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1

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

2

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

3

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

4

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

5

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

6

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

7

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

8

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

9

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

10

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

11

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

12

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

13

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

14

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

15

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

16

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

17

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

18

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

19

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

20

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

21

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

22

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

23

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

24

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

25

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

26

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

27

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

28

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

29

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

30

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.

31

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

32

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

33

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

34

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

35

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

36

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

37

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

38

Viscoelastic creep of high-temperature concrete  

SciTech Connect

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

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

1985-01-01

39

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

40

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

41

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

42

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

43

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

44

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

45

Use replication to evaluate high temperature creep  

SciTech Connect

Several major technical programs dealt with inspection and interpretation of replicas relating to creep in piping and headers in power plants. The dominant materials analyzed were 1-1/4Cr-1/2Mo and 2-1/4Cr-1Mo seamless and welded piping and forgings. A database has been assembled covering over 1,000 welds and heat affected zones operating at temperatures between 900 to 1,000{sup 0}F. Microvoiding along grain boundaries and macrocracking qualitatively related to the three stages of creep. A categorization of the development of creep first proposed by Neubauer is presented. An example of a typical intergranular creep crack with associated creep microvoids is shown. With the data collected, quantitative relationships between the amount of creep microvoids and remaining life are developed.

Strauss, B.M. (Teledyne Engineering Services, Waltham, MA (US))

1989-10-01

46

High temperature creep of modified ? + ? brasses  

Microsoft Academic Search

Good machinability and formability of technical brasses ?+? have to be preserved when alternative modifications are developed instead of alloying with toxic lead. Several model brasses of this type, which exhibit satisfactory machinability, are creep tested at 780C to compare their high temperature formability. The observed stationary creep rate and local ductility may highly differ for various alloy types. To

J. Balk; J. Faltus; M. Jane?ek

2008-01-01

47

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

48

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

49

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

50

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

51

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

52

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

53

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

54

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

55

Improvement of creep rupture life by high temperature pre-creep in magnesiumaluminum binary solid solutions  

Microsoft Academic Search

Effects of high-temperature pre-creep on creep life in magnesiumaluminum solution hardened alloys have been investigated. Creep life, at 0.55Tm (Tm is the absolute melting temperature) are drastically improved by pre-creep treatment, which is given at higher temperature, 0.7Tm. The samples show almost the same minimum creep rate, although creep rate in tertiary creep is affected by the pre-creep treatment. Improvement

Hiroyuki Sato; Kota Sawada; Kouichi Maruyama; Hiroshi Oikawa

2001-01-01

56

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

57

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

58

Stress versus temperature dependent activation energies in creep  

SciTech Connect

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

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

1990-01-01

59

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

60

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

61

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

62

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

63

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

64

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

65

Temperature-dependent transient creep and dynamics of cratonic lithosphere  

NASA Astrophysics Data System (ADS)

Large-scale mantle convection forms the upper boundary layer (lithosphere) where the vertical temperature drop is about 1300 K. Theoretical rheology and laboratory experiments with rock samples show that transient creep occurs while creep strains are sufficiently small. The transient creep is described by the temperature-dependent Andrade rheological model. Since plate tectonics allows only small deformations in lithospheric plates, creep of the lithosphere plates is transient whereas steady-state creep, described by non-Newtonian power-law rheological model, takes place in the underlying mantle. The solution of stability problem shows that the lithosphere is stable but small-scale convective oscillations are attenuated very weakly in regions of thickened lithosphere beneath continental cratons (subcratonic roots) where the thickness of the lithosphere is about 200 km. These oscillations create small-scale convective cells (the horizontal dimensions of the cells are of the order of the subcratonic lithosphere thickness). Direction of motion within the cells periodically changes (the period of convective oscillations is of the order of 3 108 yr). In this study, the oscillations of cratonic lithosphere caused by initial relief perturbation are considered. This relief perturbation is assumed to be created by overthrusting in orogenic belts surrounding cratons. The perturbation of the Earth's surface relief leads to a fast isothermal process of isostatic recovery. In the presence of vertical temperature gradient, vertical displacements, associated with the recovery process in the lithosphere interior, instantly produce the initial temperature perturbations exciting thermoconvective oscillations in the cratonic lithosphere. These small-amplitude convective oscillations cause oscillatory crustal movements which form sedimentary basins on cratons.

Birger, Boris I.

2013-11-01

66

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

67

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

68

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

69

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

70

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

71

High temperature creep-fatigue design  

Microsoft Academic Search

Generation IV fission and future fusion reactors envisage development of more efficient high temperature concepts where materials\\u000a performances are key to their success. This paper examines different types of high temperature creep-fatigue interactions\\u000a and their implications on design rules for the structural materials retained in both programmes. More precisely, the paper\\u000a examines current status of design rules for the stainless

A.-A. F. Tavassoli; B. Fournier; M. Sauzay

2010-01-01

72

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

73

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

PubMed

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

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

1993-03-01

74

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

SciTech Connect

The models developed, contain explicit dependences on constituent material properties and their changes with time, so that composite performance can be predicted. Three critical processes in ceramic composites at elevated temperatures have been modeled: (1) creep deformation of composite vs stress and time-dependent creep of fibers and matrix, and failure of these components; (2) creep deformation of ``interface`` around broken fibers; and (3) lifetime of the composite under conditions of fiber strength loss over time at temperature. In (1), general evolution formulas are derived for relaxation time of matrix stresses and steady-state creep rate of composite; the model is tested against recent data on Ti-MMCs. Calculations on a composite of Hi-Nicalon fibers in a melt-infiltrated SiC matrix are presented. In (2), numerical simulations of composite failure were made to map out time-to-failure vs applied load for several sets of material parameters. In (3), simple approximate relations are obtained between fiber life and composite life that should be useful for fiber developers and testers. Strength degradation data on Hi-Nicalon fibers is used to assess composite lifetime vs fiber lifetime for Hi-Nicalon fiber composites.

Curtin, W.A.; Fabeny, B.; Ibnabdeljalil, M.; Iyengar, N.; Reifsnider, K.L. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Engineering Science and Mechanics

1996-07-31

75

Elevated Temperature Deformation of Thoria Dispersed Nickel-Chromium.  

National Technical Information Service (NTIS)

The deformation behavior of thoria nickel-chromium (TD-NiCr) was examined over the temperature range 593 C (1100 F) to 1260 C (2300 F) in tension and compression and at 1093 C (2000 F) in creep. Major emphasis was placed on: (1) the effects of the materia...

R. D. Kane L. J. Ebert

1974-01-01

76

High temperature creep resistant austenitic alloy  

DOEpatents

An improved austenitic alloy having in wt % 19-21 Cr, 30-35 Ni, 1.5-2.5 Mn, 2-3 Mo, 0.1-0.4 Si, 0.3-0.5 Ti, 0.1-0.3 Nb, 0.1-0.5 V, 0.001-0.005 P, 0.08-0.12 C, 0.01-0.03 N, 0.005-0.01 B and the balance iron that is further improved by annealing for up to 1 hour at 1150.degree.-1200.degree. C. and then cold deforming 5-15 %. The alloy exhibits dramatically improved creep rupture resistance and ductility at 700.degree. C.

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

1989-01-01

77

Room temperature creep in saturated granite  

SciTech Connect

Cylindrical samples of granite were deformed at 26[degrees]C, constant confining pressure (60 MPa), and constant pore pressure (20 MPa). Axial and volumetric strain were determined from changes in the output of resistance foil strain gauges bonded to the rock surface. In addition, dc electrical resistivity was measured parallel to the sample axis. During each experiment (typically lasting from 1-2 weeks), the deviatoric stress [sigma] [sub d] applied to the sample was cycled between 70% and 90% of the short-term failure strength. The bulk of the experiments were conducted in tile secondary or steady state' creep regime. Inelastic volumetric strain rate was found to obey the law log[sub 10]([dot [var epsilon

Lockner, D. (Geological Survey, Menlo Park, CA (United States))

1993-01-10

78

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

SciTech Connect

The outline of this presentation is: (1) Applications of Kovar Alloy in metal/ceramic brazing; (2) Diffusion bonding of precision-photoetched Kovar parts; (3) Sample composition and annealing conditions; (4) Intermediate temperature creep properties (350-650 C); (5) Power law creep correlations--with and without modulus correction; (6) Compressive stress-strain properties (23-900 C); (7) Effect of creep deformation on grain growth; and (8) Application of the power law creep correlation to the diffusion bonding application. The summary and conclusions are: Elevated temperature creep properties of Kovar from 750-900 C obey a power law creep equation with a stress exponent equal to 4.9, modulus compensated activation energy of 47.96 kcal/mole. Grain growth in Kovar creep samples tested at 750 and 800 C is quite sluggish. Significant grain growth occurs at 850 C and above, this is consistent with isothermal grain growth studies performed on Kovar alloy wires. Finite element analysis of the diffusion bonding of Kovar predict that stresses of 30 MPa and higher are needed for good bonding at 850 C, we believe that 'sintering' effects must be accounted for to allow FEA to be predictive of actual processing conditions. Additional creep tests are planned at 250-650 C.

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

2009-01-22

79

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

80

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

81

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

82

Concrete creep at transient temperature: constitutive law and mechanism  

SciTech Connect

A constitutive law which describes the transient thermal creep of concrete is presented. Moisture and temperature are two major parameters in this constitutive law. Aside from load, creep, cracking, and thermal (shrinkage) strains, stress-induced hygrothermal strains are also included in the analysis. The theory agrees with most types of test data which include basic creep, thermal expansion, shrinkage, swelling, creep at cyclic heating or drying, and creep at heating under compression or bending. Examples are given to demonstrate agreement between the theory and the experimental data. 15 refs., 6 figs.

Chern, J.C.; Bazant, Z.P.; Marchertas, A.H.

1985-01-01

83

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

84

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

PubMed

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

Taneike, Masaki; Abe, Fujio; Sawada, Kota

2003-07-17

85

Creep behavior of materials for high-temperature reactor application  

SciTech Connect

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

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

1984-08-01

86

Long-term creep of copper at cryogenic temperatures  

SciTech Connect

Presents preliminary data on the long-term creep behavior of oxygen-free high-conductivity (OFHC) copper at 77K through a facility especially designed for long-term stability at cryogenic temperatures of both temperature and strain measurement. Uses a constant load lever arm creep machine, a vacuum thermally isolated cryostat that is cooled by a low rate of cryogen flow, and a tensile testing insert to transmit the load onto the specimen. Concludes that long-term creep testing (about 100 hrs) is necessary to study creep behavior of materials at very low temperatures.

Yen, C.T.; Roth, L.D.; Tien, J.K.; Wells, J.M.

1982-10-01

87

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

88

Elevated temperature creep properties for selected active metal braze alloys  

SciTech Connect

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

Stephens, J.J.

1997-02-01

89

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

90

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

91

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

92

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

93

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

94

Constitutive representation of high-temperature creep damage  

Microsoft Academic Search

The elastic-viscoplastic constitutive equations of Bodner-Partom were applied to modeling creep damage in a high temperature Ni-alloy, B1900 + Hf. Both tertiary creep in bulk materials and creep crack growth in flawed materials were considered. In the latter case, the energy rate line integral was used for characterizing the crack driving force, and the rate of crack extension was computed

K Chan

1988-01-01

95

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

96

High-temperature creep and kinetic decomposition of Ni2SiO4  

NASA Astrophysics Data System (ADS)

To investigate high-temperature creep and kinetic decomposition of nickel orthosilicate (Ni2SiO4), aggregates containing 3 vol% amorphous SiO2 have been deformed in uniaxial compression at a total pressure of one atomsphere. Twenty-three samples with grain sizes (d) from 9 to 30 ?m were deformed at temperatures (T) from 1573 to 1813 K, differential stresses (?) from 3 to 20 MPa, and oxygen fugacities ( f o 2) from 10-1 to 105 Pa. At temperatures up to 1773 K, the steady-state creep rate (?) can be described by the flow law 269_2004_Article_BF00202137_TeX2GIFE1.gif dot \\varepsilon = 4.0{text{ x }}10^8 {? ^{1.1} }/{d^{2.7 }}f_{O2}^0 {text{ exp }}left( {{ - 410kJ/mol}/{RT}} right)left[ {s^{ - 1} } right] Under these conditions, the dominant deformation mechanism is Coble creep, rate-limited by grain boundary diffusion of silicon. At temperatures between 1803 and 1813 K, the samples of Ni2SiO4 plus amorphous SiO2 exhibit enhanced creep rates and increased ductility. This behavior is associated with fast diffusion through a thin intergranular film produced by kinetic decomposition of Ni2SiO4 under the imposed stress gradient.

Wolfenstine, J.; Kohlstedt, D. L.

1994-08-01

97

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

98

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

99

Low-temperature creep of a carburized steel  

NASA Astrophysics Data System (ADS)

The low-temperature creep behavior of carburized 4320 steel with retained austenite contents of 35 and 14 pct and two uncarburized 4320 steels was investigated. The temperature range in the experiments was from 70 C to 195 C. The creep rate obeyed a logarithmic law when the stress level was below or near the proportional limit. A kinetic model is presented which de-scribes the low-temperature creep behavior of this steel under different stress and temperature conditions. The techniques for determining the constants in the model are given.

Neu, R. W.; Sehitoglu, Huseyin

1992-09-01

100

MEASUREMENT OF HIGH TEMPERATURE IRRADIATION CREEP IN GRAPHITE. Project DRAGON  

Microsoft Academic Search

As part of the joint Dragon\\/THTR graphite irradiation programme, experimental techniques have been evolved for measuring the irradiation creep of graphite at high temperatures. The principle of the method is to retrain the irradiation induced dimensional changes to produce a stressed assembly which gives rise to irradiation creep phenomena in the different components. Its main advantage is that little irradiation

Blackstone

1968-01-01

101

Creep of Carbon Yarns and Composites at High Temperature.  

National Technical Information Service (NTIS)

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

L. A. Feldman

1983-01-01

102

Experimental deformation of olivine single crystals at lithospheric temperatures  

NASA Astrophysics Data System (ADS)

Rheological properties of mantle minerals and rocks at temperatures (T) appropriate to much of Earth's lithosphere have remained poorly constrained, even though past experimental studies on olivine single crystals and polycrystalline aggregates have quantified the high-temperature creep mechanisms (T > 1200C). Consequently, we have performed deformation experiments on crystals of San Carlos olivine at lower temperatures, from 900 to 1200C, in triaxial compression along the [101]c direction. The experiments were carried out at a confining pressure of 300 MPa in a high-resolution gas-medium mechanical testing apparatus at differential stresses of 100 to 500 MPa. Several samples were deformed at constant displacement rate and others at constant load, in order to provide insight into possible effects of work-hardening. Under the deformation conditions investigated, little evidence of work-hardening was observed. The data follow a power-law dependence on stress, as in previous high-temperature deformation studies. The samples were, however, considerably weaker than predicted by the experimentally determined high-temperature constitutive equation for olivine crystals of this orientation from the study of Bai et al. (1991). The mechanical behavior correlates instead with the weaker of the two mechanisms (flow laws) that contribute to the high-temperature constitutive equation. Thus, our experiments demonstrate that published high-temperature constitutive equations overestimate the strength of lithospheric mantle and that the transition to low-temperature creep occurs at lower temperatures than previously inferred.

Demouchy, Sylvie; Schneider, Stephen E.; Mackwell, Stephen J.; Zimmerman, Mark E.; Kohlstedt, David L.

2009-02-01

103

Creep and slow crack growth mechanisms related to macroscopic creep behaviour of a silicon nitride ceramic at elevated temperatures  

SciTech Connect

Recent tensile creep and creep rupture test results of a hot isostatically pressed silicon nitride at 1150, 1260, and 1370{degrees}C were evaluated using microscopy in conjunction with various empirical and mathematical models to provide insight into creep and slow crack growth mechanisms. The stress and temperature sensitivities with dominant creep mechanism. Limiting cases for cavity nucleation and growth were applied to establish possible creep damage modes. At 1150{degrees}C, creep rupture was controlled by a slow crack growth mechanism. At 1260 and 1370{degrees}C, the accumulation of creep damage in the form of grain boundary cavities and cracks dominated the creep rupture behaviour. In this temperature regime, the creep rupture life was controlled by the secondary (or minimum) strain rate in accordance with a Monkman-Grant-type relation.

Jenkins, M.G.; Ferber, M.K. [Oak Ridge National Lab., TN (United States); Salem, J.A. [National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center

1992-07-01

104

Creep and slow crack growth mechanisms related to macroscopic creep behaviour of a silicon nitride ceramic at elevated temperatures  

SciTech Connect

Recent tensile creep and creep rupture test results of a hot isostatically pressed silicon nitride at 1150, 1260, and 1370{degrees}C were evaluated using microscopy in conjunction with various empirical and mathematical models to provide insight into creep and slow crack growth mechanisms. The stress and temperature sensitivities with dominant creep mechanism. Limiting cases for cavity nucleation and growth were applied to establish possible creep damage modes. At 1150{degrees}C, creep rupture was controlled by a slow crack growth mechanism. At 1260 and 1370{degrees}C, the accumulation of creep damage in the form of grain boundary cavities and cracks dominated the creep rupture behaviour. In this temperature regime, the creep rupture life was controlled by the secondary (or minimum) strain rate in accordance with a Monkman-Grant-type relation.

Jenkins, M.G.; Ferber, M.K. (Oak Ridge National Lab., TN (United States)); Salem, J.A. (National Aeronautics and Space Administration, Cleveland, OH (United States). Lewis Research Center)

1992-01-01

105

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

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

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

NASA Astrophysics Data System (ADS)

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

Liu, Cheng; Bhole, Sanjiwan; Northwood, Derek

108

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

NASA Astrophysics Data System (ADS)

The longitudinal creep behavior of two heats of coarse grained INCONEL* MA 754 have been examined at temperatures of 1000 C and above. Both heats exhibit a pronounced transition in deformation behavior. At high stresses, dislocation creep is observed and high stress exponents ( n 40) are measured. Fracture in this regime is transgranular with high creep ductilities. At lower stresses, the stress exponents are low and fracture is intergranular. In this regime, the stress exponent depends strongly on the grain morphology. Heat 1, with a uniform fiber grain morphology, exhibits significantly higher stress exponents than Heat 2, which has a duplex grain morphology consisting of coarse grains along with pockets of fine, equiaxed grains. Microstructural examination of specimens deformed at the lower stresses provides evidence that cavitation of the transverse grain boundaries occurs by means of diffusive cavity growth. In the heat with the uniform fiber morphology, cavity growth is constrained by creep of adjacent grains. Cavity growth for the heat with the duplex grain morphology is apparently limited by the sliding of pockets of fine grains. The implications of these results for optimizing creep resistance of MA 754 are discussed.

Stephens, J. J.; Nix, W. D.

1985-07-01

109

High-Temperature Deformation of Enstatite Aggregates  

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

110

Intrinsic creep of a granular column subjected to temperature changes  

NASA Astrophysics Data System (ADS)

Minute external perturbations, such as temperature variations, can lead to a creep of the fragile structures that are the granular piles. We report a study, resolved in space and time, of the dynamics associated with the slow compaction of a granular column submitted to thermal cycles. Avoiding the thermal dilations of the container, we observe that the material still creeps, even in the absence of external mechanical perturbations. The latter intrinsic creep of the material exhibits several surprising features: the compaction of the material is not homogeneous along the column height, and sudden collapses involve the entire system even if one could expect arches to screen the mechanical interaction between regions far apart from one another. In addition, the analysis of the dependence of the flow rate on the frequency of the temperature cycles suggests that the creep is mainly induced by the propagation of the temperature profile, slow temperature changes being less efficient than rapid ones in making the material flow.

