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1

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

SciTech Connect

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.

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

2

Creep Deformation of Allvac 718Plus  

NASA Astrophysics Data System (ADS)

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.

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

2015-01-01

3

Creep deformation of B2 aluminides  

NASA Technical Reports Server (NTRS)

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

Nathal, M. V.

1992-01-01

4

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

NASA Astrophysics Data System (ADS)

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

Rogowitz, Anna; Grasemann, Bernhard

2014-05-01

5

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

NASA Technical Reports Server (NTRS)

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

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

2003-01-01

6

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

NASA Technical Reports Server (NTRS)

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.

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

1988-01-01

7

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

NASA Technical Reports Server (NTRS)

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.

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

1989-01-01

8

A furnace with rotating load frame for in situ high temperature deformation and creep experiments in a neutron diffraction beam line  

NASA Astrophysics Data System (ADS)

A resistive furnace combined with a load frame was built that allows for in situ neutron diffraction studies of high temperature deformation, in particular, creep. A maximum force of 2700 N can be applied at temperatures up to 1000 C. A load control mode permits studies of, e.g., creep or phase transformations under applied uni-axial stress. In position control, a range of high temperature deformation experiments can be achieved. The examined specimen can be rotated up to 80 around the vertical compression axis allowing texture measurements in the neutron time-of-flight diffractometer HIPPO (High Pressure - Preferred Orientation). We present results from the successful commissioning, deforming a Zr-2.5 wt.% Nb cylinder at 975 C. The device is now available for the user program of the HIPPO diffractometer at the LANSCE (Los Alamos Neutron Science Center) user facility.

Reiche, H. M.; Vogel, S. C.; Mosbrucker, P.; Larson, E. J.; Daymond, M. R.

2012-05-01

9

A furnace with rotating load frame for in situ high temperature deformation and creep experiments in a neutron diffraction beam line.  

PubMed

A resistive furnace combined with a load frame was built that allows for in situ neutron diffraction studies of high temperature deformation, in particular, creep. A maximum force of 2700 N can be applied at temperatures up to 1000 C. A load control mode permits studies of, e.g., creep or phase transformations under applied uni-axial stress. In position control, a range of high temperature deformation experiments can be achieved. The examined specimen can be rotated up to 80 around the vertical compression axis allowing texture measurements in the neutron time-of-flight diffractometer HIPPO (High Pressure - Preferred Orientation). We present results from the successful commissioning, deforming a Zr-2.5 wt.% Nb cylinder at 975 C. The device is now available for the user program of the HIPPO diffractometer at the LANSCE (Los Alamos Neutron Science Center) user facility. PMID:22667627

Reiche, H M; Vogel, S C; Mosbrucker, P; Larson, E J; Daymond, M R

2012-05-01

10

Microstructure evolution and deformation features of AZ31 Mg-alloy during creep  

Microsoft Academic Search

By means of the measurement of the creep curve and the observation of SEM and transmission electron microscope (TEM), an investigation has been made into the microstructure evolution and deformation features of AZ31 Mg-alloy during high temperature creep. Results show that the deformation features of the alloy in the primary stage of creep are that significant amount of dislocation slips

Sugui Tian; Ling Wang; Keun Yong Sohn; Kyung Hyun Kim; Yongbo Xu; Zhuangqi Hu

2006-01-01

11

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

SciTech Connect

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

K. Linga (KL) Murty

2008-08-11

12

The influence of temperature on residual deformation of Phenylon and Nomex yarns following the creeprecovery process  

Microsoft Academic Search

High-performance synthetic filaments and yarns are subjected to different loads and temperature during their practical and industrial applications, resulting in changes in their mechanical properties. Knowledge of the deformation and strength properties of these polymer materials at various temperatures and different levels of preliminary stretching is therefore very important. Semi-rigid chain polymers Phenylon and Nomex yarns are popular materials for

E. S. Tsobkallo; V. A. Kvaratskheliya; J. Shen; J. Harwood

2008-01-01

13

Temperature, Thermal Stress, And Creep In A Structure  

NASA Technical Reports Server (NTRS)

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

Jenkins, Jerald M.

1991-01-01

14

A TEM Study of Creep Deformation Mechanisms in Allvac 718Plus  

SciTech Connect

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

Unocic, Raymond R [ORNL; Unocic, Kinga A [ORNL; Hayes, Robert [Metals Technology, Inc; Daehn, Glenn [Ohio State University; Mills, Michael J. [Ohio State University

2010-01-01

15

Mechanisms of creep deformation in gamma-based titanium aluminide alloys  

NASA Astrophysics Data System (ADS)

The creep behavior of gamma-based titanium aluminide alloys has been characterized phenomenologically in detail in recent years but is still not well understood mechanistically. It is apparent that a large number of variables potentially influence creep behavior; however, isolation of the effects of individual variables has been difficult. In order to understand creep deformation mechanisms and the sources which contribute to creep strain, this investigation has thoroughly examined the effect of several critical variables by conducting experiments on materials where microstructure and composition have been carefully controlled. Important variables examined include the effects of phase morphology/distribution, grain size, aluminum and molybdenum content, stress, temperature, structure stability, and prior deformation path. The resulting effects of these variables on creep properties was assessed by careful experiments examining minimum creep rates, evolution of creep rate with time and strain, sliding at grain boundaries, creep transients, and deformation substructure development. Results of the heat treatment study have shown that microstructure development in this system is highly dependent upon processing variables including heating rate, cooling rate, and annealing temperature. Controlled gamma phase grain growth can also be achieved near the binary alloy eutectoid temperature. Results of creep experiments indicate that the minimum creep rate of a wide range of multiphase structures, including equiaxed and duplex morphologies, is relatively insensitive to second phase morphology. Molybdenum present in solid solution in the gamma phase decreases minimum creep rates. A similar reduction occurs with increased aluminum content on the aluminum-lean side of stoichiometry. Grain boundary sliding contributes significantly to creep deformation for grain sizes of 10--100um with as much as 25% of the strain being attributed to sliding. Examination of dislocation substructures developed during creep indicates that creep is likely to be controlled by solute drag processes at low stresses. At high stresses, deformation appears to be controlled by glide processes involving the dragging of jogged screw dislocations. Resulting stress exponents typically transition from approximately 3 to 7 as stress is increased. Twinning occurs at 760C during creep and tensile deformation at high stresses, but does not result in a significant prior deformation path dependence of creep rate.

Ott, Eric A.

16

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

NASA Astrophysics Data System (ADS)

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.

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

2014-12-01

17

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

NASA Astrophysics Data System (ADS)

The main objective of this research was aimed at investigating the fundamental relationship between microstructure and creep deformation mechanisms using a variety of electron microscopy characterization techniques. The alloy used in this research, Rene 104, is a newer generation powder metallurgy Ni-base superalloy that was developed specifically for aircraft gas turbine disk applications with extended service durability at temperatures exceeding 650C. The influence of stress and temperature was studied first and it was found that during creep deformation at temperatures between 677--815C and stresses between 345--724MPa a variety of distinctly different creep deformation mechanisms were operative. In addition to identifying the creep deformation mechanisms an attempt was made to determine the creep rate limiting process so that an improved understanding of the fundamental processes that control deformation can be better understood. Microtwinning was found to the dominant deformation mechanism following creep at 677C/690MPa and 704C/724MPa. Microtwins form by the motion of paired a/6<112> Shockley partial dislocations that shear both the gamma matrix and gamma' precipitates. The rate limiting process in this mechanism is diffusion mediated atomic reordering that occurs in the wake of the shearing, twinning partial dislocations in order to maintain the ordered L12 structure of the gamma' precipitates. This reordering process helps to fundamentally explain the temperature and rate dependence of microtwinning under creep conditions within this temperature and stress regime. At a slightly higher temperature but lower stress (760C and 345MPa), a stacking fault related shearing mechanism, which typically spanned only a few micrometers in length, was the principle deformation mode. The faults left behind in the gamma' precipitates determined to be extrinsic in nature. During creep at the highest temperature and lowest stress (815C and 345MPa) a thermally activated climb/bypass mechanism of a/2<110> dislocations were found to be the dominant deformation mechanism. In this mechanism, the gamma' precipitates were not sheared but instead were bypassed by a/2<110> matrix dislocations. In addition to the identification of creep deformation mechanisms as a function of stress and temperature, characterization of the post creep gamma' precipitate microstructure revealed that microstructural evolution of the gamma' precipitates has occurred during creep at the higher test temperatures where the secondary gamma' precipitates have coarsened and the tertiary gamma' precipitates have dissolved. In combination with creep at low stress and high temperature, the microstructural evolution may have contributed to the transition from one deformation mode to another. In an attempt to link the influence of microstructure (gamma' precipitate size scale, distribution, volume fraction, and gamma channel width spacing) on creep deformation behavior and creep deformation mechanisms, specimens with different size scaled microstructural features were crept at the same temperature and stress (677C and 724MPa) in order to provide a direct comparison between differences in microstructure. It was found that a microstructure consisting of a bimodal distribution of gamma' precipitates with coarse secondary gamma' precipitates, a high volume fraction of tertiary gamma' precipitates and a wide gamma channel width spacing results in a less creep resistance microstructure that deformed primary by a/2<110> dislocation activity in the gamma matrix at small strain and secondary gamma' shearing via superlattice intrinsic stacking faults at higher strains. The more creep resistant microstructure consisted of a bimodal distribution of gamma' precipitates with a finer secondary gamma' precipitate size, low volume fraction of gamma' and narrow gamma channel width spacing. The combination of these microstructural features promoted a/2<110> dislocation dissociation and decorrelation of a/6<112> Shockley partial di

Unocic, Raymond R.

18

Temperature-dependent creep buckling of plates  

NASA Technical Reports Server (NTRS)

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

Ross, D. A.; Berke, L.

1981-01-01

19

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

SciTech Connect

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.

Kawai, M.; Ohashi, Y.

1987-01-01

20

High-temperature creep of polycrystalline chromium  

NASA Technical Reports Server (NTRS)

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

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

1972-01-01

21

Finite Element Analysis of Plastic Deformation During Impression Creep  

NASA Astrophysics Data System (ADS)

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.

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

2015-04-01

22

Finite Element Analysis of Plastic Deformation During Impression Creep  

NASA Astrophysics Data System (ADS)

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.

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

2015-02-01

23

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

NASA Technical Reports Server (NTRS)

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.

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

2013-01-01

24

Threshold Stress Creep Behavior of Alloy 617 at Intermediate Temperatures  

SciTech Connect

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.

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

2014-06-01

25

Creep Behavior and Deformation Mechanisms for Nanocluster-Strengthened Ferritic Steels  

SciTech Connect

Mechanically alloyed, nanostructured ferritic steels represent a class of alloys that can display high resistance to radiation and creep deformation, which are derived from the presence of nanoclusters, precipitates and solute segregation to the grain boundaries. The creep responses for a 14YWT nanostructured ferritic steel were measured over a range of temperatures and stress levels. The stress exponent was observed to vary non-linearly with applied stress; stress exponents were found to decrease with decreasing stress approaching unity at low stress. Transmission electron microscopy studies clearly demonstrated that creep deformation proceeds by a dislocation glide within nanoscale grains and that glide dislocations are attracted to and pinned by nanoclusters. In light of these observations, a new model of the creep response, inspired by the Kocks-Argon-Ashby model, is developed to explain the low creep rates and small stress exponents that are exhibited by these alloys.

Brandes, Matthew C [Ohio State University; Kovarik, L. [Ohio State University; Miller, Michael K [ORNL; Daehn, Glenn [Ohio State University; Mills, Michael J. [Ohio State University

2011-01-01

26

Creep deformation behavior in eutectic SnAg solder joints using a novel mapping technique  

Microsoft Academic Search

Creep deformation behavior was measured for 60100 m thick solder joints. The solder joints investigated consisted of: (a)\\u000a non-composite solder joints made with eutectic Sn-Ag solder, and (b) composite solder joints with eutectic Sn-Ag solder containing\\u000a 20 vol. %, 5 m diameter in-situ Cu6Sn5 intermetallic reinforcements. All creep testing in this study was carried out at room temperature. Qualitative and

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

1999-01-01

27

Creeping deformation mechanisms for mixed hydrate-sediment submarine landslides  

NASA Astrophysics Data System (ADS)

Globally widespread gas hydrates are proposed to stabilize the seafloor by increasing sediment peak shear strength; while seafloor failure localises at the base of the gas hydrate stability field (BGHS). The primary mechanism by which gas hydrates are proposed to induce slope failure is by temperature or pressure controlled dissociation of hydrate to free gas resulting in a significant pore pressure increase at the BGHS. Direct evidence for this process is lacking however, and the interaction between gas hydrate and seafloor stability remains poorly understood. We present evidence that, contrary to conventional views, gas hydrate can itself destabilize the seafloor. Morphological (Kongsberg-Simrad EM300 and EM302 multibeam) and high-resolution multichannel seismic refection data from a 100 km2 submarine landslide complex in ~450 m water depth, 20 km off the east coast of New Zealand indicate flow-like deformation within gas hydrate-bearing sediments. This "creeping" deformation occurs immediately downslope of where the BGHS reaches the seafloor, as indicated by a hydrate-indicating bottom simulating reflector (BSR) cutting through the landslide debris, suggesting involvement of gas hydrates. We propose two mechanisms to explain how the shallow gas hydrate system could control these landslides. 1) The Hydrate Valve: Overpressure and/or temperature fluctuations below low-permeability gas hydrate-bearing sediments causes hydrofracturing where the BGHS approaches the landslide base, both weakening sediments and creating a valve for transferring excess pore pressure into the upper landslide body. 2) Hydrate-sediment Glacier: Gas hydrate-bearing sediment exhibits time-dependent plastic deformation enabling glacial-style deformation. This second hypothesis is supported by recent laboratory observations of time-dependent behaviour of gas-hydrate-bearing sands. Given the ubiquitous occurrence of gas hydrates on continental slopes, our results may require a re-evaluation of slope stability following future climate-forced variation in bottom water temperatures.

Mountjoy, Joshu; Pecher, Ingo; Henrys, Stuart; Barnes, Philip; Plaza-Faverola, Andreia

2013-04-01

28

Creep of pure aluminum at cryogenic temperatures  

E-print Network

CREEP OF PURE ALUMINUM AT CRYOGENIC TEMPERATURES A Thesis by LACY CLARK MCDONALD Submitted to the Office of Graduate Studies of Texas AgrM University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August... 1989 Major Subject: Mechanical Engineering CREEP OF PURE ALUMINUM AT CRYOGENIC TEMPERATURES A Thesis by LACY CLARK MCDONALD Approved a. s to style and content by: K. Ted Hartwig (Chair ol' Committee) Walter L. Bradley (Member) Mehrda. d...

McDonald, Lacy Clark

1989-01-01

29

Prediction Procedure of Creep Rupture of Polypropylene Resin based on Time-temperature Superposition Principle  

NASA Astrophysics Data System (ADS)

In this paper, the effects of intensity of electron beam, detergent and colorant on creep rupture of polypropylene resin (PP), which is widely used in medicine containers, were investigated and the evaluation method of the long-term forecast of creep rupture was examined. Concretely, first, PP resins including colorant or not were prepared and samples that variously changed intensity of the electron beam irradiation were made. Creep rupture test of those samples was carried in detergent having various consistencies. The effects of those factors on creep rupture were considered and long-term forecast was tried by using time-temperature superposition principle about creep deformation. The following results were obtained. (1) Although creep rupture of PP resin receives the effects of the presence of colorant, intensity of electron beam irradiation and detergent, the time-temperature dependence of creep rupture of PP resin including those affecting factors can be estimated by using the time-temperature superposition principle for creep deformation of the original PP resin. Based on this equivalency, it is possible to predict the long-term forecast of creep rupture of PP resin. (2) Creep rupture is affected by the presence of colorant, intensity of electron beam irradiation and detergent and it happens earlier when the intensity of electron beam irradiation and consistency of detergent are increased.

Yamada, Hiroshi; Ikeda, Masayuki; Shimbo, Minoru; Miyano, Yasushi

30

Stress versus temperature dependent activation energies in creep  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

31

Temperature-dependent transient creep and dynamics of cratonic lithosphere  

NASA Astrophysics Data System (ADS)

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.

Birger, Boris I.

2013-11-01

32

Viscoplastic BEM analysis of creeping metallic structural components in the presence of temperature gradients  

Microsoft Academic Search

A boundary element formulation for the solution of time-dependent inelastic problems arising in creeping metallic plates at high temperatures is presented. The formulation allows the use of models of inelastic deformation using state variables for characterizing the time-dependent behaviour of metals and alloys under thermal loading conditions. The deformation of the plate is simulated using a viscoplastic model developed by

C. P. Providakis; S. G. Kourtakis

2002-01-01

33

Time-dependent brittle deformation (creep) at Mt. Etna volcano  

NASA Astrophysics Data System (ADS)

Mt. Etna is the largest and most active volcano in Europe. Time-dependent weakening mechanisms, leading to slow fracturing, have been shown to act during pre-eruptive patterns of flank eruptions at Mt. Etna volcano. Due to the high permeability of its volcanic rocks, the volcanic edifice hosts one of the biggest hydrogeologic reservoirs of Sicily (Ogniben, 1966). The presence of a fluid phase in cracks within rock has been shown to dramatically affect both mechanical and chemical interactions. Chemically, it promotes time-dependent brittle deformation through such mechanisms as stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Such crack growth is highly non-linear and accelerates towards dynamic failure over extended periods of time, even under constant applied stress; a phenomenon known as brittle creep'. Here we report results from a study of time-dependent brittle creep in water-saturated samples of Etna basalt (EB) under triaxial stress conditions (confining pressure of 50 MPa and pore fluid pressure of 20 MPa). Samples of EB were loaded at a constant strain rate of 10-5 s-1 to a pre-determined percentage of the short-term strength and left to deform under constant stress until failure. Crack damage evolution was monitored throughout each experiment by measuring the independent damage proxies of axial strain, pore volume change and output of acoustic emission (AE) energy, during brittle creep of creep strain rates ranging over four orders of magnitude. Our data not only demonstrates that basalt creeps in the brittle regime but also that the applied differential stress exerts a crucial influence on both time-to-failure and creep strain rate in EB. Furthermore, stress corrosion is considered to be responsible for the acceleratory cracking and seismicity prior to volcanic eruptions and is invoked as an important mechanism in forecasting models. Stress-stepping creep experiments were then performed to allow the influence of the effective confining stress to be studied in detail. Experiments were performed under effective stress conditions of 10, 30 and 50 MPa (whilst maintaining a constant pore fluid pressure of 20 MPa). In addition to the purely mechanical influence of water, governed by the effective stress, which results in a shift of the creep strain rate curves to lower strain rates at higher effective stresses. Our results also demonstrate that the chemically-driven process of stress corrosion cracking appears to be inhibited at higher effective stress. This results in an increase in the gradient of the creep strain rate curves with increasing effective stress. We suggest that the most likely cause of this change is a decrease in water mobility due to a reduction in crack aperture and an increase in water viscosity at higher pressure. Finally, we show that a theoretical model based on mean-field damage mechanics creep laws is able to reproduce the experimental strain-time relations. Our results indicate that the local changes in the stress field and fluid circulation can have a profound impact in the time-to-failure properties of the basaltic volcanic pile.

Heap, M. J.; Baud, P.; Meredith, P. G.; Vinciguerra, S.; Bell, A. F.; Main, I. G.

2009-04-01

34

Improved Creep Measurements for Ultra-High Temperature Materials  

NASA Technical Reports Server (NTRS)

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.

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

2010-01-01

35

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

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

36

Features of the high-temperature deformation and structural state of SB1 alloy under creep conditions in a rarefied flow of oxygen  

Microsoft Academic Search

An increase in the concentration of active impurities in rarefied atmospheres or in inert gases leads to an increase in creep resistance and in the stress-rupture strength of alloys as the result of precipitation during the gas-metal reaction of finely dispersed interstitial phases (oxides, carbides, nitrides) which may directly promote hardening, being effective stoppers in the path of advance of

O. I. Eliseeva

1984-01-01

37

Characterization of crystallographic evolution during creep deformation of a single crystal superalloy  

SciTech Connect

In the present study, the electron back scattering diffraction (EBSD) technique has been used to monitor the changes in microcrystallinity that occurs in specimens of SRR99 with complex crystal orientation when deformed to various creep strains and to failure at a range of stresses and temperatures. The current version of the anisotropic model has been used to simulate these deformations and predict the crystal rotations that will occur as a function of creep strain. The investigation compared the experimental and predicted extents and nature of crystal rotation. It also examined the wider issues of sources in variation of experimental measurements and the influence of the microstructural heterogeneities on the uniformity and consistency of crystal rotation determinations.

Shollock, B.A.; Buffiere, J.Y.; Henderson, M.B.; McLean, M. [Imperial Coll of Science, Technology and Medicine, London (United Kingdom). Dept. of Materials] [Imperial Coll of Science, Technology and Medicine, London (United Kingdom). Dept. of Materials; Curtis, R.V. [Guy`s and St. Thomas`s Hospital, London (United Kingdom). United Medical and Dental School] [Guy`s and St. Thomas`s Hospital, London (United Kingdom). United Medical and Dental School

1997-06-15

38

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

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

39

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

40

Final Report on In-Reactor Creep-Fatigue Deformation Behaviour of a  

E-print Network

V) neutrons and will experience at the same time thermo-mechanical cyclic loading (i.e. fatigue) as a resultFinal Report on In-Reactor Creep- Fatigue Deformation Behaviour of a CuCrZr Alloy: COFAT 2 B3) , J. Dekeyser3) , and J.F. Stubbins4) Title: Final Report on In-reactor Creep-fatigue Deformation

41

Improved high temperature creep resistant austenitic alloy  

DOEpatents

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.

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

1988-05-13

42

High temperature creep resistant austenitic alloy  

DOEpatents

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.

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

1989-01-01

43

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

SciTech Connect

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.

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

44

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

SciTech Connect

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.

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

2009-01-22

45

High-temperature creep of synthetic calcite aggregates: influence of Mn-content  

NASA Astrophysics Data System (ADS)

To investigate the role of impurities on the deformation of calcite rocks, we performed creep experiments on fine-grained synthetic calcite aggregates with varying Mn-content. The tests were performed in a uniaxial creep apparatus at temperatures of 700-830 C and stresses between 15 and 65 MPa, resulting in strain rates of 10 -7 to 10 -4 s -1. Varying the oxygen fugacity, fO 2, between 10 -18 and 10 -4 MPa did not affect the creep strength. Applying a power law constitutive relationship on the creep data, two distinct creep regimes were observed, a low stress regime (<15 MPa) and a high stress regime (>20-25 MPa). In the low stress regime, a stress exponent n of 1.70.3 and an activation energy of Q=30045 kJ/mol were found. The mechanical data and microstructural observations suggest that grain-boundary sliding accommodated by grain-boundary diffusion is the dominant creep mechanism. At high stresses, we obtained a stress exponent of n=3.10.6 and an activation energy of Q=49050 kJ/mol, indicating dislocation creep. Transmission-electron microscopy (TEM) observations show a dominance of recovery-related dislocation structures suggesting that dislocation climb is important. Increasing Mn-concentration from 10 to 670 ppm leads to an enhancement in creep rate in both creep regimes, but the effect is more substantial in the diffusion creep regime (one order of magnitude). In the diffusion creep regime, the enhancement of creep rate by Mn is attributed to the substitution of Ca by Mn, which may increase grain-boundary diffusivity of calcite. In the dislocation regime, it is interpreted as a combination of dislocation climb and glide with the exchange of Ca by aliovalent Mn, which may affect the point defect concentration.

Freund, Dieter; Wang, Zichao; Rybacki, Erik; Dresen, Georg

2004-10-01

46

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

SciTech Connect

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

M.C. Carroll; L.J. Carroll

2012-10-01

47

High temperature indentation creep tests on anhydrite - a promising first look  

NASA Astrophysics Data System (ADS)

Indentation creep tests are established in materials engineering, providing information on rheology, deformation mechanisms, and related microstructures of materials. Here we explore the potential of this method on natural, polycrystalline anhydrite. The tests are run at atmospheric pressure, temperatures between 700 and 920 C, and reference stresses between 7 and 30 MPa. An activation energy Q of 338 kJ mol-1 and a stress exponent n of 3.9 are derived. Deformation is localized into shear zones bounding a less deformed approximately conical plug underneath the indenter. Shear zone microstructures reveal inhomogeneous crystal-plastic deformation, subgrains, and extensive strain-induced grain boundary migration, while mechanical twinning appears not to be activated. Microstructure and mechanical data are consistent with deformation by dislocation creep.

Dorner, D.; Rller, K.; Stckhert, B.

2014-08-01

48

Elevated temperature creep properties for selected active metal braze alloys  

SciTech Connect

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

Stephens, J.J.

1997-02-01

49

Creep of an epoxy resin under transient temperatures  

E-print Network

(Member) . Saya Memb' r) August 1973 ABSTRACT Creep of an Epoxy Resin Under Transient Temperatures. (August 1973) Larry Alan Watkins, B. S. , Texas ASM Univers1ty D1rected by: Dr. R. A. Schapery Transient temperature tests were performed...

Watkins, Larry Alan

1973-01-01

50

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

SciTech Connect

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

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

2011-11-01

51

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

Microsoft Academic Search

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

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

1998-01-01

52

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

SciTech Connect

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

Unocic, Raymond R [ORNL; Zhou, Ning [Ohio State University; Kovarik, Libor [Pacific Northwest National Laboratory (PNNL); Shen, Chen [GE Global Research; Wang, Yunzhi [Ohio State University; Mills, Michael J. [Ohio State University

2011-01-01

53

Evolution of load transfer between hydroxyapatite and collagen during creep deformation of bone.  

PubMed

While the matrix/reinforcement load-transfer occurring at the micro- and nanoscale in nonbiological composites subjected to creep deformation is well understood, this topic has been little studied in biological composites such as bone. Here, for the first time in bone, the mechanisms of time-dependent load transfer occurring at the nanoscale between the collagen phase and the hydroxyapatite (HAP) platelets are studied. Bovine cortical bone samples are subjected to synchrotron X-ray diffraction to measure in situ the evolution of elastic strains in the crystalline HAP phase and the evolution of viscoelastic strains accumulating in the mineralized collagen fibrils under creep conditions at body temperature. For a constant compressive stress, both types of strains increase linearly with time. This suggests that bone, as it deforms macroscopically, is behaving as a traditional composite, shedding load from the more compliant, viscoelastic collagen matrix to the reinforcing elastic HAP platelets. This behavior is modeled by finite-element simulation carried out at the fibrillar level. PMID:21878399

Deymier-Black, A C; Yuan, F; Singhal, A; Almer, J D; Brinson, L C; Dunand, D C

2012-01-01

54

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

SciTech Connect

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

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

2011-06-01

55

High temperature creep of SiC densified using a transient liquid phase  

SciTech Connect

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

Jou, Z.C.; Virkar, A.V. (Department of Materials Science and Engineering, The University of Utah, Salt Lake City, Utah (USA)); Cutler, R.A. (Ceramatec, Inc., 2425 South 900 West, Salt Lake City, Utah (USA))

1991-09-01

56

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

Microsoft Academic Search

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

S. A. Sajjadi; S. Nategh

2001-01-01

57

High temperature creep of refractory bricks. Final report  

SciTech Connect

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

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

1991-05-15

58

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

PubMed

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

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

2000-08-01

59

The constitutive representation of high-temperature creep damage  

NASA Technical Reports Server (NTRS)

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

Chan, K. S.

1988-01-01

60

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

NASA Astrophysics Data System (ADS)

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.

Trinh, B. T.; Hackl, K.

2014-07-01

61

Creep, stress relaxation, and plastic deformation in Sn-Ag and Sn-Zn eutectic solders  

NASA Astrophysics Data System (ADS)

Because of the high homologous operation temperature of solders used in electronic devices, time and temperature dependent relaxation and creep processes affect their mechanical behavior. In this paper, two eutectic lead-free solders (96.5Sn-3.5Ag and 91Sn-9Zn) are investigated for their creep and stress relaxation behavior. The creep tests were done in load-control with initial stresses in the range of 10-22 MPa at two temperatures, 25 and 80C. The stress relaxation tests were performed under constant-strain conditions with strains in the range of 0.3-2.4% and at 25 and 80C. Since creep/relaxation processes are active even during monotonie tensile tests at ambient temperatures, stress-strain curves at different temperatures and strain rates provide insight into these processes. Activation energies obtained from the monotonic tensile, stress relaxation, and creep tests are compared and discussed in light of the governing mechanisms. These data along with creep exponents, strain rate sensitivities and damage mechanisms are useful for aiding the modeling of solder interconnects for reliability and lifetime prediction. Constitutive modeling for creep and stress relaxation behavior was done using a formulation based on unified creep plasticity theory which has been previously employed in the modeling of high temperature superalloys with satisfactory results.

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

1997-07-01

62

Nuclear Deformation at Finite Temperature  

NASA Astrophysics Data System (ADS)

Deformation, a key concept in our understanding of heavy nuclei, is based on a mean-field description that breaks the rotational invariance of the nuclear many-body Hamiltonian. We present a method to analyze nuclear deformations at finite temperature in a framework that preserves rotational invariance. The auxiliary-field Monte Carlo method is used to generate a statistical ensemble and calculate the probability distribution associated with the quadrupole operator. Applying the technique to nuclei in the rare-earth region, we identify model-independent signatures of deformation and find that deformation effects persist to temperatures higher than the spherical-to-deformed shape phase-transition temperature of mean-field theory.

Alhassid, Y.; Gilbreth, C. N.; Bertsch, G. F.

2014-12-01

63

Nuclear deformation at finite temperature.  

PubMed

Deformation, a key concept in our understanding of heavy nuclei, is based on a mean-field description that breaks the rotational invariance of the nuclear many-body Hamiltonian. We present a method to analyze nuclear deformations at finite temperature in a framework that preserves rotational invariance. The auxiliary-field Monte Carlo method is used to generate a statistical ensemble and calculate the probability distribution associated with the quadrupole operator. Applying the technique to nuclei in the rare-earth region, we identify model-independent signatures of deformation and find that deformation effects persist to temperatures higher than the spherical-to-deformed shape phase-transition temperature of mean-field theory. PMID:25615315

Alhassid, Y; Gilbreth, C N; Bertsch, G F

2014-12-31

64

The high temperature creep behavior of oxides and oxide fibers  

NASA Technical Reports Server (NTRS)

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

Jones, Linda E.; Tressler, Richard E.

1991-01-01

65

Identification of wavelengths of strain heterogeneities during creep deformation in Carrara Marble  

NASA Astrophysics Data System (ADS)

We use a new technique combining microfabrication technology and compression tests to map the strain field at a micrometric scale in polycrystalline materials. The motivation of such high-resolution mapping is to identify characteristic wavelengths of heterogeneities for different plasticity mechanisms under varying creep conditions. The micro-strain mapping technique was applied to Carrara Marble under different deformation regimes, at a confining pressure of 300 MPa and temperatures ranging from 200 to 700 C. In samples deformed to 10% strain in compression at 400C, 500C and 600C, at a 3x10-5 s-1 strain rate, strain can be up to 5 times greater along twins and grain boundaries compared to the macroscopic strain accommodated over the entire sample. Strain averaged across a particular grain may vary by as much as 100%. Moreover, there is a gradual but clear change in the accommodation of strain, from twins to grain boundaries as temperature increases. For a fixed temperature of 600C, varying strain from 10% to 30% does not appear to increase the wavelength of heterogeneities (i.e. the strain field does not homogenize). Macroscopically, strain hardening is minimal and there seems to be a constant generation of perturbations of similar wavelength.

Quintanilla-Terminel, Alejandra; Evans, Brian

2014-05-01

66

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

E-print Network

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

Fortin, Jérôme

67

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

68

Correlation of creep rate with microstructural changes during high temperature creep  

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

69

Elevated temperature deformation of thoria dispersed nickel-chromium  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

70

Post- and interseismic deformation due to both localized and distributed creep at depth (Invited)  

NASA Astrophysics Data System (ADS)

There are two end-member representations of the ductile lithosphere (i.e., the lower crust and uppermost mantle) commonly used in models of post- and interseismic deformation around strike-slip faults: either (1) laterally homogeneous ductile layers, with sharp contrasts in rheological properties between the layers, in which creep is distributed; or (2) discrete extensions of the fault at depth in which creep is fully localized. The most realistic representation of the ductile lithosphere on earthquake cycle time scales likely falls between these two end-members. Researchers have considered both distributed and localized creep when interpreting post- and interseismic deformation, although the two mechanisms are most commonly treated separately, with the localized creep often approximated by kinematic slip on planar faults. There are a few noteworthy models that considered the feedback between both distributed and localized creep, although those models were largely constrained to 2D geometries of infinite length faults. The thickness of shear zones in the ductile lithosphere may be comparable to the locking depth of the fault, and the existence of a deep shear zone does not preclude the possibility that some distributed creep occurs in the surrounding lithosphere. Furthermore, variations in rheology, including both rheological models and their parameters, may be more subtle than the discrete contrasts typically assumed. In this presentation, we consider models of postseismic deformation following a finite length, strike-slip fault, as well as models of interseismic deformation around an infinite length strike-slip fault. Both sets of models are capable of localized and distributed creep at depth, and use Maxwell viscoelasticity. We show that the horizontal surface velocities during the early postseismic period are most sensitive to the viscosity of the shear zone; however during much of the interseismic period the shear zone is not apparent from the surface deformation, which is consistent with very large uniform viscosities in the ductile lithosphere. On the other hand, the vertical postseismic surface deformation is highly sensitive to the depth-dependent distribution of viscosities, regardless of whether the model contains purely distributed creep or also includes a component of localized creep. Hence, vertical postseismic deformation can discriminate vertical contrasts in viscosity, but is not a good discriminant of localized vs. distributed creep at depth. Models that contain components of both localized and distributed creep predict transient postseismic deformation, characterized by a fast relaxation phase followed by a slower relaxation phase, even when the model only contains steady Maxwell viscosities. This transience is equivalent to that predicted in models that approximate the ductile lithosphere with transient viscoelasticity, and we discuss the implication on the lithosphere rheology inferred from deformation following the 1997 Manyi, China, earthquake. Finally, we address the mechanism in which shear zones might develop under strike-slip faults and the implication of power-law creep rheologies.

Hetland, E. A.; Zhang, G.; Hines, T.

2013-12-01

71

Plastic Deformation of Aluminum Single Crystals at Elevated Temperatures  

NASA Technical Reports Server (NTRS)

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

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

1956-01-01

72

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

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

73

Methods of investigating the deformation and strength properties of clayey soils under creep  

Microsoft Academic Search

Methods of determining the strength and deformability of soils under creep during triaxial compression are examined. A kinematic\\u000a method of determining the strength and deformability of soils with a consistency ranging from fluid to hard in accordance\\u000a with an unconsolidated-undrained scheme is proposed for such soils. It is demonstrated that the results of the experimental\\u000a investigations can be represented by

G. V. Sorokina

1996-01-01

74

Cavitation in the neck of a deformed Ti-47Al-2Nb-2Cr creep specimen  

SciTech Connect

In creep deformation, intergranular cavitation is the predominant damage process that leads to fracture. In addition to the strain rate, nucleation and growth of cavities are the most important issues to examine when considering material lifetimes. Cavities tend to grow on boundaries normal to the tensile stress axis. Constrained cavity growth models describe how the growth rate is retarded due to the need for the surrounding matrix to accommodate the volume increase. Near-{gamma} TiAl has a microstructure that is very sensitive to heat treatment and deformation history. In this study, the authors investigate a necked creep specimen upon which creep rates were evaluated in a history that started with a large stress and steadily decreased by stress changes through the end of the experiment. Since creep rates at similar stresses are as much as an order of magnitude higher than in a specimen deformed in a generally increasing stress change history, the cavitation evident in the neck is expected to be strongly affected by the particular deformation history in the material.

Sneary, P.R.; Beals, R.S.; Bieler, T.R. [Michigan State Univ., East Lansing, MI (United States). Dept. of Materials Science and Mechanics] [Michigan State Univ., East Lansing, MI (United States). Dept. of Materials Science and Mechanics

1996-05-15

75

High-Temperature Deformation of Enstatite Aggregates  

NASA Astrophysics Data System (ADS)

Although enstatite is a significant component of the upper mantle, its rheology is still poorly understood. We have performed an experimental investigation of the mechanical properties of enstatite at high pressure and temperature in the proto- and ortho-enstatite stability fields. Synthetic enstatite powders were produced by reacting San Carlos olivine powders with lab-grade quartz. Powders were hot-pressed at high PT, and were then baked at 1000C under controlled oxygen fugacity conditions to remove all hydrous defect species. The polycrystalline enstatite samples were deformed in a Paterson gas-medium apparatus at temperatures of 1200-1300C, an oxygen fugacity buffered at Ni/NiO, and confining pressures of 300 or 450 MPa. Under these conditions, samples were in the orthoenstatite field at 450 MPa and likely mainly in the protoenstatite field at 300 MPa. At both confining pressures, the mechanical data display a progressive increase of the stress exponent n from 1 to 3 as a function of differential stress, suggesting a transition from diffusional to dislocation creep. Non-linear least-square fits to the high-stress data yielded flow laws with n=3 and activation energies of 600 and 720 kJ/mol for ortho- and proto-enstatite, respectively. The measured strengths are significantly higher than those derived from Raleigh et al. (1971) and Ross and Nielsen (1978), due to the influence of water on the mechanical behavior of their samples. Deformed samples were analysed using optical microscopy, SEM and TEM. Because enstatite reverts to clinoenstatite during quenching, the microstructures present highly twinned grains composed of thin alternating domains of clino- and ortho-pyroxene. Nevertheless, the microstructures show evidence of dislocation processes in the form of undulatory extinction and kink bands. Crystallographic preferred orientations measured by EBSD are axisymmetric and indicate preferential slip on (100)[001]. High resolution TEM indicates that for samples deformed at 450MPa, the thin ortho- and clino-pyroxene lamellae are bound by partial c dislocations in (100) planes, suggesting extensive gliding of partial c dislocations on (100) in samples deformed in the orthoenstatite field. Our high-stress mechanical data for protoenstatite is in perfect agreement with the extrapolation of the flow law for dislocation creep on (100)[001], obtained for single crystals deformed in the protoenstatite stability field (Mackwell, 1991). This confirms that the deformation in our samples is likely controlled by slip on (100)[001], arguably the weakest slip system in enstatite. Comparison of our results with dislocation creep flow laws for olivine indicates that enstatite is almost half an order of magnitude stronger than olivine at our experimental conditions. However, as enstatite has a slightly higher activation energy than olivine, the difference in strength is not likely to be as high in the upper mantle.

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

2011-12-01

76

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

NASA Astrophysics Data System (ADS)

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.

