Science.gov

Sample records for creep deformation characteristics

  1. Creep deformation characteristics of ductile discontinuous fiber reinforced composites

    SciTech Connect

    Biner, S.B.

    1993-10-01

    Role of material parameters and geometric parameters of ductile reinforcing phase on the creep deformation behavior of 20% discontinuously reinforced composite was numerically investigated including debonding and pull-out mechanisms. Results indicate that for rigidly bonded interfaces, the creep rate of the composite is not significantly influenced by the material properties and geometric parameters of the ductile reinforcing phase due to development of large hydrostatic stress and constrained deformation in the reinforcement. For debonding interfaces, the geometric parameters of the reinforcing phase are important; however, event with very weak interfacial behavior low composite creep rates can be achieved by suitable selection of the geometric parameters of the ductile reinforcing phase.

  2. Creep Deformation of Allvac 718Plus

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.

  3. Creep Deformation of B2 Alumindes

    NASA Technical Reports Server (NTRS)

    Nathal, M. V.

    1991-01-01

    The creep resistance and elevated temperature deformation mechanisms in CoAl, FeAl, and NiAl are reviewed. The stress and temperature dependencies of the steady state creep rate, the primary creep behavior, the dislocation substructure, and the response during transient tests are used as the main indicators of the deformation processes. In single phase intermetallics, the influence of grain size, stoichiometry, and solid solution hardening have been examined. In addition, the effect of adding dispersoids, precipitates, and other types of reinforcements to improve creep strength are compared.

  4. Creep fracture during solute-drag creep and superplastic deformation

    SciTech Connect

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

    1996-10-01

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

  5. Deformation twinning in a creep-deformed nanolaminate structure

    NASA Astrophysics Data System (ADS)

    Hsiung, Luke L.

    2010-10-01

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

  6. Deformation twinning in a creep-deformed nanolaminate structure.

    PubMed

    Hsiung, Luke L

    2010-10-01

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

  7. Creep deformation of a soft magnetic iron-cobalt alloy

    NASA Astrophysics Data System (ADS)

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

    1999-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

    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.

  9. Tantalum alloys resist creep deformation at elevated temperatures

    NASA Technical Reports Server (NTRS)

    Buckman, R. W., Jr.

    1966-01-01

    Dispersion-strengthened tantalum-base alloys possess high strength and good resistance to creep deformation at elevated temperatures in high vacuum environments. They also have ease of fabrication, good weldability, and corrosion resistance to molten alkali metals.

  10. Creep Behavior, Deformation Mechanisms, and Creep Life of Mod.9Cr-1Mo Steel

    NASA Astrophysics Data System (ADS)

    ABE, Fujio

    2015-12-01

    The creep behavior, deformation mechanisms, and the correlation between creep deformation parameters and creep life have been investigated for Mod.9Cr-1Mo steel (Gr.91, 9Cr-1Mo-VNb) by analyzing creep strain data at 723 K to 998 K (450 °C to 725 °C), 40 to 450 MPa, and t r = 11.4 to 68,755 hours in NIMS Creep Data Sheet. The time to rupture t r is reasonably correlated with the minimum creep rate {dot{\\varepsilon }}_{ min } and the acceleration of creep rate by strain in the acceleration region dln {dot{\\varepsilon }} /d ?, as t r = 1.5/[ {dot{\\varepsilon }}_{ min } ( dln {dot{\\varepsilon }} /d ?)], where {dot{\\varepsilon }}_{ min } and dln {dot{\\varepsilon }} /d ? reflect the creep behavior in the transient and acceleration regions, respectively. The {dot{\\varepsilon }}_{ min } is inversely proportional to the time to minimum creep rate t m, while it is proportional to the strain to minimum creep rate ? m, as {dot{\\varepsilon }}_{ min } = 0.54 ( ? m/ t m). The ? m decreases with decreasing stress, suggesting that the creep deformation in the transient region becomes localized in the vicinity of prior austenite grain boundaries with decreasing stress. The duration of acceleration region is proportional to the duration of transient region, while the dln {dot{\\varepsilon }} /d ? is inversely proportional to the ? m. The t r is also correlated with the t m, as t r = g t m, where g is a constant. The present creep life equations reasonably predict the degradation in creep rupture strength at long times. The downward deviation takes place in the t r vs {dot{\\varepsilon }}_{ min } curves (Monkman-Grant plot). At the same {dot{\\varepsilon }}_{ min } , both the ? m and t m change upon the condition of t m ? ? m. The decrease in ? m with decreasing stress, corresponding to decreasing {dot{\\varepsilon }}_{ min } , causes a decrease in t m, indicating the downward deviation of the t r vs {dot{\\varepsilon }}_{ min } curves.

  11. Sharp interface model of creep deformation in crystalline solids

    NASA Astrophysics Data System (ADS)

    Mishin, Y.; McFadden, G. B.; Sekerka, R. F.; Boettinger, W. J.

    2015-08-01

    We present a rigorous irreversible thermodynamics treatment of creep deformation of solid materials with interfaces described as geometric surfaces capable of vacancy generation and absorption and moving under the influence of local thermodynamic forces. The free energy dissipation rate derived in this work permits clear identification of thermodynamic driving forces for all stages of the creep process and formulation of kinetic equations of creep deformation and microstructure evolution. The theory incorporates capillary effects and reveals the different roles played by the interface free energy and interface stress. To describe the interaction of grain boundaries with stresses, we classify grain boundaries into coherent, incoherent and semicoherent, depending on their mechanical response to the stress. To prepare for future applications, we specialize the general equations to a particular case of a linear-elastic solid with a small concentration of vacancies. The proposed theory creates a thermodynamic framework for addressing more complex cases, such as creep in multicomponent alloys and cross-effects among vacancy generation/absorption and grain boundary motion and sliding.

  12. Assessment of Tungsten Content on Tertiary Creep Deformation Behavior of Reduced Activation Ferritic-Martensitic Steel

    NASA Astrophysics Data System (ADS)

    Vanaja, J.; Laha, Kinkar

    2015-10-01

    Tertiary creep deformation behavior of reduced activation ferritic-martensitic (RAFM) steels having different tungsten contents has been assessed. Creep tests were carried out at 823 K (550 °C) over a stress range of 180 to 260 MPa on three heats of the RAFM steel (9Cr-W-0.06Ta-0.22V) with tungsten content of 1, 1.4, and 2.0 wt pct. With creep exposure, the steels exhibited minimum in creep rate followed by progressive increase in creep rate until fracture. The minimum creep rate decreased, rupture life increased, and the onset of tertiary stage of creep deformation delayed with the increase in tungsten content. The tertiary creep behavior has been assessed based on the relationship, , considering minimum creep rate () instead of steady-state creep rate. The increase in tungsten content was found to decrease the rate of acceleration of tertiary parameter ` p.' The relationships between (1) tertiary parameter `p' with minimum creep rate and time spent in tertiary creep deformation and (2) the final creep rate with minimum creep rate revealed that the same first-order reaction rate theory prevailed in the minimum creep rate as well as throughout the tertiary creep deformation behavior of the steel. A master tertiary creep curve of the steels has been developed. Scanning electron microscopic investigation revealed enhanced coarsening resistance of carbides in the steel on creep exposure with increase in tungsten content. The decrease in tertiary parameter ` p' with tungsten content with the consequent decrease in minimum creep rate and increase in rupture life has been attributed to the enhanced microstructural stability of the steel.

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

    SciTech Connect

    K. Linga Murty

    2008-08-11

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

  14. Multimechanism-Deformation Parameters of Domal Salts Using Transient Creep Analysis

    SciTech Connect

    MUNSON, DARRELL E

    1999-09-01

    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.

  15. Creep deformation behavior in eutectic Sn-Ag solder joints using a novel mapping technique

    SciTech Connect

    Lucas, J.P.; Guo, F.; McDougall, J.; Bieler, T.R.; Subramanian, K.N.; Park, J.K.

    1999-11-01

    Creep deformation behavior was measured for 60--100 {micro}m thick solder joints. The solder joints investigated consisted of: (1) non-composite solder joints made with eutectic Sn-Ag solder, and (2) composite solder joints with eutectic Sn-Ag solder containing 20 vol.%, 5 {micro}m diameter in-situ Cu{sub 6}Sn{sub 5} intermetallic reinforcements. All creep testing in this study was carried out at room temperature. Qualitative and quantitative assessment of creep deformation was characterized on the solder joints. Creep deformation was analyzed using a novel mapping technique where a geometrical-regular line pattern was etched over the entire solder joint using excimer laser ablation. During creep, the laser-ablation (LA) pattern becomes distorted due to deformation in the solder joint. By imaging the distortion of laser-ablation patterns using the SEM, actual deformation mapping for the entire solder joint is revealed. The technique involves sequential optical/digital imaging of the deformation versus time history during creep. By tracing and recording the deformation of the LA patterns on the solder over intervals of time, local creep data are obtained in many locations in the joint. This analysis enables global and localized creep shear strains and strain rate to be determined.

  16. On the creep deformation mechanisms of an advanced disk nickel-base superalloy

    NASA Astrophysics Data System (ADS)

    Unocic, Raymond R.

    The main objective of this research was aimed at investigating the fundamental relationship between microstructure and creep deformation mechanisms using a variety of electron microscopy characterization techniques. The alloy used in this research, Rene 104, is a newer generation powder metallurgy Ni-base superalloy that was developed specifically for aircraft gas turbine disk applications with extended service durability at temperatures exceeding 650°C. The influence of stress and temperature was studied first and it was found that during creep deformation at temperatures between 677--815°C and stresses between 345--724MPa a variety of distinctly different creep deformation mechanisms were operative. In addition to identifying the creep deformation mechanisms an attempt was made to determine the creep rate limiting process so that an improved understanding of the fundamental processes that control deformation can be better understood. Microtwinning was found to the dominant deformation mechanism following creep at 677°C/690MPa and 704°C/724MPa. Microtwins form by the motion of paired a/6<112> Shockley partial dislocations that shear both the gamma matrix and gamma' precipitates. The rate limiting process in this mechanism is diffusion mediated atomic reordering that occurs in the wake of the shearing, twinning partial dislocations in order to maintain the ordered L12 structure of the gamma' precipitates. This reordering process helps to fundamentally explain the temperature and rate dependence of microtwinning under creep conditions within this temperature and stress regime. At a slightly higher temperature but lower stress (760°C and 345MPa), a stacking fault related shearing mechanism, which typically spanned only a few micrometers in length, was the principle deformation mode. The faults left behind in the gamma' precipitates determined to be extrinsic in nature. During creep at the highest temperature and lowest stress (815°C and 345MPa) a thermally activated climb/bypass mechanism of a/2<110> dislocations were found to be the dominant deformation mechanism. In this mechanism, the gamma' precipitates were not sheared but instead were bypassed by a/2<110> matrix dislocations. In addition to the identification of creep deformation mechanisms as a function of stress and temperature, characterization of the post creep gamma' precipitate microstructure revealed that microstructural evolution of the gamma' precipitates has occurred during creep at the higher test temperatures where the secondary gamma' precipitates have coarsened and the tertiary gamma' precipitates have dissolved. In combination with creep at low stress and high temperature, the microstructural evolution may have contributed to the transition from one deformation mode to another. In an attempt to link the influence of microstructure (gamma' precipitate size scale, distribution, volume fraction, and gamma channel width spacing) on creep deformation behavior and creep deformation mechanisms, specimens with different size scaled microstructural features were crept at the same temperature and stress (677°C and 724MPa) in order to provide a direct comparison between differences in microstructure. It was found that a microstructure consisting of a bimodal distribution of gamma' precipitates with coarse secondary gamma' precipitates, a high volume fraction of tertiary gamma' precipitates and a wide gamma channel width spacing results in a less creep resistance microstructure that deformed primary by a/2<110> dislocation activity in the gamma matrix at small strain and secondary gamma' shearing via superlattice intrinsic stacking faults at higher strains. The more creep resistant microstructure consisted of a bimodal distribution of gamma' precipitates with a finer secondary gamma' precipitate size, low volume fraction of gamma' and narrow gamma channel width spacing. The combination of these microstructural features promoted a/2<110> dislocation dissociation and decorrelation of a/6<112> Shockley partial di

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

    E-print Network

    Fialko, Yuri

    Postseismic deformation due to the Mw 6.0 2004 Parkfield earthquake: Stress-driven creep on a fault investigate the coseismic and postseismic deformation due to the Mw 6.0 2004 Parkfield, California, earthquake deformation due to the Mw 6.0 2004 Parkfield earthquake: Stress- driven creep on a fault with spatially

  18. Deformational characteristics of thermoplastic elastomers

    NASA Astrophysics Data System (ADS)

    Indukuri, Kishore K.

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

  19. 2 Transient creep, aseismic damage and slow failure in Carrara marble 3 deformed across the brittle-ductile transition

    E-print Network

    Fortin, Jérôme

    2 Transient creep, aseismic damage and slow failure in Carrara marble 3 deformed across the brittle triaxial compression experiments were performed 8 on Carrara marble at high confining pressure, in creep 9 in Carrara marble deformed across the brittle-ductile transition, 31 Geophys. Res. Lett., 33, LXXXXX, doi:10

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

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

    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.

  1. Elevated temperature flow strength, creep resistance and diffusion welding characteristics of Ti-6Al-2Nb-1Ta-0.8Mo

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

    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.

  2. Creep Properties and Deformation Mechanisms of a FGH95 Ni-based Superalloy

    NASA Astrophysics Data System (ADS)

    Xie, Jun; Tian, Su-gui; Zhou, Xiao-ming

    2013-07-01

    By means of full heat treatment, microstructure observation, lattice parameters determination, and the measurement of creep curves, an investigation has been conducted into the microstructure and creep mechanisms of FGH95 Ni-based superalloy. Results show that after the alloy is hot isostatically pressed, coarse ?' phase discontinuously distributes along the previous particle boundaries. After solution treatment at high temperature and aging, the grain size has no obvious change, and the amount of coarse ?' phase decreases, and a high volume fraction of fine ?' phase dispersedly precipitates in the ? matrix. Moreover, the granular carbides are found to be precipitated along grain boundaries, which can hinder the grain boundaries' sliding and enhance the creep resistance of the alloy. By x-ray diffraction analysis, it is indicated that the lattice misfit between the ? and ?' phases decreases in the alloy after full heat treatment. In the ranges of experimental temperatures and applied stresses, the creep activation energy of the alloy is measured to be 630.4 kJ/mol. During creep, the deformation mechanisms of the alloy are that dislocations slip in the ? matrix or shear into the ?' phase. Thereinto, the creep dislocations move over the ?' phase by the Orowan mechanism, and the < { 1 10 } rangle super-dislocation shearing into the ?' phase can be decomposed to form the configuration of (1/3) < { 1 12 } rangle super-Shockleys' partials and the stacking fault.

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

    SciTech Connect

    Tribula, D.

    1990-06-02

    Thermal fatigue failures of solder joints in electronic devices often arise from cyclic shear strains imposed by the mismatched thermal expansion coefficients of the materials that bind the joint as temperature changes are encountered. Increased solder joint reliability demands a fundamental understanding of the metallurigical mechanisms that control the fatigue to design accurate accelerated probative tests and new, more fatigue resistant solder alloys. The high temperatures and slow strain rates that pertain to thermal fatigue imply that creep is an important deformation mode in the thermal fatigue cycle. In this work, the creep behaviour of a solder joint is studied to determine the solder's microstructural response to this type of deformation and to relate this to the more complex problem of thermal fatigue. It is shown that creep failures arise from the inherent inhomogeneity and instability of the solder microstructure and suggest that small compositional changes of the binary near-eutectic Pn-Sn alloy may defeat the observed failure mechanisms. This work presents creep and thermal fatigue data for several near-eutectic Pb-Sn solder compositions and concludes that a 58Sn-40Pb-2In and a 58Sn-40Pb-2Cd alloy show significantly enhanced fatigue resistance over that of the simple binary material. 80 refs., 33 figs., 1 tab.

  4. Microstructures of beta silicon carbide after irradiation creep deformation at elevated temperatures

    SciTech Connect

    Katoh, Yutai; Kondo, Sosuke; Snead, Lance Lewis

    2008-01-01

    Microstructures of silicon carbide were examined by transmission electron microscopy (TEM) after creep deformation under neutron irradiation. Thin strip specimens of polycrystalline and monocrystalline, chemically vapor-deposited, beta-phase silicon carbide were irradiated in the high flux isotope reactor to 0.7-4.2 dpa at nominal temperatures of 640-1080 C in an elastically pre-strained bend stress relaxation configuration with the initial stress of {approx}100 MPa. Irradiation creep caused permanent strains of 0.6 to 2.3 x 10{sup -4}. Tensile-loaded near-surface portions of the crept specimens were examined by TEM. The main microstructural features observed were dislocation loops in all samples, and appeared similar to those observed in samples irradiated in non-stressed conditions. Slight but statistically significant anisotropy in dislocation loop microstructure was observed in one irradiation condition, and accounted for at least a fraction of the creep strain derived from the stress relaxation. The estimated total volume of loops accounted for 10-45% of the estimated total swelling. The results imply that the early irradiation creep deformation of SiC observed in this work was driven by anisotropic evolutions of extrinsic dislocation loops and matrix defects with undetectable sizes.

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

    SciTech Connect

    M.C. Carroll; L.J. Carroll

    2012-10-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Hangx, Suzanne; Spiers, Christopher

    2014-05-01

    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.

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

    PubMed

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

    2014-07-01

    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

  8. Role of coupled cataclasis-pressure solution deformation in microearthquake activity along the creeping segment of the SAF: Inferences from studies of the SAFOD core samples

    NASA Astrophysics Data System (ADS)

    Hadizadeh, J.; Gratier, J.; Renard, F.; Mittempregher, S.; di Toro, G.

    2009-12-01

    Rocks encountered in the SAFOD drill hole represent deformation in the southern-most extent of the creeping segment of the SAF north of the Parkfield. At the site and toward the northwest the SAF is characterized by aseismic creep as well as strain release through repeating microearthquakes M<3. The activity is shown to be mostly distributed as clusters aligned in the slip direction, and occurring at depths of between 3 to 5 kilometers. It has been suggested that the events are due to frequent moment release from high strength asperities constituting only about 1% or less of the total fault surface area within an otherwise weak fault gouge. We studied samples selected from the SAFOD phase 3 cores (3142m -3296m MD) using high resolution scanning electron microscopy, cathodoluminescence imaging, X-ray fluorescence mapping, and energy dispersive X-ray spectroscopy. The observed microstructural deformation that is apparently relevant to the seismological data includes clear evidence of cyclic deformation events, cataclastic flow, and pressure solution creep with attendant vein sealing and fracture healing fabrics. Friction testing of drill cuttings and modeling by others suggest that the overall creep behavior in shale-siltstone gouge may be due to low bulk friction coefficient of 0.2-0.4 for the fault rock. Furthermore, the low resistivity zone extending to about 5km beneath the SAFOD-Middle Mountain area is believed to consist of a pod of fluid-filled fractured and porous rocks. Our microstructural data indicate that the foliated shale-siltstone cataclasites are, in a highly heterogeneous way, more porous and permeable than the host rock and therefore provide for structurally controlled enhanced fluid-rock interactions. This is consistent with the observed pressure solution deformation and the microstructural indications of transiently high fluid pressures. We hypothesize that while the friction laws defining stable sliding are prevalent in bulk deformation of the creeping segment, there exist the possibility of steady conditions for repetitive healing, dilation, and rupture of populations of stress-oriented patches due to operation of pressure solution creep along the fault zone. The limitation on the total area of the locked patches at any given time would be controlled primarily by the imposed tectonic and near field rates of slip and fluid flux within the local permeability structure. The available geophysical data for the creeping section of the SAF including hypocenter cluster distribution, moment release rate, seismic rupture area (? healed patch size), stress drop and return time characteristics point to a highly heterogeneous internal structure at the SAFOD site, and could be used to test the proposed coupled cataclasis-pressure solution microstructural model.

  9. Cell structure in cold worked and creep deformed phosphorus alloyed copper

    SciTech Connect

    Wu, Rui; Pettersson, Niklas; Martinsson, Åsa; Sandström, Rolf

    2014-04-01

    Transmission electron microscopy (TEM) examinations on as-received, cold worked, as well as cold worked and creep tested phosphorus-alloyed oxygen-free copper (Cu-OFP) have been carried out to study the role of the cell structure. The cell size decreased linearly with increasing plastic deformation in tension. The flow stress in the tests could also be correlated to the cell size. The observed relation between the flow stress and the cell size was in excellent agreement with previously published results. The dense dislocation walls that appeared after cold work in tension is likely to be the main reason for the dramatic increase in creep strength. The dense dislocation walls act as barriers against dislocation motion and their presence also reduces the recovery rate due to an unbalanced dislocation content.

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

    E-print Network

    Cambridge, University of

    and slows with time. The region CD stands as secondary or steady state creep, which has a relatively uniform of categories primary creep, tertiary creep, and steady state creep [7] 1.2.1 Primary Creep During primary creep, the strain rate decreases with time until a constant rate is reached. And this tends to occur over a short

  11. Analysis of Mining Terrain Deformation Characteristics with Deformation Information System

    NASA Astrophysics Data System (ADS)

    Blachowski, Jan; Milczarek, Wojciech; Grzempowski, Piotr

    2014-05-01

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

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

    NASA Astrophysics Data System (ADS)

    Wintsch, R. P.; Yi, Keewook

    2002-07-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Wintsch, R. P.

    2001-12-01

    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.

  14. Neutron Diffraction Study of Strain/Stress States and Subgrain Defects in a Creep-Deformed, Single-Crystal Superalloy

    NASA Astrophysics Data System (ADS)

    Wu, Erdong; Sun, Guangai; Chen, BO; Zhang, Jian; Ji, Vincent; Klosek, Vincent; Mathon, Marie-Helene

    2014-01-01

    A single crystal superalloy with initial sample axis 10 deg deviated from [001] was creep deformed at 1273 K (1000 °C) 235 MPa and its triaxial strain/stress state and subgrain defects were studied by neutron diffraction. Normal internal stresses with their directions close to the loading axis and their scales smaller than those perpendicular to the axis were observed and attributed to a lattice rotation toward [001] pole. The internal stress at a level approaching to the loading stress and mostly in the state of interphase stress was induced during the first stage of creep prior to rafting and associated to lattice rotation, microstrain relaxation and line-up of misoriented ?'-precipitates. The internal stress was diminished and released at final stage of creep associated with a reduction in unit-cell volume and a transition of strain/stress state between the two phases. The observation was explained by development of dislocations and raft structure during creep.

  15. Effect of titanium on the creep deformation behaviour of 14Cr-15Ni-Ti stainless steel

    NASA Astrophysics Data System (ADS)

    Latha, S.; Mathew, M. D.; Parameswaran, P.; Nandagopal, M.; Mannan, S. L.

    2011-02-01

    14Cr-15Ni-Ti modified stainless steel alloyed with additions of phosphorus and silicon is a potential candidate material for the future cores of Prototype Fast Breeder Reactor. In order to optimise the titanium content in this steel, creep tests have been conducted on the heats with different titanium contents of 0.18, 0.23, 0.25 and 0.36 wt.% at 973 K at various stress levels. The stress exponents indicated that the rate controlling deformation mechanism was dislocation creep. A peak in the variation of rupture life with titanium content was observed around 0.23 wt.% titanium and the peak was more pronounced at lower stresses. The variation in creep strength with titanium content was correlated with transmission electron microscopic investigations. The peak in creep strength exhibited by the material with 0.23 wt.% titanium is attributed to the higher volume fraction of fine secondary titanium carbide (TiC) precipitates.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    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.

  17. Dynamic Deformation Characteristics of Sedimentary Soft Rock

    NASA Astrophysics Data System (ADS)

    Fukumoto, Shun'ichi; Yoshida, Nozomu; Sahara, Mamoru

    Soil under the engineering seismic base layer is treated as elastic material in the engineering practice, however, evidence that its nonlinear behavior affects surface response begins to appear. Test data on dynamic deformation characteristics and tri-axial compression test on sedimentary soft rock are collected and compiled to consider its nonlinearity. In addition, nonlinear characteristics of soft rock and note on practical use are described. Static tri-axial compression test of the sample taken by means of diamond core drill is first carried out by using a LDT (Local deformation transducer), and shear modulus is found to keep nearly constant up to strain of about 10-3 for the undisturbed sample, whereas that decreases significantly even at strain of 10-5. Secondly, dynamic deformation test data on Pleistocene and Tertiary soft rock with SPT-N value greater than 30 or shear wave velocity greater than 300 m/s is collected and compiled. It is found that there exist data that shows similar behavior of static test described in the preceding. These samples is supposed be undisturbed, which means there exists many disturbed samples even if they are retrieved by, so called, undisturbed sampling method. Shear modulus at shear strain of 10-3, which is used as index of nonlinearity, is independent from effective confining stress, but it has positive correlation with plastic index. Finally, dynamic deformation characteristics of undisturbed samples are shown to be modeled by Ramberg-Osgood model well.

  18. Interseismic deformation and creep along the central section of the North Anatolian Fault (Turkey): InSAR observations

    E-print Network

    Fialko, Yuri

    Interseismic deformation and creep along the central section of the North Anatolian Fault (Turkey the central section of the North Anatolian Fault (NAF) in Turkey using interferometric synthetic aperture along the central section of the North Anatolian Fault (Turkey): InSAR observations and implications

  19. Interseismic deformation and creep along the central section of the North Anatolian Fault (Turkey): InSAR observations

    E-print Network

    Sandwell, David T.

    Interseismic deformation and creep along the central section of the North Anatolian Fault (Turkey Anatolian Fault (NAF) in Turkey using interferometric synthetic aperture radar data from the Advanced Land Anatolian Fault (Turkey): InSAR observations and implications for rate-and-state friction properties, J

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

    SciTech Connect

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

    2011-11-01

    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.

  1. Creep mechanisms and interface-enhanced deformation twinning in a two-phase lamellar TiAl alloy

    SciTech Connect

    Hsiung, L.M., LLNL

    1997-03-01

    Deformation mechanisms and the role of interfaces in deformation twinning of a two-phase [TiAl({gamma})/Ti{sub 3}Al({alpha}{sub 2})] lamellar alloy creep deformed at elevated temperatures have been investigated. Since the multiplication of lattice dislocations within both {gamma} and {alpha}{sub 2} lamellae is very limited at a low stress level due to a refined lamellar microstructure, the glide of interfacial dislocations on both {gamma}/{alpha}{sub 2} and {gamma}/{gamma} interfaces (i.e interface sliding) becomes an important deformation mode. Obstacles such as impinged lattice dislocations can impede the movement of interfacial dislocations, which glide in a cooperative fashion along the lamellar interfaces. The impediment of dislocation motion subsequently causes a dislocation pile-up in front of obstacles as creep strain accumulates. When the crystals deform at high stress level, deformation twinning becomes a predominant deformation mode. Deformation twins are found to nucleate from the interfaces as a result of a local stress concentration generated from dislocation pile-ups. It is suggested that the deformation twinning in lamellar TiAl/Ti{sub 3}Al crystals can be vieived as a stress relaxation process for the concentration of stress at the head of each dislocation pile-up. An interface-assisted twinning mechanism is accordingly proposed and discussed.

  2. Standard test method for flexure-creep of sandwich constructions

    SciTech Connect

    Not Available

    1980-01-01

    This method covers the determination of the creep characteristics and creep rate of sandwich constructions loaded in flexure, at any desired temperature. The determination of the creep rate provides information on the behavior of sandwich constructions under constant load. Creep is defined as deflection under constant load over a period of time beyond the initial deformation due to the application of the load. Deflection data obtained from this method can be plotted against time, and a creep rate determined. By using standard specimen constructions and constant loading, the method may also be used to evaluate creep behavior of adhesives for use in sandwich panels.

  3. The sliding mode control for different shapes and dimensions of IPMC on resisting its creep characteristics

    NASA Astrophysics Data System (ADS)

    Hao, Lina; Chen, Yang; Sun, Zhiyong

    2015-04-01

    Ionic polymer metal composite (IPMC) is a novel smart material which has been widely implemented in MEMS, biomimetic mechanical and electrical integrated system and micro operation system. While the IPMC with different shapes and dimensions has been implemented in many different types of biomechanical integrated systems, one of its inherent properties called creep characteristic is difficult to be handled, which limits the further application of different IPMCs in integrated systems. A promising control method called sliding mode control (SMC) is proposed to resist the creep characteristics in this paper. The SMC controller can regulate IPMC actuators with different shapes and dimensions effectively to resist the creep characteristics without changing parameters of the control system. Experiments of four different types of IPMC actuators were conducted on the semi-physical SMC experimental platform. All the experimental results confirm the feasibility of the SMC control approach on regulating the multi-IPMCs with different shapes and dimensions based integrated system.

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

    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.

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

    SciTech Connect

    Unocic, Raymond R; Zhou, Ning; Kovarik, Libor; Shen, Chen; Wang, Yunzhi; Mills, Michael J.

    2011-01-01

    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.

  6. The Åknes rockslide: Characteristics of subsurface deformation

    NASA Astrophysics Data System (ADS)

    Blikra, Lars; Lovisolo, Mario; Kristensen, Lene

    2010-05-01

    The Åknes rockslide represents a possible collapse of 20-55 million cubic metres, moving with a velocity of up to 10 cm/year. The risk is associated with the generation of catastrophic tsunamis, having run-up potential of up to 80 m in nearby villages. The surface monitoring systems is today based on extensometers/crackmeters, tiltmeters, single lasers, GPS, total station and a microseismic network, in addition to a climate station. Large efforts have been paid to the establishment of subsurface investigations and monitoring systems in deep boreholes. Tree boreholes have been instrumented with 50 to 120 m long active multiparametric in place columns (DMS system: Differential Monitoring of Stability). The system consists of 1 m long modules connected by special flexible junctions being free to move. Each module contains of a biaxial inclinometric sensor, a temperature sensor, and selected modules have a piezometric sensor. Also digital compass is emplaced in specific modules for controlling the direction of column. Measurements are continuous and are automatically downloaded. The DMS data has documented a well-defined upper sliding zone in two boreholes at depth of 35 and 50 m depth. This is above the water-level measured in open standpipes. The video inspection before instrumentation and the core data shows distinct fracture zones in this upper part, in addition to water inflow at some parts. The continuous temperature data from the DMS columns can also be used to measure the inflow of water through time, by the fact that the flow of water influences the temperatures. The deformation data also show that there are creeping movements in lower part, down to below 120 m depth. The mode of deformation is varying from continuous displacements through time to suddenly and abrupt steps in movement rates. Also, it is possible to detect a series of different displacements rates during small time windows. For examples, in the upper borehole, the movement velocity at 49-51 m depth beginning from November 2009 to middle of January 2010 depicts 3 velocity trends. This range from 0,1 mm/day the first month, decreasing to 0,05 mm/day the next month, and finally reducing to 0,02 mm/day the last half month. This velocity change seems to correlate broadly with the decreasing water level during the transition from relative wet autumn to colder winter conditions.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2008-12-01

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

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

    E-print Network

    Fatemi, Ali

    2002-01-01

    of Mechanical, Industrial and Manufacturing Engineering, The University of Toledo, Toledo, Ohio, USA E of a typical creep curve. turbine blade in a military aircraft engine (tR = 100 hrs) [1]. In such short life hardening, softening, and damage processes, resulting in a nearly constant creep rate. The tertiary stage

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    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.

  12. Creep Measurement Video Extensometer

    NASA Technical Reports Server (NTRS)

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

    2011-01-01

    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.

  13. Aftershocks resulting from creeping sections in a heterogeneous fault

    NASA Astrophysics Data System (ADS)

    Zöller, G.; Hainzl, S.; Holschneider, M.; Ben-Zion, Y.

    2005-02-01

    We show that realistic aftershock sequences with space-time characteristics compatible with observations are generated by a model consisting of brittle fault segments separated by creeping zones. The dynamics of the brittle regions is governed by static/kinetic friction, 3D elastic stress transfer and small creep deformation. The creeping parts are characterized by high ongoing creep velocities. These regions store stress during earthquake failures and then release it in the interseismic periods. The resulting postseismic deformation leads to aftershock sequences following the modified Omori law. The ratio of creep coefficients in the brittle and creeping sections determines the duration of the postseismic transients and the exponent p of the modified Omori law.

  14. Madelung deformity and Madelung-type deformities: a review of the clinical and radiological characteristics.

    PubMed

    Ali, Sayed; Kaplan, Summer; Kaufman, Theresa; Fenerty, Sarah; Kozin, Scott; Zlotolow, Dan A

    2015-11-01

    Madelung deformity of the distal radius results from premature closure of the medial volar aspect of the distal radial physis, leading to increased volar tilt and increased inclination of the radial articular surface, triangulation of the carpus with proximal migration of the lunate and dorsal displacement of the distal ulna. The deformity is particularly common in Leri-Weill dyschondrosteosis, but it may also occur in isolation. True Madelung deformity can be differentiated from Madelung-type deformities by the presence of an anomalous radiolunate ligament (Vickers ligament). In this article, we will review the imaging characteristics of true Madelung deformity, including the common "distal radius" variant, the less common "entire radius" variant and "reverse" Madelung deformity. We will discuss the role of the Vickers ligament in disease pathogenesis and its use in differentiating true Madelung deformity from Madelung-type deformities arising from trauma or multiple hereditary exostoses. Surgical management of these patients will also be addressed. PMID:26135644

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

    SciTech Connect

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

    1999-08-26

    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.

  16. Creep and the corrosion characteristics of Incoloy Alloy 800 in molten nitrate salts

    SciTech Connect

    Goods, S.H.

    1981-03-01

    Incoloy Alloy 800 (I800) has been proposed for use in the receiver tube panel arrays in a number of advanced solar central receiver (SCR) concepts. Because of their high heat capacity and high thermal energy density, several designs require the use of molten sodium and potassium nitrate salt mixture to act as the cooling or heat transfer fluid. The effects of deformation on the corrosion resistance of Incoloy Alloy 800 in sodium nitrate and potassium nitrate salt mixtures have been studied. Hollow tube specimens filled with the salt mixture (60%-NaNO/sub 3/-40% KNO/sub 3/) were tested in constant load tension creep at elevated temperatures (550/sup 0/ less than or equal to T less than or equal to 670/sup 0/C). Depending on the temperature and initial stress, fracture times (and therefore salt exposure times) ranged between 300 and 1000 hours. While the fracture strain of specimens tested to failure was only slightly reduced when exposed to the salt environment, metallographic observations of polished cross-sections revealed severe surface oxidation. In order to characterize the effect of total imposed strain on oxide morphology a number of creep tests were terminated prior to fracture. Increasing deformation resulted in a more extensively damaged surface oxide as well as a more rapid rate of corrosion. EDX analysis revealed that the oxide was multiphase, with a near surface iron rich oxide above a chromium-rich oxide layer. Below 630/sup 0/C the oxide-metal interface was well defined (although irregular). Above 630/sup 0/C the interface was more diffuse with fine oxide intrusions growing into the base metal and small particles of the alloy visible in the oxide near the base metal interface.

  17. Microstructural Evolution of an Extensional Shear Zone: the Transition from Dislocation Creep to Grain Boundary Sliding in Naturally Deformed Plagioclase

    NASA Astrophysics Data System (ADS)

    Miranda, E.; Hirth, G.; John, B. E.

    2014-12-01

    We present microstructural, LPO, and misorientation data from EBSD analyses to interpret the deformation mechanisms of naturally deformed plagioclase in an amphibolite-facies extensional shear zone within oceanic crust. Textural data and mineral chemistry data for thermometry were acquired on samples of gabbro mylonite collected from the footwall of the Atlantis Bank oceanic core complex; we focus on a monophase plagioclase layer with a high ratio of recrystallized matrix grains to porphyroclasts. Sample microstructures are subdivided into three regions: seven porphyroclasts, recrystallized grains immediately adjacent to those porphyroclasts, and the population of recrystallized matrix grains. All porphyroclasts exhibit subgrain development and show clustering of low-angle (3-10º) misorientation axes within the {010} plane, consistent with slip on {010}. However, only one porphyroclast is oriented for operation of the {010}<001> easy slip system. The small recrystallized grains immediately adjacent to the porphyroclasts do not show a host control relationship with their respective porphyroclasts, and these grains are also smaller than the subgrains of the porphyroclasts. Recrystallized matrix grains are fine-grained (mean grain size 8 ?m) and slightly elongate parallel to foliation, with local misorientations concentrated along grain boundaries and junctions. They exhibit a weak, nonrandom LPO suggesting the activity of the {111}<110> slip system, and their neighbor-pair misorientations are shifted towards higher angles. We interpret the distinctive relationships between the three regions as evidence of a transition from dislocation creep to dislocation-accommodated grain boundary sliding (DisGBS). Porphyroclast subgrains and misorientation axes suggest the operation of dislocation creep, but the lack of host control in the adjacent recrystallized grains precludes grain size reduction through subgrain rotation recrystallization alone. High driving force bulge nucleation likely contributed to the grain size reduction and recrystallization of matrix grains, triggering the onset of grain size sensitive DisGBS. We suggest that the transition between deformation mechanisms is an effective weakening mechanism that contributed to development of the shear zone.

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

    PubMed Central

    Mashaan, Nuha Salim; Karim, Mohamed Rehan

    2013-01-01

    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

  19. Modelling and analysis of creep deformation and fracture in a 1 Cr 1/2 Mo ferritic steel

    NASA Astrophysics Data System (ADS)

    Dyson, B. F.; Osgerby, D.

    A quantitative model, based upon a proposed new mechanism of creep deformation in particle-hardened alloys, has been validated by analysis of creep data from a 13CrMo 4 4 (1Cr 1/2 Mo) material tested under a range of stresses and temperatures. The methodology that has been used to extract the model parameters quantifies, as a first approximation, only the main degradation (damage) processes - in the case of the 1CR 1/2 Mo steel, these are considered to be the parallel operation of particle-coarsening and a progressively increasing stress due to a constant-load boundary condition. These 'global' model parameters can then be modified (only slightly) as required to obtain a detailed description and 'fit' to the rupture lifetime and strain/time trajectory of any individual test. The global model parameter approach may be thought of as predicting average behavior and the detailed fits as taking account of uncertainties (scatter) due to variability in the material. Using the global parameter dataset, predictions have also been made of behavior under biaxial stressing; constant straining rate; constant total strain (stress relaxation) and the likely success or otherwise of metallographic and mechanical remanent lifetime procedures.

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

    PubMed

    Mashaan, Nuha Salim; Karim, Mohamed Rehan

    2013-01-01

    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

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

    NASA Astrophysics Data System (ADS)

    Jaworski, A.; Ankem, S.

    2006-09-01

    The effects of ? and ? phase interactions on the room-temperature tensile and creep deformation behavior of ? + ? titanium alloys with Widmanstätten microstructures were studied using Ti-6.0 wt pct Mn and Ti-8.1 wt pct V as the model two-phase alloy systems. This article, Part I, deals with tensile deformation. It was found that when the ? phase is present as thin (<10-µm) plates in the ? + ? alloys, significant twinning occurs. No significant twinning was observed in single-phase alloys with the same chemistry and similar grain size. Additionally, the ? phase of Ti-8.1 V deforms by stress-induced hexagonal martensite (?'), while only twinning occurs in the single-phase ? alloy with the same chemistry. Twinning in the ? phase in association with stress-induced martensite (SIM) in the ? phase was observed for the first time in a two-phase titanium alloy. This behavior is explained in terms of a number of factors including elastic interaction stresses between the ? and ? phases, coherency between the ? phase and hexagonal martensite, and ? phase stability.

  2. On The Creep Behavior and Deformation Mechanisms Found in an Advanced Polycrystalline Nickel-Base Superalloy at High Temperatures

    NASA Astrophysics Data System (ADS)

    Deutchman, Hallee Zox

    Polycrystalline Ni-base superalloys are used as turbine disks in the hot section in jet engines, placing them in a high temperature and stress environment. As operating temperatures increase in search of better fuel efficiency, it becomes important to understand how these higher temperatures are affecting mechanical behavior and active deformation mechanisms in the substructure. Not only are operating temperatures increasing, but there is a drive to design next generation alloys in shorter time periods using predictive modeling capabilities. This dissertation focuses on mechanical behavior and active deformation mechanisms found in two different advanced polycrystalline alloy systems, information which will then be used to build advanced predictive models to design the next generation of alloys. The first part of this dissertation discusses the creep behavior and identifying active deformation mechanisms in an advanced polycrystalline Ni-based superalloy (ME3) that is currently in operation, but at higher temperatures and stresses than are experienced in current engines. Monotonic creep tests were run at 700°C and between 655-793MPa at 34MPa increments, on two microstructures (called M1 and M2) produced by different heat treatments. All tests were crept to 0.5% plastic strain. Transient temperature and transient stress tests were used determine activation energy and stress exponents of the M1 microstructure. Constant strain rate tests (at 10-4s-1) were performed on both microstructures as well. Following creep testing, both M1 and M2 microstructures were fully characterized using Scanning Electron Microscopy (SEM) for basic microstructure information, and Scanning Transmission Electron Microscopy (STEM) to determine active deformation mechanism. It was found that in the M1 microstructure, reorder mediated activity (such as discontinuous faulting and microtwinning) is dominant at low stresses (655-724 MPa). Dislocations in the gamma matrix, and overall planar dislocation activity were also present. At higher stresses (758-793MPa), there is still planar activity present, but now non-planar "wavy" slip appears. Wavy slip was also present in the constant strain rate sample of the M1 microstructure. M2 showed much of the same activity as M1, but wavy slip was not present in either the high stress creep conditions or the constant strain rate conditions. The second part of this dissertation focused on Alloy X, which is a next generation alloy system. Three variants were examined (decreased levels of Cr and Co, decreased levels of Cr and Co with added Hf, and decreased levels of Cr and Co with added Hf and a faster cooling rate). The variants were all tested at 700°C/690MPa, 760°C/490MPa, and 815°C/345MPa, to various strains. In Alloy X, the dominant mechanisms that appear throughout all strains, stresses, and temperatures are unpaired dislocations and discontinuous stacking faults. In the Hf bearing variants, , unpaired dislocations appear to start at grain boundaries and move in to the grains with increasing strain and temperature. Through 3D stereo imaging using STEM images, it appears that the dislocations are able to climb over precipitates at larger strains. It is postulated that the decreasing levels of Cr and Co have changed the stacking fault energy so it is unfavorable to form microtwins anymore. This was discussed in terms of the Dislocation Activity Diagram (DAD).

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

    PubMed

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

    2003-01-01

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

  4. Strain heterogeneity during creep of Carrara marble

    E-print Network

    Quintanilla Terminel, Alejandra

    2014-01-01

    Creep processes in calcite have been extensively studied, leading to the establishment of deformation mechanism maps. However, flow laws assuming a steady-state and homogeneous creep deformation cannot describe the strain ...

  5. 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)

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

    2010-12-01

    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.

