based on a fracture mechanics approach. The analysis showed that the model based on crack bridging analysis was valid at 25C and 500C, while a model based on statistical fiber failure was valid at 1200C. Microstructural studies showed that fiber failure in the crack wake occurred at or below the matrix cracking stress at 1200C, and no fiber failure occurred at the other two temperatures, which validated the results predicted by the theoretical models. Also, it was shown that the interfacial shear stress corresponding to debonding determined the matrix cracking stress, and not the frictional shear stress. This study showed for the first time, the steady state and non-steady state matrix cracking behavior at elevated temperatures, the difference in behavior between room temperature and elevated temperatures, and the validity of the various models of first matrix cracking behavior. In order to understand the creep behavior of composites, it is important to study the creep behavior of matrix, fiber, and composites under identical conditions to determine the role of various constituents. Creep studies were conducted in an inert atmosphere in four point bending and uniaxial tension modes on zircon and zircon silicon carbide fiber composites at four different temperatures of 1250C, 1300C, 1350C, and 1400C, and over the stress range of 10--200 MPa. The strain rate was measured as a function of the stress and temperature to determine the stress exponent and activation energy, and microstructural analysis was done on crept samples using scanning electron microscopy. The composites exhibited a much lower creep rate than the monolilth, indicating that the major portion of the creep load was carried by the fibers. In flexural mode, both zircon and composite samples exhibited bimodal creep behavior, with the stress exponent (n) increasing with increasing stress. For zircon, at lower-stresses n was in the range of 2.1--2.6 and increased to 7--7.9 at higher stresses. Microstructural studies showed that diffusional creep was the rate controlling mechanism at lower stresses, while the higher stress exponent observed at higher stresses, was due to linkage of cavities and damage accumulation resulting in a higher strain rate. In the case of composites, the stress exponent was ?1 at lower stresses, and increased to 3--5 at higher stresses, indicating that diffusional creep (and grain boundary sliding) was rate controlling at lower stresses, and either creep cavitation and crack growth or dislocation creep was the rate controlling mechanism at higher stresses. Anomalous creep curves with strain jumps were observed for the first time during the creep of ceramic composites at lower temperatures and higher stresses. Microstructural studies showed that matrix cracking during creep results in these strain jumps. These studies showed tha

  6. A high-temperature torsion apparatus for the high-resolution characterization of internal friction and creep in refractory metals

    E-print Network

    Cooper, Reid F.

    materials initially display a decelerating transient in the strain rate that decays to a ``steady-state'' regime of con- stant, or near-constant strain rate. This initial transient re- sponse is often ignored, it is often difficult to accurately measure the high strain rates characteristic of transient creep

  7. Plastic Creep and Brittle-Ductile Transition in Hydrated Rocks of the Plate Interface

    NASA Astrophysics Data System (ADS)

    Reynard, B.

    2014-12-01

    Geophysical observations suggest that the formation of hydrous phyllosilicate-bearing rocks such as serpentinites favor aseismic slip on the plate interface. I review our current understanding of deformation of serpentines and similar phyllosilicates in the first 100 km of subduction and discuss some pending questions on measurements and modeling of the behavior and properties of the complex serpentinite rocks. Experimental studies suggest that serpentines have low enough mechanical strength to act as a "stabilizer" of stable creep, but the actual strength of serpentinites will depend on the exact nature of the crystallographic structure and fabric of the stable serpentine variety. Low-temperature, flat-layered lizardite has strong anisotropy in strength. Lizardite-serpentinite strength will depend crystal-preferred orientation (CPO), with isotropic texture having high strength (>300 MPa) and foliated serpentinites having small strength (<100 MPa), independent of temperature, pressure, and strain rate. Thus, the transition between brittle and plastic (or stable creep) behavior may result from progressive deformation. High-temperature serpentine antigorite has a complex corrugated-layered structure, and complex deformation modes were evidenced from experimental studies. Mechanical strength shows a strong stress dependence, suggesting dislocation-creep, and low temperature dependence, suggesting plastic behavior. Extrapolation of experimental results to natural strain rates suggests that antigorite-serpentinites have low strength (<100 MPa or lower), and will favor stable-creep. However, the extrapolation relies on mechanical flow laws that may not apply to serpentine. Electron microscopy observations reveals dislocation-like deformation mechanisms that are not sufficient to explain global deformation of antigorite aggregates, and that are likely accompanied by dissolution-precipitation at low natural strain-rates. Establishing reliable flow laws relevant to the subduction interface in the 30-100 km depth range will require further experimental investigations of such mechanisms.

  8. Temperature and angular momentum dependence of the quadrupole deformation in sd-shell

    E-print Network

    P. A. Ganai; J. A. Sheikh; I. Maqbool; R. P. Singh

    2009-06-16

    Temperature and angular momentum dependence of the quadrupole deformation is studied in the middle of the sd-shell for 28Si and 27Si isotopes using the spherical shell model approach. The shell model calculations have been performed using the standard USD interaction and the canonical partition function constructed from the calculated eigen-solutions. It is shown that the extracted average quadrupole moments show a transitional behavior as a function of temperature and the inferred transitional temperature is shown to vary with angular-momentum. The quadrupole deformation of the individual eigen-states is also analyzed.

  9. Experimental Creep Life Assessment for the Advanced Stirling Convertor Heater Head

    NASA Technical Reports Server (NTRS)

    Krause, David L.; Kalluri, Sreeramesh; Shah, Ashwin R.; Korovaichuk, Igor

    2010-01-01

    The United States Department of Energy is planning to develop the Advanced Stirling Radioisotope Generator (ASRG) for the National Aeronautics and Space Administration (NASA) for potential use on future space missions. The ASRG provides substantial efficiency and specific power improvements over radioisotope power systems of heritage designs. The ASRG would use General Purpose Heat Source modules as energy sources and the free-piston Advanced Stirling Convertor (ASC) to convert heat into electrical energy. Lockheed Martin Corporation of Valley Forge, Pennsylvania, is integrating the ASRG systems, and Sunpower, Inc., of Athens, Ohio, is designing and building the ASC. NASA Glenn Research Center of Cleveland, Ohio, manages the Sunpower contract and provides technology development in several areas for the ASC. One area is reliability assessment for the ASC heater head, a critical pressure vessel within which heat is converted into mechanical oscillation of a displacer piston. For high system efficiency, the ASC heater head operates at very high temperature (850 C) and therefore is fabricated from an advanced heat-resistant nickel-based superalloy Microcast MarM-247. Since use of MarM-247 in a thin-walled pressure vessel is atypical, much effort is required to assure that the system will operate reliably for its design life of 17 years. One life-limiting structural response for this application is creep; creep deformation is the accumulation of time-dependent inelastic strain under sustained loading over time. If allowed to progress, the deformation eventually results in creep rupture. Since creep material properties are not available in the open literature, a detailed creep life assessment of the ASC heater head effort is underway. This paper presents an overview of that creep life assessment approach, including the reliability-based creep criteria developed from coupon testing, and the associated heater head deterministic and probabilistic analyses. The approach also includes direct benchmark experimental creep assessment. This element provides high-fidelity creep testing of prototypical heater head test articles to investigate the relevant material issues and multiaxial stress state. Benchmark testing provides required data to evaluate the complex life assessment methodology and to validate that analysis. Results from current benchmark heater head tests and newly developed experimental methods are presented. In the concluding remarks, the test results are shown to compare favorably with the creep strain predictions and are the first experimental evidence for a robust ASC heater head creep life.

  10. Evidence of dislocation cross-slip in MAX phase deformed at high temperature

    PubMed Central

    Guitton, Antoine; Joulain, Anne; Thilly, Ludovic; Tromas, Christophe

    2014-01-01

    Ti2AlN nanolayered ternary alloy has been plastically deformed under confining pressure at 900C. The dislocation configurations of the deformed material have been analyzed by transmission electron microscopy. The results show a drastic evolution compared to the dislocation configurations observed in the Ti2AlN samples deformed at room temperature. In particular, they evidence out-of-basal-plane dislocations and interactions. Moreover numerous cross-slip events from basal plane to prismatic or pyramidal planes are observed. These original results are discussed in the context of the Brittle-to-Ductile Transition of the nanolayered ternary alloys. PMID:25220949

  11. The influence of hydrogen on the transition from power-law creep to low-temperature plasticity of olivine at lithospheric temperatures

    NASA Astrophysics Data System (ADS)

    Tielke, Jacob; Zimmerman, Mark; Kohlstedt, David

    2015-04-01

    At high-temperature (asthenospheric) conditions, strain rate of olivine-rich mantle rocks follows a power-law dependence on stress. At lower-temperature (lithospheric) conditions, strain rate exhibits an exponential dependence on stress. However, the influence of water (hydrogen) on the transition from high-temperature to low-temperature behavior is poorly constrained. To investigate the influence of water on the transition in flow regimes at lithospheric conditions, deformation experiments on single crystals of San Carlos olivine under both wet (hydrogen-rich) and dry (hydrogen-poor) conditions were carried out. Crystals were oriented relative to the applied load to exert the maximum shear stress on the (100)[001] and (001)[100] dislocation slip systems, which are the dominate (weakest) slip systems at both low temperatures and under wet conditions. Experiments were carried out using a gas-medium apparatus with high resolution in stress (2 MPa) and temperature (2C). For the wet experiments, hydrogen was supplied to the crystals using talc sealed in nickel jackets. Deformation experiments were carried out in either triaxial compression or direct shear geometries at 1000-1300C, differential stresses of 120 to 670 MPa, and resultant strain rates of 6 x 10-6 to 4 x 10-4 s-1. At high-temperature, under dry conditions, strain rate is a power-law function of stress with a stress exponent of 3.5 and an Arrhenius function of temperature with an activation energy of 520 kJ/mol. At low-temperature and high-stress conditions, under dry conditions, strain rate increases exponentially with increasing stress with an activation energy of 360 kJ/mol. These observations are consistent with a transition from a climb-controlled dislocation mechanism at higher temperatures to a glide-controlled dislocation mechanism at lower temperatures for hydrogen-poor olivine crystals. Under wet conditions, the strain rate dependence on stress follows a power-law relationship with a stress exponent of 3.5 and an activation energy of 330 kJ/mol and does not transition to an exponential dependence on stress. Post-deformation electron-backscatter diffraction analyses indicate development of low-angle boundaries with rotation about the [010] axis, consistent with deformation resulting from glide of dislocations on the (100)[001] and (001)[100] slip systems. Water concentrations in crystals from wet experiments determined using Fourier transform infrared spectroscopy were 157 to 190 ppm H/Si, similar to values obtained from xenoliths derived from the lithospheric mantle. These analyses indicate that the presence of water in the lithospheric mantle results in considerable weakening and that power-law flow behavior of mantle rocks may operate at shallower depths than previously thought.

  12. Effects of Electromigration on the Creep and Thermal Fatigue Behavior of Sn58Bi Solder Joints

    NASA Astrophysics Data System (ADS)

    Zuo, Yong; Ma, Limin; Guo, Fu; Qiao, Lei; Shu, Yutian; Lee, Andree; Subramanian, K. N.

    2014-12-01

    Electromigration (EM), creep, and thermal fatigue (TF) are the most important aspects of the reliability of electronic solder joints, the failure mechanisms of which used to be investigated separately. However, current, mechanical loading, and temperature fluctuation usually co-exist under real service conditions, especially as the magnitude of current density is increasing with joint miniaturization. The importance of EM can no longer be simply ignored when analyzing the creep and TF behavior of a solder joint. The published literature reports that current density substantially changes creep rate, but the intrinsic mechanism is still unclear. Hence, the purpose of this study was to investigate the effects of EM on the creep and TF behavior of Sn58Bi solder joints by analyzing the evolution of electrical resistance and microstructure. The results indicated that EM shortens the lifetime of creep or TF of Sn58Bi solder joints. During creep, EM delays or suppresses the cracking and deforming process, so fracture occurs at the cathode interface. During TF, EM suppresses the cracking process and changes the interfacial structure.

  13. Estimation of long-term creep behavior of salt

    SciTech Connect

    Chun, R.C.

    1980-08-01

    A computer routine for both primary and secondary creep laws has been developed using a modified strain hardening law. The computations reveal that results from Heard's steady-state creep law and Lomenick and Bradshaw's primary creep law can differ from each other by a factor of thirty after about 6 hours of creep deformation, but the difference diminishes as time becomes large. The belief that these two creep laws may yield long-term results that are orders of magnitude apart is shown to be unfounded.

  14. Comprehensive Characterization of Voids and Microstructure in TATB-based Explosives from 10 nm to 1 cm: Effects of Temperature Cycling and Compressive Creep

    SciTech Connect

    Willey, T M; Lauderbach, L; Gagliardi, F; Cunningham, B; Lorenz, K T; Lee, J I; van Buuren, T; Call, R; Landt, L; Overturf, G

    2010-02-26

    This paper outlines the characterization of voids and Microstructure in TATB-based Explosives over several orders of magnitude, from sizes on the order of 10 nm to about 1 cm. This is accomplished using ultra small angle x-ray scattering to investigate voids from a few nm to a few microns, ultra small angle neutron scattering for voids from 100 nm to 10 microns, and x-ray computed microtomography to investigate microstructure from a few microns to a few centimeters. The void distributions of LX-17 are outlined, and the microstructure of LX-17 is presented. Temperature cycling and compressive creep cause drastically different damage to the microstructure. Temperature cycling leads to a volume expansion (ratchet growth) in TATB-based explosives, and x-ray scattering techniques that are sensitive to sizes up to a few microns indicated changes to the void volume distribution that had previously accounted for most, but not all of the change in density. This paper presents the microstructural damage larger than a few microns caused by ratchet growth. Temperature cycling leads to void creation in the binder poor regions associated with the interior portion of formulated prills. Conversely, compressive creep causes characteristically different changes to microstructure; fissures form at binder-rich prill boundaries prior to mechanical failure.

  15. Monitoring microstructural evolution of alloy 617 with non-linear acoustics for remaining useful life prediction; multiaxial creep-fatigue and creep-ratcheting

    SciTech Connect

    Lissenden, Cliff; Hassan, Tasnin; Rangari, Vijaya

    2014-10-30

    The research built upon a prior investigation to develop a unified constitutive model for design-by-analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-fatigue and creep-ratcheting tests were conducted on the nickel-base Alloy 617 at 850 and 950C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load-controlled cycling, are major concerns for NGNP design. This research project aimed at characterizing the microstructure evolution mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method was researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter was shown to correlate with microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-fatigue and creep-ratcheting deformation. Mechanical testing was conducted to provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-ratcheting. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Optical Microscopy were conducted to correlate the beta parameter with individual microstructure mechanisms. We researched application of the harmonic generation method to tubular mechanical test specimens and pipes for nondestructive evaluation. Tubular specimens and pipes act as waveguides, thus we applied the acoustic harmonic generation method to guided waves in both plates and shells. Magnetostrictive transducers were used to generate and receive guided wave modes in the shell sample and the received signals were processed to show the sensitivity of higher harmonic generation to microstructure evolution. Modeling was initiated to correlate higher harmonic generation with the microstructure that will lead to development of a life prediction model that is informed by the nonlinear acoustics measurements.

  16. The microstructure and creep behavior of cold rolled udimet 188 sheet.

    PubMed

    Boehlert, C J; Longanbach, S C

    2011-06-01

    Udimet 188 was subjected to thermomechanical processing (TMP) in an attempt to understand the effects of cold-rolling deformation on the microstructure and tensile-creep behavior. Commercially available sheet was cold rolled to varying amounts of deformation (between 5-35% reduction in sheet thickness) followed by a solution treatment at 1,464 K (1,191 C) for 1 h and subsequent air cooling. This sequence was repeated four times to induce a high-volume fraction of low-energy grain boundaries. The resultant microstructure was characterized using electron backscattered diffraction. The effect of the TMP treatment on the high-temperature [1,033-1,088 K (760-815 C)] creep behavior was evaluated. The measured creep stress exponents (6.0-6.8) suggested that dislocation creep was dominant at 1,033 K (760 C) for stresses ranging between 100-220 MPa. For stresses ranging between 25-100 MPa at 1,033 K (760 C), the stress exponents (2.3-2.8) suggested grain boundary sliding was dominant. A significant amount of grain boundary cracking was observed both on the surface and subsurface of deformed samples. To assess the mechanisms of crack nucleation, in situ scanning electron microscopy was performed during the elevated-temperature tensile-creep deformation. Cracking occurred preferentially along general high-angle grain boundaries (GHAB) and less than 25% of the cracks were found on low-angle grain boundaries (LAB) and coincident site lattice boundaries (CSLB). Creep rupture experiments were performed at T = 1,088 K (815 C) and ? = 165 MPa and the greatest average time-to-rupture was exhibited by the TMP sheet with the greatest fraction of LAB+CSLB. However, a clear correlation was not exhibited between the grain boundary character distribution and the minimum creep rates. The findings of this work suggest that although grain boundary engineering may be possible for this alloy, simply relating the fraction of grain boundary types to the creep resistance is not sufficient. PMID:21205424

  17. Deformation mechanisms of NiAl cyclicly deformed near the brittle-to-ductile transition temperature

    NASA Technical Reports Server (NTRS)

    Cullers, Cheryl L.; Antolovich, Stephen D.

    1993-01-01

    The intermetallic compound NiAl is one of many advanced materials which is being scrutinized for possible use in high temperature, structural applications. Stoichiometric NiAl has a high melting temperature, 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 temperatures near the monotonic brittle-to-ductile transition. The fatigue properties were found to change only slightly in the temperature range of 600 to 700 K; a temperature 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 temperature.

  18. Control of epoxy creep using graphene.

    PubMed

    Zandiatashbar, Ardavan; Picu, Catalin R; Koratkar, Nikhil

    2012-06-11

    The creep behavior of epoxy-graphene platelet (GPL) nanocomposites with different weight fractions of filler is investigated by macroscopic testing and nanoindentation. No difference is observed at low stress and ambient temperature between neat epoxy and nanocomposites. At elevated stress and temperature the nanocomposite with the optimal weight fraction, 0.1 wt% GPLs, creeps significantly less than the unfilled polymer. This indicates that thermally activated processes controlling the creep rate are in part inhibited by the presence of GPLs. The phenomenon is qualitatively similar at the macroscale and in nanoindentation tests. The results are compared with the creep of epoxy-single-walled (SWNT) and multi-walled carbon nanotube (MWNT) composites and it is observed that creep in both these systems is similar to that in pure epoxy, that is, faster than creep in the epoxy-GPL system considered in this work. PMID:22378720

  19. Creep effects in diffusion bonding of oxygen-free copper

    E-print Network

    Moilanen, Antti

    Diffusion is the transport of atoms or particles through the surrounding material. Various microstructural changes in metals are based on the diffusion phenomena. In solid metals the diffusion is closely related to crystallographic defects. In single-component metals the dominant mechanism of diffusion is the vacancy mechanism. Diffusion bonding is a direct technological application of diffusion. It is an advanced solidstate joining process in which the surfaces of two components are brought to contact with each other and heated under a pressing load in a controlled environment. During the process, the contact surfaces are bonded by atomic diffusion across the interface and as a result, one solid piece is formed. The condition of high temperature and low applied stress combined with relatively long process duration enables the creep effects to take place in bonded metals. Furthermore, creep causes unwanted permanent deformations in the bonded components. Some authors suggest that there could be a threshold fo...

  20. Temperature effects on deformation and serration behavior of high-entropy alloys (HEAs)

    SciTech Connect

    Antonaglia, J.; Xie, X.; Tang, Z.; Tsai, C. -W.; Qiao, J. W.; Zhang, Y.; Laktionova, M. O.; Tabachnikova, E. D.; Yeh, J. W.; Senkov, O. N.; Gao, M. C.; Uhl, J. T.; Liaw, P. K.; Dahmen, K. A.

    2014-09-16

    Many materials are known to deform under shear in an intermittent way with slip avalanches detected as acoustic emission and serrations in the stressstrain curves. Similar serrations have recently been observed in a new class of materials, called high-entropy alloys (HEAs). Here, we discuss the serration behaviors of several HEAs from cryogenic to elevated temperatures. The experimental results of slow compression and tension tests are compared with the predictions of a slip-avalanche model for the deformation of a broad range of solids. The results shed light on the deformation processes in HEAs. Temperature effects on the distributions of stress drops and the decrease of the cutoff (i.e., of the largest observed slip size) for increasing temperature qualitatively agree with the model predictions. As a result, the model is used to quantify the serration characteristics of HEAs, and pertinent implications are discussed.

  1. Viscoelastoplastic Deformation and Damage Response of Titanium Alloy, Ti-6Al-4V, at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

    Arnold, Steven M.; Lerch, Bradley A.; Saleeb, Atef F.; Kasemer, Matthew P.

    2013-01-01

    Time-dependent deformation and damage behavior can significantly affect the life of aerospace propulsion components. Consequently, one needs an accurate constitutive model that can represent both reversible and irreversible behavior under multiaxial loading conditions. This paper details the characterization and utilization of a multi-mechanism constitutive model of the GVIPS class (Generalized Viscoplastic with Potential Structure) that has been extended to describe the viscoelastoplastic deformation and damage of the titanium alloy Ti-6Al-4V. Associated material constants were characterized at five elevated temperatures where viscoelastoplastic behavior was observed, and at three elevated temperatures where damage (of both the stiffness reduction and strength reduction type) was incurred. Experimental data from a wide variety of uniaxial load cases were used to correlate and validate the proposed GVIPS model. Presented are the optimized material parameters, and the viscoelastoplastic deformation and damage responses at the various temperatures.

  2. Temperature effects on deformation and serration behavior of high-entropy alloys (HEAs)

    DOE PAGESBeta

    Antonaglia, J.; Xie, X.; Tang, Z.; Tsai, C. -W.; Qiao, J. W.; Zhang, Y.; Laktionova, M. O.; Tabachnikova, E. D.; Yeh, J. W.; Senkov, O. N.; et al

    2014-09-16

    Many materials are known to deform under shear in an intermittent way with slip avalanches detected as acoustic emission and serrations in the stressstrain curves. Similar serrations have recently been observed in a new class of materials, called high-entropy alloys (HEAs). Here, we discuss the serration behaviors of several HEAs from cryogenic to elevated temperatures. The experimental results of slow compression and tension tests are compared with the predictions of a slip-avalanche model for the deformation of a broad range of solids. The results shed light on the deformation processes in HEAs. Temperature effects on the distributions of stress dropsmoreand the decrease of the cutoff (i.e., of the largest observed slip size) for increasing temperature qualitatively agree with the model predictions. As a result, the model is used to quantify the serration characteristics of HEAs, and pertinent implications are discussed.less

  3. Sessile dislocations by reactions in NiAl severely deformed at room temperature

    DOE PAGESBeta

    Geist, D.; Gammer, C.; Rentenberger, C.; Karnthaler, H. P.

