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Sample records for cyclic deformation mechanisms

  1. Temperature Dependent Cyclic Deformation Mechanisms in Haynes 188 Superalloy

    NASA Technical Reports Server (NTRS)

    Rao, K. Bhanu Sankara; Castelli, Michael G.; Allen, Gorden P.; Ellis, John R.

    1995-01-01

    The cyclic deformation behavior of a wrought cobalt-base superalloy, Haynes 188, has been investigated over a range of temperatures between 25 and 1000 C under isothermal and in-phase thermomechanical fatigue (TMF) conditions. Constant mechanical strain rates (epsilon-dot) of 10(exp -3)/s and 10(exp -4)/s were examined with a fully reversed strain range of 0.8%. Particular attention was given to the effects of dynamic strain aging (DSA) on the stress-strain response and low cycle fatigue life. A correlation between cyclic deformation behavior and microstructural substructure was made through detailed transmission electron microscopy. Although DSA was found to occur over a wide temperature range between approximately 300 and 750 C the microstructural characteristics and the deformation mechanisms responsible for DSA varied considerably and were dependent upon temperature. In general, the operation of DSA processes led to a maximum of the cyclic stress amplitude at 650 C and was accompanied by pronounced planar slip, relatively high dislocation density, and the generation of stacking faults. DSA was evidenced through a combination of phenomena, including serrated yielding, an inverse dependence of the maximum cyclic hardening with epsilon-dot, and an instantaneous inverse epsilon-dot sensitivity verified by specialized epsilon-dot -change tests. The TMF cyclic hardening behavior of the alloy appeared to be dictated by the substructural changes occuring at the maximum temperature in the TMF cycle.

  2. Hardening mechanisms in a dynamic strain aging alloy, Hastelloy X, during isothermal and thermomechanical cyclic deformation

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    The relative contributions of the hardening mechanisms in Hastelloy X during cyclic deformation were investigated by conducting isothermal cyclic deformation tests within a total strain range of +/-0.3 pct and at several temperatures and strain rates, and thermomechanical tests within several different temperature limits. The results of the TEM examinations and special constant structure tests showed that the precipitation on dislocations of Cr23C6 contributed to hardening, but only after sufficient time above 500 C. Solute drag alone produced very considerable cyclic hardening. Heat dislocation densities, peaking around 10 exp 11 per sq cm, were found to develop at temperatures producing the greatest cyclic hardening.

  3. Unraveling cyclic deformation mechanisms of a rolled magnesium alloy using in situ neutron diffraction

    SciTech Connect

    Wu, Wei; An, Ke; Liaw, Peter K.

    2014-12-23

    In the current study, the deformation mechanisms of a rolled magnesium alloy were investigated under cyclic loading using real-time in situ neutron diffraction under a continuous-loading condition. The relationship between the macroscopic cyclic deformation behavior and the microscopic response at the grain level was established. The neutron diffraction results indicate that more and more grains are involved in the twinning and detwinning deformation process with the increase of fatigue cycles. The residual twins appear in the early fatigue life, which is responsible for the cyclic hardening behavior. The asymmetric shape of the hysteresis loop is attributed to the early exhaustion of the detwinning process during compression, which leads to the activation of dislocation slips and rapid strain-hardening. The critical resolved shear stress for the activation of tensile twinning closely depends on the residual strain developed during cyclic loading. In the cycle before the sample fractured, the dislocation slips became active in tension, although the sample was not fully twinned. The increased dislocation density leads to the rise of the stress concentration at weak spots, which is believed to be the main reason for the fatigue failure. Furthermore, the deformation history greatly influences the deformation mechanisms of hexagonal-close-packed-structured magnesium alloy during cyclic loading.

  4. Unraveling cyclic deformation mechanisms of a rolled magnesium alloy using in situ neutron diffraction

    DOE PAGESBeta

    Wu, Wei; An, Ke; Liaw, Peter K.

    2014-12-23

    In the current study, the deformation mechanisms of a rolled magnesium alloy were investigated under cyclic loading using real-time in situ neutron diffraction under a continuous-loading condition. The relationship between the macroscopic cyclic deformation behavior and the microscopic response at the grain level was established. The neutron diffraction results indicate that more and more grains are involved in the twinning and detwinning deformation process with the increase of fatigue cycles. The residual twins appear in the early fatigue life, which is responsible for the cyclic hardening behavior. The asymmetric shape of the hysteresis loop is attributed to the early exhaustionmore » of the detwinning process during compression, which leads to the activation of dislocation slips and rapid strain-hardening. The critical resolved shear stress for the activation of tensile twinning closely depends on the residual strain developed during cyclic loading. In the cycle before the sample fractured, the dislocation slips became active in tension, although the sample was not fully twinned. The increased dislocation density leads to the rise of the stress concentration at weak spots, which is believed to be the main reason for the fatigue failure. Furthermore, the deformation history greatly influences the deformation mechanisms of hexagonal-close-packed-structured magnesium alloy during cyclic loading.« less

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

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    , probing the deformation mechanisms operating in fatigue will lead to a better understanding of NiAl's unique characteristics. Low cycle fatigue properties have been reported on binary NiAl in the past year, yet those studies were limited to two temperature ranges: room temperature and near 1000 K. Eventually, fatigue property data will be needed for a wide range of temperatures and compositions. The intermediate temperature range near the brittle-to-ductile transition was chosen for this study to ascertain whether the sharp change occurring in monotonic behavior also occurs under cyclic conditions. An effort was made to characterize the dislocation structures which evolved during fatigue testing and comment on their role in the deformation process.

  6. Cyclic Deformation of Advanced High-Strength Steels: Mechanical Behavior and Microstructural Analysis

    NASA Astrophysics Data System (ADS)

    Hilditch, Timothy B.; Timokhina, Ilana B.; Robertson, Leigh T.; Pereloma, Elena V.; Hodgson, Peter D.

    2009-02-01

    The fatigue properties of multiphase steels are an important consideration in the automotive industry. The different microstructural phases present in these steels can influence the strain life and cyclic stabilized strength of the material due to the way in which these phases accommodate the applied cyclic strain. Fully reversed strain-controlled low-cycle fatigue tests have been used to determine the mechanical fatigue performance of a dual-phase (DP) 590 and transformation-induced plasticity (TRIP) 780 steel, with transmission electron microscopy (TEM) used to examine the deformed microstructures. It is shown that the higher strain life and cyclic stabilized strength of the TRIP steel can be attributed to an increased yield strength. Despite the presence of significant levels of retained austenite in the TRIP steel, both steels exhibited similar cyclic softening behavior at a range of strain amplitudes due to comparable ferrite volume fractions and yielding characteristics. Both steels formed low-energy dislocation structures in the ferrite during cyclic straining.

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

    NASA Technical Reports Server (NTRS)

    Cullers, Cheryl L.; Antolovich, Stephen D.

    1993-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Kono, Akiko; Matsushima, Takashi

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

  9. Microstructural mechanisms of cyclic deformation, fatigue crack initiation and early crack growth.

    PubMed

    Mughrabi, Haël

    2015-03-28

    In this survey, the origin of fatigue crack initiation and damage evolution in different metallic materials is discussed with emphasis on the responsible microstructural mechanisms. After a historical introduction, the stages of cyclic deformation which precede the onset of fatigue damage are reviewed. Different types of cyclic slip irreversibilities in the bulk that eventually lead to the initiation of fatigue cracks are discussed. Examples of trans- and intercrystalline fatigue damage evolution in the low cycle, high cycle and ultrahigh cycle fatigue regimes in mono- and polycrystalline face-centred cubic and body-centred cubic metals and alloys and in different engineering materials are presented, and some microstructural models of fatigue crack initiation and early crack growth are discussed. The basic difficulties in defining the transition from the initiation to the growth of fatigue cracks are emphasized. In ultrahigh cycle fatigue at very low loading amplitudes, the initiation of fatigue cracks generally occupies a major fraction of fatigue life and is hence life controlling. PMID:25713457

  10. Reversible cyclic deformation mechanism of gold nanowires by twinning-detwinning transition evidenced from in situ TEM.

    PubMed

    Lee, Subin; Im, Jiseong; Yoo, Youngdong; Bitzek, Erik; Kiener, Daniel; Richter, Gunther; Kim, Bongsoo; Oh, Sang Ho

    2014-01-01

    Mechanical response of metal nanowires has recently attracted a lot of interest due to their ultra-high strengths and unique deformation behaviours. Atomistic simulations have predicted that face-centered cubic metal nanowires deform in different modes depending on the orientation between wire axis and loading direction. Here we report, by combination of in situ transmission electron microscopy and molecular dynamic simulation, the conditions under which particular deformation mechanisms take place during the uniaxial loading of [110]-oriented Au nanowires. Furthermore, by performing cyclic uniaxial loading, we show reversible plastic deformation by twinning and consecutive detwinning in tension and compression, respectively. Molecular dynamics simulations rationalize the observed behaviours in terms of the orientation-dependent resolved shear stress on the leading and trailing partial dislocations, their potential nucleation sites and energy barriers. This reversible twinning-detwinning process accommodates large strains that can be beneficially utilized in applications requiring high ductility in addition to ultra-high strength. PMID:24398783

  11. Cyclic Plastic Deformation, Fatigue, and the Associated Micro-Mechanisms in Magnesium: From Single Crystal to Polycrystal

    NASA Astrophysics Data System (ADS)

    Yu, Qin

    Magnesium and its alloys have received substantial interests as the government initiatives on energy saving and environment protection demand an increasing use of lightweight materials in structural parts, especially in transportation industries. A good understanding of fatigue behavior in magnesium is critical to ensure the reliability and durability of the magnesium components. Unlike the body centered cubic and face centered cubic metals, fundamental knowledge concerning the cyclic deformation and fatigue in hexagonal close packed magnesium is limited. The current research aims at a better understanding of the micro-mechanisms associated with the cyclic deformation and fatigue of magnesium. Magnesium single crystal was chosen to study the fundamental twinning/detwinning process while extruded polycrystalline pure magnesium was studied for the fatigue damage mechanisms. Cyclic deformation and the corresponding morphology evolution of {1 0 1¯ 2} twinning-detwinning-retwinning are, for the first time, characterized in magnesium single crystal under fully reserved strain-controlled tension-compression utilizing in situ optical microscopy. As loading cycles are increased, the activity of twinning-detwinning-retwinning gradually decreases. Microscopy after fatigue shows that the matrix region having experienced repeated twinning-detwinning cannot be completely detwinned to its original crystal orientation. Fragmented secondary tension twins are found to result from twin-twin interactions. Various twin-twin interaction structures exist in fatigued magnesium single crystal: quilted-looking twin structure, "apparent crossing" twin structure, and double tension twin structure. According to the crystallography of magnesium, twin-twin interactions are classified into Type I for two twin variants sharing the same zone axis and Type II for two twins with different zone axes. For Type I twin-twin interactions, one twin does not transmit across the twin boundary and into the

  12. Present-day crustal movements and the mechanics of cyclic deformation

    SciTech Connect

    Thatcher, W.

    1990-01-01

    Contemporary crustal movements in California are concentrated within a plate-boundary deformation zone that is typically 50 to 200 km wide, centered approximately on the San Andreas fault. Observations of coseismic, postseismic, and interseismic movements define the earthquake deformation cycle and constrain models of strain accumulation and release for strike-slip plate boundaries. This chapter describes shear strain on the San Andreas fault system; aseismic slip, integrated displacement rates, and Pacific-North American plate motion; detailed displacement-rate patterns; and thick- and thin-lithosphere models and stress-slip-constitutive-law fault models of deformation.

  13. Strain rate change transients during cyclic deformation of copper

    SciTech Connect

    Kaschner, G.C.; Gibeling, J.C.

    1996-12-15

    In the present study, the authors have undertaken to apply the strain rate change method to mechanically probe the mechanisms of cyclic deformation in copper. The goals of this work were twofold: to carefully explore differences in results obtained under conventional displacement control with those recorded under plastic strain control and to apply the formalism for monotonic deformation described above to cyclic deformation. To achieve these goals, it has been necessary to utilize computed-variable servo-hydraulic control to develop a new test technique incorporating strain rate change tests performed during low cycle fatigue. Plastic strain is used as the control variable to ensure a constant plastic strain rate between pre-determined plastic strain limits.

  14. Analysis on sheet cyclic plastic deformation using mixed hardening model

    NASA Astrophysics Data System (ADS)

    Li, Qun; Jin, Miao; Yuxin, Zhu

    2013-05-01

    Treating the cyclic deformation problem of sheet flowing through drawbead as the object of the research, using HILL anisotropy yield criterion and mixed hardening model, the cyclic plastic deformation mechanism of sheet was studied, the deformation characteristics of sheet subjected to cyclic loads were revealed, and the influence of Bauschinger effect on stress-strain circulating relationship and the influence of bending neutral layer migration on the stress of sheet's intermediate integral point were analyzed as well. The effectiveness of the model was verified by experiments. The results of analysis were showed that the stress values influenced by Bauschinger effect were different at the yield point of reverse loading and the point of unloading during the cyclic deformation. The stress rate at the yield point of reverse loading and the point of unloading in different loading branches was also different. The stress-strain circulating relationship in different loading branches can be approximately treated as bilinear. The tangent modulus of each loading branch showed a significant downward trend as the times of the reverse loading increased. The tangent modulus calculated by the mixed hardening model after the second loading branch reduced to less than 21% of the first loading tangent modulus. Effected by the neutral layer migration, the stress-strain curve of integral point of sheet's intermediate layer showed alternating transition phenomenon of the tensile stress and compressive stress.

  15. Superplastic deformation induced by cyclic hydrogen charging

    SciTech Connect

    Choe, Heeman; Schuh, Christopher A.; Dunand, David C.

    2008-05-15

    Deformation under the combined action of external stress and cyclic hydrogen charging/discharging is studied in a model material, titanium. Cyclic charging with hydrogen is carried out at 860 deg. C, which repeatedly triggers the transformation between hydrogen-lean {alpha}-Ti and hydrogen-rich {beta}-Ti. Due to bias from the externally applied tensile stress, the internal mismatch strains produced by this isothermal {alpha}-{beta} transformation accumulate preferentially along the loading axis. These strain increments are linearly proportional to the applied stress, i.e., flow is ideally Newtonian, at small stress levels (below {approx}2 MPa). Therefore, after multiple chemical cycles, a tensile engineering strain of 100% is achieved without fracture, with an average strain rate of 10{sup -5} s{sup -1}, which demonstrates for the first time that superplastic elongations can be achieved by chemical cycling. The effect of hydrogen partial pressure, cycle time, and external stress on the value of the superplastic strain increments is experimentally measured and discussed in light of a diffusional phase transformation model. Special attention is paid to understanding the two contributions to the internal mismatch strains from the phase transformation and lattice swelling.

  16. Investigation of Cyclic Deformation and Fatigue of Polycrystalline Cu under Pure Compression Cyclic Loading Conditions

    NASA Astrophysics Data System (ADS)

    Hsu, Tzu-Yin Jean

    It is commonly accepted that fatigue crack is initiated under tensile fatigue stresses. However, practical examples demonstrate that cracks may also initiate under pure compressive fluctuating loads such as the failures observed in aircraft landing gear frames. However, the mechanism of such failures is rarely investigated. Furthermore, knowledge on cyclic deformation response under pure compressive fatigue condition is also very limited or non-existent. Our recent work already verified that fatigue cracks may nucleate from stress concentration sites under pure compression fatigue, but whether or not a form of stress concentration is always needed to initiate a crack under pure compression fatigue remains uncertain. In this study, compression fatigue tests under different peak stresses were carried out on smooth bars of fully annealed OFHC Copper. The purpose of these tests is to investigate not only the cyclic deformation response but also the possibility of crack nucleation without the stress concentrator. Results showed that overall the cyclic stress-strain response and microstructural evolution of OFHC Copper under pure compression fatigue exhibits rather dissimilar behaviour compared to those under symmetrical fatigue. The specimens hardened rapidly within 10 cycles under pure compression fatigue unlike the gradual cyclic hardening behaviour in symmetrical fatigue with the same peak stress amplitude. Compressive cyclic creep behaviour was also observed under the same testing conditions. Moreover, unlike conventional tension-compression fatigue, only moderate slip activity was detectable on the surface instead of typical PSB features detected from TEM observations. The surface observations has revealed that surface slip bands did not increase in number nor did they become more pronounced in height with increasing number of cycles. In addition, surface roughening by grain boundary extrusion was detected to become more severe as the cycling progressed. Therefore

  17. Investigation of Cyclic Deformation and Fatigue of Polycrystalline Cu under Pure Compression Cyclic Loading Conditions

    NASA Astrophysics Data System (ADS)

    Hsu, Tzu-Yin Jean

    It is commonly accepted that fatigue crack is initiated under tensile fatigue stresses. However, practical examples demonstrate that cracks may initiate under pure compressive fluctuating loads, e.g. the failures observed in aircraft landing gear frames. As the mechanism of such failures is rarely investigated, there is very limited or non-existent knowledge pool on cyclic deformation response under pure compressive fatigue condition. Our recent work verified that fatigue cracks may nucleate from stress concentration sites under pure compression fatigue, but whether or not a form of stress concentration is always needed to initiate a crack remains uncertain. In this study, compression fatigue tests under different peak stresses were carried out on smooth bars of fully annealed OFHC Copper. The purpose of these tests is to investigate not only the cyclic deformation response but also the possibility of crack nucleation without the stress concentrator. Results showed that overall the cyclic stress-strain response and microstructural evolution of OFHC Copper under pure compression fatigue exhibits rather dissimilar behaviour compared to those under symmetrical fatigue. The specimens hardened rapidly within 10 cycles under pure compression fatigue unlike the gradual cyclic hardening behaviour in symmetrical fatigue with the same peak stress amplitude. Compressive cyclic creep behaviour was also observed. Moreover, TEM observation showed that only moderate slip activity was detectable on the surface instead of typical PSB features. The surface observations revealed that surface slip bands did not increase in number nor height as cycling progressed. In addition, surface roughening by grain boundary extrusion was detected to become more severe with further cycling. Therefore, the plastic strain accommodated within the samples was not mainly related to dislocation activities. Instead, the mechanism of cyclic creep response for pure compression fatigue was correlated and

  18. Inhomogeneous deformation in INCONEL 718 during monotonic and cyclic loadings

    NASA Technical Reports Server (NTRS)

    Worthem, D. W.; Robertson, I. M.; Socie, D. F.; Altstetter, C. J.; Leckie, F. A.

    1990-01-01

    The paper concentrates on the relation between microstructural observations of the dislocation structures and the macroscopic deformation responses of both aged and homogenized precipitate-hardened alloys at room temperature. The deformation responses are compared to the cyclic deformation response of an aged precipitate-hardened alloy. Early in the deformation, one deformation band per grain and little evidence of work hardening are observed; with increased deformation, work hardening begins, more bands nucleate, and their spacing becomes similar to that in the aged material. It is pointed out that the degree of coarseness of inhomogeneous deformation is not a result of a softening process within the bands due to precipitate shearing, but it is a function of the amount of work hardening within the bands.

  19. Dynamic deformation capability of a red blood cell under a cyclically reciprocating shear stress.

    PubMed

    Watanabe, N; Yasuda, T; Kataoka, H; Takatani, S

    2004-01-01

    Red blood cells (RBCs) in the cardiovascular devices are exposed to varying degree of the shear stress from all the directions. However the RBCs' deformability or the deformation capability under such a shear stress is not well understood. In this study, we designed and built a system that can induce a cyclically reciprocating shear stress to a RBC suspension. The arm of the cyclically reciprocating shear stress device was attached to the upper piece of the parallel glass plates between which a suspension of human RBCs (1% hematocrit whole blood diluted in a 32 weight% dextran phosphate buffer solution) was contained. The cyclic reciprocating motion of the upper glass plate of 3.0 mm stroke length was produced using a slider-crank shaft mechanism that was linked to an eccentric cam-motor system. Each rotation of the motor produced a 3.0 mm stroke each in the forward and backward direction of the slider block. The clearance between the two glass plates was adjusted to 30 micrometer. The cyclic reciprocating glass plate apparatus was attached to a light microscope stage (IX71 Olympus with x40 objective lens) for illumination with a 350 watt metal halide light source. A high speed camera (MEMREMCAM fx-K3 Nac, 5000 frames per second with shutter kept open) was attached to the microscope to capture the deformation process of the RBCs under cyclic shear stress. The preliminary result indicated that the correlation between the amplitude of the maximum shear stress and the RBCs' deformability. This indicates a potential application of the cyclic reciprocating device to evaluate the temporal response of the RBCs deformability prior to its destruction. The future study will focus on the study of the relative velocity of the erythrocytes with respect to the velocity of the reciprocating plate. PMID:17271457

  20. Low Cycle Fatigue Behavior of 316LN Stainless Steel Alloyed with Varying Nitrogen Content. Part I: Cyclic Deformation Behavior

    NASA Astrophysics Data System (ADS)

    Prasad Reddy, G. V.; Sandhya, R.; Sankaran, S.; Mathew, M. D.

    2014-10-01

    In this study, the influence of cyclic strain amplitude on the evolution of cyclic stress-strain response and the associated cyclic deformation mechanisms in 316LN stainless steel with varying nitrogen content (0.07 to 0.22 wt pct) is reported in the temperature range 773 K to 873 K (500 °C to 600 °C). Two mechanisms, namely dynamic strain aging and secondary cyclic hardening, are found to strongly influence the cyclic stress response. Deformation substructures associated with both the mechanisms showed planar mode of deformation. These mechanisms are observed to be operative over certain combinations of temperature and strain amplitude. For strain amplitudes >0.6 pct, wavy or mixed mode of deformation is noticed to suppress both the mechanisms. Cyclic stress-strain curves revealed both single and dual-slope behavior depending on the test temperature. Increase in nitrogen content is found to increase the tendency toward planar mode of deformation, while increase in strain amplitude leads to transition from planar slip bands to dislocation cell/wall structure formation, irrespective of the nitrogen content in 316LN stainless steel.

  1. Cyclic deformation leads to defect healing and strengthening of small-volume metal crystals.

    PubMed

    Wang, Zhang-Jie; Li, Qing-Jie; Cui, Yi-Nan; Liu, Zhan-Li; Ma, Evan; Li, Ju; Sun, Jun; Zhuang, Zhuo; Dao, Ming; Shan, Zhi-Wei; Suresh, Subra

    2015-11-01

    When microscopic and macroscopic specimens of metals are subjected to cyclic loading, the creation, interaction, and accumulation of defects lead to damage, cracking, and failure. Here we demonstrate that when aluminum single crystals of submicrometer dimensions are subjected to low-amplitude cyclic deformation at room temperature, the density of preexisting dislocation lines and loops can be dramatically reduced with virtually no change of the overall sample geometry and essentially no permanent plastic strain. This "cyclic healing" of the metal crystal leads to significant strengthening through dramatic reductions in dislocation density, in distinct contrast to conventional cyclic strain hardening mechanisms arising from increases in dislocation density and interactions among defects in microcrystalline and macrocrystalline metals and alloys. Our real-time, in situ transmission electron microscopy observations of tensile tests reveal that pinned dislocation lines undergo shakedown during cyclic straining, with the extent of dislocation unpinning dependent on the amplitude, sequence, and number of strain cycles. Those unpinned mobile dislocations moving close enough to the free surface of the thin specimens as a result of such repeated straining are then further attracted to the surface by image forces that facilitate their egress from the crystal. These results point to a versatile pathway for controlled mechanical annealing and defect engineering in submicrometer-sized metal crystals, thereby obviating the need for thermal annealing or significant plastic deformation that could cause change in shape and/or dimensions of the specimen. PMID:26483463

  2. Cyclic deformation leads to defect healing and strengthening of small-volume metal crystals

    PubMed Central

    Wang, Zhang-Jie; Li, Qing-Jie; Cui, Yi-Nan; Liu, Zhan-Li; Ma, Evan; Li, Ju; Sun, Jun; Zhuang, Zhuo; Dao, Ming; Shan, Zhi-Wei; Suresh, Subra

    2015-01-01

    When microscopic and macroscopic specimens of metals are subjected to cyclic loading, the creation, interaction, and accumulation of defects lead to damage, cracking, and failure. Here we demonstrate that when aluminum single crystals of submicrometer dimensions are subjected to low-amplitude cyclic deformation at room temperature, the density of preexisting dislocation lines and loops can be dramatically reduced with virtually no change of the overall sample geometry and essentially no permanent plastic strain. This “cyclic healing” of the metal crystal leads to significant strengthening through dramatic reductions in dislocation density, in distinct contrast to conventional cyclic strain hardening mechanisms arising from increases in dislocation density and interactions among defects in microcrystalline and macrocrystalline metals and alloys. Our real-time, in situ transmission electron microscopy observations of tensile tests reveal that pinned dislocation lines undergo shakedown during cyclic straining, with the extent of dislocation unpinning dependent on the amplitude, sequence, and number of strain cycles. Those unpinned mobile dislocations moving close enough to the free surface of the thin specimens as a result of such repeated straining are then further attracted to the surface by image forces that facilitate their egress from the crystal. These results point to a versatile pathway for controlled mechanical annealing and defect engineering in submicrometer-sized metal crystals, thereby obviating the need for thermal annealing or significant plastic deformation that could cause change in shape and/or dimensions of the specimen. PMID:26483463

  3. Cyclic deformations in the Opalinus clay: a laboratory experiment

    NASA Astrophysics Data System (ADS)

    Huber, Emanuel; Huggenberger, Peter; Möri, Andreas; Meier, Edi

    2015-04-01

    The influence of tunnel climate on deformation cycles of joint openings and closings is often observed immediately after excavation. At the EZ-B niche in the Mt. Terri rock laboratory (Switzerland), a cyclic deformation of the shaly Opalinus clay has been monitored for several years. The deformation cycles of the joints parallel to the clay bedding planes correlate with seasonal variations in relative humidity of the air in the niche. In winter, when the relative humidity is the lowest (down to 65%), the joints open as the clay volume decreases, whereas they tend to close in the summer when the relative humidity reaches up to 100%. Furthermore, in situ measurements have shown the trend of an increasingly smaller aperture of joints with time. A laboratory experiment was carried out to reproduce the observed cyclic deformation in a climate chamber using a core sample of Opalinus clay. The main goal of the experiment was to investigate the influence of the relative humidity on the deformation of the Opalinus clay while excluding the in situ effects (e.g. confining stress). The core sample of Opalinus clay was put into a closed ended PVC tube and the space between the sample and the tube was filled with resin. Then, the sample (size: 28 cm × 14 cm × 6.5 cm) was cut in half lengthways and the open end was cut, so that the half-core sample could move in one direction. The mounted sample was exposed to wetting and drying cycles in a climate chamber. Air temperature, air humidity and sample weight were continuously recorded. Photographs taken at regular time intervals by a webcam allowed the formation/deformation of cracks on the surface of the sample to be monitored. A crackmeter consisting of a double-plate capacitor attached to the core sample was developed to measure the dynamics of the crack opening and closing. Preliminary results show that: - Deformation movements during different climate cycles can be visualized with the webcam - The crackmeter signal gives a

  4. Deformation mechanisms in experimentally deformed Boom Clay

    NASA Astrophysics Data System (ADS)

    Desbois, Guillaume; Schuck, Bernhard; Urai, Janos

    2016-04-01

    Bulk mechanical and transport properties of reference claystones for deep disposal of radioactive waste have been investigated since many years but little is known about microscale deformation mechanisms because accessing the relevant microstructure in these soft, very fine-grained, low permeable and low porous materials remains difficult. Recent development of ion beam polishing methods to prepare high quality damage free surfaces for scanning electron microscope (SEM) is opening new fields of microstructural investigation in claystones towards a better understanding of the deformation behavior transitional between rocks and soils. We present results of Boom Clay deformed in a triaxial cell in a consolidated - undrained test at a confining pressure of 0.375 MPa (i.e. close to natural value), with σ1 perpendicular to the bedding. Experiments stopped at 20 % strain. As a first approximation, the plasticity of the sample can be described by a Mohr-Coulomb type failure envelope with a coefficient of cohesion C = 0.117 MPa and an internal friction angle ϕ = 18.7°. After deformation test, the bulk sample shows a shear zone at an angle of about 35° from the vertical with an offset of about 5 mm. We used the "Lamipeel" method that allows producing a permanent absolutely plane and large size etched micro relief-replica in order to localize and to document the shear zone at the scale of the deformed core. High-resolution imaging of microstructures was mostly done by using the BIB-SEM method on key-regions identified after the "Lamipeel" method. Detailed BIB-SEM investigations of shear zones show the following: the boundaries between the shear zone and the host rock are sharp, clay aggregates and clastic grains are strongly reoriented parallel to the shear direction, and the porosity is significantly reduced in the shear zone and the grain size is smaller in the shear zone than in the host rock but there is no evidence for broken grains. Comparison of microstructures

  5. Mechanical annealing under low-amplitude cyclic loading in micropillars

    NASA Astrophysics Data System (ADS)

    Cui, Yi-nan; Liu, Zhan-li; Wang, Zhang-jie; Zhuang, Zhuo

    2016-04-01

    Mechanical annealing has been demonstrated to be an effective method for decreasing the overall dislocation density in submicron single crystal. However, simultaneously significant shape change always unexpectedly happens under extremely high monotonic loading to drive the pre-existing dislocations out of the free surfaces. In the present work, through in situ TEM experiments it is found that cyclic loading with low stress amplitude can drive most dislocations out of the submicron sample with virtually little change of the shape. The underlying dislocation mechanism is revealed by carrying out discrete dislocation dynamic (DDD) simulations. The simulation results indicate that the dislocation density decreases within cycles, while the accumulated plastic strain is small. By comparing the evolution of dislocation junction under monotonic, cyclic and relaxation deformation, the cumulative irreversible slip is found to be the key factor of promoting junction destruction and dislocation annihilation at free surface under low-amplitude cyclic loading condition. By introducing this mechanics into dislocation density evolution equations, the critical conditions for mechanical annealing under cyclic and monotonic loadings are discussed. Low-amplitude cyclic loading which strengthens the single crystal without seriously disturbing the structure has the potential applications in the manufacture of defect-free nano-devices.

  6. Modeling Cyclic Deformation of HSLA Steels Using Crystal Plasticity

    NASA Astrophysics Data System (ADS)

    Ghosh, Somnath; Xie, Chunlei

    2004-06-01

    In this paper, we propose a multi-time scale modeling technique for analyzing cyclic plastic deformation in crystalline solids subject to periodic loading. An asymptotic expansion of the variables in the time domain, together with homogenization forms the basis of multi-time scaling. In the macroscopic scale analysis, the oscillatory behavior of the load is averaged out and neglected, and the rate of averaged material behavior is quite slow in cyclic deformation. Implicitly, this means that the periodicity of some variables may be assumed for the oscillatory potion of the material behavior may be approximated. In this formulation, the governing equations are divided into two initial-boundary value problems with two different time scale: one is long time scale problem for describing the smooth averaged solution (global problem) and the other is for the remaining oscillatory potion (local problem). For the global problem, long time increments, which are longer than one cycle period, can be used and this multi-time scaling becomes an effective integrator.

  7. Modeling Step-Strain Relaxation and Cyclic Deformations of Elastomers

    NASA Technical Reports Server (NTRS)

    Johnson, A.R.; Mead, J. L.

    2000-01-01

    Data for step-strain relaxation and cyclic compressive deformations of highly viscous short elastomer cylinders are modeled using a large strain rubber viscoelastic constitutive theory with a rate-independent friction stress term added. In the tests, both small and large amplitude cyclic compressive strains, in the range of 1% to 10%, were superimposed on steady state compressed strains, in the range of 5% to 20%, for frequencies of 1 and 10 Hz. The elastomer cylinders were conditioned prior to each test to soften them. The constants in the viscoclastic-friction constitutive theory are determined by employing a nonlinear least-squares method to fit the analytical stresses for a Maxwell model, which includes friction, to measured relaxation stresses obtained from a 20% step-strain compression test. The simulation of the relaxation data with the nonlinear model is successful at compressive strains of 5%, 10%, 15%, and 20%. Simulations of hysteresis stresses for enforced cyclic compressive strains of 20% +/- 5% are made with the model calibrated by the relaxation data. The predicted hysteresis stresses are lower than the measured stresses.

  8. Monotonic and cyclic deformation behavior of a SiCw/6061 Al composite at elevated temperature

    SciTech Connect

    Wang, L.; Sun, Z.M.; Kobayashi, T.

    1996-10-15

    With the advent of new processing techniques, the technological interest and research activity in the development of metal-matrix composites have increased rapidly. Particularly, discontinuously reinforced composites, such as whisker and particle reinforced aluminum-based metal-matrix composites, exhibit attractive advantages, such as high specific modulus, high specific strength, good fatigue resistance and easy fabrication. They have emerged as a new class of structural materials for ambient and elevated temperature applications in aerospace and automobile industries. Therefore, great attention has been paid on their mechanical properties. However, a limited number of investigations on the cyclic deformation behavior have been reported, and little research has been done in this aspect at elevated temperature. The present study is based on a previous study at room temperature to investigate the monotonic and cyclic deformation behavior of a SiC whisker reinforced 6061 Al alloy composite and its unreinforced counterpart at elevated temperature.

  9. Microtensile testing and cyclic deformation of freestanding aluminum thin films

    NASA Astrophysics Data System (ADS)

    Barbosa, Nicholas, III

    2005-07-01

    Although the fatigue properties of bulk materials are well characterized for most materials, the implications of reducing the size scale of cyclically strained members to thicknesses on the order of single grains are not well defined. In this work, the cyclic deformation properties of 1 mum Al thin films are investigated. The fatigue test structures, the uniaxial load frame, the associated electronics, and the data acquisition and control software were all custom designed and fabricated in order to evaluate the monotonic and cyclic properties of thin metallic films. Test structures are 600 mum long x 100 mum wide x 1 mum thick. Monotonic tests were performed at a displacement rate of 5 mum/s and samples were pulled to failure. A value for the Young's modulus of the Al beams was determined to be 63.0 GPa +/- 5.1 GPa. The 0.2% yield stress was found to be 314.3 MPa +/- 45.2 MPa, the ultimate tensile strength was found to be 347.1 MPa +/- 56.3 MPa, and the average elongation was found to be 1.3% +/- 0.5%. Monotonic failures occurred through an oblique fracture. Fatigue tests were performed on the test structures under total strain amplitude control. Samples were fatigue under tension-tension conditions with strain amplitudes from 0.08% to 0.34%. The Al thin films were found to follow a Coffin-Manson relationship with a fatigue ductility coefficient of 0.022 and a fatigue ductility exponent of -0.278. Film fatigue fracture surfaces were similar in nature to bulk tension-tension fatigue, with the presence of slip offsets. The behavior of the 1 mum Al freestanding films, both in the monotonic and fatigue testing, was very similar to the fatigue properties of bulk materials when the significantly smaller sample grain size was considered.

  10. Influence of Cyclic Straining on Fatigue, Deformation, and Fracture Behavior of High-Strength Alloy Steel

    NASA Astrophysics Data System (ADS)

    Manigandan, K.; Srivatsan, T. S.; Vasudevan, V. K.; Tammana, D.; Poorganji, B.

    2016-01-01

    In this paper, the results of a study on microstructural influences on mechanical behavior of the high-strength alloy steel Tenax™ 310 are presented and discussed. Under the influence of fully reversed strain cycling, the stress response of this alloy steel revealed softening from the onset of deformation. Cyclic strain resistance exhibited a linear trend for the variation of both elastic strain amplitude with reversals-to-failure, and plastic strain amplitude with reversals-to-failure. Fracture morphology was essentially the same at the macroscopic level over the entire range of cyclic strain amplitudes examined. However, at the fine microscopic level, this high-strength alloy steel revealed fracture to be mixed-mode with features reminiscent of "locally" ductile and brittle mechanisms. The macroscopic mechanisms governing stress response at the fine microscopic level, resultant fatigue life, and final fracture behavior are presented and discussed in light of the mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the microstructural constituents during fully reversed strain cycling, cyclic strain amplitude, and resultant response stress.

  11. Detecting thermally driven cyclic deformation of an exfoliation sheet with lidar and radar

    USGS Publications Warehouse

    Collins, Brian D.; Stock, Greg M.

    2014-01-01

    Rock falls from steep, exfoliating cliffs are common in many landscapes. Of the many mechanisms known to trigger rock falls, thermally driven deformation is among the least quantified, despite potentially being a prevalent trigger due to its occurrence at all times of year. Here we present the results of a field-based monitoring program using instrumentation, ground-based lidar, and ground-based radar to investigate the process of thermally driven deformation of an exfoliation sheet, and the ability of remote sensing tools to capture cyclic expansion and contraction patterns. Our results indicate that thermally driven exfoliation occurs on diurnal cycles and can be measured at the submillimeter to centimeter scale using high-resolution strain gauges, short-range (2 km) radar interfer-ometry.

  12. Solute Transport in Cyclically Deformed Porous Tissue Scaffolds with Controlled Pore Cross-Sectional Geometries

    PubMed Central

    Op Den Buijs, Jorn; Lu, Lichun; Jorgensen, Steven M.; Dragomir-Daescu, Dan; Yaszemski, Michael J.

    2009-01-01

    The objective of this study was to investigate the influence of pore geometry on the transport rate and depth after repetitive mechanical deformation of porous scaffolds for tissue engineering applications. Flexible cubic imaging phantoms with pores in the shape of a circular cylinder, elliptic cylinder, and spheroid were fabricated from a biodegradable polymer blend using a combined 3D printing and injection molding technique. The specimens were immersed in fluid and loaded with a solution of a radiopaque solute. The solute distribution was quantified by recording 20 μm pixel-resolution images in an X-ray microimaging scanner at selected time points after intervals of dynamic straining with a mean strain of 8.6 ± 1.6% at 1.0 Hz. The results show that application of cyclic strain significantly increases the rate and depth of solute transport, as compared to diffusive transport alone, for all pore shapes. In addition, pore shape, pore size, and the orientation of the pore cross-sectional asymmetry with respect to the direction of strain greatly influence solute transport. Thus, pore geometry can be tailored to increase transport rates and depths in cyclically deformed scaffolds, which is of utmost importance when thick, metabolically functional tissues are to be engineered. PMID:19196145

  13. Phase Structure and Cyclic Deformation in Eutectic Tin-Lead Alloy: A Numerical Analysis

    SciTech Connect

    FANG,HUEI ELIOT; Li,W; SHEN,Y.-L

    1999-09-09

    This study is devoted to providing a mechanistic rationale of coarsening induced failure in solder alloys during thermomechanical fatigue. Micromechanical modeling of cyclic deformation of eutectic tin-lead alloy was undertaken using the finite element method. The models consist of regularly arranged tin-rich and lead-rich phases, simulating the lamellar array and colony structure in a typical eutectic system. A fine structure and a coarse structure, bearing the same phase fraction but different in the aspect ratio of each lead-rich layer and in the number of lead-rich layers in each colony, are utilized for representing the microstructure before and after coarsening, respectively. Both phases are treated as elastic-plastic solids with their respective properties. For simplicity the creep effect is ignored without compromising the main objective of this study. Cyclic loading under pure shear and uniaxial conditions is modeled. It is found that both the fine and coarse structures exhibit essentially the same macroscopic stress-strain response. The coarse structure, however, shows a greater maximum effective plastic strain on a local scale throughout the deformation. The numerical result implies that, in a solder joint, a locally coarsened region may not be mechanically weaker than its surrounding, but it is subject to early damage initiation due to accumulated plasticity. Other implications regarding solder alloy failure and micromechanical modeling of two-phase materials are discussed.

  14. Deformations and cyclic fatigue resistance of nickel-titanium instruments inside a sequence

    PubMed Central

    Gambarini, Gianluca; Plotino, Gianluca; Piasecki, Lucila; Al-Sudani, Dina; Testarelli, Luca; Sannino, Gianpaolo

    2015-01-01

    Summary Aim To compare the effect of brushing motion on torsional and cyclic fatigue resistance of TF Adaptive instruments after clinical use. Methods 20 packs of TFA small sequence (SybronEndo, Orange, CA, USA) were used for this study and divided into two groups. Each instrument prepared one resin tooth, consisting in 4 canals with a complex anatomy. In group A, no brushing motion was performed. In group B, after the green instrument reached the working length, brushing motion with circumferential filing was performed for 15 seconds in each canal (overall 1 minute). All the instruments were then subjected to cyclic fatigue test and mean values and standard deviation for time to fracture were evaluated. Data were subjected to one-way analysis of variance and Bonferroni t-test procedure with a significance set at P < 0.05. Results No instruments were broken during preparation of root canals. Two TF Adaptive green and 5 yellow showed unwinding after intracanal clinical use. No statistically significant differences were found between green instruments of both groups (P > 0.05), while a statistically significant difference was found between the yellow instruments (P < 0.05), with group B showing an higher resistance to cyclic fatigue. Conclusions A prolonged passive brushing motion did not adversely affected mechanical resistance of the instrument used for this purpose. Resistance to both deformations and cyclic fatigue of the second instrument within the TFA small sequence was enhanced by the coronal flaring provided by the brushing action of the first instrument used. PMID:26161246

  15. Twinning-detwinning behavior during cyclic deformation of magnesium alloy

    SciTech Connect

    Lee, Soo Yeol; Wang, Huamiao; Gharghouri, Michael A.

    2015-05-26

    In situ neutron diffraction has been used to examine the deformation mechanisms of a precipitation-hardened and extruded Mg-8.5wt.%Al alloy subjected to (i) compression followed by reverse tension (texture T1) and (ii) tension followed by reverse compression (texture T2). Two starting textures are used: (1) as-extruded texture, T1, in which the basal pole of most grains is normal to the extrusion axis and a small portion of grains are oriented with the basal pole parallel to the extrusion axis; (2) a reoriented texture, T2, in which the basal pole of most grains is parallel to the extrusion axis. For texture T1, the onset of extension twinning corresponds well with the macroscopic elastic-plastic transition during the initial compression stage. The non-linear macroscopic stress/strain behavior during unloading after compression is more significant than during unloading after tension. For texture T2, little detwinning occurs after the initial tension stage, but almost all of the twinned volumes are detwinned during loading in reverse compression.

  16. Twinning-detwinning behavior during cyclic deformation of magnesium alloy

    DOE PAGESBeta

    Lee, Soo Yeol; Wang, Huamiao; Gharghouri, Michael A.

    2015-05-26

    In situ neutron diffraction has been used to examine the deformation mechanisms of a precipitation-hardened and extruded Mg-8.5wt.%Al alloy subjected to (i) compression followed by reverse tension (texture T1) and (ii) tension followed by reverse compression (texture T2). Two starting textures are used: (1) as-extruded texture, T1, in which the basal pole of most grains is normal to the extrusion axis and a small portion of grains are oriented with the basal pole parallel to the extrusion axis; (2) a reoriented texture, T2, in which the basal pole of most grains is parallel to the extrusion axis. For texture T1,more » the onset of extension twinning corresponds well with the macroscopic elastic-plastic transition during the initial compression stage. The non-linear macroscopic stress/strain behavior during unloading after compression is more significant than during unloading after tension. For texture T2, little detwinning occurs after the initial tension stage, but almost all of the twinned volumes are detwinned during loading in reverse compression.« less

  17. Constitutive modeling of ultra-high molecular weight polyethylene under large-deformation and cyclic loading conditions.

