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1

Creep of crystals: High-temperature deformation processes in metals, ceramics and minerals  

Microsoft Academic Search

An introductory text describing high-temperature deformation processes in metals, ceramics, and minerals is presented. Among the specific topics discussed are: the mechanical aspects of crystal deformation; lattice defects; and phenomenological and thermodynamical analysis of quasi-steady-state creep. Consideration is also given to: dislocation creep models; the effect of hydrostatic pressure on deformation; creep polygonization; and dynamic recrystallization. The status of experimental

J. P. Poirier

1985-01-01

2

heterogeneous deformation of Cu 2 O single crystals during high temperature compression creep  

Microsoft Academic Search

Single crystals of Cu2O in parallelopipedic and cubic geometries have been deformed in high temperature creep. Depending on the compression axis, either 2 or 4 glide planes are observed. Local strain analysis performed by a visioplasticity method permits an estimation of the heterogeneity of deformation and shows clearly the imperfection of the compression test.

T. Bretheau; C. Dolin

1978-01-01

3

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

4

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

NASA Astrophysics Data System (ADS)

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

Rogowitz, Anna; Grasemann, Bernhard

2014-05-01

5

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

Microsoft Academic Search

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

Sofiane Terzi; Raphael Couturier; Laure Gutaz; Bernard Viguier

2008-01-01

6

Creep deformation of TD-nickel chromium  

NASA Technical Reports Server (NTRS)

An investigation was conducted of the mechanical behavioral characteristics of thoria-dispersed (TD) NiCr materials at elevated temperatures. The experimental procedure used is discussed along with the significance of the obtained results. Attention is given to basic creep behavior and creep thermal activation parameter measurements. It is found that the overall creep behavior of TD-NiCr can be explained on the basis of the relative contributions of two parallel-concurrent deformation mechanisms, including diffusion controlled grain boundary sliding and dislocation motion.

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

1976-01-01

7

Creep of high temperature composites  

SciTech Connect

High temperature creep deformation of composites is examined. Creep of composites depends on the interplay of many factors. One of the basic issues in the design of the creep resistant composites is the ability to predict their creep behavior from the knowledge of the creep behavior of the individual components. In this report, the existing theoretical models based on continuum mechanics principles are reviewed. These models are evaluated using extensive experimental data on molydisilicide-silicon carbide composites obtained by the authors. The analysis shows that the rule of mixture based on isostrain and isostress provides two limiting bounds wherein all other theoretical predictions fall. For molydisilicide composites, the creep is predominantly governed by the creep of the majority phase, i.e. the matrix with fibers deforming elastically. The role of back stresses both on creep rates and activation energies are shown to be minimum. Kinetics of creep in MoSi{sub 2} is shown to be controlled by the process of dislocation glide with climb involving the diffusion of Mo atoms.

Sadananda, K.; Feng, C.R. [Naval Research Lab., Washington, DC (United States). Materials Science and Technology Division

1993-12-31

8

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

2010-10-01

9

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

10

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

11

Room temperature creep of a high strength steel  

Microsoft Academic Search

The time dependent deformation at room temperature of a high strength steel was investigated. The room temperature creep tests showed that creep can occur below 1\\/3 ?0.2 (yield strength at 0.2% offset). The resulting creep behavior consists of only two stages, including primary creep and steady-state creep, each of which has its own distinctive straintime features. The effects of creep

Cheng Liu; Ping Liu; Zhenbo Zhao; Derek O. Northwood

2001-01-01

12

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

13

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

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

Substructure in a creep deformed lamellar TiAl alloy  

SciTech Connect

It has recently been demonstrated that the primary creep of a fully-lamellar (FL) TiAl alloy can be significantly reduced by a prestraining technique. Specifically, when a FL-TiAl specimen was first crept to a few percent of strain at high stresses (>240 MPa), the specimen became more resistant to a subsequent creep deformation at lower stresses (<240 MPa) even after a prolonged loading. Although changing interaction between strain hardening and recovery processes which strongly affect the creep rate at a given temperature and stress. Both strain hardening and recovery processes are intimately related to the mobilization and immobilization of dislocations. In the present study, the substructure of crept alloys is examined in order to understand how and to what extent a prestraining can affect the creep behavior of the FL-TiAl alloys. The influence of lamellar orientation (with respect to the stress axis) in the deformation substructure is also investigated.

Hsiung, L.M.; Nieh, T.G. [Lawrence Livermore National Lab., CA (United States). Materials Science Dept.] [Lawrence Livermore National Lab., CA (United States). Materials Science Dept.

1997-02-01

17

Room temperature creep of high strength steels  

Microsoft Academic Search

The room-temperature creep behavior of three high strength steels has been investigated. Several parameters such as creep stress, loading rate, stress history and heat treatment has been altered and their influence on the low temperature creep has been reported. The primary creep in all three alloys agreed well with the logarithmic creep law and the creep mechanism has been identified

A. Oehlert; A. Atrens

1994-01-01

18

Creep of pure aluminum at cryogenic temperatures  

E-print Network

Conducted on OFHC Copper . B. Equipment Used in Successful Long-term Creep Testing. . . C. Creep Mechanisms at Cryogenic Temperatures. . . . . . . . . . 8 8 11 III PRIMARY RESEARCH OBJECTIVE . . 14 IV EXPERIMENTAL SETUP AND PROCEDURES . . 15 A. Load... aluminum and NbTi. 2 Constant load creep curve showing three distinct regions. 3 Creep curves for OPHC copper taken over 200 hours. 10 4 Photograph of creep frame used in cryogenic creep tests. . . . . . . . . 5 Photograph of top of creep frame showing...

McDonald, Lacy Clark

2012-06-07

19

Short-term flexural creep deformation in synroc-C  

Microsoft Academic Search

The flexural creep behaviour of synroc-C in an inert atmosphere was studied at temperatures of 860C, 900C and 940C under constant-load conditions in four-point bending. Applied stresses ranged from 100 to 160 MPa. Individual creep curves show primary and secondary creep but little or no tertiary creep stage. The log of the creep rate was found to increase linearly with

B. A. Latella; T. Liu; K. U. Snowden; E. G. Mehrtens; G. R. Lumpkin; B. K. Gan

2003-01-01

20

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

NASA Astrophysics Data System (ADS)

Exposure of aluminum alloy to an elastic loading, during "creep-aging forming" or other manufacturing processes at relatively high temperature, may lead to the lasting creep deformation. The creep behaviors of 7075 aluminum alloy are investigated by uniaxial tensile creep experiments over wide ranges of temperature and external stress. The results show that the creep behaviors of the studied aluminum alloy strongly depend on the creep temperature, external stress, and creep time. With the increase of creep temperature and external stress, the creep strain increases quickly. In order to overcome the shortcomings of the Bailey-Norton law and ? projection method, a new constitutive model is proposed to describe the variations of creep strain with time for the studied aluminum alloy. In the proposed model, the dependences of creep strain on the creep temperature, external stress, and creep time are well taken into account. A good agreement between the predicted and measured creep strains shows that the established creep constitutive model can give an accurate description of the creep behaviors of 7075 aluminum alloy. Meanwhile, the obtained stress exponent indicates that the creep process is controlled by the dislocation glide, which is verified by the microstructural observations.

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

2014-08-01

21

Creep Behavior and Deformation Mechanisms for Nanocluster-Strengthened Ferritic Steels  

SciTech Connect

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

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

2011-01-01

22

High-temperature creep and resultant anisotropy in ultrasonic velocity in isotropic graphite  

Microsoft Academic Search

Plastic deformation of isotropic graphite in the vicinity of 2500 C was studied using an Instron-type testing machine. The load-deflection curve was found to show a proportional limit at high temperature. Creep curves of graphite were also measured and were simulated by an empirical equation based on parabolic creep. Following the creep tests, ultrasonic velocity in the elongated graphite was

M. Narisawa; M. Adachi; I. Souma

1994-01-01

23

Effect of Tungsten on Primary Creep Deformation and Minimum Creep Rate of Reduced Activation Ferritic-Martensitic Steel  

NASA Astrophysics Data System (ADS)

Effect of tungsten on transient creep deformation and minimum creep rate of reduced activation ferritic-martensitic (RAFM) steel has been assessed. Tungsten content in the 9Cr-RAFM steel has been varied between 1 and 2 wt pct, and creep tests were carried out over the stress range of 180 and 260 MPa at 823 K (550 C). The tempered martensitic steel exhibited primary creep followed by tertiary stage of creep deformation with a minimum in creep deformation rate. The primary creep behavior has been assessed based on the Garofalo relationship, , considering minimum creep rate instead of steady-state creep rate . The relationships between (i) rate of exhaustion of transient creep r' with minimum creep rate, (ii) rate of exhaustion of transient creep r' with time to reach minimum creep rate, and (iii) initial creep rate with minimum creep rate revealed that the first-order reaction-rate theory has prevailed throughout the transient region of the RAFM steel having different tungsten contents. The rate of exhaustion of transient creep r' and minimum creep rate decreased, whereas the transient strain ? T increased with increase in tungsten content. A master transient creep curve of the steels has been developed considering the variation of with . The effect of tungsten on the variation of minimum creep rate with applied stress has been rationalized by invoking the back-stress concept.

Vanaja, J.; Laha, Kinkar; Mathew, M. D.

2014-10-01

24

High-temperature deformation of plasma-sprayed ZrO 2 thermal barrier coatings  

Microsoft Academic Search

The high-temperature deformation of atmospheric plasma-sprayed ZrO2 thermal barrier coatings (TBCs) was investigated. Compression creep tests were performed at temperatures between 900 and 1300C at stresses between 1.8 and 80 MPa. During 100 h creep time a secondary creep region was not achieved. The creep behavior can be described by a power law. Besides the creep deformation, a shrinkage of

Gnter Thurn; Gerold A. Schneider; Fritz Aldinger

1997-01-01

25

Viscoelastic creep of high-temperature concrete  

SciTech Connect

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

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

1985-01-01

26

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

NASA Technical Reports Server (NTRS)

This two-part paper is the first published report on the long term, low temperature creep of hot-extruded near-stoichiometric NiTi. Constant load tensile creep tests were conducted on hot-extruded near-stoichiometric NiTi at 300, 373 and 473 K under initial applied stresses varying between 200 and 350 MPa as long as 15 months. These temperatures corresponded to the martensitic, two-phase and austenitic phase regions, respectively. Normal primary creep lasting several months was observed under all conditions indicating dislocation activity. Although steady-state creep was not observed under these conditions, the estimated creep rates varied between 10(exp -10) and 10(exp -9)/s. The creep behavior of the two phases showed significant differences. The martensitic phase exhibited a large strain on loading followed by a primary creep region accumulating a small amount of strain over a period of several months. The loading strain was attributed to the detwinning of the martensitic phase whereas the subsequent strain accumulation was attributed to dislocation glide-controlled creep. An "incubation period" was observed before the occurrence of detwinning. In contrast, the austenitic phase exhibited a relatively smaller loading strain followed by a primary creep region, where the creep strain continued to increase over several months. It is concluded that the creep of the austenitic phase occurs by a dislocation glide-controlled creep mechanism as well as by the nucleation and growth of deformation twins.

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

2013-01-01

27

Elevated temperature deformation of TD-nickel.  

NASA Technical Reports Server (NTRS)

Sensitivity of the elevated temperature (above 0.5 Tm) 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. Temperature sensitivity of the yield stress, as well as high (compared to self diffusion) apparent tensile activation enthalpies were the result of the internal stress not being proportional to the shear modulus. Creep activation enthalpies increased with increasing L/D ratio and, to a lesser extent, increasing grain diameter, reaching high values which may be apparent values. The thoria particle dispersion may have been altered by elevated temperature tensile and creep deformation.

Petrovic, J. J.; Ebert, L. J.

1973-01-01

28

Stress versus temperature dependence of activation energies for creep  

NASA Technical Reports Server (NTRS)

The activation energy for creep at low stresses and elevated temperatures is associated with lattice diffusion, where the rate controlling mechanism for deformation is dislocation climb. At higher stresses and intermediate temperatures, the rate controlling mechanism changes from dislocation climb to obstacle-controlled dislocation glide. Along with this change in deformation mechanism occurs a change in the activation energy. When the rate controlling mechanism for deformation is obstacle-controlled dislocation glide, it is shown that a temperature-dependent Gibbs free energy does better than a stress-dependent Gibbs free energy in correlating steady-state creep data for both copper and LiF-22mol percent CaF2 hypereutectic salt.

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

1992-01-01

29

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

30

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

31

In situ synchrotron radiation topography of NaCI during high temperature creep  

Microsoft Academic Search

High temperature plastic deformation is associated with large changes in the microstructure of single crystals. To observe this microstructure during the creep test, we have performed X-ray reflection topography, taking advantage of the high intensity of the synchrotron radiation. A special creep machine was designed which permits in situ observation.Creep tests and microstructural observations were performed on NaCl single crystals

E. Fries; J. Deschamps; J. Castaing

1983-01-01

32

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

NASA Astrophysics Data System (ADS)

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

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

33

Deformation properties of Finnish spruce and pine wood in tangential and radial directions in association to high temperature drying. Part III. Experimental results under drying conditions (mechano-sorptive creep)  

Microsoft Academic Search

Picea abies) and Scots pine (Pinus sylvestris) wood under conditions relevant in the high temperature drying process. This paper reports the experimental results obtained\\u000a for creep in tension under drying conditions at temperatures 95125?C. The results are compared to other researchers' measurements\\u000a of mechano-sorptive creep at conventional drying temperatures (up to 80?C). Based on this comparison the effect of temperature

A. Hanhijrvi

2000-01-01

34

Stress versus temperature dependent activation energies in creep  

NASA Technical Reports Server (NTRS)

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

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

1990-01-01

35

High temperature creep behavior of single crystal gamma prime and gamma alloys  

NASA Technical Reports Server (NTRS)

The creep behavior of single crystals of gamma-prime and gamma alloys were investigated and compared to the response of two-phase superalloys tested previously. High temperature deformation in the gamma alloys was characteristic of a climb-controlled mechanism, whereas the gamma-prime based materials exhibited glide-controlled creep behavior. The superalloys were much more creep resistant than their constituent phases, which indicates the importance of the gamma/gamma-prime interface as a barrier for dislocation motion during creep.

Nathal, M. V.; Diaz, J. O.; Miner, R. V.

1989-01-01

36

Abnormal acceleration of creep deformation rate above 700 C in the orthorhombic based Ti22Al27Nb alloy  

Microsoft Academic Search

For the past decade, Ti2AlNb-based alloys have been investigated for being applied to the structural materials in aerospace engine. In this study, creep tests of Ti22Al27Nb (at.%) alloys are conducted at a constant tensile stress of 200MPa at the various temperatures in the range from 650 to 750C. It is observed that the creep deformation rate of the O+bcc dual

Seung Jin Yang; Soo Woo Nam; Masuo Hagiwara

2004-01-01

37

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

38

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

E-print Network

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

39

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

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

40

Room Temperature Creep Of SiC/SiC Composites  

NASA Technical Reports Server (NTRS)

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

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

2001-01-01

41

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

42

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

NASA Technical Reports Server (NTRS)

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

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

2005-01-01

43

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

44

Improved high temperature creep resistant austenitic alloy  

DOEpatents

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

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

1988-05-13

45

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

46

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

47

Deformation properties of Finnish spruce and pine wood in tangential and radial directions in association to high temperature dryingPart II. Experimental results under constant conditions (viscoelastic creep)  

Microsoft Academic Search

Picea abies) and Scots pine (Pinus sylvestris) wood under conditions relevant in the high temperature drying process. This paper reports on the experimental results obtained\\u000a concerning creep in tension under constant conditions, primarily in wet (saturated, green) state at temperatures 95?C125?C.\\u000a The results are compared to some other researchers' measurements in a trial of the applicability of the timetemperaturemoisture-content\\u000a superposition

A. Hanhijrvi

1999-01-01

48

Time temperature-stress dependence of boron fiber deformation  

NASA Technical Reports Server (NTRS)

Flexural stress relaxation (FSR) and flexural internal friction (FIF) techniques were employed to measure the time-dependent deformation of boron fibers from -190 to 800 C. The principal specimens were 203 micrometers diameter fibers commercially produced by chemical vapor deposition (CVD) on a 13 micrometer tungsten substrate. The observation of complete creep strain recovery with time and temperature indicated that CVD boron fibers deform flexurally as anelastic solids with no plastic component.

Dicarlo, J. A.

1976-01-01

49

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

Microsoft Academic Search

We have performed an experimental study to quantify the high-temperature creep behavior of natural diabase rocks under dry deformation conditions. Samples of both Maryland diabase and Columbia diabase were investigated to measure the effects of temperature, oxygen fugacity, and plagioclase-to-pyroxene ratio on creep strength. Flow laws determined for creep of these diabases were characterized by an activation energy of Q

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

1998-01-01

50

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

51

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

52

JOURNAL OF MATERIALS SCIENCE 37 (2002) 2899 2907 Creep deformation and monotonic stress-strain  

E-print Network

of a typical creep curve. turbine blade in a military aircraft engine (tR = 100 hrs) [1]. In such short life-hardening exponent, or creep exponent Q Activation energy for creep R Universal gas constant R.T. Room temperature r

Fatemi, Ali

53

Nuclear deformation at finite temperature  

E-print Network

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

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

2014-08-01

54

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

55

Time-dependent deformation of austenitic stainless steels at cryogenic temperatures  

NASA Astrophysics Data System (ADS)

Creep tests and constant load rate tensile tests at cryogenic temperatures were carried out on austenitic stainless steels AISI304L, 310S and 316L. A creep rate of ? 10 -9 s -1 was observed in a 200 h creep test under the proof stress of the materials at 77 K. The creep rate at 4 K was decreased to a tenth of that at 77 K. However, an abrupt and large deformation occurs in a constant load rate tensile test at 4 K. The magnitude of the abrupt deformation depends on the work-hardening rate and the stablity of the austenitic phase. Higher proof stress materials, especially AISI310S, do not always show better characteristics for the creep or the abrupt deformation at 4 K.

Ogata, T.; Ishikawa, K.

56

Introduction Creep is a time-dependent deformation that happens when metals or other materials are  

E-print Network

(usually temperature is greater than approximately 0.4 of the absolute melting temperature T=0.4Tm) [3;3 As shown in Figure 1.1, the slope of the curve is called creep rate ( · ) and the end point of the curve E rate. DE as tertiary creep has an accelerating creep-rate and terminates at the point E by failure

Cambridge, University of

57

Creep Behavior of High Temperature Alloys for Generation IV Nuclear Energy Systems  

NASA Astrophysics Data System (ADS)

The Very High Temperature Reactor (VHTR) is one of the leading concepts of the Generation IV nuclear reactor development, which is the core component of Next Generation Nuclear Plant (NGNP). The major challenge in the research and development of NGNP is the performance and reliability of structure materials at high temperature. Alloy 617, with an exceptional combination of high temperature strength and oxidation resistance, has been selected as a primary candidate material for structural use, particularly in Intermediate Heat Exchanger (IHX) which has an outlet temperature in the range of 850 to 950C and an inner pressure from 5 to 20MPa. In order to qualify the material to be used at the operation condition for a designed service life of 60 years, a comprehensive scientific understanding of creep behavior at high temperature and low stress regime is necessary. In addition, the creep mechanism and the impact factors such as precipitates, grain size, and grain boundary characters need to be evaluated for the purpose of alloy design and development. In this study, thermomechanically processed specimens of alloy 617 with different grain sizes were fabricated, and creep tests with a systematic test matrix covering the temperatures of 850 to 1050C and stress levels from 5 to 100MPa were conducted. Creep data was analyzed, and the creep curves were found to be unconventional without a well-defined steady-state creep. Very good linear relationships were determined for minimum creep rate versus stress levels with the stress exponents determined around 3-5 depending on the grain size and test condition. Activation energies were also calculated for different stress levels, and the values are close to 400kJ/mol, which is higher than that for self-diffusion in nickel. Power law dislocation climb-glide mechanism was proposed as the dominant creep mechanism in the test condition regime. Dynamic recrystallization happening at high strain range enhanced dislocation climb and are believed to be responsible for the monotonically increasing creep rates. Apart from dislocation creep, diffusional creep in existence at low stress level in fine-grained (ASTM 8) material also contributed partly to the creep rates. A reasonable prediction on the long term performance of alloy 617 was also made by extrapolation method using optimized parameters based on creep test data. Furthermore, microstructure characterization was performed utilizing Optical Microscopy (OM), Scanning Electron Microscopy (SEM), Electron Backscattered Diffraction (EBSD), Transmission Electron Microscopy (TEM) and related analytical techniques on samples from both before and after creep, with special attention given to grain size effects, grain boundary type, and dislocation substructures. Evidences for dislocation climb and dislocation glide were found through detailed dislocation analysis by TEM, proving the dislocation climb-glide mechanism. The formation of subgrain boundary, the changes in boundary characters and grain sizes was confirmed by EBSD analysis for dynamic recrystallization. The effects of initial grain size and grain boundary character distribution on the creep behavior and mechanism were also evaluated. Through the results obtained from this experimental study, new insights were provided into how changes in microstructure take place during high temperature creep of alloy 617, creep mechanism at different conditions was identified, and the creep deformation model was discussed. The results will also serve to technological and code case development and design of materials for NGNP.

Wen, Xingshuo

58

Temperature effects on creep behavior of continuous fiber GMT composites  

Microsoft Academic Search

The effects of temperature on the tensile creep of continuous random fiber glass mat thermoplastic composite (GMT) have been studied following an accelerated characterization procedure. The objectives of this work are twofold. First, is to obtain a long-term creep model using timetemperature superposition (TTS) that can represent behavior within the linear viscoelastic regime (up to 20MPa) at room temperature. The

Prasad Dasappa; Pearl Lee-Sullivan; Xinran Xiao

2009-01-01

59

Elevated temperature deformation of thoria dispersed nickel-chromium  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

60

Circuits of thyristor temperature regulation in creep and creep limit tests  

Microsoft Academic Search

The operating principles of a thyristor-based temperature regulation circuit for a three-section testing furnace using a positional temperature regulator are described. The effectiveness of the proposed circuit is verified experimentally on a creep rupture testing machine. Deviations from the specified temperature in tests lasting 500 hr is within + or - 3 C. The use of this circuit eliminates any

B. I. Pevzner; B. M. Ovsiannikov; V. V. Mikheev; N. N. Demidov

1979-01-01

61

Plastic Deformation of Aluminum Single Crystals at Elevated Temperatures  

NASA Technical Reports Server (NTRS)

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

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

1956-01-01

62

High temperature creep of SiC densified using a transient liquid phase  

SciTech Connect

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

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

1991-09-01

63

Low-temperature creep of a carburized steel  

Microsoft Academic Search

The low-temperature creep behavior of carburized 4320 steel with retained austenite contents of 35 and 14 pct and two uncarburized\\u000a 4320 steels was investigated. The temperature range in the experiments was from 70 ?C to 195 ?C. The creep rate obeyed a logarithmic\\u000a law when the stress level was below or near the proportional limit. A kinetic model is presented

R. W. Neu; Huseyin Sehitoglu

1992-01-01

64

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

SciTech Connect

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

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

2011-06-01

65

Multiaxial Creep Behavior of Nickel-Base Heat-Resistant Alloys Hastelloy XR and Ni-Cr-W Superalloy at Elevated Temperatures  

Microsoft Academic Search

A series of uniaxial and multiaxial creep tests was carried out on Hastelloy XR and Ni-Cr-W superalloy, which were developed as the high temperature structural materials for nuclear application at the Japan Atomic Energy Research In- stitute, in order to investigate multiaxial creep behavior of these materials and to verify the laws for the description of deformation under multiaxial loadings.

Yoshiyuki KAJI; Hirokazu TSUJI; Hiroshi NISHI; Yasushi MUTO; Heinz-Josef PENKALLA; Florian SCHUBERT

2002-01-01

66

Creep behavior of epoxy resin during irradiation at cryogenic temperature  

NASA Astrophysics Data System (ADS)

Creep tests of an epoxy resin during bending and irradiation have been carried out to investigate the synergistic effects of radiation and stress on mechanical properties of the resin. Simultaneous application of stress and irradiation on the epoxy resin enhanced creep rates in comparison with the application of stress on an irradiated sample. In order to clarify the mechanism of the radiation-induced creep, measurements of solvent swelling of specimens have been performed. The swelling increased with the dose and the increase of the swelling corresponds to the increase of the chain scission. The mechanism of increased deformation of the resin during irradiation is proposed to be caused by increased chain scission following the release of the local strain energy.

Nishiura, Tetsuya; Nishijima, Shigehiro; Okada, Toichi

1999-11-01

67

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

68

Microstructure and modelling of the deformation behaviour of CoCr22Ni22W14 in hot-tensile- and creep tests  

Microsoft Academic Search

The present study describes the application of hot tension experiments in order to predict the creep and tensile behaviour of the highly loaded superalloy CoCr22Ni22W14. The results of mechanical tests and transmission electron microscopy (TEM) investigations have been used as input data in a model which describes the high temperature plastic deformation. A common log ? - log ? plot

U. Mhle; U. Martin; H. Oettel; O. Vhringer

1997-01-01

69

Evaluation of permanent deformation of unmodified and SBS modified asphalt mixtures using dynamic creep test  

Microsoft Academic Search

Recent researches show that there is a serious need for more accurate methods to evaluate polymer modified asphalt mixtures. In this research, dynamic creep test was conducted on unmodified and SBS modified samples, using UTM25 machine to this end. During this work it was attempted to compare the permanent deformation potential of the coarse graded mixtures with dense graded mixtures.

Ali Khodaii; Amir Mehrara

2009-01-01

70

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

71

Creep of precipitation-hardened nickel-base alloy single crystals at high temperatures  

Microsoft Academic Search

Single crystals of a ?? precipitation-hardened nickel-base super alloy, Mar-M200, were tested in constant load creep at 1575?F.\\u000a It was found that shear of the ?? precipitate by pairs of ?\\/2 (110) dislocations controlled deformation in both primary and\\u000a steady-state creep. This contrasts with 1400?F creep behavior where shear of ?? is dominated by ?\\/3 (112) dislocations in\\u000a primary creep,

G. R. Leverant; B. H. Kear; J. M. Oblak

1973-01-01

72

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

NASA Astrophysics Data System (ADS)

The deformation of rocks in the Earth's middle and lower crust is often localized in ductile shear zones. To better understand the initiation and propagation of high-temperature shear zones induced by the presence of structural and material heterogeneities, we performed deformation experiments in the dislocation creep regime on Carrara marble samples containing weak (limestone) or strong (novaculite) second phase inclusions. The samples were mostly deformed in torsion at a bulk shear strain rate of ? 1.9 10- 4 s- 1 to bulk shear strains ? between 0.02 and 2.9 using a Paterson-type gas deformation apparatus at 900 C temperature and 400 MPa confining pressure. At low strain, twisted specimens with weak inclusions show minor strain hardening that is replaced by strain weakening at ? > 0.1-0.2. Peak shear stress at the imposed conditions is about 20 MPa, which is ? 8% lower than the strength of intact samples. Strain progressively localized within the matrix with increasing bulk strain, but decayed rapidly with increasing distance from the inclusion tip. Microstructural analysis shows twinning and recrystallization within this process zone, with a strong crystallographic preferred orientation, dominated by {r} and (c) slip in < a >. Recrystallization-induced weakening starts at local shear strain of about 1 in the process zone, corresponding to a bulk shear strain of about 0.1. In contrast, torsion of a sample containing strong inclusions deformed at similar stress as inclusion-free samples, but do not show localization. The experiments demonstrate that the presence of weak heterogeneities initiates localized creep at local stress concentrations around the inclusion tips. Recrystallization-induced grain size reduction may only locally promote grain boundary diffusion creep. Accordingly, the bulk strength of the twisted aggregate is close to or slightly below the lower (isostress) strength bound, determined from the flow strength and volume fraction of matrix and inclusions.

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

2014-11-01

73

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

NASA Technical Reports Server (NTRS)

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

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

2007-01-01

74

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

75

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

NASA Technical Reports Server (NTRS)

We have performed an experimental study to quantify the high-temperature creep behavior of natural diabase rocks under dry deformation conditions. Samples of both Maryland diabase and Columbia diabase were investigated to measure the effects of temperature, oxygen fugacity, and plagioclase-to-pyroxene ratio on creep strength. Flow laws determined for creep of these diabases were characterized by an activation energy of Q = 485 +/- 30 kJ/mol and a stress exponent of n = 4.7 +/- 0.6, indicative of deformation dominated by dislocation creep processes. Although n and Q are the same for the two rocks within experimental error, the Maryland diabase, which has the lower plagioclase content, is significantly stronger than the Columbia diabase. Thus the modal abundance of the various minerals plays an important role in defining rock strength. Within the s ample-to-sample variation, no clear influence of oxygen fugacity on creep strength could be discerned for either rock. The dry creep strengths of both rocks are significantly greater than values previously measured on diabase under "as-received" or wet conditions. Application of these results to the present conditions in the lithosphere on Venus predicts a high viscosity crust with strong dynamic coupling between mantle convection and crustal deformation, consistent with measurements of topography and gravity for that planet.

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

1998-01-01

76

Creep deformation and fracture behaviour of a nitrogen-bearing type 316 stainless steel weld metal  

NASA Astrophysics Data System (ADS)

Creep properties of a nuclear grade type 316 stainless steel (SS) weld metal containing 0.08 wt% of nitrogen were studied at 873 and 923 K. These properties were compared with those of a type 316 SS weld metal without nitrogen. In general, the nitrogen-bearing weld metal exhibited better creep and rupture properties. The rupture strengths of the nitrogen-containing weld metal was 40% higher than that for the type 316 SS weld metal at both the temperatures. The steady-state (minimum) creep rates were up to two orders of magnitude lower for the nitrogen-containing weld metal compared to 316 SS weld metal. Rupture ductility of nitrogen-containing weld metal was lower at all the test conditions; the long-term ductility at 923 K was below 5%. The differences in creep behaviour of the two weld metals are discussed with respect to the influence of nitrogen on microstructural evolution in the two weld metals.