Blanc, Baptiste; Gminard, Jean-Christophe

2013-08-01

111

Long-term creep of copper at cryogenic temperatures  

Microsoft Academic Search

Presents preliminary data on the long-term creep behavior of oxygen-free high-conductivity (OFHC) copper at 77K through a facility especially designed for long-term stability at cryogenic temperatures of both temperature and strain measurement. Uses a constant load lever arm creep machine, a vacuum thermally isolated cryostat that is cooled by a low rate of cryogen flow, and a tensile testing insert

C. T. Yen; L. D. Roth; J. K. Tien; J. M. Wells

1982-01-01

112

High-temperature creep of the intermetallic alloy Ni 3 Al  

Microsoft Academic Search

Constant stress creep tests have been conducted on Ni3Al (Hf, B) single crystals in an attempt to characterize the high-temperature creep behavior of this alloy. In contrast to\\u000a intermediate temperature creep behavior, steady-state creep was observed at 1273 K. This extended steady-state region was\\u000a formed in less than 1 pct creep strain and lasted for the duration of the creep

K. J. Hemker; W. D. Nix

1993-01-01

113

High-temperature creep of the intermetallic alloy Ni3Al  

Microsoft Academic Search

Constant stress creep tests have been conducted on Ni3Al (Hf, B) single crystals in an attempt to characterize the high-temperature creep behavior of this alloy. In contrast to intermediate temperature creep behavior, steady-state creep was observed at 1273 K. This extended steady-state region was formed in less than 1 pct creep strain and lasted for the duration of the creep

K. J. Hemker; W. D. Nix

1993-01-01

114

Experimental investigation of the creep behavior of garnet at high temperatures and pressures  

Microsoft Academic Search

To provide constraints on the rheological properties of garnet, we have experimentally investigated the creep behavior of\\u000a garnet at high pressures and temperatures using a deformation-DIA. Samples were cold-pressed from a garnet powder and deformed\\u000a at constant displacement rates ranging from 1.110?5 to 2.610?5 s?1 at high temperatures (1 2731 473 K) and high pressures (2.44.1 GPa). Differential stress and

Shenghua Mei; Ayako M. Suzuki; David L. Kohlstedt; Lili Xu

2010-01-01

115

High temperature creep of refractory bricks. Final report  

SciTech Connect

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

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

1991-05-15

116

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

NASA Astrophysics Data System (ADS)

A model for high temperature creep of single crystal superalloys is developed, which includes constitutive laws for nonlocal damage and viscoplasticity. It is based on a variational formulation, employing potentials for free energy, and dissipation originating from plasticity and damage. Evolution equations for plastic strain and damage variables are derived from the well-established minimum principle for the dissipation potential. The model is capable of describing the different stages of creep in a unified way. Plastic deformation in superalloys incorporates the evolution of dislocation densities of the different phases present. It results in a time dependence of the creep rate in primary and secondary creep. Tertiary creep is taken into account by introducing local and nonlocal damage. Herein, the nonlocal one is included in order to model strain localization as well as to remove mesh dependence of finite element calculations. Numerical results and comparisons with experimental data of the single crystal superalloy LEK94 are shown.

Trinh, B. T.; Hackl, K.

2013-08-01

117

Creep-fatigue criteria and inelastic behavior of modified 9Cr-1Mo steel at elevated temperatures. Final report  

SciTech Connect

The ever increasing demand for safety requires that stringent and conservative methodology be developed for design and analysis of reactor components. At present modified 9Cr-1Mo steel is a candidate material for construction of steam generators in fast breeder reactors. Therefore high-temperature material properties and extensive insight into deformation behavior and creep-fatigue life are required to develop design guidelines for use of modified 9Cr-1Mo steel in actual plant components. However, existing information on creep-fatigue and deformation response of modified 9Cr-1Mo steel is insufficient, and further experimental and modeling efforts are needed. A joint effort between the Electric Power Research Institute (EPRI) in the United States and the Central Research Institute of Electric Power Industry (CRIEPI) in Japan was started in 1991 to investigate the inelastic behavior of and to develop creep-fatigue criteria for modified 9Cr-1Mo steel at elevated temperatures. The current program focuses on uniaxial and biaxial fatigue, creep, and creep-fatigue tests. Results of this effort are presented in this report. Section 2 introduces the test material and experimental arrangement. Uniaxial exploratory deformation tests and unified constitutive equations for inelastic analysis of modified 9Cr-1Mo steel are presented in Sections 3 and 4, respectively. Axial fatigue and creep-fatigue test results are discussed in Section 5. Section 6 is devoted to constant stress creep tests. Biaxial fatigue and creep-fatigue tests are described in Section 7. Progress in creep-fatigue life evaluation is reported in Section 8.

Ruggles, M.B. [Oak Ridge National Lab., TN (United States); Ogata, T. [Central Research Inst. of Electric Power Industry, Tokyo (Japan). Komae Research Lab.

1994-02-01

118

Triaxial moisture-controlled creep tests of hardened cement paste at high temperature  

Microsoft Academic Search

Creep tests of sealed specimens as well as unsealed specimens exposed to either pressurized water or air have been conducted\\u000a at various constant temperatures from 100 to 300C and durations up to 24 hours. Apart from the need to study multiaxial deformations,\\u000a the triaxial loading is required to prevent moisture escape from the sealed specimen. The specimens are sufficiently small

Z. P. Baant; S. S. Kim; S. Meiri

1979-01-01

119

The elevated temperature compression creep behavior of a calcium-aluminosilicate(anorthite) glass ceramic  

Microsoft Academic Search

An experimental investigation of compression creep in a calcium-aluminosilicate glass ceramic revealed that the deformation can be expressed as [epsilon][alpha][sigma][sup 1]exp([minus]650 kJ mol[sup [minus]1]\\/RT), where [epsilon] is the steady state strain rate, [sigma] is the imposed stress, R is the gas constant and T is the absolute temperature. The high activation energy, a stress exponent of unity and microstructural observations

R. F. Mercer; A. H. Chokski

1993-01-01

120

Constitutive representation of high-temperature creep damage  

SciTech Connect

The elastic-viscoplastic constitutive equations of Bodner-Partom were applied to modeling creep damage in a high temperature Ni-alloy, B1900 + Hf. Both tertiary creep in bulk materials and creep crack growth in flawed materials were considered. In the latter case, the energy rate line integral was used for characterizing the crack driving force, and the rate of crack extension was computed using a local damage formulation that assumed fracture was controlled by cavitation occurring within the crack-tip process zone. The results of this investigation were used to assess the evolution equation for isotropic damage utilized in the Bodner-Partom constitutive equations. 25 references.

Chan, K.S.

1988-01-01

121

Influence of a temperature change on in-reactor creep  

SciTech Connect

The results of a series of pressurized tube creep experiments were evaluated to determine the effect of a temperature change on the in-reactor creep of AISI 316 stainless steel. In contrast to prior experiments where a temperature change was imposed and only a short interval of additional fluence accumulated prior to examination, this experiment examines the long term effects of a temperature change. Data are reported from three separate experiments in which the temperature history was altered by a linear reduction with fluence, a step increase and a step decrease. Analysis of the data indicated that the long term creep rate adjusts to the new temperature. However, evidence of swelling and stress affected swelling resulting from the temperature change were found.

Chin, B.A.; Gilbert, E.R.

1984-06-18

122

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

123

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

124

The elevated temperature compression creep behavior of a calcium-aluminosilicate(anorthite) glass ceramic  

SciTech Connect

An experimental investigation of compression creep in a calcium-aluminosilicate glass ceramic revealed that the deformation can be expressed as [epsilon][alpha][sigma][sup 1]exp([minus]650 kJ mol[sup [minus]1]/RT), where [epsilon] is the steady state strain rate, [sigma] is the imposed stress, R is the gas constant and T is the absolute temperature. The high activation energy, a stress exponent of unity and microstructural observations indicate that creep deformation is enhanced by the presence of a liquid phase. The occurrence of significant cavitation at low strains suggests that the material is not likely to exhibit superplastic-like large elongations when tested in tension, although it exhibits Newtonian-viscous behavior.

Mercer, R.F.; Chokski, A.H. (Univ. of California, San Diego (United States))

1993-05-15

125

Temperature Dependent Creep in Zinc Crystals  

Microsoft Academic Search

Tensile creep measurements beginning in a tensile strain region of about 10?6 have been made upon a set of seven single crystals of zinc of 99.99+ percent purity. Measurements were made both by means of electrical resistance strain gauges and an optical lever system. Some of the measurements made in the latter apparatus lasted 100 hours or more, and in

Donald O. Thompson

1955-01-01

126

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

127

Creep of Mg-PSZ at room temperature  

SciTech Connect

Transient [beta], or Andrade, creep occurs when magnesia-partially-stabilized zirconia is loaded in tension at room temperature. The equation relating the longitudinal or tensile creep strain [var epsilon][sub l][sup c] to the tensile stress, [sigma], and to the time, t, has been determined to be [var epsilon][sub l][sup c] = A[sigma][sup m]t[sup n] in which the constants A, m, and n depend on the phase content of the zirconia. Observations are reported of the tetragonal-to-monoclinic and tetragonal-to-orthorhombic phase transformations which occur during creep: there is also a progressive development of microcracking. It is shown that a combination of these phenomena can account for the observed creep behavior.

Finlayson, T.R. (Monash Univ., Clayton, Victoria (Australia). Dept. of Physics); Gross, A.K. (Monash Univ., Clayton, Victoria (Australia). Dept. of Materials Engineering); Griffiths, J.R. (CSIRO, Kenmore, Queensland (Australia). Div. of Manufacturing Technology); Kisi, E.H. (Griffith Univ., Nathan, Queensland (Australia). Faculty of Science and Technology)

1994-03-01

128

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

129

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

130

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

131

High-temperature creep of the intermetallic alloy Ni[sub 3]Al  

Microsoft Academic Search

Constant stress creep tests have been conducted on Ni[sub 3]Al (Hf, B) single crystals in an attempt to characterize the high-temperature creep behavior of this alloy. In contrast to intermediate temperature creep behavior, steady-state creep was observed at 1273 K. This extended steady-state region was formed in less than 1 pct creep strain and lasted for the duration of the

K. J. Hemker; W. D. Nix

1993-01-01

132

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

133

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

134

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

135

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

SciTech Connect

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

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

1994-05-01

136

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

137

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

138

High-Temperature Creep Behavior of Low-Temperature-Sintered Nano-Silver Paste Films  

NASA Astrophysics Data System (ADS)

Creep behavior of nano-silver paste films has been studied over the tensile stress range from 2 MPa to 7.5 MPa and the temperature range from 100C to 175C. In this study, all creep tests were conducted on a micro uniaxial fatigue testing system (MUF-1020). It was observed that, under the above test conditions, the steady-state creep rate of the films, dot{\\varepsilon } , could be sufficiently described by a power-law creep equation in which both the tensile stress and the temperature were involved. Creep rupture life was analyzed by the following two methods: the Monkman-Grant relationship and the ? projection concept. Based on accurate measurement of the creep strain rate, the prediction of creep life by the Monkman-Grant relation is very close to the test results. The ? projection concept is not only an effective way to predict the creep life, but also an appropriate approach to determine a precise value of creep strain rate. In addition, the Kachanov damage evolution law was employed to investigate the damage evolution of the films. The study showed that the process of damage evolution of the nano-silver films was temperature independent for all tests performed.

Chen, Gang; Sun, Xiu-Hu; Nie, Peng; Mei, Yun-Hui; Lu, Guo-Quan; Chen, Xu

2012-04-01

139

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

140

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

141

Investigation of Asphalt Mixture Creep Compliance at Low Temperatures  

Microsoft Academic Search

The creep compliance is one of the main material characteristics used to describe low temperature behavior of the asphalt mixtures. It also serves as a primary input to the current thermal cracking model in the US that is used to predict thermally induced cracking in asphalt pavements over their service life. The current standard method in the US to determine

Adam Zofka; Mihai Marasteanu; Mugurel Turos

2008-01-01

142

Intrinsic creep of a granular column subjected to temperature changes.  

PubMed

Minute external perturbations, such as temperature variations, can lead to a creep of the fragile structures that are the granular piles. We report a study, resolved in space and time, of the dynamics associated with the slow compaction of a granular column submitted to thermal cycles. Avoiding the thermal dilations of the container, we observe that the material still creeps, even in the absence of external mechanical perturbations. The latter intrinsic creep of the material exhibits several surprising features: the compaction of the material is not homogeneous along the column height, and sudden collapses involve the entire system even if one could expect arches to screen the mechanical interaction between regions far apart from one another. In addition, the analysis of the dependence of the flow rate on the frequency of the temperature cycles suggests that the creep is mainly induced by the propagation of the temperature profile, slow temperature changes being less efficient than rapid ones in making the material flow. PMID:24032822

Blanc, Baptiste; Gminard, Jean-Christophe

2013-08-05

143

Single and duplex creep tests at intermediate temperatures on Ni 3Al  

Microsoft Academic Search

Creep tests and parallel transmission electron microscopy (TEM) studies on Ni3Al in the intermediate temperature regime (where strength is increasing with temperature) are described. Under certain circumstances inverse creep is observed. Lower stress and higher temperature both inhibit the transition to cube cross-slip. Pretesting at constant strain rate can both increase or decrease the subsequent creep rate, depending on the

L. P. Jones; T. S. Rong; R. E. Smallman

1997-01-01

144

Update of CSFM Creep and Creep Rupture Models for Determining Temperature Limits for Dry Storage of Spent Fuel  

SciTech Connect

Creep rupture is believed to be a dominant mode of cladding failure during dry storage of spent nuclear fuel. This paper describes a methodology to determine the maximum allowable temperature for dry SNF storage based on expected time-in-storage, cooling time after discharge, fuel rod inner pressure, burnup, and material properties of Zircalay cladding. The methodology employs a Monkman-Grant correlation to predict the time-to-rupture as a function of steady-state creep rate. The steady-state creep rate is calculated using different creep mechanisms developed from recently published experimental data. Several creep mechanisms were found to be active during dry SNF storage conditions. The methodology incorporates creep adjustment factors due to irradiation damage and thermal annealing.

Gilbert, Edgar R. (BATTELLE (PACIFIC NW LAB)); Beyer, Carl E. (BATTELLE (PACIFIC NW LAB)); Simonen, Edward P. (BATTELLE (PACIFIC NW LAB)); Medvedev, Pavel G. (ASSOC WESTERN UNIVERSITY)

2002-06-09

145

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

146

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

147

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

148

Induced creep and creep/fatigue of a nickel-base superalloy at ambient temperatures  

NASA Astrophysics Data System (ADS)

The stress controlled fatigue of Nimonic*115, a typical ?-strengthened nickel-base superalloy, was studied at ambient temperature, using a trapezoidal wave form at 1 Hz, with stresses chosen to produce failure in the lO4 to lO4 cycle range. In tests with maximum stress greater than the proportional limit, most of the fatigue damage occurs within the first few test cycles. Much of this strain is accumulated under static load and is therefore identified as creep strain. Transmission electron microscopy shows that these creep strains occur in slip bands which disrupt the ordered ? precipitates. Strain is found to follow a logarithmic time dependence, which suggests a low activation energy mechanism.

Chen, G. L.; Fritzemeier, L. G.; Xie, X.; Tien, J. K.

1982-11-01

149

Elevated temperature creep behavior of Inconel alloy 625  

Microsoft Academic Search

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

A. Purohit; W. F. Burke

1984-01-01

150

Elevated temperature creep behavior of Inconel alloy 625  

SciTech Connect

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

Purohit, A.; Burke, W.F.

1984-07-01

151

High-temperature tensile and creep tester for wire  

Microsoft Academic Search

To provide test facilities for determining the tension and short-time creep properties of small-diameter tungsten wire at high temperatures, special equipment has been designed and built, employing rf (radio frequency) heating as the means of attaining temperatures up to 2600 C.This paper describes the problems which had to be solved in designing and building the equipment, and gives results to

Bernard R. Sinwell

1962-01-01

152

High temperature creep in a <001> single crystal nickel-base superalloy  

SciTech Connect

Creep data at 982 C and 950 C have been presented for the single crystal alloy CMSX-4. At these temperatures the creep rate is initially very low and 50% of the creep life is consumed in reaching {approximately}1% strain. Some steady-state creep occurred at 950 C. Low strains are important; plots of log, strain rate versus log, strain give more weight to low strains and also showed that tertiary creep is strain controlled. A linear strain softening approach described the increase in creep rate reasonably well. Creep curves, where time had been normalized with respect to the rupture life, could be superimposed at a given temperature, in spite of widely differing rupture lives. Normalized creep curves can only be superimposed if primary creep is negligible, but could be used as a means of estimating the rupture life of a long term test after a few millistrains have been reached.

Henderson, P.J.; Lindblom, J. [Swedish Inst. for Metals Research, Stockholm (Sweden)

1997-08-15

153

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

154

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

155

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

156

Grain boundary electronic structure related to the high-temperature creep resistance in polycrystalline Al 2O 3  

Microsoft Academic Search

High-temperature creep deformation in polycrystalline Al2O3 with an average grain size of 1 ?m is suppressed by the doping of 0.1 mol% SrO, LuO1.5, SiO2 or ZrO2, while that is accelerated by MgO, CuO or TiO2-doping at 1250C. The difference in the creep resistance is considered to be originated from change in the grain boundary diffusion in Al2O3 due to

Hidehiro Yoshida; Yuichi Ikuhara; Taketo Sakuma

2002-01-01

157

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

158

A simple endochronic transient creep model of metals with applications to variable temperature creep  

Microsoft Academic Search

Similar to the theory of endochronic plasticity, modified by Valanis in 1980, a simple endochronic transient creep model of metals is proposed by using a definition of intrinsic time ?, measured within the creep strain tensor space, whose metric tensor is treated as a simple power form of creep strain-rate sensitive material function. The resulting constitutive equation of creep (Endocreep)

C. F. Lee

1996-01-01

159

Deformation and fracture of low alloy steels at high temperature  

SciTech Connect

This project formed part of the initiative in the AR TD program to characterize high temperature, time-dependent damage processes in low alloy steels, for use in the construction of coal-gasification plant. This project was broadly aimed at adding to the knowledge base for this bainitic form of 2.25Cr 1Mo steel, as it related to time-dependent performance at elevated temperature. Its original intention was to obtain information in specific grades of 2.25Cr 1Mo steel, in particular those containing reduced residual elements and microalloyed modifications, which were being considered as candidate materials at the time. This objective was subsequently modified, in the course of the contract period, to a more generic study of bainitic steel, using the 2.25Cr 1Mo material as a representative of the class. The main thrust of the project was directed initially at the detrimental effect of cyclic loading on creep resistance and manifesting itself in an apparently severe creep-fatigue interaction. Three subtasks were eventually identified. These are: a study of the evolution of microstructural changes in bainitic materials during steady load creep and under constant amplitude cyclic deformation, investigation of the effect of cyclic softening on the fatigue and creep strength of complex geometries, focusing on circumferentially notched bars, and investigation of the influence of environment as a possible cause of observed fatigue/elevated temperature interaction through its effects on crack initiation and propagation, using EDM notched specimens tested in air and vacuum. Results are discussed. 24 refs., 40 figs., 5 tabs.

Marriott, D.L.; Stubbins, J.F.; Leckie, F.A.; Muddle, B.

1988-12-01

160

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

Microsoft Academic Search

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

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

2009-01-01

161

Effect of temperature and microstructure on tensile and tensile creep properties of titanium silicon carbide in air  

NASA Astrophysics Data System (ADS)

The ternary carbide, Ti3SiC2, combines some of the best attributes of ceramics and metals. It is stable in inert atmospheres to temperatures above 2200C, stiff and yet is readily machinable, oxidation, fatigue and thermal shock resistant and damage tolerant. Thus, Ti3SiC 2 is good candidate material for high temperature structural application. The aim of this work was to characterize its tensile and tensile creep properties. The mechanical behavior of Ti3SiC2 is characterized by a brittle-to-ductile (BTD) transition that is a function of strain rate. Its high strain rate sensitivity (?0.50--0.6) is in the range that is more typical for superplastic materials, although it does not exhibit other attributes of superplasticity. Polycrystalline samples do not exhibit linear elastic behavior in tension even at room temperature. Room temperature loading-unloading tests result in closed hysteresis loops when the stress exceeds ?120 MPa, suggesting that the mechanical response can be described as anelastic (viscoelastic). At high temperatures (1200C) intense stress relaxation takes place; cycling loading-unloading tests at high temperature and low strain rates, demonstrate that the samples continue to elongate even during unloading, suggesting that Ti3SiC2 deforms viscoplastically. Tensile creep curves exhibit primary, steady state and tertiary regimes. The minimum creep rate can be represented by power law equation with a stress exponent of 1.5 for fine-grained (3--5 mum) samples, and 2 for coarse-grained (100--300 mum) ones. For both microstructures the activation energy for creep is ?450 kJ/mol. The dependence on grain size is quite weak, implying that diffusion creep and/or creep mechanisms based on grain boundary sliding do not play a central role. Results of strain transient dip tests suggest that large internal stresses are developed during creep. Those internal stresses are believed to result in recoverable (anelastic) strains during unloading. The response on small stress decreases in strain-transient creep tests suggests that the steady state creep is recovery controlled. Finally, it is important to note that the mechanical response of Ti 3SiC2 is quite similar to hexagonal ice. Both materials, if loaded rapidly are brittle, but if loaded slowly are quite plastic. This stems from the fact that both are plastically very anisotropic; deformation occurs overwhelmingly by basal slip. In both cases, stress concentrations, and the rate at which they can be relaxed, dictate the nature of the mechanical response.