    2015-02-05

    B2 ordered NiAl is known for its poor room temperature (RT) ductility; failure occurs in a brittle like manner even in ductile single crystals deforming by single slip. In the present study NiAl was severely deformed at RT using the method of high pressure torsion (HPT) enabling the hitherto impossible investigation of multiple slip deformation. Methods of transmission electron microscopy were used to analyze the dislocations formed by the plastic deformation showing that as expected dislocations with Burgers vector a(100) carry the plasticity during HPT deformation at RT. In addition, we observe that they often form a(110) dislocations by dislocationmorereactions; 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 deformation-induced embrittlement. In spite of the severe deformation, the chemical order remains unchanged.less

  4. Advances in Non-contact Measurement of Creep Properties

    NASA Technical Reports Server (NTRS)

    Hyers, Robert W.; Canepari, Stacy; Rogers, Jan. R.

    2009-01-01

    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). High-precision machined spheres of the sample are levitated in the NASA MSFC ESL, a national user facility, and heated with a laser. The laser is aligned off-center so that the absorbed photons transfer their momentum to the sample, causing it to rotate at up to 250,000+ RPM. The rapid rotation loads the sample through centripetal acceleration, causing it 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 noncontact method exploits stress gradients within the sample to determine the stress exponent in a single test. This method was validated in collaboration with the University of Tennessee for niobium at 1985 C, with agreement within the uncertainty of the conventional measurements. A similar method is being employed on Ultra-High-Temperature ZrB2- SiC composites, which may see application in rocket nozzles and sharp leading edges for hypersonic vehicles.

  5. Temperature deformations of the mirror of a radio telescope antenna

    NASA Technical Reports Server (NTRS)

    Avdeyev, V. I.; Grach, S. A.; Kozhakhmetov, K. K.; Kostenko, F. I.

    1979-01-01

    The stress informed state of the mirror of an antenna, with a diameter of 3 m, for a radio interferometer used in space, and located in a temperature field is examined. The mirror represents a parabolic shell, consisting of 19 identical parts. The problem is based on representations of the thermoelasticity of thin shells.

  6. Effects of Ce Addition on High Temperature Deformation Behavior of Cu-Cr-Zr Alloys

    NASA Astrophysics Data System (ADS)

    Zhang, Yi; Volinsky, Alex A.; Tran, Hai T.; Chai, Zhe; Liu, Ping; Tian, Baohong

    2015-10-01

    Hot deformation behavior of the Cu-Cr-Zr and Cu-Cr-Zr-Ce alloys was investigated by compressive tests using the Glee-ble-1500D thermomechanical simulator at 650-850 C and 0.001-10 s-1 strain rate. The flow stress decreased with the deformation temperature at a given stain rate. However, the flow stress increased with the strain rate at the same deformation temperature. The constitutive equations for two kinds of alloys were obtained by correlating the flow stress, the strain rate and temperature using stepwise regression analysis. The addition of Ce can refine the grain and effectively accelerate dynamic recrystallization. The processing maps were established, based on the dynamic material model. Instability zones in the flow behavior can be easily recognized. Hot deformation optimal processing parameters were obtained in the range of this experiment. The hot deformation characteristics and microstructure were also analyzed by the processing maps. The addition of Ce can optimize hot workability of the Cu-Cr-Zr alloy.

  7. Structural Benchmark Creep Testing for the Advanced Stirling Convertor Heater Head

    NASA Technical Reports Server (NTRS)

    Krause, David L.; Kalluri, Sreeramesh; Bowman, Randy R.; Shah, Ashwin R.

    2008-01-01

    The National Aeronautics and Space Administration (NASA) has identified the high efficiency Advanced Stirling Radioisotope Generator (ASRG) as a candidate power source for use on long duration Science missions such as lunar applications, Mars rovers, and deep space missions. For the inherent long life times required, a structurally significant design limit for the heater head component of the ASRG Advanced Stirling Convertor (ASC) is creep deformation induced at low stress levels and high temperatures. Demonstrating proof of adequate margins on creep deformation and rupture for the operating conditions and the MarM-247 material of construction is a challenge that the NASA Glenn Research Center is addressing. The combined analytical and experimental program ensures integrity and high reliability of the heater head for its 17-year design life. The life assessment approach starts with an extensive series of uniaxial creep tests on thin MarM-247 specimens that comprise the same chemistry, microstructure, and heat treatment processing as the heater head itself. This effort addresses a scarcity of openly available creep properties for the material as well as for the virtual absence of understanding of the effect on creep properties due to very thin walls, fine grains, low stress levels, and high-temperature fabrication steps. The approach continues with a considerable analytical effort, both deterministically to evaluate the median creep life using nonlinear finite element analysis, and probabilistically to calculate the heater head s reliability to a higher degree. Finally, the approach includes a substantial structural benchmark creep testing activity to calibrate and validate the analytical work. This last element provides high fidelity testing of prototypical heater head test articles; the testing includes the relevant material issues and the essential multiaxial stress state, and applies prototypical and accelerated temperature profiles for timely results in a highly controlled laboratory environment. This paper focuses on the last element and presents a preliminary methodology for creep rate prediction, the experimental methods, test challenges, and results from benchmark testing of a trial MarM-247 heater head test article. The results compare favorably with the analytical strain predictions. A description of other test findings is provided, and recommendations for future test procedures are suggested. The manuscript concludes with describing the potential impact of the heater head creep life assessment and benchmark testing effort on the ASC program.

  8. Deformation, Stress Relaxation, and Crystallization of Lithium Silicate Glass Fibers Below the Glass Transition Temperature

    NASA Technical Reports Server (NTRS)

    Ray, Chandra S.; Brow, Richard K.; Kim, Cheol W.; Reis, Signo T.

    2004-01-01

    The deformation and crystallization of Li(sub 2)O (center dot) 2SiO2 and Li(sub 2)O (center dot) 1.6SiO2 glass fibers subjected to a bending stress were measured as a function of time over the temperature range -50 to -150 C below the glass transition temperature (Tg). The glass fibers can be permanently deformed at temperatures about 100 C below T (sub)g, and they crystallize significantly at temperatures close to, but below T,, about 150 C lower than the onset temperature for crystallization for these glasses in the no-stress condition. The crystallization was found to occur only on the surface of the glass fibers with no detectable difference in the extent of crystallization in tensile and compressive stress regions. The relaxation mechanism for fiber deformation can be best described by a stretched exponential (Kohlrausch-Williams-Watt (KWW) approximation), rather than a single exponential model.The activation energy for stress relaxation, Es, for the glass fibers ranges between 175 and 195 kJ/mol, which is considerably smaller than the activation energy for viscous flow, E, (about 400 kJ/mol) near T, for these glasses at normal, stress-free condition. It is suspected that a viscosity relaxation mechanism could be responsible for permanent deformation and crystallization of the glass fibers below T,

  9. Deformation Behavior and Dynamic Recovery Kinetics of Ultrahigh Strength Steel BR1500HS at Elevated Temperature

    NASA Astrophysics Data System (ADS)

    Xia, Yufeng; Ji, Shuai; Zhang, Yandong; Wu, Dongsen; Quan, Guozheng

    2015-10-01

    The flow behaviors of ultrahigh strength steel BR1500HS at elevated temperature were studied by performing hot tension tests at the temperatures of 773 K, 873 K, 1023 K and 1173 K, and strain rates of 0.01 s-1, 0.1 s-1 and 1 s-1 on a Gleeble 3500 thermo-mechanical simulator. The true stress-strain curves were obtained and their characteristics were analyzed. Relationships among the maximum stress, temperature and strain rate were described by means of the conventional hyperbolic sine equation. The average deformation activation energy in the whole deformation temperatures was determined as Q = 235.257 KJ/mol by regression analysis. Based on ?(d?/d?) verse ?2 curves, the values of dynamic recovery (DRV) rate coefficient, r, saturated stress, ?rec, and yield strength, ?0, under different deformation conditions were calculated. In order to estimate the DRV volume fractions, the modified Avrami type equation including r (r = 106.911351Z-0.059) as a function of the temperature compensating parameter, Z, was established, and then the effects of deformation conditions on the DRV kinetics were described in details.

  10. The effect of high temperature deformation conditions on the secondary recrystallization of MA 754 plate

    SciTech Connect

    Lee, J.H.; Paik, K.W.; Park, L.J.; Kim, Y.G.; Tundermann, J.H.; Barbadillo, J.J. de

    1998-02-03

    Nickel-base oxide-dispersion-strengthened (ODS) alloys produced by the mechanical alloying process are being used for high temperature applications because of their excellent high temperature strength which can be useful up to relatively high fraction of their melting points. The high temperature strength of ODS alloys is attributed to the presence of inert, finely dispersed oxide particles which give dispersion strengthening effect by acting as barriers to dislocation motion. In order to develop high temperature strength, fine grains should be transformed into elongated coarse grains which contribute to the retardation of creep process and prolongation of rupture life. This is possible with a high temperature anneal during which secondary recrystallization occurs. INCONEL alloy MA 754 which has been used as a turbine vane material in advanced jet engines obtains a desired grain structure by isothermal annealing. The general objectives of thermomechanical processing (TMP) of ODS alloys is to achieve coarse grain morphologies by means of secondary recrystallization, and to increase the availability of the necessary product forms. However, subsequent secondary recrystallization depends strongly on the temperature, strain, strain rate of the prior TMP operation and such compositional factors as yttria content and the amount of excess oxygen. The problem is more severe in complex shaped parts. This study is aimed at investigating the effect of temperature and strain rate of hot compression on the microstructure and secondary recrystallization of primary rolled INCONEL alloy MA 754 plate. The relationship between as-compressed and as-annealed grain structure is also investigated.

  11. Study on creep properties of Japonica cooked rice and its relationship with rice chemical compositions and sensory evaluation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Creep properties of four varieties japonica cooked rice were tested using a Dynamic Mechanical Analyser (DMA Q800). The creep curve was described by Burgers model. The creep process of japonica cooked rice mainly consisted of retarded elastic deformation, epsilonR and viscous flow deformation, epsil...

  12. Aftershocks resulting from creeping sections in a heterogeneous fault

    NASA Astrophysics Data System (ADS)

    Zller, G.; Hainzl, S.; Holschneider, M.; Ben-Zion, Y.

    2005-02-01

    We show that realistic aftershock sequences with space-time characteristics compatible with observations are generated by a model consisting of brittle fault segments separated by creeping zones. The dynamics of the brittle regions is governed by static/kinetic friction, 3D elastic stress transfer and small creep deformation. The creeping parts are characterized by high ongoing creep velocities. These regions store stress during earthquake failures and then release it in the interseismic periods. The resulting postseismic deformation leads to aftershock sequences following the modified Omori law. The ratio of creep coefficients in the brittle and creeping sections determines the duration of the postseismic transients and the exponent p of the modified Omori law.

  13. Creep of Refractory Fibers and Modeling of Metal and Ceramic Matrix Composite Creep Behavior

    NASA Technical Reports Server (NTRS)

    Tewari, S.N.

    1995-01-01

    Our concentration during this research was on the following subprograms. (1) Ultra high vacuum creep tests on 218, ST300 and WHfC tungsten and MoHfC molybdenum alloy wires, temperature range from 1100 K to 1500 K, creep time of 1 to 500 hours. (2) High temperature vacuum tensile tests on 218, ST300 and WHfC tungsten and MoHfC molybdenum alloy wires. (3) Air and vacuum tensile creep tests on polycrystalline and single crystal alumina fibers, such as alumina-mullite Nextel fiber, yttrium aluminum ganet (YAG) and Saphikon, temperature range from 1150 K to 1470 K, creep time of 2 to 200 hours. (4) Microstructural evaluation of crept fibers, TEM study on the crept metal wires, SEM study on the fracture surface of ceramic fibers. (5) Metal Matrix Composite creep models, based on the fiber creep properties and fiber-matrix interface zone formation.

  14. High-temperature deformation in the Neoproterozoic transpressional Ribeira belt, southeast Brazil

    E-print Network

    Bascou, Jrme

    High-temperature deformation in the Neoproterozoic transpressional Ribeira belt, southeast Brazil^ncias da Universidade de Sa~o Paulo, Rua do Lago 562, Cep: 05508-080, Sa~o Paulo, SP, Brazil b Laboratoire Geologia, Universidade Federal de Ouro Preto, 35400-000, Ouro Pre^to, MG, Brazil Received 5 April 2001

  15. High temperature deformation and ternary alloying of NbCr{sub 2} Laves intermetallics

    SciTech Connect

    Takasugi, T.; Hanada, S.; Yoshida, M.

    1996-10-01

    A study has been conducted to examine the effect of ternary alloying elements on high temperature deformation of the C15 NbCr{sub 2} based intermetallics in Nb-Cr-X (X = V, Mo and W) alloy systems, which have attractive properties as high temperature structural materials. The high temperature deformation of the C15 NbCr{sub 2} intermetallics can be improved by two alloying methods. One method is based on geometrical consideration for site occupation and atomic size factor of component elements and additive elements in the single phase C15 lattice; addition of Mo and V can promote dislocation movement without introducing significant hardening. The other method is based on microstructural modification through ternary alloying; moderate addition of these elements results in a variety of duplex microstructure consisting of the C15 phase and bcc solid solution without forming any intermediate phases, and can enhance the high temperature deformability. Particularly, alloys with duplex microstructure equilibrating with Cr-rich bcc solid solution is shown to exhibit superior deformability. Also, lattice property of the additive atoms in the C15 structure and phase relation between the C15 structure and the bcc solid solution are investigated by OM, XRD, TEM and ALCHEMI observations and then discussed in association with observed mechanical behavior.

  16. Measurements for displacement and deformation at high temperature by using edge detection of digital image.

    PubMed

    Qu, Zhe; Fang, Xufei; Su, Honghong; Feng, Xue

    2015-10-10

    In this work, we propose a structural deformation measuring method based on structural feature processing (straight line/edge detection) of the recorded digital images for specimens subjected to a high-temperature environment. Both radiation light and oxidation at high temperatures challenge the optics-based measurements. The images of a rectangular piece of copper specimen are obtained by using a bandpass filtering method at high temperatures, then all the edges are detected by using an edge detection operator, and then a Hough transform is conducted to search the straight edges for the calculation of deformation. Especially, due to the severe oxidation, a special seed strategy is adopted to reduce the oxidation effect and obtain an accurate result. For validation, the structural thermal deformation and the values of coefficients of thermal expansion for the copper specimen are measured and compared with data in the literature. The results reveal that the proposed method is accurate to measure the deformation of the structures at high temperatures. PMID:26479811

  17. In-situ Phase Transformation and Deformation of Iron at High Pressure andTemperature

    SciTech Connect

    Miyagi, Lowell; Kunz, Martin; Knight, Jason; Nasiatka, James; Voltolini, Marco; Wenk, Hans-Rudolf

    2008-07-01

    With a membrane based mechanism to allow for pressure change of a sample in aradial diffraction diamond anvil cell (rDAC) and simultaneous infra-red laser heating, itis now possible to investigate texture changes during deformation and phasetransformations over a wide range of temperature-pressure conditions. The device isused to study bcc (alpha), fcc (gamma) and hcp (epislon) iron. In bcc iron, room temperature compression generates a texture characterized by (100) and (111) poles parallel to the compression direction. During the deformation induced phase transformation to hcp iron, a subset of orientations are favored to transform to the hcp structure first and generate a texture of (01-10) at high angles to the compression direction. Upon further deformation, the remaining grains transform, resulting in a texture that obeys the Burgers relationship of (110)bcc // (0001)hcp. This is in contrast to high temperature results that indicate that texture is developed through dominant pyramidal {2-1-12}<2-1-13> and basal (0001)-{2-1-10} slip based on polycrystal plasticity modeling. We also observe that the high temperature fcc phase develops a 110 texture typical for fcc metals deformed in compression.

  18. Thermal diffusivity of upper mantle rocks: Influence of temperature, pressure, and the deformation fabric

    E-print Network

    Cattin, Rodolphe

    fabric Benoit Gibert Laboratoire de Tectonophysique, Universite Montpellier II and CNRS, Montpellier), temperature (up to 1250 K), and the deformation fabric of the samples. For each sample the strain crystallographic fabric. The direction of maximum thermal diffusivity is parallel to the lineation (flow direction

  19. Probabilistic Material Strength Degradation Model for Inconel 718 Components Subjected to High Temperature, High-Cycle and Low-Cycle Mechanical Fatigue, Creep and Thermal Fatigue Effects

    NASA Technical Reports Server (NTRS)

    Bast, Callie C.; Boyce, Lola

    1995-01-01

    The development of methodology for a probabilistic material strength degradation is described. 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 five effects that typically reduce lifetime strength: high temperature, high-cycle mechanical fatigue, low-cycle mechanical fatigue, creep and thermal fatigue. 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 predictions of high-cycle mechanical fatigue and high temperature effects with experiments are presented. Results from this limited verification study strongly supported that material degradation can be represented by randomized multifactor interaction models.

  20. The role of microstructure on deformation and damage mechanisms in a Nickel-based superalloy at elevated temperatures

    NASA Astrophysics Data System (ADS)

    Maciejewski, Kimberly E.

    The overall objective of this research work is the development and implementation of a mechanistic based time-dependent crack growth model which considers the role of creep, fatigue and environment interactions on both the bulk and the grain boundary phase in ME3 disk material. The model is established by considering a moving crack tip along a grain boundary path in which damage events are described in terms of the grain boundary deformation and related accommodation processes. Modeling of these events was achieved by adapting a cohesive zone approach (an interface with internal singular surfaces) in which the grain boundary dislocation network is smeared into a Newtonian fluid element. The deformation behavior of this element is controlled by the continuum in both far field (internal state variable model) and near field (crystal plasticity model) and the intrinsic grain boundary viscosity which is characterized by microstructural parameters, including grain boundary precipitates and morphology, and is able to define the mobility of the element by scaling the motion of dislocations into a mesoscopic scale. Within the cohesive zone element, the motion of gliding dislocations in the tangential direction relates to the observed grain boundary sliding displacement, the rate of which is limited by the climb of dislocations over grain boundary obstacles. Effects of microstructural variation and orientation of the surrounding continuum are embedded in the tangential stress developing in the grain boundary. The mobility of the element in the tangential direction (i.e. by grain boundary sliding) characterizes the accumulation of irreversible displacement while the vertical movement (migration), although present, is assumed to alter stress by relaxation and, thus, is not considered a contributing factor in the damage process. This process is controlled by the rate at which the time-dependent sliding reaches a critical displacement and as such, a damage criterion is introduced by considering the mobility limit in the tangential direction leading to strain incompatibility and failure. This limit is diminished by environmental effects which are introduced as a dynamic embrittlement process that hinders grain boundary mobility due to oxygen diffusion. The concepts described herein indicate that implementation of the cohesive zone model requires the knowledge of the grain boundary external and internal deformation fields. The external field is generated by developing and coupling two continuum constitutive models including (i) a microstructure-explicit coarse scale crystal plasticity model with strength provided by tertiary and secondary gamma' precipitates. This scale is appropriate for the representation of the continuum region at the immediate crack tip, and (ii) a macroscopic internal state variable model for the purpose of modeling the response of the far field region located several grains away from the crack path. The hardening contributions of the gamma' precipitates consider dislocation/precipitate interactions in terms of gamma' particles shearing and/or Orowan by-passing mechanisms. The material parameters for these models are obtained from results of low cycle fatigue tests which were performed at three temperatures; 650, 704 and 760C. Furthermore, a series of microstructure controlled experiments were carried out in order to develop and validate the microstructure dependency feature of the continuum constitutive models. The second requirement in the implementation of the cohesive zone model is a grain boundary deformation model which has been developed, as described above, on the basis of viscous flow rules of the boundary material. This model is supported by dwell crack growth experiments carried out at the three temperatures mentioned above, in both air and vacuum environments. Results of these tests have identified the frequency range in which the grain boundary cohesive zone model is applicable and also provided data to calculate the grain boundary activation energy as well as identifying the relative contributions o

  1. Effect of Deformation Temperature on Texture and Thermoelectric Properties of Bi0.5Sb1.5Te3 Prepared by Hot-Press Deformation

    NASA Astrophysics Data System (ADS)

    Kitagawa, H.; Kurata, A.; Araki, H.; Morito, S.; Tanabe, E.

    2010-09-01

    The effects of deformation temperature on texture and thermoelectric properties of p-type Bi0.5Sb1.5Te3 sintered materials were investigated. The sintered materials were prepared by mechanical alloying and hot-press sintering. The hot-press deformation was performed at 723 K and 823 K by applying mechanical pressure in a graphite die. Then, the materials were extruded in the direction opposite to the direction of applied pressure. X-ray diffraction and electron backscattered diffraction patterns showed that the hexagonal c-plane tended to align along the extruded direction when the samples were deformed at high temperatures. The thermoelectric power factor was increased by high-temperature hot-press deformation because of the low electrical resistivity that originated from the c-plane orientation.

  2. Beyond the D-DIA: new initiatives for deformation experiments at higher pressure and temperature

    NASA Astrophysics Data System (ADS)

    Wang, Y.; Jing, Z.; Yu, T.; Hilairet, N.; Nishiyama, N.

    2011-12-01

    Advances in experimental high-pressure, high-temperature deformation have relied to a large extent on technological developments. From the pioneer work of F.D. Adams [1] in generating differential stress at high pressure to deform rocks plastically to Griggs' famous deformation apparatus [2], each new invention has enabled numerous scientific publications and brought our understanding of rock deformation to a new level. For the past few years, two major workhorses in deformation experiments above 3 GPa are the rotational deformation apparatus (RDA) [3] and the deformation DIA (D-DIA) [4]. These developments brought us to almost 20 GPa under controlled differential stress and strain rates. Several new initiatives are being undertaken at GSECARS aiming at further enhancing experimental capabilities to higher pressures, temperatures and better in situ characterization of the deforming samples. We constructed a modified RDA with microtomography capability at high pressure which is used to image, in situ and in 3D, fabric evolution in multi-phase composites under large shear strains, to shed lights on the physics of complex earth materials during deformation. A large version of D-DIA (DDIA-30) has also been developed taking advantages of the rigidity of large guide blocks for much improved alignment. A 6-6 multianvil cell (MA6-6) [5] is used for deformation experiments with various truncated edge lengths, without having to change the large first-stage anvils. This configuration has the potential to reach pressure conditions corresponding to the lower mantle. We present recent results of these developments, and their potential applications for understanding dynamic processes from the upper mantle to the lower mantle. [1] Adams, F. D. and J. T. Nicolson (1900) Phil. Trans. Roy. Soc. London. A, 195: 363-401. [2] Griggs, D.T. (1967) Geophys. J. Roy. Astr. Soc., 14:19-31. [3] Yamazaki, D., and S. Karato (2001) Rev. Sci. Instrum., 72:4207-4211. [4] Wang, Y., I. Getting, W. Durham, D. Weidner (2003) Rev. Sci. Instrum., 74:3002-3011. [5] Nishiyama, N., Y. Wang, T. Sanehira, T. Irifune, M. Rivers (2008) High Pres. Res., 28, 307-314.

