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Sample records for dynamic dislocation mechanisms

  1. Dislocation climb models from atomistic scheme to dislocation dynamics

    Science.gov (United States)

    Niu, Xiaohua; Luo, Tao; Lu, Jianfeng; Xiang, Yang

    2017-02-01

    We develop a mesoscopic dislocation dynamics model for vacancy-assisted dislocation climb by upscalings from a stochastic model on the atomistic scale. Our models incorporate microscopic mechanisms of (i) bulk diffusion of vacancies, (ii) vacancy exchange dynamics between bulk and dislocation core, (iii) vacancy pipe diffusion along the dislocation core, and (iv) vacancy attachment-detachment kinetics at jogs leading to the motion of jogs. Our mesoscopic model consists of the vacancy bulk diffusion equation and a dislocation climb velocity formula. The effects of these microscopic mechanisms are incorporated by a Robin boundary condition near the dislocations for the bulk diffusion equation and a new contribution in the dislocation climb velocity due to vacancy pipe diffusion driven by the stress variation along the dislocation. Our climb formulation is able to quantitatively describe the translation of prismatic loops at low temperatures when the bulk diffusion is negligible. Using this new formulation, we derive analytical formulas for the climb velocity of a straight edge dislocation and a prismatic circular loop. Our dislocation climb formulation can be implemented in dislocation dynamics simulations to incorporate all the above four microscopic mechanisms of dislocation climb.

  2. Dynamic mechanical behaviour and dislocation substructure evolution of Inconel 718 over wide temperature range

    Energy Technology Data Exchange (ETDEWEB)

    Lee, Woei-Shyan, E-mail: wslee@mail.ncku.edu.tw [Department of Mechanical Engineering, National Cheng Kung University, Tainan 701, Taiwan (China); Lin, Chi-Feng [National Center for High-Performance Computing, Hsin-Shi Tainan County 744, Taiwan (China); Chen, Tao-Hsing [Department of Mechanical Engineering, National Kaohsiung University of Applied Sciences, Kaohsiung 807, Taiwan (China); Chen, Hong-Wei [Department of Mechanical Engineering, National Cheng Kung University, Tainan 701, Taiwan (China)

    2011-07-25

    A compressive split-Hopkinson pressure bar and transmission electron microscope (TEM) are used to investigate the mechanical behaviour and microstructural evolution of Inconel 718 at strain rates ranging from 1000 to 5000 s{sup -1} and temperatures between -150 and 550 deg. C. The results show that the flow stress increases with an increasing strain rate or a reducing temperature. The strain rate effect is particularly pronounced at strain rates greater than 3000 s{sup -1} and a deformation temperature of -150 deg. C. A significant thermal softening effect occurs at temperatures between -150 and 25 deg. C. The microstructural observations reveal that the strengthening effect in deformed Inconel 718 alloy is a result primarily of dislocation multiplication. The dislocation density increases with increasing strain rate, but decreases with increasing temperature. By contrast, the dislocation cell size decreases with increasing strain rate, but increases with increasing temperature. It is shown that the correlation between the flow stress, the dislocation density and the dislocation cell size is well described by the Bailey-Hirsch constitutive equations.

  3. Dislocation climb in two-dimensional discrete dislocation dynamics

    NARCIS (Netherlands)

    Davoudi, K.M.; Nicola, L.; Vlassak, J.J.

    2012-01-01

    In this paper, dislocation climb is incorporated in a two-dimensional discrete dislocation dynamics model. Calculations are carried out for polycrystalline thin films, passivated on one or both surfaces. Climb allows dislocations to escape from dislocation pile-ups and reduces the strain-hardening r

  4. Dislocation Dynamics in Nanocrystalline Nickel

    OpenAIRE

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

    2007-01-01

    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...

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

    Science.gov (United States)

    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.

  6. Ultrasonic Study of Dislocation Dynamics in Lithium -

    Science.gov (United States)

    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.

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

    Science.gov (United States)

    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.

  8. Dynamic Dislocation Mechanisms For the Anomalous Slip in a Single-Crystal BCC Metal Oriented for "Single Slip"

    Energy Technology Data Exchange (ETDEWEB)

    Hsiung, L; La Cruz, C

    2007-01-11

    Dislocation substructures of high-purity Mo single crystals deformed under uniaxial compression at room temperature to an axial strain of 0.6% were investigated in order to elucidate the underlying mechanisms for the {l_brace}0{bar 1}1{r_brace} anomalous slip in bcc metals [1], which is also known as the violation of Schmid law [2]. The test sample was oriented with the stress axis parallel to a nominal ''single-slip'' orientation of [{bar 2} 9 20], in which ({bar 1}01) [111] is the primary slip system that has a maximum Schmid factor (m = 0.5), which requires the lowest stress to operate among the twelve {l_brace}{bar 1}10{r_brace} <111> slip systems. Nevertheless, the recorded stress-strain curve reveals no easy-glide or single-slip stage; work hardening starts immediately after yielding. Moreover, the result of slip trace analysis indicates the occurrence of anomalous slip on both the (011) and (0{bar 1}1) planes, which according to the Schmid law requires relatively higher stresses to operate. TEM examinations of dislocation structures formed on the (101) primary slip plane reveal that in addition to the ({bar 1}01) [111] slip system, the coplanar ({bar 1}01) [1{bar 1}1] slip system which has a much smaller Schmid factor (m = 0.167) is also operative. Similarly, (0{bar 1}1) [111] (m = 0.25) is cooperative with the coplanar (0{bar 1}1) [{bar 1}11] slip system (m = 0.287) on the (0{bar 1}1) slip plane, and (011) [1{bar 1}1] (m = 0.222) is cooperative with the coplanar (011) [11{bar 1}] slip system (m = 0.32) on the (011) plane. The occurrence of {l_brace}0{bar 1}1{r_brace} anomalous slip is accordingly proposed to be originated from the cooperative dislocation motion of the {+-} 1/2 [111] and {+-} 1/2 [1{bar 1}1] dislocations on the ({bar 1}01) slip plane; the mutual interaction and blocking of {+-} 1/2 [111] and {+-} 1/2 [1{bar 1}1] dislocations not only cause an increase of glide resistance to the dislocation motion on the ({bar 1}01) plane

  9. Interaction of 〈1 0 0〉 dislocation loops with dislocations studied by dislocation dynamics in α-iron

    Energy Technology Data Exchange (ETDEWEB)

    Shi, X.J.; Dupuy, L. [CEA, DEN, SRMA, F-91191 Gif-sur-Yvette (France); Devincre, B. [Laboratoire d’Etude des Microstructures, CNRS-ONERA, 29 av. de la Division Leclerc, 92322 Châtillon Cedex (France); Terentyev, D. [SCK–CEN, Nuclear Materials Science Institute, Boeretang 200, B-2400 Mol (Belgium); Vincent, L. [CEA, DEN, SRMA, F-91191 Gif-sur-Yvette (France)

    2015-05-15

    Highlights: • Interactions between edge dislocations and radiation-induced loops were studied by dislocation dynamics. • Dislocation dynamics results are directly compared to molecular dynamics results. • The complex elementary reactions are successfully reproduced. • The critical shear stress to overcome individual loops if reproduced quantitatively. - Abstract: Interstitial dislocation loops with Burgers vector of 〈1 0 0〉 type are formed in α-iron under neutron or heavy ion irradiation. As the density and size of these loops increase with radiation dose and temperature, these defects are thought to play a key role in hardening and subsequent embrittlement of iron-based steels. The aim of the present work is to study the pinning strength of the loops on mobile dislocations. Prior to run massive Dislocation Dynamics (DD) simulations involving experimentally representative array of radiation defects and dislocations, the DD code and its parameterization are validated by comparing the individual loop–dislocation reactions with those obtained from direct atomistic Molecular Dynamics (MD) simulations. Several loop–dislocation reaction mechanisms are successfully reproduced as well as the values of the unpinning stress to detach mobile dislocations from the defects.

  10. Evolution of geometrically necessary dislocation density from computational dislocation dynamics

    Science.gov (United States)

    Guruprasad, P. J.; Benzerga, A. A.

    2009-07-01

    This paper presents a method for calculating GND densities in dislocation dynamics simulations. Evolution of suitably defined averages of GND density as well as maps showing the spatial nonuniform distribution of GNDs are analyzed under uniaxial loading. Focus is laid on the resolution dependence of the very notion of GND density, its dependence upon physical dimensions of plastically deformed specimens and its sensitivity to initial conditions. Acknowledgments Support from the National Science Foundation (CMMI-0748187) is gratefully acknowledged.

  11. Atomistic simulation of hydrogen dynamics near dislocations in vanadium hydrides

    Energy Technology Data Exchange (ETDEWEB)

    Ogawa, Hiroshi, E-mail: h.ogawa@aist.go.jp

    2015-10-05

    Highlights: • Hydrogen–dislocation interaction was simulated by molecular dynamics method. • Different distribution of H atoms were observed at edge and screw dislocation. • Planner distribution of hydrogen may be caused by partialized edge dislocation. • Hydrogen diffusivity was reduced in both edge and screw dislocation models. • Pipe diffusion was observed for edge dislocation but not for screw dislocation. - Abstract: Kinetics of interstitial hydrogen atoms near dislocation cores were analyzed by atomistic simulation. Classical molecular dynamics method was applied to model structures of edge and screw dislocations in α-phase vanadium hydride. Simulation showed that hydrogen atoms aggregate near dislocation cores. The spatial distribution of hydrogen has a planner shape at edge dislocation due to dislocation partialization, and a cylindrical shape at screw dislocation. Simulated self-diffusion coefficients of hydrogen atoms in dislocation models were a half- to one-order lower than that of dislocation-free model. Arrhenius plot of self-diffusivity showed slightly different activation energies for edge and screw dislocations. Directional dependency of hydrogen diffusion near dislocation showed high and low diffusivity along edge and screw dislocation lines, respectively, hence so called ‘pipe diffusion’ possibly occur at edge dislocation but does not at screw dislocation.

  12. How to identify dislocations in molecular dynamics simulations?

    Science.gov (United States)

    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.

  13. CYCLIC HARDENING BEHAVIOR OF POLYCRYSTALS WITH PENETRABLE GRAIN BOUNDARIES: TWO-DIMENSIONAL DISCRETE DISLOCATION DYNAMICS SIMULATION

    Institute of Scientific and Technical Information of China (English)

    Chuantao Hou; Zhenhuan Li; Minsheng Huang; Chaojun Ouyang

    2009-01-01

    A two-dimensional discrete dislocation dynamics (DDD) technology by Giessen and Needleman (1995), which has been extended by integrating a dislocation-grain boundary interaction model, is used to computationally analyze the micro-cyclic plastic response of polycrystals containing micron-sized grains, with special attentions to significant influence of dislocationpenetrable grain boundaries (GBs) on the micro-plastic cyclic responses of polycrystals and underlying dislocation mechanism. Toward this end, a typical polycrystalline rectangular specimen under simple tension-compression loading is considered. Results show that, with the increase of cycle accumulative strain, continual dislocation accumulation and enhanced dislocation-dislocation interactions induce the cyclic hardening behavior; however, when a dynamic balance among dislocation nucleation, penetration through GB and dislocation annihilation is approximately established, cyclic stress gradually tends to saturate. In addition, other factors, including the grain size, cyclic strain amplitude and its history, also have considerable influences on the cyclic hardening and saturation.

  14. Dislocations: 75 years of Deformation Mechanisms

    Science.gov (United States)

    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.

  15. Dislocation dynamics simulations of plasticity at small scales

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Caizhi [Iowa State Univ., Ames, IA (United States)

    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.

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

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Qian [Iowa State Univ., Ames, IA (United States)

    2008-01-01

    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.

  17. Dislocation pinning effects on fracture behavior: Atomistic and dislocation dynamics simulations

    Science.gov (United States)

    Noronha, S. J.; Farkas, D.

    2002-10-01

    We introduce an approach in which results from atomistic simulations are combined with discrete dislocation dynamics simulations of crack-tip plasticity. The method is used to study the effects of dislocation pinning due to grain boundaries or secondary particles on the fracture behavior of aluminum. We find that the fracture resistance is reduced with decreasing pinning distance. The results show that the pinning of the dislocations causes a net decrease in the shear stress projected on the slip plane, preventing further dislocation emission. Semibrittle cleavage occurs after a certain number of dislocations is emitted.

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

    NARCIS (Netherlands)

    Davoudi, K.M.; Nicola, L.; Vlassak, J.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

  19. Observation of dislocation dynamics in the electron microscope

    Energy Technology Data Exchange (ETDEWEB)

    Lagow, B W; Robertson, I M; Jouiad, M; Lassila, D H; Lee, T C; Birnbaum, H K

    2001-01-17

    Deformation experiments performed in-situ in the transmission electron microscope have led to an increased understanding of dislocation dynamics. To illustrate the capability of this technique two examples will be presented. In the first example, the processes of work hardening in Mo at room temperature will be presented. These studies have improved our understanding of dislocation mobility, dislocation generation, and dislocation-obstacle interactions. In the second example, the interaction of matrix dislocations with grain boundaries will be described. From such studies predictive criteria for slip transfer through grain boundaries have been developed.

  20. Observation of Dislocation Dynamics in the Electron Microscope

    Energy Technology Data Exchange (ETDEWEB)

    Lagow, B W; Robertson, I M; Jouiad, M; Lassila, D H; Lee, T C; Birnbaum, H K

    2001-08-21

    Deformation experiments performed in-situ in the transmission electron microscope have led to an increased understanding of dislocation dynamics. To illustrate the capability of this technique two examples will be presented. In the first example, the processes of work hardening in Mo at room temperature will be presented. These studies have improved our understanding of dislocation mobility, dislocation generation, and dislocation-obstacle interactions. In the second example, the interaction of matrix dislocations with grain boundaries will be described. From such studies predictive criteria for slip transfer through grain boundaries have been developed.

  1. 3D discrete dislocation dynamics study of creep behavior in Ni-base single crystal superalloys by a combined dislocation climb and vacancy diffusion model

    Science.gov (United States)

    Gao, Siwen; Fivel, Marc; Ma, Anxin; Hartmaier, Alexander

    2017-05-01

    A three-dimensional (3D) discrete dislocation dynamics (DDD) creep model is developed to investigate creep behavior under uniaxial tensile stress along the crystallographic [001] direction in Ni-base single crystal superalloys, which takes explicitly account of dislocation glide, climb and vacancy diffusion, but neglects phase transformation like rafting of γ‧ precipitates. The vacancy diffusion model takes internal stresses by dislocations and mismatch strains into account and it is coupled to the dislocation dynamics model in a numerically efficient way. This model is helpful for understanding the fundamental creep mechanisms in superalloys and clarifying the effects of dislocation glide and climb on creep deformation. In cases where the precipitate cutting rarely occurs, e.g. due to the high anti-phase boundary energy and the lack of superdislocations, the dislocation glide in the γ matrix and the dislocation climb along the γ/γ‧ interface dominate plastic deformation. The simulation results show that a high temperature or a high stress both promote dislocation motion and multiplication, so as to cause a large creep strain. Dislocation climb accelerated by high temperature only produces a small plastic strain, but relaxes the hardening caused by the filling γ channels and lets dislocations further glide and multiply. The strongest variation of vacancy concentration occurs in the horizontal channels, where more mixed dislocations exit and tend to climb. The increasing internal stresses due to the increasing dislocation density are easily overcome by dislocations under a high external stress that leads to a long-term dislocation glide accompanied by multiplication.

  2. Riemann–Cartan Geometry of Nonlinear Dislocation Mechanics

    KAUST Repository

    Yavari, Arash

    2012-03-09

    We present a geometric theory of nonlinear solids with distributed dislocations. In this theory the material manifold-where the body is stress free-is a Weitzenböck manifold, that is, a manifold with a flat affine connection with torsion but vanishing non-metricity. Torsion of the material manifold is identified with the dislocation density tensor of nonlinear dislocation mechanics. Using Cartan\\'s moving frames we construct the material manifold for several examples of bodies with distributed dislocations. We also present non-trivial examples of zero-stress dislocation distributions. More importantly, in this geometric framework we are able to calculate the residual stress fields, assuming that the nonlinear elastic body is incompressible. We derive the governing equations of nonlinear dislocation mechanics covariantly using balance of energy and its covariance. © 2012 Springer-Verlag.

  3. Mechanisms and rate of dislocation nucleation in aluminum-copper alloys near Guinier-Preston zones

    Science.gov (United States)

    Bryukhanov, I. A.; Larin, A. V.

    2016-12-01

    This article is devoted to a molecular dynamics simulation study of partial dislocation loop nucleation with respect to its mechanism and rate, and its propagation process under high shear stress in aluminum-copper alloys. The mechanisms of dislocation nucleation near Guinier-Preston (GP) zones of various diameters and concentrations have been analyzed. Dislocation nucleation rates near plain GP Cu-zones with diameters of 3.5, 7.5, and 13.5 nm and at various concentrations have been calculated using the mean lifetime method with temperatures in range of 100 and 700 K. It has been found that depending on the temperature and applied stress, the dislocation can nucleate either from the edge, or from the plain area of a GP zone. The dislocation nucleation is preceded by a generation of defect clusters that are formed due to local opposite atomic shifts in two adjacent (111) planes by the half-length of a Burgers vector of a partial dislocation. The expansion of a partial dislocation loop can be accompanied by the formation of twins via a shift of the atoms in the internal region of the loop. The twin velocity along the direction of the partial dislocation Burgers vector inside the loop can achieve longitudinal sound speed. The speeds of the edge and screw segments of a partial dislocation loop as a function of a shear stress component along the Burgers vector have been estimated. The latter seems to be limited by the shear sound speed.

  4. Dislocation Mechanism of Twinning in Ni-Mn-Ga

    Science.gov (United States)

    Zárubová, N.; Ge, Y.; Gemperlová, J.; Gemperle, A.; Hannula, S.-P.

    2012-03-01

    Tensile tests were performed in situ in a transmission electron microscope to investigate the twinning mechanism in non-modulated Ni-Mn-Ga martensite. The reorientation of the twin variants occurs via twinning dislocations. Their generation and movement were followed; the glide plane and Burgers vector were verified. Individual twinning dislocations were visualized.

  5. Modeling of dislocation dynamics in germanium Czochralski growth

    Science.gov (United States)

    Artemyev, V. V.; Smirnov, A. D.; Kalaev, V. V.; Mamedov, V. M.; Sidko, A. P.; Podkopaev, O. I.; Kravtsova, E. D.; Shimansky, A. F.

    2017-06-01

    Obtaining very high-purity germanium crystals with low dislocation density is a practically difficult problem, which requires knowledge and experience in growth processes. Dislocation density is one of the most important parameters defining the quality of germanium crystal. In this paper, we have performed experimental study of dislocation density during 4-in. germanium crystal growth using the Czochralski method and comprehensive unsteady modeling of the same crystal growth processes, taking into account global heat transfer, melt flow and melt/crystal interface shape evolution. Thermal stresses in the crystal and their relaxation with generation of dislocations within the Alexander-Haasen model have been calculated simultaneously with crystallization dynamics. Comparison to experimental data showed reasonable agreement for the temperature, interface shape and dislocation density in the crystal between calculation and experiment.

