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1

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

2

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

3

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

4

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

5

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

6

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

7

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

8

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

9

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

10

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

11

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

12

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

13

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

14

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 860°C, 900°C and 940°C 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

15

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

16

Experimental Research on Creep Characteristics of Nansha Soft Soil  

PubMed Central

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

Luo, Qingzi; Chen, Xiaoping

2014-01-01

17

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

18

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

19

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

Microsoft Academic Search

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

Sofiane Terzi; Raphael Couturier; Laure Guétaz; Bernard Viguier

2008-01-01

20

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

21

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

22

Deformation characteristics of metal foams  

Microsoft Academic Search

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

J Banhart; J. BAUMEISTER

1998-01-01

23

Analysis of Mining Terrain Deformation Characteristics with Deformation Information System  

NASA Astrophysics Data System (ADS)

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

Blachowski, Jan; Milczarek, Wojciech; Grzempowski, Piotr

2014-05-01

24

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

25

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

26

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

27

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

28

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

29

Abnormal acceleration of creep deformation rate above 700 °C in the orthorhombic based Ti–22Al–27Nb 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 Ti–22Al–27Nb (at.%) alloys are conducted at a constant tensile stress of 200MPa at the various temperatures in the range from 650 to 750°C. It is observed that the creep deformation rate of the O+bcc dual

Seung Jin Yang; Soo Woo Nam; Masuo Hagiwara

2004-01-01

30

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

31

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

32

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

33

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

34

Characteristics of irradiation creep in the first wall of a fusion reactor  

SciTech Connect

A number of significant differences in the irradiation environment of a fusion reactor are expected with respect to the fission reactor irradiation environment. These differences are expected to affect the characteristics of irradiation creep in the fusion reactor. Special conditions of importance are identified as the (1) large number of defects produced per pka, (2) high helium production rate, (3) cyclic operation, (4) unique stress histories, and (5) low temperature operations. Existing experimental data from the fission reactor environment is analyzed to shed light on irradiation creep under fusion conditions. Theoretical considerations are used to deduce additional characteristics of irradiation creep in the fusion reactor environment for which no experimental data are available.

Coghlan, W.A.; Mansur, L.K.

1981-01-01

35

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

NASA Astrophysics Data System (ADS)

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

Rogowitz, Anna; Grasemann, Bernhard

2014-05-01

36

The irradiation creep characteristics of graphite to high fluences  

SciTech Connect

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

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

1988-01-01

37

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

38

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

39

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

40

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.

41

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

42

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

43

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

44

Energy characteristics of adiabatically-deformed Hamiltonian oscillators  

E-print Network

Energy characteristics of adiabatically-deformed Hamiltonian oscillators Matthew Kiener and Mihir in the adiabatic deformation of a classical cubic oscillator. This system has been studied in the literature on the principle of adiabatic invariance, it is shown here that the total energy of an initially excited oscillator

Sen, Mihir

45

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

46

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

47

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

48

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

49

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. Mühle; U. Martin; H. Oettel; O. Vöhringer

1997-01-01

50

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

51

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

52

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

53

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

SciTech Connect

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

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

1999-08-26

54

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

55

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

56

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

57

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

58

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

59

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

60

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

61

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

62

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

63

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

64

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

NASA Astrophysics Data System (ADS)

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

Shrestha, Triratna

65

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

66

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

67

Probing the coupled adhesion and deformation characteristics of suspension cells  

NASA Astrophysics Data System (ADS)

By combining optical trapping with fluorescence imaging, the adhesion and deformation characteristics of suspension cells were probed on single cell level. We found that, after 24 h of co-culturing, stable attachment between non-adherent K562 cells and polystyrene beads coated with fibronectin, collagen I, or G-actin can all be formed with an adhesion energy density in the range of 1 - 3 × 10 - 2 mJ/m2, which is about one order of magnitude lower than the reported values for several adherent cells. In addition, it was observed that the formation of a stronger adhesion is accompanied with the appearance of a denser actin cell cortex, especially in the region close to the cell-bead interface, resulting in a significant increase in the apparent modulus of the cell. Findings here could be important for our understanding of why the aggregation of circulating cells, like that in leukostasis, takes place in vivo as well as how such clusters of non-adherent cells behave. The method proposed can also be useful in investigating adhesion and related phenomena for other cell types in the future.

Hui, T. H.; Zhu, Q.; Zhou, Z. L.; Qian, J.; Lin, Y.

2014-08-01

68

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

69

Characteristics of tsunamis generated by 3D deformable granular landslides  

NASA Astrophysics Data System (ADS)

Landslides can trigger tsunamis with locally high amplitudes and runup, which can cause devastating effects in the near field region. The events of 1958 Lituya Bay, 1998 Papua New Guinea and 2006 Java tsunamis are reminders of the hazards associated with impulse waves. Tsunamis generated by granular landslides were studied in the three dimensional NEES tsunami wave basin (TWB) at Oregon State University (OSU) based on the generalized Froude similarity. A novel pneumatic landslide generator was deployed to simulate landslides with varying geometry and kinematics. Granular materials were used to model deformable landslides. Measurement techniques such as particle image velocimetry (PIV), multiple above and underwater video cameras, multiple acoustic transducer arrays (MTA), as well as resistance wave and runup gauges were applied. Tsunami wave generation and propagation is studied off a hill slope, in fjords and around curved headlands. The wave generation was characterized by an extremely unsteady three phase flow consisting of the slide granulate, water and air entrained into the flow. Landslide deformation is quantified and the slide kinematics with reference to slide surface velocity distribution and slide front velocity is obtained. Empirical equations for predicting the wave amplitude, period and wavelength are obtained. The generated waves depend on determined non-dimensional landslide and water body parameters such as the slide Froude number and relative slide shape at impact, among others. Attenuation functions of the leading wave crest amplitude, the lateral wave runup on the hill slope, the wave length and the time period were obtained to describe the wave behavior in the near field and to quantify the wave amplitude decay away from the landslide source. The measured wave celerity of the leading wave corresponds well to the solitary wave speed while the trailing waves are considerably slower in propagation. The individual waves in the wave train span from shallow to deep water depth regime. The energy conversion between landslide and waves is lower compared with 2D and solid block landslides due to radial spread of unidirectional landslide energy by the wave front. The slide characteristics measured in the experiment provide the landslide source for numerical landslide tsunami modeling. The measured landslide and tsunami data serve the validation and advancement of 3-dimensional numerical landslide tsunami and prediction models. Landslide impact and tsunami generation (Photo credit: Devin K. Daniels)

Mohammed, F.; Fritz, H. M.; McFall, B.

2010-12-01

70

Derivation of deformation characteristics in fast-moving glaciers  

NASA Astrophysics Data System (ADS)

Crevasse patterns are the writings in a glacier's history book—the movement, strain and deformation frozen in ice. Therefore by analysis of crevasse patterns we can learn about the ice-dynamic processes which the glacier has experienced. Direct measurement of ice movement and deformation is time-consuming and costly, in particular for large glaciers; typically, observations are lacking when sudden changes occur. Analysis of crevasse patterns provides a means to reconstruct past and ongoing deformation processes mathematically. This is especially important for fast-moving ice. Ice movement and deformation are commonly described and analyzed using continuum mechanics and measurements of ice velocities or strain rates. Here, we present a different approach to the study of ice deformation based on principles of structural geology. Fast ice movement manifests itself in the occurrence of crevasses. Because crevasses remain after the deformation event and may be transported, overprinted or closed, their analysis based on aerial videography and photography or satellite data gives information on past deformation events and resulting strain states. In our treatment, we distinguish (A) continuously fast-moving glaciers and ice streams, and (B) surge-type glaciers, based on observations of two prototypes, Jakobshavns Isbræ, Greenland, for (A), and Bering Glacier, Alaska, during the 1993-1995 surge, for (B). Classes of ice-deformation types are derived from aerial images of ice surfaces using structural geology, i.e. structural glaciology. For each type, the deformation gradient matrix is formed. Relationships between invariants used in structural geology and continuum mechanics and the singular value decomposition are established and applied to ice-surface classification. Deformation during a surge is mostly one of the extensional deformation types. Continuously, or infinitesimally repeated, deformation acting in continuously fast-moving ice causes different typical crevasse patterns. The structural-geology approach also includes a way to treat the problem of shear, as observed in the margins of fast-moving ice streams within slow-moving surrounding ice. In this paper we provide the first link between a physical analysis of ice-surface deformation and a connectionist-geostatistical analysis of the same problem.

Herzfeld, Ute C.; Clarke, Garry K. C.; Mayer, Helmut; Greve, Ralf

2004-04-01

71

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

72

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

NASA Astrophysics Data System (ADS)

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

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

73

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

74

Role of grain boundary sliding on creep deformation characteristics of discontinuous reinforced composites.  

National Technical Information Service (NTIS)

In this study, the grain boundary sliding behavior in discontinuous reinforced composites is investigated numerically. Results indicate that the stress enhancement factor for the composite is much larger than the one observed for the matrix material. In t...

S. B. Biner

1994-01-01

75

Quaternary Science Reviews 24 (2005) 123140 The deforming bed characteristics of a stratified till assemblage in  

E-print Network

Quaternary Science Reviews 24 (2005) 123­140 The deforming bed characteristics of a stratified till) and laboratory (Iverson et al., 1997, 1998) based investigations of till deformation subscribe to a plastic rheological model for till behaviour however, and recent micromorphological studies point to the presence

Hart, Jane

76

Memory characteristics of hysteresis and creep in multi-layer piezoelectric actuators: An experimental analysis  

NASA Astrophysics Data System (ADS)

In this paper we provide an experimental characterization of creep and hysteresis in a multi-layer piezoelectric actuator (PEA), taking into account their relationships in terms of memory structure. We fit the well-known log-t model to the response of the PEA when driven by piecewise-constant signals, and find that both the instantaneous and the delayed response of the PEA display hysteretic dependence on the voltage level. We investigate experimentally the dependence of the creep coefficient on the input history, by driving the PEA along first-order reversal curves and congruent minor loops, and find that it displays peculiar features like strict congruence of the minor loops and discontinuities. We finally explain the observed experimental behaviors in terms of a slow relaxation of the staircase interface line in the Preisach plane.

Biggio, Matteo; Butcher, Mark; Giustiniani, Alessandro; Masi, Alessandro; Storace, Marco

2014-02-01

77

Characteristics of Creep Damage for 60Sn40Pb Solder Material  

Microsoft Academic Search

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

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

1999-01-01

78

Postseismic relaxation and transient creep  

USGS Publications Warehouse

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

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

2005-01-01

79

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

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

80

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

81

Microstructure and creep characteristics of dissimilar T91/TP316H martensitic/austenitic welded joint with Ni-based weld metal  

SciTech Connect

This paper deals with characterization of microstructure and creep behavior of dissimilar weldment between the tempered martensitic steel T91 and the non-stabilized austenitic steel TP316H with Ni-based weld metal (Ni WM). Microstructure analyses were performed using light microscopy, scanning and transmission electron microscopy and energy-dispersive X-ray spectroscopy. The martensitic part of the welded joint exhibited a wide heat-affected zone (HAZ) with typical microstructural gradient from its coarse-grained to the fine-grained/intercritical region. In contrast, the HAZ of austenitic steel was limited to only a narrow region with coarsened polygonal grains. The microstructure of Ni WM was found to be very heterogeneous with respect to the size, morphology and distribution of grain boundaries and MC-type precipitates as a result of strong weld metal dilution effects and fast non-equilibrium solidification. Cross-weld creep tests were carried out in a temperature range from 600 to 650 Degree-Sign C at applied stresses from 60 to 140 MPa. The obtained values of apparent stress exponents and creep activation energies indicate thermally activated dislocation glide to be the governing creep deformation mechanism within the range of used testing conditions. The creep samples ruptured in the T91 intercritical HAZ region by the 'type IV cracking' failure mode and the creep fracture mechanism was identified to be the intergranular dimple tearing by microvoid coalescence at grain boundaries. The TEM observations revealed pronounced microstructural differences between the critical HAZ region and the T91 base material before as well as after the creep exposure. - Highlights: Black-Right-Pointing-Pointer Phase transformations affect the microstructures of T91 and TP316H HAZ regions. Black-Right-Pointing-Pointer High weld metal dilution results in heterogeneous microstructure with MC carbides. Black-Right-Pointing-Pointer Creep behavior of the studied weldment is controlled by its martensitic T91 part. Black-Right-Pointing-Pointer The lowest hardness of T91 ICHAZ region corresponds with its lowest creep strength.

Falat, Ladislav, E-mail: lfalat@imr.saske.sk [Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 040 01 Kosice (Slovakia)] [Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 040 01 Kosice (Slovakia); Svoboda, Milan [Institute of Physics of Materials, Academy of Sciences of Czech Republic, Zizkova 22, 616 62 Brno (Czech Republic)] [Institute of Physics of Materials, Academy of Sciences of Czech Republic, Zizkova 22, 616 62 Brno (Czech Republic); Vyrostkova, Anna; Petryshynets, Ivan; Sopko, Martin [Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 040 01 Kosice (Slovakia)] [Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 040 01 Kosice (Slovakia)

2012-10-15

82

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.

83

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 strain–time features. The effects of creep

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

2001-01-01

84

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

85

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

NASA Astrophysics Data System (ADS)

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

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

2014-01-01

86

Vibration and damping characteristics of composite laminates using shear deformable finite element  

SciTech Connect

The effects of transverse shear deformation on dynamic characteristics of composite laminated plates have been investigated. Complex modulus of an orthotropic lamina is employed to study damping effect and a modal approach to the resultant complex eigenvalue problem is introduced to save a considerable amount of computation time. The present results are in a good agreement with the solution of the modal strain energy method (MSE). The damping is very high when the composite laminated plates are subject to large transverse shear deformation.

Koo, K.N.; Lee, I. [Korea Advanced Institute of Science and Technology, Taejon (Korea, Republic of). Dept. of Aerospace Engineering

1993-12-31

87

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

88

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

89

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

90

Constraining the characteristics of tsunami waves from deformable submarine slides  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

91

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

92

EBSD investigation of the microstructure and texture characteristics of hot deformed duplex stainless steel.  

PubMed

The microstructure and crystallographic texture characteristics were studied in a 22Cr-6Ni-3Mo duplex stainless steel subjected to plastic deformation in torsion at a temperature of 1000 degrees C using a strain rate of 1 s(-1). High-resolution EBSD was successfully used for precise phase and substructural characterization of this steel. The austenite/ferrite ratio and phase morphology as well as the crystallographic texture, subgrain size, misorientation angles and misorientation gradients corresponding to each phase were determined over large sample areas. The deformation mechanisms in each phase and the interrelationship between the two are discussed. PMID:16774517

Cizek, P; Wynne, B P; Rainforth, W M

2006-05-01

93

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, François; Audemard, Franck A.; Beck, Christian; Van Welden, Aurélien; Ollarves, Reinaldo; Reinoza, Carlos

2011-05-01

94

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

95

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

96

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

97

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

NASA Astrophysics Data System (ADS)

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

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

2008-05-01

98

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

Microsoft Academic Search

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

T. Campbell McCuaig; Robert Kerrich

1998-01-01

99

Deformation structure and the tensile fracture characteristics of a cold worked 1080 pearlitic steel  

Microsoft Academic Search

The tensile mechanical properties, deformation structure, and tensile fracture characteristics of a 1080 perlitic steel were\\u000a examined at various reduction ratios of cold work. The final tensile fracture ductility exhibited an unusual behavior in that\\u000a this parameter first decreased and then increased with increasing reduction ratio. At a reduction ratio of 1.92, the cold\\u000a worked material exhibited greater tensile ductility

Joseph J. Pepe

1973-01-01

100

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

101

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

NASA Astrophysics Data System (ADS)

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

Cheema, Taqi Ahmad; Park, Cheol Woo

2013-08-01

102

Nanogranular origin of concrete creep  

PubMed Central

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

Vandamme, Matthieu; Ulm, Franz-Josef

2009-01-01

103

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

104

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

105

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

106

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

107

A mucolipidosis III patient presenting characteristic sonographic and magnetic resonance imaging findings of claw hand deformity.  

PubMed

Mucolipidosis III (ML-III), or pseudo-Hurler polydystrophy, is an autosomal recessive Hurler-like disorder without mucopolysacchariduria. The diagnosis is challenging for rheumatologists since the musculoskeletal presentation is similar to some rheumatic diseases. We report a case of ML-III in a 16-year-old Taiwanese boy. The characteristic findings of sonography and magnetic resonance imaging (MRI) of claw hand deformity are described. A 16-year-old boy was referred to our rheumatologic clinic because of progressive claw hand deformity, multiple joint stiffness and tightness of the skin over the fingers at the age of 6 years. Sonography and MRI examination disclosed tendon sheath thickening over extensor tendons of both wrists and fingers without features of active inflammation over tendons or joints nor thickening of skin. Urinary glycosaminoglycans were normal. The diagnosis of ML-III was confirmed by the presence of elevated activities of beta-glucuronidase (2141.99 nmol/mg protein/hour), arylsulfatase A (1237.7 nmol/mg protein/hour) and alpha-fucosidase (52.95 nmol/mg protein/hour) in his plasma and decreased activity of these lysosomal enzymes in cultured skin fibroblasts. Sonography and MRI screening for claw hand deformity may offer important clues enabling early diagnosis of ML-III. PMID:15361946

Chen, Hsin-Hua; Lan, Joung-Liang; Shu, San-Ging; Chen, Der-Yuan; Lan, Howard Haw-Chang

2004-09-01

108

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

PubMed Central

Objective: The objective of the following study is to compare the cleaning efficiency and deformation characteristics of Twisted File (TF) and ProTaper (PT) nickel-titanium rotary instruments in root canal preparation. Materials and Methods: A total of 52 canals from 26 extracted maxillary first molars were randomly assigned into two groups of each including 13 mesiobuccal and 12 distobuccal (DB) canals. Two DB canals were as blank controls. After preparation with TF and PT, we recorded the preparation time and evaluate the amounts of debris and smear layer at apical, middle and coronal canals under scanning electron microscopy (SEM). Three cross-sections of canals at 3 mm, 5 mm and 7 mm from the apex foramens were scanned before and after preparation under micro-computed tomography. Changes of the cross-section area (CSA) at the three levels were calculated with Photoshop CS4. File deformation was also investigated under SEM. Two groups were statistically compared with Mann-Whitney test and independent sample t-test. Results: Less debris and smear layer were found in coronal regions of canals prepared with TF (P = 0.006, P = 0.001, respectively). TF group displayed more CSA change than PT group (P = 0.045) at cross-sections of 5 mm from the apex foramens and took significantly less preparation time than PT group did (P = 9.06 × 10?28). All five TF files without obvious micro-cracks and two out of 25 PT files with many micro-cracks showed visible unwound deformation. Conclusion: Neither TF nor PT achieves complete cleanliness of canal walls. Their deformation features might indicate different fracture resistance. TF single-file technique would substantially shorten the time of root canal preparation. PMID:24966769

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

2014-01-01

109

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

110

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 600°C. 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

111

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

112

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

113

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

114

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

115

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

116

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

Microsoft Academic Search

The in-reactor behaviour of internally pressurised capsules of Zr–2.5Nb tubes is analysed in detail to separate the stress dependent component of deformation (creep). It is found by a rigorous statistical analysis that the creep rate varies with fast neutron fluence. At 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

117

An Approach to the Determination of the Deformation Characteristics of Viscoelastic Materials  

Microsoft Academic Search

An efficient method is proposed to determine the deformation function of a viscoelastic material from experimental data. The deformation function is assumed to be an integral operator with Rabotnov's fractional-exponential kernel or a sum of such kernels. This representation enables effective use of the method of operator continued fractions. To illustrate the method, deformation data for polymethylmethacrylate are used. The

A. A. Kaminskii; M. F. Selivanov

2005-01-01

118

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

SciTech Connect

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

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

2012-11-15

119

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

Microsoft Academic Search

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

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

120

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

121

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

122

Basic deformation characteristics of Bayan Hara Group in northern Tibetan Plateau  

NASA Astrophysics Data System (ADS)

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

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

2012-12-01

123

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

NASA Astrophysics Data System (ADS)

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

Samani, Babak

2013-05-01

124

Dislocation Creep of Dry Quartz  

NASA Astrophysics Data System (ADS)

Small scale shear zones formed during heterogeneous, amphibolite facies condition in the Truzzo granite in the Penninic Tambo nappe. Magmatic quartz grains recrystallized dynamically by subgrain rotation and grain boundary migration. The presence of a monoclinic shape fabric and a crystallographic preferred orientation are typical for deformation by dislocation creep. Dynamically recrystallized mean grain sizes vary between 200 and 750 ?m which indicate deformation at relatively low differential stresses (5 - 30 MPa). Fourier-Transform-Infrared (FTIR) spectroscopy reveals water contents mostly below 200 H/10^6 Si in the interior of recrystallized grains (in the form of discrete OH peaks and very little broad band absorption). This water content is in the range of values reported for dry Brazil quartz. Primary magmatic quartz grains contain fluid-inclusion-rich areas with a broad absorption band and higher water concentrations. Recrystallized grains are dry, except for postkinematic inclusion trails. These measurements present the first data on strictly intragranular water contents of dynamically recrystallized quartz in nature. Dry quartz is extremely strong and does not deform by dislocation creep in deformation experiments at the low differential stress levels that would correspond to natural deformation. In contrast, deformation experiments on wet polycrystalline quartz have produced flow laws that can be extrapolated to natural conditions, which yield satisfying results. This is in contrast with our data of the dry quartz deforming by dislocation creep at relatively low differential stresses at natural strain rates. Contrary to the conventional concept of recovery, our data and observations imply that quartz would be hardening as a consequence of grain boundary migration because fluid inclusions are expelled. The drainage of fluid inclusions and microstructures in the feldspar-mica matrix indicate that water during deformation was at least present in the grain boundary region. FTIR measurements of natural deformed quartz reported in literature include grain boundaries and usually yield concentration of up to several 1000s H/10^6 Si. Therefore it is concluded that either introduction of water into the deforming grains must have been transient or that the intragranular water concentrations which are rheologically effective in the naturally deformed Truzzo granite are much lower than those previously reported in the literature.