  3. Evolution of microstructures during creep in TiAl-base intermetallics with a different Nb content

    NASA Astrophysics Data System (ADS)

    Dlouh, A.; Orlov, A.; Kucha?ov, K.

    2010-07-01

    An evolution of microstructure has been investigated with increasing compression creep strain in intermetallic alloys Ti-48Al-2Cr-2Nb-1B (alloy Nb2) and Ti-46Al-7Nb-0.6Cr-0.2Ni-0.1Si (alloy Nb7) loaded to 350 MPa at 973 K. Scanning electron microscopy and transmission electron microscopy analysis focused on individual deformation modes and on the phase stability of the alloys. Dislocation densities and deformation twinning characteristics were systematically evaluated for strains up to 0.38. Results of these quantitative studies showed that the evolution of total and non-zero -component dislocation densities with strain was similar for all the investigated materials in spite of relevant differences in the initial ?/?2 microstructures. However, the spacing between deformation twins seemed to scale with the creep strength of the two alloys. These results are discussed in terms of the fundamental deformation modes and their contributions to the strain accumulation kinetics during high temperature creep in TiAl-base intermetallics with a different Nb content.

  4. Interaction of trapped hydrogen with dislocations at low-temperature in deformed palladium

    NASA Astrophysics Data System (ADS)

    Ju, Hyunsu

    Segregation of solute atoms to dislocations occurs due to the elastic interaction with the hydrostatic stress of edge dislocations and also due to the dislocation core-solute interaction. The characteristics of the local segregation at dislocations, Cottrell atmosphere, at low temperature and low concentration have not been investigated until the phase transformation of the deformed PdH0.0008 was recently observed at low temperature. The purpose of this study was to investigate the phase behavior of the trapped solute influenced by the distorted dislocation environment. The phase behavior of the Cottrell atmosphere in deformed Pd was investigated as a function of temperature by incoherent inelastic neutron scattering (IINS) and small angle neutron scattering (SANS) measurements. The IINS measurements of the deformed PdH0.00134 presented the characteristic vibrational density-of-states (VDOS) of hydrogen trapped at dislocation, while the spatial profile of the trapped hydrogen in the deform PdH0.00134 was determined by the SANS measurements. The VDOS of hydrogen in the deformed PdH0.00134 was obtained at 4, 100, 200, and 295 K by the IINS measurements. The VDOS at 4 K exhibited the primary peak of approximately 57 meV associated with hydrogen-rich beta-Pd hydride phase. The characteristic peak of the VDOS at 295 K corresponded to dilute solid-solution beta-Pd hydride phase, appearing at approximately 68 meV. Coexistence of the beta-phase and the alpha-phase was observed at 100 and 200 K. This suggests that hydrogen trapped at dislocations undergoes the phase transformation upon temperature change from 295 to 4 K in the deformed PdH0.00134. The spatial characterization of the Cottrell atmosphere was performed by the SANS measurements at 15, 100, and 200 K. The cylindrical geometry with the radius of 9 and the length of 50 was obtained and the dislocation density was 1.2x10-11 cm-2. Based on the spatial profile, the local concentration of the trapped hydrogen was estimated as approximately 0.2 [H]/[Pd] even at 200 K, which exceeds the dilute solid-solution regime (0.01 [H]/[Pd] at room temperature). Correlation between the local concentration and the phase behavior verified the condensation of the hydrogen-rich phase along the dislocations. Given such low hydrogen concentration in the heavily deformed Pd, this behavior is representative of hydrogen trapped at dislocations at low temperature. Correlating the spatial and the vibrational characterization of the Cottrell atmosphere demonstrated the phase behavior of the trapped solute interacting with dislocations at the distorted dislocation environment.

  5. The Fabric of Clasts, Veins and Foliations within the Actively Creeping Zones of the San Andreas Fault at SAFOD: Implications for Deformation Processes

    E-print Network

    Sills, David Wayne

    2012-02-14

    Recovered core samples from the San Andreas Fault Observatory at Depth (SAFOD), located near Parkfield, CA, offer a unique opportunity to study the products of faulting and to learn about the mechanisms of slip at 3 km depth. Casing deformation...

  6. Contribution of temperature to deformation of adsorbed vesicles studied by nanoplasmonic biosensing.

    PubMed

    Oh, Eunkyul; Jackman, Joshua A; Yorulmaz, Saziye; Zhdanov, Vladimir P; Lee, Haiwon; Cho, Nam-Joon

    2015-01-20

    With increasing temperature, biological macromolecules and nanometer-sized aggregates typically undergo complex and poorly understood reconfigurations, especially in the adsorbed state. Herein, we demonstrate the strong potential of using localized surface plasmon resonance (LSPR) sensors to address challenging questions related to this topic. By employing an LSPR-based gold nanodisk array platform, we have studied the adsorption of sub-100-nm diameter 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipid vesicles on titanium oxide at two temperatures, 23 and 50 C. Inside this temperature range, DPPC lipid vesicles undergo the gel-to-fluid phase transition accompanied by membrane area expansion, while DOPC lipid vesicles remain in the fluid-phase state. To interpret the corresponding measurement results, we have derived general equations describing the effect of deformation of adsorbed vesicles on the LSPR signal. At the two temperatures, the shape of adsorbed DPPC lipid vesicles on titanium oxide remains nearly equivalent, while DOPC lipid vesicles become less deformed at higher temperature. Adsorption and rupture of DPPC lipid vesicles on silicon oxide were also studied for comparison. In contrast to the results obtained on titanium oxide, adsorbed vesicles on silicon oxide become more deformed at higher temperature. Collectively, the findings demonstrate that increasing temperature may ultimately promote, hinder, or have negligible effect on the deformation of adsorbed vesicles. The physics behind these observations is discussed, and helps to clarify the interplay of various, often hidden, factors involved in adsorption of biological macromolecules at interfaces. PMID:25531903

  7. Modeling Long-term Creep Performance for Welded Nickel-base Superalloy Structures for Power Generation Systems

    SciTech Connect

    Shen, Chen

    2015-01-01

    We report here a constitutive model for predicting long-term creep strain evolution in ? strengthened Ni-base superalloys. Dislocation climb-bypassing ?, typical in intermediate ? volume fraction (~20%) alloys, is considered as the primary deformation mechanism. Dislocation shearing ? to anti-phase boundary (APB) faults and diffusional creep are also considered for high-stress and high-temperature low-stress conditions, respectively. Additional damage mechanism is taken into account for rapid increase in tertiary creep strain. The model has been applied to Alloy 282, and calibrated in a temperature range of 1375-1450?F, and stress range of 15-45ksi. The model parameters and a MATLAB code are provided. This report is prepared by Monica Soare and Chen Shen at GE Global Research. Technical discussions with Dr. Vito Cedro are greatly appreciated. This work was supported by DOE program DE-FE0005859

  8. High-temperature deformation behavior in Sr TiO{sub 3} ceramics.

    SciTech Connect

    Singh, D.; Lorenzo-Martin, M.; Chen, G.; Gutierrez-Mora, F.; Routbort, J. L.; Nuclear Engineering Division; Univ. de Sevilla

    2007-01-01

    The high-temperature deformation behavior of a polycrystalline strontium titanate (SrTiO{sub 3}) ceramic (6 {micro}m grain size) was investigated at temperatures of 1200-1345 C in an argon atmosphere. Compressive deformation tests were conducted at strain rates ranging from 5 x 10{sup -6} to 5 x 10{sup -5} s{sup -1}. Steady-state flow stresses were 0.05-30 MPa and increased with increasing strain rates. Stress exponents of {approx}1, at temperatures >1200 C, indicated a viscous diffusion-controlled deformation with an activation energy of {approx}628 {+-} 24 kJ/mol. Comparison of activation energy with literature data suggests diffusion of cations as the rate-controlling mechanism. Absence of cavitation and grain-shape changes were consistent with grain-boundary sliding as the principal deformation mechanism. The electron back-scattered diffraction (EBSD) technique was used to determine the grain orientation as a function of applied strain. The results indicate that some of the grains rotate with cumulative rotation as large as 7 degrees at a strain of 4%.

  9. Creep of trabecular bone from the human proximal tibia.

    PubMed

    Novitskaya, Ekaterina; Zin, Carolyn; Chang, Neil; Cory, Esther; Chen, Peter; D'Lima, Darryl; Sah, Robert L; McKittrick, Joanna

    2014-07-01

    Creep is the deformation that occurs under a prolonged, sustained load and can lead to permanent damage in bone. Creep in bone is a complex phenomenon and varies with type of loading and local mechanical properties. Human trabecular bone samples from proximal tibia were harvested from a 71-year old female cadaver with osteoporosis. The samples were initially subjected to one cycle load up to 1% strain to determine the creep load. Samples were then loaded in compression under a constant stress for 2h and immediately unloaded. All tests were conducted with the specimens soaked in phosphate buffered saline with proteinase inhibitors at 37 C. Steady state creep rate and final creep strain were estimated from mechanical testing and compared with published data. The steady state creep rate correlated well with values obtained from bovine tibial and human vertebral trabecular bone, and was higher for lower density samples. Tissue architecture was analyzed by micro-computed tomography (?CT) both before and after creep testing to assess creep deformation and damage accumulated. Quantitative morphometric analysis indicated that creep induced changes in trabecular separation and the structural model index. A main mode of deformation was bending of trabeculae. PMID:24857486

  10. Creep behavior of thin laminates of iron-cobalt alloys for use in switched reluctance motors and generators

    NASA Astrophysics Data System (ADS)

    Fingers, Richard Todd

    The United States 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 behind a new emphasis on high temperature, high strength magnetic materials for power applications. Analytical work, utilizing elasticity theory, in conjunction with design requirements, indicates a need for magnetic materials to have strengths in excess of 80 ksi up to about 1000spF. It is this combination of desired material characteristics that is the motivation for this effort to measure, model, and predict the creep behavior of such advanced magnetic materials. Hipercospler Alloy 50HS, manufactured by Carpenter Technology Corporation, is one of the leading candidates for application and is studied in this effort by subjecting mechanical test specimens to a battery of tensile and creep tests. The tensile tests provide stress versus strain behaviors that clearly indicate: a yield point, a heterogeneous deformation described as Luders 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 two distinct types of behavior. The first was a traditional response with primary, secondary and tertiary stages, while the second type could be characterized by an abrupt increase in strain rate that acted as a transition from one steady state behavior to another. This second linear region was then followed by the tertiary stage. The relationship between the tensile response and the creep responses is discussed. Analyses of the mechanical behavior includes double linear regression of empirically modeled data, scanning electron microscopy for microstructural investigations, isochronous stress-strain relations, and constant strain rate testing to relate the tensile and creep test parameters. Also, elastic and creep deformation analyses are done, which incorporate material property data and material constants determined along with stress and displacement profiles for a specific Air Force design configuration.

  11. Probabilistic material strength degradation model for Inconel 718 components subjected to high temperature, high-cycle and low-cycle mechanical fatigue, creep and thermal fatigue effects

    NASA Technical Reports Server (NTRS)

    Bast, Callie C.; Boyce, Lola

    1995-01-01

    This report presents the results of both the fifth and sixth 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 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 five effects that typically reduce lifetime strength: high temperature, high-cycle mechanical fatigue, low-cycle mechanical fatigue, creep 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 five variables, namely, high temperature, high-cycle and low-cycle mechanical fatigue, creep and thermal fatigue. Methodology to estimate standard deviations of these material constants for input into the probabilistic material strength model was developed. Using an updated version of PROMISS, entitled PROMISS93, a sensitivity study for the combined effects of high-cycle mechanical fatigue, creep and thermal fatigue was performed. Then using the current version of PROMISS, entitled PROMISS94, a second sensitivity study including the effect of low-cycle mechanical fatigue, as well as, the three previous effects 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 high-cycle mechanical fatigue and high temperature 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.

  12. Experimental study on multi-step creep properties of rat skins.

    PubMed

    Chen, Gang; Cui, Shibo; You, Lin; Li, Yan; Mei, Yun-Hui; Chen, Xu

    2015-06-01

    Tension, single-step creep, and multi-step creep of rat skins at room temperature were experimentally studied. We studied the effects of loading histories of high stress creep, low stress creep, and stress relaxation on multi-step creep. Microstructure of rat skins after prescribed tests were observed microscopically with the help of standard hematoxylin and eosin (H&E). The void ratios were also analyzed. The loading histories of high stress creep, low stress creep, and stress relaxation have significant influence on multi-step creep. We found that the creep strain and its rate in the steady-state stage and the creep-fatigue life of rat skins are sensitive to creep stress. Low stress creep after the loading history of high stress creep is characterized as a recovery of strain and a zero strain rate. Both the loading history of low stress creep and stress relaxation act as a recovery in multi-step creep, and they are driven by a same mechanism in the creep strain and the void ratio of rat skins. The loading history, of which sequence is as followings successively: low stress creep, stress relaxation, and high stress creep, helps to obtain the largest creep strain at the lowest void ratio. PMID:25771256

  13. In-situ tube burst testing and high-temperature deformation behavior of candidate materials for accident tolerant fuel cladding

    SciTech Connect

    Gussev, Maxim N.; Byun, Thak Sang; Yamamoto, Yukinori; Maloy, Stuart A.; Terrani, Kurt A.

    2015-11-01

    The high resistance of cladding to plastic deformation and burst failure is one of the most essential properties of accident tolerant fuel (ATF) for maintaining structural integrity during a loss-of-coolant accident (LOCA) since the deformation and burst behavior governs the cooling efficiency of flow channels and process of fission product release. To simulate and evaluate such deformation and burst process of thin-walled cladding, an in-situ testing and evaluation method has been developed on the basis of visual imaging and image analysis techniques. The method uses a specialized optics system consisted of a high-resolution video camera, light filtering unit, and monochromatic light sources, and the in-situ testing is performed using a 50 mm long pressurized thin-walled tubular specimen set in a programmable furnace. In this study eleven (11) candidate cladding materials for ATF, i.e., 6 FeCrAl alloys and 5 nanostructured steels, were tested using the newly developed method, and the time-dependent images were analyzed to produce detailed deformation and burst data such as true hoop stress, strain (creep) rate, and failure stress. Relatively soft FeCrAl alloys deformed and burst below 800C while negligible strain rates were measured for higher strength alloys and/or for relatively thick wall specimens.

  14. In-situ tube burst testing and high-temperature deformation behavior of candidate materials for accident tolerant fuel cladding

    NASA Astrophysics Data System (ADS)

    Gussev, M. N.; Byun, T. S.; Yamamoto, Y.; Maloy, S. A.; Terrani, K. A.

    2015-11-01

    One of the most essential properties of accident tolerant fuel (ATF) for maintaining structural integrity during a loss-of-coolant accident (LOCA) is high resistance of the cladding to plastic deformation and burst failure, since the deformation and burst behavior governs the cooling efficiency of flow channels and the process of fission product release. To simulate and evaluate the deformation and burst process of thin-walled cladding, an in-situ testing and evaluation method has been developed on the basis of visual imaging and image analysis techniques. The method uses a specialized optics system consisting of a high-resolution video camera, a light filtering unit, and monochromatic light sources. The in-situ testing is performed using a 50mm long pressurized thin-walled tubular specimen set in a programmable furnace. As the first application, ten (10) candidate cladding materials for ATF, i.e., five FeCrAl alloys and five nanostructured steels, were tested using the newly developed method, and the time-dependent images were analyzed to produce detailed deformation and burst data such as true hoop stress, strain (creep) rate, and failure stress. Relatively soft FeCrAl alloys deformed and burst below 800C, while negligible strain rates were measured for higher strength alloys.

  15. Creep substructure formation in sodium chloride single crystals in the power law and exponential creep regimes

    NASA Technical Reports Server (NTRS)

    Raj, S. V.; Pharr, G. M.

    1989-01-01

    Creep tests conducted on NaCl single crystals in the temperature range from 373 to 1023 K show that true steady state creep is obtained only above 873 K when the ratio of the applied stress to the shear modulus is less than or equal to 0.0001. Under other stress and temperature conditions, corresponding to both power law and exponential creep, the creep rate decreases monotonically with increasing strain. The transition from power law to exponential creep is shown to be associated with increases in the dislocation density, the cell boundary width, and the aspect ratio of the subgrains along the primary slip planes. The relation between dislocation structure and creep behavior is also assessed.

  16. A creep model for austenitic stainless steels incorporating cavitation and wedge cracking

    E-print Network

    Mahesh, Sivasambu

    A creep model for austenitic stainless steels incorporating cavitation and wedge cracking S Mahesh, Kalpakkam 603102. India Abstract. A model of damage evolution in austenitic stainless steels under creep experimental data for a type 316 austenitic stainless steel under uniaxial creep loading. Deformation

  17. Prediction of creep of polymer concrete

    SciTech Connect

    Khristova, Yu.; Aniskevich, K.

    1995-11-01

    We studied the applicability of the phenomenological approach to the prediction of long-time creep of polymer concrete consisting of polyester binder with diabase filler and diabase aggregate. We discovered that the principles of temperature-time analogy, of moisture-time analogy, and of temperature-moisture-time analogy are applicable to the description of the diagrams of short-time creep and to the prediction of long-time creep of polymer concrete at different temperatures and constant moisture content of the material.

  18. High temperature monotonic and cyclic deformation in a directionally solidified nickel-base superalloy

    NASA Technical Reports Server (NTRS)

    Huron, Eric S.

    1986-01-01

    Directionally solidified (DS) MAR-M246+Hf was tested in tension and fatigue, at temperatures from 20 C to 1093 C. Tests were performed on (001) oriented specimens at strain rates of 50 % and 0.5 % per minute. In tension, the yield strength was constant up to 704 C, above which the strength dropped off rapidly. A strong dependence of strength on strain rate was seen at the higher temperatures. The deformation mode was observed to change from heterogeneous to homogeneous with increasing temperature. Low Cycle Fatigue tests were done using a fully reversed waveform and total strain control. For a given plastic strain range, lives increased with increasing temperature. For a given temperature strain rate had a strong effect on life. At 704 C, decreasing strain rates decreased life, while at the higher temperatures, decreasing strain rates increased life, for a given plastic strain range. These results could be explained through considerations of the deformation modes and stress levels. At the higher temperatures, marked coarsening caused beneficial stress reductions, but oxidation limited the life. The longitudinal grain boundaries were found to influence slip behavior. The degree of secondary slip adjacent to the boundaries was found to be related to the degree of misorientation between the grains.

  19. Creep-fatigue interaction of titanium alloy Ti-6Al-2Cb-1Ta-0.8Mo at room temperature

    NASA Technical Reports Server (NTRS)

    Chu, H. P.; Mcdonald, B. A.; Arora, O. P.

    1985-01-01

    The present investigation is concerned with the mutual influence of creep and fatigue in the case of Ti-6211, which represents a new weldable, stress-corrosion resistant alloy. Attention is given to the effect of creep on fatigue, the effect of fatigue on creep, and microstructural studies. It is found that prior creep in the amounts investigated, from 0.2 percent to 2.7 percent, is beneficial to low-cycle fatigue life. Hold time at peak strain is found to be beneficial to low-cycle fatigue life. Hold time at constant stress has no effect on low-cycle fatigue when specimens are cycled only once between hold times; but increasing fatigue loading for 50 or more cycles between hold times can prolong the fatigue life. There is an acceleration of creep by cyclic loading when comparison of cyclic and static creep is based on mean stress.

  20. Evolution of interphase and intergranular strain in zirconium-niobium alloys during deformation at room temperature

    NASA Astrophysics Data System (ADS)

    Cai, Song

    Zr-2.5Nb is currently used for pressure tubes in the CANDU (CANada Deuterium Uranium) reactor. A complete understanding of the deformation mechanism of Zr-2.5Nb is important if we are to accurately predict the in-reactor performance of pressure tubes and guarantee normal operation of the reactors. This thesis is a first step in gaining such an understanding; the deformation mechanism of ZrNb alloys at room temperature has been evaluated through studying the effect of texture and microstructure on deformation. In-situ neutron diffraction was used to monitor the evolution of the lattice strain of individual grain families along both the loading and Poisson's directions and to track the development of interphase and intergranular strains during deformation. The following experiments were carried out with data interpreted using elasto-plastic modeling techniques: (1) Compression tests of a 100%betaZr material at room temperature. (2) Tension and compression tests of hot rolled Zr-2.5Nb plate material. (3) Compression of annealed Zr-2.5Nb. (4) Cyclic loading of the hot rolled Zr-2.5Nb. (5) Compression tests of ZrNb alloys with different Nb and oxygen contents. The experimental results were interpreted using a combination of finite element (FE) and elasto-plastic self-consistent (EPSC) models. The phase properties and phase interactions well represented by the FE model, the EPSC model successfully captured the evolution of intergranular constraint during deformation and provided reasonable estimates of the critical resolved shear stress and hardening parameters of different slip systems under different conditions. The consistency of the material parameters obtained by the EPSC model allows the deformation mechanism at room temperature and the effect of textures and microstructures of ZrNb alloys to be understood. This work provides useful information towards manufacturing of Zr-2.5Nb components and helps in producing ideal microstructures and material properties for pressure tubes. Also it is helpful in guiding the development of new materials for the next generation of nuclear reactors. Furthermore, the large data set obtained from this study can be used in evaluation and improving current and future polycrystalline deformation models.

  1. Scaling behavior and complexity of plastic deformation for a bulk metallic glass at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Chen, Cun; Ren, Jingli; Wang, Gang; Dahmen, Karin A.; Liaw, Peter K.

    2015-07-01

    We explore the scaling behavior and complexity in the shear-branching process during the compressive deformation of a bulk metallic glass Z r64 .13C u15 .75A l10N i10 .12 (at. %) at cryogenic temperatures. The fractal dimension of the stress rate signal ranges from 1.22 to 1.72 with decreasing temperature and a larger shear-branching rate occurs at lower temperature. A stochastic model is introduced for the shear-branching process. In particular, at a temperature of 213 K , the shear-branching process evolves as a self-similar random process. In addition, the complexity of the stress rate signal conforms to the larger activation energy of the shear transformation zone at lower temperatures.

