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. Low temperature creep of titanium alloys: Microstructure, deformation mechanisms and modeling

    Microsoft Academic Search

    Neeraj Srinivas Thirumalai

    2000-01-01

    Primary creep is the dominant mode of deformation during ambient temperature creep in titanium alloys. In this study the mechanisms causing this unusual creep behavior have been investigated both at the phenomenological and at the microstructural level. The main focus of this work is on a single phase a titanium alloy, Ti-6wt%Al(Ti-6Al). Creep behavior of Ti-6Al-2Sn-4Zr-2Mo(Ti-6242) was also investigated. Neutron

  3. Influence of the second phase on the room-temperature tensile and creep deformation mechanisms of ?-? titanium alloys, part II: Creep deformation

    Microsoft Academic Search

    A. Jaworski; Pa. S. Ankem

    2006-01-01

    This work focuses on the effect of the second phase on the ambient temperature creep deformation mechanisms of titanium alloys,\\u000a using Ti-6.0 wt pct Mn and Ti-8.1 wt pct V with Widmansttten microstructures as the model systems. In Part I it was observed\\u000a that the presence of a second phase can affect the tensile deformation behavior. Likewise, the creep deformation

  4. Deformation mechanism for high temperature creep of a directionally solidified nickel-base superalloy

    SciTech Connect

    Yuan, C. [Chinese Academy of Sciences, Shenyang (China)] [Chinese Academy of Sciences, Shenyang (China); [Northeastern Univ., Shenyang (China). School of Materials and Metallurgy; Guo, J.T.; Wang, S.H. [Chinese Academy of Sciences, Shenyang (China)] [Chinese Academy of Sciences, Shenyang (China); Yang, H.C. [Northeastern Univ., Shenyang (China). School of Materials and Metallurgy] [Northeastern Univ., Shenyang (China). School of Materials and Metallurgy

    1998-09-04

    Modern nickel-base superalloys, which contain a high volume fraction of hard cubical {gamma}{prime} precipitates embedded coherently in a softer {gamma} matrix, are used as turbine blade material due to their good resistance to creep deformation at high temperature. In this present study, the authors will analyze the relationship between the steady-state creep rate and the applied stress of DZ17G, a modern DS cast nickel-base superalloy used for producing turbine blades and vanes for aeroengine applications. On the basis of TEM observations and calculations of the threshold stress for different deformation mechanism, the authors finally propose the deformation mechanism for creep of DZ17G superalloy at high temperature.

  5. High temperature creep deformation of dispersion strengthened tungsten alloys for thermionic emitters

    SciTech Connect

    Ozaki, Y.; Gao, P.; Zee, R.H. (Materials Engineering, Auburn University, AL 36849 (United States))

    1993-01-10

    The mechanism for creep deformation in dispersion strengthened tungsten alloys was examined. The effects of three dispersoids were investigated: HfC, ZrC, and ThO[sub 2]. High temperature creep data (up to 2400 K) in these materials were analyzed based on a model that reflects the presence of dispersion carbide particles. The strengthened tungsten creeps in accordance with a dislocation process with the dispersed particles imposing a back stress. Results obtained from this model are in accord with other studies of similar materials systems. Based on this effort, critical controlling parameters were identified. Lifetime predictions were made for conditions appropriate for thermionic emitters using different creep models. It is evident that the proper selection of the model is critical to the accuracy of such predictions.

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

    SciTech Connect

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

    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.

  7. Strengthening in MULTIPHASE(MP35N) alloy: Part II. elevated temperature tensile and creep deformation

    NASA Astrophysics Data System (ADS)

    Singh, Rishi Pal; Doherty, Roger D.

    1992-01-01

    The strengthening mechanisms in the cobalt alloy MP35N have been investigated by tensile and creep deformation at elevated temperatures and by transmission electron microscopy (TEM) of the deformed alloy. A high ultimate tensile strength (UTS) of 800 to 900 MPa was maintained at all test temperatures from 300 to 873 K due to the maintenance of high strain hardening. On straining, there was the usual initial fall of the strain-hardening rate with stress, but above a critical stress of about 500 MPa, the strain-hardening rate stopped falling and was held almost constant at about 2000 MPa. At 973 and 1073 K, this high strain-hardening rate suddenly ceased during the test, while at 1123 K, negligible strain hardening was seen. At temperatures between 673 and 1073 K, tensile load drops were seen whose magnitude increased with strain, and thus stress, at a fixed temperature. The load drops also increased with increased temperature. How-ever, in conditions when the strain-hardening rate fell to a low value, the load drops ceased. In a tensile test in which small increments of strain were applied as the temperature was increased in 10 K intervals, a steadily rising flow stress with temperature was seen up to a critical temperature of 1073 K, beyond which the flow stress fell and the load drops also ceased. In conditions where the high rate of strain hardening was found, fine platelike structures were seen by transmission electron microscopy (TEM) to form on {111} planes in the face-centered cubic (fcc) matrix. Diffraction evidence showed that these were faulted hexagonal close-packed (hep) plates. Creep tests carried out above and below the critical temperature of 1073 K showed very different behavior. At 1098 K, the sample showed conventional creep behavior, while at a temperature of 973 K, the material showed sigmoidal creep strain rate. At low strains, up to a strain of about 0.02, there was an initial steady-state creep rate. The creep strain rate then increased and fell back to a second steady-state creep rate. During the accelerated creep stage, hexagonal plates were again seen to form. Strain-induced martensite forming at temperatures up to and including 1073 K, but not at higher temperatures, appears to account satisfactorily for all of the behavior seen in this study. It is proposed that the hexagonal plates form martensitically at high speed, but as proposed in Part I,[1] solute partitioning occurs between the closely spaced fcc and hcp phases. At 1025 and 1073 K, the end of both the load drops and the high strain hardening during a tensile test may be explained by the stabilization of the remaining fcc matrix by loss of hexagonal phase stabilizing solute. The critical temperature of approximately 1073 K seen in this study is close to the critical softening temperature of 1083 K, above which recrystallization of cold-worked MP35N occurs readily (Part I[1])- The critical temperature is proposed to be close to the transus temperature, above which single-phase fcc is the stable structure of MP35N.

  8. 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.

  9. Effect of microstructure on the room temperature tensile and creep deformation mechanisms of alpha-beta titanium alloys

    Microsoft Academic Search

    Allan Wayne Jaworski Jr.

    2005-01-01

    Two-phase alpha-beta titanium alloys are used in many applications because of their high specific strength, corrosion resistance, processability, and biocompatibility. The room temperature tensile and creep deformation mechanisms of alpha-beta alloys must be understood in order to design alloys with desired properties and improved creep resistance. There is a lack of understanding in this regard. The aim of this investigation

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

    Microsoft Academic Search

    Horst Biermann; Marcus Strehler; Haël Mughrabi

    1996-01-01

    High-temperature X-ray line profile measurements were performed to maximal temperatures of 1050 ?C on samples of the nickel-base\\u000a superalloy SRR 99. The samples with rod axes near the [001] direction were investigated in the initially undeformed state\\u000a and after creep deformation at different temperatures and stresses. For the measurements of the (002) and (020) line profiles,\\u000a a special X-ray double

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

    Microsoft Academic Search

    A. Jaworski; S. Ankem

    2006-01-01

    The effects of alpha and beta phase interactions on the room-temperature tensile and creep deformation behavior of alpha + beta titanium alloys with Widmanstätten 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 alpha phase is

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

    Microsoft Academic Search

    A. Jaworski; S. Ankem

    2006-01-01

    The effects of ? and ? phase interactions on the room-temperature tensile and creep deformation behavior of ? + ? titanium\\u000a alloys with Widmanstätten microstructures were studied using Ti-6.0 wt pct Mn and Ti-8.1 wt pct V as the model two-phase alloy\\u000a systems. This article, Part I, deals with tensile deformation. It was found that when the ? phase is

  13. The effect of atmosphere on the creep deformation of a particle reinforced aluminum alloy matrix composites

    Microsoft Academic Search

    Norio Matsuda; Koichi Kikuchi; Satoshi Ishikawa; Mitsuru Saitoh

    2004-01-01

    Creep behavior of the 6061 aluminum alloy matrix composite reinforced by 10vol.% of alumina particles has been investigated at temperatures from 573 to 773K in air and Ar atmospheres. Creep curves, stress dependence of the minimum creep rate, microstructures after creep deformation and the effect of the atmospheres on the creep behavior were examined. Deformation around grain boundaries was estimated

  14. High temperature creep deformation of directionally solidified Al 2O 3\\/Er 3Al 5O 12

    Microsoft Academic Search

    J. Martinez Fernandez; A. Sayir; S. C. Farmer

    2003-01-01

    The microstructure of directionally solidified Al2O3\\/Er3Al5O12 (19.5 mol% Er2O3) is analyzed and high temperature creep deformation studied using fibers in tension between 1400° C and 1550° C. The directionally solidified Al2O3\\/Er3Al5O12 system is an in situ composite and has a fine eutectic- microstructure with sub-micron phase spacing. The microstructure is elongated in the direction of growth. Transmission electron microscopy observations

  15. 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.

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

    NASA Astrophysics Data System (ADS)

    Deutchman, Hallee Zox

    Polycrystalline Ni-base superalloys are used as turbine disks in the hot section in jet engines, placing them in a high temperature and stress environment. As operating temperatures increase in search of better fuel efficiency, it becomes important to understand how these higher temperatures are affecting mechanical behavior and active deformation mechanisms in the substructure. Not only are operating temperatures increasing, but there is a drive to design next generation alloys in shorter time periods using predictive modeling capabilities. This dissertation focuses on mechanical behavior and active deformation mechanisms found in two different advanced polycrystalline alloy systems, information which will then be used to build advanced predictive models to design the next generation of alloys. The first part of this dissertation discusses the creep behavior and identifying active deformation mechanisms in an advanced polycrystalline Ni-based superalloy (ME3) that is currently in operation, but at higher temperatures and stresses than are experienced in current engines. Monotonic creep tests were run at 700°C and between 655-793MPa at 34MPa increments, on two microstructures (called M1 and M2) produced by different heat treatments. All tests were crept to 0.5% plastic strain. Transient temperature and transient stress tests were used determine activation energy and stress exponents of the M1 microstructure. Constant strain rate tests (at 10-4s-1) were performed on both microstructures as well. Following creep testing, both M1 and M2 microstructures were fully characterized using Scanning Electron Microscopy (SEM) for basic microstructure information, and Scanning Transmission Electron Microscopy (STEM) to determine active deformation mechanism. It was found that in the M1 microstructure, reorder mediated activity (such as discontinuous faulting and microtwinning) is dominant at low stresses (655-724 MPa). Dislocations in the gamma matrix, and overall planar 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 700°C/690MPa, 760°C/490MPa, and 815°C/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).

  17. Creep deformation of dispersion-strengthened copper

    SciTech Connect

    Broyles, S.E.; Anderson, K.R.; Groza, J.R.; Gibeling, J.C. [Univ. of California, Davis, CA (United States)

    1996-05-01

    The creep behavior of an internally oxidized, Al{sub 2}O{sub 3} dispersion-strengthened copper alloy, GlidCop Al-15, has been investigated in the temperature range of 745 to 994 K. The results exhibit a high apparent stress exponent (10 to 21) and a high apparent activation energy for creep (253.3 kJ/mole). To describe the creep behavior of this alloy, the Roesler-Arzt model for attractive particle/dislocation interaction is applied. The results are in good agreement with the model when account is taken of the effects of the fine elongated grains and heavily dislocated structures revealed through transmission electron microscopy. The analysis demonstrates that the dislocation/particle interaction is of moderate strength in this alloy, consistent with the observation that the particle/matrix interface is partially coherent. In addition, the analysis reveals that the choice of mechanism and corresponding activation energy for vacancy diffusion has only a small effect on the calculated model parameters. It is argued that the weak dependence of subgrain size on stress demonstrates that creep deformation is particle controlled, rather than subgrain size controlled. In addition, the poorly developed subgrain structure and high dislocation densities are attributed to the presence of the fine oxide particles. Finally, the dependence of rupture time on stress is shown to be consistent with a description of creep fracture based on diffusive cavity growth with continuous nucleation.

  18. Estimating creep deformation of glass-fiber-reinforced polycarbonate

    NASA Astrophysics Data System (ADS)

    Sakai, Takenobu; Somiya, Satoshi

    2006-09-01

    Thermoplastic resin and fiber-reinforced thermo-plastics (FRTPs) were used without post-cure treatment as “molded material.” For such materials, creep behavior and physical aging occur simultaneously. This study examined the creep behavior of polycarbonate (PC) and glass-fiber-reinforced polycarbonate (GFRPC) injection moldings, including the effect of physical aging and fiber content, and determined that the time temperature superposition principle could be applied to the creep behavior for different fiber contents. The effects of physical aging on creep behavior were evaluated quantitatively on pure resin and with various fiber contents without heat treatment. We found that the effect of physical aging could be evaluated with the proposed factor, “aging shift rate.” To discuss the linearity of viscoelasticity in FRTPs, this study used two shift factors: time and modulus shift factors. The fiber content affected creep behavior by both retarding and restraining it through changing the elastic modulus. This was shown by generating a grand master curve of creep compliance, which included the effects of time, temperature, and fiber content. Using the grand master curve of creep compliance and shift factors, it was possible to estimate the creep deformation of molded materials under varying conditions and fiber contents. The estimated creep deformation gave a very good fit to the experimental creep deformation.

  19. Creep deformation in magnesium aluminum calcium-based alloys

    Microsoft Academic Search

    Jessica Renae Terbush

    2010-01-01

    Magnesium alloys, with a lower density than steel or aluminum, have the potential to reduce the mass of automotive components. However, new alloys with improved creep resistance must be developed before Mg can be used for high temperature powertrain applications. Limiting the development of these alloys is the lack of fundamental knowledge of creep deformation in Mg alloys. This dissertation

  20. 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.

  1. Spatial fluctuations in transient creep deformation

    NASA Astrophysics Data System (ADS)

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

    2011-07-01

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

  2. Fluctuations and Scaling in Creep Deformation

    NASA Astrophysics Data System (ADS)

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

    2010-09-01

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

  3. Modeling of high homologous temperature deformation behavior using the viscoplasticity theory based on overstress (VBO). Part 1: Creep and tensile behavior

    SciTech Connect

    Tachibana, Y.; Krempl, E. [Rensselaer Polytechnic Inst., Troy, NY (United States). Mechanics of Materials Lab.

    1995-10-01

    The viscoplasticity theory based on overstress (VBO) is a state variable theory without a yield surface and without loading/unloading conditions. It contains two tensor valued state variables, the equilibrium (back) stress and the kinematic stress that is a repository for work hardening (softening). The scalar valued isotropic or time (rate)-independent stress models cyclic hardening (softening). For application to high homologous temperature, the effects of diffusion which counteracts the hardening of inelastic deformation has to be accounted for. Recovery of state terms are introduced in the growth laws for the state variables. A high homologous temperature VBO model is introduced and applied to the creep and tensile tests of Alloy 800 H between 750 C and 1,050 C. Primary, secondary and tertiary creep as well as tensile behavior were well reproduced. It is shown that the transition to fluid state can be modeled with VBO.

  4. On the role of matrix creep in the high temperature deformation of short fiber reinforced aluminum alloys

    Microsoft Academic Search

    G. Kausträter; B. Skrotzki; G. Eggeler

    2001-01-01

    The present study investigates creep of short fiber reinforced metal matrix composites (MMCs) which were produced by squeeze casting. Two types of aluminum alloys were used as matrix materials with class I (alloy type) and class II (metal type) creep behavior. The creep behavior of the resulting MMCs is similar both in terms of the shape of the individual creep

  5. Mechanisms of primary creep in ?\\/? titanium alloys at lower temperatures

    Microsoft Academic Search

    S. Suri; T. Neeraj; G. S. Daehn; D.-H. Hou; J. M. Scott; R. W. Hayes; M. J. Mills

    1997-01-01

    Creep occurs in two phase ?\\/? Ti alloys at room temperature and at stresses below the yield strength. In polycrystalline Ti alloys, creep strain exhibits two distinct power-law regimes, an initial higher exponent which exhausts to a constant value at longer times. However, the exhaustion is much more gradual than that for other metals at lower homologous temperatures. The deformation

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

    SciTech Connect

    K. Linga (KL) 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

  7. Creep of pure aluminum at cryogenic temperatures 

    E-print Network

    McDonald, Lacy Clark

    1989-01-01

    Conducted on OFHC Copper . B. Equipment Used in Successful Long-term Creep Testing. . . C. Creep Mechanisms at Cryogenic Temperatures. . . . . . . . . . 8 8 11 III PRIMARY RESEARCH OBJECTIVE . . 14 IV EXPERIMENTAL SETUP AND PROCEDURES . . 15 A. Load... aluminum and NbTi. 2 Constant load creep curve showing three distinct regions. 3 Creep curves for OPHC copper taken over 200 hours. 10 4 Photograph of creep frame used in cryogenic creep tests. . . . . . . . . 5 Photograph of top of creep frame showing...

  8. Creep Deformation of Dispersion-Strengthened Copper

    Microsoft Academic Search

    S. E. Broyles; K. R. Anderson; J. R. Groza; J. C. Gibeling

    1996-01-01

    The creep behavior of an internally oxidized, A12O3 dispersion-strengthened copper alloy, GlidCop Al-15, has been investigated in the temperature range of 745 to 994 K. The\\u000a results exhibit a high apparent stress exponent (10 to 21) and a high apparent activation energy for creep (253.3 kJ\\/mole).\\u000a To describe the creep behavior of this alloy, the Rösler-Arzt model for attractive particle\\/dislocation

  9. High-temperature creep of forsterite single crystals

    Microsoft Academic Search

    Michel Darot; Yves Gueguen

    1981-01-01

    Creep of forsterite single crystals has been studied with respect to the orientation of the differential stress. Three orientations have been investigated: [110]c, [101]c, and [011]c. Specimens were deformed at high temperature (T?1400°C) and moderate stresses (5 < sigma<110 MPa) in a load creep apparatus at room pressure and under controlled atmosphere. Assuming Assuming, that the creep law has the

  10. Creep deformation mechanisms in high-pressure die-cast magnesium-aluminum-base alloys

    Microsoft Academic Search

    W. Blum; Y. J. Li; X. H. Zeng; P. Zhang; B. von Großmann; C. Haberling

    2005-01-01

    Creep of die-cast Mg alloys is described as an integral part of their plastic deformation behavior in terms of stress-strain-rate-strain\\u000a relations. Creep tests yield information on yield stress, work hardening, maximum deformation resistance (minimum creep rate),\\u000a and work softening. Testing in compression avoids influences by fracture. Data on the alloy AJ52 (5Al, 2Sr) in the temperature\\u000a range between 135 °C

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

    NASA Astrophysics Data System (ADS)

    Benz, Julian K.; Carroll, Laura J.; Wright, Jill K.; Wright, Richard N.; Lillo, Thomas M.

    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 ?' 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 ?' precipitates, respectively. The ?' 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 ?' precipitate dislocation bypass, suggests that the climb of dislocations around the ?' 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 ?' precipitates.

  12. High temperature impression creep testing of weldments

    Microsoft Academic Search

    W. S. Gibbs; D. K. Matlock; D. L. Olson; S. H. Wang

    1985-01-01

    The impression creep test technique, a modified hot hardness test in which the time dependence of the indentor displacement correlates directly to creep properties, has been utilized to measure the localized creep properties across welded joints. High temperature creep data, as a function of position, with respect to the fusion line, were measured on an autogeneous GTA aluminum weld and

  13. Deformation and Fracture of Alumina Joints in Bending Creep

    NASA Astrophysics Data System (ADS)

    Motoie, Katsuhiko; Sasaki, Kazunori; Kawasaki, Tadashi

    Bending creep tests were conducted on alumina-alumina butt joints at temperatures of 788-888 K. The lifetimes in three-point bending tests under constant loads were measured and the specimens tested were investigated using scanning electron microscope. From the elastic stress-distribution at the joining layer calculated using the finite element method, it was confirmed that the thin metal film in the joining layer is under the conditions of triaxial tension and the hydrostatic tensile stress. The results of SEM observation of creep fractured surfaces showed numerous small and large cavities in the tension side of the joining layer. Under the assumption that the mechanism of creep deformation and fracture for the thin metal film in the joining layer were the nucleation, growth and aggregation of void with the aid of the hydrostatic tensile stress component, the lifetimes in creep bending test were predicted. Time-dependent change of stress distribution related to initial outer fiber stress in bending has been calculated with formulas based on linear elastic beam theory. Predicted lifetimes are in good agreement with the experimentally obtained lifetimes. The neutral-axis position measured from the photographs of the fracture surfaces can be explained by the predicted stress distribution in creep bending tests.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  15. Creep rupture curve for simultaneous creep deformation and degradation of geosynthetic reinforcement

    Microsoft Academic Search

    W. Kongkitkul; F. Tatsuoka; D. Hirakawa

    2007-01-01

    The viscous property of polymer geosynthetic reinforcement, which causes creep deformation, is first summarised. The creep deformation and associated creep rupture characteristics, when subjected to long-term sustained loading under the following three conditions, are numerically simulated based on a non-linear three-component rheology model: (a) the load- strain behaviour is always free from material degradation; (b) the load-strain behaviour exhibits simultaneous

  16. Couple effect between creep and plasticity of type 316 stainless steel at elevated temperature

    SciTech Connect

    Kawai, M.; Ohashi, Y.

    1987-01-01

    Interaction between creep and plastic strains is discussed for metallic materials at elevated temperature. We first estimate qualitatively an applicability of representative unified constitutive equations to combined creep and plastic deformations. Then, some actual creep-plasticity interaction of type 316 stainless steel is shown in comparison with predicted results.

  17. 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.

  18. 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.

  19. Finite Element Analysis of Plastic Deformation During Impression Creep

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  20. Room-temperature creep of tantalum tritides

    SciTech Connect

    Schober, T.; Trinkaus, H. (Institut fuer Festkoerperforschung, Forschungszentrum Juelich, 5170 Juelich, Federal Republic of Germany (DE))

    1990-06-15

    We report on long-term creep experiments on dilute tantalum tritides at room temperature. Significant deviations of the recorded strain rates from isotropic swelling are found above approximately 30 MPa. We attribute this room-temperature creep to a stress-induced preferential dislocation loop punching by bubbles in crystallographic directions close the stress axis. Quantitative estimates show that this mechanism can indeed account for the observed creep rates.

  1. On the creep deformation of nickel foams under compression

    NASA Astrophysics Data System (ADS)

    Burteau, Anthony; Bartout, Jean-Dominique; Bienvenu, Yves; Forest, Samuel

    2014-10-01

    A finite-element computational strategy is developed to study the viscoplastic deformation mechanisms at work in a nickel foam sample under compression creep. The constitutive law for pure nickel accounts for both diffusional and dislocation creep mechanisms. The finite-element results show the competition between both mechanisms due to the strong heterogeneity of the stress distribution in the foam. The initiation of the viscoplastic buckling phenomenon leading to cell crushing in tertiary creep is illustrated. The overall model prediction is compared to the results of compression creep tests performed in vacuo at 900 °C. xml:lang="fr"

  2. 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.

  3. Experimental deformation of fine-grained anhydrite: Evidence for dislocation and diffusion creep

    Microsoft Academic Search

    Lisa N. Dell'Angelo; David L. Olgaard

    1995-01-01

    Deformation experiments on two fine-grained anhydrite aggregates have revealed two high-temperature flow regimes: (1) twinning and dislocation creep at high stresses (sigma), and (2) diffusion creep accompanied by grain boundary sliding at low stresses. Each regime is characterized by a power law constitutive equation, diagnostic microstructures, and crystallographic preferred orientations (CPO). Experiments were performed at 400°-800°C, strain rates of 10-3-10-6

  4. Plastic deformation macrolocalization during serrated creep of an aluminum-magnesium Al-6 wt % Mg alloy

    NASA Astrophysics Data System (ADS)

    Shibkov, A. A.; Zolotov, A. E.; Zheltov, M. A.; Denisov, A. A.; Gasanov, M. F.

    2014-04-01

    The nonlinear dynamics of the space-time structure of macrolocalized deformation is studied by a set of high-speed in situ methods under the conditions of serrated creep in an aluminum-magnesium Al-6 wt % Mg alloy at room temperature. Macroscopic deformation jumps with an amplitude of several percent are detected in the creep curve of this alloy. It is found that a complex space-time structure of macrolocalized deformation bands moving in a correlated manner forms spontaneously in the material during the development of a deformation jump. The difference between the observed picture of deformation bands and the well-known Portevin-Le Chatelier classification of deformation bands is discussed.

  5. Creep behaviors of highly pure aluminum at lower temperatures

    Microsoft Academic Search

    Keisuke Ishikawa; Hiroshi Okuda; Yasuo Kobayashi

    1997-01-01

    We have carried out experiments on the creep behaviors of pure aluminums at lower temperatures from a phenomenological viewpoint. The creep curves are classified into three regions; the transient, steady-state and terminal ones. The creep curve changes from a logarithmic to a constant strain rate curve at a higher applied stress. The creep curves yield a constant creep rate for

  6. Creep in pure single and polycrystalline aluminum at very low stresses and high temperatures: An evaluation of Harper-Dorn creep

    Microsoft Academic Search

    Praveen Kumar

    2007-01-01

    Harper-Dorn creep was proposed for materials with large grain size deforming at very low stresses (sigma\\/G ˜ 10-6 where sigma is the applied stress and G is the shear modulus) and high temperatures (~ 0.95--0.99 Tm, where Tm is the absolute melting temperature). Recently, this creep mechanism has become controversial and several other creep mechanisms, such as 5-power law and

  7. Improvement of creep rupture life by high temperature pre-creep in magnesium–aluminum binary solid solutions

    Microsoft Academic Search

    Hiroyuki Sato; Kota Sawada; Kouichi Maruyama; Hiroshi Oikawa

    2001-01-01

    Effects of high-temperature pre-creep on creep life in magnesium–aluminum solution hardened alloys have been investigated. Creep life, at 0.55Tm (Tm is the absolute melting temperature) are drastically improved by pre-creep treatment, which is given at higher temperature, 0.7Tm. The samples show almost the same minimum creep rate, although creep rate in tertiary creep is affected by the pre-creep treatment. Improvement

  8. Interactive Effect of Stress and Temperature on Creep of PFM Alloys

    Microsoft Academic Search

    K. J. Anusavice; C. Shen; D. Hashinger; S. W. Twiggs

    1985-01-01

    The creep rates of six alloys for porcelain-fused-to-metal (PFM) restorations were determined as a function of flexural stress and temperature. Although two Pd-Cu alloys demonstrated excellent resistance to creep at low-stress, high-temperature conditions, they were especially susceptible to deformation at high stresses and temperatures near the glass transition temperature of dental porcelains. In comparison, a Ni-Cr alloy and a Pd-Co

  9. 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.

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

    NASA Astrophysics Data System (ADS)

    Birger, Boris I.

    2013-11-01

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

  11. High temperature creep-fatigue design

    Microsoft Academic Search

    A.-A. F. Tavassoli; B. Fournier; M. Sauzay

    2010-01-01

    Generation IV fission and future fusion reactors envisage development of more efficient high temperature concepts where materials\\u000a performances are key to their success. This paper examines different types of high temperature creep-fatigue interactions\\u000a and their implications on design rules for the structural materials retained in both programmes. More precisely, the paper\\u000a examines current status of design rules for the stainless

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

    SciTech Connect

    Tribula, D.

    1990-06-02

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

  14. 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. Deformation of high-temperature superconductors

    SciTech Connect

    Goretta, K.C.; Routbort, J.L.; Miller, D.J.; Chen, N. [Argonne National Lab., IL (United States); Dominguez-Rodriguez, A.; Jimenez-Melendo, M.; De Arellano-Lopez, A.R. [Universidad of Sevilla (Spain). Departamento di Fisica de la Materia Condensada

    1994-08-01

    Of the many families of high-temperature superconductors, only the properties of those discovered prior to 1989 - Y-Ba-Cu-O, Tl-Ba(Sr)-Ca-Cu-O, and Bi(Pb)-Sr-Ca-Cu-O - have been studied extensively. Deformation tests have been performed on YBa{sub 2}Cu{sub 3}O{sub x} (Y-123), YBa{sub 2}Cu{sub 4}O{sub x} (Y-124), TlBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} (Bi-2223). The tests have revealed that plasticity is generally limited in these compounds and that the rate-controlling diffusional kinetics for creep are very slow. Nevertheless, hot forming has proved to be quite successful for fabrication of bulk high-temperature superconductors, so long as deformation rates are low or large hydrostatic stresses are applied. Steady-state creep data have proved to be useful in designing optimal heat treatments for superconductors and in support of more-fundamental diffusion experiments. The high-temperature superconductors are highly complex oxides, and it is a challenge to understand their deformation responses. In this paper, results of interest and operant creep mechanisms will be reviewed.

  16. 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. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Engineering Science and Mechanics

    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.

  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. High temperature creep resistant austenitic alloy

    DOEpatents

    Maziasz, Philip J. (Oak Ridge, TN); Swindeman, Robert W. (Oak Ridge, TN); Goodwin, Gene M. (Lenoir City, TN)

    1989-01-01

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

  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. Concrete creep at transient temperature: constitutive law and mechanism

    SciTech Connect

    Chern, J.C.; Bazant, Z.P.; Marchertas, A.H.

    1985-01-01

    A constitutive law which describes the transient thermal creep of concrete is presented. Moisture and temperature are two major parameters in this constitutive law. Aside from load, creep, cracking, and thermal (shrinkage) strains, stress-induced hygrothermal strains are also included in the analysis. The theory agrees with most types of test data which include basic creep, thermal expansion, shrinkage, swelling, creep at cyclic heating or drying, and creep at heating under compression or bending. Examples are given to demonstrate agreement between the theory and the experimental data. 15 refs., 6 figs.

  1. High temperature creep strength of second phase particle strengthened tungsten alloy

    SciTech Connect

    Park, J.J. [Los Alamos National Lab., NM (United States). Reactor Design and Analytic Group; Jacobson, D.L. [Arizona State Univ., Tempe, AZ (United States). Dept. of Chemical, Bio, and Materials Engineering

    1994-12-31

    Space nuclear power systems that utilize thermionic energy conversion are currently being investigated. One of the primary life limiting factors for space nuclear thermionic power systems is emitter deformation resulting from fuel swelling. Improving the creep properties of the emitter can thus increase the performance and lifetime of thermionic power systems. Tungsten base alloys have great potential for improving thermionic emitter performance because of their high temperature creep strength. The high temperature creep behavior of tungsten-4w/o rhenium-0.32w/o hafnium carbide (W-4Re-0.32HfC) was evaluated at temperature ranges of 2,200 to 2,400 K and stress ranges of 40 to 70 MPa in a vacuum better than 1.33 {times} 10{sup {minus}6} MPa (1.0 {times} 10{sup {minus}8} torr). The stress exponent for creep was estimated to be 5.2, and the activation energy for creep was estimated to be 142 Kcal/mol. The temperature compensated creep rate of W-4Re-0.32HfC was approximately two orders of magnitude lower than that of W, and one order of magnitude lower than that of W-5Re. Transmission electron microscopy (TEM) study revealed that the high creep strength of this alloy was associated with (a) finely dispersed submicron-size HfC particles that retard dislocation movements and (b) with subgrains containing dislocation networks.

  2. Deformation of nonfired refractories based on phosphate binders. 6. Deformation under heating and creep in corundum composites

    Microsoft Academic Search

    V. S. Bakunov; U. Sh. Shayakhmetov

    2007-01-01

    The results of studying heating deformation and creep are described for two systems: electrocorundum — ?-Al2O3 — phosphate binder and electrocorundum — pyrophyllite — phosphate binder. It is shown that composites with H3PO4 experience less deformation than composites with the alumochromium-phosphate binder, whereas using pyrophyllite instead of\\u000a aluminum oxide increases creep deformation due to the presence of the liquid phase

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  4. Creep measuring device for low melting point metals 

    E-print Network

    Portal, Marc-Emmanuel Gilbert

    1987-01-01

    OF CONTENTS CHAPTER Page I INTRODUCTION II THEORY A. Introduction to creep 1. Equations of creep 2. Experimental tests B. Mechanisms of deformation 1. Deformation characteristics 2. Creep as a thermally activated process 3. Dei'orrnation I...' or temperature variations 9 9 17 20 III PREVIOUS INVESTIGATIONS 22 A. Models for creep 1. Dislocation creep 2. Diffusion creep 3. Deformation maps B. Studies of lov- melting point metals 1. Revievr of properties 2. Lead studies 22 22 2I 29 30 30...

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

    E-print Network

    Suresh, Subra

    - inant deformation mode in metallic materials when the homologous temperature, TH = T/Tm, exceeds 0.4 [1 deformation over a wide range of stress and temperature. Numerical analyses revealed that, when evaluating A solder material normally has a relatively low melting temperature, Tm. Creep deformation is the dom

  6. Effect of dynamic plastic deformation on the fluctuation stage of creep in single-crystal ?-tin at 1.6 K

    NASA Astrophysics Data System (ADS)

    Kyrichenko, G. I.; Soldatov, V. P.

    2014-08-01

    Plastic deformation is studied in single-crystal ?-tin oriented for plastic slip in the (100) <010> system. Cases are examined in which the logarithmic low-temperature creep curves are preceded by dynamic movement of dislocations. For this purpose an attachment was developed for the deformation machine that made it possible to change the external load in a standard way over identical times on the order of 0.1 s. A computer was used to record the creep process with a time resolution of 0.04 s. The logarithmic creep coefficient ? is found to decrease dramatically when the preceding dynamic component of the deformation increment is increased. Thus, correct study of low-temperature logarithmic creep and its mechanisms requires a correct choice of the experimental conditions that excludes the dynamic stage when possible.

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  8. High-temperature deformation of dry diabase with application to tectonics on Venus

    Microsoft Academic Search

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

    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

  9. 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.

  10. 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 950°C 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 1050°C 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.

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

    E-print Network

    Cambridge, University of

    the yield strength as measured in a tensile test, and yet, creep causes permanent deformation. Materials of a stress is often characterised using a tensile test, which is in generally conducted under conditions

  12. Local TimeTemperature-dependent Deformation of a Woven Composite

    E-print Network

    Sottos, Nancy R.

    ­temperature- dependent response, Moiré interferometry, creep and stress relaxation, multilayer circuit boards, textile are measured via moiré interferometry. Measured displacement fields reveal the influence of fabric architecture on woven composite response. The deformation fields in the plane of the composite for loading along both

  13. Time temperature-stress dependence of boron fiber deformation

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1976-01-01

    Flexural stress relaxation (FSR) and flexural internal friction (FIF) techniques were employed to measure the time-dependent deformation of boron fibers from -190 to 800 C. The principal specimens were 203 micrometers diameter fibers commercially produced by chemical vapor deposition (CVD) on a 13 micrometer tungsten substrate. The observation of complete creep strain recovery with time and temperature indicated that CVD boron fibers deform flexurally as anelastic solids with no plastic component.

  14. High temperature creep of refractory bricks. Final report

    SciTech Connect

    McGee, T.D. [Ames Lab., IA (United States)

    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.

  15. Measurement of Creep Deformation in Stainless Steel Welded Joints

    Microsoft Academic Search

    Y. Sakanashi; S. Gungor; P. J. Bouchard

    \\u000a This article reports early findings of an experimental programme aimed at determining local creep properties of welded joints\\u000a made from AISI Type 316H austenitic stainless steel. For this purpose, 3 mm thick, flat cross-weld specimens were cut from\\u000a a pipe and subjected to creep testing at 550°C. In order to determine local creep properties around the weld within the gauge

  16. A high temperature deformation mechanism map for the high performance Ni-base superalloy GTD-111

    Microsoft Academic Search

    S. A. Sajjadi; S. Nategh

    2001-01-01

    GTD-111, used for gas turbine first stage blades, is a new, high performance and less investigated Ni-based superalloy. This alloy, with high volume fraction of ?? phase, has excellent creep resistance. It is believed that several creep deformation mechanisms operate at various combinations of temperature and stress. The regions of the controlling mechanisms can be described in terms of a

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

    NASA Astrophysics Data System (ADS)

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

    2010-05-01

    Earthquake rupture and volcanic eruptions are the most spectacular manifestations of dynamic failure of a critically stressed crust. But these are actually rather rare events, and most of the crust spends most of its time in a highly-stressed but sub-critical state. Below a few hundred metres, the crust is saturated, and water-rock chemical reactions lead to time-dependent deformation that allows rocks to fail over extended periods of time at stresses far below their short-term strength by the mechanism of stress corrosion crack growth. This process is highly non-linear and a change in applied stress of around 5% can lead to a change in the time-to-failure of more than an order of magnitude. Theoretical calculations based on reaction rate theory suggest that such cracking may occur down to stresses as low as 20% of the rock strength, implying that time-dependent cracking will be an important deformation mechanism over geological time and at typical tectonic strain rates. A number of theoretical models have been proposed to explain this behaviour. However, it is currently not possible to discriminate between these competing models due to the relatively narrow bandwidth of strain rates that are practicably achievable in conventional laboratory experiments. Ultra-long-term experiments at very low strain rates are clearly essential to address this problem. We have therefore used the stability of the deep-sea environment to conduct ultra-long-term experiments. At depth, the temperature remains constant throughout the year and water pressure also remains essentially constant, especially in the Ionian Sea where the tidal range is minimal. We have successfully conducted a pilot experiment (CREEP-1) in which we used the constant sea-water pressure at depth to provide both a constant confining pressure and a constant deforming stress for our rock samples. Building on that success, we are now building a multi-sample deformation observatory (CREEP-2) to be deployed at approximately 2000m water depth at the NEMO-SN1 test site in the Ionian Sea using the deep-sea shuttle (DSS) operated by INGV. CREEP-2 will be connected to the underwater electro-optical cable operated by INFN and INGV that runs some 25 km from the test site to the shore station sited in the laboratory of LNS-INFN at the port of Catania. This arrangement provides for both power to the deformation apparatus and fast, real-time data transfer from the apparatus.

