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1

Creep Deformation of Allvac 718Plus  

NASA Astrophysics Data System (ADS)

The creep deformation behavior of Allvac 718Plus was studied over the temperature range of 923 K to 1005 K (650 °C to 732 °C) at initial applied stress levels ranging from 517 to 655 MPa. Over the entire experimental temperature-stress regime this alloy exhibits Class M-type creep behavior with all creep curves exhibiting a decelerating strain rate with strain or time throughout primary creep. However, unlike pure metals or simple solid solution alloys, this gamma prime strengthened superalloy does not exhibit steady-state creep. Rather, primary creep is instantly followed by a long duration of accelerating strain rate with strain or time. These creep characteristics are common among the gamma prime strengthened superalloys. Allvac 718Plus also exhibits a very high temperature dependence of creep rate. Detailed TEM examination of the deformation structures of selected creep samples reveals dislocation mechanisms similar to those found in high volume fraction gamma prime strengthened superalloys. Strong evidence of microtwinning is found in several of the deformation structures. The presence of microtwinning may account for the strong temperature dependence of creep rate observed in this alloy. In addition, due to the presence of Nb and thus, grain boundary delta phase, matrix dislocation activity which is not present in non-Nb-bearing superalloys occurs in this alloy. The creep characteristics and dislocation mechanisms are presented and discussed in detail.

Hayes, Robert W.; Unocic, Raymond R.; Nasrollahzadeh, Maryam

2014-11-01

2

Creep Deformation of Allvac 718Plus  

NASA Astrophysics Data System (ADS)

The creep deformation behavior of Allvac 718Plus was studied over the temperature range of 923 K to 1005 K (650 °C to 732 °C) at initial applied stress levels ranging from 517 to 655 MPa. Over the entire experimental temperature-stress regime this alloy exhibits Class M-type creep behavior with all creep curves exhibiting a decelerating strain rate with strain or time throughout primary creep. However, unlike pure metals or simple solid solution alloys, this gamma prime strengthened superalloy does not exhibit steady-state creep. Rather, primary creep is instantly followed by a long duration of accelerating strain rate with strain or time. These creep characteristics are common among the gamma prime strengthened superalloys. Allvac 718Plus also exhibits a very high temperature dependence of creep rate. Detailed TEM examination of the deformation structures of selected creep samples reveals dislocation mechanisms similar to those found in high volume fraction gamma prime strengthened superalloys. Strong evidence of microtwinning is found in several of the deformation structures. The presence of microtwinning may account for the strong temperature dependence of creep rate observed in this alloy. In addition, due to the presence of Nb and thus, grain boundary delta phase, matrix dislocation activity which is not present in non-Nb-bearing superalloys occurs in this alloy. The creep characteristics and dislocation mechanisms are presented and discussed in detail.

Hayes, Robert W.; Unocic, Raymond R.; Nasrollahzadeh, Maryam

2015-01-01

3

High temperature deformation characteristics of Zirlo™ tubing via ring-creep and burst tests  

Microsoft Academic Search

Fuel cladding tubing acting as a barrier between coolant and radioactive fuel pellets in light water reactors undergo a combination of mechanical and thermal effects along with corrosive conditions during normal operations as well as accident situations, such as LOCA, etc. Therefore, the mechanical integrity of the cladding tubing is of critical importance. In this study, high temperature deformation characteristics

C. S. Seok; B. Marple; Y. J. Song; S. Gollapudi; I. Charit; K. L. Murty

2011-01-01

4

Spatial fluctuations in transient creep deformation  

NASA Astrophysics Data System (ADS)

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

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

2011-07-01

5

Fluctuations and Scaling in Creep Deformation  

NASA Astrophysics Data System (ADS)

The spatial fluctuations of deformation are studied in the creep in Andrade’s power law and the logarithmic phases, using paper samples. Measurements by the digital image correlation technique show that the relative strength of the strain rate fluctuations increases with time, in both creep regimes. In the Andrade creep phase characterized by a power-law decay of the strain rate ?t˜t-?, with ??0.7, the fluctuations obey ??t˜t-?, with ??0.5. The local deformation follows a data collapse appropriate for a phase transition. Similar behavior is found in a crystal plasticity model, with a jamming or yielding transition.

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

2010-09-01

6

Estimating creep deformation of glass-fiber-reinforced polycarbonate  

NASA Astrophysics Data System (ADS)

Thermoplastic resin and fiber-reinforced thermo-plastics (FRTPs) were used without post-cure treatment as “molded material.” For such materials, creep behavior and physical aging occur simultaneously. This study examined the creep behavior of polycarbonate (PC) and glass-fiber-reinforced polycarbonate (GFRPC) injection moldings, including the effect of physical aging and fiber content, and determined that the time temperature superposition principle could be applied to the creep behavior for different fiber contents. The effects of physical aging on creep behavior were evaluated quantitatively on pure resin and with various fiber contents without heat treatment. We found that the effect of physical aging could be evaluated with the proposed factor, “aging shift rate.” To discuss the linearity of viscoelasticity in FRTPs, this study used two shift factors: time and modulus shift factors. The fiber content affected creep behavior by both retarding and restraining it through changing the elastic modulus. This was shown by generating a grand master curve of creep compliance, which included the effects of time, temperature, and fiber content. Using the grand master curve of creep compliance and shift factors, it was possible to estimate the creep deformation of molded materials under varying conditions and fiber contents. The estimated creep deformation gave a very good fit to the experimental creep deformation.

Sakai, Takenobu; Somiya, Satoshi

2006-09-01

7

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

8

On the creep deformation of nickel foams under compression  

NASA Astrophysics Data System (ADS)

A finite-element computational strategy is developed to study the viscoplastic deformation mechanisms at work in a nickel foam sample under compression creep. The constitutive law for pure nickel accounts for both diffusional and dislocation creep mechanisms. The finite-element results show the competition between both mechanisms due to the strong heterogeneity of the stress distribution in the foam. The initiation of the viscoplastic buckling phenomenon leading to cell crushing in tertiary creep is illustrated. The overall model prediction is compared to the results of compression creep tests performed in vacuo at 900 °C. xml:lang="fr"

Burteau, Anthony; Bartout, Jean-Dominique; Bienvenu, Yves; Forest, Samuel

2014-10-01

9

Deformation and Fracture Mode during Small Punch Creep Tests  

NASA Astrophysics Data System (ADS)

The creep damage condition of components under elevated temperature is a requirement to guarantee safe life extension and continued operation. Destructive and/or non-destructive assessments are regularly applied to assess the remaining life of components during service. Uniaxial creep specimens have been traditionally employed for conventional tests to examine a series of high temperature creep properties. However the ability to remove these relatively large uniaxial specimens is limited due to the required size of the specimens with respect to the component dimensions. To overcome this shortcoming, small element testing techniques such as miniature creep (MC) and small punch creep (SPC) tests have recently been proposed to investigate creep properties. However their applications are limited as there is no established standard for the testing procedures and subsequent data evaluation. In order to aid the standardization of the SPC test method, this paper investigated the deformation and fracture of interrupted SPC tests. Results showed that the creep deformation in the SPC test could be classified into three conventional stages. Firstly, the crack of about 1mm in the diameter developed on the extended surface of the disc specimen at the end of the primary creep stage. Secondly, during secondary creep, circumferential cracking progressed in the through-thickness direction by about 0.1mm. Lastly, the tertiary creep region was extremely short and only appeared just before final fracture and failure. The result showed that the ratio of load in the SPC test to stress in the uniaxial creep proposed past was smaller than the experiment value. This result was due to the early crack formation in the disc specimen and the shear type crack development, and the difference of loading ball's diameter.

Kobayashi, Ken-Ichi; Kajihara, Ikumi; Koyama, Hideo; Stratford, Gavin C.

10

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

11

Oxidation induced localized creep deformation in Zircaloy-2  

NASA Astrophysics Data System (ADS)

Extensive plastic deformation in the metal underneath the oxide scale in autoclave tested Zircaloy-2 was studied using transmission electron microscopy (TEM). It was concluded that the plastic deformation is created by creep during oxidation, and is not caused by surface treatment, sample preparation or cooling from autoclave temperatures. Evidence of large strains was found in the form of dislocation tangles, dislocation patches and sub-grain formation, and also indications of twinning were found. The heavily deformed layer is around a few ?m thick and no obvious difference could be seen between alloys with different strength or different oxide thickness.

Tejland, Pia; Andrén, Hans-Olof

2014-01-01

12

Computer solution of two-dimensional elastoplastic and creep deformation problems  

Microsoft Academic Search

This paper presents a method for the calculation of a two-dimensional stress distribution ar, ~0' TrO, and the corresponding displacements U and V, under elastic, elastoplastic, and creep deformation conditions. The method can be applied using a program written for the Ural-2 computer. Stress concentrations and the stress vs strain (a i, at) characteristics of the material are taken into

A. V. Amel'yanchik; Yu. S. Gutorova; V. T. Lapteva

1970-01-01

13

The periodic output feedback control for creep characteristics of Ionic Polymer-Metal Composite (IPMC)  

Microsoft Academic Search

IPMC (Ionic Polymer-Metal Composite) is an artificial intelligent material, and the applied low driving voltage can make it produce a large deformation. People make full use of this feature to make into a variety of biomimetic robots by IPMC materials. However, this material has creep characteristics, which does not meet the needs of the operation accuracy. Thus, this limits greatly

Ting Zhang; Lina Hao; Chunlei Wang

2010-01-01

14

Creep deformation of an unirradiated zircaloy nuclear fuel cladding tube under dry storage conditions  

NASA Astrophysics Data System (ADS)

Measurements of creep deformation were made on an internally gas pressurized tubular Zircaloy-4 specimen with plugs welded to its ends. Creep tests were conducted at temperatures between 577 and 693 K for holding times of up to 26640 ks, to formulate the creep equation needed for predicting creep strain during dry storage of spent fuel. Discussion was also given to the difference of creep behaviour between irradiated and unirradiated fuel cladding, indicating that the equation derived is applicable for predicting creep strain of spent fuel cladding during dry storage.

Mayuzumi, Masami; Onchi, Takeo

1990-05-01

15

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

16

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

E-print Network

Reactor (ITER). In service, both these components will be exposed to an intense flux of fusion (14MeFinal 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

17

Experimental research on creep characteristics of Nansha soft soil.  

PubMed

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

Luo, Qingzi; Chen, Xiaoping

2014-01-01

18

Exhumation of UHP rocks: Elastic Deformation or Shearing Creep?  

NASA Astrophysics Data System (ADS)

Since 1967, Chinese geophysicists have carried out deep seismic reflection, magnetotellulic, geothermal and potential-field observations in Sulu area where the Chinese continental scientific drilling site is located. In order to perfect interpretation of these data, we have measured physical properties of main rocks in the area at room pressure/temperature laboratories. Geophysical data reveal both external and internal structures along the UHP belt, including the Triassic collisional and subduction structures, occurrence of UHP and HP rocks in the upper crust, eclogite occurrence and magnetization history, multi-cycle ductile shear zones, etc. These features are useful to understand processes of the UHP metamorphic dynamics. The crustal structures in the area are characterized by following facts. (a) Some seismic signatures of Triassic collisional and subduction structures are remained in the current crust, but most seismic signatures illustrate extensional structures formed after the Triassic event. (b) The UHP rock slices only appear within the upper crust and are surrounded by non-UHP rocks, the seismic patterns of the middle and lower crust are typically extensional. (c) Multiple superimposed ductile shear zones densely develop in the crust and coexist with UHP rocks. (d) In the upper crust, UHP and HP rock slumps are coexist and superimposed each other with contact zones mostly the shearing faults. (e) The strike-dip of eclogite bodies is different from the shearing faults. (f) There are two groups of eclogites that have different permanent magnetization directions and magnetization history, possibly implying rotation of the UHP rock slumps. The exhumation dynamics of the UHP rocks can hardly explained by theories based on elastic deformation, which could hardly result the crustal structures mentioned above. On the contrary, the exhumation of the UHP rocks in the Sulu area might strongly relate to rheological creeps, especially complex shearing creep motions occurred in the lithosphere and upper mantle in the late Triassic. As a matter of fact, evidences of viscous flow can be seen not only in the UHP rock samples and cores, but also in the lithospheric structures, such as the ductile shearing faults. Though we have not measured the shear creep compliance of the UHP rocks, we know that these rocks have high yield strength and high fracture energy. However, their enclosing rocks, such as gneisses or most of lower-crust rocks, could act in shearing creep manners with a considerable rate under high temperature and pressure, pushing the UHP rock slices exhumed onto the upper crust.

Yang, W.

2004-12-01

19

Mechanisms of creep deformation in gamma-based titanium aluminide alloys  

NASA Astrophysics Data System (ADS)

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

Ott, Eric A.

20

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

21

Creep deformation behavior and dislocation substructures of Mg–Y binary alloys  

Microsoft Academic Search

Compressive creep behavior and deformation substructures of binary Mg–Y alloys containing 0.2–2.4 mol% Y were investigated at 550–650 K under 4–200 MPa. The addition of yttrium improves creep strength of magnesium more efficiently than aluminum and manganese. This efficiency decreases with increasing temperature. The apparent activation energy for creep is substantially greater than that for self-diffusion in magnesium. Transmission electron

Mayumi Suzuki; Hiroyuki Sato; Kouich Maruyama; Hiroshi Oikawa

2001-01-01

22

Features controlling the early stages of creep deformation of Waspaloy  

NASA Technical Reports Server (NTRS)

A model has been presented for describing primary and second stage creep. General equations were derived for the amount and time of primary creep. It was shown how the model can be used to extrapolate creep data. Applicability of the model was demonstrated for Waspaloy with gamma prime particle sizes from 75 - 1000 A creep tested in the temperature range 1000 - 1400 F (538 - 760 C). Equations were developed showing the dependence of creep parameters on dislocation mechanism, gamma prime volume fraction and size.

Ferrari, A.; Wilson, D. J.

1974-01-01

23

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

24

Post- and interseismic deformation due to both localized and distributed creep at depth (Invited)  

NASA Astrophysics Data System (ADS)

There are two end-member representations of the ductile lithosphere (i.e., the lower crust and uppermost mantle) commonly used in models of post- and interseismic deformation around strike-slip faults: either (1) laterally homogeneous ductile layers, with sharp contrasts in rheological properties between the layers, in which creep is distributed; or (2) discrete extensions of the fault at depth in which creep is fully localized. The most realistic representation of the ductile lithosphere on earthquake cycle time scales likely falls between these two end-members. Researchers have considered both distributed and localized creep when interpreting post- and interseismic deformation, although the two mechanisms are most commonly treated separately, with the localized creep often approximated by kinematic slip on planar faults. There are a few noteworthy models that considered the feedback between both distributed and localized creep, although those models were largely constrained to 2D geometries of infinite length faults. The thickness of shear zones in the ductile lithosphere may be comparable to the locking depth of the fault, and the existence of a deep shear zone does not preclude the possibility that some distributed creep occurs in the surrounding lithosphere. Furthermore, variations in rheology, including both rheological models and their parameters, may be more subtle than the discrete contrasts typically assumed. In this presentation, we consider models of postseismic deformation following a finite length, strike-slip fault, as well as models of interseismic deformation around an infinite length strike-slip fault. Both sets of models are capable of localized and distributed creep at depth, and use Maxwell viscoelasticity. We show that the horizontal surface velocities during the early postseismic period are most sensitive to the viscosity of the shear zone; however during much of the interseismic period the shear zone is not apparent from the surface deformation, which is consistent with very large uniform viscosities in the ductile lithosphere. On the other hand, the vertical postseismic surface deformation is highly sensitive to the depth-dependent distribution of viscosities, regardless of whether the model contains purely distributed creep or also includes a component of localized creep. Hence, vertical postseismic deformation can discriminate vertical contrasts in viscosity, but is not a good discriminant of localized vs. distributed creep at depth. Models that contain components of both localized and distributed creep predict transient postseismic deformation, characterized by a fast relaxation phase followed by a slower relaxation phase, even when the model only contains steady Maxwell viscosities. This transience is equivalent to that predicted in models that approximate the ductile lithosphere with transient viscoelasticity, and we discuss the implication on the lithosphere rheology inferred from deformation following the 1997 Manyi, China, earthquake. Finally, we address the mechanism in which shear zones might develop under strike-slip faults and the implication of power-law creep rheologies.

Hetland, E. A.; Zhang, G.; Hines, T.

2013-12-01

25

Identification of wavelengths of strain heterogeneities during creep deformation in Carrara Marble  

NASA Astrophysics Data System (ADS)

We use a new technique combining microfabrication technology and compression tests to map the strain field at a micrometric scale in polycrystalline materials. The motivation of such high-resolution mapping is to identify characteristic wavelengths of heterogeneities for different plasticity mechanisms under varying creep conditions. The micro-strain mapping technique was applied to Carrara Marble under different deformation regimes, at a confining pressure of 300 MPa and temperatures ranging from 200 to 700 °C. In samples deformed to 10% strain in compression at 400°C, 500°C and 600°C, at a 3x10-5 s-1 strain rate, strain can be up to 5 times greater along twins and grain boundaries compared to the macroscopic strain accommodated over the entire sample. Strain averaged across a particular grain may vary by as much as 100%. Moreover, there is a gradual but clear change in the accommodation of strain, from twins to grain boundaries as temperature increases. For a fixed temperature of 600°C, varying strain from 10% to 30% does not appear to increase the wavelength of heterogeneities (i.e. the strain field does not homogenize). Macroscopically, strain hardening is minimal and there seems to be a constant generation of perturbations of similar wavelength.

Quintanilla-Terminel, Alejandra; Evans, Brian

2014-05-01

26

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

SciTech Connect

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

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

1996-05-15

27

Elevated temperature flow strength, creep resistance and diffusion welding characteristics of Ti-6Al-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 has been conducted. Two mill-processed forms of this alloy were examined. The forged material had been processed above the beta transus (approximately 1275 K) while the rolled form had been subjected to 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.

1979-01-01

28

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

29

Creep deformation and rupture properties of unirradiated Zircaloy-4 nuclear fuel cladding tube at temperatures of 727 to 857 K  

NASA Astrophysics Data System (ADS)

Creep deformation and rupture properties of an unirradiated Zircaloy-4 tube were examined at temperatures of 727 to 857 K to obtain data for evaluating spent fuel integrity under the off-normal dry storage condition. Creep tests were carried out on internally gas pressurized tubular specimens with end plugs welded to both ends. The hoop creep strain up to the steady-state creep region was given by the following equation: ? = 0.05{1- exp[-10( ?st) 0.51]} + ?st, where ?s = 1.02 × 10 5( E/ T) exp (4060 ?/ E) exp (- Q/ RT) ( S-1), t is time (s), E is the elastic modulus (MPa), T is the temperature (K), ? is the applied stress (MPa), R is the gas constant (= 8.314 J/mol K), and Q the apparent activation energy (233 kJ/mol). The total creep deformation curve over the accelerated creep region could also be presented by the equation expressed as a function of true stress formulated on the basis of constant stress creep data. It is inferred that the transition from the steady-state to the accelerated creep region occurs without changing the deformation mechanism. It was also shown that most of the creep strain to rupture exceeded 100% and Zircaloy-4 had an extremely ductile rupture property.

Mayuzumi, Masami; Onchi, Takeo

1990-12-01

30

GRAVITATIONAL CREEP OF ROCK SLOPES AS PRE-COLLAPSE DEFORMATION AND SOME PROBLEMS IN ITS MODELLING  

Microsoft Academic Search

Pre-collapse creep is a widespread component of complex slope movements. Its study requires a preliminary kinematic classification,\\u000a based on the relations between style and rate of gravitational dislocations and geological structure of rock massifs. Complexity\\u000a and variability of slope deformations determine the shortcoming of the traditional deterministic approach. Thus, probabilistic\\u000a analysis considering different scenarios and ‘event trees’ seems to be

A. A. VARGA; Volokolamskoye Shosse

31

Marine ice deformation experiments: an empirical validation of creep parameters  

NASA Astrophysics Data System (ADS)

Marine ice is increasingly recognized as an important component of ice shelves in Antarctica. Because it mainly accretes in "weak" locations, it plays a crucial role in ice shelf stability. Little is known however on the rheology of this particular material (low salinity, no bubbles, specific fabrics). We present marine ice deformation experiments in unconfined uniaxial compression at -10 °C, -6 °C, and -3 °C. Generally, marine ice samples confirm the value of n = 3 for Glen's power law. It also appears to behave systematically "harder" than artificial or meteoric isotropic ice samples used in the past, in the studied stress condition. Bulk salinity does not seem to have a significant impact on the viscosity. All deformation curves compare well with a generalized empirical temperature/viscosity relationship. They represent the first experimental validation of the lower boundary of this rheological relationship recommended for use in modeling ice dynamics.

Dierckx, Marie; Tison, Jean-Louis

2013-01-01

32

Influence of mineral fraction on the rheological properties of forsterite + enstatite during grain-size-sensitive creep: 2. Deformation experiments  

NASA Astrophysics Data System (ADS)

order to understand the effects of secondary minerals on the flow properties of rocks, we have conducted uniaxial compression experiments on polycrystalline forsterite (Fo) + enstatite (En) samples. At constant temperature and strain rate, the flow stress of the samples decreases with increasing enstatite volume fraction ( fEn) for samples with 0 < fEn < 0.5 and increases with increasing fEn for samples with 0.5 < fEn < 1. The values of the preexponential term, stress and grain size exponents, and activation energy in the constitutive equation for a wide range of fEn were determined. Samples with a low fEn(?0.03) deformed at strain rates of 2 × 10-5 to 2 × 10-4/s exhibit creep characteristics that correspond to dislocation-accommodated grain boundary sliding creep (i.e., stress exponent, n = 3), whereas diffusion-accommodated grain boundary sliding creep is typical of high fEn samples (i.e., stress exponent, n = 1). The change of flow strength as a function of fEn during grain-size-sensitive creep is primarily due to changes in grain size of both phases and secondarily due to changes in the volume fraction of phases with different flow strengths. Viscosities of all samples can be reproduced in a viscosity model that takes into account (1) the grain sizes estimated by the grain growth laws established in our part 1 paper and (2) flow laws determined for the individual phases, in this case, forsterite and enstatite. Furthermore, we demonstrate that our model can be extended to make predictions of viscosity in other mineral assemblages.

Tasaka, Miki; Hiraga, Takehiko; Zimmerman, Mark E.

2013-08-01

33

Creep behavior during the eutectoid transformation of albite: Implications for the slab deformation in the lower mantle  

NASA Astrophysics Data System (ADS)

In order to investigate effects of the post-spinel transformation on rheological behavior of descending slabs, we conducted simultaneous deformation and eutectoid reaction experiments using an analogue reaction from albite to jadeite and quartz by a deformation-DIA apparatus. Flow stress and transformed fraction were quantitatively obtained by in-situ X-ray observations during the constant strain rate deformation. The microstructures of recovered samples as well as the flow and kinetic data suggest sequential variation of the creep mechanism from dislocation creep of the transformed eutectoid colony followed by the grain-size sensitive creep in the degenerated eutectoid structure. Our study demonstrated that the creep behavior during the eutectoid transformation involves various processes than previously thought. The slabs may not be weaken promptly after entering into the lower mantle when the size of eutectoid colony is enough large, and keep their strength (or harden) over a period of time depending on the degeneration kinetics of the colony.

Doi, Naoko; Kato, Takumi; Kubo, Tomoaki; Noda, Masahiko; Shiraishi, Rei; Suzuki, Akio; Ohtani, Eiji; Kikegawa, Takumi

2014-02-01

34

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

35

Understanding creep in sandstone reservoirs - theoretical deformation mechanism maps for pressure solution in granular materials  

NASA Astrophysics Data System (ADS)

Subsurface exploitation of the Earth's natural resources removes the natural system from its chemical and physical equilibrium. As such, groundwater extraction and hydrocarbon production from subsurface reservoirs frequently causes surface subsidence and induces (micro)seismicity. These effects are not only a problem in onshore (e.g. Groningen, the Netherlands) and offshore hydrocarbon fields (e.g. Ekofisk, Norway), but also in urban areas with extensive groundwater pumping (e.g. Venice, Italy). It is known that fluid extraction inevitably leads to (poro)elastic compaction of reservoirs, hence subsidence and occasional fault reactivation, and causes significant technical, economic and ecological impact. However, such effects often exceed what is expected from purely elastic reservoir behaviour and may continue long after exploitation has ceased. This is most likely due to time-dependent compaction, or 'creep deformation', of such reservoirs, driven by the reduction in pore fluid pressure compared with the rock overburden. Given the societal and ecological impact of surface subsidence, as well as the current interest in developing geothermal energy and unconventional gas resources in densely populated areas, there is much need for obtaining better quantitative understanding of creep in sediments to improve the predictability of the impact of geo-energy and groundwater production. The key problem in developing a reliable, quantitative description of the creep behaviour of sediments, such as sands and sandstones, is that the operative deformation mechanisms are poorly known and poorly quantified. While grain-scale brittle fracturing plus intergranular sliding play an important role in the early stages of compaction, these time-independent, brittle-frictional processes give way to compaction creep on longer time-scales. Thermally-activated mass transfer processes, like pressure solution, can cause creep via dissolution of material at stressed grain contacts, grain-boundary diffusion and precipitation on pore walls. As a first step to better describe creep in sands and sandstones, we have derived a simple model for intergranular pressure solution (IPS) within an ordered pack of spherical grains, employing existing IPS rate models, such as those derived by Renard et al. (1999) and Spiers et al. (2004). This universal model is able to predict the conditions under which each of the respective pressure solution serial processes, i.e. diffusion, precipitation or dissolution, is dominant. In essence, this creates generic deformation mechanism maps for any granular material. We have used our model to predict the amount and rate of compaction for sandstone reservoirs, and compared our predictions to known subsidence rates for reservoirs around the world. This gives a first order-comparison to verify whether or not IPS is an important mechanism in controlling reservoir compaction.

Hangx, Suzanne; Spiers, Christopher

2014-05-01

36

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

37

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

PubMed

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

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

2014-07-01

38

Dissolution and Replacement Creep:A Significant Deformation Mechanism in Mid-crustal Rocks  

NASA Astrophysics Data System (ADS)

Zoning patterns and zoning truncations in metamorphic minerals in a granodioritic orthogneiss from the Bronson Hill terrane, New England indicate that strain and S-C fabrics in these rocks were produced by dissolution, precipitation, and replacement processes, even at epidote-amphibolite facies metamorphic conditions. The metamorphic fabric is defined by alternating layers and folia dominated by quartz, feldspars, and biotite + epidote. Zoning patterns in most metamorphic plagioclase, orthoclase, epidote, and sphene are truncated at boundaries normal to the shortening direction, suggesting dissolution. Interfaces of relict igneous orthoclase phenocrysts that face the shortening direction are embayed and replaced by biotite, epidote and myrmekitic intergrowths of plagioclase and quartz. Metamorphic plagioclase grains are also replaced by epidote. We interpret these microstructures to reflect strain-enhanced dissolution. The cores of many grains show asymmetric overgrowths with at least two generations of beards, all oriented on the ends of grains that face the extension direction. We interpret these textures to reflect precipitation of components dissolved by deformation enhanced dissolution. While biotite and quartz probably deformed by dislocation creep, the overall deformation was accommodated by dissolution perpendicular to the shortening direction, and precipitation parallel to it. These chemical processes must have been activated at lower stresses than the dislocation creep predicted from extrapolations of data from experiments in dry rocks. Thus wet crust is likely to be weaker than calculated from these experimental studies. Where such processes dominate, stress may not be high enough to reach brittle failure.

Wintsch, R. P.

2001-12-01

39

Dissolution and replacement creep: a significant deformation mechanism in mid-crustal rocks  

NASA Astrophysics Data System (ADS)

Zoning patterns and zoning truncations in metamorphic minerals in a granodioritic orthogneiss indicate that strain and S- C fabrics in these rocks were produced by dissolution, precipitation, and replacement processes, even at epidote-amphibolite facies metamorphic conditions. The metamorphic fabric is defined by alternating layers and folia dominated by quartz, feldspars, and biotite+epidote. Zoning patterns in most metamorphic plagioclase, orthoclase, epidote, and sphene are truncated at boundaries normal to the shortening direction, suggesting dissolution. Interfaces of relict igneous orthoclase phenocrysts that face the shortening direction are embayed and replaced by biotite, epidote, and myrmekitic intergrowths of plagioclase and quartz. Metamorphic plagioclase grains are also replaced by epidote. We interpret these microstructures to reflect strain-enhanced dissolution. The cores of many grains show asymmetric overgrowths with at least two generations of beards, all oriented on the ends of grains that face the extension direction. We interpret these textures to reflect precipitation of components dissolved by deformation-enhanced dissolution. While biotite and quartz probably deformed by dislocation creep, the overall deformation was accommodated by dissolution perpendicular to the shortening direction, and precipitation parallel to it. These chemical processes must have been activated at lower stresses than the dislocation creep predicted from extrapolations of data from experiments in dry rocks. Thus wet crust is likely to be weaker than calculated from these experimental studies.

Wintsch, R. P.; Yi, Keewook

2002-07-01

40

The applicability of the strain-hardening rule to creep deformation of Zircaloy fuel cladding tube under dry storage condition  

NASA Astrophysics Data System (ADS)

Variable stress and temperature creep tests were carried out at temperatures between 626 and 693 K for the Zircaloy-4 tubular specimens in the hoop stress regime 55 to 125 MPa to examine the applicability of the strain hardening rule to creep deformation of Zircaloy-4 fuel cladding tube. Results were compared with those of the constant temperature/stress tests, indicating that the strain hardening rule but not the time hardening rule can be applicable for predicting creep deformation of fuel cladding tube at temperatures tested. It is also suggested that although Zircaloy-4 fuel cladding tube tends to deform under multiaxial condition, it can satisfy the requirements for the strain hardening rule at temperatures of interest during dry storage condition.

Mayuzumi, Masami; Onchi, Takeo

1991-01-01

41

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

NASA Astrophysics Data System (ADS)

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

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

2010-05-01

42

Impression Creep Characteristics of a Cast Mg Alloy  

NASA Astrophysics Data System (ADS)

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

Kondori, B.; Mahmudi, R.

2009-08-01

43

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

44

Dislocation decorrelation and relationship to deformation microtwins during creep of a y' precipitate strengthened Ni-based superalloy  

SciTech Connect

The evolution of microtwins during high temperature creep deformation in a strengthened Ni-base superalloy has been investigated through a combination of creep testing, TEM characterization, theoretical modeling and computer simulation. Experimentally, microtwin nucleation sources were identified and their evolution was tracked by characterizing the deformation substructure at different stages of the creep deformation. Initially, deformation is highly localized around stress concentrators such as carbides, borides and serrated grain boundaries, which act as sources of a/2<110> matrix type dislocations. Due to microstructural effects such as fine channels between particles and low matrix stacking fault energies, the a/2<110> matrix dislocations dissociate into a/6<112> Shockley partials, which were commonly observed to be decorrelated from one another, creating extended intrinsic stacking faults in the matrix. As deformation progress further, microtwins form via partial dislocations cooperatively shearing both and phases on adjacent {111} glide planes. The TEM observations lead directly to an analysis of dislocation-precipitate interactions. Through phase field simulations and theoretical analysis based on Orowan looping, the important processes of dislocation dissociation and decorrelation are modeled in detail, providing comprehensive insight into the microstructural features and applied stress conditions that favor the microtwinning deformation mode in strengthened Ni-based superalloys.

Unocic, R. R.; Zhou, N.; Kovarik, Libor; Shen, C.; Wang, Y.; Mills, M. J.

2011-11-01

45

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

NASA Astrophysics Data System (ADS)

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

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

2013-09-01

46

Dislocation decorrelation and relationship to deformation microtwins during creep of a precipitate strengthened Ni-based superalloy  

SciTech Connect

The evolution of microtwins during high temperature creep deformation in a strengthened Ni-base superalloy has been investigated through a combination of creep testing, transmission electron microscopy (TEM), theoretical modeling, and computer simulation. Experimentally, microtwin nucleation sources were identified and their evolution was tracked by characterizing the deformation substructure at different stages of creep deformation. Deformation is highly localized around stress concentrators such as carbides, borides and serrated grain boundaries, which act as sources of a/2<110> matrix-type dislocations. Due to fine channels between particles, coupled with the low matrix stacking fault energy, the a/2<110> matrix dislocations dissociate into a/6<112> Shockley partials, which were commonly observed to be decorrelated from one another, creating extended intrinsic stacking faults in the matrix. Microtwins are common and form via Shockley partial dislocations cooperatively shearing both and phases on adjacent {111} glide planes. The TEM observations lead directly to an analysis of dislocation-precipitate interactions. Through phase field simulations and theoretical analyses based on Orowan looping, the important processes of dislocation dissociation and decorrelation are modeled in detail, providing comprehensive insight into the microstructural features and applied stress conditions that favor the microtwinning deformation mode in strengthened Ni-based superalloys.