    PubMed

    Bergström, J S; Kurtz, S M; Rimnac, C M; Edidin, A A

    2002-06-01

    When subjected to a monotonically increasing deformation state, the mechanical behavior of UHMWPE is characterized by a linear elastic response followed by distributed yielding and strain hardening at large deformations. During the unloading phases of an applied cyclic deformation process, the response is characterized by nonlinear recovery driven by the release of stored internal energy. A number of different constitutive theories can be used to model these experimentally observed events. We compare the ability of the J2-plasticity theory, the "Arruda-Boyce" model, the "Hasan-Boyce" model, and the "Bergström-Boyce" model to reproduce the observed mechanical behavior of ultra-high molecular weight polyethylene (UHMWPE). In addition a new hybrid model is proposed, which incorporates many features of the previous theories. This hybrid model is shown to most effectively predict the experimentally observed mechanical behavior of UHMWPE. PMID:12013180

  18. Advanced defect characterization via electron microscopy and its application to cyclically deformed nickel-based superalloy R104

    NASA Astrophysics Data System (ADS)

    Phillips, Patrick J.

    Ni-based superalloys continue to be used in the hot sections of turbine engines due to their superior high temperature properties and retained strength. The present document will focus specifically on the polycrystalline alloy R104, and the deformation substructure observed during and following cyclic mechanical testing. Both low cycle fatigue (LCF) and sustained peak low cycle fatigue (SPLCF) tests are considered. Two chapters on electron microscopy technique development follow a brief introduction on general properties of Nickel superalloys. Almost exclusively, scanning transmission electron microscopy (STEM) was performed for defect characterization. Furthermore, through a systematic study of STEM-based diffraction contrast methods, including experimental and computational results, STEM is presented as a valid means of defect analysis. The second chapter in this set also uses STEM, but in a non-traditional setting: the microscope is configured for high resolution imaging, i.e., the sample is aligned along a low index zone axis and a large convergence angle is used. In this low angle annular dark field (LAADF) mode, an annular detector accepts low-angle scattering, which allows one to obtain atomic resolution images while retaining defect contrast. Both techniques described in these two chapters were used extensively throughout this research. The remaining chapters discuss the application of the microscopy techniques developed in the proceeding chapters to cyclically deformed specimens of R104. Both interrupted and failed samples were deformed in LCF at 427°C and 704°C, and interrupted SPLCF samples were tested at 704 and 760°C. The deformation mechanisms observed will be discussed at length in this document. In general, dislocation activity dominates under LCF conditions while stacking faults and stacking fault ribbons are most prominent under SPLCF conditions. Time and temperature components will be discussed in regards to the operative mechanisms. A point

  19. Cyclic Deformation Behavior of Aged FeNiCoAlTa Single Crystals

    NASA Astrophysics Data System (ADS)

    Krooß, P.; Niendorf, T.; Karaman, I.; Chumlyakov, Y.; Maier, H. J.

    2012-11-01

    The cyclic deformation behavior of [001] oriented Fe-28Ni-17Co-11.5Al-2.5Ta (at.%) shape memory single crystals was investigated under tension. Dog-bone shaped specimens were tested up to 100 cycles after different aging heat treatments in order to characterize the cyclic stress-strain response and functional degradation. The smaller particles formed as a consequence of short aging for 1 h at 700°C, as compared to longer aging for 7 h, resulted in significantly enhanced resistance to cyclic degradation.

  20. An x-ray diffraction study of microstructural deformation induced by cyclic loading of selected steels

    SciTech Connect

    Fourspring, P.M.; Pangborn, R.N.

    1996-06-01

    X-ray double crystal diffractometry (XRDCD) was used to assess cyclic microstructural deformation in a face centered cubic (fcc) steel (AISI304) and a body centered cubic (bcc) steel (SA508 class 2). The first objective of the investigation was to determine if XRDCD could be used to effectively monitor cyclic microstructural deformation in polycrystalline Fe alloys. A second objective was to study the microstructural deformation induced by cyclic loading of polycrystalline Fe alloys. The approach used in the investigation was to induce fatigue damage in a material and to characterize the resulting microstructural deformation at discrete fractions of the fatigue life of the material. Also, characterization of microstructural deformation was carried out to identify differences in the accumulation of damage from the surface to the bulk, focusing on the following three regions: near surface (0--10 {micro}m), subsurface (10--300 {micro}m), and bulk. Characterization of the subsurface region was performed only on the AISI304 material because of the limited availability of the SA508 material. The results from the XRDCD data indicate a measurable change induced by fatigue from the initial state to subsequent states of both the AISI304 and the SA508 materials. Therefore, the XRDCD technique was shown to be sensitive to the microstructural deformation caused by fatigue in steels; thus, the technique can be used to monitor fatigue damage in steels. In addition, for the AISI304 material, the level of cyclic microstructural deformation in the bulk material was found to be greater than the level in the near surface material. In contrast, previous investigations have shown that the deformation is greater in the near surface than the bulk for Al alloys and bcc Fe alloys.

  1. An x-ray diffraction study of microstructural deformation induced by cyclic loading of selected steel

    NASA Astrophysics Data System (ADS)

    Fourspring, Patrick Michael

    X-ray double crystal diffractometry (XRDCD) and X-ray scanning diffractometry (XRSD) were used to assess cyclic microstructural deformation in a face centered cubic (fcc) steel (AISI304) and a body centered cubic (bcc) steel (SA508 class 2). The objectives of the investigation were to determine if X-ray diffraction could be used effectively to monitor cyclic microstructural deformation in polycrystalline Fe alloys and to study the distribution of the microstructural deformation induced by cyclic loading in these alloys. The approach used in the investigation was to induce fatigue damage in a material and to characterize the resulting microstructural deformation at discrete fractions of the fatigue life of the material. Also, characterization of microstructural deformation was carried out to identify differences in the accumulation of damage from the surface to the bulk, focusing on the following three regions: near surface (0-10 mum), subsurface (10-300 mum), and bulk. Characterization of the subsurface region was performed only on the AISI304 material because of the limited availability of the SA508 material. The results from the XRDCD data indicate a measurable change induced by fatigue from the initial state to subsequent states of both the AISI304 and the SA508 materials. The results from the XRSD data show similar but less coherent trends than the results from the XRDCD data. Therefore, the XRDCD technique was shown to be sensitive to the microstructural deformation caused by fatigue in steels; thus, the technique can be used to monitor fatigue damage in steels. In addition, for the AISI304 material, the level of cyclic microstructural deformation in the bulk material was found to be greater than the level in the near surface material. In contrast, previous investigations have shown that the deformation is greater in the near surface than the bulk for Al alloys and bcc Fe alloys.

  2. An x-ray diffraction study of microstructural deformation induced by cyclic loading of selected steels

    SciTech Connect

    Fourspring, P.M.; Pangborn, R.N.

    1997-12-31

    X-ray double crystal diffractometry (XRDCD) was used to assess cyclic microstructural deformation in a face centered cubic (fcc) steel (AISI304) and a body centered cubic (bcc) steel (SA508 class 2). The objectives of the investigation were to determine if XRDCD could be used effectively to monitor cyclic microstructural deformation in polycrystalline Fe alloys and to study the distribution of the microstructural deformation induced by cyclic loading in these alloys. The approach used in the investigation was to induce fatigue damage in a material and to characterize the resulting microstructural deformation at discrete fractions of the fatigue life of the material. Also, characterization of microstructural deformation was carried out to identify differences in the accumulation of damage from the surface to the bulk, focusing on the following three regions: near surface (0--10 {micro}m), subsurface (10--300 {micro}m), and bulk. Characterization of the subsurface region was performed only on the AISI304 material because of the limited availability of the SA508 material. The results from the XRDCD data indicate a measurable change induced by fatigue from the initial state to subsequent states of both the AISI304 and the SA508 materials. Therefore, the XRDCD technique was shown to be sensitive to the microstructural deformation caused by fatigue in steels; thus, the technique can be used to monitor fatigue damage in steels.

  3. Cyclic fatigue mechanisms in partially stabilized zirconia

    SciTech Connect

    Hoffman, M.J.; Wakayama, Shuichi; Kawahara, Masanori; Mai, Y.W.; Kishi, Teruo

    1995-12-31

    Cyclic fatigue crack growth rate and crack resistance curve testing were undertaken on 6 different grades of Mg-PSZ. The width of the transformation zone at the flanks of the cracks was determined using Raman spectroscopy and, combined with R-curve toughening values, used to ascertain the level of crack-tip shielding during cyclic fatigue crack growth and hence the crack-tip stress intensity factor amplitude. By normalizing the crack-tip stress intensity factor amplitude with the intrinsic toughness of the material, it was found that the cyclic fatigue threshold stress intensity factor was independent of the extent of crack-tip shielding and a function of the stress intensity factor at the crack tip. In situ SEM observations of cyclic fatigue revealed crack bridging by uncracked ligaments and the precipitate phase. Under cyclic loading the precipitate bridges were postulated to undergo frictional degradation at the precipitate/matrix interface with the degree of degradation determined by the cyclic amplitude. Acoustic emission testing revealed acoustic emissions at three distinct levels during the loading cycle: firstly, near the maximum applied stress intensity factor caused by crack propagation; secondly, at the mid-range of the applied stress intensity factor attributed to crack closure near the crack tip, presumably as a result of transformation induced dilation; and thirdly, intermittently near the base of the loading cycle as a result of fracture surface contact due to surface roughness at a significant distance behind the crack tip. Crack closure near the crack tip due to dilation is proposed to significantly reduce the crack tip stress intensity factor amplitude and hence the degree of cyclic fatigue.

  4. Grain size effect on monotonic and cyclic deformation responses of electroformed copper with ultrafine and nano sized twins

    NASA Astrophysics Data System (ADS)

    Luo, Ji

    2007-12-01

    Refining of grain sizes is one of the most powerful tools for achieving enhanced properties and performance in polycrystalline metallic materials. It has been found that, by reducing the grain size to ultrafine and nano ranges, the strength of the materials can be significantly enhanced. However, interpretation of the influence of the grain size on the mechanical behaviour of this kind of materials is still in its infancy. Especially, as the grain size falls in these regions, conventional dislocation model is subjected to contradictory experimental results. A wide spread of the applications of these materials is hindered due to the lack of validated models. To develop the present understanding, a novel energy approach is attempted, in which deformation process was treated as an energetic process. This energy approach is experimentally tested and theoretically investigated. The experimental investigation includes mechanical response characterization and microstructure investigation. It was found that, with decreasing grain size, the static deformation mechanism appears to transform from lower hardening stage to higher stage. Similarly, the cyclic deformation mode also exhibits corresponding characteristics shifting. Such transitions are attributed to the material's internal energy increases with the decrease of the grain size, leading to the following conclusions: (1) A novel view on cyclic hardening, cyclic softening and cyclic creep in relation to the strain energy of the material is synthesized, based on which a microstructure evolution law is derived. (2) Quantitative grading of grain size is enabled for the first time. According to the presented grading method, the size of the ultrafine grain is equal to the critical grain size at which the energetic transition condition from Stage III hardening to Stage IV hardening is satisfied. (3) An original interpretation of the physical meaning for Hall-Petch constant is provided. The Hall-Petch slope constant is found

  5. Structure Evolution During Cyclic Deformation of an Elastic Propylene-Based Ethylene-Propylene Copolymer

    SciTech Connect

    Toki,S.; Sics, I.; Burger, C.; Fang, D.; Liu, L.; Hsiao, B.; Datta, S.; Tsou, A.

    2006-01-01

    In-situ structural evolution during uniaxial extension and subsequent retraction of a thermoplastic elastomer (TPE) based on propylene-dominant ethylene-propylene (EP) copolymer was studied. Combined measurements of time-resolved wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) as well as stress-strain curves revealed molecular mechanism responsible for the elastic behavior. During the first cycle of deformation, a fraction of the crystals was destroyed, while the rest was reoriented. At strains larger than 1.0, strain-induced {alpha}-crystals in the lamellar form took place, resulting in the creation of a network with well-oriented lamellae having their normals parallel to the stretching direction. With the increase of strain, more crystals were induced, forming an enhanced network with strain-hardening behavior. During retraction and even after complete relaxation to zero stress, the majority of the strain-induced crystalline network remains in tact as being 'permanent set', where lamellar stacks act as the network points. This strain-induced crystalline network structure is thermally stable at room temperature and is responsible for the elastic behavior during subsequent cyclic deformation, similar to a vulcanized rubber.

  6. Simulation to the Cyclic Deformation of Polycrystalline Aluminum Alloy Using Crystal Plasticity Finite Element Method

    NASA Astrophysics Data System (ADS)

    Luo, Juan; Kang, Guozheng; Shi, Mingxing

    2013-01-01

    A crystal plasticity based finite element model (i.e., FE model) is used in this paper to simulate the cyclic deformation of polycrystalline aluminum alloy plates. The Armstrong-Frederick nonlinear kinematic hardening rule is employed in the single crystal constitutive model to capture the Bauschinger effect and ratcheting of aluminum single crystal presented under the cyclic loading conditions. A simple model of latent hardening is used to consider the interaction of dislocations between different slipping systems. The proposed single crystal constitutive model is implemented numerically into a FE code, i.e., ABAQUS. Then, the proposed model is verified by comparing the simulated results of cyclic deformation with the corresponding experimental ones of a face-centered cubic polycrystalline metal, i.e., rolled 5083 aluminum alloy. In the meantime, it is shown that the model is capable of predicting local heterogeneous deformation in single crystal scale, which plays an important role in the macroscopic deformation of polycrystalline aggregates. Under the cyclic loading conditions, the effect of applied strain amplitude on the responded stress amplitude and the dependence of ratcheting strain on the applied stress level are reproduced reasonably.

  7. Experimental investigation of cyclic thermomechanical deformation in torsion

    NASA Technical Reports Server (NTRS)

    Ellis, John R.; Castelli, Michael G.; Bakis, Charles E.

    1992-01-01

    An investigation of thermomechanical testing and deformation behavior of tubular specimens under torsional loading is described. Experimental issues concerning test accuracy and control specific to thermomechanical loadings under a torsional regime are discussed. A series of shear strain-controlled tests involving the nickel-base superalloy Hastelloy X were performed with various temperature excursions and compared to similar thermomechanical uniaxial tests. The concept and use of second invariants of the deviatoric stress and strain tensors as a means of comparing uniaxial and torsional specimens is also briefly presented and discussed in light of previous thermomechanical tests conducted under uniaxial conditions.

  8. Microstructures and deformation mechanisms of experimentally deformed gabbro

    NASA Astrophysics Data System (ADS)

    Zhou, Yongsheng; He, Changrong

    2015-04-01

    The natural gabbro samples were deformed at temperature ranging from 700 to 1150 °C with strain rate steps of 1 × 10-4, 2.5 × 10-5, 6.3 × 10-6 s-1. The mechanical data show that sample experiences gradual transition from semi-brittle flow to plastic flow, corresponding to a systematically decreasing stress exponent n with the increasing temperature ranging from 16.5 to 4.1 (He et al. Sci China (D) 46(7):730-742, 2003). We investigate microstructures and deformation mechanisms of experimentally deformed gabbro under transmission electron microscope in this study. For low temperature of 700 °C to 950 °C, the deformation is mainly accommodated with dislocation glide and mechanical twinning, corresponding to stress exponent lager than 5, which means semi-brittle deformation. Whereas with higher temperature up to 1000 °C-1150 °C, the deformation is accommodated mainly with dislocation glide and climb corresponding to stress exponent of 4.1, which means plastic deformation. Evidence of dislocation climb has been found as dislocation walls in plagioclase. The observed slip system in plagioclase is (001)1/2[110] and that in clinopyroxene are (100)[001] and (010)[001]. The (010)[001] slip system in clinopyroxene is newly found in this work. Melt was found at temperature of 950 °C-1050 °C. The melt glass distributed both in melt thin film between two grain boundaries and melt tubules of triangular along three grain boundaries at temperature of 950 °C-1000 °C. The melt triangular interconnected to the melt film at temperature of 1050 °C-1150 °C, where the melt chemical composition differentiated into iron-rich dark dots and silicate-rich matrix.

  9. Dynamic Deformation and Recovery Response of Red Blood Cells to a Cyclically Reversing Shear Flow: Effects of Frequency of Cyclically Reversing Shear Flow and Shear Stress Level

    PubMed Central

    Watanabe, Nobuo; Kataoka, Hiroyuki; Yasuda, Toshitaka; Takatani, Setsuo

    2006-01-01

    Dynamic deformation and recovery responses of red blood cells (RBCs) to a cyclically reversing shear flow generated in a 30-μm clearance, with the peak shear stress of 53, 108, 161, and 274 Pa at the frequency of 1, 2, 3, and 5 Hz, respectively, were studied. The RBCs' time-varying velocity varied after the glass plate velocity without any time lag, whereas the L/W change, where L and W were the major and minor axes of RBCs' ellipsoidal shape, exhibited a rapid increase and gradual decay during the deformation and recovery phase. The time of minimum L/W occurrence lagged behind the zero-velocity time of the glass plate (zero stress), and the delay time normalized to the one-cycle duration remained constant at 8.0%. The elongation of RBCs at zero stress time became larger with the reversing frequency. A simple mechanical model consisting of an elastic linear element during a rapid elongation period and a parallel combination of elements such as a spring and dashpot during the nonlinear recovery phase was suggested. The dynamic response behavior of RBCs under a cyclically reversing shear flow was different from the conventional shape change where a steplike force was applied to and completely released from the RBCs. PMID:16766612

  10. Preferred orientation in experimentally deformed stishovite: implications for deformation mechanisms

    NASA Astrophysics Data System (ADS)

    Kaercher, P. M.; Zepeda-Alarcon, E.; Prakapenka, V.; Kanitpanyacharoen, W.; Smith, J.; Sinogeikin, S. V.; Wenk, H. R.

    2014-12-01

    The crystal structure of the high pressure SiO2 polymorph stishovite has been studied in detail, yet little is known about its deformation mechanisms. Information about how stishovite deforms under stress is important for understanding subduction of quartz-bearing crustal rocks into the mantle. Particularly, stishovite is elastically anisotropic and thus development of crystallographic preferred orientation (CPO) during deformation may contribute to seismic anomalies in the mantle. We converted a natural sample of flint to stishovite in a laser heated diamond anvil cell and compressed the stishovite aggregate up to 38 GPa. Diffraction patterns were collected in situ in radial geometry at the Advanced Light Source (ALS) and the Advanced Photon Source (APS) to examine development of CPO during deformation. We find that (001) poles preferentially align with the compression direction and infer deformation mechanisms leading to the observed CPO with visco-plastic self consistent (VPSC) polycrystal plasticity models. Our results show pyramidal and basal slip are most likely active at high pressure and ambient temperature, in agreement with transmission electron microscopy (TEM) studies of rutile (TiO2) and paratellurite (TeO2), which are isostructural to stishovite. Conversely other TEM studies of stishovite done at higher temperature suggest dominant prismatic slip. This indicates that a variety of slip systems may be active in stishovite, depending on conditions. As a result, stishovite's contribution to the seismic signature in the mantle may vary as a function of pressure and temperature and thus depth.

  11. Experimental investigation on mechanical damage characteristics of sandstone under triaxial cyclic loading

    NASA Astrophysics Data System (ADS)

    Yang, Sheng-Qi; Ranjith, P. G.; Huang, Yan-Hua; Yin, Peng-Fei; Jing, Hong-Wen; Gui, Yi-Lin; Yu, Qing-Lei

    2015-05-01

    The mechanical damage characteristics of sandstone subjected to cyclic loading is very significant to evaluate the stability and safety of deep excavation damage zones. However to date, there are very few triaxial experimental studies of sandstone under cyclic loading. Moreover, few X-ray micro-computed tomography (micro-CT) observations have been adopted to reveal the damage mechanism of sandstone under triaxial cyclic loading. Therefore, in this research, a series of triaxial cyclic loading tests and X-ray micro-CT observations were conducted to analyse the mechanical damage characteristics of sandstone with respect to different confining pressures. The results indicated that at lower confining pressures, the triaxial strength of sandstone specimens under cyclic loading is higher than that under monotonic loading; whereas at confining pressures above 20 MPa, the triaxial strength of sandstone under cyclic loading is approximately equal to that under monotonic loading. With the increase of cycle number, the crack damage threshold of sandstone first increases, and then significantly decreases and finally remains constant. Based on the damage evolution of irreversible deformation, it appears that the axial damage value of sandstone is all higher than the radial damage value before the peak strength; whereas the radial damage value is higher than the axial damage value after the peak strength. The evolution of Young's modulus and Poisson's ratio of sandstone can be characterized as having four stages: (i) Stage I: material strengthening; (ii) Stage II: material degradation; (iii) Stage III: material failure and (iv) Stage IV: structure slippage. X-ray micro-CT observations demonstrated that the CT scanning surface images of sandstone specimens are consistent with actual surface crack photographs. The analysis of the cross-sections of sandstone supports that the system of crack planes under triaxial cyclic loading is much more complicated than that under triaxial

  12. Dislocations: 75 years of Deformation Mechanisms

    NASA Technical Reports Server (NTRS)

    Schneider, Judy

    2009-01-01

    The selection of papers presented in this section reflect on themes to be explored at the "Dislocations: 75 years of Deformation Mechanisms" Symposium to be held at the Annual 2009 TMS meeting. The symposium was sponsored by the Mechanical Behavior of Materials Committee to give tribute to the evolution of a concept that has formed the basis of our mechanistic understanding of how crystalline solids plastically deform and how they fail.

  13. Cyclic mechanical reinforcement of integrin–ligand interactions

    PubMed Central

    Kong, Fang; Li, Zhenhai; Parks, William M.; Dumbauld, David W.; García, Andrés J.; Mould, A. Paul; Humphries, Martin J.; Zhu, Cheng

    2013-01-01

    Summary Cells regulate adhesion in response to internally-generated and externally-applied forces. Integrins connect the extracellular matrix to the cytoskeleton and provide cells with mechanical anchorages and signaling platforms. Here we show that cyclic forces applied to a fibronectin–integrin α5β1 bond switch the bond from a short-lived state with 1-s lifetime to a long-lived state with 100-s lifetime. We term this phenomenon “cyclic mechanical reinforcement” as the bond strength remembers the history of force application, accumulates over repeated cycles, but does not require force to be sustained. Cyclic mechanical reinforcement strengthens the fibronectin–integrin α5β1 bond through the RGD binding site of the ligand with the synergy binding site greatly facilitating the process. A flexible integrin hybrid domain is also important for cyclic mechanical reinforcement. Our results reveal a mechanical regulation of receptor–ligand interactions and identify a molecular mechanism for cell adhesion strengthening by cyclic forces. PMID:23416109

  14. Cyclic Axial-Torsional Deformation Behavior of a Cobalt-Base Superalloy

    NASA Technical Reports Server (NTRS)

    Bonacuse, Peter J.; Kalluri, Sreeramesh

    1995-01-01

    The cyclic, high-temperature deformation behavior of a wrought cobalt-base super-alloy, Haynes 188, is investigated under combined axial and torsional loads. This is accomplished through the examination of hysteresis loops generated from a biaxial fatigue test program. A high-temperature axial, torsional, and combined axial-torsional fatigue database has been generated on Haynes 188 at 760 C. Cyclic loading tests have been conducted on uniform gage section tubular specimens in a servohydraulic axial-torsional test rig. Test control and data acquisition were accomplished with a minicomputer. The fatigue behavior of Haynes 188 at 760 C under axial, torsional, and combined axial-torsional loads and the monotonic and cyclic deformation behaviors under axial and torsional loads have been previously reported. In this paper, the cyclic hardening characteristics and typical hysteresis loops in the axial stress versus axial strain, shear stress ,versus engineering shear strain, axial strain versus engineering shear strain. and axial stress versus shear stress spaces are presented for cyclic in-phase and out-of-phase axial-torsional tests. For in-phase tests, three different values of the proportionality constant lambda (the ratio of engineering shear strain amplitude to axial strain amplitude, are examined, viz. 0.86, 1.73, and 3.46. In the out-of-phase tests, three different values of the phase angle, phi (between the axial and engineering shear strain waveforms), are studied, viz., 30, 60, and 90 degrees with lambda equals 1.73. The cyclic hardening behaviors of all the tests conducted on Haynes 188 at 760 C are evaluated using the von Mises equivalent stress-strain and the maximum shear stress-maximum engineering shear strain (Tresca) curves. Comparisons are also made between the hardening behaviors of cyclic axial, torsional, and combined in-phase (lambda = 1.73 and phi = 0) and out-of-phase (lambda = 1.73 and phi = 90') axial-torsional fatigue tests. These comparisons

  15. Effect of cyclic loading on the nanoscale deformation of hydroxyapatite and collagen fibrils in bovine bone.

    PubMed

    Singhal, Anjali; Stock, Stuart R; Almer, Jonathan D; Dunand, David C

    2014-06-01

    Cyclic compressive loading tests were carried out on bovine femoral bones at body temperature (37 °C), with varying mean stresses (-55 to -80 MPa) and loading frequencies (0.5-5 Hz). At various times, the cyclic loading was interrupted to carry out high-energy X-ray scattering measurements of the internal strains developing in the hydroxyapatite (HAP) platelets and the collagen fibrils. The residual strains upon unloading were always tensile in the HAP and compressive in the fibrils, and each increases in magnitude with loading cycles, which can be explained from damage at the HAP–collagen interface and accumulation of plastic deformation within the collagen phase. The samples tested at a higher mean stress and stress amplitude, and at lower loading frequencies exhibit greater plastic deformation and damage accumulation, which is attributed to greater contribution of creep. Synchrotron microcomputed tomography of some of the specimens showed that cracks are produced during cyclic loading and that they mostly occur concentric with Haversian canals. PMID:23958833

  16. Highly deformable bones: unusual deformation mechanisms of seahorse armor.

    PubMed

    Porter, Michael M; Novitskaya, Ekaterina; Castro-Ceseña, Ana Bertha; Meyers, Marc A; McKittrick, Joanna

    2013-06-01

    Multifunctional materials and devices found in nature serve as inspiration for advanced synthetic materials, structures and robotics. Here, we elucidate the architecture and unusual deformation mechanisms of seahorse tails that provide prehension as well as protection against predators. The seahorse tail is composed of subdermal bony plates arranged in articulating ring-like segments that overlap for controlled ventral bending and twisting. The bony plates are highly deformable materials designed to slide past one another and buckle when compressed. This complex plate and segment motion, along with the unique hardness distribution and structural hierarchy of each plate, provide seahorses with joint flexibility while shielding them against impact and crushing. Mimicking seahorse armor may lead to novel bio-inspired technologies, such as flexible armor, fracture-resistant structures or prehensile robotics. PMID:23470547

  17. Preferred orientation in experimentally deformed stishovite: implications for deformation mechanisms

    NASA Astrophysics Data System (ADS)

    Kaercher, Pamela M.; Zepeda-Alarcon, Eloisa; Prakapenka, Vitali B.; Kanitpanyacharoen, Waruntorn; Smith, Jesse S.; Sinogeikin, Stanislav; Wenk, Hans-Rudolf

    2015-04-01

    Although the crystal structure of the high-pressure SiO2 polymorph stishovite has been studied in detail, little is known about the development of crystallographic preferred orientation (CPO) during deformation in stishovite. Insight into CPO and associated deformation mechanics of stishovite would provide important information for understanding subduction of quartz-bearing crustal rocks into the mantle. To study CPO development, we converted a natural sample of flint to stishovite in a laser-heated diamond anvil cell and compressed the stishovite aggregate up to 38 GPa. We collected diffraction patterns in radial geometry to examine in situ development of crystallographic preferred orientation and find that (001) poles preferentially align with the compression direction. Viscoplastic self-consistent modeling suggests the most likely slip systems at high pressure and ambient temperature are pyramidal and basal slip.

  18. Cyclic axial-torsional deformation behavior of a cobalt-base superalloy

    NASA Technical Reports Server (NTRS)

    Bonacuse, Peter J.; Kalluri, Sreeramesh

    1992-01-01

    Multiaxial loading, especially at elevated temperature, can cause the inelastic response of a material to differ significantly from that predicted by simple flow rules, i.e., von Mises or Tresca. To quantify some of these differences, the cyclic high-temperature, deformation behavior of a wrought cobalt-based superalloy, Haynes 188, is investigated under combined axial and torsional loads. Haynes 188 is currently used in many aerospace gas turbine and rocket engine applications, e.g., the combustor liner for the T800 turboshaft engine for the RAH-66 Comanche helicopter and the liquid oxygen posts in the main injector of the space shuttle main engine. The deformation behavior of this material is assessed through the examination of hysteresis loops generated from a biaxial fatigue test program. A high-temperature axial, torsional, and combined axial-torsional fatigue data base has been generated on Haynes 188 at 760 C. Cyclic loading tests have been conducted on uniform gauge section tubular specimens in a servohydraulic axial-torsional test rig. Test control and data acquisition were accomplished with a minicomputer. In this paper, the cyclic hardening characteristics and typical hysteresis loops in the axial stress versus axial strain, shear stress versus engineering shear strain, axial strain versus engineering shear strain, and axial stress versus shear stress spaces are presented for cyclic, in-phase and out-of-phase, axial torsional tests. For in-phase tests three different values of the proportionality constant, lambda (ratio of engineering shear strain amplitude to axial strain amplitude), are examined, viz., 0.86, 1.73, and 3.46. In the out-of-phase tests, three different values of the phase angle, phi (between the axial and engineering shear strain waveforms), are studied, viz., 30, 60, and 90 deg with lambda = 1.73. The cyclic hardening behaviors of all the tests conducted on Haynes 188 at 760 C are evaluated using the von Mises equivalent stress

  19. Microstructure, Cyclic Deformation and Corrosion Behavior of Laser Welded NiTi Shape Memory Wires

    NASA Astrophysics Data System (ADS)

    Mirshekari, G. R.; Kermanpur, A.; Saatchi, A.; Sadrnezhaad, S. K.; Soleymani, A. P.

    2015-09-01

    The present paper reports the effects of Nd:YAG laser welding on the microstructure, phase transformation, cyclic deformation behavior, and corrosion resistance of Ti-55 wt.% Ni wire. The results showed that the laser welding altered the microstructure of the weld metal which mainly composed of columnar dendrites grown epitaxially from the fusion line. DSC results indicated that the onset of the transformation temperatures of the weld metal differed from that of the base metal. Cyclic stress-strain behavior of laser-welded NiTi wire was comparable to the as-received material; while a little reduction in the pseudo-elastic property was noted. The weld metal exhibited higher corrosion potential, lower corrosion current density, higher breakdown potential and wider passive region than the base metal. The weld metal was therefore more resistant to corrosion than the base metal.

  20. Effects of Cyclic and Monotonic Deformations on Nonlinear Ultrasonic Response of Austenitic Stainless Steel: A Comparative Study

    NASA Astrophysics Data System (ADS)

    Zhang, Jianfeng; Xuan, Fu-Zhen; Xiang, Yanxun; Zhao, Peng

    2016-05-01

    The effect of plastic deformations on the nonlinear ultrasonic response in austenite stainless steel was investigated under the tensile, asymmetric cyclic, and symmetric cyclic loadings. Nonlinear ultrasonic wave measurement was performed on the interrupted specimens. Results show that cyclic and monotonic plastic deformations lead to the significantly different acoustic nonlinear response. The increase of dislocation density and martensite transformation causes the increase of acoustic nonlinearity. By contrast, the well-developed cell structures decrease the acoustic nonlinear response. Under the asymmetric cyclic loading condition, the lightly decrease of acoustic nonlinearity is caused by the development of cell structures, while the slight increase of acoustic nonlinearity should be attributed to the increase of martensite transformation. Comparatively, the severe increase of acoustic nonlinearity during the first stage under symmetric cyclic loading is ascribed to the fast generation of dislocation structures and martensite transformation.

  1. Structure modulation driven by cyclic deformation in nanocrystalline NiFe

    SciTech Connect

    Cheng, Sheng; Wang, Xun-Li; Zhao, Yh; Wang, Yinmin; Liaw, Peter K; Lavernia, Ej

    2010-01-01

    Theoretical modeling suggests that the grain size remains unchanged during fatigue crack growth in nanocrystalline metals. Here we demonstrate that a modulated structure is generated in a nanocrystalline Ni-Fe alloy under cyclic deformation. Substantial grain coarsening and loss of growth twins are observed in the path of fatigue cracks, while the grains away from the cracks remain largely unaffected. Statistical analyses suggest that the grain coarsening is realized through the grain lattice rotation and coalescence and the loss of growth twins may be related to the detwinning process near crack tip.

  2. Fatigueless response of spider draglines in cyclic torsion facilitated by reversible molecular deformation

    NASA Astrophysics Data System (ADS)

    Kumar, Bhupesh; Singh, Kamal P.

    2014-11-01

    We demonstrate that spider draglines exhibit a fatigueless response in extreme cyclic torsion up to its breaking limit. The well defined Raman bands at 1095 and 1245 cm-1 shifted linearly towards lower wavenumbers versus increasing twist in both clockwise and counter-clockwise directions. Under thousands of continuous loading cycles of twist strain approaching its breaking limit, all the Raman bands were preserved and the characteristic Raman peak shifts were found to be reversible. Besides, nanoscale surface profile of the worked silk appeared as good as the pristine silk. This unique fatigueless twist response of draglines, facilitated by reversible deformation of protein molecules, could find applications in durable miniatured devices.

  3. Modeling the Stress Transfer between Carbon Nanotubes and a Polymer Matrix during Cyclic Deformation

    NASA Astrophysics Data System (ADS)

    Kao, C. C.; Young, R. J.

    Raman spectroscopy was used in this study to investigate the cyclic deformation behavior of the single-walled carbon nanotubes (SWNTs)/epoxy composites. The stress transfer between the nanotube and epoxy resin has been followed through the stress-induced variation of the G' Raman band position of the nan-otubes. A hysteresis loop was found between the loading and unloading cycles and its size decreased with the increase of the deformation cycles. The energy dissipated in the composite and at the interface between the nanotube and matrix has been modeled from the loop area. The amount of interface damaged for each loading cycle was further predicted from the estimated dissipation energy.

  4. A viscoelastic coupling model for the cyclic deformation due to periodically repeated Earthquakes at subduction zones

    NASA Astrophysics Data System (ADS)

    Thatcher, Wayne; Rundle, John B.

    1984-09-01

    Vertical displacements due to periodic reverse faulting events in an elastic plate overlying a viscoelastic (Maxwell) half space are obtained and compared with the observed deformation cycle (coseismic strain release, postseismic transients, interseismic strain accumulation) from Japan. The viscoelastic effects, including the influence of buoyant restoring forces, are obtained using the method developed by Rundle, and plate convergence and strain accumulation are incorporated following the procedure suggested by Savage. The resulting deformation cycle is compared with that of an analogous elastic half-space dislocation model in which postearthquake effects are due to transient aseismic slip below the coseismic fault. Cyclic deformation is similar but not identical for the two models, and observations from southwest Japan suggest the superiority of the viscoelastic coupling model. In particular, inclusion of the effects of steady state flow in the asthenosphere overcomes a defect of the elastic half-space model and results in agreement with the observed interseismic movement pattern. Several aspects of the postseismic deformation, its landward migration, and its transition to the interseismic phase of the cycle are explained as well, but the short duration of near-trench transients relative to those observed farther inland is not matched. The success of a buried slip model in explaining early postseismic near-trench movements and asthenospheric flow in accounting for cumulative postearthquake transient motions suggests the existence of a transition zone between lithosphere and asthenosphere whose behavior is brittle/elastic in the short term and ductile for longer-term deformation, and such a modification may reconcile remaining discordant observations. However, reasonable variations in coupling model parameters cannot account for observed differences in the deformation cycle in other parts of Japan, and these regional differences remain unexplained.

  5. Dislocation Mechanics of High-Rate Deformations

    NASA Astrophysics Data System (ADS)

    Armstrong, Ronald W.; Li, Qizhen

    2015-10-01

    Four topics associated with constitutive equation descriptions of rate-dependent metal plastic deformation behavior are reviewed in honor of previous research accomplished on the same issues by Professor Marc Meyers along with colleagues and students, as follow: (1) increasing strength levels attributed to thermally activated dislocation migration at higher loading rates; (2) inhomogeneous adiabatic shear banding; (3) controlling mechanisms of deformation in shock as compared with shock-less isentropic compression experiments and (4) Hall-Petch-based grain size-dependent strain rate sensitivities exhibited by nanopolycrystalline materials. Experimental results are reviewed on the topics for a wide range of metals.

  6. Cyclic Deformation Behavior of a Rare-Earth Containing Extruded Magnesium Alloy: Effect of Heat Treatment

    NASA Astrophysics Data System (ADS)

    Mirza, F. A.; Chen, D. L.; Li, D. J.; Zeng, X. Q.

    2015-03-01

    The present study was aimed at evaluating strain-controlled cyclic deformation behavior of a rare-earth (RE) element containing Mg-10Gd-3Y-0.5Zr (GW103K) alloy in different states (as-extruded, peak-aged (T5), and solution-treated and peak-aged (T6)). The addition of RE elements led to an effective grain refinement and weak texture in the as-extruded alloy. While heat treatment resulted in a grain growth modestly in the T5 state and significantly in the T6 state, a high density of nano-sized and bamboo-leaf/plate-shaped β' (Mg7(Gd,Y)) precipitates was observed to distribute uniformly in the α-Mg matrix. The yield strength and ultimate tensile strength, as well as the maximum and minimum peak stresses during cyclic deformation in the T5 and T6 states were significantly higher than those in the as-extruded state. Unlike RE-free extruded Mg alloys, symmetrical hysteresis loops in tension and compression and cyclic stabilization were present in the GW103K alloy in different states. The fatigue life of this alloy in the three conditions, which could be well described by the Coffin-Manson law and Basquin's equation, was equivalent within the experimental scatter and was longer than that of RE-free extruded Mg alloys. This was predominantly attributed to the presence of the relatively weak texture and the suppression of twinning activities stemming from the fine grain sizes and especially RE-containing β' precipitates. Fatigue crack was observed to initiate from the specimen surface in all the three alloy states and the initiation site contained some cleavage-like facets after T6 heat treatment. Crack propagation was characterized mainly by the characteristic fatigue striations.

  7. Deformation mechanism crossover and mechanical behaviour in nanocrystalline materials.

    SciTech Connect

    Yamakov, V.; Wolf, D.; Phillpot, S. R.; Mukherjee, A. K.; Gleiter, H.; Materials Science Division; Univ. of California-Davis; Forschungszentrum Karlsruhe

    2003-06-01

    We use molecular dynamics simulations to elucidate the transition with decreasing grain size from a dislocation- to a grain-boundary-based deformation mechanism in nanocrystalline fcc metals. Our simulations reveal that this crossover is accompanied by a pronounced transition in the mechanical behaviour of the material; namely, at the grain size where the crossover occurs (the 'strongest size'), the strain rate under tensile elongation goes through a minimum. This simultaneous transition in both the deformation mechanism and the corresponding mechanical behaviour offers an explanation for the experimentally observed crossover in the yield strength of nanocrystalline materials, from Hall-Petch hardening to 'inverse Hall-Petch' softening.

  8. The cyclic deformation and fatigue behaviour of the low carbon steel SAE 1045 in the temperature regime of dynamic strain aging

    SciTech Connect

    Weisse, M.; Wamukwamba, C.K.; Christ, H.J.; Mughrabi, H. . Inst. fuer Werkstoffwissenschaften)

    1993-07-01

    The cyclic deformation behaviour of normalized SAE 1045 steel (german steel grade Ck 45) had been investigated over a range of temperatures between 20 and 375C. Special attention has been paid to the effects of dynamic strain aging, which are most pronounced around 300C. Different types of deformation tests (tension tests, incremental step tests, and constant amplitude cyclic deformation tests under stress control with a stress amplitude of 400 MPa as well as under plastic strain control with a plastic strain amplitude of 0.5%) were carried out to observe the influence of temperature on the macroscopic mechanical behaviour. These tests were followed by TEM studies on microstructural features. In the temperature range of maximum dynamic strain aging, the material was found to show maximum strength in unidirectional as well as in cyclic deformation tests. While the fatigue life is maximum at the temperature of maximum dynamic strain aging in stress-controlled tests, it is minimum in plastic strain controlled tests. At the temperature of maximum dynamic strain aging around 300C, the dislocations are arranged in dense dislocation tangles and parallel dislocation walls, whereas at room and at higher temperatures (375C) mainly dislocation cell structures are observed.

  9. Deformation Mechanisms of Gum Metals Under Nanoindentation

    NASA Astrophysics Data System (ADS)

    Sankaran, Rohini Priya

    Gum Metal is a set of multi-component beta-Ti alloys designed and developed by Toyota Central R&D Labs in 2003 to have a nearly zero shear modulus in the direction. After significant amounts of cold-work (>90%), these alloys were found to have yield strengths at a significant fraction of the predicted ideal strengths and exhibited very little work hardening. It has been speculated that this mechanical behavior may be realized through an ideal shear mechanism as opposed to conventional plastic deformation mechanisms, such as slip, and that such a mechanism may be realized through a defect structure termed "nanodisturbance". It is furthermore theorized that for near ideal strength to be attained, dislocations need to be pinned at sufficiently high stresses. It is the search for these defects and pinning points that motivates the present study. However, the mechanism of plastic deformation and the true origin of specific defect structures unique to gum metals is still controversial, mainly due to the complexity of the beta-Ti alloy system and the heavily distorted lattice exhibited in cold worked gum metals, rendering interpretation of images difficult. Accordingly, the first aim of this study is to clarify the starting as-received microstructures of gum metal alloys through conventional transmission electron microscopy (TEM) and aberration-corrected high resolution scanning transmission electron microscopy with high-angle annular dark field detector (HAADF-HRSTEM) imaging. To elucidate the effects of beta-stability and starting microstructure on the deformation behavior of gum metals and thus to provide adequate context for potentially novel deformation structures, we investigate three alloy conditions: gum metal that has undergone solution heat treatment (STGM), gum metal that has been heavily cold worked (CWGM), and a solution treated alloy of nominal gum metal composition, but leaner in beta-stabilizing content (ST Ref-1). In order to directly relate observed

  10. Cyclic evolution of the defect structure in a deformation macrolocalization zone in an HCP Zr-Nb alloy

    NASA Astrophysics Data System (ADS)

    Poletika, T. M.; Girsova, S. L.; Pshenichnikov, A. P.

    2011-10-01

    The microstructure of a Zr-1% Nb is studied in a deformation macrolocalization zone during its transformation into a neck. The related dislocation transformations are found to be cyclic, and this cyclicity is accompanied by oscillatory changes in the volumes occupied by different dislocation substructures, the scalar dislocation density, the subboundary density, and periodic relaxation of internal stresses as a result of the decomposition of low-angle subboundaries and dislocation redistribution.

