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Sample records for deformation induced dislocation

  1. Intermittent dislocation flow in viscoplastic deformation.

    PubMed

    Miguel, M C; Vespignani, A; Zapperi, S; Weiss, J; Grasso, J R

    2001-04-01

    The viscoplastic deformation (creep) of crystalline materials under constant stress involves the motion of a large number of interacting dislocations. Analytical methods and sophisticated 'dislocation dynamics' simulations have proved very effective in the study of dislocation patterning, and have led to macroscopic constitutive laws of plastic deformation. Yet, a statistical analysis of the dynamics of an assembly of interacting dislocations has not hitherto been performed. Here we report acoustic emission measurements on stressed ice single crystals, the results of which indicate that dislocations move in a scale-free intermittent fashion. This result is confirmed by numerical simulations of a model of interacting dislocations that successfully reproduces the main features of the experiment. We find that dislocations generate a slowly evolving configuration landscape which coexists with rapid collective rearrangements. These rearrangements involve a comparatively small fraction of the dislocations and lead to an intermittent behaviour of the net plastic response. This basic dynamical picture appears to be a generic feature in the deformation of many other materials. Moreover, it should provide a framework for discussing fundamental aspects of plasticity that goes beyond standard mean-field approaches that see plastic deformation as a smooth laminar flow. PMID:11287948

  2. Sessile dislocations by reactions in NiAl severely deformed at room temperature

    SciTech Connect

    Geist, D.; Gammer, C.; Rentenberger, C.; Karnthaler, H. P.

    2015-02-05

    B2 ordered NiAl is known for its poor room temperature (RT) ductility; failure occurs in a brittle like manner even in ductile single crystals deforming by single slip. In the present study NiAl was severely deformed at RT using the method of high pressure torsion (HPT) enabling the hitherto impossible investigation of multiple slip deformation. Methods of transmission electron microscopy were used to analyze the dislocations formed by the plastic deformation showing that as expected dislocations with Burgers vector a(100) carry the plasticity during HPT deformation at RT. In addition, we observe that they often form a(110) dislocations by dislocation reactions; the a(110) dislocations are considered to be sessile based on calculations found in the literature. It is therefore concluded that the frequently encountered 3D dislocation networks containing sessile a(110) dislocations are pinned and lead to deformation-induced embrittlement. In spite of the severe deformation, the chemical order remains unchanged.

  3. 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.

  4. 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.

  5. Surface dislocation nucleation controlled deformation of Au nanowires

    SciTech Connect

    Roos, B.; Kapelle, B.; Volkert, C. A.; Richter, G.

    2014-11-17

    We investigate deformation in high quality Au nanowires under both tension and bending using in-situ transmission electron microscopy. Defect evolution is investigated during: (1) tensile deformation of 〈110〉 oriented, initially defect-free, single crystal nanowires with cross-sectional widths between 30 and 300 nm, (2) bending deformation of the same wires, and (3) tensile deformation of wires containing coherent twin boundaries along their lengths. We observe the formation of twins and stacking faults in the single crystal wires under tension, and storage of full dislocations after bending of single crystal wires and after tension of twinned wires. The stress state dependence of the deformation morphology and the formation of stacking faults and twins are not features of bulk Au, where deformation is controlled by dislocation interactions. Instead, we attribute the deformation morphologies to the surface nucleation of either leading or trailing partial dislocations, depending on the Schmid factors, which move through and exit the wires producing stacking faults or full dislocation slip. The presence of obstacles such as neutral planes or twin boundaries hinder the egress of the freshly nucleated dislocations and allow trailing and leading partial dislocations to combine and to be stored as full dislocations in the wires. We infer that the twins and stacking faults often observed in nanoscale Au specimens are not a direct size effect but the result of a size and obstacle dependent transition from dislocation interaction controlled to dislocation nucleation controlled deformation.

  6. Effect of dislocation and grain boundary on deformation mechanism in ultrafine-grained interstitial-free steel

    NASA Astrophysics Data System (ADS)

    Nakazawa, K.; Itoh, S.; Matsunaga, T.; Matsukawa, Y.; Satoh, Y.; Murase, Y.; Abe, H.

    2014-08-01

    Ultrafine-grained interstitial-free steel fabricated by the accumulative roll-bonding method was subjected to tensile tests and analyses of AFM, TEM and XRD to identify the effects of interaction between dislocations and grain boundaries (GB) on the deformation mechanism. The AFM analyses indicated that the main deformation mechanism of this material changed from dislocation motion to grain boundary sliding (GBS) with decreasing strain rate. TEM observations and XRD analysis revealed showed that dislocations piled up at GB and the dislocation density decreased with increasing strain. Those suggest the dislocations are absorbed into GB during deformation, activating slip-induced GBS.

  7. Sessile dislocations by reactions in NiAl severely deformed at room temperature

    PubMed Central

    Geist, D.; Gammer, C.; Rentenberger, C.; Karnthaler, H.P.

    2015-01-01

    B2 ordered NiAl is known for its poor room temperature (RT) ductility; failure occurs in a brittle like manner even in ductile single crystals deforming by single slip. In the present study NiAl was severely deformed at RT using the method of high pressure torsion (HPT) enabling the hitherto impossible investigation of multiple slip deformation. Methods of transmission electron microscopy were used to analyze the dislocations formed by the plastic deformation showing that as expected dislocations with Burgers vector a〈100〉 carry the plasticity during HPT deformation at RT. In addition, we observe that they often form a〈110〉 dislocations by dislocation reactions; the a〈110〉 dislocations are considered to be sessile based on calculations found in the literature. It is therefore concluded that the frequently encountered 3D dislocation networks containing sessile a〈110〉 dislocations are pinned and lead to deformation-induced embrittlement. In spite of the severe deformation, the chemical order remains unchanged. PMID:25663749

  8. Sessile dislocations by reactions in NiAl severely deformed at room temperature

    DOE PAGESBeta

    Geist, D.; Gammer, C.; Rentenberger, C.; Karnthaler, H. P.

    2015-02-05

    B2 ordered NiAl is known for its poor room temperature (RT) ductility; failure occurs in a brittle like manner even in ductile single crystals deforming by single slip. In the present study NiAl was severely deformed at RT using the method of high pressure torsion (HPT) enabling the hitherto impossible investigation of multiple slip deformation. Methods of transmission electron microscopy were used to analyze the dislocations formed by the plastic deformation showing that as expected dislocations with Burgers vector a(100) carry the plasticity during HPT deformation at RT. In addition, we observe that they often form a(110) dislocations by dislocationmore » reactions; the a(110) dislocations are considered to be sessile based on calculations found in the literature. It is therefore concluded that the frequently encountered 3D dislocation networks containing sessile a(110) dislocations are pinned and lead to deformation-induced embrittlement. In spite of the severe deformation, the chemical order remains unchanged.« less

  9. Second yield via dislocation-induced premelting in copper

    NASA Astrophysics Data System (ADS)

    Wang, L.; Cai, Y.; He, A. M.; Luo, S. N.

    2016-05-01

    Premelting or virtual melting was proposed previously as an important deformation mechanism for high strain-rate loading. However, two questions remain outstanding: how premelting occurs exactly, and whether it plays a role in plastic deformation independent of, parasitic on, or synergetic with, dislocation motion. By virtue of double-shock compression, our large-scale molecular dynamics simulations reveal two yields in single-crystal copper, with the first yield achieved via dislocation motion, and the second, via dislocation-induced premelting as well. The clean capture of melting during dislocation motion suggests that premelting occurs on slip planes and at their intersections, facilitating gliding and leading to yield together with dislocation motion.

  10. Deformations of the spin currents by topological screw dislocation and cosmic dispiration

    NASA Astrophysics Data System (ADS)

    Wang, Jianhua; Ma, Kai; Li, Kang; Fan, Huawei

    2015-11-01

    We study the spin currents induced by topological screw dislocation and cosmic dispiration. By using the extended Drude model, we find that the spin dependent forces are modified by the nontrivial geometry. For the topological screw dislocation, only the direction of spin current is bent by deforming the spin polarization vector. In contrast, the force induced by cosmic dispiration could affect both the direction and magnitude of the spin current. As a consequence, the spin-Hall conductivity does not receive corrections from screw dislocation.

  11. Material yielding and irreversible deformation mediated by dislocation motion

    NASA Astrophysics Data System (ADS)

    Miguel, M.-Carmen; Laurson, L.; Alava, M. J.

    2008-08-01

    We study the collective behavior of dislocation assemblies in simplified models of plastic deformation. We first review several numerical results on long range dislocation interactions with simplified dislocation motion constraints. These typically give rise to a yielding transition separating stationary and moving dislocation phases. Furthermore, we discuss the intermittent relaxation of the plastic strain-rate observed around this transition at mesoscopic scales, and how this intermittent behavior gives rise to an average slow power law relaxation in time known in the literature as Andrade’s creep. We analyze the coherent dynamics and the average stress-strain relationship in the steady regime of plastic deformation. In this steady regime, plastic deformation proceeds in the form of plastic avalanches whose size and duration are broadly distributed and statistically characterized. One signature of the time correlations of this heterogeneous collective dislocation dynamics is a power spectrum scaling with frequency as f - a with an exponent α close to 1.5. This feature appears to be peculiar of dislocation and grain boundary motion as has been observed in other physical situations in the vicinity of a yielding transition.

  12. Inelastic deformation and dislocation structure of a nickel alloy - Effects of deformation and thermal histories

    NASA Technical Reports Server (NTRS)

    Chan, K. S.; Page, R. A.

    1988-01-01

    Inelastic deformation behavior of the cast Ni-base alloy, B1900 + Hf, was investigated using data from step-temperature tensile tests and thermomechanical cyclic tests in the temperature ranges 538-760 C and 760-982 C. The deformation results were correlated with the dislocation structures of deformed specimens, identified by TEM. It was found that, in the 760-982 C temperature range, there are no thermal history effects in the inelastic deformation behavior of B1900 + Hf. In the 538-760 range, anomalous cyclic hardening and, possibly, thermal history effects were observed in thermomechanically deformed alloy, caused by sessile (010) dislocations in the gamma-prime phase.

  13. Atomistic processes of dislocation generation and plastic deformation during nanoindentation

    SciTech Connect

    Begau, C.; Hartmaier, A.; George, Easo P; Pharr, George M

    2011-01-01

    To enable plastic deformation during nanoindentation of an initially defect-free crystal, it is necessary first to produce dislocations. While it is now widely accepted that the nucleation of the first dislocations occurs at the start of the pop-in event frequently observed in experiments, it is unclear how these initial dislocations multiply during the early stages of plastic deformation and produce pop-in displacements that are typically much larger than the magnitude of the Burgers vector. This uncertainty about the complex interplay between dislocation multiplication and strain hardening during nanoindentation makes a direct correlation between force-displacement curves and macroscopic material properties difficult. In this paper, we study the early phase of plastic deformation during nanoindentation with the help of large-scale molecular dynamics simulations. A skeletonization method to simplify defect structures in atomistic simulations enables the direct observation and quantitative analysis of dislocation nucleation and multiplication processes occurring in the bulk as well as at the surface.

  14. Stochastically forced dislocation density distribution in plastic deformation.

    PubMed

    Chattopadhyay, Amit K; Aifantis, Elias C

    2016-08-01

    The dynamical evolution of dislocations in plastically deformed metals is controlled by both deterministic factors arising out of applied loads and stochastic effects appearing due to fluctuations of internal stress. Such types of stochastic dislocation processes and the associated spatially inhomogeneous modes lead to randomness in the observed deformation structure. Previous studies have analyzed the role of randomness in such textural evolution, but none of these models have considered the impact of a finite decay time (all previous models assumed instantaneous relaxation which is "unphysical") of the stochastic perturbations in the overall dynamics of the system. The present article bridges this knowledge gap by introducing a colored noise in the form of an Ornstein-Uhlenbeck noise in the analysis of a class of linear and nonlinear Wiener and Ornstein-Uhlenbeck processes that these structural dislocation dynamics could be mapped on to. Based on an analysis of the relevant Fokker-Planck model, our results show that linear Wiener processes remain unaffected by the second time scale in the problem, but all nonlinear processes, both the Wiener type and Ornstein-Uhlenbeck type, scale as a function of the noise decay time τ. The results are expected to ramify existing experimental observations and inspire new numerical and laboratory tests to gain further insight into the competition between deterministic and random effects in modeling plastically deformed samples. PMID:27627278

  15. Local decomposition induced by dislocation motions inside precipitates in an Al-alloy

    PubMed Central

    Yang, B.; Zhou, Y. T.; Chen, D.; Ma, X. L.

    2013-01-01

    Dislocations in crystals are linear crystallographic defects, which move in lattice when crystals are plastically deformed. Motion of a partial dislocation may remove or create stacking fault characterized with a partial of a lattice translation vector. Here we report that motion of partial dislocations inside an intermetallic compound result in a local composition deviation from its stoichiometric ratio, which cannot be depicted with any vectors of the primary crystal. Along dislocation slip bands inside the deformed Al2Cu particles, redistribution of Cu and Al atoms leads to a local decomposition and collapse of the original crystal structure. This finding demonstrates that dislocation slip may induce destabilization in complex compounds, which is fundamentally different from that in monometallic crystals. This phenomenon of chemical unmixing of initially homogeneous multicomponent solids induced by dislocation motion might also have important implications for understanding the geologic evolvement of deep-focus peridotites in the Earth. PMID:23301160

  16. Local decomposition induced by dislocation motions inside precipitates in an Al-alloy.

    PubMed

    Yang, B; Zhou, Y T; Chen, D; Ma, X L

    2013-01-01

    Dislocations in crystals are linear crystallographic defects, which move in lattice when crystals are plastically deformed. Motion of a partial dislocation may remove or create stacking fault characterized with a partial of a lattice translation vector. Here we report that motion of partial dislocations inside an intermetallic compound result in a local composition deviation from its stoichiometric ratio, which cannot be depicted with any vectors of the primary crystal. Along dislocation slip bands inside the deformed Al(2)Cu particles, redistribution of Cu and Al atoms leads to a local decomposition and collapse of the original crystal structure. This finding demonstrates that dislocation slip may induce destabilization in complex compounds, which is fundamentally different from that in monometallic crystals. This phenomenon of chemical unmixing of initially homogeneous multicomponent solids induced by dislocation motion might also have important implications for understanding the geologic evolvement of deep-focus peridotites in the Earth. PMID:23301160

  17. Dislocation substructure in NiAl single crystals deformed at ambient temperature

    SciTech Connect

    Shi, X.; Pollock, T.M.; Mahajan, S.; Arunachalam, V.S.

    1997-12-31

    Dislocation substructure in NiAl single crystals oriented for single slip and deformed at ambient temperature has been studied using weak-beam transmission electron microscopy. Deformation is localized in bands that consists mostly of near-edge dislocations, with an interspersion of a high density of elongated prismatic loops. Pure screw dislocations are not observed, but dislocations having zigzag configurations that are near-screw in orientation are present. A high density of jogs is observed on both near-edge and zigzag dislocation segments. The mechanisms for the development of this substructure are discussed, emphasizing the role of double cross slip and resulting glissile and sessile jogs of varying heights.

  18. Dislocation models of interseismic deformation in the western United States

    USGS Publications Warehouse

    Pollitz, F.F.; McCrory, P.; Svarc, J.; Murray, J.

    2008-01-01

    The GPS-derived crustal velocity field of the western United States is used to construct dislocation models in a viscoelastic medium of interseismic crustal deformation. The interseismic velocity field is constrained by 1052 GPS velocity vectors spanning the ???2500-km-long plate boundary zone adjacent to the San Andreas fault and Cascadia subduction zone and extending ???1000 km into the plate interior. The GPS data set is compiled from U.S. Geological Survey campaign data, Plate Boundary Observatory data, and the Western U.S. Cordillera velocity field of Bennett et al. (1999). In the context of viscoelastic cycle models of postearthquake deformation, the interseismic velocity field is modeled with a combination of earthquake sources on ???100 known faults plus broadly distributed sources. Models that best explain the observed interseismic velocity field include the contributions of viscoelastic relaxation from faulting near the major plate margins, viscoelastic relaxation from distributed faulting in the plate interior, as well as lateral variations in depth-averaged rigidity in the elastic lithosphere. Resulting rigidity variations are consistent with reduced effective elastic plate thickness in a zone a few tens of kilometers wide surrounding the San Andreas fault (SAF) system. Primary deformation characteristics are captured along the entire SAF system, Eastern California Shear Zone, Walker Lane, the Mendocino triple junction, the Cascadia margin, and the plate interior up to ???1000 km from the major plate boundaries.

  19. Dislocation models of interseismic deformation in the western United States

    NASA Astrophysics Data System (ADS)

    Pollitz, Fred F.; McCrory, Patricia; Svarc, Jerry; Murray, Jessica

    2008-04-01

    The GPS-derived crustal velocity field of the western United States is used to construct dislocation models in a viscoelastic medium of interseismic crustal deformation. The interseismic velocity field is constrained by 1052 GPS velocity vectors spanning the ˜2500-km-long plate boundary zone adjacent to the San Andreas fault and Cascadia subduction zone and extending ˜1000 km into the plate interior. The GPS data set is compiled from U.S. Geological Survey campaign data, Plate Boundary Observatory data, and the Western U.S. Cordillera velocity field of Bennett et al. (1999). In the context of viscoelastic cycle models of postearthquake deformation, the interseismic velocity field is modeled with a combination of earthquake sources on ˜100 known faults plus broadly distributed sources. Models that best explain the observed interseismic velocity field include the contributions of viscoelastic relaxation from faulting near the major plate margins, viscoelastic relaxation from distributed faulting in the plate interior, as well as lateral variations in depth-averaged rigidity in the elastic lithosphere. Resulting rigidity variations are consistent with reduced effective elastic plate thickness in a zone a few tens of kilometers wide surrounding the San Andreas fault (SAF) system. Primary deformation characteristics are captured along the entire SAF system, Eastern California Shear Zone, Walker Lane, the Mendocino triple junction, the Cascadia margin, and the plate interior up to ˜1000 km from the major plate boundaries.

  20. The role of twinning deformation on the hardening response of polycrystalline magnesium from discrete dislocation dynamics simulations

    SciTech Connect

    Fan, Haidong; Aubry, Sylvie; Arsenlis, Athanasios; El-Awady, Jaafar A.

    2015-04-13

    The mechanical response of micro-twinned polycrystalline magnesium was studied through three-dimensional discrete dislocation dynamics (DDD). A systematic interaction model between dislocations and (1012) tension twin boundaries (TBs) was proposed and introduced into the DDD framework. In addition, a nominal grain boundary (GB) model agreeing with experimental results was also introduced to mimic the GB’s barrier effect. The current simulation results show that TBs act as a strong obstacle to gliding dislocations, which contributes significantly to the hardening behavior of magnesium. On the other hand, the deformation accommodated by twinning plays a softening role. Therefore, the concave shape of the Mg stress-strain curve results from the competition between dislocation-TB induced hardening and twinning deformation induced softening. At low strain levels, twinning deformation induced softening dominates and a decreasing hardening rate is observed in Stage-I. In Stage-II, both the hardening and softening effects decline, but twinning deformation induced softening declines faster, which leads to an increasing hardening rate.

  1. The role of twinning deformation on the hardening response of polycrystalline magnesium from discrete dislocation dynamics simulations

    DOE PAGESBeta

    Fan, Haidong; Aubry, Sylvie; Arsenlis, Athanasios; El-Awady, Jaafar A.

    2015-04-13

    The mechanical response of micro-twinned polycrystalline magnesium was studied through three-dimensional discrete dislocation dynamics (DDD). A systematic interaction model between dislocations and (1012) tension twin boundaries (TBs) was proposed and introduced into the DDD framework. In addition, a nominal grain boundary (GB) model agreeing with experimental results was also introduced to mimic the GB’s barrier effect. The current simulation results show that TBs act as a strong obstacle to gliding dislocations, which contributes significantly to the hardening behavior of magnesium. On the other hand, the deformation accommodated by twinning plays a softening role. Therefore, the concave shape of the Mgmore » stress-strain curve results from the competition between dislocation-TB induced hardening and twinning deformation induced softening. At low strain levels, twinning deformation induced softening dominates and a decreasing hardening rate is observed in Stage-I. In Stage-II, both the hardening and softening effects decline, but twinning deformation induced softening declines faster, which leads to an increasing hardening rate.« less

  2. Modeling and 2-D discrete simulation of dislocation dynamics for plastic deformation of metal

    NASA Astrophysics Data System (ADS)

    Liu, Juan; Cui, Zhenshan; Ou, Hengan; Ruan, Liqun

    2013-05-01

    Two methods are employed in this paper to investigate the dislocation evolution during plastic deformation of metal. One method is dislocation dynamic simulation of two-dimensional discrete dislocation dynamics (2D-DDD), and the other is dislocation dynamics modeling by means of nonlinear analysis. As screw dislocation is prone to disappear by cross-slip, only edge dislocation is taken into account in simulation. First, an approach of 2D-DDD is used to graphically simulate and exhibit the collective motion of a large number of discrete dislocations. In the beginning, initial grains are generated in the simulation cells according to the mechanism of grain growth and the initial dislocation is randomly distributed in grains and relaxed under the internal stress. During the simulation process, the externally imposed stress, the long range stress contribution of all dislocations and the short range stress caused by the grain boundaries are calculated. Under the action of these forces, dislocations begin to glide, climb, multiply, annihilate and react with each other. Besides, thermal activation process is included. Through the simulation, the distribution of dislocation and the stress-strain curves can be obtained. On the other hand, based on the classic dislocation theory, the variation of the dislocation density with time is described by nonlinear differential equations. Finite difference method (FDM) is used to solve the built differential equations. The dislocation evolution at a constant strain rate is taken as an example to verify the rationality of the model.

  3. Dislocation dynamics during plastic deformations of complex plasma crystals.

    PubMed

    Durniak, C; Samsonov, D; Ralph, J F; Zhdanov, S; Morfill, G

    2013-11-01

    The internal structures of most periodic crystalline solids contain defects. This affects various important mechanical and thermal properties of crystals. Since it is very difficult and expensive to track the motion of individual atoms in real solids, macroscopic model systems, such as complex plasmas, are often used. Complex plasmas consist of micrometer-sized grains immersed into an ion-electron plasma. They exist in solidlike, liquidlike, and gaseouslike states and exhibit a range of nonlinear and dynamic effects, most of which have direct analogies in solids and liquids. Slabs of a monolayer hexagonal complex plasma were subjected to a cycle of uniaxial compression and decompression of large amplitudes to achieve plastic deformations, both in experiments and simulations. During the cycle, the internal structure of the lattice exhibited significant rearrangements. Dislocations (point defects) were generated and displaced in the stressed lattice. They tended to glide parallel to their Burgers vectors under load. It was found that the deformation cycle was macroscopically reversible but irreversible at the particle scale. PMID:24329366

  4. Dislocation dynamics during plastic deformations of complex plasma crystals

    NASA Astrophysics Data System (ADS)

    Durniak, C.; Samsonov, D.; Ralph, J. F.; Zhdanov, S.; Morfill, G.

    2013-11-01

    The internal structures of most periodic crystalline solids contain defects. This affects various important mechanical and thermal properties of crystals. Since it is very difficult and expensive to track the motion of individual atoms in real solids, macroscopic model systems, such as complex plasmas, are often used. Complex plasmas consist of micrometer-sized grains immersed into an ion-electron plasma. They exist in solidlike, liquidlike, and gaseouslike states and exhibit a range of nonlinear and dynamic effects, most of which have direct analogies in solids and liquids. Slabs of a monolayer hexagonal complex plasma were subjected to a cycle of uniaxial compression and decompression of large amplitudes to achieve plastic deformations, both in experiments and simulations. During the cycle, the internal structure of the lattice exhibited significant rearrangements. Dislocations (point defects) were generated and displaced in the stressed lattice. They tended to glide parallel to their Burgers vectors under load. It was found that the deformation cycle was macroscopically reversible but irreversible at the particle scale.

  5. Transitions of Dislocation Glide to Twinning and Shear Transformation in Shock-Deformed Tantalum

    SciTech Connect

    Hsiung, L L; Campbell, G H; McNaney, J M

    2009-10-19

    tantalum. The observation of {alpha} {yields} {omega} transition in shock-compressed tantalum and tantalum-tungsten alloys at {approx}45 GPa in fact reveals the occurrence of a non-equilibrium phase transformation at such a low pressure. We therefore postulated that the equation of state (EOS) based on static thermodynamics, which asserts that the system free energy (G) is a function of volume (V), pressure (P), and temperature (T), i.e., G = F(V, P, T) is insufficient to rationalize the system free energy under dynamic-pressure conditions. Since shear deformation was found to play a crucial role in shock-induced deformation twins and {omega} phase, the density and arrangement of dislocations, which can alter and increase the system free energy, should also be taken into account to rationalize the non-equilibrium phase transformation in shocked tantalum. Typical arrangements of high-density dislocations formed in pure tantalum shocked at {approx}45 GPa are shown in Figs. 1a and 1b. Figure 1a reveals a cellular dislocation structure but no twins or {omega} phase-domains were observed in this region. The formation of low-energy type cellular dislocation structures indicates the occurrence of dynamic-recovery reactions to reduce dislocation density in this region. Figure 1b shows an evenly distributed dislocation structure with a local dislocation density ({rho}) as high as {approx}5 x 10{sup 12} cm{sup -2} according to {rho} {approx} 1/l{sup 2}, where l ({approx}4.5 nm) is the spacing between two dislocations. Here shock-induced twin plates and {omega} phase-domains can be readily seen. These observations provide us a clue that dislocation arrangement and density population, which can alter system free energy through the changes of dislocation self-energy (E{sub s}) and dislocation interaction energy (E{sub ij}), are relevant to the occurrence of shock-induced twinning and phase transformation in tantalum. The objective of this paper is to report new results obtained from

  6. High dislocation density of tin induced by electric current

    SciTech Connect

    Liao, Yi-Han; Liang, Chien-Lung; Lin, Kwang-Lung; Wu, Albert T.

    2015-12-15

    A dislocation density of as high as 10{sup 17} /m{sup 2} in a tin strip, as revealed by high resolution transmission electron microscope, was induced by current stressing at 6.5 x 10{sup 3} A/ cm{sup 2}. The dislocations exist in terms of dislocation line, dislocation loop, and dislocation aggregates. Electron Backscattered Diffraction images reflect that the high dislocation density induced the formation of low deflection angle subgrains, high deflection angle Widmanstätten grains, and recrystallization. The recrystallization gave rise to grain refining.

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

    PubMed Central

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

    2014-01-01

    Ti2AlN nanolayered ternary alloy has been plastically deformed under confining pressure at 900°C. The dislocation configurations of the deformed material have been analyzed by transmission electron microscopy. The results show a drastic evolution compared to the dislocation configurations observed in the Ti2AlN samples deformed at room temperature. In particular, they evidence out-of-basal-plane dislocations and interactions. Moreover numerous cross-slip events from basal plane to prismatic or pyramidal planes are observed. These original results are discussed in the context of the Brittle-to-Ductile Transition of the nanolayered ternary alloys. PMID:25220949

  8. Modeling of ultrasonic nonlinearities for dislocation evolution in plastically deformed materials: Simulation and experimental validation.

    PubMed

    Zhu, Wujun; Deng, Mingxi; Xiang, Yanxun; Xuan, Fu-Zhen; Liu, Changjun; Wang, Yi-Ning

    2016-05-01

    A nonlinear constitutive relationship was established to investigate nonlinear behaviors of ultrasonic wave propagation in plastically damaged media based on analyses of mixed dislocation evolution. Finite element simulations of longitudinal wave propagation in plastically deformed martensite stainless steel were performed based on the proposed nonlinear constitutive relationship, in which the contribution of mixed dislocation to acoustic nonlinearity was considered. The simulated results were validated by experimental measurements of plastically deformed 30Cr2Ni4MoV martensite stainless steels. Simulated and experimental results both reveal a monotonically increasing tendency of the normalized acoustic nonlinearity parameter as a function of plastic strain. Microscopic studies revealed that the changes of the acoustic nonlinearity are mainly attributed to dislocation evolutions, such as dislocation density, dislocation length, and the type and fraction of dislocations during plastic loading. PMID:26950888

  9. Dislocation

    MedlinePlus

    Joint dislocation ... It may be hard to tell a dislocated joint from a broken bone . Both are emergencies. You ... to repair a ligament that tears when the joint is dislocated is needed. Injuries to nerves and ...

  10. Orientation dependence of shock induced dislocations in Tantalum single crystals

    NASA Astrophysics Data System (ADS)

    Pang, Bo; Jones, I.; Chiu, Yulung; Millett, J.; Whiteman, Glenn; Bourne, N.

    2013-06-01

    Shock wave deformation of monocrystalline tantalum to a pressure of 6.2 GPa and duration of 1.7 μs generates profuse dislocations. Three orientations (100),(110),(111) were tested to examine the orientation dependence of the dislocation generation. The dislocations were characterised by transmission electron microscopy. The difference in the Burgers vectors of the primary dislocations in the specimens with different orientations showed a distinct anisotropy and will be discussed in light of the models of slip behaviour in one-dimensional strain (Smith 1958) and (Meyers 1978). The front and rear surfaces of the specimens were both investigated to examine the effects of wave duration.

  11. Contribution of mixed dislocations to the acoustic nonlinearity in plastically deformed materials

    NASA Astrophysics Data System (ADS)

    Xiang, Yanxun; Deng, Mingxi; Liu, Chang-Jun; Xuan, Fu-Zhen

    2015-06-01

    An analytical model is proposed based on dislocation line energy and variable line tension to describe the influence of mixed dislocations on acoustic nonlinearity in plastically deformed materials. Numerical results indicate that the acoustic nonlinearity parameter β is strongly dependent on the Poisson's ratio, and the fraction and type of the dislocation. For edge dislocations, β is found to increase with increasing Poisson's ratio, which is different from the behavior predicted by existing models. Moreover, this result indicates that β should be more sensitive to edge dislocations in materials with large Poisson's ratios. The proposed model is validated by experimental measurements of cold-rolled 304 stainless steel plates and plastically deformed 30Cr2Ni4MoV martensite stainless steels.

  12. X-Ray Diffraction Study on the Strain Anisotropy and Dislocation Structure of Deformed Lath Martensite

    NASA Astrophysics Data System (ADS)

    Hossein Nedjad, S.; Hosseini Nasab, F.; Movaghar Garabagh, M. R.; Damadi, S. R.; Nili Ahmadabadi, M.

    2011-08-01

    18Ni (300) maraging steel possessing lath martensite structure was deformed by four passes of equal-channel angular pressing (ECAP) at ambient temperature. Line profile analysis (LPA) of X-ray diffraction (XRD) patterns identified strong strain anisotropy and remarkable increases in the relative fraction of screw dislocations after ECAP. The strain anisotropy was reasonably accounted for by the anisotropy of elastic constants. Domination of screw dislocations in the deformed structure was attributed to the preferred annihilation of edge dislocations in the early stages of deformation along with the difficulties for annihilation of screw dislocations by cross slipping. Cobalt addition was mainly assumed to make cross slipping difficult by reducing stacking-fault energy and favoring short-range ordering.

  13. Dislocations

    MedlinePlus

    Dislocations are joint injuries that force the ends of your bones out of position. The cause is often a fall or a blow, sometimes from playing a contact sport. You can dislocate your ankles, knees, shoulders, hips, elbows and jaw. You can also dislocate your finger and toe joints. Dislocated joints often are ...

  14. Dislocation dynamics simulations of interactions between gliding dislocations and radiation induced prismatic loops in zirconium

    NASA Astrophysics Data System (ADS)

    Drouet, Julie; Dupuy, Laurent; Onimus, Fabien; Mompiou, Frédéric; Perusin, Simon; Ambard, Antoine

    2014-06-01

    The mechanical behavior of Pressurized Water Reactor fuel cladding tubes made of zirconium alloys is strongly affected by neutron irradiation due to the high density of radiation induced dislocation loops. In order to investigate the interaction mechanisms between gliding dislocations and loops in zirconium, a new nodal dislocation dynamics code, adapted to Hexagonal Close Packed metals, has been used. Various configurations have been systematically computed considering different glide planes, basal or prismatic, and different characters, edge or screw, for gliding dislocations with -type Burgers vectors. Simulations show various interaction mechanisms such as (i) absorption of a loop on an edge dislocation leading to the formation of a double super-jog, (ii) creation of a helical turn, on a screw dislocation, that acts as a strong pinning point or (iii) sweeping of a loop by a gliding dislocation. It is shown that the clearing of loops is more favorable when the dislocation glides in the basal plane than in the prismatic plane explaining the easy dislocation channeling in the basal plane observed after neutron irradiation by transmission electron microscopy.

  15. Plastic Deformation of Transition Zone Minerals: Effect of Temperature on Dislocation Mobility

    NASA Astrophysics Data System (ADS)

    Ritterbex, S.; Carrez, P.; Gouriet, K.; Cordier, P.

    2014-12-01

    Mantle convection is the fundamental process by which the Earth expels its internal heat. It is controlled at the microscopic scale by the motion of crystal defects responsable for plastic deformation at high temperature and pressure conditions of the deep Earth. In this study we focus on dislocations which are usually considered as the most efficient defects contributing to intracrystalline deformation. The influence of temperature is a key parameter in determining the behaviour of dislocations. We propose a model to describe the temperature-dependent mobility of dislocations based on a computational materials science approach, connecting the atomic to the grain scale. This provides elementary knowledge to both interpret seismic anisotropy and to improve geodynamic modelling. Here we focus on plastic deformation of the transition zone minerals wadsleyite and ringwoodite, dominating the boundary separating the upper from the lower mantle, a region over which the viscosity is thought to increase rapidly. Using the Peierls-Nabarro-Galerkin model enabled us to select potential glide planes, to predict the dislocation core structures and fundamental properties of both Mg2SiO4 high-pressure polymorphs integrating the non-elastic nature of dislocations from atomic scale based calculations. Macroscopic deformation results from the mobility of these distinct dislocations. High finite mantle temperatures activates unstable double-kink configurations on the dislocation line which allow the dislocation to move under stress. The original contribution of the present work is the formulation of a mobility law for dissociated dislocations as they occur in wadsleyite and ringwoodite. This permits us to predict the critical activation enthalpy required to overcome lattice friction associated to the onset of glide. From this, the effective glide velocities can be derived as a function of stress and temperature leading to the first lower bound estimates of transition zone viscosities

  16. Dislocation Density Tensor Characterization of Deformation Using 3D X-Ray Microscopy

    SciTech Connect

    Larson, Ben C; Tischler, Jonathan Zachary; El-Azab, Anter; Liu, Wenjun

    2008-01-01

    Three-dimensional (3D) X-ray microscopy with submicron resolution has been used to make spatially resolved measurements of lattice curvature and elastic strain over two-dimensional slices in thin deformed Si plates. The techniques and capabilities associated with white-beam 3D X-ray microscopy are discussed, and both theoretical and experimental considerations associated with the measurement of Nye dislocation density tensors in deformed materials are presented. The ability to determine the local geometrically necessary dislocation (GND) density in the form of a dislocation density tensor, with micron spatial resolution over mesoscopic length scales, is demonstrated. Results are shown for the special case of an elastically bent (dislocation free) thin Si plate and for a similar thin Si plate that was bent plastically, above the brittle-to-ductile transition temperature, to introduce dislocations. Within the uncertainties of the measurements, the known result that GND density is zero for elastic bending is obtained, and well-defined GND distributions are observed in the plastically deformed Si plate. The direct and absolute connection between experimental measurements of GND density and multiscale modeling and computer simulations of deformation microstructures is discussed to highlight the importance of submicron-resolution 3D X-ray microscopy for mesoscale characterization of material defects and to achieve a fundamental understanding of deformation in ductile materials.

  17. Dislocation density tensor characterization of deformation using 3D x-ray microscopy.

    SciTech Connect

    Larson, B. C.; Tischler, J. Z.; El-Azab, A.; Liu, W.; ORNL; Florida State Univ.

    2008-04-01

    Three-dimensional (3D) X-ray microscopy with submicron resolution has been used to make spatially resolved measurements of lattice curvature and elastic strain over two-dimensional slices in thin deformed Si plates. The techniques and capabilities associated with white-beam 3D X-ray microscopy are discussed, and both theoretical and experimental considerations associated with the measurement of Nye dislocation density tensors in deformed materials are presented. The ability to determine the local geometrically necessary dislocation (GND) density in the form of a dislocation density tensor, with micron spatial resolution over mesoscopic length scales, is demonstrated. Results are shown for the special case of an elastically bent (dislocation free) thin Si plate and for a similar thin Si plate that was bent plastically, above the brittle-to-ductile transition temperature, to introduce dislocations. Within the uncertainties of the measurements, the known result that GND density is zero for elastic bending is obtained, and well-defined GND distributions are observed in the plastically deformed Si plate. The direct and absolute connection between experimental measurements of GND density and multiscale modeling and computer simulations of deformation microstructures is discussed to highlight the importance of submicron-resolution 3D X-ray microscopy for mesoscale characterization of material defects and to achieve a fundamental understanding of deformation in ductile materials.

  18. Three-dimensional deformation analysis of two-phase dislocation substructures

    NASA Technical Reports Server (NTRS)

    Freed, Alan D.; Raj, S. V.; Walker, Kevin P.

    1992-01-01

    Three-dimensional deformation analysis of two-phase dislocation substructures was carried out, extending the Qian and Fan (1991) approach to 3D stress-strain fields by using the Budiansky and Wu (1962) criterion for strain compatibility between the 'hard' and 'soft' regions. The result is a rate-dependent viscoplastic theory, named the dislocation substructure viscoplasticity (DSV), which incorporates a self-consistent effect of dislocation substructure on material response. An algorithm developed for numerical implementation of the DSV theory is presented.

  19. Impact of dislocation cell elastic strain variations on line profiles from deformed copper.

    SciTech Connect

    Levine, L. E.; Larson, B. C.; Tischler, J. Z.; Geantil, P.; Kassner, M. E.; Liu, W.; Stoudt, M. R.; NIST; ORNL; Univ. of Southern California

    2008-01-01

    Energy scanned, sub-micrometer X-ray beams were used to obtain diffraction line profiles from individual dislocation cells in copper single crystals deformed in compression. Sub-micrometer depth resolution was provided by translating a wire through the diffracted beams and using triangulation to determine the depths of the diffracting volumes. Connection to classic volume-averaged results was made by adding the line profiles from 52 spatially resolved dislocation cell measurements. The resulting sub profile is smooth and symmetric, in agreement with early assumptions; the mean strain and full width half maximum are consistent with the average of the parameters extracted from the more exact individual dislocation cell measurements.

  20. Characterization of dislocation structures and deformation mechanisms in as-grown and deformed directionally solidified NiAl–Mo composites

    SciTech Connect

    Kwon, J.; Bowers, M. L.; Brandes, M. C.; McCreary, V.; Robertson, Ian M.; Phani, P. Sudaharshan; Bei, H.; Gao, Y. F.; Pharr, George M.; George, Easo P.; Mills, M. J.

    2015-02-26

    In this paper, directionally solidified (DS) NiAl–Mo eutectic composites were strained to plastic strain values ranging from 0% to 12% to investigate the origin of the previously observed stochastic versus deterministic mechanical behaviors of Mo-alloy micropillars in terms of the development of dislocation structures at different pre-strain levels. The DS composites consist of long, [1 0 0] single-crystal Mo-alloy fibers with approximately square cross-sections embedded in a [1 0 0] single-crystal NiAl matrix. Scanning transmission electron microscopy (STEM) and computational stress state analysis were conducted for the current study. STEM of the as-grown samples (without pre-straining) reveal no dislocations in the investigated Mo-alloy fibers. In the NiAl matrix, on the other hand, a(1 0 0)-type dislocations exist in two orthogonal orientations: along the [1 0 0] Mo fiber axis, and wrapped around the fiber axis. They presumably form to accommodate the different thermal contractions of the two phases during cool down after eutectic solidification. At intermediate pre-strain levels (4–8%), a/2(1 1 1)-type dislocations are present in the Mo-alloy fibers and the pre-existing dislocations in the NiAl matrix seem to be swept toward the interphase boundary. Some of the dislocations in the Mo-alloy fibers appear to be transformed from a(1 0 0)-type dislocations present in the NiAl matrix. Subsequently, the transformed dislocations in the fibers propagate through the NiAl matrix as a(1 1 1) dislocations and aid in initiating additional slip bands in adjacent fibers. Thereafter, co-deformation presumably occurs by (1 1 1) slip in both phases. With a further increase in the pre-strain level (>10%), multiple a/2(1 1 1)-type dislocations are observed in many locations in the Mo-alloy fibers. Interactions between these systems upon subsequent deformation could lead to stable junctions and persistent dislocation sources. Finally, the transition from stochastic to

  1. Characterization of dislocation structures and deformation mechanisms in as-grown and deformed directionally solidified NiAl–Mo composites

    DOE PAGESBeta

    Kwon, J.; Bowers, M. L.; Brandes, M. C.; McCreary, V.; Robertson, Ian M.; Phani, P. Sudaharshan; Bei, H.; Gao, Y. F.; Pharr, George M.; George, Easo P.; et al

    2015-02-26

    In this paper, directionally solidified (DS) NiAl–Mo eutectic composites were strained to plastic strain values ranging from 0% to 12% to investigate the origin of the previously observed stochastic versus deterministic mechanical behaviors of Mo-alloy micropillars in terms of the development of dislocation structures at different pre-strain levels. The DS composites consist of long, [1 0 0] single-crystal Mo-alloy fibers with approximately square cross-sections embedded in a [1 0 0] single-crystal NiAl matrix. Scanning transmission electron microscopy (STEM) and computational stress state analysis were conducted for the current study. STEM of the as-grown samples (without pre-straining) reveal no dislocations inmore » the investigated Mo-alloy fibers. In the NiAl matrix, on the other hand, a(1 0 0)-type dislocations exist in two orthogonal orientations: along the [1 0 0] Mo fiber axis, and wrapped around the fiber axis. They presumably form to accommodate the different thermal contractions of the two phases during cool down after eutectic solidification. At intermediate pre-strain levels (4–8%), a/2(1 1 1)-type dislocations are present in the Mo-alloy fibers and the pre-existing dislocations in the NiAl matrix seem to be swept toward the interphase boundary. Some of the dislocations in the Mo-alloy fibers appear to be transformed from a(1 0 0)-type dislocations present in the NiAl matrix. Subsequently, the transformed dislocations in the fibers propagate through the NiAl matrix as a(1 1 1) dislocations and aid in initiating additional slip bands in adjacent fibers. Thereafter, co-deformation presumably occurs by (1 1 1) slip in both phases. With a further increase in the pre-strain level (>10%), multiple a/2(1 1 1)-type dislocations are observed in many locations in the Mo-alloy fibers. Interactions between these systems upon subsequent deformation could lead to stable junctions and persistent dislocation sources. Finally, the transition from stochastic to

  2. Single-dislocation-based deformation mechanisms in nanolayered composites

    NASA Astrophysics Data System (ADS)

    Misra, Amit

    2004-03-01

    Nanolayered metallic composites, composed of alternating layers of soft metals, are shown to possess several GPa level strengths, often within a factor of two to three of the theoretical strength limit, when the bilayer periods are on the order of a few nanometers. Experiments on model systems such as Cu-Ni and Cu-Nb indicate that, in the micron to sub-micron range, the strengths of these materials increase with microstructural refinement according to the Hall-Petch model. However, as the layer thickness is reduced to the nm-scale, the number of dislocations in a pile-up approaches unity and the pile-up based Hall-Petch model ceases to apply. In the few to a few tens of nanometers range, the increase in yield strength of nanolaminates with decreasing layer thickness is interpreted in terms of the confined layer slip of single dislocations. As layer thickness is decreased to a couple nanometers, strength reaches a peak with weak or no dependence on layer thickness. We show that the peak strength is determined by the stress needed to transmit single dislocations across the interface. Atomistic modeling is used to estimate the single dislocation interface crossing stress for coherent (Cu-Ni), incoherent (Cu-Nb) and nanoscale twinned (austenitic stainless steel 330) interfaces, and compared with experimental data. This work is supported by the U. S. Dept. of Energy, Office of Science, Office of Basic Energy Sciences.

  3. The Interaction of Dislocations and Radiation-Induced Obstacles at High-Strain Rate

    SciTech Connect

    Young, J A; Wirth, B D; Robach, J; Robertson, I

    2003-07-14

    Improved understanding of the plastic deformation of metals during high strain rate shock loading is key to predicting their resulting material properties. This paper presents the results of molecular dynamics simulations that identify the deformation modes of aluminum over a range of applied shear stresses and examines the interaction between dislocations and irradiation induced obstacles. These simulations show that while super-sonic dislocation motion can occur during impact loading, the finite dimensions of the materials render this motion transient. Larger applied loads do not stabilize supersonic dislocations, but instead lead an alternate deformation mode, namely twinning. Finally, the atomistic mechanisms that underlie the observed changes in the mechanical properties of metals as a function of irradiation are examined. Specifically, simulations of the interactions between moving edge dislocations and nanometer-sized helium bubbles provide insight into increases of the critical shear stresses but also reveal the effect of internal gas pressure on the deformation mode. The information gained in these studies provides fundamental insight into materials behavior, as well as important inputs for multi-scale models of materials deformation.

  4. Dislocation processes in the deformation of nanocrystalline aluminium by molecular-dynamics simulation.

    PubMed

    Yamakov, Vesselin; Wolf, Dieter; Phillpot, Simon R; Mukherjee, Amiya K; Gleiter, Herbert

    2002-09-01

    The mechanical behaviour of nanocrystalline materials (that is, polycrystals with a grain size of less than 100 nm) remains controversial. Although it is commonly accepted that the intrinsic deformation behaviour of these materials arises from the interplay between dislocation and grain-boundary processes, little is known about the specific deformation mechanisms. Here we use large-scale molecular-dynamics simulations to elucidate this intricate interplay during room-temperature plastic deformation of model nanocrystalline Al microstructures. We demonstrate that, in contrast to coarse-grained Al, mechanical twinning may play an important role in the deformation behaviour of nanocrystalline Al. Our results illustrate that this type of simulation has now advanced to a level where it provides a powerful new tool for elucidating and quantifying--in a degree of detail not possible experimentally--the atomic-level mechanisms controlling the complex dislocation and grain-boundary processes in heavily deformed materials with a submicrometre grain size. PMID:12618848

  5. Dislocation processes in the deformation of nanocrystalline aluminum by molecular-dynamics simulation.

    SciTech Connect

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

    2002-09-01

    The mechanical behaviour of nanocrystalline materials (that is, polycrystals with a grain size of less than 100 nm) remains controversial. Although it is commonly accepted that the intrinsic deformation behaviour of these materials arises from the interplay between dislocation and grain-boundary processes, little is known about the specific deformation mechanisms. Here we use large-scale molecular-dynamics simulations to elucidate this intricate interplay during room-temperature plastic deformation of model nanocrystalline Al microstructures. We demonstrate that, in contrast to coarse-grained Al, mechanical twinning may play an important role in the deformation behaviour of nanocrystalline Al. Our results illustrate that this type of simulation has now advanced to a level where it provides a powerful new tool for elucidating and quantifying-in a degree of detail not possible experimentally-the atomic-level mechanisms controlling the complex dislocation and grain-boundary processes in heavily deformed materials with a submicrometre grain size.

  6. On the hierarchy of deformation processes in nanocrystalline alloys: Grain boundary mediated plasticity vs. dislocation slip

    NASA Astrophysics Data System (ADS)

    Schäfer, Jonathan; Stukowski, Alexander; Albe, Karsten

    2013-10-01

    Hybrid molecular dynamics and Monte-Carlo simulations on the deformation behavior of nanocrystalline Pd-Au are presented. A semi-grandcanonical Monte-Carlo scheme is employed during straining to allow for local relaxation by chemical equilibration and to effectively shortcut diffusional processes. Altering the balance between an imposed straining and local relaxation reveals a strong correlation of the irreversible plastic deformation and the frequency of local relaxation. Using a novel method to quantify the amount of crystal slip strain from atomistic data, it is demonstrated how plastic deformation carried by dislocations changes as a function of the local relaxation. The results indicate that conventional molecular dynamics simulations overestimate the contributions of dislocation slip to the overall plastic deformation of nanocrystalline samples.

  7. Computational modelling of mesoscale dislocation patterning and plastic deformation of single crystals

    NASA Astrophysics Data System (ADS)

    Xia, Shengxu; El-Azab, Anter

    2015-07-01

    We present a continuum dislocation dynamics model that predicts the formation of dislocation cell structure in single crystals at low strains. The model features a set of kinetic equations of the curl type that govern the space and time evolution of the dislocation density in the crystal. These kinetic equations are coupled to stress equilibrium and deformation kinematics using the eigenstrain approach. A custom finite element method has been developed to solve the coupled system of equations of dislocation kinetics and crystal mechanics. The results show that, in general, dislocations self-organize in patterns under their mutual interactions. However, the famous dislocation cell structure has been found to form only when cross slip is implemented in the model. Cross slip is also found to lower the yield point, increase the hardening rate, and sustain an increase in the dislocation density over the hardening regime. Analysis of the cell structure evolution reveals that the average cell size decreases with the applied stress, which is consistent with the similitude principle.

  8. Dislocation distributions in an Al-4. 5% Mg alloy during superplastic deformation

    SciTech Connect

    Li, F.; Roberts, W.T.; Bate, P.S. . IRC in Materials for High Performance Applications)

    1993-10-01

    Superplasticity has been studied actively for several decades. Many models of the phenomenon have been proposed, in most of which normal dislocation glide has either not been considered or been considered only as an accommodation process to maintain continuity during grain boundary sliding. Although evidence of dislocation activity during superplastic deformation has been observed several times by TEM studies following deformation, the published results appear to be inconsistent and occasionally contradict themselves, and so are unable to provide systematic and convincing evidence for the development of any theoretical model. A major experimental problem associated with those results is the delay between unloading and quenching the specimens from the high testing temperatures. Dislocations can be lost by relaxation and annealing during the unloading and also during the preparation of TEM thin foils. A facility was developed to preserve the high temperature deformation microstructure for consequent TEM examination by quenching and aging under constant stress. This technique and some preliminary results are given elsewhere. The work presented here is from a more comprehensive TEM study of the dislocation distributions in an Al-4.5%Mg alloy developed during deformation at an elevated temperature and a range of strain rates.

  9. PREFACE: DISLOCATIONS 2008 An International Conference on the Fundamentals of Plastic Deformation

    NASA Astrophysics Data System (ADS)

    Cai, Wei; Edagawa, Keiichi; Ngan, Alfonso H. W.

    2009-07-01

    Crystal dislocations are fundamental carriers of plastic deformation in crystalline materials and a good understanding of their behavior forms the scientific basis for improving our ability to manufacture new materials of high mechanical strength. After their initial proposal in 1934, crystal dislocations have become the focus of intense research following their first direct observation in a transmission electron microscope in the 1950's. The last decade has witnessed a new burst of interest and activity in the field, driven in part by the desire to understand the fundamental mechanisms of plasticity in materials at smaller scales, and enabled by significant breakthroughs in both experimental and computational tools. To facilitate information exchange and academic discussions, the ''Dislocations 200X'' international conference series was established in 2000 and has since become the major world forum on crystal dislocations taking place every four years on average. The relatively long period between the conferences leaves sufficient time for new ideas to develop and become worthy of a wide discussion. An important goal of the ''Dislocations 200X'' series is to encourage young researchers to engage in direct communications with the scientists of older generations. The scope of the ''Dislocations 200X'' conference includes fundamental research on dislocations in all types of materials and their role in plasticity. The ''Dislocations 2008'', the third in the series, was held in Hong Kong, 13-17 October 2008. The choice of this conference site reflects the desire to strengthen the connection between scientists on the continents of North America, Europe and Asia. Over 60 talks and 60 posters were presented at the Dislocations 2008 conference. Some presentations have led to papers that are published in this volume after review. Editors: Wei Cai (Stanford University, USA) Keiichi Edagawa (Tokyo University, Japan) Alfonso H W Ngan (Hong Kong University, China)

  10. In Situ Deformation of Olivine in the Transmission Electron Microscope: from Dislocation Velocity Measurements to Stress-Strain Curves

    NASA Astrophysics Data System (ADS)

    Bollinger, C.; Idrissi, H.; Boioli, F.; Cordier, P.

    2015-12-01

    There is a growing consensus to recognize that rheological law established for olivine at high-temperature (ca. >1000°C) fail when extrapolated to low temperatures relevant for the lithospheric mantle. Hence it appears necessary to fit rheological laws against data at low temperatures where olivine tends to become more and more brittle. The usual approach consists in applying confining pressure to inhibit brittleness. Here we propose an innovative approach based on the use of very small samples and numerical modelling. New commercial in situ TEM nanotensile testing equipment recently developed by Hysitron.Inc is combined with weak-beam dark-field TEM diffraction contrast imaging in order to obtain information on the elementary mechanisms controlling the plasticity of olivine: namely glide of [001] screw dislocations. The olivine tensile beams dedicated for in situ TEM nanomechanical testing were produced using microfabrication techniques based on MEMS-type procedures. The testing geometry was designed as to induce maximum resolved shear stresses on the [001](110) slip system. Under tensile loads between 2 and 3 GPa, ductile behaviour was reached with the development and propagation of dislocation loops across the sample allowing to measure the velocity of screw and non-screw dislocations as a function of stress. This information is introduced into a numerical model involving Dislocation Dynamics in order to obtain the stress-strain curves describing the mechanical response of olivine single crystals deformed in tension at room temperature.

  11. Discrete dislocation plasticity analysis of contact between deformable bodies of simple geometry

    NASA Astrophysics Data System (ADS)

    Siang, Kelvin Ng Wei; Nicola, Lucia

    2016-05-01

    A contact mechanical model is presented where both metal bodies can deform by discrete dislocation plasticity. The model intends to improve on previous dislocation dynamics models of contact, where only a plastically deformable body was considered, flattened by a rigid platen. The effect of the rigid platen was mimicked through boundary conditions acting on the deformable body. While the formulation is general, the simulations presented here are only performed for contact between a plastically deforming body with sinusoidal surface and a flat body that is either elastic or rigid. Results show that the contact conditions, i.e. frictionless and full stick, affect the morphology of the contact as well as the contact pressure distribution. This is because dislocations can glide through the frictionless contact and fragment it, but do not penetrate a sticking contact. Average quantities like mean apparent contact pressure and total plastic slip are, instead, independent of contact conditions and of the details of the contact area. A size dependence is observed in relation to the onset of plastic deformation, where surfaces with smaller wavelength and amplitude require a larger contact pressure to yield than self similar surfaces with larger wavelength. The size dependence is very pronounced when the flat body is rigid, but fades when the compliance of the flat body is large.

  12. Dislocation

    MedlinePlus

    ... likely to happen again. Follow-up with an orthopedic surgeon is recommended after a dislocation. ... SE, Mehta A, Maddow C, Luber SD. Critical orthopedic skills and procedures. Emergency Medicine Clinics of North ...

  13. Dislocation-induced superfluidity in a model supersolid

    NASA Astrophysics Data System (ADS)

    Dasbiswas, Kinjal; Goswami, Debajit; Yoo, Chi-Deuk; Dorsey, Alan

    2010-03-01

    The effect of an edge dislocation in inducing superfluidity is explored by coupling the elastic strain field of the dislocation to the superfluid density, and solving the corresponding Ginzburg-Landau theory. It is shown that superfluid density is induced along a single dislocation below a critical temperature determined by the ground state solution of a 2D Schr"odinger equation with a dipolar potential. This superfluid behavior can be described by a 1D Ginzburg-Landau equation obtained through a weakly nonlinear analysis. We then extend our analysis to a network of dislocation lines considered before by Shevchenko and Toner, which could serve as a model for superflow through solid ^4He. The effect of fluctuations and dynamics are included through a full time dependent Ginzburg-Landau theory.

  14. Transmission electron microscopy of dislocations in cementite deformed at high pressure and high temperature

    NASA Astrophysics Data System (ADS)

    Mussi, A.; Cordier, P.; Ghosh, S.; Garvik, N.; Nzogang, B. C.; Carrez, Ph.; Garruchet, S.

    2016-06-01

    Polycrystalline aggregates of cementite (Fe3C) and (Fe,Ni)3C have been synthesised at 10 GPa and 1250 °C in the multianvil apparatus. Further, deformation of the carbides by stress relaxation has been carried out at temperature of 1250 °C and for 8 h at the same pressure. Dislocations have been characterised by transmission electron microscopy. They are of the [1 0 0] and [0 0 1] type, [1 0 0] being the most frequent. [1 0 0] dislocations are dissociated and glide in the (0 1 0) plane. [0 0 1] dislocations glide in (1 0 0) and (0 1 0). Given the plastic anisotropy of cementite, the morphology of the lamellae in pearlitic steels appears to have a major role in the strengthening role played by this phase, since activation of easy slip systems is geometrically inhibited in most cases.

  15. Dynamic instability of dislocation motion at high-strain-rate deformation of crystals with high concentration of point defects

    NASA Astrophysics Data System (ADS)

    Malashenko, V. V.

    2015-12-01

    The motion of an ensemble of edge dislocations has been studied under conditions of high-strainrate deformation of a crystal with a high concentration of point defects. The conditions of existence of the region of dynamic instability of dislocation motion have been found. It has been shown that the existence of the region and its boundaries is determined by the proportion of the point defect concentration and the dislocation density.

  16. Dislocation model for aseismic crustal deformation at Hollister, California

    NASA Technical Reports Server (NTRS)

    Matsuura, Mitsuhiro; Jackson, David D.; Cheng, Abe

    1986-01-01

    A model of crustal deformation during the interseismic phase is developed and applied (using the improved Bayesian inversion algorithm described by Jackson and Matsu'ura, 1985) to trilateration data for the USGS Hollister (CA) network. In the model, rigid blocks in motion relative to each other experience friction only in a brittle upper zone, while their ductile lower zones slide freely; the Hollister model comprises five blocks and nine rectangular fault patches. The data and results are presented in tables, graphs, and maps and characterized in detail. The model predicts steady block motion on time scales between 10 yr and 1 Myr, with net motion across the San Andreas/Calaveras fault system 38 + or - 3 mm/yr and brittle/ductile transition depths ranging from 0.4 to 11 km. Two San Andreas segments with higher probabilities of moderate-to-large earthquakes are identified.

  17. Dislocations

    MedlinePlus

    ... Attempting to move or jam a dislocated bone back in can damage blood vessels, muscles, ligaments, and nerves. Apply an ice pack. Ice can ease swelling and pain in and around the joint. Use ibuprofen or acetaminophen for pain. Think Prevention! Make sure kids wear the appropriate safety gear ...

  18. Transmission electron microscopy characterization of the dislocations of phase A deformed at 11 GPa, 400°C in the multianvil apparatus

    NASA Astrophysics Data System (ADS)

    Cordier, P.; Mussi, A.; Frost, D. J.

    2011-12-01

    Several dense hydrous magnesium silicate (DHMS) phases have been identified as possible carriers for water in subducting slabs. The style and distribution of deformation in subduction zones depends on the nature and rheological properties of subducted materials. If we have reasonable estimates of the rheological properties of anhydrous high-pressure phases, the properties of DHMS are largely unconstrained. In this study, we investigate the deformation mechanisms of phase A (Mg7Si2H6O14) which is hexagonal ( a = 7.86 Å and c = 9.57 Å). Phase A has been synthesized in quasi-hydrostatic conditions from high-purity oxides at 11 GPa, 900°C in a multi-anvil apparatus. After synthesis, the high-pressure phase was recovered and placed in another high-pressure cell designed to induce deviatoric stresses during the compression at 11 GPa, 400°C, i.e. at a temperature lower to the one investigated previously (700°C). Electron transparent thin foils suitable for TEM have been prepared by ion milling at liquid nitrogen temperature. To prevent electron beam damage, TEM characterizations were carried out under low illumination conditions, with a 300 kV accelerating voltage microscope (a Philips° CM30), and a Gatan° cold stage (liquid nitrogen temperature). The grain size of the microstructure is approximately 8 ± 2 μm, with very few sub-grains and the dislocation density is in the order of 2.1013 m-2. At this temperature, we observe many dissociated dislocations with extended stacking faults (dissociation width of the order of 1 μm). Supposing that dislocations are in glide conditions, and using the Ishida's method, we could identify: Partial 1/3 <1 -1 0 0> dislocations and perfect 1/3 <1 1 -2 0> dislocations (in equivalent proportion), in the (0 0 0 1) plane; Partial 1/3 <1 -1 0 0> and 1/3 <-1 1 0 3> dislocations, resulting from the dissociation of 1/3 <2 -1 -1 3> dislocations, and to a lesser extend perfect 1/3 <2 -1 -1 3> dislocations on the {1 -2 1 -1} plane

  19. Direct measurement of hydrogen dislocation pipe diffusion in deformed polycrystalline Pd using quasielastic neutron scattering.

    PubMed

    Heuser, Brent J; Trinkle, Dallas R; Jalarvo, Niina; Serio, Joseph; Schiavone, Emily J; Mamontov, Eugene; Tyagi, Madhusudan

    2014-07-11

    The temperature-dependent diffusivity D(T) of hydrogen solute atoms trapped at dislocations-dislocation pipe diffusion of hydrogen-in deformed polycrystalline PdH(x) (x∼10(-3)  [H]/[Pd]) has been quantified with quasielastic neutron scattering between 150 and 400 K. We observe diffusion coefficients for trapped hydrogen elevated by one to two orders of magnitude above bulk diffusion. Arrhenius diffusion behavior has been observed for dislocation pipe diffusion and regular bulk diffusion, the latter in well-annealed polycrystalline Pd. For regular bulk diffusion of hydrogen in Pd we find D(T)=D(0)exp(-E(a)/kT)=0.005exp(-0.23  eV/kT)  cm(2)/s, in agreement with the known diffusivity of hydrogen in Pd. For hydrogen dislocation pipe diffusion we find D(T)≃10(-5)exp(-E(a)/kT)  cm(2)/s, where E(a)=0.042 and 0.083 eV for concentrations of 0.52×10(-3) and 1.13×10(-3)[H]/[Pd], respectively. Ab initio computations provide a physical basis for the pipe diffusion pathway and confirm the reduced barrier height. PMID:25062206

  20. Deformation localization and dislocation channel dynamics in neutron-irradiated austenitic stainless steels

    NASA Astrophysics Data System (ADS)

    Gussev, Maxim N.; Field, Kevin G.; Busby, Jeremy T.

    2015-05-01

    The dynamics of deformation localization and dislocation channel formation were investigated in situ in a neutron-irradiated AISI 304 austenitic stainless steel and a model 304-based austenitic alloy by combining several analytical techniques including optic microscopy and laser confocal microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy (TEM). Channel formation was observed at ∼70% of the polycrystalline yield stress of the irradiated materials (σ0.2). It was shown that triple junction points do not always serve as a source of dislocation channels; at stress levels below the σ0.2, channels often formed near the middle of the grain boundary. For a single grain, the role of elastic stiffness value (Young's modulus) in channel formation was analyzed; it was shown that in the irradiated 304 steels the initial channels appeared in "soft" grains with a high Schmid factor located near "stiff" grains with high elastic stiffness. The spatial organization of channels in a single grain was analyzed; it was shown that secondary channels operating in the same slip plane as primary channels often appeared at the middle or at one-third of the way between primary channels. The twinning nature of dislocation channels was analyzed for grains of different orientation using TEM. In the AISI 304 steel, channels in grains oriented close to <0 0 1>||TA (tensile axis) and <1 0 1>||TA were twin free and grain with <1 1 1>||TA and grains oriented close to a Schmid factor maximum contained deformation twins.

  1. Deformation localization and dislocation channel dynamics in neutron-irradiated austenitic stainless steels

    DOE PAGESBeta

    Gussev, Maxim N.; Field, Kevin G.; Busby, Jeremy T.

    2015-02-24

    We investigated dynamics of deformation localization and dislocation channel formation in situ in a neutron irradiated AISI 304 austenitic stainless steel and a model 304-based austenitic alloy by combining several analytical techniques including optic microscopy and laser confocal microscopy, scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. Channel formation was observed at 70% of the formal tensile yield stress for both alloys. It was shown that triple junction points do not always serve as a source of dislocation channels; at stress levels below the yield stress, channels often formed near the middle of the grain boundary. For amore » single grain, the role of elastic stiffness value (Young modulus) in the channel formation was analyzed; it was shown that in the irradiated 304 steels the initial channels appeared in soft grains with a high Schmid factor located near stiff grains with high elastic stiffness. Moreover, the spatial organization of channels in a single grain was analyzed; it was shown that secondary channels operating in the same slip plane as primary channels often appeared at the middle or at one third of the way between primary channels. The twinning nature of dislocation channels was analyzed for grains of different orientation using TEM. Finally, it was shown that in the AISI 304 steel, channels were twin-free in grains oriented close to [001] and [101] of standard unit triangle; [111]-grains and grains oriented close to Schmid factor maximum contained deformation twins.« less

  2. Deformation localization and dislocation channel dynamics in neutron-irradiated austenitic stainless steels

    SciTech Connect

    Gussev, Maxim N.; Field, Kevin G.; Busby, Jeremy T.

    2015-02-24

    We investigated dynamics of deformation localization and dislocation channel formation in situ in a neutron irradiated AISI 304 austenitic stainless steel and a model 304-based austenitic alloy by combining several analytical techniques including optic microscopy and laser confocal microscopy, scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. Channel formation was observed at 70% of the formal tensile yield stress for both alloys. It was shown that triple junction points do not always serve as a source of dislocation channels; at stress levels below the yield stress, channels often formed near the middle of the grain boundary. For a single grain, the role of elastic stiffness value (Young modulus) in the channel formation was analyzed; it was shown that in the irradiated 304 steels the initial channels appeared in soft grains with a high Schmid factor located near stiff grains with high elastic stiffness. Moreover, the spatial organization of channels in a single grain was analyzed; it was shown that secondary channels operating in the same slip plane as primary channels often appeared at the middle or at one third of the way between primary channels. The twinning nature of dislocation channels was analyzed for grains of different orientation using TEM. Finally, it was shown that in the AISI 304 steel, channels were twin-free in grains oriented close to [001] and [101] of standard unit triangle; [111]-grains and grains oriented close to Schmid factor maximum contained deformation twins.

