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1

Creep deformation characteristics of discontinuously reinforced aluminium-matrix composites  

Microsoft Academic Search

Recent developments in the study of creep behaviour of discontinuously reinforced aluminium-matrix composites (DRAMCs) at elevated temperatures are reviewed in this paper. These include the shapes of the creep curves, the origin and characteristics of the threshold stress, the creep strengthening of the DRAMCs, the nature of the rate-controlling processes, the effect of cyclic stress, and creep rupture. The DRAMCs

Z. Y. Ma; S. C. Tjong

2001-01-01

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

Creep deformation characteristics of tin and tin-based electronic solder alloys  

Microsoft Academic Search

Creep deformation characteristics of pure tin, and Sn-3.5Ag and Sn-5Sb electronic solder alloys, have been studied at various\\u000a temperatures between ambient and 473 K (homologous temperature 0.58 to 0.85). Power-law relationships between strain rate\\u000a and stress were observed at most of the temperatures. The stress exponent (n=7.6, 5.0, and 5.0) and activation energy (Q\\u000a \\u000a c\\u000a =60.3, 60.7, and 44.7 kJ\\/mol)

M. D. Mathew; H. Yang; S. Movva; K. L. Murty

2005-01-01

4

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

5

Creep fracture during solute-drag creep and superplastic deformation  

SciTech Connect

Creep fracture behavior has been studied in Al-Mg and Al-Mg-Mn alloys undergoing solute-drag creep and in microduplex stainless steel undergoing both solute-drag creep and superplastic deformation. Failure in these materials is found to be controlled by two mechanisms, neck formation and cavitation. The mechanism of creep fracture during solute-drag creep in Al-Mg is found to change from necking-controlled fracture to cavitation-controlled fracture as Mn content is increased. Binary Al-Mg material fails by neck formation during solute-drag creep, and cavities are formed primarily in the neck region due to high hydrostatic stresses. Ternary alloys of Al-Mg- Mn containing 0.25 and 0.50 wt % Mn exhibit more uniform cavitation, with the 0.50 Mn alloy clearly failing by cavity interlinkage. Failure in the microduplex stainless steel is dominated by neck formation during solute-drag creep deformation but is controlled by cavity growth and interlinkage during superplastic deformation. Cavitation was measured at several strains, and found to increase as an exponential function of strain. An important aspect of cavity growth in the stainless steel is the long latency time before significant cavitation occurs. For a short latency period, cavitation acts to significantly reduce ductility below that allowed by neck growth alone. This effect is most pronounced in materials with a high strain-rate sensitivity, for which neck growth occurs very slowly.

Taleff, E.M.; Lesuer, D.R.; Syn, C.K.; Henshall, G.A.

1996-10-01

6

Spatial fluctuations in transient creep deformation  

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

7

Fluctuations and Scaling in Creep Deformation  

NASA Astrophysics Data System (ADS)

The spatial fluctuations of deformation are studied in the creep in Andrades power law and the logarithmic phases, using paper samples. Measurements by the digital image correlation technique show that the relative strength of the strain rate fluctuations increases with time, in both creep regimes. In the Andrade creep phase characterized by a power-law decay of the strain rate ?tt-?, with ??0.7, the fluctuations obey ??tt-?, with ??0.5. The local deformation follows a data collapse appropriate for a phase transition. Similar behavior is found in a crystal plasticity model, with a jamming or yielding transition.

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

2010-09-01

8

Deformation twinning in a creep-deformed nanolaminate structure  

NASA Astrophysics Data System (ADS)

The underlying mechanism of deformation twinning occurring in a TiAl-(?)/Ti3Al-(?2) nanolaminate creep deformed at elevated temperatures has been studied. Since the multiplication and propagation of lattice dislocations in both ? and ?2 thin lamellae are very limited, the total flow of lattice dislocations becomes insufficient to accommodate the accumulated creep strains. Consequently, the movement of interfacial dislocations along the laminate interfaces, i.e., interface sliding, becomes an alternative deformation mode of the nanolaminate structure. Pile-ups of interfacial dislocations occur when interfacial ledges and impinged lattice dislocations act as obstacles to impede the movement of interfacial dislocations. Deformation twinning can accordingly take place to relieve a stress concentration resulting from the pile-up of interfacial dislocations. An interface-controlled twinning mechanism driven by the pile-up and dissociation of interfacial dislocations is accordingly proposed.

Hsiung, Luke L.

2010-10-01

9

Deformation twinning in a creep-deformed nanolaminate structure.  

PubMed

The underlying mechanism of deformation twinning occurring in a TiAl-(?)/Ti(3)Al-(?(2)) nanolaminate creep deformed at elevated temperatures has been studied. Since the multiplication and propagation of lattice dislocations in both ? and ?(2) thin lamellae are very limited, the total flow of lattice dislocations becomes insufficient to accommodate the accumulated creep strains. Consequently, the movement of interfacial dislocations along the laminate interfaces, i.e., interface sliding, becomes an alternative deformation mode of the nanolaminate structure. Pile-ups of interfacial dislocations occur when interfacial ledges and impinged lattice dislocations act as obstacles to impede the movement of interfacial dislocations. Deformation twinning can accordingly take place to relieve a stress concentration resulting from the pile-up of interfacial dislocations. An interface-controlled twinning mechanism driven by the pile-up and dissociation of interfacial dislocations is accordingly proposed. PMID:21403216

Hsiung, Luke L

2010-08-25

10

Creep deformation of a soft magnetic iron-cobalt alloy  

NASA Astrophysics Data System (ADS)

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

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

1999-04-01

11

Metallographie Observations on Creep Deformation of Magnox AL80  

Microsoft Academic Search

A study, with emphasis on metallographic observations, has been made on the creep deformation of Magnox AL 80 at 250, 300, 350 and 400C.The creep deformation at 250C is quite different from those at 300C and above. With deformation at 250C, grains break clown into cells, that are marked and are smaller in size nearer the grain boundaries. This phenomenon

Ryukichi NAGASAKI; Kensuke SHIRAISHI

1966-01-01

12

Mechanisms of Creep Deformation in Pure Sn Solder Joints  

NASA Astrophysics Data System (ADS)

The work reported here concerns the creep of pure Sn solder joints with Cu metallization (Cu||Sn||Cu). Steady-state creep tests in shear are combined with electron backscatter diffraction (EBSD) analysis of the evolution of the microstructure during creep to clarify the deformation mechanism and the nature of the microstructural evolution. The creep behavior of the joint changes significantly with temperature. At low temperature (65C), two distinct creep mechanisms are observed. Low-stress creep is apparently dominated by grain boundary sliding, as evidenced by the low stress exponent ( n ? 4), low activation energy ( Q ? 42 kJ/mole), and significant grain rotation during creep. High-stress creep is dominated by bulk deformation processes, evidenced by a high stress exponent ( n ? 9), an activation energy like that for bulk diffusion ( Q ? 70 kJ/mole), and a relatively fixed microstructure. At high temperature all aspects of its behavior are consistent with deformation by bulk creep mechanisms; the stress exponent and activation energy are high ( n ? 5 to 7, Q ? 96 kJ/mole), and despite significant grain coarsening, the microstructure retains (and strengthens) a fixed [001] texture. The results suggest that a "segmented" constitutive equation of Dorn type is most suitable for the low-temperature behavior, while a "hyperbolic" constitutive equation may be preferable at high temperature.

Lee, K.-O.; Morris, J. W.; Hua, Fay

2013-03-01

13

Stored Energy in Creep Deformed Graphite  

Microsoft Academic Search

GRAPHITE which has been strained in tensile creep releases a very large amount of stored energy when the creep stress is reduced, as happens in the dip test1. The very large amount of negative creep (actual shrinkage of the specimen while it is still under an appreciable applied tensile force) that takes place after a stress reduction is shown graphically

W. V. Green; E. G. Zukas

1970-01-01

14

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

15

Deformation by grain boundary sliding and slip creep versus diffusional creep  

SciTech Connect

A review is presented of the debates between the present authors and other investigators regarding the possible role of diffusional creep in the plastic flow of polycrystalline metals at low stresses. These debates are recorded in eleven papers over the past seventeen years. ln these papers it has been shown that the creep rates of materials in the so-called ?diffusional creep region? are almost always higher than those predicted by the diffusional creep theory. Additionally, the predictions of grain size effects and stress exponents from diffusional creep theory are often not found in the experimental data. Finally, denuded zones have been universally considered to be direct evidence for diffusional creep; but, those reported in the literature are shown to be found only under conditions where a high stress exponent is observed. Also, the locations of the denuded zones do not match those predicted. Alternative mechanisms are described in which diffusion-controlled dislocation creep and/or grain boundary sliding are the dominant deformation processes in low-stress creep. It is proposed that denuded zones are formed by stress-directed grain boundary migration with the precipitates dissolving in the moving grain boundaries. The above observations have led us to the conclusion that grain boundary sliding and slip creep are in fact the principal mechanisms for observations of plastic flow in the so-called ?diffusional creep regions. ?

Ruano, O A; Sherby, O D; Wadsworth, J

1998-11-04

16

Creep Response and Deformation Processes in Nanocluster Strengthened Ferritic Steels  

SciTech Connect

There is increasing demand for oxide-dispersion-strengthened ferritic alloys that possess both high-temperature strength and irradiation resistance. Improvement of the high-temperature properties requires an understanding of the operative deformation mechanisms. In this study, the microstructures and creep properties of the oxide-dispersion-strengthened alloy 14YWT have been evaluated as a function of annealing at 1000 C for 1 hour up to 32 days. The ultra-fine initial grain size (approx. 100nm) is stable after the shortest annealing time, and even after subsequent creep at 800 C. Longer annealing periods lead to anomalous grain growth that is further enhanced following creep. Remarkably, the minimum creep rate is relatively insensitive to this dramatic grain-coarsening. The creep strength is attributed to highly stable, Ti-rich nanoclusters that appear to pin the initial primary grains, and present strong obstacles to dislocation motion in the large, anomalously grown grains.

Hayashi, Taisuke [Ohio State University; Sarosi, P. M. [Ohio State University; Schneibel, Joachim H [ORNL; Mills, Michael J. [Ohio State University

2008-01-01

17

Creep deformation mechanisms in modified 9Cr-1Mo steel  

NASA Astrophysics Data System (ADS)

Modified 9Cr-1Mo (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). The tensile creep behavior of modified 9Cr-1Mo steel (Grade 91) was studied in the temperature range of 873-1023 K and stresses between 35 MPa and 350 MPa. Analysis of creep results yielded stress exponents of 9-11 in the higher stress regime and 1 in the lower stress regime. The high stress exponent in the power-law creep regime was rationalized by invoking the concept of threshold stress, which represents the lattice diffusion controlled dislocation climb process. Without threshold stress compensation, the activation energy was 510 51 kJ/mol, while after correcting for the threshold stress, the activation energy decreased to 225 24 kJ/mol. This value is close to the activation energy for lattice self-diffusion in ?-Fe. Threshold stress calculations were performed for the high stress regime at all test temperatures. The calculated threshold stress showed a strong dependence on temperature. 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.

Shrestha, Triratna; Basirat, Mehdi; Charit, Indrajit; Potirniche, Gabriel P.; Rink, Karl K.; Sahaym, Uttara

2012-04-01

18

Long-term creep deformation property of modified 9Cr1Mo steel  

Microsoft Academic Search

The first volume of Atlas of Creep Deformation Properties was published on modified 9Cr1Mo steels in March 2007, as a part of the NIMS (National Institute for Materials Science) Creep Data Sheet series. Creep deformation properties up to about 70,000h have been investigated. No clear steady-state creep stage has been observed, and creep deformation of the steel consists of transient

K. Kimura; H. Kushima; K. Sawada

2009-01-01

19

Interfacial Control of Creep Deformation in Ultrafine Lamellar TiAl  

SciTech Connect

Solute effect on the creep resistance of two-phase lamellar TiAl with an ultrafine microstructure creep-deformed in a low-stress (LS) creep regime [where a linear creep behavior was observed] has been investigated. The resulted deformation substructure and in-situ TEM experiment revealed that interface sliding by the motion of pre-existing interfacial dislocations is the predominant deformation mechanism in LS creep regime. Solute segregation at lamellar interfaces and interfacial precipitation caused by the solute segregation result in a beneficial effect on the creep resistance of ultrafine lamellar TiAl in LS creep regime.

Hsiung, L M

2002-11-26

20

Creep deformation of stoichiometric uranium dioxide  

Microsoft Academic Search

The plastic behavior of sintered uranium dioxide of stoichiometric ; composition was studied using a creepin-bending method. The range of temperature ; from 1250 to 1400 deg C and stresses from 700 to 16,000 psi were covered in the ; investigation. Expressions describing the dependence of steady-state creep rates ; on stress and temperature were developed. Materials possessing sintered ;

W. M. Armstrong; W. R. Irvine; R. H. Martinson

1962-01-01

21

Predicting creep deformation of heat-resistant metals  

Microsoft Academic Search

There have been many attempts at describing primary creep curves (from the initial deformation to the point of rupture) by means of analytical equations. If such an aim could be achieved with due allowance for the complicated internal processes taking place in the material, if only for a number of the principal heat-resistant metals used in the manufacture of power

V. I. Kovpak

1975-01-01

22

The transverse creep deformation and failure characteristics of SCS-6/Ti-6AI-4V metal matrix composites at 482 C  

NASA Astrophysics Data System (ADS)

While continuous fiber, unidirectional composites are primarily evaluated for their longitudinal properties, the behavior transverse to the fibers often limits their application. In this study, the tensile and creep behaviors of SCS-6/Ti-6Al-4V composites in the transverse direction at 482 C were evaluated. Creep tests were performed in air and argon environments over the stress range of 103 to 276 MPa. The composite was less creep resistant than the matrix when tested at stress values larger than 150 MPa. Below 150 MPa, the composite was more creep resistant than the unreinforced matrix. Failure of the composite occurred by the ductile propagation of cracks emanating from separated fiber interfaces. The environment in which the test was performed affected the creep behavior. At 103 MPa, the creep rate in argon was 4 times slower than the creep rate in air. The SCS-6 silicon-carbide fibers graphite coating oxidized in the air environment and encouraged the separation of the fiber-matrix interface. However, at higher stress levels, the difference in behavior between air- and argon-tested specimens was small. At these stresses, separation of the interface occurred during the initial loading of the composite and the subsequent degradation of the interface did not affect the creep behavior. Finally, the enrichment of the composites surface by molybdenum during fabrication resulted in an alloyed surface layer that failed in a brittle fashion during specimen elongation. Although this embrittled layer did not appear to degrade the properties of the composite, the existence of a similar layer on a composite with a more brittle matrix might be very detrimental.

Eggleston, M. R.; Ritter, A. M.

1995-10-01

23

Steady-state creep deformation of investment cast near-gamma titanium aluminide  

Microsoft Academic Search

The creep behavior of an investment cast near-gamma alloy Ti-48Al-2Nb-2Cr (at. pct) was investigated by determining the stress dependency and activation energy for steady-state creep deformation of this alloy, using the results of post-test microscopy to characterize the microstructural evolution after creep testing at high temperatures. The results of these examinations suggest that the mechanism of creep deformation in this

D. A. Wheeler; Larsen D. E. JR

1992-01-01

24

High-resolution analytical electron microscopy and creep deformation of silicon nitride ceramics  

NASA Astrophysics Data System (ADS)

The typical microstructure of silicon nitride consists of rigid Si3N4 grains and intergranular amorphous films associated with the liquid phase sintering process involved during densification. The presence of the amorphous films may affect the creep behaviour of silicon nitride ceramics at elevated temperatures. The advent of high resolution transmission electron microscopy (HRTEM) coupled with fine-probe chemistry analysis enables us to investigate the structure and chemical composition of the nano-scale grain boundary amorphous films and the role they play in creep deformation of silicon nitride. The materials investigated consist of beta-Si3N4 grains with and without secondary crystalline phases. All grains were covered with a thin intergranular amorphous film at both homophase and heterophase boundaries. It was found that these amorphous films have a characteristic value of thickness, independent of grain misorientation, but dependent on the chemical composition of the film and the grains on either side of the film. The creep behaviour of the materials were evaluated by compressive and tensile testing. The grain-boundary film thickness distribution was measured before and after creep using both high-resolution lattice imaging technique and Fresnel fringe imaging technique. The results show a narrow range of film widths in the uncrept material but a bimodal distribution after creep. This provides, for the first time, direct evidence for the occurrence of viscous flow of intergranular amorphous films during creep deformation of silicon nitride. Finally, a model is developed to describe the viscous flow process in multi-phase Si3N4 materials in contrast to prior models which are only applicable to "pure" Si3N 4 materials. The creep response predicted by the model is consistent with the experiment.

Jin, Qiang

25

Combination tests on TiAl involving constant strain-rate deformation, annealing and creep  

SciTech Connect

Duplex tests involving constant strain-rate deformation and creep have been performed on polycrystalline single-phase titanium aluminide of nominal atomic composition Ti-52Al. It is found that predeformation (2%) at either room temperature or 800 C speeds up the subsequent primary creep rate and increases the critical strain corresponding to the minimum creep rate, but has little influence on the corresponding time, i.e., there is no obvious change in the time duration of primary creep for the virgin and prestrained specimens. Double creep tests, consisting of creep, annealing and creep, indicate that if the creep test is interrupted for annealing in the primary creep region, the creep rate decreases with time in the subsequent creep. However, if the creep is interrupted in the region of increasing creep strain rate, the creep rate increases with time almost immediately after reloading. Microstructures after various duplex deformations were examined by optical and electron microscopy. Generally, no evidence for recrystallization was observed. These results are interpreted in terms of recovery; the acceleration in creep corresponds to an increasing misorientation across the subgrain boundaries and therefore an increased mobility of these.

Rong, T.S.; Jones, I.P.; Smallman, R.E. [Univ. of Birmingham (United Kingdom)

1998-08-10

26

Microstructural behavior of 8Cr-ODS martensitic steels during creep deformation  

NASA Astrophysics Data System (ADS)

Oxide dispersion strengthened (ODS) steels show a high anisotropy in their creep behavior because of the ?-ferrite grain elongated in the hot-rolled direction and the characteristic formation of creep cavities. In this work, the relationship between the ?-ferrite grain and the growth of creep cavities in 8Cr-ODS steels was investigated. The samples of two ODS steels with different ?-ferrite volume fractions were machined parallel and perpendicular to the hot-rolled direction. Creep rupture tests and interrupted tests were performed at 700 C and about 197 MPa. Cavities formed in the martensite along ?-ferrite grains during creep deformation. The area fraction of the cavities of all specimens increased in proportion to the cube root of test time. When the volume fraction of ?-ferrite was high and ?-ferrite grains elongated parallel to the load direction, ?-ferrite then obstructed the propagation of cracks. However, when the volume fraction of ?-ferrite was low and ?-ferrite grains elongated perpendicular to the load direction, ?-ferrite grains had little effect on crack propagation.

Shinozuka, K.; Esaka, H.; Tamura, M.; Tanigawa, H.

2011-10-01

27

Motion of a Deformed Sphere with Slip in Creeping Flows  

NASA Astrophysics Data System (ADS)

An analytical solution for the motion of a slightly deformed sphere in creeping flows with the assumption of slip on the particle surface is presented. Explicit expressions are obtained for the hydrodynamic force and torque exerted by the fluid on the deformed sphere. A perturbation method, based on previous work done by Brenner [1964] and Lamb[1945], is used to solve for the motion of a fluid influenced by the presence of a deformed sphere. Slip is assumed at the surface of the particle. Hydrodynamic force and torque exerted by the fluid on the deformed sphere are expressed explicitly for a translational and rotational deformed sphere. The equation governing the motion and orientation of a spheroid induced by homogenous flows is also presented. This evolution equation for the orientation of the spheroid is similar to the equation derived by Jeffery [1922]. Solutions of this equation show that the period of rotation of the particle with slip is longer than for the same particle without slip. Furthermore, when the slip coefficient is sufficiently low, the particle rotates to a fixed angle that corresponds to a quasi-steady state in the flow. REFERENCES Brenner, H. 1964 The Stokes resistance of a slightly deformed sphere. Chemical Engineering Science 19, 519-539 Jeffery, G.B.1922 The motion of ellipsoidal particles immersed in a viscous fluid. Proc. Soc. Lond. Math., 102, 161-179 Lamb, H. 1945 Hydrodynamics, sixth version, Dover, New York, U.S.A

Benard, Andre; Jia, Liping; Petty, Charles

2004-11-01

28

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

SciTech Connect

Investigate creep behavior of Zr-based cladding tubes with attention to basic creep mechanisms and transitions in them at low stresses and/or temperatures and study the dislocation microstructures of deformed samples for correlation with the underlying micromechanism of creep

K. Linga (KL) Murty

2008-08-11

29

Mechanisms of creep deformation in gamma-based titanium aluminide alloys  

Microsoft Academic Search

The creep behavior of gamma-based titanium aluminide alloys has been characterized phenomenologically in detail in recent years but is still not well understood mechanistically. It is apparent that a large number of variables potentially influence creep behavior; however, isolation of the effects of individual variables has been difficult. In order to understand creep deformation mechanisms and the sources which contribute

Eric A. Ott

1998-01-01

30

Small angle neutron scattering study of creep deformation and fracture of Type 304 stainless steel  

SciTech Connect

A small-angle neutron scattering (SANS) study has been performed to determine the size distribution of carbide precipitates that were formed during creep deformation in Type 304 stainless steel. The hardening mechanism during primary creep by a fine dispersion of carbide particles in the matrix was confirmed by the SANS measurement and also by direct TEM observations. The size distribution of creep-induced cavities was also determined by SANS measurements after post-creep solution heat treatment.

Yoo, M.H.; Ogle, J.C.; Schneibel, J.H.; Swindeman, R.W.

1982-01-01

31

Multimechanism-Deformation Parameters of Domal Salts Using Transient Creep Analysis  

SciTech Connect

Use of Gulf Coast salt domes for construction of very large storage caverns by solution mining has grown significantly in the last several decades. In fact, among the largest developers of storage caverns along the Gulf Coast is the Strategic Petroleum Reserve (SPR) which has purchased or constructed 62 crude oil storage caverns in four storage sites (domes). Although SPR and commercial caverns have been operated economically for many years, the caverns still exhibit some relatively poorly understood behaviors, especially involving creep closure volume loss and hanging string damage from salt falls. Since it is possible to postulate that some of these behaviors stem from geomechanical or reformational aspects of the salt, a method of correlating the cavern response to mechanical creep behavior as determined in the laboratory could be of considerable value. Recently, detailed study of the creep response of domal salts has cast some insight into the influence of different salt origins on cavern behavior. The study used a simple graphical analysis of limited non-steady state data to establish an approach or bound to steady state, as an estimate of the steady state behavior of a given salt. This permitted analysis of sparse creep databases for domal salts. It appears that a shortcoming of this steady state analysis method is that it obscures some critical differences of the salt material behavior. In an attempt to overcome the steady state analysis shortcomings, a method was developed based on integration of the Multimechanism-Deformation (M-D) creep constitutive model to obtain fits to the transient response. This integration process permits definition of all the material sensitive parameters of the model, while those parameters that are constants or material insensitive parameters are fixed independently. The transient analysis method has proven more sensitive to differences in the creep characteristics and has provided a way of defining different behaviors within a given dome. Characteristics defined by the transient analysis are related quantitatively to the volume loss creep rate of the SPR caverns. This increase in understanding of the domal material creep response already has pointed to the possibility y of delineating the existence of material spines within a specific dome. Further definition of the domal geology and structure seems possible only through expansion of the creep databases for domal salts.

MUNSON, DARRELL E

1999-09-01

32

Stress relaxation and creep of polymer gels in solvent under uniaxial and biaxial deformations  

Microsoft Academic Search

Stress relaxation and creep of polymer gels in solvent under various deformation modes such as uniaxial, strip-biaxial, and equibiaxial were theoretically investigated. The magnitudes of relaxed stress and the creep at equilibrium under each deformation mode were derived by a thermodynamic consideration of gel system. Combining a constitutive equation of gel with the equation of motion of polymer network, the

K. Urayama; T. Takigawa; T. Masuda

1994-01-01

33

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

Microsoft Academic Search

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

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

2005-01-01

34

Creep deformation and crack growth behavior of a single-crystal nickel-base superalloy  

NASA Astrophysics Data System (ADS)

Uniaxial creep deformation and crack growth data are presented on the single-crystal nickel-base superalloy SC16, which is a candidate material for industrial gas turbine applications. All testing was performed at 900 C. The uniaxial experiments were conducted with the loading direction aligned approximately along the [001] crystallographic axis of the material. Under these conditions, a small primary region followed by mainly tertiary creep was obtained, and failure initiated from cracks at interdendritic pores. The crack growth experiments were performed on single-edge notch tension specimens and compact tension test pieces containing deep side grooves to examine state-of-stress effects. A selection of crystallographic orientations was also examined. Little effect of stress state and orientation was obtained. It has been found that the creep crack growth characteristics of the alloy can be predicted satisfactorily from a model of the accumulation of damage at a crack tip using the creep fracture mechanics parameter C* and assuming plane stress conditions.

Moss, S. J.; Webster, G. A.; Fleury, E.

1996-04-01

35

Compressive creep characteristics of extruded ultrahigh-molecular-weight polyethylene.  

PubMed

The static compressive creep behavior of ultrahigh-molecular-weight polyethylene (UHMWPE) was studied under physiologic conditions. Specimens were machined from the center and periphery of extruded GUR 4150HP rod stock and were subjected to constant pressures of 2, 4, or 8 MPa for intervals as long as 10(4) min. The creep strain (creep divided by initial thickness) was compared to the pressure and duration of loading by using analysis of variance and linear regression analysis. The amount of creep strain increased rapidly in the early period of testing and was followed by a reduced rate of creep, which reached a steady state after approximately 4000 min. The amount and rate of creep strain increased linearly with pressure. Surprisingly, the rate of creep strain varied with the radial position in the rod stock: specimens obtained from the periphery had 8-19% larger creep strain rates than did specimens obtained from the center (p = 0.1 to p < 0.001). These results advance the characterization of creep's contribution to the in vivo penetration of the metallic component into the UHMWPE component, thereby facilitating the measurement of true in vivo wear. These data also help explain the azimuthally nonuniform deformation observed in retrieved acetabular cups. PMID:9457556

Lee, K Y; Pienkowski, D

1998-02-01

36

Steady-state creep deformation of investment cast near-gamma titanium aluminide  

SciTech Connect

The creep behavior of an investment cast near-gamma alloy Ti-48Al-2Nb-2Cr (at. pct) was investigated by determining the stress dependency and activation energy for steady-state creep deformation of this alloy, using the results of post-test microscopy to characterize the microstructural evolution after creep testing at high temperatures. The results of these examinations suggest that the mechanism of creep deformation in this alloy is a complex process which depends strongly on the specific stress and the temperature. 23 refs.

Wheeler, D.A.; London, B.; Larsen, D.E., JR. (Howmet Corp., Whitehall, MI (United States))

1992-03-01

37

Mechanisms of creep deformation in gamma-based titanium aluminide alloys  

NASA Astrophysics Data System (ADS)

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

Ott, Eric A.

38

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

39

Creeping deformation mechanisms for mixed hydrate-sediment submarine landslides  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

40

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

1995-09-01

41

Creep deformation in two-phase titanium aluminide alloys  

Microsoft Academic Search

The paper presents an electron microscope study of diffusion assisted creep processes in a two-phase (?2+?) titanium aluminide alloy, which had been subjected to long-term creep. The results imply that the high primary creep rate of lamellar TiAl alloys is associated with the relaxation of mismatch structures and coherency stresses present at the interfaces. Long-term creep leads to spheroidization and

F. Appel; U. Christoph; M. Oehring

2002-01-01

42

Plastic deformation and creep damage evaluations of type 316 austenitic stainless steels by EBSD  

SciTech Connect

The inspection method of plastic and/or creep deformations has been required as the quantitative damage estimation procedure for structural components especially used in electric power plants. In this study, the method using electron backscatter diffraction (EBSD) was applied to the deformation and damage evaluation of austenitic stainless steels strained by tension or compression at room temperature and also tested in creep at high temperature. It was found that the value of Grain Average Misorientation (GAM) which showed the average misorientation for the whole observed area including over several dozen grains, was a very useful parameter for quantifying the microstructural change as either the plastic or creep strain increased. The unique linear correlation was obtained between GAM and plastic strain in tension and compression. For creep damage evaluation, the difference of grain average misorientation from the value of the unstrained specimen ({Delta}GAM) showed an excellent correlation with the inelastic strain below strain at which the tertiary creep began.

Yoda, Rika, E-mail: yoda.rika@kki.kobelco.com [Electronics Division, Kobelco Research Institute Inc., 1-5-5 Takatsuka-dai, Nishi-ku, Kobe, Hyogo 651-2271 (Japan); Department of Adaptive Machine Systems, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871 (Japan); Department of Materials Science and Engineering, Graduate School of Engineering, Kyoto University, Yoshida Honmachi, Sakyo-ku, Kyoto, 606-8501 (Japan); Yokomaku, Toshinori, E-mail: yokomaku.toshinori@kki.kobelco.com [Engineering Mechanics Division, Kobelco Research Institute Inc., 1-5-5 Takatsuka-dai, Nishi-ku, Kobe, Hyogo 651-2271 (Japan); Tsuji, Nobuhiro, E-mail: nobuhiro.tsuji@ky5.ecs.kyoto-u.ac.jp [Department of Materials Science and Engineering, Graduate School of Engineering, Kyoto University, Yoshida Honmachi, Sakyo-ku, Kyoto, 606-8501 (Japan)

2010-10-15

43

Deformation and creep in the human chorioamniotic sac.  

PubMed

This paper presents a review of physical principles involved in deformation and creep in the human chorioamniotic membrane. These are definable rheological properties found in many materials. Experimental data are presented on 66 human fetal membranes. A difference in the stress tolerance between preterm and term membranes is demonstrated. A computer model has been devised which allows for the calculation of changes in thickness of the membrane at the point of fracture. This computer model allows for the study of the physical property of the tissue in ways which have not previously been suggested. The model suggests that the pathophysiology related to rupture of the membrane is based on changes in the thickness of this tissue occurring secondary to acute and chronic stress applications. The data derived in these experiments suggest a possible physical model for rupture of the membranes; they also introduce questions regarding the anatomic and biochemical makeup of the chorion and the amnion and the respective role that each plays in maintaining the integrity of the human chorioamniotic sac. PMID:453271

Lavery, J P; Miller, C E

1979-06-15

44

Deformational characteristics of thermoplastic elastomers  

NASA Astrophysics Data System (ADS)

This thesis focuses primarily on the structure-property relationships of poly (styrene-ethylene-butylene-styrene) triblock copolymer TPEs. First evidence for strain-induced crystallization occurring in certain SEBS block copolymers has been established using unique techniques like deformation calorimetry, combined in-situ small angle X-ray and wide angle X-ray diffraction (SAXD/WAXD). Also the ramifications of such strain-induced crystallization on the mechanical properties like cyclic hysteresis, stress relaxation/creep retention of these SEBS systems have been studied. In addition, the structural changes in the morphology of these systems on deformation have been investigated using combined SAXD/WAXD setup. Small angle X-ray diffraction probed the changes at the nano-scale of polystyrene (PS) cylinders, while wide angle X-ray diffraction probed the changes at molecular length scales of the amorphous/crystalline domains of the elastomeric mid-block in these systems. New structural features at both these length scales have been observed and incorporated into the overall deformation mechanisms of the material. Continuous processing techniques like extrusion have been used to obtain ultra long-range order and orientation in these SEBS systems. Thus well ordered crystal like hexagonal packing of cylinders, where in each element in this hexagonal lattice can be individually addressed without any grain boundaries can be realized using these robust techniques. The effect of long-range order/orientation on the mechanical properties has been studied. In addition, these well ordered systems serve as model systems for evaluating deformation mechanisms of these SEBS systems, where the relative contributions of each of the phases can be estimated. EPDM/i-PP thermoplastic vulcanizates (TPVs) have micron size scale phase separated morphologies of EPDM rubber dispersed in a semicrystalline i-PP matrix as a result of the dynamic vulcanization process. Confocal microscopy studies, along with scanning electron microscopy (SEM) studies show that the morphology of these EPDM/i-PP systems resembles a microcellular "filled" foam in which i-PP occupies the strut regions and EPDM the inner core. Based on this, an analytical model has been developed that takes into account composition information, molecular weight, cure state and morphology into account.

Indukuri, Kishore K.

45

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

NASA Astrophysics Data System (ADS)

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

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

2002-05-01

46

Extension of an anisotropic creep model to general high temperature deformation of a single crystal superalloy  

Microsoft Academic Search

A physics based model has been developed that accounts for the principal features of anisotropic creep deformation of single crystal superalloys. The present paper extends this model to simulate other types of high temperature deformation under strain controlled test conditions, such as stress relaxation and tension tests at constant strain rate in single crystals subject to axial loading along an

L.-M. PAN; R. N. GHOSH; M. McLEAN

1993-01-01

47

Microstructural behavior of 8Cr-ODS martensitic steels during creep deformation  

Microsoft Academic Search

Oxide dispersion strengthened (ODS) steels show a high anisotropy in their creep behavior because of the ?-ferrite grain elongated in the hot-rolled direction and the characteristic formation of creep cavities. In this work, the relationship between the ?-ferrite grain and the growth of creep cavities in 8Cr-ODS steels was investigated. The samples of two ODS steels with different ?-ferrite volume

K. Shinozuka; H. Esaka; M. Tamura; H. Tanigawa

2011-01-01

48

Creep deformation behavior and failure diagnostic diagrams of a columnar-grained nickel-based superalloy  

Microsoft Academic Search

Uniaxial creep deformation of a columnar-grained cast Ni-based superalloy has been analyzed in the temperature range of 1035-1315\\u000a K. Two-stage heat treatment of the material resulted in an average ?? particle size of 0.4 ?m and inter-particle distance\\u000a of 0.04 ?m. At 1035 K, the alloy showed predominantly primary creep with very low tertiary creep strains. At temperatures\\u000a above 1035

Gopalakrishna Magadi; V. M. Radhakrishnan

2004-01-01

49

Creep deformation of TiB2-reinforced near- ? titanium aluminides  

NASA Astrophysics Data System (ADS)

The deformation behavior under creep conditions of several unreinforced and participate (TiB2)-reinforced binary near-gamma titanium aluminide alloys has been examined. Material has been produced using both ingot-and powder-processing techniques, yielding material of varying microstructures and grain sizes. It has been found that the rate of deformation is strongly dependent on matrix grain size and microstructural stability. The presence of the dispersed phase dramatically impacts the microstructural character which evolves following isothermal forging, and this has been observed to strongly influence the creep behavior. Constitutive equations which describe the observed behavior indicate that the mechanism of creep deformation is the same for both the reinforced and unreinforced variants and is independent of processing route.

