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1

Creep deformation and rupture properties of unirradiated Zircaloy-4 nuclear fuel cladding tube at temperatures of 727 to 857 K  

NASA Astrophysics Data System (ADS)

Creep deformation and rupture properties of an unirradiated Zircaloy-4 tube were examined at temperatures of 727 to 857 K to obtain data for evaluating spent fuel integrity under the off-normal dry storage condition. Creep tests were carried out on internally gas pressurized tubular specimens with end plugs welded to both ends. The hoop creep strain up to the steady-state creep region was given by the following equation: ? = 0.05{1- exp[-10( ?st) 0.51]} + ?st, where ?s = 1.02 10 5( E/ T) exp (4060 ?/ E) exp (- Q/ RT) ( S-1), t is time (s), E is the elastic modulus (MPa), T is the temperature (K), ? is the applied stress (MPa), R is the gas constant (= 8.314 J/mol K), and Q the apparent activation energy (233 kJ/mol). The total creep deformation curve over the accelerated creep region could also be presented by the equation expressed as a function of true stress formulated on the basis of constant stress creep data. It is inferred that the transition from the steady-state to the accelerated creep region occurs without changing the deformation mechanism. It was also shown that most of the creep strain to rupture exceeded 100% and Zircaloy-4 had an extremely ductile rupture property.

Mayuzumi, Masami; Onchi, Takeo

1990-12-01

2

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

Microsoft Academic Search

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

Horst Biermann; Marcus Strehler; Hal Mughrabi

1996-01-01

3

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

4

Modelling the plastic deformation during high-temperature creep of a powder-metallurgy coarse-grained superalloy  

Microsoft Academic Search

The study of creep deformation in a coarse-grained Udimet 720 superalloy obtained by powder-metallurgy reveals a good resistance associated to a dislocational deformation mechanism. A model is proposed for simulating creep and tensile curves. This model is used to understand the effect of microstructural changes on the deformation mechanisms.

Sofiane Terzi; Raphael Couturier; Laure Gutaz; Bernard Viguier

2008-01-01

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

Estimating creep deformation of glass-fiber-reinforced polycarbonate  

NASA Astrophysics Data System (ADS)

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

Sakai, Takenobu; Somiya, Satoshi

2006-09-01

7

Constitutive equations for the description of creep and creep rupture behavior of metallic materials at temperatures above 800°C  

Microsoft Academic Search

At high temperatures, the creep deformation of metallic materials is correlated with the accumulation of creep damage. Creep crack growth leads to a decrease of bearing cross section and an increase in stationary creep. Both variables, creep strain rate and creep damage, are described by a system of coupled differential equations. The solutions of these equations are given for the

H. J. Penkalla; H. H. Over; F. Schubert

1984-01-01

8

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

Microsoft Academic Search

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

G. Kaustrter; B. Skrotzki; G. Eggeler

2001-01-01

9

Creep failure model of a tempered martensitic stainless steel integrating multiple deformation and damage mechanisms  

Microsoft Academic Search

A new model considering both deformation and damage evolution under multiple viscoplastic mechanisms is used to represent high temperature creep deformation and damage of a martensitic stainless steel in a wide range of load levels. First, an experimental database is built to characterise both creep flow and damage behaviour using tests on various kinds of specimens. The parameters of the

V. Gaffard; J. Besson; A. F. Gourgues-Lorenzon

2005-01-01

10

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

National Technical Information Service (NTIS)

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 ...

J. D. Whittenberger R. D. Noebe R. Darolia

2003-01-01

11

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

Microsoft Academic Search

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

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

2005-01-01

12

Constitutive equations for the description of creep and creep rupture behavior of metallic materials at temperatures above 800/sup 0/C  

SciTech Connect

At high temperatures, the creep deformation of metallic materials is correlated with the accumulation of creep damage. Creep crack growth leads to a decrease of bearing cross section and an increase in stationary creep. Both variables, creep strain rate and creep damage, are described by a system of coupled differential equations. The solutions of these equations are given for the boundary conditions of creep tests under constant load, for creep rupture behavior, for damage accumulation in the creep region, and for creep-regimed low-cycle fatigue. A general correlation between applied stress, cumulative strain, and cumulative damage is given.

Penkalla, H.J.; Over, H.H.; Schubert, F.

1984-09-01

13

Scale and temperature dependent creep modeling and experiments in materials  

NASA Astrophysics Data System (ADS)

Creep is non-recoverable high temperature plastic deformation occurring at low load regimes, constant stress values, and small strain rates. While mechanistic information regarding macroscale (centimeters and higher) creep deformation has been of significant attention in the past few decades, the nanoscale (few nanometers to a few hundred nanometers) and microscale (few hundred nanometers to a few hundred micrometers) creep deformation has recently emerged as an important area of research. A particular interest lies in trying to control nanoscale and microscale creep properties with a view to design materials for extreme environments and materials in small scale devices. This article presents an overview of the recent developments in modeling and experiments focused on analyzing nanoscale and microscale temperature dependent creep in materials.

Gan, Ming; Tomar, Vikas

2011-09-01

14

High-temperature creep of forsterite single crystals  

Microsoft Academic Search

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

Michel Darot; Yves Gueguen

1981-01-01

15

Creep deformation of a soft magnetic iron-cobalt alloy  

NASA Astrophysics Data System (ADS)

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

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

1999-04-01

16

Threshold Stress Creep Behavior of Alloy 617 at Intermediate Temperatures  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

17

Threshold Stress Creep Behavior of Alloy 617 at Intermediate Temperatures  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

18

Development of a creep deformation and life prediction model for a HIPed silicon nitride ceramic  

SciTech Connect

A mathematical model was developed for predicting creep deformation and creep-rupture time for a HIPed silicon nitride (Si{sub 3}N{sub 4}) ceramic subjected to thermal-mechanical loading in uniaxial tension at elevated temperatures. The model was formulated based on the deformation and rupture data obtained from a systematic experimental study on a single lot of GN-10 Si{sub 3}N{sub 4}; however, it is applicable in principle to other types of ceramic materials. The model consists of three rate-type of equations that describe changes of three variables representing creep strain, devitrification of second phase, and creep damage. Introduction of the devitrification and creep damage variables is a new approach in constitutive modelling of Si{sub 3}N{sub 4} ceramics and has significantly enhanced the ability to predict effects of annealing on creep behavior and creep rupture lifetime. Although the proposed model is exploratory in nature, it has demonstrated the capability of describing the essential features of uniaxial creep and creep rupture behavior of the material subjected to both constant and stepwise-varied loading conditions as well as the effects of high temperature annealing on the subsequent creep and creep rupture behavior. The simplicity of the model makes the closed form solutions for constant or stepwise-varied loading possible and, therefore, facilitates adoption of the proposed model in the current engineering design and analysis methods.

Ding, J.L. (Washington State Univ., Pullman, WA (United States). Dept. of Mechanical Engineering); Liu, K.C.; Brinkman, C.R. (Oak Ridge National Lab., TN (United States))

1992-01-01

19

Development of a creep deformation and life prediction model for a HIPed silicon nitride ceramic  

SciTech Connect

A mathematical model was developed for predicting creep deformation and creep-rupture time for a HIPed silicon nitride (Si{sub 3}N{sub 4}) ceramic subjected to thermal-mechanical loading in uniaxial tension at elevated temperatures. The model was formulated based on the deformation and rupture data obtained from a systematic experimental study on a single lot of GN-10 Si{sub 3}N{sub 4}; however, it is applicable in principle to other types of ceramic materials. The model consists of three rate-type of equations that describe changes of three variables representing creep strain, devitrification of second phase, and creep damage. Introduction of the devitrification and creep damage variables is a new approach in constitutive modelling of Si{sub 3}N{sub 4} ceramics and has significantly enhanced the ability to predict effects of annealing on creep behavior and creep rupture lifetime. Although the proposed model is exploratory in nature, it has demonstrated the capability of describing the essential features of uniaxial creep and creep rupture behavior of the material subjected to both constant and stepwise-varied loading conditions as well as the effects of high temperature annealing on the subsequent creep and creep rupture behavior. The simplicity of the model makes the closed form solutions for constant or stepwise-varied loading possible and, therefore, facilitates adoption of the proposed model in the current engineering design and analysis methods.

Ding, J.L. [Washington State Univ., Pullman, WA (United States). Dept. of Mechanical Engineering; Liu, K.C.; Brinkman, C.R. [Oak Ridge National Lab., TN (United States)

1992-10-01

20

Modelling of anisotropic creep deformation and damage in single crystal superalloys  

SciTech Connect

Previous studies on the creep behavior of single crystal nickel base superalloys reveal that both creep deformation behavior and stress rupture properties of single crystal alloys are strongly dependent on crystal orientation and temperature. A physical model of creep deformation in single crystal superalloys has been proposed by Ghosh et al. This model accounts for the anisotropy and asymmetry of creep by viscous glide on specific crystallographic slip systems and for the tertiary creep behavior through a damage parameter that is related to the accumulation of mobile dislocations in each slip system. The model has been applied to analyze the creep curves of the single crystal nickel base superalloy SRR99, with particular reference to [001] and [111] orientations. The model also attempts to predict the change in the anisotropy of creep behavior with stress and temperature, and the changes in the orientation and specimen cross-section with creep strain. The creep model proposed by Ghosh et al has been modified and extended to describe the anisotropic creep behavior of single crystal superalloys for multiaxial stress states. The equations must be used with a general transformation procedure to relate the crystallographic deformation to the global loading directions. Three creep rupture criteria based on material damage in single crystal superalloys have been suggested. The creep damage criterion that takes into account of the different effects of damage on octahedral and cubic slip system and includes interaction effects between the two types of slip provided the best predictions of creep rupture life for the single crystal nickel base superalloy SRR99.

Li, S.X.; Smith, D.J. [Univ. of Bristol (United Kingdom). Dept. of Mechanical Engineering] [Univ. of Bristol (United Kingdom). Dept. of Mechanical Engineering

1995-09-01

21

High temperature impression creep testing of weldments  

SciTech Connect

The impression creep test technique, a modified hot hardness test in which the time dependence of the indentor displacement correlates directly to creep properties, has been utilized to measure the localized creep properties across welded joints. High temperature creep data, as a function of position, with respect to the fusion line, were measured on an autogeneous GTA aluminum weld and on an austenitic stainless steel to ferritic steel dissimilar metal weldment. The creep resistance of the aluminum weld decreased with position on traversing from the solidified weld metal to the base metal, and the variation in creep resistance with position was shown to correlate directly to gradients in microstructure.

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

1985-06-01

22

Finite element modeling of creep deformation in cellular metals  

Microsoft Academic Search

The creep of reticulated metallic foams is studied through the finite element method using three-dimensional, periodic unit cells with four different architectures characterized by struts which deform primarily by: (i) simple bending, (ii) compression, (iii) a combination of simple bending and compression and (iv) double bending (for Kelvin space-filling tetrakaidecahedra). The creep behavior of each of these models is examined

Scott M. Oppenheimer; David C. Dunand

2007-01-01

23

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

24

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

25

Viscoelastic creep of high-temperature concrete  

SciTech Connect

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

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

1985-01-01

26

Analysis of creep deformation and creep damage in thin-walled branched shells from materials with different behavior in tension and compression  

Microsoft Academic Search

A constitutive model for describing the creep and creep damage in initially isotropic materials with different properties in tension and compression has been applied to the modeling of creep deformation and creep damage growth in thin-walled shells of revolution with the branched meridian. The approach of establishing the basic equations for axisymmetrically loaded branched shells under creep deformation and creep

A. Zolochevsky; A. Galishin; S. Sklepus; G. Z. Voyiadjis

2007-01-01

27

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

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

28

Modelling and Analysis of Creep Deformation and Fracture in a 1 Cr 1/2 Mo Ferritic Steel.  

National Technical Information Service (NTIS)

A quantitative model, based upon a proposed new mechanism of creep deformation in particle-hardened alloys, has been validated by analysis of creep data from a 13CrMo 4 4 (1Cr 1/2 Mo) material tested under a range of stresses and temperatures. The methodo...

B. F. Dyson D. Osgerby

1993-01-01

29

Estimating the creep behavior of polycarbonate with changes in temperature and aging time  

NASA Astrophysics Data System (ADS)

Thermoplastic resins are typically used without any kind of physical aging treatment. For such materials, creep behavior and physical aging, which depend on time and temperature, occur simultaneously. The effects of these processes are evident after quenching and are recorded in the material as a thermal history. This history strongly influences mechanical properties and creep behavior in particular. Thus, a more thorough understanding of the physical aging process is desirable. We examined the creep deformation of polycarbonate (PC) to reveal the effects of physical aging on creep behavior. The effects were dependent on both time and temperature. The relationship between physical aging and creep behavior exemplified superposition principles with regard to time and both pre-test aging time and pre-test aging temperature. The superposition principles allowed the calculation of creep deformations at a given temperature; the calculated results were corroborated by experimental data.

Sakai, Takenobu; Somiya, Satoshi

2012-08-01

30

Creep deformation characteristics of modified asphalt and porous asphalt mixture using TPS additive  

Microsoft Academic Search

Creep deformation characteristics of Tafpack Super (TPS) modified asphalt binders and porous asphalt mixtures were investigated in this paper. Dynamic Shear Rheometer (DSR) was chosen to conduct the shear creep test at 20 over a wide range of shear stress to determine the relation between shear creep rate, modulus and TPS modifier percents. Unconfined static uniaxial creep tests were carried

Tingwei Cao; Shaopeng Wu; Qunshan Ye; Xu Huang

2008-01-01

31

Microstructural changes in alloy 625 during high temperature creep  

Microsoft Academic Search

Microstructural changes in the nickel-base alloy 625 during creep deformation have been investigated in the temperature range of 923 to 1148 K for durations from 30 to 31,800h. Intermetallic phases such as ??-phase and ?-phase have been found to precipitate extensively within the austenitic matrix under most of the test conditions. The ??-phase was observed at 973 K and ?-phase

M. D. Mathew; P. Parameswaran; K. Bhanu Sankara Rao

2008-01-01

32

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

NASA Astrophysics Data System (ADS)

Creep of die-cast Mg alloys is described as an integral part of their plastic deformation behavior in terms of stress-strain-rate-strain relations. Creep tests yield information on yield stress, work hardening, maximum deformation resistance (minimum creep rate), and work softening. Testing in compression avoids influences by fracture. Data on the alloy AJ52 (5Al, 2Sr) in the temperature range between 135 C and 190 C are presented and compared to those for AZ91 and AS21. Die-cast Mg-Al alloys consist of fine grains with a grain boundary region containing intermetallic precipitates. Transmission electron microscopic observations indicate that basal glide is the dominant mechanism of deformation being supplemented by nonbasal glide and twinning to maintain compatiblity between the grains. The deformation resistance can be modeled with a composite approach assuming that the grain boundary region is relatively hard due to precipitation of intermetallic phases. The differences in long-term creep resistance at low stress are explained in terms of different strength and stability of precipitates in the different alloys.

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

2005-07-01

33

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

NASA Astrophysics Data System (ADS)

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

Wu, Xijia; Williams, Steve; Gong, Diguang

2012-11-01

34

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

35

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

36

Low stress deformation of garnet by incongruent dissolution precipitation creep  

NASA Astrophysics Data System (ADS)

Microstructures indicating incongruent dissolution precipitation creep of garnet in eclogite-facies graphitic micaschist (Tauern window, Eastern Alps) are investigated. Garnet dissolution is observed where garnet poikiloblasts grown at eclogite facies metamorphism approached each other as a consequence of progressive deformation during exhumation, with estimated P-T-conditions between 570 C, 1.7 GPa and 470 C, 0.9 GPa. The poikiloblasts are separated by a dissolution seam and flanked by strain shadows filled with quartz, white mica, and chlorite; there is no evidence for crystal plastic deformation of garnet. Two cases are investigated: (A) stylolitic contact zone, (B) smooth contact zone. In both cases, internal fabrics of the poikiloblasts and concentric chemical zoning are truncated. Material previously forming inclusions in the garnet poikiloblasts is now passively enriched in a dissolution seam, the original microstructure of fine-grained mica-graphite aggregates remaining preserved. Though microstructures suggest that garnet dissolution was driven by local stress concentration, the level of differential stress remained too low for plastic deformation of the fine-grained white mica-graphite aggregates set free from the stress supporting garnet. Incongruent dissolution precipitation creep appears to be a particularly effective deformation mechanism at low stress in a subduction channel.

Wassmann, Sara; Stckhert, Bernhard

2013-01-01

37

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

SciTech Connect

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

Tribula, D.

1990-06-02

38

On the creep deformation of a cast near gamma TiAl alloy Ti-48Al-1Nb  

SciTech Connect

In this paper, the steady-state creep deformation behavior of a cast two phase gamma TiAl alloy having the composition Ti--48Al--1b (at.%) is studied. Tension creep tests using the stress increment technique ([sigma][sub 1] [lt] [sigma][sub 2] [lt] [sigma][sub 3]) were conducted over the temperature range of 704--850[degrees]C at constant initial applied stress level of 103.4--241.3 MPa. The activation energy for creep over the temperature and stress regime of this study varied from 217.5 kJ/mol (137.8 MPa) up to 341.0 kJ/mol (206.8 MPa) with an average value of 326.4 kJ/mol. This is well within the range of values previously measured for gamma TiAl alloys where creep controlled by volume diffusion has been suggested as rate controlling. The stress exponents measured were 5.0 at 704[degrees]C, 4.9 at 750[degrees]C, 4.7 at 800[degrees]C and 4.46 at 850[degrees]C. Using the activation energy of 326.4 kJ/mol, the temperature compensated steady-state creep rate was plotted against log stress with all temperatures collapsing onto a single line having a slope equal to 4.95. Using conventional creep analysis, this value of the stress exponent can be taken as suggestive of dislocation climb controlled power law creep as the operative deformation mechanism within the stress and temperature regime of the present study. The boundary separating the lamellar grains in two phase gamma TiAl alloys having the duplex microstructure may be a very important aspect of this microstructure with respect to creep deformation resistance.

Hayes, R.W. (Metals Technology, Inc., Northridge, CA (United States)); London, B. (Howmet Corp., Whitehall, MI (United States))

1992-09-01

39

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

NASA Astrophysics Data System (ADS)

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

Reggiani, Barbara; Donati, Lorenzo; Tomesani, Luca

2011-05-01

40

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

41

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

42

Room Temperature Creep Of SiC/SiC Composites  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

43

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

44

Precipitate coarsening-induced plasticity: Low temperature creep behaviour of tempered SAE 52100  

Microsoft Academic Search

Hardened and tempered SAE 52100 under uniaxial compressive loading deforms even at temperatures well below the tempering temperature and compressive loads well below the yield strength. The origin of the observed creep is associated with the coarsening of the nanosized precipitates (cementite, ? and ?). The local volume changes that occur near dissolving and coarsening carbides in the presence of

P. V. Morra; S. Radelaar; M. Yandouzi; J. Chen; A. J. Bttger

2009-01-01

45

The effect of temperature, stress and microstructure on the creep of compact bovine bone.  

PubMed

Creep tests of 117 compact bovine bone specimens were conducted at three temperatures (25, 37, and 43 degrees C), with applied stresses between 71 and 115 MPa. Following testing, the amount of secondary haversian bone in the gage region of the specimens was estimated. The resulting steady-state creep rates (epsilon) were fit to an Arrhenius (e-Qc/RT) model (where Qc is the activation energy for the mechanism(s) controlling creep, R is the gas constant, and T is the absolute temperature) of the type used to describe the classic steady-state creep behavior of metals, ceramics, and metamorphic rocks. The empirical model developed was epsilon = 5.6 x 10(-9) e4.6F sigma 5.2 e-5330/T, where epsilon is the estimated mean steady-state creep rate, F is the volume fraction of secondary haversian bone, sigma is the applied stress, and T is the absolute temperature. There was a positive, significant association between the estimated mean steady-state creep rate and F, sigma, and T. Qc was determined to be 44.3 kJ mol-1, a reasonable value when compared to activation energies for creep in ceramics. It is hypothesized that permanent deformation during creep of compact bovine bone is primarily due to damage mechanisms associated with dislocations in the hydroxyapatite mineral lattice structure. PMID:8468335

Rimnac, C M; Petko, A A; Santner, T J; Wright, T M

1993-03-01

46

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

47

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

48

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

49

Creep behavior of materials for high-temperature reactor application  

SciTech Connect

Materials for high-temperature gas-cooled reactor (HTGR) application are selected according to their creep behavior. For two alloys--Incoloy-800 used for the live steam tubing of the thorium high-temperature reactor and Inconel-617 evaluated for tubings in advanced HTGRs--creep curves are measured and described by equations. A microstructural interpretation is given. An essential result is that nonstable microstructures determine the creep behavior.

Schneider, K.; Hartnagel, W.; Iischner, B.; Schepp, P.

1984-08-01

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

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

SciTech Connect

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

Hsiung, L.M., LLNL

1997-03-01

52

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

53

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

PubMed

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

Taneike, Masaki; Abe, Fujio; Sawada, Kota

2003-07-17

54

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

55

Creep behaviour of Cu-30 percent Zn at intermediate temperatures  

NASA Technical Reports Server (NTRS)

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

Raj, S. V.

1991-01-01

56

High-temperature creep and the defect structure of nickel-based superalloy single crystals after hot isostatic pressing  

NASA Astrophysics Data System (ADS)

The influence of hot isostatic pressing on the high-temperature creep of single crystals of a nickel-based superalloy containing rhenium and ruthenium is studied. The microstructural damages caused by the development of creep have been studied. Hot isostatic pressing is found to weakly influence the life and creep of the superalloy at 1150C. The distribution of deformation pores over the length and cross section of failed samples has been studied. A high pore concentration is shown to exist at the sites of severe plastic deformation.

Svetlov, I. L.; Iskhodzhanova, I. V.; Evgenov, A. G.; Naprienko, S. A.

2012-04-01

57

Creep deformation characteristics of modified asphalt and porous asphalt mixture using TPS additive  

NASA Astrophysics Data System (ADS)

Creep deformation characteristics of Tafpack Super (TPS) modified asphalt binders and porous asphalt mixtures were investigated in this paper. Dynamic Shear Rheometer (DSR) was chosen to conduct the shear creep test at 20 over a wide range of shear stress to determine the relation between shear creep rate, modulus and TPS modifier percents. Unconfined static uniaxial creep tests were carried out to study the relation between compressive creep strain, stiffness modulus and TPS percents in porous asphalt mixture. Test results indicate that the shear creep rate of asphalt binders can be decreased and the shear creep modulus can be increased by the TPS additives. Furthermore, the creep deformation is decreased and the creep stiffness modulus is increased for porous asphalt mixtures containing TPS additives. The difference results from TPS modified asphalt and porous asphalt mixture using TPS additive indicated that the use of TPS as an additive in porous asphalt mixture may decrease the mechanical properties compared with its effect on asphalt as a modifier.

Cao, Tingwei; Wu, Shaopeng; Ye, Qunshan; Huang, Xu

2008-11-01

58

Residual stress analysis in the film/substrate system with the effect of creep deformation  

NASA Astrophysics Data System (ADS)

The physical phenomenon of residual stress relaxation and redistribution in the film/substrate systems due to creep deformation is focused in this work. A new analysis model to elucidate either the film or the substrate subjected to creeping deformation is developed. Specific analyses are made on the NiCrAlY coating-based system and silicon-epoxy bilayer structure. Results reveal that the proposed model can lead to an excellent agreement with the simulated results of finite element method. Furthermore, comparisons among FE results, the present model, and Zhang's creep solution [J. Appl. Phys. 101, 083530 (2007)] have been carried out. Meanwhile, comparisons between Hsueh's viscoelastic solution [J. Appl. Phys. 91, 2760 (2002)] and our current model in the case of creep exponent n=1 have also been conducted. Effects of thickness ratio of the film to the substrate on the stress distribution and the evolution of the accumulated creep strain have also been discussed in this paper.

Chen, Qing-Qi; Xuan, Fu-Zhen; Tu, Shan-Tung

2009-08-01

59

Constitutive representation of high-temperature creep damage  

Microsoft Academic Search

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

K Chan

1988-01-01

60

Biaxial creep of zircaloy: Texture and temperature effects  

SciTech Connect

Zircaloy is commonly used as a cladding material for nuclear fuel elements. The cladding is subject to time-varying multiaxial stresses in service and the ability to accurately predict cladding behavior is necessary to maintain fuel integrity. This work investigates the biaxial creep behavior of recrystallized zircaloy at three temperatures and with four different crystallographic textures. In addition to measuring the creep behavior, the crystallographic texture is used to independently predict the creep behavior. 48 refs.

Daugherty, W.L.

1988-01-01

61

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

62

Environmental effects on ultra-high temperature creep behavior of directionally solidified oxide eutectic ceramics  

Microsoft Academic Search

Experimental studies were undertaken to assess the environmental effects on ultra-high temperature tensile creep behavior of directionally solidified Al2O3\\/Y3Al5O12(YAG) and Al2O3\\/GdAlO3(GAP) eutectic ceramics. Tensile creep deformation tests conducted under constant stress ranging 100200MPa at temperature range of 16731873K at different environmental conditions consisting of air and at different water vapor pressure, pH2O, up to 0.6MPa. These eutectic ceramics exhibited a

Yoshihisa Harada; Takayuki Suzuki; Kazumi Hirano; Narihito Nakagawa; Yoshiharu Waku

2005-01-01

63

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

64

Creep of Austenitic Stainless Steels at Room Temperature.  

National Technical Information Service (NTIS)

A notable characteristic of the room-temperature mechanical behavior of austenitic stainless steels is creep even under moderate loads. The magnitude of this creep has been studied on three steels with 0.06% C, 18% Cr and nickel contents of about 13, 8 an...

D. Rousseau R. Castro R. Tricot

1987-01-01

65

Creep of Carbon Yarns and Composites at High Temperature.  

National Technical Information Service (NTIS)

Creep of mesophase- and rayon-based carbon yarns was measured in 2 to 4 ksi tension from 2100 C to failure (2500-2700 C). Resulting creep rates increased with temperature, and activation energies were lower for mesophase- than for rayon-based yarn. Rates ...

L. A. Feldman

1983-01-01

66

The master curve and the constitutive equation for creep deformation and fracture for Cr-Mo-V steel throughout smooth, notched and precracked specimens  

Microsoft Academic Search

It has been shown experimentally that the master curve for creep deformation versus the ratio of time to fracture time, can be obtained for smooth, notched and precracked specimens of Cr-Mo-V steel, a high-temperature ductile material. A simple unified constitutive equation, i.e. a master curve equation, has been proposed. It is suggested that there is some correlation between the creep

A. T. Yokobori; T. Yokobori; M. Tabuchi

1996-01-01

67

Marine ice deformation experiments: an empirical validation of creep parameters  

NASA Astrophysics Data System (ADS)

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

Dierckx, Marie; Tison, Jean-Louis

2013-01-01

68

Irradiation creep in structural materials at ITER operating conditions.  

National Technical Information Service (NTIS)

Irradiation creep is plastic deformation of a material under the influence of irradiation and stress. Below the regime of thermal creep, there remains a deformation mechanism under irradiation that is weakly temperature dependent and clearly different fro...

M. L. Grossbeck

1994-01-01

69

Serrated creep and spatio-temporal structures of macrolocalized plastic deformation  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

70

High temperature mechanical spectroscopy and creep of calcium hexaluminate  

Microsoft Academic Search

Samples of calcium hexaluminate (CA6) were studied by four-point bending creep tests and mechanical spectroscopy at temperatures between 1300 and 1600K. By using the temperature-compensated time concept, proposed by Dorn (1954, 1956), activation enthalpies of the order of 620kJ\\/mol were deduced from both the isothermal creep and the internal friction measurements. A generic curve, master curve, is obtained by

M. Daraktchiev; R. Schaller; C. Dom??nguez; J. Chevalier; G. Fantozzi

2004-01-01

71

The Effects of Ferrite Content and Morphology on the Mechanical Properties and Room Temperature Creep of Quenched and Tempered SAE 4340 Steel  

NASA Astrophysics Data System (ADS)

The room temperature creep behavior is investigated for a commercial SAE 4340 steel containing small amounts of ferrite. Significant creep deformation occurs at stress levels below 1/3 ?0.2 (The yield strength at 0.2% offset strain). Small amounts of ferrite (0% to 4%) have no influence on the hardness and yield strength. However, these small amounts of ferrite play an important role in controlling the creep resistance. The presence of any ferrite leads to a reduction in the creep resistance. The creep deformation at room temperature increases with an increase in the amount of ferrite. The effects of ferrite morphology and an inhomogeneous microstructure on the creep resistance are discussed.

Liu, Cheng; Bhole, Sanjiwan; Northwood, Derek

72

The effect of heat treatments on microstructures and primary creep deformation of investment cast titanium aluminide alloys and polysynthetically twinned (PST) crystals  

NASA Astrophysics Data System (ADS)

Several heat treatments were developed and applied to several investment cast duplex (equiaxed+lamellar) TiAl alloys (Ti-4547Al-2Nb-2Mn+0.8v%TiB 2XDTM, Ti-47Al-2Nb-2Mn+0.8TiB2XDTM with interstitial elements, Ti-47Al-2Nb-2Cr, and Ti-47Al-2Nb-1Mn-0.5W-0.5Mo-0.2Si) in an effort to enhance creep properties. Creep behavior in polysynthetically twinned (PST) crystals with different orientations was also investigated. Primary creep resistance of W-Mo-Si alloys can be improved by about 10 times with heat treatment, and the XD alloys with additions of interstitials can be improved by about 7 times, and 47-2-2 can be improved by about 3 times, and the XD alloys can be improved slightly, or not at all when the Al level is lower. The variation in creep resistance with heat treatment can be explained by differences observed in the microstructures and textures produced by the various heat treatments. The XD alloys with high O show large lamellar volume fraction (40%), since oxygen is an alpha stabilizer. Observations indicate that strain assisted nucleation and/or growth of precipitates accounts for much of the excellent creep resistance of the W-Mo-Si alloy. The lamellar spacing in lamellar grains systematically decreased by 15--35% with increasing stress, during the first 0.2--0.5% strain at the early stage of primary creep. More refinement of lamellar spacing occurs at lower temperature and higher stress. The refinement process is a consistent microstructural feature during primary creep deformation in all investment cast TiAl alloys. The refinement occurred by mechanical twinning (easy mode deformation) or/and alpha 2 shear transformation parallel to lamellar boundary. The stress exponent and activation energy for creep in the lamellar microstructure depend on the direction of the stress tensor. In comparing activation energies of the early process in primary creep in the W-Mo-Si alloy with creep in the soft orientation in a PST crystal, the activation energies are small, near 150 kJ/mol. This indicated that the early stage deformation in TiAl alloys correlates closely with PST crystal creep in easy mode deformation. From simulations of lamellar refinement, computed local shear strains are similar or higher than effective shear strain. There are some correlations between the computed local shear strain and microstructural changes during primary creep deformation. (Abstract shortened by UMI.)