Radovic, Miladin

162

Developing Dislocation Subgrain Structures and Cyclic Softening During High-Temperature Creep-Fatigue of a Nickel Alloy  

NASA Astrophysics Data System (ADS)

The complex cyclic deformation response of Alloy 617 under creep-fatigue conditions is of practical interest both in terms of the observed detriment in failure life and the considerable cyclic softening that occurs. At the low strain ranges investigated, the inelastic strain is the sole predictor of the failure life without taking into consideration a potentially significant environmental influence. The tensile-hold creep-fatigue peak stress response can be directly correlated to the evolving dislocation substructure, which consists of a relatively homogenous distribution of subgrains. Progressive high-temperature cycling with a static hold allows for the rearrangement of loose tangles of dislocations into well-ordered hexagonal dislocation networks. The cyclic softening during tensile-hold creep-fatigue deformation is attributable to two factors: the rearrangement of dislocation substructures into lower-energy configurations, which includes a decreasing dislocation density in subgrain interiors through integration into the subgrain boundaries, and the formation of surface grain boundary cracks and cavity formation or separation at interior grain boundaries, which occurs perpendicular to the stress axis. Effects attributable to the tensile character of the hold cycle are further analyzed through variations in the creep-fatigue waveform and illuminate the effects of the hold-time character on the overall creep-fatigue behavior and evolution of the dislocation substructure.

Carroll, M. C.; Carroll, L. J.

2013-04-01

163

Fatigue perturbed creep of pure aluminum at ambient temperatures  

Microsoft Academic Search

The creep of 99.999 pct pure aluminum subject to tension-tension cyclic stressing (dynamic creep) has been studied and compared\\u000a to creep for the peak cyclic stress applied statically (static creep). The creep rate for a cyclic stress of 29.8 to 3.7 MPa\\u000a was always found to be greater than the creep rate for static application of a stress of 29.8

Walter L. Bradley; Soo W. Nam; David K. Matlock

1976-01-01

164

Elevated temperature creep of polycrystalline uranium dioxide: from microscopic mechanisms to macroscopic behaviour  

Microsoft Academic Search

Creep of polycrystalline UO2 at intermediate temperatures is studied by compression experiments and microstructural observations at different dimensional scales. Creep data exhibit two different stress regimes in the classical power law representation, but can be described on a more physical basis by a unique hyperbolic sine creep law on the whole range of stresses explored here, which is shown to

Francine Dherbey; Franois Louchet; Annick Mocellin; Sylvain Leclercq

2002-01-01

165

High-temperature deformation behavior of nickel aluminum(titanium) single crystals  

Microsoft Academic Search

Intermetallics are candidate materials to replace Ni-based superalloys for high-temperature structural applications. With proper alloying additions to improve their creep strength and ductility, NiAl-based intermetallic alloys have the potential to extend the operating temperatures of structural materials by hundreds of degrees. Here, we discuss the effects of Ti alloying additions on the high-temperature deformation behavior of NiAl(Ti) single crystals. We

Paul Harout Kitabjian

1998-01-01

166

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

167

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

168

Experimental characterization of crack tip deformation fields in Alloy 718 at high temperatures  

SciTech Connect

A series of fracture mechanics tests were conducted at temperatures of 650 C and 704 C in air, using Inconel 719. A noncontacting measurement technique, based on computer vision and digital image correlation, was applied to directly measure surface displacements and strains prior to and during creep crack growth. For the first time, quantitative comparisons at elevated temperatures are presented between experimentally measured near-crack-tip deformation fields and theoretical linear elastic and viscoelastic fracture mechanics solutions. The results establish that linear elastic conditions dominate the near-crack-tip displacements and strains at 650 C during crack growth, and confirm that K{sub 1} is a viable continuum-based fracture parameter for creep crack growth characterization. Postmortem fractographic analyses indicate that grain boundary embrittlement leads to crack extension before a significant amount of creep occurs at this temperature. At higher temperatures, however, no crack growth was observed due to crack tip blunting and concurrent stress reduction after load application.

Liu, J.; Lyons, J.; Sutton, M.; Reynolds, A. [Univ. of South Carolina, Columbia, SC (United States)

1998-01-01

169

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

170

Creep-fatigue criteria and inelastic behavior of modified 9Cr1Mo steel at elevated temperatures. Final report  

Microsoft Academic Search

The ever increasing demand for safety requires that stringent and conservative methodology be developed for design and analysis of reactor components. At present modified 9Cr-1Mo steel is a candidate material for construction of steam generators in fast breeder reactors. Therefore high-temperature material properties and extensive insight into deformation behavior and creep-fatigue life are required to develop design guidelines for use

M. B. Ruggles; T. Ogata

1994-01-01

171

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

172

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

173

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

SciTech Connect

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

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

1990-01-15

174

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

175

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

176

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

SciTech Connect

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

Haritos, G.K.; Ochoa, O.O.

1991-01-01

177

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

178

On the influence of stress state on rafting in the single crystal superalloy CMSX-6 under conditions of high temperature and low stress creep  

SciTech Connect

Single crystal superalloys have excellent high temperature strength and oxidation resistance and are therefore used as blades in aircraft engines and land based gas turbines. The microstructure of these alloys consists of two phases: (i) a high volume fraction of coherently precipitated {gamma}{prime}-cubes (L1{sub 2}) which strengthen the material separated by (ii) thin channels of face centered cubic (f.c.c.) {gamma}-matrix, as shown. However, microstructural instability (i.e. {gamma}{prime}-coarsening) is observed in these alloys during high temperature creep deformation (T > 900 C). In creep, coarsening of particles is generally considered as a softening process which increases the creep rate of an alloy. However, this process does not always dominate the overall materials response to creep loading. Thus, Mughrabi et al have clearly shown that {gamma}{prime}-coarsening can occur while the overall creep rate decreases. A number of studies on the high temperature creep deformation behavior of various single crystal superalloys have been reported in recent years. To explain rafting the authors here consider the case of a {gamma}/{gamma}{prime}-microstructure with negative misfit, i.e. where the lattice constant of the ordered {gamma}{prime}-phase is smaller than the lattice constant of the {gamma}-phase.

Kamaraj, M.; Mayr, C.; Kolbe, M.; Eggeler, G. [Ruhr-Univ., Bochum (Germany). Inst. for Materials

1998-01-13

179

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

180

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

National Technical Information Service (NTIS)

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

S. O. Davis

1964-01-01

181

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

182

Effect of Normalization Temperature on Creep Strength of Modified 9Cr-1Mo Steel  

SciTech Connect

The effect of normalization temperature from 850 to 1050C on the structure and creep-rupture properties of modified 9Cr-1Mo steel was studied. Normalization at temperatures less than 925C resulted in structures containing significant polygonized, recovered ferrite. These structures had poor creep-rupture strength; roughly two orders of magnitude increase in minimum creep rate or decrease in rupture life for 850C compared to 1050C normalization at test conditions of 600C and 145 MPa. Room-temperature strength and hardness were also reduced. Normalization at temperatures between 925C and 1000C also resulted in reduced creep strength in comparison with 1050C normalization, even though tempered martensite microstructures were formed and little change in room temperature strength was observedthe reduction was attributed to subtle differences in fine MX precipitates. The effect of reduced normalization temperature was more pronounced for higher temperature, lower stress creep-rupture conditions.

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

2006-05-01

183

Creep rupture of a GFRP composite at elevated temperatures  

Microsoft Academic Search

A study of the tension and compression behavior of glass-fiber reinforced polyester composite material under sustained loads and elevated temperature is presented. Time-dependent thermal deformation and failure stresses were measured at three different temperatures (T=25, 50, and 80C). Using curve-fitting equations a simple empirical model was developed to predict the time-to-failure. The model takes into account superposition of timetemperature effects.

Piyush K. Dutta; David Hui

2000-01-01

184

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

185

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

SciTech Connect

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

Michael J. Mills

2009-03-05

186

Kinetics and mechanisms of high temperature creep in polycrystalline aluminum nitride  

SciTech Connect

The operative and controlling mechanisms of steady-state creep in hot-pressed AlN have been determined both from kinetic data within the temperature and constant compressive stress ranges of 1470 and 1670 K and 100 to 370 MPa, respectively, and from the microstructural results of TEM. No secondary phases were detected in the bulk or at the grain boundaries using Raman spectroscopy and HREM. The stress exponent was [approx]1.0 at all temperatures. The activation energies ranged between 558 and 611 kJ/mol. The most prominent microstructural features of the crept samples were elongated grains, strain whorls, and triple-point folds. Dislocations were generated only at the strain whorls in order to relieve the localized stress caused by intraboundary mechanical interaction among the grains. They contributed little to the observed deformation. The controlling mechanism for creep was diffusion-accommodated grain-boundary sliding. This mechanism was accompanied in parallel by relatively small amounts of unaccommodated grain-boundary sliding. Cavitation was not observed.

Vasudev, A. (Department of Materials Science Engineering, Box 7907, North Carolina State University, Raleigh, North Carolina 27695-7907 (United States)); More, K.L. (Oak Ridge National Laboratory, High Temperature Materials Laboratory, Oak Ridge, Tennessee 37831-6064 (United States)); Ailey-Trent, K.S.; Davis, R.F. (Department of Materials Science Engineering, Box 7907, North Carolina State University, Raleigh, North Carolina 27695-7907 (United States))

1993-05-01

187

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

SciTech Connect

The creep performance of (001)-orientated CMSX-4 superalloy single crystals at temperatures beyond 1000 C is analyzed. Rafting of the {gamma}{prime} structure occurs rapidly, e.g., for the 1150 C/100 MPa tests rafting is completed within the first 10 h. At this stage and for a considerable time thereafter the creep strain rate decreases with increasing strain, implying a creep hardening effect which is absent at lower temperatures when the kinetics of rafting is less rapid. Once a critical strain {epsilon}* of (0.7 {+-} 0.3)% is reached, the creep strain increases dramatically and failure occurs within a few tens of hours. It is demonstrated that methods of interpretation which, assume a proportionality between the creep strain rate and creep strain, are unable to account for creep hardening which occurs as a consequence of rafting. A modification is proposed which accounts for the blocking of the glide/climb of {l{underscore}brace}111{r{underscore}brace}{l{underscore}angle}1{bar 1}0{r{underscore}angle} creep dislocations which occurs as the number of vertical {gamma} channels is reduced and cellular dislocation networks become stabilized. Consequently, failure must be taken to be associated with creep cavitation, which occurs predominantly around casting porosity. It is emphasized that more work is required to quantify the interaction between the various creep damage mechanisms.

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

1999-09-29

188

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

189

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

Microsoft Academic Search

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

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

1972-01-01

190

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

Microsoft Academic Search

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

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

1972-01-01

191

Temperature Dependence of Creep Properties of Cold-worked Hastelloy XR  

Microsoft Academic Search

The creep properties of Hastelloy XR, in a solution treated. 10% or 20% cold-worked condition, were investigated at temperatures from 800 to 1,000C for the duration of creep tests up to about 2,500ks. At 800 and 850C, the steady-state creep rate and rupture ductility decreased and the rupture life increased after cold work of 10% or 20%. Although the rupture

Yuji KURATA; Hajime NAKAJIMA

1995-01-01

192

Temperature Dependence of Creep and Hardness of Sn-Ag-Cu Lead-Free Solder  

NASA Astrophysics Data System (ADS)

The creep behavior and hardness of Sn-3.5Ag-0.7Cu solder were studied using Berkovich depth-sensing indentation at temperatures of 25C to 125C. Assuming a power-law relationship between the creep strain rate and stress, an activation energy of 40 kJ/mol and stress exponents of 7.4, 5.5, and 3.7 at 25C, 75C, and 125C, respectively, were obtained. The results revealed that, with increasing temperature, the creep penetration and steady-state creep strain rate increased whereas the stress exponent decreased. The stress exponent and activation energy results also suggested that the creep mechanism is dislocation climb, assisted by diffusion through dislocation cores in Sn. Furthermore, the hardness results exhibited a decreasing trend with increasing temperature, which is attributed to softening at high temperature.

Han, Y. D.; Jing, H. Y.; Nai, S. M. L.; Xu, L. Y.; Tan, C. M.; Wei, J.

2010-02-01

193

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

PubMed

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

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

2012-07-26

194

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

NASA Astrophysics Data System (ADS)

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

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

2013-02-01

195

Study of Tertiary Creep Instability in Several Elevated-Temperature Structural Materials.  

National Technical Information Service (NTIS)

Data for a number of common elevated temperature structural materials have been analyzed to yield mathematical predictions for the time and strain to tertiary creep at various rupture lives and temperatures. Materials examined include types 304 and 316 st...

M. K. Booker V. K. Sikka

1978-01-01

196

Study on creep-fatigue life prediction using simple high temperature low cycle fatigue testing machines  

NASA Astrophysics Data System (ADS)

A simple high temperature low cycle fatigue testing machine for long time creep fatigue tests was developed and experiments on two kinds of CrMoV steel forgings and 304 stainless steel were carried out. The experimental results indicate: (1) the data obtained by long hold time tests deviate remarkably from the linear damage fraction rule. (2) Creep rupture ductility seems to be one of important factors for creep fatigue life after long time. (3) In the case of materials the creep rupture ductility makes a remarkable change with time.

Endo, T.; Sakon, T.

1983-05-01

197

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

198

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

Microsoft Academic Search

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

Shantung Tu; Guoyan Zhou

2009-01-01

199

High temperature moir interferometry investigation of creep crack growth of inconel 783environment and ?-phase effects  

Microsoft Academic Search

The effect of ?-phase and environment on creep crack growth behavior of Inconel 783, the newly developed low thermal expansion superalloy, was investigated using high temperature moir interferometry. Results show that oxygen partial pressure plays an important role on the creep crack growth behaviors of the alloy. Stress assisted grain boundary oxygen (SAGBO) embrittlement is the principal mechanism of the

Bruce Kang; Xingbo Liu; Cezar Cisloiu; Keh-Minn Chang

2003-01-01

200

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

201

Temperature and deformation in pressing high-temperature alloy pipe  

Microsoft Academic Search

A method for calculating the hot-pressing parameters for high-temperature alloy pipe is proposed. The method includes determination\\u000a of the temperature interval of maximum plasticity, taking account of sleeve cooling during auxiliary operations; temperature\\u000a corrections as a function of the wall thickness and sleeve temperature; the metals resistance to deformation as a function\\u000a of the pressing parameters (the pipe temperature, the

N. A. Bespalova; M. I. Medvedev; A. K. Tsarkov

2009-01-01

202

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

203

Processing, Microstructure and Creep Behavior of Mo-Si-B-Based Intermetallic Alloys for Very High Temperature Structural Applications  

SciTech Connect

This research project is concerned with developing a fundamental understanding of the effects of processing and microstructure on the creep behavior of refractory intermetallic alloys based on the Mo-Si-B system. In the first part of this project, the compression creep behavior of a Mo-8.9Si-7.71B (in at.%) alloy, at 1100 and 1200 C was studied, whereas in the second part of the project, the constant strain rate compression behavior at 1200, 1300 and 1400 C of a nominally Mo-20Si-10B (in at.%) alloy, processed such as to yield five different {alpha}-Mo volume fractions ranging from 5 to 46%, was studied. In order to determine the deformation and damage mechanisms and rationalize the creep/high temperature deformation data and parameters, the microstructure of both undeformed and deformed samples was characterized in detail using x-ray diffraction, scanning electron microscopy (SEM) with back scattered electron imaging (BSE) and energy dispersive x-ray spectroscopy (EDS), electron back scattered diffraction (EBSD)/orientation electron microscopy in the SEM and transmission electron microscopy (TEM). The microstructure of both alloys was three-phase, being composed of {alpha}-Mo, Mo{sub 3}Si and T2-Mo{sub 5}SiB{sub 2} phases. The values of stress exponents and activation energies, and their dependence on microstructure were determined. The data suggested the operation of both dislocation as well as diffusional mechanisms, depending on alloy, test temperature, stress level and microstructure. Microstructural observations of post-crept/deformed samples indicated the presence of many voids in the {alpha}-Mo grains and few cracks in the intermetallic particles and along their interfaces with the {alpha}-Mo matrix. TEM observations revealed the presence of recrystallized {alpha}-Mo grains and sub-grain boundaries composed of dislocation arrays within the grains (in Mo-8.9Si-7.71B) or fine sub-grains with a high density of b = 1/2<111> dislocations (in Mo-20Si-10B), which are consistent with the values of the respective stress exponents and activation energies that were obtained and provide confirmatory evidence for the operation of diffusional (former alloy) or dislocation (latter alloy) creep mechanisms. In contrast, the intermetallic phases contained very few dislocations, but many cracks. The relative contributions of the {alpha}-Mo and the intermetallic particles to the overall deformation process, including their individual and collective dependence on temperature and strain rate are discussed in light of the present results and those from previous reports.

Vijay Vasudevan

2008-03-31

204

Development of a high-temperature deformation and life prediction model for an advanced silicon nitride ceramic  

SciTech Connect

A new deformation model inclusive of life prediction capability is introduced for describing general thermal--mechanical loading behavior of an advanced structural ceramic at high temperatures. The model is formulated using the state variable approach. Two internal state variables, namely, hardening and damage variables, are employed to characterize the current state of the material. The model consists of three rate equations: a flow rule describes the creep rate as a function of the hardening state variable, applied stress, and temperature; and two evolution rules describe the rate changes of the two internal variables. Material history is accounted for through the evolution of the internal variables. The model was characterized and evaluated based on experimental creep and creep rupture data of an advanced silicon nitride ceramic tested under constant and stepwise-varied loading conditions. A unique strength of the model, not empowered in conventional approaches such as the Norton power-law creep and Monkman-Grant creep rupture relations, is demonstrated with the aid of the hardening variable, which enables the effect of thermal annealing on subsequent creep and creep rupture behavior to be delineated.

Ding, J.L.; Liu, K.C.; Brinkman, C.R. [Oak Ridge National Lab., TN (United States). Metals and Ceramics Div.; Lin, S. [Washington State Univ., Pullman, WA (United States). Mechanical and Materials Engineering Dept.

1995-11-01

205

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

206

The influence of temperature cycling on the creep properties of Nickel 201 and Inconel 600 in combustion gas  

Microsoft Academic Search

The effect of temperature cycling on the creep behaviour of Nickel 201 and Inconel 600 in combustion gas has been studied. Specimens were tested both at constant temperature, 900 C, and at 900 C interrupted by temperarature drops down to ~510 C. The creep straining has been analysed with respect to a weighted time parameter which includes the creep contribution

J. K. Solberg; H. Thon

1984-01-01

207

Creep behavior of bone cement: a method for time extrapolation using time-temperature equivalence.  