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

2014-11-01

77

Lowering Soil Temperatures Improves Creeping Bentgrass Growth under Heat Stress  

Microsoft Academic Search

drate content in roots and shoots, and root growth and shoot growth and improved turf quality of creeping ben- High soil temperature is a major factor limiting growth of cool- tgrass up to the same level as that at optimal air and

Qingzhang Xu; Bingru Huang

2001-01-01

78

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

79

Thermomechanical analysis of solder joint fatigue and creep in a flip chip on board package subjected to temperature cycling loading  

Microsoft Academic Search

Thermo-mechanical stress analysis was conducted on a flip-chip-on-board (FCOB) package with underfill encapsulation. The solder joint fatigue and creep deformation response were modeled for a typical temperature cycling loading of -55 to 125 C. Two temperature cycling loading models with and without the curing part of the temperature history for the encapsulation process were investigated. Two-dimensional plane-strain finite element models

John H. L. Pang; Tze-Ing Tan; Suresh K. Sitaraman

1998-01-01

80

Creep deformation of a fully lamellar gamma based titanium aluminide alloy  

SciTech Connect

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

Herrouin, F.; Bowen, P.; Jones, I.P. [Univ. of Birmingham, Edgbaston (United Kingdom). School of Metallurgy and Materials

1997-12-31

81

Experimental research of the effects of preconsolidation on the time-dependent deformationscreep of marl  

NASA Astrophysics Data System (ADS)

Experimental research on marl prismatic specimens under uniaxial loading indicated that, under the constant uniaxial compressive stress, marl exhibits significant time-dependent deformations, creep. A rheological model for soft rock is defined for creep after the loading and unloading (Tomanovic in Mech. Time-Depend. Mater. 10(2):135-154, 2006), whereas material parameters for the rock concerned are determined based on the result of the creep test after the initial loading. The influence of the compressive stress preconsolidation level and the loading duration on material parameters that describe the creep represents the central part of this examination. For the purpose of quantification of material parameters of the rheological model that describes creep, the laboratory research has been resumed using series of prismatic specimens under uniaxial load. The paper presents some of the so far registered results of the marl creep behavior, following previously conducted creep tests at different stress levels and different loading duration.

Zivaljevic, S.; Tomanovic, Z.

2015-02-01

82

The creep of lead-free solders at elevated temperatures  

Microsoft Academic Search

Full implementation of the new generation of lead-free solders requires a detailed knowledge and understanding of their mechanical behavior. This paper reports an investigation of the creep behavior of three lead-free alloys: Sn-0.5 Cu, Sn-3.5 Ag, and Sn-3.8Ag-0.7Cu, at 75C, and compares their response to that of Sn-37Pb at the same temperature. In terms of stress and time to rupture,

W. J. Plumbridge; C. R. Gagg; S. Peters

2001-01-01

83

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

84

Multimechanism-Deformation Parameters of Domal Salts Using Transient Creep Analysis  

SciTech Connect

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.

MUNSON, DARRELL E

1999-09-01

85

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

NASA Technical Reports Server (NTRS)

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

Rogers, Jan R.; Hyers, Robert

2008-01-01

86

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

NASA Technical Reports Server (NTRS)

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.

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

1998-01-01

87

Nanogranular origin of concrete creep  

E-print Network

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 ...

Vandamme, Matthieu

88

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

NASA Astrophysics Data System (ADS)

Subsurface exploitation of the Earth's natural resources removes the natural system from its chemical and physical equilibrium. As such, groundwater extraction and hydrocarbon production from subsurface reservoirs frequently causes surface subsidence and induces (micro)seismicity. These effects are not only a problem in onshore (e.g. Groningen, the Netherlands) and offshore hydrocarbon fields (e.g. Ekofisk, Norway), but also in urban areas with extensive groundwater pumping (e.g. Venice, Italy). It is known that fluid extraction inevitably leads to (poro)elastic compaction of reservoirs, hence subsidence and occasional fault reactivation, and causes significant technical, economic and ecological impact. However, such effects often exceed what is expected from purely elastic reservoir behaviour and may continue long after exploitation has ceased. This is most likely due to time-dependent compaction, or 'creep deformation', of such reservoirs, driven by the reduction in pore fluid pressure compared with the rock overburden. Given the societal and ecological impact of surface subsidence, as well as the current interest in developing geothermal energy and unconventional gas resources in densely populated areas, there is much need for obtaining better quantitative understanding of creep in sediments to improve the predictability of the impact of geo-energy and groundwater production. The key problem in developing a reliable, quantitative description of the creep behaviour of sediments, such as sands and sandstones, is that the operative deformation mechanisms are poorly known and poorly quantified. While grain-scale brittle fracturing plus intergranular sliding play an important role in the early stages of compaction, these time-independent, brittle-frictional processes give way to compaction creep on longer time-scales. Thermally-activated mass transfer processes, like pressure solution, can cause creep via dissolution of material at stressed grain contacts, grain-boundary diffusion and precipitation on pore walls. As a first step to better describe creep in sands and sandstones, we have derived a simple model for intergranular pressure solution (IPS) within an ordered pack of spherical grains, employing existing IPS rate models, such as those derived by Renard et al. (1999) and Spiers et al. (2004). This universal model is able to predict the conditions under which each of the respective pressure solution serial processes, i.e. diffusion, precipitation or dissolution, is dominant. In essence, this creates generic deformation mechanism maps for any granular material. We have used our model to predict the amount and rate of compaction for sandstone reservoirs, and compared our predictions to known subsidence rates for reservoirs around the world. This gives a first order-comparison to verify whether or not IPS is an important mechanism in controlling reservoir compaction.

Hangx, Suzanne; Spiers, Christopher

2014-05-01

89

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

NASA Astrophysics Data System (ADS)

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

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

1980-04-01

90

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

SciTech Connect

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

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

1980-01-01

91

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

SciTech Connect

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

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

1990-01-15

92

Elevated temperature creep properties of NiAl cryomilled with and without Y2O3  

NASA Technical Reports Server (NTRS)

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

Whittenberger, J. Daniel; Luton, Michael J.

1995-01-01

93

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

E-print Network

on deformation characteristics. Mechanically, pressurized pore fluids reduce all the applied normal stresses. Ricard Keywords: stress corrosion brittle creep triaxial basalt Mt. Etna time-dependent deformation Time, a mechanism known as stress corrosion, allows rock to fail under a constant stress that is well below its

94

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

E-print Network

for the degree of Master of Philosophy at the University of Cambridge August 2003 #12;ii Preface This dissertation is submitted for the degree of Master of Philosophy in Modelling of Materials at the University was used to make predictions against variation of composition, stress and temperature. The dependence

Cambridge, University of

95

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

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

96

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

NASA Technical Reports Server (NTRS)

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.

Jadaan, Osama M.

1998-01-01

97

The creep of lead-free solders at elevated temperatures  

Microsoft Academic Search

Full implementation of the new generation of lead-free solders requires a detailed knowledge and understanding of their mechanical\\u000a behavior. This paper reports an investigation of the creep behavior of three lead-free alloys: Sn-0.5 Cu, Sn-3.5 Ag, and Sn-3.8Ag-0.7Cu,\\u000a at 75?C, and compares their response to that of Sn-37Pb at the same temperature. In terms of stress and time to rupture,

W. J. Plumbridge; C. R. Gagg; S. Peters

2001-01-01

98

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

NASA Technical Reports Server (NTRS)

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.

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

1977-01-01

99

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

NASA Astrophysics Data System (ADS)

The deformation of rocks in the Earth's lower crust is often localized in ductile shear zones. Strain localization in rocks deforming at high temperature and pressures may be induced by various physical, chemical, or structurally-related mechanisms. Here, we studied the initiation and propagation of localized deformation in the ductile deformation regime by high temperature deformation experiments on marble with weak or strong inclusions. As starting material we used samples of coarse-grained Carrara marble containing one or two thin artificially prepared sheets of fine-grained Solnhofen limestone or Arkansas novaculite, which act under the applied experimental conditions as soft or strong material heterogeneities, respectively. Samples were deformed in the dislocation creep regime using a Paterson-type gas deformation apparatus at 900C temperature and confining pressures of 300-400 MPa. Torsion experiments were performed on hollow cylinder samples at a bulk shear strain rate of ?1.9 x 10-4 s-1 to shear strains ? between 0.02 and 2.9. At low strain, twisted specimens with weak inclusions show minor strain hardening that is replaced by strain weakening at shear strains in excess of ?0.1- 0.2. Peak shear stress at the imposed condition is about 20MPa, which is ?8% lower than the strength of inclusion-free samples. Strain progressively localized within the weak inclusions with increasing bulk strain, approaching at ? ? 1 a strain ratio of ?24 with respect to the adjacent matrix strain. This ratio is about half of the strain ratio that is expected from the creep strength contrast between pure marble and limestone at the measured bulk stress. The localization of strain extended into narrow bands in front of the inclusions, where the degree of localization decays exponentially with increasing distance from the tip of the inclusion. Microstructural analysis shows twinning, recrystallization and the development of a strong crystallographic preferred orientation of the marble within this process zone, owing to stress concentration and associated strain localization at the tip of the inclusions. The recrystallization-induced weakening requires a minimum local shear strain of about 1 in the process zone, corresponding to a bulk shear strain of about 0.1. One sample deformed at constant torque reveals an increase of the bulk shear strain rate up to a factor of about 3 between ? ? 0.1 and 1, induced by intense recrystallization in the process zone. Additional brittle microfracturing adjacent to the inclusion tip was observed in a soft inclusion-bearing marble, deformed in triaxial compression at a bulk strain rate of 7.3 x 10-5 s-1 to an axial strain of ?0.02, induced by high stress concentrations. In contrast, strong inclusions do not show localization weakening presumably because the local strain in front of the inclusion is too low to initiate recrystallization. The experimental results demonstrate that interacting weak structural defects initiate localization of creeping carbonate rocks by enhanced dynamic recrystallization.

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

2013-12-01

100

High temperature tensile deformation behavior of Grade 92 steel  

NASA Astrophysics Data System (ADS)

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.

Alsagabi, Sultan; Shrestha, Triratna; Charit, Indrajit

2014-10-01

101

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

NASA Technical Reports Server (NTRS)

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

Haisler, W. E.

1983-01-01

102

Correlation of creep rate with microstructural changes during high temperature creep  

NASA Technical Reports Server (NTRS)

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

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

1973-01-01

103

Dislocation evolution during thermal creep deformation in V-4Cr-4Ti with various thermal and mechanical treatments  

NASA Astrophysics Data System (ADS)

Dislocation evolution during thermal creep deformation was investigated at 1023 K for V-4Cr-4Ti alloys with various thermal and mechanical treatments. Changes in the density and Burgers vector of dislocations were examined with various materials and experimental variables (e.g., cold work introducing dislocations, thermal aging introducing high density of Ti-rich precipitates, applied stress, and creep deformation levels). The Burgers vector analysis showed that, in the annealed specimens, dislocations induced by the thermal creep were predominantly of a/2<1 1 1> type. The densities of a<1 0 0> and a/2<1 1 1> type dislocations were comparable for the cold worked V-4Cr-4Ti, but the fraction of a/2<1 1 1> type dislocations increased with the creep deformation. Similar changes to the Burgers vector fraction were observed for specimens with a high density of precipitation prior to the cold work. On the other hand, cold work followed by aging (i.e., strain aging) was effective in keeping dislocation structures during the creep deformation.

Muroga, T.; Nagasaka, T.; Zheng, P. F.; Li, Y. F.; Watanabe, H.

2013-11-01

104

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

SciTech Connect

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

Michael J. Mills

2009-03-05

105

Characterizing viscous creep deformation of Martian landforms in Noachis and Hellas using MOC and MOLA data  

NASA Astrophysics Data System (ADS)

The presence of widespread "softened" terrain and large-scale debris flows on Mars has long been attributed to viscous creep and flow phenomena associated with near-surface ground ice in high latitude permafrost terrain. On the basis of Viking Orbiter images, Squyres (1989) identified two classes of creep-related landforms: (1) softened terrain, which results from in situ viscous deformation and is particularly evident in impact craters which exhibit degraded rims and flat topographic profiles, and (2) debris flows, which are produced by mass wasting along escarpments, e.g., lobate debris aprons, lineated valley fill, and concentric crater fill. Such features have been linked with evidence of ground ice in the upper hundreds of meters of soil at higher latitudes, with depths to the top of the ice less than 100-200 m (Squyres et al., 1992). We are using MOC and MOLA data to document the structural and topographic characteristics of softened landforms and debris flows in the Hellas and Noachis regions. By comparing the observed landforms to the results of finite-element models of viscous creep relaxation which incorporate recent laboratory measurements of ice/rock mixtures (Durham et al., 1997, 2000; Mangold et al., 1999), we can constrain the conditions necessary to allow such deformation on Mars. Durham W.B. (1997), JGR, 102, 16293-16302. Durham W.B. (2000) Second Intl. Conf. on Mars Polar Sci. and Exploration, LPI Contribution #1057, 28-29. Mangold N. (1999) LPSC, XXX, #1016. Squyres S. (1989) Icarus, 79, 229-288. Squyres S. (1992) in Mars, Ed. H Kieffer, Univ.Arizona Press, Tucson, 523-554.

Turtle, E. P.; Pathare, A. V.; Hartmann, W. K.; Crown, D.; Esquerdo, G. A.

2002-05-01

106

Relationship governing the effect of frequency and temperature on the fatigue resistance of creep-resisting nickel alloys  

SciTech Connect

Important components of gas turbine engines such as blades and turbine rotors made of creep-resisting nickel alloys, operate in a wide range of temperatures and loading frequencies. In conditions of high temperature, the frequency and temperature are the factors affecting the variation of the fatigue resistance characteristics of the creep-resisting nickel alloys. For this reason, the authors determine the relationships governing the effect of the cyclic loading frequency on the fatigue resistance in a wide temperature range, in order to use the multicycle fatigue characteristics usually obtained at loading frequencies of 25-50 Hz. The investigations were selected on nickel-based creep-resisting alloys: deformable EI867, EP109 alloys, and cast ZhS6k, ZhS6U, and VZhL12U alloys. Various relationships governing the effect of loading frequency on the fatigue resistance of EI867 alloy in the temperature ranges below and above 0.55-0.6 T/sub m/ were determined. It was shown that in the temperature ranges above 0.55-0.6 T/sub m/, the results of the fatigue tests carried out at various temperatures and loading frequencies can be described on the basis of the kinetic model with the piecewise-exponential dependences of the number of cycles to fracture on loading frequency at the field levels of alternating stress.

Ishchenko, I.I.; Sinaiskii, B.N.

1987-03-01

107

Creep of CMSX-4 superalloy single crystals: effects of rafting at high temperature  

Microsoft Academic Search

The creep performance of ?001?-orientated CMSX-4 superalloy single crystals at temperatures beyond 1000C is analysed. Rafting of the ?? structure occurs rapidly, e.g. for the 1150C\\/100MPa tests rafting is completed within the first 10h. At this stage and for a considerable time thereafter the creep strain rate decreases with increasing strain, implying a creep hardening effect which is absent at

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

1999-01-01

108

Effect of hydrogen on the low-temperature creep of a submicrocrystalline Ti6Al4V alloy  

Microsoft Academic Search

The effect of alloying with 0.0020.24 wt % H on the creep of the Ti-6Al-4V alloy at a temperature of ?0.15T\\u000a \\u000a m\\u000a (T\\u000a \\u000a m\\u000a is the melting temperature) is studied. The formation of a submicrocrystalline structure in the alloy is found to increase\\u000a the stress-rupture strength and the hydrogen embrittlement resistance. Possible causes of the increase in the deformation\\u000a localization

G. P. Grabovetskaya; O. V. Zabudchenko; E. N. Stepanova

2010-01-01

109

Creep mechanisms of a new Ni-Co-base disc superalloy at an intermediate temperature.  

PubMed

The microstructures of a new Ni-Co-base disc superalloy, TMW-4M3, before and after the creep test at 725 C/630 MPa have been systematically investigated by transmission electron microscopy (TEM). The crept microstructures were marked as three different deformation stages (I, II and III) corresponding to the gradually increased strain. At stage I, stacking fault (SF) shearing was the main deformation mechanism. The SF was extrinsic and lay on {111} plane. However, deformation microtwinning became the dominant mode at stage II and III. The average spacing of deformation twins decreased from 109 15 nm at stage II to 76 12 nm at stage III, whereas the twin thickness did not change significantly. The influence of stacking fault energy (SFE) of ? matrix on the deformation mechanism is discussed. It is suggested that lower SFE in TMW-4M3 is partly responsible for the enhanced creep resistance. PMID:22834947

Yuan, Y; Gu, Y F; Zhong, Z H; Osada, T; Cui, C Y; Tetsui, T; Yokokawa, T; Harada, H

2012-10-01

110

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

111

The effect of cerium on high temperature tensile and creep behavior of a superalloy  

NASA Astrophysics Data System (ADS)

The presence of trace impurities such as S and O can cause embrittlement during elevated and high temperature deformation of iron or nickel-base alloys. In this study various amounts of Ce, ranging from 0 to 0.24 wt pct, have been added to an iron-nickel base superalloy, Udimet 901, in order to study its role in the refining process of S and O in the melt, hot workability, creep and stress rupture, and microstructure. It is found that Ce addition decreases the 0 and S content in the melt and improves both the hot workability and creep ductility. An optimum residual Ce content of 30 ppm was found for which ductilities are maximum. Higher residual cerium contents result in deleterious hot embrittlement. SEM as well as TEM/STEM microscopy combined with X-ray EDS spectroscopy were used to determine the inclusion content present in the alloy as well as the fine spatial microchemistries, especially at grain boundaries.

Cosandey, F.; Li, D.; Sczerzenie, F.; Tien, J. K.

1983-03-01

112

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

113

High-Temperature Creep Behavior Of Fiber-Reinforced Niobium  

NASA Technical Reports Server (NTRS)

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

Petrasek, Donald W.; Titran, Robert H.

1990-01-01

114

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

NASA Technical Reports Server (NTRS)

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

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

1977-01-01

115

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

SciTech Connect

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.

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

1980-03-01

116

The effect of low angle boundary misorientation on creep deformation in the superalloy CM 247 LC  

NASA Astrophysics Data System (ADS)

The effect of low angle boundary misorientation on the creep properties of superalloy CM 247LC bicrystals has been investigated in the medium temperature - medium stress creep regime. Constant load tensile creep tests were performed on mixed Low Angle Boundary (LAB) samples with misorientations ranging from 3o-16o; the LABs where the boundaries were oriented approximately transverse to the tensile axis. Five repeats of each LAB sample were ruptured with an initial stress of 300 MPa and three repeats of each LAB sample were ruptured with an initial stress of 200 MPa, both at 950C. A drastic decrease in creep rupture life and strain to failure was observed in bicrystals with misorientations greater than 10. Fractography of the fracture surfaces indicated that a transition from ductile transgranular fracture to intergranular fracture coincided with the decrease in creep properties. The decrease in strain to failure was correlated to a decrease in the slip compatibility factor m'. Specimens of several misorientations were also interrupted prior to failure at strains of 2%, 5% and 10% and examined by electron microscopy techniques in an effort to better understand the sequences leading to failure. For samples that fractured intergranularly, voids formed adjacent to large MC carbides located at the LABs and propagated along the boundary, ultimately linking to cracks that initiated at the specimen edge. Electron Back Scattered Diffraction (EBSD) scans were performed and Crystal reference Orientation (CO) maps were generated from the partially crept specimens. An increase in misorientation from the crystal reference orientation was observed with increasing LAB misorientation for a given interrupted strain level indicative of the poorer slip compatibility at the higher misorientations Two bicrystals with nearly identical scalar misorientation, both 10, exhibited surprisingly different behavior with one failing intergranularly at low strain to failure and the other failing transgranularly at high strain to failure; these differences were related to the different slip compatibilities as determined by an analysis of the nature of their misorientations. In addition, grain boundary migration was prevalent in the samples that fractured transgranularly, but was rarely observed on any specimen that fractured intergranularly. Based on the collective observations, it is concluded that (1) it is necessary to consider more than just the scalar misorientation when considering whether a single crystal containing LABs should be rejected and (2) characterization of the properties of superalloy bicrystals grown using traditional Bridgman methods is difficult due to the complex, non-planar nature of the resulting LABs that is associated with their dendritic growth.

Kirsch, Mathew

117

An assessment of creep deformation and fracture behavior of 2.25Cr1Mo similar and dissimilar weld joints  

Microsoft Academic Search

The evaluation of the creep deformation and fracture behavior of a 2.25Cr-1Mo steel base metal, a 2.25Cr-1Mo\\/2.25Cr-1Mo similar\\u000a weld joint, and a 2.25Cr-1Mo\\/Alloy 800 dissimilar weld joint at 823 K over a stress range of 90 to 250 MPa has been carried\\u000a out. The specimens for creep testing were taken from single-V weld pads fabricated by a shielded metal arc-welding

K. Laha; K. S. Chandravathi; K. Bhanu Sankara Rao; S. L. Mannan; D. H. Sastry

2001-01-01

118

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)

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.

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

1998-01-01

119

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

SciTech Connect

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

Khabaz, Fardin, E-mail: rajesh.khare@ttu.edu; Khare, Ketan S., E-mail: rajesh.khare@ttu.edu; Khare, Rajesh, E-mail: rajesh.khare@ttu.edu [Department of Chemical Engineering, Texas Tech University, Lubbock, TX 79409 (United States)

2014-05-15

120

The effects of temperature, stress and salinity on the creep of frozen saline soil  

SciTech Connect

Gravel of the Prudhoe Bay area of Alaska used in the construction of artificial islands has been examined in constant load creep experiments to determine the effects of temperature, stress, and salinity on its creep behavior in unconfined compression. Over the range of conditions studied, it is found that the creep behavior is strongly dependent on each of these variables. In addition, the ice content of the specimen, itself a strong function of temperature and salinity, is found to be an important strength-determining parameter.

Nixon, M.S.; Pharr, G.M.

1984-09-01

121

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

NASA Technical Reports Server (NTRS)

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

Maile, K.

1982-01-01

122

Macro- and Micro-deformation Features of the Creeping Strand of the San Andreas Fault, and Evidence for Changes in Historic Creep Rate, Flook Ranch, Bitterwater Valley, CA  

NASA Astrophysics Data System (ADS)

Evidence of active right lateral creep on the San Andreas Fault (SAF) at Flook Ranch (latitude 36.3982 ) includes offset cultural features, prominent tectonic geomorphology, macro- to micro-scale deformation of late Holocene alluvium, and historic variations in rate of activity. At Flook Ranch, the fault zone consists of two N35 W-striking faults that bound a fault-parallel, linear swale that is bordered by two 0.5-m-high scarps. Trenches excavated at the site exposed massive silt and clay loam overlain by <1,100-year-old thin-bedded silt and gravel, and two (western and eastern) fault zones bounding, in part, the margins of the linear swale. Creep-related structures at the fault zones include 4-m-wide zones of abundant fractures extending across the eastern and western fault zones, broad synformal warping, and truncated alluvial deposits. Initial observations of faulted sand samples at the microscopic scale show many distinct, narrow (<0.5mm) faults that consist of ultra-fine grained (clay size) material and bound silt and silty sand units. Sand units immediately adjacent to faults are notable for their lack of textural features that might record faulting; no porosity reduction, grain size reduction, or localized preferred grain orientation is observed at fault contacts. At the eastern fault zone: (1) apparent vertical offsets range from <0.2 m to 1.0 m, (2) Reidel shears dip steeply to the east, strike 10 -30 clockwise from the main SAF zone, and flower upward into pervasive extensional fractures, and (3) Reidel shears, rotate clockwise into extensional fractures as they approach the ground surface. In comparison, the western fault zone is characterized by: (1) apparent vertical offsets of as much as 2 m, (2) steep west dipping Reidel shears that strike 0 -50 clockwise from the fault zone, and (3) fractures extending to the ground surface show no progressive clockwise rotation up section. A March 2003 survey of an offset 95 year-old fence line yielded a dextral offset of 1.19-1.51 m and a creep rate of 22-28 mm/yr. This creep rate is: (1) lower than a 1966 reported creep rate of 32-33 mm/yr of the same fence line (Brown and Wallace, 1968), and (2) lower than a 1983 reported historic creep rate of 28-32 mm/yr of the fence line (Cotton et al., 1986), but (3) greater than the average 26 year (1969-1995) creep rate of 16-17 mm/yr of a U.S.G.S creep meter located <10 m south of the fence (Schulz, 1989). In summary, structural relations exposed in trenches, coupled with survey data, indicate that creep is concentrated primarily within the two fault zones, and that these fault zones record different faulting styles and variability in activity and deformational histories.

Swanson, K. R.; Cashman, S. M.; Baldwin, J. N.

2004-12-01

123

Creep behavior of uranium carbide-based alloys  

NASA Technical Reports Server (NTRS)

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.

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

1975-01-01

124

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

NASA Technical Reports Server (NTRS)

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

Sheffler, K. D.

1970-01-01

125

Creep and creep rupture of strongly reinforced metallic composites  

NASA Technical Reports Server (NTRS)

A creep and creep damage theory is presented for metallic composites with strong fibers. Application is to reinforced structures in which the fiber orientation may vary throughout but a distinct fiber direction can be identified locally (local transverse isotropy). The creep deformation model follows earlier work and is based on a flow potential function that depends on invariants reflecting stress and the material symmetry. As the focus is on the interaction of creep and damage, primary creep is ignored. The creep rupture model is an extension of continuum damage mechanics and includes an isochronous damage function that depends on invariants specifying the local maximum transverse tension and the maximum longitudinal shear stress. It is posited that at high temperature and low stress, appropriate to engineering practice, these stress components damage the fiber/matrix interface through diffusion controlled void growth, eventually causing creep rupture. Experiments are outlined for characterizing a composite through creep rupture tests under transverse tension and longitudinal shear. Application is made to a thin-walled pressure vessel with reinforcing fibers at an arbitrary helical angle. The results illustrate the usefulness of the model as a means of achieving optimal designs of composite structures where creep and creep rupture are life limiting.

Robinson, D. N.; Binienda, W. K.; Miti-Kavuma, M.

1990-01-01

126

High-temperature strength and creep resistance of FeAl  

Microsoft Academic Search

In an effort to improve the high-temperature mechanical properties of FeAl, we investigated the effects of alloying addition and heat treatment temperature on the tensile and creep properties of Fe40at.% Al. Alloying of Fe40Al with titanium, molybdenum, zirconium, boron and carbon, and heat treating at 1300C resulted in significant improvement in strength and creep resistance due to solid solution and

R. S. Sundar; S. C. Deevi

2003-01-01

127

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

SciTech Connect

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

Not Available

1991-01-01

128

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

PubMed

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

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

2003-01-01

129

High temperature inelastic deformation under uniaxial loading - Theory and experiment  

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

130

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

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

131

Deformation of contour and Hawking temperature  

E-print Network

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

Chikun Ding; Jiliang Jing

2010-01-19

132

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

NASA Astrophysics Data System (ADS)

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 mlange 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.

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

2013-07-01

133

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

NASA Astrophysics Data System (ADS)

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.

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

2013-12-01

134

Creep of dry clinopyroxene aggregates  

NASA Astrophysics Data System (ADS)

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

Bystricky, Misha; Mackwell, Stephen

2001-01-01

135

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

NASA Astrophysics Data System (ADS)

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

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

2015-03-01

136

High Temperature, Non-contact, Electromagnetic Mechanical Apparatus for Creep Testing  

Microsoft Academic Search

\\u000a We describe the design and implementation of a second generation Electromagnetic Mechanical Apparatus (EMMA-2) capable of\\u000a Ultra High Temperature (UHT) creep testing. EMMA-2 uses a variable magnetic field to apply stress to ribbon specimens that\\u000a are self-heated with DC current. EMMA-2 is capable of continuous non-contact creep testing and operates in a controlled atmosphere.\\u000a Theoretical models are presented for mechanical

Sindhura Gangireddy; John W. Halloran; Zachary N. Wing

137

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

138

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

NASA Astrophysics Data System (ADS)

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.

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

2007-12-01

139

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

NASA Astrophysics Data System (ADS)

Advanced gas turbine engines, which use hot section airfoil cooling, present a wide range of design problems. The frequencies of applied loads and the natural frequencies of the blade also are important since they have significant effects on failure of the component due to fatigue phenomenon. Due to high temperature environment the thermal creep and fatigue are quite severe. One-dimensional creep model, using ANSYS has been formulated in order to predict the creep life of a gas turbine engine blade. Innovative mathematical models for the prediction of the operating life of aircraft components, specifically gas turbine blades, which are subjected to creep-fatigue at high temperatures, are proposed. The components are modeled by FEM, mathematically, and using similitude principles. Three models have been suggested and evaluated numerically and experimentally. Using FEM method for natural frequencies causes phenomena such as curve veering which is studied in more detail. The simulation studies on the life-limiting modes of failure, as well as estimating the expected lifetime of the blade, using the proposed models have been carried out. Although the scale model approach has been used for quite some time, the thermal scaling has been used in this study for the first time. The only thermal studies in literature using scaling for structures is by NASA in which materials of both the prototype and the model are the same, but in the present study materials also are different. The finite element method is employed to model the structure. Because of stress redistribution due to the creep process, it is necessary to include a full inelastic creep step in the finite element formulation. Otherwise over-conservative creep life predictions will be estimated if only the initial elastic stresses are considered. The experimental investigations are carried out in order to validate the models. The main contributions in the thesis are: (1) Using similitude theory for life prediction of components in general, and specifically using thermal scaling for the first time for prototype and model with two different materials. (2) Developing 1-D creep ANSYS macro to study creep effects to get meaningful results for industrial applications of gas turbine blade. (3) Analyzing the curve veering and flattening phenomena in rotating blade at thermal environment, using Lagrange-Bhat method. (4) Simple constitutive models in creep-fatigue interaction are proposed that can predict the lifetime in complicated situations of creep-fatigue, using the pure creep and pure fatigue test data.

Sabour, Mohammad Hossein

140

Creep and creep rupture of rock salt  

Microsoft Academic Search

A fundamental review is given of creep properties and flow processes of experimentally and naturally deformed rocksalt as background pertinent to waste repository design. Deformational behavior of halite single crystals is discussed first, followed by a brief treatment of experimentally deformed artifically prepared halite aggregates. The results of recent extensive quasi-static compression and creep tests on natural aggregates, especially on

1983-01-01

141

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

NASA Technical Reports Server (NTRS)

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

Zimmerman, Richard S.; Adams, Donald F.

1989-01-01

142

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

NASA Technical Reports Server (NTRS)

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

Zimmerman, Richard S.; Adams, Donald F.

1988-01-01

143

Creep compression behaviour of a polyurethane foam from cryogenic temperatures: size effect and long-term prediction  

NASA Astrophysics Data System (ADS)

The objective of this work was to predict the long term behavior of Polyurethane foam (PU) at very low-temperature, by applying the time-temperature superposition principle (TTSP). The experimental background of the TTSP was based on a Dynamical Mechanical Analysis technique. Two issues arise from this experimental approach: the relevance of the temperature range to apply the TTSP, and the possible size-effect associated to the small DMA samples. Firstly, on the studied temperature range (-170C; +180C) many transitions have been observed, particularly from -20C. Thus to apply the TTSP, it would be necessary to limit the temperature range (between temperature of molecular transitions, i.e. from -20C up to 80C). At very low temperatures, DMA spectra did not evidence any viscoelastic domain. However a deformation has been measured during creep tests in the same temperature range. So it would be necessary to determine which micro-mechanism is responsible for the observed deformation. Secondly, it was important to determine if the volume of DMA sample was representative. Several techniques have shown that a representative volume would be reached between 8 and 12mm3.

Denay, A. G.; Castagnet, S.; Roy, A.; Alise, G.

2010-06-01

144

Inelastic deformation and damage at high temperature  

Microsoft Academic Search

Combined experimental and theoretical investigations into the inelastic deformation and damage behavior of engineering alloys at elevated temperatures are being pursued. The analysis of previously performed strain rate change and relaxation tests on modified 9Cr-1Mo steel showed the need for inclusion of a recovery of state term in the growth laws for the state variables of the viscoplasticity theory based

E. Krempl

1992-01-01

145

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

NASA Technical Reports Server (NTRS)

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

Whittenberger, J. D.

1977-01-01

146

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

NASA Technical Reports Server (NTRS)

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

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

1987-01-01

147

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

SciTech Connect

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

Koyanagi, Takaaki [ORNL; Shimoda, Kazuya [Kyoto University, Japan; Kondo, Sosuke [Kyoto University, Japan; Hinoki, Tatsuya [Kyoto University, Japan; Ozawa, Kazumi [ORNL; Katoh, Yutai [ORNL

2014-12-01

148

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

NASA Technical Reports Server (NTRS)

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

Mathauser, Eldon E; Deveikis, William D

1957-01-01

149

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

NASA Astrophysics Data System (ADS)

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

Bo?ek, M.; Hoffmann, M.

1984-11-01

150

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

SciTech Connect

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

Cabet, Celine; Carroll, Laura; Wright, Richard

2013-10-01

151

Inelastic deformation and damage at high temperature  

NASA Astrophysics Data System (ADS)

Combined experimental and theoretical investigations into the inelastic deformation and damage behavior of engineering alloys at elevated temperatures are being pursued. The analysis of previously performed strain rate change and relaxation tests on modified 9Cr-1Mo steel showed the need for inclusion of a recovery of state term in the growth laws for the state variables of the viscoplasticity theory based on overstress (VBO). Recovery of state terms were introduced and the experimental results were satisfactorily simulated. The finite deformation theory of VBO has been developed further to include a convected derivative rationale for the choice of the objective stress rate. The reversing direct current voltage drop measurements during low cycle fatigue at elevated temperature were improved. A passive filter bank and new positioning devices for the coils were installed. Tests at 650 C and lasting several days showed excessive, uncontrollable temperature changes. It was decided to drop the test temperature to 538 C which is close to the operating temperature of type 304 stainless steel. The temperature fluctuations in torsion tests were within +/- 3 C which was considered satisfactory.

Krempl, E.

1992-06-01

152

Inelastic deformation and damage at high temperature  

SciTech Connect

Combined experimental and theoretical investigations into the inelastic deformation and damage behavior of engineering alloys at elevated temperatures are being pursued. The analysis of previously performed strain rate change and relaxation tests on modified 9Cr-1Mo steel showed the need for inclusion of a recovery of state term in the growth laws for the state variables of the viscoplasticity theory based on overstress (VBO). Recovery of state terms were introduced and the experimental results were satisfactorily simulated. The finite deformation theory of VBO has been developed further to include a convected derivative rationale for the choice of the objective stress rate. The reversing direct current voltage drop measurements during low cycle fatigue at elevated temperature were improved. A passive filter bank and new positioning devices for the coils were installed. Tests at 650{degrees}C and lasting several days showed excessive, uncontrollable temperature changes. It was decided to drop the test temperature to 538{degrees}C which is close to the operating temperature of Type 304 Stainless Steel. The temperature fluctuations in torsion tests were within {plus minus}3{degrees}C which was considered satisfactory. Testing will continue at 538{degrees}C.

Krempl, E.

1992-01-01

153

High-temperature deformation behavior of an Al-8.4Fe-3.6Ce dispersion-strengthened material  

NASA Astrophysics Data System (ADS)

The high-temperature deformation behavior of a dispersion-strengthened Al-8.4Fe-3.6Ce material studied by Yaney and Nix[1] has been reanalyzed using concepts used in the analysis of the creep behavior of Al-Fe-V-Si materials. The Al-8.4Fe-3.6Ce material presents a high volume fraction of submicron dispersoids. The stress exponent and the activation energy values are anomalously high-temperature dependent, as it is usually found in most reinforced materials. Although the creep behavior of this material has been described by the deformation of dispersoids, however, direct evidence of the deformation of the second-phase precipitates was not obtained. In this work, a new approach is further developed. This approach is based on the constant substructure slip creep equation modified by the presence of an interaction between dislocations and dispersoids. This approach is able to satisfactorily predict the creep behavior of the Al-8.4Fe-3.6Ce material.

Carreo, Fernando; Ruano, Oscar A.

1999-02-01

154

TENSILE AND CREEP PROPERTIES OF COLUMBIUM, TANTALUM, AND TITANIUM ALLOYS AT ELEVATED TEMPERATURES  

Microsoft Academic Search

S>Tensile and creep tests were conducted on niobium alloys B-33, Cb-752, ; SCb-291; tantalum alloy Ta--10W; and titanium alloy Ti-- 13Cr-- 11V--3Al at ; elevated temperatures. The niobium alloys and Ta-10W were tested at;

1962-01-01

155

Steady-state creep of single-phase crystalline matter at high temperature  

Microsoft Academic Search

Over the past 15 years important advances have been made in the experimental study of the microstructural changes occurring during the non-linear steady-state creep of single phase crystalline matter at elevated temperatures. Curiously, although the results of these painstaking studies have gone a long way toward elucidating the mechanism of this phenomenon, they have been largely ignored in favour of

S. Takeuchi; A. S. Argon

1976-01-01

156

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

DOEpatents

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

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

1987-04-28

157

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

Microsoft Academic Search

Advanced gas turbine engines, which use hot section airfoil cooling, present a wide range of design problems. The frequencies of applied loads and the natural frequencies of the blade also are important since they have significant effects on failure of the component due to fatigue phenomenon. Due to high temperature environment the thermal creep and fatigue are quite severe. One-dimensional

Mohammad Hossein Sabour

2005-01-01

158

Analysis of excessive deformation behavior of a PMMA-touch screen panel laminated material in a high temperature condition  

NASA Astrophysics Data System (ADS)

In this study, the bending and twisting deformations of a laminated material composed of PMMA (Poly Methyl Methacrylate) and TSP (Touch Screen Panel) were analyzed at a high temperature condition. At similar conditions, a PC (Polycarbonate)/TSP material had little deformation, but the PMMA-TSP material showed excessive bending deformation with twisting. To determine the factors that cause the deformation, 5 factors relating to material properties were systematically analyzed using FE (Finite element) analysis. The results demonstrated that variations in each of the 5 factors affect the deformation of material, and the strongest influence on the deformation behavior of the material at high temperature comes from the CTE, residual stress, and the creep effect. The validity of the analytical research was confirmed by comparing not only differences in the material properties of PMMA and PC, but also by comparing the results of the FE analysis of PMMA-TSP and PC-TSP. In the analysis, it was discovered that CTE, creep coefficient, and residual stress are the most significant causes of deformation of the laminated material.

Lee, Hyeon; Wang, Jaeyoon; Park, Seon-Mi; Hong, Seokmoo; Kim, Naksoo

2011-12-01

159

In-situ Creep Testing Capability Development for Advanced Test Reactor  

SciTech Connect

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

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

2010-08-01

160

Experimental deformation of olivine single crystals at mantle pressures and temperatures  

NASA Astrophysics Data System (ADS)

Deformation experiments were carried out in a deformation-DIA high-pressure apparatus (D-DIA) on oriented San Carlos olivine single crystals, at pressure ( P) ranging from 3.5 to 8.5 GPa, temperature ( T) from 1373 to 1673 K, and in poor water condition. Oxygen fugacity ( fO 2) was maintained within the olivine stability field and contact with enstatite powder ensured an orthopyroxene activity aopx = 1. Two compression directions were tested, promoting either [1 0 0] slip alone or [0 0 1] slip alone in (0 1 0) crystallographic plane, here called, respectively, a-slip and c-slip. Constant applied stress ( ?) and specimen strain rates ( ??) were monitored in situ using time-resolved X-ray synchrotron diffraction and radiography, respectively. Transmission electron microscopy (TEM) investigation of run products revealed that dislocation creep was responsible for sample deformation. Comparison of the obtained high- P deformation data with the data obtained at room- P by Bai et al. [Bai, Q., Mackwell, S.L., Kohlstedt D.L., 1991, High-temperature creep of olivine single crystals. 1. Mechanical results for buffered samples, Journal of Geophysical Research, 96, 2441-2463] - on identical materials deformed at comparable T- ?- fO 2- aopx conditions - allowed quantifying the P effect on a-slip and c-slip rheological laws. A slip transition with increasing pressure, from dominant a-slip to dominant c-slip, is documented. a-slip appears sensitive to pressure, which translates into the high activation volume Va*=124 cm/mol in the corresponding rheological law, while pressure has little effect on c-slip with Vc*=34 cm/mol. These results may explain the discrepancy between olivine low- P and high- P deformation data which has been debated in the literature for more than a decade.

