Sample records for creep deformation characteristics

  1. 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.

  2. 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

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. 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.

  8. Finite Element Analysis of Plastic Deformation During Impression Creep

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  9. 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

  10. 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.

  11. 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

  12. 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"

  13. 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

  14. 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.

  15. 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

  16. 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

  17. 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.

  18. 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

  19. 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

  20. 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

  1. 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...

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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.

  7. 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

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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

  19. Poroelastic response of articular cartilage by nanoindentation creep tests at different characteristic lengths.

    PubMed

    Taffetani, M; Gottardi, R; Gastaldi, D; Raiteri, R; Vena, P

    2014-07-01

    Nanoindentation is an experimental technique which is attracting increasing interests for the mechanical characterization of articular cartilage. In particular, time dependent mechanical responses due to fluid flow through the porous matrix can be quantitatively investigated by nanoindentation experiments at different penetration depths and/or by using different probe sizes. The aim of this paper is to provide a framework for the quantitative interpretation of the poroelastic response of articular cartilage subjected to creep nanoindentation tests. To this purpose, multiload creep tests using spherical indenters have been carried out on saturated samples of mature bovine articular cartilage achieving two main quantitative results. First, the dependence of indentation modulus in the drained state (at equilibrium) on the tip radius: a value of 500 kPa has been found using the large tip (400 ?m radius) and of 1.7 MPa using the smaller one (25 ?m). Secon, the permeability at microscopic scale was estimated at values ranging from 4.5×10(-16) m(4)/N s to 0.1×10(-16) m(4)/N s, from low to high equivalent deformation. Consistently with a poroelastic behavior, the size-dependent response of the indenter displacement disappears when characteristic size and permeability are accounted for. For comparison purposes, the same protocol was applied to intrinsically viscoelastic homogeneous samples of polydimethylsiloxane (PDMS): both indentation modulus and time response have been found size-independent. PMID:24814573

  20. 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.

  1. Stiffness and damping characteristics of aluminum in creep

    NASA Technical Reports Server (NTRS)

    Berkovits, A.

    1977-01-01

    Tensile creep tests conducted at 200 C were performed on annealed commercially pure aluminum specimens in order to measure the dominant elevated temperature dislocation processes. Testing consisted of applying small lateral loads to measure flexural stiffness, and vibrating the specimens laterally in order to measure dynamic modulus and internal damping. It was concluded that (1) the strain hardening increased static stiffness and decreased internal damping during early creep, and (2) the dynamic modulus remained essentially constant at the elastic value during creep. These results imply that primary creep may constitute a mechanism of recovery of dislocatory disorder induced by yielding the material during loading, and that the inelastic modulus utilized as a mathematical concept in several creep buckling theories is not a directly measurable material property.

  2. 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.

  3. Analysis of Mining Terrain Deformation Characteristics with Deformation Information System

    NASA Astrophysics Data System (ADS)

    Blachowski, Jan; Milczarek, Wojciech; Grzempowski, Piotr

    2014-05-01

    Mapping and prediction of mining related deformations of the earth surface is an important measure for minimising threat to surface infrastructure, human population, the environment and safety of the mining operation itself arising from underground extraction of useful minerals. The number of methods and techniques used for monitoring and analysis of mining terrain deformations is wide and increasing with the development of geographical information technologies. These include for example: terrestrial geodetic measurements, global positioning systems, remote sensing, spatial interpolation, finite element method modelling, GIS based modelling, geological modelling, empirical modelling using the Knothe theory, artificial neural networks, fuzzy logic calculations and other. The aim of this paper is to introduce the concept of an integrated Deformation Information System (DIS) developed in geographic information systems environment for analysis and modelling of various spatial data related to mining activity and demonstrate its applications for mapping and visualising, as well as identifying possible mining terrain deformation areas with various spatial modelling methods. The DIS concept is based on connected modules that include: the spatial database - the core of the system, the spatial data collection module formed by: terrestrial, satellite and remote sensing measurements of the ground changes, the spatial data mining module for data discovery and extraction, the geological modelling module, the spatial data modeling module with data processing algorithms for spatio-temporal analysis and mapping of mining deformations and their characteristics (e.g. deformation parameters: tilt, curvature and horizontal strain), the multivariate spatial data classification module and the visualization module allowing two-dimensional interactive and static mapping and three-dimensional visualizations of mining ground characteristics. The Systems's functionality has been presented on the case study of a coal mining region in SW Poland where it has been applied to study characteristics and map mining induced ground deformations in a city in the last two decades of underground coal extraction and in the first decade after the end of mining. The mining subsidence area and its deformation parameters (tilt and curvature) have been calculated and the latter classified and mapped according to the Polish regulations. In addition possible areas of ground deformation have been indicated based on multivariate spatial data analysis of geological and mining operation characteristics with the geographically weighted regression method.

  4. 3D microstructural and microchemical characteristics of SAFOD fault gouge: implications for understanding fault creep

    NASA Astrophysics Data System (ADS)

    Warr, Laurence; Wojatschke, Jasmaria; Carpenter, Brett; Marone, Chris; Schleicher, Anja; van der Pluijm, Ben

    2013-04-01

    Fault creep on the SAFOD section of the San Andreas Fault occurs along mechanically weak fault gouge characterized by high proportions of hydrous clay minerals, namely smectite, illite-smectite and chlorite-smectite phases. These minerals are concentrated along closely spaced, interconnected polished slip surfaces that give the gouge its characteristic scaly fabric. Although it is generally accepted that the creep behavior of the gouge relates to the concentration of these minerals, the precise mechanisms by which clay minerals weaken rock is currently a topic of debate. In this contribution we present the first results from a "slice-and-view" study of SAFOD gouge material by focused ion beam - scanning electron microscopy (Zeiss Auriga FIB/SEM), which allows the reconstruction of the microstructure and microchemistry of mineralized slip surfaces in 3D. The core and cuttings samples studied were selected from ca. 3297 m measured depth and represent some of the weakest materials yet recovered from the borehole, with a frictional coefficient of ca. 0.10 and a healing rate close to zero. This gouge contains abundant serpentine and smectite minerals, the latter of which was identified by X-ray diffraction to be saponite, after Mg- and glycol intercalation. Imaging and chemical analyses reveal nanometer scale thin alteration seams of saponite clay distributed throughout the ca. 50 micron thick sheared serpentinite layer that coats the slip surfaces. The base of this layer is defined by cataclastically deformed iron oxide minerals. The 3D fabric implies the orientation of the hydrated smectite minerals, which are interconnected and lie commonly sub parallel to the slip surface, are responsible for the gouge creep behavior in the laboratory. These minerals, and related interlayered varieties, are particularly weak due to their thin particle size and large quantities of adsorbed water, properties that are expected to persist down to mid-crustal depth (ca. 10 km). Creep of the San Andres Fault at Parkfield can therefore be adequately explained by the nature and abundance of smectite lattice layers that provide a nanometer-scale control on the mechanisms of fault behavior.

  5. 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

  6. 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.

  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-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.

  9. 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.

  10. 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.

  11. Stiffness and damping characteristics of aluminum in creep

    Microsoft Academic Search

    A. Berkovits

    1977-01-01

    Tensile creep tests conducted at 200 C were performed on annealed commercially pure aluminum specimens in order to measure the dominant elevated temperature dislocation processes. Testing consisted of applying small lateral loads to measure flexural stiffness, and vibrating the specimens laterally in order to measure dynamic modulus and internal damping. It was concluded that (1) the strain hardening increased static

  12. 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.

  13. 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

  14. 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

  15. 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

  16. 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.

  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. 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.

  19. Creep and drying shrinkage characteristics of concrete produced with coarse recycled concrete aggregate

    Microsoft Academic Search

    Gholamreza Fathifazl; A. Ghani Razaqpur; O. Burkan Isgor; Abdelgadir Abbas; Benoit Fournier; Simon Foo

    2011-01-01

    Laboratory tests are performed to investigate the effects of a new method of mixture proportioning on the creep and shrinkage characteristics of concrete made with recycled concrete aggregate (RCA). In this method, RCA is treated as a two component composite material consisting of residual mortar and natural aggregate; accordingly, when proportioning the concrete mixture, the relative amount and properties of

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. 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

  5. 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

  6. 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

  7. 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.

  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. 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

  10. 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

  11. 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.

  12. Characteristics of Creep Damage for 60Sn-40Pb Solder Material

    SciTech Connect

    Wei, Y.; Chow, C.L.; Fang, H.E.; Neilsen, M.K.

    1999-08-26

    This paper presents a viscoplasticity model taking into account the effects of change in grain or phase size and damage on the characterization of creep damage in 60Sn-40Pb solder. Based on the theory of damage mechanics, a two-scalar damage model is developed for isotropic materials by introducing the free energy equivalence principle. The damage evolution equations are derived in terms of the damage energy release rates. In addition, a failure criterion is developed based on the postulation that a material element is said to have ruptured when the total damage accumulated in the element reaches a critical value. The damage coupled viscoplasticity model is discretized and coded in a general-purpose finite element program known as ABAQUS through its user-defined material subroutine UMAT. To illustrate the application of the model, several example cases are introduced to analyze, both numerically and experimentally, the tensile creep behaviors of the material at three stress levels. The model is then applied to predict the deformation of a notched specimen under monotonic tension at room temperature (22 C). The results demonstrate that the proposed model can successfully predict the viscoplastic behavior of the solder material.

  13. 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.

  14. 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

  15. 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

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

    PubMed

    Mashaan, Nuha Salim; Karim, Mohamed Rehan

    2013-01-01

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

  17. 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.

  18. 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

  19. 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).

  20. Parametrization of barrier characteristics for deformed oriented nuclei

    NASA Astrophysics Data System (ADS)

    Ghodsi, O. N.; Lari, F.

    2014-05-01

    Barrier characteristics, barrier height and position, were studied on spherical-deformed fusion reactions using the proximity potential. Spherical-prolate (?21=0.0, ?22=0.340) and spherical-oblate (?21=0.0, ?22=-0.330) systems were tested in two different configurations and a pocket formula was presented that reproduced the theoretical values of barrier height and its position, with an accuracy of ±0.4% for both types of configuration. The results obtained from this work reveal the possibility of determining parametrization for barrier characteristics in deformed systems.

  1. 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 ...

  2. 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

  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. 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.

  6. 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.

  7. 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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  9. 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

  10. 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.

  11. Investigation of creep mechanical characteristics of femoral prostheses by simulated hip replacement

    PubMed Central

    LIU, GUANG-YAO; JIN, YAN; LI, PENG

    2013-01-01

    In order to provide creep mechanical parameters for the clinical application of both traditional and reserved anatomy femoral artificial joint replacements, simulated hip replacement femoral stress relaxation and creep experiments were performed. Twenty-four corpse femoral specimens were obtained, with 8 specimens being randomly assigned to the control group and 8 specimens being randomly assigned to the traditional prosthesis group. Our results showed that the retaining femoral neck prosthesis and traditional prosthesis groups have different stress relaxation and creep mechanical properties. PMID:23596489

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. Brittle and compaction creep in porous sandstone

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

  17. 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.

  18. 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.

  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. 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.

  1. 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.

  2. 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

  3. Intrinsic excitations in deformed nuclei: characteristic predictions of the IBA

    SciTech Connect

    Casten, R.F.

    1982-01-01

    Deformed nuclei represent perhaps the largest and best studied class of nuclear level schemes. The Interacting Boson Approximation (IBA) model is devised so as to provide a general framework for the description of low lying collective states in nuclei spanning vibrational, rotational (i.e., deformed) and axially asymmetric types as well as the transitional species intermediate between these limiting cases. The juxtaposition of these two statements makes it all the more surprising that until recently there had been no thorough test of the model in such nuclei. Partly, the explanation for this lies in the type of data required for an adequate test. Since the IBA predicts a broad range of collective states it requires a correspondingly thorough empirical test. Moreover, in deformed nuclei, though the characteristic predictions that distinguish the IBA from the traditional, familiar collective model of harmonic ..beta.. and ..gamma.. vibrations are important, their clearest manifestation occurs in very weak, hard-to-detect low energy transitions between excited vibrational bands (in particular between ..beta.. and ..gamma.. bands), that had not heretofore been systematically observed. The present brief summary will begin with a review of the properties of the (n,..gamma..) reaction that render it a useful empirical tool for such studies, and follow this with a description of the results of the /sup 168/Er study and the application of the IBA model to the resultant level scheme. The discussion will then be generalized to other deformed nuclei and to the inherent systematic predictions that must characterize the IBA for such nuclei. Many of these ideas will be related to the role of finite boson number in the IBA.

  4. Deformation and fracture characteristics of spent Zircaloy fuel cladding

    SciTech Connect

    Chung, H.M.; Yaggee, F.L.

    1982-09-01

    For a better understanding of Zircaloy fuel-rod failure by the pellet-cladding interaction (PCI) phenomenon, a mechanistic study of deformation and fracture behavior of spent power reactor fuel cladding under simulated PCI conditions was conducted. Zircaloy-2 cladding specimens, obtained from fuel assemblies of operating power reactors, were deformed to fracture at 325/sup 0/C by internal gas pressurization in the absence of fission product simulants. Fracture characteristics and microstructures were examined via SEM, TEM, and HVEM. Numerous dislocation tangles and cell structures, observed in TEM specimens of cladding tubes that failed in a ductile manner, were consistent with SEM observations of a limited number of dimples characteristic of microvoid coalescence. A number of brittle-type failures were produced without the influence of fission product simulants. The brittle cracks occurred near the areas compressed by the Swagelok fittings of the internally pressurized tube and propagated from the outer to the inner surface. Since the outer surface was isolated and maintained under a flowing stream of pure helium, it is unlikely that the brittle-type failure was influenced by any fission product traces. SEM fractography of the brittle-type failure revealed a large area of transgranular pseudocleavage with limited areas of ductile fluting, which were similar in appearance to the surfaces produced by in-reactor PCI-type failures. A TEM evaluation of the cladding in the vicinity of the through-wall crack revealed numerous locations that contained an extensive amount of second-phase precipitate (Zr/sub 3/O). We believe that the brittle-type failures of the irradiated spent fuel cladding in the stress rupture experiments are associated with segregation of oxygen, which leads to the formation of the order structure, an immobilization of dislocations, and minimal plastic deformation in the material.

  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. 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.

  7. 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%.

  8. Postseismic relaxation and transient creep

    USGS Publications Warehouse

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

    2005-01-01

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

  9. 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.

  10. Deformation Characteristics of Geosynthetics Retaining Wall Loaded on the Crest

    Microsoft Academic Search

    D. Hirakawa; H. Takaoka; F. Tatsuoka; T. Uchimura

    Laboratory model tests of reinforced soil retaining wall were performed to evaluate instantane- ous and residual wall deformation by monotonic, sustained and cyclic vertical loading on the wall crest. The wall deformation during primary loading was noticeably larger when reinforced with a less stiff and more ine- lastic grid of polyester. The residual wall deformation by sustained and cyclic loading

  11. 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,

  12. Magnetic and Physical Characteristics of Magnetite Associated with Deformation and Exsolution

    NASA Astrophysics Data System (ADS)

    Till, Jessica Lynn

    This thesis contains a collection of laboratory-based studies designed to characterize the magnetic properties and physical aspects of magnetite that result from deformation or high temperature growth. In Chapter 2, a detailed rock magnetic characterization of rocks containing nanoscale magnetite exsolved from volcanic glass identifies the location of domain-state thresholds through distinct transitions in remanence and susceptibility properties. This unique material is an excellent candidate for standard material to be used in studies of magnetite granulometry. In Chapter 3, theoretical timescales for the growth of sub-microscopic magnetite needles during exsolution from plagioclase are calculated using results of diffusion experiments. Measured diffusivities are modeled to calculate the amount of diffusion-limited growth possible under different conditions of nucleation temperature and cooling rate. In Chapters 4 and 5, the development and evolution of magnetic fabrics are investigated through deformation experiments on synthetic rock-analogues at high temperatures and ductile conditions. Stress-induced changes in rock magnetic properties after deformation are significant. Examination of deformation-induced remagnetization demonstrates that a primary remanence can survive conditions equivalent to moderate metamorphism in certain cases and that petrofabric can play an important role in determining the remanence stability. High-temperature deformation experiments result in a pattern of anisotropy development that indicates plastic deformation of magnetic grains, which is distinct from anisotropy development resulting from different magnetite strain responses. Experimental data are combined with theoretical magnetic anisotropy models and used to estimate effective magnetite strains and strain partitioning from magnetic fabric data in deformed samples. Finally, observations of strong shape-preferred orientation and deformation-induced microstructures in magnetite grains from high-temperature shear experiments indicate plastic deformation of magnetite. Microstructural observations place constraints on the rheological behavior of magnetite and the conditions in which dislocation creep is dominant. These observations prompt a re-examination of the previously established magnetite flow laws which are modified and used to construct new deformation mechanism maps.

  13. 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.

  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. Probing the coupled adhesion and deformation characteristics of suspension cells

    NASA Astrophysics Data System (ADS)

    Hui, T. H.; Zhu, Q.; Zhou, Z. L.; Qian, J.; Lin, Y.

    2014-08-01

    By combining optical trapping with fluorescence imaging, the adhesion and deformation characteristics of suspension cells were probed on single cell level. We found that, after 24 h of co-culturing, stable attachment between non-adherent K562 cells and polystyrene beads coated with fibronectin, collagen I, or G-actin can all be formed with an adhesion energy density in the range of 1 - 3 × 10 - 2 mJ/m2, which is about one order of magnitude lower than the reported values for several adherent cells. In addition, it was observed that the formation of a stronger adhesion is accompanied with the appearance of a denser actin cell cortex, especially in the region close to the cell-bead interface, resulting in a significant increase in the apparent modulus of the cell. Findings here could be important for our understanding of why the aggregation of circulating cells, like that in leukostasis, takes place in vivo as well as how such clusters of non-adherent cells behave. The method proposed can also be useful in investigating adhesion and related phenomena for other cell types in the future.

  16. 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

  17. 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.

  18. Deformation and fracture characteristics of spent Zircaloy fuel cladding

    Microsoft Academic Search

    H. M. Chung; F. L. Yaggee

    1982-01-01

    For a better understanding of Zircaloy fuel-rod failure by the pellet-cladding interaction (PCI) phenomenon, a mechanistic study of deformation and fracture behavior of spent power reactor fuel cladding under simulated PCI conditions was conducted. Zircaloy-2 cladding specimens, obtained from fuel assemblies of operating power reactors, were deformed to fracture at 325°C by internal gas pressurization in the absence of fission

  19. Elastic deformation effects on aerodynamic characteristics for a high-aspect-ratio supercritical-wing model

    NASA Technical Reports Server (NTRS)

    Watson, J. J.

    1982-01-01

    The results of an investigation of the deformations of a high-aspect-ratio, force/pressure, supercritical-wing model during wind tunnel tests and the effects these deformations have on the wing aerodynamics are presented. A finite element model of the wing was developed, and then, for conditions corresponding to wind tunnel test points, experimental aerodynamic loads and theoretical aerodynamic loads were applied to the finite element model. Comparisons were made between the results of these load conditions for changes in structural deflections and for changes in aerodynamic characteristics. The results show that the deformations are quite small and that the pressure data are not significantly affected by model deformation.

  20. 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.

  1. 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.

  2. Microstructural degradation mechanisms during creep in strength enhanced high Cr ferritic steels and their evaluation by hardness measurement

    NASA Astrophysics Data System (ADS)

    Ghassemi Armaki, Hassan; Chen, Ruiping; Kano, Satoshi; Maruyama, Kouichi; Hasegawa, Yasushi; Igarashi, Masaaki

    2011-09-01

    There are two creep regions with different creep characteristics: short-term creep region "H", where precipitates and subgrains are thermally stable, and long-term creep region "L", where thermal coarsening of precipitates and subgrains appear. In region "H", the normalized subgrain size (?-?0)/(??-?0) has a linear relation with creep strain and its slope is 10 ?-1. But, region L is the time range in which the static recovery and the strain-induced recovery progress simultaneously. In this region, the static recovery accelerates the strain-induced recovery, and subgrain size is larger than that line which neglects the contribution of the static recovery. In region "L", the ??/???-strain present a linear relation with a slope 35 ?-1. There is a linear relation between hardness and subgrain size. Hardness drop, H0 - H, as a function of Larson-Miller parameter can be a good measure method for assessment of hardness drop and consequently degradation of microstructure. Hardness drop shows an identical slope in creep region "H", whereas hardness drop due to thermal aging and creep in region "L" show together a similar slope. In region "H", degradation of microstructure is mainly due to recovery of subgrains controlled by creep plastic deformation, and precipitates do not have a major role. However, in creep region "L", there are three degradation mechanisms that accelerate creep failure; (1) strain-induced recovery of subgrains due to creep plastic deformation, (2) static-recovery of subgrains and precipitates and (3) strain-induced coarsening of precipitates due to the appearance of static-recovery.

  3. 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.

  4. 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.

  5. 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

  6. Deformation characteristics of corrugated composites for morphing wings

    Microsoft Academic Search

    Ruijun Ge; Bangfeng Wang; Changwei Mou; Yong Zhou

    2010-01-01

    To meet the needs of morphing and withstand aerodynamic loads of a morphing wing skin, a corrugated glass fabric-epoxy laminated\\u000a composite is prepared and investigated in this paper. This composite is flexible in the corrugated direction and stiff in\\u000a the transverse direction to the corrugation. FEM models are established and solved to predict the characteristics of the composites\\u000a by the

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-05-01

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

  9. Strength and deformation characteristics of Alaskan offshore silts

    SciTech Connect

    Fleming, L.N.

    1985-01-01

    A comprehensive series of undrained shear tests were performed on representative samples of Alaskan silts in both the normally consolidated and overconsolidated state. The type of tests performed were triaxial compression and extension, torvane and miniature laboratory vane tests. It was found that the Alaskan silt exhibited dilative behavior during undrained shear. Also, the silt is highly anisotropic with respect to the stress-strain characteristics and the undrained shear strength. Sample disturbance reduced the measured strength in the unconsolidated undrained tests. The normalized strength parameter was shown to vary from one silt to another. The importance of evaluating the properties of each new silt deposit are described.

  10. 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

  11. 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

  12. 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.

  13. Utilizing microstructural characteristics to derive insights into deformation and annealing behaviour: Numerical simulations, experiments and nature

    NASA Astrophysics Data System (ADS)

    Piazolo, Sandra; Montagnat, Maurine; Prakash, Abhishek; Borthwick, Verity; Evans, Lynn; Griera, Albert; Bons, Paul D.; Svahnberg, Henrik; Prior, David J.

    2015-04-01

    Understanding the influence of the pre-existing microstructure on subsequent microstructural development is pivotal for the correct interpretation of rocks and ice that stayed at high homologous temperatures over a significant period of time. The microstructural behaviour of these materials through time has an important bearing on the interpretation of characteristics such as grain size, for example, using grain size statistics to detect former high strain zones that remain at high temperatures but low stress. We present a coupled experimental and modelling approach to better understand the evolution of recrystallization characteristics as a function of deformation-annealing time paths in a material with a high viscoplastic anisotropy e.g. polycrystalline ice and magnesium alloys. Deformation microstructures such as crystal bending, subgrain boundaries, grain size variation significantly influence the deformation and annealing behaviour of crystalline material. For numerical simulations we utilize the microdynamic modelling platform, Elle (www.elle.ws), taking local microstructural evolution into account to simulate the following processes: recovery within grains, rotational recrystallization, grain boundary migration and nucleation. We first test the validity of the numerical simulations against experiments, and then use the model to interpret microstructural features in natural examples. In-situ experiments are performed on laboratory grown and deformed ice and magnesium alloy. Our natural example is a deformed then recrystallized anorthosite from SW Greenland. The presented approach can be applied to many other minerals and crystalline materials.

  14. Microstructural characteristics of the directionally-solidified Al-Al 3 Ni eutectic and their influence on creep fracture

    Microsoft Academic Search

    E. M. Breinan; E. R. Thompson; G. P. Mccarthy; W. J. Herman

    1972-01-01

    The microstructure and fracture mechanisms of the directionally solidified Al-Al3Ni eutectic were studied in depth in this investigation. Solidification experiments conducted at 3.5 cm per hr resulted in\\u000a the formation of a dual-orientation microstructure in which portions of the whiskers were misaligned from the normal growth\\u000a direction. This structure was found to be extremely detrimental to creep behavior. The modes

  15. 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...

  16. EBSD investigation of the microstructure and texture characteristics of hot deformed duplex stainless steel.

    PubMed

    Cizek, P; Wynne, B P; Rainforth, W M

    2006-05-01

    The microstructure and crystallographic texture characteristics were studied in a 22Cr-6Ni-3Mo duplex stainless steel subjected to plastic deformation in torsion at a temperature of 1000 degrees C using a strain rate of 1 s(-1). High-resolution EBSD was successfully used for precise phase and substructural characterization of this steel. The austenite/ferrite ratio and phase morphology as well as the crystallographic texture, subgrain size, misorientation angles and misorientation gradients corresponding to each phase were determined over large sample areas. The deformation mechanisms in each phase and the interrelationship between the two are discussed. PMID:16774517

  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. 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

  19. 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.

  20. Deformation characteristics of {delta} phase in the delta-processed Inconel 718 alloy

    SciTech Connect

    Zhang, H.Y., E-mail: haiyanzhang@imr.ac.cn [Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Zhang, S.H., E-mail: shzhang@imr.ac.cn [Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Cheng, M. [Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China); Li, Z.X. [Beijing Institute of Aeronautica1 Materials, Beijing 100095 (China)

    2010-01-15

    The hot working characteristics of {delta} phase in the delta-processed Inconel 718 alloy during isothermal compression deformation at temperature of 950 deg. C and strain rate of 0.005 s{sup -1}, were studied by using optical microscope, scanning electron microscope and quantitative X-ray diffraction technique. The results showed that the dissolution of plate-like {delta} phase and the precipitation of spherical {delta} phase particles coexisted during the deformation, and the content of {delta} phase decreased from 7.05 wt.% to 5.14 wt.%. As a result of deformation breakage and dissolution breakage, the plate-like {delta} phase was spheroidized and transferred to spherical {delta} phase particles. In the center with largest strain, the plate-like {delta} phase disappeared and spherical {delta} phase appeared in the interior of grains and grain boundaries.

  1. 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

  2. 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.

  3. 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.

  4. Creep analysis of PLLA: PGA copolymer craniofacial plates.

    PubMed

    Pietrzak, William S

    2012-09-01

    Bioabsorbable fixation device failures occur clinically on occasion, with failures often brittle in nature. However, creep failure may also occur for implants that are subjected to sustained loads whereby the device may slowly deform over time, perhaps leading to fracture. Even without fracture occurring, the device may become too distorted to function. There is little in the literature regarding creep performance of bioabsorbable devices such as plates and screws. This study investigated the creep characteristics of craniofacial plates and screws made of a copolymer of 82% poly-L-lactic acid and 18% polyglycolic acid. Four-hole straight plates were attached to 2 rectangular portions of synthetic bone substrate using 2.0-mm-diameter bioabsorbable screws (2 screws used to attach the plate to each substrate portion). The constructs were submersed in phosphate-buffered saline (pH 7.4, 37°C) and placed in tension with 3 load configurations, that is, 230, 460, and 1140 g, for at least 6 days. Creep rate was constant at a given load and was directly proportional to load (4.7, 14.3, and 33.3 ?m/h for 230-, 460-, and 1140-g loads, respectively). The data conformed well to basic creep theory analysis and provided an estimate of the absolute viscosity of the polymer of 8.7 × 10(12) ± 0.81 × 10(12) P (average ± SEM), which is intermediate between that of soft and hard tissue, although closer to the latter. Surgeons and engineers should be aware of the potential for creep to occur when designing bioabsorbable implants and investigating new clinical applications. PMID:22976647

  5. Comparison of the deformation and failure characteristics of morphologically distinct metal-glass interpenetrating phase composites

    Microsoft Academic Search

    J. J. Harris; P. M. Marquis

    2002-01-01

    Deformation and failure characteristics of two metal-glass interpenetrating phase composite (IPC) systems were compared against a single-phase glass control. The first system (Captek-P) comprised an interleaved arrangement of flake-shaped Au\\/Pt\\/Pd particles, the second (Captek-G) comprised loosely packed spherical Au particles. Both materials contained a fully interconnected network of porosity, formed by thermal fusion of particles at contact points. Glass was

  6. Effect of pre-deformation on aging characteristics and mechanical properties of Mg-Gd-Nd-Zr alloy

    Microsoft Academic Search

    Kai-yun ZHENG; Jie DONG; Xiao-qin ZENG; Wen-jiang DING

    2007-01-01

    The effect of plastic deformation prior to artificial aging on the aging characteristics and properties of a Mg-11Gd-2Nd-0.5Zr (mass fraction, %) alloy was investigated. After solution treatment at 525 °C for 4 h, the alloy was subjected to cold stretching deformation of 0%, 5% and 10%, respectively. The as-deformed specimens possess high density of dislocations and mechanical twins, which increase

  7. 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

  8. Load bearing and deformation characteristics of monofilament nylon 66 and their implications for ophthalmic surgery.

    PubMed

    Clark, D; Fleming, W; Bosanquet, R; Down, E

    1996-07-01

    The load bearing and deformation characteristics of monofilament nylon 66 have been examined. This material has been shown to have increased strength and altered deformation properties compared to bulk nylon. These features are beneficial in its role as a corneal suture. However, the load bearing performance of monofilament nylon 66 has been shown to be influenced by the manner in which it is stressed, making the task of producing identical stitches difficult. Moreover, a period of rapid relaxation has been shown to occur immediately after installation which makes the time taken to install the suture a critical factor in its subsequent performance. These factors, which are essentially beyond the control of the ophthalmic surgeon, must surely play a significant role in the inconsistent post operative results seen. PMID:8822788

  9. 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

  10. 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...