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

1999-08-01

77

Damage Accumulation in Aluminum Alloys under Plastic Deformation and Creep  

Microsoft Academic Search

The accumulation of local and bulk damage in D16 AT and 1201 T1 aluminum alloys used in aircraft engineering is studied. The local damage level is calculated from data of thermoactivation\\u000a analysis of the residual life of D16 AT alloy specimens after preliminary plastic deformation. The bulk damage level is determined from the elastic-modulus defect\\u000a by measuring the natural frequency

M. G. Petrov; A. I. Ravikovich

2006-01-01

78

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

79

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

80

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

81

High temperature tensile deformation behavior of Grade 92 steel  

NASA Astrophysics Data System (ADS)

Candidate structural materials for advanced reactors need to have superior high temperature strength and creep-rupture properties among other characteristics. The ferritic-martensitic Grade 92 steel (Fe-9Cr-2W-0.5Mo, wt.%) is considered such a candidate structural material. Tensile tests were performed at temperatures of 600, 650 and 700 C in the strain rate range of 10-5-10-3 s-1. After analyzing the tensile results using the Bird-Mukherjee-Dorn (BMD) equation, a stress exponent of about 9.5 and an activation energy of about 646 kJ/mol were obtained. In the light of high values of the stress exponent and activation energy, the threshold stress concept was used to elucidate the operating high temperature deformation mechanism. As a result of this modification, the true activation energy and stress exponent of the high temperature deformation in Grade 92 steel were found to be about 245 kJ/mol and 5, respectively. Thus, the dominant high temperature deformation mechanism was identified as the high temperature climb of edge dislocations and the appropriate constitutive equation was developed.

Alsagabi, Sultan; Shrestha, Triratna; Charit, Indrajit

2014-10-01

82

A new high-temperature deformation strenthening and toughening process for titanium alloys  

Microsoft Academic Search

A new high-temperature deformation strengthening and toughening process for titanium alloys, which consists of near beta transus forging, rapid water quenching, high-temperature toughening and low-temperature strengthening treatment, has been developed. The materials processed by this method produce a new tri-modal microstructure, which shows a high low-cycle fatigue property, high fatigue-creep interaction life, high fracture toughness and a high service temperature

Y. G. Zhou; W. D. Zeng; H. Q. Yu

1996-01-01

83

A Low-Temperature Creep Experiment Using Common Solder  

NSDL National Science Digital Library

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

Bunnell, L. R.

2012-11-07

84

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.

2013-08-01

85

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

NASA Technical Reports Server (NTRS)

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

Rogers, Jan R.; Hyers, Robert

2008-01-01

86

The high temperature creep properties of alumina composites  

SciTech Connect

Experiments were conducted to determine the creep properties at high temperatures of three different alumina composites containing 9.3, 18 or 30 vol % of SiC whiskers, respectively. Specimens were tested in air in four-point bending with the displacement recorded continuously. The experimental results show the normal three stages of creep, with primary, secondary and tertiary regions. Specimens were pulled to fracture and then examined using scanning electron microscopy. These observations show that the fracture behavior depends upon the volume percentage of SiC whiskers. In the material with 30 vol % SiC whiskers, the fracture surface shows much evidence for whisker pull out; whereas in the material with 9.3 vol % SiC whiskers, there is no evidence for any pull out of the whiskers.

Xia, K. [Comalco Research Centre, Thomastown, Victoria (Australia); Langdon, T.G. [Univ. of Southern California, Los Angeles, CA (United States). Dept. of Materials Science and Mechanical Engineering

1993-12-31

87

HIGH TEMPERATURE CREEP PROPERTIES AND MICROSTRUCTURAL EXAMINATIONS OF P92 WELDS  

E-print Network

1 HIGH TEMPERATURE CREEP PROPERTIES AND MICROSTRUCTURAL EXAMINATIONS OF P92 WELDS Kalck Charlotte1: charlotte.kalck@cea.fr Abstract The present study deals with the creep properties of welded joints made of P surfaces and the microstructural examination of welded joints prior to and after creep tests allow

Paris-Sud XI, Université de

88

The mechanism of creep in gamma prime precipitation-hardened nickel-base alloys at intermediate temperatures  

Microsoft Academic Search

The creep deformation of Mar-M200 single crystals of various orientations has been studied at a temperature of 1400F. It\\u000a was found by a combination of transmission microscopy and analysis of lattice rotations that shear of the ???? structure occurs\\u000a by the glide of loosely coupled intrinsic\\/extrinsic fault pairs with a net Burgers vector ofa . The orientation dependencies of both

Gerald R. Leverant; Bernard H. Kear

1970-01-01

89

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

NASA Astrophysics Data System (ADS)

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

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

1980-04-01

90

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

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

91

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

92

Kb A. et al. Surface Deformation of Creeping Mountain Permafrost ... The 7th International Permafrost Conference, Yellowknife 1998. Proceedings, pp. 531-537  

E-print Network

Kääb A. et al. Surface Deformation of Creeping Mountain Permafrost ... The 7th International Permafrost Conference, Yellowknife 1998. Proceedings, pp. 531-537 SURFACE DEFORMATION OF CREEPING MOUNTAIN PERMAFROST. PHOTOGRAMMETRIC INVESTIGATIONS ON ROCK GLACIER MURT?L, SWISS ALPS. Andreas Kääb1 , G. Hilmar

Kääb, Andreas

93

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

NASA Technical Reports Server (NTRS)

A study of the flow strength, creep resistance and diffusion welding characteristics of the titanium alloy Ti-6Al-2Nb-1Ta-0.8Mo was conducted. Two mill-processed forms of this alloy were examined. The forged material was essentially processed above the beta transus while the rolled form was subjected to considerable work below the beta transus. Between 1150 and 1250 K, the forged material was stronger and more creep resistant than the rolled alloy. Both forms exhibit superplastic characteristics in this temperature range. Strain measurements during diffusion welding experiments at 1200 K reveal that weld interfaces have no measurable effect on the overall creep deformation. Significant deformation appears to be necessary to produce a quality diffusion weld between superplastic materials. A 'soft' interlayer inserted between faying surfaces would seemingly allow manufacture of quality diffusion welds with little overall deformation.

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

1977-01-01

94

Modeling creep deformation of a two-phase TiAl/Ti[sub 3]Al alloy with a lamellar microstructure  

SciTech Connect

A two-phase TiAl/Ti[sub 3]Al alloy with a lamellar microstructure has been previously shown to exhibit a lower minimum creep rate than the minimum creep rates of the constituent TiAl and Ti[sub 3]Al single-phase alloys. Fiducial-line experiments described in the present article demonstrate that the creep rates of the constituent phases within the two-phase TiAl/Ti[sub 3]Al lamellar alloy tested in compression are more than an order of magnitude lower than the creep rates of single-phase TiAl and Ti[sub 3]Al alloys tested in compression at the same stress and temperature. Additionally, the fiducial-line experiments show that no interfacial sliding of the phases in the TiAl/Ti[sub 3]Al lamellar alloy occurs during creep. The lower creep rate of the lamellar alloy is attributed to enhanced hardening of the constituent phases within the lamellar microstructure. A composite-strength model has been formulated to predict the creep rate of the lamellar alloy, taking into account the lower creep rates of the constituent phases within the lamellar microstructure. Application of the model yields a very good correlation between the predicted an experimentally observed minimum creep rates over moderate stress and temperature ranges.

Bartholomeusz, M.F. (Reynolds Metal Co., Richmond, VA (United States)); Wert, J.A. (Univ. of Virginia, Charlottesville, VA (United States). Dept. of Materials Science and Engineering)

1994-10-01

95

Creep of 304 LN and 316 L stainless steels at cryogenic temperatures  

SciTech Connect

Creep behavior of Type 304 LN plate and 316 L shielded-metal-arc (SMA)-deposited stainless weld metal was investigated at 4/sup 0/K. Testing was performed at constant load in a creep machine with a cryostat designed for long-term stability. Both transient and steady-state creep were observed during tests lasting over 2000 hours. Steady-state creep rates were much greater than expected from extrapolations of 300-K creep data. Creep rates on the order of 10/sup -10/ s/sup -1/ were observed at stresses around the yield stress for both materials. The stress exponent under these conditions if approx.2.3. Possible creep mechanisms at this temperature and the impact of these results on the design of engineering structures for long-term structural stability at cryogenic temperatures are discussed.

Roth, L.D.; Manhardt, A.E.; Dalder, E.N.C.; Kershaw, R.P. Jr.

1985-08-07

96

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

97

High temperature deformation characteristics of discontinuous fiber reinforced composites  

SciTech Connect

Role of the geometrical parameters of the fibers and effects of fiber distribution in the matrix on the creep deformation behavior of 20% discontinuous fiber reinforced composite were numerically investigated, including the debonding and fiber pull-out mechanisms. During the analyses in the composite it is assumed that the matrix deforms with a power law creep relationship and the fibers are rigid. The results indicate that for a given fiber geometry and distribution parameters in the matrix, an increase in the interfacial strength or an increase in the work of separation per unit area of interface reduces the secondary creep rates. For even very weak interface characteristics, it is possible to achieve lower secondary creep rates and delayed interface failure by suitable selection of the geometrical parameters of the fibers and by controlling the distribution of the fibers in the matrix.

Biner, S.B. [Ames Lab., IA (United States)

1993-12-31

98

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

NASA Technical Reports Server (NTRS)

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

Haisler, W. E.

1983-01-01

99

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

100

Point defect and diffusion properties in oxides from high temperature creep  

Microsoft Academic Search

A study of high temperature creep properties of non-stoichiometric CU2O, CoO and NiO has been performed at various temperatures and oxygen activities (Po2). Creep rates are directly related to point defects responsible for the diffusion of the slowest species. These point defects have been tentatively identified by the Po2 dependence of creep rate which does not depend on the detailed

A. Dominguez-Rodriguez; J. Castaing

1983-01-01

101

Constitutive Modeling of High Temperature Uniaxial Creep-Fatigue and Creep-Ratcheting Responses of Alloy 617  

SciTech Connect

Inconel Alloy 617 is a high temperature creep and corrosion resistant alloy and is a leading candidate for use in Intermediate Heat Exchangers (IHX) of the Next Generation Nuclear Plants (NGNP). The IHX of the NGNP is expected to experience operating temperatures in the range of 800 degrees - 950 degrees C, which is in the creep regime of Alloy 617. A broad set of uniaxial, low-cycle fatigue, fatigue-creep, ratcheting, and ratcheting-creep experiments are conducted in order to study the fatigue and ratcheting responses, and their interactions with the creep response at high temperatures. A unified constitutive model developed at North Carolina State University is used to simulate these experimental responses. The model is developed based on the Chaboche viscoplastic model framework. It includes cyclic hardening/softening, strain rate dependence, strain range dependence, static and dynamic recovery modeling features. For simulation of the alloy 617 responses, new techniques of model parameter determination are developed for optimized simulations. This paper compares the experimental responses and model simulations for demonstrating the strengths and shortcomings of the model.

P.G. Pritchard; L.J. Carroll; T. Hassan

2013-07-01

102

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

103

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

104

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

NASA Technical Reports Server (NTRS)

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

Maile, K.

1982-01-01

105

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

Microsoft Academic Search

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

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

2010-01-01

106

In-Situ Microtomographic Characterization of Single-Cavity Growth During High-Temperature Creep of Leaded Brass  

NASA Astrophysics Data System (ADS)

Synchrotron microtomography was used for in-situ characterization of high-temperature creep damage in leaded brass. Applying image registration to subsequent tomographic reconstructions, the volumetric growth rate of single cavities with equivalent radii between 2 and 4.3 ?m was assessed. We conclude from the volume dependence of the growth rates that both the viscous flow and grain boundary (GB) diffusion mechanisms influence void growth. We show that void growth in leaded brass is retarded by negative stress triaxiality, which develops in the matrix during heating the specimen to the deformation temperature.

Isaac, A.; Dzieciol, K.; Sket, F.; Borbly, A.

2011-10-01

107

A method of testing carbon materials for radiation creep  

Microsoft Academic Search

Methods of measuring radiation creep of carbon materials in the experimental channels of reactors are described. Equations are proposed for estimating the deformation of transient radiation creep and the rate of steady-state creep as a function of dose and irradiation temperature, as well as the applied load and the strength and anisotropy of the material.

Yu. S. Virgil'ev; Yu. S. Churilov

1976-01-01

108

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

NASA Astrophysics Data System (ADS)

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

Shrestha, Triratna

109

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

110

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

Microsoft Academic Search

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

T. Endo; T. Sakon

1983-01-01

111

Creep behavior of epoxy resin during irradiation at cryogenic temperature  

Microsoft Academic Search

Creep tests of an epoxy resin during bending and irradiation have been carried out to investigate the synergistic effects of radiation and stress on mechanical properties of the resin. Simultaneous application of stress and irradiation on the epoxy resin enhanced creep rates in comparison with the application of stress on an irradiated sample. In order to clarify the mechanism of

Tetsuya Nishiura; Shigehiro Nishijima; Toichi Okada

1999-01-01

112

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

PubMed

Silicon carbide (SiC) matrix composites reinforced by SiC fibres (SiC/SiC composites) are currently being considered as alternative materials in high Ni alloys for high-temperature applications, such as aerospace components, gas-turbine energy-conversion systems and nuclear fusion reactors, because of their high specific strength and fracture toughness at elevated temperatures compared with monolithic SiC ceramics. It is important to evaluate the creep properties of SiC fibres under tensile loading in order to determine their usefulness as structural components. However, it would be hard to evaluate creep properties by monoaxial tensile properties when we have little knowledge on the microstructure of crept specimens, especially at the grain boundary. Recently, a simple fibre bend stress relaxation (BSR) test was introduced by Morscher and DiCarlo to address this problem. Interpretation of the fracture mechanism at the grain boundary is also essential to allow improvement of the mechanical properties. In this paper, effects of stress applied by BSR test on microstructural evolution in advanced SiC fibres, such as Tyranno-SA including small amounts of Al, are described and discussed along with the results of microstructure analysis on an atomic scale by using advanced microscopy. PMID:12741492

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

2003-01-01

113

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

114

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

NASA Astrophysics Data System (ADS)

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 316L(N) SS exhibited better resistance to creep deformation compared to their 316 SS 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 ? 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 ? ferrite transformation behavior and coarsening kinetics is also discussed, on the basis of extensive characterization by metallographic techniques.

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

2000-04-01

115

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

116

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

NASA Astrophysics Data System (ADS)

Around the perimeter of Antarctica, much of the ice sheet discharges to the ocean through floating ice shelves. The buttressing provided by ice shelves is critical for modulating the flux of ice into the ocean, and the presently observed thinning of ice shelves is believed to be reducing their buttressing capacity and contributing to the acceleration and thinning of the grounded ice sheet. However, relatively little attention has been paid to the role that fractures play in the ability of ice shelves to sustain and transmit buttressing stresses. Here, we present a new framework for quantifying the role that fractures play in the creep deformation and buttressing capacity of ice shelves. We apply principles of continuum damage mechanics to derive a new analytical relation for the creep of an ice shelf that accounts for the softening influence of fractures on longitudinal deformation using a state damage variable. We use this new analytical relation, combined with a temperature calculation for the ice, to partition an inverse method solution for ice shelf rigidity into independent solutions for softening damage and stabilizing backstress. Using this new approach, field and remote sensing data can be utilized to monitor the structural integrity of ice shelves, their ability to buttress the flow of ice at the grounding line, and thus their indirect contribution to ice sheet mass balance and global sea level. We apply this technique to the Larsen C ice shelf using remote sensing and Operation IceBridge data, finding damage in areas with known crevasses and rifts. Backstress is highest near the grounding line and upstream of ice rises, in agreement with patterns observed on other ice shelves. The ice in contact with the Bawden ice rise is weakened by fractures, and additional damage or thinning in this area could diminish the backstress transmitted upstream. We model the consequences for the ice shelf if it loses contact with this small ice rise, finding that flow speeds would increase by 25% or more over an area the size of the former Larsen B ice shelf. Such a perturbation could potentially destabilize the northern part of Larsen C along pre-existing lines of weakness, highlighting the importance of the feedback between buttressing and fracturing in an ice shelf.

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

2013-12-01

117

Method for determining the temperature dependence of subcritical creep crack growth of a material  

SciTech Connect

The actual operating conditions of power generating elements and parts of thermoelectric power stations, such as rotor or turbine body parts, are characterized by long-term action of temperature-load loading fields whose levels can vary in operation. In assessing their long-term working ability, the authors develop an engineering method of plotting the temperature dependence describing the kinematics of subcritical creep crack growth in materials on the basis of the criteria of fracture mechanics. Proposed here, on the basis of known approaches, is a calculation-experimental method for plotting the determining temperature relations of subcritical creep crack growth on the basis of polynomial type approximations enabling to obtain an adequate description of experiments on crack resistance under creep within a wide variation field of the temperature-load loading conditions. As an example illustrating the method discussed, the temperature dependence of subcritical creep crack growth in the 15Kh1M1FL steel is determined.

Baumshtein, M.V.

1987-03-01

118

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

119

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

SciTech Connect

Gamma TiAl is a strong candidate material for the replacement of many Ni-based superalloys in advanced gas turbine jet engines. Although gamma TiAl is targeted specifically as a high temperature material, it must also be able to demonstrate reasonable toughness such as measured by impact resistance and must demonstrate reasonable crack growth resistance under cyclic deformation conditions. Of course the main attractive feature of gamma TiAl is that its high temperature creep deformation resistance and damage tolerance is high. There are three basic microstructures which may be produced in gamma TiAl depending on composition and heat treatment. These microstructures and their corresponding properties have recently been discussed extensively by Huang and Hall and Huang. Briefly, the three microstructures are a duplex microstructure consisting of a mixture of lamellar grains containing alternate laths of alpha-2 (Ti{sub 3}Al) and gamma (TiAl) and equiaxed primary gamma grains, a fully transformed structure consisting only of coarse (d > 500{micro}m) lamellar grains and a single phase gamma structure consisting only of equiaxed gamma TiAl grains. In a recent article on microstructure-property tradeoffs in wrought TiAl, Huang has suggested that an optimum balance of each of the properties cited above may be obtained by producing a fully transformed lamellar structure but with a finer grain size than those produced by heat treatment of the two phase TiAl alloys above the alpha transus. Preliminary investigations of the uniaxial tensile properties and the fracture toughness of a fine grained fully transformed TiAl alloy Ti-48Al-2Mn-2Nb have demonstrated very promising results. However, the high temperature creep deformation and damage behavior of this material has yet to be evaluated. The intent of this paper is to present a first report on the high temperature creep deformation and damage behavior of the fine grained fully transformed Ti-48Al-2Mn-2Nb alloy.

Hayes, R.W. [Metals Technology, Inc., Northridge, CA (United States)] [Metals Technology, Inc., Northridge, CA (United States); McQuay, P.A. [AF Material Command/USAF, Tokyo (Japan). AFOSR/Asian Office of Aerospace Research] [AF Material Command/USAF, Tokyo (Japan). AFOSR/Asian Office of Aerospace Research

1994-01-15

120

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

NASA Technical Reports Server (NTRS)

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

Sheffler, K. D.

1970-01-01

121

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

122

ME 354, MECHANICS OF MATERIALS LABORATORY TIME-DEPENDENT DEFORMATION: CREEP  

E-print Network

-weight," lever arm creep test machine. · Various "dead-weight" masses of 0.5, 1.0, 2.0 and 5.0 kg. · Timing test specimen in the top grip of a creep test machine. · Install the bottom end of the test specimen in the lower grip of the creep test machine and measure the initial gripped length, Lo, of the test specimen

Sniadecki, Nathan J.

123

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

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

124

Effect of creep in titanium alloy Ti-6Al-4V at elevated temperature on aircraft design and flight test  

NASA Technical Reports Server (NTRS)

Short-term compressive creep tests were conducted on three titanium alloy Ti-6Al-4V coupons at three different stress levels at a temperature of 714 K (825 F). The test data were compared to several creep laws developed from tensile creep tests of available literature. The short-term creep test data did not correlate well with any of the creep laws obtained from available literature. The creep laws themselves did not correlate well with each other. Short-term creep does not appear to be very predictable for titanium alloy Ti-6Al-4V. Aircraft events that result in extreme, but short-term temperature and stress excursions for this alloy should be approached cautiously. Extrapolations of test data and creep laws suggest a convergence toward predictability in the longer-term situation.

Jenkins, J. M.

1984-01-01

125

Temperature dependence of optically induced cell deformations  

NASA Astrophysics Data System (ADS)

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

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

2012-02-01

126

Effect of defect structure during irradiation on the deformation of metals. II. Radiative creep  

Microsoft Academic Search

The dose dependence of radiative creep of metals has been studied with account for the evolution of accumulations of point defects induced by radiation. Several possible mechanisms of creep were considered and among those some have been found to predominate at various stages of irradiation. It was observed that vacancy loops play a decisive role in the formation of the

Y. Pyatiletov; V. Kirsanov

1981-01-01

127

High-temperature creep behavior of second-phase particle-strengthened tungsten-rhenium alloys  

SciTech Connect

The creep behavior of W{sup {minus}4}Re{sup {minus}0}.26HfC, W{sup {minus}3}.6Re{sup {minus}1}ThO{sub 2}, W{sup {minus}11}Re{sup {minus}1}ThO{sub 2}, and W{sup {minus}26}Re{sup {minus}1}ThO{sub 2} alloys were evaluated at elevated temperatures (between 1955 and 2500 K) in a custom-built high vacuum creep testing facility. These alloys are promising emitter materials for the Thermionic Energy Converter. The effects of stress and temperature on the creep rate of these alloys were determined and the stress exponents and creep activation energies of these alloys were measured. Results showed that HfC particles have a very high strengthening effect on the W{sup {minus}4}Re matrix up to 2200 K. At temperatures higher than 2200 K the coarsening rate of HfC is so high that they lose their strengthening effect rapidly. Comparing the creep strength of the arc-melted W{sup {minus}4}Re{sup {minus}0}.26HfC with that of the P/M W-Re{sup {minus}1}ThO{sub 2} alloys, it was found that at temperatures less than or equal to 2200 K, W{sup {minus}4}Re{sup {minus}0}.26HfC has the highest creep.

Chen, Borliang.

1990-01-01

128

The Fabric of Clasts, Veins and Foliations within the Actively Creeping Zones of the San Andreas Fault at SAFOD: Implications for Deformation Processes  

E-print Network

reflects active creep along two strands of the San Andreas Fault (SAF) at SAFOD. The two fault strands are referred to as the Southwest Deforming Zone (SDZ) at 3194 m measured depth (MD) and the Central Deforming Zone (CDZ) at 3301 m MD. The SDZ and CDZ...

Sills, David Wayne

2012-02-14

129

Low Temperature Creeps and Delay Times in Iron of Very Low Carbon Content  

Microsoft Academic Search

The creep curves of wet-hydrogen-treated polycrystalline irons were obtained in the range of temperature 350-77K. A rapid load testing machine, which has the same principle as Clark-Wood machine, was used for the creep tests. Delay times were observed in the range of the time 10-2--103 seconds. Observed results is analysed with the use of the strain rate equation, \\\\dot{\\\\varepsilon}{=}bnv. It

Tomoyuki Takeuchi; Shozo Ikeda

1963-01-01

130

Irradiation creep in structural materials at ITER operating conditions  

SciTech Connect

Irradiation creep is plastic deformation of a material under the influence of irradiation and stress. Below the regime of thermal creep, there remains a deformation mechanism under irradiation that is weakly temperature dependent and clearly different from thermal creep. This is irradiation creep. Both stress and irradiation are required for irradiation creep. Irradiation creep studies for applications in the past focused mostly on liquid metal fast breeder reactors where temperatures are usually above 400{degrees}C. Fusion reactors, especially nearterm devices such as the ITER will have components operating at temperatures as low as 100{degrees}C exposed to high neutron fluxes. Theories of irradiation creep based on steady-state point defect concentrations do not predict significant irradiation creep deformation at these temperatures; however, data from research reactors show that irradiation creep strains at 60{degrees}C are as high or higher than at temperatures above 300{degrees}C for austenitic stainless steels. Irradiation creep of nickel has also been observed at cryogenic temperatures.

Grossbeck, M.L.

1994-09-01

131

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

2008-01-01

132

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

133

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

NASA Technical Reports Server (NTRS)

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

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

1989-01-01

134

Apparent activation volume for creep of copper and alpha brass at intermediate temperatures  

NASA Technical Reports Server (NTRS)

Experimental measurements of the apparent activation volume for creep, V-asterisk, of Cu and Cu-30 pct Zn conducted at intermediate temperatures showed two types of strain dependencies. At the lower temperatures and higher stresses, V-asterisk decreased with increasing creep strain, while at higher temperatures and lower stresses, V-asterisk was essentially independent of strain. The low temperature-high stress behavior for Cu and Cu-30 pct Zn was found to be consistent with the dominance of a dislocation intersection mechanism. The high temperature-low stress data for the pure metals suggest that the rate-controlling process involves the nonconservative motion of jogs on screw dislocations. For the latter conditions, an additional contribution from solute drag-limited dislocation glide also appears to be important in governing the creep behavior of the alloy.

Raj, S. V.

1989-01-01

135

The Creep of Single Crystals of Aluminum  

NASA Technical Reports Server (NTRS)

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

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

1953-01-01

136

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

NASA Technical Reports Server (NTRS)

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

Zimmerman, Richard S.; Adams, Donald F.

1989-01-01

137

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

NASA Technical Reports Server (NTRS)

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

Zimmerman, Richard S.; Adams, Donald F.

1988-01-01

138

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

139

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

NASA Technical Reports Server (NTRS)

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

Whittenberger, J. D.

1977-01-01

140

Creep damage of Ni-base superalloys in helium gas at very high temperatures  

SciTech Connect

The present paper investigates creep damage of two different types of advanced Ni-base superalloys, i.e., Hastelloy XR and Inconel MA 754 at very high temperatures of up to 1,273 K in impure helium gas, simulated environment of Japanese high-temperature gas-cooled reactors. Creep strength was much higher in MA 754 than in XR at 1,273 K. MA 754 fabricated via mechanical alloying, however, showed drastic decrease in creep strength in longer life region. MA 754 also showed anisotropic creep rupture behavior with longer lives in the longitudinal or extruding direction than in the long-transversal direction. This anisotropy is attributed to grains elongated in the extruding direction. Statistical evaluation of the creep damage was made on ruptured specimens by using the A-parameter. Although this parameter is usually treated as a deterministic one, its values showed wide variations and followed two-parameter Weibull distributions in both alloys, reflecting spatial randomness of creep damage. The mean of the parameter A{sub m} remained almost constant in XR alloy. It showed different behavior in the two types of MA 754 specimens; i.e., it was increased in the longitudinal type of specimens whereas decreased in the long-transversal type ones with increasing applied stress level. This tendency was elucidated to arise from the anisotropy of elongated grains in MA 754. It is also found that maximum percent damaged grains reached as high as 20% in as-received MA 754 material.

Nakasone, Yuji [Science Univ. of Tokyo (Japan); Mutoh, Isao; Tanabe, Tatsuhiko [National Research Inst. for Metals, Tsukuba, Ibaraki (Japan)

1995-12-31

141

The influence of temperature on brittle creep in sandstones  

Microsoft Academic Search

The characterization of time-dependent brittle rock deformation is fundamental to understanding the long-term evolution and dynamics of the Earth's upper crust. The presence of water promotes time-dependent deformation through environment-dependent stress corrosion cracking that allows rocks to deform at stresses far below their short-term failure stress. Here we report results from an experimental study of the influence of an elevated

M. J. Heap; P. Baud; P. G. Meredith; S. Vinciguerra

2009-01-01

142

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

SciTech Connect

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

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

2014-01-01

143

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

NASA Astrophysics Data System (ADS)

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

Trepmann, Claudia

2014-05-01

144

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

NASA Technical Reports Server (NTRS)

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

Mathauser, Eldon E; Deveikis, William D

1957-01-01

145

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

146

Damage Susceptibility of Grain Boundaries in HT9 Steel Subjected to High-Temperature Creep  

NASA Astrophysics Data System (ADS)

HT9 steel is an attractive ferritic/martensitic steel that is used in components of nuclear and fossil power plants because of its high strength and good swelling resistance. Specific phenomena (such as segregation, voiding, cracking, etc.) are prevalent along grain boundaries since these interfaces act as efficient sources for vacancies. The accumulation of vacancies in grain boundaries may result in intergranular fracture. In this study, HT9 steel was subjected to creep tests at elevated temperature (about 0.5 T m) and two different creep conditions (where creep lifetimes were about 100 and about 1000 hours, respectively). The grain boundaries in HT9 steel after creep tests were studied by the use of scanning electron microscopy in order to establish the relationship between the grain boundary structure and creep damage. Images and data obtained using electron backscatter diffraction reveal a high susceptibility of high-angle boundaries to creep cavitation, as expected. In addition, the ?3 boundaries are also susceptible to damage under these conditions at a similar or even higher rate as compared with random high-angle boundaries.

Leng, Zhe; Field, David P.