Raterron, Paul; Amiguet, Elodie; Chen, Jiuhua; Li, Li; Cordier, Patrick

2009-01-01

161

Temperature dependence of optically induced cell deformations  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

162

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

NASA Technical Reports Server (NTRS)

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

Gates, Thomas S.; Feldman, Mark

1994-01-01

163

Creep behavior of copper at intermediate temperatures. II - Surface microstructural observations. III - A comparison with theory  

NASA Technical Reports Server (NTRS)

Three different types of microstructural slip features are noted to occur during the creep of Cu at 0.46-0.72 of absolute melting point. While single slip is associated with higher temperatures and lower stresses, complex wavy slip features are observed at higher temperatures and higher stresses as well as with increasing strains: suggesting the importance of cross-slip mechanisms. At lower temperatures and higher stresses the multiple-slip morphologies observed indicate that cross-slip mechanisms may control the creep of polycrystalline Cu only over a limited stress and temperature range. A phenomenological model is proposed which assumes that (1) cell boundaries within subgrains act as both sources of, and obstacles to, gliding dislocations, and (2) dislocation annihilation occurs at the cell boundaries by climb and cross-slip.

Raj, S. V.; Langdon, T. G.

1991-01-01

164

Microstructural changes during creep of CMSX-4 single crystal Ni base superalloy at 750 degrees C.  

PubMed

TEM studies of creep tested CMSX-4 nickel-base single crystal superalloy were performed to analyse a microstructure evolution during creep at temperature 750 degrees C, and uniaxial tensile stress of 675 MPa. Microstructural analyses were focused mainly on examination of dislocation configurations during primary and secondary creep stages of high temperature deformation. At such low temperature and high stress creep deformation proceed by cutting of gamma' particles by dislocations. It was found that primary creep is initiated by movement of dislocations with Burgers vector a/2 <110> in the gamma phase. The second type of dislocations active at primary creep stage are extended dislocation ribbons with overall a<112> Burgers vector, separated by superlattice stacking faults, cutting both the gamma and gamma' phases. The movement of the dislocation ribbons is inhibited at secondary creep stage by dislocation networks formed at gamma-gamma' interfaces. PMID:20500397

Dubiel, B T; Czyrska-Filemonowicz, A

2010-03-01

165

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

166

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

NASA Technical Reports Server (NTRS)

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

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

2013-01-01

167

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

SciTech Connect

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

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

2011-05-01

168

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

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

169

Dislocations in CaTiO 3 perovskite deformed at high-temperature: a transmission electron microscopy study  

Microsoft Academic Search

Dislocation configurations in natural single crystals of CaTiO3 perovskite deformed in high-temperature creep were examined and characterized by transmission electron microscopy. Screw dislocations with Burgers vector [100]pc and [011]pc, dissociated on the \\u000a$$(01\\\\bar 1)_{{\\\\text{pc}}} $$\\u000a\\u0009 plane, form rectangular networks with extended four-fold nodes in the shape of octagons, a configuration never observed in any of the previously investigated perovskites, except

P. Besson; J. P. Poirier; G. D. Price

1996-01-01

170

Effect of Nb and Cu on the high temperature creep properties of a high MnN austenitic stainless steel  

SciTech Connect

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

Lee, Kyu-Ho, E-mail: kyuhos@korea.ac.kr [High Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Department of Materials Science and Engineering, Korea University, Seoul 136-713 (Korea, Republic of); Suh, Jin-Yoo, E-mail: jinyoo@kist.re.kr [High Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Huh, Joo-Youl, E-mail: jyhuh@korea.ac.kr [Department of Materials Science and Engineering, Korea University, Seoul 136-713 (Korea, Republic of); Park, Dae-Bum, E-mail: parkdaebum@gmail.com [High Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Department of Materials Science and Engineering, Korea University, Seoul 136-713 (Korea, Republic of); Hong, Sung-Min, E-mail: magerit84@gmail.com [High Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Department of Materials Science and Engineering, Yonsei University, Seoul 120-749 (Korea, Republic of); Shim, Jae-Hyeok, E-mail: jhshim@kist.re.kr [High Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of); Jung, Woo-Sang, E-mail: wsjung@kist.re.kr [High Temperature Energy Materials Research Center, Korea Institute of Science and Technology, Seoul 136-791 (Korea, Republic of)

2013-09-15

171

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

SciTech Connect

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

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

1999-03-01

172

Anomalous creep behaviour of aluminium high current joint materials  

Microsoft Academic Search

During creep deformation the technical aluminium alloys EN AW-1350 (Al99.5) and EN AW-6060 (AlMgSi0.5) under certain conditions of stress and temperature show deformation thrusts of several millimetres, indicating discontinuous dynamic recrystallization. To study this anomalous creep behaviour in more detail the alloys were characterized by global and local texture measurements using neutron and electron backscatter diffraction (EBSD), respectively. In the

C.-G. Oertel; R. Tamm; W. Skrotzki; H.-G. Brokmeier

2005-01-01

173

Modeling creep behavior in a directionally solidified nickel base superalloy  

NASA Astrophysics Data System (ADS)

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

Ibanez, Alejandro R.

174

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

PubMed

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

Mashaan, Nuha Salim; Karim, Mohamed Rehan

2013-01-01

175

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

PubMed Central

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

Mashaan, Nuha Salim; Karim, Mohamed Rehan

2013-01-01

176

A neural network approach to elevated temperature creepfatigue life prediction  

Microsoft Academic Search

A new approach using a back-propagation neural network for life prediction was developed and demonstrated for predicting the elevated temperature (0.70.8Tm) creepfatigue behavior of Ni-base alloy INCONEL 690. The neural network was trained with five extrinsic parameters, characterized via a 251 fractional factorial design methodology, and an intrinsic parameter (final grain size). The back-propagation network training error, prediction error and

Vasisht Venkatesh; H. J Rack

1999-01-01

177

The transition from high temperature creep to fracture in Maryland diabase  

Microsoft Academic Search

The transition from high-temperature creep to brittle fracture in Maryland diabase was investigated as a function of confining pressure and strain rate. Experiments were conducted at 1000C. Confining pressure was varied to 450 MPa and strain rates from 210-3 s-1 to 410-6 s-1. At fixed strain rate, the rock strength first increased with pressure, reached a maximum, and then decreased

Y. Caristan

1982-01-01

178

Creep of plasma sprayed zirconia  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

179

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

180

Effect of initial gamma prime size on the elevated temperature creep properties of single crystal nickel base superalloys  

NASA Astrophysics Data System (ADS)

The influence of initial ?' size and shape on the high temperature creep properties of two single crystal nickel-base superalloys was investigated. The two alloys were chosen to represent different magnitudes of ?-?' lattice mismatch. A range of initial microstructures was produced by various quenching and aging treatments. Creep-rupture testing at 1000 C was performed under stresses where ?' directionally coarsens to form ?-?' lamellae in the early portion of the creep life. Both alloys exhibited a peak in creep resistance as a function of initial ?' size. The peak corresponded to an initial microstructure consisting of cuboidal precipitates aligned along [001] directions. These aligned cuboidal ?' particles directionally coarsened into a relatively perfect lamellar ?-?' structure in the early stages of creep, whereas the more irregularly shaped and distributed ?' particles in both under and overaged material formed more irregular lamellae with more imperfections. The alloy with a lower magnitude of mismatch was less sensitive to initial ?'size and shape.

Nathal, M. V.

1987-11-01

181

Life prediction methodology for thermal-mechanical fatigue and elevated temperature creep design  

NASA Astrophysics Data System (ADS)

Nickel-based superalloys are used for hot section components of gas turbine engines. Life prediction techniques are necessary to assess service damage in superalloy components resulting from thermal-mechanical fatigue (TMF) and elevated temperature creep. A new TMF life model based on continuum damage mechanics has been developed and applied to IN 738 LC substrate material with and without coating. The model also characterizes TMF failure in bulk NiCoCrAlY overlay and NiAl aluminide coatings. The inputs to the TMF life model are mechanical strain range, hold time, peak cycle temperatures and maximum stress measured from the stabilized or mid-life hysteresis loops. A viscoplastic model is used to predict the stress-strain hysteresis loops. A flow rule used in the viscoplastic model characterizes the inelastic strain rate as a function of the applied stress and a set of three internal stress variables known as back stress, drag stress and limit stress. Test results show that the viscoplastic model can reasonably predict time-dependent stress-strain response of the coated material and stress relaxation during hold times. In addition to the TMF life prediction methodology, a model has been developed to characterize the uniaxial and multiaxial creep behavior. An effective stress defined as the applied stress minus the back stress is used to characterize the creep recovery and primary creep behavior. The back stress has terms representing strain hardening, dynamic recovery and thermal recovery. Whenever the back stress is greater than the applied stress, the model predicts a negative creep rate observed during multiple stress and multiple temperature cyclic tests. The model also predicted the rupture time and the remaining life that are important for life assessment. The model has been applied to IN 738 LC, Mar-M247, bulk NiCoCrAlY overlay coating and 316 austenitic stainless steel. The proposed model predicts creep response with a reasonable accuracy for wide range of loading cases such as uniaxial tension, tension-torsion and tension-internal pressure loading.

Annigeri, Ravindra

182

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

SciTech Connect

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

Lumin Wang; Gary Was

2010-07-30

183

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

NASA Astrophysics Data System (ADS)

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.

Faraji, Masoumeh; Khalilpour, Hamid

2014-10-01

184

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

E-print Network

by stress differences and its rate is affected by temperature, grain size, and fluid chemistry. Pressure. Introduction [2] Pressure solution creep is a temperature- and stress- dependent deformation mechanism, the mechanochemical processes associated with pressure solution creep can be kinetically controlled by reactions

Dysthe, Dag Kristian

185

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

SciTech Connect

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

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

2014-01-01

186

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

NASA Technical Reports Server (NTRS)

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

Hebsur, Mohan G.; Miner, Robert V.

1987-01-01

187

THE DEVELOPMENT OF MICROSTRUCTURAL DAMAGE DURING HIGH TEMPERATURE CREEP-FATIGUE OF A NICKEL ALLOY  

SciTech Connect

Alloy 617 is the leading candidate material for an Intermediate Heat Exchanger (IHX) of the Very High Temperature Reactor (VHTR). To evaluate the behavior of this material in the expected service conditions, strain-controlled cyclic tests that include hold times up to 9000 s at maximum tensile strain were conducted at 950 degrees C. The fatigue resistance decreased when a hold time was added at peak tensile strain, owing to the mechanisms resulting in a change in fracture mode from transgranular in pure fatigue to intergranular in creepfatigue. Increases in the tensile hold duration beyond an initial value were not detrimental to the creepfatigue resistance. An analysis of the evolving failure modes was facilitated by interrupting tests during cycling for ex situ microstructural investigation.

L.J. Carroll; M.C. Carroll; C. Cabet; R.N. Wright

2013-02-01

188

An asperity model for fault creep and interseismic deformation in northeastern Japan  

NASA Astrophysics Data System (ADS)

We explore the potential geodetic signature of mechanical stress shadows surrounding inferred major seismic asperities along the Japan-Kurile subduction megathrust. Such stress shadows result from a decrease in creep rates late in the interseismic period. We simplify the rupture history along this megathrust as the repeated rupture of several asperities, each with its own fixed recurrence interval. In our models, megathrust creep throughout the interseismic period evolves according to velocity strengthening friction, as opposed to common kinematic back-slip models of locked or partially locked (i.e. coupled) regions of the megathrust. Such backslip models are usually constrained by onshore geodetic data and typically find spatially extensive and smooth estimates of plate coupling, a likely consequence of model regularization necessitated by poor model resolution. Of course, these large coupled regions could also correspond to seismogenic asperities, some of which have not experienced a significant earthquake historically. A subset of existing kinematic models of coupling along the Japan Trench, particularly those that use both horizontal and vertical geodetic data, have inferred a surprisingly deep (100 km) locked zone along the megathrust or have called upon complex, poorly constrained megathrust processes, such as subduction erosion, to explain the geodetic observations. Here, we posit two scenarios for distributions of asperities on a realistic 3-D megathrust interface along the Japan-Kurile Trench off NE Japan. These scenarios reflect common assumptions made before and after the 2011 Mw 9 Tohoku-oki earthquake. We find that models that include two shallow M9-class asperities (one corresponding to the 2011 Tohoku-Oki earthquake and one offshore of Hokkaido) and associated stress-shadows can explain geodetic observations of interseismic strain along the eastern halves of Honshu and Hokkaido. Specifically, models including localized fault creep can explain most of the observed long-term vertical subsidence in this region during the past century and thus appealing to processes such as deep locking or subduction erosion may not be required.

Kanda, Ravi V. S.; Hetland, Eric A.; Simons, Mark

2013-01-01

189

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

190

Creep behavior of a rapidly solidified Al-5Cr-2Zr alloy between room temperature and 823 K  

SciTech Connect

Rapidly solidified (RS) Al-Cr-Zr alloys are established contenders for applications in the aircraft industry where lower cost, lightweight substitutes for titanium alloys are being sought for use in the temperature range of 473 to 723 K. Creep resistance is one of the critical properties of any material intended for high temperature applications. Therefore, a precise knowledge of creep behavior and a clear understanding of the mechanisms controlling creep in these materials are of great importance. The good thermal stability exhibited by the RS Al-5Cr-2Zr (wt.%) alloy makes it a good candidate for applications where high creep resistance is needed. This paper presents the results of creep behavior over a wide range of temperatures (0.32 to 0.88 Tm, where Tm = 933 K is the melt temperature of pure aluminum) of an Al-5Cr-2Zr alloy processed by gas atomization and extrusion and includes a brief discussion on the creep mechanisms that may be involved.

Brahmi, A.; Gerique, T.; Lieblich, M.; Torralba, M. [Centro Nacional de Investigaciones Metalurgicas, Madrid (Spain). Dept. Metalurgia Fisica] [Centro Nacional de Investigaciones Metalurgicas, Madrid (Spain). Dept. Metalurgia Fisica

1996-12-15

191

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

NASA Astrophysics Data System (ADS)

The deformation behavior of a Ti-3Al-2.5V (wt pct) near-? alloy was investigated during in situ deformation inside a scanning electron microscopy (SEM). Two plates with distinct textures were examined. Tensile experiments were performed at 296 K and 728 K (455 C) (~0.4 T m), while a tensile-creep experiment was performed at 728 K (455 C) and 180 MPa ( ?/ ? ys = 0.72). The active deformation systems were identified in the ? phase using electron backscattered diffraction based slip-trace analysis and SEM images of the surface. Prismatic slip deformation was the dominant slip mode observed for all the experiments in both plates, which was supported by a critical resolved shear stress (CRSS) ratio analysis. However, due to the texture of plate 1, which strongly favored the activation of prismatic slip, the percentages of prismatic slip activity for specimens from plate 1 tested at 296 K and 728 K (23 C and 455 C) were higher than the specimens from plate 2 under the same testing conditions. T1 twinning was an active deformation mode at both 296 K and 728 K (23 C and 455 C), but the extent of twinning activity decreased with increased temperature. T1 twinning was more frequently observed in specimens from plate 2, which exhibited a higher fraction of twinning systems favoring activation at both 296 K and 728 K (23 C and 455 C). The tension-creep experiment revealed less slip and more grain boundary sliding than in the higher strain rate tensile experiments. Using a previously demonstrated bootstrapping statistical analysis methodology, the relative CRSS ratios of prismatic, pyramidal < a>, pyramidal < c+ a>, and T1 twinning deformation systems compared with basal slip were calculated and discussed in light of similar measurements made on CP Ti and Ti-5Al-2.5Sn (wt pct).

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

2014-12-01

192

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

SciTech Connect

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

Wu, H.F.

1987-01-01

193

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)

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.

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

2015-02-01

194

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

NASA Technical Reports Server (NTRS)

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.

Slavik, D.; Sehitoglu, H.

1988-01-01

195

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

SciTech Connect

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

Not Available

1991-12-31

196

High-temperature fatigue: Example of creep lifetime prediction for grade 2 alloy 800 at 550{degrees}C  

SciTech Connect

More sophisticated alloys are designed to allow modern factories to become more reliable. The materials used in nuclear power plants are subjected to different kinds of loading for periods which can reach 300,000 h. For example, the reliability of fast neutron reactors depends on the reliability of vapor generators. During departures, stops or in working periods, the pipes are submitted to cyclic thermal loading, which is related to the following two damage processes: fatigue and creep, as indicated on the fracture surfaces. Experimental data on the material characteristics such as tension, creep or creep-fatigue behavior are needed to verify the pipes design. Moreover, high-temperature low-cycle fatigue data are not sufficient to predict the fatigue-creep lifetime. High-temperature fatigue-creep experiments in working conditions (hold-time 1000 h and total strain amplitude 0.5%) cannot be conducted for economical reasons (experimental period up to 10 years). So, it is necessary to use fatigue-creep lifetime prediction methods.

Elgharad, A.; Azari, Z.; Pluvinage, G.

1994-12-01

197

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

PubMed

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

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

2005-11-15

198

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

USGS Publications Warehouse

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

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

2008-01-01

199

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

200

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

201

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

NASA Technical Reports Server (NTRS)

The present work is focused on studying the cycling actuation behavior of HTSMAs undergoing simultaneous creep and transformation. For the thermomechanical testing, a high temperature test setup was assembled on a MTS frame with the capability to test up to temperatures of 600 C. Constant stress thermal cycling tests were conducted to establish the actuation characteristics and the phase diagram for the chosen HTSMA. Additionally, creep tests were conducted at constant stress levels at different test temperatures to characterize the creep behavior of the alloy over the operational range. A thermodynamic constitutive model is developed and extended to take into account a) the effect of multiple thermal cycling on the generation of plastic strains due to transformation (TRIP strains) and b) both primary and secondary creep effects. The model calibration is based on the test results. The creep tests and the uniaxial tests are used to identify the viscoplastic behavior of the material. The parameters for the SMA properties, regarding the transformation and transformation induced plastic strain evolutions, are obtained from the material phase diagram and the thermomechanical tests. The model is validated by predicting the material behavior at different thermomechanical test conditions.

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

2010-01-01

202

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

PubMed

Nanostructured ferritic alloys are a new class of ultrafine-grained oxide dispersion-strengthened steels that have promising properties for service in extreme environments in future nuclear reactors. This is due to the remarkable stability of their complex microstructures containing numerous Y-Ti-O nanoclusters within grains and along grain boundaries. Although nanoclusters account primarily for the exceptional resistance to irradiation damage and high-temperature creep, little is known about the mechanical roles of the polycrystalline grains that constitute the ferritic matrix. Here we report an in situ mesoscale characterization of anisotropic responses of ultrafine ferrite grains to stresses using state-of-the-art neutron diffraction. We show the experimental determination of single-crystal elastic constants for a 14YWT alloy, and reveal a strong temperature-dependent elastic anisotropy that leads to elastic softening and instability of the ferrite. We also demonstrate, from anisotropy-induced intergranular strains, that a deformation crossover exists from low-temperature lattice hardening to high-temperature lattice softening in response to extensive plastic deformation. PMID:25300893

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

2014-01-01

203

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

NASA Astrophysics Data System (ADS)

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.

Demestral, B.; Eggeler, G.; Klam, H.-J.

1996-04-01

204

Microstructural changes of CM186LC single-crystal superalloy during creep deformation at 750 degrees C.  

PubMed

The microstructure of creep-tested CM186LC Ni-base single-crystal alloy was studied to assess its suitability for use in the gas turbine environment. Creep tests were conducted at 750 degrees C and at stresses of 560 and 675 MPa up to 11 440 h. The microstructure of fractured and terminated specimens was investigated by light microscopy, scanning electron microscopy and analytical transmission electron microscopy. Microstructural analysis revealed the differences in the microstructure of creep-tested CM186LC depending on the stress applied during creep at 750 degrees C. PMID:17100893

Dubiel, B; Czyrska-Filemonowicz, A

2006-10-01

205

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

SciTech Connect

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.

Han, G.M., E-mail: gmhan@imr.ac.cn; Yu, J.J.; Hu, Z.Q.; Sun, X.F.

2013-12-15

206

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

SciTech Connect

A high-temperature flaw assessment procedure is described. This procedure is a result of a collaborative effort between Electric Power Research Institute in the United States, Central Research Institute of Electric Power Industry in Japan, and Nuclear Electric plc in the United Kingdom. The procedure addresses preexisting defects subject to creep-fatigue loading conditions. Laws employed to calculate the crack growth per cycle are defined in terms of fracture mechanics parameters and constants related to the component material. The crack-growth laws can be integrated to calculate the remaining life of a component or to predict the amount of crack extension in a given period. Fatigue and creep crack growth per cycle are calculated separately, and the total crack extension is taken as the simple sum of the two contributions. An interaction between the two propagation modes is accounted for in the material properties in the separate calculations. In producing the procedure, limitations of the approach have been identified. 25 refs., 1 fig.

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

1990-10-01

207

Application of time-temperature-stress superposition on creep of wood-plastic composites  

NASA Astrophysics Data System (ADS)

Time-temperature-stress superposition principle (TTSSP) was widely applied in studies of viscoelastic properties of materials. It involves shifting curves at various conditions to construct master curves. To extend the application of this principle, a temperature-stress hybrid shift factor and a modified Williams-Landel-Ferry (WLF) equation that incorporated variables of stress and temperature for the shift factor fitting were studied. A wood-plastic composite (WPC) was selected as the test subject to conduct a series of short-term creep tests. The results indicate that the WPC were rheologically simple materials and merely a horizontal shift was needed for the time-temperature superposition, whereas vertical shifting would be needed for time-stress superposition. The shift factor was independent of the stress for horizontal shifts in time-temperature superposition. In addition, the temperature- and stress-shift factors used to construct master curves were well fitted with the WLF equation. Furthermore, the parameters of the modified WLF equation were also successfully calibrated. The application of this method and equation can be extended to curve shifting that involves the effects of both temperature and stress simultaneously.

Chang, Feng-Cheng; Lam, Frank; Kadla, John F.

2013-08-01

208

Probabilistic models for creep-fatigue in a steel alloy  

NASA Astrophysics Data System (ADS)

In high temperature components subjected to long term cyclic operation, simultaneous creep and fatigue damage occur. A new methodology for creep-fatigue life assessment has been adopted without the need to separate creep and fatigue damage or expended life. Probabilistic models, described by hold times in tension and total strain range at temperature, have been derived based on the creep rupture behavior of a steel alloy. These models have been validated with the observed creep-fatigue life of the material with a scatter band close to a factor of 2. Uncertainties of the creep-fatigue model parameters have been estimated with WinBUGS which is an open source Bayesian analysis software tool that uses Markov Chain Monte Carlo method to fit statistical models. Secondly, creep deformation in stress relaxation data has been analyzed. Well performing creep equations have been validated with the observed data. The creep model with the highest goodness of fit among the validated models has been used to estimate probability of exceedance at 0.6% strain level for the steel alloy.

Ibisoglu, Fatmagul

209

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

SciTech Connect

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

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

1997-09-01

210

High-temperature creep with physical and chemical aging, and associated viscoelastic constitutive equations of polyimide-matrix composites  

SciTech Connect

The high-temperature creep with physical and chemical aging of a polyimide-matrix composite has been studied with a combined experimental and analytical micromechanics approach. High-temperature aging and creep experiments are carried out to determine the effects of aging on both a neat polyimide (Avimid-N) resin and polyimide-matrix composite. The effect of aging on the polyimide resin is found to be in the form of a volume reduction and a small change in its glass- transition temperature. For both the neat polyimide resin and its composite, aging strains have been distinguished from total high-temperature strains and, thus, true mechanical creep strains can be properly determined. A micromechanics model based on the recently developed homogenization theory is used to study the viscoelastic effective constitutive equations of the composite. The effect of aging-induced property change is taken into account implicitly, through the input neat resin data in the formulation. Comparisons are made between the homogenization predictions and the experimentally obtained effective properties, and good agreement is observed. In the long-term high-temperature creep, it has been found that the complexities associated with the composite microstructural inhomogeneities and imperfection may lead to some discrepancies between the predictions and the experimental results.

Skontorp, A.; Wang, S.S. [Univ. of Houston, TX (United States)

1995-12-31

211

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

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

212

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

NASA Technical Reports Server (NTRS)

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.

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

1995-01-01

213

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

NASA Astrophysics Data System (ADS)

The Neoproterozoic Ribeira belt is subdivided in two domains with contrasting tectonic characteristics. The northern domain is dominated by shallowly dipping foliations and orogen-normal thrust tectonics. The southern domain is characterized by a 1000-km-long network of anastomosing transcurrent shear zones parallel to the belt. This contrast is interpreted as reflecting continent-continent convergence that is almost orthogonal to the margins in the northern domain and significantly oblique in the southern domain. The central, transitional, domain of the Ribeira belt displays the northern termination of the transcurrent shear zone network: the Alm Para?ba-Pdua shear zone system (APPSS). The 250-km-long Alm Para?ba-Pdua system involves granulites facies mylonites deformed through transpression. A detailed study of the microstructure and lattice preferred orientation (LPO) of the rock-forming minerals in these granulite mylonites allow a better understanding of deformation mechanisms active at high temperature in the crust. Plagioclase crystals are plastically deformed; they display curved twins and cleavages, mechanical twins, and evidence of dynamic recrystallization. LPO of plagioclase is consistent with activation of the (010) [100] and (010) [001] slip systems. LPO of orthopyroxene and amphibole indicates that these minerals have been deformed through dislocation creep with the activation of the (100) [001] slip system. Quartz in granulite mylonite displays evidence of extensive growth through grain boundary migration. The LPO of quartz is therefore the result of a static transformation of an initial, syn-kinematic LPO, and cannot be straightforwardly interpreted in terms of deformation mechanisms active during mylonitization.

Egydio-Silva, Marcos; Vauchez, Alain; Bascou, Jrme; Hippertt, Joo

2002-07-01

214

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

NASA Astrophysics Data System (ADS)

The 9Cr-2W ferritic-martensitic steel (i.e. Grade 92 steel) possesses excellent mechanical and thermophysical properties; therefore, it has been considered to suit more challenging applications where high temperature strength and creep-rupture properties are required. The high temperature deformation mechanism was investigated through a set of tensile testing at elevated temperatures. Hence, the threshold stress concept was applied to elucidate the operating high temperature deformation mechanism. It was identified as the high temperature climb of edge dislocations due to the particle-dislocation interactions and the appropriate constitutive equation was developed. In addition, the microstructural evolution at room and elevated temperatures was investigated. For instance, the microstructural evolution under loading was more pronounced and carbide precipitation showed more coarsening tendency. The growth of these carbide precipitates, by removing W and Mo from matrix, significantly deteriorates the solid solution strengthening. The MX type carbonitrides exhibited better coarsening resistance. To better understand the thermal microstructural stability, long tempering schedules up to 1000 hours was conducted at 560, 660 and 760C after normalizing the steel. Still, the coarsening rate of M23C 6 carbides was higher than the MX-type particles. Moreover, the Laves phase particles were detected after tempering the steel for long periods before they dissolve back into the matrix at high temperature (i.e. 720C). The influence of the tempering temperature and time was studied for Grade 92 steel via Hollomon-Jaffe parameter. Finally, the irradiation performance of Grade 92 steel was evaluated to examine the feasibility of its eventual reactor use. To that end, Grade 92 steel was irradiated with iron (Fe2+) ions to 10, 50 and 100 dpa at 30 and 500C. Overall, the irradiated samples showed some irradiation-induced hardening which was more noticeable at 30C. Additionally, irradiation-induced defect clusters and dislocation loops were observed and the irradiated samples did not show any bubble or void.

Alsagabi, Sultan

215

Modeling of combined high-temperature creep and cyclic plasticity in components using continuum damage mechanics  

NASA Astrophysics Data System (ADS)

A computer-based finite-element viscoplastic damage solver is presented to analyze structural components subject to combined cyclic thermal and mechanical loading. The solver is capable of predicting the combined evolution of creep and cyclic plasticity damage by solution of the combined boundary-initial value problem. The solver has been used to predict the high-temperature behavior of a slag tap component subjected to cyclic thermal loading generated by infrared heaters and water cooling ducts. It is found that the initiation of damage and microcracking occur early in the lifetime at about 3000 cycles adjacent to the cooling duct. The propagation of failure zones stabilizes at 60,000 cycles after which no further damage evolution occurs.

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

1992-06-01

216

Creep analysis of fuel plates for the Advanced Neutron Source  

SciTech Connect

The reactor for the planned Advanced Neutron Source will use closely spaced arrays of fuel plates. The plates are thin and will have a core containing enriched uranium silicide fuel clad in aluminum. The heat load caused by the nuclear reactions within the fuel plates will be removed by flowing high-velocity heavy water through narrow channels between the plates. However, the plates will still be at elevated temperatures while in service, and the potential for excessive plate deformation because of creep must be considered. An analysis to include creep for deformation and stresses because of temperature over a given time span has been performed and is reported herein.

Swinson, W.F.; Yahr, G.T.

1994-11-01

217

Temperature dependent deformation mechanisms in pure amorphous silicon  

NASA Astrophysics Data System (ADS)

High temperature nanoindentation has been performed on pure ion-implanted amorphous silicon (unrelaxed a-Si) and structurally relaxed a-Si to investigate the temperature dependence of mechanical deformation, including pressure-induced phase transformations. Along with the indentation load-depth curves, ex situ measurements such as Raman micro-spectroscopy and cross-sectional transmission electron microscopy analysis on the residual indents reveal the mode of deformation under the indenter. While unrelaxed a-Si deforms entirely via plastic flow up to 200 C, a clear transition in the mode of deformation is observed in relaxed a-Si with increasing temperature. Up to 100 C, pressure-induced phase transformation and the observation of either crystalline (r8/bc8) end phases or pressure-induced a-Si occurs in relaxed a-Si. However, with further increase of temperature, plastic flow rather than phase transformation is the dominant mode of deformation. It is believed that the elevated temperature and pressure together induce bond softening and "defect" formation in structurally relaxed a-Si, leading to the inhibition of phase transformation due to pressure-releasing plastic flow under the indenter.

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

2014-03-01

218

Temperature dependent deformation mechanisms in pure amorphous silicon  

SciTech Connect

High temperature nanoindentation has been performed on pure ion-implanted amorphous silicon (unrelaxed a-Si) and structurally relaxed a-Si to investigate the temperature dependence of mechanical deformation, including pressure-induced phase transformations. Along with the indentation load-depth curves, ex situ measurements such as Raman micro-spectroscopy and cross-sectional transmission electron microscopy analysis on the residual indents reveal the mode of deformation under the indenter. While unrelaxed a-Si deforms entirely via plastic flow up to 200?C, a clear transition in the mode of deformation is observed in relaxed a-Si with increasing temperature. Up to 100?C, pressure-induced phase transformation and the observation of either crystalline (r8/bc8) end phases or pressure-induced a-Si occurs in relaxed a-Si. However, with further increase of temperature, plastic flow rather than phase transformation is the dominant mode of deformation. It is believed that the elevated temperature and pressure together induce bond softening and defect formation in structurally relaxed a-Si, leading to the inhibition of phase transformation due to pressure-releasing plastic flow under the indenter.

Kiran, M. S. R. N., E-mail: kiran.mangalampalli@anu.edu.au; Haberl, B.; Williams, J. S.; Bradby, J. E. [Department of Electronic Materials Engineering, Research School of Physics and Engineering, Australian National University, Canberra, Australian Capital Territory 0200 (Australia)

2014-03-21

219

Effect of initial gamma prime size on the elevated temperature creep properties of single crystal nickel base superalloys  

NASA Technical Reports Server (NTRS)

The influence of initial gamma-prime size and shape on the high-temperature creep properties of two single-crystal Ni-base superalloys was investigated. The two alloys were chosen to represent different magnitudes of gamma/gamma-prime lattice mismatch. A range of initial microstructures was produced by various quenching and aging treatments. Creep-rupture testing at 1000 C was performed under stresses where gamma-prime directionally coarsens to form gamma/gamma-prime lamellae in the early portion of the creep life. Both alloys exhibited a peak in creep resistance as a function of initial gamma-prime size. The peak corresponded to an initial microstructure consisting of cuboidal precipitates aligned along 001 line directions. These aligned cuboidal gamma-prime particles directionally coarsened into a relatively perfect lamellar gamma/gamma-prime structure in the early stages of creep, whereas the more irregularly shaped and distributed gamma-prime particles in both under- and overaged material formed more irregular lamellae with more imperfections. The alloy with a lower magnitude of mismatch was less sensitive to initial gamma-prime size and shape.

Nathal, M. V.

1987-01-01

220

Correlation of Creep Behavior of Domal Salts  

SciTech Connect

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.

Munson, D.E.

1999-02-16

221

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

NASA Technical Reports Server (NTRS)

An uncoupled constitutive model for predicting the transient response of thermal and rate dependent, inelastic material behavior was developed. The uncoupled model assumes that there is a temperature below which the total strain consists essentially of elastic and rate insensitive inelastic strains only. Above this temperature, the rate dependent inelastic strain (creep) dominates. The rate insensitive inelastic strain component is modelled in an incremental form with a yield function, blow rule and hardening law. Revisions to the hardening rule permit the model to predict temperature-dependent kinematic-isotropic hardening behavior, cyclic saturation, asymmetric stress-strain response upon stress reversal, and variable Bauschinger effect. The rate dependent inelastic strain component is modelled using a rate equation in terms of back stress, drag stress and exponent n as functions of temperature and strain. A sequence of hysteresis loops and relaxation tests are utilized to define the rate dependent inelastic strain rate. Evaluation of the model has been performed by comparison with experiments involving various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy X.

Haisler, W. E.

1983-01-01

222

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

NASA Technical Reports Server (NTRS)

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

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

1984-01-01

223

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

224

Very slow creep tests on salt samples  

Microsoft Academic Search

Long-term creep tests have been performed on rock-salt and argillite samples under very small uniaxial loadings (sigma = 0.02 to 0.1 MPa) . To minimize the effects of temperature variations, testing devices were set in a mine where temperature fluctuations are of the order of one-hundredth of a degree Celsius. The mechanical loading was provided by dead weights. The deformations

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

2010-01-01

225

On the formation of {l_angle}010{r_angle}-dislocations in the {gamma}{prime}-phase of superalloy single crystals during high temperature low stress creep  

SciTech Connect

The cutting of {gamma}{prime}-particles by dislocations during shear creep deformation of CMSX 6 superalloy single crystals loaded on the macroscopic crystallographic shear system {l_angle}110{r_angle}{l_brace}111{r_brace} at T = 1,025 C and {tau} = 85 MPa is analyzed using transmission electron microscopy (TEM). The formation of a {l_angle}010{r_angle}-dislocation in the {gamma}{prime}-phase was observed and investigated by means of stereo microscopy, line trace and g{center_dot}b-analysis. Two {gamma}-matrix channel dislocations with different Burgers vectors (b) of type a{sub 0}/2<110> jointly shear the {gamma}{prime}-particle where they form a superdislocation with a total Burgers vector of a{sub 0}{l_angle}010{r_angle}. The present paper provides microstructural evidence for this high temperature cutting process. The results are discussed in relation to the evolution of the dislocation structure in the {gamma}-channels during primary creep. Peach-Koehler forces were calculated to explain the formation of the {l_angle}010{r_angle}-dislocation.

Eggeler, G. [Ruhr-Univ. Bochum (Germany). Inst. fuer Werkstoffe-Werkstoffwissenschaft] [Ruhr-Univ. Bochum (Germany). Inst. fuer Werkstoffe-Werkstoffwissenschaft; Dlouhy, A. [Academy of Sciences, Brno (Czech Republic). Inst. of Physics and Materials] [Academy of Sciences, Brno (Czech Republic). Inst. of Physics and Materials

1997-10-01

226

Temperature dependence of anelastic deformation in polycrystalline silicon nitride  

SciTech Connect

The influence of grain-boundary sliding on the evaluation of the apparent Young's modulus and plastic-deformation (flow) stress was investigated by bending tests for two types of silicon nitrides sintered with Y[sub 2]O[sub 3]-based additives. The apparent Young's moduli measured at high temperatures are consistent with those predicted from a theory based on polycrystalline anelasticity due to grain-boundary sliding. The temperature dependence of the critical bending stress for the onset of plastic deformation shows viscoplastic properties of the intergranular glass. The ductile-to-brittle transition of fracture is discussed by the bending strengths normalized by the measured Young's modulus.

Sato, Kazunori; Tanaka, Kohichi; Nakano, Yoshinori (Nagaoka Univ. of Technology, Niigata (Japan). Dept. of Mechanical Engineering); Mori, Tsutomu (Tokyo Inst. of Tech., Yokohama (Japan). Dept. of Materials Science and Engineering)

1993-08-01

227

High pressure and temperature deformation experiments on San Carlos olivine and implications for upper mantle anisotropy  

NASA Astrophysics Data System (ADS)

Crystallographic preferred orientation developed in olivine due to shearing in the mantle is thought to be the prominent reason behind seismic anisotropy in the upper mantle. Seismic anisotropy in upper mantle can be observed up to a depth of 350 km with a marked drop in the strength of anisotropy seen around 250 km. Studies on natural rock samples from the mantle and deformation experiments performed on olivine have revealed that olivine deforms mainly through dislocation creep with Burgers vectors parallel to the [100] crystallographic axis under low pressure conditions (up to 3 GPa). Under similar pressures, evidence of [001] slip has been reported due to the presence of water. In order to understand the deformation mechanism in olivine at pressures greater than 3 GPa, we have performed experiments using the deformation DIA multi-anvil apparatus. The DIA consist of 6 square faceted anvils that compress a cubic high-pressure assembly. The deformation DIA possesses two vertically acting opposing inner rams, which can be operated independently of the main compressive force to deform the sample assembly. The experimental setup consists of a hot-pressed sample of polycrystalline dry San Carlos olivine 0.2 mm cut from a 1.2 mm diameter core at 45 . This slice is sandwiched between alumina pistons also cut at 45 in simple shear geometry. Experiments have been performed at 3, 5 and 8 GPa at a deformation anvil strain rate of 1.0x10-4 s-1and temperatures between 1200-1400 C. Deformed samples were cut normal to the shear plane and parallel to the shear direction. Then the sample was polished and analyzed using electron back scattered diffraction (EBSD) to identify the crystallographic preferred orientation (CPO). The fabric that developed in olivine deformed at 3 GPa mainly resulted from the [100] slip on the (010) plane. Samples deformed at 5 GPa showed both [100] and [001] slip. On the other hand, samples deformed at 8 GPa and 1200 C, show deformation mainly through slip of the [001] slip on the {0hk} plane. These observations can be interpreted as resulting from the progressive hardening of [100] slip with respect to [001] slip with increasing pressure. TEM observations have been made on several of the recovered samples in order to correlate the developed CPO with the action of specific dislocations. Samples deformed at 8 GPa and 1200 C show straight edge dislocations in the plane normal to the diffraction vector, g: 004. Whereas, experiments performed at 1400 C and 8 GPa resulted in very few visible subgrains in the SEM orientation contrast image and only very weak CPO could be observed. TEM study on this sample shows that [001] & [100] edge dislocations were co-activated in climb-configuration which resulted in no perceptible CPO. These results lead us to believe that the transition that occurs between a-slip to c-slip with increasing pressure is rather a gradual process. On the other hand our results imply that at depths over 250 km in the upper mantle, temperatures may be high enough to reinitiate [100] slip. Co-activation of both a-slip and c-slip will not lead to any CPO and the mantle will become seismically isotropic in this scenario. This might be the reason for isotropic behavior of mantle below 250 km depth.