PubMed

The clinical lifetime of poly(methyl methacrylate) (PMMA) bone cement is considerably longer than the time over which it is convenient to perform creep testing. Consequently, it is desirable to be able to predict the long term creep behavior of bone cement from the results of short term testing. A simple method is described for prediction of long term creep using the principle of time-temperature equivalence in polymers. The use of the method is illustrated using a commercial acrylic bone cement. A creep strain of approximately 0.6% is predicted after 400 days under a constant flexural stress of 2 MPa. The temperature range and stress levels over which it is appropriate to perform testing are described. Finally, the effects of physical aging on the accuracy of the method are discussed and creep data from aged cement are reported. PMID:15348456

Morgan, R L; Farrar, D F; Rose, J; Forster, H; Morgan, I

2003-04-01

208

Elevated Temperature Behavior of Creep and Fatigue in Welded P92 Steel  

NASA Astrophysics Data System (ADS)

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

Lim, Byeongsoo; Kim, Bumjoon; Park, Moonhee; Won, Sungjoon

209

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

210

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

211

Elevated temperature creep and fracture properties of the 62Cu-35Au-3Ni braze alloy  

SciTech Connect

The Cu-Au-Ni braze alloys are used for metal/ceramic brazes in electronic assemblies because of their good wetting characteristics and low vapor pressure. The authors have studied the tensile creep properties of annealed 62Cu-35Au-3Ni alloy over the temperature range 250 C to 750 C. Two power-law equations have been developed for the minimum creep rate as a function of true stress and temperature. At the highest temperatures studied (650 C and 750 C), the minimum creep rate is well described with a stress exponent of 3.0, which can be rationalized in the context of Class 1 solid solution strengthening. The inverted shape of the creep curves observed at these temperatures is also consistent with Class 1 alloy behavior. At lower temperatures, power-law creep is well described with a stress exponent of 7.5, and normal three-stage creep curves are observed. Intergranular creep damage, along the minimum values of strain to fracture, is most apparent at 450 C and 550 C. The lower stress exponent in the Class 1 alloys regime helps to increase the strain to fracture at higher temperatures (650 and 750 C). The minimum creep rate behavior of the 62Cu-35Au-3Ni alloy is also compared with those of the 74.2Cu-25.8Au alloy and pure Cu. This comparison indicates that the 62Cu-35Au-3Ni has considerably higher creep strength than pure Cu. This fact suggests that the 62Cu-35Au-3Ni braze alloy can be used in low mismatch metal-to-ceramic braze joints such as Mo to metallized alumina ceramic with few problems. However, careful joint design may be essential for the use of this alloy in high thermal mismatch metal-to-ceramic braze joints.

Stephens, J.J.; Greulich, F.A. [Sandia National Lab., Albuquerque, NM (United States)

1995-06-01

212

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

213

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

214

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

SciTech Connect

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

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

1991-01-01

215

Inelastic deformation and damage at high temperature  

SciTech Connect

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

Krempl, E.

1992-01-01

216

Inelastic deformation and damage at high temperature  

NASA Astrophysics Data System (ADS)

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

Krempl, E.

1992-06-01

217

High temperature deformation behavior of Inconel 718 at temperatures reaching into the mushy zone  

NASA Astrophysics Data System (ADS)

The mechanical response of Inconel 718 with various microstructures (cast directionally-solidified, cast random dendritic, and equiaxed non-dendritic) in the solid and semi-solid state has been characterized. The activation energy for plastic flow in the solid phase was in good agreement with the activation energies for self diffusion and creep in pure nickel and pure iron. When the dendrites were aligned along the compression axis, the directionally solidified materials exhibited a similar activation energy for plastic flow, even at temperatures within the mushy zone. However, in samples containing either the random dendritic or equiaxed non-dendritic microstructures in the semi-solid state, the deformation exhibited a greater dependence on temperature. A simple analysis indicates that this greater temperature dependence is simply a consequence of the transition from plastic flow in the solid to viscous flow in the liquid as the fraction liquid increases (i.e., lubricated flow of the grains due to intergranular liquid in the mushy zone). The deformation behavior is compared against a number of investigations from the literature and a general constitutive equation relating peak now stress versus temperature compensated strain rate is presented. The temperature compensated strain rate is often termed the Zener-Holloman parameter, Z=?exp (QRT) , where ? is the strain rate, T is the temperature, R is the gas constant, and Q is the activation energy for plastic flow. The results obtained in this investigation for solid state deformation were in good agreement with published literature values and extended the experimental range to higher temperatures and lower strain rates.

Lewandowski, Michael Stanley

2000-10-01

218

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

SciTech Connect

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

Not Available

1991-01-01

219

Elevated Temperature Deformation of Structural Steel,  

National Technical Information Service (NTIS)

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

B. A. Fields R. J. Fields

1989-01-01

220

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

221

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

222

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

Microsoft Academic Search

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

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

2009-01-01

223

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

224

High temperature deformation behavior of solid and semi-solid alloy 718  

SciTech Connect

The mechanical response of alloy 718 with various microstructures in the solid and semi-solid state has been characterized. The experimental results presented for the lower temperature solid state deformation are in good agreement with published literature values and extend the experimental range to higher temperatures and lower strain rates. When dendrites were aligned along the compression axis, the directionally solidified materials exhibited an activation energy for plastic flow consistent with the activation energy for creep and self-diffusion in nickel, even at temperatures within the mushy zone. However, samples containing non-aligned grains in the semi-solid state exhibited a greater dependence of deformation with temperature; this was associated with lubricated flow of the grains due to the intergranular liquid in the mushy zone.

Lewandowski, M.S.; Overfelt, R.A.

1999-12-10

225

Inelastic deformation and damage at high temperature  

SciTech Connect

Combined experimental and theoretical investigations into the inelastic deformation and damage behavior of engineering alloys at elevated temperatures are being pursued. Modeling of effects of recovery of state observed in modified 9Cr-lMo steel has been completed. Finite deformation formulations of viscoplasticity theory based on overstress (VBO) include a modified growth law for the equilibrium stress and a rationale for choosing objective derivatives of stress-like state variables. Numerical simulations are in progress. Seven biaxial low-cycle fatigue tests at 538C have been completed with the reversing DC potential drop apparatus attached. A new method of data analysis and smoothing was developed which showed a significant increase in voltage drop in the area of crack formation. Correlation with solutions of Laplace's Equation for a semi-elliptical crack showed similar shapes for the voltage drop.

Krempl, E.

1993-01-01

226

Corrosion and creep behaviour of selected austenitic alloys in high temperature gaseous environments  

SciTech Connect

Features common to the environments of many fossil fuel conversion and utilization processes are high temperatures coupled with a severe corrosion potential of sulphur or carbon. Construction materials for such processes must not only be able to resist such environments but also sustain mechanical constraints. To meet these rigorous demands, austenitic steels and nickel-base alloys are traditionally considered as candidate materials. The present paper deals with the corrosion and creep behaviour of two commercial austenitic alloys, HK40 and Alloy 800H, and two pure ternary Fe-Ni-Cr alloys in the temperature range 825/sup 0/C-1050/sup 0/C (1517/sup 0/F-1922/sup 0/F). Corrosion test results are described under carburising, carburising-oxidising and sulphidising conditions whereas investigations of the interaction between corrosion and creep are limited to the carburising atmosphere. From the corrosion tests the kinetics of attack and mechanisms responsible are derived and the importance of the maintenance of a protective surface scale is confirmed. The influence of carburisation on the creep rupture and creep strain behaviour of HK40 is delineated and the role of increased carbide content in either reducing or increasing creep strength and in improving ductility is also explained with the help of microstructural investigations. Preliminary creep tests on Alloy 800H tubes are described where carburisation is observed to have a negligible influence on creep rupture properties.

Guttmann, V.; Hurst, R.C.; Kemeny, G.; Krockel, H.; Marriott, J.B.; Norton, J.F.; Van de Biest, O.; Van de Voorde, M.

1983-01-01

227

Thermal-mechanical effects of low-temperature plasticity (the Peierls mechanism) on the deformation of a viscoelastic shear zone  

NASA Astrophysics Data System (ADS)

We studied for the first time the effects of low-temperature plasticity on the formation of shear zones. A thermal-mechanical model has been developed for describing the shear deformation of Maxwell viscoelastic material with a rheology close to dry olivine. We employed a one-dimensional model with a half-width of L deforming under a constant velocity U at the boundary, and the spatially-averaged strain rate U/L was set to O(10-14) s-1. In addition to diffusion and power-law creep, we included deformation by low-temperature plasticity, called the Peierls mechanism, which is significant at low temperatures and has a strong exponential dependence on the stress. When a sufficient magnitude of heat is generated by the rapid conversion from elastically-stored energy into viscous dissipation, thermal instability takes place and the deformation localizes in a narrow region. By comparing the condition for thermal instability, we found that the low-temperature plasticity inhibits the development of thermal instability in shear zones in case of constant strain rate. The Peierls mechanism enhances deformation at a significantly lower stress compared to the rheology with solely diffusion creep and power-law creep. The enhanced deformation by low-temperature plasticity produces lower amount of dissipative heating, and thus stabilizes the shear zone. Comparing the stability between constant strain-rate and constant stress boundary conditions, we found that the Peierls mechanism exerts an opposite destabilizing effect in the case of constant stress. For dry olivine rheology and realistic magnitude of the strain rate, the effect of low-temperature plasticity is significant for temperatures between around 800 K and 1000 K. This finding suggests that the low-temperature plasticity may be crucial in determining the thermal-mechanical stability in the shallow portion of slabs.

Kameyama, Masanori; Yuen, David A.; Karato, Shun-Ichiro

1999-04-01

228

Comparative estimation of high-temperature creep and rupture of structural materials  

NASA Astrophysics Data System (ADS)

The possibility of comparing the rates of creep processes and times to rupture of materials is shown by the example of several structural alloys of different types. The creep equation is written in dimensionless form, which allows one to compare creep processes up to rupture in normalized quantities, to estimate their difference, and, in the case of coincidence of the normalized quantities for some materials under corresponding temperature-load conditions, to model the indicated processes using experimental data for one of these materials.

Sosnin, O. V.; Lyubashevskaya, I. V.; Novoselya, I. V.

2008-03-01

229

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

230

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

231

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

232

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

233

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

SciTech Connect

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

Carreno, F.; Ruano, O.A. [Centro Nacional de Investigaciones Metalurgicas, Madrid (Spain). Dept. of Physical Metallurgy

1999-02-01

234

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

235

High temperature deformation of diopside IV: predominance of {110} glide above 1000C  

NASA Astrophysics Data System (ADS)

Gem quality single crystals of diopside were deformed in orientations labelled [3] and [4] selected to promote either (100)[010] and/or (010)[100], and {110}[001], respectively. Transmission electron microscopy (TEM) investigations performed on samples deformed in orientation [3] show that (100)[010] was activated and [010] dislocations are in climb configurations. A number of 1/2<110> dislocations are also detected although the Schmid factors of {110} 1/2<110> glide systems were very low. These dislocations also lie in climb configurations. The selected thermodynamic conditions, especially the partial pressure of oxygen, allowed a large amount of partial melting to occur leading to non-intrinsic creep data. In samples deformed in orientation [4], {110}[001] glide was activated with a limited amount of partial melting. TEM investigations show that most of the dislocations are straight, and of screw character parallel to [001]. A few 1/2<110> dislocations in climb configurations are also detected. For an applied stress ? = 147 MPa and at PO2 ? 2.7 10 -16 MPa the creep law for {110}[001] glide is ln ?? = 27.33 - 518/RT ( ??in s-1, R = 8.32 kJ mol-1K-1). Comparison of all the data collected so far on high temperature creep of diopside indicate that the easiest glide systems above 1000C are {110} 1/2<110> . They are followed in activity by {110}[001], then by (100)[001]. Other potential systems appear to be appreciably stronger and should remain marginal in natural deformation of diopside and similar C2/c clinopyroxenes. Climb of 1/2<110> dislocations might become relevant at temperature above 1200C.

Raterron, P.; Doukhan, N.; Jaoul, O.; Doukhan, J. C.

1994-03-01

236

Influence of a temperature change on in-reactor creep. [LMFBR  

SciTech Connect

The results of a series of pressurized tube creep experiments were evaluated to determine the effect of a temperature change on the in-reactor creep of AISI 316 stainless steel. In contrast to prior FBR experiments where a temperature change was imposed and only a short interval of additional fluence accumulated prior to examination, this experiment examines the long term effects of a temperature change. Data are reported from three separate experiments in which the temperature history was altered by a linear reduction with fluence, a step increase and a step decrease. Analysis of the data indicated that the long term creep rate adjusts to the new temperature. However, evidence of swelling and stress affected swelling resulting from the temperature change were found.

Chin, B.A.; Gilbert, E.R.

1982-03-01

237

Untersuchung des Verformungsverhaltens Ferritischer Zweiphasiger Fe-Ni-Al-Legierungen MIT Grossen Anteilen der Intermetallischen (Fe, Ni)Al-Phase bei Hohen Temperaturen (Investigation of the Deformation Behavior of Ferritic Two-Phase Fe-Ni-Al Alloys with High Concentrations of the Intermetallic (Fe, Ni)Al Phase at High Temperatures).  

National Technical Information Service (NTIS)

Ferritic model alloys were investigated to extend the application domain of ferritic, heat resistant steels to higher temperatures. The dependence of the deformation behavior, especially of the creep behavior on structure, stress and temperature was deter...

I. Jung

1986-01-01

238

Creep behavior in TiPdNi high temperature shape memory alloy  

Microsoft Academic Search

The focus of the current effort is to characterize the viscoplastic behavior in high temperature shape memory alloys and understand the impact of creep on their actuation characteristics. For this a Ti50Pd40Ni10 alloy was cast and hot rolled. Standard creep tests and isobaric thermal cycling tests were conducted on a custom test setup. The results from the thermomechanical tests indicate

Parikshith K. Kumar; Dimitris C. Lagoudas

2009-01-01

239

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

Microsoft Academic Search

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

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

2008-01-01

240

Scanning electron microscope fractography of continuously cast high purity copper after high temperature creep  

Microsoft Academic Search

Fracture surfaces produced by high temperature creep were studied using the scanning electron microscope. The material investigated\\u000a was continuously cast high purity copper containing a nodal impurity segregation structure at which grain boundary voids are\\u000a formed during creep. The observed void shape suggests that vacancies are supplied mainly via grain boundaries, and also by\\u000a enhanced diffusion via segregation nodes; the

A. Rukwied; D. B. Ballard

1972-01-01

241

Determination of room-temperature creep of soft lead zirconate titanate piezoceramics under static electric fields  

NASA Astrophysics Data System (ADS)

This study focuses on the experimental investigation of the time-dependent effects of a commercial soft lead zirconate titanate material at room temperature. Samples in initially unpoled states were subjected to a cyclic stepwise electric field which was kept constant at different levels for 300 s. Due to ferroelectric domain switching, significant nonlinearity and hysteresis were observed in the overall polarization and strain response. In particular, the material exhibited creep behavior as the applied electric field was held constant over extended periods of time. This creep was caused by microscopic domain switching processes induced gradually during the holding time. The creep was of primary or transient type in nature and depended strongly on the magnitude of the load applied. Most pronounced creep was observed when holding the field close to the coercive field. Logarithmic representation of the polarization or strain versus time curves indicated that the creep behavior could be quantified approximately by the Andrade power law. The creep exponents were determined for different field conditions. The results may help the understanding of the creep mechanism, which in turn provides contributions to improve the performance and reliability of ultrahigh-precision positioning piezoactuators.

Zhou, Dayu; Kamlah, Marc

2005-11-01

242

Creep Effects on Design below the Temperature Limits of ASME Section III Subsection NB  

SciTech Connect

Some recent studies of material response have identified an issue that crosses over and blurs the boundary between ASME Boiler and Pressure Vessel Code Section III Subsection NB and Subsection NH. For very long design lives, the effects of creep show up at lower and lower temperature as the design life increases. Although true for the temperature at which the allowable stress is governed by creep properties, the effect is more apparent, e.g. creep effects show up sooner, at local structural discontinuities and peak thermal stress locations. This is because creep is a function of time, temperature and stress and the higher the localized stress, the lower in temperature creep begins to cause damage. If the threshold is below the Subsection NB to NH temperature boundary, 700 F for ferritic steels and 800 F for austenitic materials, then this potential failure mode will not be considered. Unfortunately, there is no experience base with very long lives at temperatures close to but under the Subsection NB to NH boundary to draw upon. This issue is of particular interest in the application of Subsection NB rules of construction to some High Temperature Gas Reactor (HTGR) concepts. The purpose of this paper is, thus, twofold; one part is about statistical treatment and extrapolation of sparse data for a specific material of interest, A533B; the other part is about how these results could impact current design procedures in Subsection NB.

Sham, Sam [ORNL; Jetter, Robert I [Consultant; Eno, D.R. [Consultant

2010-01-01

243

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

244

Mechanisms and effect of microstructure on high temperature deformation of gamma-titanium aluminide-based alloys  

NASA Astrophysics Data System (ADS)

There has been a heightened interest in the high temperature behavior of gamma-based titanium aluminide alloys in the past decade or so. Despite the large body of work done in the area of high-temperature creep, the present understanding of creep mechanisms and the effect of alloying and microstructure is limited. The first part of this investigation concentrates on the creep behavior in the equiaxed microstructure of gamma-TiAl alloys. The aim is to understand the mechanisms and develop a physically-based model for creep in the gamma phase. A modification of the classic jogged-screw model has been previously adopted to explain observations of 1/2[110]-type jogged-screw dislocations in equiaxed Ti-48Al under creep conditions. The goal of this study is to verify and validate the parameters and functional dependencies that have been assumed in that model. The original solution has been reformulated with the aid of analytical modeling, numerical simulations and Transmission Electron Microscopy. Combining the parameters and dependencies, derived both from experiment and theory, leads to an excellent prediction of creep rates and stress exponents. In the second part of this study creep behavior of the fully lamellar TiAl alloys is investigated. Dislocation structures similar to those observed in the equiaxed alloys suggests that the jogged-screw model can be adapted for lamellar alloys. The aim of the model is to predict the unique creep phenomenology of fully lamellar alloys. The strengths and shortcomings of the model are discussed. Probable low stress creep mechanisms are also suggested. The origin of fully lamellar alloys' superior creep properties stems from the constrained nature of deformation in the lamellae. The results from stress drop experiments are analysed to explore the origin of the large back stresses associated with the fully lamellar alloys. Reduction of the lamellar spacing is proposed as the best way to lower creep rates. In the final part of this study, the microstructural stability of lamellar alloys during exposure to creep conditions is investigated. A detailed investigation of the creep behavior of the aged (stabilized) and unaged (unstabilized) alloys was carried out and subsequent TEM studies were done to characterize the microstructural changes during creep. Continued loss of metastable alpha2 is proposed as the reason for the larger strain rates in all stages of creep for the alloy in the unaged condition. Dynamic recrystallization and the formation of equiaxed gamma grains are discussed. These results suggest that microstructural stability is critically important in order to achieve the highest possible creep strengths. The effect of microalloying and the role of precipitation hardening in creep are investigated. The probable mechanisms of primary, secondary and tertiary creep are discussed and methods for improving the creep properties are suggested.

Karthikeyan, Subramanian

245

High temperature deformation and fracture mechanisms in a dendritic Ni[sub 3]Al alloy  

SciTech Connect

The mechanisms that control high temperature deformation and rupture were studied in a Ni[sub 3]Al alloy that was thermo-mechanically treated to produce a non-porous dendritic grain structure. Comparisons of data corresponding to the dendritic grain morphology with that for the equiaxed grain structures indicate that the dendritic morphology results in significantly lower creep rates as well as substantially greater times to rupture. Comparison of the data with numerical calculations suggests that this difference in creep strength is due to an inherent resistance to grain boundary sliding by the dendritic grain structure. A constrained cavity growth model was adapted based on microstructural observations to account for cavitation within the dendritic microstructure. The success of the model indicates that rupture time is primarily determined by constrained cavity growth on isolated dendrite boundary segments.