  11. 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.

  12. Combination of metamorphism and deformation affect the nano-scale pore structures and macromolecule characteristics of high-rank deformed coals

    NASA Astrophysics Data System (ADS)

    Zhang, W.; Li, H.; Ju, Y.

    2013-12-01

    Coal constitutes a large proportion of total energy supply in the world. Coalbed Methane (CBM) composes the greenhouse gases, which has attracted more and more scientists' concern and attention. The adsorption/desorption characteristics and mechanism of CBM on high-rank deformed coals are in favor of enhancing gas recovery, reducing coal mining accidents and carbon emission. Although the influence factors of CBM adsorption/desorption on different coals have been intensively studied, the combined action of metamorphism and deformation on high-rank coals have been rarely researched. Nevertheless. Metamorphism and deformation are the most fundamental driving forces that cause the changes of inner structures and compositions in coal strata, and then alter the adsorption/desorption capacities of CBM on different coalbeds. South of Qinshui Basin in Shanxi province developed with abundant high-rank coals is the first demonstrate area of CBM development in China. Meanwhile Southwest of Fujian province represents high metamorphic-deformed coals region due to the intense volcanic activities. Therefore samples were taken in both areas to elaborate the adsorption/desorption characteristics and mechanism of CBM. Based on hand specimens description, coal macerals testing, proximate analysis, ultimate analysis and vitrinite reflectance testing, the physical properties and composition characteristics of high-rank deformed coals have been studied. Combined with liquid nitrogen adsorption experiments, Transmission Electron Microscopy (TEM) observation, Fourier Transform Infrared Spectrometry (FTIR) and Nuclear Magnetic Resonance (NMR) experiments, the results show that nano-pores increase and become homogenization with metamorphic-deformation enhancement, stacking of the macromolecular basic structural units (BSU) enhances, aromatic compound increases while aliphatic chain compound and oxygen-containing function groups decrease. Comparing to coal adsorption/desorption isotherm experiments indicates that adsorption/desorption capacity shows a 'U' type with nano-pores volume and specific surface area, coals with best adsorption capacity contained both vitrinite and inertinite with an approximate ratio of 4:1 or 1:4, the increase of aromatic and aliphatic content individually facilitated the adsorption of CBM. Generally speaking, the adsorption/desorption capacity of ductile deformed coals is higher than that of brittle ones, but metamorphism could dramatically affects the final results. To enhance CBM production and reduce carbon emission, the appropriate coal-bearing strata need to be chosen. Our research shows that metamorphism and deformation affect the nano-scale pore structures and macromolecule characteristics of different coals. Therefore brittle-ductile superposed zone with medium-high rank coals has high gas content and permeability which is promising to exploit and helpful to environmental protection.

  13. 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

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

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

  15. Coupled heat conduction and deformation in a viscoelastic composite cylinder

    E-print Network

    Shah, Sneha

    2010-01-16

    the Prony coefficients in the transient creep compliance, characteristic of creep time in transient creep compliance and the instantaneous elastic compliance, on the overall response of the composite cylinder. The effect of different temperature dependent...

  16. 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

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

    E-print Network

    Sills, David Wayne

    2012-02-14

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

  18. 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.

  19. 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

  20. 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

  1. 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

  2. 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.

  3. Multiaxial creep and cyclic plasticity in nickel-base superalloy C263

    Microsoft Academic Search

    A. Manonukul; F. P. E. Dunne; D. Knowles; S. Williams

    2005-01-01

    Physically-based constitutive equations for uniaxial creep deformation in nickel alloy C263 [Acta Mater. 50 (2002) 2917] have been generalised for multiaxial stress states using conventional von Mises type assumptions. A range of biaxial creep tests have been carried out on nickel alloy C263 in order to investigate the stress state sensitivity of creep damage evolution. The sensitivity has been quantified

  4. 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.

  5. 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.

  6. Modeling of high homologous temperature deformation behavior using the viscoplasticity theory based on overstress (VBO). Part 2: Characteristics of the VBO model

    Microsoft Academic Search

    Yukio Tachibana; Erhard Krempl

    1997-01-01

    Characteristics of the high homologous temperature VBO model under extreme conditions such as very fast and very slow tensile tests, long-term-creep and relaxation tests are investigated via numerical experiments and analysis. To this end, material constants of Alloy 800H determined from other tests in Part 1 were utilized for the prediction. Although no experiments are available for the extreme conditions,

  7. 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,

  8. Overprinting Deformations in Mantle Rocks, Dun Mountain, New Zealand

    E-print Network

    Donnelly, Sara

    2014-04-25

    boundaries occur between olivine and orthopyroxene grains and microscale olivine and orthopyroxene compositional bands. Olivine microstructures suggest deformation was accommodated by dislocation creep and, in harzburgite, by dislocation creep and phase...

  9. 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.

  10. Quantitative investigation of the tensile plastic deformation characteristic and microstructure for friction stir welded 2024 aluminum alloy

    SciTech Connect

    Hu, Z.L., E-mail: zhilihuhit@163.com [National Key Laboratory of Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin 150001 (China); State Key Laboratory of Advanced Welding and Joining, Harbin Institute of Technology, Harbin 150001 (China); Wang, X.S. [National Key Laboratory of Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin 150001 (China)] [National Key Laboratory of Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin 150001 (China); Yuan, S.J., E-mail: syuan@hit.edu.cn [National Key Laboratory of Precision Hot Processing of Metals, Harbin Institute of Technology, Harbin 150001 (China)

    2012-11-15

    The effect of the microstructure heterogeneity on the tensile plastic deformation characteristic of friction stir welded (FSW) 2024 aluminum alloy was investigated for the potential applications on light weight design of vehicles. The microstructure characteristics of the FSW joints, such as the grain structure, dislocation density and the distribution of precipitation, were studied by electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The tensile deformation characteristic of the FSW joints was examined using the automatic strain measuring system (ASAME) by mapping the global and local strain distribution, and then was analyzed by mechanics calculation. It is found that the tensile deformation of the FSW joints is highly heterogeneous leading to a significant decrease in global ductility. The FSW joints mainly contain two typical deformation zones, which show great effect on the regional inhomogeneous deformation. One is the nugget zone (NZ) with a region of 8 mm in width, and the other is part of the BM with a region of 10 mm in width. The BM of the joints is the weakest region where the strain localizes early and this localization extends until fracture with a strain over 30%, while the strain in the NZ is only 4%. Differences in regional strain of FSW joints, which are essentially controlled by grain structure, the distribution of precipitation and dislocation density, result in decrease on the overall mechanical properties. - Highlights: Black-Right-Pointing-Pointer Microstructure heterogeneity of welds on tensile deformation behavior is studied. Black-Right-Pointing-Pointer The welds contain two typical deformation zones, affecting the global ductility. Black-Right-Pointing-Pointer Regional strain of welds is controlled by grain structure and dislocation density. Black-Right-Pointing-Pointer Theoretical calculation is in good agreement with experimental result.

  11. Renewal creep theory

    SciTech Connect

    Bagley, R.L. [Wright Lab., Wright Patterson AFB, OH (United States); Jones, D.I.G. [Technology/Scientific Services Inc., Dayton, OH (United States); Freed, A.D. [NASA-Lewis Research Center, Cleveland, OH (United States). Materials Division

    1995-04-01

    The mathematics of probability are used to construct a framework that describes some key features of primary and secondary creep. The underlying assumption is that dislocation slip and annihilation are probabilistic events. The resulting mathematical framework takes the form of renewal theory from probability theory. Renewal creep theory provides a mathematical framework for primary creep that accommodates previously developed empirical descriptions. Renewal creep theory also predicts the existence of secondary creep as an asymptotically constant strain-rate phenomenon. Creep modeling techniques are demonstrated for three titanium.

  12. Creep, creep-fatigue, and cavitation damage

    Microsoft Academic Search

    Majumdar

    1986-01-01

    Available creep and creep-fatigue data of type 304 stainless steel are re-examined in the light of some recently generated basic cavitation data on the same material. This basic study has shown creep damage to be a highly inhomogeneous phenomenon, both in space and in time. Thus a small fraction of boundaries are so intensely cavitated by about 10--25% of life

  13. Static characteristic measurement of MEMS deformable mirror with phase-shift interferometer

    NASA Astrophysics Data System (ADS)

    Wu, Kui; Cai, Dongmei; Wang, Dong; Peng, Jia

    2014-09-01

    MEMS deformable mirrors (DM) have many merits of low drive voltage, high response speed, small power consumption, low cost and small size. Its surface shape and displacement versus applied voltage are significant factors of MEMS DM. Phase-shifting interferometer (PSI) has many advantages such as non-contact, quickness and high precision. A phase-only liquid crystal spatial light modulator (LC-SLM), as a linear phase-shifter in PSI, is linear calibrated for its phase-shift characteristics. The PSI is set up to measure the static characteristic of MEMS DM. Five-step phase-shifting method is used to calculate the phase distribution from interference fringes, and Global phase unwrapping algorithm to solve the holes, noise and breakpoint of interfere images. Compared to the measurement results using Zygo instrument, these two experimental results are very close. The experiment results show, this measuring system is very reliable, convenient and cheap. Moreover, this test system need not stitch some fringe images to get the whole surface shape of the mirror like the Zygo instrument.

  14. 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.

  15. Uniaxial creep behavior and prediction of recycled-PET polymer concrete

    Microsoft Academic Search

    Byung-Wan Jo; Ghi-Ho Tae; Chang-Hyun Kim

    2007-01-01

    In this paper, we attempt to predict long-term creep using short-term creep and to define the characteristics of creep behavior of polymer concrete (PC) bound by recycled-polyester resign. Experimental variables are compressive stress\\/strength ratios and filler contents (CaCO3 and fly-ash).The difference between the proposed model and the experimental long-term creep compliance was less than about 4%. The creep strain at

  16. Rolling-deformation characteristics of clad materials determined by model experiment and numerical simulation: experimental rolling tests using plasticine

    Microsoft Academic Search

    Akio Segawa; Takao Kawanami

    1995-01-01

    A clad material is a laminate having combined properties of strength, workability, corrosion resistance, economical efficiency, and so forth. However, a clad material is difficult to form by rolling, due to the different mechanical properties of the materials.The aim of the present research is, with regard to a double-layered clad material, to investigate the characteristics of rolling deformation by means

  17. 35. OPHIOLITIC ROCKS OF THE MIDDLE AMERICA TRENCH LANDWARD SLOPE OFF GUATEMALA: DEFORMATIONAL CHARACTERISTICS AND TECTONIC SIGNIFICANCE1

    Microsoft Academic Search

    Yujiro Ogawa; Kantaro Fujioka; Tadao Nishiyama; Seiichiro Uehara; Masaharu Nakagawa

    Dismembered ophiolitic rocks including abundant sheared, serpentinized peridotite (mostly harzburgite) and minor basalts, dolerites, gabbros, and altered metabasites (mainly altered amphibolite) were drilled at most of the sites on the upper to lower Middle America Trench landward slope off Guatemala during Leg 84 of the Deep Sea Drilling Project. These rocks show characteristic Cataclastic deformation with zeolite facies metamorphism and

  18. Creep of chemically vapor deposited SiC fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1984-01-01

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

  19. Time-aging time-stress superposition in soft glass under tensile deformation field

    E-print Network

    Asima Shaukat; Ashutosh Sharma; Yogesh M. Joshi

    2010-06-10

    We have studied the tensile deformation behaviour of thin films of aging aqueous suspension of Laponite, a model soft glassy material, when subjected to a creep flow field generated by a constant engineering normal stress. Aqueous suspension of Laponite demonstrates aging behaviour wherein it undergoes time dependent enhancement of its elastic modulus as well as its characteristic relaxation time. However, under application of the normal stress, the rate of aging decreases and in the limit of high stress, the aging stops with the suspension now undergoing a plastic deformation. Overall, it is observed that the aging that occurs over short creep times at small normal stresses is same as the aging that occurs over long creep times at large normal stresses. This observation allows us to suggest an aging time - process time - normal stress superposition principle, which can predict rheological behaviour at longer times by carrying out short time tests.

  20. Postseismic relaxation driven by brittle creep: A possible mechanism to reconcile geodetic measurements and the decay

    E-print Network

    Avouac, Jean-Philippe

    by cataclastic (brittle) processes while ductile deformation, dominated by thermally activated dislocation creep, would prevail in the lower crust. The key point for seismogenesis is that brittle deformation mayPostseismic relaxation driven by brittle creep: A possible mechanism to reconcile geodetic

  1. 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

  2. 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

  3. Modeling of creep in rock materials in terms of material degradation

    Microsoft Academic Search

    J. F. Shao; Q. Z. Zhu; K. Su

    2003-01-01

    In this paper, we present a constitutive model for creep deformation in rock materials. Starting from an elastoplastic model for the description of short term behavior, the time-dependent deformation is described in terms of evolution of microstructure, leading to progressive degradation of elastic modulus and failure strength of material. The proposed model is applied to predict material responses in creep

  4. 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.

  5. 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.

  6. Post-irradiation deformation characteristics of heavy-ion irradiated 304L SS

    SciTech Connect

    Cole, J.I. [Washington State Univ., Pullman, WA (United States); Bruemmer, S.M. [Pacific Northwest Lab., Richland, WA (United States)

    1994-06-01

    Post-irradiation deformation behavior in Ni-ion-irradiated 304L stainless steel (SS) is examined as a function of radiation dose and deformation temperature. For similar strain levels, specimens exhibit a transition from dislocation slip to deformation-induced twinning at 25C with increasing radiation dose. At 288C twinning is no longer observed and highly localized slip occurs by the formation of narrow ``channels`` containing a reduced defect density. The observations are discussed in terms of radiation-induced defect character and expected deformation mechanisms.

  7. Deformation characteristics of 2-3 km buried Hota accretionary complex, central Japan

    NASA Astrophysics Data System (ADS)

    Yamamoto, Y.; Yamaguchi, H.; Kameda, J.

    2008-12-01

    The lower to middle Miocene Hota accretionary complex is a unique example of on land accretionary complex, representing deformation and its physical/chemical properties of sediments just prior to entering the seismogenic realm. The maximum paleotemperature was estimated approximately 55-70°C (based on vitrinite reflectance) indicative of a maximum burial depth about 2-3 km assuming a paleo-geothermal gradient as 25-35°C/km. Accretionary complex in this temperature/depth range corresponds with an intermediate range between the core samples collected from the modern accretionary prism (e.g. Nankai, Barbados, and so on) and rocks in the ancient accretionary complexes on land. Deformation and physical/chemical properties of accretionary complex in this range were poorly understood because the appropriate samples have not been collected yet (scientific drilling has never reached there and most of ancient examples experienced the deeper burial depth and suffered thermal and physical overprinting). This presentation will treat the detailed structural and chemical analyses of the Hota accretionary complex to construct deformation properties of accretionary complex in its 2-3 km depth range and to discuss the interrelation between the early diagenesis (hydrocarbon/cations generation and sediment dewatering, etc.) and transition of the deformation properties. The deformation in this accretionary complex is characterized by two deformation styles: one is a few centimeter-scale phacoidal deformation representing clay minerals preferred orientation in the outer rim, whereas random fabric in the core, quite similar texture to the rocks in the present-Nankai décollement zone. The other is S-C style deformation (similar deformation to the mélanges in ancient accretionary complex on land) exhibiting block-in-matrix texture and quite intense clay minerals preferred orientation in the matrix, cutting the phacoidal deformation. Positive anomaly of illite/smectite ratio and vitrinite reflectance data (Ro) inside the latter S-C structure infers frictional heating during the deformation. Carbonate cement and calcite/dolomite-filled breccias above the S- C deformation and sandstone clasts representing hydro-fractured texture in the deformation are indicative that calcareous cement and pore-fluid pressure fluctuations seemed to be an essential control of the transition of the deformation style and position of the S-C style deformation.

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

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

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

  9. Endochronic theory of transient creep and creep recovery

    NASA Technical Reports Server (NTRS)

    Wu, H. C.; Chen, L.

    1979-01-01

    Short time creep and creep recovery were investigated by means of the endochronic theory of viscoplasticity. It is shown that the constitutive equations for constant-strain-rate stress-strain behavior, creep, creep recovery, and stress relaxation can all ber derived from the general constitutive equation by imposing appropriate constraints. In this unified approach, the effect of strain-hardening is naturally accounted for when describing creep and creep recovery. The theory predicts with reasonable accuracy the creep and creep recovery behaviors for Aluminum 1100-0 at 150 C. It was found that the strain-rate history at prestraining stage affects the subsequent creep. A critical stress was also established for creep recovery. The theory predicts a forward creep for creep recovery stress greater than the critical stress. For creep recovery stress less than the critical stress, the theory then predicts a normal strain recovery.

  10. Time-dependent deformation of metals

    NASA Astrophysics Data System (ADS)

    Nix, W. D.; Gibeling, J. C.; Hughes, D. A.

    1985-12-01

    The basic characteristics of timedependent deformation of metals are described in terms of dislocation properties. At high temperatures, diffusion controlled climb of edge dislocations is the rate limiting process, whereas at low temperatures, other forms of recovery involving cross-slip of screw dislocations operate. A composite model of plastic flow is used to describe the coupling between these recovery processes. The model is patterned after the persistent slip band structures observed in cyclically deformed fcc single crystals. Screw dislocations are allowed to move in the cell interiors and to deposit edge dislocations into the adjoining walls. Cross-slip and climb lead to dislocation rearrangement and annihilation in the two regions. These processes are coupled not only through the dislocation microstructure, but also through the mechanics of the composite structure. The model is used to describe various deformation properties of metals, including stage II, stage III, and stage IV strain hardening and saturation of the flow stress. The coupling of cross-slip and climb controlled recovery processes leads to gradual transitions in strain hardening and gives a natural account of the transition from low temperature deformation to high temperature creep. The model also leads to polarized dislocation structures, internal stresses, and anelastic creep properties.

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

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

  13. Transient Analysis for the Multimechanism-Deformation Parameters of Several Domal Salts

    SciTech Connect

    Munson, Darrell E.

    1999-08-16

    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, a nationally important Strategic Petroleum Reserve (SPR) storage occurs in large cavern arrays in some of these domes. Although caverns have been operated economically for these many years, these caverns have a range of relatively poorly understood behaviors, involving creep closure fluid loss and damage from salt falls. It is certainly possible to postulate that many of these behaviors stem from geomechanical or deformational aspects of the salt response. As a result, a method of correlating the cavern response to mechanical creep behavior as determined in the laboratory could be of considerable importance. 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 the limited non-steady state data to give a bound, or an approach to steady state, as an estimate of the steady state behavior of a given domal salt. This permitted the analysis of sparse creep databases for domal salts. It appears that a shortcoming of the steady state analysis was in masking some of the salt material differences. In an attempt to overcome the steady state analysis shortcomings, a method was developed based on the integration of the Multimechanism-Deformation (M-D) creep constitutive model to fit the transient response. This integration process essentially permits definition of the material sensitive parameters of the model, while those parameters that are either 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. Creep characteristics, as defined by the transient analysis of the creep rate, are related quantitatively to the volume loss creep rate of the caverns. This type of understanding of the domal material creep response already has pointed to the possibility of establishing various distinct material spines within a given dome. Furthermore, if the creep databases for domal salts can be expanded, one could expect additional definition of domal geology and structure.

  14. Creep and shrinkage of concrete typical of four geographical areas of Texas

    E-print Network

    Ingram, Leonard Lee

    1973-01-01

    by external loading. The addition or removal of the water content of the gel results in a volume change which contributee to creep deformation of concrete. SHRINKAGE It is well known that concrete shrinks when it dries and swells when it is saturated... information on the sub]ect of shrink- age and creep in concrete. This chapter will review the theories of creep, shrinkage and factors effecting creep and shrinkage of concrete. The four ma]or theories considered to be responsible for creep may...

  15. Effects of Si on deformation behavior and cavitation of coarse-grained Al–4.5Mg alloys exhibiting large elongation

    Microsoft Academic Search

    H. Hosokawa; H. Iwasaki; T. Mori; M. Mabuchi; T. Tagata; K. Higashi

    1999-01-01

    Deformation behavior and cavitation characteristics of Al–4.5Mg–0.09Si and Al–4.5Mg–0.2Si alloys containing Mg2Si particles have been investigated at 613–693K. Tensile elongations above 350% were obtained in both alloys. Determination of the strain rate sensitivity and activation energy showed that in both alloys viscous dislocation glide creep deformation mechanism was operative and was not influenced by Si content. However, the level of

  16. 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

  17. Characteristics of red clay creep in karst caves and loss leakage of soil in the karst rocky desertification area of Puding County, Guizhou, China

    Microsoft Academic Search

    Ping Yang; Yi-Qun Tang; Nian-Qing Zhou; Jian-Xiu Wang; Tian-Yu She; Xiao-Hui Zhang

    2011-01-01

    The loss of surface soil and water in the karst rocky desertification area of carbonate rock in Chenqi village, Puding County,\\u000a Guizhou Province was monitored in this study. The results show that the major form of surface soil loss in the area is the\\u000a loss of soil through underground channels. A creep test of red clay formed by loss through

  18. Irradiation creep induced anisotropy in a/2110 dislocation populations

    NASA Astrophysics Data System (ADS)

    Gelles, D. S.

    1984-05-01

    The contribution of anisotropy in Burgers vector distribution to irradiation creep behavior has been largely ignored in irradiation creep models. However, findings on Frank loops suggest that it may be very important. Procedures are defined to identify the orientations of a 2110 Burgers vectors for dislocations in face-centered cubic crystals. By means of these procedures the anistropy in Burgers vector populations was determined for three Nimonic PE16 pressurized tube specimens irradiated under stress. Considerable anisotropy in Burgers vector population develops during irradiation creep. It is inferred that dislocation motion during irradiaton creep is restricted primarily to a climb of a/2110 dislocations on 100 planes. Effect of these results on irradiation creep modeling and deformation induced irradiation growth is considered.

  19. 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.

  20. 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.

  1. 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

  2. The Assessment of the T* Fracture Parameter During Creep Relaxation

    NASA Astrophysics Data System (ADS)

    Walker, C.; Mc Kenzie, P.

    While most fracture mechanics investigations are concerned with crack growth, there is a class of behaviour that occurs during creep relaxation where the plastic zone develops in a regime of reducing stress and near-zero crack growth. This behaviour has been measured in the aluminium alloy 7075 T6, using moiré interferometry at 190°C, and the experimental data have been used to investigate the T* integral fracture parameter as a function of time and creep deformation.

  3. Creep influence on buckling resistance of reinforced concrete shells

    Microsoft Academic Search

    J. Bockhold; Y. S. Petryna

    2008-01-01

    The influence of concrete creep on the response of shallow reinforced concrete shells is analyzed in this contribution in the context of time-dependent shell buckling. The classical time-invariant stability analysis is extended to account for the long-term creep buckling, which is characterized by a continuous increase of deformation and time-dependent stability failure, if a certain critical load factor is exceeded.

  4. The residual strength of geosynthetic reinforcement subjected to accelerated creep testing and simulated seismic events

    Microsoft Academic Search

    C. J. F. P. Jones; D. Clarke

    2007-01-01

    All geosynthetic materials used as soil reinforcements creep and it is necessary to obtain data on their creep behaviour before they can be used. During an earthquake the structure is subjected to additional loads, as may be the case with mining subsidence, blast loading or the application of abnormal loads, which may influence the creep characteristics of the reinforcement.The stepped

  5. 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

  6. 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

  7. Scaling of the acoustic emission characteristics during plastic deformation and fracture

    NASA Astrophysics Data System (ADS)

    Lependin, A. A.; Polyakov, V. V.

    2014-07-01

    The scaling of the amplitude and time distributions of acoustic emission pulses, which reflects the self-similarity of defect structures, is revealed. The possibility of separation of independent contributions to the flow of acoustic emission events, which have substantially different scaling exponents, is shown for porous materials. The differences in the scaling exponents are related to the development of plastic deformation and fracture of the materials. The developed approach to an analysis of acoustic emission can be used to describe its predominant mechanisms during deformation.

  8. Electromechanical interaction on the deformation behavior of metallic materials

    NASA Astrophysics Data System (ADS)

    Zhao, Guangfeng

    Metallic materials play important roles in providing electrical, thermal, and mechanical functions in electronic devices and systems. The understanding of the electrical-thermal-mechanical interaction caused by the passage of electric current with high density is important to improve the performance and reliability of electronic assembly and packaging. The electromechanical interaction on the deformation behavior of copper and tin is studied in this work. The electromechanical response of Cu strips was studied by passing a DC electric current. The electric resistance linearly increased with time before the occurrence of electric fusing. The electrothermal interaction led to the buckling of the Cu strips with the maximum deflection increasing with the increase of the electric current density. The total strain was found to be proportional to the square of the electric current density. A power law relation was used to describe the dependence of the time-to-fusing on the electric current density. Using the nanoindentation technique, the effect of electric current on the indentation deformation of copper and tin was studied. The reduced contact modulus of copper and tin decreased with increasing the electric current density. With the passage of a DC electric current, the indentation hardness of copper increased slightly with increasing electric current density. With the passage of an AC electric current, the indentation hardness of copper decreased with increasing the indentation deformation. With the passage of a DC electric current, the indentation hardness of tin decreased with increasing the indentation load, showing the normal indentation size effect. Both the limit of infinite depth and the characteristic length were dependent on the electric current density. Using the tensile creep technique, the creep deformation of pure tin was studied with the passage of a DC electric current. The steady state creep rate increased with the increase in temperature, tensile stress and electrical current density. For the same tensile stress and the same chamber temperature, the steady state creep rate increased linearly with the square of the electric current density. The electric current density has no significant effect on the stress exponent and activation energy of the tensile creep of tin for the experimental conditions. KEYWORDS: Metallic Materials, Electromechanical Interaction, Joule Heat, Nanoindentation, Creep Deformation.

  9. Characteristics of plastic deformation and microstructure in copper rods striking a rigid target

    Microsoft Academic Search

    U. Gerlach; G. Paulus

    1982-01-01

    The validity of a deformation model proposed by M. L. Wilkins and M. W. Guinan is tested at a microscopic scale for copper projectiles. In particular metallographic investigations confirm the curved plastic front built up during the first microseconds of impact. At higher velocities the material present in the peripheral region of the impact end is recrystallized by thermal effects

  10. Fragmentation characteristics of a welded spherical titanium pressure vessel: Part II — Plastic deformation and fracture prediction

    Microsoft Academic Search

    G. C. Sih; B. L. Webb; Y. S. Pen; D. Sharp; J. Pfefferle

    1995-01-01

    Based on the elastic-plastic stress and energy density results in Part I for a welded spherical titanium pressure vessel, Part II carries out a details analysis of failure where plastic deformation and fragmentation take place. The volume energy density criterion predicts failure to first initiate in the heat affected zone and bottle-neck section of the vessel at an internal pressure

  11. EBSD and TEM investigation of the hot deformation substructure characteristics of a type 316L austenitic stainless steel.

    PubMed

    Cizek, P; Whiteman, J A; Rainforth, W M; Beynon, J H

    2004-03-01

    The evolution of crystallographic texture and deformation substructure was studied in a type 316L austenitic stainless steel, deformed in rolling at 900 degrees C to true strain levels of about 0.3 and 0.7. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used in the investigation and a comparison of the substructural characteristics obtained by these techniques was made. At the lower strain level, the deformation substructure observed by EBSD appeared to be rather poorly developed. There was considerable evidence of a rotation of the pre-existing twin boundaries from their original orientation relationship, as well as the formation of highly distorted grain boundary regions. In TEM, at this strain level, the substructure was more clearly revealed, although it appeared rather inhomogeneously developed from grain to grain. The subgrains were frequently elongated and their boundaries often approximated to traces of [111] slip planes. The corresponding misorientations were small and largely displayed a non-cumulative character. At the larger strain, the substructure within most grains became well developed and the corresponding misorientations increased. This resulted in better detection of sub-boundaries by EBSD, although the percentage of indexing slightly decreased. TEM revealed splitting of some sub-boundaries to form fine microbands, as well as the localized formation of microshear bands. The substructural characteristics observed by EBSD, in particular at the larger strain, generally appeared to compare well with those obtained using TEM. With increased strain level, the mean subgrain size became finer, the corresponding mean misorientation angle increased and both these characteristics became less dependent on a particular grain orientation. The statistically representative data obtained will assist in the development of physically based models of microstructural evolution during thermomechanical processing of austenitic stainless steels. PMID:15009696

  12. 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)

  13. 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.

