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1

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

2

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

3

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

4

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 Lüders 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

5

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

6

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

7

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

8

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

9

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; Stöckhert, Bernhard

2013-01-01

10

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

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 Großmann; C. Haberling

2005-01-01

12

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

13

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

14

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

15

Experimental research on creep characteristics of Nansha soft soil.  

PubMed

A series of tests were performed to investigate the creep characteristics of soil in interactive marine and terrestrial deposit of Pearl River Delta. The secondary consolidation test results show that the influence of consolidation pressure on coefficient of secondary consolidation is conditional, which is decided by the consolidation state. The ratio of coefficient of secondary consolidation and coefficient of compressibility (Ca/Cc) is almost a constant, and the value is 0.03. In the shear-box test, the direct sheer creep failure of soil is mainly controlled by shear stress rather than the accumulation of shear strain. The triaxial creep features are closely associated with the drainage conditions, and consolidation can weaken the effect of creep. When the soft soil has triaxial creep damage, the strain rate will increase sharply. PMID:24526925

Luo, Qingzi; Chen, Xiaoping

2014-01-01

16

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

17

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 Guétaz; Bernard Viguier

2008-01-01

18

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

19

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

20

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

21

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

22

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

23

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 Großmann, B.; Haberling, C.

2005-07-01

24

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

25

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

26

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

27

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

28

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

29

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

30

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 ± 1°C, 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.

31

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

32

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

33

Analysis of Mining Terrain Deformation Characteristics with Deformation Information System  

NASA Astrophysics Data System (ADS)

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

Blachowski, Jan; Milczarek, Wojciech; Grzempowski, Piotr

2014-05-01

34

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

35

Creep-characteristics of a tropical wood-polymer composite  

NASA Astrophysics Data System (ADS)

Wood polymer composite (WPC) specimens were produced by impregnating a tropical wood with methyl methacrylate and subsequently polymerised by ?-irradiation. Beam specimens of varying weight percentages of polymer were then subjected to a three point bend creep test under a constant load condition, for 250, 300 and 350 N. A Norton-Bailey (power law) mathematical model was used to describe the creep behavior, with the creep components determined by a nonlinear regression analysis. Significant creep improvements were obtained from the composite specimens as compared to the untreated wood specimens. Results indicated that maximum creep resistance is obtained when the amount of polymer loading exceeded 30%. An interfacial interaction between the polymer and the wood cell wall was used to account for the behavior of the increase in the creep resistance.

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

36

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

PubMed

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

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

2014-07-01

37

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

38

Dynamic Deformation Characteristics of Sedimentary Soft Rock  

NASA Astrophysics Data System (ADS)

Soil under the engineering seismic base layer is treated as elastic material in the engineering practice, however, evidence that its nonlinear behavior affects surface response begins to appear. Test data on dynamic deformation characteristics and tri-axial compression test on sedimentary soft rock are collected and compiled to consider its nonlinearity. In addition, nonlinear characteristics of soft rock and note on practical use are described. Static tri-axial compression test of the sample taken by means of diamond core drill is first carried out by using a LDT (Local deformation transducer), and shear modulus is found to keep nearly constant up to strain of about 10-3 for the undisturbed sample, whereas that decreases significantly even at strain of 10-5. Secondly, dynamic deformation test data on Pleistocene and Tertiary soft rock with SPT-N value greater than 30 or shear wave velocity greater than 300 m/s is collected and compiled. It is found that there exist data that shows similar behavior of static test described in the preceding. These samples is supposed be undisturbed, which means there exists many disturbed samples even if they are retrieved by, so called, undisturbed sampling method. Shear modulus at shear strain of 10-3, which is used as index of nonlinearity, is independent from effective confining stress, but it has positive correlation with plastic index. Finally, dynamic deformation characteristics of undisturbed samples are shown to be modeled by Ramberg-Osgood model well.

Fukumoto, Shun'ichi; Yoshida, Nozomu; Sahara, Mamoru

39

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

40

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

41

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

42

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 µm (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

43

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

44

The Åknes rockslide: Characteristics of subsurface deformation  

NASA Astrophysics Data System (ADS)

The Åknes rockslide represents a possible collapse of 20-55 million cubic metres, moving with a velocity of up to 10 cm/year. The risk is associated with the generation of catastrophic tsunamis, having run-up potential of up to 80 m in nearby villages. The surface monitoring systems is today based on extensometers/crackmeters, tiltmeters, single lasers, GPS, total station and a microseismic network, in addition to a climate station. Large efforts have been paid to the establishment of subsurface investigations and monitoring systems in deep boreholes. Tree boreholes have been instrumented with 50 to 120 m long active multiparametric in place columns (DMS system: Differential Monitoring of Stability). The system consists of 1 m long modules connected by special flexible junctions being free to move. Each module contains of a biaxial inclinometric sensor, a temperature sensor, and selected modules have a piezometric sensor. Also digital compass is emplaced in specific modules for controlling the direction of column. Measurements are continuous and are automatically downloaded. The DMS data has documented a well-defined upper sliding zone in two boreholes at depth of 35 and 50 m depth. This is above the water-level measured in open standpipes. The video inspection before instrumentation and the core data shows distinct fracture zones in this upper part, in addition to water inflow at some parts. The continuous temperature data from the DMS columns can also be used to measure the inflow of water through time, by the fact that the flow of water influences the temperatures. The deformation data also show that there are creeping movements in lower part, down to below 120 m depth. The mode of deformation is varying from continuous displacements through time to suddenly and abrupt steps in movement rates. Also, it is possible to detect a series of different displacements rates during small time windows. For examples, in the upper borehole, the movement velocity at 49-51 m depth beginning from November 2009 to middle of January 2010 depicts 3 velocity trends. This range from 0,1 mm/day the first month, decreasing to 0,05 mm/day the next month, and finally reducing to 0,02 mm/day the last half month. This velocity change seems to correlate broadly with the decreasing water level during the transition from relative wet autumn to colder winter conditions.

Blikra, Lars; Lovisolo, Mario; Kristensen, Lene

2010-05-01

45

The irradiation creep characteristics of graphite to high fluences  

SciTech Connect

High-temperature gas-cooled reactors (HTGR) have massive blocks of graphite with thermal and neutron-flux gradients causing high internal stresses. Thermal stresses are transient; however, stresses generated by differential growth due to neutron damage continue to increase with time. Fortunately, graphite also experiences creep under irradiation allowing relaxation of stresses to nominally safe levels. Because of complexity of irradiation creep experiments, data demonstrating this phenomenon are generally limited to fairly low fluences compared to the overall fluences expected in most reactors. Notable exceptions have been experiments at 300/degree/C and 500/degree/C run at Petten under tension and compression creep stresses to fluences greater than 4 /times/ 10/sup 26/ (E > 50 keV) neutrons/m/sup 2/. This study complements the previous results by extending the irradiation temperature to 900/degree/C. 2 refs., 3 figs.

Kennedy, C.R.; Cundy, M.; Kleist, G.

1988-01-01

46

Creep rupture life and variation of micro-structure according to aging time and creep test methods  

Microsoft Academic Search

To investigate the effect of defects on the mechanical property of 9Cr–0.5Mo–1.8W–V–Nb (ASME-P92) alloy, creep rupture and small punch creep (miniaturized disc band) tests were performed. The precipitates and micro-cavities generated during the test periods were investigated quantitatively. To evaluate the characteristics of creep rupture, the relationship between the precipitates and growth of cavities was derived. Also the creep deformation

Chan-Seo Jeong; Si-Yeon Bae; Dong-Hyun Ki; Katsuhiko Watanabe; Byeong-Soo Lim

2007-01-01

47

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

48

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 950°C 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

49

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; Haël Mughrabi

1996-01-01

50

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 µm. 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 700°C, 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 730°C 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

51

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

52

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

53

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-45˜47Al-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

54

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

55

Analysis of slip activity and heterogeneous deformation in tension and tension-creep of Ti–5Al–2.5Sn (wt %) using in-situ SEM experiments  

Microsoft Academic Search

The deformation behavior of a Ti–5Al–2.5Sn (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

56

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

57

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

58

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

59

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

60

Creep Measurement Video Extensometer  

NASA Technical Reports Server (NTRS)

Understanding material behavior under load is critical to the efficient and accurate design of advanced aircraft and spacecraft. Technologies such as the one disclosed here allow accurate creep measurements to be taken automatically, reducing error. The goal was to develop a non-contact, automated system capable of capturing images that could subsequently be processed to obtain the strain characteristics of these materials during deformation, while maintaining adequate resolution to capture the true deformation response of the material. The measurement system comprises a high-resolution digital camera, computer, and software that work collectively to interpret the image.

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

2011-01-01

61

The influence of impurity content on creep deformation, cavity stringer formation, microstructure evolution, and boundary segregation in the superplastic zinc-22wt% aluminum eutectoid  

NASA Astrophysics Data System (ADS)

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 creep deformation 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 creep characteristics, such as the existence of a threshold stress or the occurrence of extensive cavitation. In addition, the microstructural evolution of FalphaBs during superplastic deformation 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.

Yousefiani, Ahmadali

62

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. Kausträter; B. Skrotzki; G. Eggeler

2001-01-01

63

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=4×10?3\\/s) indicate that lamellar structured Ti–46.6Al–1.4Mn–2Mo (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

64

Transversal Shear Effect in Moderately Thick Shells from Materials with Characteristics Dependent on the Kind of Stress State under Creep-Damage Conditions: Theoretical Framework  

Microsoft Academic Search

The refined theory of creep deformation and creep damage in moderately thick shells of revolution which accounts for transversal shears and additionally for nonlinear distribution across its thickness of the components of the strain tensor as well as of the angles of rotation of the triad of vectors defined the position of the arbitrary point of a shell is discussed.

A. Zolochevsky; A. Galishin; A. Kühhorn; M. Springmann

65

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.

66

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

SciTech Connect

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

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

1999-08-26

67

Parametrization of barrier characteristics for deformed oriented nuclei  

NASA Astrophysics Data System (ADS)

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

Ghodsi, O. N.; Lari, F.

2014-05-01

68

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

69

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 mélange between rift flanks correlates with decreasing damage, with some rifts deforming coherently with the ice shelf as if completely healed. We quantify the stabilizing backstress caused by ice rises and lateral confinement, finding high backstress associated with two ice rises that likely stabilize the ice front in its current configuration. Though overall the ice shelf appears stable at present, the ice in contact with the Bawden ice rise is weakened by fractures, and additional damage or thinning in this area could portend significant change for the shelf. Using this new approach, field and remote sensing data can be utilized to monitor the structural integrity of ice shelves, their ability to buttress the flow of ice at the grounding line, and thus their indirect contribution to ice sheet mass balance and global sea level.

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

2013-07-01

70

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

71

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

72

Dynamic characteristics of piezoelectric shear deformable composite plates  

NASA Astrophysics Data System (ADS)

Layered composites have attracted attention for their high specific stiffness, high specific strength, and application specific tailoring of their properties. It is also recognized that layered composites are prone to delamination failure in addition to other failure modes. Consideration of transverse shear on the deformation behavior of the composites is an important aspect in the study of delamination mode failure of such plates. In this paper, we consider the effects of including the transverse shear deformation on the vibration characteristics of layered piezoelectric composites. The formulation is based on the Raleigh-Ritz method using the beam characteristic functions. MATLAB based symbollic math tool box is used in evaluating th eintegrals resulting from the Raleigh Ritz approach. Various commonly occuring boundary conditions are discussed. Results are provided showing the effects of the shear deformation on the dynamics of layered laminated composites. The effects of laminate thickness, fiber orientation, and the plate aspect ratios on the free vibration characteristics of the composite laminates are given to demonstrate the methodology described.

Kolar, Ramesh

2004-07-01

73

Microstructure and dislocation analysis after creep deformation of die-cast Mg–Al–Sr (AJ) alloy  

Microsoft Academic Search

The microstructure and creep behavior of Mg\\/Al composite crankcases cast with three alloy formulations of the Mg–Al–Sr 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 L’Esperance; Philippe Plamondon; Uwe Glatzel

2009-01-01

74

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

75

Elastic deformation characteristic of the flexspline in harmonic drive  

Microsoft Academic Search

The paper presents a method to describe the spatial deformation of a cup-type flexspline, in which the spatial deformation of the flexspline is separated into a set of deformed curves on the cross sections vertical to the axis. Based on this method, the deformation function of the neutral layer of a flexspline deformed only by wave generators, such as a

Huimin Dong; Delun Wang

2009-01-01

76

Intrinsic excitations in deformed nuclei: characteristic predictions of the IBA  

SciTech Connect

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

Casten, R.F.

1982-01-01

77

Influence of topographic and climatological characteristics on rock glacier creep rates in the Western Austrian Alps  

NASA Astrophysics Data System (ADS)

Recent advances in remote sensing technologies and data analysis tools resulted in detailed monitoring activities of rock glacier surface kinetics. In combination with geophysical methods and numerical modeling the remotely sensed data led to an increased process understanding of rock glacier creep dynamics. However, the number of studies where such method combinations are carried out is limited to a rather small number of rock glaciers. With our study we aim to contribute to an improved understanding on the significance of topographic and climatological variables on rock glacier creep rates. Therefore, creep rates of 347 intact rock glaciers in the Western Austrian Alps (Tyrol) are calculated. According to the new Tyrolean rock glacier inventory 200 of them are active and 147 inactive. In contrast to other studies, where often a few rock glaciers are investigated in detail, the 347 rock glaciers represent all rock glaciers within the study area of 887 sqkm. For the calculation of creep rates, the Open Source image-correlation software IMCORR is used and implemented into an automated work-flow. Input data for the image correlation are shaded relief raster maps with 0.5 m spatial resolution, which were obtained form airborne laser scanning data acquisition campaigns carried out in 2006 and 2010. By comparing the calculated creep rates with results from differential global positioning system data, an absolute accuracy of 0.30 m (standard deviation) could be determined. Thus, reliable interpretations can be made for creep rates > 0.30 m between 2006 and 2010. In such cases, statistical correlations between the rock glacier creep rates and topographic parameters of the rock glacier, e. g. surface gradient, thickness, length, area, elevation, aspect, potential solar radiation and surface roughness (also indicator for geological properties), as well as climatological parameters, e. g. temperature are calculated. Spatial descriptive statistics on the calculated creep rates, as well as the significance of individual topographic and climatological variables on rock glacier creep will be presented.

Bollmann, E.; Abermann, J.; Krainer, K.; Sailer, R.; Spross, M.; Stötter, J.

2012-04-01

78

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

Shrestha, Triratna

79

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

80

Characteristic creep behavior of nanocrystalline metals found for high-density gold  

NASA Astrophysics Data System (ADS)

Nanocrystalline (n) Au specimens with a density of 19.4±0.2 g/cm3 and a mean grain size of about 20 nm were prepared below 300 K by the gas deposition method, where two types of n-Au specimens were obtained as a function of a deposition rate, the type-H specimens above 800 nm/s and the type-L specimens below 800 nm/s. The anelastic and the plastic creep responses are similar qualitatively but different quantitatively between the type-H and type-L specimens. The anelastic strain ?an,GB, associated with the grain boundary (GB) regions, increases linearly with (T-Tan1)(?ap-?an1), when the temperature T is higher than a threshold temperature Tan1 of 200 K and the applied stress ?ap is higher than a threshold stress, ?an1, of a few MPa. The ratio of ?an,GB to the elastic strain is as large as 1.1 for the type-H specimens and 0.2 for the type-L specimens at 320 K for ?ap??an1. The activation energy for the GB anelastic process is 0.2 eV. We surmise that cooperative motions of many atoms in the GB regions are responsible for ?an,GB, and both Tan1 and ?an1 show a distribution depending on the number of atoms associated. The plastic creep rate ?' vs ?ap data show a letter S-like curve. We classified the creep response into three categories, region I for the linear creep rate region for ?ap between ?pc 1 and ?pc2, region II for the transient creep rate region for ?ap between ?pc2 and ?pc3, and region III for the saturation creep rate region for ?ap between ?pc3 and ?y. The threshold stresses ?pc1 and ?pc2 and the yield stress ?y are about 30, 150, and 360 MPa for the type-H specimens, and about 60, 300, and 500 MPa for the type-L specimens, respectively. ?pc3 is slightly lower than ?y. From scanning tunneling microscopy images, we surmise that the localized GB slip takes place in region I, and the mean separation between the localized GB slips decreases with increasing ?ap in region II and becomes comparable with the mean grain size in region III. The plastic creep in region III may be explained by the Ashby creep. The present view for the creep behavior explains the low-temperature creep behavior of fcc n metals.

Sakai, S.; Tanimoto, H.; Kita, E.; Mizubayashi, H.

2002-12-01

81

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

82

Tensile Creep Measurement for Plastics Design Data.  

National Technical Information Service (NTIS)

The need for the measurement of creep characteristics of engineering polymers is discussed and the most important considerations of creep characterisation presented. The development of specific creep equipment and light-weight extensometry is described. T...

B. V. Howes

1974-01-01

83

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

84

Deformation Characteristics of Geosynthetics Retaining Wall Loaded on the Crest  

Microsoft Academic Search

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

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

85

Morphologies and characteristics of deformation induced martensite during tensile deformation of 304 LN stainless steel  

Microsoft Academic Search

The austenite ? (fcc) matrix of 304 LN stainless steel transforms readily to martensites ? (hcp) and ?? (bcc) on deformation. The formation and nucleation mechanism of deformation induced martensite (DIM) during tensile deformation of 304 LN stainless steel has been studied at various strain rates in room temperature. It is investigated that the enhancement of strain rates during tensile

Arpan Das; S. Sivaprasad; M. Ghosh; P. C. Chakraborti; S. Tarafder

2008-01-01

86

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

87

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

88

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

National Technical Information Service (NTIS)

This paper presents a viscoplasticity model taking into account the effects of change in grain or phase size and damage on the characterization of creep damage in 60Sn-40Pb solder. Based on the theory of damage mechanics, a two-scalar damage model is deve...

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

1999-01-01

89

Post-seismic and interseismic fault creep I: model description  

NASA Astrophysics Data System (ADS)

We present a model of localized, aseismic fault creep during the full interseismic period, including both transient and steady fault creep, in response to a sequence of imposed coseismic slip events and tectonic loading. We consider the behaviour of models with linear viscous, non-linear viscous, rate-dependent friction, and rate- and state-dependent friction fault rheologies. Both the transient post-seismic creep and the pattern of steady interseismic creep rates surrounding asperities depend on recent coseismic slip and fault rheologies. In these models, post-seismic fault creep is manifest as pulses of elevated creep rates that propagate from the coseismic slip, these pulses feature sharper fronts and are longer lived in models with rate-state friction compared to other models. With small characteristic slip distances in rate-state friction models, interseismic creep is similar to that in models with rate-dependent friction faults, except for the earliest periods of post-seismic creep. Our model can be used to constrain fault rheologies from geodetic observations in cases where the coseismic slip history is relatively well known. When only considering surface deformation over a short period of time, there are strong trade-offs between fault rheology and the details of the imposed coseismic slip. Geodetic observations over longer times following an earthquake will reduce these trade-offs, while simultaneous modelling of interseismic and post-seismic observations provide the strongest constraints on fault rheologies.

Hetland, E. A.; Simons, M.; Dunham, E. M.

2010-04-01

90

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

91

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

NASA Technical Reports Server (NTRS)

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 creep deformation 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.

Wilson, D. J.

1975-01-01

92

Characteristics of Creep Damage for 60Sn40Pb Solder Material  

Microsoft Academic Search

This paper presents a viscoplasticity model taking into account the effects of change in grain or phase size and damage on the characterization of creep damage in 60Sn-40Pb solder. Based on the theory of damage mechanics, a two-scalar damage model is developed for isotropic materials by introducing the free energy equivalence principle. The damage evolution equations are derived in terms

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

1999-01-01

93

Active disturbance rejection control for output force creep characteristics of ionic polymer metal composites  

NASA Astrophysics Data System (ADS)

Ionic polymer metal composites (IPMCs) are a type of electroactive polymer (EAP) that can be used as both sensors and actuators. An IPMC has enormous potential application in the field of biomimetic robotics, medical devices, and so on. However, an IPMC actuator has a great number of disadvantages, such as creep and time-variation, making it vulnerable to external disturbances. In addition, the complex actuation mechanism makes it difficult to model and the demand of the control algorithm is laborious to implement. In this paper, we obtain a creep model of the IPMC by means of model identification based on the method of creep operator linear superposition. Although the mathematical model is not approximate to the IPMC accurate model, it is accurate enough to be used in MATLAB to prove the control algorithm. A controller based on the active disturbance rejection control (ADRC) method is designed to solve the drawbacks previously given. Because the ADRC controller is separate from the mathematical model of the controlled plant, the control algorithm has the ability to complete disturbance estimation and compensation. Some factors, such as all external disturbances, uncertainty factors, the inaccuracy of the identification model and different kinds of IPMCs, have little effect on controlling the output block force of the IPMC. Furthermore, we use the particle swarm optimization algorithm to adjust ADRC parameters so that the IPMC actuator can approach the desired block force with unknown external disturbances. Simulations and experimental examples validate the effectiveness of the ADRC controller.

Xiong, Yan; Chen, Yang; Sun, Zhiyong; Hao, Lina; Dong, Jie

2014-07-01

94

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

95

Postseismic relaxation and transient creep  

USGS Publications Warehouse

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

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

2005-01-01

96

Intrinsic Excitations in Deformed Nuclei: Characteristic Predictions of the IBA.  

National Technical Information Service (NTIS)

Deformed nuclei represent perhaps the largest and best studied class of nuclear level schemes. The Interacting Boson Approximation (IBA) model is devised so as to provide a general framework for the description of low lying collective states in nuclei spa...

R. F. Casten

1982-01-01

97

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

98

Current-voltage characteristics and flux creep in melt-textured YBa2Cu3O7-?  

NASA Astrophysics Data System (ADS)

We investigated the current-voltage (E - J) characteristics in melt-textured YBa2Cu3O7-icons/Journals/Common/delta" ALT="delta" ALIGN="MIDDLE"/> strips by measuring the magnetic-field sweep rate dependence of magnetization. We took account of the current density J distribution in the specimen using a previously developed method (Mawatari Y et al 1997 Appl. Phys. Lett. 70 2300). For a wide temperature and magnetic-field range (60-80 K, 0.2-5.0 T), the E - J curves in the electric-field window E = 10-10 -10-5 V m-1 exhibited power-law behaviour E icons/Journals/Common/propto" ALT="propto" ALIGN="TOP"/> Jn, and the power index n generally became smaller at higher magnetic fields and temperatures. In low magnetic fields (µ0 Ha icons/Journals/Common/le" ALT="le" ALIGN="TOP"/> 0.5 T) the n values were large (icons/Journals/Common/ge" ALT="ge" ALIGN="TOP"/> 20), and thus the Bean model becomes a good approximation. The E - J characteristics in the lower E window were also derived from the relaxation of magnetization, the flux creep, and we found that the wide-range E - J characteristics exhibit near-power-law behaviour but that there exist slight downward curvatures in the log E versus log J plots. This downward curvature reveals that the dissipation approaches zero when the current is substantially reduced. The drastic decrease of the flux creep, which was observed when the sample temperature was decreased in a fixed magnetic field, is consistent with the observed E - J characteristics.

Yamasaki, H.; Mawatari, Y.

2000-02-01

99

Characteristics of fixed-shape pulses emerging from pulsating, erupting, and creeping solitons  

NASA Astrophysics Data System (ADS)

It is known that one of the impacts of combined higher-order effects, namely the intrapulse Raman scattering, third-order dispersion, and self-steepening, on the plain-pulsating, erupting, and creeping soliton solutions of the complex Ginzburg-Landau equation is the change of its periodic behavior and its transformation into fixed-shape solutions. In this work, we numerically find the regions in the parameters space in which these solutions exist. We also characterize their velocities, shapes, and chirp.

Latas, Sofia C. V.; Ferreira, Mário F. S.; Facão, Margarida V.

2013-10-01

100

Dislocation Jamming and Andrade Creep  

Microsoft Academic Search

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 creep relaxation follows Andrade's law. Our results indicate that Andrade creep in plastically deforming crystals involves the correlated motion of dislocation structures near a dynamic transition separating a flowing from a jammed phase. Simulations in

M.-Carmen Miguel; Alessandro Vespignani; Michael Zaiser; Stefano Zapperi

2002-01-01

101

Do Materials Get Tired? Creep  

NSDL National Science Digital Library

This video explains that materials will deform slowly or “creep” under the right conditions, when constant force is applied. “Strain” is illustrated with rubber bands and we learn that engineers can calculate creep strain as a function of time.

Wpsu

2008-11-12

102

Assessing the P-wave attenuation and phase velocity characteristics of fractured media based on creep and relaxation tests  

NASA Astrophysics Data System (ADS)

Fractures are present in most geological formations and they tend to dominate not only their mechanical but also, and in particular, their hydraulic properties. For these reasons, the detection and characterization of fractures are of great interest in several fields of Earth sciences. Seismic attenuation has been recognized as a key attribute for this purpose, as both laboratory and field experiments indicate that the presence of fractures typically produces significant energy dissipation and that this attribute tends to increase with increasing fracture density. This energy loss is generally considered to be primarily due to wave-induced pressure diffusion between the fractures and the embedding porous matrix. That is, due to the strong compressibility contrast between these two domains, the propagation of seismic waves can generate a strong fluid pressure gradient and associated pressure diffusion, which leads to fluid flow and in turn results in frictional energy dissipation. Numerical simulations based on Biot's poroelastic wave equations are computationally very expensive. Alternative approaches consist in performing numerical relaxation or creep tests on representative elementary volumes (REV) of the considered medium. These tests are typically based on Biot's consolidation equations. Assuming that the heterogeneous poroelastic medium can be replaced by an effective, homogeneous viscoelastic solid, these numerical creep and relaxation tests allow for computing the equivalent seismic P-wave attenuation and phase velocity. From a practical point of view, an REV is typically characterized by the smallest volume for which rock physical properties are statistically stationary and representative of the probed medium in its entirety. A more general definition in the context of wavefield attributes is to consider an REV as the smallest volume over which the P-wave attenuation and phase velocity dispersion are independent of the applied boundary conditions. That is, the corresponding results obtained from creep and relaxation tests must be equivalent. For most analyses of media characterized by patchy saturation or double-porosity-type structures these two definitions are equivalent. It is, however, not clear whether this equivalence remains true in the presence of strong material contrasts as those prevailing in fractured rocks. In this work, we explore this question for periodically fractured media. To this end, we build a medium composed of infinite replicas of a unit volume containing one fracture. This unit volume coincides with the smallest possible volume that is statistically representative of the whole. Then, we perform several creep and relaxation tests on samples composed of an increasing number of these unit volumes. We find that the wave field signatures determined from relaxation tests are independent from the number of unit volumes. Conversely, the P-wave attenuation and phase velocity characteristics inferred from creep tests are different and vary with the number of unit volumes considered. Quite interestingly, the creep test results converge with those of the relaxation tests as the number of unit volumes increases. These findings are expected to have direct implications for corresponding laboratory measurements as well as for our understanding of seismic wave propagation in fractured media.

Milani, Marco; Germán Rubino, J.; Müller, Tobias M.; Quintal, Beatriz; Holliger, Klaus

2014-05-01

103

Deformational characteristics of rock in low permeable reservoir and their effect on permeability  

Microsoft Academic Search

In the development of oil and gas the pressure in the rocks of reservoir changes constantly and rocks are compressed and deformed. So their permeability reduces. And the production capacity of oil and gas well is affected by the permeability. This paper deals with the deformational characteristics of rocks in low permeable reservoir and their effect on the permeability. The

Hong-Xing Wang; Guan Wang; Ron C. K. Wong

2010-01-01

104

Simulation of Persistence Characteristics of Textures During Plastic Deformation  

Microsoft Academic Search

The ideal orientations of textures that develop at large strains can be identified with the help of crystal plasticity simulations. In this short review, an overview is presented on these types of simulations that helped in the identification of the deformation texture components of fcc, bcc and hcp materials in pure shear (rolling) as well as in simple shear (torsion)

László S. Tóth

2009-01-01

105

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

106

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

107

Simulation of Persistence Characteristics of Textures During Plastic Deformation  

Microsoft Academic Search

The ideal orientations of textures that develop at large strains can be identified with the help of crystal plasticity simulations.\\u000a In this short review, an overview is presented on these types of simulations that helped in the identification of the deformation\\u000a texture components of fcc, bcc and hcp materials in pure shear (rolling) as well as in simple shear (torsion)

László S. Tóth

108

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

109

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

110

Coupled micro-faulting and pressure solution creep overprinted on quartz schist deformed by intracrystalline plasticity during exhumation of the Sambagawa metamorphic rocks, southwest Japan  

NASA Astrophysics Data System (ADS)

In the Sambagawa schist, southwest Japan, while ductile deformation 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 creep 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.