  18. A physically based description for coupled plasticity and creep deformation

    Microsoft Academic Search

    X. Peng; X. Zeng; J. Fan

    1998-01-01

    Based on a simple mechanical model and an appropriate definition of generalized time, a constitutive equation without using a yield surface is obtained for coupled plasticity and creep behavior of materials. The hardening of the materials is separated into two factors related respectively to inelastic strain range and nonproportionality. The steady creep of aluminum, copper and nickel under wide variation

  19. 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.

  20. Gyro pump wear and deformation analysis in vivo study: creep deformation.

    PubMed

    Nakata, K; Yoshikawa, M; Takano, T; Maeda, T; Nonaka, K; Linneweber, J; Kawahito, S; Glueck, J; Fujisawa, A; Makinouchi, K; Yokokawa, M; Nosé, Y

    2000-08-01

    The Gyro pump has a double pivot bearing system to support its impeller. In this study, the integrity of the bearing system was examined after ex vivo studies. The pumps were implanted into calves and evaluated for different periods as a paracorporeal left ventricular assist device (LVAD). One pump was subjected to a test of 30 days, 1 for 15 days, 4 for 14 days, 1 for 10 days, 1 for 7 days, 2 for 4 days, and 4 for 2 days. One additional pump was subjected to percutaneous cardiopulmonary support (PCPS) condition for 6 days (total pressure head 500 mm Hg with a pump flow rate of 3 L/min). The anticoagulation treatment consisted of a continuous administration of heparin to maintain an achieved clotting time (ACT) of 200-250 s during the LVAD study and 250-300 s during the PCPS study. After the experiment, the pumps were disassembled, and the wear and deformation of male and female bearings were analyzed. There were no dimensional changes on male bearings but there were on female bearings. Wear and deformation of the female bearings were calculated as follows: wear and deformation = (depth of female before pumping) - (depth after pumping). Thirteen assembled Gyro pumps were disassembled to measure the depth of the female bearings before pumping. There was no statistical relationship between the wear and deformation and the motor speed x driving period. From these results, the deformation was not due to wear but to the creep or elastic deformation. This study suggested that the double pivot bearing system of the Gyro pump is highly durable. PMID:10971256

  1. Creep-fatigue criteria and inelastic behavior of modified 9Cr-1Mo steel at elevated temperatures. Final report

    SciTech Connect

    Ruggles, M.B. [Oak Ridge National Lab., TN (United States); Ogata, T. [Central Research Inst. of Electric Power Industry, Tokyo (Japan). Komae Research Lab.

    1994-02-01

    The ever increasing demand for safety requires that stringent and conservative methodology be developed for design and analysis of reactor components. At present modified 9Cr-1Mo steel is a candidate material for construction of steam generators in fast breeder reactors. Therefore high-temperature material properties and extensive insight into deformation behavior and creep-fatigue life are required to develop design guidelines for use of modified 9Cr-1Mo steel in actual plant components. However, existing information on creep-fatigue and deformation response of modified 9Cr-1Mo steel is insufficient, and further experimental and modeling efforts are needed. A joint effort between the Electric Power Research Institute (EPRI) in the United States and the Central Research Institute of Electric Power Industry (CRIEPI) in Japan was started in 1991 to investigate the inelastic behavior of and to develop creep-fatigue criteria for modified 9Cr-1Mo steel at elevated temperatures. The current program focuses on uniaxial and biaxial fatigue, creep, and creep-fatigue tests. Results of this effort are presented in this report. Section 2 introduces the test material and experimental arrangement. Uniaxial exploratory deformation tests and unified constitutive equations for inelastic analysis of modified 9Cr-1Mo steel are presented in Sections 3 and 4, respectively. Axial fatigue and creep-fatigue test results are discussed in Section 5. Section 6 is devoted to constant stress creep tests. Biaxial fatigue and creep-fatigue tests are described in Section 7. Progress in creep-fatigue life evaluation is reported in Section 8.

  2. Marine ice deformation experiments: an empirical validation of creep parameters

    NASA Astrophysics Data System (ADS)

    Dierckx, Marie; Tison, Jean-Louis

    2013-01-01

    Marine ice is increasingly recognized as an important component of ice shelves in Antarctica. Because it mainly accretes in "weak" locations, it plays a crucial role in ice shelf stability. Little is known however on the rheology of this particular material (low salinity, no bubbles, specific fabrics). We present marine ice deformation experiments in unconfined uniaxial compression at -10 °C, -6 °C, and -3 °C. Generally, marine ice samples confirm the value of n = 3 for Glen's power law. It also appears to behave systematically "harder" than artificial or meteoric isotropic ice samples used in the past, in the studied stress condition. Bulk salinity does not seem to have a significant impact on the viscosity. All deformation curves compare well with a generalized empirical temperature/viscosity relationship. They represent the first experimental validation of the lower boundary of this rheological relationship recommended for use in modeling ice dynamics.

  3. The elevated temperature compression creep behavior of a calcium-aluminosilicate(anorthite) glass ceramic

    SciTech Connect

    Mercer, R.F.; Chokski, A.H. (Univ. of California, San Diego (United States))

    1993-05-15

    An experimental investigation of compression creep in a calcium-aluminosilicate glass ceramic revealed that the deformation can be expressed as [epsilon][alpha][sigma][sup 1]exp([minus]650 kJ mol[sup [minus]1]/RT), where [epsilon] is the steady state strain rate, [sigma] is the imposed stress, R is the gas constant and T is the absolute temperature. The high activation energy, a stress exponent of unity and microstructural observations indicate that creep deformation is enhanced by the presence of a liquid phase. The occurrence of significant cavitation at low strains suggests that the material is not likely to exhibit superplastic-like large elongations when tested in tension, although it exhibits Newtonian-viscous behavior.

  4. Serrated creep and spatio-temporal structures of macrolocalized plastic deformation

    NASA Astrophysics Data System (ADS)

    Shibkov, A. A.; Zolotov, A. E.; Zheltov, M. A.; Gasanov, M. F.; Denisov, A. A.

    2014-05-01

    The dynamics and morphology of macrolocalized deformation bands have been investigated using a complex of high-speed in situ methods under the conditions of serrated creep of flat samples of the aluminum-magnesium alloy 5456 with different aspect ratios. It has been found that, at the front of a macroscopic plastic deformation jump, a complex structure of propagating deformation bands, which are considered as macrolocalized deformation "quanta," is spontaneously formed in the material. It has been shown that, with an increase in the sample length, the deformation behavior of the alloy tends to the state of self-organized criticality.

  5. Brittle creep in basalt and its application to time-dependent volcano deformation M.J. Heap a,b,

    E-print Network

    . Ricard Keywords: stress corrosion brittle creep triaxial basalt Mt. Etna time-dependent deformation Time the first experimental measurements of brittle creep in a basic igneous rock (a basalt from Mt. Etna volcano with the observed deformation history at Mt. Etna volcano. © 2011 Elsevier B.V. All rights reserved. 1. Introduction

  6. The effects of oxygen concentration and temperature on cyclic creep in niobium-oxygen alloys

    Microsoft Academic Search

    G. P. Sheldon; R. A. Yeske

    1978-01-01

    The effects of dynamic solute-dislocation interactions on cyclic creep in niobium-oxygen alloys have been examined by comparing static and cyclic creep in the dynamic strain-aging temperature range. In all comparisons, the peak stress in cyclic creep tests was identical to the constant stress in static creep tests. Niobium purified of interstitial solutes exhibits classical logarithmic creep at these temperatures under

  7. The effects of oxygen concentration and temperature on cyclic creep in niobium-oxygen alloys

    Microsoft Academic Search

    G. P. Sheldon; R. A. Yeske

    1978-01-01

    The effects of dynamic solute-dislocation interactions on cyclic creep in niobium-oxygen alloys have been examined by comparing\\u000a static and cyclic creep in the dynamic strain-aging temperature range. In all comparisons, the peak stress in cyclic creep\\u000a tests was identical to the constant stress in static creep tests.\\u000a \\u000a Niobium purified of interstitial solutes exhibits classical logarithmic creep at these temperatures under

  8. 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.

  9. Creep of an epoxy resin under transient temperatures 

    E-print Network

    Watkins, Larry Alan

    1973-01-01

    CREEP OF AN EPOXY RESIN UNDER TRANSIENT TEMPERATURES A Thesis by LARRY ALAN WATKINS Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE August 1973 Major... Subject: Civil Engineering CREEP OF AN EPOXY RESIN UNDER TRANSIENT TEMPERATURES A Thesis by LARRY ALAN MATKINS Approved as to style and content by: R. A. Schapery (Ch ai rman o f Commi t tee ) C. H. amson, (Head of Department) R. E. Martin...

  10. Creep of an epoxy resin under transient temperatures

    E-print Network

    Watkins, Larry Alan

    1973-01-01

    CREEP OF AN EPOXY RESIN UNDER TRANSIENT TEMPERATURES A Thesis by LARRY ALAN WATKINS Submitted to the Graduate College of Texas A&M University in partial fulfillment of the requirement for the degree of MASTER OF SCIENCE August 1973 Major... Subject: Civil Engineering CREEP OF AN EPOXY RESIN UNDER TRANSIENT TEMPERATURES A Thesis by LARRY ALAN MATKINS Approved as to style and content by: R. A. Schapery (Ch ai rman o f Commi t tee ) C. H. amson, (Head of Department) R. E. Martin...

  11. Dynamic internal friction of mono-crystalline aluminum during high temperature creep

    SciTech Connect

    Kong, Q.P.; Zhou, H.; Li, X.M.; Wang, X. [Academia Sinica, Hefei (China). Inst. of Solid State Physics] [Academia Sinica, Hefei (China). Inst. of Solid State Physics

    1995-04-01

    The internal friction measured during creep testing may give useful information on the dynamic process of creep. In the present paper, the authors report the results of a systematic study on the internal friction peak during high temperature creep of mono-crystalline pure Al with controlled orientation, and compare the change of internal friction with the evolution of dislocation configuration during creep.

  12. Creep of precipitation-hardened nickel-base alloy single crystals at high temperatures

    Microsoft Academic Search

    G. R. Leverant; B. H. Kear; J. M. Oblak

    1973-01-01

    Single crystals of a ?? precipitation-hardened nickel-base super alloy, Mar-M200, were tested in constant load creep at 1575?F.\\u000a It was found that shear of the ?? precipitate by pairs of ?\\/2 (110) dislocations controlled deformation in both primary and\\u000a steady-state creep. This contrasts with 1400?F creep behavior where shear of ?? is dominated by ?\\/3 (112) dislocations in\\u000a primary creep,

  13. 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.

  14. 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.

  15. 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.

  16. Creep, stress relaxation, and plastic deformation in SnAg and Sn-Zn eutectic solders

    Microsoft Academic Search

    H. Mavoori; J. Chin; S. Vaynman; B. Moran; L. Keer; M. Fine

    1997-01-01

    Because of the high homologous operation temperature of solders used in electronic devices, time and temperature dependent\\u000a relaxation and creep processes affect their mechanical behavior. In this paper, two eutectic lead-free solders (96.5Sn-3.5Ag\\u000a and 91Sn-9Zn) are investigated for their creep and stress relaxation behavior. The creep tests were done in load-control with\\u000a initial stresses in the range of 10-22 MPa

  17. Suppression of ambient temperature creep by eutectic phase for hexagonal close-packed metal

    NASA Astrophysics Data System (ADS)

    Matsunaga, Tetsuya; Abe, Tomonori; Itoh, Shun; Satoh, Yuhki; Abe, Hiroaki

    2014-03-01

    Zr-Si alloys were designed to contain eutectic phase surrounding the parent phase to suppress creep behavior of claddings. Creep tests conducted at 294-573 K showed that creep behavior was inhibited and that the creep failure time of new Zr alloy became longer than that of a conventional alloy: Zircaloy-4. Results show that the eutectic phase can suppress creep at operating temperatures prevailing in current nuclear power plants.

  18. Dynamic internal friction of mono-crystalline aluminum during constant rate deformation at high temperatures

    Microsoft Academic Search

    H. Zhou; Q. P. Kong

    1996-01-01

    Dynamic internal friction measured during mechanical testing is a useful tool to study the microscopic process of plastic deformation. Recently, the authors have investigated the dynamic internal friction of mono-crystalline pure aluminum during creep at temperatures around 0.5 Tm (Tm is the melting point). In the present paper, they extend the research to the case of constant rate deformation at

  19. High-Temperature Deformation of Enstatite Aggregates

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

  20. Microstructure and high temperature creep of platinum group metal modified nickel base superalloys

    NASA Astrophysics Data System (ADS)

    van Sluytman, Jason S.

    Increasing efficiency in aeropropulsion and energy generation systems drives the development of higher temperature structural materials with good mechanical properties and environmental resistance. Platinum group metal (PGM) additions are known to be beneficial for the oxidation and corrosion resistance of superalloys and Ni rich intermetallics. However, there is limited understanding of how they influence the microstructure and high temperature mechanical properties of gamma-gamma' superalloys. The objective of this research is to examine experimental Ni-base compositions that systematically alter PGM and non-PGM elements. The PGMs used for this study are Pt, Ir, and Ru. The non-PGM elements are ones commonly used in conventional Ni-base compositions, such as Re, W, and Ta. Partitioning studies indicates that platinum preferentially partitions to the gamma' phase, resulting in alloys that exhibit positive misfit behavior --- quite uncommon for Ni-base superalloys. Iridium influences the partitioning behavior of PGM and non-PGM elements, which could be useful in manipulating alloying chemistry. The unique partitioning behavior of the PGMs results in a wide range of lattice misfit and, therefore, gamma' morphology. Coarsening studies demonstrate that Pt slows gamma' coarsening and helps maintain unusually high volume fractions at temperatures up to 1200 °C. Such high volume fractions at these elevated temperatures could lead to impressive creep properties. High temperature creep tests at 1000 °C demonstrate variations in creep strength between PGM alloys. Alloys with precipitate boundary strengthening elements boron, carbon, and zirconium, can increase the creep resistance by at least a factor of three. For alloys that directionally coarsen, the formation of dense, interfacial dislocation networks increases creep strength. Dislocation density measurements within positive misfit alloys indicate, in some cases, that a majority of the dislocations are deposited within the precipitate phase rather than the matrix phase --- a very unusual feature for high temperature deformation. The calculation of a creep stress exponent establishes that creep is carried out in the power-law regime. A climb velocity is calculated that can be applied not only to the PGM alloys in this investigation, but other Ni-base systems as well.

  1. Induced creep and creep/fatigue of a nickel-base superalloy at ambient temperatures

    NASA Astrophysics Data System (ADS)

    Chen, G. L.; Fritzemeier, L. G.; Xie, X.; Tien, J. K.

    1982-11-01

    The stress controlled fatigue of Nimonic*115, a typical ?’-strengthened nickel-base superalloy, was studied at ambient temperature, using a trapezoidal wave form at 1 Hz, with stresses chosen to produce failure in the lO4 to lO4 cycle range. In tests with maximum stress greater than the proportional limit, most of the fatigue damage occurs within the first few test cycles. Much of this strain is accumulated under static load and is therefore identified as creep strain. Transmission electron microscopy shows that these creep strains occur in slip bands which disrupt the ordered ?’ precipitates. Strain is found to follow a logarithmic time dependence, which suggests a low activation energy mechanism.

  2. Elevated temperature creep behavior of Inconel alloy 625

    SciTech Connect

    Purohit, A.; Burke, W.F.

    1984-07-01

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

  3. High temperature deformation of 6061 Al

    SciTech Connect

    Kyungtae Park; Lavernia, E.J.; Mohamed, F.A. (Univ. of California, Irvine (United States). Dept. of Mechanical and Aerospace Engineering)

    1994-03-01

    The creep behavior of powder metallurgy (PM) 6061 Al, which has been used as a metal matrix alloy in the development of discontinuous silicon carbide reinforced aluminum (SiC-Al) composites, has been studied over six orders of magnitude of strain rate. The experimental data show that the steady-state stage of the creep curve is of short duration; that the stress dependence of creep rate is high and variable; and that the temperature dependence of creep rate is much higher than that for self-diffusion in aluminum. The above creep characteristics are different from those documented for aluminum based solid-solution alloys but are similar to those reported for discontinuous SiC-Al composites and dispersion-strengthened (DS) alloys. Analysis of the experimental data shows that while the high stress dependence of creep rate in 6061 Al, like that in DS alloys, can be explained in terms of a threshold stress for creep, the strong temperature dependence of creep rate in the alloy is incompatible with the predictions of available threshold stress models and theoretical treatments proposed for DS alloys.

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

    Microsoft Academic Search

    M. V. Nathal; L. J. Ebert

    1985-01-01

    The creep and rupture behavior of [001] oriented single crystals of the nickel-base superalloy NASAIR 100 was investigated\\u000a at temperatures of 925 and 1000 °C. In the stress and temperature ranges studied, the steady state creep rate, time to failure,\\u000a time to the onset of secondary creep, and the time to the onset of tertiary creep all exhibited power law

  5. Diffusion Creep in the Earth's Mantle

    Microsoft Academic Search

    Robert B. Gordon

    1965-01-01

    By the process of diffusion creep polycrystalline materials can deform at slow strain rates with Newtonian viscosity. Creep mechanisms involving dislocations can result in more rapid, non-Newtonian flow, but the diffusion creep rate sets an upper limit to the resist- ance to nonhydrostatic stresses. It is shown that under the conditions of temperature and pressure expected in the earth's mantle,

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

    NASA Technical Reports Server (NTRS)

    Boyce, L.

    1993-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Nakakoji, T.; Hiraga, T.

    2014-12-01

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

  8. Effect of temperature and microstructure on tensile and tensile creep properties of titanium silicon carbide in air

    NASA Astrophysics Data System (ADS)

    Radovic, Miladin

    The ternary carbide, Ti3SiC2, combines some of the best attributes of ceramics and metals. It is stable in inert atmospheres to temperatures above 2200°C, stiff and yet is readily machinable, oxidation, fatigue and thermal shock resistant and damage tolerant. Thus, Ti3SiC 2 is good candidate material for high temperature structural application. The aim of this work was to characterize its tensile and tensile creep properties. The mechanical behavior of Ti3SiC2 is characterized by a brittle-to-ductile (BTD) transition that is a function of strain rate. Its high strain rate sensitivity (?0.50--0.6) is in the range that is more typical for superplastic materials, although it does not exhibit other attributes of superplasticity. Polycrystalline samples do not exhibit linear elastic behavior in tension even at room temperature. Room temperature loading-unloading tests result in closed hysteresis loops when the stress exceeds ?120 MPa, suggesting that the mechanical response can be described as anelastic (viscoelastic). At high temperatures (1200°C) intense stress relaxation takes place; cycling loading-unloading tests at high temperature and low strain rates, demonstrate that the samples continue to elongate even during unloading, suggesting that Ti3SiC2 deforms viscoplastically. Tensile creep curves exhibit primary, steady state and tertiary regimes. The minimum creep rate can be represented by power law equation with a stress exponent of 1.5 for fine-grained (3--5 mum) samples, and 2 for coarse-grained (100--300 mum) ones. For both microstructures the activation energy for creep is ?450 kJ/mol. The dependence on grain size is quite weak, implying that diffusion creep and/or creep mechanisms based on grain boundary sliding do not play a central role. Results of strain transient dip tests suggest that large internal stresses are developed during creep. Those internal stresses are believed to result in recoverable (anelastic) strains during unloading. The response on small stress decreases in strain-transient creep tests suggests that the steady state creep is recovery controlled. Finally, it is important to note that the mechanical response of Ti 3SiC2 is quite similar to hexagonal ice. Both materials, if loaded rapidly are brittle, but if loaded slowly are quite plastic. This stems from the fact that both are plastically very anisotropic; deformation occurs overwhelmingly by basal slip. In both cases, stress concentrations, and the rate at which they can be relaxed, dictate the nature of the mechanical response.

  9. Inelastic deformation and its related life under cyclic\\/creep loadings in Si 3N 4-monolithic and Si 3N 4\\/SiCw-composite ceramics at elevated temperature

    Microsoft Academic Search

    K. Hatanaka; Y. Ishiga; R. Kawazoe; M. Hasui; J. Ohgi; H. Ogawa

    2007-01-01

    Push–pull low cycle fatigue and creep tests were performed in monolithic-Si3N4 and composite-Si3N4\\/SiCw materials at 1573K. Then cyclic stress–strain response and creep strain were measured with a newly developed extensometer. The inelastic strain, which is greatly dependent upon stress\\/strain rate, was detected in both the materials. It was found from the shape of the cyclic stress–strain hysteresis loop that inelastic

  10. Fatigue perturbed creep of pure aluminum at ambient temperatures

    Microsoft Academic Search

    Walter L. Bradley; Soo W. Nam; David K. Matlock

    1976-01-01

    The creep of 99.999 pct pure aluminum subject to tension-tension cyclic stressing (dynamic creep) has been studied and compared\\u000a to creep for the peak cyclic stress applied statically (static creep). The creep rate for a cyclic stress of 29.8 to 3.7 MPa\\u000a was always found to be greater than the creep rate for static application of a stress of 29.8

  11. Fatigue perturbed creep of pure aluminum at ambient temperatures

    Microsoft Academic Search

    Walter L. Bradley; Soo W. Nam; David K. Matlock

    1976-01-01

    The creep of 99.999 pct pure aluminum subject to tension-tension cyclic stressing (dynamic creep) has been studied and compared to creep for the peak cyclic stress applied statically (static creep). The creep rate for a cyclic stress of 29.8 to 3.7 MPa was always found to be greater than the creep rate for static application of a stress of 29.8

  12. Creep of pure aluminum at cryogenic temperatures

    E-print Network

    McDonald, Lacy Clark

    1989-01-01

    has a, lower magnetoresistivity effect. 3. The specific heat of aluminum is lower than that of copper at low temperatures, reducing cool-down costs. 4. Below about 70 Kelvin, thermal conductivity of aluminum is higher than that of copper, providing.... Fe (ppm) & 0. 7 3. Cu (ppm) 5. 5 4. Mn (ppm) & 0. 2 5. Mg (ppm) 2. 3 6. Cr (ppm) & 0. 4 7. Zn (ppm) & 0. 7 8. Ti (ppm) & 0. 3 9. B (ppm) & 0. 2 10. Na (ppm) & 0. 2 11. Ca (ppm) 0. 6 12. Li (ppm) & 0. 1 13. Be (ppm) & 0. 1 14. Ni (ppm) & 0...

  13. Creep deformation in an alumina-silicon carbide composite produced via a directed metal oxidation process

    SciTech Connect

    Lin, H.T.; Breder, K. [Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.

    1996-08-01

    Flexural creep studies were conducted in a commercially available alumina matrix composite reinforced with SiC particulates (SiC{sub p}) and aluminum metal at temperatures from 1,200 to 1,300 C under selected stress levels in air. The alumina composite (5 to 10 {micro}m alumina grain size) containing 48 vol% SiC particulates and 13 vol% aluminum alloy was fabricated via a directed metal oxidation process (DIMOX{trademark}) and had an external 15 {micro}m oxide coating. Creep results indicated that the DIMOX Al{sub 2}O{sub 3}-SiC{sub p} composite exhibited creep rates that were comparable to alumina composites reinforced with 10 vol% (8 {micro}m grain size) and 50 vol% (1.5 {micro}m grain size) SiC whiskers under the employed test conditions. The DIMOX Al{sub 2}O{sub 3}-SiC{sub p} composite exhibited a stress exponent of 2 at 1,200 C and a higher exponent value (2.6) at {ge}1,260 C, which is associated with the enhanced creep cavitation. The creep mechanism in the DIMOX alumina composite was attributed to grain boundary sliding accommodated by diffusional processes. Creep damage observed in the DIMOX Al{sub 2}O{sub 3}-SiC{sub p} composite resulted from the cavitation at alumina two-grain facets and multiple-grain junctions where aluminum alloy was present.

  14. Nanogranular origin of concrete creep

    E-print Network

    Vandamme, Matthieu

    Concrete, the solid that forms at room temperature from mixing Portland cement with water, sand, and aggregates, suffers from time-dependent deformation under load. This creep occurs at a rate that deteriorates the durability ...

  15. Damage Accumulation in Aluminum Alloys under Plastic Deformation and Creep

    Microsoft Academic Search

    M. G. Petrov; A. I. Ravikovich

    2006-01-01

    The accumulation of local and bulk damage in D16 AT and 1201 T1 aluminum alloys used in aircraft engineering is studied. The local damage level is calculated from data of thermoactivation\\u000a analysis of the residual life of D16 AT alloy specimens after preliminary plastic deformation. The bulk damage level is determined from the elastic-modulus defect\\u000a by measuring the natural frequency

  16. 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.

  17. Creep behavior comparison of CMW1 and palacos R-40 clinical bone cements

    Microsoft Academic Search

    C. Liu; S. M. Green; N. D. Watkins; P. J. Gregg; A. W. McCaskie

    2002-01-01

    The restrained dynamic creep behaviors of two clinical bone cements, Palacos R-40 and CMW1 have been investigated at room temperature and body temperature. It was found that the two cements demonstrated significantly different creep deformations, with Palacos R-40 bone cement demonstrating higher creep strain than CMW1 bone cement at each loading cycle. For both cements, two stages of creep were

  18. 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.

  19. Effect of high-temperature deformation on the mechanical properties of AISI 316 stainless steel

    NASA Astrophysics Data System (ADS)

    Shabara, Mohammed A. N.

    1997-03-01

    Accurate and reliable life predictions of mechanical components subjected to stress at elevated temperature may be difficult since the mechanical properties of the material are expected to change. The constitutive equations describing the creep behavior may also change due to softening or hardening processes caused by the applied loading conditions. In this paper the response of AISI Type 316 stainless steel at 650 degrees Celsius when subjected to a static tensile stress is examined. A testing technique has been applied to the test material to evaluate the effect of short periods of high temperature deformation on its mechanical properties. Round tensile specimens were subjected to constant tensile stress levels under high temperature of 650 degrees Celsius for periods of time varying from 2 to 8 hours. The specimens were then annealed and tested in tension under room temperature. Test results indicate that the AISI Type-316 exhibited hardening due to short period creep. Yield strength and ultimate tensile strength have increased by 58% and 20%, respectively, after 8 hours creep, over that of the virgin material. Creep was also found to cause a reduction in the ductility of the AISI Type-316 over the temperature and stress levels used in this investigation. Moreover, the changes in these properties were found to increase as creep time increased. From the present work, an empirical equation was obtained for predicting the amount of hardening in the material due to creep. Such an equation may be useful in more involved problems of combined creep and fatigue.

  20. 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.

  1. Creep-fatigue interaction in delamination crack propagation of advanced CFRPs at high temperatures

    SciTech Connect

    Uematsu, Y. [Osaka Univ., Suita, Osaka (Japan). Dept. of Mechanical Engineering and Systems; Kitamura, T.; Ohtani, R. [Kyoto Univ. (Japan). Dept. of Engineering Physics and Mechanics

    1997-12-31

    The objective of this study is to elucidate creep-fatigue interaction in Mode 1 delamination crack propagation of polymers reinforced by carbon fibers at high temperatures. The materials tested are two undirectionally reinforced laminates, AS4/PEEK (carbon fiber: AS4, matrix: poly-ether-ether-ketone) and T800H/PMR-15 (carbon fiber: T800H, matrix: polyimide). Crack propagation tests are conducted in cyclic loading conditions with and without hold(s) at maximum tension and zero load at 473 K for AS4/PEEK laminates and 573 K for T800H/PMR-15 laminates, respectively. In fatigue with high frequency, the crack propagation rate per unit cycle da/dN is correlated well with the stress intensity factor range {Delta}K. However, the crack propagation in AS4/PEEK laminates depends strongly on the load waveform, while that in T800H/PMR-15 laminates is independent of it. The crack propagation in AS4/PEEK laminates is accelerated by the tensile load hold due to the creep deformation of matrix and it is purely time-dependent. In the time-dependent crack propagation, the rate per unit time da/dt is correlated well with the stress intensity factor K at the hold. On the other hand, the time-dependent crack propagation is decelerated by the zero-load-hold because of the creep recovery of matrix.

  2. 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.

  3. 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.

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

    SciTech Connect

    Krempl, E. [Rensselaer Polytechnic Institute, Troy, NY (United States)

    1997-12-31

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

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

    NASA Astrophysics Data System (ADS)

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

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

  6. Effect of matrix and atmosphere on the creep deformation of aluminum alloy matrix composites

    Microsoft Academic Search

    Norio Matsuda; Hideki Tazawa; Satoshi Ishikawa; Mitsuru Saitoh

    2001-01-01

    Creep behavior of two types of aluminum alloy matrix composites, which were reinforced with alumina particles and have different matrix alloy, have been investigated at temperatures from 573 to 773 K. Matrices of the composites were 6061 and 2014 Al alloys. The composites contained about 10 or 20 vol.% of alumina particles, the size of which is about 10–30 ?m.

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

    SciTech Connect

    Wu, Rui; Pettersson, Niklas [Swerea KIMAB, Box 7074, SE-164 07 Kista (Sweden); Martinsson, Åsa [Swerea KIMAB, Box 7074, SE-164 07 Kista (Sweden); Now at Sandvik Materials Technology, Sandviken (Sweden); Sandström, Rolf, E-mail: rsand@kth.se [Swerea KIMAB, Box 7074, SE-164 07 Kista (Sweden); Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm (Sweden)

    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.

  8. 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.

  9. 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.

  10. On the influence of stress state on rafting in the single crystal superalloy CMSX-6 under conditions of high temperature and low stress creep

    SciTech Connect

    Kamaraj, M.; Mayr, C.; Kolbe, M.; Eggeler, G. [Ruhr-Univ., Bochum (Germany). Inst. for Materials] [Ruhr-Univ., Bochum (Germany). Inst. for Materials

    1998-01-13

    Single crystal superalloys have excellent high temperature strength and oxidation resistance and are therefore used as blades in aircraft engines and land based gas turbines. The microstructure of these alloys consists of two phases: (i) a high volume fraction of coherently precipitated {gamma}{prime}-cubes (L1{sub 2}) which strengthen the material separated by (ii) thin channels of face centered cubic (f.c.c.) {gamma}-matrix, as shown. However, microstructural instability (i.e. {gamma}{prime}-coarsening) is observed in these alloys during high temperature creep deformation (T > 900 C). In creep, coarsening of particles is generally considered as a softening process which increases the creep rate of an alloy. However, this process does not always dominate the overall materials response to creep loading. Thus, Mughrabi et al have clearly shown that {gamma}{prime}-coarsening can occur while the overall creep rate decreases. A number of studies on the high temperature creep deformation behavior of various single crystal superalloys have been reported in recent years. To explain rafting the authors here consider the case of a {gamma}/{gamma}{prime}-microstructure with negative misfit, i.e. where the lattice constant of the ordered {gamma}{prime}-phase is smaller than the lattice constant of the {gamma}-phase.

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

    SciTech Connect

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

    2013-07-01

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

  12. Effect of Normalization Temperature on Creep Strength of Modified 9Cr-1Mo Steel

    SciTech Connect

    T.C. Totemeier; H. Tian; J.A. Simpson

    2006-05-01

    The effect of normalization temperature from 850 to 1050°C on the structure and creep-rupture properties of modified 9Cr-1Mo steel was studied. Normalization at temperatures less than 925°C resulted in structures containing significant polygonized, recovered ferrite. These structures had poor creep-rupture strength; roughly two orders of magnitude increase in minimum creep rate or decrease in rupture life for 850°C compared to 1050°C normalization at test conditions of 600°C and 145 MPa. Room-temperature strength and hardness were also reduced. Normalization at temperatures between 925°C and 1000°C also resulted in reduced creep strength in comparison with 1050°C normalization, even though tempered martensite microstructures were formed and little change in room temperature strength was observed–the reduction was attributed to subtle differences in fine MX precipitates. The effect of reduced normalization temperature was more pronounced for higher temperature, lower stress creep-rupture conditions.

  13. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1971-01-01

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

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

    NASA Technical Reports Server (NTRS)

    Haisler, W. E.

    1983-01-01

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

  16. 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.

  17. Deformation and fracture of low alloy steels at high temperature

    SciTech Connect

    Marriott, D.L.; Stubbins, J.F.; Leckie, F.A.; Muddle, B.

    1988-12-01

    This project formed part of the initiative in the AR TD program to characterize high temperature, time-dependent damage processes in low alloy steels, for use in the construction of coal-gasification plant. This project was broadly aimed at adding to the knowledge base for this bainitic form of 2.25Cr 1Mo steel, as it related to time-dependent performance at elevated temperature. Its original intention was to obtain information in specific grades of 2.25Cr 1Mo steel, in particular those containing reduced residual elements and microalloyed modifications, which were being considered as candidate materials at the time. This objective was subsequently modified, in the course of the contract period, to a more generic study of bainitic steel, using the 2.25Cr 1Mo material as a representative of the class. The main thrust of the project was directed initially at the detrimental effect of cyclic loading on creep resistance and manifesting itself in an apparently severe creep-fatigue interaction. Three subtasks were eventually identified. These are: a study of the evolution of microstructural changes in bainitic materials during steady load creep and under constant amplitude cyclic deformation, investigation of the effect of cyclic softening on the fatigue and creep strength of complex geometries, focusing on circumferentially notched bars, and investigation of the influence of environment as a possible cause of observed fatigue/elevated temperature interaction through its effects on crack initiation and propagation, using EDM notched specimens tested in air and vacuum. Results are discussed. 24 refs., 40 figs., 5 tabs.

  18. High temperature tensile deformation behavior of Grade 92 steel

    NASA Astrophysics Data System (ADS)

    Alsagabi, Sultan; Shrestha, Triratna; Charit, Indrajit

    2014-10-01

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

  19. High temperature deformation of rocks and minerals

    Microsoft Academic Search

    J. A. Tullis

    1979-01-01

    The goal of research on the high temperature deformation of rocks and minerals is to determine the stress and strain history of the crust and mantle—to interpret the structures observed in naturally deformed rocks, to interpret geophysical measurements, and to allow accurate modelling. This research thus includes experimental and theoretical studies, as well as studies of naturally deformed rocks. In

  20. Plastic deformation in bulk metallic glasses characterized by nanoindentation creep

    NASA Astrophysics Data System (ADS)

    Puthoff, Jonathan B.

    Plasticity and flow in metallic glasses (MGs) is believed to be the result of the activation of defects in the amorphous structure. These defects are regions of the glass, thought to be comprised of 10--100 atoms, which can undergo a localized rearrangement in response to a shear stress (tau) and are called shear transformation zones (STZs). This dissertation is an investigation strain rate-dependence of the hardness in three, Zr-based bulk metallic glasses (BMGs) to back out information about the STZs. The primary characterization technique is nanoindentation, which is capable of determining both the static materials properties, such as hardness and elastic modulus, as well as the time-dependent properties, which include information on the activation of flow defects. Other experimental techniques, such as differential scanning calorimetry and X-ray diffraction, were applied to measure the thermophysical properties of the BMGs. The low-stress activation energies (Delta G0*) for defect rearrangement are in the range 3.5--10 eV, and the stress-dependence of the activation energy is a power-law of the form DeltaG*(tau) ˜ taun , where n is measured to be in the range 1.5--2.0. From the measurements it is possible to estimate the volume of the STZ, O*, which has not been measured previously. , O* , is found to vary anywhere from 100--300 atomic volumes. In addition to the experiments conducted on the as-cast alloys for the three different Zr-Cu-Al compositions, similar tests were carried out on the same materials after they had been subjected to heat-treatment near the glass transition temperature. Not only are the characteristics of the STZs sensitive to the composition of the BMG, but they also exhibit substantial changes upon annealing; the quantities DeltaG0* and O* decrease by 10--30%. These latter results are in good agreement with expected trends and provide some insight into the relationship between the structure and dynamics in the MG.

  1. 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.

  2. Dynamic internal friction of mono-crystalline aluminum during high temperature creep

    Microsoft Academic Search

    Q. P. Kong; H. Zhou; X. M. Li; X. Wang

    1995-01-01

    Dynamic internal friction of mono-crystalline pure aluminum has been investigated during creep at temperatures around 0.5 Tm. A pronounced peak of internal friction versus creep time (Q?1-t peak) appears in the latter part of primary creep. The internal friction exhibits an anomalous amplitude dependence effect, i.e., it increases as the strain amplitude decreases. The peak height increases linearly with a

  3. Creep and creep-rupture behavior of Alloy 718

    SciTech Connect

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

    1991-01-01

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

  4. 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.