Kampe, S. L.; Bryant, J. D.; Christodoulou, L.

1991-02-01

50

Effect of DC Current on the Creep Deformation of Tin  

NASA Astrophysics Data System (ADS)

Impression creep testing of tin was performed in the temperature range of 343 K to 398 K and under a punching stress of 12 MPa to 55 MPa. During the impression test at constant load, a direct electric current in the range of 0 A to 6 A flowed through the punch into the sample, introducing an electromechanical interaction. Steady-state creep was observed under the simultaneous action of the electric current and mechanical stress. The steady-state impression velocity increased with increasing temperature, punching stress, and electric current. A hyperbolic sine relation was used to describe the stress dependence of the steady-state impression velocity for impression creep of tin. The apparent activation energy decreased with increasing electric current.

Chen, Rong; Yang, Fuqian

2010-12-01

51

Isotropic and Anisotropic Creep Characteristics of Thick-Walled Pressure Vessels under Elastic/Plastic Stress.  

National Technical Information Service (NTIS)

By using the theory of finite deformations the isochoric creep behaviour of thick-walled high-pressure containers (multi-layer containers) which have been deformed elastoplastically at the beginning of creep due to internal and external pressure is descri...

D. Knoerzer

1985-01-01

52

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

SciTech Connect

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

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

1996-05-15

53

Precipitation in 9Cr1Mo steel after creep deformation  

Microsoft Academic Search

The carbides present after creep testing a 9Cr1Mo steel at 566C over a range of stress levels giving rupture times of up to 7300h have been characterized and identified using a transmission electron microscopy, energy-dispersive X-ray spectroscopy and electron diffraction. The initial carbide precipitates present were M7C3, (NbV)C and VC and it was determined that M6C carbide precipitates were present

H. C. Furtado; L. H. de Almeida; I.. Le May

2007-01-01

54

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

55

Deformation characteristics of metal foams  

Microsoft Academic Search

The deformation behaviour of a series of aluminium and zinc foams was investigated by uniaxial testing. Because the deformation behaviour of metal foams is expected to be anisotropic owing to the existence of a closed outer skin and with respect to the foaming direction, a series of measurements was carried out where the orientation of the outer skin and the

J Banhart; J. BAUMEISTER

1998-01-01

56

Effect of loading history on the threshold stress in the creep deformation of an austenitic stainless steel  

Microsoft Academic Search

The steady state creep rate of AISI 316L(N) SS at 923K can be described by the threshold stress compensated power law relationship. The threshold stress for creep deformation over the stress range 142230MPa has been evaluated graphically as 6010MPa from the conventional creep tests. A threshold stress of about 110MPa was computed from two stress decrease tests which is much

C. Girish Shastry; P. Parameswaran; M. D. Mathew; K. Bhanu Sankara Rao; S. D. Pathak

2008-01-01

57

Characterization of micro-scale creep deformation of an electro-active paper actuator  

NASA Astrophysics Data System (ADS)

The creep deformation process of an electro-active paper (EAPap) actuator was investigated by adapting stepwise dead-weight loading. To understand the deformation mechanism of the EAPap film, including morphological and structural changes, various loading conditions below yield strength were applied to cellophane EAPap. From the structural observation, micro-dimples and micro-cracks were detected at applied load lower than 10% of yield strength, while they were not found in higher load conditions. It is hypothesized that only short and random fibers in the amorphous region may respond to the applied stress at the low loading condition, not the fibers in the crystalline area. As a result, deformation energy at the localized spot accumulated and created micro-defects at the surface. Meanwhile, fibers in the crystalline region may sustain most of the loads as creep load increases to a high level. Molecular chains in the fiber may rotate and elongate with high load. Elongated fibers were observed only at a high level of load. From the structural change as a function of applied load, a peak shift of crystal orientation was observed only in high load conditions by wide angle x-ray measurement. This may confirm that creep deformation could give rise to structure changes in EAPap.

Lee, Sangwoo; Kim, Joo-Hyung; Kang, Kwangseon; Kim, Jaehwan; Kim, Heung Soo; Yang, Chulho

2009-09-01

58

Influence of water on plastic deformation of olivine aggregates: 2. Dislocation creep regime  

NASA Astrophysics Data System (ADS)

Triaxial compressive creep experiments have been conducted over a range of hydrous conditions to investigate the effect of water fugacity on the creep behavior of olivine aggregates in the dislocation creep regime. Samples synthesized from powders of San Carlos olivine were deformed at confining pressures of 100 to 450 MPa and temperatures between 1473 and 1573 K. Water was supplied by the dehydration of talc. Water fugacities of 80 to 520 MPa were obtained by varying the confining pressure under water-saturated conditions with the oxygen fugacity buffered at Ni/NiO. Sancles were deformed at differential stresses of 20 to 230 MPa. The transition from diffusion creep to dislocation creep occurs near 100 MPa for both the hydrous case and the anhydrous case. Under hydrous conditions creep experiments yield a stress exponent of n ? 3 and an activation energy of Q ? 470 kJ/mol. The creep rate of olivine is enhanced significantly with the presence of water. At a water fugacity of 300 MPa, samples crept 5-6 times faster than those deformed under anhydrous conditions at similar differential stresses and temperatures. Within the range of water fugacity investigated, the strain rate is proportional to water fugacity to the 0.69 to 1.25 power, assuming values for the activation volume of 0 to 3810-6 m3/mol, respectively. We argue that water influences creep rate primarily through its effect on the concentrations of intrinsic point defects and hence on ionic diffusion and dislocation climb. With increasing water fugacity the charge neutrality condition changes from [FeMe] = 2[VMe?] to [FeMe] = [HMe']. For the latter charge neutrality condition the concentration of silicon interstitials is proportional to fH2O1, suggesting that under hydrous conditions dislocation climb is rate limited by diffusion of Si occurring by an interstitial mechanism. Our experimentally determined constitutive equation permits extrapolation from laboratory to mantle conditions in order to assess the rheological behavior of regions of the upper mantle with different water contents, such as beneath a mid-ocean ridge and in the mantle wedge above a subducting slab.

Mei, S.; Kohlstedt, D. L.

2000-09-01

59

Precipitation in 9Cr-1Mo steel after creep deformation  

SciTech Connect

The carbides present after creep testing a 9Cr-1Mo steel at 566 deg. C over a range of stress levels giving rupture times of up to 7300 h have been characterized and identified using a transmission electron microscopy, energy-dispersive X-ray spectroscopy and electron diffraction. The initial carbide precipitates present were M{sub 7}C{sub 3}, (NbV)C and VC and it was determined that M{sub 6}C carbide precipitates were present in all specimens after elevated temperature exposure for greater than approximately 1700 h. No precipitation of M{sub 23}C{sub 6} was detected. The evolutionary sequence from the initially present carbides during high temperature exposure involved the formation of the stable M{sub 6}C carbide directly, without the intermediate formation of M{sub 23}C{sub 6}, as is reported to occur in other Cr-Mo steels.

Furtado, H.C. [CEPEL-Centro de Pesquisas de Energia Eletrica, C.P. 68007, 21941-590, Rio de Janeiro (Brazil); Almeida, L.H. de [PEMM-COPPE/UFRJ, C.P. 68505, 21941-972, Rio de Janeiro (Brazil); Le May, I. [PEMM-COPPE/UFRJ, C.P. 68505, 21941-972, Rio de Janeiro (Brazil) and Metallurgical Consulting Services, P.O. Box 5006, Saskatoon, Canada S7K 4E3 (Canada)]. E-mail: lemayi@metallurgicalconsulting.net

2007-01-15

60

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

NASA Astrophysics Data System (ADS)

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

Bial, J.; Trepmann, C. A.

2013-10-01

61

Deep-seated creep deformations in the crystalline cores of the tatry Mts  

Microsoft Academic Search

SummaryDeep-seated creep deformations of slopes attaining kilometres in dimensions occur quite often even in the metamorphosed rocks\\u000a and granitoids forming the crystalline core of the Tatry and Nzke Tatry Mts. They have a form of gravitational folding and\\u000a fan-like disintegration of mountain slopes. In both cases, however, a similar model of failure mechanism can be assumed on\\u000a the basis of

T. Mahr; A. Nem?ok

1977-01-01

62

Crystal preferred orientation in peridotite ultramylonites deformed by grain size sensitive creep, tang de Lers, Pyrenees, France  

NASA Astrophysics Data System (ADS)

In naturally deformed upper mantle rocks a strong olivine crystallographic preferred orientation (CPO) occurs in rocks with grain sizes larger than about 15 ?m. Finer grained peridotites tend to have weak to random olivine CPO. The different types of olivine CPO are usually interpreted in relation to the dominant deformation mechanisms: with a strong CPO indicating dislocation creep and a random CPO indicating grain size sensitive (GSS) mechanisms involving grain boundary sliding and diffusion creep. Here we report the occurrence of a weak but systematic olivine CPO in ultra-fine-grained (0.5-10 ?m) ultramylonites from the tang de Lers lherzolite, Pyrenees, France. The microstructures, with elongated grains and mixed distribution of phases in the ultramylonites indicate deformation by dominant GSS creep. In theory, an olivine CPO may develop in rocks deformed by GSS creep during dislocation accommodated boundary sliding or phase boundary controlled diffusion creep in pyroxene-rich rocks. Alternatively, the CPO may be a relict texture preserved because the elongated grain shapes limit rotation during grain boundary sliding. Our observations confirm theoretical and experimental studies, which predict that systematic CPO and an associated seismic anisotropy can occur in naturally deformed upper mantle rocks during deformation by grain boundary sliding and diffusion creep.

Drury, M. R.; Av Lallemant, H. G.; Pennock, G. M.; Palasse, L. N.

2011-12-01

63

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

NASA Astrophysics Data System (ADS)

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

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

2012-08-01

64

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

65

Deformational characteristics of thermoplastic elastomers  

Microsoft Academic Search

This thesis focuses primarily on the structure-property relationships of poly (styrene-ethylene-butylene-styrene) triblock copolymer TPEs. First evidence for strain-induced crystallization occurring in certain SEBS block copolymers has been established using unique techniques like deformation calorimetry, combined in-situ small angle X-ray and wide angle X-ray diffraction (SAXD\\/WAXD). Also the ramifications of such strain-induced crystallization on the mechanical properties like cyclic hysteresis, stress

Kishore K. Indukuri

2006-01-01

66

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

SciTech Connect

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

M.C. Carroll; L.J. Carroll

2012-10-01

67

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

68

Intragranular deformation heterogeneities during the creep of ice polycrystals: experimental measurements vs. modeling  

NASA Astrophysics Data System (ADS)

Similarly as minerals from the Earth mantle, ice exhibits a strongly anisotropic rheology resulting from the small number of independent slip systems for dislocations. Therefore, a significant heterogeneity of stress and strain distributions is expected at the inter- and intra-granular scale during polycrystal deformation, owing to the mechanical interaction between adjacent grains. A Digital Image Correlation (DIC) technique has been adapted to polycrystalline ice specimens in order to characterize the development of strain heterogeneities at an intragranular scale during transient creep deformation. Specimens exhibit a columnar microstructure so that plastic deformation is essentially 2-D with no in-depth gradients, and therefore surface DIC analyses are representative for the whole specimen volume. Local misorientations at the intragranular scale were also extracted from microstructure analyses carried out with an automatic texture analyzer before and after deformation. Highly localized strain patterns are evidenced by the DIC technique. Local equivalent strain can reach values as high as one order of magnitude larger than the macroscopic average. The structure of the strain pattern does not evolve with strain in the transient creep regime. Almost no correlation between the measured local strain and the Schmid factor of the slip plane of the underlying grain is observed, highlighting the importance of the mechanical interactions between neighboring grains resulting from the very large viscoplastic anisotropy of ice crystals. Finally, the experimental microstructure was introduced in a full-field FFT polycrystal model; simulated strain fields are in good match with experimental ones.

Grennerat, F.; Montagnat, M.; Castelnau, O.; Vacher, P.; Suquet, P.; Moulinec, H.; Duval, P.

2011-12-01

69

Creep, fatigue, and deformation of alpha and alpha-beta titanium alloys at ambient temperature  

NASA Astrophysics Data System (ADS)

Titanium and it alloys are extensively utilized in critical applications that require materials with high strength to weight ratios, rigidities, and toughnesses. This being the case, over 70 years of research have been devoted to the measurement, understanding, and tailoring of the mechanical properties of these alloys. Despite these efforts, surveys of the current knowledge base and understanding of the mechanical responses of Ti alloys demonstrate that numerous mechanical behaviors have yet to be investigated and explained. It has been noted, but generally not appreciated, that commercially important materials display modest strength differentials near room temperature when deformed under quasi-static loading conditions at modest rates (10 -5 to 10-3 s-1 ). Under static loading, subtle variations in plastic flow behavior leads to dramatically weaker materials when loaded in tension versus compression. The asymmetric material responses of single and two-phase alloys deformed under monotonic constant rate and creep conditions have been investigated and related to the fundamental slip behavior observed in single crystalline materials. Two-phase titanium alloys containing a majority volume fraction of the alpha (HCP) phase have long been known to undergo creep deformation at lower temperatures (T < Tm) and stresses (sigma < sigmays). The time dependence of this plasticity, stemming from slip in the alpha-phase, has been found to be sensitive to microstructural condition. The nature of low temperature creep in heat-treatment modified beta-annealed Ti-6Al-2Sn-4Zr-2Mo has been investigated. Microstructural features, particularly primary alpha-lathe and beta-rib structure (secondary alpha morphology and content), were systematically modified, and the resulting structures were deformed under both creep and constant strain rate loading conditions. Variations in plastic response are discussed in terms of strain hardening and strain rate sensitivity parameters. The mechanical performance of engineering Ti alloys has long been known to be sensitive to the to nature of applied load waveform. A review of the open literature elucidates several gaping holes in the current understanding of waveform induced plastic response of cyclically loaded materials. This study addresses several of those issues. Sustained load hold time effects during the fatigue an aalpha-Ti alloy is investigated with respect to loading conditions and slip planarity and compared to cyclic fatigue and creep responses at room temperature.

Brandes, Matt

70

Deformational characteristics of subgrade soils in Korea  

Microsoft Academic Search

Deformational characteristics of subgrade soils are important parameters in the mechanistic design of flexible pavement. The\\u000a subgrade soils are mostly non-plastic sandy in Korea, and seven representative subgrade soils were collected for testing from\\u000a the actual pavement projects. To evaluate the deformational characteristics of subgrade soils, RC\\/TS, TX, FF-RC, and cyclicM\\u000a \\u000a R\\u000a tests were performed. The effects of various variables

Gi-Chul Kweon; Dong-Soo Kim

2000-01-01

71

Matrix-dominated time-dependent deformation and damage of graphite/epoxy composite experimental data under creep and recovery  

SciTech Connect

The objective of this report is to disseminate experimental data of matrix-dominated time-dependent deformation and time-dependent damage in graphite-epoxy composite. The composite specimens were +- 45/sup 0/ T300/5208 laminates tested in tension under creep and creep-recovery with complete instrumentation for stress, strain, and time recordings. Experimental data was recorded and archived in digital form. Polynomial series are fitted to the experimental data for compilation, dissemination and future retrieval.

Wu, E.M.; Sanchez, R.J.; Nguyen, N.Q.

1983-06-01

72

Experimental constraints on the dynamics of the partially molten upper mantle: Deformation in the diffusion creep regime  

Microsoft Academic Search

Deformation experiments have been conducted to investigate the effect of melt fraction and grain size on the creep behavior of olivine aggregates in the diffusion creep regime. Both nominally melt-free and melt-added samples display stress exponents (n = 1.0 +\\/- 0.1) and grain size exponents (p = -3.0 +\\/- 0.5 for nominally melt-free, p = -3.2 +\\/- 1.2 for melt-added)

Greg Hirth; David L. Kohlstedt

1995-01-01

73

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

NASA Astrophysics Data System (ADS)

Two triaxial compression experiments were performed on Carrara marble at high confining pressure, in creep conditions across the brittle-ductile transition. During cataclastic deformation, elastic wave velocity decrease demonstrated damage accumulation (microcracks). Keeping differential stress constant and reducing normal stress induced transient creep events (i.e., fast accelerations in strain) due to the sudden increase of microcrack growth. Tertiary creep and brittle failure followed as damage came close to criticality. Coalescence and rupture propagation were slow (60-200 seconds with ~150 MPa stress drops and millimetric slips) and radiated little energy in the experimental frequency range (0.1-1 MHz). Microstructural analysis pointed out strong interactions between intra-crystalline plastic deformation (twinning and dislocation glide) and brittle deformation (microcracking) at the macroscopic level. Our observations highlight the dependence of acoustic efficiency on the material's rheology, at least in the ultrasonic frequency range, and the role played by pore fluid diffusion as an incubation process for delayed failure triggering.

Schubnel, A.; Walker, E.; Thompson, B. D.; Fortin, J.; Guguen, Y.; Young, R. P.

2006-09-01

74

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

NASA Astrophysics Data System (ADS)

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

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

2013-11-01

75

Plastic instability during creep deformation of a NiAl-Hf single-crystal alloy -- A case study  

SciTech Connect

Tensile samples from NiAl-Hf single crystals, having the same nominal composition and heat treated and creep tested under identical conditions at 1,144 K, were found to exhibit very different rupture lives and creep ductilities. A case study was conducted on two samples with creep rupture lives of 343.6 and 37.0 hours (with corresponding creep ductilities of 12.3 and 39.9 pct, respectively) in order to find the causes of such a large variation in creep properties. Detailed microstructural analyses using optical microscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) indicated that the sample with higher rupture life and lower ductility had deformed uniformly along the length of the gage section, whereas the sample with lower rupture life and higher ductility (sample L) deformed by localized plastic deformation resulting in shear failure. This shear failure was due to a plastic instability in sample L which was caused by the presence of a high density of large Hf-rich interdendritic particles that were formed during casting of the single-crystal ingot but did not go into solution during the homogenization heat treatment. The role of these particles in causing nonuniform deformation, which led to strain localization and a premature failure in sample L, has been described in detail.

Garg, A. [AYT Corp., Cleveland, OH (United States); Raj, S.V.; Noebe, R.D.; Nathal, M.V. [National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center; Darolia, R. [General Electric Aircraft Engines, Cincinnati, OH (United States)

1998-01-01

76

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

77

Influence of Rare-Earth Additions on Properties of Titanium Alloys. Plane-Strain Fracture Toughness, Creep, and High-Temperature Deformation of Ti-6Al-4V with Erbium and Yttrium Additions.  

National Technical Information Service (NTIS)

The influence of additions of 0.05 wt% Y and 0.1 wt% Er on the room-temperature tensile properties, plane-strain and plane-stress fracture toughness, creep, and high-temperature high-strain-rate deformation characteristics of Ti-6Al-4V was studied. 75kg i...

S. M. L. Sastry R. J. Lederich P. S. Pao J. E. O'Neal

1979-01-01

78

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

PubMed

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

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

2011-08-22

79

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

NASA Astrophysics Data System (ADS)

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

Ben-Zion, Yehuda

1996-03-01

80

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

81

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

NASA Astrophysics Data System (ADS)

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

Bial, J.; Trepmann, C. A.

2013-04-01

82

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

Microsoft Academic Search

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

A. Jaworski; S. Ankem

2006-01-01

83

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

Microsoft Academic Search

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

A. Jaworski; S. Ankem

2006-01-01

84

Creep Characterization of Superalloy IN738 Using Ultrasonic Nonlinearity Measurement  

Microsoft Academic Search

The higher harmonic generation technique has been presented to investigate the creep characteristics of nickel-based superalloy. The primary gamma' precipitates became coarsened preferentially in the direction perpendicular to the applied stress axis during the creep deformation and the Vickers hardness decreased with creep time due to loss of interfacial strain between gamma matrix and gamma' precipitate. The increase in ultrasonic

Chung Seok Kim; Chang Young Hyun; Kyoung Young Jhang

2011-01-01

85

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

86

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

87

The effect of electric field on the creep characteristics of low-density polyethylene (LDPE)  

Microsoft Academic Search

The effect of electric field on the creep characteristics and the corresponding parameters such as instantaneous strain, strain rate, activation energy, activation volume, stress-sensitivity parameter and viscosity was investigated.

M. Amin; H. M. Osman; S. S. Hamza; N. El-Nashar; S. F. Moghazy

1989-01-01

88

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

89

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

90

Impression Creep Characteristics of a Cast Mg Alloy  

NASA Astrophysics Data System (ADS)

The creep behavior of the cast Mg-6Al-0.3Mn alloy (AM60) was investigated by impression testing under constant punching stress in the range 150 to 650 MPa and at temperatures in the range 423 to 523 K, corresponding to 0.458 < T/T m < 0.567. The creep behavior can be divided into two stress regimes, with a change from the low-stress regime to the high-stress regime occurring, depending on the testing temperature, around 0.021 < ( ?/ G) < 0.033. Based on the steady-state power-law creep relationship, the stress exponents of 4 to 6 and 8 to 12 were obtained at low and high stresses, respectively. When the experimental creep rates were normalized to the pipe diffusion coefficient, however, the stress exponents of about 5 and 10 were obtained for the low- and high-stress regimes, respectively. The low-stress regime activation energies of about 76 to 84 kJ mol-1, which are close to 80 kJ mol-1 for dislocation-pipe diffusion in the Mg, and stress exponents in the range 4 to 6 suggest that the operative creep mechanism is dislocation climb. This behavior is in contrast to the high-stress regime, in which the stress exponents of 8 to 12 and activation energies of about 134 to 165 kJ mol-1 are indicative of a power-law breakdown.

Kondori, B.; Mahmudi, R.

2009-08-01

91

High temperature creep and cyclic deformation behaviour of AISI 316 L(N) austenitic steel and its modelling with unified constitutive equations  

Microsoft Academic Search

Creep tests at constant stress and low cycle fatigue (LCF) tests were performed with a view to investigating and modelling the deformation behaviour of AISI 316 L(N) austenitic stainless steel at 700 C. All experiments were done on samples taken from two different sheets of the same batch of material.The creep stresses were selected from the high stress range. The

A. Haupt; D. Munz; W. Scheibe; B. Schinke; R. Schmitt; V. Sklenicka

1996-01-01

92

Creep behavior of Ni-Cr lamellar eutectic alloy  

Microsoft Academic Search

The structural changes that occur during creep deformation at 625 and 760C, with creep and creep rupture data of a directionally\\u000a solidified Ni-Cr lamellar eutectic alloy are presented and discussed. It is shown that the characteristic features of stage\\u000a I deformation are the formation of dislocation tangles in the nickel-rich phase and shearing of the cellular structure; these\\u000a features are

Ram Kossowsky

1970-01-01

93

Zur Berechnung von Kriechverformung und Spannungen in Dickwandigen Rohren (The Calculation of Creep Deformations and Stresses in Thick-Walled Tubes).  

National Technical Information Service (NTIS)

Methods for the calculation of stresses and creep deformations in thick-walled tubes under compressive and additional axial loads were developed for heat exchangers for methane reforming processes in helium cooled high temperature reactors where temperatu...

G. Breitbach S. Kragl M. Roedig H. Penkalla

1986-01-01

94

Creep deformation and fracture behavior of types 316 and 316L(N) stainless steels and their weld metals  

SciTech Connect

The creep properties of a nuclear-grade type 316(L) stainless steel (SS) alloyed with nitrogen (316L(N)SS) and its weld metal were studied at 873 and 923 K in the range of applied stresses from 100 to 335 MPa. The results were compared with those obtained on a nuclear-grade type 316 SS, which is lean in nitrogen. The creep rupture lives of the weld metals were found to be lower than those of the respective base metals by a factor of 5 to 10. Both the base and weld metals of 314L(N)SS exhibited better resistance to creep deformation compared to their 316SS counterparts at identical test conditions. A power-law relationship between the minimum creep rate and applied stress was found to be obeyed for both the base and weld metals. Both the weld metals generally exhibited lower rupture elongation than the respective base metals; however, at 873 K, the 316 SS base and weld metals had similar rupture elongation at identical applied stresses. Comparison of the rupture lives of the two steels to the ASME curves for the expected minimum stress to rupture for 316 Ss base and weld metals showed that, for 316L(N) SS, the specifications for maximum allowable stresses based on data for 316 SS could prove overconservative. The influence of nitrogen on the creep deformation and fracture behavior, especially in terms of its modifying the precipitation kinetics, is discussed in light of the microstructural observations. In welds containing {delta} ferrite, the kinetics of its transformation and the nature of the transformation products control the deformation and fracture behavior. The influence of nitrogen on the {delta} ferrite transformation behavior and coarsening kinetics is also discussed, on the basis of extensive characterization by metallographic techniques.

Sasikala, G.; Mathew, M.D.; Bhanu Sankara Rao, K.; Mannan, S.L.

2000-04-01

95

Prediction of creep characteristic of rock under varying environment  

NASA Astrophysics Data System (ADS)

The strain developed due to creep is mainly proportional to the logarithm of the time under load, and is mostly proportional to the stress and temperature. At higher temperature the creep rate falls slowly with respect to time, and the creep strain is proportional to a fractional power of time, with the exponent increasing as the temperature increases and reaching a value approximately one-third at temperatures of about 0.5C. At these temperatures, the creep increases with stress according to a power greater than unity and possibly exponentially. It increases with temperature as (- U/ kT), where U is an activation energy and k is Boltzmans constant. There are different methods to determine the creep strain and the energy of Jog (B) including experimental methods, multivariate regression analysis, and by numerical simulation. These methods are less cumbersome and time consuming. In the present investigation, artificial neural network technique has been used for prediction of the creep strain and energy of Jog (B). Two different networks have been tested and validated. Both the networks have four input neurons and one hidden layer with five neurons, and one output neuron. The data for different rocks at temperatures up to 750C under conditions of compressive or tortional stress are taken from the literatures. The training and testing data sets used were 163 and 14, respectively. To deal with the problem of overfitting of data, Bayesian regulation has been used and network is trained with suitable training epochs. The coefficients of correlation among the predicted and observed values are found high and they improve the confidence of the users. The mean absolute percentage error obtained are also very low.

Singh, T. N.; Verma, A. K.

2005-08-01

96

Creep deformations and stresses in thick-walled cylindrical vessels of functionally graded materials subjected to internal pressure  

Microsoft Academic Search

Steady-state creep of thick-walled cylindrical vessels made of functionally graded materials subjected to internal pressure is investigated in this paper. Taking material parameters involved in Nortons law to be the functions of the radial coordinate, a simple and accurate method is developed from the strain ratestress relations, Nortons law, deformation compatibility condition and equilibrium equation of axisymmetric, plane strain problems.

L. H. You; H. Ou; Z. Y. Zheng

2007-01-01

97

Creeping Deformation by the Precise Leveling Survey at the central part of the Longitudinal valley fault, Southeast Taiwan  

NASA Astrophysics Data System (ADS)

We would like to know the distributed asperity for seismic hazard and forecast. It is closely related to slip distribution on the fault in interseismic. We focused on the accumulating process of the stress at the boundary between the creeping and the locking zone, to clear the behavior on the fault. The Longitudinal Valley Fault (LVF), 150 km long and NNE-SSW striking, passes through the eastern Taiwan, and represents the obvious surface expression of the collision boundary between the Philippine Sea plate and the Eurasian continental plate. Owing to such a high deformation rate, many earthquakes have occurred along the LVF. The 1951 earthquake sequence represents a good example. The southern of LVF segment is observed to be high speed creeping based on the creep meter and leveling survey etc. The northern of LVF segment is not observed to be creeping and are found huge earthquakes evidence by paleo-seismology study in the trench. Yuili fault is one of the active segments of the longitudinal valley faults, is located around the boundary between creeping and locking area. It is reverse fault with east dip. We established about 30km leveling route from Yuli to Changbin to detect the vertical deformation in detail. Murase et al. (2009, 2010, and 2011) established about 30 km densely leveling route from Yuli to Changbin to detect the vertical deformation across the LVF for two years. As a result, the vertical displacement is 1.7 cm in 200 m across the LVF and 2.7 cm in 1000 m, referred to the west end of our route. In addition, a synclinal deformation is detected on the hanging wall side of the fault. This result is caused by the geometry of and the slipping distribution on the fault. The deformation detected in the period from 2009 to 2010 denotes the same tendency and rate of that from 2008 to 2009. We compared to the airphotographs which are taken by Taiwanese government at different age (1978 and 2007). If the creeping on the fault has continued for 30 years, the accumulation of displacement reaches about 1m, which is significantly-distinguishable by photogrammetric method. We measure profiles across the fault on 1978 and 2007 air-photograph by photogrammetric system respectively. The comparing result is shown that there are regional differences in deformation in relatively narrow region. About this result, we think two possibility; one is the creeping is not uniformity along the fault, second is the photogrammetry is not enough quality. We should actually check the creeping or not. We made thee new leveling survey lines in last year. In this August , we carried out second leveling survey in three area. We can show the variation of the deformation pattern and uplift rate across the LVF in this presentation.

Matta, N.; Murase, M.; Ishiguro, S.; Ozawa, K.; Lin, J.; Chen, W.; Lin, C.

2011-12-01

98

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

99

The effect of environment on the creep deformation of ultra-high purity nickel-chromium-iron alloys at 360 degrees Celcius  

NASA Astrophysics Data System (ADS)

Steam generators in pressurized water nuclear power plants have experienced significant problems with intergranular stress corrosion cracking (IGSCC) on the inner diameter of steam generator tubing for over 25 years. In the course of research to understand IGSCC, it has been shown that creep deformation may play a significant role in the cracking of commercial Alloy 600 (Ni-16Cr-9Fe-0.03C). The primary water environment can cause decreases in creep resistance (i.e., faster creep rates, shorter time to failure, and higher creep strains). During corrosion under the conditions of interest, both hydrogen reduction and metal dissolution occur. One or both may contribute to the enhancement of creep. The purpose of this work was to isolate the mechanism by which the water environment causes the creep deformation to increase. Activation area and activation enthalpy for glide were measured in argon and primary water on high purity Ni-16Cr-9Fe alloys. The results indicated that the activation area was reduced by primary water, consistent with a hydrogen enhanced plasticity mechanism for enhanced creep. The stress dependence of creep was also examined in argon and primary water. The results indicated that the internal stress of the alloy is reduced by the primary water environment. Lower internal stress is consistent with both a hydrogen model as well as a vacancy-aided climb model for enhanced creep. To isolate the effect of hydrogen on the creep of the alloy, experiments were conducted in a dissociated hydrogen environment. The results indicated that hydrogen would only increase the steady state creep rate if present before loading of the samples. However, if the sample was already in steady state creep and hydrogen introduced, a transient in the creep strain was observed. The creep rate returned to the original steady state rate in a short time. The results indicate that while hydrogen does affect the steady state creep to an extent, hydrogen cannot completely account for the increase in creep rate observed in primary water. Also, the presence of the aggressive environment before loading appears to be required to increase the creep rate, indicating that the effect of environment may be significant in the primary creep regime.

Paraventi, Denise Jean

2000-10-01

100

Deformation characteristics and eigenfrequencies of press-fit acetabular cups  

Microsoft Academic Search

BackgroundElastic deformation of press-fitted acetabular cups during implantation provides primary stability. Excessive deformation can lead to chipping or improper seating of ceramic inlays and is dictated by cup stiffness, which also affects its vibrational characteristics. Purpose was to investigate the influence of cup design on deformation during press-fitting and on vibration properties.

Arne Hothan; Gerd Huber; Cornelius Weiss; Norbert Hoffmann; Michael Morlock

2011-01-01

101

Deformation and damage processes during tensile creep of ceramic-fibre-reinforced ceramicmatrix composites  

Microsoft Academic Search

The tensile creep and creep fracture properties in air at 1300C are compared for SiCf\\/SiC and SiCf\\/Al2O3 composites, each reinforced with 0.38 volume fractions of interwoven silicon carbide (Nicalon) fibre bundles aligned parallel and normal to the stress direction. The differing behaviour patterns displayed by these 0\\/90 woven composites are analysed to identify the processes controlling creep strain accumulation and

B. Wilshire; F. Carreo

2000-01-01

102

Creep and rupture properties of an austenitic Fe-30Mn-9Al-1C alloys  

SciTech Connect

The creep deformation behavior and rupture properties of as-quenched austenitic Fe-30Mn-9Al-1C alloy have been studied at 923, 948, and 973 K under applied stresses ranging from 50 to 350 MPa. The creep curves of the alloy exhibited an extended tertiary stage prior to failure. The stress and temperature dependencies of the minimum creep rate indicated two regimes of creep deformation as well as a transition from creep to power-law breakdown. These two regimes of creep deformation were identified as a low-stress creep regime having an activation energy of 140 kJ/mol and a stress exponent of about 1, and a power-law creep regime having an activation energy of 350 kJ/mol and a stress exponent of about 6. Transmission electron microscope (TEM) observations of the deformed specimens revealed that a low density of dislocations, coarse dislocation networks, and profuse slip bands were developed in the low stress, power law, and power-law breakdown regimes, respectively. Optical microscope and scanning electron microscope (SEM) observations of the ruptured specimens showed that creep cavitation shifted from round-type in the low-stress creep regime to wedge-type in the power-law breakdown regime. The observed creep and rupture characteristics of the alloy are interpreted in terms of creep mechanisms, which involve the Coble creep and dislocation climb creep.