  6. Evidence of post-seismic creep type deformations derived by tilt and acoustic emission monitoring of mining induced seismic events

    NASA Astrophysics Data System (ADS)

    Milev, Alexander; Share, Pieter-Ewald; Naoi, Makoto; Durrheim, Raymond; Yabe, Yasuo; Ogasawara, Hiroshi; Nakatani, Masao

    2015-04-01

    In this study we try to understand pre- and post-failure rock behavior associated with mining induced seismic events. This involves underground installation of various high precision instruments, including geophones, acoustic emission sensors, tilt- and strain-meters at a number of sites in deep level South African gold mines. The rate of tilt, strain and the seismic ground motion were analysed in order to understand the coseismic and aseismic deformation of the rocks. A good correspondence between the coseismic and the aseismic deformations was found. The rate of coseismic and aseismic tilt, as well as seismicity recorded by the mine seismic network, are approximately constant until the daily blasting time, which takes place from about 19:30 until shortly before 21:00. During the blasting time and the subsequent seismic events, the coseismic tilt and strain shows a rapid increase. Much of the aseismic deformation, however, occurs independently of the seismic events and blasting. In an attempt to distinguish between the different mechanisms of tilting two types of events were recognized. The "fast" seismic events characterized with sharp increase of the tilt during the seismic rupture and "slow" seismic events characterized by creep type post seismic deformations. Tilt behaviour before and after a seismic event was also analysed. The fact that no recognizable aftertilt was observed for more of the "fast" seismic events means that there is no gradual release of stress and an associated continuous strain rate change afterwards. It can therefore be concluded that a large seismic event causes a rapid change in the state of stress rather than a gradual change in the strain rate During the monitoring period a seismic event with MW 2.2 occurred in the vicinity of the instrumented site. This event was recorded by both the CSIR integrated monitoring system and JAGUARS acoustic emission network. More than 21,000 AE aftershocks were located in the first 150 hours after the main event. Using the distribution of the AE events the position of the fault in the source area was successfully delineated. The rupture area, elastic properties of the rock, the state of stress before the event occurred and frictional parameters of the rupture were used as input parameters to both numerical and analytical tools to reproduce the expected tilt. The calculated values were compared with the real values as recorded by the installed tiltmeters. A good correlation between the calculated and monitored amount of tilt was found. The tilt changes associated with this event showed a well pronounced after-tilt. The distribution of the AE events following the main shock was related to after tilt in order to quantify post slip behavior of the source. There was no evidence found for coseismic expansion of the source after the main slip. Therefore the hypothesis of the post-seismic creep behaviour of the source was proposed to explain the large amount of tilt following the main shock.

  7. Compilation of Surface Creep on California Faults and Comparison of WGCEP 2007 Deformation Model to Pacific-North American Plate Motion

    USGS Publications Warehouse

    Wisely, Beth A.; Schmidt, David A.; Weldon, Ray J., II

    2008-01-01

    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

  8. Correlation of Creep Behavior of Domal Salts

    SciTech Connect

    Munson, D.E.

    1999-02-16

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Richard, Julie; Gratier, Jean-Pierre; Doan, Mai-Linh; Boullier, Anne-Marie; Renard, François

    2013-04-01

    Creep processes can relax an important part of the tectonic stresses in active faults, either by permanent steady-state creep or by episodic post-seismic creep. Here, our goal is to better constrain the micro-physical parameters that control this transition between seismic and aseismic behavior, both in time and in space. We present new results from microstructural studies on natural samples collected from the SAFOD (San Andreas Fault Observatory at Depth) drilling project, located on the Parkfield segment of the San Andreas Fault (SAF). Seven samples were collected from the main active creeping zone: the Central Deforming Zone at 3296,6-3299,1m depth (relative to Phase 3 Core). We performed chemical and mineralogical analyses and microscope observations on twenty thin sections cut from those samples. In a previous study (Gratier et al., Geology, 2011), we have already shown that pressure solution creep is an active deformation process in the SAF. We propose a model of microstructural evolution to characterize in which conditions pressure solution creep is efficient enough to relax stress and to prevent the nucleation of moderate to large earthquakes. We show that two crucial parameters may accelerate pressure solution: the presence of phyllosilicates and the degree of rock fracturing. The initial structure and composition of the rocks may explain why pressure solution creep is efficient or not. Moreover, both the content of phyllosilicates and the degree of fracture may evolve with time at various scales during the seismic cycle: - During interseismic periods (years to millennia): fracturing activates postseismic creep. However, the progressive healing of the fracture annihilates this effect. Meanwhile, growth of phyllosilicate minerals, associated with postseismic fluid flow may also activate the creep rate. - During much longer geological periods (hundred thousands to millions of years), the composition of gouge material deformed by pressure solution evolves by the passive concentration of phyllosilicates due to the dissolution of soluble minerals. If their content is large enough, phyllosilicates could control the creep mechanism and accommodate the deformation by friction on clay layers. The steady state creeping zone of the SAF illustrates both effects thanks to very fine grains resulting from successive fracturing processes, very few amount of healing, possible growth of metamorphic clays and a general passive concentration of phyllosilicates with volume decrease. Conversely, in the nearby damaged zone, healing reduces the efficiency of pressure solution. Microseismicity, resulting from the fracturing of healed zones, may maintain a dynamic equilibrium between fracturing and healing. The southern part of the permanent creeping zones, which shows 20-30 years "Parkfield"-like earthquake cycles with postseismic creep, may illustrate the competition between healing/strengthening and creep processes that occur during interseismic periods.

  11. In-situ scanning electron microscopy (sem) observations of the tensile and tensile-creep deformation of Titanium-8Aluminum-1mo-1v (wt.%) alloy

    NASA Astrophysics Data System (ADS)

    Ghosh Dastidar, Indraroop

    Titanium (Ti) and titanium alloys (Ti alloys) are attractive for structural applications, such as in the aerospace and automotive industries due to their high specific strength, excellent corrosion resistance and good ability to withstand elevated temperatures. To develop Ti alloys with better mechanical properties, it is necessary to comprehend the deformation behavior of available Ti alloys. Previous studies performed by another graduate student, Dr. Hongmei Li, involved investigation of the deformation behavior of commercially pure (CP) Ti, Ti-5Al-2.5Sn (wt.%), Ti-3Al-2.5V (wt.%) and Ti-6Al-4V (wt.%) alloys. The current thesis focused on investigating the deformation behavior of Ti-8Al-1Mo-1V (wt.%). In-situ tensile and tensile-creep experiments were performed at temperatures ranging from room temperature (RT) to 650OC inside a scanning electron microscope (SEM), which allowed for the observation of the surface deformation evolution. Electron Back Scattered Diffraction (EBSD) was used to identify the distribution of the active deformation systems. In this thesis efforts were made to characterize the various deformation modes of the Ti-8Al-1Mo-1V (wt.%) alloy as a function of the testing conditions (stress and temperature). It was observed that prismatic slip made up the majority of the observed slip systems during the RT tensile deformation, while basal and prismatic slip were almost equally active during the 455OC tensile deformation. Grain boundary ledges were observed during the elevated temperature tensile-creep deformation and from this observation it was suggested that grain boundary sliding was an active deformation mode. This work also involved estimating the Critical Resolved Shear Stress (CRSS) ratios of the alpha-phase deformation modes. The CRSS ratios were compared with the CRSS ratios of CP Ti and other Ti alloys. Overall, this work was intended to add more data to the scientific literature of Ti alloys in order to better comprehend their deformation modes, so as to design and develop higher performance Ti alloys.

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

    NASA Astrophysics Data System (ADS)

    Larouk, Z.; Pilkington, R.

    1999-08-01

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

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

    NASA Astrophysics Data System (ADS)

    Shrestha, Triratna

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

  14. Brittle and compaction creep in porous sandstone

    NASA Astrophysics Data System (ADS)

    Heap, Michael; Brantut, Nicolas; Baud, Patrick; Meredith, Philip

    2015-04-01

    Strain localisation in the Earth's crust occurs at all scales, from the fracture of grains at the microscale to crustal-scale faulting. Over the last fifty years, laboratory rock deformation studies have exposed the variety of deformation mechanisms and failure modes of rock. Broadly speaking, rock failure can be described as either dilatant (brittle) or compactive. While dilatant failure in porous sandstones is manifest as shear fracturing, their failure in the compactant regime can be characterised by either distributed cataclastic flow or the formation of localised compaction bands. To better understand the time-dependency of strain localisation (shear fracturing and compaction band growth), we performed triaxial deformation experiments on water-saturated Bleurswiller sandstone (porosity = 24%) under a constant stress (creep) in the dilatant and compactive regimes, with particular focus on time-dependent compaction band formation in the compactive regime. Our experiments show that inelastic strain accumulates at a constant stress in the brittle and compactive regimes leading to the development of shear fractures and compaction bands, respectively. While creep in the dilatant regime is characterised by an increase in porosity and, ultimately, an acceleration in axial strain to shear failure (as observed in previous studies), compaction creep is characterised by a reduction in porosity and a gradual deceleration in axial strain. The overall deceleration in axial strain, AE activity, and porosity change during creep compaction is punctuated by excursions interpreted as the formation of compaction bands. The growth rate of compaction bands formed during creep is lower as the applied differential stress, and hence background creep strain rate, is decreased, although the inelastic strain required for a compaction band remains constant over strain rates spanning several orders of magnitude. We find that, despite the large differences in strain rate and growth rate (from both creep and constant strain rate experiments), the characteristics (geometry, thickness) of a compaction band remain essentially the same. Several lines of evidence, notably the similarity between the differential stress dependence of creep strain rate in the dilatant and compactive regimes, suggest that, as for dilatant creep, compactant creep is driven by subcritical stress corrosion cracking. We highlight the attendant implications for time-dependent porosity loss, subsidence, and permeability reduction in sandstone reservoirs.

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

    SciTech Connect

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

    1980-03-01

    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.

  16. Creep deformation behavior of Sn-3.5Ag solder/Cu couple at small length scales

    SciTech Connect

    Kerr, M.; Chawla, N

    2004-09-06

    In order to adequately characterize the behavior of solder balls in electronic devices, the mechanical behavior of solder joints needs to be studied at small length scales. The creep behavior of single solder ball Sn-Ag/Cu solder joints was studied in shear, at 25, 60, 95, and 130 deg. C, using a microforce testing system. A change in the creep stress exponent with increasing stress was observed and explained in terms of a threshold stress for bypass of Ag{sub 3}Sn particles by dislocations. The stress exponent was also temperature dependent, exhibiting an increase in exponent of two from lower to higher temperature. The activation energy for creep was found to be temperature dependant, correlating with self-diffusion of pure Sn at high temperatures, and dislocation core diffusion of pure Sn at lower temperatures. Normalizing the creep rate for activation energy and the temperature-dependence of shear modulus allowed for unification of the creep data. Microstructure characterization, including preliminary TEM analysis, and fractographic analysis were conducted in order to fully describe the creep behavior of the material.

  17. Deformation characteristics and time-dependent notch sensitivity of Udimet 700 at intermediate temperatures

    NASA Technical Reports Server (NTRS)

    Wilson, D. J.

    1974-01-01

    Time dependent notch sensitivity was observed in Udimet 700 sheet, bar, and investment castings between 1000 and 1400 F (538 -760 C), but not at 1600 F (871 C). As was the case for modified Waspaloy, Waspaloy and Inconel 718, it occurred in notched specimens loaded below the yield strength when the creep deformation was localized. For each alloy and notched specimen geometry, a stress-average particle size zone can be defined that characterizes the notch sensitive behavior.

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

    NASA Astrophysics Data System (ADS)

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

    2014-02-01

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

  19. Active disturbance rejection control for output force creep characteristics of ionic polymer metal composites

    NASA Astrophysics Data System (ADS)

    Xiong, Yan; Chen, Yang; Sun, Zhiyong; Hao, Lina; Dong, Jie

    2014-07-01

    Ionic polymer metal composites (IPMCs) are a type of electroactive polymer (EAP) that can be used as both sensors and actuators. An IPMC has enormous potential application in the field of biomimetic robotics, medical devices, and so on. However, an IPMC actuator has a great number of disadvantages, such as creep and time-variation, making it vulnerable to external disturbances. In addition, the complex actuation mechanism makes it difficult to model and the demand of the control algorithm is laborious to implement. In this paper, we obtain a creep model of the IPMC by means of model identification based on the method of creep operator linear superposition. Although the mathematical model is not approximate to the IPMC accurate model, it is accurate enough to be used in MATLAB to prove the control algorithm. A controller based on the active disturbance rejection control (ADRC) method is designed to solve the drawbacks previously given. Because the ADRC controller is separate from the mathematical model of the controlled plant, the control algorithm has the ability to complete disturbance estimation and compensation. Some factors, such as all external disturbances, uncertainty factors, the inaccuracy of the identification model and different kinds of IPMCs, have little effect on controlling the output block force of the IPMC. Furthermore, we use the particle swarm optimization algorithm to adjust ADRC parameters so that the IPMC actuator can approach the desired block force with unknown external disturbances. Simulations and experimental examples validate the effectiveness of the ADRC controller.

  20. Postseismic relaxation and transient creep

    USGS Publications Warehouse

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

    2005-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Jadaan, Osama M.

    1998-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

    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.

  3. Clash of Porphyroblasts - Mechanical and chemical interaction of strong objects in a weak deforming matrix and the acceleration of dissolution precipitation creep

    NASA Astrophysics Data System (ADS)

    Bender, Hagen; Huet, Benjamin; Grasemann, Bernhard; Schuster, Ralf

    2015-04-01

    The presence of porphyroblasts in metamorphic rocks has a strong influence on the microstructures that develop during deformation. Valuable as gauges for the sense of shear, single isolated porphyroblasts and -clasts have attracted enormous attention and vigorous discussion in the geological community. Naturally, however, porphyroblasts often occur in populations. Therefore, the understanding of multi-porphyroblast interaction is of great significance. We use amphibolite-facies garnet mica schists from the Upper Austroalpine Wölz Complex for a case study. The microstructure of mm-cm sized, densely distributed garnet porphyroblasts indicates interference of the blasts. Blasts are subjected to convergence parallel to the instantaneous shortening axis, causing (i) accumulation and deformation of strain caps, (ii) fracturing of the garnets and (iii) dissolution of garnet at collision sites. Parallel to the instantaneous stretching axis, (i) cone-shaped strain shadows are linked between neighbouring garnets and (ii) separation of garnet clusters occurs preferably. Dissolution precipitation creep accommodates the major part of deformation. Consequently, the matrix separates due to the dense population of porphyroblasts. The matrix differentiates to dissolution sites and precipitation sites in the respective quadrants of stretching and shortening around the blasts. Quantitative chemical analysis and thermodynamic modelling are utilised to examine compositional variations in minerals within the stretching and shortening domains. The results show that the present-day assemblage in these rocks records no deviations from lithostatic pressure.

  4. Influence of the Temperature of Gases on the Deformation Characteristics of Moving Water Droplets

    NASA Astrophysics Data System (ADS)

    Antonov, D. V.; Volkov, R. S.; Zhdanova, A. O.; Kuznetsov, G. V.; Strizhak, P. A.

    2015-07-01

    An experimental analysis of the influence of the temperature of gases on the deformation characteristics of water droplets moving through them is carried out. High-speed (up to 105 frames per second) photography with video cameras and cross-correlation complexes, as well as panoramic optical methods of recording the motion parameters of gaseous and liquid flows, were used. The laws governing the movement of water droplets through gases with a temperature of about 1100 K and in air at relatively low (to 280 K) and moderate (about 300 K) temperatures have been studied. The principal characteristics of the deformation of water droplets (duration, extension, and amplitudes of "deformation cycles") have been established. The differences in the characteristic shapes of droplets during their motion in gaseous media (at different temperatures of the latter) have been determined. The times during which droplets retain a certain shape in the deformation process have been calculated.

  5. 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)

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

    1998-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

    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.

  8. Powder metallurgy processing and deformation characteristics of bulk multimodal nickel

    SciTech Connect

    Farbaniec, L.; Dirras, G.; Krawczynska, A.; Mompiou, F.; Couque, H.; Naimi, F.; Bernard, F.; Tingaud, D.

    2014-08-15

    Spark plasma sintering was used to process bulk nickel samples from a blend of three powder types. The resulting multimodal microstructure was made of coarse (average size ? 135 ?m) spherical microcrystalline entities (the core) surrounded by a fine-grained matrix (average grain size ? 1.5 ?m) or a thick rim (the shell) distinguishable from the matrix. Tensile tests revealed yield strength of ? 470 MPa that was accompanied by limited ductility (? 2.8% plastic strain). Microstructure observation after testing showed debonding at interfaces between the matrix and the coarse entities, but in many instances, shallow dimples within the rim were observed indicating local ductile events in the shell. Dislocation emission and annihilation at grain boundaries and twinning at crack tip were the main deformation mechanisms taking place within the fine-grained matrix as revealed by in-situ transmission electron microscopy. Estimation of the stress from loop's curvature and dislocation pile-up indicates that dislocation emission from grain boundaries and grain boundary overcoming largely contributes to the flow stress. - Highlights: • Bulk multi-modal Ni was processed by SPS from a powder blend. • Ultrafine-grained matrix or rim observed around spherical microcrystalline entities • Yield strength (470 MPa) and ductility (2.8% plastic strain) were measured. • Debonding was found at the matrix/microcrystalline entity interfaces. • In-situ TEM showed twinning, dislocation emission and annihilation at grain boundaries.

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

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  11. Precipitation Behavior in the Heat-Affected Zone of Boron-Added 9Cr-3W-3Co Steel During Post-Weld Heat Treatment and Creep Deformation

    NASA Astrophysics Data System (ADS)

    Liu, Yuan; Tsukamoto, Susumu; Sawada, Kota; Tabuchi, Masaaki; Abe, Fujio

    2015-05-01

    In the previous paper, we demonstrated that the addition of boron was effective in preventing type IV failure due to suppression of grain refinement in the heat-affected zone at the peak temperature of around AC3 (AC3 HAZ). However, some fine prior austenite grains (PAGs) still remained around the coarse PAG boundaries, and these fine PAGs may affect the creep property of the welded joint. In the present study, the effect of these fine PAGs on the creep property of the boron-added 9Cr-3Co-3W steel (B steel) Ac3 HAZ is investigated. Different heat treatments are carried out on B steel base metal to form different Ac3 HAZ-simulated microstructures of coarse PAG with and without fine PAGs. Ac3 HAZ microstructure shows that a lot of M23C6 carbides are formed at the block boundary in the interior of coarse PAG. On the other hand, few M23C6 carbides are formed at the fine PAG boundaries, but a number of ? phases (W6Fe7 type) cover the boundary. The formation of ? phase retards the recovery of dislocation at the fine PAG boundary and contributes to stabilizing the microstructure in the primary and transient creep regions. The ? phase transforms to the Laves phase during creep. As the growth rate of Laves phase is higher than that of M23C6 carbides during creep, the creep strength of fine PAG boundary, which is strengthened only by Laves phase, becomes a little bit lower than the other boundaries strengthened by M23C6 carbides after long-term creep. The mismatch of creep strength between the fine PAG boundary and the matrix should be taken into account to attain an excellent long-term creep property of the B steel welded joint.

  12. Creep behavior of uranium carbide-based alloys

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

    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.

  13. Utilizing microstructural characteristics to derive insights into deformation and annealing behaviour: Numerical simulations, experiments and nature

    NASA Astrophysics Data System (ADS)

    Piazolo, Sandra; Montagnat, Maurine; Prakash, Abhishek; Borthwick, Verity; Evans, Lynn; Griera, Albert; Bons, Paul D.; Svahnberg, Henrik; Prior, David J.

    2015-04-01

    Understanding the influence of the pre-existing microstructure on subsequent microstructural development is pivotal for the correct interpretation of rocks and ice that stayed at high homologous temperatures over a significant period of time. The microstructural behaviour of these materials through time has an important bearing on the interpretation of characteristics such as grain size, for example, using grain size statistics to detect former high strain zones that remain at high temperatures but low stress. We present a coupled experimental and modelling approach to better understand the evolution of recrystallization characteristics as a function of deformation-annealing time paths in a material with a high viscoplastic anisotropy e.g. polycrystalline ice and magnesium alloys. Deformation microstructures such as crystal bending, subgrain boundaries, grain size variation significantly influence the deformation and annealing behaviour of crystalline material. For numerical simulations we utilize the microdynamic modelling platform, Elle (www.elle.ws), taking local microstructural evolution into account to simulate the following processes: recovery within grains, rotational recrystallization, grain boundary migration and nucleation. We first test the validity of the numerical simulations against experiments, and then use the model to interpret microstructural features in natural examples. In-situ experiments are performed on laboratory grown and deformed ice and magnesium alloy. Our natural example is a deformed then recrystallized anorthosite from SW Greenland. The presented approach can be applied to many other minerals and crystalline materials.

  14. Electrochemical control of creep in nanoporous gold

    SciTech Connect

    Ye, Xing-Long; Jin, Hai-Jun

    2013-11-11

    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.

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

    SciTech Connect

    Zhang, H.Y.; Zhang, S.H.; Cheng, M.; Li, Z.X.

    2010-01-15

    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.

  16. The Creep of Single Crystals of Aluminum

    NASA Technical Reports Server (NTRS)

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

    1953-01-01

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

  17. Creep of plasma sprayed zirconia

    NASA Technical Reports Server (NTRS)

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

    1982-01-01

    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.

  18. Estimation of long-term creep behavior of salt

    SciTech Connect

    Chun, R.C.

    1980-08-01

    A computer routine for both primary and secondary creep laws has been developed using a modified strain hardening law. The computations reveal that results from Heard's steady-state creep law and Lomenick and Bradshaw's primary creep law can differ from each other by a factor of thirty after about 6 hours of creep deformation, but the difference diminishes as time becomes large. The belief that these two creep laws may yield long-term results that are orders of magnitude apart is shown to be unfounded.

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

    PubMed Central

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

    2014-01-01

    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

  20. Evolution of microstructures during creep in TiAl-base intermetallics with a different Nb content

    NASA Astrophysics Data System (ADS)

    Dlouhý, A.; Orlová, A.; Kucha?ová, K.

    2010-07-01

    An evolution of microstructure has been investigated with increasing compression creep strain in intermetallic alloys Ti-48Al-2Cr-2Nb-1B (alloy Nb2) and Ti-46Al-7Nb-0.6Cr-0.2Ni-0.1Si (alloy Nb7) loaded to 350 MPa at 973 K. Scanning electron microscopy and transmission electron microscopy analysis focused on individual deformation modes and on the phase stability of the alloys. Dislocation densities and deformation twinning characteristics were systematically evaluated for strains up to 0.38. Results of these quantitative studies showed that the evolution of total and non-zero -component dislocation densities with strain was similar for all the investigated materials in spite of relevant differences in the initial ?/?2 microstructures. However, the spacing between deformation twins seemed to scale with the creep strength of the two alloys. These results are discussed in terms of the fundamental deformation modes and their contributions to the strain accumulation kinetics during high temperature creep in TiAl-base intermetallics with a different Nb content.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

    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.

  2. Study on creep properties of Japonica cooked rice and its relationship with rice chemical compositions and sensory evaluation

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Creep properties of four varieties japonica cooked rice were tested using a Dynamic Mechanical Analyser (DMA Q800). The creep curve was described by Burgers model. The creep process of japonica cooked rice mainly consisted of retarded elastic deformation, epsilonR and viscous flow deformation, epsil...

  3. High-temperature creep of Nb-Al-V alloys

    SciTech Connect

    Rong, T.S.; Aindow, M.

    1999-07-01

    Nb-15Al-20V alloys with about 45% by volume of an A15 phase in a B2 matrix have been subjected to creep deformation at temperatures between 1,000 C and 1,200 C and stresses from 80 MPa to 240 MPa in vacuum. The creep curves show a rapid transition from primary to steady-state creep with a well-defined activation energy. Microstructural observations show that the creep deformation occurs mainly in the B2 matrix and is controlled by dislocation mechanisms. Samples which had been cold-rolled and annealed to reduce the size of A15 precipitates and increase the yield strength were found to have lower creep resistance than those with unrefined microstructures. The significance of these observations for the creep mechanisms is discussed.

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

    NASA Technical Reports Server (NTRS)

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

    2013-01-01

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

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

    E-print Network

    Sills, David Wayne

    2012-02-14

    Recovered core samples from the San Andreas Fault Observatory at Depth (SAFOD), located near Parkfield, CA, offer a unique opportunity to study the products of faulting and to learn about the mechanisms of slip at 3 km depth. Casing deformation...

  6. Creep of trabecular bone from the human proximal tibia.

    PubMed

    Novitskaya, Ekaterina; Zin, Carolyn; Chang, Neil; Cory, Esther; Chen, Peter; D'Lima, Darryl; Sah, Robert L; McKittrick, Joanna

    2014-07-01

    Creep is the deformation that occurs under a prolonged, sustained load and can lead to permanent damage in bone. Creep in bone is a complex phenomenon and varies with type of loading and local mechanical properties. Human trabecular bone samples from proximal tibia were harvested from a 71-year old female cadaver with osteoporosis. The samples were initially subjected to one cycle load up to 1% strain to determine the creep load. Samples were then loaded in compression under a constant stress for 2h and immediately unloaded. All tests were conducted with the specimens soaked in phosphate buffered saline with proteinase inhibitors at 37 °C. Steady state creep rate and final creep strain were estimated from mechanical testing and compared with published data. The steady state creep rate correlated well with values obtained from bovine tibial and human vertebral trabecular bone, and was higher for lower density samples. Tissue architecture was analyzed by micro-computed tomography (?CT) both before and after creep testing to assess creep deformation and damage accumulated. Quantitative morphometric analysis indicated that creep induced changes in trabecular separation and the structural model index. A main mode of deformation was bending of trabeculae. PMID:24857486

  7. Effect of unloading time on interrupted creep in copper

    SciTech Connect

    Chandler, H.D. . School of Mechanical Engineering)

    1994-06-01

    The effect of unloading time on the interrupted creep behavior of polycrystalline copper specimens was investigated over the temperature range 298--773 K. Up to 553 K, cyclic creep acceleration could be explained in terms of deformation and hardening using a dislocation glide model with recovery during unloading being due to dislocation climb. At higher temperatures, recrystallization effects probably influence behavior.

  8. Influence of the pearlite fineness on the mechanical properties, deformation behavior, and fracture characteristics of carbon steel

    NASA Astrophysics Data System (ADS)

    Izotov, V. I.; Pozdnyakov, V. A.; Luk'yanenko, E. V.; Usanova, O. Yu.; Filippov, G. A.

    2007-05-01

    Specific features of plastic deformation and tensile failure of a plain carbon ( C = 0.62%) pearlitic-ferritic steel with various pearlite fineness have been investigated. It is shown that the steels with coarse lamellar pearlite and fine lamellar pearlite have similar strain-hardening coefficients, but the relative elongation of the former steel is higher. Deformation results in a uniform dislocation distribution in the fine pearlite and in the formation of a cellular substructure in the coarse pearlite. It is established that the fine pearlite undergoes plastic deformation and ductile failure as a single structure, while the coarse pearlite exhibits a structure discontinuity upon deformation. A model of microplastic pearlite deformation and the initial stage of macroplastic pearlite deformation is proposed. It is established that the strain-hardening coefficient of pearlite at the initial deformation stage does not depend on its dispersity. A size effect, which manifests itself in the dependence of the dislocation structure formed in the ferrite interlayers on their thickness, is shown to be characteristic of pearlite deformation.

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

    E-print Network

    Mahesh, Sivasambu

    A creep model for austenitic stainless steels incorporating cavitation and wedge cracking S Mahesh, Kalpakkam 603102. India Abstract. A model of damage evolution in austenitic stainless steels under creep experimental data for a type 316 austenitic stainless steel under uniaxial creep loading. Deformation

  10. Analysis of crustal deformation and strain characteristics in the Tianshan Mountains with least-squares collocation

    NASA Astrophysics Data System (ADS)

    Li, S. P.; Chen, G.; Li, J. W.

    2015-11-01

    By fitting the observed velocity field of the Tianshan Mountains from 1992 to 2006 with least-squares collocation, we established a velocity field model in this region. The velocity field model reflects the crustal deformation characteristics of the Tianshan reasonably well. From the Tarim Basin to the Junggar Basin and Kazakh platform, the crustal deformation decreases gradually. Divided at 82° E, the convergence rates in the west are obviously higher than those in the east. We also calculated the parameter values for crustal strain in the Tianshan Mountains. The results for maximum shear strain exhibited a concentration of significantly high values at Wuqia and its western regions, and the values reached a maxima of 4.4×10-8 a-1. According to isogram distributions for the surface expansion rate, we found evidence that the Tianshan Mountains have been suffering from strong lateral extrusion by the basin on both sides. Combining this analysis with existing results for focal mechanism solutions from 1976 to 2014, we conclude that it should be easy for a concentration of earthquake events to occur in regions where maximum shear strains accumulate or mutate. For the Tianshan Mountains, the possibility of strong earthquakes in Wuqia-Jiashi and Lake Issyk-Kul will persist over the long term.

  11. Diffusion creep of enstatite at high pressures

    NASA Astrophysics Data System (ADS)

    Zhang, G.; Mei, S.; Kohlstedt, D. L.

    2014-12-01

    Deformation behavior of fine-grained enstatite (g.s. ~ 8 ?m) was investigated with triaxial compressive creep experiments at high pressures (4.2 - 6.9 GPa) and high temperatures (1373 - 1573 K) using a deformation-DIA apparatus. Experiments were carried out under anhydrous conditions. In each experiment, a sample column composed of a sample and alumina pistons was assembled with a boron nitride sleeve and graphite resistance heater into a 6.2-mm edge length cubic pressure medium. Experiments were carried out at the National Synchrotron Light Source at Brookhaven National Laboratory. In a run, differential stress and sample displacement were monitored in-situ using synchrotron x-ray diffraction and radiography, respectively. Based on results from this study, the deformation behavior of enstatite under anhydrous conditions has been quantitatively presented in the form of a flow law that describes the dependence of deformation rate on stress, temperature, and pressure. Specifically, data fitting yields the dependence of creep rate on stress with an exponent of n ? 1; indicating samples were deformed in the regime of diffusion creep. Experimental results also yield the dependences of creep rate on temperature and pressure with an activation energy of ~250 kJ/mol and activation volume of ~3.5×10-6 m3/mol, respectively. The flow laws for enstatite, one important constituent component for the upper mantle, quantified from this study provides a necessary constraint for modeling the dynamic activities occurring within Earth's interior.

  12. Creep rupture of fiber bundles: A molecular dynamics investigation

    NASA Astrophysics Data System (ADS)

    Linga, G.; Ballone, P.; Hansen, Alex

    2015-08-01

    The creep deformation and eventual breaking of polymeric samples under a constant tensile load F is investigated by molecular dynamics based on a particle representation of the fiber bundle model. The results of the virtual testing of fibrous samples consisting of 40 000 particles arranged on Nc=400 chains reproduce characteristic stages seen in the experimental investigations of creep in polymeric materials. A logarithmic plot of the bundle lifetime ? versus load F displays a marked curvature, ruling out a simple power-law dependence of ? on F . A power law ? ˜F-4 , however, is recovered at high load. We discuss the role of reversible bond breaking and formation on the eventual fate of the sample and simulate a different type of creep testing, imposing a constant stress rate on the sample up to its breaking point. Our simulations, relying on a coarse-grained representation of the polymer structure, introduce new features into the standard fiber bundle model, such as real-time dynamics, inertia, and entropy, and open the way to more detailed models, aiming at material science aspects of polymeric fibers, investigated within a sound statistical mechanics framework.

  13. Creep rupture of fiber bundles: A molecular dynamics investigation.

    PubMed

    Linga, G; Ballone, P; Hansen, Alex

    2015-08-01

    The creep deformation and eventual breaking of polymeric samples under a constant tensile load F is investigated by molecular dynamics based on a particle representation of the fiber bundle model. The results of the virtual testing of fibrous samples consisting of 40000 particles arranged on Nc=400 chains reproduce characteristic stages seen in the experimental investigations of creep in polymeric materials. A logarithmic plot of the bundle lifetime ? versus load F displays a marked curvature, ruling out a simple power-law dependence of ? on F. A power law ??F-4, however, is recovered at high load. We discuss the role of reversible bond breaking and formation on the eventual fate of the sample and simulate a different type of creep testing, imposing a constant stress rate on the sample up to its breaking point. Our simulations, relying on a coarse-grained representation of the polymer structure, introduce new features into the standard fiber bundle model, such as real-time dynamics, inertia, and entropy, and open the way to more detailed models, aiming at material science aspects of polymeric fibers, investigated within a sound statistical mechanics framework. PMID:26382414

  14. Creep behavior of thin laminates of iron-cobalt alloys for use in switched reluctance motors and generators

    NASA Astrophysics Data System (ADS)

    Fingers, Richard Todd

    The United States Air Force is in the process of developing magnetic bearings as well as an aircraft Integrated Power Unit and an Internal Starter/Generator for main propulsion engines. These developments are the driving force behind a new emphasis on high temperature, high strength magnetic materials for power applications. Analytical work, utilizing elasticity theory, in conjunction with design requirements, indicates a need for magnetic materials to have strengths in excess of 80 ksi up to about 1000sp°F. It is this combination of desired material characteristics that is the motivation for this effort to measure, model, and predict the creep behavior of such advanced magnetic materials. Hipercosp°ler Alloy 50HS, manufactured by Carpenter Technology Corporation, is one of the leading candidates for application and is studied in this effort by subjecting mechanical test specimens to a battery of tensile and creep tests. The tensile tests provide stress versus strain behaviors that clearly indicate: a yield point, a heterogeneous deformation described as Luders elongation, the Portevin-LeChatelier effect at elevated temperatures, and, most often, a section of homogeneous deformation that concluded with necking and fracture. Creep testing indicated two distinct types of behavior. The first was a traditional response with primary, secondary and tertiary stages, while the second type could be characterized by an abrupt increase in strain rate that acted as a transition from one steady state behavior to another. This second linear region was then followed by the tertiary stage. The relationship between the tensile response and the creep responses is discussed. Analyses of the mechanical behavior includes double linear regression of empirically modeled data, scanning electron microscopy for microstructural investigations, isochronous stress-strain relations, and constant strain rate testing to relate the tensile and creep test parameters. Also, elastic and creep deformation analyses are done, which incorporate material property data and material constants determined along with stress and displacement profiles for a specific Air Force design configuration.

  15. Creep Mechanisms of a Ni-Co-Based-Wrought Superalloy with Low Stacking Fault Energy

    NASA Astrophysics Data System (ADS)

    Tian, Chenggang; Xu, Ling; Cui, Chuanyong; Sun, Xiaofeng

    2015-10-01

    In order to study the influences of stress and temperature on the creep deformation mechanisms of a newly developed Ni-Co-based superalloy with low stacking fault energy, creep experiments were carried out under a stress range of 345 to 840 MPa and a temperature range of 923 K to 1088 K (650 °C to 815 °C). The mechanisms operated under the various creep conditions were identified and the reasons for their transformation were well discussed. A deformation mechanism map under different creep conditions was summarized, which provides a qualitative representation of the operative creep mechanisms as a function of stress and temperature.

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

    SciTech Connect

    Koyanagi, Takaaki; Shimoda, Kazuya; Kondo, Sosuke; Hinoki, Tatsuya; Ozawa, Kazumi; Katoh, Yutai

    2014-12-01

    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.

  17. Quantitative analysis of tissue deformation dynamics reveals three characteristic growth modes and globally aligned anisotropic tissue deformation during chick limb development

    PubMed Central

    Morishita, Yoshihiro; Kuroiwa, Atsushi; Suzuki, Takayuki

    2015-01-01

    Tissue-level characterization of deformation dynamics is crucial for understanding organ morphogenetic mechanisms, especially the interhierarchical links among molecular activities, cellular behaviors and tissue/organ morphogenetic processes. Limb development is a well-studied topic in vertebrate organogenesis. Nevertheless, there is still little understanding of tissue-level deformation relative to molecular and cellular dynamics. This is mainly because live recording of detailed cell behaviors in whole tissues is technically difficult. To overcome this limitation, by applying a recently developed Bayesian approach, we here constructed tissue deformation maps for chick limb development with high precision, based on snapshot lineage tracing using dye injection. The precision of the constructed maps was validated with a clear statistical criterion. From the geometrical analysis of the map, we identified three characteristic tissue growth modes in the limb and showed that they are consistent with local growth factor activity and cell cycle length. In particular, we report that SHH signaling activity changes dynamically with developmental stage and strongly correlates with the dynamic shift in the tissue growth mode. We also found anisotropic tissue deformation along the proximal-distal axis. Morphogenetic simulation and experimental studies suggested that this directional tissue elongation, and not local growth, has the greatest impact on limb shaping. This result was supported by the novel finding that anisotropic tissue elongation along the proximal-distal axis occurs independently of cell proliferation. Our study marks a pivotal point for multi-scale system understanding in vertebrate development. PMID:25858459

  18. Deformation characteristics of the near-surface layers of zirconia ceramics implanted with aluminum ions

    NASA Astrophysics Data System (ADS)

    Ghyngazov, S. A.; Vasiliev, I. P.; Frangulyan, T. S.; Chernyavski, A. V.

    2015-10-01

    The effect of ion treatment on the phase composition and mechanical properties of the near-surface layers of zirconium ceramic composition 97 ZrO2-3Y2O3 (mol%) was studied. Irradiation of the samples was carried out by accelerated ions of aluminum with using vacuum-arc source Mevva 5-Ru. Ion beam had the following parameters: the energy of the accelerated ions E = 78 keV, the pulse current density Ji = 4mA / cm2, current pulse duration equal ? = 250 mcs, pulse repetition frequency f = 5 Hz. Exposure doses (fluence) were 1016 ? 1017 ion/cm2. The depth distribution implanted ions was studied by SIMS method. It is shown that the maximum projected range of the implanted ions is equal to 250 nm. Near-surface layers were investigated by X-ray diffraction (XRD) at fixed glancing incidence angle. It is shown that implantation of aluminum ions into the ceramics does not lead to a change in the phase composition of the near-surface layer. The influence of implanted ions on mechanical properties of ceramic near-surface layers was studied by the method of dynamic nanoindentation using small loads on the indenter P=300 mN. It is shown that in ion- implanted ceramic layer the processes of material recovery in the deformed region in the unloading mode proceeds with higher efficiency as compared with the initial material state. The deformation characteristics of samples before and after ion treatment have been determined from interpretation of the resulting P-h curves within the loading and unloading sections by the technique proposed by Oliver and Pharr. It was found that implantation of aluminum ions in the near-surface layer of zirconia ceramics increases nanohardness and reduces the Young's modulus.

  19. In-situ Creep Testing Capability Development for Advanced Test Reactor

    SciTech Connect

    B. G. Kim; J. L. Rempe; D. L. Knudson; K. G. Condie; B. H. Sencer

    2010-08-01

    Creep is the slow, time-dependent strain that occurs in a material under a constant strees (or load) at high temperature. High temperature is a relative term, dependent on the materials being evaluated. A typical creep curve is shown in Figure 1-1. In a creep test, a constant load is applied to a tensile specimen maintained at a constant temperature. Strain is then measured over a period of time. The slope of the curve, identified in the figure below, is the strain rate of the test during Stage II or the creep rate of the material. Primary creep, Stage I, is a period of decreasing creep rate due to work hardening of the material. Primary creep is a period of primarily transient creep. During this period, deformation takes place and the resistance to creep increases until Stage II, Secondary creep. Stage II creep is a period with a roughly constant creep rate. Stage II is referred to as steady-state creep because a balance is achieved between the work hardening and annealing (thermal softening) processes. Tertiary creep, Stage III, occurs when there is a reduction in cross sectional area due to necking or effective reduction in area due to internal void formation; that is, the creep rate increases due to necking of the specimen and the associated increase in local stress.

  20. Creep of chemically vapor deposited SiC fibers

    NASA Technical Reports Server (NTRS)

    Dicarlo, J. A.

    1984-01-01

    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.

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

    E-print Network

    Asima Shaukat; Ashutosh Sharma; Yogesh M. Joshi

    2010-06-10

    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.

  2. Change in characteristics of superplastic deformation of the aluminum-lithium alloy under the effect of ultrasonic vibrations

    NASA Astrophysics Data System (ADS)

    Myshlyaev, M. M.; Shpeizman, V. V.; Klubovich, V. V.; Kulak, M. M.; Lyu, G.

    2015-10-01

    The tension of samples of aluminum-lithium alloy 1420 in the superplasticity temperature region T = 320-395°C and the influence of ultrasonic vibrations on deformation characteristics have been investigated. It has been shown that the effect of ultrasound manifests itself in a decrease in resistance to deformation and an increase in total strain. The tension curves plotted in the coordinates true stresses-true strains, in contrast to the standard stress-strain curves, have an extended hardening region, the magnitude of which is larger for the samples deformed with the ultrasound. The stress-rate sensitivity coefficients m have been determined from stress jumps with variations in the tension rate. It has been shown that the quantity m can be assumed to be constant over the entire superplasticity temperature region for different strains with ultrasound and without it, m = 0.46 ± 0.04, and, correspondingly, the stress exponent in the formula for the strain rate is = 2.21 ± 0.23. The activation energies of the deformation process have been evaluated, and it has been concluded that the dislocation motion during the intragrain deformation that is characteristic of the hardening stage is facilitated under the effect of ultrasound.

  3. Influence of phosphorus on the creep ductility of copper

    NASA Astrophysics Data System (ADS)

    Sandström, Rolf; Wu, Rui

    2013-10-01

    Around 1990 it was discovered that pure copper could have extra low creep ductility in the temperature interval 180-250 °C. The material was intended for use in canisters for nuclear waste disposal. Although extra low creep ductility was not observed much below 180 °C and the temperature in the canister will never exceed 100 °C, it was feared that the creep ductility could reach low values at lower temperatures after long term exposure. If 50 ppm phosphorus was added to the copper the low creep ductility disappeared. A creep cavitation model is presented that can quantitatively describe the cavitation behaviour in uniaxial and multiaxial creep tests as well as the observed creep ductility for copper with and without phosphorus. A so-called double ledge model has been introduced that demonstrates why the nucleation rate of creep cavities is often proportional to the creep rate. The phosphorus agglomerates at the grain boundaries and limits their local deformation and thereby reduces the formation and growth of cavities. This explains why extra low creep ductility does not occur in phosphorus alloyed copper.

  4. CREEP AND CREEP-FATIGUE OF ALLOY 617 WELDMENTS

    SciTech Connect

    Wright, Jill; Carroll, Laura; Wright, Richard

    2014-08-01

    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).

  5. Unified creep-plasticity model for halite

    SciTech Connect

    Krieg, R. D.