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

    SciTech Connect

    Liu, J.; Lyons, J.; Sutton, M.; Reynolds, A. [Univ. of South Carolina, Columbia, SC (United States)

    1998-01-01

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

  6. Room temperature creep of borsic-aluminum composites

    Microsoft Academic Search

    R. H. Ericksen

    1973-01-01

    Creep of aluminum reinforced with continuous Borsic filaments has been investigated at 27°C. Composites having filaments oriented 0, 0±45, 0±60, 0±90, ±45, and 90 deg with respect to the tensile axis were tested for times up to 100 h. Creep tests were also performed on unreinforced aluminum and on the Borsic filaments. Creep in the Borsic filaments and in composites

  7. Room temperature creep of borsic-aluminum composites

    Microsoft Academic Search

    R. H. Ericksen

    1973-01-01

    Creep of aluminum reinforced with continuous Borsic filaments has been investigated at 27?C. Composites having filaments oriented\\u000a 0, 0?45, 0?60, 0?90, ?45, and 90 deg with respect to the tensile axis were tested for times up to 100 h. Creep tests were\\u000a also performed on unreinforced aluminum and on the Borsic filaments. Creep in the Borsic filaments and in composites

  8. Impurity effects on the creep of polycrystalline magnesium and aluminum oxides at elevated temperatures. Technical progress report, December 19, 1972December 18, 1973

    Microsoft Academic Search

    1973-01-01

    Nabarro- Herring creep was conclusively identified as the mechanism for ; the creep in oxygen of polycrystalline MgO doped with 0.53 cation % iron or less. ; At higher dopant levels both Nabarro-Herring creep and Coble creep contribute to ; creep deformation in air. An analytical procedure was developed to estimate from ; the creep data of polycrystalline, iron-doped MgO

  9. Impurities in silicon carbide ceramics and their role during high temperature creep

    NASA Astrophysics Data System (ADS)

    Backhaus-Ricoult, M.; Mozdzierz, N.; Eveno, P.

    1993-12-01

    The high-temperature compressive creep behaviour of hot-pressed silicon carbide ceramics with different additive packages (boron and carbon or no additive) is investigated as a function of several parameters: the microstructure, the nature of the additives and that of the impurities. Additional carbon is present in all the materials investigated, as graphite precipitates of various size and amount. In materials densified with addition of boron, large precipitates of B{25}C and small amorphous silica pockets are identified. In the case of materials containing impurities, small precipitates of FeSi, Fe or Ti5Si3 are detected. Creep experiments are conducted on materials with no additives and on others containing boron and carbon additives, at temperatures ranging from 1 773 K to 1 973 K and under stresses from 100 to 1 100 MPa. A comparison of the creep behaviour of the various materials points out to the destructive effect of carbon precipitates on the creep rate: the stationary creep rate of the material containing carbon (and boron) additives is by a factor 2.5-5 faster, eventhough its grain size is much larger! The creep of both investigated materials is described by a power law with a stress exponent of 1.5 in a low stress range and 3.5-4 in a high stress range. The corresponding activation energies are 364 kJ/mole and 453 kJ/mole in the low stress range and about 629 kJ/mole in the high stress range. At low stresses the materials deform by grain boundary sliding compensated mainly by diffusion along the grain boundaries and to a lesser extent by limited cavitation, as a result of the barrier role played by grain boundaries for dislocations. At high stresses the grain boundaries are no longer an obstacle to dislocation motion, which becomes the dominant deformation mechanism. La microstructure de deux céramiques, SiC sans ajouts et SiC avec bore et carbone, est étudiée par microscopie électronique à transmission dans le but d'évaluer l'influence des additifs sur les propriétés mécaniques à haute température. Dans tous les matériaux, des précipités de graphite de différentes tailles sont observés. Le carbure de silicium fabriqué avec du bore contient des grands précipités de B{25}C et des petites poches de silice amorphe. A partir de nos observations de la microstructure, une prévision des propriétés mécaniques des matériaux est possible. Ces prévisions sont comparées aux résultats de fluage à haute température. Les matériaux sans ajouts et ceux avec carbone et bore sont déformés entre 1 773 K et 1 973 K, sous des contraintes de 100 à 1 100 MPa. Le comportement des deux matériaux suit une loi de puissance avec un exposant de contrainte de 1,5 pour les faibles contraintes et de 3,5-4 pour les fortes contraintes. Les valeurs d'énergie d'activation des deux types de matériaux sont respectivement 364 et 453 kJ/mole dans le domaine de faibles contraintes et 629 kJ/mole aux fortes contraintes. L'observation de la microstructure des matériaux déformés montre comme mécanisme principal de fluage le glissement aux joints de grains accommodé par la diffusion et accompagné par une faible cavitation due à la non-perméabilité des joints de grains pour les dislocations. Aux plus fortes contraintes, les joints de grains deviennent plus perméables, et la déformation par mécanismes de dislocations devient alors prépondérante.

  10. Creep of brazed plate-fin structures in high temperature compact heat exchangers

    Microsoft Academic Search

    Shantung Tu; Guoyan Zhou

    2009-01-01

    In recent years, the need for high temperature heat exchangers to improve the efficiency of power and chemical conversion\\u000a systems has been growing. However, the creep design of the high temperature compact heat exchangers has been a primary concern\\u000a because the working temperature can be well above the creep limit of the materials. To establish the high temperature design\\u000a criterion

  11. Creep and Mechanical Properties of Cu6Sn5 and (Cu,Ni)6Sn5 at Elevated Temperatures

    NASA Astrophysics Data System (ADS)

    Mu, Dekui; Huang, Han; McDonald, Stuart D.; Nogita, Kazuhiro

    2013-02-01

    Cu6Sn5 is the most common and important intermetallic compound (IMC) formed between Sn-based solders and Cu substrates during soldering. The Cu6Sn5 IMC exhibits significantly different thermomechanical properties from the solder alloys and the substrate. The progress of high-density three-dimensional (3D) electrical packaging technologies has led to increased operating temperatures, and interfacial Cu6Sn5 accounts for a larger volume fraction of the fine-pitch solder joints in these packages. Knowledge of creep and the mechanical behavior of Cu6Sn5 at elevated temperatures is therefore essential to understanding the deformation of a lead-free solder joint in service. In this work, the effects of temperature and Ni solubility on creep and mechanical properties of Cu6Sn5 were investigated using energy-dispersive x-ray spectroscopy and nanoindentation. The reduced modulus and hardness of Cu6Sn5 were found to decrease as temperature increased from 25°C to 150°C. The addition of Ni increased the reduced modulus and hardness of Cu6Sn5 and had different effects on the creep of Cu6Sn5 at room and elevated temperatures.

  12. 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.

  13. 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.

  14. HIGH TEMPERATURE CREEP PROPERTIES AND MICROSTRUCTURAL EXAMINATIONS OF P92 WELDS

    E-print Network

    Paris-Sud XI, Université de

    1 HIGH TEMPERATURE CREEP PROPERTIES AND MICROSTRUCTURAL EXAMINATIONS OF P92 WELDS Kalck Charlotte1: charlotte.kalck@cea.fr Abstract The present study deals with the creep properties of welded joints made of P steels [1, 2], so that long term mechanical properties of P92 welded joints at 550°C still need further

  15. The microstructural record of porphyroclasts and matrix of serpentinite mylonites - from brittle and crystal-plastic deformation to dissolution-precipitation creep

    NASA Astrophysics Data System (ADS)

    Bial, J.; Trepmann, C. A.

    2013-04-01

    We examine the microfabric development in high-pressure, low-temperature metamorphic serpentinite mylonites exposed in the Erro-Tobbio Unit (Voltri Massif, Italy) using polarization microscopy and electron microscopy (SEM/EBSD, EMP). The mylonites are derived from mantle peridotites, were serpentinized at the ocean floor and underwent high pressure metamorphism during Alpine subduction. They contain diopside and olivine porphyroclasts embedded in a fine-grained matrix essentially consisting of antigorite. The porphyroclasts record brittle and crystal-plastic deformation of the original peridotites in the upper mantle at stresses of a few hundred MPa. After the peridotites became serpentinized, deformation occurred mainly by dissolution-precipitation creep resulting in a foliation with flattened olivine grains at phase boundaries with antigorite, crenulation cleavages and olivine and antigorite aggregates in strain shadows next to porphyroclasts. It is suggested that the fluid was provided by dehydration reactions of antigorite forming olivine and enstatite during subduction and prograde metamorphism. At sites of stress concentration around porphyroclasts antigorite reveals an associated SPO and CPO, characteristically varying grain sizes and sutured grain boundaries, indicating deformation by dislocation creep. Stresses were probably below a few tens of MPa in the serpentinites, which was not sufficiently high to allow for crystal-plastic deformation of olivine at conditions at which antigorite is stable. Accordingly, any intragranular deformation features of the newly precipitated olivine in strain shadows are absent. The porphyroclast microstructures are not associated with the microstructures of the mylonitic matrix, but are inherited from an independent earlier deformation. The porphyroclasts record a high-stress deformation in the upper mantle of the oceanic lithosphere probably related to rifting processes, whereas the antigorite matrix records deformation at low stresses during subduction and exhumation.

  16. Stress, slip, and earthquakes in models of complex single-fault systems incorporating brittle and creep deformations

    Microsoft Academic Search

    Yehuda Ben-Zion

    1996-01-01

    Numerical simulations of slip evolution along a cellular vertical strike-slip fault in an elastic half-space are performed for several models representing discrete fault systems embedded in three-dimensional elastic continua. The geometry and imposed boundary conditions correspond approximately to the central San Andreas fault. The simulations incorporate brittle and creep deformations in series; the net fault zone deformation rate is the

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  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. Stress and temperature dependence of creep in Alloy 600 in primary water

    NASA Astrophysics Data System (ADS)

    Yi, Yongsun; Was, Gary S.

    2001-10-01

    The stress and temperature dependence of creep of commercial nickel-base Alloy 600 was investigated through constant load, step-load, and step-temperature creep tests in deaerated primary water containing 40 to 60 cc/kg hydrogen. To analyze creep rates for Alloy 600 in the mill-annealed (MA) condition, effective stresses were estimated using applied stresses and instantaneous strains. The apparent activation area was determined to be 7 b 2 by the multiple regression analysis of creep rates. The apparent activation energy for creep has a weak stress dependence and was determined to lie between 188 and 281 kJ/mole for the effective stress range of 117 to 232 MPa. Creep rates were better correlated with effective stress than applied stress and the stress exponent of Alloy 600 MA was determined to be 2.2 at 337 °C and 5.1 at 360 °C. The magnitudes of the stress exponent, activation energy, and activation area can be interpreted to support a creep mechanism controlled by dislocation-climb and nonconservative motion of jogs in commercial Alloy 600 MA. The activation area agreed with that determined from carbon in solution, implying thermally activated dislocation glide as another possible creep mechanism.

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

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

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

  1. State variable approach to transient creep deformation in stress reduction experiments

    SciTech Connect

    Korhonen, M.A.; Gibeling, J.C.; Li, C.Y.

    1985-03-21

    Stress reduction experiments have been widely used to explore the internal state of a creeping material. Although there has been some criticism of the use of this method to measure internal stress directly, data from stress reduction experiments can be used to generate parameters for state variable models that are verified by other means. In this paper the predictions of a state variable approach to stress reduction experiments are explored in detail and compared to previously published data. The state variable model is shown to give a consistent description of the processes involved during the transient deformation, and the predictions and the model parameters are found to compare well with the data obtained by other means.

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

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Shrestha, Triratna

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

  6. Creep of pure metals at intermediate temperatures: Effects of stacking fault energy

    SciTech Connect

    Soliman, M.S. (King Saud Univ., Riyadh (Saudi Arabia). Mechanical Engineering Dept.)

    1993-10-01

    In the present paper, the D[sub eff] approach will be used to correlate the steady state creep rates in pure metals at intermediate temperatures with a newly-developed relation based on [var epsilon] [equals] A(D[sub l]Gb/kT)([Gamma]/Gb)[sup 3]([sigma]/G)[sup n]. It will be shown that dislocation core diffusion controlling creep in pure metals has a similar dependence on stacking fault energy as high-temperature creep. The metals are copper, aluminum, silver, nickel, and lead.

  7. 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.

  8. 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.

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

    Microsoft Academic Search

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

    2011-01-01

    Alloy 617 is the one of the leading candidate materials for Intermediate Heat eXchangers (IHX) of a Very High Temperature Reactor (VHTR). System start-ups and shut-downs as well as power transients will produce low cycle fatigue (LCF) loadings of components. Furthermore, the anticipated IHX operating temperature, up to 950°C, is in the range of creep so that creep-fatigue interaction, which

  10. 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.

  11. 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.

  12. 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.

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

    NASA Technical Reports Server (NTRS)

    Jenkins, J. M.

    1984-01-01

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

  14. 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

  15. Corrosion and creep behaviour of selected austenitic alloys in high temperature gaseous environments

    SciTech Connect

    Guttmann, V.; Hurst, R.C.; Kemeny, G.; Krockel, H.; Marriott, J.B.; Norton, J.F.; Van de Biest, O.; Van de Voorde, M.

    1983-01-01

    Features common to the environments of many fossil fuel conversion and utilization processes are high temperatures coupled with a severe corrosion potential of sulphur or carbon. Construction materials for such processes must not only be able to resist such environments but also sustain mechanical constraints. To meet these rigorous demands, austenitic steels and nickel-base alloys are traditionally considered as candidate materials. The present paper deals with the corrosion and creep behaviour of two commercial austenitic alloys, HK40 and Alloy 800H, and two pure ternary Fe-Ni-Cr alloys in the temperature range 825/sup 0/C-1050/sup 0/C (1517/sup 0/F-1922/sup 0/F). Corrosion test results are described under carburising, carburising-oxidising and sulphidising conditions whereas investigations of the interaction between corrosion and creep are limited to the carburising atmosphere. From the corrosion tests the kinetics of attack and mechanisms responsible are derived and the importance of the maintenance of a protective surface scale is confirmed. The influence of carburisation on the creep rupture and creep strain behaviour of HK40 is delineated and the role of increased carbide content in either reducing or increasing creep strength and in improving ductility is also explained with the help of microstructural investigations. Preliminary creep tests on Alloy 800H tubes are described where carburisation is observed to have a negligible influence on creep rupture properties.

  16. Treatment of material creep and nonlinearities in flexible mulitbody dynamics

    Microsoft Academic Search

    M. Xie; F. M. L. Amirouche

    1994-01-01

    This paper addresses the modeling of the generalized active forces resulting from deformable bodies when subjected to high temperature conditions, elastic-plastic deformations, creep effects, and material nonlinearities. The effects of elastic-plastic deformations are studied making use of the nonlinear stress-strain relationship and the geometrical stiffness concepts. Creep conditions resulting from high temperature are studied through several proposed models. Materials nonlinearities

  17. Constitutive modelling of anisotropic creep deformation in single crystal blade alloys SRR99 and CMSX-4

    Microsoft Academic Search

    Duncan W. MacLachlan; Lawrence W. Wright; Satish Gunturi; David M. Knowles

    2001-01-01

    A damage mechanics based model has been developed to model stress rupture and creep behaviour of the first and second generation single crystal superalloys SRR99 and CMSX-4. In this article the creep behaviour of CMSX-4 in several different orientations at 950°C is simulated using finite elements, these simulations are compared with the results of creep tests. In order that the

  18. 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.

  19. High temperature deformation of ultra-fine-grained oxide dispersion strengthened alloys

    NASA Astrophysics Data System (ADS)

    Gregory, J. K.; Gibeling, J. C.; Nix, W. D.

    1985-05-01

    The high temperature deformation properties of two oxide dispersion strengthened (ODS) alloys, MA 754 and MA 6000, with initial grain sizes of 0.67 µm and 0.26 µm, respectively, have been studied. Tensile tests have been conducted at 1173, 1273, and 1373 K at strain rates ranging from 2 X 10-4 to 5 s-1. Tension creep tests were conducted on MA 6000 at 1273 K to extend the strain rate regime to 3 X 10-8 s-1. Microstructures of both undeformed and deformed samples have been characterized by transmission electron microscopy. MA 754 exhibits a maximum elongation of 200 pct and a maximum strain rate sensitivity of 0.30 at 1273 K. MA 6000 is superplastic, exhibiting a maximum elongation of over 300 pct and a maximum strain rate sensitivity of 0.47 at 1273 K. The microstructure of MA 754 is unstable during deformation, showing recrystallized grains and grains which have grown to 1 µm in diameter. No evidence for ordinary recrystallization is found for MA 6000, and grain growth is slight. For both alloys, strain rates less than about 1 s-1 alter the initial microstructure and prevent grain coarsening on subsequent annealing at higher temperature. Deformation of the fine-grained MA 6000 can be described as a combination of power law creep and diffusional (Coble) creep, with a threshold stress caused by the presence of ?t’ particles existing only for the diffusional creep process. Structural instabilities do not permit a simple description of deformation of MA 754.

  20. Kinetics and mechanisms of high-temperature creep in silicon carbide: II, chemically vapor deposited

    Microsoft Academic Search

    C. H. Carter; J. Bentley; R. F. Davis

    1984-01-01

    Chemically vapor deposited (CVD) silicon carbide was subjected to constant compressive stresses (110 to 220 MN\\/m²) at high temperatures (1848 to 2023 K) in order to determine the controlling steady-state creep mechanisms under these conditions. An extensive TEM study was also conducted to facilitate this determination. The strong preferred crystallographic orientation of this material causes the creep rate to be

  1. Effects of pressure on high-temperature dislocation creep in olivine

    Microsoft Academic Search

    Shun-Ichiro Karato; Haemyeong Jung

    2003-01-01

    Effects of pressure on high-temperature, dislocation creep in olivine ((Mg, Fe)2SiO4) aggregates have been determined under both water-poor ('dry') and water-saturated ('wet') conditions. New experimental data were obtained at pressures of 1-2 GPa under 'dry' and 'wet' conditions using a newly developed high-resolution dislocation density measurement technique to estimate the creep strength. These data are compared with previous data at

  2. Evidence From Pyrite Microstructure For Earlier Higher Temperature Deformation History In SAFOD

    NASA Astrophysics Data System (ADS)

    Boyle, A. P.; Hadizadeh, J.

    2011-12-01

    Pyrite is commonly found in SAFOD gouge samples as diagenetic framboids in relict sedimentary clasts as well as deformed and undeformed clusters of secondary pyrite grains. We investigated the forms, distribution and deformation mechanisms of pyrite in a core sample from 3194m measured depth (T 112±2 °C) consisting of foliated shale-siltstone cataclasites to constrain the deformation history of the gouge. The gouge-pyrite microstructures were studied using HR-SEM, and pyrite deformation was characterized by EBSD, which provided orientation contrast and band contrast images, Euler angle maps and crystallographic data for pole figures. The secondary pyrite appears mostly as foliation-parallel, elongated, mm-scale clusters of small grains (~0.5-4 ?m and <100 ?m). The clusters show brittle fragmentation in contact with the gouge. The pyrite domains between these brittle fractures preserve evidence of plastic deformation, as do pyrite domains adjacent to cataclasis zones. Pole figures and misorientation sub-grain boundaries indicate a broad range of pyrite grain-scale dislocation creep activity, including deformation via sub-grain rotation mechanisms, as evidenced by core-mantle textures and clumps of similarly oriented smaller pyrite grains. The latter evidence suggests the presence of previously larger pyrite grains. Recently revised pyrite deformation mechanisms map (Barrie et al. 2011) suggests T ~260 °C for the onset of dislocation creep in pyrite under high stress regimes at 10-10s-1 to 10-12s-1 (higher T at lower stresses), over twice the temperature measured at the sample depth. Secondary pyrite also locally replaces/overprints calcite veins in fractured quartz. In some cases this pyrite preserves evidence of having been subsequently deformed plastically and/or brittlely. However, in other cases, invariant pole figures and lack of misorientation sub grain boundaries or fractures indicate that some late replacive pyrite is unaffected by any subsequent deformation. The following may be inferred from the results: 1. It is likely that secondary pyrite formed continuously to present time. 2. Where undeformed, the secondary pyrite is clearly replacive in nature. It is unclear if all the cluster pyrite formed originally by replacement since potential earlier textures have been removed where creep has occurred. 3. Brittle deformation at gouge-pyrite-cluster boundaries and overall plastic deformation of the pyrite clusters suggest a decrease in temperature with time during deformation of the pyrite. 4. Overprinting of calcite veins by plastically deformed pyrite suggests deformation-related fluid-rock processes such as pressure solution may be active well below the present SAFOD depths.

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    Around the perimeter of Antarctica, much of the ice sheet discharges to the ocean through floating ice shelves. The buttressing provided by ice shelves is critical for modulating the flux of ice into the ocean, and the presently observed thinning of ice shelves is believed to be reducing their buttressing capacity and contributing to the acceleration and thinning of the grounded ice sheet. However, relatively little attention has been paid to the role that fractures play in the ability of ice shelves to sustain and transmit buttressing stresses. Here, we present a new framework for quantifying the role that fractures play in the creep deformation and buttressing capacity of ice shelves. We apply principles of continuum damage mechanics to derive a new analytical relation for the creep of an ice shelf that accounts for the softening influence of fractures on longitudinal deformation using a state damage variable. We use this new analytical relation, combined with a temperature calculation for the ice, to partition an inverse method solution for ice shelf rigidity into independent solutions for softening damage and stabilizing backstress. Using this new approach, field and remote sensing data can be utilized to monitor the structural integrity of ice shelves, their ability to buttress the flow of ice at the grounding line, and thus their indirect contribution to ice sheet mass balance and global sea level. We apply this technique to the Larsen C ice shelf using remote sensing and Operation IceBridge data, finding damage in areas with known crevasses and rifts. Backstress is highest near the grounding line and upstream of ice rises, in agreement with patterns observed on other ice shelves. The ice in contact with the Bawden ice rise is weakened by fractures, and additional damage or thinning in this area could diminish the backstress transmitted upstream. We model the consequences for the ice shelf if it loses contact with this small ice rise, finding that flow speeds would increase by 25% or more over an area the size of the former Larsen B ice shelf. Such a perturbation could potentially destabilize the northern part of Larsen C along pre-existing lines of weakness, highlighting the importance of the feedback between buttressing and fracturing in an ice shelf.

  5. Technique for tensile creep testing of ceramics

    Microsoft Academic Search

    Daniel F. Carroll; S. M. Wiederhom; D. E. Roberts

    1989-01-01

    An experimental technique for measuring tensile creep deformation in ceramic materials to temperatures of 1500°C is described. The technique uses simple flat dog-bone-shaped specimens and a hot-grip design for the loading fixture, which provide good alignment at minimum cost. Creep deformation is measured using laser extensometry to monitor the relative displacement of flags that are attached to the gauge section

  6. Determination of room-temperature creep of soft lead zirconate titanate piezoceramics under static electric fields

    NASA Astrophysics Data System (ADS)

    Zhou, Dayu; Kamlah, Marc

    2005-11-01

    This study focuses on the experimental investigation of the time-dependent effects of a commercial soft lead zirconate titanate material at room temperature. Samples in initially unpoled states were subjected to a cyclic stepwise electric field which was kept constant at different levels for 300 s. Due to ferroelectric domain switching, significant nonlinearity and hysteresis were observed in the overall polarization and strain response. In particular, the material exhibited creep behavior as the applied electric field was held constant over extended periods of time. This creep was caused by microscopic domain switching processes induced gradually during the holding time. The creep was of primary or transient type in nature and depended strongly on the magnitude of the load applied. Most pronounced creep was observed when holding the field close to the coercive field. Logarithmic representation of the polarization or strain versus time curves indicated that the creep behavior could be quantified approximately by the Andrade power law. The creep exponents were determined for different field conditions. The results may help the understanding of the creep mechanism, which in turn provides contributions to improve the performance and reliability of ultrahigh-precision positioning piezoactuators.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. High temperature creep behavior of metal matrix aluminum-SiC composites

    SciTech Connect

    Gonzalez-Doncel, G. (Centro Nacional de Investigaciones Metalurgicas, Madrid (Spain)); Sherby, O.D. (Stanford Univ., CA (United States). Dept. of Materials Science and Engineering)

    1993-10-01

    The tensile creep behavior of Al-SiC metal matrix composites has been investigated and analyzed over the temperature range from 230 to 525 C. It is shown that plastic flow in these materials is lattice-diffusion controlled dislocation creep in the aluminum matrix. All data on Al-SiC have been assessed by a creep relation developed for creep of metals at constant structure with the added contribution of a threshold stress. The threshold stress for creep in Al-SiC composites is not a thermally-activated process and is shown to have a linear dependence with temperature becoming zero at 470 C. The threshold stress is higher for the whisker composites than for the particulate composites. The origin of the threshold stress is not well understood and cannot be explained by contemporary dislocation models involving dislocation bowing or unpinning around particles sites. The observed interparticle-interwhisker spacing is shown to influence the creep rate in the same way as observed for mechanical alloyed (MA) Al base materials.

  12. 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.

  13. Creep in shear of experimental solder joints

    SciTech Connect

    Tribula, D.; Morris, J.W. Jr.

    1989-09-01

    Thermal fatigue failures of solder joints in electronic devices are a great concern in the electronics industry. Since the fatigue load is often in shear the details of thermal fatigue failure in shear are of particular interest. Recent work indicates that similar failure mechanisms operate in both thermal fatigue in shear and unidirectional creep in shear. Additionally, since the operative temperatures during thermal fatigue represent high solder homologous temperatures, creep deformation is certainly involved. These factors and the relative ease of conducting creep experiments encourage the study of solder joints under shear creep conditions. This work presents steady state shear creep rate vs shear stress data for several solder compositions, including the binary eutectic alloy and Pb-Sn alloyed with small amounts of Bi, Cd, In, and Sb, in a joint configuration. These data indicate that conventional creep mechanisms operate in the temperature and shear strain rate ranges studied. Extensive microstructural information is also reported. The microstructural evolution under creep conditions indicates that the instability of the as-cast binary Pb-Sn eutectic microstructure initiates creep failure. Changes of the as-solidified microstructure with the third element addition are reported as are the microstructural responses of each of these alloys to creep deformation. The efficacy of postponing the microstructural instability with the addition of small amounts of ternary elements is discussed. 27 refs., 13 figs., 1 tab.

  14. High-pressure creep of serpentine, interseismic deformation and initiation of subduction

    NASA Astrophysics Data System (ADS)

    Reynard, B.; Hilairet, N.; Wang, Y.; Daniel, I.; Merkel, S.; Petitgirard, S.; Nishiyama, N.

    2007-12-01

    Serpentines, phyllosilicates resulting from mantle hydration, have a low viscosity compared with other mantle and slab materials within subduction zones. They have a global geodynamic importance on the timescale of mantle convection because a serpentinite layer may decouple the mantle wedge from the subducting slab, therefore influencing plate tectonics regime on the Earth. The seismic implications are far reaching as serpentinite rheology may govern stress build-up and downdip relaxation over the slab surface, which are critical parameters for earthquake triggering and for the downdip extent of major ruptures. However, limitation of apparatus has restricted previous high temperature deformation experiments on serpentinites to pressures below 0.7 GPa, and the lack of data at relevant P-T impeded quantification of serpentine rheology influence on subduction zones dynamics. We present in situ deformation experiments on the high-pressure variety antigorite, at low strain rates and pressure-temperature (P-T) of 1 and 4 GPa and 200 to 500C, respectively, i.e. over most of the antigorite stability field, using the Deformation-DIA (D-DIA) apparatus coupled with synchrotron X-ray at 13-BM-D at GSE-CARS (Advanced Photo Source). Strain rates and stresses were obtained respectively from in-situ monitoring the sample length with X-ray radiographs, and azimuthal dependence of d-spacings on diffraction patterns. The determined stress-strain curves were fitted to a power-law equation including both temperature and pressure dependence. Regardless of the temperature, serpentinized mantle at the slab surface has a low viscosity that allows localizing the deformation and impeding stress build-up. The consequences of such a rheology for subduction zones dynamics at short and long term include limitation of the downdip propagation of large earthquakes and viscous relaxation as an origin of post-seismic deformations and slow earthquakes. The low viscosity of serpentinized faults in the oceanic lithosphere makes them possible sites for subduction initiation.

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

    NASA Technical Reports Server (NTRS)

    Mathauser, Eldon E; Deveikis, William D

    1957-01-01

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

  16. Elevated temperature deformation of single crystal Y{sub 3}Al{sub 5}O{sub 12}

    SciTech Connect

    Wolfenstine, J. [Univ. of Texas, San Antonio, TX (United States). Div. of Engineering] [Univ. of Texas, San Antonio, TX (United States). Div. of Engineering

    1998-02-13

    Single crystal oxides with complex crystal structures having large unit cells and consequently, large Burgers vectors have recently received attention as possible fiber-reinforcements in oxide/oxide composites for use at temperatures greater than 1,500 C. One such single crystal oxide is Y{sub 3}Al{sub 5}O{sub 12} (Yttrium Aluminum Garnet or YAG). At present both dislocation glide and climb have been suggested as the rate-controlling deformation mechanism for single crystal Y{sub 3}Al{sub 5}O{sub 12} above 1,600 C at stresses below 300 MPa. The choice of the specific creep mechanism was based on the nature of the creep transient, value of the stress exponent, activation energy for creep and examination of the deformed microstructure obtained from constant strain-rate tests. The present investigation was undertaken to: (1) determine whether the creep behavior of single crystal Y{sub 3}Al{sub 5}O{sub 12} is controlled by, dislocation glide or climb by examining the nature of the creep transient upon initial loading and after a stress change using constant stress tests and (2) verify that the existing steady-state creep data for single crystal Y{sub 3}Al{sub 5}O{sub 12} obtained from constant strain-rate tests are in agreement with the constant stress tests.

  17. The effect of stacking fault energy on low temperature creep in pure metals

    Microsoft Academic Search

    P. R. Thornton; P. B. Hirsch

    1958-01-01

    Experimental results obtained by studying the low temperature creep behaviour before and after a small stress change are interpreted in terms of barriers due to intersecting dislocations. Using the data available on the temperature dependence of the flow stress in conjunction with these experimental results, estimates of jog energies are derived and compared with values obtained from flow stress data

  18. Physiology and growth response of roughstalk bluegrass and creeping bentgrass to high temperature stress

    Microsoft Academic Search

    James Marable Rutledge

    2010-01-01

    Roughstalk bluegrass (Poa trivialis L.) (RBG) is a problematic weed in creeping bentgrass fairways (Agrostis stolonifera L.) (CBG) due to its susceptibility to high temperature stress. Our objective was to describe morphological and physiological characteristics of RBG and CBG under high temperature stress to ultimately improve management and control strategies of RBG. Laser (heat-tolerant) and Pulsar (heatsensitive) RBG performed statistically

  19. A theoretical model of accelerated irradiation creep at low temperatures by transient interstitial absorption

    SciTech Connect

    Stoller, R.E.; Grossbeck, M.L.; Mansur, L.K.

    1990-01-01

    A theoretical model has been developed using the reaction rate theory of radiation effects to explain experimental results that showed higher than expected values of irradiation creep at low temperatures in the Oak Ridge Research Reactor. The customary assumption that the point defect concentrations are at steady state was not made; rather, the time dependence of the vacancy and interstitial concentrations and the creep rate were explicitly calculated. For temperatures below about 100 to 200{degree}C, the time required for the vacancy concentration to reach steady state exceeds the duration of the experiment. For example, if materials parameters typical of austenitic stainless steel are used, the calculated vacancy transient dose at 100{degree}C is about 100 dpa. At 550{degree}C this transient is over by 10{sup {minus}8} dpa. During the time that the vacancy population remains lower than its steady state value, dislocation climb is increased since defects of primarily one type are being absorbed. Using the time-dependent point defect concentrations, the dislocation climb velocity has been calculated as a function of time and a climb-enabled glide creep model had been invoked. The extended transient time for the vacancies leads to high creep rates at low temperatures. In agreement with the experimental observations, a minimum in the temperature dependence of creep is predicted at a temperature between 50 and 350{degree}C. The temperature at which the minimum occurs decreases as the irradiation dose increases. Predicted values of creep at 8 dpa are in good agreement with the results of the ORR-MFE-6J/7J experiment.

  20. Reduction in the initial wear of ultrahigh molecular weight polyethylene after compressive creep deformation

    Microsoft Academic Search

    Kwon-Yong Lee; David Pienkowski

    1997-01-01

    Although the wear of ultrahigh molecular weight polyethylene (UHMWPE) total joint implant components has received much attention, the creep of this polymer has been inadequately studied. The objectives of this study were to determine whether creep affects the wear of UHMWPE and, if so, to measure the magnitude of this effect. Cylindrical specimens were machined from GUR 4150HP extruded unirradiated

  1. Service-type creep-fatigue experiments with cruciform specimens and modelling of deformation

    Microsoft Academic Search

    A. Samir; A. Simon; A. Scholz; C. Berger

    2006-01-01

    Advanced material models for the application to component life prediction require multiaxial experiments. A biaxial testing system for cruciform test pieces has been established in order to provide data for creep, creep-fatigue and thermomechanical fatigue (TMF) experiments. For this purpose a cruciform specimen was developed with the aid of Finite element calculation and the specimen design was optimised for tension

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

    SciTech Connect

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

    2003-04-22

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

  3. Nanogranular origin of concrete creep

    PubMed Central

    Vandamme, Matthieu; Ulm, Franz-Josef

    2009-01-01

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

  4. High temperature deformation behavior of solid and semi-solid alloy 718

    SciTech Connect

    Lewandowski, M.S.; Overfelt, R.A.

    1999-12-10

    The mechanical response of alloy 718 with various microstructures in the solid and semi-solid state has been characterized. The experimental results presented for the lower temperature solid state deformation are in good agreement with published literature values and extend the experimental range to higher temperatures and lower strain rates. When dendrites were aligned along the compression axis, the directionally solidified materials exhibited an activation energy for plastic flow consistent with the activation energy for creep and self-diffusion in nickel, even at temperatures within the mushy zone. However, samples containing non-aligned grains in the semi-solid state exhibited a greater dependence of deformation with temperature; this was associated with lubricated flow of the grains due to the intergranular liquid in the mushy zone.

  5. Indentation creep study on ultrafine-grained Zn processed by powder metallurgy

    E-print Network

    Gubicza, Jenõ

    in the homologous temperature range of 0.87­0.91. The activation energy of the creep for UFG-Zn was found to be much during creep deformation, indicating a considerable dislocation activity. & 2013 Elsevier B.V. All rights reserved. 1. Introduction The deformation mechanisms in hexagonal close-packed (hcp) metals depend strongly

  6. ANALYSIS OF INDENTATION CREEP D.S. Stone,1,2

    E-print Network

    Stone, Don

    relied on indentation creep to study rate-sensitive deformation in solids [1-3]. Although not as straight the years the great majority of work in indentation creep has been performed at high homologous temperatures conditions where the elastic deformations are small and therefore relatively unimportant [2, 4

  7. TEMPERATURE DEPENDENT CREEP EXPANSION OF Ti-6Al-4V LOW DENSITY CORE SANDWICH STRUCTURES

    E-print Network

    Wadley, Haydn

    TEMPERATURE DEPENDENT CREEP EXPANSION OF Ti-6Al-4V LOW DENSITY CORE SANDWICH STRUCTURES Douglas T for the low cost manufacture of porous metal sandwich structures. These porous cored sandwich structures technique for the production of Ti-6Al-4V porous cored sandwich structures. Their process began

  8. 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.

  9. 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.

  10. Diffusion creep of fine-grained polycrystalline anorthite at high temperature

    Microsoft Academic Search

    Z. Wang; G. Dresen; R. Wirth

    1996-01-01

    We performed creep experiments on synthetic fine-grained polycrystalline anorthite (d<30 mum) at temperatures from T=1000°C to 1300°C, oxygen fugacities of fO2=10-19-10-4 MPa, and stresses of sigma=5-80 MPa at room pressure. Experimental results show creep with high strain-rate sensitivity for stresses below sigma<30 MPa. We found the empirical flow law: ?=(3.8+\\/-11.5)×1010sigma13+\\/-0.3d-2.5+\\/-0.3×exp(-420+\\/-38 kJ\\/mol\\/RT) Transmission electron microscopy shows that the material is free

  11. On the viscosity and creep mechanism of Earth's inner core

    Microsoft Academic Search

    James A. Van Orman

    2004-01-01

    The viscosity and creep mechanism of Earth's inner core are evaluated based on microphysical models of the flow properties of iron under high pressure and temperature, low stress and large grain size. Harper-Dorn creep, a Newtonian-viscous dislocation mechanism, is shown to be the likely deformation process, and the viscosity is predicted to be ?1011 Pa s, at the low end

  12. Improved prediction model for time-dependent deformations of concrete: Part 2—Basic creep

    Microsoft Academic Search

    Zden?k P. Bažant; Joong-Koo Kim

    1991-01-01

    The second part of this series presents the formulae for the prediction of basic creep of concrete, i.e. creep at no moisture\\u000a exchange. The formulae give the secant uniaxial compliance function which depends on the stress level, and, as a special case,\\u000a the compliance function for linear structural analysis according to the principle of superposition. The formulae are based\\u000a on

  13. The role of fluids in partitioning brittle deformation and ductile creep in auriferous shear zones between 500 and 700 °C

    Microsoft Academic Search

    Jochen Kolb

    2008-01-01

    The fabric, mineralogy, geochemistry, and stable isotope systematics of auriferous shear zones in various hydrothermal gold deposits were studied in order to discuss the role of fluids in rock deformation at temperatures between 500 °C and 700 °C. The strong hydrothermal alteration and gold mineralization indicates that effective permeability development goes ahead with high-temperature rock deformation. The economic gold enrichment is often

  14. Assessment of damage and life prediction of austenitic stainless steel under high temperature creep–fatigue interaction condition

    Microsoft Academic Search

    Soo Woo Nam

    2002-01-01

    It is understood that grain boundary cavitation is one of the detrimental processes for the degradation of austenitic stainless steels that reduces the creep–fatigue life at high temperatures. A new damage function based on a model for the creep–fatigue life prediction in terms of nucleation and growth of grain boundary cavities is proposed for austenitic stainless steel. This damage function

  15. Internal stress and dislocation structure of aluminum in high-temperature creep

    Microsoft Academic Search

    A. Orlová; Z. Tobolová; J. Cadek

    1972-01-01

    The dislocation structure formed in high-temperature creep of aluminum has been investigated in the transmission electron microscope. The effect of applied stress and temperature on the quantitative characteristics—dislocation density in sub-grains, subgrain size and misorientation—has been discussed. The correlation of the steady-state substructure characteristics with the macroscopic mean internal stress shows the main contribution of the internal stress field of

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

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

  17. 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.