2012-10-01

147

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

SciTech Connect

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

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

1990-01-01

148

Deformation properties of finnish spruce and pine wood in tangential and radial directions in association to high temperature drying  

Microsoft Academic Search

The set of papers sums up the results of an extensive project to quantify primarily the creep characteristics but also other\\u000a deformation properties of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) wood under conditions relevant in the high temperature drying process. The programme included tension experiments on tan-gentially\\u000a and radially oriented specimens both under wet (saturated, green) conditions

A. Hanhijrvi

1998-01-01

149

The deformation mechanisms of superplasticity  

Microsoft Academic Search

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

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

1972-01-01

150

Analyzing irradiation -induced creep of silicon carbide  

SciTech Connect

Irradiation creep, which is among the major lifetime-limiting mechanisms for nuclear structural materials, is stress-driven anisotropic plastic deformation occurring in excess of thermal creep deformation in radiation environments. In this work, experimental irradiation creep data for beta-phase silicon carbide (SiC) irradiated at intermediate temperatures is analyzed using a kinetic model with an assumed linear-coupling of creep strain rate with the rate of self interstitial atom (SIA) absorption at SIA clusters. The model reasonably explains the experimentally observed time-dependent creep rate of ion-irradiated SiC and swelling evolution of ion- and neutron-irradiated SiC. Bend stress relaxation behavior during irradiation was then simulated using the developed model to examine the experimental data obtained by neutron irradiation experiments. Recommended directions of future experiment are provided to further verify and improve the models and assumptions in this work.

Katoh, Yutai [ORNL; Snead, Lance Lewis [ORNL; Golubov, Stanislav I [ORNL

2007-01-01

151

Influence of deformation temperature on texture evolution in HPT deformed NiAl  

NASA Astrophysics Data System (ADS)

NiAl is an intermetallic compound with a brittle-to-ductile transition temperature at about 300C and ambient pressure. At standard conditions, it is very difficult to deform, but fracture stress and fracture strain are increased under high hydrostatic pressure. On account of this, deformation at low temperatures is only possible at high hydrostatic pressure, as for instance used in high pressure torsion. In order to study the influence of temperature on texture evolution, small discs of polycrystalline NiAl were deformed by high pressure torsion at temperatures ranging from room temperature to 500C. At room temperature, a typical shear texture of body centred cubic metals is found, while at 500C a strong oblique cube component dominates. These textures can be well simulated with the viscoplastic self-consistent polycrystal deformation model using the primary and secondary slip systems activated at low and high temperatures. The oblique cube component is a dynamic recrystallization component.

Trnkner, C.; Chulist, R.; Skrotzki, W.; Beausir, B.; Lippmann, T.; Horky, J.; Zehetbauer, M.

2014-08-01

152

Nanogranular origin of concrete creep  

PubMed Central

Concrete, the solid that forms at room temperature from mixing Portland cement with water, sand, and aggregates, suffers from time-dependent deformation under load. This creep occurs at a rate that deteriorates the durability and truncates the lifespan of concrete structures. However, despite decades of research, the origin of concrete creep remains unknown. Here, we measure the in situ creep behavior of calciumsilicatehydrates (CSH), the nano-meter sized particles that form the fundamental building block of Portland cement concrete. We show that CSH exhibits a logarithmic creep that depends only on the packing of 3 structurally distinct but compositionally similar CSH forms: low density, high density, ultra-high density. We demonstrate that the creep rate (?1/t) is likely due to the rearrangement of nanoscale particles around limit packing densities following the free-volume dynamics theory of granular physics. These findings could lead to a new basis for nanoengineering concrete materials and structures with minimal creep rates monitored by packing density distributions of nanoscale particles, and predicted by nanoscale creep measurements in some minute time, which are as exact as macroscopic creep tests carried out over years. PMID:19541652

Vandamme, Matthieu; Ulm, Franz-Josef

2009-01-01

153

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

Microsoft Academic Search

A theoretical model has been developed using the reaction rate theory of radiation effects to explain experimental results that showed higher than expected values of irradiation creep at low temperatures in the Oak Ridge Research Reactor. The customary assumption that the point defect concentrations are at steady state was not made; rather, the time dependence of the vacancy and interstitial

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

1990-01-01

154

TEMPERATURE DEPENDENT CREEP EXPANSION OF Ti-6Al-4V LOW DENSITY CORE SANDWICH STRUCTURES  

E-print Network

TEMPERATURE DEPENDENT CREEP EXPANSION OF Ti-6Al-4V LOW DENSITY CORE SANDWICH STRUCTURES Douglas T The application of lightweight, structurally efficient metal based honeycomb structures has been limited for the low cost manufacture of porous metal sandwich structures. These porous cored sandwich structures

Wadley, Haydn

155

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

SciTech Connect

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

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

2014-01-01

156

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

NASA Technical Reports Server (NTRS)

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

1995-01-01

157

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

158

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

159

Comparative study of creep of the die-cast Mg-alloys AZ91, AS21, AS41, AM60 and AE42  

Microsoft Academic Search

The creep resistance of five high-purity die-cast MgAl-alloys was investigated in uniaxial compression at temperatures from 70 to 150C. The evolution of deformation resistance under creep conditions is described as a function of strain ?. The work hardening in primary creep determines the times for creep by strains <0.01. Among the investigated alloys AZ91 has the highest creep resistance with

W Blum; P Zhang; B Watzinger; B. v Grossmann; H. G Haldenwanger

2001-01-01

160

Steady-state creep of bent reinforced metal-composite plates with consideration of their reduced resistance to transverse shear. 1. Deformation model  

NASA Astrophysics Data System (ADS)

The problem of deformation of reinforced metal-composite plates is formulated in rectangular Cartesian coordinates using the second version of Timoshenko theory and taking into account the reduced transverse shear resistance of the plates under steady-state creep conditions. A similar model problem of axisymmetric bending of reinforced plates is considered in polar coordinates.

Yankovskii, A. P.

2014-05-01

161

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

PubMed

Today, rapid economic and industrial growth generates increasing amounts of waste materials such as waste tyre rubber. Attempts to inspire a green technology which is more environmentally friendly that can produce economic value are a major consideration in the utilization of waste materials. The aim of this study is to evaluate the effect of waste tyre rubber (crumb rubber modifier (CRM)), in stone mastic asphalt (SMA 20) performance. The virgin bitumen (80/100) penetration grade was used, modified with crumb rubber at four different modification levels, namely, 6%, 12%, 16%, and 20% by weight of the bitumen. The testing undertaken on the asphalt mix comprises the indirect tensile (dynamic stiffness), dynamic creep, and wheel tracking tests. By the experimentation, the appropriate amount of CRM was found to be 16% by weight of bitumen. The results show that the addition of CRM into the mixture has an obvious significant effect on the performance properties of SMA which could improve the mixture's resistance against permanent deformation. Further, higher correlation coefficient was obtained between the rut depth and permanent strain as compared to resilient modulus; thus dynamic creep test might be a more reliable test in evaluating the rut resistance of asphalt mixture. PMID:24302883

Mashaan, Nuha Salim; Karim, Mohamed Rehan

2013-01-01

162

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

PubMed Central

Today, rapid economic and industrial growth generates increasing amounts of waste materials such as waste tyre rubber. Attempts to inspire a green technology which is more environmentally friendly that can produce economic value are a major consideration in the utilization of waste materials. The aim of this study is to evaluate the effect of waste tyre rubber (crumb rubber modifier (CRM)), in stone mastic asphalt (SMA 20) performance. The virgin bitumen (80/100) penetration grade was used, modified with crumb rubber at four different modification levels, namely, 6%, 12%, 16%, and 20% by weight of the bitumen. The testing undertaken on the asphalt mix comprises the indirect tensile (dynamic stiffness), dynamic creep, and wheel tracking tests. By the experimentation, the appropriate amount of CRM was found to be 16% by weight of bitumen. The results show that the addition of CRM into the mixture has an obvious significant effect on the performance properties of SMA which could improve the mixture's resistance against permanent deformation. Further, higher correlation coefficient was obtained between the rut depth and permanent strain as compared to resilient modulus; thus dynamic creep test might be a more reliable test in evaluating the rut resistance of asphalt mixture. PMID:24302883

Mashaan, Nuha Salim; Karim, Mohamed Rehan

2013-01-01

163

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

164

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

NASA Technical Reports Server (NTRS)

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

Gates, Thomas S.; Feldman, Mark

1994-01-01

165

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

Microsoft Academic Search

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

Bimal K. Kad; James H. Heatherington; C. McKamey; I. Wright; V. Sikka; R. Judkins

2003-01-01

166

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

167

Technological characteristics of creep-feed grinding. Raised cutting forces and reduced work piece temperatures, part 2  

NASA Astrophysics Data System (ADS)

Temperature measurement during creep feed and oscillating bed grinding and lubrication during deep cut grinding are discussed. A method of determining heat effects on workpiece surface layers during deep cut grinding is outlined. Results indicate that low surface temperatures occur in creep feed and oscillating bed grinding, but very high temperatures are recorded for the intervening regime. The exit velocity of lubricant from the feed nozzle must equal the grinding wheel circumferential velocity to avoid clogging.

Werner, P.; Minke, E.

1982-07-01

168

Investigation of {gamma}/{gamma}{prime} lattice mismatch in the polycrystalline nickel-base superalloy IN738LC: Influence of heat treatment and creep deformation  

SciTech Connect

The {gamma}/{gamma}{prime} lattice misfit in the polycrystalline nickel-base superalloy IN738LC has been determined by convergent beam electron diffraction (CBED) technique in a transmission electron microscope (TEM). The influence of heat treatment and creep deformation on the misfit was investigated. The chemical compositions of the {gamma} and {gamma}{prime} phases were analyzed with the help of Energy Dispersive Spectrometry (EDS). The influence of different heat treatments on the {gamma}/{gamma}{prime} misfit can be explained in terms of the dependence of the chemical compositions of {gamma} and {gamma}{prime} phases on the heat treatments. The creep deformation causes a tetragonal distortion in {gamma}{prime} precipitates and leads to considerable changes in the misfit. The tetragonality in {gamma}{prime} phase and the evolution of the misfit during creep process can be understood on the basis of a dislocation model. An estimation of the local internal stress in {gamma}{prime} phase generated by {gamma}/{gamma}{prime} interfacial dislocations formed during creep deformations shows it to be higher than the applied stress.

Li, J.; Wahi, R.P. [Hahn-Meitner-Inst. Berlin GmbH (Germany)] [Hahn-Meitner-Inst. Berlin GmbH (Germany)

1995-02-01

169

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

170

On the formation of ?010?-dislocations in the ??-phase of superalloy single crystals during high temperature low stress creep  

Microsoft Academic Search

The cutting of ??-particles by dislocations during shear creep deformation of CMSX 6 superalloy single crystals loaded on the macroscopic crystallographic shear system ?110?{111} at T = 1025C and ? = 85 MPa is analysed using transmission electron microscopy (TEM). The formation of a ?010?-dislocation in the ??-phase was observed and investigated by means of stereo microscopy, line trace andgb-analysis.

G. Eggeler; A. Dlouhy

1997-01-01

171

High-temperature deformation of diposide crystal 3. Influences of pO2 and SiO2 precipitation  

Microsoft Academic Search

Single crystals of gem quality diopside [with Fe\\/(Ca+Mg+Fe)~=0.02] were deformed in a dead load apparatus under controlled oxygen partial pressure (pO2), in the range 810-14-210-9 MPa, at two temperatures T1=1100C and T2=1200C. The aim of these experiments was to investigate the sensitivity of diopside creep rate to pO2 at these two temperatures. T1 and T2 are on both sides of

Olivier Jaoul; Paul Raterron

1994-01-01

172

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

NASA Astrophysics Data System (ADS)

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

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

2014-12-01

173

Dynamic recrystallization of olivine single crystals during high-temperature creep  

Microsoft Academic Search

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

Shun-ichiro Karato; Mitsuhiro Toriumi; Toshitsugu Fujii

1980-01-01

174

Creep Laboratory manual  

Microsoft Academic Search

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

S. Osgerby; M. S. Loveday

1992-01-01

175

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

176

Creep of plasma sprayed zirconia  

NASA Technical Reports Server (NTRS)

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

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

1982-01-01

177

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

178

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

PubMed

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

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

2014-01-01

179

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

NASA Astrophysics Data System (ADS)

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

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

2014-10-01

180

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

NASA Astrophysics Data System (ADS)

The irradiation creep behavior of nano-powder sintered silicon carbide was investigated using the bend stress relaxation method under neutron irradiation up to 1.9 dpa. The creep deformation was observed at all temperatures ranging from 380 to 1180 C mainly from the irradiation creep but with the increasing contributions from the thermal creep at higher temperatures. The apparent stress exponent of the irradiation creep slightly exceeded unity, and instantaneous creep coefficient at 380-790 C was estimated to be ?1 10-5 [MPa-1 dpa-1] at ?0.1 dpa and 1 10-7 to 1 10-6 [MPa-1 dpa-1] at ?1 dpa. The irradiation creep strain appeared greater than that for the high purity SiC. Microstructural observation and data analysis indicated that the grain-boundary sliding associated with the secondary phases contributes to the irradiation creep at 380-790 C to 0.01-0.11 dpa.

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

2014-12-01

181

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

NASA Astrophysics Data System (ADS)

Creep behavior of Al-Si hypereutectic alloys inoculated with phosphorus was investigated using the impression creep testing. The results showed that at stress regimes of up to 400-450 MPa and temperatures up to 300 C, no significant creep deformation occurred in both uninoculated and inoculated specimens; however, at temperatures above 300 C, the inoculated alloys presented better creep properties. Creep data were used to calculate the stress exponent of steady-state creep rate, n, and creep activation energy, Q, for different additive conditions where n was found varied between 5 and 8. Owing to the fact that most alloys have lower values for n (4, 5), threshold stress was estimated for studied conditions. The creep governing mechanisms for different conditions are discussed here, with a particular attention to the effect of phosphorous addition on the microstructural features, including number of primary silicon particles, mean primary silicon spacing, and morphology and distribution of eutectic silicon.

Faraji, Masoumeh; Khalilpour, Hamid

2014-10-01

182

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

NASA Technical Reports Server (NTRS)

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

Hebsur, Mohan G.; Miner, Robert V.

1987-01-01

183

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

184

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

SciTech Connect

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

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

2013-02-01

185

Deformation of FeAl single crystals at high temperatures  

Microsoft Academic Search

Single crystals of the intermetallic compound FeAl with the CsCl structure have been deformed in compression at temperatures between 470 and 1000 K to study the slip geometry and the dislocation arrangements in this material at high temperatures. At temperatures below 044 of the melting temperature, Tm, slip occurs on the {110}?111? systems, while at 044Tm, the transitions in the

Y. Umakoshi; M. Yamaguchi

1980-01-01

186

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

187

Cavitation contributes substantially to tensile creep in silicon nitride  

SciTech Connect

During tensile creep of a hot isostatically pressed (HIPed) silicon nitride, the volume fraction of cavities increases linearly with strain; these cavities produce nearly all of the measured strain. In contrast, compressive creep in the same stress and temperature range produces very little cavitation. A stress exponent that increases with stress ({dot {var_epsilon}} {proportional_to} {sigma}{sup n}, 2 < n < 7) characterizes the tensile creep response, while the compressive creep response exhibits a stress dependence of unity. Furthermore, under the same stress and temperature, the material creeps nearly 100 times faster in tension than in compression. Transmission electron microscopy (TEM) indicates that the cavities formed during tensile creep occur in pockets of residual crystalline silicate phase located at silicon nitride multigrain junctions. Small-angle X-ray scattering (SAXS) from crept material quantifies the size distribution of cavities observed in TEM and demonstrates that cavity addition, rather than cavity growth, dominates the cavitation process. These observations are in accord with a model for creep based on the deformation of granular materials in which the microstructure must dilate for individual grains t slide past one another. During tensile creep the silicon nitride grains remain rigid; cavitation in the multigrain junctions allows the silicate to flow from cavities to surrounding silicate pockets, allowing the dilation of the microstructure and deformation of the material. Silicon nitride grain boundary sliding accommodates this expansion and leads to extension of the specimen. In compression, where cavitation is suppressed, deformation occurs by solution-reprecipitation of silicon nitride.

Luecke, W.E.; Wiederhorn, S.M.; Hockey, B.J.; Krause, R.F. Jr.; Long, G.G. [National Institute of Standards and Technology, Gaithersburg, MD (United States)

1995-08-01

188

High temperature deformation of hot-pressed polycrystalline orthoenstatite. Ph.D. Thesis  

NASA Technical Reports Server (NTRS)

Artificial hot pressed polycrystalline samples were prepared from purified powder of Bamble, Norway, orthoenstatite, (Mg0.86Fe0.14)SiO3. The uniaxial creep behavior of the polycrystalline orthoenstatite was studied over stress ranges of 10-180 MPa and temperatures of 1500-1700 K (0.82-0.93 T sub m) under two different oxygen fugacities, namely equilibrium (Mo-MoO2 buffer) and a reducing (graphite heating element) atmosphere, respectively. An intergranular glassy phase of different compositions with a cavitational creep deformation were observed. In the Mo-MoO2 buffer atmosphere with PO2 approx. 10 to the minus 11 power - 10 to the minus 13 power atmospheres, the results of an analytical electron microscopy analysis indicate that the glassy phases are richer in Ca and Al due to the residual impurities after hot pressing. In the reducing atmosphere with an oxygen fugacity of PO2 approx. 10 to the minus 3 power - 10 to the minus 25 power atmospheres, the results of analytical electron microscopy analysis indicate that the glassy phase is almost pure silica with the presence of free iron precipitate on grain facets and at triple junctions due to the reduction of bulk materials.

Dehghan-Banadaki, A.

1983-01-01

189

Development of simple model for creep analysis of thick welded joints (1st report): Creep characteristics of thick welded joints and their improvement  

Microsoft Academic Search

To ensure the safety of high?temperature facilities, such as fast breeder reactors, throughout their service life, it is necessary to be able to predict their creep deformation with sufficient accuracy. The welds produced in the thick plates of these facilities have an extremely complex thermal history and therefore extremely in?homogeneous characteristics, including creep behaviour. This makes it difficult and laborious

K. Nakacho; Y. Ueda; J. Kinugawa; M. Yamazaki

1994-01-01

190

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

191

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

Microsoft Academic Search

The influence of initial ?? size and shape on the high temperature creep properties of two single crystal nickel-base superalloys\\u000a was investigated. The two alloys were chosen to represent different magnitudes of ?-?? lattice mismatch. A range of initial\\u000a microstructures was produced by various quenching and aging treatments. Creep-rupture testing at 1000 C was performed under\\u000a stresses where ?? directionally

M. V. Nathal

1987-01-01

192

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

NASA Technical Reports Server (NTRS)

An experimentally based unified creep-plasticity constitutive model was implemented for 1070 steel. Accurate rate and temperature effects were obtained for isothermal and thermo-mechanical loading by incorporating deformation mechanisms into the constitutive equations in a simple way.

Slavik, D.; Sehitoglu, H.

1988-01-01

193

New ironaluminium alloy with thermally stable coherent intermetallic nanoprecipitates for enhanced high-temperature creep strength  

Microsoft Academic Search

Poor ductility and strength at high temperatures, especially under slow strain rate or creep conditions, have prevented the use of ironaluminium alloys or aluminide intermetallics, despite decades of intensive research. The low strength at high temperature is due to the inability of hardening particles such as carbides to resist dissolution or coarsening at these temperatures. A new ironaluminium alloy with

D. G. Morris; M. A. Muoz-Morris; L. M. Requejo

2006-01-01

194

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

2008-12-01

195

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

196

Two-temperature continuum thermomechanics of deforming amorphous solids  

E-print Network

There is an ever-growing need for predictive models for the elasto-viscoplastic deformation of solids. Our goal in this paper is to incorporate recently developed out-of-equilibrium statistical concepts into a thermodynamically consistent, finite-deformation, continuum framework for deforming amorphous solids. The basic premise is that the configurational degrees of freedom of the material --- the part of the internal energy/entropy that corresponds to mechanically stable microscopic configurations --- are characterized by a configurational temperature that might differ from that of the vibrational degrees of freedom, which equilibrate rapidly with an external heat bath. This results in an approximate internal energy decomposition into weakly interacting configurational and vibrational subsystems, which exchange energy following a Fourier-like law, leading to a thermomechanical framework permitting two well-defined temperatures. In this framework, internal variables that carry information about the state of the material equilibrate with the configurational subsystem, are explicitly associated with energy and entropy of their own, and couple to a viscoplastic flow rule. The coefficients that determine the rate of flow of entropy and heat between different internal systems are proposed to explicitly depend on the rate of irreversible deformation. As an application of this framework, we discuss two constitutive models for the response of glassy materials, a simple phenomenological model and a model related to the concept of Shear-Transformation-Zones as the basis for internal variables. The models account for several salient features of glassy deformation phenomenology. Directions for future investigation are briefly discussed.

Ken Kamrin; Eran Bouchbinder

2014-01-06

197

Newtonian dislocation creep in quartzites. Implications for the rheology of the lower crust  

Microsoft Academic Search

Mechanical and microstructural evidence indicates that a natural and a synthetic quartzite deformed by Newtonian dislocation (Harper-Dorn) creep at temperatures higher than 1073 K and stresses lower than 300 megapascals. The observation of this creep in these materials suggests that the lower crust may flow like a Newtonian viscous fluid by a dislocation mechanism at stresses much smaller than those

J. N. Wang; B. E. Hobbs; A. Ord; T. Shimamoto; M. Toriumi

1994-01-01

198

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

199

Plastic deformation of nickel single crystals at low temperatures  

Microsoft Academic Search

Single crystals of nickel (purities 99.98% and 99.4%) have been deformed in tension at various temperatures between 4.2K and 300K. Shear stress-shear strain relations have been determined as well as the reversible change of flow stress with temperature. The work-hardening parameters obtained are discussed in terms of dislocation theory that has been developed mainly on the basis of data on

Peter Haasen

1958-01-01

200

Hardness and Deformation Properties of Solids at Very High Temperatures  

Microsoft Academic Search

This paper describes an experimental study of the deformation and strength properties of refractory solids at temperatures up to 2000^circC. It is difficult to make direct stress-strain measurements at elevated temperatures on small specimens of these materials, and consequently the strength property measured was indentation hardness. The problem of obtaining an indenter that is sufficiently hard and stable at these

A. G. Atkins; D. Tabor

1966-01-01

201

High temperature deformation of Bridgman melt-textured YBCO  

Microsoft Academic Search

Large bars were melt-textured using a modified Bridgman method. Neutron diffraction analysis revealed the absence of any large angle grain boundary and a FWHM of < 6 . Smaller specimens cut from the bars were deformed under flowing oxygen in the temperature range 850950 C applying strain rates from 1 10?5 to 5 10?4 s?1. These high temperature

M. Ullrich; A. Leenders; J. Krelaus; L.-O. Kautschor; H. C. Freyhardt; L. Schmidt; F. Sandiumenge; X. Obradors

1998-01-01

202

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

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

203

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

204

High temperature deformation behavior of the molybdenum alloy TZM  

NASA Astrophysics Data System (ADS)

The molybdenum alloy TZM (Mo-0.5wt%Ti-0.08wt%Zr) is a commonly used constructional material for high-temperature applications. It is well known that molybdenum and its alloys develop a distinct subgrain structure and texture during hot deformation. These microstructural aspects have a significant effect on strength at elevated temperatures. It was observed that with proceeding primary recrystallization and therefore with disappearance of subgrains the yield strength drops almost to the level of pure molybdenum. The aim of the present work was to investigate and describe the strain hardening of hot deformed TZM on a microstructural basis. For this purpose sintered and prerolled TZM rods were recrystallized and each of them deformed to a specific degree of deformation afterwards. Especially the evolution of disorientation distributions was analyzed by electron backscattering diffraction (EBSD) and used to describe the work hardening effect. The yield strength was determined by tensile tests between room temperature and 1473 K. By analyzing disorientation profiles the formation and evolution of geometrically necessary and incidental dislocation boundaries could be observed. A model developed by Pantleon was used to describe the work hardening of TZM.

Mrotzek, T.; Martin, U.; Hoffmann, A.

2010-07-01

205

The deformation mechanisms of superplasticity  

Microsoft Academic Search

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

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

1972-01-01

206

Temperature dependence of the anisotropic deformation of Zr-2.5%Nb pressure tube material during micro-indentation  

NASA Astrophysics Data System (ADS)

The effect of temperature on the anisotropic plastic deformation of textured Zr-2.5%Nb pressure tube material was studied using micro-indentation tests performed in the axial, radial, and transverse directions of the tube over the temperature range from 25 to 400 C. The ratio of the indentation stress in the transverse direction relative to that in the radial and axial directions was 1.29:1 and 1.26:1 at 25 C but decreased to 1.22:1 and 1.05:1 at 400 C. The average activation energy of the obstacles that limit the rate of indentation creep increases, from 0.72 to 1.33 eV, with increasing temperature from 25 to 300 C and is independent of indentation direction. At temperature between 300 C and 400 C the measured activation energy is considerably reduced for indentation creep in the transverse direction relative to that of either the axial or radial directions. We conclude that, over this temperature range, the strength of the obstacles that limit the time-dependent dislocation glide on the pyramidal slip system changes relative to that on the prismatic slip system. These findings provide new data on the temperature dependence of the yield stress and creep rate, particularly in the radial direction, of Zr-2.5%Nb pressure tubes and shed new light on the effect of temperature on the operation of dislocation glide on the prismatic and pyramidal slip systems which ultimately determines the degree of mechanical anisotropy in the highly textured Zr-2.5Nb pressure tube material used in CANDU nuclear reactors.

Bose, B.; Klassen, R. J.

2011-12-01

207

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

208

Strain bursts in the cyclic creep of copper single crystals at ambient temperature  

Microsoft Academic Search

In order to understand the mechanism of strain bursts previously observed in polycrystalline metal tested in cyclic creep, studies have been carried out on single crystals, variously oriented Regular stage I and stage II creep were observed under pulsating tension and a saturated hysteresis loop developed during stage II creep. For stresses above a threshold of 35 MPa in maximum

F. Lorenzo; C. Laird

1984-01-01

209

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

NASA Technical Reports Server (NTRS)

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

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

2010-01-01

210

Creep deformation and fracture of a Cr/Mo/V bolting steel containing selected trace-element additions  

NASA Astrophysics Data System (ADS)

The article reports the creep behavior, at 565 C, of 1Cr1Mo0.75V (Ti, B) (Durehete D1055) steel, in each of two grain sizes and doped with individual trace elements such as P, As, and Sn, in comparison to a reference cast of the base material containing 0.08 wt pct Ti. The addition of the trace elements P, As, or Sn (each <0.045 wt pct) appears to produce no significant effect on creep strength or creep crack-growth resistance at 565 C. The fine-grained material shows low creep strength but notch strengthening, while the coarse-grained material shows higher creep strength and exhibits notch weakening for test times up to 2750 hours. From creep crack-growth tests, it appears that the C* parameter is not appropriate for correlating the creep crack-growth rate under the present test conditions. The parameters K I or ? net are found to correlate better, but, from the present data, it is not possible to judge which of these parameters is more appropriate for general use. It is suggested that the presence of Ti in CrMoV steels has an inhibiting effect on trace-element embrittlement.

Larouk, Z.; Pilkington, R.

1999-08-01

211

Creep deformation and fracture of a Cr/Mo/V bolting steel containing selected trace-element additions  

SciTech Connect

The article reports the creep behavior, at 565 C, of 1Cr1Mo0.75V (Ti, B) (Durehete D1055) steel, in each of two grain sizes and doped with individual trace elements such as P, As, and Sn, in comparison to a reference cast of the base material containing 0.08 wt pct Ti. The addition of the trace elements P, As, or Sn (each <0.045 wt pct) appears to produce no significant effect on creep strength or creep crack-growth resistance at 565 C. The fine-grained material shows low creep strength but notch strengthening, while the coarse-grained material shows higher creep strength and exhibits notch weakening for test times up to 2750 hours. From creep crack-growth tests, it appears that the C{sup *} parameter is not appropriate for correlating the creep crack-growth rate under the present test conditions. The parameters K{sub I} or {sigma}{sub net} are found to correlate better, but, from the present data, it is not possible to judge which of these parameters is more appropriate for general use. It is suggested that the presence of Ti in CrMoV steels has an inhibiting effect on trace-element embrittlement.

Larouk, Z. [Univ. of Constantine (Algeria). Inst. of Physics; Pilkington, R. [Univ. of Manchester (United Kingdom). Materials Science Centre

1999-08-01

212

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

NASA Technical Reports Server (NTRS)

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

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

1992-01-01

213

Tensile deformation behavior of aluminum alloys at warm forming temperatures  

Microsoft Academic Search

Uniaxial tensile deformation behavior of three aluminum sheet alloys, Al 5182+1% Mn, Al 5754 and Al 6111-T4, are studied in the warm forming temperature range of 200350C and in the strain rate range of 0.0151.5 s?1. Approaches have been made to process the selected aluminum sheet alloys so that the microstructural change during warm forming provides adequate recovery favorable to

Daoming Li; Amit Ghosh

2003-01-01

214

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

Microsoft Academic Search

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

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

1996-01-01

215

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

216

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

217

Probabilistic models for creep-fatigue in a steel alloy  

NASA Astrophysics Data System (ADS)

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

Ibisoglu, Fatmagul

218

Multi-Phase High Temperature Alloys: Exploration of Alumina-Forming, Creep-Resistant Austenitic Stainless Steels.  

National Technical Information Service (NTIS)

Work in 2007 focused on the development of a new class of heat-resistant austenitic stainless steel alloys which achieved a unique combination of high-temperature creep strength and excellent oxidation resistance via protective Al(sub 2)O(sub 3) scale for...

M. P. Brady, P. J. Lu P. J. Maziasz, Y. Yamamoto, Z. P. Lu

2008-01-01

219

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

NASA Technical Reports Server (NTRS)

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

Nathal, M. V.