  6. Molecular dynamics simulation of dislocations in uranium dioxide

    Energy Technology Data Exchange (ETDEWEB)

    Fossati, Paul [CEA, DEN, DPC, SCCME, F-91191 Gif-sur-Yvette Cedex (France); Van Brutzel, Laurent, E-mail: laurent.vanbrutzel@cea.fr [CEA, DEN, DPC, SCCME, F-91191 Gif-sur-Yvette Cedex (France); Devincre, Benoît [LEM, CNRS-ONERA, 29 avenue de la Division Leclerc, F-92322 Châtillon Cedex (France)

    2013-11-15

    The plasticity of the fluorite structure in UO{sub 2} is investigated with molecular dynamics simulation and empirical potential. The stacking fault energies and the dislocation core structures with Burgers vector a/2 〈110〉 are systematically calculated. All dislocation core structures show a significant increase of the oxygen sub-lattice disorder at temperatures higher than 1500 K. The threshold stress for dislocation glide is found to decrease with increasing temperature but its values is always very high, several GPa at 0 K and several hundred of MPa at 2000 K. A relation between the dislocation mobility dependence with temperature and the increase of the oxygen sub-lattice disorder in the dislocation cores is established.

  7. Quantum dynamics of a single dislocation

    Science.gov (United States)

    de Gennes, Pierre-Gilles

    We discuss the zero temperature motions of an edge dislocation in a quantum solid (e.g., He4). If the dislocation has one kink (equal in length to its Burgers vector b) the kink has a creation energy U and can move along the line with a certain transfer integral t. When t and U are of comparable magnitude, two opposite kinks can form an extended bound state, with a size l. The overall shape of the dislocation in the ground state is then associated with a random walk of persistence length l (along the line) and hop sizes b. We also discuss the motions of kinks under an applied shear stress σ: the glide velocity is proportional to exp(-σ*/σ), where σ* is a characteristic stress, controlled by tunneling processes. Mouvements quantiques d'une dislocation. On analyse le mouvement à température nulle d'une dislocation coin dans un solide quantique (He4). La dislocation peut avoir un cran (d'énergie U) dans son plan de glissement. Le cran peut avancer ou reculer le long de la dislocation par effet tunnel, avec une certaine intégrale de transfert t. Deux crans de signe opposé peuvent former un état lié. En présence d'une contrainte extérieure σ, la ligne doit avancer avec une vitesse ~exp(-σ*/σ) où σ* est une contrainte seuil, contrôlée par l'effet tunnel.

  8. A molecular dynamics study of dislocation density generation and plastic relaxation during shock of single crystal Cu

    Science.gov (United States)

    Sichani, Mehrdad M.; Spearot, Douglas E.

    2016-07-01

    The molecular dynamics simulation method is used to investigate the dependence of crystal orientation and shock wave strength on dislocation density evolution in single crystal Cu. Four different shock directions , , , and are selected to study the role of crystal orientation on dislocation generation immediately behind the shock front and plastic relaxation as the system reaches the hydrostatic state. Dislocation density evolution is analyzed for particle velocities between the Hugoniot elastic limit ( up H E L ) for each orientation up to a maximum of 1.5 km/s. Generally, dislocation density increases with increasing particle velocity for all shock orientations. Plastic relaxation for shock in the , , and directions is primarily due to a reduction in the Shockley partial dislocation density. In addition, plastic anisotropy between these orientations is less apparent at particle velocities above 1.1 km/s. In contrast, plastic relaxation is limited for shock in the orientation. This is partially due to the emergence of sessile stair-rod dislocations with Burgers vectors of 1/3 and 1/6. The nucleation of 1/6 dislocations at lower particle velocities is mainly due to the reaction between Shockley partial dislocations and twin boundaries. On the other hand, for the particle velocities above 1.1 km/s, the nucleation of 1/3 dislocations is predominantly due to reaction between Shockley partial dislocations at stacking fault intersections. Both mechanisms promote greater dislocation densities after relaxation for shock pressures above 34 GPa compared to the other three shock orientations.

  9. Green’s function molecular dynamics meets discrete dislocation plasticity

    Science.gov (United States)

    Venugopalan, Syam P.; Müser, Martin H.; Nicola, Lucia

    2017-09-01

    Metals deform plastically at the asperity level when brought in contact with a counter body even when the nominal contact pressure is small. Modeling the plasticity of solids with rough surfaces is challenging due to the multi-scale nature of surface roughness and the length-scale dependence of plasticity. While discrete-dislocation plasticity (DDP) simulations capture size-dependent plasticity by keeping track of the motion of individual dislocations, only simple two-dimensional surface geometries have so far been studied with DDP. The main computational bottleneck in contact problems modeled by DDP is the calculation of the dislocation image fields. We address this issue by combining two-dimensional DDP with Green’s function molecular dynamics. The resulting method allows for an efficient boundary-value-method based treatment of elasticity in the presence of dislocations. We demonstrate that our method captures plasticity quantitatively from single to many dislocations and that it scales more favorably with system size than conventional methods. We also derive the relevant Green’s functions for elastic slabs of finite width allowing arbitrary boundary conditions on top and bottom surface to be simulated.

  10. Continuum simulation of dislocation dynamics: Predictions for internal friction response

    Energy Technology Data Exchange (ETDEWEB)

    Greaney, P. Alex; Friedman, Lawrence H.; Chrzan, D.C.

    2002-02-19

    The amplitude dependent mechanical loss due to bosing of an idealized Frank-Read Source is studied using both simulation and analytical techniques. Dislocations are modeled within isotropic elasticity theory, and are assumed to be in the over-damped limit.

  11. Interaction of run-in edge dislocations with twist grain boundaries in Al-a molecular dynamics study

    Science.gov (United States)

    Chandra, S.; Naveen Kumar, N.; Samal, M. K.; Chavan, V. M.; Patel, R. J.

    2016-06-01

    Grain boundaries play an important role in outlining the mechanical properties of crystalline materials. They act as sites for absorption/nucleation of dislocations, which are the main carriers of plastic deformation. In view of this, the interactions between edge dislocations and twist grain boundaries-dislocation pileup, dislocation absorption and dislocation emission were explored by performing molecular dynamics simulations in face-centered cubic Al using embedded atom method. The ?1 1 0? twist grain boundaries with various misorientation angles were selected for this purpose. It was found that the misorientation angle of boundary and stress anomalies arising from repeated dislocation absorption at the grain boundaries are the important parameters in determining the ability of the boundary to emit dislocations. Complex network of dislocations results in later stages of deformation, which may have a significant effect on the mechanical properties of the material. The peculiarities of dislocation nucleation, their emission from twist grain boundaries and the ramifications of this study towards development of higher length scale material models are discussed.

  12. Dislocation dynamics: simulation of plastic flow of bcc metals

    Energy Technology Data Exchange (ETDEWEB)

    Lassila, D H

    2001-02-20

    This is the final report for the LDRD strategic initiative entitled ''Dislocation Dynamic: Simulation of Plastic Flow of bcc Metals'' (tracking code: 00-SI-011). This report is comprised of 6 individual sections. The first is an executive summary of the project and describes the overall project goal, which is to establish an experimentally validated 3D dislocation dynamics simulation. This first section also gives some information of LLNL's multi-scale modeling efforts associated with the plasticity of bcc metals, and the role of this LDRD project in the multiscale modeling program. The last five sections of this report are journal articles that were produced during the course of the FY-2000 efforts.

  13. Strengthening effects of various grain boundaries with nano-spacing as barriers of dislocation motion from molecular dynamics simulations

    Science.gov (United States)

    Yuan, FuPing

    2017-03-01

    Strengthening in metals is traditionally achieved through the controlled creation of various grain boundaries (GBs), such as low-angle GBs, high-angle GBs, and twin boundaries (TBs). In the present study, a series of large-scale molecular dynamics simulations with spherical nanoindentation and carefully designed model were conducted to investigate and compare the strengthening effects of various GBs with nano-spacing as barriers of dislocation motion. Simulation results showed that high-angle twist GBs and TBs are similar barriers and low-angle twist GBs are less effective in obstructing dislocation motion. Corresponding atomistic mechanisms were also given. At a certain indentation depth, dislocation transmission and dislocation nucleation from the other side of boundaries were observed for low-angle twist GBs, whereas dislocations were completely blocked by high-angle twist GBs and TBs at the same indentation depth. The current findings should provide insights for comprehensive understanding of the strengthening effects of various GBs at nanoscale.

  14. Dislocation Emission at the Silicon/Silicon Nitride Interface: A Million Atom Molecular Dynamics Simulation on Parallel Computers

    Science.gov (United States)

    Bachlechner, Martina E.; Omeltchenko, Andrey; Nakano, Aiichiro; Kalia, Rajiv K.; Vashishta, Priya; Ebbsjö, Ingvar; Madhukar, Anupam

    2000-01-01

    Mechanical behavior of the Si\\(111\\)/Si3N4\\(0001\\) interface is studied using million atom molecular dynamics simulations. At a critical value of applied strain parallel to the interface, a crack forms on the silicon nitride surface and moves toward the interface. The crack does not propagate into the silicon substrate; instead, dislocations are emitted when the crack reaches the interface. The dislocation loop propagates in the \\(1¯ 1¯1\\) plane of the silicon substrate with a speed of 500 \\(+/-100\\) m/s. Time evolution of the dislocation emission and nature of defects is studied.

  15. Dislocation Emission at the Silicon/Silicon Nitride Interface: A Million Atom Molecular Dynamics Simulation on Parallel Computers

    Energy Technology Data Exchange (ETDEWEB)

    Bachlechner, Martina E.; Omeltchenko, Andrey; Nakano, Aiichiro; Kalia, Rajiv K.; Vashishta, Priya; Ebbsjoe, Ingvar; Madhukar, Anupam

    2000-01-10

    Mechanical behavior of the Si(111)/Si{sub 3}N{sub 4} (0001) interface is studied using million atom molecular dynamics simulations. At a critical value of applied strain parallel to the interface, a crack forms on the silicon nitride surface and moves toward the interface. The crack does not propagate into the silicon substrate; instead, dislocations are emitted when the crack reaches the interface. The dislocation loop propagates in the (1 11) plane of the silicon substrate with a speed of 500 ({+-}100) m/s . Time evolution of the dislocation emission and nature of defects is studied. (c) 2000 The American Physical Society.

  16. Atomic and dislocation dynamics simulations of plastic deformation in reactor pressure vessel steel

    Science.gov (United States)

    Monnet, Ghiath; Domain, Christophe; Queyreau, Sylvain; Naamane, Sanae; Devincre, Benoit

    2009-11-01

    The collective behavior of dislocations in reactor pressure vessel (RPV) steel involves dislocation properties on different phenomenological scales. In the multiscale approach, adopted in this work, we use atomic simulations to provide input data for larger scale simulations. We show in this paper how first-principles calculations can be used to describe the Peierls potential of screw dislocations, allowing for the validation of the empirical interatomic potential used in molecular dynamics simulations. The latter are used to compute the velocity of dislocations as a function of the applied stress and the temperature. The mobility laws obtained in this way are employed in dislocation dynamics simulations in order to predict properties of plastic flow, namely dislocation-dislocation interactions and dislocation interactions with carbides at low and high temperature.

  17. Atomic and dislocation dynamics simulations of plastic deformation in reactor pressure vessel steel

    Energy Technology Data Exchange (ETDEWEB)

    Monnet, Ghiath, E-mail: ghiathmonnet@yahoo.f [EDF-R and D, MMC, Avenue des Renardieres, 77818 Moret sur Loing (France); Domain, Christophe; Queyreau, Sylvain; Naamane, Sanae [EDF-R and D, MMC, Avenue des Renardieres, 77818 Moret sur Loing (France); Devincre, Benoit [LEM, CNRS-ONERA, 29 av. de la division Leclerc, 92130 Chatillon (France)

    2009-11-15

    The collective behavior of dislocations in reactor pressure vessel (RPV) steel involves dislocation properties on different phenomenological scales. In the multiscale approach, adopted in this work, we use atomic simulations to provide input data for larger scale simulations. We show in this paper how first-principles calculations can be used to describe the Peierls potential of screw dislocations, allowing for the validation of the empirical interatomic potential used in molecular dynamics simulations. The latter are used to compute the velocity of dislocations as a function of the applied stress and the temperature. The mobility laws obtained in this way are employed in dislocation dynamics simulations in order to predict properties of plastic flow, namely dislocation-dislocation interactions and dislocation interactions with carbides at low and high temperature.

  18. Atomic-level level dislocation dynamics in irradiated metals

    Energy Technology Data Exchange (ETDEWEB)

    Osetskiy, Yury N [ORNL; Bacon, David J [University of Liverpool, UK

    2015-01-01

    Primary damage and microstructure evolution in structural nuclear materials operating under conditions of a high flux of energetic atomic particles and high temperature and stress lead to formation of a high concentration, non-homogeneous distribution of defect clusters in the form of dislocation loops, voids, gas-filled bubbles and radiation-induced precipitates of nanometer scale. They cause changes in many material properties. Being obstacles to dislocation glide, they strongly affect mechanical properties in particular. This gives rise to an increase in yield and flow stress and a reduction in ductility. Atomic-scale computer simulation can provide details of how these effects are influenced by obstacle structure, applied stress, strain rate and temperature. Processes such as obstacle cutting, transformation, absorption and drag are observed. Some recent results for body-centered and face-centered cubic metals are described in this review and, where appropriate, comparisons drawn with predictions based on elasticity theory of crystal defects.

  19. Mechanisms for decoration of dislocations by small dislocation loops under cascade damage conditions

    DEFF Research Database (Denmark)

    Trinkaus, H.; Singh, B.N.; Foreman, A.J.E.

    1997-01-01

    In metals under cascade damage conditions, dislocations are frequently found to be decorated with a high density of small clusters of self-interstitial atoms (SIAs) in the form of dislocation loops, particularly during the early stages of the microstructural evolution in well annealed pure metals....... This effect may arise as a result of either (a) migration and enhanced agglomeration of single SIAs in the form of loops in the strain field of the dislocation or (b) glide and trapping of SIA loops (produced directly in the cascades) in the strain field of the dislocation, In the present paper, both...... of these possibilities are examined. It is shown that the strain field of the dislocation causes a SIA depletion in the compressive as well as in the dilatational region resulting in a reduced rather than enhanced agglomeration of SIAs. (SIA depletion may, however, induce enhanced vacancy agglomeration near dislocations...

  20. Dislocation Dynamics in Al-Li Alloys. Mean Jump Distance and Activation Length of Moving Dislocations

    NARCIS (Netherlands)

    Hosson, J.Th.M. De; Huis in 't Veld, A.; Tamler, H.; Kanert, O.

    1984-01-01

    Pulsed nuclear magnetic resonance proved to be a complementary new technique for the study of moving dislocations in Al-Li alloys. The NMR technique, in combination with transmission electron microscopy and strain-rate change experiments have been applied to study dislocation motion in Al-2.2 wt% Li

  1. Molecular dynamics simulation of kink in 《100》 edge dislocation in body centred cubic iron

    Institute of Scientific and Technical Information of China (English)

    CHEN LiQun; WANG ChongYu; YU Tao

    2007-01-01

    Using the molecular dynamics method, we have constructed two kink models corresponding to the {010} and {011} edge dislocations (EDs) in body centred cubic (bcc) Fe.It is found that the geometric structure of a kink depends on the type of edge dislocation and the structural energies of the atoms sites in the dislocation core region.The formation energies, migration energies and widths of the kinks in different types of EDs are calculated.The results show that formation and migration of the kink in the {010} edge dislocation are difficult.The {011} edge dislocation moves primarily through kink nucleation, rather than kink migration.

  2. Effect of collision cascades on dislocations in tungsten: A molecular dynamics study

    Science.gov (United States)

    Fu, B. Q.; Fitzgerald, S. P.; Hou, Q.; Wang, J.; Li, M.

    2017-02-01

    Tungsten (W) is the prime candidate material for the divertor and other plasma-facing components in DEMO. The point defects (i.e. vacancies and self-interstitials) produced in collision cascades caused by incident neutrons aggregate into dislocation loops (and voids), which strongly affect the mechanical properties. The point defects also interact with existing microstructural features, and understanding these processes is crucial for modelling the long term microstructural evolution of the material under fusion conditions. In this work, we performed molecular dynamics simulations of cascades interacting with initially straight edge dislocation dipoles. It was found that the residual vacancy number usually exceeds the residual interstitial number for cascades interacting with vacancy type dipoles, but for interstitial type dipoles these are close. We observed that a cascade near a dislocation promotes climb, i.e. it facilitates the movement of point defects along the climb direction. We also observed that the dislocations move easily along the glide direction, and that kinks are formed near the centre of the cascade, which then facilitate the movement of the dipoles. Some dipoles are sheared off by the cascade, and this is dependent on PKA energy, position, direction, and the width of dipole.

  3. Topological modes bound to dislocations in mechanical metamaterials

    Science.gov (United States)

    Paulose, Jayson; Chen, Bryan Gin-Ge; Vitelli, Vincenzo

    2015-02-01

    Mechanical metamaterials are artificial structures with unusual properties, such as negative Poisson ratio, bistability or tunable vibrational properties, that originate in the geometry of their unit cell. Often at the heart of such unusual behaviour is a soft mode: a motion that does not significantly stretch or compress the links between constituent elements. When activated by motors or external fields, soft modes become the building blocks of robots and smart materials. Here, we demonstrate the existence of topological soft modes that can be positioned at desired locations in a metamaterial while being robust against a wide range of structural deformations or changes in material parameters. These protected modes, localized at dislocations in deformed kagome and square lattices, are the mechanical analogue of topological states bound to defects in electronic systems. We create physical realizations of the topological modes in prototypes of kagome lattices built out of rigid triangular plates. We show mathematically that they originate from the interplay between two Berry phases: the Burgers vector of the dislocation and the topological polarization of the lattice. Our work paves the way towards engineering topologically protected nanomechanical structures for molecular robotics or information storage and read-out.

  4. Continuum dynamics of the formation, migration and dissociation of self-locked dislocation structures on parallel slip planes

    Science.gov (United States)

    Zhu, Yichao; Niu, Xiaohua; Xiang, Yang

    2016-11-01

    In continuum models of dislocations, proper formulations of short-range elastic interactions of dislocations are crucial for capturing various types of dislocation patterns formed in crystalline materials. In this article, the continuum dynamics of straight dislocations distributed on two parallel slip planes is modelled through upscaling the underlying discrete dislocation dynamics. Two continuum velocity field quantities are introduced to facilitate the discrete-to-continuum transition. The first one is the local migration velocity of dislocation ensembles which is found fully independent of the short-range dislocation correlations. The second one is the decoupling velocity of dislocation pairs controlled by a threshold stress value, which is proposed to be the effective flow stress for single slip systems. Compared to the almost ubiquitously adopted Taylor relationship, the derived flow stress formula exhibits two features that are more consistent with the underlying discrete dislocation dynamics: (i) the flow stress increases with the in-plane component of the dislocation density only up to a certain value, hence the derived formula admits a minimum inter-dislocation distance within slip planes; (ii) the flow stress smoothly transits to zero when all dislocations become geometrically necessary dislocations. A regime under which inhomogeneities in dislocation density grow is identified, and is further validated through comparison with discrete dislocation dynamical simulation results. Based on the findings in this article and in our previous works, a general strategy for incorporating short-range dislocation correlations into continuum models of dislocations is proposed.