  18. Plastic flow and dislocation structures in tantalum carbide: Deformation at low and intermediate homologous temperatures

    SciTech Connect

    Kim, C.; Grummon, D.S. (Michigan State Univ., East Lansing, MI (United States). Dept. of Materials Science and Mechanics); Gottstein, G. (RWTH Aachen (Germany). Inst. fuer Metallkunde und Metallphysik)

    1994-07-01

    Dislocation structures and plastic flow in TaC[sub 0.99] have been studied in material deformed by microindentation at 20 C, and in specimens crept at temperatures between 0.37 and 0.43 T[sub m] (1300--1500 C). Extensive local plastic deformation occurred during indentation, accomplished mainly by the motion of a/2<011> edge dislocation gliding on [111]. The resulting defect structure consisted primarily of long screw dislocations, suggesting a relatively high mobility for edge segments and a large Peierls stress for screw dislocation motion. This <110>[111] slip system also operated in specimens crept at 0.37-0.43 T[sub m]. Thermal activation apparently increased the mobility of screw segments, resulting in substructures containing mixed dislocations with no preferred orientation. Microstructural observations, and analysis of kinetic data for power-law creep, suggest that intermediate temperature creep deformation of TaC[sub 0.99] occurs mainly by climb-controlled grain boundary sliding with severely limited intergranular accommodation.

  19. 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.

  20. High temperature deformation of 6061 Al

    Microsoft Academic Search

    Kyungtae Park; E. J. Lavernia; F. A. Mohamed

    1994-01-01

    The creep behavior of powder metallurgy (PM) 6061 Al, which has been used as a metal matrix alloy in the development of discontinuous silicon carbide reinforced aluminum (SiC-Al) composites, has been studied over six orders of magnitude of strain rate. The experimental data show that the steady-state stage of the creep curve is of short duration; that the stress dependence

  1. 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.

  2. Properties of aluminum alloys: Tensile, creep, and fatigue data at high and low temperatures

    SciTech Connect

    Kaufman, J.G. (ed.)

    1999-01-01

    Based on work by Alcoa Laboratories over several years, this book compiles more than 300 tables listing typical average properties of a wide range of aluminum alloys. Contents include: Typical Mechanical Properties of Wrought and Cast Aluminum Alloys at Various Temperatures--tensile properties at subzero temperatures at temperature after various holding times at the test temperature, and at room temperature after exposure at various temperatures for various holding times; creep rupture strengths for various times at various temperatures; stresses required to generate various amounts of creep in various lengths of time; rotating-beam fatigue strengths; modulus of elasticity as a function of temperature; Fatigue Data--fatigue strength of wrought aluminum alloys, axial stress fatigue strength of wrought aluminum alloys (at various stress ratios, smooth and notched specimens), average fatigue strength for aluminum and aluminum alloy flat sheet specimens (under complete reversed flexure), cantilever-beam fatigue test results of aluminum alloys at elevated temperatures and following stabilization at the test temperature. The properties in this book are typical values--expected average values for representative lots produced using commercial processes and that meet industry standards, whose room temperature properties correspond to published typical values for the alloys.

  3. 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?ábek, Petr; Stünitz, 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 µm 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 µm), 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 700-750°C 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.

  4. 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.

  5. Vortex creep and the internal temperature of neutron stars The Crab pulsar and PSR 0525 + 21

    NASA Technical Reports Server (NTRS)

    Alpar, M. A.; Nandkumar, R.; Pines, D.

    1985-01-01

    The behavior of the Crab pulsar following the 1969 and 1975 glitches and the postglich behavior of the old pulsar PSR 0525 + 21 are explained as resulting from internal torques due to the thermal creep of vortex lines in pinned superfluid regions. An overview of vortex creep theory is first given, and the immediate postglitch behavior of the Crab pulsar is calculated and compared with observation. The persistent shift in the spin-down rate observed for the Crab pulsar following the 1975 glitch is considered, and the internal and surface temperatures of this pulsar are deduced. The postglich behavior expected for very old pulsars is examined, showing that PSR 0525 + 21 falls into this category. It is concluded that the behavior of the Crab pulsar following both glitches can be characterized by the same two pinning regions. A comparison of the internal temperature for the Crab and Vela pulsars provides a significant constraint on the cooling of neutron stars.

  6. A neural network approach to elevated temperature creep–fatigue life prediction

    Microsoft Academic Search

    Vasisht Venkatesh; H. J Rack

    1999-01-01

    A new approach using a back-propagation neural network for life prediction was developed and demonstrated for predicting the elevated temperature (0.7–0.8Tm) creep–fatigue behavior of Ni-base alloy INCONEL 690. The neural network was trained with five extrinsic parameters, characterized via a 25–1 fractional factorial design methodology, and an intrinsic parameter (final grain size). The back-propagation network training error, prediction error and

  7. The transition from high temperature creep to fracture in Maryland diabase

    Microsoft Academic Search

    Y. Caristan

    1982-01-01

    The transition from high-temperature creep to brittle fracture in Maryland diabase was investigated as a function of confining pressure and strain rate. Experiments were conducted at 1000°C. Confining pressure was varied to 450 MPa and strain rates from 2×10-3 s-1 to 4×10-6 s-1. At fixed strain rate, the rock strength first increased with pressure, reached a maximum, and then decreased

  8. Continuum Damage Based Constitutive Equations for Copper under High Temperature Creep and Cyclic Plasticity

    Microsoft Academic Search

    F. P. E. Dunne; D. R. Hayhurst

    1992-01-01

    Viscoplastic constitutive equations without damage for cast copper have been developed for cyclic mechanical and cyclic thermal loading over the temperature range 20-500 degrees C (nominal composition: 99.99% Cu, 0.005% O2, B.S. 10355-1037). Model predictions have been compared with experimental cyclic plasticity tests. Good agreement has been achieved. Creep and cyclic plasticity damage evolution equations have been developed. The effect

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

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

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.

    1977-01-01

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

  11. Investigation of ?\\/?? lattice mismatch in the polycrystalline nickel-base superalloy IN738LC: Influence of heat treatment and creep deformation

    Microsoft Academic Search

    J. Li; R. P. Wahi

    1995-01-01

    The ?\\/?? lattice misfit in the polycrystalline nickel-base superalloy IN738LC has been determined by convergent beam electron diffraction (CBED) technique in a transmission electron microscope (TEM). The influence of heat treatment and creep deformation on the misfit was investigated. The chemical compositions of the ? and ?? phases were analysed with the help of Energy Dispersive Spectrometry (EDS). The influence

  12. Stress, slip, and earthquakes in models of complex single-fault systems incorporating brittle and creep deformations

    NASA Astrophysics Data System (ADS)

    Ben-Zion, Yehuda

    1996-03-01

    Numerical simulations of slip evolution along a cellular vertical strike-slip fault in an elastic half-space are performed for several models representing discrete fault systems embedded in three-dimensional elastic continua. The geometry and imposed boundary conditions correspond approximately to the central San Andreas fault. The simulations incorporate brittle and creep deformations in series; the net fault zone deformation rate is the sum of creep rate and frictional slip rate. Brittle fault properties are given by various distributions of earthquake stress drops on failing segments (numerical cells). The assumed distributions represent two idealized situations corresponding to different extreme states along an evolutionary path of a fault: (1) a strongly disordered state characterized by a wide range of size scales, representing immature fault zones and extended spatial domains, and (2) a relatively regular state having a narrow range of size scales, representing mature highly-slipped faults. The assumed creep properties are identical in all cases. These are prescribed in terms of coefficients characterizing a power law dependency of creep-slip rate on stress. The combined brittle-creep process and employed parameters lead to an overall "pine-tree" stress-depth profile with a "brittle-ductile" transition depth of about 12.5 km, and variable stress-along-strike profiles with "brittle-creep" transition around 65 km NW of the 1857 rupture. The spatial patterns of simulated hypocenters are statistically similar to observed data. The results indicate that the range of size scales characterizing strong fault zone heterogeneities has important manifestations on the seismic response of a fault system. A narrow range of size scales leads to frequency-size statistics of earthquakes resembling the characteristic earthquake distribution, and quasi-periodic temporal distribution of large events as in the seismic gap hypothesis. On the other hand, a wide range of size scales leads to Gutenberg-Richter power law frequency-size statistics, and random or clustered temporal distribution of large events. The simulations demonstrate that treatment of the various observed forms of frequency-size and temporal statistics of earthquakes can be unified through the concept of range of size scales characterizing fault zone heterogeneities. This has a clear physical interpretation in terms of structural properties of a given fault zone or broad lithospheric domain, and is supported by observed earthquake and fault data. In some simulated cases the frequency-size statistics of small earthquakes fall sharply below the self-similar Gutenberg-Richter line. The results indicate that small earthquakes prepare the fault for the occurrence of a large event by smoothing, during gradual tectonic loading, the long-wavelength components of stress on the fault. This is done through short-wavelength stress roughening associated with the numerous ruptures of the small events. The above pattern of smoothing/roughening of long/short wavelengths of stress on the fault is reversed during large-scale ruptures of the big events.

  13. 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.

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

    NASA Technical Reports Server (NTRS)

    Mathauser, Eldon E; Deveikis, William D

    1955-01-01

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

  15. Creep-fatigue life prediction of in situ composite solders

    Microsoft Academic Search

    C. G. Kuo; S. M. L. Sastry; K. L. Jerina

    1995-01-01

    Eutectic tin-lead solder alloys subjected to cyclic loading at room temperature experience creep-fatigue interactions due to high homologous temperature. Intermetallic reinforcements of Ni3Sn4 and Cu6Sn5 are incorporated into eutectic tin-lead alloy by rapid solidification processes to form in situ composite solders. In this study, the in situ composite solders were subjected to combined creep and fatigue deformation at room temperature.

  16. Creep-fatigue life prediction of in situ composite solders

    Microsoft Academic Search

    C. G. Kuo; S. M. L. Sastry; K. L. Jerina

    1995-01-01

    Eutectic tin-lead solder alloys subjected to cyclic loading at room temperature experience creep-fatigue interactions due\\u000a to high homologous temperature. Intermetallic reinforcements of Ni3Sn4 and Cu6Sn5 are incorporated into eutectic tin-lead alloy by rapid solidification processes to formin situ composite solders. In this study, thein situ composite solders were subjected to combined creep and fatigue deformation at room temperature. Under cyclic

  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. 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

  19. 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

  20. Creep of chemically vapor deposited SiC fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1984-01-01

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

  1. INVESTIGATION OF THE COMPRESSIVE, BEARING, AND SHEAR CREEP-RUPTURE PROPERTIES OF AIRCRAFT STRUCTURAL METALS AND JOINTS AT ELEVATED TEMPERATURES. Period covered January-December 1955

    Microsoft Academic Search

    Yerkovich

    1956-01-01

    Cornell Aeronautical Lab., Ic., Buffalo. Various aircraft structural ; alloys have been exposed to a tension, compression, bearing, and shear creep test ; program to establish their high-temperature creep and rupture properties under ; the influence of these types of stresses. From results obtained in this ; investigation, it has been found that the test alloys display creep ; characteristics

  2. The microstructural record of porphyroclasts and matrix of partly serpentinized peridotite mylonites - from brittle and crystal-plastic deformation to dissolution-precipitation creep

    NASA Astrophysics Data System (ADS)

    Bial, J.; Trepmann, C. A.

    2013-10-01

    We present microfabrics in high-pressure, metamorphic, partly serpentinized peridotite mylonites from the Voltri Massif, in which porphyroclasts and matrix record independent deformation events. The microfabrics are analysed using polarization microscopy and electron microscopy (SEM/EBSD, EMP). The mylonites contain diopside and olivine porphyroclasts originating from the mantle protolith embedded in a fine-grained matrix consisting mainly of antigorite and minor olivine and pyroxene. The porphyroclasts record brittle and crystal-plastic deformation of the peridotite at upper-mantle conditions and differential stresses of a few hundred MPa. After the peridotites became serpentinized, deformation occurred mainly by dissolution-precipitation creep resulting in a pronounced foliation of the antigorite matrix, crenulation cleavages and newly precipitated olivine and pyroxene from the pore fluid at sites of dilation, i.e. in strain shadows next to porphyroclasts and folded fine-grained antigorite layers. Antigorite reveals a pronounced associated shape preferred orientation (SPO) and crystallographic preferred orientation (CPO) with the basal (001) cleavage plane oriented in the foliation plane. In monomineralic antigorite aggregates at sites of stress concentration around porphyroclasts, a characteristically reduced grain size and deflecting CPO as well as sutured grain boundaries indicate also some contribution of crystal-plastic deformation and grain-boundary migration of antigorite. In contrast, the absence of any intragranular deformation features in newly precipitated olivine in strain shadows reveals that stresses were not sufficiently high to allow for significant dislocation creep of olivine at conditions at which antigorite is stable. The porphyroclast microstructures are not associated with the microstructures of the mylonitic matrix, but are inherited from an independent earlier deformation. The porphyroclasts record a high-stress deformation of the peridotite with dislocation creep of olivine in the upper mantle probably related to rifting processes, whereas the serpentinite matrix records dominantly dissolution-precipitation creep and low stresses during subduction and exhumation.

  3. Plastic deformation mechanism of pure aluminum at low homologous temperatures

    Microsoft Academic Search

    C.-M. Kuo; H.-H. Chu

    2005-01-01

    Contemporary theory of metallic plastic deformation mechanism at low homologous temperatures is attributed to the physical processes of dislocations passing obstacles. Physically based deformation mechanism is generally considered as thermally activated motion of dislocations past obstacles and structural evolution of the obstacles. In order to verify the thermally activated deformation theory, stress rate change experiments, which give rapid stress changes,

  4. 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 ?.

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

    SciTech Connect

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

    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.

  6. 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 ~3.5×10-6 m3/mol, respectively. The flow laws for enstatite, one important constituent component for the upper mantle, quantified from this study provides a necessary constraint for modeling the dynamic activities occurring within Earth's interior.

  7. 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.

  8. Vortex creep and the internal temperature of neutron stars - Linear and nonlinear response to a glitch

    NASA Technical Reports Server (NTRS)

    Alpar, M. A.; Cheng, K. S.; Pines, D.

    1989-01-01

    The dynamics of pinned superfluid in neutron stars is determined by the thermal 'creep' of vortices. Vortex creep can respond to changes in the rotation rate of the neutron star crust and provide the observed types of dynamical relaxation following pulsar glitches. It also gives rise to energy dissipation, which determines the thermal evolution of pulsars once the initial heat content has been radiated away. The different possible regimes of vortex creep are explored, and it is shown that the nature of the dynamical response of the pinned superfluid evolves with a pulsar's age. Younger pulsars display a linear regime, where the response is linear in the initial perturbation and is a simple exponential relaxation as a function of time. A nonliner response, with a characteristic nonlinear dependence on the initial perturbation, is responsible for energy dissipation and becomes the predominant mode of response as the pulsar ages. The transition from the linear to the nonlinear regime depends sensitively on the temperature of the neutron star interior. A preliminary review of existing postglitch observations is given within this general evolutionary framework.

  9. 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.

  10. 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 ...

  11. 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.

  12. Photosynthetic acclimation to high temperatures associated with heat tolerance in creeping bentgrass.

    PubMed

    Liu, Xiaozhong; Huang, Bingru

    2008-12-01

    Photosynthetic responses to increasing temperatures play important roles in regulating heat tolerance. The objectives of this study were to determine photosynthetic acclimation to increasing temperatures for creeping bentgrass (Agrostis stolonifera L.) and to examine changes in major photosynthetic components (photosynthetic pigments, photochemical efficiency, ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) activity, and activation state of rubisco) involved in heat responses of photosynthesis. 'Penncross' was exposed to 20, 25, 30, and 35 degrees C for 7d at each temperature (acclimated) before being exposed to 40 degrees C for 28d or directly exposed to 40 degrees C for 28d from 20 degrees C (non-acclimated) in growth chambers. Leaf net photosynthetic rate (Pn), photochemical efficiency, rubisco activity, rubisco activation state, chlorophyll content, and carotenoid content decreased when grasses were subjected to severe heat stress at 40 degrees C for 28d. The declines in rubisco activity and activation state were most dramatic among different photosynthetic components examined in this study. Heat-acclimated plants were able to maintain significantly higher Pn, the content of chlorophyll and carotenoid, and the level of rubisco activity and activation state during subsequent exposure to severe heat stress, compared to non-acclimated plants. These results suggested that photosynthetic acclimation to increasing temperatures contributed to creeping bentgrass tolerance to severe heat stress, which was associated with the maintenance of both higher light-harvesting capacity and carbon fixation activity during heat stress. PMID:18571284

  13. Vortex creep and the internal temperature of neutron stars. II - Vela pulsar

    NASA Technical Reports Server (NTRS)

    Alpar, M. A.; Anderson, P. W.; Pines, D.; Shaham, J.

    1984-01-01

    The observed complex postglitch behavior of the Vela pulsar is explained as resulting from coupling of the crust to crustal neutron superfluid, specifically that part of the superfluid in which vortex lines are pinned to crustal nuclei. It is shown how the general theory of vortex creep provides an excellent fit to the timing observations of Downs which span the decade 1969-1979 and include four giant glitches. Relaxation times, inertial moments, and limits on superfluid pinning parameters are extracted for three distinct regions of vortex pinning in the star, with results which are consistent with microscopic theories of its internal structure. Relaxation times due to vortex creep are directly proportional to the internal temperature of the star, so that the limits obtained for pinning parameters translate to bounds on this temperature. It is concluded that the internal temperature of the Vela pulsar is about 10-million K and discuss the extent to which improved calculations of vortex pinning as well as soft X-ray observations of other stars will make possible an improved determination of the pulsar temperature.

  14. Experimental deformation of natural and synthetic dolomite

    E-print Network

    Davis, Nathan Ernest

    2005-11-01

    include undulatory extinction and fine recrystallized grains suggesting that recovery and dynamic recrystallization contribute to dislocation creep at these conditions. By comparison with lower temperature deformation, mechanical twinning is unimportant...

  15. Influence of deformation temperature on texture evolution in HPT deformed NiAl

    NASA Astrophysics Data System (ADS)

    Tränkner, C.; Chulist, R.; Skrotzki, W.; Beausir, B.; Lippmann, T.; Horky, J.; Zehetbauer, M.

    2014-08-01

    NiAl is an intermetallic compound with a brittle-to-ductile transition temperature at about 300°C and ambient pressure. At standard conditions, it is very difficult to deform, but fracture stress and fracture strain are increased under high hydrostatic pressure. On account of this, deformation at low temperatures is only possible at high hydrostatic pressure, as for instance used in high pressure torsion. In order to study the influence of temperature on texture evolution, small discs of polycrystalline NiAl were deformed by high pressure torsion at temperatures ranging from room temperature to 500°C. At room temperature, a typical shear texture of body centred cubic metals is found, while at 500°C a strong oblique cube component dominates. These textures can be well simulated with the viscoplastic self-consistent polycrystal deformation model using the primary and secondary slip systems activated at low and high temperatures. The oblique cube component is a dynamic recrystallization component.

  16. 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.

  17. 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.

  18. 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.

  19. Experimental Constraints on the Strength of Antigorite Deformed at High Temperature and Pressure

    NASA Astrophysics Data System (ADS)

    Chernak, L. J.; Hirth, G.

    2008-12-01

    Understanding the strength and deformation behavior of serpentine is crucial due to its potential effects on deformation in both the brittle and ductile regimes. In subduction zones, the presence of serpentine may control the degree of coupling between the subducting slab and the overlying mantle wedge by deforming ductily, thus controlling the thermal structure of the wedge. In addition, serpentine may give rise to stable creep when present within fault zones. High pressure and temperature experiments have been conducted on intact cores of antigorite, the high pressure and temperature polymorph of serpentine, in a Griggs-type apparatus at 550°C, 1.5 GPa, and a constant strain rate of ~10-5s-1 to characterize its strength. Despite the orientation of the weak foliation, all samples fractured at 45° to ?1 and underwent frictional sliding. The fracture strength of the sample where fracture and slip occurred parallel to the foliation was ~100 - 200 MPa less than the fracture strength when foliation was at a 45° angle to the fracture. In addition, in the sample with foliation oriented at 45° to ?1, the fracture appears to have initiated upon loading and it is possible that this is related to the mechanical anisotropy of the sample. The results from our deformation experiments can be compared to results from antigorite deformed using the deformation-DIA (D-DIA) apparatus [Hilairet et al. 2007]. Hilairet et al. ductily deformed sintered powders of antigorite at 1 and 4 GPa, 300 - 500°C, and constant strain rates of ~10-4s-1 to 10- 6s-1. Results from their experiments were used to fit a flow law for the dislocation creep of antigorite. Hilairet et al. predict flow strengths of ~550 - 850 MPa at our experimental conditions of 1.5 GPa and 550°C, significantly lower than the fracture strengths observed for antigorite in our study, which are between ~1200 and 1365 MPa. In one experiment, the fracture strength is significantly lower, ~690 MPa, and the fracture is thought to have initiated at an impurity before the peak strength was achieved. To resolve the discrepancy between the two studies we will conduct experiments on antigorite powders to more directly compare our measurements to those of Hilairet et al. [2007]. Accurate strength data for serpentine is necessary to determine flow law parameters and, ultimately, calculate a viscosity for serpentine that can be incorporated into subduction zone models.

  20. Plasticity and Diffusion Creep of Dolomite

    NASA Astrophysics Data System (ADS)

    Davis, N. E.; Kronenberg, A. K.; Newman, J.

    2005-12-01

    Coarse-grained natural and fine-grained synthetic dolomites have been shortened in triaxial compression experiments at temperatures of 400-850°C, equilibrium CO2 pore pressures, effective confining pressures of 50-400 MPa, and strain rates of 10-4 to 10-7s-1. At low temperatures (T<700°C) coarse- (240?m) and fine-grained dolomites (2?m) exhibit high crystal plastic strengths (>600 MPa); differential stresses vary little with strain rate or temperature and microstructures of coarse-grained samples are dominated by f twins and undulatory extinction. An exponential relation ?? = A exp (??) between strain rate ?? and differential stress ? describes the crystal plasticity of dolomite with ?=0.08 MPa-1 and 0.02 MPa-1 for coarse- and fine-grained materials, respectively. However, measured values of ? increase with increasing temperature, a trend that has been observed for dolomite single crystals ( Higgs and Handin, 1959; Barber et al., 1981) but cannot be described by an Arrhenius relation. At high temperatures (T?800°C for coarse, T?700°C for fine), dolomite strengths are reduced with increasing temperature and decreasing strain rate, but the mechanisms of deformation differ depending on grain size. High temperature flow strengths of coarse-grained dolomite can be described by a power law ?? = A' ?n exp (- H*/RT) with a large value of n (>5) and a ratio of parameters H*/n = 60 kJ/mol. Microstructures of coarse-grained samples deformed at T?800°C show evidence of dislocation creep and recrystallization at grain boundaries with little mechanical twinning. High temperature flow strengths of fine-grained dolomite fit a thermally activated Newtonian law, where the effective n=1.28 (±0.15) and H*=280 (±45 kJ/mol), consistent with diffusion creep. The change in mechanical response of coarse-grained dolomite represents a transition from twinning and slip to recrystallization-accommodated dislocation creep while the change in response of fine-grained dolomite represents a transition from crystal plasticity to diffusion creep. The combined results for coarse- and fine-grained dolomites define a deformation mechanism map with fields of crystal plasticity, dislocation creep, and diffusion creep. Strengths of coarse-grained dolomite in the crystal plastic and dislocation creep fields are much larger than strengths of calcite rocks deformed by similar mechanisms ( Heard and Raleigh, 1972; Schmid et al., 1980; Walker et al., 1990; Renner et al., 2002). In contrast, strengths of fine-grained dolomite deformed by diffusion creep are more comparable to those of fine-grained calcite ( Schmid et al., 1977; Walker et al., 1990; Herwegh et al., 2003), suggesting little contrast in rheology.

  1. High-temperature creep rupture of low alloy ferritic steel butt-welded pipes subjected to combined internal pressure and end loadings.

    PubMed

    Vakili-Tahami, F; Hayhurst, D R; Wong, M T

    2005-11-15

    Constitutive equations are reviewed and presented for low alloy ferritic steels which undergo creep deformation and damage at high temperatures; and, a thermodynamic framework is provided for the deformation rate potentials used in the equations. Finite element continuum damage mechanics studies have been carried out using these constitutive equations on butt-welded low alloy ferritic steel pipes subjected to combined internal pressure and axial loads at 590 and 620 degrees C. Two dominant modes of failure have been identified: firstly, fusion boundary failure at high stresses; and, secondly, Type IV failure at low stresses. The stress level at which the switch in failure mechanism takes place has been found to be associated with the relative creep resistance and lifetimes, over a wide range of uniaxial stresses, for parent, heat affected zone, Type IV and weld materials. The equi-biaxial stress loading condition (mean diameter stress equal to the axial stress) has been confirmed to be the worst loading condition. For this condition, simple design formulae are proposed for both 590 and 620 degrees C. PMID:16243708

  2. The role of pressure solution creep in the ductility of the Earth's upper crust

    E-print Network

    Boyer, Edmond

    deformation mechanisms. Pressure solution creep is a major mechanism of ductile deformation of the upper crust is modelled using brittle theories, that include friction laws (Byerlee, 1978; Marone, 1998). This modelling to plastic deformation at pressure and temperature conditions appropriate for a depth of 10-20 km (Kohlstedt

  3. 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.

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

    Microsoft Academic Search

    G. B. Reddy; D. J. Ayres

    1982-01-01

    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°F to 1200°F.

  5. A nonlinear least squares technique for determining multiple-mechanism, high-temperature creep flow laws

    NASA Astrophysics Data System (ADS)

    Parrish, David K.; Gangi, Anthony F.

    Current methods for determining flow laws for high-temperature creep in rocks, ceramics, and metals assume that a single mechanism dominates and therefore produces the observed strain rate. Our calculations show that this assumption may lead to errors in (1) the magnitudes of the critical flow law parameters and (2), consequently, conclusions about the atomic mechanisms causing the flow. An alternative approach is to assume that several independent mechanisms operate and to fit the data derived from creep experiments (?., T, ?) to a flow law of the form ?. = ?i=1I Ai?ni exp (-Qi/RT), where ?. is the total steady state strain rate resulting from I independent flow mechanisms operating at the temperature T and stress ?, and Ai, Qi, and ni are the structure constants, apparent activation energies, and stress exponents for each mechanism. Since the fitting equation above is nonlinear, an iterative, nonlinear least squares technique is used to determine the best estimates of Ai, Qi, and ni. Nonlinear least squares fits to published experimental data for Yule marble demonstrate the equivalence of the nonlinear and multilinear fitting techniques when only one mechanism is dominant. Nonlinear least,squares fits to published data for polycrystalline halite provide further examples which suggest that two or more flow mechanisms independently contribute to the total strain rate.

  6. A thermo-mechanical framework for analysis of grain size evolution during high temperature creep

    NASA Astrophysics Data System (ADS)

    Holtzman, B. K.; Chrysochoos, A.; Daridon, L.

    2013-12-01

    We develop a theoretical description of high temperature creep with microstructural evolution. The model considers non-linear thermodynamics of irreversible processes (TIP), accounting for dissipated energy associated with creep processes and microstructural changes, as well as energy stored in the microstructure. The "Generalized Standard Materials" (GSM) formalism used here allows for strong coupling among multiple processes through the use of free energy (Helmholtz) and dissipation potentials that are functions of mechanical, thermal and internal or structural state variables. We represent dislocation density and grain size as the structural state variables, to which energy dissipation and storage are associated. We develop two versions of the model, the first with only the grain size and the second with both dislocation density and grain size. These choices reflect current discussion on the physical mechanisms that determine the steady state grain size. We incorporate distinct but coupled processes such as dislocation production, annealing, grain growth, and several creep mechanisms. The first model is designed to evaluate the "field boundary hypothesis" for the steady state grain size and the second to explore the Twiss piezometer model. The hypothesis that a steady state grain size value is associated with a level of energy dissipation (e.g. the "wattmeter") can also be evaluated in the GSM framework. One general advantage of the GSM approach relative to many current grain size evolution models is that the partitioning of energy input between stored and dissipated energy rates is not assumed, but emerges from the derivation and calculation of the stored and dissipated work. We design the approach to extract as much information as possible from torsion experiments (starting with olivine), which contain a continuous range of thermodynamic states (from zero strain at the torsion axis to a maximum at the edge of the sample) during primary (transient) and secondary (steady-state) creep stages. The aim is to produce constitutive equations that are thermodynamically consistent with the evolution equations for grain size and dislocation density, to increase the robustness of extrapolations from experiments to conditions in the Earth. A critical experimental benchmark is the prediction of steady state grain size as functions of stress, total measurable work rate and temperature. At present (though a work in progress), both models can explain aspects of the current steady state grain size-stress curve for olivine, but no single model fits all, raising numerous questions on the appropriate forms of the model and the interpretation of experimental data.

  7. High temperature creep–fatigue–oxidation interactions in 9–12%Cr martensitic steels

    Microsoft Academic Search

    Benjamin Fournier; Sauzay Maxime; Caes Christel; Noblecourt Michel; Rabeau Véronique; Bougault Annick; Pineau André

    2009-01-01

    Detailed observations of fractured specimens of 9–12%Cr martensitic steels subjected to creep–fatigue loadings at 823K were carried out. Observations revealed that oxidation phenomena strongly influence the creep–fatigue lifetime whereas no creep damage (cavities) can be observed in the present loading conditions. Two main interaction mechanisms between creep, fatigue and oxidation damage were highlighted. These two damage mechanisms correspond to two

  8. 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.

  9. Plastic deformation mechanism of pure copper at low homologous temperatures

    Microsoft Academic Search

    C.-M. Kuo; C.-H. Lin; Y.-C. Huang

    2005-01-01

    Plastic deformation mechanism of pure metals at low homologous temperatures is attributed to the motion of dislocations and their interactions with each other or other kinds of obstacles. Physically based modeling of deformation mechanism is generally considered as thermally activated motion of dislocations past obstacles and structural evolution of the obstacles. In this study, stress rate change experiments, which give

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

    USGS Publications Warehouse

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

    2008-01-01

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

  11. 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.

  12. The variation of subgrain misorientation in aluminum deformed to large steady-state creep strains

    Microsoft Academic Search

    M. E. Kassner; M. E. McMahon

    1986-01-01

    Pure aluminum was deformed in torsion of 644°K to various steady-state strains up to 16.33. The character of the subgrain boundaries changes dramatically over steady state. As the torsion specimens are twisted, the original grains of the annealed aluminum spiral around the torsion axis and the axial width of the grains is reduced. The average misorientation angle of the low-angle

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

    SciTech Connect

    Han, G.M., E-mail: gmhan@imr.ac.cn; 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.

  14. In situ monitored in-pile creep testing of zirconium alloys

    NASA Astrophysics Data System (ADS)

    Kozar, R. W.; Jaworski, A. W.; Webb, T. W.; Smith, R. W.

    2014-01-01

    The experiments described herein were designed to investigate the detailed irradiation creep behavior of zirconium based alloys in the HALDEN Reactor spectrum. The HALDEN Test Reactor has the unique capability to control both applied stress and temperature independently and externally for each specimen while the specimen is in-reactor and under fast neutron flux. The ability to monitor in situ the creep rates following a stress and temperature change made possible the characterization of creep behavior over a wide stress-strain-rate-temperature design space for two model experimental heats, Zircaloy-2 and Zircaloy-2 + 1 wt%Nb, with only 12 test specimens in a 100-day in-pile creep test program. Zircaloy-2 specimens with and without 1 wt% Nb additions were tested at irradiation temperatures of 561 K and 616 K and stresses ranging from 69 MPa to 455 MPa. Various steady state creep models were evaluated against the experimental results. The irradiation creep model proposed by Nichols that separates creep behavior into low, intermediate, and high stress regimes was the best model for predicting steady-state creep rates. Dislocation-based primary creep, rather than diffusion-based transient irradiation creep, was identified as the mechanism controlling deformation during the transitional period of evolving creep rate following a step change to different test conditions.

  15. 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.

  16. Treatment of material creep and nonlinearities in flexible mulitbody dynamics

    NASA Astrophysics Data System (ADS)

    Xie, M.; Amirouche, F. M. L.

    1994-01-01

    This paper addresses the modeling of the generalized active forces resulting from deformable bodies when subjected to high temperature conditions, elastic-plastic deformations, creep effects, and material nonlinearities. The effects of elastic-plastic deformations are studied making use of the nonlinear stress-strain relationship and the geometrical stiffness concepts. Creep conditions resulting from high temperature are studied through several proposed models. Materials nonlinearities for isotropic and composites are accounted for by their tangential elasticity matrix. A general procedure used in the study of multibody systems dynamics with elastic-plastic bodies depicting the characteristics mentioned is developed. This includes an explicit formulation of the equations of motion using Kane's equations, finite element method, continuum mechanics, and modal coordinate reduction techniques. A numerical simulation of a flexible robotic arm with a prescribed angular velocity subject to high temperature conditions is analyzed. The effects of creep are discussed.

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

    SciTech Connect

    Ainsworth, R.A. (Nuclear Electric PLC, Berkeley (UK). Berkeley Nuclear Labs.); Ruggles, M.B. (Oak Ridge National Lab., TN (USA)); Takahashi, Y. (Central Research Inst. of Electric Power Industry, Komae, Tokyo (Japan). 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.

  18. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

  20. High-temperature creep in an Al8.5Fe1.3V-1.7Si alloy processed by rapid solidification

    Microsoft Academic Search

    S. J. Zhu; K. Kucha?ová; J. ?adek

    2000-01-01

    The creep behavior of an Al-8.5Fe-1.3V-1.7Si alloy processed by rapid solidification is investigated at three temperatures\\u000a ranging from 623 to 723 K. The measured minimum creep strain rates cover seven orders of magnitude. The creep behavior is\\u000a associated with the true threshold stress, decreasing with increasing temperature more strongly than the shear modulus of\\u000a aluminum. The minimum creep strain rate

  1. An Evaluation for Creep of 3013 Inner Can Lids

    SciTech Connect

    DAUGHERTY, W. L.; GIBBS, K. M.; LOUTHAN JR., M. R.; DUNN, K. A.

    2005-09-01

    The deflection of Type 304L austenitic stainless steel can lids on inner 3013 containers is monitored to identify any buildup of pressure within the container. This paper provides the technical basis to conclude that creep-induced deformation of these lids will be insignificant unless the temperature of storage exceeds 400 C. This conclusion is based on experimental literature data for Types 304 and 316 stainless steel and on a phenomenological evaluation of potential creep processes.

  2. On the influence of grain morphology on creep deformation and damage mechanisms in directionally solidified and oxide dispersion strengthened superalloys

    SciTech Connect

    DeMestral, B.; Eggeler, G. [Ruhr Univ., Bochum (Germany). Inst. fuer Werkstoffe; Klam, H.J. [ABB Powder Generation Ltd., Baden (Switzerland). Materials Technology Dept.

    1996-04-01

    Directionally solidified (DS) and oxide dispersion strengthened (ODS) superalloys like CM 247 LC and MA 760 exhibit elongated macrograins. In uniaxial creep tests, the creep strength of such alloys in the direction of the longitudinal grains is higher than that of an equiaxed grain structure, because significantly less grain boundary (GB) segments are perpendicular to the axis of the applied stress. The present study investigates how creep in the longitudinal direction of these alloys is influenced (1) by deviations of individual grain orientations from the optimum growth direction during casting (CM 247 LC) and (2) by the spatial distribution of the small transverse GB segments (MA 760) for a given grain aspect ratio. In the case of creep ductile CM 247 LC, it was shown that if there is a large fraction of grains that are oriented for single slip, this results in higher creep rates and lower rupture times than if there is only a small fraction of such grains. The study of the influence of grain morphology on creep damage accumulation in the creep-brittle and notch-sensitive ODS alloy MA 760 showed that large scatter in creep rupture lives is related to (1) the stochastic nature of creep damage accumulation on transverse GB segments and (2) the spatial distribution of transverse GB segments. It is the combination of these two factors that results in increased scatter in rupture lives as compared to equiaxed fine grain structures.