Unocic, Raymond R [ORNL; Zhou, Ning [Ohio State University; Kovarik, Libor [Pacific Northwest National Laboratory (PNNL); Shen, Chen [GE Global Research; Wang, Yunzhi [Ohio State University; Mills, Michael J. [Ohio State University

2011-01-01

47

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

NASA Astrophysics Data System (ADS)

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

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

2011-12-01

48

Effects of cold rolling deformation on microstructure, hardness, and creep behavior of high nitrogen austenitic stainless steel  

NASA Astrophysics Data System (ADS)

Effects of cold rolling deformation on the microstructure, hardness, and creep behavior of high nitrogen austenitic stainless steel (HNASS) are investigated. Microstructure characterization shows that 70% cold rolling deformation results in significant refinement of the microstructure of this steel, with its average twin thickness reducing from 6.4 ?m to 14 nm. Nanoindentation tests at different strain rates demonstrate that the hardness of the steel with nano-scale twins (nt-HNASS) is about 2 times as high as that of steel with micro-scale twins (mt-HNASS). The hardness of nt-HNASS exhibits a pronounced strain rate dependence with a strain rate sensitivity (m value) of 0.0319, which is far higher than that of mt-HNASS (m = 0.0029). nt-HNASS shows more significant load plateaus and a higher creep rate than mt-HNASS. Analysis reveals that higher hardness and larger m value of nt-HNASS arise from stronger strain hardening role, which is caused by the higher storage rate of dislocations and the interactions between dislocations and high density twins. The more significant load plateaus and higher creep rates of nt-HNASS are due to the rapid relaxation of the dislocation structures generated during loading.

Sun, Shi-Cheng; Sun, Gui-Xun; Jiang, Zhong-Hao; Ji, Chang-Tao; Liu, Jia-An; Lian, Jian-She

2014-02-01

49

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

SciTech Connect

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

Lara-Curzio, E.

2001-01-30

50

Elevated Temperature Creep Deformation in Solid Solution <001> NiAL-3.6Ti Single Crystals  

NASA Technical Reports Server (NTRS)

The 1100 to 1500 K slow plastic strain rate compressive properties of <001> oriented NiAl-3.6Ti single crystals have been measured, and the results suggests that two deformation processes exist. While the intermediate temperature/faster strain rate mechanism is uncertain, plastic flow at elevated temperature/slower strain rates in NiAl-3.6Ti appears to be controlled by solute drag as described by the Cottrell-Jaswon solute drag model for gliding b = a(sub 0)<101> dislocations. While the calculated activation energy of deformation is much higher (approximately 480 kJ/mol) than the activation energy for diffusion (approximately 290 kJ/mol) used in the Cottrell-Jaswon creep model, a forced temperature compensated - power law fit using the activation energy for diffusion was able to adequately (greater than 90%) predict the observed creep properties. Thus we conclude that the rejection of a diffusion controlled mechanism can not be simply based on a large numerical difference between the activation energies for deformation and diffusion.

Whittenberger, J. Daniel; Noebe, Ronald D.; Darolia, Ram

2003-01-01

51

Stress-deformation relationship before the onset of accelerated creep at (0.5–0.65) T m for some austenite steels  

Microsoft Academic Search

Conclusions 1.An analysis has been made of the dependence of stress sa bringing on in a given time the transition to a third creep stage, and of the deformation in the first two periods of creep, on temperature in the interval 600–900°C and time t1+2 for four brands of austenite steel. It is shown that the relationship between time to

O. A. Bannykh

1970-01-01

52

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

53

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

54

Microbending losses in double-coated optical fibers caused by axial strain-induced creep deformation of polymeric coatings  

NASA Astrophysics Data System (ADS)

The viscoelastic behavior of commercial UV-cured polymeric coatings of optical fibers is evaluated using dynamic mechanic analysis. The results indicate that relaxation of stresses and/or strains in these coatings occurs by creep deformation. The axial strain-induced viscoelastic stresses in optical fibers are derived from the exact viscoelastic behavior of the polymeric coatings. Compressive radial stress on the glass fiber produces microbending losses, and therefore, microbending losses in double-coated optical fibers that are caused by axial strain-induced creep deformation of polymeric coatings are investigated. These microbending losses can be minimized by suitably selecting the thickness and physical properties of the polymeric coatings, as follows. The radius, Poisson's ratio, and strain ratio of the primary coating should be increased, but the Young's modulus and relaxation time of the primary coating should be decreased. The radius, Young's modulus, Poisson's ratio, and strain ratio of the secondary coating should be decreased, but the relaxation time of the secondary coating should be increased. When the thickness and physical properties of the polymeric coating are chosen to minimize the microbending loss, the thickness and Young's modulus of the secondary coatings should be large enough to withstand an external mechanical force.

Hsueh, Yu-Chun; Lai, Liang-Hsun; Tseng, Tzu-Fan; Wu, Jeng-Yue; Shiue, Sham-Tsong

2010-09-01

55

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

56

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

57

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

58

The effect of low angle boundary misorientation on creep deformation in the superalloy CM 247 LC  

NASA Astrophysics Data System (ADS)

The effect of low angle boundary misorientation on the creep properties of superalloy CM 247LC bicrystals has been investigated in the medium temperature - medium stress creep regime. Constant load tensile creep tests were performed on mixed Low Angle Boundary (LAB) samples with misorientations ranging from 3o-16o; the LABs where the boundaries were oriented approximately transverse to the tensile axis. Five repeats of each LAB sample were ruptured with an initial stress of 300 MPa and three repeats of each LAB sample were ruptured with an initial stress of 200 MPa, both at 950°C. A drastic decrease in creep rupture life and strain to failure was observed in bicrystals with misorientations greater than ˜10°. Fractography of the fracture surfaces indicated that a transition from ductile transgranular fracture to intergranular fracture coincided with the decrease in creep properties. The decrease in strain to failure was correlated to a decrease in the slip compatibility factor m'. Specimens of several misorientations were also interrupted prior to failure at strains of 2%, 5% and 10% and examined by electron microscopy techniques in an effort to better understand the sequences leading to failure. For samples that fractured intergranularly, voids formed adjacent to large MC carbides located at the LABs and propagated along the boundary, ultimately linking to cracks that initiated at the specimen edge. Electron Back Scattered Diffraction (EBSD) scans were performed and Crystal reference Orientation (CO) maps were generated from the partially crept specimens. An increase in misorientation from the crystal reference orientation was observed with increasing LAB misorientation for a given interrupted strain level indicative of the poorer slip compatibility at the higher misorientations Two bicrystals with nearly identical scalar misorientation, both ˜10°, exhibited surprisingly different behavior with one failing intergranularly at low strain to failure and the other failing transgranularly at high strain to failure; these differences were related to the different slip compatibilities as determined by an analysis of the nature of their misorientations. In addition, grain boundary migration was prevalent in the samples that fractured transgranularly, but was rarely observed on any specimen that fractured intergranularly. Based on the collective observations, it is concluded that (1) it is necessary to consider more than just the scalar misorientation when considering whether a single crystal containing LABs should be rejected and (2) characterization of the properties of superalloy bicrystals grown using traditional Bridgman methods is difficult due to the complex, non-planar nature of the resulting LABs that is associated with their dendritic growth.

Kirsch, Mathew

59

Effect of boron on creep characteristics in 9Cr-1.5Mo alloys  

NASA Astrophysics Data System (ADS)

For thick-section components such as headers and pipes of the power plants, high creep rupture strength and oxidation resistance are required. It is known that the addition of boron can improve the creep strength and oxidation resistance through the stabilization of M23C6 carbides in the vicinity of prior austenite grain boundaries. In this study, the effect of boron addition with the range of 0.0033~0.0133 wt% on the creep behavior of 9Cr-1.5Mo steel was investigated. Small punch creep tests were carried out to investigate the effect of boron addition on creep properties. Microstructure observation was performed to analyze the effect of boron addition on creep strength and rupture life. Also, the relationship between the minimum creep rate and the amount of boron addition were analyzed. The addition of boron is beneficial in lowering the steady-state creep rate.

Kim, Bumjoon; Yun, Haksu; Lee, Dongbok; Lim, Byeongsoo

2009-01-01

60

Characteristics of multipath effects in GPS dynamic deformation monitoring  

Microsoft Academic Search

The multipath has long been considered a major error source in GPS applications. The characteristics of the GPS signal multipath\\u000a effects are analyzed, based on which an experiment that considers the characteristics of dynamic deformation monitoring has\\u000a been carried out. The solution results of observation data in two successive days are processed by a method, which combines\\u000a the wavelet filtering

Huang Shengxiang; Jin Xiangsheng; Yang Baocen

2006-01-01

61

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

62

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

NASA Astrophysics Data System (ADS)

Around the perimeter of Antarctica, much of the ice sheet discharges to the ocean through floating ice shelves. The buttressing provided by ice shelves is critical for modulating the flux of ice into the ocean, and the presently observed thinning of ice shelves is believed to be reducing their buttressing capacity and contributing to the acceleration and thinning of the grounded ice sheet. However, relatively little attention has been paid to the role that fractures play in the flow and stability of ice shelves and their capacity to buttress the flow of grounded ice. Here, we develop an analytical framework for describing the role that fractures play in the creep deformation and buttressing capacity of ice shelves. We apply principles of continuum damage mechanics to derive a new analytical relation for the creep of an ice shelf as a function of ice thickness, temperature, material properties, resistive backstress and damage. By combining this analytical theory with an inverse method solution for the spatial rheology of an ice shelf, both backstress and damage can be calculated. We demonstrate the applicability of this new theory using satellite remote sensing and Operation IceBridge data for the Larsen C ice shelf, finding damage associated with known crevasses and rifts. We find that increasing thickness of mélange between rift flanks correlates with decreasing damage, with some rifts deforming coherently with the ice shelf as if completely healed. We quantify the stabilizing backstress caused by ice rises and lateral confinement, finding high backstress associated with two ice rises that likely stabilize the ice front in its current configuration. Though overall the ice shelf appears stable at present, the ice in contact with the Bawden ice rise is weakened by fractures, and additional damage or thinning in this area could portend significant change for the shelf. Using this new approach, field and remote sensing data can be utilized to monitor the structural integrity of ice shelves, their ability to buttress the flow of ice at the grounding line, and thus their indirect contribution to ice sheet mass balance and global sea level.

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

2013-07-01

63

Implications of Microstructural Studies of the SAFOD Gouge for the Strength and Deformation Mechanisms in the Creeping Segment of the San Andreas Fault  

NASA Astrophysics Data System (ADS)

The San Andreas Fault zone (SAF) in the vicinity of the San Andreas Fault Observatory at Depth (SAFOD)in central California is characterized by an average 21 mm/year aseismic creep and strain release through repeating M<3 earthquakes. Seismic inversion studies indicate that the ruptures occur on clusters of stationary patches making up 1% or less of the total fault surface area. The existence of these so-called asperity patches, although not critical in determining the fault strength, suggests interaction of different deformation mechanisms. What are the deformation mechanisms, and how do the mechanisms couple and factor into the current strength models for the SAF? The SAFOD provides core samples and geophysical data including cores from two shear zones where the main borehole casing is deforming. The studies so far show a weak fault zone with about 200m of low-permeability damage zone without anomalous temperature or high fluid pressure (Zoback et al. EOS 2010). To answer the above questions, we studied core samples and thin sections ranging in measured depths (MD) from 3059m to 3991m including gouge from borehole casing deformation zones. The methods of study included high resolution scanning and transmission electron microscopy, cathodoluminescence imaging, X-ray fluorescence mapping, and energy dispersive X-ray spectroscopy. The microstructural and analytical data suggest that deformation is by a coupling of cataclastic flow and pressure solution accompanied by widespread alteration of feldspar to clay minerals and other neomineralizations. The clay contents of the gouge and streaks of serpentinite are not uniformly distributed, but weakness of the creeping segment is likely to be due to intrinsically low frictional strength of the fault material. This conclusion, which is based on the overall ratio of clay/non-clay constituents and the presence of talc in the actively deforming zones, is consistent with the 0.3-0.45 coefficient of friction for the drill cuttings tested by others. We also considered weakening by diffusion-accommodated grain boundary sliding. There are two main trends in the microstructural data that provide a basis for explaining the creep rate and seismic activity: 1. Clay content of the gouge including serpentinite and talc increases toward the 1-3m wide borehole casing deformation zones, which are expected to be deforming at above the average creep rate 2. Evidence of pressure solution creep and fracture sealing is more abundant in the siltstone cataclasites than in the shale. Such rocks could act as rigid inclusions that are repeatedly loaded to seismic failure by creep of the surrounding clay gouge. Regular cycles of fracture and restrengthening by fracture sealing in and around the inclusions are thus expected. The inclusions may be viewed as asperity patches (or cluster of patches) that predominantly deform by pressure solution at below the average creep rate.

Hadizadeh, J.; Gratier, J. L.; Mittempergher, S.; Renard, F.; Richard, J.; di Toro, G.; Babaie, H. A.

2010-12-01

64

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

65

Correlation of Creep Behavior of Domal Salts  

SciTech Connect

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 temperature to produce several time increments (stages) of different creep conditions. Clearly, the ability to analyze these limited data and to correlate them with each other could be of considerable potential value in establishing the mechanical characteristics of salt domes, both generally and specifically. In any analysis, it is necessary to have a framework of rules to provide consistency. The basis for the framework is the Multimechanism-Deformation (M-D) constitutive model. This model utilizes considerable general knowledge of material creep deformation to supplement specific knowledge of the material response of salt. Because the creep of salt is controlled by just a few micromechanical mechanisms, regardless of the origin of the salt, certain of the material parameters are values that can be considered universal to salt. Actual data analysis utilizes the methodology developed for the Waste Isolation Pilot Plant (WIPP) program, and the response of a bedded pure WIPP salt as the baseline for comparison of the domal salts. Creep data from Weeks Island, Bryan Mound, West Hackberry, Bayou Choctaw, and Big Hill salt domes, which are all sites of Strategic Petroleum Reserve (SPR) storage caverns, were analyzed, as were data from the Avery Island, Moss Bluff, and Jennings salt domes. The analysis permits the parameter value sets for the domal salts to be determined in terms of the M-D model with various degrees of completeness. In turn this permits detailed numerical calculations simulating cavern response. Where the set is incomplete because of the sparse database, reasonable assumptions permit the set to be completed. From the analysis, two distinct response groups were evident, with the salts of one group measurably more creep resistant than the other group. Interestingly, these groups correspond well with the indirectly determined creep closure of the SPR storage caverns, a correlation that probably should be expected. Certainly, the results suggest a simple laboratory determination of the creep characteristics of a salt material from a dome site can indicate the relative behavior of any potential cavern placed within that dome.

Munson, D.E.

1999-02-16

66

Investigation of creep mechanical characteristics of femoral prostheses by simulated hip replacement  

PubMed Central

In order to provide creep mechanical parameters for the clinical application of both traditional and reserved anatomy femoral artificial joint replacements, simulated hip replacement femoral stress relaxation and creep experiments were performed. Twenty-four corpse femoral specimens were obtained, with 8 specimens being randomly assigned to the control group and 8 specimens being randomly assigned to the traditional prosthesis group. Our results showed that the retaining femoral neck prosthesis and traditional prosthesis groups have different stress relaxation and creep mechanical properties. PMID:23596489

LIU, GUANG-YAO; JIN, YAN; LI, PENG

2013-01-01

67

Characteristics of the Transition from Grain-Boundary Sliding to Solute Drag Creep in Superplastic AA5083  

NASA Astrophysics Data System (ADS)

Superplastic tensile ductility has been attained when specially-processed AA5083 materials are strained in tension at relatively high strain rates, in the range of the transition from grain-boundary sliding (GBS) to solute drag creep (SDC) control of deformation. Quick plastic forming (QPF) technology involves deformation at such strain rates, and the relative contributions of GBS and SDC to the strain during deformation in this strain rate regime have been examined in this investigation. The additive, independent contributions of GBS and SDC to the elevated temperature deformation of fine-grained materials are reviewed. The transition from GBS to SDC in grain-refined AA5083 materials was evaluated by several methods, including the assessment of initial transients during straining and of transients during strain-rate change tests; the strain-rate dependence of the flow stress; the dependence of ductility on strain rate; flow localization behavior and fracture mode; cavitation growth; the evolution of microstructure and microtexture during deformation; and comparison with phenomenological models for the GBS-to-SDC transition.

McNelley, Terry R.; Oh-Ishi, Keiichiro; Zhilyaev, Alexander P.; Swaminathan, Srinivasan; Krajewski, Paul E.; Taleff, Eric M.

2008-01-01

68

ACCEPT: a three-dimensional finite element program for large deformation elastic-plastic-creep analysis of pressurized tubes (LWBR/AWBA Development Program)  

SciTech Connect

ACCEPT is a three-dimensional finite element computer program for analysis of large-deformation elastic-plastic-creep response of Zircaloy tubes subjected to temperature, surface pressures, and axial force. A twenty-mode, tri-quadratic, isoparametric element is used along with a Zircaloy materials model. A linear time-incremental procedure with residual force correction is used to solve for the time-dependent response. The program features an algorithm which automatically chooses the time step sizes to control the accuracy and numerical stability of the solution. A contact-separation capability allows modeling of interaction of reactor fuel rod cladding with fuel pellets or external supports.

Hutula, D.N.; Wiancko, B.E.

1980-03-01

69

Effect of microstructure on creep deformation of 45XD TiAl alloy at low and high stresses  

Microsoft Academic Search

A stabilized fully lamellar (stabilized FL) structure and a nearly lamellar (NL) structure were prepared by selected heat treatments in a Ti–45Al–2Nb–2Mn (wt.%)+0.8vol.% TiB2 (45XD) alloy. Tensile creep tests were performed at 760°C using applied stresses of 138 and 207MPa. The stabilized FL structure exhibits a lower minimum creep rate and a longer rupture life compared to the NL structure

Hanliang Zhu; D. Y. Seo; K. Maruyama; P. Au

2008-01-01

70

Creep and Creep Rupture of Granitic Rocks  

NASA Astrophysics Data System (ADS)

A review is given of recent experimental studies of flow properties and processes of granitic rocks deformed over a wide range of physical conditions. Preliminary new creep data for Westerly granite, deformed to low strains, were obtained in dry compression tests in a Griggs solid pressure medium apparatus at 1.0 GPa confining pressure, temperatures from 470° to 765°C, constant stress differences of from 0.6 to 1.2 GPa, all in the ? quartz stability field. High-temperature transient creep data fit an exponential decay flow law very well and were also fit to a power law, for comparison with previous work, with the result ?t = 7 × 10-5 ?2.2 t0.5 exp (-30.5/RT · 10-3) for stress in MPa, where time is in seconds and E is in kcal/mole. Steady state creep results fit a power law ?s = 1.4 × 10-9 exp (-25.3/RT · 10-3)?2.9. Because of experimental uncertainties, differences in the activation energies and stress exponents for ?t and ?s are regarded as insignificant. The experiments and analyses indicate that high-temperature transient creep gives way to steady state creep at strains less than 1% and in short times. Steady state flow should thus dominate natural creep of granitic rocks at moderate to high temperatures. Preliminary optical and TEM analyses of the specimens indicate that these low creep strains are accommodated primarily by quartz, secondarily by micas, and little, if at all, by feldspars, as seems to be true also of several naturally deformed granitic rocks examined petrographically. The close accord of the activation energies for creep of granitic rocks observed here and in previous studies with those found for steady state creep of quartzite [Koch et al., 1980] also suggests that deformation of quartz controls the creep rate of granitic rocks. Activation energies for creep of feld-spars, under most favorable conditions for low energies [Tullis and Yund, 1979b], appear to be too high to account for the results.

Carter, Neville L.; Anderson, Douglas A.; Hansen, Francis D.; Kranz, Robert L.

71

Creep deformation and stress-induced structural disorder near Tg in a Zr55Al10Ni5Cu30 glassy alloy  

NASA Astrophysics Data System (ADS)

Creep deformation under a constant applied load in a Zr55Al10Ni5Cu30 glassy alloy at the glass transition region is investigated. At an initial stress, ?0, less than a critical stress, ?c=80 MPa, the glass shows a Newtonian flow. When ?0??c, the flow viscosity, ?, initially decreases and attains a minimum. It then increases as the true stress, ?, decreases with further deformation. The initial decrease in ? and the attendance of viscosity minimum are due to the stress-induced structural disorder and the structural equilibration with the applied stress, respectively. For stress, ?, less than the viscosity minimum stress, the stress dependence of viscosity, ?(?), curves all tend to merge together, and is fitted well with a master curve, ?(?), established previously for the steady-state flow under constant strain-rate experiments. These results render further support to the hypothesis of stress-induced structural disorder and the concept of fictive stress.

Kato, H.; Inoue, A.; Chen, H. S.

2001-12-01

72

Creep: Long-term Time-Dependent Rock Deformation in a Deep-sea Laboratory in the Ionian sea: a Pilot Study  

NASA Astrophysics Data System (ADS)

Time-dependent brittle rock deformation is of first-order importance for understanding the long-term behavior of water saturated rocks in the Earth's upper crust. Interpretation of results from traditional laboratory brittle creep experiments have generally been in terms of three individual creep phases; primary (decelerating), secondary (constant strain rate or quasi-steady-state) and tertiary (accelerating or unstable). The deformation may be distributed during the first two, but localizes onto a fault plane during phase three. More recently, models have been proposed that explain the trimodal shape of creep curves in terms of the competition between a weakening mechanism and a strengthening mechanism, with the weakening mechanism eventually dominating and leading to localized failure. However, a major problem is that it is difficult to distinguish between these competing mechanisms and models given the lower limit of strain rates achievable in laboratory experiments over practicable time scales. This study aims to address that problem directly by extending significantly the range of achievable strain rates through much longer-term experiments conducted in a deep-sea laboratory in the Ionian sea. The project takes advantage of a collaboration with the NEMO Group-INFN, a consortium that is developing a large volume (1 km3) deep-sea detector for high-energy (>1019 eV) cosmic neutrinos. A suitable test site has been identified, some 20km north-east of Catania in Sicily, at a depth of 2100m. Within the CREEP deformation apparatus, confining pressure is provided by the ambient water pressure (>22MPa), and the constant axial stress is provided by an actuator that amplifies this pressure. Measurement transducers and a data acquisition system are sealed internally, with power provided for up to 6 months by an internal battery pack. The great advantage of operating in the deep sea in this way is that the system is essentially passive, has few moving parts, and requires no maintenance. The apparatus is held in place by a disposable cast-iron anchor and supported above the seabed by a deep-sea buoyage system. On completion of each experiment, an acoustic release detaches from the anchor and allows the apparatus to float to the surface to be recovered by the oceanographic research vessel.

Meredith, P. G.; Boon, S.; Vinciguerra, S.; Bowles, J.; NEMO Group,.

2003-12-01

73

Creep of rocksalt  

NASA Astrophysics Data System (ADS)

A review is presented of the fundamental flow properties and processes in experimentally deformed natural and synthetic halite single crystals and polycrystalline aggregates. Included in the summary are discussions of: (a) microstructures induced during steady-state creep; (b) creep-rupture of rocksalt; (c) experiments associated with "Project Salt Vault" and more recent field studies; and (d) brine migration. A representative steady-state flow law determined for natural aggregates and maximum natural deviatoric stresses deduced from subgrain sizes are applied briefly to considerations of creep in waste repositories and of salt dome dynamics. While the mechanical behavior of rocksalt is probably better understood than for all other rock types, further investigations, especially on load path, stress history and creep-rupture are clearly mandated. Furthermore, additional investigations of brine migration and of bench and field-scale deformations are needed, the latter incorporating realistic rocksalt flow properties into numerical simulations of natural rock-mass response.

Carter, Neville L.; Hansen, Francis D.

1983-03-01

74

Experimental high-stress deformation and annealing of peridotite : simulating coseismic deformation and postseismic creep in the upper mantle of the oceanic lithosphere.  

E-print Network

??Deformations-Prozesse im oberen Mantel der ozeanischen Lithosphäre als Folge von Spannungsumverteilungen bei großen Erdbeben, wurden experimentell simuliert. Nicht-stationäre Deformations- und isostatische Annealings-Experimente wurden bei verschiedenen… (more)

Druiventak, Anthony

2012-01-01

75

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

76

Deterministic Multiaxial Creep and Creep Rupture Enhancements for CARES/Creep Integrated Design Code  

NASA Technical Reports Server (NTRS)

High temperature and long duration applications of monolithic ceramics can place their failure mode in the creep rupture regime. A previous model advanced by the authors described a methodology by which the creep rupture life of a loaded component can be predicted. That model was based on the life fraction damage accumulation rule in association with the modified Monkman-Grant creep rupture criterion. However, that model did not take into account the deteriorating state of the material due to creep damage (e.g., cavitation) as time elapsed. In addition, the material creep parameters used in that life prediction methodology, were based on uniaxial creep curves displaying primary and secondary creep behavior, with no tertiary regime. The objective of this paper is to present a creep life prediction methodology based on a modified form of the Kachanov-Rabotnov continuum damage mechanics (CDM) theory. In this theory, the uniaxial creep rate is described in terms of sum, temperature, time, and the current state of material damage. This scalar damage state parameter is basically an abstract measure of the current state of material damage due to creep deformation. The damage rate is assumed to vary with stress, temperature, time, and the current state of damage itself. Multiaxial creep and creep rupture formulations of the CDM approach are presented in this paper. Parameter estimation methodologies based on nonlinear regression analysis are also described for both, isothermal constant stress states and anisothermal variable stress conditions This creep life prediction methodology was preliminarily added to the integrated design code CARES/Creep (Ceramics Analysis and Reliability Evaluation of Structures/Creep), which is a postprocessor program to commercially available finite element analysis (FEA) packages. Two examples, showing comparisons between experimental and predicted creep lives of ceramic specimens, are used to demonstrate the viability of Ns methodology and the CARES/Creep program.

Jadaan, Osama M.

1998-01-01

77

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

78

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

79

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

80

A Fictive Stress Model Calculation of Creep Deformation of Zr-based Bulk Metallic Glass in the Glass Transition Region under a Constant Load  

NASA Astrophysics Data System (ADS)

A model calculation based on the fictive stress is conducted on the creep deformation of a Zr55Al10Ni5Cu30 bulk metallic glass near the glass transition temperature under a constant applied load. The model successfully reproduces qualitatively the main features associated with creep viscoelastic behavior at various initial applied stresses, ?0. Whenever the value of ?0 exceeds the critical flow stress, ?c ({=}80 MPa), the flow stress curve, log?-log t, shows a dip due to stress-induced softening, and the stress dependent viscosity, ?(?), initially decreases. It attains a minimum value, ?min(?min), as the glass attains an equilibrium structure corresponding to the imposed stress, ?. For stress, ?, less than the viscosity minimum stress, the ?(?) curves all decrease and tend to merge together, and may be fit with a master curve established previously. This reveals that the model curves depend mainly on the choice of structural relaxation time, ?fic, and little on the value of Young’s modulus used in a simple Maxwell model calculation. We found a systematic deviation between the model and experimental curves, such that the model tends to overestimate the structural softening in case with smaller initial applied stress. The cause of this deviation is unclear and is a subject for future studies.

Kato, Hidemi; Inoue, Akihisa; Chen, Ho-Sou

2004-12-01

81

Room temperature creep deformation and its effect on yielding behaviour of a line pipe steel with discontinuous yielding  

Microsoft Academic Search

A study was conducted to understand post-yield creep behaviour and its effect on the subsequent tensile behaviour of X-52 line pipe steel at room temperature. As a result of the carbon-locking effect, this steel exhibits a distinct yield point followed by a range of discontinuous yielding. Although normally not observed during re-loading after the first yielding, there was a yield

Sheng-Hui Wang; Weixing Chen

2001-01-01

82

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

83

Creep and creep-rupture behavior of Alloy 718  

SciTech Connect

Data obtained from creep and creep-rupture tests conducted on 18 heats of Alloy 718 were used to formulate models for predicting high temperature time dependent behavior of this alloy. Creep tests were conducted on specimens taken from a number of commercial product forms including plate, bar, and forgoing material that had been procured and heat treated in accordance with ASTM specifications B-670 or B-637. Data were obtained over the temperature range of 427 to 760{degree}C ad at test times to about 87,000 h. Comparisons are given between experimental data and the analytical models. The analytical models for creep-rupture included one based on lot-centering regression analysis and two based on the Minimum Commitment Method. A master'' curve approach was used to develop and equation for estimating creep deformation up to the onset of tertiary creep. 11 refs., 13 figs.

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

1991-01-01

84

Creep and creep fracture of zirconium and zirconium alloys  

NASA Astrophysics Data System (ADS)

The creep and creep failure mechanisms for zirconium and zirconium alloys have not been established, yet these properties are required to establish safe conditions for the interim dry storage of spent nuclear fuel. The purpose of this research, then, is to determine the relevant creep and creep fracture mechanisms controlling the deformation and failure of zirconium and zirconium alloys at elevated temperatures. Currently, the maximum allowable temperatures for the storage of spent nuclear fuel are defined by the Nuclear Regulatory Commission based on a limited set of experimental data. Recent changes in regulations will be evaluated and recommendations made regarding their applicability. Various studies in the past have reported that zirconium and zirconium alloys exhibit anomalous creep properties. A detailed analysis of the creep properties of zirconium and zirconium alloys is presented based on an extensive literature review. Next, developments in creep fracture phenomena in engineering materials over the past several decades will be discussed and related to the creep fracture of zirconium alloys. As will be discussed, the mechanism for plasticity can be intimately tied to the fracture mechanism. The results of uniaxial creep tests on zirconium at temperatures of 350--700°C and stresses of 8--70 MPa and uniaxial creep tests on Zircaloy-2 at temperatures of 300--600°C and stresses of 24--382 MPa and subsequent microstructural investigation using a scanning electron microscope will be discussed, particularly as relevant to the fracture mechanisms for this alloy.

Hayes, Troy Allyn

85

Creep and creep rupture of strongly reinforced metallic composites  

NASA Technical Reports Server (NTRS)

A creep and creep damage theory is presented for metallic composites with strong fibers. Application is to reinforced structures in which the fiber orientation may vary throughout but a distinct fiber direction can be identified locally (local transverse isotropy). The creep deformation model follows earlier work and is based on a flow potential function that depends on invariants reflecting stress and the material symmetry. As the focus is on the interaction of creep and damage, primary creep is ignored. The creep rupture model is an extension of continuum damage mechanics and includes an isochronous damage function that depends on invariants specifying the local maximum transverse tension and the maximum longitudinal shear stress. It is posited that at high temperature and low stress, appropriate to engineering practice, these stress components damage the fiber/matrix interface through diffusion controlled void growth, eventually causing creep rupture. Experiments are outlined for characterizing a composite through creep rupture tests under transverse tension and longitudinal shear. Application is made to a thin-walled pressure vessel with reinforcing fibers at an arbitrary helical angle. The results illustrate the usefulness of the model as a means of achieving optimal designs of composite structures where creep and creep rupture are life limiting.

Robinson, D. N.; Binienda, W. K.; Miti-Kavuma, M.

1990-01-01

86

Elastic deformation effects on aerodynamic characteristics for a high-aspect-ratio supercritical-wing model  

NASA Technical Reports Server (NTRS)

The results of an investigation of the deformations of a high-aspect-ratio, force/pressure, supercritical-wing model during wind tunnel tests and the effects these deformations have on the wing aerodynamics are presented. A finite element model of the wing was developed, and then, for conditions corresponding to wind tunnel test points, experimental aerodynamic loads and theoretical aerodynamic loads were applied to the finite element model. Comparisons were made between the results of these load conditions for changes in structural deflections and for changes in aerodynamic characteristics. The results show that the deformations are quite small and that the pressure data are not significantly affected by model deformation.