Kilian, R.; Heilbronner, R.; Stunitz, H.

2011-12-01

125

Primary creep in single crystal superalloys: Origins, mechanisms and effects  

Microsoft Academic Search

Creep deformation of the CMSX-4 nickel-base single crystal superalloy is studied in the range 750–850°C. Emphasis is placed on elucidating the factors causing primary creep when the tensile stress is orientated within 20°C of the technologically important ?001? direction. It is demonstrated unambiguously that primary creep occurs only if a threshold stress of approximately 500MPa is exceeded; thereafter the accumulated

C. M. F. Rae; R. C. Reed

2007-01-01

126

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

127

Time-aging time-stress superposition in soft glass under tensile deformation field  

E-print Network

We have studied the tensile deformation behaviour of thin films of aging aqueous suspension of Laponite, a model soft glassy material, when subjected to a creep flow field generated by a constant engineering normal stress. Aqueous suspension of Laponite demonstrates aging behaviour wherein it undergoes time dependent enhancement of its elastic modulus as well as its characteristic relaxation time. However, under application of the normal stress, the rate of aging decreases and in the limit of high stress, the aging stops with the suspension now undergoing a plastic deformation. Overall, it is observed that the aging that occurs over short creep times at small normal stresses is same as the aging that occurs over long creep times at large normal stresses. This observation allows us to suggest an aging time - process time - normal stress superposition principle, which can predict rheological behaviour at longer times by carrying out short time tests.

Asima Shaukat; Ashutosh Sharma; Yogesh M. Joshi

2010-06-10

128

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 1300°C 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

Günter Thurn; Gerold A. Schneider; Fritz Aldinger

1997-01-01

129

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

130

Numerical simulation of ceramic breeder pebble bed thermal creep behavior  

E-print Network

Numerical simulation of ceramic breeder pebble bed thermal creep behavior Alice Ying *, Hulin Huang Abstract The evolution of ceramic breeder pebble bed thermal creep deformation subjected to an external load and a dif- ferential thermal stress was studied using a modified discrete numerical code

Abdou, Mohamed

131

The search for creep on the faults of northern California  

NASA Astrophysics Data System (ADS)

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

Funning, Gareth; Jin, Lizhen

2013-04-01

132

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

133

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

134

Deformation characteristics of isothermally forged UDIMET 720 nickel-base superalloy  

Microsoft Academic Search

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

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

2005-01-01

135

Effect of strain and deformation route on grain boundary characteristics and recrystallization behavior of aluminum  

NASA Astrophysics Data System (ADS)

The effect of strain and deformation route on the recrystallization behavior of aluminum sheets has been investigated using well lubricated cold rolling and continuous equal channel angular extrusion. Three different deformation routes in plane strain corresponding to (1) simple shear, (2) compression, and (3) the combination of simple shear and compression were performed on 1100 aluminum sheet. Fixed amounts of the equivalent strain of 1.28 and 1.06 were accumulated in each route. In case of the combined deformation route, the ratio of shear strain to the total equivalent strain was varied. The recrystallized grain size was finer if the combined deformation route was employed instead of the monotonic route under the same amount of equivalent strain at either strain level. The density of high angle grain boundaries that act as nucleation sites for recrystallization was higher in materials deformed by the combined route. The orientation imaging micrographs revealed that the change in deformation route is effective for introducing a larger number of new high angle grain boundaries with relatively low misorientation angle.

Sakai, Tetsuo; Utsunomiya, Hiroshi; Takahashi, Yasuo

2014-08-01

136

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

137

Diffusional creep and creep-degradation in dispersion-strengthened Ni-Cr base alloys.  

NASA Technical Reports Server (NTRS)

Dispersoid-free regions were observed in the dispersion-strengthened alloy TD-NiCr (Ni-20 Cr-2 ThO2) after slow strain rate testing (stress rupture, creep, and fatigue) in air from 1145 to 1590 K. Formation of the dispersoid-free regions appears to be the result of diffusional creep. The net effect of creep in TD-NiCr is the degradation of the alloy to a duplex microstructure. Creep degradation of TD-NiCr is further enhanced by the formation of voids and intergranular oxidation in the dispersoid-free bands. Void formation was observed after as little as 0.13% creep deformation at 1255 K. The dispersoid-free regions apparently provide sites for void formation and oxide growth since the strength and oxidation resistance of Ni-20 Cr-2 ThO2.

Whittenberger, J. D.

1973-01-01

138

Influence of Microstructure on Creep Properties of Solders  

Microsoft Academic Search

The influences of microstructure on the creep properties of Sn-37Pb, Sn-3.5Ag, Sn-3.0Ag-0.5Cu and Sn-5.0Sb solders were investigated using nano-indentation tests and tensile creep tests for fine wire solders. The nano-indentation tests enabled us to measure the indentation creep properties of each phase. For the Sn-37Pb solder, the creep deformation properties were uniform for both Sn-rich and Pb-rich phases. For the

Tatsuya NISHIYAMA; Hideyuki KOHKETSU; Kyouhei TAKAHASHI; Takeshi OGAWA; Tadashi OHSAWA

2006-01-01

139

Deuteron irradiation creep of chemically vapor deposited silicon carbide fibers  

NASA Astrophysics Data System (ADS)

Irradiation creep tests were conducted on Textron SCS-6 silicon carbide (SiC) fibers during irradiation with 14 MeV deuterons at 450 and 600°C. 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 rate, are higher at 450°C than at 600°C for doses <0.07 dpa.

Scholz, R.

1998-03-01

140

Scaling of the acoustic emission characteristics during plastic deformation and fracture  

NASA Astrophysics Data System (ADS)

The scaling of the amplitude and time distributions of acoustic emission pulses, which reflects the self-similarity of defect structures, is revealed. The possibility of separation of independent contributions to the flow of acoustic emission events, which have substantially different scaling exponents, is shown for porous materials. The differences in the scaling exponents are related to the development of plastic deformation and fracture of the materials. The developed approach to an analysis of acoustic emission can be used to describe its predominant mechanisms during deformation.

Lependin, A. A.; Polyakov, V. V.

2014-07-01

141

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

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

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

144

Nanoscale deformation irregularities of gamma-irradiated poly(methyl methacrylate)  

Microsoft Academic Search

Development of deformation jumps in the creep of poly(methyl methacrylate) (PMMA) has been studied. The structural levels of deformation have been determined from the creep rate oscillation periods (deformation jumps) measured by the interferometric method. Special attention is given to a new method of data processing, which enables one to reveal previously undetectable nanoscale deformation jumps. By the example of

V. V. Shpeizman; N. N. Peschanskaya; P. N. Yakushev; A. S. Smolyanskii; A. S. Shvedov; V. G. Cheremisov

2010-01-01

145

Fault Zone Characteristics and Deformation Mechanisms of Porous, Non-welded Bishop Tuff  

Microsoft Academic Search

Fault zone deformation features associated with normal faults within non- to poorly welded Bishop Tuff (north of Bishop, CA) were undertaken to provide the structural context for air and water permeability testing. The first site (Chalk Cove fault) has approximately 9 m of offset, a narrow fault core, a broad hanging wall damage zone, and a narrow footwall damage zone

K. K. Bradbury; D. A. Ferrill; C. L. Dinwiddie; R. W. Fedors

2002-01-01

146

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

147

Some characteristics of the fracture of diphase steels during hot plastic deformation  

Microsoft Academic Search

1.We found a boundary temperature above which and below which high-temperature plastic deformation of diphase 1Kh21N5T steel is characterized by different mechanisms. The boundary temperature is about 1200\\\\dgC and matches the sharp change in the structure from approximately equal amounts of ferrite and austenite to a structure in which ferrite predominates.At temperatures below 1200°C cracks originate in austenite and develop

M. I. Sinel'nikov; E. G. Fel'dgandler

1967-01-01

148

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

PubMed Central

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

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

2013-01-01

149

Variations in Creep Rate along the Central San Andreas Fault from InSAR and GPS Observations  

NASA Astrophysics Data System (ADS)

The San Andreas Fault is locked along most of its length, but the 170 km-long section between San Juan Bautista and Parkfield undergoes creep. Measurements from creepmeters, alignment arrays and GPS over the last 25 years have shown that surface creep rates reach about 30 mm/year in the central portion, tapering off towards the locked segments at either end. Though useful, these measurements have been spatially isolated and intermittent in time. We present InSAR observations of creep across the fault, which have superior spatial coverage than previous data, and analyse them to investigate spatial variations in creep rate along the fault segment. From multiple ERS-1 and ERS-2 descending interferograms covering 1992 to 2001, we produce a stack which gives the spatial distribution of creep rate up to about 50 km either side of the fault. We find a maximum creep rate of about 32 mm/year. Deformation is step-like most of the way along the segment, but more distributed at the northern end, where the Calaveras Fault comes very close to the San Andreas Fault. We perform a linear inversion for shallow and deep sliding velocity on these faults using both the InSAR stack and GPS velocities from continuous (PBO) and campaign networks. Creep in the top few kilometers is variable along strike, with patches of faster creep interspersed with more slowly-moving patches. Creep at intermediate depths is greatest in the centre of the segment, reaching a few mm/yr less than the relative plate rate. The deep (> 12 km) sliding velocity is constrained to be less than or equal to the estimated long term relative plate velocity, and we estimate it to be a few mm/yr less than this. We compare the depth-averaged creep rate profile along the fault segment with that estimated by Nadeau and McEvilly (2004) from characteristic repeating microearthquakes. Between them, the three datasets utilised in this study suggest that creep is a spatially heterogeneous process.

Ryder, I. M.; Burgmann, R.

2007-12-01

150

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

151

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

152

Plastic deformation characteristics of Cu/X (Xdbnd Cusbnd Zr, Zr) nanolayered materials  

NASA Astrophysics Data System (ADS)

Nanolayered materials exhibit unique plastic deformation behavior, i.e., a bulk-like to small-scale plasticity transition and a scaling behavior of extremely small activation volume (V* < 10b3) with intrinsic size. This unusual plastic transition phenomenon likely stems from the dislocations respectively emit from interfaces and Frank-Read-type bulk sources below and above a critical intrinsic size ?20 nm. We quantitatively capture the scaling relationship between strain rate sensitivity and intrinsic size by a phenomenological model based on the Orowan-Frank-Read process.

Zhang, J. Y.; Wang, Y. Q.; Liu, G.; Sun, J.

2014-12-01

153

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

154

Irreversible thermodynamics of creep in crystalline solids  

NASA Astrophysics Data System (ADS)

We develop an irreversible thermodynamics framework for the description of creep deformation in crystalline solids by mechanisms that involve vacancy diffusion and lattice site generation and annihilation. The material undergoing the creep deformation is treated as a nonhydrostatically stressed multicomponent solid medium with nonconserved lattice sites and inhomogeneities handled by employing gradient thermodynamics. Phase fields describe microstructure evolution, which gives rise to redistribution of vacancy sinks and sources in the material during the creep process. We derive a general expression for the entropy production rate and use it to identify of the relevant fluxes and driving forces and to formulate phenomenological relations among them taking into account symmetry properties of the material. As a simple application, we analyze a one-dimensional model of a bicrystal in which the grain boundary acts as a sink and source of vacancies. The kinetic equations of the model describe a creep deformation process accompanied by grain boundary migration and relative rigid translations of the grains. They also demonstrate the effect of grain boundary migration induced by a vacancy concentration gradient across the boundary.

Mishin, Y.; Warren, J. A.; Sekerka, R. F.; Boettinger, W. J.

2013-11-01

155

Influences of Microstructure and Specimen Size on Creep Properties of Solders  

NASA Astrophysics Data System (ADS)

The influences of microstructure and specimen size on creep properties of Sn-37Pb and Sn-3.5Ag solders were investigated by nano-indentation tests and tensile creep tests for fine wire solders. The nano-indentation tests enabled us to measure the indentation creep properties of the specific microstructures individually. Tensile creep experiments were performed on our original creep testing machine for fine wire solders with the diameters of 0.2, 0.5 and 1.0 mm. For the Sn-37Pb solder, the creep deformation properties were uniform for both ? and ? phases and grain boundary sliding was the dominating creep mechanism. For the Sn-3.5Ag solder, creep deformations of ? phase were observed under much smaller stress levels than those for (?+?) phase, and thus the creep deformations occurred only in ? phase, which resulted in the nucleation of microvoids around the ? phase. The tensile creep tests for wire solders revealed that the significance of specimen size on the creep properties is strongly influenced by the microstructure of the solders.

Ogawa, Takeshi; Kohketsu, Hideyuki; Takahashi, Kyouhei; Ohsawa, Tadashi

156

Nanoscale deformation irregularities of ?-irradiated poly(methyl methacrylate)  

Microsoft Academic Search

Development of deformation jumps in the creep of poly(methyl methacrylate) (PMMA) has been studied. The structural levels\\u000a of deformation have been determined from the creep rate oscillation periods (deformation jumps) measured by the interferometric\\u000a method. Special attention is given to a new method of data processing, which enables one to reveal previously undetectable\\u000a nanoscale deformation jumps. By the example of

V. V. Shpe?zman; N. N. Peschanskaya; P. N. Yakushev; A. S. Smolyanski?; A. S. Shvedov; V. G. Cheremisov

2010-01-01

157

Hot Deformation Characteristics of Functionally Graded Steels Produced by Electroslag Remelting  

NASA Astrophysics Data System (ADS)

In this work, a hot compression test was carried out at 1173 K to 1473 K (900°C to 1200 °C), with a strain rate of 0.01 to 1 s-1 up to ~50 pct height reduction on functionally graded steel (FGS) specimens comprised of ferritic, bainitic, austenitic, and martensitic layers ( ???M ?). The stress-strain curves are strongly dependent on temperature and strain rate. Compressive flow stress varied from 40 to 105 MPa depending on the applied temperature and strain rates. Variation in steady-state flow stress with temperature and strain rates was studied. The strain-rate-sensitivity exponent ( m) and deformation activation energy ( Q) for the ???M ? composite under studied condition were 0.106 and 354.8 KJ mol-1, respectively, which are within the values of boundary layers of ferrite (304.9 KJ mol-1) and austenite (454.8 KJ mol-1) layers. Given the alternative microstructure of the ???M ? FGS, a range of deformation mechanisms from dynamic recovery to dynamic recrystallization maybe prevails, where the intensity of each mechanism depends on temperature and strain rates. In accordance with the experimental results, an empirical power-law equation was developed over the range of temperatures and strain rates investigated. The equation accurately describes temperature and strain-rate dependence of the flow stress.

Naderi, B.; Aghazadeh Mohandesi, J.

2011-08-01

158

Research of dynamical Characteristics of slow deformation Waves as Massif Responses on Explosions  

NASA Astrophysics Data System (ADS)

The research of massif state with use of approaches of open system theory [1-3] was developed for investigation the criterions of dissipation regimes for real rock massifs, which are under heavy man-caused influence. For realization of that research we used the data of seismic catalogue of Tashtagol mine. As a result of the analyze of that data we defined character morphology of phase trajectories of massif response, which was locally in time in a stable state: on the phase plane with coordinates released by the massif during the dynamic event energy E and lg(dE/dt) there is a local area as a ball of twisted trajectories and some not great bursts from that ball, which are not greater than 105 joules. In some time intervals that burst can be larger, than 105 joules, achieving 106 joules and yet 109 joules. [3]. Evidently there are two reciprocal depend processes: the energy accumulation in the attracted phase trajectories area and resonance fault of the accumulated energy. But after the fault the system returns again to the same attracted phase trajectories area. For analyzing of the thin structure of the chaotic area we decided to add the method of processing of the seismic monitoring data by new parameters. We shall consider each point of explosion as a source of seismic or deformation waves. Using the kinematic approach of seismic information processing we shall each point of the massif response use as a time point of the first arrival of the deformation wave for calculation of the wave velocity, because additionally we know the coordinates of the fixed response and the coordinates of explosion. The use of additional parameter-velocity of slow deformation wave propagation allowed us with use method of phase diagrams identify their hierarchic structure, which allow us to use that information for modeling and interpretation the propagation seismic and deformation waves in hierarchic structures. It is researched with use of that suggested processing method the thin structure of the chaotic area for two responses of the massif on a high energetic explosion in the northern and southern parts of it. The results are significant for understanding the high energetic rock shock and evaluation a criterion for massif stability estimation. The work is supported by the grant RFBR 10-05-00013 and Integration Project 2012-2014 with SB RAS Key words: massif response, slow deformation waves, seismic mine catalogue, analyze of observed data, phase diagrams. References 1. Naimark Y.I.,Landa P.S. Stochastic and chaotic oscillations//Moscow: Book House "LIBROKOM", 2009.-p.424. 2. Chulichkov A.I. Mathematical models of nonlinear dynamics.Moscow: Fizmatlit, 2003.-p.294. 3. Hachay O.A.,Khachay O.Y.,Klimko V.K.,Shipeev O.V. Reflection of synergetic features of rock massif state under man-caused influence after the data of mine seismological catalogue.// Mine informational and analytical bulletin MSMU,6, 2010,p.259-271.

Hachay, Olga; Khachay, Oleg; Shipeev, Oleg

2013-04-01

159

Material Parameters for Creep Rupture of Austenitic Stainless Steel Foils  

NASA Astrophysics Data System (ADS)

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

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

2014-08-01

160

A unified approach to grain boundary sliding in creep and superplasticity  

SciTech Connect

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 when d > [lambda]. Data for superplastic metals are examined to give the rate equation for Rachinger sliding when d < [lambda]. A unified model is developed for Rachinger sliding at all grain sizes, where the rate of sliding is controlled by the rate of accommodation through intragranular slip. It is demonstrated that the predictions of this model are in good agreement with experimental data under both creep and superplastic conditions.

Langdon, T.G. (Univ. of Southern California, Los Angeles, CA (United States))

1994-07-01

161

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

162

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 95–125?°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. Hanhijärvi

2000-01-01

163

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 Mg–Al-alloys was investigated in uniaxial compression at temperatures from 70 to 150°C. 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

164

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

NASA Astrophysics Data System (ADS)

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

Kono, Akiko; Matsushima, Takashi

165

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

166

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

167

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

168

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

169

Central Cascadia subduction zone creep  

NASA Astrophysics Data System (ADS)

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

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

2014-04-01

170

Influence of Static Aeroelastic Deformation of AN Airplane on the Aerodynamic Characteristics and Flightloads  

Microsoft Academic Search

The static aeroelastic characteristics of a flexible V-tail airplane were studied by the analyses of the variations of aerodynamic derivatives and flight loads versus flight dynamic pressure. The results show that the variation trends of aerodynamic derivatives and flight loads of the flexible airplane are different from those of the rigid airplane. Therefore, it is necessary to consider the static

L. D. Deng; Z. Q. Wan; C. Yang

2005-01-01

171

Characteristics of aquifer system deformation in the Southern Yangtse Delta, China  

Microsoft Academic Search

Excessive groundwater pumpage has caused regional cones of depression and severe land subsidence in the Southern Yangtse Delta, China. The characteristics of aquifer system compaction are complex because of the difference in the types, compositions and structures of the soils that the hydrostratigraphic units are composed of, and in the histories of groundwater level change the hydrostratigraphic units have experienced.

Yun Zhang; Yu-Qun Xue; Ji-Chun Wu; Shu-Jun Ye; Zi-Xin Wei; Qin-Fen Li; Jun Yu

2007-01-01

172

Microstructure and creep behaviour of magnesium hybrid composites  

Microsoft Academic Search

A comparison is made between the creep characteristics of the unreinforced squeeze-cast AZ91 and QE22 magnesium alloys and their hybrid composites reinforced with 7vol.% short carbon fibres and 15vol.% SiC particulates. Although the creep resistance of the reinforced AZ91 alloy is considerably improved by comparison with the unreinforced matrix alloy, no beneficial effect of hybrid reinforcement on the creep resistance

M. Svoboda; M. Pahutová; K. Kucha?ová; V. Skleni?ka; K. U. Kainer

2007-01-01

173

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

NASA Astrophysics Data System (ADS)

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

Aslani, Farhad; Nejadi, Shami

2012-09-01

174

Cross-Linked Thermoplastic Blends of Polyethylene with an Elastomer. 1. Deformation and Strength Characteristics  

Microsoft Academic Search

Results of an experimental investigation into changes of some mechanical characteristics of binary blends of high- and low-density polyethylenes with an elastomer (ethylene-propylene-dicyclopentadiene terpolymer) in the course of ?-radiation and chemical cross-linking are reported for a wide range of component ratios. Data on changes in the tensile strength and total, residual, and reversible strains at break, as well the microhardness

T. Bocok; J. Zicans; M. Kalnins

2005-01-01

175

Effect of cyclic deformation on the pseudoelasticity characteristics of Ti-Ni alloys  

Microsoft Academic Search

Change in the pseudoelasticity characteristics of Ti-Ni alloys during tension cycling was investigated. The critical stress\\u000a for inducing martensites and the hysteresis of a stress-strain curve decreased with increasing number of cyclic loading, while\\u000a the permanent elongation increased. The degree of the change in these values showed a strong dependence on the maximum applied\\u000a stress during stress-induced martensitic transformation. However,

S. Miyazaki; T. Imai; Y. Igo; K. Otsuka

1986-01-01

176

Influence of Static Aeroelastic Deformation of AN Airplane on the Aerodynamic Characteristics and Flightloads  

NASA Astrophysics Data System (ADS)

The static aeroelastic characteristics of a flexible V-tail airplane were studied by the analyses of the variations of aerodynamic derivatives and flight loads versus flight dynamic pressure. The results show that the variation trends of aerodynamic derivatives and flight loads of the flexible airplane are different from those of the rigid airplane. Therefore, it is necessary to consider the static aeroelastic effects during the flexible airplane design.