  2. Scaling behavior and complexity of plastic deformation for a bulk metallic glass at cryogenic temperatures.

    PubMed

    Chen, Cun; Ren, Jingli; Wang, Gang; Dahmen, Karin A; Liaw, Peter K

    2015-07-01

    We explore the scaling behavior and complexity in the shear-branching process during the compressive deformation of a bulk metallic glass Zr(64.13)Cu(15.75)Al(10)Ni(10.12) (at. %) at cryogenic temperatures. The fractal dimension of the stress rate signal ranges from 1.22 to 1.72 with decreasing temperature and a larger shear-branching rate occurs at lower temperature. A stochastic model is introduced for the shear-branching process. In particular, at a temperature of 213K, the shear-branching process evolves as a self-similar random process. In addition, the complexity of the stress rate signal conforms to the larger activation energy of the shear transformation zone at lower temperatures. PMID:26274131

  3. High-resolution measurements of pressure solution creep

    NASA Astrophysics Data System (ADS)

    Dysthe, Dag Kristian; Renard, Francois; Feder, Jens; Jamtveit, Bjrn; Meakin, Paul; Jssang, Torstein

    2003-07-01

    Two dilatometers with high precision and stability have been developed for measurement of indentation by pressure solution creep. The indentation of gold wires or glass cylinders into sodium chloride has been measured with down to 10 accuracy and 6% precision. The indentation curves show a strong history dependence and the indentation rate decreases by three orders of magnitude over 400 h. The indentation mechanism is shown to be a pressure solution creep process in which material is dissolved at the indentor-sodium chloride contacts and transported to the free surface, where it precipitates in the proximity of the indentors. The indentation rates are not controlled by precipitation rates, the density of preexisting dislocations in the material, by change in the contact widths, or by ordinary plastic deformation. Small amplitude sinusoidal variations of temperature and normal stress are shown to have a large effect on the indentation rate. Moreover, sudden increase in normal stress from the indentor on the sodium chloride is shown to initiate an increased, time-dependent indentation rate. A model for pressure solution creep with time-dependent contact sizes explains the history dependence of the indentation data presented.

  4. Indentation creep behavior of a direct-filling silver alternative to amalgam.

    PubMed

    Xu, H H; Liao, H; Eichmiller, F C

    1998-12-01

    Amalgam creep has been identified as a key parameter associated with marginal breakdown and corrosion. The aim of this study was to evaluate the time-dependent deformation (creep) of a novel silver filling material as an alternative to amalgam. We made the silver specimens by pressing a precipitated powder at room temperature to a density that can be achieved in clinical hand consolidation. The surface of the silver was either polished or burnished. To examine local contact creep and the effect of surface finishing, we used an indentation creep method in which a Vickers indenter was loaded on the specimen surface at a load of 10 N with dwell times of 5 sec to 6x10(4) sec. We used a bonded-interface technique to examine subsurface creep mechanisms. The flexural strength (mean+/-SD; n = 10) was 86+/-20 MPa for amalgam, 180+/-21 MPa for polished silver, and 209+/-19 MPa for burnished silver-values which are significantly different from each other (family confidence coefficient = 0.95; Tukey's multiple-comparison test). Indentation creep manifested as hardness number decreasing with increased dwell time. With dwell time increasing from 5 sec to 6x10(4) sec, the hardness number of amalgam was reduced by approximately 80%; that of the polished silver and the burnished silver was reduced by only 40%. Subsurface creep in amalgam consisted of the shape change of the alloy particles from spherical to elongated shapes, and the separation of matrix grains from each other, possibly due to grain-boundary sliding. Creep of the polished silver occurred by densification reducing porosity and increasing hardness; that of the burnished silver occurred by the displacement of the burnished layer. These results suggest that, due to creep-induced subsurface work-hardening and densification, the consolidated silver exhibits a higher resistance to indentation creep than does amalgam. The hardness number of silver approaches that of amalgam after prolonged indentation loading. PMID:9839787

  5. Creep of Structural Nuclear Composites

    SciTech Connect

    Will Windes; R.W. Lloyd

    2005-09-01

    A research program has been established to investigate fiber reinforced ceramic composites to be used as control rod components within a Very High Temperature Reactor (VHTR) design. Two candidate systems have been identified, carbon fiber reinforced carbon (Cf/C) and silicon carbide fiber reinforced silicon carbide (SiCf/SiC) composites. One of the primary degradation mechanisms anticipated for these core components is high temperature thermal and irradiation enhanced creep. As a consequence, high temperature test equipment, testing methodologies, and test samples for very high temperature (up to 1600 C) tensile strength and long duration creep studies have been established. Actual testing of both tubular and flat, "dog-bone"-shaped tensile composite specimens will begin next year. Since there is no precedence for using ceramic composites within a nuclear reactor, ASTM standard test procedures are currently being established from these high temperature mechanical tests.

  6. High temperature deformation of Vitreloy bulk metallic glasses and their composite

    NASA Astrophysics Data System (ADS)

    Tao, Min

    A complete understanding of the deformation mechanisms of BMGs and their composites requires investigation of the microstructural changes and their interplay with the mechanical behavior. In this dissertation, the deformation mechanisms of a series of Vitreloy glasses and their composites are experimentally investigated over a wide range of strain rates and temperatures, with focus on the supercooled liquid regime, by combining uniaxial mechanical testing with calorimetric and microscopic examinations. Various theories of deformation of metallic glasses and the composites are examined in light of the experimental data. A comparative structural relaxation study was performed on two closely related Vitreloy alloys, Zr41.2Ti13.8Cu12.5Ni 10Be22.5 (Vit 1) and Zr46.7Ti8.3Cu 7.5Ni10Be27.5 (Vit 4). Differential scanning calorimetric studies on the specimens deformed in compression at constant-strain-rate in supercooled liquid regime showed that mechanical loading accelerated the spinodal phase separation and nanocrystallization process in Vit 1, while the relaxation in Vit 4 featured local chemical composition fluctuation accompanied by annealing out of free volume. The effect of the structural relaxation on their mechanical behavior was further studied via single and multiple jump-in-strain-rate tests. The deformation and viscosity of a new Vitreloy alloy were characterized using uniaxial compression tests in its supercooled liquid regime. A new theoretical model named Cooperative Shear Model, which correlates the evolution of the macroscopic mechanical/thermal variables such as shear modulus and viscosity with the configurational energies of atom clusters in an amorphous alloy, was critically examined in this investigation. The model was successful in predicting the Newtonian and non-Newtonian viscosities of the material, as well as the shear moduli of the deformed specimens, in a self-consistent manner. The plastic flow of an in-situ metallic glass composite, beta-Vitreloy, was investigated under uniaxial compression in its supercooled liquid regime and at various strain rates (10-4 10-1 s-1). The composite, with 25% volume fraction of crystalline beta-phase dendrites exhibited superplastic behavior similar to that of amorphous Vit 1. Significant strain hardening was observed when the material was deformed at high temperatures and low strain rates. A dual-phase composite model was employed in finite element simulations to understand the effect of the composite microstructure on its mechanical behavior.

  7. A continuum deformation theory for metal-matrix composites at high temperature

    NASA Technical Reports Server (NTRS)

    Robinson, D. N.

    1987-01-01

    A continuum theory is presented for representing the high temperature, time dependent, hereditary deformation behavior of metallic composites that can be idealized as pseudohomogeneous continua with locally definable directional characteristics. Homogenization of textured materials (molecular, granular, fibrous) and applicability of continuum mechanics in structural applications depends on characteristic body dimensions, the severity of gradients (stress, temperature, etc.) in the structure and the relative size of the internal structure (cell size) of the material. The point of view taken here is that the composite is a material in its own right, with its own properties that can be measured and specified for the composite as a whole.

  8. Compaction creep of sands due to time-dependent grain failure: Effects of chemical environment, applied stress, and grain size

    NASA Astrophysics Data System (ADS)

    Brzesowsky, R. H.; Hangx, S. J. T.; Brantut, N.; Spiers, C. J.

    2014-10-01

    Time-dependent brittle creep plays a role in controlling compaction of sands and sandstones under upper crustal conditions, influencing phenomena such as production-induced reservoir compaction, surface subsidence, and induced seismicity. Brittle creep also plays a role in determining the mechanical behavior of gouge-rich faults. We performed uniaxial creep experiments on sand to investigate the effects of chemical environment (dry versus solution flooded), grain size (d = 196-378 m), and applied effective stress (?a up to 30 MPa), at room temperature conditions favoring grain-scale brittle processes. Creep measurements were complemented with acoustic emission (AE) detection and microstructural analysis to characterize the main creep mechanism. Wet samples showed much higher creep strains than dry-tested samples. AE event counts showed a direct relation between grain failure and creep strain, with higher AE rates occurring in the wet samples. Therefore, we inferred that time-dependent deformation was dominated by subcritical crack growth, resulting in grain failure accompanied by intergranular sliding rearrangements, and that crack growth in the presence of chemically active fluids was controlled by stress corrosion. The sensitivity of the compaction rate of the sands to d and ?a can be expressed as ???di?aj where i ? 6 and j ? 21 under dry conditions and i ? 9 and j ? 15 under wet conditions. Our results were compared to a simple model based on Hertzian contact theory, linear elastic fracture mechanics, and subcritical crack growth. This model showed agreement between the observed stress and grain size sensitivities of creep, within a factor of 2.

  9. Hot Deformation Behavior of Alloy 800H at Intermediate Temperatures: Constitutive Models and Microstructure Analysis

    NASA Astrophysics Data System (ADS)

    Cao, Y.; Di, H. S.; Misra, R. D. K.; Zhang, Jiecen

    2014-12-01

    The hot deformation behavior of a Fe-Ni-Cr austenitic Alloy 800H was explored in the intermediate temperature range of 825-975 C and strain rate range of 0.01-10 s-1. The study indicates that dynamic recrystallization (DRX) occurred at 875-975 C for strain rates of 0.01-0.1 s-1 and adiabatic heating generated at high strain rates accelerated the DRX process. Based on the experimental data, the Johnson-Cook, modified Johnson-Cook, and Arrhenius-type constitutive models were established to predict the flow stress during hot deformation. A comparative study was made on the accuracy and effectiveness of the above three developed models. The microstructure analysis indicated that all the deformation structures exhibited elongated grains and evidence of some degree of DRX. The multiple DRX at 975 C and 0.01 s-1 led to an increase in the intensity of {001} <100> "cube" texture component and a significant reduction in the intensity of {011} <211> "brass" component. Additionally, the average values of grain average misorientation and grain orientation spread for deformed microstructure were inversely proportional to the fraction of DRX.

  10. Influence of Hold Time on Creep-Fatigue Behavior of an Advanced Austenitic Alloy

    SciTech Connect

    Mark Carroll; Laura Carroll

    2011-09-01

    An advanced austenitic alloy, HT-UPS (high temperature-ultrafine precipitate strengthened), is a candidate material for the structural components of fast reactors and energy-conversion systems. HT-UPS provides improved creep resistance through a composition based on 316 stainless steel (SS) with additions of Ti and Nb to form nano-scale MC precipitates in the austenitic matrix. The low cycle fatigue and creep-fatigue behavior of a HT-UPS alloy has been investigated at 650 C, 1.0% total strain, and an R ratio of -1 with hold times as long as 9000 sec at peak tensile strain. The cyclic deformation response of HT-UPS is compared to that of 316 SS. The cycles to failure are similar, despite differences in peak stress profiles and the deformed microstructures. Cracking in both alloys is transgranular (initiation and propagation) in the case of continuous cycle fatigue, while the primary cracks also propagate transgranularly during creep-fatigue cycling. Internal grain boundary damage as a result of the tensile hold is present in the form of fine cracks for hold times of 3600 sec and longer and substantially more internal cracks are visible in 316 SS than HT-UPS. The dislocation substructures observed in the deformed material are different. An equiaxed cellular structure is observed in 316 SS, whereas tangles of dislocations are present at the nanoscale MC precipitates in HT-UPS and no cellular substructure is observed.

  11. Brittle and compaction creep in porous sandstone

    NASA Astrophysics Data System (ADS)

    Heap, Michael; Brantut, Nicolas; Baud, Patrick; Meredith, Philip

    2015-04-01

    Strain localisation in the Earth's crust occurs at all scales, from the fracture of grains at the microscale to crustal-scale faulting. Over the last fifty years, laboratory rock deformation studies have exposed the variety of deformation mechanisms and failure modes of rock. Broadly speaking, rock failure can be described as either dilatant (brittle) or compactive. While dilatant failure in porous sandstones is manifest as shear fracturing, their failure in the compactant regime can be characterised by either distributed cataclastic flow or the formation of localised compaction bands. To better understand the time-dependency of strain localisation (shear fracturing and compaction band growth), we performed triaxial deformation experiments on water-saturated Bleurswiller sandstone (porosity = 24%) under a constant stress (creep) in the dilatant and compactive regimes, with particular focus on time-dependent compaction band formation in the compactive regime. Our experiments show that inelastic strain accumulates at a constant stress in the brittle and compactive regimes leading to the development of shear fractures and compaction bands, respectively. While creep in the dilatant regime is characterised by an increase in porosity and, ultimately, an acceleration in axial strain to shear failure (as observed in previous studies), compaction creep is characterised by a reduction in porosity and a gradual deceleration in axial strain. The overall deceleration in axial strain, AE activity, and porosity change during creep compaction is punctuated by excursions interpreted as the formation of compaction bands. The growth rate of compaction bands formed during creep is lower as the applied differential stress, and hence background creep strain rate, is decreased, although the inelastic strain required for a compaction band remains constant over strain rates spanning several orders of magnitude. We find that, despite the large differences in strain rate and growth rate (from both creep and constant strain rate experiments), the characteristics (geometry, thickness) of a compaction band remain essentially the same. Several lines of evidence, notably the similarity between the differential stress dependence of creep strain rate in the dilatant and compactive regimes, suggest that, as for dilatant creep, compactant creep is driven by subcritical stress corrosion cracking. We highlight the attendant implications for time-dependent porosity loss, subsidence, and permeability reduction in sandstone reservoirs.

  12. The Role of Brines in low Temperature, Fault-related Deformation of Quartz Arenites

    NASA Astrophysics Data System (ADS)

    O'Kane, A.; Onasch, C. M.; Farver, J.

    2004-12-01

    Fluids play an integral role in deformation within the Earth\\'{}s crust over a wide range of physical conditions. At low temperatures (<300 C) the effect is dominantly mechanical, largely through the effects of pore fluid pressure. At higher temperatures (>300 C), chemical processes, such as diffusive mass transfer, advective mass transfer, and hydrolytic weakening dominate. Brines, because of their greater reactivity, enhance certain chemical processes during deformation. In the transition between high and low temperature regimes, both mechanical and chemical processes operate and interact in complex ways. This study investigates the role of brines in the deformation of quartz arenite in a map scale fault zone deformed under conditions transitional between low and high temperature regimes. The fault zone is also known to have been a conduit for fluids thought to be largely basinal brines. The Cove Mountain fault zone in south central Pennsylvania contains several map-scale blocks of quartz arenite which display a wide range of brittle and ductile microstructures. Abundant evidence of fluids is present in the form of quartz veins, microveins, fluid inclusion planes, cataclastic bands, and stylolites. Three different fluids are recognized based on cathodoluminescence color of quartz, and homogenization (Th) and melting temperatures (Tm) from fluid inclusions. Blue-green luminescing quartz has a Th of 185 to 215 C and a Tm of -15 to -17 C; red luminescing quartz has a Th of 165 to 200 C and a Tm of -16 to -20 C; and zoned quartz with both red and blue-green luminescence has a Th of 180 to 220 C and a Tm of -18 to -23 C. The eutectic temperature of all three fluids is approximately -50 C suggesting that CaCl2 is the dominant salt species. Grains adjacent to fluid conduits (microfractures, cataclastic bands, and stylolites) display more crystal plastic microstructures than those farther away. Compared to quartz in veins and in undeformed portions of the rock, which have water contents of ~1,000 and ~12,000 H/106 Si, respectively (determined by FTIR), grains adjacent to fluid conduits have water contents as high as 26,000 H/106 Si indicating that water was able to penetrate these grains and thus promote ductile deformation in a dominantly brittle regime. Access of water to grain centers was provided by both microfracturing and diffusion. Evidence for diffusion is shown by the presence of quartz grains adjacent to fluid conduits which have blue luminescing centers and red rims. Water contents in these grains ranges from 2,000-22,000 H/106 Si with some correlation between water content and luminescence color. The large amount of pressure solution relative to similar rocks in the region is believed to be related to the salinity of the brines. Also, the thick accumulation of goethite in stylolites and fractures precipitated by these fluids is unusual in similar rocks in the region suggesting that the fluid chemistry was atypical. The microstructures in this fault zone indicate that water is important in controlling the operative deformation mechanisms in the transition from low to high temperature deformation. Furthermore, the chemistry of these brines may account for greater solubility of quartz and faster diffusion rates than would be the case with low salinity fluids.

  13. Tensile creep and creep rupture behavior of monolithic and SiC-whisker-reinforced silicon nitride ceramics

    SciTech Connect

    Ohji, Tatsuki; Yamauchi, Yukihiko )

    1993-12-01

    The tensile creep and creep rupture behavior of silicon nitride was investigated at 1,200 to 1,350 C using hot-pressed materials with and without SiC whiskers. Stable steady-state creep was observed under low applied stresses at 1,200 C. Accelerated creep regimes, which were absent below 1,300 C, were identified above that temperature. The appearance of accelerated creep at the higher temperatures attributable to formation of microcracks throughout a specimen. The whisker-reinforced material exhibited better creep resistance than the monolith at 1,200 C. Considerably high values 3 to 5, were obtained for the creep exponent in the overall temperature range. The exponent tended to decrease with decreasing applied stress at 1,200 C. The primary creep mechanism was considered cavitation-enhanced creep. Specimen lifetimes followed the Monkman-Grant relationship except for fractures with large accelerated creep regimes. The creep rupture behavior is discussed in association with cavity formation and crack adolescence.

  14. Predicting the time-temperature dependent axial failure of B/A1 composites

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1980-01-01

    Experimental and theoretical studies were conducted in order to understand and predict the effects of time, temperature, and stress on the axial failure modes of boron fibers and B/A1 composites. Due to the anelastic nature of boron fiber deformation, it was possible to determine simple creep functions which can be employed to accurately describe creep and fracture stress of as-produced fibers. Analysis of damping and strength data for B/6061 A1 composites indicates that fiber creep effects of creep on fiber fracture are measurably reduced by the composite fabrication process. The creep function appropriate for fibers with B/Al composites was also determined. A fracture theory is presented for predicting the time-temperature dependence of the axial tensile strength for metal matrix composites in general and B/A1 composites in particular.

  15. Localized shear deformation and softening of bulk metallic glass: stress or temperature driven?

    PubMed

    Ketov, S V; Louzguine-Luzgin, D V

    2013-01-01

    Metallic glasses due to their unique combination of physical and chemical properties have a great potential in various applications: materials for construction, medical, MEMs devices and so on. The deformation mechanism in metallic glasses is very much different from that in conventional crystalline materials and not yet fully understood. Here we are trying to find out what drives shear deformation in metallic glasses. The compression experiments of the bulk metallic glassy (BMG) samples coated with tin, Rose metal and indium were performed. There were no melting sites of the coating observed near individual shear bands. Melting occurred only near fracture surface, near microcracks and in the places of shear band concentrations. The results indicate that shear banding is rather a stress driven process while the temperature rise that was observed takes place due to friction forces in the viscous supercooled liquid thin layer in the shear bands. PMID:24100784

  16. Deformation of two C36 Laves phases by microhardness indentation at room temperature

    SciTech Connect

    Liu, Y.; Allen, S.M.; Livingston, J.D.

    1995-05-01

    Microhardness indentation and electron microscopy were used to study the room-temperature deformation behavior of two Laves phases, ZrFe{sub 2} and MgNi{sub 2}, in two-phase alloys. Evidence of extensive plastic deformation was found around the indentations. Activation of basal and nonbasal slip systems forms a distinctive cell structure in both Laves phases. Slip on planes nearly normal to the basal plane occurs in the lamellar form of ZrFe{sub 2}. Burgers vectors of the dislocations and resulting shear displacements are studied using high-resolution transmission electron microscopy (TEM). Curved or zigzag nonbasal slip surfaces in atomic scale were observed. Each slip plane can be considered to be composed of a series of small facets of high atomic density. A common Burgers vector and displacement vector component of 1/4 [0001] was found on many different slip planes. The ``zonal glide`` concept for slip on prismatic planes is discussed.

  17. Evaluation of Package Stress during Temperature Cycling using Metal Deformation Measurement and FEM Simulation

    SciTech Connect

    Hoeglauer, J.; Bohm, C.; Otremba, R.; Maerz, J.; Nelle, P.; Stecher, M.; Alpern, P.

    2006-02-07

    Plastic encapsulated devices that are exposed to Temperature Cycling (TC) tests undergo an excessive mechanical stress due to different Coefficients of Thermal Expansion (CTE) of the various materials used in the system. Especially in the corners of the die, passivation cracks and shifted metal lines can be observed, which demonstrates an increasing mechanical stress from chip center to the corners of the die. This effect has been known for a long time. This paper presents a simple measurement technique to quantify the mechanical shear stress at the chip-Mold Compound (MC) interface by measuring the deformation of a periodical metal structure. Based on this deformation measurement, we evaluated the stress distribution within the package, and the influence of different parameters such as number of cycles and chip size. Furthermore, these experimental results were compared with FEM simulation, and showed good agreement but could not account in all cases for the total amount of observed shift.