Takeshita, Toru; El-Fakharani, Abdel-Hamid

2013-01-01

111

Tensile Properties and Deformation Characteristics of a Ni-Fe-Base Superalloy for Steam Boiler Applications  

NASA Astrophysics Data System (ADS)

Ni-Fe-base superalloys due to their good manufacturability and low cost are the proper candidates for boiler materials in advanced power plants. The major concerns with Ni-Fe-base superalloys are the insufficient mechanical properties at elevated temperatures. In this paper, tensile properties, deformation, and fracture characteristics of a Ni-Fe-base superalloy primarily strengthened by ?' precipitates have been investigated from room temperature to 1073 K (800 °C). The results showed a gradual decrease in the strength up to about 973 K (700 °C) followed by a rapid drop above this temperature and a ductility minimum at around 973 K (700 °C). The fracture surfaces were studied using scanning electron microscopy and the deformation mechanisms were determined by the observation of deformed microstructures using transmission electron microscopy. An attempt has been made to correlate the tensile properties and fracture characteristics at different temperatures with the observed deformation mechanisms.

Zhong, Zhihong; Gu, Yuefeng; Yuan, Yong; Shi, Zhan

2014-01-01

112

Tensile deformation and fracture characteristics of delta-processed Inconel 718 alloy at elevated temperature  

Microsoft Academic Search

Three specimens with different initial ? phase contents have been used to study the tensile deformation and fracture characteristics of the delta-processed Inconel 718 alloy at elevated temperatures by tensile tests at 950°C. The results indicated that the tensile stress–strain curves of the three specimens were the elastic-uniform plastic curves, and there were two deformation processes during the uniform plastic

Shi-Hong Zhang; Hai-Yan Zhang; Ming Cheng

2011-01-01

113

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 700°C and detailed scanning transmission electron microscopy. Creep rupture strength of P92 is found to be more stable than that of P122 at temperatures over 600°C, which is mainly due to the difference in

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

2009-01-01

114

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

NASA Astrophysics Data System (ADS)

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

Sakai, Takenobu; Somiya, Satoshi

2011-08-01

115

Creep and shrinkage behavior of improved alternate substrates for magnetic tapes  

Microsoft Academic Search

The long-term creep deformation and shrinkage characteristics of improved alternate substrates for magnetic tapes are presented. The substrates include two polyesters (PET and PEN) and aromatic polyamide (ARAMID). PET film is currently the standard substrate used for magnetic tapes and thinner tensilized-type PET, PEN and ARAMID have recently been used as alternate substrates with improved material properties. The thickness of

Takuji Higashioji; Bharat Bhushan

2001-01-01

116

Simulation of Persistence Characteristics of Textures During Plastic Deformation  

NASA Astrophysics Data System (ADS)

The ideal orientations of textures that develop at large strains can be identified with the help of crystal plasticity simulations. In this short review, an overview is presented on these types of simulations that helped in the identification of the deformation texture components of fcc, bcc and hcp materials in pure shear (rolling) as well as in simple shear (torsion) during the last 20 years. The technique is based on the so-called persistence parameter that was introduced by Tóth, Gilormini and Jonas in 1988 [Acta Metall., 36, 3077-3091]. The formation of textures and several texture effects can be understood with the help of the persistence parameter together with the rotation field of orientations in Euler space and the divergence quantity. The stability of ideal orientations is especially investigated and it is shown that simple shear distinguishes from pure shear in a very particular way; all ideal orientations of simple shear are positioned at orientations where the divergence is zero while in rolling they are situated within a negative divergence field.

Tóth, László S.

117

Suppression of creep cavitation in precipitation-hardened austenitic stainless steel to enhance creep rupture strength  

Microsoft Academic Search

Extensive creep cavitation in Ti, Nb and Cu containing precipitation hardened austenitic steels was found to limit the usefulness\\u000a of deformation resistance to increase long-term creep rupture strength. The steels were microalloyed with boron and cerium\\u000a that resulted in increase in creep rupture strength and ductility of the steels significantly. Grain boundary sliding and\\u000a creep cavity nucleation and growth in

K. Laha; J. Kyono; N. Shinya

2010-01-01

118

The influence of plasticity in creep crack growth in steels  

Microsoft Academic Search

Much of the reported work on assessing time-dependent (creep) crack growth has focussed on creep ductile materials, with the deformation conditions ranging from small-scale creep to extensive steady state creep. This previous research on crack initiation and growth has been mainly concerned with characterising creep crack growth rates using the C? parameter.In this paper we interpret recent experimental results by

A. J Fookes; D. J Smith

2003-01-01

119

The characteristics of the deformation and flow process in the rolling of metal sheets and metal powders of composite materials  

Microsoft Academic Search

The rolling of metal sheets and metal powders of composite materials is anaasymmetric rolling process for the workpiece. The deformation of the rolled-piece, powder gains and the joining deformation of the composite interface are discussed and analyzed in this paper. Many experimental results are given for the deformation of the powder and the bending tendency of the rolled-piece. The characteristic

Shi Qingnan; Zhang Shuhong; Sun Yong; Zhang Daiming

1997-01-01

120

Calculation of Journal Bearing Dynamic Characteristics Including Journal Misalignment and Bearing Structural Deformation©  

Microsoft Academic Search

A detailed journal bearing analysis for accurate evaluation of film dynamic characteristics is presented. The new formulation is based on a local perturbation of the oil film at each computational node that captures the important effects of journal misalignment and bearing structural deformation in rotor dynamics and engine NVH applications. The new algorithm is an extension to the classical approach

OMIDREZA EBRAT; ZISSIMOS P. MOURELATOS; NICKOLAS VLAHOPOULOS; KUMAR VAIDYANATHAN

2004-01-01

121

Hot deformation characteristics of INCONEL alloy MA 754 and development of a processing map  

Microsoft Academic Search

The characteristics of hot deformation of INCONEL alloy MA 754 have been studied using processing maps obtained on the basis of flow stress data generated in compression in the temperature range 700 °C to 1150 °C and strain rate range 0.001 to 100 s-1. The map exhibited three domains. (1) A domain of dynamic recovery occurs in the temperature range

M. C. Somani; K. Muraleedharan; N. C. Birla; V. Singh; Y. V. R. K. Prasad

1994-01-01

122

3D Image Analysis for Evaluating Internal Deformation \\/ Fracture Characteristics of Materials  

Microsoft Academic Search

In the past, all methods which understand deformation \\/ fracture (D\\/F) characteristics have been limited on the surface indirectly. D\\/F characteristics are impacted by nano-scale structural features like air bubbles (pores); therefore, they need to be analyzed including inside. In this paper, we propose a system which automatically obtains the corresponding relations between pre- and post-D\\/F pores. Our system enabled

Mitsuru Nakazawa; Yoshimitsu Aoki; Hiroyuki Toda; Masakazu Kobayashi

2007-01-01

123

Continuum predictions of deformation in composites with two creeping phases. 2: Nb{sub 5}Si{sub 3}/Nb composites  

SciTech Connect

The primary and steady-state creep 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 creep constitutive law have been fitted to experimentally measured creep 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 creep rates. The models somewhat underpredict the steady-state strain rates and over predict the primary creep 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 creep 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 creep damage.

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)

1997-08-01

124

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

125

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

126

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 calcium–silicate–hydrates (C–S–H), the nano-meter sized particles that form the fundamental building block of Portland cement concrete. We show that C–S–H exhibits a logarithmic creep that depends only on the packing of 3 structurally distinct but compositionally similar C–S–H forms: low density, high density, ultra-high density. We demonstrate that the creep rate (?1/t) is likely due to the rearrangement of nanoscale particles around limit packing densities following the free-volume dynamics theory of granular physics. These findings could lead to a new basis for nanoengineering concrete materials and structures with minimal creep rates monitored by packing density distributions of nanoscale particles, and predicted by nanoscale creep measurements in some minute time, which are as exact as macroscopic creep tests carried out over years.

Vandamme, Matthieu; Ulm, Franz-Josef

2009-01-01

127

Estyuninky's Deformation Characteristics of the Iron-Ore Deposit by Gravimetric Means  

NASA Astrophysics Data System (ADS)

Gravitation is the main energy source of many processes which happen in crust. Gravity possesses the leading role in structurization; it defines a tectonic broken state and permeability of the geological medium, having significant importance at an ore deposition. Because of the gravitation density naturally changes, permeability and other properties of the geological medium changes too. Presence in crust of density heterogeneity of a various form and the sizes and properties change, show its compound stress of deformation condition. Studying of the deformations caused by gravitation, represents great expected and research interest. Theoretical basis of studying of these deformations consists on ratios between components of a pure tensor deformation and its first invariant -dilatation and results of measurement of gravity force. The method of deformation studying of the geological medium, developed on this basis, was called a method of the tektonophysic analysis of a gravitational field (MTPAGF). The detailed analysis of results of MTPAGF was made for the region of the Estyuninsky iron-ore deposit. The deposit region is characterized by a reversed dilatation. The zero isoline of dilatation divides it into two parts. To the east of this isoline where there is a deposit, a dilatation positive and rather small size. To the west - a dilatation negative and it increases as approaching a protrusion. Thus, to the east of the zero isoline the geological medium is in stretching mode, which promote relative expansion of the medium, improvement of its permeability. Thanks to it favorable conditions for an ore deposition here were created. To the west f the zero isoline medium is in a compression mode. Therefore it is characterized by smaller permeability. The border of change of a sign of a dilatation probably was important a role of the peculiar deformation barrier blocking migration through it of ore substance. It is possible to make the following conclusion of the analysis of deformation characteristics of the geological medium: small values of principal values of deformation and positive dilatation and, as a result, low level of specific energy of volume deformation, can evidence and to rather low tendency of the medium to destruction. As the deposit is located in the medium with such deformation properties, so there is some optimum broken state (permeability) of the medium optimum for an ore deposition. Extreme cases: very small and very big permeability complicate development of this process. In a little permeable medium it doesn't go at all, in very permeable - (at lack of screens) the disseminated or interspersed mineralization is formed. That work was supported by grant RFBR 10-05-00013.

Vandysheva, Ksenya; Filatov, Vladimir

2013-04-01

128

Effect of lubrication on deformation characteristics of a superplastic 5083 Al alloy during bi-axial deformation  

Microsoft Academic Search

Effect of lubrication on deformation behavior of a superplastic material has relatively been less examined, though it is important for industrial application. In this paper, a superplastic 5083 Al alloy under bi-axial deformation was investigated by deforming the sheet into a rectangular die cavity with and without lubrication. It was found that reducing the interfacial friction by use of a

Horng-Yu Wu; Chui-Hung Chiu; Jiann-Yih Wang; Shyong Lee

2006-01-01

129

Automatic Deformation Inspection Method for Digital Aerial Imagery Based on Statistical Characteristics  

NASA Astrophysics Data System (ADS)

The geometric distortion of the push-broom digital aerial imagery can be rectified according to the data of the inertial measurement unit (IMU). The low precision of IMU data will cause the undulant wavelike twist deformations of the push-broom digital aerial images after geometric rectification, directly influencing the authenticity and liability of images and their practical applications. At present, the image deformation diagnosis mainly depends on the subjective judgement of human being, which costs much time and manpower. In the paper, an automatic deformation inspection method based on statistical characteristics for digital aerial imagery is proposed to inspect the distortion caused by the low IMU data accuracy. For the undulant wavelike deformation image has the characteristic of pixel displacement in the regularly same direction, there will be a lot of wave curves in the same direction appeared in the image after geometric correction. Therefore, in the method, the positions of the wave curves in the image will be located by the extreme points of curvature of the contour lines, and then the wavelike deformations can be judged automatically through the distribution statistics of the open directions of the wave curves. The specific implement method can be described as follows: firstly, the edges of the image are detected with Canny edge detector and the vector contour lines are obtained by tracing the edges to get contour lines and fitting them with the cubic spline curve method. Then, the extreme points of curvature of the contour lines are calculated, and some of these points are determined to be the vertexes of the wave curves by judging the positional relations between each extreme point and the points around it, thus constituting a vertex set. Afterwards, the perpendicular directions of the tangent of the vertexes are used as the directions of the wave curves, and then the direction histograms of all the wave curves in the image are obtained by statistical analysis. Finally, the existence of the deformation phenomenon in the image due to the low precision of IMU data is able to be judged based on whether the directions of the wave curves are centralized in a certain direction or not. Experimental results showed that the automatic deformation inspection method presented in this paper can detect the deformation of the digital aerial images effectively caused by low accuracy of IMU data with 95% accuracy.

Yaohua, Y.; Yuan, Y.; Hai, S.; Mingjing, M.

2013-05-01

130

Tensile deformation characteristics of a nano-structured 5083 Al alloy  

Microsoft Academic Search

The microstructure and tensile deformation characteristics in the commercial 5083 Al alloy after equal channel angular pressing (ECAP) at 373 and 473K were investigated and compared with those of one reannealed at 473K for 1h after ECAP at 373K. All specimens revealed nano-structure with grains of ?300nm and no distinct grain boundaries except the reannealed alloy. The strength in the

Si-Young Chang; Byong-Du Ahn; Sung-Kil Hong; Shigeharu Kamado; Yo Kojima; Dong Hyuk Shin

2005-01-01

131

P—T—t—deformation—fluid characteristics of lode gold deposits: evidence from alteration systematics  

Microsoft Academic Search

Structurally hosted lode gold-bearing quartz vein systems in metamorphic terranes possess many characteristics in common, spatially and through time; they constitute a single class of epigenetic precious metal deposit, formed during accretionary tectonics or delamination. The ore and alteration paragenesis encode numerous intensive and extensive variables that constrain the pressure—temperature—time—deformation—fluid (P—T—t—d—f) evolution of the host terrane and hence the origin

T. Campbell McCuaig; Robert Kerrich

1998-01-01

132

Hot deformation characteristics of INCONEL alloy MA 754 and development of a processing map  

Microsoft Academic Search

The characteristics of hot deformation of INCONEL alloy MA 754 have been studied using processing maps obtained on the basis\\u000a of flow stress data generated in compression in the temperature range 700 ?C to 1150 ?C and strain rate range 0.001 to 100\\u000a s-1. The map exhibited three domains. (1) A domain of dynamic recovery occurs in the temperature range

M. C. Somani; K. Muraleedharan; N. C. Birla; V. Singh; Y. V. R. K. Prasad

1994-01-01

133

Deformation characteristics of ? phase in the delta-processed Inconel 718 alloy  

Microsoft Academic Search

The hot working characteristics of ? phase in the delta-processed Inconel 718 alloy during isothermal compression deformation at temperature of 950°C and strain rate of 0.005s?1, were studied by using optical microscope, scanning electron microscope and quantitative X-ray diffraction technique. The results showed that the dissolution of plate-like ? phase and the precipitation of spherical ? phase particles coexisted during

H. Y. Zhang; S. H. Zhang; M. Cheng; Z. X. Li

2010-01-01

134

Surface loading effects complicate the derivation of internal pressure source characteristics from volcano deformation signals  

NASA Astrophysics Data System (ADS)

An increasing number of crustal deformation studies relate volcano deformation to internal pressure sources (e.g., magma chambers). However, surface loads such as lava flows provide an additional source of deformation. The initial elastic response due to a load on the surface of the Earth is followed by a visco-elastic response of the ductile crust below the uppermost elastic layer. Thus, a deformation signal recorded in the vicinity of a volcano is often composed of at least two contributors: an internal pressure source (the magma chamber) and a surface load (a composition of previously erupted lava flows) - at the extreme the volcano edifice itself. A test case for a circular lava flow on top of a deflating magma chamber shows that the crust will adjust to the load towards final relaxed response. During this relaxation process gradual subsidence occurs that may mistakenly be interpreted as due to pressure decrease in a magma chamber since the deformation pattern of both processes are very similar. This poses a problem when characteristics of a magma chamber are to be derived. We suggest that additional factors posed by the surface load must be considered and constrained by careful measurements and interpretations of observations and eruptions histories to correct the recorded data for composed signal sources. We conclude that neglecting the surface loads (elastic and visco-elastic responses) may lead to incorrect estimates of magma chamber depths (i.e., too shallow) in magma chamber studies. We conducted a case study in which Green's functions are utilized to estimate the final relaxed response due to recent lava flows of the Icelandic volcano Mt. Hekla. We compare the model results to InSAR data and to the deformation pattern induced by pressure changes in a hypothetical shallow magma chamber. The magma chamber is modeled as a point source of pressure utilizing the so-called Mogi model. The final relaxed response fits the deformation due to the point source very well. In fact, the modeling results show almost identical deformation signals in the vertical displacement field directly under the load. In the far field, however, the response due to the Mogi model is up to 16 % below the final relaxed response. Very significant differences show up the horizontal displacement fields with the horizontal displacement in response to the pressure change in the magma chamber being and order of magnitude higher than the final relaxed response. Thus, to identify whether elastic chamber pressure response or visco-elastic deformation due to surface loads is recorded in the data we suggest to carefully look at the horizontal displacement in addition to vertical displacement.

Grapenthin, R.; Sigmundsson, F.; Pedersen, R.; Pinel, V.

2007-12-01

135

Diffusion, diffusion creep and grain growth characteristics of nanocrystalline and fine-grained monoclinic, tetragonal and cubic zirconia  

Microsoft Academic Search

The experimentally measured grain size compensated diffusion creep rates are essentially identical in cubic, tetragonal and monoclinic zirconia, suggesting a similarity in the absolute magnitudes of their grain boundary diffusion coefficients. However, grain growth is substantially slower in tetragonal zirconia due to significant grain boundary segregation.

Atul H. Chokshi

2003-01-01

136

Hydrothermal vein and deformation characteristics in the Nojima fault zone, Japan  

NASA Astrophysics Data System (ADS)

The hydrothermal vein formation and deformation in the Nojima fault zone were examined in the core recovered from a borehole drilled by the Geological Survey of Japan (GSJ) twelve months after the 1995 Hyogo-ken Nanbu (Kobe) earthquake (MJMA=7.2), southwest Japan. The borehole was drilled across a slipped portion of the fault to a depth of 747 m. The fault zone was intersected at 426 m and is characterized by a greater intensity of brittle deformation and/or hydrothermal alteration than typical host granodiorite. The fault core consists of three types of fault gouge, and occurs at the depth range of 623 m to 625 m. The fluid circulation and deformation have occurred along the fault and the fault rocks from this borehole enable to understand the hydrothermal vein formation and deformation in the fault zone. The hydrothermal veins are developed along the entire depth of the core (152 to 767 m depth). Vein materials are zeolite (laumontite and stilbite) and carbonate (calcite, siderite, ankerite and dolomite). Zeolite veins are well developed and exhibit network-like structure and opening of host rocks. These indicate the fault rocks were dilated during the zeolite vein formation. Euhedral zeolites are often included in veins. This also supports dilatation of the fault zone. Carbonate often constitutes complex veins of siderite and calcite. Most zeolite mineralization preceded carbonate mineralization. The characteristic feature in the fault zone is minor fault zones. Some of them contain zeolite and/or carbonate. Biotite is partly preserved and elongated in minor fault zones. Host rocks often suffered strong zeolitization in the fault zone. These suggest a wide variety of the hydrothermal vein formation and deformation in the fault zone. The range of 625 to 635 m depth just below the fault core contains unconsolidated low-angle minor fault zones with small carbonates. These might be products of recent fluid circulation and deformation.

Ohtani, T.; Fujimoto, K.; Boullier, A.-M.; Tanaka, H.; Ito, H.

2003-04-01

137

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

138

Electrochemical control of creep in nanoporous gold  

NASA Astrophysics Data System (ADS)

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

Ye, Xing-Long; Jin, Hai-Jun

2013-11-01

139

Electrochemical control of creep in nanoporous gold  

SciTech Connect

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

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)

2013-11-11

140

Optical 3-D metric measurements of local vocal fold deformation characteristics in an in vitro setup.  

PubMed

Understanding vocal fold dynamics presents an essential part in treating voice disorders as it is the prerequisite to appropriate medical therapy. Various physical and numerical models exist for simulation purposes, all relying on simplified material parameters. To improve current approaches, data of realistic tissue behavior, i.e., in natural surroundings, have to be considered in model development. An in vitro setup was proposed for tensile tests combined with an optical method for precise, local and metrical 3-D measurements of distinctive surface points. Compared to previous 3-D reconstruction methods, the accuracy was improved tenfold. Vertically applied forces versus resulting deformation were measured for ten porcine vocal folds. Deformation characteristics of mucosa and the two-layer structure of mucosa and muscle (MM) were investigated at three distinctive locations along the vocal fold edge. The spring rates were represented by an exponential function. For equal deflections, an increasing spring rate from posterior to anterior for MM was measured. For solely mucosa, the spring rate decreased from the posterior to the middle and subsequently increased again. The MM-layer presented a stiffer deformation behavior than mucosa. For deformations higher than 1.5 mm, the spring rates for MM were more than twice as high as for mucosa. The investigations display the importance of considering both multilayers and local differences for the improvement of vocal fold models. PMID:21427016

Huttner, Björn; Sutor, Alexander; Luegmair, Georg; Rupitsch, Stefan J; Lerch, Reinhard; Döllinger, Michael

2011-10-01

141

Creep rupture of copper and aluminium alloy under combined loadings—experiments 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

142

Crystallographic preferred orientation development by dissolution–precipitation creep  

Microsoft Academic Search

Crystallographic preferred orientations (CPOs) in deformed rocks are commonly interpreted as resulting from crystal plastic deformation mechanisms, where deformation is achieved by the movement of dislocations. In this paper we investigate the possibility of CPO-development by dissolution–precipitation creep or pressure solution. A numerical model is presented, which simulates the development of a grain aggregate that deforms by reaction-controlled dissolution–precipitation creep.

Paul D. Bons; Bas den Brok

2000-01-01

143

Characteristics of a prevalent vertebral deformity predict subsequent vertebral fracture: results from the European Prospective Osteoporosis Study (EPOS)  

Microsoft Academic Search

The presence of a prevalent vertebral deformity increases the risk of a future vertebral fracture. The aim of this study was to determine whether certain characteristics of the prevalent deformity, including its shape and location in the spine, influenced this effect. The 3100 men and 3500 women who took part in this analysis were recruited from population registers for participation

Mark Lunt; Terence W O'Neill; Dieter Felsenberg; Jonathan Reeve; John A Kanis; Cyrus Cooper; Alan J Silman

2003-01-01

144

Effect of plastic deformation on spectral characteristics of alkali halide crystals doped with indium or nickel ions  

NASA Astrophysics Data System (ADS)

The opportunity of investigation of impurity defect properties in alkali halide crystals by study of the spectral characteristics of the strongly deformed crystals is shown. The spectral characteristics of KCl-In and NaCl-Ni crystals before and after deformation, and also after X- irradiation, are given. The effect of methods of impurity doping of a host crystal on spectral properties of powdered specimens under study was examined.

Kochubey, Vyacheslav I.; Sedova, Yuliya G.

2000-03-01

145

Surface loading affects internal pressure source characteristics derived from volcano deformation signals  

NASA Astrophysics Data System (ADS)

Deformation of the Earth's surface provides critical information about the migration of material beneath a volcano. The resulting displacements, recorded by geodetic techniques such as GPS or InSAR, are used to infer characteristics of the volcanic plumbing system which are critical for hazard mitigation in volcanic regions. Given some deformation data, we search for the source model that explains the data best. Discussions of the results usually focus on the validity of the chosen model and the underlying assumptions regarding crustal composition, e.g. the level of inhomogeneity, elastic versus plastic deformation, thermal effects, depth vs. volume trade offs of the applied analytical models, or the (in-)compressibility of materials. Surface loads such as lava flows, however, provide an additional source of deformation. The initial elastic response due to a load on the surface of the Earth is followed by a visco-elastic response of the ductile crust below the uppermost elastic layer. Thus, a deformation signal recorded in the vicinity of a volcano is often composed of at least two contributors: an internal pressure source (the magma chamber) and a surface load (e.g., a composition of previously erupted lava flows) - at the extreme the volcanic edifice and its glaciers. A test case for a circular lava flow on top of a deflating magma chamber shows that the crust will adjust to the load towards final relaxed response. During this relaxation process gradual subsidence occurs that may mistakenly be interpreted as due to pressure decrease in a magma chamber since the deformation pattern of both processes are very similar. This poses a problem when characteristics of a magma chamber are to be derived. Based on the ratio of horizontal and vertical displacement and a combination of model results (Green's functions and Mogi model), we can estimate the composition of observed deformation signals. This method is applied to the Icelandic volcano Mt. Hekla where we investigate InSAR observations prior to the Hekla 2000 eruption that show circular pattern of near field subsidence and far field inflation. We compare these data to the deformation pattern expected from pressure changes in a hypothetical, shallow magma reservoir. We estimate surface loading at the volcano to account for a displacement of 13.5mm-yr based on a comparison of expected Mogi source and observed InSAR line of sight velocity. From this we estimate an effective relaxation time of tr = 100yrs for this region. We infer an elastic plate thickness of H = 3.5km which controls the 15 - 20km radius of subsidence. We find that surface load signals in volcanic regions affect magmatic source model estimates significantly ; to the point of changing the preferred source model. This effect should be considered in virtually any volcanic region that shows lava flow emplacement, glacier dynamics, or sudden load removal (i.e., lateral blasts). Deformation data that remains uncorrected will most likely result in an overestimation of depth and volume of a magma reservoir. We find that the ratio of displacements aids the identification of composite signals and suggest that the ratio for GPS data be employed more rigorously in future studies since this allows volume independent source depth estimates.

Grapenthin, Ronni; Sigmundsson, Freysteinn; Ofeigsson, Benedikt; Sturkell, Erik

2010-05-01

146

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

147

The effect of tungsten on creep  

NASA Astrophysics Data System (ADS)

The effect of tungsten on creep behavior and microstructural evolution was investigated for tempered martensitic 9Cr steels with various W concentrations from 0 to 4 wt pct. The creep rupture testing was carried out at 823, 873, and 923 K for up to 54 Ms (15,000 hours). The creep and creep rupture strength increased linearly with W concentration up to about 3 wt pct, where the steels consisted of the single constituent of the tempered martensite. It increased only slightly above 3 wt pct, where the matrix consisted of the tempered martensite and ?-ferrite. The minimum creep rate was described by a power law. The apparent activation energy for the minimum creep rate showed a tendency similar to the W concentration dependence of the creep-rupture strength and was larger than the activation energy for self-diffusion at high W concentrations above 1 wt pct. The martensite lath microstructure with fine carbides along lath boundaries was responsible for a high resistance to creep deformation. With increasing W con- centration, the martensite lath microstructure became stabilized, which decreased the minimum creep rate and increased the apparent activation energy for the minimum creep rate.