  14. Microstructure and creep of eutectic indium\\/tin on copper and nickel substrates

    Microsoft Academic Search

    J. L. Freer; J. W. Jr. Morris

    1992-01-01

    The behavior during creep in shear of eutectic indium-tin joints on copper and nickel substrates was examined in order to\\u000a determine the effect of creep deformation on the microstructure of the alloy. Primary creep was absent in all the samples\\u000a tested. The stress exponent at 20° C was much higher for samples on nickel than for those on copper, indicating

  15. A creep-immune electrostatic actuator for RF-MEMS tunable capacitor

    Microsoft Academic Search

    Etsuji Ogawa; Tamio Ikehashi; Tomohiro Saito; Hiroaki Yamazaki; Kei Masunishi; Yasushi Tomizawa; Tatsuya Ohguro; Yoshiaki Sugizaki; Yoshiaki Toyoshima; Hideki Shibata

    2011-01-01

    A high creep-immunity MEMS actuator is proposed for RF-MEMS tunable capacitor. The creep-immunity is attained using silicon nitride, SiN, for the spring portions, where the stress is concentrated. Compared with an aluminum spring, the creep-induced deformation is reduced by a factor of 23 at 100°C. We also confirmed by a billion cycle test that the SiN spring does not develop

  16. Time–aging time–stress superposition in soft glass under tensile deformation field

    Microsoft Academic Search

    Asima Shaukat; Ashutosh Sharma; Yogesh M. Joshi

    2010-01-01

    We have studied the tensile deformation behaviour of thin films of aging aqueous suspension of Laponite, a model soft glassy\\u000a material, when subjected to a creep flow field generated by a constant engineering normal stress. Aqueous suspension of Laponite\\u000a demonstrates aging behaviour wherein it undergoes time-dependent enhancement of its elastic modulus as well as its characteristic\\u000a relaxation time. However, under

  17. 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.

  18. Time-dependent behaviour of high performance concrete: influence of coarse aggregate characteristics

    NASA Astrophysics Data System (ADS)

    Makani, A.; Vidal, T.; Pons, G.; Escadeillas, G.

    2010-06-01

    This paper examines the influence of coarse aggregate characteristics on the time-dependent deformations of High Performances Concretes (HPC). Four concretes made using the same cement paste but incorporating different types of aggregate (rolled siliceous gravel, crushed granite, crushed limestone and crushed siliceous gravels) were studied in order to investigate the effect of aggregate properties on the compressive strength, modulus of elasticity, shrinkage and creep. The results indicate that the aggregate type has a significant effect on creep and shrinkage deformations of HPC. An influence of the shape of aggregate on time-dependent deformations has also been observed. On the basis of these results, long-term behaviour seems to be correlated to the characteristics of the Interfacial Transition Zone (ITZ) strongly depending on the mineralogical nature and properties of aggregates. The experimental results are compared with the values calculated using the current Eurocode 2 model in order to assess the accuracy of the predictions.

  19. Diffusion creep in the mantle may create and maintain anisotropy

    NASA Astrophysics Data System (ADS)

    Wheeler, John

    2014-05-01

    Diffusion creep is thought to play an important role in lower mantle deformation and hence must be understood in detail if Earth behaviour is to be explained. It is commonly claimed that diffusion creep gives rise to equant grain shapes and destroys any crystallographic preferred orientation (CPO), so all physical properties would be isotropic. Some experiments on olivine support the first assertion but other minerals, and polyphase rocks, commonly show inequant grain shapes in nature and experiment even when diffusion creep is thought to be a major contribution to strain. Numerical models allow rigorous exploration of the effects of deformation under conditions not easily reached in experiments. A numerical model named 'DiffForm' (Wheeler & Ford 2007) gives insight into how grain shapes and microstructures evolve during diffusion creep. Modelling shows that whilst grains may initially rotate in apparently chaotic fashion during diffusion creep, such rotations slow down as grains become inequant. Consequently, an initial CPO (formed, for example, by dislocation creep at higher strain rates) will be decreased in intensity but not destroyed. Seismic anisotropy will decrease but not disappear (Wheeler 2009). Diffusion creep is also predicted to have intense mechanical anisotropy. In simple models diffusion creep is controlled entirely by diffusion and sliding along grain boundaries; there is no crystallographic influence. An aggregate of equant grains must then be mechanically isotropic, but a model microstructure with inequant grains has marked mechanical anisotropy (Wheeler 2010) - an effect related to the fact that grain boundary sliding is an intrinsic part of diffusion creep. That work was based on a very simple microstructure with a single inequant grain shape but I present here new results showing that for more complicated microstructures, mechanical anisotropy is intense even for quite modest grain elongations. There will be feedback between strain and rheology which may control overall mantle strength. This theoretical development and some recent experiments indicate that diffusion creep is quite a different process to what was envisaged 10 years ago. This means that its relationship to seismic and mechanical anisotropy in the Earth requires reappraisal. .Wheeler, J. 2009. The preservation of seismic anisotropy in the Earth's mantle during diffusion creep. Geophysical Journal International 178, 1723-1732. Wheeler, J. 2010. Anisotropic rheology during grain boundary diffusion creep and its relation to grain rotation, grain boundary sliding and superplasticity. Philosophical Magazine 90, 2841-2864. Wheeler, J. & Ford, J. M. 2007. Diffusion Creep. In: Microdynamic simulation - From microprocess to patterns in rocks (edited by Bons, P. D., Jessell, M. & Koehn, D.). Lecture Notes in Earth Science. Springer, Berlin / Heidelberg, 161-169.

  20. Novel characteristics of energy spectrum for 3D Dirac oscillator analyzed via Lorentz covariant deformed algebra

    NASA Astrophysics Data System (ADS)

    Betrouche, Malika; Maamache, Mustapha; Choi, Jeong Ryeol

    2013-11-01

    We investigate the Lorentz-covariant deformed algebra for Dirac oscillator problem, which is a generalization of Kempf deformed algebra in 3 + 1 dimension of space-time, where Lorentz symmetry are preserved. The energy spectrum of the system is analyzed by taking advantage of the corresponding wave functions with explicit spin state. We obtained entirely new results from our development based on Kempf algebra in comparison to the studies carried out with the non-Lorentz-covariant deformed one. A novel result of this research is that the quantized relativistic energy of the system in the presence of minimal length cannot grow indefinitely as quantum number n increases, but converges to a finite value, where c is the speed of light and ? is a parameter that determines the scale of noncommutativity in space. If we consider the fact that the energy levels of ordinary oscillator is equally spaced, which leads to monotonic growth of quantized energy with the increment of n, this result is very interesting. The physical meaning of this consequence is discussed in detail.

  1. Novel characteristics of energy spectrum for 3D Dirac oscillator analyzed via Lorentz covariant deformed algebra

    PubMed Central

    Betrouche, Malika; Maamache, Mustapha; Choi, Jeong Ryeol

    2013-01-01

    We investigate the Lorentz-covariant deformed algebra for Dirac oscillator problem, which is a generalization of Kempf deformed algebra in 3 + 1 dimension of space-time, where Lorentz symmetry are preserved. The energy spectrum of the system is analyzed by taking advantage of the corresponding wave functions with explicit spin state. We obtained entirely new results from our development based on Kempf algebra in comparison to the studies carried out with the non-Lorentz-covariant deformed one. A novel result of this research is that the quantized relativistic energy of the system in the presence of minimal length cannot grow indefinitely as quantum number n increases, but converges to a finite value, where c is the speed of light and ? is a parameter that determines the scale of noncommutativity in space. If we consider the fact that the energy levels of ordinary oscillator is equally spaced, which leads to monotonic growth of quantized energy with the increment of n, this result is very interesting. The physical meaning of this consequence is discussed in detail. PMID:24225900

  2. 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.

  3. 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.

  4. 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

  5. Pressure solution creep as a mechanism of aseismic sliding in active faults: evidence from the San Andreas Fault Observatory at Depth (SAFOD)

    Microsoft Academic Search

    J. Richard; J. L. Gratier; F. Renard; S. Mittempergher; M. Doan; G. di Toro; J. Hadizadeh; A. Boullier

    2010-01-01

    Creep processes in the San Andreas Fault relax part of the tectonic stresses; consequently identifying the creep mechanism and its evolution with time and depth represents a major challenge for prediction of the long-term evolution this active faults. We show from microstructural and mineralogical studies of SAFOD samples that a pervasive and widespread deformation mechanism, pressure solution creep, explains aseismic

  6. Analysis of Multistage and Other Creep Data for Domal Salts

    SciTech Connect

    Munson, D.E.

    1998-10-01

    There have existed for some time relatively sparse creep databases for a number of domal salts. Although all of these data were analyzed at the time they were reported, to date there has not been a comprehensive, overall evaluation within the same analysis framework. Such an evaluation may prove of value. The analysis methodology is based on the Multimechanism Deformation (M-D) description of salt creep and the corresponding model parameters determined from conventional creep tests. The constitutive model of creep wss formulated through application of principles involved in micromechanical modeling. It was possible, at minimum, to obtain the steady state parameters of the creep model from the data on the domal salts. When this was done, the creep of the domal salts, as compared to the well-defined Waste Isolation Pilot Plant (WIPP) bedded clean salt, was either essentially identical to, or significantly harder (more creep resistant) than WIPP salt. Interestingly, the domal salts form two distinct groups, either sofl or hard, where the difference is roughly a factor often in creep rate between the twcl groups. As might be expected, this classification corresponds quite well to the differences in magnitude of effective creep volume losses of the Strategic Petroleum Reserve (SPR) caverns as determined by the CAVEMAN cavern pressure history analysis, depending upon the specific dome or region within the dome. Creep response shoulcl also correlate to interior cavern conditions that produce salt falls. WMle, in general, the caverns in hard sah have a noticeably greater propensity for salt falls, a smaller number of similar events are exhibited even in the caverns in soft salt.

  7. 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.

  8. 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

  9. Plastic Deformation Characteristics Of AZ31 Magnesium Alloy Sheets At Elevated Temperature

    SciTech Connect

    Park, Jingee; Lee, Jongshin [Graduate School, Kyungpook National University, Deagu 702-701 (Korea, Republic of); You, Bongsun [Department of Materials Technology, Korea Institute of Machinery and Materials, Changwon 641-831 (Korea, Republic of); Choi, Seogou [Digital Production Processing and Forming Team, Korea Institute of Industrial Technology, Incheon 406-800 (Korea, Republic of); Kim, Youngsuk [Department of Mechanical Engineering, Kyoungpook National University, Deagu 702-701 (Korea, Republic of)

    2007-05-17

    Using lightweight materials is the emerging need in order to reduce the vehicle's energy consumption and pollutant emissions. Being a lightweight material, magnesium alloys are increasingly employed in the fabrication of automotive and electronic parts. Presently, magnesium alloys used in automotive and electronic parts are mainly processed by die casting. The die casting technology allows the manufacturing of parts with complex geometry. However, the mechanical properties of these parts often do not meet the requirements concerning the mechanical properties (e.g. endurance strength and ductility). A promising alternative can be forming process. The parts manufactured by forming could have fine-grained structure without porosity and improved mechanical properties such as endurance strength and ductility. Because magnesium alloy has low formability resulted form its small slip system at room temperature it is usually formed at elevated temperature. Due to a rapid increase of usage of magnesium sheets in automotive and electronic industry it is necessary to assure database for sheet metal formability and plastic yielding properties in order to optimize its usage. Especially, plastic yielding criterion is a critical property to predict plastic deformation of sheet metal parts in optimizing process using CAE simulation. Von-Mises yield criterion generally well predicts plastic deformation of steel sheets and Hill'1979 yield criterion predicts plastic deformation of aluminum sheets. In this study, using biaxial tensile test machine yield loci of AZ31 magnesium alloy sheet were obtained at elevated temperature. The yield loci ensured experimentally were compared with the theoretical predictions based on the Von-Mises, Hill, Logan-Hosford, and Barlat model.

  10. Plastic deformation characteristics of Cu/X (Xdbnd Cusbnd Zr, Zr) nanolayered materials

    NASA Astrophysics Data System (ADS)

    Zhang, J. Y.; Wang, Y. Q.; Liu, G.; Sun, J.

    2014-12-01

    Nanolayered materials exhibit unique plastic deformation behavior, i.e., a bulk-like to small-scale plasticity transition and a scaling behavior of extremely small activation volume (V* < 10b3) with intrinsic size. This unusual plastic transition phenomenon likely stems from the dislocations respectively emit from interfaces and Frank-Read-type bulk sources below and above a critical intrinsic size ?20 nm. We quantitatively capture the scaling relationship between strain rate sensitivity and intrinsic size by a phenomenological model based on the Orowan-Frank-Read process.

  11. Irradiation Creep in Graphite

    SciTech Connect

    Ubic, Rick; Butt, Darryl; Windes, William

    2014-03-13

    An understanding of the underlying mechanisms of irradiation creep in graphite material is required to correctly interpret experimental data, explain micromechanical modeling results, and predict whole-core behavior. This project will focus on experimental microscopic data to demonstrate the mechanism of irradiation creep. High-resolution transmission electron microscopy should be able to image both the dislocations in graphite and the irradiation-induced interstitial clusters that pin those dislocations. The team will first prepare and characterize nanoscale samples of virgin nuclear graphite in a transmission electron microscope. Additional samples will be irradiated to varying degrees at the Advanced Test Reactor (ATR) facility and similarly characterized. Researchers will record microstructures and crystal defects and suggest a mechanism for irradiation creep based on the results. In addition, the purchase of a tensile holder for a transmission electron microscope will allow, for the first time, in situ observation of creep behavior on the microstructure and crystallographic defects.

  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. 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.

  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. 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. 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...

  17. Physical aging and the creep behavior of acrylic bone cements.

    PubMed

    Kuzmychov, Oleksii; Koplin, Christof; Jaeger, Raimund; Büchner, Hubert; Gopp, Udo

    2009-11-01

    The creep deformation of two acrylic bone cements, Palacos R+G and SmartSet GHV, was investigated for different physical aging times ranging from 45 min to 2 (1/2) years. The experiments were carried out in a three-point-bending set-up in 37 degrees C Ringer's solution applying 10 MPa or 25 MPa creep loads. Both bone cements exhibit a significant decrease of their creep compliance with increasing physical aging time. The experimental data were analyzed with a creep law discussed in the context of physical aging by Struik, and a modified Burgers' model which can be used to separate the strain response of the bone cements into an elastic, a visco-elastic and a creep component. The creep behavior of the bone cements could be described essentially with only one parameter of Struik's creep law. The analysis with the modified Burgers' model showed that physical aging influences all model parameters which are directly related to the mobility of the polymer chains. The effect of physical aging should be taken into account particularly if the mechanical performance of bone cements shortly after curing is investigated. PMID:19630059

  18. Fault Zone Characteristics and Deformation Mechanisms of Porous, Non-welded Bishop Tuff

    NASA Astrophysics Data System (ADS)

    Bradbury, K. K.; Ferrill, D. A.; Dinwiddie, C. L.; Fedors, R. W.

    2002-12-01

    Fault zone deformation features associated with normal faults within non- to poorly welded Bishop Tuff (north of Bishop, CA) were undertaken to provide the structural context for air and water permeability testing. The first site (Chalk Cove fault) has approximately 9 m of offset, a narrow fault core, a broad hanging wall damage zone, and a narrow footwall damage zone in a massive poorly welded ignimbrite sequence. The fault is characterized by a discrete polished surface with a 1-3 mm (0.04-0.11 in) thick fault core that widens upward to 1 m (3 ft), with distributed slip surfaces. The hanging-wall damage zone is approximately 5 m (16 ft) thick and contains abundant, open, iron oxide-stained fractures with fracture intensities of 20-40/m (6-12/ft). These fractures are arranged in an overall fanning pattern. The footwall damage zone is 0.05-1 m (0.2-3 ft) thick with fracture intensities less than or equal to 20/m (6/ft). Microstructural and grain size analyses reveal deformation mechanisms such as extensional fractures, grain comminution, and mineralization within the fault core. The second study area (crucifix/crossing faults site) includes a west dipping normal fault with 7 m displacement exposed within non-welded, finely laminated basal surge deposits. The fault has a narrow and mildly deformed hanging wall damage zone with an intensely deformed footwall damage zone. This fault is characterized by a discrete fracture surface; core thickness is 1.5-30 cm (0.6-12 in) and is composed of fine-grained gouge and zones of distributed faulting represented by numerous cm-scale faults. The immediate hanging wall damage zone extends for about 5.5 m. The footwall damage zone is about 6 m thick and contains numerous small-displacement antithetic, synthetic and en echelon faults which accommodate displacement in the footwall damage zone. Fracture networks are typically open, 1-5 mm [0.04-0.20 in] thick, and vertical to steeply dipping. Average minimum fracture intensities are approximately 36/m (11/ft) within the footwall damage zone and much greater adjacent to the main fault surfaces. Mineralized fracture surfaces up to several mm thick composed of calcite and/or silica are observed along the main fault and smaller faults within the damage zone. X-Ray diffraction analyses of host and fault rock reveal the primary constituents of the volcanic host rock include quartz, feldspar, calcite, and glass. Well-developed gouge may originate through progressive smear and comminution of wall rock. Distributed shear (or smear) forms an apparent drag geometry as some beds are entrained and attenuated for distances up to 1 m (3 ft) into the fault core. Grain comminution within fault cores may contribute to porosity reduction and barrier formation that will disrupt lateral flow within the surrounding host rock. Increased fracture intensity in the fault damage zone may locally increase permeability and enhance vertical flow. This abstract is an independent product of the CNWRA and does not necessarily reflect the views or regulatory position of the NRC.

  19. 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.

  20. 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

  1. 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.

  2. Bond characteristics of steel fiber and deformed reinforcing steel bar embedded in steel fiber reinforced self-compacting concrete (SFRSCC)

    NASA Astrophysics Data System (ADS)

    Aslani, Farhad; Nejadi, Shami

    2012-09-01

    Steel fiber reinforced self-compacting concrete (SFRSCC) is a relatively new composite material which congregates the benefits of the self-compacting concrete (SCC) technology with the profits derived from the fiber addition to a brittle cementitious matrix. Steel fibers improve many of the properties of SCC elements including tensile strength, ductility, toughness, energy absorption capacity, fracture toughness and cracking. Although the available research regarding the influence of steel fibers on the properties of SFRSCC is limited, this paper investigates the bond characteristics between steel fiber and SCC firstly. Based on the available experimental results, the current analytical steel fiber pullout model (Dubey 1999) is modified by considering the different SCC properties and different fiber types (smooth, hooked) and inclination. In order to take into account the effect of fiber inclination in the pullout model, apparent shear strengths ( ? ( app)) and slip coefficient ( ?) are incorporated to express the variation of pullout peak load and the augmentation of peak slip as the inclined angle increases. These variables are expressed as functions of the inclined angle ( ?). Furthurmore, steel-concrete composite floors, reinforced concrete floors supported by columns or walls and floors on an elastic foundations belong to the category of structural elements in which the conventional steel reinforcement can be partially replaced by the use of steel fibers. When discussing deformation capacity of structural elements or civil engineering structures manufactured using SFRSCC, one must be able to describe thoroughly both the behavior of the concrete matrix reinforced with steel fibers and the interaction between this composite matrix and discrete steel reinforcement of the conventional type. However, even though the knowledge on bond behavior is essential for evaluating the overall behavior of structural components containing reinforcement and steel fibers, information is hardly available in this area. In this study, bond characteristics of deformed reinforcing steel bars embedded in SFRSCC is investigated secondly.

  3. Bond characteristics of steel fiber and deformed reinforcing steel bar embedded in steel fiber reinforced self-compacting concrete (SFRSCC)

    NASA Astrophysics Data System (ADS)

    Aslani, Farhad; Nejadi, Shami

    2012-09-01

    Steel fiber reinforced self-compacting concrete (SFRSCC) is a relatively new composite material which congregates the benefits of the self-compacting concrete (SCC) technology with the profits derived from the fiber addition to a brittle cementitious matrix. Steel fibers improve many of the properties of SCC elements including tensile strength, ductility, toughness, energy absorption capacity, fracture toughness and cracking. Although the available research regarding the influence of steel fibers on the properties of SFRSCC is limited, this paper investigates the bond characteristics between steel fiber and SCC firstly. Based on the available experimental results, the current analytical steel fiber pullout model (Dubey 1999) is modified by considering the different SCC properties and different fiber types (smooth, hooked) and inclination. In order to take into account the effect of fiber inclination in the pullout model, apparent shear strengths (? (app)) and slip coefficient (?) are incorporated to express the variation of pullout peak load and the augmentation of peak slip as the inclined angle increases. These variables are expressed as functions of the inclined angle (?). Furthurmore, steel-concrete composite floors, reinforced concrete floors supported by columns or walls and floors on an elastic foundations belong to the category of structural elements in which the conventional steel reinforcement can be partially replaced by the use of steel fibers. When discussing deformation capacity of structural elements or civil engineering structures manufactured using SFRSCC, one must be able to describe thoroughly both the behavior of the concrete matrix reinforced with steel fibers and the interaction between this composite matrix and discrete steel reinforcement of the conventional type. However, even though the knowledge on bond behavior is essential for evaluating the overall behavior of structural components containing reinforcement and steel fibers, information is hardly available in this area. In this study, bond characteristics of deformed reinforcing steel bars embedded in SFRSCC is investigated secondly.

  4. Deformation characteristics of single helical structure with concentrated mass and axial load in hanging status

    Microsoft Academic Search

    Guohua Cao; Zhencai Zhu; Weihong Peng; Xianbiao Mao

    2010-01-01

    In order to master the mechanical characteristics of single helical structure (e.g., rope, cable, spring, etc.) and design helical structure such as the non-rotate rope used in aviation field for rescuing personnel and mine hoisting or exploitation, explicit expressions of axial strain, helix angle and laying radius for helical structure were obtained. According to two operating conditions that the bottom

  5. Analysis of Multistage and Other Creep Data for Domal Salts

    Microsoft Academic Search

    Munson

    1998-01-01

    There have existed for some time relatively sparse creep databases for a number of domal salts. Although all of these data were analyzed at the time they were reported, to date there has not been a comprehensive, overall evaluation within the same analysis framework. Such an evaluation may prove of value. The analysis methodology is based on the Multimechanism Deformation

  6. 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.

  7. Analysis of the Creep Behavior of P92 Steel Welded Joint

    NASA Astrophysics Data System (ADS)

    An, Junchao; Jing, Hongyang; Xiao, Guangchun; Zhao, Lei; Xu, Lianyong

    2011-11-01

    Different regions of heat-affected zone (HAZ) were simulated by heat treatment to investigate the mechanisms of the Type IV fracture of P92 (9Cr-2W) steel weldments. Creep deformation of simulated HAZ specimens with uniform microstructures was investigated and compared with those of the base metal (BM) and the weld metal (WM) specimens. The results show that the creep strain rate of the fine-grained HAZ (FGHAZ) is much higher than that of the BM, WM, the coarse-grained HAZ (CGHAZ), and the inter-critical HAZ (ICHAZ). According to the metallurgical investigation of stress-rupture, the FGHAZ and the ICHAZ have the most severely cavitated zones. During creep process, carbides become coarser, and form on grain boundaries again, leading to the deterioration of creep property and the decline of creep strength. In addition, the crack grows along the FGHAZ adjacent to the BM in the creep crack growth test (CCG) of HAZ.

  8. 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.

  9. Effect of cyclic deformation on the pseudoelasticity characteristics of Ti-Ni alloys

    Microsoft Academic Search

    S. Miyazaki; T. Imai; Y. Igo; K. Otsuka

    1986-01-01

    Change in the pseudoelasticity characteristics of Ti-Ni alloys during tension cycling was investigated. The critical stress\\u000a for inducing martensites and the hysteresis of a stress-strain curve decreased with increasing number of cyclic loading, while\\u000a the permanent elongation increased. The degree of the change in these values showed a strong dependence on the maximum applied\\u000a stress during stress-induced martensitic transformation. However,

  10. Crack growth in creeping solids

    Microsoft Academic Search

    V. M. Radhakrishnan; A. J. McEvily

    1981-01-01

    The creep crack growth behavior in a creep-ductile material, 6061 aluminum, and a creep brittle material, Ti-6242, has been investigated. In the creep ductile material an observed load dependency in the relation between the load-point displacement rate, ..delta.., and the crack growth rate, ..cap alpha.., precluded the straightforward application of the C* approach. For both materials tested the foregoing relationship

  11. COMBINED CREEP AND FATIGUE PROPERTIES

    Microsoft Academic Search

    Meleka

    1962-01-01

    A review is presented on combined creep and fatigue. Some service ; applications in which combined creep and fatigue stresses exist are described. ; Testing techniques and methods of presenting results are discussed. The behavior ; of commercial alloys and basic considerations are discussed. Methods of ; predicting combined creep and fatigue behavior are discussed, and evidence is ; given

  12. 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.

  13. Creep Feeding Beef Calves.

    E-print Network

    Smith, A. L. (Albert Lorenzo)

    1955-01-01

    ON THE COVER The picture on the cover was taken on the E. B. Dickenson Ranch, leased by J. C. Sale, Stanton, Texas. Fig. 1. Inexpensive creep is shown on the Robert Priess Ranch, Mast County. A. L. SMITH and UEL D. THOMPSON Extension Animal... Husbandmen in collaboration with JOHN H. JONES, Professor of Animal Husbandry and JOHN K. RIGGS, A~sociate Professor of Animal Husbandry Texas A. & M. College System "Creep feeding" beef calves may tices during the first 6 to 8 months , increase weight...

  14. Modelling of creep curves of Ni3Ge single crystals

    NASA Astrophysics Data System (ADS)

    Starenchenko, V. A.; Starenchenko, S. V.; Pantyukhova, O. D.; Solov'eva, Yu V.

    2015-01-01

    In this paper the creep model of alloys with L12 superstructure is presented. The creep model is based on the idea of the mechanisms superposition connected with the different elementary deformation processes. Some of them are incident to the ordered structure L12 (anomalous mechanisms), others are typical to pure metals with the fcc structure (normal mechanisms): the accumulation of thermal APBs by means of the intersection of moving dislocations; the formation of APB tubes; the multiplication of superdislocations; the movement of single dislocations; the accumulation of point defects, such as vacancies and interstitial atoms; the accumulation APBs at the climb of edge dislocations. This model takes into account the experimental facts of the wetting antiphase boundaries and emergence of the disordered phase within the ordered phase. The calculations of the creep curves are performed under different conditions. This model describes different kinds of the creep curves and demonstrates the important meaning of the deformation superlocalisation leading to the inverse creep. The experimental and theoretical results coincide rather well.

  15. Localized and distributed creep along the southern San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Lindsey, Eric O.; Fialko, Yuri; Bock, Yehuda; Sandwell, David T.; Bilham, Roger

    2014-10-01

    We investigate the spatial pattern of surface creep and off-fault deformation along the southern segment of the San Andreas Fault using a combination of multiple interferometric synthetic aperture radar viewing geometries and survey-mode GPS occupations of a dense array crossing the fault. Radar observations from Envisat during the period 2003-2010 were used to separate the pattern of horizontal and vertical motion, providing a high-resolution image of uplift and shallow creep along the fault trace. The data reveal pervasive shallow creep along the southernmost 50 km of the fault. Creep is localized on a well-defined fault trace only in the Mecca Hills and Durmid Hill areas, while elsewhere creep appears to be distributed over a 1-2 km wide zone surrounding the fault. The degree of strain localization is correlated with variations in the local fault strike. Using a two-dimensional boundary element model, we show that stresses resulting from slip on a curved fault can promote or inhibit inelastic failure within the fault zone in a pattern matching the observations. The occurrence of shallow, localized interseismic fault creep within mature fault zones may thus be partly controlled by the local fault geometry and normal stress, with implications for models of fault zone evolution, shallow coseismic slip deficit, and geologic estimates of long-term slip rates.

  16. Probing the Characteristic Deformation Behaviors of Transformation-Induced Plasticity Steels

    NASA Astrophysics Data System (ADS)

    Cheng, Sheng; Wang, Xun-Li; Feng, Zhili; Clausen, Bjorn; Choo, Hahn; Liaw, Peter K.

    2008-12-01

    The characteristic micromechanical behaviors of contrasting transformation-induced plasticity (TRIP) steels were investigated under tensile loading by in-situ neutron diffraction and transmission electron microscopy in detail. As demonstrated by the lattice strain development from the neutron diffraction, in the TRIP steel with ˜10 pct RA, microyielding of soft ferrite was responsible for the first stress partition, but a second stress sharing was caused by effective martensitic transformation. In the TRIP steel with less than 5 pct RA, where the contribution from the martensitic transformation was minor, stress partition took place virtually between the ferrite and bainite phase. Probing with systematic transmission electron microscopy (TEM) observations, we pin down the inherent correlation between the microstructural evolutions and the stress partition mechanism. Based on the experimental observations, the factors influencing the work-hardening behavior of TRIP steels are discussed.

  17. On the characteristic length scales associated with plastic deformation in metallic glasses

    SciTech Connect

    Murali, P.; Zhang, Y. W. [Institute of High Performance Computing, Singapore 138632 (Singapore); Gao, H. J. [School of Engineering, Brown University, Rhode Island 02912 (United States)

    2012-05-14

    Atomistic simulations revealed that the spatial correlations of plastic displacements in three metallic glasses, FeP, MgAl, and CuZr, follow an exponential law with a characteristic length scale l{sub c} that governs Poisson's ratio {nu}, shear band thickness t{sub SB}, and fracture mode in these materials. Among the three glasses, FeP exhibits smallest l{sub c}, thinnest t{sub SB}, lowest {nu}, and brittle fracture; CuZr exhibits largest l{sub c}, thickest t{sub SB}, highest {nu}, and ductile fracture, while properties of MgAl lie in between those of FeP and CuZr. These findings corroborate well with existing experimental observations and suggest l{sub c} as a fundamental measure of the shear transformation zone size in metallic glasses.

  18. On the characteristic length scales associated with plastic deformation in metallic glasses

    NASA Astrophysics Data System (ADS)

    Murali, P.; Zhang, Y. W.; Gao, H. J.

    2012-05-01

    Atomistic simulations revealed that the spatial correlations of plastic displacements in three metallic glasses, FeP, MgAl, and CuZr, follow an exponential law with a characteristic length scale ?c that governs Poisson's ratio ?, shear band thickness tSB, and fracture mode in these materials. Among the three glasses, FeP exhibits smallest ?c, thinnest tSB, lowest ?, and brittle fracture; CuZr exhibits largest ?c, thickest tSB, highest ?, and ductile fracture, while properties of MgAl lie in between those of FeP and CuZr. These findings corroborate well with existing experimental observations and suggest ?c as a fundamental measure of the shear transformation zone size in metallic glasses.