Kim, H.K.; Earthman, J.C. (Univ. of California, Irvine (United States). Dept. of Mechanical and Aerospace Engineering)

1994-03-01

246

Deformation and fracture of TiAl + W at elevated temperatures  

SciTech Connect

The ternary alloy, Ti - 49 at% Al -2 at. % W, was produced using Rotating Electrode Powder (REP) compacted by hot extrusion. The tensile properties of this alloy (strength, ductility and fracture mode) were studied from room temperature to 900{degrees}C. Constant load creep properties were measured from 700 to 900{degrees}C and analyzed using conventional power law equations to calculate the stress exponent and activation energy. These parameters were approximately 4 and 400 KJ/mole respectively. TEM examination showed that the W was held in solid solution during the tensile and creep deformation when the material was tested in the as-extruded' condition. These results are interpreted as evidence for solid solution strengthening of the TiAl matrix by the W solute. 13 refs., 3 figs., 4 tabs.

Martin, P.L. (Los Alamos National Lab., NM (USA)); Lipsitt, H.A. (Wright State Univ., Dayton, OH (USA). Dept. of Mechanical Materials Engineering)

1990-01-01

247

Evaluation of creep laws and flow criteria for two metals subjected to stepped load and temperature changes  

Microsoft Academic Search

Creep theories of metals are based often upon constitutive relations for constant-stress, constant-temperature creep data.\\u000a For variable stress and temperature processes, a hardening rule is required. In addition, a flow criterion is required for\\u000a multiaxial states of stress. In this paper, creep-design procedures are evaluated for metal members subject to multiaxial-stress\\u000a states and step changes in load and temperature. Tension-test

T. W. Pickel; O. M. Sidebottom; A. P. Boresi

1971-01-01

248

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

NASA Astrophysics Data System (ADS)

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

Sabour, Mohammad Hossein

249

Experimental deformation of olivine single crystals at mantle pressures and temperatures  

NASA Astrophysics Data System (ADS)

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

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

2009-01-01

250

High temperature radiation induced creep in graphite. Dragon Project  

Microsoft Academic Search

The irradiation creep of graphite has been determined at 600, 800, 900 and 1200 deg C by successive irradiations in the High Flux Reactor Petten, of specially designed assemblies in which two or more graphites having differing shrinkage rates are used in opposition to provide tensile or compressive stress in a specimen. The experimental technique is described and the results

R. Blackstone; L. W. Graham; M. R. Everett

1969-01-01

251

On the response of rockglacier creep to surface temperature increase  

Microsoft Academic Search

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

Andreas Kb; Regula Frauenfelder; Isabelle Roer

2007-01-01

252

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

253

Plastic flow and dislocation structures in tantalum carbide: Deformation at low and intermediate homologous temperatures  

SciTech Connect

Dislocation structures and plastic flow in TaC[sub 0.99] have been studied in material deformed by microindentation at 20 C, and in specimens crept at temperatures between 0.37 and 0.43 T[sub m] (1300--1500 C). Extensive local plastic deformation occurred during indentation, accomplished mainly by the motion of a/2<011> edge dislocation gliding on [111]. The resulting defect structure consisted primarily of long screw dislocations, suggesting a relatively high mobility for edge segments and a large Peierls stress for screw dislocation motion. This <110>[111] slip system also operated in specimens crept at 0.37-0.43 T[sub m]. Thermal activation apparently increased the mobility of screw segments, resulting in substructures containing mixed dislocations with no preferred orientation. Microstructural observations, and analysis of kinetic data for power-law creep, suggest that intermediate temperature creep deformation of TaC[sub 0.99] occurs mainly by climb-controlled grain boundary sliding with severely limited intergranular accommodation.

Kim, C.; Grummon, D.S. (Michigan State Univ., East Lansing, MI (United States). Dept. of Materials Science and Mechanics); Gottstein, G. (RWTH Aachen (Germany). Inst. fuer Metallkunde und Metallphysik)

1994-07-01

254

High temperature deformation of a submicron grained Al-12 wt% Ti alloy  

SciTech Connect

Compressive deformation behavior of a MA Al-12wt%Ti alloy has been studied at 623--773 K with strain rates from 4 {times} 10{sup {minus}5} to 1 {times} 10{sup {minus}1} s{sup {minus}1}. A high stress exponent was observed in the stress dependence of strain rate. By assuming that the presence of a threshold stress is the cause of the high stress exponent, the experimental data were analyzed and compared with existing models. The creep behavior of this alloy is found similar to the dispersion strengthened Al-Al{sub 2}O{sub 3} alloys. It is suggested that the high temperature deformation of this alloy is mainly governed by the fine carbide and oxide strengthened aluminum matrix, which can be described by lattice-diffusion controlled creep with a constant structure. In addition, a strong temperature dependence of the threshold stress was observed. It might be related to certain grain boundary processes and/or thermally activated deformation of strengthening particles.

Wang, S.H.; Kao, P.W. [National Sun Yat-Sen Univ., Kaohsiung (Taiwan, Province of China). Inst. of Materials Science and Engineering

1997-06-15

255

Prediction of Elevated Temperature Deformation of Structural Steel under Anisothermal Conditions.  

National Technical Information Service (NTIS)

Using a previously formulated equation which calculates the elastic, plastic and creep strains during loading at a constant elevated temperature, a method and a computer program have been developed that will predict the strain due to creep during anisothe...

B. A. Fields R. J. Fields

1991-01-01

256

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

257

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

SciTech Connect

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

Hall, M.M. Jr.

1993-10-01

258

Creep and slow crack growth mechanisms related to macroscopic creep behaviour of a silicon nitride ceramic at elevated temperatures.  

National Technical Information Service (NTIS)

Recent tensile creep and creep rupture test results of a hot isostatically pressed silicon nitride at 1150, 1260, and 1370(degrees)C were evaluated using microscopy in conjunction with various empirical and mathematical models to provide insight into cree...

M. G. Jenkins M. K. Ferber J. A. Salem

1992-01-01

259

Elevated-Temperature Tensile and Creep Properties of Several Ferritic Stainless Steels.  

National Technical Information Service (NTIS)

The elevated-temperature mechanical properties of several ferritic stainless steels were determined. The alloys evaluated included Armco 18SR, GE 1541, and NASA-18T-A. Tensile and creep strength properties at 1073 and 1273 K and residual room temperature ...

J. D. Whittenberger

1977-01-01

260

The effect of stacking fault energy on low temperature creep in pure metals  

Microsoft Academic Search

Experimental results obtained by studying the low temperature creep behaviour before and after a small stress change are interpreted in terms of barriers due to intersecting dislocations. Using the data available on the temperature dependence of the flow stress in conjunction with these experimental results, estimates of jog energies are derived and compared with values obtained from flow stress data

P. R. Thornton; P. B. Hirsch

1958-01-01

261

Diffusive relaxation of stress concentrations at grain boundary cavities in elevated temperature creep  

Microsoft Academic Search

Elevated temperature creep cavitation of grain boundaries under cyclic and rapidly applied loading was studied. The response of partially damaged materials (where damage is represented as crack line cavities on the grain boundaries) following load alterations at relatively low stress levels and at temperatures in the vicinity of 0.5 t sub m or higher. The interaction between grain boundary diffusion

A. A. Rubinstein

1982-01-01

262

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

National Technical Information Service (NTIS)

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

A. Ching J. D. Buch

1970-01-01

263

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

264

Impression Creep Behavior of Zn-Sn High-Temperature Lead-Free Solders  

NASA Astrophysics Data System (ADS)

This study examines the microstructure and impression creep behavior of the high-temperature Zn-20 wt.%Sn, Zn-30 wt.%Sn, and Zn-40 wt.%Sn solders under constant punch stress in the range of 25 MPa to 300 MPa and at temperatures in the range of 298 K to 425 K. Analysis of the data showed that, for all loads and temperatures, the Zn-20Sn alloy had the lowest creep rates, and thus the highest creep resistance, among all materials tested. This is attributed to the lower volume fraction of the soft Sn-rich phase with a continuous morphology which acts as the matrix encompassing the harder Zn phase. The stress exponents and activation energies were in the range of 4.0 to 6.1 and 40.0 kJ mol-1 to 45.3 kJ mol-1, respectively. Based on the obtained stress exponents and activation energy data, it is proposed that dislocation climb is the controlling creep mechanism. However, the observed decreasing trend of creep activation energy with stress suggests that two parallel mechanisms of lattice-diffusion-controlled and pipe-diffusion-controlled dislocation climb are competing. Dislocation climb controlled by dislocation pipe diffusion is the controlling mechanism at high stresses, whereas climb of edge dislocations is the controlling mechanism at low stresses.

Mahmudi, R.; Eslami, M.

2010-11-01

265

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

266

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

267

Dynamic restoration mechanisms and microstructural refinement of alpha-zirconium with large strain deformation at elevated temperatures  

NASA Astrophysics Data System (ADS)

The extensive use of zirconium as an elevated-temperature structural material in the nuclear industry since the 1950's has led to many investigations on its behavior during creep. A review of the different creep investigations of alpha zirconium is presented in the first part of this study. No agreement for the mechanism governing creep of zirconium was found among the different creep mechanisms considered for the relevant stress range. However, a review article recently showed that alpha-zirconium follows five-power law creep at intermediate modulus-compensated stress levels. This indicates that dislocation-climb is the deformation mechanism, with dynamic recovery as the restoration mechanism. This implies that the creep activation energy should be equal to the self-diffusion activation energy. However, the discrepancy between the published data of creep and self-diffusion activation energies suggests a different creep mechanism and/or an extra restoration mechanism could be occurring. Constant strain-rate tensile and torsion and constant stress tests were performed between 400 and 800C. Constant strain-rate torsion tests were utilized to calculate the variation of the activation energy with temperature. It appears that the apparent activation energy followed the same trend as the self-diffusion activation energy, suggesting dislocation climb as the rate-controlling mechanism and dynamic recovery as the restoration mechanism. The grain refinement observed during constant strain-rate tests was characterized by polarized optical microscopy, transmission electron microscopy and convergent beam electron diffraction, along with electron backscattered diffraction (EBSD). No evidence of discontinuous dynamic recrystallization was observed and dynamic recovery, via dislocation climb, appears to be the sole restoration mechanism. Also, it appears that the formation of small, equiaxed (sub)grains leading to a significant grain refinement and a bimodal distribution of boundary misorientation are due to geometric dynamic recrystallization. Texture analysis by X-ray diffraction and EBSD revealed that the softening observed above 650C is likely caused by the development of a deformation texture. Finally, a study is proposed to assess the mechanism of formation of high-angle boundaries in single crystals. This could bring insights on the controversy regarding the existence of continuous dynamic recrystallization and help develop a reliable technique to study the evolution of high-angle boundaries with plastic deformation.

Barrabes, Stephane R.

268

Optimization of High Temperature Hoop Creep Response in ODS-Fe3Al Tubes  

SciTech Connect

Oxide dispersion strengthened (ODS) Fe3Al alloys are currently being developed for heat-exchanger tubes for eventual use at operating temperatures of up to 1100 C in the power generation industry. The development challenges include (a) efforts to produce thin walled ODS-Fe3Al tubes, employing powder extrusion methodologies, with (b) adequate increased strength for service at operating temperatures to (c) mitigate creep failures by enhancing the as-processed grain size. A detailed and comprehensive research and development methodology is prescribed to produce ODS-Fe3Al thin walled tubes. Current single step extrusion consolidation methodologies typically yield 8ft. lengths of 1-3/8 inch diameter, 1/8 inch wall thickness ODS-Fe3Al tubes. The process parameters for such consolidation methodologies have been prescribed and evaluated as being routinely reproducible. Recrystallization treatments at 1200 C produce elongated grains (with their long axis parallel to the extrusion axis), typically 200-2000 {micro}m in diameter, and several millimeters long. The dispersion distribution is unaltered on a micro scale by recrystallization, but the high aspect ratio grain shape typically obtained limits grain spacing and consequently the hoop creep response. Improving hoop creep in ODS-alloys requires an understanding and manipulating the factors that control grain alignment and recrystallization behavior. Current efforts are focused on examining the processing dependent longitudinal vs. transverse creep anisotropy, and exploring post-extrusion methods to improve hoop creep response in ODS-Fe3Al alloy tubes. In this report we examine the mechanisms of hoop creep failure and describe our efforts to improve creep performance via variations in thermal-mechanical treatments.

Kad, B.K.; Heatherington, J.H.; McKamey, C.; Wright, I.; Sikka, V.; Judkins, R.

2003-04-22

269

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

270

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

271

Thermal transients and creep effects on theoretical and experimental assessment in operating high temperature steam piping  

SciTech Connect

Transient, creep and relaxation studies of operating high pressure piping in AISI 316 have been developed by the Italian Electrical Board in view of reassessing the structural and mechanical integrity of the line. The influence of the prestressing on the pipe is examined to determine the modifications on stress and strain response in time. Sectional analysis with 3D finite element computer programme, assuming elastic and elastic-plastic deformation of the material, shows the congruence of theoretical approach with the experimental data; also, local strain gauge monitoring of some sections offers a good tool for validating theoretical computations which are in acceptable agreement with the quantities recorded. Many creep-relaxation cycles are introduced to simulate the effect of further long-term exposure to the piping in creep range, up to 50,000 hours, and to understand the cold spring effect on piping stress. The examination of cycles in creep regime allows to describe the behaviour of time dependent stress redistribution along the line, and gives some estimation about the safety margin existing in the structure.

Cesari, F.; Menghini, S.; Regis, V.

1982-01-01

272

Effects of Thermal Creep on Cooling of Microflows in Short Microchannels with Constant Wall Temperature  

NASA Astrophysics Data System (ADS)

Fluid flow and heat transfer in the entrance region of rectangular microchannels of various aspect ratios are numerically investigated in the slip-flow regime with particular attention to thermal creep effects. Uniform inlet velocity and temperature profiles are prescribed in microchannels with constant wall temperature. An adiabatic section is also employed at the inlet of the channel in order to prevent unrealistically large axial temperature gradients due to the prescribed uniform inlet temperature as well as upstream diffusion associated with low Reynolds number flows. A control-volume technique is used to solve the Navier-Stokes and energy equations which are accompanied with appropriate velocity slip and temperature jump boundary conditions at the walls. Despite the constant wall temperature, axial and peripheral temperature gradients form in the gas layer adjacent to the wall due to temperature jump. The simultaneous effects of velocity slip, temperature jump and thermal creep on the flow and thermal patterns along with the key flow parameters are examined in detail for a wide range of cross-sectional aspect ratios, and Knudsen and Reynolds numbers. Present results indicate that thermal creep effects influence the flow field and the temperature distribution significantly in the early section of the channel.

Amiri-Jaghargh, Ali; Niazmand, Hamid; Renksizbulut, Metin

2012-11-01

273

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

274

Effect of Stress Variation on Creep of a Super Alloy at Elevated Temperatures.  

National Technical Information Service (NTIS)

An investigation was conducted to evaluate the effect of cyclic stress on the creep of a super alloy at elevated temperature. Special attention was given to the frequency effect, and experiments were carried out for a wide range of frequencies, from one c...

R. Koterazawa

1964-01-01

275

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

Microsoft Academic Search

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

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

1959-01-01

276

Study on Creep-Fatigue Life Prediction Using Simple High Temperature Low Cycle Fatigue Testing Machines.  

National Technical Information Service (NTIS)

The authors developed a simple high temperature low cycle fatigue testing machine for long time creep-fatigue tests and carried out experiments on two kinds of CrMoV steel forgings and 304 stainless steel. The experimental results indicate: (1) The data o...

T. Endo T. Sakon

1983-01-01

277

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

Microsoft Academic Search

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

Mohammad Hossein Sabour

2005-01-01

278

Deconstructing the high-temperature deformation of phase-separating alloys  

NASA Astrophysics Data System (ADS)

At high temperatures, a microstructure evolves in order to lower the energy (including interfacial and elastic) of the system. Microstructure evolution can be influenced by applied loads if the elastic constants are anisotropic and/or inhomogeneous. When plastic deformation occurs during microstructure coarsening (e.g., under creep conditions), dislocations modify microstructure evolution (e.g., through relaxing misfit and conversion of interfaces from coherent to semicoherent) and microstructure evolution leads to changes in the plastic deformation behavior. Here, we employ phase field simulations to examine the interplay between plasticity, phase separation and microstructural coarsening. In particular, we separately control microstructure evolution, stress effects and plastic deformation in order to deconstruct the observed deformation behavior. We show that in the absence of an applied stress, the alloy with dislocation sources coarsens more quickly than that without and that the presence of dislocations reorients two-phase interfaces. A comparison of the stress-strain curves for alloys with microstructure that evolves during deformation with those for which the microstructure is static shows that simultaneous microstructure evolution leads to (1) lower effective elastic moduli, (2) a peak in the stress-strain curve (it is monotonic in the absence of microstructural evolution) and (3) lower large-strain flow stresses. The decrease in elastic modulus is the result of the reorientation of the microstructure with time (the two phases have different stiffnesses). We elucidate the microstructural sources of these changes.

Quek, S. S.; Ahluwalia, R.; Srolovitz, D. J.

2013-10-01

279

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

280

Effect of Environment on Fatigue and Creep Crack Growth in Inconel X-750 at Elevated Temperature  

NASA Astrophysics Data System (ADS)

The fatigue crack growth rates (FCGR) of Inconel X-750 were measured in air and in vacuum at 25 C and 650 C as a function of test frequency. The wave shape was triangular and the frequency varied from 10 Hz to 0.01 Hz. The creep crack growth rates (CCGR) were also measured on single edge notch specimens at 650 C in air and in purified argon. For a given AK, the FCGR increases when temperature increases and frequency decreases. At low frequency the FCGR approach the creep crack growth rates. The mode of fracture changes from transgranular at 10 Hz to intergranular at 0.01 Hz. The effect of air environment is to accelerate the transition from transgranular to intergranular fracture modes with decreasing frequency. The role of oxidation in accelerating crack growth rate in fatigue and in creep is discussed in detail.

Gabrielli, F.; Pelloux, R. M.

1982-06-01

281

Effect of temperature changes on swelling and creep of AISI 316  

SciTech Connect

A number of previous publications have shown that the swelling of cold-worked AISI 316 is quite sensitive to changes in temperature which occur during irradiation. In this report those data are expanded and reanalyzed to show that the concurrent irradiation creep is also quite sensitive to changes in irradiation temperature. An explanation is advanced to explain this behavior in terms of the sensitivity to temperture history of the radiation-induced microchemical evolution of this steel. In particular, the sensitivity to temperature history of the radiation-stabilized gamma prime phase is invoked to explain the enhanced creep and swelling behavior of AISI 316 components which experienced either gradual or abrupt decreases in temperature. The phase development observed in this steel in response to temperature changes during irradiation is also compared to the similar behavior found in aged specimens subjected to isothermal irradiation.

Garner, F.A.; Gilbert, E.R.; Gelles, D.S.; Foster, J.P.

1980-04-01

282

Effect of the intermediate action of hydrostatic pressure on the high-temperature creep and durability of copper  

NASA Astrophysics Data System (ADS)

The intermediate action of hydrostatic pressure on the high-temperature creep of copper is studied at various creep stages. Tests performed at a constant tensile stress of 12.5 MPa at 773 K show that the application of a pressure at the creep third stage decreases the steady-state creep rate and extends the time to failure. At the steady-state stage of creep, the effect of the pressure may be ignored. At pressures of up to 1 GPa, this effect is found to be only related to healing of grain-boundary porosity. At higher pressures, the steady-state creep rate is governed by porosity healing and structural changes.

Petrov, A. I.; Razuvaeva, M. V.

2007-01-01

283

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

284

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

285

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

286

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

NASA Astrophysics Data System (ADS)

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

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

2010-07-01

287

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

SciTech Connect

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

Vijay K. Vasudevan

2005-12-21

288

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

289

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

290

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

SciTech Connect

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

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

1999-03-01

291

Properties of aluminum alloys: Tensile, creep, and fatigue data at high and low temperatures  

SciTech Connect

Based on work by Alcoa Laboratories over several years, this book compiles more than 300 tables listing typical average properties of a wide range of aluminum alloys. Contents include: Typical Mechanical Properties of Wrought and Cast Aluminum Alloys at Various Temperatures--tensile properties at subzero temperatures at temperature after various holding times at the test temperature, and at room temperature after exposure at various temperatures for various holding times; creep rupture strengths for various times at various temperatures; stresses required to generate various amounts of creep in various lengths of time; rotating-beam fatigue strengths; modulus of elasticity as a function of temperature; Fatigue Data--fatigue strength of wrought aluminum alloys, axial stress fatigue strength of wrought aluminum alloys (at various stress ratios, smooth and notched specimens), average fatigue strength for aluminum and aluminum alloy flat sheet specimens (under complete reversed flexure), cantilever-beam fatigue test results of aluminum alloys at elevated temperatures and following stabilization at the test temperature. The properties in this book are typical values--expected average values for representative lots produced using commercial processes and that meet industry standards, whose room temperature properties correspond to published typical values for the alloys.