Abe, Fujio; Nakazawa, Shizuo

1992-11-01

148

The characteristics of cavitation during superplastic deformation of a warm-rolled Al-Li-Cu-Mg-Zr alloy  

SciTech Connect

The process of superplastic forming has become important in numerous commercial applications. However, there may be some deleterious defects on the properties of superplastically-formed components due to the presence of minor levels of cavitation introduced during the forming process. Thus, it is important to obtain information on nucleation, growth and interlinkage of cavities in a wide range of superplastic materials. Two different thermomechanical processing routes may be employed to develop fine grain sizes conducive to superlasticity in Al-Li alloys. In one of them, a fine grain size microstructure is obtained by static recrystallization prior to superplastic deformation, and in another, a fine grain size microstructure is obtained by deformation-induced recrystallization during the initial stage of superplastic deformation. The deformation-induced recrystallization of a cold (or warm)-rolled Al-Li alloy is strongly dependent on the strain rate microstructural change during the initial stage of superplastic deformation due to deformation-induced recrystallization. There have been some studies dealing with cavitation in superplastic Al-Li alloys. However, there is no research work reported on the effect of deformation-induced recrystallization on the characteristics of cavitation during superplastic deformation of a warm-rolled Al-Li alloy. This paper deals with the relationship between deformation-induced recrystallization and cavitation characteristics during superplastic deformation of a warm-rolled Al-Li-Cu-Mg-Zr alloy. The results show that there are three kinds of cavities. The first includes the fine cavities formed at the beginning stage of deformation, the second the large cavities formed around the intermetallic particles and the third the grain boundary cavities. All three kinds of cavities are closely related to deformation-induced recrystallization.

Liu, Q. (Analysis and Measurement Centre, Harbin Inst. of Tech., Harbin 150006 (CN)); Huang, X.; Yang, J.; Yao, M. (Dept. of Metals and Technology, Harbin Inst. of Tech., Harbin 150006 (CN))

1991-01-01

149

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

150

Structural Characteristics of the Northern Cascadia Deformation Front: Preliminary Result of the SeaJade Experiment  

NASA Astrophysics Data System (ADS)

The Cascadia subduction zone, capable of generating megathrust earthquakes, poses the greatest seismic hazard to the Pacific Northwest. Many research projects have been initiated in the past to investigate the seismogenic structures of the Cascadia subduction zone, but few could provide sufficient constraints on the detailed velocity structures within the toe of the northern Cascadia accretionary prism and the oceanic Juan de Fuca plate seaward from the deformation front. This is mainly due to their offshore setting too far outside of station coverage of the land-based seismograph network. To address this significant knowledge gap, an international research effort was planned in 2008 to deploy 32 ocean-bottom seismographs (OBS) in the vicinity of the deformation front of the northern Cascadia accretionary prism offshore southwest of Vancouver Island (VI). The experiment, named the Seafloor Earthquake Array-Japan-Canada Cascadia Experiment (SeaJade), was conducted between July and October of 2010 and has recorded over 1400 local earthquakes. In this study, we examine the 3-component waveforms recorded by stations on both sides of the deformation front to delineate the structural characteristics of the subduction system. We first use air-gun data and the T-phase of local earthquakes to calibrate the azimuthal orientation of each OBS station. The calibrated waveforms are then systematically rotated and shifted to determine the corresponding fast axis and delay time of the crustal anisotropy beneath each station. For some stations, we also notice the existence of multiple converted phases between the P and S arrivals. Our preliminary results indicate that the fast axes are oriented consistently in the E-W direction, basically sub-normal to the trench axis, for stations located on the seaward side of the deformation front. This pattern agrees well with the mantle anisotropy observed at stations on southern VI and Puget Sound, and can be interpreted as the lattice-preferred orientation (PLO) of anisotropic minerals within the Juan de Fuca plate. The orientation of fast axes appears to be much more complicated for stations on the other side of the deformation front, perhaps resulted from the combined effects of anisotropy in the subducting oceanic plate and the deformation within the accretionary prism. The multiple converted phases are also indicative of the complex velocity structures at shallow depths near the prism toe. Our results can be used to establish a realistic boundary condition for numerical modeling of the thermo-mechanical regime of the Cascadia subduction system, which in turn controls the overall seismogenic processes of megathrust earthquakes.

Shan, S.; Kao, H.; Obana, K.

2012-12-01

151

Comparison of cleaning efficiency and deformation characteristics of Twisted File and ProTaper rotary instruments  

PubMed Central

Objective: The objective of the following study is to compare the cleaning efficiency and deformation characteristics of Twisted File (TF) and ProTaper (PT) nickel-titanium rotary instruments in root canal preparation. Materials and Methods: A total of 52 canals from 26 extracted maxillary first molars were randomly assigned into two groups of each including 13 mesiobuccal and 12 distobuccal (DB) canals. Two DB canals were as blank controls. After preparation with TF and PT, we recorded the preparation time and evaluate the amounts of debris and smear layer at apical, middle and coronal canals under scanning electron microscopy (SEM). Three cross-sections of canals at 3 mm, 5 mm and 7 mm from the apex foramens were scanned before and after preparation under micro-computed tomography. Changes of the cross-section area (CSA) at the three levels were calculated with Photoshop CS4. File deformation was also investigated under SEM. Two groups were statistically compared with Mann-Whitney test and independent sample t-test. Results: Less debris and smear layer were found in coronal regions of canals prepared with TF (P = 0.006, P = 0.001, respectively). TF group displayed more CSA change than PT group (P = 0.045) at cross-sections of 5 mm from the apex foramens and took significantly less preparation time than PT group did (P = 9.06 × 10?28). All five TF files without obvious micro-cracks and two out of 25 PT files with many micro-cracks showed visible unwound deformation. Conclusion: Neither TF nor PT achieves complete cleanliness of canal walls. Their deformation features might indicate different fracture resistance. TF single-file technique would substantially shorten the time of root canal preparation.

Li, Hang; Zhang, Chenzheng; Li, Qing; Wang, Changning; Song, Yaling

2014-01-01

152

Creep in colloidal glasses.  

PubMed

We investigate the nonlinear response to shear stress of a colloidal hard-sphere glass, identifying several regimes depending on time, sample age, and the magnitude of applied stress. This emphasizes a connection between stress-imposed deformation of soft and hard matter, in particular, colloidal and metallic systems. A generalized Maxwell model rationalizes logarithmic creep for long times and low stresses. We identify diverging time scales approaching a critical yield stress. At intermediate times, strong aging effects are seen, which we link to a stress overshoot seen in stress-strain curves. PMID:23004620

Siebenbürger, M; Ballauff, M; Voigtmann, Th

2012-06-22

153

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

154

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

155

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

NASA Astrophysics Data System (ADS)

The purpose of this investigation is to identify and clarify the perspective of the nature and origin of necessary procedures and requirements for Harper-Dorn creep. Harper-Dorn creep represents to the anomalous high temperature deformation behavior, which is first reported by Harper and Dorn in aluminum under the condition of small strains about 0.01. To accomplish the purpose of this investigation, four types of large grained materials are selected: commercial purity grade lead, high purity grade lead, high purity grade polycrystalline aluminum, and high purity grade single crystalline aluminum. Creep experiments are conducted under 0.98 melting temperature of the selected materials in long term tests. Microstructures are examed by optical microscope, scanning electron microscope and transmission electron microscope. Mechanical results represent that creep curves of commercial purity grade lead are smooth and stress exponents obeys the five-power-law at both high and low stress areas. Micro-structural results show that dynamic recovery is the proper restoration mechanism for commercial purity grade lead. Mechanical results represent that creep curves of high purity grade aluminum and lead show periodic accelerations in strain. The creep results of high purity grade aluminum verify that the present test conditions correspond to the priors. Furthermore, under the condition of large strains about 0.05, it was determined that the stress exponent of Harper-Dorn creep is about 2.6 and does not reveal Newtonian behavior. Micro-structural results indicate that dynamic re-crystallization is a dominate restoration mechanism for Harper-Dorn creep in large grain size, low dislocation density, and high purity grade materials. Therefore, this investigation provides new evidence that dynamic re-crystallization occurs during Harper-Dorn creep. The evidence is proved by the occurrence of periodic accelerations in creep curves and the transition of the stress exponents. Furthermore, micro-structural results are consistent with mechanical data, which describe the Harper-Dorn creep behavior. Above information indicate that characteristics of dynamic re-crystallization are associated with Harper-Dorn creep.

Cheng, Yu-Ching

156

Study on transmission characteristics of photonic crystal fiber gratings with periodic air hole deformation  

NASA Astrophysics Data System (ADS)

The paper studies a kind of improved photonic crystal fiber gratings fabricated by CO2 laser heating method. The effective refractive index of cladding induced by periodic air hole deformation is computed using multipole method, and the relationship between the effective refractive index and the collapse of air-holes is discussed, thereby the modulation expression of effective refractive index is obtained. The grating transmission characteristics are simulated. The results indicate that with the diameter of air-holes increasing from 3.3 ?m to 3.7 ?m, the resonance wavelength shows blue-shift, the resonance peak intensifies, and the bandwidth becomes narrow. As the collapse degree of cladding enhances, the resonance wavelength shows red-shift, the transmission increases, and the bandwidth tends to narrow.

Liu, Yan-Yan; Tian, Che; Qi, Yue-Feng; Guo, Wen-Guang

2011-11-01

157

Geodetic characteristic of the postseismic deformation following the interplate large earthquake along the Japan Trench (Invited)  

NASA Astrophysics Data System (ADS)

On March 9, 2011 at 2:45 (UTC), an M7.3 interplate earthquake (hereafter foreshock) occurred ~45 km northeast of the epicenter of the M9.0 2011 Tohoku earthquake. This foreshock preceded the 2011 Tohoku earthquake by 51 hours. Ohta et al., (2012, GRL) estimated co- and postseismic afterslip distribution based on a dense GPS network and ocean bottom pressure gauge sites. They found the afterslip distribution was mainly concentrated in the up-dip extension of the coseismic slip. The coseismic slip and afterslip distribution of the foreshock were also located in the slip deficit region (between 20-40m slip) of the coiseismic slip of the M9.0 mainshock. The slip amount for the afterslip is roughly consistent with that determined by repeating earthquake analysis carried out in a previous study (Kato et al., 2012, Science). The estimated moment release for the afterslip reached magnitude 6.8, even within a short time period of 51 hours. They also pointed out that a volumetric strainmeter time series suggests that this event advanced with a rapid decay time constant (4.8 h) compared with other typical large earthquakes. The decay time constant of the afterslip may reflect the frictional property of the plate interface, especially effective normal stress controlled by fluid. For verification of the short decay time constant of the foreshock, we investigated the postseismic deformation characteristic following the 1989 and 1992 Sanriku-Oki earthquakes (M7.1 and M6.9), 2003 and 2005 Miyagi-Oki earthquakes (M6.8 and M7.2), and 2008 Fukushima-Oki earthquake (M6.9). We used four components extensometer at Miyako (39.59N, 141.98E) on the Sanriku coast for 1989 and 1992 event. For 2003, 2005 and 2008 events, we used volumetric strainmeter at Kinka-zan (38.27N, 141.58E) and Enoshima (38.27N, 141.60E). To extract the characteristics of the postseismic deformation, we fitted the logarithmic function. The estimated decay time constants for each earthquake had almost similar range (1-15 h) with the foreshock of the 2011 Tohoku earthquake (4.8h), but relatively small compared with the typical interplate earthquakes. The comparison of decay time constant with other typical large interplate earthquakes is very difficult because of difference in the observation sensors such as GPS and strainmeter. In any case, decay time constant of postseismic deformation for the foreshock of the 2011 Tohoku earthquake is not anomalous compared with other events in this region.

Ohta, Y.; Hino, R.; Ariyoshi, K.; Matsuzawa, T.; Mishina, M.; Sato, T.; Inazu, D.; Ito, Y.; Tachibana, K.; Demachi, T.; Miura, S.

2013-12-01

158

A note on the variation of Young's modulus, absorptive power of impactive energy, fracture toughness and creep strain rate during the creep process  

Microsoft Academic Search

Most of the early research on creep was confined to obtaining data for correlating the expected rupture time of a sample with the static creep stress, the variation of the mechanical properties not having been studied during the creep process. Young's modulus decreases as the Larson-Miller parameter increases. The static load multiplied by the tensile elastic deformation caused by the

Hung-Kuk Oh

1996-01-01

159

Analogy betwen dislocation creep and relativistic cosmology  

NASA Astrophysics Data System (ADS)

A formal, physical analogy between plastic deformation, mainly dislocation creep, and Relativistic Cosmology is presented. The physical analogy between eight expressions for dislocation creep and Relativistic Cosmology have been obtained. By comparing the mathematical expressions and by using a physical analysis, two new equations have been obtained for dislocation creep. Also, four new expressions have been obtained for Relativistic Cosmology. From these four new equations, one may determine the neutron energy, UN, by knowing of the present value of the universe radius and the Einstenian gravitational constant. Another new expression gives the neutron radius, (TN), as the present value of the universe radius, R-OU divided by 10(40).

Montemayor-Aldrete, J. A.; Munoz-Andrade, J. D.; Mendoza-Allende, A.; Montemayor-Varela, A.

2005-10-01

160

Morphologies and characteristics of deformation induced martensite during low cycle fatigue behaviour of austenitic stainless steel  

Microsoft Academic Search

Quantification, formation and nucleation micro-mechanisms of deformation induced martensite during low cycle fatigue behaviour of austenitic stainless steel have been investigated at various strain amplitudes tested at ambient temperature. The evolutionary deformation induced martensite has been quantified through magnetic measurement technique. It has been found that as strain amplitude increases, the volume fraction of deformation induced martensite increases. Extensive analytical

Arpan Das; S. Sivaprasad; P. C. Chakraborti; S. Tarafder

2011-01-01

161

Dielectrophoretic-Field Flow Fractionation Analysis of Dielectric, Density and Deformability Characteristics of Cells and Particles  

PubMed Central

Dielectrophoretic field-flow fractionation (DEP-FFF) has been used to discriminate between particles and cells based on their dielectric and density properties. However, hydrodynamic lift forces (HDLF) at flow rates needed for rapid separations were not accounted for in the previous theoretical treatment of the approach. Furthermore, no method was developed to isolate particle or cell physical characteristics directly from DEP-FFF elution data. An extended theory of DEP-FFF is presented that accounts for HDLF. Using DS19 erythroleukemia cells as model particles with frequency-dependent dielectric properties, it is shown that the revised theory accounts for DEP-FFF elution behavior over a wide range of conditions and is consistent with sedimentation-FFF when the DEP force is zero. Conducting four elution runs under specified conditions, the theory allows for the derivation of the cell density distribution and provides good estimates of the distributions of the dielectric properties of the cells and their deformability characteristics that affect HDLF. The approach allows for rapid profiling of the biophysical properties of cells, the identification and characterization of subpopulations and the design of optimal DEP-FFF separation conditions. The extended DEP-FFF theory is widely applicable and the parameter measurement methods may be adapted easily to other types of particles.

Gascoyne, Peter R.C.

2009-01-01

162

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

SciTech Connect

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

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

2012-11-15

163

Creep Behavior and Life Evaluation of Aged P92 Steel  

Microsoft Academic Search

Creep strength and life of material is closely related with the microstructural characteristics. Components used under creep condition for long time are unable to maintain the stability of microstructure and experience degradation of material. From this viewpoint, it is necessary for safety and residual life of power plant to investigate creep properties of specimens prepared from the material cut directly

Bumjoon Kim; Byeongsoo Lim; Donghyun Ki

2006-01-01

164

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

165

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 Oyane’s

Hyoung Seop Kim; Dong Nyung Lee

1999-01-01

166

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?1400°C) and moderate stresses (5 < sigma<110 MPa) in a load creep apparatus at room pressure and under controlled atmosphere. Assuming Assuming, that the creep law has the

Michel Darot; Yves Gueguen

1981-01-01

167

COMPARISON OF COMPUTER SIMULATED AND OBSERVED FORCE DEFORMATION CHARACTERISTICS OF ANTI-SEISMIC DEVICES AND ISOLATED STRUCTURES  

Microsoft Academic Search

The paper discusses the finite element analysis of the force deformation characteristics of high damping rubber bearings, lead rubber bearings and natural rubber bearings. The dynamic response of structures isolated using bearings is also presented. The general purpose finite element program ABAQUS has been used for the numerical predictions under monotonic loads. For computing the dynamic response, a simplified model

S. B. BHOJE; P. CHELLAPANDI; S. CHETAL

168

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

Microsoft Academic Search

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

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

169

Tensile and creep properties of the experimental oxide dispersion strengthened iron-base sheet alloy MA-956E at 1365 K  

NASA Technical Reports Server (NTRS)

A study of the 1365 K tensile properties, creep characteristics and residual room temperature properties after creep testing of the experimental oxide dispersion strengthened iron-base alloy MA-956E (Fe-20Cr-4.5Al-0.5Ti-0.5Y2O3) was conducted. The 1365 K tensile properties, particularly ductility, are strongly dependent on strain rate. It appears that MA-956E does not easily undergo slow plastic deformation. Rather than deform under creep loading conditions, the alloy apparently fails by a crack nucleation and growth mechanism. Fortunately, there appears to be a threshold stress below which crack nucleation and/or growth does not occur.

Whittenberger, J. D.

1978-01-01

170

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

171

Creep of trabecular bone from the human proximal tibia.  

PubMed

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

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

2014-07-01

172

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

173

The search for creep on the faults of northern California  

NASA Astrophysics Data System (ADS)

Shallow aseismic fault creep is a behaviour exhibited by very few faults in the world. Instead of the stick-slip frictional regime that most faults follow, creeping faults move, steadily or episodically, throughout the interseismic period of the earthquake cycle. Creep effectively reduces the fault surface area capable of rupture in earthquakes, and thus knowledge of its extent is critical for the correct assessment of seismic hazard. In addition, by comparing the geographical locations of creeping fault areas with mapped lithologies, we may be able to better understand the underlying causes or mechanisms. We present here the results of our ongoing research into the distribution of creeping fault areas in northern California, where the majority of reported cases are located. We map the surface deformation field of the plate boundary system south and north of the San Francisco Bay Area using persistent scatterer InSAR, which provides a dense spatial coverage of surface deformation measurements across the region, and 'ground truth' these, where possible, with additional surface deformation measurements from GPS. In so doing, we identify deformation consistent with right-lateral shallow creep on sections of five major faults (the Hayward, Calaveras, San Andreas, Rodgers Creek and Concord faults). On the Hayward fault, we are able to map both the extent and distribution of creep rates at depth, constraining the location of a locked zone that is presumably the source of major earthquakes on the fault. We are not able to identify a consistent lithological control for the creep behaviour.

Funning, Gareth; Jin, Lizhen

2013-04-01

174

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

175

A generalized constitutive equation for creep of polymers at multiaxial loading  

Microsoft Academic Search

This paper introduced a unified formulation for generalized deformation models including load dependent effects (2nd order effects). It is given in more detail for stationary creep of isotropic, orthotropic, and anisotropic material behavior. A further generalization of the introduced 6-parameter constitutive equation is possible by coupling creep and damage. These generalizations include the classical theory of creep damage [13]. The

H. Altenbach; J. Altenbach; A. Zolochevsky

1996-01-01

176

Multiaxial creep and cyclic plasticity in nickel-base superalloy C263  

Microsoft Academic Search

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

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

2005-01-01

177

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

Microsoft Academic Search

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

J. L. Freer; J. W. Morris

1992-01-01

178

Phenomenology of the creep process of a precipitation-hardenable AlMgSi alloy wires for overhead power lines. Experimental tests. Simulation  

NASA Astrophysics Data System (ADS)

The article presents the results of the experimental test on the creep process of AlMgSi alloy wires (series 6xxx) under the conditions of variable stress. A theoretical analysis of equivalency rheological results of stress and temperature changes by means of Bayley-Norton function, which describes well the low-temperature aluminum alloys creep, was carried out. Therefore, the described issue became one-dimensional. On the basis of experimental tests, it has been proved that negative gradients of stress and temperature may generate three types of rheological behaviour, such as: Temporary decrease of creep speed (type 1), Temporary stop of creep deformation (‘dead’ time)—type 2 and reverse after creep (type 3). The applicable nature of tests is placed in overhead power lines, which undergo cyclical stress- and time-dependent operation. Such a nature of conductor operation creates favourable conditions to decrease creep intensity, whereas its history and value and speed of stress and temperature lowering decide whether conductor rheological activity loss will take place. The actual material parameter controlling the conductor rheological behaviour is stress and temperature rheological equivalent. The article contains exemplary results of current-carrying capacity changes of AlMgSi alloy conductor on a given temperature range, and the calculations include actual creep characteristic and cumulated rheological inactivity caused by negative gradients of stress and temperature.

Knych, Tadeusz; Mamala, Andrzej; Smyrak, Beata

2009-05-01

179

Investigating the creeping section of the San Andreas Fault using ALOS PALSAR interferometry  

NASA Astrophysics Data System (ADS)

In recent years, time-series InSAR techniques have been used to study the temporal characteristics of various geophysical phenomena that produce surface deformation including earthquakes and magma migration in volcanoes. Conventional InSAR and time-series InSAR techniques have also been successfully used to study aseismic creep across faults in urban areas like the Northern Hayward Fault in California [1-3]. However, application of these methods to studying the time-dependent creep across the Central San Andreas Fault using C-band ERS and Envisat radar satellites has resulted in limited success. While these techniques estimate the average long-term far-field deformation rates reliably, creep measurement close to the fault (< 3-4 Km) is virtually impossible due to heavy decorrelation at C-band (6cm wavelength). Shanker and Zebker (2009) [4] used the Persistent Scatterer (PS) time-series InSAR technique to estimate a time-dependent non-uniform creep signal across a section of the creeping segment of the San Andreas Fault. However, the identified PS network was spatially very sparse (1 per sq. km) to study temporal characteristics of deformation of areas close to the fault. In this work, we use L-band (24cm wavelength) SAR data from the PALSAR instrument on-board the ALOS satellite, launched by Japanese Aerospace Exploration Agency (JAXA) in 2006, to study the temporal characteristics of creep across the Central San Andreas Fault. The longer wavelength at L-band improves observed correlation over the entire scene which significantly increased the ground area coverage of estimated deformation in each interferogram but at the cost of decreased sensitivity of interferometric phase to surface deformation. However, noise levels in our deformation estimates can be decreased by combining information from multiple SAR acquisitions using time-series InSAR techniques. We analyze 13 SAR acquisitions spanning the time-period from March 2007 to Dec 2009 using the Short Baseline Subset Analysis (SBAS) time-series InSAR technique [3]. We present detailed comparisons of estimated time-series of fault creep as a function of position along the fault including the locked section around Parkfield, CA. We also present comparisons between the InSAR time-series and GPS network observations in the Parkfield region. During these three years of observation, the average fault creep is estimated to be 35 mm/yr. References [1] Bürgmann,R., E. Fielding and, J. Sukhatme, Slip along the Hayward fault, California, estimated from space-based synthetic aperture radar interferometry, Geology,26, 559-562, 1998. [2] Ferretti, A., C. Prati and F. Rocca, Permanent Scatterers in SAR Interferometry, IEEE Trans. Geosci. Remote Sens., 39, 8-20, 2001. [3] Lanari, R.,F. Casu, M. Manzo, and P. Lundgren, Application of SBAS D- InSAR technique to fault creep: A case study of the Hayward Fault, California. Remote Sensing of Environment, 109(1), 20-28, 2007. [4] Shanker, A. P., and H. Zebker, Edgelist phase unwrapping algorithm for time-series InSAR. J. Opt. Soc. Am. A, 37(4), 2010.

Agram, P. S.; Wortham, C.; Zebker, H. A.

2010-12-01

180

Hot deformation characteristics of INCONEL alloy MA 754 and development of a processing map  

SciTech Connect

The characteristics of hot deformation of INCONEL alloy MA 754 have been studies using processing maps obtained on the basis of flow stress data generated in compression in the temperature range 700 C to 1,150 C and strain rate range 0.001 to 100 s[sup [minus]1]. The map exhibited three domains. (1) A domain of dynamic recovery occurs in the temperature range 800 C to 1,075 C and strain rate range 0.02 to 2 s[sup [minus]1], with a peak efficiency of 18 pct occurring at 950 C and 0.1 s [sup [minus]1]. Transmission electron microscope (TEM) micrographs revealed stable subgrain structure in this domain with the subgrain size increasing exponentially with an increase in temperature. (2) A domain exhibiting grain boundary cracking occurs at temperatures lower than 800 C and strain rates lower than 0.01 s[sup [minus]1]. (3) A domain exhibiting intense grain boundary cavitation occurs at temperatures higher than 1075 C. The material did not exhibit a dynamic recrystallization (DRX) domain, unlike other superalloys. At strain rates higher than about 1 s[sup [minus]1], the material exhibits flow instabilities manifesting as kinking of the elongated grains and adiabatic shear bands. The materials may be safely worked in the domain of dynamic recovery but can only be statically recrystallized.

Somani, M.C.; Muraleedharan, K.; Birla, N.C. (Defence Metallurgical Research Lab., Hyderabad (India)); Singh, V. (Banaras Hindu Univ., Varanasi (India). Dept. of Metallurgical Engineering); Prasad, Y.V.R.K. (Indian Inst. of Science, Bangalore (India). Dept. of Metallurgy)

1994-08-01

181

Basic deformation characteristics of Bayan Hara Group in northern Tibetan Plateau  

NASA Astrophysics Data System (ADS)

Bayan Hara block, located in the north of Tibetan Plateau between Eastern Kunlun Orogenic Belt and Qiangtang block, an active place surrounding where Wenchuan Earthquake and some other earthquakes occurred, is widely covered by very thick Triassic stratum, Bayan Hara Group. To get a better knowledge of basic properties of Bayan Hara block, structural analysis on outcrop sections were made in three locations of the block, the east part, the center part and the west part. Early folding styles of Bayan Hara Group indicate a divisional characteristic. In the south division, there is a tightly oblique plunging fold-thrust belt with its axial plane dipping to north, and its folded north wing is gentle and the south wing is steep. A broad and gentle fold-thrust belt with the almost vertical axial plane was formed in the center division of the block. In the north division, a tight homoclinal fold-thrust belt with its axial plane dipping to south comes out. At the same time, it also shows different deformation behaviors in E-W direction for Bayan Hara Group of the block. These differences possibly imply that there is no an ancient crystallization basement, or at least not a unified old basement underneath the Bayan Hara block, giving a clue to understanding the activity of Bayan Hara block and its adjacent areas responding to dynamic evolution of Tibetan Plateau after India-Asia collision.

Zha, X.; Ji, W.; Li, R.; He, S.; Chen, F.; Gu, P.

2012-12-01

182

Hot deformation characteristics of INCONEL alloy MA 754 and development of a processing map  

NASA Astrophysics Data System (ADS)

The characteristics of hot deformation of INCONEL alloy MA 754 have been studied using processing maps obtained on the basis of flow stress data generated in compression in the temperature range 700 °C to 1150 °C and strain rate range 0.001 to 100 s-1. The map exhibited three domains. (1) A domain of dynamic recovery occurs in the temperature range 800 °C to 1075 °C and strain rate range 0.02 to 2 s-1, with a peak efficiency of 18 pct occurring at 950 °C and 0.1 s-1. Transmission electron microscope (TEM) micrographs revealed stable subgrain structure in this domain with the subgrain size increasing exponentially with an increase in temperature. (2) A domain exhibiting grain boundary cracking occurs at temperatures lower than 800 °C and strain rates lower than 0.01 s-1. (3) A domain exhibiting intense grain boundary cavitation occurs at temperatures higher than 1075 °C. The material did not exhibit a dynamic recrystallization (DRX) domain, unlike other superalloys. At strain rates higher than about 1 s-1 the material exhibits flow instabilities manifesting as kinking of the elongated grains and adiabatic shear bands. The material may be safely worked in the domain of dynamic recovery but can only be statically recrystallized.

Somani, M. C.; Muraleedharan, K.; Birla, N. C.; Singh, V.; Prasad, Y. V. R. K.

1994-08-01

183

Quartz c-axis evidence for deformation characteristics in the Sanandaj-Sirjan metamorphic belt, Iran  

NASA Astrophysics Data System (ADS)

Quartz c-axis fabric, finite strain, and kinematic vorticity analyses were carried out in well-exposed quartz mylonites to investigate the heterogeneous nature of ductile deformation within the Eghlid deformed area in the High Pressure-Low Temperature (HP-LT) Sanandaj-Sirjan metamorphic belt (Zagros Mountains, Iran). This belt belongs to a sequence of tectonometamorphic complexes with low- to high-grade metamorphic rocks affected by a polyphase deformation history. Asymmetric quartz c-axis fabrics (type I) confirm a localized top-to-the-southeast sense of shear. Quantitative finite strain analysis in the XZ, XY and YZ principal planes of the finite strain ellipsoid demonstrate that the strain ratio increases towards the thrust planes of the Zagros Thrust System. Kinematic vorticity analysis of deformed quartz grains showed sequential variation in the kinematic vorticity number from ˜0.5 to ˜0.8 between the thrust sheets. Such vorticity numbers show that both simple and pure shear components contribute to the deformation. Our results show that simple shear dominated deformation near the thrust faults, and pure shear dominated deformation far from them. Quartz c-axis opening angles suggest deformation temperatures range between 450° ± 50 °C and 600° ± 50 °C, which yield greenschist to amphibolite facies conditions during ductile deformation.