Shekhar, Sushant; Frost, Daniel J.; Walte, Nicolas; Miyajima, Nobuyoshi; Heidelbach, Florian

2010-05-01

228

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

Microsoft Academic Search

Directionally solidified (DS) and oxide dispersion strengthened (ODS) superalloys like CM 247 LC and MA 760 exhibit elongated\\u000a macrograins. In uniaxial creep tests, the creep strength of such alloys in the direction of the longitudinal grains is higher\\u000a than that of an equiaxed grain structure, because significantly less grain boundary (GB) segments are perpendicular to the\\u000a axis of the applied

B. Demestral; G. Eggeler; H.-J. Klam

1996-01-01

229

A creep apparatus to explore the quenching and ageing phenomena of PVC films  

NASA Technical Reports Server (NTRS)

A creep apparatus has been constructed for an in situ determination of length and length change. Using this apparatus, the creep behavior of PVC thin films associated with quenching and aging was studied. The more severe the quench through the glass transition temperature, the greater is the instantaneous elastic deformation and the subsequent creep behavior. As aging proceeds, the quenched films gradually lose the ductility incurred by quenching. These results agree well with the well-known phenomena of physical aging. Thus, the changes reflecting molecular mobilities due to quenching and aging can be properly monitored by such a creep apparatus.

Lee, H. H. D.; Mcgarry, F. J.

1991-01-01

230

Effect of hydrogen on the low-temperature creep of a submicrocrystalline Ti6Al4V alloy  

Microsoft Academic Search

The effect of alloying with 0.002-0.24 wt % H on the creep of the Ti-6Al-4V alloy at a temperature of 0.15 T m ( T m is the melting temperature) is studied. The formation of a submicrocrystalline structure in the alloy is found to increase the stress-rupture strength and the hydrogen embrittlement resistance. Possible causes of the increase in the

G. P. Grabovetskaya; O. V. Zabudchenko; E. N. Stepanova

2010-01-01

231

Creep of Uncoated and Cu-Cr Coated NARloy-Z  

NASA Technical Reports Server (NTRS)

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.

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

1998-01-01

232

Irradiation creep at temperatures of 400 {degrees}C and below for application to near-term fusion devices  

SciTech Connect

To study irradiation creep at 400{degrees}C and below, a series of six austenitic stainless steels and two ferritic alloys was irradiated sequentially in two research reactors where the neutron spectrum was tailored to produce a He production rate typical of a fusion device. Irradiation began in the Oak Ridge Research Reactor; and, after an atomic displacement level of 7.4 dpa, the specimens were moved to the High Flux Isotope Reactor for the remainder of the 19 dpa accumulated. Irradiation temperatures of 60, 200, 330, and 400{degrees}C were studied with internally pressurized tubes of type 316 stainless steel, PCA, HT 9, and a series of four laboratory heats of: Fe-13.5Cr-15Ni, Fe-13.5Cr-35Ni, Fe-1 3.5Cr-1 W-0.18Ti, and Fe-16Cr. At 330{degrees}C, irradiation creep was shown to be linear in fluence and stress. There was little or no effect of cold-work on creep under these conditions at all temperatures investigated. The HT9 demonstrated a large deviation from linearity at high stress levels, and a minimum in irradiation creep with increasing stress was observed in the Fe-Cr-Ni ternary alloys.

Grossbeck, M.L.; Gibson, L.T.; Mansur, L.K. [and others

1996-12-31

233

Elevated temperature creep-fatigue crack propagation in nickel-base alloys and 1 Cr-Mo-V steel  

NASA Astrophysics Data System (ADS)

The crack growth behavior of several high temperature nickel-base alloys, under cyclic and static loading, is studied and reviewed. In the oxide dispersion strengthened (ODS) MA 6000 and MA 754 alloys, the high temperature crack propagation exhibited orientation dependence under cyclic as well as under static loading. The creep crack growth (CCG) behavior of cast nickel-base IN-738 and IN-939* superalloys at 850 C could be characterized by the stress intensity factor, K 1. In the case of the alloy IN-901 at 500 C and 600 C, K 1 was found to be the relevant parameter to characterize the creep crack growth behavior. The energy rate line integral, C*, may be the appropriate loading parameter to describe the creep crack growth behavior of the nickel-iron base IN-800H alloy at 800 C. The creep crack growth data of 1 Cr-Mo-V steel, with bainitic microstructure, at 550 C could be correlated better by C * than by K 1.

Nazmy, M.; Hoffelner, W.; Wthrich, C.

1988-04-01

234

Low temperature deformation and dislocation substructure of ruthenium aluminide polycrystals  

SciTech Connect

The flow behavior and dislocation substructure present in ruthenium aluminide polycrystals due to deformation at room temperature and 77 K have been studied. Dislocations with three different types of Burgers vectors have been identified after 1--2% deformation in compression at 77 K and room temperature: {l_angle}100{r_angle}, {l_angle}110{r_angle} and {l_angle}111{r_angle}. The {l_angle}100{r_angle} and {l_angle}110{r_angle} dislocations are present with approximately equal densities, while the {l_angle}111{r_angle} are only occasionally observed. Trace analyses show that the majority of the dislocations are mixed in character and lie on {l_angle}110{r_angle} type planes. The implications of these observations with regard to the number of independent slip systems and the intrinsic deformability of this material are discussed.

Lu, D.C.; Pollock, T.M. [Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Materials Science and Engineering] [Carnegie Mellon Univ., Pittsburgh, PA (United States). Dept. of Materials Science and Engineering

1999-02-05

235

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

DOEpatents

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

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

2012-11-27

236

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

NASA Technical Reports Server (NTRS)

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.

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

1998-01-01

237

High-temperature deformation and recrystallization: A variational analysis and its application to olivine aggregates  

NASA Astrophysics Data System (ADS)

We develop a framework for a variational analysis of microstructural evolution during inelastic high-temperature deformation accommodated by dislocation mechanisms and diffusive mass transport. A polycrystalline aggregate is represented by a distribution function characterizing the state of individual grains by three variables, dislocation density, grain size, and elastic strain. The aggregate's free energy comprises elastic energy and energies of lattice distortions due to dislocations and grain boundaries. The work performed by the external loading is consumed by changes in the number of defects and their migration leading to inelastic deformation. The variational approach minimizes the rate of change of free energy with the evolution of the state variables under constraints on the aggregate volume, on a relation between changes in plastic strain and dislocation density, and on the form of the dissipation functionals for defect processes. The constrained minimization results in four basic evolution equations, one each for the evolution in grain size and dislocation density and flow laws for dislocation and diffusion creep. Analytical steady state scaling relations between stress and dislocation density and grain size (piezometers) are derived for quasi-homogeneous materials characterized by a unique relation between grain size and dislocation density. Our model matches all currently available experimental observations regarding high-temperature deformation of olivine aggregates with plausible values for the involved micromechanical model parameters. The relation between strain rate and stress for olivine aggregates maintaining a steady state microstructure is distinctly nonlinear in stark contrast to the majority of geodynamical modeling relying on linear relations, i.e., Newtonian behavior.

Hackl, Klaus; Renner, JRg

2013-03-01

238

High-temperature deformation of alumina/yttria tetragonal zirconia polycrystals particulate composites and particulate laminates  

NASA Astrophysics Data System (ADS)

Al2O3/Y-TZP particulate composites consisting of 20--80 vol% Al2O3 and Al2O3/Y-TZP particulate laminates with varying composition and ratios of layer thickness were fabricated, respectively, by tapecasting, lamination, and sintering. The resulting particulate composites and particulate laminates were tested in compression and tension at 1300--1450C over strain rates from 1.00 x 10-5 to 3.16 x 10-4 s-1. The high temperature behaviors of Al2O 3/Y-TZP particulate composites and particulate laminates were characterized under conditions in which changes to the microstructure during testing were deliberately minimized. Results show that stress exponents are approximately two for both particulate composites and particulate laminates when tested in compression and tension, consistent with a grain-boundary sliding mechanism. Particulate laminates are stronger than particulate composites with the same overall composition due to the constraint imposed by the hard layer on the soft layer during the deformation. This hard layer dominates the resistance to deformation of the particulate laminates. A limited number of elongation-to-failure tests were also conducted at 1350C at a true strain rate of 1.00 x 10-4 s-1. Although grain growth and cavitaton occurred during the elongation-to-failure tests, superplasticity was observed for Al2O3/Y-TZP particulate composites and particulate laminates. In addition, models of composite creep behavior were compared to the experimental data. A constrained isostrain model was found to provide a good prediction for the high-temperature deformation of Al2O3/Y-TZP particulate composites and particulate laminates.

Wang, Jue

239

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

SciTech Connect

The mechanical behavior and microstructure of eutectic Bi-Sn and In-Sn solders were studied in parallel in order to better understand high temperature deformation of these alloys. Bi-Sn solder joints were made with Cu substrates, and In-Sn joints were made with either Cu or Ni substrates. The as-cast microstructure of Bi-Sn is complex regular, with the two eutectic phases interconnected in complicated patterns. The as-cast microstructure of In-Sn depends on the substrate. In-Sn on Cu has a non-uniform microstructure caused by diffusion of Cu into the solder during sample preparation, with regions of the Sn-rich {gamma} phase imbedded in a matrix of the In-rich {beta} phase. The microstructure of In-Sn on Ni is uniform and lamellar and the two phases are strongly coupled. The solders deform non-uniformly, with deformation concentrating in a band along the length of the sample for Bi-Sn and In-Sn on Cu, though the deformation is more diffuse in In-Sn than in Bi-Sn. Deformation of In-Sn on Ni spreads throughout the width of the joint. The different deformation patterns affect the shape of the stress-strain curves. Stress-strain curves for Bi-Sn and In-Sn on Cu exhibit sharp decays in the engineering stress after reaching a peak. Most of this stress decay is removed for In-Sn on Ni. The creep behavior of In-Sn also depends on the substrate, with the creep deformation controlled by the soft P phase of the eutectic for In-Sn on Cu and controlled by the harder {gamma} phase for In-Sn on Ni. When In-Sn on Ni samples are aged, the microstructure coarsens and changes to an array of {gamma} phase regions in a matrix of the {beta} phase, and the creep behavior changes to resemble that of In-Sn on Cu. The creep behavior of Bi-Sn changes with temperature. Two independent mechanisms operate at lower temperatures, but there is still some question as to whether one or both of these, or a third mechanism, operates at higher temperatures.

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

1993-11-01

240

CREEP AND CREEP-FATIGUE OF ALLOY 617 WELDMENTS  

SciTech Connect

The Very High Temperature Reactor (VHTR) Intermediate Heat Exchanger (IHX) may be joined to piping or other components by welding. Creep-fatigue deformation is expected to be a predominant failure mechanism of the IHX1 and thus weldments used in its fabrication will experience varying cyclic stresses interrupted by periods of elevated temperature deformation. These periods of elevated temperature deformation are greatly influenced by a materials creep behavior. The nickel-base solid solution strengthened alloy, Alloy 617, is the primary material candidate for a VHTR-type IHX, and it is expected that Alloy 617 filler metal will be used for welds. Alloy 617 is not yet been integrated into Section III of the Boiler and Pressure Vessel Code, however, nuclear component design with Alloy 617 requires ASME (American Society of Mechanical Engineers) Code qualification. The Code will dictate design for welded construction through significant performance reductions. Despite the similar compositions of the weldment and base material, significantly different microstructures and mechanical properties are inevitable. Experience of nickel alloy welds in structural applications suggests that most high temperature failures occur at the weldments or in the heat-affected zone. Reliably guarding against this type of failure is particularly challenging at high temperatures due to the variations in the inelastic response of the constituent parts of the weldment (i.e., weld metal, heat-affected zone, and base metal) [ref]. This work focuses on the creep-fatigue behavior of nickel-based weldments, a need noted during the development of the draft Alloy 617 ASME Code Case. An understanding of Alloy 617 weldments when subjected to this important deformation mode will enable determination of the appropriate design parameters associated with their use. Specifically, the three main areas emphasized are the performance reduction due to a weld discontinuity in terms of the reduced number of the cycles to failure and whether a saturation in reduced cycle life with increased hold times is observed, the microstructural stability over long cycle times, and finally, the location of the generated weldment data on a creep-fatigue damage diagram (D-diagram).

Wright, Jill; Carroll, Laura; Wright, Richard

2014-08-01

241

Creep-constitutive behavior of Sn-3.8Ag-0.7Cu solder using an internal stress approach  

NASA Astrophysics Data System (ADS)

The experimental tensile creep deformation of bulk Sn-3.8Ag-0.7Cu solder at temperatures between 263 K and 398 K, covering lifetimes up to 3,500 h, has been rationalized using constitutive equations that incorporate structure-related internal state variables. Primary creep is accounted for using an evolving internal back stress, due to the interaction between the soft matrix phase and a more creep-resistant particle phase. Steady-state creep is incorporated using a conventional power law, modified to include the steady-state value of internal stress. It is demonstrated that the observed behavior is well-fitted using creep constants for pure tin in the modified creep power law. A preliminary analysis of damage-induced tertiary creep is also presented.

Rist, Martin A.; Plumbridge, W. J.; Cooper, S.

2006-05-01

242

Dwell effects on high temperature fatigue damage mechanisms  

Microsoft Academic Search

The mechanisms controlling deformation and failure under high temperature creep-fatigue conditions of materials are examined in this paper. The materials studied were pure alloys, solder alloys, copper alloys, low alloy steels, stainless steels, titanium alloys, tantalum alloys, and Ni-based alloys. The deformation and failure mechanisms were different (fatigue, creep, oxidation and their interactions) depending on test and material parameters employed.

Tarun Goswami; Hannu Hanninen

2001-01-01

243

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

NASA Astrophysics Data System (ADS)

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

Rayner, Garrett

244

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

PubMed

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

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

2015-01-01

245

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

NASA Technical Reports Server (NTRS)

One of the ongoing challenges of the aerospace industry is to develop more efficient turbine engines. Greater efficiency entails reduced specific strength and larger temperature gradients, the latter of which means higher operating temperatures and increased thermal conductivity. Continued development of nickel-based superalloys has provided steady increases in engine efficiency and the limits of superalloys have probably not been realized. However, other material systems are under intense investigation for possible use in high temperature engines. Ceramic, intermetallic, and various composite systems are being explored in an effort to exploit the much higher melting temperatures of these systems. NiAl is considered a potential alternative to conventional superalloys due to its excellent oxidation resistance, low density, and high melting temperature. The fact that NiAl is the most common coating for current superalloy turbine blades is a tribute to its oxidation resistance. Its density is one-third that of typical superalloys and in most temperature ranges its thermal conductivity is twice that of common superalloys. Despite these many advantages, NiAl requires more investigation before it is ready to be used in engines. Binary NiAl in general has poor high-temperature strength and low-temperature ductility. On-going research in alloy design continues to make improvements in the high-temperature strength of NiAl. The factors controlling low temperature ductility have been identified in the last few years. Small, but reproducible ductility can now be achieved at room temperature through careful control of chemical purity and processing. But the mechanisms controlling the transition from brittle to ductile behavior are not fully understood. Research in the area of fatigue deformation can aid the development of the NiAl system in two ways. Fatigue properties must be documented and optimized before NiAl can be applied to engineering systems. More importantly though, probing the deformation mechanisms operating in fatigue will lead to a better understanding of NiAl's unique characteristics. Low cycle fatigue properties have been reported on binary NiAl in the past year, yet those studies were limited to two temperature ranges: room temperature and near 1000 K. Eventually, fatigue property data will be needed for a wide range of temperatures and compositions. The intermediate temperature range near the brittle-to-ductile transition was chosen for this study to ascertain whether the sharp change occurring in monotonic behavior also occurs under cyclic conditions. An effort was made to characterize the dislocation structures which evolved during fatigue testing and comment on their role in the deformation process.

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

1992-01-01

246

Temperature Dependent Cyclic Deformation Mechanisms in Haynes 188 Superalloy  

NASA Technical Reports Server (NTRS)

The cyclic deformation behavior of a wrought cobalt-base superalloy, Haynes 188, has been investigated over a range of temperatures between 25 and 1000 C under isothermal and in-phase thermomechanical fatigue (TMF) conditions. Constant mechanical strain rates (epsilon-dot) of 10(exp -3)/s and 10(exp -4)/s were examined with a fully reversed strain range of 0.8%. Particular attention was given to the effects of dynamic strain aging (DSA) on the stress-strain response and low cycle fatigue life. A correlation between cyclic deformation behavior and microstructural substructure was made through detailed transmission electron microscopy. Although DSA was found to occur over a wide temperature range between approximately 300 and 750 C the microstructural characteristics and the deformation mechanisms responsible for DSA varied considerably and were dependent upon temperature. In general, the operation of DSA processes led to a maximum of the cyclic stress amplitude at 650 C and was accompanied by pronounced planar slip, relatively high dislocation density, and the generation of stacking faults. DSA was evidenced through a combination of phenomena, including serrated yielding, an inverse dependence of the maximum cyclic hardening with epsilon-dot, and an instantaneous inverse epsilon-dot sensitivity verified by specialized epsilon-dot -change tests. The TMF cyclic hardening behavior of the alloy appeared to be dictated by the substructural changes occuring at the maximum temperature in the TMF cycle.

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

1995-01-01

247

Diffusion to dislocation creep transition in upper-mantle from Si grain-boundary diffusion  

NASA Astrophysics Data System (ADS)

Dislocation creep causes non-Newtonian viscosity and seismic anisotropy, whereas diffusion creep causes Newtonian viscosity and no or weak seismic anisotropy. Determination of deformation mechanism in the Earth's interior is thus essential to understand mantle dynamics. Although previous deformation studies on olivine suggested the dislocation to diffusion creep transition with depth in the upper mantle, recent studies suggested possible misinterpretation of those results due to experimental difficulties. Since the olivine creep is considered to be controlled by silicon diffusion, we measured silicon grain-boundary diffusion coefficient in Mg-olivine as a function of temperature, pressure, and water content to estimate the diffusion creep rate. The experimental results show a small activation enthalpy (240-260 kJ/mol), small activation volume (1.80.2 cm3/mol), and small water-content exponent (0.220.05). The smaller activation energy of grain-boundary diffusion than that of dislocation creep predicts a diffusion to dislocation creep transition in the upper mantle, which is in contrast with the previous model. The Gutenberg discontinuity could be caused by this creep-mechanism transition. The weak seismic anisotropy in lithosphere is interpreted as fossil anisotropy formed at spreading ridges. The dominance of diffusion creep in upper lithosphere accounts for the Newtonian rheology suggested by postglacial rebound.

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

2014-05-01

248

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

NASA Technical Reports Server (NTRS)

A strain rate change technique, developed previously for distinguishing between pure-metal and alloy-type creep behavior, was used to study the elevated-temperature deformation behavior of the intermetallic compounds NiAl and CoAl. Tests on NiAl were conducted at temperatures between 1100 and 1300 K while tests on CoAl were performed at temperatures ranging from 1200 to 1400 K. NiAl exhibits pure-metal type behavior over the entire temperature range studied. CoAl, however, undergoes a transition from pure-metal to alloy-type deformation behavior as the temperature is decreased from 1400 to 1200 K. Slip appears to be inherently more difficult in CoAl than in NiAl, with lattice friction effects limiting the mobility of dislocations at a much higher tmeperature in CoAl than in NiAl. The superior strength of CoAl at elevated temperatures may, therefore, be related to a greater lattice friction strengthening effect in CoAl than in NiAl.

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

1988-01-01

249

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

SciTech Connect

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

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

1996-05-01

250

High-temperature viscoelastic creep constitutive equations for polymer composites: Homogenization theory and experiments  

SciTech Connect

In this paper, a homogenization theory is developed to determine high-temperature effective viscoelastic constitutive equations for fiber-reinforced polymer composites. The homogenization theory approximates the microstructure of a fiber composite, and determine simultaneously effective macroscopic constitutive properties of the composite and the associated microscopic strain and stress in the heterogeneous material. The time-temperature dependent homogenization theory requires that the viscoelastic constituent properties of the matrix phase at elevated temperatures, the governing equations for the composites, and the boundary conditions of the problem be Laplace transformed to a conjugate problem. The homogenized effective properties in the transformed domain are determined, using a two-scale asymptotic expansion of field variables and an averaging procedure. Field solutions in the unit cell are determined from basic and first-order governing equations with the aid of a boundary integral method (BIM). Effective viscoelastic constitutive properties of the composite at elevated temperatures are determined by an inverse transformation, as are the microscopic stress and deformation in the composite. Using this method, interactions among fibers and between the fibers and the matrix can be evaluated explicitly, resulting in accurate solutions for composites with high-volume fraction of reinforcing fibers. Examples are given for the case of a carbon-fiber reinforced thermoplastic polyamide composite in an elevated temperature environment. The homogenization predictions are in good agreement with experimental data available for the composite.

Skontorp, A.; Wang, S.S. [Univ. of Houston, TX (United States). Dept. of Mechanical Engineering; Shibuya, Y. [Akita Univ., (Japan). Dept. of Mechanical Engineering

1994-12-31

251

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

252

Creep and creep rupture of rock salt  

SciTech Connect

A fundamental review is given of creep properties and flow processes of experimentally and naturally deformed rocksalt as background pertinent to waste repository design. Deformational behavior of halite single crystals is discussed first, followed by a brief treatment of experimentally deformed artifically prepared halite aggregates. The results of recent extensive quasi-static compression and creep tests on natural aggregates, especially on southeastern New Mexico bedded salt and on Avery Island domal salt, are then reviewed in some detail. The mechanical behavior of these two very different rocksalts is remarkably similar, an observation that provides some confidence to extrapolations of the results to repository condition. The relatively scarce data for accelerating creep and creep-rupture of rocksalt are reviewed, followed by a general treatment of relevant experiments and observations from the Project Salt Vault demonstration. The question of brine migration is then discussed and pertinent observations from flow of rocksalt glaciers and diapirs are reviewed briefly. Recommendations are made for additional fundamental research in various areas and it is concluded, on the basis of all available information, that dry domal salt deposits would provide nearly ideal media for radioactive waste repositories.

Carter, N.L.

1983-06-01

253

A change in the chemical bonding strength and high-temperature creep resistance in Al2O3 with lanthanoid oxide doping  

Microsoft Academic Search

High-temperature creep resistance in polycrystalline Al2O3 is highly improved by doping with 0.05 mol% lanthanoid (Ln) oxide (Ln = Sm, Eu, Tm or Lu) at 1250C. The improvement in creep resistance probably occurs as a result of retardation of the grain-boundary diffusion in Al2O3 due to grain-boundary segregation of dopant cations. The change in chemical bonding state in grain boundaries

H. Yoshida; T. Yamamoto; Y. Ikuhara; T. Sakuma

2002-01-01

254

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

SciTech Connect

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

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

1999-07-01

255

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

NASA Astrophysics Data System (ADS)

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

Shirley, Dwayne R.

256

Continuous cavity nucleation and creep fracture  

SciTech Connect

Intergranular creep fracture under the stress and temperature conditions experienced by components in service is generally acknowledged as resulting from nucleation and growth of intergranular cavities. Firstly, there seemed to be an approximately linear reciprocal relationship between time-to-fracture and minimum rate of creep deformation. Secondly, cavity growth by stress-directed flow of atoms was shown by Hull and Rimmer to lead to lifetime being inversely proportional to the maximum principal stress providing that all cavities initiated at the start of the test. Recently, it has been demonstrated that the boundary conditions imposed by Hull and Rimmer were unnecessarily restrictive and that more realistic ones result in cavity growth rates being proportional to strain rates. Nevertheless, there is an increasing body of experimental evidence on engineering alloys and also iron which indicates that cavities are not all nucleated in a short time interval, but are nucleated continuously. This paper collates the evidence for the continous nucleation of cavities, places this within the framework of creep fracture modelling and introduces a quantitative assessment of the likely errors of measurement. A model of cavity nucleation based on the stochastic nature of transgranular creep deformation is also discussed.

Dyson, B.F.

1983-01-01

257

Standard test method for creep-fatigue crack growth testing  

E-print Network

1.1 This test method covers the determination of creep-fatigue crack growth properties of nominally homogeneous materials by use of pre-cracked compact type, C(T), test specimens subjected to uniaxial cyclic forces. It concerns fatigue cycling with sufficiently long loading/unloading rates or hold-times, or both, to cause creep deformation at the crack tip and the creep deformation be responsible for enhanced crack growth per loading cycle. It is intended as a guide for creep-fatigue testing performed in support of such activities as materials research and development, mechanical design, process and quality control, product performance, and failure analysis. Therefore, this method requires testing of at least two specimens that yield overlapping crack growth rate data. The cyclic conditions responsible for creep-fatigue deformation and enhanced crack growth vary with material and with temperature for a given material. The effects of environment such as time-dependent oxidation in enhancing the crack growth ra...

American Society for Testing and Materials. Philadelphia

2010-01-01

258

Mechanical behavior of low porosity carbonate rock: from brittle creep to ductile creep  

NASA Astrophysics Data System (ADS)

Mechanical compaction and associated porosity reduction play an important role in the diagenesis of porous rocks. They may also affect reservoir rocks during hydrocarbon production, as the pore pressure field is modified. This inelastic compaction can lead to subsidence, cause casing failure, trigger earthquake, or change the fluid transport properties. In addition, inelastic deformation can be time - dependent. In particular, brittle creep phenomena have been deeply investigated since the 90s, especially in sandstones. However knowledge of carbonates behavior is still insufficient. In this experimental study, we focus on the mechanical behavior of a low porosity (9%) white Tavel (France) carbonate rock (>98% calcite) at P-Q conditions beyond the elastic domain. It has been shown that in sandstones composed of quartz, cracks are developing under these conditions. However, in carbonates, calcite minerals can meanwhile also exhibit microplasticity. The samples were deformed in the triaxial cell of the Ecole Normale Superieure de Paris at effective confining pressures ranging from 35 MPa to 85 MPa and room temperature. Experiments were carried on dry and water saturated samples to explore the role played by the pore fluids. Time dependency was investigated by a creep steps methodology: at each step, differential stress was increased rapidly and kept constant for at least 24h. During these steps elastic wave velocities (P and S) and permeability were measured continuously. Our results show two different creep behaviors: (1) brittle creep is observed at low confining pressures, whereas (2) ductile creep is observed at higher confining pressures. These two creep behaviors have a different signature in term of elastic wave velocities and permeability changes. Indeed, in the brittle domain, the primary creep is associated with a decrease of elastic wave velocities and an increase of permeability, and no secondary creep is observed. In the ductile domain, the primary creep is also associated with a decreased in elastic wave velocity and an increase of the permeability. However, the secondary creep is associated with an increase of velocities and a decrease of permeability (pointing to recovery). This behavior observed in the ductile regime can be explained by two mechanisms: cracks propagation and plasticity. Indeed, the increase of stress induces fractures. When long term plastic phenomena take place at the tips of the cracks, these fractures close partially.

Nicolas, A.; Fortin, J.; Gueguen, Y.

2013-12-01

259

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

NASA Astrophysics Data System (ADS)

We studied the ductile creep behavior of organic-rich shales from shale gas reservoirs in North America through laboratory triaxial experiments to better understand controls on the physical behavior of these rocks over time and the effect of creep on other rock properties. Laboratory experiments conducted at room-temperature conditions show that creep deformation observed at in-situ differential stress conditions is approximately linear with the applied differential pressure. The creep behavior is also anisotropic such that creep occurs more in the bedding-perpendicular direction than in the bedding-parallel direction. The reduction in sample volume during creep suggests that the creep is accommodated by a small amount of pore compaction occurring in the clay-aggregates and/or the relatively porous kerogen in the rock. Thus, the tendency to creep (creep compliance) is generally observed to increases with clay and kerogen volume. However, the strongest correlation is found between creep compliance and Young's modulus. A strong negative correlation between creep compliance and elastic Young's modulus exists regardless of the sample orientation and despite the wide range of sample mineralogy (5-50% clay, 5-60% quartz-feldspar-pyrite, 0-80% carbonates). This correlation is quite interesting as inelastic creep and elastic stiffness depend on somewhat different physical attributes. We attempt to quantitatively explain the correlation between creep behavior and elastic stiffness by appealing to a stress-partitioning that occurs between the soft components (clay and kerogen) and stiff components (quartz, feldspar, pyrite, carbonates) of the shale rock. First, the stress-partitioning occurring within the soft and stiff components is quantified based on the rock composition, elastic properties of the individual components, and the overall average Young's modulus of the rock. By combining the stress-partitioning behavior with knowledge that the creep behavior is linear against the applied stress, we forward calculate the creep compliance of the whole rock. Results show that when creep is linear against stress, a unique relation between creep compliance and elastic modulus can be established for rocks with similar mineral assemblages, consistent with our laboratory results. Thus, our results provide insights into how creep behaviors of poly-mineralic rocks can be re-constructed from the creep properties of the individual phases composing the rock.

Sone, Hiroki; Zoback, Mark

2013-04-01

260

Creep-rupture behavior of a directionally solidified nickel-base superalloy  

NASA Astrophysics Data System (ADS)

The creep-rupture behavior of the directionally solidified (DS) nickel-base superalloy DZ17G has been investigated over a wide stress range of 60 to 950 MPa at high temperature (923 to 1323 K). In this article, the detailed creep deformation and fracture mechanisms at constant load have been studied. The results show that all creep curves exhibit a short primary and a dominant accelerated creep stage, which results in higher ductility of DS superalloy DZ17G compared to the conventionally cast alloy. From the creep parameters and transmission electron microscopy (TEM) observations, it is suggested that the dominant creep deformation mechanism has a change from gamma prime particles shearing by matrix dislocations in high stress region to dislocation climb process in low stress region. It is found that the fracture mode of DS superalloy DZ17G is transgranular, and it is controlled by the propagation rate of creep cracks initiated at both surface and inner microstructure discontinuities. The creep rupture data follows the Monkman-Grant relationship under all the explored test conditions.

Guo, J. T.; Yuan, C.; Yang, H. C.; Lupinc, V.; Maldini, M.

2001-05-01

261

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

NASA Astrophysics Data System (ADS)

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.

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

2014-10-01

262

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

SciTech Connect

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.

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

263

Mantle temperature under drifting deformable continents during the supercontinent cycle  

NASA Astrophysics Data System (ADS)