Watson, J. J.

1982-01-01

87

Transient Creep of a Composite Lower Crust. 2; A Polymineralic Basis for Rapidly Evolving Postseismic Deformation Modes  

NASA Technical Reports Server (NTRS)

Postseismic horizontal strain and displacement following the June 28, 1992, Landers, California, earthquake (M(sub W) 7.3) is broad scale and cannot be explained solely by delayed afterslip located at the rupturing fault trace. Both the observed strain at Pifion Flat Observatory (PFO) and observed Global Positioning System receiver velocities evolve rapidly after the Landers-Big Bear earthquake sequence. The observed exponential decay of these motions, with timescales of 4-34 days, may reflect a soft creep rheology in the lower crust and brittle-ductile transition zone or even within the seismogenic crust itself. Here a simple model of a two-dimensional screw dislocation in a layered Maxwell viscoelastic Earth is employed in conjunction with a composite rheology to demonstrate that the short timescale transient response modes (approx. = 4-34 days) are consistent with the behavior of a biviscous lower crust. The lowest viscosity of this system is derivable from laboratory experimental data on the long-term creep of natural quarztites, and the highest viscosity is consistent with isostasy-related lower crustal flow in a continental extensional tectonic environment. The model predicts significant stress relaxation at the base of the seismogenic crust. Near the base of the seismogenic zone, and about 4 km away from the mainshock, the rate of predicted relaxation is of the order of 0.01 MPa/ d during the first 20 days of postseismic flow. Oblate spheroidal inclusions at 5% concentration levels that are both aligned and fairly flat in shape and that have a viscosity of 3-4 x 10(exp 15) Pa s are consistent with both the amplitude and decay time of horizontal crustal strain observed at PFO after the Landers mainshock. It is speculated that the structures exposed in cross sections and in seismic reflection profiles of the lower crust that have mylonitic associations are, in part, the cause of such rapid postseismic evolution in southeastern California. Unmylonitized quartz-rich rock at sufficiently elevated temperatures could also contribute to the rapid decay modes.

Ivins, Erik R.

1996-01-01

88

Effects of Dissolution-Precipitation Creep on the Crystallographic Preferred Orientation of Quartz Within the Purgatory Conglomerate, RI.  

E-print Network

??Crystallographic Preferred Orientations (CPO) are common in deformed rocks, and usually result from crystal plastic deformation by dislocation creep. Whether deformation mechanisms that occur at… (more)

McPherren, Eric

2010-01-01

89

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

NASA Astrophysics Data System (ADS)

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

Sakai, Takenobu; Somiya, Satoshi

2011-08-01

90

Influence of deformation velocity on the limiting characteristics of rocks  

Microsoft Academic Search

Conclusions  \\u000a \\u000a \\u000a \\u000a 1. \\u000a \\u000a An apparatus and procedures have been developed, enabling us to obtain the complete “stress-strain” diagrams, including the\\u000a limiting field for extremely brittle rocks during variations in the relative deformation velocities in the range from 10?8 to 10?1 sec?1.\\u000a \\u000a \\u000a \\u000a \\u000a 2. \\u000a \\u000a Four varieties of rocks have been tested under conditions of uniaxial compression and we have established the absence of

A. N. Stavrogin; B. G. Tarasov; E. D. Fevzner

1982-01-01

91

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

92

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

Microsoft Academic Search

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

Sheng-Hui Wang; Weixing Chen

2002-01-01

93

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

94

Deterministic and Probabilistic Creep and Creep Rupture Enhancement to CARES/Creep: Multiaxial Creep Life Prediction of Ceramic Structures Using Continuum Damage Mechanics and the Finite Element Method  

NASA Technical Reports Server (NTRS)

High temperature and long duration applications of monolithic ceramics can place their failure mode in the creep rupture regime. A previous model advanced by the authors described a methodology by which the creep rupture life of a loaded component can be predicted. That model was based on the life fraction damage accumulation rule in association with the modified Monkman-Grant creep ripture criterion However, that model did not take into account the deteriorating state of the material due to creep damage (e.g., cavitation) as time elapsed. In addition, the material creep parameters used in that life prediction methodology, were based on uniaxial creep curves displaying primary and secondary creep behavior, with no tertiary regime. The objective of this paper is to present a creep life prediction methodology based on a modified form of the Kachanov-Rabotnov continuum damage mechanics (CDM) theory. In this theory, the uniaxial creep rate is described in terms of stress, temperature, time, and the current state of material damage. This scalar damage state parameter is basically an abstract measure of the current state of material damage due to creep deformation. The damage rate is assumed to vary with stress, temperature, time, and the current state of damage itself. Multiaxial creep and creep rupture formulations of the CDM approach are presented in this paper. Parameter estimation methodologies based on nonlinear regression analysis are also described for both, isothermal constant stress states and anisothermal variable stress conditions This creep life prediction methodology was preliminarily added to the integrated design code CARES/Creep (Ceramics Analysis and Reliability Evaluation of Structures/Creep), which is a postprocessor program to commercially available finite element analysis (FEA) packages. Two examples, showing comparisons between experimental and predicted creep lives of ceramic specimens, are used to demonstrate the viability of this methodology and the CARES/Creep program.

Jadaan, Osama M.; Powers, Lynn M.; Gyekenyesi, John P.

1998-01-01

95

Strength and deformation characteristics of Alaskan offshore silts  

SciTech Connect

A comprehensive series of undrained shear tests were performed on representative samples of Alaskan silts in both the normally consolidated and overconsolidated state. The type of tests performed were triaxial compression and extension, torvane and miniature laboratory vane tests. It was found that the Alaskan silt exhibited dilative behavior during undrained shear. Also, the silt is highly anisotropic with respect to the stress-strain characteristics and the undrained shear strength. Sample disturbance reduced the measured strength in the unconsolidated undrained tests. The normalized strength parameter was shown to vary from one silt to another. The importance of evaluating the properties of each new silt deposit are described.

Fleming, L.N.

1985-01-01

96

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

97

Bond characteristics of plain and deformed bars in lightweight pumice concrete  

Microsoft Academic Search

An investigation is conducted to determine the bond characteristics of plain and deformed reinforcing bars in lightweight volcanic pumice concrete (VPC) and normal concrete (NC). VPC and NC are manufactured by incorporating crushed lightweight pumice and gravel aggregates, respectively. Bond tests are conducted on 112 pullout specimens to study the influence of type of concrete (NC or VPC), type of

Khandaker M. Anwar Hossain

2008-01-01

98

Actuating characteristic of laminated PVDF actuators used on a beam with large deformation  

Microsoft Academic Search

Actuating characteristic of laminated PVDF actuator (LPA) partially covered on a beam is studied in this paper. Considering large deformation of the beam, coupled dynamic equations of the system are derived based on Hamilton principle. The formulas of nonlinear actuating forces are obtained and the parametric study is then conducted to evaluate the effects of geometric and physical properties of

Ya-hong Zhang; Shi-lin Xie; Xi-nong Zhang

2008-01-01

99

Elevated temperature flow strength, creep resistance and diffusion welding characteristics of Ti6Al2Nb1Ta0.8Mo  

Microsoft Academic Search

A study of the flow strength, creep resistance and diffusion welding characteristics of the titanium alloy Ti-6Al-2Nb-1Ta-0.8Mo\\u000a has been conducted. Two mill-processed forms of this alloy were examined. The forged material had been essentially processed\\u000a above the beta transus (?1275 K) while the rolled form had been subjected to work below the beta transus. Between 1150 and\\u000a 1250 K, the

J. Daniel Whittenberger; Thomas J. Moore

1979-01-01

100

Creeping eruption  

MedlinePLUS

... burrow into your skin. They cause an intense inflammatory response that leads to a rash and severe itching. Creeping eruption is more common in countries with warm climates. In the United States, the southeast has the highest rates of infection. ...

101

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

SciTech Connect

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

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

2010-01-15

102

Creep behavior of uranium carbide-based alloys  

NASA Technical Reports Server (NTRS)

The present work gives the results of experiments on the influence of zirconium carbide and tungsten on the creep properties of uranium carbide. The creep behavior of high-density UC samples follows the classical time-dependence pattern of (1) an instantaneous deformation, (2) a primary creep region, and (3) a period of steady-state creep. Creep rates for unalloyed UC-1.01 and UC-1.05 are several orders of magnitude greater than those measured for carbide alloys containing a Zr-C and/or W dispersoid. The difference in creep strength between alloyed and unalloyed materials varies with temperature and applied stress.

Seltzer, M. S.; Wright, T. R.; Moak, D. P.

1975-01-01

103

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

104

Constitutive modeling of creep of single crystal superalloys  

E-print Network

In this work, a constitutive theory is developed, within the context of continuum mechanics, to describe the creep deformation of single crystal superalloys. The con- stitutive model that is developed here is based on the fact that as bodies deform...

Prasad, Sharat Chand

2006-10-30

105

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

106

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

SciTech Connect

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

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

1991-01-01

107

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

NASA Astrophysics Data System (ADS)

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

Gribb, Tye Travis

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

Nonlinear dynamic characteristics of a dielectric elastomer membrane undergoing in-plane deformation  

NASA Astrophysics Data System (ADS)

This paper proposes a free energy model to study the dynamic characteristics of a dielectric elastomer membrane undergoing in-plane deformation, subject to the combined loads of a mechanical press and an electric field. The natural frequency of the small-amplitude perturbation around the state of equilibrium is calculated with focus on the damping effects and the resonance phenomenon. The numerical results, such as the oscillation, phase diagrams and Poincaré maps, are presented to show the influence of the damping on the nonlinear dynamic characteristics of the dielectric elastomer. The numerical results indicate that pre-stresses, damping effects and applied voltages could tune the natural frequency and modify the dynamic behavior of the dielectric elastomer. There is a stability transition when taking the damping effect into account. The damping effect could cause the dynamic responses to constant vibration and decrease the amplitude. These conclusions may guide the exploration of high-performance dielectric elastomers under dynamic mechanical and electrical loads.

Sheng, Junjie; Chen, Hualing; Li, Bo; Wang, Yongquan

2014-04-01

110

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

2014-12-01

111

Dislocation creep of fine-grained olivine  

NASA Astrophysics Data System (ADS)

Deformation experiments conducted in a gas medium apparatus at temperatures from 1200 to 1350°C with a fine-grained, solution-gelation derived Fe-bearing olivine show a stress dependence of the strain rate at stresses above ˜150 MPa, which is much stronger than previously reported for polycrystalline samples. The data can be fit by a power law with ???n with n ˜ 7-8, or equally well by a Peierls creep law with exponential stress dependence. Due to the observed strong stress dependence the samples deform at significantly higher strain rates at a given stress than single crystals or coarse-grained polycrystals with n ˜ 3.5. TEM observations indicate the presence of dislocations with at least two different Burgers vectors, with free dislocations predominantly of screw character. Subgrain walls are present but are only weakly developed and have small misorientation angles. Both the rheology and dislocation structures are consistent with creep rate-limited by dislocation glide or cross slip for aggregates with grain sizes smaller than or approaching the recrystallized grain size. Deformation mechanism maps extrapolated to lithospheric temperatures using the melt-free diffusion creep rheology of Faul and Jackson (2007), the dislocation creep rheology of Hirth and Kohlstedt (2003), and the results described here indicate that deformation conditions of ultramylonitic shear zones fall near the triple point of Peierls, dislocation, and diffusion creep.

Faul, U. H.; Fitz Gerald, J. D.; Farla, R. J. M.; Ahlefeldt, R.; Jackson, I.

2011-01-01

112

Prediction of deformation characteristics of sintered aluminium preforms using neural networks  

NASA Astrophysics Data System (ADS)

Neural networks (NNs) are employed to study the deformation characteristics of sintered aluminium preforms. The proposed NN model has used the measured parameters, namely the load, the aspect ratio and the initial preform fractional density ratio to predict multiple material characteristics, namely the axial stress, the hoop stress, the hydrostatic stress, the axial strain, the hoop strain and the Poisson's ratio. The model is based on a 'four layered NN' with back propagation learning algorithm. The experimental set-up available in the laboratory has been used to get the training data for the sintered aluminium with various preform densities and different aspect ratios (0.50, 0.75 and 1.00) using MoS2 as lubricant. The predicted values from the proposed NN coincide well with the experimental values. In addition, a comparative study between the regression analysis and the NN revealed that the NN can predict the material characteristics of sintered aluminium preform better than regression polynomials within a few per cent error.

Selvakumar, N.; Radha, P.; Narayanasamy, R.; Davidson, M. Joseph

2004-07-01

113

A Creep Non-Linear FEM Analysis of Glulam Timber  

Microsoft Academic Search

This work is focused on a creep formulation in bending for timber beams, of glue laminated (glulam) type, which is suited to be implemented in both geometrical and material non-linear Finite Element Method (FEM) models. It studies the performance of timber beams by accounting the deformation under increments of time and stress in a long-term. The proposed creep formulation uses

V. De Luca; A. Della Chiesa

2012-01-01

114

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

115

Multiaxial creep and cyclic plasticity in nickel-base superalloy C263  

Microsoft Academic Search

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

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

2005-01-01

116

Static characteristic measurement of MEMS deformable mirror with phase-shift interferometer  

NASA Astrophysics Data System (ADS)

MEMS deformable mirrors (DM) have many merits of low drive voltage, high response speed, small power consumption, low cost and small size. Its surface shape and displacement versus applied voltage are significant factors of MEMS DM. Phase-shifting interferometer (PSI) has many advantages such as non-contact, quickness and high precision. A phase-only liquid crystal spatial light modulator (LC-SLM), as a linear phase-shifter in PSI, is linear calibrated for its phase-shift characteristics. The PSI is set up to measure the static characteristic of MEMS DM. Five-step phase-shifting method is used to calculate the phase distribution from interference fringes, and Global phase unwrapping algorithm to solve the holes, noise and breakpoint of interfere images. Compared to the measurement results using Zygo instrument, these two experimental results are very close. The experiment results show, this measuring system is very reliable, convenient and cheap. Moreover, this test system need not stitch some fringe images to get the whole surface shape of the mirror like the Zygo instrument.

Wu, Kui; Cai, Dongmei; Wang, Dong; Peng, Jia

2014-09-01

117

Architectural characteristics of the normal and deformity mandible revealed by three-dimensional functional unit analysis.  

PubMed

The 3D architecture of the mandible contributes to the functional and morphological characteristics of the lower one third of craniofacial region. The mandible has six distinct functional units, and its architecture is the sum of balanced growth of each functional unit and surrounding matrix. A dentofacial deformity (DFD) with malocclusion can be interpreted as their unbalanced growth. In order to characterize the mandibular 3D architecture, we analyzed the 3D reconstructed computed tomography (CT) images in terms of functional units. We evaluated both sides of 30 datasets of 3D CT scans of normal controls (N = 6) and patients with prognathic (N = 17) or retrognathic (N = 7) mandibles. We first identified and evaluated reference points to define mandibular functional units and compared their linear and angular measurements of DFD with normal group. The condylar and body length, the ratio of condyle/coronoid length, and the condylar head axis angle showed the statistically significant differences between groups. From these results, we could define the 3D reference points for functional units and identify the 3D architectural characteristics of DFD mandibles. These models may help us improve diagnosis and treatment planning to let them return to the normal and balanced architecture for DFD. PMID:19823879

Park, Wonse; Kim, Bong-Chul; Yu, Hyung-Seog; Yi, Choong-Kook; Lee, Sang-Hwy

2010-12-01

118

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

119

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

120

Prevalence and characteristics of cam-type femoroacetabular deformity in 100 hips with symptomatic acetabular dysplasia: a case control study.  

PubMed

BackgroundCam-type femoroacetabular deformity in acetabular dysplasia (AD) has not been well clarified. The primary purpose of this study was to determine the prevalence and characteristics of femoroacetabular deformity in symptomatic AD patients.MethodsWe retrospectively reviewed the cases of 86 women (92 hips) and eight men (eight hips) with symptomatic AD. The mean patient age was 37.9 (range, 14¿60) years. All participants underwent lateral cross-table and lateral whole-spine radiographic examinations to measure the alpha angle and pelvic tilt. Pelvic computed tomography scans were used to measure femoral anteversion. The patients were classified into two groups: AD only group, containing hips with an alpha angle less than 55°; and AD with cam-type femoroacetabular deformity (AD¿+¿cam-type deformity) group, containing hips with an alpha angle greater than or equal to 55°.ResultsOf the patients with AD, 40 hips displayed additional radiographic evidence of cam-type morphology, while 60 hips had exclusive AD morphology. The patients in the AD¿+¿cam-type deformity group had significantly increased forward pelvic tilt in the standing position (p =0.023) and decreased femoral anteversion (p =0.047) compared with the AD only group.ConclusionsOur data revealed that 40% of patients with AD also had radiographic evidence of cam-type femoroacetabular deformity. Greater forward pelvic tilt in the standing position and decreased femoral anteversion seemed to be associated with the cam-type deformity in these patients. These results indicate the morphological features that are most likely to induce secondary symptoms to developmental hip dysplasia. It is suggested that the symptoms in the AD¿+¿cam-type deformity group could arise through femoroacetabular impingement (FAI) after periacetabular osteotomy, because a predisposition was present preoperatively. PMID:25300562

Ida, Takahiro; Nakamura, Yoshinari; Hagio, Tomonobu; Naito, Masatoshi

2014-10-10

121

Threshold Stress Creep Behavior of Alloy 617 at Intermediate Temperatures  

NASA Astrophysics Data System (ADS)

Creep of Alloy 617, a solid solution Ni-Cr-Mo alloy, was studied in the temperature range of 1023 K to 1273 K (750 °C to 1000 °C). Typical power-law creep behavior with a stress exponent of approximately 5 is observed at temperatures from 1073 K to 1273 K (800 °C to 1000 °C). Creep at 1023 K (750 °C), however, exhibits threshold stress behavior coinciding with the temperature at which a low volume fraction of ordered coherent ?' precipitates forms. The threshold stress is determined experimentally to be around 70 MPa at 1023 K (750 °C) and is verified to be near zero at 1173 K (900 °C)—temperatures directly correlating to the formation and dissolution of ?' precipitates, respectively. The ?' precipitates provide an obstacle to continued dislocation motion and result in the presence of a threshold stress. TEM analysis of specimens crept at 1023 K (750 °C) to various strains, and modeling of stresses necessary for ?' precipitate dislocation bypass, suggests that the climb of dislocations around the ?' precipitates is the controlling factor for continued deformation at the end of primary creep and into the tertiary creep regime. As creep deformation proceeds at an applied stress of 121 MPa and the precipitates coarsen, the stress required for Orowan bowing is reached and this mechanism becomes active. At the minimum creep rate at an applied stress of 145 MPa, the finer precipitate size results in higher Orowan bowing stresses and the creep deformation is dominated by the climb of dislocations around the ?' precipitates.

Benz, Julian K.; Carroll, Laura J.; Wright, Jill K.; Wright, Richard N.; Lillo, Thomas M.

2014-06-01

122

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

NASA Astrophysics Data System (ADS)

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

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

1994-08-01

123

Creep of chemically vapor deposited SiC fibers  

NASA Technical Reports Server (NTRS)

The creep, thermal expansion, and elastic modulus properties for chemically vapor deposited SiC fibers were measured between 1000 and 1500 C. Creep strain was observed to increase logarithmically with time, monotonically with temperature, and linearly with tensile stress up to 600 MPa. The controlling activation energy was 480 + or - 20 kJ/mole. Thermal pretreatments near 1200 and 1450 C were found to significantly reduce fiber creep. These results coupled with creep recovery observations indicate that below 1400 C fiber creep is anelastic with neglible plastic component. This allowed a simple predictive method to be developed for describing fiber total deformation as a function of time, temperature, and stress. Mechanistic analysis of the property data suggests that fiber creep is the result of beta-SiC grain boundary sliding controlled by a small percent of free silicon in the grain boundaries.

Dicarlo, J. A.

1984-01-01

124

CREEP AND CREEP-FATIGUE OF ALLOY 617 WELDMENTS  

SciTech Connect

The Very High Temperature Reactor (VHTR) Intermediate Heat Exchanger (IHX) may be joined to piping or other components by welding. Creep-fatigue deformation is expected to be a predominant failure mechanism of the IHX1 and thus weldments used in its fabrication will experience varying cyclic stresses interrupted by periods of elevated temperature deformation. These periods of elevated temperature deformation are greatly influenced by a materials’ creep behavior. The nickel-base solid solution strengthened alloy, Alloy 617, is the primary material candidate for a VHTR-type IHX, and it is expected that Alloy 617 filler metal will be used for welds. Alloy 617 is not yet been integrated into Section III of the Boiler and Pressure Vessel Code, however, nuclear component design with Alloy 617 requires ASME (American Society of Mechanical Engineers) Code qualification. The Code will dictate design for welded construction through significant performance reductions. Despite the similar compositions of the weldment and base material, significantly different microstructures and mechanical properties are inevitable. Experience of nickel alloy welds in structural applications suggests that most high temperature failures occur at the weldments or in the heat-affected zone. Reliably guarding against this type of failure is particularly challenging at high temperatures due to the variations in the inelastic response of the constituent parts of the weldment (i.e., weld metal, heat-affected zone, and base metal) [ref]. This work focuses on the creep-fatigue behavior of nickel-based weldments, a need noted during the development of the draft Alloy 617 ASME Code Case. An understanding of Alloy 617 weldments when subjected to this important deformation mode will enable determination of the appropriate design parameters associated with their use. Specifically, the three main areas emphasized are the performance reduction due to a weld discontinuity in terms of the reduced number of the cycles to failure and whether a saturation in reduced cycle life with increased hold times is observed, the microstructural stability over long cycle times, and finally, the location of the generated weldment data on a creep-fatigue damage diagram (D-diagram).

Jill Wright; Laura Carroll; Richard Wright

2014-08-01

125

Creep of plasma sprayed zirconia. Final Report  

SciTech Connect

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.

1982-11-01

126

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

127

Creep of Rocks Under Small Mechanical Loading  

NASA Astrophysics Data System (ADS)

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

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

128

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

SciTech Connect

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

Munson, Darrell E.

1999-08-16

129

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

130

Endochronic theory of transient creep and creep recovery  

NASA Technical Reports Server (NTRS)

Short time creep and creep recovery were investigated by means of the endochronic theory of viscoplasticity. It is shown that the constitutive equations for constant-strain-rate stress-strain behavior, creep, creep recovery, and stress relaxation can all ber derived from the general constitutive equation by imposing appropriate constraints. In this unified approach, the effect of strain-hardening is naturally accounted for when describing creep and creep recovery. The theory predicts with reasonable accuracy the creep and creep recovery behaviors for Aluminum 1100-0 at 150 C. It was found that the strain-rate history at prestraining stage affects the subsequent creep. A critical stress was also established for creep recovery. The theory predicts a forward creep for creep recovery stress greater than the critical stress. For creep recovery stress less than the critical stress, the theory then predicts a normal strain recovery.

Wu, H. C.; Chen, L.

1979-01-01

131

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

132

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

133

Creep behaviour of modified 9Cr-1Mo ferritic steel  

NASA Astrophysics Data System (ADS)

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

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

2011-05-01

134

Development of a constitutive model for creep and life prediction of advanced silicon nitride ceramics  

SciTech Connect

A constitutive model capable of describing deformation and predicting rupture life was developed for high temperature ceramic materials under general thermal-mechanical loading conditions. The model was developed based on the deformation and fracture behavior observed from a systematic experimental study on an advanced silicon nitride (Si{sub 3}N{sub 4}) ceramic material. Validity of the model was evaluated with reference to creep and creep rupture data obtained under constant and stepwise-varied loading conditions, including the effects of annealing on creep and creep rupture behavior.

Ding, J.L. [Washington State Univ., Pullman, WA (US); Liu, K.C.; Brinkman, C.R. [Oak Ridge National Lab., TN (US)

1992-12-31

135

Deformable registration of DT-MRI data based on transformation invariant tensor characteristics  

Microsoft Academic Search

Conventional deformable registration methods are mostly driven by the interface between different brain structures. In recent years, Diffusion Tensor Magnetic Resonance Imaging (DT-MRI) has been used in conjunction with other conventional Magnetic Resonance (MR) pulse sequences to provide more structural information dur- ing the registration process. Due to the geometric nature of the DT-MRI information, tensors need to be reoriented

Alexandre Guimond; Charles R. G. Guttmann; Simon K. Warfield; Carl-fredrik Westin

2002-01-01

136

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

NASA Astrophysics Data System (ADS)

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

Zolochevsky, Alexander; Obataya, Yoichi

137

A loading system for creep testing under constant compressive stress  

NASA Technical Reports Server (NTRS)

A critical analysis is made of layouts assuring constant stress under creep, pointing out the difficulties of using these layouts for compressive testing. A new mechanical system to maintain stress during creep testing is proposed. Constant stress is achieved by a definite motion of the load. The proposed system can be used in tensile or compressive testing. Practical measurements reveal that the stress constancy error is not greater than plus or minus 1.5 percent up to relative deformation of 30 percent.

Dobes, F.; Zverina, O.; Cadek, J.

1987-01-01

138

Creep behaviour of Cu-30 percent Zn at intermediate temperatures  

NASA Technical Reports Server (NTRS)

The present, intermediate-temperature (573-823 K) range investigation of creep properties for single-phase Cu-30 percent Zn alpha-brass observed inverse, linear, and sigmoidal primary-creep transients above 573 K under stresses that yield minimum creep rates in the 10 to the -7th to 2 x 10 to the -4th range; normal primary creep occurred in all other conditions. In conjunction with a review of the pertinent literature, a detailed analysis of these data suggests that no clearly defined, classes M-to-A-to-M transition exists in this alloy notwithstanding the presence of both classes' characteristics under nominally similar stresses and temperatures.

Raj, S. V.

1991-01-01

139

Estimating the creep behavior of polycarbonate with changes in temperature and aging time  

NASA Astrophysics Data System (ADS)

Thermoplastic resins are typically used without any kind of physical aging treatment. For such materials, creep behavior and physical aging, which depend on time and temperature, occur simultaneously. The effects of these processes are evident after quenching and are recorded in the material as a thermal history. This history strongly influences mechanical properties and creep behavior in particular. Thus, a more thorough understanding of the physical aging process is desirable. We examined the creep deformation of polycarbonate (PC) to reveal the effects of physical aging on creep behavior. The effects were dependent on both time and temperature. The relationship between physical aging and creep behavior exemplified superposition principles with regard to time and both pre-test aging time and pre-test aging temperature. The superposition principles allowed the calculation of creep deformations at a given temperature; the calculated results were corroborated by experimental data.

Sakai, Takenobu; Somiya, Satoshi

2012-08-01

140

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

141

On the creep rupture of structures  

NASA Astrophysics Data System (ADS)

A STUDY is made of the failure times of structures made of materials which suffer creep deformation and which crack according to the Kachanov law in which strain and damage rates are given in terms of the existing stress and state of damage. For certain types of structures, it is shown that lower bound estimates of the failure time can be made by considering the variation of a certain global parameter.

Martin, J. B.; Leckie, F. A.

1972-08-01

142

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

PubMed

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

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

2013-04-01

143

MPAA Ratings Creep  

Microsoft Academic Search

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

Ron Leone; Laurie Barowski

2011-01-01

144

Influence of Grain Boundary Character on Creep Void Formation in Alloy 617  

NASA Astrophysics Data System (ADS)

Alloy 617, a high-temperature creep-resistant, nickel-based alloy, is being considered for the primary heat exchanger for the Next Generation Nuclear Plant (NGNP), which will operate at temperatures exceeding 760 °C and a helium pressure of approximately 7 MPa. Observations of the crept microstructure using optical microscopy indicate creep stress does not significantly influence the creep void fraction at a given creep strain over the relatively narrow set of creep conditions studied. Void formation was found to occur only after significant creep in the tertiary regime (>5 pct total creep strain) had occurred. Also, orientation imaging microscopy (OIM) was used to characterize the grain boundaries in the vicinity of creep voids that develop during high-temperature creep tests (900 °C to 1000 °C at creep stresses ranging from 20 to 40 MPa) terminated at creep strains ranging from 5 to 40 pct. Preliminary analysis of the OIM data indicates voids tend to form on grain boundaries parallel, perpendicular, or 45 deg to the tensile axis, while few voids are found at intermediate inclinations to the tensile axis. Random grain boundaries intersect most voids, while coincident site lattice (CSL)-related grain boundaries did not appear to be consistently associated with void development. Similar results were found in oxygen-free, high-conductivity (OFHC) copper, severely deformed using equal channel angular extrusion, and creep tested at 450 °C and 14 MPa.

Lillo, Thomas; Cole, James; Frary, Megan; Schlegel, Scott

2009-12-01

145

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

NASA Astrophysics Data System (ADS)

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

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

2014-05-01

146

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

147

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

148

Threshold Stress Creep Behavior of Alloy 617 at Intermediate Temperatures  

SciTech Connect

Creep of Alloy 617, a solid solution Ni-Cr-Mo alloy, was studied in the temperature range of 1023 K to 1273 K (750 °C to 1000 °C). Typical power-law creep behavior with a stress exponent of approximately 5 is observed at temperatures from 1073 K to 1273 K (800 °C to 1000 °C). Creep at 1023 K (750 °C), however, exhibits threshold stress behavior coinciding with the temperature at which a low volume fraction of ordered coherent y' precipitates forms. The threshold stress is determined experimentally to be around 70 MPa at 1023 K (750 °C) and is verified to be near zero at 1173 K (900 °C)—temperatures directly correlating to the formation and dissolution of y' precipitates, respectively. The y' precipitates provide an obstacle to continued dislocation motion and result in the presence of a threshold stress. TEM analysis of specimens crept at 1023 K (750 °C) to various strains, and modeling of stresses necessary for y' precipitate dislocation bypass, suggests that the climb of dislocations around the y' precipitates is the controlling factor for continued deformation at the end of primary creep and into the tertiary creep regime. As creep deformation proceeds at an applied stress of 121 MPa and the precipitates coarsen, the stress required for Orowan bowing is reached and this mechanism becomes active. At the minimum creep rate at an applied stress of 145 MPa, the finer precipitate size results in higher Orowan bowing stresses and the creep deformation is dominated by the climb of dislocations around the y' precipitates.

J.K. Benz; L.J. Carroll; J.K. Wright; R.N. Wright; T. Lillo

2014-06-01

149

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

150

Mechanosorptive creep in nanocellulose materials  

Microsoft Academic Search

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

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

2012-01-01

151

Bend stress relaxation and tensile primary creep of a polycrystalline alpha-SiC fiber  

NASA Technical Reports Server (NTRS)

Understanding the thermomechanical behavior (creep and stress relaxation) of ceramic fibers is of both practical and basic interest. On the practical level, ceramic fibers are the reinforcement for ceramic matrix composites which are being developed for use in high temperature applications. It is important to understand and model the total creep of fibers at low strain levels where creep is predominantly in the primary stage. In addition, there are many applications where the component will only be subjected to thermal strains. Therefore, the stress relaxation of composite consituents in such circumstances will be an important factor in composite design and performance. The objective of this paper is to compare and analyze bend stress relaxation and tensile creep data for alpha-SiC fibers produced by the Carborundum Co. (Niagara Falls, NY). This fiber is of current technical interest and is similar in composition to bulk alpha-SiC which has been studied under compressive creep conditions. The temperature, time, and stress dependences will be discussed for the stress relaxation and creep results. In addition, some creep and relaxation recovery experiments were performed in order to understand the complete viscoelastic behavior, i.e. both recoverable and nonrecoverable creep components of these materials. The data will be presented in order to model the deformation behavior and compare relaxation and/or creep behavior for relatively low deformation strain conditions of practical concern. Where applicable, the tensile creep results will be compared to bend stress relaxation data.

Hee Man, Yun; Goldsby, Jon C.; Morscher, Gregory N.