    1980-11-01

    There are two national energy programs which are considering caverns in geological salt (NaCl) as a storage repository. One is the disposal of nuclear wastes and the other is the storage of oil. Both short-time and long-time structural deformations and stresses must be predictable for these applications. At 300K, the nominal initial temperature for both applications, the salt is at 0.28 of the melting temperature and exhibits a significant time dependent behavior. A constitutive model has been developed which describes the behavior observed in an extensive set of triaxial creep tests. Analysis of these tests showed that a single deformation mechanism seems to be operative over the stress and temperature range of interest so that the secondary creep data can be represented by a power of the stress over the entire test range. This simple behavior allowed a new unified creep-plasticity model to be applied with some confidence. The resulting model recognizes no inherent difference between plastic and creep strains yet models the total inelastic strain reasonably well including primary and secondary creep and reverse loadings. A multiaxial formulation is applied with a back stress. A Bauschinger effect is exhibited as a consequence and is present regardless of the time scale over which the loading is applied. The model would be interpreted as kinematic hardening in the sense of classical plasticity. Comparisons are made between test data and model behavior.

  6. Creep Laboratory manual

    NASA Astrophysics Data System (ADS)

    Osgerby, S.; Loveday, M. S.

    1992-06-01

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

  7. Creep of Rocks Under Small Mechanical Loading

    NASA Astrophysics Data System (ADS)

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

    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

  8. Material Parameters for Creep Rupture of Austenitic Stainless Steel Foils

    NASA Astrophysics Data System (ADS)

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

    2014-08-01

    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.

  9. Polycrystalline olivine rheology in dislocation creep: Revisiting experimental data to 8.1 GPa

    NASA Astrophysics Data System (ADS)

    Bollinger, Caroline; Raterron, Paul; Cordier, Patrick; Merkel, Sébastien

    2014-03-01

    The rheology of polycristalline San Carlos olivine is investigated on synchrotron beamline in the Deformation-DIA (D-DIA) at pressure (P) between 3.8 and 8.1 GPa, temperature (T) within 1373-1673 K, and at steady-state strain rates ranging from 1.1 × 10-5 to 5.8 × 10-5 s-1. Transmission electron microscopy (TEM) on run products reveals microstructures characteristic of the so-called “dislocation creep regime”. Fourier transform infrared (FTIR) measurements reveal hydroxyl concentrations within 153-1526 ppm H/Si (Paterson’s calibration), indicating ‘wet’ conditions of deformation. Analysis of our data together with previously published ‘wet’ deformation data obtained at room and high P, assuming a stress exponent n = 3.5 in classical power law, results in a linear dependence of the activation enthalpy with P, i.e., in an activation volume of V? = 12.8 ± 5 cm3 mol-1. This value of V? is also consistent with a global dataset including ‘wet’ data and ‘dry’ published deformation data for olivine aggregates. We thus conclude that, up to 8 GPa, the effect of P on ‘dry’ and ‘wet’ olivine dislocation creep is consistent with V? = 12.8 ± 5 cm3 mol-1.

  10. Interface Evolution During Transient Pressure Solution Creep

    NASA Astrophysics Data System (ADS)

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

    When aggregates of small grains are pressed together in the presence of small amounts of solvent the aggregate compacts and the grains tend to stick together. This hap- pens to salt and sugar in humid air, and to sediments when buried in the Earths crust. Stress concentration at the grain contacts cause local dissolution, diffusion of the dissolved material out of the interface and deposition on the less stressed faces of the grains{1}. This process, in geology known as pressure solution, plays a cen- tral role during compaction of sedimentary basins{1,2}, during tectonic deformation of the Earth's crust{3}, and in strengthening of active fault gouges following earth- quakes{4,5}. Experimental data on pressure solution has so far not been sufficiently accurate to understand the transient processes at the grain scale. Here we present ex- perimental evidence that pressure solution creep does not establish a steady state inter- face microstructure as previously thought. Conversely, cumulative creep strain and the characteristic size of interface microstructures grow as the cubic root of time. A sim- ilar transient phenomenon is known in metallurgy (Andrade creep) and is explained here using an analogy with spinodal dewetting. 1 Weyl, P. K., Pressure solution and the force of crystallization - a phenomenological theory. J. Geophys. Res., 64, 2001-2025 (1959). 2 Heald, M. T., Cementation of Simpson and St. Peter Sandstones in parts of Okla- homa, Arkansas and Missouri, J. Geol. Chicago, 14, 16-30 (1956). 3 Schwartz, S., Stöckert, B., Pressure solution in siliciclastic HP-LT metamorphic rocks constraints on the state of stress in deep levels of accretionary complexes. Tectonophysics, 255, 203-209 (1996). 4 Renard, F., Gratier, J.P., Jamtveit, B., Kinetics of crack-sealing, intergranular pres- sure solution, and compaction around active faults. J. Struct. Geol., 22, 1395-1407, (2000). 5 Miller, S. A., BenZion, Y., Burg, J. P.,A three-dimensional fluid-controlled earth- quake model: Behavior and implications. J. Geophys. Res., 104, 10621-10638 (1999).

  11. Creep-assisted slow crack growth in bio-inspired dental multilayers.

    PubMed

    Du, Jing; Niu, Xinrui; Soboyejo, Wole

    2015-06-01

    Ceramic crown structures under occlusal contact are often idealized as flat multilayered structures that are deformed under Hertzian contact loading. Previous models treated each layer as linear elastic materials and resulted in differences between the measured and predicted critical loads. This paper examines the combined effects of creep (in the adhesive and substrate layers) and creep-assisted slow crack growth (in the ceramic layer) on the contact-induced deformation of bio-inspired, functionally graded multilayer (FGM) structures and the conventional tri-layers. The time-dependent moduli of each of the layers were determined from constant load creep tests. The resulting modulus-time characteristics were modeled using Prony series. These were then incorporated into a finite element model for the computation of stress distributions in the sub-surface regions of the top ceramic layer, in which sub-surface radial cracks, are observed as the clinical failure mode. The time-dependent stresses are incorporated into a slow crack growth (SCG) model that is used to predict the critical loads of the dental multilayers under Hertzian contact loading. The predicted loading rate dependence of the critical loads is shown to be consistent with experimental results. The implications of the results are then discussed for the design of robust dental multilayers. PMID:25771255

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

    NASA Astrophysics Data System (ADS)

    Faraji, Masoumeh; Khalilpour, Hamid

    2014-10-01

    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.

  13. Creep behaviour of modified 9Cr-1Mo ferritic steel

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

    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.

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

    SciTech Connect

    Munson, Darrell E.

    1999-08-16

    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.

  15. Relationship between creep, gamma 2, and marginal fracture of dental amalgams.

    PubMed

    Sarkar, N K; Eyer, C S; Norling, B K

    1983-11-01

    The effect of gamma 1 and gamma 2 on the creep deformation of dental amalgams has been investigated. It has been shown that the creep of a conventional amalgam is not dependent on gamma 1 as was previously reported. Rather it is strongly influenced by gamma 2 and its volume fraction. It has been speculated that Sn-rich grain boundaries also enhance creep by facilitating grain boundary sliding. The reported correlation between creep and marginal fracture has been explained in terms of this dependence of creep on corrosion-prone Sn-rich microstructural constituents of amalgams. PMID:6580405

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

    SciTech Connect

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

    1998-03-13

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

  17. Tensile creep behavior and cyclic fatigue/creep interaction of hot- isostatically pressed Si sub 3 N sub 4

    SciTech Connect

    Liu, K.C.; Pih, H.; Stevens, C.O.; Brinkman, C.R.

    1991-01-01

    Tensile creep data are reported for a high-performance grade of hot isostatically pressed Si{sub 3}N{sub 4} that is currently being investigated as a candidate material for advanced heat engine applications. Specimens were tested in pure uniaxial tension at temperatures ranging from 1200 to 1370{degree}C. Creep strain was measured with an optical strain extensometer until creep rupture occurred, in some cases for periods in excess of 2000 h. To study the effects of various preloading material histories on creep behavior, specimens were prepared and tested in several conditions, i.e., unannealed, annealed, or precycled. Test results show that either treatment by thermal annealing or by precycling at 1370{degree}C can dramatically modify the initial transient creep behavior and enhance the resistance to creep deformation and hence the creep-rupture lifetime. However, the influence of the preloading histories on creep rate was diminished by high temperature exposure after about 500 h of testing. The rupture lifetime of the precycled specimen at 1370{degree}C was significantly higher than those of the unannealed and annealed specimens. In contrast, no significant extension of the creep-rupture lifetime was observed for a precycled specimen tested at 1300{degree}C. Steady-state creep was absent in some cases under certain conditions of temperature, stress, and heat treatment. Little or no tertiary creep was usually detected before specimen fracture occurred. The steady-state creep rate of this material was found to be a function of applied stress, temperature, and possibly the level of crystallinity in the intergranular phase. 9 refs., 15 figs.

  18. Creep behaviour of Cu-30 percent Zn at intermediate temperatures

    NASA Technical Reports Server (NTRS)

    Raj, S. V.

    1991-01-01

    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.

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

    SciTech Connect

    Bartholomeusz, M.F.; Wert, J.A. ); Qibin Yang )

    1993-08-01

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

  20. Analysis of Faulting and Sediment Velocity Characteristics Outboard of the Cascadia Deformation Front from Multi-Channel Seismic Data.

    NASA Astrophysics Data System (ADS)

    Gibson, J. C.; Carbotte, S. M.; Han, S.; Nedimovic, M. R.; Canales, J. P.; Carton, H. D.

    2014-12-01

    Faulting of the sediment section on the downgoing Juan de Fuca Plate (JdF) outboard of the Cascadia deformation front is explored using multi-channel seismic (MCS) data collected in 2012 during the JdF Ridge to Trench Survey (MGL1211). MCS data were collected along two full plate transects ("Oregon" (ORT) and "Washington" (WAT)) and one trench parallel line. Sediment velocity analysis is conducted via semblance spectrums on common mid-point super gathers spaced at a 625 m interval. Higher sediment velocities are found in the north, which may reflect the regional differences in sediment composition evident in existing drill holes located along our transects (DSDP site 174 - ORT and ODP site 1027 - WAT) that indicate higher smectite content along the ORT (bulk composition +44%). Accordingly, observations of fault frequency, dip, and throw along both transects show significant differences in faulting characteristics across the JdF plate. Faulting extends ~175 km (8.2 - 1.9 Ma plate age) from the deformation front along the WAT, and reaches a maximum fault density of ~0.48 fault/km in the region between 25 - 113 km (7.5 - 4 Ma plate age). Evidence of faulting extends ~300 km (8.9 - 2.6 Ma plate age) from the deformation front along the ORT and reaches a similar high fault density of ~0.48 fault/km in the region between 113 - 138 km (7.07 - 5.96 Ma plate age). Analysis of fault offset indicates growth faults along both transects. Along the ORT, maximum fault throws remain ~uniform at 10 - 15 m for crustal ages of 7.07 - 5.96 Ma and beginning ~75 km from the deformation front increase landward to maximum throws of 30 m, consistent with increasing fault strain due to flexural bending of the downgoing plate. In contrast, along the WAT, there is no evidence of increasing fault throw toward the deformation front. High fault dips (45 - 70°) are found in the region of highest fault density on both transects. Lower dips (35 - 60°) are measured in the region of increasing fault strain near the deformation front along the ORT. Overall, fault characteristics indicate greater subduction-bend related faulting along the ORT. Additionally, complex intra-plate stresses and/or differential compaction may contribute to the abundant faulting found within the plate interior to young crustal ages along both transects.

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

    PubMed

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

    2004-03-01

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

  2. New constraints on upper mantle creep mechanism inferred from silicon grain-boundary diffusion rates

    NASA Astrophysics Data System (ADS)

    Fei, Hongzhan; Koizumi, Sanae; Sakamoto, Naoya; Hashiguchi, Minako; Yurimoto, Hisayoshi; Marquardt, Katharina; Miyajima, Nobuyoshi; Yamazaki, Daisuke; Katsura, Tomoo

    2016-01-01

    The creep in the Earth's interior is dominated either by diffusion creep which causes Newtonian mantle flow, or by dislocation creep which results in non-Newtonian mantle flow. Although previous deformation studies on olivine claimed a transition from dislocation creep to diffusion creep with depth in the upper mantle, they might misunderstand the creep rates due to experimental difficulties. Since creep in olivine is controlled by silicon diffusion, we measured the silicon grain-boundary diffusion coefficient in well-sintered iron-free olivine aggregates as a function of temperature, pressure, and water content, showing activation energy, activation volume, and water content exponent of 220 ± 30 kJ /mol, 4.0 ± 0.7 cm3 /mol, and 0.26 ± 0.07, respectively. Our results based on Si diffusion in forsterite predict that diffusion creep dominates at low pressures and low temperatures, whereas dislocation creep dominates under high pressure and high temperature conditions. Water has negligible effects on both diffusion and dislocation creep. There is a transition from diffusion creep in the shallow upper mantle to dislocation creep in deeper regions. This explains the seismic anisotropy increases at the Gutenberg discontinuity beneath oceans and at the mid-lithosphere discontinuity beneath continents.

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

    SciTech Connect

    Gelles, David S.

    2002-09-01

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

  4. Threshold Stress Creep Behavior of Alloy 617 at Intermediate Temperatures

    SciTech Connect

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

    2014-06-01

    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.

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

    PubMed Central

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

    2013-01-01

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

  6. Changes in the expression of genetic characteristics across cohorts in skeletal deformations of farmed salmonids

    PubMed Central

    Kause, Antti; Ritola, Ossi; Paananen, Tuija

    2007-01-01

    Genetic analysis of disorder incidence in farmed animals is challenged by two factors. Disorders in different cohorts and environments could be caused by different factors, leading to changes in heritability and to less than unity genetic correlations across cohorts. Moreover, due to computational limitations, liability scale heritabilities at very low incidence may differ from those estimated at higher incidence. We tested whether these two dilemmas occur in skeletal deformations of farmed salmonids using multigeneration data from the Finnish rainbow trout breeding programme and previous salmonid studies. The results showed that heritability was close to zero in cohorts in which management practices maintained incidence at a low level. When there was a management failure and incidence was unusually high, heritability was elevated. This may be due to computational limitations at very low incidence and/or because deformations are induced by different factors in different cohorts. Most genetic correlations between deformations recorded in different generations were weakly to strongly positive. However, also negative correlations between generations were present, showing that high liability at one time can be genetically connected to low liability at another time. The results emphasise that genetic architecture of binary traits can be influenced by trait expression. PMID:17897595

  7. Wear characteristics of severely deformed aluminum sheets by accumulative roll bonding (ARB) process

    SciTech Connect

    Talachi, A. Kazemi; Eizadjou, M. Manesh, H. Danesh; Janghorban, K.

    2011-01-15

    Wear behavior of severely deformed aluminum sheets by accumulative roll bonding (ARB) process was characterized using a pin on disc wear machine at different conditions. The sheets were processed up to eight ARB cycles in order to induce a high strain ({approx} 6.4) to the samples. EBSD results showed that after eight cycles of ARB, sheets were found to contain ultrafine grains with high fraction of high angle grain boundaries. Wear experiments were conducted under different loading and operating conditions, including dry and immersion lubrication, and rotation speeds. Wear was continuously monitored by measuring the wear rates and morphologies of worn surfaces by scanning electron microscope (SEM). Contrary to expectation, the wear resistance of the ARBed Al sheets was less than the non-processed sheets. Wear rates of the ARBed Al sheets increased by increasing wear load and rotation speed, while, immersion lubrication decreased the wear rate significantly. Based on the observation and results, a model for the wear of the ARBed Al was proposed. - Research Highlights: {yields}The wear rate of the ARBed Al was higher than that of the non-processed alloy. {yields}This unexpected behavior was related to the low strain hardening capability and evolution of the ARB subsurface microstructure during the wear process. {yields}Sliding wear of the ARBed Al proceeded by surface deformation, and progressed by delamination of the deformed surface layer. {yields}The wear rate of ARBed Al increased by increasing applied load and sliding speed.

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

    PubMed

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

    2013-01-01

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

  9. Diffusion creep in the mantle may create and maintain anisotropy

    NASA Astrophysics Data System (ADS)

    Wheeler, John

    2014-05-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1995-01-01

    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.

  12. PHYSICAL REVIEW B 88, 184303 (2013) Irreversible thermodynamics of creep in crystalline solids

    E-print Network

    Mishin, Yuri

    2013-01-01

    in the material during the creep process. We derive a general expression for the entropy production rate and use number(s): 66.30.-h, 61.72.-y, 62.20.Hg, 65.40.-b I. INTRODUCTION When subject to a high homologous of materials ranging from metals and alloys to ceramics, polymers, and ice. While several creep deformation

  13. Characterization of the groundwater response to rainfall on a hillslope with fractured bedrock by creep deformation and its implication for the generation of deep-seated landslides on Mt. Wanitsuka, Kyushu Island

    NASA Astrophysics Data System (ADS)

    Padilla, Cristobal; Onda, Yuichi; Iida, Tomoyuki; Takahashi, Shinya; Uchida, Taro

    2014-01-01

    In this study, the hydrogeological response of a hillslope affected by gravitational deformation was analyzed based on the data obtained for two observation boreholes: a 10-m borehole representing a relatively superficial section of the hillslope dominated by soil and old landslide deposits and a 40-m borehole representing the bedrock aquifer. For this analysis, the precipitation events in the area, groundwater levels of the two boreholes, electrical conductivity and isotopic concentration (oxygen and hydrogen) of the groundwater in the boreholes and rainfall samples were measured. Derived from the rainfall data, the antecedent precipitation index (API) with a 6-h half-life offers a good correlation with the peaks in the groundwater levels in the bedrock aquifer. The characteristics of the groundwater response suggest the existence of a single structure in the bedrock that controls the response of the hillslope. The structure serves as a conduit, which rapidly drives the rainfall water (recharge) into the bedrock. Evidently, this process is unrelated to the superficial section represented by the observations in the 10-m borehole. The structure is associated with an area of high hydraulic conductivity in the bedrock caused by the gravitational deformation in the hillslope. The strong control of this structure in the hillslope's hydrogeological response makes it responsible for the hillslope's stability during high-precipitation events. This information is highly relevant to areas featuring the generation of several deep-seated landslides under heavy-rain conditions.

  14. Creep behavior of 6 micrometer linear low density polyethylene film

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  15. Analysis of Multistage and Other Creep Data for Domal Salts

    SciTech Connect

    Munson, D.E.

    1998-10-01

    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.

  16. Time-Dependent Behavior of Diabase and a Nonlinear Creep Model

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    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.

  17. Biaxial Creep Specimen Fabrication

    SciTech Connect

    JL Bump; RF Luther

    2006-02-09

    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.

  18. Irradiation Creep in Graphite

    SciTech Connect

    Ubic, Rick; Butt, Darryl; Windes, William

    2014-03-13

    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.

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

    NASA Technical Reports Server (NTRS)

    Slavik, D.; Sehitoglu, H.

    1988-01-01

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

  20. A model of compaction creep in carbonates

    NASA Astrophysics Data System (ADS)

    Keszthelyi, Daniel; Jamtveit, Bjørn; Dysthe, Dag Kristian

    2015-04-01

    Rocks in compressional stress conditions are subject to long-term creep deformations. We created a simple conceptual micomechanical model of creep in rocks combining microscopic fracturing and pressure solution. This was then scaled up to macroscopic scale by a statistical mechanical approach to predict strain rate at core scale. The model uses no fitting parameter and have a few input parameters: effective stress, porosity, pore size distribution, temperature and water saturation. Internal parameters are Young's modulus, interfacial energy of wet calcite and dissolution rates of calcite, all of which are measurable independently. Existing long-term creep experiments were used to verify the model which was able to predict the magnitude of the resulting strain in largely different effective stress, temperature and water saturation conditions. The model was also able to predict the compaction of a producing chalk reservoir with a good agreement. Further generalization of the model might function as a general theory of long-term creep of rocks in compressional settings.

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

    NASA Astrophysics Data System (ADS)

    Hachay, Olga; Khachay, Oleg; Shipeev, Oleg

    2013-04-01

    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.

  2. Creep properties of catalyst coated membranes for polymer electrolyte fuel cells

    NASA Astrophysics Data System (ADS)

    Sadeghi Alavijeh, Alireza; Khorasany, Ramin M. H.; Habisch, Aronne; Wang, G. Gary; Kjeang, Erik

    2015-07-01

    Creep as a time-dependent mechanical damage acting either independently or in conjunction with other degradation mechanisms is known to reduce the membrane durability of polymer electrolyte fuel cells (PEFCs). Due to the important ionomer coupling of membrane and catalyst layers in PEFCs, the present work evaluates membrane creep when constrained within a catalyst coated membrane (CCM). Three key factors dominating creep life in commonly used perfluorosulfonic acid (PFSA) ionomer membranes, including creep stress, temperature, and relative humidity, were investigated by applying ex-situ creep loading and unloading experiments under controlled temperature and humidity conditions. The creep strain and recovery of the CCM were found to be highly dependent on the environmental conditions and applied stress levels, where the temperature effect on creep strain was the most significant. Repetitive creep - recovery cycles revealed that significant creep damage can accumulate in the material over time. This accumulated creep damage was found to be independent of the loading frequency while both peak strain and permanent deformation increased with the stress duration. Based on the present findings, it is recommended to reduce the operating temperature and ensure adequate membrane hydration in order to mitigate harmful creep effects in PEFCs.

  3. Creep Resistant Zinc Alloy

    SciTech Connect

    Frank E. Goodwin

    2002-12-31

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

  4. Experimental investigations of creep in gold RF-MEMS microstructures

    NASA Astrophysics Data System (ADS)

    Somà, Aurelio; De Pasquale, Giorgio; Saleem, Muhammad Mubasher

    2015-05-01

    Lifetime prediction and reliability evaluation of micro-electro-mechanical systems (MEMS) are influenced by permanent deformations caused by plastic strain induced by creep. Creep in microstructures becomes critical in those applications where permanent loads persist for long times and thermal heating induces temperature increasing respect to the ambient. Main goal of this paper is to investigate the creep mechanism in RF-MEMS microstructures by means of experiments. This is done firstly through the detection of permanent deformation of specimens and, then, by measuring the variation of electro-mechanical parameters (resonance frequency, pull-in voltage) that provide indirect evaluation of mechanical stiffness alteration from creep. To prevent the errors caused be cumulative heating of samples and dimensional tolerances, three specimens with the same nominal geometry have been tested per each combination of actuation voltage and temperature. Results demonstrated the presence of plastic deformation due to creep, combined with a component of reversible strain linked to the viscoelastic behavior of the material.

  5. Sources of Variation in Creep Testing

    NASA Technical Reports Server (NTRS)

    Loewenthal, William S.; Ellis, David L.

    2011-01-01

    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.

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

    SciTech Connect

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

    1996-03-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Trepmann, Claudia

    2014-05-01

    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.

  8. Deformation and strain characteristics along the length of the anterior band of the inferior glenohumeral ligament.

    PubMed

    McMahon, P J; Dettling, J R; Sandusky, M D; Lee, T Q

    2001-01-01

    Efficacious surgical treatment of anterior glenohumeral instability often requires repair of the anteroinferior capsulolabral structures, including the glenoid origin of the anterior band of the inferior glenohumeral ligament. Rupture in this location, the Bankart lesion, may be accompanied by nonrecoverable stretching of the anterior band. The purpose of this study was to evaluate the amount and location of nonrecoverable stretching with tensile testing. Twelve glenoid-soft tissue-humerus complexes from fresh-frozen glenohumeral joints were studied by means of a custom jig, an Instron machine, and a video digitizing system. The joints were positioned to simulate that known to cause apprehension for anterior instability. Nonrecoverable deformation differed along the length of the anterior band but was slight in all locations. For those that failed at the glenoid insertion region, the mean nonrecoverable deformation was 0.10 +/- 0.16 mm (mean +/- SEM) at the bone-labral junction of the glenoid insertion region and 0.38 +/- 0.23 mm at the labral-ligament junction of the glenoid insertion region. It was 0.53 +/- 0.23 mm at the ligament midsubstance and 0.04 +/- 0.10 mm at the humeral insertion region. For those that failed at the glenoid insertion region, the nonrecoverable stretching was 1.4% +/- 1.9% at the bone-labral junction of the glenoid insertion region and 3.5% +/- 2.0% at the labral-ligament junction of the glenoid insertion region. It was 2.3% +/- 1.1% at the ligament midsubstance and 0.0% +/- 1.4% at the humeral insertion region. Rupture of the anterior band resulted in little nonrecoverable stretching at both the site of failure and elsewhere along the length, remote from the failure site. Surgical repairs after initial dislocation may restore the length of the anterior band of the inferior glenohumeral ligament with little shortening. PMID:11641708

  9. Time-dependent deformations on marine clays on submarine slopes

    SciTech Connect

    Silva, A.J.; Brandes, H.; Sadd, M.H.; Tian, W.M. )

    1990-06-01

    Evidence from geological and geophysical records indicates that time-dependent deformations occur on or within many submarine slopes. Laboratory studies on marine clays from the slope/rise and the ocean's basin have shown that these clays are generally quite viscous and therefore can be expected to deform in the field even under such small stresses as those caused by the downslope component of gravity on relatively gentle slopes. The nature and extent of these deformations has important geologic and engineering applications and depends on a number of factors. A research program at the University of Rhode Island is under way to study these factors, make predictions on rates of displacement, and identify environmental conditions that may lead to catastrophic mass failures. A laboratory testing program on the time-dependent characteristics of marine clays has been under way for a number of years. The data include, among others, long-term drained triaxial, one-dimensional, and direct simple shear creep tests. These results along with practical considerations are used to select a constitutive model for inclusion in the numerical code. Sediment deposits encountered on the continental slope and rise can vary substantially both in composition and behavior over relatively short distances. To analyze the integrated behavior of such a continuum, the authors have selected the finite element method. The code being developed will initially include a numerical model proposed by other investigators. With the aid of the developed methodology, creep deformations can be studied for a number of field cases of interest.

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

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

    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.

  11. Very slow creep tests on salt samples

    NASA Astrophysics Data System (ADS)

    Bérest, P.; Béraud, J. F.; Brouard, B.; Blum, P. A.; Charpentier, J. P.; de Greef, V.; Gharbi, H.; Valès, F.

    2010-06-01

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

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

    NASA Astrophysics Data System (ADS)

    Aslani, Farhad; Nejadi, Shami

    2012-09-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Aslani, Farhad; Nejadi, Shami

    2012-09-01

    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.

  14. The Characteristics of Intra-continental Deformation and Hydrocarbon Distribution Controlled by the Himalayan Tectonic Movements in China

    NASA Astrophysics Data System (ADS)

    JIA, Chengzao

    Based on previous studies and the latest insights from recent petroleum exploration programs, we propose that the characteristics of intra-continental deformation and its distribution, caused by the Himalayan tectonic movements, are controlled by basement framework formed by a collage of microcratons and lithotectonic terranes and dynamic factors such as the Indian/Eurasia collision and subduction of the Pacific plate. The evolution of Himalayan tectonic movements can be resolved by three principal dynamic mechanisms: (1) the uplift of Tibetan Plateau, (2) the coupling of orogenic belts and basins surrounding the Tibetan Plateau, and (3) extensional tectonics in eastern China. The tectonic framework and deformation that resulted from the Himalayan tectonic movements are mainly embodied in four tectonic domains: (1) the uplifted regions of the Tibetan Plateau, (2) the basin-and-range coupling of peripheral Tibetan Plateau, (3) stable regions, and (4) regions of active rifting along the western circum-Pacific margin. Sedimentary basins formed during the Himalayan tectonic movements, can be assorted into three categories: (1) rift basins due to extensional tectonics in east China, such as Bohai Bay Basin and Songliao Basin; (2) basins in central China, controlled by eastward compression of the Tibetan Plateau, which are characteristic of thrusting of basin margin and uplift-denudation in basins; (3) basins in west China such as the Tarim, Junggar and Qaidam Basins, which are associated with north-directed compression and exhibit thrust movements and flexural subsidence along basin margins. Their structural style is that of basin-and-range type. We conclude that Himalayan tectonic movements may have controlled the late hydrocarbon accumulation in China.

  15. Creep-Fatigue Behavior of Alloy 617 at 850°C

    SciTech Connect

    Carroll, Laura

    2015-05-01

    Creep-fatigue deformation is expected to be a significant contributor to the potential factors that limit the useful life of the Intermediate Heat Exchanger (IHX) in the Very High Temperature Reactor (VHTR) nuclear system.[1] The IHX of a high temperature gas reactor will be subjected to a limited number of transient cycles due to start-up and shut-down operations imparting high local stresses on the component. This cycling introduces a creep-fatigue type of interaction as dwell times occur intermittently. The leading candidate alloy for the IHX is a nickel-base solid solution strengthened alloy, Alloy 617, which must safely operate near the expected reactor outlet temperature of up to 950 °C.[1] This solid solution strengthened nickel-base alloy provides an interesting creep-fatigue deformation case study because it has characteristics of two different alloy systems for which the cyclic behavior has been extensively investigated. Compositionally, it resembles nickel-base superalloys, such as Waspalloy, IN100, and IN718, with the exception of its lower levels of Al. At temperatures above 800 °C, the microstructure of Alloy 617, however, does not contain the ordered ?’ or ?’’ phases. Thus microstructurally, it is more similar to an austenitic stainless steel, such as 316 or 304, or Alloy 800H comprised of a predominantly solid solution strengthened matrix phase with a dispersion of inter- and intragranular carbides. Previous studies of the creep-fatigue behavior of Alloy 617 at 950 °C indicate that the fatigue life is reduced when a constant strain dwell is added at peak tensile strain.[2-5] This results from the combination of faster crack initiation occurring at surface-connected grain boundaries due to oxidation from the air environment along with faster, and intergranular, crack propagation resulting from the linking of extensive interior grain boundary cracking.[3] Saturation, defined as the point at which further increases in the strain-controlled hold time duration no longer decreases the cycle life, has been observed for Alloy 617 at 950 °C at least to the investigated hold times[2,3], as illustrated through a plot of cycles to failure v. hold time in Figure 1. The 950 °C creep-fatigue data set generated by Totemeier and Tian[5] at the 0.3% and 1.0% strain range is consistent in magnitude in terms of the cycles to failure data of that of Carroll et al., however, 0.3% strain range data did not exhibit saturation at hold times of up to 10 min. At 1.0% total strain, saturation in the number of cycles to failure was observed within the investigated peak tensile hold times of up to 10 min[5]. The data of Carroll et al.[2,3] in Figure 1 and Totemeier and Tian[5] is also consistent in magnitude with the data of Rao and coworkers[4] investigated at the 0.6% strain range. It should be noted that saturation in the number of cycles to failure is not present in the data published by Rao and coworkers[4] for tensile hold times of up to 120 min. The latter testing was in a simulated primary-circuit helium gas as opposed to air and a single data point is reported for the longer hold time conditions.

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

    PubMed

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

    2010-11-16

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

  17. Effect of simulated sampling disturbance on creep behaviour of rock salt

    NASA Astrophysics Data System (ADS)

    Guessous, Z.; Gill, D. E.; Ladanyi, B.

    1987-10-01

    This article presents the results of an experimental study of creep behaviour of a rock salt under uniaxial compression as a function of prestrain, simulating sampling disturbance. The prestrain was produced by radial compressive loading of the specimens prior to creep testing. The tests were conducted on an artifical salt to avoid excessive scattering of the results. The results obtained from several series of single-stage creep tests show that, at short-term, the creep response of salt is strongly affected by the preloading history of samples. The nature of this effect depends upon the intensity of radial compressive preloading, and its magnitude is a function of the creep stress level. The effect, however, decreases with increasing plastic deformation, indicating that large creep strains may eventually lead to a complete loss of preloading memory.

  18. Creep of Uncoated and Cu-Cr Coated NARloy-Z

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

  19. Modeling the creep properties of olivine by 2.5-dimensional dislocation dynamics simulations

    NASA Astrophysics Data System (ADS)

    Boioli, Francesca; Carrez, Philippe; Cordier, Patrick; Devincre, Benoit; Marquille, Matthieu

    2015-07-01

    In this work we performed 2.5-dimensional (2.5D) dislocation dynamics simulations coupling climb with the glide dislocation motion to model the creep behavior of olivine, one of the main component of the Earth's upper mantle. In particular, we present an application of this method to determine the creep strain rate in a material with high lattice resistance, such as olivine. We show that by including the climb mechanism we reach steady state creep conditions. Moreover, we find that a creep power law with a stress exponent close to 3 can be extracted from our simulations and we provide a model based on Orowan's law to predict the creep strain rates in the high temperature and low stress regime. The model presented is relevant to describe the plastic flow of olivine in the Earth's mantle deformation conditions and can be useful to derive the high temperature creep behavior of other materials.

  20. Relation between creep compliance and elastic modulus in organic-rich shales observed through laboratory experiments.

    NASA Astrophysics Data System (ADS)

    Sone, Hiroki; Zoback, Mark

    2013-04-01

    We studied the ductile creep behavior of organic-rich shales from shale gas reservoirs in North America through laboratory triaxial experiments to better understand controls on the physical behavior of these rocks over time and the effect of creep on other rock properties. Laboratory experiments conducted at room-temperature conditions show that creep deformation observed at in-situ differential stress conditions is approximately linear with the applied differential pressure. The creep behavior is also anisotropic such that creep occurs more in the bedding-perpendicular direction than in the bedding-parallel direction. The reduction in sample volume during creep suggests that the creep is accommodated by a small amount of pore compaction occurring in the clay-aggregates and/or the relatively porous kerogen in the rock. Thus, the tendency to creep (creep compliance) is generally observed to increases with clay and kerogen volume. However, the strongest correlation is found between creep compliance and Young's modulus. A strong negative correlation between creep compliance and elastic Young's modulus exists regardless of the sample orientation and despite the wide range of sample mineralogy (5-50% clay, 5-60% quartz-feldspar-pyrite, 0-80% carbonates). This correlation is quite interesting as inelastic creep and elastic stiffness depend on somewhat different physical attributes. We attempt to quantitatively explain the correlation between creep behavior and elastic stiffness by appealing to a stress-partitioning that occurs between the soft components (clay and kerogen) and stiff components (quartz, feldspar, pyrite, carbonates) of the shale rock. First, the stress-partitioning occurring within the soft and stiff components is quantified based on the rock composition, elastic properties of the individual components, and the overall average Young's modulus of the rock. By combining the stress-partitioning behavior with knowledge that the creep behavior is linear against the applied stress, we forward calculate the creep compliance of the whole rock. Results show that when creep is linear against stress, a unique relation between creep compliance and elastic modulus can be established for rocks with similar mineral assemblages, consistent with our laboratory results. Thus, our results provide insights into how creep behaviors of poly-mineralic rocks can be re-constructed from the creep properties of the individual phases composing the rock.

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

    PubMed Central

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

    2014-01-01

    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

  2. Laser-Interferometric Creep Rate Spectroscopy of Polymers

    NASA Astrophysics Data System (ADS)

    Bershtein, Vladimir A.; Yakushev, Pavel N.

    Laser-interferometric creep rate meter (LICRM) and creep rate spectroscopy (CRS), as an original high-resolution method for discrete relaxation spectrometry and thermal analysis, were developed in the authors' Materials Dynamics Laboratory at Ioffe Physical-Technical Institute of the Russian Academy of Sciences (Saint-Petersburg). In the last few decades they have been successfully applied to solving various problems of polymer physics and materials science, especially being combined with DSC, structural, and other techniques. CRS involves measuring ultra-precisely a creep rate at small tensile or compressive stress, typically much lower than the yield stress, as a function of temperature, over the range from 100 to 800 K. LICRM setup allows one to register precisely creep rates on the basis of deformation increment of 150-300 nm. The survey describes this method and summarizes the results of numerous studies performed with the LICRM setup and CRS technique for different bulk polymeric materials, films, or thin fibers. This approach provided new experimental possibilities superior in resolution and sensitivity compared to the conventional relaxation spectrometry techniques. Among such possibilities are discrete analysis of dynamics; creep on submicro-, micro- and meso-scales; revealing relations between stepwise microplasticity and morphology; kinetic information on creep at any temperature and deformation; polymer dynamics at interfaces; analysis of microplasticity, relaxations, and phase transitions in brittle materials; using creep rate spectra for non-destructive prediction of temperature anomalies in mechanical behavior of materials, etc. Considerable attention has been paid to combined CRS/DSC analysis of the peculiarities of segmental dynamics, nanoscale dynamic, and compositional heterogeneity in different kinds of complex polymer systems and nanocomposites.

  3. FTIR Maps and Spatial Distributions of OH in Caledonide and Himalayan Shear Zones: Implications for Dislocation Creep and Water Weakening

    NASA Astrophysics Data System (ADS)

    Kronenberg, A. K.; Hasnan, H. F. B.; Holyoke, C. W., III; Kronenberg, J. A.; Law, R. D.; Thomas, J. B.

    2014-12-01

    FTIR measurements of quartz mylonites from the Moine Thrust of the NW Scotland Caledonides and the Main Central Thrust of the Himalaya reveal spatial variations in OH absorptions that correspond to deformation temperature, tectonic level within the thrust, intragranular shear, and recrystallization. Infrared spectra measured with apertures of 10-100 ?m exhibit OH absorptions characteristic of hydrogen point defects, fine fluid inclusions and micas within quartz grain interiors, and hydrous phases at grain boundaries. Moine Thrust quartzites, deformed at greenschist conditions (T ~ 350°C) by Regime II, BLG/SGR dislocation creep, have pervasive broad OH absorptions due to fine fluid inclusions and sharp OH bands that appear locally due to finely dispersed micas. Mean OH contents vary from 2250 (+/-1500) ppm (106 OH/Si) in mylonitic quartzites 2.5 m below the thrust surface to 4080 (+/-1400) ppm in weakly deformed Cambrian quartzites 70 m below the thrust. Spatial variations in OH due to fine fluid inclusions are complex, with water contents that differ significantly between neighboring grains and correlate with grain strain and recrystallization. OH absorption bands mapped at a resolution of 10 ?m vary from 280 to 9000 ppm, well above and below concentrations known to weaken quartz.Himalayan mylonites in the hanging wall of the Main Central Thrust of the Sutlej region were deformed at upper amphibolite conditions (T ~ 600°C) by Regime III, GBM dislocation creep. Given their extensive deformation and dislocation creep microstructures, quartz grains of these rocks are remarkably dry. Quartz grain spectra are dominated by sharp OH bands due to hydrogen interstitials with OH contents from 350 (+/-250) ppm (T = 600°C) to 119 (+/-62) ppm (T = 640 - 740°C). These results offer challenges to the application of experimental flow laws for water-weakened quartz to the high-grade dislocation creep of Himalayan mylonites. Much lower water contents may be sufficient for water weakening at upper amphibolite conditions and natural strain rates than are needed at experimental strain rates. Alternatively, hydrogen defects that enhance dislocation motion at these conditions may be sourced from grain boundaries or micas, diffusing over longer distances than are possible at greenschist conditions or laboratory rates.

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

    SciTech Connect

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

    2014-01-01

    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.

  5. Avoiding Project Creep.

    ERIC Educational Resources Information Center

    Kennerknecht, Norbert J.; Scarnati, James T.

    1998-01-01

    Discusses how to keep school district capital-improvement projects within budget. Examines areas where runaway costs creep into a project and ways of cutting or lessening these costs, such as using standard agreements, controlling architect's expense reimbursements, developing a quality-control process, and reducing document duplication. (GR)

  6. Creep behavior of submarine sediments

    USGS Publications Warehouse

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

    1984-01-01

    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.

  7. Stress versus temperature dependence of activation energies for creep

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    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.

  8. 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)

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

    1974-01-01

    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.

  9. Creep and fracture of dispersion-strengthened materials

    NASA Technical Reports Server (NTRS)

    Raj, Sai V.

    1991-01-01

    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.

  10. Creep behaviour and creep mechanisms of normal and healing ligaments

    NASA Astrophysics Data System (ADS)

    Thornton, Gail Marilyn

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

  11. Microscopic evaluation of creep-fatigue interaction in a nickel-based superalloy

    SciTech Connect

    Santella, Michael L; Yamamoto, Masato; Shingledecker, John P; Boehlert, C. J.; Ogata, Takashi

    2009-01-01

    In order to verify the applicability of Nickel-based alloy Alloy 263 for the thick component, a series of creep, fatigue and creep-fatigue experiments were carried out. To investigate the detailed damage process under the creep-fatigue condition, simple aged, crept, fatigued, and creep-fatigued specimens were subjected to electron back scattering diffraction (EBSD) pattern observation in the SEM. While the simple aged and fatigued specimens showed no remarkable local change in orientation (less than 1deg), the crept specimen exhibited inhomogeneous change of crystallographic orientation, at most 5 degrees, within the grains. This shows that the creep strain is inhomogeneously distributed in the grains due to the effect of relative constraint among the grains. The creep-fatigued specimen exhibited similar local inhomogeniety in strain distribution compared to the crept sample near the center of the grains. However, the creep-fatigued specimen showed remarkable local change in orientation at the vicinity of grain boundaries up to 15 degrees, indicating the occurrence of high strain concentration nearby the grain boundaries. A detailed observation of creep-fatigue damage evolution process in SEM revealed that the inhomogeneous grain deformation precedes the remarkable inhomogeneous deformation nearby the grain boundaries, and followed by the grain boundary cracking.

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

    SciTech Connect

    Han, G.M. Yu, J.J.; Hu, Z.Q.; Sun, X.F.

    2013-12-15

    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.

  13. Characterisation of Laves phase precipitation and its correlation to creep rupture strength of ferritic steels

    SciTech Connect

    Zhu, S.; Yang, M.; Song, X.L.; Tang, S.; Xiang, Z.D.

    2014-12-15

    The Laves phase precipitation process was characterised by means of field emission scanning electron microscopy to demonstrate its effect on creep rupture strength of steels with a fully ferritic matrix. To eliminate the effects of carbide and carbonitride precipitations so that the creep rupture data can be analysed exclusively in relation to the Laves phase precipitation process, an alloy Fe–9Cr–3Co–3W (wt.%) without C and N additions was used for the study. Creep rupture strengths were measured and volume fraction and particle size of Laves phase precipitates in the ruptured specimens were analysed. It was found that the creep rupture strength started to collapse (or decrease more rapidly) long before the Laves phase precipitation reached equilibrium fraction. This was related to the onset of the coarsening of Laves phase particles, which precipitated only on grain boundaries and hence contributed little to precipitation strengthening. Creep deformation had no effect either on the precipitation kinetics or on the growth kinetics of Laves phase particles. - Highlights: • Laves phase precipitation at 650 °C was characterised for Fe–9Cr–3W–3Co alloy. • Laves phase precipitated predominantly on grain boundaries. • Creep deformation had no effect on Laves phase precipitation and growth kinetics. • Creep strength started to collapse long before Laves phase precipitation is ended. • Collapse of creep strength was attributed to the coarsening of Laves phase particles.

  14. Arctic underwater noise transients from sea ice deformation: Characteristics, annual time series, and forcing in Beaufort Sea.