Seo, Dong Yi

73

High temperature plastic deformation related to grain boundary chemistry in cation-doped alumina  

Microsoft Academic Search

High temperature plastic deformation in fine-grained, polycrystalline alumina often takes place by diffusional creep or grain boundary sliding in a fairly wide stress and temperature range. Under such conditions, the high temperature creep or plastic flow behavior in alumina is sensitively affected by small amount of cation-doping, even in the dopant level of 0.1mol% or less. The dopant effect on

Hidehiro Yoshida; Yuichi Ikuhara; Taketo Sakuma

2004-01-01

74

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

75

Experiment and Simulation Study on the Creep Behavior of PMMA at Different Temperatures  

Microsoft Academic Search

In the present study, creep experiments at different stress and different temperatures were carried out to study the creep behavior of PMMA (MDYB-3). The results show that the creep behavior of PMMA is significantly dependent on temperature in the temperature range of 2075C. It was indicated that the duration curves of creep could be divided into three phases. The Chen

Z. Z. Gao; W. Liu; Z. Q. Liu; Z. F. Yue

2010-01-01

76

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

77

Constitutive representation of high-temperature creep damage  

SciTech Connect

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. 25 references.

Chan, K.S.

1988-01-01

78

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

79

Thermally activated low temperature creep and primary water stress corrosion cracking of NiCrFe alloys.  

National Technical Information Service (NTIS)

A phenomenological SCC-CGR model is developed based on an apriori assumption that the SCC-CGR is controlled by low temperature creep (LTC). This mode of low temperature time dependent deformation occurs at stress levels above the athermal flow stress by a...

M. M. Hall

1993-01-01

80

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.

2013-08-01

81

Experimental deformation of natural dunite: Effects of suppressed diffusion creep on microstructural evolution  

NASA Astrophysics Data System (ADS)

Large strain deformation experiments in torsion were conducted on a coarse grained natural dunite with a pre-existing lattice-preferred orientation (LPO) at T = 1500 K; P = 300 MPa; and strain rates of 5*10-5 - 2*10-4 s-1. The objective of these experiments is to investigate how microstructural evolution occurs when dislocation creep dominates deformation. Hence, experiments were conducted at conditions where deformation by diffusion creep is largely suppressed. Microstructural evolution was studied as a function of strain. We observe that the pre-existing LPO persists to a shear strain of at least 0.5. At larger strains, this LPO is transformed. Relict deformed grains exhibit LPO with [100] crystallographic axes at high angles to the shear plane. Unlike previous experimental studies on finer grained materials, these axes do not readily rotate into the shear plane with increasing strain. Dynamic recrystallization occurs in samples deformed to moderate strains (gamma > 0.5). Recrystallized material forms bands that mostly transect grain interiors. The inhibition of diffusion creep along relict grain boundaries may account for the relatively large strains required to observe evolution of microstructures. Our data support assertions that microstructures may record a long and complicated deformation history. Therefore, observations of LPO and seismic anisotropy may not always reflect the most recent deformation event and must be interpreted carefully.

Skemer, P. A.; Sundberg, M.; Hirth, G.; Cooper, R. F.

2010-12-01

82

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

83

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

84

Stress-induced Mobility in Polymer Glasses During Multistep Creep Deformation  

NASA Astrophysics Data System (ADS)

An optical photobleaching experiment and molecular dynamics simulations have been used to study the changes in segmental dynamics of a polymer glass during uniaxial creep deformation. Both experiment and simulation observe that segmental mobility increases more than a factor of 100 during deformation. Both show a strong correlation between strain rate and mobility in single step creep. However, in multistep creep and recovery, the correlation between strain rate and mobility is broken in both experiment and simulation; this emphasizes that no simple mechanical variable universally exhibits a simple relationship with molecular mobility. Interestingly, in contradiction to the Eyring model, both experiments and simulations show an increase in segmental mobility immediately follows a significant drop in stress.

Lee, Hau-Nan; Paeng, Keewook; Swallen, Stephen; Ediger, Mark; Riggleman, Robert; de Pablo, Juan

2009-03-01

85

Bounds on the Rate of Energy Dissipation in Bodies Deforming by Secondary Creep.  

National Technical Information Service (NTIS)

The present note extends previous methods of bounding the rate of energy dissipation in a body deforming under secondary creep according to a power law (strain-rate tensor = b signa to the n power). By an appropriate definition of the 'representative stre...

W. R. Hodgkins

1964-01-01

86

Thermal Creep Flow of Helium Gas at Cryogenic Temperatures  

NASA Astrophysics Data System (ADS)

We present a molecular dynamics (MD) simulation of nanoscale gas flow due to thermal creep at cryogenic temperatures. Helium is considered because its low liquefying temperature allows a wide range of cryogenic analysis. The thermal creep flow along a nanochannel is generated by applying temperature differences along the channel. Pressure and density variations are measured at various rarefaction conditions, covering the slip flow to the free molecular regimes. Thermo molecular pressure difference (TMPD) values are also calculated. Our results are compared with those in the literature.

Babac, G.; Reese, J. M.

2014-03-01

87

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

88

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

89

Viscoelastic properties of EA951 adhesive: A source of creep deformations of a strongback  

SciTech Connect

Both creep and relaxation functions for EA951 adhesive are presented. During this study, we have found that the adhesive used in the bonding of the facing sheet and the NOMAX of a strongback crept from 0.6% of strain to 2% in about 10 days at room temperature. Other materials, such as F263 epoxy used in the strongbacks, did not creep at room temperature. Therefore, we concluded that the creep in strongbacks observed by Schauer was due to the adhesive. We then recommended that the EA951 adhesive be replaced with FM355 adhesive. The creep phenomenon for the new strongback, constructed with the new adhesive, was eliminated. 2 refs., 8 figs.

Feng, W.W.

1987-09-28

90

High temperature creep of single crystal strontium titanate (SrTiO3): a contribution to creep systematics in perovskites  

Microsoft Academic Search

Compression tests were made on single crystals of SrTiO3 perovskite along the and directions at temperatures of 1473-1793 K (0.64-0.78Tm). The results show a power-law creep behavior with a stress exponent of 3.5 +\\/- 0.1 in both orientations. However, a strong plastic anisotropy has been observed: creep along the orientation is much easier than creep along the orientation. The activation

Zichao Wang; Shun-Ichiro Karato; Kiyoshi Fujino

1993-01-01

91

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

92

High-temperature creep of the perovskites CaTiO3 and NaNbO3  

Microsoft Academic Search

Wright, K., Price, G.D. and Poirier, J.-P., 1992. High-temperature creep of the perovskites CaTiO3 and NaNbO3. Phys. Earth Planet. Inter., 74: 922. We have performed a series of creep experiments on single crystals of the perovskites CaTiO3 and NaNbO3 at temperatures above 0.67 TM. Both are found to deform according to a dislocation-controlled power-law mechanism. Experiments performed on CaTiO3 with

Kate Wright; Geoffrey D. Price; Jean Paul Poirier

1992-01-01

93

Recoverable creep deformation and transient local stress concentration due to heterogeneous grain-boundary diffusion and sliding in polycrystalline solids  

NASA Astrophysics Data System (ADS)

Numerical simulations are used to investigate the influence of heterogeneity in grain-boundary diffusivity and sliding resistance on the creep response of a polycrystal. We model a polycrystal as a two-dimensional assembly of elastic grains, separated by sharp grain boundaries. The crystal deforms plastically by stress driven mass transport along the grain boundaries, together with grain-boundary sliding. Heterogeneity is idealized by assigning each grain boundary one of two possible values of diffusivity and sliding viscosity. We compute steady state and transient creep rates as functions of the diffusivity mismatch and relative fractions of grain boundaries with fast and slow diffusion. In addition, our results show that under transient conditions, flux divergences develop at the intersection between grain boundaries with fast and slow diffusivity, which generate high local stress concentrations. The stress concentrations develop at a rate determined by the fast diffusion coefficient, and subsequently relax at a rate determined by the slow diffusion coefficient. The influence of the mismatch in diffusion coefficient, loading conditions, and material properties on the magnitude of this stress concentration is investigated in detail using a simple model problem with a planar grain boundary. The strain energy associated with these stress concentrations also makes a small fraction of the plastic strain due to diffusion and sliding recoverable on unloading. We discuss the implications of these results for conventional polycrystalline solids at high temperatures and for nanostructured materials where grain-boundary diffusion becomes one of the primary inelastic deformation mechanisms even at room temperature.

Wei, Yujie; Bower, Allan F.; Gao, Huajian

94

Dynamic dislocation effects in low-temperature creep stimulated in ?-tin single crystals by a superconducting transition  

NASA Astrophysics Data System (ADS)

Low-temperature creep of high-purity ?-tin single crystals oriented for plastic slip in the system (100)<010>is studied. The experiments are performed in the temperature interval 0.5temperature. The samples were loaded above the yield stress and nonstationary creep was induced in them by using a magnetic field to induce a transition from the normal (N) into the superconducting (S) state. It is established that the time dependence of the post-NS-transition increase of deformation consists of three stages: transition, exponential, and logarithmic. A theory of creep is developed in the Appendix for a physical interpretation of these stages; the theory is based on the ideas of thermally activated, quantum (tunneling), and dynamic motion of dislocations in a Peierls potential relief taking account of their electronic and radiation drag. The particularities associated with the manifestation of the dynamical properties of the dislocation strings at the individual stages of creep are analyzed in detail. The transition of the samples into a superconducting state sharply decreases the electronic stopping of the dislocations and increases the contribution of the dynamic component of the dislocation flux to the creep rate. Comparing the experimental and theoretical results made it possible to obtain empirical values of some phenomenological parameters of the dislocations of the creep model.

Natsik, V. D.; Soldatov, V. P.; Kirichenko, G. I.; Ivanchenko, L. G.

2009-06-01

95

Elevated temperature creep behavior of Inconel alloy 625  

SciTech Connect

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

Purohit, A.; Burke, W.F.

1984-07-01

96

Reducing the moisture effect on the creep deformation of wood by an irradiation-induced polymer impregnation method  

NASA Astrophysics Data System (ADS)

This paper reports an attempt to reduce the sensitivity of creep deformation to moisture adsorption by impregnating a tropical wood with methyl-methacrylate and subsequent polymerization by ?-irradiation. Beam specimens both of untreated wood and polymer impregnated wood were subjected to a three-point bend creep test under a constant load of 300 N at 23 1C, at three different humidity levels of 50 5, 65 5 and 85 5%. A Norton-Bailey (power law) mathematical model successfully described the creep behaviour, with the creep components determined by a non-linear regression analysis. A significant reduction in the sensitivity of creep deformation to the humidity level was attained for the polymer impregnated wood. This could be explained by the ability of the impregnated polymer to form a strongly adhesive interface with the wood cell material, thereby acting as a physical barrier to reduce the movement of water to and from the wood cell material.

Chia, L. H. L.; Boey, F. Y. C.; Teoh, S. H.

97

Microstructural development of eutectic Bi-Sn and eutectic In-Sn during high temperature deformation  

SciTech Connect

Eutectic Bi-Sn and In-Sn solder joints were subjected to high temperature deformation in shear in order to determine whether microstructural instabilities are generated during testing. Dynamic recrystallization had previously been observed in Sn-Pb solder joints during creep and fatigue in shear. The current study shows that Bi-Sn can recrystallize during deformation in creep or at constant strain rate, whereas no microstructural changes are observed in In-Sn. Recrystallization of Bi-Sn is concentrated in a narrow band along the length of the sample, parallel to the direction of shear strain, similar to behavior in Sn-Pb. The recrystallization appears to proceed by migration of interphase boundaries rather than by a nucleation and growth mechanism. A minimum total strain is required to induce obvious recrystallization in Bi-Sn, independent of applied stress or strain rate. This value of strain is much higher than the strain at initiation of tertiary creep or at the maximum shear stress. Onset of tertiary creep and strain softening occur as a result of nonuniform deformation in the samples that is independent of the microstructural instabilities. The creep behavior of In-Sn is relatively straightforward, with a single creep mechanism operating at all temperatures tested. 36 refs., 13 figs.

Goldstein, J.L.F.; Morris, J.W. Jr. (Lawrence Berkeley Lab., CA (United States) Univ. of California, Berkeley, CA (United States))

1994-05-01

98

Elevated-temperature deformation and forming of aluminum-matrix composites  

SciTech Connect

Three related studies on the elevated-temperature deformation and forming of aluminum-matrix composites are made. In Part A, isothermal creep deformation of SiC whisker-reinforced 2124Al matrix composites (2124Al-SiCw) and a SiC whisker-reinforced aluminum matrix composite (CMSH A-40) are extensively studied at various applied stresses and temperatures. High stress exponents and activation energies for creep are observed to be general features of these composites creep tension. The anomalously high activation energy for creep observed in 2124Al-SiCw composite is partly attributed to the slightly higher activation energy exhibited by the matrix material. In Part B, thermal-cycling creep deformation of 2124Al-SiCw composites, an Al-Si eutectic alloy, and a CMSH A-40 composite is investigated. Thermal cycling can cause MMC's to creep at much higher strain rates and exhibit very high strain rate sensitivity exponent and very high tensile elongation at failure. Part C explores the possibility of using the unique mechanical properties, (e.g. high-strain-rate sensitivity exponent and high formability), which result from thermal cycling to form useful components from MMC's. Experimental results demonstrate that gas-pressure forming of MMC components via thermal cycling is feasible.

Chen, Yongchin.

1991-01-01

99

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

100

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

101

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

102

Thermally activated low temperature creep and primary water stress corrosion cracking of NiCrFe alloys  

Microsoft Academic Search

A phenomenological SCC-CGR model is developed based on an apriori assumption that the SCC-CGR is controlled by low temperature creep (LTC). This mode of low temperature time dependent deformation occurs at stress levels above the athermal flow stress by a dislocation glide mechanism that is thermally activated and may be environmentally assisted. The SCC-CGR model equations developed contain thermal activation

Hall; M. M. Jr

1993-01-01

103

Creep damage prediction of the steam pipelines with high temperature and high pressure  

Microsoft Academic Search

Creep is the significant factor that caused failure of steam pipelines with high temperature and high pressure in the period of long-term service. In this paper, the creep tests were performed at serviced temperature of 520C for 1.25Cr0.5Mo pipe material, and the creep and fracture constants were obtained by fitting the creep test data. Based on the modified KarchanovRabotnov constitutive

Xiao-Chi Niu; Jian-Ming Gong; Yong Jiang; Jun-Tao Bao

2009-01-01

104

Influence of mineral fraction on the rheological properties of forsterite + enstatite during grain-size-sensitive creep: 2. Deformation experiments  

NASA Astrophysics Data System (ADS)

order to understand the effects of secondary minerals on the flow properties of rocks, we have conducted uniaxial compression experiments on polycrystalline forsterite (Fo) + enstatite (En) samples. At constant temperature and strain rate, the flow stress of the samples decreases with increasing enstatite volume fraction ( fEn) for samples with 0 < fEn < 0.5 and increases with increasing fEn for samples with 0.5 < fEn < 1. The values of the preexponential term, stress and grain size exponents, and activation energy in the constitutive equation for a wide range of fEn were determined. Samples with a low fEn(?0.03) deformed at strain rates of 2 10-5 to 2 10-4/s exhibit creep characteristics that correspond to dislocation-accommodated grain boundary sliding creep (i.e., stress exponent, n = 3), whereas diffusion-accommodated grain boundary sliding creep is typical of high fEn samples (i.e., stress exponent, n = 1). The change of flow strength as a function of fEn during grain-size-sensitive creep is primarily due to changes in grain size of both phases and secondarily due to changes in the volume fraction of phases with different flow strengths. Viscosities of all samples can be reproduced in a viscosity model that takes into account (1) the grain sizes estimated by the grain growth laws established in our part 1 paper and (2) flow laws determined for the individual phases, in this case, forsterite and enstatite. Furthermore, we demonstrate that our model can be extended to make predictions of viscosity in other mineral assemblages.

Tasaka, Miki; Hiraga, Takehiko; Zimmerman, Mark E.

2013-08-01

105

A Low-Temperature Creep Experiment Using Common Solder  

NSDL National Science Digital Library

This experiment will help to illustrate creep in metals at room temperature. Step by step instructions are included for instructors to set up specimens to use in the demonstration. This activity would be appropriate for high school and college level students. The lesson should take about one week of class time; the class may spend a few minute per class period observing the experiment. This document will serve as a framework for instructors and may be downloaded in PDF format.

Bunnell, L. R.

2012-11-07

106

High-temperature creep of partially molten plagioclase aggregates  

Microsoft Academic Search

We have investigated the high-temperature creep of synthetic labradorite (An60Ab40) between 1323 K and 1523 K at atmospheric pressure and low stresses (2-65 MPa). Average grain size varies from 12 to 16 mum. Samples contained up to 12 vol% melt (An60Ab40 glass). Fourier transform infrared measurements indicate that trace amounts of water (~0.1-0.15 wt% H2O) were incorporated during crystallization. This

A. Dimanov; G. Dresen; R. Wirth

1998-01-01

107

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

108

Diffusion creep, grain rotation and mantle anisotropy  

NASA Astrophysics Data System (ADS)

The mantle deforms by some combination of diffusion creep and dislocation creep. It is well established that dislocation creep gives rise to crystallographic preferred orientations (CPO) which in turn lead to seismic anisotropy. Consequently seismic anisotropy may be interpreted as indicating the action of dislocation creep, and an absence of anisotropy as indicating diffusion creep. One assumption involved is that diffusion creep and the accompanying grain boundary sliding cause random grain rotations which destroy CPO. So, if a mantle rock has deformed in dislocation creep, developing a CPO, and then moves into a strain rate/temperature/grain size regime promoting diffusion creep as the dominant mechanism, the CPO will be destroyed. Here I test this assumption via a numerical model (named "DiffForm") for diffusion creep. The model is grain- scale and hence predicts the finite rotations of individual grains through time as the polycrystal deforms in grain boundary diffusion creep accompanied by sliding. The rotation evolution depends on the details of the starting microstructure, but for a variety of deformation types and initial microstructures simulations show that the rotation rates decrease through time. At large strains the microstructures reach quasi-steady states in which little further rotation occurs. This implies that diffusion creep can weaken a pre-existing CPO but not destroy it, so regions of anisotropic mantle may, in fact, be deforming by diffusion creep, with the CPO a weakened but still potent inherited feature.

Wheeler, J.

2007-12-01

109

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

NASA Astrophysics Data System (ADS)

We have performed an experimental and textural study to characterize the high-temperature creep behavior of natural diabase rock under dry deformation conditions. Samples of both Maryland diabase and Columbia diabase were investigated to measure the effects of temperature, oxygen fugacity, and ratio of plagioclase to pyroxene on the creep strength. The Maryland diabase is composed of ~56 vol% plagioclase, ~38 vol% augite, ~5 vol% pigeonite, ~1 vol% magnetite-ilmenite, and trace chlorite (altered from pyroxene); the grain size of the plagioclase is ~30 microns x 100 microns, while that of the pyroxenes is ~50 microns. The Columbia diabase is composed of ~70 vol% plagioclase, ~6 vol% augite, ~17 vol% hypersthene, ~3% magnetite-ilmenite, and ~3% chlorite (altered from pyroxene); the grain size of the plagioclase is ~100 microns x 600 microns, while that of the pyroxenes is ~200 microns. Samples of each diabase were heated in a controlled-atmosphere room-pressure apparatus at 1000 degrees C for 50 h under controlled oxygen fugacity conditions, causing the dehydration of the hydrous minerals. In subsequent deformation experiments, the more plagioclase-rich Columbia diabase (Mackwell et al. 1995) has a significantly lower strength than the more pyroxene-rich Maryland diabase.

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

1996-03-01

110

Internal stress during high-temperature creep of special grade hastelloy X alloys  

NASA Astrophysics Data System (ADS)

Creep tests and the measurement of internal stress during creep were performed at 900C for Hastelloy XR and XR-II, i.e. versions of Hastelloy X modified for nuclear applications. Creep rupture time and steady-state creep rate were influenced by the boron content, grain size and heat-treatment temperature of the alloys. It is shown that the difference in the steady-state creep rate is caused by the internal stress dependent on the boron content, grain size and solution-treatment temperature.

Kurata, Yuji; Ogawa, Yutaka

1988-09-01

111

Creep response of the lunar crust in mare regions from an analysis of crater deformation  

NASA Technical Reports Server (NTRS)

The settling trends of 318 lunar mare craters are compared with predictions of numerical finite-element models in order to determine the creep response of the upper lunar mare crust. No settling is evident in craters smaller than 5 km in diameter. Settling rates of larger craters increase as function of crater size in a manner suggesting a nonlinear lunar creep response corresponding to the power law epsilon = 8.3 x 10 to the minus 34th sigma squared where epsilon is the strain rate and sigma is the differential stress. However, the observed nonlinearity is probably an apparent nonlinearity resulting from the temperature-induced viscosity decrease with depth due to a lunar crustal temperature gradient of 3 C/km and a creep activation energy of 20 kcal/mole. It is concluded that creep in the lunar medium is essentially Newtonian, and that the effective viscosity of the upper lunar mare is (1.6 plus or minus 0.3) x 10 to the 25th poise.

Kunze, A. W. G.

1974-01-01

112

Microstructure and dislocation analysis after creep deformation of die-cast MgAlSr (AJ) alloy  

Microsoft Academic Search

The microstructure and creep behavior of Mg\\/Al composite crankcases cast with three alloy formulations of the MgAlSr alloy AJ62 have been investigated. Overall 12 components were used within this study. Multi-level creep tests were conducted to evaluate the creep properties at stresses up to 90MPa and temperatures up to 473K. Microstructure observations including phase characterization and in-depth dislocation analyses were

Martin Kunst; Andreas Fischersworring-Bunk; Gilles LEsperance; Philippe Plamondon; Uwe Glatzel

2009-01-01

113

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

114

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

115

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

116

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

NASA Astrophysics Data System (ADS)

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

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

117

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

NASA Astrophysics Data System (ADS)

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

Dyson, B. F.; Osgerby, D.

118

Elevated Temperature Tensile and Creep Properties of M-252 (Bar), Inconel 700 (Bar), and Inconel 713 (Cast) Nickel Base Alloys.  

National Technical Information Service (NTIS)

Room and elevated temperature tensile and elevated temperature creep properties to 1000 hours were determined at three representative application temperatures for M-252 (bar), Inconel 700 (bar), and Inconel 713 (cast). Tabulated tensile and creep data, de...

S. O. Davis

1964-01-01

119

Analysis of creep curves of a nickel base superalloy in a wide stress\\/temperature range  

Microsoft Academic Search

The creep behaviour of the nickel base superalloy Nimonic 263 has been studied at constant load and temperature in the 75030MPa\\/600950C range. The experimental results have shown a very strong dependence of the creep curve shape with the applied stress\\/temperature. At high stresses, when an instantaneous plastic strain occurs during the initial loading, the creep curves are characterised by an

M. Maldini; G. Angella; V. Lupinc

2007-01-01

120

Effect of normalization temperature on the creep strength of modified 9Cr1Mo steel  

Microsoft Academic Search

The effect of normalization temperature from 850 C to 1050 C on the structure and creep-rupture properties of modified 9Cr-1Mo\\u000a steel was studied. Normalization at temperatures below 925 C resulted in structures containing significant polygonized, recovered\\u000a ferrite. The ferrite structures had poor creep-rupture strength: roughly two orders of magnitude increase in minimum creep\\u000a rate or decrease in rupture life for

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

2006-01-01

121

Creep rupture of copper and aluminium alloy under combined loadingsexperiments and their various descriptions  

Microsoft Academic Search

Creep tests are carried out under tension, pure torsion, and combined tension and torsion at an elevated temperature of 523K for pure copper and 423K for an aluminium alloy. Different creep and rupture properties of the materials are observed throughout the deformation process under the different stress states. The effects of stress states on primary creep, secondary creep, the failure

J. Lin; Z. L. Kowalewski; J. Cao

2005-01-01

122

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

123

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

124

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

125

Elevated Temperature Behavior of Creep and Fatigue in Welded P92 Steel  

Microsoft Academic Search

Fatigue strength and life of weldment at high temperature is very important for high temperature materials used in power plants. In this study, creep properties of weld metal, HAZ and base metal of P92 steel were evaluated by SP (small punch) creep test method. Fatigue crack growth behaviors in weld metal, HAZ and base metal of P92 steel were investigated

Byeongsoo Lim; Bumjoon Kim; Moonhee Park; Sungjoon Won

2003-01-01

126

Creep and fatigue properties of high temperature silicides and their composites  

Microsoft Academic Search

A review of creep and fatigue behavior of high temperature silicides and their composites is presented along with new results pertaining to titanium silicides and functionally graded materials. The emphasis was placed on the molybdenum disilicides and their composites in comparison to other silicides and high temperature ceramics. It was shown that the grain size effects on creep are significant

K. Sadananda; C. R. Feng; R. Mitra; S. C. Deevi

1999-01-01

127

Creep and creep-rupture behavior of Alloy 718  

SciTech Connect

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

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

1991-01-01

128

The high-temperature creep behavior of nickel-rich Ni-W solid solutions  

Microsoft Academic Search

The steady-state creep behavior of four nickel-rich Ni-W solid solutions (1, 2, 4, and 6 wt pct W) was investigated in the temperature range 850 to 1050C. Constant stress tensile creep tests were performed in vacuum in the stress range 3000 to 7000 psi. Activation energies for creep were observed to be 71.4 2.0, 74.4 3.0, and 75.8

W. R. Johnson; C. R. Barrett; W. D. Nix

1972-01-01

129

The high-temperature creep behavior of nickel-rich Ni-W solid solutions  

Microsoft Academic Search

The steady-state creep behavior of four nickel-rich Ni-W solid solutions (1, 2, 4, and 6 wt pct W) was investigated in the\\u000a temperature range 850 to 1050C. Constant stress tensile creep tests were performed in vacuum in the stress range 3000 to\\u000a 7000 psi. Activation energies for creep were observed to be 71.4 2.0, 74.4 3.0, and 75.8

W. R. Johnson; C. R. Barrett; W. D. Nix

1972-01-01

130

Creepfatigue behavior at high temperature of a UDIMET 720 nickel-base superalloy  

Microsoft Academic Search

High temperature fatigue and creepfatigue properties of the wrought nickel-base superalloy Udimet 720 have been investigated. Tests have been performed in air at 700C under stress control with a triangular signal for fatigue and with a trapezoidal one for creepfatigue. The creep influence has been studied up to the failure for dwell times ranging from 1 to 50s. The dislocation

T. Billot; P. Villechaise; M. Jouiad; J. Mendez

2010-01-01

131

Effect of notches on high temperature fatigue\\/creep behaviour of CMSX-4 superalloy single crystals  

Microsoft Academic Search

Effect of notches on high temperature fatigue\\/creep strength of CMSX-4 single crystals has been investigated. Cylindrical bars of the orientation ?001? with circumferential notches were tested at 850 C under constant loads both without and with superimposed high frequency cyclic loads. Under creep conditions, the notched specimens exhibit a longer creep lifetime than the smooth specimens for the same net-section

P. Luk; P. Preclk; L. Kunz; J. ?adek; M. Svoboda

2002-01-01

132

Creep rupture analysis of a beam resting on high temperature foundation  

NASA Technical Reports Server (NTRS)

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

Gu, Randy J.; Cozzarelli, Francis A.

1988-01-01

133

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

NASA Astrophysics Data System (ADS)

Modified 9Cr-1 Mo (Grade 91) steel is currently considered as a candidate material for reactor pressure vessels (RPVs) and reactor internals for the Very High Temperature Reactor (VHTR), and in fossil-fuel fired power plants at higher temperatures and stresses. The tensile creep behavior of Grade 91 steel was studied in the temperature range of 600C to 750C and stresses between 35 MPa and 350 MPa. Heat treatment of Grade 91 steel was studied by normalizing and tempering the steel at various temperatures and times. Moreover, Thermo-Ca1c(TM) calculation was used to predict the precipitate stability and their evolution, and construct carbon isopleths of Grade 91 steel. Residual stress distribution across gas tungsten arc welds (GTAW) in Grade 91 steel was measured by the time-of-flight neutron diffraction using the Spectrometer for Materials Research at Temperature and Stress (SMARTS) diffractometer at Lujan Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, NM, USA. Analysis of creep results yielded stress exponents of 9-11 in the higher stress regime and 1 in the lower stress regime. The creep behavior of Grade 91 steel was described by the modified Bird-Mukherjee-Dorn relation. The rate-controlling creep deformation mechanism in the high stress regime was identified as the edge dislocation climb with a stress exponent of n = 5. On the other hand, the deformation mechanism in the Newtonian viscous creep regime (n = 1) was identified as the Nabarro-Herring creep. Creep rupture data were analyzed in terms of Monkman-Grant relation and Larson-Miller parameter. Creep damage tolerance factor and stress exponent were used to identify the cause of creep damage. The fracture surface morphology of the ruptured specimens was studied by scanning electron microscopy to elucidate the failure mechanisms. Fracture mechanism map for Grade 91 steel was developed based on the available material parameters and experimental observations. The microstructural evolution of heat treated steel was correlated with the differential scanning calorimetric study. The combination of microstructural studies with optical microscopy, scanning and transmission electron microscopy, microhardness profiles, and calorimetric plots helped in the understanding of the evolution of microstructure and precipitates in Grade 91 steel. The residual stresses were determined at the mid-thickness of the plate, 4.35 mm and 2.35 mm below the surface of the as-welded and post-weld heat treated plate. The residual stresses of the as-welded plate were compared with the post-weld heat treated plate. The post-weld heat treatment significantly reduced the residual stress in the base metal, heat affected zone, and the weld zone. Vickers microhardness profiles of the as-welded, and post-weld heat treated specimens were also determined and correlated with the observed residual stress profile and microstructure.