  3. Analysis of steady-state creep and creep fracture of directionally solidified eutectic {gamma}/{gamma}{prime}-{alpha} alloy

    SciTech Connect

    Lapin, J. [Slovak Academy of Sciences, Bratislava (Slovakia). Inst. of Materials and Machine Mechanics; Delannay, F. [Univ. Catholique de Louvain, Louvain-la-Neuve (Belgium)

    1995-08-01

    The steady-state creep behavior of directionally solidified eutectic alloy Ni-30Mo-6Al-1.6V-1.2Re (wt pct) was investigated at temperatures between 1,223 and 1,323 K using constant strain rate tension creep tests. The steady-state stress is found to depend strongly on creep rate and temperature. The apparent power law stress exponent for steady-state stress is n = 7.5 {plus_minus} 0.3, and the apparent activation energy for creep of the eutectic {gamma}/{gamma}{prime}-{alpha} composite is determined to be Q = 517 {plus_minus} 11 kJ mol{sup {minus}1}. When the steady-state creep is analyzed in terms of the effective stress and normalized with respect to the temperature dependence of the elastic modulus, the corrected activation energy for creep Q{sub c} is calculated to be between 412 and 424 kJ mol{sup {minus}1} and the stress exponent between 5.7 and 6.0. The kinetics of the steady-state creep deformation within the studied temperature range involves the contribution of both the fibers and the matrix which creep during steady-state. Analysis of the fracture surfaces of the composite shows ductile fracture mode. The composite fails by growth and coalescence of microvoids in the matrix and by fiber fragmentation.

  4. 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.

  5. 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.

  6. Creep behavior comparison of CMW1 and palacos R-40 clinical bone cements.

    PubMed

    Liu, C; Green, S M; Watkins, N D; Gregg, P J; McCaskie, A W

    2002-11-01

    The restrained dynamic creep behaviors of two clinical bone cements, Palacos R-40 and CMW1 have been investigated at room temperature and body temperature. It was found that the two cements demonstrated significantly different creep deformations, with Palacos R-40 bone cement demonstrating higher creep strain than CMW1 bone cement at each loading cycle. For both cements, two stages of creep were identified with a higher creep rate during early cycling followed by a steady-state creep rate. The test temperature had a strong effect on the creep performance of the bone cements with higher creep rate observed at body temperature. The relationship between creep deformation and loading cycles can be expressed by single logarithmic model. The SEM examinations revealed that CMW1 bone cement is more sensitive to defects within the specimen especially to the defects at the edges of the specimen than Palacos R-40 bone cement. However, in the absence of micro-cracks or defects within the inner surface layer, the dynamic loading (at less than 10.6 MPa) is unlikely to produce micro-cracks in the CMW1 bone cement. The different behaviors between the two bone cements may be attributed to differences in chemical compositions and molecular weight distributions. PMID:15348171

  7. Size effects of ?? precipitate on the creep properties of directionally solidified nickel-base super-alloys at middle temperature

    Microsoft Academic Search

    J. F. Nie; Z. L. Liu; X. M. Liu; Z. Zhuang

    2009-01-01

    Nickel-base super-alloys consist of two phases named ?-phase of nickel matrix and ??-phase of precipitates, which are dispersed uniformly in the matrix. The morphologies and sizes of ?? precipitates have strong effects on the creep properties of the alloys. At the middle temperature (850°C), the rafting effect of the precipitate is not obvious, and the size effects of precipitates are

  8. 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.

  9. 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.

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

    SciTech Connect

    Vogel, Sven C [Los Alamos National Laboratory; Sediako, Dimitry [CANADIAN NEUTRON BEAM; Shook, S [APPLIED MAGNESIUM INTERNATIONAL; Sediako, A [MCGILL UNIV

    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.

  11. STEM analysis of the local chemical composition in the nickel-based superalloy CMSX-2 after creep at high temperature

    SciTech Connect

    Buffiere, J.Y. [GEMPPM INSA Lyon, Villeurbanne (France)] [GEMPPM INSA Lyon, Villeurbanne (France); Cheynet, M.C.; Ignat, M. [Domaine Univ., Saint Martin d`Heres (France)] [Domaine Univ., Saint Martin d`Heres (France)

    1996-02-01

    High temperature creep of nickel-based superalloy single crystals is characterized by directional coalescence of the {gamma}{prime} reinforcing precipitates. The morphology of the coalesced structures depends on experimental parameters such as the sense and direction of the creep stress as well as on intrinsic parameters such as the sign of the misfit between matrix and precipitates. For single crystals of the commercial superalloy CMSX-2 submitted to <100> creep at 1,323K, the initially cuboidal {gamma}{prime} precipitates coalesce into platelets arranged perpendicular or parallel to the stress direction when the stress is in tension or in compression, respectively. So far, however, the evolution of the local chemical composition around dislocations had not been experimentally investigated in nickel-based superalloys.

  12. Creep regimes for directionally solidified Al-Al{sub 3}Ni eutectic composite

    SciTech Connect

    Himbeault, D.D. [Atomic Energy of Canada Ltd., Pinawak, Manitoba (Canada); Cahoon, J.R. [Univ. of Manitoba, Winnipeg (Canada). Dept. of Mechanical and Industrial Engineering

    1993-12-01

    Creep characteristics of Al-Al{sub 3}Ni eutectic composites directionally solidified at 2.2 {times} 10{sup {minus}2} mm/s were determined over a wide range of stress and temperature. Four distinct regions of creep were observed. The rate controlling mechanisms for the four regions appear to be high-temperature dislocation climb in the Al matrix, low-temperature climb in the Al matrix, boundary sliding, and a mechanism involving deformation of the Al{sub 3}Ni fibers. Creep rates of the Al-Al{sub 3}Ni composite are several orders of magnitude smaller than for pure Al, and apparently, in the regions where deformation of the Al matrix is rate controlling, only a very small fraction of the matrix is deforming during creep of the composite.

  13. 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.

  14. 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 760°C after normalizing the steel. Still, the coarsening rate of M23C 6 carbides was higher than the MX-type particles. Moreover, the Laves phase particles were detected after tempering the steel for long periods before they dissolve back into the matrix at high temperature (i.e. 720°C). 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 500°C. Overall, the irradiated samples showed some irradiation-induced hardening which was more noticeable at 30°C. Additionally, irradiation-induced defect clusters and dislocation loops were observed and the irradiated samples did not show any bubble or void.

  15. Influence of stacking-fault energy on high temperature creep of alpha titanium alloys

    Microsoft Academic Search

    Z. Guo; A. P. Miodownik; N. Saunders; J-Ph. Schillé

    2006-01-01

    The stacking-fault energy (SFE) has been incorporated in the calculation of the steady-state creep rate of commercially-pure titanium and Ti–(1–10)mol.% Al alloys. Their creep behaviour was found to follow power-law creep when the dependence of SFE on the aluminium content was taken into account in the calculation. The possible contribution due to the formation of short range ordered structure is

  16. 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.

  17. Constant structure experiments in high temperature primary creep of some metallic materials

    SciTech Connect

    Milicka, K. (Academy of Sciences of the Czech Republic, Brno (Czech Republic). Inst. of Physical Metallurgy)

    1994-12-01

    Constant structure creep experiments in the primary creep stage of several metallic materials were realized using the technique of sudden applied stress changes. The results were interpreted by means of the back stress concept. In a Fe-Si alloy the procedure suggested originally for the steady state and based on an assumption of single active mechanism of dislocation glide could be applied also in the primary creep. In aluminum, an aluminum alloy and an austenitic stainless steel, it is possible to interpret the primary creep as a result of two active mechanisms of dislocation glide.

  18. Vortex creep and the internal temperature of neutron stars. I - General theory

    NASA Technical Reports Server (NTRS)

    Alpar, M. A.; Pines, D.; Anderson, P. W.; Shaham, J.

    1984-01-01

    The theory of a neutron star superfluid coupled to normal matter via thermal creep against pinning forces is developed in some detail. General equations of motion for a pinned rotating superfluid and their form for vortex creep are given. Steady state creep and the way in which the system approaches the steady state are discussed. The developed formalism is applied to the postglitch relaxation of a pulsar, and detailed models are developed which permit explicit calculation of the postglitch response. The energy dissipation associated with creep and glitches is considered.

  19. Creep crack growth behavior of aluminum alloy 2519. Part 1: Experimental analysis

    SciTech Connect

    Hamilton, B.C.; Saxena, A.; McDowell, D.L. [Georgia Inst. of Tech., Atlanta, GA (United States); Hall, D.E. [Louisiana Tech Univ., Ruston, LA (United States). Dept. of Mechanical and Industrial Engineering

    1997-12-31

    The discipline of time-dependent fracture mechanics has traditionally focused on the creep crack growth behavior of high-temperature materials that display creep-ductile behavior, such as stainless steels and chromium-molybdenum steels. Elevated temperature aluminum alloys, however, have been developed that exhibit creep-brittle behavior; in this case, the creep crack growth rate correlates with the stress intensity factor, K. The fracture characteristics of aluminum alloy 2519-T87 were studied at 135 C, and the creep and creep crack growth behavior were characterized utilizing experimental and numerical methods. The strain to failure for creep deformation specimens was limited to only 1.2 to 2.0%. Creep crack growth tests revealed a unique correlation between the creep crack growth rate and K, a result consistent with creep-brittle behavior. No experimental correlation was found between the creep crack growth rate and the C{sub t} parameter. Microscopy of fracture surfaces revealed distinct regions of intergranular and transgranular fracture, and the transition between the fracture regions was found to occur at a critical K-level. Experimental results also appeared to show that initiation of crack growth (incubation) is controlled by the accumulation of a critical amount of damage ahead of the crack tip and that a correlation exists between the incubation time and K. Total time to failure is viewed as a summation of the incubation period and the crack growth period, and the design importance of incubation time is discussed.

  20. A New Creep Instability at Intermediate Homologous Temperatures with Application to Slow Earthquakes and Non-Volcanic Tremor

    NASA Astrophysics Data System (ADS)

    Sammis, C. G.; Langdon, T. G.

    2013-12-01

    Recent high-pressure torsion experiments in metals have revealed a mechanism that produces unstable creep at intermediate homologous temperatures similar to those at the base of the seismogenic zone in the crust [Edalati et al., 2013]1. In these experiments a thin disc or ring is first subjected to a normal stress in the range of 2 to 6 GPa, and then to a simple shear deformation by the rotation of one of the loading pistons. The high normal stress suppresses fracture thus allowing ductile flow at intermediate values of T/Tm. The decrease in shear strength was observed to be associated with dynamic recrystallization and the growth of crystals with a relatively low dislocation density. This new mechanism is especially promising for slow earthquakes because, unlike thermal weakening which is a run-away process, the strain-weakening associated with recrystallization is not catastrophic but extends over a large strain thereby producing the large slip-weakening displacement that leads to slow earthquakes. It is interesting that this weakening mechanism is observed in aluminum, magnesium and zinc but not in copper. Two possible explanations are: 1) Al, Mg and Zn are being deformed at a significantly higher homologous temperature and 2) the stacking fault energy in Al, Mg and Zn are significantly higher than that in Cu. The high stacking fault energy means that the separation between partial dislocations is very small (on the order of the atomic spacing). A small separation promotes easy cross-slip of the dislocations to other slip planes, which promotes the observed recrystallization. In copper, the separation between partial dislocations is on the order of 12 times the atomic spacing. Although there are no robust observations of stacking faults in olivine, it is expected to be very high because the separation between the partial dislocations is very small (l < 40 Å) [vander Sande and Kohlstedt, 1976]2. The implication is that shear weakening through dynamic recrystallization is likely in olivine at or near the brittle-ductile transition. 1Mat. Sci. and Eng. A, 559, 506-509. 2Phil. Mag. 34, 653-658.

  1. INVESTIGATION OF THE COMPRESSIVE, BEARING AND SHEAR CREEP-RUPTURE PROPERTIES OF AIRCRAFT STRUCTURAL METALS AND JOINTS AT ELEVATED TEMPERATURES. Period Covered: March 1956 to May 1957

    Microsoft Academic Search

    Yerkovich

    1957-01-01

    BS>A tabular summary of the high-temperature shorttime strength ; properties of a number of test alloys in tension, compression, bearing, and shear ; is presented. Data representing the bearing creep behavior of 2024T3 aluminum ; alloy sheet for a number of variables associated with bearing are included. The ; creep behavior of several selccted joint designs undergoing bearing and shear

  2. 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.

  3. High temperature deformation of Inconel 718

    Microsoft Academic Search

    A. Thomas; M. El-Wahabi; J. M. Cabrera; J. M. Prado

    2006-01-01

    Several technological applications demand materials able to have good mechanical performance at relatively high temperatures (as high as 650°C). This performance must be kept constant during long periods at these high temperatures. Superalloys, and particularly Ni–Cr–Fe alloys (Inconel series) appear to be candidates to accomplish such requirements. In these types of alloys, mechanical properties are achieved by precipitation of second

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

    SciTech Connect

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

    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.

  5. 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.

  6. Development of shape- and lattice-preferred orientations of amphibole grains during initial cataclastic deformation and subsequent deformation by dissolution-precipitation creep in amphibolites from the Ryoke metamorphic belt, SW Japan [review article

    NASA Astrophysics Data System (ADS)

    Imon, Reiko; Okudaira, Takamoto; Kanagawa, Kyuichi

    2004-05-01

    Amphibolites from the Ryoke metamorphic belt, SW Japan were deformed initially by cataclasis and subsequently by dissolution-precipitation creep. Initial cataclastic deformation produced a rather weak shape-preferred orientation (SPO) of brown amphibole grains with small aspect ratios as well as a poorly developed amphibole lattice-preferred orientation (LPO) with n ? (? a[100]) axes scattered subnormal to the foliation and n ? or c[001] axes scattered around the lineation. During later deformation by dissolution-precipitation creep, preferential dissolution at grain boundaries subparallel to the foliation and simultaneous compaction normal to the foliation have likely produced a distinct SPO of elongate brown amphibole grains subparallel to the foliation as well as their LPO such that their n ? or c axes are scattered around the lineation, while n ? (? a) and n ? (= b[010]) are spread along a girdle normal to the lineation. Also during this deformation green amphibole precipitated as isolated grains or in pressure shadow regions around brown amphibole grains. Nucleation and anisotropic growth of isolated green amphibole grains according to the orientations of the principal stress directions produced an LPO of these grains such that their n ? (? a) are oriented normal to foliation, n ? (= b) within the foliation normal to the lineation and n ? (or c) axes are parallel to the lineation. In addition, there is an associated SPO. Growth of green amphibole in pressure shadow regions around brown amphibole grains occurs either syntaxially or anisotropically according to the orientations of the principal stress directions.

  7. Effect of microstructure on creep deformation of 45XD TiAl alloy at low and high stresses

    Microsoft Academic Search

    Hanliang Zhu; D. Y. Seo; K. Maruyama; P. Au

    2008-01-01

    A stabilized fully lamellar (stabilized FL) structure and a nearly lamellar (NL) structure were prepared by selected heat treatments in a Ti–45Al–2Nb–2Mn (wt.%)+0.8vol.% TiB2 (45XD) alloy. Tensile creep tests were performed at 760°C using applied stresses of 138 and 207MPa. The stabilized FL structure exhibits a lower minimum creep rate and a longer rupture life compared to the NL structure

  8. 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.

  9. Buckling Analysis in Creep Conditions: Review and Comparison

    SciTech Connect

    Turbat, Andre [Framatome ANP (France); Drubay, Bernard [CEA Saclay, 91191 Gif-sur-Yvette Cedex (France)

    2002-07-01

    In the case of structures operating at high temperature in normal or accidental conditions, the influence of creep has to be considered at the design stage because this phenomenon may reduce the lifetime significantly. This is true in particular for buckling analysis: in creep conditions, the buckling sometimes occurs after a long period under a compressive load which is lower than the critical load assessed when considering an instantaneous buckling. The main reason is that creep deformations induce an amplification of the initial geometrical imperfections and consequently a reduction of the buckling load. Some Design Codes incorporate special rules and/or methods to take creep buckling into account. Creep buckling analysis methods aim at evaluating critical loading for a given hold period with creep or alternatively critical creep time for a given loading. The Codes where creep buckling is considered also define margins with respect to critical loading: it shall be demonstrated that creep instability will not occur during the whole lifetime when multiplying the specified loading by a coefficient (design factor) depending on the situation level. For the design of NPP, specific creep buckling rules exist in the US, France and Russia. In the US, ASME, Section III, Subsection NH, which is dedicated to high temperature components design, provides limits which are applicable to general geometrical configurations and loading conditions that may cause buckling due to creep behaviour of the material. For load-controlled time-dependent creep buckling, the design factors to apply to the specified loadings are 1.5 for levels A, B or C service loadings and 1.25 for level D service loadings. A design factor is not required in the case of purely strain-controlled buckling. No specific method is provided to obtain critical loading or critical time for creep instability. In France, creep buckling rules included in RCC-MR, Chapter RB or RC 3200 are similar to those of ASME, Subsection NH. In addition, a new simplified method has been developed recently to assess critical creep loading/time for a shell under mechanical loading. Diagrams, presently valid for 316 austenitic steel, have been established from a ring model with perfect plasticity. Creep buckling load is determined applying a reduction factor to Euler instantaneous buckling load, depending on temperature, hold time, thinness of the structure and geometrical imperfection amplitude. This method has been validated by experimental tests and finite element results. It will be included in Appendix A7 of RCC-MR, Edition 2000. In Russia, the document PNAE G-7-002-86 applicable to NPP equipment and pipeline strength analysis, presents stability check analytical calculations to be performed to determine the allowable loading or allowable operation lifetime for typical geometries (cylindrical shells, dished ends) and loadings (external pressure, axial force). In the case of stability analysis under creep, creep deformation is assessed using a Norton law. In Germany, a KTA project including an analytical method for creep buckling analysis had also been proposed at the beginning of 90's to be used in HTR development. Finally, in India, a creep buckling analysis method has been proposed in the framework of PFBR project. As per this approach, elastic-plastic analysis should be performed replacing the instantaneous stress-strain curve at the design temperature by the isochronous curve for the time corresponding to the lifetime of the component and the same temperature. These methods are applied in the case of cylindrical shells under external pressure and comparative results are provided. The RCC-MR method appears to be reasonably conservative and applicable with several creep law types. (authors)

  10. 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.

  11. Room temperature deformation and mechanisms of slip transmission in oriented single-colony crystals of an {alpha}/{beta} titanium alloy

    SciTech Connect

    Suri, S.; Viswanathan, G.B.; Neeraj, T.; Hou, D.H.; Mills, M.J. [Ohio State Univ., Columbus, OH (United States). Dept. of Materials Science and Engineering] [Ohio State Univ., Columbus, OH (United States). Dept. of Materials Science and Engineering

    1999-02-05

    Primary creep at low homologous temperatures and low stresses has been widely reported in {alpha}/{beta} Ti alloys. Creep in these alloys is dependent on microstructure, with the colony microstructure showing the least creep resistance. There exists a Burgers orientation relationship between the {alpha} and the {beta} phase, which has been assumed to allow for easy slip transmission across the {alpha}/{beta} interfaces. Constant strain rate and creep tests were performed on single-colony crystals of a near-{alpha} alloy oriented for slip along different prismatic slip systems in the {alpha} phase. A distinct anisotropy in the deformation behavior of different colony crystals is found. The origin of this anisotropy is due to the relative misalignment of the slip systems between the {alpha} and the {beta} phases which results in the formation of residual dislocations during slip transmission. A simple model is presented based on the accumulation of residual dislocations at both the {alpha}/{beta} interface and the {alpha} matrix, which provides insight into the mechanism of slip transmission, strain hardening and primary creep of these colony structures.

  12. 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.

  13. Review of recent irradiation-creep results

    SciTech Connect

    Coghlan, W.A.

    1982-05-01

    Materials deform faster under stress in the presence of irradiation by a process known as irradiation creep. This phenomenon is important to reactor design and has been the subject of a large number of experimental and theoretical investigations. The purpose of this work is to review the recent experimental results to obtain a summary of these results and to determine those research areas that require additional information. The investigations have been classified into four subgroups based on the different experimental methods used. These four are: (1) irradiation creep using stress relaxation methods, (2) creep measurements using pressurized tubes, (3) irradiation creep from constant applied load, and (4) irradiation creep experiments using accelerated particles. The similarity and the differences of the results from these methods are discussed and a summary of important results and suggested areas for research is presented. In brief, the important results relate to the dependence of creep on swelling, temperature, stress state and alloying additions. In each of these areas new results have been presented and new questions have arisen which require further research to answer. 65 references.

  14. Biaxial thermal creep of Inconel 617 and Haynes 230 at 850 and 950 °C

    NASA Astrophysics Data System (ADS)

    Tung, Hsiao-Ming; Mo, Kun; Stubbins, James F.

    2014-04-01

    The biaxial thermal creep behavior of Inconel 617 and Haynes 230 at 850 and 950 °C was investigated. Biaxial stresses were generated using the pressurized tube technique. The detailed creep deformation and fracture mechanism have been studied. Creep curves for both alloys showed that tertiary creep accounts for a greater portion of the materials' life, while secondary creep only accounts for a small portion. Fractographic examinations of the two alloys indicated that nucleation, growth, and coalescence of creep voids are the dominant micro-mechanisms for creep fracture. At 850 °C, alloy 230 has better creep resistance than alloy 617. When subjected to the biaxial stress state, the creep rupture life of the two alloys was considerably reduced when compared to the results obtained by uniaxial tensile creep tests. The Monkman-Grant relation proves to be a promising method for estimating the long-term creep life for alloy 617, whereas alloy 230 does not follow the relation. This might be associated with the significant changes in the microstructure of alloy 230 at high temperatures.

  15. 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. [Univ. of California, Berkeley, CA (United States). Dept. of Materials Science and Mineral Engineering; [Lawrence Berkeley Lab., CA (United States)

    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.

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

    Microsoft Academic Search

    Gary R. Halford

    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

  17. Dislocation density and high-temperature creep of aluminum alloys and fracture of silicon carbide-aluminum composites

    Microsoft Academic Search

    Feng

    1987-01-01

    A two-part investigation was undertaken to determine the correlation between dislocation density and mechanical behavior. For high-temperature creep, the relationship between logarithm of strain rate and stress is divided into a linear (power law) and a nonlinear (power-law-breakdown) region. To explain this phenomenon, an investigation was conducted. In the case of 1100 Al and Al-11 wt.% Zn alloys strained at

  18. High-pressure and high-temperature deformation experiments on polycrystalline wadsleyite using the rotational Drickamer apparatus

    NASA Astrophysics Data System (ADS)

    Farla, Robert; Amulele, George; Girard, Jennifer; Miyajima, Nobuyoshi; Karato, Shun-ichiro

    2015-07-01

    High-pressure, torsional deformation experiments on polycrystalline wadsleyite were carried out using the rotational Drickamer apparatus (RDA). The experimental conditions ranged between temperatures of 2000-2200 K at pressures of 20 ± 1 GPa. Prior to deformation, the fine-grained (1-5 µm) wadsleyite specimens were synthesized from San Carlos olivine in a Kawai-type multi-anvil apparatus. The samples were loaded in the RDA, pressurized and heated, and deformed at stepped strain rates of 5-60 × 10-6 s-1. The stress was determined through the analysis of the orientation dependence on changes in lattice spacing for the (141), (240) and (040) planes. The strain was determined from the orientation of a molybdenum strain marker. Most stepped strain-rate tests reveal the stress exponent n to be 4.7 ± 0.5, suggesting power-law dislocation creep operated. Various samples exhibit grain-size reduction (to 0.1-0.6 µm), possibly associated with dynamic recrystallization or with partial phase transformation to ringwoodite. Transmission electron microscopy and electron backscatter diffraction analyses provide information on the dominant slip system in wadsleyite as 1/2<111> slip on {101} planes, as well as slip in the [100] direction. Dislocation density, even in recrystallized grains, is very high (likely >1014 m-2), reflecting the final high stresses in the samples during deformation. The results provide greater constraints on the regimes of various deformation mechanisms in wadsleyite at various experimental conditions.

  19. Dislocation loop models for the high temperature creep of Al-5.5 at.% Mg alloy

    SciTech Connect

    An, S.U. [Korea Inst. of Science and Technology, Seoul (Korea, Republic of). Advanced Analysis Center] [Korea Inst. of Science and Technology, Seoul (Korea, Republic of). Advanced Analysis Center; Blum, W. [Univ. Erlangen-Nuernberg, Erlangen (Germany). Inst. I Fuer Werkstoffwissenschaften] [Univ. Erlangen-Nuernberg, Erlangen (Germany). Inst. I Fuer Werkstoffwissenschaften

    1995-04-15

    The Al-5.5 at.% Mg alloy is a typical class I type solution hardened material. The dislocation loop models proposed by Orlova and Cadek and by Mills et al., respectively are widely applied models in describing the high temperature creep behavior of the Al-5.5 at.% Mg alloy. These models, however, are in conflict in explaining dislocation loop theory. Orlova and Cadek suggest that in class I solution hardened alloys screw dislocations are relatively easier to migrate because they are subject to a smaller resistance in motion than edge dislocations. Consequently, the migration rate of screw dislocations is higher than that of edge dislocations. However, since dislocation loops are composed of both screw and edge components, the overall migration rate of screw dislocations are reduced by that of the edge component. Mills et al. on the contrary, used a different dislocation loop model. As the loop grows while it moves, it takes on the shape of an ellipsoid due to the unbalance in growth rate, the score segment moving much easier than the edge. Therefore, as shown in the results of the stress reduction tests, rapid elastic ({Delta} {var_epsilon}{sub el}) and anelastic contraction ({Delta} {var_epsilon}{sub an}) occur simultaneously directly after stress reduction. During the movement of the dislocation loop, the screw component hence becomes severely curved, while the edge component retains a straight line. This has been proved through dislocation structure observations by TEM.

  20. Modelling of deformations of high strength concrete at elevated temperatures

    Microsoft Academic Search

    D. Gawin; F. Pesavento; B. A. Schrefler

    2004-01-01

    A constitutive model for the analysis of deformations of concrete subject to transient temperature and pressures is proposed.\\u000a In these severe conditions concrete structures experience spalling phenomenon, which is the violent or non-violent breaking\\u000a off of layers or pieces of concrete from the surface of a structural element when it is exposed to high and rapidly rising\\u000a temperatures. This process

  1. 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.

  2. A model for creep life prediction of thin tube using strain energy density as a function of stress triaxiality under quasistatic loading employing elastic-creep & elastic-plastic-creep deformation

    NASA Astrophysics Data System (ADS)

    Mahmood, Tahir; Kanapathipillai, Sangarapillai; Chowdhury, Mahiuddin

    2013-06-01

    This paper demonstrates the application of a new multiaxial creep damage model developed by authors using stress traixiality to predict the failure time of a component made of 0.5%Cr-0.5%Mo-0.25%V low alloy steel. The model employs strain energy density and assumes that the uniaxial strain energy density of a component can be easily calculated and can be converted to multi-axial strain energy density by multiplying it to a function of stress trixiality which is a ratio of mean stress to equivalent stress. For comparison, an elastic-creep and elastic-plastic-creep finite element analysis (FEA) is performed to get multi-axial strain energy density of the component which is compared with the calculated strain energy density for both cases. The verification and application of the model are demonstrated by applying it to thin tube for which the experimental data are available. The predicted failure times by the model are compared with the experimental results. The results show that the proposed model is capable of predicting failure times of the component made of the above-mentioned material with an accuracy of 4.0%.

  3. Superplastic Deformation of ice: Experimental Observations

    NASA Technical Reports Server (NTRS)

    Goldsby, D. L.; Kohlstedt, D. L.

    2001-01-01

    Creep experiments on fine-grained ice reveal the existence of three creep regimes: (1) a dislocation creep regime; (2) a superplastic flow regime in which grain boundary sliding is an important deformation process; and (3) a basal slip creep regime in which the strain rate is limited by basal slip. Dislocation creep in ice is likely climb-limited, is characterized by a stress exponent of 4.0, and is independent of grain size. Superplastic flow is characterized by a stress exponent of 1.8 and depends inversely on grain size to the 1.4 power. Basal slip limited creep is characterized by a stress exponent of 2.4 and is independent of grain size. A fourth creep mechanism, diffusional flow, which usually occurs at very low stresses, is inaccessible at practical laboratory strain rates even for our finest grain sizes of approximately 3 micrometers. A constitutive equation based on these experimental results that includes flow laws for these four creep mechanisms is described. This equation is in excellent agreement with published laboratory creep data for coarse-grained samples at high temperatures. Superplastic flow of ice is the rate-limiting creep mechanism over a wide range of temperatures and grain sizes at stresses less than or equal to 0.1 MPa, conditions which overlap those occurring in glaciers, ice sheets, and icy planetary interiors.

  4. {1124} Deformation Twinning in Commercial Purity Titanium at Room Temperature

    E-print Network

    Lainé, S. J.; Knowles, K. M.

    2015-01-01

    during the deformation of titanium alloys [1,2]. There are four commonly observed deformation twinning modes in titanium: 1012 , 1121 and 1122 , which occur at room temperature, and {1011} which is reported above 400 °C. Experimental evidence... , as for the conjugate Type I and Type II twinning modes in ?-uranium [24,25]. However, the statement by both Yoo [5] and Christian and Mahajan [6] that 1124 twins are ‘tension’ twins, i.e., their formation causes an extension along the c- axis, is incorrect...

  5. Investigation of the low-temperature performance of asphalt mixtures via fatigue and linear contraction and creep test

    NASA Astrophysics Data System (ADS)

    Liu, Conghui; Wu, Shaopeng; Li, Bo; Wang, Jingang

    2008-11-01

    Three types of asphalt mixtures, including asphalt concrete (AC), stone mastic asphalt (SMA) and porous asphalt (PA) with a 13mm gradation, are chosen to study the fatigue behavior, linear contraction and creep performance of them. The analysis of the experimental results is summarized as follows. The asphalt mixture exhibits longer fatigue life at low temperature than that at high temperature. But the fatigue life is more sensitive to the loading stress at low temperature. At the same time, the fatigue lives of all the three mixture gradations show decreasing trends with the increasing stress, which implies that restraining over-loading of highways is quite important. The linear contractive quotiety shows great distinction with the types of asphalt mixture gradations and temperature span, which indicates that modified asphalt and lower air voids can benefit to the contractive properties of asphalt mixtures at low temperature. Additionally, the linear contractive quotiety decreases with the falling of the temperature, meanwhile the distinctions between different temperature spans tend to slower. The creep test indicates that lower air voids and larger asphalt content are beneficial to the low temperature performance of asphalt.

  6. Creep behavior of glass-ionomer restorative materials.

    PubMed

    Papadogiannis, Y; Helvatjoglou-Antoniadi, M; Lakes, R C; Sapountjis, M

    1991-01-01

    The creep of microspecimens of five glass-ionomer filling materials and one glass-ionomer-cermet cement was studied by means of a torsional creep apparatus. The glass-ionomer specimens were aged one week and conditioned in 37 degrees C water. Shear stress of 2.47 x 10(-4) N.m was maintained for three h, and recovery was followed for 50 h. Creep curves were obtained at 21, 37, and 50 degrees C. The effect of temperature increase was studied. All the glass ionomers exhibited linear visco-elastic behavior at low deformations. Their shear moduli and resistance to creep were similar to those of some composites measured by the same method. The increase of temperature influenced the creep behavior and moduli of the materials (i.e., increased creep and residual strains and decreased shear modulus). Although the applied torque was very small, there was permanent deformation, the result of viscous flow in all experiments which was more pronounced at 50 degrees C. PMID:1901812

  7. Creep in electronic ceramics

    SciTech Connect

    Routbort, J. L.; Goretta, K. C.; Arellano-Lopez, A. R.

    2000-04-27

    High-temperature creep measurements combined with microstructural investigations can be used to elucidate deformation mechanisms that can be related to the diffusion kinetics and defect chemistry of the minority species. This paper will review the theoretical basis for this correlation and illustrate it with examples from some important electronic ceramics having a perovskite structure. Recent results on BaTiO{sub 3}, (La{sub 1{minus}x}Sr){sub 1{minus}y}MnO{sub 3+{delta}}, YBa{sub 2}Cu{sub 3}O{sub x}, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x}, (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} and Sr(Fe,Co){sub 1.5}O{sub x} will be presented.

  8. Dislocation and diffusion creep of synthetic anorthite aggregates

    Microsoft Academic Search

    E. Rybacki; G. Dresen

    2000-01-01

    Synthetic fine-grained anorthite aggregates were deformed at 300 MPa confining pressure in a Paterson-type gas deformation apparatus. Creep tests were performed at temperatures ranging from 1140 to 1480 K, stresses from 30 to 600 MPa, and strain rates between 2×10-6 and 1×10-3s-1. We prepared samples with water total contents of 0.004 wt % (dry) and 0.07 wt % (wet), respectively.

  9. Effect of primary creep and plasticity in the modeling of thermal fatigue of SnPb and SnAgCu solder joints

    Microsoft Academic Search

    Dwayne R. Shirley; Hamid R. Ghorbani; Jan K. Spelt

    2008-01-01

    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.

  10. A technique to achieve uniform stress distribution in compressive creep testing of advanced ceramics at high temperatures

    SciTech Connect

    Liu, K.C.; Stevens, C.O.; Brinkman, C.R. [Oak Ridge National Lab., TN (United States); Holshauser, N.E. [North Carolina Agricultural and Technical State Univ., Greensboro, NC (United States). Dept. of Mechanical Engineering

    1996-05-01

    A technique to achieve stable and uniform uniaxial compression is offered for creep testing of advanced ceramic materials at elevated temperatures, using an innovative self-aligning load-train assembly. Excellent load-train alignment is attributed to the inherent ability of a unique hydraulic universal coupler to maintain self-aligning. Details of key elements, design concept, and pricniples of operation of the self-aligning coupler are described. A method of alignment verification using a strain-gaged specimen is then discussed. Results of verification tests indicate that bending below 1.5% is routinely achievable usin the load-train system. A successful compression creep test is demonstrated using a dumbbell-shpaed Si nitride specimen tested at 1300 C for over 4000 h.

  11. Temperature dependence of the optimum particle size for the dislocation detachment controlled creep of Al-Fe-V-Si/SiC{sub p} composite

    SciTech Connect

    Kim, I.S.; Nam, S.W. [Korea Advanced Inst. of Science and Technology, Taejon (Korea, Republic of). Dept. of Materials Science and Engineering] [Korea Advanced Inst. of Science and Technology, Taejon (Korea, Republic of). Dept. of Materials Science and Engineering; Kim, N.J. [Pohang Univ. of Science and Technology (Korea, Republic of). Center for Advanced Aerospace Materials] [Pohang Univ. of Science and Technology (Korea, Republic of). Center for Advanced Aerospace Materials

    1995-06-01

    In order to improve the models for the dislocation detachment controlled creep in the dispersion strengthened alloys, the authors analyzed the creep behavior of Al-Fe-V-Si/SiC{sub p} composite based on the attractive dislocation-particle interaction with the assumption that the optimum particle radius is not a constant value but increases with increasing temperature. And in order to verify their suggestion, the creep behavior of the rapidly solidified aluminum alloys such as FVS1212 alloy and Al-8.4wt.%Fe-3.6wt.%Ce alloy is analyzed by the suggested method and they propose a good interpretation of the dislocation detachment process during creep. The unified model has been suggested to properly explain the creep behavior of dispersion strengthened aluminum alloys. This model assumes that the optimum particle radius related to the detachment process increases with increasing temperature. Using the modified creep equation, the normalized creep rate can be shown on a single line when plotted against the stress normalized by the detachment stress.

  12. Load-relaxation studies of deformation mechanisms at elevated temperatures

    SciTech Connect

    Korhonen, M.A.; Keusseyan, R.L.; Li, L.X.; Li, C.Y.

    1982-11-30

    Load-relaxation tests generate deformation data which are usually represented in the form of logarithmic stress-logarithmic strain-rate curves. The characteristics of these curves have been used extensively at low homologous temperatures for identifying grain-matrix-controlled deformation processes. At temperatures near and above one half of the absolute melting temperature, grain-boundary sliding and thermally induced structural changes, including grain-boundary migration, will occur. The shape of load-relaxation curves has been found to reflect the various processes involved. For example, a sigmoidal-shaped curve is seen for nickel and its alloys when the contribution of grain-boundary sliding is significant. Thermally induced structural changes can be shown to produce a sufficiently high strain-rate sensitivity index required by structural superplasticity. This report is concerned mainly with mechanisms that are important at elevated temperatures. Uses of load-relaxation data are discussed to determine the deformation and material parameters required for the characterization of these processes. 6 figures.