    PubMed

    Kinda, G Bazile; Simard, Yvan; Gervaise, Cédric; Mars, Jérôme I; Fortier, Louis

    2015-10-01

    A 13-month time series of Arctic Ocean noise from the marginal ice zone of the Eastern Beaufort Sea is analyzed to detect under-ice acoustic transients isolated from ambient noise with a dedicated algorithm. Noise transients due to ice cracking, fracturing, shearing, and ridging are sorted out into three categories: broadband impulses, frequency modulated (FM) tones, and high-frequency broadband noise. Their temporal and acoustic characteristics over the 8-month ice covered period, from November 2005 to mid-June 2006, are presented and their generation mechanisms are discussed. Correlations analyses showed that the occurrence of these ice transients responded to large-scale ice motion and deformation rates forced by meteorological events, often leading to opening of large-scale leads at main discontinuities in the ice cover. Such a sequence, resulting in the opening of a large lead, hundreds by tens of kilometers in size, along the margin of landfast ice and multiyear ice plume in the Beaufort-Chukchi seas is detailed. These ice transients largely contribute to the soundscape properties of the Arctic Ocean, for both its ambient and total noise components. Some FM tonal transients can be confounded with marine mammal songs, especially when they are repeated, with periods similar to wind generated waves. PMID:26520287

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

    SciTech Connect

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

    1997-09-01

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

  16. Numerical simulation of the experiment on the measurement of salt creep

    NASA Astrophysics Data System (ADS)

    Li, Shiyuan; Abe, Steffen; Urai, Janos L.

    2010-05-01

    In this research, we collect data on salt creep and establish a database for creep of evaporite rocks at temperature up to 250°C, and compare different published creep laws based on solution-precipitation creep, and dislocation creep. The largest differences stem from lithological variations, with bischofite and epsomite being the weakest, carnalite intermediate, halite, sylvite and anhydrite being the strongest ductile evaporite. Under the same conditions, different halites can creep at two orders of magnitude different rates at a given differential stress, in agreement with observations of small scale folding in salt mines. We support this work by finite element simulations of the uniaxial compression of a cylindrical sample with variable rheologies and comparison of the computed stress-strain response with measurements, for different values of friction at the pistons. We use the commercial finite element package ABAQUS(tm), and model salt as a power-law creep material including elasticity. We find that friction at the piston produces different barreling profile for different power law exponents of the creep law, and a small but significant effect on the stress-strain response as compared to frictionless piston with homogeneous deformation. We discuss different methods to compensate for this effect and to extract the optimum creep law from such measurements.

  17. Effect of prior cold work on creep properties of a titanium modified austenitic stainless steel

    NASA Astrophysics Data System (ADS)

    Vijayanand, V. D.; Parameswaran, P.; Nandagopal, M.; Panneer Selvi, S.; Laha, K.; Mathew, M. D.

    2013-07-01

    Prior cold worked (PCW) titanium-modified 14Cr-15Ni austenitic stainless steel (SS) is used as a core-structural material in fast breeder reactor because of its superior creep strength and resistance to void swelling. In this study, the influence of PCW in the range of 16-24% on creep properties of IFAC-1 SS, a titanium modified 14Cr-15Ni austenitic SS, at 923 K and 973 K has been investigated. It was found that PCW has no appreciable effect on the creep deformation rate of the steel at both the test temperatures; creep rupture life increased with PCW at 923 K and remained rather unaffected at 973 K. The dislocation structure along with precipitation in the PCW steel was found to change appreciably depending on creep testing conditions. A well-defined dislocation substructure was observed on creep testing at 923 K; a well-annealed microstructure with evidences of recrystallization was observed on creep testing at 973 K. Creep rupture life of the steel increased with the increase in PCW at 923 K. This has been attributed to the partial retention of prior cold work induced dislocations which facilitated the extensive precipitation of secondary Ti(C,N) particles on the stable dislocation substructure. Creep rupture life of the steel did not vary with PCW at 973 K due to softening by recrystallization and absence of secondary Ti(C,N).

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

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

    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.

  19. Testing the inference of creep on Rodgers Creek Fault

    NASA Astrophysics Data System (ADS)

    Jin, L.; Funning, G. J.

    2010-12-01

    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.

  20. Observations of orientation dependent creep of Ni{sub 3}Al

    SciTech Connect

    Knobloch, C.; Glock, K.; Glatzel, U.

    1999-07-01

    The influence of crystal orientation on the high temperature creep behavior of Ni{sub 3}(Al Ti Ta) was investigated by tensile creep testing under a constant load at a temperature of 1,123K. The single crystals were oriented close to [001], [011], [111], [557] and [012]. The results show an increasing stationary creep rate from [111] over [011] to [001]. The evolution of the microstructure during creep deformation was studied, using transmission electron microscopy (TEM). Only few systems are active in the primary regime, whereas several slip systems operate in the secondary stage. habit planes of dislocation pairs separated by an antiphase boundary were examined and compared with anisotropic elastic calculations, explaining the good creep response of [111] oriented using crystals.

  1. Propagation of Crack in Glasses under Creep Conditions

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

    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.

  2. Creep Crack Initiation and Growth Behavior for Ni-Base Superalloys

    NASA Astrophysics Data System (ADS)

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

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

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

    NASA Astrophysics Data System (ADS)

    Wan, Quanhe; Quesnel, David J.

    2013-03-01

    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.

  4. Creep behavior of Fe-bearing olivine under hydrous conditions

    NASA Astrophysics Data System (ADS)

    Tasaka, Miki; Zimmerman, Mark E.; Kohlstedt, David L.

    2015-09-01

    To understand the effect of iron content on the creep behavior of olivine, (MgxFe(1 - x))2SiO4, under hydrous conditions, we have conducted tri-axial compressive creep experiments on samples of polycrystalline olivine with Mg contents of x = 0.53, 0.77, 0.90, and 1. Samples were deformed at stresses of 25 to 320 MPa, temperatures of 1050° to 1200°C, a confining pressure of 300 MPa, and a water fugacity of 300 MPa using a gas-medium high-pressure apparatus. Under hydrous conditions, our results yield the following expression for strain rate as a function of iron content for 0.53 ? x ? 0.90 in the dislocation creep regime: ??=??0.90((1-x/0.1))1/2exp[226×1030.9-x/RT]. In this equation, the strain rate of San Carlos olivine, ??0.90, is a function of T, ?, and fH2O. As previously shown for anhydrous conditions, an increase in iron content directly increases creep rate. In addition, an increase in iron content increases hydrogen solubility and therefore indirectly increases creep rate. This flow law allows us to extrapolate our results to a wide range of mantle conditions, not only for Earth's mantle but also for the mantle of Mars.

  5. Probability distributions for parameters of the Munson-Dawson salt creep model

    SciTech Connect

    Fossum, A.F.; Pfeifle, T.W.; Mellegard, K.D.

    1993-12-31

    Stress-related probability distribution functions are determined for the random variable material model parameters of the Munson-Dawson multi-mechanism deformation creep model for salt. These functions are obtained indirectly from experimental creep data for clean salt. The parameter distribution functions will form the basis for numerical calculations to generate an appropriate distribution function for room closure. Also included is a table that gives the values of the parameters for individual specimens of clean salt under different stresses.

  6. Non-Contact Measurements of Creep Properties of Refractory Materials

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  10. Autonomous Repair Mechanism of Creep Damage in Fe-Au and Fe-Au-B-N Alloys

    NASA Astrophysics Data System (ADS)

    Zhang, S.; Kwakernaak, C.; Tichelaar, F. D.; Sloof, W. G.; Kuzmina, M.; Herbig, M.; Raabe, D.; Brück, E.; van der Zwaag, S.; van Dijk, N. H.

    2015-12-01

    The autonomous repair mechanism of creep cavitation during high-temperature deformation has been investigated in Fe-Au and Fe-Au-B-N alloys. Combined electron-microscopy techniques and atom probe tomography reveal how the improved creep properties result from Au precipitation within the creep cavities, preferentially formed on grain boundaries oriented perpendicular to the applied stress. The selective precipitation of Au atoms at the free creep cavity surface results in pore filling, and thereby, autonomous repair of the creep damage. The large difference in atomic size between the Au and Fe strongly hampers the nucleation of precipitates in the matrix. As a result, the matrix acts as a reservoir for the supersaturated solute until damage occurs. Grain boundaries and dislocations are found to act as fast transport routes for solute gold from the matrix to the creep cavities. The mechanism responsible for the self-healing can be characterized by a simple model for cavity growth and cavity filling.

  11. SAR interferometry and optical remote sensing for analysis of co-seismic deformation, source characteristics and mass wasting pattern of Lushan (China, April 2013) earthquake

    NASA Astrophysics Data System (ADS)

    Mathew, John; Majumdar, Ritwik; Kumar, K. Vinod

    2015-03-01

    Co-seismic deformation associated with the Lushan (China) earthquake that occurred along the south-western segment of the Longmenshan Fault Zone (LFZ) on the 20th April 2013 has been estimated by differential interferometric SAR (DInSAR) technique using Radarsat-2 data. The Lushan earthquake resulted in the deformation of the Sichuan basin and the Longmenshan ranges in proximity to the LFZ. The line of sight (LOS) displacement values obtained from DInSAR technique mainly range between -4.0 cm to +3.0 cm. The western Sichuan basin shows oblique westward movement with predominant downward component in areas farther from LFZ and predominant westward component over the downward movement in areas closer to the source fault. Inversion modelling has been used to derive the seismic source characteristics from DInSAR derived deformation values using elastic dislocation source type. The linear inversion model converged at a double-fault source solution consisting of a deeper, steep, NW dipping fault plane-1 of 60 km × 16 km dimension and a shallower, gentle, NW dipping fault plane-2 of 60 km × 15 km dimension, with distributed slip values varying between 0 to 2.26 m. These fault planes (fault planes-1 and -2) coincide with the Dachuan-Shuangshi fault and the buried Range Front Fault, respectively. The inversion model gives a moment magnitude of 6.81 and the geodetic moment of 2.07 × 1019 Nm, comparable to those given in literature, derived using teleseismic body wave data. Thus DInSAR technique helped to quantify the co-seismic deformation and to retrieve the source characteristics from the estimated deformation values. The study also evaluated the distribution pattern of earthquake induced landslides (EIL) triggered fresh or re-activated during the Lushan earthquake and found that they show spatial association with the seismic source zone and also with various pre-conditioning factors of slope instability.

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

    SciTech Connect

    Curtin, W.A.; Fabeny, B.; Ibnabdeljalil, M.; Iyengar, N.; Reifsnider, K.L.

    1996-07-31

    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.

  13. Effect of interconnect creep on long-term performance of SOFC of one cell stacks

    SciTech Connect

    Liu, Wenning N.; Sun, Xin; Khaleel, Mohammad A.

    2008-02-01

    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 1073oK. High temperature ferritic alloys are potential candidates as interconnect (IC) materials and spacers due to their low cost and CTE compatibility with other SOFC components. Since the melting temperature of most stainless steel is around 1800oK, possible creep deformation of IC under the typical cell operating temperature should not be neglected. In this paper, the effects of interconnect creep behavior on stack geometry change and stress redistribution of different cell components are predicted and summarized. The goal of the study is to investigate the performance of the fuel cell stack by obtaining the fuel and air channel geometry changes due to creep of the ferritic stainless steel interconnect, therefore indicating possible SOFC performance change under long term operations. IC creep models were incorporated into SOFC-MP and Mentat FC, and finite element analyses were performed to quantify the deformed configuration of the SOFC stack under the long term steady state operating temperature. It is found that creep behavior of the ferritic stainless steel IC contributes to narrowing of both the fuel and the air flow channels. In addition, stress re-distribution of the cell components suggests the need for a compliant sealing material that also relaxes at operating temperature.

  14. Creep Feeding Beef Calves. 

    E-print Network

    Smith, A. L. (Albert Lorenzo)

    1955-01-01

    of cot- eed cake, and will serve about 2u calves. Blueprint No. 159 Fig. 6. This plan allows feeding from both sides. The feeder in Figure 6 feeds from both sides and is designed to care for about 80 calves. This size, 16 feet long, holds 125... any place where the cows are attracted one or more times daily is satisfactory. The Blueprint No. picture on the cover is an example Fig. 7. Wall Self Feeder. of such a location. SUGGESTED RATION FOR CREEP FEED1 SUCKLING CALVES AGE OF CALF...

  15. Deformation processes in forging ceramics

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

    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.

  16. Brittle creep and subcritical crack propagation in glass submitted to triaxial conditions

    NASA Astrophysics Data System (ADS)

    Mallet, Céline; Fortin, Jérôme; Guéguen, Yves; Bouyer, Frédéric

    2015-02-01

    An experimental work is presented that aimed at improving our understanding of the mechanical evolution of cracks under brittle creep conditions. Brittle creep may be an important slow deformation process in the Earth's crust. Synthetic glass samples have been used to observe and document brittle creep due to slow crack-propagation. A crack density of 0.05 was introduced in intact synthetic glass samples by thermal shock. Creep tests were performed at constant confining pressure (15 MPa) for water saturated conditions. Data were obtained by maintaining the differential-stress constant in steps of 24 h duration. A set of sensors allowed us to record strains and acoustic emissions during creep. The effect of temperature on creep was investigated from ambient temperature to 70°C. The activation energy for crack growth was found to be 32 kJ/mol. In secondary creep, a large dilatancy was observed that did not occur in constant strain rate tests. This is correlated to acoustic emission activity associated with crack growth. As a consequence, slow crack growth has been evidenced in glass. Beyond secondary creep, failure in tertiary creep was found to be a progressive process. The data are interpreted through a previously developed micromechanical damage model that describes crack propagation. This model allows one to predict the secondary brittle creep phase and also to give an analytical expression for the time to rupture. Comparison between glass and crystalline rock indicates that the brittle creep behavior is probably controlled by the same process even if stress sensitivity for glass is lower than for rocks.

  17. An Investigation of the Strength and Deformation Characteristics of Rock masses: A Case Study in an Excavation of Eski?ehir-Köseköy Tunnels, Turkey

    NASA Astrophysics Data System (ADS)

    Beyhan, Sunay; Abiddin Erguler, Zeynal; Ogul, Kenan

    2015-04-01

    With increasing of high-speed rail technology in last decades, Turkey has developed many big engineering projects to connect major cities. Excavations conducted for these projects provide very important contributions in term of understanding the strength and deformation characteristics of weak rock masses belongs to various geological materials. The Ankara-Istanbul high-speed railway known as a significant project among these projects was designed in two different phases. To discuss the outcomes, experiences and challenging geological materials during construction of this tunnel, the geotechnical properties of rock masses of a tunnel named as T19 are evaluated and discussed in this study. The T19 tunnel was excavated in stratified and heavily fractured four different geological formations. Rock mass rating (RMR) system, and tunnelling quality index (Q) were utilized for the preliminary design stages of this tunnel. These engineering rock mass classifications were utilized in 135 different locations to find representative RMR and Q values for encountered rock masses during excavation. The RMR and Q values, which range between 18-52 and changing between 0.017 and 1.6 respectively, indicate that the T19 tunnel was mainly constructed in very poor and poor rock masses. Thus, shotcrete immediately was applied after face advance to prevent the fall of loose rock fragments and to minimize excessive deformation in rock, particular in very poor and poor rock masses. In addition, the deformation characteristics of the tunnel were also carefully monitored and measured by 3D-optical measuring system and conventional tape extensometer, and then required further supports were installed. Finally, the rock mass-support interactions of different geological formations were comprehensively evaluated in this study for understanding strength and deformation characteristics of weak and stratified rock masses. Keywords: Convergence, high-speed rail, rock mass, support, tunnel

  18. Irradiation Creep of Chemically Vapor Deposited Silicon Carbide as Estimated by Bend Stress Relaxation Method

    SciTech Connect

    Katoh, Yutai; Snead, Lance Lewis; Hinoki, Tatsuya; Kondo, Sosuke; Kohyama, Akira

    2007-01-01

    The bend stress relaxation technique was applied for an irradiation creep study of high purity, chemically vapor-deposited beta-phase silicon carbide (CVD SiC) ceramic. A constant bend strain was applied to thin strip samples during neutron irradiation to fluences 0.2-4.2 dpa at various temperatures in the range {approx}400 to {approx}1080 C. Irradiation creep strain at <0.7 dpa exhibited only a weak dependence on irradiation temperature. However, the creep strain dependence on fluence was non-linear due to the early domination of the initial transient creep, and a transition in creep behavior was found between 950 and 1080 C. Steady-state irradiation creep compliances of polycrystalline CVD SiC at doses >0.7 dpa were estimated to be 2.7({+-}2.6) x 10{sup -7} and 1.5({+-}0.8) x 10{sup -6} (MPa dpa){sup -1} at {approx}600 to {approx}950 C and {approx}1080 C, respectively, whereas linear-averaged creep compliances of 1-2 x 10{sup -6} (MPa dpa){sup -1} were obtained for doses of 0.6-0.7 dpa at all temperatures. Monocrystalline 3C SiC samples exhibited significantly smaller transient creep strain and greater subsequent deformation when loaded along <0 1 1> direction.

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

    NASA Astrophysics Data System (ADS)

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

    2008-08-01

    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.

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

    SciTech Connect

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

    2009-01-22

    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.

  1. Creep of a Silicon Nitride Under Various Specimen/Loading Configurations

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    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.

  2. Creep-Fatigue Interaction Testing

    NASA Technical Reports Server (NTRS)

    Halford, Gary R.

    2001-01-01

    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.

  3. The plastic deformation behaviour of ceramic nuclear fuels at stress changes

    NASA Astrophysics Data System (ADS)

    Müller-Lyda, I.

    1980-01-01

    The irradiation creep experiments of the BR2 Mol-12 series in capsules allowing an in-pile variation of the stress applied on the fuel specimen showed a typical accelerated deformation of mixed oxide as well as mixed carbide fuel. Quantitative relations for the accelerated deformation depending upon the irradiation parameters are derived from the measured creep data. Magnitude and time dependence of the accelerated deformation effects are discussed and compared with the steady-state creep and swelling. Accelerated fuel deformations due to stress changes can be a beneficial effect lowering the fuel/ cladding mechanical interaction during load-follow-on operation.

  4. Fragmentation of {alpha}{sub 2} plates in a fully lamellar TiAl during creep

    SciTech Connect

    Wang, J.G.; Hsiung, L.M.; Nieh, T.G.

    1999-07-01

    The fragmentation and spheroidization of {alpha}{sub 2} laths in a fully-lamellar TiAl alloy during creep were examined. Three possible mechanisms, Rayleigh's perturbation model, subgrain boundary groove mechanism and intersection of deformation twins with {alpha}{sub 2} lamellae were presented and discussed. During creep deformation, the pile-up of interfacial dislocations leads to a change of planar interface, which, in turn, causes a difference in local chemical potential, and further results in the spheroidization of {alpha}{sub 2} lamellae. On the other hand, the deformation of the {alpha}{sub 2} phase is expected to be induced by the high local stress concentration introduced by the pile up of interfacial dislocations. The dynamic recovery process may lead to the formation of subgrain boundaries in the {alpha}{sub 2} lamellae, which results in the spheroidization and termination of {alpha}{sub 2} lamellae with the aid of diffusion during creep.

  5. 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)

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

    2010-06-01

    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

  6. Transient and steady-state creep in a tin-silver-copper lead-free solder alloy: Experiments and modeling

    NASA Astrophysics Data System (ADS)

    Shirley, Dwayne R.

    It has been conventional to simplify the thermo-mechanical modeling of solder joints by omitting the primary (transient) contributions to total creep deformation, assuming that secondary (steady-state) creep strain is dominant and primary creep is negligible. The error associated with this assumption has been difficult to assess because it depends on the properties of the solder joint and the temperature-time profile. This research examines the relative contributions of primary and secondary creep in Sn3.8Ag0.7Cu solder using the constant load creep and stress relaxation measurements for bulk tensile specimens and the finite element analysis of a chip resistor (trilayer) solder joint structure that was thermally cycled under multiple temperature ranges and ramp rates. It was found that neglect of primary creep can result in errors in the predicted stress and strain of the solder joint. In turn, these discrepancies can lead to errors in the estimation of the solder thermal fatigue life due to the changing proportion of primary creep strain to total inelastic strain under different thermal profiles. The constant-load creep and stress relaxation data for Sn3.8Ag0.7Cu span a range of strain rates 10-8s-1 < 3? < 10-4 s-1, and temperatures 25°C, 75°C and 100°C. Creep and stress relaxation measurements show that transient creep caused faster strain rates during stress relaxation for a given stress compared to the corresponding minimum creep rate from constant-load creep tests. The extent of strain hardening during primary creep was a function of temperature and strain rate. A constitutive creep model was presented for Sn3.8Ag0.7Cu that incorporates both transient and steady-state creep to provide agreement for both creep and stress relaxation data with a single set of eight coefficients. The model utilizes both temperature compensated time and strain rate to normalize minimum strain rate and saturated transient creep strain, thereby establishing equivalence between decreased temperature and increased strain rate. The apparent activation energy of steady-state creep was indicative of both dislocation core and bulk lattice diffusion was the most sensitive model parameter. A saturation threshold was defined that distinguishes whether primary or secondary creep is dominant under either static or variable loading.

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

    SciTech Connect

    Martin, R.J. III; Boyd, P.J.; Noel, J.S.; Price, R.H.

    1995-06-01

    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.

  8. Deformation mechanisms and grain size evolution in the Bohemian granulites - a computational study

    NASA Astrophysics Data System (ADS)

    Maierova, Petra; Lexa, Ondrej; Je?ábek, Petr; Fran?k, Jan; Schulmann, Karel

    2015-04-01

    A dominant deformation mechanism in crustal rocks (e.g., dislocation and diffusion creep, grain boundary sliding, solution-precipitation) depends on many parameters such as temperature, major minerals, differential stress, strain rate and grain size. An exemplary sequence of deformation mechanisms was identified in the largest felsic granulite massifs in the southern Moldanubian domain (Bohemian Massif, central European Variscides). These massifs were interpreted to result from collision-related forced diapiric ascent of lower crust and its subsequent lateral spreading at mid-crustal levels. Three types of microstructures were distinguished. The oldest relict microstructure (S1) with large grains (>1000 ?m) of feldspar deformed probably by dislocation creep at peak HT eclogite facies conditions. Subsequently at HP granulite-facies conditions, chemically- and deformation- induced recrystallization of feldspar porphyroclasts led to development of a fine-grained microstructure (S2, ~50 ?m grain size) indicating deformation via diffusion creep, probably assisted by melt-enhanced grain-boundary sliding. This microstructure was associated with flow in the lower crust and/or its diapiric ascent. The latest microstructure (S3, ~100 ?m grain size) is related to the final lateral spreading of retrograde granulites, and shows deformation by dislocation creep at amphibolite-facies conditions. The S2-S3 switch and coarsening was interpreted to be related with a significant decrease in strain rate. From this microstructural sequence it appears that it is the grain size that is critically linked with specific mechanical behavior of these rocks. Thus in this study, we focused on the interplay between grain size and deformation with the aim to numerically simulate and reinterpret the observed microstructural sequence. We tested several different mathematical descriptions of the grain size evolution, each of which gave qualitatively different results. We selected the two most elaborated and at the same time the most promising descriptions: thermodynamics-based models with and without Zener pinning. For conditions compatible with the S1 and S2 microstructures (~800 °C and strain rate ~10-13 s-1), the calculated stable grain sizes are ~30 ?m and >300 ?m in the models with and without Zener pinning, respectively. This is in agreement with the contrasting grain sizes associated with S1 and S2 microstructures implying that mainly chemically induced recrystallization of S1 feldspar porphyroclasts must had played a fundamental role in the transition into the diffusion creep. The model with pinning also explains only minor changes of mean grain size associated with S2 microstructure. The S2-S3 switch from the diffusion to dislocation creep is difficult to explain when assuming reasonable temperature and strain rate (or stress). However, a simple incorporation of the effect of melt solidification into the model with pinning can mimic this observed switch. Besides the above mentioned simple models with prescribed temperature and strain rate, we implemented the grain size evolution laws into in a 2D thermo-mechanical model setup, where stress, strain rate and temperature evolve in a more natural manner. This setup simulates a collisional evolution of an orogenic root with anomalous lower crust. The lower-crustal material is a source region for diapirs and it deforms via a combination of dislocation and grain-size-sensitive creeps. We tested the influence of selected parameters in the flow laws and in the grain-size evolution laws on the shape and other characteristics of the growing diapirs. The outputs of our simulations were then compared with the geological record from the Moldanubian granulite massifs.

  9. Elevated temperature deformation of TD-nickel base alloys

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

    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.

  10. Time-dependent cracking and brittle creep in crustal rocks: A review

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    Rock fracture under upper crustal conditions is driven not only by applied stresses, but also by time-dependent, chemically activated subcritical cracking processes. These subcritical processes are of great importance for the understanding of the mechanical behaviour of rocks over geological timescales. A macroscopic manifestation of time-dependency in the brittle field is the observation that rocks can deform and fail at constant applied stresses, a phenomenon known as brittle creep. Here, we review the available experimental evidence for brittle creep in crustal rocks, and the various models developed to explain the observations. Laboratory experiments have shown that brittle creep occurs in all major rock types, and that creep strain rates are extremely sensitive to the environmental conditions: differential stress, confining pressure, temperature and pore fluid composition. Even small changes in any of these parameters produce order of magnitude changes in creep strain rates (and times-to-failure). Three main classes of brittle creep model have been proposed to explain these observations: phenomenological, statistical, and micromechanical. Statistical and micromechanical models explain qualitatively how the increasing influence of microcrack interactions and/or the increasing accumulated damage produces the observed evolution of macroscopic deformation during brittle creep. However, no current model can predict quantitatively all of the observed features of brittle creep. Experimental data are limited by the timescale over which experiments are realistically feasible. Clearly, an extension of the range of available laboratory data to lower strain rates, and the development of new modelling approaches are needed to further improve our current understanding of time-dependent brittle deformation in rocks.

  11. Rate- and strain-dependent brittle deformation of rocks

    NASA Astrophysics Data System (ADS)

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

    2014-03-01

    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.

  12. Mechanisms of time-dependent deformation in porous limestone

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Cadek, J.

    1984-01-01

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

  14. Variational principles and optimal solutions of the inverse problems of creep bending of plates

    NASA Astrophysics Data System (ADS)

    Bormotin, K. S.; Oleinikov, A. I.

    2012-09-01

    It is shown that inverse problems of steady-state creep bending of plates in both the geometrically linear and nonlinear formulations can be represented in a variational formulation. Steady-state values of the obtained functionals corresponding to the solutions of the problems of inelastic deformation and elastic unloading are determined by applying a finite element procedure to the functionals. Optimal laws of creep deformation are formulated using the criterion of minimizing damage in the functionals of the inverse problems. The formulated problems are reduced to the problems solved by the finite element method using MSC.Marc software.

  15. A deformation-mechanism material model for NIKE 3-D

    SciTech Connect

    Raboin, P.J.

    1993-01-04

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

  16. Improved high temperature creep resistant austenitic alloy

    DOEpatents

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

    1988-05-13

    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.

  17. Defect-mediated creep of structured materials

    NASA Astrophysics Data System (ADS)

    Colby, R. H.; Nentwich, L. M.; Clingman, S. R.; Ober, C. K.

    2001-04-01

    Low-stress creep measurements on a nematic liquid crystal polymer indicate that it is a viscoelastic solid, with a modulus of 100dynes/cm2 and a yield stress of 50dynes/cm2. Both smectics and nematics are viscoelastic solids at very low stress levels, with a modulus that is related to their defect texture. At stress levels somewhat above the yield stress, there is a yielding regime where the deformation rate and defect spacing are power laws in the applied stress. We understand these power laws using the ideas developed long ago by Orowan for the motion of line defects in crystalline solids. The exponents of these power laws are different for nematics and smectics, but the nematic universality class also appears to apply to superplastic metals and ceramics.

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

    NASA Astrophysics Data System (ADS)

    Wang, Kelin; Bilek, Susan L.

    2014-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  20. Life Estimation and Creep Damage Quantification of Service Exposed Reformer Tube

    NASA Astrophysics Data System (ADS)

    Raj, A.; Roy, N.; Roy, B. N.; Ray, A. K.

    2015-11-01

    This paper deals with evaluation of creep damage of ~11 years service exposed primary hydrogen reformer tube made of HP-40 grade of steel in a petrochemical industry, which has been carried out in terms of Kachanav's continuum damage mechanics (CDM) model (K-model) and Bogdanoff model (B-model) based on Markov process. Residual life of the tubes was estimated based on hot tensile, conventional creep deformation under identical test conditions, optical microscopy and fractography. Accumulation of damage due to creep has been quantified through microstructural studies. The as received tubes did not reveal any degradation in the material like creep cavitation or voids, but there was indeed loss of tensile strength from room temperature to 870°C for the bottom portion of the tube due to ageing and overheating. Scatter in creep deformation behaviour of the material is probably due to variation in mode of fracture and scatter in voids. From statistical point of view, Weibull distribution pattern for analysing probability of rupture due to void area shifts with increase in true strain towards the higher population of void. The estimation of mean time to reach a specific damage state from K- model and B-model is in close agreement with that of experimental data and can describe the sudden changes of the creep damage in the tertiary region as well. A remnant life of >10 years is estimated at the operating stress-temperature conditions of the top as well as bottom portion of the tube.

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    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.

  2. Non-Classical Creep Behavior of Fusion-Cast Alumina Refractories

    SciTech Connect

    Hemrick, James Gordon; Wereszczak, Andrew A

    2009-01-01

    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.

  3. Microstructure and Creep Behavior of a Directional Solidification Nickel-based Superalloy

    NASA Astrophysics Data System (ADS)

    Tian, Ning; Tian, Sugui; Yu, Huichen; Li, Ying; Meng, Xianlin

    2015-07-01

    By means of creep property measurement and microstructure observation, an investigation has been made into microstructure and creep behavior of a directional solidification Ni-based superalloy at high temperatures. Results show that after full heat treatment, small cuboidal ?' precipitates distribute in the dendrite regions, while coarser ones distribute in the inter-dendrite regions. In the primary stage of creep, the ?' phase in alloy is transformed into the rafted structure along the direction vertical to stress axis, and then the creep of alloy enters the steady state stage. And dislocations slipping in the g matrix and climbing over the rafted ?' phase are thought to be the deformation mechanism of the alloy during steady creep stage. At the latter stage of creep, the alternate slipping of dislocations may shear and twist the rafted ?'/? phases, which promotes the initiation and propagation of the micro-cracks along the boundaries near the coarser rafted ?' phase. And the bigger probability of the creep damage occurs in the grain boundaries along 45° angles relative to the stress axis due to them bearing relatively bigger shearing stress.

  4. Does a dissolution-precipitation mechanism explain concrete creep in moist environments?

    E-print Network

    Isabella Pignatelli; Aditya Kumar; Rouhollah Alizadeh; Yann Le Pape; Mathieu Bauchy; Gaurav Sant

    2015-08-28

    Long-term creep (i.e., deformation under sustained load) is a significant material response that needs to be accounted for in concrete structural design. However, the nature and origin of creep remains poorly understood, and controversial. Here, we propose that concrete creep at RH (relative humidity) > 50%, but fixed moisture-contents (i.e., basic creep), arises from a dissolution-precipitation mechanism, active at nanoscale grain contacts, as is often observed in a geological context, e.g., when rocks are exposed to sustained loads, in moist environments. Based on micro-indentation and vertical scanning interferometry experiments, and molecular dynamics simulations carried out on calcium-silicate-hydrates (C-S-H's), the major binding phase in concrete, of different compositions, we show that creep rates are well correlated to dissolution rates - an observation which supports the dissolution-precipitation mechanism as the origin of concrete creep. C-S-H compositions featuring high resistance to dissolution, and hence creep are identified - analysis of which, using topological constraint theory, indicates that these compositions present limited relaxation modes on account of their optimally connected (i.e., constrained) atomic networks.

  5. Creep and shrinkage of high performance lightweight concrete: A multi-scale investigation

    NASA Astrophysics Data System (ADS)

    Lopez, Mauricio

    This multi-scale investigation aimed to provide new knowledge and understanding of creep and shrinkage of high performance lightweight concrete (HPLC) by assessing prestress losses in HPLC prestressed members in a large-scale study; by quantifying the effect of the constituent materials and external conditions on creep and shrinkage in a medium-scale study; and by improving the fundamental understanding of creep and shrinkage in a small-scale study. Creep plus shrinkage prestress losses were between two and eight times lower than those estimated for the design standards and approximately 50% of those measured in similar strength normal weight high performance concrete girders. The lower creep and shrinkage exhibited by HPLC was found to be caused by a synergy between the pre-soaked lightweight aggregate and the low water-to-cementitious material ratio matrix. That is, the water contained in the lightweight aggregate contributes to enhance hydration by providing an internal moist curing. The water in the aggregate also contributes to maintain a high internal relative humidity which reduces or eliminates autogenous shrinkage. This higher internal relative humidity also reduces creep by preventing load-induced water migration. Finally, lightweight aggregate exhibits a better elastic compatibility with the paste than normal weight aggregate. This improved elastic matching and the enhanced hydration are believed to reduce peak deformations at the ITZ which further decreases creep and shrinkage.

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

    NASA Technical Reports Server (NTRS)

    Zerwekh, R. P.

    1978-01-01

    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.

  7. Models for coupled diffusive/strain controlled growth of creep cavities

    SciTech Connect

    Lu, H.M.; Delph, T.J. )

    1993-08-01

    The importance of intergranular creep cavitation to high-temperature failure processes in metals and ceramics has been well-recognized for some time now. In general, creep cavity growth at elevated temperature is thought to occur by one of two processes. The first of these is diffusive growth, whereby matter is transported from the cavity surface and is deposited on the grain boundary. The second is strain-controlled growth, in which the cavity grows entirely as a consequence of creep deformation of the surrounding material under the action of an applied stress. Several models of cavity growth have been proposed in which these processes are coupled to each other and occur simultaneously. These models have attained some currency and have been used in several studies involving the growth of creep cavitation. The purpose of the present note is to investigate in some detail one particular class of these models.

  8. In situ tensile and creep testing of lithiated silicon nanowires

    SciTech Connect

    Boles, Steven T.; Kraft, Oliver; Thompson, Carl V.; Mönig, Reiner; Helmholtz Institute Ulm for Electrochemical Energy Storage , 89069 Ulm

    2013-12-23

    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.

  9. The mechanical creep compliance of tissue cells is gamma distributed

    E-print Network

    John M. Maloney; Krystyn J. Van Vliet

    2011-07-13

    Investigations of natural variation among cells within a population are essential for understanding the stochastic nature of tissue cell deformation under applied load. In the existing literature, the population variation of single-cell creep compliance has so far been modeled universally by using a log-normal distribution. Here we use optical stretching, a non-contact and relatively high-throughput technique for probing cell mechanics, to accumulate a sufficient data set that demonstrates robustly that cell compliance varies according to the similar but distinct gamma distribution. Additionally, we re-examine existing simulations that were originally proposed to justify a log-normal fit, and show that in fact these simulation data also correspond to the gamma distribution. Finally, we propose a general stochastic differential equation that analytically predicts a gamma distribution of creep compliance during cell stretching, as well as the Gaussian distribution of cell recovery that we observe experimentally upon removal of applied load. The population variation is well characterized by just a single parameter in each of the creep and recovery regimes. We expect our correction of a phenomenological distribution fit, enabled by an expansive data set for mesenchymal stem cells, to enable the development of more accurate constitutive laws to describe cytoskeletal deformation. These findings thus serve to replace an empirical distribution with a better-fitting model that rests on a more solid experimental and theoretical foundation, and also provides a basis to predict and understand the stochastic nature of the mechanical response of individual cells within populations.

  10. Creep Behavior of Near-Stoichiometric Polycrystalline Binary NiAl

    NASA Technical Reports Server (NTRS)

    Raj, S. V.

    2002-01-01

    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.

  11. Creep of Rocksalt: Microstructure and Hart's Mechanical Equation of State

    NASA Astrophysics Data System (ADS)

    Plookphol, T.; Cooper, R. F.; Stone, D. S.

    2001-12-01

    Hart's mechanical equation of state prescribes methods for efficiently gathering and extrapolating data pertaining to time-dependent deformation. The approach relies on the ability to characterize, first, the stress-strain rate behavior of a material at "constant structure," or "hardness state" and, second, the evolution of that structure -- work hardening and recovery -- throughout deformation. Constant structure "Hardness curves" can be generated using load relaxation experiments, which sweep out a spectrum of stress v. strain rate at nearly constant strain. It has been widely observed that hardness curves generated at different levels of work hardening scale with each other, that is, they can be translated in log-log space along lines of fixed slope so that they fit on top of each other. Despite the ubiquity of scaling among many varied materials, there has never been an experimental effort to establish a microscopic basis for such scaling. Too, there has never been a careful effort to establish the relationship between data generated from load relaxation and those obtained from creep tests. The benefit of such efforts would be to provide experimenters with tools for extending experimental techniques to lower strain rates -- short duration load relaxation experiments can routinely achieve 10-8 s-1 and, with effort, 10-10 s-1. Such efforts might also lead to a better understanding of power law creep itself, for which there is no universally accepted microscopic model. In this work we investigated the creep, stress-change, and load relaxation behavior of single crystal rock-salt at 673K and 973K deformed under compression in the [100] orientation. Subgrain size distributions of the specimens deformed at 973K were measured using light microscopy. In load relaxation experiments we found that hardness states correlated uniquely with differences in average subgrain size but not dislocation density. To within measurement error, subgrain size distributions were similar to each other differing only in the mean diameter, depending on stress, but not in the shape of the distributions; it is conjectured that microstructural similarity is the physical basis for scaling in load relaxation. A correspondence rule was established between stress relaxation and creep; the data suggest that during primary creep the material evolves through a range of hardness states until steady state strain rate is achieved.

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

    NASA Astrophysics Data System (ADS)

    Trinh, B. T.; Hackl, K.

    2014-07-01

    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.

  13. Creep of plasma-sprayed-ZrO2 thermal-barrier coatings

    NASA Technical Reports Server (NTRS)

    Firestone, R. F.; Logan, W. R.; Adams, J. W.; Bill, R. C., Jr.

    1982-01-01

    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 6900, 13,800, and 24,100 kPa (1000, 2000, and 3500 psi) and temperatures of 1100, 1250, and 1400 C. The coatings were stabilized with lime, MgO, and two different concentrations of Y2O3. 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 while the stress, particle size, and porosity had a lesser effect. Creep deformation was due to cracking and particle sliding.

  14. (Irradiation creep of graphite)

    SciTech Connect

    Kennedy, C.R.

    1990-12-21

    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.

  15. Slow and Go: Pulsing slip rates on the creeping section of the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Turner, Ryan C.; Shirzaei, Manoochehr; Nadeau, Robert M.; Bürgmann, Roland

    2015-08-01

    Rising and falling slip rates on the creeping section of the San Andreas Fault have been inferred from variations of recurrence intervals of characteristically repeating microearthquakes, but this observation has not previously been confirmed using modern geodetic data. Here we report on observations of this "pulsing" slip obtained from advanced multitemporal interferometric synthetic aperture radar (InSAR) data, confirmed using continuous GPS sites of the Plate Boundary Observatory. The surface deformation time series show a strong correlation to the previously documented slip rate variations derived from repeating earthquakes on the fault interface, at various spatial and temporal scales. Time series and spectral analyses of repeating earthquake and InSAR data reveal a quasiperiodic pulsing with a roughly 2 year period along some sections of the fault, with the earthquakes on the fault interface lagging behind the far-field deformation by about 6 months. This suggests a temporal delay between the pulsing crustal strain generated by deep-seated shear and the time-variable slip on the shallow fault interface, and that at least in some places this process may be cyclical. There exist potential impacts for time-dependent seismic hazard forecasting in California and, as it becomes better validated in the richly instrumented natural laboratory of the central San Andreas Fault, the process used here will be even more helpful in characterizing hazard and fault zone rheology in areas without California's geodetic infrastructure.

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

    SciTech Connect

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

    2007-03-30

    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.

  17. Observation of Grain Rotations to Elucidate the Development of Crystal Preferred Orientation during Diffusion Creep

    NASA Astrophysics Data System (ADS)

    Maruyama, G.; Hiraga, T.

    2014-12-01

    The seismic anisotropy in Earth's upper mantle is explained by the crystallographic preferred orientation (CPO) of rock-forming minerals, which have anisotropic elasticity. Our team showed that the CPO of forsterite is produced even during diffusion creep (Miyazaki et al. 2013). The purpose of this study is to understand the mechanism of the development of CPO of forsterite by observations of samples surface after the sample deformation where the fine-scale strain markers were imposed.We deformed cylindrical polycrystalline samples of synthesized forsterite plus 20 vol. % diopside at its diffusion creep regime. We polished the lateral side of the sample where we imposed grooves parallel to the compression axis of the sample using a focused ion beam. These marker lines allow us to observe grain rotation due to a plastic deformation of the sample. After the high temperature compression creep experiment under atmosphere, we observed the marker lines under scanning electron microscope.We succeeded to observe the marker lines after the deformation. Strain of bulk sample and of the marker line exhibit the similar value indicating the similar deformation proceeded both at bulk and surface regions of the samples. Grain rotation, which is identified by misfits of the markers at grain boundaries and rotation of intra-granular markers, were observed in all the samples. No distortion of the markers within the grains was found indicating the absence of intragranular deformation process such as a glide of dislocations; however, in the samples deformed at high stress (~300 MPa), curved intra-granular markers were observed, which is consistent with dislocation activity at high stress condition. Our results show the significant grain rotation, which is necessary process for the development of CPO, during diffusion creep as well as the ability of identification of the deformation mechanism of the bulk sample by the observation of the sample surface.

  18. Calculation of radiation-induced creep and stress relaxation

    NASA Astrophysics Data System (ADS)

    Nagakawa, Johsei

    1995-08-01

    Numerical calculation based on a computer simulation of point defect kinetics under stress was performed to predict radiation-induced deformation in an Inconel X-750 bolt in a LWR core and for a 316 stainless steel blanket in experimental fusion reactors with the water-coolant scenario. Although the displacement rate is rather low, modest irradiation creep with nearly linear stress dependence was predicted below 200 MPa at 300°C in the LWR core. This low stress dependence causes significant stress relaxation, which coincides with the experimental data to 2 dpa. An almost equal amount of enhanced irradiation creep strain was predicted at 60°C in both solution annealed and cold worker 316 stainless steel in the water-cooled blanket. The stress relaxation is practically not expected without irradiation in both the cases, but the calculation predicts that it is definitely expected under irradiation.

  19. Stress versus temperature dependent activation energies in creep

    NASA Technical Reports Server (NTRS)

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

    1990-01-01

    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.

  20. Creep effects in diffusion bonding of oxygen-free copper

    E-print Network

    Moilanen, Antti

    Diffusion is the transport of atoms or particles through the surrounding material. Various microstructural changes in metals are based on the diffusion phenomena. In solid metals the diffusion is closely related to crystallographic defects. In single-component metals the dominant mechanism of diffusion is the vacancy mechanism. Diffusion bonding is a direct technological application of diffusion. It is an advanced solidstate joining process in which the surfaces of two components are brought to contact with each other and heated under a pressing load in a controlled environment. During the process, the contact surfaces are bonded by atomic diffusion across the interface and as a result, one solid piece is formed. The condition of high temperature and low applied stress combined with relatively long process duration enables the creep effects to take place in bonded metals. Furthermore, creep causes unwanted permanent deformations in the bonded components. Some authors suggest that there could be a threshold fo...