  11. Static and cyclic mechanical loading of mesenchymal stem cells on elastomeric, electrospun polyurethane meshes.

    PubMed

    Cardwell, Robyn D; Kluge, Jonathan A; Thayer, Patrick S; Guelcher, Scott A; Dahlgren, Linda A; Kaplan, David L; Goldstein, Aaron S

    2015-07-01

    Biomaterial substrates composed of semi-aligned electrospun fibers are attractive supports for the regeneration of connective tissues because the fibers are durable under cyclic tensile loads and can guide cell adhesion, orientation, and gene expression. Previous studies on supported electrospun substrates have shown that both fiber diameter and mechanical deformation can independently influence cell morphology and gene expression. However, no studies have examined the effect of mechanical deformation and fiber diameter on unsupported meshes. Semi-aligned large (1.75 μm) and small (0.60 μm) diameter fiber meshes were prepared from degradable elastomeric poly(esterurethane urea) (PEUUR) meshes and characterized by tensile testing and scanning electron microscopy (SEM). Next, unsupported meshes were aligned between custom grips (with the stretch axis oriented parallel to axis of fiber alignment), seeded with C3H10T1/2 cells, and subjected to a static load (50 mN, adjusted daily), a cyclic load (4% strain at 0.25 Hz for 30 min, followed by a static tensile loading of 50 mN, daily), or no load. After 3 days of mechanical stimulation, confocal imaging was used to characterize cell shape, while measurements of deoxyribonucleic acid (DNA) content and messenger ribonucleic acid (mRNA) expression were used to characterize cell retention on unsupported meshes and expression of the connective tissue phenotype. Mechanical testing confirmed that these materials deform elastically to at least 10%. Cells adhered to unsupported meshes under all conditions and aligned with the direction of fiber orientation. Application of static and cyclic loads increased cell alignment. Cell density and mRNA expression of connective tissue proteins were not statistically different between experimental groups. However, on large diameter fiber meshes, static loading slightly elevated tenomodulin expression relative to the no load group, and tenascin-C and tenomodulin expression

  12. Mechanisms of Earth activity forsed by external celestial bodies:energy budjet and nature of cyclicity

    NASA Astrophysics Data System (ADS)

    Barkin, Yu. V.; Ferrandiz, J. M.

    2003-04-01

    In given report we discuss tidal and non-tidal mechanisms of forced tectonic (endogenous) activity of the Earth caused by gravitational attraction of the Moon, Sun and the planets. On the base of the classical solution of the problem of elasticity for model of the Earth with concentric mass distribution the evaluations of the tidal energy and power of Earth lunar-solar deformations, including their joint effect, were obtained. Important role of the joint energetic effect of rotational deformation of the Earth with lunar and solar tides was illustrated. Gravitational interaction of the Moon and Sun with non-spherical, non-homogeneous shells of the Earth generates big additional mechanical forces and moments of the interaction of the neighboring shells (rigid core, liquid core, mantle, lithosphere and separate plates). Acting of these forces and moments in the different time scales on the corresponding sells generates cyclic perturbations of the tensional state of the shells, their deformations, small relative translational displacements and small relative rotational oscillations of the shells. In geological period of time it leads to a fundamental tectonic reconstruction of the Earth. These additional forces and moments of the cyclic celestial-mechanical nature produce cyclic deformations of the all layers of the body and organize and control practically all natural processes. The additional force between mantle and core is cyclic and characterized by the wide basis of frequencies typical for orbital motions (of the Sun, Moon and planets), for rotational motion of the Earth, Moon and Sun and for many from observed natural processes. The problem about small relative translatory-rotary motion of the two shells separated by the thin viscous-elastic layer is studied. The differential equations of motion were obtained and have been studied in particular cases (plane motion of system; case of two axisymmetrical interacting shells and oth.) by approximate methods of small

  13. Welding of pyroclastic conduit infill: A mechanism for cyclical explosive eruptions

    NASA Astrophysics Data System (ADS)

    Kolzenburg, S.; Russell, J. K.

    2014-07-01

    Vulcanian-style eruptions are small- to moderate-sized, singular to cyclical events commonly having volcanic explosivity indices of 1-3. They produce pyroclastic flows, disperse tephra over considerable areas, and can occur as precursors to larger (e.g., Plinian) eruptions. The fallout deposits of the 2360 B.P. eruption of Mount Meager, BC, Canada, contain bread-crusted blocks of welded breccia as accessory lithics. They display a range of compaction/welding intensity and provide a remarkable opportunity to constrain the nature and timescales of mechanical processes operating within explosive volcanic conduits during repose periods between eruptive cycles. We address the deformation and porosity/permeability reduction within natural pyroclastic deposits infilling volcanic conduits. We measure the porosity, permeability, and ultrasonic wave velocities for a suite of samples and quantify the strain recorded by pumice clasts. We explore the correlations between the physical properties and deformation fabric. Based on these correlations, we reconstruct the deformation history within the conduit, model the permeability reduction timescales, and outline the implications for the repressurization of the volcanic conduit. Our results highlight a profound directionality in the measured physical properties of these samples related to the deformation-induced fabric. Gas permeability varies drastically with increasing strain and decreasing porosity along the compaction direction of the fabric but varies little along the elongation direction of the fabric. The deformation fabric records a combination of compaction within the conduit and postcompaction stretching associated with subsequent eruption. Model timescales of these processes are in good agreement with repose periods of cyclic vulcanian eruptions.

  14. Specificity of endothelial cell reorientation in response to cyclic mechanical stretching.

    PubMed

    Wang, J H; Goldschmidt-Clermont, P; Wille, J; Yin, F C

    2001-12-01

    Evidence suggests that cellular responses to mechanical stimuli depend specifically on the type of stimuli imposed. For example, when subjected to fluid shear stress, endothelial cells align along the flow direction. In contrast, in response to cyclic stretching, cells align away from the stretching direction. However, a few aspects of this cell alignment response remain to be clarified: (1) Is the cell alignment due to actual cell reorientation or selective cell detachment? (2) Does the resulting cell alignment represent a response of the cells to elongation or shortening, or both? (3) Does the cell alignment depend on the stretching magnitude or rate, or both? Finally, the role of the actin cytoskeleton and microtubules in the cell alignment response remains unclear. To address these questions, we grew human aortic endothelial cells on deformable silicone membranes and subjected them to three types of cyclic stretching: simple elongation, pure uniaxial stretching and equi-biaxial stretching. Examination of the same cells before and after stretching revealed that they reoriented. Cells subjected to either simple elongation or pure uniaxial stretching reoriented specifically toward the direction of minimal substrate deformation, even though the directions for the two types of stretching differed by only about 20 degrees. At comparable stretching durations, the extent of cell reorientation was more closely related to the stretching magnitude than the stretching rate. The actin cytoskeleton of the endothelial cell subjected to either type of stretching was reorganized into parallel arrays of actin filaments (i.e., stress fibers) aligned in the direction of the minimal substrate deformation. Furthermore, in response to equi-biaxial stretching, the actin cytoskeleton was remodeled into a "tent-like" structure oriented out of the membrane plane-again towards the direction of the minimal substrate deformation. Finally, abolishing microtubules prevented neither the

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

    NASA Technical Reports Server (NTRS)

    Jones, H. N.

    1996-01-01

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

  16. Deformation mechanisms of electrostrictive graft elastomer

    NASA Astrophysics Data System (ADS)

    Wang, Youqi; Sun, Changjie; Zhou, Eric; Su, Ji

    2004-12-01

    The electrostrictive graft elastomer is a new type of electroactive polymer. Recently developed by NASA, it consists of flexible backbone chains, each with side chains, called grafts. Neighboring backbone grafts physically cross-link and form crystal units. The flexible backbone chain and the crystal graft unit consist of polarized monomers, which contain atoms with electric partial charges, generating dipole moments. When the elastomer is placed into an electric field, external rotating moments are applied to the dipole moment. This stimulates electrostrictive strain in the graft elastomer. In this paper, the deformation of the elastomer under the action of an electric field is explained by means of two dominant mechanisms: crystal graft unit rotation and backbone chain reorientation. A two-dimensional computational model is established to analyze the deformation.

  17. Deformed Coherent State for Multiparticle Production Mechanism

    NASA Astrophysics Data System (ADS)

    Wang, W. Y.; Leong, Q.; Ng, W. K.; Dewanto, A.; Chan, A. H.; Oh, C. H.

    2014-04-01

    The deformation structure function describing the Generalised Multiplicities Distribution (GMD), Negative Binomial Distribution (NBD), Furry-Yule Distribution (FYD), and their corresponding deformed coherent states and second order correlation function g(2) are derived. A superposition model of the GMD and NBD states is then proposed as a general description of the mechanism that gives rise to the double NBD model first proposed by Giovannini. The model is applied to LHC multiplicity data at |η| ≤ 2.4 and 0.9, 2.36 and 7 TeV, from the CMS collaboration at CERN, and the second order correlation g(2) of the model is then compared with the normalised second factorial moment {F_2}/F_1^2 of the multiplicity.

  18. Deformation mechanisms of irradiated metallic nanofoams

    NASA Astrophysics Data System (ADS)

    Zepeda-Ruiz, L. A.; Martinez, E.; Caro, M.; Fu, E. G.; Caro, A.

    2013-07-01

    It was recently proposed that within a particular window in the parameter space of temperature, ion energy, dose rate, and filament diameter, nanoscale metallic foams could show radiation tolerance [Bringa et al., Nano Lett. 12, 3351 (2012)]. Outside this window, damage appears in the form of vacancy-related stacking fault tetrahedra (SFT), with no effects due to interstitials [Fu et al., Appl. Phys. Lett. 101, 191607 (2012)]. These SFT could be natural sources of dislocations within the ligaments composing the foam and determine their mechanical response. We employ molecular dynamics simulations of cylindrical ligaments containing an SFT to obtain an atomic-level picture of their deformation behavior under compression. We find that plastic deformation originates at the edges of the SFT, at lower stress than needed to create dislocations at the surface. Our results predict that nanoscale foams soften under irradiation, a prediction not yet tested experimentally.

  19. Universal mechanism of thermo-mechanical deformation in metallic glasses

    SciTech Connect

    Dmowski, W.; Tong, Y.; Iwashita, T.; Egami, Takeshi; Yokoyama, Y.

    2015-02-11

    Here we investigated the atomistic structure of metallic glasses subjected to thermo-mechanical creep deformation using high energy x-ray diffraction and molecular dynamics simulation. The experiments were performed in-situ, at high temperatures as a time dependent deformation in the elastic regime, and ex-situ on samples quenched under stress. We show that all the anisotropic structure functions of the samples undergone thermo-mechanical creep can be scaled into a single curve, regardless of the magnitude of anelastic strain, stress level and the sign of the stress, demonstrating universal behavior and pointing to unique atomistic unit of anelastic deformation. The structural changes due to creep are strongly localized within the second nearest neighbors, involving only a small group of atoms.

  20. Universal mechanism of thermo-mechanical deformation in metallic glasses

    DOE PAGESBeta

    Dmowski, W.; Tong, Y.; Iwashita, T.; Egami, Takeshi; Yokoyama, Y.

    2015-02-11

    Here we investigated the atomistic structure of metallic glasses subjected to thermo-mechanical creep deformation using high energy x-ray diffraction and molecular dynamics simulation. The experiments were performed in-situ, at high temperatures as a time dependent deformation in the elastic regime, and ex-situ on samples quenched under stress. We show that all the anisotropic structure functions of the samples undergone thermo-mechanical creep can be scaled into a single curve, regardless of the magnitude of anelastic strain, stress level and the sign of the stress, demonstrating universal behavior and pointing to unique atomistic unit of anelastic deformation. The structural changes due tomore » creep are strongly localized within the second nearest neighbors, involving only a small group of atoms.« less

  1. Deformation Mechanisms of Gum Metals Under Nanoindentation

    NASA Astrophysics Data System (ADS)

    Sankaran, Rohini Priya

    Gum Metal is a set of multi-component beta-Ti alloys designed and developed by Toyota Central R&D Labs in 2003 to have a nearly zero shear modulus in the direction. After significant amounts of cold-work (>90%), these alloys were found to have yield strengths at a significant fraction of the predicted ideal strengths and exhibited very little work hardening. It has been speculated that this mechanical behavior may be realized through an ideal shear mechanism as opposed to conventional plastic deformation mechanisms, such as slip, and that such a mechanism may be realized through a defect structure termed "nanodisturbance". It is furthermore theorized that for near ideal strength to be attained, dislocations need to be pinned at sufficiently high stresses. It is the search for these defects and pinning points that motivates the present study. However, the mechanism of plastic deformation and the true origin of specific defect structures unique to gum metals is still controversial, mainly due to the complexity of the beta-Ti alloy system and the heavily distorted lattice exhibited in cold worked gum metals, rendering interpretation of images difficult. Accordingly, the first aim of this study is to clarify the starting as-received microstructures of gum metal alloys through conventional transmission electron microscopy (TEM) and aberration-corrected high resolution scanning transmission electron microscopy with high-angle annular dark field detector (HAADF-HRSTEM) imaging. To elucidate the effects of beta-stability and starting microstructure on the deformation behavior of gum metals and thus to provide adequate context for potentially novel deformation structures, we investigate three alloy conditions: gum metal that has undergone solution heat treatment (STGM), gum metal that has been heavily cold worked (CWGM), and a solution treated alloy of nominal gum metal composition, but leaner in beta-stabilizing content (ST Ref-1). In order to directly relate observed

  2. Ruthenium Aluminides: Deformation Mechanisms and Substructure Development

    SciTech Connect

    Tresa M. Pollock

    2005-05-11

    Structural and functional materials that can operate in severe, high temperature environments are key to the operation of a wide range of energy generation systems. Because continued improvements in the energy efficiency of these systems is critical, the need for new materials with higher temperature capabilities is inevitable. Intermetallic compounds, with strong bonding and generally high melting points offer this possibility for a broad array of components such as coatings, electrode materials, actuators and/or structural elements. RuAl is a very unusual intermetallic compound among the large number of B2compounds that have been identified and investigated to date. This material has a very high melting temperature of 2050?C, low thermal expansion, high thermal conductivity and good corrosion resistance. Unlike most other high temperature B2 intermetallics, RuAl possesses good intrinsic deformability at low temperatures. In this program fundamental aspects of low and high temperature mechanical properties and deformation mechanisms in binary and higher order RuAl-based systems have been investigated. Alloying additions of interest included platinum, boron and niobium. Additionally, preliminary studies on high temperature oxidation behavior of these materials have been conducted.

  3. Cyclic Bending and Stationary Drawing Deformation of Metal Sheets : Experiments and Associated Numerical Simulations

    SciTech Connect

    Moreira, L.P.; Romao, E.C.; Vieira, L.C.A.; Ferron, G.; Sampaio, A.P.

    2005-08-05

    A simple bend-draw experimental device is employed to analyze the behavior of narrow strips submitted to a nearly cyclic bending deformation mode followed by a steady state drawing. In this bending-drawing experiment, the strip is firstly bent over a central bead and two lateral beads by applying a controlled holding load and then is pulled out of device throughout the bead radii by a drawing load. The apparatus is mounted in a standard tensile test machine where the holding and drawing loads are recorded with an acquisition data system. The specimen is a rectangular strip cut with 320 mm long and 7 mm wide. The longitudinal (1) and width (w) strip plastic strains are determined from two hardness marks 120 mm spaced whereas the corresponding thickness (t) strain is obtained by volume conservation. Previous experiments showed a correlation between the plastic strain ({epsilon}w/{epsilon}t)BD resulting from the bending-drawing and the Lankford R-values obtained from the uniaxial tensile test. However, previous 3D numerical simulations based upon Hill's quadratic and Ferron's yield criteria revealed a better correlation between the ({epsilon}w/{epsilon}t)BD and the stress ratio {sigma}PS/{sigma}({alpha}), where {sigma}PS stands for the plane-strain tension yield stress and {sigma}({alpha}) for the uniaxial yield stress in uniaxial tension along the drawing direction making an angle {alpha} with the rolling direction. In the present work, the behavior of an IF steel sheet is firstly evaluated by means of uniaxial tensile and drawing-bending experiments conducted at every 15 degrees with respect to the rolling direction. Afterwards, the bending-drawing experiment is investigated with the commercial finite element (FE) code ABAQUS/Standard in an attempt to assess the influence of cyclic loadings upon the bending-drawing strain-ratios.

  4. On the Specific Role of Microstructure in Governing Cyclic Fatigue, Deformation, and Fracture Behavior of a High-Strength Alloy Steel

    NASA Astrophysics Data System (ADS)

    Manigandan, K.; Srivatsan, T. S.

    2015-06-01

    In this paper, the results of an experimental study that focused on evaluating the conjoint influence of microstructure and test specimen orientation on fully reversed strain-controlled fatigue behavior of the high alloy steel X2M are presented and discussed. The cyclic stress response of this high-strength alloy steel revealed initial hardening during the first few cycles followed by gradual softening for most of fatigue life. Cyclic strain resistance exhibited a linear trend for the variation of elastic strain amplitude with reversals to failure, and plastic strain amplitude with reversals to failure. Fracture morphology was the same at the macroscopic level over the entire range of cyclic strain amplitudes examined. However, at the fine microscopic level, the alloy steel revealed fracture to be essentially ductile with features reminiscent of predominantly "locally" ductile and isolated brittle mechanisms. The mechanisms governing stress response at the fine microscopic level, fatigue life, and final fracture behavior are presented and discussed in light of the mutually interactive influences of intrinsic microstructural effects, deformation characteristics of the microstructural constituents during fully reversed strain cycling, cyclic strain amplitude, and resultant response stress.

  5. Cyclic ductile and brittle deformation related to coseismic thrust fault propagation: Structural record at the base of a basement nappe (Preveli, Crete)

    NASA Astrophysics Data System (ADS)

    Nüchter, Jens-Alexander; Wassmann, Sara; Stöckhert, Bernhard

    2013-09-01

    structural record at the base of a basement nappe (Preveli nappe, Crete, Greece) thrust upon sedimentary rocks is investigated, aimed on understanding mechanisms which result in decoupling of the thrust sheet from its original substratum. We identify several superimposed deformation stages, each with characteristic structural style and indications of episodic deformation at initially high differential stress. The final stage involves formation of a matrix supported breccia transected by pseudotachylytes, comprising the lowermost 30 m of the nappe. Brecciation and pseudotachylyte formation occurred in a single event, and structures were not modified afterward. Complete induration of breccia and composition of phengite crystallized during devitrification of pseudotachylytes place the sequence of events into the middle crust. We propose a model relating episodic deformation and cyclic stress history to propagation of a thrust fault in a limited number of seismic events. Terminal brecciation and frictional fusion record passage of the fault front beneath the site of observation and decoupling of the thrust sheet. Absence of discernible further deformation is consistent with negligible basal friction during transport as a nappe. Brecciation and pseudotachylyte formation mark the switch from a history of repeated coseismic loading and postseismic stress relaxation in the plastosphere, driven by seismic events on the approaching thrust fault, to passive transport with deformation localized in a weak thrust plane. For a sequence of superimposed ductile to brittle structures, our model provides an alternative to progressive cooling and exhumation concomitant with deformation over millions of years.

  6. Non-geometric fluxes, quasi-Hopf twist deformations, and nonassociative quantum mechanics

    SciTech Connect

    Mylonas, Dionysios Szabo, Richard J.; Schupp, Peter

    2014-12-15

    We analyse the symmetries underlying nonassociative deformations of geometry in non-geometric R-flux compactifications which arise via T-duality from closed strings with constant geometric fluxes. Starting from the non-abelian Lie algebra of translations and Bopp shifts in phase space, together with a suitable cochain twist, we construct the quasi-Hopf algebra of symmetries that deforms the algebra of functions and the exterior differential calculus in the phase space description of nonassociative R-space. In this setting, nonassociativity is characterised by the associator 3-cocycle which controls non-coassociativity of the quasi-Hopf algebra. We use abelian 2-cocycle twists to construct maps between the dynamical nonassociative star product and a family of associative star products parametrized by constant momentum surfaces in phase space. We define a suitable integration on these nonassociative spaces and find that the usual cyclicity of associative noncommutative deformations is replaced by weaker notions of 2-cyclicity and 3-cyclicity. Using this star product quantization on phase space together with 3-cyclicity, we formulate a consistent version of nonassociative quantum mechanics, in which we calculate the expectation values of area and volume operators, and find coarse-graining of the string background due to the R-flux.

  7. A mechanism for tectonic deformation on Venus

    NASA Technical Reports Server (NTRS)

    Phillips, Roger J.

    1986-01-01

    In the absence of identifiable physiographic features directly associated with plate tectonics, alternate mechanisms are sought for the intense tectonic deformation observed in radar images of Venus. One possible mechanism is direct coupling into an elastic lithosphere of the stresses associated with convective flow in the interior. Spectral Green's function solutions have been obtained for stresses in an elastic lithosphere overlying a Newtonian interior with an exponential depth dependence of viscosity, and a specified surface-density distribution driving the flow. At long wavelengths and for a rigid elastic/fluid boundary condition, horizontal normal stresses in the elastic lid are controlled by the vertical shear stress gradient and are directly proportional to the depth of the density disturbance in the underlying fluid. The depth and strength of density anomalies in the Venusian interior inferred by analyses of long wavelength gravity data suggest that stresses in excess of 100 MPa would be generated in a 10 km thick elastic lid unless a low viscosity channel occurring beneath the lid or a positive viscosity gradient uncouples the flow stresses. The great apparent depth of compensation of topographic features argues against this, however, thus supporting the importance of the coupling mechanism. If there is no elastic lid, stresses will also be very high near the surface, providing also that the viscosity gradient is negative.

  8. Interactive evolution concept for analyzing a rock salt cavern under cyclic thermo-mechanical loading

    NASA Astrophysics Data System (ADS)

    König, Diethard; Mahmoudi, Elham; Khaledi, Kavan; von Blumenthal, Achim; Schanz, Tom

    2016-04-01

    The excess electricity produced by renewable energy sources available during off-peak periods of consumption can be used e.g. to produce and compress hydrogen or to compress air. Afterwards the pressurized gas is stored in the rock salt cavities. During this process, thermo-mechanical cyclic loading is applied to the rock salt surrounding the cavern. Compared to the operation of conventional storage caverns in rock salt the frequencies of filling and discharging cycles and therefore the thermo-mechanical loading cycles are much higher, e.g. daily or weekly compared to seasonally or yearly. The stress strain behavior of rock salt as well as the deformation behavior and the stability of caverns in rock salt under such loading conditions are unknown. To overcome this, existing experimental studies have to be supplemented by exploring the behavior of rock salt under combined thermo-mechanical cyclic loading. Existing constitutive relations have to be extended to cover degradation of rock salt under thermo-mechanical cyclic loading. At least the complex system of a cavern in rock salt under these loading conditions has to be analyzed by numerical modeling taking into account the uncertainties due to limited access in large depth to investigate material composition and properties. An interactive evolution concept is presented to link the different components of such a study - experimental modeling, constitutive modeling and numerical modeling. A triaxial experimental setup is designed to characterize the cyclic thermo-mechanical behavior of rock salt. The imposed boundary conditions in the experimental setup are assumed to be similar to the stress state obtained from a full-scale numerical simulation. The computational model relies primarily on the governing constitutive model for predicting the behavior of rock salt cavity. Hence, a sophisticated elasto-viscoplastic creep constitutive model is developed to take into account the dilatancy and damage progress, as well as

  9. Plate-tectonic mechanism of Laramide deformation.

    USGS Publications Warehouse

    Hamilton, W.

    1981-01-01

    The Laramide compressive deformation of the craton was caused by a clockwise rotation of about 2-4o of the Colorado Plateau region relative to the continental interior, during late Late Cretaceous and early Tertiary time. Late Paleozoic and Neogene deformation of the craton also were produced by motion of a southwestern subplate relative to the continental interior. -from Author

  10. Mechanics and mechanisms of cyclic fatigue-crack propagation in transformation-toughened zirconia ceramics

    SciTech Connect

    Hoffman, M.J. Sydney Univ., NSW . Dept. of Mechanical Engineering); Dauskardt, R.H.; Ritchie, R.O. ); Mai, Y.W. . Dept. of Mechanical Engineering)

    1992-05-01

    Damage and cyclic fatigue failure under alternating loading in transformation-toughened zirconia ceramics is reviewed and compared to corresponding behavior under quasi-static loading (static fatigue). Current understanding of the role of transformation toughening in influencing cyclic fatigue-crack propagation behavior is examined based on studies which altered the extent of the tetragonal-to-monoclinic phase transformation in MG-PSZ through subeutectoid aging. These studies suggest that near-tip computations of the crack-driving force (in terms of the local stress intensity) can be used to predict crack-growth behavior under constant amplitude and variable-amplitude (spectrum) loading, using spatially resolved Raman spectroscopy to measure the extent of the transformation zones. In addition, results are reviewed which rationalize distinctions between the crack-growth behavior of preexisting, long'' (> 2 mm), through-thickness cracks and naturally-occurring, small'' (1 to 100 [mu]m), surface cracks in terms of variations in crack-tip shielding with crack size. In the present study, the effect of grain size variations on crack-growth behavior under both monotonic (R-curve) and cyclic fatigue loading are examined. Such observations are used to speculate on the mechanisms associated with cyclic crack advance, involving such processes as alternating shear via transformation-band formation, cyclic modification of the degree of transformation toughening, and uncracked-ligament (or grain) bridging.

  11. Mechanics and mechanisms of cyclic fatigue-crack propagation in transformation-toughened zirconia ceramics

    SciTech Connect

    Hoffman, M.J. |; Dauskardt, R.H.; Ritchie, R.O.; Mai, Y.W.

    1992-05-01

    Damage and cyclic fatigue failure under alternating loading in transformation-toughened zirconia ceramics is reviewed and compared to corresponding behavior under quasi-static loading (static fatigue). Current understanding of the role of transformation toughening in influencing cyclic fatigue-crack propagation behavior is examined based on studies which altered the extent of the tetragonal-to-monoclinic phase transformation in MG-PSZ through subeutectoid aging. These studies suggest that near-tip computations of the crack-driving force (in terms of the local stress intensity) can be used to predict crack-growth behavior under constant amplitude and variable-amplitude (spectrum) loading, using spatially resolved Raman spectroscopy to measure the extent of the transformation zones. In addition, results are reviewed which rationalize distinctions between the crack-growth behavior of preexisting, ``long`` (> 2 mm), through-thickness cracks and naturally-occurring, ``small`` (1 to 100 {mu}m), surface cracks in terms of variations in crack-tip shielding with crack size. In the present study, the effect of grain size variations on crack-growth behavior under both monotonic (R-curve) and cyclic fatigue loading are examined. Such observations are used to speculate on the mechanisms associated with cyclic crack advance, involving such processes as alternating shear via transformation-band formation, cyclic modification of the degree of transformation toughening, and uncracked-ligament (or grain) bridging.

  12. Structural anisotropy in metallic glasses induced by mechanical deformation

    SciTech Connect

    Dmowski, W.; Egami, T.

    2009-03-06

    We observed structural anisotropy in metallic glasses samples deformed by homogenous mechanical creep and by inhomogeneous compression using high energy X-ray diffraction. Pair distribution function analysis indicates bond anisotropy in the first atomic shell. This suggests that mechanical deformation involves rearrangements in a cluster of atoms by a bond reformation.

  13. Deformation mechanisms of antigorite serpentinite at subduction zone conditions determined from experimentally and naturally deformed rocks

    NASA Astrophysics Data System (ADS)

    Auzende, Anne-Line; Escartin, Javier; Walte, Nicolas P.; Guillot, Stéphane; Hirth, Greg; Frost, Daniel J.

    2015-02-01

    We performed deformation-DIA experiments on antigorite serpentinite at pressures of 1-3.5 GPa and temperatures of between 400 and 650 °C, bracketing the stability of antigorite under subduction zone conditions. For each set of pressure-temperature (P-T) conditions, we conducted two runs at strain rates of 5 ×10-5 and 1 ×10-4 s-1. We complemented our study with a sample deformed in a Griggs-type apparatus at 1 GPa and 400 °C (Chernak and Hirth, 2010), and with natural samples from Cuba and the Alps deformed under blueschist/eclogitic conditions. Optical and transmission electron microscopies were used for microstructural characterization and determination of deformation mechanisms. Our observations on experimentally deformed antigorite prior to breakdown show that deformation is dominated by cataclastic flow with observable but minor contribution of plastic deformation (microkinking and (001) gliding mainly expressed by stacking disorder mainly). In contrast, in naturally deformed samples, plastic deformation structures are dominant (stacking disorder, kinking, pressure solution), with minor but also perceptible contribution of brittle deformation. When dehydration occurs in experiments, plasticity increases and is coupled to local embrittlement that we attribute to antigorite dehydration. In dehydrating samples collected in the Alps, embrittlement is also observed suggesting that dehydration may contribute to intermediate-depth seismicity. Our results thus show that semibrittle deformation operates within and above the stability field of antigorite. However, the plastic deformation recorded by naturally deformed samples was likely acquired at low strain rates. We also document that the corrugated structure of antigorite controls the strain accommodation mechanisms under subduction conditions, with preferred inter- and intra-grain cracking along (001) and gliding along both a and b. We also show that antigorite rheology in subduction zones is partly controlled

  14. 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.

  15. Diversity of Cyclic Di-GMP-Binding Proteins and Mechanisms

    PubMed Central

    2015-01-01

    ABSTRACT Cyclic di-GMP (c-di-GMP) synthetases and hydrolases (GGDEF, EAL, and HD-GYP domains) can be readily identified in bacterial genome sequences by using standard bioinformatic tools. In contrast, identification of c-di-GMP receptors remains a difficult task, and the current list of experimentally characterized c-di-GMP-binding proteins is likely incomplete. Several classes of c-di-GMP-binding proteins have been structurally characterized; for some others, the binding sites have been identified; and for several potential c-di-GMP receptors, the binding sites remain to be determined. We present here a comparative structural analysis of c-di-GMP-protein complexes that aims to discern the common themes in the binding mechanisms that allow c-di-GMP receptors to bind it with (sub)micromolar affinities despite the 1,000-fold excess of GTP. The available structures show that most receptors use their Arg and Asp/Glu residues to bind c-di-GMP monomers, dimers, or tetramers with stacked guanine bases. The only exception is the EAL domains that bind c-di-GMP monomers in an extended conformation. We show that in c-di-GMP-binding signature motifs, Arg residues bind to the O-6 and N-7 atoms at the Hoogsteen edge of the guanine base, while Asp/Glu residues bind the N-1 and N-2 atoms at its Watson-Crick edge. In addition, Arg residues participate in stacking interactions with the guanine bases of c-di-GMP and the aromatic rings of Tyr and Phe residues. This may account for the presence of Arg residues in the active sites of every receptor protein that binds stacked c-di-GMP. We also discuss the implications of these structural data for the improved understanding of the c-di-GMP signaling mechanisms. PMID:26055114

  16. Diversity of Cyclic Di-GMP-Binding Proteins and Mechanisms.

    PubMed

    Chou, Shan-Ho; Galperin, Michael Y

    2016-01-01

    Cyclic di-GMP (c-di-GMP) synthetases and hydrolases (GGDEF, EAL, and HD-GYP domains) can be readily identified in bacterial genome sequences by using standard bioinformatic tools. In contrast, identification of c-di-GMP receptors remains a difficult task, and the current list of experimentally characterized c-di-GMP-binding proteins is likely incomplete. Several classes of c-di-GMP-binding proteins have been structurally characterized; for some others, the binding sites have been identified; and for several potential c-di-GMP receptors, the binding sites remain to be determined. We present here a comparative structural analysis of c-di-GMP-protein complexes that aims to discern the common themes in the binding mechanisms that allow c-di-GMP receptors to bind it with (sub)micromolar affinities despite the 1,000-fold excess of GTP. The available structures show that most receptors use their Arg and Asp/Glu residues to bind c-di-GMP monomers, dimers, or tetramers with stacked guanine bases. The only exception is the EAL domains that bind c-di-GMP monomers in an extended conformation. We show that in c-di-GMP-binding signature motifs, Arg residues bind to the O-6 and N-7 atoms at the Hoogsteen edge of the guanine base, while Asp/Glu residues bind the N-1 and N-2 atoms at its Watson-Crick edge. In addition, Arg residues participate in stacking interactions with the guanine bases of c-di-GMP and the aromatic rings of Tyr and Phe residues. This may account for the presence of Arg residues in the active sites of every receptor protein that binds stacked c-di-GMP. We also discuss the implications of these structural data for the improved understanding of the c-di-GMP signaling mechanisms. PMID:26055114

  17. Repetitive mechanical strain suppresses macrophage uptake of immunoglobulin G complexes and enhances cyclic adenosine monophosphate synthesis.

    PubMed Central

    Mattana, J.; Sankaran, R. T.; Singhal, P. C.

    1995-01-01

    Uptake of immunoglobulin G (IgG) complexes by macrophages (M phi) may play an important role in disease states characterized by increased levels of circulating immune complexes. In sites such as the glomerular mesangium M phi may be subjected to repetitive mechanical strain, although in vitro studies of M phi endocytosis are typically carried out with cells grown on rigid surfaces. We undertook the present study to determine whether repetitive mechanical strain could modulate M phi endocytosis of IgG complexes. IgG complex uptake was significantly diminished in M phi that were subjected to repetitive mechanical strain using parameters corresponding to peak and minimal intraglomerular pressures compared with control, and uptake varied according to the amount of mechanical strain applied. There was no significant difference in surface binding of IgG between M phi subjected to strain and those not. Mechanical strain did not significantly influence the rate of IgG complex degradation. Inhibition of nitric oxide synthase and guanylate cyclase activity did not alter the effect of mechanical strain, although this effect was potentiated by 3-isobutyl-1-methylxanthine (IBMX). Angiotensin II, which has been shown to reduce adenosine 3',5'-cyclic monophosphate (cAMP) production in M phi, significantly attenuated the suppressive effect of mechanical strain on IgG complex uptake as well as another inhibitor of cAMP generation, indomethacin. Enzyme immunoassay demonstrated significantly enhanced levels of cAMP in M phi that were subjected to mechanical strain compared with control, an effect that was potentiated by IBMX and attenuated by angiotensin II and indomethacin. These results demonstrate that repetitive mechanical strain significantly reduces IgG complex uptake by M phi, most likely by enhancing cAMP synthesis. Such an effect might play a significant role in macromolecule handling by M phi in sites in which they are subjected to repetitive mechanical deformation such as

  18. Inelastic deformation mechanisms in a transverse MMC lamina under compression

    NASA Technical Reports Server (NTRS)

    Newaz, Golam M.; Majumdar, Bhaskar S.

    1992-01-01

    An investigation was undertaken to study the inelastic deformation mechanisms in (90)(sub 8) Ti 15-3/SCS-6 lamina subjected to pure compression. Both mechanical behavior and microstructural evaluation were undertaken at room temperature, 538 and 650 C. Results indicate that mechanical response and deformation characteristics are significantly different in monotonic tension and compression. The inelastic deformation mechanisms in compression are controlled by radial fiber fracture, matrix plasticity and fiber-matrix debonding. The radial fiber fracture is a new damage mode observed for metal-matrix composites (MMC).

  19. Mechanisms of crustal deformation in the western US

    NASA Technical Reports Server (NTRS)

    Turcotte, Donald L.

    1986-01-01

    The deformation processes in the western United States were studied, considering both deterministic models and random or statistical models. The role of the intracrustal delamination and mechanisms of crustal thinning were also examined. The application of fractal techniques to understand how the crust is deforming was studied in complex regions. Work continued on the development of a fractal based model for deformation in the western United States. Fractal studies were also extended to the study of topography and the geoid.

  20. Deformation and failure mechanisms in metal matrix composites

    NASA Technical Reports Server (NTRS)

    Newaz, G.; Majumdar, B. S.

    1991-01-01

    An investigation was undertaken to determine the key deformation mechanisms and their interaction leading to failure of both 0 degree and 90 degree Ti 15-3/SCS-6 laminae under monotonic loading. The experimental results suggest that inelastic deformation in the 0-degree lamina is dominated by plastic deformation and that in the 90-degree lamina is dominated by both fiber-matrix debonding and plasticity. The loading-unloading response, monitoring of Poisson's ratio and microscopy were utilized to identify the key deformation mechanisms. The sequence of deformation mechanisms leading to failure are identified for both the 0 and the 90-degree specimens. The threshold strains for plasticity or damage which are referred to as 'microdeformation' in the 0 deg and 90 deg laminae are approximately 0.004 and 0.002, respectively, at room temperature. These strain levels may be considered critical in initiation based structural design with these composites.

  1. Multiscale Graphene Topographies Programmed by Sequential Mechanical Deformation.

    PubMed

    Chen, Po-Yen; Sodhi, Jaskiranjeet; Qiu, Yang; Valentin, Thomas M; Steinberg, Ruben Spitz; Wang, Zhongying; Hurt, Robert H; Wong, Ian Y

    2016-05-01

    Multigenerational graphene oxide architectures can be programmed by specific sequences of mechanical deformations. Each new deformation results in a progressively larger set of features decorated by smaller preexisting patterns, indicating a structural "memory." It is shown that these multiscale architectures are superhydrophobic and display excellent functionality as electrochemical electrodes. PMID:26996525

  2. Thermal-Mechanical Cyclic Test of a Composite Cryogenic Tank for Reusable Launch Vehicles

    NASA Technical Reports Server (NTRS)

    Messinger, Ross; Pulley, John

    2003-01-01

    This viewgraph presentation provides an overview of thermal-mechanical cyclic tests conducted on a composite cryogenic tank designed for reusable launch vehicles. Topics covered include: a structural analysis of the composite cryogenic tank, a description of Marshall Space Flight Center's Cryogenic Structure Test Facility, cyclic test plans and accomplishments, burst test and analysis and post-testing evaluation.

  3. Keratinocyte growth factor accelerates wound closure in airway epithelium during cyclic mechanical strain.

    PubMed

    Waters, C M; Savla, U

    1999-12-01

    The airway epithelium may be damaged by inhalation of noxious agents, in response to pathogens, or during endotracheal intubation and mechanical ventilation. Maintenance of an intact epithelium is important for lung fluid balance, and the loss of epithelium may stimulate inflammatory responses. Epithelial repair in the airways following injury must occur on a substrate that undergoes cyclic elongation and compression during respiration. We have previously shown that cyclic mechanical strain inhibits wound closure in the airway epithelium (Savla and Waters, 1998b). In this study, we investigated the stimulation of epithelial wound closure by keratinocyte growth factor (KGF) in vitro and the mechanisms by which KGF overcomes the inhibition due to mechanical strain. Primary cultures of normal human bronchial epithelial cells (NHBE) and a cell line of human airway epithelial cells, Calu 3, were grown on Silastic membranes, and a wound was scraped across the well. The wells were then exposed to cyclic strain using the Flexercell Strain Unit, and wound closure was measured. While cyclic elongation (20% maximum) and cyclic compression (approximately 2%) both inhibited wound closure in untreated wells, treatment with KGF (50 ng/ml) significantly accelerated wound closure and overcame the inhibition due to cyclic strain. Since wound closure involves cell spreading, migration, and proliferation, we investigated the effect of cyclic strain on cell area, cell-cell distance, and cell velocity at the wound edge. While the cell area increased in unstretched monolayers, the cell area of monolayers in compressed regions decreased significantly. Treatment with KGF increased the cell area in both cyclically elongated and compressed cells. Also, when cells were treated with KGF, cell velocity was significantly increased in both static and cyclically strained monolayers, and cyclic strain did not inhibit cell migration. These results suggest that KGF is an important factor in

  4. The mechanical deformation mechanisms in knitted fabric composites

    SciTech Connect

    Kelay, M.S.; Bader, D.L.; Reed, P.E.

    1994-12-31

    Knitted fabric composites have certain advantages over woven composites, particularly in their ability to conform to complicated contours. As a consequence, they demonstrate inferior mechanical characteristics compared to woven materials as a direct result of the presence of bent fibers. Such a knitted fabric composite made from, for example, glass fibers in a polyurethane matrix, can be used as an orthopaedic splinting bandage for immobilizing fractures of the upper and lower limbs. Relatively little research has been reported on knitted fabric composites was initiated. It was observed that knit patterns, type of fiber, size of fibers used, size of loops, coatings and lay-up procedure were all variables that could affect the structure/property relationship of knitted fabric composites. Tensile testing with optical measurement of strain was performed on knitted substrate and coated bandages in both course and wale directions. Results indicated that the knitted fabrics function as link mechanisms at the microscopic level, with knitted loops straightening and bending before the individual elements of the knitted yarn take up significant load and material deformation. Theoretical modeling of the glass knit structure, in both course and wale directions, agrees well with experimental testing.

  5. Strain gage network distinguishes between thermal and mechanical deformations

    NASA Technical Reports Server (NTRS)

    Cepollina, F. J.

    1966-01-01

    Strain gage network measures the thermal coefficient of linear expansion of composite metal structures. The network consists of a test gage and two dummy gages arranged to distinguish thermally induced deformation from mechanical strain.

  6. The high temperature deformation in cyclic loading of a single crystal nickel-base superalloy

    NASA Technical Reports Server (NTRS)

    Gabb, T. P.; Welsch, G.

    1989-01-01

    The high temperature cyclic stress softening response of the single crystal nickel-base superalloy PWA 1480 was investigated. Specimens oriented near the 001- and 111-lines were tested at 1050 C in low-cycle fatigue and then microstructurally evaluated. The 001- and 111-line specimens had dissimilar flow behavior in monotonic tensile tests, but comparable softening in low-cycle fatigue. This softening was accompanied by rapid generation of dislocation networks at the gamma-gamma-prime interfaces and by a slower time-dependent coarsening of gamma-prime precipitates. Due to the rapid formation of a dislocation substructure at the gamma-gamma-prime interfaces, the cyclic stress softening could be modeled with an existing theory which related cyclic stress to the evolving microstructure and dislocation structure.

  7. Probabilistic Simulation of Combined Thermo-Mechanical Cyclic Fatigue in Composites

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.

    2011-01-01

    A methodology to compute probabilistically-combined thermo-mechanical fatigue life of polymer matrix laminated composites has been developed and is demonstrated. Matrix degradation effects caused by long-term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress-dependent multifactor-interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability-integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/-45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical-cyclic loads and low thermal-cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical-cyclic loads and high thermal-cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

  8. Probabilistic Simulation of Combined Thermo-Mechanical Cyclic Fatigue in Composites

    NASA Technical Reports Server (NTRS)

    Chamis, Christos C.