  5. Strain energy analysis of screw dislocations in 4H-SiC by molecular dynamics

    Science.gov (United States)

    Kawamura, Takahiro; Mizutani, Mitsutoshi; Suzuki, Yasuyuki; Kangawa, Yoshihiro; Kakimoto, Koichi

    2016-03-01

    We simulated screw dislocations with the Burgers vector parallel to the [0001] direction in 4H-SiC by a classical molecular dynamics method. A stable structure of an extended dislocation generated by the dissociation of a screw dislocation was identified by calculating the strain energy caused by dislocation cores and stacking faults. As a result, we conclude that the most expected structure of the extended dislocation is made of partial dislocations with the Burgers vector b = 1/2c + 1/2c (c is equal to the thickness of one period in the c-axis direction of 4H-SiC) and the stacking fault that is parallel to the a-plane, and that the distance between the dislocation cores is less than about 44 Å.

  6. Dislocation formation and twinning from the crack tip in Ni3Al: molecular dynamics simulations

    Institute of Scientific and Technical Information of China (English)

    Xie Hong-Xian; Wang Chong-Yu; Yu Tao; Du Jun-Ping

    2009-01-01

    The mechanism of low-temperature deformation in a fracture process of L12Ni3Al is studied by molecular dynamic simulations. Owing to the unstable stacking energy, the [011] superdislocation is dissociated into partial dislocations separated by a stacking fault. The simulation results show that when the crack speed is larger than a critical speed, the Shockley partial dislocations will break forth from both the crack tip and the vicinity of the crack tip; subsequently the super intrinsic stacking faults are formed in adjacent {111} planes, meanwhile the super extrinsic stacking faults and twinning also occur. Our simulation results suggcst that at low temperatures the ductile fracture in L12Ni3Al is accompanied by twinning, which is produced by super-intrinsic stacking faults formed in adjacent {111} planes.

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

    Science.gov (United States)

    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.

  8. Two hardening mechanisms in single crystal thin films studied by discrete dislocation plasticity

    NARCIS (Netherlands)

    Nicola, L; Van der Giessen, E; Needleman, A

    2005-01-01

    thermal stress in single crystal thin films on a rigid substrate are used to study size effects. The relation between the residual stress and the dislocation structure in the films after cooling is analyzed using dislocation dynamics. A boundary layer characterized by a high stress gradient and a hi

  9. Atomic-scale structure of dislocations revealed by scanning tunneling microscopy and molecular dynamics

    DEFF Research Database (Denmark)

    Christiansen, Jesper; Morgenstern, K.; Schiøtz, Jakob;

    2002-01-01

    , the simulations can be used to determine dislocation structure and orientation in the near-surface region. In a similar way, the subsurface structure of other extended defects can be studied. The simulations show dislocations to reorient the partials in the surface region leading to an increased splitting width......The intersection between dislocations and a Ag(111) surface has been studied using an interplay of scanning tunneling microscopy (STM) and molecular dynamics. Whereas the STM provides atomically resolved information about the surface structure and Burgers vectors of the dislocations...

  10. A Dynamic Discrete Dislocation Plasticity study of elastodynamic shielding of stationary cracks

    Science.gov (United States)

    Gurrutxaga-Lerma, B.; Balint, D. S.; Dini, D.; Sutton, A. P.

    2017-01-01

    Employing Dynamic Discrete Dislocation Plasticity (D3P), an elastodynamic analysis of the shielding of a stationary crack tip by dislocations is studied. Dislocations are generated via Frank-Read sources, and make a negligible contribution to the shielding of the crack tip, whereas dislocations generated at the crack tip via homogeneous nucleation dominate the shielding. Their effect is found to be highly localised around the crack, leading to a magnification of the shielding when compared to time-independent, elastostatic predictions. The resulting attenuation of KI(t) is computed, and is found to be directly proportional to the applied load and to √{ t }.

  11. Low-temperature embrittlement and fracture of metals with different crystal lattices – Dislocation mechanisms

    Directory of Open Access Journals (Sweden)

    V.M. Chernov

    2016-12-01

    Full Text Available The state of a low-temperature embrittlement (cold brittleness and dislocation mechanisms for formation of the temperature of a ductile-brittle transition and brittle fracture of metals (mono- and polycrystals with various crystal lattices (BCC, FCC, HCP are considered. The conditions for their formation connected with a stress-deformed state and strength (low temperature yield strength as well as the fracture breaking stress and mobility of dislocations in the top of a crack of the fractured metal are determined. These conditions can be met for BCC and some HCP metals in the initial state (without irradiation and after a low-temperature damaging (neutron irradiation. These conditions are not met for FCC and many HCP metals. In the process of the damaging (neutron irradiation such conditions are not met also and the state of low-temperature embrittlement of metals is absent (suppressed due to arising various radiation dynamic processes, which increase the mobility of dislocations and worsen the strength characteristics.

  12. The role of dislocations in varied olivine deformation mechanisms investigated using high-angular resolution electron backscatter diffraction

    Science.gov (United States)

    Wallis, David; Hansen, Lars; Britton, Ben; Wilkinson, Angus

    2016-04-01

    Experimentally-derived flow laws can be used to predict the rheology of rocks deformed under natural conditions only if the same microphysical processes can be demonstrated to control the rate-limiting deformation mechanism in both cases. Olivine rheology may exert a principle control on the strength of the lithosphere, and therefore considerable research effort has been applied to assessing its rheology through experimental, geological, and geophysical approaches. Nonetheless, considerable uncertainty remains regarding the dominant deformation mechanisms in the upper mantle. This uncertainty arises in large part due to our limited understanding of the fundamental deformation processes associated with each mechanism. Future improvements to microphysical models of distinct deformation mechanisms require new insight into the contributions those fundamental processes to the macroscopic behaviour. The dynamics of dislocations is central to modelling viscous deformation of olivine, but characterisation techniques capable of constraining dislocation types, densities, and distributions over the critical grain to polycrystal length-scales have been lacking. High angular resolution electron backscatter diffraction (HR-EBSD), developed and increasingly applied in the material sciences, offers an approach capable of such analyses. HR-EBSD utilises diffraction pattern image cross-correlation to achieve dramatically improved angular resolution (~0.01°) of lattice orientation gradients compared to conventional Hough-based EBSD (~0.5°). This angular resolution allows very low densities (≥ 10^11 m^-2) of geometrically necessary dislocations (GND) to be resolved, facilitating analysis of a wide range of dislocation microstructures. We have developed the application of HR-EBSD to olivine and applied it to samples deformed both experimentally and naturally in grain-size sensitive and grain-size insensitive regimes. The results quantitatively highlight variations in the types and

  13. Cross-Split of Dislocations: An Athermal and Rapid Plasticity Mechanism

    Science.gov (United States)

    Kositski, Roman; Kovalenko, Oleg; Lee, Seok-Woo; Greer, Julia R.; Rabkin, Eugen; Mordehai, Dan

    2016-05-01

    The pathways by which dislocations, line defects within the lattice structure, overcome microstructural obstacles represent a key aspect in understanding the main mechanisms that control mechanical properties of ductile crystalline materials. While edge dislocations were believed to change their glide plane only by a slow, non-conservative, thermally activated motion, we suggest the existence of a rapid conservative athermal mechanism, by which the arrested edge dislocations split into two other edge dislocations that glide on two different crystallographic planes. This discovered mechanism, for which we coined a term “cross-split of edge dislocations”, is a unique and collective phenomenon, which is triggered by an interaction with another same-sign pre-existing edge dislocation. This mechanism is demonstrated for faceted α-Fe nanoparticles under compression, in which we propose that cross-split of arrested edge dislocations is resulting in a strain burst. The cross-split mechanism provides an efficient pathway for edge dislocations to overcome planar obstacles.

  14. Contrast mechanism in superscrew dislocation images on synchrotron back-reflection topographs

    Energy Technology Data Exchange (ETDEWEB)

    Huang, X.R.; Dudley, M.; Vetter, W.M.; Huang, W.; Wang, S. [State Univ. of New York, Stony Brook, NY (United States). Dept. of Materials Science and Engineering; Carter, C.H. Jr. [Cree Research, Inc., Durham, NC (United States)

    1998-12-31

    The topographic contrast of superscrew dislocations in 6H{single_bond}SiC crystals has been studied by synchrotron white-beam x-ray topography in the Bragg reflection geometry. The diffraction images of these dislocations are simulated using a ray-tracing method. Systematical simulations, which coincide with the dislocation images taken by back- and grazing-reflection topography, clearly reveal the kinematic diffraction mechanisms of the superscrew dislocation, and illustrate that synchrotron reflection topography is capable of providing accurate descriptions of the strain fields, the Burgers vector magnitudes, and the senses of these dislocations. In addition, the experiments and simulations demonstrate straightforwardly the relation between the topographic contrast and the lattice distortions, and therefore the general mechanisms underlying contrast formation of defect images in synchrotron reflection topographs are provided.

  15. Dislocation Reduction Mechanisms in Gallium Nitride Films Grown by Canti-Bridge Epitaxy Method

    Institute of Scientific and Technical Information of China (English)

    XING Zhi-Gang; WANG Jing; PEI Xiao-Jiang; WAN Wei; CHEN Hong; ZHOU Jun-Ming

    2007-01-01

    @@ By using the special maskless V-grooved c-plane sapphire as the substrate, we previously developed a novel GaN LEO method, or the so-called canti-bridge epitaxy (CBE), and consequently wing-tilt-free GaN films were obtained with low dislocation densities, with which all the conventional difficulties can be overcome [J. Vacuum Sci.Technol. B 23 (2005) 2476]. Here the evolution manner of dislocations in the CBE GaN films is investigated using transmission electron microscopy. The mechanisms of dislocation reduction are discussed. Dislocation behaviour is found to be similar to that in the conventional LEO GaN films except the enhanced dislocation-combination at the coalescence boundary that is a major dislocation-reduction mechanism for the bent horizontal-propagating dislocations in the CBE GaN films. The enhancement of this dislocation-combination probability is believed to result from the inclined shape and the undulate morphology of the sidewalls, which can be readily obtained in a wide range of applicable film-growth conditions during the GaN CBE process. Further development of the GaN CBE method and better crystal-quality of the GaN film both are expected.

  16. A study on the geometry of dislocation patterns in the surrounding of nanoindents in a TWIP steel using electron channeling contrast imaging and discrete dislocation dynamics simulations

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, J.-I.; Zaefferer, S., E-mail: s.zaefferer@mpie.de; Raabe, D.

    2015-06-11

    Electron channeling contrast imaging under controlled diffraction conditions (cECCI) enables observation of crystal defects, especially dislocations, stacking faults and nano-twins, close to the surface of bulk samples. In this work cECCI has been employed to observe defects around nanoindents into the surface of {100}-, {110}-, {111}-oriented grains in a Fe–22Mn–0.65C (wt%) TWIP steel sample (fcc crystal structure, stacking fault energy ~20 mJ/m²) using a cone-spherical indenter. The dislocation patterns show four- and two-fold symmetries for the {100}- and {110}-orientation, and a three-fold symmetry for the {111}-orientation which is, however, difficult to observe. Discrete dislocation dynamics (DDD) simulations of the indentation were carried out to complement the static experimental investigations. The simulations were carried out with both, cross-slip disabled and enabled conditions, where the former were found to match to the experimental results better, as may be expected for an fcc material with low stacking fault energy. The 3-dimensional geometry of the dislocation patterns of the different indents was analysed and discussed with respect to pattern formation mechanisms. The force–displacement curves obtained during indentation showed a stronger strain hardening for the {111} oriented crystal than that for the other orientations. This is in contrast to the behaviour of, for example, copper and is interpreted to be due to planar slip. Irrespective of orientation and indentation depth the radius of the plastically deformed area was found to be approximately 4 times larger than that of the indenter contact area.

  17. Molecular dynamics simulation of cross-slip and the intersection of dislocations in copper

    CERN Document Server

    Li, Maozhen; Gao, K W; Qiao, L J

    2003-01-01

    The molecular dynamics method is used to simulate cross-slip by thermal activation at 30 K and the intersection of dislocations in copper containing 1.6 x 10 sup 6 atoms using the embedded atom method potential. The results show that an extended screw dislocation can recombine through thermal activation at 30 K into a constriction on the surface because of stress imbalance and the constriction will split again in the other slip plane. Removing the constriction along the extended dislocation results in a cross-slip of the screw dislocation at low temperature. After the intersection between a moving right-hand screw dislocation DC and a perpendicular left-hand dislocation BA, whose ends are fixed on the surfaces, an extended jog corresponding to a row of one-third vacancies forms in BA and a trail of vacancies behind DC. If the intersected dislocation is a right-hand screw dislocation AB, the jog formed in AB corresponds to a row of one-third interstitials and the point defects behind DC are interstitials. Afte...

  18. Plasticity and Interfacial Dislocation Mechanisms in Epitaxial and Polycrystalline Al Films Constrained by Substrates

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    Stresses in epitaxial and textured Al films were determined by substrate-curvature measurements. It was found that in both cases the flow stresses increase with decreasing film thickness. The flow stresses in the epitaxial Al films are in agreement with a dislocation-based model, while the same model strongly underestimates the flow stresses of textured Al films. In-situ transmission electron microscopy studies indicate that dislocations channeling through epitaxial Al films on single-crystalline (0001) α-AI2O3 substrates frequently deposit dislocation segments adjacent to the interface. Furthermore, the AI/α-AI2O3 interface acted as a dislocation source. In this case, the interface is between two crystalline lattices. In contrast, the interface of textured Al films on oxidized silicon substrates is between the crystalline Al and the amorphous SiOx interlayer. It is speculated that the different nature of the interfaces changes dislocation mechanisms and thus influences the flow stresses.

  19. Bilateral Asymmetric Dislocations of Hip Joints: An Unusual Mechanism of Injury

    Directory of Open Access Journals (Sweden)

    Rajesh Kumar Kanojia

    2013-01-01

    Full Text Available Asymmetric bilateral dislocations of the hips are rare injuries. Among the small number of reports in the literature, most have attributed the cause to high-velocity motor crashes. These dislocations are often seen to be associated with fractures of the proximal femur or the acetabulum. We present a case of a 45-year-old man with bilateral asymmetric dislocation of hips which were purely ligamentous in nature, without any fracture. He sustained his injuries due to a fall while getting on a moving bus. It was an unusual mechanism of injury as compared to the other cases of asymmetric hip dislocations reported in published studies. Both hips were reduced under general anaesthesia within three hours of the trauma. Skin traction and non-weight-bearing rehabilitation were continued for six weeks. After 35 months of followup, the patient remains asymptomatic. Early diagnosis and timely reduction of such dislocations under anaesthesia are necessary for prevention of complications.

  20. Dislocation mechanism of deuterium retention in tungsten under plasma implantation.

    Science.gov (United States)

    Dubinko, V I; Grigorev, P; Bakaev, A; Terentyev, D; van Oost, G; Gao, F; Van Neck, D; Zhurkin, E E

    2014-10-01

    We have developed a new theoretical model for deuterium (D) retention in tungsten-based alloys on the basis of its being trapped at dislocations and transported to the surface via the dislocation network with parameters determined by ab initio calculations. The model is used to explain experimentally observed trends of D retention under sub-threshold implantation, which does not produce stable lattice defects to act as traps for D in conventional models. Saturation of D retention with implantation dose and effects due to alloying of tungsten with, e.g. tantalum, are evaluated, and comparison of the model predictions with experimental observations under high-flux plasma implantation conditions is presented.

  1. Deformation induced dislocation boundaries: Alignment and effect on mechanical properties

    DEFF Research Database (Denmark)

    Winther, G.; Juul Jensen, D.

    1997-01-01

    The dislocation boundaries formed during cold-rolling of FCC metals have been reported to have a preferred macroscopic direction with respect to the sample axes. However, boundaries have also been reported to form on crystallographic slip planes. The directions of the boundaries formed on crystal...

  2. Recent Progress in Discrete Dislocation Dynamics and Its Applications to Micro Plasticity

    KAUST Repository

    Po, Giacomo

    2014-09-27

    We present a self-contained review of the discrete dislocation dynamics (DDD) method for the numerical investigation of plasticity in crystals, focusing on recent development and implementation progress. The review covers the theoretical foundations of DDD within the framework of incompatible elasticity, its numerical implementation via the nodal method, the extension of the method to finite domains and several implementation details. Applications of the method to current topics in micro-plasticity are presented, including the size effects in nano-indentation, the evolution of the dislocation microstructure in persistent slip bands, and the phenomenon of dislocation avalanches in micro-pillar compression.

  3. Multiscale Analysis of Structurally-Graded Microstructures Using Molecular Dynamics, Discrete Dislocation Dynamics and Continuum Crystal Plasticity

    Science.gov (United States)

    Saether, Erik; Hochhalter, Jacob D.; Glaessgen, Edward H.; Mishin, Yuri

    2014-01-01

    A multiscale modeling methodology is developed for structurally-graded material microstructures. Molecular dynamic (MD) simulations are performed at the nanoscale to determine fundamental failure mechanisms and quantify material constitutive parameters. These parameters are used to calibrate material processes at the mesoscale using discrete dislocation dynamics (DD). Different grain boundary interactions with dislocations are analyzed using DD to predict grain-size dependent stress-strain behavior. These relationships are mapped into crystal plasticity (CP) parameters to develop a computationally efficient finite element-based DD/CP model for continuum-level simulations and complete the multiscale analysis by predicting the behavior of macroscopic physical specimens. The present analysis is focused on simulating the behavior of a graded microstructure in which grain sizes are on the order of nanometers in the exterior region and transition to larger, multi-micron size in the interior domain. This microstructural configuration has been shown to offer improved mechanical properties over homogeneous coarse-grained materials by increasing yield stress while maintaining ductility. Various mesoscopic polycrystal models of structurally-graded microstructures are generated, analyzed and used as a benchmark for comparison between multiscale DD/CP model and DD predictions. A final series of simulations utilize the DD/CP analysis method exclusively to study macroscopic models that cannot be analyzed by MD or DD methods alone due to the model size.

  4. Trends in dislocation core structures and mechanical behavior in B2 aluminides

    Energy Technology Data Exchange (ETDEWEB)

    Vailhe, C.; Farkas, D. [Virginia Polytechnic Inst., Blacksburg, VA (United States). Dept. of Materials Science and Engineering

    1995-08-01

    In an effort to understand the deformation mechanism in high temperature B2 intermetallics, atomistic simulations were carried out for dislocation cores in a series of compounds exhibiting the B2 structure (FeAl, NiAl, CoAl). A comparison was made on the basis of core structures, dislocation splittings and Peierls stress values. The (110) and (112) {gamma} surfaces were computed for these three compounds. The importance of the APB values and the maximum shear faults for explaining the dislocation behavior is discussed.

  5. Dry frictional contact of metal asperities : A dislocation dynamics analysis

    NARCIS (Netherlands)

    Sun, Fengwei; van der Giessen, Erik; Nicola, Lucia

    2016-01-01

    Discrete dislocation plasticity simulations are performed to investigate the static frictional behavior of a metal asperity on a large single crystal, in contact with a rigid platen. The focus of this study is on understanding the relative importance of contact slip opposed to plasticity in a single

  6. Bertram Hopkinson's pioneering work and the dislocation mechanics of high rate deformations and mechanically induced detonations.

    Science.gov (United States)

    Armstrong, Ronald W

    2014-05-13

    Bertram Hopkinson was prescient in writing of the importance of better measuring, albeit better understanding, the nature of high rate deformation of materials in general and, in particular, of the importance of heat in initiating detonation of explosives. This report deals with these subjects in terms of post-Hopkinson crystal dislocation mechanics applied to high rate deformations, including impact tests, Hopkinson pressure bar results, Zerilli-Armstrong-type constitutive relations, shock-induced deformations, isentropic compression experiments, mechanical initiation of explosive crystals and shear banding in metals.