  1. Sandia/Stanford Unified Creep Plasticity Damage Model for ANSYS

    Energy Science and Technology Software Center (ESTSC)

    2006-09-03

    A unified creep plasticity (UCP) model was developed, based upon the time-dependent and time-independent deformation properties of the 95.5Sn-3.9Ag-0.6Cu (wt.%) soldier that were measured at Sandia. Then, a damage parameter, D, was added to the equation to develop the unified creep plasticity damage (UCPD) model. The parameter, D, was parameterized, using data obtained at Sandia from isothermal fatigue experiments on a double-lap shear test. The softwae was validated against a BGA solder joint exposed tomore »thermal cycling. The UCPD model was put into the ANSYS finite element as a subroutine. So, the softwae is the subroutine for ANSYS 8.1.« less

  2. Low oxygen fugacity dependency for the deformation of partially molten lherzolite

    NASA Astrophysics Data System (ADS)

    Wang, Yongfeng; Zhang, Junfeng; Jin, Zhenmin; Kohlstedt, David L.

    2012-12-01

    We present the results of an experimental investigation of the influence of oxygen fugacity on the deformation of a partially molten spinel lherzolite using a 0.1 MPa gas-media creep rig under temperatures of 1160-1190 °C, stresses of 4-74 MPa and well-controlled oxygen fugacities of 10- 7 to 10- 11 MPa. The partially molten spinel lherzolite was deformed by a dislocation-mediated creep process such as dislocation creep or dislocation-accommodated grain boundary sliding (DGBS) (n = 3.5 ± 0.3) as well as in the diffusion creep regime (n = 1.2 ± 0.2). The average oxygen fugacity exponent of lherzolite is 0.04 ± 0.02, which is significantly smaller than the values measured for olivine single crystals (0.10-0.36) and dunite rocks (0.20) deformed by dislocation creep. We attribute the low oxygen fugacity exponent of partially molten lherzolite samples either to the operation of grain boundary sliding, if DGBS dominates the deformation, or to the presence of pyroxenes whose deformation has a weak or no dependency on oxygen fugacity, if dislocation creep dominates the deformation. In the latter case, the oxygen fugacity exponent decreases rapidly with decreasing volume fraction of olivine. The low oxygen fugacity exponent for our partially molten lherzolite samples implies that dislocation creep or DGBS of mantle peridotite will most likely be insensitive to variations of oxygen fugacity in the upper mantle.

  3. Transient Creep and Strain Energy Dissipation: An Experimental Perspective

    NASA Astrophysics Data System (ADS)

    Faul, Ulrich; Jackson, Ian

    2015-05-01

    Energy dissipation due to intrinsic attenuation occurs at elevated temperatures in rocks as a result of a range of processes. Examples where small-strain, transient deformation occurs are seismic waves, tidal deformation, and at longer timescales post-glacial rebound and far-field post-seismic deformation. Experiments at mantle temperatures and seismic frequencies show that grain boundary sliding is a key process that results in a broad absorption band, as indicated by seismic observations. Models of grain boundary sliding predict a smooth transition from elastic behavior through an anelastic regime toward viscous (Maxwell) behavior, consistent with experimental observations. Other mechanisms that may contribute to dissipation in Earth, at least locally, are dislocations and melt. Extrapolation of the laboratory data shows that first-order observations of planetary behavior and structure can be explained by the effects of temperature and pressure on transient creep properties, but that locally, additional mechanisms are required.

  4. Effect of Annealing Time on Microstructural Evolution and Deformation Characteristics in 10Mn1.5Al TRIP Steel

    NASA Astrophysics Data System (ADS)

    Han, Qihang; Zhang, Yulong; Wang, Li

    2015-05-01

    To investigate microstructural evolution and its effects on the deformation behaviors of cold-rolled 10Mn1.5Al TRIP steel, a series of intercritical annealing treatments with various holding times from 3 minutes to 48 hours were conducted. With the increase of the holding time from 3 minutes to 12 hours, the elongation was improved from 15 to 42 pct, while the tensile strength was only reduced from 1210 to 1095 MPa; the strength-ductility combination thus exceeded 45 GPa pct. Austenite was found to coexist with martensite within deformed grains, which reduced the strain concentration at the interface. The austenite transformation fraction, as measured from the {220} peaks, after 3 minutes annealing was half that after 12 hours annealing. This is an indication that the slip systems were more easily activated in the micro-scaled grains compared with nano-scaled grains. Therefore, although the stability of austenite would have increased during annealing, size-induced slip suppression was reduced. Thus, more strain was accommodated in the austenite, facilitating a greater strain-induced transformation and better ductility.

  5. Dimensional change of dental amalgam and a suggested correlation between marginal integrity and creep.

    PubMed

    Paffenbarger, G C; Rupp, N W; Patel, P R

    1979-07-01

    Discussion of a possible correlation of marginal integrity and degree of creep resulting from relative resistance of amalgams to deformation caused by expansion is included in this study of the effect of phase changes on the dimensional stability of amalgams. PMID:379099

  6. Characterization of the elastic and viscoelastic properties of dentin by a nanoindentation creep test.

    PubMed

    Chuang, Shu-Fen; Lin, Shih-Yun; Wei, Pal-Jen; Han, Chang-Fu; Lin, Jen-Fin; Chang, Hsien-Chang

    2015-07-16

    Dentin is the main supporting structure of teeth, but its mechanical properties may be adversely affected by pathological demineralization. The purposes of this study were to develop a quantitative approach to characterize the viscoelastic properties of dentin after de- and re-mineralization, and to examine the elastic properties using a nanoindentation creep test. Dentin specimens were prepared to receive both micro- and nano-indentation tests at wet and dry states. These tests were repeatedly performed after demineralization (1% citric acid for 3 days) and remineralization (artificial saliva immersion for 28 days). The nanoindentation test was executed in a creep mode, and the resulting displacement-time responses were disintegrated into primary (transient) and secondary (viscous) creep. The structural changes and mineral densities of dentin were also examined under SEM and microCT, respectively. The results showed that demineralization removed superficial minerals of dentin to the depth of 400 ?m, and affected its micro- and nano-hardness, especially in the hydrate state. Remineralization only repaired the minerals at the surface layer, and partially recovered the nanohardness. Both the primary the secondary creep increased in the demineralized dentin, while the hydration further enhanced creep deformation of untreated and remineralized dentin. Remineralization reduced the primary creep of dentin, but did not effectively increase the viscosity. In conclusion, water plasticization increases the transient and viscous creep strains of demineralized dentin and reduces load sustainability. The nanoindentation creep test is capable of analyzing the elastic and viscoelastic properties of dentin, and reveals crucial information about creep responses. PMID:25911251

  7. Temperature-dependent creep buckling of plates

    NASA Technical Reports Server (NTRS)

    Ross, D. A.; Berke, L.

    1981-01-01

    Time-dependent lateral deflection of flat rectangular plates is predicted by the Norton-Bailey (Norton 1929, Bailey 1935) power law for material creep. The plates have a through-thickness steady-state temperature distribution, and the effects are considered by using Maxwell's law to modify the power creep law. Equations are derived for creep exponents of 3 and 5, using the sandwich plate element to predict creep buckling of plates. Predictions of creep buckling with a temperature variation between the inner and outer plate surfaces are found to be somewhat dependent on the creep buckling relationship assumed. When significant scatter justifies a variation in the creep constants up to an order of magnitude, discrepancies in predictions using the two exponents are reasonable, and for one engineering material, the predictions have the same degree of agreement with experimental data as have the respective creep laws.

  8. Experimental Creep Life Assessment for the Advanced Stirling Convertor Heater Head

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

    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.

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

    SciTech Connect

    Cappelaere, Chantal; Limon, Roger; Duguay, Chrstelle; Pinte, Gerard; Le Breton, Michel; Bouffioux, Pol; Chabretou, Valerie; Miquet, Alain

    2012-02-15

    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)

  10. Corrosion and creep of dental amalgam.

    PubMed

    Gjerdet, N R; Espevik, S

    1978-01-01

    The influence of stress on corrosion was investigated by a potentiostatic technique. Amalgrams with low creep, both with and without gamma2-phase, revealed small increases in current with stress application while alloys with high creep exhibited large increases in current. Rupture of protective oxide due to increased strain for high creep alloys may explain the phenomenon. PMID:277492

  11. Improved Creep Measurements for Ultra-High Temperature Materials

    NASA Technical Reports Server (NTRS)

    Hyers, Robert W.; Ye, X.; Rogers, Jan R.

    2010-01-01

    Our team has developed a novel approach to measuring creep at extremely high temperatures using electrostatic levitation (ESL). This method has been demonstrated on niobium up to 2300 C, while ESL has melted tungsten (3400 C). This method has been extended to lower temperatures and higher stresses and applied to new materials, including a niobium-based superalloy, MASC. High-precision machined spheres of the sample are levitated in the NASA MSFC ESL, a national user facility and heated with a laser. The samples are rotated with an induction motor at up to 30,000 revolutions per second. The rapid rotation loads the sample through centripetal acceleration, producing a shear stress of about 60 MPa at the center, causing the sample to deform. The deformation of the sample is captured on high-speed video, which is analyzed by machine-vision software from the University of Massachusetts. The deformations are compared to finite element models to determine the constitutive constants in the creep relation. Furthermore, the non-contact method exploits stress gradients within the sample to determine the stress exponent in a single test.

  12. Advances in Non-contact Measurement of Creep Properties

    NASA Technical Reports Server (NTRS)

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

    2009-01-01

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

  13. Testing Protocol for Module Encapsulant Creep (Presentation)

    SciTech Connect

    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

    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.

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

    SciTech Connect

    Przystupa, Marek A.

    2007-12-13

    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

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

    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.

  16. Counter-intuitive Behavior of Subduction Zones: Weak Faults Rupture, Strong Faults Creep

    NASA Astrophysics Data System (ADS)

    Wang, K.; Gao, X.; Bilek, S. L.; Brown, L. N.

    2014-12-01

    Subduction interfaces that produce great earthquakes are often said to be "strongly coupled", and those that creep are said to be "weakly coupled". However, the relation between the strength and seismogenic behavior of subduction faults is far from clear. Seismological and geodetic observations of earthquake rupture usually provide information only on stress change, not fault strength. In this study, we infer fault strength by calculating frictional heating along megathrusts and comparing results with heat flow measurements. We find that stick-slip megathrusts that have produced great earthquakes such as at Japan Trench and northern Sumatra have very low apparent friction coefficients (~ 0.02 - 0.03), but megathrusts that creep such as at Northern Hikurangi and Manila Trench have higher values (up to ~0.13). The differnce cannot be explained by coseismic dynamic weakening of the stick-slip megathrusts, because the average stress drop in great earthquakes is usually less than 5 MPa, equivalent to a coseismic reduction of apparent friction coefficient by less than ~0.01. Therefore our results indicate differences in the static strength of different subduction faults. Why are the creeping faults stronger? We think it is related to their creeping mechanism. Very rugged subducting seafloor tends to cause creep and hinder great earthquake rupture (Wang and Bilek, 2014). In contrast, all giant earthquakes have occurred at subduction zones with relatively smooth subducting seafloor. Large geometrical irregularities such as seamounts generate heterogeneous structure and stresses that promote numerous small and medium size earthquakes and aseismic creep. The creeping is a process of breaking and wearing of geometrical irregularities in a deformation zone and is expected to be against relatively large resistance (strong creep). This is different from the creeping of smooth faults due to the presence of weak fault gouge (weak creep) such as along the creeping segment of the San Andreas fault. The general correlation between subducting seafloor ruggedness, creeping, and greater heat dissipation, if further verified, provides a new perspective in assessing earthquake and tsunami hazards for risk mitigation. Wang, K., and S. L. Bilek. Tectonophysics 610, 1-24 (2014).

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    SciTech Connect

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

    2010-01-02

    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.

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

    NASA Astrophysics Data System (ADS)

    Wen, Xingshuo

    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.

  20. COMPARISON OF CLADDING CREEP RUPTURE MODELS

    SciTech Connect

    P. Macheret

    2000-06-12

    The objective of this calculation is to compare several creep rupture correlations for use in calculating creep strain accrued by the Zircaloy cladding of spent nuclear fuel when it has been emplaced in the repository. These correlations are used to calculate creep strain values that are then compared to a large set of experimentally measured creep strain data, taken from four different research articles, making it possible to determine the best fitting correlation. The scope of the calculation extends to six different creep rupture correlations.

  1. Creep of CoO single crystals.

    NASA Technical Reports Server (NTRS)

    Clauer, A. H.; Seltzer, M. S.; Wilcox, B. A.

    1971-01-01

    The crystals were creep tested in compression over ranges of temperature, stress, and oxygen pressure. The creep curves were S-shaped, and only the inflection creep rate was analyzed. A formula is presented for the inflection creep rate in the range from 1000 to 1200 C, 850 to 1700 psi, and 0.001 to 1 atm oxygen. Slip was found to occur on two orthogonal slip systems. The presence of subboundaries was observed by optical and transmission electron microscopy. It is suggested that the creep rate is controlled by oxygen diffusion.

  2. Life at Mission Creep U

    ERIC Educational Resources Information Center

    Dubrow, Greg; Moseley, Bryan; Dustin, Daniel

    2006-01-01

    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…

  3. Tensile creep behavior of polycrystalline alumina fibers

    NASA Technical Reports Server (NTRS)

    Yun, H. M.; Goldsby, J. C.

    1993-01-01

    Tensile creep studies were conducted on polycrystalline Nextel 610 and Fiber FP alumina fibers with grain sizes of 100 and 300 nm, respectively. Test conditions were temperatures from 800 to 1050 C and stresses from 60 to 1000 MPa. For both fibers, only a small primary creep portion occurred followed by steady-state creep. The stress exponents for steady-state creep of Nextel 610 and Fiber FP were found to be about 3 and 1, respectively. At lower temperatures, below 1000 C, the finer grained Nextel 610 had a much higher 0.2 percent creep strength for 100 hr than the Fiber FP; while at higher temperatures, Nextel 610 had a comparable creep strength to the Fiber FP. The stress and grain size dependencies suggest Nextel 610 and Fiber FP creep rates are due to grain boundary sliding controlled by interface reaction and Nabarro-Herring mechanisms, respectively.

  4. ATOMISTIC SIMULATIONS OF DIFFUSIONAL CREEP IN A NANOCRYSTALLINE BODY-CENTERED CUBIC MATERIAL

    SciTech Connect

    Paul C. Millett; Tapan Desai; Vesselin Yamakov; Dieter Wolf

    2008-08-01

    Molecular dynamics (MD) simulations are used to study diffusion-accommodated creep deformation in nanocrystalline molybdenum, a body-centered cubic metal. In our simulations, the microstructures are subjected to constant-stress loading at levels below the dislocation nucleation threshold and at high temperatures (i.e., T > 0.75Tmelt), thereby ensuring that the overall deformation is indeed attributable to atomic self-diffusion. The initial microstructures were designed to consist of hexagonally shaped columnar grains bounded by high-energy asymmetric tilt grain boundaries (GBs). Remarkably the creep rates, which exhibit a double-exponential dependence on temperature and a double power-law dependence on grain size, indicate that both GB diffusion in the form of Coble creep and lattice diffusion in the form of Nabarro–Herring creep contribute to the overall deformation. For the first time in an MD simulation, we observe the formation and emission of vacancies from high-angle GBs into the grain interiors, thus enabling bulk diffusion.

  5. Research the dynamical characteristics of slow deformation waves as a rock massif response to explosions during its outworking

    NASA Astrophysics Data System (ADS)

    Hachay, Olga; Khachay, Oleg; Shipeev, Oleg

    2015-04-01

    As a result of long-term natural geomechanics and geophysical observation data on mines of complex ore rocks, generalization of the non-linear reaction of rock massif to heavy dynamic influences have been established. In addition, pendulum type waves have been observed and the sources of them have been located inside geoblocks of different hierarchic levels (Oparin et al., 2010). At the same time, these waves propagate with wide low (compared with seismic waves) velocity values (Kurlenja et al., 1993; Oparin et al., 2006). Research into the massif state with the use of the dynamic systems theory approach (Naimark et al., 2009; Chulichkov, 2003; Hachay et al., 2010) has been developed to ascertain the criteria of dissipative regimes changing for real rock massifs, which are under heavy man-caused influence. To realize such research we used the data from the seismic record of the Tashtagol mine for the two-year period from June 2006 up to June 2008. We used the space-time coordinates for all dynamic massif event responses, which occurred during that period inside the mine space and for the explosions - values fixed by seismic station energy (Hachay et al., 2010). The phase diagrams of the massif state for the northern and southern parts of the mine space were plotted in coordinates Ev(t) and d(Ev(t))/dt, t - time - in parts of 24 hours, Ev - the dissipated massive seismic energy - in joules. Hachay et al., (2010) analysed the morphology of seismic response phase trajectories on the explosion influences during different serial intervals in the southern part of the mine. In that period, according to data for different explosions in the mine, the majority of the total energy had been injected into the southern part of the mine. Moreover, at the end of 2007, just in the southern part, the strongest rock burst during the whole history of the working mine happened. We developed a new processing method of seismological information in real, which we can use directly in the mine to estimate the changing state of the rock burst in the massif by its outworking. As a result we have selected a typical morphology of massif response phase trajectories, which were locally, over time, in a stable state: on the phase plane the local area presented as a ball of twisted trajectories with some not far removed points from the ball, which had not exceeded energy of more than 105 joules. For some time intervals those removed points exceeded 105 joules, achieving 106 joules and even 109 joules (Hachay et al., 2010). Introduction of the additional velocity parameter of slow deformation wave propagation allowed us, with the use of phase diagrams, to identify the hierarchic structure. Further, we can use that information for the modelling and interpretation of seismic and deformation waves in hierarchic structures (Hachay et al., 2012). That method can be useful in building-up an understanding of the resonance outshooting of catastrophic dynamic events and prevent these events. References 1.Chulichkov A. (2003) Mathematical models of nonlinear dynamics. Moscow: Phismatlit. 294p. 2.Hachay O., Khachay O.Yu., Klimko V., et al. (2010) Reflection of synergetic features of rock massif state under the man-caused influence from the data of a seismological catalogue. Mining Information-Analytic Bulletin, Moscow, Mining book, 6, pp.259-271. 3.Hachay O., Khachay A.Yu. (2012) Research of stress-deforming state of hierarchic medium. Proceedings of the Third Tectonics and Physics Conference at the Institute of the Physics of the Earth 8-12 October 2012, Moscow, IFZ RAS, pp.114-117. 4.Kurlenja M., Oparin V., Vostrikov V. (1993) About forming elastic wave trains by impulse excitation of block medium. Waves of pendulum type U?. DAN USSR, V.133, 4, pp.475-481. 5.Naimark Yu., Landa P. (2009). Stochastic and chaotic oscillations. Moscow, Knigniy dom ,'LIBROKOM', 424 p. 7.Oparin V., Vostrikov V., Tapsiev A. et al. (2006) About one kinematic criterion of forecasting of the limiting massif state with use of seismological data , FTPRPI, 6, pp.3-10.

  6. Impulsive radon emanation on a creeping segment of the San Andreas fault, California

    USGS Publications Warehouse

    King, C.-Y.

    1985-01-01

    Radon emanation was continuously monitored for several months at two locations along a creeping segment of the San Andreas fault in central California. The recorded emanations showed several impulsive increases that lasted as much as five hours with amplitudes considerably larger than meteorologically induced diurnal variations. Some of the radon increases were accompanied or followed by earthquakes or fault-creep events. They were possibly the result of some sudden outbursts of relatively radon-rich ground gas, sometimes triggered by crustal deformation or vibration. ?? 1985 Birkha??user Verlag.

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

    PubMed

    Boehlert, C J; Longanbach, S C

    2011-06-01

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

  8. Monitoring microstructural evolution of alloy 617 with non-linear acoustics for remaining useful life prediction; multiaxial creep-fatigue and creep-ratcheting

    SciTech Connect

    Lissenden, Cliff; Hassan, Tasnin; Rangari, Vijaya

    2014-10-30

    The research built upon a prior investigation to develop a unified constitutive model for design-­by-­analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-­fatigue and creep-­ratcheting tests were conducted on the nickel-­base Alloy 617 at 850 and 950°C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load-­controlled cycling, are major concerns for NGNP design. This research project aimed at characterizing the microstructure evolution mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method was researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter was shown to correlate with microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-­fatigue and creep-­ratcheting deformation. Mechanical testing was conducted to provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-­fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-­ratcheting. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Optical Microscopy were conducted to correlate the beta parameter with individual microstructure mechanisms. We researched application of the harmonic generation method to tubular mechanical test specimens and pipes for nondestructive evaluation. Tubular specimens and pipes act as waveguides, thus we applied the acoustic harmonic generation method to guided waves in both plates and shells. Magnetostrictive transducers were used to generate and receive guided wave modes in the shell sample and the received signals were processed to show the sensitivity of higher harmonic generation to microstructure evolution. Modeling was initiated to correlate higher harmonic generation with the microstructure that will lead to development of a life prediction model that is informed by the nonlinear acoustics measurements.

  9. High-resolution measurements of pressure solution creep

    NASA Astrophysics Data System (ADS)

    Dysthe, Dag Kristian; Renard, Francois; Feder, Jens; Jamtveit, Bjørn; Meakin, Paul; Jøssang, Torstein

    2003-07-01

    Two dilatometers with high precision and stability have been developed for measurement of indentation by pressure solution creep. The indentation of gold wires or glass cylinders into sodium chloride has been measured with down to 10 Å accuracy and 6% precision. The indentation curves show a strong history dependence and the indentation rate decreases by three orders of magnitude over 400 h. The indentation mechanism is shown to be a pressure solution creep process in which material is dissolved at the indentor-sodium chloride contacts and transported to the free surface, where it precipitates in the proximity of the indentors. The indentation rates are not controlled by precipitation rates, the density of preexisting dislocations in the material, by change in the contact widths, or by ordinary plastic deformation. Small amplitude sinusoidal variations of temperature and normal stress are shown to have a large effect on the indentation rate. Moreover, sudden increase in normal stress from the indentor on the sodium chloride is shown to initiate an increased, time-dependent indentation rate. A model for pressure solution creep with time-dependent contact sizes explains the history dependence of the indentation data presented.

  10. Patterns of brittle deformation under extension on Venus

    NASA Technical Reports Server (NTRS)

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

    1994-01-01

    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.

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

    SciTech Connect

    Shingledecker, John P; Pharr, George Mathews

    2012-01-01

    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.

  12. Room Temperature Creep Of SiC/SiC Composites

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    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.

  13. Creep cavity observation using liquid metal embrittlement

    SciTech Connect

    Reiley, T.C.

    1981-01-01

    Grain boundary cavities, which form during high-temperature deformation and which may be considered incipient intergranular cracks, have been difficult to observe at the early growth stages. To examine grain boundaries in unfailed specimans one is normally limited to metallographic or transmission electron microscopy (TEM) techniques, the first having resolution limitations (r/sub cavity/approx.l..mu..m) and the second having limitations in the probability of seeing a cavity (especially for large-grained, low-density specimens) or of seeing a cavity which is undisturbed by the thinning process required for TEM. Other observational techniques involving hydrogen attack or low-temperature impact loading have been used to create brittle intergranular failures to observe grain boundary features, such as creep cavities on pre-crept specimens. These techniques are not, however, applicable to most metals, and as such, the need remains for a more general observational technique. Such a new technique employing liquid metal embrittlement (LME) is described below, and, given that most metals are severely embrittled by at least one liquid metal, this approach may satisfy requirements of general applicability.

  14. Effect of Nb and Cu on the high temperature creep properties of a high Mn–N austenitic stainless steel

    SciTech Connect

    Lee, Kyu-Ho; Suh, Jin-Yoo; Huh, Joo-Youl; Park, Dae-Bum; Hong, Sung-Min; Shim, Jae-Hyeok; Jung, Woo-Sang

    2013-09-15

    The effect of Nb and Cu addition on the creep properties of a high Mn–N austenitic stainless steel was investigated at 600 and 650 °C. In the original high Mn–N steel, which was initially precipitate-free, the precipitation of M{sub 23}C{sub 6} (M = Cr, Fe) and Cr{sub 2}N took place mostly on grain boudaries during creep deformation. On the other hand, the minor addition of Nb resulted in high number density of Z-phases (CrNbN) and MX (M = Nb; X = C, N) carbonitrides inside grains by combining with a high content of N, while suppressing the formation of Cr{sub 2}N. The addition of Cu gave rise to the independent precipitation of nanometer-sized metallic Cu particles. The combination of the different precipitate-forming mechanisms associated with Z-phase, MX and Cu-rich precipitates turned out to improve the creep-resistance significantly. The thermodynamics and kinetics of the precipitation were discussed using thermo-kinetic simulations. - Highlights: • The creep rupture life was improved by Nb and Cu addition. • The creep resistance of the steel A2 in this study was comparable to that of TP347HFG. • The size of Z-phase and MX carbonitride did not change significantly after creep test. • The nanometer sized Cu-rich precipitate was observed after creep. • The predicted size of precipitates by MatCalc agreed well with measured size.

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

    SciTech Connect

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

    1994-05-01

    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.

  16. The Convoluted Earthquake Cycle of a Creeping Fault

    NASA Astrophysics Data System (ADS)

    Johanson, I. A.; Taira, T.; Turner, R. C.; Nadeau, R. M.; Burgmann, R.

    2014-12-01

    The San Juan Bautista (SJB) segment of the San Andreas fault is an area of complex faulting; it experiences steady creep and produces slow slip events (SSEs) and earthquakes. While the historic record indicates as many as seven M>6 events in the 19th century, the largest earthquake in the last 100 years was the 1998 M5.1 San Juan Bautista earthquake. This earthquake occurred within an area of heterogeneously distributed creep and subsequently creepmeters and strainmeters detected a triggered SSE equivalent to a M5 that evolved over a week. Here, we present the results of a multi-pronged investigation into slip throughout the earthquake cycle on the San Juan Bautista segment. This includes a re-examination of the aftershock sequence of the 1998 M5.1 earthquake, which more clearly defines the fault area ruptured in the event. A new set of characteristically repeating earthquakes (CREs) provides insight into the decay of the triggered SSE and the distribution of interseismic creep, which compares favorably with a model from geodetic data. The analysis indicates that at seismogenic depths, the time period of enhanced creep was as much as six years, rather than one week. CREs also reveal pulses of aseismic slip in the Northern portion of the Creeping Section of the San Andreas fault near SJB. We further use 20 years of InSAR data over the San Juan Bautista region to investigate the variability of surface creep within this time span; using the Small Baseline Subset approach to generate an ordered time series from a set of interferometric pairs. While distinguishing annual variations due to groundwater changes from tectonic motions is difficult, we use principle component analysis to isolate creep variations due to the 1998 earthquake and SSE. These diverse data sets provide valuable information on the interactions between earthquakes and aseismic slip that occurs in various depth ranges in the fault zone. Results from this work provide insight into the role of aseismic fault slip transients in earthquake occurrence and clustering.

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

    SciTech Connect

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

    2013-01-01

    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.

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

    NASA Astrophysics Data System (ADS)

    Kishore, R.

    2009-04-01

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

  19. Creep of Structural Nuclear Composites

    SciTech Connect

    Will Windes; R.W. Lloyd

    2005-09-01

    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.

  20. Creep and shrinkage effects on integral abutment bridges

    NASA Astrophysics Data System (ADS)

    Munuswamy, Sivakumar

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

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

    SciTech Connect

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

    2010-11-01

    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.

  2. High temperature creep of SiC densified using a transient liquid phase

    SciTech Connect

    Jou, Z.C.; Virkar, A.V. ); Cutler, R.A. )

    1991-09-01

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

  3. Theoretical and practical differences between creep and relaxation Poisson's ratios in linear viscoelasticity

    NASA Astrophysics Data System (ADS)

    Aili, Abudushalamu; Vandamme, Matthieu; Torrenti, Jean-Michel; Masson, Benoit

    2015-08-01

    Poisson's ratio is a well-defined parameter in elasticity. For time-dependent materials, multiple definitions based on the ratios between lateral and axial deformations are available. Here, we focus ourselves on the two most widely used definitions in the time domain, which define time-dependent functions that we call relaxation Poisson's ratio and creep Poisson's ratio. Those two ratios are theoretically different, but are linked in an exact manner through an equation we derive. We show that those two functions are equal at both initial and large times and that their derivatives with respect to time also are. Based on simple rheological models for both the deviatoric and volumetric creep behaviors, we perform a parametric study and show that the difference between those two time-dependent Poisson's ratios can be significant. However, based on creep data available in the literature, we show that, for cementitious materials, this difference can be negligible or not, depending on the case.

  4. Control of epoxy creep using graphene.

    PubMed

    Zandiatashbar, Ardavan; Picu, Catalin R; Koratkar, Nikhil

    2012-06-11

    The creep behavior of epoxy-graphene platelet (GPL) nanocomposites with different weight fractions of filler is investigated by macroscopic testing and nanoindentation. No difference is observed at low stress and ambient temperature between neat epoxy and nanocomposites. At elevated stress and temperature the nanocomposite with the optimal weight fraction, 0.1 wt% GPLs, creeps significantly less than the unfilled polymer. This indicates that thermally activated processes controlling the creep rate are in part inhibited by the presence of GPLs. The phenomenon is qualitatively similar at the macroscale and in nanoindentation tests. The results are compared with the creep of epoxy-single-walled (SWNT) and multi-walled carbon nanotube (MWNT) composites and it is observed that creep in both these systems is similar to that in pure epoxy, that is, faster than creep in the epoxy-GPL system considered in this work. PMID:22378720

  5. Compression creep of filamentary composites

    NASA Technical Reports Server (NTRS)

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

    1988-01-01

    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.

  6. Structural Benchmark Creep Testing for the Advanced Stirling Convertor Heater Head

    NASA Technical Reports Server (NTRS)

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

    2008-01-01

    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.

  7. Plastic Creep and Brittle-Ductile Transition in Hydrated Rocks of the Plate Interface

    NASA Astrophysics Data System (ADS)

    Reynard, B.

    2014-12-01

    Geophysical observations suggest that the formation of hydrous phyllosilicate-bearing rocks such as serpentinites favor aseismic slip on the plate interface. I review our current understanding of deformation of serpentines and similar phyllosilicates in the first 100 km of subduction and discuss some pending questions on measurements and modeling of the behavior and properties of the complex serpentinite rocks. Experimental studies suggest that serpentines have low enough mechanical strength to act as a "stabilizer" of stable creep, but the actual strength of serpentinites will depend on the exact nature of the crystallographic structure and fabric of the stable serpentine variety. Low-temperature, flat-layered lizardite has strong anisotropy in strength. Lizardite-serpentinite strength will depend crystal-preferred orientation (CPO), with isotropic texture having high strength (>300 MPa) and foliated serpentinites having small strength (<100 MPa), independent of temperature, pressure, and strain rate. Thus, the transition between brittle and plastic (or stable creep) behavior may result from progressive deformation. High-temperature serpentine antigorite has a complex corrugated-layered structure, and complex deformation modes were evidenced from experimental studies. Mechanical strength shows a strong stress dependence, suggesting dislocation-creep, and low temperature dependence, suggesting plastic behavior. Extrapolation of experimental results to natural strain rates suggests that antigorite-serpentinites have low strength (<100 MPa or lower), and will favor stable-creep. However, the extrapolation relies on mechanical flow laws that may not apply to serpentine. Electron microscopy observations reveals dislocation-like deformation mechanisms that are not sufficient to explain global deformation of antigorite aggregates, and that are likely accompanied by dissolution-precipitation at low natural strain-rates. Establishing reliable flow laws relevant to the subduction interface in the 30-100 km depth range will require further experimental investigations of such mechanisms.

  8. Viscoelastic creep of high-temperature concrete

    SciTech Connect

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

    1985-01-01

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

  9. Application of rate-and-state friction laws to creep compaction of unconsolidated sand under hydrostatic loading conditions

    NASA Astrophysics Data System (ADS)

    Hagin, Paul; Sleep, Norman H.; Zoback, Mark D.

    2007-05-01

    Rate-and-state variable friction laws describe the time-dependent fault-normal compaction that occurs during holds in slide-hold-slide friction tests on unconsolidated materials. This time-dependent deformation is qualitatively similar to that observed during volumetric creep strain tests on unconsolidated sands and shales under hydrostatic loading conditions. To test whether rate-and-state friction laws can be used to model volumetric creep processes in unconsolidated sands, the rate-and-state formulation is expanded to include deformation under hydrostatic stress boundary conditions. Results show that the hydrostatic stress form of the rate-and-state friction law successfully describes the creep strain of unconsolidated sand. More importantly, values obtained for rate-and-state friction parameters by fitting these data are in the same range as those obtained from more traditional tests by fitting the fault-normal compaction of simulated gouge during a hold in a laboratory friction experiment.

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

    NASA Technical Reports Server (NTRS)

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

    1980-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

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

    1983-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-01-01

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

  13. Creep-fatigue as a possible cause of dental amalgam margin failure.

    PubMed

    Williams, P T; Hedge, G L

    1985-03-01

    Fracture of the margins is the most common cause of failure of dental amalgam restorations. Both corrosion and creep have been identified as possible contributors to this type of failure. The stresses that induce creep may arise from the continued setting expansion of the amalgam, the formation of corrosion products, mastication, or from the thermal expansion of the amalgam during ingestion of hot foods. The latter two are low-frequency cyclic stresses. The amalgams used in dentistry have fusion temperatures only about 40 degrees C above mouth temperature, and they experience grain boundary sliding during creep deformation. Since grain boundary sliding, low-frequency cyclic stresses, and a temperature near the fusion temperature of the alloy are prerequisites for so-called "creep-fatigue fracture", this type of fracture may contribute to amalgam margin failure. Amalgam made from seven different alloys was condensed into stainless steel dies. After being allowed to set for seven days, the specimens were thermally cycled between 4 degrees C and 50 degrees C for 500 and 1000 cycles. Amalgam margin integrity was evaluated by scanning electron microscopy both before and after each cycling period. The amount of margin fracture was calculated after 1000 cycles. Thermal cycling of amalgam restorations placed in stainless steel dies resulted in predominantly intergranular fracturing of the amalgam margins, indicating that creep-fatigue failure may be a significant contributor to in vivo margin fracturing. PMID:3855901

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

    PubMed

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

    1998-12-01

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

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

    NASA Technical Reports Server (NTRS)

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

    2007-01-01

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

  16. Rupture and creep behaviours of subduction interface controlled by fault zone heterogeneity

    NASA Astrophysics Data System (ADS)

    Wang, Kelin; Brown, Lonn; Gao, Xiang; Bilek, Susan

    2015-04-01

    The behaviour of fault slip varies tremendously, ranging from seismic rupture to aseismic creep. We explore the role of fault zone heterogeneity in controlling large-scale (> 100 km in strike dimension) rupture and creep behaviours of subduction faults. Geometrically smooth subduction faults can (although not always) provide relatively homogeneous structural and stress conditions to allow large fault patches to be locked over prolonged periods and then rupture in great earthquakes. During the rupture, however, frictional heterogeneities arising from lithological changes, pore-fluid pressure variations, and low-amplitude geometrical irregularities always cause a very heterogeneous distribution of stress drop. Although some parts of the fault may undergo high or complete stress drop (local weakening), many other parts undergo very low stress drop or stress increase (local strengthening). The mixing of stress drop and increase in different parts of the rupture zone makes the average stress drop in each great earthquake very small, of the order of a couple of MPa, as widely observed in seismological studies. We use the 2011 Mw=9 Tohoku-oki earthquake to demonstrate this averaging effect. Geometrically extremely rough subduction faults, such as those featuring multiple subducting seamounts, provide very heterogeneous structural and stress conditions that promote creep and numerous small earthquakes. A global inspection of geodetically constrained locking and creeping states of subduction zones indicates that these extremely rough faults all tend to creep (Wang and Bilek, 2014). Depending on the degree of roughness and other geological conditions (e.g., sediment and fluid), some of the rough faults may host a mixture of seismic and aseismic patches and may exhibit a variety of creep behaviour ranging from steady creep to transient creep pulses (i.e., slow slip events) of different time scales. It can be envisioned that the heterogeneity in these rough faults is generally in the form of 3D deformation in a complex zone of damage along the interface and cannot be adequately approximated by heterogeneous rate-state friction. It is also important to recognize that these creeping rough faults are not "weakly coupled", nor are the highly seismic smooth faults "strongly coupled". A global examination of frictional heating of subduction faults indicate that the creeping rough faults dissipate more heat and are statically stronger, that is, they creep against greater resistance (called strong creep) than the stress required to cause a smooth fault to rupture in great earthquakes (Gao and Wang, 2014). This observation supports the notion that these faults creep as a result of geometrical irregularities forcing through a damage zone, very different from frictional creep due to the presence of week fault gouge (called weak creep). Gao, X., and K. Wang (2014), Science, 345, 1038-1041. Wang, K., and S. L. Bilek (2014), Tectonophysics, 610, 1-24.

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

    NASA Astrophysics Data System (ADS)

    Anandakumar, Umashankar

    In this study, the first matrix cracking behavior and creep behavior of zircon matrix silicon carbide fiber composites were studied, together with the fracture and creep behavior of the monolithic zircon. These behaviors are of engineering and scientific importance, and the study was aimed at understanding the deformation mechanisms at elevated temperatures. The first matrix cracking behavior of zircon matrix uniaxially reinforced with silicon carbide fiber (SCS-6) composites and failure behavior of monolithic zircon were studied as a function of temperature (25°C, 500°C, and 1200°C) and crack length in three point bending mode. A modified vicker's indentation technique was used to vary the initial crack length in monolithic and composite samples. The interfacial shear strength was measured at these temperatures from matrix crack saturation spacing. The composites exhibited steady state and non steady state behaviors at the three different temperatures as predicted by theoretical models, while the failure stress of zircon decreased with increasing stress. The intrinsic properties of the composites were used to numerically determine the results predicted by three different matrix cracking models based on a fracture mechanics approach. The analysis showed that the model based on crack bridging analysis was valid at 25°C and 500°C, while a model based on statistical fiber failure was valid at 1200°C. Microstructural studies showed that fiber failure in the crack wake occurred at or below the matrix cracking stress at 1200°C, and no fiber failure occurred at the other two temperatures, which validated the results predicted by the theoretical models. Also, it was shown that the interfacial shear stress corresponding to debonding determined the matrix cracking stress, and not the frictional shear stress. This study showed for the first time, the steady state and non-steady state matrix cracking behavior at elevated temperatures, the difference in behavior between room temperature and elevated temperatures, and the validity of the various models of first matrix cracking behavior. In order to understand the creep behavior of composites, it is important to study the creep behavior of matrix, fiber, and composites under identical conditions to determine the role of various constituents. Creep studies were conducted in an inert atmosphere in four point bending and uniaxial tension modes on zircon and zircon silicon carbide fiber composites at four different temperatures of 1250°C, 1300°C, 1350°C, and 1400°C, and over the stress range of 10--200 MPa. The strain rate was measured as a function of the stress and temperature to determine the stress exponent and activation energy, and microstructural analysis was done on crept samples using scanning electron microscopy. The composites exhibited a much lower creep rate than the monolilth, indicating that the major portion of the creep load was carried by the fibers. In flexural mode, both zircon and composite samples exhibited bimodal creep behavior, with the stress exponent (n) increasing with increasing stress. For zircon, at lower-stresses n was in the range of 2.1--2.6 and increased to 7--7.9 at higher stresses. Microstructural studies showed that diffusional creep was the rate controlling mechanism at lower stresses, while the higher stress exponent observed at higher stresses, was due to linkage of cavities and damage accumulation resulting in a higher strain rate. In the case of composites, the stress exponent was ?1 at lower stresses, and increased to 3--5 at higher stresses, indicating that diffusional creep (and grain boundary sliding) was rate controlling at lower stresses, and either creep cavitation and crack growth or dislocation creep was the rate controlling mechanism at higher stresses. Anomalous creep curves with strain jumps were observed for the first time during the creep of ceramic composites at lower temperatures and higher stresses. Microstructural studies showed that matrix cracking during creep results in these strain jumps. These studies showed tha

  18. Creep Behaviour of Alpine Salt Rock and the Influence of Insoluble Residues in Solution Mining

    NASA Astrophysics Data System (ADS)

    Pittino, Gerhard; Golser, Johann

    In Austrian salt mining, brine is won by way of solution mining with the borehole well method. The Alpine salt rock (Haselgebirge) consists of a high share of insolubles, and therefore leached caverns are filled with clay residues, as so-called Laist, a natural backfill, according to the salt content. The creep deformations of the Haselgebirge mainly correspond with a rupture-free flow and are calculated by means of an elasto-viscous model (power-law). These deformations mobilize the passive fill-pressure in clay residue that is described as elastoplastic with isotropic hardening by means of a modified Cam-clay model. The long-term laboratory tests are supported through calculations of the creep parameter via measured convergences of drifts at various depths. The long-term behaviour of the caverns is evaluated based on numerical calculations by the volume convergence and the degree of utilization of pillar.

  19. Creep buckling of axially compressed circular cylindrical shells of a zirconium alloy: Experiment and computer simulation

    NASA Astrophysics Data System (ADS)

    Korobeynikov, S. N.; Torshenov, N. G.; Lyubashevskaya, I. V.; Larichkin, A. Yu.; Chunikhina, E. V.

    2014-01-01

    Experiments were performed to study the deformation and buckling of axially compressed circular cylindrical shells of Zr2.5Nb zirconium alloy under creep conditions. Computer simulation using the MSC.Marc 2012 software was conducted by step-by-step integration of the equations of quasistatic deformation of thin shells using Norton's law of steady creep. The results of the experiment and computer simulation show that the buckling modes are a combination of axisymmetric bulges located near one end or both ends of the shell and axisymmetric buckling modes with the formation of three or four waves in the circumferential direction. A comparison is made of the time dependences of the axial strain of the shells obtained in the experiment and by computer simulation. It is shown that for large axial compressive stresses, these dependences are in satisfactory agreement. For lower values of these stresses, the difference between the theoretical and experimental dependences is greater.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

    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.

  1. 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

  2. Evolution of Strain Partitioning during Creep of Carrara Marble

    NASA Astrophysics Data System (ADS)

    Quintanilla Terminel, A.; Evans, J. B.; Mainprice, D.; Lebensohn, R.