Deng, L. D.; Wan, Z. Q.; Yang, C.

177

A constant-stress, vacuum creep-testing apparatus  

Microsoft Academic Search

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

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

1966-01-01

178

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

179

Computer simulation on creep of amalgam in Class I cavity.  

PubMed

The creep behavior of amalgam in Class I cavity was simulated by an axi-symmetric elastic creep finite element method. In this procedure, the stress and time dependencies of the creep strain of amalgam were incorporated. Exponents of stress and time dependencies were postulated as 2.0 and 1.0, respectively. Amalgam with 1.0% of creep value (tested by American Dental Association Specification No. 1) were selected for the material to calculate. Simulation was conducted for the occlusal force of 40, 100, and 150 N, respectively, on the caps of enamel and vertical direction to the axis of the tooth. Results show that creep strain of amalgam in the cavity did not increase linearly with time because the amalgam deformed to become stress-free and creep rate was a function of the stress. It was concluded that elastic deformation of the crown with no filling material in its cavity is an important factor in determining the creep strain and the gap between the cavity and the restorative material. PMID:1458203

Asaoka, K; Kawano, F

1992-01-01

180

Irradiation creep\\/swelling interactions. [SS304  

Microsoft Academic Search

Results of a recent fast flux neutron irradiation experiment in EBR-II designed to determine the effects of high levels of prior irradiation (to 10²³n\\/cm², E greater than 0.1 MeV) on the irradiation induced deformation rate of 304 SS at 800°F are reported. The data are analyzed in terms of a model which includes enhancement of creep with increasing swelling rates.

G. L. Wire; J. L. Straalsund

1975-01-01

181

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

PubMed Central

The results of the interaction between coal failure and mining pressure field evolution during mining are presented. Not only the mechanical model of stope and its relative structure division, but also the failure and behavior characteristic of coal body under different mining stages are built and demonstrated. Namely, the breaking arch and stress arch which influence the mining area are quantified calculated. A systematic method of stress field distribution is worked out. All this indicates that the pore distribution of coal body with different compressed volume has fractal character; it appears to be the linear relationship between propagation range of internal stress field and compressed volume of coal body and nonlinear relationship between the range of outburst coal mass and the number of pores which is influenced by mining pressure. The results provide theory reference for the research on the range of mining-induced stress and broken coal wall. PMID:24967438

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

2014-01-01

182

Error correction for Moiré 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 moiré 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 moiré interference pattern. The authors assembled a creep measurement prototype for this application. By measuring the frequency change of the moiré 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

183

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

184

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

185

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. Hanhijärvi

1998-01-01

186

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

187

Effect of testing conditions and doping on superplastic creep of alumina  

E-print Network

716 Effect of testing conditions and doping on superplastic creep of alumina P. Gruffel, P. Carry superplastic deformation. Fig. 1. Strain rate variations during creep tests in compression C and tension can be arrived at. REFERENCES [1] C. Carry and A. Mocellin, in: Superplasticity Editions du C

Paris-Sud XI, Université de

188

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

189

[011] Creep in a single crystal nickel base superalloy at 1033 K  

Microsoft Academic Search

TEM investigations are performed on [011] single crystals of SRR99 after creep at 1,033 K under a load of 680 MPa. At the creep rate minimum, multiple slip in the matrix occurs on four octahedral slip systems. Octahedral cross slip or cubic slip is not activated. Due to the superposition of coherency and external stresses in small matrix channels, deformation

M. Feller-Kniepmeier; T. Kuttner

1994-01-01

190

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

191

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

192

Characterization of creep and creep damage by in-situ microtomography  

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

193

Deformation behavior and microstructure of TaC, and processing of C-TaC composites  

SciTech Connect

Deformation behavior of TaC{sub 0.99} polycrystals at elevated temperatures was investigated by compressive creep tests. From the results on creep tests at intermediate temperatures (1,400-1,500C) and stresses (105-170 MPa), the values of the stress exponent (n) and activation energy (Q{sub c}) for power-law creep of TaC{sub 0.99} were found to be n{approx}1.8 and Q{sub c}{approx}150 KJ/mol. The low activation energy and the low stress exponent suggest that the creep of TaC{sub 0.99} at intermediate temperatures is mainly controlled by grain-boundary sliding. Most dislocations formed during creep of TaC{sub 0.99} have no preferential orientation, in contrast to dislocations formed at low temperatures. The fabrication of C-fiber reinforced TaC composites was studied using combinations of powder-metallurgy techniques such as cold pressing, slurry infiltration, sintering, and hot isostatic pressing (HIP). The characteristics of the interface between carbon fibers and TaC were investigated. No chemical reaction occurred at the interface between carbon fibers and a stoichiometric TaC matrix. Carbon fibers suffered damage by indentation from tantalum carbide particles during cold compaction and HIP. A tantalum carbide coating of C-fibers prevented this indentation damage.

Kim Chulsoo.

1991-01-01

194

Diffusion creep in the mantle may create and maintain anisotropy  

NASA Astrophysics Data System (ADS)

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

Wheeler, John

2014-05-01

195

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

196

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

197

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?C–125?C.\\u000a The results are compared to some other researchers' measurements in a trial of the applicability of the time–temperature–moisture-content\\u000a superposition

A. Hanhijärvi

1999-01-01

198

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

NASA Astrophysics Data System (ADS)

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

Trepmann, Claudia

2014-05-01

199

Damage and permiability evolution in creep-failed microgranite  

NASA Astrophysics Data System (ADS)

The importance of crack generation during deformation is now becoming widely recognized as one of the key factors that control important processes involving fluid flow in rocks of low permeability e.g., hydro-thermal circulation at mid-ocean ridges, energy recovery from geothermal reservoirs, and accelerating deformation preceding volcanic eruptions. Here we describe experiments that extend the study of Meredith et al. (2000) by examining the relationship between slow deformation, the growth of micro-fractures, and permeability in Ailsa Craig microgranite (ACM) close to the fracture interconnection percolation threshold. To examine the inter-relationship between the above factors we have undertaken creep experiments on cores of ACM during which we have measured acoustic emissions, solute breakthrough curves, and electrical impedance (EI), at a strain rate of 10e(-6). The initial network of distributed damage was generated in a 38mm-diameter core of ACM by heating at 1°C/hr to 900°C then cooling to room temperature at the same rate. The treated core was then placed in a Hasler cell with integral acoustic emission and electrical impedance sensors and initially loaded to 20MPa. To measure breakthrough curves, solutions of deionized/distilled/degassed water was alternated with a degassed 1M NaCl solution at a flow rate of 1cc/hr. Differential fluid pressures were monitored by piezoelectric pressure gauges and the strain in the sample was monitored by LVDTs attached to the pistons. Initial 'breakthrough' tests under hydrostatic conditions show that the EI response detects first a linear change in impedance as the solute front advances through the core followed by a more gradual decrease as the front ‘breaks out’ of the core end. The EI response, therefore, describes both the advection and dispersion terms associated with the solute front in the core. The data allow the inter-relationship between crack generation/growth, effective cumulative aperture, permeability and hydraulic dispersion to be examined during the process of creep deformation. Of particular interest is the behaviour of the system close to failure, where rapid changes in fracture network characteristics occur.

Odling, N.; Elphick, S.; Main, I.; Meredith, P.; Ngwenya, B.

2003-04-01

200

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

201

Creep behavior of 6 micrometer linear low density polyethylene film  

NASA Technical Reports Server (NTRS)

Creep tests were performed to provide material characteristics for a 6.4-micron polyethylene film used to construct high altitude balloons. Results suggest simple power law relationships are adequate for stresses below about 4.83 MPa.

Simpson, J. M.; Schur, W. W.

1993-01-01

202

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

203

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

SciTech Connect

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

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

1996-03-01

204

Deformation characteristics of the Sheeprock and Canyon Range thrust sheets (Sevier orogenic belt) based on microstructural and strain studies  

SciTech Connect

The condition of emplacement of internal thrust sheets in the Sevier fold-and-thrust belt can be characterized by detailed studies on deformation of quartzites within these sheets. The Sheeprock and Canyon Range thrust sheets in north-central Utah both carry Proterozoic Caddy Canyon and Mutual quartzites in their hanging walls. The Caddy Canyon is a medium to coarse-grained quartzite with subrounded grains and some grain-overgrowth. The Mutual is typically coarse-grained to pebbly, has subrounded to well rounded grains with overgrowths, and is characterized by clasts showing an older metamorphic (in some cases, mylonitic) fabric. In the Sheeprock sheet both quartzites show evidence for considerable crystal-plastic deformation, including deformation lamellae, undulose extinction, and development of subgrains; the Caddy Canyon also shows considerable pressure solution. Late stage cataclasis, characterized by the development of cemented cataclasites, is also evident. In the Canyon Range, both quartzites show less plastic deformation, although the Caddy Canyon shows large amounts of pressure solution. The late stage cataclasites are coherent but not cemented, and there is locally strong plastic deformation adjacent to the cataclasite zones. The microstructures suggest an overall shallower level of deformation for the Canyon Range sheet. Strains in the quartzites are quantified using the Fry technique, and the strains are partitioned into plastic and diffusional components using deformed rutile needles within quartz grains and pressure-solved grain shapes.

Sussman, A.J.; Mitra, G. (Univ. of Rochester, NY (United States). Dept. of Geological Sciences)

1993-04-01

205

Biaxial Creep Specimen Fabrication  

SciTech Connect

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

JL Bump; RF Luther

2006-02-09

206

Dislocation and diffusion creep of synthetic anorthite aggregates  

Microsoft Academic Search

Synthetic fine-grained anorthite aggregates were deformed at 300 MPa confining pressure in a Paterson-type gas deformation apparatus. Creep tests were performed at temperatures ranging from 1140 to 1480 K, stresses from 30 to 600 MPa, and strain rates between 2×10-6 and 1×10-3s-1. We prepared samples with water total contents of 0.004 wt % (dry) and 0.07 wt % (wet), respectively.

E. Rybacki; G. Dresen

2000-01-01

207

Effects of chemical environment on dislocation creep of quartzite  

Microsoft Academic Search

The water-related chemical parameter that affects dislocation creep in quartzite has been determined from variations in sample strength and microstructure with chemical environment in buffered deformation and hydrostatic annealing experiments. Samples were weld-sealed in double capsules; fu 2, fo 2, fu2o, and a.+ were buffered using solid oxygen buffers, AgCI or CO 2. Black Hills quartzite was deformed at 900øC

Alice D. Post; Jan Tullis; Richard A. Yund

1996-01-01

208

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

209

Effect of radiation dose on radiation creep of polymers  

Microsoft Academic Search

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

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

1974-01-01

210

The effects of computed tomography image characteristics and knot spacing on the spatial accuracy of B-spline deformable image registration in the head and neck geometry  

PubMed Central

Objectives To explore the effects of computed tomography (CT) image characteristics and B-spline knot spacing (BKS) on the spatial accuracy of a B-spline deformable image registration (DIR) in the head-and-neck geometry. Methods The effect of image feature content, image contrast, noise, and BKS on the spatial accuracy of a B-spline DIR was studied. Phantom images were created with varying feature content and varying contrast-to-noise ratio (CNR), and deformed using a known smooth B-spline deformation. Subsequently, the deformed images were repeatedly registered with the original images using different BKSs. The quality of the DIR was expressed as the mean residual displacement (MRD) between the known imposed deformation and the result of the B-spline DIR. Finally, for three patients, head-and-neck planning CT scans were deformed with a realistic deformation field derived from a rescan CT of the same patient, resulting in a simulated deformed image and an a-priori known deformation field. Hence, a B-spline DIR was performed between the simulated image and the planning CT at different BKSs. Similar to the phantom cases, the DIR accuracy was evaluated by means of MRD. Results In total, 162 phantom registrations were performed with varying CNR and BKSs. MRD-values < 1.0 mm were observed with a BKS between 10–20 mm for image contrast ? ± 250 HU and noise < ± 200 HU. Decreasing the image feature content resulted in increased MRD-values at all BKSs. Using BKS = 15 mm for the three clinical cases resulted in an average MRD < 1.0 mm. Conclusions For synthetically generated phantoms and three real CT cases the highest DIR accuracy was obtained for a BKS between 10–20 mm. The accuracy decreased with decreasing image feature content, decreasing image contrast, and higher noise levels. Our results indicate that DIR accuracy in clinical CT images (typical noise levels < ± 100 HU) will not be effected by the amount of image noise. PMID:25074293

2014-01-01

211

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

NASA Technical Reports Server (NTRS)

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

Lin, J.; Sherby, O. D.

1978-01-01

212

Characteristics of High-Temperature Deformation Behavior of Ti-45Al-2Cr-3Ta-0.5W Alloy  

NASA Astrophysics Data System (ADS)

High-temperature deformation behavior tests of as-cast Ti-45Al-2Cr-3Ta-0.5W alloy were conducted over a wide range of strain rates (0.001-1.0 s-1) and temperatures (1150-1300 °C). The flow curves for the current alloy exhibited sharp peaks at low strain levels, followed by pronounced work hardening and flow localization at high strain levels. Phenomenological analysis of the strain rate and temperature dependence of peak stress data yielded an average value of the strain rate sensitivity equal to 0.25 and an apparent activation energy of ~420 kJ/mol. Processing maps were established under different deformation conditions, and the optimal condition for hot work on this material was determined to be 1250 °C/0.001 s-1. The stable deformation region was also found to decrease with increasing strain. Dynamic recrystallization (DRX) was the major softening mechanism controlling the growth of grains at the grain boundary. Meanwhile, local globularization and dynamic recovery (DR) were the main softening mechanisms in the lamellar colony. When deformed at higher temperatures (~1300 °C), the cyclic DRX and DR appeared to dominate the deformation. Moreover, the evolution of the ? phase during hot deformation played an important role in the dynamic softening of the alloy.

Luo, Y. Y.; Xi, Z. P.; Zeng, W. D.; Mao, X. N.; Yang, Y. L.; Niu, H. Z.

2014-07-01

213

Characteristics of High-Temperature Deformation Behavior of Ti-45Al-2Cr-3Ta-0.5W Alloy  

NASA Astrophysics Data System (ADS)

High-temperature deformation behavior tests of as-cast Ti-45Al-2Cr-3Ta-0.5W alloy were conducted over a wide range of strain rates (0.001-1.0 s-1) and temperatures (1150-1300 °C). The flow curves for the current alloy exhibited sharp peaks at low strain levels, followed by pronounced work hardening and flow localization at high strain levels. Phenomenological analysis of the strain rate and temperature dependence of peak stress data yielded an average value of the strain rate sensitivity equal to 0.25 and an apparent activation energy of ~420 kJ/mol. Processing maps were established under different deformation conditions, and the optimal condition for hot work on this material was determined to be 1250 °C/0.001 s-1. The stable deformation region was also found to decrease with increasing strain. Dynamic recrystallization (DRX) was the major softening mechanism controlling the growth of grains at the grain boundary. Meanwhile, local globularization and dynamic recovery (DR) were the main softening mechanisms in the lamellar colony. When deformed at higher temperatures (~1300 °C), the cyclic DRX and DR appeared to dominate the deformation. Moreover, the evolution of the ? phase during hot deformation played an important role in the dynamic softening of the alloy.

Luo, Y. Y.; Xi, Z. P.; Zeng, W. D.; Mao, X. N.; Yang, Y. L.; Niu, H. Z.

2014-10-01

214

Analysis of the Creep Behavior of P92 Steel Welded Joint  

NASA Astrophysics Data System (ADS)

Different regions of heat-affected zone (HAZ) were simulated by heat treatment to investigate the mechanisms of the Type IV fracture of P92 (9Cr-2W) steel weldments. Creep deformation of simulated HAZ specimens with uniform microstructures was investigated and compared with those of the base metal (BM) and the weld metal (WM) specimens. The results show that the creep strain rate of the fine-grained HAZ (FGHAZ) is much higher than that of the BM, WM, the coarse-grained HAZ (CGHAZ), and the inter-critical HAZ (ICHAZ). According to the metallurgical investigation of stress-rupture, the FGHAZ and the ICHAZ have the most severely cavitated zones. During creep process, carbides become coarser, and form on grain boundaries again, leading to the deterioration of creep property and the decline of creep strength. In addition, the crack grows along the FGHAZ adjacent to the BM in the creep crack growth test (CCG) of HAZ.

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

2011-11-01

215

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

216

Nanoscale deformation irregularities of ?-irradiated poly(methyl methacrylate)  

NASA Astrophysics Data System (ADS)

Development of deformation jumps in the creep of poly(methyl methacrylate) (PMMA) has been studied. The structural levels of deformation have been determined from the creep rate oscillation periods (deformation jumps) measured by the interferometric method. Special attention is given to a new method of data processing, which enables one to reveal previously undetectable nanoscale deformation jumps. By the example of PMMA specimens preliminarily exposed to ? radiation with doses D=55-330 kGy and unexposed specimens, the presence of nanoscale deformation jumps with the values dependent on the dose D and time of creep has been shown. The obtained results confirm the existence of 10-20-nm domains in amorphous polymers and make it possible to study the multilevel organization of the deformation process, starting from the nanoscale.

Shpe?zman, V. V.; Peschanskaya, N. N.; Yakushev, P. N.; Smolyanski?, A. S.; Shvedov, A. S.; Cheremisov, V. G.

2010-02-01

217

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

218

Crack growth in creeping solids  

SciTech Connect

The creep crack growth behavior in a creep-ductile material, 6061 aluminum, and a creep brittle material, Ti-6242, has been investigated. In the creep ductile material an observed load dependency in the relation between the load-point displacement rate, ..delta.., and the crack growth rate, ..cap alpha.., precluded the straightforward application of the C* approach. For both materials tested the foregoing relationship was able to describe the experimental results withoutany systematic scatter.

Radhakrishnan, V.M.; McEvily, A.J.

1981-10-01

219

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

220

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 1000°C, 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

221

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 625°C 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 625°C. 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

222

Effect of Creep and Oxidation on Reduced Creep-Fatigue life of Ni-based Alloy 617 at 850 C  

SciTech Connect

Low cycle fatigue (LCF) and creep fatigue testing of Ni-based alloy 617 was carried out at 850 C. Compared with its LCF life, the material s creep fatigue life decreases to different extents depending on test conditions. To elucidate the microstructure-fatigue property relationship for alloy 617 and the effect of creep and oxidation on its fatigue life, systematic microstructural investigations were carried out using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction (EBSD). In LCF tests, as the total strain range increased, deformations concentrated near high angle grain boundaries (HAGBs). The strain hold period in the creep fatigue tests introduced additional creep damage to the material, which revealed the detrimental effect of the strain hold time on the material fatigue life in two ways. First, the strain hold time enhanced the localized deformation near HAGBs, resulting in the promotion of intergranular cracking of alloy 617. Second, the strain hold time encouraged grain boundary sliding, which resulted in interior intergranular cracking of the material. Oxidation accelerated the initiation of intergranular cracking in alloy 617. In the crack propagation stage, if oxidation was promoted and the cyclic oxidation damage was greater than the fatigue damage, oxidation-assisted intergranular crack growth resulted in a significant reduction in the material s fatigue life.

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

2014-01-01

223

Creep Feeding Beef Calves.  

E-print Network

ON THE COVER The picture on the cover was taken on the E. B. Dickenson Ranch, leased by J. C. Sale, Stanton, Texas. Fig. 1. Inexpensive creep is shown on the Robert Priess Ranch, Mast County. A. L. SMITH and UEL D. THOMPSON Extension Animal... Husbandmen in collaboration with JOHN H. JONES, Professor of Animal Husbandry and JOHN K. RIGGS, A~sociate Professor of Animal Husbandry Texas A. & M. College System "Creep feeding" beef calves may tices during the first 6 to 8 months , increase weight...

Smith, A. L. (Albert Lorenzo)

1955-01-01

224

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

225

Creep-Feeding Range Calves  

E-print Network

, it has been found profitable to supply rain to calves during their suckling period. This may be done y what is known as creep feeding. Creeps are enclosures in nrhich the calves are fed an3 the entrances, of which are of such size that the calves can... enter but the cows cannot. A test on the Callaghan Ranch in Webb county during 1931-1932 took account of the results of creep-feeding 69 head of spring calves in com- arison with 49 calves on a similar range but not creep-fed. The creep-fed calves...