  7. Large Scale 3-D Dislocation Dynamics and Atomistic Simulations of Flow and Strain-Hardening Behavior of Metallic Micropillars

    Science.gov (United States)

    Rao, Satish

    2015-03-01

    Experimental studies show strong strengthening effects for micrometer-scale FCC as well as two-phase superalloy crystals, even at high initial dislocation densities. This talk shows results from large-scale 3-D discrete dislocation simulations (DDS) used to explicitly model the deformation behavior of FCC Ni (flow stress and strain-hardening) as well as superalloy microcrystals for diameters ranging from 1 - 20 microns. The work shows that two size-sensitive athermal hardening processes, beyond forest and precipitation hardening, are sufficient to develop the dimensional scaling of the flow stress, stochastic stress variation, flow intermittency and, high initial strain-hardening rates, similar to experimental observations for various materials. In addition, 3D dislocation dynamics simulations are used to investigate strain-hardening characteristics and dislocation microstructure evolution with strain in large 20 micron size Ni microcrystals (bulk-like) under three different loading axes: 111, 001 and 110. Three different multi-slip loading axes, , and , are explored for shear strains of ~0.03 and final dislocation densities of ~1013/m2. The orientation dependence of initial strain hardening rates and dislocation microstructure evolution with strain are discussed. The simulated strain hardening results are compared with experimental data under similar loading conditions from bulk single-crystal Ni. Finally, atomistic simulation results on the operation of single arm sources in Ni bipillars with a large angle grain boundary is discussed. The atomistic simulation results are compared with experimental mechanical behavior data on Cu bipillars with a similar large angle grain boundary. This work was supported by AFOSR (Dr. David Stargel), and by a grant of computer time from the DOD High Performance Computing Modernization Program, at the Aeronautical Systems Center/Major Shared Resource Center.

  8. Dislocation-based plasticity and strengthening mechanisms in sub-20 nm lamellar structures in pearlitic steel wire

    DEFF Research Database (Denmark)

    Zhang, Xiaodan; Hansen, Niels; Godfrey, Andrew

    2016-01-01

    at a strain of 5.4; the dislocations are stored as threading dislocations, as dislocation tangles and as cell boundaries with low to medium misorientation angles. An analysis of the evolution of microstructure and strength with increasing strain suggests that dislocation-based plasticity is a dominating...... mechanism in the wire and three strengthening mechanisms are applied: boundary strengthening, dislocation strengthening and solid solution hardening with their relative contributions to the total flow stress which change as the strain is increased. Based on linear additivity good correspondence between...

  9. Molecular Dynamics Simulation of Porous Layer-enhanced Dislocation Emission and Crack Propagation in Iron Crystal

    Institute of Scientific and Technical Information of China (English)

    D. Li; F.Y. Meng; X.Q. Ma; L.J. Qiao; W.Y. Chu

    2011-01-01

    The internal stress induced by a porous layer or passive layer can assist the applied stress to promote dislocation emission and crack propagation, e.9. when the pipeline steel is buried in the soil containing water, resulting in stress corrosion cracking (SCC). Molecular dynamics (MD) simulation is performed to study the process of dislocation emission and crack propagation in a slab of Fe crystal with and without a porous layer on the surface of the crack. The results show that when there is a porous layer on the surface of the crack, the tensile stress induced by the porous layer can superimpose on the external applied stress and then assist the applied stress to initiate crack tip dislocation emission under lowered stress intensity KI, or stress. To respond to the corrosion accelerated dislocation emission and motion, the crack begins to propagate under lowered stress intensity KI, resulting in SCC.

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

    Science.gov (United States)

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

    2015-10-01

    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 10(19.6) to 10(20.7) 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.

  11. A three dimensional discrete dislocation dynamics modelling of the early cycles of fatigue in an austenitic stainless steel 316L: dislocation microstructure and damage analysis; Modelisation physique des stades precurseurs de l'endommagement en fatigue dans l'acier inoxydable austenitique 316L

    Energy Technology Data Exchange (ETDEWEB)

    Depres, Ch

    2005-07-01

    A numerical code modelling the collective behaviour of dislocations at a mesoscopic scale (Discrete Dislocation Dynamics code) is used to analyse the cyclic plasticity that occurs in surface grains of an AISI 316L stainless steel, in order to understand the plastic mechanism involved in crack initiation in fatigue. Firstly, the analyses of both the formation and the evolution of the dislocation microstructures show the crucial role of cross-slip played in the strain localization in the form of slip bands. As the cycling proceeds, the slip bands exhibit well-organized dislocation arrangements that substitute to dislocation tangles, involving specific interaction mechanisms between primary and deviate systems. Secondly, both the surface displacements generated by plastic slip and the distortion energy induced by the dislocation microstructure have been analysed. We find that an irreversible surface relief in the form of extrusion/intrusion can be induced by cyclic slip of dislocations. The number of cycles for the crack initiation follows a Manson-Coffin type law. The analyses of the concentration of the distortion energy and its repartition in the slip bands show that beneficial energetic zones may be present at the very beginning of the cycling, and that mode-II crack propagation in the surface grains results from a succession of micro-crack initiations along primary slip plane, which is facilitated by various effects (stress concentration due to surface relief, environment effects...). Finally, a dislocation-based model for cyclic plasticity is proposed from Discrete Dislocation Dynamics results. (author)

  12. Nanoindentation of BaTiO{sub 3}: dislocation nucleation and mechanical twinning

    Energy Technology Data Exchange (ETDEWEB)

    Gaillard, Y; Anglada, M [Department of Materials Science and Metallurgy (CMEM), Universitat Politecnica de Catalunya, Avda. Diagonal 647 (ETSEIB), 08028 Barcelona (Spain); MacIas, A Hurtado [Centro de Investigacion en Materiales Avanzados, SC, Laboratorio Nacional de Nanotecnologia, Miguel de Cervantes 120, Complejo Industrial Chihuahua, Chihuahua, 31109 (Mexico); Munoz-Saldana, J; Trapaga, G, E-mail: jmunoz@qro.cinvestav.m [Centro de Investigacion y Estudios Avanzados del IPN, Unidad Queretaro Apdo, Postal 1-798, 76001 Queretaro, Qro. (Mexico)

    2009-04-21

    This paper presents a study of the deformation mechanisms of barium titanate under nanoindentation. The (0 0 1) and (1 1 0) crystallographic orientations of BaTiO{sub 3} giant grains were indented and critical mean contact pressures for dislocation nucleation were extracted from the indentation curves. The orientation of the dislocation slip lines was identified by atomic force microscopy, showing that the (1 1 0){l_brace}1 1 0{r_brace} glide systems were activated. Twin bands, observed on both orientations, also occur on the {l_brace}1 1 0{r_brace} habit planes and actively participate in the accommodation of the plastic deformation. Furthermore, dislocation pile-ups introduced by spherical indentations have shown a close relation between dislocations and twinning formation.

  13. A single theory for some quasi-static, supersonic, atomic, and tectonic scale applications of dislocations

    Science.gov (United States)

    Zhang, Xiaohan; Acharya, Amit; Walkington, Noel J.; Bielak, Jacobo

    2015-11-01

    We describe a model based on continuum mechanics that reduces the study of a significant class of problems of discrete dislocation dynamics to questions of the modern theory of continuum plasticity. As applications, we explore the questions of the existence of a Peierls stress in a continuum theory, dislocation annihilation, dislocation dissociation, finite-speed-of-propagation effects of elastic waves vis-a-vis dynamic dislocation fields, supersonic dislocation motion, and short-slip duration in rupture dynamics.

  14. Mechanisms operating during plastic deformation of metals under concurrent production of cascades and dislocations

    Energy Technology Data Exchange (ETDEWEB)

    Trinkaus, H. [Institut fuer Festkoerperforschung, Forschungszentrum Juelich (Germany); Singh, B.N. [Technical Univ. of Denmark, Risoe National Laboratory for Sustainable Energy, Materials Research Dept., Roskilde (Denmark)

    2008-04-15

    Recent in-reactor tensile tests (IRTs) on pure copper have revealed a deformation behaviour which is significantly different from that observed in post-irradiation tensile tests (PITs). In IRTs, the material deforms uniformly and homogeneously without yield drop and plastic instability as commonly observed in PITs. An increase in the pre-yield dose results in an increase in the level of hardening over the whole test periods and a decrease in the uniform elongation suggesting that the materials 'remember' the impact of the pre-yield damage level. These features are modelled in terms of the decoration of dislocations with glissile dislocation loops. During pre-yield irradiation, dislocation decoration is due to the one-dimensional (1D) diffusion of cascade induced self-interstitial (SIA) clusters and their trapping in the stress field of the static grown-in dislocations. During post-yield irradiation and deformation, moving dislocations are decorated by the sweeping of matrix loops. The interaction of dislocations with loops and between loops is discussed as a function of the relevant parameters. On this basis, the kinetics of decoration is treated in terms of fluxes of loops to and reactions with each other in a conceived 2D space of decoration. In this space, loop coalescence, alignment and mutual blocking reactions are characterised by appropriate reaction cross sections. In the kinetic equations for 'dynamic decoration' under deformation, the evolution of the dislocation density is taken into account. Simple solutions of the kinetic equations are discussed. The apparent memory of the system for the pre-yield dose is identified as the result of simultaneous and closely parallel transient evolutions of the cascade damage and the dislocations up to the end of the IRTs. The contributions of dislocation decoration to yield and flow stresses are attributed to the interaction of dislocations with aligned loops temporarily or permanently immobilized

  15. Spatiotemporal periodicity of dislocation dynamics in a two-dimensional microfluidic crystal flowing in a tapered channel

    Science.gov (United States)

    Gai, Ya; Leong, Chia Min; Cai, Wei; Tang, Sindy K. Y.

    2016-10-01

    When a many-body system is driven away from equilibrium, order can spontaneously emerge in places where disorder might be expected. Here we report an unexpected order in the flow of a concentrated emulsion in a tapered microfluidic channel. The velocity profiles of individual drops in the emulsion show periodic patterns in both space and time. Such periodic patterns appear surprising from both a fluid and a solid mechanics point of view. In particular, when the emulsion is considered as a soft crystal under extrusion, a disordered scenario might be expected based on the stochastic nature of dislocation dynamics in microscopic crystals. However, an orchestrated sequence of dislocation nucleation and migration is observed to give rise to a highly ordered deformation mode. This discovery suggests that nanocrystals can be made to deform more controllably than previously thought. It can also lead to novel flow control and mixing strategies in droplet microfluidics.

  16. Dynamics of Edge Dislocations in a Low-Stability FCC-System Irradiated by High-Energy Particles

    Science.gov (United States)

    Starostenkov, M. D.; Potekaev, A. I.; Markidonov, A. V.; Kulagina, V. V.; Grinkevich, L. S.

    2017-01-01

    Using the method of molecular dynamics, the behavior of plastic deformation and defect structure selforganization are investigated in a low-stability condensed FCC-system irradiated with high-energy particles. An analysis of the dynamics of a single edge dislocation and elementary dislocation ensembles, subjected to the action of a post-cascade shock wave, demonstrates that as a result of this action the dislocations are displaced towards the wave source. As this goes on, the roles of both collective effects and external influences on the ensembles of complex interacting defects increase. In particular, the investigation performed in this work demonstrates that the post-cascade shock waves can give rise to migration of not only single edge dislocation but also elementary dislocation ensembles. It is demonstrated that the changes in the dislocation structure of the irradiated material result from the unloading waves following the post-cascade waves, rather than from the latter waves themselves.

  17. Theory of the lattice dynamics of model crystals containing screw dislocations

    Energy Technology Data Exchange (ETDEWEB)

    Glass, N. E.

    1976-08-01

    A theoretical study of the lattice dynamics of a simple cubic model-crystal is made. The perturbation matrix of a single screw dislocation is determined and is used with the perfect lattice Green function to find four secular equations for the frequencies altered by the dislocation. The solutions yield, depending on the model parameters, up to four separate bands of optic localized-modes across the Brillouin zone. No shifts in the perfect lattice acoustical bands are found. The frequencies of the dislocation-induced localized modes are well separated from the frequencies of the perfect lattice modes and should present no difficulty in being distinguished experimentally. The Green function of the lattice containing many parallel screw dislocations is determined by following the method in use for point defects. With this imperfect-lattice Green function, the neutron cross-section for coherent one-phonon inelastic scattering by the dislocation localized-modes is obtained. Using model parameters corresponding to simple metals, the numerical evaluation yields cross-sections on the borderline of present capabilities for experimental detection and indicates the desirability of an experimental test-search. The most important parameter is found to be the ratio of the longitudinal (lambda) to the transverse (..mu..) force constants. As lambda:..mu.. increases, the localized-mode branches separate, the many-dislocation effects become noticeable, and the cross-section for inelastic scattering by the localized-modes rises. Crystals undergoing transverse mode softening, in which lambda:..mu.. grows as ..mu.. tends toward zero, may be useful in the experimental detection of dislocation-induced lattice modes.

  18. Three-dimensional molecular dynamics simulation of hydrogen-enhanced dislocation emission and crack propagation

    Institute of Scientific and Technical Information of China (English)

    2002-01-01

    A three-dimensional molecular dynamics simulation using the embedded atom method (EAM) potentials shows that for both pure Ni and Ni+H, dislocations are firstly emitted during loading and the crack propagates after enough disloca tions are emitted. In the case of hydrogen embrittlement, local plastic deformat ion is a precondition for crack propagation. For the crack along the (1 11) slip pla ne, one atom fraction in percent of hydrogen can decrease the critical stress in tensity for dislocation emission KIe from 0.42 to 0.36 MPam 1/2, and that for crack propagation KIp from 0.80 to 0.76 MPam1/2. Therefore, hydrogen enhances dislocation emission and crack pro pagation.

  19. MOLECULAR DYNAMICS SIMULATION OF THE ROLE OF DISLOCATIONS IN MICROCRACK HEALING

    Institute of Scientific and Technical Information of China (English)

    Li Shen; Gao Kewei; Qiao Lijie; Chu Wuyang; Zhou Fuxin

    2000-01-01

    The molecular dynamics method is used to simulate microcrack healing during heating or/and under compressive stress. A centre microcrack in Cu crystal would be sealed under compressive stress or by heating. The role of compressive stress and heating in crack healing was additive. During microcrack healing,dislocation generation and motion occurred. When there were pre-existing dislocations around the microcrack, the critical temperature or compressive stress necessary for microcrack healing would decrease, and, the higher the number of dislocations,the lower the critical temperature or compressive stress. The critical temperaturenecessary for microcrack healing depended upon the orientation of the crack plane.For example, the critical temperature for the crack along the (001) plane was the lowest, i.e. 770K.

  20. New mechanism of irradiation creep based on the radiation-induced vacancy emission from dislocations

    NARCIS (Netherlands)

    Dubinko, [No Value

    2005-01-01

    A new mechanism of irradiation creep is proposed, which is based on the radiation and stress induced difference in emission ( RSIDE) of vacancies from dislocations of different orientations with respect to the external stress. This phenomenon is due to the difference in vacancy formation energies, w

  1. Atomic structure of screw dislocations intersecting the Au(111) surface: A combined scanning tunneling microscopy and molecular dynamics study

    DEFF Research Database (Denmark)

    Engbæk, Jakob; Schiøtz, Jakob; Dahl-Madsen, Bjarke;

    2006-01-01

    The atomic-scale structure of naturally occurring screw dislocations intersecting a Au(111) surface has been investigated both experimentally by scanning tunneling microscopy (STM) and theoretically using molecular dynamics (MD) simulations. The step profiles of 166 dislocations were measured usi...

  2. Mechanism of void growth in irradiated NaCl based on exiton-induced formation of divacancies at dislocations

    NARCIS (Netherlands)

    Dubinko, [No Value; Vainshtein, DI; den Hartog, HW

    2005-01-01

    We propose a mechanism of void growth in di-atomic ionic crystals due to agglomeration of divacancies produced by interactions between dislocations and excitons. An exciton can cause movement of nearby dislocation jogs, resulting in the creation of equal numbers of anion and cation vacancies (Schott

  3. Dislocation glide in Ni-Al solid solutions from the atomic scale up: a molecular dynamics study; Etude du glissement des dislocations dans la solution solide Ni-Al par simulation a l'echelle atomique

    Energy Technology Data Exchange (ETDEWEB)

    Rodary, E

    2003-01-01

    The glide of an edge dislocation in solid solutions is studied by molecular dynamics, at fixed temperature and imposed external stress. We have optimized an EAM potential for Ni(1 a 8% A1): it well reproduces the lattice expansion, local atomic order, stacking fault energy as a function of composition, as well as the elastic properties of the {gamma}' phase with L1{sub 2} structure. On increasing the stress, the dislocation is first immobile, then glides with a velocity proportional to the stress and the velocity saturates on reaching the transverse sound velocity. However, only beyond a static threshold stress, {sigma}{sub s}, does the dislocation glide a distance large enough to allow macroscopic shear; the linear part of the velocity-stress curve extrapolates to zero at a dynamical threshold stress, {sigma}{sub d}, The friction coefficient, and the threshold stresses ({sigma}{sub s} and {sigma}{sub d}), increase with the A1 concentration and decrease with temperature (300 and 500 K). Close to the critical shear stress, {sigma}{sub s}, the dislocation glide is analysed with a 'stop and go' model. The latter yields the flight velocity between obstacles, the mean obstacle density and the distribution of the waiting time on each obstacle as a function of stress, composition and temperature. The obstacle to the glide is proposed to be the strong repulsion between Al atoms brought into nearest neighbour position by the glide process, and not the dislocation-solute interaction. The microscopic parameters so defined are introduced into a micro-mechanical model, which well reproduces the known behaviour of nickel base solid solutions. (author)

  4. Molecular dynamics investigation of the interaction of dislocations with carbides in BCC Fe

    Science.gov (United States)

    Granberg, F.; Terentyev, D.; Nordlund, K.

    2015-06-01

    Different types of carbides are present in many steels used as structural materials. To safely use steel in demanding environments, like nuclear power plants, it is important to know how defects will affect the mechanical properties of the material. In this study, the effect of carbide precipitates on the edge dislocation movement is investigated. Three different types of carbides were investigated by means of molecular dynamics, with a Tersoff-like bond order interatomic potential by Henriksson et al. The obstacles were 4 nm in diameter and were of Fe3C- (cementite-), Fe23C6- and Cr23C6-type. The critical unpinning stress was calculated for each type at different temperatures, to get the temperature-dependent obstacle strength. The results showed a decreasing critical stress with increasing temperature, consistent with previous studies. The critical unpinning stress was seen to be dependent on the type of carbide, but the differences were small. A difference was also observed between the obstacles with the same structure, but with different composition. This study shows the relation between the existing Cr23C6 carbide and the experimentally non-existing Fe23C6 carbide, which needs to be used as a model system for investigations with interatomic potentials not able to describe the interaction of Cr in the Fe-C-system. We found the difference to be a between 7% and 10% higher critical unpinning stress for the chromium carbide, than for the iron carbide of the same type.