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

1998-01-01

103

Observation of primary regions in the tensile creep deformation of a superplastic zirconia-alumina composite  

Microsoft Academic Search

The present experimental investigation was undertaken to characterize the shape of the creep curves at low strain rates in a superplastic zirconia-alumina composite. It is shown that there is a significant primary creep region, and it is demonstrated that the lack of proper consideration of this phenomenon may lead to an incorrect evaluation of the stress exponent. A 3 mol%

D. M. Owen; A. H. Chokshi

1993-01-01

104

Deformation and failure in polyethylene: correlation between mechanisms of creep and fatigue  

Microsoft Academic Search

Fatigue and creep tests have been conducted on medium density gas- and water-grade pipe materials using a longitudinally notched pipe geometry with internal pressurization. The failure in both types of test was brittle compared to the failure occurring when the unnotched pipe is exposed to a constant intense pressure. Further to this superficial similarity, fractographic studies revealed creep and fatigue

P. T. Reynolds; C. C. Lawrence

1991-01-01

105

The Mechanics of Creep Deformation in Polymer Derived Continuous Fiber-Reinforced Ceramic Matrix Composites  

SciTech Connect

The objective of this Cooperative Research and Development Agreement between Lockheed Martin Energy Research Corporation and Dow Corning Corporation was to study the effects of temperature, stress, fiber type and fiber architecture on the time-dependent deformation and stress-rupture behavior of polymer-derived ceramic matrix composites developed by the Dow Corning Corporation. Materials reinforced with CG-Nicalon{trademark}, Hi-Nicalon{trademark} and Sylramic{reg_sign} fibers were evaluated under fast fracture, stress-relaxation, and stress-rupture conditions at temperatures between 700 C and 1400 C in ambient air and for stresses between 50 and 200 MPa. Some of the stress-rupture tests conducted as part of this program are among the longest-duration experiments ever conducted with these materials. The possibility of using accelerated test techniques to evaluate the very-long term stress-rupture/creep behavior of these materials was investigated by means of stress-relaxation experiments. However it was found that because these materials exhibit non-linear stress-strain behavior at stresses larger than the matrix cracking stress and because of environmentally-induced changes in the micro and mesostructure of the material, particularly at elevated temperatures, this approach is impractical. However, the results of stress-relaxation experiments will be useful to predict the behavior of these materials in applications where stresses are thermally-induced and therefore driven by strains (e.g., when components are subjected to thermal gradients). The evolution of the microstructure of the fibers, matrix and fiber-matrix interface was studied as a function of stress and temperature, using analytical electron microscopy. The results from these analyses were essential to understand the relationships between environment, stress, temperature and processing on the microstructure and properties of these materials.

Lara-Curzio, E.

2001-01-30

106

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

NASA Astrophysics Data System (ADS)

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

Seo, Dong Yi

107

Prior deformation effects on creep and fracture in inconel alloy X-750  

NASA Astrophysics Data System (ADS)

Creep fracture process in Inconel alloy X-750 can be modified by room-temperature prestraining. It has been observed that fracture in the prestrained specimens occurred due to growth and interlinkage of the prenucleated voids whereas failure occurred by plastic instability in the non-prestrained specimens. Creep ductility and the times-to-rupture are found to decrease progressively with room-temperature prestraining, but there is no marked influence on the minimum creep rate. This is explained in terms of two compcting processes: a weakening effect caused by prenucleation of grain boundary voids and a hardening effect due to generation of dislocations due to the prestraining.

Pandey, M. C.; Mukherjee, A. K.; Taplin, D. M. R.

1984-07-01

108

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

109

Matrix-dominated time-dependent deformation and damage of graphite/epoxy composite. Experimental data under creep and recovery. Final report, Jan. 1981-Sep. 1982  

SciTech Connect

The objective of this report is to disseminate experimental data of matrix-dominated time-dependent deformation and time-dependent damage in graphite-epoxy composite. The composite specimens were +-45/sup 0/ T300/5208 laminates tested in tension under creep and creep-recovery with complete instrumentation for stress, strain, and time recordings. Experimental data were recorded and archived in digital form. Polynomial series are fitted to the experimental data for compilation, dissemination and future retrieval.

Wu, E.M.; Sanchez, R.J.; Nguyen, N.Q.

1983-06-01

110

Prior deformation effects on creep and fracture in inconel alloy X-750  

Microsoft Academic Search

Creep fracture process in Inconel alloy X-750 can be modified by room-temperature prestraining. It has been observed that\\u000a fracture in the prestrained specimens occurred due to growth and interlinkage of the prenucleated voids whereas failure occurred\\u000a by plastic instability in the non-prestrained specimens. Creep ductility and the times-to-rupture are found to decrease progressively\\u000a with room-temperature prestraining, but there is no

M. C. Pandey; A. K. Mukherjee; D. M. R. Taplin

1984-01-01

111

Prior deformation effects on creep and fracture in inconel alloy X-750  

Microsoft Academic Search

Creep fracture process in Inconel alloy X-750 can be modified by room-temperature prestraining. It has been observed that fracture in the prestrained specimens occurred due to growth and interlinkage of the prenucleated voids whereas failure occurred by plastic instability in the non-prestrained specimens. Creep ductility and the times-to-rupture are found to decrease progressively with room-temperature prestraining, but there is no

M. C. Pandey; A. K. Mukherjee; D. M. R. Taplin

1984-01-01

112

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

SciTech Connect

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

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

1996-08-01

113

Creep deformation of Ni3Al-Mo in situ composites  

NASA Astrophysics Data System (ADS)

High temperature ?'(Ni3A1)-?(Mo) in situ composites solidified with growth rates ranging from 0.12 cm/h to 2.4 cm/h, were creep tested at temperatures 710 C, 830 C, and 950 C under a tensile stress of 300 MPa. Creep rupture lives of rapidly grown alloys were comparable to those of ?'/?-? and Nitac eutectics whereas strain to rupture was up to three times greater. In comparison, creep rupture lives of slowly grown alloys were more than ten times and strain to rupture about two times smaller than in rapidly grown alloys. In slowly grown alloys, failure occurred by formation of shear bands caused by cooperative shear of matrix and fibers whereas no shear bands were seen in rapidly grown samples. Shear band formation was due to pile-up stresses and parallel orientation of matrix and fiber slip systems, the latter resulting from a change in the crystallographic phase relationship as growth rate decreased. There was evidence that shear band formation depended on a threshold stress. The creep behavior of rapidly grown alloys was in qualitative agreement with predictions obtained from a linear visco-elastic model composite strengthened by the mean matrix stress.

Funk, W.; Blank, E.

1988-04-01

114

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

115

Universal scaling in transient 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 happens 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. This process, in geology known as pressure solution creep, plays a central role during compaction of sedimentary basins during tectonic deformation of the Earth's crust in strengthening of active fault gouges following earthquakes and in ceramics. Experimental data on pressure solution creep has so far not been sufficiently accurate to understand the transient processes at the grain scale. Here we present experimental evidence that pressure solution creep does not establish a steady state interface microstructure as previously thought. Conversely, pressure solution creep strain and the characteristic size of interface microstructures grow as the cubic root of time. Transient creep with the same scaling is known in metallurgy (Andrade creep). The apparent universal scaling of pressure solution transient creep is explained here using an analogy with spinodal dewetting.

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

2002-12-01

116

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. Khhorn; M. Springmann

117

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

PubMed

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

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

2012-05-01

118

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

NASA Astrophysics Data System (ADS)

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

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

2012-05-01

119

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

SciTech Connect

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

Reiche, H. M. [LANSCE Lujan Center, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); New Mexico State University, Las Cruces, New Mexico 88003 (United States); Vogel, S. C.; Larson, E. J. [LANSCE Lujan Center, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Mosbrucker, P. [LANSCE Lujan Center, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States); Department of Mechanical and Materials Engineering, Queen's University, Kingston K7L 3N6 (Canada); Daymond, M. R. [Department of Mechanical and Materials Engineering, Queen's University, Kingston K7L 3N6 (Canada)

2012-05-15

120

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

121

Creep Deformation of Lead-Free Sn3.5Ag-Bi Solders  

Microsoft Academic Search

Creep rupture properties of lead-free Sn-3.5Ag-based alloys with varying amounts of Bi were investigated using dog-bone-shaped rolled and heat-treated bulk specimens. Nominal compositions of Bi additions were 0, 2.5, 4.8, 7.5, and 10 wt%, respectively. The minimum strain rates (\\\\dot{\\\\varepsilon}min) were lowest for the 2.5Bi specimens. The stress exponents (n) of \\\\dot{\\\\varepsilon}min were usually around 4 0.6, with the exception

Seung Woo Shin; Jin Yu

2003-01-01

122

Dynamic characteristic of damaged ship structures considering the warping deformations  

Microsoft Academic Search

For some largely damaged ships, the conventional methods are unadaptable to estimate their dynamic characteristics as to ships\\u000a with symmetrical hull section. Based on dry hull modal analysis of flexure torsion coupling vibration of unsymmetrical ship\\u000a structures about longitudinal center line, a transfer matrix method to calculate the dynamic characteristics is presented.\\u000a Taken both shear effect and warping deformations

Wu Nie; Bao-Hua Wen; Guo-Long Chen

2002-01-01

123

Plastic instability during creep deformation of a NiAl-Hf single-crystal alloyA case study  

Microsoft Academic Search

Tensile samples from NiAl-Hf single crystals, having the same nominal composition and heat treated and creep tested under\\u000a identical conditions at 1144 K, were found to exhibit very different rupture lives and creep ductilities. A case study was\\u000a conducted on two samples with creep rupture lives of 343.6 and 37.0 hours (with corresponding creep ductilities of 12.3 and\\u000a 39.9 pct,

A. Garg; S. V. Raj; R. D. Noebe; M. V. Nathal; R. Darolia

1998-01-01

124

Transient and steady-state creep characteristics of Cu-2wt% Sn alloy in the solid solution region  

NASA Astrophysics Data System (ADS)

Bronzes exhibit a combination of high heat conductivity and excellent mechanical strength. They have many important commercial industrial applications. Isothermal tensile creep curves of Cu-2wt% Sn were obtained in the solid solution region at temperatures 573, 623, 673 and 723K under constant stresses ranging from 64 to 111MPa. The values of the transient creep parameters ? and n showed dependence on the deformation temperatures, T, and the applied stress, ?. ? increased with both T and ? while n decreased. n is expected to be independent on the temperature at a stress of 208.3MPa. The dependence of the steady-state creep rate, ??, on the grain diameter, d, satisfies a petch type equation ??=??o+bd. ?? increases with both ? and T for any grain diameter. The stress exponent, m, is independent on d but relates to the deformation temperature, T, by the empirical formula m=0.655+4510-4T. the activation energy of the steady-state creep, Q, decreases with increasing the grain diameter. For any grain diameter, Q is slightly affected by the applied stress. The straight line obtained by the best fitting for the relation between Q and 1/d, has an intercept of 64.9kJ/mol. This value may correspond to the activation energy of the dislocation climb mechanism in a single crystal of Cu-2wt% Sn alloy.

Al-Ganainy, G. S.; Fawzy, A.; Abd El-Salam, F.

2004-02-01

125

Dynamic characteristic of damaged ship structures considering the warping deformations  

NASA Astrophysics Data System (ADS)

For some largely damaged ships, the conventional methods are unadaptable to estimate their dynamic characteristics as to ships with symmetrical hull section. Based on dry hull modal analysis of flexure torsion coupling vibration of unsymmetrical ship structures about longitudinal center line, a transfer matrix method to calculate the dynamic characteristics is presented. Taken both shear effect and warping deformations into account, the point and field transfer matrices are derived, and the influence on dynamic characteristics is computed according to different damaged positions and ranges. As examples, the damaged structures are calculated and some interesting conclusions are obtained.

Nie, Wu; Wen, Bao-Hua; Chen, Guo-Long

2002-06-01

126

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

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

127

A TEM study of deformation processes and microstructural changes during long-term tension creep of a two-phase ?-titanium aluminide alloy  

Microsoft Academic Search

Long-term tension creep tests were performed on a Ti-48 at.% Al-2 at.% Cr alloy in order to assess the material behaviour under the intended service conditions for structural parts in turbine engines. Deformation processes and microstructural changes were investigated by TEM on a specimen loaded to 140 MPa for 5988 h at 700C. At lamellar boundaries the emission of interfacial

M. Oehring; F. Appel; P. J. Ennis; R. Wagner

1999-01-01

128

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

129

Birefringence simulations for annealed ingots of the <001>-and <111>- growth calcium fluoride single crystals with consideration of creep deformation  

NASA Astrophysics Data System (ADS)

We developed an analysis system for simulating birefringence of an annealed ingot of CaF2 single crystal caused by the residual stress after annealing process. The analysis system comprises the heat conduction analysis that provides the temperature distribution during the ingot annealing, the stress analysis to calculate the residual stress after ingot annealing, and the birefringence analysis of an annealed ingot induced by the residual stress. The finite element method was applied to the heat conduction analysis and the stress analysis. In these analyses, the temperature dependence of material properties and the crystal anisotropy were taken into account. In the residual stress calculation, we considered the time-dependent nonlinear deformation behavior of a material called creep. In the birefringence analysis, the distributions of optical path difference were calculated by using average stress method with consideration of the crystal anisotropy. We can perform the birefringence analysis of an ingot of CaF2 single crystal with any growth direction, using this analysis system, and we performed the analyses of the crystals with the <001> and <111> growth directions. From these analyses, we obtained reasonable results of optical path difference in comparison with the experimental results.

Kitamura, Y.; Ogino, H.; Miyazaki, N.; Mabuchi, T.; Nawata, T.

2010-06-01

130

Quartz veins deformed by diffusion creep-accommodated grain boundary sliding during a transient, high strain-rate event in the Southern Alps, New Zealand  

NASA Astrophysics Data System (ADS)

The crystallographic preferred orientations (CPOs) and microstructures of deformed quartz veins were measured for four samples in the hanging-wall of the Alpine Fault in the Southern Alps, New Zealand. Their deformation and exhumation has occurred since 4 Ma. The quartz veins have been ductilely sheared to finite shear-strains of 5 15 in late Cenozoic shear zones at 45050 C, 31090 MPa and strain-rates between 210-11 and 210-9 s-1. The sheared veins have a polygonal microstructure with few subgrains and an average grain-size of 100 ?m. The CPO of the veins is random to very weak within the shear zones. We suggest that dislocation creep accommodated initial shear deformation, at high stresses and strain-rates. The deformation must have created a strong CPO and concomitant dynamic recrystallization reduced the grain-size significantly. Dissipation of stresses during initial deformation lead to a stress and strain-rate drop required for a switch to diffusion creep-accommodated grain boundary sliding (GBS). Continued shearing accommodated by GBS destroyed the CPO. Post-deformational grain growth gave rise to a final polygonal microstructure with a similar grain size in veins and in the wall rocks. Analysis of existing experimental data suggest that this sequence of events is possible in the time available. Rates of all processes may have been enhanced by the presence of a water-rich fluid within the shear zones. These observations of naturally deformed rocks provide a model for the processes that may occur during short-lived deformation at transiently-high stresses at mid-crustal depths or deeper.

Wightman, Ruth H.; Prior, David J.; Little, Timothy A.

2006-05-01

131

Deformation Induced Dissolution-Creep in the Ductile Lishan Fault Zone, Taiwan  

NASA Astrophysics Data System (ADS)

Slates of similar low metamorphic grade on either side of the Lishan fault zone, central Taiwan display a single pervasive cleavage defined by muscovite (mu)and chlorite (chl) folia whereas interbedded quartzites are commonly fractured. CL imaging of quartz in the slates reveals three distinct populations, namely detrital quartz of mixed provenance, authigenic overgrowths, and metamorphic overgrowths and ribbons. Textures show that metamorphic quartz with overgrowths is widespread and that boundaries of these complex grains are sharply truncated by cleavage forming mu+chl folia. Electron petrography of the phyllosilicates shows three texturally distinct generations of muscovite: detrital, pre-deformation mu-chl stacks, and metamorphic mu+chl folia. Both detrital grains and mu-chl stacks are truncated and dissolved by the younger mu+chl cleavage-forming fabric. Detrital plagioclase grains are also truncated by mica folia and are commonly overgrown by quartz pressure shadows. These observed textures qualitatively demonstrate the active role of dissolution and precipitation in the slaty cleavage development. To further assess the dissolution-precipitation process, we have applied whole-rock 40Ar/39Ar analysis, and X-ray diffraction (XRD) to bulk samples. Widely ranging Cenozoic whole-rock 40Ar/39Ar total gas ages from the slates reflect the isotopic contributions from the three muscovite age populations, and demonstrate that the slates never exceeded the Ar retention temperature for muscovite. XRD data show significant range of broadening of muscovite peaks (modeled using a strain parameter in the Rietveld refinement). We attribute to the peak broadening (high value of strain parameter) to the presence of multiple muscovite populations of varied chemical composition; this was confirmed by energy-dispersive X-ray analyses. The total gas ages decrease with the narrowing of the muscovite peaks and drop in the muscovite strain parameter. This can be explained by the disappearance of older muscovite populations (> ~15 Ma) via dissolution with the concomitant precipitation of young (< ~5 Ma) fabric-forming muscovite. The ratio of metamorphic quartz to total quartz (quantified from CL transects) correlates positively with total gas ages. However, the relative proportion of metamorphic quartz correlates inversely with the relative amount of cleavage forming muscovite as inferred from the strain parameter. These correlations suggest that quartz recrystallization induced by deformation was active, but independent of the degree of muscovite recrystallization. However, both mineral populations were actively participating in the development of the fabric. Thus the deformation-induced dissolution of detrital and authigenic minerals and precipitation of fabric-forming minerals dominated the development of slaty cleavage during lower greenschist facies deformation.

Stokes, M.; Wintsch, R. P.; Kunk, M. J.; Bish, D. L.

2011-12-01

132

Creep and creep rupture of an advanced silicon nitride ceramic  

Microsoft Academic Search

Creep and creep rupture behavior of an advanced silicon nitride ceramic were systematically characterized in the temperature range 1,150 to 1,300 C using uniaxial tensile creep tests. Absence of tertiary creep and the order-of-magnitude breaks in both creep rate and rupture lifetime at certain threshold combinations of stress and temperature were tow characteristic features of the creep behavior observed. Thermal

Jow-Lian Ding; Kenneth C. Liu; Karren L. More; C. R. Brinkman

1994-01-01

133

Creep characteristics of hand- and vacuum-mixed acrylic bone cement at elevated stress levels.  

PubMed

Compressive creep testing of cylindrical specimens machined from two commercial self-polymerizing acrylic bone cements demonstrated measurable creep strains with higher creep strains for the hand-mixed cement specimens compared to vacuum-mixed cement ones. The average creep strains of hand-mixed cement, after 6 h of constant load, ranged from 0.11% at 10.5 MPa to 14.0% at 50 MPa of applied stress. Vacuum mixing reduced the average creep strain to 6.7% after 6 h of applied stress at 50 MPa. There were no significant differences in the creep response between the two types of acrylic cements. The difference in creep resistance of the two cements was reduced after vacuum mixing (P = .013), which also significantly reduced the cement's internal porosity. PMID:7622534

Norman, T L; Kish, V; Blaha, J D; Gruen, T A; Hustosky, K

1995-04-01

134

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

SciTech Connect

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

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

1996-04-01

135

Cavitation characteristics of a superplastic 8090 Al alloy during equi-biaxial tensile deformation  

Microsoft Academic Search

Cavitation behavior of a superplastic 8090 Al alloy during equi-biaxial tensile deformation has been investigated by deforming the sheet into a right cylindrical die. Cavitation characteristics could be separated into two stages. In stage I, the sheet deformed freely as part of a spherical dome, and the cavity volume increased exponentially with deformation. The evolution of cavity volume was due

Horng-yu Wu

2000-01-01

136

A microstructural study of fault rocks from the SAFOD: Implications for the deformation mechanisms and strength of the creeping segment of the San Andreas Fault  

NASA Astrophysics Data System (ADS)

The San Andreas Fault zone in central California accommodates tectonic strain by stable slip and microseismic activity. We study microstructural controls of strength and deformation in the fault using core samples provided by the San Andreas Fault Observatory at Depth (SAFOD) including gouge corresponding to presently active shearing intervals in the main borehole. The methods of study include high-resolution optical and electron microscopy, X-ray fluorescence mapping, X-ray powder diffraction, energy dispersive X-ray spectroscopy, white light interferometry, and image processing.The fault zone at the SAFOD site consists of a strongly deformed and foliated core zone that includes 2-3 m thick active shear zones, surrounded by less deformed rocks. Results suggest deformation and foliation of the core zone outside the active shear zones by alternating cataclasis and pressure solution mechanisms. The active shear zones, considered zones of large-scale shear localization, appear to be associated with an abundance of weak phases including smectite clays, serpentinite alteration products, and amorphous material. We suggest that deformation along the active shear zones is by a granular-type flow mechanism that involves frictional sliding of microlithons along phyllosilicate-rich Riedel shear surfaces as well as stress-driven diffusive mass transfer. The microstructural data may be interpreted to suggest that deformation in the active shear zones is strongly displacement-weakening. The fault creeps because the velocity strengthening weak gouge in the active shear zones is being sheared without strong restrengthening mechanisms such as cementation or fracture sealing. Possible mechanisms for the observed microseismicity in the creeping segment of the SAF include local high fluid pressure build-ups, hard asperity development by fracture-and-seal cycles, and stress build-up due to slip zone undulations.

Hadizadeh, Jafar; Mittempergher, Silvia; Gratier, Jean-Pierre; Renard, Francois; Di Toro, Giulio; Richard, Julie; Babaie, Hassan A.

2012-09-01

137

Postseismic deformation due to the Mw 6.0 2004 Parkfield earthquake: Stress-driven creep on a fault with spatially variable rate-and-state friction parameters  

NASA Astrophysics Data System (ADS)

We investigate the coseismic and postseismic deformation due to the Mw 6.0 2004 Parkfield, California, earthquake. We produce coseismic and postseismic slip models by inverting data from an array of 14 continuous GPS stations from the SCIGN network. Kinematic inversions of postseismic GPS data over a time period of 3 years show that afterslip occurred in areas of low seismicity and low coseismic slip, predominantly at a depth of 5 km. Inversions suggest that coseismic stress increases were relaxed by predominantly aseismic afterslip on a fault plane. The kinetics of afterslip is consistent with a velocity-strengthening friction generalized to include the case of infinitesimal velocities. We performed simulations of stress-driven creep using a numerical model that evaluates the time-dependent deformation due to coseismic stress changes in a viscoelastoplastic half-space. Starting with a coseismic slip distribution, we compute the time-dependent evolution of afterslip on a fault plane and the associated displacements at the GPS stations. Data are best explained by a rate-strengthening model with frictional parameter (a - b) = 7 10-3, at a high end of values observed in laboratory experiments. We also find that the geodetic moment due to creep is a factor of 100 greater than the cumulative seismic moment of aftershocks. The rate of aftershocks in the top 10 km of the seismogenic zone mirrors the kinetics of afterslip, suggesting that postearthquake seismicity is governed by loading from the nearby aseismic creep. The San Andreas fault around Parkfield is deduced to have large along-strike variations in rate-and-state frictional properties. Velocity strengthening areas may be responsible for the separation of the coseismic slip in two distinct asperities and for the ongoing aseismic creep occurring between the velocity-weakening patches after the 2004 rupture.

Barbot, Sylvain; Fialko, Yuri; Bock, Yehuda

2009-07-01

138

Deformation and fracture characteristics of spent Zircaloy fuel cladding  

SciTech Connect

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

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

1982-09-01

139

Numerical creep analysis  

SciTech Connect

A large deformation creep algorithm is presented that includes pore pressure and fluid migration effects. Its application is illustrated by the numericl analysis of rock folding with attendant fluid migration. 6 references, 2 figures. (ACR)

Anderson, C.A.

1984-01-01

140

Deformation characteristics and history along the Ilkwang Fault, SE Korea  

NASA Astrophysics Data System (ADS)

The NNE-SSW trending Ilkwang Fault is one of the major structural features around SE Korea. It is a high angle, right-lateral strike-slip fault with a displacement of about 1.2 km. The basement around the fault is Cretaceous sedimentary and volcanic rocks forming a part of the Gyeongsang Basin in SE Korea, and it is intruded by later igneous rocks. The fault has not been studied intensively due to poor exposure along the fault. However, understanding the characteristics of the Ilkwang Fault is important because three nuclear power plants and one nuclear waste disposal site are located around the fault. We have mainly investigated along the new road-cut sections of the Busan-Ulsan Highway. Many geologic structures such as dykes, folds, and faults are measured in several studied sites. The analyzed structural patterns indicate multi-deformation including reactivation of pre-existing faults. In this study, we analyzed variation patterns of attitude on the beddings and fractures around some parts of the Ilkwang Fault. The strike/dip variation from the general attitude of the structural elements (e.g. beddings) is here used as an indicator of deformation intensity across the fault. This analysis indicates that respect distances (highly deformed area affected by faulting) along the Ilkwang Fault is about 1 km in sedimentary rocks and 200 m in volcanic rocks, respectively. It indicates that the Ilkwang Fault is a relatively big fault, and layered sedimentary rock is relatively weaker than massive volcanic rock under brittle deformation. Deformation history in the studied area, based on kinematic analysis of faults, joints and dykes, is as follows: 1) NNE-SSW trending reverse fault and fold. 2) E-W trending reverse fault and N-S trending acidic dykes. 3) ENE-WSW trending left-lateral fault, NNE-SSW trending right-lateral fault, and NE-SW trending basic dykes. 4) E-W trending normal fault. 5) N-S or NNE-SSW trending reverse fault.

Jin, K.; Kim, Y.; Yang, S.; Choi, J.

2009-12-01

141

Influence of cycling frequency on cyclic creep characteristics of nickel base single-crystal superalloy  

Microsoft Academic Search

The static and the cyclic creep load-controlled tests of the nickel base single-crystal superalloy, CMSX 3 have been studied. In this study, two different testing procedures of cyclic creep were carried out under specific loading schedules defined by the stress amplitude, the stress range, stress ratio, and cycling frequency. The different cycling frequencies for two cycling hold periods were investigated

J. Zrnik; J. A. Wang; Y. Yu; L. Peijing; P. Hornak

1997-01-01

142

High temperature creep deformation of Si/sub 3/N/sub 4/-/sub 6/Y/sub 2/O/sub 3/-/sup 2/Al/sub 2/O/sub 3/  

SciTech Connect

The creep properties of silicon nitride containing 6 wt percent yttria and 2 wt percent alumina have been determined in the temperature range 1573 to 1673 K. The stress exponent, n, in the equation epsilon dot varies as sigma sup n, was determined to be 2.00 + or - 0.15 and the true activation energy was found to be 692 + or - 25 kJ/mol. Transmission electron microscopy studies showed that deformation occurred in the grain boundary glassy phase accompanied by microcrack formation and cavitation. The steady state creep results are consistent with a diffusion controlled creep mechanism involving nitrogen diffusion through the grain boundary glassy phase.

Todd, J.A.; Xu, Z.Y.

1988-01-01

143

(Creep cavitation in nickel aluminides)  

SciTech Connect

Work on creep cavitation has been performed in collaboration with Professor L. Martinez of the Instituto de Fisica of the Universidad Nacional de Mexico in Cuernavaca, Mexico. A joint manuscript on Influencing the Shape of Creep Cavities in Nickel Aluminides by Stress Changes'' has been finalized. All details required to perform urgently needed numerical calculations on the growth of creep cavities in the presence of creep deformation have been identified and clearly defined. Ideas for incorporating the stochastic aspects of creep cavitation (coalescence) have been developed and will improve our present understanding of creep cavitation in nickel aluminides.

Schneibel, J.H.

1987-08-18

144

Creep transitions in an Al-Zn alloy  

NASA Astrophysics Data System (ADS)

The creep behavior of an Al-10 at. pct Zn alloy was investigated at temperatures in the range 573 to 800 K and in a normalized shear stress range, ?/G, extending from 106 to 103, where ? is the applied shear stress and G is the shear modulus. The results reveal the presence of four deformation regions: region I (very low stresses), region II (low stresses), region III (intermediate stresses), and region IV (high stresses). In regions II and III, the creep characteristics including the stress exponent, the shape of the creep curve, and the nature of creep transients after stress reductions are consistent with dislocation climb and viscous glide, respectively. The experimental transition stresses between region II (climb) and region III (glide) were compared with those predicted from the deformation criterion for solid-solution alloys, and it is demonstrated that the correlation between experiment and prediction becomes satisfactory when corrections concerning the appropriate diffusion coefficients for describing glide-controlled creep and climb-controlled creep, the stacking fault energy of the alloy, and the contributions of Suzuki interaction and Fisher interaction to solute atom drag forces are incorporated in the analysis. Experimental data in region IV are not sufficient to unambiguously identify the rate process, but calculations show that the values of the transition stress between region III and region IV agree reasonably well with those of the critical stress for dislocation breakaway from a solute-atom atmosphere. The characteristics of deformation in region I are still under investigation.

Soliman, Mahmoud S.; Mohamed, Farghalli A.

1984-10-01

145

Experimental Verification of Constitutive Equations for Creep and the Interaction of Creep and Plasticity under Biaxial Loading Conditions.  

National Technical Information Service (NTIS)

Creep experiments were carried out on austenitic steel WN 1.4948 to produce constitutive equations for creep deformations arising from arbitrary conditions. Constant load and program loading creep tests on solid specimens, including relaxation and recover...

F. Roode W. Dortland

1983-01-01

146

Numerical analysis of fracture and high temperature creep characteristics of composites with discontinuous ductile reinforcements.  

National Technical Information Service (NTIS)

Role of material parameters on fracture and creep behavior of discontinuous ductile fiber reinforced brittle matrix composite system was numerically investigated. For simulation of fracture behavior, the ductile fibers were modeled using a constitutive re...

S. B. Biner

1994-01-01

147

[Creep characteristics of Bis.GMA-Tri.EDMA based composite resins].  

PubMed

The creep of chemical activated and visible light activated composite resins was studied using a transverse testing instrument. In addition, the water absorption of their materials was measured, and the effect of the moisture on creep behavior was discussed. The water absorption properties of chemically activated composite resin were smaller than those of light activated composites. However, the former's creep strain increased markedly, in comparison with that of light activated resins. This result indicates that the phenomenon may derive from differences in the reaction accelerators of the composites. Increases in filler content reduced creep strain. Furthermore, the setting reaction of both types of resins was seen proceeding over a fairly long period. PMID:2535159

Tabata, Y

1989-11-01

148

Finite Creep of Closed Membranes of Revolution.  

National Technical Information Service (NTIS)

The creep of a closed membrane shell of revolution subject to uniform pressure is investigated. Large deformation incremental theory including a non-linear creep law is applied. A numerical analysis is carried out for initially ellipsoidal shapes and vari...

K. Hellan

1971-01-01

149

Magnetic and Physical Characteristics of Magnetite Associated with Deformation and Exsolution  

NASA Astrophysics Data System (ADS)

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

Till, Jessica Lynn

150

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

151

Part 2: The creep behavior of Ti-Al-Nb O + bcc orthorhombic alloys  

SciTech Connect

The intermediate-temperature (650 C to 760 C) creep behavior of orthorhombic (O) + bcc alloys containing 50 at. pct Ti was studied. Ti-25Al-25Nb, Ti-23Al-27Nb, and Ti-12Al-38Nb ingots were processed and heat treated to obtain a wide variety of microstructures. Creep deformation mechanisms and the effects of grain size, phase volume fraction, tension vs compression and aging on creep rates were examined. Unaged microstructures, which transformed during the creep experiments, exhibited larger primary creep strains than transformed microstructure, which were crept after long-term aging. The deformation observations and calculated creep exponents and activation energies suggested that separate creep mechanisms, dependent on the applied stress level, were dominating the secondary creep behavior. Coble creep characteristics, including relatively low activation energies and dislocation densities as well as stress exponents close to unity, were exhibited at low applied stresses. Experiments on fiducially marked specimens indicated that grain-boundary sliding was occurring for intermediate applied stresses. In this regime, the minimum creep rates were proportional to the applied stress squared and inversely proportional to the grain size. Overall, the minimum creep rates were dependent on microstructure and stress. Within the low-to-intermediate stress regimes, subtransus processed and heat-treated microstructures, which contained much finer grain sizes than supertransus microstructures, exhibited the poorest creep resistance. The influence of grain size was not as significant within the high-stress regime. It is shown that for low-to-intermediate stress levels, grain size is the dominant microstructural feature influencing the creep behavior of O + bcc alloys.