Shrestha, Triratna

134

Short-term creep and creep limit on the base of 110 sec of technically pure tungsten and alloy of the system W-HfC-HfO 2 at high temperatures  

Microsoft Academic Search

deformed state in the temperature range 1773-3023~ it was established that alloying of PM tungsten with up to 0.5-]~0% particles of hafnium or yttrium o>:,ides reduces its time to rupture by a factor of 1.5-3 and increases by a factor of ].5-6.0 the rate of steady creep [3]. The assumption was voiced that when tungsten contains particles of high melting

V. V. Bukhanovskii; V. K. Kharchenko; K. B. Povarova; E. K. Zavarzina; A. B. Ol'shanskii

1987-01-01

135

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

Microsoft Academic Search

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

Shantung Tu; Guoyan Zhou

2009-01-01

136

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

137

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

138

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

Microsoft Academic Search

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

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

2001-01-01

139

Dependence of irradiation creep on temperature and atom displacements in 20% cold worked type 316 stainless steel  

Microsoft Academic Search

Irradiation creep studies with pressurized tubes of 20 percent cold worked Type 316 stainless steel were conducted in EBR-2. Results showed that as atom displacements are extended above 5 dpa and temperatures are increased above 375C, the irradiation induced creep rate increases with both increasing atom displacements and increasing temperature. The stress exponent for irradiation induced creep remained near unity.

1976-01-01

140

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

141

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

142

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

143

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

NASA Astrophysics Data System (ADS)

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

Khabaz, Fardin; Khare, Ketan S.; Khare, Rajesh

2014-05-01

144

Creep and tensile behaviors of FeCrAl foils and laser microwelds at high temperature  

Microsoft Academic Search

We examine a FeCrAl foil-based material and a continuous-wave laser weld generated in ultra-fine keyhole mode undergoing tensile and creep-tension tests over a temperature range of 251000C. At all temperatures, the bead exhibits superior tensile resistance than the base material due to a homogenous reprecipitation of fine aluminum nitrides, AlN, but creeps faster at 900C, because of a finer-grained microstructure

Haitham El Kadiri; Yves Bienvenu; Kiran Solanki; Mark F. Horstemeyer; Paul T. Wang

2006-01-01

145

Effect of austenization temperature on creep resistance of steel 10Kh9V2MFBR  

Microsoft Academic Search

The effect of austenization temperature on the microstructure and on the time to failure due to creep of steel 10Kh9V2MFBR\\u000a is studied. The microstructure and the mechanical properties of the metal are determined after tempering at 730C preceded\\u000a by normalizing from 1050 and 1150C. It is shown that in order to attain the highest creep resistance the austenization temperature\\u000a of

V. A. Dudko; R. O. Kaibyshev; A. N. Belyakov; V. N. Skorobogatykh; I. A. Shchenkova

2010-01-01

146

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

Microsoft Academic Search

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

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

2011-01-01

147

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

148

A universal law for high-temperature diffusion controlled transient creep  

NASA Astrophysics Data System (ADS)

IT IS suggested that transient creep at high temperatures arises principally as a result of the dispersal of entanglements by the climb mechanism. The dispersal of the entanglements is assumed to follow a unimolecular reaction kinetics with a rate constant that depends on stress and temperature in the same way as does the secondary creep rate. The analysis shows that the strain (?) versus time ( t) relation can be represented by ?=? 0+?. 3t+ {?-1}/{K}[1- exp(-K ??3t)] , where ?0 is the instantaneous strain on loading, ??3, the secondary creep rate, K ??3 the rate constant, and ? the ratio of initial to secondary creep rate. The experimental creep data on several b.c.c. and f.c.c. metals and alloys correlate quite well with the proposed mechanism. The constants ? and K were found to be independent of temperature and stress. The proposed formulation becomes inapplicable for correlating creep data in polycrystals at low stresses because of the significant contribution of grain-boundary sliding to the total creep at these stress levels.

Amin, K. E.; Mukherjee, A. K.; Dorn, J. E.

1970-12-01

149

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

150

A strain energy density method for the prediction of creepfatigue damage in high temperature components  

Microsoft Academic Search

The accumulation of creepfatigue damage over time is the principal damage mechanism which will eventually lead to crack initiation in critical high temperature equipment. A model has been developed that assumes on a macroscopic level that the energy dissipated in the material may be taken as a measure of the creep damage induced in the material and hence the creep

Warwick M. Payten; David W. Dean; Ken U. Snowden

2010-01-01

151

Damage analysis and life prediction of a main steam pipeline at elevated temperature based on creep damage mechanics  

Microsoft Academic Search

Main steam pipelines are important components of power plants and chemical plants, which operated at elevated temperature and high pressure for the long term. Creep is a potential mechanism of failure of these pipelines. In this paper, the modified Karchanov-Rabotnov creep damage constitutive equation has been incorporated into finite element program ABAQUS through its user subroutine to predict the creep

L. Y. Geng; J. M. Gong; D. Liu; Y. Jiang

2009-01-01

152

Microstructural evolution in a ferritic-martensitic stainless steel and its relation to high-temperature deformation and rupture models  

SciTech Connect

The ferritic-martensitic stainless steel HT-9 exhibits an anomalously high creep strength in comparison to its high-temperature flow strength from tensile tests performed at moderate rates. A constitutive relation describing its high-temperature tensile behavior over a wide range of conditions has been developed. When applied to creep conditions the model predicts deformation rates orders of magnitude higher than observed. To account for the observed creep strength, a fine distribution of precipitates is postulated to evolve over time during creep. The precipitate density is calculated at each temperature and stress to give the observed creep rate. The apparent precipitation kinetics thereby extracted from this analysis is used in a model for the rupture-time kinetics that compares favorably with observation. Properly austenitized and tempered material was aged over times comparable to creep conditions, and in a way consistent with the precipitation kinetics from the model. Microstructural observations support the postulates and results of the model system. 16 refs., 10 figs.

DiMelfi, R.J.; Gruber, E.E.; Kramer, J.M.

1991-01-01

153

The Effects of Small Deformation on Creep and Stress Rupture of ODS Superalloys.  

National Technical Information Service (NTIS)

This research program aims to enhance understanding of the effects of predeformation on the creep and stress rupture of oxide dispersion strengthened (ODS) alloys and also of the cyclic creep and cyclic stress rupture behavior of ODS alloys. During the th...

T. E. Howson V. Nardone J. K. Tien

1982-01-01

154

Creep deformation mechanism of cryomilled NiCrAlY bond coat material  

Microsoft Academic Search

The effect of cryomilled bond coat material (MCrAlY) on the improvement of service life of Thermal Barrier Coatings (TBCs) was investigated. Creep resistance of the bond coat was greatly increased by the dispersoids formed during cryomilling. The creep mechanisms were found to be based on dislocation detachment from dispersoids for the cryomilled sample and grain boundary sliding for the conventional

Leonardo Ajdelsztajn; Dustin Hulbert; Amiya Mukherjee; Julie M. Schoenung

2007-01-01

155

Elevated Temperature Deformation of Structural Steel,  

National Technical Information Service (NTIS)

The results of tensile and creep tests on steels close to the American specification for ASTM A36 have been used to formulate an equation from which elastic, plastic, creep and total strains can be calculated. Correlations between measured and predicted s...

B. A. Fields R. J. Fields

1989-01-01

156

Room-temperature indentation creep of lead-free Sn5%Sb solder alloy  

Microsoft Academic Search

Creep behavior of the lead-free Sn-5%Sb solder alloy was studied by long-time Vickers indentation testing at room temperature.\\u000a Four different conditions of the material were examined. These were unhomogenized cast (UC), homogenized cast (HC), unhomogenized\\u000a wrought (UW), and homogenized wrought (HW) conditions. Based on the steady-state power-law creep relationship, the stress\\u000a exponents were determined through different methods of analysis, and

A. R. Geranmayeh; R. Mahmudi

2005-01-01

157

High-temperature creep and long-term strength of structural elements under cyclic loading  

Microsoft Academic Search

We present a method for solving problems of high-temperature cyclic creep and damage accumulation in structural elements.\\u000a The asymptotic expansion and averaging techniques both over the period of forced vibrations of a body and that of slowly varying\\u000a loads are used for the set of equations describing the creep and damage processes in thin-walled structural elements.

D. V. Breslavsky; O. K. Morachkovsky; O. A. Tatarinova

2008-01-01

158

Effect of precipitates on long-term creep deformation properties of P92 and P122 type advanced ferritic steels for USC power plants  

Microsoft Academic Search

Long-term creep rupture strengths and the microstructural stability of ASME P92 and P122 pipes have been studied using creep testing at the temperatures from 550 to 700C and detailed scanning transmission electron microscopy. Creep rupture strength of P92 is found to be more stable than that of P122 at temperatures over 600C, which is mainly due to the difference in

M. Yoshizawa; M. Igarashi; K. Moriguchi; A. Iseda; Hassan Ghassemi Armaki; K. Maruyama

2009-01-01

159

On the response of rockglacier creep to surface temperature increase  

Microsoft Academic Search

Besides its thermal characteristics creeping mountain permafrost is substantially defined by its kinematics. Due to the in general considerable ice content of rockglaciers, their dynamics respond sensitively to climate forcing. Questions arise how rockglaciers react to the current or recent climatic changes, and what the further consequences of such reactions could be. Using a one-dimensional thermo-mechanically coupled numerical

Andreas Kb; Regula Frauenfelder; Isabelle Roer

2007-01-01

160

The Creep of Single Crystals of Aluminum  

NASA Technical Reports Server (NTRS)

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

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

1953-01-01

161

High Temperature Deformation of Omphacite in Eclogite: Implications for Subducted Lithosphere  

NASA Astrophysics Data System (ADS)

Omphacite is a major component mineral in subducted oceanic crust at depth. It often develops strong lattice preferred orientation and dominates the flow properties and seismic anisotropy in eclogite. Investigation on the rheology of omphacite is important for a better understanding of geodynamic problems associated with eclogite in subduction zones. The high temperature deformation behavior of polycrystalline omphacite (Di58Jd42) is being studied at temperatures of 1300-1500 K, a confining pressure of 3 GPa, and strain rates of 10-4/s to 10-5/s. We obtained a power-law creep for the high temperature deformation of omphacite with n=3.1, Q=289 KJ/mol, and a preexponential factor of 10-1.2MPa-ns-1. These results show that the creep strength of omphacite falls between its two end members of solid solution (diopside and jadeite), which supports the previous arguments that sodic pyroxene could be significantly weaker than other pyroxenes (enstatite and diopside). A steady increase of flow strength is also observed after adding garnet. Eclogite reconstituted from powders of 50% garnet (Pry21Alm18Gro61), 40% omphacite (Di58Jd42), 10% quartz shows strength about 3 times that of polycrystalline omphacite. These data are consistent with observations of extensive deformation of omphacite in eclogite at low peak metamorphism temperatures during deep subduction and exhumation. These preliminary results also suggest that strain will concentrate into omphacite-rich domains within the subducting zones.

Zhang, J.; Green, H. W.; Jung, H.

2003-12-01

162

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

163

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

164

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

165

Oxidation and creep failure of alloy 617 foils at high temperature  

NASA Astrophysics Data System (ADS)

The microstructure of thermally grown oxides (TGO) and the creep properties of alloy 617 were investigated. Oxidation and creep tests were performed on 100 ?m thick foils at 800-1000 C in air environment, while the thickness of TGO was monitored in situ. According to energy dispersive X-ray (EDX) mapping micrographs observation, superficial dense oxides, chromia (Cr 2O 3), which was thermodynamically unstable at 1000 C, and discrete internal oxides, alumina (?-Al 2O 3), were found. Consequently, the weight of the foil specimen decreased due to the spalling and volatilization of the Cr 2O 3 oxide layer after an initial weight-gaining. Secondary and tertiary creeps were observed at 800 C, while the primary, secondary and tertiary creeps were observed at 1000 C. Dynamic recrystallization occurred at 800 C and 900 C, while partial dynamic recrystallization at 1000 C. The apparent activation energy, Qapp, for the creep deformation was 271 kJ/mol, which was independent of the applied stress.

Sharma, S. K.; Ko, G. D.; Li, F. X.; Kang, K. J.

2008-08-01

166

High-Temperature Deformation and Ductility of a Modified 5083 Al Alloy  

NASA Astrophysics Data System (ADS)

The high-temperature deformation of a 5.5% Mg and 0.6% Ca modified 5083 aluminum alloy was investigated in the temperature range from 573 to 723 K at strain rates in the range of 10-5-10-1 s-1. Ca was added to form an insoluble second phase in the range of temperatures tested to improve the high-temperature characteristics of this alloy. It was shown that the deformation behavior of the alloy could be divided into two regions with stress exponent, n of 3.5 and 13 at low and high strain rates, respectively. The apparent activation energy determined in both regions suggested that the deformation process is diffusion controlled in both regions. The slightly high value of n at the low-strain rate region (viscous glide) was attributed to the presence of threshold stress. The values of threshold stress showed an exponential increase with decreasing temperature and a dependence with an energy term Qo = 16.5 kJ mol-1. Analysis of creep data in terms of threshold stress and using diffusivity of Mg in normalizing the strain rates, revealed two types of deformation behavior. At high values of normalized strain rate (kT} {DGb}}} > 10^{{ - 9}} ), a high value of stress exponent of n = 10 is observed, and the exponential law creep takes place. At low normalized strain rates ?10-9, the n value is 3 and the true activation energy, Q, is equal to 123 kJ mol-1 suggesting viscous glide of dislocations as rate-controlling mechanism. Enhanced ductility has been observed in the region of viscous-glide controlled deformation as a result of high strain-rate sensitivity.

El-Danaf, Ehab A.; Almajid, Abdulhakim A.; Soliman, Mahmoud S.

2008-08-01

167

Analysis of slip activity and heterogeneous deformation in tension and tension-creep of Ti5Al2.5Sn (wt %) using in-situ SEM experiments  

Microsoft Academic Search

The deformation behavior of a Ti5Al2.5Sn (wt %) near-? alloy was investigated during in-situ deformation inside a scanning electron microscope. Tensile experiments were performed at 296?K and 728?K (?0.4?Tm), while tensile-creep experiments were performed at 728?K and 763?K. Active deformation systems were identified using electron backscattered diffraction-based slip trace analysis. Both basal and prismatic slip systems were active during the

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

2012-01-01

168

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

169

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

NASA Astrophysics Data System (ADS)

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

Trepmann, Claudia

2014-05-01

170

High temperature deformation processing of Monel K-500  

Microsoft Academic Search

High temperature deformation processing behavior of Monel K-500 has been studied using uniaxial compression testing performed at temperatures from 1088 to 1533 K and strain rates ranging from 0.001 to 10\\/s. Post deformation microstructural examination to correlate the flow behavior has also been conducted. The results of the mechanical testing have been correlated with presently available deformation mechanism models for

Prabir K. Chaudhury; K. G. Anand; G. Holt; J. J. Valencia

1992-01-01

171

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

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

172

Short-Time Creep Behavior of Carbon, Graphite, and Silica Phenolic Composites at Elevated Temperatures.  

National Technical Information Service (NTIS)

Short-time tensile creep behavior of carbon, graphite, and silica phenolics at elevated temperatures was determined for durations up to 40 sec. A plasma arc was used as a heat source, with test temperatures ranging from 1095 to 2760C. The results show app...

A. Ching J. D. Buch

1970-01-01

173

Thermally activated low temperature creep and primary water stress corrosion cracking of NiCrFe alloys  

SciTech Connect

A phenomenological SCC-CGR model is developed based on an apriori assumption that the SCC-CGR is controlled by low temperature creep (LTC). This mode of low temperature time dependent deformation occurs at stress levels above the athermal flow stress by a dislocation glide mechanism that is thermally activated and may be environmentally assisted. The SCC-CGR model equations developed contain thermal activation parameters descriptive of the dislocation creep mechanism. Thermal activation parameters are obtained by fitting the CGR model to SCC-CGR data obtained on Alloy 600 and Alloy X-750. These SCC-CGR activation parameters are compared to LTC activation parameters obtained from stress relaxation tests. When the high concentration of hydrogen at the tip of an SCC crack is considered, the SCC-CGR activation energies and rate sensitivities are shown to be quantitatively consistent with hydrogen reducing the activation energy and increasing the strain rate sensitivity in LTC stress relaxation tests. Stress dependence of SCC-CGR activation energy consistent with that found for the LTC activation energy. Comparisons between temperature dependence of the SCC-CGR stress sensitivity and LTC stress sensitivity provide a basis for speculation on effects of hydrogen and solute carbon on SCC crack growth rates.

Hall, M.M. Jr.

1993-10-01

174

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

175

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

SciTech Connect

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

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

1990-01-01

176

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

177

Nanogranular origin of concrete creep  

PubMed Central

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

Vandamme, Matthieu; Ulm, Franz-Josef

2009-01-01

178

Investigation of stress exponent in the room-temperature creep of Sn40Pb2.5Sb solder alloy  

Microsoft Academic Search

Creep behavior of Sn40%Pb2.5%Sb peritectic solder alloy having two different grain sizes was studied by indentation, impression, stress relaxation and conventional creep tests at room temperature (T>0.65Tm) in order to evaluate the correspondence of the creep results. Stress exponent values have been determined through these methods and in all cases the calculated exponents are in good agreement. The stress exponent

R. Mahmudi; A. Rezaee-Bazzaz; H. R. Banaie-Fard

2007-01-01

179

The deformation mechanisms of superplasticity  

Microsoft Academic Search

Under various conditions of stress and temperature various deformation mechanisms could be rate-controlling for superplastic deformation. In general at low stresses diffusion creep should be rate-controlling. At temperatures between approximately 40 and 65 pct of the absolute melting point grain boundary diffusion should be the dominant diffusion path while at higher temperatures volume diffusion should dominate. At intermediate stresses, grain

H. W. Hayden; S. Floreen; P. D. Goodell

1972-01-01

180

Creep failures of overheated boiler, superheater and reformer tubes  

Microsoft Academic Search

Internally pressurised tubes are critical components in heat-exchanger applications, such as boiler water tubes, steam superheater elements and chemical plant reformer tubes. Tubes in such applications are vulnerable to temperature excursions: as a consequence the material may enter the creep regime, and creep deformation (bulging) and even fracture (longitudinal rupture) may subsequently occur, with serious consequences. It is estimated that

D. R. H. Jones

2004-01-01

181

Power-law creep model for densification of powder compacts  

Microsoft Academic Search

Densification behaviour of powder compacts by power-law creep during pressure-assisted compaction at an elevated temperature was investigated. A constitutive model was proposed for the densification behavior of powder compacts under a power-law creep situation based on the plastic deformation theory for porous materials which satisfies the uniaxial stress condition. The proposed power-law creep model is compared with Shima and Oyanes

Hyoung Seop Kim; Dong Nyung Lee

1999-01-01

182

INVESTIGATIONS OF CREEP BEHAVIOR OF STRUCTURAL JOINTS UNDER CYCLIC LOADS AND TEMPERATURES  

Microsoft Academic Search

Eighty-two structural joint specimens were tested to evaluate the ; effects of cyclic loads and cyclic temperatures on creep and rupture. The ; specimens included riveted points of 2024-T3 clad aluminum alloy, and riveted and ; spot-welded joints of 17-7 PH (TH 1050) stainless steel. The results of these ; tests show a wide variance but indicate certain trends which

L. Mordfin; N. Halsey; G. E. Greene

1959-01-01

183

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

184

High Temperature in-Reactor Creep of 20% Cold Worked FTR Cladding.  

National Technical Information Service (NTIS)

The in-reactor creep behavior of 20% cold worked Type 316 stainless steel tubing was investigated at temperatures ranging from 410 to 720 exp 0 C for neutron fluences up to 5 x 10 exp 22 n/cm exp 2 (E > 0.1 MeV) in the experimental breeder reactor (EBR-II...

E. R. Gilbert A. J. Lovell B. A. Chin

1977-01-01

185

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

186

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

NASA Astrophysics Data System (ADS)

Optimization of the high-temperature structural properties of continuous silicon carbide fiber, silicon carbide matrix composites (SiC/SiC) requires a fundamental understanding of the relationship between fiber, matrix, and interface properties. Results of a study aimed at relating the fiber creep rate to the subcritical crack growth (SCG) rate and fracture properties of SiC/SiC composites have demonstrated that the crack growth rate in a bulk composite is controlled by the fiber creep rate. This result was demonstrated for Nicalon-CG and Hi-Nicalon fiber reinforced material where a 100C shift in the creep strength of the fiber resulted in a similar shift in the crack growth rate of the composite. Irradiation enhanced creep of SiC fibers and matrix must also be considered in the performance assessment of SiC/SiC composites. An estimate of the impact of irradiation creep of SiC fibers on the SCG of SiC/SiC will be presented.

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

1998-10-01

187

Extension of viscoplasticity based on overstress to capture the effects of prior aging on the time dependent deformation behavior of a high-temperature polymer: Experiments and modeling  

Microsoft Academic Search

The inelastic deformation behavior of PMR-15 neat resin, a high-temperature thermoset polymer, was investigated at 288 C. The experimental program was designed to explore the influence of strain rate on tensile loading, unloading, and strain recovery behaviors. In addition, the effect of the prior strain rate on the relaxation response of the material, as well as on the creep behavior

Amber J. W. McClung

2008-01-01

188

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

NASA Technical Reports Server (NTRS)

A Cu-8 at.% Cr-4 at.% Nb (Cu-8 Cr-4 Nb) alloy is under development for high-temperature, high heatflux applications, such as actively cooled, hypersonic vehicle heat exchangers and rocket engine combustion chambers. Cu-8 Cr-4 Nb offers a superior combination of strength and conductivity. It has also shown exceptional low-cycle fatigue properties. Following preliminary testing to determine the best processing route, a more detailed testing program was initiated to determine the creep lives and creep rates of Cu-8 Cr-4 Nb alloy specimens produced by extrusion. Testing was conducted at the NASA Lewis Research Center with constant-load vacuum creep units. Considering expected operating temperatures and mission lives, we developed a test matrix to accurately determine the creep properties of Cu-8 Cr-4 Nb between 500 and 800 C. Six bars of Cu-8 Cr-4 Nb were extruded. From these bars, 54 creep samples were machined and tested. The figure on the left shows the steady-state, or second-stage, creep rates for the samples. Comparison data for NARloy-Z (Cu-3 wt % Ag-0.5 wt % Zr), the alloy currently used in combustion chamber liners, were not unavailable. Therefore the steady-state creep rates for Cu at similar temperatures are presented. As expected, in comparison to pure Cu, the creep rates for Cu-8 Cr-4 Nb are much lower. The lives of the samples are presented in the figure on the right. As shown, Cu-8 Cr-4 Nb at 800 C is comparable to NARloy-Z at 648 C. At equivalent temperatures, Cu-8 Cr-4 Nb enjoys a 20 to 50 percent advantage in stress for a given life and 1 to 3 orders of magnitude greater life at a given stress. The improved properties allow for design tradeoffs and improvements in new and existing heat exchangers such as the next generation of combustion chamber liners. Average creep rates for Cu-8 Cr-4 Nb and pure Cu are shown. Average creep lives for Cu-8 Cr- 4 Nb and NARloy-Z are also shown. Currently, two companies are interested in the commercial usage of the Cu-8 Cr-4 Nb alloy. The Rocketdyne Division of Rockwell International is conducting independent testing to analyze the properties for their projected needs in advanced rocket engine applications. Metallamics, a company based in Traverse City, Michigan, is entering into a Space Act Agreement to evaluate and test Cu-Cr-Nb alloys as materials for welding electrodes that are used in robotic welding operations. Creep rate is one of the alloy properties that determines the degree to which a welding electrode will mushroom or expand at the tip. A material with a low creep rate will resist mushrooming and give the electrode a longer life, minimizing downtime. This application holds the potential for large-scale usage of the alloy in the automotive and other industries. Success here would dramatically decrease the cost of the alloy and increase availability for aerospace applications.

1995-01-01

189

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

NASA Technical Reports Server (NTRS)

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

Raj, Sai V.; Pharr, George M.

1992-01-01

190

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

191

On the transition from power law creep to Harper-Dorn creep  

SciTech Connect

At intermediate to high temperature single and polycrystalline metals, alloys, ceramics and minerals often deform by the diffusion-controlled dislocation mechanism of power law creep at high stresses, but by a mechanism of Harper-Dorn (H-D) creep at low stresses. H-D creep is characterized by a stress exponent n of unity and an activation energy equal to that for power law creep and a strain rate independent of grain size. Several dislocation mechanisms have been proposed for H-D creep. Langdon and Yavari explain H-D creep from the climb of edge dislocations under conditions of vacancy saturation. According to Weertman and Blacic, H-D creep may be produced by a low-amplitude thermal cycling effect which causes a cyclic change in equilibrium point defect concentration. Raj postulated a mechanism with the generation of dislocations from surface sources controlling the strain rate. Ardell and Lee considered H-D creep as the result of a dislocation network coarsening. Based on the assumption of the presence of internal stress, Wu and Sherby and Ruano et al. treated Harper-Dorn creep as an extension of power law creep into the low stress region. It is the intent of this communication to show that H-D creep starts to operate at stresses equal to the Peierls stress.

Wang, J.N. (Monash Univ., Clayton (Australia). Dept. of Earth Science)

1993-09-01

192

The role of grain boundary sliding on creep deformation characteristics of discontinuous reinforced composites  

SciTech Connect

In this study, the grain boundary sliding behavior in discontinuous reinforced composites is investigated numerically. Results indicate that the stress enhancement factor for the composite is much larger than the one observed for the matrix material. In the composite, the increase in the strain rates as a result of grain boundary sliding occurs in a wider stress range in comparison to the matrix. It is shown that the experimentally observed large scale triple point grain boundary cavitation in the composites could occur as a result of large grain rotations resulting from grain boundary sliding and evolution of triaxial stress state. Also, the observed larger creep exponent values or stress dependent creep exponent values for the composites may not be explained solely by the mechanism of grain boundary sliding.

Biner, S.B.

1994-10-01

193

Intergranular cracking under creep-fatigue deformation in lamellar TiAl alloy  

Microsoft Academic Search

Total strain range controlled low-cycle fatigue tests (R=?1, strain rate=410?3\\/s) indicate that lamellar structured Ti46.6Al1.4Mn2Mo (at.%) alloy shows cyclic stability behavior regardless of test conditions. Fatigue life is drastically reduced with the application of tensile hold time and this reduction of fatigue life is understood to be due to the additional creep damage occurring during tensile hold time. Microstructural analysis

Young Sam Park; Soo Woo Nam; Sun Keun Hwang

2002-01-01

194

High temperature deformation processing of Monel K-500  

NASA Astrophysics Data System (ADS)

High temperature deformation processing behavior of Monel K-500 has been studied using uniaxial compression testing performed at temperatures from 1088 to 1533 K and strain rates ranging from 0.001 to 10/s. Post deformation microstructural examination to correlate the flow behavior has also been conducted. The results of the mechanical testing have been correlated with presently available deformation mechanism models for process optimization, and a processing map for bulk forming operations has been developed. Additionally, processing conditions for Monel K-500 have been discussed in terms of microstructural phenomena that take place during high temperature deformation processing.

Chaudhury, Prabir K.; Anand, K. G.; Holt, G.; Valencia, J. J.

195

Temperature dependence of creep induced anisotropy in nanocrystalline Fe-Cu-Nb-Si-B alloys  

NASA Astrophysics Data System (ADS)

Nanocrystallisation of Fe75Cu1Nb3Si8B13 under tensile stress results in a creep induced anisotropy which, at room temperature, is characterised by a magnetic easy axis along the stress axis. However, this magnetic easy ribbon axis becomes a magnetic hard ribbon axis when the measuring temperature T decreases below a compensation temperature T 0 where the creep induced magnetic anisotropy vanishes. Accordingly, the magnetisation curve changes from a square loop for T > T 0 to a linear loop with low remanence for T < T 0. In the present case (8 at% Si), T 0 is about -2 C for the fully developed nanocrystalline state. Although slightly depending on the annealing conditions, T 0 is primarily determined by the Si content and shifts towards higher temperatures by about 50 C per at% Si with increasing Si concentration.

Herzer, Giselher; Marsilius, Mie; Polak, Christian

2013-05-01

196

Effect of thermo-mechanical processing on microstructure and creep properties of the foils of alloy 617  

NASA Astrophysics Data System (ADS)

The effect of rolling and annealing on the microstructure and high temperature creep properties of alloy 617 were investigated. Two types of foil specimens with different thickness reductions were prepared by thermo-mechanical processing. Recrystallization and grain growth were readily observed at specimens annealed at 950 and 1100 C. The uniform coarse grains increase resistance against creep deformation. The grain size effect in creep deformation was dominant up to 900 C, while dynamic recrystallization effect became dominant at 1000 C. Dynamic recrystallization was observed in all the creep deformed foils, even though some specimens had already been (statically) recrystallized during annealing. Steady state creep rates decreased with increasing annealing temperature in the less rolled foils. The apparent activation energy Qapp for the creep deformation increased from 271 to 361 kJ/mol as the annealing temperature increased from 950 to 1100 C.