  13. Asymmetric tensile and compressive creep deformation of hot-isostatically-pressed Y 2O 3-doped Si 3N 4 1 Research supported by three sources: (a) US Department of Energy Contract No. 86X-SC674C, ‘Life Prediction Methodology for Ceramic Components of Advanced Heat Engines,’ WBS Element 3.2.2.3; Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Transportation Technologies, as part of the (b) High Temperature Materials Laboratory Fellowship Program; and (c) Heavy Vehicle Propulsion System Materials Program, Oak Ridge National Laboratory, managed by Lockheed Martin Energy Research Corporation for the US Department of Energy under contract number DE-AC05-96OR22464. 1

    Microsoft Academic Search

    Andrew A Wereszczak; Mattison K Ferber; Timothy P Kirkland; Amy S Barnes; Edward L Frome; Mamballykalathil N Menon

    1999-01-01

    The uniaxial tensile and compressive creep rates of an yttria-containing hot-isostatically-pressed silicon nitride were examined at several temperatures between 1316 and 1399°C and found to have different stress dependencies. Minimum creep rates were always faster in tension than compression for an equal magnitude of stress. An empirical model was formulated which represented the minimum creep rate as a function of

  14. Tensile deformation behavior of aluminum alloys at warm forming temperatures

    Microsoft Academic Search

    Daoming Li; Amit Ghosh

    2003-01-01

    Uniaxial tensile deformation behavior of three aluminum sheet alloys, Al 5182+1% Mn, Al 5754 and Al 6111-T4, are studied in the warm forming temperature range of 200–350°C and in the strain rate range of 0.015–1.5 s?1. Approaches have been made to process the selected aluminum sheet alloys so that the microstructural change during warm forming provides adequate recovery favorable to

  15. DEVELOPMENT OF APPARATUS AND METHODS FOR MEASUREMENT OF CREEP TO TEMPERATURES OF 3500 F. Progress Report No. 18 for December 15, 1949 to January 15, 1950

    Microsoft Academic Search

    Sinnott

    1950-01-01

    Some creep data on Material 48llC to 2400 deg F have been obtained. ; Creep testing at 3000 deg F using coated Mo test specimens were attempted but ; failure in ceramic adaptors resulted. Satisfactory life-tests under intermittent ; conditions of operation using AlâOâ ceramics were obtained in the ; graphite-induction furnace at a temperature of 3350 deg F. Schematic

  16. Degradation of RSP/PM Al-8Fe-4Ce during creep

    SciTech Connect

    Mahidhara, R.K. [Tessera Inc., San Jose, CA (United States)

    1996-04-01

    The creep behavior of Al-8Fe-4Ce powder metallurgy alloy produced by rapid solidification processing (RSP/PM alloy) was studied within the 623 to 773 K temperature range and at initial stresses ranging from 10 to 52 MPa. The activation energy, Q, for creep in RSP/PM Al-Fe-Ce alloy is 2.3 Q{sub L}, where Q{sub L} is the activation energy for lattice diffusion in pure aluminum and the stress exponent is 8.6. The high-temperature creep deformation is associated with deformation of matrix and Al{sub 13}Fe{sub 4} incoherent particles. In addition, particle coarsening is an important factor in alloy degradation. The formation and growth of cavities during creep at all stress levels at 698 K is also a contributing factor.

  17. The change in phase composition of 18-8 type steels with temperature and plastic deformation

    Microsoft Academic Search

    A. N. Chukhleb; V. P. Martynov

    1959-01-01

    The principal purpose of this work was to study the effect of low temperatures and deformation on the properties of certain chromium-nickel austenitic steels. It is known that stresses and deformation may cause the martensttlc transformation to occur above the M s temperature. The extent of transformation, the temperature and deformation required to effect a particular transformation all depend on

  18. 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 Wölz 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.

  19. The strengthening effect of Al{sub 3}Ti in high temperature deformation of Al-Al{sub 3}Ti composites

    SciTech Connect

    Wang, S.H.; Kao, P.W. [National Sun Yat-Sen Univ., Kaohsiung (Taiwan, Province of China). Inst. of Materials Science and Engineering] [National Sun Yat-Sen Univ., Kaohsiung (Taiwan, Province of China). Inst. of Materials Science and Engineering

    1998-05-01

    A series of Al-Al{sub 3}Ti composites with systematic variation of Al{sub 3}Ti content were prepared by mechanical alloying. Microstructural observations have indicated that among these composites, the only distinct variable is the Al{sub 3}Ti content, while the other microstructural variables are essentially the same. The high temperature (623--773 K) deformation behavior of these composites was found to be similar to that of dispersion-hardened aluminum. By considering the presence of a threshold stress, the plastic flow in these composites can be described by lattice-diffusion controlled dislocation creep in the aluminum matrix with a constant structure. The presence of Al{sub 3}Ti particles can increase the creep strength of these alloys significantly. By considering the load-sharing effect of Al{sub 3}Ti, an analysis based on continuum mechanics approach has been conducted, which can successfully account for the creep rate of these Al-Al{sub 3}Ti composites. The threshold stress for creep in these composites was found to increase with increasing Al{sub 3}Ti content, which could be attributed to the load-shearing effect of Al{sub 3}Ti particles.

  20. Investigation of Harper-Dorn creep under the condition of large strains

    Microsoft Academic Search

    Yu-Ching Cheng

    2008-01-01

    The purpose of this investigation is to identify and clarify the perspective of the nature and origin of necessary procedures and requirements for Harper-Dorn creep. Harper-Dorn creep represents to the anomalous high temperature deformation behavior, which is first reported by Harper and Dorn in aluminum under the condition of small strains about 0.01. To accomplish the purpose of this investigation,

  1. Creep of monolithic and SiC whisker-reinforced MoSi2

    Microsoft Academic Search

    K. Sadananda; H. Jones; J. Feng; J. J. Petrovic; A. K. Vasudevan

    1991-01-01

    Creep deformation of MoSi2 with and without reinforced SiC whiskers was studed under uniaxial compression in the temperature range 1100-1400 C. The creep rates were significantly reduced by the presence of SiC whisker reinforcement. The reduction is attributed to increased resistance to plastic flow and inhibition of grain boundary sliding. From the activation energy and n values, it is concluded

  2. 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.

  3. Defects in silicon plastically deformed at room temperature

    NASA Astrophysics Data System (ADS)

    Leipner, H. S.; Wang, Z.; Gu, H.; Mikhnovich, V. V., Jr.; Bondarenko, V.; Krause-Rehberg, R.; Demenet, J.-L.; Rabier, J.

    2004-07-01

    The article [1] describes specific features of positron trapping in silicon plastically deformed at room temperature. The results are related to the dislocation core structure and the inhomogeneous deformation. The picture shows the probability density function of a positron localized in a vacancy in silicon. The calculation was performed with the superimposed-atom model. The degree of localization and consequently the defect-related positron lifetime vary for different open-volume defects, such as vacancies, voids, and dislocations.The first author, Hartmut S. Leipner, is CEO of the Center of Materials Science of the University Halle-Wittenberg. His research activities are focused on the characterization of extended defects in semiconductors.

  4. Effects of Minor Alloy Additions and Oxidation Temperature on Protective Alumina Scale Formation in Creep-Resistant Austenitic Stainless Steels

    SciTech Connect

    Brady, Michael P [ORNL; Yamamoto, Yukinori [ORNL; Santella, Michael L [ORNL; Pint, Bruce A [ORNL

    2007-01-01

    Alumina scale formation in newly developed creep-resistant austenitic stainless steels was found to be sensitive to Al, Nb, Ti, and V content and oxidation temperature. Ti and V synergistically degraded the ability to form a protective alumina scale, whereas Nb was beneficial for alumina scale formation. The ability to form external alumina scales was lost in the lower Al and Nb containing alloys between 800 and 900 aC. Compositions with the potential to form alumina at 900 aC (and possibly higher) were identified.

  5. 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.

  6. Helium effects on creep properties of Fe-14CrWTi ODS steel at 650 °C

    NASA Astrophysics Data System (ADS)

    Chen, J.; Jung, P.; Rebac, T.; Duval, F.; Sauvage, T.; de Carlan, Y.; Barthe, M. F.

    2014-10-01

    In the present paper, the effects of helium on creep properties of Fe-14CrWTi ODS steel were studied by in-beam and post He-implantation creep tests. In-situ creep was performed in an in-beam creep device under uniaxial tensile stresses from 350 to 370 MPa during homogeneous helium implantation. Helium ions of energies varying from 0 to 25 MeV were implanted at a rate of 6 × 10-3 appm/s (corresponding to a displacement dose rate of 1.5 × 10-6 dpa/s). The average temperature was controlled to 650 °C within ±2 °C. In addition, post He-implantation creep tests were conducted at 650 °C as well. Subsequently, fracture surfaces and helium bubble evolution were studied in detail by SEM and TEM observations, respectively. Preliminary creep results show that helium slightly shortens the creep life time of ODS steel at 650 °C. Fracture surfaces of reference as well as implanted specimens, show areas with various grades of deformation. Areas of highest deformation can be interpreted as necking, while areas of low deformation show in helium implanted specimens a more granular structure. The results are discussed in terms of possible embrittlement of ODS steels by helium.

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

    SciTech Connect

    Martin, R.J. III; Boyd, P.J.; Noel, J.S. [New England Research, Inc., White River Junction, VT (United States); Price, R.H. [Sandia National Labs., Albuquerque, NM (United States)

    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.

  8. 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.

  9. Low Temperature Heat Capacity of a Severely Deformed Metallic Glass

    NASA Astrophysics Data System (ADS)

    Bünz, Jonas; Brink, Tobias; Tsuchiya, Koichi; Meng, Fanqiang; Wilde, Gerhard; Albe, Karsten

    2014-04-01

    The low temperature heat capacity of amorphous materials reveals a low-frequency enhancement (boson peak) of the vibrational density of states, as compared with the Debye law. By measuring the low-temperature heat capacity of a Zr-based bulk metallic glass relative to a crystalline reference state, we show that the heat capacity of the glass is strongly enhanced after severe plastic deformation by high-pressure torsion, while subsequent thermal annealing at elevated temperatures leads to a significant reduction. The detailed analysis of corresponding molecular dynamics simulations of an amorphous Zr-Cu glass shows that the change in heat capacity is primarily due to enhanced low-frequency modes within the shear band region.

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

    SciTech Connect

    Katoh, Yutai [ORNL; Snead, Lance Lewis [ORNL; Hinoki, Tatsuya [Kyoto University, Japan; Kondo, Sosuke [ORNL; Kohyama, Akira [Kyoto University, Japan

    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.

  11. 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).

  12. A model of compaction creep in carbonates

    NASA Astrophysics Data System (ADS)

    Keszthelyi, Daniel; Jamtveit, Bjørn; 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.

  13. Analysis of creep behavior in thermoplastics based on visco-elastic theory

    NASA Astrophysics Data System (ADS)

    Sakai, Takenobu; Somiya, Satoshi

    2011-08-01

    Plastics and fiber-reinforced plastics (FRP) are used in the aerospace industry because of their mechanical properties. However, despite their excellent high-temperature mechanical properties, plastics and FRP eventually deform visco-elastically at high temperatures. Most of the research has focused on the creep behavior of FRPs, but few studies have investigated the linear visco-elastic behavior. Linear visco-elastic behavior and non-linear visco-elastic behavior occur with physical aging in these plastics. In this study, the non-linear visco-elastic behavior of plastics and FRP was investigated based on the bending creep deformation of polycarbonate (PC) and polyoxymethylene (POM). Moreover, the effects of the fiber volume fraction on the creep characteristics were investigated using glass fiber-reinforced polycarbonate (GFRPC). The creep deformation was calculated using the linear visco-elastic theory based on these effects, and comparison between experimental and estimated data showed that the creep analysis sufficiently predicted the creep behavior.

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

    E-print Network

    of geophysical and geodynamic problems. While laboratory experiments are consistent with Mohr-Coulomb brittle spanning a range of petrophysical and rheological properties and underlying deformation mechanisms rheology, and confining pressure. The fundamental strength ( f) for time-dependent deformation varies much

  15. Effect of Deformation Temperatures on High Temperature Tensile Instability of Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Bian, Hongxia; Zhu, Liang; Zhou, Hui; Tu, Peng

    2014-09-01

    The characteristics of instability have been investigated on two low nickel austenite stainless steel at the temperatures of 950-1200 °C through the uniaxial tensile test and tensile unload test. The results show geometrical instability is not concurrent with load instability in high temperature tensile. The deformation of specimens are uniform before the load instability, then appear non-uniform in some local area of specimen but they do not directly lead to the geometric instability. With the increase of deformation temperature, load instability strain and strain hardening exponent n are both no obvious variation, and load instability true strain is close to n and depends on n. The geometric instability strain and strain rate sensitivity coefficient m both increase with the increase of temperature, and the strain between load instability and geometric instability depends on m and is the main part of the geometric instability strain.

  16. 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 (1.28±0.13 °C -1). The duration of the second experiment was only 1 year but more free of systematic errors. The effective test period of this second experiment (normalized with the Arrhenius acceleration measured in the first experiment) extends in billions of years showing no sign of anomalous 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.

  17. An investigation of creep behavior in an SiC-2124 Al composite

    SciTech Connect

    Li, Y.; Mohamed, F.A. [Univ. of California, Irvine, CA (United States). Dept. of Chemical and Biochemical Engineering and Materials Science] [Univ. of California, Irvine, CA (United States). Dept. of Chemical and Biochemical Engineering and Materials Science

    1997-11-01

    The creep behavior of powder metallurgy (PM) 10 vol.% silicon carbide particulate reinforced 2124 aluminum (SiC{sub p}-2124 Al composite) was studied under experimental conditions identical with those used in an earlier investigation on the unreinforced matrix alloy, PM 2124 Al. The results show that the creep behavior of PM 10 vol.% SiC{sub p}-2124 Al composite is similar to that of PM 2124 Al with regard to: (a) the variation in both the apparent stress exponent and the apparent activation energy for creep with applied stress, (b) the value of the true stress exponent (n = 4.5), (c) the value of the true activation energy for creep (Q{sub c} {approx} Q{sub D}), (d) the interpretation of creep in terms of a threshold stress and (e) the temperature dependence of the threshold stress. These similarities indicate that deformation in the matrix alloy, 2124 Al, controls the creep of the composite, 10 vol.% SiC{sub p}-2124 Al composite; and that SiC particulates are not directly responsible for the threshold stress behavior in the composite. A comparison between the creep rates of the composite and those of the unreinforced matrix alloy reveals that, for constant temperature, strengthening arising from SiC particulates is eliminated at high strain rates and the creep strength of PM 10 vol.% SiC{sub p}-2124 Al composite becomes essentially equal to that of the unreinforced matrix alloy, PM 2124 Al.

  18. Effect of high-temperature deformation on the mechanical properties of AISI 316 stainless steel

    Microsoft Academic Search

    Mohammed A. Shabara

    1997-01-01

    Accurate and reliable life predictions of mechanical components subjected to stress at elevated temperature may be difficult since the mechanical properties of the material are expected to change. The constitutive equations describing the creep behavior may also change due to softening or hardening processes caused by the applied loading conditions. In this paper the response of AISI Type 316 stainless

  19. Characterization of creep-fatigue fracture of Type 304 stainless steel based on initiation and growth of small cracks

    SciTech Connect

    Kitamura, Takayuki; Ohtani, Ryuichi; Tada, Naoya; Zhou, W. [Kyoto Univ. (Japan). Division of Engineering Physics and Mechanics

    1995-12-01

    Creep-fatigue tests were conducted using smooth specimens of a Type 304 stainless steel at 923K through 1,073K and the characteristics of small cracks were observed. The morphology of the fracture was classified into three types; (1) transgranular cracking on the specimen surface, which is similar to that in room temperature fatigue, (2) intergranular cracking on the specimen surface due to creep, and (3) intergranular cracking inside the specimen due to creep. Type (2) was mainly caused by grain boundary sliding at the specimen surface where the constraint was weak, while Type (3) was brought about by cavities due to grain boundary diffusion coupling with creep deformation of grains, which showed the shortest fatigue lives. The creep-fatigue failure map was constructed in terms of three types of cracking in the 3D-expression of tensile strain rate, compressive strain rate and temperature.

  20. Vortex creep and the internal temperature of neutron stars Timing noise in pulsars

    NASA Technical Reports Server (NTRS)

    Alpar, M. Ali; Nandkumar, Radha; Pines, David

    1986-01-01

    Vortex creep theory is used to construct model noise power spectra for three physically distinct types of events which might give rise to pulsar timing noise. These are 'pure' events, in which vortex unpinning is the source of the initial frequency jump; 'mixed' events, in which the initial frequency jump is produced by some physical process other than vortex unpinning but leads to the unpinning of some vortices; and 'external' events, in which the initial frequency jumps responsible for noise do not involve any vortex unpinning. For the first two types of events, it is found that relaxation processes in the region responsible for the noise will give rise to structure in the observed power spectra, while for external events, the resulting noise spectra will not be influenced by vortex creep. The theoretical results are compared with observed power spectra for 25 pulsars. The absence of structure in the observed power spectra of the Crab and Vela pulsars within the range of time scales which characterize their postglitch behavior indicates that the pinning regions which play a role in postglitch behavior do not experience the small unpinning events leading to timing noise.

  1. 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.

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

    NASA Astrophysics Data System (ADS)

    Mallet, Céline; Fortin, Jérôme; Guéguen, Yves; Bouyer, Frédéric

    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 70°C. 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.

  3. Creep-induced local lattice parameter changes in a monocrystalline nickel-based superalloy

    SciTech Connect

    Mughrabi, H.; Biermann, H. (Univ. Erlangen--Nuernberg, Erlangen (Germany)); Ungar, T. (Eoetvoes Univ., Budapest (Hungary). Inst. for General Physics)

    1993-08-01

    The [gamma]-[gamma][prime] lattice mismatch of specimens of the monocrystalline nickel-base superalloy SRR 99 has been measured by a high-resolution X-ray diffraction technique for the undeformed state and after high-temperature creep deformation. During creep deformation beyond the minimum creep rate (total strain [approximately]0.5%), the lattice mismatches, measured in and perpendicular to the [001] stress axis, respectively, undergo changes in opposite directions. This reflects the buildup of a complex deformation-induced triaxial state of internal stress in the phases [gamma] and [gamma][prime]. The overall resolved shear stresses that act in [gamma][prime] and [gamma] due to the combined action of the external and internal stresses are estimated, and the conditions under which cutting of the [gamma][prime] phase by dislocations should occur are discussed.

  4. 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.

  5. Tensile creep behavior of a vitreous-bonded aluminum oxide under static and cyclic loading

    SciTech Connect

    Dey, N.; Socie, D.F.; Hsia, K.J. [Univ. of Illinois at Urbana-Champaign, IL (United States)

    1996-09-01

    Creep deformation and rupture behavior of a vitreous-bonded aluminum oxide was investigated under uniaxial static and cyclic tensile loadings at 1000, 1100, and 1175 C. The material was more creep resistant, i.e., having lower creep strain rates, under cyclic loading compared to that under static loading. For the same maximum applied stress, the ratio of steady-state creep rate under static loading to that under cyclic loading at 1100 C was approximately 100. However, the value of this ratio decreased to about 10 when the testing temperature was raised to 1175 C or lowered to 1000 C. Under static loading the material had more propensity to develop creep damage in the form of micro- and macrocracks, leading to early failure, whereas under cyclic loading the creep damage was more uniformly distributed in the form of cavities confined to the multigrain junctions. Viscous bridging by the grain boundary second phase may be the primary contributor to the lower creep deformation rate and improved lifetime under cyclic loading.

  6. Creep Strength of Nb-1Zr for SP-100 Applications

    NASA Astrophysics Data System (ADS)

    Horak, James A.; Egner, Larry K.

    1994-07-01

    Power systems that are used to provide electrical power in space are designed to optimize conversion of thermal energy to electrical energy and to minimize the mass and volume that must be launched. Only refractory metals and their alloys have sufficient long-term strength for several years of uninterrupted operation at the required temperatures of 1200 K and above. The high power densities and temperatures at which these reactors must operate require the use of liquid-metal coolants. The alloy Nb-1 wt % Zr (Nb-lZr), which exhibits excellent corrosion resistance to alkali liquid-metals at high temperatures, is being considered for the fuel cladding, reactor structural, and heat-transport systems for the SP-100 reactor system. Useful lifetime of this system is limited by creep deformation in the reactor core. Nb-lZr sheet procured to American Society for Testing and Materials (ASTM) specifications for reactor grade and commercial grade has been processed by several different cold work and annealing treatments to attempt to produce the grain structure (size, shape, and distribution of sizes) that provides the maximum creep strength of this alloy at temperatures from 1250 to 1450 K. The effects of grain size, differences in oxygen concentrations, tungsten concentrations, and electron beam and gas tungsten arc weldments on creep strength were studied. Grain size has a large effect on creep strength at 1450 K but only material with a very large grain size (150 ?m) exhibits significantly higher creep strength at 1350 K. Differences in oxygen or tungsten concentrations did not affect creep strength, and the creep strengths of weldments were equal to, or greater than, those for base metal.

  7. 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.

  8. Advanced creep-fatigue evaluation rule for fast breeder reactor components: generalization of elastic follow-up model

    Microsoft Academic Search

    Naoto Kasahara; Takashi Nagata; Koji Iwata; Hitoshi Negishi

    1995-01-01

    High temperature operative conditions of fast breeder reactors (FBRs) cause plastic and creep deformations of structures, which lead to the magnification of the creep-fatigue damage of the materials. To take these effects into account, a structural design code for the Japanese prototype FBR “Monju” has adopted an elastic follow-up model. The elastic follow-up model shows a potential for expressing both

  9. Creep-fatigue life prediction of in situ composite solders

    SciTech Connect

    Kuo, C.G.; Sastry, S.M.L.; Jerina, K.L. [Washington Univ., St. Louis, MO (United States)

    1995-12-01

    Eutectic tin-lead solder alloys subjected to cyclic loading at room temperature experience creep-fatigue interactions due to high homologous temperature. Intermetallic reinforcements of Ni{sub 3}Sn{sub 4} and Cu{sub 6}Sn{sub 5} are incorporated into eutectic tin-lead alloy by rapid solidification processes to form in situ composite solders. In this study, the in situ composite solders were subjected to combined creep and fatigue deformation at room temperature. Under cyclic deformation, the dominant damage mechanism of in situ composite solders is proposed to be growth of cavities. A constrained cavity growth model is applied to predict creep-fatigue life by taking into account the tensile loading component as well as the compressive loading component when reversed processes can occur. An algorithm to calculate cavity growth in each fatigue cycle is used to predict the number of fatigue cycles to failure, based on a critical cavity size of failure. Calculated lives are compared to experimental data under several fatigue histories, which include fully reversed stress-controlled fatigue, zero-tension stress-controlled fatigue, stress-controlled fatigue with tension hold time, fully reversed strain-controlled fatigue, and zero-tension strain-controlled fatigue. The model predicts the creep-fatigue lives within a factor of 2 with the incorporation of an appropriate compressive healing factor in most cases. Discrepancy between calculated lives and experimental results is discussed.

  10. DEVELOPMENT OF APPARATUS AND METHODS FOR MEASUREMENT OF CREEP TO TEMPERATURES OF 3500 F. Progress Report No. 17 for November 15 to December 16, 1949

    Microsoft Academic Search

    Sinnott

    1949-01-01

    ABS>A life of one-hundred hours has been obtained on a graphite ; induction heated furnace operating at 3350 deg F. Preliminary creep tests on 4811 ; ceramic specimens and on molybdenum coated with MoSiâ to temperatures of ; 2100 deg F have been made. Experimental work on the calibration and operation of ; a circuit utilizing photo-electronmultiplier tubes for measuring

  11. 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 c0 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.

  12. 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

  13. 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, Sören; Ekström, 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.

  14. Elevated temperature crack growth in aluminum alloys: Tensile deformation of 2618 and FVS0812 aluminum alloys

    NASA Technical Reports Server (NTRS)

    Leng, Yang; Gangloff, Richard P.

    1990-01-01

    Understanding the damage tolerance of aluminum alloys at elevated temperatures is essential for safe applications of advanced materials. The objective of this project is to investigate the time dependent subcritical cracking behavior of powder metallurgy FVS0812 and ingot metallurgy 2618 aluminum alloys at elevated temperatures. The fracture mechanics approach was applied. Sidegrooved compact tension specimens were tested at 175, 250, and 316 C under constant load. Subcritical crack growth occurred in each alloy at applied stress intensity levels (K) of between about 14 and 25 MPa/m, well below K (sub IC). Measured load, crack opening displacement and displacement rate, and crack length and growth rate (da/dt) were analyzed with several continuum fracture parameters including, the C-integral, C (sub t), and K. Elevated temperature growth rate data suggest that K is a controlling parameter during time dependent cracking. For FVS0812, da/dt is highest at 175 C when rates are expressed as a function of K. While crack growth rate is not controlled by C (sub t) at 175 C, da/dt appears to better correlate with C (sub t) at higher temperatures. Creep brittle cracking at intermediate temperatures, and perhaps related to strain aging, is augmented by time dependent transient creep plasticity at higher temperatures. The C (sub t) analysis is, however, complicated by the necessity to measure small differences in the elastic crack growth and creep contributions to the crack opening displacement rate. A microstructural study indicates that 2618 and FVS0812 are likely to be creep brittle materials, consistent with the results obtained from the fracture mechanics study. Time dependent crack growth of 2618 at 175 C is characterized by mixed transgranular and intergranular fracture. Delamination along the ribbon powder particle boundaries occurs in FVS0812 at all temperatures. The fracture mode of FVS0812 changes with temperature. At 175 C, it is characterized as dimpled rupture, and at 316 C as mixed matrix superplastic rupture and matrix-dipersoid debonding.

  15. Advanced Procedures for Long-Term Creep Data Prediction for 2.25 Chromium Steels

    NASA Astrophysics Data System (ADS)

    Whittaker, Mark T.; Wilshire, Brian

    2013-01-01

    A critical review of recent creep studies concluded that traditional approaches such as steady-state behavior, power law equations, and the view that diffusional creep mechanisms are dominant at low stresses should be seriously reconsidered. Specifically, creep strain rate against time curves show that a decaying primary rate leads into an accelerating tertiary stage, giving a minimum rather than a secondary period. Conventional steady-state mechanisms should therefore be abandoned in favor of an understanding of the processes governing strain accumulation and the damage phenomena causing tertiary creep and fracture. Similarly, creep always takes place by dislocation processes, with no change to diffusional creep mechanisms with decreasing stress, negating the concept of deformation mechanism maps. Alternative descriptions are then provided by normalizing the applied stress through the ultimate tensile stress and yield stress at the creep temperature. In this way, the resulting Wilshire equations allow accurate prediction of 100,00 hours of creep data using only property values from tests lasting 5000 hours for a series of 2.25 chromium steels, namely grades 22, 23, and 24.

  16. Challenges in predicting non-linear creep and recovery in glassy polymers

    NASA Astrophysics Data System (ADS)

    Medvedev, Grigori; Caruthers, James

    2014-03-01

    The phenomenon of non-linear creep of amorphous polymeric glasses is difficult to predict using the traditional viscoelastic and viscoplastic constitutive frameworks, where two features present a particular challenge: (i) the tertiary stage of the creep and (ii) the recovery from large creep upon removal of the load. Representative examples of these two nonlinear responses will be shown for lightly cross-linked PMMA and an epoxy material, where the creep and recovery behavior has been studied as a function of temperature and aging time. The acceleration of creep during the tertiary stage is not caused by damage since the original dimensions of a cross-linked sample are fully recoverable by annealing above Tg. The assumption that the relaxation time is a function of strain runs into qualitative problems when predicting multi-step constant strain rate loading experiments. Recovery from creep as predicted by the constitutive models where the relaxation time depends on the deformation history is too abrupt compared to the experiment - this known as the ``accelerated aging'' problem. A recently developed Stochastic Constitutive Model that acknowledges dynamic heterogeneity in the glass state naturally predicts both the tertiary creep and the smooth recovery from creep.

  17. Creep of laminated aluminum composites

    Microsoft Academic Search

    W. Moore; T. J. Davies

    1980-01-01

    The creep behavior of a laminate system consisting of alternate layers of pure aluminum and SAP (sintered aluminum powder)\\u000a sheet has been examined in the temperature range 323 to 473 K and in the stress range 35 to 68 MN m?2. It was observed that secondary creep strain in the laminates was greater than in elemental SAP; the secondary creep

  18. Low-temperature electrical resistivity study of deformed Inconel alloy 600

    NASA Astrophysics Data System (ADS)

    Chan, Feng Shiu; Yao, Yeong Der; Wang, Shing Hoa

    2006-09-01

    The electrical resistivity of a plastic deformed Inconel alloy 600 (alloy of Ni 72 Cr 16 Fe 8) as function of temperature between 25 K and 300 K was studied. The deformation does not affect the Curie temperature much; it is roughly near 176 K of the deflected point at electrical resistivity, except for the sample with 75% deformation. The ?-type behavior of the electrical resistivity is a typical signal for the magnetic phase transition.

  19. Effective temperature rise during propagation of shock wave and high-speed deformation in metals

    Microsoft Academic Search

    Alexander I. Ryazanov; S. A. Pavlov; M. Kiritani

    2003-01-01

    Two theoretical models are developed for the calculations of temperature rise during high-speed deformation and shock wave propagation. In the first model the calculations of the temperature distribution in metals during high-speed deformation are based on a model where the stationary high-speed deformation is considered as a propagation of shock wave with some fixed velocity in these metals. In this

  20. 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.

  1. Creep and creep recovery of cast aluminum alloys

    Microsoft Academic Search

    Jay Christian Dandrea; Roderic Lakes

    2009-01-01

    Constant load uniaxial creep tests were performed on four aluminum alloys (designated M4032-2, 332, 332RR, and 333) at stresses\\u000a of 31.5 MPa, 56.5 MPa, and 73 MPa and temperatures of 220°C and 260°C. Of the four materials, M4032-2 had the greatest resistance\\u000a to creep, while 332RR alloy had the least. In addition to creep, the creep recovery phase was observed as well.

  2. Deformation Behavior of MEMS Gyroscope Sensor Package Subjected to Temperature Change

    Microsoft Academic Search

    Jin-Won Joo; Sung-Hoon Choa

    2007-01-01

    In microelectromechanical system (MEMS) devices, the deformation of MEMS structure caused by packaging induced stress is of great concern since it directly affects the performance of the device. In this paper, deformation behavior of the MEMS gyroscope package subjected to temperature change is investigated using a high-sensitivity moire interferometry. Temperature dependent analyses of warpage and extension\\/contraction of the package are

  3. Elevated temperature tensile\\/creep test of UV-LIGA nickel thin film for design of high-density micro connector

    Microsoft Academic Search

    Yoshitada Isono; Junichi Tada; T. Watanabe; TosFnori Unno; Toshiyuki Toriyama; Susumu Sugiyama

    2003-01-01

    This paper describes mechanical properties of UV-LIGA Ni films at elevated temperatures for design of a high-density micro connector. A compact tensile tester operated under a scanning probe microscope (SPM) was newly developed, and it characterized a stress-strain relation and creep behavior of the Ni films at temperatures ranging from 300 K to 573 K. 600 ?m-long, 15 ?m-thick and

  4. Effect of microstructure on plastic deformation of Cu at low homologous temperatures

    Microsoft Academic Search

    Y. Estrin; N. V. Isaev; S. V. Lubenets; S. V. Malykhin; A. T. Pugachov; V. V. Pustovalov; E. N. Reshetnyak; V. S. Fomenko; L. S. Fomenko; S. E. Shumilin; M. Janecek; R. J. Hellmig

    2006-01-01

    The mechanical properties of polycrystalline Cu (purity 99.95%) prepared by severe plastic deformation were studied at low homologous temperatures from 0.5K to room temperature. Material with three different microstructures was prepared by annealing of ultrafine-grained Cu. At cryogenic temperatures (0.5 and 4.2K) the material exhibited an inverse temperature dependence of the yield stress and unstable plastic deformation accompanied by serrations

  5. Microdeformation experiments on chalk - fluids, fracture and creep

    NASA Astrophysics Data System (ADS)

    Bergsaker, Anne; Neuville, Amelie; Røyne, Anja; Dysthe, Dag Kristian

    2014-05-01

    Chalks are fine grained aggregates of biogenic calcite that creep and fracture and the deformation is very sensitive to the nature of the fluid present. Close to yield there is a time scale and spatial scale of transition from distributed to localized deformation. This transition is governed by the grain scale mechanism involved - subcritical crack growth, pore collapse, ion exchange in the grain contact, mechanochemical processes and others. We present a microdeformation rig with accurate control of temperature, small strains and the pore fluid. The thin chalk samples are imaged at different scales with a resolution down to 0.5 micrometers. Deformation measurements are performed by digital image correlation. Examples of localized and distributed deformation and effects of rapid change of pore fluid during deformation are presented.

  6. The effect of deformation temperature on the microstructure evolution of Inconel 625 superalloy

    NASA Astrophysics Data System (ADS)

    Guo, Qingmiao; Li, Defu; Guo, Shengli; Peng, Haijian; Hu, Jie

    2011-07-01

    Hot compression tests of Inconel 625 superalloy were conducted using a Gleeble-1500 simulator between 900 °C and 1200 °C with different true strains and a strain rate of 0.1 s -1. Scanning electron microscope (SEM) and electron backscatter diffraction technique (EBSD) were employed to investigate the effect of deformation temperature on the microstructure evolution and nucleation mechanisms of dynamic recrystallization (DRX). It is found that the relationship between the DRX grain size and the peak stress can be expressed by a power law function. Significant influence of deformation temperatures on the nucleation mechanisms of DRX are observed at different deformation stages. At lower deformation temperatures, continuous dynamic recrystallization (CDRX) characterized by progressive subgrain rotation is considered as the main mechanism of DRX at the early deformation stage. However, discontinuous dynamic recrystallization (DDRX) with bulging of the original grain boundaries becomes the operating mechanism of DRX at the later deformation stage. At higher deformation temperatures, DDRX is the primary mechanism of DRX, while CDRX can only be considered as an assistant mechanism at the early deformation stage. Nucleation of DRX can also be activated by the twinning formation. With increasing the deformation temperature, the effect of DDRX accompanied with twinning formation grows stronger, while the effect of CDRX grows weaker. Meanwhile, the position of subgrain formation shifts gradually from the interior of original grains to the vicinity of the original boundaries.

  7. 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 900°C, but they have a different resistance to high-temperature deformation.

  8. 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.

  9. Temperature dependence of lifetime statistics for single Kevlar 49 filaments in creep-rupture

    Microsoft Academic Search

    H. F. Wu; S. L. Phoenix; P. Schwartz

    1988-01-01

    Experimental data are presented for the strength and lifetime under constant stress of single Kevlar 49 aramid filaments at two elevated temperatures, 80 and 130° C. As seen in previously published work performed at room temperature (21 °C), the strength data could be fitted to a two-parameter Weibull distribution; increasing the temperature caused a decrease in the Weibull scale parameter

  10. ORNL irradiation creep facility

    SciTech Connect

    Reiley, T.C.; Auble, R.L.; Beckers, R.M.; Bloom, E.E.; Duncan, M.G.; Saltmarsh, M.J.; Shannon, R.H.

    1980-09-01

    A machine was developed at ORNL to measure the rates of elongation observed under irradiation in stressed materials. The source of radiation is a beam of 60 MeV alpha particles from the Oak Ridge Isochronous Cyclotron (ORIC). This choice allows experiments to be performed which simulate the effects of fast neutrons. A brief review of irradiation creep and experimental constraints associated with each measurement technique is given. Factors are presented which lead to the experimental choices made for the Irradiation Creep Facility (ICF). The ICF consists of a helium-filled chamber which houses a high-precision mechanical testing device. The specimen to be tested must be thermally stabilized with respect to the temperature fluctuations imposed by the particle beam which passes through the specimen. Electrical resistance of the specimen is the temperature control parameter chosen. Very high precision in length measurement and temperature control are required to detect the small elongation rates relevant to irradiation creep in the test periods available (approx. 1 day). The apparatus components and features required for the above are presented in some detail, along with the experimental procedures. The damage processes associated with light ions are discussed and displacement rates are calculated. Recent irradiation creep results are given, demonstrating the suitability of the apparatus for high resolution experiments. Also discussed is the suitability of the ICF for making high precision thermal creep measurements.

  11. Development of Advanced Corrosion-Resistant Fe-Cr-Ni Austenitic Stainless Steel Alloy with Improved High Temperature Strenth and Creep-Resistance

    SciTech Connect

    Maziasz, PJ

    2004-09-30

    In February of 1999, a Cooperative Research and Development Agreement (CRADA) was undertaken between Oak Ridge National Laboratory (ORNL) and Special Metals Corporation-Huntington Alloys (formerly INCO Alloys International, Inc.) to develop a modified wrought austenitic stainless alloy with considerably more strength and corrosion resistance than alloy 800H or 800HT, but with otherwise similar engineering and application characteristics. Alloy 800H and related alloys have extensive use in coal flue gas environments, as well as for tubing or structural components in chemical and petrochemical applications. The main concept of the project was make small, deliberate elemental microalloying additions to this Fe-based alloy to produce, with proper processing, fine stable carbide dispersions for enhanced high temperature creep-strength and rupture resistance, with similar or better oxidation/corrosion resistance. The project began with alloy 803, a Fe-25Cr-35NiTi,Nb alloy recently developed by INCO, as the base alloy for modification. Smaller commercial developmental alloy heats were produced by Special Metals. At the end of the project, three rounds of alloy development had produced a modified 803 alloy with significantly better creep resistance above 815EC (1500EC) than standard alloy 803 in the solution-annealed (SA) condition. The new upgraded 803 alloy also had the potential for a processing boost in that creep resistance for certain kinds of manufactured components that was not found in the standard alloy. The upgraded 803 alloy showed similar or slightly better oxidation and corrosion resistance relative to standard 803. Creep strength and oxidation/corrosion resistance of the upgraded 803 alloy were significantly better than found in alloy 800H, as originally intended. The CRADA was terminated in February 2003. A contributing factor was Special Metals Corporation being in Chapter 11 Bankruptcy. Additional testing, further commercial scale-up, and any potential invention disclosures were not pursued. One objective of this project was to improve the high temperature creep resistance of the recently developed 803 alloy, while another was to have a wrought modified 803 alloy with significantly better creep resistance and corrosion resistance than the commonly used alloy 800H. The project was intended to use the established expertise at ORNL to design specific microalloying element additions to appropriately tailor the microstructure during aging or creep so that fine, stable carbides develop for strength. If possible, oxidation/corrosion resistance at high temperatures would also be enhanced. Optimum processing was to be developed for plate and tube products.