  3. Probing deformation substructure by synchrotron X-ray diffraction and dislocation dynamics modelling.

    PubMed

    Korsunsky, Alexander M; Hofmann, Felix; Song, Xu; Eve, Sophie; Collins, Steve P

    2010-09-01

    Materials characterization at the nano-scale is motivated by the desire to resolve the structural aspects and deformation behavior at length scales relevant to those mechanisms that define the novel and unusual properties of nano-structured materials. A range of novel techniques has recently become accessible with the help of synchrotron X-ray beams that can be focused down to spot sizes of less than a few microns on the sample. The unique combination of tunability (energy selection), parallelism and brightness of synchrotron X-ray beams allows their use for high resolution diffraction (determination of crystal structure and transformations, analysis of dislocation sub-structures, orientation and texture analysis, strain mapping); small angle X-ray scattering (analysis of nano-scale voids and defects; orientation analysis) and imaging (radiography and tomography). After a brief review of the state-of-the-art capabilities for monochromatic and white beam synchrotron diffraction, we consider the usefulness of these techniques for the task of bridging the gap between experiment and modeling. Namely, we discuss how the experiments can be configured to provide information relevant to the validation and improvement of modeling approaches, and also how the results of various simulations can be post-processed to improve the possibility of (more or less) direct comparison with experiments. Using the example of some recent experiments carried out on beamline 116 at Diamond Light Source near Oxford, we discuss how such experimental results can be interpreted in view and in conjunction with numerical deformation models, particularly those incorporating dislocation effects, e.g., finite-element based pseudo-continuum strain gradient formulations, and discrete dislocation simulations. Post-processing of FE and discrete dislocation simulations is described, illustrating the kind of information that can be extracted from comparisons between modeling and experimental data. PMID

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

    SciTech Connect

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

    2011-11-01

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

  5. Electronic-structure study of an edge dislocation in Aluminum and the role of macroscopic deformations on its energetics

    NASA Astrophysics Data System (ADS)

    Iyer, Mrinal; Radhakrishnan, Balachandran; Gavini, Vikram

    2015-03-01

    We employed a real-space formulation of orbital-free density functional theory using finite-element basis to study the defect-core and energetics of an edge dislocation in Aluminum. Our study shows that the core-size of a perfect edge dislocation is around ten times the magnitude of the Burgers vector. This finding is contrary to the widely accepted notion that continuum descriptions of dislocation energetics are accurate beyond ∼1-3 Burgers vector from the dislocation line. Consistent with prior electronic-structure studies, we find that the perfect edge dislocation dissociates into two Shockley partials with a partial separation distance of 12.8 Å. Interestingly, our study revealed a significant influence of macroscopic deformations on the core-energy of Shockley partials. We show that this dependence of the core-energy on macroscopic deformations results in an additional force on dislocations, beyond the Peach-Koehler force, that is proportional to strain gradients. Further, we demonstrate that this force from core-effects can be significant and can play an important role in governing the dislocation behavior in regions of inhomogeneous deformations.

  6. Multifunctional Alloys Obtained via a Dislocation-Free Plastic Deformation Mechanism.

    PubMed

    Saito, Takashi; Furuta, Tadahiko; Hwang, Jung-Hwan; Kuramoto, Shigeru; Nishino, Kazuaki; Suzuki, Nobuaki; Chen, Rong; Yamada, Akira; Ito, Kazuhiko; Seno, Yoshiki; Nonaka, Takamasa; Ikehata, Hideaki; Nagasako, Naoyuki; Iwamoto, Chihiro; Ikuhara, Yuuichi; Sakuma, Taketo

    2003-04-18

    We describe a group of alloys that exhibit "super" properties, such as ultralow elastic modulus, ultrahigh strength, super elasticity, and super plasticity, at room temperature and that show Elinvar and Invar behavior. These "super" properties are attributable to a dislocation-free plastic deformation mechanism. In cold-worked alloys, this mechanism forms elastic strain fields of hierarchical structure that range in size from the nanometer scale to several tens of micrometers. The resultant elastic strain energy leads to a number of enhanced material properties. PMID:12702870

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

    SciTech Connect

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

    2011-01-01

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

  8. Role of the static and dynamic aging of dislocations in the kinetics of deformation of doped crystals

    NASA Astrophysics Data System (ADS)

    Petukhov, B. V.

    2014-06-01

    A method has been developed for calculating yield stresses in doped crystals and solid solutions with inclusion of the static and dynamic aging of dislocations. An analytical description of the kinetics of deformation of these materials in the vicinity of the upper yield stress has been proposed. The stage character of stress-strain curves due to the dislocation immobilization by impurity atmospheres formed around dislocations has been demonstrated. The theory is applicable to the calculation of the impurity and solid solution hardening of semiconductors, metals with body-centered cubic (bcc) structure, intermetallic compounds, and other materials.

  9. Effect of plastic deformation on the magnetic properties and dislocation luminescence of isotopically enriched silicon {sup 29}Si:B

    SciTech Connect

    Koplak, O. V.; Shteynman, E. A.; Tereschenko, A. N.; Morgunov, R. B.

    2015-09-15

    A correlation between the temperature dependences of the D1-line intensity of dislocation luminescence and the magnetic moment of plastically deformed isotopically enriched crystals {sup 29}Si:B is found. It is established that the magnetic susceptibility of the deformed crystals obtained by integration of the spectra of electron spin resonance and the D1-line intensity undergo similar nonmonotonic variations with temperature varying in the range of 20–32 K.

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

    NASA Astrophysics Data System (ADS)

    Rogowitz, Anna; Grasemann, Bernhard

    2014-05-01

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

  11. Stochastic dislocation kinetics and fractal structures in deforming metals probed by acoustic emission and surface topography measurements

    SciTech Connect

    Vinogradov, A.; Yasnikov, I. S.; Estrin, Y.

    2014-06-21

    We demonstrate that the fractal dimension (FD) of the dislocation population in a deforming material is an important quantitative characteristic of the evolution of the dislocation structure. Thus, we show that peaking of FD signifies a nearing loss of uniformity of plastic flow and the onset of strain localization. Two techniques were employed to determine FD: (i) inspection of surface morphology of the deforming crystal by white light interferometry and (ii) monitoring of acoustic emission (AE) during uniaxial tensile deformation. A connection between the AE characteristics and the fractal dimension determined from surface topography measurements was established. As a common platform for the two methods, the dislocation density evolution in the bulk was used. The relations found made it possible to identify the occurrence of a peak in the median frequency of AE as a harbinger of plastic instability leading to necking. It is suggested that access to the fractal dimension provided by AE measurements and by surface topography analysis makes these techniques important tools for monitoring the evolution of the dislocation structure during plastic deformation—both as stand-alone methods and especially when used in tandem.

  12. Dislocation structure in AlN films induced by in situ transmission electron microscope nanoindentation

    NASA Astrophysics Data System (ADS)

    Tokumoto, Yuki; Kutsukake, Kentaro; Ohno, Yutaka; Yonenaga, Ichiro

    2012-11-01

    To elucidate dislocation generation and propagation processes in AlN films containing a high density of grown-in threading dislocations (TDs), in situ nanoindentation (NI) was performed in a transmission electron microscope at room temperature. Dislocations with the Burgers vector b = 1/3<12¯10> were introduced not only on the primary slip plane, i.e., the (0001) basal planes, but also on the {101¯1} and {101¯2} pyramidal planes. The results are explained by considering the distribution of the resolved shear stress. It was found that the dislocations induced by NI interact with grown-in TDs: (1) for the NI-induced dislocations on pyramidal planes, edge grown-in TDs induce cross slip to basal planes, and (2) for the NI-induced dislocations on basal planes, screw grown-in TDs prevent their propagation, while edge grown-in TDs do not.

  13. Flux line lattice in deformed superconductor Nb-Mo: Collective pinning and dielastic interaction with screw dislocations

    SciTech Connect

    Grigoryeva, I.V.; Vinnikov, L.Y.

    1989-01-01

    A detailed investigation of the flux line lattice (FLL) interaction with nonuniformly distributed, mainly screw dislocations in deformed Nb-Mo single crystals has been made using the high resolution technique of decorating a sample by small Fe particles. The interaction has been considered from the point of view both of elementary pinning force summation and of the particular pinning mechanism. The FLL has been observed to split into short-range order regions at a low dislocation density and to be amorphous at densities exceeding 10/sup 10/ cm/sup /minus/2/. The dimensions of these regions determine the critical current value in agreement with the collective pinning theory. The observed distribution of the flux lines has been shown to result from the dielastic /Delta/E-interaction of the dislocations with the FLL.

  14. Hydrogen induced plastic deformation of stainless steel

    SciTech Connect

    Gadgil, V.J.; Keim, E.G.; Geijselaers, H.J.M.

    1998-12-31

    Hydrogen can influence the behavior of materials significantly. The effects of hydrogen are specially pronounced in high fugacities of hydrogen which can occur at the surface of steels in contact with certain aqueous environments. In this investigation the effect of high fugacity hydrogen on the surface of stainless steel was investigated using electrochemical cathodic charging. Microhardness was measured on the cross section. Transmission electron microscopy was used to investigate the dislocation substructure just below the surface. Computer simulation using finite element method was carried out to estimate the extent and severity of the deformation. The significance of the results are discussed in relation to the loss of ductility due to hydrogen.

  15. Spatial organization of plastic deformation in single crystals with different structure of slip dislocation

    SciTech Connect

    Kunitsyna, T. S.; Teplyakova, L. A. Koneva, N. A.; Poltaranin, M. A.

    2015-10-27

    It is established that different structure of slip dislocation at the end of the linear hardening stage results in different distribution of dislocation charges in the volume of a single crystal. In the alloy with a near atomic order the slip of single dislocations leads to formation of planar structures—layers with the excess density of dislocations. In the alloy with long-range atomic order the slip of superdislocations brings the formation of the system of parallel rod-like charged dislocation linking.

  16. Deformation-Induced Anisotropy of Polymers

    NASA Technical Reports Server (NTRS)

    Peng, S. T. J.; Landel, R. F.

    1982-01-01

    New theory calculates anisotropies induced by large deformations in polymers. Theory was developed primarily for calculating anistropy of thermal expansivity, but is also applicable to thermal conductivity, elastic moduli and other properties. Theory assumes that in isotropic state, long polymer chains are randomly coiled and not oriented in particular direction. They acquire an orientation when material is deformed. As average molecular orientation increases with deformation, properties of bulk material exhibit averaging of the microscopic anistropies of the oriented molecular segments.

  17. Ion irradiation induced disappearance of dislocations in a nickel-based alloy

    NASA Astrophysics Data System (ADS)

    Chen, H. C.; Li, D. H.; Lui, R. D.; Huang, H. F.; Li, J. J.; Lei, G. H.; Huang, Q.; Bao, L. M.; Yan, L.; Zhou, X. T.; Zhu, Z. Y.

    2016-06-01

    Under Xe ion irradiation, the microstructural evolution of a nickel based alloy, Hastelloy N (US N10003), was studied. The intrinsic dislocations are decorated with irradiation induced interstitial loops and/or clusters. Moreover, the intrinsic dislocations density reduces as the irradiation damage increases. The disappearance of the intrinsic dislocations is ascribed to the dislocations climb to the free surface by the absorption of interstitials under the ion irradiation. Moreover, the in situ annealing experiment reveals that the small interstitial loops and/or clusters induced by the ion irradiation are stable below 600 °C.

  18. Post-irradiation plastic deformation in bcc Fe grains investigated by means of 3D dislocation dynamics simulations

    NASA Astrophysics Data System (ADS)

    Gururaj, K.; Robertson, C.; Fivel, M.

    2015-04-01

    Post-irradiation tensile straining is investigated by means of three-dimensional dislocation dynamics simulations adapted to body centred cubic Fe. Namely, 1 μm Fe grains are strained at various temperatures in the 100-300 K range, in absence and in presence of radiation-induced defect dispersions. The defect-induced hardening is consistent with the disperse barrier effect up to 5 ×1021m-3 loops and is weakly dependent on the straining temperature. The dislocation-loops interaction rate augments with the accumulated plastic strain, loop density and strength; while it is mainly independent of the number of active slip systems and thermally activated screw dislocation mobility. An additional, radiation-induced hardening mechanism known as dislocation "decoration" is also implemented and tested for comparison. Those results show that the plastic flow localisation transition depends on the total yield point rise rather than on the lone, dispersed loop density. The simulation results are then rationalized through an original micro-mechanical model relating the grain-scale stress-strain behaviour to dislocation sub-structure formation and spreading. That model combines strain dependent and strain independent hardening mechanisms, which both contribute to the associated stress-strain response and plastic flow spreading.

  19. Heavy ion irradiation induced dislocation loops in AREVA's M5® alloy

    NASA Astrophysics Data System (ADS)

    Hengstler-Eger, R. M.; Baldo, P.; Beck, L.; Dorner, J.; Ertl, K.; Hoffmann, P. B.; Hugenschmidt, C.; Kirk, M. A.; Petry, W.; Pikart, P.; Rempel, A.

    2012-04-01

    Pressurized water reactor (PWR) Zr-based alloy structural materials show creep and growth under neutron irradiation as a consequence of the irradiation induced microstructural changes in the alloy. A better scientific understanding of these microstructural processes can improve simulation programs for structural component deformation and simplify the development of advanced deformation resistant alloys. As in-pile irradiation leads to high material activation and requires long irradiation times, the objective of this work was to study whether ion irradiation is an applicable method to simulate typical PWR neutron damage in Zr-based alloys, with AREVA's M5® alloy as reference material. The irradiated specimens were studied by electron backscatter diffraction (EBSD), positron Doppler broadening spectroscopy (DBS) and in situ transmission electron microscopy (TEM) at different dose levels and temperatures. The irradiation induced microstructure consisted of - and -type dislocation loops with their characteristics corresponding to typical neutron damage in Zr-based alloys; it can thus be concluded that heavy ion irradiation under the chosen conditions is an excellent method to simulate PWR neutron damage.

  20. Observations of Glide and Decomposition of a<101> Dislocations at High Temperatures in Ni-Al Single Crystals Deformed along the Hard Orientation

    NASA Technical Reports Server (NTRS)

    Srinivasan, R.; Daw, M. S.; Noebe, R. D.; Mills, M. J.

    2003-01-01

    Ni-44at.% Al and Ni-50at.% single crystals were tested in compression in the hard (001) orientations. The dislocation processes and deformation behavior were studied as a function of temperature, strain and strain rate. A slip transition in NiAl occurs from alpha(111) slip to non-alphaaaaaaaaaaa9111) slip at intermediate temperatures. In Ni-50at.% Al single crystal, only alpha(010) dislocations are observed above the slip transition temperature. In contrast, alpha(101)(101) glide has been observed to control deformation beyond the slip transition temperature in Ni-44at.%Al. alpha(101) dislocations are observed primarily along both (111) directions in the glide plane. High-resolution transmission electron microscopy observations show that the core of the alpha(101) dislocations along these directions is decomposed into two alpha(010) dislocations, separated by a distance of approximately 2nm. The temperature window of stability for these alpha(101) dislocations depends upon the strain rate. At a strain rate of 1.4 x 10(exp -4)/s, lpha(101) dislocations are observed between 800 and 1000K. Complete decomposition of a alpha(101) dislocations into alpha(010) dislocations occurs beyond 1000K, leading to alpha(010) climb as the deformation mode at higher temperature. At lower strain rates, decomposition of a alpha(101) dislocations has been observed to occur along the edge orientation at temperatures below 1000K. Embedded-atom method calculations and experimental results indicate that alpha(101) dislocation have a large Peieris stress at low temperature. Based on the present microstructural observations and a survey of the literature with respect to vacancy content and diffusion in NiAl, a model is proposed for alpha(101)(101) glide in Ni-44at.%Al, and for the observed yield strength versus temperature behavior of Ni-Al alloys at intermediate and high temperatures.

  1. A novel unified dislocation density-based model for hot deformation behavior of a nickel-based superalloy under dynamic recrystallization conditions

    NASA Astrophysics Data System (ADS)

    Lin, Y. C.; Wen, Dong-Xu; Chen, Ming-Song; Chen, Xiao-Min

    2016-09-01

    In this study, a novel unified dislocation density-based model is presented for characterizing hot deformation behaviors in a nickel-based superalloy under dynamic recrystallization (DRX) conditions. In the Kocks-Mecking model, a new softening item is proposed to represent the impacts of DRX behavior on dislocation density evolution. The grain size evolution and DRX kinetics are incorporated into the developed model. Material parameters of the developed model are calibrated by a derivative-free method of MATLAB software. Comparisons between experimental and predicted results confirm that the developed unified dislocation density-based model can nicely reproduce hot deformation behavior, DRX kinetics, and grain size evolution in wide scope of initial grain size, strain rate, and deformation temperature. Moreover, the developed unified dislocation density-based model is well employed to analyze the time-variant forming processes of the studied superalloy.

  2. A second-order phase-transformation of the dislocation structure during plastic deformation determined by in situ synchrotron X-ray diffraction

    SciTech Connect

    Schafler, E.; Simon, K.; Bernstorff, S.; Tichy, G.; Ungar, T. . E-mail: ungar@ludens.elte.hu; Zehetbauer, M.J.

    2005-01-10

    In situ X-ray diffraction peak profile analysis during plastic deformation in [0 0 1] oriented copper single crystals was carried out using synchrotron radiation. Characteristic changes of the hardening coefficient indicate that a transition occurs from stage III to stage IV which has been observed for the first time in a single crystal under low temperature deformation conditions. The long-range internal stresses, the dislocation arrangement parameters and the fluctuations of the dislocation density show non-monotonous changes at this transition suggesting that the dislocation structure, especially within the cell-wall regions, reveals a second-order phase transition. A microscopic dislocation model is introduced which not only illustrates the break of symmetry, but also describes well the development of new grains ('fragmentation') during plastic deformation.

  3. Dislocation-accommodated grain boundary sliding as the major deformation mechanism of olivine in the Earth’s upper mantle

    PubMed Central

    Ohuchi, Tomohiro; Kawazoe, Takaaki; Higo, Yuji; Funakoshi, Ken-ichi; Suzuki, Akio; Kikegawa, Takumi; Irifune, Tetsuo

    2015-01-01

    Understanding the deformation mechanisms of olivine is important for addressing the dynamic processes in Earth’s upper mantle. It has been thought that dislocation creep is the dominant mechanism because of extrapolated laboratory data on the plasticity of olivine at pressures below 0.5 GPa. However, we found that dislocation-accommodated grain boundary sliding (DisGBS), rather than dislocation creep, dominates the deformation of olivine under middle and deep upper mantle conditions. We used a deformation-DIA apparatus combined with synchrotron in situ x-ray observations to study the plasticity of olivine aggregates at pressures up to 6.7 GPa (that is, ~200-km depth) and at temperatures between 1273 and 1473 K, which is equivalent to the conditions in the middle region of the upper mantle. The creep strength of olivine deforming by DisGBS is apparently less sensitive to pressure because of the competing pressure-hardening effect of the activation volume and pressure-softening effect of water fugacity. The estimated viscosity of olivine controlled by DisGBS is independent of depth and ranges from 1019.6 to 1020.7 Pa·s throughout the asthenospheric upper mantle with a representative water content (50 to 1000 parts per million H/Si), which is consistent with geophysical viscosity profiles. Because DisGBS is a grain size–sensitive creep mechanism, the evolution of the grain size of olivine is an important process controlling the dynamics of the upper mantle. PMID:26601281

  4. Spiderweb deformation induced by electrostatically charged insects

    NASA Astrophysics Data System (ADS)

    Ortega-Jimenez, Victor Manuel; Dudley, Robert

    2013-07-01

    Capture success of spider webs has been associated with their microstructure, ornamentation, and wind-induced vibrations. Indirect evidence suggests that statically charged objects can attract silk thread, but web deformations induced by charged insects have not yet been described. Here, we show under laboratory conditions that electrostatically charged honeybees, green bottle flies, fruit flies, aphids, and also water drops falling near webs of cross-spiders (Araneus diadematus) induce rapid thread deformation that enhances the likelihood of physical contact, and thus of prey capture.

  5. Spiderweb deformation induced by electrostatically charged insects

    PubMed Central

    Ortega-Jimenez, Victor Manuel; Dudley, Robert

    2013-01-01

    Capture success of spider webs has been associated with their microstructure, ornamentation, and wind-induced vibrations. Indirect evidence suggests that statically charged objects can attract silk thread, but web deformations induced by charged insects have not yet been described. Here, we show under laboratory conditions that electrostatically charged honeybees, green bottle flies, fruit flies, aphids, and also water drops falling near webs of cross-spiders (Araneus diadematus) induce rapid thread deformation that enhances the likelihood of physical contact, and thus of prey capture. PMID:23828093

  6. Fields induced by three-dimensional dislocation loops in anisotropic magneto-electro-elastic bimaterials

    NASA Astrophysics Data System (ADS)

    Han, Xueli; Pan, Ernie; Sangghaleh, Ali

    2013-08-01

    The coupled elastic, electric and magnetic fields produced by an arbitrarily shaped three-dimensional dislocation loop in general anisotropic magneto-electro-elastic (MEE) bimaterials are derived. First, we develop line-integral expressions for the fields induced by a general dislocation loop. Then, we obtain analytical solutions for the fields, including the extended Peach-Koehler force, due to some useful dislocation segments such as straight line and elliptic arc. The present solutions contain the piezoelectric, piezomagnetic and purely elastic solutions as special cases. As numerical examples, the fields induced by a square and an elliptic dislocation loop in MEE bimaterials are studied. Our numerical results show the coupling effects among different fields, along with various interesting features associated with the dislocation and interface.

  7. The breakdown of superlubricity by driving-induced commensurate dislocations

    PubMed Central

    Benassi, A.; Ma, Ming; Urbakh, M.; Vanossi, A.

    2015-01-01

    In the framework of a Frenkel-Kontorova-like model, we address the robustness of the superlubricity phenomenon in an edge-driven system at large scales, highlighting the dynamical mechanisms leading to its failure due to the slider elasticity. The results of the numerical simulations perfectly match the length critical size derived from a parameter-free analytical model. By considering different driving and commensurability interface configurations, we explore the distinctive nature of the transition from superlubric to high-friction sliding states which occurs above the critical size, discovering the occurrence of previously undetected multiple dissipative jumps in the friction force as a function of the slider length. These driving-induced commensurate dislocations in the slider are then characterized in relation to their spatial localization and width, depending on the system parameters. Setting the ground to scale superlubricity up, this investigation provides a novel perspective on friction and nanomanipulation experiments and can serve as a theoretical basis for designing high-tech devices with specific superlow frictional features. PMID:26553308

  8. A dislocation-based, strain–gradient–plasticity strengthening model for deformation processed metal–metal composites

    SciTech Connect

    Tian, Liang; Russell, Alan; Anderson, Iver

    2014-01-03

    Deformation processed metal–metal composites (DMMCs) are high-strength, high-electrical conductivity composites developed by severe plastic deformation of two ductile metal phases. The extraordinarily high strength of DMMCs is underestimated using the rule of mixture (or volumetric weighted average) of conventionally work-hardened metals. A dislocation-density-based, strain–gradient–plasticity model is proposed to relate the strain-gradient effect with the geometrically necessary dislocations emanating from the interface to better predict the strength of DMMCs. The model prediction was compared with our experimental findings of Cu–Nb, Cu–Ta, and Al–Ti DMMC systems to verify the applicability of the new model. The results show that this model predicts the strength of DMMCs better than the rule-of-mixture model. The strain-gradient effect, responsible for the exceptionally high strength of heavily cold worked DMMCs, is dominant at large deformation strain since its characteristic microstructure length is comparable with the intrinsic material length.

  9. A dislocation-based, strain–gradient–plasticity strengthening model for deformation processed metal-metal composites

    SciTech Connect

    Tian, Liang; Russell, Alan; Anderson, Iver

    2014-01-03

    Deformation processed metal–metal composites (DMMCs) are high-strength, high-electrical conductivity composites developed by severe plastic deformation of two ductile metal phases. The extraordinarily high strength of DMMCs is underestimated using the rule of mixture (or volumetric weighted average) of conventionally work-hardened metals. In this article, a dislocation-density-based, strain–gradient–plasticity model is proposed to relate the strain-gradient effect with the geometrically necessary dislocations emanating from the interface to better predict the strength of DMMCs. The model prediction was compared with the experimental findings of Cu–Nb, Cu–Ta, and Al–Ti DMMC systems to verify the applicability of the new model. The results show that this model predicts the strength of DMMCs better than the rule-of-mixture model. The strain-gradient effect, responsible for the exceptionally high strength of heavily cold worked DMMCs, is dominant at large deformation strain since its characteristic microstructure length is comparable with the intrinsic material length.

  10. A dislocation-based, strain–gradient–plasticity strengthening model for deformation processed metal–metal composites

    DOE PAGESBeta

    Tian, Liang; Russell, Alan; Anderson, Iver

    2014-01-03

    Deformation processed metal–metal composites (DMMCs) are high-strength, high-electrical conductivity composites developed by severe plastic deformation of two ductile metal phases. The extraordinarily high strength of DMMCs is underestimated using the rule of mixture (or volumetric weighted average) of conventionally work-hardened metals. A dislocation-density-based, strain–gradient–plasticity model is proposed to relate the strain-gradient effect with the geometrically necessary dislocations emanating from the interface to better predict the strength of DMMCs. The model prediction was compared with our experimental findings of Cu–Nb, Cu–Ta, and Al–Ti DMMC systems to verify the applicability of the new model. The results show that this model predicts themore » strength of DMMCs better than the rule-of-mixture model. The strain-gradient effect, responsible for the exceptionally high strength of heavily cold worked DMMCs, is dominant at large deformation strain since its characteristic microstructure length is comparable with the intrinsic material length.« less

  11. Doping-induced suppression of dislocation formation in semiconductors

    SciTech Connect

    Walukiewicz, W.

    1989-04-15

    A mechanism explaining suppression of dislocation formation in doped semiconductors is proposed. The mechanism is based on the recently introduced concept of amphoteric native defects. It is shown that supersaturation of vacancylike defects depends on the Fermi energy and thus also on the doping level. The calculated dependence of supersaturation on the doping level quantitatively accounts for experimentally observed trends in dislocation suppression in GaAs and InP.

  12. Chloroquine-induced bilateral anterior shoulder dislocation: a unique aetiology for a rare clinical problem.

    PubMed

    Martin, Alexander Nicholas; Tsekes, Dimitris; White, William James; Rossouw, Dan

    2016-01-01

    Bilateral anterior shoulder dislocation is a rare clinical entity with few case reports and limited series published in the literature. Bilateral shoulder dislocations are rare and of them, most are posterior. We present a highly unusual case of bilateral, atraumatic, anterior shoulder dislocation with concomitant comminuted greater tuberosity fracture on the right side, secondary to seizure, in a patient without known epilepsy, induced by oral chloroquine medication. We demonstrate the treatment approach that led to a satisfactory clinical outcome, evidenced by radiological union, clinical assessment and Patient Reported Outcome Measure data, following non-operative management of both shoulders. The unusual mechanism for anterior shoulder dislocation, the asymmetric dislocation pattern and peculiar precipitant for the causative seizure all provide interesting learning points from this case. PMID:27005796

  13. Cyclic deformation behavior and dislocation substructures of hexagonal Zircaloy-4 under out-of-phase loading

    SciTech Connect

    Lin, X.

    2000-01-01

    Macroscopic response and microscopic dislocation structures of Zr-4 subjected to biaxial fatigue under different phase angles of 30{degree}, 60{degree}, 90{degree}, and different equivalent strain ranges of 0.8%, 0.6%, 0.4% were studied. The testing results show that the delay angle between the stress deviators and strain increment tensors is strongly dependent on phase angle and the equivalent strain range. When phase angle equals 60{degree}, the delay angle has the minimum variation range for all specimens. The mean value of the delay angle decreases with increasing phase angle or the equivalent strain range. The variation range and average value of the Mises equivalent stress have the maximum in S3 with the phase angle of 90{degree}. They decrease as the equivalent strain range decreases. Zr-4 displays a pronounced initial hardening followed by a continuous softening for all specimens during out-of-phase cycling. The stabilized saturation stresses of Zr-4 under out-of-phase cycling are much higher than that under uniaxial cycling. It indicates that Zr-4 displays an obvious additional hardening. As the phase angle increases, the typical dislocation structure changes from dislocation cells to tangles. The dislocation-dislocation interactions increase resulting in an additional hardening. In essence, the degree of additional hardening depends, among other factors, on the maximum shear stress ratio of resolved shear stresses and critical resolved shear stresses (RSS/CRSS).

  14. Determination of the activation enthalpy for migration of dislocations in plastically deformed 8006 Al-alloy by positron annihilation lifetime technique

    NASA Astrophysics Data System (ADS)

    Salah, Mohammed; Abdel-Rahman, M.; Badawi, Emad A.; Abdel-Rahman, M. A.

    2016-06-01

    The activation enthalpy for migration of dislocations of plastically deformed 8006 Al-alloy was investigated by positron annihilation lifetime technique. Plastic deformation using a hydraulic press produces mainly dislocations and may produce point defects. The type of defect was studied by isochronal annealing which determines the temperature range of recovery of each type. Only one type of defect (dislocations) was observed for the investigated sample and was found to be recovered within the range 455-700 K. Isothermal annealing by slow cooling was performed through this range and used in determination of the activation enthalpy of migration of dislocations which was found to be 0.26 ± 0.01 eV.

  15. Dislocation Mechanics Under Extreme Pressures

    NASA Astrophysics Data System (ADS)

    Armstrong, Ronald; Arnold, Werner; Zerilli, Frank

    2007-06-01

    The shock-induced plasticity of copper, Armco iron, and tantalum materials is attributed to strain rate control by a substantial dislocation density being generated at the shock front. A thermal activation type constitutive equation is employed for the dislocation generation based on achievement of a limiting small activation volume for the process. A linear dependence of the equivalent compressive stress on logarithm of the plastic strain rate is predicted. The prediction compares favorably with Swegle-Grady and Meyers measurements previously fitted to a power law relationship. For Armco iron and tantalum, control is matched with a dislocation description of deformation twinning at the shock front. By comparison, the uniform shock-less loading in an isentropic compression experiment (ICE) provides for plastic strain rate control by the drag-resisted movement of mobile dislocations within the resident dislocation density.

  16. Shock-induced deformation of nanocrystalline Al: Characterization with orientation mapping and selected area electron diffraction

    NASA Astrophysics Data System (ADS)

    Wang, L.; E, J. C.; Cai, Y.; Zhao, F.; Fan, D.; Luo, S. N.

    2015-02-01

    We investigate shock-induced deformation of columnar nanocrystalline Al with large-scale molecular dynamics simulations and implement orientation mapping (OM) and selected area electron diffraction (SAED) for microstructural analysis. Deformation mechanisms include stacking fault formation, pronounced twinning, dislocation slip, grain boundary (GB) sliding and migration, and lattice or partial grain rotation. GBs and GB triple junctions serve as the nucleation sites for crystal plasticity including twinning and dislocations, due to GB weakening, and stress concentrations. Grains with different orientations exhibit different densities of twins or stacking faults nucleated from GBs. GB migration occurs as a result of differential deformation between two grains across the GB. High strain rates, appropriate grain orientation and GBs contribute to deformation twinning. Upon shock compression, intra-grain dislocation and twinning nucleated from GBs lead to partial grain rotation and the formation of subgrains, while whole grain rotation is not observed. During tension, stress gradients associated with the tensile pulse give rise to intra-grain plasticity and then partial grain rotation. The simulated OM and SAED are useful to describe lattice/grain rotation, the formation of subgrains, GB migration and other microstructures.

  17. Dislocations and deformation microstructure in a B2-ordered Al28Co20Cr11Fe15Ni26 high-entropy alloy

    PubMed Central

    Feuerbacher, Michael

    2016-01-01

    High-entropy alloys are multicomponent metallic materials currently attracting high research interest. They display a unique combination of chemical disorder and crystalline long-range order, and due to their attractive properties are promising candidates for technological application. Many high-entropy alloys possess surprisingly high strength, occasionally in combination with high ductility and low density. The mechanisms effecting these attractive mechanical properties are not understood. This study addresses the deformation mechanism of a Al28Co20Cr11Fe15Ni26 high-entropy alloy, which is a two-phase material, consisting of a B2-ordered matrix and disordered body-centred inclusions. We quantitatively analyse the microstructure and dislocations in deformed samples by transmission-electron-microscopic methods including weak-beam imaging and convergent-beam electron diffraction. We find that the deformation process in the B2 phase is dominated by heterogeneous slip of screw dislocations gliding on planes. The dislocations are perfect superdislocations of the B2 lattice and show no dissociation. This indicates that the antiphase-boundary energy in the structure is very high, inhibiting spread of the dislocation core. Along with the observation of a widely extending strain field associated to the dislocations, our results provide a possible explanation for the high strength of this high-entropy alloy as a direct consequence of its dislocation structure. PMID:27430993

  18. Dislocations and deformation microstructure in a B2-ordered Al28Co20Cr11Fe15Ni26 high-entropy alloy.

    PubMed

    Feuerbacher, Michael

    2016-01-01

    High-entropy alloys are multicomponent metallic materials currently attracting high research interest. They display a unique combination of chemical disorder and crystalline long-range order, and due to their attractive properties are promising candidates for technological application. Many high-entropy alloys possess surprisingly high strength, occasionally in combination with high ductility and low density. The mechanisms effecting these attractive mechanical properties are not understood. This study addresses the deformation mechanism of a Al28Co20Cr11Fe15Ni26 high-entropy alloy, which is a two-phase material, consisting of a B2-ordered matrix and disordered body-centred inclusions. We quantitatively analyse the microstructure and dislocations in deformed samples by transmission-electron-microscopic methods including weak-beam imaging and convergent-beam electron diffraction. We find that the deformation process in the B2 phase is dominated by heterogeneous slip of screw dislocations gliding on planes. The dislocations are perfect superdislocations of the B2 lattice and show no dissociation. This indicates that the antiphase-boundary energy in the structure is very high, inhibiting spread of the dislocation core. Along with the observation of a widely extending strain field associated to the dislocations, our results provide a possible explanation for the high strength of this high-entropy alloy as a direct consequence of its dislocation structure. PMID:27430993

  19. Dislocations and deformation microstructure in a B2-ordered Al28Co20Cr11Fe15Ni26 high-entropy alloy

    NASA Astrophysics Data System (ADS)

    Feuerbacher, Michael

    2016-07-01

    High-entropy alloys are multicomponent metallic materials currently attracting high research interest. They display a unique combination of chemical disorder and crystalline long-range order, and due to their attractive properties are promising candidates for technological application. Many high-entropy alloys possess surprisingly high strength, occasionally in combination with high ductility and low density. The mechanisms effecting these attractive mechanical properties are not understood. This study addresses the deformation mechanism of a Al28Co20Cr11Fe15Ni26 high-entropy alloy, which is a two-phase material, consisting of a B2-ordered matrix and disordered body-centred inclusions. We quantitatively analyse the microstructure and dislocations in deformed samples by transmission-electron-microscopic methods including weak-beam imaging and convergent-beam electron diffraction. We find that the deformation process in the B2 phase is dominated by heterogeneous slip of screw dislocations gliding on planes. The dislocations are perfect superdislocations of the B2 lattice and show no dissociation. This indicates that the antiphase-boundary energy in the structure is very high, inhibiting spread of the dislocation core. Along with the observation of a widely extending strain field associated to the dislocations, our results provide a possible explanation for the high strength of this high-entropy alloy as a direct consequence of its dislocation structure.

  20. Vortex dislocations in wake-type flow induced by spanwise disturbances

    NASA Astrophysics Data System (ADS)

    Ling, Guo Can; Zhao, Hong Liang

    2009-07-01

    Vortex dislocations in wake-type flow induced by three types of spanwise disturbances superimposed on an upstream velocity profile are investigated by direct numerical simulations. Three distinct modes of vortex dislocations and flow transitions have been found. A local spanwise exponential decay disturbance leads to the appearance of a twisted chainlike mode of vortex dislocation. A stepped spanwise disturbance causes a streamwise periodic spotlike mode of vortex dislocation. A spanwise sinusoidal wavy disturbance with a moderate waviness causes a strong unsteadiness of wake behavior. This unsteadiness starts with a systematic periodic mode of vortex dislocation in the spanwise direction followed by the spanwise vortex shedding suppressed completely with increased time and the near wake becoming a steady shear flow. Characteristics of these modes of vortex dislocation and complex vortex linkages over the dislocation, as well as the corresponding dynamic processes related to the appearance of dislocations, are described by examining the variations of vortex lines and vorticity distribution. The nature of the vortex dislocation is demonstrated by the substantial vorticity modification of the spanwise vortex from the original spanwise direction to streamwise and vertical directions, accompanied by the appearance of noticeable vortex branching and complex vortex linking, all of which are produced at the locations with the biggest phase difference or with a frequency discontinuity between shedding cells. The effect of vortex dislocation on flow transition, either to an unsteady irregular vortex flow or suppression of the Kármán vortex shedding making the wake flow steady state, is analyzed. Distinct similarities are found in the mechanism and main flow phenomena between the present numerical results obtained in wake-type flows and the experimental-numerical results of cylinder wakes reported in previous studies.

  1. Deformation-induced {alpha}{sub 2} {yields} {gamma} phase transformation in TiAl alloys

    SciTech Connect

    Chen, C.L.; Lu, W.; Sun Dai; He, L.L.; Ye, H.Q.

    2010-11-15

    Deformation-induced {alpha}{sub 2} {yields} {gamma} phase transformation in high Nb containing TiAl alloys was investigated using high-resolution transmission electron microscopy (HREM) and energy dispersive X-ray spectroscopy (EDS). The dislocations appearing at the tip of deformation-induced {gamma} plate (DI-{gamma}) and the stacking sequence change of the {alpha}{sub 2} matrix were two key evidences for determining the occurrence of the deformation-induced {alpha}{sub 2} {yields} {gamma} phase transformation. Compositional analysis revealed that the product phase of the room-temperature transformation was not standard {gamma} phase; on the contrary, the product phase of the high-temperature transformation was standard {gamma} phase.

  2. Dislocation-nucleation-controlled deformation of Ni3Al nanocubes in molecular dynamics simulations

    NASA Astrophysics Data System (ADS)

    Shreiber, Koren; Mordehai, Dan

    2015-12-01

    The strength of Ni3Al nanocubes under compression, as well as the underlying dislocation mechanisms, are analysed in molecular dynamics simulations. For this purpose, the bond-order parameters analysis is extended to multi-atomic systems in order to identify the intrinsic planar defects in Ni3Al. We benchmarked different interatomic potentials and compared the results with experimental ones. The different potentials resulted in different elastic responses under compression but all yielded abruptly at a compressive stress of about 7-8 GPa, followed by a large strain burst. The nanocubes yielded by nucleating Shockley partial dislocations at the vertices on ≤ft\\{1 1 1\\right\\} planes, leaving a structure of faulted planes. The mechanical response was found to be size independent, which we attribute to the cubical shape of the nanoparticle and the lack of stress gradients at its vertices.

  3. Modeling of friction-induced deformation and microstructures.

    SciTech Connect

    Michael, Joseph Richard; Prasad, Somuri V.; Jungk, John Michael; Cordill, Megan J.; Bammann, Douglas J.; Battaile, Corbett Chandler; Moody, Neville Reid; Majumdar, Bhaskar Sinha (New Mexico Institure of Mining and Technology)

    2006-12-01

    Frictional contact results in surface and subsurface damage that could influence the performance, aging, and reliability of moving mechanical assemblies. Changes in surface roughness, hardness, grain size and texture often occur during the initial run-in period, resulting in the evolution of subsurface layers with characteristic microstructural features that are different from those of the bulk. The objective of this LDRD funded research was to model friction-induced microstructures. In order to accomplish this objective, novel experimental techniques were developed to make friction measurements on single crystal surfaces along specific crystallographic surfaces. Focused ion beam techniques were used to prepare cross-sections of wear scars, and electron backscattered diffraction (EBSD) and TEM to understand the deformation, orientation changes, and recrystallization that are associated with sliding wear. The extent of subsurface deformation and the coefficient of friction were strongly dependent on the crystal orientation. These experimental observations and insights were used to develop and validate phenomenological models. A phenomenological model was developed to elucidate the relationships between deformation, microstructure formation, and friction during wear. The contact mechanics problem was described by well-known mathematical solutions for the stresses during sliding friction. Crystal plasticity theory was used to describe the evolution of dislocation content in the worn material, which in turn provided an estimate of the characteristic microstructural feature size as a function of the imposed strain. An analysis of grain boundary sliding in ultra-fine-grained material provided a mechanism for lubrication, and model predictions of the contribution of grain boundary sliding (relative to plastic deformation) to lubrication were in good qualitative agreement with experimental evidence. A nanomechanics-based approach has been developed for characterizing the

  4. Gravitational effects of process-induced dislocations in silicon. [during thermal cycling

    NASA Technical Reports Server (NTRS)

    Porter, W. A.; Parker, D. L.

    1974-01-01

    Matters pertaining to semiconductor device fabrication were studied in terms of the influence of gravity on the production of dislocations in silicon wafers during thermal cycling in a controlled ambient where no impurities are present and oxidation is minimal. Both n-type and p-type silicon wafers having a diameter of 1.25 in to 1.5 in, with fixed orientation and resistivity values, were used. The surface dislocation densities were measured quantitatively by the Sirtl etch technique. The results show two significant features of the plastic flow phenomenon as it is related to gravitational stress: (1) the density of dislocations generated during a given thermal cycle is directly related to the duration of the cycle; and (2) the duration of the thermal cycle required to produce a given dislocation density is inversely related to the equilibrium temperature. Analysis of the results indicates that gravitational stress is instrumental in process-induced defect generation.

  5. Experimental Deformation of Olivine Single Crystal at Mantle P and T: Pressure Effect on Olivine Dislocation Slip-System Activities

    NASA Astrophysics Data System (ADS)

    Paul, R.; Girard, J.; Chen, J.; Amiguet, E.

    2008-12-01

    Seismic velocity anisotropies observed in the upper mantle are interpreted from lattice preferred orientations (LPO) produced experimentally in olivine, which depends on the dominant dislocation slip systems. At low pressure P<3 GPa, mantle temperature (T) and in dry conditions, olivine [100] dislocation slip dominates the less active [001] slip. This tends to align crystal fast velocity [100] axis with the principal shear direction. Yet recent high-pressure deformation experiments (Couvy et al., 2004, EJM, 16, 877; Raterron et al., 2007, Am. Min., 92, 1436; Raterron et al., 2008, Phys. Earth Planet. Int., doi:10.1016/j.pepi.2008.07.026) show that [001](010) slip system dominates [100](010) system in the (P,T) range of the deep upper mantle. This may promote a shear-parallel slow-velocity [001] axis and may explain the seismic-velocity attenuation observed at depth >200 km (Mainprice et al., 2005, Nature, 433, 731). In order to further constrain the effect of P on olivine slip system activities, which is classically quantified by the activation volume V* in power creep laws, deformation experiments were carried out in poor water condition, at P>5 GPa and T=1400°C, on pure forsterite (Fo100) and San Carlos olivine crystals, using the Deformation-DIA apparatus at the X17B2 beamline of the NSLS (Upton, NY). Ten crystals were oriented in order to active either [100] slip alone or [001] slip alone in (010) plane, or both [100](001) and [001](100) systems together. Constant applied stress σ <300 MPa and specimen strain rates were monitored in situ using time-resolved x-ray diffraction and radiography, respectively, for a total of 27 investigated steady state conditions. The obtained rheological data were compared with data previously obtained in comparable T and σ conditions, but at room P, by Darot and Gueguen (1981, JGR, 86, 6219) for Fo100 and by Bai et al. (1991, JGR, 96, 2441) for San Carlos olivine. This new set of data confirms previous deformation data

  6. Fracture toughness from atomistic simulations: Brittleness induced by emission of sessile dislocations

    SciTech Connect

    Farkas, D.

    1998-08-04

    Using atomistic simulations of crack response for intermetallic materials the author shows that when the emitted dislocations are sessile and stay in the immediate vicinity of the crack tip the emitted dislocations can actually lead to brittle failure. She present the results of an atomistic simulation study of the simultaneous dislocation emission and crack propagation process in this class of materials. She used a molecular statics technique with embedded atom (EAM) potentials developed for NiAl. The crystal structure of NiAl is the CsCl type (B2) with a lattice parameter of 0.287 nm, which is reproduced by the potential together with the cohesive energy and elastic constants. The compound stays ordered up to the melting point, indicating a strong tendency towards chemical ordering with a relatively high energy of the antiphase boundary (APB). As a result of this relatively large energy the dislocations of 1/2<111> type Burgers vectors imply a high energy and the deformation process occurs via the larger <100> type dislocations.

  7. Stress induced roughening of superclimbing dislocation in solid 4He

    NASA Astrophysics Data System (ADS)

    Aleinikava, Darya; Kuklov, Anatoly

    2011-03-01

    We investigate numerically superclimb of dislocation in solid 4 He biased by externally imposed chemical potential μ . The effective action takes into account quantum phase slips in the core superfluid as well as the core displacement in Peierls potential within the Granato-Lücke string model. The bias produces stress on the core and this can result in dislocation roughening. Such roughening is characterized by hysteretic behavior at temperatures (T) below some threshold Thyst . At T >Thyst strongresonantpeaksdevelopinthedislocationdifferentialresponse . Thesepeaksexhibitperiodicbehaviorvs μ, with the period determined by Peierls potential and dislocation length. We explain these effects by thermally assisted tunneling of jog-antijog pairs across the barrier created by Peierls potential and the bias. Since superclimbing is controlled by core superflow, speed of sound along the superfluid core exhibits dip-like features at the peak positions. We propose that this effect is seen in the mass transport experiment. We acknowledge support by NSF, grants PHY1005527 and PHY0653135,and by CUNY, grant 63071-00 41.

  8. Plastic deformation and impaction of the retroacetabular surface associated with posterior fracture-dislocation of the hip: description of two cases.

    PubMed

    Meier, Sandra; Isler, Balz; Gautier, Emanuel

    2007-10-01

    In two cases of posterior fracture-dislocation of the hip, we found an impaction and plastic deformation of the retroacetabular surface, in addition to other typically associated lesions. This deformation creates a mismatch between the stable and the free fragments of the posterior wall, and if unrecognized makes an anatomic reconstruction of the posterior wall impossible. On the computed tomography scan, the most characteristic sign is a concave deformation of the retroacetabular region as compared to the contralateral side. To our knowledge, this specific fracture-dislocation pattern has not been previously described in the literature. If orthopedic surgeons know about the existence of this deformation, then they will easily recognize the impaction on preoperative computed tomography scan and will be able to achieve an anatomic reduction of the acetabulum. Diagnostic aspects and the operative technique to approach this problem are described and illustrated in two cases. PMID:17921844

  9. Sensitivity of ion induced charge pulses to the electrical and crystallographic properties of 60° dislocations

    NASA Astrophysics Data System (ADS)

    Breese, M. B. H.; King, P. J. C.; Grime, G. W.

    1994-12-01

    This letter reports evidence that the size of MeV ion induced charge pulses measured from epitaxial Si0.875Ge0.125/Si depends on both the crystallographic and electrical properties of the 60° misfit dislocations present. The results are correlated with both backscattered and transmission ion channeling analysis. With the sample in nonchanneled alignment the measured ion induced charge pulses depend on the number of charge carriers which recombine at the dislocations. With the sample in channeled alignment the rotated (110) and (11¯0) planes around the 60° dislocations affect the local rate of carrier generation and so alter the size of the measured ion induced charge pulses.

  10. Intraplate rotational deformation induced by faults

    NASA Astrophysics Data System (ADS)

    Dembo, Neta; Hamiel, Yariv; Granot, Roi

    2015-11-01

    Vertical axis rotations provide important constraints on the tectonic history of plate boundaries. Geodetic measurements can be used to calculate interseismic rotations, whereas paleomagnetic remanence directions provide constraints on the long-term rotations accumulated over geological timescales. Here we present a new mechanical modeling approach that links between intraplate deformational patterns of these timescales. We construct mechanical models of active faults at their locked state to simulate the presumed to be elastic interseismic deformation rate observed by GPS measurements. We then apply a slip to the faults above the locking depth to simulate the long-term deformation of the crust from which we derive the accumulated rotations. We test this approach in northern Israel along the Dead Sea Fault and Carmel-Gilboa fault system. We use 12 years of interseismic GPS measurements to constrain a slip model of the major faults found in this region. Next, we compare the modeled rotations against long-term rotations determined based on new primary magnetic remanence directions from 29 sites with known age. The distributional pattern of site mean declinations is in general agreement with the vertical axis rotations predicted by the mechanical model, both showing anomalously high rotations near fault tips and bending points. Overall, the results from northern Israel validate the effectiveness of our approach and indicate that rotations induced by motion along faults may act in parallel (or alone) to rigid block rotations. Finally, the new suggested method unravels important insights on the evolution (timing, magnitude, and style) of deformation along major faults.

  11. A model for nucleation of tin whisker through dislocation behavior

    NASA Astrophysics Data System (ADS)

    Nakai, K.; Sakamoto, T.; Kobayashi, S.; Takamizawa, M.; Murakami, K.; Hino, M.

    2009-05-01

    A model for the nucleation and growth processes of Sn whisker is offered. High density of localized screw dislocations by deformation form the dense spiral steps of atomic scale on Sn surface. The spiral steps would induce the nucleation of Sn whisker. Edge dislocations localized at the same region where dense screw dislocations exist supply Sn atoms to the Sn whisker through pipe diffusion. Both screw and edge dislocations would bend along almost one direction, namely, to relax the external shear stress. The image force also helps to bend the dislocations perpendicular to the whisker side-surface. The bending of dislocations at root of whisker leads the bend of whisker. The pipe diffusion of Sn atoms through edge dislocations from bulk Sn toward whisker is suppressed at the bent part of edge dislocation, resulting in release of Sn atoms inside whisker and leading to the growth of whisker near its root.

  12. Deformation-induced dissolution of the intermetallics Ni3Ti and Ni3Al in austenitic steels at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Sagaradze, V. V.; Shabashov, V. A.; Kataeva, N. V.; Zavalishin, V. A.; Kozlov, K. A.; Kuznetsov, A. R.; Litvinov, A. V.; Pilyugin, V. P.

    2016-06-01

    An anomalous deformation-induced dissolution of the intermetallics Ni3Al and Ni3Ti in the matrix of austenitic Fe-Ni-Al(Ti) alloys has been revealed in experiment at cryogenic temperatures (down to 77 K) under rolling and high pressure torsion. The observed phenomenon is explained as the result of migration of deformation-stipulated interstitial atoms from a particle into the matrix in the stress field of moving dislocations. With increasing the temperature of deformation, the dissolution is replaced by the deformation-induced precipitation of the intermetallics, which is accelerated due to a sufficient amount of point defects in the matrix, gained as well in the course of deformation at lower temperatures.

  13. Deformation mechanism study of a hot rolled Zr-2.5Nb alloy by transmission electron microscopy. I. Dislocation microstructures in as-received state and at different plastic strains

    SciTech Connect

    Long, Fei; Daymond, Mark R. Yao, Zhongwen

    2015-03-07

    Thin foil dog bone samples prepared from a hot rolled Zr-2.5Nb alloy have been deformed by tensile deformation to different plastic strains. The development of slip traces during loading was observed in situ through SEM, revealing that deformation starts preferentially in certain sets of grains during the elastic-plastic transition region. TEM characterization showed that sub-grain boundaries formed during hot rolling consisted of screw 〈a〉 dislocations or screw 〈c〉 and 〈a〉 dislocations. Prismatic 〈a〉 dislocations with large screw or edge components have been identified from the sample with 0.5% plastic strain. Basal 〈a〉 and pyramidal 〈c + a〉 dislocations were found in the sample that had been deformed with 1.5% plastic strain, implying that these dislocations require larger stresses to be activated.

  14. Deformation mechanism study of a hot rolled Zr-2.5Nb alloy by transmission electron microscopy. I. Dislocation microstructures in as-received state and at different plastic strains

    NASA Astrophysics Data System (ADS)

    Long, Fei; Daymond, Mark R.; Yao, Zhongwen

    2015-03-01

    Thin foil dog bone samples prepared from a hot rolled Zr-2.5Nb alloy have been deformed by tensile deformation to different plastic strains. The development of slip traces during loading was observed in situ through SEM, revealing that deformation starts preferentially in certain sets of grains during the elastic-plastic transition region. TEM characterization showed that sub-grain boundaries formed during hot rolling consisted of screw ⟨a⟩ dislocations or screw ⟨c⟩ and ⟨a⟩ dislocations. Prismatic ⟨a⟩ dislocations with large screw or edge components have been identified from the sample with 0.5% plastic strain. Basal ⟨a⟩ and pyramidal ⟨c + a⟩ dislocations were found in the sample that had been deformed with 1.5% plastic strain, implying that these dislocations require larger stresses to be activated.

  15. Morphology transition of deformation-induced lenticular martensite in Fe-Ni-C alloys

    SciTech Connect

    Zhang, X.M.; Li, D.F.; Xing, Z.S. . Inst. of Metal Research); Gautier, E.; Zhang, J.S.; Simon, A. . Lab. de Science et Genie des Materiaux Metalliques)

    1993-06-01

    The morphology and habit planes of deformation-induced lenticular martensite were investigated by optical and transmission electron microscopy in Fe-30Ni and Fe-30Ni-0.11C alloys. Transitions in morphology were observed with progressive deformation levels going from lenticular to butterfly martensite for the Fe-30Ni-0.11C alloy. The habit planes changed from (225)[sub f] or (259)[sub f] for the thermal lenticular martensite to (111)[sub f] for the strain-induced martensite. The morphology and crystallography of the small butterfly martensites was also investigated. A change in the orientation relationships from K-S to N-W relations was also observed. These changes were attributed to the contribution of mobile dislocations which modified the shear mode form twinning to slip, and to a plastic accommodation of transformation strains.

  16. Investigation of dislocations in Nb-doped SrTiO{sub 3} by electron-beam-induced current and transmission electron microscopy

    SciTech Connect

    Chen, Jun Sekiguchi, Takashi; Li, Jianyong; Ito, Shun; Yi, Wei; Ogura, Atsushi

    2015-03-09

    This paper aims to clarify the electrical activities of dislocations in Nb-doped SrTiO{sub 3} substrates and the role of dislocations in the resistance switching phenomenon in Pt/SrTiO{sub 3} Schottky contacts. The electrical activities of dislocations have been studied by electron-beam-induced current (EBIC) technique. EBIC has found that dislocations can exhibit dark or bright contrast depending on their character and band bending condition. The character of dislocations has been analysed based on chemical etching and transmission electron microscopy. These data suggested that not all the dislocations contribute to the switching phenomenon. The active dislocations for resistance switching were discussed.

  17. Role of superposition of dislocation avalanches in the statistics of acoustic emission during plastic deformation.

    PubMed

    Lebyodkin, M A; Shashkov, I V; Lebedkina, T A; Mathis, K; Dobron, P; Chmelik, F

    2013-10-01

    Various dynamical systems with many degrees of freedom display avalanche dynamics, which is characterized by scale invariance reflected in power-law statistics. The superposition of avalanche processes in real systems driven at a finite velocity may influence the experimental determination of the underlying power law. The present paper reports results of an investigation of this effect using the example of acoustic emission (AE) accompanying plastic deformation of crystals. Indeed, recent studies of AE did not only prove that the dynamics of crystal defects obeys power-law statistics, but also led to a hypothesis of universality of the scaling law. We examine the sensitivity of the apparent statistics of AE to the parameters applied to individualize AE events. Two different alloys, MgZr and AlMg, both displaying strong AE but characterized by different plasticity mechanisms, are investigated. It is shown that the power-law indices display a good robustness in wide ranges of parameters even in the conditions leading to very strong superposition of AE events, although some deviations from the persistent values are also detected. The totality of the results confirms the scale-invariant character of deformation processes on the scale relevant to AE, but uncovers essential differences between the power-law exponents found for two kinds of alloys. PMID:24229184

  18. The evolution of internal stress and dislocation during tensile deformation in a 9Cr ferritic/martensitic (F/M) ODS steel investigated by high-energy X-rays

    SciTech Connect

    Zhang, Guangming; Zhou, Zhangjian; Mo, Kun; Miao, Yinbin; Liu, Xiang; Almer, Jonathan; Stubbins, James F.

    2015-12-01

    An application of high-energy wide angle synchrotron X-ray diffraction to investigate the tensile deformation of 9Cr ferritic/martensitic (F/M) ODS steel is presented. With tensile loading and in-situ Xray exposure, the lattice strain development of matrix was determined. The lattice strain was found to decrease with increasing temperature, and the difference in Young's modulus of six different reflections at different temperatures reveals the temperature dependence of elastic anisotropy. The mean internal stress was calculated and compared with the applied stress, showing that the strengthening factor increased with increasing temperature, indicating that the oxide nanoparticles have a good strengthening impact at high temperature. The dislocation density and character were also measured during tensile deformation. The dislocation density decreased with increasing of temperature due to the greater mobility of dislocation at high temperature. The dislocation character was determined by best-fit methods for different dislocation average contrasts with various levels of uncertainty. The results shows edge type dislocations dominate the plastic strain at room temperature (RT) and 300 C, while the screw type dislocations dominate at 600 C. The dominance of edge character in 9Cr F/M ODS steels at RT and 300 C is likely due to the pinning effect of nanoparticles for higher mobile edge dislocations when compared with screw dislocations, while the stronger screw type of dislocation structure at 600 C may be explained by the activated cross slip of screw segments.

  19. The evolution of internal stress and dislocation during tensile deformation in a 9Cr ferritic/martensitic (F/M) ODS steel investigated by high-energy X-rays

    NASA Astrophysics Data System (ADS)

    Zhang, Guangming; Zhou, Zhangjian; Mo, Kun; Miao, Yinbin; Liu, Xiang; Almer, Jonathan; Stubbins, James F.

    2015-12-01

    An application of high-energy wide angle synchrotron X-ray diffraction to investigate the tensile deformation of 9Cr ferritic/martensitic (F/M) ODS steel is presented. With tensile loading and in-situ X-ray exposure, the lattice strain development of matrix was determined. The lattice strain was found to decrease with increasing temperature, and the difference in Young's modulus of six different reflections at different temperatures reveals the temperature dependence of elastic anisotropy. The mean internal stress was calculated and compared with the applied stress, showing that the strengthening factor increased with increasing temperature, indicating that the oxide nanoparticles have a good strengthening impact at high temperature. The dislocation density and character were also measured during tensile deformation. The dislocation density decreased with increasing of temperature due to the greater mobility of dislocation at high temperature. The dislocation character was determined by best-fit methods for different dislocation average contrasts with various levels of uncertainty. The results shows edge type dislocations dominate the plastic strain at room temperature (RT) and 300 °C, while the screw type dislocations dominate at 600 °C. The dominance of edge character in 9Cr F/M ODS steels at RT and 300 °C is likely due to the pinning effect of nanoparticles for higher mobile edge dislocations when compared with screw dislocations, while the stronger screw type of dislocation structure at 600 °C may be explained by the activated cross slip of screw segments.

  20. Screw dislocation-induced influence of transverse modes on Hall conductivity

    NASA Astrophysics Data System (ADS)

    de Lima, André G.; Poux, Armelle; Assafrão, Denise; Filgueiras, Cleverson

    2013-11-01

    The Hall conductivity of an electron gas on an interface showing a topological defect called screw dislocation is investigated. This kind of defect induces a singular torsion on the medium which in turn induces transverse modes in the quantum Hall effect. It is shown that this topology decreases the plateaus' widths and shifts the steps in the Hall conductivity to lower magnetic fields. The Hall conductivity is neither enhanced nor diminished by the presence of this kind of defect alone. We also consider the presence of two defects on a sample, a screw dislocation together with a disclination. For a specific value of deficit angle, there is a reduction in the Hall conductivity. For an excess of angle, the steps shift to higher magnetic fields and the Hall conductivity is enhanced. Our work could be tested only in common semiconductors but we think it opens a road to the investigation on how topological defects can influence other classes of Hall effect.

  1. Silicon based light emitters utilizing radiation from dislocations; electric field induced shift of the dislocation-related luminescence

    NASA Astrophysics Data System (ADS)

    Arguirov, T.; Mchedlidze, T.; Kittler, M.; Reiche, M.; Wilhelm, T.; Hoang, T.; Holleman, J.; Schmitz, J.

    2009-05-01

    Dislocation rich regions can be controllably formed at a certain location inside a silicon wafer. We studied the light emission properties of such regions located in an electric field of a p-n junction under different excitation conditions. It was found that the luminescence spectra of the dislocations are significantly influenced by the presence of the junction. The dislocation-related luminescence peak position appears red-shifted due to the built-in electric field. A suppression of that field by photo-generation of carriers or by applying a forward bias voltage at the junction leads to a gradual decrease in the energy position of the peaks. The dependence of the peak position on the electric field was found to be a quadratic function, similar to that observed for semiconductor nanostructures. We show that the shift of the peak position is due to the Stark effect on dislocation-related excitonic states. The characteristic constant of the shift, obtained by fitting the data with the quadratic Stark effect equation, was 0.0186 meV/(kV/cm) 2. The observed effect opens new possibilities for integration of a silicon based light emitter, combining the radiation from dislocations with a Stark effect based modulator.

  2. Plasticity of Cu nanoparticles: Dislocation-dendrite-induced strain hardening and a limit for displacive plasticity

    PubMed Central

    Albe, Karsten

    2013-01-01

    Summary The plastic behaviour of individual Cu crystallites under nanoextrusion is studied by molecular dynamics simulations. Single-crystal Cu fcc nanoparticles are embedded in a spherical force field mimicking the effect of a contracting carbon shell, inducing pressure on the system in the range of gigapascals. The material is extruded from a hole of 1.1–1.6 nm radius under athermal conditions. Simultaneous nucleation of partial dislocations at the extrusion orifice leads to the formation of dislocation dendrites in the particle causing strain hardening and high flow stress of the material. As the extrusion orifice radius is reduced below 1.3 Å we observe a transition from displacive plasticity to solid-state amorphisation. PMID:23616936

  3. Primary combination of phase-field and discrete dislocation dynamics methods for investigating athermal plastic deformation in various realistic Ni-base single crystal superalloy microstructures

    NASA Astrophysics Data System (ADS)

    Gao, Siwen; Rajendran, Mohan Kumar; Fivel, Marc; Ma, Anxin; Shchyglo, Oleg; Hartmaier, Alexander; Steinbach, Ingo

    2015-10-01

    Three-dimensional discrete dislocation dynamics (DDD) simulations in combination with the phase-field method are performed to investigate the influence of different realistic Ni-base single crystal superalloy microstructures with the same volume fraction of {γ\\prime} precipitates on plastic deformation at room temperature. The phase-field method is used to generate realistic microstructures as the boundary conditions for DDD simulations in which a constant high uniaxial tensile load is applied along different crystallographic directions. In addition, the lattice mismatch between the γ and {γ\\prime} phases is taken into account as a source of internal stresses. Due to the high antiphase boundary energy and the rare formation of superdislocations, precipitate cutting is not observed in the present simulations. Therefore, the plastic deformation is mainly caused by dislocation motion in γ matrix channels. From a comparison of the macroscopic mechanical response and the dislocation evolution for different microstructures in each loading direction, we found that, for a given {γ\\prime} phase volume fraction, the optimal microstructure should possess narrow and homogeneous γ matrix channels.

  4. Dislocation density evolution during high pressure torsion of a nanocrystalline Ni-Fe alloy

    SciTech Connect

    Li, Hongqi; Wang, Y B; Ho, J C; Cao, Y; Liao, X Z; Ringer, S P; Zhu, Y T; Zhao, Y H; Lavernia, E J

    2009-01-01

    High-pressure torsion (HPT) induced dislocation density evolution in a nanocrystalline Ni-20wt.%Fe alloy was investigated using X-ray diffraction and transmission electron microscopy. Results suggest that the dislocation density evolution is different from that in coarse-grained materials. An HPT process first reduces the dislocation density within nanocrystalline grains and produces a large number of dislocations located at small-angle sub grain boundaries that are formed via grain rotation and coalescence. Continuing the deformation process eliminates the sub grain boundaries but significantly increases the dislocation density in grains. This phenomenon provides an explanation of the mechanical behavior of some nanostructured materials.

  5. Dislocation motion and instability

    NASA Astrophysics Data System (ADS)

    Zhu, Yichao; Chapman, Stephen Jonathan; Acharya, Amit

    2013-08-01

    The Peach-Koehler expression for the stress generated by a single (non-planar) curvilinear dislocation is evaluated to calculate the dislocation self stress. This is combined with a law of motion to give the self-induced motion of a general dislocation curve. A stability analysis of a rectilinear, uniformly translating dislocation is then performed. The dislocation is found to be susceptible to a helical instability, with the maximum growth rate occurring when the dislocation is almost, but not exactly, pure screw. The non-linear evolution of the instability is determined numerically, and implications for slip band formation and non-Schmid behavior in yielding are discussed.

  6. Microstructure and Deformation Behavior of Phase-Reversion-Induced Nanograined/Ultrafine-Grained Austenitic Stainless Steel

    NASA Astrophysics Data System (ADS)

    Misra, R. D. K.; Nayak, S.; Mali, S. A.; Shah, J. S.; Somani, M. C.; Karjalainen, L. P.

    2009-10-01

    Materials with submicron to nanometer-sized grains by virtue of their high grain boundary area to grain size ratio provide valuable tools for studying deformation behavior in ultrafine-grained structures. In this regard, the well-known strain-induced martensite transformation and its reversal to the parent austenite phase were used to produce nanograins/ultrafine grains via controlled annealing of heavily cold-worked metastable austenite. The results of the electron microscopy study of phase-reversion-induced microstructure and deformation behavior of nanograined/ultrafine-grained (NG/UFG) austenitic stainless steel during tensile straining are described here. The phase-reversion-induced structure was observed to depend on the cold rolling reduction and temperature-time annealing cycle. The optimized structure consisted of nanocrystalline ( d < 100 nm), ultrafine ( d ≈ 100 to 500 nm), and submicron ( d ≈ 500 to 1000 nm) grains and was characterized by a high yield strength (800 to 1000 MPa)-high ductility (30 to 40 pct) combination. Austenite nucleation during phase-reversion annealing occurred in the form of thin plates or as equiaxed grains along the martensite laths. Twinning and dislocation glide were identified as the primary deformation mechanisms, where twinning had a varied character. However, the high elongation seems to be associated with the gradual transformation of metastable austenite, with twinning having only a minor contribution.