Kaufman, J.G. (ed.)

1999-01-01

292

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

293

The transition from high temperature creep to fracture in Maryland diabase  

Microsoft Academic Search

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

Y. Caristan

1982-01-01

294

Phenomenological regularities pertinent to development of brittle local fractures at high-temperature creep  

NASA Astrophysics Data System (ADS)

Conditions under which brittle fractures occur in the elements of power equipment operating at high-temperature creep are analyzed. New local fracture criteria are proposed. An engineering method for predicting the lifetime of power equipment on the basis of a phenomenological model of brittle local fractures is developed. The use of the proposed criteria and phenomenological approach allows the lifetime of operating and newly designed power installations to be predicted with essentially better accuracy.

Lanin, A. A.

2013-01-01

295

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

Microsoft Academic Search

New explicit weldment strength criteria in the form of creep and fatigue strength-reduction factors were recently introduced into the American Society of Mechanical Engineers Code Case N-47, which governs the design of elevated-temperature nuclear plants components in the United States. This paper provides some of the background and logic for these factors and their use, and it describes the results

Corum

1989-01-01

296

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

Microsoft Academic Search

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

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

1992-01-01

297

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

Microsoft Academic Search

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

N. G. Needham; J. Orr

1980-01-01

298

INVESTIGATION OF THE COMPRESSIVE STRENGTH AND CREEP OF 7075-T6 ALUMINUM ALLOY PLATES AT ELEVATED TEMPERATURES  

Microsoft Academic Search

Elevated-temperature compressive-strength test results from room ; temperature to 600 deg F and creep test results from 350 to 500 deg F are ; presented for V-groove edge-supponted plates of 7075-T6 aluminum alloy. The test ; results are analyzed to verify procedures for estimating maximum strength from ; material stress-strain curves and creep-failure stresses from isochronous stress-; strain curves. The

Deveikis

1957-01-01

299

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

SciTech Connect

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

Lumin Wang; Gary Was

2010-07-30

300

High-temperature tensile and creep properties of a ferritic stainless steel for interconnect in solid oxide fuel cell  

Microsoft Academic Search

The purpose of this study is to investigate the high-temperature mechanical properties of a ferritic stainless steel (Crofer 22 APU) for use as an interconnect material in planar solid oxide fuel cells (pSOFCs). Tensile properties of the Crofer 22 APU steel are evaluated at temperatures of 25800C. Creep properties are evaluated by constant-load tests at 650800C. Several creep lifetime models

Yung-Tang Chiu; Chih-Kuang Lin; Jiunn-Chi Wu

301

Effect of prior creep at 1365 K on the room temperature tensile properties of several oxide dispersion strengthened alloys  

Microsoft Academic Search

A study was undertaken to determine if oxide dispersion strengthened (ODS) Ni-base alloys in wrought bar form are subject to a loss of room temperature tensile properties after elevated temperature creep similar to that found in a thin gage ODS alloy sheet. The bar products evaluated included ODS-Ni, ODS-NiCr, and advanced ODS-NiCrAl types. Tensile type test specimens were creep exposed

J. Daniel Whittenberger

1977-01-01

302

Effect of prior creep at 1365 K on the room temperature tensile properties of several oxide dispersion strengthened alloys  

Microsoft Academic Search

A study was undertaken to determine if oxide dispersion strengthened (ODS) Ni-base alloys in wrought bar form are subject\\u000a to a loss of room temperature tensile properties after elevated temperature creep similar to that found in a thin gage ODS\\u000a alloy sheet. The bar products evaluated included ODS-Ni, ODS-NiCr, and advanced ODS-NiCrAl types. Tensile type test specimens\\u000a were creep exposed

J. Daniel Whittenberger

1977-01-01

303

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

304

Temperature evolution in deformed shape memory alloy  

NASA Astrophysics Data System (ADS)

Temperature changes during tensile test and simple shear test of TiNi shape memory alloys loaded at various strain rates and at different temperatures have been presented. The temperature changes were measured by recording infrared radiation emitted by the surface of the specimen. It was found that the martensite transformation was accompanied by an increase in temperature while the reversible transformation/--temperature decrease.

Gadaj, S. P.; Nowacki, W. K.; Pieczyska, E. A.

2002-06-01

305

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

306

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

307

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

308

Elevated Temperature Creep Behavior of Inconel Alloy 625.  

National Technical Information Service (NTIS)

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

A. Purohit W. F. Burke

1984-01-01

309

Creep rupture of polypropylene sutures as a function of diameter, radiation dose and temperature.  

PubMed

The failure of polypropylene (PP) sutures was studied via creep rupture tests. Linear relationships were generated from plots of log time to break (tB) versus stress (sigma). At a constant sigma the results showed that tB was inversely proportional to the suture diameter (7-0, 6-0, 5-0 and 4-0) and to the radiation dose (0, 15, 20, 25 and 50 Mrad). Moreover, for the 6-0 suture size at a 15 Mrad dose, tB decreased with increasing temperature (26, 37, 44, 50 and 60 degrees C). For this creep rupture process the activation energy equalled 91.2 kJ/mol (21.8 kcal/mol). A mechanism for failure was presented which assumes that these sutures are bundles of oriented, semicrystalline microfibrils. PMID:3224142

Whitley, J Q; Kusy, R P

1988-11-01

310

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

311

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

312

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

NASA Astrophysics Data System (ADS)

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

Ryther, Chad E. C.

313

Creep Constitutive Relationships and Cyclic Behaviors of Sn96.5Ag3Cu0.5 Under High Temperatures  

NASA Astrophysics Data System (ADS)

As a lead-free solder, Sn96.5Ag3Cu0.5 has a wide application in electronic packaging. Since the solder materials usually work under cyclic temperature surroundings, creep constitutive relationships and cyclic behaviors are necessary to carry out the thermal stress analysis of a package with such a solder for its strength and life evaluations. This paper has investigated the creep constitutive relationships by constant (non-cyclic) loadings firstly, based on the creep test results at various stress and temperature levels. The complete form of the constitutive relationship containing both the linear viscous and hyperbola-sine creeps is proposed. Secondly, through the tests under cyclic stress loadings, the cyclic stress-strain relationships have been illustrated.

Liu, Ji-Hong; Meng, Xiang-Qi; Xu, Jin-Quan

314

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

315

High temperature deformation of Inconel 718  

Microsoft Academic Search

Several technological applications demand materials able to have good mechanical performance at relatively high temperatures (as high as 650C). This performance must be kept constant during long periods at these high temperatures. Superalloys, and particularly NiCrFe alloys (Inconel series) appear to be candidates to accomplish such requirements. In these types of alloys, mechanical properties are achieved by precipitation of second

A. Thomas; M. El-Wahabi; J. M. Cabrera; J. M. Prado

2006-01-01

316

Residual and trace element effects on the high-temperature creep strength of austenitic stainless steels  

NASA Astrophysics Data System (ADS)

The heat-to-heat variation in the creep strength and ductility of austenitic stainless steels was reviewed from the viewpoint of residual and trace element effects. Based on data reported in the literature, the creep strength of unstabilized alloys such as types 304 and 316 stainless steel increased with residual element and trace element content. Niobium appeared to be the most potent strengthener. There was no direct evidence that trace elements such as sulfur and phosphorus had a deleterious effect on either strength and ductility. It was assumed that the creep strength and ductility of the unstabilized grades of austenitic stainless steels are controlled by the precipitate characteristics. It follows from this that thermomechanical treatment or residual element additions that affect the precipitate characteristics influence subsequent time dependent mechanical properties. This view is consistant with most of the information in the literature. It was concluded that more systematic studies of trace and residual element effects would be beneficial to the improvement of steels. Incorporated into the studies should be quantitative characterization of evolving precipitate morphology and composition as they are influenced by residual elements. This information should be incorporated into modeling studies of non-equilibrium segregation. Ultimately, optimum elevated-temperature strength could be developed based on a materials science approach.

Swindeman, R. W.; Sikka, V. K.; Klueh, R. L.

1983-03-01

317

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

SciTech Connect

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

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

1994-09-01

318

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

319

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

320

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

321

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

322

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

323

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

324

Elevated Temperature Creep Properties of Conventional 50Au-50Cu and 47Au 50Cu-3Ni Braze Alloys.  

National Technical Information Service (NTIS)

The elevated temperature creep properties of the 50Au-50Cu wt% and 47Au-50Cu-3Ni braze alloys have been evaluated over the temperature range 250-850 C. At elevated temperatures, i.e., 450-850 C, both alloys were tested in the annealed condition (2 hrs. 75...

Stephens Schmale

2000-01-01

325

Photosynthetic acclimation to high temperatures associated with heat tolerance in creeping bentgrass.  

PubMed

Photosynthetic responses to increasing temperatures play important roles in regulating heat tolerance. The objectives of this study were to determine photosynthetic acclimation to increasing temperatures for creeping bentgrass (Agrostis stolonifera L.) and to examine changes in major photosynthetic components (photosynthetic pigments, photochemical efficiency, ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) activity, and activation state of rubisco) involved in heat responses of photosynthesis. 'Penncross' was exposed to 20, 25, 30, and 35 degrees C for 7d at each temperature (acclimated) before being exposed to 40 degrees C for 28d or directly exposed to 40 degrees C for 28d from 20 degrees C (non-acclimated) in growth chambers. Leaf net photosynthetic rate (Pn), photochemical efficiency, rubisco activity, rubisco activation state, chlorophyll content, and carotenoid content decreased when grasses were subjected to severe heat stress at 40 degrees C for 28d. The declines in rubisco activity and activation state were most dramatic among different photosynthetic components examined in this study. Heat-acclimated plants were able to maintain significantly higher Pn, the content of chlorophyll and carotenoid, and the level of rubisco activity and activation state during subsequent exposure to severe heat stress, compared to non-acclimated plants. These results suggested that photosynthetic acclimation to increasing temperatures contributed to creeping bentgrass tolerance to severe heat stress, which was associated with the maintenance of both higher light-harvesting capacity and carbon fixation activity during heat stress. PMID:18571284

Liu, Xiaozhong; Huang, Bingru

2008-06-20

326

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

327

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

PubMed

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

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

2005-11-15

328

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

SciTech Connect

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

Not Available

1991-12-31

329

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

SciTech Connect

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

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

1994-12-01

330

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

SciTech Connect

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

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

1980-05-01

331

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

National Technical Information Service (NTIS)

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

D. Tribula

1990-01-01

332

Further creep behavior of bedded salt from southeastern New Mexico at elevated temperature. Topical report RSI-0104  

SciTech Connect

This report presents the results of a series of triaxial compression creep experiments conducted on rock salt specimens from southeastern New Mexico. The specimens were prepared from salt core taken from the 2500-foot depth of ERDA Drillhole 9. The test matrix was prescribed by Sandia Laboratories: tests were conducted at differential stress levels ranging from 800 to 3000 psi, confining pressures from 0 to 3000 psi and temperatures to 200/sup 0/C. Duration of the experiments ranged up to 60 days. Section 2 of this report documents the core received and the specimens recored for experimentation. It describes the procedures used for testing and data acquisition and gives an account of data manipulation using a new data logger. The reduced data were recorded on magnetic tapes and sent to Sandia for independent analysis. Fundamental test results comprise the bulk of this report. Section 3, summarizes differential axial stress application. The resulting stress-strain curves are given in Appendix A. Section 4 discusses axial and lateral strain as a function of time and the corresponding strain-time curves are given in Appendices B and C, respectively. The section concludes with photographs of the deformed specimens. Section 5 discusses the results of this experimental effort in conjunction with results previously determined for New Mexico salt. The collective data are used to determine empirical constants for transient and steady-state equations and a few observations are made.

Hansen, F.D.; Mellegard, K.D.

1980-11-01

333

Microstructural examination of high temperature creep failure of Zircaloy-2 cladding in irradiated PHWR fuel pins  

NASA Astrophysics Data System (ADS)

Cladding samples taken from the ballooned region of the irradiated Zircaloy-2 cladded PHWR fuel pins which failed during isothermal heating tests carried out at 800-900 C were examined using optical and scanning electron microscopy. The examination of samples from the fuel pin tested at 900 C showed an intergranular mode of failure in the cladding due to formation of cracks, cavities and zirconium hydride precipitates on the grain boundaries in the cladding material. A thin hard ?-Zr(O) layer was observed on outer surface due to dissolution of the oxide layer formed during reactor operation. Grain boundary sliding was identified to be the main mode of creep deformation of Zircaloy-2 at 900 C. Examination of the cladding tested at 800 C showed absence of cracks or cavities in the deformed material and no localisation of hydrides was observed at the grain boundaries. The failure of the cladding occurred after necking followed by extensive wall thinning of the cladding tube.

Mishra, Prerna; Sah, D. N.; Kumar, Sunil; Anantharaman, S.

2012-10-01

334

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

335

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

Microsoft Academic Search

Various papers on creep-fatigue interaction at high temperature are presented. Individual topics addressed include: analysis of elevated temperature fatigue crack growth mechanisms in Alloy 718, physically based microcrack propagation laws for creep-fatigue-environment interaction, in situ SEM observation of short fatigue crack growth in Waspaloy at 700 C under cyclic and dwell conditions, evolution of creep-fatigue life prediction models, TMF design

George K. Haritos; O. O. Ochoa

1991-01-01

336

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

337

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

338

High temperature deformation of a commercial aluminum alloy  

Microsoft Academic Search

A study of high temperature deformation of a commercial aluminum alloy has been undertaken through tensile tests at strain\\u000a rates ranging from 5.6 10-5 s-1 to 5.6 10-2 s-1 and load relaxation testing in the temperature range 473 to 873 K. Experiments have established that maximum ductility is\\u000a reached at about 623 K and at maximum strain rates.

P. Olla; P. F. Virdis

1987-01-01

339

High temperature deformation of a commercial aluminum alloy  

Microsoft Academic Search

A study of high temperature deformation of a commercial aluminum alloy has been undertaken through tensile tests at strain\\u000a rates ranging from 5.610?5 s?1 to 5.610?2 s?1 and load relaxation testing in the temperature range 473 to 873 K. Experiments have established that maximum ductility is\\u000a reached at about 623 K and at maximum strain rates. Maximum fracture ductility corresponds

P. Olla; P. F. Virdis

1987-01-01

340

High Temperature Deformation Behavior of Gradually Pressurized Zircaloy4 Tubes  

Microsoft Academic Search

In order to obtain fundamental perspectives on fuel cladding deformation behavior under changing temperature and pressure conditions in a hypothetical loss-of-coolant accident of PWR, Zircaloy-4 tube burst test was conducted in both air and 99.97% Ar atmospheres. The tubes were directly heated by ac-current and maintained at various temperatures, and pressurized gradually until rupture occurred. Rupture circumferential strains were generally

Motoye SUZUKI

1981-01-01

341

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

342

Investigation of the low-temperature performance of asphalt mixtures via fatigue and linear contraction and creep test  

Microsoft Academic Search

Three types of asphalt mixtures, including asphalt concrete (AC), stone mastic asphalt (SMA) and porous asphalt (PA) with a 13mm gradation, are chosen to study the fatigue behavior, linear contraction and creep performance of them. The analysis of the experimental results is summarized as follows. The asphalt mixture exhibits longer fatigue life at low temperature than that at high temperature.

Conghui Liu; Shaopeng Wu; Bo Li; Jingang Wang

2008-01-01

343

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

344

Dislocations in CdTe plastically deformed at room temperature  

SciTech Connect

Two samples of cadmium telluride have been deformed in compression at room temperature. The applied stress was parallel to 110 in the matrix of the twinned crystal and to 131 in the twin. The other sample was deformed along an 132 direction. Activation of glide systems has been studied by transmission electron microscopy (TEM). The structure mainly contains segments of screw and 60/sup 0/ dislocations and edge dipoles resulting from dragging of jogs. All the dislocations are dissociated in two Shockley partials; the stacking fault energy ranges from 8.8 to 14.7 mJ x m/sup -2/.

Orlova, A.; Sieber, B.

1984-07-01

345

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

346

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

NASA Astrophysics Data System (ADS)

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

Hackl, Klaus; Renner, JRg

2013-03-01

347

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

348

High-Temperature Creep and Oxidation Behavior of Mo-Si-B Alloys with High Ti Contents  

NASA Astrophysics Data System (ADS)

Multiphase alloys in the Mo-Si-B system are potential high-temperature structural materials due to their good oxidation and creep resistance. Since they suffer from relatively high densities, the current study focuses on the influence of density-reducing Ti additions on creep and oxidation behavior at temperatures above 1273 K (1000 C). Two alloys with compositions of Mo-12.5Si-8.5B-27.5Ti and Mo-9Si-8B-29Ti (in at. pct) were synthesized by arc melting and then homogenized by annealing in vacuum for 150 hours at 1873 K (1600 C). Both alloys show similar creep behavior at stresses of 100 to 300 MPa and temperatures of 1473 K and 1573 K (1200 C and 1300 C), although they possess different intermetallic volume fractions. They exhibit superior creep resistance and lower density than a state-of-the-art Ni-base superalloy (single-crystalline CMSX-4) as well as other Mo-Si-B alloys. Solid solution strengthening due to Ti was confirmed by Vickers hardness measurements and is believed to be the reason for the significant increase in creep resistance compared to Mo-Si-B alloys without Ti, but with comparable microstructural length scales. The addition of Ti degrades oxidation resistance relative to a Mo-9Si-8B reference alloy due to the formation of a relatively porous duplex layer with titania matrix enabling easy inward diffusion of oxygen.

Schliephake, Daniel; Azim, Maria; von Klinski-Wetzel, Katharina; Gorr, Bronislava; Christ, Hans-Jrgen; Bei, Hongbin; George, Easo P.; Heilmaier, Martin

2013-08-01

349

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

350

Plastic deformation of wadsleyite and olivine at high-pressure and high-temperature using a rotational Drickamer apparatus (RDA)  

NASA Astrophysics Data System (ADS)

Large-strain plastic deformation experiments of wadsleyite and olivine were conducted using a rotational Drickamer apparatus (RDA) up to pressure and temperature conditions corresponding to the Earth's mantle transition zone. Sintered ring-shaped (Mg,Fe) 2SiO 4 wadsleyite and olivine samples were deformed at P 16 GPa and T = 1600 and 1800 K, and P 11 GPa and T = 1800 K, respectively, with equivalent strain rate of ?610-5 s. In situ observations of deforming samples were carried out using the synchrotron radiation facility at Brookhaven National Laboratory, NSLS, X17B2. Stress was measured by X-ray diffraction at six different angles with respect to the compression axis. The stress estimated by X-ray diffraction was in good agreement with the stress estimated from dislocation density (for olivine). Strain was determined using X-ray radiographs of a strain marker (Re or Mo foil). Deformation of samples with a RDA involves both uniaxial compression and simple shear. A new formulation is developed to analyze both components to determine the rheological properties of a sample. Stress-strain curves show strain-hardening up to the equivalent strain of ?E 0.2 followed by the quasi-steady state deformation. Wadsleyite is found to be stronger than olivine compared at similar conditions and the creep strength of olivine at P 11 GPa is much higher than those at lower pressures.