    2010-01-01

    A methodology to compute probabilistically-combined thermo-mechanical fatigue life of polymer matrix laminated composites has been developed and is demonstrated. Matrix degradation effects caused by long-term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress-dependent multifactor-interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability-integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/-45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical-cyclic loads and low thermal-cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical-cyclic loads and high thermal-cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

  9. Cyclic Deformation Response of β-Annealed Ti-5Al-5V-5Mo-3Cr Alloy Under Compressive Loading Conditions

    NASA Astrophysics Data System (ADS)

    Huang, Jun; Wang, Zhirui; Zhou, Jie

    2011-09-01

    This article reports the cyclic deformation behavior of the β-annealed metastable Ti-5Al-5V-5Mo-3Cr (Ti-5553) alloy under the condition of pure compressive fatigue stress. The following three aspects, namely, the mechanical response, the surface morphology evolution, and the dislocation structures, were systematically investigated. Under all testing conditions, the material demonstrated cyclic softening in the initial cycles followed by saturation. The progressive observation of surface morphology at fixed locations, but after different numbers of cycles, elucidated typical planar slip behavior and the early appearance of fatigue microcracks, which were found often to be induced by the highly localized planar slip bands. The transmission electron microscopy (TEM) study revealed dislocation annihilation upon cycling, i.e., the reduction of dislocation density as well as the simplification of dislocation configurations. In addition, detwinning and changed twin boundary structures upon cycling were also detected. Such activities, together with the intersection of coherent ω precipitates by moving dislocations, are considered to be responsible for the initial softening, whereas the dislocation dipole flip-flop mechanism is presumably responsible for the cyclic saturation behavior. An attempt was made to explain the strain-localized planar slip behavior by considering the stacking fault energy (SFE) as well as the free-electron-to-atom ( e/ a) ratio. The nanoscaled ω and α precipitation in the β matrix may also contribute to the planar slip behavior. The effect of the microstructure in the as-received material was also analyzed for the strain localization and planar-slip mode.

  10. Effect of Cyclic Thermo-Mechanical Loads on Fatigue Reliability in Polymer Matrix Composites

    NASA Technical Reports Server (NTRS)

    Shah, A. R.; Murthy, P. L. N.; Chamis, C. C.

    1996-01-01

    A methodology to compute probabilistic fatigue life of polymer matrix laminated composites has been developed and demonstrated. Matrix degradation effects caused by long term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress dependent multi-factor interaction relationship developed at NASA Lewis Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability- based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/- 45/90)(sub s) graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical cyclic loads and low thermal cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical cyclic loads and high thermal cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

  11. Hardness and deformation mechanisms of highly elastic carbon nitride thin films as studied by nanoindentation

    SciTech Connect

    Hainsworth, S.V.; Page, T.F.; Sjoestroem, H.; Sundgren, J.E.

    1997-05-01

    Carbon nitride (CN{sub x}) thin films (0.18 < x < 0.43), deposited by magnetron sputtering of C in a N{sub 2} discharge, have been observed to be extremely resistant to plastic deformation during surface contact (i.e., exhibit a purely elastic response over large strains). Elastic recoveries as high as 90% have been measured by nanoindentation. This paper addresses the problems of estimating Young`s modulus (E) and hardness (H) in such cases and shows how different strategies involving analysis of both loading and unloading curves and measuring the work of indentation each present their own problems. The results of some cyclic contact experiments are also presented and possible deformation mechanisms in the fullerene-like CN{sub x} structures discussed.

  12. Deformation twinning mechanisms in FCC and HCP metals

    SciTech Connect

    Wang, Jian; Tome, Carlos N; Beyerlein, Irene J; Misra, Amit; Mara, N

    2011-01-31

    We report the recent work on twinning and detwinning in fcc and hcp metals based on the in situ and ex situ TEM observations and molecular dynamics simulations. Three aspects are discussed in this paper. (1) Detwinning in single-phase Cu with respect to growth twins, (2) deformation twinning in Ag-Cu composites, and (3) deformation twinning mechanisms in hcp metals. The main conclusion is that atomic structures of interfaces (twin boundaries, two-phases interface, and grain boundaries) play a crucial role in nucleating and propagating of deformation twins.

  13. Techniques for in situ HVEM mechanical deformation of nanostructural materials

    SciTech Connect

    Wall, M.A.; Barbee, T.W. Jr.; Dahmen, U.

    1995-08-07

    We have developed two in-situ HVEM techniques which allow us to begin fundamental investigations into the mechanisms of deformation and fracture in nonstructured materials. A procedure for the observation of tensile deformation and failure in multilayers materials in cross-section is given and also the development of an in-situ HVEM nanoindentor of surfaces and films on surfaces in cross-section.

  14. Damage mechanisms in PBT-GF30 under thermo-mechanical cyclic loading

    SciTech Connect

    Schaaf, A. De Monte, M. Hoffmann, C.; Vormwald, M.; Quaresimin, M.

    2014-05-15

    The scope of this paper is the investigation of damage mechanisms at microscopic scale on a short glass fiber reinforced polybutylene terephthalate (PBT-GF30) under thermo-mechanical cyclic loading. In addition the principal mechanisms are verified through micro mechanical FE models. In order to investigate the fatigue behavior of the material both isothermal strain controlled fatigue (ISCF) tests at three different temperatures and thermo-mechanical fatigue (TMF) tests were conducted on plain and notched specimens, manufactured by injection molding. The goal of the work is to determine the damage mechanisms occurring under TMF conditions and to compare them with the mechanisms occurring under ISCF. For this reason fracture surfaces of TMF and ISCF samples loaded at different temperature levels were analyzed using scanning electron microscopy. Furthermore, specimens that failed under TMF were examined on microsections revealing insight into both crack initiation and crack propagation. The findings of this investigation give valuable information about the main damage mechanisms of PBT-GF30 under TMF loading and serve as basis for the development of a TMF life estimation methodology.

  15. Fluctuating Nonlinear Spring Model of Mechanical Deformation of Biological Particles

    PubMed Central

    Kononova, Olga; Snijder, Joost; Kholodov, Yaroslav; Marx, Kenneth A.; Wuite, Gijs J. L.; Roos, Wouter H.; Barsegov, Valeri

    2016-01-01

    The mechanical properties of virus capsids correlate with local conformational dynamics in the capsid structure. They also reflect the required stability needed to withstand high internal pressures generated upon genome loading and contribute to the success of important events in viral infectivity, such as capsid maturation, genome uncoating and receptor binding. The mechanical properties of biological nanoparticles are often determined from monitoring their dynamic deformations in Atomic Force Microscopy nanoindentation experiments; but a comprehensive theory describing the full range of observed deformation behaviors has not previously been described. We present a new theory for modeling dynamic deformations of biological nanoparticles, which considers the non-linear Hertzian deformation, resulting from an indenter-particle physical contact, and the bending of curved elements (beams) modeling the particle structure. The beams’ deformation beyond the critical point triggers a dynamic transition of the particle to the collapsed state. This extreme event is accompanied by a catastrophic force drop as observed in the experimental or simulated force (F)-deformation (X) spectra. The theory interprets fine features of the spectra, including the nonlinear components of the FX-curves, in terms of the Young’s moduli for Hertzian and bending deformations, and the structural damage dependent beams’ survival probability, in terms of the maximum strength and the cooperativity parameter. The theory is exemplified by successfully describing the deformation dynamics of natural nanoparticles through comparing theoretical curves with experimental force-deformation spectra for several virus particles. This approach provides a comprehensive description of the dynamic structural transitions in biological and artificial nanoparticles, which is essential for their optimal use in nanotechnology and nanomedicine applications. PMID:26821264

  16. Fluctuating Nonlinear Spring Model of Mechanical Deformation of Biological Particles.

    PubMed

    Kononova, Olga; Snijder, Joost; Kholodov, Yaroslav; Marx, Kenneth A; Wuite, Gijs J L; Roos, Wouter H; Barsegov, Valeri

    2016-01-01

    The mechanical properties of virus capsids correlate with local conformational dynamics in the capsid structure. They also reflect the required stability needed to withstand high internal pressures generated upon genome loading and contribute to the success of important events in viral infectivity, such as capsid maturation, genome uncoating and receptor binding. The mechanical properties of biological nanoparticles are often determined from monitoring their dynamic deformations in Atomic Force Microscopy nanoindentation experiments; but a comprehensive theory describing the full range of observed deformation behaviors has not previously been described. We present a new theory for modeling dynamic deformations of biological nanoparticles, which considers the non-linear Hertzian deformation, resulting from an indenter-particle physical contact, and the bending of curved elements (beams) modeling the particle structure. The beams' deformation beyond the critical point triggers a dynamic transition of the particle to the collapsed state. This extreme event is accompanied by a catastrophic force drop as observed in the experimental or simulated force (F)-deformation (X) spectra. The theory interprets fine features of the spectra, including the nonlinear components of the FX-curves, in terms of the Young's moduli for Hertzian and bending deformations, and the structural damage dependent beams' survival probability, in terms of the maximum strength and the cooperativity parameter. The theory is exemplified by successfully describing the deformation dynamics of natural nanoparticles through comparing theoretical curves with experimental force-deformation spectra for several virus particles. This approach provides a comprehensive description of the dynamic structural transitions in biological and artificial nanoparticles, which is essential for their optimal use in nanotechnology and nanomedicine applications. PMID:26821264

  17. Cyclic stretch promotes osteogenesis-related gene expression in osteoblast-like cells through a cofilin-associated mechanism

    PubMed Central

    GAO, JIE; FU, SHANMIN; ZENG, ZHAOBIN; LI, FEIFEI; NIU, QIANNAN; JING, DA; FENG, XUE

    2016-01-01

    Osteoblasts have the capacity to perceive and transduce mechanical signals, and thus, regulate the mRNA and protein expression of a variety of genes associated with osteogenesis. Cytoskeletal reconstruction, as one of the earliest perception events for external mechanical stimulation, has previously been demonstrated to be essential for mechanotransduction in bone cells. However, the mechanism by which mechanical signals induce cytoskeletal deformation remains poorly understood. The actin-binding protein, cofilin, promotes the depolymerization of actin and is understood to be important in the regulation of activities in various cell types, including endothelial, neuronal and muscle cells. However, to the best of our knowledge, the importance of cofilin in osteoblastic mechanotransduction has not been previously investigated. In the present study, osteoblast-like MG-63 cells were subjected to physiological cyclic stretch stimulation (12% elongation) for 1, 4, 8, 12 and 24 h, and the expression levels of cofilin and osteogenesis-associated genes were quantified with reverse transcription-quantitative polymerase chain reaction, immunofluorescence staining and western blotting analyses. Additionally, knockdown of cofilin using RNA interference was conducted, and the mRNA levels of osteogenesis-associated genes were compared between osteoblast-like cells in the presence and absence of cofilin gene knockdown. The results of the present study demonstrated that cyclic stretch stimulates the expression of genes associated with osteoblastic activities in MG-63 cells, including alkaline phosphatase (ALP), osteocalcin (OCN), runt-related transcription factor 2 (Runx2) and collagen-1 (COL-1). Cyclic stretch also regulates the mRNA and protein expression of cofilin in MG-63 cells. Furthermore, stretch-induced increases in the levels of osteogenesis-associated genes, including ALP, OCN, Runx2 and COL-1, were reduced following cofilin gene knockdown. Together, these results

  18. Magnetite deformation mechanism maps for better prediction of strain partitioning

    NASA Astrophysics Data System (ADS)