  7. PSGRN/PSCMP—a new code for calculating co- and post-seismic deformation, geoid and gravity changes based on the viscoelastic-gravitational dislocation theory

    NASA Astrophysics Data System (ADS)

    Wang, Rongjiang; Lorenzo-Martín, Francisco; Roth, Frank

    2006-05-01

    We present a new numerical code for modeling co- and post-seismic response of the Earth's crust to earthquakes. The code consists of two FORTRAN programs: the first program, PSGRN, calculates the time-dependent Green functions of a given layered viscoelastic-gravitational half-space for four fundamental dislocation sources [the strike-slip double-couple, the dip-slip double-couple, the compensated linear vertical dipole (CLVD) and the point inflation] at different depths. The results provide a data base for the second program, PSCMP, which automatically discretizes the earthquake's extended rupture area into a number of discrete point dislocations and calculates the co- and post-seismic deformation by linear superposition. According to the correspondence principle, the same propagator algorithm used in our previously published elastic modeling software, EDGRN/EDCMP, is adopted to compute the spectral Green functions. The temporal Green functions are then obtained by the fast Fourier transform extended with an anti-aliasing technique, that ensures numerical stability when calculating the post-seismic transients. Moreover, the new software considers the coupling between the deformation and the Earth's gravity field, so that its output includes not only the complete deformation field consisting of 3 displacement components, 6 stress (strain) components and 2 tilt components, but also the geoid and gravity changes. In particular, the gravity effect is treated using a new consistent approach that remedies an incorrect formulation used in many earlier publications. The performance of the software is shown by an example.

  8. Parallel Dislocation Simulator

    Energy Science and Technology Software Center (ESTSC)

    2006-10-30

    ParaDiS is software capable of simulating the motion, evolution, and interaction of dislocation networks in single crystals using massively parallel computer architectures. The software is capable of outputting the stress-strain response of a single crystal whose plastic deformation is controlled by the dislocation processes.

  9. Patterns of postural deformity in non-ambulant people with cerebral palsy: what is the relationship between the direction of scoliosis, direction of pelvic obliquity, direction of windswept hip deformity and side of hip dislocation?

    PubMed Central

    Michael, Shona; Kirkwood, Craig

    2008-01-01

    Objective: To investigate: (a) associations between the direction of scoliosis, direction of pelvic obliquity, direction of windswept deformity and side of hip subluxation/dislocation in non-ambulant people with cerebral palsy; and (b) the lateral distribution of these postural asymmetries. Design: Cross-sectional observational study. Setting: Posture management services in three centres in the UK. Subjects: Non-ambulant people at level five on the gross motor function classification system for cerebral palsy. Main measures: Direction of pelvic obliquity and lateral spinal curvature determined from physical examination, direction of windswept hip deformity derived from range of hip abduction/adduction, and presence/side of unilateral hip subluxation defined by hip migration percentage. Results: A total of 747 participants were included in the study, aged 6–80 years (median 18 years 10 months). Associations between the direction of scoliosis and direction of pelvic obliquity, and between the direction of windswept hip deformity and side hip subluxation/dislocation were confirmed. A significant association was also seen between the direction of scoliosis and the direction of the windswept hip deformity (P < 0.001) such that the convexity of the lateral spinal curve was more likely to be opposite to the direction of windsweeping. Furthermore, significantly more windswept deformities to the right (P = 0.007), hips subluxed on the left (P = 0.002) and lateral lumbar/lower thoracic spinal curves convex to the left (P = 0.03) were observed. Conclusions: The individual asymmetrical postural deformities are not unrelated in terms of direction and not equally distributed to the left/right. A pattern of postural deformity was observed. PMID:18042604

  10. Shock metamorphism of deformed quartz

    NASA Technical Reports Server (NTRS)

    Gratz, Andrew J.; Christie, John; Tyburczy, James; Ahrens, Thomas; Pongratz, Peter

    1988-01-01

    The effect produced by shock loading (to peak pressures of 12 and 24) on deformed synthetic quartz containing a dislocation and abundant bubbles and small inclusions was investigated, and the relationships between preexisting dislocation density shock lamellae in the target material were examined. The resultant material was found to be inhomogeneously deformed and extremely fractured. Results of TEM examinations indicate that no change in dislocation density was caused by shock loading except in regions containing shock lamellae, where the dislocation density was lowered. The shock-induced defects tend to nucleate on and be controlled by preexisting stress concentrators; shock lamellae, glassy veins, and most curviplanar defects form in tension, presumably during release. An extremely mobile silica fluid is formed and injected into fractures during release, which forcibly removes crystalline fragments from vein walls. It is concluded that shock deformation in quartz is dominated by fracture and melting.

  11. EBIC (electron beam induced current) contrast of clean, decorated and deuterium passivated Si(Ge) epitaxial misfit dislocations

    SciTech Connect

    Zhou, T.Q.; Buczkowski, A.; Radzimski, Z.J.; Rozgonyi, G.A. . Dept. of Materials Science and Engineering); Seager, C.H.; Panitz, J. )

    1991-01-01

    The electrical activity of as-grown and intentionally decorated misfit dislocations in an epitaxial Si/Si(Ge) heterostructure was examined using the electron beam induced current (EBIC) technique in a scanning electron microscope. Misfit dislocations, which were not visible initially, were subsequently activated either by an unknown processing contaminant or a backside metallic impurity. Passivation of these contaminated dislocations was then studied using low energy deuterium ion implantation in a Kaufman ion source. EBIC results show that the recombination activity of the decorated misfit dislocations was dramatically reduced by the deuterium treatment. Although a front side passivation treatment was more effective than a backside treatment, a surface ion bombardment damage problem is still evident. 5 refs., 3 figs.

  12. Hydrologically induced slope deformations detected by GPS and clinometric surveys in the Cansiglio Plateau, southern Alps

    NASA Astrophysics Data System (ADS)

    Devoti, R.; Zuliani, D.; Braitenberg, C.; Fabris, P.; Grillo, B.

    2015-06-01

    Changes in groundwater or surface water level may cause observable deformation of the drainage basins in different ways. We describe an active slope deformation monitored with GPS and tiltmeter stations in a karstic limestone plateau in southeastern Alps (Cansiglio Plateau). The observed transient GPS deformation clearly correlates with the rainfall. Both GPS and tiltmeter equipments react instantly to heavy rains displaying abrupt offsets, but with different time constants, demonstrating the response to different catchment volumes. The GPS movement is mostly confined in the horizontal plane (SSW direction) showing a systematic tendency to rebound in the weeks following the rain. Four GPS stations concur to define a coherent deformation pattern of a wide area (12 × 5km2), concerning the whole southeastern slope of the plateau. The plateau expands and rebounds radially after rain by an amount up to a few centimeters and causing only small vertical deformation. The effect is largest where karstic features are mostly developed, at the margin of the plateau where a thick succession of Cretaceous peritidal carbonates faces the Venetian lowland. A couple of tiltmeters installed in a cave at the top of the plateau, detect a much faster deformation, that has the tendency to rebound in less than 6 h. The correlation to rainfall is less straightforward, and shows a more complex behavior during rainy weather. The different responses demonstrate a fast hydrologic flow in the more permeable epikarst for the tiltmeters, drained by open fractures and fissures in the neighborhood of the cave, and a rapid tensile dislocation of the bedrock measured at the GPS stations that affect the whole slope of the mountain. In the days following the rain, both tiltmeter and GPS data show a tendency to retrieve the displacement which is consistent with the phreatic discharge curve. We propose that hydrologically active fractures recharged by rainfall are the most likely features capable to

  13. Strain-induced phase transformation at the surface of an AISI-304 stainless steel irradiated to 4.4 dpa and deformed to 0.8% strain

    NASA Astrophysics Data System (ADS)

    Gussev, M. N.; Field, K. G.; Busby, J. T.

    2014-03-01

    Surface relief due to localized deformation in a 4.4-dpa neutron-irradiated AISI 304 stainless steel was investigated using scanning electron microscopy coupled with electron backscattering diffraction and scanning transmission electron microscopy. It was found a body-centered-cubic (BCC) phase (deformation-induced martensite) had formed at the surface of the deformed specimen along the steps generated from dislocation channels. Martensitic hill-like formations with widths of ˜1 μm and depths of several microns were observed at channels with heights greater than ˜150 nm above the original surface. Martensite at dislocation channels was observed in grains along the [0 0 1]-[1 1 1] orientation but not in those along the [1 0 1] orientation.

  14. In-situ TEM observation of dynamic interaction between dislocation and cavity in BCC metals in tensile deformation

    NASA Astrophysics Data System (ADS)

    Tougou, Kouichi; Shikata, Akihito; Kawase, Uchu; Onitsuka, Takashi; Fukumoto, Ken-ichi

    2015-10-01

    To investigate the effect of irradiation hardening of structural materials due to cavity formation in BCC metals for nuclear applications, an in-situ transmission electron microscopy (TEM) observation in tensile test was performed for the helium ion-irradiated specimens of pure molybdenum and pure iron. The obstacle barrier strength, α was calculated from the bow-out dislocation based on line tension model, and the obstacle barrier strengths of cavity in pure molybdenum and pure iron were about 0.5-0.7. The fractions of cross-slip generation of dislocation of screw type due to interaction with the cavities were about 16-18 % for pure molybdenum.

  15. Finite element model predictions of static deformation from dislocation sources in a subduction zone: Sensitivities to homogeneous, isotropic, Poisson-solid, and half-space assumptions

    USGS Publications Warehouse

    Masterlark, Timothy

    2003-01-01

    Dislocation models can simulate static deformation caused by slip along a fault. These models usually take the form of a dislocation embedded in a homogeneous, isotropic, Poisson-solid half-space (HIPSHS). However, the widely accepted HIPSHS assumptions poorly approximate subduction zone systems of converging oceanic and continental crust. This study uses three-dimensional finite element models (FEMs) that allow for any combination (including none) of the HIPSHS assumptions to compute synthetic Green's functions for displacement. Using the 1995 Mw = 8.0 Jalisco-Colima, Mexico, subduction zone earthquake and associated measurements from a nearby GPS array as an example, FEM-generated synthetic Green's functions are combined with standard linear inverse methods to estimate dislocation distributions along the subduction interface. Loading a forward HIPSHS model with dislocation distributions, estimated from FEMs that sequentially relax the HIPSHS assumptions, yields the sensitivity of predicted displacements to each of the HIPSHS assumptions. For the subduction zone models tested and the specific field situation considered, sensitivities to the individual Poisson-solid, isotropy, and homogeneity assumptions can be substantially greater than GPS. measurement uncertainties. Forward modeling quantifies stress coupling between the Mw = 8.0 earthquake and a nearby Mw = 6.3 earthquake that occurred 63 days later. Coulomb stress changes predicted from static HIPSHS models cannot account for the 63-day lag time between events. Alternatively, an FEM that includes a poroelastic oceanic crust, which allows for postseismic pore fluid pressure recovery, can account for the lag time. The pore fluid pressure recovery rate puts an upper limit of 10-17 m2 on the bulk permeability of the oceanic crust. Copyright 2003 by the American Geophysical Union.

  16. Prediction of dislocation generation during Bridgman growth of GaAs crystals

    NASA Technical Reports Server (NTRS)

    Tsai, C. T.; Yao, M. W.; Chait, Arnon

    1992-01-01

    Dislocation densities are generated in GaAs single crystals due to the excessive thermal stresses induced by temperature variations during growth. A viscoplastic material model for GaAs, which takes into account the movement and multiplication of dislocations in the plastic deformation, is developed according to Haasen's theory. The dislocation density is expressed as an internal state variable in this dynamic viscoplastic model. The deformation process is a nonlinear function of stress, strain rate, dislocation density and temperature. The dislocation density in the GaAs crystal during vertical Bridgman growth is calculated using a nonlinear finite element model. The dislocation multiplication in GaAs crystals for several temperature fields obtained from thermal modeling of both the GTE GaAs experimental data and artificially designed data are investigated.

  17. Statistical characterization of dislocation ensembles

    SciTech Connect

    El-Azab, A; Deng, J; Tang, M

    2006-05-17

    We outline a method to study the spatial and orientation statistics of dynamical dislocation systems by modeling the dislocations as a stochastic fiber process. Statistical measures have been introduced for the density, velocity, and flux of dislocations, and the connection between these measures and the dislocation state and plastic distortion rate in the crystal is explained. A dislocation dynamics simulation model has been used to extract numerical data to study the evolution of these statistical measures numerically in a body-centered cubic crystal under deformation. The orientation distribution of the dislocation density, velocity and dislocation flux, as well as the dislocation correlations have been computed. The importance of the statistical measures introduced here in building continuum models of dislocation systems is highlighted.

  18. Analysis of Obstacle Hardening Models Using Dislocation Dynamics: Application to Irradiation-Induced Defects

    NASA Astrophysics Data System (ADS)

    Sobie, Cameron; Bertin, Nicolas; Capolungo, Laurent

    2015-08-01

    Irradiation hardening in -iron represents a critical factor in nuclear reactor design and lifetime prediction. The dispersed barrier hardening, Friedel Kroupa Hirsch (FKH), and Bacon Kocks Scattergood (BKS) models have been proposed to predict hardening caused by dislocation obstacles in metals, but the limits of their applicability have never been investigated for varying defect types, sizes, and densities. In this work, dislocation dynamics calculations of irradiation-induced obstacle hardening in the athermal case were compared to these models for voids, self-interstitial atom (SIA) loops, and a combination of the two types. The BKS model was found to accurately predict hardening due to voids, whereas the FKH model was superior for SIA loops. For both loops and voids, the hardening from a normal distribution of defects was compared to that from the mean size, and was shown to have no statistically significant dependence on the distribution. A mean size approach was also shown to be valid for an asymmetric distribution of voids. A non-linear superposition principle was shown to predict the hardening from the simultaneous presence of voids and SIA loops.

  19. Coseismic deformation induced by the Sumatra earthquake

    NASA Astrophysics Data System (ADS)

    Boschi, E.; Casarotti, E.; Devoti, R.; Melini, D.; Piersanti, A.; Pietrantonio, G.; Riguzzi, F.

    2006-08-01

    The giant Sumatra-Andaman earthquake of December 26, 2004 caused permanent deformations effects in a region of previously never observed extension. The GPS data from the worldwide network of permanent IGS sites show significant coseismic displacements in an area exceeding 10 7 km 2, reaching most of South-East Asia, besides Indonesia and India. We have analyzed long GPS time series histories in order to characterize the noise type of each site and, consequently, to precisely assess the formal errors of the coseismic offset estimates. The synthetic simulations of the coseismic displacement field obtained by means of a spherical model using different rupture histories indicate that a major part of the energy release took place in a fault plane similar to that obtained by Ammon et al. (2005) and Vigny et al. (2005) but with a larger amount of compressional slip on the northern segment of the fault area.

  20. Role of plastic deformation in shock-induced phase transitions

    NASA Astrophysics Data System (ADS)

    Ghimire, Punam; Germann, T. C.; Ravelo, R.

    2015-06-01

    Non-equilibrium molecular dynamics (NEMD) simulations of shock-wave propagation in fcc single crystals exhibit high elastic limits and large anisotropies in the yield strength. They can be used to explore the role of plastic deformation in the morphology and kinetics of solid-solid phase transformations. We report on large-scale atomistic simulations of defect-mediated phase transformations under shock and quasi-isentropic compression (QIC). An analytical embedded atom method (EAM) description is used to model a fcc-bcc phase transition (PT) boundary fitted to occur below or above the elastic-plastic threshold in order to model systems undergoing a PT with and without plasticity. For cases where plastic deformation precedes the phase transformation, the defect-mediated PT proceeds at faster rates than the defect-free ones. The bcc fraction growth rate can be correlated with a sharp decrease in the dislocation densities originally present in the parent phase. This work was supported by the Air Force Office of Scientific Research under AFOSR Award FA9550-12-1-0476. Work at Los Alamos was performed under the auspices of the U.S. Department of Energy (DOE) under Contract No. DE-AC52-06NA25396.

  1. Deformation twinning induced decomposition of lamellar LPSO structure and its re-precipitation in an Mg-Zn-Y alloy

    NASA Astrophysics Data System (ADS)

    Shao, X. H.; Zheng, S. J.; Chen, D.; Jin, Q. Q.; Peng, Z. Z.; Ma, X. L.

    2016-07-01

    The high hardness or yield strength of an alloy is known to benefit from the presence of small-scale precipitation, whose hardening effect is extensively applied in various engineering materials. Stability of the precipitates is of critical importance in maintaining the high performance of a material under mechanical loading. The long period stacking ordered (LPSO) structures play an important role in tuning the mechanical properties of an Mg-alloy. Here, we report deformation twinning induces decomposition of lamellar LPSO structures and their re-precipitation in an Mg-Zn-Y alloy. Using atomic resolution scanning transmission electron microscopy (STEM), we directly illustrate that the misfit dislocations at the interface between the lamellar LPSO structure and the deformation twin is corresponding to the decomposition and re-precipitation of LPSO structure, owing to dislocation effects on redistribution of Zn/Y atoms. This finding demonstrates that deformation twinning could destabilize complex precipitates. An occurrence of decomposition and re-precipitation, leading to a variant spatial distribution of the precipitates under plastic loading, may significantly affect the precipitation strengthening.

  2. Deformation twinning induced decomposition of lamellar LPSO structure and its re-precipitation in an Mg-Zn-Y alloy.

    PubMed

    Shao, X H; Zheng, S J; Chen, D; Jin, Q Q; Peng, Z Z; Ma, X L

    2016-01-01

    The high hardness or yield strength of an alloy is known to benefit from the presence of small-scale precipitation, whose hardening effect is extensively applied in various engineering materials. Stability of the precipitates is of critical importance in maintaining the high performance of a material under mechanical loading. The long period stacking ordered (LPSO) structures play an important role in tuning the mechanical properties of an Mg-alloy. Here, we report deformation twinning induces decomposition of lamellar LPSO structures and their re-precipitation in an Mg-Zn-Y alloy. Using atomic resolution scanning transmission electron microscopy (STEM), we directly illustrate that the misfit dislocations at the interface between the lamellar LPSO structure and the deformation twin is corresponding to the decomposition and re-precipitation of LPSO structure, owing to dislocation effects on redistribution of Zn/Y atoms. This finding demonstrates that deformation twinning could destabilize complex precipitates. An occurrence of decomposition and re-precipitation, leading to a variant spatial distribution of the precipitates under plastic loading, may significantly affect the precipitation strengthening. PMID:27435638

  3. Deformation twinning induced decomposition of lamellar LPSO structure and its re-precipitation in an Mg-Zn-Y alloy

    PubMed Central

    Shao, X. H.; Zheng, S. J.; Chen, D.; Jin, Q. Q.; Peng, Z. Z.; Ma, X. L.

    2016-01-01

    The high hardness or yield strength of an alloy is known to benefit from the presence of small-scale precipitation, whose hardening effect is extensively applied in various engineering materials. Stability of the precipitates is of critical importance in maintaining the high performance of a material under mechanical loading. The long period stacking ordered (LPSO) structures play an important role in tuning the mechanical properties of an Mg-alloy. Here, we report deformation twinning induces decomposition of lamellar LPSO structures and their re-precipitation in an Mg-Zn-Y alloy. Using atomic resolution scanning transmission electron microscopy (STEM), we directly illustrate that the misfit dislocations at the interface between the lamellar LPSO structure and the deformation twin is corresponding to the decomposition and re-precipitation of LPSO structure, owing to dislocation effects on redistribution of Zn/Y atoms. This finding demonstrates that deformation twinning could destabilize complex precipitates. An occurrence of decomposition and re-precipitation, leading to a variant spatial distribution of the precipitates under plastic loading, may significantly affect the precipitation strengthening. PMID:27435638

  4. 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.

  5. Temperature dependence of optically induced cell deformations

    NASA Astrophysics Data System (ADS)

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

    2012-02-01

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

  6. Elastic image registration via rigid object motion induced deformation

    NASA Astrophysics Data System (ADS)

    Zheng, Xiaofen; Udupa, Jayaram K.; Hirsch, Bruce E.

    2011-03-01

    In this paper, we estimate the deformations induced on soft tissues by the rigid independent movements of hard objects and create an admixture of rigid and elastic adaptive image registration transformations. By automatically segmenting and independently estimating the movement of rigid objects in 3D images, we can maintain rigidity in bones and hard tissues while appropriately deforming soft tissues. We tested our algorithms on 20 pairs of 3D MRI datasets pertaining to a kinematic study of the flexibility of the ankle complex of normal feet as well as ankles affected by abnormalities in foot architecture and ligament injuries. The results show that elastic image registration via rigid object-induced deformation outperforms purely rigid and purely nonrigid approaches.

  7. Freezing-induced deformation of biomaterials in cryomedicine

    NASA Astrophysics Data System (ADS)

    Ozcelikkale, Altug

    Cryomedicine utilizes low temperature treatments of biological proteins, cells and tissues for cryopreservation, materials processing and cryotherapy. Lack of proper understanding of cryodamage that occurs during these applications remains to be the primary bottleneck for development of successful tissue cryopreservation and cryosurgery procedures. An engineering approach based on a view of biological systems as functional biomaterials can help identify, predict and control the primary cryodamage mechanisms by developing an understanding of underlying freezing-induced biophysical processes. In particular, freezing constitutes the main structural/mechanical origin of cryodamage and results in significant deformation of biomaterials at multiple length scales. Understanding of these freezing-induced deformation processes and their effects on post-thaw biomaterial functionality is currently lacking but will be critical to engineer improved cryomedicine procedures. This dissertation addresses this problem by presenting three separate but related studies of freezing-induced deformation at multiple length scales including nanometer-scale protein fibrils, single cells and whole tissues. A combination of rigorous experimentation and computational modeling is used to characterize post-thaw biomaterial structure and properties, predict biomaterial behavior and assess its post-thaw biological functionality. Firstly, freezing-induced damage on hierarchical extracellular matrix structure of collagen is investigated at molecular, fibril and matrix levels. Results indicate to a specific kind of fibril damage due to freezing-induced expansion of intrafibrillar fluid. This is followed by a study of freezing-induced cell and tissue deformation coupled to osmotically driven cellular water transport. Computational and semi empirical modeling of these processes indicate that intracellular deformation of the cell during freezing is heterogeneous and can interfere with cellular water

  8. Relative Stability of Deformed Cube in Warm and Hot Deformed AA6022: Possible Role of Strain-Induced Boundary Migration

    NASA Astrophysics Data System (ADS)

    Raveendra, S.; Paranjape, H.; Mishra, S.; Weiland, H.; Doherty, R. D.; Samajdar, I.

    2009-09-01

    AA6022 samples were deformed at different temperatures and strain rates and to respective true strains of 1.0 and 2.0. Though the deformation was immediately followed by quenching, the as-deformed samples contained recrystallized grains. A convention was adopted, based on grain size and in-grain misorientation developments, to distinguish between the deformed and recrystallized grains/orientations. At the highest deformation temperature(s), a clear pattern of increase (with increase in strain) in deformed cube left\\{ {001} right\\}left< {100} rightrangle was established. Such a pattern could not be explained from Taylor type deformation texture simulations, even after allowing nonoctahedral as well as octahedral slip. Microstructural observations could link, statistically, the increased cube presence with the presence of thicker deformed cube bands. The process of thickening was hypothesized as strain-induced boundary migration (SIBM) of the deformed cube bands into the adjacent noncube.

  9. Interaction of a screw dislocation with a nano-sized, arbitrarily shaped inhomogeneity with interface stresses under anti-plane deformations.

    PubMed

    Wang, Xu; Schiavone, Peter

    2014-10-01

    We propose an elegant and concise general method for the solution of a problem involving the interaction of a screw dislocation and a nano-sized, arbitrarily shaped, elastic inhomogeneity in which the contribution of interface/surface elasticity is incorporated using a version of the Gurtin-Murdoch model. The analytic function inside the arbitrarily shaped inhomogeneity is represented in the form of a Faber series. The real periodic function arising from the contribution of the surface mechanics is then expanded as a Fourier series. The resulting system of linear algebraic equations is solved through the use of simple matrix algebra. When the elastic inhomogeneity represents a hole, our solution method simplifies considerably. Furthermore, we undertake an analytical investigation of the challenging problem of a screw dislocation interacting with two closely spaced nano-sized holes of arbitrary shape in the presence of surface stresses. Our solutions quite clearly demonstrate that the induced elastic fields and image force acting on the dislocation are indeed size-dependent. PMID:25294965

  10. Hydrogen-Induced Plastic Deformation in ZnO

    NASA Astrophysics Data System (ADS)

    Lukáč, F.; Čížek, J.; Vlček, M.; Procházka, I.; Anwand, W.; Brauer, G.; Traeger, F.; Rogalla, D.; Becker, H.-W.

    In the present work hydrothermally grown ZnO single crystals covered with Pd over-layer were electrochemically loaded with hydrogen and the influence of hydrogen on ZnO micro structure was investigated by positron annihilation spectroscopy (PAS). Nuclear reaction analysis (NRA) was employed for determination of depth profile of hydrogen concentration in the sample. NRA measurements confirmed that a substantial amount of hydrogen was introduced into ZnO by electrochemical charging. The bulk hydrogen concentration in ZnO determined by NRA agrees well with the concentration estimated from the transported charge using the Faraday's law. Moreover, a subsurface region with enhanced hydrogen concentration was found in the loaded crystals. Slow positron implantation spectroscopy (SPIS) investigations of hydrogen-loaded crystal revealed enhanced concentration of defects in the subsurface region. This testifies hydrogen-induced plastic deformation of the loaded crystal. Absorbed hydrogen causes a significant lattice expansion. At low hydrogen concentrations this expansion is accommodated by elastic straining, but at higher concentrations hydrogen-induced stress exceeds the yield stress in ZnO and plastic deformation of the loaded crystal takes place. Enhanced hydrogen concentration detected in the subsurface region by NRA is, therefore, due to excess hydrogen trapped at open volume defects introduced by plastic deformation. Moreover, it was found that hydrogen-induced plastic deformation in the subsurface layer leads to typical surface modification: formation of hexagonal shape pyramids on the surface due to hydrogen-induced slip in the [0001] direction.

  11. Imaging Dyke-Induced Deformation in the Lab

    NASA Astrophysics Data System (ADS)

    Ellwood, H.; Rivalta, E.; Wright, T. J.; O'Shea, K.; Hogg, D. C.; Boyle, R. D.

    2008-12-01

    The presence of a dike in Earth's crust can be inferred from a combination of seismological and geodetic techniques. Often, geodetic measurements (e.g. GPS and InSAR) of surface deformation near a dike are inverted for dike parameters using the equations for rectangular tensile dislocations in an elastic, homogeneous half-space, as presented in Okada (1985). Here, we create artificial dikes in the lab and simulate surface geodetic observations. Because the dike parameters are known, or can be directly observed, we are able to test the validity of standard geodetic models for dike injections. A fluid injection into gelatin is analogous to dike ascent driven by magma buoyancy in the crust; gelatin is an elastic medium (Menand and Tait, 2002) and away from the tip of a magma dike, strains are small, suggesting that deformation of the host rock may also be largely elastic (Delaney and Pollard, 1981). Gelatin has been used in several investigations into the propagation of fluid-filled cracks in the Earth's crust, including the shape and velocity of fluid-filled fractures (Takada, 1990; Dahm, 2000), propagation in layered media (Rivalta et al., 2005) and laccolith growth (Johnson and Pollard, 1973), among others. This study focuses on the deformation at the surface caused by this propagation. We seeded the upper surface of a homogeneous gelatin mass with markers and injected some fluid at the bottom of the gelatin container. We recorded the ascent of the resulting buoyancy-driven fluid-filled fracture from above with two camcorders and from the side with an additional camcorder. Surfaces markers were observed by the camcorders and tracked from one frame to the next. 3D positions were determined using photogrammetry after matching the markers. The resultant time series of surface deformation at each marker are analogous to continuous GPS observations from real dikes. The horizontal accuracy obtainable with HD camcorders was about 0.1 mm. We inverted the surface

  12. Supersonic Dislocation Bursts in Silicon

    DOE PAGESBeta

    Hahn, E. N.; Zhao, S.; Bringa, E. M.; Meyers, M. A.

    2016-06-06

    Dislocations are the primary agents of permanent deformation in crystalline solids. Since the theoretical prediction of supersonic dislocations over half a century ago, there is a dearth of experimental evidence supporting their existence. Here we use non-equilibrium molecular dynamics simulations of shocked silicon to reveal transient supersonic partial dislocation motion at approximately 15 km/s, faster than any previous in-silico observation. Homogeneous dislocation nucleation occurs near the shock front and supersonic dislocation motion lasts just fractions of picoseconds before the dislocations catch the shock front and decelerate back to the elastic wave speed. Applying a modified analytical equation for dislocation evolutionmore » we successfully predict a dislocation density of 1.5 x 10(12) cm(-2) within the shocked volume, in agreement with the present simulations and realistic in regards to prior and on-going recovery experiments in silicon.« less

  13. Supersonic Dislocation Bursts in Silicon.

    PubMed

    Hahn, E N; Zhao, S; Bringa, E M; Meyers, M A

    2016-01-01

    Dislocations are the primary agents of permanent deformation in crystalline solids. Since the theoretical prediction of supersonic dislocations over half a century ago, there is a dearth of experimental evidence supporting their existence. Here we use non-equilibrium molecular dynamics simulations of shocked silicon to reveal transient supersonic partial dislocation motion at approximately 15 km/s, faster than any previous in-silico observation. Homogeneous dislocation nucleation occurs near the shock front and supersonic dislocation motion lasts just fractions of picoseconds before the dislocations catch the shock front and decelerate back to the elastic wave speed. Applying a modified analytical equation for dislocation evolution we successfully predict a dislocation density of 1.5 × 10(12) cm(-2) within the shocked volume, in agreement with the present simulations and realistic in regards to prior and on-going recovery experiments in silicon. PMID:27264746

  14. Supersonic Dislocation Bursts in Silicon

    PubMed Central

    Hahn, E. N.; Zhao, S.; Bringa, E. M.; Meyers, M. A.

    2016-01-01

    Dislocations are the primary agents of permanent deformation in crystalline solids. Since the theoretical prediction of supersonic dislocations over half a century ago, there is a dearth of experimental evidence supporting their existence. Here we use non-equilibrium molecular dynamics simulations of shocked silicon to reveal transient supersonic partial dislocation motion at approximately 15 km/s, faster than any previous in-silico observation. Homogeneous dislocation nucleation occurs near the shock front and supersonic dislocation motion lasts just fractions of picoseconds before the dislocations catch the shock front and decelerate back to the elastic wave speed. Applying a modified analytical equation for dislocation evolution we successfully predict a dislocation density of 1.5 × 1012 cm−2 within the shocked volume, in agreement with the present simulations and realistic in regards to prior and on-going recovery experiments in silicon. PMID:27264746

  15. Supersonic Dislocation Bursts in Silicon

    NASA Astrophysics Data System (ADS)

    Hahn, E. N.; Zhao, S.; Bringa, E. M.; Meyers, M. A.

    2016-06-01

    Dislocations are the primary agents of permanent deformation in crystalline solids. Since the theoretical prediction of supersonic dislocations over half a century ago, there is a dearth of experimental evidence supporting their existence. Here we use non-equilibrium molecular dynamics simulations of shocked silicon to reveal transient supersonic partial dislocation motion at approximately 15 km/s, faster than any previous in-silico observation. Homogeneous dislocation nucleation occurs near the shock front and supersonic dislocation motion lasts just fractions of picoseconds before the dislocations catch the shock front and decelerate back to the elastic wave speed. Applying a modified analytical equation for dislocation evolution we successfully predict a dislocation density of 1.5 × 1012 cm‑2 within the shocked volume, in agreement with the present simulations and realistic in regards to prior and on-going recovery experiments in silicon.

  16. Dislocation dynamics in nanocrystalline nickel.

    PubMed

    Shan, Z W; Wiezorek, J M K; Stach, E A; Follstaedt, D M; Knapp, J A; Mao, S X

    2007-03-01

    It is believed that the dynamics of dislocation processes during the deformation of nanocrystalline materials can only be visualized by computational simulations. Here we demonstrate that observations of dislocation processes during the deformation of nanocrystalline Ni with grain sizes as small as 10 nm can be achieved by using a combination of in situ tensile straining and high-resolution transmission electron microscopy. Trapped unit lattice dislocations are observed in strained grains as small as 5 nm, but subsequent relaxation leads to dislocation recombination. PMID:17359167

  17. Spatiotemporal measurement of freezing-induced deformation of engineered tissues

    PubMed Central

    Teo, Ka Yaw; Dutton, J. Craig; Han, Bumsoo

    2010-01-01

    In order to cryopreserve functional engineered tissues (ETs), the microstructure of the extracellular matrix (ECM) should be maintained as well as the cellular viability since the functionality is closely related to the ECM microstructure. Since the post-thaw ECM microstructure is determined by the deformation of ETs during cryopreservation, freezing-induced deformation of ETs was measured with a newly developed quantum dot (QD)-mediated cell image deformetry system using dermal equivalents as a model tissue. The dermal equivalents were constructed by seeding QD-labeled fibroblasts in type I collagen matrices. After 24 hour incubation, the ETs were directionally frozen by exposing them to a spatial temperature gradient (from 4 °C to −20 °C over a distance of 6 mm). While being frozen, the ETs were consecutively imaged, and consecutive pairs of these images were two-dimensionally cross-correlated to determine the local deformation during freezing. The results showed that freezing induced the deformation of ET, and its magnitude varied with both time and location. The maximum local dilatation was 0.006 s−1 and was always observed at the phase change interface. Due to this local expansion, the unfrozen region in front of the freezing interface experienced compression. This expansion-compression pattern was observed throughout the freezing process. In the unfrozen region, the deformation rate gradually decreased away from the freezing interface. After freezing/thawing, the ET experienced an approximately 28% decrease in thickness and 8% loss in weight. These results indicate that freezing-induced deformation caused the transport of interstitial fluid and the interstitial fluid was extruded. In summary, the results suggest that complex cell-fluid-matrix interactions occur within ETs during freezing, and these interactions determine the post-thaw ECM microstructure and eventual post-thaw tissue functionality. PMID:20459191

  18. Compensation of Gravity-Induced Structural Deformations on a Beam- Waveguide Antenna Using a Deformable Mirror

    NASA Technical Reports Server (NTRS)

    Imbriale, W. A.; Moore, M.; Rochblatt, D. J.; Veruttipong, W.

    1995-01-01

    At the NASA Deep Space Network (DSN) Goldstone Complex, a 34-meter- diameter beam-waveguide antenna, DSS-13, was constructed in 1988-1990 and has become an integral part of an advanced systems program and a test bed for technologies being developed to introduce Ka-band (32 GHz) frequencies into the DSN. A method for compensating the gravity- induced structural deformations in this large antenna is presented.

  19. Texture developed during deformation of Transformation Induced Plasticity (TRIP) steels

    NASA Astrophysics Data System (ADS)

    Bhargava, M.; Shanta, C.; Asim, T.; Sushil, M.

    2015-04-01

    Automotive industry is currently focusing on using advanced high strength steels (AHSS) due to its high strength and formability for closure applications. Transformation Induced Plasticity (TRIP) steel is promising material for this application among other AHSS. The present work is focused on the microstructure development during deformation of TRIP steel sheets. To mimic complex strain path condition during forming of automotive body, Limit Dome Height (LDH) tests were conducted and samples were deformed in servo hydraulic press to find the different strain path. FEM Simulations were done to predict different strain path diagrams and compared with experimental results. There is a significant difference between experimental and simulation results as the existing material models are not applicable for TRIP steels. Micro texture studies were performed on the samples using EBSD and X-RD techniques. It was observed that austenite is transformed to martensite and texture developed during deformation had strong impact on limit strain and strain path.

  20. Understanding Gas-Induced Structural Deformation of ZIF-8.

    PubMed

    Ania, Conchi O; García-Pérez, E; Haro, M; Gutiérrez-Sevillano, J J; Valdés-Solís, T; Parra, J B; Calero, S

    2012-05-01

    ZIF-8 is a zeolitic imidazolate framework with very good thermal and chemical stability that opens up many applications that are not feasible by other metal-organic frameowrks (MOFs) and zeolites. Several works report the adsorption properties of ZIF-8 for strategic gases. However, despite the vast experimental corpus of data reported, there seems yet to be a dearth in the understanding of the gas adsorption properties. In this work we provide insights at a molecular level on the mechanisms governing the ZIF-8 structural deformation during molecular adsorption. We demonstrate that the ZIF-8 structural deformation during the adsorption of different molecules at cryogenic temperature goes beyond the gas-induced rotation of the imidazolate linkers. We combine experimental and simulation studies to demonstrate that this deformation is governed by the polarizability and molecular size and shape of the gases, and that the stepped adsorption behavior is defined by the packing arrangement of the guest inside the host. PMID:26288051

  1. A variational formulation of constrained dislocation dynamics coupled with heat and vacancy diffusion

    NASA Astrophysics Data System (ADS)

    Po, Giacomo; Ghoniem, Nasr

    2014-05-01

    We present a formulation of the discrete Dislocation Dynamics (DD) method based on Onsager's variational principle. The motion of discrete dislocations is treated as a generalized irreversible flux associated with conjugate thermodynamic forces causing internal production of entropy. Intrinsic in the variational principle is the role of physical constraints that limit the choice of generalized fluxes. We leverage the concept of constrained maximization to introduce the requirement that dislocation climb must be sustained by the flux of vacancies into the dislocation core. The constrained variational approach results naturally in the coupling between plastic deformation induced by discrete dislocations, vacancy diffusion, and heat propagation in solid crystals. In particular, this coupling requires that dislocation velocity and chemical potential of vacancies at the dislocation core be found simultaneously. A new numerical formulation of DD that accounts for generalized constraints imposed on dislocations is presented, based on a network discretization of the dislocation configuration. Applications illustrate the significance of constrained motion of dislocations confined in channels and pillars, and the attainment of heterogeneous dislocation structures.

  2. Collective dynamics of dislocations interacting with mobile solute atoms

    NASA Astrophysics Data System (ADS)

    Ovaska, Markus; Paananen, Topi; Laurson, Lasse; Alava, Mikko J.

    2016-04-01

    We study the effect of diffusing solute atoms on the collective dynamics of dislocations in plastically deforming crystals, by simulating a two-dimensional discrete dislocation dynamics model with solute atoms included. We employ various protocols to apply the external stress, including constant, oscillatory and quasistatically increasing stress, and study the resulting dynamics for various values of the solute mobility, temperature, and interaction strength with the dislocations. The values of these parameters dictate if Cottrell clouds are formed around the dislocations, and whether the dislocations are able to drag them along as they move. The relevant solute-induced processes include a temporally increasing average Cottrell cloud size due to cloud merging during the evolution of the dislocation structures subject to constant stresses, and a crossover between a solute-free ‘phase’ and a regime where solute drag is important for cyclic stresses, controlled by the solute mobility and temperature. Statistics of deformation bursts under quasistatic loading exhibit atypical scaling where the average burst size is directly proportional to its duration, and are also affected by solute-induced strain hardening in the high-stress regime.

  3. Nonlinear resonance-assisted tunneling induced by microcavity deformation

    PubMed Central

    Kwak, Hojeong; Shin, Younghoon; Moon, Songky; Lee, Sang-Bum; Yang, Juhee; An, Kyungwon

    2015-01-01

    Noncircular two-dimensional microcavities support directional output and strong confinement of light, making them suitable for various photonics applications. It is now of primary interest to control the interactions among the cavity modes since novel functionality and enhanced light-matter coupling can be realized through intermode interactions. However, the interaction Hamiltonian induced by cavity deformation is basically unknown, limiting practical utilization of intermode interactions. Here we present the first experimental observation of resonance-assisted tunneling in a deformed two-dimensional microcavity. It is this tunneling mechanism that induces strong inter-mode interactions in mixed phase space as their strength can be directly obtained from a separatrix area in the phase space of intracavity ray dynamics. A selection rule for strong interactions is also found in terms of angular quantum numbers. Our findings, applicable to other physical systems in mixed phase space, make the interaction control more accessible. PMID:25759322

  4. Defect-induced incompatability of elastic strains: dislocations within the Landau theory of martensitic phase transformations

    SciTech Connect

    Groger, Roman1; Lockman, Turab; Saxena, Avadh

    2008-01-01

    In dislocation-free martensites the components of the elastic strain tensor are constrained by the Saint-Venant compatibility condition which guarantees continuity of the body during external loading. However, in dislocated materials the plastic part of the distortion tensor introduces a displacement mismatch that is removed by elastic relaxation. The elastic strains are then no longer compatible in the sense of the Saint-Venant law and the ensuing incompatibility tensor is shown to be proportional to the gradients of the Nye dislocation density tensor. We demonstrate that the presence of this incompatibility gives rise to an additional long-range contribution in the inhomogeneous part of the Landau energy functional and to the corresponding stress fields. Competition among the local and long-range interactions results in frustration in the evolving order parameter (elastic) texture. We show how the Peach-Koehler forces and stress fields for any distribution of dislocations in arbitrarily anisotropic media can be calculated and employed in a Fokker-Planck dynamics for the dislocation density. This approach represents a self-consistent scheme that yields the evolutions of both the order parameter field and the continuous dislocation density. We illustrate our method by studying the effects of dislocations on microstructure, particularly twinned domain walls, in an Fe-Pd alloy undergoing a martensitic transformation.

  5. Texture of Nanocrystalline Nickel: Probing the Lower Size Limit of Dislocation Activity

    NASA Astrophysics Data System (ADS)

    Chen, Bin; Lutker, Katie; Raju, Selva Vennila; Yan, Jinyuan; Kanitpanyacharoen, Waruntorn; Lei, Jialin; Yang, Shizhong; Wenk, Hans-Rudolf; Mao, Ho-kwang; Williams, Quentin

    2012-12-01

    The size of nanocrystals provides a limitation on dislocation activity and associated stress-induced deformation. Dislocation-mediated plastic deformation is expected to become inactive below a critical particle size, which has been proposed to be between 10 and 30 nanometers according to computer simulations and transmission electron microscopy analysis. However, deformation experiments at high pressure on polycrystalline nickel suggest that dislocation activity is still operative in 3-nanometer crystals. Substantial texturing is observed at pressures above 3.0 gigapascals for 500-nanometer nickel and at greater than 11.0 gigapascals for 20-nanometer nickel. Surprisingly, texturing is also seen in 3-nanometer nickel when compressed above 18.5 gigapascals. The observations of pressure-promoted texturing indicate that under high external pressures, dislocation activity can be extended down to a few-nanometers-length scale.

  6. Vitamin A Deficiency Induces Congenital Spinal Deformities in Rats

    PubMed Central

    Li, Zheng; Shen, Jianxiong; Wu, William Ka Kei; Wang, Xiaojuan; Liang, Jinqian; Qiu, Guixing; Liu, Jiaming

    2012-01-01

    Most cases of congenital spinal deformities were sporadic and without strong evidence of heritability. The etiology of congenital spinal deformities is still elusive and assumed to be multi-factorial. The current study seeks to elucidate the effect of maternal vitamin A deficiency and the production of congenital spinal deformities in the offsping. Thirty two female rats were randomized into two groups: control group, which was fed a normal diet; vitamin A deficient group, which were given vitamin A-deficient diet from at least 2 weeks before mating till delivery. Three random neonatal rats from each group were killed the next day of parturition. Female rats were fed an AIN-93G diet sufficient in vitamin A to feed the rest of neonates for two weeks until euthanasia. Serum levels of vitamin A were assessed in the adult and filial rats. Anteroposterior (AP) spine radiographs were obtained at week 2 after delivery to evaluate the presence of the skeletal abnormalities especially of spinal deformities. Liver and vertebral body expression of retinaldehyde dehydrogenase (RALDHs) and RARs mRNA was assessed by reverse transcription-real time PCR. VAD neonates displayed many skeletal malformations in the cervical, thoracic, the pelvic and sacral and limbs regions. The incidence of congenital scoliosis was 13.79% (8/58) in the filial rats of vitamin A deficiency group and 0% in the control group. Furthermore, vitamin A deficiency negatively regulate the liver and verterbral body mRNA levels of RALDH1, RALDH2, RALDH3, RAR-α, RAR-β and RAR-γ. Vitamin A deficiency in pregnancy may induce congenital spinal deformities in the postnatal rats. The decreases of RALDHs and RARs mRNA expression induced by vitamin A deprivation suggest that vertebral birth defects may be caused by a defect in RA signaling pathway during somitogenesis. PMID:23071590

  7. Strong luminescence induced by elastic deformation of piezoelectric crystals

    NASA Astrophysics Data System (ADS)

    Chandra, V. K.; Chandra, B. P.; Jha, Piyush

    2013-06-01

    The luminescence induced by elastic deformation of solids, called the phenomenon of elastico-mechanoluminescence (EML), is observed in several materials. For applied pressure in the range of 17 MPa, certain crystals emit intense EML, which can be seen in day light with naked eye. In the present paper, we explore that, as the piezoelectric constant near the photo-generated electric dipoles formed by trapping of charge carriers in crystals is several times higher as compared to that at normal sites, the piezoelectrically induced detrapping of charge carriers and EML emission may take place for less value of the pressure applied onto the crystals.

  8. Radiation-induced strengthening and absorption of dislocation loops in ferritic Fe-Cr alloys: the role of Cr segregation.

    PubMed

    Terentyev, D; Bakaev, A

    2013-07-01

    The understanding of radiation-induced strengthening in ferritic FeCr-based steels remains an essential issue in the assessment of materials for fusion and fission reactors. Both early and recent experimental works on Fe-Cr alloys reveal Cr segregation on radiation-induced nanostructural features (mainly dislocation loops), whose impact on the modification of the mechanical response of the material might be key for explaining quantitatively the radiation-induced strengthening in these alloys. In this work, we use molecular dynamics to study systematically the interaction of dislocations with 1/2<111> and <100> loops in all possible orientations, both enriched by Cr atoms and undecorated, for different temperatures, loop sizes and dislocation velocities. The configurations of the enriched loops have been obtained using a non-rigid lattice Monte Carlo method. The study reveals that Cr segregation influences the interaction mechanisms with both 1/2<111> and <100> loops. The overall effect of Cr enrichment is to penalize the mobility of intrinsically glissile 1/2<111> loops, modifying the reaction mechanisms as a result. The following three most important effects associated with Cr enrichment have been revealed: (i) absence of dynamic drag; (ii) suppression of complete absorption; (iii) enhanced strength of small dislocation loops (2 nm and smaller). Overall the effect of the Cr enrichment is therefore to increase the unpinning stress, so experimentally 'invisible' nanostructural features may also contribute to radiation-induced strengthening. The reasons for the modification of the mechanisms are explained and the impact of the loading conditions is discussed. PMID:23756468

  9. Dislocation-induced Charges in Quantum Dots: Step Alignment and Radiative Emission

    NASA Technical Reports Server (NTRS)

    Leon, R.; Okuno, J.; Lawton, R.; Stevens-Kalceff, M.; Phillips, M.; Zou, J.; Cockayne, D.; Lobo, C.

    1999-01-01

    A transition between two types of step alignment was observed in a multilayered InGaAs/GaAs quantum-dot (QD) structure. A change to larger QD sizes in smaller concentrations occurred after formation of a dislocation array.

  10. The analysis of severely deformed pure Fe structure aided by X-ray diffraction profile

    NASA Astrophysics Data System (ADS)

    Forouzanmehr, Nazanin; Nili-Ahmadabadi, Mahmoud; Bönisch, Matthias

    2016-06-01

    Pure Fe was severely deformed by a combination of shaped cold rolling and cold drawing. X-ray diffraction profiles analysis was applied in accordance with the Williamson-Hall (WH) and modified Williamson-Hall (MWH) methods to identify crystallite sizes of the deformed specimens. It was found that some differences exist between the results of WH and MWH procedures using the hkl dependent Young's modulus or considering the average dislocation contrast factor. The latter method is more accurate and enables the determination of the character of dislocations in plastically deformed Fe. It was shown that by increasing deformation strain, the screw dislocations dominated. The enhancement of hardness occurs in the deformed Fe due to grain refinement, dislocation accumulation and deformation-induced vacancies.

  11. Tritium deformation interactions in FCC austenitic steels

    SciTech Connect

    Chene, J.

    2008-07-15

    Hydrogen deformation interactions are known to control the environmental degradation effects (H and He embrittlement, stress corrosion cracking,...) associated with the presence of H and its isotopes in structural materials. Different types of interaction have been investigated: trapping on stress field and strain-induced defects, enhanced diffusion along dislocation networks, transport by moving dislocation. For several reasons, the quantification of these interactions is a major challenge in nuclear systems involving the presence of tritium: prevention of tritium-induced damage, tritium inventory, management of tritiated waste... This paper reports recent results on the quantitative characterization of tritium deformation interactions in fee materials. (authors)

  12. Deformation field of the soft substrate induced by capillary force

    NASA Astrophysics Data System (ADS)

    Liu, J. L.; Nie, Z. X.; Jiang, W. G.

    2009-05-01

    Prediction on the deformation of a soft substrate induced by capillary force has been widely paid attention in the broad range of applications, such as metallurgy, material science, astronavigation, micro/nano-technology, etc., which is also a supplementary result to the classical Young's equation. We quantitatively analyzed the deformation of an elastic substrate under capillary force by means of the energy principle and the continuum mechanics method. The actual drop's morphology was investigated and was compared with that calculated based on the classical spherical shape assumption of the droplet. The displacement field of the substrate was obtained, especially, its singularity at the droplet edge was also discussed. The results are beneficial to engineering application and micro/nano-measurement.

  13. Deformation mechanisms of bent Si nanowires governed by the sign and magnitude of strain

    NASA Astrophysics Data System (ADS)

    Wang, Lihua; Kong, Deli; Xin, Tianjiao; Shu, Xinyu; Zheng, Kun; Xiao, Lirong; Sha, Xuechao; Lu, Yan; Zhang, Ze; Han, Xiaodong; Zou, Jin

    2016-04-01

    In this study, the deformation mechanisms 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 deformation mechanisms, 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 deformation 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 deformation mechanisms in bent Si nanowires.

  14. Atomic-scale configurations of synchroshear-induced deformation twins in the ionic MnS crystal

    PubMed Central

    Zhou, Y. T.; Xue, Y. B.; Chen, D.; Wang, Y. J.; Zhang, B.; Ma, X. L.

    2014-01-01

    Deformation twinning was thought as impossible in ionic compounds with rock-salt structure due to the charge effect on {111} planes. Here we report the presence and formation mechanism of deformation {111} twins in the rock-salt manganese sulphide (MnS) inclusions embedded in a hot-rolled stainless steel. Based on the atomic-scale mapping under aberration-corrected scanning transmission electron microscopy, a dislocation-based mechanism involved two synchronized shear on adjacent atomic layers is proposed to describe the dislocation glide and consequently twinning formation. First-principles calculations of the energy barriers for twinning formation in MnS and comparing with that of PbS and MgO indicate the distinct dislocation glide scheme and deformation behaviors for the rock-salt compounds with different ionicities. This study may improve our understanding of the deformation mechanisms of rock-salt crystals and other ionic compounds. PMID:24874022

  15. Atomic-scale configurations of synchroshear-induced deformation twins in the ionic MnS crystal

    NASA Astrophysics Data System (ADS)

    Zhou, Y. T.; Xue, Y. B.; Chen, D.; Wang, Y. J.; Zhang, B.; Ma, X. L.

    2014-05-01

    Deformation twinning was thought as impossible in ionic compounds with rock-salt structure due to the charge effect on {111} planes. Here we report the presence and formation mechanism of deformation {111} twins in the rock-salt manganese sulphide (MnS) inclusions embedded in a hot-rolled stainless steel. Based on the atomic-scale mapping under aberration-corrected scanning transmission electron microscopy, a dislocation-based mechanism involved two synchronized shear on adjacent atomic layers is proposed to describe the dislocation glide and consequently twinning formation. First-principles calculations of the energy barriers for twinning formation in MnS and comparing with that of PbS and MgO indicate the distinct dislocation glide scheme and deformation behaviors for the rock-salt compounds with different ionicities. This study may improve our understanding of the deformation mechanisms of rock-salt crystals and other ionic compounds.

  16. RNGCHN: a program to calculate displacement components from dislocations in an elastic half-space with applications for modeling geodetic measurements of crustal deformation

    NASA Astrophysics Data System (ADS)

    Feigl, Kurt L.; Dupré, Emmeline

    1999-07-01

    The RNGCHN program calculates a single component of the displacement field due to a finite or point-source dislocation buried in an elastic half space. This formulation approximates the surface movements produced by earthquake faulting or volcanic intrusion. As such, it is appropriate for modeling crustal deformation measured by geodetic surveying techniques, such as spirit leveling, trilateration, Very Long Baseline Interferometry (VLBI), Global Positioning System (GPS), or especially interferometric analysis of synthetic aperture radar (SAR) images. Examples suggest that this model can fit simple coseismic earthquake signatures to within their measurement uncertainties. The program's input parameters include fault position, depth, length, width, strike, dip, and three components of slip. The output consists of displacement components in the form of an ASCII list or a rectangular array of binary integers. The same program also provides partial derivatives of the displacement component with respect to all 10 input parameters. The FORTRAN source code for the program is in the public domain and available as the compressed tar file rngchn.tar.Z in the directory/pub/GRGS via the Internet by anonymous ftp to spike.cst. cnes.fr. This distribution includes worked examples and a MATLAB interface.

  17. The computation of induced drag with nonplanar and deformed wakes

    NASA Technical Reports Server (NTRS)

    Kroo, Ilan; Smith, Stephen

    1991-01-01

    The classical calculation of inviscid drag, based on far field flow properties, is reexamined with particular attention to the nonlinear effects of wake roll-up. Based on a detailed look at nonlinear, inviscid flow theory, it is concluded that many of the classical, linear results are more general than might have been expected. Departures from the linear theory are identified and design implications are discussed. Results include the following: Wake deformation has little effect on the induced drag of a single element wing, but introduces first order corrections to the induced drag of a multi-element lifting system. Far field Trefftz-plane analysis may be used to estimate the induced drag of lifting systems, even when wake roll-up is considered, but numerical difficulties arise. The implications of several other approximations made in lifting line theory are evaluated by comparison with more refined analyses.

  18. Dislocation boundaries and active slip systems

    SciTech Connect

    Wert, J.A.; Hansen, N.

    1995-11-01

    Part of the dislocations which have participated in the plastic deformation of a polycrystalline metal are stored in dislocation boundaries in a two- or three-dimensional arrangement. The dislocation in such boundaries can be analyzed by determining the misorientation between neighboring crystallites and the boundary orientation. Information about the dislocations in the boundaries can also be obtained by an analysis of active slip systems based on the crystallite orientation and the imposed stress or strain state in combination with appropriate constraint conditions. In the present paper an analysis of the boundary dislocation structure and of the slip systems has been conducted for pure aluminium cold-rolled to a von Mises strain of 0.41. The results show that a substantial majority of dislocations in different types of dislocation boundaries are from the primary and conjugate slip system in the adjoining crystallites. A basis is therefore provided for integrating deformation structure observations with plastic deformation behavior.

  19. Transition of dislocation nucleation induced by local stress concentration in nanotwinned copper

    PubMed Central

    Lu, N.; Du, K.; Lu, L.; Ye, H. Q.

    2015-01-01

    Metals with a high density of nanometre-scale twins have demonstrated simultaneous high strength and good ductility, attributed to the interaction between lattice dislocations and twin boundaries. Maximum strength was observed at a critical twin lamella spacing (∼15 nm) by mechanical testing; hence, an explanation of how twin lamella spacing influences dislocation behaviours is desired. Here, we report a transition of dislocation nucleation from steps on the twin boundaries to twin boundary/grain boundary junctions at a critical twin lamella spacing (12–37 nm), observed with in situ transmission electron microscopy. The local stress concentrations vary significantly with twin lamella spacing, thus resulting in a critical twin lamella spacing (∼18 nm) for the transition of dislocation nucleation. This agrees quantitatively with the mechanical test. These results demonstrate that by quantitatively analysing local stress concentrations, a direct relationship can be resolved between the microscopic dislocation activities and macroscopic mechanical properties of nanotwinned metals. PMID:26179409

  20. Transition of dislocation nucleation induced by local stress concentration in nanotwinned copper.

    PubMed

    Lu, N; Du, K; Lu, L; Ye, H Q

    2015-01-01

    Metals with a high density of nanometre-scale twins have demonstrated simultaneous high strength and good ductility, attributed to the interaction between lattice dislocations and twin boundaries. Maximum strength was observed at a critical twin lamella spacing (∼15 nm) by mechanical testing; hence, an explanation of how twin lamella spacing influences dislocation behaviours is desired. Here, we report a transition of dislocation nucleation from steps on the twin boundaries to twin boundary/grain boundary junctions at a critical twin lamella spacing (12-37 nm), observed with in situ transmission electron microscopy. The local stress concentrations vary significantly with twin lamella spacing, thus resulting in a critical twin lamella spacing (∼18 nm) for the transition of dislocation nucleation. This agrees quantitatively with the mechanical test. These results demonstrate that by quantitatively analysing local stress concentrations, a direct relationship can be resolved between the microscopic dislocation activities and macroscopic mechanical properties of nanotwinned metals. PMID:26179409

  1. A Multiscale Model Based On Intragranular Microstructure — Prediction Of Dislocation Patterns At The Microscopic Scale

    NASA Astrophysics Data System (ADS)

    Franz, Gérald; Abed-Meraim, Farid; Zineb, Tarak Ben; Lemoine, Xavier; Berveiller, Marcel

    2007-04-01

    A large strain elastic-plastic single crystal constitutive law, based on dislocation annihilation and storage, is implemented in a new self-consistent scheme, leading to a multiscale model which achieves, for each grain, the calculation of plastic slip activity, with help of regularized formulation drawn from visco-plasticity, and dislocation microstructure evolution. This paper focuses on the relationship between the deformation history of a BCC grain and induced microstructure during monotonic and two-stage strain paths.

  2. Dislocation Multi-junctions and Strain Hardening

    SciTech Connect

    Bulatov, V; Hsiung, L; Tang, M; Arsenlis, A; Bartelt, M; Cai, W; Florando, J; Hiratani, M; Rhee, M; Hommes, G; Pierce, T; Diaz de la Rubia, T

    2006-06-20

    At the microscopic scale, the strength of a crystal derives from the motion, multiplication and interaction of distinctive line defects--dislocations. First theorized in 1934 to explain low magnitudes of crystal strength observed experimentally, the existence of dislocations was confirmed only two decades later. Much of the research in dislocation physics has since focused on dislocation interactions and their role in strain hardening: a common phenomenon in which continued deformation increases a crystal's strength. The existing theory relates strain hardening to pair-wise dislocation reactions in which two intersecting dislocations form junctions tying dislocations together. Here we report that interactions among three dislocations result in the formation of unusual elements of dislocation network topology, termed hereafter multi-junctions. The existence of multi-junctions is first predicted by Dislocation Dynamics (DD) and atomistic simulations and then confirmed by the transmission electron microscopy (TEM) experiments in single crystal molybdenum. In large-scale Dislocation Dynamics simulations, multi-junctions present very strong, nearly indestructible, obstacles to dislocation motion and furnish new sources for dislocation multiplication thereby playing an essential role in the evolution of dislocation microstructure and strength of deforming crystals. Simulation analyses conclude that multi-junctions are responsible for the strong orientation dependence of strain hardening in BCC crystals.

  3. Thermally induced stresses and deformations in layered composite tubes

    NASA Technical Reports Server (NTRS)

    Cooper, D. E.; Cohen, D.; Rousseau, C. Q.; Hyer, M. W.; Tompkins, S. S.

    1985-01-01

    The thermally induced stresses and deformations in layered, orthotropic tubes are studied. The motivation for studying tubes is their likely application for use in space structures. Tubes are a strong candidate for this application because of their high structural efficiency, as measured by stiffness per unit weight, and their relative ease of fabrication. Also, tubes have no free edges to deteriorate or delaminate. An anticipated thermal condition for tubes in space is a circumferential temperature gradient. This type of gradient will introduce dimensional changes into the structure and may cause stresses large enough to cause damage to the material. There are potentially large differences in temperatures at different circumferential locations on the tube. Because of this, the effects of temperature dependent material properties on the stresses and deformations may be important. The study is composed of three parts: experiments to determine the functional form of the circumferential gradient and to measure tube deflections; an elasticity solution to compute the stresses and deformations; and an approximate approach to determine the effects of temperature dependent material properties.

  4. Electron Beam Induced Artifacts During in situ TEM Deformation of Nanostructured Metals.

    PubMed

    Sarkar, Rohit; Rentenberger, Christian; Rajagopalan, Jagannathan

    2015-01-01

    A critical assumption underlying in situ transmission electron microscopy studies is that the electron beam (e-beam) exposure does not fundamentally alter the intrinsic deformation behavior of the materials being probed. Here, we show that e-beam exposure causes increased dislocation activation and marked stress relaxation in aluminum and gold films spanning a range of thicknesses (80-400 nanometers) and grain sizes (50-220 nanometers). Furthermore, the e-beam induces anomalous sample necking, which unusually depends more on the e-beam diameter than intensity. Notably, the stress relaxation in both aluminum and gold occurs at beam energies well below their damage thresholds. More remarkably, the stress relaxation and/or sample necking is significantly more pronounced at lower accelerating voltages (120 kV versus 200 kV) in both the metals. These observations in aluminum and gold, two metals with highly dissimilar atomic weights and properties, indicate that e-beam exposure can cause anomalous behavior in a broad spectrum of nanostructured materials, and simultaneously suggest a strategy to minimize such artifacts. PMID:26552934

  5. Electron Beam Induced Artifacts During in situ TEM Deformation of Nanostructured Metals

    PubMed Central

    Sarkar, Rohit; Rentenberger, Christian; Rajagopalan, Jagannathan

    2015-01-01

    A critical assumption underlying in situ transmission electron microscopy studies is that the electron beam (e-beam) exposure does not fundamentally alter the intrinsic deformation behavior of the materials being probed. Here, we show that e-beam exposure causes increased dislocation activation and marked stress relaxation in aluminum and gold films spanning a range of thicknesses (80–400 nanometers) and grain sizes (50–220 nanometers). Furthermore, the e-beam induces anomalous sample necking, which unusually depends more on the e-beam diameter than intensity. Notably, the stress relaxation in both aluminum and gold occurs at beam energies well below their damage thresholds. More remarkably, the stress relaxation and/or sample necking is significantly more pronounced at lower accelerating voltages (120 kV versus 200 kV) in both the metals. These observations in aluminum and gold, two metals with highly dissimilar atomic weights and properties, indicate that e-beam exposure can cause anomalous behavior in a broad spectrum of nanostructured materials, and simultaneously suggest a strategy to minimize such artifacts. PMID:26552934

  6. Theory of magnetoresistance due to lattice dislocations in face-centred cubic metals

    NASA Astrophysics Data System (ADS)

    Bian, Q.; Niewczas, M.

    2016-06-01

    A theoretical model to describe the low temperature magneto-resistivity of high purity copper single and polycrystals containing different density and distribution of dislocations has been developed. In the model, magnetoresistivity tensor is evaluated numerically using the effective medium approximation. The anisotropy of dislocation-induced relaxation time is considered by incorporating two independent energy bands with different relaxation times and the spherical and cylindrical Fermi surfaces representing open, extended and closed electron orbits. The effect of dislocation microstructure is introduced by means of two adjustable parameters corresponding to the length and direction of electron orbits in the momentum space, which permits prediction of magnetoresistance of FCC metals containing different density and distribution of dislocations. The results reveal that dislocation microstructure influences the character of the field-dependent magnetoresistivity. In the orientation of the open orbits, the quadratic variation in magnetoresistivity changes to quasi-linear as the density of dislocations increases. In the closed orbit orientation, dislocations delay the onset of magnetoresistivity saturation. The results indicate that in the open orbit orientations of the crystals, the anisotropic relaxation time due to small-angle dislocation scattering induces the upward deviation from Kohler's rule. In the closed orbit orientations Kohler's rule holds, independent of the density of dislocations. The results obtained with the model show good agreement with the experimental measurements of transverse magnetoresistivity in deformed single and polycrystal samples of copper at 2 K.

  7. Atomistic Simulation of shock induced dislocation dynamics and evolution of different plasticity mechanisms in Single Crystal Copper

    NASA Astrophysics Data System (ADS)

    Neogi, Anupam; Mitra, Nilanjan

    Deformation and observation of different types of plasticity mechanisms of FCC metals (e.g. Copper) under shock loading of various intensities has been investigated by several groups of researchers around the globe through different types of experiments and/or atomistic simulations. However, there still exists lacuna in this well researched area. In this study the temporal details of dislocation dynamics are provided. Simulations also demonstrate different types of temporal evolution of different loops observed for single crystal Cu under different intensities of shock loading. Observance of formation of twins and their temporal evolution at higher intensities of shock loading are also demonstrated as part of this study. Comparisons of these NEMD simulations using EAM potential are discussed with regards to different experimental and simulation studies in literature.

  8. Development of regional liquefaction-induced deformation hazard maps

    USGS Publications Warehouse

    Rosinski, A.; Knudsen, K.-L.; Wu, J.; Seed, R.B.; Real, C.R.

    2004-01-01

    This paper describes part of a project to assess the feasibility of producing regional (1:24,000-scale) liquefaction hazard maps that are based-on potential liquefaction-induced deformation. The study area is the central Santa Clara Valley, at the south end of San Francisco Bay in Central California. The information collected and used includes: a) detailed Quaternary geological mapping, b) over 650 geotechnical borings, c) probabilistic earthquake shaking information, and d) ground-water levels. Predictions of strain can be made using either empirical formulations or numerical simulations. In this project lateral spread displacements are estimated and new empirical relations to estimate future volumetric and shear strain are used. Geotechnical boring data to are used to: (a) develop isopach maps showing the thickness of sediment thatis likely to liquefy and deform under earthquake shaking; and (b) assess the variability in engineering properties within and between geologic map units. Preliminary results reveal that late Holocene deposits are likely to experience the greatest liquefaction-induced strains, while Holocene and late Pleistocene deposits are likely to experience significantly less horizontal and vertical strain in future earthquakes. Development of maps based on these analyses is feasible.

  9. Deformation-induced trace element redistribution in zircon revealed using atom probe tomography

    PubMed Central

    Piazolo, Sandra; La Fontaine, Alexandre; Trimby, Patrick; Harley, Simon; Yang, Limei; Armstrong, Richard; Cairney, Julie M.