1987-01-01

220

Improving high temperature creep resistance of reduced activation steels by addition of nitrogen and intermediate heat treatment  

NASA Astrophysics Data System (ADS)

In the present study, we report an enhanced high-temperature creep resistance in reduced activation ferrite/martensite (RAFM) steels, by introducing nitrogen (0.035 wt%, M3 steel) and employing a novel intermediate heat treatment I-Q-T (intermediate treatment, quenching and tempering). In comparison with all the control groups, the uniaxial tests of the I-Q-T treated M3 steel showed significant increase in rupture time and decrease in elongation. The microstructures of the samples were further characterized to elucidate the origin of the enhanced creep resistance. It is found that, by introducing nitrogen, the primary TaC particles were refined; by employing the I-Q-T heat treatment, the dispersed fine secondary MX precipitates, as well as the lath subgrains containing high-density dislocations, were increased: all are responsible for the improved creep resistance.

Liu, W. B.; Zhang, C.; Xia, Z. X.; Yang, Z. G.

2014-12-01

221

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

222

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

NASA Technical Reports Server (NTRS)

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

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

1988-01-01

223

Microstructure Evolution in Alpha Iron during High Temperature Tensile Deformation  

NASA Astrophysics Data System (ADS)

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

Thanh, Phi Hung Xuan

224

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

NASA Technical Reports Server (NTRS)

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

Haisler, W. E.

1983-01-01

225

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

NASA Technical Reports Server (NTRS)

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

Jenkins, Jerald M.

1987-01-01

226

The correlation between the power-law coefficients in creep: the temperature dependence  

Microsoft Academic Search

In this study we investigated the relationship between the coefficients of the Norton law for low-stress high-temperature deformation results of different materials reported in the literature. These coefficients are interrelated and it is shown that this relation can be theoretically deduced from the assumption of a variation of the activation area with the inverse of the effective stress (i.e. a

A. Iost

1998-01-01

227

Superplastic Deformation of ice: Experimental Observations  

NASA Technical Reports Server (NTRS)

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 approximately 3 micrometers. 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 less than or equal to 0.1 MPa, conditions which overlap those occurring in glaciers, ice sheets, and icy planetary interiors.

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

2001-01-01

228

Low temperature heat capacity of a severely deformed metallic glass.  

PubMed

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

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

2014-04-01

229

Low Temperature Heat Capacity of a Severely Deformed Metallic Glass  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

230

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

NASA Technical Reports Server (NTRS)

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

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

1991-01-01

231

Room temperature creep-fatigue response of selected copper alloys for high heat flux applications  

NASA Astrophysics Data System (ADS)

Two copper alloys, dispersion-strengthened CuAl25 and precipitation-hardened CuCrZr, were examined under fatigue and fatigue with hold time loading conditions. Tests were carried out at room temperature and hold times were imposed at maximum tensile and maximum compressive strains. It was found that hold times could be damaging even at room temperature, well below temperatures typically associated with creep. Hold times resulted in shorter fatigue lives in the high cycle fatigue, long life regime (i.e., at low strain amplitudes) than those of materials tested under the same conditions without hold times. The influence of hold times on fatigue life in the low cycle fatigue, short life regime (i.e., at high strain amplitudes) was minimal. When hold time effects were observed, fatigue lives were reduced with hold times as short as two seconds. Appreciable stress relaxation was observed during the hold period at all applied strain levels in both tension and compression. In all cases, stresses relaxed quickly within the first few seconds of the hold period and much more gradually thereafter. The CuAl25 alloy showed a larger effect of hold time on reduction of high cycle fatigue life than did the CuCrZr alloy.

Li, Meimei; Singh, B. N.; Stubbins, J. F.

2004-08-01

232

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

233

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

234

Viscoelastic properties of epoxy resins derived from creep and relaxation tests at different temperatures  

Microsoft Academic Search

Summary Experimental data have been obtained on the creep compliance and the relaxation modulus of two epoxy resins in their transition regions. These tests were combined with birefringence measurements to follow the changes in bond orientation of the polymers as the strain or stress varies. Experimental data on the stress- and strain-optical coefficients are presented for both creep and relaxation

Pericles S. Theocaris

1962-01-01

235

Creep of Uncoated and Cu-Cr Coated NARloy-Z  

NASA Technical Reports Server (NTRS)

Stress rupture creep tests were performed on uncoated and Cu-30vol%Cr coated NARloy-Z copper alloy specimens exposed to air at 482 C to 704 C. The results showed that creep failure in air of unprotected NARloy-Z was precipitated by brittle intergranular surface cracking produced by strain assisted grain boundary oxidation (SAGBO) which in turn caused early onset of tertiary creep. For the protected specimens, the Cu-Cr coating remained adherent throughout the tests and was effective in slowing down the rate of oxygen absorption, particularly at the higher temperatures, by formation of a continuous chromium oxide scale. As the result of reducing oxygen ingress, the coating prevented SAGBO initiated early creep failure, extended creep deformation and increased the creep rupture life of NARloy-Z over the entire 482 C to 704 C test temperature range.

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

1998-01-01

236

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

237

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

238

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

239

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

USGS Publications Warehouse

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

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

1973-01-01

240

Biaxial thermal creep of Inconel 617 and Haynes 230 at 850 and 950 C  

NASA Astrophysics Data System (ADS)

The biaxial thermal creep behavior of Inconel 617 and Haynes 230 at 850 and 950 C was investigated. Biaxial stresses were generated using the pressurized tube technique. The detailed creep deformation and fracture mechanism have been studied. Creep curves for both alloys showed that tertiary creep accounts for a greater portion of the materials' life, while secondary creep only accounts for a small portion. Fractographic examinations of the two alloys indicated that nucleation, growth, and coalescence of creep voids are the dominant micro-mechanisms for creep fracture. At 850 C, alloy 230 has better creep resistance than alloy 617. When subjected to the biaxial stress state, the creep rupture life of the two alloys was considerably reduced when compared to the results obtained by uniaxial tensile creep tests. The Monkman-Grant relation proves to be a promising method for estimating the long-term creep life for alloy 617, whereas alloy 230 does not follow the relation. This might be associated with the significant changes in the microstructure of alloy 230 at high temperatures.

Tung, Hsiao-Ming; Mo, Kun; Stubbins, James F.

2014-04-01

241

Creep deformation and fracture of a Cr\\/Mo\\/V bolting steel containing selected trace-element additions  

Microsoft Academic Search

The article reports the creep behavior, at 565 C, of 1Cr1Mo0.75V (Ti, B) (Durehete D1055) steel, in each of two grain sizes\\u000a and doped with individual trace elements such as P, As, and Sn, in comparison to a reference cast of the base material containing\\u000a 0.08 wt pct Ti. The addition of the trace elements P, As, or Sn (each

Z. Larouk; R. Pilkington

1999-01-01

242

High temperature deformation behavior of a nanocrystalline titanium aluminide  

SciTech Connect

Gamma titanium intermetallic alloys are potentially attractive for elevated temperature applications. The room temperature ductility and fracture toughness have been improved considerably by the addition of ternary and quaternary elements. The synthesis of nanocrystalline materials has provided further avenues for possible improvement in the mechanical properties. The exciting prospect of low temperature superplasticity in nanocrystalline materials has been discussed. Recently, nanocrystalline {gamma}-TiAl alloys have been synthesized by hot isostatic pressing (HIP) of mechanically alloyed (MA) Ti-47.5 Al-3 Cr (at.%) powders. The purpose of this study was to evaluate the possibility of observing low temperature superplasticity in this nanocrystalline alloy. By determining the stress exponent for flow, it should be possible to comment on the micromechanism of deformation in a nanocrystalline intermetallic alloy. A number of studies have shown that superplasticity is possible in {gamma}-TiAl alloys and it is important to establish whether the scaling law extends to nanocrystalline {gamma}-TiAl regime or the flow behavior changes.

Mishra, R.S.; Mukherjee, A.K. [Univ. of California, Davis, CA (United States). Dept. of Chemical Engineering and Materials Science] [Univ. of California, Davis, CA (United States). Dept. of Chemical Engineering and Materials Science; Mukhopadhyay, D.K.; Suryanarayana, C.; Froes, F.H. [Univ. of Idaho, Moscow, ID (United States). Inst. for Materials and Advanced Processes] [Univ. of Idaho, Moscow, ID (United States). Inst. for Materials and Advanced Processes

1996-06-01

243

Swelling and radiation creep of austenitic corrosion-resistant steel irradiated by neutrons in wide dose and temperature ranges  

Microsoft Academic Search

The results of a study of the swelling and in-reactor creep of EI-847, EP-172, and ChS-68 austenitic steel after irradiation\\u000a in materials science assemblies in the range 330700C and damaging dose 2096 dpa are presented. The temperature dependences\\u000a of the volume change of steel were obtained from measurements of the diameter of unloaded ampuls. It is shown that the swelling

S. I. Porollo; S. V. Shulepin; A. A. Ivanov; Yu. V. Konobeev; N. I. Budylkin; E. G. Mironova

2011-01-01

244

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\\u000a of residual and trace element effects. Based on data reported in the literature, the creep strength of unstabilized alloys\\u000a such as types 304 and 316 stainless steel increased with residual element and trace element content. Niobium appeared to be\\u000a the most potent

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

1983-01-01

245

THE HOMOLOGOUS TEMPERATURE DEPENDENCE OF CREEP Harry W. Green, II and Robert S. Borch  

E-print Network

Tm represents the solidus of the material, the steady-state creep strength is independent of pressure to the solidus and corrected through the power-law creep equation to a common strain rate of 2X10-4 sec 1 using of the solidus is O.1K/MPa and °Tm is estimated. Experiments conducted at different pressures are symbolized

Paris-Sud XI, Université de

246

Microstructural evidence for dynamic recrystallization during creep of a duplex near-{gamma} TiAl-alloy  

SciTech Connect

Intermetallic near-{gamma} titanium aluminides (TiAl) have attractive properties such as high strength, low density, good oxidation resistance and good high temperature properties. In the present study the authors consider an alloy with duplex microstructure which is attractive in combining good creep strength with reasonable ductility. In order to be able to safely use such materials for high temperature components operating in the creep range, the mechanical creep behavior has to be well characterized and the dominating microstructural creep processes must be understood. Dynamic recrystallization can occur during high temperature plastic deformation, i.e, hot working (rolling, extrusion, forging) or creep and represents a softening process. It is presently not clear how much dynamic recrystallization affects the creep rate and what role it plays in the overall creep deformation mechanism. The objective of the present study was to (i) determine whether dynamic recrystallization occurs during creep of the duplex material studied here at stresses and temperatures which are low in comparison to the large majority of literature experiments, (ii) identify the critical condition for the onset of dynamic recrystallization and (iii) perceive the role of dynamic recrystallization as part of the creep mechanism in TiAl based alloys.

Skrotzki, B.; Rudolf, T.; Eggeler, G. [Ruhr-Univ., Bochum (Germany). Inst. for Materials] [Ruhr-Univ., Bochum (Germany). Inst. for Materials; Dlouhy, A. [Academy of Sciences of the Czech Republic, Brno (Czech Republic). Inst. of Physics and Materials] [Academy of Sciences of the Czech Republic, Brno (Czech Republic). Inst. of Physics and Materials

1998-11-03

247

Review of deformation behavior of tungsten at temperature less than 0.2 absolute melting temperature  

NASA Technical Reports Server (NTRS)

The deformation behavior of tungsten at temperatures 0.2 T sub m is reviewed, with primary emphasis on the temperature dependence of the yield stress and the ductile-brittle transition temperature. It appears that a model based on the high Peierls stress of tungsten best accounts for the observed mechanical behavior at low temperatures. Recent research is discussed which suggests an important role of electron concentration and bonding on the mechanical behavior of tungsten. It is concluded that future research on tungsten should include studies to define more clearly the correlation between electron concentration and mechanical behavior of tungsten alloys and other transition metal alloys.

Stephens, J. R.

1972-01-01

248

Error correction for Moir based creep measurement system  

NASA Astrophysics Data System (ADS)

Due to the high temperatures and stresses present in the high-pressure section of a gas turbine, the airfoils experience creep or radial stretching. Nowadays manufacturers are putting in place condition-based maintenance programs in which the condition of individual components is assessed to determine their remaining lives. To accurately track this creep effect and predict the impact on part life, the ability to accurately assess creep has become an important engineering challenge. One approach for measuring creep is using moir imaging. Using pad-print technology, a grating pattern can be directly printed on a turbine bucket, and it compares against a reference pattern built in the creep measurement system to create moir interference pattern. The authors assembled a creep measurement prototype for this application. By measuring the frequency change of the moir fringes, it is then possible to determine the local creep distribution. However, since the sensitivity requirement for the creep measurement is very stringent (0.1 micron), the measurement result can be easily offset due to optical system aberrations, tilts and magnification. In this paper, a mechanical specimen subjected to a tensile test to induce plastic deformation up to 4% in the gage was used to evaluate the system. The results show some offset compared to the readings from a strain gage and an extensometer. By using a new grating pattern with two subset patterns, it was possible to correct these offset errors.

Liao, Yi; Harding, Kevin G.; Nieters, Edward J.; Tait, Robert W.; Hasz, Wayne C.; Piche, Nicole

2014-05-01

249

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

Microsoft Academic Search

The ferritic 2-1\\/4 Cr-1 Mo steel is an important construction material for elevated-temperature applications worldwide. It is of particular interest for coal conversion pressure vessels. Tensile and creep data are presented for normalized and tempered 2-1\\/4 Cr-1 Mo steel from American, Japanese, British, French, and German sources. These include creep data obtained at temperatures from 427 to 600°C (800 to

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

1982-01-01

250

Point defects and high-temperature creep of non-stoichiometric NaCl-type oxide single crystals I. NiO  

Microsoft Academic Search

Creep of NiO single crystals has been investigated by compression along ?100? in the temperature range 06Tm to 08Tm, for stresses from 25 to 120 MPa and oxygen partial pressures pO2 from 10 to 02 atm. The data are analysed using the equation for recovery-controlled creep. The stress exponent decreases from a value of 12 to low temperature to 7

J. Carrera-Cao; A. Dominguez-Rodriguez; R. Marquez; J. Castaing; J. Philibert

1982-01-01

251

Dislocation and diffusion creep of synthetic anorthite aggregates  

Microsoft Academic Search

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

E. Rybacki; G. Dresen

2000-01-01

252

Investigation of titanium nanostructure deformed at low temperatures  

NASA Astrophysics Data System (ADS)

The bulk titanium with a grain size from nanometer to submicron was obtained using cryomechanical treatment. An investigation of nanostructure, determining unusual mechanical properties of the new material, was performed by methods of transmission electron microscopy and X-ray diffraction. The results of a comparative study of the structures formed by deformation at temperatures close to that of liquid nitrogen and room temperature in the case of different activity of sliding and twinning, showed that large degree of grain diminishment at the cryodeformation is caused by mechanical twinning. In this case, the twinning generating a set of diverse orientations due to fragmentation of grains leads to increasing the number of reflexes in X-ray diffraction patterns, providing a random character of the structure/texture. The data on a mean size of a region of coherent scattering (RCS) in crystallites and values of average microdiformations ?? were obtained. It is assumed that much smaller values of microdeformations ?? after cryorolling are caused by activated relaxation processes due to warming up to room temperature. It is shown that an X-ray amorphous phase presented in nanostructured titanium is not truly amorphous, and corresponds to RCS with the size d <~ 15 nm.

Braude, I. S.; Gal'tsov, N. N.; Moskalenko, V. A.; Smirnov, A. R.

2011-12-01

253

Mechanisms of deformation-induced grain growth of a two-dimensional nanocrystal at different deformation temperatures  

NASA Astrophysics Data System (ADS)

This work discloses the evolution of a two-dimensional nanocrystalline aggregate in the process of shear deformation under the conditions of hydrostatic compression of the material in the deformation-temperature range T = 0.5-0.7 T m. It has been shown that grain growth by the mechanism of mutual rotation with subsequent coalescence is characteristic of deformation temperatures T = 0.6 T m and below, whereas at T = 0.65 and 0.7 T m one of grains with predominant orientation grows at the expense of other grains. In all instances, the growth of the degree of shear deformation leads to the disappearance of all grain boundaries in the calculated cell under consideration.

Korznikova, E. A.; Dmitriev, S. V.

2014-06-01

254

Mechanisms governing cyclic deformation and failure during elevated temperature fatigue of aluminum alloy 7055  

Microsoft Academic Search

The cyclic stress response, deformation and damage characteristics of aluminum alloy 7055 was studied at ambient and elevated temperatures. Specimens of the alloy were cyclically deformed using tension-compression loading under total strain-amplitude control. The alloy showed evidence of softening to failure at the ambient and elevated test temperatures. The degree of cyclic softening increased with an increase in test temperature.

T. S Srivatsan

1999-01-01

255

Modeling high-temperature glass molding process by coupling heat transfer and viscous deformation analysis  

Microsoft Academic Search

Glass molding is as an effective approach to produce precision micro optical elements with complex shapes at high production efficiency. Since glass is deformed at a high temperature where the mechanical and optical properties depend strongly on temperature, modeling the heat transfer and high-temperature deformation behavior of glass is an important issue. In this paper, a two-step pressing process is

Jiwang Yan; Tianfeng Zhou; Jun Masuda; Tsunemoto Kuriyagawa

2009-01-01

256

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

SciTech Connect

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

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

1996-05-01

257

Elevated temperature load-order effects on austenitic steel life predictions  

Microsoft Academic Search

The design of nuclear pressure vessel components may typically involve a few hundred or more cyclic thermal loadings of various levels coupled with steady mechanical loads. Ordering of these loading events may not be detailed in the design specification. Thermal loading usually implies plastic deformation, and elevated temperature design must consider creep deformation and damage. Plastic creep solutions are history

1989-01-01

258

Modeling Creep in Thermoplastic Composites  

Microsoft Academic Search

A creep model for unidirectionally reinforced fiber composites was devel oped based on a one-parameter potential function. The same potential function was used to describe plastic flow and time-dependent creep deformation. The material constants in the model were determined by using the uniaxial tension test of off-axis coupon specimens. In terms of effective stress and effective creep strain, the anisotropic

Ilsup Chung; C. T. Sun; I. Y. Chang

1993-01-01

259

DEFORMATION MECHANISMS AND DAMAGE OF OXIDE DISPERSION STRENGTHENED STEELS AT HIGH TEMPERATURE  

E-print Network

DEFORMATION MECHANISMS AND DAMAGE OF OXIDE DISPERSION STRENGTHENED STEELS AT HIGH TEMPERATURE A influenced by the strain rate and the temperature. Deformation mechanisms linked to diffusion phenomena alloy, an ODS ferritic steel produced by hot extrusion at CEA are presented. Its mechanical properties

Boyer, Edmond

260

A METHOD OF SPECIMEN CORROSION PROTECTION FOR HIGH-TEMPERATURE CREEP TESTING  

Microsoft Academic Search

The method involves encasing the creep specimen in a flexible capsule ; which is capable of withstanding exposure to the atmosphere for extended periods ; at up to 1000 deg C. The capsule consists of several sections of bellows welded ; to machined parts which comprise the gage point mounting rings and specimen end-; adapters. Provisions are made to attach

J. R. Bohn; R. E. Uhrig; G. Murphy

1959-01-01

261

Point defects and high temperature creep of NiO single crystals  

Microsoft Academic Search

NiO single crystals have been crept in compression between 1 070 C and 1 550 C for stresses in the range 10 MPa-150 MPa. Oxygen partial pressures were varied between 10-5 atm. and air. The steady state creep rate seems to depend on the concentration of oxygen vacancies V\\

J. Castaing

1980-01-01

262

Thermal deformation of concentrators in an axisymmetric temperature field  

NASA Technical Reports Server (NTRS)

Axisymmetric thermal deformations of paraboloid mirrors, due to heating, are examined for a mirror with a optical axis oriented toward the Sun. A governing differential equation is derived using Mushtari-Donnel-Vlasov simplifications, and a solution is presented which makes it possible to determine the principal deformation characteristics.

Bairamov, R.; Machuev, Y. I.; Nazarov, A.; Sokolov, Y. V.; Solodovnikova, L. A.; Fokin, V. G.

1985-01-01

263

Postseismic deformation due to the Mw 6.0 2004 Parkfield earthquake: Stress-driven creep on a fault  

E-print Network

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 show that afterslip occurred in areas of low seismicity and low coseismic slip, predominantly

Fialko, Yuri

264

Severe Plastic Deformation of Difficult-to-Deform Materials at Near-Ambient Temperatures  

NASA Astrophysics Data System (ADS)

Plane-strain machining can be used to impart large plastic strains in alloys that are difficult to deform by other severe plastic deformation (SPD) processes. By cutting at low speeds, the heating caused by friction with the tool can be reduced to insignificant levels. The utility of this approach for characterizing microstructure development in SPD is demonstrated using a variety of commercial alloys that exhibit different deformation behaviors and strengthening mechanisms, including CP-titanium, aluminum alloy 6061-T6, nickel-base superalloy IN-718, and pearlitic plain-carbon steel.

Ravi Shankar, M.; Verma, R.; Rao, B. C.; Chandrasekar, S.; Compton, W. D.; King, A. H.; Trumble, K. P.

2007-09-01

265

Thermal-cycling creep apparatus  

Microsoft Academic Search

A constant load creep testing machine has been designed and built for operation under high frequency (1 to 10?2 S?1) thermal cycling conditions. The apparatus can be operated at loads up to 7 kg with temperatures up to 1000C, and under vacuum to better than 10 ?torr. A twin creep stage enables differential creep measurements. Preliminary results on foil specimens

D. Eylon; N. Kushnir; A. Rosen

1970-01-01

266

Elevated temperature crack growth in aluminum alloys: Tensile deformation of 2618 and FVS0812 aluminum alloys  

NASA Technical Reports Server (NTRS)

Understanding the damage tolerance of aluminum alloys at elevated temperatures is essential for safe applications of advanced materials. The objective of this project is to investigate the time dependent subcritical cracking behavior of powder metallurgy FVS0812 and ingot metallurgy 2618 aluminum alloys at elevated temperatures. The fracture mechanics approach was applied. Sidegrooved compact tension specimens were tested at 175, 250, and 316 C under constant load. Subcritical crack growth occurred in each alloy at applied stress intensity levels (K) of between about 14 and 25 MPa/m, well below K (sub IC). Measured load, crack opening displacement and displacement rate, and crack length and growth rate (da/dt) were analyzed with several continuum fracture parameters including, the C-integral, C (sub t), and K. Elevated temperature growth rate data suggest that K is a controlling parameter during time dependent cracking. For FVS0812, da/dt is highest at 175 C when rates are expressed as a function of K. While crack growth rate is not controlled by C (sub t) at 175 C, da/dt appears to better correlate with C (sub t) at higher temperatures. Creep brittle cracking at intermediate temperatures, and perhaps related to strain aging, is augmented by time dependent transient creep plasticity at higher temperatures. The C (sub t) analysis is, however, complicated by the necessity to measure small differences in the elastic crack growth and creep contributions to the crack opening displacement rate. A microstructural study indicates that 2618 and FVS0812 are likely to be creep brittle materials, consistent with the results obtained from the fracture mechanics study. Time dependent crack growth of 2618 at 175 C is characterized by mixed transgranular and intergranular fracture. Delamination along the ribbon powder particle boundaries occurs in FVS0812 at all temperatures. The fracture mode of FVS0812 changes with temperature. At 175 C, it is characterized as dimpled rupture, and at 316 C as mixed matrix superplastic rupture and matrix-dipersoid debonding.

Leng, Yang; Gangloff, Richard P.

1990-01-01

267

Creep of SiC-Whisker reinforced Si3N4 M. Backhaus-Ricoult (1), J. Castaing (1) and J. L. Routbort (2)  

E-print Network

temperature the creep deformation occurs at a quasiconstant strain rate. Extended cavitation in the triple for the deformation in both temperatures regions. Revue Phys. Appl. 23 (1988) 239-249 MARS 1988, Classification Physics Abstracts 62.20 - 81.40 1. Introduction. Additive containing hot-pressed or sintered silicon

Paris-Sud XI, Université de

268

Newtonian dislocation creep in quartzites: implications for the rheology of the lower crust.  

PubMed

Mechanical and microstructural evidence indicates that a natural and a synthetic quartzite deformed by Newtonian dislocation (Harper-Dorn) creep at temperatures higher than 1073 K and stresses lower than 300 megapascals. The observation of this creep in these materials suggests that the lower crust may flow like a Newtonian viscous fluid by a dislocation mechanism at stresses much smaller than those previously postulated. PMID:17787584

Wang, J N; Hobbs, B E; Ord, A; Shimamoto, T; Toriumi, M

1994-08-26

269

Effect of high-temperature plastic deformation on the properties of precipitation-hardening magnesium alloys  

Microsoft Academic Search

1.Heating the Mg-3% Nd alloy to a temperature guaranteeing a solid solution of alloying elements in magnesium and high-temperature plastic deformation (80% strain) produce higher strength characteristics at a testing temperature of 250C than those resulting from treatment T6 (quenching+aging) but lower than those resulting from treatment T8 (quenching +10% cold plastic deformation + aging).2.At room temperature the strength characteristics

M. E. Drits; Z. A. Sviderskaya; L. L. Rokhlin; A. A. Oreshkina

1968-01-01

270

The effect of deformation temperature on the microstructure evolution of Inconel 625 superalloy  

NASA Astrophysics Data System (ADS)

Hot compression tests of Inconel 625 superalloy were conducted using a Gleeble-1500 simulator between 900 C and 1200 C with different true strains and a strain rate of 0.1 s -1. Scanning electron microscope (SEM) and electron backscatter diffraction technique (EBSD) were employed to investigate the effect of deformation temperature on the microstructure evolution and nucleation mechanisms of dynamic recrystallization (DRX). It is found that the relationship between the DRX grain size and the peak stress can be expressed by a power law function. Significant influence of deformation temperatures on the nucleation mechanisms of DRX are observed at different deformation stages. At lower deformation temperatures, continuous dynamic recrystallization (CDRX) characterized by progressive subgrain rotation is considered as the main mechanism of DRX at the early deformation stage. However, discontinuous dynamic recrystallization (DDRX) with bulging of the original grain boundaries becomes the operating mechanism of DRX at the later deformation stage. At higher deformation temperatures, DDRX is the primary mechanism of DRX, while CDRX can only be considered as an assistant mechanism at the early deformation stage. Nucleation of DRX can also be activated by the twinning formation. With increasing the deformation temperature, the effect of DDRX accompanied with twinning formation grows stronger, while the effect of CDRX grows weaker. Meanwhile, the position of subgrain formation shifts gradually from the interior of original grains to the vicinity of the original boundaries.

Guo, Qingmiao; Li, Defu; Guo, Shengli; Peng, Haijian; Hu, Jie

2011-07-01

271

Mechanisms of time-dependent deformation in porous limestone  

NASA Astrophysics Data System (ADS)

We performed triaxial deformation experiments on a water-saturated porous limestone under constant strain rate and constant stress (creep) conditions. The tests were conducted at room temperature and at low effective pressures Peff=10 and Peff=20 MPa, in a regime where the rock is nominally brittle when tested at a constant strain rate of 10-5 s-1. Under these conditions and at constant stress, the phenomenon of brittle creep occurs. At Peff=10 MPa, brittle creep follows similar trends as those observed in other rock types (e.g., sandstones and granites): only small strains are accumulated before failure, and damage accumulation with increasing strain (as monitored by P wave speeds measurements during the tests) is not strongly dependent on the applied stresses. At Peff=20 MPa, brittle creep is also macroscopically observed, but when the creep strain rate is lower than ?10-7 s-1, we observe that (1) much larger strains are accumulated, (2) less damage is accumulated with increasing strain, and (3) the deformation tends to be more compactant. These observations can be understood by considering that another deformation mechanism, different from crack growth, is active at low strain rates. We explore this possibility by constructing a deformation mechanism map that includes both subcritical crack growth and pressure solution creep processes; the increasing contribution of pressure solution creep at low strain rates is consistent with our observations.

Brantut, Nicolas; Heap, Michael J.; Baud, Patrick; Meredith, Philip G.

2014-07-01

272

Deformation in metals after low temperature irradiation: Part I - Mapping macroscopic deformation modes on true stress-dose plane  

SciTech Connect

Macroscopic deformation modes, elastic, uniform plastic, and unstable plastic deformation modes, are mapped in tensile true stress-dose space for more than two dozen metallic materials consisting of 13 body-centered cubic (bcc), 11 face-centered cubic (fcc), and 2 hexagonal closed packed (hcp) metals. The boundaries between different deformation zones are set by the true stress versus dose curves for the yield stress (YS), plastic instability stress (PIS), and true fracture stress (FS) plotted as functions of dose. Values for these true stresses are obtained from uniaxial tensile tests or calculated from engineering tensile data using a linear strain-hardening model for necking deformation. The relatively low strength annealed fcc metals display large uniform plasticity regions, while unstable deformation regions are dominant in the harder bcc and hcp metals. PIS values for all materials are independent of dose except for the precipitation-hardened IN718 alloy where a decrease is noted that may result from an irradiation-induced change in the precipitate phase. In the bcc materials for high temperature application, such as 9Cr ferritic/martensitic steels, sintered molybdenum, vanadium, and tantalum, the radiation-induced embrittlement is characterized in terms of FS decreasing with dose at relatively high doses. FS is nearly dose-independent below the critical dose for embrittlement. It is concluded that the tensile stress-based deformation mode maps effectively integrate mechanical property information and characterize differences in radiation effects between crystalline structures or material groups.