Jones, J. M. (John McKinley); Jones, John H.

1932-01-01

226

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

227

Deformation behavior of particle-strengthened alloys: A Voronoi mesh approach  

SciTech Connect

A modelling approach based on the discretization of a particle-strengthened material using a Voronoi mesh is considered. The model is applied to studying the effects of particle arrangement on the deformation behavior of a particle-strengthened alloy, particularly on its creep resistance. On a local scale, i.e., within an individual Voronoi cell containing a single particle, a dislocation density-based constitutive model developed previously is applied. Interaction with adjacent Voronoi cells due to plastic incompatibilities is also included. The model predicts a dependence of the creep resistance on the character of particle distribution, notably, on the degree of particle clustering. Application to oxide dispersion strengthened (ODS) nickel-base alloys MA 754 and PM 1000, which are very similar in their metallurgical characteristics, including the volume fraction of oxide dispersoids, but differ in the dispersoid arrangement, shows an excellent predictive capability of the Voronoi mesh modelling technique.

Estrin, Y.; Arndt, S.; Heilmaier, M. [Univ. of Western Australia, Nedlands, Western Australia (Australia). Dept. of Mechanical and Materials Engineering] [Univ. of Western Australia, Nedlands, Western Australia (Australia). Dept. of Mechanical and Materials Engineering; Brechet, Y. [LTPCM-INPG, Saint Martin d`Heres (France)] [LTPCM-INPG, Saint Martin d`Heres (France)

1999-01-15

228

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

229

Creep behaviour and creep mechanisms of normal and healing ligaments  

NASA Astrophysics Data System (ADS)

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

Thornton, Gail Marilyn

230

Source characteristics of Yutian earthquake in 2008 inversed from co-seismic deformation field mapped by InSAR  

NASA Astrophysics Data System (ADS)

On 21 March 2008, an Ms7.3 earthquake occurred at Quickbird, Yutian County, Xinjiang. The earthquake is located in the depopulated Kunlun Mountains of an elevation over 5000m, featured by thin air, cold weather and extremely bad conditions, where field investigations would be formidable. Besides, there is no station for deformation measurements in an area of several hundreds km2 surrounding the epicenter. Consequently, there is little knowledge on the causative fault and coseismic deformation of this event. We attempt to fill this gap by means of satellite remote sensing and DInSAR (Differential Interferometric Synthetic Aperture Rader).We attempt to reveal the features of the causative fault of this shock and its coseismic deformation field by a sensitivity- based iterative fitting (SBIF) method. Our work is based on analysis and interpretation to high-resolution satellite images as well as DInSAR data from the satellite Envisat SAR, coupled with seismicity, focal mechanism solutions and active tectonics in this region. The result shows that the 22km-long, nearly NS trending surface rupture zone by this event lies on a range-front alluvial platform in the Qira County. It is characterized by distinct linear traces and simple structure with 1~3m-wide individual seams and maximum 6.5m width of a collapse fracture. Along the rupture zone are seen many secondary fractures and fault-bounded blocks by collapse, exhibiting remarkable extension. The coseismic deformation affected a big range 100km and 40km. D-InSAR analysis indicates that the interferometric deformation field is dominated by extensional faulting with a small strike-slip component. Along the causative fault, the western wall fell down and the eastern wall, that is the active unit, rose up, both with westerly vergence.The minimum subsidence displacement is -2.6m in the LOS, and the maximum uplift is 1.2m. The maximum relative vertical dislocation reaches 4.1m,which is located at the distance of 10km along the fault from the starting rupture point to south. The fault plane is 42km long, extending from north to south in arc shape with variable dip angles from 70° at the surface to 52° at the depth of 20km.The larger slip areas are concentrated on three areas, forming a belt with the depth less than 8km along dip, length of 30km along strike on fault plane. The largest slip area with the maximum slip 10.5m is located at the area with distance of 10km from the starting edge along the strike.

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

2009-12-01

231

Strengthening of synthetic quartz-rich sediments during time-dependent compaction due to pressure solution-precipitation compaction creep  

NASA Astrophysics Data System (ADS)

During diagenesis, incohesive sediments are compacted and gain strength against shear deformation for a geologically long time scale. The evolution of shear strength as well as the change in the mechanical and hydraulic characteristics under shear deformation is of significant importance in considering deformation at shallow part of the subduction zones and in accretionary prisms. Sediments after induration due to time-dependent diagenesis process probably deform with increases in porosity and permeability much more significantly than normally compacted incohesive sediments. An active fault in a shallow incohesive medium may favor thermal pressurization of pore fluid when slid rapidly, while the lack of time-dependent healing effect may cause stable (e.g., rate-strengthening) frictional property there. On the other hand, indurated sediments may deform with significant post-failure weakening, and thus exhibit localization of deformation or unstable behavior. In order to investigate how the time-dependent compaction and induration affect the mechanical and hydraulic characteristics of sediments under deformation, we have conducted a series of compaction experiments under hydrothermal conditions (at temperatures from R.T. to 500 °C, 200 MPa confining pressure, 100 MPa pore water pressure, and for various time), and following triaxial deformation experiments for the compacted samples, with monitoring permeability and storage capacity with pore pressure oscillation method [Fischer and Paterson, 1992]. Previous work [e.g., Niemeijer et at., 2003] reported that under the adopted conditions, quartz aggregate deforms by pressure solution-precipitation creep. The initial synthetic sediments have been prepared by depositing commercially available crushed quartzite the grain size of which is about 6 ?m on average. 4 cm long samples have been extracted from the middle of 10 cm long deposited columns. The experiments have been performed with a gas-medium apparatus in Hiroshima University. As the compaction time and temperature increases, compressional strain increases and the synthetic sediments gain shear strength, flow stress during triaxial deformation tests. An uncooked sample yielded immediately on application of differential stress, and showed strengthening during triaxial deformation test with ?1-?3 about 150 MPa at 0.1 compressional strain. On the other hand, a sample compacted at 500 °C for 5 hours (about 0.1 of isotropic compressional strain) deformed mainly elastically up to about 100 MPa differential stress. At 0.02 compressional strain ?1-?3 reached 200 MPa which is the experimental limitation due to compressional strength of porous alumina spacers. In the presentation, we will focus on the relation between mechanical behavior under shear and the compressional strain during preceding compaction experiments.

Noda, H.; Okazaki, K.; Katayama, I.

2013-12-01

232

Microdeformation experiments on chalk - fluids, fracture and creep  

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

233

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

234

Correlation of Creep Behavior of Domal Salts  

Microsoft Academic Search

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

Munson

1999-01-01

235

Propagation of Crack in Glasses under Creep Conditions  

NASA Astrophysics Data System (ADS)

The context of our study is the observation of the mechanical behaviour of glass used for the storage of radioactive wastes. This implies to measure the crack propagation characteristics in glass. Results on the investigation of the micromechanics of creep under triaxial loading conditions are presented in the framework of this study. We performed the experiments in a triaxial cell, with pore fluid pressure, on boro-silicate glass. The chemical composition of the investigated glass is very close to the composition of waste vitrified packages. The matrix of the original glass (OG) is perfectly amorphous, without porosity. A few isolated air bubbles are trapped during the glass flow. Cracks are introduced in the OG through thermal shocks. The evolution of deformation (axial and radial strain) is measured using strain gages. The elastic P and S wave velocities and the acoustic emissions (AE) are also recorded. An experiment in dry conditions was performed (the pore fluid was argon gas) with a confining pressure fixed at 15 MPa. Stress step tests were performed in order to get creep data. A similar experiment was performed in water saturated conditions. Crack-closure is first observed at very low strains. Then elastic deformation is observed up to a stress level where elastic anisotropy develops. This can be clearly detected from ? Thomsen parameter increase. At last, at a deviatoric stress of 175 MPa (in dry conditions), we observe dilatancy. This behaviour has never been observed in original glass. Indeed, the OG behaviour is perfectly elastic and brittle. In addition, the constant stress tests show that dilatancy develops during a time constant that depends on the stress level. It can be inferred that crack propagation takes place during the constant stress steps. This behaviour is under investigation. We are also quantifying the velocity of the crack propagation by modelling this phenomenon. Indeed, the crack density can be expressed as a volumic strain, ?v = ???c. Then, using a model of penny shaped cracks of a radius, "a", we can express the crack density as: ?c = N/V a3 (for N cracks in a volume V). Knowing that ? is the crack aspect ratio we can estimate ?v using in a first approximation that ? is a constant. Thus the variation of ?v with time can be directly related to crack propagation ȧ.

Mallet, C.; Fortin, J.; Guéguen, Y.; Schubnel, A.

2012-04-01

236

Characteristics of lateral electrical surface stimulation (LESS) and its effect on the degree of spinal deformity in idiopathic scoliosis  

NASA Astrophysics Data System (ADS)

Clinical studies were carried out in the period of 2003-2006 at the Provincial Children's Rehabilitation Hospital in Ameryka near Olsztyn (Poland). The study involved a group of children and youth exhibiting spinal deformity progression in idiopathic scoliosis (IS) of more than 5° per year according to the Cobb scale. Four hundred and fifty patients between 4 and 15 years of age were divided into three groups (n = 150). Group I and group II received 2-hour and 9-hour lateral electrical surface stimulation (LESS), respectively, whereas group III (control) was treated only with corrective exercises for 30 minutes twice a day. LESS was performed with the use of a battery-operated SCOL-2 stimulator manufactured by Elmech, Warsaw, Poland. The effectiveness of this method was confirmed in the treatment of spinal IS in children and youth, especially when the initial spinal deformity did not exceed 20° according to the Cobb scale. A short-duration electrostimulation (2 hours daily) was found to produce results similar to those obtained after overnight (9 h) electrostimulation. Moreover, the analysis of the Harrington prognostic index F confirms the positive effect of LESS in both groups of patients (2 h and 9 h of LESS).

Kowalski, Ireneusz M.; Palko, Tadeusz; Pasniczek, Roman; Szarek, Jozef

2009-01-01

237

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

Microsoft Academic Search

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

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

1999-01-01

238

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

Microsoft Academic Search

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

A. T. Donaldson; G. Knowles

1980-01-01

239

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

240

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

241

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

242

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

243

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

244

Continuous turbine blade creep measurement based on Moiré  

NASA Astrophysics Data System (ADS)

Moiré 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 moiré 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 moiré patterns from the turbine blade sensor at shutdown to determine creep level in individual parts by analyzing the moiré 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 moiré 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

245

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

246

Interactions between fracturing and pressure solution creep in the upper crust: evidence from natural observations and experiments  

NASA Astrophysics Data System (ADS)

Fracturing and pressure solution creep processes are very often associated in the upper crust deformation. One can see for example that mineral grains and pebbles are both fractured and dissolved under stress, that stylolites are bounded by fractures or that pressure solution spaced cleavage is associated with veins. The question is thus how pressure solution creep and fracturing processes interact in the upper crust to make it behave in both a brittle and viscous manner? Dynamic indenting experiments allow understanding how fracturing and pressure solution creep processes interact. Such experimental technique includes the static loading of a sample by an indenter and its dynamic loading by episodic shocks. The experimental results show that fracturing and comminuting processes induced by the shock accelerate the pressure solution creep rate by reducing the distance of mass transfer. However, it is also observed that after each shock the creep rate progressively decreases due to healing and sealing processes. The main healing processes, in non-porous material such as halite crystal, are crack healing and grain compaction. In porous aggregates such as plaster, the main healing processes are grain sliding, grain dissolution indenting and redeposition. In both cases, when pressure solution is the creep mechanism, fracturing and comminuting weaken the rock whereas compaction, healing and sealing strengthen it. This leads to a non-steady state creep process. This also leads to a chemical segregation of the rocks which is amplified by lithological effect: all the conditions of the deformation being the same, pressure solution creep rate is faster for a mixture of soluble and insoluble minerals than for monomineralic soluble material. Consequently in natural deformation, starting from the common mixture of soluble (quartz, calcite, feldspars…) and insoluble (oxides, phyllosilicates) minerals, successive fracturing and creep-healing events develop a segregation of the rock with the development of rock heterogeneity that is seen for example in faulted rocks with two end members: (i) weak active creep zones, which are the zones of progressive depletion in soluble species and (ii) damage zones, which are progressively strengthen by the redeposited minerals and which are the zones of potential (micro)seismicity. Actually, the microseismicity in the damage zone could even activate the pressure solution creep rate as long as deposition does not occur in the creeping zone. So fracturing and pressure solution creep are associated processes that interact in the upper crust in order to accommodate its deformation in a ductile or brittle manner depending on the geological conditions and such interactions amplify the segregation between brittle (seismic) and ductile (creep) deformation.

Gratier, Jean-Pierre

2014-05-01

247

A brick model for asperity sintering and creep of APS TBCs  

NASA Astrophysics Data System (ADS)

A micromechanical model is developed for the microstructural evolution of an air plasma sprayed (APS), thermal barrier coating: discrete, brick-like splats progressively sinter together at contacting asperities and also undergo Coble creep within each splat. The main microstructural features are captured: the shape, orientation and distribution of asperities between disc-shaped splats, and the presence of columnar grains within each splat. Elasticity is accounted for at the asperity contacts and within each splat, and the high contact compliance explains the fact that APS coatings have a much lower modulus (and thermal conductivity) than that of the parent, fully dense solid. The macroscopic elastic, sintering and creep responses are taken to be transversely isotropic, and remain so with microstructural evolution. Despite the large number of geometric and kinetic parameters, the main features of the behaviour are captured by a small number of characteristic material timescales: these reveal the competition between the deformation mechanisms and identify the rate controlling processes for both free and constrained sintering. The evolution of macroscopic strain, moduli and asperity size is compared for free and constrained sintering, and the level of in-plane stress within a constrained coating is predicted.

Cocks, Alan; Fleck, Norman; Lampenscherf, Stefan

2014-02-01

248

Creep Crack Initiation and Growth Behavior for Ni-Base Superalloys  

NASA Astrophysics Data System (ADS)

The structural components which are used in high temperature gas turbines have various shapes which may cause the notch effect. Moreover, the site of stress concentration might have the heterogeneous microstructural distribution. Therefore, it is necessary to clarify the creep fracture mechanism for these materials in order to predict the life of creep fracture with high degree of accuracy. In this study, the creep crack growth tests were performed using in-situ observational testing machine with microscope to observe the creep damage formation and creep crack growth behavior. The materials used are polycrystalline Ni-base superalloy IN100 and directionally solidified Ni-base superalloy CM247LC which were developed for jet engine turbine blades and gas turbine blades in electric power plants, respectively. The microstructural observation of the test specimens was also conducted using FE-SEM/EBSD. Additionally, the analyses of two-dimensional elastic-plastic creep finite element using designed methods were conducted to understand the effect of microstructural distribution on creep damage formation. The experimental and analytical results showed that it is important to determine the creep crack initiation and early crack growth to predict the life of creep fracture and it is indicated that the highly accurate prediction of creep fracture life could be realized by measuring notch opening displacement proposed as the RNOD characteristic.

Nagumo, Yoshiko; Yokobori, A. Toshimitsu, Jr.; Sugiura, Ryuji; Ozeki, Go; Matsuzaki, Takashi

249

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

250

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

251

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

252

Application of small punch creep test for Inconel 617 alloy weldment  

Microsoft Academic Search

In this work, SP creep tests were applied to the Inconel 617 alloy and its weldment, which is one of the candidate materials for future advanced fossil power plant. To find the creep characteristics of the weakest local part in Inconel 617 alloy weldment, test specimens of thin squares (10 10 0.5mm) were machined at three different locations: weld metal,

B. J. Kim; Y. B. Sim; J. H. Lee; M. K. Kim; B. S. Lim

2011-01-01

253

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 (1.28±0.13 °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

254

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

255

Resonant creep enhancement in austenitic stainless steels due to pulsed irradiation at low doses  

SciTech Connect

Steady-state irradiation creep of austenitic stainless steels has been extensively studied as one of the most important design parameters in fusion reactors. The steady-state irradiation creep has been evaluated using in-pile and light-ion experiments. Those creep compliances of various austenitic steels range in the vicinity of {dot {epsilon}}/G{sigma} = 10{sup {minus}6}{approximately}10{sup {minus}5} (dpa{sm_bullet}MPa){sup {minus}1}, depending on chemical composition etc. The mechanism of steady-state irradiation creep has been elucidated, essentially in terms of stress-induced preferential absorption of point defects into dislocations, and their climb motion. From this standpoint, low doses such as 10{sup {minus}3}{approximately}10{sup {minus}1} dpa would not give rise to any serious creep, and the irradiation creep may not be a critical issue for the low-dose fusion devices including ITER. It is, however, possible that pulsed irradiation causes different creep behaviors from the steady-state one due to dynamic unbalance of interstitials and vacancies. The authors have actually observed anomalous creep enhancement due to pulsed irradiation in austenitic stainless steels. The resonant behavior of creep indicates that pulsed irradiation may cause significant deformation in austenitic steels even at such low doses and slow pulsing rates, especially for the SA-materials. The first-wall materials in plasma operation of {approximately}10{sup 2} s may suffer from unexpected transient creep, even in the near-term fusion deices, such as ITER. Though this effect might be a transient effect for a relatively short period, it should be taken into account that the pulsed irradiation makes influences on stress relaxation of the fusion components and on the irradiation fatigue. The mechanism and the relevant behaviors of pulse-induced creep will be discussed in terms of a point-defect model based on the resonant interstitial enrichment.

Kishimoto, N.; Amekura, H.; Saito, T. [National Research Inst. for Metals, Ibaraki (Japan)

1994-12-31

256

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

257

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

258

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

259

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

260

Quantitative analysis of surface coseismic faulting and postseismic creep accompanying the 2003, Mw = 6.5, Chengkung earthquake  

E-print Network

Quantitative analysis of surface coseismic faulting and postseismic creep accompanying the 2003, Mw we analyzed coseismic and postseismic deformation of the 2003, Mw = 6.5, Chengkung earthquake across-wide networks the coseismic deformation of the main shock produced only about 1­2 cm of horizontal shortening

Lee, Jian-Cheng

261

COMPRESSIVE CREEP OF ULTRAFINE GRAINED MgO POLYCRYSTALS J. CRAMPON*, A. C. D. CHAKLADER** and B. ESCAIG*  

E-print Network

range 0.3 to 0.38 Tm. The specimens were fabricated by reactive hot pressing i.e. by hot-pressing of Mg contribute strongly to the deformation of these materials. On the other hand, another type of mechanism i.e. dislocation creep may also control the deformation in a significant way. As a matter of fact, it is often

Paris-Sud XI, Université de

262

Extending creep measurements to short times  

NASA Astrophysics Data System (ADS)

A standard lever arm creep machine (Satec model M-3) is modified to directly measure creep at relatively short times. The modified version of the Satec dead-weight frame can be used to determine momentary creep master curves and to measure short-time creep behavior.

Sullivan, J. L.; Blais, E. J.

1992-12-01

263

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

264

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

265

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

266

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

267

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

268

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

269

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

270

A test machine for studying the deformation and strength characteristics of structural materials during disproportional cyclic loading at normal and high temperatures  

Microsoft Academic Search

A machine has been developed for testing structural materials under disproportional cyclic loading (independent alternating torsion and tension-compression) comprising stages of creep and relaxation. The machine allows testing over a wide range of strain rates and temperatures. Test results for a Kh18N9T steel specimen at 650 C are presented as an example.

D. A. Gokhfeld; I. A. Ivanov; K. K. Dubovikov; M. V. Apaichev

1985-01-01

271

Source characteristics of the Yutian earthquake in 2008 from inversion of the co-seismic deformation field mapped by InSAR  

NASA Astrophysics Data System (ADS)

On 21 March 2008, an Ms7.3 earthquake occurred at Yutian County, Xinjiang Uygur Autonomous Region, which is in the same year as 2008 Mw 7.9 Wenchuan earthquake. These two earthquakes both took place in the Bayar Har block, while Yutian earthquake is located in the west edge and Wenchuan earthquake is in the east. The research on source characteristics of Yutian earthquake can serve to better understand Wenchuan earthquake mechanism. We attempt to reveal the features of the causative fault of Yutian shock and its co-seismic deformation field by a sensitivity-based iterative fitting (SBIF) method. Our work is based on analysis and interpretation to high-resolution satellite (Quickbird) images as well as D-InSAR data from the satellite Envisat ASAR, in conjunction with the analysis of seismicity, focal mechanism solutions and active tectonics in this region. The result shows that the 22 km long, nearly NS trending surface rupture zone by this event lies on a range-front alluvial platform in the Qira County. It is characterized by distinct linear traces and a simple structure with 1-3 m-wide individual seams and maximum 6.5 m width of a collapse fracture. Along the rupture zone are seen many secondary fractures and fault-bounded blocks by collapse, exhibiting remarkable extension. The co-seismic deformation affected a big range 100 km × 40 km. D-InSAR analysis indicates that the interferometric deformation field is dominated by extensional faulting with a small strike-slip component. Along the causative fault, the western wall fell down and the eastern wall, that is the active unit, rose up, both with westerly vergence. The maximum subsidence displacement is ˜2.6 m in the LOS, and the maximum uplift is 1.2 m. The maximum relative vertical dislocation reaches 4.1 m, which is 10 km distant from the starting rupture point to south. The 42 km-long seismogenic fault in the subsurface extends in NS direction as an arc, and it dipping angle changes from 70° near the surface to 52° at depth ˜10 km. The slip on the fault plane is concentrated in the depth range 0-8 km, forming a belt of length 30 km along strike on the fault plane. There are three areas of concentrating slip, in which the largest slip is 10.5 m located at the area 10 km distant from the initial point of the rupture.