    2016-01-01

    Trace elements diffuse negligible distances through the pristine crystal lattice in minerals: this is a fundamental assumption when using them to decipher geological processes. For example, the reliable use of the mineral zircon (ZrSiO4) as a U-Th-Pb geochronometer and trace element monitor requires minimal radiogenic isotope and trace element mobility. Here, using atom probe tomography, we document the effects of crystal–plastic deformation on atomic-scale elemental distributions in zircon revealing sub-micrometre-scale mechanisms of trace element mobility. Dislocations that move through the lattice accumulate U and other trace elements. Pipe diffusion along dislocation arrays connected to a chemical or structural sink results in continuous removal of selected elements (for example, Pb), even after deformation has ceased. However, in disconnected dislocations, trace elements remain locked. Our findings have important implications for the use of zircon as a geochronometer, and highlight the importance of deformation on trace element redistribution in minerals and engineering materials. PMID:26868040

  10. Deformation-induced trace element redistribution in zircon revealed using atom probe tomography.

    PubMed

    Piazolo, Sandra; La Fontaine, Alexandre; Trimby, Patrick; Harley, Simon; Yang, Limei; Armstrong, Richard; Cairney, Julie M

    2016-01-01

    Trace elements diffuse negligible distances through the pristine crystal lattice in minerals: this is a fundamental assumption when using them to decipher geological processes. For example, the reliable use of the mineral zircon (ZrSiO4) as a U-Th-Pb geochronometer and trace element monitor requires minimal radiogenic isotope and trace element mobility. Here, using atom probe tomography, we document the effects of crystal-plastic deformation on atomic-scale elemental distributions in zircon revealing sub-micrometre-scale mechanisms of trace element mobility. Dislocations that move through the lattice accumulate U and other trace elements. Pipe diffusion along dislocation arrays connected to a chemical or structural sink results in continuous removal of selected elements (for example, Pb), even after deformation has ceased. However, in disconnected dislocations, trace elements remain locked. Our findings have important implications for the use of zircon as a geochronometer, and highlight the importance of deformation on trace element redistribution in minerals and engineering materials. PMID:26868040

  11. Deformation-induced trace element redistribution in zircon revealed using atom probe tomography

    NASA Astrophysics Data System (ADS)

    Piazolo, Sandra; La Fontaine, Alexandre; Trimby, Patrick; Harley, Simon; Yang, Limei; Armstrong, Richard; Cairney, Julie M.

    2016-02-01

    Trace elements diffuse negligible distances through the pristine crystal lattice in minerals: this is a fundamental assumption when using them to decipher geological processes. For example, the reliable use of the mineral zircon (ZrSiO4) as a U-Th-Pb geochronometer and trace element monitor requires minimal radiogenic isotope and trace element mobility. Here, using atom probe tomography, we document the effects of crystal-plastic deformation on atomic-scale elemental distributions in zircon revealing sub-micrometre-scale mechanisms of trace element mobility. Dislocations that move through the lattice accumulate U and other trace elements. Pipe diffusion along dislocation arrays connected to a chemical or structural sink results in continuous removal of selected elements (for example, Pb), even after deformation has ceased. However, in disconnected dislocations, trace elements remain locked. Our findings have important implications for the use of zircon as a geochronometer, and highlight the importance of deformation on trace element redistribution in minerals and engineering materials.

  12. Deformation-Induced Amorphization of Copper-Titanium Intermetallics

    NASA Astrophysics Data System (ADS)

    Askenazy, Philip Douglas

    Two methods of inducing amorphization in Cu-Ti intermetallic compounds by mechanical means have been investigated. Ingots of compositions Cu_{35}Ti _{65} and Cu_ {33.3}Ti_{66.7} were rapidly quenched into ribbons. The microstructure consisted largely of microcrystals in an amorphous matrix, which were either quenched in or grown by annealing. The ribbons were cold-rolled, which reduced their effective thickness by a factor of about 8. The status of the intermetallic compound CuTi_2 was monitored by x-ray diffraction and transmission electron microscopy (TEM). The crystals were found to amorphize as rolling progressed. This behavior was not reproduced in polycrystalline samples that had no amorphous matrix present initially. The presence of the amorphous phase is thus necessary for amorphization of the crystal: it eliminates the need to nucleate the new glass, and it prevents the ribbon from disintegrating at high deformation stages. It may also change the deformation mechanism that occurs in the crystals, retarding the onset of amorphization. Diffuse scattering in close-packed directions is similar to that seen in electron irradiation experiments. It is postulated that the chemical disorder present in antiphase boundaries caused by deformation raises the free energy of the crystal higher than that of the amorphous phase. Ingots of the same compound were worn against each other in a custom-built wear apparatus. The design eliminates iron contamination of the wear sample and requires relatively small quantities of material. Alteration of the surface structure was monitored by plane-view and cross -sectional TEM. Larger subsurface crystals exhibit diffuse scattering, similar to that found in the rolled samples. A wide range of grain sizes was observed, due to the inhomogeneous nature of the wear process. An unusual phase was observed at the surface, consisting of a nanometer-scale mixture of aligned nanocrystalline regions and disordered areas. Some amorphous phase is

  13. Subtalar dislocation

    SciTech Connect

    El-Khoury, G.Y.; Yousefzadeh, D.K.; Mulligan, G.M.; Moore, T.E.

    1982-05-01

    Over a period of three years we have seen nine patients with subtalar dislocation, all of whom sustained violent trauma to the region of the ankle and hind foot. All but one patient were males. Clinically a subtalar dislocation resembles a complicated fracture dislocation of the ankle but a definitive diagnosis can only be made radiographically. The mechanism of injury and radiographic features of this injury are discussed.

  14. Formation of Nanostructures in Severely Deformed High-Strength Steel Induced by High-Frequency Ultrasonic Impact Treatment

    NASA Astrophysics Data System (ADS)

    Dutta, R. K.; Malet, L.; Gao, H.; Hermans, M. J. M.; Godet, S.; Richardson, I. M.

    2015-02-01

    Surface modification by the generation of a nanostructured surface layer induced via ultrasonic impact treatment was performed at the weld toe of a welded high-strength quenched and tempered structural steel, S690QL1 (Fe-0.16C-0.2Si-0.87Mn-0.33Cr-0.21Mo (wt pct)). Such high-frequency peening techniques are known to improve the fatigue life of welded components. The nanocrystallized structure as a function of depth from the top-treated surface was characterized via a recently developed automated crystal orientation mapping in transmission electron microscopy. Based on the experimental observations, a grain refinement mechanism induced by plastic deformation during the ultrasonic impact treatment is proposed. It involves the formation of low-angle misoriented lamellae displaying a high density of dislocations followed by the subdivision of microbands into blocks and the resulting formation of polygonal submicronic grains. These submicronic grains further breakdown into nano grains. The results show the presence of retained austenite even after severe surface plastic deformation. The average grain size of the retained austenite and martensite is 17 and 35 nm, respectively. The in-grain deformation mechanisms are different in larger and smaller grains. Larger grains show long-range lattice rotations, while smaller grains show plastic deformation through grain rotation. Also the smaller nano grains exhibit the presence of short-range disorder. Surface nanocrystallization also leads to an increased fraction of low angle and low energy coincident site lattice boundaries especially in the smaller grains ( nm).

  15. Synergy of plastic deformation and gas retention in tungsten

    NASA Astrophysics Data System (ADS)

    Terentyev, D.; De Temmerman, G.; Minov, B.; Zayachuk, Y.; Lambrinou, K.; Morgan, T. W.; Dubinko, A.; Bystrov, K.; Van Oost, G.

    2015-01-01

    Taking the example of tungsten, we demonstrate that high-flux plasma exposure of recrystallized and plastically deformed samples leads to principal differences in the gas trapping and associated surface modification. Surface of the exposed pre-deformed samples exhibits ruptured µm-sized blisters, a signature of bubbles nucleated close to the surface on the plastically induced dislocation network. Contrary to the recrystallized samples, no stage attributable to gas bubbles appeared in the desorption spectrum of the deformed samples demonstrating the strong impact of dislocations on hydrogen retention.

  16. Evidence for a transition in deformation mechanism in nanocrystalline pure titanium processed by high-pressure torsion

    NASA Astrophysics Data System (ADS)

    Yang, Chao; Song, Min; Liu, Yong; Ni, Song; Sabbaghianrad, Shima; Langdon, Terence G.

    2016-06-01

    Nanocrystalline titanium with an average grain size of about 60-70 nm was prepared by high-pressure torsion. The results of hardness and structural evolutions indicate that a strain-induced hardening-softening-hardening-softening behaviour occurs. For coarse-grained titanium, -type dislocation multiplication, twinning and a high pressure-induced α-to-ω phase transformation play major roles to accommodate deformation, leading to a significant strain hardening. As deformation proceeds, dynamic recrystallisation leads to a decrease in dislocation density, especially for -type dislocations, leading to a slight strain softening. The -component dislocation multiplication dominates the deformation when the grain size decreases to 100 nm and -component dislocation multiplication, grain refinement and the α-to-ω phase transformation contribute to the second strain hardening. The following strain softening is attributed to dynamic recovery.

  17. Determination of the inhomogeneous dislocation density in a crystallographic texture

    SciTech Connect

    Satdarova, F. F.; Kozlov, D. A.

    2007-03-15

    Diffraction analysis of the mixed dislocation structure of a polycrystal with an orthorhombic texture is reported. A significant difference in the dislocation densities in the texture components of cold-deformed low-carbon steel has been revealed.

  18. Transient luminescence induced by electrical refilling of charge carrier traps of dislocation network at hydrophilically bonded Si wafers interface

    SciTech Connect

    Bondarenko, Anton; Vyvenko, Oleg

    2014-02-21

    Dislocation network (DN) at hydrophilically bonded Si wafers interface is placed in space charge region (SCR) of a Schottky diode at a depth of about 150 nm from Schottky electrode for simultaneous investigation of its electrical and luminescent properties. Our recently proposed pulsed traps refilling enhanced luminescence (Pulsed-TREL) technique based on the effect of transient luminescence induced by refilling of charge carrier traps with electrical pulses is further developed and used as a tool to establish DN energy levels responsible for D1 band of dislocation-related luminescence in Si (DRL). In present work we do theoretical analysis and simulation of traps refilling kinetics dependence on refilling pulse magnitude (Vp) in two levels model: shallow and deep. The influence of initial charge state of deep level on shallow level occupation-Vp dependence is discussed. Characteristic features predicted by simulations are used for Pulsed-TREL experimental results interpretation. We conclude that only shallow (∼0.1 eV from conduction and valence band) energetic levels in the band gap participate in D1 DRL.

  19. AC electric field induced droplet deformation in a microfluidic T-junction.

    PubMed

    Xi, Heng-Dong; Guo, Wei; Leniart, Michael; Chong, Zhuang Zhi; Tan, Say Hwa

    2016-08-01

    We present for the first time an experimental study on the droplet deformation induced by an AC electric field in droplet-based microfluidics. It is found that the deformation of the droplets becomes stronger with increasing electric field intensity and frequency. The measured electric field intensity dependence of the droplet deformation is consistent with an early theoretical prediction for stationary droplets. We also proposed a simple equivalent circuit model to account for the frequency dependence of the droplet deformation. The model well explains our experimental observations. In addition, we found that the droplets can be deformed repeatedly by applying an amplitude modulation (AM) signal. PMID:27173587

  20. Hydrogen-induced change in core structures of {110}[111] edge and {110}[111] screw dislocations in iron

    PubMed Central

    Wang, Shuai; Hashimoto, Naoyuki; Ohnuki, Somei

    2013-01-01

    Employing the empirical embedded-atom method potentials, the evolution of edge and screw dislocation core structure is calculated at different hydrogen concentrations. With hydrogen, the core energy and Peierls potential are reduced for all dislocations. A broaden-core and a quasi-split core structure are observed for edge and screw dislocation respectively. The screw dislocation and hydrogen interaction in body-centred cubic iron is found to be not mainly due to the change of elastic modulus, but the variation of dislocation core structure. PMID:24067268

  1. Acute traumatic patellar dislocation.

    PubMed

    Duthon, V B

    2015-02-01

    Inaugural traumatic patellar dislocation is most often due to trauma sustained during physical or sports activity. Two-thirds of acute patellar dislocations occur in young active patients (less than 20 years old). Non-contact knee sprain in flexion and valgus is the leading mechanism in patellar dislocation, accounting for as many as 93% of all cases. The strong displacement of the patella tears the medial stabilizing structures, and notably the medial patellofemoral ligament (MPFL), which is almost always injured in acute patellar dislocation, most frequently at its femoral attachment. Lateral patellar glide can be assessed with the knee in extension or 20° flexion. Displacement by more than 50% of the patellar width is considered abnormal and may induce apprehension. Plain X-ray and CT are mandatory to diagnose bony risk factors for patellar dislocation, such as trochlear dysplasia or increased tibial tubercle-trochlear groove distance (TT-TG), and plan correction. MRI gives information on cartilage and capsulo-ligamentous status for treatment planning: free bodies or osteochondral fracture have to be treated surgically. If patellar dislocation occurs in an anatomically normal knee and osteochondral fracture is ruled out on MRI, non-operative treatment is usually recommended. PMID:25592052

  2. Electric field-induced deformation of polyelectrolyte gels

    SciTech Connect

    Adolf, D.; Hance, B.G.

    1995-08-01

    Water-swollen polyelectrolyte gels deform in an electric field. We observed that the sign and magnitude of the deformation is dependent on the nature of the salt bath in which the gel is immersed and electrocuted. These results are compatible with a deformation mechanism based upon creation of ion density gradients by the field which, in turn, creates osmotic pressure gradients within the gel. A consistent interpretation results only if gel mobility is allowed as well as free ion diffusion and migration.

  3. Nonlinear modeling and estimation of slew induced structural deformations

    NASA Technical Reports Server (NTRS)

    Dwyer, T. A. W., III; Karray, F.

    1988-01-01

    A model of the nonlinear dynamics of a deformable maneuvering multibody system is described, whereby elastic deformation are modeled by restoring forces and dissipative forces at point mass appendages. This model is brought into bilinear form. Estimation of deformations occasioned by rapid slewing maneuvers is carried out by a filter based on a globally equivalent linear model of the bilinear dynamics, and is shown to be an improvement over the extended Kalman filter. To further alleviate the computational burden, the estimated deformation state is propagated between observations by a low dimensional operator spline interpolator of bilinear system Volterra series, which is easily implemented.

  4. Using transverse isotropy to model arbitrary deformation-induced anisotropy

    SciTech Connect

    Brannon, R.M.

    1996-07-01

    A unifying framework is developed for the analysis of brittle materials. Heretofore diverse classes of models result from different choices for unspecified coefficient and distribution functions in the unified theory. Material response is described in terms of expectation integrals of transverse symmetry tensors. First, a canonical body containing cracks of all the same orientation is argued to possess macroscopic transverse isotropy. An orthogonal basis for the linear subspace consisting of all double-symmetric transversely-isotropic fourth-order tensors associated with a given material vector is introduced and applied to deduce the explicit functional dependence of the compliance of such contrived materials on the shared crack orientation. A principle of superposition of strain rates is used to write the compliance for a more realistic material consisting of cracks of random size and orientation as an expectation integral of the transverse compliance for each orientation times the joint distribution function for the size and orientation. Utilizing an evolving (initially exponential) size- dependence in the joint distribution, the general theory gives unprecedented agreement with measurements of the dynamic response of alumina to impact loading, especially upon release where the calculations predict the development of considerable deformation- induced anisotropy, challenging the conventional notion of shocks as isotropic phenomena.

  5. Shock induced deformation substructures in a copper bicrystal

    SciTech Connect

    Cao, Fang; Beyerlein, Irene J; Cerreta, Ellen K; Trujillo, Carl P; Gray Ill, George T; Sencer, Bulent H

    2008-01-01

    Controlled shock recovery experiments have been conducted to assess the role of shock pressure and orientation dependence on the substructure evolution of a [100]/[01{ovr 1}] copper bicrystal. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were utilized to characterize orientation variation and substructure evolution of the post-shock specimens. Well defined dislocation cell structures were displayed in both grains and the average cell size was observed to decrease with increasing shock pressure. Twinning was occasionally observed in the 5 GPa shocked [100] grain and became the dominant substructure at higher shock pressure. The stress and directional dependence of twinning in the bicrystal was analyzed with consideration of the energetically favorable dissociation of dislocations into Shockley partials and the stress-orientation effect on the partial width. Moreover, a critical 'tear apart' stress is proposed and a good agreement is obtained between the calculated value and the experimental observations.

  6. Kinetics of a Fast Moving Partial Dislocation

    NASA Astrophysics Data System (ADS)

    Daphalapurkar, Nitin; Ramesh, K. T.

    2013-03-01

    Plastic deformation in materials under extreme stresses requires a kinetic description of moving dislocations. The velocities with which the partial dislocations can propagate under an applied stress has implications for plasticity at high strain rates, specifically, the rate of plastic deformation and the rate-sensitivity. In this work, we focus our attention on motion of a twinning partial dislocation in a face-centered cubic (FCC) material, Ni. We use molecular dynamics simulations to simulate the velocity of a propagating twinning partial dislocation and investigate the effect of applied shear stress. Results suggest a limiting value for the speeds of a propagating partial dislocation. The material speeds based on the nonlinear part (under high stresses) of the stress-strain curve are shown to have an influence on the velocity with which a partial dislocation can propagate. Predicted velocities from simulations will be related to observations from high rate impact experiments. Supported by Hopkins Extreme Materials Institute

  7. Cyclic-loading-induced accumulation of geometrically necessary dislocations near grain boundaries in a an ni-based superalloy.

    SciTech Connect

    Huang, E. W.; Barabash, R. I.; Ice, G. I.; Liu, W.; Liu, Y. L.; Kai, J. J.; Liaw, P. K.; Univ.of Tennessee; ORNL; Tsing-Hua Univ.

    2009-01-01

    In this study, the fatigue-induced microstructure produced in a nickel-based polycrystalline superalloy that was subjected to cyclic loading was characterized by polychromatic x-ray microdiffraction (PXM) together with in-situ neutron diffraction and transmission-electron microscopy (TEM). In-situ neutron-diffraction measurements reveal two distinct stages of the fatigue damage: cyclic hardening followed by cyclic softening. Three-dimensional spatially resolved PXM micro-Laue measurements find an increase in the density of geometrically necessary dislocations near the grain boundaries, which is accompanied by lattice rotations and grain subdivisions. The PXM results are in agreement with the in-situ neutron-diffraction and TEM results.

  8. 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.

  9. Deformation-induced accelerated dynamics in polymer glasses

    SciTech Connect

    Warren, Mya; Rottler, Joerg

    2010-10-28

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

  10. Internal friction peaks observed in explosively deformed polycrystalline Mo, Nb, and Cu

    NASA Technical Reports Server (NTRS)

    Rieu, G. E.; Grimes, H. H.; Romain, J. P.; Defouquet, J.

    1974-01-01

    Explosive deformation (50 kbar range) induced, in Cu, Mo and Nb, internal friction peaks identical to those observed after large normal deformation. The variation of the peaks with pressure for Mo and Nb lead to an explanation of these processes in terms of double kink generation in screw and edge dislocations.

  11. Particle-Based Simulation of Shock-Induced Deformation of Elastic Bodies

    NASA Astrophysics Data System (ADS)

    Sakamura, Y.; Sugimoto, T.; Nakayama, K.

    Shock-induced deformations of solid bodies are of practical interest to those who are concerned with explosive processing of materials, demolition of buildings, precautions against accidental explosions, etc. In order to simulate the shock-induced deformations of solid bodies, a large number of numerical codes based on continuum mechanics, which are called hydrocodes, have been developed so far [1, 2]. When the amount of deformation is relatively small, Lagrangian hydrocodes have been used to simulate the dynamic response of shock-loaded materials. When the deformation is large, Eulerian hydrocodes have been utilized instead. This is because the computational grids distorted along with the deformation of materials in the Lagrangian approach make the simulations either inaccurate or unstable, while the Eulerian approach where grids are fixed in space can handle such large deformations of materials. On the contrary, material interfaces that are precisely defined in the Lagrangian approach are not traced exactly in the Eulerian one.

  12. Dislocations and crowdions in two-dimensional crystals. Part III: Plastic deformation of the crystal as a result of defect movement and defect interaction with the field of elastic stresses

    NASA Astrophysics Data System (ADS)

    Natsik, V. D.; Smirnov, S. N.

    2016-03-01

    A continuation of the theoretical study of the intrinsic properties of dislocation and crowdion structural defects in 2D crystals [V. D. Natsik and S. N. Smirnov, Fiz. Nizk. Temp. 40, 1366 (2014) and V. D. Natsik and S. N. Smirnov, Fiz. Nizk. Temp. 41, 271 (2015)]. The atomic lattice model of conservative (glide) and non-conservative (climb) defect movement is discussed in detail. It is shown that given a continuum description of the 2D crystal, an individual defect can be examined as a point carrier of plastic deformation, its value being determined by the topological charge, which is compliant with the crystal geometry defect parameters. It is found that the strain rate depends on the rate at which the defect center moves, as well as its topological charge. The elastic forces acting on the dislocation and crowdion centers in the field of applied mechanical stresses, and the forces of elastic interaction between defects, are calculated in terms of the linear theory of elasticity of a 2D crystal. The non-linear effect pertaining to the interaction between defects and bending deformation of the crystalline membrane, which is specific to 2D crystals, is also discussed.

  13. Discrete dislocation dynamics simulations in a cylinder

    NASA Astrophysics Data System (ADS)

    Li, Maosheng; Gao, Chan; Xu, Jianing

    2015-02-01

    Mechanical properties of material are closely related to the motion of dislocations, and predicting the interactions and resulting collective motion of dislocations is a major task in understanding and modelling plastically deforming materials. A discrete dislocation dynamics model is used to describe the orientation substructure within the microstructure. Discrete dislocation dynamics simulations in three dimensions have been used to examine the role of dislocation multiplication and mobility on the plasticity in small samples under uniaxial compression. In this paper we describe the application of the dislocation dynamics simulations in a cylindrical geometry. The boundary conditions for the simulation were estimated from the distribution of the geometrically necessary dislocation density which was obtained from the orientation map. Numerical studies benchmark could validate the accuracy of the algorithms and the importance of handling the singularity correctly. The results of the simulation explain the formation of the experimentally observed substructure.

  14. Local decomposition induced by dislocation motions inside tetragonal Al2Cu compound: slip system-dependent dynamics

    NASA Astrophysics Data System (ADS)

    Chen, D.; Ma, X. L.

    2013-11-01

    Dislocations in a crystal are usually classified into several independent slip systems. Motion of a partial dislocation in monometallic crystals may remove or create stacking fault characterized with a partial of a lattice translation vector. However, it is recently known that motion of partial dislocations in complex structure, such as that inside an intermetallic Al2Cu compound, lead to a local composition deviation from its stoichiometric ratio and the resultant structure collapse. Here we report such a local decomposition behaviors are strongly dependent on slip system of dislocations. Under applied external stress, we have studied dislocation motion behaviors in the three independent slip systems of [001](110), [100]() and [110]() within tetragonal Al2Cu crystal by using molecular dynamics method. We found dislocation motions in all these slip systems result in local decomposition but their physical details differ significantly.

  15. Local decomposition induced by dislocation motions inside tetragonal Al(2)Cu compound: slip system-dependent dynamics.

    PubMed

    Chen, D; Ma, X L

    2013-01-01

    Dislocations in a crystal are usually classified into several independent slip systems. Motion of a partial dislocation in monometallic crystals may remove or create stacking fault characterized with a partial of a lattice translation vector. However, it is recently known that motion of partial dislocations in complex structure, such as that inside an intermetallic Al2Cu compound, lead to a local composition deviation from its stoichiometric ratio and the resultant structure collapse. Here we report such a local decomposition behaviors are strongly dependent on slip system of dislocations. Under applied external stress, we have studied dislocation motion behaviors in the three independent slip systems of [001](110), [100]() and [110]() within tetragonal Al2Cu crystal by using molecular dynamics method. We found dislocation motions in all these slip systems result in local decomposition but their physical details differ significantly. PMID:24196169

  16. Local decomposition induced by dislocation motions inside tetragonal Al2Cu compound: slip system-dependent dynamics

    PubMed Central

    Chen, D.; Ma, X. L.

    2013-01-01

    Dislocations in a crystal are usually classified into several independent slip systems. Motion of a partial dislocation in monometallic crystals may remove or create stacking fault characterized with a partial of a lattice translation vector. However, it is recently known that motion of partial dislocations in complex structure, such as that inside an intermetallic Al2Cu compound, lead to a local composition deviation from its stoichiometric ratio and the resultant structure collapse. Here we report such a local decomposition behaviors are strongly dependent on slip system of dislocations. Under applied external stress, we have studied dislocation motion behaviors in the three independent slip systems of [001](110), [100]() and [110]() within tetragonal Al2Cu crystal by using molecular dynamics method. We found dislocation motions in all these slip systems result in local decomposition but their physical details differ significantly. PMID:24196169

  17. The inhibiting effect of dislocation helices on the stress-induced orientation of S' precipitates in Al–Cu–Mg alloy

    SciTech Connect

    Guo, Xiaobin; Deng, Yunlai; Zhang, Jin; Zhang, Xinming

    2015-09-15

    The phenomenon of restrained stress-induced preferential orientation of S′ precipitates is investigated using a single-crystal of Al–1.23Cu–0.43 Mg alloy. Al–1.23Cu–0.43 Mg single-crystal specimens are subjected to stress aging, and the microstructure is analyzed by transmission electron microscopy (TEM). It is found that the stress-induced preferential orientation of S′ precipitates is restrained owing to the dislocations produced by a higher stress. The effect of dislocations on the oriented precipitates depends on the total length of the intersection lines for precipitate habit planes and dislocation glide planes. This investigation not only provides important insight into solving the anisotropy problem attributed to precipitation strengthening, but also offers a benchmark for choosing the appropriate stress range in manufacturing of Al–Cu–Mg alloys. - Highlights: • Single crystals of an Al–Cu–Mg alloy were prepared for the investigations. • A phenomenon of restrained stress-induced preferential orientation of S′ precipitates was found. • The influence of dislocation helices on precipitation during stress-aging was studied. • Difference of orientation degree of S′ precipitates and θ′ precipitates was explained. • A basis for choosing the appropriate stress range in manufacturing of Al–Cu–Mg alloys is provided.

  18. Smectic Edge Dislocations under Shear

    NASA Astrophysics Data System (ADS)

    Chen, Peilong; Lu, Chun-Yi David

    2011-09-01

    Layer structures around an edge dislocation in a smectic phase under shear are studied with both phase field and order parameter models. It is shown that, contrast to a crystal solid, the conventional picture of the Peach--Koehler force experienced by dislocations when the sample is under a shear stress cannot be readily applied to the smectic phases. Under a uniform shear flow, we obtain the phase field and order parameter solutions around an edge dislocation. The solutions elucidate properties such as the layer distortion range around the dislocation and scaling of inter-dislocation interaction on dislocation separation. Calculations on energy dissipation indicate the extreme shear-thinning behavior that an edge dislocation induces a shear stress independent of the shear rate. Finally in a bulk sample with dislocation forming loops and networks, we argue that the uniform flow component around the dislocation is important to the energy dissipation and we show that its scaling exponent with the shear rate is very close to results from many previous rheology measurements.

  19. Plastic deformation of a magnesium oxide 001-plane surface produced by cavitation

    NASA Technical Reports Server (NTRS)

    Hattori, S.; Miyoshi, K.; Buckley, D. H.; Okada, T.

    1986-01-01

    An investigation was conducted to examine plastic deformation of a cleaved single-crystal magnesium oxide 001-plane surface exposed to cavitation. Cavitation damage experiments were carried out in distilled water at 25 C by using a magnetostrictive oscillator in close proximity (2 mm) to the surface of the cleaved specimen. The dislocation-etch-pit patterns induced by cavitation were examined and compared with that of microhardness indentations. The results revealed that dislocation-etch-pit patterns around hardness indentations contain both screw and edge dislocations, while the etch-pit patterns on the surface exposed to cavitation contain only screw dislocations. During cavitation, deformation occurred in a thin surface layer, accompanied by work-hardening of the ceramic. The row of screw dislocations underwent a stable growth, which was analyzed crystallographically.

  20. Deformation behaviour and 6H-LPSO structure formation at nanoindentation in lamellar high Nb containing TiAl alloy

    NASA Astrophysics Data System (ADS)

    Song, L.; Xu, X. J.; Peng, C.; Wang, Y. L.; Liang, Y. F.; Shang, S. L.; Liu, Z. K.; Lin, J. P.

    2015-02-01

    Microstructure and deformation mechanisms at a nanoindentation in the lamellar colony of high Nb containing TiAl alloy have been studied using the focused ion beam and the transmission electron microscopy. Considerable deformation twins are observed around the nanoindentation, and a strain gradient is generated. A continuous change in the bending angle of the lamellar structure can be derived, and a strain-induced grain refinement process is observed as various active deformations split the γ grains into subgrains. In addition to all possible deformation mechanisms (ordinary dislocation, super-dislocation and deformation twining) activated due to the heavy plastic deformation, a 6-layer hexagonal (6H) long-period stacking ordered structure is identified for the first time near the contact zone and is thought to be closely related to the glide of partial dislocations.

  1. Deformation-induced damage and recovery in model hydrogels - A molecular dynamics simulation

    NASA Astrophysics Data System (ADS)

    Zidek, Jan; Milchev, Andrey; Jancar, Josef; Vilgis, Thomas A.

    2016-09-01

    Using molecular dynamics simulation of a model hybrid cross-link hydrogel, we investigate the network damage evolution and the related structure transformations. We model the hydrogel structure as a network-connected assembly of crosslinked clusters whereby deformation-induced damage is considered along with network recovery. The two principal mechanisms involved in hydrogel recovery from deformation include segment hops of the building structure units (segments) between clusters and cluster shape modification. These mechanisms act either instantaneously, or with a certain time delay after the onset of deformation. By elucidating the conditions under which one of the mechanisms prevails, one may design hydrogel materials with a desired response to deformation.

  2. Knee Dislocations

    PubMed Central

    Schenck, Robert C.; Richter, Dustin L.; Wascher, Daniel C.

    2014-01-01

    Background: Traumatic knee dislocation is becoming more prevalent because of improved recognition and increased exposure to high-energy trauma, but long-term results are lacking. Purpose: To present 2 cases with minimum 20-year follow-up and a review of the literature to illustrate some of the fundamental principles in the management of the dislocated knee. Study Design: Review and case reports. Methods: Two patients with knee dislocations who underwent multiligamentous knee reconstruction were reviewed, with a minimum 20-year follow-up. These patients were brought back for a clinical evaluation using both subjective and objective measures. Subjective measures include the following scales: Lysholm, Tegner activity, visual analog scale (VAS), Short Form–36 (SF-36), International Knee Documentation Committee (IKDC), and a psychosocial questionnaire. Objective measures included ligamentous examination, radiographic evaluation (including Telos stress radiographs), and physical therapy assessment of function and stability. Results: The mean follow-up was 22 years. One patient had a vascular injury requiring repair prior to ligament reconstruction. The average assessment scores were as follows: SF-36 physical health, 52; SF-36 mental health, 59; Lysholm, 92; IKDC, 86.5; VAS involved, 10.5 mm; and VAS uninvolved, 2.5 mm. Both patients had excellent stability and were functioning at high levels of activity for their age (eg, hiking, skydiving). Both patients had radiographic signs of arthritis, which lowered 1 subject’s IKDC score to “C.” Conclusion: Knee dislocations have rare long-term excellent results, and most intermediate-term studies show fair to good functional results. By following fundamental principles in the management of a dislocated knee, patients can be given the opportunity to function at high levels. Hopefully, continued advances in the evaluation and treatment of knee dislocations will improve the long-term outcomes for these patients in the

  3. Characterization of Plastic Deformation Induced by Shot-Peening in a Ni-Base Superalloy

    NASA Astrophysics Data System (ADS)

    Messé, O. M. D. M.; Stekovic, S.; Hardy, M. C.; Rae, C. M. F.

    2014-12-01

    The shot-peening process is currently employed in most industries to improve the longevity of components by inhibiting crack initiation as well as crack growth at the surface. The protective effect of shot peening has been mainly attributed to compressive stresses within the deformed layer. Intensive research has been carried out to quantify the near-surface residual stresses on entry into service and evolution throughout life. In nickel-base superalloys, the focus of research on the effects of shot-peening has performed using x-rays from either laboratory or synchrotron-based sources. However, this approach cannot evaluate in detail the deformation mechanisms nor the role of the γ' precipitates in a nickel-base superalloy; the latter is responsible for its unique properties. Our study uses a complementary range of techniques to investigate in detail the microstructure and deformation mechanisms associated with shot-peening in a coarse-grained nickel-based superalloy strengthened with coherent γ' precipitates. These include scanning electron microscopy and transmission electron microscopy, nanoindentation and micropillar compression. Accurate mapping of the dislocation structure produced throughout the deformed layers have been performed. Using an unconventional specimen preparation technique, it provides the basis for a more complete interpretation of how shot-peening inhibits fatigue cracking.

  4. Evaluating Deformation-Induced Grain Orientation Change in a Polycrystal During In Situ Tensile Deformation using EBSD.

    PubMed

    Buchheit, Thomas E; Carroll, Jay D; Clark, Blythe G; Boyce, Brad L

    2015-08-01

    Using an in situ load frame within a scanning electron microscope, a microstructural section on the surface of an annealed tantalum (Ta) polycrystalline specimen was mapped at successive tensile strain intervals, up to ~20% strain, using electron backscatter diffraction. A grain identification and correlation technique was developed for characterizing the evolving microstructure during loading. Presenting the correlated results builds on the reference orientation deviation (ROD) map concept where individual orientation measurements within a grain are compared with a reference orientation associated with that grain. In this case, individual orientation measurements in a deformed grain are measured relative to a reference orientation derived from the undeformed (initial) configuration rather than the current deformed configuration as has been done for previous ROD schemes. Using this technique helps reveal the evolution of crystallographic orientation gradients and development of deformation-induced substructure within grains. Although overall crystallographic texture evolved slowly during deformation, orientation spread within grains developed quickly. In some locations, misorientation relative to the original orientation of a grain exceeded 20° by 15% strain. The largest orientation changes often appeared near grain boundaries suggesting that these regions were preferred locations for the initial development of subgrains. PMID:26189352

  5. Solute drag on perfect and extended dislocations

    NASA Astrophysics Data System (ADS)

    Sills, R. B.; Cai, W.

    2016-04-01

    The drag force exerted on a moving dislocation by a field of mobile solutes is studied in the steady state. The drag force is numerically calculated as a function of the dislocation velocity for both perfect and extended dislocations. The sensitivity of the non-dimensionalized force-velocity curve to the various controlling parameters is assessed, and an approximate analytical force-velocity expression is given. A non-dimensional parameter S characterizing the strength of the solute-dislocation interaction, the background solute fraction ?, and the dislocation character angle ?, are found to have the strongest influence on the force-velocity curve. Within the model considered here, a perfect screw dislocation experiences no solute drag, but an extended screw dislocation experiences a non-zero drag force that is about 10 to 30% of the drag on an extended edge dislocation. The solutes can change the spacing between the Shockley partials in both stationary and moving extended dislocations, even when the stacking fault energy remains unaltered. Under certain conditions, the solutes destabilize an extended dislocation by either collapsing it into a perfect dislocation or causing the partials to separate unboundedly. It is proposed that the latter instability may lead to the formation of large faulted areas and deformation twins in low stacking fault energy materials containing solutes, consistent with experimental observations of copper and stainless steel containing hydrogen.

  6. Particle deformation induced by AFM tapping under different setpoint voltages

    NASA Astrophysics Data System (ADS)

    Wu, Chung-Lin; Farkas, Natalia; Dagata, John A.; He, Bo-Ching; Fu, Wei-En

    2014-09-01

    The measured height of polystyrene nanoparticles varies with setpoint voltage during atomic force microscopy (AFM) tapping-mode imaging. Nanoparticle height was strongly influenced by the magnitude of the deformation caused by the AFM tapping forces, which was determined by the setpoint voltage. This influence quantity was studied by controlling the operational AFM setpoint voltage. A test sample consisting of well-dispersed 60-nm polystyrene and gold nanoparticles co-adsorbed on poly-l-lysine-coated mica was studied in this research. Gold nanoparticles have not only better mechanical property than polystyrene nanoparticles, but also obvious facets in AFM phase image. By using this sample of mixed nanoparticles, it allows us to confirm that the deformation resulted from the effect of setpoint voltage, not noise. In tapping mode, the deformation of polystyrene nanoparticles increased with decreasing setpoint voltage. Similar behavior was observed with both open loop and closed loop AFM instruments.

  7. Monitoring of deformation induced microcracking in polycrystalline NiAl

    SciTech Connect

    Wanner, A.; Schietinger, B.; Bidlingmaier, T.; Zalkind, H.; Arzt, E.

    1995-08-01

    Microcracking in polycrystalline near-stoichiometric NiAl produced by room temperature plastic deformation under uniaxial compression was investigated by means of optical microscopy, velocity of sound measurements, and acoustic emission monitoring. Results show that strains greater than 2% are required to produce microcrack populations which can be evaluated by microscopical investigation or velocity of sound measurements. However, acoustic emission monitoring during compression testing indicates that microcracking starts at about 0.7% compressive plastic strain which is identical with the typical tensile fracture strain for NiAl. Thus it is concluded that there is little or no stable microcracking prior to failure in tension. Acoustic emission results show also that the process of microcracking does not primarily occur during the applied compressive deformation. A considerable fraction of the microcracking takes place during the quasi-elastic unloading following deformation.

  8. Distribution of dislocations in nanostructured bainite

    SciTech Connect

    Cornide, J; Miyamoto, G; Caballero, Francesca G.; Furuhara, T; Miller, Michael K; Garcia-Mateo, C.

    2011-01-01

    The dislocation density in ferrite and austenite of a bainitic microstructure obtained by transformation at very low temperature (300 C) has been determined using transmission electron microscopy. Observations revealed that bainitic ferrite plates consist of two distinctive regions with different substructures. A central region in the ferrite plate is observed with dislocations that may result from lattice-invariant deformation at the earlier stage of bainite growth. As plastic deformation occurs in the surrounding austenite to accommodate the transformation strain as growth progresses, the Ferrite/Austenite interface has also a very distinctive dislocation profile. In addition, atom-probe tomography suggested that dislocation tangles observed in the vicinity of the ferrite/austenite interface might trap higher amount of carbon than single dislocations inside the bainitic ferrite plate.

  9. Response properties of axion insulators and Weyl semimetals driven by screw dislocations and dynamical axion strings

    NASA Astrophysics Data System (ADS)

    You, Yizhi; Cho, Gil Young; Hughes, Taylor L.

    2016-08-01

    In this paper, we investigate the theory of dynamical axion strings emerging from chiral symmetry breaking in three-dimensional Weyl semimetals. The chiral symmetry is spontaneously broken by a charge density wave (CDW) order which opens an energy gap and converts the Weyl semimetal into an axion insulator. Indeed, the phase fluctuations of the CDW order parameter act as a dynamical axion field θ (x ⃗,t ) and couple to electromagnetic field via Lθ=θ/(x ⃗,t ) 32 π2 ɛσ τ ν μFσ τFν μ. Additionally, when the axion insulator is coupled to deformations of the background geometry/strain fields via torsional defects, e.g., screw dislocations, there is interesting interplay between the crystal dislocations and dynamical axion strings. For example, the screw dislocation traps axial charge, and there is a Berry phase accumulation when an axion string (which carries axial flux) is braided with a screw dislocation. In addition, a cubic coupling between the axial current and the geometry fields is nonvanishing and indicates a Berry phase accumulation during a particular three-loop braiding procedure where a dislocation loop is braided with another dislocation and they are both threaded by an axion string. We also observe a chiral magnetic effect induced by a screw dislocation density in the absence of a nodal energy imbalance between Weyl points and describe an additional chiral geometric effect and a geometric Witten effect.

  10. Hot deformation induced defects and performance enhancement in FeSb2 thermoelectric materials

    NASA Astrophysics Data System (ADS)

    Wang, Yongzheng; Fu, Chenguang; Zhu, Tiejun; Hu, Lipeng; Jiang, Guangyu; Zhao, Guanghui; Huo, Dexuan; Zhao, Xinbing

    2013-11-01

    The effect of hot deformation induced defects and texture on thermoelectric properties of FeSb2 bulk crystals has been investigated. The transport properties of the samples along both parallel and perpendicular direction of pressing were measured from 3 K to 300 K. The results showed that thermal conductivity of the deformed samples was significantly reduced. After twice deformation, the thermal conductivity of the sample along the perpendicular direction of pressing was decreased to 4 W/mK, which was only one third of that before deformation. Transmission electron microscopy observation revealed the presence of high density of lattice defects in the deformed samples. The lattice thermal conductivity was analyzed using the Debye-Callaway approximation, and the results showed that the deformation induced lattice imperfections play an important role in enhancing phonon scattering. In addition, both the electrical resistivity and Seebeck coefficient exhibited a weak anisotropy in the deformed samples. The figure of merit ZT of the bulk FeSb2 was significantly improved from 0.010 to 0.021 after deformation.

  11. Hot deformation induced defects and performance enhancement in FeSb{sub 2} thermoelectric materials

    SciTech Connect

    Wang, Yongzheng; Fu, Chenguang; Zhu, Tiejun E-mail: zhaoxb@zju.edu.cn; Hu, Lipeng; Jiang, Guangyu; Zhao, Xinbing E-mail: zhaoxb@zju.edu.cn; Zhao, Guanghui; Huo, Dexuan

    2013-11-14

    The effect of hot deformation induced defects and texture on thermoelectric properties of FeSb{sub 2} bulk crystals has been investigated. The transport properties of the samples along both parallel and perpendicular direction of pressing were measured from 3 K to 300 K. The results showed that thermal conductivity of the deformed samples was significantly reduced. After twice deformation, the thermal conductivity of the sample along the perpendicular direction of pressing was decreased to 4 W/mK, which was only one third of that before deformation. Transmission electron microscopy observation revealed the presence of high density of lattice defects in the deformed samples. The lattice thermal conductivity was analyzed using the Debye-Callaway approximation, and the results showed that the deformation induced lattice imperfections play an important role in enhancing phonon scattering. In addition, both the electrical resistivity and Seebeck coefficient exhibited a weak anisotropy in the deformed samples. The figure of merit ZT of the bulk FeSb{sub 2} was significantly improved from 0.010 to 0.021 after deformation.

  12. Structural Anisotropy in Metallic Glasses Induced by Mechanical Deformation

    SciTech Connect

    Dmowski, Wojtek; Egami, Takeshi

    2008-01-01

    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 deformed 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 deformed 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) mechanical deformation. The observation of the

  13. Multiscale modeling of dislocation-precipitate interactions in Fe: From molecular dynamics to discrete dislocations

    NASA Astrophysics Data System (ADS)

    Lehtinen, Arttu; Granberg, Fredric; Laurson, Lasse; Nordlund, Kai; Alava, Mikko J.

    2016-01-01

    The stress-driven motion of dislocations in crystalline solids, and thus the ensuing plastic deformation process, is greatly influenced by the presence or absence of various pointlike defects such as precipitates or solute atoms. These defects act as obstacles for dislocation motion and hence affect the mechanical properties of the material. Here we combine molecular dynamics studies with three-dimensional discrete dislocation dynamics simulations in order to model the interaction between different kinds of precipitates and a 1/2 <111 > {110 } edge dislocation in BCC iron. We have implemented immobile spherical precipitates into the ParaDis discrete dislocation dynamics code, with the dislocations interacting with the precipitates via a Gaussian potential, generating a normal force acting on the dislocation segments. The parameters used in the discrete dislocation dynamics simulations for the precipitate potential, the dislocation mobility, shear modulus, and dislocation core energy are obtained from molecular dynamics simulations. We compare the critical stresses needed to unpin the dislocation from the precipitate in molecular dynamics and discrete dislocation dynamics simulations in order to fit the two methods together and discuss the variety of the relevant pinning and depinning mechanisms.

  14. Multiscale modeling of dislocation-precipitate interactions in Fe: From molecular dynamics to discrete dislocations.

    PubMed

    Lehtinen, Arttu; Granberg, Fredric; Laurson, Lasse; Nordlund, Kai; Alava, Mikko J

    2016-01-01

    The stress-driven motion of dislocations in crystalline solids, and thus the ensuing plastic deformation process, is greatly influenced by the presence or absence of various pointlike defects such as precipitates or solute atoms. These defects act as obstacles for dislocation motion and hence affect the mechanical properties of the material. Here we combine molecular dynamics studies with three-dimensional discrete dislocation dynamics simulations in order to model the interaction between different kinds of precipitates and a 1/2〈111〉{110} edge dislocation in BCC iron. We have implemented immobile spherical precipitates into the ParaDis discrete dislocation dynamics code, with the dislocations interacting with the precipitates via a Gaussian potential, generating a normal force acting on the dislocation segments. The parameters used in the discrete dislocation dynamics simulations for the precipitate potential, the dislocation mobility, shear modulus, and dislocation core energy are obtained from molecular dynamics simulations. We compare the critical stresses needed to unpin the dislocation from the precipitate in molecular dynamics and discrete dislocation dynamics simulations in order to fit the two methods together and discuss the variety of the relevant pinning and depinning mechanisms. PMID:26871192

  15. Experimental Deformation of Olivine Crystals at Mantle P and T: Evidences for a Pressure-Induced Slip Transition and Implications for Upper-Mantle Seismic Anisotropy and Low Viscosity Zone

    NASA Astrophysics Data System (ADS)

    Raterron, P.; Chen, J.; Geenen, T.; Girard, J.

    2009-04-01

    Recent developments in high-pressure deformation devices coupled with synchrotron radiation allow investigating the rheology of mantle minerals and aggregates at the extreme pressure (P) and temperature (T) of their natural occurrence in the Earth. This is particularly true in the case of olivine, which rheology has been recently investigated in the Deformation-DIA apparatus (D-DIA, see Wang et al., 2003, Rev. Scientific Instr., 74, 3002) at upper-mantle P and T conditions. Olivine deforms by dislocation creep in the shallow upper-mantle, as revealed by the seismic velocity anisotropy observed in this region. The attenuation of seismic anisotropy at depth greater than 200 km is interpreted as a pressure-induced change in olivine main deformation mechanism. It was first attributed to a transition from dislocation creep to diffusion creep (Karato and Wu, 1993, Science, 260, 771). This interpretation has been challenged by deformation data obtained at high pressure (P > 3 GPa) in the dislocation creep regime (Couvy et al., 2004, EJM, 16, 877; Raterron et al., 2007, Am. Miner., 92, 1436; Raterron et al., 2009, PEPI, 72, 74), which support a second interpretation: a transition in olivine dominant dislocation slip, from [100] slip at low P to [001] slip at high P (e.g., Mainprice et al., 2005, Nature, 433, 731). Such a P -induced [100]/[001] slip transition is also supported by recent theoretical studies based on first-principle calculations of olivine dislocation slips (Durinck et al., 2005, PCM, 32, 646; Durinck et al., 2007, Eur. J. Mineral., 19, 631). In order to further constrain the effect of pressure on olivine slip system activities, deformation experiments were carried out in poor water condition at P > 5 GPa and T =1400˚ C, on pure forsterite (Fo100) and San Carlos olivine crystals, using the D-DIA at the X17B2 beamline of the NSLS (Upton, NY, USA). Crystals were oriented in order to active either [100] slip alone or [001] slip alone in (010) plane, or both

  16. Dislocation patterning in a two-dimensional continuum theory of dislocations

    NASA Astrophysics Data System (ADS)

    Groma, István; Zaiser, Michael; Ispánovity, Péter Dusán

    2016-06-01

    Understanding the spontaneous emergence of dislocation patterns during plastic deformation is a long standing challenge in dislocation theory. During the past decades several phenomenological continuum models of dislocation patterning were proposed, but few of them (if any) are derived from microscopic considerations through systematic and controlled averaging procedures. In this paper we present a two-dimensional continuum theory that is obtained by systematic averaging of the equations of motion of discrete dislocations. It is shown that in the evolution equations of the dislocation densities diffusionlike terms neglected in earlier considerations play a crucial role in the length scale selection of the dislocation density fluctuations. It is also shown that the formulated continuum theory can be derived from an averaged energy functional using the framework of phase field theories. However, in order to account for the flow stress one has in that case to introduce a nontrivial dislocation mobility function, which proves to be crucial for the instability leading to patterning.

  17. Coupling between meniscus and smectic-A films: circular and catenoid profiles, induced stress, and dislocation dynamics

    PubMed

    Picano; Holyst; Oswald

    2000-09-01

    In this paper we discuss the formation and shape of the meniscus between a free-standing film of a smectic-A phase and a wall (in practice the frame that supports the film). The wall may be flat or circular, and the system with or without a reservoir of particles. The formation of the meniscus is always an irreversible thermodynamic process, since it involves the creation of dislocations in the bulk (therefore it involves friction). The four basic shapes of meniscus discussed are the following: exponential, algebraic (x(3/2)), circular, and catenoid. Three principal regions of the whole meniscus must be distinguished: close to the wall with a high density of dislocations, away from the wall with medium density of dislocations, and far from the wall (i.e., close to the film) with a low density of dislocations (vicinal regime). The region with medium density of dislocations is observable using a microscope, and is determined by the competition between surface tension, energy of dislocations, and pressure difference set by the mass of the meniscus or by the reservoir. Its profile is circular as observed in recent experiments [J.-C. Geminard, R. Holyst, and P. Oswald, Phys. Rev. Lett. 78, 1924 (1997)]. By contrast, the vicinal regime with low density of dislocations is never observable with an optical microscope. In the regime with a high density of dislocations, the reasons why the dislocations tend to gather by forming giant dislocations and rows of focal conics are discussed. Finally, we discuss the stability of a smectic film with respect to the formation of a dislocation loop. We show experimentally that the critical radius of the loop is proportional to the curvature radius of the meniscus in its circular part, in agreement with the theory. In addition, we show that the mobility of edge dislocations measured in thick films is in agreement with that found in bulk samples from a creep experiment. This result confirms again our model of the meniscus. PMID:11088891

  18. Shear-Induced Deformation of Surfactant Multilamellar Vesicles

    NASA Astrophysics Data System (ADS)

    Pommella, Angelo; Caserta, Sergio; Guida, Vincenzo; Guido, Stefano

    2012-03-01

    Surfactant multilamellar vesicles (SMLVs) play a key role in the formulation of many industrial products, such as detergents, foodstuff, and cosmetics. In this Letter, we present the first quantitative investigation of the flow behavior of single SMLVs in a shearing parallel plate apparatus. We found that SMLVs are deformed and oriented by the action of shear flow while keeping constant volume and exhibit complex dynamic modes (i.e., tumbling, breathing, and tank treading). This behavior can be explained in terms of an excess area (as compared to a sphere of the same volume) and of microstructural defects, which were observed by 3D shape reconstruction through confocal microscopy. Furthermore, the deformation and orientation of SMLVs scale with radius R in analogy with emulsion droplets and elastic capsules (instead of R3, such as in unilamellar vesicles). A possible application of the physical insight provided by this Letter is in the rationale design of processing methods of surfactant-based systems.

  19. A Unified Material Description for Light Induced Deformation in Azobenzene Polymers

    PubMed Central

    Bin, Jonghoon; Oates, William S.

    2015-01-01

    Complex light-matter interactions in azobenzene polymers have limited our understanding of how photoisomerization induces deformation as a function of the underlying polymer network and form of the light excitation. A unified modeling framework is formulated to advance the understanding of surface deformation and bulk deformation of polymer films that are controlled by linear or circularly polarized light or vortex beams. It is shown that dipole forces strongly respond to polarized light in contrast to higher order quadrupole forces that are often used to describe surface relief grating deformation through a field gradient constitutive law. The modeling results and comparisons with a broad range of photomechanical data in the literature suggest that the molecular structure of the azobenzene monomers dramatically influences the photostrictive behavior. The results provide important insight for designing azobenzene monomers within a polymer network to achieve enhanced photo-responsive deformation. PMID:26437598

  20. A Unified Material Description for Light Induced Deformation in Azobenzene Polymers

    NASA Astrophysics Data System (ADS)

    Bin, Jonghoon; Oates, William S.

    2015-10-01

    Complex light-matter interactions in azobenzene polymers have limited our understanding of how photoisomerization induces deformation as a function of the underlying polymer network and form of the light excitation. A unified modeling framework is formulated to advance the understanding of surface deformation and bulk deformation of polymer films that are controlled by linear or circularly polarized light or vortex beams. It is shown that dipole forces strongly respond to polarized light in contrast to higher order quadrupole forces that are often used to describe surface relief grating deformation through a field gradient constitutive law. The modeling results and comparisons with a broad range of photomechanical data in the literature suggest that the molecular structure of the azobenzene monomers dramatically influences the photostrictive behavior. The results provide important insight for designing azobenzene monomers within a polymer network to achieve enhanced photo-responsive deformation.

  1. Bauschinger effect in thin metal films: Discrete dislocation dynamics study

    NASA Astrophysics Data System (ADS)

    Davoudi, Kamyar M.; Nicola, Lucia; Vlassak, Joost J.

    2014-01-01

    The effects of dislocation climb on plastic deformation during loading and unloading are studied using a two-dimensional discrete dislocation dynamics model. Simulations are performed for polycrystalline thin films passivated on both surfaces. Dislocation climb lowers the overall level of the stress inside thin films and reduces the work hardening rate. Climb decreases the density of dislocations in pile-ups and reduces back stresses. These factors result in a smaller Bauschinger effect on unloading compared to simulations without climb. As dislocations continue to climb at the onset of unloading and the dislocation density continues to increase, the initial unloading slope increases with decreasing unloading rate. Because climb disperses dislocations, fewer dislocations are annihilated during unloading, leading to a higher dislocation density at the end of the unloading step.

  2. Sound Emission of Rotor Induced Deformations of Generator Casings

    NASA Technical Reports Server (NTRS)

    Polifke, W.; Mueller, B.; Yee, H. C.; Mansour, Nagi (Technical Monitor)

    2001-01-01

    The casing of large electrical generators can be deformed slightly by the rotor's magnetic field. The sound emission produced by these periodic deformations, which could possibly exceed guaranteed noise emission limits, is analysed analytically and numerically. From the deformation of the casing, the normal velocity of the generator's surface is computed. Taking into account the corresponding symmetry, an analytical solution for the acoustic pressure outside the generator is round in terms of the Hankel function of second order. The normal velocity or the generator surface provides the required boundary condition for the acoustic pressure and determines the magnitude of pressure oscillations. For the numerical simulation, the nonlinear 2D Euler equations are formulated In a perturbation form for low Mach number Computational Aeroacoustics (CAA). The spatial derivatives are discretized by the classical sixth-order central interior scheme and a third-order boundary scheme. Spurious high frequency oscillations are damped by a characteristic-based artificial compression method (ACM) filter. The time derivatives are approximated by the classical 4th-order Runge-Kutta method. The numerical results are In excellent agreement with the analytical solution.

  3. Flow-induced compaction of a deformable porous medium

    NASA Astrophysics Data System (ADS)

    Hewitt, Duncan R.; Nijjer, Japinder S.; Worster, M. Grae; Neufeld, Jerome A.

    2016-02-01

    Fluid flowing through a deformable porous medium imparts viscous drag on the solid matrix, causing it to deform. This effect is investigated theoretically and experimentally in a one-dimensional configuration. The experiments consist of the downwards flow of water through a saturated pack of small, soft, hydrogel spheres, driven by a pressure head that can be increased or decreased. As the pressure head is increased, the effective permeability of the medium decreases and, in contrast to flow through a rigid medium, the flux of water is found to increase towards a finite upper bound such that it becomes insensitive to changes in the pressure head. Measurements of the internal deformation, extracted by particle tracking, show that the medium compacts differentially, with the porosity being lower at the base than at the upper free surface. A general theoretical model is derived, and the predictions of the model give good agreement with experimental measurements from a series of experiments in which the applied pressure head is sequentially increased. However, contrary to theory, all the experimental results display a distinct and repeatable hysteresis: the flux through the material for a particular applied pressure drop is appreciably lower when the pressure has been decreased to that value compared to when it has been increased to the same value.

  4. Flow-induced compaction of a deformable porous medium.

    PubMed

    Hewitt, Duncan R; Nijjer, Japinder S; Worster, M Grae; Neufeld, Jerome A

    2016-02-01

    Fluid flowing through a deformable porous medium imparts viscous drag on the solid matrix, causing it to deform. This effect is investigated theoretically and experimentally in a one-dimensional configuration. The experiments consist of the downwards flow of water through a saturated pack of small, soft, hydrogel spheres, driven by a pressure head that can be increased or decreased. As the pressure head is increased, the effective permeability of the medium decreases and, in contrast to flow through a rigid medium, the flux of water is found to increase towards a finite upper bound such that it becomes insensitive to changes in the pressure head. Measurements of the internal deformation, extracted by particle tracking, show that the medium compacts differentially, with the porosity being lower at the base than at the upper free surface. A general theoretical model is derived, and the predictions of the model give good agreement with experimental measurements from a series of experiments in which the applied pressure head is sequentially increased. However, contrary to theory, all the experimental results display a distinct and repeatable hysteresis: the flux through the material for a particular applied pressure drop is appreciably lower when the pressure has been decreased to that value compared to when it has been increased to the same value. PMID:26986422

  5. Bipolar dislocation of the clavicle.

    PubMed

    Jiang, Wei; Gao, Shu-Guang; Li, Yu-Sheng; Lei, Guang-Hua

    2012-11-01

    Bipolar dislocation of the clavicle at acromioclavicular and sternoclavicular joint is an uncommon traumatic injury. The conservative treatments adopted in the past is associated with redislocation dysfunction and deformity. A 41 years old lady with bipolar dislocation of right shoulder is treated surgically by open reduction and internal fixation by oblique T-plate at sternoclavicular joint and Kirschner wire stabilization at acromioclavicular joint. The patient showed satisfactory recovery with full range of motion of the right shoulder and normal muscular strength. The case reported in view of rarity and at 2 years followup. PMID:23325981

  6. Predictive Model for Temperature-Induced Deformation of Robot Mechanical Systems

    NASA Astrophysics Data System (ADS)

    Poonyapak, Pranchalee

    The positioning accuracy and repeatability of a robot are critical for many industrial applications. Drift in repeatability can occur with changes in environmental and internal conditions, such as those seen with temperature-induced deformation. Thermal instability causes dimensional deformation, and a warm-up cycle is typically required to bring the robot to a thermally stable working condition. The elimination of warm-up cycles will ultimately enhance the positioning accuracy of the robots, their productivity, and reduce unnecessary energy consumption. The main objective of this research was to develop a robot controller algorithm that would provide, a priori, compensation for temperature-induced deformation associated with warm-up in robot mechanical systems. The research started at the fundamental stage of gaining insight into the thermal behaviour and corresponding temperature-induced deformation of simplified, i.e., one-dimensional, robot mechanical systems consisting of slender links and heat sources. The systems were studied using concomitant experimental, numerical and analytical models to provide cross-checking of the results. For the experimental model, the deformation was measured by tracking the drift of a laser diode spot across a charge-coupled device (CCD) camera chip. A non-contact measurement system consisting of an infrared camera, a CCD camera and a laser diode was developed to provide high accuracy measurement for the deformation. The numerical model was generated with a coupled thermal-mechanical finite element analysis incorporating thermal effects due to conduction and convection. The models were tested with the analytical model that was further extended using a finite difference technique. Once the three models showed excellent agreement, it was possible to develop a controller algorithm. Deformations predicted by the finite difference model were used as input for a validation experiment of the compensation algorithm. Results of the

  7. 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.

  8. Modeling of porous scaffold deformation induced by medium perfusion.

    PubMed

    Podichetty, Jagdeep T; Madihally, Sundararajan V

    2014-05-01

    In this study, we tested the possibility of calculating permeability of porous scaffolds utilized in soft tissue engineering using pore size and shape. We validated the results using experimental measured pressure drop and simulations with the inclusion of structural deformation. We prepared Polycaprolactone (PCL) and Chitosan-Gelatin (CG) scaffolds by salt leaching and freeze drying technique, respectively. Micrographs were assessed for pore characteristics and mechanical properties. Porosity for both scaffolds was nearly same but the permeability varied 10-fold. Elastic moduli were 600 and 9 kPa for PCL and CG scaffolds, respectively, while Poisson's ratio was 0.3 for PCL scaffolds and ∼1.0 for CG scaffolds. A flow-through bioreactor accommodating a 10 cm diameter and 0.2 cm thick scaffold was used to determine the pressure-drop at various flow rates. Additionally, computational fluid dynamic (CFD) simulations were performed by coupling fluid flow, described by Brinkman equation, with structural mechanics using a dynamic mesh. The experimentally obtained pressure drop matched the simulation results of PCL scaffolds. Simulations were extended to a broad range of permeabilities (10(-10) m(2) to 10(-14) m(2) ), elastic moduli (10-100,000 kPa) and Poisson's ratio (0.1-0.49). The results showed significant deviation in pressure drop due to scaffold deformation compared to rigid scaffold at permeabilities near healthy tissues. Also, considering the scaffold as a nonrigid structure altered the shear stress profile. In summary, scaffold permeability can be calculated using scaffold pore characteristics and deformation could be predicted using CFD simulation. These relationships could potentially be used in monitoring tissue regeneration noninvasively via pressure drop. PMID:24259467

  9. Deformation mechanism study of a hot rolled Zr-2.5Nb alloy by transmission electron microscopy. II. In situ transmission electron microscopy study of deformation mechanism change of a Zr-2.5Nb alloy upon heavy ion irradiation.

    SciTech Connect

    Long, Fei; Daymond, Mark R.; Yao, Zhongwen; Kirk, Marquis A.

    2015-03-14

    The effect of heavy-ion irradiation on deformation mechanisms of a Zr-2.5Nb alloy was investigated by using the in situ transmission electron microscopy deformation technique. The gliding behavior of prismatic < a > dislocations has been dynamically observed before and after irradiation at room temperature and 300 degrees C. Irradiation induced loops were shown to strongly pin the gliding dislocations. Unpinning occurred while loops were incorporated into or eliminated by < a > dislocations. In the irradiated sample, loop depleted areas with a boundary parallel to the basal plane trace were found by post-mortem observation after room temperature deformation, supporting the possibility of basal channel formation in bulk neutron irradiated samples. Strong activity of pyramidal slip was also observed at both temperatures, which might be another important mechanism to induce plastic instability in irradiated zirconium alloys. Finally, {01 (1) over bar1}< 0 (1) over bar 12 > twinning was identified in the irradiated sample deformed at 300 degrees C.

  10. Vibration-induced elastic deformation of Fabry-Perot cavities

    SciTech Connect

    Chen Lisheng; Hall, John L.; Ye Jun; Yang Tao; Zang Erjun; Li Tianchu

    2006-11-15

    We perform a detailed numerical analysis of Fabry-Perot cavities used for state-of-the-art laser stabilization. Elastic deformation of Fabry-Perot cavities with various shapes and mounting methods is quantitatively analyzed using finite-element analysis. We show that with a suitable choice of mounting schemes it is feasible to minimize the susceptibility of the resonator length to vibrational perturbations. This investigation offers detailed information on stable optical cavities that may benefit the development of ultrastable optical local oscillators in optical atomic clocks and precision measurements probing the fundamental laws of physics.

  11. Method to adjust multilayer film stress induced deformation of optics

    DOEpatents

    Mirkarimi, Paul B.; Montcalm, Claude

    2000-01-01

    A buffer-layer located between a substrate and a multilayer for counteracting stress in the multilayer. Depositing a buffer-layer having a stress of sufficient magnitude and opposite in sign reduces or cancels out deformation in the substrate due to the stress in the multilayer. By providing a buffer-layer between the substrate and the multilayer, a tunable, near-zero net stress results, and hence results in little or no deformation of the substrate, such as an optic for an extreme ultraviolet (EUV) lithography tool. Buffer-layers have been deposited, for example, between Mo/Si and Mo/Be multilayer films and their associated substrate reducing significantly the stress, wherein the magnitude of the stress is less than 100 MPa and respectively near-normal incidence (5.degree.) reflectance of over 60% is obtained at 13.4 nm and 11.4 nm. The present invention is applicable to crystalline and non-crystalline materials, and can be used at ambient temperatures.

  12. Automated identification and indexing of dislocations in crystal interfaces

    SciTech Connect

    Stukowski, Alexander; Bulatov, Vasily V.; Arsenlis, Athanasios

    2012-10-31

    Here, we present a computational method for identifying partial and interfacial dislocations in atomistic models of crystals with defects. Our automated algorithm is based on a discrete Burgers circuit integral over the elastic displacement field and is not limited to specific lattices or dislocation types. Dislocations in grain boundaries and other interfaces are identified by mapping atomic bonds from the dislocated interface to an ideal template configuration of the coherent interface to reveal incompatible displacements induced by dislocations and to determine their Burgers vectors. Additionally, the algorithm generates a continuous line representation of each dislocation segment in the crystal and also identifies dislocation junctions.

  13. Automated identification and indexing of dislocations in crystal interfaces

    DOE PAGESBeta

    Stukowski, Alexander; Bulatov, Vasily V.; Arsenlis, Athanasios

    2012-10-31

    Here, we present a computational method for identifying partial and interfacial dislocations in atomistic models of crystals with defects. Our automated algorithm is based on a discrete Burgers circuit integral over the elastic displacement field and is not limited to specific lattices or dislocation types. Dislocations in grain boundaries and other interfaces are identified by mapping atomic bonds from the dislocated interface to an ideal template configuration of the coherent interface to reveal incompatible displacements induced by dislocations and to determine their Burgers vectors. Additionally, the algorithm generates a continuous line representation of each dislocation segment in the crystal andmore » also identifies dislocation junctions.« less

  14. Theory of interacting dislocations on cylinders

    NASA Astrophysics Data System (ADS)

    Amir, Ariel; Paulose, Jayson; Nelson, David R.

    2013-04-01

    We study the mechanics and statistical physics of dislocations interacting on cylinders, motivated by the elongation of rod-shaped bacterial cell walls and cylindrical assemblies of colloidal particles subject to external stresses. The interaction energy and forces between dislocations are solved analytically, and analyzed asymptotically. The results of continuum elastic theory agree well with numerical simulations on finite lattices even for relatively small systems. Isolated dislocations on a cylinder act like grain boundaries. With colloidal crystals in mind, we show that saddle points are created by a Peach-Koehler force on the dislocations in the circumferential direction, causing dislocation pairs to unbind. The thermal nucleation rate of dislocation unbinding is calculated, for an arbitrary mobility tensor and external stress, including the case of a twist-induced Peach-Koehler force along the cylinder axis. Surprisingly rich phenomena arise for dislocations on cylinders, despite their vanishing Gaussian curvature.

  15. 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.

  16. 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.