    2014-12-01

    We measured the local strain and strain heterogeneity produced during creep deformation of split cylinders of Carrara marble under conventional triaxial loading to inelastic strains of 11% at a strain rate of 3x10-5s-1, confining pressure of 300 MPa and 400deformed to strains of 11%, 22% and 36% at 600ºC and the same rate and confining pressure. Microscale strain mapping at a scale of 10 micrometers (MSSM) show that the partitioning of strain amongst twinning, dislocation slip, and grain boundary sliding mechanisms change with T. Preliminary results using a VPFFT model that gives more importance to dislocation slip predict strain heterogeneities with larger wavelength. Interestingly, at all T, although sliding occurred on some boundaries, on average, strain in regions near boundaries was less than that in grain interiors suggesting the formation of a core-mantle structure observed in naturally deformed rocks. The production of local crystallographic texture also depends on T (and presumably, partitioning amongst the mechanisms). In all the experiments, the texture index (TI) of local areas decreased after deformation, but the path of the evolution differed with changing T. Reductions in TI were greatest for samples deformed at 400ºC, where twin activity was greatest, and at 700ºC, where boundary sliding was more prevalent, and less for intermediate T. The wavelength and amplitude of the heterogeneity in local strain decreased with increasing strain at 600ºC, suggesting that the strain (and perhaps, structures) were being homogenized. From this data and previous observations, we conclude that the evolution of deformation structures in marble takes place over a substantial interval in strain; that the duration of this interval probably depends on strain rate, temperature, and pressure; and that extrapolation of mechanical behavior from lab to natural conditions will need to account for changes in strain partitioning.

  3. Creep resistant high temperature martensitic steel

    DOEpatents

    Hawk, Jeffrey A.; Jablonski, Paul D.; Cowen, Christopher J.

    2015-11-13

    The disclosure provides a creep resistant alloy having an overall composition comprised of iron, chromium, molybdenum, carbon, manganese, silicon, nickel, vanadium, niobium, nitrogen, tungsten, cobalt, tantalum, boron, and potentially additional elements. In an embodiment, the creep resistant alloy has a molybdenum equivalent Mo(eq) from 1.475 to 1.700 wt. % and a quantity (C+N) from 0.145 to 0.205. The overall composition ameliorates sources of microstructural instability such as coarsening of M.sub.23C.sub.6 carbides and MX precipitates, and mitigates or eliminates Laves and Z-phase formation. A creep resistant martensitic steel may be fabricated by preparing a melt comprised of the overall composition followed by at least austenizing and tempering. The creep resistant alloy exhibits improved high-temperature creep strength in the temperature environment of around 650.degree. C.

  4. Microstructural study of the partition between seismic and aseismic deformation along the North Anatolian Fault zone, Turkey

    NASA Astrophysics Data System (ADS)

    Kaduri, M.; Gratier, J. P.; Renard, F.; Cakir, Z.; Lasserre, C.

    2014-12-01

    Along the North Anatolian Fault (Turkey), fault sliding is accommodated both by earthquakes and by aseismic creep. The creep processes develop either as transient (post-seismic or interseismic) sliding or as permanent sliding along zones localized on specific segments of the fault. Creep processes relax the stress and contribute to stress redistribution within the seismogenic zone. They participate to the deformation budget during the seismic cycle, sometimes delaying or on the contrary helping triggering the occurrence of large earthquakes. Identifying the mechanisms controlling creep and their evolution with time and space represents a major challenge for predicting the mechanical evolution of active faults. Our goal is to answer three main questions: How to identify at the outcrop scale permanent creep from transient creep? Is aseismic creep controlled by lithology? How does creep evolve before and after earthquakes? The challenge is to understand which key parameters control the shift from seismic to aseismic deformation, such as the effect of fabric, rock lithology, fault roughness, strain-rate, fluid pressure or stress.We collected samples from a dozen of fresh and well-preserved fault outcrops along creeping and locked segments of the North Anatolian Fault. We used various methods such as microscopic and geological observations, SEM, XRD analysis, strain measurements from image processing approaches in order to quantitatively characterize the amount of deformation and the mechanisms involved. Results show different relationships between lithology and mechanisms of deformation: (i) Along the locked segments of the North Anatolian Fault, in massive limestone, we found evidence of large earthquakes followed by pre- or post-seismic (i.e. afterslip) creep. (ii) Along some creeping segments, we observed gouges with weak clay (saponite) that could accommodate (or have accommodated in the past) large permanent creep. (iii) Along other creeping segments, we observed deformed serpentine bodies attesting of creep episodes, the strain values of which remaining to be evaluated, but also evidences of past earthquakes, suggesting in such areas a mixed-mode of seismic and aseismic deformation.

  5. Haglund's Deformity

    MedlinePLUS

    ... Is Haglund’s Deformity? Haglund’s deformity is a bony enlargement on the back of the heel. The soft ... the Achilles tendon becomes irritated when the bony enlargement rubs against shoes. This often leads to painful ...

  6. Relative strength of mafic and felsic rocks during amphibolite facies metamorphism and deformation

    NASA Astrophysics Data System (ADS)

    Pearce, Mark A.; Wheeler, John; Prior, David J.

    2011-04-01

    Field observations of mafic dykes intruded into felsic rocks from the Lewisian Complex, NW Scotland, suggest that the mafic rocks are weaker than the felsic ones, contrary to experimental results. In order to resolve this conflict, samples were studied to constrain the deformation mechanisms active under amphibolite facies conditions. Crystallographic preferred orientation (CPO) in plagioclase is used to infer deformation by dislocation creep on the (112)[11¯0], (11¯2)[110], (001)[11¯0], and (001)[11¯0] slip systems. With increasing strain, this CPO became weaker due to grain-boundary sliding that accompanied diffusion creep. In rocks where grain size reduction of plagioclase occurred by chemically-dominated recrystallisation there is no CPO suggesting deformation was wholly accommodated by diffusion creep and grain-boundary sliding. In metamorphosed dykes, plagioclase grains have orientations that are not consistent with dislocation creep deformation. Amphibole has a CPO consistent with either dislocation creep on {100}<001> or deformation by diffusion creep with anisotropic dissolution and precipitation rates. It is inferred that metamorphism of the dykes lead to the production of fine-grained amphibole and plagioclase, both of which deform by diffusion creep, but that anisotropic dissolution and precipitation in the amphibole produced a CPO. The mafic dykes are weaker than the felsic gneisses because grain size reduction is more extreme in the dykes even though both may be deforming primarily by grain size sensitive mechanisms. This work highlights the variation in processes active in polyphase rocks and how these can lead to variations in CPO of the same mineral among different rock types.

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

    SciTech Connect

    Mark Carroll; Laura Carroll

    2011-09-01

    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.

  8. Madelung Deformity.

    PubMed

    Kozin, Scott H; Zlotolow, Dan A

    2015-10-01

    Madelung deformity of the wrist is more common in females and is often associated with Leri Weill dyschondrosteosis, a mesomelic form of dwarfism. Patients with Madelung deformity often report wrist deformity resulting from the prominence of the relatively long ulna. The typical Madelung deformity is associated with a Vickers ligament that creates a tether across the volar-ulnar radial physis that restricts growth across this segment. The distal radius deforms in the coronal (increasing radial inclination) and the sagittal (increasing volar tilt) planes. There is lunate subsidence and the proximal carpal row adapts to the deformity by forming an upside-down pyramid shape or triangle. Treatment depends on the age at presentation, degree of deformity, and magnitude of symptoms. Mild asymptomatic deformity warrants a period of nonsurgical management with serial x-ray examinations because the natural history is unpredictable. Many patients never require surgical intervention. Progressive deformity in the young child with considerable growth potential remaining requires release of Vickers ligament and radial physiolysis to prevent ongoing deterioration Concomitant ulnar epiphysiodesis may be necessary. Advanced asymptomatic deformity in older children with an unacceptable-appearing wrist or symptomatic deformity are indications for surgery. A dome osteotomy of the radius allows 3-dimensional correction of the deformity. Positive radiographic and clinical results after dome osteotomy have been reported. PMID:26341718

  9. Creep-rupture reliability analysis

    NASA Technical Reports Server (NTRS)

    Peralta-Duran, A.; Wirsching, P. H.

    1984-01-01

    A probabilistic approach to the correlation and extrapolation of creep-rupture data is presented. Time temperature parameters (TTP) are used to correlate the data, and an analytical expression for the master curve is developed. The expression provides a simple model for the statistical distribution of strength and fits neatly into a probabilistic design format. The analysis focuses on the Larson-Miller and on the Manson-Haferd parameters, but it can be applied to any of the TTP's. A method is developed for evaluating material dependent constants for TTP's. It is shown that optimized constants can provide a significant improvement in the correlation of the data, thereby reducing modelling error. Attempts were made to quantify the performance of the proposed method in predicting long term behavior. Uncertainty in predicting long term behavior from short term tests was derived for several sets of data. Examples are presented which illustrate the theory and demonstrate the application of state of the art reliability methods to the design of components under creep.

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

    E-print Network

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

    2008-03-03

    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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    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.

  12. Elevated temperature creep properties for selected active metal braze alloys

    SciTech Connect

    Stephens, J.J.

    1997-02-01

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

  13. Strain localization during deformation of Westerly granite

    NASA Technical Reports Server (NTRS)

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

    1984-01-01

    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.

  14. Creep mechanisms of fully-lamellar TiAl based upon interface sliding

    SciTech Connect

    Hsiung, L.M.; Nieh, T.G.

    1999-07-01

    Deformation mechanisms of fully lamellar TiAl with a refined microstructure ({gamma} lamellae: 100 {approximately} 300 nm thick, {alpha}{sub 2} lamellae: 10 {approximately} 50 nm thick) crept at 760 C have been investigated. As a result of a fine structure, the motion and multiplication of lattice dislocations within both {gamma} and {alpha}{sub 2} lamellae are limited at low creep stresses ({lt}400 MPa). Therefore, the glide and climb of lattice dislocations are insignificant to creep deformation. The cooperative motion of interfacial dislocations on {gamma}/{alpha}{sub 2} and {gamma}/{gamma} interfaces (i.e., interface sliding) is proposed to be the dominant deformation mechanism at low stresses. Lattice dislocations impinged on lamellar interfaces are found to be the major obstacles impeding the motion of interfacial dislocations. The number of impinged lattice dislocations increases as the applied stress increases and, subsequently, causes the pileup of interfacial dislocations along the interfaces. Accordingly, deformation twinning activated by the pileup of interfacial dislocations is proposed to be the dominant deformation mechanism at high stresses ({gt}400 MPa).

  15. Models for rupture mechanics of plate boundaries and crustal deformation

    NASA Technical Reports Server (NTRS)

    Nur, A.

    1983-01-01

    The role of pull aparts and pushups in transcurrent systems, the rotation of faults and blocks within transcurrent fault systems, the role of accretion tectonics in plate boundary deformation, and power law creep behavior and the yielding at plate boundaries were investigated.

  16. Effect of Creep of Ferritic Interconnect on Long-Term Performance of Solid Oxide Fuel Cell Stacks

    SciTech Connect

    Liu, Wenning N.; Sun, Xin; Khaleel, Mohammad A.

    2010-08-01

    High-temperature ferritic alloys are potential candidates as interconnect (IC) materials and spacers due to their low cost and coefficient of thermal expansion (CTE) compatibility with other components for most of the solid oxide fuel cells (SOFCs) . However, creep deformation becomes relevant for a material when the operating temperature exceeds or even is less than half of its melting temperature (in degrees of Kelvin). The operating temperatures for most of the SOFCs under development are around 1,073 K. With around 1,800 K of the melting temperature for most stainless steel, possible creep deformation of ferritic IC under the typical cell operating temperature should not be neglected. In this paper, the effects of IC creep behavior on stack geometry change and the stress redistribution of different cell components are predicted and summarized. The goal of the study is to investigate the performance of the fuel cell stack by obtaining the changes in fuel- and air-channel geometry due to creep of the ferritic stainless steel IC, therefore indicating possible changes in SOFC performance under long-term operations. The ferritic IC creep model was incorporated into software SOFC-MP and Mentat-FC, and finite element analyses were performed to quantify the deformed configuration of the SOFC stack under the long-term steady-state operating temperature. It was found that the creep behavior of the ferritic stainless steel IC contributes to narrowing of both the fuel- and the air-flow channels. In addition, stress re-distribution of the cell components suggests the need for a compliant sealing material that also relaxes at operating temperature.

  17. Materials Science and Technology, Volume 6, Plastic Deformation and Fracture of Materials

    NASA Astrophysics Data System (ADS)

    Mughrabi, Hael

    1996-12-01

    This self-contained handbook focuses on the mechanisms of plastic deformation and fracture affecting a wide variety of materials. From the Contents: Mughrabi: Introduction. Gil Sevillano: Flow Stress and Work Hardening. Leffers/Van Houtte/Aernoudt: Deformation and Textures of Metals at Large Strain. Kubin: Dislocation Patterning. Neuhäuser/Schwink: Solid Solution Strengthening. Umakoshi: Deformation of Intermettalic Compounds. Reppich: Particle Strengthening. Blum: High Temperature Deformation and Creep of Crystalline Solids. Mukherjee: Superplasticity in Metals, Ceramics and Intermetallics. Argon: Inelastic Deformation and Fracture of Glassy Solids. Suresh: Cyclic Deformation and Fatigue. Riedel: Frature Mechanisms. Kato: Friction and Wear.

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

    NASA Astrophysics Data System (ADS)

    Hol, Sander; Zoback, Mark

    2013-04-01

    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.

  19. Compaction creep of sands due to time-dependent grain failure: Effects of chemical environment, applied stress, and grain size

    NASA Astrophysics Data System (ADS)

    Brzesowsky, R. H.; Hangx, S. J. T.; Brantut, N.; Spiers, C. J.

    2014-10-01

    Time-dependent brittle creep plays a role in controlling compaction of sands and sandstones under upper crustal conditions, influencing phenomena such as production-induced reservoir compaction, surface subsidence, and induced seismicity. Brittle creep also plays a role in determining the mechanical behavior of gouge-rich faults. We performed uniaxial creep experiments on sand to investigate the effects of chemical environment (dry versus solution flooded), grain size (d = 196-378 µm), and applied effective stress (?a up to 30 MPa), at room temperature conditions favoring grain-scale brittle processes. Creep measurements were complemented with acoustic emission (AE) detection and microstructural analysis to characterize the main creep mechanism. Wet samples showed much higher creep strains than dry-tested samples. AE event counts showed a direct relation between grain failure and creep strain, with higher AE rates occurring in the wet samples. Therefore, we inferred that time-dependent deformation was dominated by subcritical crack growth, resulting in grain failure accompanied by intergranular sliding rearrangements, and that crack growth in the presence of chemically active fluids was controlled by stress corrosion. The sensitivity of the compaction rate of the sands to d and ?a can be expressed as ???di?aj where i ? 6 and j ? 21 under dry conditions and i ? 9 and j ? 15 under wet conditions. Our results were compared to a simple model based on Hertzian contact theory, linear elastic fracture mechanics, and subcritical crack growth. This model showed agreement between the observed stress and grain size sensitivities of creep, within a factor of 2.

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

    NASA Technical Reports Server (NTRS)

    Tewari, S.N.

    1995-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

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

  2. Prediction of creep of polymer concrete

    SciTech Connect

    Khristova, Yu.; Aniskevich, K.

    1995-11-01

    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.

  3. Creep of plain weave polymer matrix composites

    NASA Astrophysics Data System (ADS)

    Gupta, Abhishek

    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.

  4. Creep behavior of an A286 type stainless steel

    SciTech Connect

    DeCicco, H. . E-mail: decicco@cnea.gov.ar; Luppo, M.I.; Raffaeli, H.; Di Gaetano, J.; Gribaudo, L.M.; Ovejero-Garcia, J.

    2005-08-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

    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.

  7. Deformation Mechanisms of Antigorite Serpentinite at Subduction Zone Conditions Determined from Experimentally and Naturally Deformed Rocks

    NASA Astrophysics Data System (ADS)

    Auzende, A. L.; Escartin, J.; Walte, N.; Guillot, S.; Hirth, G.; Frost, D. J.

    2014-12-01

    The rheology of serpentinite, and particularly that of antigorite-bearing rocks, is of prime importance for understanding subduction zone proceses, including decoupling between the downwelling slab and the overriding plate, exhumation of high-pressure rocks, fluids pathways and, more generally, mantle wedge dynamics. We present results from deformation-DIA experiments on antigorite serpentinite performed under conditions relevant of subduction zones (1-3.5 GPa ; 400-650°C). We complemented our study with a sample deformed in a Griggs-type apparatus at 1 GPa and 400°C (Chernak and Hirth, EPSL, 2010), and with natural samples from Cuba and the Alps deformed under blueschist/eclogitic conditions. Our observations on experimental samples of antigorite deformed within its stability field show that deformation is dominated by cataclastic flow; we can only document a minor contribution of plastic deformation. In naturally deformed samples, deformation-related plastic structures largely dominate strain accommodation, but we also document a minor contribution of brittle deformation. When dehydration occurs in experiments, plasticity increases, and is coupled to local embrittlement attributed to hydraulic fracturating due to the migration of dehydration fluids. Our results thus show that semibrittle deformation operates within and above the stability field of antigorite. We also document that the corrugated structure of antigorite has a control on the strain accommodation mechanisms under subduction conditions, with preferred inter and intra-cracking along (001) and gliding along both a and b. Deformation dominated by brittle processes, as observed in experiments, may occur during deformation at elevated (seismic?) strain rates, while plastic deformation, as observed in naturally deformed rocks, may correspond instead to low strain rates instead (aseismic creep?). We also discuss the role of antigorite rheology and mode of deformation on fluid transport.

  8. Characteristics of AFRP Bars for Prestressing Applications 

    E-print Network

    Medina, Jose

    2012-02-14

    sustainability of beams prestressed with AFRP composite materials. The objective of this research is to effectively characterize the material properties based on the short-term and long-term characteristics of AFRP bars. Tensile, creep-rupture, and relaxation...

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

    NASA Astrophysics Data System (ADS)

    Leopold, Philip; Draganits, Erich; Heiss, Gerhard

    2010-05-01

    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

  10. Deformation behaviour of feldspar in greenschist facies granitoide shear zones from the Austroalpine basement to the south of the western Tauern window, Eastern Alps

    NASA Astrophysics Data System (ADS)

    Hentschel, Felix; Trepmann, Claudia

    2015-04-01

    Objective of this study is to elucidate the feldspar deformation behaviour at greenschist facies conditions relevant for the long-term rheological properties of continental crust. Uncertainties in models for the rheological properties are partly due to a poor knowledge of the deformation mechanisms taking place in granitoid rocks at inaccessible depth. The deformation behaviour of feldspar, the most abundant mineral in the continental crust, is characterized by an interaction of brittle, dissolution-precipitation and crystal-plastic processes, which is difficult to evaluate in experiments given the problematic extrapolation of experimental conditions to reasonable natural conditions. However, microfabrics of metamorphic granitoid rocks record the grain-scale deformation mechanisms and involved chemical reactions proceeding during their geological history. This usually includes deformation and modification through several stages in space (depth, i.e., P, T conditions) and/or time. For deciphering the rock's record this implies both, challenge and chance to resolve these different stages. Here, we use the deformation record of mylonitic pegmatites from the Austroalpine basement south to the western Tauern window. The structural, crystallographic and chemical characteristics of the feldspar microfabrics are determined via micro-analytical techniques (polarized light microscopy, scanning electron microscopy, SEM, electron back scatter diffraction, EBSD) to identify the relevant deformation mechanisms and deformation conditions. The pegmatites represent a relatively simple Ca-poor granitoid system, mineralogically dominated by albite-rich plagioclase, K-feldspar and quartz. The matrix of the mylonitic pegmatites is composed of alternating monomineralic albite and quartz ribbons defining the foliation. Fragmented tourmaline and K-feldspar porphyroclasts occur isolated within the matrix. At sites of dilation along the stretching lineation K-feldspar porphyroclasts show serrated boundaries to matrix albite grains. In intragranular zones within K-feldspar porphyroclasts, small albite but also K-feldspar grains and "subgrains" (K-feldspar domains with a small misorientation angle to the host K-feldspar porphyroclast) occur. Strain shadows around porphyroclasts are composed of polymineralic aggregates of albite, K-feldspar and quartz. The albite grains in ribbons show a shape preferred orientation (SPO) with a long axis of about 50-100 µm in the foliation plane and EBSD data reveal an absent to very weak crystallographic orientation (CPO). These microfabrics show indication of a sequence of brittle behaviour, localized dislocation glide-controlled deformation and dissolution-precipitation creep of feldspar. Monomineralic quartz ribbons and shear bands show evidence of dislocation glide by a pronounced CPO, implying dislocation creep. The microfabric is interpreted to have evolved during different stages of episodic deformation at transient high stresses with subsequent viscous flow at decreasing stresses.

  11. Creep-fatigue of low cobalt superalloys

    NASA Technical Reports Server (NTRS)

    Halford, G. R.

    1982-01-01

    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.

  12. Compression and Creep of Venice Lagoon Sands

    E-print Network

    Sanzeni, Alex

    A laboratory test program was conducted to evaluate the one-dimensional (1D) compression and creep properties of intact sand (and silty-sand) samples from a deep borehole at the Malamocco Inlet to the Venice Lagoon. The ...

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

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  14. Composites of Polystyrene/Wood Fiber, Processing Effect to Creep Resistance

    SciTech Connect

    Romero-Balderrama, L.; Mendoza-Duarte, M. E.; Flores-Gallardo, S. G.; Ibarra-Gomez, R.; Gaspar-Rosas, A.

    2008-07-07

    In the present work, PS/wood fiber composites were studied in relation to their creep response as to be affected by the incorporation of a silane type coupling agent. Two elaboration variables were also considered in the experiments: wood fiber content and type of composites processing (compression, extrusion and injection molding). A series of weight ratios PS/wood fiber, with and without coupling agent, were prepared, 90/10, 80/20, 70/30 and 60/40. For the compatibilized series, 1% wt of silane coupling agent in relation to the polystyrene weight was employed. The creep tests were performed inside the lineal viscoelastic region at 80 deg. C. A general improvement of the creep resistance for the compatibilized composites was observed independently of the elaboration process. However, the injection molded samples showed by far the lowest deformation with time. This behavior suggests that the high orientation of the fibers generated by the injection molding process, in relation to the extrusion and compression molding, promotes a higher superficial area of treated fiber to be in contact with the PS matrix, which enhances the adhesion and in consequence the resistance to creep.

  15. Can grain size sensitive creep lubricate faults during earthquake propagation?

    NASA Astrophysics Data System (ADS)

    De Paola, N.; Holdsworth, R.; Viti, C.; Collettini, C.; Bullock, R. J.; Faoro, I.

    2014-12-01

    In the shallow portion of crustal fault zones, fracturing and cataclasis are thought to be the dominant processes during earthquake propagation. In the lower crust/upper mantle, viscous flow is inferred to facilitate aseismic creep along shear zones. Recent studies show that slip zones (SZs), in natural and experimental carbonate seismic faults, are made of nanograins with a polygonal texture, a microstructure consistent with deformation by grain boundary sliding (GBS) mechanisms. Friction experiments performed on calcite fine-grained gouges, at speed v = 1 ms-1, normal stress sn = 18 MPa, displacements d = 0.009-1.46 m, and room temperature and humidity, show a four stage-evolution of the fault strength: SI) attainment of initial value, f = 0.67; SII) increase up to peak value f = 0.82; SIII) sudden decrease to low steady-state value, f = 0.18; and SIV) sudden increase to final value, f = 0.44, during sample deceleration. Samples recovered at the end of each displacement-controlled experiments (Stages I-IV) show the following microstructures evolution of the SZ material, which is: SI) poorly consolidated, and made of fine-grained (1 < D < 5 microns), angular clasts formed by brittle fracturing and cataclasis; SII) cohesive, and made of larger clasts of calcite (D ? 1 microns), exhibiting a high density of free dislocations and hosting subgrains (D ? 200 nm), dispersed within calcite nanograins. SIII) made of nanograin aggregates exhibiting polygonal grain boundaries, and 120° triple junctions between equiaxial grains. The grains display no preferred elongation, no crystal preferred orientation and low free dislocation densities, possibly due to high temperature (> 900 C) GBS creep deformation. Our microstructural observations suggest that GBS mechanisms can operate in geological materials deformed at high strain rates along frictionally heated seismogenic slip surfaces. The observed microstructures in experimental slip zones are strikingly similar to those predicted by theoretical studies, and to those observed during experiments on metals and fine-grained carbonates deformed at T > 900 °C, where superplastic behaviour due to GBS has been inferred. A regime of frictionally-induced GBS could thus account for the dynamic weakening of carbonate faults during earthquake propagation in nature.

  16. Onset of sediment transport is a continuous transition driven by fluid shear and granular creep

    PubMed Central

    Houssais, Morgane; Ortiz, Carlos P.; Durian, Douglas J.; Jerolmack, Douglas J.

    2015-01-01

    Fluid-sheared granular transport sculpts landscapes and undermines infrastructure, yet predicting the onset of sediment transport remains notoriously unreliable. For almost a century, this onset has been treated as a discontinuous transition at which hydrodynamic forces overcome gravity-loaded grain–grain friction. Using a custom laminar-shear flume to image slow granular dynamics deep into the bed, here we find that the onset is instead a continuous transition from creeping to granular flow. This transition occurs inside the dense granular bed at a critical viscous number, similar to granular flows and colloidal suspensions and inconsistent with hydrodynamic frameworks. We propose a new phase diagram for sediment transport, where ‘bed load’ is a dense granular flow bounded by creep below and suspension above. Creep is characteristic of disordered solids and reminiscent of soil diffusion on hillslopes. Results provide new predictions for the onset and dynamics of sediment transport that challenge existing models. PMID:25751296

  17. Onset of sediment transport is a continuous transition driven by fluid shear and granular creep.

    PubMed

    Houssais, Morgane; Ortiz, Carlos P; Durian, Douglas J; Jerolmack, Douglas J

    2015-01-01

    Fluid-sheared granular transport sculpts landscapes and undermines infrastructure, yet predicting the onset of sediment transport remains notoriously unreliable. For almost a century, this onset has been treated as a discontinuous transition at which hydrodynamic forces overcome gravity-loaded grain-grain friction. Using a custom laminar-shear flume to image slow granular dynamics deep into the bed, here we find that the onset is instead a continuous transition from creeping to granular flow. This transition occurs inside the dense granular bed at a critical viscous number, similar to granular flows and colloidal suspensions and inconsistent with hydrodynamic frameworks. We propose a new phase diagram for sediment transport, where 'bed load' is a dense granular flow bounded by creep below and suspension above. Creep is characteristic of disordered solids and reminiscent of soil diffusion on hillslopes. Results provide new predictions for the onset and dynamics of sediment transport that challenge existing models. PMID:25751296

  18. Microstructural effects on the creep and crack propagation behaviors of {gamma}-Ti aluminide alloy

    SciTech Connect

    Lupinc, V.; Onofrio, G.; Nazmy, M.; Staubli, M.

    1999-07-01

    Gamma titanium aluminides class of materials possess several unique physical and mechanical properties. These characteristics can be attractive for specific industrial applications. By applying different heat treatment schedules one can change the microstructural features of this class of materials. In the present investigation, two heat treatment schedules were used to produce two different microstructures, duplex (D) and nearly lamellar (NL) in the cast and HIP'ed Ti-47Al-2W-0.5Si alloy. The tensile strength and creep behavior, in the 700--850 C temperature range, of this alloy have been determined and correlated to the corresponding microstructures. In addition, the fatigue crack propagation behavior in this alloy has been studied at different temperatures. The results on the creep behavior showed that the alloy with nearly lamellar microstructure has a strongly improved creep strength as compared with that of the duplex microstructure.

  19. Low strain creep and aging of aluminum alloy 2219-T87 sheet

    NASA Technical Reports Server (NTRS)

    Navrotski, G.; Rummler, D. R.

    1981-01-01

    The constant load creep and isothermal aging characteristics of aluminum alloy 2219-T87 sheet have been studied experimentally and analytically in the temperature range 250 to 650 F at stress levels between 2.9 and 4.0 ksi (20 to 283 MPa). Testing variables were closely and automatically monitored. The data generated agree somewhat with the literature data base at lower temperatures, but above 500 F, discrepancies of greater than an order of magnitude in the time to 1% creep strain occur. Good correlation was found with the Larson-Miller parameter as modeled by a second-order polynomial in stress. Constitutive equations for time to 0.1%, 0.2%, 0.5%, and 1.0% creep are given. Information on residual mechanical properties and electrical conductivity is also provided.

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

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

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

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

    SciTech Connect

    Shen, Chen

    2015-01-01

    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

  2. Creep Events and Shear Localization in a Polyphase Material: Insight into the Brittle-Ductile Transition

    NASA Astrophysics Data System (ADS)

    Reber, J. E.; Hayman, N. W.; Lavier, L. L.; Jammes, S.

    2014-12-01

    The co-occurrence of brittle and ductile deformation underlies many large-scale tectonic processes, geodetically and seismologically monitored strain transients, and even several applied geoscience problems in hydrocarbon production and CO2 sequestration. Evidence for such mixed-deformation is preserved in the rock record, such as in mid-crustal shear zones where, depending on the temperature and pressure conditions, some mineral phases undergo brittle and others ductile deformation during the same overall bulk deformation. Here we combine physical experiments with an analytical approach to investigate the impact of the semi-brittle material on the deformation localization and on stick-slip and creep events. Two sets of experiments are performed: 1) shear of a mixture of elastic-frictional grains within a viscously deforming media, and 2) propagation of wetted fractures in a visco-elasto-plastic interlinked polymer gel during shear. We measure the force and displacement while imaging the shear cell. In both cases the rock analogues show a semi-brittle behavior where the deformation localization is enhanced and slip events get damped leading to creep. Several parameters were then extracted from the experiments and directly used as input parameters in an analytical solution for semi-brittle flow. In the analytical model localization and slip is modeled as a damped oscillator mimicking the behavior of discrete fractures originating in a strong material that get viscously damped in a surrounding continuous weaker material. That the measured and calculated decay times of slip events lead to comparable results is supportive of the models physical premise. This study suggest that in a mixed brittle-ductile system, localization can be efficient, frictional responses can be dampened but still present, and basic rheological descriptions may apply, all of which has implications for understanding strain transients and coseismic release.

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

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

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

  4. Polygonal deformation bands

    NASA Astrophysics Data System (ADS)

    Antonellini, Marco; Mollema, Pauline Nella

    2015-12-01

    We report for the first time the occurrence of polygonal faults in sandstone, which is compelling given that layer-bound polygonal fault systems have been observed so far only in fine-grained sediments such as clay and chalk. The polygonal faults are shear deformation bands that developed under shallow burial conditions via strain hardening in dm-wide zones. The edges of the polygons are 1-5 m long. The shear deformation bands are organized as conjugate faults along each edge of the polygon and form characteristic horst-like structures. The individual deformation bands have slip magnitudes ranging from a few mm to 1.5 cm; the cumulative average slip magnitude in a zone is up to 10 cm. The deformation bands heaves, in aggregate form, accommodate a small isotropic horizontal extension (strain <0.005). The individual shear deformation bands show abutting T-junctions, veering, curving, and merging where they mechanically interact. Crosscutting relationships are rare. The interactions of the deformation bands are similar to those of mode I opening fractures. The documented fault networks have important implications for evaluating the geometry of km-scale polygonal fault systems in the subsurface, top seal integrity, as well as constraining paleo-tectonic stress regimes.

  5. Weakening of rock salt by water during long-term creep

    NASA Astrophysics Data System (ADS)

    Urai, Janos L.; Spiers, Christopher J.; Zwart, Hendrik J.; Lister, Gordon S.

    1986-12-01

    The rheological properties of rock salt are of fundamental importance in predicting the long-term evolution of salt-based radioactive waste repositories and strategic storage caverns, and in modelling the formation of salt diapirs and associated oil traps1,2. The short-term, high-stress rheology of rock salt is well known from laboratory experiments; however, extrapolation to appropriately low stresses fails to predict the rapid flow seen in certain natural structures. Furthermore, experiments have failed to reproduce the recrystallized microstructure of naturally deformed salt. Here we report experiments indicating that the above discrepancies can be explained by taking into account the influence of trace amounts of brine. Trace brine is always present in natural salt but sometimes escapes during experiments. Our tests on dry dilated salt show more or less conventional dislocation creep behaviour, but brine-bearing samples show marked weakening at low strain rates. This is associated with dynamic recrystallization and a change of deformation mechanism to solution transfer creep. Because natural rock salt always contains some brine, these results cast substantial doubt on the validity of presently accepted dislocation creep laws for predicting the long-term rheological behaviour of salt in nature.

  6. Transient Liquid Phase Bonding Single-Crystal Superalloys with Orientation Deviations: Creep Properties

    NASA Astrophysics Data System (ADS)

    Sheng, Naicheng; Liu, Jide; Jin, Tao; Sun, Xiaofeng; Hu, Zhuangqi

    2015-12-01

    Superalloys single crystals with various orientation deviations were bonded using transient liquid phase bonding method, then the creep properties of the bonded specimens were tested at 1033 K (760 °C)/780 MPa. It is found that the creep life of the bonded specimens decreases with the increase of the relative orientation deviations. Despite the fracture of the specimens appears on the bonding region, the deformation mechanism changes from specimens with low angle boundary to high angle boundary. In low angle boundary specimens, cleavage originated from the defects grows perpendicularly to the tensile stress and connects through the different slip planes around the cleavage planes. In this case, the deformation proceeds by the dislocations and stacking faults on multi-planes. With increasing orientation deviation, dislocation and stacking faults moved on single plane. As a result, the dislocations interact with the grain boundary and lead to fracture. Based on the present investigation, the orientation of the bonded superalloys single crystal should be controlled so that the introduced grain boundaries are relatively small and exhibit higher creep strength.

  7. Microstructural influence on high temperature creep flow of Zr-1%NbO alloy in near- ?, ( ? + ?), and ? temperature ranges in a high vacuum environment

    NASA Astrophysics Data System (ADS)

    Kaddour, Djilali; Gourgues-Lorenzon, Anne-Françoise; Brachet, Jean-Christophe; Portier, Laurence; Pineau, André

    2011-01-01

    Uniaxial tensile creep tests were carried out at 650-1100 °C in a high vacuum environment on Zr-1%NbO tubes with various microstructures. The effect of microstructure on creep flow in the ( ? + ?) temperature range is significant (the creep rate being modified by up to three orders of magnitude) under stresses lower than 10 MPa, that is, for stress values of one order of magnitude lower than those characteristic of prototypical Loss-of-coolant-accident (LOCA) conditions. Under stresses higher than about 20 MPa, this effect is much smaller. No transformation-induced plasticity was detected from anisothermal creep tests, once the creep strain was thoroughly taken into account to process experimental strain vs. time data.

  8. Preliminary deformation model for National Seismic Hazard map of Indonesia

    SciTech Connect

    Meilano, Irwan; Gunawan, Endra; Sarsito, Dina; Prijatna, Kosasih; Abidin, Hasanuddin Z.; Susilo,; Efendi, Joni

    2015-04-24

    Preliminary deformation model for the Indonesia’s National Seismic Hazard (NSH) map is constructed as the block rotation and strain accumulation function at the elastic half-space. Deformation due to rigid body motion is estimated by rotating six tectonic blocks in Indonesia. The interseismic deformation due to subduction is estimated by assuming coupling on subduction interface while deformation at active fault is calculated by assuming each of the fault‘s segment slips beneath a locking depth or in combination with creeping in a shallower part. This research shows that rigid body motion dominates the deformation pattern with magnitude more than 15?mm/year, except in the narrow area near subduction zones and active faults where significant deformation reach to 25?mm/year.

  9. Correlation of creep rate with microstructural changes during high temperature creep

    NASA Technical Reports Server (NTRS)

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

    1973-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Cohen, S. C.

    1981-01-01

    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.

  11. Fluid-present deformation aids chemical modification of chromite: Insights from chromites from Golyamo Kamenyane, SE Bulgaria

    NASA Astrophysics Data System (ADS)

    Satsukawa, Takako; Piazolo, Sandra; González-Jiménez, José María; Colás, Vanessa; Griffin, William L.; O'Reilly, Suzanne Y.; Gervilla, Fernando; Fanlo, Isabel; Kerestedjian, Thomas N.

    2015-07-01

    Chemical signatures of chromitites are commonly used to track the evolution of the Earth's mantle. However, chemical modification during deformation may have important implications for the interpretation of chromites' signatures. Here, we describe the details of how deformation promotes chemical modification in chromite. Physicochemical characteristics of the chromites were quantified by measuring crystallographic orientation relationships using Electron Back-Scattered Diffraction (EBSD) and electron microprobe analysis (EMP). Chromites show porphyroclastic textures with coarse-grained porphyroclasts (ca. 0.2-5 mm) and fine-grained neoblasts (< 200 ?m). Coarse-grained chromites are chemically zoned in terms of major elements from core to rim, preserving this initial igneous feature in the cores, while the outer rims reveal a metamorphic signature. Large chromite grains are characterized by local crystal-plastic deformation, exhibiting distinct inter-crystalline deformation including continuous crystal bending and subgrain boundaries as well as chemical modification in their outer, deformed parts. Two types of fine-grained chromite, F1 and F2, are present. While F1 exhibits a well-developed polygonal texture, straight grain boundaries and low intercrystal misorientation (< 1°), F2 shows low-angle boundaries and significant intercrystalline misorientation (2-8°). Both F1 and F2 have higher Fe3 + and Cr and lower Mg# values than the cores of large grains. We interpret F1 and F2 to represent chromite recrystallized by heterogeneous nucleation and subgrain rotation recrystallization, respectively. Crystallographic preferred orientation (CPO) and misorientation data on the well-developed low-angle (subgrain) boundaries in coarse grains and F2 grains indicate that deformation in chromite was accommodated mainly by dislocation creep with the dominant activation of the {111}<100 > slip system. The retrograde P-T exhumation path predicted by thermodynamic and chemical modeling suggests that these fine-grained chromites were produced when the initial chromitites reacted with oxidizing fluids during retrograde metamorphism ( 1.0 GPa and 500-700 °C). Our results show that deformation in the dislocation-creep regime in a chemically open system has induced chemical modification and homogenization within chromite aggregates as well as strain localization. This close physicochemical link offers new avenues of interpreting the chemical signatures of chromites, utilizing their microstructurally controlled variation or lack thereof.

  12. A creep-damage model for mesoscale simulations of concrete expansion-degradation phenomena

    SciTech Connect

    Giorla, Alain B; Le Pape, Yann

    2015-01-01

    Long-term performance of aging concrete in nuclear power plants (NPPs) requires a careful examination of the physical phenomena taking place in the material. Concrete under high neutron irradiation is subjected to large irreversible deformations as well as mechanical damage, caused by a swelling of the aggregates. However, these results, generally obtained in accelerated conditions in test reactors, cannot be directly applied to NPP irradiated structures, i.e., the biological shield, operating conditions due to difference in time scale and environmental conditions (temperature, humidity). Mesoscale numerical simulations are performed to separate the underlying mechanisms and their interactions. The cement paste creep-damage model accounts for the effect of the loading rate on the apparent damage properties of the material and uses an event-based approach to capture the competition between creep and damage. The model is applied to the simulation of irradiation experiments from the literature and shows a good agreement with the experimental data.

  13. Creep crack-growth: A new path-independent T sub o and computational studies

    NASA Technical Reports Server (NTRS)

    Stonesifer, R. B.; Atluri, S. N.

    1981-01-01

    Two path independent integral parameters which show some degree of promise as fracture criteria are the C* and delta T sub c integrals. The mathematical aspects of these parameters are reviewed. This is accomplished by deriving generalized vector forms of the parameters using conservation laws which are valid for arbitrary, three dimensional, cracked bodies with crack surface tractions (or applied displacements), body forces, inertial effects and large deformations. Two principal conclusions are that delta T sub c is a valid crack tip parameter during nonsteady as well as steady state creep and that delta T sub c has an energy rate interpretation whereas C* does not. An efficient, small displacement, infinitestimal strain, displacement based finite element model is developed for general elastic/plastic material behavior. For the numerical studies, this model is specialized to two dimensional plane stress and plane strain and to power law creep constitutive relations.

  14. Irradiation creep of SA 304L and CW 316 stainless steels: Mechanical behaviour and microstructural aspects. Part I: Experimental results

    NASA Astrophysics Data System (ADS)

    Garnier, J.; Bréchet, Y.; Delnondedieu, M.; Pokor, C.; Dubuisson, P.; Renault, A.; Averty, X.; Massoud, J. P.

    2011-06-01

    Solution annealed 304L (SA 304L) and cold work 316 (CW 316) austenitic stainless steel irradiation creep behaviour have been studied thoroughly. Irradiations were carried out in fast breeder reactors BOR-60 (at 330 °C, up to 120 dpa) and EBR-II (at 375 °C, up to 10.5 dpa), and in the OSIRIS mixed spectrum reactor (at 330 °C, up to 9.8 dpa). After an incubation threshold, the irradiation creep of the austenitic stainless steels is linear in stress and in dose. Creep appears to be athermal in this temperature range. A significant difference in the behaviour is measured between the creep of SA 304L and CW 316. In order to study the anisotropy of loop population, which would be the signature of a possible stress induced preferential absorption (SIPA) mechanism for irradiation creep, special attention was given to the measurement of anisotropy of loop distribution between the four families. The anisotropy induced by an applied stress has been shown to be in the range of the statistical scatter in the situation where no stress is applied. TEM microstructural analyses performed on this sample show slight difference between the microstructure of specimens deformed under irradiation and the microstructure of specimens irradiated without stress under the same irradiation conditions.

  15. Deformation (& deformation modes) Parameters in Deformation

    E-print Network

    Subramaniam, Anandh

    . In uniaxial tension test (loading of specimen in uniaxial tension), dislocation `activity' starts well below), dislocation activity can lead to surface intrusions and extrusions (plastic deformation at the microscopic: a fundamental perspective #12;What can happen to a `material' body (solid) on the application of external loads

  16. Geological and structural characterisation of deformation zones of deep seated rockslides in metamorphic rocks

    NASA Astrophysics Data System (ADS)

    Strauhal, T.; Zangerl, C.; Fellin, W.; Brandner, R.

    2012-04-01

    Generally, deep-seated slowly moving rockslides, characterised by average slope velocities in the range of some mm to dm per year, are frequently observed in foliated metamorphic rock masses such as gneisses, schists and phyllites. Many case studies show that this activity behaviour results from deformation, i.e. sliding/creeping along one or several discrete deformation zones which originate from initial rockslide formation processes. From a geological and structural point of view such deformation zones are extremely heterogeneous and are composed of uncemented fault breccias and gouges. The material that is newly formed through cataclasis and fragmentation of the rock during shearing processes possesses soil-like mechanical as well as hydraulical properties. Consequently, slope stability and temporal deformation behaviour of rockslides is dominated by hydro-mechanical deformation zone characteristics rather than by the properties of the overall mass movement. In this study preliminary investigation results about the geological structure and mechanical behaviour of deformation zones of deep-seated rock slides are presented. The case studies herein are located in paragneissic rock masses of the polymetamorphic Austroalpine Ötztal-Stubai complex (Tyrol, Austria). In order to focus on the characterisation of the structure of deformation zones the degree of fragmentation, the spatial distribution of clay-gouges and breccias, moisture content and porosity, the distribution of shear planes, the mineralogical composition and grain shapes as well as grain alignment are investigated. Furthermore the shear strength properties (residual friction angles) are determined by ring shear tests. The results obtained are analysed in combination with geological, structural and geometrical observations of the rockslides from detailed field mapping, borehole and investigation adit data as well as slope deformation measurements. Preliminary results show a complex geological and structural architecture at the basal contact between the rockslide mass and the stable bedrock below. There a several decimetre thick layer of clayey-silty fault gouge zone with variable orientated small-scale slickenslide surfaces were found. Residual friction angle results from shear tests and mineralogical analyses indicate the occurrence of high amounts of sheet silicates but without any swellable minerals. Below and above the gouge layer cohesionless fault breccias (gravelly-sandy) are located with lateral variations in thickness and degree of fragmentation (i.e. block in matrix structures). The new findings increase the process understanding of the deformation behaviour of slow to extremely slow rockslides in metamorphic rocks and provide new fundamentals for comprehensive slope stability analysis.