  19. Deformation Failure Characteristics of Coal Body and Mining Induced Stress Evolution Law

    PubMed Central

    Wen, Zhijie; Wen, Jinhao; Shi, Yongkui; Jia, Chuanyang

    2014-01-01

    The results of the interaction between coal failure and mining pressure field evolution during mining are presented. Not only the mechanical model of stope and its relative structure division, but also the failure and behavior characteristic of coal body under different mining stages are built and demonstrated. Namely, the breaking arch and stress arch which influence the mining area are quantified calculated. A systematic method of stress field distribution is worked out. All this indicates that the pore distribution of coal body with different compressed volume has fractal character; it appears to be the linear relationship between propagation range of internal stress field and compressed volume of coal body and nonlinear relationship between the range of outburst coal mass and the number of pores which is influenced by mining pressure. The results provide theory reference for the research on the range of mining-induced stress and broken coal wall. PMID:24967438

  20. Deformation failure characteristics of coal body and mining induced stress evolution law.

    PubMed

    Wen, Zhijie; Qu, Guanglong; Wen, Jinhao; Shi, Yongkui; Jia, Chuanyang

    2014-01-01

    The results of the interaction between coal failure and mining pressure field evolution during mining are presented. Not only the mechanical model of stope and its relative structure division, but also the failure and behavior characteristic of coal body under different mining stages are built and demonstrated. Namely, the breaking arch and stress arch which influence the mining area are quantified calculated. A systematic method of stress field distribution is worked out. All this indicates that the pore distribution of coal body with different compressed volume has fractal character; it appears to be the linear relationship between propagation range of internal stress field and compressed volume of coal body and nonlinear relationship between the range of outburst coal mass and the number of pores which is influenced by mining pressure. The results provide theory reference for the research on the range of mining-induced stress and broken coal wall. PMID:24967438

  1. Creep-Feeding Range Calves

    E-print Network

    Jones, J. M. (John McKinley); Jones, John H.

    1932-01-01

    , it has been found profitable to supply rain to calves during their suckling period. This may be done y what is known as creep feeding. Creeps are enclosures in nrhich the calves are fed an3 the entrances, of which are of such size that the calves can... enter but the cows cannot. A test on the Callaghan Ranch in Webb county during 1931-1932 took account of the results of creep-feeding 69 head of spring calves in com- arison with 49 calves on a similar range but not creep-fed. The creep-fed calves...

  2. Creep and low-cycle fatigue behavior of ferritic Fe-24Cr-4Al alloy in the dynamic strain aging regime: Effect of aluminum addition

    SciTech Connect

    Tjong, S.C.; Zhu, S.M. [City Univ. of Hong Kong, Kowloon (Hong Kong). Dept. of Physics and Materials Science

    1997-06-01

    Creep and low-cycle fatigue behavior of ferritic Fe-24Cr-04Al alloy was studied in the temperature range of 673 to 873 K, where dynamic strain aging (DSA) occurrence was found. The DSA of the alloy manifested in the form of serrated flow, negative strain rate sensitivity, and the peak or plateau in the variations of yield strength (YS) and ultimate tensile strength (UTS) with temperature. The characteristic creep behavior of the alloy was experimentally verified as that for a class I solid solution. However, this ferritic alloy showed an anomalous high stress exponent (n = 5.7) and high activation energy (Q{sub c} = 285 kJ/mol) of the secondary creep, which were commonly exhibited by class II solid solutions. During cyclic deformation, the alloy displayed serration in the stress-strain hysteresis loops, increased cyclic hardening, and enhanced planarity of dislocations. On the basis of the observed experimental results and proper analysis, it was proposed that there was strong elastic interaction between solute aluminum atoms and dislocations in the DSA temperature domain. The anomalous creep and fatigue features were interpreted in terms of the interaction of aluminum with the dislocations.

  3. Stress versus temperature dependence of activation energies for creep

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

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

  4. On Creep and Relaxation

    Microsoft Academic Search

    I. L. Hopkins; R. W. Hamming

    1957-01-01

    The creep function for the ``National Bureau of Standards'' polyisobutylene at 25°C is calculated from the relaxation function, using the integral equation connecting them. The calculated function is shown to be correct in its initial slope, to satisfy the inequality ?(t)&psgr;(t)?1 throughout, and to approach satisfactorily the independently determined asymptote.

  5. 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...

  6. Prediction and verification of creep behavior in metallic materials and components, for the space shuttle thermal protection system. Volume 1, phase 1: Cyclic materials creep predictions

    NASA Technical Reports Server (NTRS)

    Davis, J. W.; Cramer, B. A.

    1974-01-01

    Cyclic creep response was investigated and design methods applicable to thermal protection system structures were developed. The steady-state (constant temperature and load) and cyclic creep response characteristics of four alloys were studied. Steady-state creep data were gathered through a literature survey to establish reference data bases. These data bases were used to develop empirical equations describing creep as a function of time, temperature, and stress and as a basis of comparison for test data. Steady-state creep tests and tensile cyclic tests were conducted. The following factors were investigated: material thickness and rolling direction; material cyclic creep response under varying loads and temperatures; constant stress and temperature cycles representing flight conditions; changing stresses present in a creeping beam as a result of stress redistribution; and complex stress and temperature profiles representative of space shuttle orbiter trajectories. A computer program was written, applying creep hardening theories and empirical equations for creep, to aid in analysis of test data. Results are considered applicable to a variety of structures which are cyclicly exposed to creep producing thermal environments.

  7. Creep and fracture of dispersion-strengthened materials

    NASA Technical Reports Server (NTRS)

    Raj, Sai V.

    1991-01-01

    The creep and fracture of dispersion strengthened materials is reviewed. A compilation of creep data on several alloys showed that the reported values of the stress exponent for creep varied between 3.5 and 100. The activation energy for creep exceeded that for lattice self diffusion in the matrix in the case of some materials and a threshold stress behavior was generally reported in these instances. The threshold stress is shown to be dependent on the interparticle spacing and it is significantly affected by the initial microstructure. The effect of particle size and the nature of the dispersoid on the threshold stress is not well understood at the present time. In general, most studies indicate that the microstructure after creep is similar to that before testing and very few dislocations are usually observed. It is shown that the stress acting on a dispersoid due to a rapidly moving dislocation can exceed the particle yield strength of the G sub p/1000, where G sub p is the shear modulus of the dispersoid. The case when the particle deforms is examined and it is suggested that the dislocation creep threshold stress of the alloy is equal to the yield strength of the dispersoid under these conditions. These results indicate that the possibility that the dispersoid creep threshold stress is determined by either the particle yield strength or the stress required to detach a dislocation from the dispersoid matrix interface. The conditions under which the threshold stress is influenced by one or the other mechanism are discussed and it is shown that the particle yield strength is important until the extent of dislocation core relaxation at the dispersoid matrix interface exceeds about 25 pct. depending on the nature of the particle matrix combination. Finally, the effect of grain boundaries and grain morphology on the creep and fracture behavior of dispersoid strengthened alloys is examined.

  8. 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.

  9. A review of water contents and ductile deformation mechanisms of olivine: Implications for the lithosphere-asthenosphere boundary of continents

    NASA Astrophysics Data System (ADS)

    Wang, Qin

    2010-11-01

    Water plays an important role in the ductile deformation and evolution of the upper mantle. Water contents of natural olivine from 240 samples reveal a wide variation of 0-170 ppm H 2O, suggesting heterogeneous water distribution in the continental upper mantle. The average water contents (17 ± 13 ppm H 2O) in kimberlite nodules provide the best estimation of water concentrations in olivine in the lithosphere beneath cratons. The very low water contents (7 ± 9 ppm H 2O) of olivine from basalt xenoliths are caused by significant hydrogen loss during transport, while the high values (44 ± 34 ppm H 2O) in olivine megacrysts from kimberlites reflect restricted fluid-rich conditions in the upper mantle. To compare deformation in different tectonic environments, the western Superior Province (Canada), the Dabie Mountains and the North Jiangsu basin (China) are selected to represent an Archean craton, an orogenic belt and a rift basin, respectively. Using recent flow laws of olivine, deformation maps of dry and wet olivine are constructed under P- T conditions of the three tectonic units and in a continental subduction zone characterized by P = 6.28 GPa and T = 900 °C. For dry olivine, diffusion creep is the dominant mechanism in all the cases, which is contrary to the widely observed crystal preferred orientation of olivine in peridotites and seismic anisotropy observations. For wet olivine, only a small amount of water (50 H/10 6 Si) can remarkably decrease the stress of dislocation creep and increase contribution of dislocation creep to the deformation of olivine. The strain rate profiles of olivine indicate a transition from dislocation creep to diffusion creep at a depth of ˜ 220 km, which can be related with the Lehmann discontinuity characterized by a rapid decrease in seismic anisotropy. However, the pressure-induced fabric transition from [100] slip to [001] slip may be responsible for the Lehmann discontinuity in subduction zones. Therefore rheology of the continental upper mantle is controlled by power-law creep of wet olivine, and diffusion creep is the dominant deformation mechanism in the deep upper mantle, especially for fine-grained peridotites. The mechanical lithosphere-asthenosphere boundary (LAB) can be defined by the characteristic pressure derivative of effective viscosity. The sharp LAB beneath the Dabie Mountains and the Sulu terrane favors the lithosphere-asthenosphere decoupling, while the diffuse LAB beneath the western Superior Province will protect the continental root from convective erosion and mantle metasomatism. The long-term preservation of the continental roots can be attributed to a large viscosity contrast (temperature contrast) at a depth of < 150 km, and a thick and diffuse LAB at a depth of > 150 km.

  10. 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.

  11. Creep behaviour and creep mechanisms of normal and healing ligaments

    NASA Astrophysics Data System (ADS)

    Thornton, Gail Marilyn

    Patients with knee ligament injuries often undergo ligament reconstructions to restore joint stability and, potentially, abate osteoarthritis. Careful literature review suggests that in 10% to 40% of these patients the graft tissue "stretches out". Some graft elongation is likely due to creep (increased elongation of tissue under repeated or sustained load). Quantifying creep behaviour and identifying creep mechanisms in both normal and healing ligaments is important for finding clinically relevant means to prevent creep. Ligament creep was accurately predicted using a novel yet simple structural model that incorporated both collagen fibre recruitment and fibre creep. Using the inverse stress relaxation function to model fibre creep in conjunction with fibre recruitment produced a superior prediction of ligament creep than that obtained from the inverse stress relaxation function alone. This implied mechanistic role of fibre recruitment during creep was supported using a new approach to quantify crimp patterns at stresses in the toe region (increasing stiffness) and linear region (constant stiffness) of the stress-strain curve. Ligament creep was relatively insensitive to increases in stress in the toe region; however, creep strain increased significantly when tested at the linear region stress. Concomitantly, fibre recruitment was evident at the toe region stresses; however, recruitment was limited at the linear region stress. Elevating the water content of normal ligament using phosphate buffered saline increased the creep response. Therefore, both water content and fibre recruitment are important mechanistic factors involved in creep of normal ligaments. Ligament scars had inferior creep behaviour compared to normal ligaments even after 14 weeks. In addition to inferior collagen properties affecting fibre recruitment and increased water content, increased glycosaminoglycan content and flaws in scar tissue were implicated as potential mechanisms of scar creep. Similarly, ligament autografts had persistently abnormal creep behaviour and creep recovery after 2 years likely due to infiltration by scar tissue. Short-term immobilization of autografts had long-term detrimental consequences perhaps due to re-injury of the graft at remobilization. Treatments that restore normal properties to these mechanistic factors in order to control creep would improve joint healing by restoring joint kinematics and maintaining normal joint loading.

  12. ARTICLE IN PRESS New evidence for dislocation creep from 3-D geodynamic

    E-print Network

    Ritzwolle, Mike

    July 2005 Editor: R.D. van der Hilst Abstract Laboratory studies on deformation of olivine in response to applied stress suggest two distinct deformation mechanisms in the earth's upper mantle: diffusion creep of the mantle and the development of mantle fabric. Due to the lack of in situ observations, it is unclear which

  13. Modeling of high homologous temperature deformation behavior using the viscoplasticity theory based on overstress (VBO). Part 2: Characteristics of the VBO model

    SciTech Connect

    Tachibana, Yukio; Krempl, E. [Rensselaer Polytechnic Inst., Troy, NY (United States)

    1997-01-01

    Characteristics of the high homologous temperature VBO model under extreme conditions such as very fast and very slow tensile tests, long-term-creep and relaxation tests are investigated via numerical experiments and analysis. To this end, material constants of Alloy 800H determined from other tests in Part 1 were utilized for the prediction. Although no experiments are available for the extreme conditions, the predictions are plausible. For cyclic, strain controlled hold-time tests the predictions compare well with sparse experimental data. The results give confidence that VBO can be used to predict the long-term behavior at high homologous temperature once the constants have been determined from regular, short-term tests.

  14. Intracrystalline deformation of calcite

    Microsoft Academic Search

    J. H. P. de Bresser

    1991-01-01

    It is well established from observations on natural calcite tectonites that\\u000aintracrystalline plastic mechanisms are important during the deformation of calcite\\u000arocks in nature. In this thesis, new data are presented on fundamental aspects of\\u000adeformation behaviour of calcite under conditions where 'dislocation creep'\\u000amechanisms dominate. The data provide a better understanding of the rheological\\u000abehaviour of calcite rocks, and

  15. 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.

  16. 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).

  17. 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.

  18. Irradiation creep induced anisotropy in a/2<110> dislocation populations

    SciTech Connect

    Gelles, D.S.

    1984-05-01

    The contribution of anisotropy in Burgers vector distribution to irradiation creep behavior has been largely ignored in irradiation creep models. However, findings on Frank loops suggest that it may be very important. Procedures are defined to identify the orientations of a/2<110> Burgers vectors for dislocations in face-centered cubic crystals. By means of these procedures the anisotropy in Burgers vector populations was determined for three Nimonic PE16 pressurized tube specimens irradiated under stress. Considerable anisotropy in Burgers vector population develops during irradiation creep. It is inferred that dislocation motion during irradiation creep is restricted primarily to a climb of a/2<110> dislocations on 100 planes. Effect of these results on irradiation creep modeling and deformation induced irradiation growth is considered.

  19. 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

  20. 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.

  1. 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.

  2. Variability of Tissue Mineral Density Can Determine Physiological Creep of Human Vertebral Cancellous Bone

    PubMed Central

    Kim, Do-Gyoon; Shertok, Daniel; Tee, Boon Ching; Yeni, Yener N.

    2011-01-01

    Creep is a time-dependent viscoelastic deformation observed under a constant prolonged load. It has been indicated that progressive vertebral deformation due to creep may increase the risk of vertebral fracture in the long-term. The objective of this study was to examine the relationships of creep with trabecular architecture and tissue mineral density (TMD) parameters in human vertebral cancellous bone at a physiological static strain level. Architecture and TMD parameters of cancellous bone were analyzed using microcomputerized tomography (micro-CT) in specimens cored out of human vertebrae. Then, creep and residual strains of the specimens were measured after a two-hour physiological compressive constant static loading and unloading cycle. Creep developed (3877±2158 ??) resulting in substantial levels of non-recoverable post-creep residual strain (1797±1391 ??). A strong positive linear correlation was found between creep and residual strain (r=0.94, p<0.001). The current results showed that smaller thickness, larger surface area, greater connectivity of trabeculae, less mean tissue mineral density (TMD, represented by gray levels) and higher variability of TMD are associated with increasing logarithmic creep rate. The TMD variability (GLCOV) was the strongest correlate of creep rate (r=0.79, p<0.001). This result suggests that TMD variability may be a useful parameter for estimating the long-term deformation of a whole vertebral body. The results further suggest that the changes in TMD variability resulting from bone remodeling are of importance and may provide an insight into the understanding of the mechanisms underlying progressive failure of vertebral bodies and development of a clinical fracture. PMID:21481880

  3. 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.

  4. 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

  5. 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,

  6. 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

  7. Degree of hydration based Kelvin model for the basic creep of early age concrete

    Microsoft Academic Search

    G. De Schutter

    1999-01-01

    Based on simple but fundamental physical observations, a simple Kelvin model with degree of hydration based stiffnesses and\\u000a viscosity is developed for the simulation of the visco-elastic behaviour of early age concrete, including instantaneous deformation\\u000a and basic creep. The validity of the model is verified by means of creep tests under constant or varying stresses. A good\\u000a agreement with the

  8. 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.

  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. 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.

  11. Dislocation Substructure Gradient Formation in Aluminum by Creep under Weak Potential

    Microsoft Academic Search

    Sergey V. Konovalov; Yuri F. Ivanov; Oksana A. Stolboushkina; Victor E. Gromov

    2011-01-01

    Transmission diffraction electron microscopy of thin foils was used to study the dislocation substructure gradient of aluminum\\u000a destroyed during creep. Creep under +1 V potential resulted in the formation of a dislocation substructure gradient, which\\u000a was observed as a regular change in quantitative structural characteristics upon moving away from the sample fracture surface.

  12. 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.

  13. A brick model for asperity sintering and creep of APS TBCs

    NASA Astrophysics Data System (ADS)

    Cocks, Alan; Fleck, Norman; Lampenscherf, Stefan

    2014-02-01

    A micromechanical model is developed for the microstructural evolution of an air plasma sprayed (APS), thermal barrier coating: discrete, brick-like splats progressively sinter together at contacting asperities and also undergo Coble creep within each splat. The main microstructural features are captured: the shape, orientation and distribution of asperities between disc-shaped splats, and the presence of columnar grains within each splat. Elasticity is accounted for at the asperity contacts and within each splat, and the high contact compliance explains the fact that APS coatings have a much lower modulus (and thermal conductivity) than that of the parent, fully dense solid. The macroscopic elastic, sintering and creep responses are taken to be transversely isotropic, and remain so with microstructural evolution. Despite the large number of geometric and kinetic parameters, the main features of the behaviour are captured by a small number of characteristic material timescales: these reveal the competition between the deformation mechanisms and identify the rate controlling processes for both free and constrained sintering. The evolution of macroscopic strain, moduli and asperity size is compared for free and constrained sintering, and the level of in-plane stress within a constrained coating is predicted.

  14. 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

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

    SciTech Connect

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

    2008-02-01

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

  16. 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. 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.

  18. Deformation characteristics and associated clay-mineral variation in 2-3 km buried Hota accretionary complex, central Japan

    NASA Astrophysics Data System (ADS)

    Yamamoto, Y.; Kameda, J.; Yamaguchi, H.

    2009-12-01

    Although deformation and physical/chemical properties variation in aseismic-seismic transition zone were essential to examine critical changes in environmental parameters that result in earthquake, they are poorly understood because the appropriate samples buried 2-4 km have not been collected yet (scientific drilling has never reached there and most of ancient examples experienced the deeper burial depth and suffered thermal and physical overprinting). The lower to middle Miocene Hota accretionary complex is a unique example of on land accretionary complex, representing deformation and its physical/chemical properties of sediments just prior to entering the seismogenic realm. The maximum paleotemperature was estimated approximately 55-70°C (based on vitrinite reflectance) indicative of a maximum burial depth about 2-3 km assuming a paleo-geothermal gradient as 25-35°C/km. Accretionary complex in this temperature/depth range corresponds with an intermediate range between the core samples collected from the modern accretionary prism (e.g. Nankai, Barbados, and so on) and rocks in the ancient accretionary complexes on land. This presentation will treat the detailed structural and chemical analyses of the Hota accretionary complex to construct deformation properties of décollement zone and accretionary complex in its 2-3 km depth range and to discuss the interrelation between the early diagenesis (hydrocarbon/cations generation and sediment dewatering, etc.) and transition of the deformation properties. The deformation in this accretionary complex is characterized by two deformation styles: one is a few centimeter-scale phacoidal deformation representing clay minerals preferred orientation in the outer rim, whereas random fabric in the core, quite similar texture to the rocks in the present-Nankai décollement. The other is S-C style deformation (similar deformation to the mélanges in ancient accretionary complex on land) exhibiting block-in-matrix texture and quite intense clay minerals preferred orientation in the matrix, cutting the phacoidal deformation. The host and faulted (S-C structure) rocks composed of hemipelagic siltstone containing 70-80% of clay minerals. Considerable-smectite reduction and positive anomaly of illite/smectite ratio were clearly identified inside the latter S-C structure, which would cause remarkable increase in friction coefficient. Such strain hardening associated with dynamic clay-mineral variation would be the primary mechanism in décollement -zone and/or mélange-zone thickening and fundamental mechanical transition just prior to entering the seismogenic zone. Positive anomaly of the vitrinite reflectance data (Ro) inside infers frictional heating during the deformation plausibly caused the clay mineral variation.

  19. Characteristics of High-Temperature Deformation Behavior of Ti-45Al-2Cr-3Ta-0.5W Alloy

    NASA Astrophysics Data System (ADS)

    Luo, Y. Y.; Xi, Z. P.; Zeng, W. D.; Mao, X. N.; Yang, Y. L.; Niu, H. Z.

    2014-10-01

    High-temperature deformation behavior tests of as-cast Ti-45Al-2Cr-3Ta-0.5W alloy were conducted over a wide range of strain rates (0.001-1.0 s-1) and temperatures (1150-1300 °C). The flow curves for the current alloy exhibited sharp peaks at low strain levels, followed by pronounced work hardening and flow localization at high strain levels. Phenomenological analysis of the strain rate and temperature dependence of peak stress data yielded an average value of the strain rate sensitivity equal to 0.25 and an apparent activation energy of ~420 kJ/mol. Processing maps were established under different deformation conditions, and the optimal condition for hot work on this material was determined to be 1250 °C/0.001 s-1. The stable deformation region was also found to decrease with increasing strain. Dynamic recrystallization (DRX) was the major softening mechanism controlling the growth of grains at the grain boundary. Meanwhile, local globularization and dynamic recovery (DR) were the main softening mechanisms in the lamellar colony. When deformed at higher temperatures (~1300 °C), the cyclic DRX and DR appeared to dominate the deformation. Moreover, the evolution of the ? phase during hot deformation played an important role in the dynamic softening of the alloy.

  20. An Investigation of the Strength and Deformation Characteristics of Rock masses: A Case Study in an Excavation of Eski?ehir-Köseköy Tunnels, Turkey

    NASA Astrophysics Data System (ADS)

    Beyhan, Sunay; Abiddin Erguler, Zeynal; Ogul, Kenan

    2015-04-01

    With increasing of high-speed rail technology in last decades, Turkey has developed many big engineering projects to connect major cities. Excavations conducted for these projects provide very important contributions in term of understanding the strength and deformation characteristics of weak rock masses belongs to various geological materials. The Ankara-Istanbul high-speed railway known as a significant project among these projects was designed in two different phases. To discuss the outcomes, experiences and challenging geological materials during construction of this tunnel, the geotechnical properties of rock masses of a tunnel named as T19 are evaluated and discussed in this study. The T19 tunnel was excavated in stratified and heavily fractured four different geological formations. Rock mass rating (RMR) system, and tunnelling quality index (Q) were utilized for the preliminary design stages of this tunnel. These engineering rock mass classifications were utilized in 135 different locations to find representative RMR and Q values for encountered rock masses during excavation. The RMR and Q values, which range between 18-52 and changing between 0.017 and 1.6 respectively, indicate that the T19 tunnel was mainly constructed in very poor and poor rock masses. Thus, shotcrete immediately was applied after face advance to prevent the fall of loose rock fragments and to minimize excessive deformation in rock, particular in very poor and poor rock masses. In addition, the deformation characteristics of the tunnel were also carefully monitored and measured by 3D-optical measuring system and conventional tape extensometer, and then required further supports were installed. Finally, the rock mass-support interactions of different geological formations were comprehensively evaluated in this study for understanding strength and deformation characteristics of weak and stratified rock masses. Keywords: Convergence, high-speed rail, rock mass, support, tunnel

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Creep of a Silicon Nitride Under Various Specimen/Loading Configurations

    NASA Technical Reports Server (NTRS)

    Choi, Sung R.; Powers, Lynn M.; Holland, Frederic A.; Gyekenyesi, John P.; Holland, F. A. (Technical Monitor)

    2000-01-01

    Extensive creep testing of a hot-pressed silicon nitride (NC132) was performed at 1300 C in air using five different specimen/loading configurations, including pure tension, pure compression, four-point uniaxial flexure, ball-on-ring biaxial flexure, and ring-on-ring biaxial flexure. Nominal creep strain and its rate for a given nominal applied stress were greatest in tension, least in compression, and intermediate in uniaxial and biaxial flexure. Except for the case of compressive loading, nominal creep strain generally decreased with time, resulting in less-defined steady-state condition. Of the four different creep formulations - power-law, hyperbolic sine, step, redistribution models - the conventional power-law model still provides the most convenient and reasonable means to estimate simple, quantitative creep parameters of the material. Predictions of creep deformation for the case of multiaxial stress state (biaxial flexure) were made based on pure tension and compression creep data by using the design code CARES/Creep.

  7. 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.

  8. 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.

  9. 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.

  10. Coupling creep and damage in concrete under high sustained loading: Experimental investigation on bending beams and application of Acoustic Emission technique

    NASA Astrophysics Data System (ADS)

    Saliba, J.; Loukili, A.; Grondin, F.

    2010-06-01

    Creep and damage in concrete govern the long-term deformability of concrete. Thus, it is important to understand the interaction between creep and damage in order to design reliable civil engineering structures subjected to high level loading during a long time. Many investigations have been performed on the influence of concrete mixture, the effect of the bond between the matrix and the aggregates, temperature, aging and the size effect on the cracking mechanism and fracture parameters of concrete. But there is a lack of results on the influence of the creep loading history. In the present paper, an experimental investigation on the fracture properties of concrete beams submitted to three point bending tests with high levels of sustained load that deals with creep is reported. The results aim first to investigate the ranges of variation of the time response due to creep damage coupled effects under constant load and secondly to evaluate the residual capacity after creep. For this purpose a series of tests were carried out on geometrically similar specimens of size 100x200x800mm with notch to depth ratio of 0.2 in all the test specimens. The exchange of moisture was prevented and beams were subjected to a constant load of 70% and 90% of the maximum capacity. Three point bending test were realized on specimen at the age of 28 days to determine the characteristics of concrete and the maximum load so we could load the specimens in creep. Threepoint bend creep tests were performed on frames placed in a climate controlled chamber [1]. Then after four months of loading, the beams subjected to creep were removed from the creep frames and then immediately subjected to three-point bending test loading up to failure with a constant loading rate as per RILEM-FMC 50 recommendations. The residual capacity on the notched beams and the evolution of the characteristics of concrete due to the basic creep was considered. The results show that sustained loading had a strengthening effect on concrete, probably because of the consolidation of the hardened cement paste. The influence of creep on fracture energy, fracture toughness, and characteristic length of concrete is also studied. The fracture energy and the characteristic length of concrete increases slightly when creep occurs prior to failure and the size of the fracture process zone increases too. The load-CMOD relationship is linear in the ascending portion and gradually drops off after the peak value in the descending portion. The length of the tail end portion of the softening curve increases with beams subjected to creep. Relatively more ductile fracture behavior was observed with beams subjected to creep. The contribution of non-destructive and instrumental investigation methods is currently exploited to check and measure the evolution of some negative structural phenomena, such as micro-and macro-cracking, finally resulting in a creep-like behaviour. Among these methods, the non-destructive technique based on acoustic Emission proves to be very effective, especially to check and measure micro-cracking that takes place inside a structure under mechanical loading. Thus as a part of the investigation quantitative acoustic emission techniques were applied to investigate microcracking and damage localization in concrete beams. The AE signals were captured with the AE WIN software and further analyzed with Noesis software analysis of acoustic emission data. AE waveforms were generated as elastic waves in concrete due to crack nucleation. And a multichannel data acquisition system was used to record the AE waveforms. During the three point bending tests, quantitative acoustic emission (AE) techniques were used to monitor crack growth and to deduce micro fracture mechanics in concrete beams before and after creep. Several specimens are experimented in order to match each cluster with corresponding damage mechanism of the material under loading. At the same time acoustic emission was used to investigate characteristic of the fracture process zone (length width and macro crack propagation

  11. Penetrative Deformation of Dolostones during Contact Metamorphism and the Forceful Emplacement of the Tungstonia Granite, Kern Mountains, Nevada

    E-print Network

    Goodson, Kyle

    2014-08-05

    rates in experimental studies. Penetrative deformation of dolostones closest to the granite-carbonate contact may involve a mixture of both dislocation and diffusion creep, while deformation further from the contact appears to be dominated...

  12. 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.