  17. Dislocation creep of dry quartz

    NASA Astrophysics Data System (ADS)

    Kilian, Rüdiger; Heilbronner, Renée.; Holyoke, Caleb W.; Kronenberg, Andreas K.; Stünitz, Holger

    2016-05-01

    Small-scale shear zones within the Permian Truzzo meta-granite developed during the Alpine orogeny at amphibolite facies conditions. In these shear zones magmatic quartz deformed by dislocation creep and recrystallized dynamically by grain boundary migration with minor subgrain rotation recrystallization to a grain size of around 250-750 µm, consistent with flow at low differential stresses. Fourier transform infrared (FTIR) spectroscopy reveals very low water contents in the interior of recrystallized grains (in the form of discrete OH peaks, ~20 H/106Si and very little broad band absorption, <100 H/106Si). The spectral characteristics are comparable to those of dry Brazil quartz. In FTIR spectra, magmatic quartz grains show a broad absorption band related with high water concentrations only in those areas where fluid inclusions are present while other areas are dry. Drainage of fluid inclusions and synkinematic growth of hydrous minerals indicates that a hydrous fluid has been available during deformation. Loss of intragranular water during grain boundary migration recrystallization did not result in a microstructure indicative of hardening. These FTIR measurements provide the first evidence that quartz with extremely low intragranular water contents can deform in nature by dislocation creep at low differential stresses. Low intragranular water contents in naturally deformed quartz may not be necessarily indicative of a high strength, and the results are contrary to implications taken from deformation experiments where very high water contents are required to allow dislocation creep in quartz. It is suggested that dislocation creep of quartz in the Truzzo meta-granite is possible to occur at low differential stresses because sufficient amounts of intergranular water ensure a high recovery rate by grain boundary migration while the absence of significant amounts of intragranular water is not crucial at natural conditions.

  18. Dislocation creep of fine-grained olivine

    NASA Astrophysics Data System (ADS)

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

    2011-01-01

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

  19. Deformation-induced changes in hydraulic head during ground-water withdrawal

    USGS Publications Warehouse

    Hsieh, Paul A.

    1996-01-01

    Ground-water withdrawal from a confined or semiconfined aquifer causes three-dimensional deformation in the pumped aquifer and in adjacent layers (overlying and underlying aquifers and aquitards). In response to the deformation, hydraulic head in the adjacent layers could rise or fall almost immediately after the start of pumping. This deformation-induced effect suggest that an adjacent layer undergoes horizontal compression and vertical extension when pumping begins. Hydraulic head initially drops in a region near the well and close to the pumped aquifer, but rises outside this region. Magnitude of head change varies from a few centimeters to more than 10 centimeters. Factors that influence the development of deformation-induced effects includes matrix rigidity (shear modulus), the arrangement of aquifer and aquitards, their thicknesses, and proximity to land surface. Induced rise in hydraulic head is prominent in an aquitard that extends from land surface to a shallow pumped aquifer. Induced drop in hydraulic head is likely observed close to the well in an aquifer that is separated from the pumped aquifer by a relatively thin aquitard. Induced effects might last for hours in an aquifer, but could persist for many days in an aquitard. Induced effects are eventually dissipated by fluid flow from regions of higher head to regions of lower head, and by propagation of drawdown from the pumped aquifer into adjacent layers.

  20. Multiscale Theory of Dislocation Climb

    NASA Astrophysics Data System (ADS)

    Geslin, Pierre-Antoine; Appolaire, Benoît; Finel, Alphonse

    2015-12-01

    Dislocation climb is a ubiquitous mechanism playing a major role in the plastic deformation of crystals at high temperature. We propose a multiscale approach to model quantitatively this mechanism at mesoscopic length and time scales. First, we analyze climb at a nanoscopic scale and derive an analytical expression of the climb rate of a jogged dislocation. Next, we deduce from this expression the activation energy of the process, bringing valuable insights to experimental studies. Finally, we show how to rigorously upscale the climb rate to a mesoscopic phase-field model of dislocation climb. This upscaling procedure opens the way to large scale simulations where climb processes are quantitatively reproduced even though the mesoscopic length scale of the simulation is orders of magnitude larger than the atomic one.

  1. Multiscale Theory of Dislocation Climb.

    PubMed

    Geslin, Pierre-Antoine; Appolaire, Benoît; Finel, Alphonse

    2015-12-31

    Dislocation climb is a ubiquitous mechanism playing a major role in the plastic deformation of crystals at high temperature. We propose a multiscale approach to model quantitatively this mechanism at mesoscopic length and time scales. First, we analyze climb at a nanoscopic scale and derive an analytical expression of the climb rate of a jogged dislocation. Next, we deduce from this expression the activation energy of the process, bringing valuable insights to experimental studies. Finally, we show how to rigorously upscale the climb rate to a mesoscopic phase-field model of dislocation climb. This upscaling procedure opens the way to large scale simulations where climb processes are quantitatively reproduced even though the mesoscopic length scale of the simulation is orders of magnitude larger than the atomic one. PMID:26765003

  2. [Traumatic hip dislocation in childhood].

    PubMed

    Stachel, P; Hofmann-v Kap-herr, S; Schild, H

    1989-06-01

    The article reports on eight cases of traumatic dislocation of the hip in children. Six of these were genuine dislocations and two dislocation fractures. The children were between 5 and 13 years of age at the time of injury. Seven of these 8 children could be followed up one to 21 years after the accident. All 7 children were free from complaints at the time of follow-up examination; in one case only we found a moderate loss of function in the injured hip joint. In this patient the x-ray film showed deformation of the head of the femur after partial necrosis of the femoral head, as well as initial signs of coxarthrosis. Prognosis of this rare injury in children is favourable if repositioning is performed in time and if relief of the hip is effected for the proper period of time, depending on the individual case. PMID:2665382

  3. Droplet-induced deformation of a polymer microfiber

    NASA Astrophysics Data System (ADS)

    Liu, Jianlin; Sun, Jing; Mei, Yue

    2013-07-01

    Capillary force of a liquid drop embedded in a microfiber has great influence on the mechanics behavior of the microfiber. In this study, we investigated the buckling and finite deformation of a microfiber filled with a droplet. First, the critical load for the buckling of the microfiber was presented under the combined action of the surface tension and Laplace pressure. Both global buckling based on slender rod model and local buckling according to thin shell model has been considered. Then in use of the Mooney-Rivlin model, we calculated the true axial stress of the microfiber, and clearly showed that the microfiber takes a different load carrying capability due to the capillary force. These investigations emphasize the important role of capillary force in microfibers, and the conclusions hold great potentials in micro/nanotechnologies, fabrics, blood vessels, and animal/plant surfaces.

  4. Formation and subdivision of deformation structures during plastic deformation.

    PubMed

    Jakobsen, Bo; Poulsen, Henning F; Lienert, Ulrich; Almer, Jonathan; Shastri, Sarvjit D; Sørensen, Henning O; Gundlach, Carsten; Pantleon, Wolfgang

    2006-05-12

    During plastic deformation of metals and alloys, dislocations arrange in ordered patterns. How and when these self-organization processes take place have remained elusive, because in situ observations have not been feasible. We present an x-ray diffraction method that provided data on the dynamics of individual, deeply embedded dislocation structures. During tensile deformation of pure copper, dislocation-free regions were identified. They showed an unexpected intermittent dynamics, for example, appearing and disappearing with proceeding deformation and even displaying transient splitting behavior. Insight into these processes is relevant for an understanding of the strength and work-hardening of deformed materials. PMID:16690859

  5. Large-Amplitude Deformation and Bond Breakage in Shock-Induced Reactions of Explosive Molecules

    NASA Astrophysics Data System (ADS)

    Kay, Jeffrey

    The response of explosive molecules to large-amplitude mechanical deformation plays an important role in shock-induced reactions and the initiation of detonation in explosive materials. In this presentation, the response of a series of explosive molecules (nitromethane, 2,4,6-trinitrotoluene [TNT], and 2,4,6-triamino-1,3,5-trinitrobenzene [TATB]) to a variety of large-amplitude deformations are examined using ab initio quantum chemical calculations. Large-amplitude motions that result in bond breakage are described, and the insights these results provide into both previous experimental observations and previous theoretical predictions of shock-induced reactions are discussed.

  6. Tip-induced deformation of a phospholipid bilayer: Theoretical perspective of sum frequency generation imaging

    SciTech Connect

    Volkov, Victor

    2014-10-21

    The paper addresses theory of Sum Frequency Generation imaging of an atomic force microscopy tip-induced deformation of a bilayer phospholipid membrane deposited over a pore: known as a nano-drum system. Image modeling employed nonlinearities of the normal modes specific to hydrocarbon terminal methyls, which are distributed about the deformed surfaces of inner and outer leaflets. The deformed profiles are according to the solutions of shape equation for Canham-Helfrich Hamiltonian accounting properties of four membranes, which differ in elasticity and adhesion. The results indicate that in continuous deformed surfaces, the difference in the curvature of the outer and inner leaflets dominates in the imaged nonlinearity. This is different comparing to the results for a perfect bilayer spherical cap system (the subject of previous study), where nonlinear image response is dominated by the mismatch of the inner and outer leaflets’ surface areas (as projected to the image plane) at the edge of perfectly spherical structure. The results of theoretical studies, here, demonstrate that Sum Frequency Generation imaging in continuous and deformed bilayer surfaces are helpful to address curvature locally and anticipate mechanical properties of membrane. The articles discuss applicability and practical limitations of the approach. Combination of Atomic Force Microscopy and Sum Frequency Generation imaging under controlled tip-induced deformation provides a good opportunity to probe and test membranes physical properties with rigor of adopted theory.

  7. Tip-induced deformation of a phospholipid bilayer: theoretical perspective of sum frequency generation imaging.

    PubMed

    Volkov, Victor

    2014-10-21

    The paper addresses theory of Sum Frequency Generation imaging of an atomic force microscopy tip-induced deformation of a bilayer phospholipid membrane deposited over a pore: known as a nano-drum system. Image modeling employed nonlinearities of the normal modes specific to hydrocarbon terminal methyls, which are distributed about the deformed surfaces of inner and outer leaflets. The deformed profiles are according to the solutions of shape equation for Canham-Helfrich Hamiltonian accounting properties of four membranes, which differ in elasticity and adhesion. The results indicate that in continuous deformed surfaces, the difference in the curvature of the outer and inner leaflets dominates in the imaged nonlinearity. This is different comparing to the results for a perfect bilayer spherical cap system (the subject of previous study), where nonlinear image response is dominated by the mismatch of the inner and outer leaflets' surface areas (as projected to the image plane) at the edge of perfectly spherical structure. The results of theoretical studies, here, demonstrate that Sum Frequency Generation imaging in continuous and deformed bilayer surfaces are helpful to address curvature locally and anticipate mechanical properties of membrane. The articles discuss applicability and practical limitations of the approach. Combination of Atomic Force Microscopy and Sum Frequency Generation imaging under controlled tip-induced deformation provides a good opportunity to probe and test membranes physical properties with rigor of adopted theory. PMID:25338888

  8. In situ spectroscopic study of the plastic deformation of amorphous silicon under nonhydrostatic conditions induced by indentation

    DOE PAGESBeta

    Gerbig, Yvonne B.; Michaels, C. A.; Bradby, Jodie E.; Haberl, Bianca; Cook, Robert F.

    2015-12-17

    Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique (IIT). The occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were observed. Furthermore, the obtained experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a model for the deformation behavior of a-Si under indentation loading.

  9. Can Stress Relaxation Experiments be Used to Assess Deformation Induced Mobility in Glassy Polymers?

    NASA Astrophysics Data System (ADS)

    Kropka, Jamie; Long, Kevin

    The observance of an increase in glassy polymer relaxation rates under a mechanical deformation is often referred to as deformation induced mobility (DIM). It has been argued that stress relaxation experiments can provide indirect evidence of this phenomenon. Recently, stress relaxation experiments have been interpreted as demonstrating a mobility decrease with increased deformation when very slow strain rates, 1.2 x 10-5 s-1, are used to apply the deformation. This would suggest against generality of DIM and would have significant implications to constitutive models founded on this principle. Here, a mathematical exercise is performed to evaluate the implications of DIM on stress relaxation response. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under Contract DE-AC04-94AL85000.

  10. Dislocation-driven surface dynamics on solids.

    PubMed

    Kodambaka, S; Khare, S V; Swiech, W; Ohmori, K; Petrov, I; Greene, J E

    2004-05-01

    Dislocations are line defects that bound plastically deformed regions in crystalline solids. Dislocations terminating on the surface of materials can strongly influence nanostructural and interfacial stability, mechanical properties, chemical reactions, transport phenomena, and other surface processes. While most theoretical and experimental studies have focused on dislocation motion in bulk solids under applied stress and step formation due to dislocations at surfaces during crystal growth, very little is known about the effects of dislocations on surface dynamics and morphological evolution. Here we investigate the near-equilibrium dynamics of surface-terminated dislocations using low-energy electron microscopy. We observe, in real time, the thermally driven nucleation and shape-preserving growth of spiral steps rotating at constant temperature-dependent angular velocities around cores of dislocations terminating on the (111) surface of TiN in the absence of applied external stress or net mass change. We attribute this phenomenon to point-defect migration from the bulk to the surface along dislocation lines. Our results demonstrate that dislocation-mediated surface roughening can occur even in the absence of deposition or evaporation, and provide fundamental insights into mechanisms controlling nanostructural stability. PMID:15129275

  11. Deformation-induced grain growth and twinning in nanocrystalline palladium thin films

    PubMed Central

    Lohmiller, Jochen; Schäfer, Jonathan; Kerber, Michael; Castrup, Anna; Kashiwar, Ankush; Gruber, Patric A; Albe, Karsten; Hahn, Horst

    2013-01-01

    Summary The microstructure and mechanical properties of nanocrystalline Pd films prepared by magnetron sputtering have been investigated as a function of strain. The films were deposited onto polyimide substrates and tested in tensile mode. In order to follow the deformation processes in the material, several samples were strained to defined straining states, up to a maximum engineering strain of 10%, and prepared for post-mortem analysis. The nanocrystalline structure was investigated by quantitative automated crystal orientation mapping (ACOM) in a transmission electron microscope (TEM), identifying grain growth and twinning/detwinning resulting from dislocation activity as two of the mechanisms contributing to the macroscopic deformation. Depending on the initial twin density, the samples behaved differently. For low initial twin densities, an increasing twin density was found during straining. On the other hand, starting from a higher twin density, the twins were depleted with increasing strain. The findings from ACOM-TEM were confirmed by results from molecular dynamics (MD) simulations and from conventional and in-situ synchrotron X-ray diffraction (CXRD, SXRD) experiments. PMID:24205451

  12. The Kinetics of Dislocation Loop Formation in Ferritic Alloys Through the Aggregation of Irradiation Induced Defects

    NASA Astrophysics Data System (ADS)

    Kohnert, Aaron Anthony

    The mechanical properties of materials are often degraded over time by exposure to irradiation environments, a phenomenon that has hindered the development of multiple nuclear reactor design concepts. Such property changes are the result of microstructural changes induced by the collision of high energy particles with the atoms in a material. The lattice defects generated in these recoil events migrate and interact to form extended damage structures. This study has used theoretical models based on the mean field chemical reaction rate theory to analyze the aggregation of isolated lattice defects into larger microstructural features that are responsible for long term property changes, focusing on the development of black dot damage in ferritic iron based alloys. The purpose of such endeavors is two-fold. Primarily, such models explain and quantify the processes through which these microstructures form. Additionally, models provide insight into the behavior and properties of the point defects and defect clusters which drive general microstructural evolution processes. The modeling effort presented in this work has focused on physical fidelity, drawing from a variety of sources of information to characterize the unobservable defect generation and agglomeration processes that give rise to the observable features reported in experimental data. As such, the models are based not solely on isolated point defect creation, as is the case with many older rate theory approaches, but instead on realistic estimates of the defect cluster population produced in high energy cascade damage events. Experimental assessments of the microstructural changes evident in transmission electron microscopy studies provide a means to measure the efficacy of the kinetic models. Using common assumptions of the mobility of defect clusters generated in cascade damage conditions, an unphysically high density of damage features develops at the temperatures of interest with a temperature dependence

  13. Continuum dislocation dynamics: Towards a physical theory of crystal plasticity

    NASA Astrophysics Data System (ADS)

    Hochrainer, Thomas; Sandfeld, Stefan; Zaiser, Michael; Gumbsch, Peter

    2014-02-01

    The plastic deformation of metals is the result of the motion and interaction of dislocations, line defects of the crystalline structure. Continuum models of plasticity, however, remain largely phenomenological to date, usually do not consider dislocation motion, and fail when materials behavior becomes size dependent. In this work we present a novel plasticity theory based on systematic physical averages of the kinematics and dynamics of dislocation systems. We demonstrate that this theory can predict microstructure evolution and size effects in accordance with experiments and discrete dislocation simulations. The theory is based on only four internal variables per slip system and features physical boundary conditions, dislocation pile ups, dislocation curvature, dislocation multiplication and dislocation loss. The presented theory therefore marks a major step towards a physically based theory of crystal plasticity.

  14. Scale-free phase field theory of dislocations.

    PubMed

    Groma, István; Vandrus, Zoltán; Ispánovity, Péter Dusán

    2015-01-01

    According to recent experimental and numerical investigations, if a characteristic length (such as grain size) of a specimen is in the submicron size regime, several new interesting phenomena emerge during the deformation. Since in such systems boundaries play a crucial role, to model the plastic response it is crucial to determine the dislocation distribution near the boundaries. In this Letter, a phase-field-type continuum theory of the time evolution of an ensemble of parallel edge dislocations with identical Burgers vectors, corresponding to the dislocation geometry near internal boundaries, is presented. Since the dislocation-dislocation interaction is scale free (1/r), apart from the average dislocation spacing the theory cannot contain any length scale parameter. As shown, the continuum theory suggested is able to recover the dislocation distribution near boundaries obtained by discrete dislocation dynamics simulations. PMID:25615479

  15. Scale-Free Phase Field Theory of Dislocations

    NASA Astrophysics Data System (ADS)

    Groma, István; Vandrus, Zoltán; Ispánovity, Péter Dusán

    2015-01-01

    According to recent experimental and numerical investigations, if a characteristic length (such as grain size) of a specimen is in the submicron size regime, several new interesting phenomena emerge during the deformation. Since in such systems boundaries play a crucial role, to model the plastic response it is crucial to determine the dislocation distribution near the boundaries. In this Letter, a phase-field-type continuum theory of the time evolution of an ensemble of parallel edge dislocations with identical Burgers vectors, corresponding to the dislocation geometry near internal boundaries, is presented. Since the dislocation-dislocation interaction is scale free (1 /r ), apart from the average dislocation spacing the theory cannot contain any length scale parameter. As shown, the continuum theory suggested is able to recover the dislocation distribution near boundaries obtained by discrete dislocation dynamics simulations.

  16. Neglected isolated plantar dislocation of middle cuneiform : a case report

    PubMed Central

    Verma, Ashu; Sharma, Vinod Kumar; Batra, Sumit; Rohria, Mahender Singh

    2007-01-01

    Background Four cases of plantar dislocation of middle cuneiform have been reported in the english literature. All of them were fresh cases and treated with open reduction. We are reporting a case of neglected plantar dislocation of middle cuneiform which was treated with excision. Case presentation A farmer presented with a painful plantar dislocation of middle cuneiform bone after 9 months of injury. The bone was deformed and was excised by a plantar incision. It resulted in painless foot with no disability. Conclusion The neglected plantar dislocated middle cuneiform bone becomes deformed due to repeated weight bearing. The gap gets filled with Fibrous tissue. Excision of the cuneiform gives good results. PMID:17229316

  17. Tracking the deformation of a tissue phantom induced by ultrasound-driven bubble oscillations

    NASA Astrophysics Data System (ADS)

    Tinguely, M.; Matar, O. K.; Garbin, V.

    2015-12-01

    Microbubbles are used as contrast agents in ultrasound medical imaging. Once the microbubbles are injected into the body, they flow through the vascular system, confined by viscoelastic boundaries. The proximity of the boundaries affects the dynamics of the bubbles in ultrasound, in a manner that depends on the boundary's viscoelastic properties. Experiments on violently collapsing bubbles have revealed the dynamics of deformation of blood vessel walls. However, the deformation field induced by a bubble undergoing small-amplitude oscillations, relevant for ultrasound imaging, is difficult to access in experiment, and has not been reported yet. We present an experimental method to measure the deformation field induced by a bubble oscillating inside a microchannel within a tissue phantom. We use high-speed video microscopy to track the displacement of tracer particles embedded in the phantom, along with the dynamics of the bubble.

  18. Defect structure and deformation mechanisms in naturally deformed augite and enstatite

    NASA Astrophysics Data System (ADS)

    Skrotzki, W.

    1994-01-01

    enstatite are either SFs on (100) or CMFs on (010). The SFs represent layers of proto- or clinoenstatite. The CMFs in both phases are amphibole-type defects, the formation of which requires a certain solubility of OH ions in the lattice. Broadening of the CMFs occurs by movement of partial dislocations along the fault leading to clinoand orthoamphibole lamellae. Diffusion of the necessary ions most probably is along the dislocation core of the partials. The main deformation mechanisms in augite and enstatite are dislocation creep and the stress-induced ortho/clinoenstatite inversion, respectively. Dislocation dissociation hinders dynamical recovery by climb and cross slip, exsolution leads to precipitation hardening. These processes may account for the different rheological behaviour between pyroxenes and olivine. A comparison of the microstructure in orthopyroxene lamellae deformed within the augite matrix with that in orthopyroxene grains deformed within an olivine environment shows that additional independent slip systems are activated if orthopyroxene is embedded in a less ductile matrix. Nevertheless, similar to clinopyroxenes, five independent slip systems required for full strain compatibility are not activated because slip on planes cutting the chains does not take place.

  19. Holographic investigation of residual deformations induced by a pulsed ion implanter.

    PubMed

    Kaufmann, G H; Feugeas, J N; Marino, B; Galizzi, G E

    1991-01-01

    A new use of holographic interferometry to investigate the residual deformations induced in nitrogen implanted specimens by a plasma focus device is reported. The method is simple and nondestructive. Experimental results obtained for AISI 304 stainless steel specimens are presented. PMID:20581951

  20. Evolution, Interaction, and Intrinsic Properties of Dislocations in Intermetallics: Anisotropic 3D Dislocation Dynamics Approach

    SciTech Connect

    Qian Chen

    2008-08-18

    The generation, motion, and interaction of dislocations play key roles during the plastic deformation process of crystalline solids. 3D Dislocation Dynamics has been employed as a mesoscale simulation algorithm to investigate the collective and cooperative behavior of dislocations. Most current research on 3D Dislocation Dynamics is based on the solutions available in the framework of classical isotropic elasticity. However, due to some degree of elastic anisotropy in almost all crystalline solids, it is very necessary to extend 3D Dislocation Dynamics into anisotropic elasticity. In this study, first, the details of efficient and accurate incorporation of the fully anisotropic elasticity into 3D discrete Dislocation Dynamics by numerically evaluating the derivatives of Green's functions are described. Then the intrinsic properties of perfect dislocations, including their stability, their core properties and disassociation characteristics, in newly discovered rare earth-based intermetallics and in conventional intermetallics are investigated, within the framework of fully anisotropic elasticity supplemented with the atomistic information obtained from the ab initio calculations. Moreover, the evolution and interaction of dislocations in these intermetallics as well as the role of solute segregation are presented by utilizing fully anisotropic 3D dislocation dynamics. The results from this work clearly indicate the role and the importance of elastic anisotropy on the evolution of dislocation microstructures, the overall ductility and the hardening behavior in these systems.

  1. Ultrasound visualization of internal crystalline lens deformation using laser-induced microbubbles

    NASA Astrophysics Data System (ADS)

    Karpiouk, Andrei B.; Aglyamov, Salavat R.; Glasser, Adrian; Emelianov, Stanislav Y.

    2014-02-01

    The progressive loss of accommodation of the eye, called presbyopia, affects people with age and can result in a complete loss of accommodation by about age 55 years. It is generally accepted that presbyopia is due to an increase in stiffness of the lens. With increasing age, the stiffness of the crystalline lens nucleus increases faster than that of the cortex. During accommodation, the deformation of different parts of the crystalline lens is different and likely changes with age. However, a direct observation of crystalline lens deformation and strain distribution is difficult because although imaging methods such as OCT or Scheimpflug imaging can distinguish cortex and nucleus, they cannot determine their regional deformation. Here, patterns of laser-induced microbubbles were created in gelatin phantoms and different parts of excised animal crystalline lenses and their displacements in response to external deformation were tracked by ultrasound imaging. In the animal lenses, the deformation of the lens cortex was greater than that of nucleus and this regional difference is greater for a 27-month-old bovine lens than for a 6-month-old porcine lens. This approach enables visualization of localized, regional deformation of crystalline lenses and, if applied to lenses from animal species that undergo accommodation, may help to understand the mechanisms of accommodation and presbyopia, improve diagnostics, and, potentially, aid in the development of new methods of lens modifying presbyopia treatments.

  2. Dislocations: do you want them moving or in 3D ?

    NASA Astrophysics Data System (ADS)

    Cordier, Patrick; Boioli, Francesca; Bollinger, Caroline; Idrissi, Hosni; Mussi, Alexandre; Clitton Nzogang, Billy; Schryvers, Dominique

    2016-04-01

    Plastic deformation of minerals and rocks can be explained in most cases by the presence of crystal defects. Among those, dislocations represent the most efficient strain-producing actors of deformation. The physics of deformation by dislocations is complex since it is intrinsically multiscale. At the atomic scale, the dislocation core structure controls a fundamental property: their mobility. However, the plastic strain results from the collective behavior of dislocations which can be understood only at the mesoscopic scale. Multiscale numerical modeling has provided a lot of insights on these aspects in the recent years, also in mineral physics. These progress were calling for parallel developments in experiments and characterization. Here we present two studies on dislocations in olivine deformed under lithospheric conditions based in recent developments in transmission electron microscopy. We present plastic deformation experiments performed on olivine in situ, in the transmission electron microscope, at room temperature. The ductile behavior is made possible thanks to the very small size of the specimens (maximum dimension < 5μm) which are prepared by focused ion beam and strained in a special Micro-Electro-Mechanical-System (MEMS) device called push-to-pull (PI 95 TEM PicoIndenter from Hysitron). By performing experiments under constant load, the velocity of [001] screw dislocations has been measured as a function of stress. This mobility law has then been introduced in a Dislocation Dynamics model to determine the stress strain curves. We present also some recent developments on electron tomography of dislocations performed on olivine. The difficulty is here to keep diffraction conditions strictly constant over a wide range of tilt acquisitions. We present some examples obtained by imaging dislocations in weak-beam dark-field using precession electron diffraction. The analysis of dislocation microstructures in 3D is used to characterize dislocations glide

  3. Phase with pressure-induced shuttlewise deformation in dense solid atomic hydrogen

    NASA Astrophysics Data System (ADS)

    Ishikawa, Takahiro; Nagara, Hitose; Oda, Tatsuki; Suzuki, Naoshi; Shimizu, Katsuya

    2014-09-01

    A phase which shows pressure-induced shuttlewise structural deformation between orthorhombic Fddd and tetragonal I41/amd structures has been predicted in solid atomic hydrogen by means of the first-principles calculations, including harmonic zero-point energy contributions of proton motions. The Fddd structure is formed by shear distortion from the I41/amd structure, and the angle specifying the distortion changes with pressure in the range 84-96∘ around 90∘, which corresponds to I41/amd. In the shuttlewise deforming phase, the electron-phonon interaction is enhanced owing to phonon softenings, which brings about superconductivity at elevated temperatures.

  4. Analytical and Experimental Characterization of Gravity Induced Deformations In Subscale Gossamer Structures

    NASA Technical Reports Server (NTRS)

    Johnston, John D.; Blandino, Joseph R.; McEvoy, Kiley C.

    2004-01-01

    The development of gossamer space structures such as solar sails and sunshields presents many challenges due to their large size and extreme flexibility. The post-deployment structural geometry exhibited during ground testing may significantly depart from the in-space configuration due to the presence of gravity-induced deformations (gravity sag) of lightly preloaded membranes. This paper describes a study carried out to characterize gravity sag in two subscale gossamer structures: a single quadrant from a 2 m, 4 quadrant square solar sail and a 1.7 m membrane layer from a multi-layer sunshield The behavior of the test articles was studied over a range of preloads and in several orientations with respect to gravity. An experimental study was carried out to measure the global surface profiles using photogrammetry, and nonlinear finite element analysis was used to predict the behavior of the test articles. Comparison of measured and predicted surface profiles shows that the finite dement analysis qualitatively predicts deformed shapes comparable to those observed in the laboratory. Quantitatively, finite element analysis predictions for peak gravity-induced deformations in both test articles were within 10% of measured values. Results from this study provide increased insight into gravity sag behavior in gossamer structures, and demonstrates the potential to analytically predict gravity-induced deformations to within reasonable accuracy.

  5. Intraoperative measurement of indenter-induced brain deformation: a feasibility study

    NASA Astrophysics Data System (ADS)

    Ji, Songbai; Fan, Xiaoyao; Roberts, David W.; Paulsen, Keith D.

    2014-03-01

    Accurate measurement of soft tissue material properties is critical for characterizing its biomechanical behaviors but can be challenging especially for the human brain in vivo. In this study, we investigated the feasibility of inducing and detecting cortical surface deformation intraoperatively for patients undergoing open skull neurosurgeries. A custom diskshaped indenter made of high-density tungsten (diameter of 15 mm with a thickness of 6 mm) was used to induce deformation on the brain cortical surface immediately after dural opening. Before and after placing the indenter, sequences (typically 250 frames at 15 frames-per-second, or ~17 seconds) of high-resolution stereo image pairs were acquired to capture the harmonic motion of the exposed cortical surface as due to blood pressure pulsation and respiration. For each sequence with the first left image serving as a baseline, an optical-flow motion-tracking algorithm was used to detect in-sequence cortical surface deformation. The resulting displacements of the exposed features within the craniotomy were spatially averaged to identify the temporal frames corresponding to motion peak magnitudes. Corresponding image pairs were then selected to reconstruct full-field three-dimensional (3D) cortical surfaces before and after indentation, respectively, from which full 3D displacement fields were obtained by registering their projection images. With one clinical patient case, we illustrate the feasibility of the technique in detecting indenter-induced cortical surface deformation in order to allow subsequent processing to determine material properties of the brain in vivo.

  6. The relationship between strain geometry and geometrically necessary dislocations

    NASA Astrophysics Data System (ADS)

    Hansen, Lars; Wallis, David

    2016-04-01

    The kinematics of past deformations are often a primary goal in structural analyses of strained rocks. Details of the strain geometry, in particular, can help distinguish hypotheses about large-scale tectonic phenomena. Microstructural indicators of strain geometry have been heavily utilized to investigate large-scale kinematics. However, many of the existing techniques require structures for which the initial morphology is known, and those structures must undergo the same deformation as imposed macroscopically. Many deformed rocks do not exhibit such convenient features, and therefore the strain geometry is often difficult (if not impossible) to ascertain. Alternatively, crystallographic textures contain information about the strain geometry, but the influence of strain geometry can be difficult to separate from other environmental factors that might affect slip system activity and therefore the textural evolution. Here we explore the ability for geometrically necessary dislocations to record information about the deformation geometry. It is well known that crystallographic slip due to the motion of dislocations yields macroscopic plastic strain, and the mathematics are established to relate dislocation glide on multiple slip systems to the strain tensor of a crystal. This theoretical description generally assumes that dislocations propagate across the entire crystal. However, at any point during the deformation, dislocations are present that have not fully transected the crystal, existing either as free dislocations or as dislocations organized into substructures like subgrain boundaries. These dislocations can remain in the lattice after deformation if the crystal is quenched sufficiently fast, and we hypothesize that this residual dislocation population can be linked to the plastic strain geometry in a quantitative manner. To test this hypothesis, we use high-resolution electron backscatter diffraction to measure lattice curvatures in experimentally deformed

  7. Tissue deformation induced by radiation force from Gaussian transducers.

    PubMed

    Myers, Matthew R

    2006-05-01

    Imaging techniques based upon the tissue mechanical response to an acoustic radiation force are being actively researched. In this paper a model for predicting steady-state tissue displacement induced by a radiation force arising from the absorption of Gaussian ultrasound beams is presented. A simple analytic expression is derived that agrees closely with the numerical quadrature of the displacement convolution integrals. The analytic result reveals the dependence of the steady-state axial displacement upon the operational parameters, e.g., an inverse proportional relationship to the tissue shear modulus. The derivation requires that the transducer radius be small compared to the focal length, but accurate results were obtained for transducer radii comparable to the focal length. Favorable comparisons with displacement predictions for non-Gaussian transducers indicate that the theory is also useful for a broader range of transducer intensity profiles. PMID:16708969

  8. Thermophoretically induced large-scale deformations around microscopic heat centers

    NASA Astrophysics Data System (ADS)

    Puljiz, Mate; Orlishausen, Michael; Köhler, Werner; Menzel, Andreas M.

    2016-05-01

    Selectively heating a microscopic colloidal particle embedded in a soft elastic matrix is a situation of high practical relevance. For instance, during hyperthermic cancer treatment, cell tissue surrounding heated magnetic colloidal particles is destroyed. Experiments on soft elastic polymeric matrices suggest a very long-ranged, non-decaying radial component of the thermophoretically induced displacement fields around the microscopic heat centers. We theoretically confirm this conjecture using a macroscopic hydrodynamic two-fluid description. Both thermophoretic and elastic effects are included in this theory. Indeed, we find that the elasticity of the environment can cause the experimentally observed large-scale radial displacements in the embedding matrix. Additional experiments confirm the central role of elasticity. Finally, a linearly decaying radial component of the displacement field in the experiments is attributed to the finite size of the experimental sample. Similar results are obtained from our theoretical analysis under modified boundary conditions.

  9. Thermoplastic deformation of silicon surfaces induced by ultrashort pulsed lasers in submelting conditions

    SciTech Connect

    Tsibidis, G. D.; Stratakis, E.; Aifantis, K. E.

    2012-03-01

    A hybrid theoretical model is presented to describe thermoplastic deformation effects on silicon surfaces induced by single and multiple ultrashort pulsed laser irradiation in submelting conditions. An approximation of the Boltzmann transport equation is adopted to describe the laser irradiation process. The evolution of the induced deformation field is described initially by adopting the differential equations of dynamic thermoelasticity while the onset of plastic yielding is described by the von Mises stress. Details of the resulting picometre sized crater, produced by irradiation with a single pulse, are discussed as a function of the imposed conditions and thresholds for the onset of plasticity are computed. Irradiation with multiple pulses leads to ripple formation of nanometre size that originates from the interference of the incident and a surface scattered wave. It is suggested that ultrafast laser induced surface modification in semiconductors is feasible in submelting conditions, and it may act as a precursor of the incubation effects observed at multiple pulse irradiation of materials surfaces.

  10. Atraumatic Anterior Dislocation of the Hip Joint

    PubMed Central

    Ohtsuru, Tadahiko; Morita, Yasuyuki; Murata, Yasuaki; Itou, Junya; Morita, Yuji; Munakata, Yutaro; Kato, Yoshiharu

    2015-01-01

    Dislocation of the hip joint in adults is usually caused by high-energy trauma such as road traffic accidents or falls from heights. Posterior dislocation is observed in most cases. However, atraumatic anterior dislocation of the hip joint is extremely rare. We present a case of atraumatic anterior dislocation of the hip joint that was induced by an activity of daily living. The possible causes of this dislocation were anterior capsule insufficiency due to developmental dysplasia of the hip, posterior pelvic tilt following thoracolumbar kyphosis due to vertebral fracture, and acetabular anterior coverage changes by postural factor. Acetabular anterior coverage changes in the sagittal plane were measured using a tomosynthesis imaging system. This system was useful for elucidation of the dislocation mechanism in the present case. PMID:26819791

  11. Nodal effects in a-iron dislocation mobility in the presence of helium bubbles

    SciTech Connect

    Kumar, N. Naveen; Martinez, E; Dutta, B. K.; Dey, G. K.; Caro, J. A.

    2013-02-13

    Dislocations and dislocation networks act as sinks for irradiation-induced point defects such as vacancies and interstitials, or impurities such as helium. Recently, it has been found that the intersection points of the screw dislocation network formed at twist grain boundaries in Au (experimental) and Cu (simulations) act as nucleation sites for He bubbles, which form an array at the interface [ J. Hetherly, E. Martinez, Z. F. Di, M. Nastasi and A. Caro Scr. Mater. 66 17 (2012)]. The modeling part of that study was based on Monte Carlo algorithms. Here, using molecular dynamics simulations, we have performed shear deformation simulations of small-angle twist grain boundaries in α-iron. We report on the mechanical properties of this interface in pure as well as He-segregated samples. We find that this particular dislocation array in pure Fe is extremely mobile, with a Peierls stress ten times smaller than the value for a single straight screw dislocation, and that He bubbles induce a colossal increase (>50 times) in Peierls stress with respect to the pristine network. We interpret the results in terms of preexisting kinks and no shear transmission across the He bubbles.

  12. Microstructures of deformed VTiCrSi type alloys after neutron irradiation

    NASA Astrophysics Data System (ADS)

    Satou, Manabu; Abe, Katsunori; Kayano, Hideo

    1996-10-01

    The alloy of V5Ti5Cr1SiAl,Y (nominal composition, weight percentage) was developed to improve oxidation properties and high temperature strength, and has been studied as one of the candidates for fusion applications. This alloy showed low swelling properties and enough tensile ductility after neutron irradiation to high fluence levels. The dislocation microstructures after tensile deformation and defect microstructures in the neutron-irradiated alloy to high fluences were studied. Irradiation was conducted in the Materials Open Test Assembly of the Fast Flux Test Facility (FFTF/MOTA-2A) at 406°C to 46 dpa and the deformation microstructures were examined by transmission electron microscopy. Slip dislocations were developed inhomogeneously in the specimen deformed at ambient temperature after neutron irradiation. Dislocation loops contributed mainly to hardening of the alloy after irradiation; however, cavities and radiation-induced precipitates did not so much.

  13. Dislocation generation during early stage sintering.

    NASA Technical Reports Server (NTRS)

    Sheehan, J. E.; Lenel, F. V.; Ansell, G. S.

    1973-01-01

    Discussion of the effects of capillarity-induced stresses on dislocations during early stage sintering. A special version of Hirth's (1963) theoretical calculation procedures modified to describe dislocation nucleation on planes meeting the sintering body's neck surface obliquely is shown to predict plastic flow at stress levels know to exist between micron size metal particles in the early stages of sintering.

  14. Wind induced surface deformation of the Nobeyama 45-m radio telescope

    NASA Astrophysics Data System (ADS)

    Ukita, N.

    2008-07-01

    Reflector surface deformation due to wind loading on the Nobeyama 45-m antenna has been measured with four LED lamps on the surface at r = 20 m and two CCD cameras on the central hub as it rotates in azimuth with elevation angles of 90 and 11 degrees. The side-wind loading of 8.4 m s-1 caused a tilt of 12 arcseconds and an astigmatic deformation of 0.8 mm. The front- and back-wind loading of 9.9 m s-1 induced a vertical displacement variation of 2.3 mm. These largescale surface deformation profiles have been compared with those of finite element calculations and coefficients of axial force and yaw moment predicted by a JPL wind tunnel data excerpt.

  15. The equivalence between dislocation pile-ups and cracks

    NASA Technical Reports Server (NTRS)

    Liu, H. W.; Gao, Q.

    1990-01-01

    Cracks and dislocation pile-ups are equivalent to each other. In this paper, the physical equivalence between cracks and pile-ups is delineated, and the relationshps between crack-extension force, force on the leading dislocation, stress-intensity factor, and dislocation density are reviewed and summarized. These relations make it possible to extend quantitatively the recent advances in the concepts and practices of fracture mechanics to the studies of microfractures and microplastic deformations.

  16. Ultrahigh strength of dislocation-free Ni3Al nanocubes.

    PubMed

    Maaß, Robert; Meza, Lucas; Gan, Bin; Tin, Sammy; Greer, Julia R

    2012-06-25

    Individual Ni(3) Al nanocubes under pressure are investigated by comparing the compressive strength of both dislocation-free and irradiated Ni(3) Al nanocubes. The results are dicussed in light of the size-dependent and size-independent strength of face-centered cubic (fcc) nanocrystals in the framework of dislocation nucleation at free surfaces. This study sheds more light on the understanding of fundamental deformation mechanisms and size-affected strength in dislocation-free metallic nanocrystals. PMID:22454244

  17. NANOSECOND INTERFEROMETRIC STUDIES OF SURFACE DEFORMATIONS OF DIELECTRICS INDUCED BY LASER IRRADIATION

    SciTech Connect

    S. GREENFIELD; ET AL

    2000-05-01

    Transient surface deformations in dielectric materials induced by laser irradiation were investigated with time-resolved interferometry. Deformation images were acquired at various delay times after exposure to single pulses (100 ps at 1.064 {micro}m) on fresh sample regions. Above the ablation threshold, we observe prompt ejection of material and the formation of a single unipolar compressional surface acoustic wave propagating away from the ablation crater. For calcite, no deformation--either transient or permanent--is discernable at laser fluences below the threshold for material ejection. Above and below-threshold behavior was investigated using a phosphate glass sample with substantial near infrared absorption (Schott filter KG3). Below threshold, KG3 exhibits the formation of a small bulge roughly the size of the laser spot that reaches its maximum amplitude by {approx}5 ns. By tens of nanoseconds, the deformations become quite complex and very sensitive to laser fluence. The above-threshold behavior of KG3 combines the ablation-induced surface acoustic wave seen in calcite with the bulge seen below threshold in KG3. A velocity of 2.97 {+-} 0.03 km/s is measured for the KG3 surface acoustic wave, very close to the Rayleigh wave velocity calculated from material elastic parameters. Details of the transient interferometry system will also be given.

  18. In vitro deposition of hydroxyapatite on cortical bone collagen stimulated by deformation-induced piezoelectricity.

    PubMed

    Noris-Suárez, Karem; Lira-Olivares, Joaquin; Ferreira, Ana Marina; Feijoo, José Luis; Suárez, Nery; Hernández, Maria C; Barrios, Esteban

    2007-03-01

    In the present work, we have studied the effect of the piezoelectricity of elastically deformed cortical bone collagen on surface using a biomimetic approach. The mineralization process induced as a consequence of the piezoelectricity effect was evaluated using scanning electron microscopy (SEM), thermally stimulated depolarization current (TSDC), and differential scanning calorimetry (DSC). SEM micrographs showed that mineralization occurred predominantly over the compressed side of bone collagen, due to the effect of piezoelectricity, when the sample was immersed in the simulated body fluid (SBF) in a cell-free system. The TSDC method was used to examine the complex collagen dielectric response. The dielectric spectra of deformed and undeformed collagen samples with different hydration levels were compared and correlated with the mineralization process followed by SEM. The dielectric measurements showed that the mineralization induced significant changes in the dielectric spectra of the deformed sample. DSC and TSDC results demonstrated a reduction of the collagen glass transition as the mineralization process advanced. The combined use of SEM, TSDC, and DSC showed that, even without osteoblasts present, the piezoelectric dipoles produced by deformed collagen can produce the precipitation of hydroxyapatite by electrochemical means, without a catalytic converter as occurs in classical biomimetic deposition. PMID:17261065

  19. Roles of deformation and orientation in heavy-ion collisions induced by light deformed nuclei at intermediate energy

    SciTech Connect

    Cao, X. G.; Zhang, G. Q.; Cai, X. Z.; Ma, Y. G.; Guo, W.; Chen, J. G.; Tian, W. D.; Fang, D. Q.; Wang, H. W.

    2010-06-15

    The reaction dynamics of axisymmetric deformed {sup 24}Mg+{sup 24}Mg collisions has been investigated systematically by an isospin-dependent quantum molecular dynamics model. It is found that different deformations and orientations result in apparently different properties of reaction dynamics. We reveal that some observables such as nuclear stopping power (R), multiplicity of fragments, and elliptic flow are very sensitive to the initial deformations and orientations. There exists an eccentricity scaling of elliptic flow in central body-body collisions with different deformations. In addition, the tip-tip and body-body configurations turn out to be two extreme cases in central reaction dynamical process.

  20. The deformation units in metallic glasses revealed by stress-induced localized glass transition

    NASA Astrophysics Data System (ADS)

    Huo, L. S.; Ma, J.; Ke, H. B.; Bai, H. Y.; Zhao, D. Q.; Wang, W. H.

    2012-06-01

    We report that even in quasi-static cyclic compressions in the apparent elastic regimes of the bulk metallic glasses, the precisely measured stress-strain curve presents a mechanical hysteresis loop, which is commonly perceived to occur only in high-frequency dynamic tests. A phenomenological viscoelastic model is established to explain the hysteresis loop and demonstrate the evolutions of the viscous zones in metallic glasses during the cyclic compression. The declining of the viscosity of the viscous zones to at least 1 × 1012 Pa s when stress applied indicates that stress-induced localized glass to supercooled liquid transition occurs. We show that the deformation units of metallic glasses are evolved from the intrinsic heterogeneous defects in metallic glasses under stress and the evolution is a manifestation of the stress-induced localized glass transition. Our study might provide a new insight into the atomic-scale mechanisms of plastic deformation of metallic glasses.

  1. The influence of the dislocation distribution heterogeneity degree on the formation of a non-misoriented dislocation cell substructures in f.c.c. metals

    NASA Astrophysics Data System (ADS)

    Cherepanov, D. N.; Selivanikova, O. V.; Matveev, M. V.

    2016-06-01

    Dislocation loops emitted by Frank-Reed source during crossing dislocations of the non-coplanar slip systems are accumulates jogs on the own dislocation line, resulting in the deceleration of the segments of dislocation loops with high jog density. As a result, bending around of the slowed segments the formation of dynamic dipoles in the shear zone occurs. In the present paper we consider formation mechanism of non-misoriented dislocation cell substructure during plastic deformation of f.c.c. metals and conclude that the increase in the degree heterogeneity of dislocation distribution leads to an increase in the jog density and reduce the mean value of arm dynamic dipoles.

  2. [Spectrum research on metamorphic and deformation of tectonically deformed coals].

    PubMed

    Li, Xiao-Shi; Ju, Yi-Wen; Hou, Quan-Lin; Lin, Hong

    2011-08-01

    The structural and compositive evolution of tectonically deformed coals (TDCs) and their influencing factors were investigated and analyzed in detail through Fourier transform infrared spectroscopy (FTIR) and laser Raman spectra analysis. The TDC samples (0.7% < Ro,max <3.1%) were collected from Huaibei coalfield with different deformation mechanisms and intensity. The FTIR of TDCs shows that the metamorphism and the deformation affect the degradation and polycondensation process of macromolecular structure to different degree. The Raman spectra analysis indicates that secondary structure defects can be produced mainly by structural deformation, also the metamorphism influences the secondary structure defects and aromatic structure. Through comprehensive analysis, it was discussed that the ductile deformation could change to strain energy through the increase and accumulation of dislocation in molecular structure units of TDC, and it could make an obvious influence on degradation and polycondensation. While the brittle deformation could change to frictional heat energy and promote the metamorphism and degradation of TDC structure, but has less effect on polycondensation. Furthermore, degradation is the main reason for affecting the structural evolution of coal in lower metamorphic stage, and polycondensation is the most important controlling factor in higher metamorphic stage. Under metamorphism and deformation, the small molecules which break and fall off from the macromolecular tructure of TDC are preferentially replenished and embedded into the secondary structure defects or the residual aromatic rings were formed into aromatic structure by polycondensation. This process improved the stability of coal structure. It is easier for ductile deformation of coal to induce the secondary structure defects than brittle deformation. PMID:22007412

  3. Understanding of edge and screw dislocations in nanostructures by modeling and simulations

    NASA Astrophysics Data System (ADS)

    Dontsova, Evgeniya

    The role of the extended dislocation defects in nanostructures only recently began to be explored. In bulk materials, dislocations are modeled only away from their cores within the framework of the continuum mechanics. It is known that applying continuum modeling in the core region leads to divergences. In nanostructures, the core region dominates and new investigation methods are needed. This work contributes to the fundamental understanding of the role of dislocations in important carbon and zinc oxide nanostructures, by using atomistic investigation methods. In quasi-zero-dimensional structures, thesis describes the first attempt to rationalize dislocation processes in carbon nano-onions. Experiments show that carbon nano-onions exhibit an unusual dislocation dynamics with unexpected attraction of outer edge dislocation towards the core. Atomistic calculations combined with rigorous energy analysis attribute this behavior to an unusual inward driving force on the outer edge dislocation associated with a reduction in the number of dangling bonds. Moving on to quasi-one-dimensional nanostructures, we study the stability of screw-dislocated zinc oxide structures in the wurtzite phase with a symmetry-adapted molecular dynamics methodology, which introduces a significant simplification in the simulation domain size by accounting for the helical symmetry explicitly. The goal is to provide the theoretical support for a universal screw-dislocation-driven growth mechanism suggested by recent experiments. Moreover, the effects of axial screw dislocations on the electronic properties in helical zinc oxide nanowires and nanotubes are explored. We demonstrate significant screw-dislocation-induced band gap modifications that originate in the highly distorted cores. Finally, using the same objective technique, we investigate the stability against torsional deformations of quasi-one-dimensional graphene nanoribbons with bare, F-, and OH-saturated armchair edges. The prevalence

  4. Quantum dislocations in solid Helium-4

    NASA Astrophysics Data System (ADS)

    Aleinikava, Darya

    In this thesis the following problems on properties of solid 4He are considered: (i) the role of long-range interactions in suppression of dislocation roughening at T = 0; (ii) the combined effect of 3He impurities and Peierls potential on shear modulus softening; (iii) the dislocation superclimb and its connection to the phenomenon of "giant isochoric compressibility"; (iv) non-linear dislocation response to the applied stress and stress-induces dislocation roughening as a I-order phase transition in 1D at finite temperature. First we investigate the effect of long-range interactions on the state of edge dislocation at T = 0. Such interactions are induced by elastic forces of the solid. We found that quantum roughening transition of a dislocation at T = 0 is completely suppressed by arbitrarily small long-range interactions between kinks. A heuristic argument is presented and the result has been verified by numerical Monte-Carlo simulations using Worm Algorithm in J-current model. It was shown that the Peierls potential plays a crucial role in explaining the elastic properties of dislocations, namely shear modulus softening phenomenon. The crossover from T = 0 to finite temperatures leads to intrinsic softening of the shear modulus and is solely controlled by kink typical energy. It was demonstrated that the mechanism, involving only the binding of 3He impurities to the dislocations, requires an unrealistically high concentrations of defects (or impurities) in order to explain the shear modulus phenomenon and therefore an inclusion of Peierls potential in consideration is required. Superclimbing dislocations, that is the edge dislocations with the superfluidity along the core, were investigated. The theoretical prediction that superclimb is responsible for the phenomenon of "giant isochoric compressibility" was confirmed by Monte-Carlo simulations. It was demonstrated that the isochoric compressibility is suppressed at low temperatures. The dependence of

  5. The role of purinergic signaling on deformation induced injury and repair responses of alveolar epithelial cells.

    PubMed

    Belete, Hewan A; Hubmayr, Rolf D; Wang, Shaohua; Singh, Raman-Deep

    2011-01-01

    Cell wounding is an important driver of the innate immune response of ventilator-injured lungs. We had previously shown that the majority of wounded alveolus resident cells repair and survive deformation induced insults. This is important insofar as wounded and repaired cells may contribute to injurious deformation responses commonly referred to as biotrauma. The central hypothesis of this communication states that extracellular adenosine-5' triphosphate (ATP) promotes the repair of wounded alveolus resident cells by a P2Y2-Receptor dependent mechanism. Using primary type 1 alveolar epithelial rat cell models subjected to micropuncture injury and/or deforming stress we show that 1) stretch causes a dose dependent increase in cell injury and ATP media concentrations; 2) enzymatic depletion of extracellular ATP reduces the probability of stretch induced wound repair; 3) enriching extracellular ATP concentrations facilitates wound repair; 4) purinergic effects on cell repair are mediated by ATP and not by one of its metabolites; and 5) ATP mediated cell salvage depends at least in part on P2Y2-R activation. While rescuing cells from wounding induced death may seem appealing, it is possible that survivors of membrane wounding become governors of a sustained pro-inflammatory state and thereby perpetuate and worsen organ function in the early stages of lung injury syndromes. Means to uncouple P2Y2-R mediated cytoprotection from P2Y2-R mediated inflammation and to test the preclinical efficacy of such an undertaking deserve to be explored. PMID:22087324

  6. Revisiting Bangham's law of adsorption-induced deformation: changes of surface energy and surface stress.

    PubMed

    Gor, Gennady Y; Bernstein, Noam

    2016-04-14

    When fluids are adsorbed on a solid surface they induce noticeable stresses, which cause the deformation of the solid. D. H. Bangham and co-authors performed a series of experimental measurements of adsorption-induced strains, and concluded that physisorption causes expansion, which is proportional to the lowering of the surface energy Δγ. This statement is referred to as the Bangham effect or Bangham's law. However, it is known that the quantity that controls the deformation is actually the change in surface stress Δf rather than surface energy Δγ, but this difference has not been considered in the context of adsorption-induced deformation of mesoporous materials. We use the Brunauer-Emmett-Teller (BET) theory to derive both values and show the difference between them. We find the condition when the difference between the two vanishes, and Bangham's law is applicable; it is likely that this condition is satisfied in most cases, and prediction of strain based on Δγ is a good approximation. We show that this is the case for adsorption of argon and water on Vycor glass. Finally, we show that the difference between Δγ and Δf can explain some of the experimental data that contradicts Bangham's law. PMID:27001041

  7. The Work Softening by Deformation-Induced Disordering and Cold Rolling of 6.5 wt pct Si Steel Thin Sheets

    NASA Astrophysics Data System (ADS)

    Wang, Xianglong; Li, Haoze; Zhang, Weina; Liu, Zhenyu; Wang, Guodong; Luo, Zhonghan; Zhang, Fengquan

    2016-06-01

    As-cast strip of 6.5 wt pct Si steel was fabricated by twin-roll strip casting. After hot rolling at 1323 K (1050 °C), thin sheets with the thickness of 0.35 mm were produced by warm rolling at 373 K (100 °C) with rolling reductions of 15, 25, 35, 45, 55, and 65 pct. Influence of warm rolling reduction on ductility was investigated by room temperature bending test. The measurement of macro-hardness showed that "work softening" could begin when the warm rolling reduction exceeded 35 pct. The room temperature ductility of the thin sheets gradually increased with the increase of warm rolling reductions, and the plastic deformation during bending began to form when the warm rolling reduction was greater than 45 pct, the 65 pct rolled thin sheet exhibited the maximum plastic deformation of about 0.6 pct during bending at room temperature, with a few small dimples having been observed on the fracture surfaces. B2-ordered domains were formed in the 15, 25, 35, 45, and 55 pct rolled specimens, and their average size decreased with the increase of warm rolling reductions. By contrast, no B2-ordered domain could be found in the 65 pct rolled specimen. It had been observed that large-ordered domains could be split into several small parts by the slip of partial super-dislocations during warm rolling, which led to significant decrease of the order degree to cause the phenomenon of deformation-induced disordering. On the basis of these results, cold rolling schedule was developed to successfully fabricate 0.25-mm-thick sheets with good surface qualities and magnetic properties from warm rolled sheets.

  8. Effect of Friction-Induced Deformation on the Structure, Microhardness, and Wear Resistance of Austenitic Chromium—Nickel Stainless Steel Subjected to Subsequent Oxidation

    NASA Astrophysics Data System (ADS)

    Korshunov, L. G.; Chernenko, N. L.

    2016-03-01

    The effect of plastic deformation that occurs in the zone of the sliding friction contact on structural transformations in the 12Kh18N9T austenitic steel subjected to subsequent 1-h oxidation in air at temperatures of 300-800°C, as well as on its wear resistance, has been studied. It has been shown that severe deformation induced by dry sliding friction produces the two-phase nanocrystalline γ + α structure in the surface layer of the steel ~10 μm thick. This structure has the microhardness of 5.2 GPa. Subsequent oxidation of steel at temperatures of 300-500°C leads to an additional increase in the microhardness of its deformed surface layer to the value of 7.0 GPa. This is due to the active saturation of the austenite and the strain-assisted martensite (α') with the oxygen atoms, which diffuse deep into the metal over the boundaries of the γ and α' nanocrystals with an increased rate. The concentration of oxygen in the surface layer of the steel and in wear products reaches 8 wt %. The atoms of the dissolved oxygen efficiently pin dislocations in the γ and α' phases, which enhances the strength and wear resistance of the surface of the 12Kh18N9T steel. The oxidation of steel at temperatures of 550-800°C under a light normal load (98 N) results in the formation of a large number of Fe3O4 (magnetite) nanoparticles, which increase the resistance of the steel to thermal softening and its wear resistance during dry sliding friction in a pair with 40Kh13 steel. Under a heavy normal load (196 N), the toughness of 12Kh18N9T steel and, therefore, the wear resistance of its surface layer decrease due to the presence of the brittle oxide phase.

  9. The Work Softening by Deformation-Induced Disordering and Cold Rolling of 6.5 wt pct Si Steel Thin Sheets

    NASA Astrophysics Data System (ADS)

    Wang, Xianglong; Li, Haoze; Zhang, Weina; Liu, Zhenyu; Wang, Guodong; Luo, Zhonghan; Zhang, Fengquan

    2016-09-01

    As-cast strip of 6.5 wt pct Si steel was fabricated by twin-roll strip casting. After hot rolling at 1323 K (1050 °C), thin sheets with the thickness of 0.35 mm were produced by warm rolling at 373 K (100 °C) with rolling reductions of 15, 25, 35, 45, 55, and 65 pct. Influence of warm rolling reduction on ductility was investigated by room temperature bending test. The measurement of macro-hardness showed that "work softening" could begin when the warm rolling reduction exceeded 35 pct. The room temperature ductility of the thin sheets gradually increased with the increase of warm rolling reductions, and the plastic deformation during bending began to form when the warm rolling reduction was greater than 45 pct, the 65 pct rolled thin sheet exhibited the maximum plastic deformation of about 0.6 pct during bending at room temperature, with a few small dimples having been observed on the fracture surfaces. B2-ordered domains were formed in the 15, 25, 35, 45, and 55 pct rolled specimens, and their average size decreased with the increase of warm rolling reductions. By contrast, no B2-ordered domain could be found in the 65 pct rolled specimen. It had been observed that large-ordered domains could be split into several small parts by the slip of partial super-dislocations during warm rolling, which led to significant decrease of the order degree to cause the phenomenon of deformation-induced disordering. On the basis of these results, cold rolling schedule was developed to successfully fabricate 0.25-mm-thick sheets with good surface qualities and magnetic properties from warm rolled sheets.

  10. Theory of light-induced deformation of azobenzene elastomers: Influence of network structure

    NASA Astrophysics Data System (ADS)

    Toshchevikov, V. P.; Saphiannikova, M.; Heinrich, G.

    2012-07-01

    Azobenzene elastomers have been extensively explored in the last decade as photo-deformable smart materials which are able to transform light energy into mechanical stress. Presently, there is a great need for theoretical approaches to accurately predict the quantitative response of these materials based on their microscopic structure. Recently, we proposed a theory of light-induced deformation of azobenzene elastomers using a simple regular cubic network model [V. Toshchevikov, M. Saphiannikova, and G. Heinrich, J. Phys. Chem. B 116, 913 (2012), 10.1021/jp206323h]. In the present study, we extend the previous theory using more realistic network models which take into account the random orientation of end-to-end vectors of network strands as well as the molecular weight distribution of the strands. Interaction of the chromophores with the linearly polarized light is described by an effective orientation potential which orients the chromophores perpendicular to the polarization direction. We show that both monodisperse and polydisperse azobenzene elastomers can demonstrate either a uniaxial expansion or contraction along the polarization direction. The sign of deformation (expansion/contraction) depends on the orientation distribution of chromophores with respect to the main chains which is defined by the chemical structure and by the lengths of spacers. The degree of cross-linking and the polydispersity of network strands do not affect the sign of deformation but influence the magnitude of light-induced deformation. We demonstrate that photo-mechanical properties of mono- and poly-disperse azobenzene elastomers with random spatial distribution of network strands can be described in a very good approximation by a regular cubic network model with an appropriately chosen length of the strands.

  11. Anisotropy of remanent and induced magnetization in hematite ore deformed in torsion

    NASA Astrophysics Data System (ADS)

    Machek, Matěj; Petrovský, Eduard; Roxerová, Zuzana; Kusbach, Vladimír; Siemes, Heinrich

    2016-04-01

    Induced and remanent magnetization measurements, e.g. shape of hysteresis loops, FORC diagrams and decomposition of isothermal remanent magnetization (IRM) acquisition curves, became routine tools in rock-magnetic measurements, interpreted mostly in terms of composition and grain-size distribution of iron oxides. It is assumed that the substances investigate are with respect to these measurements isotropic and single measurement of one sample is sufficient for interpretation. This assumption is valid for powdered samples, but solid rock samples in general behave anisotropically. In our contribution we report on magnetic measurements of hematite ore samples deformed in torsion, which show significant anisotropy of shape of hysteresis loops and IRM acquisition curves; the degree of anisotropy reflecting the degree of deformation. Samples, measured in different directions, showed different shape of hysteresis loop, from regular, which may be interpreted either as randomly oriented multi-domain grains, or with different degree of distortion (wasp-waistedness), reflecting different distribution of contrasting coercivities. Also decomposition of IRM acquisition curves, measured in different direction, yielded different interpretation in terms of relative contributions of components with different coercivities. The increasing strain is reflected in the strength and orientation of microstructure and crystallographic preferred orientation (CPO). The AMS in deformed samples is not controlled by hematite CPO. It is rather dominated by occurrence of magnetite grains along samples edges parallel to shear plane, probably due to the diffusion of Fe ions from iron jacket, even though samples were shielded by a silver (70)/palladium (30) sleeve of 0.5 mm thickness. We interpret this anisotropy as result of deformation, causing preferred orientation of basal planes of hematite. Moreover, the anisotropy is asymmetric. Our results suggest that, at least in deformed rocks containing

  12. Deformation twinning in small-sized face-centred cubic single crystals: Experiments and modelling

    NASA Astrophysics Data System (ADS)

    Liang, Z. Y.; Huang, M. X.

    2015-12-01

    Small-sized crystals generally show deformation behaviour distinct from their bulk counterparts. In addition to dislocation slip, deformation twinning in small-sized face-centred cubic (FCC) single crystals has been reported to follow a different mechanism which involves coherent emission of partial dislocations on successive { 111 } planes from free surface. The present work employed a twinning-induced plasticity (TWIP) steel with a low stacking fault energy to systematically investigate the twin evolution in small-sized FCC single crystals. Micrometre-sized single crystal pillars of TWIP steel were fabricated by focus ion beam and then strained to different levels by compression experiments. Detailed transmission electron microscopy characterization was carried out to obtain a quantitative evaluation of the deformation twins, which contribute to most of the plastic strain. Emissions of partial dislocations from free surface (surface sources) and pre-existing perfect dislocations inside the pillar (inner sources) are found as the essential processes for the formation of deformation twins. Accordingly, a physically-based model, which integrates source introduction methods and source activation criterions for partial dislocation emission, is developed to quantitatively predict the twin evolution. The model is able to reproduce the experimental twin evolution, in terms of the total twin formation, the twin morphology and the occurrence of twinning burst.

  13. Laser shock peening effect on the dislocation transitions and grain refinement of Al–Mg–Si alloy

    SciTech Connect

    Trdan, U.; Skarba, M.; Grum, J.

    2014-11-15

    This paper systematically investigates the effect of laser shock peening without coating parameters on the microstructural evolution, and dislocation configurations induced by ultra-high plastic strains and strain rates. Based on an analysis of optical microscopy, polarized light microscopy, transmission electron microscopy observations and residual stress analysis, the significant influence of laser shock peening parameters due to the effect of plasma generation and shock wave propagation has been confirmed. Although the optical microscopy results revealed no significant microstructural changes after laser shock peening, i.e. no heat effect zone and differences in the distribution of second-phase particles, expressive influence of laser treatment parameters on the laser shock induced craters was confirmed. Moreover, polarized light microscopy results have confirmed the existence of well-defined longish grains up to 455 μm in length in the centre of the plate due to the rolling effect, and randomly oriented smaller grains (20 μm × 50 μm) in the surface due to the static recrystallization effect. Laser shock peening is reflected in an exceptional increase in dislocation density with various configurations, i.e. dislocation lines, dislocation cells, dislocation tangles, and the formation of dense dislocation walls. More importantly, the microstructure is considerably refined due to the effect of strain deformations induced by laser shock peening process. The results have confirmed that dense dislocation structures during ultra-high plastic deformation with the addition of shear bands producing ultra-fine (60–200 nm) and nano-grains (20–50 nm). Furthermore, dislocation density was increased by a factor of 2.5 compared to the untreated material (29 × 10{sup 13} m{sup −2} vs. 12 × 10{sup 13} m{sup −2}). - Highlights: • LSPwC imparts high compressive residual stresses up to − 362 ± 31 MPa. • After LSPwC the microstructure is considerably refined via

  14. Quenched pinning and collective dislocation dynamics

    PubMed Central

    Ovaska, Markus; Laurson, Lasse; Alava, Mikko J.

    2015-01-01

    Several experiments show that crystalline solids deform in a bursty and intermittent fashion. Power-law distributed strain bursts in compression experiments of micron-sized samples, and acoustic emission energies from larger-scale specimens, are the key signatures of the underlying critical-like collective dislocation dynamics - a phenomenon that has also been seen in discrete dislocation dynamics (DDD) simulations. Here we show, by performing large-scale two-dimensional DDD simulations, that the character of the dislocation avalanche dynamics changes upon addition of sufficiently strong randomly distributed quenched pinning centres, present e.g. in many alloys as immobile solute atoms. For intermediate pinning strength, our results adhere to the scaling picture of depinning transitions, in contrast to pure systems where dislocation jamming dominates the avalanche dynamics. Still stronger disorder quenches the critical behaviour entirely. PMID:26024505

  15. Quenched pinning and collective dislocation dynamics.

    PubMed

    Ovaska, Markus; Laurson, Lasse; Alava, Mikko J

    2015-01-01

    Several experiments show that crystalline solids deform in a bursty and intermittent fashion. Power-law distributed strain bursts in compression experiments of micron-sized samples, and acoustic emission energies from larger-scale specimens, are the key signatures of the underlying critical-like collective dislocation dynamics - a phenomenon that has also been seen in discrete dislocation dynamics (DDD) simulations. Here we show, by performing large-scale two-dimensional DDD simulations, that the character of the dislocation avalanche dynamics changes upon addition of sufficiently strong randomly distributed quenched pinning centres, present e.g. in many alloys as immobile solute atoms. For intermediate pinning strength, our results adhere to the scaling picture of depinning transitions, in contrast to pure systems where dislocation jamming dominates the avalanche dynamics. Still stronger disorder quenches the critical behaviour entirely. PMID:26024505

  16. Electronic modification of Cu-based chalcopyrite semiconductors induced by lattice deformation and composition alchemy

    NASA Astrophysics Data System (ADS)

    Jiang, F. D.; Feng, J. Y.