  12. Effect of deformation temperature on mechanical properties of austenitic steels

    Microsoft Academic Search

    A. N. Chukhleb; V. P. Martynov

    1961-01-01

    In several steels a complex relationship has been noted between the ; degree of deforraation and the ability of the alloy to undergo martensitic ; transformation upon cooling it was found that a slight amount of preliminary ; deformation of austenitic stainless steels enhances the martensitic ; transformation while a strong deformation results in the partial stabilization of ; the

  13. Plastic Instability in Amorphous Selenium near its Glass Transition Temperature

    SciTech Connect

    Su, Caijun [ORNL; Lamanna Jr, James [ORNL; Gao, Yanfei [ORNL; Oliver, Warren C. [MTS Nanoinstruments Innovation Center, Oak Ridge; Pharr, George M [University of Tennessee, Knoxville (UTK) & Oak Ridge National Laboratory (ORNL)

    2010-01-01

    Deformation behavior of amorphous selenium near its glass transition temperature (31 C) has been investigated by uniaxial compression and nanoindentation creep tests. Cylindrical specimens compressed at high temperatures and low strain rates deform into drum-like shape, while tests at low temperatures and high strain rates lead to fragmentation. These results agree nicely with the stress exponent and kinetic activation parameters extracted from the nanoindentation creep tests by using a similarity analysis. The dependence of deformation modes on temperature and strain rate is understood as a consequence of material instability and strain localization in the rate-dependent solids.

  14. Tensile, creep, and ABI tests on sn5%sb solder for mechanical property evaluation

    NASA Astrophysics Data System (ADS)

    Murty, K. Linga; Haggag, Fahmy M.; Mahidhara, Rao K.

    1997-07-01

    Sn5%Sb is one of the materials considered for replacing lead containing alloys for soldering in electronic packaging. We evaluated the tensile properties of the bulk material at varied strain-rates and temperatures (to 473K) to determine the underlying deformation mechanisms. Stress exponents of about three and seven were observed at low and high stresses, respectively, and very low activation energies for creep (about 16.7 and 37.7 kJ/mole) were noted. A maximum ductility of about 350% was noted at ambient temperature. Creep tests performed in the same temperature regime also showed two distinct regions, albeit with slightly different exponents (three and five) and activation energy (about 54.4 kJ/mole). Ball indentation tests were performed on the shoulder portions of the creep samples (prior to creep tests) using a Stress-Strain Microprobe@ (Advanced Technology Corporation) at varied indentation rates (strain-rates). The automated ball indentation (ABI) data were at relatively high strain-rates; however, they were in excellent agreement with creep data, while both these results deviated from the tensile test data. Work is planned to perform creep at high stresses at ambient and extend ABI tests to elevated temperatures.

  15. Tension/compression asymmetry in creep behavior of a Ni-based superalloy

    SciTech Connect

    Kakehi, K. [Tokyo Metropolitan Univ., Hachioji, Tokyo (Japan). Dept. of Mechanical Engineering] [Tokyo Metropolitan Univ., Hachioji, Tokyo (Japan). Dept. of Mechanical Engineering

    1999-08-06

    Orientation and temperature dependence of yield stress or CRSS (Critical Resolved Shear Stress) and tension/compression anisotropy of the yield stress of CRSS have been shown by Shah and Duhl, Heredia and Pope, and Miner et al. Tension/compression asymmetry in the yield strength of Ni-based superalloys has been explained in terms of the core width effect. Shah and Duhl observed the tension/compression asymmetry in creep deformation, which is similar to that observed in the yield strength, and indicated that it can be attributed to cross slip and dislocation core-constriction mechanisms associated with octahedral slip. However, little is known about the mechanism of tension/compression asymmetry in creep. In the present study, single crystals of a Ni-base superalloy were subjected to tensile and compressive creep tests. Tension/compression asymmetry in creep behavior was examined in detail for each orientation.

  16. On the viscosity and creep mechanism of Earth's inner core

    NASA Astrophysics Data System (ADS)

    Van Orman, James A.

    2004-10-01

    The viscosity and creep mechanism of Earth's inner core are evaluated based on microphysical models of the flow properties of iron under high pressure and temperature, low stress and large grain size. Harper-Dorn creep, a Newtonian-viscous dislocation mechanism, is shown to be the likely deformation process, and the viscosity is predicted to be ~1011 Pa s, at the low end of previous estimates. Such a low viscosity implies that the inner core can adjust its shape to maintain alignment with the gravitational field imposed by the mantle on a timescale of approximately one minute. It also implies that strain sufficient to produce significant lattice preferred orientation could develop in a few years to a few hundred years, which suggests that seismic anisotropy of the inner core is the product of active deformation and has no memory of primary crystallization.

  17. Temperature-dependent mechanical deformation of silicon at the nanoscale: Phase transformation versus defect propagation

    NASA Astrophysics Data System (ADS)

    Kiran, M. S. R. N.; Tran, T. T.; Smillie, L. A.; Haberl, B.; Subianto, D.; Williams, J. S.; Bradby, J. E.

    2015-05-01

    This study uses high-temperature nanoindentation coupled with in situ electrical measurements to investigate the temperature dependence (25-200 °C) of the phase transformation behavior of diamond cubic (dc) silicon at the nanoscale. Along with in situ indentation and electrical data, ex situ characterizations, such as Raman and cross-sectional transmission electron microscopy, have been used to reveal the indentation-induced deformation mechanisms. We find that phase transformation and defect propagation within the crystal lattice are not mutually exclusive deformation processes at elevated temperature. Both can occur at temperatures up to 150 °C but to different extents, depending on the temperature and loading conditions. For nanoindentation, we observe that phase transformation is dominant below 100 °C but that deformation by twinning along {111} planes dominates at 150 °C and 200 °C. This work, therefore, provides clear insight into the temperature dependent deformation mechanisms in dc-Si at the nanoscale and helps to clarify previous inconsistencies in the literature.

  18. 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 (800-1000°C). 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.

  19. 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, François; Audemard, Franck A.; Beck, Christian; Van Welden, Aurélien; 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.

  20. On the subgrain size evolution in high temperature deformation

    SciTech Connect

    Dobes, F. [Academy of Sciences of the Czech Republic, Brno (Czech Republic). Inst. of Physics of Materials] [Academy of Sciences of the Czech Republic, Brno (Czech Republic). Inst. of Physics of Materials

    1996-09-01

    Subgrain formation represents one of the best documented microstructural phenomena in many metallic and non-metallic materials. In spite of its obvious technical importance a profound quantitative description of strain and time dependence of subgrain size is still missing. That is why in attempts to model creep behavior empirical or semiempirical relations were employed. Recently, Nes tried to explain flow stress on the basis of microstructural characteristics. In the present paper the principal ideas of Nes` approach will be used for the correlation of subgrain size and the plastic strain.

  1. Diffusion creep of dry, melt-free olivine

    NASA Astrophysics Data System (ADS)

    Faul, Ulrich H.; Jackson, Ian

    2007-04-01

    Deformation experiments were conducted on fine-grained (3-6 ?m), fully synthetic Fo90 olivine aggregates in a gas-medium apparatus at 300 MPa confining pressure and temperatures of 1150-1360°C. The strain rates of the solution-gelation-derived and therefore genuinely melt-free, dry samples are about two orders of magnitude lower than the strain rates for nominally melt-free aggregates at the same pressure and temperature conditions and grain size. Benchmark deformation tests with Anita Bay dunite and mild steel reproduce published data. The creep strength of melt-added sol-gel olivine is similar to the published creep strength of dry, melt-bearing olivine derived from natural rocks. Nonlinear least-squares fits to the melt-free deformation data give an activation energy of 484 kJ/mol, a stress exponent of 1.4, and a grain-size exponent of 3 over a range of stresses from 15 to 210 MPa. These results suggest that small amounts of melt may be similarly effective in reducing the creep strength of upper mantle rocks as small amounts of water. However, a possible contribution of grain boundary composition to the observed differences in rheology in the absence of melt cannot be conclusively ruled out by the current experiments.

  2. 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

  3. HP-HT deformation of olivine: new in-situ insights into P-T dependent creep mechanisms from monochromatic X-Ray Diffraction

    NASA Astrophysics Data System (ADS)

    Hilairet, N.; Wang, Y.; Sanehira, T.; Mei, S.

    2009-12-01

    Olivine is a major mineral of the upper mantle. Therefore rheological properties of olivine are critical input parameters in modeling geodynamic processes in the upper mantle, such as evolution of subduction zones, resulting seismic patterns, or post-seismic mantle relaxation. In the last few decades, olivine and its rock counterpart dunite have been extensively studied and their flow behavior has been well documented at low pressures (< 2 GPa). Even so, some parameters for the flow of olivine are still not well constrained with the lack of studies carried out at higher pressures. Particularly, published values of laboratory determined activation volume, describing the pressure dependence of strain rate at a given flow stress, varies from 0 to 25 cm3/mol. This leads to a huge uncertainty in estimating the viscosity of the mantle in mantle flow and calls for more experimental investigations at higher pressures (> 2 GPa). We present results from HP-HT deformation experiments of sintered San-Carlos olivine under controlled strain rates from 7e-6 to 3e-5 s-1. Samples were deformed using a deformation-DIA at high pressures (3.3 to 7.6 GPa) and high temperatures (1073 to 1623 K) with final strains up to 18%. This dataset has been acquired at GSECARS, sector 13 at the APS, with monochromatic synchrotron X-ray diffraction and radiography for in-situ stress and strain measurements. For stress calculation we used lattice strains from five to six lattice planes of deforming samples, from complete 2D X-ray diffraction patterns. These data bring therefore more information for evaluation of stress and identification of deformation regimes, complementing and allowing more documented interpretation of the previously published work.

  4. 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 earth’s 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

  5. ELEVATED-TEMPERATURE CREEP AND TENSILE PROPERTIES OF THREE COLUMBIUM-BASE ALLOYS

    Microsoft Academic Search

    J. A. DeMastry; F. R. Shober; R. F. Dickerson

    1963-01-01

    In work to develop materials for elevated temperature applications, ; binary niobium alloys containing either 2.37 wt% chromium, 3.34 wt% zirconium, or ; 5.21 wt% vanadrum were fabricated to sheet by forging at 550 deg C and rolling at ; room temperature. All three alloys were completely recrystallized after 90% cold ; work (reduction in thickness) and a one hour

  6. 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 [CEA Saclay, DEN, Serv Etud Mat Irradies, F-91191 Gif Sur Yvette, (France); Bouffioux, Pol [EDF R et D Renardieres, F-77818 Ecuelles, Moret Sur Loing, (France); Chabretou, Valerie [AREVA NP SAS, AREVA, F-69456 Lyon 6, (France); Miquet, Alain [EDF SEPTEN, F-69628 Villeurbanne, (France)

    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)

  7. Field theory and diffusion creep predictions in polycrystalline aggregates

    NASA Astrophysics Data System (ADS)

    Villani, A.; Busso, E. P.; Forest, S.

    2015-07-01

    In polycrystals, stress-driven vacancy diffusion at high homologous temperatures leads to inelastic deformation. In this work, a novel continuum mechanics framework is proposed to describe the strain fields resulting from such a diffusion-driven process in a polycrystalline aggregate where grains and grain boundaries are explicitly considered. The choice of an anisotropic eigenstrain in the grain boundary region provides the driving force for the diffusive creep processes. The corresponding inelastic strain rate is shown to be related to the gradient of the vacancy flux. Dislocation driven deformation is then introduced as an additional mechanism, through standard crystal plasticity constitutive equations. The fully coupled diffusion-mechanical model is implemented into the finite element method and then used to describe the biaxial creep behaviour of FCC polycrystalline aggregates. The corresponding results revealed for the first time that such a coupled diffusion-stress approach, involving the gradient of the vacancy flux, can accurately predict the well-known macroscopic strain rate dependency on stress and grain size in the diffusion creep regime. They also predict strongly heterogeneous viscoplastic strain fields, especially close to grain boundaries triple junctions. Finally, a smooth transition from Herring and Coble to dislocation creep behaviour is predicted and compared to experimental results for copper.

  8. Deformation twinning in polycrystalline copper at room temperature and low strain rate

    Microsoft Academic Search

    C. X. Huang; K. Wang; S. D. Wu; Z. F. Zhang; G. Y. Li; S. X. Li

    2006-01-01

    Deformation twins were widely observed in polycrystalline Cu with grain sizes varying from micrometers to nanometers during the process of equal channel angular pressing at room temperature and low strain rate (?10?2s?1). The microstructures of deformation twins were characterized by a transmission electron microscope (TEM) and a high-resolution TEM. It was found that deformation twinning in coarse-grained Cu occurred mainly

  9. Creep crack growth behavior of several structural alloys

    NASA Astrophysics Data System (ADS)

    Sadananda, K.; Shahinian, P.

    1983-07-01

    Creep crack growth behavior of several high temperature alloys, Inconel 600, Inconel 625, Inconel X-750, Hastelloy X, Nimonic PE-16, Incoloy 800, and Haynes 25 (HS-25) was examined at 540, 650, 760, and 870 °C. Crack growth rates were analyzed in terms of both linear elastic stress intensity factor and J*-integral parameter. Among the alloys Inconel 600 and Hastelloy X did not show any observable crack growth. Instead, they deformed at a rapid rate resulting in severe blunting of the crack tip. The other alloys, Inconel 625, Inconel X-750, Incoloy 800, HS-25, and PE-16 showed crack growth at one or two temperatures and deformed continuously at other temperatures. Crack growth rates of the above alloys in terms ofJ* parameter were compared with the growth rates of other alloys published in the literature. Alloys such as Inconel X-750, Alloy 718, and IN-100 show very high growth rates as a result of their sensitivity to an air environment. Based on detailed fracture surface analysis, it is proposed that creep crack growth occurs by the nucleation and growth of wedge-type cracks at triple point junctions due to grain boundary sliding or by the formation and growth of cavities at the boundaries. Crack growth in the above alloys occurs only in some critical range of strain rates or temperatures. Since the service conditions for these alloys usually fall within this critical range, knowledge and understanding of creep crack growth behavior of the structural alloys are important.

  10. Influence of grain size on the creep behavior of HfC-dispersed NiAl

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.; Ray, Ranjan; Jha, Sunil C.

    1992-01-01

    Rapid solidification technology has been utilized to produce a NiAl-4(wt pct)HfC composite containing about 0.3 vol pct HfC as dispersed 50 nm particles. Study of the 1300 K compressive creep properties demonstrated that the initial, small grain size microstructure was unstable under slow strain rate deformation conditions. The grain growth which occurred during testing led to considerable strengthening. Subsequent measurements of the creep properties of the coarse grained specimens revealed that this strength was achieved by a large increase in the activation energy for deformation without any change in the stress exponent. Based on this work, it is concluded that large grain microstructures will be required for optimum elevated temperature creep properties in dispersed NiAl.

  11. Creep Effects in the Toroidal Field Coils of the Ignitor machine

    NASA Astrophysics Data System (ADS)

    Salvetti, M. F.; Titus, P. H.

    2002-11-01

    Ignitor is a copper coil high density machine whose structural integrity relies on an optimized combination of "bucking" between the TF coils and the central solenoid and "wedging" between the inner legs of the TF coils. Creep is the slow deformation of the materials under stress that results in a permanent deformation. The creep behavior of the TF coils is investigated resorting to FEM simulations, using the ANSYS code, to quantify the amount of preload that will be lost during the operative life of the machine. Simulations are still limited by the small amount of creep curves of copper at cryogenic temperature. Ignitor will be preloaded mostly at cryogenic temperature, or at room temperature during maintenance, thus all the simulations consider creep behavior at 30 K and 293 K. At present, the TF coils are modeled as equivalent isotropic material structures, up-coming computational routines will allow in the future to consider the orthotropic properties. Results show that creep has minimal effect over time on magnet performance mostly because the beneficial presence of an active preload system (magnetic press).

  12. 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 ...

  13. Laminated metal composites—High temperature deformation behavior

    Microsoft Academic Search

    R. B. Grishaber; A. V. Sergueeva; R. S. Mishra; A. K. Mukherjee

    2005-01-01

    A constitutive model for deformation of a novel laminated metal composite (LMC) which is comprised of 21 alternating layers of Al 5182 alloy and Al 6090\\/SiC\\/25p metal matrix composite (MMC) has been proposed. The LMC as well as the constituent or neat structures have been deformed in uniaxial tension within a broad range of strain-rates (i.e. 10?6 to 10+1s?1) and

  14. 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.

  15. 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.

  16. 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.

  17. Method for measuring temperature of crystals during elastic and plastic deformation

    Microsoft Academic Search

    D. Ronnpagel; H. Neuhauser

    1972-01-01

    A method of measurement developed for the investigation of energy relations during plastic deformation of metal crystals is described. The energy stored in the crystal is obtained from the difference in work expended and energy converted into heat. The heat evolved per unit of time is determined by measuring the crystal temperature during plastic deformation by means of small thermistors.

  18. 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.

  19. 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.

  20. Creep of posterior dental composites.

    PubMed

    Papadogianis, Y; Boyer, D B; Lakes, R S

    1985-01-01

    The creep of microspecimens of posterior dental composites was studied using a torsional creep apparatus. Shear stresses were maintained for 3 h and recovery was followed for 50 h. Creep curves were obtained at 21, 37, and 50 degrees C and four torque levels. The effect of conditioning the specimens in water up to 8 weeks was studied. The posterior composites exhibited linear viscoelastic behavior at low deformations. They had higher shear moduli and greater resistance to creep than conventional and microfilled composites. In aging experiments, maximum shear moduli occurred when specimens were 48 h to 1 week old. Subsequent softening was attributed to water absorption. Residual strain was highest when the composites were stressed within 24 h of initiating polymerization. Residual strain was very low in specimens 48 h to 8 weeks of age. PMID:4077874

  1. Probabilistic material strength degradation model for Inconel 718 components subjected to high temperature, mechanical fatigue, creep and thermal fatigue effects. Final report

    SciTech Connect

    Bast, C.C.S.

    1994-03-01

    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.

  2. An investigation of creep and substructure formation in 2124 Al

    Microsoft Academic Search

    Yong LI; Steven R. Nutt; Farghalli A. Mohamed

    1997-01-01

    The effect of stress on the creep behavior of powder metallurgy (PM) 2124 Al was investigated in the temperature range 618–678 K. In addition, substructure that developed during creep was examined by means of transmission electron microscopy (TEM). The creep data, which extend over seven orders of magnitude of strain rate, show that the apparent stress exponent, na, for creep

  3. Creep of sandwich beams with metallic foam cores

    Microsoft Academic Search

    O. Kesler; L. K. Crews; L. J. Gibson

    2003-01-01

    The steady state creep deflection rates of sandwich beams with metallic foam cores were measured and compared with analytical and numerical predictions of the creep behavior. The deflection rate depends on the geometry of the sandwich beam, the creep behavior of the foam core and the loading conditions (stress state, temperature). Although there was a considerable scatter in the creep

  4. Influence of precipitate morphology on intermediate temperature creep properties of a nickel-base superalloy single crystal

    Microsoft Academic Search

    M. V. Nathal; R. A. MacKay; R. V. Miner

    1989-01-01

    The influence of ?’ precipitate morphology on the-creep behavior of the single crystal nickel-base superalloy NASAIR 100 at\\u000a 760-?C was investigtated. As-heat treated crystals with cuboidal ?’ particles and crystals given an additional pre-rafting\\u000a treatment to form a continuous lamellar structure were creep tested at stress levels which produced rupture lives ranging\\u000a from 40 to 2500 hours. At high applied

  5. Creep Behavior of Bi-Containing Lead-Free Solder Alloys

    NASA Astrophysics Data System (ADS)

    Witkin, David

    2012-02-01

    The creep behavior of Sn-3.0Ag-0.5Cu (SAC305), Sn-3.4Ag-1.0Cu-3.3Bi (SAC-Bi), and Sn-3.4Ag-4.8Bi (SnAg-Bi, all wt.%) was studied in constant-stress creep tests from room temperature to 125°C. The alloys were tested in two microstructural conditions. As-cast alloys had a composite eutectic-primary Sn structure, while in aged alloys the eutectic regions were replaced by a continuous Sn matrix with coarsened intermetallic (Cu6Sn5 and Ag3Sn) particles. After aging, Bi in SAC-Bi and SnAg-Bi was found as precipitates at grain boundaries and grain interiors. The creep resistance of of-cast SAC305 was higher than that of as-cast Bi-containing alloys, but after aging the SAC305 had the lowest creep resistance. The creep strain rates in SAC-Bi and SnAg-Bi were much less affected by aging. The apparent activation energy for creep was also changed more for SAC305 than for the other two alloys. The creep behavior of SAC-Bi and SnAg-Bi can be understood by considering the solubility of Bi in Sn. The difference in creep behavior between as-cast and aged SAC-Bi is greatly reduced when room-temperature test results are excluded from analysis. This suggests that the strongest influence on creep in these alloys is due to Bi solute interaction with moving dislocations during deformation.

  6. Reactive infiltration processing and secondary compressive creep of NiAl and NiAl-W composites

    SciTech Connect

    Venkatesh, T.A.; Dunand, D.C.

    2000-03-01

    Reactive infiltration processing was used to fabricate bulk NiAl and fiber-reinforced NiAl composites. Homogeneous, pore-free materials were obtained by chemical reaction between nickel and aluminum after complete infiltration with liquid aluminum of performs of nickel wires (containing tungsten wires for the composites) with low surface-to-volume ratio, high permeability, and regular infiltration paths. Reactively-processed, monolithic NiAl exhibited compressive creep properties at 715 C and 1,025 C in good agreement with those of conventionally processed NiAl. The compressive creep behavior of NiAl composites reinforced with 5 to 20 vol pct W was also characterized at the same temperatures. At 715 C, the NiAl-W composites exhibited secondary creep with little primary and tertiary creep, while at 1,025 C, the composites displayed all three stages. Microstructurally, secondary creep was characterized by pure uniaxial compression of tungsten fibers. The measured composite secondary creep rates could be predicted reasonably well with the role-of-mixtures isostrain model developed for composites where both phases undergo creep deformation using tensile creep data measured on the as-received tungsten fibers.

  7. Constitutive modeling of creep of single crystal superalloys

    E-print Network

    Prasad, Sharat Chand

    2006-10-30

    In this work, a constitutive theory is developed, within the context of continuum mechanics, to describe the creep deformation of single crystal superalloys. The con- stitutive model that is developed here is based on the fact that as bodies deform...

  8. Creep and stress relaxation in a longitudinal polymer liquid crystal: Prediction of the temperature shift factor

    E-print Network

    North Texas, University of

    University of Technology, 412-96 Gothenburg, Sweden Robert Maksimovd) Institute of Polymer Mechanics 17 February 1999 The polymer liquid crystal PLC is the PET/0.6PHB copolymer; PET poly ethylene data for a polymer liquid crystal PLC . The PLC in its service temperature range contains four phases,2

  9. High-temperature deformation of Sr(FeCo){sub 1.5}O{sub x} ceramics.

    SciTech Connect

    de Arellano-Lopez, A. R.; Balachandran, U.; Goretta, K. C.; Ma, B.; Routbort, J. L.; Energy Technology; Univ. de Sevilla

    2001-01-01

    Compressive creep of polycrystalline SrFe{sub 1.2}Co{sub 0.3}O{sub x} and SrFeCo{sub 0.5}O{sub x} ceramics has been investigated at 940-1000 C in constant-load and constant-displacement-rate experiments. At low stresses, the stress exponent was {approx}1 and the activation energy was {approx}110-135 kJ/mol. At higher stresses, a transition occurred and the stress exponent became {approx}2.4-3.1 and the activation energy became {approx}425-453 kJ/mol. At higher stresses, there was no dependence of the steady-state flow stress on oxygen partial pressure from 10-10{sup 5} Pa. The creep parameters and scanning and transmission electron microscopy observations of the deformed samples suggested that deformation was controlled by diffusion at low stresses and dislocation glide at high stresses.

  10. LONG-TERM CREEP RESPONSE OF BORATE-MODIFIED ORIENTED STRANDBOARD

    Microsoft Academic Search

    Qinglin Wu; N. Lee

    Creep performance of zinc and calcium borate-modified OSB was assessed under both constant and varying moisture conditions. The influence of initial borate content, wood species, and stress level on the creep deformation was studied. Under the constant moisture condition, there was practically no difference in creep for boards at various borate levels for both types of borate. The creep data

  11. 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.

  12. Analysis of creep transients in pure metals following stress changes

    SciTech Connect

    Biberger, M. [Varian Associates, Palo Alto, CA (United States)] [Varian Associates, Palo Alto, CA (United States); Gibeling, J.C. [Univ. of California, Davis, CA (United States). Dept. of Chemical Engineering and Materials Science] [Univ. of California, Davis, CA (United States). Dept. of Chemical Engineering and Materials Science

    1995-09-01

    The analysis of creep transients associated with stress change tests is reviewed, with an emphasis on using the results of these experiments to characterize the kinetics of deformation under conditions of nominally constant structure. In order to develop a common framework for the description of results obtained by various authors, operational definitions of the characteristic strain rates observed after stress changes are adopted. The data for aluminum reported by numerous investigators provide a consistent picture over a broad range of temperatures and initial creep stresses. These results show that transient creep after stress reductions occurs by two parallel processes of dislocation glide within subgrain interiors and dynamic recovery associated with subgrain boundary migration. Following relatively large stress reductions, the creep transient is dominated by the subgrain boundary migration processes. After relatively small changes in stress, thermally activated motion of dislocation within subgrain interiors is the predominant mechanism of deformation. In this regime, the creep transients can be described by a thermally activated rate law, thereby enabling various activation parameters to be evaluated from the data. Limited results for other f.c.c. metals and related materials are shown to follow the trends established for aluminum. In particular, it is demonstrated that the data for pure copper and LiF at high temperatures and after small stress changes are also consistent with a description based on thermally activated glide. However, the true activation areas in copper are about five times greater than the dislocation spacing. This difference between copper and aluminum is attributed to the fact that the former has a substantially lower stacking fault energy.

  13. Evolution of Precipitate Microstructure During Creep of an AA7449 T7651 Aluminum Alloy

    NASA Astrophysics Data System (ADS)

    Fribourg, G.; Bréchet, Y.; Chemin, J. L.; Deschamps, A.

    2011-12-01

    Creep forming is a process where plastic deformation is applied at the material's aging temperature. It enables to obtain parts of complex shape with reduced internal stresses and finds applications, for instance, in the aerospace industry. In this article, we report in-situ small-angle X-ray scattering measurements during creep experiments carried out on an AA7449 Al-Zn-Mg-Cu alloy in the T7651 temper. In the range of temperatures of 413 K to 453 K (140 °C to 180 °C), we show that the initial microstructure is not stable with respect to the applied stress/strain. Accelerated precipitation coarsening is shown to occur, clearly related to the plastic deformation. This strain-induced microstructure evolution is shown to happen even at temperatures well below the aging temperature that has led to the initial temper.

  14. Oxygen self-diffusion in forsterite: Implications for the high-temperature creep mechanism

    Microsoft Academic Search

    O. Jaoul; C. Froidevaux; W. B. Durham; M. Michaut

    1980-01-01

    The diffusivity of 18O in forsterite Mg2SiO4 has been measured in the temperature range 1150-1600°C. The activation energy of oxygen self-diffusion in this silicate is found to equal 0.32 +\\/- 0.04 MJ\\/mol (77 +\\/- 10 kcal\\/mol), and there is no dependence of the diffusivity upon the oxygen partial pressure surrounding the samples. The diffusion profiles were analysed either with an

  15. Influence of temperature on dissociation of dislocations and plastic deformation in spinel oxides

    Microsoft Academic Search

    P. Veyssière; J. Rabier; H. Garem; J. Grilhé

    1978-01-01

    Depending upon the temperature at which spinel oxides are deformed, different dissociation configurations of dislocations have been observed. At elevated temperatures, edge dislocations are dissociated over several hundreds angstroms by a process involving climb of partials. At low temperatures, the long screw dipoles resulting from indentation tests suggest a classical dissociation of dislocations out of the preferred glide plane. These

  16. Elevated temperature cyclic deformation of stainless-steel and interaction effects with other modes of deformation

    Microsoft Academic Search

    A. P. L

    1976-01-01

    Since pertinent information concerning the deformation history of a material is stored in its current structure, an attempt has been made to determine the number of state variables necessary to uniquely describe the material's present condition. An experimental program has been carried out to determine the number of state variables which is required to describe the tensile test, cyclic, and

  17. On the creep of directionally solidified MoSi{sub 2}-Mo{sub 5}Si{sub 3} eutectics

    SciTech Connect

    Mason, D.P. [Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Materials Science and Engineering] [Univ. of Michigan, Ann Arbor, MI (United States). Dept. of Materials Science and Engineering; Van Aken, D.C. [Univ. of Missouri, Rolla, MO (United States). Dept. of Metallurgical Engineering] [Univ. of Missouri, Rolla, MO (United States). Dept. of Metallurgical Engineering

    1995-03-01

    The high temperature deformation behavior of MoSi{sub 2}-Mo{sub 5}Si{sub 3} eutectics has been investigated as a function of lamellar spacing over the temperature range 1,100--1,400 C and strain rates ({dot {epsilon}}) of 1 {times} 10{sup {minus}4} to 1 {times} 10{sup {minus}6} s{sup {minus}1}. Specimens with lamellar morphologies were produced by directional solidification using the Czochralski method at pull rates of 25--210 mm/h giving lamellar spacings ({lambda}) of 2.6 to 1.09 {mu}m. The measured flow stress was found to increase as the lamellar spacing decreased for a given strain rate. A constitutive model for creep that incorporates reinforcement spacing for creeping fibers in a creeping matrix was found to describe the creep behavior of the eutectic, i.e. {dot {epsilon}}{alpha}{lambda}{sup m} with m = 1. Creep deformation of the eutectic was controlled by {1/2}<110>(001) partial dislocations in the Mo{sub 5}Si{sub 3} phase. The creep behavior of a [314] oriented Mo{sub 5}Si{sub 3} single crystal was also investigated.

  18. Hot strength of creep resistant ferritic steels and relationship to creep rupture data

    E-print Network

    Cambridge, University of

    Hot strength of creep resistant ferritic steels and relationship to creep rupture data R. C relationship between the temperature dependence of hot tensile strength and creep rupture stress. Keywords: Hot in which the hot strength of austenite has been modelled, primarily as an aid to the simulation of the hot

  19. Aging effects on high-temperature creep properties of a solid oxide fuel cell glass-ceramic sealant

    NASA Astrophysics Data System (ADS)

    Lin, Chih-Kuang; Lin, Kun-Liang; Yeh, Jing-Hong; Shiu, Wei-Hong; Liu, Chien-Kuo; Lee, Ruey-Yi

    2013-11-01

    Creep properties at 800 °C are investigated for a newly developed solid oxide fuel cell BaO-B2O3-Al2O3-SiO2 glass-ceramic sealant (GC-9) in variously aged conditions using a ring-on-ring test technique. GC-9 specimens are thermally aged at 750 °C for 4 h (designated as non-aged), 100 h, or 1000 h after sintering at 850 °C. Results show a longer thermal aging treatment leads to a higher crystallinity and greater creep resistance for the given glass-ceramic sealant. When subjected to an applied constant load at 800 °C, the 1000 h-aged GC-9 lasts much longer than the non-aged and 100 h-aged ones before rupture. The 1000 h-aged GC-9 also exhibits a creep strain rate much smaller than that in the non-aged and 100 h-aged samples. The value of creep stress exponent increases from 6 to 29 as the aging treatment time is increased from 4 h to 1000 h. The creep strength at a rupture time of 1000 h for the non-aged, 100 h-aged, and 1000 h-aged GC-9 is about 21%, 28%, and 39%, respectively, of the corresponding Weibull characteristic strength at 800 °C.

  20. 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.

  1. 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.

  2. Creep deformation of the human trunk in response to prolonged and repetitive flexion: measuring and modeling the effect of external moment and flexion rate.

    PubMed

    Toosizadeh, Nima; Nussbaum, Maury A

    2013-06-01

    While viscoelastic responses of isolated trunk soft tissues have been characterized in earlier studies, the effects of external loading and flexion rate on these responses in the intact human trunk are largely unknown. Two experiments were conducted to measure trunk viscoelastic behaviors, one involving prolonged flexion with several extra loads (attached to the wrists) and the other repetitive trunk flexion with different extra loads and flexion rates. Direct outcome measures included initial trunk angle, creep angle, and residual/cumulative creep. Viscoelastic behaviors in both experiments were characterized using different Kelvin-solid models. For prolonged flexion, extra load significantly affected initial angle, creep angle, and viscoelastic model parameters, while residual creep remained unchanged. For repetitive flexion, cumulative creep angle significantly increased with both extra load and flexion rate. Nonlinear viscoelastic behavior of the trunk was evident in both experiments, which also indicated better predictive performance using Kelvin-solid models with ?2 retardation time constants. Understanding trunk viscoelastic behaviors in response to flexion exposures can help in future modeling and in assessing how such exposures alter the synergy between active and passive trunk tissues. PMID:23525750

  3. 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.

  4. On temperature dependence of deformation mechanism and the brittle{endash}ductile transition in semiconductors

    SciTech Connect

    Pirouz, P.; Samant, A.V.; Hong, M.H. [Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, Ohio 44106-7204 (United States); Moulin, A.; Kubin, L.P. [LEM, CNRS-ONERA, B.P. 72, 29, Av. de la Division Leclerc, 92322 Chatillon Cedex (France)

    1999-07-01

    Recent deformation experiments on semiconductors have shown the occurrence of a break in the variation of the critical resolved shear stress of the crystal as a function of temperature. These and many other examples in the literature evidence a critical temperature at which a transition occurs in the deformation mechanism of the crystal. In this paper, the occurrence of a similar transition in two polytypes of SiC is reported and correlated to the microstructure of the deformed crystals investigated by transmission electron microscopy, which shows evidence for partial dislocations carrying the deformation at high stresses and low temperatures. Based on these results and data in the literature, the explanation is generalized to other semiconductors and a possible relationship to their brittle-ductile transition is proposed. {copyright} {ital 1999 Materials Research Society.}

  5. 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 Nabarro–Herring 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.

  6. Determination of temperature rise during high strain rate deformation

    Microsoft Academic Search

    Rajeev Kapoor; Sia Nemat-Nasser

    1998-01-01

    The energy converted to heat during high strain rate plastic deformation is measured directly using an infra-red method for Ta?2.5% W alloy and, indirectly, using UCSD's recovery Hopkinson bar technique for the same alloy, as well as for commercially pure Ti, 1018 steel, 6061 Al and OFHC Cu. The infra-red measurement yields a 70% conversion of work to heat for

  7. Recommendations for a modification of ASTM E 1457 to include creep-brittle materials

    Microsoft Academic Search

    Karl-Heinz Schwalbe; Robert A Ainsworth; Ashok Saxena; Takeo Yokobori

    1999-01-01

    VAMAS Technical Working Area 19 on High Temperature Fracture of Brittle Materials has developed several new recommendations for determining and analysing the creep crack extension behaviour of creep-brittle materials. These recommendations, most of which are also useful for creep-ductile materials, include: machining narrow starter notches for brittle materials; definition of creep crack initiation; definition of creep toughness; recommendations for conducting

  8. Development of Advanced Corrosion-Resistant Fe-Cr-Ni Austenitic Stainless Steel Alloy with Improved High-Temperature Strength and Creep-Resistance

    SciTech Connect

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

    2001-06-15

    In February of 1999, a Cooperative Research and Development Agreement (CRADA) was undertaken between Oak Ridge National Laboratory (ORNL) and Special Metals Corporation - Huntington Alloys (formerly INCO Alloys International, Inc.) to develop a modified wrought austenitic stainless alloy with considerably more strength and corrosion resistance than alloy 800H or 800HT, but with otherwise similar engineering and application characteristics. Alloy 800H and related alloys have extensive use in coal flue gas environments, as well as for tubing or structural components in chemical and petrochemical applications. The main concept of the project was make small, deliberate elemental microalloying additions to this Fe-based alloy to produce, with proper processing, fine stable carbide dispersions for enhanced high temperature creep-strength and rupture resistance, with similar or better oxidation/corrosion resistance. The project began with alloy 803, a Fe-25Cr-35NiTi,Nb alloy recently developed by INCO, as the base alloy for modification. Smaller commercial developmental alloy heats were produced by Special Metal. At the end of the project, three rounds of alloy development had produced a modified 803 alloy with significantly better creep resistance above 815 C (1500 C) than standard alloy 803 in the solution-annealed (SA) condition. The new upgraded 803 alloy also had the potential for a processing boost in that creep resistance for certain kinds of manufactured components that was not found in the standard alloy. The upgraded 803 alloy showed similar or slightly better oxidation and corrosion resistance relative to standard 803. Creep strength and oxidation/corrosion resistance of the upgraded 803 alloy were significantly better than found in alloy 800 H, as originally intended. The CRADA was terminated in February 2003. A contributing factor was Special Metals Corporation being in Chapter 11 Bankruptcy. Additional testing, further commercial scale-up, and any potential invention disclosures were not pursued.