Samani, Babak

2013-05-01

184

Creep in electronic ceramics  

SciTech Connect

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

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

2000-04-27

185

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

NASA Astrophysics Data System (ADS)

The United States Air Force is in the process of developing magnetic bearings as well as an aircraft Integrated Power Unit and an Internal Starter/Generator for main propulsion engines. These developments are the driving force behind a new emphasis on high temperature, high strength magnetic materials for power applications. Analytical work, utilizing elasticity theory, in conjunction with design requirements, indicates a need for magnetic materials to have strengths in excess of 80 ksi up to about 1000sp°F. It is this combination of desired material characteristics that is the motivation for this effort to measure, model, and predict the creep behavior of such advanced magnetic materials. Hipercosp°ler Alloy 50HS, manufactured by Carpenter Technology Corporation, is one of the leading candidates for application and is studied in this effort by subjecting mechanical test specimens to a battery of tensile and creep tests. The tensile tests provide stress versus strain behaviors that clearly indicate: a yield point, a heterogeneous deformation described as Luders elongation, the Portevin-LeChatelier effect at elevated temperatures, and, most often, a section of homogeneous deformation that concluded with necking and fracture. Creep testing indicated two distinct types of behavior. The first was a traditional response with primary, secondary and tertiary stages, while the second type could be characterized by an abrupt increase in strain rate that acted as a transition from one steady state behavior to another. This second linear region was then followed by the tertiary stage. The relationship between the tensile response and the creep responses is discussed. Analyses of the mechanical behavior includes double linear regression of empirically modeled data, scanning electron microscopy for microstructural investigations, isochronous stress-strain relations, and constant strain rate testing to relate the tensile and creep test parameters. Also, elastic and creep deformation analyses are done, which incorporate material property data and material constants determined along with stress and displacement profiles for a specific Air Force design configuration.

Fingers, Richard Todd

186

Endochronic Theory of Transient Creep and Creep Recovery.  

National Technical Information Service (NTIS)

Short time creep and creep recovery were investigated by means of the endochronic theory of viscoplasticity. It is shown that the constitutive equations for constant-strain-rate stress-strain behavior, creep, creep recovery, and stress relaxation can all ...

H. C. Wu L. Chen

1979-01-01

187

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

188

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

189

In Situ Test for Soil Creep.  

National Technical Information Service (NTIS)

The Iowa bore-hole shear apparatus, modified to monitor time deformational behavior in soils, produced both primary and tertiary type creep curves from in-situ tests on soils. Laboratory simple shear tests produced comparable results. An examination of th...

R. A. Lohnes A. Millan T. Demirel R. L. Handy

1971-01-01

190

Adhesion, friction, and deformation characteristics of Ti(Ca,Zr)-(C,N,O,P) coatings for orthopedic and dental implants  

Microsoft Academic Search

This paper reports on the results of a comparative investigation into the physical, mechanical, and tribological characteristics\\u000a of Ti-(Ca,Zr)-(C,N,O,P) coatings. The hardness, elastic modulus, elastic recovery, adhesion strength, friction coefficient,\\u000a and wear rate of the coatings are determined. The specific features revealed in the deformation and fracture of the coatings\\u000a deposited on various substrates in the course of adhesion tests

D. V. Shtansky; M. I. Petrzhik; I. A. Bashkova; F. V. Kiryukhantsev-Korneev; A. N. Sheve?ko; E. A. Levashov

2006-01-01

191

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

192

Deformation characteristics of isothermally forged UDIMET 720 nickel-base superalloy  

Microsoft Academic Search

The hot deformation behavior of nickel-base superalloy UDIMET 720 in solution-treated conditions, simulating the forging process\\u000a of the alloy, was studied using hot compression experiments. Specimens were deformed in the temperature range of 1000 C to\\u000a 1175 C with strain rates of 10?3 to 1 s?1 and total strain of 0.8. Below 1100 C, all specimens showed flow localization as

H. Monajati; A. K. Taheri; M. Jahazi; S. Yue

2005-01-01

193

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.

194

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

195

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 700°C 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

196

Deformation-induced martensitic characteristics in 304 and 316 stainless steels during room-temperature rolling  

Microsoft Academic Search

The effect of grain size on the deformation-induced martensite (alpha') in 304 and 316 stainless steels (SS) during room-temperature rolling has been studied. Samples of four grain sizes of 52, 180, 229, and 285 mu in 304 and three grain sizes of 77, 125, and 200 \\/mum in 316 SS have been rolled from 16 to 63 pct reduction in

Vijay Shrinivas; S. K. Varma; L. E. Murr

1995-01-01

197

Material Parameters for Creep Rupture of Austenitic Stainless Steel Foils  

NASA Astrophysics Data System (ADS)

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

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

2014-06-01

198

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

199

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

NASA Astrophysics Data System (ADS)

The rheology of polycristalline San Carlos olivine is investigated on synchrotron beamline in the Deformation-DIA (D-DIA) at pressure (P) between 3.8 and 8.1 GPa, temperature (T) within 1373-1673 K, and at steady-state strain rates ranging from 1.1 × 10-5 to 5.8 × 10-5 s-1. Transmission electron microscopy (TEM) on run products reveals microstructures characteristic of the so-called “dislocation creep regime”. Fourier transform infrared (FTIR) measurements reveal hydroxyl concentrations within 153-1526 ppm H/Si (Paterson’s calibration), indicating ‘wet’ conditions of deformation. Analysis of our data together with previously published ‘wet’ deformation data obtained at room and high P, assuming a stress exponent n = 3.5 in classical power law, results in a linear dependence of the activation enthalpy with P, i.e., in an activation volume of V? = 12.8 ± 5 cm3 mol-1. This value of V? is also consistent with a global dataset including ‘wet’ data and ‘dry’ published deformation data for olivine aggregates. We thus conclude that, up to 8 GPa, the effect of P on ‘dry’ and ‘wet’ olivine dislocation creep is consistent with V? = 12.8 ± 5 cm3 mol-1.

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

2014-03-01

200

Wear and creep of highly crosslinked polyethylene against cobalt chrome and ceramic femoral heads.  

PubMed

The wear and creep characteristics of highly crosslinked ultrahigh-molecular-weight polyethylene (UHMWPE) articulating against large-diameter (36mm) ceramic and cobalt chrome femoral heads have been investigated in a physiological anatomical hip joint simulator for 10 million cycles. The crosslinked UHMWPE/ceramic combination showed higher volume deformation due to creep plus wear during the first 2 million cycles, and a steady-state wear rate 40 per cent lower than that of the crosslinked UHMWPE/cobalt chrome combination. Wear particles were isolated and characterized from the hip simulator lubricants. The wear particles were similar in size and morphology for both head materials. The particle isolation methodology used could not detect a statistically significant difference between the particles produced by the cobalt chrome and alumina ceramic femoral heads. PMID:21138235

Galvin, A L; Jennings, L M; Tipper, J L; Ingham, E; Fisher, J

2010-10-01

201

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

202

Continuous deformation versus episodic deformation at high stress - the microstructural record  

NASA Astrophysics Data System (ADS)

The microstructural record of continuous high stress deformation is compared to that of episodic high stress deformation on two examples: 1. Folding of quartz veins in metagreywacke from Pacheco Pass, California, undergoing deformation by dissolution precipitation creep at temperatures of 300 ± 50°C. The microfabric of the folded quartz veins indicates deformation by dislocation creep accompanied by subgrain rotation. The small recrystallized grain size of ~8±6 µm in average implies relatively high differential stresses of a few hundred MPa. The stress concentration in the vein is due to a high contrast in effective viscosities between the single phase material and the polyphase fine-grained host metagreywacke deforming by dissolution precipitation creep. Smoothly curved, but generally not sutured, grain boundaries as well as the small size and a relatively high dislocation density of recrystallized grains suggest that strain-induced grain boundary migration was of minor importance. This is suspected to be a consequence of low strain gradients, which are due to the relative rates of dynamic recovery and continuous dislocation production during climb-controlled creep, at high stress and the given low temperature. Subgrain rotation recrystallization is thus proposed to be characteristic for continuous deformation at high differential stress. 2. Episodic deformation in the middle crust at the tip of a seismic active fault zone. The microfabric of mid-crustal rocks exhumed in tectonically active regions can record episodic high stress deformation at the base of the seismogenic layer. The quartz veins from St. Paul la Roche in the Massif Central, France, are very coarse grained. On the scale of a thin section they are basically single crystalline. However, they show a very heterogeneous microstructure with a system of healed microcracks that are decorated by subgrains and more rarely by small recrystallized grains. Undulating deformation lamellae that do not show a preferred crystallographic orientation are found by transmission electron microscopy to represent dislocation walls with a high density of dislocations. They are interpreted as a modified microstructure that reflects a stage of initial high stress deformation with restricted dynamic recovery. The missing aggregates of recrystallized grains rule out dynamic recrystallization, which is proposed to be due to a high strain rate, preventing effective dislocation climb. Instead, localized single grains in random orientations that are aligned along fractures indicate quasi-static recrystallization and recovery at a subsequent stage of low stress and temperatures of ~300 ± 50°C. Such a microstructure is characteristic of initial short-term high stress glide-controlled deformation accompanied by microcracking during coseismic loading and subsequent modification by recovery and recrystallization at rapidly decreasing stresses during postseismic relaxation in the middle crust below the seismogenic layer. Both examples indicate deformation of quartz at similar conditions in terms of temperature (~300 ± 50°C) and high stress. However, the deformation and recrystallization processes and the resulting microfabrics are completely different due to the different loading time and rate.

Trepmann, C. A.; Stöckhert, B.

2009-04-01

203

Interface Evolution During Transient Pressure Solution Creep  

NASA Astrophysics Data System (ADS)

When aggregates of small grains are pressed together in the presence of small amounts of solvent the aggregate compacts and the grains tend to stick together. This hap- pens to salt and sugar in humid air, and to sediments when buried in the Earths crust. Stress concentration at the grain contacts cause local dissolution, diffusion of the dissolved material out of the interface and deposition on the less stressed faces of the grains{1}. This process, in geology known as pressure solution, plays a cen- tral role during compaction of sedimentary basins{1,2}, during tectonic deformation of the Earth's crust{3}, and in strengthening of active fault gouges following earth- quakes{4,5}. Experimental data on pressure solution has so far not been sufficiently accurate to understand the transient processes at the grain scale. Here we present ex- perimental evidence that pressure solution creep does not establish a steady state inter- face microstructure as previously thought. Conversely, cumulative creep strain and the characteristic size of interface microstructures grow as the cubic root of time. A sim- ilar transient phenomenon is known in metallurgy (Andrade creep) and is explained here using an analogy with spinodal dewetting. 1 Weyl, P. K., Pressure solution and the force of crystallization - a phenomenological theory. J. Geophys. Res., 64, 2001-2025 (1959). 2 Heald, M. T., Cementation of Simpson and St. Peter Sandstones in parts of Okla- homa, Arkansas and Missouri, J. Geol. Chicago, 14, 16-30 (1956). 3 Schwartz, S., Stöckert, B., Pressure solution in siliciclastic HP-LT metamorphic rocks constraints on the state of stress in deep levels of accretionary complexes. Tectonophysics, 255, 203-209 (1996). 4 Renard, F., Gratier, J.P., Jamtveit, B., Kinetics of crack-sealing, intergranular pres- sure solution, and compaction around active faults. J. Struct. Geol., 22, 1395-1407, (2000). 5 Miller, S. A., BenZion, Y., Burg, J. P.,A three-dimensional fluid-controlled earth- quake model: Behavior and implications. J. Geophys. Res., 104, 10621-10638 (1999).

Dysthe, D. K.; Podladchikov, Y. Y.; Renard, F.; Jamtveit, B.; Feder, J.

204

Deformation-induced martensitic characteristics in 304 and 316 stainless steels during room-temperature rolling  

Microsoft Academic Search

The effect of grain size on the deformation-induced martensite (??) in 304 and 316 stainless steels (SS) during room-temperature\\u000a rolling has been studied. Samples of four grain sizes of 52, 180, 229, and 285 ? in 304 and three grain sizes of 77, 125,\\u000a and 200 \\/?m in 316 SS have been rolled from 16 to 63 pct reduction in

Vijay Shrinivas; S. K. Varma; L. E. Murr

1995-01-01

205

Creep behaviour of modified 9Cr-1Mo ferritic steel  

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

206

Wear characteristics of severely deformed aluminum sheets by accumulative roll bonding (ARB) process  

SciTech Connect

Wear behavior of severely deformed aluminum sheets by accumulative roll bonding (ARB) process was characterized using a pin on disc wear machine at different conditions. The sheets were processed up to eight ARB cycles in order to induce a high strain ({approx} 6.4) to the samples. EBSD results showed that after eight cycles of ARB, sheets were found to contain ultrafine grains with high fraction of high angle grain boundaries. Wear experiments were conducted under different loading and operating conditions, including dry and immersion lubrication, and rotation speeds. Wear was continuously monitored by measuring the wear rates and morphologies of worn surfaces by scanning electron microscope (SEM). Contrary to expectation, the wear resistance of the ARBed Al sheets was less than the non-processed sheets. Wear rates of the ARBed Al sheets increased by increasing wear load and rotation speed, while, immersion lubrication decreased the wear rate significantly. Based on the observation and results, a model for the wear of the ARBed Al was proposed. - Research Highlights: {yields}The wear rate of the ARBed Al was higher than that of the non-processed alloy. {yields}This unexpected behavior was related to the low strain hardening capability and evolution of the ARB subsurface microstructure during the wear process. {yields}Sliding wear of the ARBed Al proceeded by surface deformation, and progressed by delamination of the deformed surface layer. {yields}The wear rate of ARBed Al increased by increasing applied load and sliding speed.

Talachi, A. Kazemi; Eizadjou, M., E-mail: m.eizadjou@gmail.com; Manesh, H. Danesh; Janghorban, K.

2011-01-15

207

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

PubMed Central

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

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

2013-01-01

208

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

PubMed

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

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

2013-01-01

209

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

210

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

211

Central Cascadia subduction zone creep  

NASA Astrophysics Data System (ADS)

Cascadia between 43°N and 46°N has reduced interseismic uplift observed in geodetic data and coseismic subsidence seen in multiple thrust earthquakes, suggesting elevated persistent fault creep in this section of the subduction zone. We estimate subduction thrust "decade-scale" locking and crustal block rotations from three-component continuous Global Positioning System (GPS) time series from 1997 to 2013, as well as 80 year tide gauge and leveling-derived uplift rates. Geodetic observations indicate coastal central Oregon is rising at a slower rate than coastal Washington, southern Oregon and northern California. Modeled locking distributions suggest a wide locking transition zone that extends inland under central Oregon. Paleoseismic records of multiple great earthquakes along Cascadia indicate less subsidence in central Oregon. The Cascade thrust under central Oregon may be partially creeping for at least 6500 years (the length of the paleoseismic record) reducing interseismic uplift and resulting in reduced coseismic subsidence. Large accretions of Eocene age basalt (Siletzia terrane) between 43°N and 46°N may be less permeable compared to surrounding terranes, potentially increasing pore fluid pressures along the fault interface resulting in a wide zone of persistent fault creep. In a separate inversion, three-component GPS time series from 1 July 2005 to 1 January 2011 are used to estimate upper plate deformation, locking between slow-slip events (SSEs), slip from 16 SSEs and an earthquake mechanism. Cumulative SSEs and tectonic tremor are weakest between 43°N and 46°N where partial fault creep is increased and Siletzia terrane is thick, suggesting that surrounding rock properties may influence the mode of slip.

Schmalzle, Gina M.; McCaffrey, Robert; Creager, Kenneth C.

2014-04-01

212

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

213

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 850°C 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 800°C 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, Jörg; Herwegh, Marco; Evans, Brian

2009-03-01

214

Hot Tensile Deformation Characteristics and Processing Map of Extruded AZ80 Mg Alloys  

NASA Astrophysics Data System (ADS)

The hot deformation behaviors of extruded AZ80 Mg alloys were investigated using tension tests. True stress-true strain curves were obtained for deformation at temperatures from 250 to 450 °C with the strain rate range from 0.001 to 0.08 s-1. Optical microscopy analysis was performed to correlate microstructural changes to the flow behaviors. Based on the flow stress, the processing map at a strain of 0.18 was developed using the dynamic materials model theory and can be divided into three zones, including stability zones, change-over region, and instability zones. In stability zones, there are two dynamic recrystallization regions: one region with a peak efficiency of 58% at 350 °C and a strain rate of 0.001 s-1 called domain I; another region with a peak efficiency of 58% at 400 °C and a strain rate of 0.01 s-1 taken as domain II. The apparent activation energy for domain I was estimated to be 100.71 kJ/mol, indicating that short-circuit diffusion process is along the grain boundaries and falls at lower temperatures and lower strain rates. A lattice self-diffusion is considered to be rate controlling mechanism with the apparent activation energy estimated as 140.32 kJ/mol at higher temperatures and higher strain rates in domain II. The change-over region is the zone from domain I to domain II, in which the grains abnormally grow. In instability zones, twins, local deformation band, wedge cracking, and matrix cracking were observed, suggesting that these processing parameters for hot tension in this zone are inapplicable.

Lou, Yan; Chen, Heng; Ke, Changxing; Long, Min

2014-05-01

215

Hot Tensile Deformation Characteristics and Processing Map of Extruded AZ80 Mg Alloys  

NASA Astrophysics Data System (ADS)

The hot deformation behaviors of extruded AZ80 Mg alloys were investigated using tension tests. True stress-true strain curves were obtained for deformation at temperatures from 250 to 450 °C with the strain rate range from 0.001 to 0.08 s-1. Optical microscopy analysis was performed to correlate microstructural changes to the flow behaviors. Based on the flow stress, the processing map at a strain of 0.18 was developed using the dynamic materials model theory and can be divided into three zones, including stability zones, change-over region, and instability zones. In stability zones, there are two dynamic recrystallization regions: one region with a peak efficiency of 58% at 350 °C and a strain rate of 0.001 s-1 called domain I; another region with a peak efficiency of 58% at 400 °C and a strain rate of 0.01 s-1 taken as domain II. The apparent activation energy for domain I was estimated to be 100.71 kJ/mol, indicating that short-circuit diffusion process is along the grain boundaries and falls at lower temperatures and lower strain rates. A lattice self-diffusion is considered to be rate controlling mechanism with the apparent activation energy estimated as 140.32 kJ/mol at higher temperatures and higher strain rates in domain II. The change-over region is the zone from domain I to domain II, in which the grains abnormally grow. In instability zones, twins, local deformation band, wedge cracking, and matrix cracking were observed, suggesting that these processing parameters for hot tension in this zone are inapplicable.

Lou, Yan; Chen, Heng; Ke, Changxing; Long, Min

2014-03-01

216

Plastic Deformation Characteristics Of AZ31 Magnesium Alloy Sheets At Elevated Temperature  

NASA Astrophysics Data System (ADS)

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

Park, Jingee; Lee, Jongshin; You, Bongsun; Choi, Seogou; Kim, Youngsuk

2007-05-01

217

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

218

Tension-Compression Asymmetry of Creep and Unilateral Creep Damage in Aluminum for Isothermal and Nonisothermal Processes  

NASA Astrophysics Data System (ADS)

A constitutive model is proposed to describe the damage development in aluminum alloys under creep conditions for both isothermal and nonisothermal processes. Special emphasis is laid on four specific phenomena: tension-compression asymmetry of creep, damage induced anisotropy, unilateral creep damage and damage deactivation. Within the framework of the phenomenological approach in the Continuum Damage Mechanics, the nonlinear tensor constitutive equation for creep deformation and damage evolution equation are proposed to account for different orientation of microcracks in aluminum alloys under tensile and compressive loading types. After a determination of the material parameters in the obtained constitutive equation and damage growth equation, the proposed model is applied to the describing creep behavior of the aluminum alloy under uniaxial nonproportional and multiaxial nonproportional loading for both isothermal and nonisothermal processes.

Zolochevsky, Alexander; Obataya, Yoichi

219

Influence of preliminary ultrasonic treatment upon the steady-state creep of metals of different stacking fault energies.  

PubMed

This paper addresses the issue of the ultrasound effects upon the creep deformation of metals with different levels of stacking fault energy. The influence of preliminary ultrasound irradiation time upon the steady state creep rate is considered. Synthetic theory of irrecoverable deformation is taken as a mathematical apparatus. The analytical results show good agreement with experimental data. PMID:23876435

Rusinko, A

2014-01-01

220

Calculation of radiation-induced deformation in the ITER vacuum vessel  

NASA Astrophysics Data System (ADS)

Numerical calculation was carried out to evaluate the radiation induced deformation at the blanket side of the vacuum vessel (120°C) and the rear portion of the blanket module (200°C) in ITER. The calculation was performed for solution-annealed 316 stainless steel mainly at 1×10 -9 dpa/s and 100 MPa. Enhanced transient creep characteristic of the low temperature irradiation is evident at 120°C. However, the total accumulated creep strain in the vacuum vessel is only below 0.01% for the lifetime irradiation so that serious consequence would not be anticipated. At the rear portion of the blanket the creep strain would be about 0.01% and not serious either. Radiation-induced stress relaxation at the vacuum vessel is only several per cent during the lifetime. At the rear portion of the blanket, on the other hand, the relaxation could be of the order of 10% and should not be completely neglected.

Nagakawa, Johsei

1998-10-01

221

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

Microsoft Academic Search

We extended a previous study on the influence of Mg solute impurity on diffusion creep in calcite to include deformation under\\u000a a broader range of stress conditions and over a wider range of Mg contents. Synthetic marbles were produced by hot isostatic\\u000a pressing (HIP) mixtures of calcite and dolomite powders for different intervals (2–30 h) at 850°C and 300 MPa confining pressure.

Lili Xu; Jörg Renner; Marco Herwegh; Brian Evans

2009-01-01

222

Characterization of the groundwater response to rainfall on a hillslope with fractured bedrock by creep deformation and its implication for the generation of deep-seated landslides on Mt. Wanitsuka, Kyushu Island  

NASA Astrophysics Data System (ADS)

In this study, the hydrogeological response of a hillslope affected by gravitational deformation was analyzed based on the data obtained for two observation boreholes: a 10-m borehole representing a relatively superficial section of the hillslope dominated by soil and old landslide deposits and a 40-m borehole representing the bedrock aquifer. For this analysis, the precipitation events in the area, groundwater levels of the two boreholes, electrical conductivity and isotopic concentration (oxygen and hydrogen) of the groundwater in the boreholes and rainfall samples were measured. Derived from the rainfall data, the antecedent precipitation index (API) with a 6-h half-life offers a good correlation with the peaks in the groundwater levels in the bedrock aquifer. The characteristics of the groundwater response suggest the existence of a single structure in the bedrock that controls the response of the hillslope. The structure serves as a conduit, which rapidly drives the rainfall water (recharge) into the bedrock. Evidently, this process is unrelated to the superficial section represented by the observations in the 10-m borehole. The structure is associated with an area of high hydraulic conductivity in the bedrock caused by the gravitational deformation in the hillslope. The strong control of this structure in the hillslope's hydrogeological response makes it responsible for the hillslope's stability during high-precipitation events. This information is highly relevant to areas featuring the generation of several deep-seated landslides under heavy-rain conditions.

Padilla, Cristobal; Onda, Yuichi; Iida, Tomoyuki; Takahashi, Shinya; Uchida, Taro

2014-01-01

223

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

224

DEFORMATION CHARACTERISTICS OF CRUSHED-STONE LAYER UNDER CYCLIC IMPACT LOADING FROM MICRO-MECHANICAL VIEW  

NASA Astrophysics Data System (ADS)

'Hanging sleepers', which have gaps between sleepers and ballast layer are often found in the neighborhood of rail joints or rugged surface rails. This suggests that differential settlement of the ballast layer is due to impact loading generated by the contact between running wheel and rugged surface rail. Then cyclic loading tests were performed on crushed-stone layer with two loading patterns, the one is a cyclic impact loading and the other one is cyclic 'standard' loading controlled at 1/10 loading velocity of the impact loading. It was shown that the crashed-stone layer deforms with volumetric expansion during every off-loading processes under the cyclic impact loading. This phenomena prevents crushed stone layer from forming stable grain columns, then the residual settlement under the cyclic impact loading is larger than that under the cyclic 'standard' loading. A simple mass-spring model simulates that two masses move in the opposite direction with increased frequency of harmonic excitation.

Kono, Akiko; Matsushima, Takashi

225

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

226

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

227

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

228

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

229

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

230

Irradiation Creep Behavior of Vanadium Alloys during Neutron Irradiation in a Liquid Metal Environment  

NASA Astrophysics Data System (ADS)

The manufacturing process of creep specimens and an irradiation technique in a liquid metal environment for in-pile and creep measurements of irradiated samples are established for highly purified V-4Cr-4Ti, NIFS-HEAT alloys. Irradiation experiments with sodium-enclosed irradiation capsules in JOYO and lithiumenclosed irradiation capsules in HFIR-17J were conducted using pressurized creep tubes. From thermal creep experiments, the activation energy of creep deformation using pressurized creep tubes was determined to be 210 kJ/mol·K, the creep stress factor was 4.9 for an 800°C creep test, and its mechanism was determined to be a climb-assisted glide of dislocation motion. It was found that the creep strain rate exhibited a linear relationship with effective stress up to 150 MPa from 425 to 600°C under JOYO and HFIR irradiation. The activation energy of irradiation creep was estimated to be 46 kJ/mol·K. No significant difference in irradiation creep behavior between the liquid sodium and liquid lithium environments was observed. A set of essential physical data of irradiation creep properties was obtained for V-4Cr-4Ti alloys.

Fukumoto, Kenichi; Narui, Minoru; Matsui, Hideki; Nagasaka, Takuya; Muroga, Takeo

231

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

232

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 500°C (up to 160 × 103 h) and 600°C (up to 94 × 103 h). 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-Françoise Gourgues-Lorenzon

2011-01-01

233

On the Prediction of Creep Damage by Bending of Thin-Walled Structures  

Microsoft Academic Search

Analysis of thin-walled structures operating at elevated temperaturesneeds a consideration of time-dependent creep-damage behaviour. Within theframework of the creep theory and the CDM the irreversible deformations ofthe structural elements can be described by constitutive equations withinternal state variables. The paper deals with an application ofphysically based creep-damage constitutive model with two damageparameters, proposed by Hayhurst, to the stress analysis of

Holm Altenbach; Johannes Altenbach; Konstantin Naumenko

1997-01-01

234

An integrated process for modelling of precipitation hardening and springback in creep age-forming  

Microsoft Academic Search

Creep age-forming (CAF) process has been developed and used to manufacture complex-shaped panel components in aerospace applications. CAF is based on the complex combination of stress relaxation, creep and age hardening. The aim of this paper is to introduce an integrated technique to model stress–relaxation, creep deformation, precipitate hardening and springback in a CAF process. Firstly, a new set of

J. Lin; K. C. Ho; T. A. Dean

2006-01-01

235

Creep and creep rupture of ERNiCr-3 weld metal  

NASA Astrophysics Data System (ADS)

Creep and creep-rupture tests were made on AWS A5.14 Class ERNiCr-3 weld metal, commonly known as Inconel 82. Specimens from gas tungsten-arc welds were tested over the range 454-732°C. Tests at 454, 510, and 566°C displayed different characteristics from those at 621, 677, and 732°C. The lower temperature creep curves showed a rapid transient, a long steady-state stage, and little tertiary creep. At elevated temperatures the transient stage was slower, the steady-state stage was shorter, and the tertiary stage was longer. Creep-rupture curves and stress-minimum creep rate curves were much flatter at lower temperatures. Certain tests at 454, 510, and 566°C exhibited an "instantaneous elongation" or "strain burst" phenomenon, in which the creep curves contained strain jumps. At these same temperatures several specimens failed prematurely. The difference in behavior in the two temperature regimes was attributed to short-range order.