Boehlert, C.J. [Johns Hopkins Univ., Baltimore, MD (United States). Dept. of Mechanical Engineering; Miracle, D.B. [Air Force Research Lab., Wright-Patterson AFB, OH (United States)

1999-09-01

152

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

153

An Experimental Study on Creep Characteristics of Salt Rock and Gypsum-salt Rock in Puguang Gas Field  

Microsoft Academic Search

Through the determination of mineralogical compositions of the salt rock and gypsum-salt rock in Puguang gas field and the creep experiments on these rocks, the authors analyze the impacts of mineralogical compositions, deviatoric stress, temperature, and confining pressure on creep behavior and proposes the constitutive equation of steady-state creep rate by combining with the creep curve and rock parameters obtained

P. Li; J. C. Deng; W. L. Zhao; Y. C. Feng

2012-01-01

154

Room temperature fracture and high temperature creep deformation properties of alumina reinforced with 20 vol % particulate niobium  

SciTech Connect

For this material, an increase in RT crack growth resistance of {ge} 300% was achieved; this property increases with increasing Nb particle size. SEM and in-situ crack growth observations show that crack bridging is the primary toughening mechanism for the increased crack growth resistance. A model was presented which uses existing models to determine the steady state bridging length given a stress intensity due to crack bridging. This model showed that the specimen size used for determining the RT fracture toughness was too small. It was also determined that the creep strain rate is in the same range as and comparable to existing studies of Al{sub 2}O{sub 3} and Al{sub 2}O{sub 3} systems. The creep mechanism of the composite material was found to be similar to that of unreinforced Al{sub 2}O{sub 3} with a stress redistribution to the particle/matrix interface.

Lane, S.

1994-10-20

155

Dynamic behavior of the dislocation network in monocrystalline NaCl during creep deformation at elevated temperatures  

Microsoft Academic Search

A series of constant-stress creep tests on monocrystalline NaCl compressed parallel to (100) was conducted under various conditions of temperature (T = 650 and 700 C) and stress ( = 0.39, 0.59, and 0.78 MPa). Tests were terminated at various values of strain within the primary stage, as well as in steady state. For each sample tested, the dislocation density,

P. Lin; A. J. Ardell

2008-01-01

156

GENOTYPE RESPONSES AND PLANT CHARACTERISTICS ASSOCIATED WITH DOLLAR SPOT RESISTANCE IN CREEPING BENTGRASS (AGROSTIS PALUSTRIS HUDS.)  

Technology Transfer Automated Retrieval System (TEKTRAN)

Dollar spot, incited by Sclerotinia homoeocarpa F.T. Bennet, is one of the principle diseases affecting creeping bentgrass (Agrostis palustris Huds.) greens, fairways, and tees. Genetic resistance is the most promising of the disease control strategies. A study was initiated to: 1) evaluate dollar...

157

Extreme ductile deformation of fine-grained salt by coupled solution-precipitation creep and microcracking: Microstructural evidence from perennial Zechstein sequence (Neuhof salt mine, Germany)  

NASA Astrophysics Data System (ADS)

Microstructural study revealed that the ductile flow of intensely folded fine-grained salt exposed in an underground mine (Zechstein-Werra salt sequence, Neuhof mine, Germany) was accommodated by coupled activity of solution-precipitation (SP) creep and microcracking of the halite grains. The grain cores of the halite aggregates contain remnants of sedimentary microstructures with straight and chevron shaped fluid inclusion trails (FITs) and are surrounded by two concentric mantles reflecting different events of salt precipitation. Numerous intra-granular or transgranular microcracks originate at the tips of FITs and propagate preferentially along the interface between sedimentary cores and the surrounding mantle of reprecipitated halite. These microcracks are interpreted as tensional Griffith cracks. Microcracks starting at grain boundary triple junctions or grain boundary ledges form due to stress concentrations generated by grain boundary sliding (GBS). Solid or fluid inclusions frequently alter the course of the propagating microcracks or the cracks terminate at these inclusions. Because the inner mantle containing the microcracks is corroded and is surrounded by microcrack-free outer mantle, microcracking is interpreted to reflect transient failure of the aggregate. Microcracking is argued to play a fundamental role in the continuation and enhancement of the SP-GBS creep during halokinesis of the Werra salt, because the transgranular cracks (1) provide the ingress of additional fluid in the grain boundary network when cross-cutting the FITs and (2) decrease grain size by splitting the grains. More over, the ingress of additional fluids into grain boundaries is also provided by non-conservative grain boundary migration that advanced into FITs bearing cores of grains. Described readjustments of the microstructure and mechanical and chemical feedbacks for the grain boundary diffusion flow in halite-brine system are proposed to be comparable to other rock-fluid or rock-melt aggregates deforming by the grain boundary sliding (GBS) coupled deformation mechanisms.

Zvada, Prokop; Desbois, Guillaume; Schwedt, Alexander; Lexa, Ondrej; Urai, Janos L.

2012-04-01

158

Small Strain Deformation Characteristics of Granular Materials in Torsional Shear and Triaxial Tests with Local Deformation Measurements  

NASA Astrophysics Data System (ADS)

The soil behaviour under normal working loads usually mobilizes strain increments that are less than 0.1 %. Therefore it is very important to measure the small deformation of soil by laboratory experiments accurately. Among others, the local deformation transducer (LDT) has been used to measure locally small deformation of cylindrical or rectangular specimens in triaxial tests. In this study, a hollow cylindrical specimen was used in torsional shear and triaxial tests. By using a modified version of LDT, called PLDT (Pin-typed LDT), to comply with shear deformation of hollow cylindrical specimen under torsional loading, it was confirmed that the modified version could be successfully used to evaluate quasi-elastic deformation properties. The small deformation characteristics of Toyoura sand, Hime gravel and glass beads were investigated using both PLDTs for the local static measurement and gap sensors and a potentiometer for the external static measurement. In addition, a dynamic measurement system by using a set of small triggers and accelerometers was used to evaluate S wave velocity of glass beads. The specimens at different densities were subjected to small vertical and torsional cyclic loadings during otherwise isotropic consolidation from 50 kPa to 400 kPa and isotropic unloading from 400 kPa to 50 or 100 kPa.

Kiyota, T.; De Silva, L. I. N.; Sato, T.; Koseki, J.

159

Increased Variability of Bone Tissue Mineral Density Resulting from Estrogen Deficiency Influences Creep Behavior in a Rat Vertebral Body  

PubMed Central

Progressive vertebral deformation increases the fracture risk of a vertebral body in the postmenopausal patient. Many studies have observed that bone can demonstrate creep behavior, defined as continued time-dependent deformation even when mechanical loading is held constant. Creep is a characteristic of viscoelastic behavior, which is common in biological materials. We hypothesized that estrogen deficiency-dependent alteration of the mineral distribution of bone at the tissue level could influence the progressive postmenopausal vertebral deformity that is observed as the creep response at the organ level. The objective of this study was thus to examine whether the creep behavior of vertebral bone is changed by estrogen deficiency, and to determine which bone property parameters are responsible for the creep response of vertebral bone at physiological loading levels using an ovariectomized (OVX) rat model. Correlations of creep parameters with bone mineral density (BMD), tissue mineral density (TMD) and architectural parameters of both OVX and sham surgery vertebral bone were tested. As the vertebral creep was not fully recovered during the post-creep unloading period, there was substantial residual displacement for both the sham and OVX groups. A strong positive correlation between loading creep and residual displacement was found (r=0.868, p<0.001). Of the various parameters studied, TMD variability was the parameter that best predicted the creep behavior of the OVX group (p<0.038). The current results indicated that creep caused progressive, permanent reduction in vertebral height for both the sham and OVX groups. In addition, estrogen deficiency-induced active bone remodeling increased variability of trabecular TMD in the OVX group. Taken together, these results suggest that increased variability of trabecular TMD resulting from high bone turnover influence creep behavior of the OVX vertebrae.

Kim, Do-Gyoon; Navalgund, Anand R.; Tee, Boon Ching; Noble, Garrett J.; Hart, Richard T.; Lee, Hye Ri

2012-01-01

160

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

161

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

162

Universal Scaling in Transient Creep  

NASA Astrophysics Data System (ADS)

We present experimental evidence that pressure solution creep does not establish a steady-state interface microstructure as previously thought. Conversely, pressure solution controlled strain and the characteristic length scale of interface microstructures grow as the cubic root of time. Transient creep with the same scaling is known in metallurgy (Andrade creep). The apparent universal scaling of pressure solution transient creep is explained using an analogy with spinodal dewetting.

Dysthe, Dag Kristian; Podladchikov, Yuri; Renard, Francois; Feder, Jens; Jamtveit, Bjrn

2002-11-01

163

Characteristics of aluminum alloy microplastic deformation in different structural states  

SciTech Connect

The solution to the problem of improving the mechanical properties (including cyclic strength) of structural materials is largely dependent on our knowledge of the laws governing the development of microplastic deformations in them. The effect of heat and mechanical treatment on the elastoplastic properties and fatigue resistance of the commercial aluminum alloys AK4-1 and D16 is analyzed.

Seregin, G.V.; Efimenko, L.L.; Leonov, M.V. [Novosibirsk Pedagogical Inst. (Russian Federation)

1995-07-01

164

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 (0 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

165

Magnetic characteristics of HPT deformed soft-magnetic materials  

NASA Astrophysics Data System (ADS)

Five sets of soft-magnetic metals, such as pure Fe, pure Ni, Fe-3 wt% Si, Fe-6.5 wt% Si and Fe-17 wt% Co, were subjected to high pressure torsion (HPT) up to strain levels where a saturation of the microstructural refinement is observed. Following HPT at 77, 293 and 723 K, transmission electron microscopy (TEM) was used to study the grain size and grain shape of the severely deformed metals. The coercivity HC was characterized in a magnetic closed system by using ring shaped samples. Magnetic measurements obtained on ring shaped samples give a much higher accuracy for determining the coercivity. Depending on the material the mean microstructural sizes in the steady state vary from 300 nm at 723 K to 30 nm at 77 K, respectively. The coercivity of the deformed materials first increases with decrease in grain size. Once the crystallite size is far below 100 nm the coercivity shows a strong decrease.

Scheriau, S.; Kriegisch, M.; Kleber, S.; Mehboob, N.; Grssinger, R.; Pippan, R.

2010-10-01

166

High temperature deformation properties of nial single crystals  

Microsoft Academic Search

The high-temperature deformation properties of stoichiometric NiAl single crystals have been studied in the temperature range\\u000a from 850 C and 1200 C. We have established a basic data set for and have explored the high-temperature deformation characteristics\\u000a of this intermetallic compound. The results provide a basis for determining the controlling mechanisms of high-temperature\\u000a deformation. Constant stress tension creep and constant

K. R. Forbes; U. Glatzel; R. Darolia; W. D. Nix

1996-01-01

167

High temperature deformation properties of nial single crystals  

Microsoft Academic Search

The high-temperature deformation properties of stoichiometric NiAl single crystals have been studied in the temperature range from 850 C and 1200 C. We have established a basic data set for and have explored the high-temperature deformation characteristics of this intermetallic compound. The results provide a basis for determining the controlling mechanisms of high-temperature deformation. Constant stress tension creep and constant

K. R. Forbes; U. Glatzel; R. Darolia; W. D. Nix

1996-01-01

168

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

2013-08-01

169

Effects of microstructural evolution on superplastic deformation characteristics of a rapidly solidified Al-Li alloy  

Microsoft Academic Search

This study is concerned with the effects of microstructural modification on superplastic deformation characteristics of a\\u000a rapidly solidified (RS) Al-3Li-1Cu-0.5Mg-0.5Zr (wt pct) alloy. This Al-Li alloy has a very fine grain structure desirable\\u000a for improved superplasticity. The results of superplastic deformation indicated that the alloy exhibited a high superplastic\\u000a ductility, e.g., elongation of approximately 800 pct, when deformed at temperatures

Yong Namkwon; Hyang Jin Koh; Sunghak Lee; Nack J. Kim; Young Won Chang

2001-01-01

170

Deformations of classical Lie algebras with homogeneous root system in characteristic two. I  

NASA Astrophysics Data System (ADS)

Spaces of local deformations of classical Lie algebras with a homogeneous root system over a field K of characteristic 2 are studied. By a classical Lie algebra over a field K we mean the Lie algebra of a simple algebraic Lie group or its quotient algebra by the centre. The description of deformations of Lie algebras is interesting in connection with the classification of the simple Lie algebras.

Chebochko, N. G.

2005-10-01

171

Deformation characteristics of Ti6Al4V alloy under isothermal forging conditions  

Microsoft Academic Search

An investigation was undertaken to determine the influence of forge temperature, ram rate, and starting microstructure on\\u000a the deformation characteristics of isothermally forged Ti-6A1-4V alloy. Both yielding and finish forge pressures were measured\\u000a in the practical range of forge temperatures and ram rates. With the absence of die-chilling, the results obtained can be\\u000a quantitatively related to the hot deformation properties.

C. C. Chen; J. E. Coyne

1976-01-01

172

Two-dimensional boundary element analysis of creep continuum damage problems with plastic effects  

Microsoft Academic Search

In this paper, a quadratic boundary element formulation for elasto-plastic creep damage problems in which strains and deformations are mainly creep dominant is presented. In order to cover both plastic and creep deformations, the initial strain formulation is employed. The Euler method with automatic time-step control scheme is implemented for time integrations. Creep rupture life is predicted using a continuum

H. Gun

2008-01-01

173

Creep Properties of Single Crystals of Nickel-Base Superalloys. 1: High Temperature Creep (980 C).  

National Technical Information Service (NTIS)

The creep properties of homogeneous and finely dendritic single crystals of MAR M200 at 980 C are described. The results and observations of the microstructures after deformation reveal that this industrial alloy has the same elementary deformation mechan...

C. Carry C. Houis J. L. Strudel

1981-01-01

174

A study on the pre-cyclic-load-induced burst of creep deformation of a pipeline steel under subsequent static load  

Microsoft Academic Search

Room temperature creep of X-52 pipeline steel was studied under various loading conditions. Due to cyclic hardening, the steel exhibits cyclic creep retardation, which is less pronounced at lower stress-ratio and under cyclic load with periodical hold at peak stress. Pre-cyclic loading has significant effect on subsequent static creep. Up to 40 cycles, pre-cyclic load results in a smaller cumulative

Sheng-Hui Wang; Weixing Chen

2002-01-01

175

Cyclic deformation and fracture behavior of Al alloy 6061 under the action of positive mean stresses  

NASA Astrophysics Data System (ADS)

Cyclic deformation and fatigue fracture behavior of Al alloy 6061 were studied over an extensive range of positive mean stress. In the regime of low cyclic stress amplitude, both secondary stage creep rate and fracture process are retarded by decreasing mean stress, but they are accelerated if the cyclic stress ratio is smaller than 0. 75. The superimposition of cyclic compressive stress is found to decrease the creep rate, but it has no effect on the relationship between fatigue life and mean stress. Characteristic patterns on the specimen fracture surfaces, representing the interaction between creep and fatigue and also the mechanism of the fatigue-creep deformation in different mean stress ranges, are discussed analytically. Finally, the concept of equivalent creep rate is proposed and a method to predict fatigue life with positive mean stresses is established and verified using the present experimental results.

Yang, Zhi'an; Wang, Zhirui

1993-09-01

176

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 Tth, 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.

Tth, Lszl S.

177

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

178

Pressure solution as a mechanism of creep and sealing in active faults: evidence from the SAFOD samples  

NASA Astrophysics Data System (ADS)

Active faults in the upper crust may either break or creep depending on the geodynamic context. Moreover, on the same fault creeping periods may alternate with episodes of seismic ruptures coupled to post-seismic healing processes. Identifying creep and sealing mechanisms in active faults, and their evolution with time and depth, represents a major challenge to predict the long-term evolution of such active faults. The San Andreas Fault Observatory at Depth (SAFOD) provides the opportunity to obtain samples from creeping fault zones that are periodically broken by major seismic events and that have recorded deformation mechanisms that characterize the rheology of active seismic-aseismic systems. The SAFOD drilling site lies at the northern end of a SAF segment where 6 repeating M6 earthquakes occurred since 1887. The last 2004 M6 Parkfield event induced both long-term perturbation of crustal properties revealed by seismic velocity change, and related post-seismic stress relaxation revealed by afterslip creep. Observations of core samples show that at least five major faults were crossed, including an actively creeping segment of the SAF system that is causing casing deformation at a depth of 3295-3313 m. Using a detailed microstructural study of core samples retrieved from this creeping zone, we propose that pressure solution is the main mechanism of creep and a significant mechanism of sealing. Pressure solution viscous creep is evidenced by solution cleavage (100-300 microns spacing) that lies at low angle to the SAF. Stress driven dissolution of several minerals, including feldspars, accommodates the shortening perpendicular to the cleavage. Calcite minerals precipitate in veins oriented perpendicularly to this cleavage. The extension marked by the veins is rather large (20-30%) and the amount of finite deformation is compatible with an active creeping process along the SAF. Within and nearby this creeping zone, fragmented pieces of solution cleavage and associated vein structures are found re-worked and embedded in fault zones indicating that seismic events have periodically cut through this SAF section. Cross-cuttings of fault gouges and associated network of sealed veins also attest to repeating seismic events. Relying on laboratory experiments that show how the kinetics of pressure solution creep is drastically activated by fracturing episodes due to short cuts of diffusive mass transfer, we propose a model of continuously creeping fault zones that are intermittently broken by earthquakes. The model involves (i) porosity increase during earthquake due to intense fracturing; (ii) co-seismic fracturing that activates pressure solution afterslip creep rate both in gouges and damaged zones (iii) sealing of the fractures that restrengthens the faults and slow down the creep rate with characteristic exponential time dependence until the next earthquake.

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

2009-12-01

179

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

180

Assessment of local vocal fold deformation characteristics in an in vitro static tensile test  

PubMed Central

Voice quality is strongly dependent on vocal fold dynamics, which in turn are dependent on lung pressure and vocal fold biomechanics. Numerical and physical models are often used to investigate the interactions of these different subsystems. However, the utility of numerical and physical models is limited unless appropriately validated with data from physiological models. Hence a method that enables analysis of local vocal fold deformations along the entire surface is presented. In static tensile tests, forces are applied to distinctive working points being located in cover and muscle, respectively, so that specific layer properties can be investigated. The forces are directed vertically upward and are applied along or above the vocal fold edge. The resulting deformations are analyzed using multiple perspectives and three-dimensional reconstruction. Deformation characteristics of four human vocal folds were investigated. Preliminary results showed two phases of deformation: a range with a small slope for small deformations fading into a significant nonlinear deformation trend with a high slope. An increase of tissue stiffness from posterior to anterior was detected. This trend is more significant for muscle and in the mid-anterior half of the vocal fold.

Dollinger, M.; Berry, D. A.; Huttner, B.; Bohr, C.

2011-01-01

181

Constraining the characteristics of tsunami waves from deformable submarine slides  

NASA Astrophysics Data System (ADS)

The last decade has produced unprecedented increase in national and international relevance of coastal cities. Coastal cities are important links in the quickly globalizing economy. As a marine hazard, submarine slope failures have the potential to directly destroy offshore infrastructure, and, if a tsunami in generated, it also endangers the life of those who life and/or work at the coastline. Tsunami generated by earthquakes can be constrained by independent measurements of the parent earthquake by seismographs. Such measurements are impossible in case of landslides. Hence, the use of simulation tools in less effective and reliable due to the introduced unpredictable uncertainty. This uncertainty has to decrease. To lower the uncertainty, we present a method that determines material parameters for the slide body that result in a more realistic rheological behavior and a constraint of the generated tsunami waves. Our method employs the distribution of landslide run-out masses and their comparison with simulations. If the characteristic of observed run-out masses is reproduced with a certain amount of confidence, then it is assumed that the dynamical behavior of the slide is known, and the tsunami waves are constraint. To demonstrate our method, we make use of Valdes run-out masses off the Chilean coast. Even though our method suffers from the basic assumption that the parameters describing the rheological behavior of the slide do not change during the slide motion, our method represents a first step toward a better and more constraint understanding of risk and hazard from tsunami waves generated by submarine landslides.

Weiss, R.; Krastel, S.; Anasetti, A.

2012-04-01

182

Dislocation creep of polycrystalline dolomite  

NASA Astrophysics Data System (ADS)

The field of dislocation creep and rheological parameters for coarse-grained (d = 240 ?m) natural dolomite has been determined through experiments performed at temperatures of 700-1000 C, effective pressures of 300-900 MPa and strain rates of 10- 4/s to 10- 7/s. At low strain (< 7%), dolomite aggregates deform homogeneously and define a power law between strain rate and differential stress with a stress exponent of 3.0 +/- 0.1, but at higher strains, through-going, fine-grained (< 10 ?m) shear zones develop in the dolomite aggregates concomitant with strain weakening. Recrystallization is limited at low strain and microstructures observed in the low strain samples include undulatory extinction, twins, grain boundary bulging, limited recrystallization along twins and fluid inclusion trails. These same microstructures are present outside of the narrow, through-going shear zones in high strain samples; however, within the shear zones the grain size is small (< 10 ?m) with some larger porphyroclasts (20-50 ?m). Shear zones nucleate at fine-grained zones formed at twin boundaries, twin-twin intersections and fluid inclusion trails and is likely due to a switch in deformation mechanism due to the large strength contrast between the fine-grained zones deforming by diffusion creep and the coarse-grained protolith. The activation energy (Q) for creep of coarse-grained dolomite at low strain is 145 kJ/mol. In contrast to other activation energies for dislocation and diffusion creep of minerals, Q for dislocation creep of dolomite is considerably less than that for diffusion creep (248 kJ/mol). The results of this study indicate that coarse-grained dolomite will initially deform by dislocation creep at natural strain rates and temperatures between 200 and 550 C, but due to limited recovery mechanisms, fine-grained shear zones will nucleate and diffusion creep may control the rheology of these fine-grained shear zones in nature at temperatures above ~ 300 C.

Holyoke, Caleb W.; Kronenberg, Andreas K.; Newman, Julie

2013-04-01

183

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

SciTech Connect

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

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

2010-01-15

184

High temperature deformation characteristics of Ti(41--52) at% Al alloys  

SciTech Connect

Titanium aluminide alloys of engineering interest contain 46 to 50 atomic percent aluminum and typically up to 20 volume percent of alpha-2 (Ti[sub 3]Al) as a second phase in the gamma (TiAl) matrix. The volume percent and aluminum content of the alpha phase in Ti-48Al vary substantially between 1,200 C and 1,300 C where near-gamma titanium aluminides are usually worked. The microstructures of the alloys in this temperature range consist of a mixture of gamma and disordered alpha. The volume fractions of gamma and disordered alpha present between 1,200 C and 1,300 C have significant effects on high temperature workability of the alloys. Upon cooling to room temperature, the alpha phase transforms to alpha-2 and gamma lamellae, and as a result, the volume percents of the phases present at room temperature are functions of the exact composition of the alloy, the deformation temperature, and cooling rates. The gamma and alpha-2 phase are ordered at room temperature and the relative volume fraction and morphology of each phase have significant effect on the resultant room temperature properties. To optimize both workability and room temperature mechanical properties, a precise knowledge of the effects of alloy composition and varying amounts of gamma and alpha-2 phases on high temperature deformation is essential. The high temperature deformation characteristics at 1,200--1,300 C and effective strain rates of 10[sup [minus]3]--10[sup [minus]1] s[sup [minus]1] of Ti-xAl (x = 41, 48, 52 at%) alloy were studied with the objective of understanding the deformation of two phase gamma + alpha-2 alloys in terms of the deformation characteristics of individual phases. The goal of this research is to develop a model which describes the deformation behavior of two phase titanium aluminides as a function of constituent phases, test temperature, and strain rate.

Sabinash, C.M. (McDonnell Douglas Corp., St. Louis, MO (United States)); Sastry, S.M.L.; Jerina, K.L. (Washington Univ., St. Louis, MO (United States). Material Research Lab.)

1994-06-01

185

Characteristics of deformation of saturated soft clay under the load of Shanghai subway line No. 2  

NASA Astrophysics Data System (ADS)

Shanghai subway Line No. 2 passes through the center of Shanghai from Songhong Road station in the west to Zhangjianggaoke station in the east. The total length of Shanghai subway Line No. 2 is 25 km. The tunnel mostly lies in the saturated soft clay and the environment issue can not be ignored. The response frequency and response stress of soil around the tunnel are monitored when the subway train passes through. The cyclic triaxial test of the saturated soft clay around the subway tunnel is conducted using the data monitored. The characteristics of deformation of the saturated soft clay of Shanghai under the subway load are analyzed. The results show that when the subway train Line No. 2 begins to run, a small and vertical rebound first occurs in the saturated soft clay at the side wall of the tunnel. Although a large deformation does not occur in the saturated soft clay at the side wall of the tunnel when the subway train has run for a period of time, yet with the lapse of time, a perceptive and non-uniform deformation will still occur. The vertical rebound is transitory and a plastic deformation occurs immediately in the saturated soft clay at the bottom of the tunnel, the large deformation at the bottom of the tunnel is 30 times that of the saturated soft clay at the side wall of the tunnel.

Tang, Yi-Qun; Yang, Ping; Zhao, Shu-Kai; Zhang, Xi; Wang, Jian-Xiu

2008-05-01

186

Predicting the Creep Lifetime of HMPE Mooring Rope Applications  

Microsoft Academic Search

Under constant loading HMPE fibers and ropes show an irreversible deformation (creep) behavior that is strongly dependent upon load and temperature. This paper presents an updated model that seeks to accurately predict the creep rate at various temperature ranges and to estimate creep life of HMPE on fiber level, and demonstrates the apparent validity of this model to rope applications

M. P. Vlasblom; M. R. L. Bosman

2006-01-01

187

Low temperature deformation characteristics of neutron irradiated vanadium-titanium alloys  

Microsoft Academic Search

An investigation was undertaken to determine the effect of neutron irradiation on the low temperature deformation characteristics of vanadium-titanium alloys. The effect can be divided into two groups: for low titanium concentrations (0.75 and 1.6 wt. per cent Ti) a weakening effect appeared which was apparent for the complete temperature range investigated for the 0.75 per cent Ti but to

E. Pink; R. J. Arsenault

1971-01-01

188

Technique for tensile creep testing of ceramics  

Microsoft Academic Search

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

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

1989-01-01

189

Numerical investigation of hyperelastic wall deformation characteristics in a micro-scale stenotic blood vessel  

NASA Astrophysics Data System (ADS)

Stenosis is the drastic reduction of blood vessel diameter because of cholesterol accumulation in the vessel wall. In addition to the changes in blood flow characteristics, significant changes occur in the mechanical behavior of a stenotic blood vessel. We conducted a 3-D study of such behavior in micro-scale blood vessels by considering the fluid structure interaction between blood flow and vessel wall structure. The simulation consisted of one-way coupled analysis of blood flow and the resulting structural deformation without a moving mesh. A commercial code based on a finite element method with a hyperelastic material model (Neo-Hookean) of the wall was used to calculate wall deformation. Three different cases of stenosis severity and aspect ratios with and without muscles around the blood vessel were considered. The results showed that the wall deformation in a stenotic channel is directly related to stenosis severity and aspect ratio. The presence of muscles reduces the degree of deformation even in very severe stenosis.

Cheema, Taqi Ahmad; Park, Cheol Woo

2013-08-01

190

Deformation characteristics during Y-shaped tube hydroforming of 6061 aluminum alloy  

NASA Astrophysics Data System (ADS)

To manufacture lightweight tube components for aerospace oil circuit systems, an experiment was run to investigate the deformation characteristics on Y-shaped tube hydroforming of 6061 aluminum alloy. Both strain state and metallurgical structure indicate that there are four kinds of prevailing defects during Y-shaped tube hydroforming: bursting, lack of cylindricity, wrinkling, and thinning due to the poor plastic property of 6061 aluminum alloy. The danger of bursting prevails at the early stage of the operation as a result of excessively high internal pressure. In contrast, wrinkling prevails after the middle stage of the operation as a result of excessively axial feeding and cannot be eliminated during subsequent deformation. Lack of cylindricity is mainly because of insufficient axial feeding and internal pressure but can be eliminated by increasing internal pressure. Elongation and compression deformations are originated on protrusion and main pipe of Y-shape tube respectively all the way through the bulging process. Consequently, minimum and maximum thicknesses are at the top of protrusion and the bottom of Y-shape tube respectively, which induces a V-shape borderline of thickness distribution. According to the excessive plastic deformation, microstructure evolution is originated. Crystal grain of protrusion is elongated and its grain size is about 150 ?m. In contrast, crystal grain of the middle zone of main tube is refined greatly, which grain size is 50 ?m, decreased by 75%. These are useful to improve the component.

Chu, Guannan; Li, Feng; Liu, Wenjian

2011-02-01

191

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

Microsoft Academic Search

Several heat treatments were developed and applied to several investment cast duplex (equiaxed+lamellar) TiAl alloys (Ti-4547Al-2Nb-2Mn+0.8v%TiB 2XDTM, Ti-47Al-2Nb-2Mn+0.8TiB2XDTM with interstitial elements, Ti-47Al-2Nb-2Cr, and Ti-47Al-2Nb-1Mn-0.5W-0.5Mo-0.2Si) in an effort to enhance creep properties. Creep behavior in polysynthetically twinned (PST) crystals with different orientations was also investigated. Primary creep resistance of W-Mo-Si alloys can be improved by about 10 times with heat treatment,

Dong Yi Seo

1998-01-01

192

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

Microsoft Academic Search

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

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

2005-01-01

193

Deuteron irradiation creep of chemically vapor deposited silicon carbide fibers  

Microsoft Academic Search

Irradiation creep tests were conducted on Textron SCS-6 silicon carbide (SiC) fibers during irradiation with 14 MeV deuterons at 450 and 600C. The fibers are produced by a CVD procedure; their microstructure may therefore be representative for the matrix of a SiC composite. There is a significant radiation induced increase in creep deformation. Both quantities, irradiation creep strain and creep

R. Scholz

1998-01-01

194

Creep behaviour of modified 9Cr1Mo ferritic steel  

Microsoft Academic Search

Creep deformation and fracture behaviour of indigenously developed modified 9Cr1Mo steel for steam generator (SG) tube application has been examined at 823, 848 and 873K. Creep tests were performed on flat creep specimens machined from normalised and tempered SG tubes at stresses ranging from 125 to 275MPa. The stress dependence of minimum creep rate obeyed Nortons power law. Similarly, the

B. K. Choudhary; E. Isaac Samuel

2011-01-01

195

Creep in shear of experimental solder joints  

SciTech Connect

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

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

1989-09-01

196

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

197

Creep and creep rupture of an advanced silicon nitride ceramic  

SciTech Connect

Creep and creep rupture behavior of an advanced silicon nitride ceramic were systematically characterized in the temperature range 1,150 to 1,300 C using uniaxial tensile creep tests. Absence of tertiary creep and the order-of-magnitude breaks in both creep rate and rupture lifetime at certain threshold combinations of stress and temperature were tow characteristic features of the creep behavior observed. Thermal annealing was found to have enhanced both subsequent creep resistance and creep rupture life. The stress exponent (n) and the activation energy (Q) defined in the Norton relation were found to be 12.6 and 1645 kJ/mol for the material investigated. Both values appear to fall in the general range of those reported for other but similar types of Si[sub 3]N[sub 4] ceramic materials. The stress exponent, m, equivalent to the slope of the Larson-Miller equation was found to be in the range 13 to 14.4, and that defined as p in the Monkman-Grant relation to be 0.91, based on the available experimental data. The values of m, n, and p obtained above approximately support the interrelationship of the three exponents given by p = m/n.

Ding, J.L.; Liu, K.C.; More, K.L.; Brinkman, C.R. (Oak Ridge National Lab., TN (United States). Metals and Ceramics Division)

1994-04-01

198

Creep analysis of PLLA: PGA copolymer craniofacial plates.  

PubMed

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

Pietrzak, William S

2012-09-01

199

Rupture and Internal Pressurization Creep of Nb-Modified Zircaloy-4 Tubing: Application to Dry Storage Feasibility  

SciTech Connect

Burst rupture properties of Zircaloy-4 and Nb-Modified Zircaloy-4 are investigated at temperatures ranging from 638 K to 843 K by internal pressurization of closed-end tubing samples. Various pressurization levels were imposed and rupture times were noted. The data enabled an evaluation of Larson-Miller parameter and the present experimental results on Zircaloy-4 were in excellent agreement with those reported in the literature. The effect of 1% Nb addition to Zircaloy-4 was studied since these materials are now known to resist long-time corrosion in water reactors and are thus considered for high burn-up applications. Negligible differences were noted in the rupture characteristics between the standard Zircaloy-4 and Nb-added Zircaloy-4. In addition, a limited amount of testing was performed to characterize the hoop creep behavior of these materials using a creep tester with hoop strain monitored in-situ by a Laser telemetric extensometer. Both the alloys followed an exponential stress variation of the creep-rate at high (>10{sup -3} E) stresses. At very low stresses, viscous creep (n=1) was noted identifiable with Coble creep corresponding to small grain sized materials. These results have significance on the feasibility of surface storage of spent fuel where the creep deformation of the cladding could be a failure mode because of the residual heat and fission products following exposure to neutron irradiation in commercial nuclear plants. Blind extrapolation of short-term creep results to low stresses encountered during dry storage lead to nonconservative estimates of the creep-rates and creep-strains due to contributions of viscous creep to the total strain. (authors)

Murty, K.K.; Zhou, Y.; Devarajan, B. [North Carolina State University, Nuclear Engineering Department, Raleigh, NC 27695-7909 (United States)

2002-07-01

200

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

201

Comparison of the creep and creep rupture performance of two HIPed silicon nitride ceramics  

SciTech Connect

Measurements of the tensile creep and creep rupture behavior were used to evaluate the long-term mechanical reliability of a commercially available and a developmental hot isostatically pressed (HIPed) silicon nitride. Measurements were conducted at 1,260 and 1,370 C utilizing button-head tensile specimens. The stress and temperature sensitivities of the secondary creep rates were used to estimate the stress exponent and activation energy associated with the dominant creep mechanism. The stress and temperature dependencies of creep rupture life were determined by continuing individual creep tests to specimen failure. Creep deformation in both materials was associated with cavitation at multigrain junctions. Two-grain cavitation was also observed in the commercial material. Failure in both materials resulted from the evolution of an extensive damage zone. The failure times were uniquely related to the creep rates, suggesting that the zone growth was constrained by the bulk creep response. The fact that the creep and creep rupture behaviors of the developmental silicon nitride were significantly improved compared to those of the commercial material was attributed to the absence of cavitation along two-grain junctions in the developmental material.