  18. Deformability and stability of erythrocytes in high-frequency electric fields down to subzero temperatures.

    PubMed Central

    Krueger, M; Thom, F

    1997-01-01

    High-frequency electric fields can be used to induce deformation of red blood cells. In the temperature domain T = 0 degrees to -15 degrees C (supercooled suspension) and for 25 degrees C this paper examines for human erythrocytes (discocytes, young cell population suspended in a low ionic strength solution with conductivity sigma(25 degrees) = 154 microS/cm) in a sinusoidal electric field (nu = 1 MHz, E0 = 0-18 kV/cm) the following properties and effects as a function of field strength and temperature: 1) viscoelastic response, 2) (shear) deformation (steady-state value obtained from the viscoelastic response time), 3) stability (by experimentally observed breakdown of cell polarization and hemolysis), 4) electrical membrane breakdown and field-induced hemolysis (theoretical calculations for ellipsoidal particles), and 5) mechanical hemolysis. The items 2-4 were also examined for the frequency nu = 100 kHz and for a nonionic solution of very low conductivity (sigma(25 degrees) = 10 microS/cm) to support our interpretations of the results for 1 MHz. Below 0 degrees C with decreasing temperature the viscoelastic response time tau(res)(T) for the cells to reach steady-state deformation values d(infinity,E) increases and the deformation d(infinity,E)(T) decreases strongly. Both effects are especially high for low field strengths. The longest response time of approximately 30 s was obtained for -15 degrees C and small deformations. For 1 MHz the cells can be highly elongated up to 2.3 times their initial diameter a0 for 25 degrees and 0 degrees C, 2.1a0 for -10 degrees C and still 1.95a0 for -15 degrees C. For T > or = 0 degrees C the deformation is limited by hemolysis of the cells, which sets in for E0(lysis)(25 degrees) approximately 8 kV/cm and E0(lysis)(0 degrees) approximately 14 kV/cm. These values are approximately three times higher than the corresponding calculated critical field strengths for electrically induced pore formation. Nevertheless, the observed depolarization and hemolysis of the cells is provoked by electrical membrane breakdown rather than by mechanical forces due to the high deformation. For the nonionic solution, where no electrical breakdown is expected in the whole range for E0, the cells can indeed be deformed to even higher values with a low hemolytic rate. Below 0 degrees C we observe no hemolysis at all, not even for the frequency 100 kHz, where the cells hemolyze at 25 degrees C for the much lower field strength E0(lysis) approximately 2.5 kV/cm. Obviously, pore formation and growth are weak for subzero temperatures. Images FIGURE 7 PMID:9370459

  19. Deformation twinning at low temperatures in a Hf-V-Nb cubic laves phase

    SciTech Connect

    Luzzi, D.E.; Rao, G.; Dobbins, T.A.; Pope, D.P.

    1998-05-01

    Deformation twinning in the C15 cubic laves phase of the Hf-V-Nb alloy system is analyzed at temperatures between 77 K and room temperature by conventional and high-resolution TEM. In order to reduce the stacking fault energy (SFE), alloy compositions are chosen such that the cubic laves phase composition is close to a region of C14 phase stability. A high density of stacking defects of intrinsic character in the as-homogenized alloy confirms that the SFE has been reduced. Twinning is observed at all temperatures placing a low upper limit on any thermally activated deformation process. Twin clusters are observed which are narrow and have a similar distribution to the stacking defects in the undeformed alloy. The structure of twins and stacking defects is solved via HREM combined with image calculations. Finally, the mechanism of twinning is discussed and the use of alloying to control the SFE or to refine the microstructure in order to increase the low temperature ductility in these intermetallic compounds with complex cubic crystal structures is proposed.

  20. Deformation and Phase Transformation Processes in Polycrystalline NiTi and NiTiHf High Temperature Shape Memory Alloys

    NASA Technical Reports Server (NTRS)

    Benafan, Othmane

    2012-01-01

    The deformation and transformation mechanisms of polycrystalline Ni49.9Ti50.1 and Ni50.3Ti29.7Hf20 (in at.%) shape memory alloys were investigated by combined experimental and modeling efforts aided by an in situ neutron diffraction technique at stress and temperature. The thermomechanical response of the low temperature martensite, the high temperature austenite phases, and changes between these two states during thermomechanical cycling were probed and reported. In the cubic austenite phase, stress-induced martensite, deformation twinning and slip processes were observed which helped in constructing a deformation map that contained the limits over which each of the identified mechanisms was dominant. Deformation of the monoclinic martensitic phase was also investigated where the microstructural changes (texture, lattice strains, and phase fractions) during room-temperature deformation and subsequent thermal cycling were compared to the bulk macroscopic response. When cycling between these two phases, the evolution of inelastic strains, along with the shape setting procedures were examined and used for the optimization of the transformation properties as a function of deformation levels and temperatures. Finally, this work was extended to the development of multiaxial capabilities at elevated temperatures for the in situ neutron diffraction measurements of shape memory alloys on the VULCAN Diffractometer at Oak Ridge National Laboratory.

  1. Tensile Creep of Polycrystalline Near-Stoichiometric NiAl

    NASA Technical Reports Server (NTRS)

    Raj, Sai V.

    2002-01-01

    Long term tensile creep studies were conducted on binary NiAl in the temperature range 700-1200 K with the objectives of characterizing and understanding the creep mechanisms. Inverse and normal primary creep curves were observed depending on stress and temperature. It was concluded that the creep of NiAl is limited by dislocation mobility. The stress exponent for creep, n, increased from 5.5 at 1200 K to 13.9 at 700 K. The true activation energy for creep, Qc, was constant and equal to about 400 kJ per mole between 20 and 50 MPa but decreased to a constant value of 250 kJ per mole between 50 and 110 MPa. The activation energy was observed to be stress dependent above 110 MPa. The tensile creep results reported in this investigation were compared with compression creep data reported in the literature. A detailed discussion of the probable dislocation creep mechanisms governing compressive and tensile creep of NiAl is presented. It is concluded that the non-conservative motion of jogs on screw dislocations influenced the nature of the primary creep curves, where the climb of these jogs involves either the next nearest neighbor or the six-jump cycle vacancy diffusion mechanism. The probable nature of the atom vacancy exchange that occur within the core of an edge dislocation undergoing climb in NiAl are schematically examined.

  2. Creep and shrinkage effects on integral abutment bridges

    NASA Astrophysics Data System (ADS)

    Munuswamy, Sivakumar

    Integral abutment bridges provide bridge engineers an economical design alternative to traditional bridges with expansion joints owing to the benefits, arising from elimination of expensive joints installation and reduced maintenance cost. The superstructure for integral abutment bridges is cast integrally with abutments. Time-dependent effects of creep, shrinkage of concrete, relaxation of prestressing steel, temperature gradient, restraints provided by abutment foundation and backfill and statical indeterminacy of the structure introduce time-dependent variations in the redundant forces. An analytical model and numerical procedure to predict instantaneous linear behavior and non-linear time dependent long-term behavior of continuous composite superstructure are developed in which the redundant forces in the integral abutment bridges are derived considering the time-dependent effects. The redistributions of moments due to time-dependent effects have been considered in the analysis. The analysis includes nonlinearity due to cracking of the concrete, as well as the time-dependent deformations. American Concrete Institute (ACI) and American Association of State Highway and Transportation Officials (AASHTO) models for creep and shrinkage are considered in modeling the time dependent material behavior. The variations in the material property of the cross-section corresponding to the constituent materials are incorporated and age-adjusted effective modulus method with relaxation procedure is followed to include the creep behavior of concrete. The partial restraint provided by the abutment-pile-soil system is modeled using discrete spring stiffness as translational and rotational degrees of freedom. Numerical simulation of the behavior is carried out on continuous composite integral abutment bridges and the deformations and stresses due to time-dependent effects due to typical sustained loads are computed. The results from the analytical model are compared with the published laboratory experimental and field data. The behavior of the laterally loaded piles supporting the integral abutments is evaluated and presented in terms of the lateral deflection, bending moment, shear force and stress along the pile depth.

  3. Material Parameters for Creep Rupture of Austenitic Stainless Steel Foils

    NASA Astrophysics Data System (ADS)

    Osman, H.; Borhana, A.; Tamin, M. N.

    2014-08-01

    Creep rupture properties of austenitic stainless steel foil, 347SS, used in compact recuperators have been evaluated at 700 C in the stress range of 54-221 MPa to establish the baseline behavior for its extended use. Creep curves of the foil show that the primary creep stage is brief and creep life is dominated by tertiary creep deformation with rupture lives in the range of 10-2000 h. Results are compared with properties of bulk specimens tested at 98 and 162 MPa. Thin foil 347SS specimens were found to have higher creep rates and higher rupture ductility than their bulk specimen counterparts. Power law relationship was obtained between the minimum creep rate and the applied stress with stress exponent value, n = 5.7. The value of the stress exponent is indicative of the rate-controlling deformation mechanism associated with dislocation creep. Nucleation of voids mainly occurred at second-phase particles (chromium-rich M23C6 carbides) that are present in the metal matrix by decohesion of the particle-matrix interface. The improvement in strength is attributed to the precipitation of fine niobium carbides in the matrix that act as obstacles to the movement of dislocations.

  4. Postseismic relaxation and transient creep

    USGS Publications Warehouse

    Savage, J.C.; Svarc, J.L.; Yu, S.-B.

    2005-01-01

    Postseismic deformation has been observed in the epicentral area following the 1992 Landers (M = 7.3), 1999 Chi-Chi (M = 7.6), 1999 Hector Mine (M = 7.1), 2002 Denali (M = 7.9), 2003 San Simeon (M = 6.5), and 2004 Parkfield (M = 6.0) earthquakes. The observations consist of repeated GPS measurements of the position of one monument relative to another (separation ???100 km). The early observations (t < 0.1 year) are well fit by the function a' + c'log(t), where t is the time after the earthquake and a' and c' are constants chosen to fit the data. Because a log(t) time dependence is characteristic of transient (primary) creep, the early postseismic response may be governed by transient creep as Benioff proposed in 1951. That inference is provisional as the stress conditions prevailing in postseismic relaxation are not identical to the constant stress condition in creep experiments. The observed logarithmic time dependence includes no characteristic time that might aid in identifying the micromechanical cause.

  5. Creep-fatigue of low cobalt superalloys

    NASA Technical Reports Server (NTRS)

    Halford, G. R.

    1982-01-01

    Testing for the low cycle fatigue and creep fatigue resistance of superalloys containing reduced amounts of cobalt is described. The test matrix employed involves a single high temperature appropriate for each alloy. A single total strain range, again appropriate to each alloy, is used in conducting strain controlled, low cycle, creep fatigue tests. The total strain range is based upon the level of straining that results in about 10,000 cycles to failure in a high frequency (0.5 Hz) continuous strain-cycling fatigue test. No creep is expected to occur in such a test. To bracket the influence of creep on the cyclic strain resistance, strain hold time tests with ore minute hold periods are introduced. One test per composition is conducted with the hold period in tension only, one in compression only, and one in both tension and compression. The test temperatures, alloys, and their cobalt compositions that are under study are given.

  6. Creep behavior of an A286 type stainless steel

    SciTech Connect

    DeCicco, H. . E-mail: decicco@cnea.gov.ar; Luppo, M.I.; Raffaeli, H.; Di Gaetano, J.; Gribaudo, L.M.; Ovejero-Garcia, J.

    2005-08-15

    A model for steady state deformation of the commercial {gamma}' precipitation hardened alloy A286 at moderately high temperature is presented. This model is mainly based on the theory of thermally activated glide. The activation parameters such as the maximum free energy necessary to overcome obstacles to glide, the threshold stress for jerky glide and the activation volume of the rate controlling process are derived from experimental results and allowed rationalization of all the measurements in the range of stresses and temperatures investigated. Creep tests were carried out at constant stress in the range of 180-750 MPa at 600, 640, 670 and 700 deg. C in air. Transmission electron microscopy has permitted determination of the size of the {gamma}' particles and the average distance between them.

  7. Irradiation creep of SA 304L and CW 316 stainless steels: Mechanical behaviour and microstructural aspects. Part I: Experimental results

    NASA Astrophysics Data System (ADS)

    Garnier, J.; Brchet, Y.; Delnondedieu, M.; Pokor, C.; Dubuisson, P.; Renault, A.; Averty, X.; Massoud, J. P.

    2011-06-01

    Solution annealed 304L (SA 304L) and cold work 316 (CW 316) austenitic stainless steel irradiation creep behaviour have been studied thoroughly. Irradiations were carried out in fast breeder reactors BOR-60 (at 330 C, up to 120 dpa) and EBR-II (at 375 C, up to 10.5 dpa), and in the OSIRIS mixed spectrum reactor (at 330 C, up to 9.8 dpa). After an incubation threshold, the irradiation creep of the austenitic stainless steels is linear in stress and in dose. Creep appears to be athermal in this temperature range. A significant difference in the behaviour is measured between the creep of SA 304L and CW 316. In order to study the anisotropy of loop population, which would be the signature of a possible stress induced preferential absorption (SIPA) mechanism for irradiation creep, special attention was given to the measurement of anisotropy of loop distribution between the four families. The anisotropy induced by an applied stress has been shown to be in the range of the statistical scatter in the situation where no stress is applied. TEM microstructural analyses performed on this sample show slight difference between the microstructure of specimens deformed under irradiation and the microstructure of specimens irradiated without stress under the same irradiation conditions.

  8. Sources of Variation in Creep Testing

    NASA Technical Reports Server (NTRS)

    Loewenthal, William S.; Ellis, David L.

    2011-01-01

    Creep rupture is an important material characteristic for the design of rocket engines. It was observed during the characterization of GRCop-84 that the complete data set had nearly 4 orders of magnitude of scatter. This scatter likely confounded attempts to determine how creep performance was influenced by manufacturing. It was unclear if this variation was from the testing, the material, or both. Sources of variation were examined by conducting tests on identically processed specimens at the same specified stresses and temperatures. Significant differences existed between the five constant-load creep frames. The specimen temperature was higher than the desired temperature by as much as 43 C. It was also observed that the temperature gradient was up to 44 C. Improved specimen temperature control minimized temperature variations. The data from additional tests demonstrated that the results from all five frames were comparable. The variation decreased to 1/2 order of magnitude from 2 orders of magnitude for the baseline data set. Independent determination of creep rates in a reference load frame closely matched the creep rates determined after the modifications. Testing in helium tended to decrease the sample temperature gradient, but helium was not a significant improvement over vacuum.

  9. The Effect of Cold Plastic Straining of Submicrocrystalline and Coarse-Grained Titanium on the Temperature Behavior of Flow Stress in the Stage of Microplastic Deformation

    NASA Astrophysics Data System (ADS)

    Dudarev, E. F.; Pochivalova, G. P.; Kolobov, Yu. R.; Bakach, G. P.; Skosyrskii, A. B.; Zhorovkov, M. F.; Goraynov, ?. ?.

    2013-10-01

    The results of an experimental investigation of the effect of mechanical-thermal treatment of submicrocrystalline and coarse-grained titanium on the deformation behavior in the stage of microplastic deformation at room and elevated temperatures are reported. The structural factors giving rise to the flowstress changes in the stage of microplastic deformation as a result of mechanical-thermal treatment are discussed. The general tendencies and special features of the effect of annealing and testing temperatures on the deformation behavior and flow stress in the first and second stages of microplastic deformation of submicrocrystalline and coarse-grained titanium subjected to large plastic deformation at 295 K are clarified.

  10. Deformation mechanisms in ARB processed aluminium alloy AA6016 at low temperatures

    NASA Astrophysics Data System (ADS)

    Hollang, L.; Scharnweber, J.; Reuther, K.; Skrotzki, W.

    2010-07-01

    The deformation behaviour of the aluminium alloy AA6016 at low temperatures was investigated in the initial state and after 4 and 8 cycles of accumulative roll bonding (ARB). Tensile tests at 25 K, 77 K, 180 K and 296 K were performed at constant strain rate 10-4 s-1. Stress relaxation experiments performed during the tensile tests were used to determine the experimental rate sensitivity ? as a function of the flow stress ?. In all cases ? (?) is found to be linear revealing that the Cottrell-Stokes law holds. The effect of grain size on ? can be adequately described through an additive athermal stress contribution ?d, which is the higher the higher the degree of pre-deformation is. Moreover, the temperature dependence of the strain rate sensitivity m(T) indicates that the rate controlling mechanism in the initial state is local single slip. The ARB states deviate from the single slip behaviour already at 25 K. The reason probably is the occurrence of additional thermally activated slip processes in the ARB states.

  11. Creep behaviour of modified 9Cr-1Mo ferritic steel

    NASA Astrophysics Data System (ADS)

    Choudhary, B. K.; Isaac Samuel, E.

    2011-05-01

    Creep deformation and fracture behaviour of indigenously developed modified 9Cr-1Mo steel for steam generator (SG) tube application has been examined at 823, 848 and 873 K. Creep tests were performed on flat creep specimens machined from normalised and tempered SG tubes at stresses ranging from 125 to 275 MPa. The stress dependence of minimum creep rate obeyed Norton's power law. Similarly, the rupture life dependence on stress obeyed a power law. The fracture mode remained transgranular at all test conditions examined. The analysis of creep data indicated that the steel obey Monkman-Grant and modified Monkman-Grant relationships and display high creep damage tolerance factor. The tertiary creep was examined in terms of the variations of time to onset of tertiary creep with rupture life, and a recently proposed concept of time to reach Monkman-Grant ductility, and its relationship with rupture life that depends only on damage tolerance factor. SG tube steel exhibited creep-rupture strength comparable to those reported in literature and specified in the nuclear design code RCC-MR.

  12. Magnetoelastic effect during the low-temperature deformation of 316LN-IG stainless steel

    NASA Astrophysics Data System (ADS)

    Krivykh, A. V.; Irodova, A. V.; Keilin, V. E.

    2015-01-01

    The segments of tubes made of austenitic 316LN-IG stainless steel that are cut along the tube axis are subjected to tensile tests in liquid and gaseous helium at temperatures below 7 K. The tubes are intended for the conductor conduits of the toroidal magnetic system of ITER. The time evolution of the strain, the temperature, and the strain-induced magnetization of specimens in the form of the normal component of the magnetic field on their surfaces is studied as a function of the applied load. The behavior of local deformation near slip bands is complicated: the areas near slip planes undergo unloading and shrinking. A magnetoelastic effect is detected; it indicates a negative longitudinal magnetostriction for the initial ? phase and the strain-induced ? phase. The cases of absent local heating during strain jumps are explained by the magnetocaloric effect in the areas unloaded during slip.

  13. Deformation and failure of bulk metallic glasses under different initial temperatures

    NASA Astrophysics Data System (ADS)

    Li, J. C.; Chen, X. W.; Huang, F. L.

    2015-09-01

    Based on the coupled thermo-mechanical model, a constitutive model for bulk metallic glasses (BMGs), which is generalized to the multi-axial stress state and considers the effects of free volume, heat and hydrostatic stress, has been modified in the present paper. Besides, a failure criterion of critical free volume concentration is introduced based on the coalescence mechanism of free volume. The constitutive model as well as the failure criterion is implemented into the LS-DYNA commercial software by user material subroutine (UMAT). Then FEM simulations for different initial material temperatures are conducted and the evolutions of material parameter as well as corresponding macroscopic mechanical behaviour of material are analyzed. Relative analysis shows that the initial material temperature significantly affects the deformation and failure of material.

  14. Syn-deformation temperature and fossil fluid pathways along an exhumed detachment zone, khao khwang fold-thrust belt, Thailand

    NASA Astrophysics Data System (ADS)

    Hansberry, Rowan L.; Collins, Alan S.; King, Rosalind C.; Morley, Christopher K.; Gi?e, Andy P.; Warren, John; Lhr, Stefan C.; Hall, P. A.

    2015-08-01

    Shale detachment zones, their influence on deformational style, and their internal mechanisms of deformation are an understudied aspect of fold-thrust belts. Properties such as deformational temperature, lithology, and mineralogy are often recognized as having a key influence on the rheology and deformational style of detachment zones and overlying fold-thrust belts. However, little work has been conducted on rock properties of known detachment zones. A recently described upper-level detachment zone in the exhumed Khao Khwang Fold-Thrust Belt of central Thailand provides an ideal natural laboratory for investigation of the deformation conditions of the detachment zone, and association with its complex deformational style. The low-grade metamorphic indicator illite crystallinty is used to broadly constrain deformational temperatures, while oxygen and carbon stable isotope analysis provides insight into fluid flow history and fluid-rock interaction. Illite crystallinity data indicate deep diagenetic, to low anchizonal conditions, and temperatures of ~ 160-210 C in the shale detachment, interpreted as reflecting peak metamorphic conditions during the Triassic Indosinian Orogeny. No trend between the intensity (spacing, complexity) of structures and illite crystallinty is observed. However, shale shear zones of continuous-style deformation and inferred higher finite strain display uniformly higher illite crystallinty than surrounding packages of discontinuously faulted shales. We also note a positive association between total organic carbon content in the shales and the spacing and complexity of deformational structures. Data from limestones and syn-tectonic vein fills detail the history of fluid-rock interaction during early mesogenesis, through to orogenesis. The early covariant trend of increasingly negative ?13C and ?18O values is attributed to increasing burial, while a divergent orogenic trend of increasingly negative ?18O values is interpreted as the result of a loss of matrix permeability and interruption of fluid-rock re-equilibration. These hottest fluids were concentrated along large thrusts which facilitated fluid movement during orogenesis.

  15. Carbonates in thrust faults: High temperature investigations into deformation processes in calcite-dolomite systems

    NASA Astrophysics Data System (ADS)

    Kushnir, A.; Kennedy, L.; Misra, S.; Benson, P.

    2012-04-01

    The role of dolomite on the strength and evolution of calcite-dolomite fold and thrust belts and nappes (as observed in the Canadian Rockies, the Swiss Alps, the Italian Apennines, and the Naukluft Nappe Complex) is largely unknown. Field investigations indicate that strain in natural systems is localized in calcite, resulting in a ductile response, while dolomite deforms in a dominantly brittle manner. To date, experimental studies on polymineralic carbonate systems are limited to homogeneous, fine-grained, calcite-dolomite composites of relatively low dolomite content. The effect of dolomite on limestone rheology, the onset of crystal-plastic deformation in dolomite in composites, and the potential for strain localization in composites have not yet been fully quantified. Constant displacement rate (3x10-4 s-1and 10-4 s-1), high confining pressure (300 MPa) and high temperature (750 C and 800 C) torsion experiments were conducted to address the role of dolomite on the strength of calcite-dolomite composites. Experiments were performed on samples produced by hot isostatic pressing (HIP) amalgams of a natural, pure dolomite and a reagent, pure calcite. We performed experiments on the following mixtures (given as dolomite%): 25%, 35%, 50%, and 75%. These synthetic HIP products eliminated concerns of mineralogical impurities and textural anomalies due to porosity, structural fabrics (e.g., foliation) and fossil content. The samples were deformed up to a maximum finite shear strain of 5.0 and the experimental set up was unvented to inhibit sample decarbonation. Mechanical data shows a considerable increase in sample yield strength with increasing dolomite content. Experimental products with low starting dolomite content (dol%: 25% and 35%) display macroscopic strain localization along compositionally defined foliation. Experimental products with high dolomite content (dol%: 50% and 75%) demonstrate no macroscopic foliation. Post-deformation microstructure analysis shows that small dolomite grains (~50 ?m) are characterized by well-defined grain boundaries and cleavage controlled fracture. There is evidence of the interruption of foliation development due to the presence of large-grained dolomite. Calcite grains are characterized by triple junction grain boundaries, providing evidence for recrystallization. Ongoing microstructural analyses (including: thin section analysis, EBSD, SEM, and Microprobe analysis) are being conducted to better constrain the deformation mechanisms and the degree of strain localization in these composites. Our experiments provide insights into the processes controlling rheology within bimodal calcite-dolomite systems, which can be used to improve models of the evolution of fold and thrust belt systems.