Abstract The thermal heterogeneity of the Earth's mantle under the drifting continents during a supercontinent cycle is a controversial issue in earth science. Here, a series of numerical simulations of mantle convection are performed in 3-D spherical-shell geometry, incorporating drifting <span class="hlt">deformable</span> continents and self-consistent plate tectonics, to evaluate the subcontinental mantle <span class="hlt">temperature</span> during a supercontinent cycle. Results show that the laterally averaged <span class="hlt">temperature</span> anomaly of the subcontinental mantle remains within several tens of degrees (50C) throughout the simulation time. Even after the formation of the supercontinent and the development of subcontinental plumes due to the subduction of the oceanic plates, the laterally averaged <span class="hlt">temperature</span> anomaly of the deep mantle under the continent is within +10C. This implies that there is no substantial <span class="hlt">temperature</span> difference between the subcontinental and suboceanic mantles during a supercontinent cycle. The <span class="hlt">temperature</span> anomaly immediately beneath the supercontinent is generally positive owing to the thermal insulation effect and the active upwelling plumes from the core-mantle boundary. In the present simulation, the formation of a supercontinent causes the laterally averaged subcontinental <span class="hlt">temperature</span> to increase by a maximum of 50C, which would produce sufficient tensional force to break up the supercontinent. The regular periodicity of the supercontinent cycles observed in previous 2-D and 3-D simulation models with rigid nondeformable continents and without self-consistent plate tectonics is not confirmed.</p> <div class="credits"> <p class="dwt_author">Yoshida, Masaki</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">264</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://pubs.er.usgs.gov/publication/70030748"> <span id="translatedtitle">The instantaneous rate dependence in low <span class="hlt">temperature</span> laboratory rock friction and rock <span class="hlt">deformation</span> experiments</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">Earthquake occurrence probabilities that account for stress transfer and time-dependent failure depend on the product of the effective normal stress and a lab-derived dimensionless coefficient a. This coefficient describes the instantaneous dependence of fault strength on <span class="hlt">deformation</span> rate, and determines the duration of precursory slip. Although an instantaneous rate dependence is observed for fracture, friction, crack growth, and low <span class="hlt">temperature</span> plasticity in laboratory experiments, the physical origin of this effect during earthquake faulting is obscure. We examine this rate dependence in laboratory experiments on different rock types using a normalization scheme modified from one proposed by Tullis and Weeks [1987]. We compare the instantaneous rate dependence in rock friction with rate dependence measurements from higher <span class="hlt">temperature</span> dislocation glide experiments. The same normalization scheme is used to compare rate dependence in friction to rock fracture and to low-<span class="hlt">temperature</span> crack growth tests. For particular weak phyllosilicate minerals, the instantaneous friction rate dependence is consistent with dislocation glide. In intact rock failure tests, for each rock type considered, the instantaneous rate dependence is the same size as for friction, suggesting a common physical origin. During subcritical crack growth in strong quartzofeldspathic and carbonate rock where glide is not possible, the instantaneous rate dependence measured during failure or <span class="hlt">creep</span> tests at high stress has long been thought to be due to crack growth; however, direct comparison between crack growth and friction tests shows poor agreement. The crack growth rate dependence appears to be higher than the rate dependence of friction and fracture by a factor of two to three for all rock types considered. Copyright 2007 by the American Geophysical Union.</p> <div class="credits"> <p class="dwt_author">Beeler, N.M.; Tullis, T.E.; Kronenberg, A.K.; Reinen, L.A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">265</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013JNuM..438...51V"> <span id="translatedtitle">Effect of prior cold work on <span class="hlt">creep</span> properties of a titanium modified austenitic stainless steel</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Prior cold worked (PCW) titanium-modified 14Cr-15Ni austenitic stainless steel (SS) is used as a core-structural material in fast breeder reactor because of its superior <span class="hlt">creep</span> strength and resistance to void swelling. In this study, the influence of PCW in the range of 16-24% on <span class="hlt">creep</span> properties of IFAC-1 SS, a titanium modified 14Cr-15Ni austenitic SS, at 923 K and 973 K has been investigated. It was found that PCW has no appreciable effect on the <span class="hlt">creep</span> <span class="hlt">deformation</span> rate of the steel at both the test <span class="hlt">temperatures</span>; <span class="hlt">creep</span> rupture life increased with PCW at 923 K and remained rather unaffected at 973 K. The dislocation structure along with precipitation in the PCW steel was found to change appreciably depending on <span class="hlt">creep</span> testing conditions. A well-defined dislocation substructure was observed on <span class="hlt">creep</span> testing at 923 K; a well-annealed microstructure with evidences of recrystallization was observed on <span class="hlt">creep</span> testing at 973 K. <span class="hlt">Creep</span> rupture life of the steel increased with the increase in PCW at 923 K. This has been attributed to the partial retention of prior cold work induced dislocations which facilitated the extensive precipitation of secondary Ti(C,N) particles on the stable dislocation substructure. <span class="hlt">Creep</span> rupture life of the steel did not vary with PCW at 973 K due to softening by recrystallization and absence of secondary Ti(C,N).</p> <div class="credits"> <p class="dwt_author">Vijayanand, V. D.; Parameswaran, P.; Nandagopal, M.; Panneer Selvi, S.; Laha, K.; Mathew, M. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">266</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/25037333"> <span id="translatedtitle">Effect of particle size and <span class="hlt">temperature</span> on rheology and <span class="hlt">creep</span> behavior of barley ?-d-glucan concentrate dough.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Concentrated ?-D-glucan has been added in the formulation of food products development that attributing human health. The purpose of this study is to assess the role of particle size (74, 105, 149, 297 and 595 ?m) of barley ?-D-glucan concentrate (BGC) on two fundamental rheological properties namely oscillatory rheology and <span class="hlt">creep</span> in a dough system (sample to water = 1:2). The water holding capacity, sediment volume fraction and protein content increased with an increase in particle size from 74 ?m to 595 ?m, which directly influences the mechanical strength and visco-elasticity of the dough. The dough exhibited predominating solid-like behavior (elastic modulus, G'>viscous modulus, G"). The G' decreased systematically with increasing <span class="hlt">temperature</span> from 25 to 85 C at the frequency range of 0.1-10 Hz except for the dough having particle size of 105 ?m, which could be associated with increase in protein content in the fraction. A discrete retardation spectrum is employed to the <span class="hlt">creep</span> data to obtain retardation time and compliance parameters which varied significantly with particle size and the process <span class="hlt">temperature</span>. All those information could be helpful to identify the particle size range of BGC that could be useful to produce a ?-D-glucan enriched designed food. PMID:25037333</p> <div class="credits"> <p class="dwt_author">Ahmed, Jasim</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-10-13</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">267</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/61196664"> <span id="translatedtitle"><span class="hlt">CREEP</span> RATE OF SOME THERMAL INSULATING MATERIALS UNDER 100 PSI LOAD AT 2100 F HOT-FACE <span class="hlt">TEMPERATURE</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The <span class="hlt">creep</span> rate and thermal conductivity of several thermal insulating ; materials were determined. Alsimag 202 and 504'' materials had the lowest ; <span class="hlt">creep</span> rate, while a Perlite'' base material had the lowest thermal conductivity ; and specific weight. (auth);</p> <div class="credits"> <p class="dwt_author">Eckard</p> <p class="dwt_publisher"></p> <p class="publishDate">1960-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">268</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.2670Y"> <span id="translatedtitle">Mantle <span class="hlt">temperature</span> under drifting <span class="hlt">deformable</span> continents during the supercontinent cycle</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The thermal heterogeneity of the Earth's mantle under the drifting continents during a supercontinent cycle is a controversial issue in earth science. Here, a series of numerical simulations of mantle convection are performed in 3D spherical-shell geometry, incorporating drifting <span class="hlt">deformable</span> continents and self-consistent plate tectonics, to evaluate the subcontinental mantle <span class="hlt">temperature</span> during a supercontinent cycle. Results show that the laterally averaged <span class="hlt">temperature</span> anomaly of the subcontinental mantle remains within several tens of degrees (50 C) throughout the simulation time. Even after the formation of the supercontinent and the development of subcontinental plumes due to the subduction of the oceanic plates, the laterally averaged <span class="hlt">temperature</span> anomaly of the deep mantle under the continent is within +10 C. This implies that there is no substantial <span class="hlt">temperature</span> difference between the subcontinental and suboceanic mantles during a supercontinent cycle. The <span class="hlt">temperature</span> anomaly immediately beneath the supercontinent is generally positive owing to the thermal insulation effect and the active upwelling plumes from the core-mantle boundary. In the present simulation, the formation of a supercontinent causes the laterally averaged subcontinental <span class="hlt">temperature</span> to increase by a maximum of 50 C, which would produce sufficient tensional force to break up the supercontinent. The periodic assembly and dispersal of continental fragments, referred to as the supercontinent cycle, bear close relation to the evolution of mantle convection and plate tectonics. Supercontinent formation involves complex processes of introversion, extroversion or a combination of these in uniting dispersed continental fragments, as against the simple opening and closing of individual oceans envisaged in Wilson cycle. In the present study, I evaluate supercontinent processes in a realistic mantle convection regime. Results show that the assembly of supercontinents is accompanied by a combination of introversion and extroversion processes. The regular periodicity of the supercontinent cycles observed in previous 2D and 3D simulation models with rigid nondeformable continents is not confirmed. The small-scale thermal heterogeneity is dominated in deep mantle convection during the supercontinent cycle, although the large-scale, active upwelling plumes intermittently originate under drifting continents and/or the supercontinent. Results suggest that active subducting cold plates along continental margins generate thermal heterogeneity with short-wavelength structures, which is consistent with the thermal heterogeneity in the present-day mantle convection inferred from seismic tomography models. References: [1] Yoshida, M. Mantle <span class="hlt">temperature</span> under drifting <span class="hlt">deformable</span> continents during the supercontinent cycle, Geophys. Res. Lett., 2013, in press. [2] Yoshida, M. and M. Santosh, Mantle convection modeling of supercontinent cycle: Introversion, extroversion, or combination?, 2013, submitted.</p> <div class="credits"> <p class="dwt_author">Yoshida, Masaki</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">269</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2015MMTA..tmp...97H"> <span id="translatedtitle">Grain Breakup During Elevated <span class="hlt">Temperature</span> <span class="hlt">Deformation</span> of an HCP Metal</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A combination of mechanical testing, EBSD and crystal plasticity finite element modeling were used to investigate the influence of <span class="hlt">temperature</span> on the fragmentation of grains in a zirconium alloy. The results demonstrate that grains of Zircaloy-4 fragment more as the <span class="hlt">temperature</span> rises. This trend can be explained by an increasing difference between the CRSS values for <c+a> slip and <a> slip as <span class="hlt">temperature</span> rises. This change in relative slip activities with <span class="hlt">temperature</span> is supported by experimental observations of macroscopic anisotropy and in-grain misorientation axes calculated from EBSD data, as well as plasticity modeling. By tracking the microstructural evolution during <span class="hlt">deformation</span>, it is shown that the two major texture components fragment to different degrees under the action of prismatic slip. Grains in the < {11overline{2} 0} rangle fiber are significantly more stable than those in the < {10overline{1} 0} rangle fiber, which break up. Grains of the latter fiber fragment heterogeneously as portions of the grain rotate in opposite directions, and some do not rotate at all.</p> <div class="credits"> <p class="dwt_author">Honniball, Peter D.; Preuss, Michael; Rugg, David; Quinta da Fonseca, Joo</p> <p class="dwt_publisher"></p> <p class="publishDate">2015-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">270</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013SuScT..26e5023L"> <span id="translatedtitle">On the possibility of explaining the high rate of flux <span class="hlt">creep</span> at ultra-low <span class="hlt">temperatures</span> using the Anderson model</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The nonvanishing magnetic relaxation rate and noticeable resistance in the resistive measurements in high-<span class="hlt">temperature</span> superconductors (HTSCs) at ultra-low <span class="hlt">temperatures</span>, which have recently been discussed as evidence of the quantum tunneling of vortices, is argued to be caused by electromagnetic noise in the framework of the modified Anderson theory. This explains the main features of this phenomenon, which cannot be described by quantum tunneling theory. Thus, the modified Anderson theory, which incorporates flux flow, the distribution of activation energies, the mutual interaction of the vortices, and the spatial variation of the pinning energy into the conventional Anderson theory, provides an explanation of the main features of magnetic flux <span class="hlt">creep</span> in HTSCs.</p> <div class="credits"> <p class="dwt_author">Lykov, A. N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">271</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008NIMPA.593..597V"> <span id="translatedtitle">Extended-time-scale <span class="hlt">creep</span> measurement on Maraging cantilever blade springs</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Two controlled <span class="hlt">temperature</span> facilities were built to induce an accelerated <span class="hlt">creep</span> rate in a Maraging steel GAS spring and to measure the material's <span class="hlt">creep</span> over an artificially extended period of time. The data acquisition of the first experiment lasted for almost a year, but then the blades were allowed to <span class="hlt">creep</span> for six more years before measuring the permanent <span class="hlt">deformation</span> integrated over time. The data from this first experiment was polluted by a defect in the data acquisition software, but yielded overall <span class="hlt">creep</span> limits and an evaluation of the Arrhenius acceleration of <span class="hlt">creep</span> speed with <span class="hlt">temperature</span> (1.280.13 C -1). The duration of the second experiment was only 1 year but more free of systematic errors. The effective test period of this second experiment (normalized with the Arrhenius acceleration measured in the first experiment) extends in billions of years showing no sign of anomalous <span class="hlt">creep</span>. The result of both experiments also produced a simple procedure capable of eliminating all practical effects of <span class="hlt">creep</span> from the Advanced LIGO seismic isolation and suspensions. Measurements of <span class="hlt">creep</span> under various stress levels, and of the thermal variations of Young's modulus (2.023 (0.013)10 -4 C -1) are reported as well.</p> <div class="credits"> <p class="dwt_author">Virdone, Nicole; Agresti, Juri; Bertolini, Alessandro; DeSalvo, Riccardo; Stellacci, Rosalia; Kamp, Justin; Mantovani, Maddalena; Sannibale, Virginio; Tarallo, Marco; Kaltenegger, Lisa</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">272</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/10188601"> <span id="translatedtitle"><span class="hlt">Creep</span> behavior in SiC whisker-reinforced alumina composite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Grain boundary sliding (often accompanied by cavitation) is a major contributor to compressive and tensile <span class="hlt">creep</span> <span class="hlt">deformation</span> in fine-grained aluminas, both with and without whisker-reinforcement. Studies indicate that the <span class="hlt">creep</span> response of alumina composites reinforced with SiC whiskers can be tailored by controlling the composite microstructure and composition. The addition of SiC whiskers (< 30 vol%) significantly increases the <span class="hlt">creep</span> resistance of fine-grained (1--2 {mu}m) alumina in air at <span class="hlt">temperatures</span> of 1,200 and 1,300 C. However, at higher whisker contents (30 and 50 vol%), the <span class="hlt">creep</span> resistance is degraded due to enhanced surface oxidation reactions accompanied by extensive <span class="hlt">creep</span> cavitation. Densification aids (i.e., Y{sub 2}O{sub 3}), which facilitate silica glass formation and thus liquid phase densification of the composites, can also result in degradation of <span class="hlt">creep</span> resistance. On the other hand, increasing the matrix grain size or decreasing the whisker aspect ratio (increased whisker number density) results in raising the <span class="hlt">creep</span> resistance of the composites. These observations not only explain the variability in the <span class="hlt">creep</span> response of various SiC whisker-reinforced alumina composites but also indicate factors that can be used to enhance the elevated <span class="hlt">temperature</span> performance.</p> <div class="credits"> <p class="dwt_author">Lin, H.T.; Becher, P.F. [Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">273</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1997JGR...102..875D"> <span id="translatedtitle">Uniaxial compaction <span class="hlt">creep</span> of wet gypsum aggregates</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The uniaxial compaction <span class="hlt">creep</span> behavior of wet, granular gypsum is investigated under both chemically closed (i.e., drained) and open (i.e., flow through) conditions known to favor pressure solution. The experiments were performed using applied stresses of 0.5 to 2.5 MPa and grain sizes of 32-280 ?m, at room <span class="hlt">temperature</span>, using pore fluids saturated with respect to unstressed sample material. All wet-tested samples crept rapidly. In contrast, control experiments using dry and oil-saturated samples showed no measurable <span class="hlt">creep</span>. The microstructures developed in the wet tests provide classical evidence for the operation of grain boundary diffusional pressure solution. To enable detailed comparison with theory, it is demonstrated that despite minor effects of the water of crystallization, conventional pressure solution <span class="hlt">creep</span> models, for closed systems, are applicable to gypsum. However, the mechanical behavior observed in the closed-system experiments does not fully match these models for either dissolution, diffusion, or precipitation control. Nonetheless, independent crystal growth data suggest that precipitation is most likely to be rate controlling. Additional evidence for this was provided by the experiments with through-flowing solution. In such experiments, precipitation can no longer control the rate of <span class="hlt">deformation</span>, so that dissolution or diffusion are expected to take over as the rate-limiting process, thus enhancing the <span class="hlt">creep</span> rate. Indeed, a 10 to 30 times increase in compaction <span class="hlt">creep</span> rate was observed in the flow-through tests, confirming that <span class="hlt">creep</span> in the closed-system case probably occurred by precipitation-controlled grain boundary diffusional pressure solution.</p> <div class="credits"> <p class="dwt_author">de Meer, Siese; Spiers, Christopher J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">274</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/11981365"> <span id="translatedtitle">On the Nonlinear <span class="hlt">Creep</span> and Recovery of Open Cell Earplug Foams</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The compressive <span class="hlt">creep</span> and recovery of foam earplugs was studied at various applied stresses leading to different fi nal <span class="hlt">creep</span> strains. <span class="hlt">Deformation</span> was determined from digital videos of the earplugs via image processing software. <span class="hlt">Creep</span> could not be modeled by a single exponential in time; <span class="hlt">creep</span> approximated a power law in time. Nonlinear viscoelasticity was observed: <span class="hlt">creep</span> compliance depends on</p> <div class="credits"> <p class="dwt_author">B. Calcagno; C. Lopez Garcia; M. Kuhns; R. S Lakes</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">275</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5119743"> <span id="translatedtitle">Influence of environment and <span class="hlt">creep</span> on fatigue crack growth in a high <span class="hlt">temperature</span> aluminum alloy 8009</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Frequency effects on fatigue crack growth rates are examined in aluminum alloy 8009 in sheet and extruded product forms. The investigations show that frequency effects on the fatigue crack growth rates are pronounced in the sheet but minimal in the extrusion. The influence of <span class="hlt">creep</span> cracking on fatigue crack growth rate is studied through tests with a 60 s hold-time at maximum load at several stress intensity ranges. A 60 s hold-time at maximum load at 315 C tends to retard fatigue crack growth in both the sheet and the extrusion. The mechanism by which this retardation occurs is attributed to stress relaxation at the crack tip. At 204 C a 60 s hold at P[sub max] accelerates crack growth rate in the sheet but not in the extrusion. Vacuum and laboratory air tests show that fatigue crack growth rates in vacuum are lower than in air by about a factor of four. A 60 s hold-time at minimum load has only a minor effect on the fatigue crack growth rates at 315 C and no effect at 204 C, confirming the absence of any strong environmental contribution to crack growth rate. Fracture modes in fatigue, <span class="hlt">creep</span> crack growth and hold-time at P[sub max] are significantly different. The fractographic results are discussed in relation to the mechanical property data.</p> <div class="credits"> <p class="dwt_author">Jata, K.V.; Nicholas, T. (Wright Lab., Wright-Patterson AFB, OH (United States)); Maxwell, D. (Univ. of Dayton, OH (United States). Research Inst.)</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">276</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/540906"> <span id="translatedtitle">High energy X-ray diffraction measurement of the superstructure reflection (100) for a <span class="hlt">creep</span> <span class="hlt">deformed</span> AM1 single crystal superalloy specimen</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Due to its importance for industrial applications, the microstructural behavior of single crystal nickel base superalloys as a function of the thermo-mechanical history of the material is the subject of many studies. However, some controversies remain concerning parameters which are driving the coarsening of {gamma}{prime} precipitates. In particular the role of the lattice parameter mismatch between the {gamma} and {gamma}{prime} phases (usually defined as {Delta}d/d = (a{gamma}{prime} {minus} a{gamma})/<a> where a{gamma}{prime} and a{gamma} represent respectively the lattice parameter value of the {gamma}{prime} and {gamma} phases) and of the internal stresses at the interfaces has to be clarified. An experiment was performed on a <span class="hlt">creep</span> <span class="hlt">deformed</span> sample using high energy synchrotron radiation and a Triple Crystal Diffractometer set-up (TCD) which allow nondestructive measurements and probe the bulk of the sample. With this method the superstructure reflection (100) was measured with a good accuracy and a reasonable statistics.</p> <div class="credits"> <p class="dwt_author">Royer, A. [European Synchrotron Radiation Facility, Grenoble (France)] [European Synchrotron Radiation Facility, Grenoble (France); Bastie, P.; Veron, M. [Univ. Joseph Fourier Grenoble I-CNRS, Saint-Martin-d`Heres (France)] [Univ. Joseph Fourier Grenoble I-CNRS, Saint-Martin-d`Heres (France)</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-10-15</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">277</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2015JGRB..120..879M"> <span id="translatedtitle">Brittle <span class="hlt">creep</span> and subcritical crack propagation in glass submitted to triaxial conditions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">An experimental work is presented that aimed at improving our understanding of the mechanical evolution of cracks under brittle <span class="hlt">creep</span> conditions. Brittle <span class="hlt">creep</span> may be an important slow <span class="hlt">deformation</span> process in the Earth's crust. Synthetic glass samples have been used to observe and document brittle <span class="hlt">creep</span> due to slow crack-propagation. A crack density of 0.05 was introduced in intact synthetic glass samples by thermal shock. <span class="hlt">Creep</span> tests were performed at constant confining pressure (15 MPa) for water saturated conditions. Data were obtained by maintaining the differential-stress constant in steps of 24 h duration. A set of sensors allowed us to record strains and acoustic emissions during <span class="hlt">creep</span>. The effect of <span class="hlt">temperature</span> on <span class="hlt">creep</span> was investigated from ambient <span class="hlt">temperature</span> to 70C. The activation energy for crack growth was found to be 32 kJ/mol. In secondary <span class="hlt">creep</span>, a large dilatancy was observed that did not occur in constant strain rate tests. This is correlated to acoustic emission activity associated with crack growth. As a consequence, slow crack growth has been evidenced in glass. Beyond secondary <span class="hlt">creep</span>, failure in tertiary <span class="hlt">creep</span> was found to be a progressive process. The data are interpreted through a previously developed micromechanical damage model that describes crack propagation. This model allows one to predict the secondary brittle <span class="hlt">creep</span> phase and also to give an analytical expression for the time to rupture. Comparison between glass and crystalline rock indicates that the brittle <span class="hlt">creep</span> behavior is probably controlled by the same process even if stress sensitivity for glass is lower than for rocks.</p> <div class="credits"> <p class="dwt_author">Mallet, Cline; Fortin, Jrme; Guguen, Yves; Bouyer, Frdric</p> <p class="dwt_publisher"></p> <p class="publishDate">2015-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">278</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3195673"> <span id="translatedtitle">Influence of impurities and <span class="hlt">deformation</span> <span class="hlt">temperature</span> on the saturation microstructure and ductility of HPT-<span class="hlt">deformed</span> nickel</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">Ni with different purities between 99.69 and 99.99wt.% was <span class="hlt">deformed</span> by high-pressure torsion (HPT) to high strains, where no further refinement of the microstructure is observed. The HPT <span class="hlt">deformation</span> <span class="hlt">temperature</span> varied between ?196 and 400C. Both impurities and <span class="hlt">temperature</span> significantly affect the lower limit of the grain size obtained by HPT. In the investigated samples, carbon was the most important impurity element in controlling the limit of grain refinement. The decrease in grain size due to an increase in the carbon content from 0.008 to 0.06wt.% for HPT-<span class="hlt">deformed</span> Ni samples at room <span class="hlt">temperature</span> enhanced the ultimate tensile strength from 1000 to 1700MPa. Surprisingly, the carbon content did not deteriorate the ductility, defined as the reduction in area, which is mainly limited by the total amount of impurities besides carbon. Furthermore, the <span class="hlt">deformation</span> <span class="hlt">temperature</span> dependency on ductility was not very pronounced and only visible for <span class="hlt">deformation</span> <span class="hlt">temperatures</span> above 200C. PMID:22163380</p> <div class="credits"> <p class="dwt_author">Rathmayr, Georg B.; Pippan, Reinhard</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">279</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011MSMSE..19a5005M"> <span id="translatedtitle">A <span class="hlt">creep</span> model for austenitic stainless steels incorporating cavitation and wedge cracking</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A model of damage evolution in austenitic stainless steels under <span class="hlt">creep</span> loading at elevated <span class="hlt">temperatures</span> is proposed. The initial microstructure is idealized as a space-tiling aggregate of identical rhombic dodecahedral grains, which undergo power-law <span class="hlt">creep</span> <span class="hlt">deformation</span>. Damage evolution in the form of cavitation and wedge cracking on grain-boundary facets is considered. Both diffusion- and <span class="hlt">deformation</span>-driven grain-boundary cavity growth are treated. Cavity and wedge-crack length evolution are derived from an energy balance argument that combines and extends the models of Cottrell (1961 Trans. AIME 212 191-203), Williams (1967 Phil. Mag. 15 1289-91) and Evans (1971 Phil Mag. 23 1101-12). The time to rupture predicted by the model is in good agreement with published experimental data for a type 316 austenitic stainless steel under uniaxial <span class="hlt">creep</span> loading. <span class="hlt">Deformation</span> and damage evolution at the microscale predicted by the present model are also discussed.</p> <div class="credits"> <p class="dwt_author">Mahesh, S.; Alur, K. C.; Mathew, M. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">280</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19940018140&hterms=creep+continuum+damage+finite+element&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dcreep%2Bcontinuum%2Bdamage%2Bfinite%2Belement"> <span id="translatedtitle">Brief summary of the evolution of high-<span class="hlt">temperature</span> <span class="hlt">creep</span>-fatigue life prediction models for crack initiation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The evolution of high-<span class="hlt">temperature</span>, <span class="hlt">creep</span>-fatigue, life-prediction methods used for cyclic crack initiation is traced from inception in the late 1940's. The methods reviewed are material models as opposed to structural life prediction models. Material life models are used by both structural durability analysts and by material scientists. The latter use micromechanistic models as guidance to improve a material's crack initiation resistance. Nearly one hundred approaches and their variations have been proposed to date. This proliferation poses a problem in deciding which method is most appropriate for a given application. Approaches were identified as being combinations of thirteen different classifications. This review is intended to aid both developers and users of high-<span class="hlt">temperature</span> fatigue life prediction methods by providing a background from which choices can be made. The need for high-<span class="hlt">temperature</span>, fatigue-life prediction methods followed immediately on the heels of the development of large, costly, high-technology industrial and aerospace equipment immediately following the second world war. Major advances were made in the design and manufacture of high-<span class="hlt">temperature</span>, high-pressure boilers and steam turbines, nuclear reactors, high-<span class="hlt">temperature</span> forming dies, high-performance poppet valves, aeronautical gas turbine engines, reusable rocket engines, etc. These advances could no longer be accomplished simply by trial and error using the 'build-em and bust-em' approach. Development lead times were too great and costs too prohibitive to retain such an approach. Analytic assessments of anticipated performance, cost, and durability were introduced to cut costs and shorten lead times. The analytic tools were quite primitive at first and out of necessity evolved in parallel with hardware development. After forty years more descriptive, more accurate, and more efficient analytic tools are being developed. These include thermal-structural finite element and boundary element analyses, advanced constitutive stress-strain-<span class="hlt">temperature</span>-time relations, and <span class="hlt">creep</span>-fatigue-environmental models for crack initiation and propagation. The high-<span class="hlt">temperature</span> durability methods that have evolved for calculating high-<span class="hlt">temperature</span> fatigue crack initiation lives of structural engineering materials are addressed. Only a few of the methods were refined to the point of being directly useable in design. Recently, two of the methods were transcribed into computer software for use with personal computers.</p> <div class="credits"> <p class="dwt_author">Halford, Gary R.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_13");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return showDiv("page_9");' href="#">9</a> <a onClick='return showDiv("page_10");' href="#">10</a> <a onClick='return showDiv("page_11");' href="#">11</a> <a onClick='return showDiv("page_12");' href="#">12</a> <a onClick='return showDiv("page_13");' href="#">13</a> <a style="font-weight: bold;">14</a> <a onClick='return showDiv("page_15");' href="#">15</a> <a onClick='return showDiv("page_16");' href="#">16</a> <a onClick='return showDiv("page_17");' href="#">17</a> <a onClick='return showDiv("page_18");' href="#">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a 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showDiv("page_16");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">281</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1993cmfa.nasa..121H"> <span id="translatedtitle">Brief summary of the evolution of high-<span class="hlt">temperature</span> <span class="hlt">creep</span>-fatigue life prediction models for crack initiation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The evolution of high-<span class="hlt">temperature</span>, <span class="hlt">creep</span>-fatigue, life-prediction methods used for cyclic crack initiation is traced from inception in the late 1940's. The methods reviewed are material models as opposed to structural life prediction models. Material life models are used by both structural durability analysts and by material scientists. The latter use micromechanistic models as guidance to improve a material's crack initiation resistance. Nearly one hundred approaches and their variations have been proposed to date. This proliferation poses a problem in deciding which method is most appropriate for a given application. Approaches were identified as being combinations of thirteen different classifications. This review is intended to aid both developers and users of high-<span class="hlt">temperature</span> fatigue life prediction methods by providing a background from which choices can be made. The need for high-<span class="hlt">temperature</span>, fatigue-life prediction methods followed immediately on the heels of the development of large, costly, high-technology industrial and aerospace equipment immediately following the second world war. Major advances were made in the design and manufacture of high-<span class="hlt">temperature</span>, high-pressure boilers and steam turbines, nuclear reactors, high-<span class="hlt">temperature</span> forming dies, high-performance poppet valves, aeronautical gas turbine engines, reusable rocket engines, etc. These advances could no longer be accomplished simply by trial and error using the 'build-em and bust-em' approach. Development lead times were too great and costs too prohibitive to retain such an approach. Analytic assessments of anticipated performance, cost, and durability were introduced to cut costs and shorten lead times. The analytic tools were quite primitive at first and out of necessity evolved in parallel with hardware development. After forty years more descriptive, more accurate, and more efficient analytic tools are being developed. These include thermal-structural finite element and boundary element analyses, advanced constitutive stress-strain-<span class="hlt">temperature</span>-time relations, and <span class="hlt">creep</span>-fatigue-environmental models for crack initiation and propagation. The high-<span class="hlt">temperature</span> durability methods that have evolved for calculating high-<span class="hlt">temperature</span> fatigue crack initiation lives of structural engineering materials are addressed. Only a few of the methods were refined to the point of being directly useable in design. <Recently, two of the methods were transcribed into computer software for use with personal computers.</p> <div class="credits"> <p class="dwt_author">Halford, Gary R.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">282</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/250691"> <span id="translatedtitle">Recrystallization at ambient <span class="hlt">temperature</span> of heavily <span class="hlt">deformed</span> ETP copper wire</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Recrystallization of electrolytic tough pitch (ETP) copper wire at room <span class="hlt">temperature</span> has been reported by several authors. The phenomenon changes the mechanical properties of the wire which can cause a loss of process control, but remains largely unpredictable. The aim of this study is to get a better understanding of the conditions under which partial recrystallization can be expected. It is observed that the recrystallization pattern is non-homogeneous across the cross-section of the wire. Recrystallization starts in a cylindrical zone with diameter 0.5 to 0.8 times the wire diameter. The core and the surface of the wire recrystallize at a later stage. It is proposed that this is due to different modes of <span class="hlt">deformation</span> along the wire diameter. The progress of recrystallization at room <span class="hlt">temperature</span> depends on a large extent on the chemical composition of the material. It is well known that all impurity elements slow down recrystallization, but some elements, such as Se, Te, Bi, S and Pb are more deleterious than others. It is shown that a few tenths of ppm`s of these impurities determine whether the wire is stable in time or not.</p> <div class="credits"> <p class="dwt_author">Schamp, J.; Verlinden, B.; Van Humbeeck, J. [Katholieke Univ. Leuven (Belgium). Dept. of Metallurgy and Materials Engineering] [Katholieke Univ. Leuven (Belgium). Dept. of Metallurgy and Materials Engineering</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">283</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19900013338&hterms=Tensile+aluminum&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DTensile%2Baluminum"> <span id="translatedtitle">Elevated <span class="hlt">temperature</span> crack growth in aluminum alloys: Tensile <span class="hlt">deformation</span> of 2618 and FVS0812 aluminum alloys</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Understanding the damage tolerance of aluminum alloys at elevated <span class="hlt">temperatures</span> is essential for safe applications of advanced materials. The objective of this project is to investigate the time dependent subcritical cracking behavior of powder metallurgy FVS0812 and ingot metallurgy 2618 aluminum alloys at elevated <span class="hlt">temperatures</span>. The fracture mechanics approach was applied. Sidegrooved compact tension specimens were tested at 175, 250, and 316 C under constant load. Subcritical crack growth occurred in each alloy at applied stress intensity levels (K) of between about 14 and 25 MPa/m, well below K (sub IC). Measured load, crack opening displacement and displacement rate, and crack length and growth rate (da/dt) were analyzed with several continuum fracture parameters including, the C-integral, C (sub t), and K. Elevated <span class="hlt">temperature</span> growth rate data suggest that K is a controlling parameter during time dependent cracking. For FVS0812, da/dt is highest at 175 C when rates are expressed as a function of K. While crack growth rate is not controlled by C (sub t) at 175 C, da/dt appears to better correlate with C (sub t) at higher <span class="hlt">temperatures</span>. <span class="hlt">Creep</span> brittle cracking at intermediate <span class="hlt">temperatures</span>, and perhaps related to strain aging, is augmented by time dependent transient <span class="hlt">creep</span> plasticity at higher <span class="hlt">temperatures</span>. The C (sub t) analysis is, however, complicated by the necessity to measure small differences in the elastic crack growth and <span class="hlt">creep</span> contributions to the crack opening displacement rate. A microstructural study indicates that 2618 and FVS0812 are likely to be <span class="hlt">creep</span> brittle materials, consistent with the results obtained from the fracture mechanics study. Time dependent crack growth of 2618 at 175 C is characterized by mixed transgranular and intergranular fracture. Delamination along the ribbon powder particle boundaries occurs in FVS0812 at all <span class="hlt">temperatures</span>. The fracture mode of FVS0812 changes with <span class="hlt">temperature</span>. At 175 C, it is characterized as dimpled rupture, and at 316 C as mixed matrix superplastic rupture and matrix-dipersoid debonding.</p> <div class="credits"> <p class="dwt_author">Leng, Yang; Gangloff, Richard P.</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">284</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/50416216"> <span id="translatedtitle">Relevance of primary <span class="hlt">creep</span> in thermo-mechanical cycling for life-time prediction in Sn-based solders</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The time and <span class="hlt">temperature</span> dependant <span class="hlt">creep</span> <span class="hlt">deformation</span> of solder alloys has to be studied to describe material characteristics and failure behaviour in order to use it for lifetime evaluation by FE-simulations. It is often found in the literature that material behaviour of eutectic SnPb and lead-free such as SnAgCu solders is described considering only secondary <span class="hlt">creep</span>. To improve the material</p> <div class="credits"> <p class="dwt_author">S. Deplanque; W. Nuchter; M. Spraul; B. Wunderie; R. Dudek; B. Michel</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">285</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/205259"> <span id="translatedtitle"><span class="hlt">Creep</span>-fatigue life prediction of in situ composite solders</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Eutectic tin-lead solder alloys subjected to cyclic loading at room <span class="hlt">temperature</span> experience <span class="hlt">creep</span>-fatigue interactions due to high homologous <span class="hlt">temperature</span>. 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 <span class="hlt">creep</span> and fatigue <span class="hlt">deformation</span> at room <span class="hlt">temperature</span>. Under cyclic <span class="hlt">deformation</span>, 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 <span class="hlt">creep</span>-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 <span class="hlt">creep</span>-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.</p> <div class="credits"> <p class="dwt_author">Kuo, C.G.; Sastry, S.M.L.; Jerina, K.L. [Washington Univ., St. Louis, MO (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-12-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">286</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20060016347&hterms=contact&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dcontact"> <span id="translatedtitle">Non-Contact Measurements of <span class="hlt">Creep</span> Properties of Refractory Materials</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">State-of-the-art technologies for hypersonic aircraft, nuclear electric/thermal propulsion for spacecraft, and more efficient jet engines are driving ever more demanding needs for high-<span class="hlt">temperature</span> (>2000 C) materials. At such high <span class="hlt">temperatures</span>, <span class="hlt">creep</span> rises as one of the most important design factors to be considered. Since conventional measurement techniques for <span class="hlt">creep</span> resistance are limited to about 17OO0C, a new technique is in demand for higher <span class="hlt">temperatures</span>. This paper presents a non-contact method using electrostatic levitation (ESL) which is applicable to both metallic and non-metallic materials. The samples were rotated quickly enough to cause <span class="hlt">creep</span> <span class="hlt">deformation</span> by centrifugal acceleration. The <span class="hlt">deformation</span> of the samples was captured with a high speed camera and then the images were analyzed to estimate <span class="hlt">creep</span> resistance. Finite element analyses were performed and compared to the experiments to verify the new method. Results are presented for niobium and tungsten, representative refractory materials at 2300 C and 2700 C respectively.</p> <div class="credits"> <p class="dwt_author">Lee, Jonghyun; Bradshaw, Richard C.; Hyers, Robert W.; Rogers, Jan R.; Rathz, Thomas J.; Wall, James J.; Choo, Hahn; Liaw, Peter</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">287</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19720025884&hterms=Larry&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DLarry%2Bd."> <span id="translatedtitle">Effect of high <span class="hlt">temperature</span> <span class="hlt">creep</span> and oxidation on residual room <span class="hlt">temperature</span> properties for several thin sheet superalloys</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Superalloys are being considered for the primary heat shields and supports in the thermal protection system of both hypersonic transport and space shuttle vehicles. Since conservative design philosophy dictates designs based on residual material properties at the end of the service life, material characterization after exposure to the environmental conditions imposed by the flight requirements of these two classes of vehicles is needed on the candidate alloys. An investigation was conducted to provide some of the necessary data, with emphasis placed on oxidation, <span class="hlt">creep</span>, and residual properties of thin-gage sheet material.</p> <div class="credits"> <p class="dwt_author">Royster, D. M.; Lisagor, W. B.</p> <p class="dwt_publisher"></p> <p class="publishDate">1972-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">288</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014JNuM..444..283B"> <span id="translatedtitle">Characterization of a 14Cr ODS steel by means of small punch and uniaxial testing with regard to <span class="hlt">creep</span> and fatigue at elevated <span class="hlt">temperatures</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A 14Cr ODS steel was characterized at elevated <span class="hlt">temperatures</span> with regard to its behavior in small punch and uniaxial <span class="hlt">creep</span> tests and in low cycle fatigue tests. A comparison of small punch and uniaxial <span class="hlt">creep</span> tests at 650 C revealed a strong anisotropy of the material when strained parallel and perpendicular to the extrusion direction with rupture times being several orders of magnitude lower for the perpendicular direction. The stress-rupture and Larson-Miller plots show a very large scatter of the <span class="hlt">creep</span> data. This scatter is strongly reduced when rupture time is plotted against minimum deflection rate or minimum <span class="hlt">creep</span> rate (Monkman-Grant plot). Fatigue tests have been carried out at 650 C and 750 C. The alloy is cyclically very stable with practically no hardening/softening. Results from the tests at both <span class="hlt">temperatures</span> can be described by a common power law. An increase in the test <span class="hlt">temperature</span> has little influence on the fatigue ductility exponent. For a given total strain level, the fatigue life of the alloy is reduced with increasing <span class="hlt">temperature</span>.</p> <div class="credits"> <p class="dwt_author">Bruchhausen, M.; Turba, K.; de Haan, F.; Hhner, P.; Austin, T.; de Carlan, Y.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">289</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014MMTA...45..663K"> <span id="translatedtitle">Tensile, Fatigue, and <span class="hlt">Creep</span> Properties of Aluminum Heat Exchanger Tube Alloys for <span class="hlt">Temperatures</span> from 293 K to 573 K (20 C to 300 C)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Since automotive heat exchangers are operated at varying <span class="hlt">temperatures</span> and under varying pressures, both static and dynamic mechanical properties should be known at different <span class="hlt">temperatures</span>. Tubes are the most critical part of the most heat exchangers made from aluminum brazing sheet. We present tensile test, stress amplitude-fatigue life, and <span class="hlt">creep</span>-rupture data of six AA3XXX series tube alloys after simulated brazing for <span class="hlt">temperatures</span> ranging from 293 K to 573 K (20 C to 300 C). While correlations between several mechanical properties are strong, ranking of alloys according to one property cannot be safely deduced from the known ranking according to another property. The relative reduction in <span class="hlt">creep</span> strength with increasing <span class="hlt">temperature</span> is very similar for all six alloys, but the general trends are also strong with respect to tensile and fatigue properties; an exception is one alloy that exhibits strong Mg-Si precipitation activity during fatigue testing at elevated <span class="hlt">temperatures</span>. Interrupted fatigue tests indicated that the crack growth time is negligible compared to the crack initiation time. Fatigue lifetimes are reduced by <span class="hlt">creep</span> processes for <span class="hlt">temperatures</span> above approximately 423 K (150 C). When mechanical properties were measured at several <span class="hlt">temperatures</span>, interpolation to other <span class="hlt">temperatures</span> within the same <span class="hlt">temperature</span> range was possible in most cases, using simple and well-established equations.