1995-01-01

152

Modeling the Role of Dislocation Substructure During Class M and Exponential Creep. Revised  

NASA Technical Reports Server (NTRS)

The different substructures that form in the power-law and exponential creep regimes for single phase crystalline materials under various conditions of stress, temperature and strain are reviewed. The microstructure is correlated both qualitatively and quantitatively with power-law and exponential creep as well as with steady state and non-steady state deformation behavior. These observations suggest that creep is influenced by a complex interaction between several elements of the microstructure, such as dislocations, cells and subgrains. The stability of the creep substructure is examined in both of these creep regimes during stress and temperature change experiments. These observations are rationalized on the basis of a phenomenological model, where normal primary creep is interpreted as a series of constant structure exponential creep rate-stress relationships. The implications of this viewpoint on the magnitude of the stress exponent and steady state behavior are discussed. A theory is developed to predict the macroscopic creep behavior of a single phase material using quantitative microstructural data. In this technique the thermally activated deformation mechanisms proposed by dislocation physics are interlinked with a previously developed multiphase, three-dimensional. dislocation substructure creep model. This procedure leads to several coupled differential equations interrelating macroscopic creep plasticity with microstructural evolution.

Raj, S. V.; Iskovitz, Ilana Seiden; Freed, A. D.

1995-01-01

153

Synchrotron 3D microtomography of halite aggregates during experimental pressure solution creep and evolution of  

E-print Network

is present, rock salt can creep and deform in the pressure solution regime [Rutter, 1976; Spiers of the pores. The aim of this study is twofold: 1) quantify how the porosity and the permeability of salt1 Synchrotron 3D microtomography of halite aggregates during experimental pressure solution creep

Paris-Sud XI, Université de

154

Mathematical modeling of the deformation behavior of heterophase alloys at various characteristics of the strengthening phase  

NASA Astrophysics Data System (ADS)

Further development of techniques and technologies urgently requires the creation of new materials with unique properties. One of the most popular and promising areas in materials science is the creation of composite materials with desired properties. Currently, in practice peening by dispersed particles is widely used to improve the properties of metal materials. It is necessary to investigate in detail the influence of various factors on the behavior of dispersion-hardened materials in a variety of conditions to control the properties of materials. Physical experiment, in addition to large investments, often takes a long time. This paper presents a mathematical model of plastic deformation of dispersion-hardened materials with a face-centered cubic (fcc) matrix and with incoherent and coherent nanoscale particles. Application of this model can significantly reduce the time of research and necessary amount of physical experiment. The results allow optimizing of experiment, identifying ways to improve the properties of the materials.

Daneyko, O. I.; Kovalevskaya, T. A.; Kolupaeva, S. N.; Kulaeva, N. A.

2015-01-01

155

Creep damage mechanisms in composites  

SciTech Connect

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

Nutt, S.R.

1994-10-17

156

Analysis of Multistage and Other Creep Data for Domal Salts  

SciTech Connect

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

Munson, D.E.

1998-10-01

157

Time-Dependent Behavior of Diabase and a Nonlinear Creep Model  

NASA Astrophysics Data System (ADS)

Triaxial creep tests were performed on diabase specimens from the dam foundation of the Dagangshan hydropower station, and the typical characteristics of creep curves were analyzed. Based on the test results under different stress levels, a new nonlinear visco-elasto-plastic creep model with creep threshold and long-term strength was proposed by connecting an instantaneous elastic Hooke body, a visco-elasto-plastic Schiffman body, and a nonlinear visco-plastic body in series mode. By introducing the nonlinear visco-plastic component, this creep model can describe the typical creep behavior, which includes the primary creep stage, the secondary creep stage, and the tertiary creep stage. Three-dimensional creep equations under constant stress conditions were deduced. The yield approach index (YAI) was used as the criterion for the piecewise creep function to resolve the difficulty in determining the creep threshold value and the long-term strength. The expression of the visco-plastic component was derived in detail and the three-dimensional central difference form was given. An example was used to verify the credibility of the model. The creep parameters were identified, and the calculated curves were in good agreement with the experimental curves, indicating that the model is capable of replicating the physical processes.

Yang, Wendong; Zhang, Qiangyong; Li, Shucai; Wang, Shugang

2014-07-01

158

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

159

Irradiation Creep in Graphite  

SciTech Connect

An understanding of the underlying mechanisms of irradiation creep in graphite material is required to correctly interpret experimental data, explain micromechanical modeling results, and predict whole-core behavior. This project will focus on experimental microscopic data to demonstrate the mechanism of irradiation creep. High-resolution transmission electron microscopy should be able to image both the dislocations in graphite and the irradiation-induced interstitial clusters that pin those dislocations. The team will first prepare and characterize nanoscale samples of virgin nuclear graphite in a transmission electron microscope. Additional samples will be irradiated to varying degrees at the Advanced Test Reactor (ATR) facility and similarly characterized. Researchers will record microstructures and crystal defects and suggest a mechanism for irradiation creep based on the results. In addition, the purchase of a tensile holder for a transmission electron microscope will allow, for the first time, in situ observation of creep behavior on the microstructure and crystallographic defects.

Ubic, Rick; Butt, Darryl; Windes, William

2014-03-13

160

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

161

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

162

Sources of Variation in Creep Testing  

NASA Technical Reports Server (NTRS)

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

Loewenthal, William S.; Ellis, David L.

2011-01-01

163

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

164

Creep Behavior and Life Evaluation of Aged P92 Steel  

NASA Astrophysics Data System (ADS)

Creep strength and life of material is closely related with the microstructural characteristics. Components used under creep condition for long time are unable to maintain the stability of microstructure and experience degradation of material. From this viewpoint, it is necessary for safety and residual life of power plant to investigate creep properties of specimens prepared from the material cut directly from the operating service components. The small punch test has been developed as a useful method to estimate mechanical properties because of its miniaturized specimen size. In this study, small punch creep tests were carried out to investigate the effect of aging time on creep properties using P92 steel aged from 0~12100 hrs at 600°C.

Kim, Bumjoon; Lim, Byeongsoo; Ki, Donghyun

165

Creep damage characterization using nonlinear ultrasonic guided wave method: A mesoscale model  

NASA Astrophysics Data System (ADS)

The early deformations in materials such as creep, plasticity, and fatigue damages have been proved to have a close relationship with the nonlinear effect of ultrasonic waves propagating in them. In the present paper, a theoretical mesoscale model of an ultrasonic non-destructive method has been proposed to evaluate creep deformed states based on nonlinear guided waves. The model developed here considers the nonlinear generation of Lamb waves response from precipitates variation in the dislocation network, which can be applicable to all precipitate stages including coherent and semi-coherent precipitates in the metallic alloy undergoing creep degradation. To verify the proposed model, experiments of titanium alloy Ti60 plates were carried out with different creep strains. An "increase-decrease" change of the acoustic nonlinearity of guided wave versus the creep life fraction has been observed. Based on microscopic images analyses, the mesoscale model was then applied to these creep damaged Ti60 specimens, which revealed a good accordance with the measured results of the nonlinear guided waves. It is shown that the change of the nonlinear Lamb wave depends on the variations of the ?2 precipitation volume fraction, the dislocation density, the growth of the creep-voids, and the increasing mismatch of the phase velocities during the creep deformation process. The results indicate that the effect of the precipitate-dislocation interactions on the nonlinear guided wave is likely the dominant mechanism responsible for the change of nonlinear guided wave propagation in the crept materials.

Xiang, Yanxun; Deng, Mingxi; Xuan, Fu-Zhen

2014-01-01

166

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

167

Creep Strain and Strain Rate Response of 2219 Al Alloy at High Stress Levels  

NASA Technical Reports Server (NTRS)

As a result of high localized plastic deformation experienced during proof testing in an International Space Station connecting module, a study was undertaken to determine the deformation response of a 2219-T851 roll forging. After prestraining 2219-T851 Al specimens to simulate strains observed during the proof testing, creep tests were conducted in the temperature range from ambient temperature to 107 C (225 F) at stress levels approaching the ultimate tensile strength of 2219-T851 Al. Strain-time histories and strain rate responses were examined. The strain rate response was extremely high initially, but decayed rapidly, spanning as much as five orders of magnitude during primary creep. Select specimens were subjected to incremental step loading and exhibited initial creep rates of similar magnitude for each load step. Although the creep rates decreased quickly at all loads, the creep rates dropped faster and reached lower strain rate levels for lower applied loads. The initial creep rate and creep rate decay associated with primary creep were similar for specimens with and without prestrain; however, prestraining (strain hardening) the specimens, as in the aforementioned proof test, resulted in significantly longer creep life.

Taminger, Karen M. B.; Wagner, John A.; Lisagor, W. Barry

1998-01-01

168

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

PubMed Central

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

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

2010-01-01

169

Deformation failure characteristics of coal body and mining induced stress evolution law.  

PubMed

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; Qu, Guanglong; Wen, Jinhao; Shi, Yongkui; Jia, Chuanyang

2014-01-01

170

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

171

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

NASA Astrophysics Data System (ADS)

Atomistic simulations revealed that the spatial correlations of plastic displacements in three metallic glasses, FeP, MgAl, and CuZr, follow an exponential law with a characteristic length scale ?c that governs Poisson's ratio ?, shear band thickness tSB, and fracture mode in these materials. Among the three glasses, FeP exhibits smallest ?c, thinnest tSB, lowest ?, and brittle fracture; CuZr exhibits largest ?c, thickest tSB, highest ?, and ductile fracture, while properties of MgAl lie in between those of FeP and CuZr. These findings corroborate well with existing experimental observations and suggest ?c as a fundamental measure of the shear transformation zone size in metallic glasses.

Murali, P.; Zhang, Y. W.; Gao, H. J.

2012-05-01

172

ORNL irradiation creep facility  

SciTech Connect

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

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

1980-09-01

173

Effect of hydrogen on creep behavior of Ti-6AI-4V alloy at room temperature  

NASA Astrophysics Data System (ADS)

Room temperature creep was investigated for a commercial Ti-6Al-4V alloy containing 80 ppm to 720 ppm hydrogen. It was shown that dissolved hydrogen promoted the creep of this alloy at room temperature, markedly increasing both the creep strain and rate in the primary stage. The results indicated that dissolved hydrogen does not change the primary creep mechanism, but rather increases mobility of glide dislocations. It is suggested that dissolved hydrogen atoms soften the alloy at the beginning of deformation due to this increase in dislocation mobility. The initial deformation results in hydrogen build-up near the subboundaries due to the "sweeping" effect of the glide dislocations, thereby causing hydrogen embrittlement in a later stage of deformation.

Gao, G. Y.; Dexter, S. C.

1991-01-01

174

Effect of hydrogen on creep behavior of Ti-6AI-4V alloy at room temperature  

NASA Astrophysics Data System (ADS)

Room temperature creep was investigated for a commercial Ti-6Al-4V alloy containing 80 ppm to 720 ppm hydrogen. It was shown that dissolved hydrogen promoted the creep of this alloy at room temperature, markedly increasing both the creep strain and rate in the primary stage. The results indicated that dissolved hydrogen does not change the primary creep mechanism, but rather increases mobility of glide dislocations. It is suggested that dissolved hydrogen atoms soften the alloy at the beginning of deformation due to this increase in dislocation mobility. The initial deformation results in hydrogen build-up near the subboundaries due to the "sweeping" effect of the glide dislocations, thereby causing hydrogen embrittlement in a later stage of deformation.

Gao, G. Y.; Dexter, S. C.

1987-01-01

175

Modelling of creep curves of Ni3Ge single crystals  

NASA Astrophysics Data System (ADS)

In this paper the creep model of alloys with L12 superstructure is presented. The creep model is based on the idea of the mechanisms superposition connected with the different elementary deformation processes. Some of them are incident to the ordered structure L12 (anomalous mechanisms), others are typical to pure metals with the fcc structure (normal mechanisms): the accumulation of thermal APBs by means of the intersection of moving dislocations; the formation of APB tubes; the multiplication of superdislocations; the movement of single dislocations; the accumulation of point defects, such as vacancies and interstitial atoms; the accumulation APBs at the climb of edge dislocations. This model takes into account the experimental facts of the wetting antiphase boundaries and emergence of the disordered phase within the ordered phase. The calculations of the creep curves are performed under different conditions. This model describes different kinds of the creep curves and demonstrates the important meaning of the deformation superlocalisation leading to the inverse creep. The experimental and theoretical results coincide rather well.

Starenchenko, V. A.; Starenchenko, S. V.; Pantyukhova, O. D.; Solov'eva, Yu V.

2015-01-01

176

Creep-constitutive behavior of Sn-3.8Ag-0.7Cu solder using an internal stress approach  

NASA Astrophysics Data System (ADS)

The experimental tensile creep deformation of bulk Sn-3.8Ag-0.7Cu solder at temperatures between 263 K and 398 K, covering lifetimes up to 3,500 h, has been rationalized using constitutive equations that incorporate structure-related internal state variables. Primary creep is accounted for using an evolving internal back stress, due to the interaction between the soft matrix phase and a more creep-resistant particle phase. Steady-state creep is incorporated using a conventional power law, modified to include the steady-state value of internal stress. It is demonstrated that the observed behavior is well-fitted using creep constants for pure tin in the modified creep power law. A preliminary analysis of damage-induced tertiary creep is also presented.

Rist, Martin A.; Plumbridge, W. J.; Cooper, S.

2006-05-01

177

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

NASA Astrophysics Data System (ADS)

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

Kayran, Altan; Yavuzbalkan, Erdem

2009-01-01

178

Localized and distributed creep along the southern San Andreas Fault  

NASA Astrophysics Data System (ADS)

We investigate the spatial pattern of surface creep and off-fault deformation along the southern segment of the San Andreas Fault using a combination of multiple interferometric synthetic aperture radar viewing geometries and survey-mode GPS occupations of a dense array crossing the fault. Radar observations from Envisat during the period 2003-2010 were used to separate the pattern of horizontal and vertical motion, providing a high-resolution image of uplift and shallow creep along the fault trace. The data reveal pervasive shallow creep along the southernmost 50 km of the fault. Creep is localized on a well-defined fault trace only in the Mecca Hills and Durmid Hill areas, while elsewhere creep appears to be distributed over a 1-2 km wide zone surrounding the fault. The degree of strain localization is correlated with variations in the local fault strike. Using a two-dimensional boundary element model, we show that stresses resulting from slip on a curved fault can promote or inhibit inelastic failure within the fault zone in a pattern matching the observations. The occurrence of shallow, localized interseismic fault creep within mature fault zones may thus be partly controlled by the local fault geometry and normal stress, with implications for models of fault zone evolution, shallow coseismic slip deficit, and geologic estimates of long-term slip rates.

Lindsey, Eric O.; Fialko, Yuri; Bock, Yehuda; Sandwell, David T.; Bilham, Roger

2014-10-01

179

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

180

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

181

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

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

182

Creep property and microstructure evolution of a nickel-base single crystal superalloy in [011] orientation  

SciTech Connect

The creep property and microstructure evolution of a single crystal superalloy with [011] orientation were investigated at the temperatures of 700 °C, 900 °C and 1040 °C. It is shown that there exist stages of primary, steady-state, and tertiary creep under the lower temperature 700 °C. As the temperature increases to high temperatures of 900 °C and 1040 °C, steady-state creep stage is reduced or disappears and the shape of creep curves is dominated by an extensive tertiary stage. The minimum creep strain rate exhibits power law dependence on the applied stress; the stress exponents at 700 °C, 900 °C and 1040 °C are 28, 13 and 6.5, respectively. Microstructure observation shows that the morphologies of ?? phase almost keep original shape at the lower temperature 700 °C and high applied stress. With the increasing creep temperature, ?? precipitates tend to link together and form lamellar structure at an angle of 45° inclined to the applied stress. Transmission electron microscopy (TEM) investigations reveal that multiple < 110 > (111) slip systems gliding in the matrix channels and shearing ?? precipitates by stacking faults or bending dislocation pairs are the main deformation mechanism at the lower temperature of 700 °C. At the high temperatures of 900 °C and 1040 °C, dislocation networks are formed at ?/?? interfaces and the ?? rafts are sheared by dislocation pairs. - Highlights: • Creep properties of < 011 >-oriented single crystal superalloys were investigated. • ?? phases become rafting at an angle of 45° inclined to the applied stress. • Creep deformation mechanisms depend on temperature and stress.

Han, G.M., E-mail: gmhan@imr.ac.cn; Yu, J.J.; Hu, Z.Q.; Sun, X.F.

2013-12-15

183

Creep and fracture of dispersion-strengthened materials  

NASA Technical Reports Server (NTRS)

The creep and fracture of dispersion strengthened materials is reviewed. A compilation of creep data on several alloys showed that the reported values of the stress exponent for creep varied between 3.5 and 100. The activation energy for creep exceeded that for lattice self diffusion in the matrix in the case of some materials and a threshold stress behavior was generally reported in these instances. The threshold stress is shown to be dependent on the interparticle spacing and it is significantly affected by the initial microstructure. The effect of particle size and the nature of the dispersoid on the threshold stress is not well understood at the present time. In general, most studies indicate that the microstructure after creep is similar to that before testing and very few dislocations are usually observed. It is shown that the stress acting on a dispersoid due to a rapidly moving dislocation can exceed the particle yield strength of the G sub p/1000, where G sub p is the shear modulus of the dispersoid. The case when the particle deforms is examined and it is suggested that the dislocation creep threshold stress of the alloy is equal to the yield strength of the dispersoid under these conditions. These results indicate that the possibility that the dispersoid creep threshold stress is determined by either the particle yield strength or the stress required to detach a dislocation from the dispersoid matrix interface. The conditions under which the threshold stress is influenced by one or the other mechanism are discussed and it is shown that the particle yield strength is important until the extent of dislocation core relaxation at the dispersoid matrix interface exceeds about 25 pct. depending on the nature of the particle matrix combination. Finally, the effect of grain boundaries and grain morphology on the creep and fracture behavior of dispersoid strengthened alloys is examined.

Raj, Sai V.

1991-01-01

184

Creep in chipboard  

Microsoft Academic Search

Matched samples to those used in a previously reported investigation (under constant environments employing eight board materials and solid wood) were subjected to five different levels of stress under four different cyclic environments for periods of six months. Relative creep increased slightly and linearly with respect to stress within the range of stress levels adopted, as well as increasing with

J. M. Dinwoodie; Jo-Anne Higgins; B. H. Paxton; D. J. Robson

1992-01-01

185

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

186

Creep behavior of submarine sediments  

USGS Publications Warehouse

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

Silva, Armand J.; Booth, J.S.

1984-01-01

187

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

NASA Astrophysics Data System (ADS)

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

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

2010-12-01

188

High temperature tensile and creep behaviour of low pressure plasma-sprayed Ni-Co-Cr-Al-Y coating alloy  

NASA Technical Reports Server (NTRS)

The high temperature tensile and creep behavior of low pressure plasma-sprayed plates of a typical Ni-Co-Cr-Al-Y alloy has been studied. From room temperature to 800 K, the Ni-Co-Cr-Al-Y alloy studied has nearly a constant low ductility and a high strength. At higher temperatures, it becomes weak and highly ductile. At and above 1123 K, the behavior is highly dependent on strain rate and exhibits classic superplastic characteristics with a high ductility at intermediate strain rates and a strain rate sensitivity of about 0.5. At either higher or lower strain rates, the ductility decreases and the strain rate sensitivities are about 0.2. In the superplastic deformation range, the activation energy for creep is 120 + or - 20 kJ/mol, suggesting a diffusion-aided grain boundary sliding mechanism. Outside the superplastic range, the activation energy for creep is calculated to be 290 + or - 20 kJ/mol.

Hebsur, M. G.; Miner, R. V.

1986-01-01

189

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

190

Testing the inference of creep on Rodgers Creek Fault  

NASA Astrophysics Data System (ADS)

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

Jin, L.; Funning, G. J.

2010-12-01

191

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

192

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

NASA Astrophysics Data System (ADS)

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

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

2008-07-01

193

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

194

High temperature creep behavior of oxide dispersion strengthened NiAl intermetallics  

SciTech Connect

The intermetallic compound NiAl is a promising candidate material for high-temperature applications, provided its creep strength can be raised by some strengthening strategy. Oxide-dispersion strengthened (ODS) NiAl has been produced by powder-metallurgical methods and its creep behavior at temperatures up to 1,723 K (1,450 C) has been studied. Exceptional creep properties, with high stresses and stress sensitivities when compared to dispersoid-free NiAl, are found, which confirms the effectiveness of dispersion strengthening in this material. The creep behavior is interpreted in the light of creep models. Detachment-controlled models satisfactorily describe the deformation in coarse-grained ODS-NiAl, but modifications are necessary for fine-grained material. In technical terms, ODS-NiAl recommends itself as a strong, light and oxidation-resistant high-temperature alloy for applications up to 1,700 K.

Arzt, E.; Grahle, P. [Univ. of Stuttgart (Germany)] [Univ. of Stuttgart (Germany)

1998-05-01

195

Creep in chipboard  

Microsoft Academic Search

Deflection under 4-point bending of a range of board types was measured for up to six months. Results were obtained under steady-state conditions of stress level (30%, 45%, 60%, 67.5% and 75% of the short term breaking stress), relative humidity (30%, 65% and 90% rh) and temperature (10°C, 20°C and 30°C). These results are presented in terms of relative creep

J. M. Dinwoodie; D. J. Robson; B. H. Paxton; J. S. Higgins

1991-01-01

196

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

197

Deformation processes in forging ceramics  

NASA Technical Reports Server (NTRS)

The deformation processes involved in the forging of refractory ceramic oxides were investigated. A combination of mechanical testing and forging was utilized to investigate both the flow and fracture processes involved. Deformation studies of very fine grain Al203 revealed an apparent transition in behavior, characterized by a shift in the strain rate sensitivity from 0.5 at low stresses to near unity at higher stresses. The behavior is indicative of a shift in control between two dependent mechanisms, one of which is indicated to be cation limited diffusional creep with significant boundary enhancement. The possible contributions of slip, indicated by crystallographic texture, interface control of the diffusional creep and inhomogeneous boundary sliding are also discussed. Additional experiments indicated an independence of deformation behavior on MgO doping and retained hot pressing impurities, at least for ultrafine grained material, and also an independence of test atmosphere.

Cannon, R. M.; Rhodes, W. H.

1973-01-01

198

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

199

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

200

Effects of NaCl, pH, and Potential on the Static Creep Behavior of AA1100  

NASA Astrophysics Data System (ADS)

The creep rates of AA1100 are measured during exposure to a variety of aggressive environments. NaCl solutions of various concentrations have no influence on the steady-state creep behavior, producing creep rates comparable to those measured in lab air at room temperature. However, after an initial incubation period of steady strain rate, a dramatic increase of strain rate is observed on exposure to HCl solutions and NaOH solutions, as well as during cathodic polarization of specimens in NaCl solutions. Creep strain produces a continuous deformation and elongation of the sample surface that is comparable to slow strain rates at crack tips thought to control the kinetics of crack growth during stress corrosion cracking (SCC). In this experiment, we separate the strain and surface deformation from the complex geometry of the crack tip to better understand the processes at work. Based on this concept, two possible explanations for the environmental influences on creep strain rates are discussed relating to the anodic dissolution of the free surface and hydrogen influences on deformation mechanisms. Consistencies of pH dependence between corrosion creep and SCC at low pH prove a creep-involved SCC mechanism, while the discrepancies between corrosion creep behavior and previous SCC results at high pH indicate a rate-limit step change in the crack propagation of the SCC process.

Wan, Quanhe; Quesnel, David J.

2013-03-01

201

Correlation between permanent deformation-related performance parameters of asphalt concrete mixes and binders  

NASA Astrophysics Data System (ADS)

This paper examines methods to predict the performance of hot asphalt concrete mixes based on performance parameters of binders. Specifically, relationships between binder parameters determined from multiple stress creep and recovery tests were correlated to the creep parameters of hot asphalt concrete mixes obtained from cyclic load compression testing. For the determination of creep parameters, a modified expression of the creep curve is proposed to cover the entire spectrum of permanent deformation; including the tertiary creep phase. Non-recoverable compliance, unrecovered strain, and recoverable strain of binders show good correlation to creep parameters of hot asphalt concrete mixes such as creep rate and high temperature performance ratio. Additionally, unrecovered strain and non-recoverable compliance of binders correlates well with mean rut depth of asphalt concrete mixes. However, no correlation has been detected between the difference in non-recoverable compliance of binders and permanent deformation parameters of asphalt concrete mixes.

Adorjányi, Kálmán; Füleki, Péter

2013-09-01

202

Influence of creep anisotropy on the stress-strain state of channel tubes  

SciTech Connect

The authors compile a mathematical model depicting creep behavior and swelling under the effects of neutron irradiation and temperature in zirconium alloy reactor channels. The model accounts for coolant pressure and thermoradiational creep anisotropy and performs a stress-strain analysis which incorporates elastic and plastic deformation and possible mechanical interference with graphite moderators. Test results against experimental conditions encountered in the RBMK-1000 reactor are given.

Zheltukhin, K.K.; Tutnov, A.A.; Ul'yanov, A.I.

1988-02-01

203

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

204

Water Weakening of Clinopyroxene in the Dislocation Creep Regime  

NASA Astrophysics Data System (ADS)

In our experimental studies, we investigated water weakening in the dislocation creep regime of natural Sleaford Bay clinopyroxenite containing diopside of compostion Ca1.0Mg0.8Fe0.2Si2O6. Samples were deformed in a gas-medium apparatus at confining pressures of 300 to 400 MPa and temperatures of 1373 to 1498 K with the oxygen fugacity buffered by the solid state reaction between Ni and NiO. A small amount of free water was added to each sample to obtain water-saturated conditions. Based on results from compressive creep experiments on seven samples deformed under hydrous condition, coarse-grained natural clinopyroxene yielded a stress exponent of n = 3.6+/- 0.6 and an activation energy of Q = 520+/-63KJ/mol. Compared to published data for dislocation creep of dry clinopyroxene, the wet aggregate flows up to 150 times faster at a given stress and temperature. Together with creep data for olivine, which show that olivine flows less than 10 times faster under hydrous condition than under anhydrous condition, the water weakening effect is much more significant in clinopyroxene than in olivine.

Chen, S.; Kohlstedt, D. L.

2003-12-01

205

Differential Response of Legumes and Creep Feeding on Gut Morphology and Faecal Composition in Weanling Pigs  

Microsoft Academic Search

The effects of creep feeding and different levels of soybean meal (SBM) and cowpea meal on the intestinal morphology and faecal characteristics were investigated in weaners. Prior to the feeding trial, one group of piglets was creep-fed and the other noncreep-fed. The two groups of piglets were weaned at 28 days and randomly assigned to four different diets, the main

M. O. Makinde; E. Umapathy; B. T. Akingbemi; K. T. Mandisodza; E. Skadhauge

1997-01-01

206

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

SciTech Connect

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

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

1996-07-31

207

Elevated temperature deformation of TD-nickel base alloys  

NASA Technical Reports Server (NTRS)

Sensitivity of the elevated temperature deformation of TD-nickel to grain size and shape was examined in both tension and creep. Elevated temperature strength increased with increasing grain diameter and increasing L/D ratio. Measured activation enthalpies in tension and creep were not the same. In tension, the internal stress was not proportional to the shear modulus. Creep activation enthalpies increased with increasing L/D ratio and increasing grain diameter, to high values compared with that of the self diffusion enthalpy. It has been postulated that two concurrent processes contribute to the elevated temperature deformation of polycrystalline TD-nickel: (1) diffusion controlled grain boundary sliding, and (2) dislocation motion.

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

1972-01-01

208

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

NASA Astrophysics Data System (ADS)

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

Whittaker, Mark T.; Wilshire, Brian

2013-01-01

209

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

210

Creep of a Silicon Nitride Under Various Specimen/Loading Configurations  

NASA Technical Reports Server (NTRS)

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

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

2000-01-01

211

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

SciTech Connect

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

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

2009-01-22

212

Dislocation creep behavior in Mg–Al–Zn alloys  

Microsoft Academic Search

The climb-controlled dislocation creep behavior was investigated in Mg–Al–Zn alloys of AZ31, AZ61 and AZ91 with different aluminum contents. The flow stress increased with the increase of aluminum content under the same deformation conditions. At high temperatures, the stress exponent was 5 and the activation energy was close to that for lattice diffusion of magnesium, whereas at low temperatures the

Hidetoshi Somekawa; Kinji Hirai; Hiroyuki Watanabe; Yorinobu Takigawa; Kenji Higashi

2005-01-01

213

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

214

Rate- and strain-dependent brittle deformation of rocks  

NASA Astrophysics Data System (ADS)

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

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

2014-03-01

215

Coupling creep and damage in concrete under high sustained loading: Experimental investigation on bending beams and application of Acoustic Emission technique  

NASA Astrophysics Data System (ADS)

Creep and damage in concrete govern the long-term deformability of concrete. Thus, it is important to understand the interaction between creep and damage in order to design reliable civil engineering structures subjected to high level loading during a long time. Many investigations have been performed on the influence of concrete mixture, the effect of the bond between the matrix and the aggregates, temperature, aging and the size effect on the cracking mechanism and fracture parameters of concrete. But there is a lack of results on the influence of the creep loading history. In the present paper, an experimental investigation on the fracture properties of concrete beams submitted to three point bending tests with high levels of sustained load that deals with creep is reported. The results aim first to investigate the ranges of variation of the time response due to creep damage coupled effects under constant load and secondly to evaluate the residual capacity after creep. For this purpose a series of tests were carried out on geometrically similar specimens of size 100x200x800mm with notch to depth ratio of 0.2 in all the test specimens. The exchange of moisture was prevented and beams were subjected to a constant load of 70% and 90% of the maximum capacity. Three point bending test were realized on specimen at the age of 28 days to determine the characteristics of concrete and the maximum load so we could load the specimens in creep. Threepoint bend creep tests were performed on frames placed in a climate controlled chamber [1]. Then after four months of loading, the beams subjected to creep were removed from the creep frames and then immediately subjected to three-point bending test loading up to failure with a constant loading rate as per RILEM-FMC 50 recommendations. The residual capacity on the notched beams and the evolution of the characteristics of concrete due to the basic creep was considered. The results show that sustained loading had a strengthening effect on concrete, probably because of the consolidation of the hardened cement paste. The influence of creep on fracture energy, fracture toughness, and characteristic length of concrete is also studied. The fracture energy and the characteristic length of concrete increases slightly when creep occurs prior to failure and the size of the fracture process zone increases too. The load-CMOD relationship is linear in the ascending portion and gradually drops off after the peak value in the descending portion. The length of the tail end portion of the softening curve increases with beams subjected to creep. Relatively more ductile fracture behavior was observed with beams subjected to creep. The contribution of non-destructive and instrumental investigation methods is currently exploited to check and measure the evolution of some negative structural phenomena, such as micro-and macro-cracking, finally resulting in a creep-like behaviour. Among these methods, the non-destructive technique based on acoustic Emission proves to be very effective, especially to check and measure micro-cracking that takes place inside a structure under mechanical loading. Thus as a part of the investigation quantitative acoustic emission techniques were applied to investigate microcracking and damage localization in concrete beams. The AE signals were captured with the AE WIN software and further analyzed with Noesis software analysis of acoustic emission data. AE waveforms were generated as elastic waves in concrete due to crack nucleation. And a multichannel data acquisition system was used to record the AE waveforms. During the three point bending tests, quantitative acoustic emission (AE) techniques were used to monitor crack growth and to deduce micro fracture mechanics in concrete beams before and after creep. Several specimens are experimented in order to match each cluster with corresponding damage mechanism of the material under loading. At the same time acoustic emission was used to investigate characteristic of the fracture process zone (length width and macro crack propagation

Saliba, J.; Loukili, A.; Grondin, F.

2010-06-01

216

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

PubMed

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

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

2009-04-01

217

Creep fracture of zirconium alloys  

NASA Astrophysics Data System (ADS)

Theoretical approaches utilized to predict the lifetime of spent nuclear fuel in interim dry storage assumed that diffusion controlled cavity growth controlled the failure time under these conditions. DCCG, however, fails to account for the fact that the failure time is related to the strain rate in Zircaloys according to the Monkman-Grant relationship. This paper will show that constrained cavity growth, which can account for the Monkman-Grant relationship but was not considered in the spent nuclear fuel lifetime prediction models, is more relevant to failure of spent nuclear fuel in dry storage. Contrary to reports in the past, constant stress creep tests performed in this study on Zircaloy-2 suggest that creep cavity nucleation and/or growth occurs prior to tertiary creep. Constant strain rate creep rupture tests on Zircaloy-2 show strong evidence of extensive cavity nucleation and growth near and at the fracture surface, indicating a creep cavitation failure mechanism under these conditions.

Hayes, Troy A.; Rosen, Robert S.; Kassner, Michael E.