    Till, J. L.; Moskowitz, Bruce

    2013-02-01

    Abstract A meta-analysis of existing experimental <span class="hlt">deformation</span> data for magnetite and other spinel-structured ferrites reveals that previously published flow laws are inadequate to describe the general <span class="hlt">deformation</span> behavior of magnetite. Using updated rate equations for oxygen diffusion in magnetite, we present new flow laws that closely predict creep rates similar to those found in <span class="hlt">deformation</span> experiments and that can be used to predict strain partitioning between cubic Fe oxides and other phases in the Earth's crust. New <span class="hlt">deformation</span> <span class="hlt">mechanism</span> maps for magnetite have been constructed as functions of temperature and grain size. Using the revised creep parameters, estimates of strain partitioning between magnetite, ilmenite, and plagioclase indicate that concentrated zones of Fe-Ti oxides in oceanic crust near slow-spreading ridges could accommodate significant amounts of strain at moderate temperatures and may contribute to aseismic creep along spreading-segment faults.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19820058833&hterms=aluminum+alloys+applications&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Daluminum%2Balloys%2Bapplications','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19820058833&hterms=aluminum+alloys+applications&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Daluminum%2Balloys%2Bapplications"><span id="translatedtitle"><span class="hlt">Cyclic</span>-inelastic <span class="hlt">deformation</span> and fatigue resistance of notched-thin aluminum plates</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Leis, B. N.; Frey, N. D.</p> <p>1982-01-01</p> <p>The results of experiments designed to develop data to assess the accuracy and utility of the critical location concept in applications of fatigue-crack nucleation analysis at notch roots are presented and discussed. Fully reversed and nonzero mean-stress data are presented over a range of lives which encompass both elastic and inelastic <span class="hlt">deformations</span> for thin-notched specimens and smooth specimens made of 2024 T351 aluminum-alloy sheet. Notch-root strains were measured via an extensometer, whereas the formation of small cracks was detected via an eddy-current transducer. Data reported indicated the validity of the assumption that smooth and notched specimens form cracks at the same cycle number when identical <span class="hlt">deformation</span> histories are imposed at their respective critical locations. They also serve to demonstrate the accuracy and utility of the critical-location approach in analysis to predict the formation of small cracks at notches in coupons and components.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://pubs.er.usgs.gov/publication/70030702','USGSPUBS'); return false;" href="http://pubs.er.usgs.gov/publication/70030702"><span id="translatedtitle">Inference of postseismic <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> of the 1923 Kanto earthquake</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Pollitz, F.F.; Nyst, M.; Nishimura, T.; Thatcher, W.</p> <p>2006-01-01</p> <p>Coseismic slip associated with the M7.9, 1923 Kanto earthquake is fairly well understood, involving slip of up to 8 m along the Philippine Sea-Honshu interplate boundary under Sagami Bay and its onland extension. Postseismic <span class="hlt">deformation</span> after the 1923 earthquake, however, is relatively poorly understood. We revisit the available <span class="hlt">deformation</span> data in order to constrain possible <span class="hlt">mechanisms</span> of postseismic <span class="hlt">deformation</span> and to examine the consequences for associated stress changes in the surrounding crust. Data from two leveling lines and one tide gage station over the first 7-8 years postseismic period are of much greater amplitude than the corresponding expected interseismic <span class="hlt">deformation</span> during the same period, making these data suitable for isolating the signal from postseismic <span class="hlt">deformation</span>. We consider both viscoelastic models of asthenosphere relaxation and afterslip models. A distributed coseismic slip model presented by Pollitz et al. (2005), combined with prescribed parameters of a viscoelastic Earth model, yields predicted postseismic <span class="hlt">deformation</span> that agrees with observed <span class="hlt">deformation</span> on mainland Honshu from Tokyo to the Izu peninsula. Elsewhere (southern Miura peninsula; Boso peninsula), the considered viscoelastic models fail to predict observed <span class="hlt">deformation</span>, and a model of ???1 in shallow afterslip in the offshore region south of the Boso peninsula, with equivalent moment magnitude Mw = 7.0, adequately accounts for the observed <span class="hlt">deformation</span>. Using the distributed coseismic slip model, layered viscoelastic structure, and a model of interseismic strain accumulation, we evaluate the post-1923 stress evolution, including both the coseismic and accumulated postseismic stress changes and those stresses contributed by interseismic loading. We find that if account is made for the varying tectonic regime in the region, the occurrence of both immediate (first month) post-1923 crustal aftershocks as well as recent regional crustal seismicity is consistent with the predicted</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_4");'>4</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li class="active"><span>6</span></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_6 --> <div id="page_7" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="121"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5577060','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5577060"><span id="translatedtitle"><span class="hlt">Mechanical</span> threshold of dynamically <span class="hlt">deformed</span> copper and Nitronic 40</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Follansbee, P.S.; Kocks, U.F.; Regazzoni, G.</p> <p>1985-01-01</p> <p>Measurements of the <span class="hlt">mechanical</span> threshold, or threshold stress, are reported on quasi-statically and dynamically <span class="hlt">deformed</span> copper and Nitronic 40. Results for copper show that the increase of the threshold stress with strain rate is similar to that of the flow stress. In Nitronic 40 the results show that the ratio of the flow stress to the threshold stress is approx.0.6. Both results indicate that the increased rate sensitivity found in these materials at high strain rates is not due to the predominance of a viscous drag <span class="hlt">deformation</span> <span class="hlt">mechanism</span>, as has been previously suggested.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/26444553','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/26444553"><span id="translatedtitle">On-chip assessment of human primary cardiac fibroblasts proliferative responses to uniaxial <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> strain.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Ugolini, Giovanni Stefano; Rasponi, Marco; Pavesi, Andrea; Santoro, Rosaria; Kamm, Roger; Fiore, Gianfranco Beniamino; Pesce, Maurizio; Soncini, Monica</p> <p>2016-04-01</p> <p>Cardiac cell function is substantially influenced by the nature and intensity of the <span class="hlt">mechanical</span> loads the cells experience. Cardiac fibroblasts (CFs) are primarily involved in myocardial tissue remodeling: at the onset of specific pathological conditions, CFs activate, proliferate, differentiate, and critically alter the amount of myocardial extra-cellular matrix with important consequences for myocardial functioning. While <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> strain has been shown to increase matrix synthesis of CFs in vitro, the role of <span class="hlt">mechanical</span> cues in CFs proliferation is unclear. We here developed a multi-chamber cell straining microdevice for cell cultures under uniform, uniaxial <span class="hlt">cyclic</span> strain. After careful characterization of the strain field, we extracted human heart-derived CFs and performed <span class="hlt">cyclic</span> strain experiments. We subjected cells to 2% or 8% <span class="hlt">cyclic</span> strain for 24 h or 72 h, using immunofluorescence to investigate markers of cell morphology, cell proliferation (Ki67, EdU, phospho-Histone-H3) and subcellular localization of the mechanotransduction-associated transcription factor YAP. Cell morphology was affected by <span class="hlt">cyclic</span> strain in terms of cell area, cell and nuclear shape and cellular alignment. We additionally observed a strain intensity-dependent control of cell growth: a significant proliferation increase occurred at 2% <span class="hlt">cyclic</span> strain, while time-dependent effects took place upon 8% <span class="hlt">cyclic</span> strain. The YAP-dependent mechano-transduction pathway was similarly activated in both strain conditions. These results demonstrate a differential effect of <span class="hlt">cyclic</span> strain intensity on human CFs proliferation control and provide insights into the YAP-dependent mechano-sensing machinery of human CFs. Biotechnol. Bioeng. 2016;113: 859-869. © 2015 Wiley Periodicals, Inc. PMID:26444553</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3155904','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3155904"><span id="translatedtitle">3D video-based <span class="hlt">deformation</span> measurement of the pelvis bone under dynamic <span class="hlt">cyclic</span> loading</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p></p> <p>2011-01-01</p> <p>Background Dynamic three-dimensional (3D) <span class="hlt">deformation</span> of the pelvic bones is a crucial factor in the successful design and longevity of complex orthopaedic oncological implants. The current solutions are often not very promising for the patient; thus it would be interesting to measure the dynamic 3D-<span class="hlt">deformation</span> of the whole pelvic bone in order to get a more realistic dataset for a better implant design. Therefore we hypothesis if it would be possible to combine a material testing machine with a 3D video motion capturing system, used in clinical gait analysis, to measure the sub millimetre <span class="hlt">deformation</span> of a whole pelvis specimen. Method A pelvis specimen was placed in a standing position on a material testing machine. Passive reflective markers, traceable by the 3D video motion capturing system, were fixed to the bony surface of the pelvis specimen. While applying a dynamic sinusoidal load the 3D-movement of the markers was recorded by the cameras and afterwards the 3D-<span class="hlt">deformation</span> of the pelvis specimen was computed. The accuracy of the 3D-movement of the markers was verified with 3D-displacement curve with a step function using a manual driven 3D micro-motion-stage. Results The resulting accuracy of the measurement system depended on the number of cameras tracking a marker. The noise level for a marker seen by two cameras was during the stationary phase of the calibration procedure ± 0.036 mm, and ± 0.022 mm if tracked by 6 cameras. The detectable 3D-movement performed by the 3D-micro-motion-stage was smaller than the noise level of the 3D-video motion capturing system. Therefore the limiting factor of the setup was the noise level, which resulted in a measurement accuracy for the dynamic test setup of ± 0.036 mm. Conclusion This 3D test setup opens new possibilities in dynamic testing of wide range materials, like anatomical specimens, biomaterials, and its combinations. The resulting 3D-<span class="hlt">deformation</span> dataset can be used for a better estimation of material</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2763927','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2763927"><span id="translatedtitle">In Situ <span class="hlt">Deformation</span> of Cartilage in <span class="hlt">Cyclically</span> Loaded Tibiofemoral Joints by Displacement-Encoded MRI</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Chan, D.D.; Neu, C.P.; Hull, M.L.</p> <p>2009-01-01</p> <p>Objectives Cartilage displacement and strain patterns were documented noninvasively in intact tibiofemoral joints in situ by magnetic resonance imaging (MRI). This study determined the number of compressive loading cycles required to precondition intact joints prior to imaging, the spatial distribution of displacements and strains in cartilage using displacement-encoded MRI, and the depth-dependency of these measures across specimens. Design Juvenile porcine tibiofemoral joints were <span class="hlt">cyclically</span> compressed at one and two times body weight at 0.1 Hz to achieve quasi-steady state load-displacement response. A 7T MRI scanner was used for displacement-encoded stimulated echoes with a fast spin echo acquisition (DENSE-FSE) in eight intact joints. Two-dimensional displacements and strains were determined throughout the thickness of the tibial and femoral cartilage and then normalized over the tissue thickness. Results Two-dimensional displacements and strains were heterogeneous through the depth of femoral and tibial cartilage under <span class="hlt">cyclic</span> compression. Strains in the loading direction were compressive and were maximal in the middle zone of femoral and tibial cartilage, and tensile strains were observed in the direction transverse to loading. Conclusions This study determined the depth-dependent displacements and strains in intact juvenile porcine tibiofemoral joints using displacement-encoded imaging. Displacement and strain distributions reflect the heterogeneous biochemistry of cartilage and the biomechanical response of the tissue to compression in the loading environment of an intact joint. This unique information about the biomechanics of cartilage has potential for comparisons of healthy and degenerated tissue and in the design of engineered replacement tissues. PMID:19447213</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003SMaS...12..993T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003SMaS...12..993T"><span id="translatedtitle">Reliability of piezoceramic patch sensors under <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> loading</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Thielicke, Bärbel; Gesang, Thomas; Wierach, Peter</p> <p>2003-12-01</p> <p>Piezoceramic patch sensors have to withstand the primary stresses and strains of a structure during operation. In the leading project 'Adaptronics' a lifespan of 106 cycles at 0.1% strain was required for sensors applied on components of steel and carbon fibre reinforced plastic (CFRP). In order to test the reliability of the patches themselves and of their adhesion on the substrate, special four-point bending tests were carried out under quasistatic loading and under <span class="hlt">cyclic</span> loading at different strain levels. The specimens consisted in sheets of steel and CFRP as substrates on which the newly developed patches with embedded piezoelectric foils and fibres were glued. In the quasistatic bending tests the performance of each sensor was characterized by measuring the sensor signal (charge) as a function of strain before and after cycling. Damage of the specimens would result in a decreasing slope of the charge-strain-curve after cycling. However, all the specimens tested survived 107 cycles up to 0.12% strain without marked loss of performance.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19870005870','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870005870"><span id="translatedtitle">High temperature monotonic and <span class="hlt">cyclic</span> <span class="hlt">deformation</span> in a directionally solidified nickel-base superalloy</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Huron, Eric S.</p> <p>1986-01-01</p> <p>Directionally solidified (DS) MAR-M246+Hf was tested in tension and fatigue, at temperatures from 20 C to 1093 C. Tests were performed on (001) oriented specimens at strain rates of 50 % and 0.5 % per minute. In tension, the yield strength was constant up to 704 C, above which the strength dropped off rapidly. A strong dependence of strength on strain rate was seen at the higher temperatures. The <span class="hlt">deformation</span> mode was observed to change from heterogeneous to homogeneous with increasing temperature. Low Cycle Fatigue tests were done using a fully reversed waveform and total strain control. For a given plastic strain range, lives increased with increasing temperature. For a given temperature strain rate had a strong effect on life. At 704 C, decreasing strain rates decreased life, while at the higher temperatures, decreasing strain rates increased life, for a given plastic strain range. These results could be explained through considerations of the <span class="hlt">deformation</span> modes and stress levels. At the higher temperatures, marked coarsening caused beneficial stress reductions, but oxidation limited the life. The longitudinal grain boundaries were found to influence slip behavior. The degree of secondary slip adjacent to the boundaries was found to be related to the degree of misorientation between the grains.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JAP...115p4305Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JAP...115p4305Z"><span id="translatedtitle"><span class="hlt">Mechanical</span> <span class="hlt">deformations</span> of boron nitride nanotubes in crossed junctions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhao, Yadong; Chen, Xiaoming; Park, Cheol; Fay, Catharine C.; Stupkiewicz, Stanislaw; Ke, Changhong</p> <p>2014-04-01</p> <p>We present a study of the <span class="hlt">mechanical</span> <span class="hlt">deformations</span> of boron nitride nanotubes (BNNTs) in crossed junctions. The structure and <span class="hlt">deformation</span> of the crossed tubes in the junction are characterized by using atomic force microscopy. Our results show that the total tube heights are reduced by 20%-33% at the crossed junctions formed by double-walled BNNTs with outer diameters in the range of 2.21-4.67 nm. The measured tube height reduction is found to be in a nearly linear relationship with the summation of the outer diameters of the two tubes forming the junction. The contact force between the two tubes in the junction is estimated based on contact <span class="hlt">mechanics</span> theories and found to be within the range of 4.2-7.6 nN. The Young's modulus of BNNTs and their binding strengths with the substrate are quantified, based on the <span class="hlt">deformation</span> profile of the upper tube in the junction, and are found to be 1.07 ± 0.11 TPa and 0.18-0.29 nJ/m, respectively. Finally, we perform finite element simulations on the <span class="hlt">mechanical</span> <span class="hlt">deformations</span> of the crossed BNNT junctions. The numerical simulation results are consistent with both the experimental measurements and the analytical analysis. The results reported in this paper contribute to a better understanding of the structural and <span class="hlt">mechanical</span> properties of BNNTs and to the pursuit of their applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22273525','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22273525"><span id="translatedtitle"><span class="hlt">Mechanical</span> <span class="hlt">deformations</span> of boron nitride nanotubes in crossed junctions</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Zhao, Yadong; Chen, Xiaoming; Ke, Changhong; Park, Cheol; Fay, Catharine C.; Stupkiewicz, Stanislaw</p> <p>2014-04-28</p> <p>We present a study of the <span class="hlt">mechanical</span> <span class="hlt">deformations</span> of boron nitride nanotubes (BNNTs) in crossed junctions. The structure and <span class="hlt">deformation</span> of the crossed tubes in the junction are characterized by using atomic force microscopy. Our results show that the total tube heights are reduced by 20%–33% at the crossed junctions formed by double-walled BNNTs with outer diameters in the range of 2.21–4.67 nm. The measured tube height reduction is found to be in a nearly linear relationship with the summation of the outer diameters of the two tubes forming the junction. The contact force between the two tubes in the junction is estimated based on contact <span class="hlt">mechanics</span> theories and found to be within the range of 4.2–7.6 nN. The Young's modulus of BNNTs and their binding strengths with the substrate are quantified, based on the <span class="hlt">deformation</span> profile of the upper tube in the junction, and are found to be 1.07 ± 0.11 TPa and 0.18–0.29 nJ/m, respectively. Finally, we perform finite element simulations on the <span class="hlt">mechanical</span> <span class="hlt">deformations</span> of the crossed BNNT junctions. The numerical simulation results are consistent with both the experimental measurements and the analytical analysis. The results reported in this paper contribute to a better understanding of the structural and <span class="hlt">mechanical</span> properties of BNNTs and to the pursuit of their applications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013APS..SHK.M1058L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013APS..SHK.M1058L"><span id="translatedtitle">Regenerated Spider Silk Possess <span class="hlt">Mechanical</span> Properties of Super- and <span class="hlt">Cyclic</span> Contraction in Response to Environmental Humidity</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lu, Shan; Swaminathan, Ganesh; Evans, Samuel; Blackledge, Todd</p> <p>2013-06-01</p> <p>Major Ampullate (MA) spider silk is among the most impressive biomaterials due to its unparalleled <span class="hlt">mechanical</span> properties, such as super-contraction and <span class="hlt">cyclic</span> response to changes in humidity. Electro-spinning enables the generation of engineered silk fibers with controlled parameters and dimentions for various medical and commercial applications. However, their applications hinge on the ability to reproduce the <span class="hlt">mechanical</span> properties such as a precise expansion-contraction response existed in natural silk fibers. Here, we successfully reproduced MA spider-silk fibers from solutions of natural MA silk proteins via electrospinning, which exhibit the super-contraction and <span class="hlt">cyclic</span> response to humidity change in a manner mirroring the natural fibers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007PhDT........61Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007PhDT........61Y"><span id="translatedtitle"><span class="hlt">Deformation</span>, lava dome evolution, and eruption <span class="hlt">cyclicity</span> at Merapi volcano, Indonesia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Young, Kirby D.</p> <p></p> <p><span class="hlt">Deformation</span> monitoring results are reported here for the period 1988-1998 at Merapi volcano, one of the most active and dangerous volcanoes in Indonesia. Comprehensive databases of various geophysical parameters were concurrently studied and analyzed to 2000, and similar data were subsequently considered during periods of eruption crisis in 2001 and 2006. Of particular emphasis was the study of lava eruption rates based on dome volume estimates and seismic proxies for dome collapse volumes. The detailed study period of <span class="hlt">deformation</span> includes a major resumption in lava effusion in January 1992 and major dome collapses in November 1994, January 1997, and July 1998. Monitoring techniques employed in the field are of two types. Translational movements were recorded via electronic distance measurements (EDM) on a summit trilateration network, slope distance changes measured to the upper flanks, and other data collected from 1988 to 1995. Tilt changes were detected by a summit and flank network of tilt stations that operated at various times from 1993 to 1998. A major consequence of the <span class="hlt">deformation</span> results is the documentation of a significant 4-year period of <span class="hlt">deformation</span> precursory to the 1992 eruption. Cross-crater strain rates accelerated from less than 3 x 10-6/day between 1988 and 1990 to more than 11 x 10-6/day just prior to the January 1992 activity, representing a general, asymmetric extension of the summit during highlevel conduit pressurization. After the vent opened and effusion of lava resumed, strain occurred at a much reduced rate of less than 2 x 10-6/day. The Gendol breach, a pronounced depression formed by the juxtaposition of old lava coulees on the southeast flank, functioned as a major displacement discontinuity. An elevated phase of magma production with respect to the long-term rate for the 20th Century characterized the activity at Merapi volcano, Central Java/Yogyakarta, Indonesia, for the period 1992-2006. Most large (0.2 - 3.4 x 106 m3) dome</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JPhA...48R5208O','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JPhA...48R5208O"><span id="translatedtitle">Sine-square <span class="hlt">deformation</span> and supersymmetric quantum <span class="hlt">mechanics</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Okunishi, Kouichi; Katsura, Hosho</p> <p>2015-11-01</p> <p>We investigate the sine-square <span class="hlt">deformation</span> (SSD) of free fermions in one-dimensional continuous space. On the basis of supersymmetric quantum <span class="hlt">mechanics</span>, we prove the correspondence between the many-body ground state of the system with SSD and that of the uniform system with periodic boundary conditions. We also discuss the connection between the SSD in the continuous space and its lattice version, where the geometric correction due to the real-space <span class="hlt">deformation</span> plays an important role in relating the eigenstates of the lattice SSD with those of the continuous SSD.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2529232','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2529232"><span id="translatedtitle">Different <span class="hlt">mechanisms</span> of adaptation to <span class="hlt">cyclic</span> water stress in two South Australian bread wheat cultivars</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Izanloo, Ali; Condon, Anthony G.; Langridge, Peter; Tester, Mark; Schnurbusch, Thorsten</p> <p>2008-01-01</p> <p>In the South Australian wheat belt, <span class="hlt">cyclic</span> drought is a frequent event represented by intermittent periods of rainfall which can occur around anthesis and post-anthesis in wheat. Three South Australian bread wheat (Triticum aestivum L.) cultivars, Excalibur, Kukri, and RAC875, were evaluated in one greenhouse and two growth-room experiments. In the first growth-room experiment, where plants were subjected to severe <span class="hlt">cyclic</span> water-limiting conditions, RAC875 and Excalibur (drought-tolerant) showed significantly higher grain yield under <span class="hlt">cyclic</span> water availability compared to Kukri (drought-susceptible), producing 44% and 18% more grain compared to Kukri, respectively. In the second growth-room experiment, where plants were subjected to a milder drought stress, the differences between cultivars were less pronounced, with only RAC875 showing significantly higher grain yield under the <span class="hlt">cyclic</span> water treatment. Grain number per spike and the percentage of aborted tillers were the major components that affected yield under <span class="hlt">cyclic</span> water stress. Excalibur and RAC875 adopted different morpho-physiological traits and <span class="hlt">mechanisms</span> to reduce water stress. Excalibur was most responsive to <span class="hlt">cyclic</span> water availability and showed the highest level of osmotic adjustment (OA), high stomatal conductance, lowest ABA content, and rapid recovery from stress under <span class="hlt">cyclic</span> water stress. RAC875 was more conservative and restrained, with moderate OA, high leaf waxiness, high chlorophyll content, and slower recovery from stress. Within this germplasm, the capacity for osmotic adjustment was the main physiological attribute associated with tolerance under <span class="hlt">cyclic</span> water stress which enabled plants to recover from water deficit. PMID:18703496</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930018132','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930018132"><span id="translatedtitle"><span class="hlt">Deformation</span> of supersymmetric and conformal quantum <span class="hlt">mechanics</span> through affine transformations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Spiridonov, Vyacheslav</p> <p>1993-01-01</p> <p>Affine transformations (dilatations and translations) are used to define a <span class="hlt">deformation</span> of one-dimensional N = 2 supersymmetric quantum <span class="hlt">mechanics</span>. Resulting physical systems do not have conserved charges and degeneracies in the spectra. Instead, superpartner Hamiltonians are q-isospectral, i.e. the spectrum of one can be obtained from another (with possible exception of the lowest level) by q(sup 2)-factor scaling. This construction allows easily to rederive a special self-similar potential found by Shabat and to show that for the latter a q-<span class="hlt">deformed</span> harmonic oscillator algebra of Biedenharn and Macfarlane serves as the spectrum generating algebra. A general class of potentials related to the quantum conformal algebra su(sub q)(1,1) is described. Further possibilities for q-<span class="hlt">deformation</span> of known solvable potentials are outlined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22271185','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22271185"><span id="translatedtitle">Temperature dependent <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> in pure amorphous silicon</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kiran, M. S. R. N. Haberl, B.; Williams, J. S.; Bradby, J. E.</p> <p>2014-03-21</p> <p>High temperature nanoindentation has been performed on pure ion-implanted amorphous silicon (unrelaxed a-Si) and structurally relaxed a-Si to investigate the temperature dependence of <span class="hlt">mechanical</span> <span class="hlt">deformation</span>, including pressure-induced phase transformations. Along with the indentation load-depth curves, ex situ measurements such as Raman micro-spectroscopy and cross-sectional transmission electron microscopy analysis on the residual indents reveal the mode of <span class="hlt">deformation</span> under the indenter. While unrelaxed a-Si <span class="hlt">deforms</span> entirely via plastic flow up to 200 °C, a clear transition in the mode of <span class="hlt">deformation</span> is observed in relaxed a-Si with increasing temperature. Up to 100 °C, pressure-induced phase transformation and the observation of either crystalline (r8/bc8) end phases or pressure-induced a-Si occurs in relaxed a-Si. However, with further increase of temperature, plastic flow rather than phase transformation is the dominant mode of <span class="hlt">deformation</span>. It is believed that the elevated temperature and pressure together induce bond softening and “defect” formation in structurally relaxed a-Si, leading to the inhibition of phase transformation due to pressure-releasing plastic flow under the indenter.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4086985','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4086985"><span id="translatedtitle">Analysis of Internal Crack Healing <span class="hlt">Mechanism</span> under Rolling <span class="hlt">Deformation</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Gao, Haitao; Ai, Zhengrong; Yu, Hailiang; Wu, Hongyan; Liu, Xianghua</p> <p>2014-01-01</p> <p>A new experimental method, called the ‘hole filling method’, is proposed to simulate the healing of internal cracks in rolled workpieces. Based on the experimental results, the evolution in the microstructure, in terms of diffusion, nucleation and recrystallisation were used to analyze the crack healing <span class="hlt">mechanism</span>. We also validated the phenomenon of segmented healing. Internal crack healing involves plastic <span class="hlt">deformation</span>, heat transfer and an increase in the free energy introduced by the cracks. It is proposed that internal cracks heal better under high plastic <span class="hlt">deformation</span> followed by slow cooling after rolling. Crack healing is controlled by diffusion of atoms from the matrix to the crack surface, and also by the nucleation and growth of ferrite grain on the crack surface. The diffusion <span class="hlt">mechanism</span> is used to explain the source of material needed for crack healing. The recrystallisation <span class="hlt">mechanism</span> is used to explain grain nucleation and growth, accompanied by atomic migration to the crack surface. PMID:25003518</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25003518','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/25003518"><span id="translatedtitle">Analysis of internal crack healing <span class="hlt">mechanism</span> under rolling <span class="hlt">deformation</span>.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gao, Haitao; Ai, Zhengrong; Yu, Hailiang; Wu, Hongyan; Liu, Xianghua</p> <p>2014-01-01</p> <p>A new experimental method, called the 'hole filling method', is proposed to simulate the healing of internal cracks in rolled workpieces. Based on the experimental results, the evolution in the microstructure, in terms of diffusion, nucleation and recrystallisation were used to analyze the crack healing <span class="hlt">mechanism</span>. We also validated the phenomenon of segmented healing. Internal crack healing involves plastic <span class="hlt">deformation</span>, heat transfer and an increase in the free energy introduced by the cracks. It is proposed that internal cracks heal better under high plastic <span class="hlt">deformation</span> followed by slow cooling after rolling. Crack healing is controlled by diffusion of atoms from the matrix to the crack surface, and also by the nucleation and growth of ferrite grain on the crack surface. The diffusion <span class="hlt">mechanism</span> is used to explain the source of material needed for crack healing. The recrystallisation <span class="hlt">mechanism</span> is used to explain grain nucleation and growth, accompanied by atomic migration to the crack surface. PMID:25003518</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013APS..MAR.A5011C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013APS..MAR.A5011C"><span id="translatedtitle">Effects of interatomic potentials on <span class="hlt">mechanical</span> <span class="hlt">deformation</span> of glasses</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, Wei-Ren; Iwashita, Takuya; Egami, Takeshi</p> <p>2013-03-01</p> <p>Apparently glasses behave like an elastic solid, which shows a linear relationship between stress and strain in <span class="hlt">mechanical</span> <span class="hlt">deformation</span>. However the understanding of the <span class="hlt">mechanical</span> response of glasses remains elusive because of structural disorder. <span class="hlt">Mechanical</span> <span class="hlt">deformation</span> of monatomic model glasses was studied using athermal quasi-static shear (AQS) simulation and with three different potentials. As the interatomic potentials we employed the 12-6 Lennard-Jones (LJ) potential, modified Johnson (mJ) potential, and Dzugutov (Dz) potential, respectively. For mJ and Dz glasses the shear modulus keeps constant below a critical strain, below which it decreases rapidly or discontinuously with strain. Such changes in shear modulus were mostly related to the change in local topology of atomic connectivity or anelasticity. In contrast LJ glass shows a gradual decrease in shear modulus in a continuous manner. The results indicated that the difference arises from the nature of the potentials if the topology of atomic connectivity can be clearly defined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..MARV37008C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..MARV37008C"><span id="translatedtitle">A micro-<span class="hlt">mechanical</span> model to determine changes of collagen fibrils under <span class="hlt">cyclic</span> loading</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chen, Michelle L.; Susilo, Monica E.; Ruberti, Jeffrey A.; Nguyen, Thao D.</p> <p></p> <p>Dynamic <span class="hlt">mechanical</span> loading induces growth and remodeling in biological tissues. It can alter the degradation rate and intrinsic <span class="hlt">mechanical</span> properties of collagen through cellular activity. Experiments showed that repeated <span class="hlt">cyclic</span> loading of a dense collagen fibril substrate increased collagen stiffness and strength, lengthened the substrate, but did not significantly change the fibril areal fraction or fibril anisotropy (Susilo, et al. ``Collagen Network Hardening Following <span class="hlt">Cyclic</span> Tensile Loading'', Interface Focus, submitted). We developed a model for the collagen fibril substrate (Tonge, et al. ``A micromechanical modeling study of the <span class="hlt">mechanical</span> stabilization of enzymatic degradation of collagen tissues'', Biophys J, in press.) to probe whether changes in the fibril morphology and <span class="hlt">mechanical</span> properties can explain the tissue-level properties observed during <span class="hlt">cyclic</span> loading. The fibrils were modeled as a continuous distribution of wavy elastica, based on experimental measurements of fibril density and collagen anisotropy, and can experience damage after a critical stress threshold. Other <span class="hlt">mechanical</span> properties in the model were fit to the stress response measured before and after the extended <span class="hlt">cyclic</span> loading to determine changes in the strength and stiffness of collagen fibrils.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/20803471','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/20803471"><span id="translatedtitle"><span class="hlt">Cyclic</span> <span class="hlt">deformation</span> fatigue behaviour of Ti6Al4V thermochemically nitrided for articular prostheses.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gil, F J; Manero, J M; Rodriguez, D; Planell, J A</p> <p>2003-01-01</p> <p>Titanium and its alloys have many attractive properties including high specific strength, low density, and excellent corrosion resistance. Titanium and the Ti6Al4V alloy have long been recognized as materials with high biocompatibility. These properties have led to the use of these materials in biomedical applications. Despite these advantages, the lack of good wear resistance makes the use of titanium and Ti6Al4V difficult in some biomedical applications, for example, articulating components of prostheses. To overcome this limitation, nitriding has been investigated as a surface-hardening method for titanium. Although nitriding greatly improves the wear resistance, this method reduces the fatigue strength. Low cycle fatigue performance in air of nitrided Ti6Al4V at different <span class="hlt">deformation</span> amplitudes has been studied. Results show a reduction of low cycle fatigue life of up to 10% compared to the non-treated material. Studies suggest it is not related to the titanium nitride surface layer, but to microstructural changes caused by the high temperature treatment. (Journal of Applied Biomaterial & Biomechanics 2003; 1: 43-7). PMID:20803471</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/290256','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/290256"><span id="translatedtitle">Some observations on <span class="hlt">cyclic</span> <span class="hlt">deformation</span> structures in the high-strength commercial aluminum alloy AA 7150</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Hanlon, D.N.; Rainforth, W.M.</p> <p>1998-11-01</p> <p>Load-controlled fatigue testing of the aluminum alloy AA 7150 has been conducted using four-point bending with an R ratio of + 0.1 over a range of maximum stress levels from 60 to 120% of the 0.2% proof stress. The alloy, in the form of 12.5-mm rolled plate, was investigated in underaged (UA), peak-aged (PA), and overaged (OA) conditions, corresponding to a change in average precipitate sizes from 5 nm in the UA condition to 21 nm in the OA condition. Three orientations of the plate were investigated. Orientation and aging condition influenced the degree of surface topographical development but not fatigue life. Detailed transmission electron microscopy (TEM) of the fatigued surface indicated that <span class="hlt">deformation</span> in all aging conditions occurred by planar slip. Slip was generally restricted to a single slip system within each grain, and subgrain boundaries offered little resistance to dislocation movement facilitating long slip line lengths (measured up to 310 {micro}m) between adjacent high-angle grain boundaries. Planar slip observed in the OA condition is attributed to shearing of large strengthening precipitates, which is promoted by long slip line lengths. No evidence of surface specific changes in slip character was observed.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_5");'>5</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li class="active"><span>7</span></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_7 --> <div id="page_8" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="141"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4758181','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4758181"><span id="translatedtitle">Data related to <span class="hlt">cyclic</span> <span class="hlt">deformation</span> and fatigue behavior of direct laser deposited Ti–6Al–4V with and without heat treatment</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Sterling, Amanda J.; Torries, Brian; Shamsaei, Nima; Thompson, Scott M.</p> <p>2016-01-01</p> <p>Data is presented describing the strain-controlled, fully-reversed uniaxial <span class="hlt">cyclic</span> <span class="hlt">deformation</span> and fatigue behavior of Ti–6Al–4V specimens additively manufactured via Laser Engineered Net Shaping (LENS) – a Direct Laser Deposition (DLD) process. The data was collected by performing multiple fatigue tests on specimens with various microstructural states/conditions, i.e. in their ‘as-built’, annealed (below the beta transus temperature), or heat treated (above the beta transus temperature) condition. Such data aids in characterizing the <span class="hlt">mechanical</span> integrity and fatigue resistance of DLD parts. Data presented herein also allows for elucidating the strong microstructure coupling of the fatigue behavior of DLD Ti–6Al–4V, as the data trends were found to vary with material condition (i.e. as-built, annealed or heat treated) [1]. This data is of interest to the additive manufacturing and fatigue scientific communities, as well as the aerospace and biomedical industries, since additively-manufactured parts cannot be reliably deployed for public use, until their <span class="hlt">mechanical</span> properties are understood with high certainty. PMID:26949728</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/26949728','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/26949728"><span id="translatedtitle">Data related to <span class="hlt">cyclic</span> <span class="hlt">deformation</span> and fatigue behavior of direct laser deposited Ti-6Al-4V with and without heat treatment.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Sterling, Amanda J; Torries, Brian; Shamsaei, Nima; Thompson, Scott M</p> <p>2016-03-01</p> <p>Data is presented describing the strain-controlled, fully-reversed uniaxial <span class="hlt">cyclic</span> <span class="hlt">deformation</span> and fatigue behavior of Ti-6Al-4V specimens additively manufactured via Laser Engineered Net Shaping (LENS) - a Direct Laser Deposition (DLD) process. The data was collected by performing multiple fatigue tests on specimens with various microstructural states/conditions, i.e. in their 'as-built', annealed (below the beta transus temperature), or heat treated (above the beta transus temperature) condition. Such data aids in characterizing the <span class="hlt">mechanical</span> integrity and fatigue resistance of DLD parts. Data presented herein also allows for elucidating the strong microstructure coupling of the fatigue behavior of DLD Ti-6Al-4V, as the data trends were found to vary with material condition (i.e. as-built, annealed or heat treated) [1]. This data is of interest to the additive manufacturing and fatigue scientific communities, as well as the aerospace and biomedical industries, since additively-manufactured parts cannot be reliably deployed for public use, until their <span class="hlt">mechanical</span> properties are understood with high certainty. PMID:26949728</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010SPIE.7997E..1BM','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010SPIE.7997E..1BM"><span id="translatedtitle"><span class="hlt">Mechanical</span> bearing bore similarity law of non-thermal <span class="hlt">deformation</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miao, Enming; Niu, Pengcheng; Ji, Xianrui; Lin, Nan; Fei, Yetai</p> <p>2010-12-01</p> <p>The gear transmission is widely used in <span class="hlt">mechanical</span> engineering. During the work time, the size of the bearing hole has changed due to temperature increase, leading to the size, shape and position tolerances of shaft and bearing with the components deviates from the original design requirements, thus making the spatial location of axis , gear with the gap and tooth contact angle changed, noise increasing, gear life shorten. In this paper, the thermal <span class="hlt">deformation</span> experiments of the commonly used <span class="hlt">mechanical</span> engineering machinery bearing hole has been carrying on. Using self-developed experimental device, in the -10 ~ 80°C temperature range, a single hole is measured accurately on the different radial direct, and measurement data is analyzed, combined with the structure and size of surrounding of hole. The results of theory and test analysis show that the thermal <span class="hlt">deformation</span> feature of hole is not only closely related to the physical attributes of material, but still affected by its own structure and size of parts. That means thermal <span class="hlt">deformation</span> of parts has non-similar thermal <span class="hlt">deformation</span> features.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011SPIE.7997E..1BM','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011SPIE.7997E..1BM"><span id="translatedtitle"><span class="hlt">Mechanical</span> bearing bore similarity law of non-thermal <span class="hlt">deformation</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Miao, Enming; Niu, Pengcheng; Ji, Xianrui; Lin, Nan; Fei, Yetai</p> <p>2011-05-01</p> <p>The gear transmission is widely used in <span class="hlt">mechanical</span> engineering. During the work time, the size of the bearing hole has changed due to temperature increase, leading to the size, shape and position tolerances of shaft and bearing with the components deviates from the original design requirements, thus making the spatial location of axis , gear with the gap and tooth contact angle changed, noise increasing, gear life shorten. In this paper, the thermal <span class="hlt">deformation</span> experiments of the commonly used <span class="hlt">mechanical</span> engineering machinery bearing hole has been carrying on. Using self-developed experimental device, in the -10 ~ 80°C temperature range, a single hole is measured accurately on the different radial direct, and measurement data is analyzed, combined with the structure and size of surrounding of hole. The results of theory and test analysis show that the thermal <span class="hlt">deformation</span> feature of hole is not only closely related to the physical attributes of material, but still affected by its own structure and size of parts. That means thermal <span class="hlt">deformation</span> of parts has non-similar thermal <span class="hlt">deformation</span> features.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016APS..MARE17005L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016APS..MARE17005L"><span id="translatedtitle">Tuning transport properties on graphene multiterminal structures by <span class="hlt">mechanical</span> <span class="hlt">deformations</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Latge, Andrea; Torres, Vanessa; Faria, Daiara</p> <p></p> <p>The realization of <span class="hlt">mechanical</span> strain on graphene structures is viewed as a promise route to tune electronic and transport properties such as changing energy band-gaps and promoting localization of states. Using continuum models, <span class="hlt">mechanical</span> <span class="hlt">deformations</span> are described by effective gauge fields, mirrored as pseudomagnetic fields that may reach quite high values. Interesting symmetry features are developed due to out of plane <span class="hlt">deformations</span> on graphene; lift sublattice symmetry was predicted and observed in centrosymmetric bumps and strained nanobubbles. Here we discuss the effects of Gaussian-like strain on a hexagonal graphene flake connected to three leads, modeled as perfect graphene nanoribbons. The Green function formalism is used within a tight-binding approximation. For this particular <span class="hlt">deformation</span> sharp resonant states are achieved depending on the strained structure details. We also study a fold-strained structure in which the three leads are <span class="hlt">deformed</span> extending up to the very center of the hexagonal flake. We show that conductance suppressions can be controlled by the strain intensity and important transport features are modeled by the electronic band structure of the leads.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/1049842','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/1049842"><span id="translatedtitle">Structural Anisotropy in Metallic Glasses Induced by <span class="hlt">Mechanical</span> <span class="hlt">Deformation</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Dmowski, Wojtek; Egami, Takeshi</p> <p>2008-01-01</p> <p>Metallic glasses have been studied vigorously since the first report on amorphous gold-silicon alloy back in 1960.[1] Initially soft magnetic properties were the most promising features for industrial applications. The recent development of bulk metallic glasses (BMGs)[2 5] initiated interests in engineering applications such as structural or biomedical materials because of attractive properties such as high strength,[6] high elasticity,[7,8] and good corrosion resistance,[9,10] among others. In addition, high temperature processing of BMGs allows for near-net-shape formability,[11 13] which could simplify and possibly reduce the cost of the final product. The glasses retain the disordered atomic structure of a liquid, and ideally are isotropic solids. Frequently because of processing conditions, such as directional heat flow, some structural anisotropy is produced during quenching, and has been observed by structural investigations. Usually, annealing at high temperatures results in an isotropic structure. Also, formation of uniaxial magnetic anisotropy[14] had been observed in studies of creep <span class="hlt">deformed</span> ferromagnetic metallic glasses. Samples with a near-zero magnetostriction coefficient had been studied to establish the origin of the magnetic anisotropy. It was concluded that anisotropy resulted from the atomic level anisotropy[15] and not the heterogeneous internal stress distribution. Indeed X-ray diffraction study of the creep <span class="hlt">deformed</span> metallic glass showed bond anisotropy.[ 16,17] Such structural studies had been cumbersome and lengthy because they required measurement of many orientations with high statistics. Recently we have shown that use of an area detector and high energy X-rays at a synchrotron source can speed up data collection without compromising statistics.[18] In this contribution, we present data showing structural anisotropy in glassy samples after homogenous (creep) and inhomogeneous (compression) <span class="hlt">mechanical</span> <span class="hlt">deformation</span>. The observation of the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016Nanos...814420D&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016Nanos...814420D&link_type=ABSTRACT"><span id="translatedtitle">Nanoparticle <span class="hlt">mechanics</span>: <span class="hlt">deformation</span> detection via nanopore resistive pulse sensing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Darvish, Armin; Goyal, Gaurav; Aneja, Rachna; Sundaram, Ramalingam V. K.; Lee, Kidan; Ahn, Chi Won; Kim, Ki-Bum; Vlahovska, Petia M.; Kim, Min Jun</p> <p>2016-07-01</p> <p>Solid-state nanopores have been widely used in the past for single-particle analysis of nanoparticles, liposomes, exosomes and viruses. The shape of soft particles, particularly liposomes with a bilayer membrane, can greatly differ inside the nanopore compared to bulk solution as the electric field inside the nanopores can cause liposome electrodeformation. Such <span class="hlt">deformations</span> can compromise size measurement and characterization of particles, but are often neglected in nanopore resistive pulse sensing. In this paper, we investigated the <span class="hlt">deformation</span> of various liposomes inside nanopores. We observed a significant difference in resistive pulse characteristics between soft liposomes and rigid polystyrene nanoparticles especially at higher applied voltages. We used theoretical simulations to demonstrate that the difference can be explained by shape <span class="hlt">deformation</span> of liposomes as they translocate through the nanopores. Comparing our results with the findings from electrodeformation experiments, we demonstrated that the rigidity of liposomes can be qualitatively compared using resistive pulse characteristics. This application of nanopores can provide new opportunities to study the <span class="hlt">mechanics</span> at the nanoscale, to investigate properties of great value in fundamental biophysics and cellular mechanobiology, such as virus <span class="hlt">deformability</span> and fusogenicity, and in applied sciences for designing novel drug/gene delivery systems.Solid-state nanopores have been widely used in the past for single-particle analysis of nanoparticles, liposomes, exosomes and viruses. The shape of soft particles, particularly liposomes with a bilayer membrane, can greatly differ inside the nanopore compared to bulk solution as the electric field inside the nanopores can cause liposome electrodeformation. Such <span class="hlt">deformations</span> can compromise size measurement and characterization of particles, but are often neglected in nanopore resistive pulse sensing. In this paper, we investigated the <span class="hlt">deformation</span> of various</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015MMTA...46.1610S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015MMTA...46.1610S"><span id="translatedtitle"><span class="hlt">Cyclic</span> <span class="hlt">Deformation</span> Behavior of Fe-18Cr-18Mn-0.63N Nickel-Free High-Nitrogen Austenitic Stainless Steel</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shao, C. W.; Shi, F.; Li, X. W.</p> <p>2015-04-01</p> <p><span class="hlt">Cyclic</span> <span class="hlt">deformation</span> and damage behavior of a Ni-free high-nitrogen austenitic stainless steel with a composition of Fe-18Cr-18Mn-0.63N (weight pct) were studied, and the internal stress and effective stress were estimated by partitioning the hysteresis loop during <span class="hlt">cyclic</span> straining at total strain amplitudes ranging from 3.0 × 10-3 to 1.0 × 10-2. It is found that immediate <span class="hlt">cyclic</span> softening takes place at all strain amplitudes and subsequently a saturation or quasi-saturation state develops and occupies the main part of the whole fatigue life. The internal stress increases with increasing strain amplitude, while the variation of effective stress with strain amplitude is somewhat complicated. Such a phenomenon is discussed in terms of dislocation structures and the short-range ordering caused by the interaction between nitrogen atoms and substitutional atoms. The relationship of fatigue life vs plastic strain amplitude ( N f-Δ ɛ pl/2) follows a bilinear Coffin-Manson rule, resulting from the variation in slip <span class="hlt">deformation</span> mode with the applied strain amplitude. At the low strain amplitude, cracks initiate along slip bands, and planar slip dislocation configurations dominate the major characteristic of internal microstructures. At high strain amplitudes, intergranular (mostly along grain boundaries and few along twin boundaries) cracks are generally found, and the <span class="hlt">deformation</span> microstructures are mainly composed of dislocation cells, stacking faults and a small amount of <span class="hlt">deformation</span> twins, in addition to planar slip dislocation structures.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/441489','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/441489"><span id="translatedtitle"><span class="hlt">Mechanical</span> behavior of adhesive joints subjected to <span class="hlt">cyclic</span> thermal loading</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Humfeld, G.R.; Dillard, D.A.</p> <p>1996-12-31</p> <p>Stresses induced in bimaterial systems due to changing temperature has been the subject of much study since the publication of Timoshenko`s classic paper of 1925. An adhesive bond is one example of a bimaterial system in which thermal stress can play an important role. However, adhesives are viscoelastic in nature, and their <span class="hlt">mechanical</span> behavior is dictated by the temperature- and time-dependence of their material properties; analytical solutions for elastic materials do not adequately describe their true behavior. The effect of the adhesive`s viscoelasticity on stress in an adhesive bond subjected to changing temperature is therefore of compelling interest and importance for the adhesives industry. The objective of this research is to develop an understanding of the viscoelastic effect in an adhesive bond subjected to cycling temperature, particularly when the temperature range spans a transition temperature of the adhesive. Numerical modeling of a simplified geometry was first undertaken to isolate the influence of viscoelasticity on the stress state from any particular specimen geometry effect. Finite element modeling was then undertaken to examine the <span class="hlt">mechanical</span> behavior of the adhesive in a layered geometry. Both solution methods predicted development of residual tensile stresses in the adhesive. For the layered geometry this was found to correspond with residual tensile peel stresses, which are thought to be the cause of interfacial debonding.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1992RSPSA.437..567D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1992RSPSA.437..567D"><span id="translatedtitle">Modeling of combined high-temperature creep and <span class="hlt">cyclic</span> plasticity in components using continuum damage <span class="hlt">mechanics</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dunne, F. P. E.; Hayhurst, D. R.</p> <p>1992-06-01</p> <p>A computer-based finite-element viscoplastic damage solver is presented to analyze structural components subject to combined <span class="hlt">cyclic</span> thermal and <span class="hlt">mechanical</span> loading. The solver is capable of predicting the combined evolution of creep and <span class="hlt">cyclic</span> plasticity damage by solution of the combined boundary-initial value problem. The solver has been used to predict the high-temperature behavior of a slag tap component subjected to <span class="hlt">cyclic</span> thermal loading generated by infrared heaters and water cooling ducts. It is found that the initiation of damage and microcracking occur early in the lifetime at about 3000 cycles adjacent to the cooling duct. The propagation of failure zones stabilizes at 60,000 cycles after which no further damage evolution occurs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/290933','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/290933"><span id="translatedtitle">A <span class="hlt">mechanics</span> model for the <span class="hlt">deformation</span> of swirl-mat composites</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Elahi, M.; Weitsman, Y.J.</p> <p>1998-11-01</p> <p>Swirl-mat polymeric composites are considered as representative materials for application in the automotive industry. This article summarizes a three-year long effort to characterize, model, and predict the <span class="hlt">deformation</span> of these composites under stress, temperature, <span class="hlt">cyclic</span> loadings, and the ingress of fluids. The effort involved several hundred characterization tests of various kinds and the formulation of a constitutive model based upon fundamental principles of irreversible thermodynamics and continuum <span class="hlt">mechanics</span>. The above-mentioned experiments and model development were performed interactively. Subsequently, the model was employed in a predictive manner to anticipate experimental data collected under complex load and temperature histories, as well as to predict long-term behavior from short-term data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/16199413','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/16199413"><span id="translatedtitle"><span class="hlt">Cyclic</span> <span class="hlt">mechanical</span> stretch augments hyaluronan production in cultured human uterine cervical fibroblast cells.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Takemura, Maki; Itoh, Hiroaki; Sagawa, Norimasa; Yura, Shigeo; Korita, Daizo; Kakui, Kazuyo; Kawamura, Makoto; Hirota, Naoyoshi; Maeda, Hiroshi; Fujii, Shingo</p> <p>2005-09-01</p> <p>Hyaluronan (HA) a glycosaminoglycan with high affinity for water molecules stimulates local inflammatory reactions. Parturition causes a dramatic increase in the amount of HA fragments in the uterine cervix, thereby contributing to a rapid softening as well as opening of the cervical canal, i.e. cervical ripening. The aim of this study was to investigate the possible involvement of <span class="hlt">cyclic</span> distension caused by labour in the augmentation of HA production during cervical ripening. Immunohistochemistry and/or RT-PCR detected hyaluronan synthase (HAS)1, 2 and 3 in samples of human cervical tissue obtained from pregnant women. Labour-like <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> stretch for 24, 36 and 48 h significantly enhanced the secretion of HA, from cultured human uterine cervical fibroblast (CxF) cells, 128.7, 151.4 and 173.2%, respectively, concomitant with a significant augmentation of HAS1 (36, 48 h), HAS2 (24, 36 and 48 h) and HAS3 (48 h) mRNA expression. <span class="hlt">Cyclic</span> <span class="hlt">mechanical</span> stretch for 12, 36 and 48 h increased molecular size of the HA secreted from CxF cells. In conclusion, <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> stretch of the uterine cervix caused by the presenting part of the fetus in labour may contribute to the increase in the secretion of HA during the process of cervical ripening. PMID:16199413</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/27321911','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/27321911"><span id="translatedtitle">Nanoparticle <span class="hlt">mechanics</span>: <span class="hlt">deformation</span> detection via nanopore resistive pulse sensing.