</p> <div class="credits"> <p class="dwt_author">Kahl, Sren; Ekstrm, Hans-Erik; Mendoza, Jesus</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">290</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/52934516"> <span id="translatedtitle"><span class="hlt">Creeping</span> soil</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Soil <span class="hlt">creep</span> is the most widespread and perhaps the least understood process of erosion on soil-mantled hillslopes. Soil is slowly ``stirred'' by burrowing creatures, and particles are displaced in wetting-drying cycles. These actions can cause downslope <span class="hlt">creep</span> by processes analogous to particle diffusion. Other possible transport mechanisms include shear and viscous-like <span class="hlt">creep</span>, such that precise characterization of the entire process</p> <div class="credits"> <p class="dwt_author">Arjun M. Heimsath; John Chappell; Nigel A. Spooner; Danile G. Questiaux</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">291</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19950011631&hterms=Ionization+Rhenium&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DIonization%2BRhenium"> <span id="translatedtitle">Influence of high pressure hydrogen environment on <span class="hlt">creep</span> <span class="hlt">deformation</span> of Mo-Re, Haynes 188, and NARloy-Z alloys</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The present study focuses on the investigation of the influence of hydrogen on the mechanical properties of three types of alloys at elevated <span class="hlt">temperatures</span>. The reasons for the consideration of hydrogen effects are the potential use of hydrogen as a coolant in gas-cooled reactors and fuel in advanced hypersonic vehicles. The materials used in hydrogen atmosphere must not be embrittled by hydrogen at ambient <span class="hlt">temperature</span> and should have good strength in hydrogen atmosphere at elevated <span class="hlt">temperature</span>. The paucity of information concerning the mechanical performance in hydrogen atmosphere at elevated <span class="hlt">temperature</span> has been a limiting factor in the selection and design of structural components for operation in hydrogen environment.</p> <div class="credits"> <p class="dwt_author">Sastry, S. M. L.; Yang, Charles C.; Ouyang, Shewang; Jerina, K. L.; Schwartz, D. S.</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">292</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/437788"> <span id="translatedtitle"><span class="hlt">Temperature</span> dependence of the <span class="hlt">deformation</span> behavior of type 316 stainless steel after low <span class="hlt">temperature</span> neutron irradiation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">A single heat of solution annealed 316 ss was irradiated to 7 and 18 dpa at 60, 200, 330, and 400 C. Tensile properties were studied vs dose and <span class="hlt">temperature</span>. Large changes in yield strength, <span class="hlt">deformation</span> mode, strain to necking (STN), and strain hardening capacity were seen. Magnitude of the changes are dependent on both irradiation <span class="hlt">temperature</span> and neutron dose. Irradiation can more than triple the yield strength and decrease STN to <0.5% under certain conditions. A maximum increase in yield strength and a minimum in STN occur after irradiation at 330 C but failure mode remains ductile.</p> <div class="credits"> <p class="dwt_author">Robertson, J.P.; Rowcliffe, A.F.; Grossbeck, M.L. [Oak Ridge National Lab., TN (United States); Ioka, Ikuo; Jitsukawa, Shiro [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Dept. of Materials Science and Engineering</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-12-31</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">293</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5559875"> <span id="translatedtitle"><span class="hlt">Creep</span> behavior of beams using the viscoplasticity theory based on total strain and overstress</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The viscoplasticity theory based on total strain and overstress can reproduce rate-dependent inelastic <span class="hlt">deformation</span> without distinction between plastic and <span class="hlt">creep</span> strain using two material functions. A viscosity function and an equilibrium stress-strain curve characterize rate-dependency and work hardening, respectively. The theory is used to analyze the <span class="hlt">creep</span> behavior of a beam subjected to a linearly increasing moment which is subsequently held constant. The analysis shows the existence of two possible states of equilibrium: termination of primary <span class="hlt">creep</span> or secondary <span class="hlt">creep</span>. They occur when the equilibrium stress-strain curve has positive or zero slope in the plastic strain range. The numerical experiments illustrate that the stress distribution at the end of the moment increase depends on the moment rate. The rate effects disappear with time when stress is redistributed. The equilibrium solution is obtained before 10/sup 7/ sec, when the material functions representing AISI Type 304 Stainless Steel at room <span class="hlt">temperature</span> are used. The other equilibrium solution (secondary <span class="hlt">creep</span>) is reached after primary <span class="hlt">creep</span> when the constant moment is above the limiting equilibrium moment which corresponds to the plastic hinge moment of plasticity theory. The stress distribution during stationary <span class="hlt">creep</span> is shown to be the solution corresponding to the Norton Law of <span class="hlt">creep</span> theory.</p> <div class="credits"> <p class="dwt_author">Hiroe, T.; Krempl, E.</p> <p class="dwt_publisher"></p> <p class="publishDate">1982-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">294</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.springerlink.com/index/funtqbvu6uxwedpr.pdf"> <span id="translatedtitle"><span class="hlt">Temperature</span> and water content effects on the viscoelastic behavior of Tilia americana (Tiliaceae) sapwood</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The effects of <span class="hlt">temperature</span> and water content on the viscoelasticity of living and dehydrated Tilia americana sapwood were examined using transient <span class="hlt">creep</span> (time- and load-dependent <span class="hlt">deformation</span>) tests under sustained bending loads. <span class="hlt">Creep</span> tests were performed at 21.1C and 20.5C to determine the magnitudes and types of strains in living and dehydrated samples. <span class="hlt">Temperature</span> had no effect on the <span class="hlt">creep</span> rate</p> <div class="credits"> <p class="dwt_author">Christopher J. Hogan; Karl J. Niklas</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">295</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011JNuM..414..440G"> <span id="translatedtitle">The effect of <span class="hlt">deformation</span> <span class="hlt">temperature</span> on the microstructure evolution of Inconel 625 superalloy</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Hot compression tests of Inconel 625 superalloy were conducted using a Gleeble-1500 simulator between 900 C and 1200 C with different true strains and a strain rate of 0.1 s -1. Scanning electron microscope (SEM) and electron backscatter diffraction technique (EBSD) were employed to investigate the effect of <span class="hlt">deformation</span> <span class="hlt">temperature</span> on the microstructure evolution and nucleation mechanisms of dynamic recrystallization (DRX). It is found that the relationship between the DRX grain size and the peak stress can be expressed by a power law function. Significant influence of <span class="hlt">deformation</span> <span class="hlt">temperatures</span> on the nucleation mechanisms of DRX are observed at different <span class="hlt">deformation</span> stages. At lower <span class="hlt">deformation</span> <span class="hlt">temperatures</span>, continuous dynamic recrystallization (CDRX) characterized by progressive subgrain rotation is considered as the main mechanism of DRX at the early <span class="hlt">deformation</span> stage. However, discontinuous dynamic recrystallization (DDRX) with bulging of the original grain boundaries becomes the operating mechanism of DRX at the later <span class="hlt">deformation</span> stage. At higher <span class="hlt">deformation</span> <span class="hlt">temperatures</span>, DDRX is the primary mechanism of DRX, while CDRX can only be considered as an assistant mechanism at the early <span class="hlt">deformation</span> stage. Nucleation of DRX can also be activated by the twinning formation. With increasing the <span class="hlt">deformation</span> <span class="hlt">temperature</span>, the effect of DDRX accompanied with twinning formation grows stronger, while the effect of CDRX grows weaker. Meanwhile, the position of subgrain formation shifts gradually from the interior of original grains to the vicinity of the original boundaries.</p> <div class="credits"> <p class="dwt_author">Guo, Qingmiao; Li, Defu; Guo, Shengli; Peng, Haijian; Hu, Jie</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">296</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19860012506&hterms=NaZArov&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DNaZArov"> <span id="translatedtitle">Thermal <span class="hlt">deformation</span> of concentrators in an axisymmetric <span class="hlt">temperature</span> field</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Axisymmetric thermal <span class="hlt">deformations</span> of paraboloid mirrors, due to heating, are examined for a mirror with a optical axis oriented toward the Sun. A governing differential equation is derived using Mushtari-Donnel-Vlasov simplifications, and a solution is presented which makes it possible to determine the principal <span class="hlt">deformation</span> characteristics.</p> <div class="credits"> <p class="dwt_author">Bairamov, R.; Machuev, Y. I.; Nazarov, A.; Sokolov, Y. V.; Solodovnikova, L. A.; Fokin, V. G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">297</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19830041055&hterms=ZrO2&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DZrO2"> <span id="translatedtitle"><span class="hlt">Creep</span> of plasma-sprayed-ZrO2 thermal-barrier coatings</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Specimens of plasma-sprayed-zirconia thermal-barrier coatings with three different porosities and different initial particle sizes were <span class="hlt">deformed</span> in compression at initial loads of 6900, 13,800, and 24,100 kPa (1000, 2000, and 3500 psi) and <span class="hlt">temperatures</span> of 1100, 1250, and 1400 C. The coatings were stabilized with lime, MgO, and two different concentrations of Y2O3. <span class="hlt">Creep</span> began as soon as the load was applied and continued at a constantly decreasing rate until the load was removed. <span class="hlt">Temperature</span> and stabilization had a pronounced effect on <span class="hlt">creep</span> rate while the stress, particle size, and porosity had a lesser effect. <span class="hlt">Creep</span> <span class="hlt">deformation</span> was due to cracking and particle sliding.</p> <div class="credits"> <p class="dwt_author">Firestone, R. F.; Logan, W. R.; Adams, J. W.; Bill, R. C., Jr.</p> <p class="dwt_publisher"></p> <p class="publishDate">1982-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">298</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/939198"> <span id="translatedtitle">MOLECULAR DYNAMICS STUDY OF DIFFUSIONAL <span class="hlt">CREEP</span> IN NANOCRYSTALLINE UO2</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We present the results of molecular dynamics (MD) simulations to study hightemperature <span class="hlt">deformation</span> of nanocrystalline UO2. In qualitative agreement with experimental observations, the oxygen sub-lattice undergoes a structural transition at a <span class="hlt">temperature</span> of about 2200 K (i.e., well below the melting point of 3450 K of our model system), whereas the uranium sub-lattice remains unchanged all the way up to melting. At <span class="hlt">temperatures</span> well above this structural transition, columnar nanocrystalline model microstructures with a uniform grain size and grain shape were subjected to constantstress loading at levels low enough to avoid microcracking and dislocation nucleation from the GBs. Our simulations reveal that in the absence of grain growth, the material <span class="hlt">deforms</span> via GB diffusion <span class="hlt">creep</span> (also known as Coble <span class="hlt">creep</span>). Analysis of the underlying self-diffusion behavior in undeformed nanocrystalline UO2 reveals that, on our MD time scale, the uranium ions diffuse only via the grain boundaries (GBs) whereas the much faster moving oxygen ions diffuse through both the lattice and the GBs. As expected for the Coble-<span class="hlt">creep</span> mechanism, the <span class="hlt">creep</span> activation energy agrees well with that for GB diffusion of the slowest moving species, i.e., of the uranium ions.</p> <div class="credits"> <p class="dwt_author">Tapan G. Desai; Paul C. Millett; Dieter Wolf</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">299</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2015PMM...116..200D"> <span id="translatedtitle">Investigation of the structure of two heat-<span class="hlt">temperature</span> nickel-based alloys after high-<span class="hlt">temperature</span> <span class="hlt">deformation</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The structural tests of turbine blades made from two commercial high-<span class="hlt">temperature</span> nickel-based alloys were carried out after their test operation at elevated <span class="hlt">temperature</span> and stresses. Both alloys contain 40% of a hardening intermetallic phase and the upper operating <span class="hlt">temperature</span> of both alloys is limited to 900C, but they have a different resistance to high-<span class="hlt">temperature</span> <span class="hlt">deformation</span>.</p> <div class="credits"> <p class="dwt_author">Davydov, D. I.; Vinogradova, N. I.; Kazantseva, N. V.; Stepanova, N. N.</p> <p class="dwt_publisher"></p> <p class="publishDate">2015-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">300</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40489160"> <span id="translatedtitle">Dislocation <span class="hlt">creep</span> of fine-grained recrystallized plagioclase under low-<span class="hlt">temperature</span> conditions</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Lattice preferred orientation (LPO) and dislocation substructure of fine-grained plagioclase were investigated in ultramylonite from a shear zone along the Hatagawa fault zone in northeast Japan. In the shear zone, the orthoclase mole fraction of the recrystallized alkali-feldspar is not less than 0.94. This composition suggests that <span class="hlt">deformation</span> occurred below 500C. Selected area diffraction by transmission electron microscopy (TEM) for</p> <div class="credits"> <p class="dwt_author">Norio Shigematsu; Hidemi Tanaka</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_14");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a 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class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_15");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' href="#">4</a> <a onClick='return showDiv("page_5");' href="#">5</a> <a onClick='return showDiv("page_6");' href="#">6</a> <a onClick='return showDiv("page_7");' href="#">7</a> <a onClick='return showDiv("page_8");' href="#">8</a> <a onClick='return 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title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">301</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014EGUGA..1614902B"> <span id="translatedtitle">Microdeformation experiments on chalk - fluids, fracture and <span class="hlt">creep</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Chalks are fine grained aggregates of biogenic calcite that <span class="hlt">creep</span> and fracture and the <span class="hlt">deformation</span> 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 <span class="hlt">deformation</span>. 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 <span class="hlt">temperature</span>, small strains and the pore fluid. The thin chalk samples are imaged at different scales with a resolution down to 0.5 micrometers. <span class="hlt">Deformation</span> measurements are performed by digital image correlation. Examples of localized and distributed <span class="hlt">deformation</span> and effects of rapid change of pore fluid during <span class="hlt">deformation</span> are presented.</p> <div class="credits"> <p class="dwt_author">Bergsaker, Anne; Neuville, Amelie; Ryne, Anja; Dysthe, Dag Kristian</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">302</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AGUFMMR33C..02K"> <span id="translatedtitle">In Situ <span class="hlt">Creep</span> Strength Measurements on Ringwoodite at 18 GPa and 1700K Using a <span class="hlt">Deformation</span>-DIA Apparatus Combined with Synchrotron Radiation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In order to study rheology of deep Earth materials at pressure-<span class="hlt">temperature</span> conditions of the lower mantle transition zone, technical improvements in <span class="hlt">deformation</span> experiments with a <span class="hlt">deformation</span>-DIA (D-DIA) apparatus have been made. We optimized dimensions of anvil truncation, a pressure medium and gasket to achieve the <span class="hlt">deformation</span> experiments at 18 GPa at relatively low press load (0.5 MN) to minimize damage of X-ray transparent second-stage anvils. Stress and strain of a sample were determined quantitatively by means of in situ X-ray radial diffraction and radiography, respectively, in conjunction with synchrotron radiation at BL04B1 beamline, SPring-8. We adopted low X-ray absorption materials (e.g. cubic BN anvils, graphite window in a LaCrO3 heater) along an X-ray path to enable the in situ stress-strain measurements. Based on the developed technique, the <span class="hlt">deformation</span> experiments on ringwoodite were carried out in uniaxial geometry at pressures of 17-18 GPa and <span class="hlt">temperatures</span> of 1500-1700 K with strain rates of 3.38-5.56 10-5 s-1 and strains up to 26.0 %. In the present study, the pressure condition of the in situ stress-strain measurements in the D-DIA apparatus was successfully expanded from 14.5 GPa to 18 GPa at <span class="hlt">temperatures</span> of 1500-1700 K. The present technical improvements in the in situ stress-strain measurements with the D-DIA apparatus should greatly contribute to studies on rheology of the deep Earth materials.</p> <div class="credits"> <p class="dwt_author">Kawazoe, T.; Nishihara, Y.; Ohuchi, T.; Maruyama, G.; Higo, Y.; Funakoshi, K.; Irifune, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">303</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009PMM...107..409D"> <span id="translatedtitle"><span class="hlt">Deformation</span> mechanisms in Cr20Ni80 alloy at elevated <span class="hlt">temperatures</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The mechanisms of plastic <span class="hlt">deformation</span> of Cr20Ni80 nichrome with an initial grain size of 80 ?m were studied in the <span class="hlt">temperature</span> range 600-950C and the strain-rate range 1.5 10-6-5 10-2s-1. Nichrome is shown to exhibit anomalously high values of stress exponent n and a high <span class="hlt">deformation</span> activation energy Q. These unusual properties were found to be caused by threshold stresses below which <span class="hlt">deformation</span> does not occur. An analysis of the <span class="hlt">deformation</span> behavior with allowance for threshold stresses reveals the regions of hot, warm, and cold <span class="hlt">deformation</span> in nichrome. At normalized strain rates dot \\varepsilon kT/ D 1 Gb < 10-8, the true values of n and Q are 4 and 285 30 kJ/mol, respectively. In the normalized-strain range 10-8-10-4 n 6 and the <span class="hlt">deformation</span> activation energy decreases to 175 30 kJ/mol. This change in the <span class="hlt">deformation</span>-behavior characteristics is explained by the transition from high-<span class="hlt">temperature</span> dislocation climb, which is controlled by lattice self-diffusion, to low-<span class="hlt">temperature</span> dislocation climb, which is controlled by pipe diffusion, as the <span class="hlt">temperature</span> decreases. At dot \\varepsilon kT/ D 1 Gb = 10-4, a power law break-down takes place and an exponential law (which describes the <span class="hlt">deformation</span> behavior in the range of cold <span class="hlt">deformation</span>) becomes operative.</p> <div class="credits"> <p class="dwt_author">Dudova, N. R.; Kaibyshev, R. O.; Valitov, V. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">304</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011JGeo...51..398J"> <span id="translatedtitle">Present-day <span class="hlt">deformation</span> along the El Pilar Fault in eastern Venezuela: Evidence of <span class="hlt">creep</span> along a major transform boundary</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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 <span class="hlt">deformation</span> 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.</p> <div class="credits"> <p class="dwt_author">Jouanne, Franois; Audemard, Franck A.; Beck, Christian; Van Welden, Aurlien; Ollarves, Reinaldo; Reinoza, Carlos</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">305</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4308006"> <span id="translatedtitle">Sessile dislocations by reactions in NiAl severely <span class="hlt">deformed</span> at room <span class="hlt">temperature</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">B2 ordered NiAl is known for its poor room <span class="hlt">temperature</span> (RT) ductility; failure occurs in a brittle like manner even in ductile single crystals <span class="hlt">deforming</span> by single slip. In the present study NiAl was severely <span class="hlt">deformed</span> at RT using the method of high pressure torsion (HPT) enabling the hitherto impossible investigation of multiple slip <span class="hlt">deformation</span>. Methods of transmission electron microscopy were used to analyze the dislocations formed by the plastic <span class="hlt">deformation</span> showing that as expected dislocations with Burgers vector a?100? carry the plasticity during HPT <span class="hlt">deformation</span> at RT. In addition, we observe that they often form a?110? dislocations by dislocation reactions; the a?110? dislocations are considered to be sessile based on calculations found in the literature. It is therefore concluded that the frequently encountered 3D dislocation networks containing sessile a?110? dislocations are pinned and lead to <span class="hlt">deformation</span>-induced embrittlement. In spite of the severe <span class="hlt">deformation</span>, the chemical order remains unchanged. PMID:25663749</p> <div class="credits"> <p class="dwt_author">Geist, D.; Gammer, C.; Rentenberger, C.; Karnthaler, H.P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2015-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">306</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20110011967&hterms=videos&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dvideos"> <span id="translatedtitle"><span class="hlt">Creep</span> Measurement Video Extensometer</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Understanding material behavior under load is critical to the efficient and accurate design of advanced aircraft and spacecraft. Technologies such as the one disclosed here allow accurate <span class="hlt">creep</span> measurements to be taken automatically, reducing error. The goal was to develop a non-contact, automated system capable of capturing images that could subsequently be processed to obtain the strain characteristics of these materials during <span class="hlt">deformation</span>, while maintaining adequate resolution to capture the true <span class="hlt">deformation</span> response of the material. The measurement system comprises a high-resolution digital camera, computer, and software that work collectively to interpret the image.</p> <div class="credits"> <p class="dwt_author">Jaster, Mark; Vickerman, Mary; Padula, Santo, II; Juhas, John</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">307</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/7243995"> <span id="translatedtitle">Petrology and micromechanics of experimentally <span class="hlt">deformed</span> natural rock salt: Physical processes: Topical report</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Effects of impurities and microprocesses on the <span class="hlt">creep</span> of natural salt samples are presented. Salts are analyzed from four sites (Palo Duro Unit 4 and Palo Duro Unit 5, Texas; Avery Island, Louisiana; and Salina Basin, Michigan). The salts have been <span class="hlt">deformed</span> at <span class="hlt">temperatures</span> and pressures that simulate repository conditions. Bulk chemistry, optical petrology, and microprobe analyses are used to identify the species and to quantify the amount of each impurity. General effects of impurities on the rheology of natural salt are discussed. The physical processes that control <span class="hlt">creep</span> <span class="hlt">deformation</span> of salt are identified by etchpit techniques. The nature of desolation motion which controls the <span class="hlt">creep</span> behavior of salt changes dramatically over the <span class="hlt">temperature</span> range of 25 to 200/degree/C. Physical bases for constitutive modeling are established through observations documented in this report. Composition of the salts range from nearly pure, uniform halite to a heterogeneous composite of halite and anhydrite. Impurities evidently increase <span class="hlt">creep</span> resistance at lower test <span class="hlt">temperatures</span>. At higher test <span class="hlt">temperatures</span>, <span class="hlt">creep</span> <span class="hlt">deformation</span> is much less sensitive to the presence of impurities. Anhydrite is the only mineral species that correlates strongly with <span class="hlt">creep</span> response. Generally, greater amounts of anhydrite increase the <span class="hlt">creep</span> resistance. 13 refs., 11 figs., 12 tabs.</p> <div class="credits"> <p class="dwt_author">Hansen, F.D.</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">308</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/39857738"> <span id="translatedtitle"><span class="hlt">Temperature</span> dependence of lifetime statistics for single Kevlar 49 filaments in <span class="hlt">creep</span>-rupture</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Experimental data are presented for the strength and lifetime under constant stress of single Kevlar 49 aramid filaments at two elevated <span class="hlt">temperatures</span>, 80 and 130 C. As seen in previously published work performed at room <span class="hlt">temperature</span> (21 C), the strength data could be fitted to a two-parameter Weibull distribution; increasing the <span class="hlt">temperature</span> caused a decrease in the Weibull scale parameter</p> <div class="credits"> <p class="dwt_author">H. F. Wu; S. L. Phoenix; P. Schwartz</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">309</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dspace.mit.edu/handle/1721.1/45602"> <span id="translatedtitle">High <span class="hlt">temperature</span> <span class="hlt">deformation</span> mechanisms and strain heterogeneities in calcite rocks</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/eprints/">E-print Network</a></p> <p class="result-summary">In nature, carbonates often accumulate large amounts of strain in localized shear zones. Such marble sequences play a key role in crustal <span class="hlt">deformation</span> processes. Despite extensive field and laboratory investigation, many ...</p> <div class="credits"> <p class="dwt_author">Xu, Lili, Sh. D. Massachusetts Institute of Technology</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">310</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/5135718"> <span id="translatedtitle">ORNL irradiation <span class="hlt">creep</span> facility</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">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 <span class="hlt">creep</span> and experimental constraints associated with each measurement technique is given. Factors are presented which lead to the experimental choices made for the Irradiation <span class="hlt">Creep</span> 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 <span class="hlt">temperature</span> fluctuations imposed by the particle beam which passes through the specimen. Electrical resistance of the specimen is the <span class="hlt">temperature</span> control parameter chosen. Very high precision in length measurement and <span class="hlt">temperature</span> control are required to detect the small elongation rates relevant to irradiation <span class="hlt">creep</span> 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 <span class="hlt">creep</span> 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 <span class="hlt">creep</span> measurements.</p> <div class="credits"> <p class="dwt_author">Reiley, T.C.; Auble, R.L.; Beckers, R.M.; Bloom, E.E.; Duncan, M.G.; Saltmarsh, M.J.; Shannon, R.H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1980-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">311</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/885787"> <span id="translatedtitle">Development of Advanced Corrosion-Resistant Fe-Cr-Ni Austenitic Stainless Steel Alloy with Improved High <span class="hlt">Temperature</span> Strenth and <span class="hlt">Creep</span>-Resistance</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">In February of 1999, a Cooperative Research and Development Agreement (CRADA) was undertaken between Oak Ridge National Laboratory (ORNL) and Special Metals Corporation-Huntington Alloys (formerly INCO Alloys International, Inc.) to develop a modified wrought austenitic stainless alloy with considerably more strength and corrosion resistance than alloy 800H or 800HT, but with otherwise similar engineering and application characteristics. Alloy 800H and related alloys have extensive use in coal flue gas environments, as well as for tubing or structural components in chemical and petrochemical applications. The main concept of the project was make small, deliberate elemental microalloying additions to this Fe-based alloy to produce, with proper processing, fine stable carbide dispersions for enhanced high <span class="hlt">temperature</span> <span class="hlt">creep</span>-strength and rupture resistance, with similar or better oxidation/corrosion resistance. The project began with alloy 803, a Fe-25Cr-35NiTi,Nb alloy recently developed by INCO, as the base alloy for modification. Smaller commercial developmental alloy heats were produced by Special Metals. At the end of the project, three rounds of alloy development had produced a modified 803 alloy with significantly better <span class="hlt">creep</span> resistance above 815EC (1500EC) than standard alloy 803 in the solution-annealed (SA) condition. The new upgraded 803 alloy also had the potential for a processing boost in that <span class="hlt">creep</span> resistance for certain kinds of manufactured components that was not found in the standard alloy. The upgraded 803 alloy showed similar or slightly better oxidation and corrosion resistance relative to standard 803. <span class="hlt">Creep</span> strength and oxidation/corrosion resistance of the upgraded 803 alloy were significantly better than found in alloy 800H, as originally intended. The CRADA was terminated in February 2003. A contributing factor was Special Metals Corporation being in Chapter 11 Bankruptcy. Additional testing, further commercial scale-up, and any potential invention disclosures were not pursued. One objective of this project was to improve the high <span class="hlt">temperature</span> <span class="hlt">creep</span> resistance of the recently developed 803 alloy, while another was to have a wrought modified 803 alloy with significantly better <span class="hlt">creep</span> resistance and corrosion resistance than the commonly used alloy 800H. The project was intended to use the established expertise at ORNL to design specific microalloying element additions to appropriately tailor the microstructure during aging or <span class="hlt">creep</span> so that fine, stable carbides develop for strength. If possible, oxidation/corrosion resistance at high <span class="hlt">temperatures</span> would also be enhanced. Optimum processing was to be developed for plate and tube products.</p> <div class="credits"> <p class="dwt_author">Maziasz, PJ</p> <p class="dwt_publisher"></p> <p class="publishDate">2004-09-30</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">312</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/175208"> <span id="translatedtitle">Damage-enhanced <span class="hlt">creep</span> and <span class="hlt">creep</span> rupture in fiber composites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary"><span class="hlt">Creep</span> in fiber composites at high <span class="hlt">temperatures</span> is an important phenomenon that can lead to accelerated failure in several different ways. For systems with matrix <span class="hlt">creep</span> rates larger than those of the fibers, <span class="hlt">creep</span> transfers load onto the fibers and the fibers undergo progressive damage under the increasing load. This leads to enhanced composite <span class="hlt">creep</span> rates, relative to non-breaking fibers, in both ceramic and metal matrix composites. In metal composites, <span class="hlt">creep</span> rupture can then occur by excessive damage accumulation even in the absence of explicit high-<span class="hlt">temperature</span> fiber degradation mechanisms. In ceramic composites, <span class="hlt">creep</span> rupture occurs following fiber degradation such as slow crack growth, a process accelerated by the enhanced stress on the fibers. Here, these phenomena are discussed within the framework of the composite model of Curtin, which is generalized to include <span class="hlt">creep</span> and <span class="hlt">creep</span> rupture. The model generally accounts for the statistical evolution of fiber damage and for the interfacial slip between fibers and matrix that occur in both CMC and MMC materials, both of which can be functions of time at elevated <span class="hlt">temperatures</span>. Application of the theory to <span class="hlt">creep</span> rupture in titanium matrix composites reinforced with SiC fibers shows good agreement with experimental results for <span class="hlt">creep</span> rates and failure times versus applied load. Application to <span class="hlt">creep</span> rupture in ceramic matrix composites in which the fibers undergo slow crack growth demonstrates the dependence of lifetime on load and crack growth rate. A much longer lifetime for composites, as compared to the lifetime of individual fibers tested in the laboratory, is demonstrated; this is a result of the small effective gauge length of fibers in the composite relative to the typical gauge lengths tested in single fiber stress rupture tests.</p> <div class="credits"> <p class="dwt_author">Curtin, W.A.; Fabeny, B.; Iyengar, N. [Virginia State Univ., Blacksburg, VA (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-12-31</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">313</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19850061828&hterms=creep+fatigue&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dcreep%2Bfatigue"> <span id="translatedtitle">Application of two <span class="hlt">creep</span> fatigue life models for the prediction of elevated <span class="hlt">temperature</span> crack initiation of a nickel base alloy</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Cyclic Damage Accumulation (CDA) and Total Strain-Strain Range Partitioning (TS-SRP) models for predicting the <span class="hlt">creep</span>-fatigue crack initiation life of high <span class="hlt">temperature</span> alloys are presented. The models differ in their fundamental assumptions regarding the controlling parameters for fatigue crack initiation and in the amount of data required to determine model constants. The CDA model represents a ductility exhaustion approach and uses stress quantities to calculate the cyclic fatigue damage. The TS-SRP model is based on the use of total mechanical strain and earlier concepts of the Strain Range Partitioning Method. Both models were applied to a well controlled fatigue data set at a high <span class="hlt">temperature</span> nickel base alloy, B1900 + Hf, tested at 1600 F and 1800 F. The tests were divided into a baseline data set required to determine model constants and a verification data set for evaluation of the predictive capability of the models. Both models correlated the baseline data set to within factors of two in life, and predicted the verification data set to within a factor of three or better. In addition, sample calculations to demonstrate the application of each model and discusions of the predictive capabilities and areas requiring further development are presented.</p> <div class="credits"> <p class="dwt_author">Moreno, V.; Nissley, D. M.; Halford, G. R.; Saltsman, J. F.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">314</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/51737081"> <span id="translatedtitle">Experimental pressure solution <span class="hlt">creep</span> of polymineralic aggregates</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Unexpected <span class="hlt">creep</span> behavior is obtained when experimentally compacting an aggregate containing two different minerals. Sieved mixtures of calcite and halite grains are experimentally compacted in pressure cells in the presence of a saturated aqueous solution. The individual halite grains <span class="hlt">deform</span> easily by pressure solution <span class="hlt">creep</span> whereas calcite grains act as hard objects and resist compaction. The fastest rate of compaction</p> <div class="credits"> <p class="dwt_author">S. Zoubtsov; F. Renard; J.-P. Gratier; R. Guiguet; D. K. Dysthe; V. Traskine</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">315</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1997JEMat..26..839M"> <span id="translatedtitle">Tensile, <span class="hlt">creep</span>, and ABI tests on sn5%sb solder for mechanical property evaluation</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Sn5%Sb is one of the materials considered for replacing lead containing alloys for soldering in electronic packaging. We evaluated the tensile properties of the bulk material at varied strain-rates and <span class="hlt">temperatures</span> (to 473K) to determine the underlying <span class="hlt">deformation</span> mechanisms. Stress exponents of about three and seven were observed at low and high stresses, respectively, and very low activation energies for <span class="hlt">creep</span> (about 16.7 and 37.7 kJ/mole) were noted. A maximum ductility of about 350% was noted at ambient <span class="hlt">temperature</span>. <span class="hlt">Creep</span> tests performed in the same <span class="hlt">temperature</span> regime also showed two distinct regions, albeit with slightly different exponents (three and five) and activation energy (about 54.4 kJ/mole). Ball indentation tests were performed on the shoulder portions of the <span class="hlt">creep</span> samples (prior to <span class="hlt">creep</span> tests) using a Stress-Strain Microprobe@ (Advanced Technology Corporation) at varied indentation rates (strain-rates). The automated ball indentation (ABI) data were at relatively high strain-rates; however, they were in excellent agreement with <span class="hlt">creep</span> data, while both these results deviated from the tensile test data. Work is planned to perform <span class="hlt">creep</span> at high stresses at ambient and extend ABI tests to elevated <span class="hlt">temperatures</span>.</p> <div class="credits"> <p class="dwt_author">Murty, K. Linga; Haggag, Fahmy M.; Mahidhara, Rao K.</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">316</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013JNuM..440..467F"> <span id="translatedtitle">Anisotropic <span class="hlt">deformation</span> of Zr-2.5Nb pressure tube material at high <span class="hlt">temperatures</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Zr-2.5Nb alloy is used for the pressure tubes in CANDU reactor fuel channels. In reactor, the pressure tube normally operates at 300 C and experiences a primary coolant fluid internal pressure of approximately 10 MPa. Manufacturing and processing procedures generate an anisotropic state in the pressure tube which makes the tube stronger in the hoop (transverse) direction than in the axial (longitudinal) direction. This anisotropy condition is present for <span class="hlt">temperatures</span> less than 500 C. During postulated accident conditions where the material <span class="hlt">temperature</span> could reach 1000 C, it might be assumed that the high <span class="hlt">temperature</span> and subsequent phase change would reduce the inherent anisotropy, and thus affect the <span class="hlt">deformation</span> behaviour (ballooning) of the pressure tube. From constant-load, rapid-<span class="hlt">temperature</span>-ramp, uniaxial <span class="hlt">deformation</span> tests, the <span class="hlt">deformation</span> rate in the longitudinal direction of the tube behaves differently than the <span class="hlt">deformation</span> rate in the transverse direction of the tube. This anisotropic mechanical behaviour appears to persist at <span class="hlt">temperatures</span> up to 1000 C. This paper presents the results of high-<span class="hlt">temperature</span> <span class="hlt">deformation</span> tests using longitudinal and transverse specimens taken from as-received Zr-2.5Nb pressure tubes. It is shown that the anisotropic <span class="hlt">deformation</span> behaviour observed at high <span class="hlt">temperatures</span> is largely due to the stable crystallographic texture of the ?-Zr phase constituent in the material that was previously observed by neutron diffraction measurements during heating at <span class="hlt">temperatures</span> up to 1050 C. The <span class="hlt">deformation</span> behaviour is also influenced by the phase transformation occurring at high <span class="hlt">temperatures</span> during heating. The effects of texture and phase transformation on the anisotropic <span class="hlt">deformation</span> of as-received Zr-2.5Nb pressure tube material are discussed in the context of the tube ballooning behaviour. Because of the high <span class="hlt">temperatures</span> in postulated accident scenarios, any irradiation damage will be annealed from the pressure tube material and thus the unirradiated material results presented in this paper are also applicable to irradiated pressure tubes.</p> <div class="credits"> <p class="dwt_author">Fong, R. W. L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">317</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013PhDT........40K"> <span id="translatedtitle"><span class="hlt">Creep</span>, fatigue and <span class="hlt">creep</span>-fatigue interactions in modified 9% Chromium - 1% Molybdenum (P91) steels</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Grade P91 steel, from the class of advanced high-chrome ferritic steels, is one of the preferred materials for many elevated <span class="hlt">temperature</span> structural components. <span class="hlt">Creep</span>-fatigue (C-F) interactions, along with oxidation, can accelerate the kinetics of damage accumulation and consequently reduce such components' life. Hence, reliable C-F test data is required for meticulous consideration of C-F interactions and oxidation, which in turn is vital for sound design practices. It is also imperative to develop analytical constitutive models that can simulate and predict material response under various long-term in-service conditions using experimental data from short-term laboratory experiments. Consequently, the major objectives of the proposed research are to characterize the <span class="hlt">creep</span>, fatigue and C-F behavior of grade P91 steels at 625 C and develop robust constitutive models for simulating/predicting their microstructural response under different loading conditions. This work will utilize experimental data from 16 laboratories worldwide that conducted tests (<span class="hlt">creep</span>, fatigue and C-F) on grade P91 steel at 625C in a round-robin (RR) program. Along with 7 <span class="hlt">creep</span> <span class="hlt">deformation</span> and rupture tests, 32 pure fatigue and 46 C-F tests from the RR are considered in this work. A phenomenological constitutive model formulated in this work needs just five fitting parameters to simulate/predict the monotonic, pure fatigue and C-F behavior of grade P91 at 625 C. A modified version of an existing constitutive model is also presented for particularly simulating its isothermal <span class="hlt">creep</span> <span class="hlt">deformation</span> and rupture behavior. Experimental results indicate that specimen C-F lives, as measured by the 2% load drop criterion, seem to decrease with increasing strain ranges and increasing hold times at 625C. Metallographic assessment of the tested specimens shows that the damage mode in both pure fatigue and 600 seconds hold time cyclic tests is predominantly transgranular fatigue with some presence of oxidation spikes. The damage mode in 1800 second hold time cyclic tests is an interaction of transgranular fatigue with dominant oxide spikes and <span class="hlt">creep</span> cavitation. Other experimental results including the statistical analysis and inter- and intra-laboratory variability in the C-F lifetimes are provided in the text. Scatter factor for any of <span class="hlt">creep</span>, monotonic, pure fatigue and C-F simulations is shown to be at a maximum of 1.3, in comparison to > 5 expected for a RR. Moreover, the microstructural variability between nominally homogeneous specimens can be inherently accounted by the formulated constitutive model.</p> <div class="credits"> <p class="dwt_author">Kalyanasundaram, Valliappa</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">318</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/1986GMS....36..117H"> <span id="translatedtitle">Experimental <span class="hlt">deformation</span> of rocksalt</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Using newly designed apparatus for triaxial-compression testing of 10 by 20-cm cores of Avery Island rocksalt at constant strain-rates between 10-4 and 10-6/s, <span class="hlt">temperatures</span> between 100 and 200C, and confining pressures of 3.4 and 20 MPa, comparing our data with those of other workers on the same material, and observing natural <span class="hlt">deformations</span> of rocksalt, we find that (1) constant-strain-rate and quasi-constant stress-rate tests (both often called quasi-static compression tests) yield essentially similar stress-strain relations, and these depend strongly on strain rate and <span class="hlt">temperature</span>, but not confining pressure; (2) fracture excluded, the <span class="hlt">deformation</span> mechanisms observed for differential stresses between 0.5 and 20 MPa are intracrystal-line slip (dislocation glide and cross-slip) and polygonization (dislocation glide and climb by ion-vacancy pipe diffusion); (3) the same steady-state strain rate ?., and flow stress are reached at the same <span class="hlt">temperature</span> in both constant-strain-rate and constant-stress (<span class="hlt">creep</span>) tests, but the strain-time data from transient <span class="hlt">creep</span> tests do not match the strain-hardening data unless the initial strain, ?0 (time-dependent in rocksalt) is accounted for; in <span class="hlt">creep</span> tests the clock is not started until the desired constant stress is reached; (4) because the stress-strain curve contains the entire history of the <span class="hlt">deformation</span>, the constant-strain-rate test rather than the <span class="hlt">creep</span> test may well be preferred as the source of constitutive data; (5) furthermore, if the stress or <span class="hlt">temperature</span> of the <span class="hlt">creep</span> test is too low to achieve the steady state in laboratory time, one cannot predict the steady-state flow stress or strain rate from the transient response alone, whereas we can estimate them rather well from constant-strain-rate data even when strain rates are too high or <span class="hlt">temperatures</span> too low to reach the steady state within a few hours; (6) the so-called "baseline <span class="hlt">creep</span> law", giving <span class="hlt">creep</span> strain, ? = ea[1-exp(-?t)]+?. ss t, where ea, ?, and ?. ss are regarded as material properties as well as fitting parameters, can be valid, if at all, only over intervals of stress and <span class="hlt">temperature</span> where the same <span class="hlt">deformation</span> mechanisms operate and only if it is independent of structural changes, that is of loading path, and it poorly predicts constant-stress-rate response in triaxial-compression tests and long-term, low-stress response from data taken over short time at high stress; (7) a potentially more useful, semi-empirical constitutive model, incorporating stress (?), strain (?), strain rate (?.), and absolute <span class="hlt">temperature</span> (T), and capable of matching at least limited constant-strain-rate, constant-stress-rate, constant-stress (<span class="hlt">creep</span>), and relaxation (nearly constant strain) data even though constant structure is assumed, is ?=K?. q exp(B/T)[1={exp(-r1?) + exp(-r2?)}/2], where K, q, B, r1, and r2 are to be treated as fitting parameters until their physical significance is better understood; (8) however, we doubt that any single, perfectly general constitutive equation can be written to satisfy all conditions pertinent to repository design, say 25 ? T ? 300C and 1 ? ? ? 20 MPa, and also to be workable in numerical modeling; (9) hence, no matter how abundant and precise site-specific laboratory data may become, one can expect only to approximate the rheological behavior of the prototype.</p> <div class="credits"> <p class="dwt_author">Handin, J.; Russell, J. E.; Carter, N. L.</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">319</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/1001116"> <span id="translatedtitle"><span class="hlt">Creep</span> Properties of Solid Oxide Fuel Cell Glass-Ceramic Seal G18</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This study utilizes nanoindentation to investigate and measure <span class="hlt">creep</span> properties of a barium calcium aluminosilicate glass-ceramic used for solid oxide fuel cell seals (SOFCs). Samples of the glassceramic seal material were aged for 5h, 50h, and 100h to obtain different degrees of crystallinity. Instrumented nanoindentation was performed on the samples with different aging times at different <span class="hlt">temperatures</span> to investigate the strain rate sensitivity during inelastic <span class="hlt">deformation</span>. The <span class="hlt">temperature</span> dependent behavior is important since SOFCs operate at high <span class="hlt">temperatures</span> (800-1000C). Results show that the samples with higher crystallinity were more resistant to <span class="hlt">creep</span>, and the <span class="hlt">creep</span> compliance tended to decrease with increasing <span class="hlt">temperature</span>, especially with further aged samples.