2006-07-01

218

Creep-Fatigue Interaction Testing  

NASA Technical Reports Server (NTRS)

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

Halford, Gary R.

2001-01-01

219

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

220

Viscoelastic creep elimination in dielectric elastomer actuation by preprogrammed voltage  

NASA Astrophysics Data System (ADS)

Viscoelasticity causes a time-dependent deformation and lowers the response speed and energy conversion efficiency of VHB-based dielectric elastomers (DEs), thus seriously restricting a wide range of applications of this otherwise versatile soft smart material. The viscoelastic deformation of a prestretched VHB film in a circular actuator configuration is studied both theoretically and experimentally. By adjusting the applied voltage, viscoelastic creep can be dispelled and an invariable strain is obtained by simulation. Subsequently, an experiment was designed to validate the simulation and the results indicate that a constant strain can be achieved by preprogramming the applied actuation voltage.

Zhang, Junshi; Wang, Yanjie; McCoul, David; Pei, Qibing; Chen, Hualing

2014-11-01

221

High temperature indentation creep tests on anhydrite - a promising first look  

NASA Astrophysics Data System (ADS)

Indentation creep tests are established in materials engineering, providing information on rheology, deformation mechanisms, and related microstructures of materials. Here we explore the potential of this method on natural, polycrystalline anhydrite. The tests are run at atmospheric pressure, temperatures between 700 and 920 °C, and reference stresses between 7 and 30 MPa. An activation energy Q of 338 kJ mol-1 and a stress exponent n of 3.9 are derived. Deformation is localized into shear zones bounding a less deformed approximately conical plug underneath the indenter. Shear zone microstructures reveal inhomogeneous crystal-plastic deformation, subgrains, and extensive strain-induced grain boundary migration, while mechanical twinning appears not to be activated. Microstructure and mechanical data are consistent with deformation by dislocation creep.

Dorner, D.; Röller, K.; Stöckhert, B.

2014-08-01

222

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

PubMed

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

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

2012-10-01

223

Active fault creep variations at Chihshang, Taiwan, revealed by creep meter monitoring, 19982001  

E-print Network

Active fault creep variations at Chihshang, Taiwan, revealed by creep meter monitoring, 1998] The daily creep meter data recorded at Chihshang in 1998­2001 are presented. The Chihshang creep meter similar annual shortening rates: 16.2 mm at the Tapo site (comprising two connected creep meters) and 15

Lee, Jian-Cheng

224

High temperature creep properties of zirconium and Zircaloy-4 in vacuum and oxygen environments  

NASA Astrophysics Data System (ADS)

A special set-up has been used to follow the evolution of mechanical parameters under various applied stresses in in situ conditions (controlled temperature and atmosphere). This experimental set-up is used to study the creep behavior of zirconium and Zircaloy-4 in the temperature range 723-823 K. The influence of applied stresses, atmosphere and alloy grade on the deformation and oxidation processes are specifically analyzed. The results underline the presence of two distinct deformation domains for both alloy grades, depending on the applied stress value and the temperature. The results show that the presence of an oxide scale only leads to slight modifications of the creep behavior.

Moulin, G.; El Tahhan, R.; Favergeon, J.; Bigerelle, M.; Viennot, M.

2007-05-01

225

Extensional deformation along the southern boundary of the Gyeonggi Massif, South Korea: structural characteristics, age constraints, and tectonic implications  

NASA Astrophysics Data System (ADS)

The Permo-Triassic collision of the North and South China blocks caused the development of the Dabie-Sulu Orogen in China and Songrim Orogen in the Korean Peninsula. Extension after this collision is known from the Dabie-Sulu Orogen, but post-orogenic extension is not well defined in the Korean Peninsula. Extensional deformation along the southern boundary of the Gyeonggi Massif in Korea is characterized by top-down-to-the-south ductile shearing and subsequent brittle normal faulting, and was predated by regional metamorphism and north-vergent contractional deformation. Extension occurred between ~220 and 185 Ma based on the ages of pre-extensional regional metamorphism and post-extensional pluton emplacement. 40Ar/39Ar dating of syn-extensional muscovite in quartz-mica mylonite yields an age of 187.8 ± 5.6 (2 ?) Ma, in agreement with constraints from structural relationships. Together with the extensional deformation identified along the northern boundary of the Gyeonggi Massif (~226 Ma), the extension along the southern boundary is probably related to the exhumation of the massif during late-orogenic or post-orogenic extension associated with the Songrim Orogeny of the Korean Peninsula and forms an important event in the Phanerozoic crustal evolution of East Asia.

Han, Raehee; Min, Kyoungwon; Ree, Jin-Han; Foster, David A.

2014-04-01

226

Creep Ruptures in Heterogeneous Materials  

NASA Astrophysics Data System (ADS)

We present creep experiments on fiber composite materials with different controlled heterogeneity. All samples exhibit a power-law relaxation of the strain rate in the primary creep regime (Andrade's law) followed by a power-law acceleration up to rupture. We discover that the rupture time is proportional to the duration of the primary creep regime, showing the interplay between the two regimes and offering a method of rupture prediction. These experimental results are rationalized by a mean-field model of representative elements with nonlinear viscoelastic rheology and with a large heterogeneity of strengths.

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

2005-01-01

227

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

228

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

229

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

230

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

231

Study of creep crack growth in 2618 and 8009 aluminum alloys  

NASA Astrophysics Data System (ADS)

Creep crack growth (CCG) has been investigated in an 8009 (Al-Fe-V-S) P/M alloy at 175 °, 250 °, and 316 ° and in a 2618 ingot alloy at 150 °, 175 °, and 200 °. Under sustained load, subcritical crack growth is observed at stress intensity levels lower than K ic ; for 2618, at 200 °, crack growth is observed at stress intensities more than 40 pct lower than K ic . Alloys 8009 and 2618 exhibit creep brittle behavior, i.e., very limited creep deformation, during CCG. The CCG rates do not correlate with CCG parameters C* and C but correlate with the stress intensity factor, K, and the J integral. Generally, crack growth rates increase with increasing temperature. Micromechanisms of CCG have been studied with regard to microstructural deg-radation, environmental attack, and creep damage. Although theoretical estimation indicates that CCG resistance decreases with second-phase coarsening, such coarsening has not been observed at the crack tip. Also, no evidence is found for hydrogen- or oxygen-induced crack growth in comparing test results in moist air and in vacuum. Creep deformation and cavitation ahead of crack tip are responsible for observed time-dependent crack growth. Based on the cavitation damage in the elastic field, a micromechanical model is proposed which semiquantitatively explains the correlations between the creep crack growth rate and stress intensity factor, K.

Leng, Yang

1995-02-01

232

Creep fatigue life prediction for engine hot section materials (isotropic)  

NASA Technical Reports Server (NTRS)

The first two years of a two-phase program aimed at improving the high temperature crack initiation life prediction technology for gas turbine hot section components are discussed. In Phase 1 (baseline) effort, low cycle fatigue (LCF) models, using a data base generated for a cast nickel base gas turbine hot section alloy (B1900+Hf), were evaluated for their ability to predict the crack initiation life for relevant creep-fatigue loading conditions and to define data required for determination of model constants. The variables included strain range and rate, mean strain, strain hold times and temperature. None of the models predicted all of the life trends within reasonable data requirements. A Cycle Damage Accumulation (CDA) was therefore developed which follows an exhaustion of material ductility approach. Material ductility is estimated based on observed similarities of deformation structure between fatigue, tensile and creep tests. The cycle damage function is based on total strain range, maximum stress and stress amplitude and includes both time independent and time dependent components. The CDA model accurately predicts all of the trends in creep-fatigue life with loading conditions. In addition, all of the CDA model constants are determinable from rapid cycle, fully reversed fatigue tests and monotonic tensile and/or creep data.

Moreno, Vito; Nissley, David; Lin, Li-Sen Jim

1985-01-01

233

Numerical analysis for elucidation of nonlinear frictional characteristics of a deformed erythrocyte moving on a plate in medium subject to inclined centrifugal force.  

PubMed

Complex interactions between blood cells, plasma proteins, and glycocalyx in the endothelial surface layer are crucial in microcirculation. To obtain measurement data of such interactions, we have previously performed experiments using an inclined centrifuge microscope, which revealed that the nonlinear velocity-friction characteristics of erythrocytes moving on an endothelia-cultured glass plate in medium under inclined centrifugal force are much larger than those on plain or material-coated glass plates. The purpose of this study was to elucidate the nonlinear frictional characteristics of an erythrocyte on plain or material-coated glass plates as the basis to clarify the interaction between the erythrocyte and the endothelial cells. We propose a model in which steady motion of the cell is realized as an equilibrium state of the force and moment due to inclined centrifugal force and hydrodynamic flow force acting on the cell. Other electrochemical effects on the surfaces of the erythrocyte and the plate are ignored for the sake of simplicity. Numerical analysis was performed for a three-dimensional flow of a mixture of plasma and saline around a rigid erythrocyte model of an undeformed biconcave shape and a deformed shape with a concave top surface and a flat bottom surface. A variety of conditions for the concentration of plasma in a medium, the velocity of the cell, and the minimum gap width and the angle of attack of the cell from the plate, were examined to obtain the equilibrium states. A simple flat plate model based on the lubrication theory was also examined to elucidate the physical meaning of the model. The equilibrium angle of attack was obtained only for the deformed cell model and was represented as a power function of the minimum gap width. A simple flat plate model qualitatively explains the power function relation of the frictional characteristics, but it cannot explain the equilibrium relation, confirming the computational result that the deformation of the cell is necessary for the equilibrium. The frictional characteristics obtained from the present computation qualitatively agree with those of former experiments, showing the validity of the proposed model. PMID:25271707

Oshibe, Takashi; Hayase, Toshiyuki; Funamoto, Kenichi; Shirai, Atsushi

2014-12-01

234

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

235

Non-Classical Creep Behavior of Fusion-Cast Alumina Refractories  

SciTech Connect

The compressive creep behavior of a typical 50% ?-/50% ?-alumina fusion-cast refractory block was examined as a function of temperature. Test temperatures (1450-1650oC) were chosen to correspond to those typical of service conditions, while relatively high compressive test stresses (0.6 and 1.0 MPa compared to 0.2-0.4 MPa which is typical of service) were chosen to promote exaggerated deformation and to more accurately measure the resulting creep strain. It was found that the measured creep strain responses in this alumina were a sum of (contracting) compressive creep strain and expansion strain due to time and temperature dependent microcracking. Long term, isothtermal expansion tests were also conducted, and their results allowed for the deconvolution of the compressive creep and expansion strains present in the measured creep strain test data. The analysis shows that despite complications associated with conflicting expansion and contraction effects, classical creep analysis may be used with this alumina refractory after the strains associated with the non-steady-state mechanism are considered and accounted for.

Hemrick, James Gordon [ORNL; Wereszczak, Andrew A [ORNL

2009-01-01

236

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

237

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

238

Optimal combination of InSAR and GPS for measuring interseismic crustal deformation  

NASA Astrophysics Data System (ADS)

High spatial resolution measurements of interseismic deformation along major faults are critical for understanding the earthquake cycle and for assessing earthquake hazard. We propose a new remove/filter/restore technique to optimally combine GPS and InSAR data to measure interseismic crustal deformation, considering the spacing of GPS stations in California and the characteristics of interseismic signal and noise using InSAR. To constrain the longer wavelengths (>40 km) we use GPS measurements, combined with a dislocation model, and for the shorter wavelength information we rely on InSAR measurements. Expanding the standard techniques, which use a planar ramp to remove long wavelength error, we use a Gaussian filter technique. Our method has the advantage of increasing the signal-to-noise ratio, controlling the variance of atmosphere error, and being isotropic. Our theoretical analysis indicates this technique can improve the signal-to-noise ratio by up to 20%. We test this method along three segments of the San Andreas Fault (Southern section near Salton Sea, Creeping section near Parkfield and Mojave/Big Bend section near Los Angeles), and find improvements of 26%, 11% and 8% in these areas, respectively. Our data shows a zone of uplift to the west of the Creeping section of the San Andreas Fault and an area of subsidence near the city of Lancaster. This work suggests that after only 5 years of data collection, ALOS interferograms will provide a major improvement in measuring details of interseismic deformation.

Wei, Meng; Sandwell, David; Smith-Konter, Bridget

2010-07-01

239

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

240

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

241

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

242

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

243

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

244

Creep Behavior of Near-Stoichiometric Polycrystalline Binary NiAl  

NASA Technical Reports Server (NTRS)

New and published constant load creep and constant engineering strain rate data on near-stoichiometric binary NiAl in the intermediate temperature range 700 to 1300 K are reviewed. Both normal and inverse primary creep curves are observed depending on stress and temperature. Other characteristics relating to creep of NiAl involving grain size, stress and temperature dependence are critically examined and discussed. At stresses below 25 MPa and temperatures above 1000 K, a new grain boundary sliding mechanism was observed with n approx. 2, Qc approx. 100 kJ/ mol and a grain size exponent of about 2. It is demonstrated that Coble creep and accommodated grain boundary sliding models fail to predict the experimental creep rates by several orders of magnitude.

Raj, S. V.

2002-01-01

245

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

NASA Astrophysics Data System (ADS)

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

Trinh, B. T.; Hackl, K.

2014-07-01

246

Influence of grain size on the creep behavior of HfC-dispersed NiAl  

NASA Technical Reports Server (NTRS)

Rapid solidification technology has been utilized to produce a NiAl-4(wt pct)HfC composite containing about 0.3 vol pct HfC as dispersed 50 nm particles. Study of the 1300 K compressive creep properties demonstrated that the initial, small grain size microstructure was unstable under slow strain rate deformation conditions. The grain growth which occurred during testing led to considerable strengthening. Subsequent measurements of the creep properties of the coarse grained specimens revealed that this strength was achieved by a large increase in the activation energy for deformation without any change in the stress exponent. Based on this work, it is concluded that large grain microstructures will be required for optimum elevated temperature creep properties in dispersed NiAl.

Whittenberger, J. D.; Ray, Ranjan; Jha, Sunil C.

1992-01-01

247

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

248

"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

249

Creep of cold-worked Zry-4 at 673 K  

NASA Astrophysics Data System (ADS)

Creep data, at 673 K, up to times of about 400 h and stresses between 117.6 and 264.7 MPa, in flat specimens of cold-worked Zry-4, are reported. When viewed in a ?-/.? diagram, the data can be represented by Hart's equation of state /.? = /.? ?[ln(? ?/?)] {-1}/{?}, where ? ? and /.? ? are related to the plastic strain and ? is a constant, with a value similar to that obtained by measurements of the stress-relaxation in bending of the same material and at the same temperature. No distinction is made between primary and steady-state creep, indicating that the same mechanism is controlling the plastic deformation in both regions. The apparent activation energy was found to be independent of stress with a value close to that for self diffusion.

Povolo, F.; Marzocca, A. J.

1981-04-01

250

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

251

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

252

(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

253

Simulation and prediction of engineering deformation through comparisons of time serial and wavelet decomposition  

Microsoft Academic Search

Deformation on earth's surface covers crust displacement due to tectonism and land slide or subsidence caused by human activities or natural evolvement. The former is explained by tectonician through geologic investigation and researches. The local creep deformation arisen from engineering activities on earth's surface is complex and is often related with local engineering safety. So this kind of deformation attracts

Linyuan Xia; Guoxin Peng; Hui Tian; Zhongyi Wu

2008-01-01

254

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

255

Brittle creep, damage, and time to failure in rocks  

NASA Astrophysics Data System (ADS)

We propose a numerical model based on static fatigue laws in order to model the time-dependent damage and deformation of rocks under creep. An empirical relation between time to failure and applied stress is used to simulate the behavior of each element of our finite element model. We review available data on creep experiments in order to study how the material properties and the loading conditions control the failure time. The main parameter that controls the failure time is the applied stress. Two commonly used models, an exponential tf-exp (-b?/?0) and a power law function tf-?b' fit the data as well. These time-to-failure laws are used at the scale of each element to simulate its damage as a function of its stress history. An element is damaged by decreasing its Young's modulus to simulate the effect of increasing crack density at smaller scales. Elastic interactions between elements and heterogeneity of the mechanical properties lead to the emergence of a complex macroscopic behavior, which is richer than the elementary one. In particular, we observe primary and tertiary creep regimes associated respectively with a power law decay and increase of the rate of strain, damage event and energy release. Our model produces a power law distribution of damage event sizes, with an average size that increases with time as a power law until macroscopic failure. Damage localization emerges at the transition between primary and tertiary creep, when damage rate starts accelerating. The final state of the simulation shows highly damaged bands, similar to shear bands observed in laboratory experiments. The thickness and the orientation of these bands depend on the applied stress. This model thus reproduces many properties of rock creep, which were previously not modeled simultaneously.

Amitrano, David; Helmstetter, AgnèS.

2006-11-01

256

Seismological characteristics of the 2011 unrest in Santorini caldera: Implications for observed deformation and volcano-tectonics  

NASA Astrophysics Data System (ADS)

Santorini caldera has experienced several explosive eruptions in the past, the most well-known of these being the Late Bronze Age (ca. 1628 BC) eruption that may have been responsible for the demise of the Minoan civilization. Since the early 1950's the volcano has been dormant without exhibiting any significant activity except from discharge of low-temperature hydrothermal fluids. In January 2011 both deformation and seismic activity increased considerably signaling a period of unrest which however, did not result in an eruption. One permanent and seven temporary seismic stations equipped with three-component sensors were deployed by the National Observatory of Athens. These were combined with seismic stations from the University of Thessaloniki, seven with only a vertical component and four with three-component sensors and all operated under the Hellenic Unified Seismic Network, thus densely monitoring the Santorini Volcano. These seismic stations have recorded the seismic activity from its start up to now. About 290 micro-earthquakes recorded by at least 5 stations were analyzed for the purpose of obtaining accurate epicentral and hypocentral locations using both catalog and differential travel times from waveform cross-correlation. All of these events exhibit clear P- and S-phases indicating that they resulted from shear failure of rock rather than fluid-flow within volcanic conduits. Results show two well-defined clusters in Palea and Nea Kameni islands within the caldera with hypocentral depths ranging between 5-10 km. Interestingly, one more cluster of events with depths between 15-19 km appears near the area of Cape Coloumbo and developed almost simultaneously with the clusters within the caldera. The Mogi source depth inferred from geodetic observations previously is shallower (~4 km) and does not coincide spatially with the clusters within the caldera. This points to the possibility that seismicity and deformation may be excited by deeper pressure changes. Shear wave splitting measurements have also been performed using all available waveform data in order to understand the nature and spatial variation of the stress field during the unrest. Fast polarization directions exhibit some orientations consistent with the regional NW-SE extension in the area, but also orientations along NE-SW that signify the presence of a local stress field as well.

Konstantinou, Konstantinos; Evangelidis, Christos; Melis, Nikolaos; Liang, Wen-Tzong

2013-04-01

257

Plastic deformation of protein monolayers.  

PubMed Central

Globular proteins are peculiar solids that display both local stability of their conformation and the ability to undergo large cooperative changes of shape (conformational changes). If one forces a large deformation of the molecule, such that the structure is necessarily changed, it is not obvious whether the deformed globule can still remain a solid or whether it will melt. Is it possible to plastically deform a protein? Here we investigate this question with a micro-mechanical experiment on a small region (approximately 10 molecules) of a protein monolayer adsorbed on a rigid surface. For the two proteins studied, albumin and myoglobin, we observed that the molecules can be substantially deformed (approximately 1-2 nm deformation) by comparatively small stresses applied for sufficiently long times. The deformation is irreversible, and the protein remains in the solid state (i.e., displays a nonzero shear modulus). The dynamics of the deformation is approximately logarithmic in time, similar to creep in solids. These results show that globular proteins adsorbed on a surface can be plastically deformed. PMID:12324438

Singh-Zocchi, Mukta; Hanne, Jeungphill; Zocchi, Giovanni

2002-01-01

258

Experimental Creep Life Assessment for the Advanced Stirling Convertor Heater Head  

NASA Technical Reports Server (NTRS)

The United States Department of Energy is planning to develop the Advanced Stirling Radioisotope Generator (ASRG) for the National Aeronautics and Space Administration (NASA) for potential use on future space missions. The ASRG provides substantial efficiency and specific power improvements over radioisotope power systems of heritage designs. The ASRG would use General Purpose Heat Source modules as energy sources and the free-piston Advanced Stirling Convertor (ASC) to convert heat into electrical energy. Lockheed Martin Corporation of Valley Forge, Pennsylvania, is integrating the ASRG systems, and Sunpower, Inc., of Athens, Ohio, is designing and building the ASC. NASA Glenn Research Center of Cleveland, Ohio, manages the Sunpower contract and provides technology development in several areas for the ASC. One area is reliability assessment for the ASC heater head, a critical pressure vessel within which heat is converted into mechanical oscillation of a displacer piston. For high system efficiency, the ASC heater head operates at very high temperature (850 C) and therefore is fabricated from an advanced heat-resistant nickel-based superalloy Microcast MarM-247. Since use of MarM-247 in a thin-walled pressure vessel is atypical, much effort is required to assure that the system will operate reliably for its design life of 17 years. One life-limiting structural response for this application is creep; creep deformation is the accumulation of time-dependent inelastic strain under sustained loading over time. If allowed to progress, the deformation eventually results in creep rupture. Since creep material properties are not available in the open literature, a detailed creep life assessment of the ASC heater head effort is underway. This paper presents an overview of that creep life assessment approach, including the reliability-based creep criteria developed from coupon testing, and the associated heater head deterministic and probabilistic analyses. The approach also includes direct benchmark experimental creep assessment. This element provides high-fidelity creep testing of prototypical heater head test articles to investigate the relevant material issues and multiaxial stress state. Benchmark testing provides required data to evaluate the complex life assessment methodology and to validate that analysis. Results from current benchmark heater head tests and newly developed experimental methods are presented. In the concluding remarks, the test results are shown to compare favorably with the creep strain predictions and are the first experimental evidence for a robust ASC heater head creep life.

Krause, David L.; Kalluri, Sreeramesh; Shah, Ashwin R.; Korovaichuk, Igor

2010-01-01

259

High-Temperature Deformation and Ductility of a Modified 5083 Al Alloy  

NASA Astrophysics Data System (ADS)

The high-temperature deformation of a 5.5% Mg and 0.6% Ca modified 5083 aluminum alloy was investigated in the temperature range from 573 to 723 K at strain rates in the range of 10-5-10-1 s-1. Ca was added to form an insoluble second phase in the range of temperatures tested to improve the high-temperature characteristics of this alloy. It was shown that the deformation behavior of the alloy could be divided into two regions with stress exponent, n of 3.5 and 13 at low and high strain rates, respectively. The apparent activation energy determined in both regions suggested that the deformation process is diffusion controlled in both regions. The slightly high value of n at the low-strain rate region (viscous glide) was attributed to the presence of threshold stress. The values of threshold stress showed an exponential increase with decreasing temperature and a dependence with an energy term Qo = 16.5 kJ mol-1. Analysis of creep data in terms of threshold stress and using diffusivity of Mg in normalizing the strain rates, revealed two types of deformation behavior. At high values of normalized strain rate (kT} {DGb}}} > 10^{{ - 9}} ), a high value of stress exponent of n = 10 is observed, and the exponential law creep takes place. At low normalized strain rates ?10-9, the n value is 3 and the true activation energy, Q, is equal to 123 kJ mol-1 suggesting viscous glide of dislocations as rate-controlling mechanism. Enhanced ductility has been observed in the region of viscous-glide controlled deformation as a result of high strain-rate sensitivity.

El-Danaf, Ehab A.; Almajid, Abdulhakim A.; Soliman, Mahmoud S.

2008-08-01

260

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

261

Reactive infiltration processing and secondary compressive creep of NiAl and NiAl-W composites  

SciTech Connect

Reactive infiltration processing was used to fabricate bulk NiAl and fiber-reinforced NiAl composites. Homogeneous, pore-free materials were obtained by chemical reaction between nickel and aluminum after complete infiltration with liquid aluminum of performs of nickel wires (containing tungsten wires for the composites) with low surface-to-volume ratio, high permeability, and regular infiltration paths. Reactively-processed, monolithic NiAl exhibited compressive creep properties at 715 C and 1,025 C in good agreement with those of conventionally processed NiAl. The compressive creep behavior of NiAl composites reinforced with 5 to 20 vol pct W was also characterized at the same temperatures. At 715 C, the NiAl-W composites exhibited secondary creep with little primary and tertiary creep, while at 1,025 C, the composites displayed all three stages. Microstructurally, secondary creep was characterized by pure uniaxial compression of tungsten fibers. The measured composite secondary creep rates could be predicted reasonably well with the role-of-mixtures isostrain model developed for composites where both phases undergo creep deformation using tensile creep data measured on the as-received tungsten fibers.

Venkatesh, T.A.; Dunand, D.C.

2000-03-01

262

Vortex creep dynamics: theory and observations  

NASA Astrophysics Data System (ADS)

Contents: (1) Introduction. (2) Outline of vortex creep theory. (3) The equation of motion. (4) Two regimes of vortex creep. (5) The linear regime. (6) The nonlinear regime. (7) Ambiguities in distinguishing linear and nonlinear response. (8) Linear vs non-linear creep in the evolution of a pulsar. (9) Information from relaxation times.

Alpar, M. A.; Pines, D.

263

Cleavage and creep fracture of rock salt  

Microsoft Academic Search

The dominant failure mechanism in rock salt at ambient temperature is either cleavage or creep fracture. Since the transition of creep fracture to cleavage in a compressive stress field is not well understood, failure of rock salt by cleavage and creep fracture is analyzed in this paper to elucidate the effect of stress state on the competition between these two

K. S. Chan; D. E. Munson; S. R. Bodner; A. F. Fossum

1996-01-01

264

Testing Protocol for Module Encapsulant Creep (Presentation)  

SciTech Connect

Recently there has been an interest in the use of thermoplastic encapsulant materials in photovoltaic modules to replace chemically crosslinked materials, e.g., ethylene-vinyl acetate. The related motivations include the desire to: reduce lamination time or temperature; use less moisture-permeable materials; or use materials with better corrosion characteristics. However, the use of any thermoplastic material in a high-temperature environment raises safety and performance concerns, as the standardized tests currently do not expose the modules to temperatures in excess of 85C, yet modules may experience temperatures above 100C in operation. Here we constructed eight pairs of crystalline-silicon modules and eight pairs of glass/encapsulation/glass mock modules using different encapsulation materials of which only two were designed to chemically crosslink. One module set was exposed outdoors with insulation on the back side in Arizona in the summer, and an identical set was exposed in environmental chambers. High precision creep measurements and performance measurements indicate that despite many of these polymeric materials being in the melt state at some of the highest outdoor temperatures achievable, very little creep was seen because of their high viscosity, temperature heterogeneity across the modules, and in the case of the crystalline-silicon modules, the physical restraint of the backsheet. These findings have very important implications for the development of IEC and UL qualification and safety standards, and in regards to the necessary level of cure during the processing of crosslinking encapsulants.

Kempe, M. D.; Miller, D. C.; Wohlgemuth, J. H.; Kurtz, S. R.; Moseley, J. M.; Shah, Q.; Tamizhmani, G.; Sakurai, K.; Inoue, M.; Doi, T.; Masuda, A.

2012-02-01

265

Microstructural Characterization of Dislocation Networks During Harper-Dorn Creep of fcc, bcc, and hcp Metals and Alloys  

SciTech Connect

Harper-Dorn (H-D) creep is observed in metals and geological materials exposed to very low stresses at temperatures close to the melting point. It is one of several types of creep processes wherein the steady-state strain rate is proportional to the applied stress, Nabarro-Herring creep and Coble creep being two other important processes. H-D creep can be somewhat insidious because the creep rates are much larger than those expected for Nabarro-Herring or Coble creep. Since the working conditions of structural components of power plants and propulsion systems, as well as the motion of the earth’s mantle all involve very low stresses, an understanding of the factors controlling H-D creep is critical in preventing failures associated with those higher-than-expected creep rates. The purpose of this investigation was to obtain missing microstructural information on the evolution of the dislocation structures during static annealing of materials with fcc, bcc and hcp structure and use obtained results to test predictive capabilities of the dislocation network theory of H-D creep. In our view the evolutionary processes during static annealing and during Harper-Dorn creep are intimately related. The materials used in this study were fcc aluminum, hcp zinc and bcc tin. All characterizations of dislocation structures, densities and dislocation link length distributions were carried out using the etch pit method. To obtain quantitative information on the evolution of the dislocation networks during annealing the pure fcc aluminum samples were pre-deformed by creep at 913 and 620 K and then annealed. The higher deformation temperature was selected to generate starting dislocation networks similar to those forming during Harper-Dorn creep and the lower, to obtain higher dislocation densities suitable for reliable estimates of the parameters of the network growth law. The measured experimental link length distribution were, after scaling, (1) the same for all annealing temperatures, (2) time invariant and (3) identical to the distributions obtained previously for Harper-Dorn creep. This has never been shown before and confirms our theoretical expectations that evolution of the dislocation networks during annealing and H-D creep is governed by the same growth law. Obtained results were also used to predict H-D steady creep rates from annealing kinetics data using equations of the dislocation network theory. For the three considered stresses the theory predicts systematically smaller creep rates by the average factor of 4.5. Considering that the creep rates have been predicted from the annealing data alone and without any adjustable parameters, this results shout be considered as outstanding. In case of hcp zinc the samples were pre-deformed in compression at constant stress of 4 MPa at temperature of 573 K and subsequently annealed at the same temperature. During annealing samples readily recrystallized, but it was possible to obtain information on the link length distributions from several unrecrystallized grains. The results showed that the scaled link length distributions were time invariant and similar to those of the aluminum. The annealing studies on bcc tin were also curtailed by the concurrent recrystallization. It was only possible to obtain link length distribution for samples deformed in compression at constant load of 2 MPa at 423 K after unloading. The link length distribution was also in this case similar to that of the aluminum and zinc. These results suggest that the scaled link length distribution is universal and the same for the three considered crystal structures. This supports theoretical findings of these studies that appropriately scaled dislocation link length distribution should both universal and time invariant. We have also investigated the possibility of using alternative methods of estimating local dislocation densities from etch pits which could give more precise estimates of the dislocation link-lengths. The two most promising method are based on the use of Voronoi diagrams and uniform 3-connected nets

Przystupa, Marek A.

2007-12-13

266

Patterns of brittle deformation under extension on Venus  

NASA Technical Reports Server (NTRS)

The development of fractures at regular length scales is a widespread feature of Venusian tectonics. Models of lithospheric deformation under extension based on non-Newtonian viscous flow and brittle-plastic flow develop localized failure at preferred wavelengths that depend on lithospheric thickness and stratification. The characteristic wavelengths seen in rift zones and tessera can therefore provide constraints on crustal and thermal structure. Analytic solutions were obtained for growth rates in infinitesimal perturbations imposed on a one-dimensional, layered rheology. Brittle layers were approximated by perfectly-plastic, uniform strength, overlying ductile layers exhibiting thermally-activated power-law creep. This study investigates the formation of faults under finite amounts of extension, employing a finite-element approach. Our model incorporates non-linear viscous rheology and a Coulomb failure envelope. An initial perturbation in crustal thickness gives rise to necking instabilities. A small amount of velocity weakening serves to localize deformation into planar regions of high strain rate. Such planes are analogous to normal faults seen in terrestrial rift zones. These 'faults' evolve to low angle under finite extension. Fault spacing, orientation and location, and the depth to the brittle-ductile transition, depend in a complex way on lateral variations in crustal thickness. In general, we find that multiple wavelengths of deformation can arise from the interaction of crustal and mantle lithosphere.

Neumann, G. A.; Zuber, M. T.

1994-01-01

267

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

268

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

269

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

270

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

271

Associations between characters in populations of creeping-rooted lucerne (Medicago sativa L.)  

Microsoft Academic Search

Correlations were calculated between some non-creeping characters first season of growth. The non-creeping characters were: length of seed pods, the number of pod spirals, and autumn growth score.Correlations between the different measures of the size of the plant were consistently highly significant. Correlations between traits considered characteristic of M. falcata were not as close or consistent, and were considered to

M. W. Dunbier

1971-01-01

272

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

273

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

274

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

1998-12-01

275

Effect of high-energy X-ray irradiation on creep mechanisms in bone and dentin.  