  5. Multiple time step molecular dynamics simulation for interaction between dislocations and grain boundaries

    Institute of Scientific and Technical Information of China (English)

    Xiaoyan Li; Wei Yang

    2005-01-01

    A multiple time step algorithm, called reversible reference system propagator algorithm, is introduced for thelong time molecular dynamics simulation. In contrast to the conventional algorithms, the multiple time method has better convergence, stability and efficiency. The method is validated by simulating free relaxation and the hypervelocity impact of nano-clusters. The time efficiency of the multiple time step method enables us to investigate the long time interaction between lattice dislocations and low-angle grain boundaries.

  6. Are Self-Organised Critical Dislocation Dynamics Relevant to Ice Sheet Flow?

    OpenAIRE

    Louchet, François; Duval,Paul; Montagnat, Maurine; Weiss, Jérôme

    2009-01-01

    It was recently shown thai crystals (including ice) plastically deform in an intermittent manner in usual laboratory conditions. The present paper aims at discussing whether such self-organised critical dynamics still apply to polar ice sheet conditions. Field data suggest that grains should contain between zero and one dislocation moving at a time. However, this is nothing but an average estimate. Field data also show that strong back-stresses are present, collesponding to a significant dens...

  7. Enabling microstructural changes of FCC/BCC alloys in 2D dislocation dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Ilker Topuz, Ahmet, E-mail: aitopuz@gmail.com

    2015-03-11

    Dimension reduction procedure is the recipe to represent defects in two dimensional dislocation dynamics according to the changes in the geometrical properties of the defects triggered by different conditions such as radiation, high temperature, or pressure. In the present study, this procedure is extended to incorporate further features related to the presence of defects with a special focus on face-centered cubic/body-centered cubic alloys used for diverse engineering purposes. In order to reflect the microstructural state of the alloy on the computational cell of two dimensional dislocation dynamics, the distribution of the multi-type defects over slip lines is implemented by using corresponding strength and line spacing for each type of defect. Additionally, a simple recursive incremental relation is set to count the loop accumulation on the precipitates. In the case of continuous resistance against the motion of edge dislocations on the slip lines, an expression of friction is introduced to see its contribution on the yield strength. Each new property is applied independently on a different material by using experimental information about defect properties and grain sizes under the condition of plain strain deformation: both constant and dynamically increasing obstacle strength for precipitate coarsening in prime-aged and heat-treated copper-chromium-zirconium, internal friction in tantalum-2.5tungsten, and mixed hardening due to the presence of precipitates and prismatic loops in irradiated oxide dispersion strengthened EUROFER with 0.3% yttria.

  8. The Dislocation Mechanism of Stress Corrosion Embrittlement in Ti-6Al-2Sn-4Zr-6Mo

    Science.gov (United States)

    Chapman, Tamara P.; Vorontsov, Vassili A.; Sankaran, Ananthi; Rugg, David; Lindley, Trevor C.; Dye, David

    2016-01-01

    An observation of the dislocation mechanisms operating below a naturally initiated hot-salt stress corrosion crack is presented, suggesting how hydrogen may contribute to embrittlement. The observations are consistent with the hydrogen-enhanced localized plasticity mechanism. Dislocation activity has been investigated through post-mortem examination of thin foils prepared by focused ion beam milling, lifted directly from the fracture surface. The results are in agreement with the existing studies, suggesting that hydrogen enhances dislocation motion. It is found that the presence of hydrogen in (solid) solution results in dislocation motion on slip systems that would not normally be expected to be active. A rationale is presented regarding the interplay of dislocation density and the hydrogen diffusion length.

  9. Mechanism and energetics of dislocation cross-slip in hcp metals

    Science.gov (United States)

    Wu, Zhaoxuan; Curtin, W. A.

    2016-10-01

    Hexagonal close-packed (hcp) metals such as Mg, Ti, and Zr are lightweight and/or durable metals with critical structural applications in the automotive (Mg), aerospace (Ti), and nuclear (Zr) industries. The hcp structure, however, brings significant complications in the mechanisms of plastic deformation, strengthening, and ductility, and these complications pose significant challenges in advancing the science and engineering of these metals. In hcp metals, generalized plasticity requires the activation of slip on pyramidal planes, but the structure, motion, and cross-slip of the associated dislocations are not well established even though they determine ductility and influence strengthening. Here, atomistic simulations in Mg reveal the unusual mechanism of dislocation cross-slip between pyramidal I and II planes, which occurs by cross-slip of the individual partial dislocations. The energy barrier is controlled by a fundamental step/jog energy and the near-core energy difference between pyramidal dislocations. The near-core energy difference can be changed by nonglide stresses, leading to tension-compression asymmetry and even a switch in absolute stability from one glide plane to the other, both features observed experimentally in Mg, Ti, and their alloys. The unique cross-slip mechanism is governed by common features of the generalized stacking fault energy surfaces of hcp pyramidal planes and is thus expected to be generic to all hcp metals. An analytical model is developed to predict the cross-slip barrier as a function of the near-core energy difference and applied stresses and quantifies the controlling features of cross-slip and pyramidal I/II stability across the family of hcp metals.

  10. Discrete Dislocation Dynamics Simulations of Twin Size-Effects in Magnesium

    Science.gov (United States)

    2015-01-01

    size-effects in magnesium Haidong Fan1,2*, Sylvie Aubry3, A. Arsenlis3, Jaafar A. El-Awady1* 1 Department of Mechanical Engineering, Johns Hopkins...structural metal, magnesium (Mg) and its alloys have been of practical interest due to their potential use in automotive, aerospace and defense...applications. Magnesium has a hexagonal closed packed (HCP) lattice structure with low crystal symmetry, thus, in addition to dislocation-mediated

  11. In situ observation of dislocation dynamics at the TOPO-TOMO beamline at the synchrotron light source ANKA

    Energy Technology Data Exchange (ETDEWEB)

    Danilewsky, Andreas; Wittge, Jochen; Croell, Arne; Hess, Adam [Kristallographie, Universitaet Freiburg (Germany); Allen, David; McNally, Patrik [RINCE, Dublin City University (Ireland); Vagovic, Patrick; Li, Zhijuan; Baumbach, Tilo [ANKA, ISS, Research Center Karlsruhe (Germany); GorosteguiColinas, Eider; Garagorri, Jorge; Elizalde, Reyes [CIT, San Sebastian (Spain); Fossati, Matteo; Bowen, Keith; Tanner, Brian [Physics Dept., Durham (United Kingdom)

    2010-07-01

    White beam X-ray topography at the Topo-Tomo beamline of the synchrotron light source ANKA (Research Centre Karlsruhe) is used to monitor in situ the origin and the dynamics of dislocations in silicon at high temperatures. The (100)Si sample with well defined, artificial defects from a nanoindenter was heated in a mirror heater up to 1000 C. During the heating the transmission X-ray topographs were taken with a CCD-camera system continuously every second resulting in a movie of the formation and motion of dislocations. It will be shown, that the indents act as the source for dislocation loops. The dislocations move with about 3.4.10{sup -5} m/sec inside two opposite inclined {l_brace}111{r_brace} glide planes. Finally slip bands of 60 -dislocations are formed. The experimental details of the high temperature topography, the analysis of dislocations as well as the first results of the dislocation dynamics and slip band formation are presented.

  12. A convergent scheme for a non-local coupled system modelling dislocations densities dynamics

    Science.gov (United States)

    Hajj, A. El; Forcadel, N.

    2008-06-01

    In this paper, we study a non-local coupled system that arises in the theory of dislocations densities dynamics. Within the framework of viscosity solutions, we prove a long time existence and uniqueness result for the solution of this model. We also propose a convergent numerical scheme and we prove a Crandall-Lions type error estimate between the continuous solution and the numerical one. As far as we know, this is the first error estimate of Crandall-Lions type for Hamilton-Jacobi systems. We also provide some numerical simulations.

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

    Science.gov (United States)

    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.

  14. Atlantoaxial dislocation

    Directory of Open Access Journals (Sweden)

    Vijendra K Jain

    2012-01-01

    Full Text Available Atlanto-axial dislocations (AADs may be classified into four varieties depending upon the direction and plane of the dislocation i.e. anteroposterior, rotatory, central, and mixed dislocations. However, from the surgical point of view these are divided into two categories i.e. reducible (RAADs and irreducible (IAADs. Posterior fusion is the treatment of choice for RAAD. Transarticular screw fixation with sub-laminar wiring is the most stable& method of posterior fusion. Often, IAAD is due to inadequate extension in dynamic X-ray study which may also be due to spasm of muscles. If the anatomy at the occipito-atlanto-axial region {O-C1-C2; O: occiput, C1: atlas, C2: axis} is normal on X-ray, the dislocation should be reducible. In case congenital anomalies at O-C1-C2 and IAAD are seen on flexion/extension studies of the cervical spine, the C1-C2 joints should be seen in computerized tomography scan (CT. If the C1-C2 joint facet surfaces are normal, the AAD should be reducible by cervical traction or during surgery by mobilizing the joints. The entity termed "dolichoodontoid" does not exist. It is invariably C2-C3 (C3- third cervical vertebra fusion which gives an appearance of dolichoodontoid on plain X-ray or on mid-saggital section of magnetic resonance imaging (MRI or CT scan. The central dislocation and axial invagination should not be confused with basilar invagination. Transoral odontoidectomy alone is never sufficient in cases of congenital IAAD, adequate generous three-dimensional decompression while protecting the underlying neural structures should be achieved. Chronic post-traumatic IAAD are usually Type II odontoid fractures which get malunited or nonunited with pseudoarthrosis in dislocated position. All these dislocations can be reduced by transoral removal of the offending bone, callous and fibrous tissue.

  15. Mechanical properties of irradiated nanowires – A molecular dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Figueroa, Emilio [Grupo de NanoMateriales, Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla, 653 Santiago (Chile); Departamento de Física, Facultad de Ciencias Naturales, Matemática y del Medio Ambiente, Universidad Tecnológica Metropolitana, Santiago 7800002 (Chile); Tramontina, Diego [Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo, 5500 Mendoza (Argentina); Instituto de Bioingeniería, Universidad de Mendoza, 5500 Mendoza (Argentina); Gutiérrez, Gonzalo, E-mail: gonzalo@fisica.ciencias.uchile.cl [Grupo de NanoMateriales, Departamento de Física, Facultad de Ciencias, Universidad de Chile, Casilla, 653 Santiago (Chile); Bringa, Eduardo [Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo, 5500 Mendoza (Argentina)

    2015-12-15

    In this work we study, by means of molecular dynamics simulation, the change in the mechanical properties of a gold nanowire with pre-existing radiation damage. The gold nanowire is used as a simple model for a nanofoam, made of connected nanowires. Radiation damage by keV ions leads to the formation of a stacking fault tetrahedron (SFT), and this defect leads to a reduced plastic threshold, as expected, when the nanowire is subjected to tension. We quantify dislocation and twin density during the deformation, and find that the early activation of the SFT as a dislocation source leads to reduced dislocation densities compared to the case without radiation damage. In addition, we observed a total destruction of the SFT, as opposed to a recent simulation study where it was postulated that SFTs might act as self-generating dislocation sources. The flow stress at large deformation is also found to be slightly larger for the irradiated case, in agreement with recent experiments. - Highlights: • Stacking Fault Tetrahedra (SFT) formation proceeds by cascades, containing typically a vacancy cluster and interstitials. • Applied tension leads to the destruction of the SFT, in contrast to a recently reported case of a SFT which soften the NW. • After the initial dislocation activity, strength is controlled by a few surviving dislocations.

  16. Crystal Dislocations

    Directory of Open Access Journals (Sweden)

    Ronald W. Armstrong

    2016-01-01

    Full Text Available Crystal dislocations were invisible until the mid-20th century although their presence had been inferred; the atomic and molecular scale dimensions had prevented earlier discovery. Now they are normally known to be just about everywhere, for example, in the softest molecularly-bonded crystals as well as within the hardest covalently-bonded diamonds. The advent of advanced techniques of atomic-scale probing has facilitated modern observations of dislocations in every crystal structure-type, particularly by X-ray diffraction topography and transmission electron microscopy. The present Special Issue provides a flavor of their ubiquitous presences, their characterizations and, especially, their influence on mechanical and electrical properties.

  17. Tailoring dislocation structures and mechanical properties of nanostructured metals produced by plastic deformation

    DEFF Research Database (Denmark)

    Huang, Xiaoxu

    2009-01-01

    The presence of a dislocation structure associated with low-angle dislocation boundaries and interior dislocations is a common and characteristic feature in nanostructured metals produced by plastic deformation, and plays an important role in determining both the strength and ductility of the nan...

  18. A Novel Approach for Dynamic Testing of Total Hip Dislocation under Physiological Conditions.

    Science.gov (United States)

    Herrmann, Sven; Kluess, Daniel; Kaehler, Michael; Grawe, Robert; Rachholz, Roman; Souffrant, Robert; Zierath, János; Bader, Rainer; Woernle, Christoph

    2015-01-01

    Constant high rates of dislocation-related complications of total hip replacements (THRs) show that contributing factors like implant position and design, soft tissue condition and dynamics of physiological motions have not yet been fully understood. As in vivo measurements of excessive motions are not possible due to ethical objections, a comprehensive approach is proposed which is capable of testing THR stability under dynamic, reproducible and physiological conditions. The approach is based on a hardware-in-the-loop (HiL) simulation where a robotic physical setup interacts with a computational musculoskeletal model based on inverse dynamics. A major objective of this work was the validation of the HiL test system against in vivo data derived from patients with instrumented THRs. Moreover, the impact of certain test conditions, such as joint lubrication, implant position, load level in terms of body mass and removal of muscle structures, was evaluated within several HiL simulations. The outcomes for a normal sitting down and standing up maneuver revealed good agreement in trend and magnitude compared with in vivo measured hip joint forces. For a deep maneuver with femoral adduction, lubrication was shown to cause less friction torques than under dry conditions. Similarly, it could be demonstrated that less cup anteversion and inclination lead to earlier impingement in flexion motion including pelvic tilt for selected combinations of cup and stem positions. Reducing body mass did not influence impingement-free range of motion and dislocation behavior; however, higher resisting torques were observed under higher loads. Muscle removal emulating a posterior surgical approach indicated alterations in THR loading and the instability process in contrast to a reference case with intact musculature. Based on the presented data, it can be concluded that the HiL test system is able to reproduce comparable joint dynamics as present in THR patients.

  19. A Novel Approach for Dynamic Testing of Total Hip Dislocation under Physiological Conditions.

    Directory of Open Access Journals (Sweden)

    Sven Herrmann

    Full Text Available Constant high rates of dislocation-related complications of total hip replacements (THRs show that contributing factors like implant position and design, soft tissue condition and dynamics of physiological motions have not yet been fully understood. As in vivo measurements of excessive motions are not possible due to ethical objections, a comprehensive approach is proposed which is capable of testing THR stability under dynamic, reproducible and physiological conditions. The approach is based on a hardware-in-the-loop (HiL simulation where a robotic physical setup interacts with a computational musculoskeletal model based on inverse dynamics. A major objective of this work was the validation of the HiL test system against in vivo data derived from patients with instrumented THRs. Moreover, the impact of certain test conditions, such as joint lubrication, implant position, load level in terms of body mass and removal of muscle structures, was evaluated within several HiL simulations. The outcomes for a normal sitting down and standing up maneuver revealed good agreement in trend and magnitude compared with in vivo measured hip joint forces. For a deep maneuver with femoral adduction, lubrication was shown to cause less friction torques than under dry conditions. Similarly, it could be demonstrated that less cup anteversion and inclination lead to earlier impingement in flexion motion including pelvic tilt for selected combinations of cup and stem positions. Reducing body mass did not influence impingement-free range of motion and dislocation behavior; however, higher resisting torques were observed under higher loads. Muscle removal emulating a posterior surgical approach indicated alterations in THR loading and the instability process in contrast to a reference case with intact musculature. Based on the presented data, it can be concluded that the HiL test system is able to reproduce comparable joint dynamics as present in THR patients.

  20. Periodic dislocation dynamics in two-dimensional concentrated emulsion flowing in a tapered microchannel

    Science.gov (United States)

    Gai, Ya; Leong, Chia Min; Cai, Wei; Tang, Sindy K. Y.

    2016-11-01

    Here we report a surprising order in concentrated emulsion when flowing as a monolayer in a tapered microfluidic channel. The flow of droplets in micro-channels can be non-trivial, and may lead to unexpected phenomena such as long-period oscillations and chaos. Previously, there have been studies on concentrated emulsions in straight channels and channels with bends. The dynamics of how drops flow and rearrange in a tapered geometry has not yet been characterized. At sufficiently slow flow rates, the drops arrange into a hexagonal lattice. At a given x-position, the time-averaged droplet velocities are uniform. The instantaneous drop velocities, however, reveal a different, wave-like pattern. Within the rearrangement zone where the number of rows of drops decreases from N to N-1, there is always a drop moved faster than the others. Close examination reveals the anomalous velocity profile arises from a series of dislocations that are both spatial and temporal periodic. To our knowledge, such reproducible dislocation motion has not been reported before. Our results are useful in novel flow control and mixing strategies in droplet microfluidics as well as modeling crystal plasticity in low-dimensional nanomaterials.

  1. Dynamically assisted Schwinger mechanism.

    Science.gov (United States)

    Schützhold, Ralf; Gies, Holger; Dunne, Gerald

    2008-09-26

    We study electron-positron pair creation from the Dirac vacuum induced by a strong and slowly varying electric field (Schwinger effect) which is superimposed by a weak and rapidly changing electromagnetic field (dynamical pair creation). In the subcritical regime where both mechanisms separately are strongly suppressed, their combined impact yields a pair creation rate which is dramatically enhanced. Intuitively speaking, the strong electric field lowers the threshold for dynamical particle creation--or, alternatively, the fast electromagnetic field generates additional seeds for the Schwinger mechanism. These findings could be relevant for planned ultrahigh intensity lasers.

  2. Mechanism and patterns of cervical spine fractures-dislocations in vertebral artery injury

    Directory of Open Access Journals (Sweden)

    Pankaj Gupta

    2012-01-01

    Full Text Available Purpose: To identify the fracture patterns and mechanism of injury, based on subaxial cervical spine injury classification system (SLIC, on non-contrast computed tomography (NCCT of cervical spine predictive of vertebral artery injury (VAI. Patients and Methods: We retrospectively analyzed cervical spine magnetic resonance imaging (MRI of 320 patients who were admitted with cervical spine injury in our level I regional trauma center over a period of two years (April 2010 to April 2012. Diagnosis of VAI was based on hyperintensity replacing the flow void on a T2-weighted axial image. NCCT images of the selected 43 patients with MRI diagnosis of VAI were then assessed for the pattern of injury. The cervical spinal injuries were classified into those involving the C1 and C2 and subaxial spine. For the latter, SLIC was used. Results: A total of 47 VAI were analyzed in 43 patients. Only one patient with VAI on MRI had no detectable abnormality on NCCT. C1 and C2 injuries were found in one and six patients respectively. In subaxial injuries, the most common mechanism of injury was distraction (37.5% with facet dislocation with or without fracture representing the most common pattern of injury (55%. C5 was the single most common affected vertebral level. Extension to foramen transversarium was present in 20 (42.5% cases. Conclusion: CT represents a robust screening tool for patients with VAI. VAI should be suspected in patients with facet dislocation with or without fractures, foramina transversarium fractures and C1-C3 fractures, especially type III odontoid fractures and distraction mechanism of injury.