Shan, Xinjian; Zhang, Guohong; Wang, Chisheng; Qu, Chunyan; Song, Xiaogang; Zhang, Guifang; Guo, Liming

2011-03-01

272

Diffusion-controlled dislocation creep: a defense  

Microsoft Academic Search

A defense is made to the criticisms of Poirier against diffusion-controlled dislocation creep. The criticism that values of the activation volumes of creep offer no strong support to diffusion-controlled dislocation creep is turned around and is shown to be strong evidence against non-diffusion-controlled dislocation creep. It is shown that, just as in very fine grain material Coble creep takes over

O. D. Sherby; J. Weertman

1979-01-01

273

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

274

Ductile shear localization in experimentally and naturally deformed dolomite  

NASA Astrophysics Data System (ADS)

Experimental deformation studies of polycrystalline olivine by Post and Griggs first revealed conditions that favor ductile faulting over homogeneous deformation by a combination of dislocation creep and recrystallization processes that change defect populations and/or deformation mechanisms. The development of recrystallized shear zones at large angles (>35°) to the maximum compressive stress direction associated with significant strain weakening has since been reported in a number of silicates, including clinopyroxene and feldspars. Recent studies of dolomite deformation, both in the lab and in nature, show that strain localization in this nominally strong carbonate occurs over a wide range of conditions. Compression experiments conducted on coarse-grained dolomite at 700-1050°C, effective pressures of 300-900 MPa and strain rates of 10-4 to 10-7/s reach high peak stresses associated with dislocation creep, followed by continuous reductions in flow stress as narrow shear zones of finely recrystallized grains transect samples. These observations indicate that dislocation creep in dolomite gives way to diffusion creep after limited internal deformation, so that displacement is localized within these narrow zones. Similarly, in exposures of dolomite in the southern Appalachians of TN exhumed from a depth of ~9 km (and estimated 250°C), deformation is localized in narrow fine-grained zones that are associated with grain size reduction by dynamic recrystallization. Dynamic recrystallization of coarse-grained silicates and carbonates often leads to a transition from dislocation creep to mixed deformation mechanisms at the transition between dislocation and diffusion creep fields. When grain nucleation and growth rates balance to yield steady-state size populations under these transitional conditions, flow stresses may reach a well-defined steady state at low strains and the aggregate deforms homogeneously. Grain growth of dolomite is very slow compared with grain growth kinetics of many rock-forming minerals. As a result, nucleation of fine grains in dolomite may lead to a large over-step into the diffusion creep field, rather than reaching (without overstepping) the boundary between the dislocation and diffusion creep fields. Flow stresses associated with this over-step will drop significantly rather than reach a steady state, and localized deformation in fine-grained zones may persist to large displacements. The conditions under which strain localizes within recrystallized zones in olivine, pyroxene, and feldspar aggregates may likewise correspond to conditions of limited grain growth for these minerals.

Kronenberg, A. K.; Holyoke, C. W.; Wells, R. K.; Newman, J.

2011-12-01

275

The development of methods for the prediction of primary creep behavior in metals  

NASA Technical Reports Server (NTRS)

The applicability of a thermodynamic constitutive theory of deformation to the prediction of primary creep and creep strain relaxation behavior in metals is examined. Constitutive equations derived from the theory are subjected to a parametric analysis in order to determine the influence of several parameters on the curve forms generated by the equations. A computer program is developed which enables the solution of a generalized constitutive equation using experimental data as input. Several metals were tested to form a data base of primary creep and relaxation behavior. The extent to which these materials conformed to the constitutive equation showed wide variability, with the alloy Ti-6Al-4V exhibiting the most consistent results. Accordingly, most of the analysis is concentrated upon data from that alloy, although creep and relaxation data from all the materials tested are presented. Experimental methods are outlined as well as some variations in methods of analysis. Various theoretical and practical implications of the work are discussed.

Zerwekh, R. P.

1978-01-01

276

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

277

In situ tensile and creep testing of lithiated silicon nanowires  

SciTech Connect

We present experimental results for uniaxial tensile and creep testing of fully lithiated silicon nanowires. A reduction in the elastic modulus is observed when silicon nanowires are alloyed with lithium and plastic deformation becomes possible when the wires are saturated with lithium. Creep testing was performed at fixed force levels above and below the tensile strength of the material. A linear dependence of the strain-rate on the applied stress was evident below the yield stress of the alloy, indicating viscous deformation behavior. The observed inverse exponential relationship between wire radius and strain rate below the yield stress indicates that material transport was controlled by diffusion. At stress levels approaching the yield strength of fully lithiated silicon, power-law creep appears to govern the strain-rate dependence on stress. These results have direct implications on the cycling conditions, rate-capabilities, and charge capacity of silicon and should prove useful for the design and construction of future silicon-based electrodes.

Boles, Steven T.; Kraft, Oliver [Institute for Applied Materials, KIT, 76344 Eggenstein-Leopoldshafen (Germany)] [Institute for Applied Materials, KIT, 76344 Eggenstein-Leopoldshafen (Germany); Thompson, Carl V. [Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts 02139 (United States)] [Department of Materials Science and Engineering, MIT, Cambridge, Massachusetts 02139 (United States); Mönig, Reiner [Institute for Applied Materials, KIT, 76344 Eggenstein-Leopoldshafen (Germany) [Institute for Applied Materials, KIT, 76344 Eggenstein-Leopoldshafen (Germany); Helmholtz Institute Ulm for Electrochemical Energy Storage (HIU), 89069 Ulm (Germany)

2013-12-23

278

In situ tensile and creep testing of lithiated silicon nanowires  

NASA Astrophysics Data System (ADS)

We present experimental results for uniaxial tensile and creep testing of fully lithiated silicon nanowires. A reduction in the elastic modulus is observed when silicon nanowires are alloyed with lithium and plastic deformation becomes possible when the wires are saturated with lithium. Creep testing was performed at fixed force levels above and below the tensile strength of the material. A linear dependence of the strain-rate on the applied stress was evident below the yield stress of the alloy, indicating viscous deformation behavior. The observed inverse exponential relationship between wire radius and strain rate below the yield stress indicates that material transport was controlled by diffusion. At stress levels approaching the yield strength of fully lithiated silicon, power-law creep appears to govern the strain-rate dependence on stress. These results have direct implications on the cycling conditions, rate-capabilities, and charge capacity of silicon and should prove useful for the design and construction of future silicon-based electrodes.

Boles, Steven T.; Thompson, Carl V.; Kraft, Oliver; Mönig, Reiner

2013-12-01

279

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

280

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

281

Creep-compensated fatigue testing of polyethylene under reversed loading conditions  

Microsoft Academic Search

A machine capable of testing polymers under creep-compensated strain-controlled cyclic deformation has been constructed, and used initially to study fatigue behaviour in low-density polyethylene. Reversed loading conditions have been used with total strain amplitude up to 6.5%. Crack propagation is inhibited by the compressive component of the deformation. Within the range of testing employed, the slowest crack-growth rates are obtained

J. W. Teh; J. R. White; E. H. Andrews

1975-01-01

282

Arc Hyperbolic sine creep theory applied to torsion-tension member of circular cross section  

Microsoft Academic Search

A multiaxial creep theory is presented in this paper which will predict the total deformations of a load-carrying member at any specified time after load. Load-deformation relations are derived based on the assumption that the isochronous stress-strain diagram of the material can be represented by an arc hyperbolic sine function [see, eq (2)]. A closed solution was obtained for the

S. Dharmarajan; O. M. Sidebottom

1963-01-01

283

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

284

Rheological Characteristics of Weak Rock Mass and Effects on the Long-Term Stability of Slopes  

NASA Astrophysics Data System (ADS)

The creep deformation behavior of the northern slope of an open-pit mine is introduced. Direct shear creep tests are then conducted for the samples taken from the northern slope to study the rheological characteristics of the rock mass. The experimental results are analyzed afterwards using an empirical method to develop a rheological model for the rock mass. The proposed rheological model is finally applied to understand the creep behavior of the northern slope, predict the long-term stability, and guide appropriate measures to be taken at suitable times to increase the factor of safety to ensure stability. Through this study, a failure criterion is proposed to predict the long-term stability of the slope based on the rheological characteristics of the rock mass and a critical deformation rate is adopted to determine when appropriate measures should be taken to ensure slope stability. The method has been successfully applied for stability analysis and engineering management of the toppling and slippage of the northern slope of the open-pit mine. This success in application indicates that it is theoretically accurate, practically feasible, and highly cost-effective.

Yang, Tianhong; Xu, Tao; Liu, Hongyuan; Zhang, Chunming; Wang, Shanyong; Rui, Yongqin; Shen, Li

2014-11-01

285

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

286

Creep processes in magnesium alloys and their composites  

NASA Astrophysics Data System (ADS)

A comparison is made between the creep characteristics of two squeeze-cast magnesium alloys (AZ 91 and QE 22) reinforced with 20 vol pct Al2O3 short fibers and the unreinforced AZ 91 and QE 22 matrix alloys. The results show the creep resistance of the reinforced materials is considerably improved by comparison with the unreinforced matrix alloys. It is suggested that creep strengthening in these short-fiber composites arises primarily from the existence of a threshold stress and the effect of load transfer. By testing samples to failure, it is demonstrated that the unreinforced and reinforced materials exhibit similar times to failure at the higher stress levels. A detailed microstructural investigation by transmission electron microscopy (TEM) reveals no substantial changes in matrix microstructure due to the presence of the reinforcement. This suggests that direct composite strengthening dominates over indirect effects.

Skleni?ka, V.; Pahutová, M.; Kucha?ová, K.; Svoboda, M.; Langdon, T. G.

2002-03-01

287

Significance of primary irradiation creep in graphite  

NASA Astrophysics Data System (ADS)

Traditionally primary irradiation creep is introduced into graphite analysis by applying the appropriate amount of creep strain to the model at the initial time-step. This is valid for graphite components that are subjected to high fast neutron flux fields and constant stress fields, but it does not allow for the effect of movement of stress locations around a graphite component during life, nor does it allow primary creep to be applied rate-dependently to graphite components subject to lower fast neutron flux. This paper shows that a differential form of primary irradiation creep in graphite combined with the secondary creep formulation proposed by Kennedy et al. performs well when predicting creep behaviour in experimental samples. The significance of primary irradiation creep in particular in regions with lower flux is investigated. It is shown that in low flux regions with a realistic operating lifetime primary irradiation creep is significant and is larger than secondary irradiation creep.

Erasmus, Christiaan; Kok, Schalk; Hindley, Michael P.

2013-05-01

288

Creep behaviour of natural rock salt and its description with the composite model  

Microsoft Academic Search

Natural rock salt in deep underground structures is planned to act as the host material for the permanent storage of radioactive and toxic wastes. Dimensioning and safety analysis of such repositories require a model which allows to predict the creep behaviour of rock salt on the basis of the microstructure and the physical mechanisms of deformation. Already before testing natural

P. Weidinger; A. Hampel; W. Blum; U. Hunsche

1997-01-01

289

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

290

Properties of shallow creep on the Southern San Andreas Fault from InSAR and GPS  

NASA Astrophysics Data System (ADS)

We present a detailed characterization of surface creep and off-fault deformation along the Coachella Valley segment of the San Andreas Fault from 33.3-33.7 deg. North using a combination of campaign GPS and multiple InSAR viewing geometries. An array of 30 survey monuments spanning 3km across the fault at Painted Canyon was occupied with campaign-mode GPS between 2007 and 2012, providing a direct measurement of creep at that location; the rate of 3+/-1mm/yr is in good agreement with long-term geologic estimates of 2-4 mm/yr (Sieh and Williams, 1990). A combination of over 400 radar interferograms from ascending and descending Envisat (Tracks 356 and 77), ALOS (Tracks 213-214) (Tong et. al, 2012), and ERS (Track 356) were used to isolate the creep signal from other non-tectonic sources of deformation, providing a high-resolution image of the near-fault horizontal deformation pattern. The results indicate a creep rate consistent with the GPS at Painted Canyon, and reveal along-strike variations in both the creep rate and effective shear zone width. This width varies from less than a few meters at Painted Canyon to as wide as 4km along the North Shore section of the fault. In this area, previous geologic and geodetic observations have not identified localized surface creep. Instead, the satellite data indicates 3-4 mm/yr of fault-parallel surface deformation is distributed over a wide shear zone. We compare the geodetic data to numerical simulations of earthquake cycles incorporating laboratory-derived rate and state friction, allowing us to constrain the depth extent of the velocity-strengthening and velocity-weakening layers and the process of stress evolution in the seismogenic zone.

Lindsey, E. O.; Fialko, Y.; Bock, Y.

2012-12-01

291

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

292

Electrochemical Creeping and Actuation of Polypyrrole in Ionic Liquid  

NASA Astrophysics Data System (ADS)

The electrochemical creeping and actuation of polypyrrole films operated in an ionic liquid are reported. The electrochemical deformation was initiated by the reduction and swelling of the films by 15-20% with soaking in ionic liquid. An electrochemical strain of 3% and a blocked stress of 1.7 MPa showing cation movement were obtained. The film showed creeping at tensile loads larger than 0.5 MPa. The electrochemical strain obtained in a mixed solution of an ionic liquid and propylene carbonate was 15% at the initial stage, showing anion movement together with swelling induced by soaking in solvents. However, the electrochemical strain became negligible after several electrochemical cycles, resulting from the loss of electrochemical activity and conductivity upon swelling.

Kaneto, Keiichi; Shinonome, Teruyuki; Tominaga, Kazuo; Takashima, Wataru

2011-09-01

293

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

294

(Irradiation creep of graphite)  

SciTech Connect

The traveler attended the Conference, International Symposium on Carbon, to present an invited paper, Irradiation Creep of Graphite,'' and chair one of the technical sessions. There were many papers of particular interest to ORNL and HTGR technology presented by the Japanese since they do not have a particular technology embargo and are quite open in describing their work and results. In particular, a paper describing the failure of Minor's law to predict the fatigue life of graphite was presented. Although the conference had an international flavor, it was dominated by the Japanese. This was primarily a result of geography; however, the work presented by the Japanese illustrated an internal program that is very comprehensive. This conference, a result of this program, was better than all other carbon conferences attended by the traveler. This conference emphasizes the need for US participation in international conferences in order to stay abreast of the rapidly expanding HTGR and graphite technology throughout the world. The United States is no longer a leader in some emerging technologies. The traveler was surprised by the Japanese position in their HTGR development. Their reactor is licensed and the major problem in their graphite program is how to eliminate it with the least perturbation now that most of the work has been done.

Kennedy, C.R.

1990-12-21

295

"A New Class of Creep Resistant Oxide/Oxide Ceramic Matrix Composites"  

SciTech Connect

Despite recent progress in the development of SiC-SiC ceramic matrix composites (CMCs), their application in industrial gas turbines for distributed energy (DE) systems has been limited. The poor oxidation resistance of the non-oxide ceramics warrants the use of envrionmental barrier coatings (EBCs), which in turn lead to issues pertaining to life expectancy of the coatings. On the other hand, oxide/oxide CMCs are potential replacements, but their use has been limited until now due to the poor creep resistance at high temperatures, particularly above 1200 oC: the lack of a creep resistant matrix has been a major limiting factor. Using yttrium aluminum garnet (YAG) as the matrix material system, we have advanced the state-of-the-art in oxide/oxide CMCs by introducing innovations in both the structure and composition of the matrix material, thereby leading to high temperature matrix creep properties not achieved until now. An array of YAG-based powders with a unique set of particle characteristics were produced in-house and sintered to full density and compressive creep data was obtained. Aided in part by the composition and the microstructure, the creep rates were found to be two orders of magnitude smaller than the most creep resistant oxide fiber available commercially. Even after accounting for porosity and a smaller matrix grain size in a practical CMC component, the YAG-based matrix material was found to creep slower than the most creep resistant oxide fiber available commercially.

Dr. Mohit Jain, Dr. Ganesh Skandan, Prof. Roger Cannon, Rutgers University

2007-03-30

296

Granular and semi-brittle descriptions of slip and creep  

NASA Astrophysics Data System (ADS)

Crustal deformation generates a wide range of creep and slip behaviors. Coseismic fault slip, aseismic creep, long-term strain transients, and slow-slip events all accommodate a great deal of tectonic strain and cause or contribute to destructive geohazards. Moreover, all have different time scales and exhibit differing degrees of periodicity. The dynamic frictional response of fault surfaces and fault rocks to slip may control a great deal of crustal slip and creep behaviors. Such is also the case for effective stress changes through fluid-pressure fluctuation and remote triggering. Yet, few existing friction and effective-stress models address the heterogeneity, range of metamorphic conditions, and range of deformational time scales that characterize natural shear zones. A useful framework for addressing this geological diversity is to treat natural shear zones as granular media. Physical experiments using analog materials provide some insight into such an approach. Shear zones of dry, granular materials produce stick-slip events via jamming phenomena, including influencing the periodicity and duration of events. When added to such granular mixtures, viscous materials enhance localization and smooth stick-slip events. Though such experimental approaches are difficult to simulate numerically, analytical and numerical solutions for fracture propagation into semi-brittle media can produce strain transients with a wide range of durations and recurrence intervals. A good example of how to use these concepts is in the characterization of possible slip behaviors for now-exhumed mid-crustal shear zones. Such shear zones tend to have deformed via predominantly viscous crystal plastic mechanisms, yet their creep behavior may well have produced strain transients including episodic tremor and slip. Fracture propagation into creeping media comprising mixtures of strong and weak materials could explain the generation of such phenomena. Geological observations of strong mafic lenses within weaker quartz-rich gneiss, cut by syntectonic quartz veins, are widely observed structural records of such behavior. Extending this analysis into the upper crust, however, will require a more complete framework for describing the strength of granular materials in the crust.

Hayman, N. W.; Lavier, L. L.

2013-12-01

297

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

298

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

299

The Rate of Creep Deformation St Edmund's College, Cambridge  

E-print Network

Department of Materials Science and Metallurgy Pembroke Street, Cambridge CB2 3QZ A dissertation submitted. Bhadeshia and Dr T. Sourmail in the Department of Materials Science and Metallurgy, University of Cambridge

Cambridge, University of

300

Ris-R-1528(EN) Creep-Fatigue Deformation Behaviour  

E-print Network

the monotonic yield strength of the material. The reduction in the yield strength due to overaging heat. The increase in the yield strength due to neutron irradiation at 333 K, on the other hand, causes an increase

301

Jumpwise deformation of polymethyl methacrylate in the microplasticity region  

NASA Astrophysics Data System (ADS)

The deformation rate with a step of 325 nm has been measured under uniaxial compression at the initial stage of creep and shape recovery of a polymethyl methacrylate (PMMA) sample after unloading. The effect of low ?-ray doses and magnetic fields on the deformation has been studied. It has been shown that a weak pre-exposure of the PMMA sample structure to radiation and magnetic fields can cause a slight hardening in the microplasticity region. The deformation jump sizes have been determined on micro- and nanoscales. The effect of irradiation and magnetic fields manifests itself as redistributed contributions of various jumps to the deformation.

Shpeizman, V. V.; Yakushev, P. N.; Mukhina, Zh. V.; Kuznetsov, E. V.; Smolyanskii, A. S.

2013-05-01

302

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

303

Creep and rupture behavior of Cu wire\\/lead-free solder-alloy joint specimen  

Microsoft Academic Search

Creep and rupture behavior of Cu wire\\/lead-free solder-alloy joint specimens have been investigated using Sn-3.5% Ag and Sn-0.5%\\u000a Cu alloys. A Sn-37% Pb solder alloy is also used as a reference material. The present authors have fabricated a creep-rupture\\u000a testing machine for Cu wire\\/solder-alloy joint specimens, performed creep and rupture tests at 303 K and 403 K, analyzed the\\u000a characteristics

Kepeng Wu; Makoto Aoyama; Noboru Wade; Jie Cui; Shinji Yamada; Kazuya Miyahara

2003-01-01

304

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

305

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

306

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

307

Characterization of load dependent creep behavior in medically relevant absorbable polymers.  