  17. Unified Creep Plasticity Damage (UCPD) Model for Rigid Polyurethane Foams.

    SciTech Connect

    Neilsen, Michael K.; Lu, Wei-Yang; Scherzinger, William M.; Hinnerichs, Terry D.; Lo, Chi S.

    2015-06-01

    Numerous experiments were performed to characterize the mechanical response of several different rigid polyurethane foams (FR3712, PMDI10, PMDI20, and TufFoam35) to large deformation. In these experiments, the effects of load path, loading rate, and temperature were investigated. Results from these experiments indicated that rigid polyurethane foams exhibit significant volumetric and deviatoric plasticity when they are compressed. Rigid polyurethane foams were also found to be very strain-rate and temperature dependent. These foams are also rather brittle and crack when loaded to small strains in tension or to larger strains in compression. Thus, a new Unified Creep Plasticity Damage (UCPD) model was developed and implemented into SIERRA with the name Foam Damage to describe the mechanical response of these foams to large deformation at a variety of temperatures and strain rates. This report includes a description of recent experiments and experimental findings. Next, development of a UCPD model for rigid, polyurethane foams is described. Selection of material parameters for a variety of rigid polyurethane foams is then discussed and finite element simulations with the new UCPD model are compared with experimental results to show behavior that can be captured with this model.

  18. Application of Radar Interferometry for Monitoring the Landslide Creeping of Jiufen Area, Northern Taiwan

    NASA Astrophysics Data System (ADS)

    Tai, YuHeng; Chang, ChungPai

    2015-04-01

    Taiwan is one of the most active landslide areas in the world because of its high precipitation and active tectonic. Landslide, which destroys buildings and human lives, causes a lot of hazard and economical loss in the recent years. Jiufen, which have been determined as a creeping area with previous studies, is one of the famous tourist place in northern Taiwan. Therefore, detection and monitoring of landslide and creeping thus play an important role in risk management and help us decrease the damage from such mass movement. In this study, we apply Interferometric Synthetic Aperture Radar (InSAR) techniques at Jiufen area to monitor the creeping of slope. InSAR observations are obtained from ERS and ENVISAT, which were launched by European Space Agency, spaning from 1994 to 2008. Persistent Scatterer InSAR (PSInSAR) method is also applied to reduce the phase contributed from atmosphere and topography and help us get more precise measurement. We compare the result with previous studies carried out by fieldwork to confirm the possibility of InSAR techniques applying on landslide monitoring. Moreover, the time-series analysis helps us to understand the motion of the creeping along with time. After completion of some amelioration measures, time-series can illustrate the effect of these structures. Then, the result combining with fieldwork survey will give good suggestion of future remediation works. Furthermore, we estimate the measuring error and possible factors, such as slope direction, dip angle, etc., affecting InSAR result and. The result helps us to verify the reliability of this method and gives us more clear deformation pattern of the creeping area.

  19. Structural characteristics and LA-ICP-MS U-Pb zircon geochronology of the deformed granitic rocks from the Mesozoic Xingcheng-Taili ductile shear zone in the North China Craton

    NASA Astrophysics Data System (ADS)

    Liang, Chenyue; Liu, Yongjiang; Neubauer, Franz; Jin, Wei; Zeng, Zuoxun; Genser, Johann; Li, Weimin; Li, Wei; Han, Guoqing; Wen, Quanbo; Zhao, Yingli; Cai, Libin

    2015-05-01

    We describe the recently detected ENE-trending Xingcheng-Taili ductile strike-slip shear zone, which is an important Mesozoic low- to middle-grade tectonic element formed during the reactivation of the North China Craton (NCC) at the eastern termination of the Yanshanian orogenic belt. Within the Xingcheng-Taili ductile shear zone, the degree of deformation weakens gradually from NW to SE. Three main types of banded granitic gneisses represent low- to middle-grade metamorphic tectonites. New U-Pb zircon dating gives a wide range of protolith ages. Neoarchean granitic rocks with an emplacement age of 2498.4 ± 6.3 Ma have obvious E-W trending banded structures. Upper Triassic granitic rocks with U-Pb zircon ages of 219.7 ± 1.1 Ma, 218.74 ± 0.61 Ma, 212.1 ± 1.6 Ma and 212.3 ± 1.9 Ma are considered to relate to the collision of the NCC and Yangtze craton in early Mesozoic times. The emplacement of biotite adamellite bodies with ages of 159.0 ± 0.8 Ma and 152.4 ± 1.9 Ma is related to the thinning of the NCC's continental crust. An ENE-trending sinistral ductile shear zone developed within these granites. The strongly deformed biotite adamellite bodies bear a gneissosity with S-C fabrics, ENE-trending sinistral shear zones and show the deformation characteristics of a shallow crustal level, reflecting decratonization of the NCC. Crystal lattice preferred orientations (LPO) of quartz, determined by electron back-scatter diffraction, suggest sinistral strike-slip shear and a deformation temperature at about 400 to 500 °C. Quartz mainly shows low-temperature fabrics with a dominant {0001}-slip system similar to the temperature estimated by the micro-structural characteristics of quartz and feldspar. This deformation event might have occurred in Early Cretaceous times and is related to the lithospheric thinning and extension of the North China Craton triggered by an ongoing roll-back of the Pacific Plate beneath the eastern North China Craton.

  20. Creep of whisker-reinforced ceramics

    SciTech Connect

    Routbort, J.L; Goretta, K.C. ); Dominguez-Rodriguez, A.; de Arellano-Lopez, A.R. )

    1991-01-01

    The results of high-temperature creep of various ceramic composites will be reviewed. In particular, creep results for Al{sub 2}O{sub 3} and Si{sub 3}N{sub 4} matrices reinforced with SiC whiskers will be emphasized. For a given temperature, stress and grain size, the creep rate of the Al{sub 2}O{sub 3} composite is usually lower than that of the ceramic matrix. In general, creep at low stresses occurs by grain boundary sliding accommodated by diffusion, whereas higher stresses lead to damage accumulation processes which are manifested by triple point cavitation and cracking. The quasi-steady-state creep rates depend on grain size, whisker concentration, and the amount of glass phase present between the boundary of the whisker and the matrix. Unless all of the parameters are known, including the fabrication and loading histories, comparisons between various studies that used samples prepared in different ways are difficult. 44 refs., 7 figs., 2 tabs.

  1. Atmospheric pressure creep experiments using highly dense fine-grained mineral aggregates

    NASA Astrophysics Data System (ADS)

    Hiraga, T.; Miyazaki, T.; Tasaka, M.; Sueyoshi, K.; Nakakoji, S.; Koizumi, S.; Yoshida, H.

    2012-12-01

    Historically in mineral and rock physics, atmospheric pressure creep tests have been used extensively to study the rheological properties of minerals through deformation of single crystals. This technique has several advantages including minimal friction effects on the loading column, which allows excellent stress resolution on the sample, and stable temperature control, which allows long duration experiments at relatively slow strain rates. The downside of atmospheric pressure experiments on polycrystalline samples is that cavities and cracks are easily introduced during the test, resulting in brittle failure of the specimen. It is generally found that the confining pressure should be larger than the applied differential stress to avoid failure due to microcracking. Consequently very few creep experiments under atmospheric pressure have been conducted on polycrystalline samples. We revisit this classic method of atmospheric pressure creep experiments by developing a technique to synthesize very fine grained aggregates with essentially zero porosity. So far, we are able to reach even 200 micron grain size for certain type of mineral assemblies. During grain size sensitive creep, we expect that the differential stress applied to the samples can be reduced 100 to 1000 times the stress to deform coarser grained samples at the same strain rate condition by reducing grain size of one order of magnitude. Taking into account of ~10 micron grain size as a common value in conventional experiments, we should be able to reduce the applied stress of > 2500 times. Such lowering the applied stress will help to prevent cracking and/or cavitation in the samples. Using this technique, we have been able to demonstrate (i) superplasticity, (ii) microstructural development comparable to that in observed natural mylonites, (iii) flow strength as a function of stress, grain size and temperature, (iv) the effect of the fraction of second phase on flow strength in poly-phase materials, (v) fabric development as a function of strain, (vi) grain growth behavior during deformation, (vii) deformation during chemical reaction, and (viii) the effect of melt on deformation microstructures of synthetic geomaterials.

  2. A Phenomenological Description of Primary Creep in Class M Materials

    NASA Technical Reports Server (NTRS)

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

    1999-01-01

    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.

  3. Data from theodolite measurements of creep rates on San Francisco Bay region faults, California, 1979-2012

    USGS Publications Warehouse

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

    2009-01-01

    From 1979 until his retirement from the project in 2001, Jon Galehouse of San Francisco State University (SFSU) and many student research assistants measured creep (aseismic slip) rates on these faults. The creep measurement project, which was initiated by Galehouse, continued through the Geosciences Department at SFSU from 2001-2006 under the direction of Karen Grove and John Caskey (Grove and Caskey, 2005) and since 2006 under Caskey (2007). Forrest McFarland has managed most of the technical and logistical project operations, as well as data processing and compilation since 2001. Data from 2001-2007 are found in McFarland and others (2007). From 2009 onward, we have released the raw data annually using this report (OF2009-1119) as a permanent publication link, while publishing more detailed analyses of these data in the scientific literature, such as Lienkaemper and others (2014a). 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 links to 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 Web site.

  4. The use of thick-walled hollow cylinder creep tests for evaluating flow criteria for rock salt

    SciTech Connect

    Morgan, H.S.; Wawersik, W.R.

    1990-01-01

    Finite element simulations of two laboratory creep tests on thick-walled hollow cylinders of rock salt are evaluated to determine if such bench-scale experiments can be used to establish applicability of either von Mises or Tresca stress measures and associated flow conditions. In the tests, the cylinders were loaded axially and pressurized both internally and externally to produce stress fields similar to those found around underground excavations in rock salt. Several different loading stages were used in each test. The simulations show that for each of two creep models studied, quite different deformations of the cylinders are predicted with the Mises and Tresca flow criteria, especially if friction between the cylinders and axial loading platens is ignored. When friction is included in the simulations, the differences in deformation are changed but are sill clearly distinguishable. 10 refs., 10 figs.

  5. Spinal deformity.

    PubMed

    Bunnell, W P

    1986-12-01

    Spinal deformity is a relatively common disorder, particularly in teenage girls. Early detection is possible by a simple, quick visual inspection that should be a standard part of the routine examination of all preteen and teenage patients. Follow-up observation will reveal those curvatures that are progressive and permit orthotic treatment to prevent further increase in the deformity. Spinal fusion offers correction and stabilization of more severe degrees of scoliosis. PMID:3786010

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

    USGS Publications Warehouse

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

    2007-01-01

    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.

  7. Computational implementation of the multi-mechanism deformation coupled fracture model for salt

    SciTech Connect

    Koteras, J.R.; Munson, D.E.

    1996-05-01

    The Multi-Mechanism Deformation (M-D) model for creep in rock salt has been used in three-dimensional computations for the Waste Isolation Pilot Plant (WIPP), a potential waste, repository. These computational studies are relied upon to make key predictions about long-term behavior of the repository. Recently, the M-D model was extended to include creep-induced damage. The extended model, the Multi-Mechanism Deformation Coupled Fracture (MDCF) model, is considerably more complicated than the M-D model and required a different technology from that of the M-D model for a computational implementation.

  8. Creep on a composite resin in water.

    PubMed

    Hirano, S; Hirasawa, T

    1989-06-01

    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

  9. Block versus continuum deformation in the Western United States

    USGS Publications Warehouse

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

    1994-01-01

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

  10. Edge di raction of creeping rays S. J. Chapman

    E-print Network

    Chapman, Jon

    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

  11. Constant structure creep of copper at 973K

    SciTech Connect

    Broyles, S.E.; Gibeling, J.C.

    1995-09-01

    The results from studies indicate there is no change in the constant structure glide kinetics of copper across the 673 to 973K temperature range. The values of the obstacle strength parameter, g{sub o}, are in the range of 0.701 and 0.785, which is characteristic of medium strength obstacles such as forest dislocations. Also, the true activation area results are in agreement with the results of other FCC metals,a nd are of the order expected for forest dislocation cutting. The linear relationship between {beta} and {mu}(T)/T{sigma} does not change in this temperature range, and is in good agreement with the results from other FCC metals. Most importantly, the values of {Delta}G are similar across all of the temperatures and lie in the range of 112 to 123 kJ/mole. A good correlation exists between {Delta}G and the activation energies for creep reported by Barrett and Sherby, 117 kJ/mole, and Feltham, and Meakin, 125.5 kJ/mole, for the temperature range of 673 to 873K. The results of these constant structure creep tests demonstrate that there is no change in the dislocation glide kinetics over the temperature rage 673 to 973K.

  12. 20 years of SAR measurements along the NAFS: interseismic deformation

    NASA Astrophysics Data System (ADS)

    Stramondo, S.; Walter, T. R.; Ergintav, S.; Diao, F.; Wang, R.; Polcari, M.; Serpelloni, E.; Devoti, R.

    2014-12-01

    A comprehensive analysis of the earthquake cycle is a key issue for the definition of the hazard in seismic areas. Advanced SAR Interferometry (A-InSAR) techniques have today a key role in Earth Sciences thanks to the capability to detect and measure slow surface movements along wide areas, and to follow the evolution of signal along a certain time periods. A-InSAR techniques have been applied to large datasets of SAR images spanning long time intervals and, together with in-situ surveys and ground measurements, can provide suitable information about the causes of post seismic (deformation rebound or residual strain release) and interseismic (seismic, creep) movements. In the framework of FP7 MARSITE (Marmara Supersite) project we have investigated the Western sector of North Anatolian Fault System (NAFS) from Istanbul toward Duzce area. From West toward the Marmara Sea region (Mudurnu/Akyaz) the NAFS begins to lose its single fault line character and splays into a complex fault system. The main Marmara Fault is argued to be a very young structure and exhibits typical characteristics of a major strike slip fault. In 1999 the August 17th Izmit earthquake was followed few months later by the Duzce mainshock. We compare the A-InSAR results to permanent GPS stations installed in the region after the Izmit/Duzce earthquakes. These observations allow studying the post-seismic deformation of the 1999 Izmit/Düzce earthquake. We investigate the response of the eastern Marmara Fault to the quasi-static loading caused by Izmit/Düzce earthquakes. Overlapped post-seismic processes of fault creep (or afterslip) and viscoelastic relaxation of the lower crust and the upper mantle were investigated. We firstly estimated the viscoelastic relaxation effect using well covered long-term GPS data. This relaxation effect was subtracted from the InSAR data and the remaining InSAR data was inverted to identify localized slip variation along the MMF. Our inversion results imply that part of the MMF segment is subject to aseismic fault movement. The fault movement might be triggered by the 1999 Izmit/Düzce earthquakes, and has partially released the strain accumulated on this segment, challenging previous interpretations on a possible rupture of this segment of the fault.

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

    PubMed

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

    2009-06-18

    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

  14. Effects of misalignment on mechanical behavior of metals in creep

    NASA Technical Reports Server (NTRS)

    Wu, H. C.

    1981-01-01

    Creep tests were conducted by means of a closed loop servocontrolled materials test system. The strain history prior to creep is carefully monitored. Tests were performed for aluminum alloy 6061-O at 150 C and were monitored by a PDP 11/04 minicomputer at a preset constant plastic strain rate prehistory. The results show that the plastic strain rate prior to creep plays a significant role in creep behavior. The endochronic theory of viscoplasticity was applied to describe the observed creep curves. Intrinsic time and strain rate sensitivity function concepts are employed and modified according to the present observation.

  15. Penetrative Deformation of Dolostones during Contact Metamorphism and the Forceful Emplacement of the Tungstonia Granite, Kern Mountains, Nevada 

    E-print Network

    Goodson, Kyle

    2014-08-05

    &M University in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE Chair of Committee, Andreas Kronenberg Committee Members, Will Lamb Julie Newman David Sparks Ibrahim Karaman Head of Department, Rick Giardino... dislocation and diffusion creep, while deformation further from the contact appears to be dominated by intracrystalline dislocation creep. iv ACKNOWLEDGEMENTS I would like to thank my committee chair, Dr. Andreas...

  16. Crustal deformation in southern California using SAR interferometry

    USGS Publications Warehouse

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

    1997-01-01

    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.

  17. Polycrystal creep in the microplastic stress range

    NASA Astrophysics Data System (ADS)

    Dudarev, E. F.; Pochivalova, G. P.

    1993-06-01

    A microcreep theory has been developed for polycrystalline materials, which incorporates the microplastic strain in the aggregate on static loading. Experiments have been performed on the creep laws for polycrystalline metals and alloys, and it is found that the theory fits the experiments. The mobile-dislocation density decreases during microcreep.

  18. Quantum deformations

    SciTech Connect

    Zachos, C.K.

    1990-01-01

    I review and illustrate applications of explicit functionals we have found which map SU(2) algebra generators to those of several quantum deformations of this Lie algebra. I indicate how virtually any such quantized algebra can be mapped to any other, and how representations of such algebras can be expressed as simple functions of SU(2) representations. The representation theory and its comultiplication rules are thus systematized and streamlined by direct reference to their SU(2) correspondents, and may be rapidly surveyed. I further provide a candidate quantum deformation of the Virasoro algebra. 19 refs.

  19. Quaternary deformation

    SciTech Connect

    Brown, R.D. Jr.

    1990-01-01

    Displaced or deformed rock units and landforms record the past 2 m.y. of faulting, folding, uplift, and subsidence in California. Properly interpreted, such evidence provides a quantitative basis for predicting future earthquake activity and for relating many diverse structures and landforms to the 5 cm/yr of horizontal motion at the boundary between the North American and Pacific plates. Modern techniques of geologic dating and expanded research on earthquake hazards have greatly improved our knowledge of the San Andreas fault system. Much of this new knowledge has been gained since 1965, and that part which concerns crustal deformation during the past 2 m.y. is briefly summarized here.

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

    SciTech Connect

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

    2011-06-01

    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.

  1. Tensile Creep of Polycrystalline Near-Stoichiometric NiAl

    NASA Technical Reports Server (NTRS)

    Raj, Sai V.

    2002-01-01

    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.

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

    NASA Technical Reports Server (NTRS)

    Rogers, Jan R.; Hyers, Robert

    2008-01-01

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

  3. Suppression of creep-regime dynamics in epitaxial ferroelectric BiFeO3 films

    PubMed Central

    Shin, Y. J.; Jeon, B. C.; Yang, S. M.; Hwang, I.; Cho, M. R.; Sando, D.; Lee, S. R.; Yoon, J.-G.; Noh, T. W.

    2015-01-01

    Switching dynamics of ferroelectric materials are governed by the response of domain walls to applied electric field. In epitaxial ferroelectric films, thermally-activated ‘creep’ motion plays a significant role in domain wall dynamics, and accordingly, detailed understanding of the system’s switching properties requires that this creep motion be taken into account. Despite this importance, few studies have investigated creep motion in ferroelectric films under ac-driven force. Here, we explore ac hysteretic dynamics in epitaxial BiFeO3 thin films, through ferroelectric hysteresis measurements, and stroboscopic piezoresponse force microscopy. We reveal that identically-fabricated BiFeO3 films on SrRuO3 or La0.67Sr0.33MnO3 bottom electrodes exhibit markedly different switching behaviour, with BiFeO3/SrRuO3 presenting essentially creep-free dynamics. This unprecedented result arises from the distinctive spatial inhomogeneities of the internal fields, these being influenced by the bottom electrode’s surface morphology. Our findings further highlight the importance of controlling interface and defect characteristics, to engineer ferroelectric devices with optimised performance. PMID:26014521

  4. Steady-state creep of bent reinforced metal-composite plates with consideration of their reduced resistance to transverse shear 2. Analysis of calculated results

    NASA Astrophysics Data System (ADS)

    Yankovskii, A. P.

    2014-07-01

    Deformation of annular plates with different structures of helical reinforcement is studied. It is demonstrated that the use of the classical theory for calculating steady-state creep for thick reinforced plates subjected to bending leads to underprediction of the compliance of thin-walled metal-composite structures. It is also shown that there are significant shear strain rates in the binder of such plates, which has to be taken into account and which is mainly responsible for creep strain accumulation. Results calculated by two different models, which take into account the composite structure, are compared.

  5. Plastic Deformation of Aluminum Single Crystals at Elevated Temperatures

    NASA Technical Reports Server (NTRS)

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

    1956-01-01

    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.

  6. Creep rupture as a non-homogeneous Poissonian process

    PubMed Central

    Danku, Zsuzsa; Kun, Ferenc

    2013-01-01

    Creep rupture of heterogeneous materials occurring under constant sub-critical external loads is responsible for the collapse of engineering constructions and for natural catastrophes. Acoustic monitoring of crackling bursts provides microscopic insight into the failure process. Based on a fiber bundle model, we show that the accelerating bursting activity when approaching failure can be described by the Omori law. For long range load redistribution the time series of bursts proved to be a non-homogeneous Poissonian process with power law distributed burst sizes and waiting times. We demonstrate that limitations of experiments such as finite detection threshold and time resolution have striking effects on the characteristic exponents, which have to be taken into account when comparing model calculations with experiments. Recording events solely within the Omori time to failure the size distribution of bursts has a crossover to a lower exponent which is promising for forecasting the imminent catastrophic failure. PMID:24045539

  7. Characterization of strain rate sensitivity in pharmaceutical materials using indentation creep analysis.

    PubMed

    Katz, Jeffrey M; Buckner, Ira S

    2013-02-14

    Understanding how a material's response to stress changes as the stress is applied at different rates is important in predicting performance of pharmaceutical powders during tablet compression. Widely used methods for determining strain rate sensitivity (SRS) are empirically based and can often provide inconsistent or misleading results. Indentation creep data, collected during hardness tests on compacts formed from several common tableting excipients, were used to predict each material's relative sensitivity to changes in strain rate. Linear relationships between Ln(indentation hardness) and Ln(strain rate) were observed for all materials tested. The slope values taken from these relationships were compared to traditional strain rate sensitivity estimates based on in-die Heckel analysis. Overall, the results from the two methods were quite similar, but several advantages were evident in the creep data. The most notable advantage was the ability to characterize strain rate sensitivity derived from plastic behavior with little influence of elastic deformation. For example, two grades of corn starch had very similar creep behavior, but their yield pressures were affected very differently when the compaction rate was increased. This inconsistency was related to the difference in the viscoelastic recovery exhibited by these two materials. This new method promises to allow a better understanding of strain rate effects observed during tablet manufacturing. PMID:22985770

  8. Creep fatigue of low-cobalt superalloys: Waspalloy, PM U 700 and wrought U 700

    NASA Technical Reports Server (NTRS)

    Leis, B. N.; Rungta, R.; Hopper, A. T.

    1983-01-01

    The influence of cobalt content on the high temperature creep fatigue crack initiation resistance of three primary alloys was evaluated. These were Waspalloy, Powder U 700, and Cast U 700, with cobalt contents ranging from 0 up to 17 percent. Waspalloy was studied at 538 C whereas the U 700 was studied at 760 C. Constraints of the program required investigation at a single strain range using diametral strain control. The approach was phenomenological, using standard low cycle fatigue tests involving continuous cycling tension hold cycling, compression hold cycling, and symmetric hold cycling. Cycling in the absence of or between holds was done at 0.5 Hz, whereas holds when introduced lasted 1 minute. The plan was to allocate two specimens to the continuous cycling, and one specimen to each of the hold time conditions. Data was taken to document the nature of the cracking process, the deformation response, and the resistance to cyclic loading to the formation of small cracks and to specimen separation. The influence of cobalt content on creep fatigue resistance was not judged to be very significant based on the results generated. Specific conclusions were that the hold time history dependence of the resistance is as significant as the influence of cobalt content and increased cobalt content does not produce increased creep fatigue resistance on a one to one basis.

  9. Elevated temperature creep properties of NiAl cryomilled with and without Y2O3

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. Daniel; Luton, Michael J.

    1995-01-01

    The creep properties of lots of NiAl cryomilled with and without Y2O3 have been determined in compression and tension. Although identical cryomilling procedures were used, differences in composition were found between the lot ground with 0.5 vol% yttria and the lot ground without Y2O3. Compression testing between 1000 and 1300 K yielded similar creep strengths for both materials, while tensile creep rupture testing indicated that the yttria-containing alloy was slightly stronger than the Y2O3-free version. Both compression and tensile testing showed two deformation regimes; whereas the stress state did not affect the high stress exponent (n approximately equals 10) mechanism, the low stress exponent regime n was approximately 6 in tension and approximately 2 in compression. The strengths in tension were somewhat less than those measured in compression, but the estimated activation energies (Q) of approximately 600 kJ/mol for tensile testing were closer to the previously measured values (approximately 700 kJ/mol) for NiAl-AlN and very different from the Q's of 400 and 200 kJ/mol for compression tests in the high and low stress exponent regimes, respectively. A Larson-Miller comparison indicated that cryomilling can produce an alloy with long-term, high-temperature strength at least equal to conventional superalloys.

  10. A comparison of long-baseline strain data and fault creep records obtained near Hollister, California

    USGS Publications Warehouse

    Slater, L.E.; Burford, R.O.

    1979-01-01

    A comparison of creepmeter records from nine sites along a 12-km segment of the Calaveras fault near Hollister, California and long-baseline strain changes for nine lines in the Hollister multiwavelength distance-measuring (MWDM) array has established that episodes of large-scale deformation both preceded and accompanied periods of creep activity monitored along the fault trace during 1976. A concept of episodic, deep-seated aseismic slip that contributes to loading and subsequent aseismic failure of shallow parts of the fault plane seems attractive, implying that the character of aseismic slip sensed along the surface trace may be restricted to a relatively shallow (~ 1-km) region on the fault plane. Preliminary results from simple dislocation models designed to test the concept demonstrate that extending the time-histories and amplitudes of creep events sensed along the fault trace to depths of up to 10 km on the fault plane cannot simulate adequately the character and amplitudes of large-scale episodic movements observed at points more than 1 km from the fault. Properties of a 2-3-km-thick layer of unconsolidated sediments present in Hollister Valley, combined with an essentially rigid-block behavior in buried basement blocks, might be employed in the formulation of more appropriate models that could predict patterns of shallow fault creep and large-scale displacements much more like those actually observed. ?? 1979.

  11. Bimodal distribution of creep event amplitudes on the San Andreas fault, California

    USGS Publications Warehouse

    Burford, R.O.

    1977-01-01

    EPISODIC fault creep, at several instrument sites along the San Andreas and associated faults in central California consists of a few small and large slip events per year generally superimposed on a background of gradual yielding at low rates1-3. Most of the events are aseismic, but a few minor displacement steps have occured in association with local earthquakes 12. After removal of earthquake steps, event lists for several sites include significant numbers of small events about an order or magnitude below the typical 1-4-mm amplitude range for large events1, 3. Recent experimental rock-deformation results demonstrate that under biaxial loading some rocks show episodic slip on pre-cut surfaces9,10. It is not yet clear how the laboratory and field observations are related, but the data presented here indicate that episodic fault creep in nature may be more complex than previously realised. In light of the laboratory results, it is more important than ever to consider all the details of the field data concerning fault creep. ?? 1977 Nature Publishing Group.

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

    NASA Astrophysics Data System (ADS)

    Hangx, S. J. T.; Spiers, C. J.; Peach, C. J.

    2010-09-01

    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 injection of CO2 and the concomitant acidification of the pore fluid inhibited microcracking in both the quartz and feldspar samples in line with known effects of pH on stress corrosion cracking. We infer that the injection of CO2 into quartz- and plagioclase-bearing sandstones will inhibit grain scale microcracking process and that related geomechanical effects, such as reservoir compaction and surface subsidence, will be negligible compared with the poroelastic response.

  13. Assessment of Creep Capability of HSR-EPM Turbine Airfoil Alloys

    NASA Technical Reports Server (NTRS)

    MacKay, Rebecca A.; Garg, Anita; Ritzert, Frank J.; Locci, Ivan E.

    2007-01-01

    The High Speed Civil Transport (HSCT) mission of the High Speed Research-Enabling Propulsion Materials (HSR-EPM) Program represented a unique challenge for turbine airfoil materials because the highest operating temperatures occur during climb and supersonic cruise. The accumulated hot time of an HSCT engine before overhaul is many thousands of hours. This is significantly different from subsonic engines, where the maximum operating temperatures occur during takeoff and thrust reverse after landing, and the accumulated hot time before overhaul is about 300 hr. The goal of airfoil alloy development under the HSR-EPM Program was to develop an alloy with a 75 F increase in creep rupture capability over the average Rene N5/PWA 1484 baseline. Airfoil alloy development under the HSR-EPM Program pursued a path that led to evolutionary mechanical behavior improvements, resulting from increased amounts of high density, refractory metals. The purpose of the present paper is to describe the experimental work that was performed at NASA Glenn Research Center after the HSR-EPM Program ended. Emphasis will be placed on the creep behavior of coated specimens, as well as on the development and progression of phase instabilities during creep deformation. Mitigation techniques that were used to reduce phase instabilities are also discussed. Most of the work described in this report was performed at NASA Glenn during the years 2000 and 2001.

  14. Tensile creep and creep rupture behavior of monolithic and SiC-whisker-reinforced silicon nitride ceramics

    SciTech Connect

    Ohji, Tatsuki; Yamauchi, Yukihiko )

    1993-12-01

    The tensile creep and creep rupture behavior of silicon nitride was investigated at 1,200 to 1,350 C using hot-pressed materials with and without SiC whiskers. Stable steady-state creep was observed under low applied stresses at 1,200 C. Accelerated creep regimes, which were absent below 1,300 C, were identified above that temperature. The appearance of accelerated creep at the higher temperatures attributable to formation of microcracks throughout a specimen. The whisker-reinforced material exhibited better creep resistance than the monolith at 1,200 C. Considerably high values 3 to 5, were obtained for the creep exponent in the overall temperature range. The exponent tended to decrease with decreasing applied stress at 1,200 C. The primary creep mechanism was considered cavitation-enhanced creep. Specimen lifetimes followed the Monkman-Grant relationship except for fractures with large accelerated creep regimes. The creep rupture behavior is discussed in association with cavity formation and crack adolescence.

  15. Experimental study of cyclic creep and high-cycle fatigue of welded joints of St3 steel by the DIC technique

    NASA Astrophysics Data System (ADS)

    Kibitkin, Vladimir V.; Solodushkin, Andrey I.; Pleshanov, Vasily S.

    2015-10-01

    In the paper the mechanisms of plastic deformation and fracture of welded joints of steel St3 were investigated at high-cycle fatigue and cyclic creep by the digital image correlation (DIC) technique. The evolution of strain rate is studied for the following regions: base metal, HAZ, and fusion zone. This strain rate evolution can be considered as a mechanical response of material. Three stages of deformation evolution are shown: deformation hardening (I), fatigue crack initiation (II), and the last stage is related to main crack (III). Two criteria are offered to evaluate the current mechanical state of welded joints.

  16. A high-temperature torsion apparatus for the high-resolution characterization of internal friction and creep in refractory metals

    E-print Network

    Cooper, Reid F.

    materials initially display a decelerating transient in the strain rate that decays to a ``steady-state'' regime of con- stant, or near-constant strain rate. This initial transient re- sponse is often ignored, it is often difficult to accurately measure the high strain rates­ characteristic of transient creep

  17. Multi-scale InSAR analysis of aseismic creep across the San Andreas, Calevaras,and Hayward Fault systems

    NASA Astrophysics Data System (ADS)

    Agram, P. S.; Simons, M.

    2011-12-01

    We apply the Multi-scale Interferometric Time-series (MInTS) technique, developed at Caltech,to study spatial variations in aseismic creep across the San Andreas, Calaveras and Hayward Faultsystems in Central California.Interferometric Synthetic Aperture Radar (InSAR) Time-series methods estimate the spatio-temporal evolution of surface deformation using multiple SAR interferograms. Traditional time-series analysis techniques like persistent scatterers and short baseline methods assume the statistical independence of InSAR phase measurements over space and time when estimating deformation. However, existing atmospheric phase screen models clearly show that noise in InSAR phase observations is correlated over the spatial domain. MInTS is an approach designed to exploit the correlation of phase observations over space to significantly improve the signal-to-noise ratio in the estimated deformation time-series compared to the traditional time-series InSAR techniques. The MInTS technique reduces the set of InSAR observations to a set of almost uncorrelated observations at various spatial scales using wavelets. Traditional inversion techniques can then be applied to the wavelet coefficients more effectively. Creep across the Central San Andreas Fault and the Hayward Fault has been studied previously using C-band (6 cm wavelength) ERS data, but detailed analysis of the transition zone between the San Andreas and Hayward Faults was not possible due to severe decorrelation. Improved coherence at L-band (24 cm wavelength) significantly improves the spatial coverage of the estimated deformation signal in our ALOS PALSAR data set. We analyze 450 ALOS PALSAR interferograms processed using 175 SAR images acquired between Dec 2006 and Dec 2010 that cover the area along the San Andreas Fault System from Richmond in the San Francisco Bay Area to Maricopa in the San Joaquin Valley.We invert the InSAR phase observations to estimate the constant Line-of-Sight (LOS) deformation velocity and the periodic seasonal terms using the MInTS technique. We model the estimated LOS velocity field using simple fault models.The average surface creep across the Central San Andreas, Hayward and the Calaveras Faults are estimated at 35+-4 mm/yr, 7+-2 mm/yr and 15+-4 mm/yr respectively, assuming zero vertical deformation along the faults. We observe spatial variations in creep across the Central San Andreas Fault,in agreement with previously published work. We also observe a deformation signal along the length of the southern Calaveras Fault, suggesting possible interaction between the Hayward and the Calaveras Faults which is consistent with earlier geological studies.

  18. Shape Memory Characteristics of Ti(sub 49.5)Ni(sub 25)Pd(sub 25)Sc(sub 0.5) High-Temperature Shape Memory Alloy After Severe Plastic Deformation

    NASA Technical Reports Server (NTRS)

    Atli, K. C.; Karaman, I.; Noebe, R. D.; Garg, A.; Chumlyakov, Y. I.; Kireeva, I. V.

    2011-01-01

    A Ti(49.5)Ni25Pd25Sc(0.5) high-temperature shape memory alloy is thermomechanically processed to obtain enhanced shape-memory characteristics: in particular, dimensional stability upon repeated thermal cycles under constant loads. This is accomplished using severe plastic deformation via equal channel angular extrusion (ECAE) and post-processing annealing heat treatments. The results of the thermomechanical experiments reveal that the processed materials display enhanced shape memory response, exhibiting higher recoverable transformation and reduced irrecoverable strain levels upon thermal cycling compared with the unprocessed material. This improvement is attributed to the increased strength and resistance of the material against defect generation upon phase transformation as a result of the microstructural refinement due to the ECAE process, as supported by the electron microscopy observations.

  19. Effect of Overheating on Creep-rupture Properties of S-816 Alloy at 1,500 F

    NASA Technical Reports Server (NTRS)

    Rowe, John P; Freeman, J W

    1957-01-01

    The effects of overheats to temperatures of 1650, 1800, 1900, and 2000 F were evaluated in terms of the changes in creep-rupture characteristics at 1500 F of S-816 alloy under stresses within the range of rupture strengths of the alloy for 100 to 1000 hours. Overheat periods were predominantly of 2-minute duration and were applied cyclically at approximately 5- or 12-hour intervals. The possible damage from overheating was believed to include internal metal structure changes induced by exposure to the higher temperatures and loss of life by creep if stress was present during the overheats.

  20. Implications of recent asperity failures and aseismic creep for time-dependent earthquake hazard on the Hayward fault

    NASA Astrophysics Data System (ADS)

    Shirzaei, Manoochehr; Bürgmann, Roland; Taira, Taka'aki

    2013-06-01

    The probability of large seismic events on a particular fault segment may vary due to external stress changes imparted by nearby deformation events, including other earthquakes and aseismic processes, such as fault creep and postseismic relaxation. The Hayward fault (HF), undergoing both seismic and aseismic fault slip, provides a unique opportunity to study the mutual relation of seismic and aseismic processes on a fault system. We use surface deformation data obtained from InSAR (interferometric synthetic aperture radar), creepmeters and alinement arrays, together with constraints provided by repeating earthquakes to investigate the kinematics of fault creep on the northern HF and its relation to two seismic clusters (Mw?4.1) in October 2011 and March 2012, and an Mw 4.2 event in July 2007. Recurrences of nearby repeating earthquakes show that these episodes involved both seismic and aseismic slip. We model the stress changes due to fault creep and the recent seismic activity on the locked central asperity of the HF, which is believed to be the rupture zone of past and future M~7 earthquakes. The results show that the shallow fault creep stresses the major locked central patch at an average rate of 0.001-0.003 MPa/yr, in addition to background stressing at 0.01-0.015 MPa/yr. Given the time-dependent nature of the creep, occasional deviations from this stressing rate occur. We find that the 2011 seismic cluster occurred in areas on the fault that are stressed up to 0.01 MPa/yr due to aseismic slip on the surrounding segments, suggesting that the occurrence of these events was encouraged by the fault creep. Changes in the probability of major earthquakes can be estimated from the imparted stress from the recent earthquakes and associated fault creep transients. We estimate that the 1-day probability of a large event on the HF only increased by up to 0.18% and 0.05% due to the static stress increase and stressing rate change by the 2011 and 2012 clusters. For the July 2007 south Oakland event (Mw 4.2) the estimated increase of short-term probabilities is 50%, highlighting the importance of short-term probability changes due to transient stress changes.

  1. Axial creep-rupture time of boron-aluminum composites

    SciTech Connect

    Goda, Koichi; Hamada, Jun`ichi

    1995-11-01

    Axial creep tests of a 10vol% boron-aluminum hotpressed monolayer composite were carried out under several constant loads at 300 C in air. The composite behaved with slight primary creep, but did not show appreciable secondary creep. Several specimens encountered a momentary increase of strain during the creep test which separated the creep curve into two regions, because of the individual fiber breaks in the composite. And then, almost all the specimens suddenly fractured without tertiary creep. From the viewpoint of reliability engineering the statistical properties of the creep-rupture time were investigated. The average creep-rupture time decreased with an increase in the applied stress, and the relatively large coefficient of variation was estimated in every case, being around 1,000%. However, these scatters were estimated to be smaller than the scatter of creep-rupture time in the boron fiber itself. That means, the reliability of the fiber`s creep-rupture time is improved by compositing with matrix material.

  2. Fluid Assisted Compaction and Deformation of Reservoir Lithologies

    SciTech Connect

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

    2002-02-13

    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.

  3. Elevated temperature deformation of thoria dispersed nickel-chromium

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

    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.

  4. Dynamic triggering of creep events in the Salton Trough, Southern California by regional M ? 5.4 earthquakes constrained by geodetic observations and numerical simulations

    NASA Astrophysics Data System (ADS)

    Wei, Meng; Liu, Yajing; Kaneko, Yoshihiro; McGuire, Jeffrey J.; Bilham, Roger

    2015-10-01

    Since a regional earthquake in 1951, shallow creep events on strike-slip faults within the Salton Trough, Southern California have been triggered at least 10 times by M ? 5.4 earthquakes within 200 km. The high earthquake and creep activity and the long history of digital recording within the Salton Trough region provide a unique opportunity to study the mechanism of creep event triggering by nearby earthquakes. Here, we document the history of fault creep events on the Superstition Hills Fault based on data from creepmeters, InSAR, and field surveys since 1988. We focus on a subset of these creep events that were triggered by significant nearby earthquakes. We model these events by adding realistic static and dynamic perturbations to a theoretical fault model based on rate- and state-dependent friction. We find that the static stress changes from the causal earthquakes are less than 0.1 MPa and too small to instantaneously trigger creep events. In contrast, we can reproduce the characteristics of triggered slip with dynamic perturbations alone. The instantaneous triggering of creep events depends on the peak and the time-integrated amplitudes of the dynamic Coulomb stress change. Based on observations and simulations, the stress change amplitude required to trigger a creep event of a 0.01-mm surface slip is about 0.6 MPa. This threshold is at least an order of magnitude larger than the reported triggering threshold of non-volcanic tremors (2-60 kPa) and earthquakes in geothermal fields (5 kPa) and near shale gas production sites (0.2-0.4 kPa), which may result from differences in effective normal stress, fault friction, the density of nucleation sites in these systems, or triggering mechanisms. We conclude that shallow frictional heterogeneity can explain both the spontaneous and dynamically triggered creep events on the Superstition Hills Fault.

  5. Aseismic slip and fault-normal strain along the central creeping section of the San Andreas fault

    USGS Publications Warehouse

    Rolandone, F.; Burgmann, R.; Agnew, D.C.; Johanson, I.A.; Templeton, D.C.; d'Alessio, M. A.; Titus, S.J.; DeMets, C.; Tikoff, B.

    2008-01-01

    We use GPS data to measure the aseismic slip along the central San Andreas fault (CSAF) and the deformation across adjacent faults. Comparison of EDM and GPS data sets implies that, except for small-scale transients, the fault motion has been steady over the last 40 years. We add 42 new GPS, velocities along the CSAF to constrain the regional strain distribution. Shear strain rates are less than 0.083 ?? 0.010 ??strain/yr adjacent to the creeping SAF, with 1-4.5 mm/yr of contraction across the Coast Ranges. Dislocation modeling of the data gives a deep, long-term slip rate of 31-35 mm/yr and a shallow (0-12 km) creep rate of 28 mm/yr along the central portion of the CSAF, consistent with surface creep measurements. The lower shallow slip rate may be due to the effect of partial locking along the CSAF or reflect reduced creep rates late in the earthquake cycle of the adjoining SAF rupture zones. Copyright 2008 by the American Geophysical Union.

  6. Microscopic View of Accelerated Dynamics in Deformed Polymer Glasses

    SciTech Connect

    Warren, Mya; Rottler, Joerg

    2010-05-21

    A molecular level analysis of segmental trajectories obtained from molecular dynamics simulations is used to obtain the full relaxation time spectrum in aging polymer glasses subject to three different deformation protocols. As in experiments, dynamics can be accelerated by several orders of magnitude, and a narrowing of the distribution of relaxation times during creep is directly observed. Additionally, the acceleration factor describing the transformation of the relaxation time distributions is computed and found to obey a universal dependence on the strain, independent of age and deformation protocol.