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Darvish, Armin; Goyal, Gaurav; Aneja, Rachna; Sundaram, Ramalingam V K; Lee, Kidan; Ahn, Chi Won; Kim, Ki-Bum; Vlahovska, Petia M; Kim, Min Jun</p> <p>2016-08-14</p> <p>Solid-state nanopores have been widely used in the past for single-particle analysis of nanoparticles, liposomes, exosomes and viruses. The shape of soft particles, particularly liposomes with a bilayer membrane, can greatly differ inside the nanopore compared to bulk solution as the electric field inside the nanopores can cause liposome electrodeformation. Such <span class="hlt">deformations</span> can compromise size measurement and characterization of particles, but are often neglected in nanopore resistive pulse sensing. In this paper, we investigated the <span class="hlt">deformation</span> of various liposomes inside nanopores. We observed a significant difference in resistive pulse characteristics between soft liposomes and rigid polystyrene nanoparticles especially at higher applied voltages. We used theoretical simulations to demonstrate that the difference can be explained by shape <span class="hlt">deformation</span> of liposomes as they translocate through the nanopores. Comparing our results with the findings from electrodeformation experiments, we demonstrated that the rigidity of liposomes can be qualitatively compared using resistive pulse characteristics. This application of nanopores can provide new opportunities to study the <span class="hlt">mechanics</span> at the nanoscale, to investigate properties of great value in fundamental biophysics and cellular mechanobiology, such as virus <span class="hlt">deformability</span> and fusogenicity, and in applied sciences for designing novel drug/gene delivery systems. PMID:27321911</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/pages/biblio/1321726-constitutive-law-flow-mechanism-diamond-deformation','SCIGOV-DOEP'); return false;" href="http://www.osti.gov/pages/biblio/1321726-constitutive-law-flow-mechanism-diamond-deformation"><span id="translatedtitle">Constitutive Law and Flow <span class="hlt">Mechanism</span> in Diamond <span class="hlt">Deformation</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/pages">DOE PAGESBeta</a></p> <p>Yu, Xiaohui; Raterron, Paul; Zhang, Jianzhong; Lin, Zhijun; Wang, Liping; Zhao, Yusheng</p> <p>2012-11-19</p> <p>Constitutive laws and crystal plasticity in diamond <span class="hlt">deformation</span> have been the subjects of substantial interest since synthetic diamond was made in 1950's. To date, however, little is known quantitatively regarding its brittle-ductile properties and yield strength at high temperatures. In this paper, we report, for the first time, the strain-stress constitutive relations and experimental demonstration of <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> under confined high pressure. The <span class="hlt">deformation</span> at room temperature is essentially brittle, cataclastic, and mostly accommodated by fracturing on {111} plane with no plastic yielding at uniaxial strains up to 15%. At elevated temperatures of 1000°C and 1200°C diamond crystals exhibit significantmore » ductile flow with corresponding yield strength of 7.9 and 6.3 GPa, indicating that diamond starts to weaken when temperature is over 1000°C. Finally, at high temperature the plastic <span class="hlt">deformation</span> and ductile flow is meditated by the <110>{111} dislocation glide and a very active {111} micro-twinning.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1321726','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1321726"><span id="translatedtitle">Constitutive Law and Flow <span class="hlt">Mechanism</span> in Diamond <span class="hlt">Deformation</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Yu, Xiaohui; Raterron, Paul; Zhang, Jianzhong; Lin, Zhijun; Wang, Liping; Zhao, Yusheng</p> <p>2012-11-19</p> <p>Constitutive laws and crystal plasticity in diamond <span class="hlt">deformation</span> have been the subjects of substantial interest since synthetic diamond was made in 1950's. To date, however, little is known quantitatively regarding its brittle-ductile properties and yield strength at high temperatures. In this paper, we report, for the first time, the strain-stress constitutive relations and experimental demonstration of <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> under confined high pressure. The <span class="hlt">deformation</span> at room temperature is essentially brittle, cataclastic, and mostly accommodated by fracturing on {111} plane with no plastic yielding at uniaxial strains up to 15%. At elevated temperatures of 1000°C and 1200°C diamond crystals exhibit significant ductile flow with corresponding yield strength of 7.9 and 6.3 GPa, indicating that diamond starts to weaken when temperature is over 1000°C. Finally, at high temperature the plastic <span class="hlt">deformation</span> and ductile flow is meditated by the <110>{111} dislocation glide and a very active {111} micro-twinning.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3500768','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3500768"><span id="translatedtitle">Constitutive Law and Flow <span class="hlt">Mechanism</span> in Diamond <span class="hlt">Deformation</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Yu, Xiaohui; Raterron, Paul; Zhang, Jianzhong; Lin, Zhijun; Wang, Liping; Zhao, Yusheng</p> <p>2012-01-01</p> <p>Constitutive laws and crystal plasticity in diamond <span class="hlt">deformation</span> have been the subjects of substantial interest since synthetic diamond was made in 1950's. To date, however, little is known quantitatively regarding its brittle-ductile properties and yield strength at high temperatures. Here we report, for the first time, the strain-stress constitutive relations and experimental demonstration of <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> under confined high pressure. The <span class="hlt">deformation</span> at room temperature is essentially brittle, cataclastic, and mostly accommodated by fracturing on {111} plane with no plastic yielding at uniaxial strains up to 15%. At elevated temperatures of 1000°C and 1200°C diamond crystals exhibit significant ductile flow with corresponding yield strength of 7.9 and 6.3 GPa, indicating that diamond starts to weaken when temperature is over 1000°C. At high temperature the plastic <span class="hlt">deformation</span> and ductile flow is meditated by the <110>{111} dislocation glide and a very active {111} micro-twinning. PMID:23166859</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/764611','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/764611"><span id="translatedtitle">Final Report: Hardening and Strain Localization in Single and Polycrystalline Materials Under <span class="hlt">Cyclic</span> and Monotonic <span class="hlt">Deformation</span>, January 11, 1985 - July 31, 1997</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Laird, Campbell; Bassani, John L.</p> <p>2000-03-03</p> <p>The subject program on substructure evolution initially focused on strain localization produced by fatigue cycling and especially how such localization affects the <span class="hlt">cyclic</span> response of polycrystalline pure metal. The latter stages have dealt with strain localization in the heavy monotonic <span class="hlt">deformation</span> of alloys, which eventually produces forms of localized <span class="hlt">deformation</span> that include coarse slip bands (CSB's), which are aligned to slip planes and macroscopic shear bands (MSB's), which are not aligned to slip planes. These forms of strain localization are important in that they limit the usable ductility of the material in forming processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhRvD..88h4009C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhRvD..88h4009C"><span id="translatedtitle">Generalized coherent states under <span class="hlt">deformed</span> quantum <span class="hlt">mechanics</span> with maximum momentum</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ching, Chee Leong; Ng, Wei Khim</p> <p>2013-10-01</p> <p>Following the Gazeau-Klauder approach, we construct generalized coherent states (GCS) as the quantum simulator to examine the <span class="hlt">deformed</span> quantum <span class="hlt">mechanics</span>, which exhibits an intrinsic maximum momentum. We study <span class="hlt">deformed</span> harmonic oscillators and compute their probability distribution and entropy of states exactly. Also, a particle in an infinite potential box is studied perturbatively. In particular, unlike usual quantum <span class="hlt">mechanics</span>, the present <span class="hlt">deformed</span> case increases the entropy of the Planck scale quantum optical system. Furthermore, for simplicity, we obtain the modified uncertainty principle (MUP) with the perturbative treatment up to leading order. MUP turns out to increase generally. However, for certain values of γ (a parameter of GCS), it is possible that the MUP will vanish and hence will exhibit the classical characteristic. This is interpreted as the manifestation of the intrinsic high-momentum cutoff at lower momentum in a perturbative treatment. Although the GCS saturates the minimal uncertainty in a simultaneous measurement of physical position and momentum operators, thus constituting the squeezed states, complete coherency is impossible in quantum gravitational physics. The Mandel Q number is calculated, and it is shown that the statistics can be Poissonian and super-/sub-Poissonian depending on γ. The equation of motion is studied, and both Ehrenfest’s theorem and the correspondence principle are recovered. Fractional revival times are obtained through the autocorrelation, and they indicate that the superposition of a classical-like subwave packet is natural in GCS. We also contrast our results with the string-motivated (Snyder) type of <span class="hlt">deformed</span> quantum <span class="hlt">mechanics</span>, which incorporates a minimum position uncertainty rather than a maximum momentum. With the advances of quantum optics technology, it might be possible to realize some of these distinguishing quantum-gravitational features within the domain of future experiments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/23290516','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/23290516"><span id="translatedtitle"><span class="hlt">Deformation</span> behavior and <span class="hlt">mechanical</span> properties of amyloid protein nanowires.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Solar, Max; Buehler, Markus J</p> <p>2013-03-01</p> <p>Amyloid fibrils are most often associated with their pathological role in diseases like Alzheimer's disease and Parkinson's disease, but they are now increasingly being considered for uses in functional engineering materials. They are among the stiffest protein fibers known but they are also rather brittle, and it is unclear how this combination of properties affects the behavior of amyloid structures at larger length scales, such as in films, wires or plaques. Using a coarse-grained model for amyloid fibrils, we study the <span class="hlt">mechanical</span> response of amyloid nanowires and examine fundamental <span class="hlt">mechanical</span> properties, including <span class="hlt">mechanisms</span> of <span class="hlt">deformation</span> and failure under tensile loading. We also explore the effect of varying the breaking strain and adhesion strength of the constituent amyloid fibrils on the properties of the larger structure. We find that <span class="hlt">deformation</span> in the nanowires is controlled by a combination of fibril sliding and fibril failure and that there exists a transition from brittle to ductile behavior by either increasing the fibril failure strain or decreasing the strength of adhesion between fibrils. Furthermore, our results reveal that the <span class="hlt">mechanical</span> properties of the nanowires are quite sensitive to changes in the properties of the individual fibrils, and the larger scale structures are found to be more <span class="hlt">mechanically</span> robust than the constituent fibrils, for all cases considered. More broadly, this work demonstrates the promise of utilizing self-assembled biological building blocks in the development of hierarchical nanomaterials. PMID:23290516</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1813444H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1813444H"><span id="translatedtitle">Thermal and <span class="hlt">mechanical</span> controls on magma supply and volcanic <span class="hlt">deformation</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hickey, James; Gottsmann, Jo; Nakamichi, Haruhisa; Iguchi, Masato</p> <p>2016-04-01</p> <p>Ground <span class="hlt">deformation</span> often precedes volcanic eruptions, and results from complex interactions between source processes and the thermomechanical behaviour of surrounding rock. Geodetic models aimed at constraining source processes consequently require the implementation of realistic <span class="hlt">mechanical</span> and thermal rock properties. However, most generic models ignore this requirement and employ oversimplified <span class="hlt">mechanical</span> assumptions without regard for thermal effects. Here we show how spatio-temporal <span class="hlt">deformation</span> and magma reservoir evolution are fundamentally controlled by three-dimensional thermomechanical heterogeneity. Using the example of continued inflation at Aira caldera, Japan, we demonstrate that despite on-going eruptions magma is accumulating faster than it can be ejected, and the current uplift is approaching the level inferred prior to the 1914 Plinian eruption. Our results from inverse and forward numerical models are consistent with petrological constraints and highlight how the location, volume, and rate of magma supply, 0.014 km3/yr, are thermomechanically controlled. Magma storage conditions coincide with estimates for the caldera-forming reservoir ˜29,000 years ago, and the inferred magma supply rate indicates a ˜130-year timeframe to amass enough magma to feed a future 1914-sized eruption. These new inferences are important for eruption forecasting and risk mitigation, and have significant implications for the interpretations of volcanic <span class="hlt">deformation</span> worldwide.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_6");'>6</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li class="active"><span>8</span></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_8 --> <div id="page_9" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="161"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/7032767','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/7032767"><span id="translatedtitle">Computer modelling of <span class="hlt">cyclic</span> <span class="hlt">deformation</span> of high-temperature materials. Progress report</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Duesbery, M.S.; Louat, N.P.</p> <p>1992-11-16</p> <p>Current methods of lifetime assessment leave much to be desired. Typically, the expected life of a full-scale component exposed to a complex environment is based upon empirical interpretations of measurements performed on microscopic samples in controlled laboratory conditions. Extrapolation to the service component is accomplished by scaling laws which, if used at all, are empirical; little or no attention is paid to synergistic interactions between the different components of the real environment. With the increasingly hostile conditions which must be faced in modern aerospace applications, improvement in lifetime estimation is mandated by both cost and safety considerations. This program aims at improving current methods of lifetime assessment by building in the characteristics of the micro-<span class="hlt">mechanisms</span> known to be responsible for damage and failure. The broad approach entails the integration and, where necessary, augmentation of the micro-scale research results currently available in the literature into a macro-scale model with predictive capability. In more detail, the program will develop a set of hierarchically structured models at different length scales, from atomic to macroscopic, at each level taking as parametric input the results of the model at the next smaller scale. In this way the known microscopic properties can be transported by systematic procedures to the unknown macro-scale region. It may not be possible to eliminate empiricism completely, because some of the quantities involved cannot yet be estimated to the required degree of precision. In this case the aim will be at least to eliminate functional empiricism.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016PMM...117..518V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016PMM...117..518V"><span id="translatedtitle">Production, structure, texture, and <span class="hlt">mechanical</span> properties of severely <span class="hlt">deformed</span> magnesium</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Volkov, A. Yu.; Antonova, O. V.; Kamenetskii, B. I.; Klyukin, I. V.; Komkova, D. A.; Antonov, B. D.</p> <p>2016-05-01</p> <p>Methods of the severe plastic <span class="hlt">deformation</span> (SPD) of pure magnesium at room temperature, namely, transverse extrusion and hydroextrusion in a self-destroyed shell, have been developed. The maximum true strain of the samples after the hydroextrusion was e ~ 3.2; in the course of transverse extrusion and subsequent cold rolling, a true strain of e ~ 6.0 was achieved. The structure and <span class="hlt">mechanical</span> properties of the magnesium samples have been studied in different structural states. It has been shown that the SPD led to a decrease in the grain size d to ~2 μm; the relative elongation at fracture δ increased to ~20%. No active twinning has been revealed. The reasons for the high plasticity of magnesium after SPD according to the <span class="hlt">deformation</span> modes suggested are discussed from the viewpoint of the hierarchy of the observed structural states.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/27177232','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/27177232"><span id="translatedtitle"><span class="hlt">Cyclic</span> stretch promotes osteogenesis-related gene expression in osteoblast-like cells through a cofilin-associated <span class="hlt">mechanism</span>.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gao, Jie; Fu, Shanmin; Zeng, Zhaobin; Li, Feifei; Niu, Qiannan; Jing, Da; Feng, Xue</p> <p>2016-07-01</p> <p>Osteoblasts have the capacity to perceive and transduce <span class="hlt">mechanical</span> signals, and thus, regulate the mRNA and protein expression of a variety of genes associated with osteogenesis. Cytoskeletal reconstruction, as one of the earliest perception events for external <span class="hlt">mechanical</span> stimulation, has previously been demonstrated to be essential for mechanotransduction in bone cells. However, the <span class="hlt">mechanism</span> by which <span class="hlt">mechanical</span> signals induce cytoskeletal <span class="hlt">deformation</span> remains poorly understood. The actin‑binding protein, cofilin, promotes the depolymerization of actin and is understood to be important in the regulation of activities in various cell types, including endothelial, neuronal and muscle cells. However, to the best of our knowledge, the importance of cofilin in osteoblastic mechanotransduction has not been previously investigated. In the present study, osteoblast‑like MG‑63 cells were subjected to physiological <span class="hlt">cyclic</span> stretch stimulation (12% elongation) for 1, 4, 8, 12 and 24 h, and the expression levels of cofilin and osteogenesis-associated genes were quantified with reverse transcription‑quantitative polymerase chain reaction, immunofluorescence staining and western blotting analyses. Additionally, knockdown of cofilin using RNA interference was conducted, and the mRNA levels of osteogenesis‑associated genes were compared between osteoblast‑like cells in the presence and absence of cofilin gene knockdown. The results of the present study demonstrated that <span class="hlt">cyclic</span> stretch stimulates the expression of genes associated with osteoblastic activities in MG‑63 cells, including alkaline phosphatase (ALP), osteocalcin (OCN), runt‑related transcription factor 2 (Runx2) and collagen‑1 (COL‑1). <span class="hlt">Cyclic</span> stretch also regulates the mRNA and protein expression of cofilin in MG‑63 cells. Furthermore, stretch‑induced increases in the levels of osteogenesis-associated genes, including ALP, OCN, Runx2 and COL‑1, were reduced following cofilin gene knockdown</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050169941','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050169941"><span id="translatedtitle">Fatigue Behavior and <span class="hlt">Deformation</span> <span class="hlt">Mechanisms</span> in Inconel 718 Superalloy Investigated</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>2005-01-01</p> <p>The nickel-base superalloy Inconel 718 (IN 718) is used as a structural material for a variety of components in the space shuttle main engine (SSME) and accounts for more than half of the total weight of this engine. IN 718 is the bill-of-material for the pressure vessels of nickel-hydrogen batteries for the space station. In the case of the space shuttle main engine, structural components are typically subjected to startup and shutdown load transients and occasional overloads in addition to high-frequency vibratory loads from routine operation. The nickel-hydrogen battery cells are prooftested before service and are subjected to fluctuating pressure loads during operation. In both of these applications, the structural material is subjected to a monotonic load initially, which is subsequently followed by fatigue. To assess the life of these structural components, it is necessary to determine the influence of a prior monotonic load on the subsequent fatigue life of the superalloy. An insight into the underlying <span class="hlt">deformation</span> and damage <span class="hlt">mechanisms</span> is also required to properly account for the interaction between the prior monotonic load and the subsequent fatigue loading. An experimental investigation was conducted to establish the effect of prior monotonic straining on the subsequent fatigue behavior of wrought, double-aged, IN 718 at room temperature. First, monotonic strain tests and fully-reversed, strain-controlled fatigue tests were conducted on uniform-gage-section IN 718 specimens. Next, fully reversed fatigue tests were conducted under strain control on specimens that were monotonically strained in tension. Results from this investigation indicated that prior monotonic straining reduced the fatigue resistance of the superalloy particularly at the lowest strain range. Some of the tested specimens were sectioned and examined by transmission electron microscopy to reveal typical microstructures as well as the active <span class="hlt">deformation</span> and damage <span class="hlt">mechanisms</span> under each of</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/15949544','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/15949544"><span id="translatedtitle">The effect of crystallinity on the <span class="hlt">deformation</span> <span class="hlt">mechanism</span> and bulk <span class="hlt">mechanical</span> properties of PLLA.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Renouf-Glauser, Annette C; Rose, John; Farrar, David F; Cameron, Ruth Elizabeth</p> <p>2005-10-01</p> <p>Poly (l-lactide) is a widely studied biomaterial, currently approved for use in a range of medical devices, however, most in vitro studies have so far focussed upon either the bulk properties during degradation and/or <span class="hlt">deformation</span>, or on the microstructure of the unloaded material during degradation. This study aimed to combine these approaches through the technique of simultaneous small-angle X-ray scattering and tensile testing at various stages of degradation up to 8 months, on material with a range of induced microstructures. Results showed that the amorphous material <span class="hlt">deformed</span> by crazing in the dry, wet and degraded states, however, the <span class="hlt">mechanism</span> by which the craze developed changed significantly on hydration. Despite this difference, there was little change in the bulk <span class="hlt">mechanical</span> properties. Crystalline materials <span class="hlt">deformed</span> through crystal-mediated <span class="hlt">deformation</span>, with contributions from both cavitation and fibrillated shear, but surprisingly, differences in the length scales within the spherulitic structure caused by annealing at different temperatures had very little effect on the <span class="hlt">mechanism</span> of <span class="hlt">deformation</span>, though differences were seen in the bulk properties. Furthermore, hydration had little effect on the crystalline materials, though degradation over 8 months resulted in loss of <span class="hlt">mechanical</span> properties for samples produced at higher annealing temperatures. In conclusion, the introduction of crystallinity had a huge effect on both bulk and microscopic properties of PLLA, but the spherulitic structure of the crystalline material affected the bulk properties significantly more than it did the micromechanism of <span class="hlt">deformation</span>. PMID:15949544</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1994Tectp.229...43S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1994Tectp.229...43S"><span id="translatedtitle">Defect structure and <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> in naturally <span class="hlt">deformed</span> augite and enstatite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Skrotzki, W.</p> <p>1994-01-01</p> <p>The defect structure of naturally <span class="hlt">deformed</span> augite containing enstatite lamellae has been investigated by conventional and high resolution transmission electron microscopy in order to obtain information on the <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> of these important rock-forming minerals. The aggregate under investigation originates from a coarse-grained websterite dyke of the Balmuccia Massif which is located within the Ivrea Zone (NW-Italy). Dyke formation may have taken place during intrusion of the peridotite massif into the lower crust at temperatures of about 1000°C. <span class="hlt">Deformation</span> of the pyroxenite dykes may be due to subsequent tilting of the Ivrea Zone at lower temperatures (about 650°C). Cooling of the augites led to exsolution of orthopyroxene, clinoamphibole and two generations of pigeonite lamellae. The microstructure observed in the augite matrix and the enstatite exsolution lamellae consists of dislocations, planar faults and subgrain boundaries. Burgers vectors and dislocation line directions in augite indicate the activation of the (100)[001], {110} {1}/{2}<110>, {110} {1}/{2}1/2<112>, (100)[010], (010)[100], (010)<101> and {110}<111> slip systems, the first two being the most active. Dislocation reactions are common, as well as heterogeneous precipitation of pigeonite at [001] dislocations. The subgrain boundaries observed are { hkO} tilt boundaries with [001] tilt axis and (010) twist boundaries. Occasionally (100) twin lamellae exist. The dislocations in the <span class="hlt">deformed</span> enstatite lamellae have [001], [010] and [100]Burgers vectors, as well as combinations of these. In general, all dislocations are dissociated. The subgrain boundaries observed are { hkO} tilt boundaries with [001] tilt axis. The planar faults produced by dissociation of [001], [010] and <111> dislocations in augite are stacking faults (SFs) on (100), (010) and {110}, respectively, that of {1}/{2}<112> and <101> dislocations are chain multiplicity faults (CMFs) on (010). The planar faults produced in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3834291','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3834291"><span id="translatedtitle">Molecular <span class="hlt">Mechanisms</span> of Gonadotropin-Releasing Hormone Signaling: Integrating <span class="hlt">Cyclic</span> Nucleotides into the Network</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Perrett, Rebecca M.; McArdle, Craig A.</p> <p>2013-01-01</p> <p>Gonadotropin-releasing hormone (GnRH) is the primary regulator of mammalian reproductive function in both males and females. It acts via G-protein coupled receptors on gonadotropes to stimulate synthesis and secretion of the gonadotropin hormones luteinizing hormone and follicle-stimulating hormone. These receptors couple primarily via G-proteins of the Gq/ll family, driving activation of phospholipases C and mediating GnRH effects on gonadotropin synthesis and secretion. There is also good evidence that GnRH causes activation of other heterotrimeric G-proteins (Gs and Gi) with consequent effects on <span class="hlt">cyclic</span> AMP production, as well as for effects on the soluble and particulate guanylyl cyclases that generate cGMP. Here we provide an overview of these pathways. We emphasize <span class="hlt">mechanisms</span> underpinning pulsatile hormone signaling and the possible interplay of GnRH and autocrine or paracrine regulatory <span class="hlt">mechanisms</span> in control of <span class="hlt">cyclic</span> nucleotide signaling. PMID:24312080</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JMEP...19.1005T','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JMEP...19.1005T"><span id="translatedtitle">Effect of <span class="hlt">Cyclic</span> Aging on <span class="hlt">Mechanical</span> Properties and Microstructure of Maraging Steel 250</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Tariq, Fawad; Naz, Nausheen; Baloch, Rasheed Ahmed</p> <p>2010-10-01</p> <p>The effects of thermal <span class="hlt">cyclic</span> aging on <span class="hlt">mechanical</span> properties and microstructure of maraging steel 250 were studied using hardness tester, tensile testing machine, impact tester, optical, scanning electron, and stereo microscopy. Samples were solution annealed at 1093 K for 1 h followed by air cooling to form bcc martensite. <span class="hlt">Cyclic</span> aging treatments were carried out at 753 and 773 K for varying time periods. Increase in hardness and strength with corresponding decrease in ductility and impact strength was observed with increasing aging cycles. Reverted austenite was detected by x-ray diffraction technique formed as a result of <span class="hlt">cyclic</span> aging. The presence of reverted γ was also confirmed by EDX-SEM analysis and attributed to the formation of Mo- and Ni-rich regions which transformed to γ on cooling. Heterogeneity in composition and amount of reverted γ was found to increase with increase in aging cycles and aging time. Fractography reveals the change in fracture mode from ductile dimple-like to brittle cleavage with increase in hardness and strength due to <span class="hlt">cyclic</span> aging.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=20040141407&hterms=cattle&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dcattle','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=20040141407&hterms=cattle&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dcattle"><span id="translatedtitle"><span class="hlt">Mechanical</span> control of <span class="hlt">cyclic</span> AMP signalling and gene transcription through integrins</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Meyer, C. J.; Alenghat, F. J.; Rim, P.; Fong, J. H.; Fabry, B.; Ingber, D. E.</p> <p>2000-01-01</p> <p>This study was carried out to discriminate between two alternative hypotheses as to how cells sense <span class="hlt">mechanical</span> forces and transduce them into changes in gene transcription. Do cells sense <span class="hlt">mechanical</span> signals through generalized membrane distortion or through specific transmembrane receptors, such as integrins? Here we show that <span class="hlt">mechanical</span> stresses applied to the cell surface alter the <span class="hlt">cyclic</span> AMP signalling cascade and downstream gene transcription by modulating local release of signals generated by activated integrin receptors in a G-protein-dependent manner, whereas distortion of integrins in the absence of receptor occupancy has no effect.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998APS..MAR.U3834H&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1998APS..MAR.U3834H&link_type=ABSTRACT"><span id="translatedtitle"><span class="hlt">Deformation</span> and Fracture <span class="hlt">Mechanisms</span> of Polymer-Silicate Nanocomposites</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Harcup, Jason; Yee, Albert</p> <p>1998-03-01</p> <p>The <span class="hlt">deformation</span> and fracture behavior of a series of nanocomposites comprising polyamide, silicate and in some cases rubber has been studied. <span class="hlt">Mechanical</span> properties including Young modulus and fracture toughness were measured and it was found that compared to conventional composites, the nanocomposites exhibited far greater improvement in properties over the neat matrix for a given silicate fraction. It was also found that the addition of the rubber phase produced an increase in toughness. The arrested crack tip process zone was obtained using the Double Notch Four Point Bend test geometry and the process zone morphology was studied using TEM and TOM. Fracture surfaces were probed with XEDS and SEM. The use of these techniques enabled the <span class="hlt">mechanisms</span> which occur during fracture to be studied and related to the <span class="hlt">mechanical</span> properties and toughening of these materials.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/21362167','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/21362167"><span id="translatedtitle">A <span class="hlt">deformation</span> quantization theory for noncommutative quantum <span class="hlt">mechanics</span></span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Costa Dias, Nuno; Prata, Joao Nuno; Gosson, Maurice de; Luef, Franz</p> <p>2010-07-15</p> <p>We show that the <span class="hlt">deformation</span> quantization of noncommutative quantum <span class="hlt">mechanics</span> previously considered by Dias and Prata ['Weyl-Wigner formulation of noncommutative quantum <span class="hlt">mechanics</span>', J. Math. Phys. 49, 072101 (2008)] and Bastos, Dias, and Prata ['Wigner measures in non-commutative quantum <span class="hlt">mechanics</span>', e-print arXiv:math-ph/0907.4438v1; Commun. Math. Phys. (to appear)] can be expressed as a Weyl calculus on a double phase space. We study the properties of the star-product thus defined and prove a spectral theorem for the star-genvalue equation using an extension of the methods recently initiated by de Gosson and Luef ['A new approach to the *-genvalue equation', Lett. Math. Phys. 85, 173-183 (2008)].</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/83356','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/83356"><span id="translatedtitle">Rheology and <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> of an isotropic mica schist</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Shea, W.T.; Kronenberg, A.K.</p> <p>1992-10-10</p> <p>The authors have investigated the transitional, semibrittle <span class="hlt">deformation</span> of a mica schist ({approximately} 75% biotite) by shortening cylinders cored at 0{degrees}, 45{degrees}, and 90{degrees} to foliation to varying strains, at confining pressures P{sub c} to 500 MPa, constant strain rates {epsilon} from 1.5 x 10{sup {minus}7} to 1.6 x 10{sup {minus}4} s{sup {minus}1}, and temperatures T from 25{degrees} to 400{degrees}C. <span class="hlt">Deformation</span> is concentrated within one or more throughgoing, millimeter-wide shear zones at all conditions; these localize at low strains ({epsilon} < 2%) through the nucleation and coalescence of dense sets of intragranular microkink bands (MKBs). Despite distinct differences in the relative number of mica grains oriented favorably for slip and kinking in different loading directions, the differential stresses required for shear zone development vary little with fabric orientation. Biotite schist undergoes a transition from strain-softening to steady strength <span class="hlt">mechanical</span> response at confining pressures in the range 75 to 150 MPa. The pressure sensitivity of strength (characterized by the slope {mu} of the Mohr envelope) decreases from {mu} {approximately} 0.5 (at P{sub c} < 100 MPa) to {mu} < 0.1 at pressures greater than 200 MPa, reflecting the increasing contribution of glide and kinking in biotite at higher pressures. However, dilatancy associated with microcracking and void formation along MKB boundaries persists to at least 500 MPa. Application of the results to crustal <span class="hlt">deformation</span> suggests that mica-rich aggregates are weaker than other common rock types throughout a broad midcrustal depth range, supporting the inference that retrograde reaction to phyllosilicates may be important in localizing crustal <span class="hlt">deformations</span> within large faults and shear zones. 111 refs., 24 figs., 4 tabs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFMMR41A2340D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFMMR41A2340D"><span id="translatedtitle">Significance of grain sliding <span class="hlt">mechanisms</span> for ductile <span class="hlt">deformation</span> of rocks</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dimanov, A.; Bourcier, M.; Gaye, A.; Héripré, E.; Bornert, M.; Raphanel, J.; Ludwig, W.</p> <p>2013-12-01</p> <p>Ductile shear zones at depth present polyphase and heterogeneous rocks and multi-scale strain localization patterns. Most strain concentrates in ultramylonitic layers, which exhibit microstructural signatures of several concomitant <span class="hlt">deformation</span> <span class="hlt">mechanisms</span>. The latter are either active in volume (dislocation creep), or in the vicinity and along interfaces (grain sliding and solution mass transfer). Because their chronology of appearance and interactions are unclear, inference of the overall rheology seems illusory. We have therefore characterized over a decade the rheology of synthetic lower crustal materials with different compositions and fluid contents, and for various microstructures. Non-Newtonian flow clearly related to dominant dislocation creep. Conversely, Newtonian behavior involved grain sliding <span class="hlt">mechanisms</span>, but crystal plasticity could be identified as well. In order to clarify the respective roles of these <span class="hlt">mechanisms</span> we underwent a multi-scale investigation of the ductile <span class="hlt">deformation</span> of rock analog synthetic halite with controlled microstructures. The <span class="hlt">mechanical</span> tests were combined with in-situ optical microscopy, scanning electron microscopy and X ray computed tomography, allowing for digital image correlation (DIC) techniques and retrieval of full strain field. Crystal plasticity dominated, as evidenced by physical slip lines and DIC computed slip bands. Crystal orientation mapping allowed to identify strongly active easy glide {110} <110> systems. But, all other slip systems were observed as well, and especially near interfaces, where their activity is necessary to accommodate for the plastic strain incompatibilities between neighboring grains. We also evidenced grain boundary sliding (GBS), which clearly occurred as a secondary, but necessary, accommodation <span class="hlt">mechanism</span>. The DIC technique allowed the quantification of the relative contribution of each <span class="hlt">mechanism</span>. The amount of GBS clearly increased with decreasing grain size. Finite element (FE) modeling</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..16.5556K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..16.5556K"><span id="translatedtitle">Welding of Pyroclastic Conduit Infill: A <span class="hlt">Mechanism</span> for <span class="hlt">Cyclical</span> Explosive Eruptions</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kolzenburg, Stephan; Russell, James K.</p> <p>2014-05-01</p> <p>Vulcanian style eruptions are small to moderate sized singular to <span class="hlt">cyclical</span> events commonly having volcanic explosivity indices (VEI) of 1-3. They produce pyroclastic flows, disperse tephra over considerable areas and can occur as precursors to larger (e.g. Plinian) eruptions. Here we present a study on the evolution of the physical properties (strain, porosity, permeability and ultrasonic wave velocities) of breadcrust bombs recovered from the deposits of the 2350 B.P. eruption of Mt Meager, BC, Canada. These accessory lithics are fragments of welded intra vent deposits formed during compaction and <span class="hlt">deformation</span> processes operating in the shallow (less than 2 km) conduit. The <span class="hlt">deformation</span> experienced by these samples is a combination of compaction within the conduit and post-compaction stretching associated with the subsequent eruption. Our results highlight a profound directionality in the measured physical properties of these samples related to the <span class="hlt">deformation</span>-induced fabric. Gas permeability varies drastically with increasing strain and decreasing porosity along the compaction direction of the fabric. However, permeability varies little along the elongation direction of the fabric. Similarly, ultrasonic wave velocities increase along the compaction direction and remain unaffected along the direction of fabric stretching; Poisons ratio increases along the fabric stretching direction. We combine these physical property measurements with models describing the timescales of porosity loss and to explore the timescales of permeability reduction and re-pressurization of the edifice. Modelling results and reconstruction of the <span class="hlt">deformation</span> history also suggest the potential for a low-cost technique for monitoring the pressure build-up within volcanic systems based on fumarolic activity.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4430365','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4430365"><span id="translatedtitle"><span class="hlt">Cyclic</span> <span class="hlt">mechanical</span> loading promotes bacterial penetration along composite restoration marginal gaps</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Khvostenko, D.; Salehi, S.; Naleway, S. E.; Hilton, T. J.; Ferracane, J. L.; Mitchell, J. C.; Kruzic, J. J.</p> <p>2015-01-01</p> <p>Objectives Secondary caries is the most common reason for composite restoration replacement and usually forms between dentin and the filling. The objective of this study was to investigate the combined effect of <span class="hlt">cyclic</span> loading and bacterial exposure on bacterial penetration into gaps at the interface between dentin and resin composite restorative material using a novel bioreactor system and test specimen design. Methods Human molars were machined into 3 mm thick disks with 2 mm deep × 5 mm diameter cavity preparations into which composite restorations were placed. A ∼15-30 micrometer (small) or ∼300 micrometer wide (large) dentin-restoration gap was introduced along half of the interface between the dentin and restoration. Streptococcus mutans UA 159 biofilms were grown on each sample prior to testing in a bioreactor both with and without <span class="hlt">cyclic</span> loading. Both groups of samples were tested for 2 weeks and post-test biofilm viability was confirmed with a live-dead assay. Samples were fixed, mounted and cross-sectioned to reveal the gaps and observe the depth of bacterial penetration. Results It was shown that for large gap samples the bacteria easily penetrated to the full depth of the gap independent of loading or non-loading conditions. The results for all <span class="hlt">cyclically</span> loaded small gap samples show a consistently deep bacterial penetration down 100% of the gap while the average penetration depth was only 67% for the non-loaded samples with only two of six samples reaching 100%. Significance A new bioreactor was developed that allows combining <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> loading and bacterial exposure of restored teeth for bacterial biofilm and demineralization studies. <span class="hlt">Cyclic</span> loading was shown to aid bacterial penetration into narrow marginal gaps, which could ultimately promote secondary caries formation. PMID:25900624</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22412962','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22412962"><span id="translatedtitle"><span class="hlt">Deformation</span> <span class="hlt">mechanisms</span> of Cu nanowires with planar defects</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Tian, Xia Yang, Haixia; Wan, Rui; Cui, Junzhi; Yu, Xingang</p> <p>2015-01-21</p> <p>Molecular dynamics simulations are used to investigate the <span class="hlt">mechanical</span> behavior of Cu nanowires (NWs) with planar defects such as grain boundaries (GBs), twin boundaries (TBs), stacking faults (SFs), etc. To investigate how the planar defects affect the <span class="hlt">deformation</span> and fracture <span class="hlt">mechanisms</span> of naowires, three types of nanowires are considered in this paper: (1) polycrystalline Cu nanowire; (2) single-crystalline Cu nanowire with twin boundaries; and (3) single-crystalline Cu nanowire with stacking faults. Because of the large fraction of atoms at grain boundaries, the energy of grain boundaries is higher than that of the grains. Thus, grain boundaries are proved to be the preferred sites for dislocations to nucleate. Moreover, necking and fracture prefer to occur at the grain boundary interface owing to the weakness of grain boundaries. For Cu nanowires in the presence of twin boundaries, it is found that twin boundaries can strength nanowires due to the restriction of the movement of dislocations. The pile up of dislocations on twin boundaries makes them rough, inducing high energy in twin boundaries. Hence, twin boundaries can emit dislocations, and necking initiates at twin boundaries. In the case of Cu nanowires with stacking faults, all pre-existing stacking faults in the nanowires are observed to disappear during <span class="hlt">deformation</span>, giving rise to a fracture process resembling the samples without stacking fault.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JNuM..423..110S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JNuM..423..110S"><span id="translatedtitle">Creep <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> in modified 9Cr-1Mo steel</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shrestha, Triratna; Basirat, Mehdi; Charit, Indrajit; Potirniche, Gabriel P.; Rink, Karl K.; Sahaym, Uttara</p> <p>2012-04-01</p> <p>Modified 9Cr-1Mo (Grade 91) steel is currently considered as a candidate material for reactor pressure vessels (RPVs) and reactor internals for the Very High Temperature Reactor (VHTR). The tensile creep behavior of modified 9Cr-1Mo steel (Grade 91) was studied in the temperature range of 873-1023 K and stresses between 35 MPa and 350 MPa. Analysis of creep results yielded stress exponents of ∼9-11 in the higher stress regime and ∼1 in the lower stress regime. The high stress exponent in the power-law creep regime was rationalized by invoking the concept of threshold stress, which represents the lattice diffusion controlled dislocation climb process. Without threshold stress compensation, the activation energy was 510 ± 51 kJ/mol, while after correcting for the threshold stress, the activation energy decreased to 225 ± 24 kJ/mol. This value is close to the activation energy for lattice self-diffusion in α-Fe. Threshold stress calculations were performed for the high stress regime at all test temperatures. The calculated threshold stress showed a strong dependence on temperature. The creep behavior of Grade 91 steel was described by the modified Bird-Mukherjee-Dorn relation. The rate controlling creep <span class="hlt">deformation</span> <span class="hlt">mechanism</span> in the high stress regime was identified as the edge dislocation climb with a stress exponent of n = 5. On the other hand, the <span class="hlt">deformation</span> <span class="hlt">mechanism</span> in the Newtonian viscous creep regime (n = 1) was identified as the Nabarro-Herring creep.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012SPIE.8252E..0NK&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012SPIE.8252E..0NK&link_type=ABSTRACT"><span id="translatedtitle">Miniature non-<span class="hlt">mechanical</span> zoom camera using <span class="hlt">deformable</span> MOEMS mirrors</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kaylor, Brant M.; Wilson, Christopher R.; Greenfield, Nathan J.; Roos, Peter A.; Seger, Eric M.; Moghimi, Mohammad J.; Dickensheets, David L.</p> <p>2012-03-01</p> <p>We present a miniature non-<span class="hlt">mechanical</span> zoom camera using <span class="hlt">deformable</span> MOEMS mirrors. Bridger Photonics, Inc. (Bridger) in collaboration with Montana State University (MSU), has developed electrostatically actuated <span class="hlt">deformable</span> MEMS mirrors for use in compact focus control and zoom imaging systems. Applications including microscopy, endomicroscopy, robotic surgery and cell-phone cameras. In comparison to conventional systems, our MEMS-based designs require no <span class="hlt">mechanically</span> moving parts. Both circular and elliptical membranes are now being manufactured at the wafer level and possess excellent optical surface quality (membrane flatness < λ/4). The mirror diameters range from 1 - 4 mm. For membranes with a 25 μm air gap, the membrane stroke is 10 μm. In terms of the optical design, the mirrors are considered variable power optical elements. A device with 2 mm diameter and 10 μm stroke can vary its optical power over 40 diopters or 0.04mm∧(-1). Equivalently, this corresponds to a focal length ranging from infinity to 25 mm. We have designed and demonstrated a zoom system using two MOEMS elements and exclusively commercial off-the-shelf optical components to achieve an optical zoom of 1.9x with a 15° full field of view. The total optical track length of the system is 36 mm. The design is approximately 30 mm x 30 mm x 20 mm including the optomechanical housing and image sensor. With custom optics, we anticipate achieving form factors that are compatible with incorporation into cell phones.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015SPIE.9677E..0WD','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015SPIE.9677E..0WD"><span id="translatedtitle">Distributed <span class="hlt">deformation</span> measurement of large space deployable <span class="hlt">mechanism</span> based on FBG sensors</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dong, Yanfang; Zhou, Zude; Liu, Yi; Liu, Mingyao; Li, Ruiya; Li, Tianliang</p> <p>2015-10-01</p> <p>Space deployable <span class="hlt">mechanisms</span> are widely used, important and multi-purpose components in aerospace fields. In order to ensure the <span class="hlt">mechanism</span> in normal situation after unfolded, detecting the <span class="hlt">deformation</span> caused by huge temperature difference in real-time is necessary. This paper designed a deployable <span class="hlt">mechanism</span> setup, completed its distributed <span class="hlt">deformation</span> measurement by means of fiber Bragg grating (FBG) sensors and BP neural network, proved the <span class="hlt">mechanism</span> distributed strain takes place sequence and FBG sensor is capable for space deployable <span class="hlt">mechanisms</span> <span class="hlt">deformation</span> measuring.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014MS%26E...62a2028W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014MS%26E...62a2028W"><span id="translatedtitle">Tensile <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> of ABS/PMMA/EMA blends</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, S. H.; Gao, J.; Lin, S. X.; Zhang, P.; Huang, J.; Xu, L. L.</p> <p>2014-08-01</p> <p>The tensile <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> of acrylonitrile - butadiene - styrene (ABS) / polymethyl methacrylate (PMMA) blends toughened by ethylene methacrylate (EMA) copolymer was investigated by analysing the fracture morphology. ABS/PMMA was blended with EMA copolymer by melt mixing technique using co-rotating twin extruder. Tensile tests show that the elongation at break of ABS/PMMA blends can be efficiently improved with the increase in EMA content. Fracture morphology of ABS/PMMA/EMA blends reveals that the material yield induced by hollowing-out of EMA particles and its propagation into yield zone is the main toughening <span class="hlt">mechanism</span>. Moreover, the appearance that EMA particles in the central area are given priority to hollowing-out may be related to the skin-core structure of the injection moulded parts caused by the different cooling rate between surface and inside in the process of injection moulding.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_7");'>7</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li class="active"><span>9</span></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_9 --> <div id="page_10" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="181"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/14715680','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/14715680"><span id="translatedtitle">Mathematical modeling of airway epithelial wound closure during <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> strain.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Savla, Ushma; Olson, Lars E; Waters, Christopher M</p> <p>2004-02-01</p> <p>The repair of airway epithelium after injury is crucial in restoring epithelial barrier integrity. Because the airways are stretched and compressed due to changes in both circumferential and longitudinal dimensions during respiration and may be overdistended during <span class="hlt">mechanical</span> ventilation, we investigated the effect of <span class="hlt">cyclic</span> strain on the repair of epithelial wounds. Both <span class="hlt">cyclic</span> elongation and compression significantly slowed repair, with compression having the greatest effect. We developed a mathematical model of the <span class="hlt">mechanisms</span> involved in airway epithelial cell wound closure. The model focuses on the differences in spreading, migration, and proliferation with <span class="hlt">cyclic</span> strain by using separate parameters for each process and incorporating a time delay for the mitotic component. Numerical solutions of model equations determine the shape of the diffusive wave solutions of cell density that correspond to the influx of cells into the wound during the initial phase of reepithelialization. Model simulations were compared with experimental measurements of cell density and the rate of wound closure, and parameters were determined based on measurements from airway epithelial cells from several different sources. The contributions of spreading, migration, and mitosis were investigated both numerically and experimentally by using cytochalasin D to inhibit cell motility and mitomycin C to inhibit proliferation. PMID:14715680</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PhDT.......120K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PhDT.......120K"><span id="translatedtitle">EBSD characterization of low temperature <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> in modern alloys</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kozmel, Thomas S., II</p> <p></p> <p>For structural applications, grain refinement has been shown to enhance <span class="hlt">mechanical</span> properties such as strength, fatigue resistance, and fracture toughness. Through control of the thermos-<span class="hlt">mechanical</span> processing parameters, dynamic recrystallization <span class="hlt">mechanisms</span> were used to produce microstructures consisting of sub-micron grains in 9310 steel, 4140 steel, and Ti-6Al-4V. In both 9310 and 4140 steel, the distribution of carbides throughout the microstructure affected the ability of the material to dynamically recrystallize and determined the size of the dynamically recrystallized grains. Processing the materials at lower temperatures and higher strain rates resulted in finer dynamically recrystallized grains. Microstructural process models that can be used to estimate the resulting microstructure based on the processing parameters were developed for both 9310 and 4140 steel. Heat treatment studies performed on 9310 steel showed that the sub-micron grain size obtained during <span class="hlt">deformation</span> could not be retained due to the low equilibrium volume fraction of carbides. Commercially available aluminum alloys were investigated to explain their high strain rate <span class="hlt">deformation</span> behavior. Alloys such as 2139, 2519, 5083, and 7039 exhibit strain softening after an ultimate strength is reached, followed by a rapid degradation of <span class="hlt">mechanical</span> properties after a critical strain level has been reached. Microstructural analysis showed that the formation of shear bands typically preceded this rapid degradation in properties. Shear band boundary misorientations increased as a function of equivalent strain in all cases. Precipitation behavior was found to greatly influence the microstructural response of the alloys. Additionally, precipitation strengthened alloys were found to exhibit similar flow stress behavior, whereas solid solution strengthened alloys exhibited lower flow stresses but higher ductility during dynamic loading. Schmid factor maps demonstrated that shear band formation behavior</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/17112531','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/17112531"><span id="translatedtitle"><span class="hlt">Mechanics</span> and <span class="hlt">deformation</span> of the nucleus in micropipette aspiration experiment.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Vaziri, Ashkan; Mofrad, Mohammad R Kaazempur</p> <p>2007-01-01</p> <p>Robust biomechanical models are essential for the study of nuclear <span class="hlt">mechanics</span> and <span class="hlt">deformation</span> and can help shed light on the underlying <span class="hlt">mechanisms</span> of stress transition in nuclear elements. Here, we develop a computational model for an isolated nucleus undergoing micropipette aspiration. Our model includes distinct components representing the nucleoplasm and nuclear envelope. The nuclear envelope itself comprises three layers: inner and outer nuclear membranes and one thicker layer representing the nuclear lamina. The nucleoplasm is modeled as a viscoelastic Maxwell material with a single time constant, while a modified Maxwell model, equivalent to a spring and a dashpot in series and both in parallel with a spring, is adopted for the inner and outer nuclear membranes. The nuclear envelope layer is taken as a linear elastic material. The proposed computational model, validated using experimental observations of Guilak et al. [2000. Viscoelastic properties of the cell nucleus. Biochemical and Biophysical Research Communications 269, 781-786] and Deguchi et al. [2005, Flow-induced hardening of endothelial nucleus as an intracellular stress-bearing organelle. Journal of Biomechanics 38, 1751-1759], is employed to study nuclear <span class="hlt">mechanics</span> and <span class="hlt">deformation</span> in micropipette aspiration and to shed light on the contribution of individual nuclear components on the response. The results indicate that the overall response of an isolated nucleus in micropipette aspiration is highly sensitive to the apparent stiffness of the nuclear lamina. This observation suggests that micropipette aspiration is an effective technique for examining the influence of various kinds of alteration in the nuclear lamina, such as mutations in the gene encoding lamin A, and also structural remodeling due to <span class="hlt">mechanical</span> perturbation. PMID:17112531</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1160164','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1160164"><span id="translatedtitle">Investigating <span class="hlt">Deformation</span> and Failure <span class="hlt">Mechanisms</span> in Nanoscale Multilayer Metallic Composites</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Zbib, Hussein M; Bahr, David F</p> <p>2014-10-22</p> <p>Over the history of materials science there are many examples of materials discoveries that have made superlative materials; the strongest, lightest, or toughest material is almost always a goal when we invent new materials. However, often these have been a result of enormous trial and error approaches. A new methodology, one in which researchers design, from the atoms up, new ultra-strong materials for use in energy applications, is taking hold within the science and engineering community. This project focused on one particular new classification of materials; nanolaminate metallic composites. These materials, where two metallic materials are intimately bonded and layered over and over to form sheets or coatings, have been shown over the past decade to reach strengths over 10 times that of their constituents. However, they are not yet widely used in part because while extremely strong (they don’t permanently bend), they are also not particularly tough (they break relatively easily when notched). Our program took a coupled approach to investigating new materials systems within the laminate field. We used computational materials science to explore ways to institute new <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> that occurred when a tri-layer, rather than the more common bi-layer system was created. Our predictions suggested that copper-nickel or copper-niobium composites (two very common bi-layer systems) with layer thicknesses on the order of 20 nm and then layered 100’s of times, would be less tough than a copper-nickel-niobium metallic composite of similar thicknesses. In particular, a particular mode of permanent <span class="hlt">deformation</span>, cross-slip, could be activated only in the tri-layer system; the crystal structure of the other bi-layers would prohibit this particular mode of <span class="hlt">deformation</span>. We then experimentally validated this predication using a wide range of tools. We utilized a DOE user facility, the Center for Integrated Nanotechnology (CINT), to fabricate, for the first time, these</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1073049','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1073049"><span id="translatedtitle">STATISTICAL <span class="hlt">MECHANICS</span> MODELING OF MESOSCALE <span class="hlt">DEFORMATION</span> IN METALS</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Anter El-Azab</p> <p>2013-04-08</p> <p>The research under this project focused on a theoretical and computational modeling of dislocation dynamics of mesoscale <span class="hlt">deformation</span> of metal single crystals. Specifically, the work aimed to implement a continuum statistical theory of dislocations to understand strain hardening and cell structure formation under monotonic loading. These aspects of crystal <span class="hlt">deformation</span> are manifestations of the evolution of the underlying dislocation system under <span class="hlt">mechanical</span> loading. The project had three research tasks: 1) Investigating the statistical characteristics of dislocation systems in <span class="hlt">deformed</span> crystals. 