Klueh, R. L.; King, J. F.

1981-05-01

236

Detection of a honeybee iflavirus with intermediate characteristics between kakugo virus and deformed wing virus.  

PubMed

Iflavirus RNA was detected in honeybee colonies displaying unduly aggressive behavior and with no evidence of morphological alterations. Sequence analysis of the RNA-dependent RNA polymerase (RdRp) revealed that the iflavirus strain was more similar (> 99% aa) to Deformed Wing Virus (DWV), that has been associated with morphological alterations in bees, rather than to the newly-described Kakugo Virus (KV) (about 95% aa), that has been associated with increased aggressiveness. Therefore, the iflavirus strain detected in the Italian hives genetically resembled DWV but was apparently associated with a KV-like phenotype. RT-PCR detected the iflavirus RNA in the abdomen of the workers, and only in one case was the virus detected in the head. No viral RNA was detected in the drones, a pattern of virus distribution across the honeybee casts that is in apparent conflict with the higher rates of infestation of drones by the mite Varroa distructor. The identification of a virus with apparently intermediate features between DWV and KV open new perspectives on the patho-biological role of iflaviruses in honeybees. PMID:19123297

Terio, Valentina; Martella, Vito; Camero, Michele; Decaro, Nicola; Testini, Gabriella; Bonerba, Elisabetta; Tantillo, Giuseppina; Buonavoglia, Canio

2008-10-01

237

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

NASA Astrophysics Data System (ADS)

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

Aslani, Farhad; Nejadi, Shami

2012-09-01

238

The Characteristics of Intra-continental Deformation and Hydrocarbon Distribution Controlled by the Himalayan Tectonic Movements in China  

NASA Astrophysics Data System (ADS)

Based on previous studies and the latest insights from recent petroleum exploration programs, we propose that the characteristics of intra-continental deformation and its distribution, caused by the Himalayan tectonic movements, are controlled by basement framework formed by a collage of microcratons and lithotectonic terranes and dynamic factors such as the Indian/Eurasia collision and subduction of the Pacific plate. The evolution of Himalayan tectonic movements can be resolved by three principal dynamic mechanisms: (1) the uplift of Tibetan Plateau, (2) the coupling of orogenic belts and basins surrounding the Tibetan Plateau, and (3) extensional tectonics in eastern China. The tectonic framework and deformation that resulted from the Himalayan tectonic movements are mainly embodied in four tectonic domains: (1) the uplifted regions of the Tibetan Plateau, (2) the basin-and-range coupling of peripheral Tibetan Plateau, (3) stable regions, and (4) regions of active rifting along the western circum-Pacific margin. Sedimentary basins formed during the Himalayan tectonic movements, can be assorted into three categories: (1) rift basins due to extensional tectonics in east China, such as Bohai Bay Basin and Songliao Basin; (2) basins in central China, controlled by eastward compression of the Tibetan Plateau, which are characteristic of thrusting of basin margin and uplift-denudation in basins; (3) basins in west China such as the Tarim, Junggar and Qaidam Basins, which are associated with north-directed compression and exhibit thrust movements and flexural subsidence along basin margins. Their structural style is that of basin-and-range type. We conclude that Himalayan tectonic movements may have controlled the late hydrocarbon accumulation in China.

JIA, Chengzao

239

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

240

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

241

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

242

Diffusion creep in the mantle may create and maintain anisotropy  

NASA Astrophysics Data System (ADS)

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

Wheeler, John

2014-05-01

243

Characterization of creep and creep damage by in-situ microtomography  

NASA Astrophysics Data System (ADS)

Application of in-situ microtomography to characterization of power law creep and creep damage in structural materials is presented. It is shown first that the successively reconstructed volumes are adequately monitoring the macroscopic sample shape and that microtomography is an optimal tool to characterize inhomogeneous specimen deformation. Based on a two-step image correlation technique the evolution of single voids is revealed and the basis of a pioneering approach to creep damage studies is presented. The method allows the unequivocal separation of three concurrent damage mechanisms: nucleation, growth, and coalescence of voids. The results indicate that growth rate of voids with equivalent diameters in the range of 2-5 mm is of about one order of magnitude higher than the prediction of continuum solid mechanics. Analysis of void coalescence points out the presence of two stable growth regimes related to coalescence between primary and secondary voids, respectively.

Borbély, András; Dzieciol, Krzysztof; Sket, Federico; Isaac, Augusta; di Michiel, Marco; Buslaps, Thomas; Kaysser-Pyzalla, Anke R.

2011-07-01

244

Mechanosorptive creep in nanocellulose materials  

Microsoft Academic Search

The creep behavior of nanocellulose films and aerogels are studied in a dynamic moisture environment, which is crucial to their performance in packaging applications. For these materials, the creep rate under cyclic humidity conditions exceeds any constant humidity creep rate within the cycling range, a phenomenon known as mechanosorptive creep. By varying the sample thickness and relative humidity ramp rate,

S. B. Lindström; E. Karabulut; A. Kulachenko; H. Sehaqui; L. Wågberg

2012-01-01

245

Determination of creep rate and extent at Ismetpasa section of the North Anatolian Fault using Persistent Scatterer InSAR and GPS  

NASA Astrophysics Data System (ADS)

Although fault creep was discovered over half a century ago along the Ismetpasa section of the North Anatolian Fault, its spatiotemporal nature is still poorly known due to lack of geodetic and seismological studies along the fault. Despite the difficulties arising from atmospheric artifacts and low coherency, classical long-term InSAR analysis of ERS (C-band) data between 1992 and 2001 suggested an average creep rate of 9±3 mm along a fault segment of ~70 km long (Cakir et al., 2005). Even though these estimations were obtained from a limited number of available images, these results have been supported by a recent study of stacked PALSAR (L-band) interferograms spanning the period between 2007 and 2010 (Fialko et al., 2011). In this study, we use the Persistent Scatterer InSAR technique to better constrain spatiotemporal characteristics of the surface creep. We analyzed 55 Envisat ASAR images on 2 descending tracks (479 and 207) between 2003 and 2010 and calculated InSAR time series. The PS-InSAR results show clearly the gradual transition between the creeping and locked sections of the NAF west of Ismetpasa. On the contrary, its eastern boundary is crudely determined near 33.4E since the signal is disturbed by the postseismic deformation of the Orta earthquake (June 6, 2000, Mw=6.0). The extent of the creeping section therefore appears to be approximately 81.5 km. The creep rate is also robustly constrained and found to be in the range of 10±2 mm/yr near to Ismetpasa, consistent with the GPS measurements from a small-aperture geodetic network near Ismetpasa and recently reported PALSAR measurements (Fialko et al., 2011). Furthermore, elastic dislocation modeling suggests shallow creeping depth (< 5 km).

Cetin, E.; Cakir, Z.; Dogan, U.; Akoglu, A. M.; Ozener, H.; Ergintav, S.; Meghraoui, M.

2012-12-01

246

Mineralogy of Faults in the San Andreas System That are Characterized by Creep  

NASA Astrophysics Data System (ADS)

The San Andreas Fault Observatory at Depth (SAFOD) is a deep-drilling program sited in the central creeping section of the San Andreas Fault (SAF) near Parkfield, California. Core was recovered from two locations at ~2.7 km vertical depth that correspond to the places where the well casing is being deformed in response to fault creep. The two creeping strands are narrow zones of fault gouge, 1.6 and 2.6 m in width, respectively, that are the products of shear-enhanced metasomatic reactions between serpentinite tectonically entrained in the fault and adjoining sedimentary wall rocks. Both gouge zones consist of porphyroclasts of serpentinite and sedimentary rock dispersed in a foliated matrix of Mg-rich, saponitic ± corrensitic clays, and porphyroclasts of all types are variably altered to the same Mg-rich clays as the gouge matrix. Some serpentinite porphyroclasts also contain the assemblage talc + actinolite + chlorite + andradite garnet, which is characteristic of reaction zones developed between ultramafic and crustal rocks at greenschist- to subgreenschist-facies conditions. The presence of this higher-temperature assemblage raises the possibility that the serpentinite and its alteration products may extend to significantly greater depths in the fault. Similar fault gouge has also been identified in a serpentinite outcrop near the drill site that forms part of a sheared serpentinite body mapped for several kilometers within the creeping section of the SAF. The SAFOD core thus supports the long-held view that serpentinite is implicated in the origin of creep, as does at least one other creeping fault of the San Andreas System. The Bartlett Springs Fault (BSF) is a right-lateral strike-slip fault located north of San Francisco, California. Its slip rate currently is estimated to be 6 +/- 2 mm/yr, and along a segment that crosses Lake Pillsbury half the surface slip rate is taken up by creep. An exposure of this fault segment near Lake Pillsbury consists of sheared serpentinite that has risen buoyantly through late Pleistocene to Holocene (?) fluvial deposits and extruded onto the ground surface. Lighter-colored portions of the sheared body are dominated by antigorite serpentinite, with some retrograde recrystallization to chrysotile and lizardite. Darker zones are rich in porphyroclasts containing one or more of the minerals talc, chlorite, and actinolite in a sheared matrix of the same minerals. Incipient low-temperature alteration accompanying shear has produced Mg-rich smectitic clays, with local development of a foliated, clay-rich gouge that corresponds texturally and mineralogically to the SAFOD gouge zones. This outcrop of the BSF may thus illustrate the early stages in the development of the SAFOD gouge zones.

Moore, D. E.; Rymer, M. J.; McLaughlin, R. J.; Lienkaemper, J. J.

2011-12-01

247

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

248

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

249

Effects of Creep and Shrinkage on the Behavior of Reinforced Concrete Gable Roof Hyperbolic-Paraboloids.  

National Technical Information Service (NTIS)

Time-dependent deformations due to creep and shrinkage modify the response of structures sensitive to small geometrical changes such as the hyperbolic-parabola. In the investigation, a general finite element program is extended to consider time dependent ...

S. Gallegos-Cazares W. C. Schobrich

1988-01-01

250

Analysis of Multistage and Other Creep Data for Domal Salts  

SciTech Connect

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

Munson, D.E.

1998-10-01

251

Micromechanics of Brittle Creep Under Triaxial Loading Conditions  

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 (i) at stresses far below their short-term failure strength, and (ii) even at constant applied stress ("brittle creep"). Here we provide a micromechanical model and experimental results describing time-dependent brittle creep of water-saturated granite 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 microcracks in compression are derived from the sliding wing-crack model of Ashby and Sammis (1990). Crack length evolution is computed from Charles' law. The macroscopic strain and strain rates are then computed from the change in energy potential due to microcrack growth. They are non-linear, and compare well with complementary experimental results obtained on granite samples. Primary creep (decelerating strain) corresponds to decreasing crack growth rate , 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 merely an inflexion between the two end-member phases.

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

2011-12-01

252

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

253

Irradiation induced creep of graphite  

NASA Astrophysics Data System (ADS)

The status of graphite irradiation induced creep strain prediction is reviewed and major creep models are described. The ability of the models to quantitatively predict the irradiation induced creep strain of graphite is reported. Potential mechanisms of in-crystal creep are reviewed as are mechanisms of pore generation under stress. The case for further experimental work is made and the need for improved creep models across multi-scales is highlighted.

Burchell, T. D.; Murty, K. L.; Eapen, J.

2010-09-01

254

Crystallographic preferred orientation development by dissolution?precipitation creep  

NASA Astrophysics Data System (ADS)

Crystallographic preferred orientations (CPOs) in deformed rocks are commonly interpreted as resulting from crystal plastic deformation mechanisms, where deformation is achieved by the movement of dislocations. In this paper we investigate the possibility of CPO-development by dissolution-precipitation creep or pressure solution. A numerical model is presented, which simulates the development of a grain aggregate that deforms by reaction-controlled dissolution-precipitation creep. Grains are simulated as rectangular boxes that change their shape by growth, or dissolution of their surfaces, depending on the normal stresses acting on the individual surfaces. Grains can also rotate due to an applied vorticity (for non-coaxial deformation) and if they have a non-equidimensional shape. For each strain increment, stress that is applied to the grains is the same for all grains, while individual grains deform and rotate by different amounts. A variety of CPOs develop at moderate strains, depending on the reaction rates of the different crystal-surfaces and type of deformation (uni-axial shortening, plane strain pure shear and simple shear). The modelling results confirm that dissolution-precipitation creep may play a role in CPO-development in rocks.

Bons, Paul D.; den Brok, Bas

2000-11-01

255

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

SciTech Connect

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

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

2012-05-14

256

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

PubMed Central

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

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

2014-01-01

257

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

258

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

259

Multiaxial Creep Testing of Rock and Concrete  

Microsoft Academic Search

The finite element method of simulating tunnel excavations in squeezing ground requires experimental data on multiaxial creep relationships and related characteristics of rock and concrete as input. A servo-controlled test frame, for applying multiaxial stress states to cubical specimens through three independent actuators, was developed. This test system allows the simulation of typical stress levels and stress paths involved during

Kwok-Hung Leung

1980-01-01

260

Extending the theory of creep to viscoplasticity  

Microsoft Academic Search

A viscoplastic theory is developed that reduces to creep theory analytically under steady-state conditions. A fairly simple model is constructed from this theoretical framework by defining material functions that have close ties to the physics of inelasticity; consequently, the model is characterized easily. The computational characteristics of the model are enhanced, in general, by converting the kinetics equation from a

A. D. Freed; M. J. Verrilli; K. P. Walker

1994-01-01

261

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 µm 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

262

Diffusion-controlled creep in mixed-conducting oxides  

SciTech Connect

Steady-state creep rate of the mixed conducting oxides La{sub 1-x}Sr{sub x}MnO{sub 3} (x=0.1, 0.15, 0.25) and La{sub 0.7}Ca{sub 0.3}MnO{sub 3} has been investigated between 1150 and 1300 C. Creep parameters and TEM indicate that deformation is controlled by lattice diffusion of one of the cations. Dependence of creep rate on Sr concentration, combined with a point-defect model, confirms this hypothesis; however the oxygen partial pressure dependence of creep (from 10{sup -1} to 2x10{sup 4} Pa) cannot be accounted for within the framework of a simple point-defect model.

Routbort, J.L.; Goretta, K.C.; Cook, R.E. [Argonne National Lab., IL (United States); Wolfenstine, J. [California Coll. of Medicine, Irvine, CA (United States); Armstrong, T.R. [Pacific Northwest Lab., Richland, WA (United States); Clauss, C.; Dominguez-Rodriguez, A. [Seville Univ. (Spain). Dept. Materia Condensada

1996-06-01

263

Biaxial Creep Specimen Fabrication  

SciTech Connect

This report documents the results of the weld development and abbreviated weld qualification efforts performed by Pacific Northwest National Laboratory (PNNL) for refractory metal and superalloy biaxial creep specimens. Biaxial creep specimens were to be assembled, electron beam welded, laser-seal welded, and pressurized at PNNL for both in-pile (JOYO reactor, O-arai, Japan) and out-of-pile creep testing. The objective of this test campaign was to evaluate the creep behavior of primary cladding and structural alloys under consideration for the Prometheus space reactor. PNNL successfully developed electron beam weld parameters for six of these materials prior to the termination of the Naval Reactors program effort to deliver a space reactor for Project Prometheus. These materials were FS-85, ASTAR-811C, T-111, Alloy 617, Haynes 230, and Nirnonic PE16. Early termination of the NR space program precluded the development of laser welding parameters for post-pressurization seal weldments.

JL Bump; RF Luther

2006-02-09

264

A theory for creep crack growth. [in wrought nickel-base superalloys  

NASA Technical Reports Server (NTRS)

The paper derives an analytical expression for creep crack growth rate based on a model in which the higher and concentrated stresses ahead of the crack tip enhance creep deformation, thus progressively causing stress rupture and continuous crack advance. The equation derived for creep crack growth rate is expressed in terms of a geometrical factor in the stress intensity expression and in terms of the crack tip radius whose lower limit estimate is the fracture mechanics crack-tip opening displacement. The functional features of the derived creep crack growth rate equation can be compared with those of a pertinent empirical equation. The analytical expression provides some guidelines for alloy and microstructure design.

Purushothaman, S.; Tien, J. K.

1976-01-01

265

A constitutive model for representing coupled creep, fracture, and healing in rock salt  

SciTech Connect

The development of a constitutive model for representing inelastic flow due to coupled creep, damage, and healing in rock salt is present in this paper. This model, referred to as Multimechanism Deformation Coupled Fracture model, has been formulated by considering individual mechanisms that include dislocation creep, shear damage, tensile damage, and damage healing. Applications of the model to representing the inelastic flow and fracture behavior of WIPP salt subjected to creep, quasi-static loading, and damage healing conditions are illustrated with comparisons of model calculations against experimental creep curves, stress-strain curves, strain recovery curves, time-to-rupture data, and fracture mechanism maps.

Chan, K.S.; Bodner, S.R. [Southwest Research Inst., San Antonio, TX (United States); Munson, D.E.; Fossum, A.F. [Sandia National Labs., Albuquerque, NM (United States)

1996-03-01

266

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

267

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

268

Creep Resistant Zinc Alloy  

SciTech Connect

This report covers the development of Hot Chamber Die Castable Zinc Alloys with High Creep Strengths. This project commenced in 2000, with the primary objective of developing a hot chamber zinc die-casting alloy, capable of satisfactory service at 140 C. The core objectives of the development program were to: (1) fill in missing alloy data areas and develop a more complete empirical model of the influence of alloy composition on creep strength and other selected properties, and (2) based on the results from this model, examine promising alloy composition areas, for further development and for meeting the property combination targets, with the view to designing an optimized alloy composition. The target properties identified by ILZRO for an improved creep resistant zinc die-casting alloy were identified as follows: (1) temperature capability of 1470 C; (2) creep stress of 31 MPa (4500 psi); (3) exposure time of 1000 hours; and (4) maximum creep elongation under these conditions of 1%. The project was broadly divided into three tasks: (1) Task 1--General and Modeling, covering Experimental design of a first batch of alloys, alloy preparation and characterization. (2) Task 2--Refinement and Optimization, covering Experimental design of a second batch of alloys. (3) Task 3--Creep Testing and Technology transfer, covering the finalization of testing and the transfer of technology to the Zinc industry should have at least one improved alloy result from this work.

Frank E. Goodwin

2002-12-31

269

Sources of Variation in Creep Testing  

NASA Technical Reports Server (NTRS)

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

Loewenthal, William S.; Ellis, David L.

2011-01-01

270

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 2×10-6 and 1×10-3s-1. We prepared samples with water total contents of 0.004 wt % (dry) and 0.07 wt % (wet), respectively.

E. Rybacki; G. Dresen

2000-01-01

271

Intermittent dislocation flow in viscoplastic deformation  

Microsoft Academic Search

The viscoplastic deformation (creep) of crystalline materials under constant stress involves the motion of a large number of interacting dislocations. Analytical methods and sophisticated `dislocation dynamics' simulations have proved very effective in the study of dislocation patterning, and have led to macroscopic constitutive laws of plastic deformation. Yet, a statistical analysis of the dynamics of an assembly of interacting dislocations

M.-Carmen Miguel; Alessandro Vespignani; Stefano Zapperi; Jérôme Weiss; Jean-Robert Grasso

2001-01-01

272

Creep of oxide dispersion strengthened materials (with special reference to TD nichrome)  

NASA Technical Reports Server (NTRS)

It was shown that the creep behavior of oxide dispersion strengthened (ODS) alloys is controlled principally by the creep properties of the matrix of the alloy devoid of particles. Thus, diffusion controlled slip process determine the rate controlling step in such materials. The role of the particles is to stabilize a fine substructure which is invariant with the creep stress over a wide range of stress. This characteristic leads to negligible strain hardening during creep and suggests that creep relations developed for pure metals and many solid solution alloys at constant structure should be used to describe the creep of ODS alloys. A second characteristics of the ODS alloys is that a stress may exist below which creep will not occur (threshold stress).

Lin, J.; Sherby, O. D.

1978-01-01

273

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 (1.8±0.2 cm3/mol), and small water-content exponent (0.22±0.05). 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

274

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

275

Modeling the densification of powder composites by power law creep  

Microsoft Academic Search

A model describing the densification under isotropic pressure of a powder composite, consisting of viscoplastic particles deforming by power law creep mixed with rigid inclusions of the same size, is presented. A description of the behavior of each type of contacts is first proposed, from which an expression for the densification rate of the mixture is deduced. The evolution of

Bouvard

1993-01-01

276

Tensile and creep behavior of cryomilled Inco 625  

Microsoft Academic Search

The tensile and creep behavior of a cyromilled Inconel 625 alloy have been investigated. The microstructure is duplex with grain sizes ranging from 200 nm at the smallest to about 10 ?m at the largest. Normal work hardening is observed in uniaxial tension and the stress-strain behavior follows a power law. Deformation of this material is accomplished by dislocation motion

R. Rodriguez; R. W. Hayes; P. B. Berbon; E. J. Lavernia

2003-01-01

277

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

278

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

279

On the stability of the creep substructure in NaCl single crystals  

NASA Technical Reports Server (NTRS)

Microstructural observations were conducted on NaCl single crystals after creep. The microstructure after a stress increase followed by a stress decrease consisted primarily of cells; no significant number of subgrains were observed although they were present in the microstructures produced during uninterrupted tests. Prestraining in the exponential creep regime produced an uniform distribution of dislocations and a few subboundaries which transformed to equiaxed subgrains when tested in the power law creep region. This substructure was similar to that observed in an as-received specimen deformed to an equivalent strain. Prior creep in the power law creep region produced equiaxed subgrains whose boundaries were found to be mechanically stable when the specimen was retested in the exponential creep region. The role of subboundary migration in the formation of new subgrains is discussed.

Raj, S. V.; Whittenberger, J. D.; Pharr, G. M.

1989-01-01

280

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

NASA Astrophysics Data System (ADS)

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

Wang, Qin

2010-11-01

281

Postseismic relaxation associated with transient creep rheology  

NASA Astrophysics Data System (ADS)

Perfettini and Avouac (2004) postulated that both the aftershock rate (assumed proportional to the local stressing rate) and the postseismic relaxation are driven by the loading imposed by postseismic slip on the brittle creep fault zone (BCFZ), the downdip extension of the fault zone below the coseismic rupture. I explore the consequences of that hypothesis for a long, strike-slip fault in the case where the BCFZ rheology is compatible with ordinary transient creep (creep strain proportional to loge(1 + t/?2)). Because the important relaxation occurs near the bottom of the coseismic rupture, I calculate the postearthquake response with a model in which the BCFZ is represented by a viscoelastic half-space below the coseismic rupture. I find that both the predicted postseismic relaxation and the cumulative number of aftershocks can be approximated by the same temporal dependence NMO(t) = aMO(1-(1 + t/?)1-p)/(p - 1), where t is the time after the earthquake and aMO, ?, and p are the constants chosen to fit either data set. Notice that dNMO(t)/dt = (aMO/?)/(1 + t/?)p is the modified Omori law used to describe the rate of aftershock occurrence. Thus, the modified Omori law can be understood as a consequence of the Perfettini-Avouac hypothesis (aftershocks driven by slip on the BCFZ) and a BCFZ rheology compatible with ordinary transient creep. Moreover, the temporal dependence NMO(t) has been shown to fit postseismic surface deformation following at least 9 earthquakes. I also show that the conventional, one-dimensional, spring-block model of a BFCZ with a rheology compatible with ordinary transient creep leads to the same temporal dependence (NMO(t)).

Savage, J. C.

2007-05-01

282

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

283

ORNL irradiation creep facility  

SciTech Connect

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

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

1980-09-01

284

In-Reactor Creep Measurements.  

National Technical Information Service (NTIS)

Creep studies have produced experimental results which are being used for design and performance analyses of fast breeder reactors. These programs enabled the development of experimental methods which have produced in-reactor creep data over a broad range...

E. R. Gilbert B. A. Chin

1978-01-01

285

Modelling creep behaviour and failure of 9Cr–0.5Mo–1.8W–VNb 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 550–750°C.In a first step, the results of creep tests performed at 575°C are presented and compared to other literature results in order to bring the main mechanisms of P92 steel creep behaviour into

C. Pétry; G. Lindet

2009-01-01

286

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

287

Laser-Interferometric Creep Rate Spectroscopy of Polymers  

NASA Astrophysics Data System (ADS)

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

Bershtein, Vladimir A.; Yakushev, Pavel N.

288

Nanodisturbances in deformed nanowires.  

PubMed

A new physical mechanism of plastic deformation in nanowires is suggested and theoretically described. This mechanism represents formation of near-surface nanodisturbances-nanoscopic areas of plastic shear with tiny shear vectors-in deformed nanowires. We calculated the energy characteristics for nanodisturbance formation and compared them with those for conventional dislocation generation. It is shown that the nanodisturbance deformation mode tends to dominate in Au nanowires deformed at high stresses and zero temperature. PMID:19905521

Bobylev, S V; Ovid'ko, I A

2009-09-25

289

Spatio-temporal characteristics of acoustic emission during the deformation of rock samples with compressional and extensional en-echelon faults  

Microsoft Academic Search

The spatio-temporal characteristics of acoustic emission (AE) during the deformation of rock samples with compressional and\\u000a extensional en-echelon faults have been studied. The results show that the pre-existing structure can significantly influence\\u000a the patterns of AE spatial distribution. With increasing of differential stress, AE events firstly cluster around the two\\u000a ends of pre-existing faults inside the jog and then along

Hai-Kun Jiang; Shengli Ma; Liu Zhang; Hai-Feng Hou; Wen-Hai Cao

2002-01-01

290

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

291

Copper, Boron, and Cerium Additions in Type 347 Austenitic Steel to Improve Creep Rupture Strength  

NASA Astrophysics Data System (ADS)

Type 347 austenitic stainless steel (18Cr-12Ni-Nb) was alloyed with copper (3 wt pct), boron (0.01 to 0.06 wt pct), and cerium (0.01 wt pct) with an aim to increase the creep rupture strength of the steel through the improved deformation and cavitation resistance. Short-term creep rupture strength was found to increase with the addition of copper in the 347 steel, but the long-term strength was inferior. Extensive creep cavitation deprived the steel of the beneficial effect of creep deformation resistance induced by nano-size copper particles. Boron and cerium additions in the copper-containing steel increased its creep rupture strength and ductility, which were more for higher boron content. Creep deformation, grain boundary sliding, and creep cavity nucleation and growth in the steel were found to be suppressed by microalloying the copper-containing steel with boron and cerium, and the suppression was more for higher boron content. An auger electron spectroscopic study revealed the segregation of boron instead of sulfur on the cavity surface of the boron- and cerium-microalloyed steel. Cerium acted as a scavenger for soluble sulfur in the steels through the precipitation of cerium sulfide (CeS). This inhibited the segregation of sulfur and facilitated the segregation of boron on cavity surface. Boron segregation on the nucleated cavity surface reduced its growth rate. Microalloying the copper-containing 347 steel with boron and cerium thus enabled to use the full extent of creep deformation resistance rendered by copper nano-size particle by increase in creep rupture strength and ductility.

Laha, Kinkar; Kyono, J.; Shinya, Norio

2012-04-01

292

Nonlinear physical stress - strain relationship of cellular polymers and glass plastics under conditions of attenuating creep  

Microsoft Academic Search

The coupling equations of hard cellular polymers and glass plastics based on these are analyzed. The material is considered as an elastically relaxing medium for the case of small deformations. The physical relationship between the rubber-elastic stresses and strains is derived in explicit form for the case of attenuating creep and a uniform three-dimensional stressed state. The total deformations are

G. Zakhariev; L. Khadzhikov

1972-01-01

293

Experimental deformation of rocksalt  

NASA Astrophysics Data System (ADS)

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, temperatures between 100° and 200°C, and confining pressures of 3.4 and 20 MPa, comparing our data with those of other workers on the same material, and observing natural deformations 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 temperature, but not confining pressure; (2) fracture excluded, the deformation 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 temperature in both constant-strain-rate and constant-stress (creep) tests, but the strain-time data from transient creep tests do not match the strain-hardening data unless the initial strain, ?0 (time-dependent in rocksalt) is accounted for; in creep 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 deformation, the constant-strain-rate test rather than the creep test may well be preferred as the source of constitutive data; (5) furthermore, if the stress or temperature of the creep 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 temperatures too low to reach the steady state within a few hours; (6) the so-called "baseline creep law", giving creep 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 temperature where the same deformation 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 temperature (T), and capable of matching at least limited constant-strain-rate, constant-stress-rate, constant-stress (creep), 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 ? 300°C 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.