  16. Influence of Plastic Deformation on Low-Temperature Surface Hardening of Austenitic Stainless Steel by Gaseous Nitriding

    NASA Astrophysics Data System (ADS)

    Bottoli, Federico; Winther, Grethe; Christiansen, Thomas L.; Somers, Marcel A. J.

    2015-06-01

    This article addresses an investigation of the influence of plastic deformation on low-temperature surface hardening by gaseous nitriding of two commercial stainless steels: EN 1.4369 and AISI 304. The materials were plastically deformed to several levels of equivalent strain by conventional tensile straining, plane strain compression, and shear. Gaseous nitriding of the strained material was performed in ammonia gas at atmospheric pressure at various temperatures. Microstructural characterization of the as-deformed state and the nitrided case produced included X-ray diffraction analysis, reflected-light microscopy, and microhardness testing. The results demonstrate that a case of expanded austenite develops and that the presence of plastic deformation has a significant influence on the morphology of the nitrided case. The presence of strain-induced martensite favors the formation of CrN, while a high dislocation density in a fully austenitic structure does not lead to such premature nucleation of CrN.

  17. Strain hardening behavior of TWIP steel in plastic deformation with temperature

    NASA Astrophysics Data System (ADS)

    Dan, W. J.; Liu, F.; Zhang, W. G.

    2015-03-01

    Considering dynamic recovery/recrystallization and twinning effects, in this paper we develop a dislocation-based model to study the strain hardening behavior of TWIP steel. In the model, the dislocation evolution is controlled through a dynamic recovery/recrystallization process at high temperatures, and is primarily dominated by a twinning-induced plasticity (TWIP) process at moderate/ambient temperatures. The corresponding dislocation evolution model is established based on irreversible thermodynamics at high temperatures and conventional plasticity theory at moderate/ambient temperatures, respectively. A factor of ? is introduced to reflect the mixture effect of dynamic recovery/recrystallization and twinning on dislocation evolution, and ? increases with deformation temperature. The stress-strain response and strain hardening behavior of TWIP steel (Fe-22Mn-0.6C) are validated at 293, 473, 573, 673, 773 and 873 K. Moreover, the mixture influence of dynamic recovery/recrystallization and twinning on the strain hardening behavior of TWIP steel is analyzed at 293, 473 and 573 K.

  18. Creep cavity observation using liquid metal embrittlement

    SciTech Connect

    Reiley, T.C.

    1981-01-01

    Grain boundary cavities, which form during high-temperature deformation and which may be considered incipient intergranular cracks, have been difficult to observe at the early growth stages. To examine grain boundaries in unfailed specimans one is normally limited to metallographic or transmission electron microscopy (TEM) techniques, the first having resolution limitations (r/sub cavity/approx.l..mu..m) and the second having limitations in the probability of seeing a cavity (especially for large-grained, low-density specimens) or of seeing a cavity which is undisturbed by the thinning process required for TEM. Other observational techniques involving hydrogen attack or low-temperature impact loading have been used to create brittle intergranular failures to observe grain boundary features, such as creep cavities on pre-crept specimens. These techniques are not, however, applicable to most metals, and as such, the need remains for a more general observational technique. Such a new technique employing liquid metal embrittlement (LME) is described below, and, given that most metals are severely embrittled by at least one liquid metal, this approach may satisfy requirements of general applicability.

  19. Relationship between creep, gamma 2, and marginal fracture of dental amalgams.

    PubMed

    Sarkar, N K; Eyer, C S; Norling, B K

    1983-11-01

    The effect of gamma 1 and gamma 2 on the creep deformation of dental amalgams has been investigated. It has been shown that the creep of a conventional amalgam is not dependent on gamma 1 as was previously reported. Rather it is strongly influenced by gamma 2 and its volume fraction. It has been speculated that Sn-rich grain boundaries also enhance creep by facilitating grain boundary sliding. The reported correlation between creep and marginal fracture has been explained in terms of this dependence of creep on corrosion-prone Sn-rich microstructural constituents of amalgams. PMID:6580405

  20. Creep of plain weave polymer matrix composites

    NASA Astrophysics Data System (ADS)

    Gupta, Abhishek

    Polymer matrix composites are increasingly used in various industrial sectors to reduce structural weight and improve performance. Woven (also known as textile) composites are one class of polymer matrix composites with increasing market share mostly due to their lightweight, their flexibility to form into desired shape, their mechanical properties and toughness. Due to the viscoelasticity of the polymer matrix, time-dependent degradation in modulus (creep) and strength (creep rupture) are two of the major mechanical properties required by engineers to design a structure reliably when using these materials. Unfortunately, creep and creep rupture of woven composites have received little attention by the research community and thus, there is a dire need to generate additional knowledge and prediction models, given the increasing market share of woven composites in load bearing structural applications. Currently, available creep models are limited in scope and have not been validated for any loading orientation and time period beyond the experimental time window. In this thesis, an analytical creep model, namely the Modified Equivalent Laminate Model (MELM), was developed to predict tensile creep of plain weave composites for any orientation of the load with respect to the orientation of the fill and warp fibers, using creep of unidirectional composites. The ability of the model to predict creep for any orientation of the load is a "first" in this area. The model was validated using an extensive experimental involving the tensile creep of plain weave composites under varying loading orientation and service conditions. Plain weave epoxy (F263)/ carbon fiber (T300) composite, currently used in aerospace applications, was procured as fabrics from Hexcel Corporation. Creep tests were conducted under two loading conditions: on-axis loading (0) and off-axis loading (45). Constant load creep, in the temperature range of 80-240C and stress range of 1-70% UTS of the composites, was experimentally evaluated for time periods ranging from 1--120 hours under both loading conditions. The composite showed increase in creep with increase in temperature and stress. Creep of composite increased with increase in angle of loading, from 1% under on-axis loading to 31% under off-axis loading, within the tested time window. The experimental creep data for plain weave composites were superposed using TTSP (Time Temperature Superposition Principle) to obtain a master curve of experimental data extending to several years and was compared with model predictions to validate the model. The experimental and model results were found in good agreement within an error range of +/-1-3% under both loading conditions. A parametric study was also conducted to understand the effect of microstructure of plain weave composites on its on-axis and off-axis creep. Generation of knowledge in this area is also "first". Additionally, this thesis generated knowledge on time-dependent damage m woven composites and its effect on creep and tensile properties and their prediction.

  1. Polycrystalline olivine rheology in dislocation creep: Revisiting experimental data to 8.1 GPa

    NASA Astrophysics Data System (ADS)

    Bollinger, Caroline; Raterron, Paul; Cordier, Patrick; Merkel, Sbastien

    2014-03-01

    The rheology of polycristalline San Carlos olivine is investigated on synchrotron beamline in the Deformation-DIA (D-DIA) at pressure (P) between 3.8 and 8.1 GPa, temperature (T) within 1373-1673 K, and at steady-state strain rates ranging from 1.1 10-5 to 5.8 10-5 s-1. Transmission electron microscopy (TEM) on run products reveals microstructures characteristic of the so-called dislocation creep regime. Fourier transform infrared (FTIR) measurements reveal hydroxyl concentrations within 153-1526 ppm H/Si (Patersons calibration), indicating wet conditions of deformation. Analysis of our data together with previously published wet deformation data obtained at room and high P, assuming a stress exponent n = 3.5 in classical power law, results in a linear dependence of the activation enthalpy with P, i.e., in an activation volume of V? = 12.8 5 cm3 mol-1. This value of V? is also consistent with a global dataset including wet data and dry published deformation data for olivine aggregates. We thus conclude that, up to 8 GPa, the effect of P on dry and wet olivine dislocation creep is consistent with V? = 12.8 5 cm3 mol-1.

  2. A creep-damage model for mesoscale simulations of concrete expansion-degradation phenomena

    SciTech Connect

    Giorla, Alain B; Le Pape, Yann

    2015-01-01

    Long-term performance of aging concrete in nuclear power plants (NPPs) requires a careful examination of the physical phenomena taking place in the material. Concrete under high neutron irradiation is subjected to large irreversible deformations as well as mechanical damage, caused by a swelling of the aggregates. However, these results, generally obtained in accelerated conditions in test reactors, cannot be directly applied to NPP irradiated structures, i.e., the biological shield, operating conditions due to difference in time scale and environmental conditions (temperature, humidity). Mesoscale numerical simulations are performed to separate the underlying mechanisms and their interactions. The cement paste creep-damage model accounts for the effect of the loading rate on the apparent damage properties of the material and uses an event-based approach to capture the competition between creep and damage. The model is applied to the simulation of irradiation experiments from the literature and shows a good agreement with the experimental data.

  3. Diffusional creep and diffusion-controlled dislocation creep and their relation to denuded zones in Mg-ZrH{sub 2} materials

    SciTech Connect

    Ruano, O.A.; Sherby, O.D.; Wadsworth, J.; Wolfenstine, J.

    1998-03-13

    Langdon`s contention that creep of Mg-0.5 wt% Zr is well characterized by diffusional creep at 400 C is in error. It is shown that Langdon and Gifkins` single analysis of denuded zones formed during creep at 2 MPa, purporting to occur as a result of diffusional creep, in fact, took place in the power-law dislocation creep range where solute atoms are interacting with moving dislocations. This observation supports the earlier conclusions made for creep and denuded zones observed in the hydrided Mg-Zr alloy at 500 C. Furthermore, it is shown that Pickles` data at stresses below 2 MPa at 400 C are not related to diffusional creep as considered by Langdon. In this region, denuded zones appear in both longitudinal and transverse boundaries indicating that grain boundary sliding, accompanied by grain boundary migration, is the principal deformation process. It is proposed that denuded zones are caused by dissolution of precipitates at moving grain boundaries.

  4. Thermally Activated Deformation Behavior of ufg-Au: Environmental Issues During Long-Term and High-Temperature Nanoindentation Testing

    NASA Astrophysics Data System (ADS)

    Maier, Verena; Leitner, Alexander; Pippan, Reinhard; Kiener, Daniel

    2015-09-01

    For testing time-dependent material properties by nanoindentation, in particular for long-term creep or relaxation experiments, thermal drift influences on the displacement signal are of prime concern. To address this at room and elevated temperatures, we tested fused quartz at various contact depths at room temperature and ultra-fine grained (ufg) Au at various temperatures. We found that the raw data for fused quartz are strongly affected by thermal drift, but corrected by use of dynamic stiffness measurements all the datasets collapse. The situation for the ufg Au shows again that the data are only useful with drift correction, but with this applied it turns out that there is a significant change of elastic and plastic properties when exceeding 200C, which is also reflected by an increasing strain rate sensitivity.

  5. High Temperature Mechanical Behavior of Ti-45Al-8Nb and Its Cavity Evolution in Deformation

    NASA Astrophysics Data System (ADS)

    Du, Zhihao; Zhang, Kaifeng; Jiang, Shaosong; Zhu, Ruican; Li, Shuguang

    2015-10-01

    The tensile property of a high Nb containing TiAl-based alloy (Ti-45Al-8Nb) was investigated in the temperature range of 900-1050 C and strain rate range of 1 10-3 to 2.5 10-2 s-1. The results revealed that the yield stress decreased with increasing temperature and decreasing strain rate, while the tensile elongation increased with an increase in temperature and a decrease in strain rate. Hence, The minimum yield stress of 119.2 MPa and the maximum elongation of 237% were obtained at the temperature of 1050 C and strain rate of 1 10-3 s-1. Based on the experimental data, the activation energy of the alloy was calculated to be 360 kJ/mol. Moreover, the microstructure and the fracture morphology of the specimens were observed, and the results revealed that the distribution of cavities was related to deformation parameters and the fracture mode was typically dimple-type.

  6. Deformation at ambient and high temperature of in situ Laves phases-ferrite composites

    NASA Astrophysics Data System (ADS)

    Donnadieu, Patricia; Pohlmann, Carsten; Scudino, Sergio; Blandin, Jean-Jacques; Babu Surreddi, Kumar; Eckert, Jrgen

    2014-06-01

    The mechanical behavior of a Fe80Zr10Cr10 alloy has been studied at ambient and high temperature. This Fe80Zr10Cr10 alloy, whoose microstructure is formed by alternate lamellae of Laves phase and ferrite, constitutes a very simple example of an in situ CMA phase composite. The role of the Laves phase type was investigated in a previous study while the present work focuses on the influence of the microstructure length scale owing to a series of alloys cast at different cooling rates that display microstructures with Laves phase lamellae width ranging from 50 nm to 150 nm. Room temperature compression tests have revealed a very high strength (up to 2 GPa) combined with a very high ductility (up to 35%). Both strength and ductility increase with reduction of the lamella width. High temperature compression tests have shown that a high strength (900 MPa) is maintained up to 873 K. Microstructural study of the deformed samples suggests that the confinement of dislocations in the ferrite lamellae is responsible for strengthening at both ambient and high temperature. The microstructure scale in addition to CMA phase structural features stands then as a key parameter for optimization of mechanical properties of CMA in situ composites.

  7. Formation behavior of basal texture under the high temperature plane strain compression deformation in AZ80 magnesium alloy

    NASA Astrophysics Data System (ADS)

    Kim, K.; Okayasu, K.; Fukutomi, H.

    2015-04-01

    The formation behavior of basal texture during high temperature deformation of AZ80 magnesium alloys in single phase was investigated by plane strain compression deformation. Three kinds of specimens with different initial textures were machined out from an extruded bar having a <1010> texture. Plane strain compression tests were conducted at temperatures of 623K and 723K and a strain rate of 5.010-2s-1, with a strain range of between - 0.4 and -1.0. After deformation, the specimens were immediately quenched in oil. Texture measurement was carried out on the compression planes by the Schulz reflection method using nickel filtered Cu K? radiation. Electron backscatter diffraction (EBSD) measurements were also conducted in order to examine the spatial distribution of orientations. Three kinds of specimens named A, B and C were prepared from the same extruded bar. In the specimens A, B and C, {0001} was distributed preferentially parallel to ND, TD, and RD, respectively. After deformation, texture evaluation was conducted on the mid-plane section. At the plane strain compression deformation, peaks appeared in the true stress-true strain curves irrespective of the kinds of specimen used. It was found that the main components and the pole densities of the textures vary depending on deformation condition and initial texture. Six kinds of texture components were observed after deformation. The (0001)<1010> has formed regardless of the initial texture. There are two types of texture components; one exists before the deformation, and the other does not. Either types are considered to have stable orientations for plane strain compression. Also, the basal texture is composed of two crystal orientation components - (0001)<1010> and (0001)<1120>. When (0001) existed before deformation, an extremely sharp (0001) (compression plane) texture is formed.

  8. Creep Events and Shear Localization in a Polyphase Material: Insight into the Brittle-Ductile Transition

    NASA Astrophysics Data System (ADS)

    Reber, J. E.; Hayman, N. W.; Lavier, L. L.; Jammes, S.

    2014-12-01

    The co-occurrence of brittle and ductile deformation underlies many large-scale tectonic processes, geodetically and seismologically monitored strain transients, and even several applied geoscience problems in hydrocarbon production and CO2 sequestration. Evidence for such mixed-deformation is preserved in the rock record, such as in mid-crustal shear zones where, depending on the temperature and pressure conditions, some mineral phases undergo brittle and others ductile deformation during the same overall bulk deformation. Here we combine physical experiments with an analytical approach to investigate the impact of the semi-brittle material on the deformation localization and on stick-slip and creep events. Two sets of experiments are performed: 1) shear of a mixture of elastic-frictional grains within a viscously deforming media, and 2) propagation of wetted fractures in a visco-elasto-plastic interlinked polymer gel during shear. We measure the force and displacement while imaging the shear cell. In both cases the rock analogues show a semi-brittle behavior where the deformation localization is enhanced and slip events get damped leading to creep. Several parameters were then extracted from the experiments and directly used as input parameters in an analytical solution for semi-brittle flow. In the analytical model localization and slip is modeled as a damped oscillator mimicking the behavior of discrete fractures originating in a strong material that get viscously damped in a surrounding continuous weaker material. That the measured and calculated decay times of slip events lead to comparable results is supportive of the models physical premise. This study suggest that in a mixed brittle-ductile system, localization can be efficient, frictional responses can be dampened but still present, and basic rheological descriptions may apply, all of which has implications for understanding strain transients and coseismic release.

  9. Deformation mechanisms in granodiorite at effective pressures to 100 MPa and temperatures to partial melting

    SciTech Connect

    Friedman, M.; Handin, J.; Bauer, S.J.

    1981-01-01

    Deformation mechanisms in room-dry and water-saturated specimens of Charcoal Granodiorite, shortened at 10/sup -4/s/sup -1/, at effective pressures (Pe) to 100 MPa and temperatures to partial melting (less than or equal to 1050/sup 0/C) are documented with a view toward providing criteria to recognize and characterize the deformation for geological and engienering applications. Above 800/sup 0/C strength decreases dramatically at effective pressures greater than or equal to 50 MPa and water-weakening reduces strength an additional 30 to 40% at Pe = 100 MPa. Strains at failure are only 0.1 to 2.2% with macroscopic ductility (within this range) increasing as the effective pressures are increased and in wet versus dry tests. Shattering (multiple faulting) gives way to faulting along a single zone to failure without macroscopic faulting as ductility increases. Microscopically, cataclasis (extension microfracturing and thermal cracking with rigid-body motions) predominates at all conditions. Dislocation gliding contributes little to the strain. Precursive extension microfractures coalesce to produce the throughgoing faults with gouge zones exhibiting possible Riedel shears. Incipient melting, particularly in wet tests, produces a distinctive texture along feldspar grain boundaries that suggests a grain-boundary-softening effect contributes to the weakening. In addition, it is demonstrated that the presence of water does not lead to more microfractures, but to a reduction in the stresses required to initiate and propagate them.

  10. Creep of a fine-grained, fully-lamellar, two-phase TiAl alloy at 760{degree}C

    SciTech Connect

    Wang, J.N.; Schwartz, A.J.; Nieh, T.G.; Liu, C.T.; Sikka, V.K.; Clemens, D.

    1995-02-01

    Creep of a TiAl alloy, having a composition of Ti-47Al-2Cr-2Nb (in atom %) and a fine-grained, fully-lamellar structure, was carried out at 760 C and stresses between 69--723 MPa. It was found that, in addition to having good room temperature properties, the alloy exhibits higher creep resistance than other TiAl alloys with a similar composition. Both the creep data and microstructures of the alloy suggest that there exists a change in deformation mechanism from a glide-controlled process at high stresses to a recovery-controlled process at low stresses. Also, microstructural evidence indicates that the rate-controlling recovery mechanism is the climb of dislocation segments pinned by ledges at {gamma}/{alpha}{sub 2} interfacial boundaries.

  11. Evolution of Strain Partitioning during Creep of Carrara Marble

    NASA Astrophysics Data System (ADS)

    Quintanilla Terminel, A.; Evans, J. B.; Mainprice, D.; Lebensohn, R.

    2014-12-01

    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% at a strain rate of 3x10-5s-1, confining pressure of 300 MPa and 400deformed to strains of 11%, 22% and 36% at 600C and the same rate and confining pressure. Microscale strain mapping at a scale of 10 micrometers (MSSM) show that the partitioning of strain amongst twinning, dislocation slip, and grain boundary sliding mechanisms change with T. Preliminary results using a VPFFT model that gives more importance to dislocation slip predict strain heterogeneities with larger wavelength. Interestingly, at all T, although sliding occurred on some boundaries, on average, strain in regions near boundaries was less than that in grain interiors suggesting the formation of a core-mantle structure observed in naturally deformed rocks. The production of local crystallographic texture also depends on T (and presumably, partitioning amongst the mechanisms). In all the experiments, the texture index (TI) of local areas decreased after deformation, but the path of the evolution differed with changing T. Reductions in TI were greatest for samples deformed at 400C, where twin activity was greatest, and at 700C, where boundary sliding was more prevalent, and less for intermediate T. The wavelength and amplitude of the heterogeneity in local strain decreased with increasing strain at 600C, suggesting that the strain (and perhaps, structures) were being homogenized. From this data and previous observations, we conclude that the evolution of deformation structures in marble takes place over a substantial interval in strain; that the duration of this interval probably depends on strain rate, temperature, and pressure; and that extrapolation of mechanical behavior from lab to natural conditions will need to account for changes in strain partitioning.

  12. Alpha-Case Kinetics and Surface Crack Growth in the High-Temperature Alloy TIMETAL 834 Under Creep Conditions

    NASA Astrophysics Data System (ADS)

    Abdallah, Zakaria; Perkins, Karen; Williams, Steve

    2012-12-01

    Investigations of Timetal 834 crept specimens showed that a uniform alpha-case layer was developed at the surfaces of all specimens tested in air at 823 K to 923 K (550 C to 650 C). The formation of this alpha-case was a result of the inward diffusion of oxygen, which is an alpha stabilizer, and other elements promoting the transformation of the beta matrix into an alpha phase and, thus, modifying the microstructure at the surfaces of these test pieces. The thickness of this alpha-case was increasing in a parabolic manner with increasing exposure time and temperature. Cracks were clearly observed at the surface of the crept specimens whose depths were greater at lower stresses. Interestingly, an alpha-case was also developed at the surfaces of the penetrating cracks with the case thickness decreasing towards the crack tip. This information was used to calculate the times at which the cracks initiated.

  13. Atmospheric pressure creep experiments using highly dense fine-grained mineral aggregates

    NASA Astrophysics Data System (ADS)

    Hiraga, T.; Miyazaki, T.; Tasaka, M.; Sueyoshi, K.; Nakakoji, S.; Koizumi, S.; Yoshida, H.