Ferber, M.K.; Jenkins, M.G.; Nolan, T.A. (Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.); Yeckley, R.L. (Norton Co., Northboro, MA (United States))

1994-03-01

202

Dislocation Jamming and Andrade Creep  

NASA Astrophysics Data System (ADS)

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 the presence of dislocation multiplication and noise confirm the robustness of this finding and highlight the importance of metastable structure formation for the relaxation process.

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

2002-09-01

203

Dislocation jamming and andrade creep.  

PubMed

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 the presence of dislocation multiplication and noise confirm the robustness of this finding and highlight the importance of metastable structure formation for the relaxation process. PMID:12398733

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

2002-09-26

204

Deformation characteristics of surrounding rock of broken and soft rock roadway  

Microsoft Academic Search

A similar material model and a numerical simulation were constructed and are described herein. The deformation and failure of surrounding rock of broken and soft roadway are studied by using these models. The deformation of the roof and floor, the relative deformation of the two sides and the deformation of the deep surrounding rock are predicted using the model. Measurements

Jin-xi WANG; Ming-yue LIN; Duan-xin TIAN; Cun-liang ZHAO

2009-01-01

205

Refutation of the relationship between denuded zones and diffusional creep  

SciTech Connect

The first direct microstructural observation used as evidence for diffusional creep is from the work of Squires, Weiner, and Phillips (S-W-P). They observed denuded zones at grain boundaries after creep in a Mg-0.5 wt.% Zr alloy that contained inert precipitates. It is the purpose of this paper to show that the reported creep data for the Mg-0.5 wt.%Zr alloy was, in fact, obtained in a region where dislocation creep, rather than diffusional creep, was the dominant deformation mechanism. Details of the denuded zone formation will also be presented which question the relation of denuded zones to diffusional creep. Therefore, it is contended that the microstructurally-observed denuded zones cannot be a result of diffusional creep. This contention supports previously-published views by the present authors that conclusive proof for diffusional creep in polycrystalline materials remains elusive.

Wolfenstine, J. (Univ. of California, Irvine, CA (United States)); Ruano, O.A. (Centro Nacional de Investigaciounes Metalurgicas, Madrid (Spain)); Wadsworth, J. (Lawrence Livermore National Lab., CA (United States)); Sherby, O.D. (Stanford Univ., CA (United States). Dept. of Materials Science and Engineering)

1993-08-15

206

Dislocation Creep in Magnesium Calcite  

NASA Astrophysics Data System (ADS)

To investigate the effect of dissolved Mg on plastic deformation of calcite, we performed triaxial deformation experiments on synthetic calcite with varying amount of Mg content. Mixtures of powders of calcite and dolomite were isostatically hot pressed (HIP) at 850 C and 300 MPa confining pressure for different intervals (2 to 20hrs) resulting in homogeneous aggregates of high-magnesium calcite; Mg content varied from 0.07 to 0.17 mol%. Creep tests were performed at differential stresses from 20 to 160 MPa at 700 to 800 C. Grain sizes before and after deformation were determined from the images obtained from scanning electron microscope (SEM) and optical microscope. Grain sizes are in the range of 5 to 20 microns depending on the HIP time, and decrease with increasing magnesium content. Both BSE images and chemical analysis suggest that all dolomite are dissolved and the Mg distribution is homogeneous through the sample, after 2 hrs HIP. At stresses below 40 MPa, the samples deformed in diffusion region (Coble creep), as described previously by Herwegh. The strength decreases with increasing magnesium content, owing to the difference of grain size. At stresses above 80 MPa, the stress exponent is greater than 3, indicating an increased contribution of dislocation creep. The transition between diffusion to dislocation creep occurs at higher stresses for the samples with higher magnesium content and smaller grain size. Preliminary data suggests a slight increase in strength with increasing magnesium content, but more tests are needed to verify this effect. In a few samples, some strain weakening may have been evident. The activation energy in the transition region (at 80 MPa) is 200 KJ/mol with no dependence on magnesium content, agreeing with previous measurements of diffusion creep in natural and synthetic marbles.

Xu, L.; Xiao, X.; Evans, B. J.

2003-12-01

207

Tensioning of Prolene reduces creep under cyclical load: relevance to a simple pre-operative manoeuvre.  

PubMed

A longitudinal stretch or 'pre-tensioning' is a method employed by some surgeons to improve the handling characteristics of a suture. We used a tensile tester to assess the effect of pre-tensioning on the mechanical properties of two suture materials (3-0 Prolene and 3-0 Ethibond) commonly used for flexor tendon repair. A cyclical loading programme was used to simulate an early rehabilitation regime. All sutures were subsequently tested to failure (for ultimate tensile strength). The pre-tensioned Prolene sutures showed significantly less creep after cyclical loading in comparison to controls. Conversely pre-tensioning had no measurable effect on the deformation of Ethibond by creep. There was no effect on ultimate tensile strength for either material. The propensity of Prolene to creep (and thereby form a 'gap' in tendon repairs) can be reduced by pre-tensioning. PMID:22117015

Smith, G H; Huntley, J S; Anakwe, R E; Wallace, R J; McEachan, J E

2011-11-24

208

Shear creep and attenuation in Newtonian-viscous, polycrystalline olivine and olivine-based partial melts  

NASA Astrophysics Data System (ADS)

High-temperature (1100sp C{-}1285sp C), driven torsional attenuation and creep experiments have been performed on both nominally melt-free (MF) and melt-bearing (MB; 5 wt% synthetic high-potassium basalt), fine-grained (d{}3?m) synthetic dunites. Both materials are mechanically linear (i.e., strain, strain rate are both proportional to the applied stress) over the entirety of the testing conditions, implying that deformation is accomplished via a diffusional mechanism. The creep response of both materials is characterized by a decelerating transient in the creep rate that leads to an apparent steady state, and is accurately modeled by the Andrade creep function. Both aggregates display an activation energy of 700\\ kJ{*}molsp{-1} for the entirety of the creep response, with the MB aggregates displaying creep rates approximately six times higher than the MF aggregates, in agreement with solution-precipitation-enhanced diffusional creep models. No additional transient response is evident in the MB materials. At temperatures above 1100sp C, both materials display relatively high shear attenuation ({cal Q}sbsp{G}{-1}) values ({-2 < logsb{10}}({cal Q}sbsp{G}{-1}) < 0.5) that are moderately dependent upon frequency (f), with {cal Q}sbsp{G}{-1}{}fsp{-0.35}, consistent with seismic observations. The {cal Q}sbsp{G}{-1} behavior in both materials can be predicted directly from Andrade-model fits to the creep response. At identical experimental conditions, the values of {cal Q}sbsp{G}{-1} for the MB aggregates are consistently 0.35 logsb{10} units higher than those for the MF aggregates. The difference in magnitude of {cal Q}sbsp{G}{-1} is shown to be solely a consequence of the enhanced creep rates in the MB material and is not related to any other, unique, melt-based attenuation mechanism. The transient creep and corresponding {cal Q}sbsp{G}{-1} behavior observed in both aggregates is due to the evolution of the grain boundary tractions from an initial state, one characterized by large tractions at triple junctions and low values elsewhere along the grain face, to a nominally parabolic distribution that allows for steady-state creep. This transient is intrinsic to diffusional creep; in a uniform-grain-sized aggregate it will produce the characteristic power-law-of-time signature of the transient in the Andrade model. Thus, an attenuation "band", i.e., {cal Q}sbsp{G}{-1}{}fsp{-q} with 0.25? q? 0.5 can arise from the grain-boundary-diffusion response; a broad spatial distribution of a microstructural feature is not a priori required.

Gribb, Tye Travis

209

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

210

Deformation characteristics at 300 K of single-crystalline molybdenum sheet prepared by secondary recrystallization  

SciTech Connect

The present work was carried out to examine the slip behavior under tension and the role of island grain on the deformation and fracture in a Mo single crystal. The tensile deformation characteristics of single-crystalline molybdenum sheet containing Ca and Mg of 50ppm and oxygen of 270ppm, which was prepared by secondary recrystallization, were investigated at 300 K and compared with that of the crystal containing a low level of oxygen (10ppm) in view of slip geometry and fracture behavior. Stress was applied approximately in the [011] direction. Conclusions are as follows: (1) slip system of ({bar 3}12)[111] dominated deformation at the beginning of yield and this slip system continued up to a strain of 0.09; (2) ({bar 2}11)[111] and ({bar 1}{bar 1}2)[111] began to act as another vital slip systems at a strain over 1.00; (3) stress drop phenomenon at a strain of 0.10 might be due to the change of slip system from ({bar 3}12)[111] to ({bar 2}11)[111] and/or ({bar 1}{bar 1}2)[111] by the rotation of crystal axis against the tensile axis; (4) cracks were generated from the island grain having different orientations from the matrix and separated from the matrix intergranularly. Subsequently the crack propagated along the ({bar 1}{bar 1}2) plane. It might be attributed to the pile-up of dislocations and the grain boundary weakening by the segregation of oxygen.

Yoo, M.K.; Choi, J. [Korea Inst. of Science and Technology, Seoul (Korea, Republic of). Div. of Metals; Hiraoka, Yutaka [Okayama Univ. of Science (Japan). Dept. of Applied Physics

1995-11-01

211

Rheological model of soft rock creep based on the tests on marl  

Microsoft Academic Search

Basic task in mathematical description of time dependent deformations of a certain material is to define deformations as a function of time, stress and temperature. In order to formulate the rheological model of time dependent deformations of soft rocks, which is presented in this paper, laboratory tests on marl creep have been carried out. Experimental research on marl creep has

Zvonko Tomanovic

2006-01-01

212

Characteristics of a Novel ICP Source with a Deformable Bifilar Coil  

NASA Astrophysics Data System (ADS)

The characteristics of a low pressure inductively-coupled plasma (ICP) source which employs a novel coil design to maximize the source's operation window will be described. A uniform plasma density over an area larger than the wafer size is one of the most important requirements for the plasma sources used in ULSI processing tools. By making the coil deformable, the plasma density uniformity can be maintained over a wider operation window as system's parameters, such as gas chemistry, gas pressure, and chuck RF bias power, are varied to meet different process requirements, as compared to the ICP sources based on conventional fixed coil design. The other feature of the new coil design is that it has two sets of winding connected in parallel but 180 degrees opposite azymuthally. This arrangement in principle provides a better azymuthal symmetry than the conventional single winding planar coil. The system was characterized with several plasma diagnostic tools: a 2D RF-compensated Langmuir probe, a B-Dot probe, a heterodyne interferometer and spectroscopy/imaging of plasma-induced emissions. A wafer-type grided ion energy analyzer has also been developed to measure ion energy distribuition at different locations on the wafer. Experimental results show that the radial profile of plasma density changes as the coil is deformed. The effect is more pronounced at higher gas pressures where electron's mean free path becomes shorter and the plasma density profile is basically determined by the distribution of RF power deposition. The detailed experimental results will be presented.

Leou, K. C.; Cheng, J. H.; Chen, T. S.; Hsu, C. R.; Wu, W. C.; Chiang, W. Y.; Lin, T. L.; Tsai, C. H.

1998-10-01

213

Creep and relaxation behavior of Inconel-617  

SciTech Connect

The static and dynamic creep behavior of Inconel alloy 617 has been determined in constant load creep tests, relaxation tests, and stress reduction tests in the temperature range 1023 to 1273 K. The results have been interpreted using the internal stress concept: The dependence of the internal stress on the applied stress and test temperature was determined. In a few experiments, the influence of cold deformation prior to the creep test on the magnitude of the internal stress was also investigated. It was found that the experimentally observed relaxation behavior could be more satisfactorily described using the Norton creep equation modified by incorporation of the internal stress than by the conventional Norton creep equation.

Osthoff, W.; Ennis, P.J.; Nickel, H.; Schuster, H.

1984-08-01

214

Investigation of radiation creep of reactor graphite  

Microsoft Academic Search

The results of investigations of the radiation creep of GR-280 graphite under a high compression load (about 15 MPa) after\\u000a irradiation in a BOR-60 reactor at 520C to fast-neutron fluence 1.21022 cm?2 are presented. It is shown that the fluence dependence of the creep deformation, calculated using the standard relation as\\u000a the difference of the change in the dimensions of

A. V. Subbotin; A. S. Pokrovskii; D. V. Kharkov

2008-01-01

215

Deformation of salt rock joints in time  

Microsoft Academic Search

The results are presented for the deformation testing of joints of salt rocks. The tests on shear with compression were conducted at creep and various loading rates. A structural rheological model of the joint deformation is constructed. Basing on the linear heredity theory, the relations are obtained for describing the process of creep and relaxation.

V. A. Asanov; I. L. Pankov

2004-01-01

216

Dielectrophoretic-field flow fractionation analysis of dielectric, density, and deformability characteristics of cells and particles.  

PubMed

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. With the use of 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. PMID:19791772

Gascoyne, Peter R C

2009-11-01

217

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

218

Creep induced substructures in titanium aluminide  

NASA Astrophysics Data System (ADS)

Many investigations have examined the creep properties of titanium aluminides. Attempts to classify observed behaviors with existing models for high temperature deformation have been met with limited success. Several researchers have shown that an understanding of substructural evolution in the early stages of the creep curve may offer insight into the mechanisms, which control the rate of deformation. Creep deformation has been shown to include twinning, recrystallization, grain boundary sliding, ordinary and super dislocation activity, and faulting depending on the microstructure of the alloy and testing conditions. However, the environments that these alloys are likely to be exposed to are not similar to the test conditions in the literature. Furthermore the emphasis of much of the research into this group of alloys has been on the effects of microstructure particularly, the volume fraction of lamellar phase and ternary elemental additions. With all of these studies little information is available on the deformation behavior of the gamma phase. The alloys in these studies are mostly composed of the gamma phase and yet its creep behavior is not well understood. For this reason single phase binary gamma titanium aluminides were investigated in this study. To understand the effects of aluminum, interstitial oxygen content, and stress on creep, five alloys of varying Al concentrations and interstitial oxygen contents were deformed at temperatures ranging from 700--800C and at stresses of 150, 200, and 250MPa. Full creep curves were developed under these conditions and phenomenological parameters for creep were calculated from these data. Additional tests were interrupted during primary and secondary creep at 760C. Specimens from the interrupted tests as well as from the as-processed materials were examined optically and by TEM. Creep data and the microscopy were analyzed in concert to determine rate-controlling mechanisms for creep. Evolution of the substructure with strain and as a function of interstitial oxygen content and stress will be discussed. Finally, mechanisms for the formation of deformation twins and accommodation reactions for the stresses associated with twins terminating within the TiAl matrix will be presented.

Cerreta, Ellen Kathleen

219

Stress dependence of the creep behavior of silicon carbide whisker-reinforced alumina  

SciTech Connect

Creep tests of Silicon carbide-whicker reinforced alumina at 1500 C yielded creep strain vs. time curves exhibiting typical primary, secondary and tertiary creep. The initial creep rate, which is proportional to the matrix creep rate, exhibited a stress exponent of 1.59, typical for single-phase polycrystalline alumina, while the apparent stress exponent for secondary (steady-state) creep was 2.88. The presence of the whiskers appeared to suppress cavitation or other damage, thereby eliminating any contribution from elastic creep by crack growth or crack-enhanced creep to creep deformation. Analysis of the creep behavior of short elastic fiber reinforced matrix composite based on the theory of Kelly and Street indicated that stress dependent sliding at the silicon carbide-alumina interface and stress dependent partial whisker fracture, resulting in a decrease in average aspect ratio, could be the mechanisms responsible for the higher apparent stress exponent in the secondary regime.

Donaldson, K.Y.; Venkateswaran, A.; Hasselman, D.P.

1989-01-01

220

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

221

Creep rupture of polymers-a statistical model  

Microsoft Academic Search

The paper focuses on the micromechanical origins and mechanisms of creep failure of epoxy-resins. Microstructure of the material is modeled by a 2D lattice. The probabilistic nature of the creep deformation process is based on the kinetic theory of rupture. The macroscopic manifestation of the process: evolution of strain, degradation of stiffness and endurance are defined in terms of the

Milena Vujosevic; Dusan Krajcinovic

1997-01-01

222

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

223

Creep property comparisons for ceramic-fibre-reinforced ceramicmatrix composites  

Microsoft Academic Search

The tensile creep and creep fracture properties are analysed for seven different ceramicmatrix composites, reinforced with silicon carbide or alumina fibres. For this broad product range, the processes controlling creep deformation and damage evolution are identified, showing that the longitudinal fibres govern the rates of strain accumulation and crack development, with the matrices and fibre\\/matrix interfaces influencing the times and

B Wilshire

2002-01-01

224

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

225

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

226

Determining the Thermoviscoplastic State of Shells of Revolution Subject to Creep Damage  

Microsoft Academic Search

A technique is developed for determining the thermoviscoplastic state of shells of revolution with allowance for creep damage. The technique is based on the hypotheses of rectilinear element and the theory of deformation along paths of small curvature. The equivalent stress appearing in the kinetic equations of damage and creep is determined using a creep-rupture criterion that accounts for the

A. Z. Galishin

2004-01-01

227

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

SciTech Connect

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

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

1994-06-01

228

A first report on the creep deformation and damage behavior of a fine grained fully transformed lamellar gamma TiAl alloy  

Microsoft Academic Search

Gamma TiAl is a strong candidate material for the replacement of many Ni-based superalloys in advanced gas turbine jet engines. Although gamma TiAl is targeted specifically as a high temperature material, it must also be able to demonstrate reasonable toughness such as measured by impact resistance and must demonstrate reasonable crack growth resistance under cyclic deformation conditions. Of course the

R. W. Hayes; P. A. McQuay

1994-01-01

229

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] Brgmann,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

230

Creep-fatigue interactions in eutectic tin-lead-based solder alloys. Ph.D. Thesis  

SciTech Connect

Eutectic tin-lead solder alloys subjected to cyclic loading at room temperature experience creep-fatigue interactions due to high homologous temperature. At temperature above 0.5 melting point, the dominant damage mechanism can be cavity nucleation and growth, especially for alloys that have fine grain structure and a large volume fraction of dispersoids. The objective of the present study is to model the damage evolution during creep-fatigue interactions and experimentally validate the damage evolution based life predictions in rapidly solidified solder alloys. Four types of solder alloys were considered in this research, namely, conventional 63Sn-37Pb, rapidly solidified 63Sn-37Pb, dispersion-strengthened eutectic solders, and solid solution strengthened eutectic solders. Mechanical properties of the solder alloys and the life times under creep-fatigue conditions were evaluated. Damage produced in the course of creep or fatigue deformation was studied by metallography, scanning electron microscopy, precision density measurement, and the observation of grain boundary sliding. Based on the damage characteristics, the dominant failure mechanism was proved to be cavity growth. Three cavity growth models were applied to four types of solder alloys to predict creep-fatigue life by taking into account the tensile loading component as well as the compressive loading component when reversed process can occur. An algorithm to calculate cavity growth in each fatigue cycle is used to predict the number of fatigue cycles to failure, where failure is defined as a critical cavity size. Calculated lives are compared to experimental data under six types of creep-fatigue loading histories. The method predicts the creep-fatigue lives within a factor of two with the incorporation of appropriate compressive healing factor. Discrepancy between calculated lives and experimental results is discussed.

Kuo, C.W.

1994-01-01

231

Evaluation of deformation-strength characteristics of Fiber-cement-stabilized soil by using Distinct Element Method  

NASA Astrophysics Data System (ADS)

Fiber-cement-stabilized soil method is an effective way to recycle high-water content mud. The modified soil has several advantages such as high failure stress and high failure strain. However, the quality of the modified soil is not constant and depends on the water content of the mud and additives. Therefore, experimental verification to obtain the strength characteristics of the modified soil is necessary, but conducting experiments under various conditions is ineffective and uneconomic. In this study, a numerical model to estimate deformation-strength characteristics of the modified soil is investigated by using Distinct Element Method (DEM). It was shown that the developed model was effective way to estimate deformation-strength characteristics. Moreover, it was confirmed that the modified soil had high earthquake resistance.

Satomi, Tomoaki; Konda, Naoki; Takahashi, Hiroshi

232

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 1000spF. 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. Hipercospler 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

233

Comparison of tension, compression, and flexure creep for alumina and silicon nitride ceramics  

SciTech Connect

The stress sensitivity of the creep rate of commercially available Al{sub 2}O{sub 3} and Si{sub 3}N{sub 4} ceramics was measured at elevated temperatures using tension, compression, and flexure specimens. Pronounced differences in creep deformation behavior measured in compression and tension were observed for both ceramics. Fractographic studies suggested that these differences were attributed to the effects of creep cavitation which occurred under tensile loading. Data generated from the flexure creep testing were found to be in fair agreement with results predicted from existing creep deformation models. 16 refs., 8 figs.

Ferber, M.K.; Jenkins, M.G.; Tennery, V.J.

1989-01-01

234

On the response of rockglacier creep to surface temperature increase  

NASA Astrophysics Data System (ADS)

Besides its thermal characteristics creeping mountain permafrost is substantially defined by its kinematics. Due to the in general considerable ice content of rockglaciers, their dynamics respond sensitively to climate forcing. Questions arise how rockglaciers react to the current or recent climatic changes, and what the further consequences of such reactions could be. Using a one-dimensional thermo-mechanically coupled numerical model we simulate the potential response of rockglacier creep to a change in surface temperature (Section 2). It turns out that variations in temperature could indeed affect rockglacier creep in the currently observed order of magnitude. Other influences, however, clearly act as well. Among these, the occurrence and complex influence of liquid water in the frozen material might be the most important factor for permafrost close to 0 C, though difficult to model. As a next step in this contribution, we plot globally observed rockglacier speeds against mean annual air temperature (Section 3). In fact, air temperature can be statistically identified as a major factor determining rockglacier speed. The remaining scatter clearly points to other influences such as slope, debris content, column thickness or liquid water. In a further step, we summarize current monitoring results on rockglacier speed (Section 4). A surprisingly large number of Alpine rockglaciers showed an increase in speed during recent years. This large number points to other than solely local influences, but rather to some regional-scale impact such as the observed increase in air temperatures. Our monitoring and modelling work clearly shows that rockglaciers with ground temperatures close to 0 C creep in general faster than colder ones. Furthermore, our findings suggest that the creep of permafrost close to 0 C is more sensitive to thermal forcing than the creep of colder one. From this, we conclude that increasing rockglacier temperatures may lead to a marked, but both spatially and temporally highly variable speed-up, before a significant loss of ice content by melt-out is able to reduce the deformation rate of the frozen mass towards its entire deactivation. By means of three scenarios, we exemplify the possible consequences of an increase in rockglacier temperature and subsequent acceleration: (1) increasing sensitivity of rockglacier creep to seasonal influences, (2) activation of so far stable frozen debris slopes, and (3) rockglacier destabilization.

Kb, Andreas; Frauenfelder, Regula; Roer, Isabelle

2007-03-01

235

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

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

236

Metal Creep.  

National Technical Information Service (NTIS)

The book is intended for scientific workers, engineering personnel and aspirants investigating the mechanism of plastic deformation and carrying on research on the use of heat-resistant alloys. The book may also be useful to students of metallurgical and ...

V. M. Rozenberg

1969-01-01

237

EXPERIMENTAL EVALUATION OF DEFORMATION AND CONSTRAINT CHARACTERISTICS IN PRECRACKED CHARPY AND OTHER THREE-POINT BEND SPECIMENS  

SciTech Connect

To enable determination of the fracture toughness reference temperature, T0, with reactor pressure vessel surveillance specimens, the precracked Charpy (PCVN) three-point bend, SE(B), specimen is of interest. Compared with the 25-mm (1 in.) thick compact, 1TC(T), specimen, tests with the PCVN specimen (10x10x55 mm) have resulted in T0 temperatures as much as 40 XC lower (a so-called specimen bias effect). The Heavy-Section Steel Irradiation (HSSI) Program at Oak Ridge National Laboratory developed a two-part project to evaluate the C(T) versus PCVN differences, (1) calibration experiments concentrating on test practices, and (2) a matrix of transition range tests with various specimen geometries and sizes, including 1T SE(B) and 1TC(T). The test material selected was a plate of A533 grade B class 1 steel. The calibration experiments included assessment of the computational validity of J-integral determinations, while the constraint characteristics of various specimen types and sizes were evaluated using key curves and notch strength determinations. The results indicate that J-integral solutions for the small PCVN specimen are comparable in terms of J-integral validity with 1T bend specimens. Regarding constraint evaluations, Phase I deformation is defined where plastic deformation is confined to crack tip plastic zone development, whereas Phase II deformation is defined where plastic hinging deformation develops. In Phase II deformation, the 0.5T SE(B) B B specimen (slightly larger than the PCVN specimen) consistently showed the highest constraint of all SE(B) specimens evaluated for constraint comparisons. The PCVN specimen begins the Phase II type of deformation at relatively low KR levels, with the result that KJc values above about 70 MPa m from precracked Charpy specimens are under extensive plastic hinging deformation.

Nanstad, Randy K [ORNL; Sokolov, Mikhail A [ORNL; Merkle, John Graham [ORNL; McCabe, Donald E [ORNL

2007-01-01

238

Creep anisotropy of a continuous-fiber-reinforced silicon carbide/calcium aluminosilicate composite  

SciTech Connect

Creep studies conducted on a unidirectional silicon carbide/calcium aluminosilicate composite indicate that the Nicalon fibers provide longitudinal creep strengthening at 1,200 C. The deformation is transient in nature because grain growth in the fibers enhances their creep resistance. The transverse creep strength is considerably smaller, being dominated by the matrix, resulting in appreciable creep anisotropy. This anisotropy leads to severe distortion when off-axis loadings are imposed. Residual stresses develop upon unloading after creep, and cause superficial matrix cracking.

Weber, C.H.; Loefvander, J.P.A.; Evans, A.G. (Univ. of California, Santa Barbara, CA (United States). Materials Dept.)

1994-07-01

239

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

240

Finite element study for determination of materials creep parameters from small punch test  

Microsoft Academic Search

Compared with the conventional tensile creep test, it is much more difficult to obtain the creep properties of a material\\u000a by the small punch creep test due to the complex deformation response and stress distribution in the miniature specimen of\\u000a the material. Although creep behavior has been investigated by the small punch test, most studies have been limited to a

Jianjun Chen; Young Wha Ma; Kee Bong Yoon

2010-01-01

241

Grain-scale creep processes in MgAlCa base alloys: Implications for alloy design  

Microsoft Academic Search

Grain-scale creep straining processes in die-cast and permanent-mold-cast MgAlCa alloys have been studied. High-temperature strain mapping with electron backscattered diffraction analysis reveals favorably oriented grains deforming preferentially during creep. Displacements of microstructural-scale markers applied along grain boundaries and within grain interiors demonstrate no significant contribution of grain boundary sliding to creep. Creep rates at 175C display an inverse dependence on

N. D. Saddock; A. Suzuki; J. W. Jones; T. M. Pollock

2010-01-01

242

Intragranular strain field in columnar ice during elasto-viscoplatic transient creep regime  

Microsoft Academic Search

Transient effects in the creep of polycrystalline ice could play a crucial role for several ice flows (e.g. interaction between Antarctic ice shelves and ocean tides) and also ave a major impact concerning deformation mechanisms of ice. During creep deformation of polycrystalline ice, strong stress and strain-rate intragranular heterogeneities are expected. These heterogeneities come from the very large viscoplastic anisotropy

F. Grennerat; M. Montagnat; O. Castelnau; P. Duval; P. Vacher

2010-01-01

243

Intragranular strain field in columnar ice during transient creep regime and relation with the local microstucture  

Microsoft Academic Search

Transient effects in the creep of polycrystalline ice could play a crucial role for several ice flows (e.g. interaction between Antarctic ice shelves and ocean tides) and also have a major impact concerning deformation mechanisms of ice. During creep deformation of polycrystalline ice, strong stress and strain-rate intragranular heterogeneities are expected. These heterogeneities come from the very large viscoplastic anisotropy

F. Grennerat; M. Montagnat; O. Castelnau; P. Vacher; P. Duval

2010-01-01

244

New evidence for dislocation creep from 3-D geodynamic modeling of the Pacific upper mantle structure  

Microsoft Academic Search

Laboratory studies on deformation of olivine in response to applied stress suggest two distinct deformation mechanisms in the earth's upper mantle: diffusion creep through diffusion of atoms along grain boundaries and dislocation creep by slipping along crystallographic glide planes. Each mechanism has very different and important consequences on the dynamical evolution of the mantle and the development of mantle fabric.

Jeroen van Hunen; Shijie Zhong; Nikolai M. Shapiro; Michael H. Ritzwoller

2005-01-01

245

Nanoindentation Creep Behavior of Nanocomposite Sn-Ag-Cu Solders  

NASA Astrophysics Data System (ADS)

High-density, ultrasmall-pitch electronic applications require miniaturized solder bumps with improved thermomechanical performance. In addition, novel techniques which are able to precisely characterize these solder bumps are needed. One approach to meeting both of these requirements is to make use of recently developed nanocomposite solders with enhanced creep resistance, and to characterize these solders using a nanoindentation technique. In the present study, the creep behavior of ceria-reinforced nanocomposite solder foils fabricated by the accumulative roll-bonding process was characterized using a depth-sensing nanoindentation technique. It was found that the creep resistance of the composites increased with increasing volume fraction of CeO2 reinforcement, and it was deduced that the creep deformation of this nanocomposite proceeded by deformation of the matrix, with the role of the reinforcement being to increase the creep resistance by reducing the effective stress acting on the matrix. The values of the creep exponent suggested that the dominant creep deformation mechanisms involved were diffusion creep and grain boundary sliding.

Roshanghias, A.; Kokabi, A. H.; Miyashita, Y.; Mutoh, Y.; Ihara, I.; Guan Fatt, R. G.; Madaah-Hosseini, H. R.

2012-08-01

246

The effect of alloying additions on the high temperature deformation characteristics of Ti48Al (at%) alloys  

Microsoft Academic Search

Addition of ternary and quaternary alloying elements at levels between one and three atomic percent increase the room temperature ductility of Ti-48Al (at%) based titanium aluminides. In this investigation the deformation characteristics of Ti-48Al-2X (X = Cr, Mn) alloys at temperatures of 1,200 C to 1,300 C and strain rates of 10⁻³s⁻¹ to 10⁻¹s⁻¹ were studied and compared with the

C. M. Sabinash; S. M. L. Sastry; K. L. Jerina

1995-01-01

247

Plastic flow characteristics of ultrafine grained low carbon steel during tensile deformation  

Microsoft Academic Search

In order to explain steady-state plastic deformation, i.e. the absence of strain hardening in ultrafine grained low carbon\\u000a steel during tensile deformation, steel of different ferrite grain sizes was prepared by intense plastic straining followed\\u000a by static annealing and then tensile-tested at room temperature. A comparison between the ferrite grain size of ultrafine\\u000a grained steel and the dislocation cell size

Dong Hyuk Shin

2001-01-01

248

Creep failure criteria for high temperature alloys  

Microsoft Academic Search

The evolution of creep failure criteria is discussed from the early considerations of strain limits to avoid excessive deformation to the current concepts where rupture is used as the basic parameter for most cumulative damage laws. In addition to these modes of failure, the strain to crack initiation itself is considered as a possible overriding criterion for modern cast high

W. L. Chambers; W. J. Ostergren; J. H. Wood

1979-01-01

249

Creep of metal-type organic compounds. 3: Friction stress models for creep in particle-hardened systems  

SciTech Connect

The effect of a dispersed phase of small, hard particles on the creep behavior of two plastic crystals, camphene and succinonitrile, is investigated experimentally. Three models describing the creep deformation of a material containing hard particles are compared to the experimental data. Previous work has considered the particles to result in a constant friction stress which opposes creep deformation. The experimental results for plastic crystals are shown to be equally consistent with a model in which the friction stress is a linear function of the applied stress.

Davies, G.C.; Jones, D.R.H. [Univ. of Cambridge (United Kingdom). Engineering Dept.

1996-08-15

250

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

SciTech Connect

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

Munson, Darrell E.

1999-08-16

251

Postseismic deformation due to the M w 6.0 2004 Parkfield earthquake: Stress-driven creep on a fault with spatially variable rate-and-state friction parameters  

Microsoft Academic Search

We also find that the geodetic moment due to creep is a factor of 100 greater than the cumulative seismic moment of aftershocks. The rate of aftershocks in the top 10 km of the seismogenic zone mirrors the kinetics of afterslip, suggesting that postearthquake seismicity is governed by loading from the nearby aseismic creep. The San Andreas fault around Parkfield

Sylvain Barbot; Yuri Fialko; Yehuda Bock

2009-01-01

252

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.  

National Technical Information Service (NTIS)

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-sta...