Handin, J.; Russell, J. E.; Carter, N. L.

294

Avoiding Project Creep.  

ERIC Educational Resources Information Center

Discusses how to keep school district capital-improvement projects within budget. Examines areas where runaway costs creep into a project and ways of cutting or lessening these costs, such as using standard agreements, controlling architect's expense reimbursements, developing a quality-control process, and reducing document duplication. (GR)

Kennerknecht, Norbert J.; Scarnati, James T.

1998-01-01

295

Creep behavior of submarine sediments  

USGS Publications Warehouse

A series of experiments on drained creep of marine sediment indicates that strength degradation results from the creep process, which implies an associated reduction in slope stability. Furthermore, the highest creep potential of a sediment may be at its preconsolidation stress. Results from the experiments on samples from Georges Bank continental slope were also used in conjunction with a preliminary theoretical model to predict creep displacements. For the case illustrated in this report, steep slopes (>20??) and thick sections (>30 m) give rise to substantial creep and probable creep rupture; as angles or thicknesses decrease, displacements rapidly become negligible. Creep may be a significant geologic process on many marine slopes. Not only can it cause major displacements of surface sediment, but it may also be the precursor to numerous slope failures. ?? 1985 Springer-Verlag New York Inc.

Silva, A. J.; Booth, J. S.

1984-01-01

296

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

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

297

Creep behaviour and creep mechanisms of normal and healing ligaments  

NASA Astrophysics Data System (ADS)

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

Thornton, Gail Marilyn

298

Importance of Mantle Viscosity in Interseismic Deformation  

NASA Astrophysics Data System (ADS)

The role of mantle viscosity in subduction earthquake cycles was postulated when the plate tectonics theory had just gained wide acceptance. The process was described using Elsasser's 1-D model for diffusion of stress from the subduction boundary to the plate interior. Main features of interseismic surface deformation predicted by this elegantly simple model were later verified by GPS observations following giant subduction earthquakes. However, and intriguingly, the vast majority of interseismic deformation models developed in the era of space geodesy assume an elastic Earth, incorrectly regarding interseismic deformation as a subdued mirror image of coseismic deformation. The reason is four-fold. (1) The 1-D model and subsequent 2-D viscoelastic models failed to recognize the role of rupture length in the strike direction and could not self-consistently explain deformation following medium and small earthquakes. (2) Based on global mantle viscosity models derived from glacial isostatic adjustment studies, the viscoelastic mantle should indeed behave elastically in earthquake cycles of a few hundred years. (3) The effect of viscous mantle deformation can often be equivalently described by deep fault creep in a purely elastic Earth. (4) The use of an elastic model provides convenience in inverting geodetic data to determine fault locking and creep. Here we use 3D finite element models to show that the main characteristics of surface deformation following subduction earthquakes of all sizes can be explained with a viscoelastic Earth in which the mantle wedge is less viscous than global upper-mantle average of 1020 - 1021 Pa s by one to two orders of magnitude. Following giant earthquakes, such as 1700 Cascadia, 1960 Chile, 1964 Alaska, 2004 Sumatra, and 2011 Japan, upper-plate land deformation undergoes phases of wholesale seaward motion, opposing motion of coastal and inland areas, and wholesale landward motion. The "speed" of the evolution scales inversely with the seismic moment of the earthquake, such that for small events, the first two phases are brief or even absent. With modern geodetic observations and advanced modeling demonstrating the first-order importance of mantle viscosity in interseismic deformation, we argue that it is time to revise all the elastic interseismic models to address the effect of mantle viscosity. Using an elastic model to represent the real Earth of very low mantle-wedge viscosity leads to under- or over-estimates of the downdip width of the zone of fault locking or "partial locking", depending on the time since the previous earthquake. The effect of viscoelastic relaxation is strong regardless of how long after the earthquake and whether the deformation field is still changing with time. The use of an elastic model may also cause the interseismic elastic strain to be misidentified as due to permanent upper-plate deformation (commonly described in terms of block motion). Revising these models therefore will improve our view of subduction zone earthquake/tsunami hazards and geodynamic processes.

Wang, K.; He, J.; Hu, Y.

2012-12-01

299

Effect of in situ TiB 2 particle reinforcement on the creep resistance of hypoeutectic Al–12Si alloy  

Microsoft Academic Search

The effect of in situ TiB2 particle reinforcement on the tensile creep deformation of an Al–12Si alloy prepared by the technique of salt–metal reactions was studied in a wide temperature range of 573–673K 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

300

Creep-fatigue damage and life prediction in P92 alloy by focused ultrasound measurements  

Microsoft Academic Search

In the present study, the characteristics of creep damage in P92 alloy were investigated via nondestructive evaluation. Generally,\\u000a as the hold time of a static load increases, the degradation of the material becomes more severe along with a reduction of\\u000a service life. Therefore, in power plants, the reduction of creep-fatigue strength and the creep-fatigue life of high pressure\\u000a vessels at

Bum-joon Kim; Hak-joon Kim; Byeong-soo Lim

2008-01-01

301

Rate- and strain-dependent brittle deformation of rocks  

NASA Astrophysics Data System (ADS)

We develop a unifying framework to quantify rate-dependent deformation in the brittle field and establish links between the microscale time-dependent crack growth processes and the macroscopically observed rate dependency. Triaxial deformation experiments have been performed under both constant strain rate and constant stress (creep) conditions on three types of sandstone. The measured relative evolution of P wave speeds as a function of inelastic axial strain is similar for both types of test, despite differences in strain rate of up to 3 orders of magnitude. This similarity indicates that there exists a direct, time-independent link between the microstructural state (as reflected by the variations in P wave speed) and the inelastic axial strain. Comparison of applied stresses between constant strain rate and creep experiments as a function of inelastic strain indicates that creep deformation requires less mechanical work to bring the sample to failure. This energy deficit corresponds to a stress deficit, which can be related to a deficit in energy release rate of the microcracks. We establish empirically that the creep strain rate is given by ???exp(?Q/??), where ?Q is the stress deficit (negative) and ?? is an activation stress. This empirical exponential relation between creep strain rate and stress deficit is analogous to rate-and-state friction law. We develop a micromechanical approach based on fracture mechanics to determine the evolution of an effective stress intensity factor at crack tips during creep deformation and estimate the activation volume of the stress corrosion reaction responsible for brittle creep.

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

2014-03-01

302

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

SciTech Connect

The behavior during creep in shear of eutectic indium-tin joints on copper and nickel substrates was examined in order to determine the effect of creep deformation on the microstructure of the alloy. Primary creep was absent in all the samples tested. The stress exponent at 20[degree] C was much higher for samples on nickel than for those on copper, indicating a different creep deformation mechanism. Also, the microstructure within the indium-tin joints differed significantly with a change of substrate. Samples with a nickel substrate showed a colony microstructure that was not observed in those with a copper substrate. Thus, eutectic morphology is important in determining deformation mechanism during creep. The microstructure within the joints in tested and untested regions of the samples was effectively the same. This is quite distinct from the behavior of eutectic lead-tin observed in previous work. Lead-tin formed a recrystallized band of material along a region of concentrated shear deformation. While the deformation pattern in the indium-tin samples appeared to be the same as for lead-tin, the microstructural changes did not occur. This implies that the behavior observed in lead-tin is not universal to eutectic alloys. 8 refs., 7 figs.

Freer, J.L.; Morris, J.W. Jr. (Lawrence Berkeley Lab., CA (United States))

1992-06-01

303

Microdeformation experiments on chalk - fluids, fracture and creep  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

304

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

PubMed Central

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

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

2011-01-01

305

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 1150°C. 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

306

Experimental and Numerical Studies on Mudstone's Creep Behavior During Water Injection and Its Effect on Casing Damage  

NASA Astrophysics Data System (ADS)

During the process of water injection production in oilfield, when water cuts into the mudstone, as a result, large numbers of casings are damaged because of mudstone's creep characteristic. In order to analyze this phenomenon, the uniaxial compression experiments and creep experiments of mudstone from Daqing Oil Field under different saturation conditions were done, it was studied that how the mudstone's mechanical parameters and creep characteristic would change with the increment of water contents. The results indicate that the rock strength and elastic modulus are decreased rapidly with the increment of water contents, on the other hand, the creep strain and steady state creep strain rate are increased with the increment of water contents, and also the steady state creep strain rate is enhanced with the increment of deviatoric stress. Through the creep characteristic curves, a nonlinear creeping constitutive equation of mudstone considering the changes of water contents was established. In the deep stratum of the oilfield, the calculation model of casing-cement sheath-mudstone was built, based on the experiment results of mudstone and its creep constitutive equation, mudstone's creep pressure with time under different water contents was simulated. The simulation results show that the increasing water content accelerates the incremental rate of the creep pressure of mudstone, so the time of reaching yield state of casing will descend greatly, which means service time of casing becomes much shorter.

Huang, X. L.; Yang, C. H.; Liu, J. J.; He, X.; Xiong, J.

2008-07-01

307

Analysis of the Creep Behavior of P92 Steel Welded Joint  

Microsoft Academic Search

Different regions of heat-affected zone (HAZ) were simulated by heat treatment to investigate the mechanisms of the Type IV\\u000a fracture of P92 (9Cr-2W) steel weldments. Creep deformation of simulated HAZ specimens with uniform microstructures was investigated\\u000a and compared with those of the base metal (BM) and the weld metal (WM) specimens. The results show that the creep strain rate\\u000a of

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

308

Extended Creep Recovery via Oscillatory Shear and Bending Beam Rheometers  

NASA Astrophysics Data System (ADS)

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 creep. The overall range of relaxation times can be expanded by means of the time-temperature superposition. In the case of bituminous materials studied, creep experiments at lower temperatures involve different testing geometry, e.g. a bending beam rheometer (BBR). The challenge is to combine the spectra obtained from the oscillatory and creep/recovery in shear deformation with the spectra obtained from the extended flexural deformation. We demonstrate a technique of combining the spectra obtained for a conventional bitumen (asphalt), with a practical application to modeling a multiple creep and recovery test.

Kazatchkov, Igor B.; Stastna, Jiri; Zanzotto, Ludo

2008-07-01

309

Non-Contact Measurements of Creep Properties of Refractory Materials  

NASA Technical Reports Server (NTRS)

State-of-the-art technologies for hypersonic aircraft, nuclear electric/thermal propulsion for spacecraft, and more efficient jet engines are driving ever more demanding needs for high-temperature (>2000 C) materials. At such high temperatures, creep rises as one of the most important design factors to be considered. Since conventional measurement techniques for creep resistance are limited to about 17OO0C, a new technique is in demand for higher temperatures. This paper presents a non-contact method using electrostatic levitation (ESL) which is applicable to both metallic and non-metallic materials. The samples were rotated quickly enough to cause creep deformation by centrifugal acceleration. The deformation of the samples was captured with a high speed camera and then the images were analyzed to estimate creep resistance. Finite element analyses were performed and compared to the experiments to verify the new method. Results are presented for niobium and tungsten, representative refractory materials at 2300 C and 2700 C respectively.

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

2006-01-01

310

The characteristics of three-dimensional crustal deformation around the Longmen Shan fault before the 2008 Wenchuan earthquake  

NASA Astrophysics Data System (ADS)

The Wenchuan earthquake took place within the context of long-term uplift of the Longmen Shan range. There is a very close relationship between them. In order to study the uplift rate of the region before the event, this work obtains the kinematic model about the active fault and crustal deformation, by using the 324 GPS data, 414 leveling data and slip rates of some active faults from geology as constraints, the OKADA dislocation model as the fault model, and the least-squares as the inversion method. That mean the major fault slip rate of the study area have been obtained. The dip slip rate and the strike slip rate of Longmen Shan fault is 2.6×0.2 mm/a and 1.6×0.2 mm/a each. Based on the major fault slip rate of kinematc model and using the OKADA dislocation model to forward interpolation velocity, I acquire the three-dimensional crustal deformation and the horizonal strain rate field around the Longmen Shan region. So the main results of this work are described as follows: 1).The horizontal deformation of the Longmen Shan fault is not obvious compared to the adjacent Xianshuihe-Xiaojiang fault and the East Kunlun fault. 2).In the action of Longmen Shan fault and MinShan fault, the Longmen Shan region is continued uplift. The uplift rate of it is about 1.8×0.2 mm/a relative the Sichuan Basin in nowadays. 3).The Gongga Mountains is another notable vertical deformation region in the study area. Its uplift rate is about 2.9×0.2mm/a relative the Sichuan Basin, which is lower than less 5.8mm/a observed by leveling data. This may reflect that the deformation of the region cannot be explained by the dislocation model and the crustal flow model is more appropriate. The strain rate around Longmen Shan region. The vertical deformation around Longmen Shan region.

Weitao, C.; Gan, W.; Genru, X.; Yuebing, W.

2013-12-01

311

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

312

Detection of Creep displacement along the North Anatolian Fault by SAR Interferometry  

NASA Astrophysics Data System (ADS)

North Anatolian Fault (NAF) has several records of a huge earthquake occurrence in the last one century, which is well-known as a risky active fault. Some signs indicating a creep displacement could be observed on the Ismetpasa segment. It is reported so far that the San Andreas fault in California, the Longitudinal Valley fault in Taiwan and the Valley Fault System in Metro Manila also exhibit fault creep. The fault with creep deformation is aseismic and never generate the large scale earthquakes. But the scale and rate of fault creep are important factors to watch the fault behavior and to understand the cycle of earthquake. The purpose of this study is to investigate the distribution of spatial and temporal change on the ground motion due to fault creep in the surrounding of the Ismetpasa, NAF. DInSAR is capable to catch a subtle land displacement less than a centimeter and observe a wide area at a high spatial resolution. We applied InSAR time series analysis using PALSAR data in order to measure long-term ground deformation from 2007 until 2011. As a result, the land deformation that the northern and southern parts of the fault have slipped to east and west at a rate of 7.5 and 6.5 mm/year in line of sight respectively were obviously detected. In addition, it became clear that the fault creep along the NAF extended 61 km in east to west direction.

Deguchi, Tomonori; Kutoglu, Hakan

2012-07-01

313

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

314

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

315

Numerical and experimental studies on thermal deformation of ceramic breeder pebble bed systems  

NASA Astrophysics Data System (ADS)

The goal of this work is to develop modeling capabilities for understanding and predicting thermo-mechanical behavior of ceramic breeder pebble bed systems at elevated temperatures (600-800°C). The thermo-mechanical behavior of solid breeder pebble beds is a critical issue for the solid breeder blanket designs and is different from the behaviors of solid materials. The issue includes potential breakage of pebble materials and change in heat transfer characteristics across the breeder materials and cladding interface. Furthermore, at elevated temperatures, thermal creep deformation plays an uncertain role related to the contact stresses in the pebble beds. To understand these effects, the following efforts have been undertaken: First, experiments of a typical breeder blanket design have been conducted to study the thermal creep behaviors of the pebble bed system. Other than providing data for benchmarking numerical simulation, the experimental results show that the thermal deformation behaviors of typical pebble materials, such as Li2O and Li4SiO4 lithium ceramics, are nonlinear with respect to time and temperature. Under fixed temperatures (higher than 600°C), stresses generated from differential thermal expansion begin to decrease as a result of creep deformation. Second, a new numerical program, based on discrete element method (DEM), has been developed to simulate the fundamental mechanical behaviors of the packed pebble bed system. Considering the effects in a high temperature situation, inelastic contact models have been derived to predict thermal creep deformation. Our DEM program is mainly used to derive the effective mechanical constitutive equations for a pebble bed system. Besides that, it can provide the stress distribution inside the pebble bed and the force evolution related to the changes of boundary loadings. Last, a numerical program based on the finite element analysis (FEA) has been utilized to simulate the stress magnitude and deformation characteristics/evolution of the breeding zone in a fusion blanket. The advantage of FEA modeling is that it can analyze a larger-scale material system, and also provide important information for blanket design and performance evaluation. One of the numerical results has illustrated the thermo-mechanical behaviors of breeding blanket unit cells under pulsed heating operation.

An, Zhiyong

316

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

NASA Astrophysics Data System (ADS)

A model of damage evolution in austenitic stainless steels under creep loading at elevated temperatures is proposed. The initial microstructure is idealized as a space-tiling aggregate of identical rhombic dodecahedral grains, which undergo power-law creep deformation. Damage evolution in the form of cavitation and wedge cracking on grain-boundary facets is considered. Both diffusion- and deformation-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 creep loading. Deformation and damage evolution at the microscale predicted by the present model are also discussed.

Mahesh, S.; Alur, K. C.; Mathew, M. D.

2011-01-01

317

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 31,800 h. 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

318

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

NASA Astrophysics Data System (ADS)

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

Whittaker, Mark T.; Wilshire, Brian

2013-01-01

319

Creep behavior in SiC whisker-reinforced alumina composite  

SciTech Connect

Grain boundary sliding (often accompanied by cavitation) is a major contributor to compressive and tensile creep deformation in fine-grained aluminas, both with and without whisker-reinforcement. Studies indicate that the creep 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 creep resistance of fine-grained (1--2 {mu}m) alumina in air at temperatures of 1,200 and 1,300 C. However, at higher whisker contents (30 and 50 vol%), the creep resistance is degraded due to enhanced surface oxidation reactions accompanied by extensive creep 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 creep resistance. On the other hand, increasing the matrix grain size or decreasing the whisker aspect ratio (increased whisker number density) results in raising the creep resistance of the composites. These observations not only explain the variability in the creep response of various SiC whisker-reinforced alumina composites but also indicate factors that can be used to enhance the elevated temperature performance.

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

1994-10-01

320

Prediction of creep-rupture life of unidirectional titanium matrix composites subjected to transverse loading  

NASA Astrophysics Data System (ADS)

Titanium matrix composites (TMCs) incorporating unidirectional fiber reinforcement are considered as enabling materials technology for advanced engines which require high specific strength and elevated temperature capability. The resistance of unidirectional TMCs to deformation under longitudinally applied sustained loading at elevated temperatures 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 creep-rupture life of TMCs subjected to different transverse stress levels over a wide range of temperatures. In this article, we propose a model to predict the creep-rupture life of unidirectional TMC subjected to transverse loading based on the creep-rupture life of unidirectional TMC subjected to transverse loading based on the creep-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 creep-rupture strength and the fibers do not contribute to the creep 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 creep behavior. The results show that the creep-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.

John, Reji; Khobaib, M.; Smith, Paul R.

1996-10-01

321

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

322

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

323

Creep of a Silicon Nitride Under Various Specimen/Loading Configurations  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

324

Creep and Structure of Ceramics  

Microsoft Academic Search

The effects of pores and low-melting phases on the creep in multiphase oxide ceramics are analyzed using experimental data. It is shown that the high stress level produced by pores has no effect on the creep behavior of the ceramics. The pores reduce the contact cross section, which is smaller than the effective cross section taking into account only the

V. S. Bakunov; A. V. Belyakov

2000-01-01

325

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

NASA Astrophysics Data System (ADS)

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

Shirley, Dwayne R.

326

Creep-Fatigue Interaction Testing  

NASA Technical Reports Server (NTRS)

Fatigue fives in metals are nominally time independent below 0.5 T(sub Melt). At higher temperatures, fatigue lives are altered due to time-dependent, thermally activated creep. Conversely, creep rates are altered by super. imposed fatigue loading. Creep and fatigue generally interact synergistically to reduce material lifetime. Their interaction, therefore, is of importance to structural durability of high-temperature structures such as nuclear reactors, reusable rocket engines, gas turbine engines, terrestrial steam turbines, pressure vessel and piping components, casting dies, molds for plastics, and pollution control devices. Safety and lifecycle costs force designers to quantify these interactions. Analytical and experimental approaches to creep-fatigue began in the era following World War II. In this article experimental and life prediction approaches are reviewed for assessing creep-fatigue interactions of metallic materials. Mechanistic models are also discussed briefly.

Halford, Gary R.

2001-01-01

327

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

NASA Astrophysics Data System (ADS)

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

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

2013-07-01

328

PREDICTION OF CREEP IN BENDING FROM TENSION-AND COMPRESSION-CREEP DATA WHEN CREEP COEFFICIENTS ARE UNEQUAL  

Microsoft Academic Search

The method of predicting creep in bending from data on creep in tension ; previously described was extended to the prediction of creep in bending when the ; creep in tension and compression are unequal, and when the time-dependent and ; time-independent stress functions are unequal. It was shown that the stress ; distribution and position of the neutral axis

W. N. Findley; J. J. Poczatek; P. N. Mathur

1958-01-01

329

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

NASA Astrophysics Data System (ADS)

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

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

2012-09-01

330

Magnetite deformation mechanism maps for better prediction of strain partitioning  

NASA Astrophysics Data System (ADS)