  13. Deformation mechanisms and grain size evolution in the Bohemian granulites - a computational study

    NASA Astrophysics Data System (ADS)

    Maierova, Petra; Lexa, Ondrej; Je?ábek, Petr; Fran?k, Jan; Schulmann, Karel

    2015-04-01

    A dominant deformation mechanism in crustal rocks (e.g., dislocation and diffusion creep, grain boundary sliding, solution-precipitation) depends on many parameters such as temperature, major minerals, differential stress, strain rate and grain size. An exemplary sequence of deformation mechanisms was identified in the largest felsic granulite massifs in the southern Moldanubian domain (Bohemian Massif, central European Variscides). These massifs were interpreted to result from collision-related forced diapiric ascent of lower crust and its subsequent lateral spreading at mid-crustal levels. Three types of microstructures were distinguished. The oldest relict microstructure (S1) with large grains (>1000 ?m) of feldspar deformed probably by dislocation creep at peak HT eclogite facies conditions. Subsequently at HP granulite-facies conditions, chemically- and deformation- induced recrystallization of feldspar porphyroclasts led to development of a fine-grained microstructure (S2, ~50 ?m grain size) indicating deformation via diffusion creep, probably assisted by melt-enhanced grain-boundary sliding. This microstructure was associated with flow in the lower crust and/or its diapiric ascent. The latest microstructure (S3, ~100 ?m grain size) is related to the final lateral spreading of retrograde granulites, and shows deformation by dislocation creep at amphibolite-facies conditions. The S2-S3 switch and coarsening was interpreted to be related with a significant decrease in strain rate. From this microstructural sequence it appears that it is the grain size that is critically linked with specific mechanical behavior of these rocks. Thus in this study, we focused on the interplay between grain size and deformation with the aim to numerically simulate and reinterpret the observed microstructural sequence. We tested several different mathematical descriptions of the grain size evolution, each of which gave qualitatively different results. We selected the two most elaborated and at the same time the most promising descriptions: thermodynamics-based models with and without Zener pinning. For conditions compatible with the S1 and S2 microstructures (~800 °C and strain rate ~10-13 s-1), the calculated stable grain sizes are ~30 ?m and >300 ?m in the models with and without Zener pinning, respectively. This is in agreement with the contrasting grain sizes associated with S1 and S2 microstructures implying that mainly chemically induced recrystallization of S1 feldspar porphyroclasts must had played a fundamental role in the transition into the diffusion creep. The model with pinning also explains only minor changes of mean grain size associated with S2 microstructure. The S2-S3 switch from the diffusion to dislocation creep is difficult to explain when assuming reasonable temperature and strain rate (or stress). However, a simple incorporation of the effect of melt solidification into the model with pinning can mimic this observed switch. Besides the above mentioned simple models with prescribed temperature and strain rate, we implemented the grain size evolution laws into in a 2D thermo-mechanical model setup, where stress, strain rate and temperature evolve in a more natural manner. This setup simulates a collisional evolution of an orogenic root with anomalous lower crust. The lower-crustal material is a source region for diapirs and it deforms via a combination of dislocation and grain-size-sensitive creeps. We tested the influence of selected parameters in the flow laws and in the grain-size evolution laws on the shape and other characteristics of the growing diapirs. The outputs of our simulations were then compared with the geological record from the Moldanubian granulite massifs.

  14. 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.

  15. Is diffusion creep the cause for the inverse Hall-Petch effect in nanocrystalline materials?

    SciTech Connect

    T. G. Desai; P. Millett; D. Wolf

    2008-10-01

    It has previously been demonstrated by means of molecular-dynamics (MD) simulation that for the very smallest grain sizes (typically below 20-30 nm), nanocrystalline fcc metals deform via grain-boundary diffusion creep, provided the applied stress is low enough to avoid microcracking and dislocation nucleation from the grain boundaries. Experimentally, however, the nature of the deformation process in this “inverse Hall-Petch” regime (in which the yield stress decreases with decreasing grain size) remains controversial. Here we illustrate by MD simulation that in the absence of grain growth a nanocrystalline model bcc metal, Mo, and a model metal oxide, UO2, also deform via diffusion creep. However, in the case of Mo both grain-boundary and lattice diffusion are observed to contribute to the creep rate; i.e., the deformation mechanism involves a combination of Coble and Nabarro-Herring creep. While our results on Mo and UO2 are still preliminary, they lend further support to the observation of diffusion creep previously documented in fcc metals and in covalently bonded Si.

  16. 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.

  17. Viscoelastic creep elimination in dielectric elastomer actuation by preprogrammed voltage

    NASA Astrophysics Data System (ADS)

    Zhang, Junshi; Wang, Yanjie; McCoul, David; Pei, Qibing; Chen, Hualing

    2014-11-01

    Viscoelasticity causes a time-dependent deformation and lowers the response speed and energy conversion efficiency of VHB-based dielectric elastomers (DEs), thus seriously restricting a wide range of applications of this otherwise versatile soft smart material. The viscoelastic deformation of a prestretched VHB film in a circular actuator configuration is studied both theoretically and experimentally. By adjusting the applied voltage, viscoelastic creep can be dispelled and an invariable strain is obtained by simulation. Subsequently, an experiment was designed to validate the simulation and the results indicate that a constant strain can be achieved by preprogramming the applied actuation voltage.

  18. 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.

  19. 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

  20. Variational principles and optimal solutions of the inverse problems of creep bending of plates

    NASA Astrophysics Data System (ADS)

    Bormotin, K. S.; Oleinikov, A. I.

    2012-09-01

    It is shown that inverse problems of steady-state creep bending of plates in both the geometrically linear and nonlinear formulations can be represented in a variational formulation. Steady-state values of the obtained functionals corresponding to the solutions of the problems of inelastic deformation and elastic unloading are determined by applying a finite element procedure to the functionals. Optimal laws of creep deformation are formulated using the criterion of minimizing damage in the functionals of the inverse problems. The formulated problems are reduced to the problems solved by the finite element method using MSC.Marc software.

  1. 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.

  2. 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.

  3. 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.

  4. 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

  5. A renewal theory of creep and inelasticity

    SciTech Connect

    Bagley, R.L. [Wright-Patterson AFB, Dayton, OH (United States); Jones, D.I.G. [TSSI Inc., Dayton, OH (United States); Freed, A.D. [NASA Lewis Research Center, Cleveland, OH (United States)

    1995-12-31

    A summary of the development of the renewal theory of creep and inelasticity is presented. The creep theory development is outlined to motivate the mathematical form of the uniaxial creep equation. The concept of intrinsic or internal time is then introduced and used to transform the creep theory into the more general inelasticity theory. Measured creep data is then used to construct an inelasticity model for a steel. The model is used to predict a stress-strain curve for the steel.

  6. Experimental and numerical study of the method to determine the creep parameters from the indentation creep testing

    Microsoft Academic Search

    Y. J. Liu; B. Zhao; B. X. Xu; Z. F. Yue

    2007-01-01

    Indentation creep testing and uniaxial creep testing were carried out in this paper in order to set up the relationship between them. The aim of this work is to present a experimental validated method to determine the material creep parameters (nm, creep stress exponent; cm, creep factor, ??=cm?nm, ??, tensile creep strain rate at the steady state; ?, creep stress,

  7. 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.

  8. 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.

  9. Properties of Creep Fronts on Rate-and-State Faults

    NASA Astrophysics Data System (ADS)

    Rubin, A. M.

    2009-12-01

    Creep fronts invariably arise in rate-and-state friction models when velocity-weakening regions too large for purely steady sliding are loaded by creep of their surroundings. Examples include models of repeating earthquakes and episodic slow slip in subduction zones. For several reasons it is worth understanding the behavior of these creep fronts better. First, this creep produces a large fraction of the aseismic slip in the simulations of Chen and Lapusta [2009], which appear to explain the surprising relationship between moment and recurrence interval that Nadeau and Johnson [1998] observed for repeating earthquakes. Second, creep fronts often produce large transient slip velocities when they collide, which, given how ubiquitous these fronts are in the presence of heterogeneity, provides a possible explanation for tremor accompanying slow slip. Third, when it leads to elastodynamic rupture this creep represents a style of nucleation quite distinct from that explored by Rubin/Ampuero and Ampuero/Rubin [2005; 2008], who considered a heterogeneous pre-stress on a fault with uniform material properties. It is not known how their analytical estimates of nucleation size translate to cases where the velocity-weakening region is loaded from the edge. Other unanswered questions include: How far can a creep front propagate before going unstable? When two fronts collide, what are the characteristics of the ensuing high-velocity slip? How do the answers to these questions depend upon the adopted friction law? Here I take a stab at these questions, and discuss their implications for models of slow slip, tremor, and repeating earthquakes.

  10. Strengthening mechanisms, creep, and fatigue processes in dispersion-hardened niobium alloy. Annual technical report, 1 Feb 90-31 Jan 91

    SciTech Connect

    Mukherjee, A.K.; Gibeling, J.C.

    1991-05-01

    The creep properties of Nb-1% Zr alloy was investigated at intermediate temperatures. A model is proposed based on the operation of two parallel mechanisms. The first mechanism is based on dislocation glide-controlled creep and controls creep rate at higher stresses where the influence of the threshold stress due to the particles is negligible. At lower stresses (below 135 MPa), the threshold stress of the particles come into play and becomes the rate-controlling mechanism. The resultant effect of the operation of these two parallel mechanisms produced quite satisfactory correlation between theoretical predictions and experimental data. The author's have also studied the cyclic deformation of commercially pure niobium and Nb-1Zr at ambient temperature. They have conducted tests at slow strain rates, where these materials exhibit high temperature dislocation glide kinetics, and at fast strain rates, where the behavior is characteristic of the low temperature regime. They are presently exploring additional aspects of the fatigue response using a Bauschinger analysis and by testing at very low plastic strain amplitudes to see if a fatigue limit is observed. The focus of this research program is on the development and characterization of refractory metals for advanced aerospace craft and structural applications at elevated temperatures. These applications include space nuclear power reactors and hypersonic vehicles such as the National Aerospace Plane.

  11. 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.

  12. Creep and friction of ice.

    PubMed

    Tabor, D; Walker, J C

    1970-10-10

    The creep of polycrystalline ice in uniaxial compression has been studied over a very wide range of strain rates. The creep is far too slow to explain the friction of ice observed at very low sliding speeds, but experiments with single crystals show that sliding produces recrystallization at the interface, the ice presenting an orientation favourable to easy glide in directions tangential to the interface. PMID:16058445

  13. Line creep in paper peeling

    Microsoft Academic Search

    Jari Rosti; Juha Koivisto; Paola Traversa; Xavier Illa; Jean-Robert Grasso; Mikko J. Alava

    2008-01-01

    The dynamics of a “peeling front” or an elastic line is studied under creep (constant load) conditions. Our experiments show\\u000a in most cases an exponential dependence of the creep velocity on the inverse force (mass) applied. In particular, the dynamical\\u000a correlations of the avalanche activity are discussed here. We compare various avalanche statistics to those of a line with\\u000a non-local

  14. 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.

  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. A nonlocal continuum damage mechanics approach to simulation of creep fracture in ice sheets

    NASA Astrophysics Data System (ADS)

    Duddu, Ravindra; Waisman, Haim

    2013-06-01

    We present a Lagrangian finite element formulation aimed at modeling creep fracture in ice-sheets using nonlocal continuum damage mechanics. The proposed formulation is based on a thermo-viscoelastic constitutive model and a creep damage model for polycrystalline ice with different behavior in tension and compression. In this paper, mainly, we detail the nonlocal numerical implementation of the constitutive damage model into commercial finite element codes (e.g. Abaqus), wherein a procedure to handle the abrupt failure (rupture) of ice under tension is proposed. Then, we present numerical examples of creep fracture under four-point bending, uniaxial tension, and biaxial tension in order to illustrate the viability of the current approach. Finally, we present simulations of creep crack propagation in idealized rectangular ice slabs so as to estimate calving rates at low deformation rates. The examples presented demonstrate the mesh size and mesh directionality independence of the proposed nonlocal implementation.

  17. 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.

  18. 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.

  19. Creep Behavior of Ice in Polar Ice Sheets

    NASA Astrophysics Data System (ADS)

    Duval, Paul

    Major advances in the understanding of the plasticity of ice Ih have been made with the development of studies of the flow of glaciers and, recently, with the analysis of deep ice cores in Antarctica and Greenland. Evidence is presented that indicates deformation, in glaciers and ice sheets, is essentially produced by basal slip. Other deformation modes are required for compatibility reasons: non-basal slip, dislocation climb, cross-slip and/or grain boundary sliding. Diffusion processes cannot be invoked as a significant deformation mode, even at low stresses. A grain size effect is expected for secondary creep, as soon as the stress exponent of the flow law is lower than 2. A threshold stress could explain the apparent high stress exponent found at the ice divides in polar ice sheets. It is shown that the presence of a liquid phase at grain boundaries or around particles significantly reduces the ice viscosity. Dynamic recrystallization is very active in glaciers and ice sheets. Grain boundary migration associated with normal grain growth and dynamic recrystallization is considered as an efficient accommodation process of basal slip. Migration recrystallization, which is associated with tertiary creep and with the rapid migration of grain boundaries between dislocation-free nuclei and deformed grains, produces an interlocking grain structure and grains well oriented for basal slip.

  20. Significance of primary irradiation creep in graphite

    NASA Astrophysics Data System (ADS)

    Erasmus, Christiaan; Kok, Schalk; Hindley, Michael P.

    2013-05-01

    Traditionally primary irradiation creep is introduced into graphite analysis by applying the appropriate amount of creep strain to the model at the initial time-step. This is valid for graphite components that are subjected to high fast neutron flux fields and constant stress fields, but it does not allow for the effect of movement of stress locations around a graphite component during life, nor does it allow primary creep to be applied rate-dependently to graphite components subject to lower fast neutron flux. This paper shows that a differential form of primary irradiation creep in graphite combined with the secondary creep formulation proposed by Kennedy et al. performs well when predicting creep behaviour in experimental samples. The significance of primary irradiation creep in particular in regions with lower flux is investigated. It is shown that in low flux regions with a realistic operating lifetime primary irradiation creep is significant and is larger than secondary irradiation creep.

  1. In situ tensile and creep testing of lithiated silicon nanowires

    SciTech Connect

    Boles, Steven T.; Kraft, Oliver [Institute for Applied Materials, KIT, 76344 Eggenstein-Leopoldshafen (Germany)] [Institute for Applied Materials, KIT, 76344 Eggenstein-Leopoldshafen (Germany); Thompson, Carl V. [Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts 02139 (United States)] [Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts 02139 (United States); Mönig, Reiner [Institute for Applied Materials, KIT, 76344 Eggenstein-Leopoldshafen (Germany) [Institute for Applied Materials, KIT, 76344 Eggenstein-Leopoldshafen (Germany); Helmholtz Institute Ulm for Electrochemical Energy Storage (HIU), 89069 Ulm (Germany)

    2013-12-23

    We present experimental results for uniaxial tensile and creep testing of fully lithiated silicon nanowires. A reduction in the elastic modulus is observed when silicon nanowires are alloyed with lithium and plastic deformation becomes possible when the wires are saturated with lithium. Creep testing was performed at fixed force levels above and below the tensile strength of the material. A linear dependence of the strain-rate on the applied stress was evident below the yield stress of the alloy, indicating viscous deformation behavior. The observed inverse exponential relationship between wire radius and strain rate below the yield stress indicates that material transport was controlled by diffusion. At stress levels approaching the yield strength of fully lithiated silicon, power-law creep appears to govern the strain-rate dependence on stress. These results have direct implications on the cycling conditions, rate-capabilities, and charge capacity of silicon and should prove useful for the design and construction of future silicon-based electrodes.

  2. In situ tensile and creep testing of lithiated silicon nanowires

    NASA Astrophysics Data System (ADS)

    Boles, Steven T.; Thompson, Carl V.; Kraft, Oliver; Mönig, Reiner

    2013-12-01

    We present experimental results for uniaxial tensile and creep testing of fully lithiated silicon nanowires. A reduction in the elastic modulus is observed when silicon nanowires are alloyed with lithium and plastic deformation becomes possible when the wires are saturated with lithium. Creep testing was performed at fixed force levels above and below the tensile strength of the material. A linear dependence of the strain-rate on the applied stress was evident below the yield stress of the alloy, indicating viscous deformation behavior. The observed inverse exponential relationship between wire radius and strain rate below the yield stress indicates that material transport was controlled by diffusion. At stress levels approaching the yield strength of fully lithiated silicon, power-law creep appears to govern the strain-rate dependence on stress. These results have direct implications on the cycling conditions, rate-capabilities, and charge capacity of silicon and should prove useful for the design and construction of future silicon-based electrodes.

  3. Tectonic creep in the Hayward fault zone, California

    USGS Publications Warehouse

    Radbruch-Hall, Dorothy H.; Bonilla, M.G.

    1966-01-01

    Tectonic creep is slight apparently continuous movement along a fault. Evidence of creep has been noted at several places within the Hayward fault zone--a zone trending northwestward near the western front of the hills bordering the east side of San Francisco Bay. D. H. Radbruch of the Geological Survey and B. J. Lennert, consulting engineer, confirmed a reported cracking of a culvert under the University of California stadium. F. B. Blanchard and C. L. Laverty of the East Bay Municipal Utility District of Oakland studied cracks in the Claremont water tunnel in Berkeley. M. G. Bonilla of the Geological Survey noted deformation of railroad tracks in the Niles district of Fremont. Six sets of tracks have been bent and shifted. L. S. Cluff of Woodward-Clyde-Sherard and Associates and K. V. Steinbrugge of the Pacific Fire Rating Bureau noted that the concrete walls of a warehouse in the Irvington district of Fremont have been bent and broken, and the columns forced out of line. All the deformations noted have been right lateral and range from about 2 inches in the Claremont tunnel to about 8 inches on the railroad tracks. Tectonic creep almost certainly will continue to damage buildings, tunnels, and other structures that cross the narrow bands of active movement within the Hayward fault zone.

  4. The mechanical creep compliance of tissue cells is gamma distributed

    E-print Network

    John M. Maloney; Krystyn J. Van Vliet

    2011-07-13

    Investigations of natural variation among cells within a population are essential for understanding the stochastic nature of tissue cell deformation under applied load. In the existing literature, the population variation of single-cell creep compliance has so far been modeled universally by using a log-normal distribution. Here we use optical stretching, a non-contact and relatively high-throughput technique for probing cell mechanics, to accumulate a sufficient data set that demonstrates robustly that cell compliance varies according to the similar but distinct gamma distribution. Additionally, we re-examine existing simulations that were originally proposed to justify a log-normal fit, and show that in fact these simulation data also correspond to the gamma distribution. Finally, we propose a general stochastic differential equation that analytically predicts a gamma distribution of creep compliance during cell stretching, as well as the Gaussian distribution of cell recovery that we observe experimentally upon removal of applied load. The population variation is well characterized by just a single parameter in each of the creep and recovery regimes. We expect our correction of a phenomenological distribution fit, enabled by an expansive data set for mesenchymal stem cells, to enable the development of more accurate constitutive laws to describe cytoskeletal deformation. These findings thus serve to replace an empirical distribution with a better-fitting model that rests on a more solid experimental and theoretical foundation, and also provides a basis to predict and understand the stochastic nature of the mechanical response of individual cells within populations.

  5. 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.

  6. EBSD study of the orientation dependence of substructure characteristics in a model Fe-30wt%Ni alloy subjected to hot deformation.

    PubMed

    Cizek, P; Bai, F; Palmiere, E J; Rainforth, W M

    2005-02-01

    The aim of the present investigation was to determine the orientation dependence of substructure characteristics in an austenitic Fe-30wt%Ni model alloy subjected to hot plane strain compression. Deformation was carried out at a temperature of 950 degrees C using a strain rate of 10 s(-1) to equivalent strain levels of approximately 0.2, 0.4, 0.6 and 0.8. The specimens obtained were analysed using a fully automatic electron backscatter diffraction technique. The crystallographic texture was characterized for all the strain levels studied and the subgrain structure was quantified in detail at a strain of 0.4. The substructure characteristics displayed pronounced orientation dependence. The major texture components, namely the copper, S, brass, Goss and rotated Goss, generally contained one or two prominent families of parallel larger-angle extended subboundaries, the traces of which on the longitudinal viewing plane appeared systematically aligned along the {111} slip plane traces, bounding long microbands subdivided into slightly elongated subgrains by short lower-angle transverse subboundaries. Relatively rare cube-orientated grains displayed pronounced subdivision into coarse deformation bands containing large, low-misorientated subgrains. The misorientation vectors across subboundaries largely showed a tendency to cluster around the sample transverse direction. Apart from the rotated Goss texture component, the stored energy levels for the remaining components were principally consistent with the corresponding Taylor factor values. PMID:15683411

  7. 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.

  8. Grain-size effect on compressive creep of silicon-carbide-whisker-reinforced aluminum oxide.

    SciTech Connect

    De Arellano-Lopez, A. R.; Melendez-Martinez, J. J.; Dominguez-Rodriguez, A.; Routbort, J. L.; Lin, H.-T.; Becher, P. F.; Energy Technology; Univ. de Sevilla; ORNL

    2001-01-01

    The steady-state compressive creep of Al{sub 2}O{sub 3} with 10 vol% SiC whiskers having grain sizes of 1.2, 2.3, and 4.0 {mu}m has been measured at 1400 C in argon. The creep rate is related to the free volume within the whisker network, not the nominal grain size. The results are consistent with diffusional-controlled creep with different contributions from grain-boundary sliding. Under low stresses, only Liftshitz sliding is possible and the diffusional process controls deformation, while at stresses over a threshold, Rachinger sliding is the mechanism controlling deformation. The evolution between Liftshitz and Rachinger sliding is marked by a significant increase in the value of the stress exponent.

  9. 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.

  10. 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.

  11. Spectral and dynamic analysis of plastic instabilities during serrated creep of the aluminum-magnesium alloy

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    The force response to the development of a macroscopic plastic deformation jump under the conditions of serrated creep of the aluminummagnesium alloy 5456 has been studied using spectral and dynamic analysis methods. The flicker-noise structure of the force response indicating the self-organized criticality state has been revealed. It has been found that a short-term state of plastic instability flatter spontaneously appears during the development of the macroscopic deformation step.

  12. 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.

  13. Creep-compensated fatigue testing of polyethylene under reversed loading conditions

    Microsoft Academic Search

    J. W. Teh; J. R. White; E. H. Andrews

    1975-01-01

    A machine capable of testing polymers under creep-compensated strain-controlled cyclic deformation has been constructed, and used initially to study fatigue behaviour in low-density polyethylene. Reversed loading conditions have been used with total strain amplitude up to 6.5%. Crack propagation is inhibited by the compressive component of the deformation. Within the range of testing employed, the slowest crack-growth rates are obtained

  14. Numerical analysis for elucidation of nonlinear frictional characteristics of a deformed erythrocyte moving on a plate in medium subject to inclined centrifugal force.

    PubMed

    Oshibe, Takashi; Hayase, Toshiyuki; Funamoto, Kenichi; Shirai, Atsushi

    2014-12-01

    Complex interactions between blood cells, plasma proteins, and glycocalyx in the endothelial surface layer are crucial in microcirculation. To obtain measurement data of such interactions, we have previously performed experiments using an inclined centrifuge microscope, which revealed that the nonlinear velocity-friction characteristics of erythrocytes moving on an endothelia-cultured glass plate in medium under inclined centrifugal force are much larger than those on plain or material-coated glass plates. The purpose of this study was to elucidate the nonlinear frictional characteristics of an erythrocyte on plain or material-coated glass plates as the basis to clarify the interaction between the erythrocyte and the endothelial cells. We propose a model in which steady motion of the cell is realized as an equilibrium state of the force and moment due to inclined centrifugal force and hydrodynamic flow force acting on the cell. Other electrochemical effects on the surfaces of the erythrocyte and the plate are ignored for the sake of simplicity. Numerical analysis was performed for a three-dimensional flow of a mixture of plasma and saline around a rigid erythrocyte model of an undeformed biconcave shape and a deformed shape with a concave top surface and a flat bottom surface. A variety of conditions for the concentration of plasma in a medium, the velocity of the cell, and the minimum gap width and the angle of attack of the cell from the plate, were examined to obtain the equilibrium states. A simple flat plate model based on the lubrication theory was also examined to elucidate the physical meaning of the model. The equilibrium angle of attack was obtained only for the deformed cell model and was represented as a power function of the minimum gap width. A simple flat plate model qualitatively explains the power function relation of the frictional characteristics, but it cannot explain the equilibrium relation, confirming the computational result that the deformation of the cell is necessary for the equilibrium. The frictional characteristics obtained from the present computation qualitatively agree with those of former experiments, showing the validity of the proposed model. PMID:25271707

  15. (Irradiation creep of graphite)

    SciTech Connect

    Kennedy, C.R.

    1990-12-21

    The traveler attended the Conference, International Symposium on Carbon, to present an invited paper, Irradiation Creep of Graphite,'' and chair one of the technical sessions. There were many papers of particular interest to ORNL and HTGR technology presented by the Japanese since they do not have a particular technology embargo and are quite open in describing their work and results. In particular, a paper describing the failure of Minor's law to predict the fatigue life of graphite was presented. Although the conference had an international flavor, it was dominated by the Japanese. This was primarily a result of geography; however, the work presented by the Japanese illustrated an internal program that is very comprehensive. This conference, a result of this program, was better than all other carbon conferences attended by the traveler. This conference emphasizes the need for US participation in international conferences in order to stay abreast of the rapidly expanding HTGR and graphite technology throughout the world. The United States is no longer a leader in some emerging technologies. The traveler was surprised by the Japanese position in their HTGR development. Their reactor is licensed and the major problem in their graphite program is how to eliminate it with the least perturbation now that most of the work has been done.

  16. Evidence for dynamic recrystallization during Harper–Dorn creep

    Microsoft Academic Search

    Timothy J. Ginter; Farghalli A. Mohamed

    2002-01-01

    Harper–Dorn creep refers to the anomalous creep behavior first reported in 1957 by Harper and Dorn in their study on the creep behavior of large-grained aluminum. The creep rates associated with Harper–Dorn creep are two orders of magnitude faster than those predicted by Nabarro–Herring creep (diffusional creep). The present investigation provides new evidence that dynamic recrystallization occurs during Harper–Dorn creep.

  17. Changes in complex resistivity during creep in granite

    USGS Publications Warehouse

    Lockner, D.A.; Byerlee, J.D.

    1986-01-01

    A sample of Westerly granite was deformed under constant stress conditions: a pore pressure of 5 MPa, a confining pressure of 10 MPa, and an axial load of 170 MPa. Pore volume changes were determined by measuring the volume of pore fluid (0.01 M KClaq) injected into the sample. After 6 days of creep, characterized by accelerating volumetric stain, the sample failed along a macroscopic fault. Measurements of complex resistivity over the frequency range 0.001-300 Hz, taken at various times during creep, showed a gradual increase in both conductivity and permittivity. When analysed in terms of standard induced polarization (IP) techniques, the changing complex resistivity resulted in systematic changes in such parameters as percent frequency effect and chargeability. These results suggest that it may be possible to monitor the development of dilatancy in the source region of an impending earthquake through standard IP techniques. ?? 1986 Birka??user Verlag.

  18. Creep-Fatigue Interactions in a 9 Pct Cr1 Pct Mo Martensitic Steel: Part I. Mechanical Test Results

    Microsoft Academic Search

    B. Fournier; M. Sauzay; C. Caës; M. Noblecourt; M. Mottot; L. Allais; I. Tournie; A. Pineau

    2009-01-01

    Creep-fatigue (CF) tests are carried out on a modified 9 pct Cr-1 pct Mo (P91) steel at 550 °C. These CF tests are strain\\u000a controlled during the cyclic part of the stress-strain hysteresis loop and then load controlled when the stress is maintained\\u000a at its maximum value, to produce a prescribed value of the creep strain before cyclic deformation is reversed under

  19. 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

  20. 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.

  1. Rheological Characteristics of Weak Rock Mass and Effects on the Long-Term Stability of Slopes

    NASA Astrophysics Data System (ADS)

    Yang, Tianhong; Xu, Tao; Liu, Hongyuan; Zhang, Chunming; Wang, Shanyong; Rui, Yongqin; Shen, Li

    2014-11-01

    The creep deformation behavior of the northern slope of an open-pit mine is introduced. Direct shear creep tests are then conducted for the samples taken from the northern slope to study the rheological characteristics of the rock mass. The experimental results are analyzed afterwards using an empirical method to develop a rheological model for the rock mass. The proposed rheological model is finally applied to understand the creep behavior of the northern slope, predict the long-term stability, and guide appropriate measures to be taken at suitable times to increase the factor of safety to ensure stability. Through this study, a failure criterion is proposed to predict the long-term stability of the slope based on the rheological characteristics of the rock mass and a critical deformation rate is adopted to determine when appropriate measures should be taken to ensure slope stability. The method has been successfully applied for stability analysis and engineering management of the toppling and slippage of the northern slope of the open-pit mine. This success in application indicates that it is theoretically accurate, practically feasible, and highly cost-effective.

  2. Coupling between pressure solution creep and diffusive mass transport in porous rocks

    E-print Network

    Dysthe, Dag Kristian

    Coupling between pressure solution creep and diffusive mass transport in porous rocks Elisabeth solution is widely regarded as a mechanism of ductile deformation in the upper crust. It is driven or by grain indentation. For a system closed at a grain scale, pressure solution is traditionally described

  3. 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

  4. Characterization of the elastic and viscoelastic properties of dentin by a nanoindentation creep test.

    PubMed

    Chuang, Shu-Fen; Lin, Shih-Yun; Wei, Pal-Jen; Han, Chang-Fu; Lin, Jen-Fin; Chang, Hsien-Chang

    2015-07-16

    Dentin is the main supporting structure of teeth, but its mechanical properties may be adversely affected by pathological demineralization. The purposes of this study were to develop a quantitative approach to characterize the viscoelastic properties of dentin after de- and re-mineralization, and to examine the elastic properties using a nanoindentation creep test. Dentin specimens were prepared to receive both micro- and nano-indentation tests at wet and dry states. These tests were repeatedly performed after demineralization (1% citric acid for 3 days) and remineralization (artificial saliva immersion for 28 days). The nanoindentation test was executed in a creep mode, and the resulting displacement-time responses were disintegrated into primary (transient) and secondary (viscous) creep. The structural changes and mineral densities of dentin were also examined under SEM and microCT, respectively. The results showed that demineralization removed superficial minerals of dentin to the depth of 400?m, and affected its micro- and nano-hardness, especially in the hydrate state. Remineralization only repaired the minerals at the surface layer, and partially recovered the nanohardness. Both the primary the secondary creep increased in the demineralized dentin, while the hydration further enhanced creep deformation of untreated and remineralized dentin. Remineralization reduced the primary creep of dentin, but did not effectively increase the viscosity. In conclusion, water plasticization increases the transient and viscous creep strains of demineralized dentin and reduces load sustainability. The nanoindentation creep test is capable of analyzing the elastic and viscoelastic properties of dentin, and reveals crucial information about creep responses. PMID:25911251

  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. 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.