Sharma, S. K.; Jang, C.; Kang, K. J.

2009-06-01

197

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

198

High temperature deformation in engineering alloys - modelling for strain or load control  

SciTech Connect

A generalized constitutive description of deformation of engineering alloys that exhibit a dominant tertiary creep is presented that extends a previous treatment of creep deformation. The model parameters of the constitutive equations that are determined by analysis of creep curves are supplemented by the Young's modulus to provide a database from which illustrative calculations are made. Simulations of constant strain rate, stress relaxation and high strain low cycle fatigue (both strain and stress control) are made for the superalloy IN738LC; the predictions are compared with limited available experimental data. 22 refs.

Ghosh, R.N.; Mclean, M. (National Metallurgical Lab., Jamshedpur (India) Imperial College of Science, Technology, and Medicine, London (United Kingdom))

1992-11-01

199

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

200

Creep, Damage and Life Prediction for High Temperature Materials.  

National Technical Information Service (NTIS)

The high temperature static failure mechanisms of several representative superalloys (Inconel 718, 800 and 783) were studied under controlled loading and environmental conditions. As part of this experimental program, high temperature Digital Image Correl...

M. A. Sutton B. Y. Chao X. Deng J. S. Lyons

1997-01-01

201

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

SciTech Connect

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

Vijay K. Vasudevan

2005-12-21

202

Effects of 14 MeV neutron irradiation on creep of nickel and niobium  

NASA Astrophysics Data System (ADS)

Flux, stress and temperature effects on the creep strength of nickel and niobium were observed in situ at the RTNS-II 14 MeV neutron source at Lawrence Livermore National Laboratory. Creep tests were done on Ni and Nb near 0.3 T m with stresses to 280 MPa in a high vacuum test unit using a digital computer for control and data acquisition. Cyclic flux tests produced dramatic changes in creep rate. This creep behavior is attributed to the point defect fluctuations in the crystal structure. Analysis of creep and stress relaxation under steady state flux indicates that an intermediate temperature, thermally activated deformation mechanism is rate controlling.

Barmore, W.; Ruotola, A.; Raymond, E.; Mukherjee, A.

1983-07-01

203

Cyclic creep of Type 304 stainless steel during unbalanced tension-compression loading at elevated temperature  

SciTech Connect

Samples of Type 304 stainless steel were subjected to cyclic stresses with a positive mean stress at 300 and 560/sup 0/C. Very rapid net elongation was observed whenever the stress limits were such as to produce a plastic strain amplitude of the same order of magnitude as the elastic strain at the peak stress. The maximum mean strain-rate, or cyclic creep rate, for a given peak tensile stress was achieved when the mean stress was just slightly above zero. Increasing the mean stress caused the mean strain rate to decrease. The sensitive dependence of the mean strain-rate on the plastic strain amplitude and inverse dependence on the mean stress indicates that remobilization of dislocations by the reverse strain is an important mechanism for cyclic-creep acceleration. Although rapid cyclic creep was observed at both temperatures, a measurable mean strain rate was found for a much narrower range of stress conditions at 560 than at 300/sup 0/C. The strain accumulated during cyclic creep did not produce any strain hardening, but did influence the shape of the stress-strain curve in a subsequent tensile test.

Turner, A.P.L.; Martin, T.J.

1980-03-01

204

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

205

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.

206

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

NASA Astrophysics Data System (ADS)

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

Chernak, L. J.; Hirth, G.

2008-12-01

207

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

208

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

NASA Technical Reports Server (NTRS)

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

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

1985-01-01

209

Evaluation of weldment creep and fatigue strength-reduction factors for elevated-temperature design  

SciTech Connect

New explicit weldment strength criteria in the form of creep and fatigue strength-reduction factors were recently introduced into the American Society of Mechanical Engineers Code Case N-47, which governs the design of elevated-temperature nuclear plants components in the United States. This paper provides some of the background and logic for these factors and their use, and it describes the results of a series of long-term, confirmatory, creep-rupture and fatigue tests of simple welded structures. The structures (welded plates and tubes) were made of 316 stainless steel base metal and 16-8-2 weld filler metal. Overall, the results provide further substantiation of the validity of the strength-reduction factor approach for ensuring adequate life in elevated-temperature nuclear component weldments. 16 refs., 7 figs.

Corum, J.M.

1989-01-01

210

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

NASA Astrophysics Data System (ADS)

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. The apparent stress exponent of the irradiation creep slightly exceeded unity, and instantaneous creep coefficient at 380-790 C was estimated to be ?1 10-5 [MPa-1 dpa-1] at ?0.1 dpa and 1 10-7 to 1 10-6 [MPa-1 dpa-1] at ?1 dpa. The irradiation creep strain appeared greater than that for the high purity SiC. Microstructural observation and data analysis indicated that the grain-boundary sliding associated with the secondary phases contributes to the irradiation creep at 380-790 C to 0.01-0.11 dpa.

Koyanagi, T.; Shimoda, K.; Kondo, S.; Hinoki, T.; Ozawa, K.; Katoh, Y.

2014-12-01

211

AISI 316Ti (1.4571) steelMechanical, creep and fracture properties versus temperature  

Microsoft Academic Search

In this paper some useful, experimentally obtained, results regarding material properties of austenitic stainless steel 1.4571 are presented. Tests were performed at low and elevated temperatures. During uniaxial tests, mechanical properties such as ultimate tensile strength, 0.2% offset yield strength and short-time creep behaviour were determined. Charpy impact energy was also determined using the Charpy impact machine. Engineering stress-strain diagrams

J. Brnic; G. Turkalj; M. Canadija; D. Lanc

2011-01-01

212

The Effect of Residuals on the Elevated Temperature Properties of Some Creep Resistant Steels  

Microsoft Academic Search

The effect of residuals and other deliberate minor additions on the elevated temperature properties of austenitic, CrMo and CrMoV steels is reviewed and those that affect these properties are identified. The elements boron, molybdenum, nitrogen and phosphorus in austenitic steels all increased creep rupture life although only boron and molybdenum were beneficial to rupture ductility. In the ferritic steels the

N. G. Needham; J. Orr

1980-01-01

213

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

Microsoft Academic Search

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

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

1992-01-01

214

Damage Accumulation at High Temperature Creep of a Single-Crystal Superalloy  

Microsoft Academic Search

The micromechanics of the high temperature creep and damage acumulation in single crystal nickel base superalloy is the subject\\u000a of this study. These alloys are used in turbine blade and vane applications in advanced commercial and military gas turbines\\u000a and in turbopumps for the space shuttle main engines. The objective of this program was to develop a robust predictive tool

A. Staroselsky; B. Cassenti

215

Dynamic recrystallization of olivine single crystals during high-temperature creep  

Microsoft Academic Search

High-temperature creep experiments were made on olivine single crystals under compressional stress to large strains. At strains larger than about 40 to 60%, dynamic recrystllization occurs and cellular wall dislocation structure is formed. Recrystallized grain size dg(mum) and cell wall spacing ds(mum) are dependent upon applied stress sigma(MPa) as: dg?(times)=103sigma1.18+\\/-0.11 and ds?(times)=102sigma-0.67+\\/-0.10.

Shun-ichiro Karato; Mitsuhiro Toriumi; Toshitsugu Fujii

1980-01-01

216

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

217

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

218

Elevated Temperature Mechanical Behavior of Severely Deformed Titanium  

NASA Astrophysics Data System (ADS)

In this investigation, compression tests were performed at a strain rate of 0.001-0.1 s-1 in the range of 600-900 C to study the high temperature deformation behavior and flow stress model of commercial purity (CP) titanium after severe plastic deformation (SPD). It was observed that SPD via equal channel angular extrusion can considerably enhance the flow strength of CP titanium deformed at 600 and 700 C. Post-compression microstructures showed that, a fine grained structure can be retained at a deformation temperature of 600 C. Based on the kinematics of dynamic recovery and recrystallization, the flow stress constitutive equations were established. The validity of the model was demonstrated with reasonable agreement by comparing the experimental data with the numerical results. The error values were less than 5% at all deformation temperatures except 600 C.

Sajadifar, Seyed Vahid; Yapici, Guney Guven

2014-05-01

219

Low-temperature creep behavior of ultrafine-grained 5083 Al alloy processed by equal-channel angular pressing  

Microsoft Academic Search

Low temperature creep behavior of ECAPed Al 5083 alloy with grain sizes of approximately 300 nm was investigated at temperatures\\u000a of 498, 523 and 548 K. The value of the stress exponent was found to be 3.5 at a low stress level and increased to 5.0 at\\u000a a high stress level. At the low stress level, the creep curve exhibits

Ho-Kyung Kim

2010-01-01

220

Elevated Temperature Creep Behavior of Inconel Alloy 625.  

National Technical Information Service (NTIS)

Inconel 625 in the solution-annealed condition has been selected as the clad material for the fuel and control rod housing assemblies of the Upgraded Transient Reactor Test Facility (TREAT Upgrade or TU). The clad is expected to be subjected to temperatur...

A. Purohit W. F. Burke

1984-01-01

221

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

222

Diffusion creep, grain rotation and mantle anisotropy  

Microsoft Academic Search

The mantle deforms by some combination of diffusion creep and dislocation creep. It is well established that dislocation creep gives rise to crystallographic preferred orientations (CPO) which in turn lead to seismic anisotropy. Consequently seismic anisotropy may be interpreted as indicating the action of dislocation creep, and an absence of anisotropy as indicating diffusion creep. One assumption involved is that

J. Wheeler

2007-01-01

223

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

SciTech Connect

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

Ding, J.L. [Washington State Univ., Pullman, WA (US); Liu, K.C.; Brinkman, C.R. [Oak Ridge National Lab., TN (US)

1992-12-31

224

Instability of creeping flow past a deformable wall: the role of depth-dependent modulus.  

PubMed

Linear stability analysis is carried out to examine the effect of a depth-dependent modulus on the stability of creeping flow of a Newtonian fluid past an incompressible and impermeable linear elastic solid. Two different systems are considered: (i) Couette flow past a solid with a continuously varying modulus, and (ii) Couette flow past two adjacent solids with different thicknesses and moduli. For the first system, we find that between two configurations having the same average modulus, the more stable configuration is the one that has the higher modulus at the interface. In the case of two different configurations having the same interfacial modulus and the same average modulus, the more stable configuration is the one that has the higher modulus right below the interface. For the second system, we find that stability depends in a non-monotonic way on the modulus ratio (top modulus to bottom modulus) of the two solids. If the thickness of the top solid is less than a critical value, then increasing the modulus ratio initially causes the system to be less stable. Since this critical thickness decreases as the modulus ratio increases, increasing the modulus ratio beyond a certain point causes the system to be more stable. An analysis of the solid-solid interfacial boundary conditions suggests that the relationship between the stiffness of the top solid and the stability of the system is due to a jump in the base-state displacement gradient at the interface which creates a net perturbation displacement. PMID:16605454

Gkanis, Vasileios; Kumar, Satish

2006-02-01

225

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

226

Unified Creep-Plasticity Model Suitable for Thermo-Mechanical Loading.  

National Technical Information Service (NTIS)

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 constitut...

D. Slavik H. Sehitoglu

1988-01-01

227

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

228

High temperature creep properties of eutectic and near eutectic silver-copper alloys: Application to metal\\/ceramic joining  

Microsoft Academic Search

Calculations of residual stresses in eutectic Ag-Cu braze joints are often required to validate designs for a variety of metal\\/ceramic joining applications. In particular, Finite Element Analysis (FEA) codes have the capability of incorporating either elastic-plastic or minimum creep rate constitutive models for the braze material. Unfortunately, neither high temperature stress-strain or creep data are available in the literature for

J. J. Stephens; S. N. Burchett; F. M. Hosking

1991-01-01

229

Effect of heat treatment temperature on creep-rupture properties of Fe{sub 3}Al-based alloys  

SciTech Connect

The effects of heat treatment at 1100 to 1250C on the creep-rupture properties of an Fe{sub 3}Al-based alloy were studied. Tests were conducted at 593C (1100F) and 207 MPa (30 ksi) in air. The modes of fracture were identified using optical metallography and scanning electron microscopy. Analytical electron microscopy was also used to study characteristics of the microstructure, including dislocations, ordered domains, and precipitates. The creep results showed maximum creep-rupture resistance with a heat treatment at approximately 1150C, with significant decreases in rupture life after heat treatments at both lower and higher temperatures. The peak in creep life was associated with fine precipitates that were observed after the 1150C heat treatment and persisted during prolonged creep at 593C. Heat treatment at 1150C appeared to cause dissolution of coarser precipitates which then reprecipitated as new fine particles upon cooling or during creep. These fine precipitates then pinned dislocations and grain boundaries to produce strength during creep.

McKamey, C.G.; Maziasz, P.J.

1994-09-01

230

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

NASA Astrophysics Data System (ADS)

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

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

2011-01-01

231

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

SciTech Connect

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

Boccaccini, A.R.; Kern, H. [Technische Univ., Ilmenau (Germany). Fachgebiet Werkstofftechnik; West, G.; Lewis, M.H. [Univ. of Warwick, Coventry (United Kingdom); Janczak, J. [Swiss Federal Labs. for Materials Testing and Research, Thun (Switzerland)

1997-06-01

232

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

233

The effect of elevated temperature on the inelastic deformation behavior of PMR-15 solid polymer  

NASA Astrophysics Data System (ADS)

The inelastic deformation behavior of PMR-15 neat resin, a high-temperature thermoset polymer, was investigated at temperatures in the 274--316 C range. The experimental program was developed to explore the influence of temperature on strain-controlled tensile loading, relaxation and creep behaviors. The experimental results clearly demonstrate that the mechanical behavior of PMR-15 polymer exhibits a strong dependence on temperature. During strain-controlled tensile loading, the slope of the stress-strain curve in the quasi-elastic region decreases and the slope of the stress-strain curve in the flow stress region increases with increasing temperature. At a given strain rate, the flow stress level decreases with increasing temperature. Furthermore, the transition from quasi-elastic behavior to inelastic flow becomes less pronounced with increasing temperature. During relaxation, the amount of the stress drop for a given prior strain rate decreases with increasing temperature. At a given prior strain rate and creep stress level, increasing temperature results in increased creep strain accumulation. Based on the experimental results the Viscoplasticity Based on Overstress for Polymers (VBOP) theory was augmented to account for the effects of elevated temperature. Several model parameters were determined to depend on temperature. Those parameters were developed into functions of temperature. The augmented VBOP was then employed to predict the response of the PMR-15 polymer under various test histories at temperatures in the 274--316 C range. An enhanced procedure for determining VBOP model parameters that utilizes a McLean type dip test to assess the equilibrium stress was developed. Model predictions were considerably improved by employing an enhanced model characterization procedure. Additionally, the effects of prior isothermal aging at various temperatures in the 260--316 C range on the inelastic deformation behavior of PMR-15 at 288 C were evaluated. For PMR-15 aged at 260--302 C, the initial slope of the stress-strain curve and the flow stress increase with prior aging duration. The shape of the knee of the stress-strain curve becomes more pronounced and the departure from quasi-linear behavior is delayed with increasing prior aging time. Experimental results reveal that there is no relationship between prior aging temperature and elastic modulus, tangent modulus, the shape of the knee of the stress-strain curve or departure from quasi-linear behavior. This implies that for aging temperatures in the 260--302 C range, mechanical behavior depends only on prior aging duration and not on prior aging temperature. However, testing of PMR-15 aged at 316 C revealed a decrease in flow stress with increasing prior aging duration. This suggests that a degradation mechanism, not present at lower aging temperatures, is in effect during aging at 316 C.

Ryther, Chad E. C.

234

Modelling and experimental study of the tertiary creep stage of Grade 91 steel  

Microsoft Academic Search

This article addresses experimental studies and analytical simulations of the tertiary creep stage of Grade 91 steel tested\\u000a at various stresses and temperatures between 500C (up to 160 103h) and 600C (up to 94נ103h). The strain rate increases after its minimum mainly because of the softening of the material which microstructure evolves\\u000a strongly during creep deformation. An interrupted creep test

Rattanak Lim; Maxime Sauzay; France Dalle; Ivan Tournie; Patrick Bonnaillie; Anne-Franoise Gourgues-Lorenzon

2011-01-01

235

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

236

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

SciTech Connect

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

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

1980-05-01

237

Effect of fast neutron fluence on the creep anisotropy of Zr 2.5Nb tubes  

NASA Astrophysics Data System (ADS)

The in-reactor behaviour of internally pressurised capsules of Zr-2.5Nb tubes is analysed in detail to separate the stress dependent component of deformation (creep). It is found by a rigorous statistical analysis that the creep rate varies with fast neutron fluence. At 555 K the axial creep rate increases while the transverse creep rate decreases with fluence. At 588 K the creep rate in both the axial and transverse directions increases with fluence. It is also shown that the creep anisotropy ratio R, i.e., the ratio of axial to transverse creep rate for a pressurised tube, varies with fluence, stress and irradiation temperature. These findings are discussed in terms of the irradiation-induced evolution in microstructure. The possible impact of the evolution of the dislocation substructure is discussed with reference to a self-consistent polycrystalline model that takes into account the crystallographic texture and the grain interaction strains present in zirconium alloys. The lower temperature creep behaviour is consistent with an increase with fast fluence of the single crystal creep compliance related to prismatic dislocation climb and glide, or a decrease in the single crystal creep compliances relating to basal and pyramidal slip. The creep behaviour at the higher irradiation temperature is more complicated, and there may be an influence of phase changes as well as dislocation structure. It appears that all three eigenvalues describing the single crystal creep behaviour depend on fast fluence.

Holt, R. A.; Bickel, G. A.; Christodoulou, N.

2008-02-01

238

Influence of Grain Boundary Character on Creep Void Formation in Alloy 617  

NASA Astrophysics Data System (ADS)

Alloy 617, a high-temperature creep-resistant, nickel-based alloy, is being considered for the primary heat exchanger for the Next Generation Nuclear Plant (NGNP), which will operate at temperatures exceeding 760 C and a helium pressure of approximately 7 MPa. Observations of the crept microstructure using optical microscopy indicate creep stress does not significantly influence the creep void fraction at a given creep strain over the relatively narrow set of creep conditions studied. Void formation was found to occur only after significant creep in the tertiary regime (>5 pct total creep strain) had occurred. Also, orientation imaging microscopy (OIM) was used to characterize the grain boundaries in the vicinity of creep voids that develop during high-temperature creep tests (900 C to 1000 C at creep stresses ranging from 20 to 40 MPa) terminated at creep strains ranging from 5 to 40 pct. Preliminary analysis of the OIM data indicates voids tend to form on grain boundaries parallel, perpendicular, or 45 deg to the tensile axis, while few voids are found at intermediate inclinations to the tensile axis. Random grain boundaries intersect most voids, while coincident site lattice (CSL)-related grain boundaries did not appear to be consistently associated with void development. Similar results were found in oxygen-free, high-conductivity (OFHC) copper, severely deformed using equal channel angular extrusion, and creep tested at 450 C and 14 MPa.

Lillo, Thomas; Cole, James; Frary, Megan; Schlegel, Scott

2009-12-01

239

On rafting in a single crystal nickel-base superalloy after high and low temperature creep  

SciTech Connect

Rafting (also known as directional coarsening) was first studied more than 25 years ago in SX Udimet 700. At intermediate temperatures, 700--800 C, no microstructural changes were seen during the creep of SX alloys in tests which lasted less than a few thousand hours. In a study of CMSX-4 crept at 750 C the immediate area of the fracture contained many cracks, but away from the fracture the microstructure looked identical to that of the uncrept material. It was not possible to see a change in the material with scanning electron microscopy. The aim of the work presented here was to find a way of imaging low and intermediate temperature creep damage using simple techniques and equipment readily available in most laboratories. This area is one of practical importance as SX alloys are being introduced into industrial gas turbines for power generation and principles for condition assessment need to be developed which are relevant to the temperature of usage. As a first step towards finding a solution it was necessary to study the conditions under which rafting occurred in other SX alloys and a brief summary of some important findings is given.

Henderson, P. [Vattenfall AB, Stockholm (Sweden)] [Vattenfall AB, Stockholm (Sweden); Berglin, L.; Jansson, C. [ABB STAL AB, Finspaang (Sweden)] [ABB STAL AB, Finspaang (Sweden)

1998-12-18

240

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

NASA Astrophysics Data System (ADS)

Creep processes can relax an important part of the tectonic stresses in active faults, either by permanent steady-state creep or by episodic post-seismic creep. Here, our goal is to better constrain the micro-physical parameters that control this transition between seismic and aseismic behavior, both in time and in space. We present new results from microstructural studies on natural samples collected from the SAFOD (San Andreas Fault Observatory at Depth) drilling project, located on the Parkfield segment of the San Andreas Fault (SAF). Seven samples were collected from the main active creeping zone: the Central Deforming Zone at 3301-3303m depth. We performed chemical and mineralogical analyses and microscope observations on twenty thin sections cut from those samples. In a previous study (Gratier et al., Geology, 2011), we have already shown that pressure solution creep is an active deformation process in the SAF. We propose a model of microstructural evolution to characterize in which conditions pressure solution creep is efficient enough to relax stress and to prevent the nucleation of moderate to large earthquakes. We show that two crucial parameters may accelerate pressure solution: the presence of phyllosilicates and the degree of rock fracturing. The initial structure and composition of the rocks may explain why pressure solution creep is efficient or not. Moreover, both the content of phyllosilicates and the degree of fracture may evolve with time at various scales during the seismic cycle: - During interseismic periods (years to millennia): fracturing activates postseismic creep. However, the progressive healing of the fracture annihilates this effect. Meanwhile, growth of phyllosilicate minerals, associated with postseismic fluid flow may also activate the creep rate. - During much longer geological periods (hundred thousands to millions of years), the composition of gouge material deformed by pressure solution evolves by the passive concentration of phyllosilicates due to the dissolution of soluble minerals. If their content is large enough, phyllosilicates could control the creep mechanism and accommodate the deformation by friction on clay layers. The steady state creeping zone of the SAF illustrates both effects thanks to very fine grains resulting from successive fracturing processes, very few amount of healing, possible growth of metamorphic clays and a general passive concentration of phyllosilicates with volume decrease. Conversely, in the nearby damaged zone, healing reduces the efficiency of pressure solution. Microseismicity, resulting from the fracturing of healed zones, may maintain a dynamic equilibrium between fracturing and healing. The southern part of the permanent creeping zones, which shows 20-30 years "Parkfield"-like earthquake cycles with postseismic creep, may illustrate the competition between healing/strengthening and creep processes that occur during interseismic periods.

Richard, J.; Gratier, J.; Doan, M.; Renard, F.; Boullier, A.

2012-12-01

241

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

National Technical Information Service (NTIS)

Thermal fatigue failures of solder joints in electronic devices often arise from cyclic shear strains imposed by the mismatched thermal expansion coefficients of the materials that bind the joint as temperature changes are encountered. Increased solder jo...

D. Tribula

1990-01-01

242

Micromechanics of brittle creep in rocks  

NASA Astrophysics Data System (ADS)

In the upper crust, the chemical influence of pore water promotes time dependent brittle deformation through sub-critical crack growth. Sub-critical crack growth allows rocks to deform and fail at stresses well below their short-term failure strength, and even at constant applied stress (brittle creep). Here we provide a micromechanical model describing time dependent brittle creep of water-saturated rocks under triaxial stress conditions. Macroscopic brittle creep is modeled on the basis of microcrack extension under compressive stresses due to sub-critical crack growth. The incremental strains due to the growth of cracks in compression are derived from the sliding wing crack model of Ashby and Sammis (1990), and the crack length evolution is computed from Charles' law. The macroscopic strains and strain rates computed from the model are non linear, and compare well with experimental results obtained on granite, low porosity sandstone and basalt rock samples. Primary creep (decelerating strain) corresponds to decelerating crack growth, due to an initial decrease in stress intensity factor with increasing crack length in compression. Tertiary creep (accelerating strain as failure is approached) corresponds to an increase in crack growth rate due to crack interactions. Secondary creep with apparently constant strain rate arises as an inflexion between those two end-member phases. The minimum strain rate at the inflexion point can be estimated analytically as a function of model parameters, effective confining pressure and temperature, which provides an approximate creep law for the process. The creep law is used to infer the long term strain rate as a function of depth in the upper crust due to the action of the applied stresses: in this way, sub-critical cracking reduces the failure stress in a manner equivalent to a decrease in cohesion. We also investigate the competition with pressure solution in porous rocks, and show that the transition from sub-critical cracking to pressure solution dominated creep occurs with increasing depth and decreasing strain rates.

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

2012-08-01

243

Determination of Creep Behavior of Thermal Barrier Coatings Under Laser Imposed Temperature and Stress Gradients.  

National Technical Information Service (NTIS)

In the present study, a laser sintering/creep technique has been established to quantitatively determine the creep behavior of thermal barrier coatings under steady state high heat flux/high thermal gradient conditions. An approach is proposed to separate...

D. Zhu R. A. Miller

1997-01-01

244

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

245

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

Microsoft Academic Search

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

G. B. Reddy; D. J. Ayres

1982-01-01

246

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

SciTech Connect

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

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

1982-12-01

247

Electromagnetic detection and monitoring of creep induced damage in high temperature resistant steels  

NASA Astrophysics Data System (ADS)

Monitoring and remaining life assessment of ferritic-martensitic alloys exposed to creep was addressed using electromagnetic evaluation. In order to determine the correlation between the creep damage and the change in magnetic properties, two steels were exposed to different extent of creep and magnetic properties were evaluated for each sample. A close evaluation of the creep damage was performed in each sample using optical microscopy, as well as SEM and TEM techniques. It was found that the microstructural changes occurring during the creep progress have a correlation with variations in the magnetic response at the different levels of creep damage. Saturation decreases as creep damage progress due to the increases of demagnetized sites. Remanence shows the characteristic behavior of isotropic materials and coercivity changes as a function of the progress of the creep damage. Even though this established correlation may be used to directly monitoring the creep damage evolution, a magnetically determined damage factor was defined using the relationship of the hysteretic Jiles-Atherton factors with the extent pf creep damage. On the base of existing Continuous Damage Mechanics (CDM) models for creep, a model has been proposed for the monitoring and assessment of creep damage using the described magnetic damage factor.

Polar, Alberto

248

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

249

In situ monitored in-pile creep testing of zirconium alloys  

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

250

Treatment of material creep and nonlinearities in flexible mulitbody dynamics  

SciTech Connect

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

Xie, M.; Amirouche, F.M.L. [Univ. of Illinois, Chicago, IL (United States)

1994-01-01

251

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

SciTech Connect

Tensile creep data are reported for a high-performance grade of hot isostatically pressed Si{sub 3}N{sub 4} that is currently being investigated as a candidate material for advanced heat engine applications. Specimens were tested in pure uniaxial tension at temperatures ranging from 1200 to 1370{degree}C. Creep strain was measured with an optical strain extensometer until creep rupture occurred, in some cases for periods in excess of 2000 h. To study the effects of various preloading material histories on creep behavior, specimens were prepared and tested in several conditions, i.e., unannealed, annealed, or precycled. Test results show that either treatment by thermal annealing or by precycling at 1370{degree}C can dramatically modify the initial transient creep behavior and enhance the resistance to creep deformation and hence the creep-rupture lifetime. However, the influence of the preloading histories on creep rate was diminished by high temperature exposure after about 500 h of testing. The rupture lifetime of the precycled specimen at 1370{degree}C was significantly higher than those of the unannealed and annealed specimens. In contrast, no significant extension of the creep-rupture lifetime was observed for a precycled specimen tested at 1300{degree}C. Steady-state creep was absent in some cases under certain conditions of temperature, stress, and heat treatment. Little or no tertiary creep was usually detected before specimen fracture occurred. The steady-state creep rate of this material was found to be a function of applied stress, temperature, and possibly the level of crystallinity in the intergranular phase. 9 refs., 15 figs.

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

1991-01-01

252

Multixial creep life prediction of ceramic structures using continuum damage mechanics and the finite element method  

SciTech Connect

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 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 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 named Ceramics Analysis and Reliability Evaluation of Structures/Creep (CARES/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 CARES/Creep program.

Jadaan, O.M.; Powers, L.M.; Gyenkenyesi, J.P.

1999-10-01

253

The deformation mechanisms of superplasticity  

Microsoft Academic Search

Under various conditions of stress and temperature various deformation mechanisms could be rate-controlling for superplastic\\u000a deformation. In general at low stresses diffusion creep should be rate-controlling. At temperatures between approximately\\u000a 40 and 65 pct of the absolute melting point grain boundary diffusion should be the dominant diffusion path while at higher\\u000a temperatures volume diffusion should dominate. At intermediate stresses, grain

H. W. Hayden; S. Floreen; P. D. Goodell

1972-01-01

254

Creep behavior of bagasse fiber reinforced polymer composites.  