  9. 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

  10. 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.

  11. Influence of high temperature on cadmium-induced skeletal deformities in juvenile mosquitofish (Gambusia affinis).

    PubMed

    Sassi, Asma; Annabi, Ali; Kessabi, Kaouthar; Kerkeni, Abdelhamid; Saïd, Khaled; Messaoudi, Imed

    2010-09-01

    The aim of this study was to assess the effect of high temperature on cadmium (Cd)-induced skeletal deformities in juvenile Mosquitofish, Gambusia affinis. For this purpose, 188 juveniles (1 day old) were equally divided into the control group, which was maintained in Cd-free water at 24 degrees C, and three treated groups exposed either to Cd (0.4 mg/l as Cd Cl(2)) at 24 degrees C, to high temperature (32 degrees C), or to Cd at 32 degrees C for 30 days. The results showed that Cd exposure at 24 degrees C significantly increased the Cd accumulation (P < 0.0001) in the whole tissues of juveniles as well as the incidence of skeletal deformities (P < 0.01) compared with control animals. Exposure to high temperature also led to a significant increase in the incidence of skeletal deformities (P < 0.01) with respect to the control group. Interestingly, our results showed that the combined exposure to Cd and high temperature led to a more significant increase in Cd accumulation and in the frequency of spinal deformities than exposure to Cd or high temperature alone. These results confirm that temperature increases Cd toxicity and needs to be taken into account for the accurate prediction and assessment of Cd-induced spinal deformities in fish. PMID:19229646

  12. 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.

  13. Electrically induced temperature difference and deformation in hardened cement pastes

    SciTech Connect

    Sun Mingqing [Department of Engineering Structures and Mechanics, Wuhan University of Technology, Wuhan 430070 (China)]. E-mail: sunmingqing@yahoo.com; Wang Xiaoying [Department of Engineering Structures and Mechanics, Wuhan University of Technology, Wuhan 430070 (China); Zhao Kairui [Department of Engineering Structures and Mechanics, Wuhan University of Technology, Wuhan 430070 (China); Li Zhuoqiu [Department of Engineering Structures and Mechanics, Wuhan University of Technology, Wuhan 430070 (China)

    2006-12-15

    Electromechanical effect of hardened cement paste beam is investigated in this paper. When an external electrical current is applied to the electrodes attached to opposite surfaces of a cement beam, it is found that temperature on the positive electrode is always higher than that on the negative electrode. The sign of electrically induced temperature difference is determined by the direction of applied electrical current. Electrically induced temperature difference makes the beam bend towards the surface with a higher temperature. Both electrically induced temperature difference and electroosmosis lead to electromechanical effect of hardened cement paste. Finally, electromechanical effect becomes more obvious by adding NaCl to cement paste.

  14. Creep rupture behavior of unidirectional advanced composites

    NASA Technical Reports Server (NTRS)

    Yeow, Y. T.

    1980-01-01

    A 'material modeling' methodology for predicting the creep rupture behavior of unidirectional advanced composites is proposed. In this approach the parameters (obtained from short-term tests) required to make the predictions are the three principal creep compliance master curves and their corresponding quasi-static strengths tested at room temperature (22 C). Using these parameters in conjunction with a failure criterion, creep rupture envelopes can be generated for any combination of in-plane loading conditions and ambient temperature. The analysis was validated experimentally for one composite system, the T300/934 graphite-epoxy system. This was done by performing short-term creep tests (to generate the principal creep compliance master curves with the time-temperature superposition principle) and relatively long-term creep rupture tensile tests of off-axis specimens at 180 C. Good to reasonable agreement between experimental and analytical results is observed.

  15. 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 (±2°C). 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 1000-1300°C, 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.

  16. Plastic flow and dislocation structures in tantalum carbide: Deformation at low and intermediate homologous temperatures

    Microsoft Academic Search

    C. Kim; G. Gottstein; D. S. Grummon

    1994-01-01

    Dislocation structures and plastic flow in TaC(0.99) have been studied in material deformed by microindentation at 20 C, and in specimens crept at temperatures between 0.37 and 0.43 T(sub m) (1300-1500 C). Extensive local plastic deformation occurred during indentation, accomplished mainly by the motion of a\\/2(011) edge dislocations gliding on (111). The resulting defect structure consisted primarily of long screw

  17. TEM observations of dislocations in aluminium nitride after high temperature deformation

    Microsoft Academic Search

    M. Azzaz; J. P. Michel; V. Feregotto; A. George

    2000-01-01

    AlN ceramics were deformed up to 10% strain in compression at elevated temperatures (1820–1920 K) under constant stress in the range 150–250 MPa or at a constant fixed strain rate of 5×10?6 s?1. Several kinds of dislocations were identified by TEM in deformed crystals. Most of them have a? type Burgers vectors and were seen to glide in the basal

  18. Dislocation structure of intermetallic Ti 3 Al subjected to high-temperature deformation

    Microsoft Academic Search

    L. E. Kar’kina; O. A. Elkina; L. I. Yakovenkova

    2008-01-01

    Transmission electron microscopy was used to examine the dislocation structure of intermetallic Ti3Al subjected to deformation at tempertures T = 1073–1273 K. The microstructure of samples subjected to high-temperature deformation is established to contain mobile superdislocations\\u000a of a and 2c + a types, and single dislocations with Burgers vector [0001] are also observed on the prismatic planes. Possible models of

  19. High temperature deformation behavior of Al–Cu–Mg alloys micro-alloyed with Sn

    Microsoft Academic Search

    Sanjib Banerjee; P. S. Robi; A. Srinivasan; Lakavath Praveen Kumar

    2010-01-01

    Deformation behavior of Al–6.2%Cu–0.6%Mg alloy and Al–6.2%Cu–0.6%Mg alloy containing 0.06wt.% of Sn was studied by hot compression tests conducted at various temperatures and strain rates. During the deformation process, the flow stress of the Al–Cu–Mg alloy increased due to trace addition of Sn. The peak flow stress for both the alloys increased with increase in strain rate and decrease in

  20. 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.

  1. A PM 2124Al-20SiC{sub p} composite: Disappearance of true threshold creep behavior at high testing temperatures

    SciTech Connect

    Cadek, J.; Kucharova, K.; Sustek, V. [Academy of Sciences of the Czech Republic, Brno (Czech Republic). Inst. of Physics of Materials] [Academy of Sciences of the Czech Republic, Brno (Czech Republic). Inst. of Physics of Materials

    1999-05-07

    During the recent several years it has been well recognized that the creep behavior in discontinuous aluminum and aluminum alloy matrix composites processed by powder metallurgy is associated with a true threshold stress at least up to a temperature of about 700 K. In the present paper, an attempt is made to interpret the disappearance of the true threshold behavior in terms of transition from the athermal to thermally activated detachment of dislocations from fine ``interacting`` alumina particles present in the PM 2124Al-20SiC{sub p} composite matrix.

  2. Creep analysis of solid oxide fuel cell with bonded compliant seal design

    NASA Astrophysics Data System (ADS)

    Jiang, Wenchun; Zhang, Yucai; Luo, Yun; Gong, J. M.; Tu, S. T.

    2013-12-01

    Solid oxide fuel cell (SOFC) requires good sealant because it works in harsh conditions (high temperature, thermal cycle, oxidative and reducing gas environments). Bonded compliant seal (BCS) is a new sealing method for planar SOFC. It uses a thin foil metal to bond the window frame and cell, achieving the seal between window frame and cell. At high temperature, a comprehensive evaluation of its creep strength is essential for the adoption of BCS design. In order to characterize the creep behavior, the creep induced by thermal stresses in SOFC with BCS design is simulated by finite element method. The results show that the foil is compressed and large thermal stresses are generated. The initial peak thermal stress is located in the thin foil because the foil acts as a spring stores the thermal stresses by elastic and plastic deformation in itself. Serving at high temperature, initial thermal displacement is partially recovered because of the creep relaxation, which becomes a new discovered advantage for BCS design. It predicts that the failures are likely to happen in the middle of the cell edge and BNi-2 filler metal, because the maximum residual displacement and creep strain are located.

  3. 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.

  4. Temperature and strain-rate effects on deformation mechanisms in irradiated stainless steel

    SciTech Connect

    Brimhall, J.L.; Cole, J.I.; Vetrano, J.S.; Bruemmer, S.M.

    1994-11-01

    Analysis of the deformation microstructures in ion-irradiated stainless steel shows twinning to be the predominant deformation mode at room temperature. Dislocation channelling also occurs under slow strain rate conditions. Stresses required for twinning were calculated by the model of Venables and are compatible with observed yield stresses in neutron-irradiated material if loops are the principal twin source. Computation of the expected radiation hardening from the defect structure, based on a simple model, is consistent with yield strengths measured on neutron-irradiated steels. Lower yield stresses and greater thermal energy at 288 C lessen the probability of twinning and dislocation channeling becomes the primary deformation mode at the higher temperature. However, preliminary early results show that some twinning does occur in the irradiated stainless steel even at the higher temperature when higher strain rates are used.

  5. Vesicle growth and deformation in a surfactant solution below the Krafft temperature.

    PubMed

    Kawabata, Youhei; Shinoda, Tomoaki; Kato, Tadashi

    2011-02-28

    We have studied vesicle growth and deformation in aqueous solutions of nonionic surfactant C(16)E(7) below the Krafft temperature by means of an optical microscope. It has been found that vesicles become larger by fusing together, and that the growth rate is slower than that of the unilamellar vesicle or emulsion systems due to the multilamellar structures of shells in a vesicle. The deformation of the vesicles depends on the temperature quench depth, and we found the transformation from spherical vesicles to string-like domains at a certain quench-temperature. From the small angle X-ray scattering and confocal microscope experiments, it can be deduced that the deformation of vesicles would be induced by osmotic pressure due to the micellar concentration difference between inside and outside of vesicles. PMID:21243142

  6. 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.

  7. 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

  8. High-temperature deformation and grain-boundary characteristics of titanium alloys with an equiaxed microstructure

    Microsoft Academic Search

    Jeoung Han Kim; S. L. Semiatin; Chong Soo Lee

    2008-01-01

    The high-temperature deformation behavior of single-phase ? (Ti–7.0Al–1.5V), near-? (Ti–6.85Al–1.6V), and two-phase (Ti–6Al–4V) titanium alloys with an equiaxed microstructure was examined, and the results were compared within the framework of an internal-variable theory of inelastic deformation. For this purpose, load-relaxation and tension tests were conducted at various temperatures. Stress–strain-rate curves obtained by load-relaxation tests for the three alloys were well

  9. Deformation of carbon nanotubes colliding with a silicon surface and its dependence on temperature.

    PubMed

    Saha, Leton C; Mian, Shabeer A; Kim, Hyojeong; Saha, Joyanta K; Jang, Joonkyung

    2012-01-01

    Using molecular dynamics simulation, we investigated the carbon nanotubes (CNTs) colliding with a silicon surface at a speed of 600 m/s, mimicking cold spray experiments of CNTs. Depending on temperature (300-900 K), the CNT is deposited on or bounces off the surface after impact on the surface. The CNT was more deformed as its temperature rose. The deformation of CNT was maximal for the collision geometry where the long axis of CNT lies parallel to the surface plane. However, its vibrational energy was maximal when the CNT collided with its long axis perpendicular to the surface. PMID:22524038

  10. Effect of trace impurities in helium on the creep behavior of Alloy 617 for very high temperature reactor applications

    NASA Astrophysics Data System (ADS)

    Shankar, P. S.; Natesan, K.

    2007-06-01

    The effect of trace impurities, methane and oxygen, in helium on the creep behavior of Alloy 617, has been investigated. The creep rupture life at relatively low applied stresses was shortest in a helium environment containing 500 vppm oxygen (He + O 2), while it was the longest in helium containing 675 vppm methane (He + CH 4). However, the rupture strain was significantly lower in the He + CH 4 environment compared to that in pure helium (He) and He + O 2. The low rupture strain in the He + CH 4 is caused by cleavage fracture. In the He + CH 4 environment, the fracture mode was cleavage at lower applied stresses and ductile at higher applied stresses while in the He and He + O 2, a ductile fracture was observed at all stress levels. The apparent activation energy for creep was determined in all three environments, and it appears to be independent of stress in the He, dependent in the He + CH 4, while in the He + O 2 environment the stress dependence could not be conclusively established.

  11. Creep Studies of Aluminum Conductor Alloys

    Microsoft Academic Search

    Calvin Roest

    1969-01-01

    The results of a comprehensive laboratory test program on the creep characteristics of EC-H19, 5005-H19, and 6201- T81 aluminum alloy conductor wires are presented. Creep curves for those alloys are illustrated over a stress range of 15 to 25 percent minimum average strengths and a temperature range of 25 to 100°C. The importance of creep history as a function of

  12. Creep-fatigue interactions in eutectic tin-lead-based solder alloys. Ph.D. Thesis

    SciTech Connect

    Kuo, C.W.

    1994-01-01

    Eutectic tin-lead solder alloys subjected to cyclic loading at room temperature experience creep-fatigue interactions due to high homologous temperature. At temperature above 0.5 melting point, the dominant damage mechanism can be cavity nucleation and growth, especially for alloys that have fine grain structure and a large volume fraction of dispersoids. The objective of the present study is to model the damage evolution during creep-fatigue interactions and experimentally validate the damage evolution based life predictions in rapidly solidified solder alloys. Four types of solder alloys were considered in this research, namely, conventional 63Sn-37Pb, rapidly solidified 63Sn-37Pb, dispersion-strengthened eutectic solders, and solid solution strengthened eutectic solders. Mechanical properties of the solder alloys and the life times under creep-fatigue conditions were evaluated. Damage produced in the course of creep or fatigue deformation was studied by metallography, scanning electron microscopy, precision density measurement, and the observation of grain boundary sliding. Based on the damage characteristics, the dominant failure mechanism was proved to be cavity growth. Three cavity growth models were applied to four types of solder alloys to predict creep-fatigue life by taking into account the tensile loading component as well as the compressive loading component when reversed process can occur. An algorithm to calculate cavity growth in each fatigue cycle is used to predict the number of fatigue cycles to failure, where failure is defined as a critical cavity size. Calculated lives are compared to experimental data under six types of creep-fatigue loading histories. The method predicts the creep-fatigue lives within a factor of two with the incorporation of appropriate compressive healing factor. Discrepancy between calculated lives and experimental results is discussed.

  13. 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.

  14. Modelling of creep rupture experiments using a coupled damage-viscoplasticity model

    SciTech Connect

    Strub, C.; Devos, J. [Commissariat a l`Energie Atomique, Gif-sur-Yvette (France). Service d`Etudes Mecaniques et Thermiques

    1996-12-31

    Creep rupture of real RPV`s in severe accident would probably occur after complex load and temperature histories, allowing creep deformation, stress relaxation, material damaging and plastic instability. To properly deal with all these mechanisms and their possible interactions, CEA has generalized a model due to Lemaitre and Chaboche, in which damaging and viscoplastic flow are treated in a coupled way. It has been used to predict creep experiments of tube submitted to internal pressure and a localized heating (RUPTHER program). The results show a marked difference with analyses based on more conventional models, in terms of times to failure. The paper gives the basic features of the model, the principles of parameter identification and its application to an experiment prediction.

  15. 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,

  16. Grain-boundary diffusion creep in nanocrystalline palladium by molecular-dynamics simulation

    Microsoft Academic Search

    V. Yamakov; D. Wolf; S. R. Phillpot; H. Gleiter; Forschungszentrum Karlsruhe

    2002-01-01

    Molecular-dynamics (MD) simulations of fully three-dimensional (3D), model nanocrystalline face-centered cubic metal microstructures are used to study grain-boundary (GB) diffusion creep, one mechanism considered to contribute to the deformation of nanocrystalline materials. To overcome the well-known limitations associated with the relatively short time interval used in our MD simulation (typically <10?8 s), our simulations are performed at elevated temperatures where

  17. 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.

  18. 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.

  19. Plastic deformation in high critical current melt-textured YBa2Cu3O7

    Microsoft Academic Search

    B. Martínez; F. Sandiumenge; N. Vilalta; S. Piñol; X. Obradors; J. Rabier

    1996-01-01

    The effect of high-temperature creep under different conditions in melt-textured YBa2Cu3O7–Y2BaCuO5 composites, with high critical currents before deformation, is investigated. Transmission electron microscopy studies show that the low-temperature oxygenation process causes a strong modification of the as-deformed microstructure and leads to a clear degradation of the superconducting performances. This behavior of the superconducting properties is well correlated with the formation

  20. Transient creep and convective instability of the lithosphere

    NASA Astrophysics Data System (ADS)

    Birger, Boris I.

    2012-12-01

    Laboratory experiments with rock samples show that transient creep, at which strain grows with time and strain rate decrease at constant stress, occurs while creep strains are sufficiently small. The transient creep at high temperatures is described by the Andrade rheological model. Since plate tectonics allows only small deformations in lithospheric plates, creep of the lithosphere plates is transient whereas steady-state creep, described by non-Newtonian power-law rheological model, takes place in the underlying mantle. At the transient creep, the effective viscosity, found in the study of postglacial flows, differs significantly from the effective viscosity, which characterizes convective flow, since timescales of these flows are very different. Besides, the transient creep changes the elastic crust thickness estimated within the power-law rheology of the lithosphere. Two problems of convective stability for the lithosphere with the Andrade rheology are solved. The solution of the first problem shows that the state, in which large-scale convective flow in the mantle occurs under lithospheric plates, is unstable and must bifurcate into another more stable state at which the lithospheric plates become mobile and plunge into the mantle at subduction zones. If the lithosphere had the power-law fluid rheology, the effective viscosity of the stagnant lithospheric plates would be extremely high and the state, in which large-scale convection occurs under the stagnant plates, would be stable that contradicts plate tectonics. The mantle convection forms mobile lithospheric plates if the effective viscosity of the plate is not too much higher than the effective viscosity of the underlying mantle. The Andrade rheology lowers the plate effective viscosity corresponding to the power-law fluid rheology and, thus, leads to instability of the state in which the plates are stagnant. The solution of the second stability problem shows that the state, in which the lithospheric plate moves as a whole with constant velocity, is stable but small-amplitude oscillations are imposed on this motion in regions of thickened lithosphere beneath continental cratons (subcratonic roots) where the thickness of the lithosphere is about 200 km. These oscillations create small-scale convective cells (the horizontal dimensions of the cells are of the order of the subcratonic lithosphere thickness). Direction of motion within the cells periodically changes (the period of oscillations is of the order of 108 yr). The small-amplitude convective oscillations cause small strains and do not destroy the thickening of the lithosphere beneath cratons. Thus, the transient creep of the lithosphere explains not only mobility of the lithospheric plates but longevity of subcratonic roots as well.

  1. Acquiring a novel constitutive equation of a TC6 alloy at high-temperature deformation

    NASA Astrophysics Data System (ADS)

    Li, Miaoquan; Cheng, Shenhui; Xiong, Aiming; Wang, Hairong; Su, Shaobo; Sun, Lichuang

    2005-04-01

    The TC6 alloy produced in Baoji nonferrous metals work, Xian, China, is one of the best titanium alloys with good resistance against heat and corrosion and is widely used in the aviation and aerospace industries. In this paper, isothermal compression tests were conducted on the TC6 alloy in the Thermecmastor Z simulator, at temperatures between 800 and 1040 °C at strain rates between 0.001 and 50 s-1 to a 50% height reduction. The experimental results are presented as variations of flow stress with deformation temperature, strain rate, and strain. On the basis of the present experimental results and deformation behavior, a constitutive equation for the TC6 alloy was proposed by employing an Arrhenius-type equation. The activation energy of deformation (Q) and work-hardening index (n) are found to be a function of strain. The present equation is in good agreement with the experimental data.

  2. Research on Softening of A95456 Alloy Deformed Under Elevated Temperatures

    SciTech Connect

    Petrov, Pavel A.; Perfilov, Victor I. [Department of Autobody building and metal forming, Moscow State Technical University 'MAMI', 107023, B.Semenovskaya str., 38, GPS, Moscow (Russian Federation)

    2007-04-07

    The present paper describes the results of the research on the softening of aluminium alloy A95456 deformed at elevated temperatures. The investigations were carried out within the temperature range of 310-450 deg. C and strain rate of 0.01-0.4 s-1. The strain rate was either constant or variable in performed experiments. In case of variable strain rate two different schemes were observed. Firstly, the deformation of alloy A95456 was performed at constant die velocity and so the strain rate increased monotonically. Secondly, the die velocity was changed suddenly during the deformation of A95456 alloy. In turn, it caused the sudden strain rate change. To describe the softening behaviour of A95456 alloy several equations were investigated. The accuracy of each equation was estimated. Some practical recommendations for use of those equations were given.

  3. Evidence for dislocation glide controlled creep in niobium-base alloys

    SciTech Connect

    Wadsworth, J.; Dougherty, S.E.; Nieh, T.G. (Lockheed Missiles and Space Co., Research and Development Div., Palo Alto, CA (US)); Kramer, P.A. (Lawrence Berkeley Lab., Center for Advanced Materials, Materials Science Div., Berkeley, CA (US))

    1992-07-01

    It was shown several years ago that a coarse-grained Nb-5.4Hf-2.0Ti alloy (known commercially as C103) could exhibit large tensile elongations of over 200%; the phenomenon was observed at intermediate homologous temperatures (about 0.7 T{sub m}, where T{sub m} is the absolute melting temperature) and at intermediate strain rates (of about 10{sup {minus}3} s{sup {minus}1}). The extended ductility in C103 was attributed to the fact that it is representative of a special group of alloys known as Class I solid solutions. This paper reports that based on these descriptions, Class I solid solutions are found in alloys that have relatively large atomic size mismatches for a given value of elastic modulus, although it has been pointed out that the solute concentration, stress level, and the ratio of climb to glide diffusivities are also important variables. Often there is little or no subgrain formation, and the deformation behavior of the alloys does not exhibit a direct dependence on the stacking fault energy. During creep, the alloys exhibit either little primary creep or an inversion of primary creep that often enters directly into tertiary, or accelerating, creep. The activation energy for creep in Class I solid solutions is for chemical interdiffusion and is often below the activation energy for self-diffusion of the matrix metal.

  4. Dynamic strain aging in stress controlled creep–fatigue tests of 316L stainless steel under different loading conditions

    Microsoft Academic Search

    Huifeng Jiang; Xuedong Chen; Zhichao Fan; Jie Dong; Heng Jiang; Shouxiang Lu

    2009-01-01

    Stress controlled fatigue–creep tests were carried out for 316L stainless steel under different loading conditions, i.e. different loading levels at the fixed temperature (loading condition 1, LC1) and different temperatures at the fixed loading level (loading condition 2, LC2). Cyclic deformation behaviors were investigated with respect to the evolutions of strain amplitude and mean strain. Abrupt mean strain jumps were

  5. 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...

  6. 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.

  7. 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.

  8. Effects of Temperature and Grain Size Evolution on the Deformation and Stability of a 1-D Viscoelastic Shear Zone

    NASA Astrophysics Data System (ADS)

    Homburg, J. M.; Spiegelman, M.; Kelemen, P. B.; Hirth, G.

    2011-12-01

    Viscous shear heating instabilities may provide a possible mechanism for some intermediate depth earthquakes where high confining pressure makes it difficult to achieve the conditions for frictional failure. While many studies have looked at the feedback between temperature-dependant strain rate and strain rate-dependant shear heating (e.g. Braeck and Podladchikov, 2007), fewer have examined the feedbacks between grain size, temperature and viscosity. We have developed a 1-D numerical model that describes the behavior of a Maxwell viscoelastic body with the rheology of dry olivine, driven at a constant velocity at its boundary and initiated with a fine-grained shear zone. Specific contributions to viscous strain include diffusion and dislocation creep, dislocation accommodated grain boundary sliding (disGBS), and low-temperature plasticity (LTP - Peierls mechanism). Grain size is allowed to evolve according to the parameterization described in Austin and Evans (2007). However, unlike Austin and Evans (2007) we allow strain accommodated by both dislocation creep and disGBS to contribute to grain size evolution. This is because both mechanisms rely on similar microphysical processes to accommodate strain. We contrast the stability of the system with and without grain size evolution and evaluate the consequences that grain size evolution has on overall system behavior. Including grain size evolution modifies the behavior of the basic model in several ways. First, due to the combined processes of grain growth and grain size reduction, a wide range of initial shear zone grain sizes (1 ?m - 500 ?m) evolves during the elastic loading phase to a common shear zone grain size (~2 ?m) at the peak stress, nearly eliminating a previously observed dependence of peak stress on initial shear zone grain size. Second, we observe an expansion, by an order of magnitude both faster and slower, in the range of applied strain rate conditions under which moderately rapid and complex unloading (stress relaxation rates of ~1 MPa/yr - ~100 MPa/yr within a single run) and reloading of the system occurs. For example, for a domain size of 2 km and a 8 m wide shear zone, initial background and shear zone grain sizes of 10 mm and 2 ?m respectively, and an initial temperature of 650°C, the ranges of background strain rates for which this type of behavior is observed are <2 x 10-13 - 2 x 10-10 and 2 x 10-12 - 2 x 10-11 s-1, with and without grain size evolution, respectively. Finally, we observe a shift to slightly higher applied background strain rates for the occurrence of dramatic, self-localizing instabilities during which the system unloads all of its stress, up to ~1 GPa, almost instantaneously. For example, for the same run conditions described above, this transition occurs for background strain rates of 2 x 10-10 and 2 x 10-11 s-1, with and without grain size evolution, respectively. We are now systematically evaluating the behavior of the model over a wide range of geologically reasonable parameter space to investigate the implications of viscous shear heating instabilities for deformation in the earth.

  9. Creep and fracture kinetics of polymers

    NASA Astrophysics Data System (ADS)

    Makarov, A. G.; Slutsker, G. Ya.; Drobotun, N. V.

    2015-02-01

    The creep kinetics and the fracture kinetics of oriented linear polymer (polypropylene) are compared. The distributions (scatter) of the specimen lives and the steady-state creep rate are studied on series of identical specimens loaded under the same conditions (load, temperature). It is found that the scatter of the specimen lives is significantly larger than the scatter of the creep rates at the same activation energy of fracture (the measure of which is the life) and creep. This finding reflects a localized character of fracture (break) of specimens and a delocalized character (involvement of the entire specimen volume) of creep. It is concluded that the equality of the activation energies of both processes is caused by the elementary acts of fracture of an oriented polymer (breaking of chain molecules), and they open up possibilities for creep acts, i.e., conformation transitions, in a polymer.

  10. 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 760°C. 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

  11. Study of microstructure and mechanical properties of oriented single colony crystals of a near-alpha titanium alloy at room temperature

    Microsoft Academic Search

    Satyarth Suri

    2000-01-01

    Two phase alpha\\/beta titanium alloys have been widely reported to deform by primary creep at low homologous temperatures (T\\/Tm < 0.2) and at fractions (as low as 0.6) of the 0.2% yield strength. There exists little understanding of the mechanisms of creep deformation in these alloys. The mechanism of slip transmission across the alpha\\/beta interfaces is also not well understood.

  12. Effect of deformation temperature on the mechanical behavior and deformation mechanisms of Al-Al[sub 2]O[sub 3] metal matrix composites

    SciTech Connect

    Mazen, A.A. (American Univ. in Cairo (Egypt). Dept. of Engineering)

    1999-08-01

    Aluminum-alumina (Al-Al[sub 2]O[sub 3]) metal matrix composite (MMC) materials were fabricated using the powder metallurgy (PM) techniques of hot pressing followed by hot extrusion. Different reinforcement weight fractions were used, that is, 0, 2.5, 5, and 10 wt% Al[sub 2]O[sub 3]. The effect of deformation temperature was investigated through hot tensile deformation conducted at different temperatures. The microstructures of the tested specimens were also investigated to characterize the operative softening mechanisms. The yield and tensile strength of the Al-Al[sub 2]O[sub 3] were found to improve as a function of reinforcement weight fraction. With the exception of Al-10wt%Al[sub 2]O[sub 3], the MMC showed better strength and behavior at high temperatures than the unreinforced matrix. The uniform deformation range was found to decrease for the same reinforcement weight fraction, as a function of temperature. For the same deformation temperature, it increases as a function of reinforcement weight fraction. Both dynamic recovery and dynamic recrystallization were found to be operative in Al-Al[sub 2]O[sub 3] MMC as a function of deformation temperature. Dynamic recovery is dominant in the lower temperature range, while dynamic recrystallization is more dominant at the higher range. The increase in reinforcement weight fraction was found to lead to early nucleation of recrystallization. No direct relationship was established as far as the number of grains nucleated due to each reinforcement particle.

  13. Effect of deformation temperature on the mechanical behavior and deformation mechanisms of Al-Al2O3 metal matrix composites

    NASA Astrophysics Data System (ADS)

    Mazen, A. A.

    1999-08-01

    Aluminum-alumina (Al-Al2O3) metal matrix composite (MMC) materials were fabricated using the powder metallurgy (PM) techniques of hot pressing followed by hot extrusion. Different reinforcement weight fractions were used, that is, 0, 2.5, 5, and 10 wt% Al2O3. The effect of deformation temperature was investigated through hot tensile deformation conducted at different temperatures. The microstructures of the tested specimens were also investigated to characterize the operative softening mechanisms. The yield and tensile strength of the Al-Al2O3 were found to improve as a function of reinforcement weight fraction. With the exception of Al-10wt%Al2O3, the MMC showed better strength and behavior at high temperatures than the unreinforced matrix. The uniform deformation range was found to decrease for the same reinforcement weight fraction, as a function of temperature. For the same deformation temperature, it increases as a function of reinforcement weight fraction. Both dynamic recovery and dynamic recrystallization were found to be operative in Al-Al2O3 MMC as a function of deformation temperature. Dynamic recovery is dominant in the lower temperature range, while dynamic recrystallization is more dominant at the higher range. The increase in reinforcement weight fraction was found to lead to early nucleation of recrystallization. No direct relationship was established as far as the number of grains nucleated due to each reinforcement particle.

  14. Thermally activated dislocation creep model for primary water stress corrosion cracking of NiCrFe alloys

    SciTech Connect

    Hall, M.M., Jr

    1995-12-31

    There is a growing awareness that awareness that environmentally assisted creep plays an important role in integranular stress corrosion cracking (IGSCC) of NiCrFe alloys in the primary coolant water environment of a pressurized water reactor (PWR). The expected creep mechanism is the thermally activated glide of dislocations. This mode of deformation is favored by the relatively low temperature of PWR operation combined with the large residual stresses that are most often identified as responsible for the SCC failure of plant components. Stress corrosion crack growth rate (CGR) equations that properly reflect the influence of this mechanism of crack tip deformation are required for accurate component life predictions. A phenomenological IGSCC-CGR model, which is based on an apriori assumption that the IGSCC-CGR is controlled by a low temperature dislocation creep mechanism, is developed in this report. Obstacles to dislocation creep include solute atoms such as carbon, which increase the lattice friction force, and forest dislocations, which can be introduced by cold prestrain. Dislocation creep also may be environmentally assisted due to hydrogen absorption at the crack tip. The IGSCC-CGR model developed here is based on an assumption that crack growth occurs by repeated fracture events occurring within an advancing crack-tip creep-fracture zone. Thermal activation parameters for stress corrosion cracking are obtained by fitting the CGR model to IGSCC-CGR data obtained on NiCrFe alloys, Alloy X-750 and Alloy 600. These IGSCC-CGR activation parameters are compared to activation parameters obtained from creep and stress relaxation tests. Recently reported CGR data, which exhibit an activation energy that depends on yield stress and the applied stress intensity factor, are used to benchmark the model. Finally, the effects of matrix carbon concentration, grain boundary carbides and absorbed hydrogen concentration are discussed within context of the model.

  15. Dislocation substructure in NiAl single crystals deformed at ambient temperature

    SciTech Connect

    Shi, X.; Pollock, T.M.; Mahajan, S.; Arunachalam, V.S. [Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Materials Science and Engineering

    1997-12-31

    Dislocation substructure in NiAl single crystals oriented for single slip and deformed at ambient temperature has been studied using weak-beam transmission electron microscopy. Deformation is localized in bands that consists mostly of near-edge dislocations, with an interspersion of a high density of elongated prismatic loops. Pure screw dislocations are not observed, but dislocations having zigzag configurations that are near-screw in orientation are present. A high density of jogs is observed on both near-edge and zigzag dislocation segments. The mechanisms for the development of this substructure are discussed, emphasizing the role of double cross slip and resulting glissile and sessile jogs of varying heights.

  16. Evaluation of hoop creep behaviors in long-term dry storage condition of pre-hydrided and high burn-up nuclear fuel cladding

    SciTech Connect

    Kim, Sun-Ki; Bang, J.G.; Kim, D.H.; Yang, Y.S. [Korea Atomic Energy Research Institute, P.O. Box 150, Yuseong, Daejeon, Korea, 305-600 (Korea, Republic of)

    2007-07-01

    Related to the degradation of the mechanical properties of Zr-based nuclear fuel cladding tubes under long term dry storage condition, the mechanical tests which can simulate the degradation of the mechanical properties properly are needed. Especially, the degradation of the mechanical properties by creep mechanism seems to be dominant under long term dry storage condition. Accordingly, in this paper, ring creep tests were performed in order to evaluate the creep behaviors of high burn-up fuel cladding under a hoop loading condition in a hot cell. The tests are performed with Zircaloy-4 fuel cladding whose burn-up is approximately {approx}60,000 MWd/tU in the temperature range from 350 deg. to 550 deg.. The tests are also performed with pre-hydrided Zircaloy-4 and ZIRLO up to 1,000 ppm. First of all, the hoop loading grip for the ring creep test was designed in order that a constant curvature of the specimen was maintained during the creep deformation, and the graphite lubricant was used to minimize the friction between the outer surface of the die insert and the inner surface of the ring specimen. The specimen for the ring creep test was designed to limit the deformation within the gauge section and to maximize the uniformity of the strain distribution. It was confirmed that the mechanical properties under a hoop loading condition can be correctly evaluated by using this test technique. In this paper, secondary creep rate with increasing hydrogen content are drawn, and then kinetic data such as pre-exponential factor and activation energy for creep process are also drawn. In addition, creep life are predicted by obtaining LMP (Larson-Miller parameter) correlation in the function of hydrogen content and applied stress to yield stress ratio. (authors)

  17. 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

  18. Effect of prior deformation on the elevated temperature fatigue behavior in Nimonic PE16 alloy

    SciTech Connect

    Sundararaman, M. (Bhabha Atomic Research Centre, Bombay (India). Metallurgy Div.); Chen, W.; Wahi, R.P. (Hahn-Meitner-Inst., Berlin (Germany))

    1994-05-01

    It is well known that prior deformation (either monotonic or cyclic) affects the subsequent fatigue behavior of some metals and alloys. A study of this history dependence of cyclic deformation behavior is important, because in engineering application, components quite often experience varying loads and temperatures. Results reported so far indicate that the fatigue behavior of materials, with low/intermediate stacking fault energy, depends very much on the prior history of the sample whereas the behavior of the wavy slip mode materials is not so dependent. The authors chose for the present investigation, a nickel base superalloy, Nimonic PE16, strengthened by the precipitation of [gamma][prime] particles (Ni[sub 3]Al,Ti), having spherical morphology, low volume fraction and uniform distribution in the austenite matrix. This paper reports the results obtained on the effect on prior room temperature cyclic deformation on the elevated temperature fatigue behavior of this alloy, corresponding to two initial microstructural conditions. The results are interpreted in the light of the present understanding of the mechanism of fatigue deformation and the results of transmission electron microscopic (TEM) examination of fatigued samples.

  19. Analysis of the Dependence of Material Properties on Temperature - Steel 1.4122

    NASA Astrophysics Data System (ADS)

    Brnic, Josip; Turkalj, Goran; Vukelic, Goran; Brcic, Marino

    2012-06-01

    This article presents an analysis of experimental data with reference to material properties, short-time creep and relaxation phenomena of 1.4122 steel (AISI 420RM) at high temperatures. The behaviour of the material subjected to uniaxial stress is indicated by engineering stress - strain diagrams. The data referring to tensile strength, 0.2 percent offset yield strength, the modulus of elasticity and total deformation, are shown through tables and curves presenting the dependence of these quantities on temperature. Creep and relaxation curves regarding certain level of stresses at selected temperatures are also shown. In addition, modelling of both creep and relaxation phenomena is presented.

  20. PLASTIC DEFORMATIONPLASTIC DEFORMATION Modes of Deformation

    E-print Network

    Subramaniam, Anandh

    original shape. A steel piece is easier to deform when heated (as compared to when it is cold). Let us Deformation in Crystalline Materials Twinning Phase Transformation Creep Mechanisms Grain boundary sliding in the current chapter #12; One of the simplest test which can performed to evaluate the mechanical properties