  3. Equivalent Plastic Strain Gradient Plasticity with Grain Boundary Hardening and Comparison to Discrete Dislocation Dynamics

    CERN Document Server

    Bayerschen, E; Wulfinghoff, S; Weygand, D; Böhlke, T

    2015-01-01

    The gradient crystal plasticity framework of Wulfinghoff et al. [53] incorporating an equivalent plastic strain and grain boundary yielding, is extended with additional grain boundary hardening. By comparison to averaged results from many discrete dislocation dynamics (DDD) simulations of an aluminum type tricrystal under tensile loading, the new hardening parameter in the continuum model is calibrated. It is shown that although the grain boundaries (GBs) in the discrete simulations are impenetrable, an infinite GB yield strength corresponding to microhard GB conditions, is not applicable in the continuum model. A combination of a finite GB yield strength with an isotropic bulk Voce hardening relation alone also fails to model the plastic strain profiles obtained by DDD. Instead, a finite GB yield strength in combination with GB hardening depending on the equivalent plastic strain at the GBs is shown to give a better agreement to DDD results. The differences in the plastic strain profiles obtained in DDD simu...

  4. Modelling of Dynamic Strain Aging with a Dislocation-Based Isotropic Hardening Model and Investigation of Orthogonal Loading

    NARCIS (Netherlands)

    Berisha, B.; Hora, P.; Tong, L.; Wahlen, A.; Boogaard, van den A.H.

    2008-01-01

    Based on experimental results, a dislocation material model describing the dynamic strain aging effect at different temperatures is presented. One and two stage loading tests were performed in order to investigate the influence of the loading direction as well as the temperature influence due to the

  5. Atomistic insights into dislocation-based mechanisms of void growth and coalescence

    Science.gov (United States)

    Mi, Changwen; Buttry, Daniel A.; Sharma, Pradeep; Kouris, Demitris A.

    2011-09-01

    One of the low-temperature failure mechanisms in ductile metallic alloys is the growth of voids and their coalescence. In the present work we attempt to obtain atomistic insights into the mechanisms underpinning cavitation in a representative metal, namely Aluminum. Often the pre-existing voids in metallic alloys such as Al have complex shapes (e.g. corrosion pits) and the defromation/damage mechanisms exhibit a rich size-dependent behavior across various material length scales. We focus on these two issues in this paper through large-scale calculations on specimens of sizes ranging from 18 thousand to 1.08 million atoms. In addition to the elucidation of the dislocation propagation based void growth mechanism we highlight the observed length scale effect reflected in the effective stress-strain response, stress triaxiality and void fraction evolution. Furthermore, as expected, the conventionally used Gurson's model fails to capture the observed size-effects calling for a mechanistic modification that incorporates the mechanisms observed in our (and other researchers') simulation. Finally, in our multi-void simulations, we find that, the splitting of a big void into a distribution of small ones increases the load-carrying capacity of specimens. However, no obvious dependence of the void fraction evolution on void coalescence is observed.

  6. Atomistic modeling of dislocation-interface interactions

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Jian [Los Alamos National Laboratory; Valone, Steven M [Los Alamos National Laboratory; Beyerlein, Irene J [Los Alamos National Laboratory; Misra, Amit [Los Alamos National Laboratory; Germann, T. C. [Los Alamos National Laboratory

    2011-01-31

    Using atomic scale models and interface defect theory, we first classify interface structures into a few types with respect to geometrical factors, then study the interfacial shear response and further simulate the dislocation-interface interactions using molecular dynamics. The results show that the atomic scale structural characteristics of both heterophases and homophases interfaces play a crucial role in (i) their mechanical responses and (ii) the ability of incoming lattice dislocations to transmit across them.

  7. Differential Histopathological and Behavioral Outcomes Eight Weeks after Rat Spinal Cord Injury by Contusion, Dislocation, and Distraction Mechanisms

    Science.gov (United States)

    Chen, Kinon; Liu, Jie; Assinck, Peggy; Bhatnagar, Tim; Streijger, Femke; Zhu, Qingan; Dvorak, Marcel F.; Kwon, Brian K.; Tetzlaff, Wolfram

    2016-01-01

    Abstract The objective of this study was to compare the long-term histological and behavioral outcomes after spinal cord injury (SCI) induced by one of three distinct biomechanical mechanisms: dislocation, contusion, and distraction. Thirty male Sprague-Dawley rats were randomized to incur a traumatic cervical SCI by one of these three clinically relevant mechanisms. The injured cervical spines were surgically stabilized, and motor function was assessed for the following 8 weeks. The spinal cords were then harvested for histologic analysis. Quantification of white matter sparing using Luxol fast blue staining revealed that dislocation injury caused the greatest overall loss of white matter, both laterally and along the rostrocaudal axis of the injured cord. Distraction caused enlarged extracellular spaces and structural alteration in the white matter but spared the most myelinated axons overall. Contusion caused the most severe loss of myelinated axons in the dorsal white matter. Immunohistochemistry for the neuronal marker NeuN combined with Fluoro Nissl revealed that the dislocation mechanism resulted in the greatest neuronal cell losses in both the ventral and dorsal horns. After the distraction injury mechanism, animals displayed no recovery of grip strength over time, in contrast to the animals subjected to contusion or dislocation injuries. After the dislocation injury mechanism, animals displayed no improvement in the grooming test, in contrast to the animals subjected to contusion or distraction injuries. These data indicate that different SCI mechanisms result in distinct patterns of histopathology and behavioral recovery. Understanding this heterogeneity may be important for the future development of therapeutic interventions that target specific neuropathology after SCI. PMID:26671448

  8. Discrete dislocation dynamic simulation for PCD indentation behavior%聚晶金刚石压痕行为的离散位错动力学仿真分析

    Institute of Scientific and Technical Information of China (English)

    白清顺; 白锦轩; 泽华; 姜丽辉; 梁迎春

    2014-01-01

    According to dislocation theory,PCD indentation simulation model was established by coupling discrete dislocation dynamics and finite element model.Through the discrete dislocation simulation,we got the PCD dislocation cloud under the action of micro indentation,obtained the influence law of PCD indentation characteristic which was caused by various granularities and diamond volume fractions,and analyzed PCD dislocation evolution mechanism and failure behavior.Result showed that the PCD dislocation movement could be accurately described by discrete dislocation dynamic analysis method,that the crystal dislocation slip degree increased with enlarging granularities, and that the dislocation nucleation density increased as the diamond volume fractions increased.Such changes would lead to the decline of fracture strength finally.This paper introduced discrete dislocation theory into the analysis of PCD dislocation evolution behavior,and it provided a theoretical basis for the study on materials failure behavior of PCD cutting tool in engineering application.%依据位错理论,建立了聚晶金刚石(polycrystalline diamond,PCD)离散位错动力学-有限元耦合的压痕仿真模型。通过离散位错动力学仿真,获得了在微压痕作用下 PCD 的位错云图,揭示了金刚石微粉颗粒尺寸及颗粒体积分数对聚晶金刚石压痕特性的影响规律,并分析了聚晶金刚石的位错演化机制及其失效行为。研究结果表明:采用离散位错动力学分析方法能够准确描述 PCD 的位错运动过程,PCD 微粉颗粒尺寸增加会增大晶体位错滑移程度,金刚石颗粒体积分数增加则导致位错形核密度增加,最终将引起聚晶金刚石材料断裂强度下降。将离散位错理论引入到为分析聚晶金刚石位错演化的行为中,将为研究 PCD 在切削刀具等工程应用中材料的失效行为提供理论基础。

  9. Statistical characterization of dislocation ensembles

    Energy Technology Data Exchange (ETDEWEB)

    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.

  10. Mechanism and kinetics of spontaneous nanotube growth driven by screw dislocations.

    Science.gov (United States)

    Morin, Stephen A; Bierman, Matthew J; Tong, Jonathan; Jin, Song

    2010-04-23

    Single-crystal nanotubes are commonly observed, but their formation is often not understood. We show that nanotube growth can be driven by axial screw dislocations: Self-perpetuating growth spirals enable anisotropic growth, and the dislocation strain energy overcomes the surface energy required for creating a new inner surface forming hollow tubes spontaneously. This was demonstrated through solution-grown zinc oxide nanotubes and nanowires by controlling supersaturation using a flow reactor and confirmed using microstructural characterization. The agreement between experimental growth kinetics and those predicted from fundamental crystal growth theories confirms that the growth of these nanotubes is driven by dislocations.

  11. Dynamic drag of edge dislocation by circular prismatic loops and point defects

    Energy Technology Data Exchange (ETDEWEB)

    Malashenko, V.V., E-mail: malashenko@kinetic.ac.donetsk.u [Donetsk Institute for Physics and Engineering of NASU, 83114 Donetsk (Ukraine); Donetsk National Technical University, 83000 Donetsk (Ukraine)

    2009-11-15

    Motion of edge dislocation in the presence of prismatic loops and point defects is studied analytically. It is shown that at certain conditions, the velocity dependence of the drag force has two maximums and two minimums.

  12. a Study of Static and Dynamic Properties of Dislocations in Smectic Liquid Crystals.

    Science.gov (United States)

    Chiang, Chien

    Edge dislocations in Smectic liquid Crystals can be observed optically as phase boundaries in a wedged shaped sample near the Smectic A to C phase transition temperature. When C and A phases coexist, two lines can be observed under crossed polarizers. One with an abrupt change in contrast is the dislocation line; the other line, which has a gradual change in contrast, is a continuous phase transition line. Using piezoelectric transducers to apply stress to a sample, we can make the dislocations move. Measuring the velocity of the dislocation line and the relative position of the transition line, we can deduce the driving force on the dislocation and therefore measure its climb mobility. We have developed a theoretical model for the climb mobility in terms of viscous flow within the layers and diffusion between layers. It agrees reasonably well with our experimental data. Pinned dislocations adopt a curved configuration between pinning pints; the curvature is proportional to the driving force applied to them. By measuring the curvature and the driving force, we can deduce the line tension, or self energy, of the dislocation. To study these phenomena experimentally, we have developed a computerized video system which can record pictures from the microscope with frame numbers from the computer simultaneously. Examining the video tape frame by frame, we can make measurements on each frame to study both static and time dependent structures. Besides the quantitative studies that motivated these experiments, a number of qualitative observations have been made, as well as some tentative conclusions concerning the core energy and the relative stability of dislocations of different Burgers vectors.

  13. Behavior of dislocations in silicon

    Energy Technology Data Exchange (ETDEWEB)

    Sumino, Koji [Nippon Steel Corp., Chiba Prefecture (Japan)

    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.

  14. Dislocational Rock Mechanisms As a Basis for Seismic Methods in the Search for Hydrocarbons La géomécanique de dislocation en tant que base des méthodes sismiques de la recherche des hydrocarbures

    Directory of Open Access Journals (Sweden)

    Pissetski V. B.

    2006-11-01

    Full Text Available The analysis of the geological and geophysical data points out the inadequacy of the classical concept of a stratified continuous sedimentary medium on one hand. In the second hand it helps to introduce a serie of key physical concepts. The general formulation of the proposed concept can be presented as follows :(a The discrete character clearly observed during the sedimentation process ensures that changes of sedimentary cycles (hiatuses are marked by fine layers or surfaces which correspond to regular structures of strength defects later. (b The changes in gravity or tectonic load induce a destruction mechanism which regular growth changes a stratified continuous medium with defects into a dicrete medium. This destruction mechanism is a final process : each discrete element is limited in space by horizontal and vertical surfaces of disruption (dislocations. The final medium is a critical piling of elements which reacts easily to any change of the mechanical stress field. From this point of view, if we analyse outcrops and well data one notices a strong correspondance between the actual cracks and the main sedimentary limits. The main feature of the destruction mechanism is well reproduced in the laboratory by physical models built layer by layer with cristallisation pauses between layers. The theoretical analysis of the stress field of discrete media shows the predominance of vertical displacements and consequently the block aspect of the stress distribution within a compensation scheme. Thus, the key element in such a discrete medium model is the dislocation structure and the associated stress or pressure distribution. It becomes obvious that the main parameters of the fluid behaviour are determined by the density of dislocations and the value of the general pressure over the volume of the formation. The general pressure is defined as the sum of geostatic pressure and the anornafic pressure linked to the characteristic variability of the

  15. Evaluation of the mechanism and principles of management of temporomandibular joint dislocation. Systematic review of literature and a proposed new classification of temporomandibular joint dislocation

    Science.gov (United States)

    2011-01-01

    Background Virtually all the articles in literature addressed only a specific type of dislocation. The aim of this review was to project a comprehensive understanding of the pathologic processes and management of all types of dislodgement of the head of the mandibular condyle from its normal position in the glenoid fossa. In addition, a new classification of temporomandibular joint dislocation was also proposed. Method and materials A thorough computer literature search was done using the Medline, Cochrane library and Embase database. Key words like temporo-mandibular joint dislocation were used for the search. Additional manual search was done by going through published home-based and foreign articles. Case reports/series, and original articles that documented the type of dislocation, number of cases treated in the series and original articles. Treatment done and outcome of treatment were included in the study. Result A total of 128 articles were reviewed out which 79 were found relevant. Of these, 26 were case reports, 17 were case series and 36 were original articles. 79 cases were acute dislocations, 35 cases were chronic protracted TMJ dislocations and 311 cases were chronic recurrent TMJ dislocations. Etiology was predominantly trauma in 60% of cases and other causes contributed about 40%. Of all the cases reviewed, only 4 were unilateral dislocation. Various treatment modalities are outlined in this report as indicated for each type of dislocation. Conclusion The more complex and invasive method of treatment may not necessarily offer the best option and outcome of treatment, therefore conservative approaches should be exhausted and utilized appropriately before adopting the more invasive surgical techniques. PMID:21676208

  16. Evaluation of the mechanism and principles of management of temporomandibular joint dislocation. Systematic review of literature and a proposed new classification of temporomandibular joint dislocation

    Directory of Open Access Journals (Sweden)

    Akinbami Babatunde O

    2011-06-01

    Full Text Available Abstract Background Virtually all the articles in literature addressed only a specific type of dislocation. The aim of this review was to project a comprehensive understanding of the pathologic processes and management of all types of dislodgement of the head of the mandibular condyle from its normal position in the glenoid fossa. In addition, a new classification of temporomandibular joint dislocation was also proposed. Method and materials A thorough computer literature search was done using the Medline, Cochrane library and Embase database. Key words like temporo-mandibular joint dislocation were used for the search. Additional manual search was done by going through published home-based and foreign articles. Case reports/series, and original articles that documented the type of dislocation, number of cases treated in the series and original articles. Treatment done and outcome of treatment were included in the study. Result A total of 128 articles were reviewed out which 79 were found relevant. Of these, 26 were case reports, 17 were case series and 36 were original articles. 79 cases were acute dislocations, 35 cases were chronic protracted TMJ dislocations and 311 cases were chronic recurrent TMJ dislocations. Etiology was predominantly trauma in 60% of cases and other causes contributed about 40%. Of all the cases reviewed, only 4 were unilateral dislocation. Various treatment modalities are outlined in this report as indicated for each type of dislocation. Conclusion The more complex and invasive method of treatment may not necessarily offer the best option and outcome of treatment, therefore conservative approaches should be exhausted and utilized appropriately before adopting the more invasive surgical techniques.

  17. Traumatic cervical cord transection without facet dislocations--a proposal of combined hyperflexion-hyperextension mechanism: a case report.

    Science.gov (United States)

    Cha, Yoo-Hyun; Cho, Tai-Hyoung; Suh, Jung-Keun

    2010-08-01

    A patient is presented with a cervical spinal cord transection which occurred after a motor vehicle accident in which the air bag deployed and the seat belt was not in use. The patient had complete quadriplegia below the C5 level and his imaging study showed cervical cord transection at the level of the C5/6 disc space with C5, C6 vertebral bodies and laminar fractures. He underwent a C5 laminectomy and a C4-7 posterior fusion with lateral mass screw fixation. Previous reports have described central cord syndromes occurring in hyperextension injuries, but in adults, acute spinal cord transections have only developed after fracture-dislocations of the spine. A case involving a post-traumatic spinal cord transection without any evidence of radiologic facet dislocations is reported. Also, we propose a combined hyperflexion-hyperextension mechanism to explain this type of injury.

  18. The inverse hall-petch relation in nanocrystalline metals: A discrete dislocation dynamics analysis

    Science.gov (United States)

    Quek, Siu Sin; Chooi, Zheng Hoe; Wu, Zhaoxuan; Zhang, Yong Wei; Srolovitz, David J.

    2016-03-01

    When the grain size in polycrystalline materials is reduced to the nanometer length scale (nanocrystallinity), observations from experiments and atomistic simulations suggest that the yield strength decreases (softening) as the grain size is decreased. This is in contrast to the Hall-Petch relation observed in larger sized grains. We incorporated grain boundary (GB) sliding and dislocation emission from GB junctions into the classical DDD framework, and recovered the smaller is weaker relationship observed in nanocrystalline materials. This current model shows that the inverse Hall-Petch behavior can be obtained through a relief of stress buildup at GB junctions from GB sliding by emitting dislocations from the junctions. The yield stress is shown to vary with grain size, d, by a d 1 / 2 relationship when grain sizes are very small. However, pure GB sliding alone without further plastic accomodation by dislocation emission is grain size independent.

  19. Supersonic Dislocation Bursts in Silicon

    Science.gov (United States)

    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.

  20. Dynamic fracture mechanics

    Science.gov (United States)

    Kobayashi, A. S.; Ramulu, M.

    1985-01-01

    Dynamic fracture and crack propagation concepts for ductile materials are reviewed. The equations for calculating dynamic stress integrity and the dynamic energy release rate in order to study dynamic crack propagation are provided. The stress intensity factor versus crack velocity relation is investigated. The uses of optical experimental techniques and finite element methods for fracture analyses are described. The fracture criteria for a rapidly propagating crack under mixed mode conditions are discussed; crack extension and fracture criteria under combined tension and shear loading are based on maximum circumferential stress or energy criteria such as strain energy density. The development and use of a Dugdale model and finite element models to represent crack and fracture dynamics are examined.

  1. [Dislocation of the closing element of the disk mechanical graft at aortic valve replacement].

    Science.gov (United States)

    Korostelev, A N; Kuntsevich, G I; Zotikov, A E; Chernyak, B B; Il'ina, M V; Ter-Khachaturova, I E; Solopova, G V

    2003-01-01

    Presented herein is the first case of dislocation of the closing element of the artificial low-profile aortic valve to the abdominal aorta, which happened during replacement. Toward completion of extracorporeal circulation a 37-year-old man showed the signs of aortic insufficiency because of dislocation of the closing element. After resumption of extracorporeal circulation repeated replacement was accomplished. To detect the site of graft cusp embolism, transesophageal echocardiography and duplex scanning of the abdominal aorta were employed. On the 18th day following the first intervention the patient developed thromboembolism to the distal arterial bed. Emergency thrombectomy from the arteries of the right lower extremity was performed and a foreign body was removed from the abdominal aorta, using left-sided thoracophrenolumbotomy. The patient was discharged from the clinic in a satisfactory condition.