PubMed

The creep behavior of bagasse-based composites with virgin and recycled polyvinyl chloride (B/PVC) and high density polyethylene (B/HDPE) as well as a commercial wood and HDPE composite decking material was investigated. The instantaneous deformation and creep rate of all composites at the same loading level increased at higher temperatures. At a constant load level, B/PVC composites had better creep resistance than B/HDPE systems at low temperatures. However, B/PVC composites showed greater temperature-dependence. Several creep models (i.e., Burgers model, Findley's power law model, and a simpler two-parameter power law model) were used to fit the measured creep data. Time-temperature superposition (TTS) was attempted for long-term creep prediction. The four-element Burgers model and the two-parameter power law model fitted creep curves of the composites well. The TTS principle more accurately predicted the creep response of the PVC composites compared to the HDPE composites. PMID:20064712

Xu, Yanjun; Wu, Qinglin; Lei, Yong; Yao, Fei

2010-05-01

255

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

256

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

257

High temperature deformation behavior of the molybdenum alloy TZM  

Microsoft Academic Search

The molybdenum alloy TZM (Mo-0.5wt%Ti-0.08wt%Zr) is a commonly used constructional material for high-temperature applications. It is well known that molybdenum and its alloys develop a distinct subgrain structure and texture during hot deformation. These microstructural aspects have a significant effect on strength at elevated temperatures. It was observed that with proceeding primary recrystallization and therefore with disappearance of subgrains the

T. Mrotzek; U. Martin; A. Hoffmann

2010-01-01

258

Modelling of deformations of high strength concrete at elevated temperatures  

Microsoft Academic Search

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

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

2004-01-01

259

Recovery and recrystallization during high temperature deformation of ?-iron  

Microsoft Academic Search

The high temperature deformation of vacuum-melted iron and zone-refined iron has been studied in the temperature range 500\\u000a to 800C over a wide range of strain rates in torsion. Changes in stress-strain behavior and metallographic observations show\\u000a a transition in the dynamic restoration process from recovery at high stresses to recrystallization at low stresses. The results\\u000a are discussed in terms

G. Glover; C. M. Sellars

1973-01-01

260

Effect of in situ TiB 2 particle reinforcement on the creep resistance of hypoeutectic Al12Si alloy  

Microsoft Academic Search

The effect of in situ TiB2 particle reinforcement on the tensile creep deformation of an Al12Si alloy prepared by the technique of saltmetal reactions was studied in a wide temperature range of 573673K under a constant stress in air. At the investigated temperature and stress condition, TiB2 particles significantly increase creep deformation resistance. High values of the apparent stress exponent

Minhwa Huang; Xianfeng Li; Hongzhan Yi; Naiheng Ma; Haowei Wang

2005-01-01

261

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

262

Stress Relaxation and Creep of High-Temperature Gas-Cooled Reactor Core Support Ceramic Materials: A Literature Search.  

National Technical Information Service (NTIS)

Creep and stress relaxation in structural ceramics are important properties to the high-temperature design and safety analysis of the core support structure of the HTGR. The ability of the support structure to function for the lifetime of the reactor is d...

J. E. Selle V. J. Tennery

1980-01-01

263

Creep Behavior of Ni-Base Heat Resistant Alloys for High Temperature Gas-Cooled Reactors in Decarburizing Helium Environment.  

National Technical Information Service (NTIS)

Creep and corrosion tests of Ni-base heat resistant alloys (Hastelloy XR and XR-II) for high temperature gas-cooled reactors (HTGR) were conducted at 950C in several kinds of helium environments with different impurity compositions in order to examine the...

Y. Kurata H. Nakajima Y. Ogawa

1988-01-01

264

High-Temperature Elastic-Plastic and Creep Properties for SA533 Grade B Class I and SA508 Materials.  

National Technical Information Service (NTIS)

High temperature elastic-plastic and creep properties are presented for SA533 Grade B Class I and SA508 Class II materials. These properties are derived from tests conducted at Combustion Engineering Material and Metallurgical Laboratories and cover the t...

D. J. Ayres G. B. Reddy

1982-01-01

265

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

266

Elastic stress in single crystal Ni-base superalloys and the driving force for their microstructural evolution under high temperature creep conditions  

SciTech Connect

Microstructural stability of blade materials used in land based gas turbine systems has become a critical issue for the reliability and economy of entire power generation systems since the materials must be sound during increasingly longer intervals between inspections. A mechanism for rafting in Ni-base superalloys under high temperature creep conditions is discussed in terms of elastic strain energy. The elastic deformation is analyzed by the finite element method and approximate analytical expressions are also deduced for it. The difference between the elastic strain energies at {gamma} channels parallel and perpendicular to the stress axis is derived in closed form, which is used to evaluate the local equilibrium concentration of component elements. The rate of rafting estimated with a simple diffusion model and the concentration distribution data obtained in the present theory agree well with the magnitude of the measured growth rate.

Ohashi, Tetsuya; Hidaka, Kishio; Imano, Shinya [Hitachi Ltd., Omika, Hitachi (Japan). Hitachi Research Lab.] [Hitachi Ltd., Omika, Hitachi (Japan). Hitachi Research Lab.

1997-05-01

267

Creep: Long-term Time-Dependent Rock Deformation in a Deep-sea Laboratory in the Ionian sea: a Pilot Study  

NASA Astrophysics Data System (ADS)

Time-dependent brittle rock deformation is of first-order importance for understanding the long-term behavior of water saturated rocks in the Earth's upper crust. Interpretation of results from traditional laboratory brittle creep experiments have generally been in terms of three individual creep phases; primary (decelerating), secondary (constant strain rate or quasi-steady-state) and tertiary (accelerating or unstable). The deformation may be distributed during the first two, but localizes onto a fault plane during phase three. More recently, models have been proposed that explain the trimodal shape of creep curves in terms of the competition between a weakening mechanism and a strengthening mechanism, with the weakening mechanism eventually dominating and leading to localized failure. However, a major problem is that it is difficult to distinguish between these competing mechanisms and models given the lower limit of strain rates achievable in laboratory experiments over practicable time scales. This study aims to address that problem directly by extending significantly the range of achievable strain rates through much longer-term experiments conducted in a deep-sea laboratory in the Ionian sea. The project takes advantage of a collaboration with the NEMO Group-INFN, a consortium that is developing a large volume (1 km3) deep-sea detector for high-energy (>1019 eV) cosmic neutrinos. A suitable test site has been identified, some 20km north-east of Catania in Sicily, at a depth of 2100m. Within the CREEP deformation apparatus, confining pressure is provided by the ambient water pressure (>22MPa), and the constant axial stress is provided by an actuator that amplifies this pressure. Measurement transducers and a data acquisition system are sealed internally, with power provided for up to 6 months by an internal battery pack. The great advantage of operating in the deep sea in this way is that the system is essentially passive, has few moving parts, and requires no maintenance. The apparatus is held in place by a disposable cast-iron anchor and supported above the seabed by a deep-sea buoyage system. On completion of each experiment, an acoustic release detaches from the anchor and allows the apparatus to float to the surface to be recovered by the oceanographic research vessel.

Meredith, P. G.; Boon, S.; Vinciguerra, S.; Bowles, J.; NEMO Group,.

2003-12-01

268

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

269

Thermally activated dislocation creep model for primary water stress corrosion cracking of NiCrFe alloys  

Microsoft Academic Search

There is a growing awareness that awareness that environmentally assisted creep plays an important role in integranular stress corrosion cracking (IGSCC) of NiCrFe alloys in the primary coolant water environment of a pressurized water reactor (PWR). The expected creep mechanism is the thermally activated glide of dislocations. This mode of deformation is favored by the relatively low temperature of PWR

Hall

1995-01-01

270

Stabilization of martensitic microstructure in advanced 9Cr steel during creep at high temperature  

Microsoft Academic Search

In order to improve the long-term creep strength of 9%Cr steel, the stabilization of martensitic microstructure in the vicinity of prior austenite grain boundaries during creep has been investigated by the addition of boron and by a dispersion of nano-size MX nitrides. Creep tests were carried out at 923K for up to about 3104h. Boron is enriched in the M23C6

F Abe; T Horiuchi; M Taneike; K Sawada

2004-01-01

271

Modelling creep behaviour and failure of 9Cr0.5Mo1.8WVNb steel  

Microsoft Academic Search

In this paper, a continuum viscoplastic model including damage effects is used to describe the creep deformation and damage mechanisms of P92 steel in the temperature range 550750C.In a first step, the results of creep tests performed at 575C are presented and compared to other literature results in order to bring the main mechanisms of P92 steel creep behaviour into

C. Ptry; G. Lindet

2009-01-01

272

Temperature dependent cyclic deformation mechanisms in Haynes 188 superalloy  

NASA Astrophysics Data System (ADS)

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.

1995-08-01

273

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

274

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

275

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

276

Experimental Validation of Two-dimensional Finite Element Method for Simulating Constitutive Response of Polycrystals During High Temperature Plastic Deformation  

NASA Astrophysics Data System (ADS)

A finite element method was recently designed to model the mechanisms that cause superplastic deformation (A.F. Bower and E. Wininger, A Two-Dimensional Finite Element Method for Simulating the Constitutive Response and Microstructure of Polycrystals during High-Temperature Plastic Deformation, J. Mech. Phys. Solids, 2004, 52, p 1289-1317). The computations idealize the solid as a collection of two-dimensional grains, separated by sharp grain boundaries. The grains may deform plastically by thermally activated dislocation motion, which is modeled using a conventional crystal plasticity law. The solid may also deform by sliding on the grain boundaries, or by stress-driven diffusion of atoms along grain boundaries. The governing equations are solved using a finite element method, which includes a front-tracking procedure to monitor the evolution of the grain boundaries and surfaces in the solid. The goal of this article is to validate these computations by systematically comparing numerical predictions to experimental measurements of the elevated-temperature response of aluminum alloy AA5083 (M.-A. Kulas, W.P. Green, E.M. Taleff, P.E. Krajewski, and T.R. McNelley, Deformation Mechanisms in Superplastic AA5083 materials. Metall. Mater. Trans. A, 2005, 36(5), p 1249-1261). The experimental work revealed that a transition occurs from grain-boundary sliding to dislocation (solute-drag) creep at approximately 0.001/s for temperatures between 425 and 500 C. In addition, increasing the grain size from 7 to 10 ?m decreased the transition to significantly lower strain rates. Predictions from the finite element method accurately predict the effect of grain size on the transition in deformation mechanisms.

Agarwal, Sumit; Briant, Clyde L.; Krajewski, Paul E.; Bower, Allan F.; Taleff, Eric M.

2007-04-01

277

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

NASA Technical Reports Server (NTRS)

Temperature, thermal stresses, and residual creep stresses were studied by comparing laboratory values measured on a built-up titanium structure with values calculated from finite-element models. Several such models were used to examine the relationship between computational thermal stresses and thermal stresses measured on a built-up structure. Element suitability, element density, and computational temperature discrepancies were studied to determine their impact on measured and calculated thermal stress. The optimum number of elements is established from a balance between element density and suitable safety margins, such that the answer is acceptably safe yet is economical from a computational viewpoint. It is noted that situations exist where relatively small excursions of calculated temperatures from measured values result in far more than proportional increases in thermal stress values. Measured residual stresses due to creep significantly exceeded the values computed by the piecewise linear elastic strain analogy approach. The most important element in the computation is the correct definition of the creep law. Computational methodology advances in predicting residual stresses due to creep require significantly more viscoelastic material characterization.

Jenkins, Jerald M.

1987-01-01

278

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

279

Permanent deformation in armos fibre at a temperature below the glass transition temperature  

Microsoft Academic Search

The character of accumulation of permanent deformation of Armos fiber as a function of the temperature was established. The\\u000a important change in the character of ?per.(ass.) in the temperature region of 80100C can be attributed to breaking of hydrogen bonds of the polymer-water-polymer type.\\u000a The special character of accumulation of permanent deformation is observed in dried Armos fibre. This is

E. S. Tsobkallo; O. I. Nachinkin; V. A. Kvartskheliya

1999-01-01

280

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

281

High-temperature deformation measurements using digital-image correlation  

Microsoft Academic Search

The ability of the computer-vision technique of digital-image correlation to measure full-field in-plane surface deformations at elevated temperatures was evaluated by a series of experiments. Samples were subjected to pure translation, free thermal expansion and uniform tensile loads. Results are presented which show that the digital-image-correlation technique remains fully capable of accurate measurement of the displacements and strains on the

J. S. Lyons; J. Liu; M. A. Sutton

1996-01-01

282

Creep of Cr{sub 2}Hf + Cr in situ intermetallic composites  

SciTech Connect

Intermetallics are attractive for high temperature applications due to their high melting temperature and high temperature strength. One of the principal requirements for high temperature use is the creep strength. At present very little information on creep is available in intermetallics and it is even rare in the case of two phase intermetallic composites indicated above. In previous studies, the effects of microstructure and heat treatment on the mechanical behavior as a function of temperature, including flexure strength, ductility and fracture toughness of Cr{sub 2}Hf + Cr composites were investigated. The objective of the present study is to investigate the creep deformation characteristics of Cr{sub 2}Hf + cr composite. Creep data for one hypoeutectic microstructure and for the eutectic microstructure in this composite system were determined at 1,200 C and are compared with that of pure Cr. Estimates of composite creep behavior, made using known models, are also presented.

Ravichandran, K.S. [Univ. of Utah, Salt Lake City, UT (United States). Dept. of Metallurgical Engineering] [Univ. of Utah, Salt Lake City, UT (United States). Dept. of Metallurgical Engineering

1996-06-15

283

Anomalous deformation twinning in fcc metals at high temperatures  

NASA Astrophysics Data System (ADS)

Nanotwinned structures have shown strong promise as optimal motifs for strength, ductility, and grain stability in fcc metals--in sharp contrast to their nano-grained counterparts where gains in strength are disappointingly offset by loss of ductility. However, their high temperature stability has remained relatively unaddressed. Here we investigate the high temperature response of twin boundaries that constitute these nanostructured metals, by way of molecular dynamics simulations. At low and intermediate temperatures, the twin boundaries exhibit normal motion coupled to shear deformation as expected. However, our simulations at higher temperatures (above 0.5-0.7 Tm), reveal considerable deformation twinning, an occurrence that has not been observed before in fcc metals. Although the origins of this intriguing behavior are not yet clear to us, we discuss a possible conjecture by addressing the following questions: (i) Why is the high temperature response of some fcc metals different? (ii) Why do we observe a transition from twin migration to stacking fault nucleation and subsequent twin formation at high temperatures?

Sinha, Tanushree; Kulkarni, Yashashree

2011-06-01

284

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

Microsoft Academic Search

The crack growth behavior of several high temperature nickel-base alloys, under cyclic and static loading, is studied and\\u000a reviewed. In the oxide dispersion strengthened (ODS) MA 6000 and MA 754 alloys, the high temperature crack propagation exhibited\\u000a orientation dependence under cyclic as well as under static loading. The creep crack growth (CCG) behavior of cast nickel-base\\u000a IN-738 and IN-939* superalloys

M. Nazmy; W. Hoffelner; C. Wthrich

1988-01-01

285

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

286

Low temperature deformation detwinning - a reverse mode of twinning.  

SciTech Connect

The origin of the plasticity in bulk nanocrystalline metals have, to date, been attributed to the grain-boundary-mediated process, stress-induced grain coalescence, dislocation plasticity, and/or twinning. Here we report a different mechanism - detwinning, which operates at low temperatures during the tensile deformation of an electrodeposited Cu with a high density of nanosized growth twins. Both three-dimensional XRD microscopy using the Laue method with a submicron-sized polychromatic beam and high-energy XRD technique with a monochromatic beam provide the direct experimental evidences for low temperature detwinning of nanoscale twins.

Wang, Y. D.; Liu, W.; Lu, L.; Ren, Y.; Nie, Z. H.; Almer, J.; Cheng, S.; Shen, Y. F.; Zuo, L.; Liaw, P. K.; Lu, K. (X-Ray Science Division); (Beijing Inst. of Tech.); (Chinese Academy of Sciences); (Univ. of Tennessee); (Northeastern Univ. - China)

2010-01-01

287

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

288

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

SciTech Connect

Four-point flexure creep deformation of ZrB2-30 vol% SiC ceramics in argon atmosphere under a static load of 19 MPa for 0-100 h at 1500 and 1600 C was investigated. The strain rate at 1600 oC was 3.7 times higher than that at 1500 oC. Microstructural evolution during creep consisted of nucleation and growth of triple-point cavitations which were always associated with SiC particles. Due to the low stress, only isolated cavitations were nucleated, and no microcracks were formed. For up to 100 h at 1500 and 1600 C, the grains maintained their size and shape. The cavitations in both size and number showed no obvious difference from 26 to 100 h at 1500 C, whereas that showed a significant increase from 26 to 100 h at 1600 C. Present study suggested that ZrB2-30 vol% SiC exhibited relatively good microstructural stability and creep resistance at 1500 C in argon atmosphere.

Guo, Wei-Ming [Shanghai Institute of Ceramics, Chinese Academy of Sciences (SICCAS); Zhang, Guo-Jun [Shanghai Institute of Ceramics, Chinese Academy of Sciences (SICCAS); Lin, Hua-Tay [ORNL

2012-01-01

289

Review of recent irradiation-creep results  

SciTech Connect

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

Coghlan, W.A.

1982-05-01

290

Microstructure Evolution in Alpha Iron during High Temperature Tensile Deformation  

NASA Astrophysics Data System (ADS)

The microstructural evolution of alpha iron under tensile deformation at high temperature (TH 0.5) and slow strain-rate (10-5 s-1 to 10-5 s-1) was investigated. The impetus for this study was the recent observation of Dynamic Abnormal Grain Growth (DAGG) in pure molybdenum under the same testing conditions. A high temperature tensile testing system was refurbished and assembled for this study. The testing system consists of an Centorr 2229 furnace system mounted on an Instron 1331 load frame. I designed the tensile grip and programmed the testing program to obtain data in the stress and strain regime of interest. Testing were done at both UC Davis and Los Alamos National Labs (LANL). Metallography techniques and electron backscattering diffraction (EBSD) technique in a scanning electron microscope were used to characterize the samples after testing. In addition to normal tensile tests at constant strain-rates where DAGG is proposed to occur, a series of strain-rate change tests were designed and performed. Strain-rate change tests were employed to extract activation area information that provided insight into the active mechanism of deformation of the material in addition to the information obtained from analysis of the stress-strain curve and the microstructure via optical microscopy and EBSD. The obtained stress-train curve data were compared with the stress-strain curves data in the literature for alpha iron in similar regime of deformation indicating that the dominant mechanism of deformation is dynamic recovery. The comparison includes past stress-strain curves and the data recorded in the Ashby Map. Optical and EBSD analysis showed that normal grain growth occurred in alpha iron during this testing regime. This lack of grain boundary pinning by impurity differs from that observed in Mo that exhibited DAGG. Activation area analysis showed that the activation area values of Fe are consistent with friction drag from the lattice being the active deformation mechanism. The same activation area analysis reveals that the active mechanism of deformation in the Mo material that exhibited DAGG is impurity drag. These analyses reveal the microstructure evolution of pure alpha iron and provide thought about the difference between Fe and Mo. Although both Fe and Mo have a BCC structure and undergo dynamic recovery for the processing conditions considered, DAGG did not occur in pure Fe. Dynamic recovery and normal grain growth occurred in Fe instead; there was no grain boundary pinning.

Thanh, Phi Hung Xuan

291

Creep: long-term time-dependent rock deformation in a deep-sea laboratory in the ionian sea: a pilot study  

NASA Astrophysics Data System (ADS)

Time-dependent brittle rock deformation is of first-order importance for understanding the long-term behaviour of water saturated rocks in the Earth's upper crust. The traditional way of investigating this has been to carry out laboratory "brittle creep" experiments. Results have been interpreted involving three individual creep phases; primary (decelerating), secondary (constant strain rate or steady state) and tertiary (accelerating or unstable). The deformation may be distributed during the first two, but localizes onto a fault plane during phase three. However, it is difficult to distinguish between competing mechanisms and models given the lower limit of strain rates practicably achievable in the laboratory. The study reported here aims to address this problem directly by extending significantly the range of achievable strain rates through much longer-term experiments conducted in a deep-sea laboratory in the Ionian sea. The project takes advantage of a collaboration with the Laboratori Nazionali del Sud (LNS) of the Italian National Institute of Nuclear Physics (INFN), that is developing a deep-sea laboratory for a very large volume (1 km3) deep-sea detector of high-energy (>1019 eV) cosmic neutrinos (NEMO). A suitable deep-sea site has been identified, some 20km south-west of Catania in Sicily, with flat bathymetry at a depth of 2100m. The CREEP deformation apparatus is driven by an actuator that amplifies the ambient water pressure, while the confining pressure around the rock sample is provided by the ambient water pressure (>20MPa). Measurement transducers and a low-energy data acquisition system are sealed internally, with power provided for up to 6 months by an internal battery pack. The great advantage of operating in the deep sea in this way is that the system is simple; it is "passive", has few moving parts, and requires no maintenance. The apparatus is fixed approximately 10m above the seabed; held in place by a disposable concrete anchor and supported by a deep-sea buoyage system. On completion of each experiment, an acoustic release detaches the anchor and allows the apparatus to float to the surface to be recovered by the oceanographic research vessel.

Meredith, P.; Boon, S.; Vinciguerra, S.; Bowles, J.; Hughes, N.; Migneco, E.; Musumeci, M.; Piattelli, P.; Riccobene, G.; Vinciguerra, D.

2003-04-01

292

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

293

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

NASA Astrophysics Data System (ADS)

A substantial amount of considerations regarding localization during high-temperature creep ranks around the relation between grain-size and dislocation-density piezometer and flow laws. The piezometers are considered expressions for a microstructural steady state ultimately achieved at a given loading condition while the flow laws describe the instantaneous response of an aggregate to imposed stress or strain rate boundary conditions. The missing link between these concepts is a set of evolution equations for microstructural parameters as a function of the external thermodynamic variables. While well designed experiments may constrain the parameters in such evolution equations the equations must be first formulated by theoretical approaches. We develop a framework for a variational analysis of microstrutural evolution during inelastic high-temperature deformation accommodated by dislocation mechanisms and diffusive mass transport. In our approach, a polycrystalline aggregate is characterized by a distribution function that characterizes the state of individual grains by dislocation density, grain size, and strain. The Gibbs free energy of the aggregate is considered to have contributions from the elastic energy and from lattice distortions associated with dislocations and grain boundaries. The work performed on a representative volume by the external loading is dissipated by changes in the number of defects and their migration. The variational approach minimizes the rate of change of free energy with the evolution of the state variables. The minimization is done under constraints on the aggregate volume, on a link between changes in plastic strain and dislocation density, and on the form of the dissipation functionals for the various considered diffusion processes. As a result of the constrained minimization we gain three basic evolution equations, a grain growth law and two flow laws comparing favorably to classic results. For quasi-homogeneous materials characterized by a unique relation between grain size and dislocation density, an analytical set of evolution equations can be derived that constrains piezometers. Our model is capable of matching all currently available experimental observations regarding the high-temperature deformation of olivine aggregates with plausible values for the involved micromechanical model parameters apt for a process-oriented discussion of high-temperature deformation.

Hackl, K.; Renner, J.

2011-12-01

294

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

USGS Publications Warehouse

The problem of applying laboratory silicate-flow data to the mantle, where conditions can be vastly different, is approached through a critical review of high-temperature flow mechanisms in ceramics and their relation to empirical flow laws. The intimate association of solid-state diffusion and high-temperature creep in pure metals is found to apply to ceramics as well. It is shown that in ceramics of moderate grain size, compared on the basis of self-diffusivity and elastic modulus, normalized creep rates compare remarkably well. This comparison is paralleled by the near universal occurrence of similar creep-induced structures, and it is thought that the derived empirical flow laws can be associated with dislocation creep. Creep data in fine-grained ceramics, on the other hand, are found to compare poorly with theories involving the stress-directed diffusion of point defects and have not been successfully correlated by self-diffusion rates. We conclude that these fine-grained materials creep primarily by a quasi-viscous grain-boundary sliding mechanism which is unlikely to predominate in the earth's deep interior. Creep predictions for the mantle reveal that under most conditions the empirical dislocation creep behavior predominates over the mechanisms involving the stress-directed diffusion of point defects. The probable role of polymorphic transformations in the transition zone is also discussed. ?? 1973.

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

1973-01-01

295

Inelastic deformation behavior of PMR15 high temperature polymer at 316 C  

Microsoft Academic Search

The strain rate (time)-dependent mechanical behavior of PMR-15 neat resin, a thermoset polymer, was investigated at 316degC. In order to investigate the inelastic deformation behavior of PMR-15, experimental program was designed to explore the effect of prior strain rate on monotonic loading and unloading, and relaxation behaviors. In addition, the recovery of strain at zero stress and the creep behavior

O. Ozmen

2009-01-01

296

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

NASA Technical Reports Server (NTRS)

Time dependent notch sensitivity was observed in Udimet 700 sheet, bar, and investment castings between 1000 and 1400 F (538 -760 C), but not at 1600 F (871 C). As was the case for modified Waspaloy, Waspaloy and Inconel 718, it occurred in notched specimens loaded below the yield strength when the creep deformation was localized. For each alloy and notched specimen geometry, a stress-average particle size zone can be defined that characterizes the notch sensitive behavior.

Wilson, D. J.

1974-01-01

297

The effect of neutron irradiation on the fatigue and fatigue-creep behaviour of structural material  

NASA Astrophysics Data System (ADS)

The primary circuit of a pulsed type fusion reactor will be subjected to cyclic loads at high temperature. Deformation rates will be in the range from below 10 -6 s -1 (creep) to 1 s -1 (fatigue) leading to creep-fatigue interaction in the neutron irradiated structural materials. The effects of neutron irradiation on fatigue and fatigue-creep interaction are reviewed. The study of austenitic stainless steel is most advanced, but the test conditions are still far from the first wall operating conditions, leaving a lot of uncertainties. It is expected that irradiation reduces the fatigue-creep endurance of austenites to very low levels, because of enhanced intergranular cracking. Two classes of alloys in an early stage of development, low activation steels and vanadium base alloys, hold the promise to be more fatigue-creep resistant due to their more ductile creep behaviour.

van der Schaaf, B.

1988-07-01

298

Hot deformation behaviour of alloys for applications at elevated temperatures  

NASA Astrophysics Data System (ADS)

The present study investigated the deformation behaviour, microstructure evolution and fracture behaviour under hot working conditions of alloys designed for elevated-temperature applications. For this purpose, iron-aluminum and titanium-aluminum alloys were selected and their compositions are: Fe-8.5wt%Al-5.5Cr-2.0Mo-0.2Zr-0.03C, Fe-16.5Al-5.5Cr-1.0Nb-0.05C and Ti-33.3Al-2.8Mn-4.8Nb. These alloys were tested in the as-cast condition and in the form of hot-rolled + annealed plate for the iron-aluminum alloys and in the HIP'ed condition for the titanium-aluminum alloy. Isothermal compression tests were carried out with a Gleeble 2000 over a range of temperatures from 800 to 1250C and constant strain rates from 10-3 to 10 s-1. In general, the flow curves are marked by a peak stress and softening which decline as temperature rises, and a flow stress which diminishes with rise in temperature and decrease in strain rate. The flow behaviour at peak stress (sigmap) and 0.5 true strain of these materials was described well by the Zener-Hollomon parameter Z=3?exp /RTQHW , where Z=K3sinha sn . A numerical curve-fitting method was used to yield values of the following parameters: (i) stress exponent, n and (ii) activation energy, QHW . The dynamic material modeling approach was performed to extract from hot compression data: (i) the strain rate sensitivity parameter, m, (ii) the efficiency of power dissipation, eta, and (iii) the instability parameter, xi. The microstructure evolution and fracture behaviour were assessed using optical and electron microscopy. The deformation processes occuring were determined by correlation of the sigma-epsilon curves, m and microstructural observations. The resulting deformation map indicates that at lower temperatures and higher strain rates, the dominant restoration occurs by dynamic recovery, while at lower strain rates and higher temperatures dynamic recrystallization is the operative mode. At the highest temperatures, dynamic recrystallization followed by grain coarsening occurs. Hot workability maps were constructed based on xi, cracking observations and sigmap. These maps indicate good workability can be achieved over a wider range of temperatures and strain rates with wrought alloys compared with as-cast alloys. The beneficial effect of dynamic recrystallization on hot workability has been clearly demonstrated. Finally, the application of hot workability maps is demonstrated and approaches to improving the hot workability of selected materials are presented.

Voyzelle, Benoit

299

Low Temperature Heat Capacity of a Severely Deformed Metallic Glass  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

300

Low temperature heat capacity of a severely deformed metallic glass.  

PubMed

The low temperature heat capacity of amorphous materials reveals a low-frequency enhancement (boson peak) of the vibrational density of states, as compared with the Debye law. By measuring the low-temperature heat capacity of a Zr-based bulk metallic glass relative to a crystalline reference state, we show that the heat capacity of the glass is strongly enhanced after severe plastic deformation by high-pressure torsion, while subsequent thermal annealing at elevated temperatures leads to a significant reduction. The detailed analysis of corresponding molecular dynamics simulations of an amorphous Zr-Cu glass shows that the change in heat capacity is primarily due to enhanced low-frequency modes within the shear band region. PMID:24745435

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

2014-04-01

301

Development of a Simple Test to Determine the Low Temperature Creep Compliance of Asphalt Mixtures.  

National Technical Information Service (NTIS)

The idea of performing creep tests on asphalt mixture beam specimens with the Bending Beam Rheometer (BBR) was investigated in this project. In the first part of the investigation a detailed beam preparation procedure was developed for both laboratory com...

A. Zofka A. C. Falchetto M. Marastean R. Velasquez

2008-01-01

302

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

Microsoft Academic Search

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

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

1999-01-01

303

The use of computational creep continuum damage mechanics to optimize materials selection for high-temperature weldments  

Microsoft Academic Search

It is shown how mechanisms-based constitutive equations may be formulated which are based on single-state damage variables for ferritic steels undergoing high-temperature creep and damage. In addition, it is shown how this description may be used to express the constitutive equations for weld and heat-affected-zone (HAZ) materials in terms of the same description of parent material behaviour and of simple

D. R. Hayhurst

1994-01-01

304

A correlation of creep and fatigue crack growth in high density poly(ethylene) at various temperatures  

Microsoft Academic Search

The creep crack growth (CCG) and fatigue crack growth (FCG) behaviour of two PE-HD pipe grades was studied based on a linear elastic fracture mechanics (LEFM) methodology. The FCG-tests were performed under a sinusoidal load at a frequency of 1 Hz and R-ratios (Fmin\\/Fmax) of 0.1, 0.3 and 0.5; the test temperatures were 23 (only FCG), 60 and 80 C.