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 temperature 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 temperatures 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">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/1999JChPh.111.2235B"> <span id="translatedtitle">Physical aging by periodic <span class="hlt">creep</span> and interrupted <span class="hlt">creep</span> experiments</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 newly developed ``interrupted <span class="hlt">creep</span>'' experiment has been used to study the physical aging of a low molecular weight polystyrene, Tg~69 °C. The results of the new experiment are compared to those obtained from traditional ``periodic <span class="hlt">creep</span>'' experiments. The interrupted <span class="hlt">creep</span> experiment provides information about the viscosity, the recoverable <span class="hlt">creep</span> compliance and the steady-state compliance, Js, during aging. Low molecular weight polystyrene was chosen because it exhibits a steady-state compliance that is a strong function of temperature. Aging was conducted at three temperatures, 68.2, 65.7 and 61.0 °C, using both down-jump and up-jump experiments. The behavior observed in the new experiments mirrors the behavior observed in the traditional experiments. In addition, the new experiments allow the first ever determination of how Js evolves during aging. The change of Js with aging time was calculated using the relationship between the shift factors, obtained from the recoverable <span class="hlt">creep</span> compliance data, and the average relaxation times, obtained from the viscosity. The advantage of the new experiment is that it provides both the short-time recoverable <span class="hlt">creep</span> compliance information and the long-time viscous flow. By combining these contributions to the <span class="hlt">creep</span> compliance in a simple additive fashion, one can obtain a more complete picture of how the material is behaving during aging.</p> <div class="credits"> <p class="dwt_author">Bernatz, Kevin M.; Giri, Lily; Simon, Sindee L.; Plazek, Donald J.</p> <p class="dwt_publisher"></p> <p class="publishDate">1999-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">332</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://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 temperature 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 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.springerlink.com/index/v53267607wq21121.pdf"> <span id="translatedtitle">Cyclic <span class="hlt">creep</span> and failure in the stress concentration zone in low-cycle loading. Report 2. Prediction of the life of plates with stress raisers in cyclic <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">The results of experimental investigation of the process of low-cycle <span class="hlt">deformation</span> and failure of a plate with a hole presented in Report 1 showed that for prediction of the life of elements of structures with stress raisers it is insufficient to have available data on the low-cycle fatigue of the material in cyclic <span class="hlt">creep</span> under conditions of the linear stressed</p> <div class="credits"> <p class="dwt_author">G. S. Pisarenko; V. A. Strizhalo; V. I. Skripchenko</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">334</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/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 temperature 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">335</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.agu.org/journals/jb/v103/iB01/97JB02671/97JB02671.pdf"> <span id="translatedtitle">High-temperature <span class="hlt">deformation</span> of dry diabase with application to tectonics on Venus</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 have performed an experimental study to quantify the high-temperature <span class="hlt">creep</span> behavior of natural diabase rocks under dry <span class="hlt">deformation</span> 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 <span class="hlt">creep</span> strength. Flow laws determined for <span class="hlt">creep</span> of these diabases were characterized by an activation energy of Q</p> <div class="credits"> <p class="dwt_author">S. J. Mackwell; M. E. Zimmerman; D. L. Kohlstedt</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">336</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.T51H2454U"> <span id="translatedtitle">Plasticity and <span class="hlt">creep</span> of polycrystalline magnesite</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">Carbonates may be incorporated in the mantle at collisional plate boundaries by a number of processes, including subduction of weathered oceanic crust and fault-bounded tectonic slivers of seamounts that are not left behind in the accretionary wedge. High-magnesium carbonates, dolomite and magnesite have been observed in ultra-deep metamorphic collisional terrains and they have been observed (or inferred) in mantle xenoliths from well-preserved (or partially back-reacted) inclusions. Magnesite can also be formed in the mantle by reaction with CO2-rich fluids, and is commonly found within serpentinized peridotite bodies. Once magnesite is formed in subducting slabs, it is likely to remain as an important carbon-bearing phase, as its stability extends over a wide range of (upper, transitional and possibly lower) mantle conditions. In order to quantify the mechanical properties of magnesite aggregates, we performed a series of triaxial compression experiments on cylinders of a natural, fine-grained (d~1 ?m) magnesite aggregate at temperatures of 400-775°C and strain rates of 10-4/s - 10-6/s at a constant effective pressure of 300 MPa using a Heard-type gas confining medium <span class="hlt">deformation</span> apparatus. Experiments performed at 1*10-5/s, show that the strength of magnesite is weakly temperature dependent from 400 to 600°C and becomes strongly temperature dependent at T ? 600°C as strengths decrease from 500 MPa to 5 MPa (at 775°C). The microstructures in the sample <span class="hlt">deformed</span> at 500°C include angular grains and pores, similar to those observed in the starting material. However, the grains and pore boundaries in the sample <span class="hlt">deformed</span> at 775°C are considerably more rounded. These first <span class="hlt">deformation</span> experiments on polycrystalline magnesite reveal results indicate a transition in the dominant <span class="hlt">deformation</span> mechanism with increasing temperature. Based on comparisons with <span class="hlt">deformation</span> mechanisms of other carbonates, and their associated mechanical responses, we expect that magnesite <span class="hlt">deforms</span> by low-temperature crystal plasticity at temperatures less than 600°C (at 1*10-5/s) and it <span class="hlt">deforms</span> by diffusion (coble) <span class="hlt">creep</span> at higher temperatures. Comparisons of magnesite, calcite, dolomite and olivine strengths along a P-T path within a subducting slab indicate that calcite is the weakest phase in the upper 100 km, where it is stable, but magnesite becomes weaker than all of the other phases at greater depths. These results indicate that magnesite may play a significant role as a weak phase that affects the rheology of subducting slabs.</p> <div class="credits"> <p class="dwt_author">Ulrich, C. A.; Holyoke, C. W.; Kronenberg, A. K.; Newman, J.</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">337</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/6409723"> <span id="translatedtitle">Improved high temperature <span class="hlt">creep</span> resistant austenitic alloy</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 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 <span class="hlt">deforming</span> 5-15%. The alloy exhibits dramatically improved <span class="hlt">creep</span> rupture resistance and ductility at 700/degree/C. 2 figs.</p> <div class="credits"> <p class="dwt_author">Maziasz, P.J.; Swindeman, R.W.; Goodwin, G.M.</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-05-13</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">338</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/doepatents/biblio/867041"> <span id="translatedtitle">High temperature <span class="hlt">creep</span> resistant austenitic alloy</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 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 <span class="hlt">deforming</span> 5-15 %. The alloy exhibits dramatically improved <span class="hlt">creep</span> rupture resistance and ductility at 700.degree. C.</p> <div class="credits"> <p class="dwt_author">Maziasz, Philip J. (Oak Ridge, TN); Swindeman, Robert W. (Oak Ridge, TN); Goodwin, Gene M. (Lenoir City, TN)</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-01-01</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://ntrs.nasa.gov/search.jsp?R=20050207572&hterms=contact&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dcontact"> <span id="translatedtitle">Non-contact <span class="hlt">Creep</span> Resistance Measurement for Ultra-high temperature 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">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 <span class="hlt">creep</span> properties very important. <span class="hlt">Creep</span> 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 <span class="hlt">creep</span> 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 <span class="hlt">creep</span> <span class="hlt">deformation</span> 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 <span class="hlt">creep</span> <span class="hlt">deformation</span>. <span class="hlt">Creep</span> 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.</p> <div class="credits"> <p class="dwt_author">Hyers, Robert W.; Lee, Jonghuyn; Bradshaw, Richard C.; Rogers, Jan; Rathz, Thomas J.; Wall, James J.; Choo, Hahn; Liaw, Peter K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2005-01-01</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://ntrs.nasa.gov/search.jsp?R=19890000460&hterms=piecewise&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3D%2522piecewise%2522"> <span id="translatedtitle">Piecewise-Linear Computation Of <span class="hlt">Creep</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">Theory of elastic and inelastic stresses and strains in isotropic materials blended with finite-element computer programs to calculate residual stresses due to <span class="hlt">creep</span> in structures. Analogy drawn between thermal expansion and <span class="hlt">creep</span>, enabling use of thermal-stress computational approach to calculate <span class="hlt">creep</span> stresses and strains. Overall transient solution obtained by piecewise-linear iterations. <span class="hlt">Creep</span> stresses in structure computed in iterative process in which cumulative <span class="hlt">creep</span> strains treated as fictitious changes in coefficients of thermal expansion.</p> <div class="credits"> <p class="dwt_author">Jenkins, Jerald</p> <p class="dwt_publisher"></p> <p class="publishDate">1989-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_16");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" 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<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 style="font-weight: bold;">18</a> <a onClick='return showDiv("page_19");' href="#">19</a> <a onClick='return showDiv("page_20");' href="#">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_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://academic.research.microsoft.com/Publication/40785036"> <span id="translatedtitle">Diffusion-controlled dislocation <span class="hlt">creep</span>: a defense</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 defense is made to the criticisms of Poirier against diffusion-controlled dislocation <span class="hlt">creep</span>. The criticism that values of the activation volumes of <span class="hlt">creep</span> offer no strong support to diffusion-controlled dislocation <span class="hlt">creep</span> is turned around and is shown to be strong evidence against non-diffusion-controlled dislocation <span class="hlt">creep</span>. It is shown that, just as in very fine grain material Coble <span class="hlt">creep</span> takes over</p> <div class="credits"> <p class="dwt_author">O. D. Sherby; J. Weertman</p> <p class="dwt_publisher"></p> <p class="publishDate">1979-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">342</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5093930"> <span id="translatedtitle">Extending the theory of <span class="hlt">creep</span> to viscoplasticity</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 viscoplastic theory is developed that reduces to <span class="hlt">creep</span> theory analytically under steady-state conditions. A fairly simple model is constructed from this theoretical framework by defining material functions that have close ties to the physics of inelasticity; consequently, the model is characterized easily. The computational <span class="hlt">characteristics</span> of the model are enhanced, in general, by converting the kinetics equation from a hyperbolic relationship to a power-law relationship. The resulting model is applied to copper and to the copper alloy, NARloy Z.</p> <div class="credits"> <p class="dwt_author">Freed, A.D.; Verrilli, M.J. (National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center); Walker, K.P. (Engineering Science Software, Inc., Smithfield, RI (United States))</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">343</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/41026229"> <span id="translatedtitle">A high temperature <span class="hlt">deformation</span> mechanism map for the high performance Ni-base superalloy GTD-111</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">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 <span class="hlt">creep</span> resistance. It is believed that several <span class="hlt">creep</span> <span class="hlt">deformation</span> mechanisms operate at various combinations of temperature and stress. The regions of the controlling mechanisms can be described in terms of a</p> <div class="credits"> <p class="dwt_author">S. A. Sajjadi; S. Nategh</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">344</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/5967011"> <span id="translatedtitle">On the response of rockglacier <span class="hlt">creep</span> to surface temperature increase</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">Besides its thermal <span class="hlt">characteristics</span> <span class="hlt">creeping</span> 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</p> <div class="credits"> <p class="dwt_author">Andreas Kääb; Regula Frauenfelder; Isabelle Roer</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">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.port.ac.uk/departments/academic/mde/research/RAEPublicationsHide/filetodownload,61588,en.pdf"> <span id="translatedtitle">Microphase separation, stress relaxation, and <span class="hlt">creep</span> behavior of polyurethane nanocomposites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The stress relaxation and <span class="hlt">creep</span> behavior of blank polyurethane (PU) and PU\\/clay nanocomposites were investigated. The relaxation time spectrum and re- tardant time spectrum were derived according to the gen- eralized Maxwell model and Voigt model with a Tikhonov regularization method, respectively. The <span class="hlt">characteristic</span> relaxation time was identified with the corresponding relaxation process. At a small strain, the relaxation was</p> <div class="credits"> <p class="dwt_author">Hesheng Xia; Mo Song; Zhongyi Zhang; Mel Richardson</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">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.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3388749"> <span id="translatedtitle">Mechanical Interferometry Imaging for <span class="hlt">Creep</span> Modeling of the Cornea</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">Purpose. A novel nanoindentation technique was used to biomechanically characterize each of three main layers of the cornea by using Hertzian viscoelastic formulation of <span class="hlt">creep</span>, the <span class="hlt">deformation</span> resulting from sustained-force application. Methods. The nanoindentation method known as mechanical interferometry imaging (MII) with <1-nm displacement precision was used to observe indentation of bovine corneal epithelium, endothelium, and stroma by a spherical ferrous probe in a calibrated magnetic field. For each specimen, <span class="hlt">creep</span> testing was performed using two different forces for 200 seconds. Measurements for single force were used to build a quantitative Hertzian model that was then used to predict <span class="hlt">creep</span> behavior for another imposed force. Results. For all three layers, displacement measurements were highly repeatable and were well predicted by Hertzian models. Although short- and long-term stiffnesses of the endothelium were highest of the three layers at 339.2 and 20.2 kPa, respectively, both stromal stiffnesses were lowest at 100.4 and 3.6 kPa, respectively. Stiffnesses for the epithelium were intermediate at 264.6 and 12.2 kPa, respectively. Conclusions. Precise, repeatable measurements of corneal <span class="hlt">creep</span> behavior can be conveniently obtained using MII at mechanical scale as small as one cell thickness. When interpreted in analytical context of Hertzian viscoelasticity, MII technique proved to be a powerful tool for biomechanical characterization of time-dependent biomechanics of corneal regions.</p> <div class="credits"> <p class="dwt_author">Yoo, Lawrence; Reed, Jason; Gimzewski, James K.</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">347</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=19870008684&hterms=Fatigue+Testing+Piping+Components&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DFatigue%2BTesting%2BPiping%2BComponents"> <span id="translatedtitle"><span class="hlt">Creep</span> fatigue life prediction for engine hot section materials (isotropic)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The first two years of a two-phase program aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components are discussed. In Phase 1 (baseline) effort, low cycle fatigue (LCF) models, using a data base generated for a cast nickel base gas turbine hot section alloy (B1900+Hf), were evaluated for their ability to predict the crack initiation life for relevant <span class="hlt">creep</span>-fatigue loading conditions and to define data required for determination of model constants. The variables included strain range and rate, mean strain, strain hold times and temperature. None of the models predicted all of the life trends within reasonable data requirements. A Cycle Damage Accumulation (CDA) was therefore developed which follows an exhaustion of material ductility approach. Material ductility is estimated based on observed similarities of <span class="hlt">deformation</span> structure between fatigue, tensile and <span class="hlt">creep</span> tests. The cycle damage function is based on total strain range, maximum stress and stress amplitude and includes both time independent and time dependent components. The CDA model accurately predicts all of the trends in <span class="hlt">creep</span>-fatigue life with loading conditions. In addition, all of the CDA model constants are determinable from rapid cycle, fully reversed fatigue tests and monotonic tensile and/or <span class="hlt">creep</span> data.</p> <div class="credits"> <p class="dwt_author">Moreno, Vito; Nissley, David; Lin, Li-Sen Jim</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">348</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://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 temperature 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 odd" lang="en"> <div class="resultNumber element">349</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/12867976"> <span id="translatedtitle"><span class="hlt">Creep</span>-strengthening of steel at high temperatures using nano-sized carbonitride dispersions.</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"><span class="hlt">Creep</span> is a time-dependent mechanism of plastic <span class="hlt">deformation</span>, 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 <span class="hlt">creep</span> at high temperatures, usually by a process called dispersion strengthening, in which fine particles are evenly distributed throughout the matrix. For example, high-temperature <span class="hlt">creep</span>-resistant ferritic steels achieve optimal <span class="hlt">creep</span> 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 <span class="hlt">creep</span>-resistant steels. This improvement in <span class="hlt">creep</span> 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 <span class="hlt">creep</span>-resistant steels and to the economical manufacture of large-scale steel components for high-temperature applications. PMID:12867976</p> <div class="credits"> <p class="dwt_author">Taneike, Masaki; Abe, Fujio; Sawada, Kota</p> <p class="dwt_publisher"></p> <p class="publishDate">2003-07-17</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">350</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2005PhDT.......194L"> <span id="translatedtitle"><span class="hlt">Creep</span> and shrinkage of high performance lightweight concrete: A multi-scale investigation</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 multi-scale investigation aimed to provide new knowledge and understanding of <span class="hlt">creep</span> and shrinkage of high performance lightweight concrete (HPLC) by assessing prestress losses in HPLC prestressed members in a large-scale study; by quantifying the effect of the constituent materials and external conditions on <span class="hlt">creep</span> and shrinkage in a medium-scale study; and by improving the fundamental understanding of <span class="hlt">creep</span> and shrinkage in a small-scale study. <span class="hlt">Creep</span> plus shrinkage prestress losses were between two and eight times lower than those estimated for the design standards and approximately 50% of those measured in similar strength normal weight high performance concrete girders. The lower <span class="hlt">creep</span> and shrinkage exhibited by HPLC was found to be caused by a synergy between the pre-soaked lightweight aggregate and the low water-to-cementitious material ratio matrix. That is, the water contained in the lightweight aggregate contributes to enhance hydration by providing an internal moist curing. The water in the aggregate also contributes to maintain a high internal relative humidity which reduces or eliminates autogenous shrinkage. This higher internal relative humidity also reduces <span class="hlt">creep</span> by preventing load-induced water migration. Finally, lightweight aggregate exhibits a better elastic compatibility with the paste than normal weight aggregate. This improved elastic matching and the enhanced hydration are believed to reduce peak <span class="hlt">deformations</span> at the ITZ which further decreases <span class="hlt">creep</span> and shrinkage.</p> <div class="credits"> <p class="dwt_author">Lopez, Mauricio</p> <p class="dwt_publisher"></p> <p class="publishDate"></p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">351</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2002JNuM..305..209P"> <span id="translatedtitle">Influence of chemical composition, prior <span class="hlt">deformation</span> and prolonged thermal aging on the sensitization <span class="hlt">characteristics</span> of austenitic stainless 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">Sensitization behaviour of austenitic stainless steels are greatly influenced by several metallurgical factors such as chemical composition, degree of prior <span class="hlt">deformation</span>, grain size, aging temperature-time. The need for generation of data on sensitization kinetics for specific composition of stainless steels to take care of the heat to heat variation for the fabrication of critical components is often questioned. An attempt was made in this investigation to understand this aspect by establishing time-temperature-sensitization diagrams, continuous-cooling-sensitization diagrams and critical cooling rate for three sets of AISI 316 stainless steel in which as the wt% of carbon decreases, that of nitrogen increases so as to encompass the normal span of concentration range usually encountered in different heats. A systematic trend is observed in these experimentally determined sensitization data of these typical stainless steels. This would eliminate the need for the independent generation of sensitization data for stainless steel of specified composition which is within the range investigated here. The database reported for these alloys will also help to recommend the limits of critical cooling rate to avoid sensitization during fabrication.</p> <div class="credits"> <p class="dwt_author">Parvathavarthini, N.; Dayal, R. K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-10-01</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://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 temperature dependence of yield stress or CRSS (Critical Resolved Shear Stress) and tension/compression anisotropy of the yield stress of CRSS have been shown by Shah and Duhl, Heredia and Pope, and Miner et al. Tension/compression asymmetry in the yield strength of Ni-based superalloys has been explained in terms of the core width effect. Shah and Duhl observed the tension/compression asymmetry in <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 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://ntrs.nasa.gov/search.jsp?R=19790009840&hterms=EHR+meaningful+analysis&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3DEHR%2Bmeaningful%2Banalysis"> <span id="translatedtitle">The development of methods for the prediction of primary <span class="hlt">creep</span> behavior in metals</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 applicability of a thermodynamic constitutive theory of <span class="hlt">deformation</span> to the prediction of primary <span class="hlt">creep</span> and <span class="hlt">creep</span> strain relaxation behavior in metals is examined. Constitutive equations derived from the theory are subjected to a parametric analysis in order to determine the influence of several parameters on the curve forms generated by the equations. A computer program is developed which enables the solution of a generalized constitutive equation using experimental data as input. Several metals were tested to form a data base of primary <span class="hlt">creep</span> and relaxation behavior. The extent to which these materials conformed to the constitutive equation showed wide variability, with the alloy Ti-6Al-4V exhibiting the most consistent results. Accordingly, most of the analysis is concentrated upon data from that alloy, although <span class="hlt">creep</span> and relaxation data from all the materials tested are presented. Experimental methods are outlined as well as some variations in methods of analysis. Various theoretical and practical implications of the work are discussed.</p> <div class="credits"> <p class="dwt_author">Zerwekh, R. P.</p> <p class="dwt_publisher"></p> <p class="publishDate">1978-01-01</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://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 temperature alloys, Inconel 600, Inconel 625, Inconel X-750, Hastelloy X, Nimonic PE-16, Incoloy 800, and Haynes 25 (HS-25) was examined at 540, 650, 760, and 870 °C. Crack growth rates were analyzed in terms of both linear elastic stress intensity factor and J*-integral parameter. Among the alloys Inconel 600 and Hastelloy X did not show any observable crack growth. Instead, they <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 temperatures and <span class="hlt">deformed</span> continuously at other temperatures. Crack growth rates of the above alloys in terms ofJ* parameter were compared with the growth rates of other alloys published in the literature. Alloys such as Inconel X-750, Alloy 718, and IN-100 show very high growth rates as a result of their sensitivity to an air environment. Based on detailed fracture surface analysis, it is proposed that <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 temperatures. 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 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://www.osti.gov/scitech/biblio/22253218"> <span id="translatedtitle">In situ tensile and <span class="hlt">creep</span> testing of lithiated silicon nanowires</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p class="result-summary">We present experimental results for uniaxial tensile and <span class="hlt">creep</span> testing of fully lithiated silicon nanowires. A reduction in the elastic modulus is observed when silicon nanowires are alloyed with lithium and plastic <span class="hlt">deformation</span> becomes possible when the wires are saturated with lithium. <span class="hlt">Creep</span> testing was performed at fixed force levels above and below the tensile strength of the material. A linear dependence of the strain-rate on the applied stress was evident below the yield stress of the alloy, indicating viscous <span class="hlt">deformation</span> behavior. The observed inverse exponential relationship between wire radius and strain rate below the yield stress indicates that material transport was controlled by diffusion. At stress levels approaching the yield strength of fully lithiated silicon, power-law <span class="hlt">creep</span> appears to govern the strain-rate dependence on stress. These results have direct implications on the cycling conditions, rate-capabilities, and charge capacity of silicon and should prove useful for the design and construction of future silicon-based electrodes.</p> <div class="credits"> <p class="dwt_author">Boles, Steven T.; Kraft, Oliver [Institute for Applied Materials, KIT, 76344 Eggenstein-Leopoldshafen (Germany)] [Institute for Applied Materials, KIT, 76344 Eggenstein-Leopoldshafen (Germany); Thompson, Carl V. [Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts 02139 (United States)] [Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts 02139 (United States); Mönig, Reiner [Institute for Applied Materials, KIT, 76344 Eggenstein-Leopoldshafen (Germany) [Institute for Applied Materials, KIT, 76344 Eggenstein-Leopoldshafen (Germany); Helmholtz Institute Ulm for Electrochemical Energy Storage (HIU), 89069 Ulm (Germany)</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-12-23</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://pubs.usgs.gov/circ/1966/0525/report.pdf"> <span id="translatedtitle">Tectonic <span class="hlt">creep</span> in the Hayward fault zone, California</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">Tectonic <span class="hlt">creep</span> is slight apparently continuous movement along a fault. Evidence of <span class="hlt">creep</span> has been noted at several places within the Hayward fault zone--a zone trending northwestward near the western front of the hills bordering the east side of San Francisco Bay. D. H. Radbruch of the Geological Survey and B. J. Lennert, consulting engineer, confirmed a reported cracking of a culvert under the University of California stadium. F. B. Blanchard and C. L. Laverty of the East Bay Municipal Utility District of Oakland studied cracks in the Claremont water tunnel in Berkeley. M. G. Bonilla of the Geological Survey noted <span class="hlt">deformation</span> of railroad tracks in the Niles district of Fremont. Six sets of tracks have been bent and shifted. L. S. Cluff of Woodward-Clyde-Sherard and Associates and K. V. Steinbrugge of the Pacific Fire Rating Bureau noted that the concrete walls of a warehouse in the Irvington district of Fremont have been bent and broken, and the columns forced out of line. All the <span class="hlt">deformations</span> noted have been right lateral and range from about 2 inches in the Claremont tunnel to about 8 inches on the railroad tracks. Tectonic <span class="hlt">creep</span> almost certainly will continue to damage buildings, tunnels, and other structures that cross the narrow bands of active movement within the Hayward fault zone.</p> <div class="credits"> <p class="dwt_author">Radbruch-Hall, Dorothy H.; Bonilla, M. G.</p> <p class="dwt_publisher"></p> <p class="publishDate">1966-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">357</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008JMEP...17..572E"> <span id="translatedtitle">High-Temperature <span class="hlt">Deformation</span> and Ductility of a Modified 5083 Al 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">The high-temperature <span class="hlt">deformation</span> 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 <span class="hlt">characteristics</span> of this alloy. It was shown that the <span class="hlt">deformation</span> 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 <span class="hlt">deformation</span> 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 <span class="hlt">creep</span> data in terms of threshold stress and using diffusivity of Mg in normalizing the strain rates, revealed two types of <span class="hlt">deformation</span> 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 <span class="hlt">creep</span> 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 <span class="hlt">deformation</span> as a result of high strain-rate sensitivity.</p> <div class="credits"> <p class="dwt_author">El-Danaf, Ehab A.; Almajid, Abdulhakim A.; Soliman, Mahmoud S.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-08-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">358</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013CMT...tmp...36T"> <span id="translatedtitle">A model for high temperature <span class="hlt">creep</span> of single crystal superalloys based on nonlocal damage and viscoplastic material behavior</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 for high temperature <span class="hlt">creep</span> 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 <span class="hlt">creep</span> in a unified way. Plastic <span class="hlt">deformation</span> in superalloys incorporates the evolution of dislocation densities of the different phases present. It results in a time dependence of the <span class="hlt">creep</span> rate in primary and secondary <span class="hlt">creep</span>. Tertiary <span class="hlt">creep</span> 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.</p> <div class="credits"> <p class="dwt_author">Trinh, B. T.; Hackl, K.</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-08-01</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://academic.research.microsoft.com/Publication/42362006"> <span id="translatedtitle">Anisotropic plastic <span class="hlt">deformation</span> of indium antimonide</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">By virtue of the structure, positive and negative dislocations in InSb should have different mobilities. This was demonstrated experimentally by <span class="hlt">creep</span> tests in reverse bending. The S-shaped strain–time curves and their <span class="hlt">characteristic</span> parameters (incubation time ti, stationary <span class="hlt">creep</span> rate ?w) were calculated as functions of stress ? and temperature T using a simple model. It was assumed that dislocation movement</p> <div class="credits"> <p class="dwt_author">E. Peissker; P. Haasen; H. Alexander</p> <p class="dwt_publisher"></p> <p class="publishDate">1962-01-01</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/2014PhSS...56..889S"> <span id="translatedtitle">Spectral and dynamic analysis of plastic instabilities during serrated <span class="hlt">creep</span> of the aluminum-magnesium 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">The force response to the development of a macroscopic plastic <span class="hlt">deformation</span> jump under the conditions of serrated <span class="hlt">creep</span> of the aluminummagnesium alloy 5456 has been studied using spectral and dynamic analysis methods. The flicker-noise structure of the force response indicating the self-organized criticality state has been revealed. It has been found that a short-term state of plastic instability flatter spontaneously appears during the development of the macroscopic <span class="hlt">deformation</span> step.</p> <div class="credits"> <p class="dwt_author">Shibkov, A. A.; Zolotov, A. E.; Zheltov, M. A.; Denisov, A. A.; Gasanov, M. F.</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-05-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_17");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_18");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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 style="font-weight: bold;">19</a> <a onClick='return showDiv("page_20");' href="#">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_20");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">361</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ncbi.nlm.nih.gov/pubmed/19680702"> <span id="translatedtitle"><span class="hlt">Deformation</span>-induced hydrolysis of a degradable polymeric cylindrical annulus.</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">A thermodynamically consistent framework for describing the response of materials undergoing <span class="hlt">deformation</span>-induced degradation is developed and applied to a particular biodegradable polymer system. In the current case, energy is dissipated through the mechanism of hydrolytic degradation and its effects are incorporated in the constitutive model by appropriately stipulating the forms for the rate of dissipation and for the degradation-dependent Helmholtz potential which changes with the extent of the degradation of the material. When degradation does not occur, the response of the material follows the response of a power-law generalized neo-Hookean material that fits the response of the non-degraded poly(L: -lactic acid) under uniaxial extension. We study the inflation and extension of a degrading cylindrical annulus and the influence of the <span class="hlt">deformation</span> on the mechanism of degradation and its consequent mechanical response. Depreciation of mechanical properties due to degradation confers time-dependent <span class="hlt">characteristics</span> to the response of the biodegradable material: the material <span class="hlt">creeps</span> when subjected to constant loads and stresses necessary to keep a fixed <span class="hlt">deformation</span> relax. PMID:19680702</p> <div class="credits"> <p class="dwt_author">Soares, João S; Rajagopal, Kumbakonam R; Moore, James E</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-04-01</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://ntrs.nasa.gov/search.jsp?R=20020038217&hterms=O2O&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3D%2522O2O%2522"> <span id="translatedtitle"><span class="hlt">Creep</span> Behavior of Near-Stoichiometric Polycrystalline Binary NiAl</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">New and published constant load <span class="hlt">creep</span> and constant engineering strain rate data on near-stoichiometric binary NiAl in the intermediate temperature range 700 to 1300 K are reviewed. Both normal and inverse primary <span class="hlt">creep</span> curves are observed depending on stress and temperature. Other <span class="hlt">characteristics</span> relating to <span class="hlt">creep</span> of NiAl involving grain size, stress and temperature dependence are critically examined and discussed. At stresses below 25 MPa and temperatures above 1000 K, a new grain boundary sliding mechanism was observed with n approx. 2, Qc approx. 100 kJ/ mol and a grain size exponent of about 2. It is demonstrated that Coble <span class="hlt">creep</span> and accommodated grain boundary sliding models fail to predict the experimental <span class="hlt">creep</span> rates by several orders of magnitude.</p> <div class="credits"> <p class="dwt_author">Raj, S. V.