PubMed

Under long-term loading creep conditions, mineralized biological tissues like bone are expected to behave in a similar manner to synthetic composites where the creeping matrix sheds load to the elastic reinforcement as creep deformation progresses. To study this mechanism in biological composites, creep experiments were performed at 37 °C on bovine compact bone and dentin. Static compressive stresses were applied to the samples, while wide- and small-angle scattering patterns from high energy synchrotron X-rays were used to determine, respectively, the elastic strain in the hydroxyapatite (HAP) platelets and the strain in the mineralized collagen fibril, as a function of creep time. In these highly irradiated biological composites, the reinforcing hydroxyapatite platelets progressively transfer some of their stress back to the softer protein matrix during creep. While such behavior can be explained by damage at the interface between the two phases, it is not consistent with measurements of the apparent moduli--the ratio of applied stress to elastic HAP strain measured throughout the creep experiments by elastic unload/load segments--which remained constant throughout the experiment and thus indicated good HAP/protein bonding. A possible explanation is a combination of X-ray and load induced interfacial damage explaining the shedding of load from the HAP during long term creep, coupled with interfacial re-bonding of the load-disrupted reversible bonds upon unloading, explaining the unaffected elastic load partitioning during unload/load segments. This hypothesis is further supported by finite element modeling which shows results mirroring the experimental strain measurements when considering interfacial delamination and a compliant interstitial space at the ends of the HAP platelets. PMID:23454365

Deymier-Black, Alix C; Singhal, Anjali; Yuan, Fang; Almer, Jonathan D; Brinson, L Catherine; Dunand, David C

2013-05-01

276

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

277

Multiple-creep-test apparatus  

NASA Technical Reports Server (NTRS)

Simplified, compact apparatus uses fixtures that can test three samples at once for flexure, compression, or double-shear creep. Each fixture uses series of rods and plates to divide one load equally among three samples. Fixtures could be expanded to carry more samples by adding more rods and plates.

Haehner, C. L.

1980-01-01

278

Microstructural evolution of uranium dioxide following compression creep tests: An EBSD and image analysis study  

NASA Astrophysics Data System (ADS)

Sintered UO2 pellets with relatively large grains (?25 ?m) are tested at 1500 °C under a compressive stress of 50 MPa, at different deformation levels up to 12%. Electron Back Scattered Diffraction (EBSD) is used to follow the evolution, with deformation, of grains (size, shape, orientation) and sub-grains. Image analyses of SEM images are performed to characterize emergence of a population of micron size voids. For the considered microstructure and test conditions, the results show that the deformation process of UO2 globally corresponds to grain boundary sliding, partly accommodated by a dislocational creep within the grains, leading to a highly sub-structured state.

Iltis, X.; Gey, N.; Cagna, C.; Hazotte, A.; Sornay, Ph.

2015-01-01

279

The Role of Eta Phase Formation on the Creep Strength and Ductility of INCONEL Alloy 740 at 1023 K (750 °C)  

NASA Astrophysics Data System (ADS)

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, J. P.; Pharr, G. M.

2012-06-01

280

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

281

Adaptive inverse control based on the creep property of IPMC  

Microsoft Academic Search

IPMC is one kind of electro-active polymer materials, which is called artificial muscle. Like piezoelectric material, the creep property also exists in IPMC. In this paper we explained how the creep property created in IPMC, modified the creep model based on piezoelectric in order to get a creep model which fitted IPMC. For the creep property of IPMC changes with

Li Zhi; Hao Lina

2009-01-01

282

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

283

Triaxial creep measurements on rock salt from the Jennings dome, Louisiana, borehole LA-1, core {number_sign}8  

SciTech Connect

Tejas Power Company requested that facilities in the Rock Mechanics Laboratory at Sandia National Laboratories be used to assess the time-dependent properties of rock salt from the Jennings dome in Acadia Parish, Louisiana. Nominally 2.5-inch diameter slat core from borehole LA-1, core 8 (depth 3924.8 to 3837.8 ft; 1196.8--1197.1 m) was provided to accomplish two tasks: (1) Using the smallest possible number of experiments, evaluate the tendency of Jennings salt to undergo time-dependent deformation (creep) under constant applied stresses, and compare the creep of Jennings salt with creep data for rock salt from other locations. (2) Assess the applicability of published laboratory-derived creep properties for rock salt from several bedded and domal sites in finite element analyses concerning the design of new gas storage caverns in the Jennings dome. The characterization of Jennings salt followed the same strategy that was applied in earlier laboratory experiments on core from the Moss Bluff dome near Houston, Texas. This report summarizes the relevant details of five creep experiments on a sample from depth 3927.5 ft, the results obtained, and how these results compared with laboratory creep measurements gathered on rock salt from other locations including the West Hackberry, Bryan Mound and Moss Bluff domes. The report also considers the estimates of specific creep parameters commonly used in numerical engineering design analyses.

Wawersik, W.R.; Zimmerer, D.J.

1994-05-01

284

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

285

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

286

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

287

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

288

Creep of Structural Nuclear Composites  

SciTech Connect

A research program has been established to investigate fiber reinforced ceramic composites to be used as control rod components within a Very High Temperature Reactor (VHTR) design. Two candidate systems have been identified, carbon fiber reinforced carbon (Cf/C) and silicon carbide fiber reinforced silicon carbide (SiCf/SiC) composites. One of the primary degradation mechanisms anticipated for these core components is high temperature thermal and irradiation enhanced creep. As a consequence, high temperature test equipment, testing methodologies, and test samples for very high temperature (up to 1600º C) tensile strength and long duration creep studies have been established. Actual testing of both tubular and flat, "dog-bone"-shaped tensile composite specimens will begin next year. Since there is no precedence for using ceramic composites within a nuclear reactor, ASTM standard test procedures are currently being established from these high temperature mechanical tests.

Will Windes; R.W. Lloyd

2005-09-01

289

Structural Benchmark Creep Testing for the Advanced Stirling Convertor Heater Head  

NASA Technical Reports Server (NTRS)

The National Aeronautics and Space Administration (NASA) has identified the high efficiency Advanced Stirling Radioisotope Generator (ASRG) as a candidate power source for use on long duration Science missions such as lunar applications, Mars rovers, and deep space missions. For the inherent long life times required, a structurally significant design limit for the heater head component of the ASRG Advanced Stirling Convertor (ASC) is creep deformation induced at low stress levels and high temperatures. Demonstrating proof of adequate margins on creep deformation and rupture for the operating conditions and the MarM-247 material of construction is a challenge that the NASA Glenn Research Center is addressing. The combined analytical and experimental program ensures integrity and high reliability of the heater head for its 17-year design life. The life assessment approach starts with an extensive series of uniaxial creep tests on thin MarM-247 specimens that comprise the same chemistry, microstructure, and heat treatment processing as the heater head itself. This effort addresses a scarcity of openly available creep properties for the material as well as for the virtual absence of understanding of the effect on creep properties due to very thin walls, fine grains, low stress levels, and high-temperature fabrication steps. The approach continues with a considerable analytical effort, both deterministically to evaluate the median creep life using nonlinear finite element analysis, and probabilistically to calculate the heater head s reliability to a higher degree. Finally, the approach includes a substantial structural benchmark creep testing activity to calibrate and validate the analytical work. This last element provides high fidelity testing of prototypical heater head test articles; the testing includes the relevant material issues and the essential multiaxial stress state, and applies prototypical and accelerated temperature profiles for timely results in a highly controlled laboratory environment. This paper focuses on the last element and presents a preliminary methodology for creep rate prediction, the experimental methods, test challenges, and results from benchmark testing of a trial MarM-247 heater head test article. The results compare favorably with the analytical strain predictions. A description of other test findings is provided, and recommendations for future test procedures are suggested. The manuscript concludes with describing the potential impact of the heater head creep life assessment and benchmark testing effort on the ASC program.

Krause, David L.; Kalluri, Sreeramesh; Bowman, Randy R.; Shah, Ashwin R.

2008-01-01

290

Compression creep of filamentary composites  

NASA Technical Reports Server (NTRS)

Axial and transverse strain fields induced in composite laminates subjected to compressive creep loading were compared for several types of laminate layups. Unidirectional graphite/epoxy as well as multi-directional graphite/epoxy and graphite/PEEK layups were studied. Specimens with and without holes were tested. The specimens were subjected to compressive creep loading for a 10-hour period. In-plane displacements were measured using moire interferometry. A computer based data reduction scheme was developed which reduces the whole-field displacement fields obtained using moire to whole-field strain contour maps. Only slight viscoelastic response was observed in matrix-dominated laminates, except for one test in which catastrophic specimen failure occurred after a 16-hour period. In this case the specimen response was a complex combination of both viscoelastic and fracture mechanisms. No viscoelastic effects were observed for fiber-dominated laminates over the 10-hour creep time used. The experimental results for specimens with holes were compared with results obtained using a finite-element analysis. The comparison between experiment and theory was generally good. Overall strain distributions were very well predicted. The finite element analysis typically predicted slightly higher strain values at the edge of the hole, and slightly lower strain values at positions removed from the hole, than were observed experimentally. It is hypothesized that these discrepancies are due to nonlinear material behavior at the hole edge, which were not accounted for during the finite-element analysis.

Graesser, D. L.; Tuttle, M. E.

1988-01-01

291

Cumulative creep damage for polycarbonate and polysulfone  

NASA Technical Reports Server (NTRS)

The literature for creep to failure cumulative damage laws are reviewed. Creep to failure tests performed on polycarbonate and polysulfone under single and two step loadings are discussed. A cumulative damage law or modified time fraction rule is developed using a power law for transient creep response as the starting point. Experimental results are approximated well by the new rule. Damage and failure mechanisms associated with the two materials are suggested.

Zhang, M.; Brinson, H. F.

1985-01-01

292

Model for transient creep of southeastern New Mexico rock salt  

SciTech Connect

In a previous analysis, existing experimental data pertaining to creep tests on rock salt from the Salado formation of S.E. New Mexico were fitted to an exponential transient creep law. While very early time portions of creep strain histories were not fitted very well for tests at low temperatures and stresses, initial creep rates in particular generally being underestimated, the exponential creep law has the property that the transient creep strain approaches a finite limit with time, and is therefore desirable from a creep modelling point of view. In this report, an analysis of transient creep is made. It is found that exponential transient creep can be related to steady-state creep through a universal creep curve. The resultant description is convenient for creep analyses where very early time behavior is not important.

Herrmann, W; Wawersik, W R; Lauson, H S

1980-11-01

293

Fiber Creep Evaluation by Stress Relaxation Measurements  

NASA Technical Reports Server (NTRS)

A simple bend stress relaxation (BSR) test has been used to measure the creep related properties of a chemically vapor-deposited SiC fiber. Time, temperature, and strain dependent BSR data were analyzed to ascertain the ability of the stress relaxation results to predict tensile creep as a function of the same parameters. The predictions compared very well to actual creep data obtained by axial measurements, indicating that the BSR test could be used for determining both creep and stress relaxation of polycrystalline ceramic fibers under tensile loading.

Morscher, Gregory N.; Dicarlo, James A.; Wagner, Timothy

1991-01-01

294

Fiber creep evaluation by stress relaxation measurements  

SciTech Connect

A simple bend stress relaxation (BSR) test has been used to measure the creep related properties of a chemically vapor-deposited SiC fiber. Time, temperature, and strain dependent BSR data were analyzed to ascertain the ability of the stress relaxation results to predict tensile creep as a function of the same parameters. The predictions compared very well to actual creep data obtained by axial measurements, indicating that the BSR test could be used for determining both creep and stress relaxation of polycrystalline ceramic fibers under tensile loading. 10 refs.

Morscher, G.N.; Dicarlo, J.A.; Wagner, T.

1991-08-01

295

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

296

Creep analysis of solid oxide fuel cell with bonded compliant seal design  

NASA Astrophysics Data System (ADS)

Solid oxide fuel cell (SOFC) requires good sealant because it works in harsh conditions (high temperature, thermal cycle, oxidative and reducing gas environments). Bonded compliant seal (BCS) is a new sealing method for planar SOFC. It uses a thin foil metal to bond the window frame and cell, achieving the seal between window frame and cell. At high temperature, a comprehensive evaluation of its creep strength is essential for the adoption of BCS design. In order to characterize the creep behavior, the creep induced by thermal stresses in SOFC with BCS design is simulated by finite element method. The results show that the foil is compressed and large thermal stresses are generated. The initial peak thermal stress is located in the thin foil because the foil acts as a spring stores the thermal stresses by elastic and plastic deformation in itself. Serving at high temperature, initial thermal displacement is partially recovered because of the creep relaxation, which becomes a new discovered advantage for BCS design. It predicts that the failures are likely to happen in the middle of the cell edge and BNi-2 filler metal, because the maximum residual displacement and creep strain are located.

Jiang, Wenchun; Zhang, Yucai; Luo, Yun; Gong, J. M.; Tu, S. T.

2013-12-01

297

Dislocation Jamming and Andrade Creep M.Carmen Miguel, 1 Alessandro Vespignani, 2 Michael Zaiser, 3 and Stefano Zapperi 4  

E-print Network

Dislocation Jamming and Andrade Creep M.­Carmen Miguel, 1 Alessandro Vespignani, 2 Michael Zaiser the correlated motion of dislocation structures near a dynamic transition separating a flowing from a jammed activity of ice crystals [13]. Other phenomena in plastically deforming crystals, such as hardening

Miguel-Lopez, Carmen

298

Shear Correction Factors in Creep-Damage Analysis of Beams, Plates and Shells  

NASA Astrophysics Data System (ADS)

Modern design rules for thin-walled structures which operate at elevated temperatures are based on the demand that the creep and may be the damage behaviour should be taken into account. In the last four decades various models including the scalar or tensor valued hardening and damage variables are established. These models reflect the influence of the deformation or the damage induced anisotropy on the creep response. One problem in creep analysis of thin-walled structures is the selection of the structural mechanics model which has to be adequate to the choice of the constitutive equations. Considering complex loading conditions the structural mechanics model has to reflect for instance the different constitutive behaviour in tension and compression. Below the applicability of classical engineering models for beams, plates and shells to the creep-damage analysis is discussed. It will be shown that a first improvement of the classical approach can be given within the assumptions of the first order shear deformation theory. Based on the beam equations we demonstrate that the shear correction factors have to be modified within the time-step analysis.

Altenbach, Holm; Naumenko, Konstantin

299

Deformation Characteristics, Geometry and Kinematics of Active Fold Scarp: A Case Study from the Mingyaole Anticline, Southern Foreland of Chinese Tian Shan  

NASA Astrophysics Data System (ADS)

The fold scarp, a type of geomorphic scarp formed by folding without fault offsets on the surface, can be used to constrain folding and slip rates and kinematics and to reconstruct a folding history despite a lack of full constraints on the subsurface structure. Recently, the conceptual, geometric, and kinematic model of fold scarps formed by fault-bend folding (fault-bend fold scarp) were developed. But for other types of fold scarp, there are few detailed investigations till now. Located at southern foreland of Chinese Tian Shan, the Mingyaole anticline is interpreted to be a detachment fold. Along the Kangoulvke river valley, a series of detachment fold scarps occur on the fluvial terrace surfaces in both fold limbs. In the south limb, height and slope of fold scarps on the T3 and T1 terraces are ~46m/~26° and ~6m/~16° respectively. The scarp locations are correlated with an underlying narrow synclinal hinge separating a 58° dip and a 16°dip domain) and the strike of the scarp is parallel with the hinge. On the north limb, the height and slope of fold scarp on the T3 are ~44 m and ~8° and are correlated with a wide synclinal hinge zone in which the dip decreases gradually from 70° to 14° across a width of ~300 m. At SW tip of the fold, fold scarps also occur on high terraces: slopes of fold scarps on the T3a and T4a are ~6° and ~7°, respectively. Detailed geologic and geomorphic mapping and dGPS survey data indicate the fold scarps along the Kalangoulvke river valley and at the fold's SW tip are formed by hinge migration and strong limb rotation, respectively. We investigated deformation characteristics, kinematics, and geometry of these detachment fold scarps. Despite similarities with fault-bend fold scarps, detachment-fold scarps have some pronounced differences, which suggests that the type of fold scarp should be defined prior to calculating folding rates.

Li, T.; Chen, J.; Jessica, T.; Burbank, D. W.

2013-12-01

300

Creep and stress-rupture behavior of Y 2O 3–Nd 2O 3-doped silicon nitrides with different additive contents  

Microsoft Academic Search

Tensile creep tests were performed on two grades of gas-pressure sintered silicon nitride. Silicon nitride SN4 contained 2.0 mol% Nd2O3 and 2.0 mol% Y2O3 as sintering aids, and the additives for silicon nitride SN1 were 0.5 mol% Nd2O3 and 0.5 mol% Y2O3. The delayed failure of SN4 was thought to result from creep rupture because considerable creep deformation was found

Jian-Wu Cao; Akira Okada; Naoto Hirosaki

2002-01-01

301

Non-contact measurements of creep properties of niobium at 1985?°C  

NASA Astrophysics Data System (ADS)

The stress exponent in the power-law creep of niobium at 1985?°C was measured by a non-contact technique using an electrostatic levitation facility at NASA MSFC. This method employs a distribution of stress to allow the stress exponent to be determined from each test, rather than from the curve fit through measurements from multiple samples that is required by conventional methods. The sample is deformed by the centripetal acceleration from the rapid rotation, and the deformed shapes are analyzed to determine the strain. Based on a mathematical proof, which revealed that the stress exponent was determined uniquely by the ratio of the polar to equatorial strains, a series of finite-element analyses with the models of different stress exponents were also performed to determine the stress exponent corresponding to the measured strain ratio. The stress exponent from the ESL experiment showed a good agreement with those from the literature and the conventional creep test.

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

2015-01-01

302

Experimental pressure solution compaction of chalk in aqueous solutions Part 1. Deformation behavior and chemistry  

E-print Network

Experimental pressure solution compaction of chalk in aqueous solutions Part 1. Deformation solution creep, chalk from the Paris basin (France) was deformed in a tri- axial press with fluids. The major goal of this investigation was to study the physico-chemical reactions that occur when chalk

303

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

304

Strain localization during deformation of Westerly granite  

NASA Technical Reports Server (NTRS)

A specimen of Westerly granite was cyclically loaded to near failure at 50 MPa confining pressure. Holographic interferometry provided detailed measurements of localized surface deformations during loading and unloading. The data are consistent with deformation occurring primarily elastically at low differential stress; in conjunction with one incipient fault zone between approximately 350 and 520 MPa differential stress; and in conjunction with a second incipient fault zone above 580 MPa and/or during creep. During unloading only one fault zone, that which is active at the intermediate stress levels during loading, is seen to recede.

Brodsky, N. S.; Spetzler, H. A.

1984-01-01

305

Effect of aqueous and carbonic fluids on the dislocation creep strength of quartz  

Microsoft Academic Search

Dislocation creep experiments conducted on quartzite indicate that the presence of CO2 can cause strengthening or weakening depending on the oxygen fugacity (fO2) of the deformation environment. Under oxidizing conditions (ferrosilite-hematite-quartz), the presence of CO2 reduces the water fugacity (fH2O) and results in strengthening of the quartz. Under moderately reducing conditions (?Ni-NiO), CO2 reacts with H2 from the sample assembly

Linda J. Chernak; Greg Hirth; Jane Selverstone; Jan Tullis

2009-01-01

306

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

307

Effect of initial microstructure on microstructural instability and creep resistance of XD TiAl alloys  

Microsoft Academic Search

A number of lamellar structures were produced in XD TiAl alloys (Ti-45 at. pct and 47 at. pct Al-2 at. pct Nb-2 at. pct Mn+0.8\\u000a vol pct TiB2) by selected heat treatments. During creep deformation, microstructural degradation of the lamellar structure was characterized\\u000a by coarsening and spheroidization, resulting in the formation of fine globular structures at the grain boundaries. Grain

Hanliang Zhu; K. Maruyama; D. Y. Seo; P. Au

2006-01-01

308

Failure of a welded pressure vessel due to creep: damage initiation, evolution and reheat cracking  

Microsoft Academic Search

Continuum damage mechanics (CDM)-based constitutive equations are reviewed and presented for austenitic AISI 316H stainless steels, which undergo creep deformation and damage at 550°C. Two multi-axial stress rupture functions\\/criteria have been utilised. Equations and the finite element computer code, DAMAGE XX, were used to carry out CDM studies of the weldment in an axi-symmetric equivalent of the flank section of

F. Vakili-Tahami; Hayhurst

2007-01-01

309

Deformation mechanisms during low-and high-temperature superplasticity in 5083 Al-Mg alloy  

NASA Astrophysics Data System (ADS)

The controlling deformation mechanisms and grain boundary sliding behavior during low-, medium-, and high-temperature superplasticity (LTSP, MTSP, and HTSP) in fine-grained 5083 Al-Mg base alloys are systematically examined as a function of strain. Grain boundary sliding was observed to proceed at temperatures as low as 200 °C. With increasing LTSP straining from the initial (?<0.5) to later stages (?>1.0), the strain rate sensitivity m, plastic anisotropy factor R, high-angle grain boundary fraction, grain size exponent p, and grain boundary sliding contribution all increased. During the initial LTSP stage, there was little grain size dependence and the primary deformation mechanisms were solute drag creep plus minor power-law creep. At later stages, grain size dependence increased and grain boundary sliding gradually controlled the deformation. During MTSP and HTSP, solute drag creep and grain boundary sliding were the dominant deformation mechanisms.

Hsiao, I. C.; Huang, J. C.

2002-05-01

310

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

311

Cumulative creep damage for polycarbonate and polysulfone  

NASA Technical Reports Server (NTRS)

Creep to failure tests performed on polycarbonate and polysulfone under single and two step loadings are discussed. A cumulative damage law or modified time fraction rule is developed using a power law for transient creep response as the starting point. Experimental results are approximated well by the new rule. Damage and failure mechanisms associated with the two materials are suggested.

Zhang, M. J.; Straight, M. R.; Brinson, H. F.

1985-01-01

312

Time-dependent deformation of gas shales - role of rock framework versus reservoir fluids  

NASA Astrophysics Data System (ADS)

Hydraulic fracturing operations are generally performed to achieve a fast, drastic increase of permeability and production rates. Although modeling of the underlying short-term mechanical response has proven successful via conventional geomechanical approaches, predicting long-term behavior is still challenging as the formation interacts physically and chemically with the fluids present in-situ. Recent experimental work has shown that shale samples subjected to a change in effective stress deform in a time-dependent manner ("creep"). Although the magnitude and nature of this behavior is strongly related to the composition and texture of the sample, also the choice of fluid used in the experiments affects the total strain response - strongly adsorbing fluids result in more, recoverable creep. The processes underlying time-dependent deformation of shales under in-situ stresses, and the long-term impact on reservoir performance, are at present poorly understood. In this contribution, we report triaxial mechanical tests, and theoretical/thermodynamic modeling work with the aim to identify and describe the main mechanisms that control time-dependent deformation of gas shales. In particular, we focus on the role of the shale solid framework versus the type and pressure of the present pore fluid. Our experiments were mainly performed on Eagle Ford Shale samples. The samples were subjected to cycles of loading and unloading, first in the dry state, and then again after equilibrating them with (adsorbing) CO2 and (non-adsorbing) He at fluid pressures of 4 MPa. Stresses were chosen close to those persisting under in-situ conditions. The results of our tests demonstrate that likely two main types of deformation mechanisms operate that relate to a) the presence of microfractures as a dominating feature in the solid framework of the shale, and b) the adsorbing potential of fluids present in the nanoscale voids of the shale. To explain the role of adsorption in the observed compaction creep, we postulate a serial coupling between 1) stress-driven desorption of the fluid species, 2) diffusion of the desorbed species out of the solid, and 3) consequent shrinkage. We propose a model in which the total shrinkage of the solid (Step 3) that is measured as bulk compaction, is driven by a change in stress state (Step 1), and evolves in time controlled by the diffusion characteristics of the system (Step 2). Our experimental and modeling study shows that both the nature of the solid framework of the shale, as well as the type and pressure of pore fluids affect the long-term in-situ mechanical behavior of gas shale reservoirs.

Hol, Sander; Zoback, Mark

2013-04-01

313

Influence of Hold Time on Creep-Fatigue Behavior of an Advanced Austenitic Alloy  

SciTech Connect

An advanced austenitic alloy, HT-UPS (high temperature-ultrafine precipitate strengthened), is a candidate material for the structural components of fast reactors and energy-conversion systems. HT-UPS provides improved creep resistance through a composition based on 316 stainless steel (SS) with additions of Ti and Nb to form nano-scale MC precipitates in the austenitic matrix. The low cycle fatigue and creep-fatigue behavior of a HT-UPS alloy has been investigated at 650 C, 1.0% total strain, and an R ratio of -1 with hold times as long as 9000 sec at peak tensile strain. The cyclic deformation response of HT-UPS is compared to that of 316 SS. The cycles to failure are similar, despite differences in peak stress profiles and the deformed microstructures. Cracking in both alloys is transgranular (initiation and propagation) in the case of continuous cycle fatigue, while the primary cracks also propagate transgranularly during creep-fatigue cycling. Internal grain boundary damage as a result of the tensile hold is present in the form of fine cracks for hold times of 3600 sec and longer and substantially more internal cracks are visible in 316 SS than HT-UPS. The dislocation substructures observed in the deformed material are different. An equiaxed cellular structure is observed in 316 SS, whereas tangles of dislocations are present at the nanoscale MC precipitates in HT-UPS and no cellular substructure is observed.

Mark Carroll; Laura Carroll

2011-09-01

314

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

315

Experimental deformation and grain growth of pure water ice aggregates  

NASA Astrophysics Data System (ADS)

Water ice is the principal constituent of the low density moons of the outer solar system, and the flow behavior of ice is of great importance in dynamic processes on icy moons. Our interest here is on the influence that grain growth has on the flow behavior of ice. By understanding grain growth in combination with flow mechanisms it is possible to reconstruct thermal evolutions and tectonic histories of icy moons. Grain growth is expected to influence the evolution of strength of ice by altering the relative contributions to strain rate by grain-size-sensitive (GSS) creep mechanisms, such as diffusion and grain-boundary sliding, and grain-size-insensitive (GSI) creep mechanisms, such as dislocation creep. In particular, we are interested in examining the so-called field boundary hypothesis wherein grain size evolution and GSI and GSS creep mechanisms eventually lead to a dynamic balance involving a distribution of grain sizes and significant operation of both types creep mechanisms. We studied grain size evolution both during static annealing and during deformation. Static anneals ran for up to two weeks at 213 ? T ? 268 K and hydrostatic pressures 0.1 MPa and 100 MPa. Static grain growth observations allow us to calibrate values for the grain size exponent m and the activation energy Q as used in conventional grain growth laws. We simulated grain growth of ice based on the microphysical model of Kellermann Slotemaker (2006 - PhD thesis Utrecht University, the Netherlands). This model takes into account full grain size distributions. Triaxial deformation experiments were carried out for a variety of starting grain sizes, from 2 to 250 microns, of both narrow and broad size distributions. Small grain sizes promote GSS creep; large sizes promote GSI creep and a mixture of large and small will result in mixed-mechanism deformation, in a ratio that will change as the grain size distribution evolves. All deformation runs were performed at temperatures > 170 K, pressures ranging between 30 MPa and 100 MPa and strain rates between 1e-8/s and 1e-4/s. The fine-grained ice (< 2 microns) which is used for the grain growth experiments and the deformation experiments starting in the GSS-creep field was generated by a special pressure-release technique described by Stern et al. (1997 - J. Geoph. Res, 102). The fine-grained ice material can be cold-pressed resulting in dense ice aggregates with a porosity < 0.5% and randomly oriented ice crystals. Grain sizes, grain size distributions and grain topologies of the different types of experiments were measured by cryogenic SEM and image analysis techniques.

Diebold, S.; de Bresser, J. H.; Durham, W. B.; Stern, L. A.

2010-12-01

316

InSAR measurements around active faults: creeping Philippine Fault and un-creeping Alpine Fault  

NASA Astrophysics Data System (ADS)

Recently, interferometric synthetic aperture radar (InSAR) time-series analyses have been frequently applied to measure the time-series of small and quasi-steady displacements in wide areas. Large efforts in the methodological developments have been made to pursue higher temporal and spatial resolutions by using frequently acquired SAR images and detecting more pixels that exhibit phase stability. While such a high resolution is indispensable for tracking displacements of man-made and other small-scale structures, it is not necessarily needed and can be unnecessarily computer-intensive for measuring the crustal deformation associated with active faults and volcanic activities. I apply a simple and efficient method to measure the deformation around the Alpine Fault in the South Island of New Zealand, and the Philippine Fault in the Leyte Island. I use a small-baseline subset (SBAS) analysis approach (Berardino, et al., 2002). Generally, the more we average the pixel values, the more coherent the signals are. Considering that, for the deformation around active faults, the spatial resolution can be as coarse as a few hundred meters, we can severely 'multi-look' the interferograms. The two applied cases in this study benefited from this approach; I could obtain the mean velocity maps on practically the entire area without discarding decorrelated areas. The signals could have been only partially obtained by standard persistent scatterer or single-look small-baseline approaches that are much more computer-intensive. In order to further increase the signal detection capability, it is sometimes effective to introduce a processing algorithm adapted to the signal of interest. In an InSAR time-series processing, one usually needs to set the reference point because interferograms are all relative measurements. It is difficult, however, to fix the reference point when one aims to measure long-wavelength deformation signals that span the whole analysis area. This problem can be solved by adding the displacement offset in each interferogram as a model parameter and solving the system of equations with the minimum norm condition. This way, the unknown offsets can be automatically determined. By applying this method to the ALOS/PALSAR data acquired over the Alpine Fault, I obtained the mean velocity map showing the right-lateral relative motion of the blocks north and south of the fault and the strain concentration (large velocity gradient) around the fault. The velocity gradient around the fault has along-fault variation, probably reflecting the variation in the fault locking depth. When one aims to detect fault creeps, i.e., displacement discontinuity in space, one can additionally introduce additional parameters to describe the phase ramps in the interferograms and solve the system of equations again with the minimum norm condition. Then, the displacement discontinuity appears more clearly in the result at the cost of suppressing long-wavelength displacements. By applying this method to the ALOS/PALSAR data acquired over the Philippine Fault in Leyte Island, I obtained the mean velocity map showing fault creep at least in the northern and central parts of Leyte at a rate of around 10 mm/year.

Fukushima, Y.

2013-12-01

317

Microstructural Evolution of INCONEL® Alloy 740H® Fusion Welds During Creep  

NASA Astrophysics Data System (ADS)

Electron microscopy techniques have been used to investigate the cause of premature creep failure in the fusion zone of INCONEL® Alloy 740H® (INCONEL and 740H are registered trademarks of Special Metals Corporation) welds. The reduced creep rupture lives of all-weld-metal and cross-weld creep specimens (relative to base metal specimens) have been attributed to the presence of large grain boundary regions that were denuded in fine ?' but contained coarse, elongated particles. Investigation of creep rupture specimens has revealed four factors that influence the formation of these coarsened zones, and the large particles found within them have been identified as ?'. Comparisons of the microstructural characteristics of these zones to the characteristics that are typical of denuded zones formed by a variety of mechanisms identified in the literature have been made. It is concluded that the mechanism of ?'-denuded zone formation in alloy 740H is discontinuous coarsening of the ?' phase. The discontinuous reaction is catalyzed by the grain boundary migration and sliding which occur during creep and likely promoted by the inhomogeneous weld metal microstructure that results from solute segregation during solidification. The increased susceptibility to the formation of the observed ?'-denuded zones in the weld metal as compared to the base metal is discussed in the context of differences in the contributions to the driving force for the discontinuous coarsening reaction.