G. Pinter; W. Balika; R. W. Lang

2002-01-01

305

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

306

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

NASA Astrophysics Data System (ADS)

This thesis presents the on-going development of methodology for a probabilistic material strength degradation model. The probabilistic model, in the form of a postulated randomized multifactor equation, provides for quantification of uncertainty in the lifetime material strength of aerospace propulsion system components subjected to a number of diverse random effects. This model is embodied in the computer program entitled PROMISS, which can include up to eighteen different effects. Presently, the model includes four effects that typically reduce lifetime strength: high temperature, mechanical fatigue, creep, and thermal fatigue. Statistical analysis was conducted on experimental Inconel 718 data obtained from the open literature. This analysis provided regression parameters for use as the model's empirical material constants, thus calibrating the model specifically for Inconel 718. Model calibration was carried out for four variables, namely, high temperature, mechanical fatigue, creep, and thermal fatigue. Methodology to estimate standard deviations of these material constants for input into the probabilistic material strength model was developed. Using the current version of PROMISS, entitled PROMISS93, a sensitivity study for the combined effects of mechanical fatigue, creep, and thermal fatigue was performed. Results, in the form of cumulative distribution functions, illustrated the sensitivity of lifetime strength to any current value of an effect. In addition, verification studies comparing a combination of mechanical fatigue and high temperature effects by model to the combination by experiment were conducted. Thus, for Inconel 718, the basic model assumption of independence between effects was evaluated. Results from this limited verification study strongly supported this assumption.

Bast, Callie Corinne Scheidt

1994-03-01

307

Transient creep and semibrittle behavior of crystalline rocks  

USGS Publications Warehouse

We review transient creep and semibrittle behavior of crystalline solids. The results are expected to be pertinent to crystalline rocks undergoing deformation in the depth range 5 to 20 km, corresponding to depths of focus of many major earthquakes. Transient creep data for crystalline rocks at elevated temperatures are analyzed but are poorly understood because of lack of information on the deformation processes which, at low to moderate pressure, are likely to be semibrittle in nature. Activation energies for transient creep at high effective confining pressure are much higher than those found for atmospheric pressure tests in which thermally-activated microfracturing probably dominates the creep rate. Empirical transient creep equations are extrapolated at 200?? to 600??C, stresses from 0.1 to 1.0 kbar, to times ranging from 3.17??102 to 3.17??108 years. At the higher temperatures, appreciable transient creep strains may take place but the physical significance of the results is in question because the flow mechanisms have not been determined. The purpose of this paper is to stimulate careful research on this important topic. ?? 1978 Birkha??user Verlag.

Carter, N. L.; Kirby, S. H.

1978-01-01

308

Dislocation and diffusion creep of synthetic anorthite aggregates  

Microsoft Academic Search

Synthetic fine-grained anorthite aggregates were deformed at 300 MPa confining pressure in a Paterson-type gas deformation apparatus. Creep tests were performed at temperatures ranging from 1140 to 1480 K, stresses from 30 to 600 MPa, and strain rates between 210-6 and 110-3s-1. We prepared samples with water total contents of 0.004 wt % (dry) and 0.07 wt % (wet), respectively.

E. Rybacki; G. Dresen

2000-01-01

309

Creep of Li 2O  

NASA Astrophysics Data System (ADS)

The tritium breeding material with the highest lithium atom density, Li 2O has been observed to incur significant swelling ( > 4%) under fast reactor irradiation. Such swelling, if unrestrained leads to either unacceptable, induced-strains in adjacent structural material or undesirable design compromises. Fortunately, however, Li 2O deform at low temperatures so that swelling strains may be internally accommodated. Laboratory dilational creep experiments were conducted on unirradiated Li 2O between 500 and 700C in order to provide data for structural analysis of in-reactor experiments and blanket design studies. A densification model agreed with most of the available data.

Hollenberg, G. W.; Liu, Y. Y.; Arthur, B.

1985-08-01

310

The effect of dissolved magnesium on creep of calcite II: transition from diffusion creep to dislocation creep  

NASA Astrophysics Data System (ADS)

We extended a previous study on the influence of Mg solute impurity on diffusion creep in calcite to include deformation under a broader range of stress conditions and over a wider range of Mg contents. Synthetic marbles were produced by hot isostatic pressing (HIP) mixtures of calcite and dolomite powders for different intervals (2-30 h) at 850C and 300 MPa confining pressure. The HIP treatment resulted in high-magnesian calcite aggregates with Mg content ranging from 0.5 to 17 mol%. Both back-scattered electron images and chemical analysis suggested that the dolomite phase was completely dissolved, and that Mg distribution was homogeneous throughout the samples at the scale of about two micrometers. The grain size after HIP varied from 8 to 31 ?m, increased with time at temperature, and decreased with increasing Mg content (>3.0 mol%). Grain size and time were consistent with a normal grain growth equation, with exponents from 2.4 to 4.7, for samples containing 0.5-17.0 mol% Mg, respectively. We deformed samples after HIP at the same confining pressure with differential stresses between 20 and 200 MPa using either constant strain rate or stepping intervals of loading at constant stresses in a Paterson gas-medium deformation apparatus. The deformation tests took place at between 700 and 800C and at strain rates between 10-6 and 10-3 s-1. After deformation to strains of about 25%, a bimodal distribution of large protoblasts and small recrystallized neoblasts coexisted in some samples loaded at higher stresses. The deformation data indicated a transition in mechanism from diffusion creep to dislocation creep. At stresses below 40 MPa, the strength was directly proportional to grain size and decreased with increasing Mg content due to the reductions in grain size. At about 40 MPa, the sensitivity of log strain rate to log stress, ( n), became greater than 1 and eventually exceeded 3 for stresses above 80 MPa. At a given strain rate and temperature, the stress at which that transition occurred was larger for samples with higher Mg content and smaller grain size. At given strain rates, constant temperature, and fixed grain size, the strength of calcite in the dislocation creep regime increased with solute content, while the strength in the diffusion creep regime was independent of Mg content. The results suggest that chemical composition will be an important element to consider when solid substitution can occur during natural deformation.