2) Formulating kinetic equations of dislocations and coupling these kinetics equations and crystal <span class="hlt">mechanics</span>. 3) Computational solution of coupled crystal <span class="hlt">mechanics</span> and dislocation kinetics. Comparison of dislocation dynamics predictions with experimental results in the area of statistical properties of dislocations and their field was also a part of the proposed effort. In the first research task, the dislocation dynamics simulation method was used to investigate the spatial, orientation, velocity, and temporal statistics of dynamical dislocation systems, and on the use of the results from this investigation to complete the kinetic description of dislocations. The second task focused on completing the formulation of a kinetic theory of dislocations that respects the discrete nature of crystallographic slip and the physics of dislocation motion and dislocation interaction in the crystal. Part of this effort also targeted the theoretical basis for establishing the connection between discrete and continuum representation of dislocations and the analysis of discrete dislocation simulation results within the continuum framework. This part of the research enables the enrichment of the kinetic description with information representing the discrete dislocation systems behavior. The third task focused on the development of physics-inspired numerical methods of solution of the coupled</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MMTA..tmp..199P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MMTA..tmp..199P"><span id="translatedtitle">Effects of Crack Closure and <span class="hlt">Cyclic</span> <span class="hlt">Deformation</span> on Thermomechanical Fatigue Crack Growth of a Near α Titanium Alloy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Prasad, Kartik; Kumar, Vikas; Bhanu Sankara Rao, K.; Sundararaman, M.</p> <p>2016-04-01</p> <p>In this study, closure corrected in-phase (IP) and out-of-phase (OP) thermomechanical fatigue crack growth rates at two temperature intervals viz. 573 K to 723 K (300 °C to 450 °C) and 723 K to 873 K (450 °C to 600 °C) of Timetal 834 near α titanium alloy are presented. It is found that closure <span class="hlt">mechanisms</span> significantly influence the stage I crack growth behavior. Surface roughness-induced crack closure (RICC) predominantly modifies the crack growth rate of near-threshold region at 573 K to 723 K (300 °C to 450 °C) test conditions. However, oxide-induced crack closure further strengthens RICC at 723 K to 873 K (450 °C to 600 °C) TMF loading. In stage II crack growth behavior, the alloy shows higher crack growth rates at 723 K to 873 K (450 °C to 600 °C) OP-TMF loading which is attributed to the combined effect of <span class="hlt">cyclic</span> hardening occurring at the crack tip and weakening of interlamellar regions due to oxidation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MMTA...47.3713P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MMTA...47.3713P"><span id="translatedtitle">Effects of Crack Closure and <span class="hlt">Cyclic</span> <span class="hlt">Deformation</span> on Thermomechanical Fatigue Crack Growth of a Near α Titanium Alloy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Prasad, Kartik; Kumar, Vikas; Bhanu Sankara Rao, K.; Sundararaman, M.</p> <p>2016-07-01</p> <p>In this study, closure corrected in-phase (IP) and out-of-phase (OP) thermomechanical fatigue crack growth rates at two temperature intervals viz. 573 K to 723 K (300 °C to 450 °C) and 723 K to 873 K (450 °C to 600 °C) of Timetal 834 near α titanium alloy are presented. It is found that closure <span class="hlt">mechanisms</span> significantly influence the stage I crack growth behavior. Surface roughness-induced crack closure (RICC) predominantly modifies the crack growth rate of near-threshold region at 573 K to 723 K (300 °C to 450 °C) test conditions. However, oxide-induced crack closure further strengthens RICC at 723 K to 873 K (450 °C to 600 °C) TMF loading. In stage II crack growth behavior, the alloy shows higher crack growth rates at 723 K to 873 K (450 °C to 600 °C) OP-TMF loading which is attributed to the combined effect of <span class="hlt">cyclic</span> hardening occurring at the crack tip and weakening of interlamellar regions due to oxidation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012PhDT........20J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012PhDT........20J"><span id="translatedtitle"><span class="hlt">Deformation</span> <span class="hlt">mechanisms</span> in nanoscale single crystalline electroplated copper pillars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Jennings, Andrew T.</p> <p></p> <p>Scientific research in nanotechnology has enabled advances in a diverse range of applications, such as: electronics, chemical sensing, and cancer treatment. In order to transition these nanotechnology-driven innovations out of the laboratory and into real-world applications, the resilience and <span class="hlt">mechanical</span> reliability of nanoscale structures must be well understood in order to preserve functionality under real-world operating environments. Understanding the <span class="hlt">mechanical</span> properties of nanoscale materials is especially important because several authors have shown that single crystalline metal pillars produced through focused-ion-beam milling have unique properties when the pillar diameter, D, approaches nanotechnology-relevant dimensions. The strength, sigma, of these pillars is size-dependent and is well described through a power-law relation showing that smaller is stronger: sigma∝D-n , where n is the exponent and is found to be 0.5≤n≤1.0 in face-centered-cubic metals. In this work, the fundamental <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> governing the size-dependent <span class="hlt">mechanical</span> properties are investigated through uniaxial compression and tension tests of electroplated single crystalline copper pillars with diameters between 75 nm and 1000 nm. At larger pillar diameters, D >125 nm, these copper pillars are shown to obey a similar size-dependent regime, demonstrating that the "smaller is stronger" phenomenon is a function of the pillar microstructure, as opposed to the fabrication route. Furthermore, the dominant dislocation <span class="hlt">mechanism</span> in this size-dependent regime is shown to be the result of single-arm, or spiral, sources. At smaller pillar diameters, D≤125 nm, a strain-rate-dependent <span class="hlt">mechanism</span> transition is observed through both the size-strength relation and also quantitative, experimental measures of the activation volume. This new <span class="hlt">deformation</span> regime is characterized by a size-independent strength and is governed by surface dislocation nucleation, a thermally activated</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004APS..MARJ21002R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004APS..MARJ21002R"><span id="translatedtitle">Molecular <span class="hlt">mechanisms</span> of <span class="hlt">deformation</span> and failure in glassy materials</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rottler, Joerg</p> <p>2004-03-01</p> <p>Understanding the molecular origins of macroscopic <span class="hlt">mechanical</span> properties is a fundamental scientific challenge. Fracture of both amorphous and crystalline materials involves many length scales reaching from the continuum to atomic level processes near a crack tip. Using molecular simulations of simple models for amorphous glassy materials, we first study elastoplastic <span class="hlt">deformation</span> and discuss the nature of the shear yield stress and its dependence on loading conditions, strain rate and temperature. We then focus on the <span class="hlt">deformation</span> of glassy polymeric systems into crazes at large strains. In the craze, polymers ( 0.5 nm diameter) are bundled into an intricate network of 10 nm diameter fibrils that extends 10 micrometers on either side of a mm crack tip. Analysis of local geometry and stresses provide insight into the real-space nature of the entanglements that control craze formation as well as melt dynamics. Crazes are also shown to share many features with jammed systems such as granular media and foams, but are unique in jamming under a tensile load. This allows explanations for the exponential force distribution in jammed systems to be tested. The force distribution strongly influences the ultimate breakdown of the craze fibrils either through disentanglement or chain scission. We conclude by quantifying the contribution of crazing to the unusually large fracture energy of glassy polymers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008SMaS...17d5025W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008SMaS...17d5025W"><span id="translatedtitle">Structural integrity and failure <span class="hlt">mechanisms</span> of a smart piezoelectric actuator under a <span class="hlt">cyclic</span> bending mode</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Woo, Sung-Choong; Goo, Nam Seo</p> <p>2008-08-01</p> <p>Information on the onset and evolution of damage within materials is essential for guaranteeing the integrity of actuator systems. The authors have evaluated the structural integrity and the failure <span class="hlt">mechanisms</span> of smart composite actuators with a PZT ceramic plate under electric <span class="hlt">cyclic</span> loading. For this, two kinds of actuators, actuator 1 and actuator 2, were manufactured. Prior to the main testing, performance testing was performed on the actuators to determine their resonant frequencies. Electric <span class="hlt">cyclic</span> tests were conducted up to twenty million cycles. An acoustic emission technique was used for monitoring the damage evolution in real time. We observed the extent of the damage after testing using scanning electron microscopy and reflected optical microscopy to support characteristics in the acoustic emission behavior that corresponded to specific types of damage <span class="hlt">mechanisms</span>. It was shown that the initial damage <span class="hlt">mechanism</span> of the smart composite actuator under electric <span class="hlt">cyclic</span> loading originated from the transgranular micro-fatigue damage in the PZT ceramic layer. With increasing cycles, a local intergranular crack initiated and developed onto the surface of the PZT ceramic layer or propagated into the internal layer. Finally, short-circuiting led to the electric breakdown of the actuator. These results were different depending on the drive frequencies and the configuration of the actuators. Moreover, we differentiated between the aforementioned damage <span class="hlt">mechanisms</span> via AE signal pattern analyses based on the primary frequency and the waveform. From our results, we conclude that the drive frequency and the existence of a protecting layer are dominant factors in the structural integrity of the smart composite actuator.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020061832','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020061832"><span id="translatedtitle"><span class="hlt">Cyclic</span> Failure <span class="hlt">Mechanisms</span> of Thermal and Environmental Barrier Coating Systems Under Thermal Gradient Test Conditions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Zhu, Dongming; Lee, Kang N.; Miller, Robert A.</p> <p>2002-01-01</p> <p>Plasma-sprayed ZrO2-8wt%Y2O3 and mullite+BSAS/Si multilayer thermal and environmental barrier coating (TBC-EBC) systems on SiC/SiC ceramic matrix composite (CMC) substrates were thermally <span class="hlt">cyclic</span> tested under high thermal gradients using a laser high-heat-flux rig in conjunction with furnace exposure in water-vapor environments. Coating sintering and interface damage were assessed by monitoring the real-time thermal conductivity changes during the laser heat-flux tests and by examining the microstructural changes after exposure. Sintering kinetics of the coating systems were also independently characterized using a dilatometer. It was found that the coating failure involved both the time-temperature dependent sintering and the cycle frequency dependent <span class="hlt">cyclic</span> fatigue processes. The water vapor environments not only facilitated the initial coating conductivity increases due to enhanced sintering and interface reaction, but also promoted later conductivity reductions due to the accelerated coating cracking and delamination. The failure <span class="hlt">mechanisms</span> of the coating systems are also discussed based on the <span class="hlt">cyclic</span> test results and are correlated to the sintering and thermal stress behavior under the thermal gradient test conditions.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/22003897','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/22003897"><span id="translatedtitle">Theoretical studies on the heats of formation, detonation properties, and pyrolysis <span class="hlt">mechanisms</span> of energetic <span class="hlt">cyclic</span> nitramines.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Wang, Fang; Wang, Guixiang; Du, Hongchen; Zhang, Jianying; Gong, Xuedong</p> <p>2011-12-01</p> <p>Density functional theory calculations were performed to find comprehensive relationships between the structures and performance of a series of highly energetic <span class="hlt">cyclic</span> nitramines. The isodesmic reaction method was employed to estimate the heat of formation. The detonation properties were evaluated by using the Kamlet-Jacobs equations based on the theoretical densities and HOFs. Results indicate the N-NO(2) group and aza N atom are effective substituents for enhancing the detonation performance. All <span class="hlt">cyclic</span> nitramines except C11 and C21 exhibit better detonation performance than HMX. The decomposition <span class="hlt">mechanism</span> and thermal stability of these <span class="hlt">cyclic</span> nitramines were analyzed via the bond dissociation energies. For most of these nitramines, the homolysis of N-NO(2) is the initial step in the thermolysis, and the species with the bridged N-N bond are more sensitive than others. Considering the detonation performance and thermal stability, twelve derivatives may be the promising candidates of high energy density materials (HEDMs). The results of this study may provide basic information for the further study of this kind of compounds and molecular design of novel HEDMs. PMID:22003897</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4564076','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4564076"><span id="translatedtitle"><span class="hlt">Cyclic</span> <span class="hlt">mechanical</span> stretch promotes energy metabolism in osteoblast-like cells through an mTOR signaling-associated <span class="hlt">mechanism</span></span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>ZENG, ZHAOBIN; JING, DA; ZHANG, XIAODONG; DUAN, YINZHONG; XUE, FENG</p> <p>2015-01-01</p> <p>Energy metabolism is essential for maintaining function and substance metabolism in osteoblasts. However, the role of <span class="hlt">cyclic</span> stretch in regulating osteoblastic energy metabolism and the underlying <span class="hlt">mechanisms</span> remain poorly understood. In this study, we found that <span class="hlt">cyclic</span> stretch (10% elongation at 0.1 Hz) significantly enhanced glucose consumption, lactate levels (determined using a glucose/lactate assay kit), intracellular adenosine triphosphate (ATP) levels (quantified using rLuciferase/Luciferin reagent) and the mRNA expression of energy metabolism-related enzymes [mitochondrial ATP synthase, L-lactate dehydrogenase A (LDHA) and enolase 1; measured by RT-qPCR], and increased the phosphorylation levels of Akt, mammalian target of rapamycin (mTOR) and p70s6k (measured by western blot analysis) in human osteoblast-like MG-63 cells. Furthermore, the inhibition of Akt or mTOR with an antagonist (wortmannin or rapamycin) suppressed the stretch-induced increase in glucose consumption, lactate levels, intracellular ATP levels and the expression of mitochondrial ATP synthase and LDHA, indicating the significance of the Akt/mTOR/p70s6k pathway in regulating osteoblastic energy metabolism in response to <span class="hlt">mechanical</span> stretch. Thus, we concluded that <span class="hlt">cyclic</span> stretch regulates energy metabolism in MG-63 cells partially through the Akt/mTOR/p70s6k signaling pathway. The present findings provide novel insight into osteoblastic mechanobiology from the perspective of energy metabolism. PMID:26251974</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25474149','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/25474149"><span id="translatedtitle">Structure, dynamics and implied gating <span class="hlt">mechanism</span> of a human <span class="hlt">cyclic</span> nucleotide-gated channel.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Gofman, Yana; Schärfe, Charlotta; Marks, Debora S; Haliloglu, Turkan; Ben-Tal, Nir</p> <p>2014-12-01</p> <p><span class="hlt">Cyclic</span> nucleotide-gated (CNG) ion channels are nonselective cation channels, essential for visual and olfactory sensory transduction. Although the channels include voltage-sensor domains (VSDs), their conductance is thought to be independent of the membrane potential, and their gating regulated by cytosolic <span class="hlt">cyclic</span> nucleotide-binding domains. Mutations in these channels result in severe, degenerative retinal diseases, which remain untreatable. The lack of structural information on CNG channels has prevented mechanistic understanding of disease-causing mutations, precluded structure-based drug design, and hampered in silico investigation of the gating <span class="hlt">mechanism</span>. To address this, we built a 3D model of the cone tetrameric CNG channel, based on homology to two distinct templates with known structures: the transmembrane (TM) domain of a bacterial channel, and the <span class="hlt">cyclic</span> nucleotide-binding domain of the mouse HCN2 channel. Since the TM-domain template had low sequence-similarity to the TM domains of the CNG channels, and to reconcile conflicts between the two templates, we developed a novel, hybrid approach, combining homology modeling with evolutionary coupling constraints. Next, we used elastic network analysis of the model structure to investigate global motions of the channel and to elucidate its gating <span class="hlt">mechanism</span>. We found the following: (i) In the main mode of motion, the TM and cytosolic domains counter-rotated around the membrane normal. We related this motion to gating, a proposition that is supported by previous experimental data, and by comparison to the known gating <span class="hlt">mechanism</span> of the bacterial KirBac channel. (ii) The VSDs could facilitate gating (supplementing the pore gate), explaining their presence in such 'voltage-insensitive' channels. (iii) Our elastic network model analysis of the CNGA3 channel supports a modular model of allosteric gating, according to which protein domains are quasi-independent: they can move independently, but are coupled to each</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4398456','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=4398456"><span id="translatedtitle">Evidence for a Novel <span class="hlt">Mechanism</span> of Antimicrobial Action of a <span class="hlt">Cyclic</span> R-,W-Rich Hexapeptide</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Scheinpflug, Kathi; Krylova, Oxana; Nikolenko, Heike; Thurm, Charley; Dathe, Margitta</p> <p>2015-01-01</p> <p>The development of antimicrobial peptides as new class of antibiotic agents requires structural characterisation and understanding of their diverse <span class="hlt">mechanisms</span> of action. As the <span class="hlt">cyclic</span> hexapeptide cWFW (cyclo(RRRWFW)) does not exert its rapid cell killing activity by membrane permeabilisation, in this study we investigated alternative <span class="hlt">mechanisms</span> of action, such as peptide translocation into the cytoplasm and peptide interaction with components of the phospholipid matrix of the bacterial membrane. Using fluorescence microscopy and an HPLC-based strategy to analyse peptide uptake into the cells we could confirm the cytoplasmic membrane as the major peptide target. However, unexpectedly we observed accumulation of cWFW at distinct sites of the membrane. Further characterisation of peptide-membrane interaction involved live cell imaging to visualise the distribution of the lipid cardiolipin (CL) and isothermal titration calorimetry to determine the binding affinity to model membranes with different bacterial lipid compositions. Our results demonstrate a distribution of the <span class="hlt">cyclic</span> peptide similar to that of cardiolipin within the membrane and highly preferred affinity of cWFW for CL-rich phosphatidylethanolamine (POPE) matrices. These observations point to a novel <span class="hlt">mechanism</span> of antimicrobial killing for the <span class="hlt">cyclic</span> hexapeptide cWFW which is neither based on membrane permeabilisation nor translocation into the cytoplasm but rather on preferred partitioning into particular lipid domains. As the phospholipids POPE/CL play a key role in the dynamic organisation of bacterial membranes we discuss the consequences of this peptide-lipid-interaction and outline the impact on antimicrobial peptide research. PMID:25875357</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=20020033735&hterms=pure+individual&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dpure%2Bindividual','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=20020033735&hterms=pure+individual&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dpure%2Bindividual"><span id="translatedtitle"><span class="hlt">Deformation</span> and Tensile <span class="hlt">Cyclic</span> Fatigue of Plasma-Sprayed ZrO2-8wt% Y2O3 Thermal Barrier Coatings</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Choi, Sung R.; Zhu, Dong-Ming; Miller, Robert A.</p> <p>2001-01-01</p> <p><span class="hlt">Deformation</span> (constitutive relations) of free-standing, thick thermal barrier coatings of sprayed ZrO2-8Wt% Y2O3 was determined at ambient temperature in both pure tension and pure compression using cylindrical bar test specimens. The material exhibited both significant nonlinearity and hysteresis in its load-strain curves, The load-strain relations in four-point uniaxial flexure were determined from tension and compression sides and were compared with individual pure tension and compression constitutive data. Effect of sintering on <span class="hlt">deformation</span> behavior was significant, resulting in a dramatic change in constitutive relation. <span class="hlt">Cyclic</span> fatigue testing of the coating material in tension-tension at room temperature showed an insignificant susceptibility to fatigue, similar to the slow crack growth behavior of the material in flexure in 800 C air.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012AGUFMMR51A..04P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012AGUFMMR51A..04P"><span id="translatedtitle"><span class="hlt">Deformation</span> <span class="hlt">mechanisms</span> of antigorite and strain localization during dehydration</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Proctor, B.; Hirth, G.</p> <p>2012-12-01</p> <p>Antigorite, the high temperature and pressure serpentine polytype, is thought to exist along subduction zones between the mantle wedge and the subducting oceanic crust (e.g., Wada et al., 2008). Understanding how the rheology of antigorite changes with depth along the slab may be key to understanding seismicity along the upper plate boundary (e.g., Hacker et al., 2003). To explore this phenomenon we are conducting constant strain rate general shear experiments on antigorite-rich serpentinite at shear strain rates of 5*10^-7/s to 10^-5/s, confining pressures from 1-2 GPa and temperatures from 400-700°C. We are using microstructural observations to constrain <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> and investigate conditions where strain localization occurs. In some experiments we employ either strain rate stepping or temperature ramping to examine the stress dependence of viscosity (i.e., determine stress exponent) and syntectonic reaction during heating. The results of our general shear experiments suggest the rheologic behavior of antigorite varies significantly with changes in temperature and pressure, similar to previous work in axial compression (e.g., Chernak and Hirth, 2010). At 400°C and 1GPa confining pressure antigorite <span class="hlt">deforms</span> initially via steady-state ductile flow with strengths as high as 1.4 GPa at a strain rate of 10^-5/s. With increasing strain we observe weakening events that correlate with the development of shear fractures within the sample. At 2GPa pressure, the flow strength of antigorite increases to ~1.8 GPa at 10^-6/s and <span class="hlt">deformation</span> is distributed at low strain. Strain rate stepping at these conditions suggests a very weak strain rate dependence on strength with a 5-10% change in stress for an order of magnitude strain rate step. At 700C and 1 GPa, above the thermal stability of antigorite, the steady-state strength is ~120 MPa at 10^-5/s. In these samples olivine becomes the dominant phase as antigorite progressively reacts to olivine and pyroxene. At the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2808707','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=2808707"><span id="translatedtitle"><span class="hlt">Mechanism</span> of <span class="hlt">Cyclic</span> Dye Regeneration During Eosin-Sensitized Photoinitiation in the Presence of Polymerization Inhibitors</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Avens, Heather J.; Bowman, Christopher N.</p> <p>2009-01-01</p> <p>A visible light photoinitiator, eosin, in combination with a tertiary amine coinitiator is found to initiate polymerization despite the presence of at least 1000-fold excess dissolved oxygen which functions as an inhibitor of radical polymerizations. Additionally, 0.4 µM eosin is able to overcome 100-fold excess (40 µM) 2,2,6,6-Tetramethyl-1-piperidinyloxy (TEMPO) inhibitor, initiating polymerization after only a 2 minute inhibition period. In contrast, 40 µM Irgacure-2959, a standard cleavage-type initiator, is unable to overcome even an equivalent amount of inhibitor (40 µM TEMPO). Through additional comparisons of these two initiation systems, a reaction <span class="hlt">mechanism</span> is developed which is consistent with the kinetic data and provides an explanation for eosin’s relative insensitivity to oxygen, TEMPO and other inhibitors. A <span class="hlt">cyclic</span> <span class="hlt">mechanism</span> is proposed in which semi-reduced eosin radicals react by disproportionation with radical inhibitors and radical intermediates in the inhibition process to regenerate eosin and effectively consume inhibitor. In behavior similar to that of eosin, rose bengal, fluorescein, and riboflavin are also found to initiate polymerization despite the presence of excess TEMPO, indicating that <span class="hlt">cyclic</span> regeneration likely enhances the photoinitiation kinetics of many dye photosensitizers. Selection of such dye initiation systems constitutes a valuable strategy for alleviating inhibitory effects in radical polymerizations. PMID:20098667</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22212283','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22212283"><span id="translatedtitle"><span class="hlt">Cyclic</span> <span class="hlt">mechanical</span> strain maintains Nanog expression through PI3K/Akt signaling in mouse embryonic stem cells</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Horiuchi, Rie; Akimoto, Takayuki; Hong, Zhang; Ushida, Takashi</p> <p>2012-08-15</p> <p><span class="hlt">Mechanical</span> strain has been reported to affect the proliferation/differentiation of many cell types; however, the effects of mechanotransduction on self-renewal as well as pluripotency of embryonic stem (ES) cells remains unknown. To investigate the effects of <span class="hlt">mechanical</span> strain on mouse ES cell fate, we examined the expression of Nanog, which is an essential regulator of self-renewal and pluripotency as well as Nanog-associated intracellular signaling during uniaxial <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> strain. The mouse ES cell line, CCE was plated onto elastic membranes, and we applied 10% strain at 0.17 Hz. The expression of Nanog was reduced during ES cell differentiation in response to the withdrawal of leukemia inhibitory factor (LIF); however, two days of <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> strain attenuated this reduction of Nanog expression. On the other hand, the <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> strain promoted PI3K-Akt signaling, which is reported as an upstream of Nanog transcription. The <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> strain-induced Akt phosphorylation was blunted by the PI3K inhibitor wortmannin. Furthermore, cytochalasin D, an inhibitor of actin polymerization, also inhibited the <span class="hlt">mechanical</span> strain-induced increase in phospho-Akt. These findings imply that <span class="hlt">mechanical</span> force plays a role in regulating Nanog expression in ES cells through the actin cytoskeleton-PI3K-Akt signaling. -- Highlights: Black-Right-Pointing-Pointer The expression of Nanog, which is an essential regulator of 'stemness' was reduced during embryonic stem (ES) cell differentiation. Black-Right-Pointing-Pointer <span class="hlt">Cyclic</span> <span class="hlt">mechanical</span> strain attenuated the reduction of Nanog expression. Black-Right-Pointing-Pointer <span class="hlt">Cyclic</span> <span class="hlt">mechanical</span> strain promoted PI3K-Akt signaling and <span class="hlt">mechanical</span> strain-induced Akt phosphorylation was blunted by the PI3K inhibitor and an inhibitor of actin polymerization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/15804809','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/15804809"><span id="translatedtitle">Theoretical predictions of chemical degradation reaction <span class="hlt">mechanisms</span> of RDX and other <span class="hlt">cyclic</span> nitramines derived from their molecular structures.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Qasim, M; Fredrickson, H; McGrath, C; Furey, J; Bajpai, R</p> <p>2005-06-01</p> <p>Analysis of environmental degradation pathways of contaminants is aided by predictions of likely reaction <span class="hlt">mechanisms</span> and intermediate products derived from computational models of molecular structure. Quantum <span class="hlt">mechanical</span> methods and force-field molecular <span class="hlt">mechanics</span> were used to characterize <span class="hlt">cyclic</span> nitramines. Likely degradation <span class="hlt">mechanisms</span> for hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) include hydroxylation utilizing addition of hydroxide ions to initiate proton abstraction via 2nd order rate elimination (E2) or via nucleophilic substitution of nitro groups, reductive chemical and biochemical degradation, and free radical oxidation. Due to structural similarities, it is predicted that, under homologous circumstances, certain RDX environmental degradation pathways should also be effective for octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and similar <span class="hlt">cyclic</span> nitramines. Computational models provided a theoretical framework whereby likely transformation <span class="hlt">mechanisms</span> and transformation products of <span class="hlt">cyclic</span> nitramines were predicted and used to elucidate in situ degradation pathways. PMID:15804809</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_8");'>8</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li class="active"><span>10</span></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_10 --> <div id="page_11" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="201"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/1179294','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/1179294"><span id="translatedtitle"><span class="hlt">Deformation</span> and Failure <span class="hlt">Mechanisms</span> of Shape Memory Alloys</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Daly, Samantha Hayes</p> <p>2015-04-15</p> <p>The goal of this research was to understand the fundamental <span class="hlt">mechanics</span> that drive the <span class="hlt">deformation</span> and failure of shape memory alloys (SMAs). SMAs are difficult materials to characterize because of the complex phase transformations that give rise to their unique properties, including shape memory and superelasticity. These phase transformations occur across multiple length scales (one example being the martensite-austenite twinning that underlies macroscopic strain localization) and result in a large hysteresis. In order to optimize the use of this hysteretic behavior in energy storage and damping applications, we must first have a quantitative understanding of this transformation behavior. Prior results on shape memory alloys have been largely qualitative (i.e., mapping phase transformations through cracked oxide coatings or surface morphology). The PI developed and utilized new approaches to provide a quantitative, full-field characterization of phase transformation, conducting a comprehensive suite of experiments across multiple length scales and tying these results to theoretical and computational analysis. The research funded by this award utilized new combinations of scanning electron microscopy, diffraction, digital image correlation, and custom testing equipment and procedures to study phase transformation processes at a wide range of length scales, with a focus at small length scales with spatial resolution on the order of 1 nanometer. These experiments probe the basic connections between length scales during phase transformation. In addition to the insights gained on the fundamental <span class="hlt">mechanisms</span> driving transformations in shape memory alloys, the unique experimental methodologies developed under this award are applicable to a wide range of solid-to-solid phase transformations and other strain localization <span class="hlt">mechanisms</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/960886','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/960886"><span id="translatedtitle">Precipitation under <span class="hlt">cyclic</span> strain in solution-treated Al4wt%Cu I: <span class="hlt">mechanical</span> behavior</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Farrow, Adam M; Laird, Campbell</p> <p>2008-01-01</p> <p>Solution-treated AL-4wt%Cu was strain-cycled at ambient temperature and above, and the precipitation and <span class="hlt">deformation</span> behaviors investigated by TEM. Anomalously rapid growth of precipitates appears to have been facilitated by a vacancy super-saturation generated by <span class="hlt">cyclic</span> strain and the presence of a continually refreshed dislocation density to provide heterogeneous nucleation sites. Texture effects as characterized by Orientation Imaging Microscopy appear to be responsible for latent hardening in specimens tested at room temperature, with increasing temperatures leading to a gradual hardening throughout life due to precipitation. Specimens exhibiting rapid precipitation hardening appear to show a greater effect of texture due to the increased stress required to cut precipitates in specimens machined from rolled plate at an angle corresponding to a lower average Schmid factor. The accelerated formation of grain boundary precipitates appears to be partially responsible for rapid inter-granular fatigue failure at elevated temperatures, producing fatigue striations and ductile dimples coexistent on the fracture surface.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=207529','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=207529"><span id="translatedtitle"><span class="hlt">Mechanism</span> of action of <span class="hlt">cyclic</span> beta-1,2-glucan synthetase from Agrobacterium tumefaciens: competition between cyclization and elongation reactions.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Williamson, G; Damani, K; Devenney, P; Faulds, C B; Morris, V J; Stevens, B J</p> <p>1992-01-01</p> <p>We have examined some aspects of the <span class="hlt">mechanism</span> of <span class="hlt">cyclic</span> beta-1,2-glucan synthetase from Agrobacterium tumefaciens (235-kDa protein, gene product of the chvB region). The enzyme produces <span class="hlt">cyclic</span> beta-1,2-glucans containing 17 to 23 glucose residues from UDP-glucose. In the presence of added <span class="hlt">cyclic</span> beta-1,2-glucans (> 0.5 mg/ml) (containing 17 to 23 glucose residues), the enzyme instead synthesizes larger <span class="hlt">cyclic</span> beta-1,2-glucans containing 24 to 30 glucose residues. This is achieved by de novo synthesis and not by disproportion reactions with the added product. This is interpreted as inhibition of the specific cyclization reaction for the synthesis of <span class="hlt">cyclic</span> beta-1,2-glucans containing 17 to 23 glucose residues but with no concomitant effect on the elongation (polymerization) reaction. Temperature and detergents both affect the distribution of sizes of <span class="hlt">cyclic</span> beta-1,2-glucans, but glucans containing 24 to 30 glucose residues are not produced. We suggest that the size distribution of <span class="hlt">cyclic</span> beta-1,2-glucan products depends on competing elongation and cyclization reactions. PMID:1459942</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012JMEP...21.2255W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012JMEP...21.2255W"><span id="translatedtitle">A True-Stress Creep Model Based on <span class="hlt">Deformation</span> <span class="hlt">Mechanisms</span> for Polycrystalline Materials</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wu, Xijia; Williams, Steve; Gong, Diguang</p> <p>2012-11-01</p> <p>A true-stress creep model has been developed based on well-recognized <span class="hlt">deformation</span> <span class="hlt">mechanisms</span>, i.e., dislocation glide, dislocation climb, and grain boundary sliding. The model provides a physics-based description of the entire creep <span class="hlt">deformation</span> process with regards to the strain-time history (primary, secondary, and tertiary creep), rupture strain and lifetime, which finds good agreement with experimental observations for Waspaloy. A <span class="hlt">deformation-mechanism</span> map is constructed for Waspaloy, and a creep failure criterion is defined by the dominant <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> leading to intergranular/transgranular fracture. Thus, the model is a self-consistent tool for creep life prediction.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011PMag...91.1070D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011PMag...91.1070D"><span id="translatedtitle"><span class="hlt">Deformation</span> <span class="hlt">mechanisms</span> in gold nanowires and nanoporous gold</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dou, R.; Derby, B.</p> <p>2011-03-01</p> <p>We present a study of the <span class="hlt">deformation</span> of gold nanowires of diameter 30-70 nm and nanoporous gold specimens with ligament diameter 5-10 nm, both produced by electrodeposition into anodised aluminium oxide templates. The nanowires show extensive surface slip steps and low dislocation densities with a few perfect dislocation loops, Shockley partial dislocations and microtwins observed after <span class="hlt">deformation</span>. Nanoporous specimens show <span class="hlt">deformation</span> localised to the nodes between the ligaments of the foamed structure, with high densities of microtwins and Shockley partial dislocations in these regions. Similar dislocation structures are seen in larger nanowires <span class="hlt">deformed</span> in bending. This is shown to be consistent with a strain gradient plasticity model for the <span class="hlt">deformation</span> of nanoporous gold, with the strain gradient accommodated by geometrically necessary twins and partial dislocations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015PIAHS.372..231C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015PIAHS.372..231C"><span id="translatedtitle">Study of the <span class="hlt">deformation</span> <span class="hlt">mechanism</span> of the Gaoliying ground fissure</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cheng, G.; Wang, H.; Luo, Y.; Guo, H.</p> <p>2015-11-01</p> <p>The Gaoliying ground fissure in Beijing has caused building cracking and road damage, and has seriously influenced city construction. Based on investigations and trenching, the influences of the fault and the variation of groundwater levels on the formation <span class="hlt">mechanism</span> of the Gaoliying ground fissure were investigated by using FLAC3D. The results indicated that (1) the surface location of Gaoliying fissure is controlled by the underlying normal fault activity, and over pumping further exacerbates development of the ground fissure; (2) when the groundwater level declines, obvious differential settlement occurs at both sides of the ground fissure, in which greater settlement occurs in the vicinity of the hanging wall, the greater the distance from the hanging wall, the smaller the ground subsidence, however smaller ground subsidence occurs in the vicinity of the footwall, the greater the distance from the footwall, the greater the ground subsidence; (3) the vertical velocity of the ground fissure triggered by the fault activity and groundwater decline ranges from 15.5 to 18.3 mm a-1, which is basically in line with the monitoring data. The fault activity contributes about 28-39 %, and the groundwater contributes about 61-72 % to the <span class="hlt">deformation</span> of the ground fissure, respectively.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012SPIE.8409E..31Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012SPIE.8409E..31Y"><span id="translatedtitle">Molecular modelling of structure and <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> of auxetic behaviour in the α-quartz structures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yao, Yong Tao; Alderson, Andrew; Alderson, Kim Lesley</p> <p>2012-04-01</p> <p>Force field based simulation has been employed to predict the <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> of auxetic nano-materials having tetrahedral framework. The structure of α-quartz was studied in detail for subjecting to uniaxial loading along the Z direction. The cooperative dilation and rotation of tetrahedra acting concurrently were demonstrated to be the main <span class="hlt">deformation</span> <span class="hlt">mechanism</span> of α-quartz, confirming previous analytical model. Slight tetrahedral distortion also existed for undeformed and <span class="hlt">deformed</span> structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011SPIE.8409E..31Y','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011SPIE.8409E..31Y"><span id="translatedtitle">Molecular modelling of structure and <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> of auxetic behaviour in the α-quartz structures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Yao, Yong Tao; Alderson, Andrew; Alderson, Kim Lesley</p> <p>2011-11-01</p> <p>Force field based simulation has been employed to predict the <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> of auxetic nano-materials having tetrahedral framework. The structure of α-quartz was studied in detail for subjecting to uniaxial loading along the Z direction. The cooperative dilation and rotation of tetrahedra acting concurrently were demonstrated to be the main <span class="hlt">deformation</span> <span class="hlt">mechanism</span> of α-quartz, confirming previous analytical model. Slight tetrahedral distortion also existed for undeformed and <span class="hlt">deformed</span> structure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011AIPC.1315..303B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011AIPC.1315..303B"><span id="translatedtitle">FEA Based Tool Life Quantity Estimation of Hot Forging Dies Under <span class="hlt">Cyclic</span> Thermo-<span class="hlt">Mechanical</span> Loads</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Behrens, B.-A.; Bouguecha, A.; Schäfer, F.; Hadifi, T.</p> <p>2011-01-01</p> <p>Hot forging dies are exposed during service to a combination of <span class="hlt">cyclic</span> thermo-<span class="hlt">mechanical</span>, tribological and chemical loads. Besides abrasive and adhesive wear on the die surface, fatigue crack initiation with subsequent fracture is one of the most frequent causes of failure. In order to extend the tool life, the finite element analysis (FEA) may serve as a means for process design and process optimisation. So far the FEA based estimation of the production cycles until initial cracking is limited as tool material behaviour due to repeated loading is not captured with the required accuracy. Material models which are able to account for <span class="hlt">cyclic</span> effects are not verified for the fatigue life predictions of forging dies. Furthermore fatigue properties from strain controlled fatigue tests of relevant hot work steels are to date not available to allow for a close-to-reality fatigue life prediction. Two industrial forging processes, where clear fatigue crack initiation has been observed are considered for a fatigue analysis. For this purpose the relevant tool components are modelled with elasto-plastic material behaviour. The predicted sites, where crack initiation occurs, agree with the ones observed on the real die component.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/1711631','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/1711631"><span id="translatedtitle">Dual <span class="hlt">mechanism</span> of the relaxing effect of nicorandil by stimulation of <span class="hlt">cyclic</span> GMP formation and by hyperpolarization.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kukovetz, W R; Holzmann, S; Braida, C; Pöch, G</p> <p>1991-04-01</p> <p>In addition to previous results from our laboratory showing that nicorandil relaxed vascular smooth muscle by increasing <span class="hlt">cyclic</span> GMP levels, it was shown to activate K-channels as well, an effect that also leads to relaxation. In the present study, we attempted to differentiate quantitatively between these two effects in isolated bovine coronary artery strips with simultaneous isotonic measurement of length and radioimmunoassay (RIA) determination of <span class="hlt">cyclic</span> GMP. When the strips were contracted by the thromboxane A2 analogue U 46619 (1 microM) with 10 microM methylene blue added, nicorandil produced 30-50% relaxation without significant changes in <span class="hlt">cyclic</span> GMP. When in U 46619-contracted strips the hyperpolarizing effect of nicorandil was suppressed by increasing extracellular K+ to 80.4 mM (30-fold), nicorandil caused only 52% relaxation, whereas <span class="hlt">cyclic</span> GMP increases were not significantly suppressed. Quantitative separation of both <span class="hlt">mechanisms</span> of relaxation by nicorandil was further achieved through calculation of the <span class="hlt">cyclic</span> GMP-mediated component from a correlation between increases in <span class="hlt">cyclic</span> GMP and percentage of relaxation as produced by nicorandil under conditions of inhibited hyperpolarization, i.e., in strips contracted with 1 microM U 46619 or 26.8 mM K+ (10-fold) and exposed to either 30-fold K+ or 10 mM Ba2+. Under both conditions, similar correlations between <span class="hlt">cyclic</span> GMP and relaxation were obtained. Because U 46619, in addition to its contractile effect, partially antagonized the relaxation by nicorandil without changing <span class="hlt">cyclic</span> GMP, the correlation was corrected for this effect and indicated a participation of <span class="hlt">cyclic</span> GMP in the overall relaxant response of approximately 30-40% at low and less than or equal to 80-90% at high concentrations of nicorandil. PMID:1711631</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Cryo...73...14W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Cryo...73...14W"><span id="translatedtitle"><span class="hlt">Mechanical</span> behaviors of multi-filament twist superconducting strand under tensile and <span class="hlt">cyclic</span> loading</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Xu; Li, Yingxu; Gao, Yuanwen</p> <p>2016-01-01</p> <p>The superconducting strand, serving as the basic unit cell of the cable-in-conduit-conductors (CICCs), is a typical multi-filament twist composite which is always subjected to a <span class="hlt">cyclic</span> loading under the operating condition. Meanwhile, the superconducting material Nb3Sn in the strand is sensitive to strain frequently relating to the performance degradation of the superconductivity. Therefore, a comprehensive study on the <span class="hlt">mechanical</span> behavior of the strand helps understanding the superconducting performance of the strained Nb3Sn strands. To address this issue, taking the LMI (internal tin) strand as an example, a three-dimensional structural finite element model, named as the Multi-filament twist model, of the strand with the real configuration of the LMI strand is built to study the influences of the plasticity of the component materials, the twist of the filament bundle, the initial thermal residual stress and the breakage and its evolution of the filaments on the <span class="hlt">mechanical</span> behaviors of the strand. The effective properties of superconducting filament bundle with random filament breakage and its evolution versus strain are obtained based on the damage theory of fiber-reinforced composite materials proposed by Curtin and Zhou. From the calculation results of this model, we find that the occurrence of the hysteresis loop in the <span class="hlt">cyclic</span> loading curve is determined by the reverse yielding of the elastic-plastic materials in the strand. Both the initial thermal residual stress in the strand and the pitch length of the filaments have significant impacts on the axial and hysteretic behaviors of the strand. The damage of the filaments also affects the axial <span class="hlt">mechanical</span> behavior of the strand remarkably at large axial strain. The critical current of the strand is calculated by the scaling law with the results of the Multi-filament twist model. The predicted results of the Multi-filament twist model show an acceptable agreement with the experiment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JSG....32..606C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JSG....32..606C"><span id="translatedtitle">Orientation-related <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> of naturally <span class="hlt">deformed</span> amphibole in amphibolite mylonites from the Diancang Shan, SW Yunnan, China</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cao, Shuyun; Liu, Junlai; Leiss, Bernd</p> <p>2010-05-01</p> <p>Sheared amphibolite rocks from Diancang Shan high-grade metamorphic complex along the Ailao Shan-Red River shear zone, southwestern Yunnan, China, show typical mylonitic microstructures. The mylonites are characterized by porphyroclastic microstructures and the ultramylonites are highly lineated with alternating amphibole- and quartzofeldspathic domains. Microstructural analysis and P/T estimation suggest that the amphibole grains in the mylonitic rocks are <span class="hlt">deformed</span> and dynamically recrystallized at amphibolite facies. In the mylonitic amphibolites, there are two types of amphibole porphyroclasts, i.e. type I "hard" and type II "soft" porphyroclasts. They have their [001] crystallographic orientations subnormal and sub-parallel to the stretching lineation of the rocks, respectively. The two types of porphyroclasts show distinct <span class="hlt">deformation</span> microstructures and sub-microstructures formed by various <span class="hlt">deformation</span> <span class="hlt">mechanisms</span>, which contribute in different ways to the generation of the fine-grained matrix. Shape preferred orientation analysis, misorientation analysis of the two types of porphyroclasts and new fine grains around them further prove the generation of the fine grains in matrix from the type II porphyroclasts. The type I "hard" porphyroclasts are <span class="hlt">deformed</span> mainly by <span class="hlt">mechanical</span> rotation, work hardening and intragranular microfracturing. In contrast, the <span class="hlt">deformation</span> of the type II "soft" porphyroclasts is mainly attributed to crystalline plasticity, i.e. twinning, dislocation creep and dynamic recrystallization. During the <span class="hlt">deformation</span> of the type II porphyroclasts, the (100) [001] slip system plays a dominant role during <span class="hlt">deformation</span> and grain size reduction of amphibole. Twinning along the active (100) slip system, in combination with dislocation creep (gliding and climbing) governs the nucleation of subgrains and formation of dynamically recrystallized fine grains, a process here named Twinning Nucleation Recrystallization.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5148420','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5148420"><span id="translatedtitle">Differences in responsiveness of intrapulmonary artery and vein to arachidonic acid: <span class="hlt">mechanism</span> of arterial relaxation involves <span class="hlt">cyclic</span> guanosine 3':5'-monophosphate and <span class="hlt">cyclic</span> adenosine 3':5'-monophosphate</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Ignarro, L.J.; Harbison, R.G.; Wood, K.S.; Wolin, M.S.; McNamara, D.B.; Hyman, A.L.; Kadowitz, P.J.</p> <p>1985-06-01</p> <p>The objective of this study was to examine the relationship between responses of bovine intrapulmonary artery and vein to arachidonic acid and <span class="hlt">cyclic</span> nucleotide levels in order to better understand the <span class="hlt">mechanism</span> of relaxation elicited by arachidonic acid and acetylcholine. Arachidonic acid relaxed phenylephrine-precontracted arterial rings and elevated both <span class="hlt">cyclic</span> GMP and <span class="hlt">cyclic</span> AMP levels in arteries with intact endothelium. In contrast, endothelium-damaged arterial rings contracted to arachidonic acid without demonstrating significant changes in <span class="hlt">cyclic</span> nucleotide levels. Indomethacin partially inhibited endothelium-dependent relaxation and abolished <span class="hlt">cyclic</span> AMP accumulation whereas methylene blue, a guanylate cyclase inhibitor, partially inhibited relaxation and abolished <span class="hlt">cyclic</span> GMP accumulation in response to arachidonic acid. All vessel responses were blocked by a combination of the two inhibitors. Prostaglandin (PG) I2 relaxed arterial rings and elevated <span class="hlt">cyclic</span> AMP levels whereas PGE2 and PGF2 alpha caused contraction, suggesting that the indomethacin-sensitive component of arachidonic acid-elicited relaxation is due to PGI2 formation and <span class="hlt">cyclic</span> AMP accumulation. The methylene blue-sensitive component is attributed to an endothelium-dependent but cyclooxygenase-independent generation of a substance causing <span class="hlt">cyclic</span> GMP accumulation. Intrapulmonary veins contracted to arachidonic acid with no changes in <span class="hlt">cyclic</span> nucleotide levels and PGI2 was without effect. Homogenates of intrapulmonary artery and vein formed 6-keto-PGF1 alpha, PGF2 alpha and PGE2 from (/sup 14/C)arachidonic acid, which was inhibited by indomethacin. Thus, bovine intrapulmonary vein may not possess receptors for PGI2.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/27007978','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/27007978"><span id="translatedtitle">Catalytic <span class="hlt">Mechanism</span> of Nitrile Hydratase Subsequent to <span class="hlt">Cyclic</span> Intermediate Formation: A QM/MM Study.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Kayanuma, Megumi; Shoji, Mitsuo; Yohda, Masafumi; Odaka, Masafumi; Shigeta, Yasuteru</p> <p>2016-04-01</p> <p>The catalytic <span class="hlt">mechanism</span> of an Fe-containing nitrile hydratase (NHase) subsequent to the formation of a <span class="hlt">cyclic</span> intermediate was investigated using a hybrid quantum <span class="hlt">mechanics</span>/molecular <span class="hlt">mechanics</span> (QM/MM) method. We identified the following <span class="hlt">mechanism</span>: (i) proton transfer from βTyr72 to the substrate via αSer113, and cleavage of the S-O bond of αCys114-SO(-) and formation of a disulfide bond between αCys109 and αCys114; (ii) direct attack of a water molecule on the sulfur atom of αCys114, which resulted in the generation of both an imidic acid and a renewed sulfenic cysteine; and (iii) isomerization of the imidic acid to the amide. In addition, to clarify the role of βArg56K, which is one of the essential amino residues in the enzyme, we analyzed a βR56K mutant in which βArg56 was replaced by Lys. The results suggest that βArg56 is necessary for the formation of disulfide intermediate by stabilizing the cleavage of the S-O bond via a hydrogen bond with the oxygen atom of αCys114-SO(-). PMID:27007978</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3881892','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3881892"><span id="translatedtitle">Load-bearing capacity of screw-retained CAD/CAM-produced titanium implant frameworks (I-Bridge®2) before and after <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> loading</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>DITTMER, Marc Philipp; NENSA, Moritz; STIESCH, Meike; KOHORST, Philipp</p> <p>2013-01-01</p> <p>Implant-supported screw-retained fixed dental prostheses (FDPs) produced by CAD/ CAM have been introduced in recent years for the rehabilitation of partial or total endentulous jaws. However, there is a lack of data about the long-term <span class="hlt">mechanical</span> characteristics. Objective The aim of this study was to investigate the failure mode and the influence of extended <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> loading on the load-bearing capacity of these frameworks. Material and Methods Ten five-unit FDP frameworks simulating a free-end situation in the mandibular jaw were manufactured according to the I-Bridge®2-concept (I-Bridge®2, Biomain AB, Helsingborg, Sweden) and each was screw-retained on three differently angulated Astra Tech implants (30º buccal angulation/0º angulation/30º lingual angulation). One half of the specimens was tested for static load-bearing capacity without any further treatment (control), whereas the other half underwent five million cycles of <span class="hlt">mechanical</span> loading with 100 N as the upper load limit (test). All specimens were loaded until failure in a universal testing machine with an occlusal force applied at the pontics. Load-displacement curves were recorded and the failure mode was macro- and microscopically analyzed. The statistical analysis was performed using a t-test (p=0.05). Results All the specimens survived <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> loading and no obvious failure could be observed. Due to the <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> loading, the load-bearing capacity decreased from 8,496 N±196 N (control) to 7,592 N±901 N (test). The <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> loading did not significantly influence the load-bearing capacity (p=0.060). The failure mode was almost identical in all specimens: large <span class="hlt">deformations</span> of the framework at the implant connection area were obvious. Conclusion The load-bearing capacity of the I-Bridge®2 frameworks is much higher than the clinically relevant occlusal forces, even with considerably angulated implants. However, the performance under functional loading in vivo</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011EL.....9627005Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011EL.....9627005Z"><span id="translatedtitle">NMR study on <span class="hlt">mechanisms</span> of ionic polymer-metal composites <span class="hlt">deformation</span> with water content</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhu, Zicai; Chen, Hualing; Wang, Yongquan; Luo, Bin; Chang, Longfei; Li, Bo; Chen, Luping</p> <p>2011-10-01</p> <p>Ionic polymer-metal composites (IPMCs) exhibit a large dynamic bending <span class="hlt">deformation</span> under exterior electric field. The states and proportions of water within the IPMCs have great effect on the IPMCs <span class="hlt">deformation</span> properties. This letter investigates the influence of the proportion changes of different types of water on the <span class="hlt">deformation</span>, which may disclose the working <span class="hlt">mechanisms</span> of the IPMCs. We give a <span class="hlt">deformation</span> trend of IPMCs with the reduction of water content firstly. Then by the method of nuclear magnetic resonance, various water types (water bonded to sulfonates, loosely bound water and free water) of IPMCs and their proportions are investigated in the drying process which corresponds to their different <span class="hlt">deformation</span> states. It is obtained that the <span class="hlt">deformation</span> properties of IPMCs depend strongly on their water content and the excess free water is responsible for the relaxation <span class="hlt">deformation</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016JOM...tmp..208V&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016JOM...tmp..208V&link_type=ABSTRACT"><span id="translatedtitle">Acoustic Emission as a Tool for Exploring <span class="hlt">Deformation</span> <span class="hlt">Mechanisms</span> in Magnesium and Its Alloys In Situ</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vinogradov, Alexei; Máthis, Kristian</p> <p>2016-06-01</p> <p>Structural performance of magnesium alloys depends strongly on specific <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> operating during <span class="hlt">mechanical</span> loading. Therefore, in situ monitoring of the acting <span class="hlt">mechanisms</span> is a key to performance tailoring. We review the capacity of the advanced acoustic emission (AE) technique to understand the interplay between two primary <span class="hlt">deformation</span> mechanisms—dislocation slip and twinning—in real time scale. Details of relative contributions of dislocation slip and <span class="hlt">deformation</span> twinning to the <span class="hlt">mechanical</span> response of pure Mg and Mg-Al alloy are discussed in view of AE results obtained with the aid of recently proposed spectral and signal categorization algorithms in conjunction with with neutron diffraction data.