  2. Dynamical systems in classical mechanics

    CERN Document Server

    Kozlov, V V

    1995-01-01

    This book shows that the phenomenon of integrability is related not only to Hamiltonian systems, but also to a wider variety of systems having invariant measures that often arise in nonholonomic mechanics. Each paper presents unique ideas and original approaches to various mathematical problems related to integrability, stability, and chaos in classical dynamics. Topics include… the inverse Lyapunov theorem on stability of equilibria geometrical aspects of Hamiltonian mechanics from a hydrodynamic perspective current unsolved problems in the dynamical systems approach to classical mechanics

  3. DYNAMIC MODELING OF METAMORPHIC MECHANISM

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    The concept of metamorphic mechanism is put forward according to the change of configurations from one state to another. Different configurations of metamorphic mechanism are described through the method of Huston lower body arrays. Kinematics analyses for metamorphic mechanism with generalized topological structure, including the velocity, angular velocity, acceleration and angular acceleration, are given. Dynamic equations for an arbitrary configuration, including close-loop constraints, are formed by using Kane's equations. For an arbitrary metamorphic mechanism, the transformation matrix of generalized speeds between configuration (*)and(*)+1 is obtained for the first time. Furthermore, configuration-complete dynamic modeling of metamorphic mechanism including all configurations is completely established.

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

    Science.gov (United States)

    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.

  5. Dynamic plantar pressure distribution, strength capacity and postural control after Lisfranc fracture-dislocation

    DEFF Research Database (Denmark)

    Mehlhorn, Alexander T; Walther, Markus; Yilmaz, Tayfun

    2017-01-01

    of life. 17 consecutive patients suffering from a Lisfranc fracture dislocation were registered, underwent open reduction and internal fixation and were followed-up for 50.5±25.7months (Mean±SDM). Biomechanical analysis of muscle strength capacities, postural control and plantar pressure distribution...... correlated well with clinical outcome. Altered postural control was evident by a significant reduction in unilateral stance time, from which we calculated a strong correlation between stance time and the isokinetic strength measurement. Plantar pressure measurements revealed a significant reduction in peak...... pressure under the midfoot and of Force-Time Integral beneath the second metatarsal. Sufficient rehabilitation is crucial to the clinical outcome following anatomical open reduction of Lisfranc fracture-dislocation. The present study supports a rehabilitation approach focussing on restoring proprioception...

  6. Dislocation Pile-Ups, Material Strength Levels, and Thermal Activation

    Science.gov (United States)

    Armstrong, Ronald W.

    2016-12-01

    A review dedicated to James C.M. Li is given of dislocation pile-ups and their connection to the Hall-Petch dependence of polycrystalline strength and fracture mechanics properties on an inverse square root of grain size basis, with such grain size dependence now very importantly extended to nanopolycrystalline material behaviors. An analogous H-P dependence is described for the inverse activation volume parameter obtained from the strain rate (and thermal) dependencies contained in the model dislocation thermal activation-strain rate analysis, also relating to pioneering contributions of Li to the topic of thermally activated dislocation dynamics.

  7. Reactions between a <111> screw dislocation and <100> interstitial dislocation loops in alpha-iron modelled at atomic-scale

    Energy Technology Data Exchange (ETDEWEB)

    Terentyev, Dmitry [Belgian Nuclear Research Centre, SCK-CEN; Bacon, David J [University of Liverpool; Osetskiy, Yury N [ORNL

    2010-03-01

    Interstitial dislocation loops with Burgers vector of <100> type are observed in {alpha}-iron irradiated by neutrons or heavy ions, and their population increases with increasing temperature. Their effect on motion of a 1/2<111> edge dislocation was reported earlier 1. Results are presented of a molecular dynamics study of interactions between a 1/2<111> screw dislocation and <100> loops in iron at temperature in the range 100 to 600 K. A variety of reaction mechanisms and outcomes are observed and classified in terms of the resulting dislocation configuration and the maximum stress required for the dislocation to break away. The highest obstacle resistance arises when the loop is absorbed to form a helical turn on the screw dislocation line, for the dislocation cannot glide away until the turn closes and a loop is released with the same Burgers vector as the line. Other than one situation found, in which no dislocation-loop reaction occurs, the weakest obstacle strength is found when the original <100> loop is restored at the end of the reaction. The important role of the cross-slip and the influence of model boundary conditions are emphasised and demonstrated by examples.

  8. Towards a quantification of stress corrosion mechanisms: numerical simulations of hydrogen-dislocations at the very crack tip; Vers une quantification des mecanismes de corrosion sous contrainte: simulations numeriques des interactions hydrogene-dislocations en pointe de fissure

    Energy Technology Data Exchange (ETDEWEB)

    Chateau, J.P

    1999-01-05

    We discuss the respective roles played by anodic dissolution and hydrogen in SCC mechanisms of f.c.c. materials, by studying the fracture of copper in nitrite for which we compare the results with that previously obtained in 316L steel in hot chloride. It is surprising to note that even the crystallographies at the scale of the micron are different, the macroscopic inclination of the fracture surfaces are the same. In the case of 316L steel, the formation of strong pile-ups in the presence of hydrogen leads to a zigzag fracture along alternated slip planes in the most general case. In the absence of hydrogen, as in copper, this mechanism effectively disappears. Furthermore, numerical simulations of crack shielding by dislocations emitted on one plane predict the macroscopic inclination. It shows that it is due to the mere dissolution which confines slip activity at the very crack tip in f.c.c. materials. In order to quantify the mechanism involved in 316L steel, we developed simulations which numerically solve the coupled diffusion and elasticity equations for hydrogen in the presence of a crack and shielding dislocations. They reproduce the mechanisms of hydrogen segregation on edge dislocations and of a localised softening effect by decreasing pair interactions. These mechanisms lead to i) a localisation of hydrogen embrittlement along the activated slip planes, ii) an increase of the dislocation density in pile-ups, and iii) a decrease of the cross slip probability. These three factors enhance micro-fracture at the head of a pile-up, which is responsible of thezigzag fracture. Introducing the free surface effects for hydrogen, we point out a new mechanism: the inhibition of dislocation sources at the crack tip, which is relevant with the brittle fracture surfaces observed in some cases in 316L steel. The quantification of these different mechanisms allows to give a relation between the local fracture possibility and the macroscopic parameters. A general law for

  9. Treatment of congenital dislocation of the hip by the Pavlik harness. Mechanism of reduction and usage.

    Science.gov (United States)

    Iwasaki, K

    1983-07-01

    The Pavlik harness was used in the treatment of complete congenital dislocation of one or both hips in a series of infants, on either an outpatient or an inpatient basis. The results in the two groups were compared. For the children treated as outpatients the incidence of avascular necrosis of the femoral head was 7.2 per cent and for the group treated as inpatients the rate was 28 per cent. Application of the Pavlik harness allowed reduction of the hip by shifting the femoral head first to the posterior part of the acetabulum through flexion of the hip, followed by movement of the femoral head anteriorly into the acetabulum through abduction of the hip, which is possible because of stretching of the adductor muscles by the weight of the lower extremity. When the reduction is obtained by forced abduction there is a greater danger of avascular necrosis of the femoral head.

  10. Structural Mechanics and Dynamics Branch

    Science.gov (United States)

    Stefko, George

    2003-01-01

    The 2002 annual report of the Structural Mechanics and Dynamics Branch reflects the majority of the work performed by the branch staff during the 2002 calendar year. Its purpose is to give a brief review of the branch s technical accomplishments. The Structural Mechanics and Dynamics Branch develops innovative computational tools, benchmark experimental data, and solutions to long-term barrier problems in the areas of propulsion aeroelasticity, active and passive damping, engine vibration control, rotor dynamics, magnetic suspension, structural mechanics, probabilistics, smart structures, engine system dynamics, and engine containment. Furthermore, the branch is developing a compact, nonpolluting, bearingless electric machine with electric power supplied by fuel cells for future "more electric" aircraft. An ultra-high-power-density machine that can generate projected power densities of 50 hp/lb or more, in comparison to conventional electric machines, which generate usually 0.2 hp/lb, is under development for application to electric drives for propulsive fans or propellers. In the future, propulsion and power systems will need to be lighter, to operate at higher temperatures, and to be more reliable in order to achieve higher performance and economic viability. The Structural Mechanics and Dynamics Branch is working to achieve these complex, challenging goals.

  11. Nonlinear Dynamic Phenomena in Mechanics

    CERN Document Server

    Warminski, Jerzy; Cartmell, Matthew P

    2012-01-01

    Nonlinear phenomena should play a crucial role in the design and control of engineering systems and structures as they can drastically change the prevailing dynamical responses. This book covers theoretical and applications-based problems of nonlinear dynamics concerned with both discrete and continuous systems of interest in civil and mechanical engineering. They include pendulum-like systems, slender footbridges, shape memory alloys, sagged elastic cables and non-smooth problems. Pendulums can be used as a dynamic absorber mounted in high buildings, bridges or chimneys. Geometrical nonlinear

  12. Jaw Dislocation

    Science.gov (United States)

    ... This Article Medical Dictionary Also of Interest (Quiz) Biology of the Mouth (Video) Root Canal Additional Content Medical News Jaw Dislocation By David F. Murchison, DDS, MMS, Clinical Professor, Department of Biological Sciences;Clinical Professor, The University ...

  13. Dislocated Shoulder

    Science.gov (United States)

    ... bruising Intense pain Inability to move the joint Shoulder dislocation may also cause numbness, weakness or tingling near the injury, such as in your neck or down your arm. The muscles in your shoulder may spasm from the disruption, ...

  14. Dislocation Multi-junctions and Strain Hardening

    Energy Technology Data Exchange (ETDEWEB)

    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.

  15. Dislocations and vacancies in two-dimensional mixed crystals of spheres and dimers

    KAUST Repository

    Gerbode, Sharon J.

    2010-10-15

    In colloidal crystals of spheres, dislocation motion is unrestricted. On the other hand, recent studies of relaxation in crystals of colloidal dimer particles have demonstrated that the dislocation dynamics in such crystals are reminiscent of glassy systems. The observed glassy dynamics arise as a result of dislocation cages formed by certain dimer orientations. In the current study, we use experiments and simulations to investigate the transition that arises when a pure sphere crystal is doped with an increasing concentration of dimers. Specifically, we focus on both dislocation caging and vacancy motion. Interestingly, we find that any nonzero fraction of dimers introduces finite dislocation cages, suggesting that glassy dynamics are present for any mixed crystal. However, we have also identified a vacancy-mediated uncaging mechanism for releasing dislocations from their cages. This mechanism is dependent on vacancy diffusion, which slows by orders of magnitude as the dimer concentration is increased. We propose that in mixed crystals with low dimer concentrations vacancy diffusion is fast enough to uncage dislocations and delay the onset of glassy dislocation dynamics. © 2010 The American Physical Society.

  16. Formation of disorientations in dislocation structures during plastic deformation

    DEFF Research Database (Denmark)

    Pantleon, W.

    2002-01-01

    Disorientations developing during plastic deformation in dislocation structures are investigated. Based on expected mechanisms for the formation of different types of dislocation boundaries (statistical trapping of dislocations or differently activated slip systems) the formation of the disorient...

  17. Role of quaternary additions on dislocated martensite, retain austenite and mechanical properties of Fe/Cr/C structural steels

    Energy Technology Data Exchange (ETDEWEB)

    Rao, B.V.N.

    1978-02-01

    The influence of quaternary alloy additions of Mn and Ni to Fe/Cr/C steels which have been designed to provide superior mechanical properties has been investigated. Transmission electron microscopy and x-ray analysis revealed increasing amounts of retained austenite with Mn up to 2 w/o and with 5 w/o Ni additions after quenching from 1100/sup 0/C. This is accompanied by a corresponding improvement in toughness properties of the quaternary alloys. In addition, the generally attractive combinations of strength and toughness in these quaternary alloys is attributed to the production of dislocated lath martensite from a homogeneous austenite phase free from undissolved alloy carbides. Grain-refining resulted in a further increase in the amount of retained austenite.

  18. System dynamics for mechanical engineers

    CERN Document Server

    Davies, Matthew

    2015-01-01

    This textbook is ideal for mechanical engineering students preparing to enter the workforce during a time of rapidly accelerating technology, where they will be challenged to join interdisciplinary teams. It explains system dynamics using analogies familiar to the mechanical engineer while introducing new content in an intuitive fashion. The fundamentals provided in this book prepare the mechanical engineer to adapt to continuous technological advances with topics outside traditional mechanical engineering curricula by preparing them to apply basic principles and established approaches to new problems. This book also: ·         Reinforces the connection between the subject matter and engineering reality ·         Includes an instructor pack with the online publication that describes in-class experiments with minimal preparation requirements ·         Provides content dedicated to the modeling of modern interdisciplinary technological subjects, including opto-mechanical systems, high...

  19. Rigid body dynamics of mechanisms

    CERN Document Server

    Hahn, Hubert

    2003-01-01

    The second volume of Rigid Body Dynamics of Mechanisms covers applications via a systematic method for deriving model equations of planar and spatial mechanisms. The necessary theoretical foundations have been laid in the first volume that introduces the theoretical mechanical aspects of mechatronic systems. Here the focus is on the application of the modeling methodology to various examples of rigid-body mechanisms, simple planar ones as well as more challenging spatial problems. A rich variety of joint models, active constraints, plus active and passive force elements is treated. The book is intended for self-study by working engineers and students concerned with the control of mechanical systems, i.e. robotics, mechatronics, vehicles, and machine tools. The examples included are a likely source from which to choose models for university lectures.

  20. Advanced dynamics of mechanical systems

    CERN Document Server

    Cheli, Federico

    2015-01-01

    This book introduces a general approach for schematization of mechanical systems with rigid and deformable bodies. It proposes a systems approach to reproduce the interaction of the mechanical system with different force fields such as those due to the action of fluids or contact forces between bodies, i.e., with forces dependent on the system states, introducing the concepts of the stability of motion. In the first part of the text mechanical systems with one or more degrees of freedom with large motion and subsequently perturbed in the neighborhood of the steady state position are analyzed. Both discrete and continuous systems (modal approach, finite elements) are analyzed. The second part is devoted to the study of mechanical systems subject to force fields, the rotor dynamics, techniques of experimental identification of the parameters, and random excitations. The book will be especially valuable for students of engineering courses in Mechanical Systems, Aerospace, Automation, and Energy but will also b...

  1. Characterization of crystallite size, dislocation characteristics and stacking faults in nanostructured mechanically alloyed Cu–Fe system using an advanced X-ray diffraction analysis method

    Energy Technology Data Exchange (ETDEWEB)

    Soleimanian, V., E-mail: vishtasb@iust.ac.ir [Department of Physics, Faculty of Sciences, Shahrekord University, P.O. Box 115, Shahrekord (Iran, Islamic Republic of); Nanotechnology Research Center, Shahrekord University, 8818634141 Shahrekord (Iran, Islamic Republic of); Mojtahedi, M.; Goodarzi, M.; Aboutalebi, M.R. [School of Materials Science and Engineering, Iran University of Science and Technology, Farjam Street, Narmak Tehran 16846-13114 (Iran, Islamic Republic of)

    2014-03-25

    Highlights: • Various microstructural features of mechanically alloyed Cu–Fe are investigated simultaneously. • The crystallite size and size distribution are calculated via refinement of XRD profiles. • Using the eCMWP method, characteristics of dislocations are studied as a function of milling time and composition. • The probability of stacking faults are calculated. -- Abstract: Developments in the synthesis of nanostructured materials have expanded the need for appropriate characterization methods. The aim of this work is to apply new X-ray diffraction analysis methods for simultaneous investigation of various microstructural characteristics. For this purpose, the structure of mechanically alloyed Cu–Fe system with three compositions of 30 wt%, 50% and 70% of iron was studied. By applying the modified Williamson-Hall method, the type of dislocations in the FCC phase is distinguished. Afterwards by modification of previous XRD analysis methods, the proportion of edge/screw dislocations was characterized. Moreover, the outer cut-off radius, the density and energy of dislocations were calculated as a function of the composition and the milling time. On the other hand, using the extended convolutional multiple whole profile fitting procedure, the variations in the crystallite size and size distribution of FCC and BCC phases were studied. Finally, the stacking fault probability was calculated in different milled samples. It is revealed that smaller steady state crystallite size of samples with higher Fe content, is relevant to reduction of the outer cut-off radius of dislocation. On the other hand, the density of dislocations and stacking faults increased continuously up to 96 h of milling.

  2. Dynamics of micromechanisms controlling the mechanical behaviour of industrial single crystal superalloys

    Indian Academy of Sciences (India)

    M Benyoucef; A Coujou; F Pettinari-Sturmel; S Raujol; B Boubker; N Clément

    2003-02-01

    When deforming bulk material, micromechanisms involving moving defects result in mechanical characteristics observed at a macroscopic scale. In situ straining of microsamples in a Transmission Electron Microscope. provides the unique advantage of observing the dislocation dynamics involved in such microdeformation processes under the combined effects of stress and temperature. Here the efficiency of this technique is illustrated by describing the different obstacles controlling the movement of dislocations in a two-phase industrial single crystal superalloy. At 25° and 850°C, different core structures of the moving dislocations as well as several ways of crossing obstacles are described, which concern the movement of dislocations in channels, at $\\gamma /\\gamma' $ interfaces and while shearing $\\gamma' $ precipitates. From these observations, a quantitative analysis is developed leading to the evaluation of the critical propagation stresses involved in the channels of the matrix and when crossing the interfaces. This allows to discuss the various sites of resistance opposed to the dislocation movements and controlling the macroscopic deformation.

  3. Dislocation dynamics in Al-Mg-Zn alloys : A nuclear magnetic resonance and transmission electron microscopic study

    NARCIS (Netherlands)

    Hosson, J.Th.M. De; Kanert, O.; Schlagowski, U.; Boom, G.

    1988-01-01

    Pulsed nuclear magnetic resonance (NMR) proved to be a complementary new technique for the study of moving dislocations in Al-Mg-Zn alloys. The NMR technique, in combination with transmission electron microscopy (TEM), has been applied to study dislocation motion in Al-0.6 at. % Mg-1 at. % Zn and

  4. The effect of isotope on the dynamic behavior of <1 0 0> vacancy-type dislocation loop in deuterium-implanted Fe

    Energy Technology Data Exchange (ETDEWEB)

    Liu, P.P.; Zhu, Y.M.; Zhao, M.Z.; Jiang, S.N. [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Liu, C.X.; Wang, Y.M. [Faculty of Engineering, Hokkaido University, Sapporo 060-8628 (Japan); Wan, F.R. [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China); Ohnuki, S. [Faculty of Engineering, Hokkaido University, Sapporo 060-8628 (Japan); Zhan, Q., E-mail: qzhan@mater.ustb.edu.cn [School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083 (China)

    2015-06-15

    Highlights: • Vacancy-loop formed in D-implanted Fe after anneal at high temperature. • V-loop formation temperature in D-implanted Fe is higher than that in H-implanted one. • Dynamic behavior of <1 0 0> vacancy-loop in D-implanted Fe has been in situ observed. • Growth and shrink rate of both type loops increase with increase of the damage rate. • The origin for the behavior of both type loops was discussed in detail. - Abstract: The dynamic behavior of individual loops of the both interstitial and vacancy types is believed to be strongly connected to the degradation processes that affect radiation-resistant materials used in nuclear-fission and fusion devices. Meanwhile, the isotopic effect of hydrogen on irradiation damage has attracted wide interest. In situ transmission electron microscopy investigation of the dynamic behavior of dislocation loops under high-energy electron irradiation was carried out in pure Fe with deuterium implantation at room temperature and aged at different temperatures. Shrinkage of dislocation loop was observed in implanted sample annealed at 753 K, except the popular growth of dislocation loop. The loop shrinkage was also observed in H implanted sample annealed at relatively lower temperature. The shrinking loop is identified to be <1 0 0> vacancy-type loop by acknowledged “inside–outside” method. Origin for the dynamic behavior of both type loops and the isotopic effect on the behavior were discussed.