Byun, Thak Sang [ORNL

2008-01-01

273

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

SciTech Connect

A laboratory investigation has been carried out to determine the effects of elevated temperature and stress on the creep deformation of welded tuffs recovered from Busted Butte in the vicinity of Yucca Mountain, Nevada. Water saturated specimens of tuff from thermal/mechanical unit TSw2 were tested in creep at a confining pressure of 5.0 MPa, a pore pressure of 4.5 MPa, and temperatures of 25 and 250 C. At each stress level the load was held constant for a minimum of 2.5 {times} 10{sup 5} seconds and for as long as 1.8 {times} 10{sup 6} seconds. One specimen was tested at a single stress of 80 MPa and a temperature of 250 C. The sample failed after a short time. Subsequent experiments were initiated with an initial differential stress of 50 or 60 MPa; the stress was then increased in 10 MPa increments until failure. The data showed that creep deformation occurred in the form of time-dependent axial and radial strains, particularly beyond 90% of the unconfined, quasi-static fracture strength. There was little dilatancy associated with the deformation of the welded tuff at stresses below 90% of the fracture strength. Insufficient data have been collected in this preliminary study to determine the relationship between temperature, stress, creep deformation to failure, and total failure time at a fixed creep stress.

Martin, R.J. III; Boyd, P.J.; Noel, J.S. [New England Research, Inc., White River Junction, VT (United States); Price, R.H. [Sandia National Labs., Albuquerque, NM (United States)

1995-06-01

274

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

NASA Astrophysics Data System (ADS)

In the present paper, the effects of helium on creep properties of Fe-14CrWTi ODS steel were studied by in-beam and post He-implantation creep tests. In-situ creep was performed in an in-beam creep device under uniaxial tensile stresses from 350 to 370 MPa during homogeneous helium implantation. Helium ions of energies varying from 0 to 25 MeV were implanted at a rate of 6 10-3 appm/s (corresponding to a displacement dose rate of 1.5 10-6 dpa/s). The average temperature was controlled to 650 C within 2 C. In addition, post He-implantation creep tests were conducted at 650 C as well. Subsequently, fracture surfaces and helium bubble evolution were studied in detail by SEM and TEM observations, respectively. Preliminary creep results show that helium slightly shortens the creep life time of ODS steel at 650 C. Fracture surfaces of reference as well as implanted specimens, show areas with various grades of deformation. Areas of highest deformation can be interpreted as necking, while areas of low deformation show in helium implanted specimens a more granular structure. The results are discussed in terms of possible embrittlement of ODS steels by helium.

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

2014-10-01

275

Deformation of reinforced polymer bearing elements on full-scale compressive strength and creep tests under yielding conditions  

Microsoft Academic Search

Ultra high molecular weight polyethylene (UHMWPE) reinforced with a carbon fibre\\/epoxy ring (hybrid polymer pad) is used as bearing elements in a ball-joint for rotation of a storm surge barrier, requiring high strength and dimensional stability. The concave bearing surfaces contain 500 pads with diameter 250mm incorporated in machined holes. As they are used as functional parts, high deformation will

P. Samyn; L. Van Schepdael; J. S. Leendertz; W. Van Paepegem; P. De Baets; J. Degrieck

2006-01-01

276

CREEP: LONG-TERM TIME-DEPENDENT ROCK DEFORMATION IN THE NEMO DEEP-SEA LABORATORY: A PILOT STUDY  

Microsoft Academic Search

The time-dependent properties of brittle rock deformation are of first-order importance for understanding the long-term behaviour of the Earth's upper crust, as well as for the temporal evolution of mid-term precursories before earthquakes (Meredith et al., 1990; Main et al., 1992) and eruptions (Vinciguerra, 1999;2002). Water saturated rocks are ubiquitous in the crust, and the chemical influence of water leads

P. G. Meredith; E. Migneco; P. Piattelli; G. Riccobene; D. Vinciguerra

277

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

SciTech Connect

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

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

1993-08-01

278

High temperature deformation mechanisms and strain heterogeneities in calcite rocks  

E-print Network

In nature, carbonates often accumulate large amounts of strain in localized shear zones. Such marble sequences play a key role in crustal deformation processes. Despite extensive field and laboratory investigation, many ...

Xu, Lili, Sh. D. Massachusetts Institute of Technology

2008-01-01

279

High-temperature deformation of uniaxially aligned lamellar TiAl/Ti{sub 3}Al  

SciTech Connect

Uniaxially aligned polysynthetically twinned two-phase TiAl/Ti{sub 3}Al material is produced by induction zone melting and deformed in uniaxial compression. Above 1,000 K the strain rate sensitivity is independent of the lamellar orientation and increases strongly with increasing deformation temperature. Results for the strain rate sensitivity parameters are somewhat lower than those obtained for {gamma}-TiAl single- and polycrystals. If the lamellae are oriented parallel or perpendicular to the deformation axis, the flow stress decreases with increasing strain. After plastic deformation the dislocation density in the lamellae is remarkably low indicating recovery processes. At the lamellar interfaces misfit dislocations and periodic arrangements of dislocations with Burgers vectors inclined to the lamellar boundaries are found. In contrast to deformation at lower temperatures, deformation twinning is rare.

Heinrich, H.; Abaecherli, V.; Wilkins, D.J.; Kostorz, G.

1999-07-01

280

The investigations of hot-deformability and structure of high-temperature Fe-Ni alloy  

Microsoft Academic Search

Purpose: This study describes the influence of initial austenite grain size and parameters of hot plastic deformation on the deformability and structure of high-temperature Fe-Ni austenitic alloy of A-286 type. Design\\/methodology\\/approach: The hot deformation characteristics of the alloy were investigated by hot torsion tests using torsion plastometer. The tests were executed at constant strain rates of 0.1 and 1.0 s-1,

K. J. Ducki; D. Kuc

281

Low-temperature plastic deformation of AZ31 magnesium alloy with different microstructures  

Microsoft Academic Search

The plastic deformation of AZ31 magnesium alloy under tension at temperatures of 4.2-295 K is studied as a function of its microstructure following squeeze casting (SC) and after severe plastic deformation (SPD) by hot rolling and equal-channel angular pressing. SPD reduces the average grain size and creates a texture that favors basal-plane dislocation glide. It is found that plastic deformation

Yu. Z. Estrin; P. A. Zabrodin; I. S. Braude; T. V. Grigorova; N. V. Isaev; V. V. Pustovalov; V. S. Fomenko; S. E. Shumilin

2010-01-01

282

Effect of deformation temperature on microstructure evolution in aluminum alloy 2219 during hot ECAP  

Microsoft Academic Search

The effect of deformation temperature on microstructure evolution during equal channel angular pressing (ECAP) was studied in a coarse-grained aluminum alloy 2219 in a wide temperature interval from 250 to 475C. The structural changes taking place during ECAP up to strains of 12 are classified into the following three stages irrespective of deformation temperatures: i.e. (1) an incubation period for

I. Mazurina; T. Sakai; H. Miura; O. Sitdikov; R. Kaibyshev

2008-01-01

283

The Dislocation Microstructure of Cyclically Deformed Nickel Single Crystals at Different Temperatures  

Microsoft Academic Search

Using transmission electron microscopy a systematic study of the dislocation microstructure after cyclic deformation of nickel single crystals was undertaken in order to describe quantitatively the influence of deformation temperature on microstructural parameters. The frequency distributions of the heights and lengths of edge dislocation dipoles were measured in the walls and channels of persistent slip bands and in the matrix

B. Tippelt; J. Breitschneider; P. Hhner

1997-01-01

284

The deformation of AgMg single crystals at high temperatures  

Microsoft Academic Search

Pronounced yield points have been observed in AgMg single crystals which deformed in compression at temperatures above 450 K. The mechanism of the deformation of single crystals of the compound in the presence of the yield point is discussed in terms of atmosphere-dragging-controlled glide.

M. Yamaguchi; Y. Umakoshi

1979-01-01

285

Free volume model: high temperature deformation of a Zr based bulk metallic glass  

E-print Network

1 Free volume model: high temperature deformation of a Zr based bulk metallic glass M. Bletry1 deformation of a zirconium based bulk metallic glass is investigated in the glass transition range being of the same order of magnitude for the studied alloy when compared with other metallic glasses

Paris-Sud XI, Université de

286

Numerical investigation of grain boundary effects on elevated-temperature deformation and fracture  

Microsoft Academic Search

A three-dimensional (3D) polycrystal intergranular model that accounts for grain boundary deformation and intergranular weakening at elevated temperatures is presented. The effects of grain boundaries on the accumulated slip deformation of grain interiors and lattice rotation have been investigated through a comparison between results from a model including grain boundary region (GBM) and a model representing only the grain interiors

Yan-Qing Wu; Hui-Ji Shi; Ke-Shi Zhang; Hsien-Yang Yeh

2006-01-01

287

The creep damage behavior of the plasma-sprayed thermal barrier coating system NiCr22Co12Mo9-NiCoCrAlY-ZrO{sub 2}/7%Y{sub 2}O{sub 3}  

SciTech Connect

During creep loading metallic substrates impose deformation on deposited ceramic thermal barrier coatings (TBC). Strain accommodation of the TBC is not attained by plastic deformation, but by means of crack initiation, crack opening, crack propagation or sliding of adjacent crack faces. In technical applications a distinction is made between tolerated or desired cracks perpendicular to the surface, and detrimental cracks parallel to the substrate-coating interface. Thus, TBC can respond to creep deformation by segmentation or spallation, the latter being referred to as failure. The parameters influencing the probability of either segmentation or spallation are temperature, creep rate, magnitude of creep deformation, layer thickness, and microstructure of the TBC. It can be stated that spallation failure probability increases with increasing creep rate, creep deformation, and layer thickness. The presence of pores between single spraying layers also strongly augments the likelihood of spallation. No significant influence of temperature on spallation failure probability can be found in the range from 850 C to 1,050 C. Light microscopy and scanning electron microscopy investigation show that the microstructure of the ceramic TBC changes during creep, and that the density of cracks detected on micrographs with low magnification (x50) increases with increasing creep deformation. On the other hand, the density of microcracks visible with high magnification (x500) is constant, or even decreases with increasing creep deformation. These findings are explained by sintering processes enabled by stress relaxation due to formation of macroscopic cracks perpendicular to the surface as a response to creep deformation. A relationship between microstructural changes and the emission of signals recorded during creep is presented.

Schmidt, U.T.; Voehringer, O.; Loehe, D.

1999-10-01

288

Point defects and high-temperature creep of non-stoichiometric NaCl-type oxide single crystals II. CoO  

Microsoft Academic Search

High-temperature creep of CoO single crystals has been investigated by compression along ?100? in the temperature range 06Tm to 08Tm, for stresses of 5 to 25 MPa and oxygen partial pressures pO2 from 10?5 to 02 atm. The stress exponent decreases from a value of 85 at low temperature to 65 at high temperature; the activation energy is 5 eV

A. Dominguez-Rodriguez; M. Sanchez; R. Marquez; J. Castaing; C. Monty; J. Philibert

1982-01-01

289

Plastic deformation and fracture behavior of Ti{sub 3}Al single crystals deformed at high temperatures under cyclic loading  

SciTech Connect

Temperature dependence of cyclic deformation behavior in Ti{sub 3}Al single crystals was investigated between 300 C and 800 C focusing on the cyclic hardening, deformation substructure and orientation dependence of fatigue life and fracture behavior. The saturated bundled structure (SBS) composed of numerous edge dislocations parallel to [0001] was observed below 500 C accompanied by edge dislocation dipoles and debris, while dislocation networks composed of three different a/3{l_angle}1{bar 2}10>{r_angle}-type dislocations were formed at 800 C. Cyclic hardening was moderated with increasing temperature but anomalous cyclic hardening was observed at 800 C due to the formation of the dislocation networks. The fatigue life at 800 C showed strong orientation dependence: the fatigue resistance was related to the Schmid law under prism slip but when the basal or pyramidal slip is expected to be operative instead of the prism slip, fracture occurred at a lower stress before yielding.

Koizumi, Y.; Nakano, T.; Umakoshi, Y. [Osaka Univ., Suita, Osaka (Japan). Dept. of Materials Science and Engineering] [Osaka Univ., Suita, Osaka (Japan). Dept. of Materials Science and Engineering

1999-05-28

290

The Effect of Temperature Condition on Material Deformation and Die Wear  

NASA Astrophysics Data System (ADS)

The characteristics of temperature change on die and billet are very complex during the deformation process because of the interaction between them and some unstable external factors. In this paper, the numerical simulation model for the crank shaft die forging was established by means of the rigid-plastic FEM method. The model was validated by optical non-contact 3D measurementATOS. Based on available research results, this paper explored the effect of temperature conditions on material deformation and die wear. Three parameters, press velocity and initial temperature of billet and die, were chosen to illustrate the effects. From the experimental results, the effect of process parameters on deformation ability of the material is simple, while the effect on die wear is relatively complicated. The press velocity plays an important role on die wear when the initial temperature of the billet has larger influence on material deformation. A conclusion can be drawn that when the initial temperature of the billet is 1100 C, the initial temperature of the die is 250 C, and the velocity is kept in the range of 200-300 mm/s, the optimum solution for deformation ability of the material and die wear can be obtained. It is possible for the conclusion to be extended further for the control of temperature condition to optimize die life and material deformation.

Zhi, Jia; Jie, Zhou; Jin-jin, Ji; Liang, Huang; Hai, Yang

2013-07-01

291

Extended-time-scale creep measurement on Maraging cantilever blade springs  

NASA Astrophysics Data System (ADS)

Two controlled temperature facilities were built to induce an accelerated creep rate in a Maraging steel GAS spring and to measure the material's creep over an artificially extended period of time. The data acquisition of the first experiment lasted for almost a year, but then the blades were allowed to creep for six more years before measuring the permanent deformation integrated over time. The data from this first experiment was polluted by a defect in the data acquisition software, but yielded overall creep limits and an evaluation of the Arrhenius acceleration of creep speed with temperature (1.280.13 C -1). The duration of the second experiment was only 1 year but more free of systematic errors. The effective test period of this second experiment (normalized with the Arrhenius acceleration measured in the first experiment) extends in billions of years showing no sign of anomalous creep. The result of both experiments also produced a simple procedure capable of eliminating all practical effects of creep from the Advanced LIGO seismic isolation and suspensions. Measurements of creep under various stress levels, and of the thermal variations of Young's modulus (2.023 (0.013)10 -4 C -1) are reported as well.

Virdone, Nicole; Agresti, Juri; Bertolini, Alessandro; DeSalvo, Riccardo; Stellacci, Rosalia; Kamp, Justin; Mantovani, Maddalena; Sannibale, Virginio; Tarallo, Marco; Kaltenegger, Lisa

2008-08-01

292

Creep behavior in SiC whisker-reinforced alumina composite  

SciTech Connect

Grain boundary sliding (often accompanied by cavitation) is a major contributor to compressive and tensile creep deformation in fine-grained aluminas, both with and without whisker-reinforcement. Studies indicate that the creep response of alumina composites reinforced with SiC whiskers can be tailored by controlling the composite microstructure and composition. The addition of SiC whiskers (< 30 vol%) significantly increases the creep resistance of fine-grained (1--2 {mu}m) alumina in air at temperatures of 1,200 and 1,300 C. However, at higher whisker contents (30 and 50 vol%), the creep resistance is degraded due to enhanced surface oxidation reactions accompanied by extensive creep cavitation. Densification aids (i.e., Y{sub 2}O{sub 3}), which facilitate silica glass formation and thus liquid phase densification of the composites, can also result in degradation of creep resistance. On the other hand, increasing the matrix grain size or decreasing the whisker aspect ratio (increased whisker number density) results in raising the creep resistance of the composites. These observations not only explain the variability in the creep response of various SiC whisker-reinforced alumina composites but also indicate factors that can be used to enhance the elevated temperature performance.

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

1994-10-01

293

High-temperature texture in naturally deformed Carrara marble from the Alpi Apuane, Italy  

Microsoft Academic Search

From deformation experiments and numerical modelling, a large type variety of crystallographic preferred orientations (textures) are known for calcite. In contrast, naturally deformed samples usually show the low-temperature (LT)-texture type with only minor texture variations. The high-temperature (HT)-texture type is rarely described and mostly not very well defined. Based on neutron diffraction measurements and a quantitative texture analysis by means

Bernd Leiss; Giancarlo Molli

2003-01-01

294

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

NASA Astrophysics Data System (ADS)

A model of damage evolution in austenitic stainless steels under creep loading at elevated temperatures is proposed. The initial microstructure is idealized as a space-tiling aggregate of identical rhombic dodecahedral grains, which undergo power-law creep deformation. Damage evolution in the form of cavitation and wedge cracking on grain-boundary facets is considered. Both diffusion- and deformation-driven grain-boundary cavity growth are treated. Cavity and wedge-crack length evolution are derived from an energy balance argument that combines and extends the models of Cottrell (1961 Trans. AIME 212 191-203), Williams (1967 Phil. Mag. 15 1289-91) and Evans (1971 Phil Mag. 23 1101-12). The time to rupture predicted by the model is in good agreement with published experimental data for a type 316 austenitic stainless steel under uniaxial creep loading. Deformation and damage evolution at the microscale predicted by the present model are also discussed.

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

2011-01-01

295

Effect of High-Temperature Severe Plastic Deformation on Microstructure and Mechanical Properties of IF Steel  

NASA Astrophysics Data System (ADS)

Extensive research work has been carried out on interstitial-free steel to understand its response to deformation; particularly, the behavior during severe plastic deformation (SPD). However, most of these studies were mainly undertaken in the ferritic regime. The present investigation reports the initial results of our attempt to employ accumulative roll bonding (ARB), one of the variants of SPD, at a high temperature (950 C). A considerable grain refinement has been observed, which may be attributed to the severity of deformation and recrystallisation at high temperatures. Nanoindentation tests have been performed at various stages of ARB process to understand the evolution of mechanical properties.

Jindal, Vikas; Rupa, P. K. P.; Mandal, G. K.; Srivastava, V. C.

2014-06-01

296

Back stress in dislocation creep. Part 1: Basic concepts and measuring techniques  

NASA Technical Reports Server (NTRS)

A theory is proposed whereby the plastic deformation of metal materials is determined by the difference between the applied stress and the back stress which characterizes the resistance of the material to plastic deformation. The back stress is usually equivalent to the internal stress or the friction stress and depends on the magnitude of the applied stress and temperature. The concept of back stress is applied to the case of the dislocation creep of precipitation-hardened or dispersion-strengthened metal materials. An additivity rule is formulated which can be useful in interpreting the creep behavior of such materials.

Cadek, J.

1984-01-01

297

Present-day deformation along the El Pilar Fault in eastern Venezuela: Evidence of creep along a major transform boundary  

NASA Astrophysics Data System (ADS)

The right-lateral strike-slip El Pilar Fault is one of the major structures that accommodate the relative displacement between the Caribbean and South-America Plates. This fault, which trends East-West along the northeastern Venezuela margin, is a seismogenic source, and shows numerous evidence for active tectonics, including deformation of the Quaternary sediments filling the Cariaco Gulf. Because the main El Pilar Fault strand belongs to a set of strike-slip faults and thrusts between the stable Guyana shield (South) and the Caribbean oceanic floor (North), a GPS network was designed and installed to measure the relative motion of the El Pilar Fault and other faults. The results obtained from the comparison of 2003 and 2005 surveys indicate: (i) a lack of significant displacement (especially shortening) in the Serrania del Interior (Neogene cordillera overthrusted above the Guyana craton), (ii) an eastward displacement (relative to fixed south America plate) up to 22 mm/year of benchmarks located north of the El Pilar Fault. Velocities simulations using dislocations in an elastic half-space show: (1) the concentration along the El Pilar Fault of the whole Caribbean-South America relative displacement, (2) the existence of an important component of aseismic displacement along the upper part of the El Pilar Fault. Between 12 km depth and the surface, only 40% of displacement is locked for the western segment and 50% for the eastern segment. This last phenomenon may be related to the existence of serpentinite lenses along the fault zone as observed for segments of San Andreas and North Anatolian faults.

Jouanne, Franois; Audemard, Franck A.; Beck, Christian; Van Welden, Aurlien; Ollarves, Reinaldo; Reinoza, Carlos

2011-05-01

298

Creep properties of eutectic Sn3.5Ag solder joints reinforced with mechanically incorporated Ni particles  

Microsoft Academic Search

The creep deformation behavior of eutectic Sn-3.5Ag based Ni particle rein forced composite solder joints was investigated.\\u000a The Ni particle reinforced composite solder was prepared by mechanically dispersing 15 vol.% of Ni particles into eutectic\\u000a Sn-3.5Ag solder paste. Static-loading creep tests were carried out on solder joint specimens at 25 C, 65 C, and 105 C, representing\\u000a homologous temperatures ranging

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

2001-01-01

299

High-temperature deformation and microstructural analysis for Si3N4-Sc2O3  

NASA Technical Reports Server (NTRS)

It was indicated that Si3N4 doped with Sc2O3 may exhibit high temperature mechanical properties superior to Si3N4 systems with various other oxide sintered additives. High temperature deformation of samples was studied by characterizing the microstructures before and after deformation. It was found that elements of the additive, such as Sc and O, exist in small amounts at very thin grain boundary layers and most of them stay in secondary phases at triple and multiple grain boundary junctions. These secondary phases are devitrified as crystalline Sc2Si2O7. Deformation of the samples was dominated by cavitational processes rather than movements of dislocations. Thus the excellent deformation resistance of the samples at high temperature can be attributed to the very small thickness of the grain boundary layers and the crystalline secondary phase.

Cheong, Deock-Soo; Sanders, William A.

1990-01-01

300

Subglacial deformation at sub-freezing temperatures? Evidence from Hagafellsjkull-Eystri, Iceland  

NASA Astrophysics Data System (ADS)

We report evidence of deformation at sub-freezing temperatures beneath Hagafellsjkull-Eystri, an Icelandic surge-type glacier. The bed of a piedmont lobe that advanced during the 1999 surge comprises deformed blocks of glacier ice set within frozen sediment. This material has also been injected through overlying ice to form a network of crevasse-squeeze ridges. This layer contains evidence for two phases of deformation under contrasting rheological conditions: (1) deformation under relatively warm conditions, when the blocks of glacier ice acted as competent clasts within an unfrozen deforming matrix and (2) subsequent deformation at sub-freezing temperatures when the ice blocks were attenuated into the surrounding frozen matrix along fractures and planar shears enriched with excess ice. This suggests that the basal thermal regime of the advancing ice margin changed from warm-based to cold-based during the surge event. The persistence and potential prevalence of subglacial sediment deformation at sub-freezing temperatures has fundamental implications for our understanding of the dynamic behaviour, sediment flux and geomorphic ability of cold-based glaciers.

Bennett, Matthew R.; Waller, Richard I.; Midgley, Nicholas G.; Huddart, David; Gonzalez, Silvia; Cook, Simon J.; Tomio, Alexandre

2003-04-01

301

Non-Contact Measurements of Creep Properties of Refractory Materials  

NASA Technical Reports Server (NTRS)

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

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

2006-01-01

302

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

SciTech Connect

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

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

1994-06-01

303

Creep Strength of Nb-1Zr for SP-100 Applications  

NASA Astrophysics Data System (ADS)

Power systems that are used to provide electrical power in space are designed to optimize conversion of thermal energy to electrical energy and to minimize the mass and volume that must be launched. Only refractory metals and their alloys have sufficient long-term strength for several years of uninterrupted operation at the required temperatures of 1200 K and above. The high power densities and temperatures at which these reactors must operate require the use of liquid-metal coolants. The alloy Nb-1 wt % Zr (Nb-lZr), which exhibits excellent corrosion resistance to alkali liquid-metals at high temperatures, is being considered for the fuel cladding, reactor structural, and heat-transport systems for the SP-100 reactor system. Useful lifetime of this system is limited by creep deformation in the reactor core. Nb-lZr sheet procured to American Society for Testing and Materials (ASTM) specifications for reactor grade and commercial grade has been processed by several different cold work and annealing treatments to attempt to produce the grain structure (size, shape, and distribution of sizes) that provides the maximum creep strength of this alloy at temperatures from 1250 to 1450 K. The effects of grain size, differences in oxygen concentrations, tungsten concentrations, and electron beam and gas tungsten arc weldments on creep strength were studied. Grain size has a large effect on creep strength at 1450 K but only material with a very large grain size (150 ?m) exhibits significantly higher creep strength at 1350 K. Differences in oxygen or tungsten concentrations did not affect creep strength, and the creep strengths of weldments were equal to, or greater than, those for base metal.

Horak, James A.; Egner, Larry K.

1994-07-01

304

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

SciTech Connect

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). The operating temperatures for most of the solid oxide fuel cells (SOFC) under development in the SECA program are around 800oC, which exceeds the glass transition temperature Tg for most glass ceramic materials. The goal of the study is to develop a creep model to capture the creep behavior of glass ceramic materials at high temperature and to investigate the effect of creep of glass ceramic sealant materials on stresses in glass seal and on the various interfaces of glass seal with other layers. The self-consistent creep models were incorporated into SOFC-MP and Mentat FC, and finite element analyses were performed to quantify the stresses in various parts. The stress in glass seals were released due to its creep behavior during the operating environments.

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

2010-01-02

305

Cryogenic deformation of high temperature superconductive composite structures  

DOEpatents

An improvement in a process of preparing a composite high temperature oxide superconductive wire is provided and involves conducting at least one cross-sectional reduction step in the processing preparation of the wire at sub-ambient temperatures.

Roberts, Peter R. (Groton, MA); Michels, William (Brookline, MA); Bingert, John F. (Jemez Springs, NM)

2001-01-01

306

A unified approach to grain boundary sliding in creep and superplasticity  

Microsoft Academic Search

Rachinger grain boundary sliding is a characteristic of high temperature deformation in both creep when the grain size is large (d > [lambda]) and superplasticity when the grain size is small (d < [lambda]), where d and [lambda] are the grain size and the subgrain size, respectively. An analytical procedure is used to determine the rate equation for Rachinger sliding

T LANGDON

1994-01-01

307

The high temperature creep and fracture behavior of a 1pct CrMoV rotor steel  

Microsoft Academic Search

The creep and fracture behavior of a low alloy ferritic steel has been studied between 220 and 340 MN\\/m2 at 823 and 838 K. Over most of the creep life the creep strain could be represented by: ?-?o + ?T\\u000a (l-e-mt ) + ?st + ?L\\u000a e\\u000a p\\u000a (t-t\\u000a t) where ?o is the instantaneous strain on loading, ?T the

D. Side

1976-01-01

308

Influence of precipitate morphology on intermediate temperature creep properties of a nickel-base superalloy single crystal  

NASA Technical Reports Server (NTRS)

The relative creep behavior of cuboidal (as-heat treated) and rafted (precrept at 1000 C) gamma-prime microstructures in the single-crystal Ni-based superalloy NASAIR 100 at 760 C was investigated using SEM and TEM examinations of materials at various stages of creep. It was found that, at high applied stresses, the crystals with cuboidal gamma-prime structure had both lower minimum creep rates and longer rupture lives than the crystals with lamellar gamma-prime. At lower stress levels, the initially cuboidal gamma-prime microstructure maintained a lower creep rate, but exhibited a similar rupture life compared to the prerafted crystals.

Nathal, M. V.; Mackay, R. A.; Miner, R. V.

1989-01-01

309

Microdeformation experiments on chalk - fluids, fracture and creep  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

310

Effects of grain growth on grain-boundary diffusion creep by molecular-dynamics simulation  

Microsoft Academic Search

Molecular-dynamics simulations are used to elucidate the effects of grain growth on grain-boundary diffusion creep and grain-boundary sliding during high-temperature deformation of a nanocrystalline Pd model microstructure. The initial microstructure consists of a 25-grain polycrystal with an average grain size of about 15 nm and a columnar grain shape. Prior to the onset of significant grain growth, the deformation proceeds

A. J. Haslam; V. Yamakov; D. Moldovan; D. Wolf; S. R. Phillpot; H. Gleiter; Forschungszentrum Karlsruhe

2004-01-01

311

Flow unit perspective on room temperature homogeneous plastic deformation in metallic glasses.  

PubMed

A mandrel winding method, which can realize remarkable homogeneous plastic deformation at room temperature for various metallic glasses, is applied to characterize plastic flow units and study their relationship with macroscopic deformations and relaxations. The method can provide information on the activation energy, activation time, size, intrinsic relaxation time, distribution, and density of flow units. We find the plasticity of a metallic glass can be controlled through modulating the features of flow units. The results have benefits for better understanding the structural origins of deformations and relaxations, and for designing metallic glasses with improved performances. PMID:25105632

Lu, Z; Jiao, W; Wang, W H; Bai, H Y

2014-07-25

312

Flow Unit Perspective on Room Temperature Homogeneous Plastic Deformation in Metallic Glasses  

NASA Astrophysics Data System (ADS)

A mandrel winding method, which can realize remarkable homogeneous plastic deformation at room temperature for various metallic glasses, is applied to characterize plastic flow units and study their relationship with macroscopic deformations and relaxations. The method can provide information on the activation energy, activation time, size, intrinsic relaxation time, distribution, and density of flow units. We find the plasticity of a metallic glass can be controlled through modulating the features of flow units. The results have benefits for better understanding the structural origins of deformations and relaxations, and for designing metallic glasses with improved performances.

Lu, Z.; Jiao, W.; Wang, W. H.; Bai, H. Y.

2014-07-01

313

Evidence of dislocation cross-slip in MAX phase deformed at high temperature  

NASA Astrophysics Data System (ADS)

Ti2AlN nanolayered ternary alloy has been plastically deformed under confining pressure at 900C. The dislocation configurations of the deformed material have been analyzed by transmission electron microscopy. The results show a drastic evolution compared to the dislocation configurations observed in the Ti2AlN samples deformed at room temperature. In particular, they evidence out-of-basal-plane dislocations and interactions. Moreover numerous cross-slip events from basal plane to prismatic or pyramidal planes are observed. These original results are discussed in the context of the Brittle-to-Ductile Transition of the nanolayered ternary alloys.