    2008-02-01

    Using first principles calculation, we systematically investigate the electronic modification of Cu-based chalcopyrite semiconductors induced by lattice deformation and composition alchemy. It is shown that the optical band gap Eg is remarkably sensitive to the anion displacement μ, resulting from the opposite shifts of conduction band minimum and valence band maximum. Meanwhile, the dependence of structural parameters of alloyed compounds on alloy composition x is demonstrated for both cation and anion alloying. The d orbitals of group-III cations are found to be of great importance in the calculation. Abnormal changes in the optical band gap Eg induced by anion alloying are addressed.

  17. Nanoscale silicon-on-insulator deformation induced by stressed liner structures

    SciTech Connect

    Murray, Conal E.; Ying, A.; Polvino, S. M.; Noyan, I. C.; Holt, M.; Maser, J.

    2011-04-15

    Rotation and strain fields were mapped across silicon-on-insulator (SOI) regions induced by overlying stressed Si{sub 3}N{sub 4} features using x-ray nanobeam diffraction. The distribution in SOI tilt exhibited an antisymmetric distribution with a maximum magnitude of 7.9 milliradians, representing one of the first direct measurements of the lattice tilt conducted in situ within buried layers using a spot size of less than 100 nm. The measured rotation distribution corresponds to simulated values generated by boundary element method modeling, indicating that the strain transfer into the underlying SOI primarily induces elastic deformation.

  18. Thermodynamic forces in single crystals with dislocations

    NASA Astrophysics Data System (ADS)

    Van Goethem, Nicolas

    2014-06-01

    A simple model for the evolution of macroscopic dislocation regions in a single crystal is presented. This model relies on maximal dissipation principle within Kröner's geometric description of the dislocated crystal. Mathematical methods and tools from shape optimization theory provide equilibrium relations at the dislocation front, similarly to previous work achieved on damage modelling (J Comput Phys 33(16):5010-5044, 2011). The deformation state variable is the incompatible strain as related to the dislocation density tensor by a relation involving the Ricci curvature of the crystal underlying elastic metric. The time evolution of the model variables follows from a novel interpretation of the Einstein-Hilbert flow in terms of dislocation microstructure energy. This flow is interpreted as the dissipation of non-conservative dislocations, due to the climb mechanism, modelled by an average effect of mesoscopic dislocations moving normal to their glide planes by adding or removing points defects. The model equations are a fourth-order tensor parabolic equation involving the operator "incompatibility," here appearing as a tensorial counterpart of the scalar Laplacian. This work encompasses and generalizes results previously announced (C R Acad Sci Paris Ser I 349:923-927, 2011), with in addition a series of physical interpretations to give a meaning to the newly introduced concepts.

  19. Ultrasonic Study of Dislocation Dynamics in Lithium -

    NASA Astrophysics Data System (ADS)

    Han, Myeong-Deok

    1987-09-01

    Experimental studies of dislocation dynamics in LiF single crystals, using ultrasonic techniques combined with dynamic loading, were performed to investigate the time evolution of the plastic deformation process under a short stress pulse at room temperature, and the temperature dependence of the dislocation damping mechanism in the temperature range 25 - 300(DEGREES)K. From the former, the time dependence of the ultrasonic attenuation was understood as resulting from dislocation multiplication followed by the evolution of mobile dislocations to immobile ones under large stress. From the latter, the temperature dependence of the ultrasonic attenuation was interpreted as due to the motion of the dislocation loops overcoming the periodic Peierls potential barrier in a manner analogous to the motion of a thermalized sine-Gordon chain under a small stress. The Peierls stress obtained from the experimental results by application of Seeger's relaxation model with exponential dislocation length distribution was 4.26MPa, which is consistent with the lowest stress for the linear relation between the dislocation velocity and stress observed by Flinn and Tinder.

  20. Dislocated shoulder - aftercare

    MedlinePlus

    Shoulder dislocation - aftercare; Shoulder subluxation - aftercare; Shoulder reduction - aftercare ... You most likely dislocated your shoulder from a sports injury or accident, such as a fall. You have likely injured (stretched or torn) some of the muscles, ...

  1. Dislocated shoulder - aftercare

    MedlinePlus

    Shoulder dislocation - aftercare; Shoulder subluxation - aftercare; Shoulder reduction - aftercare ... Horn AE, Ufberg JW. Management of common dislocations. In: ... Extremity 6th ed. Philadelphia, PA: ElsevierMosby; 2011:chap 92.

  2. Thermally induced stresses and deformations in angle-ply composite tubes

    NASA Technical Reports Server (NTRS)

    Hyer, M. W.; Rousseau, Carl Q.

    1987-01-01

    Cure-induced uniform temperature change effects on the stresses, axial expansion, and thermally-induced twist of four specific angle-ply tube designs are discussed with a view to the tubes' use as major space structure components. The stresses and deformations in the tubes are studied as a function of the four designs, the off-axis angle, and the single-material and hybrid reinforcing-material construction used. It is found that tube design has a minor influence on the stresses, axial stiffness, and axial thermal expansion characteristics, which are more directly a function of off-axis angle and material selection; tube design is, however, the primary influence in the definition of thermally-induced twist and torsional stiffness characteristics. None of the designs is free of thermally induced twist.

  3. Temporomandibular joint dislocation.

    PubMed

    Sharma, Naresh Kumar; Singh, Akhilesh Kumar; Pandey, Arun; Verma, Vishal; Singh, Shreya

    2015-01-01

    Temporomandibular joint (TMJ) dislocation is an uncommon but debilitating condition of the facial skeleton. The condition may be acute or chronic. Acute TMJ dislocation is common in clinical practice and can be managed easily with manual reduction. Chronic recurrent TMJ dislocation is a challenging situation to manage. In this article, we discuss the comprehensive review of the different treatment modalities in managing TMJ dislocation. PMID:26668447

  4. Temporomandibular joint dislocation

    PubMed Central

    Sharma, Naresh Kumar; Singh, Akhilesh Kumar; Pandey, Arun; Verma, Vishal; Singh, Shreya

    2015-01-01

    Temporomandibular joint (TMJ) dislocation is an uncommon but debilitating condition of the facial skeleton. The condition may be acute or chronic. Acute TMJ dislocation is common in clinical practice and can be managed easily with manual reduction. Chronic recurrent TMJ dislocation is a challenging situation to manage. In this article, we discuss the comprehensive review of the different treatment modalities in managing TMJ dislocation. PMID:26668447

  5. Simulating root-induced rhizosphere deformation and its effect on water flow

    NASA Astrophysics Data System (ADS)

    Aravena, J. E.; Ruiz, S.; Mandava, A.; Regentova, E. E.; Ghezzehei, T.; Berli, M.; Tyler, S. W.

    2011-12-01

    Soil structure in the rhizosphere is influenced by root activities, such as mucilage production, microbial activity and root growth. Root growth alters soil structure by moving and deforming soil aggregates, affecting water and nutrient flow from the bulk soil to the root surface. In this study, we utilized synchrotron X-ray micro-tomography (XMT) and finite element analysis to quantify the effect of root-induced compaction on water flow through the rhizosphere to the root surface. In a first step, finite element meshes of structured soil around the root were created by processing rhizosphere XMT images. Then, soil deformation by root expansion was simulated using COMSOL Multiphysics° (Version 4.2) considering the soil an elasto-plastic porous material. Finally, fluid flow simulations were carried out on the deformed mesh to quantify the effect of root-induced compaction on water flow to the root surface. We found a 31% increase in water flow from the bulk soil to the root due to a 56% increase in root diameter. Simulations also show that the increase of root-soil contact area was the dominating factor with respect to the calculated increase in water flow. Increase of inter-aggregate contacts in size and number were observed within a couple of root diameters away from the root surface. But their influence on water flow was, in this case, rather limited compared to the immediate soil-root contact.

  6. Temperature and strain-rate dependence of surface dislocation nucleation.

    PubMed

    Zhu, Ting; Li, Ju; Samanta, Amit; Leach, Austin; Gall, Ken

    2008-01-18

    Dislocation nucleation is essential to the plastic deformation of small-volume crystalline solids. The free surface may act as an effective source of dislocations to initiate and sustain plastic flow, in conjunction with bulk sources. Here, we develop an atomistic modeling framework to address the probabilistic nature of surface dislocation nucleation. We show the activation volume associated with surface dislocation nucleation is characteristically in the range of 1-10b3, where b is the Burgers vector. Such small activation volume leads to sensitive temperature and strain-rate dependence of the nucleation stress, providing an upper bound to the size-strength relation in nanopillar compression experiments. PMID:18232884

  7. Elastic anisotropy and shear-induced atomistic deformation of tetragonal silicon carbon nitride

    SciTech Connect

    Yan, Haiyan; Zhang, Meiguang; Zhao, Yaru; Zhou, Xinchun; Wei, Qun

    2014-07-14

    First-principles calculations are employed to provide a fundamental understanding of the structural features, elastic anisotropy, shear-induced atomistic deformation behaviors, and its electronic origin of the recently proposed superhard t-SiCN. According to the dependences of the elastic modulus on different crystal directions, the t-SiCN exhibits a well-pronounced elastic anisotropy which may impose certain limitations and restrictions on its applications. The further mechanical calculations demonstrated that t-SiCN shows lower elastic moduli and ideal shear strength than those of typical hard substances of TiN and TiC, suggesting that it cannot be intrinsically superhard as claimed in the recent works. We find that the failure modes of t-SiCN at the atomic level during shear deformation can be attributed to the breaking of C-C bonds through the bonding evolution and electronic localization analyses.

  8. Deformation-induced melting in the margins of the West Antarctic ice streams

    NASA Astrophysics Data System (ADS)

    Suckale, Jenny; Platt, John D.; Perol, Thibaut; Rice, James R.

    2014-05-01

    Flow of glacial ice in the West Antarctic Ice Sheet localizes in narrow bands of fast-flowing ice streams bordered by ridges of nearly stagnant ice, but our understanding of the physical processes that generate this morphology is incomplete. Here we study the thermal and mechanical properties of ice-stream margins, where flow transitions from rapid to stagnant over a few kilometers. Our goal is to explore under which conditions the intense shear deformation in the margin may lead to deformation-induced melting. We propose a 2-D model that represents a cross section through the ice stream margin perpendicular to the downstream flow direction. We limit temperature to the melting point to estimate melt rates based on latent heat. Using rheology parameters as constrained by laboratory data and observations, we conclude that a zone of temperate ice is likely to form in active shear margins.

  9. Tip-Induced Deformation of Graphene on SiO2 Assessed by Capacitance Measurement

    NASA Astrophysics Data System (ADS)

    Naitou, Yuichi

    2012-11-01

    Tip-induced deformation of graphene on a SiO2 substrate was probed through a combination of scanning capacitance microscopy (SCM) and dynamic force microscopy (DFM). Spectroscopic analysis revealed that the resonant frequency shift (Δf) of the probe tip oscillation and the modulated capacitance (ΔC) simultaneously measured on graphene depend on the externally applied bias voltage while keeping the tip-sample distance constant. This finding is interpreted as a result of a local displacement of the graphene surface caused by the electrostatic force between the probe tip and graphene. The approach curve of the SCM tip toward graphene can be used to calibrate the observed ΔC spectra, quantitatively yielding an average deformation of approximately 0.31 nm in trilayer graphene and 0.21 nm in single-layer graphene.

  10. Eye-Specific IOP-Induced Displacements and Deformations of Human Lamina Cribrosa

    PubMed Central

    Sigal, Ian A.; Grimm, Jonathan L.; Jan, Ning-Jiun; Reid, Korey; Minckler, Don S.; Brown, Donald J.

    2014-01-01

    Purpose. To measure high-resolution eye-specific displacements and deformations induced within the human LC microstructure by an acute increase in IOP. Methods. Six eyes from donors aged 23 to 82 were scanned using second harmonic-generated (SHG) imaging at various levels of IOP from 10 to 50 mm Hg. An image registration technique was developed, tested, and used to find the deformation mapping between maximum intensity projection images acquired at low and elevated IOP. The mappings were analyzed to determine the magnitude and distribution of the IOP-induced displacements and deformations and contralateral similarity. Results. Images of the LC were obtained and the registration technique was successful. IOP increases produced substantial, and potentially biologically significant, levels of in-plane LC stretch and compression (reaching 10%–25% medians and 20%–30% 75th percentiles). Deformations were sometimes highly focal and concentrated in regions as small as a few pores. Regions of largest displacement, stretch, compression, and shear did not colocalize. Displacements and strains were not normally distributed. Contralateral eyes did not always have more similar responses to IOP than unrelated eyes. Under elevated IOP, some LC regions were under bi-axial stretch, others under bi-axial compression. Conclusions. We obtained eye-specific measurements of the complex effects of IOP on the LC with unprecedented resolution in uncut and unfixed human eyes. Our technique was robust to electronic and speckle noise. Elevated IOP produced substantial in-plane LC stretch and compression. Further research will explore the effects of IOP on the LC in a three-dimensional framework. PMID:24334450

  11. The role of dislocation-induced scattering in electronic transport in GaxIn1-xN alloys

    NASA Astrophysics Data System (ADS)

    Donmez, Omer; Gunes, Mustafa; Erol, Ayse; Arikan, Cetin M.; Balkan, Naci; Schaff, William J.

    2012-08-01

    Electronic transport in unintentionally doped GaxIn1-xN alloys with various Ga concentrations ( x = 0.06, 0.32 and 0.52) is studied. Hall effect measurements are performed at temperatures between 77 and 300 K. Temperature dependence of carrier mobility is analysed by an analytical formula based on two-dimensional degenerate statistics by taking into account all major scattering mechanisms for a two-dimensional electron gas confined in a triangular quantum well between GaxIn1-xN epilayer and GaN buffer. Experimental results show that as the Ga concentration increases, mobility not only decreases drastically but also becomes less temperature dependent. Carrier density is almost temperature independent and tends to increase with increasing Ga concentration. The weak temperature dependence of the mobility may be attributed to screening of polar optical phonon scattering at high temperatures by the high free carrier concentration, which is at the order of 1014 cm-2. In our analytical model, the dislocation density is used as an adjustable parameter for the best fit to the experimental results. Our results reveal that in the samples with lower Ga compositions and carrier concentrations, alloy and interface roughness scattering are the dominant scattering mechanisms at low temperatures, while at high temperatures, optical phonon scattering is the dominant mechanism. In the samples with higher Ga compositions and carrier concentrations, however, dislocation scattering becomes more significant and suppresses the effect of longitudinal optical phonon scattering at high temperatures, leading to an almost temperature-independent behaviour.

  12. Dynamics of dislocation interactions with stacking-fault tetrahedra at high temperature

    NASA Astrophysics Data System (ADS)

    Briceño, M.; Kacher, J.; Robertson, I. M.

    2013-02-01

    The interaction process between dislocations and large stacking-fault tetrahedra was observed in real time at high temperature during deformation experiments in situ in the transmission electron microscope. Dislocation interactions with tetrahedra resulted in them being annihilated and converted to another defect type. Dislocation bypass of the tetrahedra occurred by cross-slip. The latter interaction occurred slowly and halted the progress of the dislocation. Annihilation versus bypass by dislocation cross-slip was dictated by the location at which the slip plane intersected the tetrahedron - on the face or along the edges with the stair-rod dislocations. In general, the interactions, at best, were weakly temperature dependent.

  13. Effect of plastic deformation on deuterium retention and release in tungsten

    NASA Astrophysics Data System (ADS)

    Terentyev, D.; De Temmerman, G.; Morgan, T. W.; Zayachuk, Y.; Lambrinou, K.; Minov, B.; Dubinko, A.; Bystrov, K.; Van Oost, G.

    2015-02-01

    The effect of severe plastic deformation on the deuterium retention in tungsten exposed to high-flux low-energy plasma (flux ˜ 1024 D/m2/s, energy ˜ 50 eV, and fluence up to 3 × 1026 D/m2) at the plasma generator Pilot-PSI was studied by thermal desorption spectroscopy and scanning electron microscopy. The desorption spectra in both reference and plastically deformed samples were deconvolved into three contributions attributed to the detrapping from dislocations, deuterium-vacancy clusters, and pores, respectively. The plastically induced deformation, resulting in high dislocation density, does not change the positions of the three peaks, but alters their amplitudes as compared to the reference material. The appearance of blisters detected by scanning electron microscopy and the desorption peak attributed to the release from pores (i.e., deuterium bubbles) were suppressed in the plastically deformed samples but only up to a certain fluence. Beyond 5 × 1025 D/m2, the release from the bubbles in the deformed material is essentially higher than in the reference material. Based on the presented results, we suggest that a dense dislocation network increases the incubation dose needed for the appearance of blisters, associated with deuterium bubbles, by offering numerous nucleation sites for deuterium clusters eventually transforming into deuterium-vacancy clusters by punching out jogs on dislocation lines.

  14. Effect of plastic deformation on deuterium retention and release in tungsten

    SciTech Connect

    Terentyev, D. Lambrinou, K.; Minov, B.; De Temmerman, G.; Morgan, T. W.; Zayachuk, Y.; Bystrov, K.; Dubinko, A.; Van Oost, G.

    2015-02-28

    The effect of severe plastic deformation on the deuterium retention in tungsten exposed to high-flux low-energy plasma (flux ∼ 10{sup 24 }D/m{sup 2}/s, energy ∼ 50 eV, and fluence up to 3 × 10{sup 26 }D/m{sup 2}) at the plasma generator Pilot-PSI was studied by thermal desorption spectroscopy and scanning electron microscopy. The desorption spectra in both reference and plastically deformed samples were deconvolved into three contributions attributed to the detrapping from dislocations, deuterium-vacancy clusters, and pores, respectively. The plastically induced deformation, resulting in high dislocation density, does not change the positions of the three peaks, but alters their amplitudes as compared to the reference material. The appearance of blisters detected by scanning electron microscopy and the desorption peak attributed to the release from pores (i.e., deuterium bubbles) were suppressed in the plastically deformed samples but only up to a certain fluence. Beyond 5 × 10{sup 25 }D/m{sup 2}, the release from the bubbles in the deformed material is essentially higher than in the reference material. Based on the presented results, we suggest that a dense dislocation network increases the incubation dose needed for the appearance of blisters, associated with deuterium bubbles, by offering numerous nucleation sites for deuterium clusters eventually transforming into deuterium-vacancy clusters by punching out jogs on dislocation lines.

  15. A TEM Study of Creep Deformation Mechanisms in Allvac 718Plus

    SciTech Connect

    Unocic, Raymond R; Unocic, Kinga A; Hayes, Robert; Daehn, Glenn; Mills, Michael J.

    2010-01-01

    A preliminary study on the evolution of creep deformation substructure in Ni-base superalloy Allvac 718Plus has been performed. Specimens crept at 620 MPa and at temperatures ranging from 690-732 C were examined utilizing diffraction contrast TEM characterization techniques. Creep was interrupted at 1-2.5% strain in order to study the deformation substructure following a limited amount of deformation. The dominant deformation modes at each of the test temperatures were highly planar in nature and involved shearing of the matrix and precipitates on {111} glide planes. In addition, paired a/2<110> dislocations were evident which suggest an antiphase boundary shearing mechanism. Creep induced microtwinning was also observed at the highest creep temperature which was created by identical a/6<112> Shockley partial dislocations that shear the matrix and precipitates on consecutive close packed {111} glide planes.

  16. Continuous deformation versus episodic deformation at high stress - the microstructural record

    NASA Astrophysics Data System (ADS)

    Trepmann, C. A.; Stöckhert, B.

    2009-04-01

    The microstructural record of continuous high stress deformation is compared to that of episodic high stress deformation on two examples: 1. Folding of quartz veins in metagreywacke from Pacheco Pass, California, undergoing deformation by dissolution precipitation creep at temperatures of 300 ± 50°C. The microfabric of the folded quartz veins indicates deformation by dislocation creep accompanied by subgrain rotation. The small recrystallized grain size of ~8±6 µm in average implies relatively high differential stresses of a few hundred MPa. The stress concentration in the vein is due to a high contrast in effective viscosities between the single phase material and the polyphase fine-grained host metagreywacke deforming by dissolution precipitation creep. Smoothly curved, but generally not sutured, grain boundaries as well as the small size and a relatively high dislocation density of recrystallized grains suggest that strain-induced grain boundary migration was of minor importance. This is suspected to be a consequence of low strain gradients, which are due to the relative rates of dynamic recovery and continuous dislocation production during climb-controlled creep, at high stress and the given low temperature. Subgrain rotation recrystallization is thus proposed to be characteristic for continuous deformation at high differential stress. 2. Episodic deformation in the middle crust at the tip of a seismic active fault zone. The microfabric of mid-crustal rocks exhumed in tectonically active regions can record episodic high stress deformation at the base of the seismogenic layer. The quartz veins from St. Paul la Roche in the Massif Central, France, are very coarse grained. On the scale of a thin section they are basically single crystalline. However, they show a very heterogeneous microstructure with a system of healed microcracks that are decorated by subgrains and more rarely by small recrystallized grains. Undulating deformation lamellae that do not show a

  17. Free energy of dislocations in a multi-slip geometry

    NASA Astrophysics Data System (ADS)

    Kooiman, M.; Hütter, M.; Geers, M. G. D.

    2016-03-01

    The collective dynamics of dislocations is the underlying mechanism of plastic deformation in metallic crystals. Dislocation motion in metals generally occurs on multiple slip systems. The simultaneous activation of different slip systems plays a crucial role in crystal plasticity models. In this contribution, we study the energetic interactions between dislocations on different slip systems by deriving the free energy in a multi-slip geometry. In this, we restrict ourselves to straight and parallel edge dislocations. The obtained free energy has a long-range mean-field contribution, a statistical contribution and a many-body contribution. The many-body contribution is a local function of the total dislocation density on each slip system, and can therefore not be written in terms of the net dislocation density only. Moreover, this function is a strongly non-linear and non-convex function of the density on different slip systems, and hence the coupling between slip systems is of great importance.

  18. Pattern formation in a minimal model of continuum dislocation plasticity

    NASA Astrophysics Data System (ADS)

    Sandfeld, Stefan; Zaiser, Michael

    2015-09-01

    The spontaneous emergence of heterogeneous dislocation patterns is a conspicuous feature of plastic deformation and strain hardening of crystalline solids. Despite long-standing efforts in the materials science and physics of defect communities, there is no general consensus regarding the physical mechanism which leads to the formation of dislocation patterns. In order to establish the fundamental mechanism, we formulate an extremely simplified, minimal model to investigate the formation of patterns based on the continuum theory of fluxes of curved dislocations. We demonstrate that strain hardening as embodied in a Taylor-type dislocation density dependence of the flow stress, in conjunction with the structure of the kinematic equations that govern dislocation motion under the action of external stresses, is already sufficient for the formation of dislocation patterns that are consistent with the principle of similitude.

  19. Glassy dislocation dynamics in colloidal dimer crystals

    NASA Astrophysics Data System (ADS)

    Gerbode, Sharon

    2012-02-01

    Dislocation mobility is central to both the mechanical response and the relaxation mechanisms of crystalline materials. Recent experiments have explored the role of novel particle anisotropies in affecting the rules of defect motion in crystals. ``Peanut-shaped'' colloidal dimer particles consisting of two connected spherical lobes form densely packed crystals in 2D. In these ``degenerate crystals,'' the particle lobes occupy triangular lattice sites while the particle axes are randomly oriented among the three crystalline directions. One consequence of the random orientations of the dimers is that dislocation glide is severely limited by certain particle arrangements in the degenerate crystals. Using optical tweezers to manipulate single lobe-sized spherical intruder particles, we locally deform the crystal, creating defects. During subsequent relaxation, the dislocations formed during the deformation leave the crystal grain, either via annihilation with other dislocations or by moving to a grain boundary. Interestingly, in large crystalline grains this dislocation relaxation occurs through a two-stage process reminiscent of slow relaxations in glassy systems, suggesting the novel concept that glassy phenomena may be introduced to certain kinds of colloidal crystals via simple anisotropic constituents.

  20. Aluminizing a Ni sheet through severe plastic deformation induced by ball collisions

    NASA Astrophysics Data System (ADS)

    Romankov, S.; Shchetinin, I. V.; Park, Y. C.

    2015-07-01

    Aluminizing a Ni sheet was performed through severe plastic deformation induced by ball collisions. The Ni sheet was fixed in the center of a mechanically vibrated vial between two connected parts. The balls were loaded into the vial on both sides of the Ni disk. Al disks, which were fixed on the top and the bottom of the vial, served as the sources of Al contamination. During processing, the Ni sheet was subject to intense ball collisions. The Al fragments were transferred and alloyed to the surface of the Ni sheet by these collisions. The combined effects of deformation-induced plastic flow, mechanical intermixing, and grain refinement resulted in the formation of a dense, continuous nanostructured Al layer on the Ni surface on both sides of the sheet. The Al layer consisted of Al grains with an average size of about 40 nm. The Al layer was reinforced with nano-sized Ni flakes that were introduced from the Ni surface during processing. The local amorphization at the Ni/Al interface revealed that the bonding between Ni and Al was formed by mechanical intermixing of atomic layers at the interface. The hardness of the fabricated Al layer was 10 times that of the initial Al plate. The ball collisions destroyed the initial rolling texture of the Ni sheet and induced the formation of the mixed [1 0 0] + [1 1 1] fiber texture. The laminar rolling structure of the Ni was transformed into an ultrafine grain structure.

  1. Process-induced stress and deformation in thick-section thermosetting composites

    SciTech Connect

    Bogetti, T.A.

    1989-01-01

    The cure and process-induced stress and deformation development in thick-section thermosetting composites is presented. A two-dimensional anisotropic cure simulation analysis is developed to predict temperature and degree of cure distributions within arbitrary cross-sectional geometries as a function of the autoclave temperature history. Correlation between experimentally measured and predicted through-the-thickness temperature profiles in glass/polyester laminates are presented for various arbitrary temperature cure cycle histories. Several typical glass/polyester and graphite/epoxy structural elements of arbitrary cross-section are analyzed. Spatial gradients in degree of cure are shown to be strongly dependent on part geometry, thermal anisotropy, cure kinetics, and the autoclave temperature cure cycle. The cure simulation analysis is coupled to an incremental laminated plate theory model and a quasi-three-dimensional finite element analysis to study the complex relationships between gradients in temperature and degree of cure and process-induced stress and deformation unique to thick sections. Material models are developed to describe composite behavior during cure. Thermal expansion and cure shrinkage contribute to changes in material specific volume and represent important sources of internal loading included in the analysis. The effects of the autoclave temperature cure cycle, laminate thickness, resin shrinkage and laminate stacking sequence on the evolution of processing-induced stress and deformation are presented. Significant macroscopic stresses are shown to develop during the curing process of thick-section laminates. The results presented demonstrate that the mechanics and performance of thick-section thermosets are strongly dependent on processing history.

  2. In situ spectroscopic study of the plastic deformation of amorphous silicon under nonhydrostatic conditions induced by indentation

    NASA Astrophysics Data System (ADS)

    Gerbig, Y. B.; Michaels, C. A.; Bradby, J. E.; Haberl, B.; Cook, R. F.

    2015-12-01

    Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique. Quantitative analyses of the generated in situ Raman maps provide unique insight into the phase behavior of as-implanted a-Si. In particular, the occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were measured. The experimental results are linked with previously published papers on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a sequence for the development of deformation of a-Si under indentation loading. The sequence involves three distinct deformation mechanisms of a-Si: (1) reversible deformation, (2) increase in coordination defects (onset of plastic deformation), and (3) phase transformation. Estimated conditions for the occurrence of these mechanisms are given with respect to relevant intrinsic and extrinsic parameters, such as indentation stress, volumetric strain, and bond angle distribution (a measure for the structural order of the amorphous network). The induced volumetric strains are accommodated solely by reversible deformation of the tetrahedral network when exposed to small indentation stresses. At greater indentation stresses, the increased volumetric strains in the tetrahedral network lead to the formation of predominately fivefold coordination defects, which seems to mark the onset of irreversible or plastic deformation of the a-Si thin film. Further increase in the indentation stress appears to initiate the formation of sixfold coordinated atomic arrangements. These sixfold coordinated arrangements may maintain their amorphous tetrahedral structure with a high density of coordination defects or nucleate as a new crystalline

  3. In situ spectroscopic study of the plastic deformation of amorphous silicon under non-hydrostatic conditions induced by indentation

    PubMed Central

    Gerbig, Y.B; Michaels, C.A.; Bradby, J.E.; Haberl, B.; Cook, R.F.

    2016-01-01

    Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique. Quantitative analyses of the generated in situ Raman maps provide unique, new insight into the phase behavior of as-implanted a-Si. In particular, the occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were measured. The experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a sequence for the development of deformation of a-Si under indentation loading. The sequence involves three distinct deformation mechanisms of a-Si: (1) reversible deformation, (2) increase in coordination defects (onset of plastic deformation), and (3) phase transformation. Estimated conditions for the occurrence of these mechanisms are given with respect to relevant intrinsic and extrinsic parameters, such as indentation stress, volumetric strain, and bond angle distribution (a measure for the structural order of the amorphous network). The induced volumetric strains are accommodated solely by reversible deformation of the tetrahedral network when exposed to small indentation stresses. At greater indentation stresses, the increased volumetric strains in the tetrahedral network lead to the formation of predominately five-fold coordination defects, which seems to mark the onset of irreversible or plastic deformation of the a-Si thin film. Further increase in the indentation stress appears to initiate the formation of six-fold coordinated atomic arrangements. These six-fold coordinated arrangements may maintain their amorphous tetrahedral structure with a high density of coordination defects or nucleate as a new crystalline

  4. Grain boundary deformation-induced integranular stress corrosion cracking of nickel-chromium(16)-iron(9) in 360 degrees Celsius water

    NASA Astrophysics Data System (ADS)

    Alexandreanu, Bogdan

    The objective of this study was to determine whether grain boundary deformation plays a direct role in intergranular stress corrosion cracking of Ni-16Cr-9Fe in high temperature water. The difference in deformation and cracking behavior between special grain boundaries, or coincident site lattice boundaries (CLSB), and high angle boundaries (HAB) is exploited to determine if a cause-and-effect exists between grain boundary deformation and IGSCC. It was hypothesized that coincident site lattice boundaries (CSLBs) are less susceptible to deformation than general (random) high angle boundaries (HABs), and are, therefore, less susceptible to cracking. The hypothesis was substantiated by showing that (1) the dislocation absorption kinetics differs substantially between CSLBs and HABs, resulting in different susceptibilities to deformation, and (2) grain boundary deformation is a precursor to intergranular cracking. The difference in dislocation annihilation kinetics at CSLBs and HABs was determined by TEM on samples annealed at 360°C. Results showed that extrinsic grain boundary dislocations (EGBDs) are annihilated at HABs at a rate that is, on average, 3 times that at CSLBs, implying a grain boundary diffusion coefficient in CSLBs is 12 times lower than that in HABs. The expectation that a reduced EGBD absorption at CSLBs would lead to greater matrix hardening was investigated using nanohardness measurements. Results showed that the hardness in the vicinity of CSLBs is greater than near HABs, and the sample-average hardness increases with the fraction of CSLBs. The difference in deformation behavior was investigated by SEM examination of samples strained at 360°C in an inert environment. Following 10% plastic straining in 360°C Ar, 52% of the HABs and 15% of the CSLBs were found to display deformation. The relationship between grain boundary deformation and IGSCC was demonstrated by further exposing these samples to 5% strain in 360°C primary water. Resulting

  5. Dislocation pileup as a representation of strain accumulation on a strike-slip fault

    USGS Publications Warehouse

    Savage, J.C.

    2006-01-01

    The conventional model of strain accumulation on a vertical transform fault is a discrete screw dislocation in an elastic half-space with the Burgers vector of the dislocation increasing at the rate of relative plate motion. It would be more realistic to replace that discrete dislocation by a dislocation distribution, presumably a pileup in which the individual dislocations are in equilibrium. The length of the pileup depends upon the applied stress and the amount of slip that has occurred at depth. I argue here that the dislocation pileup (the transition on the fault from no slip to slip at the full plate rate) occupies a substantial portion of the lithosphere thickness. A discrete dislocation at an adjustable depth can reproduce the surface deformation profile predicted by a pileup so closely that it will be difficult to distinguish between the two models. The locking depth (dislocation depth) of that discrete dislocation approximation is substantially (???30%) larger than that (depth to top of the pileup) in the pileup model. Thus, in inverting surface deformation data using the discrete dislocation model, the locking depth in the model should not be interpreted as the true locking depth. Although dislocation pileup models should provide a good explanation of the surface deformation near the fault trace, that explanation may not be adequate at greater distances from the fault trace because approximating the expected horizontally distributed deformation at subcrustal depths by uniform slip concentrated on the fault is not justified.

  6. Quantification of Crack Interaction in Loading-Induced Rock Deformation Tests

    NASA Astrophysics Data System (ADS)

    Reyes-Montes, J. M.; Goodfellow, S. D.; Nasseri, M. H.; Young, R.

    2013-12-01

    The coalescence of microcracks into major fractures marks the onset of major damage in rock and induces significant changes in its geotechnical and sealing properties. The interaction between neighbouring fractures affects the deformation process leading to this major failure. This study presents the analysis of load-induced fracture using spatial and temporal patterns of recorded acoustic emission (AE) events to investigate the role of crack interaction during fracturing processes Two methods based on event separation are used to estimate correlation and interaction distances between events. The first method uses the spacing of sequential and non-sequential event pairs, thus, the distance bin where both distributions converge can be interpreted as an upper bound for the interaction distance of correlated events in each of the experiments. The second method compares the distribution of inter-event separation of recorded events with the distribution obtained for a random population of events, quantifying the divergence between both distributions and its variation with time. A positive deviation for a distance range including up to the interaction distance observed in the previous approach indicates spatial clustering and process dominated by interactive events. This deviation is used to quantify the degree of event interaction or degree of non-randomness (NR) during the process. Two load-stress induced fracturing tests, carried out at two different scales, are analysed in this study to investigate the role of crack interaction in the deformation and fracturing process. The first test registered a total of 15,198 AE events from a pillar created between two deposition holes at SKB's Aspö Pillar Stability Experiment. The results show a good correlation between maxima of NR and minima in b-value in the time period immediately preceding and during the development of the observed major damage in form of spalling. The result can be interpreted as an indication of spalling

  7. Chemopreventive activity of sesquiterpene lactones (SLs) from yacon against TPA-induced Raji cells deformation.

    PubMed

    Siriwan, D; Miyawaki, C; Miyamoto, T; Naruse, T; Okazaki, K; Tamura, H

    2011-05-15

    Yacon is a medicinal plant used as a traditional medicine by the natives in South America. In Japan, it becomes popular as a health food. Sesquiterpene Lactones (SLs) from yacon leaves were investigated and the active SLs such as enhydrin, uvedalin and sonchifolin, bearing alpha-methylene-gamma-lactone and epoxides as the active functional groups, were identified by 1H-6000 MHz-NMR. Chemopreventive and cytotoxic activities were determined using different primary screening methods. In this study, all tested SLs strongly inhibited TPA-induced deformed of Raji cells. The IC50 values of yacon SLs from anti-deforming assay were 0.04-0.4 microM. Interestingly, yacon SLs showed more potential of chemo preventive activity than both curcumin and parthenolide. However, the cytotoxicity on Raji cells was observed at high concentration of yacon SLs. The degree of anti-deformation was ranked in order: enhydrin >uvedalin >sonchifolin >parthenolide >curcumin. As according to structure-activity relationship, the high activities of enhydrin, uvedalin and sonchifolin may be due to the 2-methyl-2-butenoate and its epoxide moiety. PMID:22097098

  8. Shock-induced deformation features in terrestrial peridot and lunar dunite

    NASA Technical Reports Server (NTRS)

    Snee, L. W.; Ahrens, T. J.

    1975-01-01

    Single crystals of terrestrial olivine were experimentally shock-loaded along the 010 line to peak pressures 280, 330, and 440 kbar, and the resulting deformation features were compared to those in olivine from lunar dunite 72415. Recovered fragments were examined to determine the orientation of the planar fractures. With increasing pressure the percentage of pinacoids and prisms decreases, whereas the percentage of bipyramids increases. The complexity of the distribution of bipyramids also increases with increasing pressure. Other shock-induced deformation features, including varying degrees of recrystallization, are found to depend on pressure, as observed by others. Lunar dunite 72415 was examined and found to contain olivine with well-developed shock-deformation features. The relative proportion of pinacoid, prism, and bipyramid planar fractures measured for olivine from 72415 indicates that this rock appears to have undergone shock pressure in the range 330-440 kbar. If this dunite was brought to the surface of the moon as a result of excavation of an Imbrium event-sized impact crater, the shock-pressure range experienced by the sample and the results of cratering calculations suggest that it could have originated no deeper than 50-150 km.

  9. Evaluation of deformation-induced transformation and reversion processes of stainless steel by acoustic microscope

    NASA Astrophysics Data System (ADS)

    Kasuga, Yukio; Endo, Tomio; Miyasaka, Chiaki; Kasano, Hideaki

    1999-02-01

    Deformation-induced martensite and reversed austenite of a metastable austenitic stainless steel sheet were evaluated by a scanning acoustic microscope with frequencies 600MHz and 800 MHz. The sheet was elongated up to 40 percent at and below the room temperature to produce martensite, followed by annealing for reversion. First martensite content was measured by a Feritscope. Next using a complex V(z) curve, leaky Rayleigh wave velocity was measured. The deformed and annealed grain structure s were observed with the frequency 800MHz and compared with those by the optical microscope. Rayleigh wave velocity is dependent on the elongation and ambient temperature in elongation and the annealing temperature, which agrees well with the one by the Feritscope. Deformed grains are more clearly observed by the scanning acoustic microscope with 800MHz. The measured value of the velocity is compared with the theoretical one which can be calculated by Young's modulus, Poisson's ratio and the density. The measured Rayleigh wave velocity is well agreement with the theoretical one.

  10. Effect of strain rate and dislocation density on the twinning behavior in tantalum

    NASA Astrophysics Data System (ADS)

    Florando, Jeffrey N.; El-Dasher, Bassem S.; Chen, Changqiang; Swift, Damian C.; Barton, Nathan R.; McNaney, James M.; Ramesh, K. T.; Hemker, Kevin J.; Kumar, Mukul

    2016-04-01

    The conditions which affect twinning in tantalum have been investigated across a range of strain rates and initial dislocation densities. Tantalum samples were subjected to a range of strain rates, from 10-4/s to 103/s under uniaxial stress conditions, and under laser-induced shock-loading conditions. In this study, twinning was observed at 77K at strain rates from 1/s to 103/s, and during laser-induced shock experiments. The effect of the initial dislocation density, which was imparted by deforming the material to different amounts of pre-strain, was also studied, and it was shown that twinning is suppressed after a given amount of pre-strain, even as the global stress continues to increase. These results indicate that the conditions for twinning cannot be represented solely by a critical global stress value, but are also dependent on the evolution of the dislocation density. In addition, the analysis shows that if twinning is initiated, the nucleated twins may continue to grow as a function of strain, even as the dislocation density continues to increase.

  11. Radiation enhanced basal plane dislocation glide in GaN

    NASA Astrophysics Data System (ADS)

    Yakimov, Eugene B.; Vergeles, Pavel S.; Polyakov, Alexander Y.; Lee, In-Hwan; Pearton, Stephen J.

    2016-05-01

    A movement of basal plane segments of dislocations in GaN films grown by epitaxial lateral overgrowth under low energy electron beam irradiation (LEEBI) was studied by the electron beam induced current (EBIC) method. Only a small fraction of the basal plane dislocation segments were susceptible to irradiation and the movement was limited to relatively short distances. The effect is explained by the radiation enhanced dislocation glide (REDG) in the structure with strong pinning. A dislocation velocity under LEEBI with a beam current lower than 1 nA was estimated as about 10 nm/s. The results assuming the REDG for prismatic plane dislocations were presented.

  12. Screw dislocation-induced growth spirals as emissive exciton localization centers in Al-rich AlGaN/AlN quantum wells

    NASA Astrophysics Data System (ADS)

    Funato, Mitsuru; Banal, Ryan G.; Kawakami, Yoichi

    2015-11-01

    Screw dislocations in Al-rich AlGaN/AlN quantum wells cause growth spirals with an enhanced Ga incorporation, which create potential minima. Although screw dislocations and their surrounding potential minima suggest non-radiative recombination processes within growth spirals, in reality, screw dislocations are not major non-radiative sinks for carriers. Consequently, carriers localized within growth spirals recombine radiatively without being captured by non-radiative recombination centers, resulting in intense emissions from growth spirals.

  13. Screw dislocation-induced growth spirals as emissive exciton localization centers in Al-rich AlGaN/AlN quantum wells

    SciTech Connect

    Funato, Mitsuru Banal, Ryan G.; Kawakami, Yoichi

    2015-11-15

    Screw dislocations in Al-rich AlGaN/AlN quantum wells cause growth spirals with an enhanced Ga incorporation, which create potential minima. Although screw dislocations and their surrounding potential minima suggest non-radiative recombination processes within growth spirals, in reality, screw dislocations are not major non-radiative sinks for carriers. Consequently, carriers localized within growth spirals recombine radiatively without being captured by non-radiative recombination centers, resulting in intense emissions from growth spirals.

  14. A preliminary study on surface ground deformation near shallow foundation induced by strike-slip faulting

    NASA Astrophysics Data System (ADS)

    Wong, Pei-Syuan; Lin, Ming-Lang

    2016-04-01

    According to investigation of recent earthquakes, ground deformation and surface rupture are used to map the influenced range of the active fault. The zones of horizontal and vertical surface displacements and different features of surface rupture are investigated in the field, for example, the Greendale Fault 2010, MW 7.1 Canterbury earthquake. The buildings near the fault rotated and displaced vertically and horizontally due to the ground deformation. Besides, the propagation of fault trace detoured them because of the higher rigidity. Consequently, it's necessary to explore the ground deformation and mechanism of the foundation induced by strike-slip faulting for the safety issue. Based on previous study from scaled analogue model of strike-slip faulting, the ground deformation is controlled by material properties, depth of soil, and boundary condition. On the condition controlled, the model shows the features of ground deformation in the field. This study presents results from shear box experiment on small-scale soft clay models subjected to strike-slip faulting and placed shallow foundations on it in a 1-g environment. The quantifiable data including sequence of surface rupture, topography and the position of foundation are recorded with increasing faulting. From the result of the experiment, first en echelon R shears appeared. The R shears rotated to a more parallel angle to the trace and cracks pulled apart along them with increasing displacements. Then the P shears crossed the basement fault in the opposite direction appears and linked R shears. Lastly the central shear was Y shears. On the other hand, the development of wider zones of rupture, higher rising surface and larger the crack area on surface developed, with deeper depth of soil. With the depth of 1 cm and half-box displacement 1.2 cm, en echelon R shears appeared and the surface above the fault trace elevated to 1.15 mm (Dv), causing a 1.16 cm-wide zone of ground-surface rupture and deformation

  15. Dislocation Creep in Magnesium Calcite

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

    To investigate the effect of dissolved Mg on plastic deformation of calcite, we performed triaxial deformation experiments on synthetic calcite with varying amount of Mg content. Mixtures of powders of calcite and dolomite were isostatically hot pressed (HIP) at 850° C and 300 MPa confining pressure for different intervals (2 to 20hrs) resulting in homogeneous aggregates of high-magnesium calcite; Mg content varied from 0.07 to 0.17 mol%. Creep tests were performed at differential stresses from 20 to 160 MPa at 700 to 800° C. Grain sizes before and after deformation were determined from the images obtained from scanning electron microscope (SEM) and optical microscope. Grain sizes are in the range of 5 to 20 microns depending on the HIP time, and decrease with increasing magnesium content. Both BSE images and chemical analysis suggest that all dolomite are dissolved and the Mg distribution is homogeneous through the sample, after 2 hrs HIP. At stresses below 40 MPa, the samples deformed in diffusion region (Coble creep), as described previously by Herwegh. The strength decreases with increasing magnesium content, owing to the difference of grain size. At stresses above 80 MPa, the stress exponent is greater than 3, indicating an increased contribution of dislocation creep. The transition between diffusion to dislocation creep occurs at higher stresses for the samples with higher magnesium content and smaller grain size. Preliminary data suggests a slight increase in strength with increasing magnesium content, but more tests are needed to verify this effect. In a few samples, some strain weakening may have been evident. The activation energy in the transition region (at 80 MPa) is ˜200 KJ/mol with no dependence on magnesium content, agreeing with previous measurements of diffusion creep in natural and synthetic marbles.

  16. Intensification of deformation-induced diffusion processes of the dissolution of intermetallic compounds in iron-based alloys at cryogenic temperatures

    NASA Astrophysics Data System (ADS)

    Sagaradze, V. V.; Shabashov, V. A.; Kozlov, K. A.; Kataeva, N. V.; Zavalishin, V. A.; Afanas'ev, S. V.; Zamatovskii, A. E.; Litvinov, A. V.; Lyashkov, K. A.

    2015-10-01

    In an aging austenitic iron-based alloy (Fe-35.8Ni-2.6Ti), when the deformation temperature decreases from 573 to 203-77 K, a sharp intensification of anomalous processes of the dissolution of nanoparticles of the coherent γ'-Ni3Ti phase has been detected upon the interaction with dislocations. This is connected with the suppression (at cryogenic temperatures) of alternative diffusion processes of the precipitation of particles initiated by point defects.

  17. Theoretical investigations of compositional inhomogeneity around threading dislocations in III–nitride semiconductor alloys

    NASA Astrophysics Data System (ADS)

    Sakaguchi, Ryohei; Akiyama, Toru; Nakamura, Kohji; Ito, Tomonori

    2016-05-01

    The compositional inhomogeneity of group III elements around threading dislocations in III–nitride semiconductors are theoretically investigated using empirical interatomic potentials and Monte Carlo simulations. We find that the calculated atomic arrangements around threading dislocations in Al0.3Ga0.7N and In0.2Ga0.8N depend on the lattice strain around dislocation cores. Consequently, compositional inhomogeneity arises around edge dislocation cores to release the strain induced by dislocation cores. In contrast, the compositional inhomogeneity in screw dislocation is negligible owing to relatively small strain induced by dislocation cores compared with edge dislocation. These results indicate that the strain relief around dislocation cores is decisive in determining the atomic arrangements and resultant compositional inhomogeneity around threading dislocations in III–nitride semiconductor alloys.

  18. Advances in the theory of the Hall-Petch relation, dislocation pileups and dislocation sources

    NASA Astrophysics Data System (ADS)

    Friedman, Lawrence Henry

    Advances in the theory of dislocations are reported. The Hall-Petch relation is extended, and a continuum level simulation of curvilinear dislocations is developed and used to study the operation of Frank-Read sources. The Hall-Petch relation states that the yield stress, sigma y, or strength against plastic deformation of polycrystalline materials is enhanced by decreasing the grain diameter: sigma y = Kd--1/2 + sigma 0, with K and sigma0 constants. One explanation of this relation is that yielding results from stress concentrated by queues of dislocations known as pileups. The pileup theory of the Hall-Petch relation is extended in two ways. First, two important aspects of pileup formation are incorporated into the theory: the existence of a threshold stress for dislocation production and the necessity of a finite-sized dislocation-free region in which a dislocation source may operate. Using a continuum theory of dislocation pileups, a closed form expression is obtained for the dependence of yield stress on grain size and source characteristics. The continuum model agrees closely with the corresponding discrete dislocation model. Second, a scaling theory describing the strength of lamellar materials is developed. The Hall-Petch relation is found to result from the similarity between dislocation densities of pileups of different lengths and under different applied stresses. For multilayers, the scaling theory predicts sigma y = KΛ--a + sigma0, where Λ is the compositional wavelength of the multilayer and a is a material dependent exponent. The scaling theory is then enlarged to incorporate parameters important to the operation of dislocation sources. The simulation of curvilinear dislocations, based on linear isotropic elasticity theory, includes self stress and dislocation-dislocation interactions. The operation stress of a Frank-Read source is found as a function of source size. Additionally, the plastic strain produced by a continuously operating source was

  19. A preliminary investigation of dislocation cell structure formation in metals using continuum dislocation dynamics

    NASA Astrophysics Data System (ADS)

    Xia, S. X.; El-Azab, A.

    2015-08-01

    A continuum dislocation dynamics model capable of capturing the cellular arrangements of dislocations in deformed crystals is presented. A small strain formulation of the model is given, followed by sample results of stress-strain behaviour, dislocation density evolution, dislocation cell pattern, lattice rotation, and geometrically necessary dislocation density and strain energy density distributions. An important finding of the current work is that dislocations form patterns under all circumstances due to their long range interactions. It is found, however, that the famous cell structure pattern forms when cross slip is activated. It is also found that cells are 3D sub-regions surrounded by dislocations walls in all directions, and they form, disappear, and reappear as a result of the motion of cell walls and formation of new walls by cross slip. It is further found that the average cell size is connected with the applied resolved shear stress according to the similitude principle observed in related experiments. The importance of these results is briefly discussed in the context of recrystallization.

  20. Efficient Meshfree Large Deformation Simulation of Rainfall Induced Soil Slope Failure

    NASA Astrophysics Data System (ADS)

    Wang, Dongdong; Li, Ling

    2010-05-01

    An efficient Lagrangian Galerkin meshfree framework is presented for large deformation simulation of rainfall-induced soil slope failure. Detailed coupled soil-rainfall seepage equations are given for the proposed formulation. This nonlinear meshfree formulation is featured by the Lagrangian stabilized conforming nodal integration method where the low cost nature of nodal integration approach is kept and at the same time the numerical stability is maintained. The initiation and evolution of progressive failure in the soil slope is modeled by the coupled constitutive equations of isotropic damage and Drucker-Prager pressure-dependent plasticity. The gradient smoothing in the stabilized conforming integration also serves as a non-local regularization of material instability and consequently the present method is capable of effectively capture the shear band failure. The efficacy of the present method is demonstrated by simulating the rainfall-induced failure of two typical soil slopes.

  1. A Wireless Intracranial Brain Deformation Sensing System for Blast-Induced Traumatic Brain Injury

    PubMed Central

    Song, S.; Race, N. S.; Kim, A.; Zhang, T.; Shi, R.; Ziaie, B.

    2015-01-01

    Blast-induced traumatic brain injury (bTBI) has been linked to a multitude of delayed-onset neurodegenerative and neuropsychiatric disorders, but complete understanding of their pathogenesis remains elusive. To develop mechanistic relationships between bTBI and post-blast neurological sequelae, it is imperative to characterize the initiating traumatic mechanical events leading to eventual alterations of cell, tissue, and organ structure and function. This paper presents a wireless sensing system capable of monitoring the intracranial brain deformation in real-time during the event of a bTBI. The system consists of an implantable soft magnet and an external head-mounted magnetic sensor that is able to measure the field in three dimensions. The change in the relative position of the soft magnet WITH respect to the external sensor as the result of the blast wave induces changes in the magnetic field. The magnetic field data in turn is used to extract the temporal and spatial motion of the brain under the blast wave in real-time. The system has temporal and spatial resolutions of 5 μs and 10 μm. Following the characterization and validation of the sensor system, we measured brain deformations in a live rodent during a bTBI. PMID:26586273

  2. A Wireless Intracranial Brain Deformation Sensing System for Blast-Induced Traumatic Brain Injury.

    PubMed

    Song, S; Race, N S; Kim, A; Zhang, T; Shi, R; Ziaie, B

    2015-01-01

    Blast-induced traumatic brain injury (bTBI) has been linked to a multitude of delayed-onset neurodegenerative and neuropsychiatric disorders, but complete understanding of their pathogenesis remains elusive. To develop mechanistic relationships between bTBI and post-blast neurological sequelae, it is imperative to characterize the initiating traumatic mechanical events leading to eventual alterations of cell, tissue, and organ structure and function. This paper presents a wireless sensing system capable of monitoring the intracranial brain deformation in real-time during the event of a bTBI. The system consists of an implantable soft magnet and an external head-mounted magnetic sensor that is able to measure the field in three dimensions. The change in the relative position of the soft magnet WITH respect to the external sensor as the result of the blast wave induces changes in the magnetic field. The magnetic field data in turn is used to extract the temporal and spatial motion of the brain under the blast wave in real-time. The system has temporal and spatial resolutions of 5 μs and 10 μm. Following the characterization and validation of the sensor system, we measured brain deformations in a live rodent during a bTBI. PMID:26586273

  3. Magneto-induced large deformation and high-damping performance of a magnetorheological plastomer

    NASA Astrophysics Data System (ADS)

    Liu, Taixiang; Gong, Xinglong; Xu, Yangguang; Pang, Haoming; Xuan, Shouhu

    2014-10-01

    A magnetorheological plastomer (MRP) is a new kind of soft magneto-sensitive polymeric composite. This work reports on the large magneto-deforming effect and high magneto-damping performance of MRPs under a quasi-statical shearing condition. We demonstrate that an MRP possesses a magnetically sensitive malleability, and its magneto-mechanical behavior can be analytically described by the magneto-enhanced Bingham fluid-like model. The magneto-induced axial stress, which drives the deformation of the MRP with 70 wt % carbonyl iron powder, can be tuned in a large range from nearly 0.0 kPa to 55.4 kPa by an external 662.6 kA m-1 magnetic field. The damping performance of an MRP has a significant correlation with the magnetic strength, shear rate, carbonyl iron content and shear strain amplitude. For an MRP with 60 wt % carbonyl iron powder, the relative magneto-enhanced damping effect can reach as high as 716.2% under a quasi-statically shearing condition. Furthermore, the related physical mechanism is proposed, and we reveal that the magneto-induced, particle-assembled microstructure directs the magneto-mechanical behavior of the MRP.

  4. Understanding the microscopic processes that govern the charge-induced deformation of carbon nanotubes

    NASA Astrophysics Data System (ADS)

    Pastewka, Lars; Koskinen, Pekka; Elsässer, Christian; Moseler, Michael

    2009-10-01

    While carbon nanotubes have technological potential as actuators, the underlying actuation mechanisms remain poorly understood. We calculate charge-induced stresses and strains for electrochemical actuation of carbon nanotubes with different chiralities and defects, using density-functional theory and various tight-binding models. For a given deformation mode the concept of bonding and antibonding orbitals can be redefined depending on the sign of a differential band-structure stress. We use this theoretical framework to analyze orbital contributions to the actuation. These show charge asymmetric behavior which is due to next-nearest-neighbor hopping while Coulombic contributions account for approximately charge-symmetric isotropic deformations. In the typical case of a (10,10) tube strains around 0.1% with 1 nN force along the tube axis are obtained. Defects and functional groups have negligible influence on the actuation. In multiwall tubes we find charge inversion on the inner tubes due to Friedel-type oscillations which could lead to a slight magnification of charge-induced strains. Finally, we consider photoactuation of nanotubes and predict that transitions between van-Hove singularities can be expected to expand the tubes.

  5. Modeling deformation-induced fluid flow in cortical bone's canalicular-lacunar system.

    PubMed

    Gururaja, S; Kim, H J; Swan, C C; Brand, R A; Lakes, R S

    2005-01-01

    To explore the potential role that load-induced fluid flow plays as a mechano-transduction mechanism in bone adaptation, a lacunar-canalicular scale bone poroelasticity model is developed and implemented. The model uses micromechanics to homogenize the pericanalicular bone matrix, a system of straight circular cylinders in the bone matrix through which bone fluids can flow, as a locally anisotropic poroelastic medium. In this work, a simplified two-dimensional model of a periodic array of lacunae and their surrounding systems of canaliculi is used to quantify local fluid flow characteristics in the vicinity of a single lacuna. When the cortical bone model is loaded, microscale stress, and strain concentrations occur in the vicinity of individual lacunae and give rise to microscale spatial variations in the pore fluid pressure field. Furthermore, loading of the bone matrix containing canaliculi generates fluid pressures in the contained fluids. Consequently, loading of cortical bone induces fluid flow in the canaliculi and exchange of fluid between canaliculi and lacunae. For realistic bone morphology parameters, and a range of loading frequencies, fluid pressures and fluid-solid drag forces in the canalicular bone are computed and the associated energy dissipation in the models compared to that measured in physical in vitro experiments on human cortical bone. The proposed model indicates that deformation-induced fluid pressures in the lacunar-canalicular system have relaxation times on the order of milliseconds as opposed to the much shorter times (hundredths of milliseconds) associated with deformation-induced pressures in the Haversian system. PMID:15709702

  6. Understanding dislocation mechanics at the mesoscale using phase field dislocation dynamics.

    PubMed

    Beyerlein, I J; Hunter, A

    2016-04-28

    In this paper, we discuss the formulation, recent developments and findings obtained from a mesoscale mechanics technique called phase field dislocation dynamics (PFDD). We begin by presenting recent advancements made in modelling face-centred cubic materials, such as integration with atomic-scale simulations to account for partial dislocations. We discuss calculations that help in understanding grain size effects on transitions from full to partial dislocation-mediated slip behaviour and deformation twinning. Finally, we present recent extensions of the PFDD framework to alternative crystal structures, such as body-centred cubic metals, and two-phase materials, including free surfaces, voids and bi-metallic crystals. With several examples we demonstrate that the PFDD model is a powerful and versatile method that can bridge the length and time scales between atomistic and continuum-scale methods, providing a much needed understanding of deformation mechanisms in the mesoscale regime. PMID:27002063

  7. Dislocation Formation in Alloys

    NASA Astrophysics Data System (ADS)

    Minami, Akihiko; Onuki, Akira

    2006-05-01

    An interaction between dislocations and phase transitions is studied by a phase field model both in two and three dimensional systems. Our theory is a simple extension of the traditional linear elastic theory, and the elastic energy is a periodic function of local strains which is reflecting the periodicity of crystals. We find that the dislocations are spontaneously formed by quenching. Dislocations are formed from the interface of binary alloys, and slips are preferentially gliding into the soft metals. In three dimensional systems, formation of dislocations under applied strain is studied in two phase state. We find that the dislocation loops are created from the surface of hard metals. We also studied the phase separation above the coexisting temperature which is called as the Cottrell atmosphere. Clouds of metals cannot catch up with the motion of dislocations at highly strained state.

  8. Dislocation dynamics of web type silicon ribbon

    NASA Technical Reports Server (NTRS)

    Dillon, O. W., Jr.; Tsai, C. T.; De Angelis, R. J.

    1987-01-01

    Silicon ribbon grown by the dendritic web process passes through a rapidly changing thermal profile in the growth direction. This rapidly changing profile induces stresses which produce changes in the dislocation density in the ribbon. A viscoplastic material response function (Haasen-Sumino model) is used herein to calculate the stresses and the dislocation density at each point in the silicon ribbon. The residual stresses are also calculated.

  9. Do normal hips dislocate?

    PubMed

    Alshameeri, Zeiad; Rehm, Andreas

    2014-11-01

    There have been a small number of case reports describing late normal-hip dislocations in children who were later diagnosed with developmental dysplasia of the hip. Here, we contest the assumption that normal hips can dislocate. We argue that (as in our case) the ultrasound scans in all published case reports on late dislocated normal hips did not show results that were entirely normal and therefore, so far, there has been no convincing evidence of a dislocation of a normal hip. We also want to highlight the importance of meticulous ultrasound and clinical assessments of high-risk children by an experienced orthopaedic surgeon. PMID:25144883

  10. Formation of helical dislocations in ammonothermal GaN substrate by heat treatment

    NASA Astrophysics Data System (ADS)

    Horibuchi, Kayo; Yamaguchi, Satoshi; Kimoto, Yasuji; Nishikawa, Koichi; Kachi, Tetsu

    2016-03-01

    GaN substrate produced by the basic ammonothermal method and an epitaxial layer on the substrate was evaluated using synchrotron radiation x-ray topography and transmission electron microscopy. We revealed that the threading dislocations present in the GaN substrate are deformed into helical dislocations and the generation of the voids by heat treatment in the substrate for the first observation in the GaN crystal. These phenomena are formed by the interactions between the dislocations and vacancies. The helical dislocation was formed in the substrate region, and not in the epitaxial layer region. Furthermore, the evaluation of the influence of the dislocations on the leakage current of Schottky barrier diodes fabricated on the epitaxial layer is discussed. The dislocations did not affect the leakage current characteristics of the epitaxial layer. Our results suggest that the deformation of dislocations in the GaN substrate does not adversely affect the epitaxial layer.

  11. Deformation mechanisms in gold nanowires and nanoporous gold

    NASA Astrophysics Data System (ADS)

    Dou, R.; Derby, B.

    2011-03-01

    We present a study of the deformation 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 deformation. Nanoporous specimens show deformation 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 deformed in bending. This is shown to be consistent with a strain gradient plasticity model for the deformation of nanoporous gold, with the strain gradient accommodated by geometrically necessary twins and partial dislocations.

  12. Longitudinal and transverse deformation of human Achilles tendon induced by isometric plantar flexion at different intensities.

    PubMed

    Iwanuma, Soichiro; Akagi, Ryota; Kurihara, Toshiyuki; Ikegawa, Shigeki; Kanehisa, Hiroaki; Fukunaga, Tetsuo; Kawakami, Yasuo

    2011-06-01

    The present study determined in vivo deformation of the entire Achilles tendon in the longitudinal and transverse directions during isometric plantar flexions. Twelve young women and men performed isometric plantar flexions at 0% (rest), 30%, and 60% of the maximal voluntary contraction (MVC) while a series of oblique longitudinal and cross-sectional magnetic resonance (MR) images of the Achilles tendon were taken. At the distal end of the soleus muscle belly, the Achilles tendon was divided into the aponeurotic (ATapo) and the tendinous (ATten) components. The length of each component was measured in the MR images. The widths of the Achilles tendon were determined at 10 regions along ATapo and at four regions along ATten. Longitudinal and transverse strains were calculated as changes in relative length and width compared with those at rest. The ATapo deformed in both longitudinal and transverse directions at 30%MVC and 60%MVC. There was no difference between the strains of the ATapo at 30%MVC and 60%MVC either in the longitudinal (1.1 and 1.6%) or transverse (5.0∼11.4 and 5.0∼13.9%) direction. The ATten was elongated longitudinally (3.3%) to a greater amount than ATapo, while narrowing transversely in the most distal region (-4.6%). The current results show that the magnitude and the direction of contraction-induced deformation of Achilles tendon are different for the proximal and distal components. This may be related to the different functions of Achilles tendon, i.e., force transmission or elastic energy storage during muscle contractions. PMID:21415176

  13. Metallurgy: Starting and stopping dislocations

    NASA Astrophysics Data System (ADS)

    Minor, Andrew M.

    2015-09-01

    A comparison of dislocation dynamics in two hexagonal close-packed metals has revealed that dislocation movement can vary substantially in materials with the same crystal structure, associated with how the dislocations relax when stationary.

  14. Dislocation gliding and cross-hatch morphology formation in AIII-BV epitaxial heterostructures

    SciTech Connect

    Kovalskiy, V. A. Vergeles, P. S.; Eremenko, V. G.; Fokin, D. A.

    2014-12-08

    An approach for understanding the origin of cross-hatch pattern (CHP) on the surface of lattice mismatched GaMnAs/InGaAs samples grown on GaAs (001) substrates is developed. It is argued that the motion of threading dislocations in the (111) slip planes during the relaxation of InGaAs buffer layer is more complicated process and its features are similar to the ones of dislocation half-loops gliding in plastically deformed crystals. The heterostructures were characterized by atomic force microscopy and electron beam induced current (EBIC). Detailed EBIC experiments revealed contrast features, which cannot be accounted for by the electrical activity of misfit dislocations at the buffer/substrate interface. We attribute these features to specific extended defects (EDs) generated by moving threading dislocations in the partially relaxed InGaAs layers. We believe that the core topology, surface reconstruction, and elastic strains from these EDs accommodated in slip planes play an important role in the CHP formation. The study of such electrically active EDs will allow further understanding of degradation and changes in characteristics of quantum devices based on strained heterostructures.

  15. Dislocation gliding and cross-hatch morphology formation in AIII-BV epitaxial heterostructures

    NASA Astrophysics Data System (ADS)

    Kovalskiy, V. A.; Vergeles, P. S.; Eremenko, V. G.; Fokin, D. A.; Dorokhin, M. V.; Danilov, Yu. A.; Zvonkov, B. N.

    2014-12-01

    An approach for understanding the origin of cross-hatch pattern (CHP) on the surface of lattice mismatched GaMnAs/InGaAs samples grown on GaAs (001) substrates is developed. It is argued that the motion of threading dislocations in the {111} slip planes during the relaxation of InGaAs buffer layer is more complicated process and its features are similar to the ones of dislocation half-loops gliding in plastically deformed crystals. The heterostructures were characterized by atomic force microscopy and electron beam induced current (EBIC). Detailed EBIC experiments revealed contrast features, which cannot be accounted for by the electrical activity of misfit dislocations at the buffer/substrate interface. We attribute these features to specific extended defects (EDs) generated by moving threading dislocations in the partially relaxed InGaAs layers. We believe that the core topology, surface reconstruction, and elastic strains from these EDs accommodated in slip planes play an important role in the CHP formation. The study of such electrically active EDs will allow further understanding of degradation and changes in characteristics of quantum devices based on strained heterostructures.

  16. Deformation mechanisms of Cu nanowires with planar defects

    SciTech Connect

    Tian, Xia Yang, Haixia; Wan, Rui; Cui, Junzhi; Yu, Xingang

    2015-01-21

    Molecular dynamics simulations are used to investigate the mechanical 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 deformation and fracture mechanisms 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 deformation, giving rise to a fracture process resembling the samples without stacking fault.

  17. Indentation-induced localized deformation and elastic strain partitioning in composites at submicron length scale

    SciTech Connect

    Barabash, R.I.; Bei, H.; Gao, Y.F.; Ice, G.E.