J. W. Davis B. A. Cramer

1974-01-01

253

Influence of phosphorus on the creep ductility of copper  

NASA Astrophysics Data System (ADS)

Around 1990 it was discovered that pure copper could have extra low creep ductility in the temperature interval 180250 C. The material was intended for use in canisters for nuclear waste disposal. Although extra low creep ductility was not observed much below 180 C and the temperature in the canister will never exceed 100 C, it was feared that the creep ductility could reach low values at lower temperatures after long term exposure. If 50 ppm phosphorus was added to the copper the low creep ductility disappeared. A creep cavitation model is presented that can quantitatively describe the cavitation behaviour in uniaxial and multiaxial creep tests as well as the observed creep ductility for copper with and without phosphorus. A so-called double ledge model has been introduced that demonstrates why the nucleation rate of creep cavities is often proportional to the creep rate. The phosphorus agglomerates at the grain boundaries and limits their local deformation and thereby reduces the formation and growth of cavities. This explains why extra low creep ductility does not occur in phosphorus alloyed copper.

Sandstrm, Rolf; Wu, Rui

2013-10-01

254

Creep, creep-fatigue, and cavitation damage  

Microsoft Academic Search

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

Majumdar

1986-01-01

255

Plasticity and Diffusion Creep of Dolomite  

NASA Astrophysics Data System (ADS)

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

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

2005-12-01

256

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 50C. The microfabric of the folded quartz veins indicates deformation by dislocation creep accompanied by subgrain rotation. The small recrystallized grain size of ~86 m 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 50C. 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 50C) 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.; Stckhert, B.

2009-04-01

257

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

258

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

PubMed

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

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

2004-03-01

259

Creep of Rocks Under Small Mechanical Loading  

NASA Astrophysics Data System (ADS)

Study of rocks under small (typically s = 0.1 MPa) mechanical loading is of great importance both for a better understanding of geological deformation features and for the analysis of rock mass behavior at large distance from underground openings. A very small amount of experimental data is available. Very long-term tests are required, as the creep rates induced by such small mechanical loading are exceedingly small (10 13 to 10-12s-1). Accurate displacement measurements and a thorough control of both hygrometry and temperature must be used. We used high resolution displacements sensors, whose resolution is 10-9m, designed for purpose by P.A.Blum from IPG Paris. The creep test system were set in a 20-m deep gallery where hygrometry is close to 100%PHs suburbs ; and in a 200-m deep salt mine where hygrometry is 54+/-2% RH . In both sites daily temperature fluctuations are smaller than a few hundredth of a Celsius degree, allowing for quite constant ambient conditions during several month long tests, the observed displacement-versus-time curves can be corrected from the thermoelastic effects. Creep of salt samples was measured in the 200-m deep mine ; transient creep, steady-state creep and the effcts of stress drop were observed during a 18-month long test. The measured steady-state creep rates (10-12s-1) are much faster than the values extrapolated from standard tests performed under larger mechanical loading. Argillite creep was measured in the 20-m deep gallery. High hygrometry conditions result in relatively fast clay swelling. In this context, argillite creep rate, which is slower than swelling rate by one order of magnitude, is difficult to identify

Berest, P.; Charpentier, J. P.; Vales, F.

260

Ring shear test on creep in soils in help to the early warning on rainfall induced landslides  

NASA Astrophysics Data System (ADS)

Using prefailure creep for time prediction has become popular with the works of Saito and Uezawa (1961), Voight (1983), Fukuzono (1985) and others. The term of creep has been adopted from the mechanics of solids and defined as "time dependent deformation". Creep in different materials was found to show three distinctive phases - primary, when the rate of deformation decreases, secondary with constant rate of deformation and tertiary when acceleration in the rate is observed and eventually leads to rupture. Those phases have been also observed clearly in many natural slope slides. The characteristics of the tertiary creep gave opportunity for developing few time prediction models. In recent years the ring shear tests have proved to be reliable for simulating close to natural conditions rainfall induced landslides. We worked out our calculations based on the well-known and vastly used Fukuzono's method (1985). He provided the description of the tertiary creep phase with the equation d2x/dt2=A(dx/dt)? where x is the surface displacement, t is time and A and ? are constants. Our aim was to simulate creep in soils by raising the pore water pressure and investigate the mechanism of shear zone development during the creep. We examined the characteristics of the pre-failure deformations - displacement and rate of displacement as to provide new details on prediction of time of failure based on them. DPRI-5 is an intelligent ring shear apparatus initially aimed on testing the residual strength of sheared soils and simulation of earthquake induced landslides (detailed description on DPRI-5 and its application can be found in Sassa et al., 2004). We chose the ring shear apparatus for its biggest advantage to the direct shear test and the triaxial test of providing predetermined shear zone, which does not change during the test and possibility of monitoring of the pore water pressure in vicinity to the exact shear zone is possible. We have conducted 15 ring shear tests and analyzed in details the prefailure creep movement in soils triggered by gradually increasing positive pore water pressure. The soil samples were placed in the shear box of the apparatus and brought to a state of full saturation. Then normal stress and shear stress were applied. Backpressure was applied in the shear box from its upper outlets in "naturally drained" conditions until failure occurred. Based on the shear displacement we calculated the velocity and the acceleration as to determine the beginning of the tertiary creep and to obtain the parameters A and ? for each test. We found that ? tends to become bigger with the higher Bentonite or Illite content and with the higher total normal stress ? and smaller over-consolidation ratio. As the parameter ? determines the inclination of the velocity-acceleration line in the double-logarithmic relation between them it means that the higher ? the bigger the inclination. The inclination corresponds to the rate the velocity is increasing and thereafter the speed of which soil is losing its strength. A higher ? will mean the soil is collapsing faster. That can be an alarm criterion when we have initial data for accelerated movement. From the above paragraphs the following conclusion could be made. A soil with higher content of Bentonite clay or Illite mineral is going to fail quicker when the tertiary creep is initiated. The same will happen for deeper seated shear zones. As for the effect of OCR - a soil with higher OCR and density respectively has a smaller ? therefore its tertiary creep will last longer and the acceleration will be smaller than it is for a normally consolidated specimen

Georgieva, E.; Fukuoka, I.

2009-04-01

261

Deformation characteristics of rolled zirconium alloys: a study by X-ray diffraction line profile analysis  

SciTech Connect

Different techniques of the X-ray diffraction line profile analysis (XRDLPA) have been used to study the microstructural parameters of the heavily deformed solid polycrystalline Zircaloy-2 and Zr-2.5%Nb alloys. The domain size, microstrain within the domain, dislocation density and the stacking fault probabilities have been estimated by the Simplified Breadth Method, Williamson-Hall technique and the Modified Rietveld Method. A clear signature of the anisotropy in the domain shape was revealed. The domain size (D{sub e}) was quantified along the different crystallographic directions. In these deformed alloys, the dislocation density ({rho}{sub e}) was of the order of 10{sup 15} m{sup -2} but the stacking fault probabilities were almost negligible. For the first time, we could establish an empirical relationship between D{sub e} and ({rho}e)-12 for these hexagonal closed packed alloys.

Mukherjee, P. [Variable Energy Cyclotron Centre, Department of Atomic Energy, Block 1/AF Bidhannagar, Kolkata 700064 (India)]. E-mail: paramita@veccal.ernet.in; Sarkar, A. [Variable Energy Cyclotron Centre, Department of Atomic Energy, Block 1/AF Bidhannagar, Kolkata 700064 (India); Barat, P. [Variable Energy Cyclotron Centre, Department of Atomic Energy, Block 1/AF Bidhannagar, Kolkata 700064 (India); Bandyopadhyay, S.K. [Variable Energy Cyclotron Centre, Department of Atomic Energy, Block 1/AF Bidhannagar, Kolkata 700064 (India); Sen, Pintu [Variable Energy Cyclotron Centre, Department of Atomic Energy, Block 1/AF Bidhannagar, Kolkata 700064 (India); Chattopadhyay, S.K. [Regional Engineering College, Durgapur 713209 (India); Chatterjee, P. [Department of Physics, Vivekananda Mahavidyalaya, Haripal, Hooghly 712405 (India); Chatterjee, S.K. [Regional Engineering College, Durgapur 713209 (India); Mitra, M.K. [Faculty of Engineering and Technology, Jadavpur University, Kolkata 700032 (India)

2004-11-08

262

Amorphization and crystallization characteristics of TiNi shape memory alloys by severe plastic deformation  

Microsoft Academic Search

Differential scanning calorimetry (DSC) was used to determine the crystallization fraction and rate in TiNi alloys by severe\\u000a plastic deformation. Results showed that the reverse martensitic transformation peak was not observed during the first heating\\u000a at the rate of 40 K\\/min in the as-rolled samples, but one exothermic peak was observed at 620 K, which was associated with\\u000a the amorphous

Jun-tao Li; Wei-dong Miao; Yu-ling Hu; Yan-jun Zheng; Li-shan Cui

2009-01-01

263

Deep penetration of a non-deformable projectile with different geometrical characteristics  

Microsoft Academic Search

A general non-dimensional formula based on the dynamic cavity-expansion model is proposed to predict penetration depth into several mediums subjected to a normal impact of a non-deformable projectile. The proposed formula depends on two dimensionless numbers and shows good agreement with penetration tests on metal, concrete and soil for a range of nose shapes and impact velocities. The validity of

X. W. Chen; Q. M. Li

2002-01-01

264

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

265

Uniaxial creep behavior of V-4Cr-4Ti alloy.  

SciTech Connect

We are undertaking a systematic study at Argonne National Laboratory to evaluate the uniaxial creep behavior of V-Cr-Ti alloys in a vacuum environment as a function of temperature in the range of 650-800 C and at applied stress levels of 75-380 MPa. Creep strain in the specimens is measured by a linear-variable-differential transducer, which is attached between the fixed and movable pull rods of the creep assembly. Strain is measured at sufficiently frequent intervals during testing to define the creep strain/time curve. A linear least-squares analysis function is used to ensure consistent extraction of minimum creep rate, onset of tertiary creep, and creep strain at the onset of tertiary creep. Creep test data, obtained at 650, 700, 725, and 800 C, showed power-law creep behavior. Extensive analysis of the tested specimens is conducted to establish hardness profiles, oxygen content, and microstructural characteristics. The data are also quantified by the Larson-Miller approach, and correlations are developed to relate time to rupture, onset of tertiary creep, times for 1 and 2% strain, exposure temperature, and applied stress.

Natesan, K.; Soppet, W.K.; Purohit, A.

2002-04-15

266

Creep deformation of a two-phase TiAl/Ti[sub 3]Al lamellar alloy and the individual TiAl and Ti[sub 3]Al constituent phases  

SciTech Connect

Two-phase TiAl/Ti[sub 3]Al alloys in which the constituent phases form a lamellar microstructure are reported to possess good combinations of low-temperature fracture toughness, tensile strength and fatigue resistance. However, information about the high-temperature creep properties of the two-phase TiAl/Ti[sub 3]Al alloys with lamellar microstructures (referred to as lamellar alloys in the remainder of the paper) is limited. Based on a simple rule of mixtures model of strength, it would be expected that the creep rates of the lamellar alloy would be between the creep rates of TiAl and Ti[sub 3]Al. In contrast to composite model predictions of strength, Polvani and coworkers found that the minimum creep rates of two duplex alloys, a [gamma]/[gamma][prime] nickel-base superalloy and NiAl/Ni[sub 2]AlTi, were significantly lower than the minimum creep rates of either of the constituent phases. They also reported that most dislocations in the two-phase NiAl/Ni[sub 2]AlTi alloy were contained within the semi-coherent interfacial dislocation networks between the two phases. Based on this observation they proposed that the creep rate is controlled by the rate at which dislocations moving through both phases are emitted and absorbed by the interphase dislocation networks. The greater strain hardening rate of the lamellar TiAl/Ti[sub 3]Al alloy suggests that it may exhibit lower steady-state creep rates that the individual constituent phases. The objective of the present study is to evaluate the creep properties of a TiAl/ Ti[sub 3]Al lamellar alloy and of the individual constituent phases. In this paper, the results of this investigation will be presented and compared with previously published results for this alloy system.

Bartholomeusz, M.F.; Wert, J.A. (Univ. of Virgina, Charlottesville, VA (United States)); Qibin Yang (Inst. of Metals Research, Shenyang (China))

1993-08-01

267

Creep Laboratory manual  

NASA Astrophysics Data System (ADS)

A manual for the NPL Creep Laboratory, a collective name given to two testing laboratories, the Uniaxial Creep Laboratory and the Advanced High Temperature Mechanical Testing Laboratory, is presented. The first laboratory is devoted to uniaxial creep testing and houses approximately 50 high sensitivity creep machines including 10 constant stress cam lever machines. The second laboratory houses a low cycle fatigue testing machine of 100 kN capacity driven by a servo-electric actuator, five machines for uniaxial tensile creep testing of engineering ceramics at temperatures up to 1600C, and an electronic creep machine. Details of the operational procedures for carrying out uniaxial creep testing are given. Calibration procedures to be followed in order to comply with the specifications laid down by British standards, and to provide traceability back to the primary standards are described.

Osgerby, S.; Loveday, M. S.

1992-06-01

268

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., Stckert, 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.

269

Diffusional creep and diffusion-controlled dislocation creep and their relation to denuded zones in Mg-ZrH{sub 2} materials  

SciTech Connect

Langdon`s contention that creep of Mg-0.5 wt% Zr is well characterized by diffusional creep at 400 C is in error. It is shown that Langdon and Gifkins` single analysis of denuded zones formed during creep at 2 MPa, purporting to occur as a result of diffusional creep, in fact, took place in the power-law dislocation creep range where solute atoms are interacting with moving dislocations. This observation supports the earlier conclusions made for creep and denuded zones observed in the hydrided Mg-Zr alloy at 500 C. Furthermore, it is shown that Pickles` data at stresses below 2 MPa at 400 C are not related to diffusional creep as considered by Langdon. In this region, denuded zones appear in both longitudinal and transverse boundaries indicating that grain boundary sliding, accompanied by grain boundary migration, is the principal deformation process. It is proposed that denuded zones are caused by dissolution of precipitates at moving grain boundaries.

Ruano, O.A. [C.S.I.C., Madrid (Spain). Centro Nacional de Investigaciones Metalurgicas; Sherby, O.D. [Stanford Univ., CA (United States). Dept. of Materials Science and Engineering; Wadsworth, J. [Lawrence Livermore National Lab., CA (United States); Wolfenstine, J. [Univ. of Texas, San Antonio, TX (United States). Div. of Engineering

1998-03-13

270

Deformation characteristics and microstructural evolution of SnAgCu solder joints  

Microsoft Academic Search

Three SnAgCu solder alloys (Sn2AgO.5Cu, Sn3.4AgO.8Cu, Sn4AgO.5Cu) have been tested to determine their deformation behavior in the temperature range 23-110C, strain-rates varying 10-7-10-1 1\\/s. It is shown by optical micro-graphs of CSP solder joints that microstructure of SnAgCu may undergo through significant changes due to various loading conditions, which can occur during usage of microelectronic devices, such as thermal cycling,

T. O. Reinikainen; P. Marjamaki; J. K. Kivilahti

2005-01-01

271

Scaling laws of creep rupture of fiber bundles.  

PubMed

We study the creep rupture of fiber composites in the framework of fiber bundle models. Two fiber bundle models are introduced based on different microscopic mechanisms responsible for the macroscopic creep behavior. Analytical and numerical calculations show that above a critical load the deformation of the creeping system monotonically increases in time resulting in global failure at a finite time t(f), while below the critical load the system suffers only partial failure and the deformation tends to a constant value giving rise to an infinite lifetime. It is found that approaching the critical load from below and above the creeping system is characterized by universal power laws when the fibers have long-range interaction. The lifetime of the composite above the critical point has a universal dependence on the system size. PMID:16241249

Kun, Ferenc; Hidalgo, Raul Cruz; Herrmann, Hans J; Pl, Kroly F

2003-06-23

272

Scaling laws of creep rupture of fiber bundles  

NASA Astrophysics Data System (ADS)

We study the creep rupture of fiber composites in the framework of fiber bundle models. Two fiber bundle models are introduced based on different microscopic mechanisms responsible for the macroscopic creep behavior. Analytical and numerical calculations show that above a critical load the deformation of the creeping system monotonically increases in time resulting in global failure at a finite time tf, while below the critical load the system suffers only partial failure and the deformation tends to a constant value giving rise to an infinite lifetime. It is found that approaching the critical load from below and above the creeping system is characterized by universal power laws when the fibers have long-range interaction. The lifetime of the composite above the critical point has a universal dependence on the system size.

Kun, Ferenc; Hidalgo, Raul Cruz; Herrmann, Hans J.; Pl, Kroly F.

2003-06-01

273

Irradiation creep induced anisotropy in a/2110 dislocation populations  

NASA Astrophysics Data System (ADS)

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

Gelles, D. S.

1984-05-01

274

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

2013-06-28

275

Time-dependent brittle creep in Darley Dale sandstone  

Microsoft Academic Search

The characterization of time-dependent brittle rock deformation is fundamental to understanding the long-term evolution and dynamics of the Earth's crust. The chemical influence of pore water promotes time-dependent deformation through stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure strength. Here, we report results from a study of time-dependent brittle creep in water-saturated samples

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

2009-01-01

276

Creep indentation of single cells.  

PubMed

An apparatus for creep indentation of individual adherent cells was designed, developed, and experimentally validated. The creep cytoindentation apparatus (CCA) can perform stress-controlled experiments and measure the corresponding deformation of single anchorage-dependent cells. The apparatus can resolve forces on the order of 1 nN and cellular deformations on the order of 0.1 micron. Experiments were conducted on bovine articular chondrocytes using loads on the order of 10 nN. The experimentally observed viscoelastic behavior of these cells was modeled using the punch problem and standard linear solid. The punch problem yielded a Young's modulus of 1.11 +/- 0.48 kPa. The standard linear solid model yielded an instantaneous elastic modulus of 8.00 +/- 4.41 kPa, a relaxed modulus of 1.09 +/- 0.54 kPa, an apparent viscosity of 1.50 +/- 0.92 kPa-s, and a time constant of 1.32 +/- 0.65 s. To our knowledge, this is the first time that stress-controlled indentation testing has been applied at the single cell level. This methodology represents a new tool in understanding the mechanical nature of anchorage-dependent cells and mechanotransductional pathways. PMID:12929237

Koay, Eugene J; Shieh, Adrian C; Athanasiou, Kyriacos A

2003-06-01

277

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

NASA Astrophysics Data System (ADS)

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

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

2009-03-01

278

Elastic deformation characteristics and constitutive equations of light weight flexible robot manipulators  

NASA Astrophysics Data System (ADS)

Theoretical techniques have been developed to determine the tip positional errors of statically loaded flexible manipulators for any position and orientation. Two different approaches were taken in the analysis of flexible components of manipulator arms. One of which employs the strain energy invariance principle with respect to the elemental and the system reference coordinate frames in conjunction with the differential equations used in the classical beam theory to derive the desired combined flexural-joint stiffness matrix of the robotic structure. The second approach takes advantage of the (4 by 4) Denavit-Hartenberg homogeneous transformations to describe the kinematics of light weight flexible robotic arms under static loading. These methods are general in the sense that they may be applied to n-axis flexible manipulator arms. However, to simplify the derivations without deteriorating the techniques, only models of two link manipulator arms with flexible members are considered. To verify performance, these methods are simulated on an 11/780 Vax computer. Furthermore, sample of a two link motor arm were designed and constructed where the comparison between experimental and the theoretical results is quite satisfactory. The deformational inaccuracies of a current (so called rigid) manipulator such as the PUMA 560 robot is also examined and definite elastic deformation trends have been observed and discussed.

Meghdari, Ali

279

The coseismic deformation characteristic of the Wenchuan Ms 8.0 earthquake in 2008  

NASA Astrophysics Data System (ADS)

We used the radar data from the satellite ALOS/PALSAR of Japan and the differential interferometric synthetic aperture radar (D-InSAR) technology to derive the coseismic displacement field produced by the Wenchuan, Sichucan Province, China Ms 8.0 earthquake on 12 May 2008. Based on processing SAR data of 7 swaths and 112 scenes by the two-pass method, we obtained the interferometric map of 450km * 450km covering the causative fault and determined the distribution range of incoherent zones. Proper phase unwrapping was performed to these zones of continuous and discontinuous phases, yielding digital image of the interferometric displacement field, which is analyzed by displacement contours and the profile across the fault. The result shows that the Wenchuan Ms 8.0 earthquake has produced a vast area of surface deformation along the Yingxiu-Beichuan fault, primarily concentrated in a near-field range of 100km width on the northern and southern sides of the causative fault. In this field the 250km-long and 15~35km wide incoherent zone nearby the fault has suffered the largest deformation with surface ruptures, of which the amount is too large to measure by InSAR. The secondary deformed areas are 70km wide on each side of the incoherent zone, where envelope-like fringes are clear, continuous and converging towards the fault indicative of increasing gradient and amplitude of displacements which exhibit sunk north wall and uplifted south wall in sight line. With respect to the north and south edges of the data zone, the maximum subsidence in the north wall is 110~120cm appearing northeast of Wenhcuan and Maoxian, and a big range of descents of 55~60cm occurred nearby the epicenter south of Lixian. The largest uplift 120~135cm in the south wall is present at the epicenter west of Yingxiu, north to Dujiangyan and around Beichuan. The maximum relative displacement between the north and south walls is up to 240cm that appears nearby the epicenter west of Yingxiu and north to Dujiangyan. In the far-field 70km away from the incoherent zones on the both sides of the causative fault, there are sparse fringes indicative of displacements less than 10cm. The profile across the fault indicates that deformation is highly variable gradients with profound heterogeneity near the fault and in its hanging wall, while relatively uniform in the foot wall. These differences of deformation can be attributed to complicated thrust faulting. Our analysis suggests that the fault rupture of the Wenchuan earthquake is not a uni-direction thrust of its hanging wall to the footwall, instead a relative thrust between the two walls of the fault.

Qu, C.; Shan, X.; Song, X.; Zhang, G.

2009-12-01

280

A constant-stress, vacuum creep-testing apparatus  

Microsoft Academic Search

A mathematical analysis is presented for a direct-linkage tensile and compression creep-testing mechanism. A particular design,\\u000a employing a dead weight, a cam and a linkage system, achieves constant stress in a tensile specimen during uniform creep deformation.\\u000a Superiority has been achieved over previous designs in: (1) compactness with mechanical advantages up to 10:1, (2) higher\\u000a structural rigidity and (3) higher

J. F. Wilson; F. Garofalo; W. F. Domis; E. P. R. Reiche

1966-01-01

281

An Evaluation for Creep of 3013 Inner Can Lids  

SciTech Connect

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

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

2005-09-01

282

Elastic and creep properties of alumina-based single fibers  

SciTech Connect

Young`s moduli, creep properties, and time to failure under steady loads were measured for two types of alumina-based single fibers. Microstructural changes during deformation (grain growth and cavitation) have been analyzed. Experimental dispersion has been correlated to fiber diameter scatter. It has been shown that the fibers` behavior is similar to the behavior of bulk materials. Addition of zirconia particles slightly improved the creep and rupture properties of the materials.

Lavaste, V.; Besson, J.; Berger, M.H.; Bunsell, A.R. [Ecole des Mines de Paris, Evry (France). Centre des Materiaux

1995-11-01

283

Transitions in creep mechanisms and creep anisotropy in Zr?1Nb?1Sn?0.2Fe sheet  

Microsoft Academic Search

The creep characteristics of a Zr?1Nb?1Sn?0.2Fe alloy sheet were investigated at temperatures from 773 to 923 K and at stresses ranging from 9 to 150 MPa along both the rolling and transverse directions. Transitions in creep mechanisms are noted, with diffusional viscous creep at low stresses, viscous-glide-controlled microcreep in the intermediate stress regime and the climb of edge dislocations at

K. Linga Murty; J. Ravi; Wiratmo

1995-01-01

284

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

285

Deformation kinetics based rheological model for the time-dependent and moisture induced deformation of wood  

Microsoft Academic Search

A new general rheological model for the calculation of the creep of wood is presented. The flow equation derived in the theory of molecular deformation kinetics is adjusted to account for creep flow, moisture content change induced swelling\\/shrinkage and their combined effect by making an assumption that both of these processes activate the same bond breaking and reforming process. The

A. Hanhijrvi

1995-01-01

286

Hot Deformation Characteristics of GH625 and Development of a Processing Map  

NASA Astrophysics Data System (ADS)

The hot deformation behavior of GH625 is investigated by a compression test in the temperature range of 950-1150 C and the strain rate of 10-3-5 s-1. It is found that the flow stress behavior is described by the hyperbolic sine constitutive equation with average activation energy of 421 kJ/mol. Through the flow stresses' curves, the processing maps are constructed and analyzed according to the dynamic materials model. In the processing map, the variation of the efficiency of the power dissipation is plotted as a function of temperature and strain rate, and the maps exhibit a significant feature with a domain of dynamic recrystallization occurring at the temperature range of 950-1150 C and in the strain rate range of 0.005-0.13 s-1, which are the optimum parameters for hot working of the alloy. Meanwhile, the instability zones of flow behavior can also be recognized by the maps.

Zhou, H. T.; Liu, R. R.; Liu, Z. C.; Zhou, X.; Peng, Q. Z.; Zhong, F. H.; Peng, Y.

2013-09-01

287

Timing and characteristics of Paleozoic deformation and metamorphism in the Alabama Inner Piedmont  

SciTech Connect

The Opelika Complex in the Inner Piedmont of Alabama and Georgia records multiple periods of Paleozoic deformation and metamorphism. Rb-Sr isochron ages and thermobarometric data are reported for pelitic schists and spatially associated metagranite. A whole-rock Rb-Sr isochron age of 369 {plus minus} 5 Ma for Farmville Metagranite is interpreted as the time of syntectonic emplacement and crystallization within Auburn Gneiss and Loachapoka Schist of the Opelika Complex. Metapelitic units from the Auburn Gneiss and Loachapoka Schist exhibit a dominant S{sub 1} foliation which is continuous into Farmville Metagranite. Metamorphic assemblages defining this foliation (garnet + biotite + plagioclase + quartz + muscovite {plus minus} kyanite {plus minus} staurolite) indicate middle- to upper-amphibolite-facies conditions. Garnet-biotite geothermometry yields temperature estimates for final equilibration of 541{degree} to 580{degree}C, and garnet-plagioclase-kyanite-quartz and/or garnet-plagioclase-biotite-muscovite geobarometry indicate pressures of 6.8 to 8.2 kb for the matrix assemblage. This schistosity is retrograded by a S{sub 2} crenulation cleavage exhibiting greenschist-facies assemblages. The S{sub 2} cleavage in the Opelika Complex represents a late-stage (D{sub 2}) deformational event showing similar fabric and kinematic relationships to spatially associated mylonites from the Towaliga fault. Two feldspar thermometry from an extensional shear band in Farmville Metagranite yields temperatures of 302{degree} to 406{degree}C. A Rb-Sr mineral isochron from a strongly foliated sample of Farmville Metagranite yields an age of 296 {plus minus} 4 Ma. This age is interpreted as the time of Sr isotopic reequilibration, apparently in response to a period of uplift or thrusting associated with the Alleghanian orogeny.

Goldberg, S.A. (Univ. of North Carolina, Chapel Hill (USA)); Steltenpohl, M.G. (Auburn Univ., AL (USA))

1990-12-01

288

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

289

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 (230h) at 850C and 300MPa confining pressure.

Lili Xu; Jrg Renner; Marco Herwegh; Brian Evans

2009-01-01

290

Effect of stress and temperature on the micromechanics of creep in highly irradiated bone and dentin.  

PubMed

Synchrotron X-ray diffraction is used to study in situ the evolution of phase strains during compressive creep deformation in bovine bone and dentin for a range of compressive stresses and irradiation rates, at ambient and body temperatures. In all cases, compressive strains in the collagen phase increase with increasing creep time (and concomitant irradiation), reflecting macroscopic deformation of the sample. By contrast, compressive elastic strains in the hydroxyapatite (HAP) phase, created upon initial application of compressive load on the sample, decrease with increasing time (and irradiation) for all conditions; this load shedding behavior is consistent with damage at the HAP-collagen interface due to the high irradiation doses (from ~100 to ~9,000 kGy). Both the HAP and fibril strain rates increase with applied compressive stress, temperature and irradiation rate, which is indicative of greater collagen molecular sliding at the HAP-collagen interface and greater intermolecular sliding (i.e., plastic deformation) within the collagen network. The temperature sensitivity confirms that testing at body temperature, rather than ambient temperature, is necessary to assess the in vivo behavior of bone and teeth. The characteristic pattern of HAP strain evolution with time differs quantitatively between bone and dentin, and may reflect their different structural organization. PMID:23827597

Singhal, Anjali; Deymier-Black, Alix C; Almer, Jonathan D; Dunand, David C

2012-12-23

291

MICROSTRUCTURAL EXAMINATION OF V-4CR-4TI PRESSURIZED THERMAL CREEP TUBES  

SciTech Connect

Two further failed thermal creep pressurized tubes of V-4Cr-4Ti tested at 700 and 800 degrees C have been examined using optical microscopy and transmission electron microscopy in order to understand failure and creep mechanisms. These conditions represent lower stress states than were previously examined. Creep deformation at lower stress is shown to be controlled by sub-boundary formation and mis-orientation between sub-grains arising from climb of dislocations within the boundary.

Gelles, David S.

2002-09-01

292

The effect of grain morphology on longitudinal creep properties of INCONEL MA 754 at elevated temperatures  

Microsoft Academic Search

The longitudinal creep behavior of two heats of coarse grained INCONEL* MA 754 have been examined at temperatures of 1000\\u000a C and above. Both heats exhibit a pronounced transition in deformation behavior. At high stresses, dislocation creep is observed\\u000a and high stress exponents (n ?40) are measured. Fracture in this regime is transgranular with high creep ductilities. At lower stresses,

J. J. Stephens; W. D. Nix

1985-01-01

293

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 stressrelaxation, 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

294

Creep behavior of FeC alloys at high temperatures and high strain rates  

Microsoft Academic Search

The creep behavior of FeC alloys (11.8%C) has been studied at high temperatures (0.70.9Tm) and high strain rates (1100 s?1). The dominant deformation resistance has been found to be climb-controlled dislocation creep and thus the creep rates are a function of elastic modulus, lattice diffusivity and stacking fault energy. The self-diffusion coefficient of iron in austenite was found to be

D. R Lesuer; C. K Syn; J. D Whittenberger; M Carsi; O. A Ruano; O. D Sherby

2001-01-01

295

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

296

Effect of creep stress on microstructure of a Ni-Cr-W-Al-Ti superalloy  

Microsoft Academic Search

Creep stress changes the morphology and distribution of the precipitates in the precipitation-hardened alloys. It leads to the formation of precipitate free zones (PFZs) near the grain boundaries. From the microstructural observation of the creep tested specimens of a Ni-Cr-W-Al-Ti superalloy, the relation between PFZs and the amount of plastic deformation in the creep-ruptured specimen is established and the validity

Jung-Man Doh; Kyung-Keun Yoo; Hong-Ku Baik; Ju Choi; Sung-Kang Hur

1996-01-01

297

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/molK, the creep stress factor was 4.9 for an 800C 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 600C under JOYO and HFIR irradiation. The activation energy of irradiation creep was estimated to be 46 kJ/molK. 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

298

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

299

Development of a steady state creep behavior model of polycrystalline tungsten for bimodal space reactor application  

SciTech Connect

The fuel element for one of the many reactor concepts being currently evaluated for bimodal applications in space consists of spherical fuel particles clad with tungsten or alloys of tungsten. The fuel itself consists of stabilized UO{sub 2}. One of the life limiting phenomena for the fuel element is failure of the cladding because of creep deformation. This report summarizes the information available in literature regarding the creep deformation of tungsten and its alloys and proposes a relation to be used for calculating the creep strains for elevated temperatures in the low stress region ({sigma} {le} 20 MPa). Also, results of the application of this creep relation to one of the reactor design concepts (NEBA-3) are discussed. Based on the traditional definition of creep deformation, the temperatures of 1500 K to 2900 K for tungsten and its alloys are considered to be in the {open_quotes}high{close_quotes} temperature range. In this temperature range, the rate controlling mechanisms for creep deformation are believed to be non-conservative motion of screw dislocations and short circuit diffusional paths. Extensive theoretical work on creep and in particular for creep of tungsten and its alloys have been reported in the literature. These theoretical efforts have produced complex mathematical models that require detailed materials properties. These relations, however, are not presently suitable for the creep analysis because of lack of consistent material properties required for their use. Variations in material chemistry and thermomechanical pre-treatment of tungsten have significant effects on creep and the mechanical properties. Analysis of the theoretical models and limited data indicates that the following empirical relation originally proposed by M. Jacox of INEL and the Air Force Phillips Laboratory, for calculating creep deformation of tungsten cladding, can be used for the downselection of preliminary bimodal reactor design concepts.

Purohit, A.; Hanan, N.A.; Bhattacharyya, S.K.; Gruber, E.E.

1995-02-01

300

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

301

Characteristic features of the dynamic deformation of a circular plate with a hole  

Microsoft Academic Search

Many aspects of the edge mode characteristic for elastic bodies of finite dimensions are not well understood at the present time. It is also safe to say that the formation of this mode is explained qualitatively as the formation of a standing wave with inhomogeneous traveling waves. The variability of the stress (strain) field in this wave is characterized by

V. T. Grinchenko; V. P. Targonya

1995-01-01

302

Superplastic deformation of ice: Experimental observations  

NASA Astrophysics Data System (ADS)

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

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

2001-06-01

303

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

304

Creep analysis of fuel plates for the Advanced Neutron Source  

SciTech Connect

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

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

1994-11-01

305

Thermodynamic model of creep at constant stresses and constant strain rates  

Microsoft Academic Search

A thermodynamic model has been developed that for the first time describes the entire creep process, including primary, secondary, and tertiary creep, and failure for both constant stress (CS) tests (sigma = const.) and constant strain rate (CSR) tests (epsilon = const.), in the form of a unified constitutive equation and unified failure criteria. Deformation and failure are considered as

A. M. Fish

1983-01-01

306

An Evaluation of the Potential for Creep of 3013 Inner Can Lids  

Microsoft Academic Search

This report provides the technical basis to conclude that creep induced deformation of Type 304L austenitic stainless steel can lids on inner 3013 containers will be insignificant unless the temperature of storage exceeds 400 C. This conclusion is based on experimental literature data for Types 304 and 316 stainless steel and on a phenomenological evaluation of potential creep processes.