</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/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 temperatures 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">364</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 1450 °C. Above this temperature, 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">365</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 temperatures 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">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/26463050"> <span id="translatedtitle">Precipitate coarsening-induced plasticity: Low temperature <span class="hlt">creep</span> behaviour of tempered SAE 52100</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">Hardened and tempered SAE 52100 under uniaxial compressive loading <span class="hlt">deforms</span> even at temperatures well below the tempering temperature and compressive loads well below the yield strength. The origin of the observed <span class="hlt">creep</span> 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> <div class="credits"> <p class="dwt_author">P. V. Morra; S. Radelaar; M. Yandouzi; J. Chen; A. J. Böttger</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">367</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.osti.gov/scitech/biblio/5034018"> <span id="translatedtitle">High temperature impression <span class="hlt">creep</span> testing of weldments</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 impression <span class="hlt">creep</span> test technique, a modified hot hardness test in which the time dependence of the indentor displacement correlates directly to <span class="hlt">creep</span> properties, has been utilized to measure the localized <span class="hlt">creep</span> properties across welded joints. High temperature <span class="hlt">creep</span> 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 <span class="hlt">creep</span> resistance of the aluminum weld decreased with position on traversing from the solidified weld metal to the base metal, and the variation in <span class="hlt">creep</span> resistance with position was shown to correlate directly to gradients in microstructure.</p> <div class="credits"> <p class="dwt_author">Gibbs, W.S.; Matlock, D.K.; Olson, D.L.; Wang, S.H.</p> <p class="dwt_publisher"></p> <p class="publishDate">1985-06-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">368</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dx.doi.org/10.1007/BF00879603"> <span id="translatedtitle">Changes in complex resistivity during <span class="hlt">creep</span> in granite</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">A sample of Westerly granite was <span class="hlt">deformed</span> under constant stress conditions: a pore pressure of 5 MPa, a confining pressure of 10 MPa, and an axial load of 170 MPa. Pore volume changes were determined by measuring the volume of pore fluid (0.01 M KClaq) injected into the sample. After 6 days of <span class="hlt">creep</span>, characterized by accelerating volumetric stain, the sample failed along a macroscopic fault. Measurements of complex resistivity over the frequency range 0.001-300 Hz, taken at various times during <span class="hlt">creep</span>, showed a gradual increase in both conductivity and permittivity. When analysed in terms of standard induced polarization (IP) techniques, the changing complex resistivity resulted in systematic changes in such parameters as percent frequency effect and chargeability. These results suggest that it may be possible to monitor the development of dilatancy in the source region of an impending earthquake through standard IP techniques. ?? 1986 Birka??user Verlag.</p> <div class="credits"> <p class="dwt_author">Lockner, D. A.; Byerlee, J. D.</p> <p class="dwt_publisher"></p> <p class="publishDate">1986-01-01</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://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3065521"> <span id="translatedtitle">The Effect of Holding Time on Nanoindentation Measurements of <span class="hlt">Creep</span> in Bone</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p class="result-summary">Viscoelasticity may affect both the elastic and fracture <span class="hlt">characteristics</span> of bone. Nanoindentation can be used to measure the <span class="hlt">creep</span> behavior of bone by fitting the depth vs. time data at constant load to rheological models. However, the <span class="hlt">creep</span> data may be influenced by latent effects arising during the loading phase of indentation. As such, the loading protocol, particularly the holding time, may affect the measured <span class="hlt">creep</span> time constants. To characterize the effect of holding time on the measures, four cortical bone samples were prepared from four bovine femora and subjected to nanoindentation to measure the <span class="hlt">creep</span> behavior. The <span class="hlt">creep</span> time constants were found by fitting the indentation depth vs. time curve to three different rheological models: the standard linear solid, Burgers model, and a two-dashpot Kelvin model. All three models provided good fits to the data, which were relatively insensitive to the initial parameter estimates. The calculated <span class="hlt">creep</span> time constants increased monotonically with increasing holding time for all three models. However, the relative differences between measurements within a single osteon, within a single sample, and between samples were maintained for <span class="hlt">creep</span> holding times over 16 s. Hence, while the <span class="hlt">creep</span> time constants measured by nanoindentation with hold times up to 30 s may not provide accurate property measurements, comparisons between samples are valid if all are assessed at the same holding time. Considering the long-term viscosity of bone tissue, Burgers model provided the best performance in terms of stability and goodness of fit, and is recommended for future studies.</p> <div class="credits"> <p class="dwt_author">Wu, Ziheng; Baker, Tyler A.; Ovaert, Timothy C.; Niebur, Glen L</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">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/1998PhDT.......326C"> <span id="translatedtitle">Time-dependent <span class="hlt">deformation</span> in unconsolidated reservoir sands</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 dissertation discusses observations, implications, and micromechanical mechanisms of time-dependent <span class="hlt">deformation</span> in dry reservoir sands from the Wilmington Field, Long Beach, California, and the South Eugene Island Field, Gulf of Mexico, with grain sizes between 10 to 300 mum under elevated pressures. Experimental results obtained in a triaxial loading system at confining pressures of 20-30 MPa and axial stresses of 40 MPa provide evidence of viscoelasticity as indicated by time-dependent <span class="hlt">deformation</span> and ultrasonic pulse transmission data. <span class="hlt">Creep</span> strain data suggests that dry sand <span class="hlt">deformed</span> under high pressures has a fundamental <span class="hlt">creep</span> and relaxation time constant. These results may provide a mechanism that explains <span class="hlt">creep</span>, dispersion, and low differential stress observed in unconsolidated reservoir rocks. The combination of <span class="hlt">creep</span> and relaxation implies that the dry rock matrix is viscoelastic which may result in dispersion even in the absence of pore fluids. The viscoelasticity of the dry sand matrix adds an additional relaxation time constant besides those associated with pore fluid motion thus complicating previous descriptions of frequency dependent moduli. Control groups of Ottawa sand mixed with small amounts of Montmorillonite clay suggest that the phenomena is controlled by the <span class="hlt">deformation</span> of intergranular clay and not the <span class="hlt">deformation</span> of quartz grains. <span class="hlt">Creep</span> tests on synthetic idealized "two grain" models could replicate the <span class="hlt">creep</span> strain observed in the sands with equal volume fractions of Montmorillonite clay indicating clay's role in the overall matrix rheology. It appears that microporosity reduction in the clays allows the quartz sand matrix to viscously rearrange its grains hence leading to time-dependent <span class="hlt">deformation</span>.</p> <div class="credits"> <p class="dwt_author">Chang, Carl Tingyu</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">371</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 temperatures (650°C to 850°C) 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 704°C/24 hr. or 871°C/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 704°C/862 MPa and produced a slight dependence of the tensile properties of PWA 1480 on aging heat treatment temperature. For all test temperatures, the high temperature 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 temperature. 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 704°C, but significantly shorter at 760°C and 815°C. PWA 1480+Re, however, displayed the longest lifetime of all three alloys at both 704°C and 815°C (PWA 1480+Re was not tested at 760°C). 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 " 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://ntrs.nasa.gov/search.jsp?R=20100039318&hterms=Second+Life+environment&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3DSecond%2BLife%25C2%25AE%2Benvironment"> <span id="translatedtitle">Experimental <span class="hlt">Creep</span> Life Assessment for the Advanced Stirling Convertor Heater Head</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">The United States Department of Energy is planning to develop the Advanced Stirling Radioisotope Generator (ASRG) for the National Aeronautics and Space Administration (NASA) for potential use on future space missions. The ASRG provides substantial efficiency and specific power improvements over radioisotope power systems of heritage designs. The ASRG would use General Purpose Heat Source modules as energy sources and the free-piston Advanced Stirling Convertor (ASC) to convert heat into electrical energy. Lockheed Martin Corporation of Valley Forge, Pennsylvania, is integrating the ASRG systems, and Sunpower, Inc., of Athens, Ohio, is designing and building the ASC. NASA Glenn Research Center of Cleveland, Ohio, manages the Sunpower contract and provides technology development in several areas for the ASC. One area is reliability assessment for the ASC heater head, a critical pressure vessel within which heat is converted into mechanical oscillation of a displacer piston. For high system efficiency, the ASC heater head operates at very high temperature (850 C) and therefore is fabricated from an advanced heat-resistant nickel-based superalloy Microcast MarM-247. Since use of MarM-247 in a thin-walled pressure vessel is atypical, much effort is required to assure that the system will operate reliably for its design life of 17 years. One life-limiting structural response for this application is <span class="hlt">creep</span>; <span class="hlt">creep</span> <span class="hlt">deformation</span> is the accumulation of time-dependent inelastic strain under sustained loading over time. If allowed to progress, the <span class="hlt">deformation</span> eventually results in <span class="hlt">creep</span> rupture. Since <span class="hlt">creep</span> material properties are not available in the open literature, a detailed <span class="hlt">creep</span> life assessment of the ASC heater head effort is underway. This paper presents an overview of that <span class="hlt">creep</span> life assessment approach, including the reliability-based <span class="hlt">creep</span> criteria developed from coupon testing, and the associated heater head deterministic and probabilistic analyses. The approach also includes direct benchmark experimental <span class="hlt">creep</span> assessment. This element provides high-fidelity <span class="hlt">creep</span> testing of prototypical heater head test articles to investigate the relevant material issues and multiaxial stress state. Benchmark testing provides required data to evaluate the complex life assessment methodology and to validate that analysis. Results from current benchmark heater head tests and newly developed experimental methods are presented. In the concluding remarks, the test results are shown to compare favorably with the <span class="hlt">creep</span> strain predictions and are the first experimental evidence for a robust ASC heater head <span class="hlt">creep</span> life.</p> <div class="credits"> <p class="dwt_author">Krause, David L.; Kalluri, Sreeramesh; Shah, Ashwin R.; Korovaichuk, Igor</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">373</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/26466000"> <span id="translatedtitle"><span class="hlt">Creep</span> damage in small punch <span class="hlt">creep</span> specimens of Type 304 stainless 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">Small punch <span class="hlt">creep</span> tests on Type 304 stainless steel have been performed at 650°C. Based on these tests, a finite element model, with modified Kachanov–Rabotnov <span class="hlt">creep</span> damage constitutive equations, was established. The variation of central deflection and <span class="hlt">creep</span> strain with time and the evolution of <span class="hlt">creep</span> damage under constant loads were analysed by using the finite element model. The central</p> <div class="credits"> <p class="dwt_author">Xiang Ling; Yangyan Zheng; Yingjun You; Yuxin Chen</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">374</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/54667313"> <span id="translatedtitle">Experimental and Numerical Studies on Mudstone's <span class="hlt">Creep</span> Behavior During Water Injection and Its Effect on Casing 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">During the process of water injection production in oilfield, when water cuts into the mudstone, as a result, large numbers of casings are damaged because of mudstone's <span class="hlt">creep</span> <span class="hlt">characteristic</span>. In order to analyze this phenomenon, the uniaxial compression experiments and <span class="hlt">creep</span> experiments of mudstone from Daqing Oil Field under different saturation conditions were done, it was studied that how the</p> <div class="credits"> <p class="dwt_author">X. L. Huang; C. H. Yang; J. J. Liu; X. He; J. Xiong</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">375</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/6828684"> <span id="translatedtitle">High temperature <span class="hlt">deformation</span> in engineering alloys - modelling for strain or load control</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 generalized constitutive description of <span class="hlt">deformation</span> of engineering alloys that exhibit a dominant tertiary <span class="hlt">creep</span> is presented that extends a previous treatment of <span class="hlt">creep</span> <span class="hlt">deformation</span>. The model parameters of the constitutive equations that are determined by analysis of <span class="hlt">creep</span> 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.</p> <div class="credits"> <p class="dwt_author">Ghosh, R.N.; Mclean, M. (National Metallurgical Lab., Jamshedpur (India) Imperial College of Science, Technology, and Medicine, London (United Kingdom))</p> <p class="dwt_publisher"></p> <p class="publishDate">1992-11-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">376</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013AGUFM.T33C2647H"> <span id="translatedtitle">Granular and semi-brittle descriptions of slip 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">Crustal <span class="hlt">deformation</span> generates a wide range of <span class="hlt">creep</span> and slip behaviors. Coseismic fault slip, aseismic <span class="hlt">creep</span>, long-term strain transients, and slow-slip events all accommodate a great deal of tectonic strain and cause or contribute to destructive geohazards. Moreover, all have different time scales and exhibit differing degrees of periodicity. The dynamic frictional response of fault surfaces and fault rocks to slip may control a great deal of crustal slip and <span class="hlt">creep</span> behaviors. Such is also the case for effective stress changes through fluid-pressure fluctuation and remote triggering. Yet, few existing friction and effective-stress models address the heterogeneity, range of metamorphic conditions, and range of <span class="hlt">deformational</span> time scales that characterize natural shear zones. A useful framework for addressing this geological diversity is to treat natural shear zones as granular media. Physical experiments using analog materials provide some insight into such an approach. Shear zones of dry, granular materials produce stick-slip events via jamming phenomena, including influencing the periodicity and duration of events. When added to such granular mixtures, viscous materials enhance localization and smooth stick-slip events. Though such experimental approaches are difficult to simulate numerically, analytical and numerical solutions for fracture propagation into semi-brittle media can produce strain transients with a wide range of durations and recurrence intervals. A good example of how to use these concepts is in the characterization of possible slip behaviors for now-exhumed mid-crustal shear zones. Such shear zones tend to have <span class="hlt">deformed</span> via predominantly viscous crystal plastic mechanisms, yet their <span class="hlt">creep</span> behavior may well have produced strain transients including episodic tremor and slip. Fracture propagation into <span class="hlt">creeping</span> media comprising mixtures of strong and weak materials could explain the generation of such phenomena. Geological observations of strong mafic lenses within weaker quartz-rich gneiss, cut by syntectonic quartz veins, are widely observed structural records of such behavior. Extending this analysis into the upper crust, however, will require a more complete framework for describing the strength of granular materials in the crust.</p> <div class="credits"> <p class="dwt_author">Hayman, N. W.; Lavier, L. L.</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">377</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/145986"> <span id="translatedtitle"><span class="hlt">Deformable</span> models</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">.38>. Original modelFFD-example6FFD-example. ExampleFFD-example7<span class="hlt">Deformation</span> of articulatedstructures. <span class="hlt">Deform</span> FFD patches attached to the skeleton<span class="hlt">Deformation</span> of articulatedstructures. Define ad-hoc laws. EX: muscle8Extended FFD. Noncubic patches. Cubic parametrizationExtendedFFDexample9Animating <span class="hlt">deformation</span>Factor curves. Interpolating a transform over space andtime. Ex: ) ( ) (0t f w f t w q q =10Human face animation. Geometric model. Skin...</p> <div class="credits"> <p class="dwt_author">Demetri Terzopoulos; Kurt W. Fleischer</p> <p class="dwt_publisher"></p> <p class="publishDate">1988-01-01</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://ntrs.nasa.gov/search.jsp?R=19810062007&hterms=norton+bailey&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dnorton%2Bbailey"> <span id="translatedtitle">Temperature-dependent <span class="hlt">creep</span> buckling of plates</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 lateral deflection of flat rectangular plates is predicted by the Norton-Bailey (Norton 1929, Bailey 1935) power law for material <span class="hlt">creep</span>. The plates have a through-thickness steady-state temperature distribution, and the effects are considered by using Maxwell's law to modify the power <span class="hlt">creep</span> law. Equations are derived for <span class="hlt">creep</span> exponents of 3 and 5, using the sandwich plate element to predict <span class="hlt">creep</span> buckling of plates. Predictions of <span class="hlt">creep</span> buckling with a temperature variation between the inner and outer plate surfaces are found to be somewhat dependent on the <span class="hlt">creep</span> buckling relationship assumed. When significant scatter justifies a variation in the <span class="hlt">creep</span> 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 <span class="hlt">creep</span> laws.</p> <div class="credits"> <p class="dwt_author">Ross, D. A.; Berke, L.</p> <p class="dwt_publisher"></p> <p class="publishDate">1981-01-01</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://ntrs.nasa.gov/search.jsp?R=20100033127&hterms=creep&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3D%2522creep%2522"> <span id="translatedtitle">Improved <span class="hlt">Creep</span> Measurements for Ultra-High Temperature 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">Our team has developed a novel approach to measuring <span class="hlt">creep</span> 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 <span class="hlt">deform</span>. The <span class="hlt">deformation</span> of the sample is captured on high-speed video, which is analyzed by machine-vision software from the University of Massachusetts. The <span class="hlt">deformations</span> are compared to finite element models to determine the constitutive constants in the <span class="hlt">creep</span> relation. Furthermore, the non-contact method exploits stress gradients within the sample to determine the stress exponent in a single test.</p> <div class="credits"> <p class="dwt_author">Hyers, Robert W.; Ye, X.; Rogers, Jan R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">380</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://ntrs.nasa.gov/search.jsp?R=20090028680&hterms=contact&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dcontact"> <span id="translatedtitle">Advances in Non-contact Measurement of <span class="hlt">Creep</span> Properties</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p class="result-summary">Our team has developed a novel approach to measuring <span class="hlt">creep</span> at extremely high temperatures using electrostatic levitation (ESL). This method has been demonstrated on niobium up to 2300 C, while ESL has melted tungsten (3400 C). High-precision machined spheres of the sample are levitated in the NASA MSFC ESL, a national user facility, and heated with a laser. The laser is aligned off-center so that the absorbed photons transfer their momentum to the sample, causing it to rotate at up to 250,000+ RPM. The rapid rotation loads the sample through centripetal acceleration, causing it to <span class="hlt">deform</span>. The <span class="hlt">deformation</span> of the sample is captured on high-speed video, which is analyzed by machine-vision software from the University of Massachusetts. The <span class="hlt">deformations</span> are compared to finite element models to determine the constitutive constants in the <span class="hlt">creep</span> relation. Furthermore, the noncontact method exploits stress gradients within the sample to determine the stress exponent in a single test. This method was validated in collaboration with the University of Tennessee for niobium at 1985 C, with agreement within the uncertainty of the conventional measurements. A similar method is being employed on Ultra-High-Temperature ZrB2- SiC composites, which may see application in rocket nozzles and sharp leading edges for hypersonic vehicles.</p> <div class="credits"> <p class="dwt_author">Hyers, Robert W.; Canepari, Stacy; Rogers, Jan. R.</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-01-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_18");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous Page" /></a> <span id="PageLinks" class="pageLinks"> <span> <a onClick='return showDiv("page_1");' href="#">1</a> <a onClick='return showDiv("page_2");' href="#">2</a> <a onClick='return showDiv("page_3");' href="#">3</a> <a onClick='return showDiv("page_4");' 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onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">381</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.springerlink.com/index/21rlylnl0thyl7hk.pdf"> <span id="translatedtitle">Transient moisture effects on wood <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">To gain insight into the physical nature of the coupling between mechanical stress and humidity variations, the behaviour\\u000a of thin wood strips was studied using specially developed apparatus for <span class="hlt">creep</span>\\/recovery and relaxation\\/blotting-out tests in\\u000a a controlled humidity environment. The load time and the rate of viscoelastic <span class="hlt">creep</span> were found to have little influence on\\u000a mechano-sorptive <span class="hlt">creep</span>. Moreover, <span class="hlt">creep</span> trajectory curves</p> <div class="credits"> <p class="dwt_author">P. Navi; V. Pittet; C. J. G. Plummer</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">382</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/10.1046/j.1365-246X.2002.01628.x"> <span id="translatedtitle">Seismic anisotropy and mantle <span class="hlt">creep</span> in young orogens</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">Seismic anisotropy provides evidence for the physical state and tectonic evolution of the lithosphere. We discuss the origin of anisotropy at various depths, and relate it to tectonic stress, geotherms and rheology. The anisotropy of the uppermost mantle is controlled by the orthorhombic mineral olivine, and may result from ductile <span class="hlt">deformation</span>, dynamic recrystallization or annealing. Anisotropy beneath young orogens has been measured for the seismic phase Pn that propagates in the uppermost mantle. This anisotropy is interpreted as being caused by <span class="hlt">deformation</span> during the most recent thermotectonic event, and thus provides information on the process of mountain building. Whereas tectonic stress and many structural features in the upper crust are usually orientated perpendicular to the structural axis of mountain belts, Pn anisotropy is aligned parallel to the structural axis. We interpret this to indicate mountain-parallel ductile (i.e. <span class="hlt">creeping</span>) <span class="hlt">deformation</span> in the uppermost mantle that is a consequence of mountain-perpendicular compressive stresses. The preferred orientation of the fast axes of some anisotropic minerals, such as olivine, is known to be in the <span class="hlt">creep</span> direction, a consequence of the anisotropy of strength and viscosity of orientated minerals. In order to explain the anisotropy of the mantle beneath young orogens we extend the concept of crustal 'escape' (or 'extrusion') tectonics to the uppermost mantle. We present rheological model calculations to support this hypothesis. Mountain-perpendicular horizontal stress (determined in the upper crust) and mountain-parallel seismic anisotropy (in the uppermost mantle) require a zone of ductile decoupling in the middle or lower crust of young mountain belts. Examples for stress and mountain-parallel Pn anisotropy are given for Tibet, the Alpine chains, and young mountain ranges in the Americas. Finally, we suggest a simple model for initiating mountain parallel <span class="hlt">creep</span>.</p> <div class="credits"> <p class="dwt_author">Meissner, R.; Mooney, W. D.; Artemieva, I.</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">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.ncbi.nlm.nih.gov/pubmed/20092098"> <span id="translatedtitle"><span class="hlt">Deformation</span> mechanisms and impact attenuation <span class="hlt">characteristics</span> of thin-walled collapsible air chambers used in head protection.</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">Head injuries are a major cause of morbidity and mortality worldwide, many resulting from sporting activities. There is a constant need in the head protection industry for improved methods to manage impacts and to reduce the risk of mild and severe head injuries. Contemporary head protection primarily consists of foam with several inherent disadvantages, including a limited ability to provide effective energy absorption under both low and high impact velocities. Recently, thin-walled collapsible chambers were engineered to address this problem and have been implemented into sport helmets. The chambers consist of four engineering elements which define their dynamic performance: geometry, air volume, material, and venting system. This research analysed the contribution of air flow through an orifice to the chamber's management of impact energy. The objective of this study was to determine the effect of the chamber's vent diameter and material stiffness on peak force and venting rate during an impact. Two material stiffnesses (thermoplastic polyurethane 45D and thermoplastic polyurethane 90A) and five vent diameters (1 mm, 2 mm, 3 mm, 4 mm, and 5 mm) were tested at three inbound velocities (1.3 m/s, 2.3 m/s, and 3.0 m/s). Each chamber was impacted ten times using a monorail drop system. Analysis of the results revealed that the material stiffness, vent diameter, and inbound velocity all had a significant effect on peak force and venting rate (p < 0.001). Under low inbound velocities the largest vent diameters transmitted a lower force than the smallest vent, while this relationship reversed at high inbound velocities. Under low velocities the air flowrate was negatively correlated and the flow duration was positively correlated to the peak force. Under high velocities, the air flowrate was positively correlated and the duration was negatively correlated to the peak force. This suggested that, under low velocities, chambers performed optimally when air was dissipated quickly, for a short duration; however, as the chamber approached a critical failure region, the increased duration and decreased velocity of air released prevented higher peak forces. This research confirmed that the differences in vent diameter and material stiffness significantly affected the impact force <span class="hlt">characteristics</span> of engineered thin-walled collapsible chambers. PMID:20092098</p> <div class="credits"> <p class="dwt_author">Lamb, L; Hoshizaki, T B</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-11-01</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/2012CoMP..163..403B"> <span id="translatedtitle">Brittle-plastic <span class="hlt">deformation</span> in initially dry rocks at fluid-present conditions: transient behaviour of feldspar at mid-crustal levels</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 present detailed microstructural and chemical analyses from an initially dry anorthositic rock <span class="hlt">deformed</span> during wet amphibolite facies conditions. Three different domains representing the microstructural variation of the <span class="hlt">deformed</span> samples are investigated in detail in terms of fracture morphology and mode, grain <span class="hlt">characteristics</span> and chemistry of present phases. Results show transient <span class="hlt">deformational</span> behaviour where a close interaction between brittle, plastic and fluid-assisted <span class="hlt">deformation</span> mechanisms can be observed. Our analysis allows us to describe the succession, interrelationships and effects of active mechanisms with progressively increasing strain in three so-called stages. In Stage 1, initial fracturing along cleavage planes promoted fluid influx that caused fragmentation and chemical reactions, producing fine-grained mineral assemblages in the fractures. <span class="hlt">Deformation</span> twins and dislocations developed in clast pieces due to stress relaxation. Passive rotation of conjugate fracture sets and interconnection of intracrystalline fractures formed micro-shear-zones, constituting S tage 2. Microstructures and grain relationships indicate the activity and fluctuation between fracturing, dissolution-precipitation <span class="hlt">creep</span>, grain boundary sliding and locally dislocation <span class="hlt">creep</span>, reflecting the transient behaviour of brittle and plastic <span class="hlt">deformation</span> mechanisms. Further rotation and widening of fractures into overall foliation parallel shear-bands ( Stage 3) promoted strain partitioning into these areas through increased fluid influx, influence of fluid-assisted grain boundary sliding, phase mixing and presence of weak phases such as white mica. We suggest that local differences in fluid availability, volume fraction of weak phases produced by fluid present metamorphic reactions coupled with volume increase and local variations in stress concentration induced transient brittle-plastic behaviour. The studied shear-zone represents an example of the transformation of a rigid dry rock to a soft wet rock during <span class="hlt">deformation</span> through syntectonic fracturing.</p> <div class="credits"> <p class="dwt_author">Brander, Linus; Svahnberg, Henrik; Piazolo, Sandra</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-03-01</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.osti.gov/scitech/biblio/136977"> <span id="translatedtitle"><span class="hlt">Creep</span> and intergranular cracking behavior of nickel-chromium-iron-carbon alloys in 360 C water</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">Mechanical testing of controlled-purity Ni-x% Cr-9% Fe-y% C alloys at 360 C revealed an environmental enhancement in intergranular (IG) cracking and time-dependent <span class="hlt">deformation</span> in high-purity (HP) and primary water (PW) over that exhibited in argon. Dimples on the IG facets indicated a <span class="hlt">creep</span> void nucleation and growth failure mode. IG cracking was located primarily in the interior of the specimen and was not necessarily linked to the environment. Controlled-potential constant extension rate tensile (CERT) experiments showed increases in IG cracking as the applied potential decreased, suggesting that hydrogen was detrimental to the mechanical properties. It was proposed that the environment, through the presence of hydrogen, enhanced IG cracking by enhancing the matrix dislocation mobility. This conclusion was based on observations that dislocation <span class="hlt">creep</span> controlled IG cracking of controlled-purity Ni-x% Cr-9% Fe-y% C in argon at 360 C. Grain-boundary cavitation (GBC) and sliding (GBS) results showed environmental enhancement of the <span class="hlt">creep</span> rate primarily resulted from an increase in matrix plastic <span class="hlt">deformation</span>. However, controlled-potential constant load tensile (CLT) experiments did not indicate a change in the <span class="hlt">creep</span> rate as the applied potential decreased. While this result did not support hydrogen-assisted <span class="hlt">creep</span>, the material already may have been saturated with hydrogen at these applied potentials, and thus, no effect was realized. Chromium and carbon decreased IG cracking in HP and PW by increasing the <span class="hlt">creep</span> resistance. The surface film did not play a significant role in the <span class="hlt">creep</span> or IG cracking behavior under the conditions investigated.</p> <div class="credits"> <p class="dwt_author">Angeliu, T.M.; Paraventi, D.J.; Was, G.S. [Univ. of Michigan, Ann Arbor, MI (United States)</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">386</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 temperature of solid oxide fuel cells require that sealant must function at high temperature between 600o and 900oC and in the oxidizing and reducing environments of fuel and air. It should be noted that <span class="hlt">creep</span> <span class="hlt">deformation</span> becomes relevant for a material when the operating temperature is near or exceeds half of its melting temperature (in degrees of Kelvin). The operating temperatures for most of the solid oxide fuel cells (SOFC) under development in the SECA program are around 800oC, which exceeds the glass transition temperature Tg for most glass ceramic materials. The goal of the study is to develop a <span class="hlt">creep</span> model to capture the <span class="hlt">creep</span> behavior of glass ceramic materials at high temperature 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">387</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/24211356"> <span id="translatedtitle">Characterization of load dependent <span class="hlt">creep</span> behavior in medically relevant absorbable polymers.</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">While synthetic absorbable polymers have a substantial history of use in medical devices, their use is expanding and becoming more prevalent for devices where long term loading and structural support is required. In addition, there is evidence that current absorbable medical devices may experience permanent <span class="hlt">deformations</span>, warping (out of plane twisting), and geometric changes in vivo. For clinical indications with long term loading or structural support requirements, understanding the material's viscoelastic properties becomes increasingly important whereas these properties have not been used historically as preclinical indications of performance or design considerations. In this study we measured the static <span class="hlt">creep</span>, <span class="hlt">creep</span> recovery and cyclic <span class="hlt">creep</span> responses of common medically relevant absorbable materials (i.e., poly(l-lactide, PLLA) and poly(l-co-glycolide, PLGA) over a range of physiologically relevant loading magnitudes. The results indicate that both PLLA and PLGA exhibit <span class="hlt">creep</span> behavior and failure at loads significantly less than the yield or ultimate properties of the material and that significant material specific responses to loading exist. In addition, we identified a strong correlation between the extent of <span class="hlt">creep</span> in the material and its crystallinity. Results of the study provide new information on the <span class="hlt">creep</span> behavior of PLLA and PLGA and support the use of viscoelastic properties of absorbable polymers as part of the material selection process. PMID:24211356</p> <div class="credits"> <p class="dwt_author">Dreher, Maureen L; Nagaraja, Srinidhi; Bui, Hieu; Hong, Danny</p> <p class="dwt_publisher"></p> <p class="publishDate">2014-01-01</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://adsabs.harvard.edu/abs/2013JGRB..118.1733S"> <span id="translatedtitle">Time-dependent model of <span class="hlt">creep</span> on the Hayward fault from joint inversion of 18 years of InSAR and surface <span class="hlt">creep</span> data</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">Spatial and temporal variations of aseismic fault <span class="hlt">creep</span> influence the size and timing of large earthquakes along partially coupled faults. To solve for a time-dependent model of <span class="hlt">creep</span> on the Hayward fault, we invert 18 years of surface <span class="hlt">deformation</span> data (1992-2010), obtained by interferometric processing of 52 and 50 SAR images acquired by the ERS1/2 and Envisat satellites, respectively, and surface <span class="hlt">creep</span> data obtained at 19 alinement and 4 creepmeter stations. For multi-temporal analysis of the SAR data we developed a method for identifying stable pixels using wavelet multi-resolution analysis. We also implement a variety of wavelet-based filters for reducing the effects of environmental artifacts. Using a reweighted least squares approach, we inverted the interferometric data to generate a time series of surface <span class="hlt">deformation</span> over the San Francisco Bay Area with a precision of better than a few millimeters. To jointly invert the InSAR displacement time series and the surface <span class="hlt">creep</span> data for a time-dependent model of fault <span class="hlt">creep</span>, we use a robust inversion approach combined with a Kalman filter. The time-dependent model constrains a zone of high slip deficit that may represent the locked rupture asperity of past and future M?7 earthquakes. We identify several additional temporal variations in <span class="hlt">creep</span> rate along the Hayward fault, the most important one being a zone of accelerating slip just northwest of the major locked zone. We estimate that a slip-rate deficit equivalent to Mw 6.3-6.8 has accumulated on the fault, since the last event in 1868.</p> <div class="credits"> <p class="dwt_author">Shirzaei, M.; Bürgmann, R.</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">389</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/60224444"> <span id="translatedtitle">Mechanisms of damage accumulation in time-dependent cyclic <span class="hlt">deformation</span>. Progress report, January 1, 1981December 31, 1981</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">Problems of cyclic <span class="hlt">creep</span> and time-dependent cyclic <span class="hlt">deformation</span> are being increasingly recognized in machines used for energy conversion and storage, but few studies have been done in exploration of the relevant damage phenomena. Accordingly the proposal called for the parallel study of two kinds of damage produced in cyclic <span class="hlt">creep</span>: (1) change in dislocation density and arrangement, to be studied</p> <div class="credits"> <p class="dwt_author">Laird</p> <p class="dwt_publisher"></p> <p class="publishDate">1981-01-01</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://academic.research.microsoft.com/Publication/60244291"> <span id="translatedtitle">Mechanisms of damage accumulation in time-dependent cyclic <span class="hlt">deformation</span>. Progress report, January 1, 1984December 31, 1984</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">Problems of cyclic <span