    2010-10-26

    Three-dimensional spatially resolved strains were mapped in a model NiAl/Mo composite after nanoindentation. The depth-dependent strain distributed in the two phases and partitioned across the composite interfaces is directly measured at submicron length scale using X-ray microdiffraction and compared with a detailed micromechanical stress analysis. It is shown that indentation-induced deformation in the composite material is distinct from deformation expected in a single-phase material. This difference arises in part from residual thermal strains in both phases of the composite in the as-grown state. Interplay between residual thermal strains and external mechanical strain results in a complex distribution of dilatational strain in the Mo fibers and NiAl matrix and is distinct in different locations within the indented area. Reversal of the strain sign (e.g., alternating tensile/compressive/tensile strain distribution) is observed in the NiAl matrix. Bending of the Mo fibers during indentation creates relatively large 1.5{sup o} misorientations between the different fibers and NiAl matrix. Compressive strain along the <0 0 1> direction reached -0.017 in the Mo fibers and -0.007 in the NiAl matrix.

  18. Dislocation-stacking fault tetrahedron interaction: what can we learn from atomic scale modelling.

    SciTech Connect

    Osetskiy, Yury N; Stoller, Roger E; Matsukawa, Yoshitaka

    2004-01-01

    The high number density of stacking fault tetrahedra (SFTs) observed in irradiated fcc metals suggests that they should contribute to radiation-induced hardening and, therefore, taken into account when estimating mechanical properties changes of irradiated materials. The central issue is describing the individual interaction between a moving dislocation and an SFT, which is characterized by a very fine size scale, {approx}100 nm. This scale is amenable to both in situ TEM experiments and large-scale atomic modelling. In this paper we present results of an atomistic simulation of dislocation-SFT interactions using molecular dynamics (MD). The results are compared with observations from in situ deformation experiments. It is demonstrated that in some cases the simulations and experimental observations are quite similar, suggesting a reasonable interpretation of experimental observations.

  19. Dislocation in Spoken French.

    ERIC Educational Resources Information Center

    Calve, Pierre

    1985-01-01

    Discusses dislocation, a construction in which one element, usually a noun, is isolated either at the beginning or at the end of a sentence while being represented in the body of the sentence by a pronoun. Discusses the place of dislocation in linguistic studies and its pedagogical implications. (SED)

  20. Dislocations in yttrium orthovanadate

    NASA Astrophysics Data System (ADS)

    Eakins, D. E.; LeBret, J. B.; Norton, M. G.; Bahr, D. F.

    2004-06-01

    Dislocation structures in single crystals of yttrium orthovanadate have been identified by transmission electron microscopy. Electron diffraction was used to predict possible Burgers vectors for the dislocations. Results suggest vectors of the type {1}/{2}[1 1 1] or {1}/{4}[0 2 1] . Arguments for the likelihood of each possible vector have been presented.

  1. Nonconvex energy minimization and dislocation structures in ductile single crystals

    NASA Astrophysics Data System (ADS)

    Ortiz, M.; Repetto, E. a.

    1999-02-01

    Plastically deformed crystals are often observed to develop intricate dislocation patterns such as the labyrinth, mosaic, fence and carpet structures. In this paper, such dislocation structures are given an energetic interpretation with the aid of direct methods of the calculus of variations. We formulate the theory in terms of deformation fields and regard the dislocations as manifestations of the incompatibility of the plastic deformation gradient field. Within this framework, we show that the incremental displacements of inelastic solids follow as minimizers of a suitably defined pseudoelastic energy function. In crystals exhibiting latent hardening, the energy function is nonconvex and has wells corresponding to single-slip deformations. This favors microstructures consisting locally of single slip. Deformation microstructures constructed in accordance with this prescription are shown to be in correspondence with several commonly observed dislocation structures. Finally, we show that a characteristic length scale can be built into the theory by taking into account the self energy of the dislocations. The extended theory leads to scaling laws which appear to be in good qualitative and quantitative agreement with observation.

  2. THEORETICAL INVESTIGATION OF MICROSTRUCTURE EVOLUTION AND DEFORMATION OF ZIRCONIUM UNDER CASCADE DAMAGE CONDITIONS

    SciTech Connect

    Barashev, Alexander V; Golubov, Stanislav I; Stoller, Roger E

    2012-06-01

    This work is based on our reaction-diffusion model of radiation growth of Zr-based materials proposed recently in [1]. In [1], the equations for the strain rates in unloaded pure crystal under cascade damage conditions of, e.g., neutron or heavy-ion irradiation were derived as functions of dislocation densities, which include contributions from dislocation loops, and spatial distribution of their Burgers vectors. The model takes into account the intra-cascade clustering of self-interstitial atoms and their one-dimensional diffusion; explains the growth stages, including the break-away growth of pre-annealed samples; and accounts for some striking observations, such as of negative strain in prismatic direction, and co-existence of vacancy- and interstitial-type prismatic loops. In this report, the change of dislocation densities due to accumulation of sessile dislocation loops is taken into account explicitly to investigate the dose dependence of radiation growth. The dose dependence of climb rates of dislocations is calculated, which is important for the climb-induced glide model of radiation creep. The results of fitting the model to available experimental data and some numerical calculations of the strain behavior of Zr for different initial dislocation structures are presented and discussed. The computer code RIMD-ZR.V1 (Radiation Induced Microstructure and Deformation of Zr) developed is described and attached to this report.

  3. Role of interfacial dislocations on creep of a fully lamellar tial

    SciTech Connect

    Hsiung, L M; Nieh, T G

    1999-08-16

    Deformation mechanisms of a fully lamellar TiAl ({gamma} lamellae: 100 {approximately} 300 nm thick, {alpha}{sub 2} lamellae: 10 {approximately} 50 nm thick) crept at 760 C have been investigated. It was found that, as a result of a fine structure, the motion and multiplication of dislocations within both {gamma} and {alpha}{sub 2} lamellae are limited at low creep stresses (< 400 MPa). Thus, the glide and climb of lattice dislocations have insignificant contribution to creep deformation. In contrast, the motion of interfacial dislocations on {gamma}{alpha}{sub 2} and {gamma}{gamma} interfaces (i.e. interface sliding) dominates the deformation at low stresses. The major obstacles impeding the motion of interfacial dislocations was found to be lattice dislocations impinging on lamellar interfaces. The number of impinging lattice dislocations increases as the applied stress increases and, subsequently, causes the pileup of interfacial dislocations on the interfaces. The pileup further leads to the formation of deformation twins. Deformation twinning activated by the pileup of interfacial dislocations is suggested to be the dominant deformation mechanism at high stresses (> 400 MPa).

  4. Analysis of thermal cycle-induced dislocation reduction in HgCdTe/CdTe/Si(211) by scanning transmission electron microscopy

    NASA Astrophysics Data System (ADS)

    Jacobs, R. N.; Benson, J. D.; Stoltz, A. J.; Almeida, L. A.; Farrell, S.; Brill, G.; Salmon, M.; Newell, A.

    2013-03-01

    High threading dislocation densities limit the operability of infrared focal plane arrays based on large lattice-mismatched heterostructures such as HgCdTe/CdTe/Si. Recently it has been shown that post-growth thermal cycle annealing can routinely reduce the surface etch pit density from >5×106 cm-2 to as low as 9×105 cm-2. To fully exploit the procedure, a deeper understanding of the inherent dislocation dynamics is needed. In this work, we employ scanning transmission electron microscopy to analyze cross-sectional samples of HgCdTe/CdTe/Si prepared using site-specific focused ion beam milling. A key factor in this work is the use of defect decorated samples, which has allowed for a correlation of surface etch pits to dislocation segments observed in cross-section images. We have observed that the previously reported oval-shaped etch pits are likely associated with Shockley partial type dislocations, and that triangular etch pits are associated with perfect dislocations. This suggests the likelihood that interaction between mobile Shockley partial and other dislocation types are responsible in part for the observed reduction in top surface etch pit density. These studies provide a deeper understanding of dislocation reduction processes which are critical for the realization of high performance infrared detectors based on low-cost, lattice-mismatched substrates.

  5. In situ spectroscopic study of the plastic deformation of amorphous silicon under nonhydrostatic conditions induced by indentation

    SciTech Connect

    Gerbig, Yvonne B.; Michaels, C. A.; Bradby, Jodie E.; Haberl, Bianca; Cook, Robert F.

    2015-12-17

    Indentation-induced plastic deformation of amorphous silicon (a-Si) thin films was studied by in situ Raman imaging of the deformed contact region of an indented sample, employing a Raman spectroscopy-enhanced instrumented indentation technique (IIT). The occurrence and evolving spatial distribution of changes in the a-Si structure caused by processes, such as polyamorphization and crystallization, induced by indentation loading were observed. Furthermore, the obtained experimental results are linked with previously published work on the plastic deformation of a-Si under hydrostatic compression and shear deformation to establish a model for the deformation behavior of a-Si under indentation loading.

  6. Electromechanical simulations of dislocations

    NASA Astrophysics Data System (ADS)

    Skiba, Oxana; Gracie, Robert; Potapenko, Stanislav

    2013-04-01

    Improving the reliability of micro-electronic devices depends in part on developing a more in-depth understanding of dislocations because dislocations are barriers to charge carriers. To this end, the quasi-static simulation of discrete dislocations dynamics in materials under mechanical and electrical loads is presented. The simulations are based on the extended finite element method, where dislocations are modelled as internal discontinuities. The strong and weak forms of the boundary value problem for the coupled system are presented. The computation of the Peach-Koehler force using the J-integral is discussed. Examples to illustrate the accuracy of the simulations are presented. The motion of the network of the dislocations under different electrical and mechanical loads is simulated. It was shown that even in weak piezoelectric materials the effect of the electric field on plastic behaviour is significant.

  7. Electronic properties of dislocations

    NASA Astrophysics Data System (ADS)

    Reiche, M.; Kittler, M.; Uebensee, H.; Pippel, E.; Haehnel, A.; Birner, S.

    2016-04-01

    Dislocations exhibit a number of exceptional electronic properties resulting in a significant increase in the drain current of MOSFETs if defined numbers of these defects are placed in the channel. Measurements on individual dislocations in Si refer to a supermetallic conductivity. A model of the electronic structure of dislocations is proposed based on experimental measurements and tight-binding simulations. It is shown that the high strain level on the dislocation core—exceeding 10 % or more—causes locally dramatic changes in the band structure and results in the formation of a quantum well along the dislocation line. This explains experimental findings (two-dimensional electron gas, single-electron transitions). The energy quantization within the quantum well is most important for supermetallic conductivity.

  8. Rotating Rig Development for Droplet Deformation/Breakup and Impact Induced by Aerodynamic Surfaces

    NASA Technical Reports Server (NTRS)

    Feo, A.; Vargas, M.; Sor, A.

    2012-01-01

    This work presents the development of a Rotating Rig Facility by the Instituto Nacional de Tecnica Aeroespacial (INTA) in cooperation with the NASA Glenn Research Center. The facility is located at the INTA installations near Madrid, Spain. It has been designed to study the deformation, breakup and impact of large droplets induced by aerodynamic bodies. The importance of these physical phenomena is related to the effects of Supercooled Large Droplets in icing clouds on the impinging efficiency of the droplets on the body, that may change should these phenomena not be taken into account. The important variables and the similarity parameters that enter in this problem are presented. The facility's components are described and some possible set-ups are explained. Application examples from past experiments are presented in order to indicate the capabilities of the new facility.

  9. Poroelastic theory applied to the adsorption-induced deformation of vitreous silica.

    PubMed

    Coasne, Benoit; Weigel, Coralie; Polian, Alain; Kint, Mathieu; Rouquette, Jérome; Haines, Julien; Foret, Marie; Vacher, René; Rufflé, Benoit

    2014-12-11

    When vitreous silica is submitted to high pressures under a helium atmosphere, the change in volume observed is much smaller than expected from its elastic properties. It results from helium penetration into the interstitial free volume of the glass network. We present here the results of concurrent spectroscopic experiments using either helium or neon and molecular simulations relating the amount of gas adsorbed to the strain of the network. We show that a generalized poromechanical approach, describing the elastic properties of microporous materials upon adsorption, can be applied successfully to silica glass in which the free volume exists only at the subnanometer scale. In that picture, the adsorption-induced deformation accounts for the small apparent compressibility of silica observed in experiments. PMID:25383694

  10. Infrared-Laser-Induced Thermocapillary Deformation and Destabilization of Thin Liquid Films on Moving Substrates

    NASA Astrophysics Data System (ADS)

    Wedershoven, H. M. J. M.; Berendsen, C. W. J.; Zeegers, J. C. H.; Darhuber, A. A.

    2015-02-01

    We study the thermocapillary deformation, induced by infrared laser irradiation, of thin liquid films on moving substrates. We develop numerical models for the temperature distribution and film thickness evolution. Steady-state film thickness profiles are measured for different values of substrate speed and laser power. The experimental results compare well with the simulations. In the case of partially wettable substrates, the thin liquid films tend to become unstable. We find that, for certain ranges of the laser power and substrate speed, the film ruptures in a single location and subsequently dewets without the occurrence of residual droplets. Such "clean" dewetting is highly desirable in the context of immersion lithography or solution processing of organic electronic devices.

  11. Ritually induced growth disturbances and deformities of the orofacial system--a contribution to cranial morphogenesis.

    PubMed

    Dietze, S; Winkelmann, D; Garve, R; Blens, T; Fanghänel, J; Proff, P; Gedrange, T; Maile, S

    2007-01-01

    Numerous ritual acts involving the skull result in orofacial changes. The present study focuses on ritual acts of Brazilian Zoé Indians. A distinct deformation effect of the ritual act (wearing a lip-plug) on the morphology of the orofacial system is demonstrated and documented using jaw models. The studies show that the lip-plug significantly influences tooth position and jaw growth. While the maxilla displays palatal displacement of the lateral incisors and elevation of the palate, retraction occurs in the mandible depending upon plug size. Additionally, both the plug and the nutritional habits of the Indians induce marked abrasion of all teeth. Moreover, it is shown that the duration of lip-plug wear is an essential determinant of sustained orofacial changes. PMID:17534041

  12. Fine Tuning of Chlorophyll Spectra by Protein-Induced Ring Deformation.

    PubMed

    Bednarczyk, Dominika; Dym, Orly; Prabahar, Vadivel; Peleg, Yoav; Pike, Douglas H; Noy, Dror

    2016-06-01

    The ability to tune the light-absorption properties of chlorophylls by their protein environment is the key to the robustness and high efficiency of photosynthetic light-harvesting proteins. Unfortunately, the intricacy of the natural complexes makes it very difficult to identify and isolate specific protein-pigment interactions that underlie the spectral-tuning mechanisms. Herein we identify and demonstrate the tuning mechanism of chlorophyll spectra in type II water-soluble chlorophyll binding proteins from Brassicaceae (WSCPs). By comparing the molecular structures of two natural WSCPs we correlate a shift in the chlorophyll red absorption band with deformation of its tetrapyrrole macrocycle that is induced by changing the position of a nearby tryptophan residue. We show by a set of reciprocal point mutations that this change accounts for up to 2/3 of the observed spectral shift between the two natural variants. PMID:27098554

  13. Measurement and compensation of laser-induced wavefront deformations and focal shifts in near IR optics.

    PubMed

    Stubenvoll, Martin; Schäfer, Bernd; Mann, Klaus

    2014-10-20

    We demonstrate the feasibility of passive compensation of the thermal lens effect in fused silica optics, placing suitable optical materials with negative dn/dT in the beam path of a high power near IR fiber laser. Following a brief overview of the involved mechanisms, photo-thermal absorption measurements with a Hartmann-Shack sensor are described, from which coefficients for surface/coating and bulk absorption in various materials are determined. Based on comprehensive knowledge of the 2D wavefront deformations resulting from absorption, passive compensation of thermally induced aberrations in complex optical systems is possible, as illustrated for an F-Theta objective. By means of caustic measurements during high-power operation we are able to demonstrate a 60% reduction of the focal shift in F-Theta lenses through passive compensation. PMID:25401572

  14. Is the fracto-mechanoluminescence of ZnS:Mn phosphor dominated by charged dislocation mechanism or piezoelectrification mechanism?

    PubMed

    Chandra, B P; Chandra, V K; Jha, Piyush; Pateria, Deepti; Baghel, R N

    2016-02-01

    Mathematical approaches made for both the charged dislocation model and piezoelectrically induced electron bombardment model of fracto-mechanoluminescence (FML), the luminescence induced by fracture of solids, in ZnS:Mn phosphor indicate that the piezoelectrically induced electron bombardment model provides a dominating process for the FML of ZnS phosphors. The concentration of 3000 ppm Mn(2+) is optimal for ML intensity of ZnS:Mn phosphor. The decay time of ML gives the relaxation time of the piston used to deform the sample and the time tm of maximum of ML is controlled by both the relaxation time of the piston and decay time of charges on the newly created surfaces of crystals. As the product of the velocity of dislocations and pinning time of dislocations gives the mean free path of a moving dislocation. Both factors play an important role in the ML excitation of impurity doped II-VI semiconductors. The linear increase of total ML intensity IT with the impact velocity indicates that the damage increases linearly with impact velocity of the load. Thus, the ML measurement can be used remotely to monitor the real-time damage in the structures, and therefore, the ML of ZnS:Mn phosphor has also the potential for a structural health monitoring system. PMID:25991045

  15. Strange behavior of dislocations of a certain type: Self-locking

    NASA Astrophysics Data System (ADS)

    Greenberg, B. A.; Ivanov, M. A.

    2016-04-01

    The results of studying the self-locking of dislocations, namely, the transformation of glissile dislocations into blocked dislocations in the absence of an applied stress, are generalized. The existence of selflocking is theoretically grounded and experimentally proved via the observation of dislocation extension along a preferred direction upon loading-free heating after preliminary plastic deformation. The following concept is developed to explain the experimental results: an effective force appears in the case of a two-valley dislocation potential relief; it is proportional to the difference between the valley depths and causes the transformation of a dislocation into an indestructible barrier. The temperature anomaly of yield strength and the dislocation self-locking are shown to have the same nature—a two-valley dislocation potential relief. Both effects were observed in Ni3Al- and TiAl-type intermetallics and a pure metal (magnesium).

  16. Basics of luminescent diagnostics of the dislocation structure of SiC crystals

    NASA Astrophysics Data System (ADS)

    Gorban, Ivan S.; Mishinova, Galina N.

    1998-04-01

    The result of the studies of dislocation luminescence in SiC crystals are presented in the report. This semiconductor forms great number of polytypes which differs by periodical alternation of cubic and hexagonal layers in basic planes. High probability of periodic pack infringement caused by very little energy of stacking fault leads to variation of dislocation structures in different glide planes of this crystals. Shockly and Frank partial dislocations are sufficiently important. The dislocation luminescence as growth origin so as dislocations included in result of plastic deformation or high temperature annealing. In this case the spectra of dislocation luminescence are the indicators of processes of phase transitions. The influence of impurities on the dislocation luminescence centers is investigated. The models of structure of dislocation centers and the mechanism of radiative transitions are proposed.

  17. Direct nanoimprinting of single crystalline gold: Experiments and dislocation dynamics simulations

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Zhang, Y.; Mara, N. A.; Lou, J.; Nicola, L.

    2014-01-01

    This paper addresses the feasibility of direct nanoimprinting and highlights the challenges involved in this technique. Our study focuses on experimental work supported by dislocation dynamics simulations. A gold single crystal is imprinted by a tungsten indenter patterned with parallel lines of various spacings. Dedicated dislocation dynamics simulations give insight in the plastic deformation occurring into the crystal during imprinting. We find that good pattern transfer is achieved when the lines are sufficiently spaced such that dislocation activity can be effective in assisting deformation of the region underneath each line. Yet, the edges of the obtained imprints are not smooth, partly due to dislocation glide.

  18. Dislocation mean free paths and strain hardening of crystals.

    PubMed

    Devincre, B; Hoc, T; Kubin, L

    2008-06-27

    Predicting the strain hardening properties of crystals constitutes a long-standing challenge for dislocation theory. The main difficulty resides in the integration of dislocation processes through a wide range of time and length scales, up to macroscopic dimensions. In the present multiscale approach, dislocation dynamics simulations are used to establish a dislocation-based continuum model incorporating discrete and intermittent aspects of plastic flow. This is performed through the modeling of a key quantity, the mean free path of dislocations. The model is then integrated at the scale of bulk crystals, which allows for the detailed reproduction of the complex deformation curves of face-centered cubic crystals. Because of its predictive ability, the proposed framework has a large potential for further applications. PMID:18583605

  19. Dislocation structure produced by an ultrashort shock pulse

    SciTech Connect

    Matsuda, Tomoki Hirose, Akio; Sano, Tomokazu; Arakawa, Kazuto

    2014-11-14

    We found an ultrashort shock pulse driven by a femtosecond laser pulse on iron generates a different dislocation structure than the shock process which is on the nanosecond timescale. The ultrashort shock pulse produces a highly dense dislocation structure that varies by depth. According to transmission electron microscopy, dislocations away from the surface produce microbands via a network structure similar to a long shock process, but unlike a long shock process dislocations near the surface have limited intersections. Considering the dislocation motion during the shock process, the structure near the surface is attributed to the ultrashort shock duration. This approach using an ultrashort shock pulse will lead to understanding the whole process off shock deformation by clarifying the early stage.

  20. Neglected Posterior Dislocation of Hip in Children - A Case Report

    PubMed Central

    Pal, Chandra Prakash; Kumar, Deepak; Sadana, Ashwani; Dinkar, Karuna Shankar

    2014-01-01

    Introduction: Traumatic dislocation of the hip in children is a rare injury. We report the outcome of 2 patients of neglected hip dislocation which were treated by open reduction and internal fixation by k-wires. Case Report: We treat 2 children both girls (one was of 4 years and other was 7 years of age). In both cases dislocation was unilateral and was not associated with any facture. Both cases were of posterior dislocation. in both cases open reduction and internal fixation was done by k wires. Hip spica was applied post operatively in both cases. The k wire was removed at 3 to 4 weeks. Patients were allowed to bear weight from gradual to full weight bearing after 6 weeks. Conclusion: We conclude that open reduction is a satisfactory treatment for neglected hip dislocation. It prevents not only deformity but also maintains limb length. PMID:27298953

  1. Basic study of intrinsic elastography: Relationship between tissue stiffness and propagation velocity of deformation induced by pulsatile flow

    NASA Astrophysics Data System (ADS)

    Nagaoka, Ryo; Iwasaki, Ryosuke; Arakawa, Mototaka; Kobayashi, Kazuto; Yoshizawa, Shin; Umemura, Shin-ichiro; Saijo, Yoshifumi

    2015-07-01

    We proposed an estimation method for a tissue stiffness from deformations induced by arterial pulsation, and named this proposed method intrinsic elastography (IE). In IE, assuming that the velocity of the deformation propagation in tissues is closely related to the stiffness, the propagation velocity (PV) was estimated by spatial compound ultrasound imaging with a high temporal resolution of 1 ms. However, the relationship between tissue stiffness and PV has not been revealed yet. In this study, the PV of the deformation induced by the pulsatile pump was measured by IE in three different poly(vinyl alcohol) (PVA) phantoms of different stiffnesses. The measured PV was compared with the shear wave velocity (SWV) measured by shear wave imaging (SWI). The measured PV has trends similar to the measured SWV. These results obtained by IE in a healthy male show the possibility that the mechanical properties of living tissues could be evaluated by IE.

  2. Dislocations in extruded Co-49.3 at. pct Al

    NASA Technical Reports Server (NTRS)

    Yaney, D. L.; Nix, W. D.; Pelton, A. R.

    1986-01-01

    Polycrystalline Co-49.3 at. pct Al, which had been extruded at 1505 K, was examined using transmission electron microscopy. Diffraction contrast analysis showed that b = 100 as well as b = 111 line dislocations contribute to elevated temperature deformation in CoAl. Therefore, it was concluded that sufficient slip systems exist in CoAl to allow for general plasticity in the absence of diffusional mechanisms. Line dislocations of the type b = 001 were observed on both 110 and 100 planes while b = 111 line dislocations were observed on 1 -1 0 planes.

  3. Bilateral posterior sternoclavicular dislocation.

    PubMed

    Baumann, Matthias; Vogel, Tobias; Weise, Kuno; Muratore, Tim; Trobisch, Per

    2010-07-01

    Posterior sternoclavicular dislocations are a rare injury, representing <5% of all sternoclavicular dislocations and 1 in 1600 shoulder girdle injuries. Proper imaging with computed tomography and prompt diagnosis are essential steps in preventing potentially lethal complications observed in approximately 3% of all posterior sternoclavicular dislocations. Surgical treatment is necessary if closed reduction fails. With the medial clavicular epiphysis being the last to close (between ages 22 and 25), children and adolescents typically present with epiphyseal fractures rather than joint dislocations. If closed reduction fails, open reduction and internal fixation (ORIF) should be considered in fractures, whereas complex reconstructions with tendon graft procedures have been recommended for joint dislocations. This article presents a case of a traumatic bilateral posterior sternoclavicular dislocation due to an epiphyseal fracture in a 15-year-old boy. To our knowledge, this is the first reported case of a bilateral posterior sternoclavicular dislocation. Attempted closed reduction failed with redislocation after 2 days. The patient subsequently required ORIF. This article describes our technique with anterior retraction of the medial clavicle, closure of the posterior periosteum, and ORIF using nonabsorbable sutures. Postoperative shoulder mobilization was started on day 1. At final follow-up, the patient was completely asymptomatic. PMID:20608625

  4. Collective behaviour of dislocations in a finite medium

    NASA Astrophysics Data System (ADS)

    Kooiman, M.; Hütter, M.; Geers, M. G. D.

    2014-04-01

    We derive the grand-canonical partition function of straight and parallel dislocation lines without making a priori assumptions on the temperature regime. Such a systematic derivation for dislocations has, to the best of our knowledge, not been carried out before, and several conflicting assumptions on the free energy of dislocations have been made in the literature. Dislocations have gained interest as they are the carriers of plastic deformation in crystalline materials and solid polymers, and they constitute a prototype system for two-dimensional Coulomb particles. Our microscopic starting level is the description of dislocations as used in the discrete dislocation dynamics (DDD) framework. The macroscopic level of interest is characterized by the temperature, the boundary deformation and the dislocation density profile. By integrating over state space, we obtain a field theoretic partition function, which is a functional integral of the Boltzmann weight over an auxiliary field. The Hamiltonian consists of a term quadratic in the field and an exponential of this field. The partition function is strongly non-local, and reduces in special cases to the sine-Gordon model. Moreover, we determine implicit expressions for the response functions and the dominant scaling regime for metals, namely the low-temperature regime.

  5. Dislocation Starvation and Exhaustion Hardening in Mo-alloy Nanofibers

    SciTech Connect

    Chisholm, Claire; Bei, Hongbin; Lowry, M. B.; Oh, Jason; Asif, S.A. Syed; Warren, O.; Shan, Zhiwei; George, Easo P; Minor, Andrew

    2012-01-01

    The evolution of defects in Mo alloy nanofibers with initial dislocation densities ranging from 0 to 1.6 1014 m2 were studied using an in situ push-to-pull device in conjunction with a nanoindenter in a transmission electron microscope. Digital image correlation was used to determine stress and strain in local areas of deformation. When they had no initial dislocations the Mo alloy nanofibers suffered sudden catastrophic elongation following elastic deformation to ultrahigh stresses. At the other extreme fibers with a high dislocation density underwent sustained homogeneous deformation after yielding at much lower stresses. Between these two extremes nanofibers with intermediate dislocation densities demonstrated a clear exhaustion hardening behavior, where the progressive exhaustion of dislocations and dislocation sources increases the stress required to drive plasticity. This is consistent with the idea that mechanical size effects ( smaller is stronger ) are due to the fact that nanostructures usually have fewer defects that can operate at lower stresses. By monitoring the evolution of stress locally we find that exhaustion hardening causes the stress in the nanofibers to surpass the critical stress predicted for self-multiplication, supporting a plasticity mechanism that has been hypothesized to account for the rapid strain softening observed in nanoscale bcc materials at high stresses.

  6. How to identify dislocations in molecular dynamics simulations?

    NASA Astrophysics Data System (ADS)

    Li, Duo; Wang, FengChao; Yang, ZhenYu; Zhao, YaPu

    2014-12-01

    Dislocations are of great importance in revealing the underlying mechanisms of deformed solid crystals. With the development of computational facilities and technologies, the observations of dislocations at atomic level through numerical simulations are permitted. Molecular dynamics (MD) simulation suggests itself as a powerful tool for understanding and visualizing the creation of dislocations as well as the evolution of crystal defects. However, the numerical results from the large-scale MD simulations are not very illuminating by themselves and there exist various techniques for analyzing dislocations and the deformed crystal structures. Thus, it is a big challenge for the beginners in this community to choose a proper method to start their investigations. In this review, we summarized and discussed up to twelve existing structure characterization methods in MD simulations of deformed crystal solids. A comprehensive comparison was made between the advantages and disadvantages of these typical techniques. We also examined some of the recent advances in the dynamics of dislocations related to the hydraulic fracturing. It was found that the dislocation emission has a significant effect on the propagation and bifurcation of the crack tip in the hydraulic fracturing.

  7. The development of physically based micro-mechanics - Based on the characteristic tip field of dislocation pileup

    NASA Technical Reports Server (NTRS)

    Gao, Q.; Liu, H. W.

    1990-01-01

    Based on the analytical solution by Eshelby et al. (1951) and the numerical calculations by Chou and Li (1969) and Armstrong et al. (1962), it is shown that the force, F, on the locked leading dislocation of a discrete dislocation pileup is capable of characterizing uniquely the stress, strain, and displacement field at the tip of the pileup, including the positions of the discrete mobile dislocations next to the leading dislocation. Conversely, the positions of the mobile dislocations can be used to measure F. The F thus measured can be used to study micro-plastic deformation and micro-fractures at grain boundaries or any other dislocation barriers.

  8. Mechanism of grain growth during severe plastic deformation of a nanocrystalline Ni-Fe alloy

    SciTech Connect

    Li, Hongqi; Wang, Y B; Ho, J C; Liao, X Z; Zhu, Y T; Ringer, S P

    2009-01-01

    Deformation induced grain growth has been widely reported in nanocrystalline materials. However, the grain growth mechanism remains an open question. This study applies high-pressure torsion to severely deform bulk nanocrystalline Ni-20 wt % Fe disks and uses transmission electron microscopy to characterize the grain growth process. Our results provide solid evidence suggesting that high pressure torsion induced grain growth is achieved primarily via grain rotation for grains much smaller than 100 nm. Dislocations are mainly seen at small-angle subgrain boundaries during the grain growth process but are seen everywhere in grains after the grains have grown large.

  9. Quantitative evaluation of the broadening of x-ray diffraction, Raman, and photoluminescence lines by dislocation-induced strain in heteroepitaxial GaN films

    NASA Astrophysics Data System (ADS)

    Kaganer, Vladimir M.; Jenichen, Bernd; Ramsteiner, Manfred; Jahn, Uwe; Hauswald, Christian; Grosse, Frank; Fernández-Garrido, Sergio; Brandt, Oliver

    2015-09-01

    Experimental x-ray diffraction, Raman, and photoluminescence line profiles from GaN films with different densities of threading dislocations are modeled using Monte Carlo calculations of the strain distribution due to these dislocations. We quantitatively analyze and compare the respective line broadenings predicted by these calculations for different dislocation densities. X-ray diffraction and Raman measurements reveal the strain in the whole volume of the film, due to the large penetration depth of the corresponding radiation, while photoluminescence measurements are sensitive to the strain close to the film surface, in a layer limited by the penetration depth of the radiation used for excitation. This difference in information depths becomes especially important for films in which the threading dislocation density is continuously decreasing during growth, as it can be achieved by vapor phase epitaxy methods. An additional narrowing of photoluminescence lines occurs due to two effects: first, the elastic relaxation of the dislocation strain at the free surface, and second, the suppression of luminescence from the most highly strained regions around the dislocation cores which act as centers of nonradiative recombination.

  10. Mathematical modelling of swelling-induced surface instabilities in deformable porous media

    NASA Astrophysics Data System (ADS)

    Hennessy, Matthew; Vitale, Alessandra; Cabral, Joao; Matar, Omar

    2015-11-01

    The swelling of a deformable porous medium as it absorbs liquid can generate large compressive stresses which, in turn, can induce a rich variety of surface instabilities. When controlled, these instabilities can be used to drive the self-assembly of microscale structures that find practical applications in fields such as surface patterning, imprint lithography, optically-active surfaces, and flexible electronics. Recent experiments by our group have suggested that a swelling-induced instability can occur at a surface of crosslinked polymer gels exposed to a good solvent. In this talk, we present a mathematical model for a swelling porous medium and use it to describe spontaneous pattern formation on gel surfaces. The model is based on nonlinear poroelasticity and the flow of liquid is described by a generalisation of Darcy's law that accounts for the thermodynamics of mixing. A combination of linear stability theory and finite-element simulations is used to explore the surface morphologies in the linear and nonlinear regimes. We show that the model is able to accurately reproduce experimental observations. EPSRC Grant number EP/L022176/1.

  11. The effect of length scale on the determination of geometrically necessary dislocations via EBSD continuum dislocation microscopy.

    PubMed

    Ruggles, T J; Rampton, T M; Khosravani, A; Fullwood, D T

    2016-05-01

    Electron backscatter diffraction (EBSD) dislocation microscopy is an important, emerging field in metals characterization. Currently, calculation of geometrically necessary dislocation (GND) density is problematic because it has been shown to depend on the step size of the EBSD scan used to investigate the sample. This paper models the change in calculated GND density as a function of step size statistically. The model provides selection criteria for EBSD step size as well as an estimate of the total dislocation content. Evaluation of a heterogeneously deformed tantalum specimen is used to asses the method. PMID:26986021

  12. Dislocation damping and anisotropic seismic wave attenuation in Earth's upper mantle.

    PubMed

    Farla, Robert J M; Jackson, Ian; Fitz Gerald, John D; Faul, Ulrich H; Zimmerman, Mark E

    2012-04-20

    Crystal defects form during tectonic deformation and are reactivated by the shear stress associated with passing seismic waves. Although these defects, known as dislocations, potentially contribute to the attenuation of seismic waves in Earth's upper mantle, evidence for dislocation damping from laboratory studies has been circumstantial. We experimentally determined the shear modulus and associated strain-energy dissipation in pre-deformed synthetic olivine aggregates under high pressures and temperatures. Enhanced high-temperature background dissipation occurred in specimens pre-deformed by dislocation creep in either compression or torsion, the enhancement being greater for prior deformation in torsion. These observations suggest the possibility of anisotropic attenuation in relatively coarse-grained rocks where olivine is or was deformed at relatively high stress by dislocation creep in Earth's upper mantle. PMID:22517856

  13. Cell membrane deformation and bioeffects produced by tandem bubble-induced jetting flow

    PubMed Central

    Yuan, Fang; Yang, Chen; Zhong, Pei

    2015-01-01

    Cavitation with bubble–bubble interaction is a fundamental feature in therapeutic ultrasound. However, the causal relationships between bubble dynamics, associated flow motion, cell deformation, and resultant bioeffects are not well elucidated. Here, we report an experimental system for tandem bubble (TB; maximum diameter = 50 ± 2 μm) generation, jet formation, and subsequent interaction with single HeLa cells patterned on fibronectin-coated islands (32 × 32 μm) in a microfluidic chip. We have demonstrated that pinpoint membrane poration can be produced at the leading edge of the HeLa cell in standoff distance Sd ≤ 30 μm, driven by the transient shear stress associated with TB-induced jetting flow. The cell membrane deformation associated with a maximum strain rate on the order of 104 s−1 was heterogeneous. The maximum area strain (εA,M) decreased exponentially with Sd (also influenced by adhesion pattern), a feature that allows us to create distinctly different treatment outcome (i.e., necrosis, repairable poration, or nonporation) in individual cells. More importantly, our results suggest that membrane poration and cell survival are better correlated with area strain integral (∫​εA2dt) instead of εA,M, which is characteristic of the response of materials under high strain-rate loadings. For 50% cell survival the corresponding area strain integral was found to vary in the range of 56 ∼ 123 μs with εA,M in the range of 57 ∼ 87%. Finally, significant variations in individual cell’s response were observed at the same Sd, indicating the potential for using this method to probe mechanotransduction at the single cell level. PMID:26663913

  14. Effects of Dislocations on Minority Carrier Lifetime in Dislocated Float Zone Silicon

    SciTech Connect

    Karoui, A.; Zhang, R.; Rozgonyi, G. A.; Ciszek, T. F.

    2002-08-01

    We present a correlation of Microwave Photoconductance Decay minority carrier lifetime with dislocation density in high purity Float Zone silicon. Electron Beam Induced Current (EBIC) images were carefully aligned to lifetime maps and depth profiling of individual defect electrical activity was done by varying the bias of Schottky diodes. The data presented provides a relationship between lifetime variations and EBIC contrast, based on dislocation density and impurity decoration in the near surface zone.

  15. Multiscale characterization of dislocation processes in Al 5754

    NASA Astrophysics Data System (ADS)

    Kacher, Josh; Mishra, Raja K.; Minor, Andrew M.

    2015-07-01

    Multiscale characterization was performed on an Al-Mg alloy, Al 5754 O-temper, including in situ mechanical deformation in both the scanning electron microscope and the transmission electron microscope. Scanning electron microscopy characterization showed corresponding inhomogeneity in the dislocation and Mg distribution, with higher levels of Mg correlating with elevated levels of dislocation density. At the nanoscale, in situ transmission electron microscopy straining experiments showed that dislocation propagation through the Al matrix is characterized by frequent interactions with obstacles smaller than the imaging resolution that resulted in the formation of dislocation debris in the form of dislocation loops. Post-mortem chemical characterization and comparison to dislocation loop behaviour in an Al-Cr alloy suggests that these obstacles are small Mg clusters. Previous theoretical work and indirect experimental evidence have suggested that these Mg nanoclusters are important factors contributing to strain instabilities in Al-Mg alloys. This study provides direct experimental characterization of the interaction of glissile dislocations with these nanoclusters and the stress needed for dislocations to overcome them.

  16. A novel fusionless vertebral physeal device inducing spinal growth modulation for the correction of spinal deformities

    PubMed Central

    Schmid, Eliane C.; Moreau, Alain; Sarwark, John; Parent, Stefan

    2008-01-01

    Current fusionless scoliosis surgical techniques span the intervertebral disc. This alters the spine stiffness, disc pressure equilibrium and possibly may lead to disc degeneration. A new fusionless physeal device was developed that locally modulates vertebral growth by compressing the physeal ring, while maintaining maximum segmental spinal mobility without spanning the intervertebral disc. This study’s objective was to test the feasibility of the device on a small animal model by inducing a scoliotic deformity (inverse approach) while analyzing the growth modifications. This study was conducted on caudal vertebrae of 21 rats (26-day-old) divided into 3 groups: (1) “experimental” (n = 11) with 4 instrumented vertebrae, (2) sham (n = 5) and (3) control (n = 5). Radiographs were taken at regular intervals during the 7-week experimental period. Tissues were embedded in methyl metacrylate (MMA), prepared by the cutting/grinding method, and then stained (Toluidine blue). The discs physiological alterations were qualitatively assessed and classified by inspection of the histological sections. A mean maximum Cobb angle of 30º (±6º) and a mean maximum vertebral wedge angle of 10º (±3º) were obtained between the 23rd and 35th day postoperative in the subgroup that underwent a long-term response from the device. The sham group underwent no growth alterations when compared to the control group. Descriptive histological analyses of the operated segments showed that 69% had no alterations to the intervertebral disc. This study presents experimental evidence that the device induces a significant and controlled wedging of the vertebrae while maintaining regular flexibility. In most discs, there were no visible morphological alterations induced. Further analysis of the discs and testing of this device on a larger animal is recommended with the long-term objective of developing an early treatment of progressive idiopathic scoliosis. PMID:18712419

  17. GPU accelerated dislocation dynamics

    NASA Astrophysics Data System (ADS)

    Ferroni, Francesco; Tarleton, Edmund; Fitzgerald, Steven

    2014-09-01

    In this paper we analyze the computational bottlenecks in discrete dislocation dynamics modeling (associated with segment-segment interactions as well as the treatment of free surfaces), discuss the parallelization and optimization strategies, and demonstrate the effectiveness of Graphical Processing Unit (GPU) computation in accelerating dislocation dynamics simulations and expanding their scope. Individual algorithmic benchmark tests as well as an example large simulation of a thin film are presented.

  18. Electronic selection rules controlling dislocation glide in bcc metals.

    PubMed

    Jones, Travis E; Eberhart, Mark E; Clougherty, Dennis P; Woodward, Chris

    2008-08-22

    The validity of the structure-property relationships governing the low-temperature deformation behavior of many bcc metals was brought into question with recent ab initio density functional studies of isolated screw dislocations in Mo and Ta. These relationships were semiclassical in nature, having grown from atomistic investigations of the deformation properties of the group V and VI transition metals. We find that the correct form for these structure-property relationships is fully quantum mechanical, involving the coupling of electronic states with the strain field at the core of long a/<2111> screw dislocations. PMID:18764636

  19. Electronic Selection Rules Controlling Dislocation Glide in bcc Metals

    NASA Astrophysics Data System (ADS)

    Jones, Travis E.; Eberhart, Mark E.; Clougherty, Dennis P.; Woodward, Chris

    2008-08-01

    The validity of the structure-property relationships governing the low-temperature deformation behavior of many bcc metals was brought into question with recent ab initio density functional studies of isolated screw dislocations in Mo and Ta. These relationships were semiclassical in nature, having grown from atomistic investigations of the deformation properties of the group V and VI transition metals. We find that the correct form for these structure-property relationships is fully quantum mechanical, involving the coupling of electronic states with the strain field at the core of long a/2⟨111⟩ screw dislocations.

  20. Dislocation dynamics in SiGe alloys

    NASA Astrophysics Data System (ADS)

    Yonenaga, I.

    2013-11-01

    The dislocation velocities and mechanical strength of bulk crystals of SixGe1-x alloys grown by the Czochralski method have been investigated by the etch pit technique and compressive deformation tests, respectively. Velocity of dislocations in the SiGe alloys of the composition range 0.004 < x < 0.08 decreases monotonically with an increase in Si content at temperature 450-700°C and under stress 3-24MPa. In contrast, velocity of dislocations in the composition range 0.92 < x < 1 first increases, then decreases and again increases with a decrease in Si content at temperature 750-850°C and under stress 3-30MPa. The velocity of dislocations was quantitatively evaluated as functions of stress and temperature. Stress-strain behaviour in the yield region of the SiGe alloys of composition 0 < x < 0.4 is similar to that of Ge at temperatures lower than about 600°C. However, the yield stress becomes temperature-insensitive at high temperatures and increases with increasing Si content. The stress-strain curves of the SiGe alloys of composition 0.95 < x < 1 are similar to those of pure Si at temperatures 800-1000°C and the yield stress increases with decreasing Si content down to x = 0.95. The yield stress of the SiGe alloys is dependent on the composition, being proportional to x(1-x), showing a maximum around x ≈ 0.5. Built-in stress fields related to local fluctuation of the alloy composition and the dynamic development of a solute atmosphere around the dislocations, may suppress the activities of dislocations and lead to the hardening of SiGe alloys.

  1. In-situ Synchrotron X-ray Microdiffraction Study of Lattice Rotation in Polycrystalline Materials during Uniaxial Deformations

    SciTech Connect

    Joo, H.D.; Bark, C.W.; Koo, Y.M.; Kim, K.H.; Tamura, N.

    2004-05-12

    Recent experiments have shown that formation of dislocation cell structures and rotation of structural elements at the macroscopic level are fundamental to the development of plastic deformation. However, attention should also be focused on micro-volumes because local stress and strain can significantly differ from their averaged values at the macroscale. In-situ orientation measurements in copper polycrystals during uniaxial deformation were performed using synchrotron x-ray microdiffraction at the Advanced Light Source. We observed heterogeneities in deformation-induced microstructure within individual grains. Different slip systems in particular can be simultaneously activated among neighboring volume elements of individual grains.

  2. In-situ synchrotron X-ray microdiffraction study of lattice rotation in polycrystalline materials during uniaxial deformations

    SciTech Connect

    Joo, H.D.; Kim, K.H.; Bark, C.W.; Koo, Y.M.; Tamura, N.

    2004-07-19

    Recent experiments have shown that formation of dislocation cell structures and rotation of structural elements at the macroscopic level are fundamental to the development of plastic deformation. However, attention should also be focused on micro-volumes because local stress and strain can significantly differ from their averaged values at the macroscale. In-situ orientation measurements in copper polycrystals during uniaxial deformation were performed using synchrotron x-ray microdiffraction at the Advanced Light Source. We observed heterogeneities in deformation-induced microstructure within individual grains. Different slip systems in particular can be simultaneously activated among neighboring volume elements of individual grains.

  3. Orientation dependence of the dislocation microstructure in compressed body-centered cubic molybdenum

    SciTech Connect

    Wang, S.; Wang, M.P.; Chen, C.; Xiao, Z.; Jia, Y.L.; Li, Z.; Wang, Z.X.

    2014-05-01

    The orientation dependence of the deformation microstructure has been investigated in commercial pure molybdenum. After deformation, the dislocation boundaries of compressed molybdenum can be classified, similar to that in face-centered cubic metals, into three types: dislocation cells (Type 2), and extended planar boundaries parallel to (Type 1) or not parallel to (Type 3) a (110) trace. However, it shows a reciprocal relationship between face-centered cubic metals and body-centered cubic metals on the orientation dependence of the deformation microstructure. The higher the strain, the finer the microstructure is and the smaller the inclination angle between extended planar boundaries and the compression axis is. - Highlights: • A reciprocal relationship between FCC metals and BCC metals is confirmed. • The dislocation boundaries can be classified into three types in compressed Mo. • The dislocation characteristic of different dislocation boundaries is different.

  4. Ultrasonic excitation of a bubble inside a deformable tube: implications for ultrasonically induced hemorrhage.

    PubMed

    Miao, Hongyu; Gracewski, Sheryl M; Dalecki, Diane

    2008-10-01

    Various independent investigations indicate that the presence of microbubbles within blood vessels may increase the likelihood of ultrasound-induced hemorrhage. To explore potential damage mechanisms, an axisymmetric coupled finite element and boundary element code was developed and employed to simulate the response of an acoustically excited bubble centered within a deformable tube. As expected, the tube mitigates the expansion of the bubble. The maximum tube dilation and maximum hoop stress were found to occur well before the bubble reached its maximum radius. Therefore, it is not likely that the expanding low pressure bubble pushes the tube wall outward. Instead, simulation results indicate that the tensile portion of the acoustic excitation plays a major role in tube dilation and thus tube rupture. The effects of tube dimensions (tube wall thickness 1-5 microm), material properties (Young's modulus 1-10 MPa), ultrasound frequency (1-10 MHz), and pressure amplitude (0.2-1.0 MPa) on bubble response and tube dilation were investigated. As the tube thickness, tube radius, and acoustic frequency decreased, the maximum hoop stress increased, indicating a higher potential for tube rupture and hemorrhage. PMID:19062875

  5. Exercise effects on erythrocyte deformability in exercise-induced arterial hypoxemia.

    PubMed

    Alis, R; Sanchis-Gomar, F; Ferioli, D; La Torre, A; Blesa, J R; Romagnoli, M

    2015-04-01

    Exercise-induced arterial hypoxemia (EIAH) is often found in endurance-trained subjects at high exercise intensity. The role of erythrocyte deformability (ED) in EIAH has been scarcely explored. We aimed to explore the role of erythrocyte properties and lactate accumulation in the response of ED in EIAH. ED was determined in 10 sedentary and in 16 trained subjects, both before and after a maximal incremental test, and after recovery, along with mean corpuscular volume (MCV) and red blood cell lactate concentrations. EIAH was found in 6 trained subjects (∆SaO2=-8.25±4.03%). Sedentary and non-EIAH trained subjects showed reduced ED after exercise, while no effect on ED was found in EIAH trained subjects. After exercise, lactate concentrations rose and MCV increased equally in all groups. ED is strongly driven by cell volume, but the different ED response to exercise in EIAH shows that other cellular mechanisms may be implicated. Interactions between membrane and cytoskeleton, which have been found to be O2-regulated, play a role in ED. The drop in SaO2 in EIAH subjects can improve ED response to exercise. This can be an adaptive mechanism that enhances muscular and pulmonary perfusion, and allows the achievement of high exercise intensity in EIAH despite lower O2 arterial transport. PMID:25429547

  6. Ultrasonic excitation of a bubble inside a deformable tube: Implications for ultrasonically induced hemorrhage

    PubMed Central

    Miao, Hongyu; Gracewski, Sheryl M.; Dalecki, Diane

    2008-01-01

    Various independent investigations indicate that the presence of microbubbles within blood vessels may increase the likelihood of ultrasound-induced hemorrhage. To explore potential damage mechanisms, an axisymmetric coupled finite element and boundary element code was developed and employed to simulate the response of an acoustically excited bubble centered within a deformable tube. As expected, the tube mitigates the expansion of the bubble. The maximum tube dilation and maximum hoop stress were found to occur well before the bubble reached its maximum radius. Therefore, it is not likely that the expanding low pressure bubble pushes the tube wall outward. Instead, simulation results indicate that the tensile portion of the acoustic excitation plays a major role in tube dilation and thus tube rupture. The effects of tube dimensions (tube wall thickness 1–5 μm), material properties (Young’s modulus 1–10 MPa), ultrasound frequency (1–10 MHz), and pressure amplitude (0.2–1.0 MPa) on bubble response and tube dilation were investigated. As the tube thickness, tube radius, and acoustic frequency decreased, the maximum hoop stress increased, indicating a higher potential for tube rupture and hemorrhage. PMID:19062875

  7. Reservoir-induced deformation and continental rheology in vicinity of Lake Mead, Nevada

    NASA Astrophysics Data System (ADS)

    Kaufmann, Georg; Amelung, Falk

    2000-07-01

    Lake Mead is a large reservoir in Nevada, formed by the construction of the 221-m-high Hoover Dam in the Black Canyon of the Colorado River. The lake encompasses an area of 635 km2, and the total volume of the reservoir is 35.5 km3. Filling started in February 1935. On the basis of a first-order leveling in 1935, several levelings were carried out to measure the deformation induced by the load of the reservoir. Subsidence in the central parts of the lake relative to the first leveling was around 120 mm (1941), 218 mm (1950), and 200 mm (1963). The subsidence pattern clearly shows relaxation of the underlying basement due to the water load of the lake, which ceased after 1950. Modeling of the relaxation process by means of layered, viscoelastic, compressible flat Earth models with a detailed representation of the spatial and temporal distribution of the water load shows that the thickness of the elastic crust underneath Lake Mead is 30±3 km. The data are also consistent with a 10-km-thick elastic upper crust and a 20-km-thick viscoelastic lower crust, with 1020 Pa s as a lower bound for its viscosity. The subcrust has an average viscosity of 1018±0.2 Pa s, a surprisingly low value. The leveling data constrain the viscosity profile down to ˜200 km depth.

  8. A remotely driven and controlled micro-gripper fabricated from light-induced deformation smart material

    NASA Astrophysics Data System (ADS)

    Huang, Chaolei; Lv, Jiu-an; Tian, Xiaojun; Wang, Yuechao; Liu, Jie; Yu, Yanlei

    2016-09-01

    Micro-gripper is an important tool to manipulate and assemble micro-scale objects. Generally, as micro-gripper is too small to be directly driven by general motors, it always needs special driving devices and suitable structure design. In this paper, two-finger micro-grippers are designed and fabricated, which utilize light-induced deformation smart material to make one of the two fingers. As the smart material is directly driven and controlled by remote lights instead of lines and motors, this light-driven mode simplifies the design of the two-finger micro-gripper and avoids special drivers and complex mechanical structure. In addition, a micro-manipulation experiment system is set up which is based on the light-driven micro-gripper. Experimental results show that this remotely light-driven micro-gripper has ability to manipulate and assemble micro-scale objects both in air and water. Furthermore, two micro-grippers can also work together for cooperation which can further enhance the assembly ability. On the other hand, this kind of remotely controllable micro-gripper that does not require on-board energy storage, can be used in mobile micro-robot as a manipulation hand.

  9. High-Strain-Induced Deformation Mechanisms in Block-Graft and Multigraft Copolymers

    SciTech Connect

    Schlegel, Ralf; Duan, Y. X.; Weidisch, Roland; Holzer, Suzette R; Schneider, Ken R; Stamm, M.; Uhrig, David; Mays, Jimmy; Heinrich, G.; Hadjichristidis, Nikolaos

    2011-01-01

    The molecular orientation behavior and structural changes of morphology at high strains for multigraft and block graft copolymers based on polystyrene (PS) and polyisoprene (PI) were investigated during uniaxial monotonic loading via FT-IR and synchrotron SAXS. Results from FT-IR revealed specific orientations of PS and PI segments depending on molecular architecture and on the morphology, while structural investigations revealed a typical decrease in long-range order with increasing strain. This decrease was interpreted as strain-induced dissolution of the glassy blocks in the soft matrix, which is assumed to affect an additional enthalpic contribution (strain-induced mixing of polymer chains) and stronger retracting forces of the network chains during elongation. Our interpretation is supported by FT-IR measurements showing similar orientation of rubbery and glassy segments up to high strains. It also points to highly deformable PS domains. By synchrotron SAXS, we observed in the neo-Hookean region an approach of glassy domains, while at higher elongations the intensity of the primary reflection peak was significantly decreasing. The latter clearly verifies the assumption that the glassy chains are pulled out from the domains and are partly mixed in the PI matrix. Results obtained by applying models of rubber elasticity to stressstrain and hysteresis data revealed similar correlations between the softening behavior and molecular and morphological parameters. Further, an influence of the network modality was observed (randomgrafted branches). For sphere formingmultigraft copolymers the domain functionality was found to be less important to achieve improved mechanical properties but rather size and distribution of the domains.

  10. Shock-induced deformation phenomena in magnetite and their consequences on magnetic properties

    NASA Astrophysics Data System (ADS)

    Reznik, Boris; Kontny, Agnes; Fritz, Jörg; Gerhards, Uta

    2016-06-01

    This study investigates the effects of shock waves on magnetic and microstructural behavior of multidomain magnetite from a magnetite-bearing ore, experimentally shocked to pressures of 5, 10, 20, and 30 GPa. Changes in apparent crystallite size and lattice parameter were determined by X-ray diffraction, and grain fragmentation and defect accumulation were studied by scanning and transmission electron microscopy. Magnetic properties were characterized by low-temperature saturation isothermal remanent magnetization (SIRM), susceptibility measurements around the Verwey transition as well as by hysteresis parameters at room temperature. It is established that the shock-induced refinement of magnetic domains from MD to SD-PSD range is a result of cooperative processes including brittle fragmentation of magnetite grains, plastic deformation with shear bands and twins as well as structural disordering in form of molten grains and amorphous nanoclusters. Up to 10 GPa, a decrease of coherent crystallite size, lattice parameter, saturation magnetization (Ms), and magnetic susceptibility and an increase in coercivity, SIRM, and width of Verwey transition are mostly associated with brittle grain fragmentation. Starting from 20 GPa, a slight recovery is documented in all magnetic and nonmagnetic parameters. In particular, the recovery in SIRM is correlated with an increase of the lattice constant. The recovery effect is associated with the increasing influence of shock heating/annealing at high shock pressures. The strong decrease of Ms at 30 GPa is interpreted as a result of strong lattice damage and distortion. Our results unravel the microstructural mechanisms behind the loss of magnetization and the modification of magnetic properties of magnetite and contribute to our understanding of shock-induced magnetic phenomena in impacted rocks on earth and in meteorites.

  11. Deformation analysis on F138 austenitic stainless steel: ECAE and rolling

    NASA Astrophysics Data System (ADS)

    De Vincentis, N. S.; Avalos, M. C.; Kliauga, A. M.; Sordi, V. L.; Schell, N.; Brokmeier, H.-G.; Bolmaro, R. E.

    2014-08-01

    Twinning is an alternative mechanism to achieve ultra-fine grain structures through severe plastic deformation. The properties induced in a plastically deformed material are highly dependent on the degree of deformation, accumulated deformation energy and details on grain sizes and microstructure, which are on the scale of some tens of nanometers; therefore it is very important to understand misorientation distributions and dislocation arrays developed in the samples. In this work an F138 austenitic stainless steel was solution heat treated, deformed by Equal Channel Angular Extrusion (ECAE) at room temperature up to four passes, and rolled up to 70% thickness reduction at room temperature. The microstructure evolution was analyzed by x-ray diffraction and domain sizes calculated by Convolutional Multiple Whole Profile (CMWP) model, the misorientation boundaries were measured by electron backscattered diffraction (EBSD), and transmission electron microscopy. Mechanical behavior was tested by tensile tests.

  12. Impact-induced brittle deformation, porosity loss, and aqueous alteration in the Murchison CM chondrite

    NASA Astrophysics Data System (ADS)

    Hanna, Romy D.; Ketcham, Richard A.; Zolensky, Mike; Behr, Whitney M.

    2015-12-01

    X-ray computed tomographic scanning of a 44 g Murchison stone (USNM 5487) reveals a preferred alignment of deformed, partially altered chondrules, which define a prominent foliation and weak lineation in 3D. The presence of a lineation and evidence for a component of rotational, noncoaxial shear suggest that the deformation was caused by impact. Olivine optical extinction indicates that the sample can be classified as shock stage S1, and electron backscatter diffraction (EBSD) and electron microscopy reveal that plastic deformation within the chondrules was minimal and that brittle deformation in the form of fracturing, cataclasis, and grain boundary sliding was the dominant microstructural strain-accommodating mechanism. Textural evidence such as serpentine veins parallel to the foliation fabric and crosscutting alteration veins strongly suggest that some aqueous alteration post-dated or was contemporaneous with the deformation and that multiple episodes of fracturing and mineralization occurred. Finally, using the deformed shape of the chondrules we estimate that the strain experienced by Murchison was 17-43%. This combined with the current measured porosity of Murchison suggests that the original bulk porosity of Murchison prior to its deformation was 32.2-53.4% and likely at the upper end of this range due to chondrule compressibility, providing a unique estimate of pre-deformation porosity for a carbonaceous chondrite. Our findings suggest that significant porosity loss, deformation, and compaction from impact can occur on chondrite parent bodies whose samples may record only a low level of shock, and that significant chondrule deformation resulting in a chondrite foliation fabric can occur primarily through brittle processes and does not require plastic deformation of grains.

  13. Kinematic assumptions and their consequences on the structure of field equations in continuum dislocation theory

    NASA Astrophysics Data System (ADS)

    Silbermann, C. B.; Ihlemann, J.

    2016-03-01

    Continuum Dislocation Theory (CDT) relates gradients of plastic deformation in crystals with the presence of geometrically necessary dislocations. Therefore, the dislocation tensor is introduced as an additional thermodynamic state variable which reflects tensorial properties of dislocation ensembles. Moreover, the CDT captures both the strain energy from the macroscopic deformation of the crystal and the elastic energy of the dislocation network, as well as the dissipation of energy due to dislocation motion. The present contribution deals with the geometrically linear CDT. More precise, the focus is on the role of dislocation kinematics for single and multi-slip and its consequences on the field equations. Thereby, the number of active slip systems plays a crucial role since it restricts the degrees of freedom of plastic deformation. Special attention is put on the definition of proper, well-defined invariants of the dislocation tensor in order to avoid any spurious dependence of the resulting field equations on the coordinate system. It is shown how a slip system based approach can be in accordance with the tensor nature of the involved quantities. At first, only dislocation glide in one active slip system of the crystal is allowed. Then, the special case of two orthogonal (interacting) slip systems is considered and the governing field equations are presented. In addition, the structure and symmetry of the backstress tensor is investigated from the viewpoint of thermodynamical consistency. The results will again be used in order to facilitate the set of field equations and to prepare for a robust numerical implementation.

  14. Deformation induced topographic effects in inversion of temporal gravity changes: First look at Free Air and Bouguer terms

    NASA Astrophysics Data System (ADS)

    Vajda, Peter; Zahorec Pavol, Pavol; Papčo, Juraj; Kubová, Anna

    2015-06-01

    We review here the gravitational effects on the temporal (time-lapse) gravity changes induced by the surface deformation (vertical displacements). We focus on two terms, one induced by the displacement of the benchmark (gravity station) in the ambient gravity field, and the other imposed by the attraction of the masses within the topographic deformation rind. The first term, coined often the Free Air Effect (FAE), is the product of the vertical gradient of gravity (VGG) and the vertical displacement of the benchmark. We examine the use of the vertical gradient of normal gravity, typically called the theoretical or normal Free Air Gradient (normal FAG), as a replacement for the true VGG in the FAE, as well as the contribution of the topography to the VGG. We compute a topographic correction to the normal FAG, to offer a better approximation of the VGG, and evaluate its size and shape (spatial behavior) for a volcanic study area selected as the Central Volcanic Complex (CVC) on Tenerife, where this correction reaches 77% of the normal FAG and varies rapidly with terrain. The second term, imposed by the attraction of the vertically displaced topo-masses, referred to here as the Topographic Deformation Effect (TDE) must be computed by numerical evaluation of the Newton volumetric integral. As the effect wanes off quickly with distance, a high resolution DEM is required for its evaluation. In practice this effect is often approximated by the planar or spherical Bouguer deformation effect (BDE). By a synthetic simulation at the CVC of Tenerife we show the difference between the rigorously evaluated TDE and its approximation by the planar BDE. The complete effect, coined here the Deformation Induced Topographic Effect (DITE) is the sum of FAE and TDE. Next we compare by means of synthetic simulations the DITE with two approximations of DITE typically used in practice: one amounting only to the first term in which the VGG is approximated by normal FAG, the other adopting a

  15. Correlation of photothermal conversion on the photo-induced deformation of amorphous carbon nitride films prepared by reactive sputtering

    SciTech Connect

    Harata, T.; Aono, M. Kitazawa, N.; Watanabe, Y.

    2014-08-04

    The photo-induced deformation of hydrogen-free amorphous carbon nitride (a-CN{sub x}) films was investigated under visible-light illumination. The films gave rise to photothermal conversion by irradiation. In this study, we investigated the effects of thermal energy generated by irradiation on the deformation of a-CN{sub x}/ultrathin substrate bimorph specimens. The films were prepared on both ultrathin Si and SiO{sub 2} substrates by reactive radio-frequency magnetron sputtering from a graphite target in the presence of pure nitrogen gas. The temperature of the film on the SiO{sub 2} substrate increased as the optical band-gap of the a-CN{sub x} was decreased. For the film on Si, the temperature remained constant. The deformation degree of the films on Si and SiO{sub 2} substrates were approximately the same. Thus, the deformation of a-CN{sub x} films primarily induced by photon energy directly.

  16. Simplified dynamic analysis to evaluate liquefaction-induced lateral deformation of earth slopes: a computational fluid dynamics approach

    NASA Astrophysics Data System (ADS)

    Jafarian, Yaser; Ghorbani, Ali; Ahmadi, Omid

    2014-09-01

    Lateral deformation of liquefiable soil is a cause of much damage during earthquakes, reportedly more than other forms of liquefaction-induced ground failures. Researchers have presented studies in which the liquefied soil is considered as viscous fluid. In this manner, the liquefied soil behaves as non-Newtonian fluid, whose viscosity decreases as the shear strain rate increases. The current study incorporates computational fluid dynamics to propose a simplified dynamic analysis for the liquefaction-induced lateral deformation of earth slopes. The numerical procedure involves a quasi-linear elastic model for small to moderate strains and a Bingham fluid model for large strain states during liquefaction. An iterative procedure is considered to estimate the strain-compatible shear stiffness of soil. The post-liquefaction residual strength of soil is considered as the initial Bingham viscosity. Performance of the numerical procedure is examined by using the results of centrifuge model and shaking table tests together with some field observations of lateral ground deformation. The results demonstrate that the proposed procedure predicts the time history of lateral ground deformation with a reasonable degree of precision.

  17. Deformation-induced diagenesis and microbial activity in the Nankai accretionary prism

    NASA Astrophysics Data System (ADS)

    Famin, V.; Andreani, M.; Boullier, A. M.; Raimbourg, H.; Magnin, V.

    2014-12-01

    We performed a microscopic and chemical study of diagenetic reactions in deformation microstructures within deep mud sediments from the Nankai accretionary prism (SW Japan) collected during IODP Expedition 315. Our study reveals that deformation microstructures localize the crystallization of pyrite, a diagenetic reaction also found in large megasplay faults of the prism. Textural observation shows that pyrite crystallization is synchronous of the sediment deformation. The framboidal shape of pyrite crystals, the barium depletion and the strong arsenic enrichment observed in deformation microstructures compared with the sediment matrix, suggest that pyrite crystallization is mediated by the proliferation of anoxic archae. During scientific drilling expeditions IODP 315, 316 and 319, microbial life has been evidenced at depths of up to 800 m below the sea floor by the presence of biogenic methane and sulfate reducers in sediments. We suggest that deformation structures localize microbial proliferation because the fracturing of silicate minerals produces hydrogen, a necessary compound for bacteria under anoxic conditions. Bacteria proliferate as long as active deformation supplies hydrogen, and vanish when the deformation stops. The development of bacteria in deformation structures impacts our mechanical understanding of fault zones in accretionary prisms: Firstly, bacterial activity converts carbon from organic matter and hydrogen into methane and/or water, which may alter the fluid budget of fault zones and the recurrence of dynamic ruptures in megathrusts. Secondly, the abundance of bacteria could be used to recognize active fault zones from inactive ones in drilling cores.

  18. Tensile response of passivated films with climb-assisted dislocation glide

    NASA Astrophysics Data System (ADS)

    Ayas, C.; Deshpande, V. S.; Geers, M. G. D.

    2012-09-01

    The tensile response of single crystal films passivated on two sides is analysed using climb enabled discrete dislocation plasticity. Plastic deformation is modelled through the motion of edge dislocations in an elastic solid with a lattice resistance to dislocation motion, dislocation nucleation, dislocation interaction with obstacles and dislocation annihilation incorporated through a set of constitutive rules. The dislocation motion in the films is by glide-only or by climb-assisted glide whereas in the surface passivation layers dislocation motion occurs by glide-only and penalized by a friction stress. For realistic values of the friction stress, the size dependence of the flow strength of the oxidised films was mainly a geometrical effect resulting from the fact that the ratio of the oxide layer thickness to film thickness increases with decreasing film thickness. However, if the passivation layer was modelled as impenetrable, i.e. an infinite friction stress, the plastic hardening rate of the films increases with decreasing film thickness even for geometrically self-similar specimens. This size dependence is an intrinsic material size effect that occurs because the dislocation pile-up lengths become on the order of the film thickness. Counter-intuitively, the films have a higher flow strength when dislocation motion is driven by climb-assisted glide compared to the case when dislocation motion is glide-only. This occurs because dislocation climb breaks up the dislocation pile-ups that aid dislocations to penetrate the passivation layers. The results also show that the Bauschinger effect in passivated thin films is stronger when dislocation motion is climb-assisted compared to films wherein dislocation motion is by glide-only.