Guitton, Antoine; Joulain, Anne; Thilly, Ludovic; Tromas, Christophe

2014-09-01

314

High temperature deformation behavior and mechanism of spray deposited Al-Fe-V-Si alloy  

Microsoft Academic Search

Al-8.5Fe-1.3V-1.7Si alloy was prepared by spray deposition and hot extrusion. The high temperature plastic deformation behavior of the spray deposited Al-8.5Fe-1.3V-1.7Si alloy was investigated in the strain rate range of 2.77 10?4?2.77 10?2s?1 and temperature range of 350550 C by Gleebe-1500 thermomechanical simulator. The mechanism of the high temperature plastic deformation of the alloys was studied by TEM

Yu-de XIAO; Wei WANG; Wen-xian LI

2007-01-01

315

Vacuum confinement at finite temperature for scalar QED in magnetic field and deformed boundary condition  

E-print Network

We investigate the Casimir effect at finite temperature for a charged scalar field in the presence of an external uniform and constant magnetic field, perpendicular to the Casimir plates. We have used a boundary condition characterized by a deformation parameter $\\theta$; for $\\theta=0$ we have a periodic condition and for $\\theta=\\pi$, an antiperiodic one, for intermediate values, we have a deformation. The temperature was introduced using the imaginary time formalism and both the lagrangian and free energy were obtained from Schwinger proper time method for computing the effective action. We also computed the permeability and its asymptotic expressions for low and high temperatures.

M. V. Cougo-Pinto; C. Farina; J. F. M. Mendes; A. Tort

2001-10-15

316

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

NASA Technical Reports Server (NTRS)

The intermetallic compound NiAl is one of many advanced materials which is being scrutinized for possible use in high temperature, structural applications. Stoichiometric NiAl has a high melting temperature, excellent oxidation resistance, and good thermal conductivity. Past research has concentrated on improving monotonic properties. The encouraging results obtained on binary and micro-alloyed NiAl over the past ten years have led to the broadening of NiAl experimental programs. The purpose of this research project was to determine the low cycle fatigue properties and dislocation mechanisms of stoichiometric NiAl at temperatures near the monotonic brittle-to-ductile transition. The fatigue properties were found to change only slightly in the temperature range of 600 to 700 K; a temperature range over which monotonic ductility and fracture strength increase markedly. The shape of the cyclic hardening curves coincided with the changes observed in the dislocation structures. The evolution of dislocation structures did not appear to change with temperature.

Cullers, Cheryl L.; Antolovich, Stephen D.

1993-01-01

317

Failure prediction of magnesium alloy sheets deforming at warm temperatures using the Zener-Holloman parameter  

Microsoft Academic Search

In the present study, a new method of predicting fracture in magnesium alloy sheet deforming under warm-working conditions has been developed. The effects of temperature and strain rate have been incorporated into the ductile fracture criteria by formulating the damage growth resistance as a function of strain rate and temperature based on the finding of correlation between the fracture strain

Heung-Kyu Kim; Woo-Jin Kim

2010-01-01

318

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

NASA Astrophysics Data System (ADS)

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

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

2014-07-01

319

Deformations of glassy polymers in very low temperature regime within cylindrical micropores  

E-print Network

The deformation kinetics for glassy polymers confined in microscopic domain at very low temperature regime was investigated using a transition-rate-state dependent model considering the shear thinning behavior which means, once material being subjected to high shear rates, the viscosity diminishes with increasing shear rate. The preliminary results show that there might be nearly frictionless fields for rate of deformation due to the almost vanishing shear stress in micropores at very low temperature regime subjected to some surface conditions : The relatively larger roughness (compared to the macroscopic domain) inside micropores and the slip. As the pore size decreases, the surface-to-volume ratio increases and therefore, surface roughness will greatly affect the deformation kinetics in micropores. By using the boundary perturbation method, we obtained a class of temperature and activation energy dependent fields for the deformation kinetics at low temperature regime with the presumed small wavy roughness distributed along the walls of an cylindrical micropore. The critical deformation kinetics of the glassy matter is dependent upon the temperature, activation energy, activation volume, orientation dependent and is proportional to the (referenced) shear rate, the slip length, the amplitude and the orientation of the wavy-roughness.

Guanghua Zhu

2008-08-28

320

Plastic Instability in Amorphous Selenium near its Glass Transition Temperature  

SciTech Connect

Deformation behavior of amorphous selenium near its glass transition temperature (31 C) has been investigated by uniaxial compression and nanoindentation creep tests. Cylindrical specimens compressed at high temperatures and low strain rates deform into drum-like shape, while tests at low temperatures and high strain rates lead to fragmentation. These results agree nicely with the stress exponent and kinetic activation parameters extracted from the nanoindentation creep tests by using a similarity analysis. The dependence of deformation modes on temperature and strain rate is understood as a consequence of material instability and strain localization in the rate-dependent solids.

Su, Caijun [ORNL; Lamanna Jr, James [ORNL; Gao, Yanfei [ORNL; Oliver, Warren C. [MTS Nanoinstruments Innovation Center, Oak Ridge; Pharr, George M [University of Tennessee, Knoxville (UTK) & Oak Ridge National Laboratory (ORNL)

2010-01-01

321

Procedure for describing the deformation of materials to fracture under conditions of near-superplasticity  

SciTech Connect

The ability of metallic materials to deform by hundreds or even thousand of percent, with a substantial drop in resistance to deformation is known as the superplasticity effect. Here the titanium allow VT-9 (as received rod of diameter 16 mm) under pure tension is used as an example to show that the defining equations proposed for the description of creep and creep-rupture strength at a moderate temperature can be extended to the range of temperatures close to superplasticity, T > 0.6T{sup pl}. The defining equations used have one scalar damageability parameter, which is found by means of the quantities {omega} = {epsilon}/{epsilon}{sub *} ({epsilon} are instantaneous strains and {epsilon}{sub *} are breaking strains). A method is given for determining the parameters of the creep and damageability equations with allowance for tertiary creep over wide ranges of temperature and force.

Gorev, B.V.; Klopotov, I.D.; Zakharova, T.E.

1995-07-01

322

Role of the grain-boundary phase on the elevated-temperature strength, toughness, fatigue and creep resistance of silicon carbide sintered with Al, B and C  

Microsoft Academic Search

The high-temperature mechanical properties, specifically strength, fracture toughness, cyclic fatigue-crack growth and creep behavior, of an in situ toughened silicon carbide, with Al, B and C sintering additives (ABC-SiC), have been examined at temperatures from ambient to 1500C with the objective of characterizing the role of the grain-boundary film\\/phase. It was found that the high strength, cyclic fatigue resistance and

D. Chen; M. E. Sixta; X. F. Zhang; L. C. De Jonghe; R. O. Ritchie

2000-01-01

323

Temperature Effects on Deformation and Serration Behavior of High-Entropy Alloys (HEAs)  

NASA Astrophysics Data System (ADS)

Many materials are known to deform under shear in an intermittent way with slip avalanches detected as acoustic emission and serrations in the stress-strain curves. Similar serrations have recently been observed in a new class of materials, called high-entropy alloys (HEAs). Here, we discuss the serration behaviors of several HEAs from cryogenic to elevated temperatures. The experimental results of slow compression and tension tests are compared with the predictions of a slip-avalanche model for the deformation of a broad range of solids. The results shed light on the deformation processes in HEAs. Temperature effects on the distributions of stress drops and the decrease of the cutoff (i.e., of the largest observed slip size) for increasing temperature qualitatively agree with the model predictions. The model is used to quantify the serration characteristics of HEAs, and pertinent implications are discussed.

Antonaglia, J.; Xie, X.; Tang, Z.; Tsai, C.-W.; Qiao, J. W.; Zhang, Y.; Laktionova, M. O.; Tabachnikova, E. D.; Yeh, J. W.; Senkov, O. N.; Gao, M. C.; Uhl, J. T.; Liaw, P. K.; Dahmen, K. A.

2014-09-01

324

Temperature Effects on Deformation and Serration Behavior of High-Entropy Alloys (HEAs)  

NASA Astrophysics Data System (ADS)

Many materials are known to deform under shear in an intermittent way with slip avalanches detected as acoustic emission and serrations in the stress-strain curves. Similar serrations have recently been observed in a new class of materials, called high-entropy alloys (HEAs). Here, we discuss the serration behaviors of several HEAs from cryogenic to elevated temperatures. The experimental results of slow compression and tension tests are compared with the predictions of a slip-avalanche model for the deformation of a broad range of solids. The results shed light on the deformation processes in HEAs. Temperature effects on the distributions of stress drops and the decrease of the cutoff (i.e., of the largest observed slip size) for increasing temperature qualitatively agree with the model predictions. The model is used to quantify the serration characteristics of HEAs, and pertinent implications are discussed.

Antonaglia, J.; Xie, X.; Tang, Z.; Tsai, C.-W.; Qiao, J. W.; Zhang, Y.; Laktionova, M. O.; Tabachnikova, E. D.; Yeh, J. W.; Senkov, O. N.; Gao, M. C.; Uhl, J. T.; Liaw, P. K.; Dahmen, K. A.

2014-10-01

325

Creep Measurement Video Extensometer  

NASA Technical Reports Server (NTRS)

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

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

2011-01-01

326

Effects of strain rate, temperature and thermomechanical coupling on the finite strain deformation of glassy polymers  

Microsoft Academic Search

The effects of strain rate and temperature on the inelastic response of a glassy polymer have been studied. Deformation tests in uniaxial compression to strains of ?1.0 were conducted on polymethylmethacrylate (PMMA) over a range of temperatures at a strain rate of ?0.001\\/s providing nearly isothermal test conditions and thus documenting the temperature dependence of yield, strain softening, and strain

Ellen M. Arruda; Mary C. Boyce; R. Jayachandran

1995-01-01

327

Application of two creep fatigue life models for the prediction of elevated temperature crack initiation of a nickel base alloy  

NASA Technical Reports Server (NTRS)

Cyclic Damage Accumulation (CDA) and Total Strain-Strain Range Partitioning (TS-SRP) models for predicting the creep-fatigue crack initiation life of high temperature alloys are presented. The models differ in their fundamental assumptions regarding the controlling parameters for fatigue crack initiation and in the amount of data required to determine model constants. The CDA model represents a ductility exhaustion approach and uses stress quantities to calculate the cyclic fatigue damage. The TS-SRP model is based on the use of total mechanical strain and earlier concepts of the Strain Range Partitioning Method. Both models were applied to a well controlled fatigue data set at a high temperature nickel base alloy, B1900 + Hf, tested at 1600 F and 1800 F. The tests were divided into a baseline data set required to determine model constants and a verification data set for evaluation of the predictive capability of the models. Both models correlated the baseline data set to within factors of two in life, and predicted the verification data set to within a factor of three or better. In addition, sample calculations to demonstrate the application of each model and discusions of the predictive capabilities and areas requiring further development are presented.

Moreno, V.; Nissley, D. M.; Halford, G. R.; Saltsman, J. F.

1985-01-01

328

Mechanisms governing deformation and damage during elevated-temperature fatigue of an aluminum-magnesium-silicon alloy  

Microsoft Academic Search

The cyclic deformation and fracture characteristics of aluminum alloy 6061 are presented and discussed. The specimens were\\u000a cyclically deformed using fully reversed tension-compression loading under total strain-amplitude control, over a range of\\u000a temperatures. The alloy showed evidence of softening to failure at all test temperatures. The degree of softening during fully\\u000a reversed deformation increased with test temperature. The presence of

T. S. Srivatsan; S. Anand; N. Narendra

1997-01-01

329

High temperature deformation behavior of YBa2Cu3O6+X superconducting ceramic materials. Technical report  

SciTech Connect

Superplastic deformation is being explored as a means to turn the new ceramic superconducting YBa2Cu3O(6+x) into useful Naval hardware. The deformation experiments that were conducted on fine YBa2Cu3O(6+x) powders suggest that the maximum deformation that can be achieved without the degradation of superconductivity is about 62 % at 850 deg C. The addition of silver improves the maximum deformation and the addition of alumina has a devastating effect on the deformation mode.... High temperature, Deformation, Superplasticity silver, Alumina, Superconductivity.

Rao, A.S.; Aprigliano, L.F.; Arora, O.P.

1993-05-15

330

Creep Resistant Zinc Alloy  

SciTech Connect

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

Frank E. Goodwin

2002-12-31

331

Dimensional Changes and Radiation Creep in Graphite at Very High Neutron Doses  

Microsoft Academic Search

RADIATION creep1-4 is the deformation produced by the combined effect of stress and irradiation in a nuclear reactor. In graphite, radiation creep consists of a permanent set, transient creep, and steady-state creep. The permanent set and transient creep are comparable with the elastic strain and it is normally assumed that the steady-state creep is proportional to the stress and the

J. H. W. Simmons; A. J. Perks

1965-01-01

332

Deformation, Stress Relaxation, and Crystallization of Lithium Silicate Glass Fibers Below the Glass Transition Temperature  

NASA Technical Reports Server (NTRS)

The deformation and crystallization of Li(sub 2)O (center dot) 2SiO2 and Li(sub 2)O (center dot) 1.6SiO2 glass fibers subjected to a bending stress were measured as a function of time over the temperature range -50 to -150 C below the glass transition temperature (Tg). The glass fibers can be permanently deformed at temperatures about 100 C below T (sub)g, and they crystallize significantly at temperatures close to, but below T,, about 150 C lower than the onset temperature for crystallization for these glasses in the no-stress condition. The crystallization was found to occur only on the surface of the glass fibers with no detectable difference in the extent of crystallization in tensile and compressive stress regions. The relaxation mechanism for fiber deformation can be best described by a stretched exponential (Kohlrausch-Williams-Watt (KWW) approximation), rather than a single exponential model.The activation energy for stress relaxation, Es, for the glass fibers ranges between 175 and 195 kJ/mol, which is considerably smaller than the activation energy for viscous flow, E, (about 400 kJ/mol) near T, for these glasses at normal, stress-free condition. It is suspected that a viscosity relaxation mechanism could be responsible for permanent deformation and crystallization of the glass fibers below T,

Ray, Chandra S.; Brow, Richard K.; Kim, Cheol W.; Reis, Signo T.

2004-01-01

333

Creep behavior of magnesium die-cast alloy ZA85  

Microsoft Academic Search

The compressive creep behavior of a magnesium die-cast alloy with 8 wt.% Zn and 5 wt.% Al was investigated. We argue that grain boundary sliding does not contribute to the deformation. Creep data and microstructural analysis strongly support dislocation creep, influenced by the formation and over-aging of precipitates, as the dominant mechanism.

M. Vogel; O. Kraft; E. Arzt

2003-01-01

334

Creep Properties of Solid Oxide Fuel Cell Glass-Ceramic Seal G18  

SciTech Connect

This study utilizes nanoindentation to investigate and measure creep properties of a barium calcium aluminosilicate glass-ceramic used for solid oxide fuel cell seals (SOFCs). Samples of the glassceramic seal material were aged for 5h, 50h, and 100h to obtain different degrees of crystallinity. Instrumented nanoindentation was performed on the samples with different aging times at different temperatures to investigate the strain rate sensitivity during inelastic deformation. The temperature dependent behavior is important since SOFCs operate at high temperatures (800-1000C). Results show that the samples with higher crystallinity were more resistant to creep, and the creep compliance tended to decrease with increasing temperature, especially with further aged samples.

Milhans, Jacqueline; Khaleel, Mohammad A.; Sun, Xin; Tehrani, Mehran; Al-Haik, Marwan; Garmestani, Hamid

2010-11-01

335

CREEP CRACK GROWTH ASSESSMENT METHODS  

Microsoft Academic Search

This paper describes engineering methods for assessing defects in components operating at elevated temperatures where creep crack growth needs to be considered. Practical aspects such as the treatment of secondary and residual stresses and the inclusion of realistic creep laws are included. Recent finite element results for complex loading are described, as validation of the assessment methods. The British Energy

R A Ainsworth; Y Lei

336

Creep, fatigue and creep-fatigue interactions in modified 9% Chromium - 1% Molybdenum (P91) steels  

NASA Astrophysics Data System (ADS)

Grade P91 steel, from the class of advanced high-chrome ferritic steels, is one of the preferred materials for many elevated temperature structural components. Creep-fatigue (C-F) interactions, along with oxidation, can accelerate the kinetics of damage accumulation and consequently reduce such components' life. Hence, reliable C-F test data is required for meticulous consideration of C-F interactions and oxidation, which in turn is vital for sound design practices. It is also imperative to develop analytical constitutive models that can simulate and predict material response under various long-term in-service conditions using experimental data from short-term laboratory experiments. Consequently, the major objectives of the proposed research are to characterize the creep, fatigue and C-F behavior of grade P91 steels at 625 C and develop robust constitutive models for simulating/predicting their microstructural response under different loading conditions. This work will utilize experimental data from 16 laboratories worldwide that conducted tests (creep, fatigue and C-F) on grade P91 steel at 625C in a round-robin (RR) program. Along with 7 creep deformation and rupture tests, 32 pure fatigue and 46 C-F tests from the RR are considered in this work. A phenomenological constitutive model formulated in this work needs just five fitting parameters to simulate/predict the monotonic, pure fatigue and C-F behavior of grade P91 at 625 C. A modified version of an existing constitutive model is also presented for particularly simulating its isothermal creep deformation and rupture behavior. Experimental results indicate that specimen C-F lives, as measured by the 2% load drop criterion, seem to decrease with increasing strain ranges and increasing hold times at 625C. Metallographic assessment of the tested specimens shows that the damage mode in both pure fatigue and 600 seconds hold time cyclic tests is predominantly transgranular fatigue with some presence of oxidation spikes. The damage mode in 1800 second hold time cyclic tests is an interaction of transgranular fatigue with dominant oxide spikes and creep cavitation. Other experimental results including the statistical analysis and inter- and intra-laboratory variability in the C-F lifetimes are provided in the text. Scatter factor for any of creep, monotonic, pure fatigue and C-F simulations is shown to be at a maximum of 1.3, in comparison to > 5 expected for a RR. Moreover, the microstructural variability between nominally homogeneous specimens can be inherently accounted by the formulated constitutive model.

Kalyanasundaram, Valliappa

337

Continuous turbine blade creep measurement based on Moir  

NASA Astrophysics Data System (ADS)

Moir imaging has been used to measure creep in the airfoil section of gas turbine blades. The ability to accurately assess creep and other failure modes has become an important engineering challenge, because gas turbine manufacturers are putting in place condition-based maintenance programs. In such maintenance programs, the condition of individual components is assessed to determine their remaining lives. Using pad-print technology, a grating pattern was printed directly on a turbine blade for localized creep detection using the spacing change of moir pattern fringes. A creep measurement prototype was assembled for this application which contained a lens, reference grating, camera and lighting module. This prototype comprised a bench-top camera system that can read moir patterns from the turbine blade sensor at shutdown to determine creep level in individual parts by analyzing the moir fringes. Sensitivity analyses and noise factor studies were performed to evaluate the system. Analysis software was also developed. A correlation study with strain gages was performed and the measurement results from the moir system align well with the strain gage readings. A mechanical specimen subjected to a one cycle tensile test at high temperature to induce plastic deformation in the gage was used to evaluate the system and the result of this test exhibited good correlation to extensometer readings.

Liao, Yi; Tait, Robert; Harding, Kevin; Nieters, Edward J.; Hasz, Wayne C.; Piche, Nicole

2012-11-01

338

Effects of grain growth on grain-boundary diffusion creep by molecular-dynamics simulation.  

SciTech Connect

Molecular-dynamics simulations are used to elucidate the effects of grain growth on grain-boundary diffusion creep and grain-boundary sliding during high-temperature deformation of a nanocrystalline Pd model microstructure. The initial microstructure consists of a 25-grain polycrystal with an average grain size of about 15 nm and a columnar grain shape. Prior to the onset of significant grain growth, the deformation proceeds via the mechanism of Coble creep accompanied by grain-boundary sliding. While grain growth is generally known to decrease the creep rate due to the increase of the average grain size, the results obtained in this study reveal an enhanced creep rate at the onset of the grain growth, when rapid grain-boundary migration occurs. The enhanced creep rate is shown to arise from topological changes during the initial growth phases, which enhance both the stress-induced grain-boundary diffusive fluxes and grain-boundary sliding. Dislocations generated as a result of grain-rotation-induced grain coalescence and grain-boundary decomposition in the vicinity of certain triple junctions also contribute to the deformation.

Haslam, A. J.; Yamakov, V.; Moldovan, D.; Wolf, D.; Phillpot, S. R.; Gleiter, H.; Materials Science Division; Forschungszentrum Karlsruhe

2004-04-01

339

Evolution of uranium dislocation structure at different-rate deformation and different-temperature annealing  

NASA Astrophysics Data System (ADS)

The Williamson-Hall method based on analyzing the angular dependence of diffraction maximum broadening is used to study the dislocation structure. Densities of chaotically arranged dislocations on samples after their different-rate deformation are measured. Consideration is given to the dislocation structure of a spherical uranium sample after its shock-wave loading, as well as to the dislocation structure of model samples deformed at the rate of 10-3s-1 up to 5%, 20%, and 60% relative deformation. After deformation, samples were vacuum annealed at 200C, 400C, 600C, 720C, and 850C (in alpha-, beta-, and gamma-phases). Samples were cooled at the rate of 10?/min. Results for samples subjected to different-rate deformation and different-temperature annealing are compared. In the dislocation structure of the sample recovered after shock-wave loading, special features that cannot be described with the help of mechanisms observed at the low-rate deformation and cooling were elucidated. Systematic investigations of the uranium dislocation structure at the increasing speed of loading are to be continued).

Shestakov, A. E.; Artamonov, I. V.

2012-08-01

340

GRAVITY-DRIVEN SLOW CREEPING FLOW OF A THERMOVISCOUS BODY AT ELEVATED TEMPERATURES  

Microsoft Academic Search

The flow of a thermoviscous body at elevated temperature under gravity is described by the mass, momentum, and energy balances of an incompressible, homogeneous, heat conducting, nonlinearly viscous fluid, in which the shear response includes a strongly temperature?dependent rate factor. A scale analysis and coordinate stretching, appropriate for flows down an inclined surface, reflect the properties that depth?to?length ratios are

Kolumban Hutter; Laurent Vulliet

1985-01-01

341

Creep crack growth behavior of several structural alloys  

NASA Astrophysics Data System (ADS)

Creep crack growth behavior of several high temperature alloys, Inconel 600, Inconel 625, Inconel X-750, Hastelloy X, Nimonic PE-16, Incoloy 800, and Haynes 25 (HS-25) was examined at 540, 650, 760, and 870 C. Crack growth rates were analyzed in terms of both linear elastic stress intensity factor and J*-integral parameter. Among the alloys Inconel 600 and Hastelloy X did not show any observable crack growth. Instead, they deformed at a rapid rate resulting in severe blunting of the crack tip. The other alloys, Inconel 625, Inconel X-750, Incoloy 800, HS-25, and PE-16 showed crack growth at one or two temperatures and deformed continuously at other temperatures. Crack growth rates of the above alloys in terms ofJ* parameter were compared with the growth rates of other alloys published in the literature. Alloys such as Inconel X-750, Alloy 718, and IN-100 show very high growth rates as a result of their sensitivity to an air environment. Based on detailed fracture surface analysis, it is proposed that creep crack growth occurs by the nucleation and growth of wedge-type cracks at triple point junctions due to grain boundary sliding or by the formation and growth of cavities at the boundaries. Crack growth in the above alloys occurs only in some critical range of strain rates or temperatures. Since the service conditions for these alloys usually fall within this critical range, knowledge and understanding of creep crack growth behavior of the structural alloys are important.

Sadananda, K.; Shahinian, P.

1983-07-01

342

Thermal creep model for CWSR zircaloy-4 cladding taking into account the annealing of the irradiation hardening  

SciTech Connect

After irradiation and cooling in a pool, spent nuclear fuel assemblies are either transported for wet storage to a devoted site or loaded in casks for dry storage. During dry transportation or at the beginning of dry storage, the cladding is expected to be submitted to creep deformation under the hoop stress induced by the internal pressure of the fuel rod. The thermal creep is a potential mechanism that might lead to cladding failure. A new creep model was developed, based on a database of creep tests on as-received and irradiated cold-worked stress-relieved Zircaloy-4 cladding in a wide range of temperatures (310 degrees C to 470 degrees C) and hoop stress (80 to 260 MPa). Based on three laws-a flow law, a strain-hardening recovery law, and an annealing of irradiation hardening law this model allows the simulation of not only the transient creep and the steady-state creep, but also the early creep acceleration observed on irradiated samples tested in severe conditions, which was not taken into account in the previous models. The extrapolation of the creep model in the conditions of very long-term creep tests is reassuring, proving the robustness of the chosen formalism. The creep model has been assessed in progressively decreasing stress conditions, more representative of a transport. Set up to predict the cladding creep behavior under variable temperature and stress conditions, this model can easily be implemented into codes in order to simulate the thermomechanical behavior of spent fuel rods in various scenarios of postirradiation phases. (authors)

Cappelaere, Chantal; Limon, Roger; Duguay, Chrstelle; Pinte, Gerard; Le Breton, Michel [CEA Saclay, DEN, Serv Etud Mat Irradies, F-91191 Gif Sur Yvette, (France); Bouffioux, Pol [EDF R et D Renardieres, F-77818 Ecuelles, Moret Sur Loing, (France); Chabretou, Valerie [AREVA NP SAS, AREVA, F-69456 Lyon 6, (France); Miquet, Alain [EDF SEPTEN, F-69628 Villeurbanne, (France)

2012-02-15

343

Mechanism and kinetics of coagulation of ? ? -phase in nickel alloys at temperatures of hot plastic deformationin nickel alloys at temperatures of hot plastic deformation  

Microsoft Academic Search

It is known that hot plastic deformation of hard-to-deform complexly alloyed heat-resistant nickel alloys is easier to conduct\\u000a at temperatures of the double-phase region than at those of the single-phase region. In heating such alloys before deformation\\u000a and in the process of deformation cooling of them the amount of strengthening ??-phase and its sizes and distribution change, which exerts a

A. S. Kleshchev; O. N. Vlasova

1997-01-01

344

The effect of grain size on the high temperature plastic deformation of nb3sn  

Microsoft Academic Search

A study of high temperature plastic deformation has been undertaken on 10, 20, and 60 mum grain size Nb3Sn. The materials were produced by the hot isostatic pressing of powder blends. The 20 and 60 mum grain size material involved a stoichiometric blend of Nb and Sn powder, whereas the 10 mum grain size material involved a blend of 30.2

James B. Clark; George B. Hopple; Roger N. Wright

1983-01-01

345

Effects of Hydrothermal Cooling and Magma Injection on Mid-Ocean Ridge Temperature Structure, Deformation, and  

E-print Network

Effects of Hydrothermal Cooling and Magma Injection on Mid-Ocean Ridge Temperature Structure, Deformation, and Axial Morphology Mark D. Behn1, Jian Lin2, and Maria T. Zuber3 Fault development at mid-ocean ridge spreading centers is strongly dependent on the thermal state of the axial lithosphere. Thermal

Zuber, Maria

346

Invited review paper: Fault creep caused by subduction of rough seafloor relief  

NASA Astrophysics Data System (ADS)

Among the wide range of thermal, petrologic, hydrological, and structural factors that potentially affect subduction earthquakes, the roughness of the subducting seafloor is among the most important. By reviewing seismic and geodetic studies of megathrust locking/creeping state, we find that creeping is the predominant mode of subduction in areas of extremely rugged subducting seafloor such as the Kyushu margin, Manila Trench, northern Hikurangi, and southeastern Costa Rica. In Java and Mariana, megathrust creeping state is not yet constrained by geodetic observations, but the very rugged subducting seafloor and lack of large earthquakes also suggest aseismic creep. Large topographic features on otherwise relatively smooth subducting seafloor such as the Nazca Ridge off Peru, the Investigator Fracture Zone off Sumatra, and the Joban seamount chain in southern Japan Trench also cause creep and often stop the propagation of large ruptures. Similar to all other known giant earthquakes, the Tohoku earthquake of March 2011 occurred in an area of relatively smooth subducting seafloor. The Tohoku event also offers an example of subducting seamounts stopping rupture propagation. Very rugged subducting seafloor not only retards the process of shear localization, but also gives rise to heterogeneous stresses. In this situation, the fault zone creeps because of distributed deformation of fractured rocks, and the creep may take place as transient events of various spatial and temporal scales accompanied with small and medium-size earthquakes. This process cannot be described as stable or unstable friction along a single contact surface. The association of large earthquakes with relatively smooth subducting seafloor and creep with very rugged subducting seafloor calls for further investigation. Seafloor near-trench geodetic monitoring, high-resolution imaging of subduction fault structure, studies of exhumed ancient subduction zones, and laboratory studies of low-temperature creep will greatly improve our understanding of the seismogenic and creep processes and their hazard implications.

Wang, Kelin; Bilek, Susan L.