PubMed

While synthetic absorbable polymers have a substantial history of use in medical devices, their use is expanding and becoming more prevalent for devices where long term loading and structural support is required. In addition, there is evidence that current absorbable medical devices may experience permanent deformations, warping (out of plane twisting), and geometric changes in vivo. For clinical indications with long term loading or structural support requirements, understanding the material's viscoelastic properties becomes increasingly important whereas these properties have not been used historically as preclinical indications of performance or design considerations. In this study we measured the static creep, creep recovery and cyclic creep responses of common medically relevant absorbable materials (i.e., poly(l-lactide, PLLA) and poly(l-co-glycolide, PLGA) over a range of physiologically relevant loading magnitudes. The results indicate that both PLLA and PLGA exhibit creep behavior and failure at loads significantly less than the yield or ultimate properties of the material and that significant material specific responses to loading exist. In addition, we identified a strong correlation between the extent of creep in the material and its crystallinity. Results of the study provide new information on the creep behavior of PLLA and PLGA and support the use of viscoelastic properties of absorbable polymers as part of the material selection process. PMID:24211356

Dreher, Maureen L; Nagaraja, Srinidhi; Bui, Hieu; Hong, Danny

2014-01-01

308

Time-dependent model of creep on the Hayward fault from joint inversion of 18 years of InSAR and surface creep data  

NASA Astrophysics Data System (ADS)

Spatial and temporal variations of aseismic fault creep influence the size and timing of large earthquakes along partially coupled faults. To solve for a time-dependent model of creep on the Hayward fault, we invert 18 years of surface deformation data (1992-2010), obtained by interferometric processing of 52 and 50 SAR images acquired by the ERS1/2 and Envisat satellites, respectively, and surface creep data obtained at 19 alinement and 4 creepmeter stations. For multi-temporal analysis of the SAR data we developed a method for identifying stable pixels using wavelet multi-resolution analysis. We also implement a variety of wavelet-based filters for reducing the effects of environmental artifacts. Using a reweighted least squares approach, we inverted the interferometric data to generate a time series of surface deformation over the San Francisco Bay Area with a precision of better than a few millimeters. To jointly invert the InSAR displacement time series and the surface creep data for a time-dependent model of fault creep, we use a robust inversion approach combined with a Kalman filter. The time-dependent model constrains a zone of high slip deficit that may represent the locked rupture asperity of past and future M?7 earthquakes. We identify several additional temporal variations in creep rate along the Hayward fault, the most important one being a zone of accelerating slip just northwest of the major locked zone. We estimate that a slip-rate deficit equivalent to Mw 6.3-6.8 has accumulated on the fault, since the last event in 1868.

Shirzaei, M.; Bürgmann, R.

2013-04-01

309

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

310

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 950°C 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 1050°C 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

311

Study on hot deformation characteristics of 12%Cr ultra-super-critical rotor steel using processing maps and Zener–Hollomon parameter  

Microsoft Academic Search

The hot deformation behavior of a 12%Cr ultra-super-critical rotor steel was investigated in the temperature range of 900–1200°C and strain rate range of 0.01–10s?1. The processing maps of the material were derived by using dynamic materials model and Prasad instability criterion. The deformation mechanisms of different regions in the processing maps and corresponding microstructures were discussed in combination of the

Zhenhua Wang; Wantang Fu; Baozhong Wang; Wenhui Zhang; Zhiqing Lv; Ping Jiang

2010-01-01

312

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

313

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

314

Creep behaviour and microstructural evolution in AISI 316LN + Nb steels at 650 °C  

Microsoft Academic Search

The paper deals with the effect of niobium in the wrought AISI 316LN steels on the long-term creep characteristics at 650°C. Casts B and C contained 0.1 and 0.3wt.%Nb, respectively. As a reference material the niobium free Cast A was used. Small additions of niobium to the AISI 316LN steel resulted in a significant reduction of the minimum creep rate

Vlastimil Vodárek

2011-01-01

315

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 (1250°C). 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

316

Creep of wet gypsum aggregates under hydrostatic loading conditions  

NASA Astrophysics Data System (ADS)

Gypsum-dominated evaporite sequences are known to play an important role in controlling the mechanics of foreland thrust and nappe tectonics, as well as occasionally forming large-scale halokinetic structures associated with oil and gas accumulations. However, relatively little is known regarding the relevant deformation mechanisms and mechanical behaviour of gypsum. In this study, attention is focused on determining the compaction creep behaviour of wet granular gypsum aggregates with the aim of assessing the importance of pressure solution. Hydrostatic compaction experiments were performed at room temperature and applied effective pressures in the range 0.4-3.9 MPa, using grain sizes ranging from 15 to 125 ?m. The microstructure of the wet-tested samples showed that compaction occurred by a process of dissolution within grain contacts and precipitation on pore walls. In addition, for most of the range of conditions investigated, the mechanical data were found to be broadly consistent with models for interface-reaction-controlled grain boundary diffusional pressure solution. Combining the mechanical data with kinetic data taken from the crystal growth / dissolution literature it is suggested that for the bulk of conditions studied, creep of our wet granular gypsum aggregates was probably rate-limited by precipitation on the pore walls. This is in sharp contrast to the diffusion-controlled pressure solution creep behaviour recently reported for highly soluble salts, such as NaCl and NaNO 3, under similar conditions.

de Meer, Siese; Spiers, Christopher J.

1995-05-01

317

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

318

Transient Creep in Pure Metals  

Microsoft Academic Search

A constant stress testing machine of small inertia and with continuous strain recording has been built. The loading was by air contained in metallic bellows whose wall stiffness was compensated by a `negative spring'. The initial strain rate was standardized at 1% per second. Polycrystalline copper and aluminium have been investigated between -196°C and 140°C. At low temperatures, the creep

O H Wyatt

1953-01-01

319

Life at Mission Creep U  

ERIC Educational Resources Information Center

The term "mission creep" was originally coined nearly a hundred years ago to describe the gradual process by which a military mission's stated methods and goals change, and recently the term has been applied to incremental organizational changes. In this article, the term is used to describe what happens when a teaching-oriented college or…

Dubrow, Greg; Moseley, Bryan; Dustin, Daniel

2006-01-01

320

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

321

Influence of mineral fraction on the rheological properties of forsterite + enstatite during grain size sensitive creep: 3. Application of grain growth and flow laws on peridotite ultramylonite  

NASA Astrophysics Data System (ADS)

of a layered peridotite ultramylonite from the Oman ophiolite are compared with that of experimentally deformed samples. Average grain sizes and grain size ratios of olivine and pyroxene from each layer are compared with respect to the fraction of pyroxene (fpx) in the layer. Grain size of the pyroxene is almost constant among different fpx layers, whereas olivine grain size decreases significantly with increasing fpx, both of which were characteristic features found in forsterite + enstatite aggregates after grain growth experiments (Tasaka and Hiraga, ). Furthermore, the Zener relationship (log dol/dpx versus log fpx) found in the ultramylonite is remarkably comparable to that observed in our experiments. These observations indicate effective pinning of olivine grain growth due to the presence of pyroxene grains during the deformation of the rocks. Olivine grains in layers with fpx ? 0.03 do not exhibit lattice-preferred orientation (LPO), whereas the grains in layers with fpx < 0.03 exhibit LPO, indicating that deformation proceeded via diffusion- and dislocation-accommodated creep in the former and the latter layers, respectively. We simulated the evolution of grain size and viscosity in the shear zone based on our grain growth and flow laws obtained for diffusion creep of forsterite + enstatite (Tasaka and Hiraga, ; Tasaka et al., ) and successfully reproduced the observed grain sizes in the ultramylonite. We therefore conclude that the relative values of the kinetic parameters, some of which are functions of the fpx, are applicable to nature.

Tasaka, Miki; Hiraga, Takehiko; Michibayashi, Katsuyoshi

2014-02-01

322

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

323

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

324

Effect of hydrogen on the creep behavior of Zr-2.5%Nb alloy at 723 K  

NASA Astrophysics Data System (ADS)

Increased plasticity is reported in Ti alloys, stainless steels and Pd by the introduction of hydrogen. The dissolved hydrogen in zirconium and its alloys which have similar properties as those of titanium and its alloys, can modify the creep properties of the matrix. Hydrogen, formed during the corrosion reaction of Zr-2.5%Nb pressure tube, in a CANDU design nuclear reactor, with the coolant can ingress into the metal matrix. This absorbed hydrogen can lead to an unexpected increase in length and in diameter of the pressure tube. In order to evaluate the effect of hydrogen on the creep behavior of the pressure tube material, tensile specimens with longitudinal and transverse orientations were hydrided to 65 and 160 wt ppm and creep tested at 723 K over a stress range. The combined influence of hydrogen and specimen orientations on creep rate is evaluated, and an attempt is made to explain the results using the deformation mechanisms reported in literature.

Kishore, R.

2009-04-01

325

Creep and shrinkage effects on integral abutment bridges  

NASA Astrophysics Data System (ADS)

Integral abutment bridges provide bridge engineers an economical design alternative to traditional bridges with expansion joints owing to the benefits, arising from elimination of expensive joints installation and reduced maintenance cost. The superstructure for integral abutment bridges is cast integrally with abutments. Time-dependent effects of creep, shrinkage of concrete, relaxation of prestressing steel, temperature gradient, restraints provided by abutment foundation and backfill and statical indeterminacy of the structure introduce time-dependent variations in the redundant forces. An analytical model and numerical procedure to predict instantaneous linear behavior and non-linear time dependent long-term behavior of continuous composite superstructure are developed in which the redundant forces in the integral abutment bridges are derived considering the time-dependent effects. The redistributions of moments due to time-dependent effects have been considered in the analysis. The analysis includes nonlinearity due to cracking of the concrete, as well as the time-dependent deformations. American Concrete Institute (ACI) and American Association of State Highway and Transportation Officials (AASHTO) models for creep and shrinkage are considered in modeling the time dependent material behavior. The variations in the material property of the cross-section corresponding to the constituent materials are incorporated and age-adjusted effective modulus method with relaxation procedure is followed to include the creep behavior of concrete. The partial restraint provided by the abutment-pile-soil system is modeled using discrete spring stiffness as translational and rotational degrees of freedom. Numerical simulation of the behavior is carried out on continuous composite integral abutment bridges and the deformations and stresses due to time-dependent effects due to typical sustained loads are computed. The results from the analytical model are compared with the published laboratory experimental and field data. The behavior of the laterally loaded piles supporting the integral abutments is evaluated and presented in terms of the lateral deflection, bending moment, shear force and stress along the pile depth.

Munuswamy, Sivakumar

326

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

327

Viscoplastic response and creep failure time prediction of polymers based on the transient network model  

NASA Astrophysics Data System (ADS)

The nonlinear viscoelastic/viscoplastic response of polymeric materials is described by a new model based on previous works in terms of monotonic loading, stress-relaxation, and creep. In the proposed analysis, following a constitutive equation of viscoelasticity, based on the transient network theory, essential modifications are introduced, which account for the nonlinearity and viscoplasticity at small elastic and finite plastic strain regime. In addition, viscoplastic response is successfully analyzed by a proper kinematic formulation, which is combined with a functional form of the rate of plastic deformation. A three-dimensional constitutive equation is then derived for an isotropic incompressible medium. This analysis is capable of capturing the main aspects of inelastic response and the instability stage taking place at the tertiary creep, related to the creep failure. Model simulations described successfully the experimental data of polypropylene, which were performed elsewhere.

Kontou, E.; Spathis, G.

2014-05-01

328

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 (800-1000°C). 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

329

FURTHER OBSERVATIONS ON V-4Cr-4Ti PRESSURIZED CREEP TUBES  

SciTech Connect

Further observations are provided for pressurized thermal creep tubes of V-4Cr-4Ti examined following testing in the range 650 to 800°C for tests lasting up to ~104 h. Precipitate particles have been analyzed by EELS to define interstitial contents, and are shown to be either C or O rich with only minor N contents. Grain shape aspect ratios as a function of strain have been measured and these data shows shape change as a result of effective mid-wall strains as high as 12.7%. Deformation mechanisms are considered to explain Newtonian viscous flow response at 800°C below effective midwall stresses of 70 MPa, and it is concluded that grain boundary sliding probably is the predominant mechanism based on the microstructural information presented here, but there is evidence that Harper-Dorn creep may also be a contributing creep mechanism under these conditions.

Gelles, David S.; Kurtz, Richard J.; Toloczko, Mychailo B.; Thomas, Larry E.

2006-03-01

330

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

331

Using UAVSAR to Estimate Creep Along the Superstition Hills Fault, Southern California  

NASA Astrophysics Data System (ADS)

UAVSAR data were first acquired over the Salton Trough region, just north of the Mexican border in October 2009. Second passes of data were acquired on 12 and 13 April 2010, about one week following the 5 April 2010 M 7.2 El Mayor - Cucapah earthquake. The earthquake resulted in creep on several faults north of the main rupture, including the Yuha, Imperial, and Superstition Hills faults. The UAVSAR platform acquires data about every six meters in swaths about 15 km wide. Tropospheric effects and residual aircraft motion contribute to error in the estimation of surface deformation in the Repeat Pass Interferometry products. The Superstition Hills fault shows clearly in the associated radar interferogram; however, error in the data product makes it difficult to infer deformation from long profiles that cross the fault. Using the QuakeSim InSAR Profile tool we extracted line of site profiles on either side of the fault delineated in the interferogram. We were able to remove much of the correlated error by differencing profiles 250 m on either side of the fault. The result shows right-lateral creep of 1.5±.4 mm along the northern 7 km of the fault in the interferogram. The amount of creep abruptly changes to 8.4±.4 mm of right lateral creep along at least 9 km of the fault covered in the image to the south. The transition occurs within less than 100 m along the fault. We also extracted 2 km long line of site profiles perpendicular to this section of the fault. Averaging these profiles shows a step across the fault of 14.9±.3 mm with greater creep on the order of 20 mm on the northern two profiles and lower creep of about 10 mm on the southern two profiles. Nearby GPS stations P503 and P493 are consistent with this result. They also confirm that the creep event occurred at the time of the El Mayor - Cucapah earthquake. By removing regional deformation resulting from the main rupture we were able to invert for the depth of creep from the surface. Results indicate that the slip occurred from the surface to 10-20 km, not shallowly, as previously suggested.

Donnellan, A.; Parker, J. W.; Pierce, M.; Wang, J.

2012-12-01

332

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 300°C and 500°C 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 400°C and of carbides below about 700°C, 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.

Schüle, Wolfgang; Hausen, Hermann

1994-09-01

333

Characteristics and deformation mechanism of salt-related structures in the western Kuqa depression, Tarim basin: Insights from scaled sandbox modeling  

NASA Astrophysics Data System (ADS)

Three scaled analog (sandbox) models are constructed to simulate the evolution of thick-skinned shortening on broad and narrow salt basins. These models simulate the evolution of the Cenozoic salt (salt-related) structures in the westernmost Kuqa salt-bearing depression (Quele area), Tarim basin. The formation mechanism and the controlling factors of structural deformation in this area are investigated and discussed systematically. Model results show that the variable depositional width of the salt basin has a major controlling influence on the differential structural deformation in different longitudinal segmentations from east (broad) to west (narrow) in the western Kuqa depression (Quele area). Model results also demonstrate that the early salt structure (salt diapir) has an important controlling role on the subsequent compressional structural deformation. The pre-existing thin overburden Quele diapir, which acts as a stress concentration zone during the subsequent shortening, is deformed to the Quele salt nappe. On the basis of the model results, it is suggested that the formation of the long-distance Quele allochthonous salt sheet is related with the pre-existing Quele diapir, which displaces up paralleling the hanging wall and flows to the surface during the subsequent shortening.

Wu, Zhenyun; Yin, Hongwei; Wang, Xin; Zhao, Bo; Jia, Dong

2014-02-01

334

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 = 1025°C 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 andg·b-analysis.

G. Eggeler; A. Dlouhy

1997-01-01

335

Effects of Steel Slag Usage as Aggregate on Indirect Tensile and Creep Modulus of Hot Mix Asphalt  

Microsoft Academic Search

In this study indirect tensile modulus and long term deformation behaviour of the hot mix asphalt (HMA) containing steel slag, basalt and limestone were investigated using 5 pulses Universal Testing Machine. Optimum bitumen content was determined for three types of mixtures according to the Marshall procedure. Indirect tensile modulus ITM (Sm) and creep modulus (S) tests were applied in order

Baha Vural KÖK

336

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

337

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

338

Creep of garnet in eclogite: Mechanisms and implications  

NASA Astrophysics Data System (ADS)

The rheological properties of subducting rocks represent a fundamental parameter in the dynamics of subduction zones. Making robust predictions about these properties and the general strength evolution of subducting plates is hampered by a relatively restricted understanding of the mechanisms by which rocks deform at high- and ultrahigh pressure. This uncertainty is relates to the discrepancy between experimental and field-based observations of eclogite deformation and, in particular, the role of garnet. To further investigate this important aspect, we performed a textural and micro-structural investigation, applying optical microscopy, element mapping, and electron backscatter diffraction on deformed garnet polycrystals from an eclogite mylonite. The results were compared to those from a study of undeformed polycrystals that formed from a supercooled frictional melt at HP conditions. The mylonites' polycrystals are flattened parallel to the main high-pressure foliation in the rock and individual grains were shortened by an average 15%. Although dislocation creep is commonly presumed to dominate garnet straining in eclogites, no record of this mechanism was found. Instead, the garnet grains have dissolution surfaces indicative of deformation by intergranular pressure solution. The observations provide compelling evidence for the role of fluids and syn-tectonic porosity in the weakening of garnet: a supposedly rigid eclogite component. Such weakening represents a crucial step in the fundamental feedback loop between fluid ingress, metamorphism and near-instantaneous competence loss in rocks undergoing deep subduction.

Smit, Matthijs A.; Scherer, Erik E.; John, Timm; Janssen, Arne

2011-11-01

339

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

340

Empirical law for fault-creep events  

USGS Publications Warehouse

Fault-creep events measured on the San Andreas and related faults near Hollister, California, can be described by a rheological model consisting of a spring, power-law dashpotand sliding block connected in series. An empirical creep-event law, derived from many creep-event records analyzed within the constraints of the model, provides a remarkably simple and accurate representation of creep-event behavior. The empirical creep law is expressed by the equation: D(t)= Df [1-1/{ct(n-1)Dfn-1+1}/(n-1)] where D is the value of displacement at time t following the onset of an event, Df is the final equilibrium value of the event displacementand C is a proportionality constant. This discovery should help determine whether the time-displacement character of creep events is controlled by the material properties of fault gouge, or by other parameters. ?? 1977.

Crough, S.T.; Burford, R.O.

1977-01-01

341

Errors in shearography measurements due to the creep of the PZT shearing actuator  

NASA Astrophysics Data System (ADS)

Shearography is a modern optical interferometric measurement technique. It uses the interferometric properties of coherent laser light to measure deformation gradients on the µm m?-?1 level. In the most common shearography setups, the ones employing a Michelson interferometer, the deformation gradients in both the x- and y-directions can be identified by setting angles on the shearing mirror. One of the mechanisms for setting the desired shearing angles in the Michelson interferometer is using the PZT actuators. This paper will reveal that the time-dependent creep behaviour of the PZT actuators is a major source of measurement errors. Measurements at long time spans suffer severely from this creep behaviour. Even for short time spans, which are typical for shearographic experiments, the creep behaviour of the PZT shear actuator induces considerable deviation in the measured response. In this paper the mechanism and the effect of PZT creep is explored and demonstrated with measurements. For long time-span measurements in shearography, noise is a limiting factor. Thus, the time-dependent evolution of noise is considered in this paper, with particular interest in the influence of external vibrations. Measurements with and without external vibration isolation are conducted and the difference between the two setups is analyzed. At the end of the paper some recommendations are given for minimizing and correcting the here-studied time-dependent effects.

Zastavnik, Filip; Pyl, Lincy; Sol, Hugo; Kersemans, Mathias; Van Paepegem, Wim

2014-08-01

342

Rock bending creep and disturbance effects  

Microsoft Academic Search

The bending creep and its disturbance effects of red sandstone rock beam and oil shale rock beam were studied by adopting\\u000a the self-developed gravitation level style rock creep test machine and bending creep test system, and the constitutive equations\\u000a were established. It is found that fracture morphology of rock beams under no disturbance load is regular, cracking position\\u000a of fractures

Zhi-liang Fu; Ying-ren Zheng; Yuan-xue Liu

2008-01-01

343

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

344

Superplastic creep of eutectic tinlead solder joints  

Microsoft Academic Search

This paper presents experimental evidence that as-solidified eutectic Pb-Sn solder joints can exhibit superplastic behavior\\u000a in shear creep loading. Stepped load creep tests of as-solidified joints show a change in the stress exponent from a high\\u000a value typical of con-ventional creep at high stress and strain rate to a superplastic value near 2 at lower stress and strain\\u000a rates. In

Z. Mei; D. Grivas; M. C. Shine; J. W. Morris

1990-01-01

345

Development of a simplified procedure for rocket engine thrust chamber life prediction with creep  

NASA Technical Reports Server (NTRS)

An analytical method for predicting engine thrust chamber life is developed. The method accounts for high pressure differentials and time-dependent creep effects both of which are significant in limiting the useful life of the shuttle main engine thrust chamber. The hot-gas-wall ligaments connecting adjacent cooling channels ribs and separating the coolant flow from the combustion gas are subjected to a high pressure induced primary stress superimposed on an alternating cyclic thermal strain field. The pressure load combined with strain-controlled cycling produces creep ratcheting and consequent bulging and thinning of these ligaments. This mechanism of creep-enhanced ratcheting is analyzed for determining the hot-gas-wall deformation and accumulated strain. Results are confirmed by inelastic finite element analysis. Fatigue and creep rupture damage as well as plastic tensile instability are evaluated as potential failure modes. It is demonstrated for the NARloy Z cases analyzed that when pressure differentials across the ligament are high, creep rupture damage is often the primary failure mode for the cycle times considered.

Badlani, M. L.; Porowski, J. S.; Odonnell, W. J.; Peterson, D. B.