Nishihara, Yu; Tinker, David; Kawazoe, Takaaki; Xu, Yousheng; Jing, Zhicheng; Matsukage, Kyoko N.; Karato, Shun-ichiro

2008-11-01

351

(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

352

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

353

Analysis of elevated-temperature tensile and creep properties of normalized and tempered 2 1\\/4 Cr1 Mo steel  

Microsoft Academic Search

Tensile and creep data were collected for normalized and tempered 2 1\\/4 Cr-1 Mo steel from American, Japanese, British, French, and German sources. These included creep data obtained at temperatures from 427 to 600°C (800 to 1112°F) and tensile data from room temperature to 550°C (1022°F). Properties examined included yield strength, ultimate tensile strength, 10⁵-h creep-rupture strength, and 10⁻⁵%\\/h creep

M. K. Booker; B. L. P. Booker; R. W. Swindeman

1982-01-01

354

High-temperature deformation processing of Ti-24Al-20Nb  

NASA Astrophysics Data System (ADS)

Power dissipation maps have been generated in the temperature range of 900 C to 1150 C and strain rate range of 10-3 to 10 s-1 for a cast aluminide alloy Ti-24Al-20Nb using dynamic material model. The results define two distinct regimes of temperature and strain rate in which efficiency of power dissipation is maximum. The first region, centered around 975 C/0.1 s-1, is shown to correspond to dynamic recrystallization of the ?2 phase and the second, centered around 1150 C/0.001 s-1, corresponds to dynamic recovery and superplastic deformation of the ? phase. Thermal activation analysis using the power law creep equation yielded apparent activation energies of 854 and 627 kJ/mol for the first and second regimes, respectively. Reanalyzing the data by alternate methods yielded activation energies in the range of 170 to 220 kJ/mol and 220 to 270 kJ/mol for the first and second regimes, respectively. Cross slip was shown to constitute the activation barrier in both cases. Two distinct regimes of processing instabilityone at high strain rates and the other at the low strain rates in the lower temperature regionshave been identified, within which shear bands are formed.

Sagar, P. K.; Banerjee, D.; Muraleedharan, K.; Prasad, Y. V. R. K.

1996-09-01

355

High-temperature deformation processing of Ti-24Al-20Nb  

SciTech Connect

Power dissipation maps have been generated in the temperature range of 900 C to 1,150 C and strain rate range of 10{sup {minus}3} to 10 s{sup {minus}1} for a cast aluminide alloy Ti-24Al-20Nb using dynamic material model. The results define two distinct regimes of temperature and strain rate in which efficiency of power dissipation is maximum. The first region, centered around 975 C/0.1 s{sup {minus}1}, is shown to correspond to dynamic recrystallization of the {alpha}{sub 2} phase and the second, centered around 1,150 C/0.001 s{sup {minus}1}, corresponds to dynamic recovery and superplastic deformation of the {beta} phase. Thermal activation analysis using the power law creep equation yielded apparent activation energies of 854 and 627 kJ/mol for the first and second regimes, respectively. Reanalyzing the data by alternate methods yielded activation energies in the range of 170 to 220 kJ/mol and 220 to 270 kJ/mol for the first and second regimes, respectively. Cross slip was shown to constitute the activation barrier in both cases. Two distinct regimes of processing instability--one at high strain rates and the other at the low strain rates in the lower temperature regions--have been identified, within which shear bands are formed.

Sagar, P.K.; Banerjee, D.; Muraleedharan, K. [Defence Metallurgical Research Lab., Hyderabad (India); Prasad, Y.V.R.K. [Indian Inst. of Science, Bangalore (India). Dept. of Metallurgy

1996-09-01

356

Deformation behavior of polycrystalline Galfenol at elevated temperatures  

NASA Astrophysics Data System (ADS)

Magnetostrictive Galfenol (Fe-Ga) is a promising new active material. Single crystals of Galfenol have been shown to exhibit up to 400 ppm magnetostrictive strains with saturating fields of several hundred oersteds. Its robustness and ability to actuate in either tension or compression allows for new actuator and sensor designs. However, due to the high permeability of Galfenol, it needs to be in thin sheet form for many device applications to minimize eddy current losses. Work is underway to develop conventional rolling processes to produce large quantities of thin Galfenol sheet, while retaining a preferred <100> crystallographic texture to optimize magnetostrictive performance. Knowledge of deformation behavior at elevated temperature is crucial to understanding formability and crystallographic texture evolution during rolling. In this work, the high-temperature plasticity and the deformation behavior of polycrystalline Galfenol were investigated using conventional axial compression tests and rolling experiments. As the temperature increased, significant softening of the material occurred in the temperature range from about 450C to 800C. The results also suggested that significant dynamic recovery and recrystallization occurred during deformation at above 800C.

Cheng, Leon M.; Nolting, Allison E.; Voyzelle, Benoit; Galvani, Claude

2007-04-01

357

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

NASA Astrophysics Data System (ADS)

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

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

2012-10-01

358

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

NASA Astrophysics Data System (ADS)

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

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

2013-08-01

359

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

360

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

361

A study of the deformation kinetics of gold using high-temperature nano-indentation testing technique  

NASA Astrophysics Data System (ADS)

Effect of temperature on the length-scale dependence of deformation kinetics of a fcc metal, gold is investigated by using nanoindentation testing technique. The indentation tests consisting of constant-loading rate stage followed by a constant-load stage are performed at indentation depths ranging from 100nm to 5000nm at several temperatures; 300K, 473K, 623K and 773K. The indentation stress displayed a clear depth and temperature dependence. The indentation strain rate data are modeled in terms of an obstacle-limited dislocation glide mechanism and its stress dependence during the constant-load stage of the tests indicates that the activation energy DeltaG0 of the deformation process increases from 0.16 mub3 at 300K to 0.52mub 3 at 773K with increasing temperature. DeltaG0 was, however, relatively insensitive at a given temperature across the indentation depth range from 100 nm to 5000 nm. A Haasen plot activation analysis of the deformation process indicates that more mechanical work must be applied during the constant-loading rate stage of the nanoindentation test, due to the predominance of work-hardening, compared to the constant-load stage where considerably more dislocation recovery occurs. These findings are supported by TEM observations from the plastic zone beneath the indenter, where the dislocation configuration clearly undergoes increasing reorganization into dense cell structures with increasing creep time and increasing temperature until dynamic recrystallization occurs beneath the nanoindentations at about 773 K. Keywords: Indentation Size Effect (ISE), Deformation Kinetics, High-temperature Nanoindentation, Gold, Transmission Electron Microscopy (TEM)

Bhakhri, Vineet

362

Heat flux distribution model by sequential algorithm of inverse heat transfer for determining workpiece temperature in creep feed grinding  

Microsoft Academic Search

The purpose of this study is to determine the heat flux distribution and to estimate the workpiece temperature in creep feed grinding. The sequential algorithm of the inverse heat transfer was used for determining the heat flux distribution. The amount of heat flux to the workpiece, the energy partition and the convective heat transfer coefficients both at the front and

Hae-Ji Kim; Nam-Kyung Kim; Jae-Seob Kwak

2006-01-01

363

High impact deformation of metal cylinders at elevated temperatures  

SciTech Connect

We have used a ''reverse gun'' that fires a ceramic plate at a preheated metal target to study the dependence of flow stress on temperature. Impact velocity versus L/sub f/ /L/sub 0/ isotherms have been determined for Al, two types of Cu, 4340 steel, and Ta at 295, 730, and 1235 K, and for U at 295 and 725 K. A modified Steinberg--Guinan constitutive model and a Grueneisen equation of state were used to obtain hydrodynamic code simulations of the deformation process. A strong temperature dependence of the length ratio was clearly evident for all materials.

Gust, W.H.

1982-05-01

364

High temperature creep of a helium-implanted titanium aluminide alloy  

NASA Astrophysics Data System (ADS)

The creep properties of an intermetallic alloy Ti-46Al-2W-0.5Si (at%) including strain rate and time to fracture were investigated in vacuum using helium-implanted and non-implanted samples, at a temperature of 1073 K and a stress of 200 MPa. The implantation was performed using 24 MeV He-ions, homogeneously implanting the samples with up to 1333 appm (atomic parts per million) helium. The size and location of helium bubbles were determined with transmission electron microscopy (TEM). Samples implanted with helium content above 10 appm exhibited strong helium embrittlement, reducing both the time to fracture and the elongation at fracture. The corresponding critical helium bubble size rc was determined to 10 nm.

Magnusson, Per; Chen, Jiachao; Hoffelner, Wolfgang

2011-09-01

365

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

NASA Astrophysics Data System (ADS)

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

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

1992-06-01

366

Stress-Strain Rate Relations in Ultra High Carbon Steels Deformed in the Ferrite Range of Temperature  

SciTech Connect

The stress-strain rate relations in ultrahigh carbon steels (UHCSs) have been analyzed at high temperatures in the ferrite range where dislocation slip is the principal deformation mechanism. Specifically, the present investigation centers on the factors influencing the strength of UHCS in the ferrite range of 500 to 700 C and in the strain rate range of 10{sup -3} to 10{sup 3} s{sup -1}. These steels contain iron carbide as a second phase either in the form of spheroidite or pearlite and vary in the grain size according to the processing history. The new variables that need to be taken into account are the effect of ferromagnetism and its change with temperature on the creep strength of the ferritic UHCSs. Recent studies have shown that ferromagnetism strongly influences the lattice and dislocation pipe diffusion coefficient and the elastic modulus of iron in the ferrite range of temperature. These variables are shown to influence the creep strength of ferrite-base steels and explain the high activation energies that are observed in many of the ferritic UHCSs.

Syn, C K; Lesuer, D R; Sherby, O D; Taleff, E M

2003-02-20

367

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

368

Influence of stacking-fault energy on high temperature creep of alpha titanium alloys  

Microsoft Academic Search

The stacking-fault energy (SFE) has been incorporated in the calculation of the steady-state creep rate of commercially-pure titanium and Ti(110)mol.% Al alloys. Their creep behaviour was found to follow power-law creep when the dependence of SFE on the aluminium content was taken into account in the calculation. The possible contribution due to the formation of short range ordered structure is

Z. Guo; A. P. Miodownik; N. Saunders; J-Ph. Schill

2006-01-01

369

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

370

Defects in silicon plastically deformed at room temperature  

NASA Astrophysics Data System (ADS)

The article [1] describes specific features of positron trapping in silicon plastically deformed at room temperature. The results are related to the dislocation core structure and the inhomogeneous deformation. The picture shows the probability density function of a positron localized in a vacancy in silicon. The calculation was performed with the superimposed-atom model. The degree of localization and consequently the defect-related positron lifetime vary for different open-volume defects, such as vacancies, voids, and dislocations.The first author, Hartmut S. Leipner, is CEO of the Center of Materials Science of the University Halle-Wittenberg. His research activities are focused on the characterization of extended defects in semiconductors.

Leipner, H. S.; Wang, Z.; Gu, H.; Mikhnovich, V. V., Jr.; Bondarenko, V.; Krause-Rehberg, R.; Demenet, J.-L.; Rabier, J.

2004-07-01

371

Analysis of Elevated-Temperature Tensile and Creep Properties of Normalized and Tempered 2 1/4 Cr-1 Mo Steel.  

National Technical Information Service (NTIS)

Tensile and creep data were collected for normalized and tempered 2 1/4 Cr-1 Mo steel from American, Japanese, British, French, and German sources. These included creep data obtained at temperatures from 427 to 600 exp 0 C (800 to 1112 exp 0 F) and tensil...

M. K. Booker B. L. P. Booker R. W. Swindeman

1982-01-01

372

Creep Behavior of Glass\\/Ceramic Sealant Used in Solid Oxide Fuel Cells  

Microsoft Academic Search

High operating temperature of solid oxide fuel cells require that sealant must function at high temperature between 600o and 900oC and in the oxidizing and reducing environments of fuel and air. It should be noted that creep deformation becomes relevant for a material when the operating temperature is near or exceeds half of its melting temperature (in degrees of Kelvin).

Wenning N. Liu; Xin Sun; Brian J. Koeppel; Mohammad A. Khaleel

2010-01-01

373

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.

374

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

375

Overview of Strategies for High-Temperature Creep and Oxidation Resistance of Alumina-Forming Austenitic Stainless Steels  

NASA Astrophysics Data System (ADS)

A family of creep-resistant, alumina-forming austenitic (AFA) stainless steel alloys is under development for structural use in fossil energy conversion and combustion system applications. The AFA alloys developed to date exhibit comparable creep-rupture lives to state-of-the-art advanced austenitic alloys, and superior oxidation resistance in the ~923 K to 1173 K (650 C to 900 C) temperature range due to the formation of a protective Al2O3 scale rather than the Cr2O3 scales that form on conventional stainless steel alloys. This article overviews the alloy design approaches used to obtain high-temperature creep strength in AFA alloys via considerations of phase equilibrium from thermodynamic calculations as well as microstructure characterization. Strengthening precipitates under evaluation include MC-type carbides or intermetallic phases such as NiAl-B2, Fe2(Mo,Nb)-Laves, Ni3Al-L12, etc. in the austenitic single-phase matrix. Creep, tensile, and oxidation properties of the AFA alloys are discussed relative to compositional and microstructural factors.

Yamamoto, Y.; Brady, M. P.; Santella, M. L.; Bei, H.; Maziasz, P. J.; Pint, B. A.

2010-07-01

376

Overview of Strategies for High-Temperature Creep and Oxidation Resistance of Alumina-Forming Austenitic Stainless Steels  

NASA Astrophysics Data System (ADS)

A family of creep-resistant, alumina-forming austenitic (AFA) stainless steel alloys is under development for structural use in fossil energy conversion and combustion system applications. The AFA alloys developed to date exhibit comparable creep-rupture lives to state-of-the-art advanced austenitic alloys, and superior oxidation resistance in the ~923 K to 1173 K (650 C to 900 C) temperature range due to the formation of a protective Al2O3 scale rather than the Cr2O3 scales that form on conventional stainless steel alloys. This article overviews the alloy design approaches used to obtain high-temperature creep strength in AFA alloys via considerations of phase equilibrium from thermodynamic calculations as well as microstructure characterization. Strengthening precipitates under evaluation include MC-type carbides or intermetallic phases such as NiAl-B2, Fe2(Mo,Nb)-Laves, Ni3Al-L12, etc. in the austenitic single-phase matrix. Creep, tensile, and oxidation properties of the AFA alloys are discussed relative to compositional and microstructural factors.

Yamamoto, Y.; Brady, M. P.; Santella, M. L.; Bei, H.; Maziasz, P. J.; Pint, B. A.

2011-04-01

377

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

SciTech Connect

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

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

1996-12-31

378

Overview of strategies for high-temperature creep and oxidation resistance of alumina-forming austenitic stainless steels  

SciTech Connect

A family of creep-resistant, alumina-forming austenitic (AFA) stainless steel alloys is under development for structural use in fossil energy conversion and combustion system applications. The AFA alloys developed to date exhibit comparable creep-rupture lives to state-of-the-art advanced austenitic alloys, and superior oxidation resistance in the {approx}923 K to 1173 K (650 C to 900 C) temperature range due to the formation of a protective Al{sub 2}O{sub 3} scale rather than the Cr{sub 2}O{sub 3} scales that form on conventional stainless steel alloys. This article overviews the alloy design approaches used to obtain high-temperature creep strength in AFA alloys via considerations of phase equilibrium from thermodynamic calculations as well as microstructure characterization. Strengthening precipitates under evaluation include MC-type carbides or intermetallic phases such as NiAl-B2, Fe{sub 2}(Mo,Nb)-Laves, Ni{sub 3}Al-L1{sub 2}, etc. in the austenitic single-phase matrix. Creep, tensile, and oxidation properties of the AFA alloys are discussed relative to compositional and microstructural factors.

Yamamoto, Yukinori [ORNL; Brady, Michael P [ORNL; Santella, Michael L [ORNL; Bei, Hongbin [ORNL; Maziasz, Philip J [ORNL; Pint, Bruce A [ORNL

2001-01-01

379

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

380

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

381

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

382

Influence of Stacking Fault Energy on High Temperature Creep of Pure Metals.  

National Technical Information Service (NTIS)

The creep characteristics of four pure metals with widely varying stacking fault energies (Ag, Cu, Ni and Al) were evaluated above 0.5 Tm. Creep tests were performed under conditions of constant atomic diffusivity and constant stress over the elastic modu...

C. R. Barrett O. D. Sherby

1965-01-01

383

Residual and trace element effects on the high-temperature creep strength of austenitic stainless steels  

Microsoft Academic Search

The heat-to-heat variation in the creep strength and ductility of austenitic stainless steels was reviewed from the viewpoint of residual and trace element effects. Based on data reported in the literature, the creep strength of unstabilized alloys such as types 304 and 316 stainless steel increased with residual element and trace element content. Niobium appeared to be the most potent

R. W. Swindeman; V. K. Sikka; R. L. Klueh

1983-01-01

384

The strengthening effect of Al{sub 3}Ti in high temperature deformation of Al-Al{sub 3}Ti composites  

SciTech Connect

A series of Al-Al{sub 3}Ti composites with systematic variation of Al{sub 3}Ti content were prepared by mechanical alloying. Microstructural observations have indicated that among these composites, the only distinct variable is the Al{sub 3}Ti content, while the other microstructural variables are essentially the same. The high temperature (623--773 K) deformation behavior of these composites was found to be similar to that of dispersion-hardened aluminum. By considering the presence of a threshold stress, the plastic flow in these composites can be described by lattice-diffusion controlled dislocation creep in the aluminum matrix with a constant structure. The presence of Al{sub 3}Ti particles can increase the creep strength of these alloys significantly. By considering the load-sharing effect of Al{sub 3}Ti, an analysis based on continuum mechanics approach has been conducted, which can successfully account for the creep rate of these Al-Al{sub 3}Ti composites. The threshold stress for creep in these composites was found to increase with increasing Al{sub 3}Ti content, which could be attributed to the load-shearing effect of Al{sub 3}Ti particles.

Wang, S.H.; Kao, P.W. [National Sun Yat-Sen Univ., Kaohsiung (Taiwan, Province of China). Inst. of Materials Science and Engineering

1998-05-01

385

High temperature plastic deformation of multilayered YTZP/ZTA composites obtained by tape casting  

SciTech Connect

Laminar composites containing layers of 3 mol% yttria-stabilized tetragonal ZrO{sub 2} (YTZP) and a mixture of Al{sub 2}O{sub 3}/3YTZP (60/40 vol.%) have been fabricated via a tape casting process that allowed formation of multilayers with strong and sharp interfaces. Compressive tests at constant strain rate and constant load were carried out on these materials in air at temperatures between 1,200 and 1,400 C with the stress axis both parallel and perpendicular to the layer interfaces. Microstructural observations of strained composites indicated that deformation is achieved primarily by grain boundary sliding. The stress exponent n and the activation energy for flow Q decrease from 2 to 1 and from 650 to 550 kJ/mol, respectively, with increasing stress. Such a trend has already been observed in the monolithic constituents, suggesting that the same rate controlling mechanisms may operate in the composites. The creep behavior of the softer phase (YTZP) is strongly influenced by the laminar microstructure, increasing the flow stress with respect to the bulk material.