  7. Alignment of olivine crystals during diffusion creep in oceanic peridotite mylonites

    NASA Astrophysics Data System (ADS)

    Deems, N. J.; Warren, J. M.; Wolfson-Schwehr, M.

    2014-12-01

    At small grain sizes (<10 µm), olivine is expected to deform by diffusion creep at lithospheric conditions. Microstructural analysis by electron backscatter diffraction of 13 peridotite mylonites from St. Paul's Rocks (SPR) indicates that olivine has a pronounced axial-[010] lattice preferred orientation (i.e. [010] clusters perpendicular to foliation, while [100] and [001] are dispersed in the foliation plane) and a mean grain size of ~7µm. Holtzman et al. (2003) has observed similar LPOs in partially molten samples experimentally deformed under simple shear at lithospheric conditions. The occurrence of a lattice preferred orientation (LPO) is typically interpreted as indicating deformation by dislocation creep. In addition, compositional maps of the samples show that amphibole (pargasite) is ubiquitous. As the presence of pargasite in peridotites is controlled in part by the activity of plagioclase and water at high temperatures (Lynkins and Jenkins, 1992), we infer this as evidence for the presence of pre- to syn-tectonic trapped melt. In order to explain the observed LPO in SPR mylonites, we evaluate the hypothesis that alignment occurred during diffusion creep, such as observed in experiments by Sundberg and Cooper (2008) and Miyazaki et al., (2013). To explore this hypothesis, we conducted analyses of low angle (2-10°) rotation axis inverse pole figures (IPFs), which can often provide insight into the operative slip system(s). Analyses of low angle IPFs from SPR, however, showed no definitive correlation to any one particular slip system. On the other hand, high angle IPFs showed intense clustering of rotational axes at 75-90° about [010], indicating that [100] and [001] align nearly perpendicular to [010]. Based on the IPF analysis and evidence of pre- to syn-tectonic melt, we conclude that the presence of melt lubricated grain boundaries, which resulted in rigid rotation of grains and alignment of the [010] axes controlled by the orthorhombic crystal habit of olivine. That is, as [010] is shortest in terms of habit, this allows [010] to align perpendicular to the shear plane, while the [100] and [001] axes are dispersed in the plane parallel to shear. Thus, SPR mylonites represent a natural example of olivine LPO formation during diffusion creep.

  8. Fatigue and Creep Crack Propagation behaviour of Alloy 617 in the Annealed and Aged Conditions

    SciTech Connect

    Julian K. Benz; Richard N. Wright

    2013-10-01

    The crack propagation behaviour of Alloy 617 was studied under various conditions. Elevated temperature fatigue and creep-fatigue crack growth experiments were conducted at 650 and 800 degrees C under constant stress intensity (triangle K) conditions and triangular or trapezoidal waveforms at various frequencies on as-received, aged, and carburized material. Environmental conditions included both laboratory air and characteristic VHTR impure helium. As-received Alloy 617 displayed an increase in the crack growth rate (da/dN) as the frequency was decreased in air which indicated a time-dependent contribution component in fatigue crack propagation. Material aged at 650°C did not display any influence on the fatigue crack growth rates nor the increasing trend of crack growth rate with decreasing frequency even though significant microstructural evolution, including y’ (Ni3Al) after short times, occurred during aging. In contrast, carburized Alloy 617 showed an increase in crack growth rates at all frequencies tested compared to the material in the standard annealed condition. Crack growth studies under quasi-constant K (i.e. creep) conditions were also completed at 650 degrees C and a stress intensity of K = 40 MPa9 (square root)m. The results indicate that crack growth is primarily intergranular and increased creep crack growth rates exist in the impure helium environment when compared to the results in laboratory air. Furthermore, the propagation rates (da/dt) continually increased for the duration of the creep crack growth either due to material aging or evolution of a crack tip creep zone. Finally, fatigue crack propagation tests at 800 degrees C on annealed Alloy 617 indicated that crack propagation rates were higher in air than impure helium at the largest frequencies and lowest stress intensities. The rates in helium, however, eventually surpass the rates in air as the frequency is reduced and the stress intensity is decreased which was not observed at 650 degrees C.

  9. REVIEW doi:10.1038/nature11032 Deformation cycles of subduction

    E-print Network

    Fialko, Yuri

    earthquake cycle (SEC). When the theory of plate tectonics had just gained wide acceptance, the role of mantle creep in SEC was postulated1,2 to reconcile the overall steady motion of tectonic plates (Fig. 1a). Its prediction that the strongest elastic deformation should be found near plate boundaries

  10. Single-contact pressure solution creep on calcite monocrystals

    E-print Network

    Zubtsov, Sergei; Gratier, Jean-Pierre; Dysthe, Dag; Traskine, Vladimir

    2005-01-01

    Pressure solution creep rates and interface structures have been measured by two methods on calcite single crystals. In the first kind of experiments, calcite monocrystals were indented at 40 degrees C for six weeks using ceramic indenters under stresses in the 50-200 MPa range in a saturated solution of calcite and in a calcite-saturated aqueous solution of NH4Cl. The deformation (depth of the hole below the indenter) is measured ex-situ at the end of the experiment. In the second type of experiment, calcite monocrystals were indented by spherical glass indenters for 200 hours under stresses in the 0-100 MPa range at room temperature in a saturated aqueous solution of calcite. The displacement of the indenter was continuously recorded using a specially constructed differential dilatometer. The experiments conducted in a calcite-saturated aqueous solution of NH4Cl show an enhanced indentation rate owing to the fairly high solubility of calcite in this solution. In contrast, the experiments conducted in a calc...

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

    NASA Technical Reports Server (NTRS)

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

    2010-01-01

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

  12. Creep rupture behavior of Stirling engine materials

    NASA Technical Reports Server (NTRS)

    Titran, R. H.; Scheuerman, C. M.; Stephens, J. R.

    1985-01-01

    The automotive Stirling engine, being investigated jointly by the Department of Energy and NASA Lewis as an alternate to the internal combustion engine, uses high-pressure hydrogen as the working fluid. The long-term effects of hydrogen on the high temperature strength properties of materials is relatively unknown. This is especially true for the newly developed low-cost iron base alloy NASAUT 4G-A1. This iron-base alloy when tested in air has creep-rupture strengths in the directionally solidified condition comparable to the cobalt base alloy HS-31. The equiaxed (investment cast) NASAUT 4G-A1 has superior creep-rupture to the equiaxed iron-base alloy XF-818 both in air and 15 MPa hydrogen.

  13. A universal function of creep rate

    NASA Astrophysics Data System (ADS)

    Li, Jing-Tian; Rong, Xi-Ming; Wang, Jian-Lu; Zhang, Bang-Qiang; Ning, Xi-Jing

    2015-09-01

    In this paper, we derive a universal function from a model based on statistical mechanics developed recently, and show that the function is well fitted to all the available experimental data which cannot be described by any function previously established. With the function predicting creep rate, it is unnecessary to consider which creep mechanism dominates the process, but only perform several experiments to determine the three constants in the function. It is expected that the new function would be widely used in industry in the future. Project supported by the National Natural Science Foundation of China (Grant Nos. 11274073 and 51071048), the Shanghai Leading Academic Discipline Project, China (Grant No. B107), and the Key Discipline Innovative Training Program of Fudan University, China.

  14. Modeling Creep in the Lower Mantle: Insights from the Atomic Scale

    NASA Astrophysics Data System (ADS)

    Hirel, P.; Carrez, P.; Cordier, P.

    2014-12-01

    Convection and plastic deformation in the Earth's lower mantle are expected to occur by processes at various scales, including grain boundary sliding, diffusion, and dislocation creep. Although the composition of the Earth's lower mantle is dominated by the (Mg,Fe,Al)(Si,Al)O3 perovskite, the mechanical properties of this phase, its microstructure, and the relative importance of the mechanisms cited above for its plastic deformation, are still a matter of debate. Given the thermodynamic conditions, both dislocation glide and climb are expected to contribute significantly to the plastic flow, however the activation energies and rates of these mechanisms are still to be determined. In this study we utilize numerical simulations at the atomic scale in MgSiO3 perovskite to investigate the climb of dislocations, at pressure relevant to Earth's lower mantle. The interaction of vacancies with dislocations, as elementary mechanism for dislocation climb, is explicitly computed. It is shown to be dominated by electrostatic effects due to the ionic character of this material, and allow to give scenarios for climb mechanisms. These results give insight into the importance of dislocation creep in the rheology of the mantle. This work was supported by funding from the European Research Council under the Seventh Framework Program (FP7), ERC grant N.290424 - RheoMan.

  15. Creep of a fine-grained, fully-lamellar, two-phase TiAl alloy at 760{degree}C

    SciTech Connect

    Wang, J.N.; Schwartz, A.J.; Nieh, T.G.; Liu, C.T.; Sikka, V.K.; Clemens, D.

    1995-02-01

    Creep of a TiAl alloy, having a composition of Ti-47Al-2Cr-2Nb (in atom %) and a fine-grained, fully-lamellar structure, was carried out at 760 C and stresses between 69--723 MPa. It was found that, in addition to having good room temperature properties, the alloy exhibits higher creep resistance than other TiAl alloys with a similar composition. Both the creep data and microstructures of the alloy suggest that there exists a change in deformation mechanism from a glide-controlled process at high stresses to a recovery-controlled process at low stresses. Also, microstructural evidence indicates that the rate-controlling recovery mechanism is the climb of dislocation segments pinned by ledges at {gamma}/{alpha}{sub 2} interfacial boundaries.

  16. Shark skin effect in creeping films

    E-print Network

    Scholle, M

    2006-01-01

    If a body in a stream is provided with small ridges aligned in the local flow direction, a remarkable drag reduction can be reached under turbulent flow conditions. This surprising phenomenon is called the 'shark skin effect'. We demonstrate, that a reduction of resistance can also be reached in creeping flows if the ridges are aligned perpendicular to the flow direction. We especially consider in gravity-driven film flows the effect of the bottom topography on the mean transport velocity.

  17. A practical method based on stress evaluation ({sigma}{sub d} criterion) to predict initiation of crack under creep and creep-fatigue conditions

    SciTech Connect

    Moulin, D.; Drubay, B.; Acker, D.; Laiarinandrasana, L.

    1995-11-01

    In some parts of primary circuit of fast breeder reactor, where the temperature is higher than 427 C, preservice inspection has revealed indications that were conservatively assumed to be sharp cracks. These pipes are made of 316 SPH material, an austenitic material close to 316L. This material is subjected to creep behavior at this temperature. Here, the behavior of defects like cracks in nuclear components operating at high temperature, where creep is significant, must be under control. There exists the need to have a practical method of analysis, which can be used by engineers, to calculate the time of initiation for defects existing at the start of life of nuclear components. This study presents the background, the development, the application, and results concerning validation work made for a simplified method named {sigma}{sub d} of prediction of initiation for nuclear structures made of 316L austenitic steel and operating at temperature where creep is significant. This method relies on the evaluation of real stress-strain history on a small distance d (d = 0.05 mm) close to the crack front and material characteristics (limiting stresses) that are available in nuclear codes like ASME Code cases or RCC-MR.

  18. Dislocation modeling of creep-related tilt changes

    USGS Publications Warehouse

    McHugh, S.; Johnston, M.J.S.

    1979-01-01

    Tilt changes associated with 1-5 mm of fault creep have been detected at several different locations on the San Andreas fault on tiltmeters within 500 m of the creep observation point. The creep-related tilts have amplitudes of 0??.5 ??rad and durations comparable to the creep events. No changes $ ??10-2 ??rad have been observed on tiltmeters at distances $ ??1 km from the fault at the time of the creep events. Dislocation models capable of replicating the creep-related tilt events have been constructed to examine the relationship of the model parameters to details of the tilt waveforms. The tilt time histories and bounded assumptions of the source-station configurations, and the displacement time history, can be used to infer the type and amount of displacement, the propagation direction and depth of the slip zone. The shallow depth and finite size of the slip zone indicated by these models constrasts with the horizontal extent. ?? 1979.

  19. Hydrocarbon reservoirs with rocksalt caprocks: time dependence of subsidence effects and the influence of the rocksalt creep model

    NASA Astrophysics Data System (ADS)

    Marketos, George; Govers, Rob; Spiers, Chris

    2015-04-01

    Rocksalt is the caprock for a large number of hydrocarbon reservoirs. Understanding its response to extraction-induced stress perturbations can therefore be very important when calculating the resulting deformation and associated subsidence above such fields. We investigate how flow in the rocksalt leads to time-dependent deformation of the ground surface using numerical models that simulate the mechanical response of the subsurface. Rock mechanical experiments have demonstrated that rocksalt can flow by linear creep or power-law creep, depending on stress and grain size among others. Given that we often do not have data from cores that constrain these quantities, we investigate the two rocksalt flow laws as alternatives. Here, we focus specifically on differences in the surface imprints of these two types of flow. Mechanical models for linear creep show that the rocksalt exhibits two time scales in response to the reservoir pumping. The first, and shortest, time scale reflects flow that is driven by relaxation of stresses in the vicinity of the reservoir. At the surface, this results in maximum subsidence that is increasing with time. The second time scale reflects closed-conduit flow within the rocksalt layer that is driven by mean stresses equilibration. Interestingly, this results in a decrease in the maximum subsidence above the reservoir.

  20. Magnetic field annealing for improved creep resistance

    DOEpatents

    Brady, Michael P.; Ludtka, Gail M.; Ludtka, Gerard M.; Muralidharan, Govindarajan; Nicholson, Don M.; Rios, Orlando; Yamamoto, Yukinori

    2015-12-22

    The method provides heat-resistant chromia- or alumina-forming Fe-, Fe(Ni), Ni(Fe), or Ni-based alloys having improved creep resistance. A precursor is provided containing preselected constituents of a chromia- or alumina-forming Fe-, Fe(Ni), Ni(Fe), or Ni-based alloy, at least one of the constituents for forming a nanoscale precipitate MaXb where M is Cr, Nb, Ti, V, Zr, or Hf, individually and in combination, and X is C, N, O, B, individually and in combination, a=1 to 23 and b=1 to 6. The precursor is annealed at a temperature of 1000-1500.degree. C. for 1-48 h in the presence of a magnetic field of at least 5 Tesla to enhance supersaturation of the M.sub.aX.sub.b constituents in the annealed precursor. This forms nanoscale M.sub.aX.sub.b precipitates for improved creep resistance when the alloy is used at service temperatures of 500-1000.degree. C. Alloys having improved creep resistance are also disclosed.

  1. Creep as a mechanism for sealing amalgams.

    PubMed

    Osborne, John W

    2006-01-01

    Dental amalgam seals itself over time. The reduction of microleakage in amalgam restorations has been explained by corrosion products filling in the interface gap between amalgam and tooth structure in order to seal the restoration interface. This concept has been widely accepted; yet, curiously, there is little research supporting this theory. The creep mechanism may be a plausible alternative to explaining why microleakage is reduced over time in amalgam restorations. Amalgam restorations are confined to the fixed space of the cavity preparation; expansion of the amalgam through internal phase changes in this confined area must be relieved. The resultant creep-expansion of the amalgam restoration fills in the tooth/amalgam interface gap. Once the interfacial gap is filled and amalgam has made intimate contact with the cavity wall, the dental amalgam slides along the tooth preparation plane as predicted by classic metallurgical studies. The results of the creep of amalgam have been observed clinically as the extrusion of amalgam from the cavity preparation. This explanation for amalgam sealing the tooth/amalgam gap fits many clinical observations and certain research data. PMID:16827016

  2. Experimental study on multi-step creep properties of rat skins.

    PubMed

    Chen, Gang; Cui, Shibo; You, Lin; Li, Yan; Mei, Yun-Hui; Chen, Xu

    2015-06-01

    Tension, single-step creep, and multi-step creep of rat skins at room temperature were experimentally studied. We studied the effects of loading histories of high stress creep, low stress creep, and stress relaxation on multi-step creep. Microstructure of rat skins after prescribed tests were observed microscopically with the help of standard hematoxylin and eosin (H&E). The void ratios were also analyzed. The loading histories of high stress creep, low stress creep, and stress relaxation have significant influence on multi-step creep. We found that the creep strain and its rate in the steady-state stage and the creep-fatigue life of rat skins are sensitive to creep stress. Low stress creep after the loading history of high stress creep is characterized as a recovery of strain and a zero strain rate. Both the loading history of low stress creep and stress relaxation act as a recovery in multi-step creep, and they are driven by a same mechanism in the creep strain and the void ratio of rat skins. The loading history, of which sequence is as followings successively: low stress creep, stress relaxation, and high stress creep, helps to obtain the largest creep strain at the lowest void ratio. PMID:25771256

  3. Heated mine room and pillar secondary creep response

    SciTech Connect

    Tillerson, J.R.; Dawson, P.R.

    1980-04-01

    Heated salt mine room and pillar simulations have been performed to provide information regarding parameters affecting room closure rates to designers of radioactive waste isolation facilities. A coupled secondary creep and heat transfer formulation with large strain capabilities was used to assess the effects of variations in creep law parameters, thermal properties, imposed boundary conditions, temporal integration, and meshing resolution on room closure rates. Results indicate that the greatest effect results from variations in parameters appearing in the creep constitutive equation.

  4. Survivability of fossils in deformed and recrystallized carbonate rocks

    NASA Astrophysics Data System (ADS)

    Lee, S.; Ree, J.

    2013-12-01

    Carbonates rocks commonly contain fossils that are useful for age constraints of deposition and interpretation of depositional environment. Fossils in deformed carbonate rocks are hard to be preserved because of low flow strength and relatively low recrystallization temperature of carbonate minerals. Despite of the potential importance of the fossil survivability in deformed rocks, the effect of deformation/recrystallization on the fossil preservation in carbonate rocks has never been studied. Here we report fossil preservation in deformed carbonate rocks (Ordovician Joseon Supergroup) in Jeongseon area, South Korea. The carbonate rocks are multiply deformed and strongly transposed with their constituent minerals (calcite and dolomite) deformed by intracrystalline plasticity. These strongly deformed marbles do not contain any fossils. In some outcrops, weakly deformed or little deformed carbonate rocks occur as lenses in transposed layered marbles and preserve fossils such as crinoid, gastropod and mollusk. In weakly deformed marble, crinoid (0.3 - 3 mm long) occurs as a single crystal of calcite exhibiting thin deformation twins. Some twins show features of twin boundary migration and there is a bulging recrystallization along twin boundaries. The matrix grains (3-100 ?m) in the weakly deformed marbles show a foam texture with bimodal size distribution. The matrix grains are equiaxed and carry few twins. In intermediately deformed marbles, there are remnants of crinoid (mostly 500 ?m long) with thicker deformation twins most of which exhibit features of twin boundary migration. Some twins of the crinoid crystals are bent or kinked. Recrystallized grains along twin boundaries are larger than those of the weakly deformed marbles. The equiaxed matrix grains (10-80 ?m) in the intermediately deformed marbles also show a foam texture with seriate grain size distribution and many of the grains contain thin deformation twins. In the strongly deformed marbles, the remnants of crinoid occur as calcite grain aggregates with their grain size (50-500 ?m) larger than the matrix grains (10-50 ?m). The calcite grains within the crinoid remnants are elongated with wavy or lobate grain boundaries. The matrix grains (10-100 ?m) in the strongly deformed marbles are also highly elongated and their boundaries are lobate or amoeboid, suggesting dynamic recrystallization by grain boundary migration. In the transposed marbles (most strongly deformed), calcite/dolomite grains are highly elongated with microstructures of dislocation creep and there are no traces of fossils. We are conducting lattice orientation mapping of thin sections using electron backscattered diffraction (EBSD) analysis with the expectation that traces of fossils can be recognized even in the transposed marbles.

  5. Quantum creep of ?-Sn in the normal and superconducting states. Influence of the NS transition on work hardening

    NASA Astrophysics Data System (ADS)

    Natsik, V. D.; Soldatov, V. P.; Ivanchenko, L. G.; Kirichenko, G. I.

    2006-12-01

    Previously we investigated the kinetics of transient logarithmic creep of ?-tin single crystals at very low temperatures 0.5K deformation in the normal (N) electronic state. In a continuation of that research, here we determine the boundary temperature Tg?1.3K separating the regions of thermally activated (T>Tg) and quantum (Tcreep, its quantum character in the region T creep in the quantum region can yield empirical estimates for the work hardening coefficient ? of the samples. It is found to increase significantly at the NS transition: along the whole deformation curve the work hardening in the S state occurs more intensely, and, on the average, ?S?1.5?N. Such an effect has been observed previously in a study of the plasticity of a series of fcc metals by the method of active deformation at a constant rate (V. V. Pustovalov, I. N. Kuz'menko, N. V. Isaev, V. S. Fomenko, S. É. Shumlin, Fiz. Nizk. Temp. 30, 109 (2004) [Low Temp. Phys. 30, 82 (2004)]). A comparison of the results of this study with previous results suggests that the increase in intensity of the work hardening at the superconducting transition is of a general nature for metallic superconductors and is manifested for other deformation regimes as well. The possible causes of the effect are discussed in the general conceptual framework of dislocation physics.

  6. Deformation of Unentangled Swollen Gels

    NASA Astrophysics Data System (ADS)

    Sariyer, Ozan; Panyukov, Sergey; Rubinstein, Michael

    2014-03-01

    We study the deformation characteristics (Poisson's ratios and stress-strain relations) of unentangled gels swollen and uniaxially or biaxially deformed in excess solvent by considering the balance of osmotic pressure and elastic stress in unconstrained dimensions. Our scaling theory predicts a crossover from theta solvent behavior to marginal solvent behavior upon stretching gels that are in concentrated regime at swelling equilibrium - a phenomenon that was experimentally observed long ago, but not understood theoretically. For gels that are in the semidilute good solvent regime at swelling equilibrium, we predict a crossover to theta solvent behavior upon compression and a crossover to marginal solvent behavior upon stretching. Our theory reproduces the previously known results for equilibrium swelling degree as well as known deformation characteristics in theta and athermal solvents.

  7. Collect Available Creep-Fatigue Data and Study Existing Creep-Fatigue Evaluation Procedures for Grade 91 and Hastelloy XR

    SciTech Connect

    Tai Asayama; Yukio Tachibana

    2007-09-30

    This report describes the results of investigation on Task 5 of DOE/ASME Materials Project based on a contract between ASME Standards Technology, LLC (ASME ST-LLC) and Japan Atomic Energy Agency (JAEA). Task 5 is to collect available creep-fatigue data and study existing creep-fatigue evaluation procedures for Grade 91 steel and Hastelloy XR. Part I of this report is devoted to Grade 91 steel. Existing creep-fatigue data were collected (Appendix A) and analyzed from the viewpoints of establishing a creep-fatigue procedure for VHTR design. A fair amount of creep-fatigue data has been obtained and creep-fatigue phenomena have been clarified to develop design standards mainly for fast breeder reactors. Following this, existing creep-fatigue procedures were studied and it was clarified that the creep-fatigue evaluation procedure of the ASME-NH has a lot of conservatisms and they were analyzed in detail from the viewpoints of the evaluation of creep damage of material. Based on the above studies, suggestions to improve the ASME-NH procedure along with necessary research and development items were presented. Part II of this report is devoted to Hastelloy XR. Existing creep-fatigue data used for development of the high temperature structural design guideline for High Temperature Gas-cooled Reactor (HTGR) were collected. Creep-fatigue evaluation procedure in the design guideline and its application to design of the intermediate heat exchanger (IHX) for High Temperature Engineering Test Reactor (HTTR) was described. Finally, some necessary research and development items in relation to creep-fatigue evaluation for Gen IV and VHTR reactors were presented.

  8. Could lithospheric instability cause the San Andreas Fault to creep ?

    NASA Astrophysics Data System (ADS)

    Le Pourhiet, L.; Saleeby, J.

    2013-12-01

    The Southern Sierra Nevada mountains range rapidly uplifted at ? 3.5 Ma simultaneously with a pulse of basaltic volcanism. Xenoliths recovered from volcanics indicate that the range lost a dense crustal root after the Miocene. The vertical motions and removal of the root have been linked to a fast seismic velocity anomaly that extends ? 200 km into the mantle but is offset to the west of the range. With visco-elasto-plastic thermo-mechanical numerical models, we have tested the influence of crustal strength on the kinematics of removal and on the amount of associated uplift. We find that delamination of the dense root is the most likely mechanism for gravitational instability to occur. In this class of models, the Great Valley deforms by elastic flexure in response to the load exerted by the delaminated root. We therefore explore the influence of the strength of the Great Valley on the wavelength of the flexure and complement 2D models by flexural 3D models. The study shows that for a Te=10 km, the flexural anomaly resulting from the drip pull outlines the limit between the area where the Quaternary sediments are found on-lapping or off-lapping the western flank of the Sierra. On the Western edge of the Sierra Nevada micro plate, the flexural anomaly crosses the San Andreas Fault. Where uplift is predicted Miocene strata are eroding, and where subsidence is predicted Quaternary sediments are at the surface. These geological limits also coincide with the limit of the creeping segment of the Fault. Geological evidence (especially fold kinematics) suggests that the extreme weakness of the San Andreas Fault in that area started during the Pliocene (~3 Ma). This timing also coincides with the rapid uplift of the Sierra Nevada. Simple coincidences or real mechanical link between these two anomalous behaviors? We will present and discuss how flexure could promote lithostatic fluid pressure in the depth range of 7 to 15 km along the creeping segment of the fault, and therefore influence the seismic behavior of the fault and, compare the prediction of this model with various sets of observations.

  9. Numerical modeling of carbon dioxide sequestration on the rate of pressure solution creep in limestone: Preliminary results

    E-print Network

    Renard, Francois; Hellmann, Roland; Collombet, Marielle; Guen, Yvi Le

    2008-01-01

    When carbon dioxide (CO2) is injected into an aquifer or a depleted geological reservoir, its dissolution into solution results in acidification of the pore waters. As a consequence, the pore waters become more reactive, which leads to enhanced dissolution-precipitation processes and a modification of the mechanical and hydrological properties of the rock. This effect is especially important for limestones given that the solubility and reactivity of carbonates is strongly dependent on pH and the partial pressure of CO2. The main mechanism that couples dissolution, precipitation and rock matrix deformation is commonly referred to as intergranular pressure solution creep (IPS) or pervasive pressure solution creep (PSC). This process involves dissolution at intergranular grain contacts subject to elevated stress, diffusion of dissolved material in an intergranular fluid, and precipitation in pore spaces subject to lower stress. This leads to an overall and pervasive reduction in porosity due to both grain indent...

  10. Creep-rupture performance of 0.07C-23Cr-45Ni-6W-Ti,Nb austenitic alloy (HR6W) tubes

    SciTech Connect

    Evans, Neal D; Shingledecker, John P

    2010-01-01

    A series of base metal and cross-weld creep-rupture tests were conducted on the advanced austenitic alloy, HR6W, to evaluate the material for use at advanced ultrasupercritical (A-USC) steam conditions. Creep deformation and rupture were evaluated by traditional methods and data were compared with other studies to evaluate the creep response of the material. Optical and scanning electron microscopy revealed changes in failure mode and precipitation behavior. Thermodynamic predictions of phase stability were conducted and the results were compared with the experimental data. This research confirmed the important role of W and the precipitation of laves phase in the alloy system, but a direct relationship between laves phase content and creep strength was not observed. Furthermore, Cr content was investigated as an additional factor which may be important in the microstructural stability of the alloy which had not been previously considered. Finally, when compared to commercially available stainless steels, this heat of HR6W showed no creep strength advantage for A-USC application.

  11. Creep Life of Ceramic Components Using a Finite-Element-Based Integrated Design Program (CARES/CREEP)

    NASA Technical Reports Server (NTRS)

    Gyekenyesi, J. P.; Powers, L. M.; Jadaan, O. M.

    1998-01-01

    The desirable properties of ceramics at high temperatures have generated interest in their use for structural applications such as in advanced turbine systems. Design lives for such systems can exceed 10,000 hours. The long life requirement necessitates subjecting the components to relatively low stresses. The combination of high temperatures and low stresses typically places failure for monolithic ceramics in the creep regime. The objective of this paper is to present a design methodology for predicting the lifetimes of structural components subjected to creep rupture conditions. This methodology utilized commercially available finite element packages and takes into account the time-varying creep strain distributions (stress relaxation). The creep life of a component is discretized into short time steps, during which the stress and strain distributions are assumed constant. The damage is calculated for each time step based on a modified Monkman-Grant creep rupture criterion. Failure is assumed to occur when the normalized accumulated damage at any point in the component is greater than or equal to unity. The corresponding time will be the creep rupture life for that component. Examples are chosen to demonstrate the CARES/CREEP (Ceramics Analysis and Reliability Evaluation of Structures/CREEP) integrated design programs, which is written for the ANSYS finite element package. Depending on the component size and loading conditions, it was found that in real structures one of two competing failure modes (creep or slow crack growth) will dominate. Applications to benechmark problems and engine components are included.

  12. Creep Life of Ceramic Components Using a Finite-Element-Based Integrated Design Program (CARES/CREEP)

    NASA Technical Reports Server (NTRS)

    Powers, L. M.; Jadaan, O. M.; Gyekenyesi, J. P.

    1998-01-01

    The desirable properties of ceramics at high temperatures have generated interest in their use for structural application such as in advanced turbine engine systems. Design lives for such systems can exceed 10,000 hours. The long life requirement necessitates subjecting the components to relatively low stresses. The combination of high temperatures and low stresses typically places failure for monolithic ceramics in the creep regime. The objective of this paper is to present a design methodology for predicting the lifetimes of structural components subjected to creep rupture conditions. This methodology utilizes commercially available finite element packages and takes into account the time-varying creep strain distributions (stress relaxation). The creep life, of a component is discretized into short time steps, during which the stress and strain distributions are assumed constant. The damage is calculated for each time step based on a modified Monkman-Grant creep rupture criterion. Failure is assumed to occur when the normalized accumulated damage at any point in the component is greater than or equal to unity. The corresponding time will be the creep rupture life for that component. Examples are chosen to demonstrate the Ceramics Analysis and Reliability Evaluation of Structures/CREEP (CARES/CREEP) integrated design program, which is written for the ANSYS finite element package. Depending on the component size and loading conditions, it was found that in real structures one of two competing failure modes (creep or slow crack growth) will dominate. Applications to benchmark problems and engine components are included.

  13. Creep and creep-rupture behavior of a continuous strand, swirl mat reinforced polymer composite in automotive environments

    SciTech Connect

    Ren, W.; Brinkman, C.R.

    1998-12-31

    Creep and creep-rupture behavior of an isocyanurate based polyurethane matrix with a continuous strand, swirl mat E-glass reinforcement was investigated for automotive applications. The material under stress was exposed to various automobile service environments. Results show that environment has substantial effects on its creep and creep-rupture properties. Proposed design guide lines and stress reduction factors were developed for various automotive environments. These composites are considered candidate structural materials for light weight and fuel efficient automobiles of the future.

  14. The relationship between fluid infiltration, metamorphism and deformation: an example from the Bergen Arcs, Norway

    NASA Astrophysics Data System (ADS)

    Putnis, Andrew; Austrheim, Håkon; Mukai, Hiroki

    2015-04-01

    The Bergen Arcs are a classic field area for the study of fluid infiltration into dry, low permeability granulites, resulting in amphibolite and eclogite facies parageneses typically developed along fluid fronts and shear zones. The relationship between fluid infiltration and mineral reactions can be mapped at outcrop as well as micro-scale, and it is now a widely accepted generalization that the metamorphism requires fluids for reactions to proceed. Given that the metamorphic reactions and deformation in the shear zones are clearly related, raises the question of how appropriate are our "solid state" notions of deformation mechanisms under these conditions. Although deformation mechanisms in minerals have been studied for many decades, experiments have largely been on monomineralic non-reacting samples and mechanisms related to the theories first derived in metals and ceramics. Thus high temperature dislocation glide, diffusion creep both by grain boundary diffusion (Coble creep) and volume diffusion (Nabarro-Herring creep) have been recognised in quartz and feldspar. In a similar way, the strength of rocks has been equated with the dry strength of component minerals, and rock weakening due to fluids attributed to the formation of 'softer' minerals such as micas. When fluid-induced weakening of individual minerals such as quartz and feldspar was recognized, there was still the tendency to explain this in solid state terms e.g. "fluid enhanced dislocation glide". An EBSD study of feldspars taken from a sequence of rocks in the Bergen Arcs, across a section from relatively undeformed and unreacted granulites into a highly deformed shear zone shows that crystallographic orientations from groups of feldspar grains within the shear zone can be related to individual parent feldspar grains within the granulite, that is, the crystallographic preferred orientation (CPO) is inherited. The feldspar textures and analysis of the misorientation angle distributions for neighbouring and random pairs of feldspar grains suggest that the deformation mechanism is by dissolution-precipitation creep rather than dislocation creep. The loss of strength of the rock is dependent on the reactivity of the minerals in the specific fluid and not simply on inherent physical properties of the minerals themselves. A future challenge will be to determine the conditions under which dissolution-precipitation creep is dominant over dislocation creep as the principal deformation mechanism.

  15. Microstructure and crystallographic preferred orientation of polycrystalline microgarnet aggregates developed during progressive creep, recovery, and grain boundary sliding

    USGS Publications Warehouse

    Massey, M.A.; Prior, D.J.; Moecher, D.P.

    2011-01-01

    Optical microscopy, electron probe microanalysis, and electron backscatter diffraction methods have been used to examine a broad range of garnet microstructures within a high strain zone that marks the western margin of a major transpression zone in the southern New England Appalachians. Garnet accommodated variable states of finite strain, expressed as low strain porphyroclasts (Type 1), high strain polycrystalline aggregates (Type 2), and transitional morphologies (Type 3) that range between these end members. Type 1 behaved as rigid porphyroclasts and is characterized by four concentric Ca growth zones. Type 2 help define foliation and lineation, are characterized by three Ca zones, and possess a consistent bulk crystallographic preferred orientation of (100) symmetrical to the tectonic fabric. Type 3 show variable degrees of porphyroclast associated with aggregate, where porphyroclasts display complex compositional zoning that corresponds to lattice distortion, low-angle boundaries, and subgrains, and aggregate CPO mimics porphyroclast orientation. All aggregates accommodated a significant proportion of greenschist facies deformation through grain boundary sliding, grain rotation and impingement, and pressure solution, which lead to a cohesive behavior and overall strain hardening of the aggregates. The characteristic CPO could not have been developed in this manner, and was the result of an older phase of partitioned amphibolite facies dislocation creep, recovery including chemical segregation, and recrystallization of porphyroclasts. This study demonstrates the significance of strain accommodation within garnet and its affect on composition under a range of PT conditions, and emphasizes the importance of utilizing EBSD methods with studies that rely upon a sound understanding of garnet. ?? 2010 Elsevier Ltd.

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

    SciTech Connect

    Vijay Vasudevan

    2008-03-31

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

  17. Correlation of creep rate with microstructural changes during high temperature creep

    NASA Technical Reports Server (NTRS)

    Young, C. T.; Sommers, B. R.; Lytton, J. L.

    1977-01-01

    Creep tests were conducted on Haynes 188 cobalt-base alloy and alpha titanium. The tests on Haynes 188 were conducted at 1600 F and 1800 F for stresses from 3 to 20 ksi, and the as-received, mill-annealed results were compared to specimens given 5%, 10%, and 15% room temperature prestrains and then annealed one hour at 1800 F. The tests on alpha titanium were performed at 7,250 and 10,000 psi at 500 C. One creep test was done at 527 C and 10,000 psi to provide information on kinetics. Results for annealed titanium were compared to specimens given 10% and 20% room temperature prestrains followed by 100 hours recovery at 550 C. Electron microscopy was used to relate dislocation and precipitate structure to the creep behavior of the two materials. The results on Haynes 188 alloy reveal that the time to reach 0.5% creep strain at 1600 F increases with increasing prestrain for exposure times less than 1,000 hours, the increase at 15% prestrain being more than a factor of ten.

  18. Variations in creep rate along the Hayward Fault, California, interpreted as changes in depth of creep

    NASA Astrophysics Data System (ADS)

    Simpson, R. W.; Lienkaemper, J. J.; Galehouse, J. S.

    Variations in surface creep rate along the Hayward fault are modeled as changes in locking depth using 3D boundary elements. Model creep is driven by screw dislocations at 12 km depth under the Hayward and other regional faults. Inferred depth to locking varies along strike from 4-12 km. (12 km implies no locking.) Our models require locked patches under the central Hayward fault, consistent with a M6.8 earthquake in 1868, but the geometry and extent of locking under the north and south ends depend critically on assumptions regarding continuity and creep behavior of the fault at its ends. For the northern onshore part of the fault, our models contain 1.4-1.7 times more stored moment than the model of Bürgmann et al. [2000]; 45-57% of this stored moment resides in creeping areas. It is important for seismic hazard estimation to know how much of this moment is released coseismically or as aseismic afterslip.

  19. Diffusional creep and creep degradation in the dispersion-strengthened alloy TD-NiCr

    NASA Technical Reports Server (NTRS)

    Whittenberger, J. D.

    1972-01-01

    Dispersoid-free regions were observed in TD-NiCr (Ni-20Cr-2ThO2) after slow strain rate testing in air from 1145 to 1590 K. Formation of the dispersoid-free regions appears to be the result of diffusional creep. The net effect of this creep is the degradation of TD-NiCr to a duplex microstructure. Degradation is further enhanced by the formation of voids and integranular oxidation in the thoria-free regions. These regions apparently provided sites for void formation and oxide growth since the strength and oxidation resistance of Ni-20Cr is much less than Ni-20Cr-2ThO2. This localized oxidation does not appear to reduce the static load bearing capacity of TD-NiCr since long stress rupture lives were observed even with heavily oxidized microstructures. But this oxidation does significantly reduce the ductility and impact resistance of the material. Dispersoid-free bands and voids were also observed for two other dispersion strengthened alloys, TD-NiCrAl and IN-853. Thus, it appears that diffusional creep is charactertistic of dispersion-strengthened alloys and can play a major role in the creep degradation of these materials.

  20. The fate of fluid inclusions during high-temperature experimental deformation of olivine aggregates

    NASA Astrophysics Data System (ADS)

    Carter, Matthew J.; Zimmerman, Mark E.; Teyssier, Christian

    2015-05-01

    Torsion experiments on initially wet and dry olivine aggregates at equivalent deformation conditions investigated the fate of fluid inclusions (FIs) during high-temperature deformation. Wet samples were produced by adding water to San Carlos olivine powders before hot pressing; those hot pressed without water are considered dry. After hot pressing, wet and dry aggregates have comparable grain sizes, but wet aggregates have more abundant primary FIs. Talc jackets were fitted around some wet and dry samples prior to deformation to hydrate samples during deformation via talc dehydration at elevated temperature, whereas other samples were deformed without talc. At similar strain rates (~1.0 × 10-4 s-1), the peak shear stress for the dry sample (no talc) was 190-220 MPa, whereas all other samples reached 180 MPa; the strengths of wet (± talc) and dry (+ talc) specimens appear similar. Deformed samples reveal abundant FIs, reduced grain size, shape preferred orientation of olivine, and a pervasive low-angle fabric (C') to the shear plane defined by aligned FIs. Samples deformed with talc have FI-rich and FI-depleted domains; where FIs are abundant, the C' fabric is better developed and grain size is smaller. Electron backscatter diffraction pole figures suggest that olivine deformed in the dislocation creep regime via the (010)[100] slip system. Results of these experiments suggest that FIs are redistributed during dislocation creep, leading to the development of grain-scale, high-diffusivity pathways.

  1. In-reactor deformation of cold-worked Zr 2.5Nb pressure tubes

    NASA Astrophysics Data System (ADS)

    Holt, R. A.

    2008-01-01

    Over forty years of in-reactor testing and over thirty years of operating experience in power reactors have provided a broad understanding of the in-reactor deformation of cold-worked Zr-2.5Nb pressure tubes, and an extensive data-base upon which to base models for managing the life of existing reactors and for designing new ones. The effects of the major operating variables and many of the metallurgical variables are broadly understood. The deformation is often considered to comprise three components: thermal creep, irradiation growth and irradiation creep. Of the three, irradiation growth is best understood - it is thought to be driven by the diffusional anisotropy difference (DAD). It is still not clear whether the enhancement of creep by irradiation is due to climb-plus-glide (CPG), stress-induced preferred absorption (SIPA) or elasto-diffusion (ED). The least understood area is the transition between thermal creep and irradiation where the fast neutron flux may either suppress or enhance the creep rate. The three components are generally treated as additive in the models, although it is recognized that this is only a crude approximation of reality. There are still significant gaps in our knowledge besides the thermal- to irradiation-creep transition, for example, the effect of Mo which is produced from Nb by transmutation in the thermal neutron flux is not known, and on-going work is required in a number of areas. This paper reviews the current state of knowledge of the in-reactor deformation of cold-worked Zr-2.5Nb pressure tubes, and highlights areas for further research.

  2. High Precision Measurements of Temperature Dependence of Creep Rate of Polycrystalline Forsterite

    NASA Astrophysics Data System (ADS)

    Nakakoji, T.; Hiraga, T.

    2014-12-01

    Obtaining temperature dependence of creep rate, that is, activation energy for the creep is critical in geophysics, since its value can indicate deformation mechanism and also allows to extrapolate the creep rate measured in the room experiments to geological conditions when the creep mechanism is identical in both cases. Although numerous experimental results have been obtained so far, the obtained activation energy often contains error range of >50 kJ/mol, which often causes large uncertainties in strain rate at applied geological conditions. To minimize this error, it is important to collect strain rates at many different temperatures with high accuracy. We conducted high temperature compression experiments on synthetic forsterite (90%vol) and enstatite (10vol %) aggregates under increasing and decreasing temperatures. We applied a constant load of ~20 MPa using uniaxial testing machine (Shimadzu AG-X 50kN). The temperature was changed from 1360°C to 1240°C by furnace attached to the machine. Prior to the applying the load to the samples the grain size was saturated at 1360°C for 24 hours to minimize grain growth during the test. Decreasing-rate of temperature was 0.11min/°C and 0.02min/°C at temperature ranges of 1360 to 1300 and 1300 to 1240 respectively. The increasing-rate of the temperature was the same as the decreasing-rate. Strain rates from every 1 degree were obtained successfully. After the experiment, we analyzed the microstructure of the sample with scanning electron microscopy to measure the grain diameter. Arrhenius plots of strain rate demonstrate very linear distribution at > 1300 °C giving an activation energy of 649 ± 14 kJ/mol, whereas weak transition to lower activation energy 550 ± 23 kJ/mol below 1300°C was observed. Tasaka et al. (2013) obtained the activation energy of 370 ± 50 kJ/mol from similar temperature ranges used in our study but finer-grained samples. Combining these results, we interpret our results of high activation energy to lattice diffusion of Si and lower activation energy to apparent values where deformation mechanism transits from volume diffusion to grain boundary diffusion at lower temperature cond