2014-01-01

347

Effect of long-time high-temperature aging on creep of an Nb-Zr-C alloy in a vacuum  

Microsoft Academic Search

The present work investigates the effect of holding metal in stressed and unstressed states for 5000 and 10,000 h at 900~ on creep characteristics. The test material was an Nb-1% Zr-0.1% C alloy. The tests were conducted in a multiposition unit [21 designed for high-temperature tests In a vacuum_< 5-10 -6 mm Hg created by means of NORD-250 magneto-discharg e

E. M. Lyutyi; A. G. Arakelov; G. G. Maksimo vich; L. P. Onisenko; O. S. Tsvikilevich

1978-01-01

348

Low-temperature AMS and the quantification of subfabrics in deformed rocks  

NASA Astrophysics Data System (ADS)

We evaluate the application and significance of Low-Temperature Anisotropy of Magnetic Susceptibility (LT-AMS) measurements in deformed mudrocks. Originally conceived as a way to enhance paramagnetic relative to ferromagnetic susceptibility, LT-AMS studies offer significant potential in constraining the coexistence of subfabrics that are due to phyllosilicate grains with different preferred orientations. In this study we report a detailed procedure to obtain such directional susceptibilities, measuring samples in multiple orientations at liquid nitrogen temperatures in order to determine the LT-AMS. Due to unequal changes of magnetic susceptibility in micas at low-temperature, the enhancement of standard AMS at low-temperature better separates interacting fabrics in natural rocks, particularly depositional fabrics versus deformational fabrics. LT-AMS is a non-destructive technique that readily offers an ability to separate ferromagnetic and paramagnetic fabrics, and allows the characterization and quantification of multiple fabrics in natural rocks.

Pars, Josep M.; van der Pluijm, Ben A.

2014-08-01

349

Effect of deformation temperature on microstructure and mechanical behaviour of warm working vanadium microalloyed steels  

Microsoft Academic Search

Plane strain compression tests of two V microalloyed steels and one plain CMn steel have been done to analyse the influence\\u000a of the deformation temperature, in the warm working range, on the final microstructure and subsequent mechanical behaviour.\\u000a In the case of V microalloyed steels, the reheating temperature has an effect on the amount of vanadium in solution prior\\u000a to

C. Garca-Mateo; B. Lpez; J. M. Rodriguez-Ibabe

2011-01-01

350

Dislocations and extended defects in AlN deformed at high temperatures  

Microsoft Academic Search

Polycrystalline AlN could be deformed up to 10% strain in compression at elevated temperatures (18201920 K) under constant stress in the range 150250 MPa or at a fixed strain rate of 5.6 10?6 s?1. Stress-strain curves show a marked temperature dependence. TEM investigations point to cavitation at grain boundaries as the main source of damage. Intragranular plasticity is achieved

Virginia Feregotto; Amand George; Jean-Pierre Michel

1997-01-01

351

Low cycle fatigue and creep-fatigue behavior of Ni-based alloy 230 at 850 C  

SciTech Connect

Strain-controlled low cycle fatigue (LCF) and creep-fatigue testing of Ni-based alloy 230 were carried out at 850 C. The material creep-fatigue life decreased compared with its low cycle fatigue life at the same total strain range. Longer hold time at peak tensile strain further reduced the material creep-fatigue life. Based on the electron backscatter diffraction, a novel material deformation characterization method was applied, which revealed that in low cycle fatigue testing as the total strain range increased, the deformation was segregated to grain boundaries since the test temperature was higher than the material equicohesive temperature and grain boundaries became weaker regions compared with grains. Creep-fatigue tests enhanced the localized deformation, resulting in material interior intergranular cracking, and accelerated material damage. Precipitation in alloy 230 helped slip dispersion, favorable for fatigue property, but grain boundary cellular precipitates formed after material exposure to the elevated temperature had a deleterious effect on the material low cycle fatigue and creep-fatigue property.

Chen, Xiang [ORNL; Yang, Zhiqing [ORNL; Sokolov, Mikhail A [ORNL; ERDMAN III, DONALD L [ORNL; Mo, Kun [ORNL; Stubbins, James [ORNL

2013-01-01

352

Low-temperature plastic deformation and strain-hardening of nanocrystalline titanium  

NASA Astrophysics Data System (ADS)

Patterns of plastic deformation of nanocrystalline (NC) technical grade VT1-0 titanium, are studied in quasi-static tensile experiments, with the average size of the grain d, ranging from 35 nm to 2 ?m, at the temperature interval 4.2 K < T < 395 K. The wide range of grain size, and grain size distribution, was made possible by cryomechanical grain fragmentation, which involves rolling at liquid nitrogen temperature, and subsequent annealing. At temperatures of T ? 30 K, smooth deformation curves become wavy, and as the temperature is continually lowered to Tjump ? 22 K, they become jagged. A correlation is found between the relative amplitude of the stress jump ??/? and the rate of strain hardening ? = (??/?e)?. A significant increase in plasticity is observed, especially noticeable at temperatures T ?140 K, if a small fraction (?15%) of submicron-sized grains is present. This is explained by a combination of dynamic grain growth under the influence of tensile stress, and nanotwinning activated in submicron grains. At cryogenic temperatures, abnormal grain growth favors nanotwinning during deformation. In nanometer-sized grains (d ? 50 nm), twinning is not observed.

Moskalenko, V. A.; Smirnov, A. R.; Smolyanets, R. V.

2014-09-01

353

Electrochemical control of creep in nanoporous gold  

SciTech Connect

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

Ye, Xing-Long; Jin, Hai-Jun, E-mail: hjjin@imr.ac.cn [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)] [Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016 (China)

2013-11-11

354

Deuteron irradiation creep of chemically vapor deposited silicon carbide fibers  

Microsoft Academic Search

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

R. Scholz

1998-01-01

355

Elevated Temperature Strength, Aging Response and Creep of Aluminum Matrix Composites  

Microsoft Academic Search

Aluminum matrix composites with reinforcement of planar-random graphite fibers, SiC whiskers, or alumina particulates have been evaluated for their high temperature performance. The composites were aged at 150 and 200C for up to 500 hours. Microhardness results indicate accelerated aging of the composites in comparison with that of wrought 6061 Al resolutionized and aged under identical conditions. The aging response

Ram B. Bhagat; Maurice F. Amateau; Michael B. House; Kenneth C. Meinert; Paul Nisson

1992-01-01

356

High-temperature behavior of a deformed Fermi gas obeying interpolating statistics.  

PubMed

An outstanding idea originally introduced by Greenberg is to investigate whether there is equivalence between intermediate statistics, which may be different from anyonic statistics, and q-deformed particle algebra. Also, a model to be studied for addressing such an idea could possibly provide us some new consequences about the interactions of particles as well as their internal structures. Motivated mainly by this idea, in this work, we consider a q-deformed Fermi gas model whose statistical properties enable us to effectively study interpolating statistics. Starting with a generalized Fermi-Dirac distribution function, we derive several thermostatistical functions of a gas of these deformed fermions in the thermodynamical limit. We study the high-temperature behavior of the system by analyzing the effects of q deformation on the most important thermostatistical characteristics of the system such as the entropy, specific heat, and equation of state. It is shown that such a deformed fermion model in two and three spatial dimensions exhibits the interpolating statistics in a specific interval of the model deformation parameter 0 < q < 1. In particular, for two and three spatial dimensions, it is found from the behavior of the third virial coefficient of the model that the deformation parameter q interpolates completely between attractive and repulsive systems, including the free boson and fermion cases. From the results obtained in this work, we conclude that such a model could provide much physical insight into some interacting theories of fermions, and could be useful to further study the particle systems with intermediate statistics. PMID:22680435

Algin, Abdullah; Senay, Mustafa

2012-04-01

357

Inelastic deformation behavior of thermal barrier coatings exposed at a high-temperature environment  

NASA Astrophysics Data System (ADS)

Thermal barrier coatings (TBCs) are usually deposited onto the surface of the high-temperature component such as gas turbine, in order to protect it from a hightemperature environment. Coating stress generated by such a high-temperature brings serious damages in TBCs in service. For predicting numerically it, it is necessary to develop the constitutive equation suite to plasam-sprayed TBCs. Previous studies have made clear that the freestanding ceramic coat peeled from TBC coated substrate deforms nonlinearly with a mechanical loading, however the results there have been restricted to the test done using as-sprayed sample. In this study, effect of deposition parameter and high-temperature exposure condition on stress-strain curve of the freestanding ceramic coating sample was examined. The associated deformation process was discussed with the microstructure changes observed after performing a bending test for the exposed sample.

Arai, M.; Wu, X.

2010-06-01

358

The influence of deformation on high temperature corrosion of CRONIFER 45 TM  

SciTech Connect

The present work deals with an investigation into the corrosion behavior of CRONIFER 45 TM (Ni-27Cr-23Fe-2.8Si) under tensile strains in a non-equilibrated S-O-C bearing atmosphere which served to simulate a typical coal gasification environment. The investigations have been carried out at 600 C for different creep strains. The material formed external and internal corrosion products which were composed of mixed oxides and sulphides. After 1% strain the continuous internal corrosion zone showed first indications of cracking, but the cracks did not penetrate into the sound metal. After 2% deformation or more, transgranular crack propagation into the alloy occurred which was accompanied by severe corrosion around the cracks. Strain enhanced corrosion could be described in summary as an alternating process of local corrosion beneath a through crack in the internal corrosion zone, the extension of such a crack into the corroded area, corrosive attack around the crack tip and further crack propagation.

Stein, K.; Guttmann, V. [Petten Establishment (Netherlands). Inst. for Advanced Materials; Bakker, W.T. [Electric Power Research Inst., Palo Alto, CA (United States)

1995-12-31

359

Effects of Temperature and Grain Size Evolution on the Deformation and Stability of a 1-D Viscoelastic Shear Zone  

NASA Astrophysics Data System (ADS)

Viscous shear heating instabilities may provide a possible mechanism for some intermediate depth earthquakes where high confining pressure makes it difficult to achieve the conditions for frictional failure. While many studies have looked at the feedback between temperature-dependant strain rate and strain rate-dependant shear heating (e.g. Braeck and Podladchikov, 2007), fewer have examined the feedbacks between grain size, temperature and viscosity. We have developed a 1-D numerical model that describes the behavior of a Maxwell viscoelastic body with the rheology of dry olivine, driven at a constant velocity at its boundary and initiated with a fine-grained shear zone. Specific contributions to viscous strain include diffusion and dislocation creep, dislocation accommodated grain boundary sliding (disGBS), and low-temperature plasticity (LTP - Peierls mechanism). Grain size is allowed to evolve according to the parameterization described in Austin and Evans (2007). However, unlike Austin and Evans (2007) we allow strain accommodated by both dislocation creep and disGBS to contribute to grain size evolution. This is because both mechanisms rely on similar microphysical processes to accommodate strain. We contrast the stability of the system with and without grain size evolution and evaluate the consequences that grain size evolution has on overall system behavior. Including grain size evolution modifies the behavior of the basic model in several ways. First, due to the combined processes of grain growth and grain size reduction, a wide range of initial shear zone grain sizes (1 ?m - 500 ?m) evolves during the elastic loading phase to a common shear zone grain size (~2 ?m) at the peak stress, nearly eliminating a previously observed dependence of peak stress on initial shear zone grain size. Second, we observe an expansion, by an order of magnitude both faster and slower, in the range of applied strain rate conditions under which moderately rapid and complex unloading (stress relaxation rates of ~1 MPa/yr - ~100 MPa/yr within a single run) and reloading of the system occurs. For example, for a domain size of 2 km and a 8 m wide shear zone, initial background and shear zone grain sizes of 10 mm and 2 ?m respectively, and an initial temperature of 650C, the ranges of background strain rates for which this type of behavior is observed are <2 x 10-13 - 2 x 10-10 and 2 x 10-12 - 2 x 10-11 s-1, with and without grain size evolution, respectively. Finally, we observe a shift to slightly higher applied background strain rates for the occurrence of dramatic, self-localizing instabilities during which the system unloads all of its stress, up to ~1 GPa, almost instantaneously. For example, for the same run conditions described above, this transition occurs for background strain rates of 2 x 10-10 and 2 x 10-11 s-1, with and without grain size evolution, respectively. We are now systematically evaluating the behavior of the model over a wide range of geologically reasonable parameter space to investigate the implications of viscous shear heating instabilities for deformation in the earth.

Homburg, J. M.; Spiegelman, M.; Kelemen, P. B.; Hirth, G.

2011-12-01

360

Temperature dependence of yield stress, deformation mode and deformation structure in single crystals of TiAl (Ti56 at.% Al)  

Microsoft Academic Search

The plastic deformation behaviour of single crystals of TiAl with a composition of Ti-56 at.% Al has been studied in compression as a function of crystal orientation in the temperature range from ?196 to 1100C. The profile of yield stress-temperature curves for all orientations studied can be divided into three temperature regions; the yield stress rapidly decreases with increasing temperature

H. Inui; M. Matsumuro; D.-H. Wu; M. Yamaguchi

1997-01-01

361

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 microstructure, bend strength and compressive creep behavior of a Mo-3Si-1B (in wt.%) alloy were studied. 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. The elastic limit strength of the alloy remained quite high until 1200 C with a value of 800MPa, but dropped rapidly thereafter to a value of 220 MPa at 1400 C. Results of compressive creep tests at 1200 C showed that the creep rates were quite high and varied nearly linearly with stress between 250 and 500 MPa, which suggests that diffusional mechanisms dominate the creep process. 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. These results and presented and discussed.

Vijay K. Vasudevan

2005-02-08

362

Creep and Fracture Behavior of Peak-Aged Mg-11Y-5Gd-2Zn-0.5Zr (wt pct)  

NASA Astrophysics Data System (ADS)

The tensile-creep and creep-fracture behavior of peak-aged Mg-11Y-5Gd-2Zn-0.5Zr (wt pct) (WGZ1152) was investigated at temperatures between 523 K (250 C) to 598 K (325 C) (0.58 to 0.66 T m) and stresses between 30 MPa to 140 MPa. The minimum creep rate of the alloy was almost two orders of magnitude lower than that for WE54-T6 and was similar to that for HZ32-T5. The creep behavior exhibited an extended tertiary creep stage, which was believed to be associated with precipitate coarsening. The creep stress exponent value was 4.5, suggesting that dislocation creep was the rate-controlling mechanism during secondary creep. At T = 573 K (300 C), basal slip was the dominant deformation mode. The activation energy for creep ( Q avg = 221 20 kJ/mol) was higher than that for self-diffusion in magnesium and was believed to be associated with the presence of second-phase particles as well as the activation of nonbasal slip and cross slip. This finding was consistent with the slip-trace analysis and surface deformation observations, which revealed that the nonbasal slip was active. The minimum creep rate and time-to-fracture followed the original and modified Monkman-Grant relationships. The microcracks and cavities nucleated preferentially at grain boundaries and at the interface between the matrix phase and the second phase. In-situ creep experiments highlighted the intergranular cracking evolution.

Yin, D. D.; Wang, Q. D.; Boehlert, C. J.; Janik, V.

2012-09-01

363

The Role of Eta Phase Formation on the Creep Strength and Ductility of INCONEL Alloy 740 t 1023 k (750 Degrees C)  

SciTech Connect

INCONEL alloy 740 is an age-hardenable nickel-based superalloy proposed for advanced ultrasupercritical steam boiler applications operating at high stress and long times above 973 K (700 C), where creep will be the dominate deformation mode. During high-temperature exposure, the alloy can form eta phase platelets that many have suggested may be detrimental to creep strength and ductility. In this study, creep-rupture tests were conducted on smooth and notched bars of INCONEL alloy 740 at 1023 K (750 C) for times up to 20,000 hours. Examination of the creep-rupture life, creep ductility, failure modes, and microstructure by quantitative electron microscopy shows that a small amount of eta phase does not diminish the creep performance. Applied stress appears to have a minor effect on the precipitation of the eta phase but not its growth rate. Based on the observation that the microstructure after 20,000 hours of creep exposure has reached equilibrium in comparison to thermodynamic calculations, it is concluded that 20,000 hour creep tests are adequate for prediction of long-term creep performance.

Shingledecker, John P [ORNL; Pharr, George Mathews [ORNL

2012-01-01

364

Investigations on Flux Pinning and Creep in High Critical Transition Temperature Superconductors  

NASA Astrophysics Data System (ADS)

Available from UMI in association with The British Library. Requires signed TDF. The paraelastic interaction between an isolated flux line (FL) and periodically spaced planar arrays of oxygen vacancies parallel to the bc crystallographic planes in Y_1Ba_2Cu _3O_{rm 7-delta} (YBCO) was calculated. The calculation was extended to include the interaction with several superlattices reported to occur in YBCO by superposition of solutions. The paraelastic interaction between FL's and ferroelectric domains in YBCO was calculated both for the limits of low and high fields. The interaction is proportional to the spontaneous strain in the ferroelectric domain, which is proportional to the square of the polarization. The paraelastic interaction energy between a FL impinging perpendicularly through the plane interface between a disk shaped inclusion which undergoes a change of form and the matrix was calculated as a function of position across the inclusion. An analytical expression for the interaction force near the centre was obtained. This force is proportional to the strain in the inclusion and inversely proportional to its radius. Such results motivated an experimental study involving composites of YBCO containing 5% wt. BaTiO_3 particles as inclusions, made by the 'melt-and-quench' technique. Magnetization measurements have confirmed that stronger pinning was actually achieved due to the direct and indirect generation of pinning centres related to the presence of inclusions. A new model for magnetization decay in ceramic superconductors is proposed in which the FL's are assumed as breaking into disks, which are eliminated by a network of normal barriers separating superconducting cells in the material. The time-logarithmic decay of the magnetization is predicted, as well as the occurrence of a maximum in the relative magnetization decay rate at a certain sample -dependent temperature, in agreement with experimental results reported in the literature.

Schilling Neto, Osvaldo F.

365

Processing and creep behaviour of silicon carbide-platelet reinforced alumina  

NASA Astrophysics Data System (ADS)

The creep rates of SiC whisker reinforced Al2O3 have been found to be one or two orders of magnitude lower than the creep rate of unreinforced alumina. However, whiskers are a serious health hazard due to their asbestos-like geometry, they are expensive (thousands of dollars per kilogram), and they tend to get damaged during processing. Platelets have been proposed as an alternative to whiskers due to their reinforcement potential comparable to that of whiskers, forgiving geometry (with respect to safety), better thermal stability, lower price (hundreds of dollars per kilogram) and ease of processing. Up to now, research in platelet reinforced ceramics has concentrated mainly in room temperature properties and little is known about their high temperature mechanical properties. The aim of this work was to study the way in which different reinforcement network morphologies affect the creep behaviour of SiC-platelet/Al2O3 composites and to determine the important deformation mechanisms at the studied temperature (1250C). To this end, composites with different platelet volume fractions (0 to 30%) and orientation distributions were fabricated. The samples were subjected to flexure and compression creep tests and characterized using optical and electron microscopy, dilatometry, and neutron diffraction. The analysis of the creep behaviour was found to be complicated by the differences in impurity content in the samples and the increase in glass content with the platelets volume fraction. However, the results clearly indicate a strong influence of the reinforcement morphology on the creep properties. Special attention was given to an unusual time-dependent transition from high to low creep strain rate in some of the composites. The phenomenon was ascribed to the possible relief of bending strains in the platelets. In addition, some of the possible main mechanisms responsible for the increased creep resistance in SiC-whisker reinforced ceramics were found not be operative in platelet-reinforced ceramics.

Ham-Su, Rosaura

366

The effect of grain size on the high temperature plastic deformation of nb 3 sn  

Microsoft Academic Search

A study of high temperature plastic deformation has been undertaken on 10, 20, and 60 ?m grain size Nb3Sn. The materials were produced by the hot isostatic pressing of powder blends. The 20 and 60 ?m grain size material involved\\u000a a stoichiometric blend of Nb and Sn powder, whereas the 10 ?m grain size material involved a blend of 30.2

James B. Clark; George B. Hopple; Roger N. Wright

1983-01-01

367

Superplasticity in thin magnesium alloy sheets and deformation mechanism maps for magnesium alloys at elevated temperatures  

Microsoft Academic Search

Rolling processes for fabricating thin AZ61 and AZ31 alloy sheets adequate for superplastic forming have been developed. Superplastic behavior of the sheets was evaluated in the temperature range 573693 K and compared that of the initial materials having relatively coarse grains. Existing deformation mechanism maps for face-centered cubic and body-centered cubic metals were reviewed and found to be deficient in

W.-J Kim; S. W Chung; C. S Chung; D Kum

2001-01-01

368

The deformation and fracture of TiAl at elevated temperatures  

Microsoft Academic Search

The tensile properties of the intermetallic compound TiAl have been determined at several temperatures in the range 25 to\\u000a 1000C. Additional variables studied were the influence of strain rate and the effect of exposure to oxidizing conditions\\u000a prior to testing. The modes of deformation under the various testing conditions were studied in the electron microscope, the\\u000a modes of fracture were

Harry A. Lipsitt; Dan Shechtman; Robert E. Schafrik

1975-01-01

369

Nature and dissociation of the dislocations in TiAl deformed at room temperature  

Microsoft Academic Search

TiAl polycrystalline specimens, having the L10 structure, have been deformed at room temperature and examined by transmission electron microscopy. The observations revealed a new type of slip superdislocations a\\/2?112? gliding in the (111) planes, in addition to the a?101? and a\\/2?110? dislocations previously described in L10 compounds. Dissociation configurations of the superdislocations a\\/2?112? and a?101? have been observed: they explain

G. Hug; A. Loiseau; A. Lasalmonie

1986-01-01

370

The effect of deformation temperature on the microstructure evolution of Inconel 625 superalloy  

Microsoft Academic Search

Hot compression tests of Inconel 625 superalloy were conducted using a Gleeble-1500 simulator between 900C and 1200C with different true strains and a strain rate of 0.1s?1. Scanning electron microscope (SEM) and electron backscatter diffraction technique (EBSD) were employed to investigate the effect of deformation temperature on the microstructure evolution and nucleation mechanisms of dynamic recrystallization (DRX). It is found

Qingmiao Guo; Defu Li; Shengli Guo; Haijian Peng; Jie Hu

2011-01-01

371

Plastic deformation and damage of polyoxymethylene in the large strain range at elevated temperatures  

Microsoft Academic Search

The deformation behaviour of polyoxymethylene has been studied in plane strain compression at temperatures from 120C up to 165C and in uniaxial tension and simple shear at 160C for strain rates from 10?4 to 1s?1. In uniaxial tension the stressstrain behaviour was determined by a novel video-controlled testing system. The measurements showed that there was a very significant evolution of

J. Mohanraj; D. C. Barton; I. M. Ward; A. Dahoun; J. M. Hiver; C. G'Sell

2006-01-01

372

Influence of the temperature on the plastic deformation in TiAl  

SciTech Connect

A new alloy, Ti-48.6Al-1.9Cr-1.9Nb-1B, with a near-equiaxed {gamma} microstructure and with a lamellar microstructure is investigated by compression tests between 20 and 800 C and transmission electron microscopy (TEM). The yield stress exhibits no anomaly as a function of the temperature, while an anomaly, related to strain hardening, is found at 400 C in the hardening rate and the activation volume for both the lamellar and nonlamellar structure. Above 700 C, a change in the deformation mechanism occurs and the material becomes remarkably softer. The TEM micrographs highlight the importance of ordinary dislocation motion for both structures at all temperatures. The comparison with previously reported TEM observations on single-phase TiAl alloys shows definitely that the density of ordinary dislocations is higher in the investigated two-phase TiAl alloy deformed at room temperature. Also, the presence of the lamellar interfaces drastically changes the mechanical properties of the alloy and the deformation mechanism. In contrast to the nonlamellar samples, superdislocations are rare, and twinning is very frequent in the lamellar structure.

Parrini, L.

1999-11-01

373

Influence of stress, temperature, and strain on calcite twins constrained by deformation experiments  

NASA Astrophysics Data System (ADS)

A series of low-strain triaxial compression and high-strain torsion experiments were performed on marble and limestone samples to examine the influence of stress, temperature, and strain on the evolution of twin density, the percentage of grains with 1, 2, or 3 twin sets, and the twin widthall parameters that have been suggested as either paleopiezometers or paleothermometers. Cylindrical and dog-bone-shaped samples were deformed in the semibrittle regime between 20 C and 350 C, under confining pressures of 50-400 MPa, and at strain rates of 10- 4-10- 6 s- 1. The samples sustained shear stresses, ?, up to 280 MPa, failing when deformed to shear strains ? > 1. The mean width of calcite twins increased with both temperature and strain, and thus, measurement of twin width provides only a rough estimation of peak temperature, unless additional constraints on deformation are known. In Carrara marble, the twin density, NL (no of twins/mm), increased as the rock hardened with strain and was approximately related to the peak differential stress, ? (MPa), by the relation ?=19.59.8?{N}. Dislocation tangles occurred along twin boundaries, resulting in a complicated cell structure, which also evolved with stress. As previously established, the square root of dislocation density, observed after quench, also correlated with peak stress. Apparently, both twin density and dislocation cell structure are important state variables for describing the strength of these rocks.

Rybacki, E.; Evans, B.; Janssen, C.; Wirth, R.; Dresen, G.

2013-08-01

374

High-strain-rate deformation of pure aluminum reinforced with 25% alumina submicron particles near the solidus temperature  

SciTech Connect

Recently, the mechanical properties at room and elevated temperatures of dispersion-strengthened-cast aluminum (DSC-Al) with high volume fractions (>25 vol.%) of submicron Al{sub 2}O{sub 3} oxide dispersoids have been investigated. The material has characteristics of both Al-MMCs (e.g., high modulus, strength, and low coefficient of thermal expansion) and conventional PM oxide-dispersion-strengthened aluminum with lower reinforcement content (e.g., high creep resistance). While the room-temperature ductility of DSC-Al is quite high (9.4% for extruded DSC-Al with 25 vol.% Al{sub 2}O{sub 3} oxide particles), its formability at elevated temperatures is limited by its high creep strength and low creep ductility. Because of the similarity of microstructure between DSC-Al and other Al-MMCs, the question arises whether DSC-Al containing 25% Al{sub 2}O{sub 3} particles can exhibit high-strain-rate superplasticity near the solidus temperature. The purpose of the present note is to investigate this issue.

Han, B.Q.; Agnew, S.R.; Dunand, D.C. [Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science and Engineering] [Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science and Engineering

1999-03-05

375

Surface temperature and synthetic spectral energy distributions for rotationally deformed stars  

E-print Network

The spectral energy distribution (SED) of a non-spherical star could differ significantly from the SED of a spherical star with the same average temperature and luminosity. Calculation of the SED of a deformed star is often approximated as a composite of several spectra, each produced by a plane parallel model of given effective temperature and gravity. The weighting of these spectra over the stellar surface, and hence the inferred effective temperature and luminosity, will be dependent on the inclination of the rotation axis of the star with respect to the observer, as well as the temperature and gravity distribution on the stellar surface. Here we calculate the surface conditions of rapidly rotating stars with a 2D stellar structure and evolution code and compare the effective temperature distribution to that predicted by von Zeipel's law. We calculate the composite spectrum for a deformed star by interpolating within a grid of intensity spectra of plane parallel model atmospheres and integrating over the surface of the star. Using this method, we find that the deduced variation of effective temperature with inclination can be as much as 3000 K for an early B star, depending on the details of the underlying model.

C. C. Lovekin; R. G. Deupree; C. I. Short

2006-02-03

376

High Temperature Deformation Behavior of As-Cast Al-3Mg-0.25Sc Alloy  

NASA Astrophysics Data System (ADS)

High temperature deformation behavior of as-cast Al-3Mg-0.25Sc alloy was characterized in a wide range of temperatures 573 K to 773 K (300 C to 500 C) and strain rates (0.001 to 10 s-1). A threshold stress behavior is observed in the temperature range of 573 K to 673 K (300 C to 400 C) due to interaction of dislocations with precipitates. In the temperature range of 573 K to 623 K (300 C to 350 C), the dislocations are pinned by precipitates, following Orowan-bowing mechanism. At 673 K (400 C), the dislocations bypass the particles by climb process. At high temperature and low strain rate of 723 K (450 C), and 0.001 s-1, respectively, the alloy exhibited high efficiency of power dissipation for optimal hot working process.

Suresh Kumar, M.; Ambresha; Venkateswarlu, K.; Ranganath, V. R.

2014-07-01

377

Characterization and Analysis of Cavity Development During Creep of Ceramics at Elevated Temperature. Progress Report for 1983.  

National Technical Information Service (NTIS)

The early stages of creep cavitation in sintered alumina are characterized using small angle neutron scattering (SANS). It is found that the initial cavity density is on the order of 10 exp 11 cm exp -3 , and that the average initial pore is approximately...

R. A. Page, J. Lankford

1983-01-01

378

Characterization and Analysis of Cavity Development During Creep of Ceramics at Elevated Temperature. Progress Report for 1983.  

National Technical Information Service (NTIS)

The early stages of creep cavitation in sintered alumina are characterized using small angle neutron scattering (SANS). It is found that the initial cavity density is on the order of 10 exp 11 cm exp -3 , and that the average initial pore is aproximately ...

R. A. Page, J. Lankford

1983-01-01

379

Creep behaviour of Cu30% Zn at intermediate temaperatures  

Microsoft Academic Search

The creep properties of single-phase Cu-30% Zn alpha brass were investigated in the intermediate temperature range 573823 K (0.480.70Tm, whereTm is the absolute melting point). Inverse, linear, and sigmoidal primary creep transients were usually observed above 573 K under stresses resulting in minimum creep rates between 10-7 and 210-4s-1, while normal primary creep occurred under all other conditions. The creep

S. V. Raj

1991-01-01

380

The effect of surfactant redistribution on interactions of deformable drops in gravity and a temperature gradient  

NASA Astrophysics Data System (ADS)

Trajectories are calculated by the boundary-integral method for two contaminated deformable drops under the combined influence of buoyancy and a constant temperature gradient at low Reynolds number and with negligible thermal convection. The surfactant is bulk-insoluble, and its coverage is determined by solution of the time-dependent convective-diffusion equation. Two limits are considered. For small drops, the deformation is small, and thermocapillary and buoyant effects are of the same order of magnitude. In this case, comparison is made with incompressible surfactant results to determine when surfactant redistribution becomes important. Convection of surfactant can lead to elimination of saddle points in the relative-trajectory phase plane and can increase the difference between the drops' velocities. For larger drops, deformation can be significant, leading to breakup or capture, and buoyant motion dominates thermocapillary migration. In this case, convection of surfactant can increase deformation and offset previously observed inhibition of breakup for clean drops when the driving forces are opposed.