  7. 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.

  8. 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

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  10. 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)

  11. 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.

  12. 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

  13. Weep hole inspection by circumferential creeping waves

    E-print Network

    Nagy, Peter B.

    Weep hole inspection by circumferential creeping waves Peter B. Nagy*, Mark Blodgettt and Matthew circumferential creeping waves was adapted to inspect for these cracks. The conventional creeping wave technique. The cracks have been found to grow in the upward or downward or both directions. The fatigue cracks initially

  14. Components of the Creep Strength of Welds

    E-print Network

    Cambridge, University of

    ://www.msm.cam.ac.uk ABSTRACT Modern power plant steels and welding alloys, designed to resist creep deforma- tion at high in determining the ultimate creep properties. In this work, we have used a combination of models and a knowledge of the mechanical properties and microstructure, to factorise the long#21;term creep rupture strength

  15. 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.

  16. Improved Creep Measurements for Ultra-High Temperature Materials

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  17. Testing Protocol for Module Encapsulant Creep (Presentation)

    SciTech Connect

    Kempe, M. D.; Miller, D. C.; Wohlgemuth, J. H.; Kurtz, S. R.; Moseley, J. M.; Shah, Q.; Tamizhmani, G.; Sakurai, K.; Inoue, M.; Doi, T.; Masuda, A.

    2012-02-01

    Recently there has been an interest in the use of thermoplastic encapsulant materials in photovoltaic modules to replace chemically crosslinked materials, e.g., ethylene-vinyl acetate. The related motivations include the desire to: reduce lamination time or temperature; use less moisture-permeable materials; or use materials with better corrosion characteristics. However, the use of any thermoplastic material in a high-temperature environment raises safety and performance concerns, as the standardized tests currently do not expose the modules to temperatures in excess of 85C, yet modules may experience temperatures above 100C in operation. Here we constructed eight pairs of crystalline-silicon modules and eight pairs of glass/encapsulation/glass mock modules using different encapsulation materials of which only two were designed to chemically crosslink. One module set was exposed outdoors with insulation on the back side in Arizona in the summer, and an identical set was exposed in environmental chambers. High precision creep measurements and performance measurements indicate that despite many of these polymeric materials being in the melt state at some of the highest outdoor temperatures achievable, very little creep was seen because of their high viscosity, temperature heterogeneity across the modules, and in the case of the crystalline-silicon modules, the physical restraint of the backsheet. These findings have very important implications for the development of IEC and UL qualification and safety standards, and in regards to the necessary level of cure during the processing of crosslinking encapsulants.

  18. 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).

  19. 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

  20. Observations and modeling of shallow fault creep along the San Andreas Fault system

    NASA Astrophysics Data System (ADS)

    Wei, Meng

    This dissertation focuses on observations and modeling of fault creep in California aiming to understand the relationship between creep and earthquakes and assess the earthquake hazards in California. Chapter 1 gives an introduction of fault creep research in California, geodetic methods used to measure fault creep, and mechanism of fault creep. Chapter 2 documents an investigate on a creep event on the Supersitition Hills Fault in Southern California and the spatial and temporal variations in slip history between 1992 and 2008 using ERS, and Envisat Satellite data confirming that the fault creep is confined within the sediments layer and is probably due to the low normal stress in unconsolidated sediments. Chapter 3 presents a study on triggered slip on faults in the Salton Trough by the 2010 El Mayor-Cucapah Mw 7.2 earthquake. Chapter 4 compiles geodetic data and investigates the relationship between shallow stress accumulating rate and creep rate. Chapter 5 and 6 explores two technical projects related to fault creep observations in California. Chapter 5 analyzes decorrelation of L-band and C-band interferograms in California with implications for future fault creep study. Chapter 6 proposes an optimal way to combine GPS and InSAR to measure interseismic deformation, including fault creep. The proposed method is compared with other method and the improvements are observed. Chapter 7 presents the conclusions of the previous six chapters. Chapter 8 presents my work in the first two years in graduate school, which is not related to fault creep. We compute global maps of surface minus basal heat flow that show qualitative agreement with heat flow based on the inverse square root of age relation. In the beginning of each chapter, I provide you an earthquake safety tip. I borrowed them from an interesting website for your safety and interests. Hopefully it could be one more motivation to read through my thesis. I didn't bother to invent them, as Ralph Waldo Emerson noted "All my best thoughts were stolen by the ancients."

  1. Associations between characters in populations of creeping-rooted lucerne (Medicago sativa L.)

    Microsoft Academic Search

    M. W. Dunbier

    1971-01-01

    Correlations were calculated between some non-creeping characters first season of growth. The non-creeping characters were: length of seed pods, the number of pod spirals, and autumn growth score.Correlations between the different measures of the size of the plant were consistently highly significant. Correlations between traits considered characteristic of M. falcata were not as close or consistent, and were considered to

  2. 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.

  3. An evaluation of permanent deformation properties of crumb rubber modified (CRM) asphalt concrete mixtures

    E-print Network

    Makunike, Danai Ellarin

    1995-01-01

    that are associated with permanent deformation. These include Hveem stability, air voids, permeability, creep response, and compressive strength. Three CRMAC mixtures were used, each containing different amounts of RAP. The study aimed at defining how these properties...

  4. 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.

  5. Plastic deformation of protein monolayers.

    PubMed Central

    Singh-Zocchi, Mukta; Hanne, Jeungphill; Zocchi, Giovanni

    2002-01-01

    Globular proteins are peculiar solids that display both local stability of their conformation and the ability to undergo large cooperative changes of shape (conformational changes). If one forces a large deformation of the molecule, such that the structure is necessarily changed, it is not obvious whether the deformed globule can still remain a solid or whether it will melt. Is it possible to plastically deform a protein? Here we investigate this question with a micro-mechanical experiment on a small region (approximately 10 molecules) of a protein monolayer adsorbed on a rigid surface. For the two proteins studied, albumin and myoglobin, we observed that the molecules can be substantially deformed (approximately 1-2 nm deformation) by comparatively small stresses applied for sufficiently long times. The deformation is irreversible, and the protein remains in the solid state (i.e., displays a nonzero shear modulus). The dynamics of the deformation is approximately logarithmic in time, similar to creep in solids. These results show that globular proteins adsorbed on a surface can be plastically deformed. PMID:12324438

  6. Creep of ice: Further studies

    NASA Technical Reports Server (NTRS)

    Heard, H. C.; Durham, W. B.; Kirby, S. H.

    1987-01-01

    Detailed studies have been done of ice creep as related to the icy satellites, Ganymede and Callisto. Included were: (1) the flow of high-pressure water ices II, III, and V, and (2) frictional sliding of ice I sub h. Work was also begun on the study of the effects of impurities on the flow of ice. Test results are summarized.

  7. Solidification theory for aging creep

    Microsoft Academic Search

    Z BAZANT; Santosh Prasannan

    1988-01-01

    The paper presents a new theory for the basic creep of concrete which takes aging into account in a manner which is better justified physi- cally, better agrees with test results, and is more efficient computa- tionally. The aging is treated as a consequence of volume growth of the load-bearing solidified matter (hydrated cement) whose properties are nonaging and are

  8. 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.

  9. 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.

  10. 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

  11. Impulsive radon emanation on a creeping segment of the San Andreas fault, California

    USGS Publications Warehouse

    King, C.-Y.

    1985-01-01

    Radon emanation was continuously monitored for several months at two locations along a creeping segment of the San Andreas fault in central California. The recorded emanations showed several impulsive increases that lasted as much as five hours with amplitudes considerably larger than meteorologically induced diurnal variations. Some of the radon increases were accompanied or followed by earthquakes or fault-creep events. They were possibly the result of some sudden outbursts of relatively radon-rich ground gas, sometimes triggered by crustal deformation or vibration. ?? 1985 Birkha??user Verlag.

  12. Deformation-induced hydrolysis of a degradable polymeric cylindrical annulus

    PubMed Central

    Soares, João S.; Rajagopal, Kumbakonam R.; Moore, James E.

    2009-01-01

    A thermodynamically consistent framework for describing the response of materials undergoing deformation-induced degradation is developed and applied to a particular biodegradable polymer system. In the current case, energy is dissipated through the mechanism of hydrolytic degradation and its effects are incorporated in the constitutive model by appropriately stipulating the forms for the rate of dissipation and for the degradation-dependent Helmholtz potential which changes with the extent of the degradation of the material. When degradation does not occur, the response of the material follows the response of a power-law generalized neo-Hookean material that fits the response of the non-degraded poly(L-lactic acid) under uniaxial extension. We study the inflation and extension of a degrading cylindrical annulus and the influence of the deformation on the mechanism of degradation and its consequent mechanical response. Depreciation of mechanical properties due to degradation confers time-dependent characteristics to the response of the biodegradable material: the material creeps when subjected to constant loads and stresses necessary to keep a fixed deformation relax. PMID:19680702

  13. 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.

  14. Patterns of brittle deformation under extension on Venus

    NASA Technical Reports Server (NTRS)

    Neumann, G. A.; Zuber, M. T.

    1994-01-01

    The development of fractures at regular length scales is a widespread feature of Venusian tectonics. Models of lithospheric deformation under extension based on non-Newtonian viscous flow and brittle-plastic flow develop localized failure at preferred wavelengths that depend on lithospheric thickness and stratification. The characteristic wavelengths seen in rift zones and tessera can therefore provide constraints on crustal and thermal structure. Analytic solutions were obtained for growth rates in infinitesimal perturbations imposed on a one-dimensional, layered rheology. Brittle layers were approximated by perfectly-plastic, uniform strength, overlying ductile layers exhibiting thermally-activated power-law creep. This study investigates the formation of faults under finite amounts of extension, employing a finite-element approach. Our model incorporates non-linear viscous rheology and a Coulomb failure envelope. An initial perturbation in crustal thickness gives rise to necking instabilities. A small amount of velocity weakening serves to localize deformation into planar regions of high strain rate. Such planes are analogous to normal faults seen in terrestrial rift zones. These 'faults' evolve to low angle under finite extension. Fault spacing, orientation and location, and the depth to the brittle-ductile transition, depend in a complex way on lateral variations in crustal thickness. In general, we find that multiple wavelengths of deformation can arise from the interaction of crustal and mantle lithosphere.

  15. Microstructural evolution of uranium dioxide following compression creep tests: An EBSD and image analysis study

    NASA Astrophysics Data System (ADS)

    Iltis, X.; Gey, N.; Cagna, C.; Hazotte, A.; Sornay, Ph.

    2015-01-01

    Sintered UO2 pellets with relatively large grains (?25 ?m) are tested at 1500 °C under a compressive stress of 50 MPa, at different deformation levels up to 12%. Electron Back Scattered Diffraction (EBSD) is used to follow the evolution, with deformation, of grains (size, shape, orientation) and sub-grains. Image analyses of SEM images are performed to characterize emergence of a population of micron size voids. For the considered microstructure and test conditions, the results show that the deformation process of UO2 globally corresponds to grain boundary sliding, partly accommodated by a dislocational creep within the grains, leading to a highly sub-structured state.

  16. Research the dynamical characteristics of slow deformation waves as a rock massif response to explosions during its outworking

    NASA Astrophysics Data System (ADS)

    Hachay, Olga; Khachay, Oleg; Shipeev, Oleg

    2015-04-01

    As a result of long-term natural geomechanics and geophysical observation data on mines of complex ore rocks, generalization of the non-linear reaction of rock massif to heavy dynamic influences have been established. In addition, pendulum type waves have been observed and the sources of them have been located inside geoblocks of different hierarchic levels (Oparin et al., 2010). At the same time, these waves propagate with wide low (compared with seismic waves) velocity values (Kurlenja et al., 1993; Oparin et al., 2006). Research into the massif state with the use of the dynamic systems theory approach (Naimark et al., 2009; Chulichkov, 2003; Hachay et al., 2010) has been developed to ascertain the criteria of dissipative regimes changing for real rock massifs, which are under heavy man-caused influence. To realize such research we used the data from the seismic record of the Tashtagol mine for the two-year period from June 2006 up to June 2008. We used the space-time coordinates for all dynamic massif event responses, which occurred during that period inside the mine space and for the explosions - values fixed by seismic station energy (Hachay et al., 2010). The phase diagrams of the massif state for the northern and southern parts of the mine space were plotted in coordinates Ev(t) and d(Ev(t))/dt, t - time - in parts of 24 hours, Ev - the dissipated massive seismic energy - in joules. Hachay et al., (2010) analysed the morphology of seismic response phase trajectories on the explosion influences during different serial intervals in the southern part of the mine. In that period, according to data for different explosions in the mine, the majority of the total energy had been injected into the southern part of the mine. Moreover, at the end of 2007, just in the southern part, the strongest rock burst during the whole history of the working mine happened. We developed a new processing method of seismological information in real, which we can use directly in the mine to estimate the changing state of the rock burst in the massif by its outworking. As a result we have selected a typical morphology of massif response phase trajectories, which were locally, over time, in a stable state: on the phase plane the local area presented as a ball of twisted trajectories with some not far removed points from the ball, which had not exceeded energy of more than 105 joules. For some time intervals those removed points exceeded 105 joules, achieving 106 joules and even 109 joules (Hachay et al., 2010). Introduction of the additional velocity parameter of slow deformation wave propagation allowed us, with the use of phase diagrams, to identify the hierarchic structure. Further, we can use that information for the modelling and interpretation of seismic and deformation waves in hierarchic structures (Hachay et al., 2012). That method can be useful in building-up an understanding of the resonance outshooting of catastrophic dynamic events and prevent these events. References 1.Chulichkov A. (2003) Mathematical models of nonlinear dynamics. Moscow: Phismatlit. 294p. 2.Hachay O., Khachay O.Yu., Klimko V., et al. (2010) Reflection of synergetic features of rock massif state under the man-caused influence from the data of a seismological catalogue. Mining Information-Analytic Bulletin, Moscow, Mining book, 6, pp.259-271. 3.Hachay O., Khachay A.Yu. (2012) Research of stress-deforming state of hierarchic medium. Proceedings of the Third Tectonics and Physics Conference at the Institute of the Physics of the Earth 8-12 October 2012, Moscow, IFZ RAS, pp.114-117. 4.Kurlenja M., Oparin V., Vostrikov V. (1993) About forming elastic wave trains by impulse excitation of block medium. Waves of pendulum type U?. DAN USSR, V.133, 4, pp.475-481. 5.Naimark Yu., Landa P. (2009). Stochastic and chaotic oscillations. Moscow, Knigniy dom ,'LIBROKOM', 424 p. 7.Oparin V., Vostrikov V., Tapsiev A. et al. (2006) About one kinematic criterion of forecasting of the limiting massif state with use of seismological data , FTPRPI, 6, pp.3-10.

  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. 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.

  19. 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

  20. A phenomenological model for transient creep behaviors based on the steady state creep properties

    SciTech Connect

    Lee, B.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; Hong, J.H. [Korea Atomic Energy Research Inst., Taejon (Korea, Republic of). Nuclear Structural Steel Lab.] [Korea Atomic Energy Research Inst., Taejon (Korea, Republic of). Nuclear Structural Steel Lab.

    1996-08-01

    Traditionally, empirical equations were used to quantify the primary creep behavior in which the creep rate should not only be a function of test conditions, but also be a function of time. Even though many mathematical formulations were proposed to express the primary creep behavior, those equations are mostly descriptive but not predictive. In the present work, the authors examined the relationship between primary creep and steady state creep by measuring internal stress values with creep strain, using 99.95% pure aluminum specimens at 573 K. There are two important findings: Firstly, there exists a unique relationship among the primary creep rates, the secondary creep rates, and the ratio of the internal stresses to the applied stress. Secondly, the creep equation, including the primary stage as well as the steady state, could be rationalized with two stress terms; the applied stress and the effective stress. It is the aim of this paper to suggest a new constitutive creep rate equation, describing both the normal primary and the steady state creep behaviors, by means of using the effective stress which is changing with primary creep strain. Using this equation, the prediction of the transient creep behavior after a stress change is made, and compared with the experimental data.

  1. Triaxial creep measurements on rock salt from the Jennings dome, Louisiana, borehole LA-1, core {number_sign}8

    SciTech Connect

    Wawersik, W.R.; Zimmerer, D.J.

    1994-05-01

    Tejas Power Company requested that facilities in the Rock Mechanics Laboratory at Sandia National Laboratories be used to assess the time-dependent properties of rock salt from the Jennings dome in Acadia Parish, Louisiana. Nominally 2.5-inch diameter slat core from borehole LA-1, core 8 (depth 3924.8 to 3837.8 ft; 1196.8--1197.1 m) was provided to accomplish two tasks: (1) Using the smallest possible number of experiments, evaluate the tendency of Jennings salt to undergo time-dependent deformation (creep) under constant applied stresses, and compare the creep of Jennings salt with creep data for rock salt from other locations. (2) Assess the applicability of published laboratory-derived creep properties for rock salt from several bedded and domal sites in finite element analyses concerning the design of new gas storage caverns in the Jennings dome. The characterization of Jennings salt followed the same strategy that was applied in earlier laboratory experiments on core from the Moss Bluff dome near Houston, Texas. This report summarizes the relevant details of five creep experiments on a sample from depth 3927.5 ft, the results obtained, and how these results compared with laboratory creep measurements gathered on rock salt from other locations including the West Hackberry, Bryan Mound and Moss Bluff domes. The report also considers the estimates of specific creep parameters commonly used in numerical engineering design analyses.

  2. Effect of hydrogen on the creep behavior of Zr-2.5%Nb alloy at 723 K

    NASA Astrophysics Data System (ADS)

    Kishore, R.

    2009-04-01

    Increased plasticity is reported in Ti alloys, stainless steels and Pd by the introduction of hydrogen. The dissolved hydrogen in zirconium and its alloys which have similar properties as those of titanium and its alloys, can modify the creep properties of the matrix. Hydrogen, formed during the corrosion reaction of Zr-2.5%Nb pressure tube, in a CANDU design nuclear reactor, with the coolant can ingress into the metal matrix. This absorbed hydrogen can lead to an unexpected increase in length and in diameter of the pressure tube. In order to evaluate the effect of hydrogen on the creep behavior of the pressure tube material, tensile specimens with longitudinal and transverse orientations were hydrided to 65 and 160 wt ppm and creep tested at 723 K over a stress range. The combined influence of hydrogen and specimen orientations on creep rate is evaluated, and an attempt is made to explain the results using the deformation mechanisms reported in literature.

  3. 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.

  4. 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.

  5. Creep of Structural Nuclear Composites

    SciTech Connect

    Will Windes; R.W. Lloyd

    2005-09-01

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

  6. Empirical law for fault-creep events

    USGS Publications Warehouse

    Crough, S.T.; Burford, R.O.

    1977-01-01

    Fault-creep events measured on the San Andreas and related faults near Hollister, California, can be described by a rheological model consisting of a spring, power-law dashpotand sliding block connected in series. An empirical creep-event law, derived from many creep-event records analyzed within the constraints of the model, provides a remarkably simple and accurate representation of creep-event behavior. The empirical creep law is expressed by the equation: D(t)= Df [1-1/{ct(n-1)Dfn-1+1}/(n-1)] where D is the value of displacement at time t following the onset of an event, Df is the final equilibrium value of the event displacementand C is a proportionality constant. This discovery should help determine whether the time-displacement character of creep events is controlled by the material properties of fault gouge, or by other parameters. ?? 1977.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Compression creep of filamentary composites

    NASA Technical Reports Server (NTRS)

    Graesser, D. L.; Tuttle, M. E.

    1988-01-01

    Axial and transverse strain fields induced in composite laminates subjected to compressive creep loading were compared for several types of laminate layups. Unidirectional graphite/epoxy as well as multi-directional graphite/epoxy and graphite/PEEK layups were studied. Specimens with and without holes were tested. The specimens were subjected to compressive creep loading for a 10-hour period. In-plane displacements were measured using moire interferometry. A computer based data reduction scheme was developed which reduces the whole-field displacement fields obtained using moire to whole-field strain contour maps. Only slight viscoelastic response was observed in matrix-dominated laminates, except for one test in which catastrophic specimen failure occurred after a 16-hour period. In this case the specimen response was a complex combination of both viscoelastic and fracture mechanisms. No viscoelastic effects were observed for fiber-dominated laminates over the 10-hour creep time used. The experimental results for specimens with holes were compared with results obtained using a finite-element analysis. The comparison between experiment and theory was generally good. Overall strain distributions were very well predicted. The finite element analysis typically predicted slightly higher strain values at the edge of the hole, and slightly lower strain values at positions removed from the hole, than were observed experimentally. It is hypothesized that these discrepancies are due to nonlinear material behavior at the hole edge, which were not accounted for during the finite-element analysis.

  12. Effects of the regimes of heat treatment and of the magnitude and temperature of the inducing deformation on the characteristics of the shape-memory effect in the 43Ti-46Ni-9Nb-2Zr alloy

    NASA Astrophysics Data System (ADS)

    Popov, N. N.; Sysoeva, T. I.; Shchedrina, E. V.; Presnyakov, D. V.; Grishin, E. N.

    2015-06-01

    The influence of the types and regimes of heat treatment, as well as of the temperature and magnitude of the shape-memory-inducing deformation on the structural changes, martensitic transformations, parameters of the crystal lattice and substructure, and the mechanical and thermomechanical characteristics have been studied in the new shape-memory alloy of composition 43Ti-46Ni-9Nb-2Zr (at %). The conditions of the appearance and realization of the shape-memory effect have been determined. The relationship between the structural features and the values of the thermomechanical characteristics of the alloy has been revealed. The regimes of the heat treatment and of the deformation that induces the shape-memory effect, which provide in this alloy the obtaining of high thermomechanical characteristics, have been determined.

  13. 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.

  14. Creep and thermal effects in aging solids

    SciTech Connect

    Anderson, C.A.

    1983-01-01

    The purpose of this paper is to describe three constitutive models that have been developed for rocks, concrete and filled polymers to represent creep, thermal, stress, and aging effects. Also described in the paper are how these constitutive models are being used to numerically predict the behavior of solids in such diverse situations as aging creep of concrete structures and creeping mantle convection. In all cases low strain rate, compressive material behavior is the main interest.

  15. The Rate of Creep Deformation St Edmund's College, Cambridge

    E-print Network

    Cambridge, University of

    of Cambridge. The research described herein was conducted under the supervision of Professor H. K. D. H Acknowledgement I would like to express my sincere gratitude to Professor H. K. D. H. Bhadeshia for his guidance and Yokota Tomuyuki. It was an enormous pleasure to work with them. Thanks also to my friends

  16. A phenomenological model for transient creep behaviors based on the steady state creep properties

    Microsoft Academic Search

    Bong Sang Lee; Soo Woo Nam; Jun Hwa Hong

    1996-01-01

    Traditionally, empirical equations were used to quantify the primary creep behavior in which the creep rate should not only be a function of test conditions, but also be a function of time. Even though many mathematical formulations were proposed to express the primary creep behavior, those equations are mostly descriptive but not predictive. In the present work, the authors examined

  17. 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

  18. 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

  19. 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

  20. 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.

  1. 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.

  2. Biaxial Thermal Creep of V-4Cr-4Ti AT 700C and 800C

    SciTech Connect

    Kurtz, Richard J.; Hamilton, Margaret L.

    2000-09-01

    A study of the thermal creep properties of V-4Cr-4Ti was performed using pressurized tube specimens. Creep tubes nominally 4.57 mm OD by 0.25 mm wall thickness were pressurized with high-purity helium gas to mid-wall effective stresses below the uniaxial yield strength. Specimens were heated to 700 and 800C in an ultra-high vacuum furnace and periodically removed to measure the change in OD with a high-precision laser profilometer. The secondary creep rate was found to be power-law dependent on the applied stress with a stress exponent of 3.7 at 700C and 2.7 at 800C. The average activation energy for creep of V-4Cr-4Ti was 299 kJ/mole, which is quite close to the activation energy for self-diffusion in pure vanadium in this temperature regime. The predominant mechanism of creep deformation for the conditions employed in this study is most likely climb assisted dislocation motion.

  3. 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

  4. Creep and plasticity of glacier ice: a material science perspective Paul DUVAL, Maurine MONTAGNAT, Fanny GRENNERAT, Jerome WEISS,

    E-print Network

    Weiss, Jérôme

    Creep and plasticity of glacier ice: a material science perspective Paul DUVAL, Maurine MONTAGNAT the plasticity of ice have been made during the past 60 years with the development of studies of the flow experimental investigations clearly show that the plastic deformation of the ice single crystal and polycrystal

  5. Tertiary creep test by ring shear apparatus in predicting initiation time of rainfall-induced-shallow landslide

    Microsoft Academic Search

    A. Dok; H. Fukuoka

    2010-01-01

    Landslides are complex geo-disaters that frequently occur due to certain causes, but only one trigger such as earthquake or heavy rainfall or other related natural phenomenas. A slope failure seldom occurs without any creep deformation. Failure time of a slope as found by Fukuzono (1985) and Siato (1965) based on graphical analysis of extensometer monitoring data through large scale flume

  6. Rupture and creep behaviours of subduction interface controlled by fault zone heterogeneity

    NASA Astrophysics Data System (ADS)

    Wang, Kelin; Brown, Lonn; Gao, Xiang; Bilek, Susan

    2015-04-01

    The behaviour of fault slip varies tremendously, ranging from seismic rupture to aseismic creep. We explore the role of fault zone heterogeneity in controlling large-scale (> 100 km in strike dimension) rupture and creep behaviours of subduction faults. Geometrically smooth subduction faults can (although not always) provide relatively homogeneous structural and stress conditions to allow large fault patches to be locked over prolonged periods and then rupture in great earthquakes. During the rupture, however, frictional heterogeneities arising from lithological changes, pore-fluid pressure variations, and low-amplitude geometrical irregularities always cause a very heterogeneous distribution of stress drop. Although some parts of the fault may undergo high or complete stress drop (local weakening), many other parts undergo very low stress drop or stress increase (local strengthening). The mixing of stress drop and increase in different parts of the rupture zone makes the average stress drop in each great earthquake very small, of the order of a couple of MPa, as widely observed in seismological studies. We use the 2011 Mw=9 Tohoku-oki earthquake to demonstrate this averaging effect. Geometrically extremely rough subduction faults, such as those featuring multiple subducting seamounts, provide very heterogeneous structural and stress conditions that promote creep and numerous small earthquakes. A global inspection of geodetically constrained locking and creeping states of subduction zones indicates that these extremely rough faults all tend to creep (Wang and Bilek, 2014). Depending on the degree of roughness and other geological conditions (e.g., sediment and fluid), some of the rough faults may host a mixture of seismic and aseismic patches and may exhibit a variety of creep behaviour ranging from steady creep to transient creep pulses (i.e., slow slip events) of different time scales. It can be envisioned that the heterogeneity in these rough faults is generally in the form of 3D deformation in a complex zone of damage along the interface and cannot be adequately approximated by heterogeneous rate-state friction. It is also important to recognize that these creeping rough faults are not "weakly coupled", nor are the highly seismic smooth faults "strongly coupled". A global examination of frictional heating of subduction faults indicate that the creeping rough faults dissipate more heat and are statically stronger, that is, they creep against greater resistance (called strong creep) than the stress required to cause a smooth fault to rupture in great earthquakes (Gao and Wang, 2014). This observation supports the notion that these faults creep as a result of geometrical irregularities forcing through a damage zone, very different from frictional creep due to the presence of week fault gouge (called weak creep). Gao, X., and K. Wang (2014), Science, 345, 1038-1041. Wang, K., and S. L. Bilek (2014), Tectonophysics, 610, 1-24.

  7. Creep buckling of axially compressed circular cylindrical shells of a zirconium alloy: Experiment and computer simulation

    NASA Astrophysics Data System (ADS)

    Korobeynikov, S. N.; Torshenov, N. G.; Lyubashevskaya, I. V.; Larichkin, A. Yu.; Chunikhina, E. V.

    2014-01-01

    Experiments were performed to study the deformation and buckling of axially compressed circular cylindrical shells of Zr2.5Nb zirconium alloy under creep conditions. Computer simulation using the MSC.Marc 2012 software was conducted by step-by-step integration of the equations of quasistatic deformation of thin shells using Norton's law of steady creep. The results of the experiment and computer simulation show that the buckling modes are a combination of axisymmetric bulges located near one end or both ends of the shell and axisymmetric buckling modes with the formation of three or four waves in the circumferential direction. A comparison is made of the time dependences of the axial strain of the shells obtained in the experiment and by computer simulation. It is shown that for large axial compressive stresses, these dependences are in satisfactory agreement. For lower values of these stresses, the difference between the theoretical and experimental dependences is greater.

  8. 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.