1983-01-01

346

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, José

2014-01-01

347

Deformation Zone Distribution  

NSDL National Science Digital Library

The distribution of vorticity centres along an axis of maximum winds follows a fairly predictable pattern based on the characteristics of the flow. By diagnosing these characteristics, the meteorologist is able to quickly deduce the location and relative intensities of the associated vorticity centres as well as the relative sizes of the associated circulations. This information is summarized within the shape and orientation of the associated deformation zones. The deformation zones in turn reveal important details regarding feature motion and thermal advection and thus their diagnosis should be a critical part of the forecast process. This module takes 30-40 minutes to complete. It is part of the series: "Dynamic Feature Identification: The Satellite Palette".

Comet

2008-03-21

348

Dislocation Creep in Magnesium Calcite  

Microsoft Academic Search

To investigate the effect of dissolved Mg on plastic deformation of calcite, we performed triaxial deformation experiments on synthetic calcite with varying amount of Mg content. Mixtures of powders of calcite and dolomite were isostatically hot pressed (HIP) at 850° C and 300 MPa confining pressure for different intervals (2 to 20hrs) resulting in homogeneous aggregates of high-magnesium calcite; Mg

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

2003-01-01

349

ROCK DEFORMATION 2010 GORDON RESEARCH CONFERENCE, AUGUST 8-13, 2010  

Microsoft Academic Search

Creep in the crust and mantle is commonly considered a steady-state process. This view prevails despite the fact that earthquakes do not represent steady-state and at the base of the seismogenic zone, for example, the stresses that drive creep must vary with the earthquake cycle. The contribution of transient versus steady-state behavior is not easy to determine from naturally-deformed brittle

David Prior

2010-01-01

350

Indentation creep behavior of a direct-filling silver alternative to amalgam.  

PubMed

Amalgam creep has been identified as a key parameter associated with marginal breakdown and corrosion. The aim of this study was to evaluate the time-dependent deformation (creep) of a novel silver filling material as an alternative to amalgam. We made the silver specimens by pressing a precipitated powder at room temperature to a density that can be achieved in clinical hand consolidation. The surface of the silver was either polished or burnished. To examine local contact creep and the effect of surface finishing, we used an indentation creep method in which a Vickers indenter was loaded on the specimen surface at a load of 10 N with dwell times of 5 sec to 6x10(4) sec. We used a bonded-interface technique to examine subsurface creep mechanisms. The flexural strength (mean+/-SD; n = 10) was 86+/-20 MPa for amalgam, 180+/-21 MPa for polished silver, and 209+/-19 MPa for burnished silver-values which are significantly different from each other (family confidence coefficient = 0.95; Tukey's multiple-comparison test). Indentation creep manifested as hardness number decreasing with increased dwell time. With dwell time increasing from 5 sec to 6x10(4) sec, the hardness number of amalgam was reduced by approximately 80%; that of the polished silver and the burnished silver was reduced by only 40%. Subsurface creep in amalgam consisted of the shape change of the alloy particles from spherical to elongated shapes, and the separation of matrix grains from each other, possibly due to grain-boundary sliding. Creep of the polished silver occurred by densification reducing porosity and increasing hardness; that of the burnished silver occurred by the displacement of the burnished layer. These results suggest that, due to creep-induced subsurface work-hardening and densification, the consolidated silver exhibits a higher resistance to indentation creep than does amalgam. The hardness number of silver approaches that of amalgam after prolonged indentation loading. PMID:9839787

Xu, H H; Liao, H; Eichmiller, F C

1998-12-01

351

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

352

Coupling between leaching and creep of concrete  

SciTech Connect

In a radioactive waste disposal, concrete containment structures must be studied over extended periods during which it is necessary to account for a possible degradation by calcium leaching due to on-site water. An experimental investigation is described where the effects of an accelerated calcium leaching process of concrete on creep of concrete are highlighted. The comparison with a creep test where the sample is immersed in water shows that leaching generates tertiary creep and rupture of the specimen. A Dirichlet series coupled to a mechanical damage are used to model the coupled tertiary creep. With this method we can evaluate the lifetime of concrete structures subjected to chemical and mechanical loading.

Torrenti, J.M. [LCPC, Paris (France); ENS Cachan, LMT (France)], E-mail: jean-michel.torrenti@lcpc.fr; Nguyen, V.H. [LAMI/Institut Navier/ENPC-LCPC, Marne la Vallee (France); Colina, H. [ATILH, Paris (France); Le Maou, F. [LCPC, Paris (France); Benboudjema, F. [ENS Cachan, LMT (France); Deleruyelle, F. [IRSN, DSU, SSIAD, BERIS, Fontenay-aux-Roses (France)

2008-06-15

353

Observation of zero creep in piezoelectric actuators  

NASA Astrophysics Data System (ADS)

Piezoelectric actuators are frequently used nowadays in a wide variety of positioning devices. Although very suitable for small displacements in the range of nm to several hundreds of ?m, the actuators always suffer from hysteresis and creep between the input voltage and resulting displacements. In scanning applications, the input voltage is often used as an indicator of the induced displacement. This procedure can result in a large position error depending on the amount of hysteresis and creep. In order to describe and control hysteretic systems various models for hysteresis have been published but little is known about relaxation and creep in piezo materials. In this paper we present detailed studies of the hysteretic behavior and piezo relaxation and creep. We have identified certain locations on the hysteresis loop that exhibit zero creep. From this observation, a more fundamental relation between the amount of creep and the local slope of the hysteresis loop and the virgin curve is presented. This observation could be useful in both open-loop and closed-loop position control, since it allows quantification of the creep. Futhermore, the experimentally observed relation between the creep and the hysteresis suggests a reduction of the creep for non-hysteretic transfers. First measurements on a system with reduced hysteresis support this hypothesis.

Koops, K. R.; Scholte, P. M. L. O.; de Koning, W. L.

354

Earthquakes and fault creep on the northern San Andreas fault  

USGS Publications Warehouse

At present there is an absence of both fault creep and small earthquakes on the northern San Andreas fault, which had a magnitude 8 earthquake with 5 m of slip in 1906. The fault has apparently been dormant after the 1906 earthquake. One possibility is that the fault is 'locked' in some way and only produces great earthquakes. An alternative possibility, presented here, is that the lack of current activity on the northern San Andreas fault is because of a lack of sufficient elastic strain after the 1906 earthquake. This is indicated by geodetic measurements at Fort Ross in 1874, 1906 (post-earthquake), and 1969, which show that the strain accumulation in 1969 (69 ?? 10-6 engineering strain) was only about one-third of the strain release (rebound) in the 1906 earthquake (200 ?? 10-6 engineering strain). The large difference in seismicity before and after 1906, with many strong local earthquakes from 1836 to 1906, but only a few strong earthquakes from 1906 to 1976, also indicates a difference of elastic strain. The geologic characteristics (serpentine, fault straightness) of most of the northern San Andreas fault are very similar to the characteristics of the fault south of Hollister, where fault creep is occurring. Thus, the current absence of fault creep on the northern fault segment is probably due to a lack of sufficient elastic strain at the present time. ?? 1979.

Nason, R.

1979-01-01

355

Creep and stress rupture of a mechanically alloyed oxide dispersion and precipitation strengthened nickel-base superalloy  

NASA Technical Reports Server (NTRS)

The creep and stress rupture behavior of a mechanically alloyed oxide dispersion strengthened (ODS) and gamma-prime precipitation strengthened nickel-base alloy (alloy MA 6000E) was studied at intermediate and elevated temperatures. At 760 C, MA 6000E exhibits the high creep strength characteristic of nickel-base superalloys and at 1093 C the creep strength is superior to other ODS nickel-base alloys. The stress dependence of the creep rate is very sharp at both test temperatures and the apparent creep activation energy measured around 760 C is high, much larger in magnitude than the self-diffusion energy. Stress rupture in this large grain size material is transgranular and crystallographic cracking is observed. The rupture ductility is dependent on creep strain rate, but usually is low. These and accompanying microstructural results are discussed with respect to other ODS alloys and superalloys and the creep behavior is rationalized by invoking a recently-developed resisting stress model of creep in materials strengthened by second phase particles.

Howson, T. E.; Tien, J. K.; Mervyn, D. A.

1980-01-01

356

Creep rupture mechanisms in annealed and overheated 7075 Al under multiaxial stress states  

Microsoft Academic Search

The creep deformation and rupture behavior of annealed and overheated 7075 A1 was investigated under uniaxial, biaxial, and\\u000a triaxial stress states. Examinations of samples prior to and after testing using optical microscopy, scanning electron microscopy\\u000a (SEM), and transmission electron microscopy (TEM) were also performed to develop a better understanding of the microstructural\\u000a mechanisms governing this behavior. These observations combined with

AHMADALI YOUSEFIANI; Farghalli A. Mohamed; James C. Earthman

2000-01-01

357

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

358

Failure processes of a body element as a result of creep-induced material damage  

Microsoft Academic Search

Shevchendo and Mazur and Belov indicate that calculations of creep-induced material damage in structural elements using Rabotnov`s damage function agree well with experimental data, if different long-term-strength criteria are used in selecting the equivalent stress as the tangential-stress intensity increases in the elements of the body: the criterion of maximum normal stress is used in the elastic stage of deformation,

Yu. N. Shevchenko; R. G. Terekhov; N. S. Braikovskaya; S. M. Zakharov

1994-01-01

359

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

360

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 (?1300°C) oxide melt is prepared in a SiC-crucible placed in

B. R Sehgal; R. R Nourgaliev; T. N Dinh

2002-01-01

361

Rate-dependent deformation of rocks in the brittle regime  

NASA Astrophysics Data System (ADS)

Rate-dependent brittle deformation of rocks, a phenomenon relevant for long-term interseismic phases of deformation, is poorly understood quantitatively. Rate-dependence can arise from chemically-activated, subcritical crack growth, which is known to occur in the presence of aqueous fluids. Here we attempt to establish quantitative links between this small scale process and its macroscopic manifestations. We performed a series of brittle deformation experiments in porous sandstones, in creep (constant stress) and constant strain rate conditions, in order to investigate the relationship between their short- and long-term mechanical behaviors. Elastic wave velocities measurements indicate that the amount of microcracking follows the amount of inelastic strain in a trend which does not depend upon the timescale involved. The comparison of stress-strain curves between constant strain rate and creep tests allows us to define a stress difference between the two, which can be viewed as a difference in energy release rate. We empirically show that the creep strain rates are proportional to an exponential function of this stress difference. We then establish a general method to estimate empirical micromechanical functions relating the applied stresses to mode I stress intensity factors at microcrack tips, and we determine the relationship between creep strain rates and stress intensity factors in our sandstone creep experiments. We finally provide an estimate of the sub-critical crack growth law parameters, and find that they match -within the experimental errors and approximations of the method- the typical values observed in independent single crack tests. Our approach provides a comprehensive and unifying explanation for the origin and the macroscopic manifestation of time-dependent brittle deformation in brittle rocks.

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

2013-12-01

362

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

363

An old question revisited: the mechanics of shallow creep events on strike-slip faults and their triggering by nearby earthquakes  

NASA Astrophysics Data System (ADS)

Tectonic displacement on faults can occur as seismic slip, continuous aseismic creep, or transient creep events. Shallow creep events on strike-slip faults can take place in a coupled process with earthquake afterslip, spontaneously, or be triggered by nearby earthquakes. Despite more than five decades of observations, the mechanics of shallow creep events and their implications for seismic hazard are still not fully understood. To understand the mechanics and triggering of creep events, we developed a physics-based model to simulate shallow creep events on a strike-slip fault with rate-and-state frictional properties that vary both in depth and along strike. Our 1D simulation shows that a simple 2-layer model as proposed by Bilham and Behr [1992] cannot explain both the rapid afterslip and shallow creep events that were observed on the Superstition Hills Fault following the 1987 earthquake. Therefore, we propose a 3-layer model that can reproduce all the known surface deformation observations, including the co-seismic slip, afterslip, and the creep events. Using the strike-slip fault model, we also study the triggering process of creep events, by a static, a dynamic or a combined stress perturbation induced on the fault by a nearby earthquake. Preliminary results show that the magnitude of the perturbation relative to the ambient stress level and the timing of perturbation are the important parameters. By developing state-of-the-art models and constraining parameters with rich datasets from the Salton Trough, we aim to transition from a conceptual understanding of fault creep towards a quantitative and predictive understanding of the physical mechanism of creep events on strike-slip faults.

Wei, M.; Liu, Y.; McGuire, J. J.

2012-12-01

364

Aging in a colloidal glass in creep flow: Time-stress superposition  

NASA Astrophysics Data System (ADS)

We study the aging behavior of aqueous laponite suspension, a model soft glassy material, in creep. We observe that the viscoelastic behavior is time dependent and is strongly influenced by the deformation field; the effect is known to arise due to aging and rejuvenation. We show that irrespective of the strength of the deformation field (shear stress) and age, when the imposed time scale is normalized with a dominating relaxation mode of the system, universal aging behavior is obtained, demonstrating time-stress superposition, a phenomenon that may be generic in a variety of soft materials.

Joshi, Yogesh M.; Reddy, G. Ranjith K.

2008-02-01

365

Aging in a Colloidal Glass in Creep Flow: Time-Stress Superposition  

E-print Network

In this work, we study ageing behavior of aqueous laponite suspension, a model soft glassy material, in creep. We observe that viscoelastic behavior is time dependent and is strongly influenced by the deformation field; the effect is known to arise due to ageing and rejuvenation. We show that irrespective of strength of deformation field (shear stress) and age, when imposed time-scale is normalized with dominating relaxation mode of the system, universal ageing behavior is obtained demonstrating time-stress superposition; the phenomena that may be generic in variety of soft materials.

Yogesh M. Joshi; G. Ranjith; K. Reddy

2007-10-28

366

A multilayer model of time dependent deformation following an earthquake on a strike-slip fault  

NASA Technical Reports Server (NTRS)

A multilayer model of the Earth to calculate finite element of time dependent deformation and stress following an earthquake on a strike slip fault is discussed. The model involves shear properties of an elastic upper lithosphere, a standard viscoelastic linear solid lower lithosphere, a Maxwell viscoelastic asthenosphere and an elastic mesosphere. Systematic variations of fault and layer depths and comparisons with simpler elastic lithosphere over viscoelastic asthenosphere calculations are analyzed. Both the creep of the lower lithosphere and astenosphere contribute to the postseismic deformation. The magnitude of the deformation is enhanced by a short distance between the bottom of the fault (slip zone) and the top of the creep region but is less sensitive to the thickness of the creeping layer. Postseismic restressing is increased as the lower lithosphere becomes more viscoelastic, but the tendency for the width of the restressed zone to growth with time is retarded.

Cohen, S. C.

1981-01-01

367

Block versus continuum deformation in the Western United States  

USGS Publications Warehouse

The relative role of block versus continuum deformation of continental lithosphere is a current subject of debate. Continuous deformation is suggested by distributed seismicity at continental plate margins and by cumulative seismic moment sums which yield slip estimates that are less than estimates from plate motion studies. In contrast, block models are favored by geologic studies of displacement in places like Asia. A problem in this debate is a lack of data from which unequivocal conclusions may be reached. In this paper we apply the techniques of study used in regions such as the Alpine-Himalayan belt to an area with a wealth of instrumental data-the Western United States. By comparing plate rates to seismic moment release rates and assuming a typical seismogenic layer thickness of 15 km it appears that since 1850 about 60% of the Pacific-North America motion across the plate boundary in California and Nevada has occurred seismically and 40% aseismically. The San Francisco Bay area shows similar partitioning between seismic and aseismic deformation, and it can be shown that within the seismogenic depth range aseismic deformation is concentrated near the surface and at depth. In some cases this deformation can be located on creeping surface faults, but elsewhere it is spread over a several kilometer wide zone adjacent to the fault. These superficial creeping deformation zones may be responsible for the palaeomagnetic rotations that have been ascribed elsewhere to the surface expression of continuum deformation in the lithosphere. Our results support the dominant role of non-continuum deformation processes with the implication that deformation localization by strain softening must occur in the lower crust and probably the upper mantle. Our conclusions apply only to the regions where the data are good, and even within the Western United States (i.e., the Basin and Range) deformation styles remain poorly resolved. Nonetheless, we maintain that block motion is the deformation style of choice for those continental regions where the data are best. ?? 1994.

King, G.; Oppenheimer, D.; Amelung, F.

1994-01-01

368

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

369

Enhancement of the Creep Resistance of Metals.  

National Technical Information Service (NTIS)

Creep data are reported for three materials titanium (6Al-4V), Haynes 188, and 321 steel. In all threee cases, a specimen which had been prestressed below the proportional limit and whose surface layer had been eliminated creeps at much lower rates compar...

I. R. Kramer, N. Balasubramanian

1971-01-01

370

Creep Cavitation in a Nickel Aluminide.  

National Technical Information Service (NTIS)

Intergranular cavities formed during creep of a nickel aluminide (Ni-23.5 Al-0.5 Hf-0.2 B, at. %) have been studied as a function of creep time and strain. Cavity growth rates as a function of cavity size have been evaluated from metallographically determ...

J. H. Schneibel, L. Martinez

1987-01-01

371

Creep Cavitation in a Nickel Aluminide.  

National Technical Information Service (NTIS)

A nickel aluminide with the composition Ni-23.5, Al-0.5 Hf-0.2 B (at. %) has been creep-tested in tension at constant load (initial stress 250 MPa, temperature 1033K). The creep rate reaches a minimum at a strain of approximately 0.3%. Its increase at lal...

J. H. Schneibel, L. Martinez

1986-01-01

372

EFFECT OF RADIATION ON CREEP OF POLYETHYLENE  

Microsoft Academic Search

An investigation was conducted of the influence of radiation on the ; creep of polyethylene in tension and compression. The influence of five ; radiation doses and four stress levels were considered in this study. The tests ; were conducted for periods of 1000 hr. Even for small doses of radiation, it was ; found that the creep resistance of

Joseph Marin; Paul B. Griesacker

1963-01-01

373

Literature review Precipitation in creep resistant austenitic  

E-print Network

Literature review Precipitation in creep resistant austenitic stainless steels T. Sourmail of precipitates. Although the precipitation processes have been studied extensively, there remain important profoundly in¯uence the evolution of the microstructure. This review focuses on precipitation in creep

Cambridge, University of

374

Flux Creep in Type-II Superconductors  

Microsoft Academic Search

We have made measurements of the evanescent decay of the irreversible magnetization induced by magnetic cycling of solid superconducting cylinders in order to elucidate the mechanisms of Anderson's thermally activated flux-creep process. A superconducting quantum interferometer device coupled to the creep specimen by a superconducting flux transformer made possible observations of flux changes with a resolution of one part in

M. R. Beasley; R. Labusch; W. W. Webb

1969-01-01

375

Comprehensive Database on Concrete Creep and Shrinkage  

E-print Network

Comprehensive Database on Concrete Creep and Shrinkage Zdenek P. Bazant and Guang-Hua Li Structural Database on Concrete Creep and Shrinkage Zdenek P. Bazant1 and Guang-Hua Li2 Abstract: As a sequel to the first large database created at Northwestern University in 1978, the paper presents a further

376

In vivo age- and sex-related creep of human lumbar motion segments and discs in pure centric tension.  

PubMed

In vivo creep of human lumbar motion segments and discs subject to pure centric tension is presented, in terms of aging, sex and disc level. Time-related elongations of segments L3-4, L4-5 and L5-S1 were measured during the usual 20 min long traction hydrotherapy of patients, by using a computerized subaqual ultrasound measuring method [Kurutz et al., 2002a. Orvosi Hetilap 143 (13), 673-684; Kurutz et al., 2003. Journal of Bioengineering and Biomechanics 5 (1), 67-92]. Elongation of segments was considered as a change of the distance between two adjacent spinous processes. Based on these experiments, in vivo creep of human lumbar FSUs was investigated in centric tension, in terms of sex, age and disc level. Three-parameter rheological models were used to determine viscoelastic tensile moduli of human lumbar FSUs and discs. From three time-related measured elongation values, in vivo damping constants with creep functions were calculated for each segment, in terms of sex, aging and disc level. It has been demonstrated that initial elastic elongations decrease, concerning stiffness increase with aging. Similarly, tensile creep elongations decrease, damping properties increase with aging. Former observations concerning the difference in deformation propagation of men and women in time, have been verified by means of creep analysis: although males have higher initial elastic deformability, due to a smaller damping of females, the deformation propagation of women overtakes men in creep process. This tendency is more significant with aging. Increasing damping was observed in distal direction, both for males and females. PMID:15925372

Kurutz, Marta

2006-01-01

377

Irradiation creep of vanadium-base alloys.  

SciTech Connect

A study of irradiation creep in vanadium-base alloys is underway with experiments in the Advanced Test Reactor (ATR) and the High Flux Isotope Reactor (HFIR) in the US. Test specimens are thin-wall sealed tubes with internal pressure loading. The results from the initial ATR irradiation at low temperature (200-300 C) to a neutron damage level of 4.7 dpa show creep rates ranging from {approx}0 to 1.2 x 10{sup {minus}5}/dpa/MPa for a 500-kg heat of V-4Cr-4Ti alloy. These rates were generally lower than reported from a previous experiment in BR-10. Because both the attained neutron damage levels and the creep strains were low in the present study, however, these creep rates should be regarded as only preliminary. Substantially more testing is required before a data base on irradiation creep of vanadium alloys can be developed and used with confidence.