Xu, Lili; Renner, Jrg; Herwegh, Marco; Evans, Brian

2009-03-01

311

Low-temperature electrical resistivity study of deformed Inconel alloy 600  

Microsoft Academic Search

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

Feng Shiu Chan; Yeong Der Yao; Shing Hoa Wang

2006-01-01

312

Low-temperature electrical resistivity study of deformed Inconel alloy 600  

Microsoft Academic Search

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

Feng Shiu Chan; Yeong Der Yao; Shing Hoa Wang

2006-01-01

313

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">314</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/755861"> <span id="translatedtitle"><span class="hlt">Creep</span> in electronic ceramics</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> <span class="hlt">creep</span> measurements combined with microstructural investigations can be used to elucidate <span class="hlt">deformation</span> mechanisms that can be related to the diffusion kinetics and defect chemistry of the minority species. This paper will review the theoretical basis for this correlation and illustrate it with examples from some important electronic ceramics having a perovskite structure. Recent results on BaTiO{sub 3}, (La{sub 1{minus}x}Sr){sub 1{minus}y}MnO{sub 3+{delta}}, YBa{sub 2}Cu{sub 3}O{sub x}, Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub x}, (Bi,Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub x} and Sr(Fe,Co){sub 1.5}O{sub x} will be presented.</p> <div class="credits"> <p class="dwt_author">Routbort, J. L.; Goretta, K. C.; Arellano-Lopez, A. R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-04-27</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/2008SPIE.7375E..52L"> <span id="translatedtitle">Investigation of the low-<span class="hlt">temperature</span> performance of asphalt mixtures via fatigue and linear contraction and <span class="hlt">creep</span> test</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">Three types of asphalt mixtures, including asphalt concrete (AC), stone mastic asphalt (SMA) and porous asphalt (PA) with a 13mm gradation, are chosen to study the fatigue behavior, linear contraction and <span class="hlt">creep</span> performance of them. The analysis of the experimental results is summarized as follows. The asphalt mixture exhibits longer fatigue life at low <span class="hlt">temperature</span> than that at high <span class="hlt">temperature</span>. But the fatigue life is more sensitive to the loading stress at low <span class="hlt">temperature</span>. At the same time, the fatigue lives of all the three mixture gradations show decreasing trends with the increasing stress, which implies that restraining over-loading of highways is quite important. The linear contractive quotiety shows great distinction with the types of asphalt mixture gradations and <span class="hlt">temperature</span> span, which indicates that modified asphalt and lower air voids can benefit to the contractive properties of asphalt mixtures at low <span class="hlt">temperature</span>. Additionally, the linear contractive quotiety decreases with the falling of the <span class="hlt">temperature</span>, meanwhile the distinctions between different <span class="hlt">temperature</span> spans tend to slower. The <span class="hlt">creep</span> test indicates that lower air voids and larger asphalt content are beneficial to the low <span class="hlt">temperature</span> performance of asphalt.</p> <div class="credits"> <p class="dwt_author">Liu, Conghui; Wu, Shaopeng; Li, Bo; Wang, Jingang</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-11-01</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://academic.research.microsoft.com/Publication/41034738"> <span id="translatedtitle"><span class="hlt">Deformation</span>-induced martensite formation during cyclic <span class="hlt">deformation</span> of metastable austenitic steel: Influence of <span class="hlt">temperature</span> and carbon content</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">To study the influence of the parameters carbon content, <span class="hlt">temperature</span> and total strain amplitude on the <span class="hlt">deformation</span>-induced martensite formation in metastable 301 austenitic steel, hollow cylindrical fatigue specimens were carburized and decarburized in methanehydrogen gas mixtures. Fatigue experiments were carried out in a <span class="hlt">temperature</span> range between RT and T=?100C while monitoring the fraction of <span class="hlt">deformation</span>-induced martensite versus the number of</p> <div class="credits"> <p class="dwt_author">U. Krupp; H.-J. Christ</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-01-01</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://dx.doi.org/10.1029/2005JB003772"> <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 " 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/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">319</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://cmn.fisica.unimo.it/zapperi/reprints/MiguelPRL65501_2002.pdf"> <span id="translatedtitle">Dislocation Jamming and Andrade <span class="hlt">Creep</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">We simulate the glide motion of an assembly of interacting dislocations under the action of an external shear stress and show that the associated plastic <span class="hlt">creep</span> relaxation follows Andrade's law. Our results indicate that Andrade <span class="hlt">creep</span> in plastically <span class="hlt">deforming</span> crystals involves the correlated motion of dislocation structures near a dynamic transition separating a flowing from a jammed phase. Simulations in</p> <div class="credits"> <p class="dwt_author">M.-Carmen Miguel; Alessandro Vespignani; Michael Zaiser; Stefano Zapperi</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</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://www.pbslearningmedia.org/resource/psu06-nano.sci.creep/"> <span id="translatedtitle">Do Materials Get Tired? <span class="hlt">Creep</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://nsdl.org/nsdl_dds/services/ddsws1-1/service_explorer.jsp">NSDL National Science Digital Library</a></p> <p class="result-summary">This video explains that materials will <span class="hlt">deform</span> slowly or “<span class="hlt">creep</span>” under the right conditions, when constant force is applied. “Strain” is illustrated with rubber bands and we learn that engineers can calculate <span class="hlt">creep</span> strain as a function of time.</p> <div class="credits"> <p class="dwt_author">Wpsu</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-11-12</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="#" 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" 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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://academic.research.microsoft.com/Publication/41846069"> <span id="translatedtitle">A comparison of impression, indentation and impression-relaxation <span class="hlt">creep</span> of lead-free Sn9Zn and Sn8Zn3Bi solders 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"><span class="hlt">Creep</span> behavior of Sn9% Zn and Sn8% Zn3% Bi solder alloys was studied by impression, indentation, and impression-relaxation\\u000a tests at room <span class="hlt">temperature</span> (T>0.6T\\u000a \\u000a m\\u000a ) in order to evaluate the correspondence of the <span class="hlt">creep</span> results obtained by different testing techniques, and to evaluate the\\u000a effect of Bi on the <span class="hlt">creep</span> response of the eutectic Sn9Zn alloy. Stress exponent values were</p> <div class="credits"> <p class="dwt_author">R. Mahmudi; A. R. Geranmayeh; H. Noori; H. Khanbareh; N. Jahangiri</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">322</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/2008PMM...105..395P"> <span id="translatedtitle">Structure factor of acoustic emission upon high-<span class="hlt">temperature</span> <span class="hlt">deformation</span> of aluminum</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 accumulation of <span class="hlt">deformation</span> and acoustic emission upon high-<span class="hlt">temperature</span> loading of aluminum has been studied. It has been established that in aluminum the accumulation of <span class="hlt">deformation</span> in the course of a thermomechanical cycle brings about the formation of <span class="hlt">deformation</span> bands whose density is of a pronounced quasi-periodic character depending on the <span class="hlt">temperature</span>. The minimum and the maximum of the density of <span class="hlt">deformation</span> bands correspond to the <span class="hlt">temperature</span> of jumplike development of <span class="hlt">deformation</span> and to the monotonic character of <span class="hlt">deformation</span> accumulation, respectively. The monotonic accumulation of <span class="hlt">deformation</span> is accompanied by a monotonic growth of the root-mean-square voltage of acoustic emission, while the jumplike development of <span class="hlt">deformation</span>, by high-amplitude single acoustic signals. The amplitude of single acoustic signals correlates with the strain rate.</p> <div class="credits"> <p class="dwt_author">Plotnikov, V. A.; Makarov, S. V.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-04-01</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://adsabs.harvard.edu/abs/2009PhDT.......473S"> <span id="translatedtitle">Transient and steady-state <span class="hlt">creep</span> in a tin-silver-copper lead-free solder alloy: Experiments and modeling</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">It has been conventional to simplify the thermo-mechanical modeling of solder joints by omitting the primary (transient) contributions to total <span class="hlt">creep</span> <span class="hlt">deformation</span>, assuming that secondary (steady-state) <span class="hlt">creep</span> strain is dominant and primary <span class="hlt">creep</span> 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 <span class="hlt">temperature</span>-time profile. This research examines the relative contributions of primary and secondary <span class="hlt">creep</span> in Sn3.8Ag0.7Cu solder using the constant load <span class="hlt">creep</span> 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 <span class="hlt">temperature</span> ranges and ramp rates. It was found that neglect of primary <span class="hlt">creep</span> 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 <span class="hlt">creep</span> strain to total inelastic strain under different thermal profiles. The constant-load <span class="hlt">creep</span> and stress relaxation data for Sn3.8Ag0.7Cu span a range of strain rates 10-8s-1 < 3? < 10-4 s-1, and <span class="hlt">temperatures</span> 25C, 75C and 100C. <span class="hlt">Creep</span> and stress relaxation measurements show that transient <span class="hlt">creep</span> caused faster strain rates during stress relaxation for a given stress compared to the corresponding minimum <span class="hlt">creep</span> rate from constant-load <span class="hlt">creep</span> tests. The extent of strain hardening during primary <span class="hlt">creep</span> was a function of <span class="hlt">temperature</span> and strain rate. A constitutive <span class="hlt">creep</span> model was presented for Sn3.8Ag0.7Cu that incorporates both transient and steady-state <span class="hlt">creep</span> to provide agreement for both <span class="hlt">creep</span> and stress relaxation data with a single set of eight coefficients. The model utilizes both <span class="hlt">temperature</span> compensated time and strain rate to normalize minimum strain rate and saturated transient <span class="hlt">creep</span> strain, thereby establishing equivalence between decreased <span class="hlt">temperature</span> and increased strain rate. The apparent activation energy of steady-state <span class="hlt">creep</span> 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 <span class="hlt">creep</span> is dominant under either static or variable loading.</p> <div class="credits"> <p class="dwt_author">Shirley, Dwayne R.</p> <p class="dwt_publisher"></p> <p class="publishDate"></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://ntrs.nasa.gov/search.jsp?R=19720006900&hterms=tungsten+carbide+cladding&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dtungsten%2Bcarbide%2Bcladding"> <span id="translatedtitle">Review of <span class="hlt">deformation</span> behavior of tungsten at <span class="hlt">temperature</span> less than 0.2 absolute melting <span class="hlt">temperature</span></span></a>  </p> <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 <span class="hlt">deformation</span> behavior of tungsten at <span class="hlt">temperatures</span> 0.2 T sub m is reviewed, with primary emphasis on the <span class="hlt">temperature</span> dependence of the yield stress and the ductile-brittle transition <span class="hlt">temperature</span>. It appears that a model based on the high Peierls stress of tungsten best accounts for the observed mechanical behavior at low <span class="hlt">temperatures</span>. Recent research is discussed which suggests an important role of electron concentration and bonding on the mechanical behavior of tungsten. It is concluded that future research on tungsten should include studies to define more clearly the correlation between electron concentration and mechanical behavior of tungsten alloys and other transition metal alloys.</p> <div class="credits"> <p class="dwt_author">Stephens, J. R.</p> <p class="dwt_publisher"></p> <p class="publishDate">1972-01-01</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://academic.research.microsoft.com/Publication/41026766"> <span id="translatedtitle"><span class="hlt">Creep</span> behavior and stability of MX precipitates at high <span class="hlt">temperature</span> in 9Cr0.5Mo1.8WVNb steel</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 growth behavior of MX carbonitrides during aging and <span class="hlt">creep</span> was investigated for 9Cr0.5Mo1.8WVNb steel (ASME-P92). The stress exponent of minimum <span class="hlt">creep</span> rate decreases with increasing testing <span class="hlt">temperature</span>. The value of stress exponent is 5.7 at 1023 K over a wide range of stress examined, while the value is 12.7 at 923 K. The low stress exponent at 1023 K</p> <div class="credits"> <p class="dwt_author">K. Sawada; K. Kubo; F. Abe</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">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.ntis.gov/search/product.aspx?ABBR=ADA556160"> <span id="translatedtitle">Effect of Elevated <span class="hlt">Temperature</span> on the Inelastic <span class="hlt">Deformation</span> Behavior of PMR-15 Solid Polymer.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">The inelastic <span class="hlt">deformation</span> behavior of PMR-15 neat resin, a high- <span class="hlt">temperature</span> thermoset polymer, was investigated at <span class="hlt">temperatures</span> in the 274-316 deg C range. The experimental program was developed to explore the influence of <span class="hlt">temperature</span> on tensile loading,...</p> <div class="credits"> <p class="dwt_author">C. E. Ryther</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">327</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/40291865"> <span id="translatedtitle">Microstructural evolution and nanostructure formation in copper during dynamic plastic <span class="hlt">deformation</span> at cryogenic <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">The microstructural evolution and formation mechanism of nanostructures in bulk pure Cu samples induced by dynamic plastic <span class="hlt">deformation</span> (DPD) at high strain rates and cryogenic <span class="hlt">temperatures</span> were investigated using transmission electron microscopic characterization. Three different mechanisms were identified for the plastic <span class="hlt">deformation</span> and microstructural refinement, including dislocation manipulation and rearrangement, <span class="hlt">deformation</span> twinning forming nanoscale twin\\/matrix (T\\/M) lamellae in bundles, and</p> <div class="credits"> <p class="dwt_author">Y. S. Li; N. R. Tao; K. Lu</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">328</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/2013AGUFMMR13A2220N"> <span id="translatedtitle">Mechanical behavior of low porosity carbonate rock: from brittle <span class="hlt">creep</span> to ductile <span class="hlt">creep</span></span></a>  </p> <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">Mechanical compaction and associated porosity reduction play an important role in the diagenesis of porous rocks. They may also affect reservoir rocks during hydrocarbon production, as the pore pressure field is modified. This inelastic compaction can lead to subsidence, cause casing failure, trigger earthquake, or change the fluid transport properties. In addition, inelastic <span class="hlt">deformation</span> can be time - dependent. In particular, brittle <span class="hlt">creep</span> phenomena have been deeply investigated since the 90s, especially in sandstones. However knowledge of carbonates behavior is still insufficient. In this experimental study, we focus on the mechanical behavior of a low porosity (9%) white Tavel (France) carbonate rock (>98% calcite) at P-Q conditions beyond the elastic domain. It has been shown that in sandstones composed of quartz, cracks are developing under these conditions. However, in carbonates, calcite minerals can meanwhile also exhibit microplasticity. The samples were <span class="hlt">deformed</span> in the triaxial cell of the Ecole Normale Superieure de Paris at effective confining pressures ranging from 35 MPa to 85 MPa and room <span class="hlt">temperature</span>. Experiments were carried on dry and water saturated samples to explore the role played by the pore fluids. Time dependency was investigated by a <span class="hlt">creep</span> steps methodology: at each step, differential stress was increased rapidly and kept constant for at least 24h. During these steps elastic wave velocities (P and S) and permeability were measured continuously. Our results show two different <span class="hlt">creep</span> behaviors: (1) brittle <span class="hlt">creep</span> is observed at low confining pressures, whereas (2) ductile <span class="hlt">creep</span> is observed at higher confining pressures. These two <span class="hlt">creep</span> behaviors have a different signature in term of elastic wave velocities and permeability changes. Indeed, in the brittle domain, the primary <span class="hlt">creep</span> is associated with a decrease of elastic wave velocities and an increase of permeability, and no secondary <span class="hlt">creep</span> is observed. In the ductile domain, the primary <span class="hlt">creep</span> is also associated with a decreased in elastic wave velocity and an increase of the permeability. However, the secondary <span class="hlt">creep</span> 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.</p> <div class="credits"> <p class="dwt_author">Nicolas, A.; Fortin, J.; Gueguen, Y.</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">329</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=PB2001108650"> <span id="translatedtitle">Influence of <span class="hlt">Temperature</span> on Autogenous <span class="hlt">Deformation</span> and RH-Change in Hardening Cement Paste.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">This report treats the influence of <span class="hlt">temperature</span> on autogenous <span class="hlt">deformation</span> and autogenous relative humidity change in hardening cement pastes. The subject is delt with both theoretically and experimentally.</p> <div class="credits"> <p class="dwt_author">O. M. Jensen</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-01-01</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://adsabs.harvard.edu/abs/2011AGUFM.T43C2349N"> <span id="translatedtitle">Experimental <span class="hlt">Deformation</span>, Partial Melting, and Compositional Changes in Perthitic K-feldspar 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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">In order to study the relationship between partial melting, cracking and transition to diffusion <span class="hlt">creep</span> processes, we have performed (i) axial compression experiments on natural perthitic K-feldspar single crystals (compression normal to the {010} plane), (ii) shear experiments (on 10-20 ?m grain size powder obtained from the same perthitic K-feldspar) and (iii) hydrostatic experiments (on powder and single crystals) with a solid medium Griggs-type <span class="hlt">deformation</span> apparatus at T=900C, Pc varying from 0.75-1.5 GPa and axial shortening ranging from 3 to 40% at a constant strain rate of 10-6 s-1. Samples were <span class="hlt">deformed</span> as-is and with added H2O (up to 0.2 wt %). <span class="hlt">Deformation</span> in the single crystal samples at 900C is largely accommodated by shear fractures. The mechanical data, however, show an inverse normal stress dependence (flow stress at 1.5 GPa is 330 MPa, at 1.0 GPa it is 450-500MPa, and at 0.75GPa it is 680 MPa) and peak stresses below the Goetze criterion, indicating that along the cracks <span class="hlt">deformation</span> is not dominantly friction controlled. Melt (less than 7%vol.) is distributed along cracks and shear zones are oriented at 40 to ?1 . EPMA analysis reveals inhomogenous melt compositions, suggesting that the melt pockets along cracks are not interconnected. Hydrostatic experiments performed at the same P, T conditions for the same amount of time as the <span class="hlt">deformation</span> experiments do not contain any melt, indicating that melt kinetics are - at least in part - controlled by the cracking process (solidus T=725C). Chemical homogenization is evident in the fine-grained fragments of the fault gouges, which have variable intermediate chemical compositions between the K-feldspar (Ab8 An0 Or92) and the albite lamellae (Ab98 An1 Or1) of the starting material. In powder shear experiments the melt fraction is higher than in single crystals. Melt is distributed along shear bands and around single grains, which are completely homogenized (Ab21 An0 Or79). The strength of the material is as high (100-150 MPa) as the strength of pure labradorite <span class="hlt">deformed</span> in shear, where no melt was detected. These observations suggest that the <span class="hlt">deformation</span> of single feldspar crystals at high pressure and <span class="hlt">temperature</span> is controlled by a simultaneous formation of micro-cracks and melt. The formation of wet melt is accelerated by cracking as demonstrated by the absence of melt in hydrostatic experiments. Melt formation occurs faster at higher confining pressure, and weakens the sample as demonstrated by the inverse dependence of peak-strength with confining pressure. The melt along the cracks accommodates the <span class="hlt">deformation</span> by viscous processes, but it does not dramatically weaken the samples because the melt pockets are not interconnected at the low melt fraction of 7%. The coalescence of the initial micro-cracks generates conjugate cracks in which the fine grained fragments of the gouge undergoes chemical homogenization. The <span class="hlt">deformation</span> mechanism in the gouge is likely to be melt-enhanced diffusion <span class="hlt">creep</span>, which is likely to also assist the chemical homogenization process.</p> <div class="credits"> <p class="dwt_author">Negrini, M.; Stunitz, H.; Menegon, L.; Nasipuri, P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-12-01</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/1999PhDT........89Y"> <span id="translatedtitle">The influence of impurity content on <span class="hlt">creep</span> <span class="hlt">deformation</span>, cavity stringer formation, microstructure evolution, and boundary segregation in the superplastic zinc-22wt% aluminum eutectoid</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 detailed investigation was conducted using six grades of Zn-22wt%Al, containing different levels and types of impurities, to study the influence of impurity content on the properties of superplastic flow in the alloy. Aspects of <span class="hlt">creep</span> <span class="hlt">deformation</span> and cavitation at low stresses were studied by examining the effect of Fe, Cu, and Mg as selected impurities. Characteristics associated with high purity grades of the alloy, doped with either Cu or Mg, were essentially identical to those reported previously for high-purity Zn-22wt%Al but different from those documented for a grade of the alloy containing a comparable atomic concentration of Fe (1290 at. %). These results suggest that Cu and Mg, unlike Fe, have little or no tendency to segregate at boundaries and clearly indicate that superplastic flow and cavitation at low stresses are controlled not only by impurity level but also by its type. Further evidence for this suggestion was obtained by studying the effect of impurities on former alpha boundaries (FalphaBs), which are residual grain boundaries that originate during the heat treatment required for grain refinement in Zn-22wt%Al. In this regard, it was found that the characteristics associated with FalphaBs directly correspond with the level and type of impurities in Zn-22wt%Al. This correspondence, according to the detailed results obtained on FalphaB growth kinetics in the six grades of Zn-22wt%Al, results from impurity segregation at FalphaBs and tends strong support to the interpretation of superplastic behavior at low stresses in terms of phenomena arising from boundary segregation. It is suggested that information on FalphaB growth kinetics can be utilized to predict low-stress <span class="hlt">creep</span> characteristics, such as the existence of a threshold stress or the occurrence of extensive cavitation. In addition, the microstructural evolution of FalphaBs during superplastic <span class="hlt">deformation</span> was examined to provide insight into the origin of cavity stringers that form parallel to the tensile axis in the alloy. A comparison between the behavior of FalphaBs and the characteristics of cavity stringers reveals a direct correspondence between these two substructural features. On this basis, a mechanism that explains the formation of cavity stringers in Zn-22wt%Al has also been proposed.</p> <div class="credits"> <p class="dwt_author">Yousefiani, Ahmadali</p> <p class="dwt_publisher"></p> <p class="publishDate"></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://academic.research.microsoft.com/Publication/46562098"> <span id="translatedtitle">Finite element analysis on <span class="hlt">creep</span> damage</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">An implicit, iterative semi-analytical integration scheme is proposed to integrate the Leckie-Hayhurst isotropic <span class="hlt">creep</span> damage evolution equation as well as the Bailey-Norton <span class="hlt">creep</span> constitutive equation. This scheme is incorporated to a finite element programme dealing with thermal elastic plastic <span class="hlt">creep</span> problems. <span class="hlt">Creep</span> damage evolution and rupture time in a high <span class="hlt">temperature</span> structure can be predicted.</p> <div class="credits"> <p class="dwt_author">X. N. Wang; X. C. Wang</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-01-01</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/978760"> <span id="translatedtitle">Effects of Minor Alloy Additions and Oxidation <span class="hlt">Temperature</span> on Protective Alumina Scale Formation in <span class="hlt">Creep</span>-Resistant Austenitic Stainless Steels</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">Alumina scale formation in newly developed <span class="hlt">creep</span>-resistant austenitic stainless steels was found to be sensitive to Al, Nb, Ti, and V content and oxidation <span class="hlt">temperature</span>. Ti and V synergistically degraded the ability to form a protective alumina scale, whereas Nb was beneficial for alumina scale formation. The ability to form external alumina scales was lost in the lower Al and Nb containing alloys between 800 and 900 aC. Compositions with the potential to form alumina at 900 aC (and possibly higher) were identified.</p> <div class="credits"> <p class="dwt_author">Brady, Michael P [ORNL; Yamamoto, Yukinori [ORNL; Santella, Michael L [ORNL; Pint, Bruce A [ORNL</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">334</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/2013GeoRL..40..697T"> <span id="translatedtitle">Magnetite <span class="hlt">deformation</span> mechanism maps for better prediction of strain partitioning</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"><title type="main">Abstract A meta-analysis of existing experimental <span class="hlt">deformation</span> data for magnetite and other spinel-structured ferrites reveals that previously published flow laws are inadequate to describe the general <span class="hlt">deformation</span> behavior of magnetite. Using updated rate equations for oxygen diffusion in magnetite, we present new flow laws that closely predict <span class="hlt">creep</span> rates similar to those found in <span class="hlt">deformation</span> experiments and that can be used to predict strain partitioning between cubic Fe oxides and other phases in the Earth's crust. New <span class="hlt">deformation</span> mechanism maps for magnetite have been constructed as functions of <span class="hlt">temperature</span> and grain size. Using the revised <span class="hlt">creep</span> parameters, estimates of strain partitioning between magnetite, ilmenite, and plagioclase indicate that concentrated zones of Fe-Ti oxides in oceanic crust near slow-spreading ridges could accommodate significant amounts of strain at moderate <span class="hlt">temperatures</span> and may contribute to aseismic <span class="hlt">creep</span> along spreading-segment faults.</p> <div class="credits"> <p class="dwt_author">Till, J. L.; Moskowitz, Bruce</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-02-01</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://adsabs.harvard.edu/abs/2010poch.book...73B"> <span id="translatedtitle">Laser-Interferometric <span class="hlt">Creep</span> Rate Spectroscopy of Polymers</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">Laser-interferometric <span class="hlt">creep</span> rate meter (LICRM) and <span class="hlt">creep</span> rate spectroscopy (CRS), as an original high-resolution method for discrete relaxation spectrometry and thermal analysis, were developed in the authors' Materials Dynamics Laboratory at Ioffe Physical-Technical Institute of the Russian Academy of Sciences (Saint-Petersburg). In the last few decades they have been successfully applied to solving various problems of polymer physics and materials science, especially being combined with DSC, structural, and other techniques. CRS involves measuring ultra-precisely a <span class="hlt">creep</span> rate at small tensile or compressive stress, typically much lower than the yield stress, as a function of <span class="hlt">temperature</span>, over the range from 100 to 800 K. LICRM setup allows one to register precisely <span class="hlt">creep</span> rates on the basis of <span class="hlt">deformation</span> increment of 150-300 nm. The survey describes this method and summarizes the results of numerous studies performed with the LICRM setup and CRS technique for different bulk polymeric materials, films, or thin fibers. This approach provided new experimental possibilities superior in resolution and sensitivity compared to the conventional relaxation spectrometry techniques. Among such possibilities are discrete analysis of dynamics; <span class="hlt">creep</span> on submicro-, micro- and meso-scales; revealing relations between stepwise microplasticity and morphology; kinetic information on <span class="hlt">creep</span> at any <span class="hlt">temperature</span> and <span class="hlt">deformation</span>; polymer dynamics at interfaces; analysis of microplasticity, relaxations, and phase transitions in brittle materials; using <span class="hlt">creep</span> rate spectra for non-destructive prediction of <span class="hlt">temperature</span> anomalies in mechanical behavior of materials, etc. Considerable attention has been paid to combined CRS/DSC analysis of the peculiarities of segmental dynamics, nanoscale dynamic, and compositional heterogeneity in different kinds of complex polymer systems and nanocomposites.</p> <div class="credits"> <p class="dwt_author">Bershtein, Vladimir A.; Yakushev, Pavel N.</p> <p class="dwt_publisher"></p> <p class="publishDate"></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://ntrs.nasa.gov/search.jsp?R=19750054660&hterms=Mat&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DMat"> <span id="translatedtitle"><span class="hlt">Deformation</span> characteristics and time-dependent notch sensitivity of Udimet 700 at intermediate <span class="hlt">temperatures</span></span></a>  </p> <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 notch sensitivity of Udimet 700 sheet, bar, and investment castings was observed between 1000 and 1400 F (538-760 C) but not at 1600 F (871 C). As was the case for Modified Waspaloy, Waspaloy, Rene 41, Inconel 718, and TD-NiCr, it occurred when notched specimens were loaded below the yield strength and when <span class="hlt">creep</span> <span class="hlt">deformation</span> was localized. For each gamma-prime strengthened alloy and notched specimen geometry, a stress-average particle size zone can be defined to characterize the notch-sensitive behavior.</p> <div class="credits"> <p class="dwt_author">Wilson, D. J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1975-01-01</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/1996MMTA...27.3074J"> <span id="translatedtitle">Prediction of <span class="hlt">creep</span>-rupture life of unidirectional titanium matrix composites subjected to transverse 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">Titanium matrix composites (TMCs) incorporating unidirectional fiber reinforcement are considered as enabling materials technology for advanced engines which require high specific strength and elevated <span class="hlt">temperature</span> capability. The resistance of unidirectional TMCs to <span class="hlt">deformation</span> under longitudinally applied sustained loading at elevated <span class="hlt">temperatures</span> has been well documented. Many investigators have shown that the primary weakness of the unidirectional TMC is its susceptibility to failure under very low transverse loads, especially under sustained loading. Hence, a reliable model is required to predict the <span class="hlt">creep</span>-rupture life of TMCs subjected to different transverse stress levels over a wide range of <span class="hlt">temperatures</span>. In this article, we propose a model to predict the <span class="hlt">creep</span>-rupture life of unidirectional TMC subjected to transverse loading based on the <span class="hlt">creep</span>-rupture life of unidirectional TMC subjected to transverse loading based on the <span class="hlt">creep</span>-rupture behavior of the corresponding fiberless matrix. The model assumes that during transverse loading, the effective load-carrying matrix ligament along a row of fibers controls the <span class="hlt">creep</span>-rupture strength and the fibers do not contribute to the <span class="hlt">creep</span> resistance of the composite. The proposed model was verified using data obtained from different TMC fabricated using three matrix compositions, which exhibited distinctly different types of <span class="hlt">creep</span> behavior. The results show that the <span class="hlt">creep</span>-rupture life of the transverse TMC decreases linearly with increasing ratio of the fiber diameter to the ply thickness. The creeprupture life is also predicted to be independent of fiber spacing along the length of the specimen.</p> <div class="credits"> <p class="dwt_author">John, Reji; Khobaib, M.; Smith, Paul R.</p> <p class="dwt_publisher"></p> <p class="publishDate">1996-10-01</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.springerlink.com/index/7bc57hheb51t5jh1.pdf"> <span id="translatedtitle">Uniaxial <span class="hlt">deformation</span> behavior of different polypropylene cast films at <span class="hlt">temperatures</span> near the melting point</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">A new apparatus for stretching polypropylenes at elevated <span class="hlt">temperatures</span> below the melting point at high <span class="hlt">deformation</span> speeds (up to 750 mm\\/s) is described. In the <span class="hlt">temperature</span> range of 140-160 C the tensile behavior of polypropylene undergoes a shift from the ductile to the quasi-rubber-like <span class="hlt">deformation</span> behavior. Furthermore, the <span class="hlt">deformation</span> behavior is strongly affected by the strain rate. The homogeneity of</p> <div class="credits"> <p class="dwt_author">Stefan Rettenberger; Ludovic Capt; Helmut Mnstedt; Klaus Stopperka; Johannes Snze</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">339</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/2013JSG....46..142T"> <span id="translatedtitle">Coupled micro-faulting and pressure solution <span class="hlt">creep</span> overprinted on quartz schist <span class="hlt">deformed</span> by intracrystalline plasticity during exhumation of the Sambagawa metamorphic rocks, southwest Japan</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 the Sambagawa schist, southwest Japan, while ductile <span class="hlt">deformation</span> pervasively occurred at D1 phase during exhumation, low-angle normal faulting was locally intensive at D2 phase under the conditions of frictional-viscous transition of quartz (c. 300 C) during further exhumation into the upper crustal level. Accordingly, the formation of D2 shear bands was overprinted on type I crossed girdle quartz c-axis fabrics and microstructures formed by intracrystalline plasticity at D1 phase in some quartz schists. The quartz c-axis fabrics became weak and finally random with increasing shear, accompanied by the decreasing degree of undulation of recrystallized quartz grain boundaries, which resulted from the increasing portion of straight grain boundaries coinciding with the interfaces between newly precipitated quartz and mica. We interpreted these facts as caused by increasing activity of pressure solution: the quartz grains were dissolved mostly at platy quartz-mica interface, and precipitated with random orientation and pinned by mica, thus having led to the obliteration of existing quartz c-axis fabrics. In the sheared quartz schist, the strength became reduced by the enhanced pressure solution <span class="hlt">creep</span> not only due to the reduction of diffusion path length caused by increasing number of shear bands, but also to enhanced dissolution at the interphase boundaries.</p> <div class="credits"> <p class="dwt_author">Takeshita, Toru; El-Fakharani, Abdel-Hamid</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">340</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/2011MTDM...15..293S"> <span id="translatedtitle">Analysis of <span class="hlt">creep</span> behavior in thermoplastics based on visco-elastic theory</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">Plastics and fiber-reinforced plastics (FRP) are used in the aerospace industry because of their mechanical properties. However, despite their excellent high-<span class="hlt">temperature</span> mechanical properties, plastics and FRP eventually <span class="hlt">deform</span> visco-elastically at high <span class="hlt">temperatures</span>. Most of the research has focused on the <span class="hlt">creep</span> behavior of FRPs, but few studies have investigated the linear visco-elastic behavior. Linear visco-elastic behavior and non-linear visco-elastic behavior occur with physical aging in these plastics. In this study, the non-linear visco-elastic behavior of plastics and FRP was investigated based on the bending <span class="hlt">creep</span> <span class="hlt">deformation</span> of polycarbonate (PC) and polyoxymethylene (POM). Moreover, the effects of the fiber volume fraction on the <span class="hlt">creep</span> characteristics were investigated using glass fiber-reinforced polycarbonate (GFRPC). The <span class="hlt">creep</span> <span class="hlt">deformation</span> was calculated using the linear visco-elastic theory based on these effects, and comparison between experimental and estimated data showed that the <span class="hlt">creep</span> analysis sufficiently predicted the <span class="hlt">creep</span> behavior.</p> <div class="credits"> <p class="dwt_author">Sakai, Takenobu; Somiya, Satoshi</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-08-01</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 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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_19");' 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">341</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=IFRT&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DIFRT"> <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 " 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.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 85C at the frequency range of 0.1-10Hz 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">343</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 " 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/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">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/scitech/biblio/5574188"> <span id="translatedtitle">Acoustic emission in plastic <span class="hlt">deformation</span> of metals (review). Report 1</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 review focuses on attempts to establish quantitative relationships for construction of a theory of acoustic emission in plastic <span class="hlt">deformation</span>. The authors also discuss acoustic emission in <span class="hlt">deformation</span> of production steels and the role of plastic <span class="hlt">deformation</span> at the crack tip. The parameters most frequently determined in experimental investigation of acoustic emission are presented. The influence of the grain size of a polycrystalline material is investigated and acoustic emission in <span class="hlt">creep</span> of polycrystalline A1, Cd, and Pb at room <span class="hlt">temperature</span> is discussed.</p> <div class="credits"> <p class="dwt_author">Yudin, A.A.; Ivanov, V.I.</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-02-01</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.springerlink.com/index/l9m3644255771632.pdf"> <span id="translatedtitle">Suppression of <span class="hlt">creep</span> cavitation in precipitation-hardened austenitic stainless steel to enhance <span class="hlt">creep</span> rupture strength</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">Extensive <span class="hlt">creep</span> cavitation in Ti, Nb and Cu containing precipitation hardened austenitic steels was found to limit the usefulness\\u000a of <span class="hlt">deformation</span> resistance to increase long-term <span class="hlt">creep</span> rupture strength. The steels were microalloyed with boron and cerium\\u000a that resulted in increase in <span class="hlt">creep</span> rupture strength and ductility of the steels significantly. Grain boundary sliding and\\u000a <span class="hlt">creep</span> cavity nucleation and growth in</p> <div class="credits"> <p class="dwt_author">K. Laha; J. Kyono; N. Shinya</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</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://academic.research.microsoft.com/Publication/26465629"> <span id="translatedtitle">The influence of plasticity in <span class="hlt">creep</span> crack growth in 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">Much of the reported work on assessing time-dependent (<span class="hlt">creep</span>) crack growth has focussed on <span class="hlt">creep</span> ductile materials, with the <span class="hlt">deformation</span> conditions ranging from small-scale <span class="hlt">creep</span> to extensive steady state <span class="hlt">creep</span>. This previous research on crack initiation and growth has been mainly concerned with characterising <span class="hlt">creep</span> crack growth rates using the C? parameter.In this paper we interpret recent experimental results by</p> <div class="credits"> <p class="dwt_author">A. J Fookes; D. J Smith</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-01-01</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://www.osti.gov/scitech/servlets/purl/931001"> <span id="translatedtitle">Multi-Phase High <span class="hlt">Temperature</span> Alloys: Exploration of Alumina-Forming, <span class="hlt">Creep</span>-Resistant Austenitic Stainless Steels</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">Work in 2007 focused on the development of a new class of heat-resistant austenitic stainless steel alloys which achieved a unique combination of high-<span class="hlt">temperature</span> <span class="hlt">creep</span> strength and excellent oxidation resistance via protective Al{sub 2}O{sub 3} scale formation. Strengthening is achieved via the formation of stable nano NbC carbides with/without Fe{sub 2}Nb and related intermetallic phase dispersions, with controlled levels of Al to enable Al{sub 2}O{sub 3} scale formation in both air and air + water vapor environments up to {approx}800-900 C. The developed alloys exhibit comparable <span class="hlt">creep</span> resistance to that of the best commercial heat-resistant austenitic stainless steels, and the protective Al{sub 2}O{sub 3} scale formation provides oxidation resistance superior to that of advanced Cr{sub 2}O{sub 3}-forming heat-resistant austenitic alloys. Preliminary screening also indicated that the developed Al-modified alloys were amenable to welding.</p> <div class="credits"> <p class="dwt_author">Brady, Michael P [ORNL; Yamamoto, Yukinori [ORNL; Lu, Zhao Ping [ORNL; Maziasz, Philip J [ORNL; Santella, Michael L [ORNL; Pint, Bruce A [ORNL</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">349</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">350</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/5209108"> <span id="translatedtitle"><span class="hlt">Deformation</span> twinning in polycrystalline copper at room <span class="hlt">temperature</span> and low strain rate</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">Deformation</span> twins were widely observed in polycrystalline Cu with grain sizes varying from micrometers to nanometers during the process of equal channel angular pressing at room <span class="hlt">temperature</span> and low strain rate (?10?2s?1). The microstructures of <span class="hlt">deformation</span> twins were characterized by a transmission electron microscope (TEM) and a high-resolution TEM. It was found that <span class="hlt">deformation</span> twinning in coarse-grained Cu occurred mainly</p> <div class="credits"> <p class="dwt_author">C. X. Huang; K. Wang; S. D. Wu; Z. F. Zhang; G. Y. Li; S. X. Li</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">351</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/40057611"> <span id="translatedtitle"><span class="hlt">Creep</span> properties of eutectic Sn3.5Ag solder joints reinforced with mechanically incorporated Ni particles</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> <span class="hlt">deformation</span> behavior of eutectic Sn-3.5Ag based Ni particle rein forced composite solder joints was investigated.\\u000a The Ni particle reinforced composite solder was prepared by mechanically dispersing 15 vol.% of Ni particles into eutectic\\u000a Sn-3.5Ag solder paste. Static-loading <span class="hlt">creep</span> tests were carried out on solder joint specimens at 25 C, 65 C, and 105 C, representing\\u000a homologous <span class="hlt">temperatures</span> ranging</p> <div class="credits"> <p class="dwt_author">F. Guo; J. Lee; J. P. Lucas; K. N. Subramanian; T. R. Bieler</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">352</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/41036465"> <span id="translatedtitle">High <span class="hlt">temperature</span> <span class="hlt">deformation</span> of ZrB 2SiCAlN ceramic 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">ZrB2 ceramic composites are powerful candidates for use in ultra-high <span class="hlt">temperature</span> structural materials given their strength under high <span class="hlt">temperatures</span>, superb ablation resistance, and good oxidation resistance. Unfortunately, ZrB2 ceramic composites are difficult to <span class="hlt">deform</span> due to inherent brittle property, which impedes large-scale application. High <span class="hlt">temperature</span> <span class="hlt">deformation</span> of ZrB2SiCAlN ceramic composite at 1900C with inert gas protection is investigated using deep</p> <div class="credits"> <p class="dwt_author">Wenbo Han; Xinghong Zhang; Weibin Tai; Jiecai Han</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</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://academic.research.microsoft.com/Publication/39762951"> <span id="translatedtitle">Effect of preliminary plastic <span class="hlt">deformation</span> on the mechanical properties of austenitic steel at low <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">Many authors have investigated the laws of straln-hardenlng of austenitic steels at low <span class="hlt">temperatures</span> [i, 2]. This is due to the wide use of these materials in cryogenics. Also, the features of their low-<span class="hlt">temperature</span> <span class="hlt">deformation</span> are of great scientific interest. It is known that the low-<span class="hlt">temperature</span> <span class="hlt">deformation</span> of austenitic steels with a low-stability solid solution is accompanied by phase transformations</p> <div class="credits"> <p class="dwt_author">A. A. Lebedev; V. N. Rudenko; B. I. Koval'chuk</p> <p class="dwt_publisher"></p> <p class="publishDate">1983-01-01</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.osti.gov/scitech/servlets/purl/772055"> <span id="translatedtitle">Elevated <span class="hlt">Temperature</span> <span class="hlt">Creep</span> Properties of Conventional 50Au-50Cu and 47Au 50Cu-3Ni Braze 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">The elevated <span class="hlt">temperature</span> <span class="hlt">creep</span> properties of the 50Au-50Cu wt% and 47Au-50Cu-3Ni braze alloys have been evaluated over the <span class="hlt">temperature</span> range 250-850 C. At elevated <span class="hlt">temperatures</span>, i.e., 450-850 C, both alloys were tested in the annealed condition (2 hrs. 750 C/water quenched). The minimum strain rate properties over this <span class="hlt">temperature</span> range are well fit by the Garofalo sinh equation. At lower <span class="hlt">temperatures</span> (250 and 350 C), power law equations were found to characterize the data for both alloys. For samples held long periods of time at 375 C (96 hrs.) and slowly cooled to room <span class="hlt">temperature</span>, an ordering reaction was observed. For the case of the 50Au-50Cu braze alloy, the stress necessary to reach the same, strain rate increased by about 15% above the baseline data. The limited data for ordered 47Au-50Cu-3Ni alloy reflected a,smaller strength increase. However, the sluggishness of this ordering reaction in both alloys does not appear to pose a problem for braze joints cooled at reasonable rates following brazing.</p> <div class="credits"> <p class="dwt_author">STEPHENS JR.,JOHN J.; SCHMALE,DAVID T.</p> <p class="dwt_publisher"></p> <p class="publishDate">2000-12-18</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://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 " 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.osti.gov/scitech/biblio/978516"> <span id="translatedtitle"><span class="hlt">Creep</span> Behavior of Glass/Ceramic Sealant Used in Solid Oxide Fuel Cells</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 operating <span class="hlt">temperature</span> of solid oxide fuel cells require that sealant must function at high <span class="hlt">temperature</span> between 600o and 900oC and in the oxidizing and reducing environments of fuel and air. It should be noted that <span class="hlt">creep</span> <span class="hlt">deformation</span> becomes relevant for a material when the operating <span class="hlt">temperature</span> is near or exceeds half of its melting <span class="hlt">temperature</span> (in degrees of Kelvin). The operating <span class="hlt">temperatures</span> for most of the solid oxide fuel cells (SOFC) under development in the SECA program are around 800oC, which exceeds the glass transition <span class="hlt">temperature</span> Tg for most glass ceramic materials. The goal of the study is to develop a <span class="hlt">creep</span> model to capture the <span class="hlt">creep</span> behavior of glass ceramic materials at high <span class="hlt">temperature</span> and to investigate the effect of <span class="hlt">creep</span> of glass ceramic sealant materials on stresses in glass seal and on the various interfaces of glass seal with other layers. The self-consistent <span class="hlt">creep</span> models were incorporated into SOFC-MP and Mentat FC, and finite element analyses were performed to quantify the stresses in various parts. The stress in glass seals were released due to its <span class="hlt">creep</span> behavior during the operating environments.