    2012-12-01

    Historically in mineral and rock physics, atmospheric pressure creep tests have been used extensively to study the rheological properties of minerals through deformation of single crystals. This technique has several advantages including minimal friction effects on the loading column, which allows excellent stress resolution on the sample, and stable temperature control, which allows long duration experiments at relatively slow strain rates. The downside of atmospheric pressure experiments on polycrystalline samples is that cavities and cracks are easily introduced during the test, resulting in brittle failure of the specimen. It is generally found that the confining pressure should be larger than the applied differential stress to avoid failure due to microcracking. Consequently very few creep experiments under atmospheric pressure have been conducted on polycrystalline samples. We revisit this classic method of atmospheric pressure creep experiments by developing a technique to synthesize very fine grained aggregates with essentially zero porosity. So far, we are able to reach even 200 micron grain size for certain type of mineral assemblies. During grain size sensitive creep, we expect that the differential stress applied to the samples can be reduced 100 to 1000 times the stress to deform coarser grained samples at the same strain rate condition by reducing grain size of one order of magnitude. Taking into account of ~10 micron grain size as a common value in conventional experiments, we should be able to reduce the applied stress of > 2500 times. Such lowering the applied stress will help to prevent cracking and/or cavitation in the samples. Using this technique, we have been able to demonstrate (i) superplasticity, (ii) microstructural development comparable to that in observed natural mylonites, (iii) flow strength as a function of stress, grain size and temperature, (iv) the effect of the fraction of second phase on flow strength in poly-phase materials, (v) fabric development as a function of strain, (vi) grain growth behavior during deformation, (vii) deformation during chemical reaction, and (viii) the effect of melt on deformation microstructures of synthetic geomaterials.

  14. Change in high-temperature strength properties of 12Kh1MF steel in long-term loading under creep conditions

    SciTech Connect

    Shron, R.Z.; Mints, I.I.; Shul`gina, N.G.

    1995-01-01

    Stress-rupture strength tests were made of metal steam pipe (12Kh1MF steel) in various conditions, the original, after aging under laboratory conditions (580{degrees}C, 10,000 h), and after long service. It was shown that the more the steel is hardened by heat treatment or cold plastic working in the original condition, the less it hardens in creep. It was established that softening in creep of steel with a moderate yield strength is caused primarily by aging and with a high yield strength by pore formation.

  15. Effects of microstructure and temperature on the plastic deformation mechanisms of synthetic halite : a micromechanical approach

    NASA Astrophysics Data System (ADS)

    Bourcier, M.; Dimanov, A.; Hripr, E.; Bornert, M.; Raphanel, J.

    2012-04-01

    Halite is a rock forming mineral with geotechnical applications for storage in underground caverns (hydrocarbons, compressed air, wastes...). Halite is also a convenient analog polycristalline material, used to study deformation mechanisms (crystal plasticity, recrystallization, pressure solution ...). In this work we present an investigation of intragranular plastic deformation and grain boundary sliding in pure synthetic NaCl polycrystals produced by hot isostatic pressing. Uniaxial compression tests are performed in a Scanning Electron Microscope (SEM) at two temperatures, 20C and 400 C, on cm - sized samples. The displacement rate is kept constant at 1m/s and the maximum axial strain is between 5 and 10 %. The surface of the samples is marked by gold micro-spheres and analyzed by 2D digital image correlation (DIC) using the CorrelManuV software, which provides full field measures of surface displacements and strains. The dominant mechanism is intracrystalline plasticity, as revealed by the direct observation of slip lines and by DIC results showing intragranular deformation bands. Using crystal orientation mapping, the latter are related to the traces of crystallographic slip planes. However, limited grain boundary sliding (GBS) also occurs, as a secondary but necessary mechanism for accommodation of local strain incompatibilities. The relative contribution of each mechanism clearly depends on the microstructure, i.e. grain size and grain size distribution. At room temperature the strain is more heterogeneous than at high temperature, at both the aggregate scale and within individual grains, where the local activity of slip systems strongly depends on the relative crystalline and interfacial orientations. In particular, the easy glide planes ({110} planes) are not the only active ones. In some instance, wavy slip bands clearly indicate cross slip. The above kinematic analysis should be complemented by the knowledge of the local stress states in order to compute for each slip system of each grain a resolved shear stress and thus find which system is likely to be activated. If one assumes that the local stress state is representative of the macroscopic uniaxial compression, the analysis provides straightforwardly the appropriate Schmid factors showing which slip systems experience the largest resolved shear stresses. However, owing to local interactions between the different mechanisms and the neighboring grains, this is only a first order approximation, and one needs numerical simulations in order to compute the stress distribution at the local level. One will thus (i) characterize an observed area of a few grains in terms of geometry and initial orientation (measured by electron back-scattering diffraction, EBSD), (ii) determine the boundary conditions (including by implementing the measured displacement field) and (iii) simulate its deformation by crystal plasticity with finite element code. However, since the real 3D microstructure is unknown the actual influence of the underlying layers of grains cannot be well asserted. For this purpose, 3D reconstruction based on X-ray diffraction techniques is needed.

  16. Collect Available Creep-Fatigue Data and Study Existing Creep-Fatigue Evaluation Procedures for Grade 91 and Hastelloy XR

    SciTech Connect

    Tai Asayama; Yukio Tachibana

    2007-09-30

    This report describes the results of investigation on Task 5 of DOE/ASME Materials Project based on a contract between ASME Standards Technology, LLC (ASME ST-LLC) and Japan Atomic Energy Agency (JAEA). Task 5 is to collect available creep-fatigue data and study existing creep-fatigue evaluation procedures for Grade 91 steel and Hastelloy XR. Part I of this report is devoted to Grade 91 steel. Existing creep-fatigue data were collected (Appendix A) and analyzed from the viewpoints of establishing a creep-fatigue procedure for VHTR design. A fair amount of creep-fatigue data has been obtained and creep-fatigue phenomena have been clarified to develop design standards mainly for fast breeder reactors. Following this, existing creep-fatigue procedures were studied and it was clarified that the creep-fatigue evaluation procedure of the ASME-NH has a lot of conservatisms and they were analyzed in detail from the viewpoints of the evaluation of creep damage of material. Based on the above studies, suggestions to improve the ASME-NH procedure along with necessary research and development items were presented. Part II of this report is devoted to Hastelloy XR. Existing creep-fatigue data used for development of the high temperature structural design guideline for High Temperature Gas-cooled Reactor (HTGR) were collected. Creep-fatigue evaluation procedure in the design guideline and its application to design of the intermediate heat exchanger (IHX) for High Temperature Engineering Test Reactor (HTTR) was described. Finally, some necessary research and development items in relation to creep-fatigue evaluation for Gen IV and VHTR reactors were presented.

  17. Research on the Hot Deformation Behavior of Al-Zn-Mg-Sc-Zr Alloy During Compression at Elevated Temperature

    NASA Astrophysics Data System (ADS)

    Li, Bo; Pan, Qinglin; Zhang, Zhiye; Zhou, Jian

    2013-02-01

    The flow behavior of Al-Zn-Mg-Sc-Zr alloy during hot compression deformation was studied by isothermal compression test using Gleeble-1500 thermo-mechanical equipment. Compression tests were performed in the temperature range of 340-500 C and in the strain rate range of 0.001-10 s-1.The results indicate that the flow stress of the alloy increases with increasing strain rate at a given temperature, and decreases with increasing temperature at a given imposed strain rate. The relationship between flow stress and strain rate and temperature was derived by analyzing the experimental data. The constitutive equation of Al-Zn-Mg-Sc-Zr alloy during hot compression deformation can be described by the Arrhenius relationship of the hyperbolic sine form. The values of A, n, and ? in the analytical expression of strain rate are fitted to be 1.49 1010 s-1, 7.504, and 0.0114 MPa-1, respectively. The hot deformation activation energy of the alloy during compression is 150.25 kJ/mol. The temperature and strain rate have great influences on microstructure evolution of Al-Zn-Mg-Sc-Zr alloy during hot compression deformation. According to microstructure evolution, the dynamic flow softening is mainly caused by dynamic recovery and dynamic recrystallization in this present experiment.

  18. Deformation temperatures and flow vorticities near the base of the Greater Himalayan Series, Sutlej Valley and Shimla Klippe, NW India

    NASA Astrophysics Data System (ADS)

    Law, R. D.; Stahr, D. W.; Francsis, M. K.; Ashley, K. T.; Grasemann, B.; Ahmad, T.

    2013-09-01

    We report new deformation temperature and flow vorticity data from the base of the Greater Himalayan Series (GHS) exposed in the Sutlej Valley and Shimla Klippe of NW India. We focus on three groups of transects across the hanging wall of the Main Central Thrust (MCT). In order of relative foreland - hinterland positions, they are the Shimla Klippe, Western and Eastern Sutlej transects. Deformation temperatures indicated by quartz c-axis fabric opening-angles increase both from foreland to hinterland at a given structural distance above the MCT and up structural section from the MCT within individual transects. Deformation temperatures in the immediate hanging wall to the MCT are estimated at 510-535, 535-550 and 610 C on the Shimla, Western Sutlej and Eastern Sutlej transects, respectively. The steepest inferred field gradients in deformation temperatures are recorded adjacent to the MCT and progressively decrease up structural section following a power law relationship. Comparison with temperature estimates based on multi-mineral phase equilibria data suggests that penetrative shearing occurred at close to peak metamorphic conditions. Vorticity analyses indicate that shearing along the base of the GHS occurred under sub-simple shear conditions (Wm values of 0.9-1.0) with a minor component of pure shear.

  19. Determination of Creep Behavior of Thermal Barrier Coatings Under Laser Imposed High Thermal and Stress Gradient Conditions

    NASA Technical Reports Server (NTRS)

    Zhu, Dongming; Miller, Robert A.

    1999-01-01

    A laser sintering/creep technique has been established to determine the creep behavior of thermal barrier coatings under steady-state high heat flux conditions. For a plasma sprayed zirconia-8 wt. % yttria coating, a significant primary creep strain and a low apparent creep activation energy were observed. Possible creep mechanisms involved include stress induced mechanical sliding and temperature and stress enhanced cation diffusion through the splat and grain boundaries. The elastic modulus evolution, stress response, and total accumulated creep strain variation across the ceramic coating are simulated using a finite difference approach. The modeled creep response is consistent with experimental observations.

  20. Research on the hot deformation behavior of a Fe-Ni-Cr alloy (800H) at temperatures above 1000C

    NASA Astrophysics Data System (ADS)

    Cao, Yu; Di, Hongshuang

    2015-10-01

    Considering the pinning effect of fine carbides on grain boundaries, hot compression tests were performed above the dissolution temperature of Cr23C6 to investigate the hot deformation behavior of a Fe-Ni-Cr alloy (800H). The results show that the single peak stress associated with dynamic recrystalization (DRX) became more distinct at higher temperature and lower strain rate. The process of DRX was thoroughly stimulated when deformed above 1000C. Constitutive equations for hot deformation were established by regression analysis of conventional hyperbolic sine equation. The relationships between Zener-Hollomon parameter (Z) and the characteristic points of flow curves were established using the power law relation. Furthermore, kernel average misorientation (KAM) and grain orientation spread (GOS) were used to map the distribution of local misorientation and estimate the fraction of DRX, respectively. The critical strain and peak strain were used to predict the kinetics of DRX with the Avrami-type equation.

  1. MICROSTRUCTURAL EXAMINATION OF V-4CR-4TI PRESSURIZED THERMAL CREEP TUBES

    SciTech Connect

    Gelles, David S.

    2002-09-01

    Two further failed thermal creep pressurized tubes of V-4Cr-4Ti tested at 700 and 800 degrees C have been examined using optical microscopy and transmission electron microscopy in order to understand failure and creep mechanisms. These conditions represent lower stress states than were previously examined. Creep deformation at lower stress is shown to be controlled by sub-boundary formation and mis-orientation between sub-grains arising from climb of dislocations within the boundary.

  2. Application Of Shakedown Analysis To Cyclic Creep Damage Limits

    SciTech Connect

    Carter, Peter; Jetter, Robert I; Sham, Sam

    2012-01-01

    Shakedown analysis may be used to provide a conservative estimate of local rupture and hence cyclic creep damage for use in a creep-fatigue assessment. The shakedown analysis is based on an elastic-perfectly plastic material with a temperature-dependent pseudo yield stress defined to guarantee that a shakedown solution exists which does not exceed rupture stress and temperature for a defined life. The ratio of design life to the estimated maximum cyclic life is the shakedown creep damage. The methodology does not require stress classification and is also applicable to cycles over the full range of temperature above and below the creep regime. Full cyclic creep and damage analysis is the alternative when shakedown analysis appears to be excessively conservative.

  3. Unified Creep Plasticity Damage (UCPD) Model for Rigid Polyurethane Foams.

    SciTech Connect

    Neilsen, Michael K.; Lu, Wei-Yang; Scherzinger, William M.; Hinnerichs, Terry D.; Lo, Chi S.

    2015-06-01

    Numerous experiments were performed to characterize the mechanical response of several different rigid polyurethane foams (FR3712, PMDI10, PMDI20, and TufFoam35) to large deformation. In these experiments, the effects of load path, loading rate, and temperature were investigated. Results from these experiments indicated that rigid polyurethane foams exhibit significant volumetric and deviatoric plasticity when they are compressed. Rigid polyurethane foams were also found to be very strain-rate and temperature dependent. These foams are also rather brittle and crack when loaded to small strains in tension or to larger strains in compression. Thus, a new Unified Creep Plasticity Damage (UCPD) model was developed and implemented into SIERRA with the name Foam Damage to describe the mechanical response of these foams to large deformation at a variety of temperatures and strain rates. This report includes a description of recent experiments and experimental findings. Next, development of a UCPD model for rigid, polyurethane foams is described. Selection of material parameters for a variety of rigid polyurethane foams is then discussed and finite element simulations with the new UCPD model are compared with experimental results to show behavior that can be captured with this model.

  4. Improving the Performance of Creep-Strength-Enhanced Ferritic Steels

    E-print Network

    Pennycook, Steve

    Improving the Performance of Creep-Strength- Enhanced Ferritic Steels Background Creep strength for superheater tubing and main steam piping in coal-fired steam boilers, as well as in heat-recovery steam generators used in combined cycle gas turbine units. Improvements in the high temperature capability of CSEF

  5. Large-strain time-temperature equivalence in high density polyethylene for prediction of extreme deformation and damage

    NASA Astrophysics Data System (ADS)

    Furmanski, J.; Brown, E. N.; Clements, B.; Cady, C. M.; Gray, G. T.

    2012-08-01

    Time-temperature equivalence is a widely recognized property of many time-dependent material systems, where there is a clear predictive link relating the deformation response at a nominal temperature and a high strain-rate to an equivalent response at a depressed temperature and nominal strain-rate. It has been found that high-density polyethylene (HDPE) obeys a linear empirical formulation relating test temperature and strain-rate. This observation was extended to continuous stress-strain curves, such that material response measured in a load frame at large strains and low strain-rates (at depressed temperatures) could be translated into a temperature-dependent response at high strain-rates and validated against Taylor impact results. Time-temperature equivalence was used in conjuction with jump-rate compression tests to investigate isothermal response at high strain-rate while exluding adiabatic heating. The validated constitutive response was then applied to the analysis of Dynamic-Tensile-Extrusion of HDPE, a tensile analog to Taylor impact developed at LANL. The Dyn-Ten-Ext test results and FEA found that HDPE deformed smoothly after exiting the die, and after substantial drawing appeared to undergo a pressure-dependent shear damage mechanism at intermediate velocities, while it fragmented at high velocities. Dynamic-Tensile-Extrusion, properly coupled with a validated constitutive model, can successfully probe extreme tensile deformation and damage of polymers.

  6. Creep Life of Ceramic Components Using a Finite-Element-Based Integrated Design Program (CARES/CREEP)

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, J. P.; Powers, L. M.; Jadaan, O. M.

    1998-01-01

    The desirable properties of ceramics at high temperatures have generated interest in their use for structural applications such as in advanced turbine systems. Design lives for such systems can exceed 10,000 hours. The long life requirement necessitates subjecting the components to relatively low stresses. The combination of high temperatures and low stresses typically places failure for monolithic ceramics in the creep regime. The objective of this paper is to present a design methodology for predicting the lifetimes of structural components subjected to creep rupture conditions. This methodology utilized commercially available finite element packages and takes into account the time-varying creep strain distributions (stress relaxation). The creep life of a component is discretized into short time steps, during which the stress and strain distributions are assumed constant. The damage is calculated for each time step based on a modified Monkman-Grant creep rupture criterion. Failure is assumed to occur when the normalized accumulated damage at any point in the component is greater than or equal to unity. The corresponding time will be the creep rupture life for that component. Examples are chosen to demonstrate the CARES/CREEP (Ceramics Analysis and Reliability Evaluation of Structures/CREEP) integrated design programs, which is written for the ANSYS finite element package. Depending on the component size and loading conditions, it was found that in real structures one of two competing failure modes (creep or slow crack growth) will dominate. Applications to benechmark problems and engine components are included.

  7. Creep Life of Ceramic Components Using a Finite-Element-Based Integrated Design Program (CARES/CREEP)

    NASA Technical Reports Server (NTRS)

    Powers, L. M.; Jadaan, O. M.; Gyekenyesi, J. P.

    1998-01-01

    The desirable properties of ceramics at high temperatures have generated interest in their use for structural application such as in advanced turbine engine systems. Design lives for such systems can exceed 10,000 hours. The long life requirement necessitates subjecting the components to relatively low stresses. The combination of high temperatures and low stresses typically places failure for monolithic ceramics in the creep regime. The objective of this paper is to present a design methodology for predicting the lifetimes of structural components subjected to creep rupture conditions. This methodology utilizes commercially available finite element packages and takes into account the time-varying creep strain distributions (stress relaxation). The creep life, of a component is discretized into short time steps, during which the stress and strain distributions are assumed constant. The damage is calculated for each time step based on a modified Monkman-Grant creep rupture criterion. Failure is assumed to occur when the normalized accumulated damage at any point in the component is greater than or equal to unity. The corresponding time will be the creep rupture life for that component. Examples are chosen to demonstrate the Ceramics Analysis and Reliability Evaluation of Structures/CREEP (CARES/CREEP) integrated design program, which is written for the ANSYS finite element package. Depending on the component size and loading conditions, it was found that in real structures one of two competing failure modes (creep or slow crack growth) will dominate. Applications to benchmark problems and engine components are included.

  8. In situ observation of crystallographic preferred orientation of deforming olivine at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Ohuchi, Tomohiro; Nishihara, Yu; Seto, Yusuke; Kawazoe, Takaaki; Nishi, Masayuki; Maruyama, Genta; Hashimoto, Mika; Higo, Yuji; Funakoshi, Ken-ichi; Suzuki, Akio; Kikegawa, Takumi; Irifune, Tetsuo

    2015-06-01

    Simple-shear deformation experiments on polycrystalline olivine and olivine single-crystal were conducted at pressures of 1.3-3.8 GPa and temperatures of 1223-1573 K to understand the achievement of steady-state fabric strength and the process of dynamic recrystallization. Development of crystallographic preferred orientation (CPO) of olivine was evaluated from two-dimensional X-ray diffraction patterns, and shear strain was measured from X-ray radiographs. The steady-state fabric strength of the A-type fabric was achieved within total shear strain of ? = 2. At strains higher than ? = 1, an increase in concentration of the [0 1 0] axes mainly contributes to an increase in fabric strength. At strains higher than ? = 2, the magnitude of VSH/VSV (i.e., ratio of horizontally and vertically polarized shear wave velocities) scarcely increased in most of the runs. The VSH/VSV of peridotite (70 vol.% olivine + 30 vol.% minor phases) having the steady-state A-type olivine fabric coincides with that of recent global one-dimensional models under the assumption of horizontal flow, suggesting that the seismic anisotropy observed in the shallow upper mantle is mostly explained by the development of A-type olivine fabric. Experimental results on the deformation of single-crystal olivine showed that the CPO of olivine is influenced by the initial orientation of the starting single crystal because strain is concentrated in the recrystallized areas and the relic of the starting single crystal remains. In the upper mantle, the old CPO of olivine developed in the past may affect the olivine CPO developed in the present.

  9. A High-load, High-temperature Deformation Apparatus For Volcanological Studies

    NASA Astrophysics Data System (ADS)

    Hess, K.; Dingwell, D. B.

    2004-12-01

    The need for an adequate understanding of the nature and extent of physico-chemical processes involved in explosive volcanism is considerable. In recent years much effort has been concentrated on rhyolitic melts under conditions relevant to explosive volcanism. Especially the description of single-phase rhyolitic melt properties such as the temperature, pressure and compositional dependence of viscosity has been greatly improved. Yet, modelling of the emplacement and eruption of silicic domes is still hampered by the lack of a sufficiently accurate rheological database for multi-phase lavas with crystals and vesicles and no simple expression can be used to describe their rheology. We have developed a unique high-load, high-temperature deformation apparatus for studying in situ the non-Newtonian flow behaviour of magmas. The apparatus accommodates samples that are up to 100 mm in diameter and 100 mm long, and can be used to run constant displacement rate and constant load experiments. The rig is ideal for volcanological studies because it uses experimental conditions that closely match those found in volcanic processes: temperature (25 to 1300 ), stress (0 to > 500 MPa), strain rates (10-6 to 10-2 s), and total strain (0 to 100%). The apparatus still has to be optimised, but we can already present some preliminary results. To study the flow behaviour of a reference melt, we performed a viscosity study at a constant temperature on a "NIST 710a" soda-lime composition. The sample was placed between the two pistons of the apparatus and heated up to the desired temperature (609 ) above the calorimetric glass transition temperature (550 ). After allowing the system to reach thermal equilibrium (6 hours) in a parallel plate type experiment, load was applied (10, 50, 100, 200, 250 kN), holding that load for several 10 seconds. For applied loads < 100 kN (which correspond to stresses < 80 MPa), the stress versus strain rate relationship always behaves linearly and the viscosity remains constant with time (Newtonian flow regime). If the applied load was > 200 kN (which corresponds to stresses > 160 MPa), the stress versus strain rate relationship curves and the apparent viscosity decrease with time (non-Newtonian flow regime). If the applied load is raised to 250 kN "hot" cracks are produced and the sample is partly fragmented. A major advance is, that we can use sample sizes in the range of several 105 mm3, which means we are able to measure natural samples that contain large phenocrysts in cm size, like the Unzen conduit material. Finally, with this facility, it will be possible to measure reliable temperature distributions due to viscous heating in situ during the deformation process, using several thermocouples inside the sample. Experiments on obsidian are underway.