Tsai, H.; Matsui, H.; Billone, M. C.; Strain, R. V.; Smith, D. L.

1998-05-18

378

Brittle-viscous deformation, slow slip, and tremor  

NASA Astrophysics Data System (ADS)

Geophysical observations have illuminated a spectrum of fault slip styles from continuous aseismic sliding to fast earthquake slip. We study exhumed intercalated lenses of oceanic crust and sedimentary rocks, deformed to high shear strains. Deformation was partitioned between fractured, rigid blocks, with lengths of tens to hundreds of meters, and surrounding metapelites characterized by interconnected phyllosilicate networks. Under inferred conditions of low effective stress at temperatures > 500°C, locally and transiently elevated shear strain rate in phyllosilicates deforming by dislocation creep can reach those needed for transient slow slip. Concurrently, increased matrix strain rate likely stimulates brittle failure in rigid lenses. The ubiquitous presence of quartz veins and microfractures within rigid material provides evidence for brittle deformation occurring coincident with viscous shearing flow. We suggest that geophysically observed tremor and slow slip may be a manifestation of strain partitioning, where deformation is accommodated viscously in a matrix enveloping rigid lenses.

Fagereng, Åke; Hillary, Graeme W. B.; Diener, Johann F. A.

2014-06-01

379

Deformation-induced accelerated dynamics in polymer glasses  

NASA Astrophysics Data System (ADS)

Molecular dynamics simulations are used to investigate the effects of deformation on the segmental dynamics in an aging polymer glass. Individual particle trajectories are decomposed into a series of discontinuous hops, from which we obtain the full distribution of relaxation times and displacements under three deformation protocols: step stress (creep), step strain, and constant strain rate deformation. As in experiments, the dynamics can be accelerated by several orders of magnitude during deformation, and the history dependence is entirely erased during yield (mechanical rejuvenation). Aging can be explained as a result of the long tails in the relaxation time distribution of the glass, and similarly, mechanical rejuvenation is understood through the observed narrowing of this distribution during yield. Although the relaxation time distributions under deformation are highly protocol specific, in each case they may be described by a universal acceleration factor that depends only on the strain.

Warren, Mya; Rottler, Jörg

2010-10-01

380

Activation volume for dislocation creep of forsterite and of iron-free enstatite  

NASA Astrophysics Data System (ADS)

A good knowledge of the mechanical behavior of olivine and enstatite at high pressure and high temperature is essential to model Earth upper mantle dynamics. In this study, we have performed deformation experiments on forsterite and on iron-free enstatite polycrystalline aggregates at upper mantle pressures and temperatures. Fine-grained forsterite powders were obtained by crushing a commercial forsterite in WC or zirconia grinders and dried at high temperature. Enstatite powders were synthesized by solid state reaction between mixed fine-grained powders of silica and forsterite in a conventional furnace. The powders were sintered by Spark Plasma Sintering (SPS) at 1000-1300°C and 100 MPa. We obtained aggregates with very low porosities (>99% dense), low water content and well equilibrated microstructures with mean grain sizes of a few microns. Compression deformation experiments were conducted on both types of aggregates in a D-DIA apparatus coupled with synchrotron white X-ray beam at the X17-B2 beamline at the National Synchrotron Light Source (Brookhaven National Laboratory, NY, USA). Strain and stress were measured in situ during deformation. Macroscopic strains were determined by measurements of sample shortening on X-ray radiographies. Stress and pressure were determined from the analysis of 5 to 8 diffraction peaks in the X-ray diffractograms of forsterite or enstatite collected on detectors arranged in different orientations with respect to the maximum principal stress. Experiments were performed at pressures between 3 and 11 GPa and temperatures ranging from 1100 to 1300°C. 14 different samples were deformed to total strains of up to 30% with deformation rates ranging from 8 10-6 to 6 10-5 s-1. Microstructures analyzed using high resolution SEM showed features characteristic of dislocation creep. Analysis of the deformation data for forsterite at 5-7 GPa yielded a stress exponent of 2.5 to 3 at different temperatures, similar to values obtained at room pressure (Relandeau, 1981). The apparent activation energy appears lower than for forsterite or San Carlos olivine at low pressures but is subject to large errors due to the diffficulty to control temperature precisely. An activation volume V* of 8 cm3/mol was determined at constant temperature (1100°C and 1200°C). Extrapolation of the data using V* to low pressures gives strengths that are consistent with those calculated using low pressure flow laws for olivine. Interestingly, this V* value is intermediate between the activation volumes for forsterite single crystals oriented for [100](010) slip, which dominates at low pressures and high temperatures, and those oriented for [001](010) slip, which becomes increasingly active at high pressures (15 and 0 cm3/mol, respectively; Raterron et al. 2011). Iron-free enstatite aggregates were deformed in the ortho- and high clino- enstatite fields. Results indicate that orthoenstatite has a stress exponent of 3-4. It tends to be stronger than forsterite, but the strength contrast between the two phases depends on pressure and temperature conditions. We will discuss the effect of pressure on the rheology of enstatite and on the relative viscosities of enstatite and forsterite.

Bystricky, M.; Bejina, F.; Baticle, J.

2013-12-01

381

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

382

Controlling factors for crack growth under creep conditions  

SciTech Connect

The creep crack growth behavior of a class I solid solution alloy, Cu-2.7 at.% Sn, has been investigated. The characteristics of creep crack growth of this class I solid solution alloy are found to be the same as those of pure metals and class II solid solution alloys. Crack growth involves a transient stage and a constant growth rate stage. The crack growth behavior in the transient stage can be characterized by the line integral C/sub 1/, while at steady state neither the path independent line integral C/sub 1/ nor the stress intensity factor applies. However, steady state crack growth can be characterized by the power release rate C/sub rho/ measured using a technique developed by Landes and Begley. The results suggest that the HRR stress field does not exist when extensive damage occurs and that steady state creep crack growth is not due to a stress singularity. Rather, crack growth appears to occur in a progressive manner because of a damage gradient which develops during the transient stage.

Wang, J.S.; Kim, Y.S.; Nix, W.D.

1987-10-01

383

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

384

Deformation and Seismicity Within the Salton Trough  

NASA Astrophysics Data System (ADS)

We examine ground deformation and seismicity within the Salton Trough of Southern California with Interferometric Synthetic Aperture Radar (InSAR). The Salton Trough is the landward extension of the spreading centers and transforms within the Gulf of California, and is associated with a higher heat flow than is found further north along the San Andreas system. The Salton Trough region is characterized by seismicity swarms similar to those that are characteristic of fault systems on the East Pacific Rise. Transient episodes of shallow and deep creep occur on the southern San Andreas, Imperial, and Superstition Hills faults, and pronounced afterslip and triggered slip are associated with local and regional earthquakes. Documentation of the temporal and spatial evolution of transient and triggered slip phenomena is vital to development of stress transfer and strain partitioning models explaining the dynamics of interactions within the North America-Pacific plate boundary. We determine the extent to which aseismic fault slip can be observed with SAR data, and perform specific investigations of the time periods surrounding several of the ~10 major earthquake swarms that have occurred within the Salton Trough since 1992. We seek to determine whether seismic swarm activity is associated with aseismic slip transients. Extensive agricultural activity in the region limits the utility of traditional InSAR, so we explore use of the persistent scatterer method to isolate roads, buildings and other features that retain interferometric coherence over time. Because a large number of SAR acquisitions are available (>30), and because of the large spatial and temporal variations in coherence between urban, agricultural, water-covered and desert landscapes within the scene, the Salton trough provides an interesting test scenario for the persistent scatterer method. We use spatially and temporally varying fault slip to model observed activity on the Superstition Hills fault. We explore methods for including the structure of atmospheric water vapor variations in inversions using phase observations at persistent scatterers. Although the source of deformation is equivocal, since extensive groundwater pumping can produce similar signals, our modeling provides a test scenario describing the types of confidence intervals that we can place on inversions of persistent scatterer data.

Lohman, R. B.; McGuire, J. J.

2005-12-01

385

The role of creep in stress strain curves for copper  

NASA Astrophysics Data System (ADS)

A model for plastic deformation in pure copper taking work hardening, dynamic recovery and static recovery into account, has been formulated using basic dislocation mechanisms. The model is intended to be used in finite-element computations of the long term behaviour of structures in Cu-OFP for storage of nuclear waste. The relation between the strain rate and the maximum flow stress in the model has been demonstrated to correspond to strain rate versus stress in creep tests for oxygen free copper alloyed with phosphorus Cu-OFP. A further development of the model can also represent the primary and secondary stage of creep curves. The model is compared to stress strain curves in compression and tension for Cu-OFP. The compression tests were performed at room temperature for strain rates between 5 × 10-5 and 5 × 10-3 s-1. The tests in tension covered the temperature range 20-175 °C for strain rates between 1 × 10-7 and 1 × 10-4 s-1. Consequently, it is demonstrated that the model can represent mechanical test data that have been generated both at constant load and at constant strain rate without the use of any fitting parameters.

Sandström, Rolf; Hallgren, Josefin

2012-03-01

386

Effects of processing history on the creep strength of Nb-1Zr  

SciTech Connect

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 temperatures required (e.g., >1200 K). The high power densities and temperatures at which these reactors must operate require the use of liquid-metal coolants. The alloy Nb-1 wt % (Nb-1Zr), 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 current space exploration missions. Useful lifetimes of these power systems are limited by creep deformation in the reactor core. Nb-1Zr sheet procured to American Society for Testing and Materials (ASTM) specifications for rector 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 much less of an effect 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, J.A.; Egner, L.K.

1993-06-01

387

Superplastic deformation in two microduplex stainless steels  

SciTech Connect

The deformation behavior and mechanisms of superplastic flow in two microduplex stainless steels (SuperDux64 and Nitronic 19D) were studied at {similar_to}0.7T{sub m}. The two steels differed in initial grain size by a factor of 3. Both steels exhibited solute-drag-controlled grain boundary sliding in a high temperature {gamma}+{delta} phase field. In a lower temperature {gamma}+{sigma} phase field, the fine-grained steel ({bar L}=5{mu}m) exhibited climb-controlled grain boundary sliding and the coarser- grained steel ({bar L}=15{mu}m) exhibited solute-drag-controlled slip creep.

Lesuer, D.R.; Nieh, T.G.; Syn, C.K. [Lawrence Livermore National Lab., CA (United States); Taleff, E.M. [Texas Univ., Austin, TX (United States)

1996-09-01

388

Experimental investigation of creep behavior of reactor vessel lower head  

SciTech Connect

The objective of the USNRC supported Lower Head Failure (LHF) Experiment Program at Sandia National Laboratories is to experimentally investigate and characterize the failure of the reactor pressure vessel (RPV) lower head due to the thermal and pressure loads of a severe accident. The experimental program is complemented by a modeling program focused on the development of a constitutive formulation for use in standard finite element structure mechanics codes. The problem is of importance because: lower head failure defines the initial conditions of all ex-vessel events; the inability of state-of-the-art models to simulate the result of the TMI-II accident (Stickler, et al. 1993); and TMI-II results suggest the possibility of in-vessel cooling, and creep deformation may be a precursor to water ingression leading to in-vessel cooling.

Chu, T.Y.; Pilch, M.; Bentz, J.H. [Sandia National Labs., Albuquerque, NM (United States); Behbahani, A. [NRC, Washington, DC (United States)

1998-03-01

389

Creep behavior of an A286 type stainless steel  

SciTech Connect

A model for steady state deformation of the commercial {gamma}' precipitation hardened alloy A286 at moderately high temperature is presented. This model is mainly based on the theory of thermally activated glide. The activation parameters such as the maximum free energy necessary to overcome obstacles to glide, the threshold stress for jerky glide and the activation volume of the rate controlling process are derived from experimental results and allowed rationalization of all the measurements in the range of stresses and temperatures investigated. Creep tests were carried out at constant stress in the range of 180-750 MPa at 600, 640, 670 and 700 deg. C in air. Transmission electron microscopy has permitted determination of the size of the {gamma}' particles and the average distance between them.

DeCicco, H. [Comision Nacional de Energia Atomica, Departamento Materiales, Av. del Libertador 8250, Buenos Aires C1429BNO (Argentina)]. E-mail: decicco@cnea.gov.ar; Luppo, M.I. [Comision Nacional de Energia Atomica, Departamento Materiales, Av. del Libertador 8250, Buenos Aires C1429BNO (Argentina); Raffaeli, H. [Comision Nacional de Energia Atomica, Departamento Materiales, Av. del Libertador 8250, Buenos Aires C1429BNO (Argentina); Di Gaetano, J. [Comision Nacional de Energia Atomica, Departamento Materiales, Av. del Libertador 8250, Buenos Aires C1429BNO (Argentina); Gribaudo, L.M. [Comision Nacional de Energia Atomica, Departamento Materiales, Av. del Libertador 8250, Buenos Aires C1429BNO (Argentina); Ovejero-Garcia, J. [Comision Nacional de Energia Atomica, Departamento Materiales, Av. del Libertador 8250, Buenos Aires C1429BNO (Argentina)

2005-08-15

390

Creep and brittle failure of a protein gel under stress  

E-print Network

Biomaterials such as protein or polysaccharide gels are known to behave qualitatively as soft solids and to rupture under an external load. Combining optical and ultrasonic imaging to shear rheology we show that the failure scenario of a protein gel is typical of brittle solids: after a power-law creep regime fully accounted for by linear viscoelasticity and homogeneous deformation, fractures nucleate and grow logarithmically perpendicularly to shear up to sudden rupture. A single equation accounting for those two successive processes nicely captures the full rheological response. The failure time follows a decreasing power-law with the applied shear stress strongly reminiscent of the Basquin law of fatigue for solids. These results are in excellent agreement with recent fiber-bundle models that include damage accumulation on elastic fibers and exemplify protein gels as model brittle soft solids.

Leocmach, Mathieu; Divoux, Thibaut; Manneville, Sébastien

2014-01-01

391

Crustal deformation in southern California using SAR interferometry  

USGS Publications Warehouse

By combining pairs of ERS-1/2 SAR images of Southern California spanning long time intervals (1-4 years), we were able to measure the rate of slow deformation processes along faults activated during the Landers 1992 earthquake. Interferograms revealed several centimeters of post-seismic rebound in step-overs of the 1992 break, with a characteristic decay rate of -280 days. We interpreted this process as due to pore fluid flow as pore pressure gradients caused by coseismic stress changes dissipate. The data also revealed evidence of after-slip on different sections of the fault. The southern branches of the 1992 break experienced surface creep producing sharp phase cuts hi the interferometric maps. The same approach was used in the Los Angeles basin, which is currently undergoing NS shortening at a rate of ???8 mm/yr. The tectonic signal in imerferograms of the Los Angeles basin is intermingled with signals due to other sources such as ground subsidence caused by oil and water withdrawal.

Peltzer, G.; Rosen, P.; Rogez, F.; Hudnut, K.

1997-01-01

392

Creep substructure formation in sodium chloride single crystals in the power law and exponential creep regimes  

NASA Technical Reports Server (NTRS)

Creep tests conducted on NaCl single crystals in the temperature range from 373 to 1023 K show that true steady state creep is obtained only above 873 K when the ratio of the applied stress to the shear modulus is less than or equal to 0.0001. Under other stress and temperature conditions, corresponding to both power law and exponential creep, the creep rate decreases monotonically with increasing strain. The transition from power law to exponential creep is shown to be associated with increases in the dislocation density, the cell boundary width, and the aspect ratio of the subgrains along the primary slip planes. The relation between dislocation structure and creep behavior is also assessed.

Raj, S. V.; Pharr, G. M.

1989-01-01

393

Creep of Refractory Fibers and Modeling of Metal and Ceramic Matrix Composite Creep Behavior  

NASA Technical Reports Server (NTRS)

Our concentration during this research was on the following subprograms. (1) Ultra high vacuum creep tests on 218, ST300 and WHfC tungsten and MoHfC molybdenum alloy wires, temperature range from 1100 K to 1500 K, creep time of 1 to 500 hours. (2) High temperature vacuum tensile tests on 218, ST300 and WHfC tungsten and MoHfC molybdenum alloy wires. (3) Air and vacuum tensile creep tests on polycrystalline and single crystal alumina fibers, such as alumina-mullite Nextel fiber, yttrium aluminum ganet (YAG) and Saphikon, temperature range from 1150 K to 1470 K, creep time of 2 to 200 hours. (4) Microstructural evaluation of crept fibers, TEM study on the crept metal wires, SEM study on the fracture surface of ceramic fibers. (5) Metal Matrix Composite creep models, based on the fiber creep properties and fiber-matrix interface zone formation.

Tewari, S.N.

1995-01-01

394

Creep in amalgam class V restorations.  

PubMed

The purpose of the investigation was to examine the creep rate in an amalgam Class V restoration. The stresses in a central bucco-lingual plane of a loaded bicuspid with a Class V restoration were computed with aid of the finite element method. When the stresses were known, the creep rate was calculated. The results showed that the creep rate of a load of 150 N varied between 0.6% and 3.5% per 104 s for amalgams with large differences between their viscoelastic behaviors. A gap between the restoration and the cavity margin will thus occur if a tooth is often heavily loaded. PMID:1068408

Dérand, T

1976-01-01

395

Simple Creep Test For Ceramic Fibers  

NASA Technical Reports Server (NTRS)

Simple bend-stress-relaxation test yields information on creep-related properties of polycrystalline ceramic fibers. Determination of these properties important part of efforts to develop ceramic composite materials that retain mechanical strength and resistance to creep at high temperatures. Present test measures effects of time, temperature, and applied strain on creep-related relaxation of bend stress in ceramic fiber of almost any diameter in almost any environment, without need for contact sensors. Degree of relaxation of bend stress determined from radii of curvature.

Dicarlo, James A.; Morscher, Gregory N.

1994-01-01

396

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 573–823 K (0.48–0.70Tm, 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 2×10-4s-1, while normal primary creep occurred under all other conditions. The creep

S. V. Raj

1991-01-01

397

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

398

Rates of surficial rock creep on hillslopes in Western colorado.  

PubMed

The average rate of downslope movement of rock fragments on shale hillslopes is directly proportional to the sine of the slope angle or that component of the gravitational force which acts parallel to the hillslope. The rates of surficial rock creep range from a few millimeters per year on a 3degree slope to almost 70 millimeters per year on a 40-degree slope, but these rates vary with natural variations in soil characteristics and microclimate, as well as with accidental disturbances. PMID:17737406

Schumm, S A

1967-02-01

399

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

400

Static recrystallization after hot deformation of ? iron  

Microsoft Academic Search

The dependence of static recrystallization characteristics on deformation and annealing conditions has been examined for vacuum\\u000a melted and zone-refined iron deformed in torsion at high temperatures in the ? range. The kinetics of recrystallization are\\u000a strongly accelerated by increasing deformation at low strains, but are virtually independent of strain in the “steady-state”\\u000a region of the high temperature flow curve. In

G. Glover; C. M. SELLARS

1972-01-01

401

Damage Assessment of Creep Tested and Thermally Aged Metallic Alloys Using Acousto-Ultrasonics  

NASA Technical Reports Server (NTRS)

In recent years emphasis has been placed on the early detection of material changes experienced in turbine powerplant components. During the scheduled overhaul of a turbine, the current techniques of examination of various hot section components aim to find flaws such as cracks, wear, and erosion, as well as excessive deformations. Thus far, these localized damage modes have been detected with satisfactory results. However, the techniques used to find these flaws provide no information on life until the flaws are actually detected. Major improvements in damage assessment, safety, as well as more accurate life prediction could be achieved if nondestructive evaluation (NDE) techniques could be utilized to sense material changes that occur prior to the localized defects mentioned. Because of elevated temperatures and excessive stresses, turbine components may experience creep behavior. As a result, it is desirable to monitor and access the current condition of such components. Research at the NASA Glenn Research Center involves developing and utilizing an NDE technique that discloses distributed material changes that occur prior to the localized damage detected by the current methods of inspection. In a recent study, creep processes in a nickel-base alloy were the life-limiting condition of interest, and the NDE technique was acousto-ultrasonics (AU). AU is an NDE technique that utilizes two ultrasonic transducers to interrogate the condition of a test specimen. The sending transducer introduces an ultrasonic pulse at a point on the surface of the specimen while a receiving transducer detects the signal after it has passed through the material. The goal of the method is to correlate certain parameters of the detected waveform to characteristics of the material between the two transducers. Here, the waveform parameter of interest is the attenuation due to internal damping for which information is being garnered from the frequency domain. The parameters utilized to indirectly quantify the attenuation are the ultrasonic decay rate as well as various moments of the frequency power spectrum. A new, user-friendly, graphical interface AU system was developed at NASA Glenn. This system is an all-inclusive, multifunction system that controls the sending and receiving ultrasonic transducers as well as all posttest signal analysis. The system's postprocessing software calculates the multiple parameters used to study the material of interest.

Gyekenyesi, Andrew L.; Kautz, Harold E.; Baaklini, George Y.

2001-01-01

402

Effect of hot corrosion on the creep properties of types 321 and 347 stainless steels  

NASA Astrophysics Data System (ADS)

Problems caused by hot corrosion and creep damage on superheater and reheater tubes of power plants using heavy oil as fuel inhibit the continuous service of the boilers and shorten their design lives. The