</p> <div class="credits"> <p class="dwt_author">Milhans, Jacqueline; Khaleel, Mohammad A.; Sun, Xin; Tehrani, Mehran; Al-Haik, Marwan; Garmestani, Hamid</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">320</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012SPIE.8563E..0HL"> <span id="translatedtitle">Continuous turbine blade <span class="hlt">creep</span> measurement based on Moir</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Moir imaging has been used to measure <span class="hlt">creep</span> in the airfoil section of gas turbine blades. The ability to accurately assess <span class="hlt">creep</span> and other failure modes has become an important engineering challenge, because gas turbine manufacturers are putting in place condition-based maintenance programs. In such maintenance programs, the condition of individual components is assessed to determine their remaining lives. Using pad-print technology, a grating pattern was printed directly on a turbine blade for localized <span class="hlt">creep</span> detection using the spacing change of moir pattern fringes. A <span class="hlt">creep</span> measurement prototype was assembled for this application which contained a lens, reference grating, camera and lighting module. This prototype comprised a bench-top camera system that can read moir patterns from the turbine blade sensor at shutdown to determine <span class="hlt">creep</span> level in individual parts by analyzing the moir fringes. Sensitivity analyses and noise factor studies were performed to evaluate the system. Analysis software was also developed. A correlation study with strain gages was performed and the measurement results from the moir system align well with the strain gage readings. A mechanical specimen subjected to a one cycle tensile test at high <span class="hlt">temperature</span> to induce plastic <span class="hlt">deformation</span> in the gage was used to evaluate the system and the result of this test exhibited good correlation to extensometer readings.</p> <div class="credits"> <p class="dwt_author">Liao, Yi; Tait, Robert; Harding, Kevin; Nieters, Edward J.; Hasz, Wayne C.; Piche, Nicole</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-11-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_15");' href="#" 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onClick='return showDiv("page_23");' href="#">23</a> <a onClick='return showDiv("page_24");' href="#">24</a> <a onClick='return showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_18");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">321</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/920925"> <span id="translatedtitle">Microstructural Characterization of Dislocation Networks During Harper-Dorn <span class="hlt">Creep</span> of fcc, bcc, and hcp Metals and Alloys</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Harper-Dorn (H-D) <span class="hlt">creep</span> is observed in metals and geological materials exposed to very low stresses at <span class="hlt">temperatures</span> close to the melting point. It is one of several types of <span class="hlt">creep</span> processes wherein the steady-state strain rate is proportional to the applied stress, Nabarro-Herring <span class="hlt">creep</span> and Coble <span class="hlt">creep</span> being two other important processes. H-D <span class="hlt">creep</span> can be somewhat insidious because the <span class="hlt">creep</span> rates are much larger than those expected for Nabarro-Herring or Coble <span class="hlt">creep</span>. Since the working conditions of structural components of power plants and propulsion systems, as well as the motion of the earths mantle all involve very low stresses, an understanding of the factors controlling H-D <span class="hlt">creep</span> is critical in preventing failures associated with those higher-than-expected <span class="hlt">creep</span> 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 <span class="hlt">creep</span>. In our view the evolutionary processes during static annealing and during Harper-Dorn <span class="hlt">creep</span> 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-<span class="hlt">deformed</span> by <span class="hlt">creep</span> at 913 and 620 K and then annealed. The higher <span class="hlt">deformation</span> <span class="hlt">temperature</span> was selected to generate starting dislocation networks similar to those forming during Harper-Dorn <span class="hlt">creep</span> 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 <span class="hlt">temperatures</span>, (2) time invariant and (3) identical to the distributions obtained previously for Harper-Dorn <span class="hlt">creep</span>. This has never been shown before and confirms our theoretical expectations that evolution of the dislocation networks during annealing and H-D <span class="hlt">creep</span> is governed by the same growth law. Obtained results were also used to predict H-D steady <span class="hlt">creep</span> rates from annealing kinetics data using equations of the dislocation network theory. For the three considered stresses the theory predicts systematically smaller <span class="hlt">creep</span> rates by the average factor of 4.5. Considering that the <span class="hlt">creep</span> 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-<span class="hlt">deformed</span> in compression at constant stress of 4 MPa at <span class="hlt">temperature</span> of 573 K and subsequently annealed at the same <span class="hlt">temperature</span>. 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 <span class="hlt">deformed</span> 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</p> <div class="credits"> <p class="dwt_author">Przystupa, Marek A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-12-13</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">322</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22274005"> <span id="translatedtitle">Thermal <span class="hlt">creep</span> model for CWSR zircaloy-4 cladding taking into account the annealing of the irradiation hardening</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">After irradiation and cooling in a pool, spent nuclear fuel assemblies are either transported for wet storage to a devoted site or loaded in casks for dry storage. During dry transportation or at the beginning of dry storage, the cladding is expected to be submitted to <span class="hlt">creep</span> <span class="hlt">deformation</span> under the hoop stress induced by the internal pressure of the fuel rod. The thermal <span class="hlt">creep</span> is a potential mechanism that might lead to cladding failure. A new <span class="hlt">creep</span> model was developed, based on a database of <span class="hlt">creep</span> tests on as-received and irradiated cold-worked stress-relieved Zircaloy-4 cladding in a wide range of <span class="hlt">temperatures</span> (310 degrees C to 470 degrees C) and hoop stress (80 to 260 MPa). Based on three laws-a flow law, a strain-hardening recovery law, and an annealing of irradiation hardening law this model allows the simulation of not only the transient <span class="hlt">creep</span> and the steady-state <span class="hlt">creep</span>, but also the early <span class="hlt">creep</span> acceleration observed on irradiated samples tested in severe conditions, which was not taken into account in the previous models. The extrapolation of the <span class="hlt">creep</span> model in the conditions of very long-term <span class="hlt">creep</span> tests is reassuring, proving the robustness of the chosen formalism. The <span class="hlt">creep</span> model has been assessed in progressively decreasing stress conditions, more representative of a transport. Set up to predict the cladding <span class="hlt">creep</span> behavior under variable <span class="hlt">temperature</span> and stress conditions, this model can easily be implemented into codes in order to simulate the thermomechanical behavior of spent fuel rods in various scenarios of postirradiation phases. (authors)</p> <div class="credits"> <p class="dwt_author">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)</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-02-15</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">323</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20010064392&hterms=single+screw+reactor+model&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dsingle%2Bscrew%2Breactor%2Bmodel"> <span id="translatedtitle"><span class="hlt">Creep</span>-Fatigue Interaction Testing</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Fatigue fives in metals are nominally time independent below 0.5 T(sub Melt). At higher <span class="hlt">temperatures</span>, fatigue lives are altered due to time-dependent, thermally activated <span class="hlt">creep</span>. Conversely, <span class="hlt">creep</span> rates are altered by super. imposed fatigue loading. <span class="hlt">Creep</span> and fatigue generally interact synergistically to reduce material lifetime. Their interaction, therefore, is of importance to structural durability of high-<span class="hlt">temperature</span> structures such as nuclear reactors, reusable rocket engines, gas turbine engines, terrestrial steam turbines, pressure vessel and piping components, casting dies, molds for plastics, and pollution control devices. Safety and lifecycle costs force designers to quantify these interactions. Analytical and experimental approaches to <span class="hlt">creep</span>-fatigue began in the era following World War II. In this article experimental and life prediction approaches are reviewed for assessing <span class="hlt">creep</span>-fatigue interactions of metallic materials. Mechanistic models are also discussed briefly.</p> <div class="credits"> <p class="dwt_author">Halford, Gary R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">324</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014Tectp.610....1W"> <span id="translatedtitle">Invited review paper: Fault <span class="hlt">creep</span> caused by subduction of rough seafloor relief</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Among the wide range of thermal, petrologic, hydrological, and structural factors that potentially affect subduction earthquakes, the roughness of the subducting seafloor is among the most important. By reviewing seismic and geodetic studies of megathrust locking/<span class="hlt">creeping</span> state, we find that <span class="hlt">creeping</span> is the predominant mode of subduction in areas of extremely rugged subducting seafloor such as the Kyushu margin, Manila Trench, northern Hikurangi, and southeastern Costa Rica. In Java and Mariana, megathrust <span class="hlt">creeping</span> state is not yet constrained by geodetic observations, but the very rugged subducting seafloor and lack of large earthquakes also suggest aseismic <span class="hlt">creep</span>. Large topographic features on otherwise relatively smooth subducting seafloor such as the Nazca Ridge off Peru, the Investigator Fracture Zone off Sumatra, and the Joban seamount chain in southern Japan Trench also cause <span class="hlt">creep</span> and often stop the propagation of large ruptures. Similar to all other known giant earthquakes, the Tohoku earthquake of March 2011 occurred in an area of relatively smooth subducting seafloor. The Tohoku event also offers an example of subducting seamounts stopping rupture propagation. Very rugged subducting seafloor not only retards the process of shear localization, but also gives rise to heterogeneous stresses. In this situation, the fault zone <span class="hlt">creeps</span> because of distributed <span class="hlt">deformation</span> of fractured rocks, and the <span class="hlt">creep</span> may take place as transient events of various spatial and temporal scales accompanied with small and medium-size earthquakes. This process cannot be described as stable or unstable friction along a single contact surface. The association of large earthquakes with relatively smooth subducting seafloor and <span class="hlt">creep</span> with very rugged subducting seafloor calls for further investigation. Seafloor near-trench geodetic monitoring, high-resolution imaging of subduction fault structure, studies of exhumed ancient subduction zones, and laboratory studies of low-<span class="hlt">temperature</span> <span class="hlt">creep</span> will greatly improve our understanding of the seismogenic and <span class="hlt">creep</span> processes and their hazard implications.</p> <div class="credits"> <p class="dwt_author">Wang, Kelin; Bilek, Susan L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">325</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19930033677&hterms=sunil+sunil+sunil&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dsunil%2Bsunil%2Bsunil"> <span id="translatedtitle">Influence of grain size on the <span class="hlt">creep</span> behavior of HfC-dispersed NiAl</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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 <span class="hlt">creep</span> properties demonstrated that the initial, small grain size microstructure was unstable under slow strain rate <span class="hlt">deformation</span> conditions. The grain growth which occurred during testing led to considerable strengthening. Subsequent measurements of the <span class="hlt">creep</span> properties of the coarse grained specimens revealed that this strength was achieved by a large increase in the activation energy for <span class="hlt">deformation</span> without any change in the stress exponent. Based on this work, it is concluded that large grain microstructures will be required for optimum elevated <span class="hlt">temperature</span> <span class="hlt">creep</span> properties in dispersed NiAl.</p> <div class="credits"> <p class="dwt_author">Whittenberger, J. D.; Ray, Ranjan; Jha, Sunil C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">326</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/1087118"> <span id="translatedtitle">Corrosion and <span class="hlt">Creep</span> of Candidate Alloys in High <span class="hlt">Temperature</span> Helium and Steam Environments for the NGNP</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This project aims to understand the processes by which candidate materials degrade in He and supercritical water/steam environments characteristic of the current NGNP design. We will focus on understanding the roles of <span class="hlt">temperature</span>, and carbon and oxygen potential in the 750-850 degree C range on both uniform oxidation and selective internal oxidation along grain boundaries in alloys 617 and 800H in supercritical water in the <span class="hlt">temperature</span> range 500-600 degree C; and examining the application of static and cyclic stresses in combination with impure He environments in the <span class="hlt">temperature</span> rang 750-850 degree C; and examining the application of static and cyclic stresses in combination with impure He environments in the <span class="hlt">temperature</span> range 750-850 degree C over a range of oxygen and carbon potentials in helium. Combined, these studies wil elucidate the potential high damage rate processes in environments and alloys relevant to the NGNP.</p> <div class="credits"> <p class="dwt_author">Was, Gary; Jones, J. W.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-06-21</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">327</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19930004102&hterms=open+data+community&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3D%2522open%2Bdata%2522%2Bcommunity"> <span id="translatedtitle">Computational simulation of probabilistic lifetime strength for aerospace materials subjected to high <span class="hlt">temperature</span>, mechanical fatigue, <span class="hlt">creep</span> and thermal fatigue</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">This report presents the results of a fourth year effort of a research program, conducted for NASA-LeRC by the University of Texas at San Antonio (UTSA). The research included on-going development of methodology that provides probabilistic lifetime strength of aerospace materials via computational simulation. A probabilistic material strength degradation model, in the form of a randomized multifactor interaction equation, is postulated for strength degradation of structural components of aerospace propulsion systems subject to a number of effects or primitive variables. These primitive variables may include high <span class="hlt">temperature</span>, fatigue or <span class="hlt">creep</span>. In most cases, strength is reduced as a result of the action of a variable. This multifactor interaction strength degradation equation has been randomized and is included in the computer program, PROMISS. Also included in the research is the development of methodology to calibrate the above-described constitutive equation using actual experimental materials data together with regression analysis of that data, thereby predicting values for the empirical material constants for each effect or primitive variable. This regression methodology is included in the computer program, PROMISC. Actual experimental materials data were obtained from industry and the open literature for materials typically for applications in aerospace propulsion system components. Material data for Inconel 718 has been analyzed using the developed methodology.</p> <div class="credits"> <p class="dwt_author">Boyce, Lola; Bast, Callie C.; Trimble, Greg A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">328</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19920024899&hterms=creep+damage+constitutive+equations&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dcreep%2Bdamage%2Bconstitutive%2Bequations"> <span id="translatedtitle">Computational simulation of probabilistic lifetime strength for aerospace materials subjected to high <span class="hlt">temperature</span>, mechanical fatigue, <span class="hlt">creep</span>, and thermal fatigue</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The results of a fourth year effort of a research program conducted for NASA-LeRC by The University of Texas at San Antonio (UTSA) are presented. The research included on-going development of methodology that provides probabilistic lifetime strength of aerospace materials via computational simulation. A probabilistic material strength degradation model, in the form of a randomized multifactor interaction equation, is postulated for strength degradation of structural components of aerospace propulsion systems subjected to a number of effects or primitive variables. These primitive variables may include high <span class="hlt">temperature</span>, fatigue, or <span class="hlt">creep</span>. In most cases, strength is reduced as a result of the action of a variable. This multifactor interaction strength degradation equation was randomized and is included in the computer program, PROMISC. Also included in the research is the development of methodology to calibrate the above-described constitutive equation using actual experimental materials data together with regression analysis of that data, thereby predicting values for the empirical material constants for each effect or primitive variable. This regression methodology is included in the computer program, PROMISC. Actual experimental materials data were obtained from industry and the open literature for materials typically for applications in aerospace propulsion system components. Material data for Inconel 718 was analyzed using the developed methodology.</p> <div class="credits"> <p class="dwt_author">Boyce, Lola; Bast, Callie C.; Trimble, Greg A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">329</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19930021749&hterms=Poly+fiber&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DPoly%2Bfiber"> <span id="translatedtitle">Tensile <span class="hlt">creep</span> behavior of polycrystalline alumina fibers</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Tensile <span class="hlt">creep</span> studies were conducted on polycrystalline Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Test conditions were <span class="hlt">temperatures</span> from 800 to 1050 C and stresses from 60 to 1000 MPa. For both fibers, only a small primary <span class="hlt">creep</span> portion occurred followed by steady-state <span class="hlt">creep</span>. The stress exponents for steady-state <span class="hlt">creep</span> of Nextel 610 and Fiber FP were found to be about 3 and 1, respectively. At lower <span class="hlt">temperatures</span>, below 1000 C, the finer grained Nextel 610 had a much higher 0.2 percent <span class="hlt">creep</span> strength for 100 hr than the Fiber FP; while at higher <span class="hlt">temperatures</span>, Nextel 610 had a comparable <span class="hlt">creep</span> strength to the Fiber FP. The stress and grain size dependencies suggest Nextel 610 and Fiber FP <span class="hlt">creep</span> rates are due to grain boundary sliding controlled by interface reaction and Nabarro-Herring mechanisms, respectively.</p> <div class="credits"> <p class="dwt_author">Yun, H. M.; Goldsby, J. C.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">330</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/22254042"> <span id="translatedtitle">Electrochemical control of <span class="hlt">creep</span> in nanoporous gold</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We have investigated the mechanical stability of nanoporous gold (npg) in an electrochemical environment, using in situ dilatometry and compression experiments. It is demonstrated that the gold nano-ligaments <span class="hlt">creep</span> under the action of surface stress which leads to spontaneous volume contractions in macroscopic npg samples. The <span class="hlt">creep</span> of npg, under or without external forces, can be controlled electrochemically. The <span class="hlt">creep</span> rate increases with increasing potential in double-layer potential region, and deceases to almost zero when the gold surface is adsorbed with oxygen. Surprisingly, we also noticed a correlation between <span class="hlt">creep</span> and surface diffusivity, which links the <span class="hlt">deformation</span> of nanocrystals to mobility of surface atoms.</p> <div class="credits"> <p class="dwt_author">Ye, Xing-Long; Jin, Hai-Jun, E-mail: hjjin@imr.ac.cn [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)] [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-11-11</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">331</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012JEMat..41..190W"> <span id="translatedtitle"><span class="hlt">Creep</span> Behavior of Bi-Containing Lead-Free Solder Alloys</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The <span class="hlt">creep</span> 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 <span class="hlt">creep</span> tests from room <span class="hlt">temperature</span> to 125C. 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 <span class="hlt">creep</span> resistance of of-cast SAC305 was higher than that of as-cast Bi-containing alloys, but after aging the SAC305 had the lowest <span class="hlt">creep</span> resistance. The <span class="hlt">creep</span> strain rates in SAC-Bi and SnAg-Bi were much less affected by aging. The apparent activation energy for <span class="hlt">creep</span> was also changed more for SAC305 than for the other two alloys. The <span class="hlt">creep</span> behavior of SAC-Bi and SnAg-Bi can be understood by considering the solubility of Bi in Sn. The difference in <span class="hlt">creep</span> behavior between as-cast and aged SAC-Bi is greatly reduced when room-<span class="hlt">temperature</span> test results are excluded from analysis. This suggests that the strongest influence on <span class="hlt">creep</span> in these alloys is due to Bi solute interaction with moving dislocations during <span class="hlt">deformation</span>.</p> <div class="credits"> <p class="dwt_author">Witkin, David</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">332</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011MMTA...42.1990K"> <span id="translatedtitle">Microstructure and Impression <span class="hlt">Creep</span> Characteristics of Cast Mg-5Sn- xBi Magnesium Alloys</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The microstructure and <span class="hlt">creep</span> behavior of a cast Mg-5Sn alloy with 1, 2, and 3 wt pct Bi additions were studied by impression tests in the <span class="hlt">temperature</span> range 423 K to 523 K (150 C to 250 C) under punching stresses in the range 125 to 475 MPa for dwell times up to 3600 seconds. The alloy containing 3 wt pct Bi showed the lowest <span class="hlt">creep</span> rates and, thus, the highest <span class="hlt">creep</span> resistance among all materials tested. This is attributed to the favorable formation of the more thermally stable Mg3Bi2 intermetallic compound, the reduction in the volume fraction of the less stable Mg2Sn phase, and the dissolution of Bi in the remaining Mg2Sn particles. These particles strengthen both the matrix and grain boundaries during <span class="hlt">creep</span> <span class="hlt">deformation</span> of the investigated system. The <span class="hlt">creep</span> behavior of the Mg-5Sn alloy can be divided into the low- and high-stress regimes, with the respective average stress exponents of 5.5 and 10.5 and activation energies of 98.3 and 163.5 kJ mol-1. This is in contrast to the <span class="hlt">creep</span> behavior of the Bi-containing alloys, which can be expressed by a single linear relationship over the whole stress and <span class="hlt">temperature</span> ranges studied, yielding stress exponents in the range 7 to 8 and activation energies of 101.0 to 107.0 kJ mol-1. Based on the obtained stress exponents and activation energies, it is proposed that the dominant <span class="hlt">creep</span> mechanism in Mg-5Sn is pipe-diffusion controlled dislocation viscous glide the low-stress regime and dislocation climb <span class="hlt">creep</span> with back stress in the high-stress regime. For the Mg-5Sn- xBi alloys, however, the controlling <span class="hlt">creep</span> mechanism is dislocation climb with an additional particle strengthening effect, which is characterized by the higher stress exponent of 7 to 8.</p> <div class="credits"> <p class="dwt_author">Keyvani, Mahsa; Mahmudi, Reza; Nayyeri, Ghazal</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">333</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/1057497"> <span id="translatedtitle">Low cycle fatigue and <span class="hlt">creep</span>-fatigue behavior of Ni-based alloy 230 at 850 C</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Strain-controlled low cycle fatigue (LCF) and <span class="hlt">creep</span>-fatigue testing of Ni-based alloy 230 were carried out at 850 C. The material <span class="hlt">creep</span>-fatigue life decreased compared with its low cycle fatigue life at the same total strain range. Longer hold time at peak tensile strain further reduced the material <span class="hlt">creep</span>-fatigue life. Based on the electron backscatter diffraction, a novel material <span class="hlt">deformation</span> characterization method was applied, which revealed that in low cycle fatigue testing as the total strain range increased, the <span class="hlt">deformation</span> was segregated to grain boundaries since the test <span class="hlt">temperature</span> was higher than the material equicohesive <span class="hlt">temperature</span> and grain boundaries became weaker regions compared with grains. <span class="hlt">Creep</span>-fatigue tests enhanced the localized <span class="hlt">deformation</span>, resulting in material interior intergranular cracking, and accelerated material damage. Precipitation in alloy 230 helped slip dispersion, favorable for fatigue property, but grain boundary cellular precipitates formed after material exposure to the elevated <span class="hlt">temperature</span> had a deleterious effect on the material low cycle fatigue and <span class="hlt">creep</span>-fatigue property.</p> <div class="credits"> <p class="dwt_author">Chen, Xiang [ORNL; Yang, Zhiqing [ORNL; Sokolov, Mikhail A [ORNL; ERDMAN III, DONALD L [ORNL; Mo, Kun [ORNL; Stubbins, James [ORNL</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">334</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40290842"> <span id="translatedtitle">Room-<span class="hlt">temperature</span> <span class="hlt">creep</span> of soft PZT under static electrical and compressive stress loading</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">This study focuses on the experimental investigation of time-dependent effects of a commercial piezoceramic material at room <span class="hlt">temperature</span>. Specimens in the unpoled or poled state were subjected to an electric field or a compressive stress loading increasing from zero and then kept constant at a certain level. Due to ferroelectric or ferroelastic domain switching, significant nonlinearity and hysteresis were observed</p> <div class="credits"> <p class="dwt_author">Dayu Zhou; Marc Kamlah</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">335</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/971584"> <span id="translatedtitle">Analysis of Tensile <span class="hlt">Deformation</span> and Failure in Austenitic Stainless Steels: Part I- <span class="hlt">Temperature</span> Dependence</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This paper describes the <span class="hlt">temperature</span> dependence of <span class="hlt">deformation</span> and failure behaviors in the austenitic stainless steels (annealed 304, 316, 316LN, and 20% cold-worked 316LN) in terms of equivalent true stress-true strain curves. The true stress-true strain curves up to the final fracture were calculated from the tensile test data obtained at -150 ~ 450oC using an iterative technique of finite element simulation. Analysis was largely focused on the necking <span class="hlt">deformation</span> and fracture: Key parameters such as the strain hardening rate, equivalent fracture stress, fracture strain, and tensile fracture energy were evaluated, and their <span class="hlt">temperature</span> dependencies were investigated. It was shown that a significantly high strain hardening rate was still retained during unstable <span class="hlt">deformation</span> although overall strain hardening rate beyond the onset of necking was lower than that of the uniform <span class="hlt">deformation</span>. The values of the parameters except for fracture strain decreased with <span class="hlt">temperature</span> up to 200oC and were saturated as the <span class="hlt">temperature</span> came close to the maximum test <span class="hlt">temperature</span> 450oC. The fracture strain increased and had a maximum at -50oC to 20oC before decreasing with <span class="hlt">temperature</span>. It was explained that these <span class="hlt">temperature</span> dependencies of fracture properties were associated with a change in the dominant strain hardening mechanism with test <span class="hlt">temperature</span>. Also, it was seen that the pre-straining of material has little effect on the strain hardening rate during necking <span class="hlt">deformation</span> and on fracture properties.</p> <div class="credits"> <p class="dwt_author">Kim, Jin Weon [ORNL; Byun, Thak Sang [ORNL</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">336</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/530707"> <span id="translatedtitle"><span class="hlt">Creep</span> behavior and lifetime of Si{sub 3}N{sub 4}/SiC nanocomposites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary"><span class="hlt">Creep</span> behavior and lifetime of various Si{sub 3}N{sub 4}/SiC nanocomposite materials were investigated and compared with the properties of monolithic silicon nitride materials. The composites differed in the type and amount of the submicron-sized SiC particles incorporated. <span class="hlt">Creep</span> and time-to-failure were studied in four-point bending in air at <span class="hlt">temperatures</span> ranging from 1400 to 1600{degrees}C and stresses up to 600 MPa. The <span class="hlt">creep</span> resistance was strongly dependent both on the impurity level and the volume content of the SiC particles. Increasing the SiC content caused the <span class="hlt">creep</span> rate to go through a minimum located at about 10 - 15 wt.% SiC. The effect of stress on the <span class="hlt">creep</span> behavior could be described by the occurrence of two different stress regimes. At low and intermediate stresses, the <span class="hlt">creep</span> behavior was characterized by a homogeneous bulk <span class="hlt">deformation</span>, a high <span class="hlt">creep</span> resistance, low <span class="hlt">creep</span> damage, and a long lifetime. However, at stresses exceeding a certain threshold level (200 - 550 MPa, depending on the specific material), the mechanical behavior was controlled by subcritical crack growth, leading to pronounced damage and premature failure due to cracking.</p> <div class="credits"> <p class="dwt_author">Rendtel, A.; Huebner, H. [Technische Universitaet, Hamburg (Germany)</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-12-31</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">337</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2015PhRvB..91f0101D"> <span id="translatedtitle">Universal mechanism of thermomechanical <span class="hlt">deformation</span> in metallic glasses</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We investigated the atomistic structure of metallic glasses subjected to thermomechanical <span class="hlt">creep</span> <span class="hlt">deformation</span> using high energy x-ray diffraction and molecular dynamics simulation. The experiments were performed in situ at high <span class="hlt">temperatures</span> as a time dependent <span class="hlt">deformation</span> in the elastic regime, and ex situ on samples quenched under stress. We show that all the anisotropic structure functions of the samples that have undergone thermomechanical <span class="hlt">creep</span> can be scaled into a single curve, regardless of the magnitude of anelastic strain, stress level, and the sign of the stress, demonstrating universal behavior and pointing to a unique atomistic unit of anelastic <span class="hlt">deformation</span>. The structural changes due to <span class="hlt">creep</span> are strongly localized within the second nearest neighbors, involving only a small group of atoms.</p> <div class="credits"> <p class="dwt_author">Dmowski, W.; Tong, Y.; Iwashita, T.; Yokoyama, Y.; Egami, T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2015-02-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">338</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6292008"> <span id="translatedtitle">High-<span class="hlt">temperature</span> <span class="hlt">deformation</span> and microstructural analysis for Si3N4-Sc2O3</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">It was indicated that Si3N4 doped with Sc2O3 may exhibit high <span class="hlt">temperature</span> mechanical properties superior to Si3N4 systems with various other oxide sintered additives. High <span class="hlt">temperature</span> <span class="hlt">deformation</span> of samples was studied by characterizing the microstructures before and after <span class="hlt">deformation</span>. It was found that elements of the additive, such as Sc and O, exist in small amounts at very thin grain boundary layers and most of them stay in secondary phases at triple and multiple grain boundary junctions. These secondary phases are devitrified as crystalline Sc2Si2O7. <span class="hlt">Deformation</span> of the samples was dominated by cavitational processes rather than movements of dislocations. Thus the excellent <span class="hlt">deformation</span> resistance of the samples at high <span class="hlt">temperature</span> can be attributed to the very small thickness of the grain boundary layers and the crystalline secondary phase.</p> <div class="credits"> <p class="dwt_author">Cheong, Deocksoo; Sanders, W.A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">339</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19900019424&hterms=Rare+Earth+Metals&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3D%2522Rare%2BEarth%2BMetals%2522"> <span id="translatedtitle">High-<span class="hlt">temperature</span> <span class="hlt">deformation</span> and microstructural analysis for Si3N4-Sc2O3</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">It was indicated that Si3N4 doped with Sc2O3 may exhibit high <span class="hlt">temperature</span> mechanical properties superior to Si3N4 systems with various other oxide sintered additives. High <span class="hlt">temperature</span> <span class="hlt">deformation</span> of samples was studied by characterizing the microstructures before and after <span class="hlt">deformation</span>. It was found that elements of the additive, such as Sc and O, exist in small amounts at very thin grain boundary layers and most of them stay in secondary phases at triple and multiple grain boundary junctions. These secondary phases are devitrified as crystalline Sc2Si2O7. <span class="hlt">Deformation</span> of the samples was dominated by cavitational processes rather than movements of dislocations. Thus the excellent <span class="hlt">deformation</span> resistance of the samples at high <span class="hlt">temperature</span> can be attributed to the very small thickness of the grain boundary layers and the crystalline secondary phase.</p> <div class="credits"> <p class="dwt_author">Cheong, Deock-Soo; Sanders, William A.</p> <p class="dwt_publisher"></p> <p class="publishDate">1990-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">340</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/60503428"> <span id="translatedtitle">Analysis of elevated <span class="hlt">temperature</span> cyclic <span class="hlt">deformation</span> of austenitic stainless steels</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The stress relaxation behavior of 304 and 316 stainless steels during cyclic <span class="hlt">deformation</span> at 538 and 650°C with various hold times and strain amplitudes has been analyzed in terms of a power-law equation of state which includes internal stress and drag stress as structure variables. At 650°C the internal sress in 304 appears to be zero and microstructural recovery plays</p> <div class="credits"> <p class="dwt_author">R. W. Rohde; J. C. Swearengen</p> <p class="dwt_publisher"></p> <p class="publishDate">1977-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_16");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">341</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/991576"> <span id="translatedtitle">Effect of <span class="hlt">Creep</span> of Ferritic Interconnect on Long-Term Performance of Solid Oxide Fuel Cell Stacks</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">High-<span class="hlt">temperature</span> 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, <span class="hlt">creep</span> <span class="hlt">deformation</span> becomes relevant for a material when the operating <span class="hlt">temperature</span> exceeds or even is less than half of its melting <span class="hlt">temperature</span> (in degrees of Kelvin). The operating <span class="hlt">temperatures</span> for most of the SOFCs under development are around 1,073 K. With around 1,800 K of the melting <span class="hlt">temperature</span> for most stainless steel, possible <span class="hlt">creep</span> <span class="hlt">deformation</span> of ferritic IC under the typical cell operating <span class="hlt">temperature</span> should not be neglected. In this paper, the effects of IC <span class="hlt">creep</span> 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 <span class="hlt">creep</span> of the ferritic stainless steel IC, therefore indicating possible changes in SOFC performance under long-term operations. The ferritic IC <span class="hlt">creep</span> model was incorporated into software SOFC-MP and Mentat-FC, and finite element analyses were performed to quantify the <span class="hlt">deformed</span> configuration of the SOFC stack under the long-term steady-state operating <span class="hlt">temperature</span>. It was found that the <span class="hlt">creep</span> 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 <span class="hlt">temperature</span>.</p> <div class="credits"> <p class="dwt_author">Liu, Wenning N.; Sun, Xin; Khaleel, Mohammad A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">342</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/290955"> <span id="translatedtitle">Mechanisms responsible for texture development in a 5182 aluminum alloy <span class="hlt">deformed</span> at elevated <span class="hlt">temperature</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">The textures that develop in a 5182 aluminum alloy as a result of monotonic high-<span class="hlt">temperature</span> compression have been investigated. The authors found that the <span class="hlt">deformation</span> texture was a function of <span class="hlt">temperature</span>. For compressive <span class="hlt">deformation</span> at 300 C and below the material formed the classic (101) <span class="hlt">deformation</span> texture, while the material develops a texture that is a combination of the classical uniaxial compression <span class="hlt">deformation</span> texture, (101), and static recrystallization texture, (001), as a result of the <span class="hlt">deformation</span> alone when the <span class="hlt">deformation</span> <span class="hlt">temperature</span> was at and above 400 C. The investigation has focused on determining the mechanism responsible for the development of this unusual progression of <span class="hlt">deformation</span> textures. In addition the authors have performed orientation imaging microscopy (OIM) to identify the shapes of grains with particular orientations and grain-to-grain orientation relationships. The conclusions are summarized as follows: The texture development is not a result of static processes, i.e. static recrystallization at the various hold times altered neither the textures nor the constitutive behavior. Simulation using a crystal plasticity model indicates that the combination of a cube component prevalent in the original texture, slip activity on 011 planes, and increased rate sensitivity leads to a combined (001) and (101) texture. Finally, the microscopic OIM results are consistent with these observations.</p> <div class="credits"> <p class="dwt_author">Stout, M.G.; Chen, S.R.; Kocks, U.F. [Los Alamos National Lab., NM (United States); Schwartz, A.J. [Lawrence Livermore National Lab., CA (United States); MacEwen, S.R. [Alcan International Ltd., Kingston, Ontario (Canada); Beaudoin, A.J. [Univ. of Illinois, Urbana, IL (United States). Dept. of Mechanical and Industrial Engineering</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">343</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2006JGRB..111.8203C"> <span id="translatedtitle">Water weakening of clinopyroxene in the dislocation <span class="hlt">creep</span> regime</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We performed a series of triaxial compressive <span class="hlt">creep</span> experiments at two different water fugacities to investigate the effect of water on the <span class="hlt">creep</span> strength of a natural clinopyroxenite. Samples were <span class="hlt">deformed</span> under water-saturated conditions at <span class="hlt">temperatures</span> between 1373 and 1473 K, confining pressures of 150 and 300 MPa, and differential stresses from 34 to 261 MPa. Strain rates were in the range 10-7 to 10-5 s-1. Water fugacity was controlled at either 140 or 280 MPa. The <span class="hlt">creep</span> results yield a stress exponent of 2.7 0.3 and an activation energy of 670 40 kJ/mol. Compared to dry clinopyroxene, wet samples <span class="hlt">creep</span> over 100 times faster at a given <span class="hlt">temperature</span>, confining pressure, water fugacity, and differential stress. The <span class="hlt">creep</span> rate of clinopyroxene is proportional to the water fugacity to the 3.0 0.6 power, with an activation volume of 0 m3/mol. One possible water-weakening mechanism is an enhancement of the rate of dislocation climb associated with increases in the concentration of jogs and the diffusivity of silicon ions. Compared to other major minerals in Earth's lower crust, specifically olivine and plagioclase, the water-weakening effect is most significant for clinopyroxene. Under hydrous conditions the strengths of clinopyroxene and anorthite are comparable over the investigated stress range, and both phases are weaker than olivine. Since the mineral assemblages in Earth's lower continental crust are often dominated by plagioclase and pyroxene, in places where a wet flow law applies, the mechanical behavior of clinopyroxene will have a substantial effect on <span class="hlt">creep</span> strength.</p> <div class="credits"> <p class="dwt_author">Chen, S.; Hiraga, T.; Kohlstedt, D. L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">344</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/1049204"> <span id="translatedtitle">The Role of Eta Phase Formation on the <span class="hlt">Creep</span> Strength and Ductility of INCONEL Alloy 740 t 1023 k (750 Degrees C)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">INCONEL alloy 740 is an age-hardenable nickel-based superalloy proposed for advanced ultrasupercritical steam boiler applications operating at high stress and long times above 973 K (700 C), where <span class="hlt">creep</span> will be the dominate <span class="hlt">deformation</span> mode. During high-<span class="hlt">temperature</span> exposure, the alloy can form eta phase platelets that many have suggested may be detrimental to <span class="hlt">creep</span> strength and ductility. In this study, <span class="hlt">creep</span>-rupture tests were conducted on smooth and notched bars of INCONEL alloy 740 at 1023 K (750 C) for times up to 20,000 hours. Examination of the <span class="hlt">creep</span>-rupture life, <span class="hlt">creep</span> ductility, failure modes, and microstructure by quantitative electron microscopy shows that a small amount of eta phase does not diminish the <span class="hlt">creep</span> performance. Applied stress appears to have a minor effect on the precipitation of the eta phase but not its growth rate. Based on the observation that the microstructure after 20,000 hours of <span class="hlt">creep</span> exposure has reached equilibrium in comparison to thermodynamic calculations, it is concluded that 20,000 hour <span class="hlt">creep</span> tests are adequate for prediction of long-term <span class="hlt">creep</span> performance.</p> <div class="credits"> <p class="dwt_author">Shingledecker, John P [ORNL; Pharr, George Mathews [ORNL</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">345</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/doepatents/biblio/874043"> <span id="translatedtitle">Cryogenic <span class="hlt">deformation</span> of high <span class="hlt">temperature</span> superconductive composite structures</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/doepatents">DOEpatents</a></p> <p class="result-summary">An improvement in a process of preparing a composite high <span class="hlt">temperature</span> oxide superconductive wire is provided and involves conducting at least one cross-sectional reduction step in the processing preparation of the wire at sub-ambient <span class="hlt">temperatures</span>.</p> <div class="credits"> <p class="dwt_author">Roberts, Peter R. (Groton, MA); Michels, William (Brookline, MA); Bingert, John F. (Jemez Springs, NM)</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">346</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/19229646"> <span id="translatedtitle">Influence of high <span class="hlt">temperature</span> on cadmium-induced skeletal <span class="hlt">deformities</span> in juvenile mosquitofish (Gambusia affinis).</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">The aim of this study was to assess the effect of high <span class="hlt">temperature</span> on cadmium (Cd)-induced skeletal <span class="hlt">deformities</span> in juvenile Mosquitofish, Gambusia affinis. For this purpose, 188 juveniles (1 day old) were equally divided into the control group, which was maintained in Cd-free water at 24 degrees C, and three treated groups exposed either to Cd (0.4 mg/l as Cd Cl(2)) at 24 degrees C, to high <span class="hlt">temperature</span> (32 degrees C), or to Cd at 32 degrees C for 30 days. The results showed that Cd exposure at 24 degrees C significantly increased the Cd accumulation (P < 0.0001) in the whole tissues of juveniles as well as the incidence of skeletal <span class="hlt">deformities</span> (P < 0.01) compared with control animals. Exposure to high <span class="hlt">temperature</span> also led to a significant increase in the incidence of skeletal <span class="hlt">deformities</span> (P < 0.01) with respect to the control group. Interestingly, our results showed that the combined exposure to Cd and high <span class="hlt">temperature</span> led to a more significant increase in Cd accumulation and in the frequency of spinal <span class="hlt">deformities</span> than exposure to Cd or high <span class="hlt">temperature</span> alone. These results confirm that <span class="hlt">temperature</span> increases Cd toxicity and needs to be taken into account for the accurate prediction and assessment of Cd-induced spinal <span class="hlt">deformities</span> in fish. PMID:19229646</p> <div class="credits"> <p class="dwt_author">Sassi, Asma; Annabi, Ali; Kessabi, Kaouthar; Kerkeni, Abdelhamid; Sad, Khaled; Messaoudi, Imed</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-09-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">347</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19870008684&hterms=Hot+Melt&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DHot%2BMelt"> <span id="translatedtitle"><span class="hlt">Creep</span> fatigue life prediction for engine hot section materials (isotropic)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The first two years of a two-phase program aimed at improving the high <span class="hlt">temperature</span> 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 <span class="hlt">creep</span>-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 <span class="hlt">temperature</span>. 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 <span class="hlt">deformation</span> structure between fatigue, tensile and <span class="hlt">creep</span> 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 <span class="hlt">creep</span>-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 <span class="hlt">creep</span> data.</p> <div class="credits"> <p class="dwt_author">Moreno, Vito; Nissley, David; Lin, Li-Sen Jim</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">348</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2006AGUFM.G33A0048B"> <span id="translatedtitle">Vein Patterns Record Earthquake-Related Brittle and Ductile <span class="hlt">Deformation</span> at <span class="hlt">Temperatures</span> of 500C in the footwall of a Low Angle Normal Fault</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The mechanics of low angle normal faults are poorly understood and the seismological record of fault activity at greater depths appears to be equivocal. Here we present the record of quartz veins, which indicates episodic brittle and ductile <span class="hlt">deformation</span>, presumably driven by earthquakes, and stages of very high permeability in the footwall of the Nordfjord-Sogne Detachment Zone (NSDZ) in western Norway. At the NSDZ ultrahigh-pressure metamorphic rocks became exhumed from depths of 100 km into the upper crust within a few million years. The peculiar record is found in an eclogite-amphibolite slice of about 200 m length and 30 m thickness embedded in gneisses on Rugsundoya Island. For analysis, the vein record is subdivided into three stages: (1) crack initiation, propagation, and arrest, (2) opening of fractures and precipitation of minerals from the fluid phase, (3) <span class="hlt">deformation</span> of the vein. The Rugsundoya quartz veins originate from fractures, that crosscut all pre-existing structures and are oriented at a high angle to the foliation. Fracture branching is common. Both features indicate rapid crack propagation at high differential stress and consequently preclude quasi-static hydraulic fracturing at pfluid>?3. The cracks were arrested within a few milliseconds after propagating over a distance on the order of 10^{0} to 101 meters. Opening of the fractures was controlled by ductile <span class="hlt">deformation</span> of the host rock. At that stage, the fractures remained open cavities progressively sealed by quartz precipitated from the percolating fluid. The final shape of the quartz veins reflects an inhomogeneous and partly high strain <span class="hlt">deformation</span> of the host rock, with structures controlled by the cohesionless fissures and developing cavities. In contrast, <span class="hlt">deformation</span> of the completely sealed veins is subordinate. This indicates that the stage of considerable ductile <span class="hlt">deformation</span> of the host rock was entirely concomitant with fluid flow and vein formation, and followed on quasi-instantaneous loading and brittle failure at <span class="hlt">temperatures</span> near 500C. All these features indicate a rapid, episodic process. The record is therefore interpreted to reflect co-seismic loading by stress-redistribution near a seismogenic fault (stage 1), followed by ductile <span class="hlt">deformation</span> of a higly permeable crust with an initially high strain rate, referred to as postseismic <span class="hlt">creep</span> (stage 2). All subsequent <span class="hlt">deformation</span> of the completed veins (stage 3) is comparatively insignificant and has in part taken place at a later stage at lower <span class="hlt">temperatures</span>. If this is true, coseismic stress re-distribution in the middle crust at <span class="hlt">temperatures</span> as high as 500C can lead to fracturing and subsequent rapid ductile <span class="hlt">deformation</span> of the fractured rock during postseismic stress relaxation. Development of cavities controlled by ductile flow occurs at a rate exceeding the rate of sealing, with a transient very high permeability. Identification of such record in exhumed rocks provides insight into details of distributed coseismic failure and postseismic <span class="hlt">creep</span> at depth, which may become important for an improved understanding of the earthquake cycle and the inversion of geodetic data.