  10. Similarity and scaling properties in dislocation microstructures generated during high-temperature load relaxation and creep of rock salt and San Carlos olivine single crystals

    NASA Astrophysics Data System (ADS)

    Plookphol, Thawatchai

    This work explores the physical basis for Hart's [1970] mechanical equation of state behavior in rock salt and olivine. Specifically, the experiments were designed to identify a possible microstructural basis for the scaling relation and the "hardness" parameter, sigma*, associated with each load relaxation curve, which Hart interpreted to represent constant "structure." They were also designed to examine the relationship between creep and load relaxation and the significance of steady-state, power-law creep within the context of the mechanical equation of state. Constant-stress creep, stress-change, and load-relaxation experiments were conducted on synthetic rock salt (NaCl) at 400C and 700C and on natural San Carlos (AZ) olivine ([Mg, Fe]2 SiO4) single crystals at 1500C and pO2 = 10-10 atm. The two minerals behaved very differently, with rock salt exhibiting classic mechanical-equation-of-state behavior and olivine, under the conditions studied, exhibiting almost no path effects. We found that in the creep of rock salt at constant stress, the material passes through a continuum of structural states during transient creep, each state represented by a constant sigma* curve measured using load-relaxation experiments. It was surmised that each load-relaxation curve corresponds to the behavior of the material at constant (or nearly constant) average subgrain diameter, and that subgrain size distributions are similar (or nearly similar) to each other. The hardness parameter is found to follow the relation sigma* ? 50Gb/DI where G is the shear modulus, b is the Burgers vector, and DI is the mean intercept diameter. In contrast, it was found that for olivine, load-relaxation data are equivalent to steady-state creep data. In olivine, as in rock salt, the density of mobile dislocations responds rapidly to changes in stress, but, unlike rock salt, subgrain formation in olivine is very slow or nonexistent under the conditions tested, resulting in the direct correspondence between creep and load relaxation.

  11. Dislocation-dynamics based crystal plasticity law for the low-and high-temperature deformation regimes of bcc crystal

    E-print Network

    Devincre, Benoit

    Dislocation-dynamics based crystal plasticity law for the low- and high-temperature deformation online 29 July 2013 Abstract Based on recent dislocation dynamics simulations investigations, a set of constitutive equations and model parameters for the descrip- tion of plasticity of body-centered cubic

  12. Quantum creep of ?-Sn in the normal and superconducting states. Influence of the NS transition on work hardening

    NASA Astrophysics Data System (ADS)

    Natsik, V. D.; Soldatov, V. P.; Ivanchenko, L. G.; Kirichenko, G. I.

    2006-12-01

    Previously we investigated the kinetics of transient logarithmic creep of ?-tin single crystals at very low temperatures 0.5K deformation in the normal (N) electronic state. In a continuation of that research, here we determine the boundary temperature Tg?1.3K separating the regions of thermally activated (T>Tg) and quantum (Tcreep, its quantum character in the region T temperature (TgS?TgN?1.3K ). Analysis of the curves of the logarithmic creep in the quantum region can yield empirical estimates for the work hardening coefficient ? of the samples. It is found to increase significantly at the NS transition: along the whole deformation curve the work hardening in the S state occurs more intensely, and, on the average, ?S?1.5?N. Such an effect has been observed previously in a study of the plasticity of a series of fcc metals by the method of active deformation at a constant rate (V. V. Pustovalov, I. N. Kuz'menko, N. V. Isaev, V. S. Fomenko, S. . Shumlin, Fiz. Nizk. Temp. 30, 109 (2004) [Low Temp. Phys. 30, 82 (2004)]). A comparison of the results of this study with previous results suggests that the increase in intensity of the work hardening at the superconducting transition is of a general nature for metallic superconductors and is manifested for other deformation regimes as well. The possible causes of the effect are discussed in the general conceptual framework of dislocation physics.

  13. Room Temperature Deformation Mechanisms of Alumina Particles Observed from In Situ Micro-compression and Atomistic Simulations

    NASA Astrophysics Data System (ADS)

    Sarobol, Pylin; Chandross, Michael; Carroll, Jay D.; Mook, William M.; Bufford, Daniel C.; Boyce, Brad L.; Hattar, Khalid; Kotula, Paul G.; Hall, Aaron C.

    2015-09-01

    Aerosol deposition (AD) is a solid-state deposition technology that has been developed to fabricate ceramic coatings nominally at room temperature. Sub-micron ceramic particles accelerated by pressurized gas impact, deform, and consolidate on substrates under vacuum. Ceramic particle consolidation in AD coatings is highly dependent on particle deformation and bonding; these behaviors are not well understood. In this work, atomistic simulations and in situ micro-compressions in the scanning electron microscope, and the transmission electron microscope (TEM) were utilized to investigate fundamental mechanisms responsible for plastic deformation/fracture of particles under applied compression. Results showed that highly defective micron-sized alumina particles, initially containing numerous dislocations or a grain boundary, exhibited no observable shape change before fracture/fragmentation. Simulations and experimental results indicated that particles containing a grain boundary only accommodate low strain energy per unit volume before crack nucleation and propagation. In contrast, nearly defect-free, sub-micron, single crystal alumina particles exhibited plastic deformation and fracture without fragmentation. Dislocation nucleation/motion, significant plastic deformation, and shape change were observed. Simulation and TEM in situ micro-compression results indicated that nearly defect-free particles accommodate high strain energy per unit volume associated with dislocation plasticity before fracture. The identified deformation mechanisms provide insight into feedstock design for AD.

  14. A Mechanism-Based Framework for the Numerical Analysis of Creep in Zircaloy-4

    E-print Network

    Thouless, Michael

    on the forms of the relationships between stress, temperature and strain rate. This identification allowed-developed. In this context, the framework is illustrated primarily by the use of steady-state creep models. #12; 3 in a continuum-level creep calculation. The mechanisms of steady-state creep that are valid when

  15. Assessment of Creep Capability of HSR-EPM Turbine Airfoil Alloys

    NASA Technical Reports Server (NTRS)

    MacKay, Rebecca A.; Garg, Anita; Ritzert, Frank J.; Locci, Ivan E.

    2007-01-01

    The High Speed Civil Transport (HSCT) mission of the High Speed Research-Enabling Propulsion Materials (HSR-EPM) Program represented a unique challenge for turbine airfoil materials because the highest operating temperatures occur during climb and supersonic cruise. The accumulated hot time of an HSCT engine before overhaul is many thousands of hours. This is significantly different from subsonic engines, where the maximum operating temperatures occur during takeoff and thrust reverse after landing, and the accumulated hot time before overhaul is about 300 hr. The goal of airfoil alloy development under the HSR-EPM Program was to develop an alloy with a 75 F increase in creep rupture capability over the average Rene N5/PWA 1484 baseline. Airfoil alloy development under the HSR-EPM Program pursued a path that led to evolutionary mechanical behavior improvements, resulting from increased amounts of high density, refractory metals. The purpose of the present paper is to describe the experimental work that was performed at NASA Glenn Research Center after the HSR-EPM Program ended. Emphasis will be placed on the creep behavior of coated specimens, as well as on the development and progression of phase instabilities during creep deformation. Mitigation techniques that were used to reduce phase instabilities are also discussed. Most of the work described in this report was performed at NASA Glenn during the years 2000 and 2001.

  16. Creep-Fatigue Behavior of Alloy 617 at 850C

    SciTech Connect

    Carroll, Laura

    2015-05-01

    Creep-fatigue deformation is expected to be a significant contributor to the potential factors that limit the useful life of the Intermediate Heat Exchanger (IHX) in the Very High Temperature Reactor (VHTR) nuclear system.[1] The IHX of a high temperature gas reactor will be subjected to a limited number of transient cycles due to start-up and shut-down operations imparting high local stresses on the component. This cycling introduces a creep-fatigue type of interaction as dwell times occur intermittently. The leading candidate alloy for the IHX is a nickel-base solid solution strengthened alloy, Alloy 617, which must safely operate near the expected reactor outlet temperature of up to 950 C.[1] This solid solution strengthened nickel-base alloy provides an interesting creep-fatigue deformation case study because it has characteristics of two different alloy systems for which the cyclic behavior has been extensively investigated. Compositionally, it resembles nickel-base superalloys, such as Waspalloy, IN100, and IN718, with the exception of its lower levels of Al. At temperatures above 800 C, the microstructure of Alloy 617, however, does not contain the ordered ? or ? phases. Thus microstructurally, it is more similar to an austenitic stainless steel, such as 316 or 304, or Alloy 800H comprised of a predominantly solid solution strengthened matrix phase with a dispersion of inter- and intragranular carbides. Previous studies of the creep-fatigue behavior of Alloy 617 at 950 C indicate that the fatigue life is reduced when a constant strain dwell is added at peak tensile strain.[2-5] This results from the combination of faster crack initiation occurring at surface-connected grain boundaries due to oxidation from the air environment along with faster, and intergranular, crack propagation resulting from the linking of extensive interior grain boundary cracking.[3] Saturation, defined as the point at which further increases in the strain-controlled hold time duration no longer decreases the cycle life, has been observed for Alloy 617 at 950 C at least to the investigated hold times[2,3], as illustrated through a plot of cycles to failure v. hold time in Figure 1. The 950 C creep-fatigue data set generated by Totemeier and Tian[5] at the 0.3% and 1.0% strain range is consistent in magnitude in terms of the cycles to failure data of that of Carroll et al., however, 0.3% strain range data did not exhibit saturation at hold times of up to 10 min. At 1.0% total strain, saturation in the number of cycles to failure was observed within the investigated peak tensile hold times of up to 10 min[5]. The data of Carroll et al.[2,3] in Figure 1 and Totemeier and Tian[5] is also consistent in magnitude with the data of Rao and coworkers[4] investigated at the 0.6% strain range. It should be noted that saturation in the number of cycles to failure is not present in the data published by Rao and coworkers[4] for tensile hold times of up to 120 min. The latter testing was in a simulated primary-circuit helium gas as opposed to air and a single data point is reported for the longer hold time conditions.

  17. Deformities in larvae and juvenile European lobster (Homarus gammarus) exposed to lower pH at two different temperatures

    NASA Astrophysics Data System (ADS)

    Agnalt, A.-L.; Grefsrud, E. S.; Farestveit, E.; Larsen, M.; Keulder, F.

    2013-12-01

    The ongoing warming and acidification of the world's oceans are expected to influence the marine ecosystems, including benthic marine resources. Ocean acidification may especially have an impact on calcifying organisms, and the European lobster (Homarus gammarus) is among those species at risk. A project was initiated in 2011 aiming to investigate long-term effects of ocean acidification on the early life-cycle of lobster under two temperatures. Larvae were exposed to pCO2 levels of ambient water (water intake at 90 m depth), medium 750 (pH = 7.79) and high 1200 ?atm pCO2 (pH = 7.62) at temperatures 10 and 18 C. The water parameters in ambient water did not stay stable and were very low towards the end of the experiment in the larval phase at 10 C,with pH between 7.83 and 7.90. At 18, pH in ambient treatment was even lower, between 7.76 and 7.83, i.e. close to medium pCO2 treatment. Long-term exposure lasted 5 months. At 18 C the development from stage 1 to 4 lasted 14 to 16 days, as predicted under optimal water conditions. Growth was very slow at 10 C and resulted in three larvae reaching stage 4 in high pCO2 treatment only. There were no clear effects of pCO2 treatment, on either carapace length or dry weight. However, deformities were observed in both larvae and juveniles. The proportion of larvae with deformities increased with increasing pCO2 exposure, independent of temperature. In the medium treatment about 23% were deformed, and in the high treatment about 43% were deformed. None of the larvae exposed to water of pH >7.9 developed deformities. Curled carapace was the most common deformity found in larvae raised in medium pCO2 treatment, irrespective of temperature, but damages in the tail fan occurred in addition to a bent rostrum. Curled carapace was the only deformity found in high pCO2 treatment at both temperatures. Occurrence of deformities after five months of exposure was 33 and 44% in juveniles raised in ambient and low pCO2 levels, respectively, and 21% in juveniles exposed to high pCO2. Deformed claws were most often found in ambient and medium treatment (56%, followed by stiff/twisted walking legs (39%) and puffy carapace (39%). In comparison, at high pCO2 levels 71% of the deformed juveniles had developed a puffy carapace. Overall, about half of the deformed juveniles from the ambient and medium pCO2 treatment displayed two or three different abnormalities; 70% had multiple deformities in the high pCO2 treatment. Some of the deformities in the juveniles may affect respiration (carapace), the ability to find food, or sexual partners (walking legs, claw and antenna), and ability to swim (tail-fan damages).

  18. Diffusion creep in the mantle may create and maintain anisotropy

    NASA Astrophysics Data System (ADS)

    Wheeler, John

    2014-05-01

    Diffusion creep is thought to play an important role in lower mantle deformation and hence must be understood in detail if Earth behaviour is to be explained. It is commonly claimed that diffusion creep gives rise to equant grain shapes and destroys any crystallographic preferred orientation (CPO), so all physical properties would be isotropic. Some experiments on olivine support the first assertion but other minerals, and polyphase rocks, commonly show inequant grain shapes in nature and experiment even when diffusion creep is thought to be a major contribution to strain. Numerical models allow rigorous exploration of the effects of deformation under conditions not easily reached in experiments. A numerical model named 'DiffForm' (Wheeler & Ford 2007) gives insight into how grain shapes and microstructures evolve during diffusion creep. Modelling shows that whilst grains may initially rotate in apparently chaotic fashion during diffusion creep, such rotations slow down as grains become inequant. Consequently, an initial CPO (formed, for example, by dislocation creep at higher strain rates) will be decreased in intensity but not destroyed. Seismic anisotropy will decrease but not disappear (Wheeler 2009). Diffusion creep is also predicted to have intense mechanical anisotropy. In simple models diffusion creep is controlled entirely by diffusion and sliding along grain boundaries; there is no crystallographic influence. An aggregate of equant grains must then be mechanically isotropic, but a model microstructure with inequant grains has marked mechanical anisotropy (Wheeler 2010) - an effect related to the fact that grain boundary sliding is an intrinsic part of diffusion creep. That work was based on a very simple microstructure with a single inequant grain shape but I present here new results showing that for more complicated microstructures, mechanical anisotropy is intense even for quite modest grain elongations. There will be feedback between strain and rheology which may control overall mantle strength. This theoretical development and some recent experiments indicate that diffusion creep is quite a different process to what was envisaged 10 years ago. This means that its relationship to seismic and mechanical anisotropy in the Earth requires reappraisal. .Wheeler, J. 2009. The preservation of seismic anisotropy in the Earth's mantle during diffusion creep. Geophysical Journal International 178, 1723-1732. Wheeler, J. 2010. Anisotropic rheology during grain boundary diffusion creep and its relation to grain rotation, grain boundary sliding and superplasticity. Philosophical Magazine 90, 2841-2864. Wheeler, J. & Ford, J. M. 2007. Diffusion Creep. In: Microdynamic simulation - From microprocess to patterns in rocks (edited by Bons, P. D., Jessell, M. & Koehn, D.). Lecture Notes in Earth Science. Springer, Berlin / Heidelberg, 161-169.

  19. A review of the deformation behavior of tungsten at temperatures less than 0.2 of the melting point /K/

    NASA Technical Reports Server (NTRS)

    Stephens, J. R.

    1974-01-01

    The deformation behavior of tungsten at temperatures below 0.2 times the absolute melting temperature is reviewed with primary emphasis on the temperature dependence of the yield stress and the ductile-brittle transition. It is concluded that a model based on the high Peierls stress of tungsten best accounts for the observed mechanical behavior at low temperatures. Recent research suggests an important role of electron concentration and bonding on the mechanical behavior of tungsten. Future research on tungsten should include studies to define more clearly the correlation between electron concentration and mechanical behavior of alloys of tungsten and other transition metal alloys.

  20. PHYSICAL REVIEW B 88, 184303 (2013) Irreversible thermodynamics of creep in crystalline solids

    E-print Network

    Mishin, Yuri

    2013-01-01

    in the material during the creep process. We derive a general expression for the entropy production rate and use number(s): 66.30.-h, 61.72.-y, 62.20.Hg, 65.40.-b I. INTRODUCTION When subject to a high homologous of materials ranging from metals and alloys to ceramics, polymers, and ice. While several creep deformation

  1. Long-term deformational simulation of PC bridges based on the thermo-hygro model of micro-pores in cementitious composites

    SciTech Connect

    Maekawa, Koichi Chijiwa, Nobuhiro; Ishida, Tetsuya

    2011-12-15

    Creep deflections that greatly exceed the predicted values by the linear creep law are being found in measurements on actual PC bridge viaducts. In this study, structural creep deformations were reproduced by using the multi-scale coupled thermo-hygro and mechanical modeling which enables to deal with an interaction of chemo-physical events of differing dimensions ranging from the kinematics of moisture in micro-pores to the macroscopic structural mechanics, and the effect of various factors was analytically investigated. The numerical analysis approximately reproduced the excessive deflection measured on an actual bridge viaduct. It was confirmed that the creep bending of the viaduct having the hollow cross-section varies significantly due to the ambient temperature, humidity and the structural specific surface area. The macroscopic structural responses in association with the thermodynamic state of moisture in the micro-pores are also discussed.

  2. Dislocation-accommodated grain boundary sliding as the major deformation mechanism of olivine in the Earth's upper mantle.

    PubMed

    Ohuchi, Tomohiro; Kawazoe, Takaaki; Higo, Yuji; Funakoshi, Ken-Ichi; Suzuki, Akio; Kikegawa, Takumi; Irifune, Tetsuo

    2015-10-01

    Understanding the deformation mechanisms of olivine is important for addressing the dynamic processes in Earth's upper mantle. It has been thought that dislocation creep is the dominant mechanism because of extrapolated laboratory data on the plasticity of olivine at pressures below 0.5 GPa. However, we found that dislocation-accommodated grain boundary sliding (DisGBS), rather than dislocation creep, dominates the deformation of olivine under middle and deep upper mantle conditions. We used a deformation-DIA apparatus combined with synchrotron in situ x-ray observations to study the plasticity of olivine aggregates at pressures up to 6.7 GPa (that is, ~200-km depth) and at temperatures between 1273 and 1473 K, which is equivalent to the conditions in the middle region of the upper mantle. The creep strength of olivine deforming by DisGBS is apparently less sensitive to pressure because of the competing pressure-hardening effect of the activation volume and pressure-softening effect of water fugacity. The estimated viscosity of olivine controlled by DisGBS is independent of depth and ranges from 10(19.6) to 10(20.7) Pas throughout the asthenospheric upper mantle with a representative water content (50 to 1000 parts per million H/Si), which is consistent with geophysical viscosity profiles. Because DisGBS is a grain size-sensitive creep mechanism, the evolution of the grain size of olivine is an important process controlling the dynamics of the upper mantle. PMID:26601281

  3. Dislocation-accommodated grain boundary sliding as the major deformation mechanism of olivine in the Earths upper mantle

    PubMed Central

    Ohuchi, Tomohiro; Kawazoe, Takaaki; Higo, Yuji; Funakoshi, Ken-ichi; Suzuki, Akio; Kikegawa, Takumi; Irifune, Tetsuo

    2015-01-01

    Understanding the deformation mechanisms of olivine is important for addressing the dynamic processes in Earths upper mantle. It has been thought that dislocation creep is the dominant mechanism because of extrapolated laboratory data on the plasticity of olivine at pressures below 0.5 GPa. However, we found that dislocation-accommodated grain boundary sliding (DisGBS), rather than dislocation creep, dominates the deformation of olivine under middle and deep upper mantle conditions. We used a deformation-DIA apparatus combined with synchrotron in situ x-ray observations to study the plasticity of olivine aggregates at pressures up to 6.7 GPa (that is, ~200-km depth) and at temperatures between 1273 and 1473 K, which is equivalent to the conditions in the middle region of the upper mantle. The creep strength of olivine deforming by DisGBS is apparently less sensitive to pressure because of the competing pressure-hardening effect of the activation volume and pressure-softening effect of water fugacity. The estimated viscosity of olivine controlled by DisGBS is independent of depth and ranges from 1019.6 to 1020.7 Pas throughout the asthenospheric upper mantle with a representative water content (50 to 1000 parts per million H/Si), which is consistent with geophysical viscosity profiles. Because DisGBS is a grain sizesensitive creep mechanism, the evolution of the grain size of olivine is an important process controlling the dynamics of the upper mantle. PMID:26601281

  4. Elevated Temperature Primary Load Design Method Using Pseudo Elastic-Perfectly Plastic Model

    SciTech Connect

    Carter, Peter; Sham, Sam; Jetter, Robert I

    2012-01-01

    A new primary load design method for elevated temperature service has been developed. Codification of the procedure in an ASME Boiler and Pressure Vessel Code, Section III Code Case is being pursued. The proposed primary load design method is intended to provide the same margins on creep rupture, yielding and creep deformation for a component or structure that are implicit in the allowable stress data. It provides a methodology that does not require stress classification and is also applicable to a full range of temperature above and below the creep regime. Use of elastic-perfectly plastic analysis based on allowable stress with corrections for constraint, steady state stress and creep ductility is described. This approach is intended to ensure that traditional primary stresses are the basis for design, taking into account ductility limits to stress re-distribution and multiaxial rupture criteria.

  5. Deformation Temperature, Kinematics, and Internal Strain during Emplacement of Greater Himalayan Rocks in North-Central and Northeastern Bhutan

    NASA Astrophysics Data System (ADS)

    Penfold, M. L.; Long, S. P.; Gordon, S. M.; Seward, G.; Agustsson, K. S.; Zeiger, K. J.

    2014-12-01

    Across the Himalayan orogen, high-grade Greater Himalayan (GH) rocks are juxtaposed between low-grade metasedimentary rocks, and the deformation mechanisms that led to their emplacement are debated. In this study, geologic mapping and microstructural analysis are utilized to understand the deformation conditions and exhumation path of GH rocks in northern Bhutan. Three north-south transects of GH rocks were mapped, corresponding to structural thicknesses of 11-15 km, and schist, paragneiss, and quartz veins were the main lithologies sampled and analyzed. Quantitative temperature estimates (~430C, 545C, 595C, and 630C) from quartz crystallographic preferred-orientation plot opening angles, collected from an electron backscatter diffraction detector on a scanning electron microscope, combined with semi-quantitative deformation temperature estimates obtained from cataloguing quartz recrystallization mechanisms in thin-section, show that GH rocks were initially deformed at temperatures between ~500-750C, and were later overprinted by a lower-temperature (~400-500C) recrystallization event. The higher-temperature event is interpreted to be associated with ca. 22-15 Ma displacement on the Main Central thrust, at or near peak metamorphic conditions. The lower-temperature overprint is interpreted to have occurred at a shallower point along the deformation path as GH rocks were exhumed, structurally-elevated, and passively translated southward, concurrent with ca. 18-10 Ma duplexing of Lesser Himalayan rocks. During the multiple stages of deformation, the GH rocks experienced a combination of pure- and simple-shear components of strain, as indicated by multiple outcrops that exhibit both top-to-the-north and top-to-the-south kinematic indicators. In addition, mean kinematic vorticity numbers, obtained from the oblique quartz shape-preferred orientation method, ranged from 0.61-0.94 (22-57% pure shear) during the higher-temperature event and 0.18-0.58 (60-88% pure shear) during the lower-temperature overprint. A significant pure-shear component observed on all three transects indicates that emplacement of GH rocks in Bhutan was accompanied by layer-normal flattening strain.