Rother, Michael

2010-11-01

381

Hot Deformation Behavior of Alloy 800H at Intermediate Temperatures: Constitutive Models and Microstructure Analysis  

NASA Astrophysics Data System (ADS)

The hot deformation behavior of a Fe-Ni-Cr austenitic Alloy 800H was explored in the intermediate temperature range of 825-975 C and strain rate range of 0.01-10 s-1. The study indicates that dynamic recrystallization (DRX) occurred at 875-975 C for strain rates of 0.01-0.1 s-1 and adiabatic heating generated at high strain rates accelerated the DRX process. Based on the experimental data, the Johnson-Cook, modified Johnson-Cook, and Arrhenius-type constitutive models were established to predict the flow stress during hot deformation. A comparative study was made on the accuracy and effectiveness of the above three developed models. The microstructure analysis indicated that all the deformation structures exhibited elongated grains and evidence of some degree of DRX. The multiple DRX at 975 C and 0.01 s-1 led to an increase in the intensity of {001} <100> "cube" texture component and a significant reduction in the intensity of {011} <211> "brass" component. Additionally, the average values of grain average misorientation and grain orientation spread for deformed microstructure were inversely proportional to the fraction of DRX.

Cao, Y.; Di, H. S.; Misra, R. D. K.; Zhang, Jiecen

2014-09-01

382

Hot deformation behavior of 7150 aluminum alloy during compression at elevated temperature  

SciTech Connect

Hot compression tests of 7150 aluminum alloy were preformed on Gleeble-1500 system in the temperature range from 300 deg. C to 450 deg. C and at strain rate range from 0.01 s{sup -1} to 10 s{sup -1}, and the associated structural changes were studied by observations of metallographic and transmission electron microscope. The results show that the true stress-true strain curves exhibit a peak stress at a critical strain, after which the flow stresses decrease monotonically until high strains, showing a dynamic flow softening. The peak stress level decreases with increasing deformation temperature and decreasing strain rate, which can be represented by a Zener-Hollomon parameter in the hyperbolic-sine equation with the hot deformation activation energy of 229.75 kJ/mol. In the deformed structures appear the elongated grains with serrations developed in the grain boundaries, decreasing of Z value leads to more adequate proceeding of dynamic recrystallization and coarser recrystallized grains. The subgrains exhibit high-angle sub-boundaries with a certain amount of dislocations and large numbers of dynamic precipitates in subgrain interiors as increasing Z value. The dynamic recovery and recrystallization are the main reasons for the flow softening at low Z value, but the dynamic precipitates and successive dynamic particles coarsening have been assumed to be responsible for the flow softening at high Z value.

Jin Nengping [College of Materials Science and Engineering, Hunan University, Changsha 410082 (China); Zhang Hui, E-mail: zhanghui63hunu@163.com [College of Materials Science and Engineering, Hunan University, Changsha 410082 (China); Han Yi; Wu Wenxiang [Suzhou Institute for Nonferrous Metal Processing Technology, Suzhou 215026 (China); Chen Jianghua [College of Materials Science and Engineering, Hunan University, Changsha 410082 (China)

2009-06-15

383

Effect of fast neutron fluence on the creep anisotropy of Zr2.5Nb tubes  

Microsoft Academic Search

The in-reactor behaviour of internally pressurised capsules of Zr2.5Nb tubes is analysed in detail to separate the stress dependent component of deformation (creep). It is found by a rigorous statistical analysis that the creep rate varies with fast neutron fluence. At 555K the axial creep rate increases while the transverse creep rate decreases with fluence. At 588K the creep rate

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

2008-01-01

384

Production of ultrafine grained aluminum by cyclic severe plastic deformation at ambient temperature  

NASA Astrophysics Data System (ADS)

In the present study the possibilities of grain refinement was investigated by applying large-scale of cyclic plastic deformation to aluminum at ambient temperature. The specimens are processed by multiaxial forging, which is one of the severe plastic deformation techniques. The aim of the experiments with the aluminum alloy 6082M was the determination of the equivalent stress and strain by multiaxial forging and the investigation of evolution of mechanical properties in relation with the accumulated deformation in the specimen. The mechanical properties of raw material was determined by plane strain compression test as well as by hardness measurements. The forming experiments were carried out on Gleeble 3800 physical simulator with MaxStrain System. The mechanical properties of the forged specimens were investigated by micro hardness measurements and tensile tests. A mechanical model, based on the principle of virtual velocities was developed to calculate the flow curves using the measured dimensional changes of the specimen and the measured force. With respect to the evolution of these curves, the cyclic growth of the flow stress can be observed at every characteristic points of the calculated flow curves. In accordance with this tendency, the evolution of the hardness along the middle cross section of the deformed volume has also a nonmonotonous characteristic and the magnitudes of these values are much smaller than by the specimen after plane strain compression test. This difference between the flow stresses respect to the monotonic and non-monotonic deformation can be also observed. The formed microstructure, after a 10-passes multiaxial forging process, consists of mainly equiaxial grains in the submicron grain scale.

Bereczki, P.; Szombathelyi, V.; Krallics, G.

2014-08-01

385

Integrity of repair welds in high temperature plant operating under creep and creepfatigue conditions a new European Commission supported initiative  

Microsoft Academic Search

Repair welds and welds fabricated during component replacement procedures are commonly found in high temperature plants. Our validated understanding about remnant life or crack initiation and growth behaviour of such welds which will contain different heat affected zones in virgin and service exposed materials is more limited. Recently, a research project was started to obtain information about the integrity of

A. Klenk; J. A. Williams; I. A. Shibli; S. Issler

2001-01-01

386

Effects of Electromigration on the Creep and Thermal Fatigue Behavior of Sn58Bi Solder Joints  

NASA Astrophysics Data System (ADS)

Electromigration (EM), creep, and thermal fatigue (TF) are the most important aspects of the reliability of electronic solder joints, the failure mechanisms of which used to be investigated separately. However, current, mechanical loading, and temperature fluctuation usually co-exist under real service conditions, especially as the magnitude of current density is increasing with joint miniaturization. The importance of EM can no longer be simply ignored when analyzing the creep and TF behavior of a solder joint. The published literature reports that current density substantially changes creep rate, but the intrinsic mechanism is still unclear. Hence, the purpose of this study was to investigate the effects of EM on the creep and TF behavior of Sn58Bi solder joints by analyzing the evolution of electrical resistance and microstructure. The results indicated that EM shortens the lifetime of creep or TF of Sn58Bi solder joints. During creep, EM delays or suppresses the cracking and deforming process, so fracture occurs at the cathode interface. During TF, EM suppresses the cracking process and changes the interfacial structure.

Zuo, Yong; Ma, Limin; Guo, Fu; Qiao, Lei; Shu, Yutian; Lee, Andree; Subramanian, K. N.

2014-08-01

387

Grain-boundary diffusion creep in nanocrystalline palladium by molecular-dynamics simulation.  

SciTech Connect

Molecular-dynamics (MD) simulations of fully three-dimensional (3D), model nanocrystalline face-centered cubic metal microstructures are used to study grain-boundary (GB) diffusion creep, one mechanism considered to contribute to the deformation of nanocrystalline materials. To overcome the well-known limitations associated with the relatively short time interval used in our MD simulation (typically <10{sup -8} s), our simulations are performed at elevated temperatures where the distinct effects of GB diffusion are clearly identifiable. In order to prevent grain growth and thus to enable steady-state diffusion creep to be observed, our input microstructures were tailored to (1) have a uniform grain shape and a uniform grain size of nm dimensions and (2) contain only high-energy GBs which are known to exhibit rather fast, liquid-like self-diffusion. Our simulations reveal that under relatively high tensile stresses these microstructures, indeed, exhibit steady-state diffusion creep that is homogeneous, with a strain rate that agrees quantitatively with that given by the Coble-creep formula. The grain-size scaling of the Coble creep is found to decrease from d{sup -3} to d{sup -2} when the grain diameter becomes of the order of the GB width. For the first time a direct observation of the grain-boundary sliding as an accommodation mechanism for the Coble creep, known as Lifshitz sliding, is reported.

Yamakov, V.; Wolf, D.; Phillpot, S. R.; Gleiter, H.; Materials Science Division; Forschungszentrum Karlsruhe

2002-01-08

388

Inelastic deformation and damage at high temperature. Progress report April 1, 1992--April 30, 1993  

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.

1993-08-01

389

Localized shear deformation and softening of bulk metallic glass: stress or temperature driven?  

PubMed

Metallic glasses due to their unique combination of physical and chemical properties have a great potential in various applications: materials for construction, medical, MEMs devices and so on. The deformation mechanism in metallic glasses is very much different from that in conventional crystalline materials and not yet fully understood. Here we are trying to find out what drives shear deformation in metallic glasses. The compression experiments of the bulk metallic glassy (BMG) samples coated with tin, Rose metal and indium were performed. There were no melting sites of the coating observed near individual shear bands. Melting occurred only near fracture surface, near microcracks and in the places of shear band concentrations. The results indicate that shear banding is rather a stress driven process while the temperature rise that was observed takes place due to friction forces in the viscous supercooled liquid thin layer in the shear bands. PMID:24100784

Ketov, S V; Louzguine-Luzgin, D V

2013-01-01

390

The microstructure and creep behavior of cold rolled udimet 188 sheet.  

PubMed

Udimet 188 was subjected to thermomechanical processing (TMP) in an attempt to understand the effects of cold-rolling deformation on the microstructure and tensile-creep behavior. Commercially available sheet was cold rolled to varying amounts of deformation (between 5-35% reduction in sheet thickness) followed by a solution treatment at 1,464 K (1,191 C) for 1 h and subsequent air cooling. This sequence was repeated four times to induce a high-volume fraction of low-energy grain boundaries. The resultant microstructure was characterized using electron backscattered diffraction. The effect of the TMP treatment on the high-temperature [1,033-1,088 K (760-815 C)] creep behavior was evaluated. The measured creep stress exponents (6.0-6.8) suggested that dislocation creep was dominant at 1,033 K (760 C) for stresses ranging between 100-220 MPa. For stresses ranging between 25-100 MPa at 1,033 K (760 C), the stress exponents (2.3-2.8) suggested grain boundary sliding was dominant. A significant amount of grain boundary cracking was observed both on the surface and subsurface of deformed samples. To assess the mechanisms of crack nucleation, in situ scanning electron microscopy was performed during the elevated-temperature tensile-creep deformation. Cracking occurred preferentially along general high-angle grain boundaries (GHAB) and less than 25% of the cracks were found on low-angle grain boundaries (LAB) and coincident site lattice boundaries (CSLB). Creep rupture experiments were performed at T = 1,088 K (815 C) and ? = 165 MPa and the greatest average time-to-rupture was exhibited by the TMP sheet with the greatest fraction of LAB+CSLB. However, a clear correlation was not exhibited between the grain boundary character distribution and the minimum creep rates. The findings of this work suggest that although grain boundary engineering may be possible for this alloy, simply relating the fraction of grain boundary types to the creep resistance is not sufficient. PMID:21205424

Boehlert, C J; Longanbach, S C

2011-06-01

391

First Cycle Heterogeneous Deformation Behavior and Cyclic Shakedown Phenomena of Nitinol Near A(sub f) Temperatures  

NASA Technical Reports Server (NTRS)

Experimental observations on the cyclic behavior of a NiTi alloy (Nitinol) at temperatures in the neighborhood of the A(sub f) (austenite finish) temperature are presented. The strongly heterogeneous nature of the deformation behavior of this material at temperatures within this regime during the first cycle is examined with emphasis placed on the difficulties that the existence of such phenomena pose on the formulation of realistic constitutive relations. It is further demonstrated that this heterogeneity of deformation persists on subsequent cycles with the result that the hysteretic cyclic behavior of these alloys can exhibit a point to point variation in an otherwise uniform geometry. The experimental observations on the deformation behavior of this alloy show that it is strongly dependent on temperature and prior deformation history of the sample, thus resulting in an almost intractable problem with respect to capturing an adequate constitutive description from either experiment or modeling.

Jones, H. N.

1996-01-01

392

An experimental and theoretical investigation of the low temperature creep deformation behavior of single phase titanium alloys  

Microsoft Academic Search

Titanium alloys are used for many applications due to their desirable properties, including its high strength-to-weight ratio, corrosion resistance, and biocompatibility. Titanium alloys are used extensively for aerospace, chemical, nuclear, industrial, biomedical, and consumer applications. In many applications, titanium components may be subject to stresses for extended periods of time. It has long been known that single-phase hexagonally close-packed (HCP)

P. Gregory Oberson

2006-01-01

393

Effect of trace impurities in helium on the creep behavior of Alloy 617 for very high temperature reactor applications  

NASA Astrophysics Data System (ADS)

The effect of trace impurities, methane and oxygen, in helium on the creep behavior of Alloy 617, has been investigated. The creep rupture life at relatively low applied stresses was shortest in a helium environment containing 500 vppm oxygen (He + O 2), while it was the longest in helium containing 675 vppm methane (He + CH 4). However, the rupture strain was significantly lower in the He + CH 4 environment compared to that in pure helium (He) and He + O 2. The low rupture strain in the He + CH 4 is caused by cleavage fracture. In the He + CH 4 environment, the fracture mode was cleavage at lower applied stresses and ductile at higher applied stresses while in the He and He + O 2, a ductile fracture was observed at all stress levels. The apparent activation energy for creep was determined in all three environments, and it appears to be independent of stress in the He, dependent in the He + CH 4, while in the He + O 2 environment the stress dependence could not be conclusively established.

Shankar, P. S.; Natesan, K.

2007-06-01

394

Deformation and Phase Transformation Processes in Polycrystalline NiTi and NiTiHf High Temperature Shape Memory Alloys  

NASA Technical Reports Server (NTRS)

The deformation and transformation mechanisms of polycrystalline Ni49.9Ti50.1 and Ni50.3Ti29.7Hf20 (in at.%) shape memory alloys were investigated by combined experimental and modeling efforts aided by an in situ neutron diffraction technique at stress and temperature. The thermomechanical response of the low temperature martensite, the high temperature austenite phases, and changes between these two states during thermomechanical cycling were probed and reported. In the cubic austenite phase, stress-induced martensite, deformation twinning and slip processes were observed which helped in constructing a deformation map that contained the limits over which each of the identified mechanisms was dominant. Deformation of the monoclinic martensitic phase was also investigated where the microstructural changes (texture, lattice strains, and phase fractions) during room-temperature deformation and subsequent thermal cycling were compared to the bulk macroscopic response. When cycling between these two phases, the evolution of inelastic strains, along with the shape setting procedures were examined and used for the optimization of the transformation properties as a function of deformation levels and temperatures. Finally, this work was extended to the development of multiaxial capabilities at elevated temperatures for the in situ neutron diffraction measurements of shape memory alloys on the VULCAN Diffractometer at Oak Ridge National Laboratory.

Benafan, Othmane

2012-01-01

395

Rheology of Anhydrite during deformation in nature: a first look  

NASA Astrophysics Data System (ADS)

The rheology of Anhydrite under conditions of natural deformation is largely unconstrained, although it has many important effects in salt tectonics and in long-tem predictions of engineering structures in salt. A review of laboratory triaxial experiments at low temperature indicate brittle, pressure dependent behavior. At temperatures above 400 C experimental deformation shows power law creep, with contributions of dislocation creep and diffusional creep. In naturally deformed Anhydrite rocks microstructures indicate recrystallization, solution - precipitation processes and pressure solution producing stylolites. Analysis of Anhydrite layers embedded in rock salt shows complex behavior. Bedding-parallel stretching leads to boudinage, with variable amounts of pinch-and-swell before rupture and precipitation of Halite in the boudin-neck. Bedding-parallel shortening of single layers embedded in salt leads to folding of the Anhydrite layers, with the fold shapes suggesting an effective viscosity contrast between 10 and 100. This is also in agreement with the absence of extension fracture in the outer arcs of the folds. Although much remains to be done in accurately constraining Anhydrite rheology in nature, and for example its dependence on pore fluid pressure and chemistry, these results provide a first order estimate of Anhydrite rheology in nature, to be used in numerical simulations. A challenging task is to find a unified flow law which describes power law creep and fracturing dependent on effective stress.

Markus Schmalholz, Stefan; Urai, Janos

2014-05-01

396

Advances in Non-contact Measurement of Creep Properties  

NASA Technical Reports Server (NTRS)

Our team has developed a novel approach to measuring creep at extremely high temperatures using electrostatic levitation (ESL). This method has been demonstrated on niobium up to 2300 C, while ESL has melted tungsten (3400 C). High-precision machined spheres of the sample are levitated in the NASA MSFC ESL, a national user facility, and heated with a laser. The laser is aligned off-center so that the absorbed photons transfer their momentum to the sample, causing it to rotate at up to 250,000+ RPM. The rapid rotation loads the sample through centripetal acceleration, causing it to deform. The deformation of the sample is captured on high-speed video, which is analyzed by machine-vision software from the University of Massachusetts. The deformations are compared to finite element models to determine the constitutive constants in the creep relation. Furthermore, the noncontact method exploits stress gradients within the sample to determine the stress exponent in a single test. This method was validated in collaboration with the University of Tennessee for niobium at 1985 C, with agreement within the uncertainty of the conventional measurements. A similar method is being employed on Ultra-High-Temperature ZrB2- SiC composites, which may see application in rocket nozzles and sharp leading edges for hypersonic vehicles.

Hyers, Robert W.; Canepari, Stacy; Rogers, Jan. R.

2009-01-01

397

Defects interaction processes in deformed high purity polycrystalline molybdenum at elevated temperatures  

NASA Astrophysics Data System (ADS)

Mechanical spectroscopy (damping and elastic modulus as a function of temperature) and transmission electron microscopy studies have been performed in high purity polycrystalline molybdenum plastically deformed to different values of tensile and torsion strain. Mechanical spectroscopy measurements were performed from room temperature up to 1285 K. A relaxation peak in polycrystalline molybdenum related to the movement of dislocations into lower energy configurations near grain boundaries has been discovered to appear around 1170 K. The activation energy of the peak is 4.2 eV 0.5 eV. This relaxation phenomenon involves the interaction between vacancies and mobile dislocations near the grain boundaries. It should be highlighted that this relaxation process is controlled by the arrangement of vacancies and dislocations which occur at temperature below 1070 K.

Lambri, O. A.; Bonifacich, F. G.; Bozzano, P. B.; Zelada, G. I.; Plazaola, F.; Garca, J. A.

2014-10-01

398

Neutron irradiation creep in stainless steel alloys  

NASA Astrophysics Data System (ADS)

Irradiation creep elongations were measured in the HFR at Petten on AMCR steels, on 316 CE-reference steels, and on US-316 and US-PCA steels varying the irradiation temperature between 300C and 500C and the stress between 25 and 300 MPa. At the beginning of an irradiation a type of "primary" creep stage is observed for doses up to 3-5 dpa after which dose the "secondary" creep stage begins. The "primary" creep strain decreases in cold-worked steel materials with decreasing stress and decreasing irradiation temperature achieving also negative creep strains depending also on the pre-treatment of the materials. These "primary" creep strains are mainly attributed to volume changes due to the formation of radiation-induced phases, e.g. to the formation of ?-ferrite below about 400C and of carbides below about 700C, and not to irradiation creep. The "secondary" creep stage is found for doses larger than 3 to 5 dpa and is attributed mainly to irradiation creep. The irradiation creep rate is almost independent of the irradiation temperature ( Qirr = 0.132 eV) and linearly dependent on the stress. The total creep elongations normalized to about 8 dpa are equal for almost every type of steel irradiated in the HFR at Petten or in ORR or in EBR II. The negative creep elongations are more pronounced in PCA- and in AMCR-steels and for this reason the total creep elongation is slightly smaller at 8 dpa for these two steels than for the other steels.

Schle, Wolfgang; Hausen, Hermann

1994-09-01

399

Plastic Deformation Characteristics Of AZ31 Magnesium Alloy Sheets At Elevated Temperature  

NASA Astrophysics Data System (ADS)

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

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

2007-05-01

400

Plastic Deformation Characteristics Of AZ31 Magnesium Alloy Sheets At Elevated Temperature  

SciTech Connect

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

Park, Jingee; Lee, Jongshin [Graduate School, Kyungpook National University, Deagu 702-701 (Korea, Republic of); You, Bongsun [Department of Materials Technology, Korea Institute of Machinery and Materials, Changwon 641-831 (Korea, Republic of); Choi, Seogou [Digital Production Processing and Forming Team, Korea Institute of Industrial Technology, Incheon 406-800 (Korea, Republic of); Kim, Youngsuk [Department of Mechanical Engineering, Kyoungpook National University, Deagu 702-701 (Korea, Republic of)

2007-05-17

401

Stresses and deformations in cross-ply composite tubes subjected to a uniform temperature change  

NASA Technical Reports Server (NTRS)

This study investigates the effects of a uniform temperature change on the stresses and deformations of composite tubes and determines the accuracy of an approximate solution based on the principle of complementary virtual work. Interest centers on tube response away from the ends and so a planar elasticity approach is used. For the approximate solution a piecewise linear variation of stresses with the radial coordinate is assumed. The results from the approximate solution are compared with the elasticity solution. The stress predictions agree well, particularly peak interlaminar stresses. Surprisingly, the axial deformations also agree well, despite the fact that the deformations predicted by the approximate solution do not satisfy the interface displacement continuity conditions required by the elasticity solution. The study shows that the axial thermal expansion coefficient of tubes with a specific number of axial and circumferential layers depends on the stacking sequence. This is in contrast to classical lamination theory, which predicts that the expansion will be independent of the stacking arrangement. As expected, the sign and magnitude of the peak interlaminar stresses depend on stacking sequence. For tubes with a specific number of axial and circumferential layers, thermally induced interlaminar stresses can be controlled by altering stacking arrangement.

Hyer, M. W.; Cooper, D. E.; Cohen, D.

1986-01-01

402

Tensile and creep strengths of hot-pressed Si 3 N 4  

Microsoft Academic Search

Tensile, creep, and stress-rupture data for Norton HS-110 and HS-130 hot-pressed Si3N4 are presented. It is shown that the strength of the material is controlled by the grain-boundary glass phase. At elevated temperatures, >1000 C, deformation is controlled by grain-boundary sliding. A model based on the concept of geometrically necessary wedge cracks is then developed which accounts for the observed

Ram Kossowsky; D. G. Miller; E. S. Diaz

1975-01-01

403

Grain-boundary diffusion creep in nanocrystalline palladium by molecular-dynamics simulation  

Microsoft Academic Search

Molecular-dynamics (MD) simulations of fully three-dimensional (3D), model nanocrystalline face-centered cubic metal microstructures are used to study grain-boundary (GB) diffusion creep, one mechanism considered to contribute to the deformation of nanocrystalline materials. To overcome the well-known limitations associated with the relatively short time interval used in our MD simulation (typically <10?8 s), our simulations are performed at elevated temperatures where

V. Yamakov; D. Wolf; S. R. Phillpot; H. Gleiter; Forschungszentrum Karlsruhe

2002-01-01

404

Characterization of heat transfer processes in a melt pool convection and vessel-creep experiment  

Microsoft Academic Search

The results of an integral experiment on melt pool convection and vessel-creep deformation are presented and analyzed. The experiment is performed on a test facility, named Failure Of REactor VEssel Retention (FOREVER). The facility employs a 1\\/10-scaled 15Mo3-(German)-steel vessel of 400-mm diameter, 15-mm wall thickness and 750-mm height. A high-temperature (?1300C) oxide melt is prepared in a SiC-crucible placed in

B. R Sehgal; R. R Nourgaliev; T. N Dinh

2002-01-01

405

Compressive Creep Behavior of Spark Plasma Sintered 8 mol% Yttria Stabilized Cubic Zirconia  

NASA Astrophysics Data System (ADS)

The present paper describes compressive creep behavior of cubic 8 mol% Yttria-stabilized Zirconia, fabricated by spark plasma sintering, in the temperature range of 1300-1330 C at a stress level of 78-193 MPa in vacuum. The pre- and post-creep microstructures, along with the values of the stress exponent ( n = 1.7-2.7) and the activation energy ( Q = 711-757 kJ/mol) suggest that a mixed mode of plastic deformation, dominated by grain boundary sliding, occurred in this material. The relatively high activation energy observed was related to the pinning of the grain boundaries by voids during creep, leading to microcrack formation, shear strain-induced grain exfoliation, and finally creation of new voids at grain boundaries.

Robles Arellano, K. D.; Bichler, L.; Mondal, K.; Fong, R.

2014-10-01

406

Control of epoxy creep using graphene.  

PubMed

The creep behavior of epoxy-graphene platelet (GPL) nanocomposites with different weight fractions of filler is investigated by macroscopic testing and nanoindentation. No difference is observed at low stress and ambient temperature between neat epoxy and nanocomposites. At elevated stress and temperature the nanocomposite with the optimal weight fraction, 0.1 wt% GPLs, creeps significantly less than the unfilled polymer. This indicates that thermally activated processes controlling the creep rate are in part inhibited by the presence of GPLs. The phenomenon is qualitatively similar at the macroscale and in nanoindentation tests. The results are compared with the creep of epoxy-single-walled (SWNT) and multi-walled carbon nanotube (MWNT) composites and it is observed that creep in both these systems is similar to that in pure epoxy, that is, faster than creep in the epoxy-GPL system considered in this work. PMID:22378720

Zandiatashbar, Ardavan; Picu, Catalin R; Koratkar, Nikhil

2012-06-11

407

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  

Microsoft Academic Search

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

Sylvain Barbot; Yuri Fialko; Yehuda Bock

2009-01-01

408

Transient creep and convective instability of the lithosphere  

NASA Astrophysics Data System (ADS)

Laboratory experiments with rock samples show that transient creep, at which strain grows with time and strain rate decrease at constant stress, occurs while creep strains are sufficiently small. The transient creep at high temperatures is described by the 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. At the transient creep, the effective viscosity, found in the study of postglacial flows, differs significantly from the effective viscosity, which characterizes convective flow, since timescales of these flows are very different. Besides, the transient creep changes the elastic crust thickness estimated within the power-law rheology of the lithosphere. Two problems of convective stability for the lithosphere with the Andrade rheology are solved. The solution of the first problem shows that the state, in which large-scale convective flow in the mantle occurs under lithospheric plates, is unstable and must bifurcate into another more stable state at which the lithospheric plates become mobile and plunge into the mantle at subduction zones. If the lithosphere had the power-law fluid rheology, the effective viscosity of the stagnant lithospheric plates would be extremely high and the state, in which large-scale convection occurs under the stagnant plates, would be stable that contradicts plate tectonics. The mantle convection forms mobile lithospheric plates if the effective viscosity of the plate is not too much higher than the effective viscosity of the underlying mantle. The Andrade rheology lowers the plate effective viscosity corresponding to the power-law fluid rheology and, thus, leads to instability of the state in which the plates are stagnant. The solution of the second stability problem shows that the state, in which the lithospheric plate moves as a whole with constant velocity, is stable but small-amplitude oscillations are imposed on this motion 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 oscillations is of the order of 108 yr). The small-amplitude convective oscillations cause small strains and do not destroy the thickening of the lithosphere beneath cratons. Thus, the transient creep of the lithosphere explains not only mobility of the lithospheric plates but longevity of subcratonic roots as well.

Birger, Boris I.

2012-12-01

409

Finite element analysis of plastic deformation of CP-Ti by multi-pass equal channel angular extrusion at medium hot-working temperature  

Microsoft Academic Search

The plastic deformation of commercially pure (CP) titanium by multi-pass equal channel angular extrusion (ECAE), at medium hot-working temperature, was simulated using finite element method. The effect of ECAE deformation was to uniformly deform the middle billet by simple shear and to induce a side shift of un-deformed and un-moved billet-ends so as to preserve its original shape during deformation.

Z. J. Zhang; I. H. Son; Y. T. Im; J. K. Park

2007-01-01

410

CREEP STRAIN CORRELATION FOR IRRADIATED CLADDING  

SciTech Connect

In an attempt to predict the creep deformation of spent nuclear fuel cladding under the repository conditions, different correlations have been developed. One of them, which will be referred to as Murty's correlation in the following, and whose expression is given in Henningson (1998), was developed on the basis of experimental points related to unirradiated Zircaloy cladding (Henningson 1998, p. 56). The objective of this calculation is to adapt Murty's correlation to experimental points pertaining to irradiated Zircaloy cladding. The scope of the calculation is provided by the range of experimental parameters characterized by Zircaloy cladding temperature between 292 C and 420 C, hoop stress between 50 and 630 MPa, and test time extending to 8000 h. As for the burnup of the experimental samples, it ranges between 0.478 and 64 MWd/kgU (i.e., megawatt day per kilogram of uranium), but this is not a parameter of the adapted correlation.

P. Macheret

2001-01-23

411

Effects of low temperature neutron irradiation on deformation behavior of austenitic stainless steels  

SciTech Connect

An austenitic stainless steel, designated 316LN-IG, has been chosen for the first wall/shield (FW/S) structure for the International Thermonuclear Experimental Reactor (ITER). The proposed operational temperature range for the structure (100 to 250{degree}C) is below the temperature regimes for void swelling (400-600{degree}C) and for helium embrittlement (500-700{degree}C). However, the proposed neutron dose is such that large changes in yield strength, deformation mode, and strain hardening capacity could be encountered which could significantly affect fracture properties. Definition of the irradiation regimes in which this phenomenon occurs is essential to the establishment of design rules to protect against various modes of failure.

Pawel, J.E.; Rowcliffe, A.F.; Alexander, D.J.; Grossbeck, M.L. [Oak Ridge National Laboratory, TN (United States); Shiba, K.

1996-04-01