2005-01-01

307

Matrix cracking and creep behavior of monolithic zircon and zircon silicon carbide fiber composites  

Microsoft Academic Search

In this study, the first matrix cracking behavior and creep behavior of zircon matrix silicon carbide fiber composites were studied, together with the fracture and creep behavior of the monolithic zircon. These behaviors are of engineering and scientific importance, and the study was aimed at understanding the deformation mechanisms at elevated temperatures. The first matrix cracking behavior of zircon matrix

Umashankar Anandakumar

2000-01-01

308

Creep and tensile behavior of lead-rich, lead-tin solder alloys  

Microsoft Academic Search

The tensile and creep deformation of a series of high lead solders with 2% to 10% tin over a temperature range of 0C to 100C is discussed. The yield strength is strongly influenced by the precipitation of the tin phase, which depends on temperature and tin content. The creep rupture behavior follows the Monkman-Grant relationship. It is found that the

H. J. Frost; R. T. Howard; P. R. Lavery; S. D. Lutender

1988-01-01

309

Finite element method for studying the transient nonlinear thermal creep of geological structures  

Microsoft Academic Search

A finite element theory, suitable for describing the long term transient thermal creep of geomechanical structures where the material obeys an arbitrary type of creep law, is presented. The method takes into account large deformation effects, is stable for the large time steps required to model geophysical phenomena, and accurately simulates changing, incompressible, plastic flow fields. Applications of the theory

C. A. Anderson; R. J. Bridwell

1979-01-01

310

MPAA Ratings Creep  

Microsoft Academic Search

The term ratings creep refers to the belief that various types of adult content escalate in films with the same rating over time. The purpose of this study was to test the ratings creep hypothesis through a quantitative analysis of films from 1988, 1997, and 2006 in the PG-13 rating category used by the Motion Picture Association of America (MPAA).

Ron Leone; Laurie Barowski

2011-01-01

311

Plastic deformation of silicate garnets. II. Deformation microstructures in natural samples  

NASA Astrophysics Data System (ADS)

We have used Transmission Electron Microscopy to characterize the deformation microstructures in natural garnets from several localities: eclogites from Sesia Lanzo (Alps), eclogites and garnet amphibolite from Bragana (Portugal), garnet pyroxenite from Lherz (France) and eclogites from Yakutia pipe (Siberia). Two characteristic microstructures have been identified. The first, found in eclogites from the Alps, consists of microplasticity associated with microcracking that suggests brittle behavior. The remaining samples show a microstructure characteristic of dislocation creep with recovery (sub-grain boundaries). The transition between these deformation regimes occurs at ?600C, i.e., at the boundary between group C and group B eclogites. The deformation microstructures suggest that the dislocations experience strong lattice friction below ?600C whereas at high temperature, diffusion assists dislocation glide and climb (recovery). We observed the following glide systems in the whole temperature range: 1/2<111>{110}, 1/2<111>{112}, 1/2<111>{123}, <100>{010}, and <100>{011}. No correlation could be established between the dislocation microstructure and the hydrous component or the chemistry of the garnets among the pyralspites. Comparison of the natural deformation microstructures and those generated in high-pressure experiments [Voegel et al., 1998 (Part I)] validates the extrapolation of experimental data to nature.

Voegel, V.; Cordier, P.; Sautter, V.; Sharp, T. G.; Lardeaux, J. M.; Marques, F. O.

312

Failure-mechanism models for creep and creep rupture  

Microsoft Academic Search

This tutorial illustrates design situations where creep and creep rupture of components can compromise system performance over time, thereby acting as a wearout failure mechanism. Polycrystalline materials, such as metals and ceramics, and polymers are treated. Analytic microstructural creep mechanisms leading to failure of these materials are presented. Continuum microscale models for predicting long-term creep are explained for practical design

Junhui Li; Abhijit Dasgupta

1993-01-01

313

Elastic-plastic indentation creep of glassy poly(methyl methacrylate) and polystyrene: characterization using uniaxial compression and indentation tests  

NASA Astrophysics Data System (ADS)

This paper discusses the time-dependent mechanical response of poly(methyl methacrylate) (PMMA) and polystyrene (PS) subjected to a shallow indentation made by a 750 m radius steel ball at 25 C. The penetration depth was measured as a time-response to a prescribed loading history of the indenter. The tests were performed in the intermediate elastic-plastic regime, which is of paramount importance when dealing with the mechanics of a multicontact interface between rough bodies. The creep characteristics under constant load were analysed with an Eyring law relating the average stress and the strain rate in the deformed volume. The results were compared to data obtained by a standard uniaxial compression test on the bulk material. We have deduced a simple empirical rule which accounts for the heterogeneous stress and strain fields under the indenter and reduces the intricate problem of elastic-plastic indentation creep to an effective scalar rule.

Berthoud, P.; G'Sell, C.; Hiver, J.-M.

1999-11-01

314

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

315

Porosity evolution in a creeping single crystal  

NASA Astrophysics Data System (ADS)

Experimental observations on tensile specimens in Srivastava et al (2012 in preparation) indicated that the growth of initially present processing induced voids in a nickel-based single crystal superalloy played a significant role in limiting creep life. Also, creep tests on single crystal superalloy specimens typically show greater creep strain rates and/or reduced creep life for thinner specimens than predicted by current theories. In order to quantify the role of void growth in single crystals in creep loading, we have carried out three-dimensional finite deformation finite element analyses of unit cells containing a single initially spherical void. The materials are characterized by a rate-dependent crystal plasticity constitutive relation accounting for primary and secondary creep. Two types of imposed loading are considered: an applied true stress (force/unit current area) that is time independent; and an applied nominal stress (force/unit initial area) that is time independent. Isothermal conditions are assumed. The evolution of porosity is calculated for various values of stress triaxiality and of the Lode parameter. The evolution of porosity with time is sensitive to whether constant true stress or constant nominal stress loading is applied. However, the evolution of porosity with the overall unit cell strain is insensitive to the mode of loading. At high values of stress triaxiality, the response is essentially independent of the value of the Lode parameter. At sufficiently low values of the stress triaxiality, the porosity evolution depends on the value of the Lode parameter and void collapse can occur. Also, rather large stress concentrations can develop which could play a role in the observed thickness dependence.

Srivastava, A.; Needleman, A.

2012-04-01

316

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

317

Irradiation induced creep of graphite  

Microsoft Academic Search

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

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

2010-01-01

318

Irradiation Induced Creep of Graphite  

Microsoft Academic Search

The current status of graphite irradiation induced creep strain prediction is reviewed and the 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

Timothy D Burchell; K. L. Murty; Jacob Eapen

2010-01-01

319

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

320

Creep response of a 9Cr-1Mo-V-Nb steel to varying stresses and temperatures  

SciTech Connect

Deformation data were collected on specimens from a plate of a 9Cr-1Mo-V-Nb steel (SA 387 Grade 91) tested under constant and variable load conditions to 10,000 h. Data included results from relaxation, step-stress creep, cyclic creep, and a few nonisothermal tests. Ignoring short time transient effects, the use of a simple creep law in combination with the strain-hardening rule produced a reasonable correlation between observed and calculated creep rates for a variety of non-steady conditions in the primary and secondary creep regimes. 12 refs. 8 figs.

Swindeman, R.W.

1991-01-01

321

Transient Deformation at the Seismic-Aseismic Transition in a Mature Plate Boundary Fault Zone - New Zealand's Alpine Fault  

NASA Astrophysics Data System (ADS)

During the seismic cycle, stresses and strain rates fluctuate in the viscously-deforming zones down-dip of large faults. These transient events produce geological records that can be preserved in exhumed fault zones that have experienced single ruptures (e.g. Sesia Zone, European Western Alps). On the other hand, in major faults that have not experienced a simple, single rupture history, coseismic structures are likely to be destroyed during subsequent cycles of postseismic creep. New Zealand's active Alpine Fault has likely experienced upwards of 20,000 Mw~8 earthquakes, on average one every 200-300 years, over the last ?5 million years of dextral-reverse slip. Fault rocks generated during these events are exhumed in the hangingwall, exposing materials deformed throughout the seismogenic zone at the surface. We have recognised a structural record of transient events in these rocks that differs from that previously reported elsewhere. Mylonites were formed by viscous shearing of a metasedimentary protolith downdip of the seismogenic structure. Rheological models predict these mylonites should have passed through a crustal strength peak (? ?100 MPa) around the brittle-viscous transition. Immediately prior to passing through this transition, they should have developed a small recrystallised grainsize (~10-15?m) and a crystallographic preferred orientation (CPO) indicating slip on the basal system during quartz dislocation creep, as well as a retrograde greenschist-facies mineralogy. However, the high-strain mylonites preserve a large recrystallised grainsize (>~30?m), amphibolite-facies mineralogy and CPO characteristic of prism slip. This suggests they were not significantly deformed at temperatures below ~450C, significantly above the lower temperature limit for quartz crystal-plasticity at steady-state strain rates in the fault zone Microstructural observations and textural data indicate variable deformation style through the seismic cycle. Large fault ruptures propagated down-dip of the interseismically locked portion of the fault, so that a significant amount of deformation within the shear zone was released by slip on a single surface or surfaces, sometimes generating pseudotachylyte. High-stress immediate post-seismic creep resulted in activation of the uncharacteristic (harder?) prism slip system during quartz dislocation creep. On the other hand, creep strain rates in the interseismic period were much lower, so flow stresses were an order of magnitude less than expected if the shear zone deformation was evenly distributed over time. This postseismic creep must have been sufficient to develop a steady-state microstructure, so that the large quartz recrystallised grainsize developed while the ratio of recovery to deformation was high, but may have been insufficient to modify the prism CPO.

Toy, V. G.; Norris, R. J.; Prior, D. J.

2008-12-01

322

Creep damage mechanisms in composites  

SciTech Connect

During the past year, research has focused on processing and characterization of intermetallic composites synthesized by plasma spray deposition. This versatile process allows rapid synthesis of a variety of different composite systems with potential applications for coatings, functionally gradient materials, rapid proto-typing and 3d printing, as well as near-net-shape processing of complex shapes. We have been pursuing an experimental program of research aimed at a fundamental understanding of the microstructural processes involved in the synthesis of intermetallic composites, including diffusion, heat transfer, grain boundary migration, and the dependence of these phenomena on deposition parameters. The work has been motivated by issues arising from composite materials manufacturing technologies. Recent progress is described in section B on the following topics: (1) Reactive atomization and deposition of intermetallic composites (Ni3Al); (2) Reactive synthesis of MoSi2-SiC composites; (3) Mechanical alloying of nanocrystalline alloys; (4) Tensile creep deformation of BMAS glass-ceramic composites.

Nutt, S.R.

1994-10-17

323

The transient creep of vapor deposited Ti-6Al-4V  

SciTech Connect

Titanium matrix composites can be synthesized by the consolidation of ceramic fibers (for example, alumina and silicon carbide monofilaments) coated with titanium alloy deposited on the fiber by physical vapor deposition (PVD). Consolidation involves deformation of the matrix coating by both transient and steady-state creep. In a recent paper the mechanisms responsible for steady-state creep in PVD Ti-6Al-4V, between 600 and 900 C, were determined. The analysis of the data first presented has been extended here to consider the transient creep behavior of the material and identify an analogous constitutive law for use in simulating the transient creep contribution to consolidation.

Warren, J. [Philips Lighting Co., Bath, NY (United States). High Intensity Discharge Lamp Development Lab.; Wadley, H.N.G. [Univ. of Virginia, Charlottesville, VA (United States). Dept. of Materials Science and Engineering

1996-03-15

324

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

325

Minimum strain rate and primary transient creep analysis of a fine structure orthorhombic titanium aluminide  

SciTech Connect

The purpose of the present paper is to present a preliminary analysis of the primary transient creep behavior of an orthorhombic titanium aluminide having a very fine microstructure. In order to analyze and understand the creep behavior within the primary transient regime it is necessary to understand the mechanisms controlling deformation within the minimum strain rate region. Therefore an analysis of the minimum strain rate behavior is also presented. It will be shown that the primary transient creep behavior is dependent upon whether creep in the minimum strain rate region is controlled by a viscous flow mechanism or a dislocation mechanism.

Hayes, R.W. [Metals Technology Inc., Northridge, CA (United States)

1996-03-15

326

Irradiation creep in the US fusion alloy PCA at fusion He/dpa levels  

SciTech Connect

Irradiation creep has been studied in fast reactors where little helium is generated and in research reactors where very high levels of helium are generated in stainless steels. A summary of the conclusions made from the viewgraph information of this paper follows: the creep rate is 4 to 10 times higher for the fusion He/dpa ratio compared to the breeder reactor results; higher creep rate can only result from differences in the neutron spectrum; a higher level of irradiation creep could be beneficial in relieving swelling stresses, but detrimental in causing deformation under primary loads in the structure. (LSP)

Grossbeck, M.L.

1987-01-01

327

Irradiation Induced Creep of Graphite  

SciTech Connect

The current status of graphite irradiation induced creep strain prediction is reviewed and the 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, Timothy D [ORNL; Murty, Prof K.L. [North Carolina State University; Eapen, Dr. Jacob [North Carolina State University

2010-01-01

328

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

329

Development of Creep Constitutive Equation for Low-Alloy Steel  

SciTech Connect

High-temperature creep tests were performed with an SA533B1 low-alloy steel under both constant load and constant stress conditions. Using the measured minimum creep strain rates as a function of stress and temperature, least-square fittings were made into a Bailey-Norton-type power law equation. Based on the constant stress test results, a constitutive equation was developed for steady-state creep. The constitutive equation was then implemented in elastic-viscoplastic analysis of the lower head of a pressurized water reactor's reactor pressure vessel using a commercial FEM code named ABAQUS 5.8. The FEM model was validated using measured data from the lower head failure experiment conducted at the Sandia National Laboratories. The FEM model using the creep constitutive equation was shown to be capable of accurately predicting the lower head deformation behavior. Additional work, however, is needed to rationalize apparent inconsistency between the constant load data and constant stress data.

Jeong, Kwang J. [Seoul National University (Korea, Republic of); Lim, Joon [Seoul National University (Korea, Republic of); Hwang, Il S. [Seoul National University (Korea, Republic of); Kim, Hee D. [Korea Atomic Energy Research Institute (Korea, Republic of); Pilch, Martin M. [Sandia National Laboratories (United States); Chu, Tze Y. [Sandia National Laboratories (United States)

2003-09-15

330

The effect of cement creep and cement fatigue damage on the micromechanics of the cement-bone interface.  

PubMed

The cement-bone interface provides fixation for the cement mantle within the bone. The cement-bone interface is affected by fatigue loading in terms of fatigue damage or microcracks and creep, both mostly in the cement. This study investigates how fatigue damage and cement creep separately affect the mechanical response of the cement-bone interface at various load levels in terms of plastic displacement and crack formation. Two FEA models were created, which were based on micro-computed tomography data of two physical cement-bone interface specimens. These models were subjected to tensile fatigue loads with four different magnitudes. Three deformation modes of the cement were considered: 'only creep', 'only damage' or 'creep and damage'. The interfacial plastic deformation, the crack reduction as a result of creep and the interfacial stresses in the bone were monitored. The results demonstrate that, although some models failed early, the majority of plastic displacement was caused by fatigue damage, rather than cement creep. However, cement creep does decrease the crack formation in the cement up to 20%. Finally, while cement creep hardly influences the stress levels in the bone, fatigue damage of the cement considerably increases the stress levels in the bone. We conclude that at low load levels the plastic displacement is mainly caused by creep. At moderate to high load levels, however, the plastic displacement is dominated by fatigue damage and is hardly affected by creep, although creep reduced the number of cracks in moderate to high load region. PMID:20692663

Waanders, Daan; Janssen, Dennis; Mann, Kenneth A; Verdonschot, Nico

2010-08-07

331

Semi-analytical study of free vibration characteristics of shear deformable filament wound anisotropic shells of revolution  

NASA Astrophysics Data System (ADS)

Free vibration characteristics of filament wound anisotropic shells of revolution are investigated by using multisegment numerical integration technique in combination with a modified frequency trial method. The applicability of multisegment numerical integration technique is extended to the solution of free vibration problem of anisotropic composite shells of revolution through the use of finite exponential Fourier transform of the fundamental shell equations. The governing shell equations comprise the full anisotropic form of the constitutive relations, including first-order transverse shear deformation, and all components of translatory and rotary inertia. The variation of the stiffness coefficients along the axis of the shell is also incorporated into the solution method. Filaments are assumed to be placed along the geodesic fiber path on the shell of revolution resulting in the variation of the stiffness coefficients along the axis of the composite shell of revolution with general meridional curvature. Sample solutions have been performed on the effect of the variation of the stiffness coefficients on the free vibration behavior of filament wound truncated conical and spherical shells of revolution.

Kayran, Altan; Yavuzbalkan, Erdem

2009-01-01

332

Control and measurement of compressive creep at constant stress  

Microsoft Academic Search

An improved tech nique has been developed for elevated temperature compressive creep testing at constant stress. The maintenance of stress is through a servo control involving load and strain signals, and is based on the assumptions of constant volume and uniform deformation in the material. Strain is measured directly off the gauge length of a waisted specimen to avoid `bedding-in'

G P Tilly

1970-01-01

333

A Constant Stress Creep Apparatus for Superplastic Metals  

Microsoft Academic Search

In conducting constant stress creep tests of ductile metals means must be provided to alter the applied load in response to changes in specimen geometry. Over the years a variety of automatic devices has been developed which compensates for the limited range of geometrical change usually encountered. Interest in superplastic metals exhibiting homogeneous plastic deformations of several hundred percent and

T. D. Dudderar

1969-01-01

334

Mechanisms of Creep in a Precipitation Hardened Alloy  

Microsoft Academic Search

The binary alloy 97% copper-3% silver was selected as the most ideal alloy for research on the creep process in a precipitation hardened alloy. A heat treatment was divised which gave a slightly overaged Widmanstatten structure of high internal hardness and maximum stability. Wires of the alloy were subjected to deformation over a range of constant stresses at temperatures from

G C E Olds

1954-01-01

335

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

336

Creep modeling of rock salts for geoenvironmental application  

Microsoft Academic Search

Before using a rock salt as a nuclear waste repository, it is necessary to have adequate knowledge of the mechanical and thermomechanical behavior of the host geologic media. In rock salt, such mechanical and thermomechanical behavior is dominated, among other factors, by the time-dependent deformation commonly referred to as creep. The paper discusses a rate-dependent constitutive model to describe the

M. I. Hossain; M. O. Faruque; M. Zaman

1995-01-01

337

Effect of radiation dose on radiation creep of polymers  

Microsoft Academic Search

In investigations of radiation creep and service life of polymers the question arises: Are these radiation effects not determined by increasing doses of ionizing radiation? The effect of a radiation dose may be manifested, in particular, in rupture of the chemical bonds responsible for the strength of the polymer, as loading might cause supplemental deformation; and, when irradiation takes place

V. F. Stepanov; S. . Vaisberg; V. L. Karpov

1974-01-01

338

Creep Behavior and Life Evaluation of Aged P92 Steel  

NASA Astrophysics Data System (ADS)

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 from the operating service components. The small punch test has been developed as a useful method to estimate mechanical properties because of its miniaturized specimen size. In this study, small punch creep tests were carried out to investigate the effect of aging time on creep properties using P92 steel aged from 0~12100 hrs at 600C.

Kim, Bumjoon; Lim, Byeongsoo; Ki, Donghyun

339

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

340

Elastic-Plastic-Creep Simulation of Pb\\/Sn Solder Alloys by Separation of Plastic and Creep  

Microsoft Academic Search

This paper describes a constitutive model for solder alloys and a method to determine the material parameters of the model. First, a constitutive model that divides the inelastic deformation into plastic and creep parts is proposed. Next, a numerical method for the determination of the material parameters used in the model is developed. In this method, the material parameters for

Ken-Ichi Ohguchi; Katsuhiko Sasaki

2003-01-01

341

Very slow creep tests on salt samples  

NASA Astrophysics Data System (ADS)

Long-term creep tests have been performed on rock-salt and argillite samples under very small uniaxial loadings (? = 0.02 to 0.1 MPa) . To minimize the effects of temperature variations, testing devices were set in a mine where temperature fluctuations are of the order of one-hundredth of a degree Celsius. The mechanical loading was provided by dead weights. The deformations were measured through special displacement sensors with a resolution of ?? = 10-8. Strain rates as small as ? = 7 10-13s-1 were measured. These tests allow rock-sample creep to be investigated at very small strain rates. The tests also prove that extrapolation of constitutive laws at very small rates is often incorrect.

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

2010-06-01

342

Impression Creep Behavior of a Cast AZ91 Magnesium Alloy  

NASA Astrophysics Data System (ADS)

The creep behavior of the cast AZ91 magnesium alloy was investigated by impression testing. The tests were carried out under constant punching stress in the range 100 to 650 MPa, corresponding to 0.007 ? ? imp/ G ? 0.044, at temperatures in the range 425 to 570 K. Assuming a power-law relationship between the impression velocity and stress, depending on the testing temperature, stress exponents of 4.2 to 6.0 were obtained. When the experimental creep rates were normalized to the grain size and effective diffusion coefficient, a stress exponent of approximately 5 was obtained, which is in complete agreement with stress exponents determined by the conventional creep testing of the same material reported in the literature. Calculation of the activation energy showed a slight decrease in the activation energy with increasing stress such that the creep-activation energy of 122.9 kJ/mol at ? imp/ G = 0.020 decreases to 94.0 kJ/mol at ? imp/ G = 0.040. Based on the obtained stress exponents and activation energy data, it is proposed that dislocation climb is the controlling creep mechanism. However, due to the decreasing trend of creep-activation energy with stress, it is suggested that two parallel mechanisms of lattice and pipe-diffusion-controlled dislocation climb are competing. To elucidate the contribution of each mechanism to the overall creep deformation, the creep rates were calculated based on the effective activation energy. This yielded a criterion that showed that, in the high-stress regimes, the experimental activation energies fall in the range in which the operative creep mechanism is dislocation climb controlled by dislocation pipe diffusion. In the low-stress regime, however, the lattice-diffusion dislocation climb is dominant.

Kabirian, F.; Mahmudi, R.

2009-01-01

343

Elevated Temperature Deformation of Td-Nickel Base Alloys.  

National Technical Information Service (NTIS)

Sensitivity of the elevated temperature deformation of TD-nickel to grain size and shape was examined in both tension and creep. Elevated temperature strength increased with increasing grain diameter and increasing L/D ratio. Measured activation enthalpie...

J. J. Petrovic R. D. Kane L. J. Ebert

1972-01-01

344

Characteristics of the Cenozoic crustal deformations in SE Korea and its vicinity due to major tectonic events  

NASA Astrophysics Data System (ADS)

The southeastern Korean Peninsula has experienced multiple crustal deformations according to changes of global tectonic setting during the Cenozoic. Characteristics of the crustal deformations in relation to major Cenozoic tectonic events are summarized as follows. (1) Collision of Indian and Eurasian continents and abrupt change of movement direction of the Pacific plate (50 ~ 43 Ma): The collision of Indian and Eurasian continents caused the eastward extrusion of East Asia block as a trench-rollback, and then the movement direction of the Pacific plate was abruptly changed from NNW to WNW. As a result, the strong suction-force along the plate boundary produced a tensional stress field trending EW or WNW-ESE in southeastern Korea, which resultantly induced the passive intrusion of NS or NNE trending mafic dike swarm pervasively. (2) Opening of the East Sea (25 ~ 16 Ma): The NS or NNW-SSE trending opening of the East Sea generated a dextral shear stress regime trending NNW-SSE along the eastern coast line of the Korean Peninsula. As a result, pull-apart basins were developed in right bending and overstepping parts along major dextral strike slip faults trending NNW-SSE in southeastern Korea. The basins can be divided into two types on the basis of geometry and kinematics: Parallelogram-shaped basin (rhombochasm) and wedged-shaped basin (sphenochasm), respectively. At that time, the basins and adjacent basement blocks experienced clockwise rotation and northwestward tilting, and the eastward propagating rifting also occurred. At about 17 Ma, the Yeonil Tectonic Line, which is the westernmost border fault of the Miocene crustal deformation in southeastern Korea, began to move as a major dextral strike slip fault. (3) Clockwise rotation of southeastern Japan Island (16~15 Ma): The collision of the Izu-Bonin Arc and southeastern Japan Island, as a result of northward movement of the Philippine sea-plate, induced the clockwise rotation of southeastern Japan Islands. The event caused a NW-SE compression in the Korea Strait as a tectonic inversion, which resultantly terminated the basin extension and caused locally counterclockwise rotation of blocks in southeastern Korea. At that time, the folding of the San'in folded zone commenced. The folding in the Tsushima Island was almost completely accomplished at about 15 Ma and then an extensive intrusion of felsic magma occurred in the southern part of the island which led the island to be tilted about 20 into northeast. Simultaneously, the Tsushima-Goto fault was reactivated as major sinistral strike-slip faults owing to the accumulated NNW-trending compressional stress. The adjacent blocks to the fault were rotated horizontally about 28 counterclockwise due to the sinistral movement, and resultantly the western part of the San'in folded zone was dragged counterclockwise. (4) E-W compression in the East Asia (after about 5 Ma): Decreasing subduction angle of the Pacific plate and eastward movement of the Amurian plate have constructed the-top-to-west thrusts and become a major cause for earthquakes in southeastern Korea.

Son, M.; Kim, J.; Song, C.; Sohn, Y.; Kim, I.

2010-12-01

345

THE INFLUENCE OF COLDWORK LEVEL ON THE IRRADIATION CREEP AND The Influence of ColdWork Level on The Irradiation Creep and Swelling of AISI 316 Stainless Steel Irradiated as Pressurized Tubes In The EBR-II Fast Reactor  

Microsoft Academic Search

Pressurized tubes of AISI 316 stainless steel irradiated in the P-1 experiment in the EBR-II fast reactor have been measured to determine the dependence of irradiation-induced strains resulting from plastic deformation, irradiation creep, void swelling and precipitation. It is shown that the Soderberg relation predicting no axial creep strains in biaxially-loaded tubes is correct for both plastic and creep strains.

Edgar R. Gilbert; Francis A. Garner

2006-01-01

346

Bending induced by creeping of plasticized poly(vinyl chloride) gel  

NASA Astrophysics Data System (ADS)

Poly(vinyl chloride) (PVC) plasticized with large amount of plasticizer has been investigated as a material for artificial muscle or actuator that can be actuated by applying an electric field. This material shows "creep deformation" on an electrode. The deformation looks like a pseudopodial deformation of amoeba. The deformation can be utilized for swift bending motility. In this paper, we investigated the mechanism of the creep deformation. Microscopic Raman spectroscopy revealed that the orientation of polymer network or plasticizer molecule was hardly detectable under the experimental conditions employed for the electrical actuation. Orientation of plasticizer was detected only slightly at higher field application. Small angle X-ray scattering analysis clarified that the PVC gel (plasticized PVC) sustains network structure even at the very high plasticizer content like 90wt%. With the increase of plasticizer content, space distance increased linearly, implying the network structure is sustained. This nature of the PVC gel plays a critical roll in the elastic creep deformation. The network structure of the gel depends on the chemical nature of the plasticizer itself. When the increase of plasticizer content caused serious deterioration of the physical network of PVC polymer chain, the PVC gel only deformed irreversibly by creep. The bending deformation also investigated from the viewpoint of electrode asymmetry. The results suggest effective charge injection and the charge concentration on the electrode is the controlling factor of this amoeba-like deformation.

Hirai, Toshihiro; Kobayashi, Shigeyuki; Hirai, Mitsuhiro; Yamaguchi, Masaki; Uddin, Md. Zulhash; Watanabe, Masashi; Shirai, Hirofusa

2004-07-01

347

Tensile creep of dental amalgam.  

PubMed

Rather than the usual compressive dental creep, various types of one week old dental amalgams were continuously monitored in tensile creep. Testing was done at 37, 45 and 50 degrees C, in a specially designed apparatus capable of 0 to 60 degrees C while maintaining a constant true tensile stress of 17 MPa. For the first time, the classical four stages of creep were observed at elevated temperatures in the low Cu amalgams, including creep rupture. The high Cu systems displayed only transient creep up to 50 degrees C and no rupture. Approximately one half the stress was needed in tension to provide the equivalent creep in compression. PMID:7082735

Greener, E H; Szurgot, K; Lautenschlager, E P

1982-04-01

348

On the earthquake potential of creeping faults: Insights from labscale fault analogues  

NASA Astrophysics Data System (ADS)

A paradigm of creeping faults is that they are not seismogenic, i.e. that creeping segments do not generate earthquakes. Based on original stick-slip experiments on a laboratory fault we here demonstrate, however, that significant interseismic creep and large earthquakes may not be mutually exclusive phenomena and that creep signals vary systematically with the fault's seismic potential. The experimental setup used for this study includes granular material sheared in a ring-shear tester under controlled normal loads with varying velocity, both over a wide range of values (1 - 16 kPa, 0.1 - 25 mm/min) mimicking upper crustal deformation conditions at hydrostatic to lithostatic fluid pressures. According to our labscale analogue observations, transience of interseismic fault creep scales with fault strength and seismic coupling as well as with the maturity of the seismic cycle. Timescale independence of creep transience suggest that it should be possible to estimate longterm fault properties and behavior from shortterm observations, e.g. during triggered slip or aftershocks. The number of episodic creep events increase steadily towards the end of the seismic cycle giving a unique observable of the fault stress state relative to its seismic cycle. For very weak faults in a late stage of their seismic cycle, the observed creep systematics may lead to the chimera of a perennially creeping fault releasing stress by continuous creep and/or transient slow slip instead of large earthquakes.

Rosenau, M.; Oncken, O.

2012-04-01

349

Speculation on the creep behavior of silicon carbide whisker-reinforced alumina  

SciTech Connect

The creep behavior of SiC whisker-reinforced alumina matrix composites at 1500 deg C was investigated. The creep strain vs time exhibited typical primary, secondary,and tertiary creep. The initial creep rate in the primary regime exhibited a stress exponent of I.59, which is typical for single-phase polycrystalline alumina. The apparent stress exponent for secondary (Steady-state) creep was found to have a value of 2.88, well in excess of the expected value for creep of the alumina matrix. The presence of the whiskers appeared to suppress cavitation or other damage, thereby eliminating any contribution from elastic creep by crack growth or crack-enhanced creep to the total creep deformation. An analysis of the creep behavior of a short elastic fiber-reinforced matrix based on the theory of Kelly and Street was carried out.The results of this analysis suggested that stress dependent sliding at the SiC-alumina interface and stress dependent partial whisker fracture, with associated decrease in the average value of aspect ratio, appear to be the most likely mechanisms responsible for the high value of the apparent stress exponent in the secondary regime.

Donaldson, K.Y.; Venkateswaran, A.; Hasselman, D.P.; Rhodes, J.F.

1989-01-01

350

Irradiation creep of the US Heat 832665 of V-4Cr-4Ti  

SciTech Connect

The paper presents irradiation creep data for V-4Cr-4Ti irradiated to 3.7 dpa at 425 and 600 _C in the HFIR-17J experiment. Creep deformation was characterized by measuring diametral changes of pressur-ized creep tubes before and after irradiation. It was found that the creep strain rate of the US Heat 832665 of V-4Cr-4Ti exhibited a linear relationship with stress up to _180 MPa at 425 _C with a creep coefficient of 2.50 _10_6 MPa_1 dpa_1. A linear relationship between creep rate and applied stress was observed below _110 MPa at 600 _C with a creep coefficient of 5.41 _10_6 MPa_1 dpa_1; non-linear creep behavior was observed above _110 MPa, and it may not be fully accounted by invoking thermal creep. The bilinear creep behavior observed in the same alloy irradiated in BR-10 was not observed in this study.

Li, Meimei; Hoelzer, D. T.; Grossbeck, Martin L.; Rowcliffe, A. F.; Zinkle, Steven J.; Kurtz, Richard J.

2009-04-30

351

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

352

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 200C, and confining pressures of 3.4 and 20 MPa, comparing our data with those of other workers on the same material, and observing natural 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 ? 300C and 1 ? ? ? 20 MPa, and also to be workable in numerical modeling; (9) hence, no matter how abundant and precise site-specific laboratory data may become, one can expect only to approximate the rheological behavior of the prototype.