Bechetti, Daniel H.; DuPont, John N.; de Barbadillo, John J.; Baker, Brian A.; Watanabe, Masashi

2015-02-01

318

Microstructural Evolution of INCONEL® Alloy 740H® Fusion Welds During Creep  

NASA Astrophysics Data System (ADS)

Electron microscopy techniques have been used to investigate the cause of premature creep failure in the fusion zone of INCONEL® Alloy 740H® (INCONEL and 740H are registered trademarks of Special Metals Corporation) welds. The reduced creep rupture lives of all-weld-metal and cross-weld creep specimens (relative to base metal specimens) have been attributed to the presence of large grain boundary regions that were denuded in fine ?' but contained coarse, elongated particles. Investigation of creep rupture specimens has revealed four factors that influence the formation of these coarsened zones, and the large particles found within them have been identified as ?'. Comparisons of the microstructural characteristics of these zones to the characteristics that are typical of denuded zones formed by a variety of mechanisms identified in the literature have been made. It is concluded that the mechanism of ?'-denuded zone formation in alloy 740H is discontinuous coarsening of the ?' phase. The discontinuous reaction is catalyzed by the grain boundary migration and sliding which occur during creep and likely promoted by the inhomogeneous weld metal microstructure that results from solute segregation during solidification. The increased susceptibility to the formation of the observed ?'-denuded zones in the weld metal as compared to the base metal is discussed in the context of differences in the contributions to the driving force for the discontinuous coarsening reaction.

Bechetti, Daniel H.; DuPont, John N.; de Barbadillo, John J.; Baker, Brian A.; Watanabe, Masashi

2014-12-01

319

Slow crack propagation in glass and creep prediction  

NASA Astrophysics Data System (ADS)

The context of our study is the observation of the time-dependent deformation of cracked glass. The aim of our study is to observe the slow crack propagation, to quantify it and to predict finally the creep behavior. We performed creep experiments in compaction conditions in a triaxial cell, on cracked boro-silicate glass samples. 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. Strain and acoustic emission (AE) are recorded. Several experiments are performed at different confining pressures (15 or 25 MPa), different pore fluid conditions (with argon gas, considered as the dry case, with tap water saturated porosity, or with distilled water) and different temperatures (ambiant temperature, 50oC or 80oC). Linear increase of the volumetric strain is first observed. A dilatancy increase is recorded. Note that dilatancy does not appear in constant strain rate tests. Constant stress tests show that dilatancy develops during a time interval that depends on the stress level. In addition AE rate are recorded. A non zero AE rate is an evidence of crack propagation. We use a micro-mechanical model that gives the stress intensity factor at the crack tips. This factor depends on stress and geometrical parameters (all known). An exponential law describe the rate of crack propagation, as a function of temperature, environment and applied stresses. This model allows us to predict the creep rate in glass. Assuming a constant crack aspect ratio, crack length and volumetric strain are related. The volumetric strain rate is calculated from model and compared to the data.

Mallet, Celine; Fortin, Jerome; Gueguen, Yves

2013-04-01

320

COMPARISON BETWEEN CREEP FAILURE ANALYSIS AND MAGNETIC BARKAHUSEN NOISE RESULTS  

Microsoft Academic Search

On this work we compared the results obtained after a c onventional creep failure analysis and magnetic Barkhausen noise. We chose one region without creep damage that was named as standard. Two other regions with creep damage were named as T1 and T2. The sample T1 after optical metallographic analysis has presented level A and B of creep damage according

Jonhson D. ANGELO; Linilson R. PADOVESE; Manuel ALBERTERIS

321

Analysis of test system misalignment in the creep test  

NASA Technical Reports Server (NTRS)

Sheet type rectangular 1100-0 aluminum specimens were tested. The creep strain at the geometric centerline of the specimen is different than that at the neutral axis, and decreases with time. The effect of misalignment, which decreases with creep time, is minimized when creep tests are conducted with long pullrods and large initial strain level (high creep stress).

Wu, H. C.; Wang, T. P.

1980-01-01

322

Characterization of elastic and time-dependent deformations in high performance lightweight concrete by image analysis  

Microsoft Academic Search

Image analysis and strain mapping were used to examine the nature of elastic, creep and shrinkage strains in high performance lightweight concrete (HPLC). The strain maps showed non-uniform deformations related to microstructural features. Both average strain and non-uniformity increased with time under testing. Paste-rich regions exhibited higher creep plus shrinkage than the lightweight aggregate (LWA) particles examined herein; it is

Mauricio Lopez; Lawrence F. Kahn; Kimberly E. Kurtis

2009-01-01

323

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

324

Finite deformation biphasic material properties of bovine articular cartilage from confined compression experiments  

Microsoft Academic Search

In 1990, Holmes and Mow [Journal of Biomechanics23, 1145–1156] developed a hyperelastic biphasic theory to describe finite deformation behaviors of articular cartilage. To date, however, no experimental finite deformation studies have been made to assess the ability of this constitutive model to describe its finite deformation behaviors (e.g. kinetic creep and stress-relaxation, and equilibrium responses). The objectives of this study

G. A. Ateshian; W. H. Warden; J. J. Kim; R. P. Grelsamer; V. C. Mow

1997-01-01

325

Annealing studies of ?-titanium aluminides alloyed with light elements for creep strengthening  

Microsoft Academic Search

A fully-lamellar ?-titanium aluminide alloy containing carbon and silicon additions has been found to have superior creep resistance. The aging characteristics of this alloy, which also contains Nb, Cr, and W, have been studied by means of transmission electron microscopy techniques and are correlated to the post-crept microstructures. Precipitation of carbides and silicides along ?? interlamellar boundaries was observed during

P.-I. Gouma; K. Subramanian; Y.-W. Kim; M. J. Mills

1998-01-01

326

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

327

Prediction of creep of polymer concrete  

SciTech Connect

We studied the applicability of the phenomenological approach to the prediction of long-time creep of polymer concrete consisting of polyester binder with diabase filler and diabase aggregate. We discovered that the principles of temperature-time analogy, of moisture-time analogy, and of temperature-moisture-time analogy are applicable to the description of the diagrams of short-time creep and to the prediction of long-time creep of polymer concrete at different temperatures and constant moisture content of the material.

Khristova, Yu.; Aniskevich, K. [Central Lab. of Physicochemical Mechanics, Sofia (Bulgaria)

1995-11-01

328

A soft creeping robot actuated by dielectric elastomer  

NASA Astrophysics Data System (ADS)

Dielectric elastomer actuator showed significant advantages at high energy density, large deformation with comparing to other artificial muscle. The robot actuated by dielectric elastomer will be more lightweight and have lower cost, which shows great potential in field of future planetary exploration based on a group of micro-robot. In this context, a quite simple structure for creeping was designed to make the robot more lightweight. The actuation unit of the robot is made of an ellipse frame which can expand and contract with membrane under electric field. After joining four actuation units, the robot can move forward in a cooperative manner. Fabrication and some preliminary experiments of the robot were presented and the proposed motion principle was demonstrated.

Zhao, Jianwen; Niu, Junyang; Liu, Liwu; Yu, Jiangcheng

2014-03-01

329

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

330

Creep of plain weave polymer matrix composites  

NASA Astrophysics Data System (ADS)

Polymer matrix composites are increasingly used in various industrial sectors to reduce structural weight and improve performance. Woven (also known as textile) composites are one class of polymer matrix composites with increasing market share mostly due to their lightweight, their flexibility to form into desired shape, their mechanical properties and toughness. Due to the viscoelasticity of the polymer matrix, time-dependent degradation in modulus (creep) and strength (creep rupture) are two of the major mechanical properties required by engineers to design a structure reliably when using these materials. Unfortunately, creep and creep rupture of woven composites have received little attention by the research community and thus, there is a dire need to generate additional knowledge and prediction models, given the increasing market share of woven composites in load bearing structural applications. Currently, available creep models are limited in scope and have not been validated for any loading orientation and time period beyond the experimental time window. In this thesis, an analytical creep model, namely the Modified Equivalent Laminate Model (MELM), was developed to predict tensile creep of plain weave composites for any orientation of the load with respect to the orientation of the fill and warp fibers, using creep of unidirectional composites. The ability of the model to predict creep for any orientation of the load is a "first" in this area. The model was validated using an extensive experimental involving the tensile creep of plain weave composites under varying loading orientation and service conditions. Plain weave epoxy (F263)/ carbon fiber (T300) composite, currently used in aerospace applications, was procured as fabrics from Hexcel Corporation. Creep tests were conducted under two loading conditions: on-axis loading (0°) and off-axis loading (45°). Constant load creep, in the temperature range of 80-240°C and stress range of 1-70% UTS of the composites, was experimentally evaluated for time periods ranging from 1--120 hours under both loading conditions. The composite showed increase in creep with increase in temperature and stress. Creep of composite increased with increase in angle of loading, from 1% under on-axis loading to 31% under off-axis loading, within the tested time window. The experimental creep data for plain weave composites were superposed using TTSP (Time Temperature Superposition Principle) to obtain a master curve of experimental data extending to several years and was compared with model predictions to validate the model. The experimental and model results were found in good agreement within an error range of +/-1-3% under both loading conditions. A parametric study was also conducted to understand the effect of microstructure of plain weave composites on its on-axis and off-axis creep. Generation of knowledge in this area is also "first". Additionally, this thesis generated knowledge on time-dependent damage m woven composites and its effect on creep and tensile properties and their prediction.

Gupta, Abhishek

331

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

332

Creep: An underrated type of mass movement on gently dipping hill slopes - examples from the Eastern Alpine foreland  

NASA Astrophysics Data System (ADS)

Creep, as a very slow type of mass movement was first described by Terzahgi (1950) und Haefeli (1954, 1967). Terzaghi (1950) pointed out that creep represents an own type of mass movement cannot be compared with other types, such as slides, as creep occurs without rupture. According to him other mechanical laws than those that typically apply for mass movements, have to be determined for creep. In a more recent classification of mass movements, creep is described as slow earthflow within the flow type of movement (Highland & Bobrowsky, 2008). Aside from different ways of categorization of landslides, a very slow, imperceptible rate of movement is still considered characteristic for creep. Recent geological and geomorphological investigations of all kind of mass movements in the Eastern Alpine foreland in Austria (Eastern part of the Styrian basin, Oberpullendorf basin, Eisenstadt basin) showed that creep is not only widespread, but is in fact the most common type of mass movement in the Neogene sediments of the basins. More than 180 previously unrecognized zones of creep have been classified. Statistical analysis indicates that in some of the investigated areas creep occurs typically on slopes with gradients between only 10-35°. Movement rates are very low, inclinometer and other measurements show displacement rates in the range of a few centimeters per year. Therefore these mass movements have previously remained unnoticed by the population, local authorities and engineers. As a result there have been misjudgments in the land use-, building- and infrastructure planning which have caused a number of damages. Aside from the immediate implications creep has even more severe and longer term consequences. As a landforming process creep acts very constant over a very long period of time. Already Haefeli (1967) realized that creep occurs at a much lower rate of shear stress than the shear strength of the soil material. The rate of shear stress where creep starts to occur is called critical shear stress or boundary of creep (Prinz & Strauß, 2006). If the critical shear stress impacts the slope material over a long period of time (decades or centuries) the displaced slope material will react by reducing its shear strength. That causes a reduction of the original shear strength in the displaced mass up to the residual shear strength of the former unaffected mass. In case of heavy precipitation, water acts among other effects as an additional weight-component in the displaced mass. Zones of creep with their reduced shear strength are in this case much more vulnerable to form fast moving slides and flows than slopes without creep. This relationship became very obvious during extremely heavy rains in the study area in June/July 2009, causing floods and hundreds of fast mass movements. The induced slides and flows caused severe damages on buildings and infrastructure. Many of these slides and flows occurred in areas that have been affected by creep before. In summary the present investigation shows that creep acts in two different time scales: The short-term effects caused directly by the slow but continuous movement of a slope, and the long-term effects causing reduced stability of the slope related to lowered shear strength. As a result the areas of creep are more vulnerable for fast and much more dangerous mass movements. References: Haefeli, R. (1954): Kriechprobleme im Boden, Schnee und Eis. Wasser- und Energiewirtschaft, 46 Jg., Nr. 3, p. 51-67. Mitt. Vers. Anst. Wassbau Erdbau ETH Zürich, No. 30, Zürich. Haefeli, R. (1967): Kriechen und progressiver Bruch im Schnee, Boden, Fels und Eis. - Schweizerische Bauzeitung, 85(1): p. 1-9, Zürich. Highland, L.M. & Bobrowsky, P. (2008): The Landslide Handbook - A Guide to Understanding Landslides. U.S. Geological Survey Circular 1325, 129 p., Reston, Virginia. Prinz, H. & Strauß, R. (2006): Abriss der Ingenieurgeologie. 671 p., 4. Aufl., Spektrum Akad. - Elsevier, München. Terzaghi, K. (1950): Mechanism of Landslides. In: Application of Geology to Engineering Pract

Leopold, Philip; Draganits, Erich; Heiss, Gerhard

2010-05-01

333

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

334

Effect of 15 MPa hydrogen on creep-rupture properties of iron-base superalloys  

NASA Technical Reports Server (NTRS)

Six wrought alloys (A-286, Incoloy 800H, N-155, 19-9DL, 12RN72, and CG-27) and four cast alloys (XF-813, CRM-6D, HS-31, and SA-F11), candidate materials for use in Stirling engines, were evaluated with reference to creep-rupture characteristics in 15-MPa H2 at 705 and 925 C. An analysis of the test results indicates that hydrogen has no effect on the rupture life and the minimum creep rate of the alloys investigated. Rupture ductility in hydrogen is lower than in air, but the mode of fracture is not significantly affected.

Bhattacharyya, S.; Titran, R. H.

1986-01-01

335

Modeling of multiaxial creep behavior for Incoloy 800 tubes under internal pressure  

SciTech Connect

In order to validate the long-term behavior of fast breeder reactor steam generator tubes, a creep test monitoring program has been undertaken. A series of over one hundred tests were performed on small specimen tubes which were cut from the as-received tube material of Incoloy 800, similar to those used in generator applications. In contrast to uniaxial conditions in which constant load conditions usually apply, multiaxial experiments were performed assuming constant stress conditions. Thin-walled tube approximation was used to estimate the stresses across the tube wall thickness required for given internal tube pressures. This paper deals with a refined numerical modeling of stresses and strains in the pressurized test specimens, taking into account: internal pressure changes, nonlinear geometrical effects and creep deformation during all the test procedure cycles. Comparison of the numerical results with the experimental measurements shows a good agreement which validates the multiaxial generalization of the RCC-MR strain creep laws which were used in the calculations. A multiaxial creep rupture criterion is discussed.

Koundy, V.; Forgeron, T.; Le Naour, F. [CEA-CEREM, Gif-Sur-Yvette (France). Service de Recherches Metallurgiques Appliquees

1996-12-01

336

Creep tests on clean and argillaceous salt from the Waste Isolation Pilot Plant  

SciTech Connect

Fifteen triaxial compression creep tests were performed on clean and argillaceous salt from the Waste Isolation Pilot Plant (WIPP). The temperatures in the tests were either 25{degrees}C or 100{degrees}C while the stress difference ranged from 3.5 MPa to 21.0 MPa. In all tests, the confining pressure was 15 MPa. Test duration ranged from 23 to 613 days with an average duration of 300 days. The results of the creep tests supplemented earlier testing and were used to estimate two parameters in the Modified Munson-Dawson constitutive law for the creep behavior of salt. The two parameters determined from each test were the steady-state strain rate and the transient strain limit. These estimates were combined with parameter estimates determined from previous testing to study the dependence of both transient and steady-state creep deformation on stress difference. The exponents on stress difference determined in this study were found to be consistent with revised estimates of the exponents reported by other investigators.

Mellegard, K.D.; Pfeifle, T.W. [RE/SPEC Inc., Rapid City, SD (US)

1993-05-01

337

Creep-fatigue of low cobalt superalloys  

NASA Technical Reports Server (NTRS)

Testing for the low cycle fatigue and creep fatigue resistance of superalloys containing reduced amounts of cobalt is described. The test matrix employed involves a single high temperature appropriate for each alloy. A single total strain range, again appropriate to each alloy, is used in conducting strain controlled, low cycle, creep fatigue tests. The total strain range is based upon the level of straining that results in about 10,000 cycles to failure in a high frequency (0.5 Hz) continuous strain-cycling fatigue test. No creep is expected to occur in such a test. To bracket the influence of creep on the cyclic strain resistance, strain hold time tests with ore minute hold periods are introduced. One test per composition is conducted with the hold period in tension only, one in compression only, and one in both tension and compression. The test temperatures, alloys, and their cobalt compositions that are under study are given.

Halford, G. R.

1982-01-01

338

Simultaneous Modeling of Transient Creep and Grain Boundary Sliding  

NASA Astrophysics Data System (ADS)

Grain boundary sliding (GBS) has been identified as an important contributor to the plastic deformation of polycrystalline solids. This phenomenon, whether accommodated by grain boundary diffusion or dislocation slip, has implications for rheological behavior and microstructural evolution during creep. Because GBS is not an independent deformation mechanism, but rather acts in kinetic series with some other (typically) rate-limiting process, direct investigation of the precise sliding mechanism(s) is difficult during conventional large-strain creep testing. Direct observations of grain boundary sliding can be obtained, however, by: (1) observing the mechanical response of a polycrystalline solid to an oscillating load as a function of frequency using the internal friction technique, and (2) studying the short duration transient response of a polycrystalline solid to a step-function change in stress. To this end, we have conducted an experimental study of low-frequency (10-2.25creep responses of the material. Experiments were conducted in an ambient pressure, reciprocating torsion apparatus using a maximum shear stress of ~90 kPa on a very fine grained (d~5?m) aggregate of olivine and orthopyroxene (39 vol%). The attenuation spectra reveal “high-temperature background” behavior at low to moderate frequencies where attenuation diminishes smoothly and mildly with increasing frequency (QG-1 ~ f -0.3). At higher frequencies (f >10-0.5 Hz), the attenuation spectra reveal the onset of an apparent Debye peak in the attenuation spectra, likely due to elastically-accommodated GBS (GBS being rate-limiting). Previous experimental studies have demonstrated that the Andrade viscoelastic model can accurately predict both the transient creep response and the high-temperature background portion of the attenuation spectra in fine-grained polycrystalline solids. This viscoelastic model does not, however, explicitly incorporate the effects of GBS. Consequently, we have modified the Andrade model to incorporate both the high-temperature background and the Debye-peak associated with elastically-accommodated GBS. We demonstrate that this model accurately describes the microcreep curves in our experiments. We then demonstrate that inversion of this viscoelastic models allows us to accurately predict the entirety of the attenuation and shear modulus dispersion spectra we observe in our reciprocating torsion experiments in an internally consistent way. We use this model to evaluate different models for the relaxation strength associated with elastically accommodated GBS. Based on this technique we determine a grain boundary viscosity of 6x105 Pa s at T=1200°C. Finally, the implications of this result for seismic wave attenuation in the Earth’s mantle and geodetic observations of post-seismic creep are discussed.

Cooper, R. F.; Sundberg, M.

2009-12-01

339

Relationship between swelling and irradiation creep in cold-worked PCA stainless steel irradiated to {approximately}178 dpa at {approximately}400{degrees}C  

SciTech Connect

The eighth and final irradiation segment for pressurized tubes constructed from the fusion Prime Candidate Alloy (PCA) has been completed in FFTF. At 178 dpa and {approximately}400{degrees}C, the irradiation creep of 20% cold-worked PCA has become dominated by the {open_quotes}creep disappearance{close_quotes} phenomenon. The total diametral deformation rate has reached the limiting value of 0.33%/dpa at the three highest stress levels employed in this test. The stress-enhancement of swelling tends to camouflage the onset of creep disappearance, however, requiring the use of several non-traditional techniques to extract the creep coefficients. No failures occurred in these tubes, even though the swelling ranged from {approximately}20 to {approximately}40%.

Toloczko, M.B. [Univ. of California, Santa Barbara, CA (United States). Dept. of Chemical and Nuclear Engineering; Garner, F.A. [Pacific Northwest Lab., Richland, WA (United States)

1993-09-01

340

Creep of pure aluminum at cryogenic temperatures  

E-print Network

CREEP OF PURE ALUMINUM AT CRYOGENIC TEMPERATURES A Thesis by LACY CLARK MCDONALD Submitted to the Office of Graduate Studies of Texas AgrM University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE August... 1989 Major Subject: Mechanical Engineering CREEP OF PURE ALUMINUM AT CRYOGENIC TEMPERATURES A Thesis by LACY CLARK MCDONALD Approved a. s to style and content by: K. Ted Hartwig (Chair ol' Committee) Walter L. Bradley (Member) Mehrda. d...

McDonald, Lacy Clark

2012-06-07

341

Creep cavitation in 304 stainless steel  

Microsoft Academic Search

Creep cavitation in 304 stainless steel at 0.5 T\\/sub m\\/ was investigated. Two specially developed techniques were used to study the nucleation and growth of grain-boundary cavities. It was found that cavities nucleated heterogeneously throughout the creep history and those observed were well in their growth stage. Comparison of these observations with the theory for cavity nucleation requires that a

I. W. Chen; A. S. Argon

1981-01-01

342

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

343

Creep Transients and Fault Interaction from Repeating Earthquakes Near San Juan Bautista, California  

NASA Astrophysics Data System (ADS)

Along creeping sections of the San Andreas and other faults, small asperities in the fault zone load and fail in characteristic repeating earthquake sequences which can be used as subsurface creepmeters. Here, we use these virtual creepmeters to examine and compare slip rates on both the northwestern end of the creeping section of the San Andreas Fault near San Juan Bautista and on the nearby sub-parallel Sargent Fault, previously observed to have ~3mm/year of right-lateral creep. While creep on the San Andreas increases dramatically in response to the 1989 Loma Prieta earthquake and takes about ten years to resume interseismic rates, the Sargent shows little immediate response. The Sargent rather exhibits a very gradual increase of activity after the Loma Prieta earthquake, consistent with its generally lower interseismic slip rate and with static stress change models that show only a minor increase in the stress along the Sargent. When the SAF resumes its interseismic rate, it begins creeping coherently in time with the Sargent, indicating a mutual driving force in the system. Background seismicity in gray points, newly discovered repeaters in black circles (inset). Boxes show study area. Stars show epicenters of 1989 Loma Prieta EQ, 1998 San Juan Bautista EQ, and 2004 Parkfield EQ.

Turner, R. C.; Nadeau, R. M.; Burgmann, R.

2012-12-01

344

Modeling Long-term Creep Performance for Welded Nickel-base Superalloy Structures for Power Generation Systems  

SciTech Connect

We report here a constitutive model for predicting long-term creep strain evolution in ?’ strengthened Ni-base superalloys. Dislocation climb-bypassing ?’, typical in intermediate ?’ volume fraction (~20%) alloys, is considered as the primary deformation mechanism. Dislocation shearing ?’ to anti-phase boundary (APB) faults and diffusional creep are also considered for high-stress and high-temperature low-stress conditions, respectively. Additional damage mechanism is taken into account for rapid increase in tertiary creep strain. The model has been applied to Alloy 282, and calibrated in a temperature range of 1375-1450?F, and stress range of 15-45ksi. The model parameters and a MATLAB code are provided. This report is prepared by Monica Soare and Chen Shen at GE Global Research. Technical discussions with Dr. Vito Cedro are greatly appreciated. This work was supported by DOE program DE-FE0005859

Shen, Chen

2015-01-01

345

Torsional deformity.  

PubMed

Torsional deformity should be localized, quantitated, and usually managed by "observation," an approach that is set forth in detail in this article. Shoe modifications and daytime braces are inappropriate. Night splints or operative procedures are rarely indicated. PMID:3786004

Staheli, L T

1986-12-01

346

Experimental study on creep-fatigue loading history effect  

SciTech Connect

In order to extend the applicability of a creep-fatigue life prediction method based on the overstress to a loading history effect, a series of creep-fatigue tests has been conducted with 316FR stainless steel at 923K in a high vacuum environment. The creep-fatigue test program includes changes of strain wave form: changed from creep-fatigue type to fatigue type and that from fatigue type to creep-fatigue type. Additional tests have been conducted to simulate an effect of a safe shutdown earthquake (SSE) on a creep-fatigue. A fatigue type strain cycling with a large strain range from 50 to 120 cycles is introduced into the creep-fatigue cycling. It was experimentally investigated how the fatigue loading with a larger strain range affects the total creep-fatigue life. In these tests the conventional linear cumulative damage rule is used in evaluating the creep-fatigue life under the complex loading history.

Nakai, Tatsuro; Ishikawa, Akiyoshi; Asada, Yasuhide [Univ. of Tokyo (Japan). Dept. of Mechanical Engineering

1995-12-31

347

Experimental pressure solution compaction of chalk in aqueous solutions. Part 2. Deformation examined by SEM, porosimetry, synthetic permeability,  

E-print Network

Experimental pressure solution compaction of chalk in aqueous solutions. Part 2. Deformation@obs.ujf-grenoble.fr) Abstract--To investigate pressure solution creep, chalk from the Paris basin (France) was deformed of the chalk. The binarized SEM images were also used to calculate the transport properties of the samples

348

Enhanced deformation of limestone and sandstone in the presence of high PCO2 fluids Yvi Le Guen,  

E-print Network

Enhanced deformation of limestone and sandstone in the presence of high PCO2 fluids Yvi Le Guen of two limestones and one sandstone were continuously measured during separate experiments for several into the sandstone resulted in deformation rates one order of magnitude smaller than the limestones. The creep

Paris-Sud XI, Université de

349

Numerical modeling of the deformations associated with large subduction earthquakes through the seismic cycle  

NASA Astrophysics Data System (ADS)

A 3D finite element code (Zebulon-Zset) is used to model deformations through the seismic cycle in the areas surrounding the last three large subduction earthquakes: Sumatra, Japan and Chile. The mesh featuring a broad spherical shell portion with a viscoelastic asthenosphere is refined close to the subduction zones. The model is constrained by 6 years of postseismic data in Sumatra area and over a year of data for Japan and Chile plus preseismic data in the three areas. The coseismic displacements on the subduction plane are inverted from the coseismic displacements using the finite element program and provide the initial stresses. The predicted horizontal postseismic displacements depend upon the thicknesses of the elastic plate and of the low viscosity asthenosphere. Non-dimensionalized by the coseismic displacements, they present an almost uniform value between 500km and 1500km from the trench for elastic plates 80km thick. The time evolution of the velocities is function of the creep law (Maxwell, Burger or power-law creep). Moreover, the forward models predict a sizable far-field subsidence, also with a spatial distribution which varies with the geometry of the asthenosphere and lithosphere. Slip on the subduction interface does not induce such a subsidence. The observed horizontal velocities, divided by the coseismic displacement, present a similar pattern as function of time and distance from trench for the three areas, indicative of similar lithospheric and asthenospheric thicknesses and asthenospheric viscosity. This pattern cannot be fitted with power-law creep in the asthenosphere but indicates a lithosphere 60 to 90km thick and an asthenosphere of thickness of the order of 100km with a burger rheology represented by a Kelvin-Voigt element with a viscosity of 3.1018Pas and ?Kelvin=?elastic/3. A second Kelvin-Voigt element with very limited amplitude may explain some characteristics of the short time-scale signal. The postseismic subsidence is conspicuous over Thailand and Malaysia (Satirapod et al., ASR, 2012). A low viscosity wedge, with a viscosity of the order of 3. 1018 Pas is necessary to explain data in the middle-field (volcanic arc area). Post-seismic slip on the fault plane (15% of the cosismic slip) in the months after the earthquakes explains near-field deformations. The creep law and geometry deduced from postseismic data can be used to predict deformations through the seismic cycle. Far away (500 to 1500km) sizable (5mm/yr to 1cm/yr) interseismic horizontal velocities are expected. Although one should not deny the presence of long-term intraplate geologic deformations, the seismic cycle contributes significantly to the intraplate compressive preseismic deformations in the Sunda and Amurian plates. The interseismic peak in vertical velocity, predicted by elastic backslip models over the end of the locked portion of the interface can be, in viscoelastic models, pushed over the continentward border of the LVW. This may explain the pattern of vertical velocities in Northern Honshu previous to Tohoku earthquake. The deviatoric stresses associated with the seismic cycle add up to the long-term tectonic stresses and are predicted to induce a peak in extensional stress in the subducting and overriding plates with a time delay which increases with the distance to the subduction zone.

Fleitout, L.; Trubienko, O.; Garaud, J.; Vigny, C.; Cailletaud, G.; Simons, W. J.; Satirapod, C.; Shestakov, N.

2012-12-01

350

Correlation of creep rate with microstructural changes during high temperature creep  

NASA Technical Reports Server (NTRS)

The techniques of electron microscopy were used to examine the microstructural changes which occur during primary creep for two important types of engineering alloys: (1) alloys strengthened by solid-solution additions, and (2) dispersion-strengthened alloys. The metals chosen for study are unalloyed titanium, Ti-6Al-4V, and the cobalt-base alloy, Haynes 188. Results to date on NGR 47-004-108 show that development of prior dislocation substructure in Haynes 188 by 10% prestrain and annealing for one hour at 1800 F increases the time to reach 0.5% creep strain at 1600 F by more than an order of magnitude for creep stresses from 3 to 20 ksi. For creep at 1800 F, similar results were obtaind for stresses above 7 ksi, but the prior substructure decreases creep resistance below 7 ksi. This effect appears to be related to instability of grain structure at 1800 F in prestrained material.

Young, C. T.; Hochella, W. A.; Lytton, J. L.

1973-01-01

351

Creep performance of Zr-1Nb-0.75Sn-0.1Fe cladding tubes with optimized Sn content  

NASA Astrophysics Data System (ADS)

Creep properties of stress-relieved Zr-1Nb-0.75Sn-0.1Fe alloy with a lower Sn content were studied. Zr-1Nb-0.75Sn-0.1Fe alloy was found to have stress exponents of 6-7, independent of stress level, unlike Zr-1Nb-1Sn-0.1Fe alloy, in which the transition of stress exponent with increase of stress was observed. The constancy of stress exponent, without the transition observed in Zr-1Nb-0.75Sn-0.1Fe alloy with lower Sn content, is associated with the decrease of Sn atoms. The activation energies for creep deformation were calculated to be between 210 and 260 kJ/mol for the Zr-1Nb-0.75Sn-0.1Fe alloy with a lower Sn content. The slightly smaller creep activation energy in Zr-1Nb-0.75Sn-0.1Fe, compared with that of Zr-1Nb-1Sn-0.1Fe alloy, is thought to be attributed to the lower Sn content. The creep data obtained at different temperatures and stress fell close to a single line, suggesting the creep life of Zr-1Nb-0.75Sn-0.1Fe alloy with a lower Sn content is well expressed by the Larson-Miller Parameter.

Kim, Won Nyeon; Choi, Yong; Hong, Sun Ig

2014-12-01

352

Relationship between fatigue life in the creep-fatigue region and stress-strain response  

NASA Technical Reports Server (NTRS)

On the basis of mechanical tests and metallographic studies, strainrange partitioned lives were predicted by introducing stress-strain materials parameters into the Universal Slopes Equation. This was the result of correlating fatigue damage mechanisms and deformation mechanisms operating at elevated temperatures on the basis of observed mechanical and microstructural behavior. Correlation between high temperature fatigue and stress strain properties for nickel base superalloys and stainless steel substantiated the method. Parameters which must be evaluated for PP- and CC- life are the maximum stress achievable under entirely plastic and creep conditions respectively and corresponding inelastic strains, and the elastic modulus. For plasticity/creep interaction conditions (PC and CP) two more pairs of stress strain parameters must be ascertained.

Berkovits, A.; Nadiv, S.

1988-01-01

353

Does a threshold stress for creep exist in HfC-dispersed NiAl?  

NASA Technical Reports Server (NTRS)

Recently it was proposed (Jha et al., 1989; Whittenberger et al., 1990) on the basis of constant velocity testing at 1300 K that dispersion strengthened NiAl composites containing about 4 wt pct HfC possess threshold stresses for creep. Further, 1300 K compression testing has been conducted on NiAl+4HfC, and diametrically opposite behavior has been found: for constant load creep tests a normal power law behavior was observed. However, additional constant velocity testing still indicates that the flow stress is essentially independent of strain rate below 10 exp -6/s. Examination of NiAl+4.3HfC specimens deformed under constant velocity conditions revealed that the original hot extruded small grain structure could be converted to large, elongated grains during testing. Such a transformation appears to be responsible for the apparent threshold stress behavior in HfC dispersed NiAl.

Whittenberger, J. D.; Ray, Ranjan; Jha, Sunil C.