Jimenez-Melendo, M.; Clauss, C.; Dominguez-Rodriguez, A. [Univ. de Sevilla (Spain). Dept. de Fisica de la Materia Condensada; De Portu, G.; Roncari, E.; Pinasco, P. [CNR-Research Inst. for Ceramic Technology, Faenza (Italy)

1998-07-01

386

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

SciTech Connect

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

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

2012-01-01

387

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

388

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

DOEpatents

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

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

2012-11-27

389

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

390

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

391

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

392

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

393

Experimental characterization of crack tip deformation fields in Alloy 718 at high temperatures  

Microsoft Academic Search

A series of fracture mechanics tests were conducted at temperatures of 650 C and 704 C in air, using Inconel 719. A noncontacting measurement technique, based on computer vision and digital image correlation, was applied to directly measure surface displacements and strains prior to and during creep crack growth. For the first time, quantitative comparisons at elevated temperatures are presented

Jin Liu; Jed Lyons; Michael Sutton; Anthony Reynolds

1998-01-01

394

Mantle temperature under drifting deformable continents during the supercontinent cycle  

NASA Astrophysics Data System (ADS)

Abstract The thermal heterogeneity of the Earth's mantle under the drifting continents during a supercontinent cycle is a controversial issue in earth science. Here, a series of numerical simulations of mantle convection are performed in 3-D spherical-shell geometry, incorporating drifting <span class="hlt">deformable</span> continents and self-consistent plate tectonics, to evaluate the subcontinental mantle <span class="hlt">temperature</span> during a supercontinent cycle. Results show that the laterally averaged <span class="hlt">temperature</span> anomaly of the subcontinental mantle remains within several tens of degrees (50C) throughout the simulation time. Even after the formation of the supercontinent and the development of subcontinental plumes due to the subduction of the oceanic plates, the laterally averaged <span class="hlt">temperature</span> anomaly of the deep mantle under the continent is within +10C. This implies that there is no substantial <span class="hlt">temperature</span> difference between the subcontinental and suboceanic mantles during a supercontinent cycle. The <span class="hlt">temperature</span> anomaly immediately beneath the supercontinent is generally positive owing to the thermal insulation effect and the active upwelling plumes from the core-mantle boundary. In the present simulation, the formation of a supercontinent causes the laterally averaged subcontinental <span class="hlt">temperature</span> to increase by a maximum of 50C, which would produce sufficient tensional force to break up the supercontinent. The regular periodicity of the supercontinent cycles observed in previous 2-D and 3-D simulation models with rigid nondeformable continents and without self-consistent plate tectonics is not confirmed.</p> <div class="credits"> <p class="dwt_author">Yoshida, Masaki</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-02-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">395</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://dx.doi.org/10.1029/2005JB003772"> <span id="translatedtitle">The instantaneous rate dependence in low <span class="hlt">temperature</span> laboratory rock friction and rock <span class="hlt">deformation</span> experiments</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p class="result-summary">Earthquake occurrence probabilities that account for stress transfer and time-dependent failure depend on the product of the effective normal stress and a lab-derived dimensionless coefficient a. This coefficient describes the instantaneous dependence of fault strength on <span class="hlt">deformation</span> rate, and determines the duration of precursory slip. Although an instantaneous rate dependence is observed for fracture, friction, crack growth, and low <span class="hlt">temperature</span> plasticity in laboratory experiments, the physical origin of this effect during earthquake faulting is obscure. We examine this rate dependence in laboratory experiments on different rock types using a normalization scheme modified from one proposed by Tullis and Weeks [1987]. We compare the instantaneous rate dependence in rock friction with rate dependence measurements from higher <span class="hlt">temperature</span> dislocation glide experiments. The same normalization scheme is used to compare rate dependence in friction to rock fracture and to low-<span class="hlt">temperature</span> crack growth tests. For particular weak phyllosilicate minerals, the instantaneous friction rate dependence is consistent with dislocation glide. In intact rock failure tests, for each rock type considered, the instantaneous rate dependence is the same size as for friction, suggesting a common physical origin. During subcritical crack growth in strong quartzofeldspathic and carbonate rock where glide is not possible, the instantaneous rate dependence measured during failure or <span class="hlt">creep</span> tests at high stress has long been thought to be due to crack growth; however, direct comparison between crack growth and friction tests shows poor agreement. The crack growth rate dependence appears to be higher than the rate dependence of friction and fracture by a factor of two to three for all rock types considered. Copyright 2007 by the American Geophysical Union.</p> <div class="credits"> <p class="dwt_author">Beeler, N. M.; Tullis, T. E.; Kronenberg, A. K.; Reinen, L. A.</p> <p class="dwt_publisher"></p> <p class="publishDate">2007-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">396</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2006PhyC..441..122J"> <span id="translatedtitle"><span class="hlt">Creep</span> and dimensional stability of high purity niobium electron-beam welds</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">A study was conducted to characterize the microstructure of electron beam welds in high purity niobium and its effect on <span class="hlt">creep</span> behaviour at room <span class="hlt">temperature</span>. 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 <span class="hlt">temperature</span> <span class="hlt">creep</span> <span class="hlt">deformation</span> below the yield stress, but room <span class="hlt">temperature</span> <span class="hlt">creep</span> of weld specimens caused up to 10% strain in the weld region at 75% of the yield strength, over 1 2 months. <span class="hlt">Creep</span> <span class="hlt">deformation</span> 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 <span class="hlt">creep</span> <span class="hlt">deformation</span> behavior was highly dependent on the actual microstructure and loading history. An initial prestrain with unloading shut down the <span class="hlt">creep</span> <span class="hlt">deformation</span> 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.</p> <div class="credits"> <p class="dwt_author">Jiang, H.; Bieler, T. R.; Compton, C.; Grimm, T. L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2006-07-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">397</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.physik.tu-dresden.de/ifp/downloads/publications/wasserbaech.2002.1v.pdf"> <span id="translatedtitle">Low-<span class="hlt">Temperature</span> Internal Friction and Thermal Conductivity of Plastically <span class="hlt">Deformed</span>, High-Purity Monocrystalline Niobium</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The low-<span class="hlt">temperature</span> internal friction Q-1 and thermal conductivity ? of plastically <span class="hlt">deformed</span>, high-purity niobium monocrystals have been investigated and compared with measurements on an amorphous SiO2 (a-SiO2) specimen. After plastic <span class="hlt">deformation</span> at intermediate <span class="hlt">temperatures</span>, an approximately <span class="hlt">temperature</span> independent internal friction Q-1 was observed with a magnitude comparable to that of the a-SiO2 specimen. Plastic <span class="hlt">deformation</span> at low <span class="hlt">temperatures</span> leads to</p> <div class="credits"> <p class="dwt_author">W. Wasserbch; S. Sahling; R. O. Pohl; E. Thompson</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">398</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2012JSG....37...89Z"> <span id="translatedtitle">Extreme ductile <span class="hlt">deformation</span> of fine-grained salt by coupled solution-precipitation <span class="hlt">creep</span> and microcracking: Microstructural evidence from perennial Zechstein sequence (Neuhof salt mine, Germany)</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">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) <span class="hlt">creep</span> 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 <span class="hlt">creep</span> 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 <span class="hlt">deforming</span> by the grain boundary sliding (GBS) coupled <span class="hlt">deformation</span> mechanisms.</p> <div class="credits"> <p class="dwt_author">Zvada, Prokop; Desbois, Guillaume; Schwedt, Alexander; Lexa, Ondrej; Urai, Janos L.</p> <p class="dwt_publisher"></p> <p class="publishDate">2012-04-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">399</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=DE91006471"> <span id="translatedtitle">Microstructural evolution in a ferritic-martensitic stainless steel and its relation to high-<span class="hlt">temperature</span> <span class="hlt">deformation</span> and rupture models.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">The ferritic-martensitic stainless steel HT-9 exhibits an anomalously high <span class="hlt">creep</span> strength in comparison to its high-<span class="hlt">temperature</span> flow strength from tensile tests performed at moderate rates. A constitutive relation describing its high-<span class="hlt">temperature</span> tensile b...</p> <div class="credits"> <p class="dwt_author">R. J. DiMelfi E. E. Gruber J. M. Kramer</p> <p class="dwt_publisher"></p> <p class="publishDate">1991-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">400</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2009CoMP..157..339X"> <span id="translatedtitle">The effect of dissolved magnesium on <span class="hlt">creep</span> of calcite II: transition from diffusion <span class="hlt">creep</span> to dislocation <span class="hlt">creep</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">We extended a previous study on the influence of Mg solute impurity on diffusion <span class="hlt">creep</span> in calcite to include <span class="hlt">deformation</span> 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 <span class="hlt">temperature</span>, 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 <span class="hlt">deformed</span> 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 <span class="hlt">deformation</span> apparatus. The <span class="hlt">deformation</span> tests took place at between 700 and 800C and at strain rates between 10-6 and 10-3 s-1. After <span class="hlt">deformation</span> to strains of about 25%, a bimodal distribution of large protoblasts and small recrystallized neoblasts coexisted in some samples loaded at higher stresses. The <span class="hlt">deformation</span> data indicated a transition in mechanism from diffusion <span class="hlt">creep</span> to dislocation <span class="hlt">creep</span>. 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 <span class="hlt">temperature</span>, the stress at which that transition occurred was larger for samples with higher Mg content and smaller grain size. At given strain rates, constant <span class="hlt">temperature</span>, and fixed grain size, the strength of calcite in the dislocation <span class="hlt">creep</span> regime increased with solute content, while the strength in the diffusion <span class="hlt">creep</span> 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 <span class="hlt">deformation</span>.</p> <div class="credits"> <p class="dwt_author">Xu, Lili; Renner, Jrg; Herwegh, Marco; Evans, Brian</p> <p class="dwt_publisher"></p> <p class="publishDate">2009-03-01</p> </div> </div> </div> </div> <div id="filter_results_form" class="filter_results_form floatContainer" style="visibility: visible;"> <div style="width:100%" id="PaginatedNavigation" class="paginatedNavigationElement"> <a id="FirstPageLink" onclick='return showDiv("page_1");' href="#" title="First Page"> <img id="FirstPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.first.18x20.png" alt="First Page" /></a> <a id="PreviousPageLink" onclick='return showDiv("page_19");' href="#" title="Previous Page"> <img id="PreviousPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.previous.18x20.png" alt="Previous 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showDiv("page_25");' href="#">25</a> </span> </span> <a id="NextPageLink" onclick='return showDiv("page_22");' href="#" title="Next Page"> <img id="NextPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.next.18x20.png" alt="Next Page" /></a> <a id="LastPageLink" onclick='return showDiv("page_25.0");' href="#" title="Last Page"> <img id="LastPageLinkImage" class="Icon" src="http://www.science.gov/scigov/images/icon.last.18x20.png" alt="Last Page" /></a> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">401</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2010JMEP..tmp..201L"> <span id="translatedtitle"><span class="hlt">Creep</span> Constitutive Model and Component Lifetime Estimation: The Case of Niobium-Modified 9Cr-1Mo Steel Weldments</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The ?-projection parametric method was used to analyze the <span class="hlt">creep</span> 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 <span class="hlt">creep</span> lifetimes, for specified sets of design stress, <span class="hlt">temperature</span>, and strains. Furthermore, it is suggested that the <span class="hlt">creep</span> strain results may be consistent with dislocation climb being the <span class="hlt">creep</span> <span class="hlt">deformation</span> mechanism in the alloy.</p> <div class="credits"> <p class="dwt_author">Lewis, Gladius; Shaw, Kevin M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2010-10-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">402</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2011JMEP...20.1310L"> <span id="translatedtitle"><span class="hlt">Creep</span> Constitutive Model and Component Lifetime Estimation: The Case of Niobium-Modified 9Cr-1Mo Steel Weldments</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The ?-projection parametric method was used to analyze the <span class="hlt">creep</span> 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 <span class="hlt">creep</span> lifetimes, for specified sets of design stress, <span class="hlt">temperature</span>, and strains. Furthermore, it is suggested that the <span class="hlt">creep</span> strain results may be consistent with dislocation climb being the <span class="hlt">creep</span> <span class="hlt">deformation</span> mechanism in the alloy.</p> <div class="credits"> <p class="dwt_author">Lewis, Gladius; Shaw, Kevin M.</p> <p class="dwt_publisher"></p> <p class="publishDate">2011-10-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">403</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2013EGUGA..15.2670Y"> <span id="translatedtitle">Mantle <span class="hlt">temperature</span> under drifting <span class="hlt">deformable</span> continents during the supercontinent cycle</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The thermal heterogeneity of the Earth's mantle under the drifting continents during a supercontinent cycle is a controversial issue in earth science. Here, a series of numerical simulations of mantle convection are performed in 3D spherical-shell geometry, incorporating drifting <span class="hlt">deformable</span> continents and self-consistent plate tectonics, to evaluate the subcontinental mantle <span class="hlt">temperature</span> during a supercontinent cycle. Results show that the laterally averaged <span class="hlt">temperature</span> anomaly of the subcontinental mantle remains within several tens of degrees (50 C) throughout the simulation time. Even after the formation of the supercontinent and the development of subcontinental plumes due to the subduction of the oceanic plates, the laterally averaged <span class="hlt">temperature</span> anomaly of the deep mantle under the continent is within +10 C. This implies that there is no substantial <span class="hlt">temperature</span> difference between the subcontinental and suboceanic mantles during a supercontinent cycle. The <span class="hlt">temperature</span> anomaly immediately beneath the supercontinent is generally positive owing to the thermal insulation effect and the active upwelling plumes from the core-mantle boundary. In the present simulation, the formation of a supercontinent causes the laterally averaged subcontinental <span class="hlt">temperature</span> to increase by a maximum of 50 C, which would produce sufficient tensional force to break up the supercontinent. The periodic assembly and dispersal of continental fragments, referred to as the supercontinent cycle, bear close relation to the evolution of mantle convection and plate tectonics. Supercontinent formation involves complex processes of introversion, extroversion or a combination of these in uniting dispersed continental fragments, as against the simple opening and closing of individual oceans envisaged in Wilson cycle. In the present study, I evaluate supercontinent processes in a realistic mantle convection regime. Results show that the assembly of supercontinents is accompanied by a combination of introversion and extroversion processes. The regular periodicity of the supercontinent cycles observed in previous 2D and 3D simulation models with rigid nondeformable continents is not confirmed. The small-scale thermal heterogeneity is dominated in deep mantle convection during the supercontinent cycle, although the large-scale, active upwelling plumes intermittently originate under drifting continents and/or the supercontinent. Results suggest that active subducting cold plates along continental margins generate thermal heterogeneity with short-wavelength structures, which is consistent with the thermal heterogeneity in the present-day mantle convection inferred from seismic tomography models. References: [1] Yoshida, M. Mantle <span class="hlt">temperature</span> under drifting <span class="hlt">deformable</span> continents during the supercontinent cycle, Geophys. Res. Lett., 2013, in press. [2] Yoshida, M. and M. Santosh, Mantle convection modeling of supercontinent cycle: Introversion, extroversion, or combination?, 2013, submitted.</p> <div class="credits"> <p class="dwt_author">Yoshida, Masaki</p> <p class="dwt_publisher"></p> <p class="publishDate">2013-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">404</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/49065233"> <span id="translatedtitle">A correlation of <span class="hlt">creep</span> and fatigue crack growth in high density poly(ethylene) at various <span class="hlt">temperatures</span></span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The <span class="hlt">creep</span> crack growth (CCG) and fatigue crack growth (FCG) behaviour of two PE-HD pipe grades was studied based on a linear elastic fracture mechanics (LEFM) methodology. The FCG-tests were performed under a sinusoidal load at a frequency of 1 Hz and R-ratios (Fmin\\/Fmax) of 0.1, 0.3 and 0.5; the test <span class="hlt">temperatures</span> were 23 (only FCG), 60 and 80 C.</p> <div class="credits"> <p class="dwt_author">G. Pinter; W. Balika; R. W. Lang</p> <p class="dwt_publisher"></p> <p class="publishDate">2002-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">405</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/60283940"> <span id="translatedtitle">Dislocation density and high-<span class="hlt">temperature</span> <span class="hlt">creep</span> of aluminum alloys and fracture of silicon carbide-aluminum composites</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">A two-part investigation was undertaken to determine the correlation between dislocation density and mechanical behavior. For high-<span class="hlt">temperature</span> <span class="hlt">creep</span>, the relationship between logarithm of strain rate and stress is divided into a linear (power law) and a nonlinear (power-law-breakdown) region. To explain this phenomenon, an investigation was conducted. In the case of 1100 Al and Al-11 wt.% Zn alloys strained at</p> <div class="credits"> <p class="dwt_author">Feng</p> <p class="dwt_publisher"></p> <p class="publishDate">1987-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">406</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/55902223"> <span id="translatedtitle">The use of computational <span class="hlt">creep</span> continuum damage mechanics to optimize materials selection for high-<span class="hlt">temperature</span> weldments</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">It is shown how mechanisms-based constitutive equations may be formulated which are based on single-state damage variables for ferritic steels undergoing high-<span class="hlt">temperature</span> <span class="hlt">creep</span> and damage. In addition, it is shown how this description may be used to express the constitutive equations for weld and heat-affected-zone (HAZ) materials in terms of the same description of parent material behaviour and of simple</p> <div class="credits"> <p class="dwt_author">D. R. Hayhurst</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">407</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://adsabs.harvard.edu/abs/2008PMM...105..395P"> <span id="translatedtitle">Structure factor of acoustic emission upon high-<span class="hlt">temperature</span> <span class="hlt">deformation</span> of aluminum</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p class="result-summary">The accumulation of <span class="hlt">deformation</span> and acoustic emission upon high-<span class="hlt">temperature</span> loading of aluminum has been studied. It has been established that in aluminum the accumulation of <span class="hlt">deformation</span> in the course of a thermomechanical cycle brings about the formation of <span class="hlt">deformation</span> bands whose density is of a pronounced quasi-periodic character depending on the <span class="hlt">temperature</span>. The minimum and the maximum of the density of <span class="hlt">deformation</span> bands correspond to the <span class="hlt">temperature</span> of jumplike development of <span class="hlt">deformation</span> and to the monotonic character of <span class="hlt">deformation</span> accumulation, respectively. The monotonic accumulation of <span class="hlt">deformation</span> is accompanied by a monotonic growth of the root-mean-square voltage of acoustic emission, while the jumplike development of <span class="hlt">deformation</span>, by high-amplitude single acoustic signals. The amplitude of single acoustic signals correlates with the strain rate.</p> <div class="credits"> <p class="dwt_author">Plotnikov, V. A.; Makarov, S. V.</p> <p class="dwt_publisher"></p> <p class="publishDate">2008-04-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">408</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://academic.research.microsoft.com/Publication/61216508"> <span id="translatedtitle">Analysis of elevated-<span class="hlt">temperature</span> tensile and <span class="hlt">creep</span> properties of normalized and tempered 2-1\\/4 Cr1 Mo steel</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://academic.research.microsoft.com/">Microsoft Academic Search </a></p> <p class="result-summary">The ferritic 2-1\\/4 Cr-1 Mo steel is an important construction material for elevated-<span class="hlt">temperature</span> applications worldwide. It is of particular interest for coal conversion pressure vessels. Tensile and <span class="hlt">creep</span> data are presented for normalized and tempered 2-1\\/4 Cr-1 Mo steel from American, Japanese, British, French, and German sources. These include <span class="hlt">creep</span> data obtained at <span class="hlt">temperatures</span> from 427 to 600°C (800 to</p> <div class="credits"> <p class="dwt_author">M. K. Booker; B. L. P. Booker; R. W. Swindeman</p> <p class="dwt_publisher"></p> <p class="publishDate">1982-01-01</p> </div> </div> </div> </div> <div class="floatContainer result odd" lang="en"> <div class="resultNumber element">409</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=DE95010236"> <span id="translatedtitle">Numerical analysis of fracture and high <span class="hlt">temperature</span> <span class="hlt">creep</span> characteristics of composites with discontinuous ductile reinforcements.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">Role of material parameters on fracture and <span class="hlt">creep</span> 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...</p> <div class="credits"> <p class="dwt_author">S. B. Biner</p> <p class="dwt_publisher"></p> <p class="publishDate">1994-01-01</p> </div> </div> </div> </div> <div class="floatContainer result " lang="en"> <div class="resultNumber element">410</div> <div class="resultBody element"> <p class="result-title"><a target="resultTitleLink" href="http://science.gov/scigov/link.html?type=RESULT&redirectUrl=http://www.ntis.gov/search/product.aspx?ABBR=PB2010101388"> <span id="translatedtitle">Development of a Simple Test to Determine the Low <span class="hlt">Temperature</span> <span class="hlt">Creep</span> Compliance of Asphalt Mixtures.</span></a>  </p> <div class="result-meta"> <p class="source"><a target="_blank" id="logoLink" href="http://www.ntis.gov/search/index.aspx">National Technical Information Service (NTIS)</a></p> <p class="result-summary">The idea of performing <span class="hlt">creep</span> tests on asphalt mixture beam specimens with the Bending Beam Rheometer (BBR) was investigated in this project. In the first part of the investigation a detailed beam preparation procedure was developed for both laboratory com...</p> <div class="credits"> <p class="dwt_author">A. Zofka A. C. Falchetto M. Marastean R. Velasquez</p>