</p> <div class="credits"> <p class="dwt_author">Birtel, S.; Stoeckhert, B.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-12-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">349</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/6092263"> <span id="translatedtitle"><span class="hlt">Deformation</span> mechanisms of experimentally <span class="hlt">deformed</span> Salina Basin bedded salt</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Petrofabrics of <span class="hlt">deformed</span> salt from the Cleveland area within the Salina Basin are presented. Quasi-static compression at room <span class="hlt">temperature</span> and 1 MPa confining pressure is dominated by fracture. Incipient failure is evidenced by wide zones of coalesced fractures at an axial strain of 5%. Strain hardening, evidenced by photoelastic effects, abounds under these conditions. At 5 MPa far fewer fractures are found at axial strains of 13%. Photoelastic effects are appreciably diminished at 5 MPa, which must mean more homogeneous ductile flow ensues, perhaps owing to activation of many dislocation mills. Clearly, the brittle-to-ductile transition requires additional petrographic work for documentation. Because the dominant mechanism is very pressure sensitive at relative low mean stresses, it appears necessary to include confining pressure in the <span class="hlt">deformation</span> mechanism map. <span class="hlt">Creep</span> at 15 MPa and <span class="hlt">temperatures</span> >100/sup 0/C is dominated by thermally activated diffusion. Fracture and photoelastic effects are almost totally suppressed relative to quasi-static experiments at lower confining pressure and <span class="hlt">temperature</span>. The mechanism of climb into stable polygons is fully documented by etch pit studies in samples that are <span class="hlt">deformed</span> well into steady state. <span class="hlt">Creep</span> properties of Cleveland and Avery Island salt are very similar under conditions of elevated <span class="hlt">temperature</span> and intermediate stresses. As <span class="hlt">temperature</span> is reduced the predicted flow stress of Cleveland becomes greater than that of Avery Island. However, extrapolation of either flow law to low <span class="hlt">temperature</span> is not justified because the governing mechanisms change from climb to fracture and glide.</p> <div class="credits"> <p class="dwt_author">Hansen, F.D.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">350</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2002JSMEA..45...90H"> <span id="translatedtitle">The Use of CDM Analysis Techniques in High <span class="hlt">Temperature</span> <span class="hlt">Creep</span> Failure of Welded Structures</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Techniques are reviewed for the calibration of constitutive relationships for the different phases of the weld. It is shown how the calibration is carried out using property ratios, and a knowledge of the constitutive equations of the parent material. The results of CDM analyses, obtained using the two-dimensional solver Damage XX, are reviewed for: a butt-welded pipe at 565C and, a welded cylinder-sphere pipe intersection at 590C. Results are then presented of a three-dimensional CDM solution for a three-degree slice of the welded cylinder-sphere pipe intersection, and shown to be in close agreement with the two-dimensional, Damage XX, solution. Then the paper examines damage growth at a constant <span class="hlt">temperature</span> of 590C in a ferritic steel butt-welded pipe subjected to a combined constant internal pressure of 4MPa and a constant global bending moment of 49kNm. The CDM results for a three-dimensional analysis are compared with qualitative experimental results, and good correlation is indicated.</p> <div class="credits"> <p class="dwt_author">Hayhurst, David R.; Wong, Man Tak; Vakili-Tahami, Farid</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">351</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://arxiv.org/pdf/0906.2942v1"> <span id="translatedtitle"><span class="hlt">Temperature</span> and angular momentum dependence of the quadrupole <span class="hlt">deformation</span> in sd-shell</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/eprints/">E-print Network</a></p> <p class="result-summary"><span class="hlt">Temperature</span> and angular momentum dependence of the quadrupole <span class="hlt">deformation</span> is studied in the middle of the sd-shell for 28Si and 27Si isotopes using the spherical shell model approach. The shell model calculations have been performed using the standard USD interaction and the canonical partition function constructed from the calculated eigen-solutions. It is shown that the extracted average quadrupole moments show a transitional behavior as a function of <span class="hlt">temperature</span> and the inferred transitional <span class="hlt">temperature</span> is shown to vary with angular-momentum. The quadrupole <span class="hlt">deformation</span> of the individual eigen-states is also analyzed.</p> <div class="credits"> <p class="dwt_author">P. A. Ganai; J. A. Sheikh; I. Maqbool; R. P. Singh</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-06-16</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">352</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19830026099&hterms=history+of+plastic&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3D%2528%2528history%2Bof%2529%2Bplastic%2529"> <span id="translatedtitle">Constrained Self-adaptive Solutions Procedures for Structure Subject to High <span class="hlt">Temperature</span> Elastic-plastic <span class="hlt">Creep</span> Effects</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">This paper will develop a new solution strategy which can handle elastic-plastic-<span class="hlt">creep</span> problems in an inherently stable manner. This is achieved by introducing a new constrained time stepping algorithm which will enable the solution of <span class="hlt">creep</span> initiated pre/postbuckling behavior where indefinite tangent stiffnesses are encountered. Due to the generality of the scheme, both monotone and cyclic loading histories can be handled. The presentation will give a thorough overview of current solution schemes and their short comings, the development of constrained time stepping algorithms as well as illustrate the results of several numerical experiments which benchmark the new procedure.</p> <div class="credits"> <p class="dwt_author">Padovan, J.; Tovichakchaikul, S.</p> <p class="dwt_publisher"></p> <p class="publishDate">1983-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">353</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2015MMTA...46...32Z"> <span id="translatedtitle">Increase of Austenite Grain Coarsening <span class="hlt">Temperature</span> in Banded Ferrite/Pearlite Steel by Cold <span class="hlt">Deformation</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The grain coarsening <span class="hlt">temperature</span> ( T c) is quite low in a ferrite/pearlite (F/P) banded steel as compared with a non-banded steel. Here it is shown that the low T c in the F/P banded steel can be increased significantly by applying cold <span class="hlt">deformation</span> prior to austenitizing. The kinetics of abnormal grain coarsening above T c is also largely retarded by cold <span class="hlt">deformation</span>. These observations should be attributed to the uniform distribution of fine AlN precipitates caused by cold <span class="hlt">deformation</span>.</p> <div class="credits"> <p class="dwt_author">Zhang, Xianguang; Matsuura, Kiyotaka; Ohno, Munekazu</p> <p class="dwt_publisher"></p> <p class="publishDate">2015-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">354</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4163670"> <span id="translatedtitle">Evidence of dislocation cross-slip in MAX phase <span class="hlt">deformed</span> at high <span class="hlt">temperature</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">Ti2AlN nanolayered ternary alloy has been plastically <span class="hlt">deformed</span> under confining pressure at 900C. The dislocation configurations of the <span class="hlt">deformed</span> material have been analyzed by transmission electron microscopy. The results show a drastic evolution compared to the dislocation configurations observed in the Ti2AlN samples <span class="hlt">deformed</span> at room <span class="hlt">temperature</span>. In particular, they evidence out-of-basal-plane dislocations and interactions. Moreover numerous cross-slip events from basal plane to prismatic or pyramidal planes are observed. These original results are discussed in the context of the Brittle-to-Ductile Transition of the nanolayered ternary alloys. PMID:25220949</p> <div class="credits"> <p class="dwt_author">Guitton, Antoine; Joulain, Anne; Thilly, Ludovic; Tromas, Christophe</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">355</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014NatSR...4E6358G"> <span id="translatedtitle">Evidence of dislocation cross-slip in MAX phase <span class="hlt">deformed</span> at high <span class="hlt">temperature</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Ti2AlN nanolayered ternary alloy has been plastically <span class="hlt">deformed</span> under confining pressure at 900C. The dislocation configurations of the <span class="hlt">deformed</span> material have been analyzed by transmission electron microscopy. The results show a drastic evolution compared to the dislocation configurations observed in the Ti2AlN samples <span class="hlt">deformed</span> at room <span class="hlt">temperature</span>. In particular, they evidence out-of-basal-plane dislocations and interactions. Moreover numerous cross-slip events from basal plane to prismatic or pyramidal planes are observed. These original results are discussed in the context of the Brittle-to-Ductile Transition of the nanolayered ternary alloys.</p> <div class="credits"> <p class="dwt_author">Guitton, Antoine; Joulain, Anne; Thilly, Ludovic; Tromas, Christophe</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-09-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">356</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.springerlink.com/index/a5u7675245787986.pdf"> <span id="translatedtitle">Modeling thermal <span class="hlt">deformation</span> of VLBI antennas with a new <span class="hlt">temperature</span> model</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary"><span class="hlt">Temperature</span> variations at very long baseline interferometry (VLBI) sites cause thermal <span class="hlt">deformations</span> of the VLBI antennas and\\u000a corresponding displacements of the VLBI reference points. The thermal <span class="hlt">deformation</span> effects typically contain seasonal and daily\\u000a signatures. The amplitudes of the annual vertical motion of the antenna reference point can reach several millimeters, depending\\u000a on the design of the antenna structure, on the</p> <div class="credits"> <p class="dwt_author">Joerg Wresnik; Rdiger Haas; Johannes Boehm; Harald Schuh</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">357</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/935788"> <span id="translatedtitle">ATOMISTIC SIMULATIONS OF DIFFUSIONAL <span class="hlt">CREEP</span> IN A NANOCRYSTALLINE BODY-CENTERED CUBIC MATERIAL</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Molecular dynamics (MD) simulations are used to study diffusion-accommodated <span class="hlt">creep</span> <span class="hlt">deformation</span> 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 <span class="hlt">temperatures</span> (i.e., T > 0.75Tmelt), thereby ensuring that the overall <span class="hlt">deformation</span> 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 <span class="hlt">creep</span> rates, which exhibit a double-exponential dependence on <span class="hlt">temperature</span> and a double power-law dependence on grain size, indicate that both GB diffusion in the form of Coble <span class="hlt">creep</span> and lattice diffusion in the form of NabarroHerring <span class="hlt">creep</span> contribute to the overall <span class="hlt">deformation</span>. 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.</p> <div class="credits"> <p class="dwt_author">Paul C. Millett; Tapan Desai; Vesselin Yamakov; Dieter Wolf</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">358</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/940246"> <span id="translatedtitle">Development of Advanced Corrosion-Resistant Fe-Cr-Ni Austenitic Stainless Steel Alloy with Improved High-<span class="hlt">Temperature</span> Strength and <span class="hlt">Creep</span>-Resistance</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">In February of 1999, a Cooperative Research and Development Agreement (CRADA) was undertaken between Oak Ridge National Laboratory (ORNL) and Special Metals Corporation - Huntington Alloys (formerly INCO Alloys International, Inc.) to develop a modified wrought austenitic stainless alloy with considerably more strength and corrosion resistance than alloy 800H or 800HT, but with otherwise similar engineering and application characteristics. Alloy 800H and related alloys have extensive use in coal flue gas environments, as well as for tubing or structural components in chemical and petrochemical applications. The main concept of the project was make small, deliberate elemental microalloying additions to this Fe-based alloy to produce, with proper processing, fine stable carbide dispersions for enhanced high <span class="hlt">temperature</span> <span class="hlt">creep</span>-strength and rupture resistance, with similar or better oxidation/corrosion resistance. The project began with alloy 803, a Fe-25Cr-35NiTi,Nb alloy recently developed by INCO, as the base alloy for modification. Smaller commercial developmental alloy heats were produced by Special Metal. At the end of the project, three rounds of alloy development had produced a modified 803 alloy with significantly better <span class="hlt">creep</span> resistance above 815 C (1500 C) than standard alloy 803 in the solution-annealed (SA) condition. The new upgraded 803 alloy also had the potential for a processing boost in that <span class="hlt">creep</span> resistance for certain kinds of manufactured components that was not found in the standard alloy. The upgraded 803 alloy showed similar or slightly better oxidation and corrosion resistance relative to standard 803. <span class="hlt">Creep</span> strength and oxidation/corrosion resistance of the upgraded 803 alloy were significantly better than found in alloy 800 H, as originally intended. The CRADA was terminated in February 2003. A contributing factor was Special Metals Corporation being in Chapter 11 Bankruptcy. Additional testing, further commercial scale-up, and any potential invention disclosures were not pursued.</p> <div class="credits"> <p class="dwt_author">Maziasz, P.J.; Swindeman, R.W.</p> <p class="dwt_publisher"></p> <p class="publishDate">2001-06-15</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">359</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014RuPhJ..57..197S"> <span id="translatedtitle"><span class="hlt">Temperature</span> Variation in the Process of <span class="hlt">Deformation</span> of Single Crystals of the Ni3Ge Alloy with the [001] and Orientations of the <span class="hlt">Deformation</span> Axis</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Experiments on <span class="hlt">temperature</span> variation in the process of <span class="hlt">deformation</span> of single crystals of the Ni3Ge alloy with the [001] and orientations of the <span class="hlt">deformation</span> axis have revealed a linear dependence of the stress jump on the applied stress similar to the dependence observed in pure metals and called the Cottrell-Stokes law. Results obtained for single crystals of both orientations of the <span class="hlt">deformation</span> axis are compared.</p> <div class="credits"> <p class="dwt_author">Solov'eva, Yu. V.; Starenchenko, S. V.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">360</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19930017046&hterms=ocpd&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Docpd"> <span id="translatedtitle"><span class="hlt">Deformation</span> mechanisms of NiAl cyclicly <span class="hlt">deformed</span> near the brittle-to-ductile transition <span class="hlt">temperature</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The intermetallic compound NiAl is one of many advanced materials which is being scrutinized for possible use in high <span class="hlt">temperature</span>, structural applications. Stoichiometric NiAl has a high melting <span class="hlt">temperature</span>, excellent oxidation resistance, and good thermal conductivity. Past research has concentrated on improving monotonic properties. The encouraging results obtained on binary and micro-alloyed NiAl over the past ten years have led to the broadening of NiAl experimental programs. The purpose of this research project was to determine the low cycle fatigue properties and dislocation mechanisms of stoichiometric NiAl at <span class="hlt">temperatures</span> near the monotonic brittle-to-ductile transition. The fatigue properties were found to change only slightly in the <span class="hlt">temperature</span> range of 600 to 700 K; a <span class="hlt">temperature</span> range over which monotonic ductility and fracture strength increase markedly. The shape of the cyclic hardening curves coincided with the changes observed in the dislocation structures. The evolution of dislocation structures did not appear to change with <span class="hlt">temperature</span>.</p> <div class="credits"> <p class="dwt_author">Cullers, Cheryl L.; Antolovich, Stephen D.</p> <p class="dwt_publisher"></p> <p class="publishDate">1993-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_17");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a 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showDiv("page_20");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">361</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/21243142"> <span id="translatedtitle">Vesicle growth and <span class="hlt">deformation</span> in a surfactant solution below the Krafft <span class="hlt">temperature</span>.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">We have studied vesicle growth and <span class="hlt">deformation</span> in aqueous solutions of nonionic surfactant C(16)E(7) below the Krafft <span class="hlt">temperature</span> by means of an optical microscope. It has been found that vesicles become larger by fusing together, and that the growth rate is slower than that of the unilamellar vesicle or emulsion systems due to the multilamellar structures of shells in a vesicle. The <span class="hlt">deformation</span> of the vesicles depends on the <span class="hlt">temperature</span> quench depth, and we found the transformation from spherical vesicles to string-like domains at a certain quench-<span class="hlt">temperature</span>. From the small angle X-ray scattering and confocal microscope experiments, it can be deduced that the <span class="hlt">deformation</span> of vesicles would be induced by osmotic pressure due to the micellar concentration difference between inside and outside of vesicles. PMID:21243142</p> <div class="credits"> <p class="dwt_author">Kawabata, Youhei; Shinoda, Tomoaki; Kato, Tadashi</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-02-28</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">362</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20130010717&hterms=alloy&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dalloy"> <span id="translatedtitle">Viscoelastoplastic <span class="hlt">Deformation</span> and Damage Response of Titanium Alloy, Ti-6Al-4V, at Elevated <span class="hlt">Temperatures</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Time-dependent <span class="hlt">deformation</span> and damage behavior can significantly affect the life of aerospace propulsion components. Consequently, one needs an accurate constitutive model that can represent both reversible and irreversible behavior under multiaxial loading conditions. This paper details the characterization and utilization of a multi-mechanism constitutive model of the GVIPS class (Generalized Viscoplastic with Potential Structure) that has been extended to describe the viscoelastoplastic <span class="hlt">deformation</span> and damage of the titanium alloy Ti-6Al-4V. Associated material constants were characterized at five elevated <span class="hlt">temperatures</span> where viscoelastoplastic behavior was observed, and at three elevated <span class="hlt">temperatures</span> where damage (of both the stiffness reduction and strength reduction type) was incurred. Experimental data from a wide variety of uniaxial load cases were used to correlate and validate the proposed GVIPS model. Presented are the optimized material parameters, and the viscoelastoplastic <span class="hlt">deformation</span> and damage responses at the various <span class="hlt">temperatures</span>.</p> <div class="credits"> <p class="dwt_author">Arnold, Steven M.; Lerch, Bradley A.; Saleeb, Atef F.; Kasemer, Matthew P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">363</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20100039318&hterms=united+states+paper+consumption&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dunited%2Bstates%2Bpaper%2Bconsumption"> <span id="translatedtitle">Experimental <span class="hlt">Creep</span> Life Assessment for the Advanced Stirling Convertor Heater Head</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">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 <span class="hlt">temperature</span> (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 <span class="hlt">creep</span>; <span class="hlt">creep</span> <span class="hlt">deformation</span> is the accumulation of time-dependent inelastic strain under sustained loading over time. If allowed to progress, the <span class="hlt">deformation</span> eventually results in <span class="hlt">creep</span> rupture. Since <span class="hlt">creep</span> material properties are not available in the open literature, a detailed <span class="hlt">creep</span> life assessment of the ASC heater head effort is underway. This paper presents an overview of that <span class="hlt">creep</span> life assessment approach, including the reliability-based <span class="hlt">creep</span> criteria developed from coupon testing, and the associated heater head deterministic and probabilistic analyses. The approach also includes direct benchmark experimental <span class="hlt">creep</span> assessment. This element provides high-fidelity <span class="hlt">creep</span> 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 <span class="hlt">creep</span> strain predictions and are the first experimental evidence for a robust ASC heater head <span class="hlt">creep</span> life.</p> <div class="credits"> <p class="dwt_author">Krause, David L.; Kalluri, Sreeramesh; Shah, Ashwin R.; Korovaichuk, Igor</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">364</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19800002663&hterms=Jeg&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DJeg%2B3"> <span id="translatedtitle"><span class="hlt">Temperature</span> <span class="hlt">deformations</span> of the mirror of a radio telescope antenna</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The stress informed state of the mirror of an antenna, with a diameter of 3 m, for a radio interferometer used in space, and located in a <span class="hlt">temperature</span> field is examined. The mirror represents a parabolic shell, consisting of 19 identical parts. The problem is based on representations of the thermoelasticity of thin shells.</p> <div class="credits"> <p class="dwt_author">Avdeyev, V. I.; Grach, S. A.; Kozhakhmetov, K. K.; Kostenko, F. I.</p> <p class="dwt_publisher"></p> <p class="publishDate">1979-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">365</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/978424"> <span id="translatedtitle">Comprehensive Characterization of Voids and Microstructure in TATB-based Explosives from 10 nm to 1 cm: Effects of <span class="hlt">Temperature</span> Cycling and Compressive <span class="hlt">Creep</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">This paper outlines the characterization of voids and Microstructure in TATB-based Explosives over several orders of magnitude, from sizes on the order of 10 nm to about 1 cm. This is accomplished using ultra small angle x-ray scattering to investigate voids from a few nm to a few microns, ultra small angle neutron scattering for voids from 100 nm to 10 microns, and x-ray computed microtomography to investigate microstructure from a few microns to a few centimeters. The void distributions of LX-17 are outlined, and the microstructure of LX-17 is presented. <span class="hlt">Temperature</span> cycling and compressive <span class="hlt">creep</span> cause drastically different damage to the microstructure. <span class="hlt">Temperature</span> cycling leads to a volume expansion (ratchet growth) in TATB-based explosives, and x-ray scattering techniques that are sensitive to sizes up to a few microns indicated changes to the void volume distribution that had previously accounted for most, but not all of the change in density. This paper presents the microstructural damage larger than a few microns caused by ratchet growth. <span class="hlt">Temperature</span> cycling leads to void creation in the binder poor regions associated with the interior portion of formulated prills. Conversely, compressive <span class="hlt">creep</span> causes characteristically different changes to microstructure; fissures form at binder-rich prill boundaries prior to mechanical failure.</p> <div class="credits"> <p class="dwt_author">Willey, T M; Lauderbach, L; Gagliardi, F; Cunningham, B; Lorenz, K T; Lee, J I; van Buuren, T; Call, R; Landt, L; Overturf, G</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-02-26</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">366</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/49429388"> <span id="translatedtitle">Influence of grain size on <span class="hlt">deformation</span> mechanisms in rolled Mg3Al3Sn alloy at room <span class="hlt">temperature</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The <span class="hlt">deformation</span> mechanisms for rolled Mg3Al3Sn alloys were strongly dependent on grain sizes at room <span class="hlt">temperature</span>. For grain sizes of ?622?m, the <span class="hlt">deformation</span> in tension was mainly dominated by dislocation-slip, which, however, turned to be mediated by <span class="hlt">deformation</span>-twinning for those of ?2241?m. Moreover, as <span class="hlt">deformation</span> proceeded, HallPetch slopes for slip-controlled-plasticity (kS) decreased gradually due to continuous activation of non-basal slips,</p> <div class="credits"> <p class="dwt_author">Hui-Yuan Wang; En-Song Xue; Wei Xiao; Zhang Liu; Jin-Biao Li; Qi-Chuan Jiang</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">367</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/21205424"> <span id="translatedtitle">The microstructure and <span class="hlt">creep</span> behavior of cold rolled udimet 188 sheet.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p class="result-summary">Udimet 188 was subjected to thermomechanical processing (TMP) in an attempt to understand the effects of cold-rolling <span class="hlt">deformation</span> on the microstructure and tensile-<span class="hlt">creep</span> behavior. Commercially available sheet was cold rolled to varying amounts of <span class="hlt">deformation</span> (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-<span class="hlt">temperature</span> [1,033-1,088 K (760-815 C)] <span class="hlt">creep</span> behavior was evaluated. The measured <span class="hlt">creep</span> stress exponents (6.0-6.8) suggested that dislocation <span class="hlt">creep</span> 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 <span class="hlt">deformed</span> samples. To assess the mechanisms of crack nucleation, in situ scanning electron microscopy was performed during the elevated-<span class="hlt">temperature</span> tensile-<span class="hlt">creep</span> <span class="hlt">deformation</span>. 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). <span class="hlt">Creep</span> 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 <span class="hlt">creep</span> 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 <span class="hlt">creep</span> resistance is not sufficient. PMID:21205424</p> <div class="credits"> <p class="dwt_author">Boehlert, C J; Longanbach, S C</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">368</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/82958"> <span id="translatedtitle"><span class="hlt">Creep</span> modeling of rock salts for geoenvironmental application</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">Before using a rock salt as a nuclear waste repository, it is necessary to have adequate knowledge of the mechanical and thermomechanical behavior of the host geologic media. In rock salt, such mechanical and thermomechanical behavior is dominated, among other factors, by the time-dependent <span class="hlt">deformation</span> commonly referred to as <span class="hlt">creep</span>. The paper discusses a rate-dependent constitutive model to describe the <span class="hlt">creep</span> <span class="hlt">deformation</span> of rock salts. The model is based on the dislocation-related micromechanisms; the concept of effective stress is utilized by incorporating the back stress as an internal variable. The model is used to predict the <span class="hlt">creep</span> potential of rock salt under general thermo-mechanical loading. The experimental test results from Avery Island dome salt are used in this work. The associated five model parameters are evaluated by using an optimization technique, called box algorithm. The parameters are then used with the model to predict unoptimized experimental data sets. The influence of <span class="hlt">temperature</span> and confining pressure are investigated in detail for the selected rock salt. Overall, excellent correlations are observed.</p> <div class="credits"> <p class="dwt_author">Hossain, M.I. [SEARCH, Inc., Norman, OK (United States); Faruque, M.O.; Zaman, M. [Univ. of Oklahoma, Norman, OK (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-06-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">369</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2000JGR...10526017R"> <span id="translatedtitle">Dislocation and diffusion <span class="hlt">creep</span> of synthetic anorthite aggregates</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">Synthetic fine-grained anorthite aggregates were <span class="hlt">deformed</span> at 300 MPa confining pressure in a Paterson-type gas <span class="hlt">deformation</span> apparatus. <span class="hlt">Creep</span> tests were performed at <span class="hlt">temperatures</span> ranging from 1140 to 1480 K, stresses from 30 to 600 MPa, and strain rates between 210-6 and 110-3 s-1. We prepared samples with water total contents of 0.004 wt % (dry) and 0.07 wt % (wet), respectively. The wet (dry) material contained <0.7 (0.2) vol % glass, associated with fluid inclusions or contained at triple junctions. The arithmetic mean grain size of the specimens varied between 2.70.1 ?m for the dry material and 3.40.2 ?m for wet samples. Two different <span class="hlt">creep</span> regimes were identified for dry and wet anorthite aggregates. The data could be fitted to a power law. At stresses >120 MPa we found a stress exponent of n = 3 irrespective of the water content, indicating dislocation <span class="hlt">creep</span>. However, the activation energy of wet samples is 3569 kJ mol-1, substantially lower than for dry specimens with 64820 kJ mol-1. The preexponential factor is log A = 2.6 (12.7) MPa-n s-1 for wet (dry) samples. Microstructural observations suggest that grain boundary migration recrystallization is important in accommodating dislocation <span class="hlt">creep</span>. In the low-stress regime we observed a stress exponent of n = 1, suggesting diffusion <span class="hlt">creep</span>. The activation energies for dry and wet samples are 467 16 and 170 6 kJ mol-1, respectively. Log A is 12.1 MPa-n ?mm s-1 for the dry material and 1.7 MPa-n ?mm s-1 for wet anorthite. The data show that the strengths of anorthite aggregates decrease with increasing water content in both the dislocation and diffusion <span class="hlt">creep</span> regimes. A comparison of the <span class="hlt">creep</span> data of synthetic plagioclase from this study with published data for feldspar, olivine, and quartz indicates a linear relationship between activation energy and log A similar to the suggested compensation law for diffusion in silicates.</p> <div class="credits"> <p class="dwt_author">Rybacki, E.; Dresen, G.</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">370</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012JSG....38..200P"> <span id="translatedtitle">Semi-brittle <span class="hlt">deformation</span> of granitoid gouges in shear experiments at elevated pressures and <span class="hlt">temperatures</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The physical and chemical processes acting in the 'brittle-to-plastic' transition are of great interest for a better understanding of fault rheology. We performed a series of experiments on granitoid gouge material under high confining pressures (Pc = 500-1500 MPa), <span class="hlt">temperatures</span> (T = 300 C and 500 C) and fast shear strain rates (1.8 10-4 s-1) where the material <span class="hlt">deforms</span> by semi-brittle flow. Samples <span class="hlt">deformed</span> at 500 C are systematically weaker than samples <span class="hlt">deformed</span> at 300 C over the whole examined confining pressure range indicating a non-frictional component of the <span class="hlt">deformation</span>. All samples develop an S-C' fabrics and <span class="hlt">deformation</span> localizes in slip zones containing 'amorphous' feldspar material with an intermediate composition (Na, Ca and K-rich). Further, we observe changes in composition of feldspars (enrichment in the albite component) in the highly fragmented - but crystalline - regions with increasing finite shear strain. Our results indicate that mass-transfer processes keep pace with frictional <span class="hlt">deformation</span> even at high strain rates and together with viscous flow of the 'amorphous' material are responsible for the observed strength difference.</p> <div class="credits"> <p class="dwt_author">Pec, Matej; Stnitz, Holger; Heilbronner, Rene</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-05-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">371</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/18797611"> <span id="translatedtitle">Subgrain boundaries and dissociations of dislocations in yttrium iron garnet <span class="hlt">deformed</span> at high <span class="hlt">temperatures</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Sub-grain boundaries in YIG single crystals <span class="hlt">deformed</span> at high <span class="hlt">temperatures</span> (08-09 TM) have been studied by transmission electron microscopy. Dislocation networks form mainly by climb; they are formed from dislocations with ?\\/2 ?111? Burgers vectors. Dislocation junctions with ? ?100? Burgers vectors are usually found in networks; however, junctions with ? ?110? Burgers vectors are occasionally observed. They are dissociated</p> <div class="credits"> <p class="dwt_author">J. Rabier; P. Veyssiere; H. Garem; J. Grilh</p> <p class="dwt_publisher"></p> <p class="publishDate">1979-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">372</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://perso.univ-st-etienne.fr/bascjero/Egydio_et_al,Tectono,(2002).pdf"> <span id="translatedtitle">High-<span class="hlt">temperature</span> <span class="hlt">deformation</span> in the Neoproterozoic transpressional Ribeira belt, southeast Brazil</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/eprints/">E-print Network</a></p> <p class="result-summary">High-<span class="hlt">temperature</span> <span class="hlt">deformation</span> in the Neoproterozoic transpressional Ribeira belt, southeast Brazil^ncias da Universidade de Sa~o Paulo, Rua do Lago 562, Cep: 05508-080, Sa~o Paulo, SP, Brazil b Laboratoire Geologia, Universidade Federal de Ouro Preto, 35400-000, Ouro Pre^to, MG, Brazil Received 5 April 2001</p> <div class="credits"> <p class="dwt_author">Bascou, Jrme</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">373</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/60074193"> <span id="translatedtitle">Inelastic <span class="hlt">deformation</span> and damage at high <span class="hlt">temperature</span>. Progress report, April 1, 1991March 31, 1992</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Combined experimental and theoretical investigations into the inelastic <span class="hlt">deformation</span> and damage behavior of engineering alloys at elevated <span class="hlt">temperatures</span> are being pursued. The analysis of previously performed strain rate change and relaxation tests on modified 9Cr-1Mo steel showed the need for inclusion of a recovery of state term in the growth laws for the state variables of the viscoplasticity theory based</p> <div class="credits"> <p class="dwt_author">Krempl</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">374</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/servlets/purl/950969"> <span id="translatedtitle">In-situ Phase Transformation and <span class="hlt">Deformation</span> of Iron at High Pressure and<span class="hlt">Temperature</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">With a membrane based mechanism to allow for pressure change of a sample in aradial diffraction diamond anvil cell (rDAC) and simultaneous infra-red laser heating, itis now possible to investigate texture changes during <span class="hlt">deformation</span> and phasetransformations over a wide range of <span class="hlt">temperature</span>-pressure conditions. The device isused to study bcc (alpha), fcc (gamma) and hcp (epislon) iron. In bcc iron, room <span class="hlt">temperature</span> compression generates a texture characterized by (100) and (111) poles parallel to the compression direction. During the <span class="hlt">deformation</span> induced phase transformation to hcp iron, a subset of orientations are favored to transform to the hcp structure first and generate a texture of (01-10) at high angles to the compression direction. Upon further <span class="hlt">deformation</span>, the remaining grains transform, resulting in a texture that obeys the Burgers relationship of (110)bcc // (0001)hcp. This is in contrast to high <span class="hlt">temperature</span> results that indicate that texture is developed through dominant pyramidal<a+c> {2-1-12}<2-1-13> and basal (0001)-{2-1-10} slip based on polycrystal plasticity modeling. We also observe that the high <span class="hlt">temperature</span> fcc phase develops a 110 texture typical for fcc metals <span class="hlt">deformed</span> in compression.</p> <div class="credits"> <p class="dwt_author">Miyagi, Lowell; Kunz, Martin; Knight, Jason; Nasiatka, James; Voltolini, Marco; Wenk, Hans-Rudolf</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">375</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014Tectp.629...55P"> <span id="translatedtitle">Low-<span class="hlt">temperature</span> AMS and the quantification of subfabrics in <span class="hlt">deformed</span> rocks</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We evaluate the application and significance of Low-<span class="hlt">Temperature</span> Anisotropy of Magnetic Susceptibility (LT-AMS) measurements in <span class="hlt">deformed</span> mudrocks. Originally conceived as a way to enhance paramagnetic relative to ferromagnetic susceptibility, LT-AMS studies offer significant potential in constraining the coexistence of subfabrics that are due to phyllosilicate grains with different preferred orientations. In this study we report a detailed procedure to obtain such directional susceptibilities, measuring samples in multiple orientations at liquid nitrogen <span class="hlt">temperatures</span> in order to determine the LT-AMS. Due to unequal changes of magnetic susceptibility in micas at low-<span class="hlt">temperature</span>, the enhancement of standard AMS at low-<span class="hlt">temperature</span> better separates interacting fabrics in natural rocks, particularly depositional fabrics versus <span class="hlt">deformational</span> fabrics. LT-AMS is a non-destructive technique that readily offers an ability to separate ferromagnetic and paramagnetic fabrics, and allows the characterization and quantification of multiple fabrics in natural rocks.</p> <div class="credits"> <p class="dwt_author">Pars, Josep M.; van der Pluijm, Ben A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">376</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012JNuM..420..226L"> <span id="translatedtitle">High <span class="hlt">temperature</span> <span class="hlt">deformation</span> and fracture behaviour of 316L stainless steel under high strain rate loading</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The high <span class="hlt">temperature</span> <span class="hlt">deformation</span> and fracture behaviour of 316L stainless steel under high strain rate loading conditions are investigated by means of a split Hopkinson pressure bar. Impact tests are performed at strain rates ranging from 1 10 3 s -1 to 5 10 3 s -1 and <span class="hlt">temperatures</span> between 25 C and 800 C. The experimental results indicate that the flow response and fracture characteristics of 316L stainless steel are significantly dependent on the strain rate and <span class="hlt">temperature</span>. The fracture analysis results indicate that the 316L specimens fail predominantly as the result of intensive localised shearing. Furthermore, it is shown that the flow localisation effect leads to the formation of adiabatic shear bands. The fracture surfaces of the <span class="hlt">deformed</span> 316L specimens are characterised by a dimple-like structure with knobby features. The knobby features are thought to be the result of a rise in the local <span class="hlt">temperature</span> to a value greater than the melting point.</p> <div class="credits"> <p class="dwt_author">Lee, Woei-Shyan; Lin, Chi-Feng; Chen, Tao-Hsing; Luo, Wen-Zhen</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">377</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20090028680&hterms=contact&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dcontact"> <span id="translatedtitle">Advances in Non-contact Measurement of <span class="hlt">Creep</span> Properties</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Our team has developed a novel approach to measuring <span class="hlt">creep</span> at extremely high <span class="hlt">temperatures</span> 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 <span class="hlt">deform</span>. The <span class="hlt">deformation</span> of the sample is captured on high-speed video, which is analyzed by machine-vision software from the University of Massachusetts. The <span class="hlt">deformations</span> are compared to finite element models to determine the constitutive constants in the <span class="hlt">creep</span> 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-<span class="hlt">Temperature</span> ZrB2- SiC composites, which may see application in rocket nozzles and sharp leading edges for hypersonic vehicles.</p> <div class="credits"> <p class="dwt_author">Hyers, Robert W.; Canepari, Stacy; Rogers, Jan. R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">378</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2014JMEP...23.3680R"> <span id="translatedtitle">Compressive <span class="hlt">Creep</span> Behavior of Spark Plasma Sintered 8 mol% Yttria Stabilized Cubic Zirconia</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The present paper describes compressive <span class="hlt">creep</span> behavior of cubic 8 mol% Yttria-stabilized Zirconia, fabricated by spark plasma sintering, in the <span class="hlt">temperature</span> range of 1300-1330 C at a stress level of 78-193 MPa in vacuum. The pre- and post-<span class="hlt">creep</span> microstructures, along with the values of the stress exponent ( n = 1.7-2.7) and the activation energy ( Q = 711-757 kJ/mol) suggest that a mixed mode of plastic <span class="hlt">deformation</span>, dominated by grain boundary sliding, occurred in this material. The relatively high activation energy observed was related to the pinning of the grain boundaries by voids during <span class="hlt">creep</span>, leading to microcrack formation, shear strain-induced grain exfoliation, and finally creation of new voids at grain boundaries.</p> <div class="credits"> <p class="dwt_author">Robles Arellano, K. D.; Bichler, L.; Mondal, K.; Fong, R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">379</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/26496570"> <span id="translatedtitle">Thermal postbuckling behavior of shear <span class="hlt">deformable</span> FGM plates with <span class="hlt">temperature</span>-dependent properties</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Thermal postbuckling analysis is presented for a simply supported, shear <span class="hlt">deformable</span> functionally graded plate under thermal loading. Two cases of <span class="hlt">temperature</span> field, i.e. in-plane non-uniform parabolic <span class="hlt">temperature</span> distribution and heat conduction are considered. The material properties of functionally graded materials (FGMs) are assumed to be graded in the thickness direction according to a simple power-law distribution in terms of the</p> <div class="credits"> <p class="dwt_author">Hui-Shen Shen</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">380</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/40475841"> <span id="translatedtitle">High <span class="hlt">temperature</span> <span class="hlt">deformation</span> behavior of Al 2124SiC p composite</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The high <span class="hlt">temperature</span> <span class="hlt">deformation</span> of 2124\\/SiCp (17 vol.%) Composite material was investigated over the <span class="hlt">temperature</span> range from 698 K to 823 K. It was shown that the 2124\\/SiCp composite did not behave superplastically at strain rates of from 10?4 to 10?1 s?1. The strain rate sensitivity was found to be about 0.17, which was apparently below that (0.5) of a</p> <div class="credits"> <p class="dwt_author">B. Q. Han; K. C. Chan; T. M. Yue; W. S. Lau</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_18");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">381</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.springerlink.com/index/971l5x8241334j42.pdf"> <span id="translatedtitle">Superplastic <span class="hlt">deformation</span> behavior of hot-rolled AZ31 magnesium alloy sheet at elevated <span class="hlt">temperatures</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">Uniaxial tensile tests were carried out in the <span class="hlt">temperature</span> range of 250450C and the strain rate range of 0.710?31.410?1 s?1 to evaluate the superplasticity of AZ31 Mg alloy. The threshold stress which characterizes the difficulty for grain boundary\\u000a sliding was calculated at various <span class="hlt">temperatures</span>. The surface relieves of superplastically <span class="hlt">deformed</span> specimens were observed\\u000a by using a scanning electronic microscope (SEM).</p> <div class="credits"> <p class="dwt_author">Zhang Kaifeng; Yin Deliang; Wang Guofeng; Han Wenbo</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">382</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013PhDT........74M"> <span id="translatedtitle">The role of microstructure on <span class="hlt">deformation</span> and damage mechanisms in a Nickel-based superalloy at elevated <span class="hlt">temperatures</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The overall objective of this research work is the development and implementation of a mechanistic based time-dependent crack growth model which considers the role of <span class="hlt">creep</span>, fatigue and environment interactions on both the bulk and the grain boundary phase in ME3 disk material. The model is established by considering a moving crack tip along a grain boundary path in which damage events are described in terms of the grain boundary <span class="hlt">deformation</span> and related accommodation processes. Modeling of these events was achieved by adapting a cohesive zone approach (an interface with internal singular surfaces) in which the grain boundary dislocation network is smeared into a Newtonian fluid element. The <span class="hlt">deformation</span> behavior of this element is controlled by the continuum in both far field (internal state variable model) and near field (crystal plasticity model) and the intrinsic grain boundary viscosity which is characterized by microstructural parameters, including grain boundary precipitates and morphology, and is able to define the mobility of the element by scaling the motion of dislocations into a mesoscopic scale. Within the cohesive zone element, the motion of gliding dislocations in the tangential direction relates to the observed grain boundary sliding displacement, the rate of which is limited by the climb of dislocations over grain boundary obstacles. Effects of microstructural variation and orientation of the surrounding continuum are embedded in the tangential stress developing in the grain boundary. The mobility of the element in the tangential direction (i.e. by grain boundary sliding) characterizes the accumulation of irreversible displacement while the vertical movement (migration), although present, is assumed to alter stress by relaxation and, thus, is not considered a contributing factor in the damage process. This process is controlled by the rate at which the time-dependent sliding reaches a critical displacement and as such, a damage criterion is introduced by considering the mobility limit in the tangential direction leading to strain incompatibility and failure. This limit is diminished by environmental effects which are introduced as a dynamic embrittlement process that hinders grain boundary mobility due to oxygen diffusion. The concepts described herein indicate that implementation of the cohesive zone model requires the knowledge of the grain boundary external and internal <span class="hlt">deformation</span> fields. The external field is generated by developing and coupling two continuum constitutive models including