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

353

Creep of Fine-grained Gabbro in dry Condition  

NASA Astrophysics Data System (ADS)

Natural fine-grained gabbro were deformed at 300MPa confining pressure in a paterson-type deformation apparatus in GFZ. Creep tests were performed at temperatures ranging from 950-1150'C, stresses from 25-500 MPa, and strain rates between2.3x10-4 to 6.7x10-8s-1. The fine-grained gabbro is composed of 60 vol percent plagioclase, 30 vol percent pyroxene, 10 vol percent magnetite and ilmenite. The samples were dried at 1000`C for 167 hours before experiments. FTIR measurements show a water content of 0.008 wt percent H2O for starting samples, and 0.03 wt percent H2O for deformed samples. We performed three kinds of tests: stress step creep tests, temperature step creep test and constant stress creep with a long creep time. The data of stress-stepping creep tests and the constant stress creep test with long creep time show that the strain rates under the same stress level were increasing with cumulated creep time beyond a threshold time, which is 24 hours for temperature up to 1050 `C and 5 hours for temperature of 1100 `C, and a linear relation with slope of 1.0 was found between logarithm of strain rate and logarithm of accumulated time, suggesting time-proportional strain-rate enhancement, or equivalently, time-weakening effect of flow strength. Microstructural observations of deformed samples show that melt films occurred between grain boundaries of samples, and the melt contents increase with the creep time, indicating the mechanism of the weakening behavior. The strain rate enhancement related to melt fraction agrees to the data of Dimanov et al. [2000], and is fitted well with the model of Paterson [2000]. In order to determine a steady-state flow law with the effect of melt film excluded, the original steady-state strain rates are converted to the case with t=24 hours for experiments with temperatures up to 1050 `C, and data for temperature of 1100 `C are converted to the case with t=5 hours. The time-corrected creep data were fitted to the most commonly used power flow law, deriving a stress exponent of n=4, activation energy of Q= 644 kJmol-1, and pre-exponential factor in log scale of log A=10.3 MPans-1. The microstructures observed indicate that the deformation of the samples is in the dislocation creep regime. Free dislocations were observed in both pyroxene and plagioclase grains and dislocation walls and subgrain rotation were observed in pyroxene grains. Very fine-grained pyroxene and olivine altered from pyroxene grains suggest that dynamic recrystallization or reaction-accompanied dynamic recrystallization occurred in the samples during deformation with temperatures over 1000 `C. The value of stress exponent and activation energy determined in this study lie between the two end-member values of anorthite [Rybacki and Dresen, 2000] and diopside [Dimanov et al., 2005]. References Dimanov, A., R. Wirth, G. Dresen, 2000. Tectonophysics, 328. Dimanov, A., and G. Dresen, 2005. J. Geophys. Res., 110(B7). Paterson, M.S., 2000. Tectonophysics. Rybacki, E., and G. Dresen, 2000. J. Geophys. Res., 105.

Zhou, Y.; Rybacki, E.; Dresen, G.; He, C.

2008-12-01

354

Creep and creep-rupture behavior of Alloy 718.  

National Technical Information Service (NTIS)

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 commerc...

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

1991-01-01

355

Creep and creep-rupture behavior of Alloy 718  

Microsoft Academic Search

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

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

1991-01-01

356

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

357

Finite element method for studying the transient nonlinear thermal creep of geological structures. [Theory and application of SANGRE code  

Microsoft Academic Search

A finite element theory, suitable for describing the long-term transient thermal creep of geomechanical structures where the material obeys an arbitrary type of creep law, is presented. The method takes into account large deformation effects, is stable for the large time steps required to model geophysical phenomena, and accurately simulates changing, incompressible, plastic flow fields. Applications of the theory to

C. A. Anderson; R. J. Bridwell

1979-01-01

358

High-temperature creep and cavitation of polycrystalline aluminum nitride  

SciTech Connect

Dense, polycrystalline AIN samples of grain size between 1.8 and 19 {mu}m were fabricated by hot-pressing. Bar-shaped samples were subjected to creep in four-point bending under static loads in nitrogen atmosphere. The outer fiber stress was varied between 20 and 140 MPa and the temperature between 1650 and 1940 K. Steady-state creep was established in each of the tests. This paper reports that the steady-state creep rate, d{epsilon}/dt was proportional to {sigma}{sup n}d{sup m} where the stress exponent, n, was between 1.27 and 1.43 and grain-size exponent, m, between {approximately}2.2 and {approximately}2.4. The activation energy for creep ranged between 529 and 625 kJ/mol. Both round (r type) and wedge-shaped (w type) cavities were observed in electron micrographs of the deformed samples. No noticeable change in the dislocation density was observed. Contribution of cavitation to the creep rate was estimated using an unconstrained cavity model. Based on this study it is concluded that the dominant mechanism of creep in polycrystalline AIN is diffusional.

Jou, Z.C.; Virkar, A.V. (Utah Univ., Salt Lake City, UT (USA). Dept. of Materials Science and Engineering)

1990-07-01

359

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

360

Irradiation induced creep of graphite  

Microsoft Academic Search

The status of graphite irradiation induced creep strain prediction is reviewed and major creep models are described. The ability\\u000a of the models to quantitatively predict the irradiation induced creep strain of graphite is reported. Potential mechanisms\\u000a of in-crystal creep are reviewed as are mechanisms of pore generation under stress. The case for further experimental work\\u000a is made and the need

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

2010-01-01

361

Creep rupture of polymer composites  

Microsoft Academic Search

A creep-rupture model, based on a creep model which was successfully applied in a previous paper to model and predict the creep of a unidirectional carbon-fiber-reinforced epoxy composite and that of the epoxy matrix, and a critical energy fracture criterion, are presented. The results of the successful application of this model to predict the creep rupture of AS4\\/3501-6 composite specimens

J. Raghavan; M. Meshii

1997-01-01

362

Calculation of a turbine disk subject to repeated loadings, allowing for the mutual influence of short- and long-term processes of inelastic deformation  

Microsoft Academic Search

Conclusions 1.For disk-loading conditions involving the alternation of rapid, inelastic deformations and creep processes, the effects associated with the mutual influence of the viscous and plastic deformations (involving the appearance of a phase of transient creep in each cycle, and the softening of the rapid-deformation diagram after creep of the reverse sign), which were demonstrated experimentally in [1], are of

D. A. Gokhfel'd; V. . Gokhberg; K. M. Kononov; O. S. Sadakov

1976-01-01

363

Constant Stress Continuous Load Compression Creep Machine for Small Single Crystals  

Microsoft Academic Search

In order to learn more about the fundamental aspects of high temperature deformation, a machine was designed and built which can be used to study compression creep of small samples at constant stress and temperature. Constant stress is maintained in the deforming sample through the use of a specially curved arm which increases the applied load to compensate for the

W. A. Coghlan; R. J. Widlar

1972-01-01

364

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

365

Creep Rupture Modelling of Polymers  

Microsoft Academic Search

Damage by creep related fracture process is of primary importance in en gineering polymers and their composites. Modelling of creep rupture is useful for engi neering design especially in obtaining design stresses. Previously, the creep rupture times of polyethylene and polypropylene have been described successfully using a three element model with a critical elastic stored energy criterion. The modelling is

S. H. Teoh; B. W. Cherry; H. H. Kausch

1992-01-01

366

Creep Ruptures in Heterogeneous Materials  

Microsoft Academic Search

We present creep experiments on fiber composite materials with different controlled heterogeneity. All samples exhibit a power-law relaxation of the strain rate in the primary creep regime (Andrade's law) followed by a power-law acceleration up to rupture. We discover that the rupture time is proportional to the duration of the primary creep regime, showing the interplay between the two regimes

H. Nechad; A. Helmstetter; R. El Guerjouma; D. Sornette

2005-01-01

367

Calculation of Stress Relaxation Curves in Metals from Their Creep Diagrams . Berechnung der Spannungsrelaxationskurven von Metallen Aus Ihren Kriechkurven.  

National Technical Information Service (NTIS)

Creep curves from a number of metals and temperatures are used to calculate stress relaxation properties. Good agreement between theory and experiment is observed for the case where the degree of deformation is the independent variable in a high temperatu...

A. K. Hammami

1971-01-01

368

Simplified Inelastic (Plastic and Creep) Analysis of Pipe Elbows Subjected to Inplane and out-of-Plane Bending.  

National Technical Information Service (NTIS)

The inelastic analysis of elbows typical of use in Liquid Metal Fast Reactor piping systems is described. Detailed information on stresses, plastic and creep strains, and deformations throughout the elbow bodies resulting from elastic/plastic, elastic/pla...

R. M. Mello J. D. Scheller

1974-01-01

369

Finite Element Prediction of Creep-Plastic Ratchetting and Low Cycle Creep-Fatigue for a Large SPF Tool  

NASA Astrophysics Data System (ADS)

Industrial experience shows that large superplastic forming (SPF) tools suffer from distortion due to thermal cycling, which apparently causes high temperature creep and plasticity. In addition to distortion, thermomechanical fatigue and fatigue-creep interaction can lead to cracking. The aim of this study is to predict the life-limiting thermomechanical behavior of a large SPF tool under realistic forming conditions using elastic-plastic-creep FE analyses. Nonlinear time-dependent, sequentially coupled FE analyses are performed using temperature-dependent monotonic and cyclic material data for a high-nickel, high-chromium tool material, XN40F (40% Ni and 20% Cr). The effect of monotonic and cyclic material data is compared vis--vis the anisothermal, elastic-plastic-stress response of the SPF tool. An uncoupled cyclic plasticity-creep material model is employed. Progressive deformation (ratchetting) is predicted locally, transverse to the predominant direction of the creep-fatigue cycling, but at the same spatial location, due to creep and cyclic plasticity, during the so-called minor cycles, which correspond to comparatively small-amplitude temperature changes associated with opening of the press doors during part loading and unloading operations.

Deshpande, A. A.; Leen, S. B.; Hyde, T. H.

2010-06-01

370

A deformation-mechanism material model for NIKE 3-D  

SciTech Connect

The structural, finite element code, NIKE2D has a, new material model called the Deformation-Mechanism Model (DMM). This model uses kinetic equations to predict deformation rates for specific deformation-mechanisms. These mechanisms depend on temperature, applied stress, a strength parameter and grain size. Five kinetic equations are available, and they model Obstacle Controlled Plasticity, Power Law Creep, Power Law Breakdown, Diffusion Controlled Deformation and Slip Creep. A strength parameter models isotropic strain hardening and dynamic recovery. Grain size changes are modeled with a dynamic grain growth equation which depends on temperature, current grain size and the deformation rate. These kinetic equations and their evolutionary parameters are capable of predicting rate-dependent deformation behavior for many metals. In addition, multiple deformation-mechanisms can be combined in this material model to predict the rate dependent behavior of a material across several regimes of deformation behavior.

Raboin, P.J.

1993-01-04

371

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

SciTech Connect

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

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

1997-09-01

372

Early age stresses and creep-shrinkage interaction of restrained concrete  

NASA Astrophysics Data System (ADS)

Experimental and numerical analyses were performed to characterize the early age tensile creep and shrinkage behavior of concrete. A uniaxial restrained shrinkage test was developed. The experiment tested two identical specimens: restrained and unrestrained. The test was controlled by computer, and the shrinkage deformation was checked continuously and compared to a threshold value of 5 mum, which when exceeded, triggered an increase in tensile load to recover the shrinkage strain in the restrained specimen. Thus, a restrained condition is achieved and the stress generated by shrinkage mechanisms was measurable. The experiment revealed how shrinkage stresses developed and how creep mechanisms reduced shrinkage strain. The tests revealed that shrinkage stresses in the first days after casting are significant and caused fracture of the concrete. The rate of stress evolution influenced the time and stress of first cracking. The tensile creep of concrete formed a substantial part of the time dependent deformation and reduced the shrinkage stresses by 50%. A method separating drying creep mechanisms of concrete into stress-induced shrinkage and microcracking was developed. The method required measurement of creep and shrinkage of concrete under drying, sealed, and moist curing conditions. The moist-curing test produce the basic creep; the sealed test provided data on basic creep and stress-induced shrinkage, and the drying test provided data on basic creep, stress-induced shrinkage and microcracking. The basic creep results of young concrete indicated a high creep rate in the initial 10--20 hours after loading. Then, the rate decreased and the creep function approached a stable value. The initial rate of creep was sensitive to age at loading in the first two days, and became age-independent after a few days. The analysis revealed stress-induced shrinkage as a major mechanism of drying creep for plain and fiber reinforced concrete (FRC). Microcracking forms a significant portion of drying creep of plain concrete, but it is less significant in FRC. Therefore, creep of FRC is dominated by real mechanisms, whereas apparent mechanisms induced by microcracking is significant in plain concrete. The real creep mechanisms are beneficial because they provide tensile stress relaxation, but the apparent mechanisms are associated with microstructural damage and are detrimental. Therefore, FRC enhances stress relaxation and delays the time of shrinkage cracking.

Altoubat, Salah Ahmed

2000-10-01

373

Creep and dimensional stability of high purity niobium electron-beam welds  

NASA Astrophysics Data System (ADS)

A study was conducted to characterize the microstructure of electron beam welds in high purity niobium and its effect on creep behaviour at room temperature. The parent material was 2 mm sheet with a 50 ?m grain size. The weld fusion zone had 1 mm grains, implying that these grains all intersected the free surface. The parent material showed no room temperature creep deformation below the yield stress, but room temperature creep of weld specimens caused up to 10% strain in the weld region at 75% of the yield strength, over 1 2 months. Creep deformation was not smooth or continuous; the strain saturated at some value, and then after an incubation time, the strain increased and saturated again several times over 1 2 months. The magnitude of the strain for several specimens was similar but the creep deformation behavior was highly dependent on the actual microstructure and loading history. An initial prestrain with unloading shut down the creep deformation mechanism at the prior stress due to a dislocation-locking effect. The local stresses in the weld fusion zone arose from anisotropic elastic interactions due to different crystal orientations that caused local regions to exceed the yield strength.

Jiang, H.; Bieler, T. R.; Compton, C.; Grimm, T. L.

2006-07-01

374

In Situ Neutron-Diffraction Studies on the Creep Behavior of a Ferritic Superalloy  

NASA Astrophysics Data System (ADS)

Precipitate strengthening effects toward the improved creep behavior have been investigated in a ferritic superalloy with B2-type (Ni,Fe)Al precipitates. In situ neutron diffraction has been employed to study the evolution of the average phase strains, (hkl) plane-specific lattice strains, interphase lattice misfit, and grain-orientation texture during creep deformation of the ferritic superalloy at 973 K (700 C). The creep mechanisms and particle-dislocation interactions have been studied from the macroscopic creep behavior. At a low stress level of 107 MPa, the dislocation-climb-controlled power-law creep is dominant in the matrix phase, and the load partition between the matrix and the precipitate phases remains constant. However, intergranular stresses develop progressively during the primary creep regime with the load transferred to 200 and 310 oriented grains along the axial loading direction. At a high stress level of 150 MPa, deformation is governed by the thermally activated dislocation glide (power-law breakdown) accompanied by the accelerated texture evolution. Furthermore, an increase in stress level also leads to load transfer from the plastically deformed matrix to the elastically deformed precipitates in the axial direction, along with an increase in the lattice misfit between the matrix and the precipitate phases.

Huang, Shenyan; Brown, Donald W.; Clausen, Bjrn; Teng, Zhenke; Gao, Yanfei; Liaw, Peter K.

2012-05-01

375

An Approach for Impression Creep of Lead Free Microelectronic Solders  

Microsoft Academic Search

Currently, the microelectronics industry is transitioning from lead-containing to lead-free solders in response to legislation in the EU and Japan. Before an alternative alloy can be designated as a replacement for current Pb-Sn extensive testing must be accomplished. One major characteristic of the alloy that must be considered is creep. Traditionally, creep testing requires numerous samples and a long tin,

Onofrio A. Anastasio

2002-01-01

376

Developing natural convection with thermal creep in a vertical microchannel  

Microsoft Academic Search

Thermal creep occurs in anisothermal gas microflow. It is highly desirable to understand the creep effect on the flow and heat transfer characteristics for developing natural convective microflow. In this study, we investigate the steady developing natural convective flow in an open-ended vertical parallel-plate microchannel with asymmetric wall temperature distributions. The boundary-layer equations subject to the boundary conditions with respect

Cha'o-Kuang Chen; Huei Chu Weng

2006-01-01

377

High temperature deformation behavior of physical vapor deposited Ti-6Al-4V  

SciTech Connect

A detailed study has been conducted of the high temperature creep and microstructural evolution accompanying in the creep deformation of an initially nanocrystalline Ti-6Al-4V alloy. For test temperatures of 600 and 680 C the alloy transformed from an ({alpha} + {alpha}{prime}) to a single phase {alpha} during creep testing and exhibited exceptionally low creep resistance. During testing between 760 and 900 C, the alloy transformed to a conventional ({alpha} + {beta}) microstructure and exhibited up to ten times the creep rates of conventional grain size (super-plastic) Ti-6Al-4V. Creep models based on grain boundary sliding, dislocation and diffusional creep were combined with relationships for phase evolution and grain growth to predict stress-strain rate relationships at each test temperature. The analysis indicates that in the low temperature region dislocation accommodated GBS, in conjunction with diffusional flow, are responsible for creep whilst in the high temperature region diffusion accommodated GBS is the dominant mechanism.

Warren, J.; Hsiung, L.M.; Wadley, H.N.G. [Univ. of Virginia, Charlottesville, VA (United States). Dept. of Materials Science and Engineering

1995-07-01

378

THE INFLUENCE OF COLD?WORK LEVEL ON THE IRRADIATION CREEP AND The Influence of Cold?Work Level on The Irradiation Creep and Swelling of AISI 316 Stainless Steel Irradiated as Pressurized Tubes In The EBR-II Fast Reactor  

SciTech Connect

Pressurized tubes of AISI 316 stainless steel irradiated in the P-1 experiment in the EBR-II fast reactor have been measured to determine the dependence of irradiation-induced strains resulting from plastic deformation, irradiation creep, void swelling and precipitation. It is shown that the Soderberg relation predicting no axial creep strains in biaxially-loaded tubes is correct for both plastic and creep strains. Swelling strains are shown to be isotropically distributed both for stress-free and stress-affected swelling, while precipitation strains are somewhat anisotropic in their distribution. When corrected for stress-enhancement of swelling, the derived irradiation creep strains appear to be identical for both annealed and 20% cold-worked specimens, and also for tubes strained by rise to power increases in pressure. For relatively small creep strains it is often difficult to separate the creep and non-creep components of deformation.

Gilbert, Edgar R.; Garner, Francis A.

2006-09-01

379

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

SciTech Connect

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, the authors 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 creep-rupture life is also predicted to be independent of fiber spacing along the length of the specimen.

John, R.; Khobaib, M. [Univ. of Dayton Research Inst., OH (United States); Smith, P.R. [WL/MLLN, Wright-Patterson AFB, OH (United States). Materials Directorate

1996-10-01

380

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

NASA Astrophysics Data System (ADS)

Harper-Dorn creep was proposed for materials with large grain size deforming at very low stresses (sigma/G 10-6 where sigma is the applied stress and G is the shear modulus) and high temperatures (~ 0.95--0.99 Tm, where Tm is the absolute melting temperature). Recently, this creep mechanism has become controversial and several other creep mechanisms, such as 5-power law and Nabarro-Herring creep, have been proposed as governing the creep mechanism in the Harper-Dorn regime. An extensive study was conducted to evaluate several features of creep in the Harper-Dorn regime in order to determine an unambiguous creep mechanism. Compressive creep tests were conducted in the Harper-Dorn regime using single and polycrystalline samples of high purity aluminum. A stress exponent of 3 was observed for single crystal samples whereas polycrystalline samples did not show any transition in the stress exponent value from the 5-power law regime to the Harper-Dorn regime. An etch-pits study for single crystals showed that the dislocation density varies as the square of the applied stress in the Harper-Dorn regime and is in accordance with 5-power law creep. The marker line method was applied to study grain boundary sliding in the polycrystalline samples and it showed an abrupt decrease in the grain boundary sliding contribution to the total strain at the transition stress for the 5-power law regime to the Harper-Dorn regime with sliding remaining negligible in the Harper-Dorn regime. A review was conducted to compare the results obtained in the present investigation with the earlier studies supporting the conventional Harper-Dorn creep and in most of the cases a good consistency was observed. In the Harper-Dorn regime, natural 3-power law is proposed as the governing creep mechanism for the single crystals and a qualitative analysis showing grain boundary effects on the dislocation motion is presented for the polycrystals.

Kumar, Praveen

381

Creep Constitutive Model and Component Lifetime Estimation: The Case of Niobium-Modified 9Cr-1Mo Steel Weldments  

NASA Astrophysics Data System (ADS)

The ?-projection parametric method was used to analyze the creep strain versus time data, obtained in uniaxial tension, from weldments fabricated using a niobium-modified 9Cr-1Mo steel as the weld metal (Ellis, Private communication, 1991, provided the data). We used these data to illustrate a methodology whereby the ?-projection method may be used to obtain estimates of component design creep lifetimes, for specified sets of design stress, temperature, and strains. Furthermore, it is suggested that the creep strain results may be consistent with dislocation climb being the creep deformation mechanism in the alloy.

Lewis, Gladius; Shaw, Kevin M.

2010-10-01

382

Creep Constitutive Model and Component Lifetime Estimation: The Case of Niobium-Modified 9Cr-1Mo Steel Weldments  

NASA Astrophysics Data System (ADS)

The ?-projection parametric method was used to analyze the creep strain versus time data, obtained in uniaxial tension, from weldments fabricated using a niobium-modified 9Cr-1Mo steel as the weld metal (Ellis, Private communication, 1991, provided the data). We used these data to illustrate a methodology whereby the ?-projection method may be used to obtain estimates of component design creep lifetimes, for specified sets of design stress, temperature, and strains. Furthermore, it is suggested that the creep strain results may be consistent with dislocation climb being the creep deformation mechanism in the alloy.

Lewis, Gladius; Shaw, Kevin M.

2011-10-01

383

Application of kinetic theory to the analysis of high-temperature creep rupture of metals under complex stress (review)  

NASA Astrophysics Data System (ADS)

This paper gives an analytical review of the results obtained using the kinetic theory of creep and creep rupture to analyze the creep rupture of metals under complex stress. Special note is made of the outstanding contribution of Soviet scientists L. M. Kachanov and Yu. N. Rabotnov, who introduced the concept of material damage and developed the fundamentals of the kinetic theory. Different versions of this theory are used in studies of Russian and foreign scientists. The possibility of applying the kinetic theory to model the deformation and fracture of metals under creep conditions using scalar, vector, and tensor damage parameters and their combinations is considered.

Lokoshchenko, A. M.

2012-07-01

384

Limit Analysis Via Creep.  

National Technical Information Service (NTIS)

A variational method is presented for the limit analysis of an ideal plastic solid. This method has been denominated as Modified Secundary Creep and enables to find the collapse loads through a minimization of a functional and a limit process. Given an id...

E. Taroco R. A. Feijoo

1981-01-01

385

Testing the inference of creep on Rodgers Creek Fault  

NASA Astrophysics Data System (ADS)

The Rodgers Creek fault (RCF), one of the major through-going structures in the northern San Francisco Bay area, links two known active creeping faults - the Hayward fault and the Maacama fault. Historic earthquakes that occurred on the fault prove that this fault is seismically active. However, whether or not it creeps like its neighbors remains a question. A previous study (Funning et al., 2007) identified a right-lateral fault creep at rates up to 6 mm/yr between 1992 and 2001. The estimate remains controversial, however, since the evidence on the ground is limited. Another explanation for the velocity step is a vertical hydrological signal. Here, we use Permanent Scaterers InSAR data from both ascending and descending viewing geometries to test these two hypotheses. Under the assumption that fault-related deformation acts in the fault-parallel direction, it is possible to separate the deformation measured in the two viewing geometries into its horizontal and vertical components. Therefore, we put our efforts to validate/refute our initial hypothesis of creep on RCF by processing a 39-image ascending track dataset (track 478, frame 765) and a 33-image descending track dataset (track 342, frame 2835) from the ESA Envisat satellite spanning the interval 2003-2010, using the StaMPS/MTI code (Hooper, 2008). Assuming there is a creep on RCF, we would expect to see vertical deformations in both datasets but horizontal deformations only in track 342. In order to compare the PS velocities on either side of the fault, we plot cross-fault profiles through both datasets at ~5 km intervals and detrend the profiles by fitting parallel straight lines to windows of datapoints either side of the fault. The gradients of the lines reflect the regional component of deformation, along with any residual error in satellite orbital position, while the separations represent fault offset rates. Our preliminary results show positive (towards the satellite) velocities in the Cotati Basin and negative (away from the satellite) in the Santa Rosa plain in both datasets. In these areas, we believe, the ground is experiencing vertical deformations due to the subsurface fluid exchanges. Also, the results exhibit velocities change from negative to positive from west to east crossing RCF near the Foutaingrove Lake (FL) and the Annadel State Park (ASP), but in track 342 only. Based on the results, we find that our data are consistent with creep on RCF between FL and ASP from 2003 to 2010.

Jin, L.; Funning, G. J.

2010-12-01

386

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

NASA Astrophysics Data System (ADS)

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

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

2004-10-01

387

Dependence of deformability of geometries and characteristics of intramolecular hydrogen bonds in canonical 2'-deoxyribonucleotides on DNA conformations.  

PubMed

The molecular structure and deformability (with respect to average geometry) of methyl ethers of canonical 2'-deoxyribonucleotides thymidine-5'-phosphate (mTMP), 2-deoxycytidine-5'-phosphate (mCMP), 2-deoxyadenosine-5'-phosphate (mAMP) and 2'-deoxyguanosine-5'-phosphate (mGMP) in different types of DNA have been calculated using B3LYP/cc-pvdz method. Comparison of energy at equilibrium conformations of nucleotides and conformations with torsion angles of backbone fixed to average values for different types of DNA reveals that incorporation of nucleotides to A-DNA macromolecules requires the minimum amount of deformation energy. Therefore, this type of DNA should be the least strained from viewpoint of intramolecular deformations of monomers. Modeling of environmental effects within the PCM approach reveals that the immersion of nucleotides in polar medium results in significant decrease of energy differences between anti conformers of all DNTs and syn conformers of mGMP. This also leads to reduction by almost a half nucleotides' deformation energy facilitating formation of DNA macromolecule. Change of DNTs conformation causes switch between different types of intramolecular H bonds. Every type of DNA possesses unique set of intramolecular hydrogen bonds in nucleotides. PMID:19236114

Palamarchuk, Gennady V; Shishkin, Oleg V; Gorb, Leonid; Leszczynski, Jerzy

2009-04-01

388

Experimental evidence of increased deformation potential at MOS interface and its impact on characteristics of ETSOI FETs  

Microsoft Academic Search

Deformation potential (Dac), which determines the strength of electron-phonon scattering, is one of the most important physical parameters of Si. A longstanding unresolved question in Dac is that Dac for MOSFETs is considered to be much greater than Dac for bulk Si. In this work, we have demonstrated for the first time that Dac increases sharply at MOS interfaces within

Teruyuki Ohashi; Tsunaki Takahashi; Nobuyasu Beppu; Shunri Oda; Ken Uchida

2011-01-01

389

Mechanistic understanding of creep in gamma-base titanium aluminide alloys  

Microsoft Academic Search

The paper describes an experimental study of creep processes in two-phase titanium aluminide alloys. The investigations involve long-term creep test at relatively low stresses and temperatures. These test conditions lead to very low strain rates, which are characteristic of the intended service conditions. The creep tests were coupled with detailed electron microscope observations involving high-resolution imaging techniques and in situ

Fritz Appel

2001-01-01

390

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

SciTech Connect

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

Gelles, D.S.

1984-05-01

391

Irradiation creep behavior of the fusion heats of HT9 and modified 9Cr-1Mo  

SciTech Connect

In-reactor creep data on the fusion heats of HT9 and a modified 9Cr-1Mo steel have been obtained from irradiation of pressurized tube specimens in the FFTF reactor. These irradiations were conducted on specimens which reached /approximately/50 dpa at 400--540/degree/C and which utilized hoop stresses ranging from 0 to 200 Mpa. The creep behavior of these two alloys was found to be similar and to be consistent with creep data on related alloys irradiated in either EBR-II or FFTF. A correlation describing the irradiation-induced creep component of deformation has been developed and compared to the available data. These ferritic steels were also shown to exhibit a superior resistance to creep and swelling at temperatures <520/degree/C when compared to that of the AISI 316 and PCA austenitic alloys also irradiated in the fusion materials program. 18 refs., 5 figs., 2 tabs.

Puigh, R.J.; Garner, F.A.

1988-09-01

392

Microstructural softening creep of Cr-Mo ferritic/martensitic steels  

SciTech Connect

The effects of nitrogen on creep rupture strength and microstructure evolution in Cr- Mo steels have been studied. Creep tests were carried out at 600 deg. C and 650 deg. C under constant load conditions. The prior austenite grain size and martensite lath width were decreased by addition of nitrogen. And Cr{sub 2}X precipitates were stabilized at 750 deg. C as the nitrogen content increased. Creep rupture strength increased with increasing nitrogen content. Cr{sub 2}X precipitates were not dissolved after creep deformation. So these fine and stable Cr{sub 2}X precipitates may contribute to resist the microstructural softening of Cr-Mo steels during creep. (authors)

Woo Seog Ryu; Sung Ho Kim; Byoung Joon Song; Jong Hwa Chang [Korea Atomic Energy Research Institute, 150 Duckjin-Dong, Yuseong-Ku, Daejeon, 305-600 (Korea, Republic of)

2004-07-01

393

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

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

394

Creep rupture of viscoelastic fiber bundles  

NASA Astrophysics Data System (ADS)

We study the creep rupture of bundles of viscoelastic fibers occurring under uniaxial constant tensile loading. A fiber bundle model is introduced that combines the viscoelastic constitutive behavior and the strain controlled breaking of fibers. Analytical and numerical calculations showed that above a critical external load the deformation of the system monotonically increases in time resulting in global failure at a finite time tf, while below the critical load the deformation tends to a constant value giving rise to an infinite lifetime. Our studies revealed that the nature of the transition between the two regimes, i.e., the behavior of tf at the critical load ?c, strongly depends on the range of load sharing: for global load sharing tf has a power law divergence at ?c with a universal exponent of 0.5, however, for local load sharing the transition becomes abrupt: at the critical load tf jumps to a finite value, analogous to second- and first-order phase transitions, respectively. The acoustic response of the bundle during creep is also studied.

Hidalgo, Raul Cruz; Kun, Ferenc; Herrmann, Hans. J.

2002-03-01

395

Correlation of Creep Behavior of Domal Salts  

Microsoft Academic Search

The experimentally determined creep responses of a number of domal salts have been reported in, the literature. Some of these creep results were obtained using standard (conventional) creep tests. However, more typically, the creep data have come from multistage creep tests, where the number of specimens available for testing was small. An incremental test uses abrupt changes in stress and

Munson

1999-01-01

396

A numerical procedure for retrieving material creep properties from bending creep tests  

Microsoft Academic Search

In the present study, we show how bending creep testing of a material can be used to determine the creep parameters of a material. Assuming a simple Norton type of creep law (??=B?n, where ?? is the secondary creep rate, B the creep constant and ? is the applied stress), we present two procedures based on creep finite element stress

B. X. Xu; Z. F. Yue; G. Eggeler

2007-01-01

397

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 (600-800C). 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 600C), 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

398

An electronic constant-stress device - Its application in creep tests  

Microsoft Academic Search

An electronic device is described which will maintain stress constant to within plus or minus 0.1% during creep tests. The device is used in conjunction with conventional dead-load creep apparatus and, in common with all constant-stress methods, requires that the deformation of the test specimen occurs uniformly and at constant volume. The device is not strain-limited and will maintain stress

A. T. Donaldson; G. Knowles

1980-01-01

399

Flip chip solder joint reliability analysis using viscoplastic and elastic-plastic-creep constitutive models  

Microsoft Academic Search

Both elastic-plastic-creep and viscoplastic constitutive models may be used for inelastic deformation analysis of solder joints. In this paper, a phenomenological approach using elastic-plastic-creep analysis and an Anand viscoplastic model is reported for solder joint reliability. Flip chip soldered assemblies with 63Sn-37Pb solder joints were subjected to a thermal cyclic loading condition of -40 to +125degC to assess the solder

Alfred Yeo; Charles Lee; John H. L. Pang

2006-01-01

400

Prestrain effects on creep ductility of a 316 stainless steel light forging  

Microsoft Academic Search

Specimens were machined from a section of 316 stainless steel header which was in service for approximately 30?000h. Constant stress creep tests were performed at 450MPa and 575C on materials subjected to various levels of prestrain to determine the effect of prior deformation on subsequent creep behaviour. The results show that, provided the prestrain exceeds the initial strain on loading

M. Willis; A. McDonaugh-Smith; R. Hales

1999-01-01

401

Damage of low-alloy high temperature steels loaded by low-cycle fatigue and creep  

Microsoft Academic Search

Present-day models used for calculations of life at combinations of low-cycle fatigue loading and creep mostly work with experimental curves of life at constant amplitude of deformation. However, during such a type of loading, a relative proportion of damage caused by low-cycle fatigue and creep is changed.On the basis of large-extension experimental measurement made on low-alloy CrNiMoV and CrMoV steels,

Miroslav Kneifl; Ivo ?ern; Vladim??r B??na

2001-01-01

402

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

403

Experimental deformation of partially-melted granite  

Microsoft Academic Search

An account is given of the experimental deformation of partially-melted granite with melt fractions up to 25% at 800 C and 300 MPa confining pressure in constant strainrate tests between 10-3 and 10-6 S-1, creep tests and cycling tests. Microscopic study reveals that under these conditions most of the uniform deformation prior to macroscopic shear failure is accomplished by melt

I. van der Molen; M. S. Paterson

1979-01-01

404

Creep-fatigue life prediction of in situ composite solders  

SciTech Connect

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

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

1995-12-01

405

Creep-fatigue life prediction of in situ composite solders  

NASA Astrophysics Data System (ADS)

Eutectic tin-lead solder alloys subjected to cyclic loading at room temperature experience creep-fatigue interactions due to high homologous temperature. Intermetallic reinforcements of Ni3Sn4 and Cu6Sn5 are incorporated into eutectic tin-lead alloy by rapid solidification processes to form in situ composite solders. In this study, the in situ composite solders were subjected to combined creep and fatigue deformation at room temperature. Under cyclic deformation, the dominant damage mechanism of in situ composite solders is proposed to be growth of cavities. A constrained cavity growth model is applied to predict creep-fati