  9. Non-contact measurements of creep properties of niobium at 1985?°C

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    The stress exponent in the power-law creep of niobium at 1985?°C was measured by a non-contact technique using an electrostatic levitation facility at NASA MSFC. This method employs a distribution of stress to allow the stress exponent to be determined from each test, rather than from the curve fit through measurements from multiple samples that is required by conventional methods. The sample is deformed by the centripetal acceleration from the rapid rotation, and the deformed shapes are analyzed to determine the strain. Based on a mathematical proof, which revealed that the stress exponent was determined uniquely by the ratio of the polar to equatorial strains, a series of finite-element analyses with the models of different stress exponents were also performed to determine the stress exponent corresponding to the measured strain ratio. The stress exponent from the ESL experiment showed a good agreement with those from the literature and the conventional creep test.

  10. 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.

  11. 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.

  12. Evolution of Strain Partitioning during Creep of Carrara Marble

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  13. Creep events at the brittle ductile transition

    NASA Astrophysics Data System (ADS)

    Lavier, Luc L.; Bennett, Richard A.; Duddu, Ravindra

    2013-09-01

    We present an analytic formulation to model creep events at the transition between brittle behavior in the crust and viscous behavior in ductile shear zones. We assume that creep events at the brittle ductile transition (BDT) are triggered by slip on optimally oriented fractures or network of fractures filled with weak ductile material. These events are expressed as transient flow in ductile shear zones likely aided by the release of crustal fluids. We show that the creep in the shear zone can be modeled as the motion of a forced damped oscillator composed of a brittle viscoelastic crust, a ductile shear zone and a creeping zone of fractures at the BDT. The time scale of the events varies between seconds to thousands of years depending on the viscous, elastic and brittle-plastic properties of the fractured BDT, the shear zone and the crust. The nature of the events depends on the aspect ratio, ? of the shear zone thickness, Hw to the length of the fractured zone, w. We find that thick shear zones with small fractures at the BDT are stiff and generate creep oscillations. Thin shear zones with well-connected fractures over a large width have very small stiffness and are well lubricated. They generate slow creep events or steady creep event. The former are similar to transient slip events and the latter to creep at the far field tectonic rates. The viscosity of the shear zone, ?w enhances lubrication if it is small and stiffness if it is large.

  14. 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

  15. Interaction of Bearing and Tensile Loads on Creep Properties of Joints

    NASA Technical Reports Server (NTRS)

    Bodine, E G; Carlson, R L; Manning, G K

    1956-01-01

    The interaction of bearing and tensile loads on the creep behavior of joints was studied. A specimen was designed for this study which possessed some of the general features of pin and rivet joint connections and an apparatus was constructed to apply both bearing and tensile loads to the joint model. Deformation measurements were made by use of a photogrid printed on the joint model.

  16. Effect of aqueous and carbonic fluids on the dislocation creep strength of quartz

    Microsoft Academic Search

    Linda J. Chernak; Greg Hirth; Jane Selverstone; Jan Tullis

    2009-01-01

    Dislocation creep experiments conducted on quartzite indicate that the presence of CO2 can cause strengthening or weakening depending on the oxygen fugacity (fO2) of the deformation environment. Under oxidizing conditions (ferrosilite-hematite-quartz), the presence of CO2 reduces the water fugacity (fH2O) and results in strengthening of the quartz. Under moderately reducing conditions (?Ni-NiO), CO2 reacts with H2 from the sample assembly

  17. Experimental pressure solution compaction of chalk in aqueous solutions Part 1. Deformation behavior and chemistry

    E-print Network

    Experimental pressure solution compaction of chalk in aqueous solutions Part 1. Deformation solution creep, chalk from the Paris basin (France) was deformed in a tri- axial press with fluids. The major goal of this investigation was to study the physico-chemical reactions that occur when chalk

  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. Mechanisms of Dynamic Deformation and Failure in Ultra-High Molecular Weight Polyethylene Fiber-Polymer

    E-print Network

    Wadley, Haydn

    in the fiber direction is ~25 times greater than that of conventional steels, weak (van der Waals) bonds direction. This weak intermolecular strength also leads to creep deformation under prolonged loading properties and dynamic deformation and failure mechanisms during the ballistic impact of these UHMWPE

  20. 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.

  1. Developing and testing models for creep of polycrystalline ice: new laboratory approaches

    NASA Astrophysics Data System (ADS)

    Prior, D. J.; Caswell, T. E.; Durham, W. B.; Golding, N.; Goldsby, D. L.; Lilly, K.; Piazolo, S.; Seidemann, M.; Vaughan, M.; Wilson, C.

    2013-12-01

    Laboratory creep experiments provide invaluable constraints on ice rheology. If laboratory and natural deformation rates are similar then experiments that use 'natural' glacial ice as starting materials are appropriate. Often however, laboratory data have to be extrapolated across orders of magnitude of strain-rate to be applicable to natural deformation conditions. Since the strain-rate sensitivities of grain-size insensitive (GSI: e.g. dislocation creep) and grain-size sensitive (GSS: e.g. grain boundary sliding and/or diffusion creep) creep mechanisms are different, experiments that simulate natural behavior need starting materials with a different mean grain-size to natural samples in order to balance correctly the relative contributions of GSI and GSS mechanisms. Of particular interest are fine-grained (~1 - 500?m) polycrystalline ice samples that can be used in the laboratory to understand the mechanisms and mechanics associated with slower background creep rates in natural systems. Furthermore very fine-grained (<150?m) enable quantification of GSS creep where it is dominant. These data can be integrated with the larger data set from coarse-grained ice to generate mechanism maps that enable the microstructural and rheological effects of strain-rates changes with time (tidal cycle, seasonal etc) to be assessed. Although we have been able to get mechanical data for fine-grained ices for some time, good quality microstructural and fabric data have been harder to obtain. We have adapted the electron backscatter diffraction (EBSD) method in the scanning electron microscope so that we can collect quantitative microstructural maps and fabric data from fine-grained ice in a relatively routine manner. We will outline the methods used in sample preparation and data acquisition. We will use EBSD data to illustrate the microstructural differences in samples fabricated by different methods. Additionally we will show microstructural data related to fine-grained ice deformed in well-constrained laboratory experiments and will discuss the implications of these data for understanding deformation mechanisms and rheology of ice in natural systems.

  2. 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.

  3. 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.

  4. InSAR measurements around active faults: creeping Philippine Fault and un-creeping Alpine Fault

    NASA Astrophysics Data System (ADS)

    Fukushima, Y.

    2013-12-01

    Recently, interferometric synthetic aperture radar (InSAR) time-series analyses have been frequently applied to measure the time-series of small and quasi-steady displacements in wide areas. Large efforts in the methodological developments have been made to pursue higher temporal and spatial resolutions by using frequently acquired SAR images and detecting more pixels that exhibit phase stability. While such a high resolution is indispensable for tracking displacements of man-made and other small-scale structures, it is not necessarily needed and can be unnecessarily computer-intensive for measuring the crustal deformation associated with active faults and volcanic activities. I apply a simple and efficient method to measure the deformation around the Alpine Fault in the South Island of New Zealand, and the Philippine Fault in the Leyte Island. I use a small-baseline subset (SBAS) analysis approach (Berardino, et al., 2002). Generally, the more we average the pixel values, the more coherent the signals are. Considering that, for the deformation around active faults, the spatial resolution can be as coarse as a few hundred meters, we can severely 'multi-look' the interferograms. The two applied cases in this study benefited from this approach; I could obtain the mean velocity maps on practically the entire area without discarding decorrelated areas. The signals could have been only partially obtained by standard persistent scatterer or single-look small-baseline approaches that are much more computer-intensive. In order to further increase the signal detection capability, it is sometimes effective to introduce a processing algorithm adapted to the signal of interest. In an InSAR time-series processing, one usually needs to set the reference point because interferograms are all relative measurements. It is difficult, however, to fix the reference point when one aims to measure long-wavelength deformation signals that span the whole analysis area. This problem can be solved by adding the displacement offset in each interferogram as a model parameter and solving the system of equations with the minimum norm condition. This way, the unknown offsets can be automatically determined. By applying this method to the ALOS/PALSAR data acquired over the Alpine Fault, I obtained the mean velocity map showing the right-lateral relative motion of the blocks north and south of the fault and the strain concentration (large velocity gradient) around the fault. The velocity gradient around the fault has along-fault variation, probably reflecting the variation in the fault locking depth. When one aims to detect fault creeps, i.e., displacement discontinuity in space, one can additionally introduce additional parameters to describe the phase ramps in the interferograms and solve the system of equations again with the minimum norm condition. Then, the displacement discontinuity appears more clearly in the result at the cost of suppressing long-wavelength displacements. By applying this method to the ALOS/PALSAR data acquired over the Philippine Fault in Leyte Island, I obtained the mean velocity map showing fault creep at least in the northern and central parts of Leyte at a rate of around 10 mm/year.

  5. Nondestructive detection of creep and creep-fatigue damages in welded joints by ultrasonic technique

    SciTech Connect

    Okazaki, M. [Nagaoka Univ. of Technology (Japan). Dept. of Mechanical Engineering; Hashimoto, M. [Babcock Hitachi K.K., Kure (Japan). Kure Research Center

    1995-12-01

    The non-destructive detection of creep and creep-fatigue damages was studied by employing an ultrasonic technique, taking account of the applicability to welded joints. Particular attention was paid to the change of ultrasonic wave attenuation and that of the anisotropy during the creep and creep-fatigue failures. The experimental results, using the welded joint of 2 1/4 Cr-1 Mo steel and the dissimilar metal welded joint between 2 1/4 Cr-1 Mo and Type 316 steels, showed that the development process of creep damage ad that of creep-fatigue one were successfully reflected on the change of the ultrasonic attenuation as follows: the ultrasonic wave attenuation remarkably increased with creep and the creep-fatigue damages, especially at the final rupture zone, while the change was not noticeable at the other zones accompanying with negligible damage. In addition, the attenuation exhibited a comparable change to the other useful engineering parameters, such as the A-parameter; i.e., the change was satisfied,or competent for detection. These results indicate that the ultrasonic attenuation properties provide the useful information to detect the creep and creep-fatigue damages nondestructively, as well as to find out the dangerous sites to failure, in welded joints.

  6. 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.

  7. 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)

  8. Models for rupture mechanics of plate boundaries and crustal deformation

    NASA Technical Reports Server (NTRS)

    Nur, A.

    1983-01-01

    The role of pull aparts and pushups in transcurrent systems, the rotation of faults and blocks within transcurrent fault systems, the role of accretion tectonics in plate boundary deformation, and power law creep behavior and the yielding at plate boundaries were investigated.

  9. Edge dislocation climb over non-deformable circular inclusions

    Microsoft Academic Search

    J. H. Holbrook; W. D. Nix

    1974-01-01

    Edge dislocation climb over non-deformable circular inclusions is studied as a possible rate limiting mechanism for creep of dispersion strengthened metals. The inclusion and matrix are assumed to exhibit no misfit and to be elastically isotropic, with the inclusion, more rigid than the matrix. The climb motion of the dislocation is assumed to be diffusion controlled and very much slower

  10. 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

  11. 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

  12. 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

  13. Post-deformational annealing of calcite rocks

    NASA Astrophysics Data System (ADS)

    Barnhoorn, Auke; Bystricky, Misha; Burlini, Luigi; Kunze, Karsten

    2005-07-01

    The evolution of microstructure and crystallographic preferred orientation (CPO) during post-deformational annealing was studied on three calcite rock types differing in purity and grain size: Carrara marble (98% calcite, mean grain size of 115 ?m), Solnhofen limestone (96%, 5 ?m) and synthetic calcite aggregates (99%, 7 ?m). Samples were first deformed in torsion at 727 °C at a shear strain rate of 3 × 10 - 4 s - 1 to a shear strain of 5 and subsequently heat-treated at 727 °C for various durations between 0 and 24 h. Microstructures and CPOs were analysed by optical microscopy, image analysis and electron backscatter diffraction (EBSD). All rock types deformed in the dislocation creep field at the same applied conditions, but their microstructures and CPOs after deformation and after annealing differed depending on starting grain size and material composition. In Carrara marble and in the synthetic calcite aggregate, a strong CPO developed during deformation accompanied by dynamic recrystallisation with significant changes in grain size. During annealing, widespread grain growth and subtle changes of CPO occurred, and equilibrated foam microstructures were approached after long annealing times. The CPO is the only feature in annealed samples indicating an earlier deformation phase, although it is not always identical to the CPO formed during deformation. In the more impure Solnhofen limestone, secondary phases on grain boundaries suppressed grain boundary mobility and prevented both the formation of a recrystallisation CPO during deformation and grain size modification during deformation and annealing.

  14. Rheological Evolution of Faults During the Seismic Cycle: the Role of Pressure Solution Creep and Sealing Processes

    NASA Astrophysics Data System (ADS)

    Gratier, J.; Renard, F.; Richard, J.; Doan, M.; Vial, B.

    2011-12-01

    Active faults in the upper crust can either slide steadily by aseismic creep, or abruptly causing earthquakes. However, seismic and aseismic processes are often closely related: i.e. earthquakes are often followed by afterslip creep. In this case, postseismic displacement rates progressively decrease with time after several months, years or decades, and may reach an equivalent geodetic moment greater than the seismic moment released by the earthquake itself. In parallel, evidence of coseismic rock damage and postseismic healing of the same fault zone are recorded. So, at least at regional scale, postseismic healing rate and displacement rate seems to slow down similarly with time. Several questions arise from such observations: how seismic fracturing could trigger, or accelerate, afterslip creep? and why this effect progressively slows down with time? Conjugate studies of naturally deformed zone at depth and experimental deformation bring some answers. Microstructural studies of samples collected from the San Andreas Fault Observatory at Depth (SAFOD) show that pressure solution creep, a stress driven mass transfer process, accommodates at least part of the aseismic creep of the San Andreas Fault. Mass transfer occurs from solution cleavage to fracture. Moreover, the creep rate was accelerated by the last M6 Parkfield event. Consequently pressure solution is clearly associated with fracturing process. Here, we present pressure solution indenter experiments that show how grain-scale fracturing induced by dynamic stress loading drastically accelerates the displacement rate accommodated by pressure solution creep: fracturing opens new paths for solute transport along fluid-filled fractures, which decreases the distance of diffusion. However, as the fractures progressively seal, this effect disappears as sealing increases the distance of mass transfer and, consequently, reduces the displacement rate. We investigate the time-dependent evolution of indenter displacement after dynamic stress loading (i.e. ball drop on the indenter) and compare it with postseismic non-linear displacement in nature. Experimental displacement/time relations can most often be fitted by power laws with some variations in the power exponents that depend on the roughness of the dissolution surface, the nature of the minerals, the texture and initial porosity of the rocks. In conclusion, both observation of natural deformation and experimental results show the crucial role of pressure solution creep and sealing processes in the dynamic interaction of pressure solution and fracturing: fracturing associated with earthquakes activates pressure solution creep rate by reducing the distance of mass transfer; and dissolution increases soluble species content in the fluid facilitating the progressive healing of the coseismic fracture network and strengthening the fault.

  15. The kinetics of microstructural evolution during deformation of calcite

    NASA Astrophysics Data System (ADS)

    Austin, Nicholas; Evans, Brian

    2009-09-01

    There is a strong coupling between the microstructure and the strength of rocks that is thought to play a key role in the evolution of shear zones and in our ability to interpret the mechanics of natural deformation processes. To investigate the microstructural evolution of calcite-rich rocks, we have performed a series of hydrostatic and deformation experiments on synthetic calcite aggregates at 1023 K and 300 MPa. The mechanical data from our experiments were broadly consistent with a composite flow law for concurrent dislocation and diffusion creep. Recrystallization rates responded to the deformation conditions. When the bulk strain rate was dominated by diffusion creep, calcite grains grew at the same rate as occurs by normal grain growth under isostatic conditions. When the dominant deformation mechanism was dislocation creep, the matrix grain size was reduced at a rate that varied directly with product of stress, strain rate, and the square of grain size. Thus, reduction rate was proportional to mechanical work rate. If the stable grain size achieved during deformation depends on the product of stress and strain rate, rather than stress alone, then that grain size is an indication of the work rate and can be used as a paleowattmeter. Following this line of thought suggests that the gradient of recrystallized grain sizes that is often observed in the highly deformed portions of shear zones would not require a gradient in stress but could also be explained by material softening, resulting in locally elevated strain rates under constant stresses.

  16. A model for analysis of the effect of final annealing on the in- and out-of-reactor creep behavior of Zircaloy cladding

    SciTech Connect

    Limbaeck, M. [ABB Atom AB, Vaesteraas (Sweden). Nuclear Fuel Div.; Andersson, T. [AB Sandvik Steel, Sandviken (Sweden)

    1996-12-31

    The creep behavior of Zircaloy cladding materials depends on materials texture, degree of recrystallization, and chemical composition. This study is devoted mainly to the analysis of the effect of the final annealing on the creep characteristics. For this purpose, data from a series of thermal creep tests are presented and evaluated. The out-of-reactor tests are performed under internal pressurization, and the test matrix covers seven conditions with temperatures from 330 to 400 C and hoop stresses between 80 and 160 MPa. Three lots of Zircaloy-2 claddings and one lot of Zircaloy-4 are considered. The difference between the three Zircaloy-2 lots is in their final annealing conditions. The claddings are either stress relief annealed (SRA), recrystallization annealed (RXA), or partially recrystallization annealed (PRXA). The materials used when fabricating the Zircaloy-2 claddings are from the same ingot, and the chemical compositions of the three types of claddings are almost identical. The Zircaloy-4 cladding included in the test is SRA, and the tin content in this material is similar to that in the Zircaloy-2 materials. The creep data are analyzed by separating the primary and the secondary creep. In this analysis, the Matsuo creep model, which accounts for both primary and secondary creep, is modified, calibrated, and verified using the new thermal creep data. Based on in-reactor data, the thermal creep model is extended to cover also the creep behavior under irradiation. The claddings considered in the in-reactor test were of both SRA and RXA types, and the experiments were made under external pressure. It is observed that for moderate hoop stresses the measured hoop creep rates, both out-of-reactor and in-reactor, decrease with increasing final annealing temperature. However, for higher stresses, the steady state creep rate has a minimum for partially recrystallized claddings.

  17. Role of interfacial and matrix creep during thermal cycling of continuous fiber reinforced metal-matrix composites

    SciTech Connect

    Dutta, I.

    2000-03-14

    A uni-dimensional micro-mechanical model for thermal cycling of continuous fiber reinforced metal-matrix composites is developed. The model treats the fiber and matrix as thermo-elastic and thermo-elasto-plastic-creeping solids, respectively, and allows the operation of multiple matrix creep mechanisms at various stages of deformation through the use of unified creep laws. It also incorporates the effect of interfacial sliding by an interface-diffusion-controlled diffusional creep mechanism proposed earlier (Funn and Dutta, Acta mater., 1999, 47, 149). The results of thermal cycling simulations based on a graphite fiber reinforced pure aluminum-matrix composite were compared with experimental data on a P100 graphite-6061 Al composite. The model successfully captured all the important features of the observed heating/cooling rate dependence, strain hysteresis, residual permanent strain at the end of a cycle, as well as both intrusion and protrusion of the fiber-ends relative to the matrix at the completion of cycling. The analysis showed that the dominant deformation mechanism operative in the matrix changes continually during thermal cycling due to continuous stress and temperature revision. Based on these results, a framework for the construction of a transient deformation mechanism map for thermal excursions of continuous fiber composites is proposed.

  18. Deformation characteristics of the heel region of the shod foot during a simulated heel strike: The effect of varying midsole hardness

    Microsoft Academic Search

    P. Aerts; D. De Clercq

    1993-01-01

    Impact tests using a pendulum were performed on the shod heel region of nine subjects. Both soft? and hard?soled shoes were used. The deformations involved were calculated from the registered decelerations during impact. Thus, load?deformation cycles were recorded for various impact velocities. In contrast to in vivo force?platform recordings, peak loadings for the soft? and hard?soled conditions differed significantly (614

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  20. Effects of processing history on the creep strength of Nb-1Zr

    SciTech Connect

    Horak, J.A.; Egner, L.K.

    1993-06-01

    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 temperatures required (e.g., >1200 K). The high power densities and temperatures at which these reactors must operate require the use of liquid-metal coolants. The alloy Nb-1 wt % (Nb-1Zr), 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 current space exploration missions. Useful lifetimes of these power systems are limited by creep deformation in the reactor core. Nb-1Zr sheet procured to American Society for Testing and Materials (ASTM) specifications for rector 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 much less of an effect 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.

  1. Creep Failure of Roof Stratum Above Mined-Out Area

    NASA Astrophysics Data System (ADS)

    Wang, J.-A.; Li, D. Z.; Shang, X. C.

    2012-07-01

    By taking into account the rheological behavior of the rock mass, the creep failure of a roof stratum seated on pillars in mined-out area is analyzed through a newly developed visco-elastic model. The time-dependent deflection of the roof stratum is obtained by numerical inversion of Laplace transform. The study shows that when creep properties of both the pillars and roof stratum are considered, the expected deflection in the roof stratum increases with time. Consequently, the roof would fail when the critical tensile stress is reached as the result of the increased deflection. To demonstrate the present analytical procedure, the failure time of roof stratum of the Xingtai Gypsum Mine in China was estimated, and the results obtained agreed with the observation. The case study indicates that the analytic approach provides a new way to assess the potential impact of the time-dependence of the roof stratum deformation and is useful in predicting its stability above a mined-out area.

  2. 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

  3. Activation volume for dislocation creep of forsterite and of iron-free enstatite

    NASA Astrophysics Data System (ADS)

    Bystricky, M.; Bejina, F.; Baticle, J.

    2013-12-01

    A good knowledge of the mechanical behavior of olivine and enstatite at high pressure and high temperature is essential to model Earth upper mantle dynamics. In this study, we have performed deformation experiments on forsterite and on iron-free enstatite polycrystalline aggregates at upper mantle pressures and temperatures. Fine-grained forsterite powders were obtained by crushing a commercial forsterite in WC or zirconia grinders and dried at high temperature. Enstatite powders were synthesized by solid state reaction between mixed fine-grained powders of silica and forsterite in a conventional furnace. The powders were sintered by Spark Plasma Sintering (SPS) at 1000-1300°C and 100 MPa. We obtained aggregates with very low porosities (>99% dense), low water content and well equilibrated microstructures with mean grain sizes of a few microns. Compression deformation experiments were conducted on both types of aggregates in a D-DIA apparatus coupled with synchrotron white X-ray beam at the X17-B2 beamline at the National Synchrotron Light Source (Brookhaven National Laboratory, NY, USA). Strain and stress were measured in situ during deformation. Macroscopic strains were determined by measurements of sample shortening on X-ray radiographies. Stress and pressure were determined from the analysis of 5 to 8 diffraction peaks in the X-ray diffractograms of forsterite or enstatite collected on detectors arranged in different orientations with respect to the maximum principal stress. Experiments were performed at pressures between 3 and 11 GPa and temperatures ranging from 1100 to 1300°C. 14 different samples were deformed to total strains of up to 30% with deformation rates ranging from 8 10-6 to 6 10-5 s-1. Microstructures analyzed using high resolution SEM showed features characteristic of dislocation creep. Analysis of the deformation data for forsterite at 5-7 GPa yielded a stress exponent of 2.5 to 3 at different temperatures, similar to values obtained at room pressure (Relandeau, 1981). The apparent activation energy appears lower than for forsterite or San Carlos olivine at low pressures but is subject to large errors due to the diffficulty to control temperature precisely. An activation volume V* of 8 cm3/mol was determined at constant temperature (1100°C and 1200°C). Extrapolation of the data using V* to low pressures gives strengths that are consistent with those calculated using low pressure flow laws for olivine. Interestingly, this V* value is intermediate between the activation volumes for forsterite single crystals oriented for [100](010) slip, which dominates at low pressures and high temperatures, and those oriented for [001](010) slip, which becomes increasingly active at high pressures (15 and 0 cm3/mol, respectively; Raterron et al. 2011). Iron-free enstatite aggregates were deformed in the ortho- and high clino- enstatite fields. Results indicate that orthoenstatite has a stress exponent of 3-4. It tends to be stronger than forsterite, but the strength contrast between the two phases depends on pressure and temperature conditions. We will discuss the effect of pressure on the rheology of enstatite and on the relative viscosities of enstatite and forsterite.

  4. Prediction of creep of polymer concrete

    SciTech Connect

    Khristova, Yu.; Aniskevich, K. [Central Lab. of Physicochemical Mechanics, Sofia (Bulgaria)

    1995-11-01

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

  5. Modeling creep behavior of fiber composites

    NASA Technical Reports Server (NTRS)

    Chen, J. L.; Sun, C. T.

    1988-01-01

    A micromechanical model for the creep behavior of fiber composites is developed based on a typical cell consisting of a fiber and the surrounding matrix. The fiber is assumed to be linearly elastic and the matrix nonlinearly viscous. The creep strain rate in the matrix is assumed to be a function of stress. The nominal stress-strain relations are derived in the form of differential equations which are solved numerically for off-axis specimens under uniaxial loading. A potential function and the associated effective stress and effective creep strain rates are introduced to simplify the orthotropic relations.

  6. Experimental creep buckling of aluminum cylinders in axial compression

    Microsoft Academic Search

    R. Papirno; R. Goldman

    1969-01-01

    Creep-buckling tests were conducted on aluminum alloy 2024-0 circular cylinders in axial compression at 500° F having nominalR\\/t values of 90 and 50. Creep-buckling times for a variety of applied creep-stress values were compared with theoretical predictions of Gerard's unified theory of creep buckling of columns, plates and shells. In this theory, creep-buckling solutions are analogous to plastic-buckling solutions, provided

  7. Creep and microstructure of magnesium-aluminum-calcium based alloys

    Microsoft Academic Search

    Alan A. Luo; Bob R. Powell; Michael P. Balogh

    2002-01-01

    This article describes the creep and microstructure of Mg-Al-Ca-based magnesium alloys (designated as ACX alloys, where A\\u000a stands for aluminum; C for calcium; and X for strontium or silicon) developed for automotive powertrain applications. Important\\u000a creep parameters, i.e., secondary creep rate and creep strength, for the new alloys are reported. Creep properties of the new alloys are significantly\\u000a better than

  8. 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.

  9. Creep and brittle failure of a protein gel under stress

    E-print Network

    Leocmach, Mathieu; Divoux, Thibaut; Manneville, Sébastien

    2014-01-01

    Biomaterials such as protein or polysaccharide gels are known to behave qualitatively as soft solids and to rupture under an external load. Combining optical and ultrasonic imaging to shear rheology we show that the failure scenario of a protein gel is typical of brittle solids: after a power-law creep regime fully accounted for by linear viscoelasticity and homogeneous deformation, fractures nucleate and grow logarithmically perpendicularly to shear up to sudden rupture. A single equation accounting for those two successive processes nicely captures the full rheological response. The failure time follows a decreasing power-law with the applied shear stress strongly reminiscent of the Basquin law of fatigue for solids. These results are in excellent agreement with recent fiber-bundle models that include damage accumulation on elastic fibers and exemplify protein gels as model brittle soft solids.

  10. A soft creeping robot actuated by dielectric elastomer

    NASA Astrophysics Data System (ADS)

    Zhao, Jianwen; Niu, Junyang; Liu, Liwu; Yu, Jiangcheng

    2014-03-01

    Dielectric elastomer actuator showed significant advantages at high energy density, large deformation with comparing to other artificial muscle. The robot actuated by dielectric elastomer will be more lightweight and have lower cost, which shows great potential in field of future planetary exploration based on a group of micro-robot. In this context, a quite simple structure for creeping was designed to make the robot more lightweight. The actuation unit of the robot is made of an ellipse frame which can expand and contract with membrane under electric field. After joining four actuation units, the robot can move forward in a cooperative manner. Fabrication and some preliminary experiments of the robot were presented and the proposed motion principle was demonstrated.

  11. Effects of Si on deformation behavior and cavitation of coarse-grained Al-4.5Mg alloys exhibiting large elongation

    SciTech Connect

    Hosokawa, H.; Iwasaki, H.; Mori, T. [Himeji Inst. of Technology, Hyogo (Japan). Dept. of Materials Science and Engineering] [Himeji Inst. of Technology, Hyogo (Japan). Dept. of Materials Science and Engineering; Mabuchi, M. [National Industrial Research Inst. of Nagoya (Japan)] [National Industrial Research Inst. of Nagoya (Japan); Tagata, T. [SKY Aluminum Co., Ltd., Fukaya, Saitama (Japan)] [SKY Aluminum Co., Ltd., Fukaya, Saitama (Japan); Higashi, K. [Osaka Prefecture Univ., Sakai, Osaka (Japan). Dept. of Metallurgy and Materials Science] [Osaka Prefecture Univ., Sakai, Osaka (Japan). Dept. of Metallurgy and Materials Science

    1999-04-23

    Deformation behavior and cavitation characteristics of Al-4.5Mg-0.09Si and Al-4.5Mg-0.2Si alloys containing Mg{sub 2}Si particles have been investigated at 613--693 K. Tensile elongations above 350% were obtained in both alloys. Determination of the strain rate sensitivity and activation energy showed that in both alloys viscous dislocation glide creep deformation mechanism was operative and was not influenced by Si content. However, the level of cavitation was increased by the large addition of Si because Mg{sub 2}Si particles promoted more extensive cavity nucleation. Cavitation reduced the post forming tensile properties of both alloys. Investigation of the spatial distribution of cavitation revealed that the intragranular particles were more likely to nucleate cavities than the intergranular particles.