  19. Crystallization-aided extraordinary plastic deformation in nanolayered crystalline Cu/amorphous Cu-Zr micropillars

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    Metallic glasses are lucrative engineering materials owing to their superior mechanical properties such as high strength and great elastic strain. However, the Achilles' heel of metallic amorphous materials -- low plasticity caused by instantaneous catastrophic shear banding, significantly undercut their structural applications. Here, the nanolayered crystalline Cu/amorphous Cu-Zr micropillars with equal layer thickness spanning from 20-100 nm are uniaxially compressed and it is found that the Cu/Cu-Zr micropillars exhibit superhigh homogeneous deformation (>= 30% strain) rather than localized shear banding at room temperature. This extraordinary plasticity is aided by the deformation-induced devitrification via absorption/annihilation of abundant dislocations, triggering the cooperative shearing of shear transformation zones in glassy layers, which simultaneously renders the work-softening. The synthesis of such heterogeneous nanolayered structure not only hampers shear band generation but also provides a viable route to enhance the controllability of plastic deformation in metallic glassy composites via deformation-induced devitrification mechanism.

  20. Simulations of gravity-induced trapping of a deformable drop in a three-dimensional constriction.

    PubMed

    Ratcliffe, Thomas; Zinchenko, Alexander Z; Davis, Robert H

    2012-10-01

    An efficient algorithm is developed to determine the three-dimensional shape of a deformable drop trapped under gravity in a constriction, employing an artificial evolution to a steady state. During the simulation, the drop surface is advanced using a rationally-devised normal "velocity", based on local deviation from the Young-Laplace equation and the adjacent solid shape, to approach the trapped drop shape. The artificial "time-dependent" evolution of the drop to the static, trapped shape requires that the free portions of the drop interface eventually satisfy the Young-Laplace equation, and the drop-solid contact portions of the drop interface conform to the solid surface. The significant advantage of this solution method is that a simple, numerically-efficient "velocity" is used to construct the evolution to the steady state; the coated areas where the drop is in near contact with solid boundaries of the constriction do not have to be specified a priori, but are found in the course of the solution. Alternative methods (e.g., boundary integral) based on realistic time-marching would be much more costly for determining the trapped state. Trapping conditions and drop shapes are studied for gravity-induced settling of a deformable drop into a three-dimensional constriction. For conditions near critical, where the trapped-drop steady state ceases to exist, severe surface-mesh distortions are treated by a combination of 'passive mesh stabilization', mesh relaxation and topological mesh transformations through node reconnections. For Bond numbers above a critical value, the drop is deformable enough to pass through the hole of the constriction, with no trapping. Critical Bond numbers are determined by linearly fitting minima of the root-mean-squared (rms) surface velocities versus corresponding Bond numbers greater than critical, and then extrapolating the Bond number to where the minimum rms velocity is zero (i.e., the drop becomes trapped). For ring and hyperbolic

  1. Low steady-state stresses in the cold lithospheric mantle inferred from dislocation dynamics models of dislocation creep in olivine

    NASA Astrophysics Data System (ADS)

    Boioli, Francesca; Tommasi, Andrea; Cordier, Patrick; Demouchy, Sylvie; Mussi, Alexandre

    2015-12-01

    Transmission electron microscopy observations on olivine crystals deformed at moderate (≤1273 K) temperature evidenced dislocations interactions explaining the hardening observed in the experiments, but also recovery mechanisms by the absorption or emission of point defects. Thus we investigate the possibility that, at geological strain-rates, these recovery processes allow steady-state deformation by dislocation creep at low to moderate temperatures in the lithospheric mantle. We test this hypothesis using a 2.5-D dislocation dynamics (DD) model, which combines dislocation glide and recovery by climb. This model shows that diffusion-controlled recovery processes allow for steady-state deformation by dislocation creep in the lithospheric mantle at stresses <500 MPa. For stresses of 50-200 MPa, steady-state strain-rates of 10-15 s-1 may be attained at temperatures as low as 900 K. Fitting of the DD model produces a flow law, which represents a lower bound for the lithospheric mantle strength, since the models describe the deformation of an olivine single crystal in an easy slip orientation. Comparison of strain-rates and Moho temperatures inferred for different geodynamic environments and the predictions of this model-based flow law implies, nevertheless, that, except in incipient rifts, most of the observed deformation may be produced by stress levels ≤200 MPa, consistent with those inferred to be produced by convection. This convergence suggests that the present models, which explicitly calculate the time-dependent dislocation dynamics, may provide a correct first order estimate of the mechanical behaviour of the lithospheric mantle, which cannot be derived directly from any existing data.

  2. Interfacial dislocation motion and interactions in single-crystal superalloys

    SciTech Connect

    Liu, B.; Raabe, D.; Roters, F.; Arsenlis, A.

    2014-10-01

    The early stage of high-temperature low-stress creep in single-crystal superalloys is characterized by the rapid development of interfacial dislocation networks. Although interfacial motion and dynamic recovery of these dislocation networks have long been expected to control the subsequent creep behavior, direct observation and hence in-depth understanding of such processes has not been achieved. Incorporating recent developments of discrete dislocation dynamics models, we simulate interfacial dislocation motion in the channel structures of single-crystal superalloys, and investigate how interfacial dislocation motion and dynamic recovery are affected by interfacial dislocation interactions and lattice misfit. Different types of dislocation interactions are considered: self, collinear, coplanar, Lomer junction, glissile junction, and Hirth junction. The simulation results show that strong dynamic recovery occurs due to the short-range reactions of collinear annihilation and Lomer junction formation. The misfit stress is found to induce and accelerate dynamic recovery of interfacial dislocation networks involving self-interaction and Hirth junction formation, but slow down the steady interfacial motion of coplanar and glissile junction forming dislocation networks. The insights gained from these simulations on high-temperature low-stress creep of single-crystal superalloys are also discussed.

  3. A parallel algorithm for 3D dislocation dynamics

    NASA Astrophysics Data System (ADS)

    Wang, Zhiqiang; Ghoniem, Nasr; Swaminarayan, Sriram; LeSar, Richard

    2006-12-01

    Dislocation dynamics (DD), a discrete dynamic simulation method in which dislocations are the fundamental entities, is a powerful tool for investigation of plasticity, deformation and fracture of materials at the micron length scale. However, severe computational difficulties arising from complex, long-range interactions between these curvilinear line defects limit the application of DD in the study of large-scale plastic deformation. We present here the development of a parallel algorithm for accelerated computer simulations of DD. By representing dislocations as a 3D set of dislocation particles, we show here that the problem of an interacting ensemble of dislocations can be converted to a problem of a particle ensemble, interacting with a long-range force field. A grid using binary space partitioning is constructed to keep track of node connectivity across domains. We demonstrate the computational efficiency of the parallel micro-plasticity code and discuss how O(N) methods map naturally onto the parallel data structure. Finally, we present results from applications of the parallel code to deformation in single crystal fcc metals.

  4. STATISTICAL MECHANICS MODELING OF MESOSCALE DEFORMATION IN METALS

    SciTech Connect

    Anter El-Azab

    2013-04-08

    The research under this project focused on a theoretical and computational modeling of dislocation dynamics of mesoscale deformation 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 deformation are manifestations of the evolution of the underlying dislocation system under mechanical loading. The project had three research tasks: 1) Investigating the statistical characteristics of dislocation systems in deformed crystals. 2) Formulating kinetic equations of dislocations and coupling these kinetics equations and crystal mechanics. 3) Computational solution of coupled crystal mechanics 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

  5. Dislocation-mediated creep process in nanocrystalline Cu

    NASA Astrophysics Data System (ADS)

    Mu, Jun-Wei; Sun, Shi-Cheng; Jiang, Zhong-Hao; Lian, Jian-She; Jiang, Qing

    2013-03-01

    Nanocrystalline Cu with average grain sizes ranging from ~ 24.4 to 131.3 nm were prepared by the electric brush-plating technique. Nanoindentation tests were performed within a wide strain rate range, and the creep process of nanocrystalline Cu during the holding period and its relationship to dislocation and twin structures were examined. It was demonstrated that creep strain and creep strain rate are considerably significant for smaller grain sizes and higher loading strain rates, and are far higher than those predicted by the models of Cobble creep and grain boundary sliding. The analysis based on the calculations and experiments reveals that the significant creep deformation arises from the rapid absorption of high density dislocations stored in the loading regime. Our experiments imply that stored dislocations during loading are highly unstable and dislocation activity can proceed and lead to significant post-loading plasticity.

  6. Strain fields and line energies of dislocations in uranium dioxide

    NASA Astrophysics Data System (ADS)

    Parfitt, David C.; Bishop, Clare L.; Wenman, Mark R.; Grimes, Robin W.

    2010-05-01

    Computer simulations are used to investigate the stability of typical dislocations in uranium dioxide. We explain in detail the methods used to produce the dislocation configurations and calculate the line energy and Peierls barrier for pure edge and screw dislocations with the shortest Burgers vector {1\\over 2} \\langle 110 \\rangle . The easiest slip system is found to be the {100}lang110rang system for stoichiometric UO2, in agreement with experimental observations. We also examine the different strain fields associated with these line defects and the close agreement between the strain field predicted by atomic scale models and the application of elastic theory. Molecular dynamics simulations are used to investigate the processes of slip that may occur for the three different edge dislocation geometries and nudged elastic band calculations are used to establish a value for the Peierls barrier, showing the possible utility of the method in investigating both thermodynamic average behaviour and dynamic processes such as creep and plastic deformation.

  7. Measuring surface dislocation nucleation in defect-scarce nanostructures.

    PubMed

    Chen, Lisa Y; He, Mo-rigen; Shin, Jungho; Richter, Gunther; Gianola, Daniel S

    2015-07-01

    Linear defects in crystalline materials, known as dislocations, are central to the understanding of plastic deformation and mechanical strength, as well as control of performance in a variety of electronic and photonic materials. Despite nearly a century of research on dislocation structure and interactions, measurements of the energetics and kinetics of dislocation nucleation have not been possible, as synthesizing and testing pristine crystals absent of defects has been prohibitively challenging. Here, we report experiments that directly measure the surface dislocation nucleation strengths in high-quality 〈110〉 Pd nanowhiskers subjected to uniaxial tension. We find that, whereas nucleation strengths are weakly size- and strain-rate-dependent, a strong temperature dependence is uncovered, corroborating predictions that nucleation is assisted by thermal fluctuations. We measure atomic-scale activation volumes, which explain both the ultrahigh athermal strength as well as the temperature-dependent scatter, evident in our experiments and well captured by a thermal activation model. PMID:25985457

  8. Aspects of Dislocation Behavior in SiC

    SciTech Connect

    Dudley, M.; Chen, Y; Huang, X

    2009-01-01

    A review is presented of the current understanding of the dislocation configurations observed in PVT-grown 4H- and 6H-SiC boules and CVD-grown 4H-SiC homoepitaxial layers. In both PVT-grown boules and CVD-grown epilayers, dislocation configurations are classified according to whether they are growth dislocations, i.e., formed during growth via the replication of dislocations which thread the moving crystal growth front, or result from deformation processes (under either mechanical or electrical stress) immediately following growth, during post growth cooling, i.e., behind the crystal growth front or during device operation. Possible formation mechanisms of growth defects in the PVT grown boules, such as axial screw dislocations and threading edge dislocation walls are proposed. Similarly, possible origins of growth defect configurations in CVD-grown epilayers, such as Frank faults bounded by Frank partials, BPDs and TEDs, are also discussed. In a similar way, the origins of BPD configurations resulting from relaxation of thermal stresses during post-growth cooling of the PVT boules are discussed. Finally, the susceptibility of BPD configurations replicated into CVD grown epilayers from the substrate towards Recombination Enhanced Dislocation Glide (REDG) is discussed.

  9. Tectonic and gravity-induced deformation along the active Talas-Fergana Fault, Tien Shan, Kyrgyzstan

    NASA Astrophysics Data System (ADS)

    Tibaldi, A.; Corazzato, C.; Rust, D.; Bonali, F. L.; Pasquarè Mariotto, F. A.; Korzhenkov, A. M.; Oppizzi, P.; Bonzanigo, L.

    2015-08-01

    This paper shows, by field palaeoseismological data, the Holocene activity of the central segment of the intracontinental Talas-Fergana Fault (TFF), and the relevance of possible future seismic shaking on slope stability around a large water reservoir. The fault, striking NW-SE, is marked by a continuous series of scarps, deflected streams and water divides, and prehistoric earthquakes that offset substrate and Holocene deposits. Fault movements are characterised by right-lateral strike-slip kinematics with a subordinate component of uplift of the NE block. Structural, geological and geomorphological field data indicate that shallow and deep landslides are aligned along the TFF, and some of them are active. Where the TFF runs close to the reservoir, the fault trace is obscured by a series of landslides, affecting rock and soil materials and ranging in size from small slope instabilities to deep-seated gravity-induced slope deformations (DGSDs). The largest of these, which does not show clear evidence of present-day activity, involves a volume of about 1 km3 and is associated with smaller but active landslides in its lower part, with volumes in the order of 2.5 × 104 m3 to 1 × 106 m3. Based on the spatial and temporal relations between landslides and faults, we argue that at least some of these slope failures may have a coseismic character. Stability analyses by means of limit equilibrium methods (LEMs), and stress-strain analysis by finite difference numerical modelling (FDM), were carried out to evaluate different hazard scenarios linked to these slope instabilities. The results indicate concern for the different threats posed, ranging from the possible disruption of the M-41 highway, the main transportation route in central Asia, to the possible collapse of huge rock masses into the reservoir, possibly generating a tsunami.

  10. Quantitative observations of dislocation mechanisms in gamma TiAl

    SciTech Connect

    Viguier, B.; Cieslar, M.; Martin, J.L.; Hemker, K.J.

    1995-08-01

    Quantitative TEM observations have been made on a series of gamma Ti{sub 47}Al{sub 51}Mn{sub 2} polycrystals that were deformed at different temperatures. Special attention has been given to determining the statistical variation of defect densities that occur at the different temperatures. The results, which are in good agreement with mechanical testing, indicate that three different mechanisms control deformation in this alloy: lattice friction and the formation of faulted dipoles at low temperatures, the pinning of ordinary dislocations at intermediate temperatures, and the bowing and looping of dislocations at high temperatures. The anomalous flow strength of this alloy has been found to be related to the intrinsic pinning of ordinary dislocations. Details of this pinning and subsequent unzipping process, which are the basis for the new local-pinning-unzipping (LPU) models, are outlined within.

  11. Energetics and Noise in dislocation patterning.

    SciTech Connect

    Thomson, R. M.; Koslowski, M.; LeSar, R. ,

    2004-01-01

    The competition between energy and noise in the patterning transition in deformation is explored by employing a 2D model of parallel straight edge dislocations. We define a generalized force for ordering and show that at mechanical equilibrium, the ordering force is equal to the average back stress noise on the slip plane. We consider a system subjected to a total external strain that is a uniform linear function of time. When the external stress reaches a critical value that depends on the instantaneous state of strain and dislocation content, a discrete strain event occurs (what we have called elsewhere a percolation event) with the formation of one or perhaps a few micro slip steps on the surface. Within these micro slip bands, the dislocation content increases in a time short compared to the time between strain events. After the stress drop associated with the stain event, the strain stops. During the time between events, the configuration relaxes to a new equilibrium configuration, which may include thermally generated recovery. As the stress again builds owing to the continuously increasing total strain, it reaches a new critical stress determined by the newly achieved dislocation configuration. Our modeling addresses the changes during the relaxation of the system in the time between events. In our model, the initial state is a random configuration i.e., it does not contain any memory of the previous state of the deforming system. This is an extreme assumption, because in a real system, the order will evolve from one event to the next. Nevertheless, if the real system does order, we expect this to be captured in the model - we will simply be careful not to predict the quantitative order in the evolving system from our modeling.

  12. Design of a Deformed Flat Plate to Compensate the Gain Loss Due to the Gravity-Induced Surface Distortion of Large Reflector Antennas

    NASA Technical Reports Server (NTRS)

    Imbriale, W.; Rengarajan, S.; Cramer, P., Jr.

    1998-01-01

    This paper presents a novel design of a deformed flat plate, wherein known amounts of distortion are introduced in a compensating flat plate, to recover the gain-loss due to the gravity-induced surface deformations of a large reflector antenna.

  13. Dislocation of the hip (image)

    MedlinePlus

    A dislocation is an injury in which a bone is displaced from its proper position. Unless there are accompanying fractures or tissue damage, a simple dislocation may be manipulated back into place. Recovery may ...

  14. Some effects of thermal-cycle-induced deformation in rocket thrust chambers

    NASA Technical Reports Server (NTRS)

    Hannum, N. P.; Price, R. G., Jr.

    1981-01-01

    The deformation process observed in the hot gas side wall of rocket combustion chambers was investigaged for three different liner materials. Five thrust chambers were cycled to failure by using hydrogen and oxygen as propellants at a chamber pressure of 4.14 MN/cu m. The deformation was observed nondestructively at midlife points and destructively after failure occurred. The cyclic life results are presented with an accompanying discussion about the problems of life prediction associated with the types of failures encountered in the present work. Data indicating the deformation of the thrust chamber liner as cycles are accumulated are presented for each of the test thrust chambers. From these deformation data and observation of the failure sites it is evident that modeling the failure process as classic low cycle thermal fatigue is inadequate as a life prediction method.

  15. Locked volar distal radioulnar joint dislocation

    PubMed Central

    Bouri, Fadi; Fuad, Mazhar; Elsayed Abdolenour, Ayman

    2016-01-01

    Introduction Volar dislocation of the distal radioulnar joint is a rare injury which is commonly missed in the emergency departments. A thorough review of literature showed very few reported cases and the cause for irreducibility varied in different cases, Lack of suspicion and improper X-ray can delay the diagnosis. Case presentation Our article discusses a case 40 year old construction worker, who presented to the Emergency with work-related injury, complaining of left wrist pain, deformity and inability to rotate his forearm. X-rays revealed a volar dislocation of distal ulna which was reducible after manipulation under General Anesthesia (GA). The joint was stable after the reduction. Discussion Isolated dislocation of the distal radioulnar joint can be either volar or dorsal, although dorsal dislocation is more common. The distal radioulnar articulation plays an important role in the rotational movement of the forearm. It allows pronation and supination which are essential for the function of the upper limb. Pronator Quadratus muscle spasm is an important blockade to reduction and was preventing reduction in this case. Methods The work has been reported in line with the CARE criteria [9]. Conclusion Volar locked dislocation of Distal Radio ulnar joint is a rare injury. High degree of clinical suspicion and proper X-ray is required for prompt detection. The importance of this case is to raise the awareness among physicians in treating these kind of injuries by careful assessment of the patient and radiographs, and to consider pronator quadratus as an important cause for the blockade to reduction. PMID:27016647

  16. Deformation Mechanisms in Austenitic TRIP/TWIP Steel as a Function of Temperature

    NASA Astrophysics Data System (ADS)

    Martin, Stefan; Wolf, Steffen; Martin, Ulrich; Krüger, Lutz; Rafaja, David

    2016-01-01

    A high-alloy austenitic CrMnNi steel was deformed at temperatures between 213 K and 473 K (-60 °C and 200 °C) and the resulting microstructures were investigated. At low temperatures, the deformation 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 deformation bands. Deformation twinning of the austenite became the dominant deformation mechanism at 373 K (100 °C), whereas the conventional dislocation glide represented the prevailing deformation mode at 473 K (200 °C). The change of the deformation mechanisms 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 deformation 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.

  17. The influence of deformation-induced martensite on the cryogenic behavior of 300-series stainless steels

    SciTech Connect

    Morris, J.W. Jr.; Chan, J.W.; Mei, Z.

    1992-06-01

    The 300-series stainless steels that are commonly specified for the structures of high field superconducting magnets are metastable austenitic alloys that undergo martensitic transformations when deformed at low temperature. The martensitic tranformation is promoted by plastic deformation and by exposure to high magnetic fields. The transformation significantly influences the mechanical properties of the alloy. The mechanisms of this influence are reviewed, with emphasis on fatigue crack growth effects and magnetomechanical phenomena that have only recently been recognized.

  18. Oscillation of structure characteristics in polycrystalline nickel during plastic deformation

    SciTech Connect

    Dvorovienko, N.A.; Gernov, S.A.; Sirenko, A.F. . Dept. of Solid State Physics); Hamana, D. . Research Unit of Materiale Physic)

    1993-07-01

    The variation of X-ray diffraction characteristics (breadth at half maximum intensity, integrated intensity, dislocation density and residual stresses), as a function of plastic deformation rate, which occurs by uniaxial tensile test, has been studied. At room temperature the observed oscillation of studied characteristics in deformed polycrystalline nickel is due to the deformation mechanism change. The latter can be a translational displacement due to dislocations or a rotational displacement due to disclination.

  19. Comparison of geomechanical deformation induced by megatonne-scale CO2 storage at Sleipner, Weyburn, and In Salah.

    PubMed

    Verdon, James P; Kendall, J-Michael; Stork, Anna L; Chadwick, R Andy; White, Don J; Bissell, Rob C

    2013-07-23

    Geological storage of CO2 that has been captured at large, point source emitters represents a key potential method for reduction of anthropogenic greenhouse gas emissions. However, this technology will only be viable if it can be guaranteed that injected CO2 will remain trapped in the subsurface for thousands of years or more. A significant issue for storage security is the geomechanical response of the reservoir. Concerns have been raised that geomechanical deformation induced by CO2 injection will create or reactivate fracture networks in the sealing caprocks, providing a pathway for CO2 leakage. In this paper, we examine three large-scale sites where CO2 is injected at rates of ~1 megatonne/y or more: Sleipner, Weyburn, and In Salah. We compare and contrast the observed geomechanical behavior of each site, with particular focus on the risks to storage security posed by geomechanical deformation. At Sleipner, the large, high-permeability storage aquifer has experienced little pore pressure increase over 15 y of injection, implying little possibility of geomechanical deformation. At Weyburn, 45 y of oil production has depleted pore pressures before increases associated with CO2 injection. The long history of the field has led to complicated, sometimes nonintuitive geomechanical deformation. At In Salah, injection into the water leg of a gas reservoir has increased pore pressures, leading to uplift and substantial microseismic activity. The differences in the geomechanical responses of these sites emphasize the need for systematic geomechanical appraisal before injection in any potential storage site. PMID:23836635

  20. Comparison of geomechanical deformation induced by megatonne-scale CO2 storage at Sleipner, Weyburn, and In Salah

    PubMed Central

    Verdon, James P.; Kendall, J.-Michael; Stork, Anna L.; Chadwick, R. Andy; White, Don J.; Bissell, Rob C.

    2013-01-01

    Geological storage of CO2 that has been captured at large, point source emitters represents a key potential method for reduction of anthropogenic greenhouse gas emissions. However, this technology will only be viable if it can be guaranteed that injected CO2 will remain trapped in the subsurface for thousands of years or more. A significant issue for storage security is the geomechanical response of the reservoir. Concerns have been raised that geomechanical deformation induced by CO2 injection will create or reactivate fracture networks in the sealing caprocks, providing a pathway for CO2 leakage. In this paper, we examine three large-scale sites where CO2 is injected at rates of ∼1 megatonne/y or more: Sleipner, Weyburn, and In Salah. We compare and contrast the observed geomechanical behavior of each site, with particular focus on the risks to storage security posed by geomechanical deformation. At Sleipner, the large, high-permeability storage aquifer has experienced little pore pressure increase over 15 y of injection, implying little possibility of geomechanical deformation. At Weyburn, 45 y of oil production has depleted pore pressures before increases associated with CO2 injection. The long history of the field has led to complicated, sometimes nonintuitive geomechanical deformation. At In Salah, injection into the water leg of a gas reservoir has increased pore pressures, leading to uplift and substantial microseismic activity. The differences in the geomechanical responses of these sites emphasize the need for systematic geomechanical appraisal before injection in any potential storage site. PMID:23836635

  1. Opposite photo-induced deformations in azobenzene-containing polymers with different molecular architecture: Molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Ilnytskyi, Jaroslav M.; Neher, Dieter; Saphiannikova, Marina

    2011-07-01

    Photo-induced deformations in azobenzene-containing polymers (azo-polymers) are central to a number of applications, such as optical storage and fabrication of diffractive elements. The microscopic nature of the underlying opto-mechanical coupling is yet not clear. In this study, we address the experimental finding that the scenario of the effects depends on molecular architecture of the used azo-polymer. Typically, opposite deformations in respect to the direction of light polarization are observed for liquid crystalline and amorphous azo-polymers. In this study, we undertake molecular dynamics simulations of two different models that mimic these two types of azo-polymers. We employ hybrid force field modeling and consider only trans-isomers of azobenzene, represented as Gay-Berne sites. The effect of illumination on the orientation of the chromophores is considered on the level of orientational hole burning and emphasis is given to the resulting deformation of the polymer matrix. We reproduce deformations of opposite sign for the two models being considered here and discuss the relevant microscopic mechanisms in both cases.

  2. Opposite photo-induced deformations in azobenzene-containing polymers with different molecular architecture: Molecular dynamics study

    SciTech Connect

    Ilnytskyi, Jaroslav M.; Neher, Dieter; Saphiannikova, Marina

    2011-07-28

    Photo-induced deformations in azobenzene-containing polymers (azo-polymers) are central to a number of applications, such as optical storage and fabrication of diffractive elements. The microscopic nature of the underlying opto-mechanical coupling is yet not clear. In this study, we address the experimental finding that the scenario of the effects depends on molecular architecture of the used azo-polymer. Typically, opposite deformations in respect to the direction of light polarization are observed for liquid crystalline and amorphous azo-polymers. In this study, we undertake molecular dynamics simulations of two different models that mimic these two types of azo-polymers. We employ hybrid force field modeling and consider only trans-isomers of azobenzene, represented as Gay-Berne sites. The effect of illumination on the orientation of the chromophores is considered on the level of orientational hole burning and emphasis is given to the resulting deformation of the polymer matrix. We reproduce deformations of opposite sign for the two models being considered here and discuss the relevant microscopic mechanisms in both cases.

  3. Opposite photo-induced deformations in azobenzene-containing polymers with different molecular architecture: molecular dynamics study.

    PubMed

    Ilnytskyi, Jaroslav M; Neher, Dieter; Saphiannikova, Marina

    2011-07-28

    Photo-induced deformations in azobenzene-containing polymers (azo-polymers) are central to a number of applications, such as optical storage and fabrication of diffractive elements. The microscopic nature of the underlying opto-mechanical coupling is yet not clear. In this study, we address the experimental finding that the scenario of the effects depends on molecular architecture of the used azo-polymer. Typically, opposite deformations in respect to the direction of light polarization are observed for liquid crystalline and amorphous azo-polymers. In this study, we undertake molecular dynamics simulations of two different models that mimic these two types of azo-polymers. We employ hybrid force field modeling and consider only trans-isomers of azobenzene, represented as Gay-Berne sites. The effect of illumination on the orientation of the chromophores is considered on the level of orientational hole burning and emphasis is given to the resulting deformation of the polymer matrix. We reproduce deformations of opposite sign for the two models being considered here and discuss the relevant microscopic mechanisms in both cases. PMID:21806155

  4. Effect of drug-binding-induced deformation on the vibrational spectrum of a DNA.daunomycin complex

    NASA Astrophysics Data System (ADS)

    Chen, Y. Z.; Szabó, A.; Schroeter, D. F.; Powell, J. W.; Lee, S. A.; Prohofsky, E. W.

    1997-06-01

    Vibrational frequencies of a DNA.daunomycin complex and those of a free DNA helix and an isolated daunomycin are calculated and compared with the infrared spectrum of similar systems at frequencies above 600 cm-1. Our study indicates that the binding induces a considerable change in the vibrational spectrum of both DNA and the binding drug. The frequency shifts appear to be closely related to the conformational deformation in the complex caused by drug binding. Significant frequency shift is found in the normal modes in the DNA.drug complex that are primarily vibrations localized to the sugar-phosphate backbone of the binding site. Sizable frequency change is also found in the modes associated with base atoms involved in the drug binding and in the modes in regions of the binding daunomycin that are deformed by the binding. In contrast the frequency of the modes in the region with no significant deformation is relatively unchanged. The modification of the DNA dynamical force field by the nonbonded interactions between DNA and the drug is found to have little effect on the modes in DNA above 600 cm-1. The modification to the daunomycin dynamical force field appears to be sizable since the frequency of several daunomycin modes is changed by several cm-1. The close relationship between structure and spectrum revealed in this work is of potential application in the identification of sites and types of deformation of a biomolecule from Raman and infrared spectra.

  5. Dislocation dynamics in confined geometry

    NASA Astrophysics Data System (ADS)

    Gómez-García, D.; Devincre, B.; Kubin, L.

    1999-05-01

    A simulation of dislocation dynamics has been used to calculate the critical stress for a threading dislocation moving in a confined geometry. The optimum conditions for conducting simulations in systems of various sizes, down to the nanometer range, are defined. The results are critically compared with the available theoretical and numerical estimates for the problem of dislocation motion in capped layers.

  6. Behavior of dislocations in silicon

    SciTech Connect

    Sumino, Koji

    1995-08-01

    A review is given of dynamic behavior of dislocations in silicon on the basis of works of the author`s group. Topics taken up are generation, motion and multiplication of dislocations as affected by oxygen impurities and immobilization of dislocations due to impurity reaction.

  7. Deformation mechanism study of a hot rolled Zr-2.5Nb alloy by transmission electron microscopy. II. In situ transmission electron microscopy study of deformation mechanism change of a Zr-2.5Nb alloy upon heavy ion irradiation

    SciTech Connect

    Long, Fei; Daymond, Mark R. Yao, Zhongwen; Kirk, Marquis A.

    2015-03-14

    The effect of heavy-ion irradiation on deformation mechanisms of a Zr-2.5Nb alloy was investigated by using the in situ transmission electron microscopy deformation technique. The gliding behavior of prismatic 〈a〉 dislocations has been dynamically observed before and after irradiation at room temperature and 300 °C. Irradiation induced loops were shown to strongly pin the gliding dislocations. Unpinning occurred while loops were incorporated into or eliminated by 〈a〉 dislocations. In the irradiated sample, loop depleted areas with a boundary parallel to the basal plane trace were found by post-mortem observation after room temperature deformation, supporting the possibility of basal channel formation in bulk neutron irradiated samples. Strong activity of pyramidal slip was also observed at both temperatures, which might be another important mechanism to induce plastic instability in irradiated zirconium alloys. Finally, (011{sup ¯}1)〈01{sup ¯}12〉 twinning was identified in the irradiated sample deformed at 300 °C.

  8. Deformation mechanism study of a hot rolled Zr-2.5Nb alloy by transmission electron microscopy. II. In situ transmission electron microscopy study of deformation mechanism change of a Zr-2.5Nb alloy upon heavy ion irradiation

    NASA Astrophysics Data System (ADS)

    Long, Fei; Daymond, Mark R.; Yao, Zhongwen; Kirk, Marquis A.

    2015-03-01

    The effect of heavy-ion irradiation on deformation mechanisms of a Zr-2.5Nb alloy was investigated by using the in situ transmission electron microscopy deformation technique. The gliding behavior of prismatic dislocations has been dynamically observed before and after irradiation at room temperature and 300 °C. Irradiation induced loops were shown to strongly pin the gliding dislocations. Unpinning occurred while loops were incorporated into or eliminated by dislocations. In the irradiated sample, loop depleted areas with a boundary parallel to the basal plane trace were found by post-mortem observation after room temperature deformation, supporting the possibility of basal channel formation in bulk neutron irradiated samples. Strong activity of pyramidal slip was also observed at both temperatures, which might be another important mechanism to induce plastic instability in irradiated zirconium alloys. Finally, {01 1 ¯ 1 }⟨0 1 ¯ 12 ⟩ twinning was identified in the irradiated sample deformed at 300 °C.

  9. Congenital hip dislocation (image)

    MedlinePlus

    ... by a blow, fall, or other trauma, a dislocation can also occur from birth. The cause is unknown but genetic factors may play a role. Problems resulting from very mild developmental dysplasia of the hip may not become apparent until the person is ...

  10. Dislocated Worker Project.

    ERIC Educational Resources Information Center

    1988

    Due to the severe economic decline in the automobile manufacturing industry in southeastern Michigan, a Dislocated Workers Program has been developed through the partnership of the Flint Area Chamber of Commerce, three community colleges, the National Center for Research in Vocational Education, the Michigan State Department of Education, the…

  11. Impact-Induced Chondrule Deformation and Aqueous Alteration of CM2 Murchison

    NASA Technical Reports Server (NTRS)

    Hanna, R. D.; Zolensky, M.; Ketcham, R. A.; Behr, W. M.; Martinez, J. E.

    2014-01-01

    Deformed chondrules in CM2 Murchison have been found to define a prominent foliation [1,2] and lineation [3] in 3D using X-ray computed tomography (XCT). It has been hypothesized that chondrules in foliated chondrites deform by "squeezing" into surrounding pore space [4,5], a process that also likely removes primary porosity [6]. However, shock stage classification based on olivine extinction in Murchison is consistently low (S1-S2) [4-5,7] implying that significant intracrystalline plastic deformation of olivine has not occurred. One objective of our study is therefore to determine the microstructural mechanisms and phases that are accommodating the impact stress and resulting in relative displacements within the chondrules. Another question regarding impact deformation in Murchison is whether it facilitated aqueous alteration as has been proposed for the CMs which generally show a positive correlation between degree of alteration and petrofabric strength [7,2]. As pointed out by [2], CM Murchison represents a unique counterpoint to this correlation: it has a strong petrofabric but a relatively low degree of aqueous alteration. However, Murchison may not represent an inconsistency to the proposed causal relationship between impact and alteration, if it can be established that the incipient aqueous alteration post-dated chondrule deformation. Methods: Two thin sections from Murchison sample USNM 5487 were cut approximately perpendicular to the foliation and parallel to lineation determined by XCT [1,3] and one section was additionally polished for EBSD. Using a combination of optical petrography, SEM, EDS, and EBSD several chondrules were characterized in detail to: determine phases, find microstructures indicative of strain, document the geometric relationships between grain-scale microstructures and the foliation and lineation direction, and look for textural relationships of alteration minerals (tochilinite and Mg-Fe serpentine) that indicate timing of their

  12. Influence of misfit stresses on dislocation glide in single crystal superalloys: A three-dimensional discrete dislocation dynamics study

    NASA Astrophysics Data System (ADS)

    Gao, Siwen; Fivel, Marc; Ma, Anxin; Hartmaier, Alexander

    2015-03-01

    In the characteristic γ / γ ‧ microstructure of single crystal superalloys, misfit stresses occur due to a significant lattice mismatch of those two phases. The magnitude of this lattice mismatch depends on the chemical composition of both phases as well as on temperature. Furthermore, the lattice mismatch of γ and γ ‧ phases can be either positive or negative in sign. The internal stresses caused by such lattice mismatch play a decisive role for the micromechanical processes that lead to the observed macroscopic athermal deformation behavior of these high-temperature alloys. Three-dimensional discrete dislocation dynamics (DDD) simulations are applied to investigate dislocation glide in γ matrix channels and shearing of γ ‧ precipitates by superdislocations under externally applied uniaxial stresses, by fully taking into account internal misfit stresses. Misfit stress fields are calculated by the fast Fourier transformation (FFT) method and hybridized with DDD simulations. For external loading along the crystallographic [001] direction of the single crystal, it was found that the different internal stress states for negative and positive lattice mismatch result in non-uniform dislocation movement and different dislocation patterns in horizontal and vertical γ matrix channels. Furthermore, positive lattice mismatch produces a lower deformation rate than negative lattice mismatch under the same tensile loading, but for an increasing magnitude of lattice mismatch, the deformation resistance always diminishes. Hence, the best deformation performance is expected to result from alloys with either small positive, or even better, vanishing lattice mismatch between γ and γ ‧ phase.

  13. An electron microscopy study of dislocation structures in Mg single crystals compressed along [0 0 0 1] at room temperature

    DOE PAGESBeta

    Kumar, K. S.; Chisholm, Matthew F.; Geng, J.; Mishra, R. K.

    2016-01-09

    We compressed Mg single crystals along [0 0 0 1] at room temperature to various stress levels (40, 80, 120, 160 and 320 MPa) and the evolution of dislocation structure with stress increment was investigated by TEM slip is confirmed to be the dominant deformation mode; the predominance of edge dislocation debris lying along the <1 0more » $$\\bar{1}$$ 0> implies that screw dislocations are more mobile than their edge counterpart. The edge dislocation may dissociate into and dislocations, and the latter can extend further on the basal plane and bound a basal-stacking fault.« less

  14. Low temperature deformation detwinning - a reverse mode of twinning.

    SciTech Connect

    Wang, Y. D.; Liu, W.; Lu, L.; Ren, Y.; Nie, Z. H.; Almer, J.; Cheng, S.; Shen, Y. F.; Zuo, L.; Liaw, P. K.; Lu, K.

    2010-01-01

    The origin of the plasticity in bulk nanocrystalline metals have, to date, been attributed to the grain-boundary-mediated process, stress-induced grain coalescence, dislocation plasticity, and/or twinning. Here we report a different mechanism - detwinning, which operates at low temperatures during the tensile deformation of an electrodeposited Cu with a high density of nanosized growth twins. Both three-dimensional XRD microscopy using the Laue method with a submicron-sized polychromatic beam and high-energy XRD technique with a monochromatic beam provide the direct experimental evidences for low temperature detwinning of nanoscale twins.

  15. Computational study of dislocation based mechanisms in FCC materials

    NASA Astrophysics Data System (ADS)

    Yellakara, Ranga Nikhil

    Understanding the relationships between microstructures and properties of materials is a key to developing new materials with more suitable qualities or employing the appropriate materials in special uses. In the present world of material research, the main focus is on microstructural control to cost-effectively enhance properties and meet performance specifications. This present work is directed towards improving the fundamental understanding of the microscale deformation mechanisms and mechanical behavior of metallic alloys, particularly focusing on face centered cubic (FCC) structured metals through a unique computational methodology called three-dimensional dislocation dynamics (3D-DD). In these simulations, the equations of motion for dislocations are mathematically solved to determine the evolution and interaction of dislocations. Microstructure details and stress-strain curves are a direct observation in the simulation and can be used to validate experimental results. The effect of initial dislocation microstructure on the yield strength has been studied. It has been shown that dislocation density based crystal plasticity formulations only work when dislocation densities/numbers are sufficiently large so that a statistically accurate description of the microstructure can be obtainable. The evolution of the flow stress for grain sizes ranging from 0.5 to 10 mum under uniaxial tension was simulated using an improvised model by integrating dislocation pile-up mechanism at grain boundaries has been performed. This study showed that for a same initial dislocation density, the Hall--Petch relationship holds well at small grain sizes (0.5--2 mum), beyond which the yield strength remains constant as the grain size increases. Various dislocation-particle interaction mechanisms have been introduced and investigations were made on their effect on the uniaxial tensile properties. These studies suggested that increase in particle volume fraction and decrease in particle

  16. Cyclicity of the dislocation restructuring in necking in an hcp Zr-Nb alloy

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

    Cyclic dislocation transformations are detected in the deformation macrolocalization zone during tension of a Zr-1% Nb alloy, and this cyclicity is accompanied by periodic relaxation of internal stresses as a result of the decomposition of sub-boundaries and dislocation redistribution. The oscillatory instability of deformation localization in the hardening-softening mode at the parabolic stage of plastic flow in zirconium alloys is found to be related to the cyclicity of dislocation transformations in the macrolocalization zone during its transformation into a neck.

  17. Strength and Dislocation Structure Evolution of Small Metals under Vibrations

    NASA Astrophysics Data System (ADS)

    Ngan, Alfonso

    2015-03-01

    It is well-known that ultrasonic vibration can soften metals, and this phenomenon has been widely exploited in industrial applications concerning metal forming and bonding. In this work, we explore the effects of a superimposed small oscillatory load on metal plasticity, from the nano- to macro-size range, and from audible to ultrasonic frequency ranges. Macroscopic and nano-indentation were performed on aluminum, copper and molybdenum, and the results show that the simultaneous application of oscillatory stresses can lower the hardness of these samples. More interestingly, EBSD and TEM observations show that subgrain formation and reduction in dislocation density generally occurred when stress oscillations were applied. These findings point to an important knowledge gap in metal plasticity - the existing understanding of ultrasound softening in terms of the vibrations either imposing additional stress waves to augment the quasi-static applied load, or heating up the metal, whereas the metal's intrinsic deformation resistance or dislocation interactive processes are assumed unaltered by the ultrasound, is proven wrong by the present results. Furthermore, in the case of nanoindentation, the Continuous Stiffness Measurement technique for contact stiffness measurement assumes that the imposed signal-carrier oscillations do not intrinsically alter the material properties of the specimen, and again, the present results prove that this can be wrong. To understand the enhanced subgrain formation and dislocation annihilation, Discrete Dislocation Dynamics (DDD) simulations were carried out and these show that when an oscillatory stress is superimposed on a quasi-static applied stress, reversals of motion of dislocations may occur, and these allow the dislocations to revisit repeatedly suitable configurations for annihilation. DDD, however, was unable to predict the observed subgrain formation presumably because the number of dislocations that can be handled is not large

  18. Film-edge-induced dislocation generation in silicon substrates. II. Application of the theoretical model for local oxidation processes on (001) silicon substrates

    NASA Astrophysics Data System (ADS)

    Vanhellemont, J.; Amelinckx, S.; Claeys, C.

    1987-03-01

    A theoretical model which allows prediction of the type and of the equilibrium configuration of dislocations generated or captured in fcc substrates at the edges of thin films is applied to local oxidation processes on (001) Czochralski silicon substrates. Nitride film structures aligned along the two most interesting crystallographic directions on the (001) surface, i.e., the <110> and the <100> directions, are studied by high-voltage electron microscopy. The model allows to explain the observed dislocation types including most of the previous reports in the literature. Some numerical examples are given which illustrate the strength of the model to obtain even quantitative information both on the film stresses and on the critical glide force from the observed equilibrium configuration of the defects. Good agreement is obtained between the observed shape and position of the defects and computer simulations based on the model.

  19. Contributions of Cu-rich clusters, dislocation loops and nanovoids to the irradiation-induced hardening of Cu-bearing low-Ni reactor pressure vessel steels

    NASA Astrophysics Data System (ADS)

    Bergner, F.; Gillemot, F.; Hernández-Mayoral, M.; Serrano, M.; Török, G.; Ulbricht, A.; Altstadt, E.

    2015-06-01

    Dislocation loops, nanovoids and Cu-rich clusters (CRPs) are known to represent obstacles for dislocation glide in neutron-irradiated reactor pressure vessel (RPV) steels, but a consistent experimental determination of the respective obstacle strengths is still missing. A set of Cu-bearing low-Ni RPV steels and model alloys was characterized by means of SANS and TEM in order to specify mean size and number density of loops, nanovoids and CRPs. The obstacle strengths of these families were estimated by solving an over-determined set of linear equations. We have found that nanovoids are stronger than loops and loops are stronger than CRPs. Nevertheless, CRPs contribute most to irradiation hardening because of their high number density. Nanovoids were only observed for neutron fluences beyond typical end-of-life conditions of RPVs. The estimates of the obstacle strength are critically compared with reported literature data.

  20. Height bias and scale effect induced by antenna gravitational deformations in geodetic VLBI data analysis

    NASA Astrophysics Data System (ADS)

    Sarti, Pierguido; Abbondanza, Claudio; Petrov, Leonid; Negusini, Monia

    2011-01-01

    The impact of signal path variations (SPVs) caused by antenna gravitational deformations on geodetic very long baseline interferometry (VLBI) results is evaluated for the first time. Elevation-dependent models of SPV for Medicina and Noto (Italy) telescopes were derived from a combination of terrestrial surveying methods to account for gravitational deformations. After applying these models in geodetic VLBI data analysis, estimates of the antenna reference point positions are shifted upward by 8.9 and 6.7 mm, respectively. The impact on other parameters is negligible. To simulate the impact of antenna gravitational deformations on the entire VLBI network, lacking measurements for other telescopes, we rescaled the SPV models of Medicina and Noto for other antennas according to their size. The effects of the simulations are changes in VLBI heights in the range [-3, 73] mm and a net scale increase of 0.3-0.8 ppb. The height bias is larger than random errors of VLBI position estimates, implying the possibility of significant scale distortions related to antenna gravitational deformations. This demonstrates the need to precisely measure gravitational deformations of other VLBI telescopes, to derive their precise SPV models and to apply them in routine geodetic data analysis.

  1. Experiments of dike-induced deformation: Insights on the long-term evolution of divergent plate boundaries

    NASA Astrophysics Data System (ADS)

    Trippanera, D.; Ruch, J.; Acocella, V.; Rivalta, E.

    2015-10-01

    The shallow transport of magma occurs through dikes causing surface deformation. Our understanding of the effects of diking at the surface is limited, especially on the long term, for repeated intrusive episodes. We use analogue models to study the upper crustal deformation induced by dikes. We insert metal plates within cohesive sand with three setups: in setup A, the intrusion rises upward with constant thickness and in setups B and C, the intrusion thickens at a fixed depth, with final rectangular (setup B) or triangular (setup C) shape in section. Setup A creates a doming delimited by reverse faults, with secondary apical graben, without close correspondence in nature. In setups B and C, a depression flanked by two uplifted areas is bordered by inward dipping normal faults propagating downward and, for deeper intrusions in setup B, also by inner faults, reverse at the surface; this deformation is similar to what is observed in nature, suggesting a consistent physical behavior. Dikes in nature initially propagate developing a mode I fracture at the tip, subsequently thickened by magma intrusion, without any host rock translation in the propagation direction (as in setup A). The deformation pattern in setups B and C depends on the intrusion depth and thickness, consistently to what is observed along divergent plate boundaries. The early deformation in setups B and C is similar to that from a single rifting episode (i.e., Lakagigar, Iceland, and Dabbahu, Afar), whereas the late stages resemble the structure of mature rifts (i.e., Krafla, Iceland), confirming diking as a major process in shaping divergent plate boundaries.

  2. Application and Evaluation of ALOS PALSAR Data for Monitoring of Mining Induced Surface Deformations Using Interferometric Techniques

    NASA Astrophysics Data System (ADS)

    Walter, Diana; Wegmuller, Urs; Spreckels, Volker; Busch, Wolfgang

    2008-11-01

    The main objective of the projects "Determination of ground motions in mining areas by interferometric analyses of ALOS data" (ALOS ADEN 3576, ESA) and "Monitoring of mining induced surface deformation" (ALOS-RA-094, JAXA) is to evaluate PALSAR data for surface deformation monitoring, using interferometric techniques. We present monitoring results of surface movements for an active hard coal colliery of the German hard coal mining company RAG Deutsche Steinkohle (RAG). Underground mining activities lead to ground movements at the surface with maximum subsidence rates of about 10cm per month for the test site. In these projects the L-band sensor clearly demonstrates the good potential for deformation monitoring in active mining areas, especially in rural areas. In comparison to C-band sensors we clearly observe advantages in resolving the high deformation gradients that are present in this area and we achieve a more complete spatial coverage than with C-band. Extensive validation data based on levelling data and GPS measurements are available within RAǴs GIS based database "GeoMon" and thus enable an adequate analysis of the quality of the interferometric results. Previous analyses confirm the good accuracy of PALSAR data for deformation monitoring in mining areas. Furthermore, we present results of special investigations like precision geocoding of PALSAR data and corner reflector analysis. At present only DInSAR results are obtained due to the currently available number of PALSAR scenes. For the future we plan to also apply Persistent Scatterer Interferometry (PSI) using longer series of PALSAR data.

  3. Fault-induced deformation in a poorly consolidated, siliciclastic growth basin: A study from the Devonian in Norway

    NASA Astrophysics Data System (ADS)

    Braathen, A.; Osmundsen, P. T.; Hauso, H.; Semshaug, S.; Fredman, N.; Buckley, S. J.

    2013-02-01

    The extensional Berge fault (Devonian Kvamshesten Basin, West Norway) displays 430 m of syntectonic stratigraphy with fluvial sandstones and red fines exposed in a hanging wall growth section. The fault consists of three linked strands, where the offset diminishes and tips out stratigraphically upwards. Folds in the growth basin include a rollover and drag fold that record cumulative deformation during the main phases of fault slip, and a monocline that records the death and burial of the fault. Deformation styles in both the subbasin fill and the fault core indicate that the sediments were unconsolidated to poorly lithified during deformation. The upward-narrowing fault core consists of indurated breccias derived from footwall conglomerates, and mainly laminated fault gouge of subbasin affinity. Towards the hanging wall there is a mixed layer of sandstone lenses enclosed in fault gouge; this unit is variably sheared. In the damage zone deeper in the subbasin, truncating-style small-scale tabular shear bands show a general increase in frequency towards the fault, with abundant peaks in frequency next to the fault core. Smearing-style shear bands are merely encountered near the master fault. In the upper monocline realm, an overall broad zone of deformation reveals a moderate frequency of shear bands, characterized by clear distinctions between variably deformed layers. Some tabular dilation structures are found locally as layer-confined strain throughout the basin. We reason that the mixed layer is a product of fluid mobilization in/along the fault core. Fluid induced weakening combined with differential compaction would augment aseismic creep, as advocated for the creation of the smearing shear bands. We discuss a conceptual model in which damage zones grow by repeated rejuvenation and expand during propagation events, advocating that a distinctive damage zone becomes better expressed with increasing faulting events and depth (consolidation) in a growth basin.

  4. Learning intervention-induced deformations for non-rigid MR-CT registration and electrode localization in epilepsy patients

    PubMed Central

    Onofrey, John A.; Staib, Lawrence H.; Papademetris, Xenophon

    2015-01-01

    This paper describes a framework for learning a statistical model of non-rigid deformations induced by interventional procedures. We make use of this learned model to perform constrained non-rigid registration of pre-procedural and post-procedural imaging. We demonstrate results applying this framework to non-rigidly register post-surgical computed tomography (CT) brain images to pre-surgical magnetic resonance images (MRIs) of epilepsy patients who had intra-cranial electroencephalography electrodes surgically implanted. Deformations caused by this surgical procedure, imaging artifacts caused by the electrodes, and the use of multi-modal imaging data make non-rigid registration challenging. Our results show that the use of our proposed framework to constrain the non-rigid registration process results in significantly improved and more robust registration performance compared to using standard rigid and non-rigid registration methods. PMID:26900569

  5. Correlation between the Sorption-Induced Deformation of Nanoporous Glass and the Continuous Freezing of Adsorbed Argon.

    PubMed

    Schappert, Klaus; Reiplinger, Nicolas; Pelster, Rolf

    2016-08-01

    In this article we study the dependence of the sorption-induced deformation of nanoporous glass on the liquid-solid phase transition of adsorbed argon. During cooling we observe a continuous reduction of the expansion of the porous glass matrix caused by the adsorbate. The contraction is attended by a likewise continuous change of the adsorbed argon's phase state from liquid to solid. This simultaneous behavior evidences that the liquid-solid phase transition leads to a reduction of the pressure the adsorbate exerts on the pore walls. Furthermore, the study shows that small temperature changes can temporarily cause strong deformations of the porous material that decay in long time intervals of up to 1 week. We expect that our observations for the model system of argon and porous glass can be generalized to other systems. Consequently, this study will have implications when considering porous materials for applications, e.g., as a medium for storage. PMID:27398774

  6. Structural defects in natural plastically deformed diamonds: Evidence from EPR spectroscopy

    NASA Astrophysics Data System (ADS)

    Mineeva, R. M.; Titkov, S. V.; Speransky, A. V.

    2009-06-01

    Structural defects formed as a result of plastic deformation in natural diamond crystals have been studied by EPR spectroscopy. The spectra of brown, pink-brown, black-brown, pink-purple, and gray plastically deformed diamonds of type Ia from deposits in Yakutia and the Urals were recorded. The results of EPR spectroscopy allowed us to identify various deformation centers in the structure of natural diamonds and to show that nitrogen centers were transformed under epigenetic mechanical loading. Abundant A centers, consisting of two isomorphic nitrogen atoms located in neighboring structural sites, were destroyed as a result of this process to form a series of N1, N4, W7, M2, and M3 nitrogen centers. Such centers are characterized by an anisotropic spatial distribution and a positive charge, related to the mechanism of their formation. In addition, N2 centers (probably, deformation-produced dislocations decorated by nitrogen) were formed in all plastically deformed diamonds and W10 and W35 centers (the models have not been finally ascertained) were formed in some of them. It has been established that diamonds with various types of deformation-induced color contain characteristic associations of these deformation centers. The diversity of associations of deformation centers indicates appreciable variations in conditions of disintegration of deep-seated rocks, transfer of diamonds to the Earth’s surface, and formation of kimberlitic deposits. Depending on the conditions of mechanical loading, the diamond crystals were plastically deformed by either dislocation gliding or mechanical twinning. Characteristic features of plastic deformation by dislocation gliding are the substantial prevalence of the N2 centers over other deformation centers and the occurrence of the high-spin W10 and W35 centers. The attributes of less frequent plastic deformation by mechanical twinning are unusual localization of the M2 centers and, in some cases, the N1 centers in microtwinned

  7. A field theory of piezoelectric media containing dislocations

    SciTech Connect

    Taupin, V. Fressengeas, C.; Ventura, P.; Lebyodkin, M.

    2014-04-14

    A field theory is proposed to extend the standard piezoelectric framework for linear elastic solids by accounting for the presence and motion of dislocation fields and assessing their impact on the piezoelectric properties. The proposed theory describes the incompatible lattice distortion and residual piezoelectric polarization fields induced by dislocation ensembles, as well as the dynamic evolution of these fields through dislocation motion driven by coupled electro-mechanical loading. It is suggested that (i) dislocation mobility may be enhanced or inhibited by the electric field, depending on the polarity of the latter, (ii) plasticity mediated by dislocation motion allows capturing long-term time-dependent properties of piezoelectric polarization. Due to the continuity of the proposed electro-mechanical framework, the stress/strain and polarization fields are smooth even in the dislocation core regions. The theory is applied to gallium nitride layers for validation. The piezoelectric polarization fields associated with bulk screw/edge dislocations are retrieved and surface potential modulations are predicted. The results are extended to dislocation loops.

  8. Madelung Deformity and Extensor Tendon Rupture.

    PubMed

    Shahcheraghi, Gholam Hossain; Peyman, Maryam; Mozafarian, Kamran

    2015-07-01

    Extensor tendon rupture in chronic Madelung deformity, as a result of tendon attrition on the dislocated distal ulna, is a rare occurrence. It is, however, seen more often in rheumatoid arthritis. There are few case reports in the English-language literature on this issue. We report a case of multiple tendon ruptures in a previously undiagnosed Madelung deformity. PMID:26161772

  9. Ion adsorption and its influence on direct current electric field induced deformations of flexoelectric nematic layers

    NASA Astrophysics Data System (ADS)

    Derfel, Grzegorz; Buczkowska, Mariola

    2011-07-01

    The influence of ion adsorption on the behavior of the nematic liquid crystal layers is studied numerically. The homeotropic flexoelectric layer subjected to the dc electric field is considered. Selective adsorption of positive ions is assumed. The analysis is based on the free energy formalism for ion adsorption. The distributions of director orientation angle, electric potential, and ion concentrations are calculated by numerical resolving of suitable torques equations and Poisson equation. The threshold voltages for the deformations are also determined. It was shown that adsorption affects the distributions of both cations and anions. Sufficiently large number of adsorbed ions leads to spontaneous deformation arising without any threshold if the total number of ions creates sufficiently strong electric field with significant field gradients in the neighborhood of electrodes. The spontaneous deformations are favored by strong flexoelectricity, large thickness, large ion concentrations, weak anchoring, and large adsorption energy.

  10. The Spectrum of Recovery From Fracture-Induced Vertebral Deformity in Pediatric Leukemia.

    PubMed

    Dal Osto, Leo C; Konji, Victor N; Halton, Jacqueline; Matzinger, Mary Ann; Bassal, Mylène; Rauch, Frank; Ward, Leanne M

    2016-06-01

    Vertebral fractures (VF) are a frequent complication of acute lymphoblastic leukemia. Some children with VF undergo vertebral body reshaping to the point of complete restoration of normal vertebral dimensions. Others are left with permanent vertebral deformity if the degree of reshaping has been incomplete by the time of final adult height attainment. In this report, we describe three children with painful VF at leukemia diagnosis or during chemotherapy. Each patient highlights different clinical trajectories in their recovery from VF and underscores the need for osteoporosis intervention trials with the goal to prevent permanent vertebral deformity in selected patients. PMID:26878592

  11. 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.

  12. Molecular Dynamic Study of a Single Dislocation in a Two-Dimensional Lennard Jones System

    NASA Astrophysics Data System (ADS)

    Robles, Miguel; Mustonen, Ville; Kaski, Kimmo

    In this work the motion of a single dislocation in a two-dimensional triangular lattice is studied by using classical Molecular Dynamics method with the Lennard Jones inter-atomic potential. The dislocation motion is investigated with an interactive simulation program developed to track automatically the movement of lattice defects. Constant strain and constant strain-rate deformations were applied to the system. From constant strain simulations a curve of shear stress versus dislocation velocity is obtained, showing a nonlinear power law relation. An equation of motion for the dislocation is proposed and found to be applicable when the movement of dislocation follows a quasi-static process. Numerical simulations at different strain rates show an elastic-to-plastic transition that modifies the dynamics of the dislocation motion.

  13. Dislocation Ledge Sources: Dispelling the Myth of Frank-Read Source Importance

    NASA Astrophysics Data System (ADS)

    Murr, L. E.

    2016-01-01

    In the early 1960s, J.C.M. Li questioned the formation of dislocation pileups at grain boundaries, especially in high-stacking-fault free-energy fcc metals and alloys, and proposed grain boundary ledge sources for dislocations in contrast to Frank-Read sources. This article reviews these proposals and the evolution of compelling evidence for grain boundary or related interfacial ledge sources of dislocations in metals and alloys, including unambiguous observations using transmission electron microscopy. Such observations have allowed grain boundary ledge source emission profiles of dislocations to be quantified in 304 stainless steel (with a stacking-fault free energy of ~23 mJ/m2) and nickel (with a stacking-fault free energy of ~128 mJ/m2) as a function of engineering strain. The evidence supports the conclusion that FR dislocation sources are virtually absent in metal and alloy deformation with ledges at interfaces dominating as dislocation sources.

  14. Dislocation dynamics simulations of plasticity at small scales

    SciTech Connect

    Zhou, Caizhi

    2010-01-01

    As metallic structures and devices are being created on a dimension comparable to the length scales of the underlying dislocation microstructures, the mechanical properties of them change drastically. Since such small structures are increasingly common in modern technologies, there is an emergent need to understand the critical roles of elasticity, plasticity, and fracture in small structures. Dislocation dynamics (DD) simulations, in which the dislocations are the simulated entities, offer a way to extend length scales beyond those of atomistic simulations and the results from DD simulations can be directly compared with the micromechanical tests. The primary objective of this research is to use 3-D DD simulations to study the plastic deformation of nano- and micro-scale materials and understand the correlation between dislocation motion, interactions and the mechanical response. Specifically, to identify what critical events (i.e., dislocation multiplication, cross-slip, storage, nucleation, junction and dipole formation, pinning etc.) determine the deformation response and how these change from bulk behavior as the system decreases in size and correlate and improve our current knowledge of bulk plasticity with the knowledge gained from the direct observations of small-scale plasticity. Our simulation results on single crystal micropillars and polycrystalline thin films can march the experiment results well and capture the essential features in small-scale plasticity. Furthermore, several simple and accurate models have been developed following our simulation results and can reasonably predict the plastic behavior of small scale materials.

  15. Single crystal plasticity by modeling dislocation density rate behavior

    SciTech Connect

    Hansen, Benjamin L; Bronkhorst, Curt; Beyerlein, Irene; Cerreta, E. K.; Dennis-Koller, Darcie

    2010-12-23

    The goal of this work is to formulate a constitutive model for the deformation of metals over a wide range of strain rates. Damage and failure of materials frequently occurs at a variety of deformation rates within the same sample. The present state of the art in single crystal constitutive models relies on thermally-activated models which are believed to become less reliable for problems exceeding strain rates of 10{sup 4} s{sup -1}. This talk presents work in which we extend the applicability of the single crystal model to the strain rate region where dislocation drag is believed to dominate. The elastic model includes effects from volumetric change and pressure sensitive moduli. The plastic model transitions from the low-rate thermally-activated regime to the high-rate drag dominated regime. The direct use of dislocation density as a state parameter gives a measurable physical mechanism to strain hardening. Dislocation densities are separated according to type and given a systematic set of interactions rates adaptable by type. The form of the constitutive model is motivated by previously published dislocation dynamics work which articulated important behaviors unique to high-rate response in fcc systems. The proposed material model incorporates thermal coupling. The hardening model tracks the varying dislocation population with respect to each slip plane and computes the slip resistance based on those values. Comparisons can be made between the responses of single crystals and polycrystals at a variety of strain rates. The material model is fit to copper.

  16. Thermomechanical Modeling of Laser-Induced Structural Relaxation and Deformation of Glass: Volume Changes in Fused Silica at High Temperatures [Thermo-mechanical modeling of laser-induced structural relaxation and deformation of SiO2 glass

    SciTech Connect

    Vignes, Ryan M.; Soules, Thomas F.; Stolken, James S.; Settgast, Randolph R.; Elhadj, Selim; Matthews, Manyalibo J.; Mauro, J.

    2012-12-17

    In a fully coupled thermomechanical model of the nanoscale deformation in amorphous SiO2 due to laser heating is presented. Direct measurement of the transient, nonuniform temperature profiles was used to first validate a nonlinear thermal transport model. Densification due to structural relaxation above the glass transition point was modeled using the Tool-Narayanaswamy (TN) formulation for the evolution of structural relaxation times and fictive temperature. TN relaxation parameters were derived from spatially resolved confocal Raman scattering measurements of Si–O–Si stretching mode frequencies. These thermal and microstructural data were used to simulate fictive temperatures which are shown to scale nearly linearly with density, consistent with previous measurements from Shelby et al. Volumetric relaxation coupled with thermal expansion occurring in the liquid-like and solid-like glassy states lead to residual stresses and permanent deformation which could be quantified. But, experimental surface deformation profiles between 1700 and 2000 K could only be reconciled with our simulation by assuming a roughly 2 × larger liquid thermal expansion for a-SiO2 with a temperature of maximum density ~150 K higher than previously estimated by Bruckner et al. Calculated stress fields agreed well with recent laser-induced critical fracture measurements, demonstrating accurate material response prediction under processing conditions of practical interest.

  17. Experimental characterisation and modelling of deformation- induced microstructure in an A6061 aluminium alloy

    NASA Astrophysics Data System (ADS)

    Kreyca, J. F.; Falahati, A.; Kozeschnik, E.

    2016-03-01

    For industry, the mechanical properties of a material in form of flow curves are essential input data for finite element simulations. Current practice is to obtain flow curves experimentally and to apply fitting procedures to obtain constitutive equations that describe the material response to external loading as a function of temperature and strain rate. Unfortunately, the experimental procedure for characterizing flow curves is complex and expensive, which is why the prediction of flow-curves by computer modelling becomes increasingly important. In the present work, we introduce a state parameter based model that is capable of predicting the flow curves of an A6061 aluminium alloy in different heat-treatment conditions. The model is implemented in the thermo-kinetic software package MatCalc and takes into account precipitation kinetics, subgrain formation, dynamic recovery by spontaneous annihilation and dislocation climb. To validate the simulation results, a series of compression tests is performed on the thermo-mechanical simulator Gleeble 1500.

  18. Distinguishing shocked from tectonically deformed quartz by the use of the SEM and chemical etching

    USGS Publications Warehouse

    Gratz, A.J.; Fisler, D.K.; Bohor, B.F.

    1996-01-01

    Multiple sets of crystallographically-oriented planar deformation features (PDFs) are generated by high-strain-rate shock waves at pressures of > 12 GPa in naturally shocked quartz samples. On surfaces, PDFs appear as narrow (50-500 nm) lamellae filled with amorphosed quartz (diaplectic glass) which can be etched with hydrofluoric acid or with hydrothermal alkaline solutions. In contrast, slow-strain-rate tectonic deformation pressure produces wider, semi-linear and widely spaced arrays of dislocation loops that are not glass filled. Etching samples with HF before examination in a scanning electron microscope (SEM) allows for unambiguous visual distinction between glass-filled PDFs and glass-free tectonic deformation arrays in quartz. This etching also reveals the internal 'pillaring' often characteristic of shock-induced PDFs. This technique is useful for easily distinguishing between shock and tectonic deformation in quartz, but does not replace optical techniques for characterizing the shock features.

  19. 2DEG on a cylindrical shell with a screw dislocation

    NASA Astrophysics Data System (ADS)

    Filgueiras, Cleverson; Silva, Edilberto O.

    2015-09-01

    A two dimensional electron gas on a cylindrical surface with a screw dislocation is considered. More precisely, we investigate how both the geometry and the deformed potential due to a lattice distortion affect the Landau levels of such system. The case showing the deformed potential can be thought in the context of 3D common semiconductors where the electrons are confined on a cylindrical shell. We will show that important quantitative differences exist due to this lattice distortion. For instance, the effective cyclotron frequency is diminished by the deformed potential, which in turn enhances the Hall conductivity.

  20. Deformation-induced structural transition in body-centred cubic molybdenum

    PubMed Central

    Wang, S. J.; Wang, H.; Du, K.; Zhang, W.; Sui, M. L.; Mao, S. X.

    2014-01-01

    Molybdenum is a refractory metal that is stable in a body-centred cubic structure at all temperatures before melting. Plastic deformation via structural transitions has never been reported for pure molybdenum, while transformation coupled with plasticity is well known for many alloys and ceramics. Here we demonstrate a structural transformation accompanied by shear deformation from an original <001>-oriented body-centred cubic structure to a <110>-oriented face-centred cubic lattice, captured at crack tips during the straining of molybdenum inside a transmission electron microscope at room temperature. The face-centred cubic domains then revert into <111>-oriented body-centred cubic domains, equivalent to a lattice rotation of 54.7°, and ~15.4% tensile strain is reached. The face-centred cubic structure appears to be a well-defined metastable state, as evidenced by scanning transmission electron microscopy and nanodiffraction, the Nishiyama–Wassermann and Kurdjumov–Sachs relationships between the face-centred cubic and body-centred cubic structures and molecular dynamics simulations. Our findings reveal a deformation mechanism for elemental metals under high-stress deformation conditions. PMID:24603655