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3603568','PMC'); return false;" href="http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3603568"><span id="translatedtitle">Influence of <span class="hlt">Cyclic</span> <span class="hlt">Mechanical</span> Stretch and Tissue Constraints on Cellular and Collagen Alignment in Fibroblast-Derived Cell Sheets</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pmc">PubMed Central</a></p> <p>Weidenhamer, Nathan K.</p> <p>2013-01-01</p> <p><span class="hlt">Mechanical</span> forces play an important role in shaping the organization of the extracellular matrix (ECM) in developing and mature tissues. The resulting organization gives the tissue its unique functional properties. Understanding how <span class="hlt">mechanical</span> forces influence the alignment of the ECM is important in tissue engineering, where recapitulating the alignment of the native tissue is essential for appropriate <span class="hlt">mechanical</span> anisotropy. In this work, a novel method was developed to create and stretch tubular cell sheets by seeding neonatal dermal fibroblasts onto a rotating silicone tube. We show the fibroblasts proliferated to create a confluent monolayer around the tube and a collagenous, isotropic tubular tissue over 4 weeks of static culture. These silicone tubes with overlying tubular tissue constructs were mounted into a <span class="hlt">cyclic</span> distension bioreactor and subjected to <span class="hlt">cyclic</span> circumferential stretch at 5% strain, 0.5 Hz for 3 weeks. We found that the tissue subjected to <span class="hlt">cyclic</span> stretch compacted axially over the silicone tube in comparison to static controls, leading to a circumferentially aligned tissue with higher membrane stiffness and maximum tension. In a subsequent study, the tissue constructs were constrained against axial compaction during <span class="hlt">cyclic</span> stretching. The resulting alignment of fibroblasts and collagen was perpendicular (axial) to the stretch direction (circumferential). When the cells were devitalized with sodium azide before stretching, similarly constrained tissue did not develop strong axial alignment. This work suggests that both <span class="hlt">mechanical</span> stretching and <span class="hlt">mechanical</span> constraints are important in determining tissue organization, and that this organization is dependent on an intact cytoskeleton. PMID:23126441</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19840010642','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19840010642"><span id="translatedtitle">Influence of <span class="hlt">deformation</span> behavior, oxydation, and temperature on the long time <span class="hlt">cyclic</span> stress behavior of high temperature steels</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Maile, K.</p> <p>1982-01-01</p> <p>The influence of different parameters on the creep-fatigue behavior of several steel alloys was investigated. The higher the temperature the lower the crack initiation value. Pauses during the cycle reduce the damage. Oxidation reduces and protective gas increases the lifetime. Prior loading and prior <span class="hlt">deformation</span> reduce the lifetime. Short annealing slightly affects the cycle stress behavior. The test results do not satisfactorily agree with methods of extrapolation and damage accumulation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2014SMaS...23i5010W&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2014SMaS...23i5010W&link_type=ABSTRACT"><span id="translatedtitle"><span class="hlt">Mechanics</span> of dielectric elastomer-activated <span class="hlt">deformable</span> transmission grating</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Yin; Zhou, Jinxiong; Sun, Wenjie; Wu, Xiaohong; Zhang, Ling</p> <p>2014-09-01</p> <p>Laminating a thin layer of elastomeric grating on the surface of a prestretched dielectric elastomer (DE) membrane forms a basic design of electrically tunable transmission grating. We analyze the inhomogeneous <span class="hlt">deformation</span> of a circular multiple-region configuration. Variation of the geometric and material parameters, as well as of the critical condition determined by loss of tension instability, is probed to aid the design of a DE-based <span class="hlt">deformable</span> grating. The predicted changes in the grating period agree substantially with the experimental results reported by Aschwanden et al (Aschwanden et al 2007 IEEE Photon. Technol. Lett. 19 1090).</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li class="active"><span>11</span></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_11 --> <div id="page_12" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="221"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010JPhCS.241a2056L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010JPhCS.241a2056L"><span id="translatedtitle"><span class="hlt">Cyclic</span> <span class="hlt">deformation</span> and nano-contact adhesion of MEMS nano-bridges by in-situ TEM nanomechanical testing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lockwood, A. J.; Bobji, M. S.; Bunyan, R. J. T.; Inkson, B. J.</p> <p>2010-07-01</p> <p>MEMS nano-bridges fabricated by FIB have been <span class="hlt">deformed</span> in-situ in the TEM. The polysilicon bridges show high levels of flexibility but also, at increased indentation depths, residual plastic <span class="hlt">deformation</span> after fully unloading the bridges. Here, a significant number of cycles were applied to the centre of a bridge by a W-probe. This resulted in the formation of an adhesive contact with the W-probe. On unloading the nano-bridge regained its original shape and then <span class="hlt">deformed</span> upwards, adhered to the W-probe. A significant high tensile force of -17μN was required to sever the nano-contact. Analysis of the W-probe and polysilicon nano-bridge indicate that carbon migration along the W-probe and local contact heating due to the associated fatigue cycles were responsible for the adhesive bond, with initial carbon contamination layer on the W-probe of 2nm, thickening during the loading cycles to 25nm.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..1110039A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..1110039A"><span id="translatedtitle">Experimental <span class="hlt">Deformation</span> of Diopside Single Crystals at Mantle P and T: <span class="hlt">Mechanical</span> Data and <span class="hlt">Deformation</span> Microstructures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Amiguet, E.; Raterron, P.; Cordier, P.; Couvy, H.; Chen, J.</p> <p>2009-04-01</p> <p>Clinopyroxenes (cpx) are major constituents of eclogites and are present in excess of 10 vol.% at most depths in the pyrolitic upper mantle. Among mantle minerals, they exhibit the strongest anisotropy for seismic wave propagation. Cpx plastic properties may thus significantly affect both mantle rheology and seismic anisotropy. Yet, no study of cpx rheology at high-pressure (typically P > 3 GPa) has been reported so far, while recent developments in high-pressure <span class="hlt">deformation</span> devices coupled with synchrotron radiation allow now investigating the rheology of mantle minerals and aggregates at the extreme pressure and temperature (T) of their natural occurrence in the Earth. In order to investigate the effect of P on cpx rheology, steady state <span class="hlt">deformation</span> experiments were carried out on gem quality oriented diopside crystals in the <span class="hlt">Deformation</span>-DIA apparatus (D-DIA, see Wang et al., 2003, Rev. Scientific Instr., 74, 3002) that equipped the X17B2 beamline of the NSLS (Upton, NY, USA), at P ranging from 3.8 to 8.8 GPa, T in the range 1100˚ -1400˚ C, and with differential stress () ranging between 0.2 and 1.7 GPa. Three compression directions were chosen in order to activate either 1 •2 {1¯10} dislocation slip (duplex) systems together, or [100](010) and [010](100) systems together, or again [001] dislocation slip in (100), (010) and {110} planes. Constant and specimen strain rates (ɛ˙) were monitored in situ using time-resolved synchrotron X-ray diffraction and radiography, respectively. Transmission electron microscopy (TEM) investigation of the run products revealed that dislocation creep was responsible for sample <span class="hlt">deformation</span>. Comparison of the present high-P <span class="hlt">deformation</span> data with data obtained at room-P - on similar diopside crystals <span class="hlt">deformed</span> at comparable T- conditions (Raterron and Jaoul, 1991, JGR, 96, 14277) - allows quantifying the effect of P on the activity of 1 •2 {1¯10} duplex systems. This translates into an activation volume V * = 17 ± 6 cm</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/474160','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/474160"><span id="translatedtitle">Subcritical crack-growth behavior of borosilicate glass under <span class="hlt">cyclic</span> loads: Evidence of a <span class="hlt">mechanical</span> fatigue effect</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Dill, S.J.; Dauskardt, R.H.; Bennison, S.J.</p> <p>1997-03-01</p> <p>Amorphous glasses are generally considered immune to <span class="hlt">mechanical</span> fatigue effects associated with <span class="hlt">cyclic</span> loading. In this study surprising new evidence is presented for a <span class="hlt">mechanical</span> fatigue effect in borosilicate glass, in both moist air and dry nitrogen environments. The fatigue effect occurs at near threshold subcritical crack-growth rates (da/dt < 3 {times} 10{sup {minus}8} m/s) as the crack extension per cycle approaches the dimensions of the borosilicate glass network. While subcritical crack growth under <span class="hlt">cyclic</span> loads at higher load levels is entirely consistent with environmentally assisted crack growth, lower growth rates actually exceed those measured under monotonic loads. This suggests a <span class="hlt">mechanical</span> fatigue effect which accelerates subcritical crack-growth rates. Likely <span class="hlt">mechanisms</span> for the <span class="hlt">mechanical</span> fatigue effect are presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/5529140','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/5529140"><span id="translatedtitle"><span class="hlt">Mechanisms</span> for high-frequency <span class="hlt">cyclicity</span> in the Upper Jurassic limestone of northeastern Mexico</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Johnson, C.R.; Ward, W.C. ); Goldhammer, R.K. )</p> <p>1991-03-01</p> <p>The 520 m of Upper Jurassic Zuloaga Limestone exposed in the Sierra de Bunuelos in southern Coahuila comprise 118 cycles of peritidal carbonate rock deposited on a gently dipping ramp. Field studies with Fischer plots and time-series analysis suggest that a Milankovitchian glacioeustasy <span class="hlt">mechanism</span> is inadequate to describe the Zuloaga cycles. Autocyclic progradation may have been the major influence on depositional <span class="hlt">cyclicity</span>. Depositional cycles in the Zuloaga Formation typically are a few meters thick and asymmetric with subtidal wackestone and packstone grading upward into subtidal grainstone or into intertidal stromatolites. Width of the carbonate ramp is estimated to have been about 150 km. Sedimentation rates for these peritidal carbonate environments apparently exceeded subsidence rates inasmuch as most of the carbonate platform remained near sea level during Zuloaga deposition. The area was tectonically quiescent during the late Jurassic. Autocyclic shoreline progradation is a feasible <span class="hlt">mechanism</span> for producing the high-frequency cycles, as suggested by (1) poor correlation with predicted Milankovitch periodicity shown by time-series analysis, (2) little evidence of subaerial exposure, (3) development of complete peritidal cycles, (4) general progradational sequences within each third-order unit, and (5) absence of polar glaciation during Late Jurassic.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19990094229','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19990094229"><span id="translatedtitle"><span class="hlt">Cyclic</span> Cryogenic Thermal-<span class="hlt">Mechanical</span> Testing of an X-33/RLV Liquid Oxygen Tank Concept</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Rivers, H. Kevin</p> <p>1999-01-01</p> <p>An important step in developing a cost-effective, reusable, launch vehicle is the development of durable, lightweight, insulated, cryogenic propellant tanks. Current cryogenic tanks are expendable so most of the existing technology is not directly applicable to future launch vehicles. As part of the X-33/Reusable Launch Vehicle (RLV) Program, an experimental apparatus developed at the NASA Langley Research Center for evaluating the effects of combined, <span class="hlt">cyclic</span>, thermal and <span class="hlt">mechanical</span> loading on cryogenic tank concepts was used to evaluate cryogenic propellant tank concepts for Lockheed-Martin Michoud Space Systems. An aluminum-lithium (Al 2195) liquid oxygen tank concept, insulated with SS-1171 and PDL-1034 cryogenic insulation, is tested under simulated mission conditions, and the results of those tests are reported. The tests consists of twenty-five simulated Launch/Abort missions and twenty-five simulated flight missions with temperatures ranging from -320 F to 350 F and a maximum <span class="hlt">mechanical</span> load of 71,300 lb. in tension.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..1817733B&link_type=ABSTRACT','NASAADS'); return false;" href="http://adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2016EGUGA..1817733B&link_type=ABSTRACT"><span id="translatedtitle">Thermo-<span class="hlt">mechanical</span> modelling of <span class="hlt">cyclic</span> gas storage applications in salt caverns</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Böttcher, Norbert; Watanabe, Norihiro; Görke, Uwe-Jens; Kolditz, Olaf; Nagel, Thomas</p> <p>2016-04-01</p> <p>Due to the growing importance of renewable energy sources it becomes more and more necessary to investigate energy storage potentials. One major way to store energy is the power-to-gas concept. Excessive electrical energy can be used either to produce hydrogen or methane by electrolysis or methanation or to compress air, respectively. Those produced gases can then be stored in artificial salt caverns, which are constructed in large salt formations by solution mining. In combination with renewable energy sources, the power-to-gas concept is subjected to fluctuations. Compression and expansion of the storage gases lead to temperature differences within the salt rock. The variations can advance several metres into the host rock, influencing its material behaviour, inducing thermal stresses and altering the creep response. To investigate the temperature influence on the cavern capacity, we have developed a numerical model to simulate the thermo-<span class="hlt">mechanical</span> behaviour of salt caverns during <span class="hlt">cyclic</span> gas storage. The model considers the thermodynamic behaviour of the stored gases as well as the heat transport and the temperature dependent material properties of the host rock. Therefore, we utilized well-known constitutive thermo-visco-plastic material models, implemented into the open source-scientific software OpenGeoSys. Both thermal and <span class="hlt">mechanical</span> processes are solved using a finite element approach, connected via a staggered coupling scheme. The model allows the assessment of the structural safety as well as the convergence of the salt caverns.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1983stan.reptQ....N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983stan.reptQ....N"><span id="translatedtitle">Models for rupture <span class="hlt">mechanics</span> of plate boundaries and crustal <span class="hlt">deformation</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Nur, A.</p> <p>1983-02-01</p> <p>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 <span class="hlt">deformation</span>, and power law creep behavior and the yielding at plate boundaries were investigated.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/15519346','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/15519346"><span id="translatedtitle">On the <span class="hlt">mechanism</span> of cell lysis by <span class="hlt">deformation</span>.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Takamatsu, Hiroshi; Takeya, Ryu; Naito, Seiji; Sumimoto, Hideki</p> <p>2005-01-01</p> <p>In this study, we identify the extent of <span class="hlt">deformation</span> that causes cell lysis using a simple technique where a drop of cell suspension is compressed by two flat plates. The viability of human prostatic adenocarcinoma PC-3 cells in solutions of various concentrations of NaCl is determined as a function of the gap size between the plates. The viability declines with decreasing gap size in the following order: 700 mM >150 mM >75 mM NaCl. This is considered to be due to the difference in cell size, which is caused by the osmotic volume change before <span class="hlt">deformation</span>; cell diameter becomes smaller in a solution of higher NaCl concentration, which appears to increase the survival ratio in a given gap size. The <span class="hlt">deformation</span>-induced decrease in cell viability is correlated with the cell surface strain, which is dependent on the increase in surface area, irrespective of NaCl concentration. In addition, the treatment of cells with cytochalasin D results in the disappearance of cortical actin filaments and a marked drop in the viability, indicating that cell lysis is closely related to the <span class="hlt">deformation</span> of the cytoskeleton. PMID:15519346</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/16014803','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/16014803"><span id="translatedtitle"><span class="hlt">Cyclic</span> <span class="hlt">mechanical</span> strain-induced proliferation and migration of human airway smooth muscle cells: role of EMMPRIN and MMPs.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Hasaneen, Nadia A; Zucker, Stanley; Cao, Jian; Chiarelli, Christian; Panettieri, Reynold A; Foda, Hussein D</p> <p>2005-09-01</p> <p>Airway smooth muscle (ASM) proliferation and migration are major components of airway remodeling in asthma. Asthmatic airways are exposed to <span class="hlt">mechanical</span> strain, which contributes to their remodeling. Matrix metalloproteinase (MMP) plays an important role in remodeling. In the present study, we examined if the <span class="hlt">mechanical</span> strain of human ASM (HASM) cells contributes to their proliferation and migration and the role of MMPs in this process. HASM were exposed to <span class="hlt">mechanical</span> strain using the FlexCell system. HASM cell proliferation, migration and MMP release, activation, and expression were assessed. Our results show that <span class="hlt">cyclic</span> strain increased the proliferation and migration of HASM; <span class="hlt">cyclic</span> strain increased release and activation of MMP-1, -2, and -3 and membrane type 1-MMP; MMP release was preceded by an increase in extracellular MMP inducer; Prinomastat [a MMP inhibitor (MMPI)] significantly decreased <span class="hlt">cyclic</span> strain-induced proliferation and migration of HASM; and the strain-induced increase in the release of MMPs was accompanied by an increase in tenascin-C release. In conclusion, <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> strain plays an important role in HASM cell proliferation and migration. This increase in proliferation and migration is through an increase in MMP release and activation. Pharmacological MMPIs should be considered in the pursuit of therapeutic options for airway remodeling in asthma. PMID:16014803</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/15255281','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/15255281"><span id="translatedtitle"><span class="hlt">Cyclic</span> <span class="hlt">mechanical</span> stretching and interleukin-1alpha synergistically up-regulate prostacyclin secretion in cultured human uterine myometrial cells.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Korita, D; Itoh, H; Sagawa, N; Yura, S; Yoshida, M; Kakui, K; Takemura, M; Nuamah, M A; Fujii, S</p> <p>2004-03-01</p> <p>Prostacyclin (PGI2), a potent uterine smooth muscle relaxant, is postulated to be a major prostaglandin (PG) secreted from the human myometrium. PGI2 metabolite concentrations in the maternal plasma were reported to be elevated during pregnancy, especially during labor. Recently, we developed cultured human myometrial cells from pregnant women and reported that <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> stretching mimicking labor increased PGI2 secretion from these cells by up-regulating PGI2 synthase promoter activities. Since elevation of cervical/vaginal interleukin-1alpha (IL-1alpha) concentrations is also a characteristic feature of delivery, and IL-1alpha is a known stimulator of PG synthesis, we investigated a possible synergistic effect of <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> stretching and IL-1alpha on PGI2 production in cultured human myometrial cells. Treatment with IL-1alpha (10 ng/ml) significantly augmented (4- to 60-fold) the secretion of PGI2, prostaglandin E2 (PGE2), prostaglandin F2alpha (PGF2alpha) and thromboxane A2 (TXA2) from cultured human myometrial cells obtained from non-pregnant and pregnant women as well as in cultured human umbilical artery and cultured human coronary artery smooth muscle cells (p < 0.05 for all comparisons). However, labor-like <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> stretching up-regulated IL-1alpha-augmented PGI2 secretion from myometrial cells obtained from non-pregnant and pregnant women 2.1- to 2.8-fold (p < 0.05 for all comparisons), but not PGE2, PGF2alpha nor TXA2. Moreover, such an augumentation of PGI2 secretion by <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> stretching was not observed in cultured human umbilical artery nor in cultured human coronary artery smooth muscle cells. These results suggest that <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> stretching by labor, in concert with IL-1alpha stimulation, contributes to the increase in myometrial PGI2 secretion during delivery. PMID:15255281</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001MMTB...32..697L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001MMTB...32..697L"><span id="translatedtitle">Physical modeling of the <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> of semisolid bodies and a <span class="hlt">mechanical</span> criterion for hot tearing</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lahaie, D. J.; Bouchard, M.</p> <p>2001-08-01</p> <p>The <span class="hlt">mechanical</span> response of a semisolid body to an applied, uniaxial strain rate has been expressed as a function of strain by modifying an existing analysis based on an idealized representation of the microstructure. An existing <span class="hlt">mechanical</span> criterion for hot tearing of the semisolid body has been adapted to the <span class="hlt">deformation</span> <span class="hlt">mechanisms</span>. The resulting hot tearing model shows that the strength of the body depends on the strain, the viscosity of the intergranular fluid, the solid fraction, the isothermal compressibility of the fluid, the surface tension of the liquid, the limiting liquid-film thickness for viscous flow and a parameter m, which describes microstructure. The effect of each parameter on the <span class="hlt">mechanical</span> response and the onset of hot tearing has been examined for ranges of values relevant to aluminum alloys and the direct-chill (DC) casting process. The parameter testing has shown that the <span class="hlt">mechanical</span> response predicted by the model agrees well with some experimental data for both the <span class="hlt">mechanisms</span> of fracture and the parameters that govern the process. An adjustment of unknown model parameters to experimental data would permit use of the model as a constitutive law and a fracture criterion for numerical modeling of hot tearing during the solidification of Al alloys by DC casting.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010AGUFM.T41A2102W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010AGUFM.T41A2102W"><span id="translatedtitle">Evidence for <span class="hlt">Cyclic</span> Brittle-Ductile <span class="hlt">Deformation</span> from San Andreas Fault Observatory at Depth (SAFOD) Phase 3 Cores</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>White, J. C.; Kennedy, L.</p> <p>2010-12-01</p> <p>Microstructural development in core retrieved from SAFOD Phase 3 drilling has been examined in three locations utilizing light, scanning electron (SEM) and transmission electron microscopy (TEM): (1) within the Salinian Terrane near its contact with the presumed Great Valley sequence (Hole E-Run 1-Section 4 & 6); (2) proximal to the Southwest <span class="hlt">Deformation</span> Zone (SDZ) with which are associated casing <span class="hlt">deformation</span> and seismic aftershocks indicative of active faulting (Hole G-Run-1-Section 2 & Hole G-Run 2-Section 3); and (3) within the Central <span class="hlt">Deformation</span> Zone (CDZ) in the centre of the damage zone identified in Phase 2 drilling (Hole G-Run 4-Section 2). The sampling locations translate to an across-strike distance from outside the damage zone to its centre of approximately 125 meters, and a change in current measured depth from 2610 m to 2685m. Common to all cores are: (1) a significant fractional volume (<1μm) of very fine-grained material, both primary grains and tectonized particles; (2) evidence of extensive fluid flux in the form of stress-induced dissolution seams (pressure solution), grain precipitation and veining; and (3) complex, non-systematically varying phyllosilicate intergrowths (illite, muscovite, phengite, chlorite). The Salinian terrane material (E14, E16) comprises coarse-grained quartz and perthitic feldspar clasts that locally form slightly foliated cataclasite. The matrix is commonly chloritic with very fine-grained aggregates and zones of quartz and/or feldspar. Microbrecciation is ubiquitous. There are both fluid-corroded clasts, particularly of quartz, and globular infillings of calcite with sutured contacts. Quartz and feldspar grains are coated by chlorite. Amorphous silica and secondary Ti-Fe oxides occur within cataclasite. Foliated siltstone-shale cataclasites (G12, G23) at the edge of the damage zone close to the SDZ exhibit brecciation and cataclasis at different scales; <span class="hlt">deformation</span> is episodic as there are distinct overprinting</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://ntrs.nasa.gov/search.jsp?R=19910053191&hterms=anisotropic+material&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Danisotropic%2Bmaterial','NASA-TRS'); return false;" href="http://ntrs.nasa.gov/search.jsp?R=19910053191&hterms=anisotropic+material&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Danisotropic%2Bmaterial"><span id="translatedtitle"><span class="hlt">Deformation</span> <span class="hlt">mechanisms</span> in negative Poisson's ratio materials - Structural aspects</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lakes, R.</p> <p>1991-01-01</p> <p>Poisson's ratio in materials is governed by the following aspects of the microstructure: the presence of rotational degrees of freedom, non-affine <span class="hlt">deformation</span> kinematics, or anisotropic structure. Several structural models are examined. The non-affine kinematics are seen to be essential for the production of negative Poisson's ratios for isotropic materials containing central force linkages of positive stiffness. Non-central forces combined with pre-load can also give rise to a negative Poisson's ratio in isotropic materials. A chiral microstructure with non-central force interaction or non-affine <span class="hlt">deformation</span> can also exhibit a negative Poisson's ratio. Toughness and damage resistance in these materials may be affected by the Poisson's ratio itself, as well as by generalized continuum aspects associated with the microstructure.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2005JMPSo..53..525B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2005JMPSo..53..525B"><span id="translatedtitle">Finite <span class="hlt">deformations</span> of metal cylinders subjected to electromagnetic fields and <span class="hlt">mechanical</span> forces</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bilyk, S. R.; Ramesh, K. T.; Wright, T. W.</p> <p>2005-03-01</p> <p>Strong electromagnetic (EM) fields coupled with <span class="hlt">mechanical</span> loads may have a profound effect on <span class="hlt">deforming</span> bodies. The continuum description of the plastic <span class="hlt">deformation</span> of solids under electric fields and <span class="hlt">mechanical</span> loads essentially involves the coupling of the field equations of continuum <span class="hlt">mechanics</span> with Maxwell's equations. This analysis considers the effects of large EM fields on solid metal cylinders undergoing plastic <span class="hlt">deformations</span>. Other researchers have used an electroplastic effect to explain previous EM and <span class="hlt">mechanically</span> loaded experimental results. We examine whether it is necessary to invoke this controversial <span class="hlt">mechanism</span>. First, we consider only EM loading and solve the transient EM distribution in a solid metal cylinder. This determines the EM time scales as compared to thermal diffusion time scales. Next, at the continuum level, we present the <span class="hlt">mechanical</span> problem of quasi-static finite compressive <span class="hlt">deformations</span> incorporating thermal expansion, strain hardening, strain rate sensitivity, thermal softening, and heat conduction. A viscoplastic model that is applicable over a wide range of strain rates (10 -4-10 6 s -1) characterizes the material response. Finally, we consider a metal cylinder subjected to uni-axial <span class="hlt">mechanical</span> loading as well as high axial current pulses. The material is assumed to be isotropic with the plastic incompressibility constraint. The <span class="hlt">deformations</span> are assumed to remain axisymmetric and no instabilities in the cylinder are considered. Coupled effects of Joule heating and the Lorentz force on the quasi-static <span class="hlt">deformations</span> are examined.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22204925','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22204925"><span id="translatedtitle"><span class="hlt">Cyclic</span> stretch induces upregulation of endothelin-1 with keratinocytes in vitro: Possible role in <span class="hlt">mechanical</span> stress-induced hyperpigmentation</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kurita, Masakazu; Okazaki, Mutsumi; Fujino, Takashi; Takushima, Akihiko; Harii, Kiyonori</p> <p>2011-05-27</p> <p>Highlights: {yields} Influence of <span class="hlt">cyclic</span> stretch on melanogenetic paracrine cytokines was investigated. {yields} Keratinocyte-derived endothelin-1 was upregulated with <span class="hlt">cyclic</span> stretch. {yields} Degree of upregulation increases dose-dependently. {yields} This upregulation possibly plays a role in the pathogenesis of pigmented disorders. -- Abstract: The aim of this study was to investigate the possible pathological relation between <span class="hlt">mechanical</span> stress and hyperpigmentation. We did this by investigating the influence of <span class="hlt">cyclic</span> stretch on the expression of keratinocyte- and fibroblast-derived melanogenetic paracrine cytokines in vitro. Using primary human keratinocytes and fibroblasts, alterations of mRNA expression of melanogenetic paracrine cytokines due to <span class="hlt">cyclic</span> stretch were investigated using a real-time polymerase chain reaction (PCR). The cytokines included basic fibroblast growth factor (bFGF), stem cell factor (SCF), granulocyte/macrophage colony-stimulating factor, interleukin-1{alpha}, and endothelin-1 (ET-1) for keratinocytes and bFGF, SCF, and hepatocyte growth factor for fibroblasts. The dose dependence of keratinocyte-derived ET-1 upregulation was further investigated using real-time PCR and an enzyme-linked immunosorbent assay. We also investigated the effects of <span class="hlt">cyclic</span> stretch on the proliferation and differentiation of keratinocytes. Among the melanogenetic paracrine cytokines investigated, keratinocyte-derived ET-1 was consistently upregulated in all four cell lines. The degree of upregulation increased with the degree of the length and frequency of the stretch; in contrast, cell number and differentiation markers showed no obvious alterations with <span class="hlt">cyclic</span> stretch. Keratinocyte-derived ET-1 upregulation possibly plays a significant role in the pathogenesis of pigmented disorders, such as friction melanosis, caused by <span class="hlt">mechanical</span> stress.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/22063676','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/22063676"><span id="translatedtitle"><span class="hlt">Mechanical</span> and microstructural characterization of 6061 aluminum alloy strips severely <span class="hlt">deformed</span> by Dissimilar Channel Angular Pressing</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Tan, Evren; Kibar, Alp Aykut; Guer, C. Hakan</p> <p>2011-04-15</p> <p>Dissimilar Channel Angular Pressing (DCAP) is a severe plastic <span class="hlt">deformation</span> technique to improve the <span class="hlt">mechanical</span> properties of flat products by producing ultrafine grains. In this study, the changes in the microstructure and <span class="hlt">mechanical</span> properties of 6061 Al-alloy strips <span class="hlt">deformed</span> by various numbers of DCAP passes were investigated. Some DCAPed samples were also held at 200 deg. C and 350 deg. C to investigate the effect of post-annealing. <span class="hlt">Mechanical</span> properties were determined by hardness and tension tests; and microstructural changes were investigated by TEM analysis. Up to a critical level of plastic strain, remarkable improvements have been observed in the strength and hardness of the severely <span class="hlt">deformed</span> strips; and the improvements have been explained by variations in grain size, dislocation structure, and formation of subgrains. - Research Highlights: {yields}Dissimilar Channel Angular Pressing (DCAP). {yields}Severe plastic <span class="hlt">deformation</span> (SPD). {yields}Transmission Electron Microscopy of the 6061 Al alloy. {yields}<span class="hlt">Mechanical</span> Properties of 6061 Al alloy.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/23584980','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/23584980"><span id="translatedtitle"><span class="hlt">Cyclical</span> <span class="hlt">mechanical</span> stretch enhances degranulation and IL-4 secretion in RBL-2H3 mast cells.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Komiyama, Hidenori; Miyake, Koichi; Asai, Kuniya; Mizuno, Kyoichi; Shimada, Takashi</p> <p>2014-01-01</p> <p>Mast cells are widely distributed in the body and affect their surrounding environment through degranulation and secretion of cytokines. Conversely, mast cells are influenced by environmental stimuli such as <span class="hlt">cyclical</span> <span class="hlt">mechanical</span> stretch (CMS), such as that induced by heartbeat and respiration. Peripherally distributed mast cells are surrounded by extracellular matrix, where they bind IgE on their surface by expressing the high-affinity Fc receptor for IgE (FcεRI), and they release mediators after cross-linking of surface-bound IgE by allergen. To analyse how CMS affects mast cell responses, we examined the effect of applying CMS on the behaviour of IgE-bound mast cells (RBL-2H3 cell line) adhering to fibronectin as a substitute for extracellular matrix. We found that CMS enhanced FcεRI-mediated secretion in the presence of antigen (2,4-dinitrophenol-bovine serum albumin). CMS increased expression of IL-4 mRNA and secretion of IL-4 protein. Western blot analysis showed that CMS changes the signal transduction in mitogen-activated protein kinases and AKT, which in turn alters the regulation of IL-4 and increases the secretion of IL-4. These results suggest that CMS modulates the effect of mast cells on inflammation and resultant tissue remodelling. Understanding how CMS affects mast cell responses is crucial for developing therapies to treat mast cell-related diseases. PMID:23584980</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/27151628','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/27151628"><span id="translatedtitle">Graphene Topographies: Multiscale Graphene Topographies Programmed by Sequential <span class="hlt">Mechanical</span> <span class="hlt">Deformation</span> (Adv. Mater. 18/2016).</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Chen, Po-Yen; Sodhi, Jaskiranjeet; Qiu, Yang; Valentin, Thomas M; Steinberg, Ruben Spitz; Wang, Zhongying; Hurt, Robert H; Wong, Ian Y</p> <p>2016-05-01</p> <p>P.-Y. Chen, R. H. Hurt, I. Y. Wong and co-workers demonstrate a hierarchical graphene surface architecture generated by using various sequences and combinations of extreme <span class="hlt">mechanical</span> <span class="hlt">deformation</span>, as shown in the false-colored SEM image. As described on page 3564, the sequential patterning approach enables the design of feature sizes and orientations across multiple length scales which are retained during <span class="hlt">mechanical</span> <span class="hlt">deformations</span> of similar extent. This results in sequence-dependent surface topographies with structural memory. PMID:27151628</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013PhDT.......314D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013PhDT.......314D"><span id="translatedtitle">Characterization of a 3D multi-<span class="hlt">mechanism</span> SMA material model for the prediction of the <span class="hlt">cyclic</span> "evolutionary" response of NiTi for use in actuations</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dhakal, Binod</p> <p></p> <p>The intermetallic NiTi-based alloys are known as Shape Memory material. They exhibit unique ability to remember a shape after large <span class="hlt">deformation</span>. They are desirable in various engineering applications, such as actuators, biomedical devices, vibration damping, etc, as they can absorb and dissipate <span class="hlt">mechanical</span>/thermal energies by undergoing a reversible hysteretic shape change under the applied <span class="hlt">mechanical</span>/thermal <span class="hlt">cyclic</span> loadings. This reflects the effect of micro-structural changes occurring during phase transformation between Austenite(A) and Martensite(M), as well as differently-oriented M-variants. As typically utilized in applications, a particular shape memory alloy (SMA) device or component operates under a large number of thermo-<span class="hlt">mechanical</span> cycles, hence, the importance of accounting for the <span class="hlt">cyclic</span> behavior characteristics in modeling and characterization of these systems. A detailed study of the multi-<span class="hlt">mechanism</span>-based, comprehensive, thus complex modeling framework (by Saleeb et al) and the determination of its material parameters responsible for the physical significance of the shape memory effect are made. This formulation utilizes multiple, inelastic <span class="hlt">mechanisms</span> to regulate the partitioning of energy dissipation and storage governing the evolutionary thermo-<span class="hlt">mechanical</span> behavior. Equipped with the understanding of the physical significance of the model parameters and utilizing the SMA modeling strategy effectively, a comprehensive characterization of the evolutionary, <span class="hlt">cyclic</span> response of the complex real SMA, known as 55NiTi (Ni49.9Ti50.1) is carried out. The detailed comparisons between the SMA model and experimental results provided the necessary validation of the modeling capabilities of the framework to calibrate the complex alloys like 55NiTi. In addition, the details of interplays between the internal <span class="hlt">mechanisms</span> to describe the material behavior within all the important response characteristic regions provides a convenient means to compliment the theoretical</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016MMTA...47...49M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016MMTA...47...49M"><span id="translatedtitle"><span class="hlt">Deformation</span> <span class="hlt">Mechanisms</span> in Austenitic TRIP/TWIP Steel as a Function of Temperature</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Martin, Stefan; Wolf, Steffen; Martin, Ulrich; Krüger, Lutz; Rafaja, David</p> <p>2016-01-01</p> <p>A high-alloy austenitic CrMnNi steel was <span class="hlt">deformed</span> at temperatures between 213 K and 473 K (-60 °C and 200 °C) and the resulting microstructures were investigated. At low temperatures, the <span class="hlt">deformation</span> was mainly accompanied by the direct martensitic transformation of γ-austenite to α'-martensite (fcc → bcc), whereas at ambient temperatures, the transformation via ɛ-martensite (fcc → hcp → bcc) was observed in <span class="hlt">deformation</span> bands. <span class="hlt">Deformation</span> twinning of the austenite became the dominant <span class="hlt">deformation</span> <span class="hlt">mechanism</span> at 373 K (100 °C), whereas the conventional dislocation glide represented the prevailing <span class="hlt">deformation</span> mode at 473 K (200 °C). The change of the <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> was attributed to the temperature dependence of both the driving force of the martensitic γ → α' transformation and the stacking fault energy of the austenite. The continuous transition between the ɛ-martensite formation and the twinning could be explained by different stacking fault arrangements on every second and on each successive {111} austenite lattice plane, respectively, when the stacking fault energy increased. A continuous transition between the transformation-induced plasticity effect and the twinning-induced plasticity effect was observed with increasing <span class="hlt">deformation</span> temperature. Whereas the formation of α'-martensite was mainly responsible for increased work hardening, the stacking fault configurations forming ɛ-martensite and twins induced additional elongation during tensile testing.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li class="active"><span>12</span></li> <li><a href="#" onclick='return showDiv("page_13");'>13</a></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_12 --> <div id="page_13" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_9");'>9</a></li> <li><a href="#" onclick='return showDiv("page_10");'>10</a></li> <li><a href="#" onclick='return showDiv("page_11");'>11</a></li> <li><a href="#" onclick='return showDiv("page_12");'>12</a></li> <li class="active"><span>13</span></li> <li><a href="#" onclick='return showDiv("page_13");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="241"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/25348252','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/25348252"><span id="translatedtitle"><span class="hlt">Cyclic</span> <span class="hlt">mechanical</span> strain induces TGFβ1-signalling in dermal fibroblasts embedded in a 3D collagen lattice.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Peters, Andreas S; Brunner, Georg; Krieg, Thomas; Eckes, Beate</p> <p>2015-03-01</p> <p>Many tissues are constantly exposed to <span class="hlt">mechanical</span> stress, e.g. shear stress in vascular endothelium, compression forces in cartilage or tensile strain in the skin. Dermal fibroblasts can differentiate into contractile myofibroblasts in a process requiring the presence of TGFβ1 in addition to <span class="hlt">mechanical</span> load. We aimed at investigating the effect of <span class="hlt">cyclic</span> <span class="hlt">mechanical</span> strain on dermal fibroblasts grown in a three-dimensional environment. Therefore, murine dermal fibroblasts were cultured in collagen gels and subjected to <span class="hlt">cyclic</span> tension at a frequency of 0.1 Hz (6 cycles/min) with a maximal increase in surface area of 10 % for 24 h. This treatment resulted in a significant increase in active TGFβ1 levels, leaving the amount of total TGFβ1 unaffected. TGFβ1 activation led to pSMAD2-mediated transcriptional elevation of downstream mediators, such as CTGF, and an auto-induction of TGFβ1, respectively. PMID:25348252</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/1149405','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/1149405"><span id="translatedtitle">Revealing <span class="hlt">cyclic</span> hardening <span class="hlt">mechanism</span> of a TRIP steel by real-time in situ neutron diffraction</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Yu, Dunji; An, Ke; Chen, Yan; Chen, Xu</p> <p>2014-01-01</p> <p>Real-time in situ neutron diffraction was performed on a transformation-induced plasticity (TRIP) steel under <span class="hlt">cyclic</span> loading at room temperature. By Rietveld refinement and single peak analysis, the volume fraction and average stress estimates as well as dislocation density of individual phases (austenite and martensite phase) were derived. The results reveal that the volume fraction of martensite phase, instead of individual phase strengthening, should be accounted for the remarkable secondary <span class="hlt">cyclic</span> hardening.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/servlets/purl/5987','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/servlets/purl/5987"><span id="translatedtitle"><span class="hlt">Deformation</span> <span class="hlt">Mechanisms</span> is a-Phase Silicon Nitride Ceramics</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>J. A. Schneider; A. K. Mukherjee</p> <p>1998-08-12</p> <p>Changes of phase composition and morphology were investigated in Si{sub 3}N{sub 4} both before and after compressive <span class="hlt">deformation</span> testing. Si{sub 3}N{sub 4} specimens, with 5 wt% Y{sub 2}O{sub 3} and 5 wt% MgAl{sub 2}O{sub 4} additives, were rapidly consolidated to preserve the initial, metastable {alpha}-phase present in the Si{sub 3}N{sub 4} starting powders. Constant strain rate compression tests were used to evaluate the strain rate dependency of the flow stress. At 1723 K, a flow stress dependency value of n = 2 was observed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ApPhL.108o1903W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ApPhL.108o1903W"><span id="translatedtitle"><span class="hlt">Deformation</span> <span class="hlt">mechanisms</span> of bent Si nanowires governed by the sign and magnitude of strain</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wang, Lihua; Kong, Deli; Xin, Tianjiao; Shu, Xinyu; Zheng, Kun; Xiao, Lirong; Sha, Xuechao; Lu, Yan; Zhang, Ze; Han, Xiaodong; Zou, Jin</p> <p>2016-04-01</p> <p>In this study, the <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> of bent Si nanowires are investigated at the atomic scale with bending strain up to 12.8%. The sign and magnitude of the applied strain are found to govern their <span class="hlt">deformation</span> <span class="hlt">mechanisms</span>, in which the dislocation types (full or partial dislocations) can be affected by the sign (tensile or compressive) and magnitude of the applied strain. In the early stages of bending, plastic <span class="hlt">deformation</span> is controlled by 60° full dislocations. As the bending increases, Lomer dislocations can be frequently observed. When the strain increases to a significant level, 90° partial dislocations induced from the tensile surfaces of the bent nanowires are observed. This study provides a deeper understanding of the effect of the sign and magnitude of the bending strain on the <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> in bent Si nanowires.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016SMaS...25e4002S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016SMaS...25e4002S"><span id="translatedtitle">The influence of large <span class="hlt">deformations</span> on <span class="hlt">mechanical</span> properties of sinusoidal ligament structures</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Strek, Tomasz; Jopek, Hubert; Wojciechowski, Krzysztof W.</p> <p>2016-05-01</p> <p>Studies of <span class="hlt">mechanical</span> properties of materials, both theoretical and experimental, usually deal with linear characteristics assuming a small range of <span class="hlt">deformations</span>. In particular, not much research has been published devoted to large <span class="hlt">deformations</span> of auxetic structures – i.e. structures exhibiting negative Poisson’s ratio. This paper is focused on <span class="hlt">mechanical</span> properties of selected structures that are subject to large <span class="hlt">deformations</span>. Four examples of structure built of sinusoidal ligaments are studied and for each geometry the impact of <span class="hlt">deformation</span> size and geometrical parameters on the effective <span class="hlt">mechanical</span> properties of these structures are investigated. It is shown that some of them are auxetic when compressed and non-auxetic when stretched. Geometrical parameters describing sinusoidal shape of ligaments strongly affect effective <span class="hlt">mechanical</span> properties of the structure. In some cases of <span class="hlt">deformation</span>, the increase of the value of amplitude of the sinusoidal shape decreases the effective Poisson’s ratio by 0.7. Therefore the influence of geometry, as well as the arrangement of ligaments allows for smart control of <span class="hlt">mechanical</span> properties of the sinusoidal ligament structure being considered. Given the large <span class="hlt">deformation</span> of the structure, both a linear elastic material model, and a hyperelastic Neo-Hookean material model are used.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015MMTA...46.1704G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015MMTA...46.1704G"><span id="translatedtitle">Microstructures and <span class="hlt">Mechanical</span> Properties of High-Mn TRIP Steel Based on Warm <span class="hlt">Deformation</span> of Martensite</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Guo, Zhikai; Li, Longfei; Yang, Wangyue; Sun, Zuqing</p> <p>2015-04-01</p> <p>High-Mn TRIP steel with about 5 wt pct Mn was prepared by a thermo-<span class="hlt">mechanical</span> treatment based on warm <span class="hlt">deformation</span> of martensite and subsequent short-time annealing in the intercritical region. The microstructural evolution and the <span class="hlt">mechanical</span> properties of the used steel during such treatment were investigated. The results indicate that during warm <span class="hlt">deformation</span> of martensite in the intercritical region, the decomposition of martensite was accelerated by warm <span class="hlt">deformation</span> and the occurrence of dynamic recrystallization of ferrite led to the formation of equiaxed ferrite grains. Meanwhile, the reverse transformation of austenite was accelerated by warm <span class="hlt">deformation</span> to some extent. During subsequent annealing in the intercritical region, static recrystallization of ferrite led to the increase in the fraction of equiaxed ferrite grains, and the formation of the reversed austenite was accelerated by the addition of the <span class="hlt">deformation</span>-stored energy, while the stability of the reversed austenite was improved by the accelerated diffusions of C atoms and Mn atoms. As a whole, the <span class="hlt">mechanical</span> properties of the used steel by the thermo-<span class="hlt">mechanical</span> treatment based on warm <span class="hlt">deformation</span> of martensite and subsequent short-time annealing in the intercritical region were comparable to the steels with similar compositions subjected to intercritical annealing for hours after cold rolling of martensite.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160006095','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160006095"><span id="translatedtitle">Representing Matrix Cracks Through Decomposition of the <span class="hlt">Deformation</span> Gradient Tensor in Continuum Damage <span class="hlt">Mechanics</span> Methods</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Leone, Frank A., Jr.</p> <p>2015-01-01</p> <p>A method is presented to represent the large-<span class="hlt">deformation</span> kinematics of intraply matrix cracks and delaminations in continuum damage <span class="hlt">mechanics</span> (CDM) constitutive material models. The method involves the additive decomposition of the <span class="hlt">deformation</span> gradient tensor into 'crack' and 'bulk material' components. The response of the intact bulk material is represented by a reduced <span class="hlt">deformation</span> gradient tensor, and the opening of an embedded cohesive interface is represented by a normalized cohesive displacement-jump vector. The rotation of the embedded interface is tracked as the material <span class="hlt">deforms</span> and as the crack opens. The distribution of the total local <span class="hlt">deformation</span> between the bulk material and the cohesive interface components is determined by minimizing the difference between the cohesive stress and the bulk material stress projected onto the cohesive interface. The improvements to the accuracy of CDM models that incorporate the presented method over existing approaches are demonstrated for a single element subjected to simple shear <span class="hlt">deformation</span> and for a finite element model of a unidirectional open-hole tension specimen. The material model is implemented as a VUMAT user subroutine for the Abaqus/Explicit finite element software. The presented <span class="hlt">deformation</span> gradient decomposition method reduces the artificial load transfer across matrix cracks subjected to large shearing <span class="hlt">deformations</span>, and avoids the spurious secondary failure modes that often occur in analyses based on conventional progressive damage models.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.osti.gov/scitech/biblio/7123363','SCIGOV-STC'); return false;" href="http://www.osti.gov/scitech/biblio/7123363"><span id="translatedtitle"><span class="hlt">Deformation</span> <span class="hlt">mechanisms</span> adjacent to a thrust fault, Sangre de Cristo Mountains, Colorado</span></a></p> <p><a target="_blank" href="http://www.osti.gov/scitech">SciTech Connect</a></p> <p>Kelly, J.C.; McConnell, D.A.; Friberg, V.M. . Dept. of Geology)</p> <p>1994-04-01</p> <p>The purpose of this study is to examine the character of grain-scale <span class="hlt">deformation</span> adjacent to a Laramide thrust fault in the Sangre de Cristo Mountains. This site represents a window through the hanging wall of a thrust sheet which juxtaposes Precambrian rocks over Pennsylvanian rocks. It provides a rare opportunity to examine <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> in the footwall of a basement-involved thrust. Brittle <span class="hlt">deformation</span> is evident at both outcrop and grain-scale. Filled fractures and slickensides composed of quartz and epidote are present throughout the area, and increase in abundance adjacent to the fault zone, as does the frequency of mesoscopic faulting. Variations in <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> can be seen between the Precambrian rocks of the thrust sheet and the Pennsylvanian metasedimentary rocks, and between the metamorphosed arkoses and metapelites within the Pennsylvanian section. Cataclastic textures are present in <span class="hlt">deformed</span> Precambrian rocks, and the degree of cataclasis is greatest immediately adjacent to the fault zone. <span class="hlt">Deformation</span> in the Pennsylvanian rocks is largely dependent upon the abundance of fine-grained matrix within each sample. The degree of brittle <span class="hlt">deformation</span> is negatively correlated to the percentage of matrix. Coarser-grained sections show microscopic faults which offset quartz and feldspar grains. Offsets decrease on the faults as they pass from coarse grains into the matrix.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016ApSS..371..407Z','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016ApSS..371..407Z"><span id="translatedtitle">Detailed analysis of surface asperity <span class="hlt">deformation</span> <span class="hlt">mechanism</span> in diffusion bonding of steel hollow structural components</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Zhang, C.; Li, H.; Li, M. Q.</p> <p>2016-05-01</p> <p>This study focused on the detailed analysis of surface asperity <span class="hlt">deformation</span> <span class="hlt">mechanism</span> in similar diffusion bonding as well as on the fabrication of high quality martensitic stainless steel hollow structural components. A special surface with regular patterns was processed to be joined so as to observe the extent of surface asperity <span class="hlt">deformation</span> under different bonding pressures. Results showed that an undamaged hollow structural component has been obtained with full interfacial contact and the same shear strength to that of base material. Fracture surface characteristic combined with surface roughness profiles distinctly revealed the enhanced surface asperity <span class="hlt">deformation</span> as the applied pressure increases. The influence of surface asperity <span class="hlt">deformation</span> <span class="hlt">mechanism</span> on joint formation was analyzed: (a) surface asperity <span class="hlt">deformation</span> not only directly expanded the interfacial contact areas, but also released <span class="hlt">deformation</span> heat and caused defects, indirectly accelerating atomic diffusion, then benefits to void shrinkage; (b) surface asperity <span class="hlt">deformation</span> readily introduced stored energy difference between two opposite sides of interface grain boundary, resulting in strain induced interface grain boundary migration. In addition, the influence of void on interface grain boundary migration was analyzed in detail.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://www.ncbi.nlm.nih.gov/pubmed/26866939','PUBMED'); return false;" href="http://www.ncbi.nlm.nih.gov/pubmed/26866939"><span id="translatedtitle">Large <span class="hlt">Deformation</span> <span class="hlt">Mechanisms</span>, Plasticity, and Failure of an Individual Collagen Fibril With Different Mineral Content.</span></a></p> <p><a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Depalle, Baptiste; Qin, Zhao; Shefelbine, Sandra J; Buehler, Markus J</p> <p>2016-02-01</p> <p>Mineralized collagen fibrils are composed of tropocollagen molecules and mineral crystals derived from hydroxyapatite to form a composite material that combines optimal properties of both constituents and exhibits incredible strength and toughness. Their complex hierarchical structure allows collagen fibrils to sustain large <span class="hlt">deformation</span> without breaking. In this study, we report a mesoscale model of a single mineralized collagen fibril using a bottom-up approach. By conserving the three-dimensional structure and the entanglement of the molecules, we were able to construct finite-size fibril models that allowed us to explore the <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> which govern their <span class="hlt">mechanical</span> behavior under large <span class="hlt">deformation</span>. We investigated the tensile behavior of a single collagen fibril with various intrafibrillar mineral content and found that a mineralized collagen fibril can present up to five different <span class="hlt">deformation</span> <span class="hlt">mechanisms</span> to dissipate energy. These <span class="hlt">mechanisms</span> include molecular uncoiling, molecular stretching, mineral/collagen sliding, molecular slippage, and crystal dissociation. By multiplying its sources of energy dissipation and <span class="hlt">deformation</span> <span class="hlt">mechanisms</span>, a collagen fibril can reach impressive strength and toughness. Adding mineral into the collagen fibril can increase its strength up to 10 times and its toughness up to 35 times. Combining crosslinks with mineral makes the fibril stiffer but more brittle. We also found that a mineralized fibril reaches its maximum toughness to density and strength to density ratios for a mineral density of around 30%. This result, in good agreement with experimental observations, attests that bone tissue is optimized <span class="hlt">mechanically</span> to remain lightweight but maintain strength and toughness. 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