  12. Characteristics of AFRP Bars for Prestressing Applications

    E-print Network

    Medina, Jose

    2012-02-14

    sustainability of beams prestressed with AFRP composite materials. The objective of this research is to effectively characterize the material properties based on the short-term and long-term characteristics of AFRP bars. Tensile, creep-rupture, and relaxation...

  13. Deformation behaviour of feldspar in greenschist facies granitoide shear zones from the Austroalpine basement to the south of the western Tauern window, Eastern Alps

    NASA Astrophysics Data System (ADS)

    Hentschel, Felix; Trepmann, Claudia

    2015-04-01

    Objective of this study is to elucidate the feldspar deformation behaviour at greenschist facies conditions relevant for the long-term rheological properties of continental crust. Uncertainties in models for the rheological properties are partly due to a poor knowledge of the deformation mechanisms taking place in granitoid rocks at inaccessible depth. The deformation behaviour of feldspar, the most abundant mineral in the continental crust, is characterized by an interaction of brittle, dissolution-precipitation and crystal-plastic processes, which is difficult to evaluate in experiments given the problematic extrapolation of experimental conditions to reasonable natural conditions. However, microfabrics of metamorphic granitoid rocks record the grain-scale deformation mechanisms and involved chemical reactions proceeding during their geological history. This usually includes deformation and modification through several stages in space (depth, i.e., P, T conditions) and/or time. For deciphering the rock's record this implies both, challenge and chance to resolve these different stages. Here, we use the deformation record of mylonitic pegmatites from the Austroalpine basement south to the western Tauern window. The structural, crystallographic and chemical characteristics of the feldspar microfabrics are determined via micro-analytical techniques (polarized light microscopy, scanning electron microscopy, SEM, electron back scatter diffraction, EBSD) to identify the relevant deformation mechanisms and deformation conditions. The pegmatites represent a relatively simple Ca-poor granitoid system, mineralogically dominated by albite-rich plagioclase, K-feldspar and quartz. The matrix of the mylonitic pegmatites is composed of alternating monomineralic albite and quartz ribbons defining the foliation. Fragmented tourmaline and K-feldspar porphyroclasts occur isolated within the matrix. At sites of dilation along the stretching lineation K-feldspar porphyroclasts show serrated boundaries to matrix albite grains. In intragranular zones within K-feldspar porphyroclasts, small albite but also K-feldspar grains and "subgrains" (K-feldspar domains with a small misorientation angle to the host K-feldspar porphyroclast) occur. Strain shadows around porphyroclasts are composed of polymineralic aggregates of albite, K-feldspar and quartz. The albite grains in ribbons show a shape preferred orientation (SPO) with a long axis of about 50-100 µm in the foliation plane and EBSD data reveal an absent to very weak crystallographic orientation (CPO). These microfabrics show indication of a sequence of brittle behaviour, localized dislocation glide-controlled deformation and dissolution-precipitation creep of feldspar. Monomineralic quartz ribbons and shear bands show evidence of dislocation glide by a pronounced CPO, implying dislocation creep. The microfabric is interpreted to have evolved during different stages of episodic deformation at transient high stresses with subsequent viscous flow at decreasing stresses.

  14. Experimental deformation and grain growth of pure water ice aggregates

    NASA Astrophysics Data System (ADS)

    Diebold, S.; de Bresser, J. H.; Durham, W. B.; Stern, L. A.

    2010-12-01

    Water ice is the principal constituent of the low density moons of the outer solar system, and the flow behavior of ice is of great importance in dynamic processes on icy moons. Our interest here is on the influence that grain growth has on the flow behavior of ice. By understanding grain growth in combination with flow mechanisms it is possible to reconstruct thermal evolutions and tectonic histories of icy moons. Grain growth is expected to influence the evolution of strength of ice by altering the relative contributions to strain rate by grain-size-sensitive (GSS) creep mechanisms, such as diffusion and grain-boundary sliding, and grain-size-insensitive (GSI) creep mechanisms, such as dislocation creep. In particular, we are interested in examining the so-called field boundary hypothesis wherein grain size evolution and GSI and GSS creep mechanisms eventually lead to a dynamic balance involving a distribution of grain sizes and significant operation of both types creep mechanisms. We studied grain size evolution both during static annealing and during deformation. Static anneals ran for up to two weeks at 213 ? T ? 268 K and hydrostatic pressures 0.1 MPa and 100 MPa. Static grain growth observations allow us to calibrate values for the grain size exponent m and the activation energy Q as used in conventional grain growth laws. We simulated grain growth of ice based on the microphysical model of Kellermann Slotemaker (2006 - PhD thesis Utrecht University, the Netherlands). This model takes into account full grain size distributions. Triaxial deformation experiments were carried out for a variety of starting grain sizes, from 2 to 250 microns, of both narrow and broad size distributions. Small grain sizes promote GSS creep; large sizes promote GSI creep and a mixture of large and small will result in mixed-mechanism deformation, in a ratio that will change as the grain size distribution evolves. All deformation runs were performed at temperatures > 170 K, pressures ranging between 30 MPa and 100 MPa and strain rates between 1e-8/s and 1e-4/s. The fine-grained ice (< 2 microns) which is used for the grain growth experiments and the deformation experiments starting in the GSS-creep field was generated by a special pressure-release technique described by Stern et al. (1997 - J. Geoph. Res, 102). The fine-grained ice material can be cold-pressed resulting in dense ice aggregates with a porosity < 0.5% and randomly oriented ice crystals. Grain sizes, grain size distributions and grain topologies of the different types of experiments were measured by cryogenic SEM and image analysis techniques.

  15. Deformation Mechanisms of Antigorite Serpentinite at Subduction Zone Conditions Determined from Experimentally and Naturally Deformed Rocks

    NASA Astrophysics Data System (ADS)

    Auzende, A. L.; Escartin, J.; Walte, N.; Guillot, S.; Hirth, G.; Frost, D. J.

    2014-12-01

    The rheology of serpentinite, and particularly that of antigorite-bearing rocks, is of prime importance for understanding subduction zone proceses, including decoupling between the downwelling slab and the overriding plate, exhumation of high-pressure rocks, fluids pathways and, more generally, mantle wedge dynamics. We present results from deformation-DIA experiments on antigorite serpentinite performed under conditions relevant of subduction zones (1-3.5 GPa ; 400-650°C). We complemented our study with a sample deformed in a Griggs-type apparatus at 1 GPa and 400°C (Chernak and Hirth, EPSL, 2010), and with natural samples from Cuba and the Alps deformed under blueschist/eclogitic conditions. Our observations on experimental samples of antigorite deformed within its stability field show that deformation is dominated by cataclastic flow; we can only document a minor contribution of plastic deformation. In naturally deformed samples, deformation-related plastic structures largely dominate strain accommodation, but we also document a minor contribution of brittle deformation. When dehydration occurs in experiments, plasticity increases, and is coupled to local embrittlement attributed to hydraulic fracturating due to the migration of dehydration fluids. Our results thus show that semibrittle deformation operates within and above the stability field of antigorite. We also document that the corrugated structure of antigorite has a control on the strain accommodation mechanisms under subduction conditions, with preferred inter and intra-cracking along (001) and gliding along both a and b. Deformation dominated by brittle processes, as observed in experiments, may occur during deformation at elevated (seismic?) strain rates, while plastic deformation, as observed in naturally deformed rocks, may correspond instead to low strain rates instead (aseismic creep?). We also discuss the role of antigorite rheology and mode of deformation on fluid transport.

  16. Creep: An underrated type of mass movement on gently dipping hill slopes - examples from the Eastern Alpine foreland

    NASA Astrophysics Data System (ADS)

    Leopold, Philip; Draganits, Erich; Heiss, Gerhard

    2010-05-01

    Creep, as a very slow type of mass movement was first described by Terzahgi (1950) und Haefeli (1954, 1967). Terzaghi (1950) pointed out that creep represents an own type of mass movement cannot be compared with other types, such as slides, as creep occurs without rupture. According to him other mechanical laws than those that typically apply for mass movements, have to be determined for creep. In a more recent classification of mass movements, creep is described as slow earthflow within the flow type of movement (Highland & Bobrowsky, 2008). Aside from different ways of categorization of landslides, a very slow, imperceptible rate of movement is still considered characteristic for creep. Recent geological and geomorphological investigations of all kind of mass movements in the Eastern Alpine foreland in Austria (Eastern part of the Styrian basin, Oberpullendorf basin, Eisenstadt basin) showed that creep is not only widespread, but is in fact the most common type of mass movement in the Neogene sediments of the basins. More than 180 previously unrecognized zones of creep have been classified. Statistical analysis indicates that in some of the investigated areas creep occurs typically on slopes with gradients between only 10-35°. Movement rates are very low, inclinometer and other measurements show displacement rates in the range of a few centimeters per year. Therefore these mass movements have previously remained unnoticed by the population, local authorities and engineers. As a result there have been misjudgments in the land use-, building- and infrastructure planning which have caused a number of damages. Aside from the immediate implications creep has even more severe and longer term consequences. As a landforming process creep acts very constant over a very long period of time. Already Haefeli (1967) realized that creep occurs at a much lower rate of shear stress than the shear strength of the soil material. The rate of shear stress where creep starts to occur is called critical shear stress or boundary of creep (Prinz & Strauß, 2006). If the critical shear stress impacts the slope material over a long period of time (decades or centuries) the displaced slope material will react by reducing its shear strength. That causes a reduction of the original shear strength in the displaced mass up to the residual shear strength of the former unaffected mass. In case of heavy precipitation, water acts among other effects as an additional weight-component in the displaced mass. Zones of creep with their reduced shear strength are in this case much more vulnerable to form fast moving slides and flows than slopes without creep. This relationship became very obvious during extremely heavy rains in the study area in June/July 2009, causing floods and hundreds of fast mass movements. The induced slides and flows caused severe damages on buildings and infrastructure. Many of these slides and flows occurred in areas that have been affected by creep before. In summary the present investigation shows that creep acts in two different time scales: The short-term effects caused directly by the slow but continuous movement of a slope, and the long-term effects causing reduced stability of the slope related to lowered shear strength. As a result the areas of creep are more vulnerable for fast and much more dangerous mass movements. References: Haefeli, R. (1954): Kriechprobleme im Boden, Schnee und Eis. Wasser- und Energiewirtschaft, 46 Jg., Nr. 3, p. 51-67. Mitt. Vers. Anst. Wassbau Erdbau ETH Zürich, No. 30, Zürich. Haefeli, R. (1967): Kriechen und progressiver Bruch im Schnee, Boden, Fels und Eis. - Schweizerische Bauzeitung, 85(1): p. 1-9, Zürich. Highland, L.M. & Bobrowsky, P. (2008): The Landslide Handbook - A Guide to Understanding Landslides. U.S. Geological Survey Circular 1325, 129 p., Reston, Virginia. Prinz, H. & Strauß, R. (2006): Abriss der Ingenieurgeologie. 671 p., 4. Aufl., Spektrum Akad. - Elsevier, München. Terzaghi, K. (1950): Mechanism of Landslides. In: Application of Geology to Engineering Pract

  17. A microscopic view of deformation-accelerated dynamics in polymer glasses

    NASA Astrophysics Data System (ADS)

    Warren, Mya; Rottler, Joerg

    2010-03-01

    When amorphous polymers are deformed, the slow glassy dynamics resulting from broad distributions of relaxation times becomes accelerated and permits plastic flow. We use molecular dynamics simulations as a computational microscope to obtain insight into the origin of the deformation-accelerated dynamics and its relationship to aging in a model polymer glass. Segmental trajectories are analyzed to identify individual relaxation events, and the full distribution of relaxation times is obtained under three deformation protocols: step stress (creep), step strain, and constant strain rate deformation. As in experiments, the dynamics are accelerated by several orders of magnitude by the deformation, and a narrowing of the distribution of relaxation times during creep is directly observed. Additionally, the acceleration factor describing the transformation of the relaxation time distributions was computed and found to obey a universal dependence on the strain, independent of the age and deformation protocol.

  18. Sintering and creep behavior of plasma-sprayed zirconia- and hafnia-based thermal barrier coatings

    Microsoft Academic Search

    Dongming Zhu; Robert A. Miller

    1998-01-01

    The sintering and creep of plasma-sprayed ceramic thermal barrier coatings under high temperature conditions are complex phenomena. Changes in thermomechanical and thermophysical properties and in the stress response of these coating systems as a result of the sintering and creep processes are detrimental to coating thermal fatigue resistance and performance. In this paper, the sintering characteristics of ZrO2–8wt%Y2O3, ZrO2–25wt%CeO2–2.5wt%Y2O3, ZrO2–6w%NiO–9wt%Y2O3,

  19. 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.

  20. Compression and Creep of Venice Lagoon Sands

    E-print Network

    Sanzeni, Alex

    A laboratory test program was conducted to evaluate the one-dimensional (1D) compression and creep properties of intact sand (and silty-sand) samples from a deep borehole at the Malamocco Inlet to the Venice Lagoon. The ...

  1. Investigations of fault creep in southern California using interferometric synthetic aperture radar and GPS

    NASA Astrophysics Data System (ADS)

    Lyons, Suzanne Noelle

    This dissertation presents an array of remote sensing methods that can be utilized in deformation studies. The main focus is on the detection of creep and how it relates to earthquake hazard assessments. Chapter I outlines how both the Global Positioning System (GPS) and Synthetic Aperture Radar Interferometry (InSAR) can be used to detect small creep signatures near strike-slip faults. Chapter 2 presents the results from rapid-static GPS surveys of the dense Imperial Valley geodetic network. Chapter 3 investigates the southern San Andreas Fault, near the Salton Sea, where geodetic monuments are sparse. We utilize InSAR in this region and stack interferograms to isolate the creep signature along the fault. The use of permanent scatterers is introduced and its effects on improving image coherence are analyzed. Our photographic survey of permanent scatterers in the Coachella Valley/Salton Sea area is presented in Appendix 3A, while Chapter 4 summarizes various studies of creep on California faults. Research from my first two years is presented in Chapter 5, which details how one can determine the elastic thickness of oceanic lithosphere using shipboard bathymetry and satellite gravity.

  2. Composites of Polystyrene/Wood Fiber, Processing Effect to Creep Resistance

    SciTech Connect

    Romero-Balderrama, L.; Mendoza-Duarte, M. E.; Flores-Gallardo, S. G.; Ibarra-Gomez, R. [Centro de Investigacion en Materiales Avanzados. Miguel de Cervantes 120, Complejo Industrial Chihuahua, 31109. Chihuahua, Chih. (Mexico); Gaspar-Rosas, A. [TA Instruments-Waters LLC. 109 Lukens Drive New Castle, DE 19720 (United States)

    2008-07-07

    In the present work, PS/wood fiber composites were studied in relation to their creep response as to be affected by the incorporation of a silane type coupling agent. Two elaboration variables were also considered in the experiments: wood fiber content and type of composites processing (compression, extrusion and injection molding). A series of weight ratios PS/wood fiber, with and without coupling agent, were prepared, 90/10, 80/20, 70/30 and 60/40. For the compatibilized series, 1% wt of silane coupling agent in relation to the polystyrene weight was employed. The creep tests were performed inside the lineal viscoelastic region at 80 deg. C. A general improvement of the creep resistance for the compatibilized composites was observed independently of the elaboration process. However, the injection molded samples showed by far the lowest deformation with time. This behavior suggests that the high orientation of the fibers generated by the injection molding process, in relation to the extrusion and compression molding, promotes a higher superficial area of treated fiber to be in contact with the PS matrix, which enhances the adhesion and in consequence the resistance to creep.

  3. Creep Behavior of Lead-Free Sn-Ag-Cu + Ni-Ge Solder Alloys

    NASA Astrophysics Data System (ADS)

    Hidaka, N.; Watanabe, H.; Yoshiba, M.

    2009-05-01

    We developed a new lead-free solder alloy, an Sn-Ag-Cu base to which a small amount of Ni and Ge is added, to improve the mechanical properties of solder alloys. We examined creep deformation in bulk and through-hole (TH) form for two lead-free solder alloys, Sn-3.5Ag-0.5Cu-Ni-Ge and Sn-3.0Ag-0.5Cu, at elevated temperatures, finding that the creep rupture life of the Sn-3.5Ag-0.5Cu-Ni-Ge solder alloy was over three times better than that of the Sn-3.0Ag-0.5Cu solder at 398 K. Adding Ni to the solder appears to make microstructural development finer and more uniform. The Ni added to the solder readily combined with Cu to form stable intermetallic compounds of (Cu, Ni)6Sn5 capable of improving the creep behavior of solder alloys. Moreover, microstructural characterization based on transmission electron microscopy analyses observing creep behavior in detail showed that such particles in the Sn-3.5Ag-0.5Cu-Ni-Ge solder alloy prevent dislocation and movement.

  4. In-sodium creep behavior of alloys M-813 and Nimonic PE16

    SciTech Connect

    Anantatmula, R.P.; Gilbert, E.R.

    1980-04-01

    The in-sodium biaxial creep deformation of internally pressurized tube specimens of alloys M-813 and Nimonic PE16 was measured at 650/sup 0/C under constant stress conditions after 4000 hours of sodium exposure. Each alloy had specimens at two different stress levels, viz., 0 and 165 MPa (24,000 psi). The data showed negative diameter changes at zero stress, which were attributed to material densification associated with precipitation. Although material densification was also seen in comparable in-argon experiments, the in-sodium creep strains at 165 MPa and 650/sup 0/C were much lower than the corresponding in-argon values. The higher creep strains in argon are explained on the basis of two parallel mechanisms involving oxygen, which is present at a low level in sodium (1 ppM) as compared with approximately 1000 ppM in the argon environment. The trends in the current data are consistent with observations by earlier authors. Sodium exposure of Nimonic PE16 also resulted in 4 ..mu..m deep intergranular penetration, which did not have any apparent effect on its biaxial creep behavior.

  5. Strong amphibole fabric development during diffusion creep of hydrated mafic rocks

    NASA Astrophysics Data System (ADS)

    Getsinger, A.; Hirth, G.

    2013-12-01

    Numerous observations of naturally deformed, hydrated mafic rocks show that amphibole is a common reaction product in the lower continental crust. Although plagioclase lattice preferred orientation (LPO) in these lithologies may be weak, amphibole LPO is usually strong, suggesting that dislocation creep was the active deformation mechanism. However, the lack of internally strained amphibole grains coupled with the lack of strong fabric in plagioclase suggests that diffusion creep is the dominant deformation mechanism. To examine the processes associated with synkinematic amphibole fabric development, we conducted general shear deformation experiments on powdered basalt with 1 wt% H2O added at pressure and temperature conditions similar to those at the base of the continental crust and within the amphibole stability field (800° C, 1 GPa). Similar to observations from natural shear zones, amphibole forms via the following hydration reaction: plagioclase + pyroxene + H2O = amphibole + less calcic plagioclase. Amphibole formed under hydrostatic conditions exhibits a random LPO, and amphibole growing during deformation exhibits both a strong shape preferred orientation (SPO) and LPO with a [001] maximum aligned sub-parallel to the shear direction. Plagioclase in both hydrostatic and deformed samples exhibits a very weak to random LPO. At low strain rates (10-6 to 10-7/s), strain rate stepping experiments indicate a stress exponent n = ~0.9 to ~1.4, consistent with diffusion creep. Because amphibole grains are elongate parallel to the [001] axis (i.e., parallel to the SPO), we hypothesize that the LPO results from rigid grain rotation and growth of amphibole during deformation. While this interpretation has previously been suggested as a way to produce amphibole LPO in natural shear zones, no experimental investigations have demonstrated this mechanism for producing strong fabric in syntectonically-generated amphibole. These experiments replicate not only the amphibole-forming hydration reactions but also the plagioclase and amphibole fabric observed in naturally deformed, mafic lithologies. Understanding the deformation mechanisms associated with lithologies dominated by amphibole/plagioclase rheology is important for the extrapolation of flow laws to the conditions of the lower continental crust. To first order, both our laboratory and field analyses indicate that plagioclase rheology provides a reasonable rheological constraint of the lower crust.

  6. Thermomechanical theory of materials undergoing large elastic and viscoplastic deformation (AWBA development program)

    Microsoft Academic Search

    S. E. Martin; J. B. Newman

    1980-01-01

    A thermomechanical theory of large deformation elastic-inelastic material behavior is developed which is based on a multiplicative decomposition of the strain. Very general assumptions are made for the elastic and inelastic constitutive relations and effects such as thermally-activated creep, fast-neutron-flux-induced creep and growth, annealing, and strain recovery are compatible with the theory. Reduced forms of the constitutive equations are derived

  7. Pressure solution creep under cyclic loading

    Microsoft Academic Search

    Vladimir Traskine; Zoya Skvortsova; Alexey Muralev; Dmitry Zubov

    2009-01-01

    Pressure solution creep was studied on sodium chloride, calcium carbonate and ammonium nitrate in respective saturated aqueous\\u000a solutions under static loading and cyclic unloading. Ball indentation and powder compaction curves show that each transition\\u000a from static to cyclic regime produces an increase—sometimes manifold—in creep rate which lasts over the whole time of cyclic\\u000a impact. After returning to static regime, the

  8. Simultaneous Modeling of Transient Creep and Grain Boundary Sliding

    NASA Astrophysics Data System (ADS)

    Cooper, R. F.; Sundberg, M.

    2009-12-01

    Grain boundary sliding (GBS) has been identified as an important contributor to the plastic deformation of polycrystalline solids. This phenomenon, whether accommodated by grain boundary diffusion or dislocation slip, has implications for rheological behavior and microstructural evolution during creep. Because GBS is not an independent deformation mechanism, but rather acts in kinetic series with some other (typically) rate-limiting process, direct investigation of the precise sliding mechanism(s) is difficult during conventional large-strain creep testing. Direct observations of grain boundary sliding can be obtained, however, by: (1) observing the mechanical response of a polycrystalline solid to an oscillating load as a function of frequency using the internal friction technique, and (2) studying the short duration transient response of a polycrystalline solid to a step-function change in stress. To this end, we have conducted an experimental study of low-frequency (10-2.25creep responses of the material. Experiments were conducted in an ambient pressure, reciprocating torsion apparatus using a maximum shear stress of ~90 kPa on a very fine grained (d~5?m) aggregate of olivine and orthopyroxene (39 vol%). The attenuation spectra reveal “high-temperature background” behavior at low to moderate frequencies where attenuation diminishes smoothly and mildly with increasing frequency (QG-1 ~ f -0.3). At higher frequencies (f >10-0.5 Hz), the attenuation spectra reveal the onset of an apparent Debye peak in the attenuation spectra, likely due to elastically-accommodated GBS (GBS being rate-limiting). Previous experimental studies have demonstrated that the Andrade viscoelastic model can accurately predict both the transient creep response and the high-temperature background portion of the attenuation spectra in fine-grained polycrystalline solids. This viscoelastic model does not, however, explicitly incorporate the effects of GBS. Consequently, we have modified the Andrade model to incorporate both the high-temperature background and the Debye-peak associated with elastically-accommodated GBS. We demonstrate that this model accurately describes the microcreep curves in our experiments. We then demonstrate that inversion of this viscoelastic models allows us to accurately predict the entirety of the attenuation and shear modulus dispersion spectra we observe in our reciprocating torsion experiments in an internally consistent way. We use this model to evaluate different models for the relaxation strength associated with elastically accommodated GBS. Based on this technique we determine a grain boundary viscosity of 6x105 Pa s at T=1200°C. Finally, the implications of this result for seismic wave attenuation in the Earth’s mantle and geodetic observations of post-seismic creep are discussed.

  9. Low strain creep and aging of aluminum alloy 2219-T87 sheet

    NASA Technical Reports Server (NTRS)

    Navrotski, G.; Rummler, D. R.

    1981-01-01

    The constant load creep and isothermal aging characteristics of aluminum alloy 2219-T87 sheet have been studied experimentally and analytically in the temperature range 250 to 650 F at stress levels between 2.9 and 4.0 ksi (20 to 283 MPa). Testing variables were closely and automatically monitored. The data generated agree somewhat with the literature data base at lower temperatures, but above 500 F, discrepancies of greater than an order of magnitude in the time to 1% creep strain occur. Good correlation was found with the Larson-Miller parameter as modeled by a second-order polynomial in stress. Constitutive equations for time to 0.1%, 0.2%, 0.5%, and 1.0% creep are given. Information on residual mechanical properties and electrical conductivity is also provided.

  10. Onset of sediment transport is a continuous transition driven by fluid shear and granular creep

    PubMed Central

    Houssais, Morgane; Ortiz, Carlos P.; Durian, Douglas J.; Jerolmack, Douglas J.

    2015-01-01

    Fluid-sheared granular transport sculpts landscapes and undermines infrastructure, yet predicting the onset of sediment transport remains notoriously unreliable. For almost a century, this onset has been treated as a discontinuous transition at which hydrodynamic forces overcome gravity-loaded grain–grain friction. Using a custom laminar-shear flume to image slow granular dynamics deep into the bed, here we find that the onset is instead a continuous transition from creeping to granular flow. This transition occurs inside the dense granular bed at a critical viscous number, similar to granular flows and colloidal suspensions and inconsistent with hydrodynamic frameworks. We propose a new phase diagram for sediment transport, where ‘bed load’ is a dense granular flow bounded by creep below and suspension above. Creep is characteristic of disordered solids and reminiscent of soil diffusion on hillslopes. Results provide new predictions for the onset and dynamics of sediment transport that challenge existing models. PMID:25751296

  11. Relationship between swelling and irradiation creep in cold-worked PCA stainless steel irradiated to {approximately}178 dpa at {approximately}400{degrees}C

    SciTech Connect

    Toloczko, M.B. [Univ. of California, Santa Barbara, CA (United States). Dept. of Chemical and Nuclear Engineering; Garner, F.A. [Pacific Northwest Lab., Richland, WA (United States)

    1993-09-01

    The eighth and final irradiation segment for pressurized tubes constructed from the fusion Prime Candidate Alloy (PCA) has been completed in FFTF. At 178 dpa and {approximately}400{degrees}C, the irradiation creep of 20% cold-worked PCA has become dominated by the {open_quotes}creep disappearance{close_quotes} phenomenon. The total diametral deformation rate has reached the limiting value of 0.33%/dpa at the three highest stress levels employed in this test. The stress-enhancement of swelling tends to camouflage the onset of creep disappearance, however, requiring the use of several non-traditional techniques to extract the creep coefficients. No failures occurred in these tubes, even though the swelling ranged from {approximately}20 to {approximately}40%.

  12. 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)

  13. 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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  15. Deformable Surface Matching for Statistical Shape Analysis

    Microsoft Academic Search

    Hae-jeong Park; James Levitt; Robert W. Mccarley; Carl-fredrik Westin

    Abstract. We propose a deformable surface model for matching anatomically homologous points for a specific region of interest (ROI), based on both sur-rounding intensity structures and shape characteristics. The initial estimate of the deformable mesh for the individual ROI was derived by transforming the template mesh to the individual image space using nonlinear warping. For the deformable surface model, we

  16. 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.

  17. 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.

  18. 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

  19. Heritability of dollar spot resistance in creeping bentgrass.

    PubMed

    Bonos, Stacy A

    2006-08-01

    ABSTRACT The dollar spot disease incited by Sclerotinia homoeocarpa is an important disease of creeping bentgrass (Agrostis stolonifera). Genetic resistance is an important control strategy and could reduce fungicide use. Despite recent research, the genetic mechanism of dollar spot resistance in turfgrasses is still not fully understood. The objectives of this study were to (i) determine narrow-sense heritability and predicted gain from selection for dollar spot resistance in creeping bentgrass and (ii) evaluate inheritance characteristics of dollar spot disease resistance. Inheritance characteristics such as the detection of major genes, heterosis, maternal effects, and combining ability were determined by evaluating the disease severity of progeny from crosses between resistant and susceptible bent-grass clones. Parental clones and progenies from crosses were established in a field trial in a randomized complete block design and inoculated with one isolate of S. homoeocarpa applied at a rate of 0.25 g m(-2) of prepared inoculum. Differences in progeny means between crosses were observed over both years. Progeny from resistant x resistant crosses had significantly less disease severity than resistant x susceptible and susceptible x susceptible crosses. High narrow-sense heritability estimates (0.79 [2002], 0.79 [2003]) and large mean squares for general combining ability support the idea that additive gene action plays a significant role in disease resistance and support previous research that dollar spot resistance is most likely quantitatively inherited. PMID:18943744

  20. Characteristics and deformation mechanism of salt-related structures in the western Kuqa depression, Tarim basin: Insights from scaled sandbox modeling

    NASA Astrophysics Data System (ADS)

    Wu, Zhenyun; Yin, Hongwei; Wang, Xin; Zhao, Bo; Jia, Dong

    2014-02-01

    Three scaled analog (sandbox) models are constructed to simulate the evolution of thick-skinned shortening on broad and narrow salt basins. These models simulate the evolution of the Cenozoic salt (salt-related) structures in the westernmost Kuqa salt-bearing depression (Quele area), Tarim basin. The formation mechanism and the controlling factors of structural deformation in this area are investigated and discussed systematically. Model results show that the variable depositional width of the salt basin has a major controlling influence on the differential structural deformation in different longitudinal segmentations from east (broad) to west (narrow) in the western Kuqa depression (Quele area). Model results also demonstrate that the early salt structure (salt diapir) has an important controlling role on the subsequent compressional structural deformation. The pre-existing thin overburden Quele diapir, which acts as a stress concentration zone during the subsequent shortening, is deformed to the Quele salt nappe. On the basis of the model results, it is suggested that the formation of the long-distance Quele allochthonous salt sheet is related with the pre-existing Quele diapir, which displaces up paralleling the hanging wall and flows to the surface during the subsequent shortening.