1991-01-01

354

1400 and 1500 K Compressive Creep Properties of an NiAl/AlN Composite  

NASA Technical Reports Server (NTRS)

Compressive creep properties of an NiAl/AlN(p) composite produced by a reaction milling process were investigated at 1400 and 1500 K and at slow strain rates, to investigate the relative strength of this composite at high temperatures, and to determine if the consolidation technique affects the 1400 K creep properties. Results indicate that the stress exponent of the NiAl/AlN(p) composite was similar to that for unreinforced NiAl. However, the activation energy for the composite was found to be more than twice that measured in the unreinforced matrix. Oxidation did not affect the composite at 1400 K, but a significant attack was observed in a sample subjected to fast deformation at 1500 K.

Whittenberger, J. D.; Arzt, Eduard; Luton, Michael J.

1992-01-01

355

Improved creep strength and creep ductility of type 347 austenitic stainless steel through the self-healing effect of boron for creep cavitation  

NASA Astrophysics Data System (ADS)

Composition of type 347 austenitic stainless steel was modified with the addition of boron and cerium. An improvement of creep strength coupled with creep ductility of the steel was observed with boron and cerium additions. The observation of enhanced precipitation of carbonitrides in boron-containing steel over that of boron-free steel may in part contribute to the increase in creep strength. Both grain boundary sliding and nucleation and growth of intergranular creep cavities were found to be suppressed in steel-containing boron. This results in an increase in creep strength and creep ductility. Auger electron spectroscopic analysis of the chemistry of creep cavity surfaces (exposed by breaking the creep-exposed steel specimen at liquid nitrogen temperature under impact loading) revealed the segregation of elemental boron on the creep cavity surface. Boron segregation, on the creep cavity surface in the absence of sulfur contamination, suppressed the cavity growth and provided the steel with a self-healing effect for creep cavitation. Cerium additions enabled boron to segregate on the cavity surface by effectively removing the traces of free sulfur in the matrix by the formation of ceriumoxysulfide (Ce2O2S).

Laha, K.; Kyono, J.; Sasaki, T.; Kishimoto, S.; Shinya, N.

2005-02-01

356

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

357

Thermal creep of irradiated zircaloy cladding.  

SciTech Connect

As part of an effort to investigate spent-fuel behavior during dry-cask storage, thermal creep tests are being performed with defueled Zircaloy-4 cladding segments from two pressurized water reactors - Surry at {approx} 36 GWd/MTU burnup and H. B. Robinson at {approx} 67 GWd/MTU burnup, with corresponding fast (E > 1 MeV) fluence levels of 7 x 10{sup 25} and 14 x 10{sup 25} n/m{sup 2}. The Surry rods are particularly relevant because they were stored in an inert-atmosphere (He) cask for 15 years. The Robinson rods were received after reactor discharge and pool storage. Commensurate with their high burnup, the Robinson cladding has significant waterside corrosion and hydrogen uptake. Test results to-date indicate good creep ductility for both claddings in the 360 400 C and 160-250 MPa (hoop-stress) regime. Partial recovery of radiation hardening may have occurred during the long tests at 400 C, which led to improved creep ductility. Creep-rate sensitivity is significant for stress and even more so for temperature. The higher hydrogen content in the Robinson material appears to have no detrimental effect on creep behavior at the test temperature. One Robinson sample, which ruptured in the weld region at 205 C during cooling from 400 C under stress (190 MPa), precipitated all visible hydrides in the radial direction.

Tsai, H.; Billone, M. C.; Energy Technology

2005-01-01

358

A Phenomenological Description of Primary Creep in Class M Materials  

NASA Technical Reports Server (NTRS)

Observations of creep microstructures in the primary creep region in class M materials show a remarkable similarity with those formed in the exponential creep regime. As a result, it is proposed that the constitutive creep law for normal primary creep is similar to that for the exponential creep regime. A phenomenological description is discussed to rationalize these microstructural observations in terms of a normalized strain rate vs. stress plot. The implications of this plot in describing different testing procedures, steady-state flow, and on the observed deviations from the universal creep law are discussed. The plot is also extended to explain the observed similarities in the transient creep behavior in pre-strained materials and in stress change experiments.

Raj, S. V.; Freed, A. D.

1999-01-01

359

Data from Theodolite Measurements of Creep Rates on San Francisco Bay Region Faults, California: 1979-2007  

USGS Publications Warehouse

Introduction Our purpose is to update with six additional years of data, our creep data archive on San Francisco Bay region active faults for use by the scientific research community. Earlier data (1979-2001) were reported in Galehouse (2002) and were analyzed and described in detail in a summary report (Galehouse and Lienkaemper, 2003). A complete analysis of our earlier results obtained on the Hayward fault was presented in Lienkaemper, Galehouse and Simpson (2001). Jon Galehouse of San Francisco State University (SFSU) and many student research assistants measured creep (aseismic slip) rates on these faults from 1979 until his retirement from the project in 2001. The creep measurement project, which was initiated by Galehouse, has continued through the Geosciences Department at SFSU from 2001-2006 under the direction of Co-P.I.'s Karen Grove and John Caskey (Grove and Caskey, 2005), and by Caskey since 2006. Forrest McFarland has managed most of the technical and logistical project operations as well as data processing and compilation since 2001. We plan to publish detailed analyses of these updated creep data in future publications. We maintain a project web site (http://funnel.sfsu.edu/creep/) that includes the following information: project description, project personnel, creep characteristics and measurement, map of creep measurement sites, creep measurement site information, and data plots for each measurement site. Our most current, annually updated results are therefore accessible to the scientific community and to the general public. Information about the project can currently be requested by the public by an email link (fltcreep@sfsu.edu) found on our project website.

McFarland, Forrest S.; Lienkaemper, James J.; Caskey, S. John; Grove, Karen

2007-01-01

360

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

361

A microstructural investigation of steady state creep of zircaloy-4 at 973 K  

NASA Astrophysics Data System (ADS)

The creep behaviour of Zircaloy-4 at 973 K displays a transition at an applied stress of ? T ? 25 MPa. In particular, only at stresses above this level does the loading strain exceed one elastic deflection, the primary creep strain vary systematically with stress or the strain rate at high strain approach a power law dependence. At stresses ? 25 MPa, steady state is not achieved even at strains of 0.5. The present paper describes observations of the microstructures produced by creep. It is found that the average dislocation density p can be described by the empirical equation. ? = ?0 + 0.9 Gb? ?, where ?0 = 10 MPa. The dislocation is dominated by {1}/{3}a<11 2¯0> defects, which are most easily mobile on prismatic {011¯0} planes, though evidence of the operation of basal slip and of the climb of {1}/{3}a<11 2¯0> dislocations out of their prismatic planes is also presented. At all stresses above ? T, well-developed subgrains are observed whose average size is inversely proportional to stress. At ? T, the subgrain size is equal to the grain size of as-received material ( 9 ?m), though grain growth occurs during creep testing. A reduced power-law for the steady-state creep rate above ? T is proposed ? ? ( ? — ?T) 3, or, in terms of dislocation density ? ? (?-? 0) {3}/{2}. The value of ?0is 8 × 10 -12m-2, which is suggested to represent the minimum dislocation density which is able to achieve pure dislocation strain, and which corresponds to the density at ? T. At stresses below ? T, the dislocation population is insufficient to allow the general grain shape change required by von Mises criterion. Only the more favourable slip systems on average are operative at all stresses above ? 0. Observations of the microstructure at applied stresses above ? T are compatible with steady state creep being recovery controlled in that regime. At lower stress, some further deformation mechanism is required to act in conjunction with dislocation glide in order to achieve the observed strain while maintaining material continuity at grain boundaries. Observations of grain boundary structure suggest that this further mechanism involves long range grain boundary diffusion. The latter allows the movement of grain boundary dislocations, which in general will also cause migration and grain growth. Further, this is consistent firstly with the absence of steady state at low stresses, since the diffusion creep rate decreases as the grain size increases, and secondly with the equality of the subgrain and initial grain sizes at ? T, since all the matrix dislocation accommodation processes must then involve grain boundary diffusion.

Ecob, R. C.; Donaldson, A. T.

1985-06-01

362

Creep on a composite resin in water.  

PubMed

The compressive creep test of a composite resin (0-3.5 kg/mm2 stress levels) was conducted in water for 500 h. Linear regressions were obtained between the creep strains and the compressive stress levels at various hours. It is possible to predict the creep strain of the composite from the regression when it reaches water absorbed equilibrium after 500 h. The stress of the hygroscopic expansion was calculated from the linear regressions. The maximum stress due to the hygroscopic examination of the composite was 0.74 kg/mm2 at equilibrium of the water absorbed of the composite. The linear regressions at several compressive stress levels were obtained within 30-50 hr in the strain-log time diagrams. PMID:2638964

Hirano, S; Hirasawa, T

1989-06-01

363

Effect of Boron on Creep Ductility and Creep Rupture Life in 9CR-1.5MO Steel  

NASA Astrophysics Data System (ADS)

In this study, the relationship between the creep ductility and rupture life of 9Cr-1.5Mo steel with boron addition at 600°C was investigated by small punch (SP) creep test from the viewpoint of the modified Monkman-Grant relation. The amount of boron addition ranged from 0.0076wt% to 0.0196 wt%. The general concept of Monkman-Grant ductility for uniaxial creep was introduced and then particularly modified for the SP creep. The microstructure of the steel was observed to analyze the effect of boron addition on the creep ductility and rupture life. Based on the modified Monkman-Grant ductility for SP creep, it was found that the boron addition improved the creep ductility and rupture life of the 9Cr-1.5Mo steel. Also, the relationship between the minimum creep displacement rate and the amount of boron addition was analyzed.

Kim, Bumjoon; Im, Jiwoo; Kim, Moon K.; Lee, Jonghoon; Lim, Byeongsoo

364

Applicability of flow laws to naturally deformed polyphase rocks  

NASA Astrophysics Data System (ADS)

Small scale shear zones formed in the Gran Paradiso metagranodiorite under lower amphibolite facies conditions (~550°C/0.8 GPa LeGoff & Ballevre, 1990; Brouwer et al.,2002). Based on detailed microstructural work the deformation mechanisms of the different rheological phases have been identified. Polycrystalline quartz aggregates deform by dislocation creep (gbm recrystallization), whereas the polymineralic matrix deforms by diffusion creep (Kilian et al., 2011). Iso - stress conditions (Sachs-average) are assumed based on a constant recrystallized quartz grain size and the formation of shear-parallel layers. Deformed quartz aggregates show higher rotation angle / lower aspect ratio relations, little coalescence, and only minor pinch and swell structures, which altogether suggest that quartz represents the more viscous phase in a somewhat lower viscous matrix. At high strain quartz is completely recrystallized and forms parallel layers with the matrix and does not boudinage. Experimental flow laws for quartz and feldspar from the literature as well as the theoretically derived flow law for Coble creep with the appropriate parameters can reproduce the observed relation between quartz aggregates and matrix suggesting a strain rate ratio below 2 orders of magnitude. A comparison of data from different granitic rocks deformed between 450° to ~ 600°C suggests that a combination of a quartz creep law and a Coble creep law can be used for extrapolation at medium grade, natural conditions. These results provide an indication for the range of reasonable flow law parameters and viscosity ratios which are useful for modeling purposes. References: Kilian, R., Heilbronner, R., Stünitz, H. Quartz grain size reduction in a granitoid rock and the transition from dislocation to diffusion creep. JSG 33,1265-1284,2011. LeGoff, E., Ballevre, M. Geothermobarometry in albite-garnet orthogneisses - a case-study from the Gran-Paradiso Nappe (Western Alps). Lithos, 25,261-280,1990. F. Brouwer, F., Vissers, R., Lamb, E. Structure and metamorphism of the Gran Paradiso massif, western Alps, Italy. Cont.Min.Pet., 143,450-470,2002.

Kilian, Rüdiger; Heilbronner, Renée; Stünitz, Holger

2013-04-01

365

Edge di raction of creeping rays S. J. Chapman  

E-print Network

Edge di#11;raction of creeping rays S. J. Chapman J. R. Ockendon V. H. Saward #3; OCIAM by the scalar two-dimensional Helmholtz equation for the #12;eld that is di#11;racted when surface creeping rays Introduction Creeping rays are real rays that exist in the shadow region of a #12;nite scatterer that is illu

Chapman, Jon

366

Flexural creep behaviour of PP matrix woven composite  

Microsoft Academic Search

In this work the flexural creep behaviour of polypropylene and glass fibre commingled woven composite (Twintex®) sheets has been studied. Test samples were obtained in a compression moulding apparatus at different plate temperatures. Short-term flexural creep tests were run at multiple stress levels. Varying the applied stress level and using the Boltzmann superposition principle the linearity of creep behaviour was

Antonio Greco; Claudio Musardo; Alfonso Maffezzoli

2007-01-01

367

On creep of unidirectional fiber composites with fiber damage  

Microsoft Academic Search

The roles of broken fibers in the creep of continuous fiber reinforced composites are studied theoretically. The unidirectional fiber composite is modeled using a cylindrical cell consisting of a single broken fiber and a shell of the fiber material embedded in an elastic-power law creeping matrix. The time-dependent creep behavior of the composite is calculated using finite elements; both longitudinal

Y. Song; G. Bao; C. Y. Hui

1995-01-01

368

Microstructure and transient creep in an austenitic stainless steel  

Microsoft Academic Search

The dislocation substructures associated with normal and inverted transient creep in annealed and prestrained type 304 austenitic stainless steel were investigated using transmission electron microscopy. Normal primary creep was accompanied by subgrain formation, a process which was accelerated by pre-straining. A prolonged accelerating creep stage was observed under certain test conditions. The associated microstructures revealed that this type of transient

O. Ajaja; A. J. Ardell

1979-01-01

369

Creep, fatigue, and creep-fatigue properties of modified 9Cr-1Mo steel weldments  

SciTech Connect

In this paper, the results of creep-rupture, fatigue, and creep-fatigue tests obtained for the weldments of modified 9Cr-1Mo steel at elevated temperatures (500, 550 and 600 C) are presented. The fatigue properties of weldment, such as fatigue life, stress-strain response, and failure location, can be predicted well by the bi-element model of base metal and weld metal which have their corresponding mechanical properties. Furthermore, the creep-fatigue life of weldment can be predicted well by the bi-linear model.

Taguchi, Kosei; Maruyama, Shigeki [Toshiba Corp., Yokohama (Japan); Fujioka, Terutaka [Japan Atomic Power Co., Tokyo (Japan); Yamashita, Yoshihiro [Hitachi, Ltd. (Japan); Koto, Hiroyuki [Mitsubishi Heavy Industries, Ltd., Takasago (Japan); Takahashi, Koun [Ishikawajima-Harima Heavy Industries Co., Ltd., Tokyo (Japan); Toya, Yuji [Kawasaki Heavy Industries, Ltd., Noda (Japan); Sato, Takashi [Babcock-Hitachi K.K., Kure (Japan)

1996-12-01

370

Heterogeneous microstructures and macroscopic creep behavior of polycrystalline ice (Invited)  

NASA Astrophysics Data System (ADS)

We present results of two complementary formulations, a full-field approach based on fast Fourier transforms (FFT) [1] and a mean-field approach based on rigorous nonlinear homogenization [2] to study the influence of different microstructural features on the macroscopic behavior of polycrystalline ice. The FFT-based model is used for the prediction of local fields in columnar ice polycrystals deforming in compression by dislocation creep [3]. The predicted intragranular mechanical fields are in qualitative good agreement with experimental observations, in particular those involving the formation of shear and kink bands. These localization bands are associated with the large internal stresses that develop during creep in such anisotropic material, and their location, intensity, morphology and extension are found to depend strongly on the crystallographic orientation of the grains and on their interaction with neighbor crystals. In turn, this numerically-intensive full-field formulation is used to validate the predictions of different, more efficient homogenization approaches. We show that a recent second-order formulation, which explicitly uses information on average intragranular field fluctuations, implemented within the widely used ViscoPlastic Self-Consistent (VPSC) code [4], yields the most accurate results. References: [1] H. Moulinec and P. Suquet, Comput. Methods Appl. Mech. Eng. 157, 69 (1998). [2] P. Ponte Castañeda, J. Mech. Phys. Solids 50, 737 (2002). [3] R.A. Lebensohn, M. Montagnat, P. Mansuy et al. Acta Mater. 57, 1405, (2009). [4] R.A. Lebensohn, C.N. Tomé and P. Ponte Castañeda. Phil. Mag. 87, 4287 (2007).

Lebensohn, R.

2009-12-01

371

Timescales in creep and yielding of attractive gels.  

PubMed

The stress-induced yielding scenario of colloidal gels is investigated under rough boundary conditions by means of rheometry coupled with local velocity measurements. Under an applied shear stress ?, the fluidization of gels made of attractive carbon black particles dispersed in a mineral oil is shown to involve a previously unreported shear rate response ? dot above(t) characterized by two well-defined and separated timescales ?c and ?f. First ? dot above decreases as a weak power law strongly reminiscent of the primary creep observed in numerous crystalline and amorphous solids, coined the "Andrade creep". We show that the bulk deformation remains homogeneous at the micron scale, which demonstrates that whether plastic events take place or whether any shear transformation zone exists, such phenomena occur at a smaller scale. As a key result of this paper, the duration ?c of this creep regime decreases as a power law of the viscous stress, defined as the difference between the applied stress and the yield stress ?c, i.e. ?c ? (? - ?c)(-?), with ? = 2-3 depending on the gel concentration. The end of this first regime is marked by a jump of the shear rate by several orders of magnitude, while the gel slowly slides as a solid block experiencing strong wall slip at both walls, despite rough boundary conditions. Finally, a second sudden increase of the shear rate is concomitant with the full fluidization of the material which ends up being homogeneously sheared. The corresponding fluidization time ?f robustly follows an exponential decay with the applied shear stress, i.e. ?f = ?0?exp(-?/?0), as already reported for smooth boundary conditions. Varying the gel concentration C in a systematic fashion shows that the parameter ?0 and the yield stress ?c exhibit similar power-law dependences with C. Finally, we highlight a few features that are common to attractive colloidal gels and to solid materials by discussing our results in the framework of theoretical approaches of solid rupture (kinetic, fiber bundle, and transient network models). PMID:24651869

Grenard, Vincent; Divoux, Thibaut; Taberlet, Nicolas; Manneville, Sébastien

2014-03-14

372

Geotechnical simulation of tertiary creep behavior of landslides induced by extreme rainfall  

NASA Astrophysics Data System (ADS)

Rainstorm indirectly provokes landslides because of its ability to level up the groundwater table after certain hours dropping. This process causes excess pore water pressure generation and soil liquefaction at the sliding surface and determines the behavior of landslides triggered by extreme rainfall. Creep deformations are commonly observed in a slope before sliding down. Creep behavior, in particular tertiary creep behavior, is therefore the main focus in predicting the final failure time of a slope. Progressive failure/tertiary creep deformation is the stage when strain rate exponentially increases just before final collapse. This study aims at simulating geotechnical model of tertiary creep behavior in soils, which was empirically discovered by Saito (1965) and Fukuzono (1985) to help issue warning of rainfall-induced landslides in developing countries where there is no implemented methodology for issuing effective warming of landslides yet. Tertiary creep to failure is reproduced by pore-pressure-controlled test in ring shear apparatus, through which obvious relationship of A and ? (alpha) values was obtained, following consistent range with those found in previous studies under slightly deviated trend due to different test condition: pore-pressure-controlled and shear stress development tests. Constant shear speed test under shear speed of v=1cm/s was conducted in the ring shear apparatus to obtain the relation curve of shear resistance and shear displacement, from which exponential expression of creep behavior is originated. The model formula is governed by two constants: m and ? (gamma) whose relation with constants A and alpha was examined. Geotechnical simulation of creep behavior is then constructed by assuming that shear strength of soil increases and remains constant after reaching its maximum value in residual condition. This is to quantify normally consolidated condition of soils in natural slope. Shear resistance diminishes, while pore pressure is gradually generated through time until shear resistance is smaller than initial shear stress, and failure encounters. The large shear displacement took place after failure is used to calculate velocity and acceleration of virtual surface displacement. A and alpha values are measured through the plot of velocity and acceleration in log scale and compared with those of laboratory tests. In similar way, additional formulation of shear stress development condition to failure was also investigated. Consequently, model simulation of creep behavior to develop a most appropriate method for landslide early warning is successfully developed through very good correlation with experimental results. The constant m and ? are corresponded to A and ? respectively. A value gets smaller when m is higher, whereas alpha and gamma increase accordingly. The m value best fitted with experimental result is 0.1. Deviated trends were also observed in pore pressure control and shear stress increase simulations. The result shows that higher alpha value, higher landslide susceptibility is expected.

Dok, Atitkagna; Fukuoka, Hiroshi

2013-04-01

373

Damage evolution during creep of steels  

Microsoft Academic Search

Using high-precision constant-stress machines, normal creep curves are recorded over tensile stress ranges giving creep lives up to about 1000h or more for 0.5Cr–0.5Mo–0.25V ferritic steel, 1Cr–1Mo–0.25V bainitic steel, 316L austenitic steel and the oxide-dispersion-strengthened 14% Cr ferritic steel, Incoloy MA957. Although the curve shapes are material and test condition sensitive, a minimum rate rather than a secondary or steady-state

B. Wilshire; H. Burt

2008-01-01

374

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

375

Metasomatic Origin of Fault Gouge Comprising the Two Actively Creeping Strands at SAFOD  

NASA Astrophysics Data System (ADS)

Fault creep at SAFOD, evidenced by well-casing deformation, is highly localized to two narrow zones of fault gouge that differ significantly in mineralogy and bulk composition from adjoining sedimentary rocks. The 2.6-m-wide Central Deforming Zone (CDZ), situated near the middle of the ~200-m-wide damage zone of the San Andreas Fault (SAF), takes up the majority of the creep. The less active, 1.6-m-wide Southwest Deforming Zone (SDZ) marks the southwestern margin of the currently active SAF. Preliminary petrographic examination of recently obtained core samples indicates that both gouge zones are the product of shear-enhanced metasomatic reactions between serpentinite migrating diapirically up the fault and adjacent sedimentary rocks. Both gouge zones consist of porphyroclasts of serpentinite and sedimentary rock dispersed in a foliated matrix of the Mg-rich (~22-25 wt% MgO; Mg/[Mg + Fe] = 0.8-0.9) clay minerals saponite ± corrensite. Porphyroclasts of all types are variably altered to the same Mg-rich clays as the gouge matrix, and fractures lined with Mg-clays extend for a short distance (<1 m) into the sedimentary damage-zone rocks adjoining the gouge zones. Differences in texture and mineral composition between the CDZ and SDZ are attributable to their different slip rates. Similar fault gouge has been identified in a serpentinite outcrop, located ~2.4 km north of the SAFOD drill site, that forms part of a sheared serpentinite body mapped for several kilometers within the creeping section of the SAF. Some serpentinite porphyroclasts in both gouge zones at depth also contain the assemblage talc + tremolite/actinolite + chlorite + andradite garnet, which is typical of greenschist-facies reaction zones developed between serpentinite and crustal rocks. The presence of this higher-temperature alteration assemblage raises the possibility that these gouge zones may extend to significantly greater depths in the fault.

Moore, D. E.; Rymer, M. J.

2010-12-01

376

Creep cavitation can establish a dynamic granular fluid pump in ductile shear zones.  

PubMed

The feedback between fluid migration and rock deformation in mid-crustal shear zones is acknowledged as being critical for earthquake nucleation, the initiation of subduction zones and the formation of mineral deposits. The importance of this poorly understood feedback is further highlighted by evidence for shear-zone-controlled advective flow of fluids in the ductile lower crust and the recognition that deformation-induced grain-scale porosity is a key to large-scale geodynamics. Fluid migration in the middle crust cannot be explained in terms of classical concepts. The environment is considered too hot for a dynamic fracture-sustained permeability as in the upper crust, and fluid pathways are generally too deformed to be controlled by equilibrium wetting angles that apply to hotter, deeper environments. Here we present evidence that mechanical and chemical potentials control a syndeformational porosity generation in mid-crustal shear zones. High-resolution synchrotron X-ray tomography and scanning electron microscopy observations allow us to formulate a model for fluid migration in shear zones where a permeable porosity is dynamically created by viscous grain-boundary sliding, creep cavitation, dissolution and precipitation. We propose that syndeformational fluid migration in our 'granular fluid pump' model is a self-sustained process controlled by the explicit role of the rate of entropy production of the underlying irreversible mechanical and chemical microprocesses. The model explains fluid transfer through the middle crust, where strain localization in the creep regime is required for plate tectonics, the formation of giant ore deposits, mantle degassing and earthquake nucleation. Our findings provide a key component for the understanding of creep instabilities in the middle crust. PMID:19536262

Fusseis, F; Regenauer-Lieb, K; Liu, J; Hough, R M; De Carlo, F

2009-06-18

377

Creep bending of thin-walled shells and plates by consideration of finite deflections  

NASA Astrophysics Data System (ADS)

A phenomenological constitutive model for the characterization of creep-damage processes of metals is applied to the numerical analysis of thin-walled shells and plates. The governing equations of the theory of shallow shells are used taking into account geometrical nonlinearities connected with finite time-dependent deflections by moderate bending. The solutions of the initial-boundary value problem are obtained for thin rectangular plates in order to show the influence of geometrical nonlinearity on results of time-dependent deformation and stress redistribution as well as on estimations of the failure time.

Altenbach, H.; Naumenko, K.

378

Spinal deformity.  

PubMed

Early results of scoliosis screening programs have demonstrated that mild spinal deformity is common, usually nonprogressive, and often requires no specific treatment. The role of the primary care physician is an important one in identifying the rare case, which is secondary to some underlying disorder which itself requires treatment, and the progressive curves, which should be managed by bracing. The informed physician can make this separation efficiently with minimum cost to the family and minimum radiation exposure to the patient. PMID:7373257

Staheli, L T

1980-06-01

379

Impression creep testing and microstructurally adaptive creep modeling of lead free solder interconnects  

Microsoft Academic Search

Creep plays an important role in the reliability of solder joints under thermo-mechanical fatigue conditions encountered by a microelectronic package during service. In addition, the fine intermetallic precipitates (Ag3Sn and\\/or Cu6Sn5) in the microstructures of the new lead-free solders (Sn-Ag and Sn-Ag-Cu) can undergo significant in situ strain-enhanced coarsening during TMC, resulting in in-service evolution of the creep behavior of

I. Dutta; D. Pan; S. Jadhav

2005-01-01

380

Fluid Assisted Compaction and Deformation of Reservoir Lithologies  

SciTech Connect

The compaction and diagenesis of sandstones that form reservoirs to hydrocarbons depend on mechanical compaction processes, fluid flow at local and regional scales, and chemical processes of dissolution, precipitation and diffusional solution transport. The compaction and distortional deformation of quartz aggregates exposed to reactive aqueous fluids have been investigated experimentally at varying critical and subcritical stress states and time scales. Pore fluid compositions and reaction rates during deformation have been measured and compared with creep rates. Relative contributions of mechanical and chemical processes to deformation and pore structure evolution have been evaluated using acoustic emission (AE) measurements and scanning electron microscope (SEM) observations. At the subcritical conditions investigated, creep rates and acoustic emission rates fit transient logarithmic creep laws. Based on AE and SEM observations, we conclude that intragranular cracking and grain rearrangement are the dominant strain mechanisms. Specimens show little evidence of stress-enhanced solution transfer. At long times under wet conditions, the dominant strain mechanism gradually shifts from critical cracking at grain contacts with high stress concentrations to fluid-assisted sub-critical cracking.

Kronenberg, A.K.; Chester, F.M.; Chester, J.S.; Hajash, A.; He, W.; Karner, S.; Lenz, S.

2002-02-13

381

Elevated temperature deformation of thoria dispersed nickel-chromium  

NASA Technical Reports Server (NTRS)

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

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

1974-01-01

382

Tensile Creep of Polycrystalline Near-Stoichiometric NiAl  

NASA Technical Reports Server (NTRS)

Long term tensile creep studies were conducted on binary NiAl in the temperature range 700-1200 K with the objectives of characterizing and understanding the creep mechanisms. Inverse and normal primary creep curves were observed depending on stress and temperature. It was concluded that the creep of NiAl is limited by dislocation mobility. The stress exponent for creep, n, increased from 5.5 at 1200 K to 13.9 at 700 K. The true activation energy for creep, Qc, was constant and equal to about 400 kJ per mole between 20 and 50 MPa but decreased to a constant value of 250 kJ per mole between 50 and 110 MPa. The activation energy was observed to be stress dependent above 110 MPa. The tensile creep results reported in this investigation were compared with compression creep data reported in the literature. A detailed discussion of the probable dislocation creep mechanisms governing compressive and tensile creep of NiAl is presented. It is concluded that the non-conservative motion of jogs on screw dislocations influenced the nature of the primary creep curves, where the climb of these jogs involves either the next nearest neighbor or the six-jump cycle vacancy diffusion mechanism. The probable nature of the atom vacancy exchange that occur within the core of an edge dislocation undergoing climb in NiAl are schematically examined.

Raj, Sai V.

2002-01-01

383

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

SciTech Connect

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

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

2011-06-01

384

Multiaxial creep of natural rock salt  

Microsoft Academic Search

Long-term multiaxial creep tests were performed on large, thin-walled cylinders of natural rock salt to investigate the relationship between the inelastic strain rate tensor and the stress tensor. The axial load, internal pressure, and external pressure on the specimens were controlled to obtain desired values of mean stress, octahedral shear stress, and Lode angle. The loads on the specimen were

K. D. Mellegard; G. D. Callahan; P. E. Senseny

1992-01-01

385

Moss Control in Creeping Bentgrass Putting Greens  

Microsoft Academic Search

Summary. Moss (Bryum argenteum) continues to become one of the most problematic weeds in creeping bentgrass (Agrostis palustris) putting greens. Control of moss can be approached in many differ- ent ways, including chemical applications, and cultural practices such as correcting shading or poor drainage. A study was conduct- ed at Springdale Country Club (Springdale, Ark.) to evaluate the effectiveness of

J. H. McCalla Jr; M. D. Richardson; D. E. Karcher; L. R. Fry

386

Weep hole inspection by circumferential creeping waves  

E-print Network

." fatigue cracks, creeping waves, ultrasonic testing Weep holes are drilled through risers in wet of a novel ultrasonic inspection technique that detects radial fatigue cracks on the far side of thin by conventional ultrasonic inspection techniques, particularly for short cracks. A special technique using

Nagy, Peter B.

387

H-451 graphite irradiation creep design model; Revision 1  

SciTech Connect

Available irradiation creep data on H-451 graphite area analyzed and fitted to the proposed creep model in a standard linear solid (a linear viscoelastic model). A creep equation is obtained and recommended for preliminary design use. It is found that the regression is significant and the creep equation is a good predictor. The standard error (SE) of the estimate is smaller than that used in the core graphite criteria development. This smaller SE shall be used in all future work related to criteria development. The creep coefficient and/or model can be further improved if additional creep data can be obtained. For this purpose several creep experiments are recommended. The immediate one is to capsule 87M-2A currently under design.

NONE

1988-07-01

388

DEFORMATION MECHANISMS OF SALT UNDER REPOSITORY CONDITIONS F. D. Hansen, RE/SPEC Inc., P. 0. Box 725, Rapid City, SD 57709, U.S.A.  

E-print Network

the various processes of plastic defor- mation. Creep of natural rock salt in the laboratory under repository711 DEFORMATION MECHANISMS OF SALT UNDER REPOSITORY CONDITIONS F. D. Hansen, RE/SPEC Inc., P. 0, the strain rate should be a function of stress différence, temperature, and structure. Deformation of salt

Paris-Sud XI, Université de

389

Creep of simulated reservoir sands and coupled chemical-mechanical effects of CO2 injection  

NASA Astrophysics Data System (ADS)

Geological storage of CO2 in clastic reservoirs and aquifers is expected to have a variety of coupled chemical-mechanical effects. To investigate the effects of CO2 injection on creep phenomena, we performed uniaxial compaction experiments on granular aggregates of quartz and feldspar under both wet and dry control conditions. The experiments were performed in constant stress mode. Grain size, temperature, CO2 partial pressure, and effective stress were varied in order to determine their individual effect. Pore fluid pH was varied by the injection of CO2 and by addition of acidic and alkaline additives. Pore fluid salinity was increased by the addition of NaCl. Wet samples showed instantaneous compaction upon load application, followed by time-dependent creep. From the mechanical data and microstructures, the main compaction mechanism was inferred to be chemically enhanced microcracking in both quartz and feldspar, with subcritical crack growth, i.e., stress corrosion cracking, controlling deformation in the creep stage. The injectio