</p> <div class="credits"> <p class="dwt_author">Liu, Wenning N.; Sun, Xin; Koeppel, Brian J.; Khaleel, Mohammad A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-02</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://ntrs.nasa.gov/search.jsp?R=19940018140&hterms=Fatigue+Testing+Piping+Components&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DFatigue%2BTesting%2BPiping%2BComponents"> <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 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://academic.research.microsoft.com/Publication/18846266"> <span id="translatedtitle"><span class="hlt">Temperature</span> dependence of electron beam induced current contrast of <span class="hlt">deformation</span>-induced defects in silicon</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">Electron beam induced current (EBIC) investigations of plastically <span class="hlt">deformed</span> silicon in the <span class="hlt">temperature</span> range from 90 K to 300 K were carried out. It is found that the dislocation trails left behind moving dislocations are the main defects revealed by the EBIC in crystals <span class="hlt">deformed</span> in clean conditions. With an increase of the contamination level, the dislocation contrast in p-type</p> <div class="credits"> <p class="dwt_author">O. V. Feklisova; E. B. Yakimov; N. Yarykin; B. Pichaud</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">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/2013MMTA...44..136W"> <span id="translatedtitle">Advanced Procedures for Long-Term <span class="hlt">Creep</span> Data Prediction for 2.25 Chromium Steels</span></a>  </p> <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 critical review of recent <span class="hlt">creep</span> studies concluded that traditional approaches such as steady-state behavior, power law equations, and the view that diffusional <span class="hlt">creep</span> mechanisms are dominant at low stresses should be seriously reconsidered. Specifically, <span class="hlt">creep</span> strain rate against time curves show that a decaying primary rate leads into an accelerating tertiary stage, giving a minimum rather than a secondary period. Conventional steady-state mechanisms should therefore be abandoned in favor of an understanding of the processes governing strain accumulation and the damage phenomena causing tertiary <span class="hlt">creep</span> and fracture. Similarly, <span class="hlt">creep</span> always takes place by dislocation processes, with no change to diffusional <span class="hlt">creep</span> mechanisms with decreasing stress, negating the concept of <span class="hlt">deformation</span> mechanism maps. Alternative descriptions are then provided by normalizing the applied stress through the ultimate tensile stress and yield stress at the <span class="hlt">creep</span> <span class="hlt">temperature</span>. In this way, the resulting Wilshire equations allow accurate prediction of 100,00 hours of <span class="hlt">creep</span> data using only property values from tests lasting 5000 hours for a series of 2.25 chromium steels, namely grades 22, 23, and 24.</p> <div class="credits"> <p class="dwt_author">Whittaker, Mark T.; Wilshire, Brian</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">360</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 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 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 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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");' 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 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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">361</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 " 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://academic.research.microsoft.com/Publication/40989553"> <span id="translatedtitle">Mechanical spectroscopy connected to <span class="hlt">creep</span> and stress relaxation in a high resistant silicon nitride</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">Silicon nitride processed by gas pressure sintering contains a very small amount of glassy phase and consequently exhibits a strong resistance to <span class="hlt">deformation</span> until 1450C. Above this <span class="hlt">temperature</span>, both relaxation kinetics and <span class="hlt">creep</span> rate rapidly increase. To explain such a behaviour, the formation of a liquid phase by dissolution of YSiAlON phases was proposed. The present paper shows that mechanical</p> <div class="credits"> <p class="dwt_author">S Testu; R Schaller; J. L Besson; T Rouxel; G Bernard-Granger</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">363</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/27205362"> <span id="translatedtitle">Shear Correction Factors in <span class="hlt">Creep</span>-Damage Analysis of Beams, Plates and Shells</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">Modern design rules for thin-walled structures which operate at elevated <span class="hlt">temperatures</span> are based on the demand that the <span class="hlt">creep</span> and may be the damage behaviour should be taken into account. In the last four decades various models including the scalar or tensor valued hardening and damage variables are established. These models reflect the influence of the <span class="hlt">deformation</span> or the damage</p> <div class="credits"> <p class="dwt_author">Holm Altenbach; Konstantin Naumenko</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</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://www.osti.gov/scitech/biblio/532880"> <span id="translatedtitle">Continuum predictions of <span class="hlt">deformation</span> in composites with two <span class="hlt">creeping</span> phases. 2: Nb{sub 5}Si{sub 3}/Nb 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">The primary and steady-state <span class="hlt">creep</span> behavior of ductile-phase toughened Nb{sub 5}Si{sub 3}/Nb in situ composites has been simulated using the analytical and finite element (FE) continuum techniques described in Part 1 of this paper. The material constants in the <span class="hlt">creep</span> constitutive law have been fitted to experimentally measured <span class="hlt">creep</span> properties of the bulk Nb{sub 5}Si{sub 3} and Nb solid-solution phases. The composite microstructure has been idealized to facilitate the modeling, with a variety of microstructural idealizations resulting in very similar predicted composite <span class="hlt">creep</span> rates. The models somewhat underpredict the steady-state strain rates and over predict the primary <span class="hlt">creep</span> strains for the Nb-10 at.% Si composite studied experimentally. Several potential causes for these discrepancies have been identified, including internal damage effects and a possible increase in the Nb{sub 5}Si{sub 3} stress exponent at high stress. However, the models correctly make the important prediction that the <span class="hlt">creep</span> strength of the Nb-rich composite is dominated by the strong Nb{sub 5}Si{sub 3} phase. FE predictions of large internal tensile stresses in the matrix are consistent with experimental observations of <span class="hlt">creep</span> damage.</p> <div class="credits"> <p class="dwt_author">Henshall, G.A.; Strum, M.J. [Lawrence Livermore National Lab., CA (United States)] [Lawrence Livermore National Lab., CA (United States); Subramanian, P.R.; Mendiratta, M.G. [UES, Inc., Dayton, OH (United States)] [UES, Inc., Dayton, OH (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-08-01</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://adsabs.harvard.edu/abs/2014JEMat..43.2530T"> <span id="translatedtitle">A Method to Identify Steady <span class="hlt">Creep</span> Strain from Indentation <span class="hlt">Creep</span> Using a New Reference Area of Indentation</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">For the design of high-density electronic packages, finite element method (FEM) analyses to evaluate strength reliabilities of solder joints should be conducted by employing the material parameters which can precisely reflect the <span class="hlt">creep</span> properties of solder joints in actual electronic equipment. To obtain accurate results of the structural analyses of the solder joints, a method to evaluate the steady-state <span class="hlt">creep</span> <span class="hlt">deformation</span> in situ must be developed. The indentation <span class="hlt">creep</span> test is an effective method to evaluate the <span class="hlt">creep</span> properties of the solder joints in situ; however, the <span class="hlt">creep</span> properties obtained by this method do not give the same results as those obtained by tensile <span class="hlt">creep</span> tests using bulk specimens. In this paper, the indentation <span class="hlt">creep</span> test at 1 N loading for 9,000 s duration was experimentally conducted to confirm that the steady-state <span class="hlt">creep</span> <span class="hlt">deformation</span> obtained by the indentation <span class="hlt">creep</span> test did not coincide with that by the tensile <span class="hlt">creep</span> tests using bulk specimens. To identify the reason, the indentation <span class="hlt">creep</span> simulation was conducted by FEM analysis. As a result, it was found that the reference area used to obtain the <span class="hlt">creep</span> strain from the indentation <span class="hlt">creep</span> test should be modified. A method to obtain the new reference area is proposed from comparisons of experiments with simulations. Finally, this paper shows that the <span class="hlt">creep</span> properties obtained by the indentation <span class="hlt">creep</span> test using the new reference area coincided with those obtained by tensile <span class="hlt">creep</span> tests using bulk specimens.</p> <div class="credits"> <p class="dwt_author">Takita, Atsuko; Sasaki, Katsuhiko; Ohguchi, Ken-ichi</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-07-01</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/41023395"> <span id="translatedtitle">Room <span class="hlt">temperature</span> <span class="hlt">creep</span> behavior of nanocrystalline nickel produced by an electrodeposition technique</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">Deformation</span> processes of nanocrystalline (640 nm) nickel produced by an electrodeposition technique were studied. First, the results of unidirectional tensile tests were discussed with respect to the deviation from the Hall-Petch relationship. It was suggested that such a mechanical behavior exhibited by nanocrystalline materials could be described by a composite model proposed previously. Further experimental work on static and dynamic</p> <div class="credits"> <p class="dwt_author">Ning Wang; Zhirui Wang; K. T. Aust; U. Erb</p> <p class="dwt_publisher"></p> <p class="publishDate">1997-01-01</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://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">368</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/49428515"> <span id="translatedtitle">Flow stress and ductility of AA7075-T6 aluminum alloy at low <span class="hlt">deformation</span> <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">The present investigation has been conducted in order to develop a rational approach able to describe the changes in flow stress of AA7075-T6 aluminum alloy with <span class="hlt">deformation</span> <span class="hlt">temperature</span> and strain rate, when this material is <span class="hlt">deformed</span> at <span class="hlt">temperatures</span> in the range of 123298K at strain rates in the range of 410?4 to 510?2s?1. The constitutive formulation that has been advanced</p> <div class="credits"> <p class="dwt_author">E. S. Puchi-Cabrera; M. H. Staia; E. Ochoa-Prez; J. G. La Barbera-Sosa; C. Villalobos-Gutierrez; A. Brenlla-Caires</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">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/2008AIPC.1027.1357K"> <span id="translatedtitle">Extended <span class="hlt">Creep</span> Recovery via Oscillatory Shear and Bending Beam Rheometers</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">Relaxation and retardation spectra are often used to describe the linear viscoelastic properties of polymer melts, asphalts, and other viscoelastic materials, since the spectra contain sufficient information from which other linear material functions can be easily calculated. The applicability of these functions strongly depends on the range of frequencies or relaxation times over which the experimental data were obtained. Various techniques can be employed to expand the range of relaxation times, which involves using different types of tests, such as oscillatory shear or <span class="hlt">creep</span>. The overall range of relaxation times can be expanded by means of the time-<span class="hlt">temperature</span> superposition. In the case of bituminous materials studied, <span class="hlt">creep</span> experiments at lower <span class="hlt">temperatures</span> involve different testing geometry, e.g. a bending beam rheometer (BBR). The challenge is to combine the spectra obtained from the oscillatory and <span class="hlt">creep</span>/recovery in shear <span class="hlt">deformation</span> with the spectra obtained from the extended flexural <span class="hlt">deformation</span>. We demonstrate a technique of combining the spectra obtained for a conventional bitumen (asphalt), with a practical application to modeling a multiple <span class="hlt">creep</span> and recovery test.</p> <div class="credits"> <p class="dwt_author">Kazatchkov, Igor B.; Stastna, Jiri; Zanzotto, Ludo</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-07-01</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/2014JMEP..tmp..129J"> <span id="translatedtitle">Effect of High-<span class="hlt">Temperature</span> Severe Plastic <span class="hlt">Deformation</span> on Microstructure and Mechanical Properties of IF Steel</span></a>  </p> <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">Extensive research work has been carried out on interstitial-free steel to understand its response to <span class="hlt">deformation</span>; particularly, the behavior during severe plastic <span class="hlt">deformation</span> (SPD). However, most of these studies were mainly undertaken in the ferritic regime. The present investigation reports the initial results of our attempt to employ accumulative roll bonding (ARB), one of the variants of SPD, at a high <span class="hlt">temperature</span> (950 C). A considerable grain refinement has been observed, which may be attributed to the severity of <span class="hlt">deformation</span> and recrystallisation at high <span class="hlt">temperatures</span>. Nanoindentation tests have been performed at various stages of ARB process to understand the evolution of mechanical properties.</p> <div class="credits"> <p class="dwt_author">Jindal, Vikas; Rupa, P. K. P.; Mandal, G. K.; Srivastava, V. C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-04-01</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://www.osti.gov/scitech/servlets/purl/212679"> <span id="translatedtitle">High <span class="hlt">temperature</span> <span class="hlt">deformation</span> in 2036 Al and 0.2 wt % Zr-2036 A1</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 microstructure and high-<span class="hlt">temperature</span> <span class="hlt">deformation</span> of 2036 Al and a 0.2 wt % Zr modified 2036 Al were characterized. A particle-simulated- nucleation process was applied to refine grain structure in both alloys. Thermomechanically processed materials were tested from 450 to 500 C and strain rates from 2{times}10{sup {minus}1} to 2{times}10{sup {minus}4}s{sup {minus}1}. Strain rate sensitivity exponent, activation energy, and total elongation were measured, and the <span class="hlt">deformation</span> mechanism was proposed. Effect of Zr on microstructure and <span class="hlt">deformation</span> of 2036 Al at elevated <span class="hlt">temperatures</span> was discussed.</p> <div class="credits"> <p class="dwt_author">Huang, J.S.; Schwartz, A.J.; Nieh, T.G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1995-11-01</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://adsabs.harvard.edu/abs/2014JMEP...23.1954J"> <span id="translatedtitle">Effect of High-<span class="hlt">Temperature</span> Severe Plastic <span class="hlt">Deformation</span> on Microstructure and Mechanical Properties of IF Steel</span></a>  </p> <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">Extensive research work has been carried out on interstitial-free steel to understand its response to <span class="hlt">deformation</span>; particularly, the behavior during severe plastic <span class="hlt">deformation</span> (SPD). However, most of these studies were mainly undertaken in the ferritic regime. The present investigation reports the initial results of our attempt to employ accumulative roll bonding (ARB), one of the variants of SPD, at a high <span class="hlt">temperature</span> (950 C). A considerable grain refinement has been observed, which may be attributed to the severity of <span class="hlt">deformation</span> and recrystallisation at high <span class="hlt">temperatures</span>. Nanoindentation tests have been performed at various stages of ARB process to understand the evolution of mechanical properties.</p> <div class="credits"> <p class="dwt_author">Jindal, Vikas; Rupa, P. K. P.; Mandal, G. K.; Srivastava, V. C.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-06-01</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://ntrs.nasa.gov/search.jsp?R=20110011967&hterms=Work+measurement&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DWork%2Bmeasurement"> <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 " 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://adsabs.harvard.edu/abs/2013JSG....52...17B"> <span id="translatedtitle">Time-dependent cracking and brittle <span class="hlt">creep</span> in crustal rocks: A review</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">Rock fracture under upper crustal conditions is driven not only by applied stresses, but also by time-dependent, chemically activated subcritical cracking processes. These subcritical processes are of great importance for the understanding of the mechanical behaviour of rocks over geological timescales. A macroscopic manifestation of time-dependency in the brittle field is the observation that rocks can <span class="hlt">deform</span> and fail at constant applied stresses, a phenomenon known as brittle <span class="hlt">creep</span>. Here, we review the available experimental evidence for brittle <span class="hlt">creep</span> in crustal rocks, and the various models developed to explain the observations. Laboratory experiments have shown that brittle <span class="hlt">creep</span> occurs in all major rock types, and that <span class="hlt">creep</span> strain rates are extremely sensitive to the environmental conditions: differential stress, confining pressure, <span class="hlt">temperature</span> and pore fluid composition. Even small changes in any of these parameters produce order of magnitude changes in <span class="hlt">creep</span> strain rates (and times-to-failure). Three main classes of brittle <span class="hlt">creep</span> model have been proposed to explain these observations: phenomenological, statistical, and micromechanical. Statistical and micromechanical models explain qualitatively how the increasing influence of microcrack interactions and/or the increasing accumulated damage produces the observed evolution of macroscopic <span class="hlt">deformation</span> during brittle <span class="hlt">creep</span>. However, no current model can predict quantitatively all of the observed features of brittle <span class="hlt">creep</span>. Experimental data are limited by the timescale over which experiments are realistically feasible. Clearly, an extension of the range of available laboratory data to lower strain rates, and the development of new modelling approaches are needed to further improve our current understanding of time-dependent brittle <span class="hlt">deformation</span> in rocks.</p> <div class="credits"> <p class="dwt_author">Brantut, N.; Heap, M. J.; Meredith, P. G.; Baud, P.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-07-01</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://ntrs.nasa.gov/search.jsp?R=19900019424&hterms=Rare+Earth+Metals&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%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">376</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=19930036471&hterms=scandium&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dscandium"> <span id="translatedtitle">High-<span class="hlt">temperature</span> <span class="hlt">deformation</span> and microstructural analysis for silicon nitride-scandium(III) oxide</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 tripple 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">1992-01-01</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://adsabs.harvard.edu/abs/2012LTP....38...80I"> <span id="translatedtitle">Microstructure and low-<span class="hlt">temperature</span> plastic <span class="hlt">deformation</span> of Al-Li alloy</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">Features of the plastic <span class="hlt">deformation</span> of solid Al-Li solutions with microstructures formed by direct and angular hydroextrusion are studied under tension at <span class="hlt">temperatures</span> of 4.2-350 K. It is found that the grain size reductions, increases in the average density of defects, and changes in the orientational textures during combined hydroextrusion lead to increased strength and reduced plasticity of the microcrystalline alloy relative to initially large-grained samples. The high yield stress of the microcrystalline alloy is explained by a higher grain density and the evolution of an orientational texture. The strong <span class="hlt">temperature</span> dependence of the yield stress is typical of thermally activated interactions between dislocations and local obstacles in the form of <span class="hlt">deformation</span> defects produced during hydroextrusion. The low plasticity of the microcrystalline alloy, which already shows up as a localization of plastic <span class="hlt">deformation</span> with small <span class="hlt">deformations</span>, is caused by a low rate of work hardening owing to enhanced dynamic recovery of fine grains even at low <span class="hlt">temperatures</span>. The rate of dynamic recovery decreases, while uniform <span class="hlt">deformation</span> increases, at <span class="hlt">temperatures</span> of 77 K and below. Based on data on the high stress rate sensitivity at <span class="hlt">temperatures</span> above 77 K and the low activation volume for plastic <span class="hlt">deformation</span> of microcrystalline Al-Li, it is proposed that high-angle grain boundaries may serve as highly efficient sources and sinks of mobile dislocations.</p> <div class="credits"> <p class="dwt_author">Isaev, N. V.; Zabrodin, P. A.; Spuskanyuk, V. Z.; Davydenko, A. A.; Pustovalov, V. V.; Fomenko, V. S.; Braude, I. S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-01-01</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://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">379</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/809087"> <span id="translatedtitle"><span class="hlt">Creep</span> Resistant Zinc Alloy</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 report covers the development of Hot Chamber Die Castable Zinc Alloys with High <span class="hlt">Creep</span> Strengths. This project commenced in 2000, with the primary objective of developing a hot chamber zinc die-casting alloy, capable of satisfactory service at 140 C. The core objectives of the development program were to: (1) fill in missing alloy data areas and develop a more complete empirical model of the influence of alloy composition on <span class="hlt">creep</span> strength and other selected properties, and (2) based on the results from this model, examine promising alloy composition areas, for further development and for meeting the property combination targets, with the view to designing an optimized alloy composition. The target properties identified by ILZRO for an improved <span class="hlt">creep</span> resistant zinc die-casting alloy were identified as follows: (1) <span class="hlt">temperature</span> capability of 1470 C; (2) <span class="hlt">creep</span> stress of 31 MPa (4500 psi); (3) exposure time of 1000 hours; and (4) maximum <span class="hlt">creep</span> elongation under these conditions of 1%. The project was broadly divided into three tasks: (1) Task 1--General and Modeling, covering Experimental design of a first batch of alloys, alloy preparation and characterization. (2) Task 2--Refinement and Optimization, covering Experimental design of a second batch of alloys. (3) Task 3--<span class="hlt">Creep</span> Testing and Technology transfer, covering the finalization of testing and the transfer of technology to the Zinc industry should have at least one improved alloy result from this work.</p> <div class="credits"> <p class="dwt_author">Frank E. Goodwin</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-12-31</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://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 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 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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_19");' 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 onClick='return showDiv("page_14");' href="#">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 style="font-weight: bold;">20</a> <a onClick='return showDiv("page_21");' href="#">21</a> <a onClick='return showDiv("page_22");' href="#">22</a> <a 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_21");' 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">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.osti.gov/scitech/biblio/691329"> <span id="translatedtitle">Tension/compression asymmetry in <span class="hlt">creep</span> behavior of a Ni-based superalloy</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">Orientation and <span class="hlt">temperature</span> dependence of yield stress or CRSS (Critical Resolved Shear Stress) and tension/compression anisotropy of the yield stress of CRSS have been shown by Shah and Duhl, Heredia and Pope, and Miner et al. Tension/compression asymmetry in the yield strength of Ni-based superalloys has been explained in terms of the core width effect. Shah and Duhl observed the tension/compression asymmetry in <span class="hlt">creep</span> <span class="hlt">deformation</span>, which is similar to that observed in the yield strength, and indicated that it can be attributed to cross slip and dislocation core-constriction mechanisms associated with octahedral slip. However, little is known about the mechanism of tension/compression asymmetry in <span class="hlt">creep</span>. In the present study, single crystals of a Ni-base superalloy were subjected to tensile and compressive <span class="hlt">creep</span> tests. Tension/compression asymmetry in <span class="hlt">creep</span> behavior was examined in detail for each orientation.</p> <div class="credits"> <p class="dwt_author">Kakehi, K. [Tokyo Metropolitan Univ., Hachioji, Tokyo (Japan). Dept. of Mechanical Engineering] [Tokyo Metropolitan Univ., Hachioji, Tokyo (Japan). Dept. of Mechanical Engineering</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-08-06</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://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">383</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/20871551"> <span id="translatedtitle">Electrically induced <span class="hlt">temperature</span> difference and <span class="hlt">deformation</span> in hardened cement pastes</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">Electromechanical effect of hardened cement paste beam is investigated in this paper. When an external electrical current is applied to the electrodes attached to opposite surfaces of a cement beam, it is found that <span class="hlt">temperature</span> on the positive electrode is always higher than that on the negative electrode. The sign of electrically induced <span class="hlt">temperature</span> difference is determined by the direction of applied electrical current. Electrically induced <span class="hlt">temperature</span> difference makes the beam bend towards the surface with a higher <span class="hlt">temperature</span>. Both electrically induced <span class="hlt">temperature</span> difference and electroosmosis lead to electromechanical effect of hardened cement paste. Finally, electromechanical effect becomes more obvious by adding NaCl to cement paste.</p> <div class="credits"> <p class="dwt_author">Sun Mingqing [Department of Engineering Structures and Mechanics, Wuhan University of Technology, Wuhan 430070 (China)]. E-mail: sunmingqing@yahoo.com; Wang Xiaoying [Department of Engineering Structures and Mechanics, Wuhan University of Technology, Wuhan 430070 (China); Zhao Kairui [Department of Engineering Structures and Mechanics, Wuhan University of Technology, Wuhan 430070 (China); Li Zhuoqiu [Department of Engineering Structures and Mechanics, Wuhan University of Technology, Wuhan 430070 (China)</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-12-15</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">384</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/2008PhDT........76W"> <span id="translatedtitle">The primary <span class="hlt">creep</span> behavior of single crystal, nickel base superalloys PWA 1480 and PWA 1484</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">Primary <span class="hlt">creep</span> occurring at intermediate <span class="hlt">temperatures</span> (650C to 850C) and loads greater than 500 MPa has been shown to result in severe <span class="hlt">creep</span> strain, often exceeding 5-10%, during the first few hours of <span class="hlt">creep</span> testing. This investigation examines how the addition of rhenium and changes in aging heat treatment affect the primary <span class="hlt">creep</span> behavior of PWA 1480 and PWA 1484. To aid in the understanding of rhenium's role in primary <span class="hlt">creep</span>, 3wt% Re was added to PWA 1480 to create a second generation version of PWA 1480. The age heat treatments used for <span class="hlt">creep</span> testing were either 704C/24 hr. or 871C/32hr. All three alloys exhibited the presence of secondary gamma' confirmed by scanning electron microscopy and local electrode atom probe techniques. These aging heat treatments resulted in the reduction of the primary <span class="hlt">creep</span> strain produced in PWA 1484 from 24% to 16% at 704C/862 MPa and produced a slight dependence of the tensile properties of PWA 1480 on aging heat treatment <span class="hlt">temperature</span>. For all test <span class="hlt">temperatures</span>, the high <span class="hlt">temperature</span> age resulted in a significant decrease in primary <span class="hlt">creep</span> behavior of PWA 1484 and a longer lifetime for all but the lowest test <span class="hlt">temperature</span>. The primary <span class="hlt">creep</span> behavior of PWA 1480 and PWA 1480+Re did not display any significant dependence on age heat treatment. The <span class="hlt">creep</span> rupture life of PWA 1480 is greater than PWA 1484 at 704C, but significantly shorter at 760C and 815C. PWA 1480+Re, however, displayed the longest lifetime of all three alloys at both 704C and 815C (PWA 1480+Re was not tested at 760C). Qualitative TEM analysis revealed that PWA 1484 <span class="hlt">deformed</span> by large dislocation "ribbons" spanning large regions of material. PWA 1480, however, <span class="hlt">deformed</span> primarily due to matrix dislocations and the creation of interfacial dislocation networks between the gamma and gamma' phases. PWA 1480+ contained stacking faults as well, though they acted on multiple slip systems generating work hardening and forcing the onset of secondary <span class="hlt">creep</span>. X-ray diffraction and JMatPro calculations were also used to gain insight into the cause of the differences in behaviors.</p> <div class="credits"> <p class="dwt_author">Wilson, Brandon Charles</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">385</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 " lang="en"> <div class="resultNumber element">386</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/2008PhDT.......233M"> <span id="translatedtitle">Extension of viscoplasticity based on overstress to capture the effects of prior aging on the time dependent <span class="hlt">deformation</span> behavior of a high-<span class="hlt">temperature</span> polymer: Experiments and modeling</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 inelastic <span class="hlt">deformation</span> behavior of PMR-15 neat resin, a high-<span class="hlt">temperature</span> thermoset polymer, was investigated at 288 C. The experimental program was designed to explore the influence of strain rate on tensile loading, unloading, and strain recovery behaviors. In addition, the effect of the prior strain rate on the relaxation response of the material, as well as on the <span class="hlt">creep</span> behavior following strain controlled loading were examined. The material exhibits positive, nonlinear strain rate sensitivity in monotonic loading. Nonlinear, "curved" stress-strain behavior during unloading is observed at all strain rates. The recovery of strain at zero stress is strongly affected by prior strain rate. The prior strain rate also has a profound influence on relaxation behavior. The rest stresses measured at the termination of relaxation tests form the relaxation boundary which resembles a nonlinear stress-strain curve. Likewise, <span class="hlt">creep</span> response is significantly influenced by prior strain rate. The experimental results suggest that the inelastic behavior of the PMR-15 solid polymer at 288C can be represented using a unified constitutive model with an overstress dependence of the inelastic rate of <span class="hlt">deformation</span>. The experimental data were modeled with the Viscoplasticity Based on Overstress (VBO) theory. A systematic procedure for determining model parameters was developed and the model was employed to predict the response of the material under various test histories. Additionally the effects of prior aging at 288 C in argon on the time (rate)-dependent behavior of the PMR-15 polymer were evaluated in a series of strain and load controlled experiments. Based on experimental results, the VBO theory was extended to capture the environmentally induced changes in the material response. Several of the VBO material parameters were expanded as functions of prior aging time. The resulting model was used to predict the high-<span class="hlt">temperature</span> behavior of the PMR-15 polymer subjected to prior aging of various durations.</p> <div class="credits"> <p class="dwt_author">McClung, Amber J. W.</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">387</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/1981MTA....12.1003S"> <span id="translatedtitle"><span class="hlt">Temperature</span> Dependent <span class="hlt">Deformation</span> Mechanisms of Alloy 718 in Low Cycle Fatigue</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">Recent developments in the area of water cooled gas turbine design have created a need for low cycle fatigue test data for alloy 718 in the <span class="hlt">temperature</span> range of 204 to 649 C. To support this need, data were generated in the room <span class="hlt">temperature</span> to 649 C range. As noted by previous investigators, there was a crossover in fatigue lives at low strain depending on <span class="hlt">temperature</span>. At high strain ranges the lowest fatigue life was exhibited at the higher <span class="hlt">temperatures</span>. However, in the low strain, long life regime this trend reversed with the fatigue life at a given strain range exhibiting a peak at some intermediate <span class="hlt">temperature</span>. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) studies were conducted on the fatigue specimens to determine the nature of the cyclic <span class="hlt">deformation</span> process as a function of strain range and <span class="hlt">temperature</span>, the principal mode of <span class="hlt">deformation</span> was by mechanical twinning. However, at the two highest <span class="hlt">temperatures</span>, the primary process for <span class="hlt">deformation</span> was slip. The principal difference between the strain-life behavior of the specimens cycled at 538 and 649 C, and those cycled at the three lower <span class="hlt">temperatures</span> (204, 316, 427 C) is interpreted in light of this change in <span class="hlt">deformation</span> process with <span class="hlt">temperature</span>.</p> <div class="credits"> <p class="dwt_author">Sanders, T. H.; Frishmuth, R. E.; Embley, G. T.</p> <p class="dwt_publisher"></p> <p class="publishDate">1981-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">388</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/5094149"> <span id="translatedtitle">The effect of multiaxiality on the evaluation of weldment strength reduction factors in high-<span class="hlt">temperature</span> <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">The conventional way to define the weldment <span class="hlt">creep</span> strength reduction factor is usually based on uniaxial <span class="hlt">creep</span> data of weld metals and parent metals. In order to take the multiaxial effect into consideration, this paper has defined a structural transfer function which can be evaluated from general <span class="hlt">creep</span> stress analysis. An analytical model is then proposed in the light of the function. Two numerical examples of typical weld properties show that the transfer function has a load-independent feature, which allows one to obtain multiaxial stress components in a weldment through minimal computation effort. Fairly good estimation of the stress level in the weld metal is achieved. On the basis of the present semi-analytical procedure, the weldment <span class="hlt">creep</span> strength reduction factors are evaluated. For a 0.5Cr0.5Mo0.25 V butt-welded tube under internal pressure, which has a higher weld metal <span class="hlt">creep</span>-rupture strength, and lower weld metal <span class="hlt">creep</span> strain rate, the reduction factors range from 0.9 to 0.95. For the AISI 316 butt-welded tube of cold-worked parent metal and <span class="hlt">creep</span> soft weld metal, lower strength reduction factors are found, but they may still be nonconservative due to stress enhancement in the heat-affected zone.</p> <div class="credits"> <p class="dwt_author">Sandstroem, R.; Tu, S.T. (Royal Inst. of Tech., Stockholm (Sweden). Dept. of Materials Science and Engineering)</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">389</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=N19980228107"> <span id="translatedtitle">Deterministic Multiaxial <span class="hlt">Creep</span> and <span class="hlt">Creep</span> Rupture Enhancements for CARES/<span class="hlt">Creep</span> Integrated Design Code.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">High <span class="hlt">temperature</span> and long duration applications of monolithic ceramics can place their failure mode in the <span class="hlt">creep</span> rupture regime. A previous model advanced by the authors described a methodology by which the <span class="hlt">creep</span> rupture life of a loaded component can be ...</p> <div class="credits"> <p class="dwt_author">O. M. Jadaan</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">390</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/2010PhDT.......200P"> <span id="translatedtitle">Predictive Model for <span class="hlt">Temperature</span>-Induced <span class="hlt">Deformation</span> of Robot Mechanical Systems</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 positioning accuracy and repeatability of a robot are critical for many industrial applications. Drift in repeatability can occur with changes in environmental and internal conditions, such as those seen with <span class="hlt">temperature</span>-induced <span class="hlt">deformation</span>. Thermal instability causes dimensional <span class="hlt">deformation</span>, and a warm-up cycle is typically required to bring the robot to a thermally stable working condition. The elimination of warm-up cycles will ultimately enhance the positioning accuracy of the robots, their productivity, and reduce unnecessary energy consumption. The main objective of this research was to develop a robot controller algorithm that would provide, a priori, compensation for <span class="hlt">temperature</span>-induced <span class="hlt">deformation</span> associated with warm-up in robot mechanical systems. The research started at the fundamental stage of gaining insight into the thermal behaviour and corresponding <span class="hlt">temperature</span>-induced <span class="hlt">deformation</span> of simplified, i.e., one-dimensional, robot mechanical systems consisting of slender links and heat sources. The systems were studied using concomitant experimental, numerical and analytical models to provide cross-checking of the results. For the experimental model, the <span class="hlt">deformation</span> was measured by tracking the drift of a laser diode spot across a charge-coupled device (CCD) camera chip. A non-contact measurement system consisting of an infrared camera, a CCD camera and a laser diode was developed to provide high accuracy measurement for the <span class="hlt">deformation</span>. The numerical model was generated with a coupled thermal-mechanical finite element analysis incorporating thermal effects due to conduction and convection. The models were tested with the analytical model that was further extended using a finite difference technique. Once the three models showed excellent agreement, it was possible to develop a controller algorithm. <span class="hlt">Deformations</span> predicted by the finite difference model were used as input for a validation experiment of the compensation algorithm. Results of the validation experiment confirmed that <span class="hlt">temperature</span>-induced <span class="hlt">deformation</span> of the simplified robot mechanical system can be accurately compensated for using a simple algorithm implemented in a robot controller.</p> <div class="credits"> <p class="dwt_author">Poonyapak, Pranchalee</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">391</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/49429113"> <span id="translatedtitle">Tensile <span class="hlt">deformation</span> and fracture characteristics of delta-processed Inconel 718 alloy at elevated <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">Three specimens with different initial ? phase contents have been used to study the tensile <span class="hlt">deformation</span> and fracture characteristics of the delta-processed Inconel 718 alloy at elevated <span class="hlt">temperatures</span> by tensile tests at 950C. The results indicated that the tensile stressstrain curves of the three specimens were the elastic-uniform plastic curves, and there were two <span class="hlt">deformation</span> processes during the uniform plastic</p> <div class="credits"> <p class="dwt_author">Shi-Hong Zhang; Hai-Yan Zhang; Ming Cheng</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">392</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/21175954"> <span id="translatedtitle">Homogeneous <span class="hlt">deformation</span> of Au-based metallic glass micropillars in compression at elevated <span class="hlt">temperatures</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">We performed high-<span class="hlt">temperature</span> microcompression tests on micron-sized pillar samples fabricated from Au{sub 49}Ag{sub 5.5}Pd{sub 2.3}Cu{sub 26.9}Si{sub 16.3} metallic glass near the glass transition <span class="hlt">temperature</span> to investigate the homogeneous <span class="hlt">deformation</span> behavior. Samples were invariably <span class="hlt">deformed</span> uniformly. The strength was observed to decrease with increasing <span class="hlt">temperature</span> and decreasing strain rate. Plastic flow behavior can be described by a shear transition zone model. The activation energy and the size of the basic flow unit were both deduced and compared favorably with the theory.</p> <div class="credits"> <p class="dwt_author">Song, S. X.; Nieh, T. G. [Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996 (United States); Lai, Y. H.; Huang, J. C. [Department of Materials and Optoelectronic Science and Center for Nanoscience and Nanotechnology, National Sun Yat-Sen University, Kaohsiung 804, Taiwan (China)</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-02-09</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">393</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=microscop&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dmicroscop"> <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 class="floatContainer result " lang="en"> <div class="resultNumber element">394</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/ma9ll9fter8etj6b.pdf"> <span id="translatedtitle">The Influence of Superimposed <span class="hlt">Creep</span> Loadings on the Thermal-Mechanical Fatigue Behaviour of the Ni-Base Superalloy IN 792 CC</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 effect of superimposed <span class="hlt">creep</span> loadings on the cyclic <span class="hlt">deformation</span> andthe lifetime behaviour of the Ni-base superalloy IN 792 CC underout-of-phase TMF loadings is presented and discussed. The mean stressand the stress amplitude are not affected significantly by the creeploading. A slight cyclic hardening is observed even for cycles withsuperimposed <span class="hlt">creep</span> loadings at a maximum <span class="hlt">temperature</span> of 920C whichmeans that</p> <div class="credits"> <p class="dwt_author">T. Beck; K.-H. Lang; G. Pitz; D. Lhe</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">395</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/1983MTA....14.1467S"> <span id="translatedtitle"><span class="hlt">Creep</span> crack growth behavior of several structural 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"><span class="hlt">Creep</span> crack growth behavior of several high <span class="hlt">temperature</span> alloys, Inconel 600, Inconel 625, Inconel X-750, Hastelloy X, Nimonic PE-16, Incoloy 800, and Haynes 25 (HS-25) was examined at 540, 650, 760, and 870 C. Crack growth rates were analyzed in terms of both linear elastic stress intensity factor and J*-integral parameter. Among the alloys Inconel 600 and Hastelloy X did not show any observable crack growth. Instead, they <span class="hlt">deformed</span> at a rapid rate resulting in severe blunting of the crack tip. The other alloys, Inconel 625, Inconel X-750, Incoloy 800, HS-25, and PE-16 showed crack growth at one or two <span class="hlt">temperatures</span> and <span class="hlt">deformed</span> continuously at other <span class="hlt">temperatures</span>. Crack growth rates of the above alloys in terms ofJ* parameter were compared with the growth rates of other alloys published in the literature. Alloys such as Inconel X-750, Alloy 718, and IN-100 show very high growth rates as a result of their sensitivity to an air environment. Based on detailed fracture surface analysis, it is proposed that <span class="hlt">creep</span> crack growth occurs by the nucleation and growth of wedge-type cracks at triple point junctions due to grain boundary sliding or by the formation and growth of cavities at the boundaries. Crack growth in the above alloys occurs only in some critical range of strain rates or <span class="hlt">temperatures</span>. Since the service conditions for these alloys usually fall within this critical range, knowledge and understanding of <span class="hlt">creep</span> crack growth behavior of the structural alloys are important.</p> <div class="credits"> <p class="dwt_author">Sadananda, K.; Shahinian, P.</p> <p class="dwt_publisher"></p> <p class="publishDate">1983-07-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">396</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/619458"> <span id="translatedtitle">Rate sensitivities for low <span class="hlt">temperature</span> <span class="hlt">deformation</span> in ruthenium aluminide 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">Because of the need for new high <span class="hlt">temperature</span> structural materials, a number of binary and multicomponent B2 aluminides have been investigated in recent years. Some alloys based on FeAl and Nb-Ti-Al are relatively ductile at low <span class="hlt">temperatures</span>, but suffer from environmental embrittlement and/or relatively low melting <span class="hlt">temperatures</span>. One apparent exception to the brittle behavior of the higher <span class="hlt">temperature</span> B2 aluminides is ruthenium aluminide, RuAl, which has a melting point of approximately 2,060 C. Fleischer et al. have reported a high room <span class="hlt">temperature</span> toughness and high compressive ductilities for a number of alloys based on RuAl, compared to a variety of other intermetallic compounds. The objective of the experiments reported here was to measure room <span class="hlt">temperature</span> rate sensitivities for a number of the same RuAl-based alloys, to determine if the phenomenological flow parameters that relate to dislocation glide processes are also unusual, compared to other higher <span class="hlt">temperature</span> B2 compounds.</p> <div class="credits"> <p class="dwt_author">Eow, K.; Lu, D.; Pollock, T.M. [Carnegie Mellon Univ., Pittsburgh, PA (United States)] [Carnegie Mellon Univ., Pittsburgh, PA (United States)</p> <p class="dwt_publisher"></p> <p class="publishDate">1998-03-03</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">397</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=Fatigue+Testing+Piping+Components&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DFatigue%2BTesting%2BPiping%2BComponents"> <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">398</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/2013ApPhL.103t1912Y"> <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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</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</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-11-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">399</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 " lang="en"> <div class="resultNumber element">400</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/u5515428254g7361.pdf"> <span id="translatedtitle">Evolution Equation of <span class="hlt">Creep</span> Damage Under Stress Variation</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">Design and assessment of structural components at elevated <span class="hlt">temperature</span> are very significant for ensuring the safety. Lear\\u000a damage accumulation (summation of <span class="hlt">creep</span> time fraction) is widely used to predict <span class="hlt">creep</span> rupture time under stress and <span class="hlt">temperature</span>\\u000a variation. Life prediction of <span class="hlt">creep</span> under stress variation by <span class="hlt">creep</span> damage mechanics of Kachanov-Rabotnov concides with that\\u000a of linear damage accumulation model. However, <span class="hlt">creep</span></p> <div class="credits"> <p class="dwt_author">Yukio Sanomura; Kzutaka Saitoh</p> <p class="dwt_publisher"></p> <p class="publishDate"></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_19");' 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");' 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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">401</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/1992STIN...9234143B"> <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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</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">1992-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">402</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/1992STIN...9313290B"> <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://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</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 mater