  5. A continuum theory of edge dislocations

    Science.gov (United States)

    Berdichevsky, V. L.

    2017-09-01

    dislocation phase space is strikingly simple. Dislocation phase space is split in a family of subspaces corresponding to constant values of dislocation polarizations; in each equipolarization subspace there are many local minima of energy; for zero external stresses the system is stuck in a local minimum of energy; for non-zero slowly changing external stress, dislocation polarization evolves, while the system moves over local energy minima of equipolarization subspaces. Such a simple picture of dislocation dynamics is due to the presence of two time scales, slow evolution of dislocation polarization and fast motion of the system over local minima of energy. The existence of two time scales is justified for a neutral system of edge dislocations.

  6. Statistical Mechanics of Dynamical Systems

    Science.gov (United States)

    Mori, H.; Hata, H.; Horita, T.; Kobayashi, T.

    A statistical-mechanical formalism of chaos based on the geometry of invariant sets in phase space is discussed to show that chaotic dynamical systems can be treated by a formalism analogous to that of thermodynamic systems if one takes a relevant coarse-grained quantity, but their statistical laws are quite different from those of thermodynamic systems. This is a generalization of statistical mechanics for dealing with dissipative and hamiltonian (i.e., conservative) dynamical systems of a few degrees of freedom. Thus the sum of the local expansion rate of nearby orbits along relevant orbit over a long but finite time has been introduced in order to describe and characterize (1) a drastic change of the structure of a chaotic attractor at a bifurcation and anomalous phenomena associated, (2) a critical scaling of chaos in the neighborhood of a critical point for the bifurcation to a nonexotic state, and a self-similar temporal structure of a critical orbit on the critical 2^∞ attractor an the critical golden tori without mixing, (3) the critical KAM torus, diffusion and repeated sticking of a chaotic orbit to a critical torus in hamiltonian systems. Here a q-phase transition, analogous to the ferromagnetic phase transition, plays an important role. They are illustrated numerically and theoretically by treating the driven damped pendulum, the driven Duffing equation, the Henon map, and the dissipative and conservative standard maps. This description of chaos breaks the time-reversal symmetry of hamiltonian dynamical laws analogously to statistical mechanics of irreversible processes. The broken time-reversal symmetry is brought about by orbital instability of chaos.

  7. THERMODYNAMIC VARIATIONAL APPROACH FOR CLIMB OF AN EDGE DISLOCATION

    Institute of Scientific and Technical Information of China (English)

    Yunxin Gao; A.C.F. Cocks

    2009-01-01

    A general thermodynamic variational approach is applied to study the force on an edge dislocation, which drives the dislocation to climb. Our attention is focused on the physical mechanism responsible for dislocation climb. A dislocation in a material element climbs as a result of vacancies diffusing into or out from the dislocation core, with the dislocation acting as a source or a sink for vacancy diffusion in the material element. The basic governing equations for dislocation climb and the climb forces on the dislocation are obtained naturally as a result of the present thermodynamic variational approach.

  8. Hybrid dislocated control and general hybrid projective dislocated synchronization for the modified Lue chaotic system

    Energy Technology Data Exchange (ETDEWEB)

    Xu Yuhua [College of Information Science and Technology, Donghua University, Shanghai 201620 (China) and Department of Maths, Yunyang Teacher' s College, Hubei 442000 (China)], E-mail: yuhuaxu2004@163.com; Zhou Wuneng [College of Information Science and Technology, Donghua University, Shanghai 201620 (China)], E-mail: wnzhou@163.com; Fang Jianan [College of Information Science and Technology, Donghua University, Shanghai 201620 (China)

    2009-11-15

    This paper introduces a modified Lue chaotic system, and some basic dynamical properties are studied. Based on these properties, we present hybrid dislocated control method for stabilizing chaos to unstable equilibrium and limit cycle. In addition, based on the Lyapunov stability theorem, general hybrid projective dislocated synchronization (GHPDS) is proposed, which includes complete dislocated synchronization, dislocated anti-synchronization and projective dislocated synchronization as its special item. The drive and response systems discussed in this paper can be strictly different dynamical systems (including different dimensional systems). As examples, the modified Lue chaotic system, Chen chaotic system and hyperchaotic Chen system are discussed. Numerical simulations are given to show the effectiveness of these methods.

  9. The Role of Misfit Dislocations in Strength Enhancement of Cu/Ni Microlaminates

    Institute of Scientific and Technical Information of China (English)

    CHENG Dong; YAN Li; YAN Zhi-jun

    2004-01-01

    This paper simulated the nanoindentations of Cu/Ni thin films with 2D Molecular Dynamics Simulations (MDS) and examined the effects of the misfit dislocations on the mechanical properties of the microlaminates. The misfit dislocation network plays an important role in strength enhancement of Cu/Ni microlaminates because of its resistance to glide dislocations. But the strengthening also relies on the wavelength, which is defined as the thickness of adjacent two layers in microlaminates. When the wavelength is less than the critical value λc, the stress concentration caused by the movement of misfit dislocations will make Cu/Ni microlaminates weaken. Also, the critical wavelength should be more than the depth at which the dislocation nucleates in the homogeneous layer.

  10. STATISTICAL MECHANICS MODELING OF MESOSCALE DEFORMATION IN METALS

    Energy Technology Data Exchange (ETDEWEB)

    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

  11. Convoluted dislocation loops induced by helium irradiation in reduced-activation martensitic steel and their impact on mechanical properties

    Energy Technology Data Exchange (ETDEWEB)

    Luo, Fengfeng [Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, Hubei Nuclear Solid Physics Key Laboratory, School of Physics and Technology, Wuhan University, Wuhan 430072 (China); Yao, Z. [Department of Mechanical and Materials Engineering, Queen' s University, Kingston, ON, Canada K7L 3N6 (Canada); Guo, Liping, E-mail: guolp@whu.edu.cn [Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, Hubei Nuclear Solid Physics Key Laboratory, School of Physics and Technology, Wuhan University, Wuhan 430072 (China); Suo, Jinping [State Key Laboratory of Mould Technology, Institute of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074 (China); Wen, Yongming [Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education, Hubei Nuclear Solid Physics Key Laboratory, School of Physics and Technology, Wuhan University, Wuhan 430072 (China)

    2014-06-01

    Helium irradiation induced dislocation loops in reduced-activation martensitic steels were investigated using transmission electron microscopy. The specimens were irradiated with 100 keV helium ions to 0.8 dpa at 350 °C. Unexpectedly, very large dislocation loops were found, significantly larger than that induced by other types of irradiations under the same dose. Moreover, the large loops were convoluted and formed interesting flower-like shape. The large loops were determined as interstitial type. Loops with the Burgers vectors of b=〈100〉 were only observed. Furthermore, irradiation induced hardening caused by these large loops was observed using the nano-indentation technique.

  12. Mechanical properties and crack growth behavior of polycrystalline copper using molecular dynamics simulation

    Science.gov (United States)

    Qiu, Ren-Zheng; Li, Chi-Chen; Fang, Te-Hua

    2017-08-01

    This study investigated the mechanical properties and crack propagation behavior of polycrystalline copper using a molecular dynamics simulation. The effects of temperature, grain size, and crack length were evaluated in terms of atomic trajectories, slip vectors, common neighbor analysis, the material’s stress-strain diagram and Young’s modulus. The simulation results show that the grain boundary of the material is more easily damaged at high temperatures and that grain boundaries will combine at the crack tip. From the stress-strain diagram, it was observed that the maximum stress increased as the temperature decreased. In contrast, the maximum stress was reduced by increasing the temperature. With regard to the effect of the grain size, when the grain size was too small, the structure of the sample deformed due to the effect of atomic interactions, which caused the grain boundary structure to be disordered in general. However, when the grain size was larger, dislocations appeared and began to move from the tip of the crack, which led to a new dislocation phenomenon. With regards to the effect of the crack length, the tip of the crack did not affect the sample’s material when the crack length was less than 5 nm. However, when the crack length was above 7.5 nm, the grain boundary was damaged, and twinning structures and dislocations appeared on both sides of the crack tip. This is because the tip of the crack was blunt at first before sharpening due to the dislocation effect.

  13. Dynamical Symmetries in Classical Mechanics

    Science.gov (United States)

    Boozer, A. D.

    2012-01-01

    We show how symmetries of a classical dynamical system can be described in terms of operators that act on the state space for the system. We illustrate our results by considering a number of possible symmetries that a classical dynamical system might have, and for each symmetry we give examples of dynamical systems that do and do not possess that…

  14. Prediction of intragranular strains in metallic polycrystals with a two-level homogenisation approach: Influence of dislocation microstructure on the mechanical behaviour

    Energy Technology Data Exchange (ETDEWEB)

    Gloaguen, D. [GeM, Institut de Recherche en Genie Civil et Mecanique, Universite de Nantes, Ecole Centrale de Nantes, CNRS UMR 6183, 37 Boulevard de l' Universite, BP 406, 44 602 Saint-Nazaire (France); Francois, M. [Laboratoire des Systemes Mecaniques et d' Ingenierie Simultanee (LASMIS FRE CNRS 2719), Universite de Technologie de Troyes, 12 Rue Marie Curie, BP 2060, 10010 Troyes cedex (France)

    2006-06-15

    A two-level homogenisation approach is applied to the micro-mechanical modelling of the elasto-plasticity of polycrystalline materials during various strain-path changes. The model is tested by simulating the development of intragranular strains during different complex loads. Mechanical tests measurements are used as a reference in order to validate the model. The anisotropy of plastic deformation in relation to the evolution of the dislocation structure is analysed. The results demonstrate the relevance of this approach for FCC polycrystals. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  15. Theory of interacting dislocations on cylinders.

    Science.gov (United States)

    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.

  16. X-ray diffraction analysis and metal physics modeling of static strain aging and thermal dislocation recovery in the mechanically affected zone of surface finished hardened steel

    Energy Technology Data Exchange (ETDEWEB)

    Gegner, Juergen [SKF GmbH, Dept. of Material Physics, Schweinfurt (Germany)

    2009-07-01

    After heat treatment, finish machining of the hardened steel represents the last manufacturing step of machine elements. The practically most important operation of grinding is applied to achieve edge zone compressive residual stresses, best surface quality and dimensional accuracy. Metal removal involves high plastic deformation work. Glide and intersection processes raise the density and produce lower energy substructures of dislocations. The temperature and time behavior of post-machining thermal treatment is analyzed on ground and honed martensitic SAE 52100 rolling bearing steel. Microstructure stabilization is reflected in a large XRD line width decrease on the surface. The kinetics is modeled by rate-controlling carbide dissolution as the carbon source for Cottrell-type segregation at dislocations. This static strain aging is verified by the formation of a slight white etching surface layer. The metal physics model is extended to also consider superimposed thermal dislocation recovery. Both effects are separable. In rolling contact fatigue tests under mixed friction running conditions, air reheating of the samples below the tempering temperature, which avoids hardness loss, leads to a significant lifetime increase. Thermal post-treatment after cold working results in similar changes of the XRD line width in the larger mechanically affected edge zone.

  17. Dislocation mechanisms and 3D twin architectures generate exceptional strength-ductility-toughness combination in CrCoNi medium-entropy alloy

    Science.gov (United States)

    Zhang, Zijiao; Sheng, Hongwei; Wang, Zhangjie; Gludovatz, Bernd; Zhang, Ze; George, Easo P.; Yu, Qian; Mao, Scott X.; Ritchie, Robert O.

    2017-02-01

    Combinations of high strength and ductility are hard to attain in metals. Exceptions include materials exhibiting twinning-induced plasticity. To understand how the strength-ductility trade-off can be defeated, we apply in situ, and aberration-corrected scanning, transmission electron microscopy to examine deformation mechanisms in the medium-entropy alloy CrCoNi that exhibits one of the highest combinations of strength, ductility and toughness on record. Ab initio modelling suggests that it has negative stacking-fault energy at 0K and high propensity for twinning. With deformation we find that a three-dimensional (3D) hierarchical twin network forms from the activation of three twinning systems. This serves a dual function: conventional twin-boundary (TB) strengthening from blockage of dislocations impinging on TBs, coupled with the 3D twin network which offers pathways for dislocation glide along, and cross-slip between, intersecting TB-matrix interfaces. The stable twin architecture is not disrupted by interfacial dislocation glide, serving as a continuous source of strength, ductility and toughness.

  18. Stress Field of Straight Edge Dislocation in Magnetic Field

    Institute of Scientific and Technical Information of China (English)

    LIU Zhao-long; HU Hai-yun; FAN Tian-you

    2007-01-01

    To study the changes in mechanical properties of materials within magnetic fields and the motion of dislocations,stress fields of dislocation in magnetic field need to be calculated.The straight edge dislocation is of basic importance in various defects.The stress field of straight edge dislocation in an external static magnetic field is determined by the theory of elasticity and electrodynamics according to the Volterra dislocation model for continuous media.This reduces to the known stress field when the magnet field is zero.The results can be used for further study on the strain energy of dislocations and the interactions between dislocations in magnetic fields.

  19. MOVING SCREW DISLOCATION IN CUBIC QUASICRYSTAL

    Institute of Scientific and Technical Information of China (English)

    ZHOU Wang-min; SONG Yu-hai

    2005-01-01

    The elasticity theory of the dislocation of cubic quasicrystals is developed.The governing equations of anti-plane elasticity dynamics problem of the quasicrystals were reduced to a solution of wave equations by introducing displacement functions,and the analytical expressions of displacements, stresses and energies induced by a moving screw dislocation in the cubic quasicrystalline and the velocity limit of the dislocation were obtained. These provide important information for studying the plastic deformation of the new solid material.

  20. A Numeric Study on Chaotic Dislocation Emission

    Institute of Scientific and Technical Information of China (English)

    HonglaiTan; WeiYang

    1996-01-01

    Crack tip atom-string model is devised to study non-linear features of dislocation emission processes under mode II loads.Dynamic analysis shows that the atom motion at the crack tip changes from periodic to chaotic as the stress intensity factor increases.Study on the dislocation emission band reveals the phenomenon of cloud-like drifting of the dislocation core ahead of the crack tip.

  1. A visualization of threading dislocations formation and dynamics in mosaic growth of GaN-based light emitting diode epitaxial layers on (0001) sapphire

    Science.gov (United States)

    Ravadgar, P.; Horng, R. H.; Ou, S. L.

    2012-12-01

    A clear visualization of the origin and characteristics of threading dislocations (TDs) of GaN-based light emitting diode epitaxial layers on (0001) sapphire substrates have been carried out. Special experimental set up and chemical etchant along with field emission scanning electron microscopy are employed to study the dynamics of GaN TDs at different growth stages. Cross-sectional transmission electron microscopy analysis visualized the formation of edge TDs is arising from extension of coalescences at boundaries of different tilting-twining nucleation grains "mosaic growth." Etch pits as representatives of edge TDs are in agreement with previous theoretical models and analyses of TDs core position and characteristics.

  2. Based on Mechanical Transmission the Meshing of Dislocating Fault Analysis and Prevention%基于机械式变速器脱挡故障分析与预防

    Institute of Scientific and Technical Information of China (English)

    马利东

    2014-01-01

    The meshing of dislocating is one of the most common fault of the auto transmission, in this article one analyze the meshing of dislocating fault, proposes effective preventive measures, and improve mechanical transmission and reliable performance from the mechanical transmission’s the meshing of dislocating fault phenomena and two aspects of the vehicle and the transmission of the meshing of dislocating fault analysis.%脱挡是汽车变速器的常见故障之一,笔者从机械式变速器脱挡故障现象入手,从整车和变速器两方面对脱挡故障展开分析,并提出了预防解决措施,提升机械式变速器可靠性能。

  3. The Role of Twinning Deformation on the Hardening Response of Polycrystalline Magnesium from Discrete Dislocation Dynamics Simulations

    Science.gov (United States)

    2015-01-01

    to the basal plane leading to predominant basal slip, as shown in Fig. 4(a), since the Schmid factor on these planes is maxi - mum. The low yield...slip is the hardest slip mode. It is also observed from Fig. 3 that regardless of the loading directions, all single crystals results exhibit weak ...In Section 3.1, the dislocation forest hardening effect for single crystals was observed to be weak (see Fig. 3). Furthermore, GBs do produce

  4. Single crystal plasticity by modeling dislocation density rate behavior

    Energy Technology Data Exchange (ETDEWEB)

    Hansen, Benjamin L [Los Alamos National Laboratory; Bronkhorst, Curt [Los Alamos National Laboratory; Beyerlein, Irene [Los Alamos National Laboratory; Cerreta, E. K. [Los Alamos National Laboratory; Dennis-Koller, Darcie [Los Alamos National Laboratory

    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.

  5. A review of higher order strain gradient theories of plasticity: Origins, thermodynamics and connections with dislocation mechanics

    Indian Academy of Sciences (India)

    Suman Guha; Sandeep Sangal; Sumit Basu

    2015-06-01

    In this paper we review developments in higher order strain gradient theories. Several variants of these theories have been proposed in order to explain the effects of size on plastic properties that are manifest in several experiments with micron sized metallic structures. It is generally appreciated that the size effect arises from the storage of geometrically necessary dislocations (GNDs) over and above the statistically stored dislocations (SSDs) required for homogeneous deformations. We review developments that show that the GNDs result from the non-homogeneous nature of the deformation field. Though the connection between GNDs and strain gradients are established in the framework of single crystal plasticity, generalisations to polycrystal plasticity has been made. Strain gradient plasticity inherently involves an intrinsic length scale. In our review, we show, through a few illustrative problems, that conventional plasticity solutions can always be reduced to a scale independent form. The same problems are solved with a simple higher order strain gradient formulation to capture the experimentally observed size effects. However, higher order theories need to be thermodynamically consistent. It has recently been shown that only a few of the existing theories pass this test. We review a few that do. Higher order theories require higher order boundary conditions that enable us to model effects of dislocation storage at impermeable boundaries. But these additional boundary conditions also lead to unique conceptual issues that are not encountered in conventional theories. We review attempts at resolving these issues pertaining to higher order boundary conditions. Finally, we review the future of such theories, their relevance and experimental validation.

  6. Dynamics of mechanical systems with variable mass

    CERN Document Server

    Belyaev, Alexander

    2014-01-01

    The book presents up-to-date and unifying formulations for treating dynamics of different types of mechanical systems with variable mass. The starting point is overview of the continuum mechanics relations of balance and jump for open systems from which extended Lagrange and Hamiltonian formulations are derived. Corresponding approaches are stated at the level of analytical mechanics with emphasis on systems with a position-dependent mass and at the level of structural mechanics. Special emphasis is laid upon axially moving structures like belts and chains, and on pipes with an axial flow of fluid. Constitutive relations in the dynamics of systems with variable mass are studied with particular reference to modeling of multi-component mixtures. The dynamics of machines with a variable mass are treated in detail and conservation laws and the stability of motion will be analyzed. Novel finite element formulations for open systems in coupled fluid and structural dynamics are presented.

  7. Epidemiology of Isolated Acromioclavicular Joint Dislocation

    Directory of Open Access Journals (Sweden)

    Claudio Chillemi

    2013-01-01

    Full Text Available Background. Acromioclavicular (AC joint dislocation is a common shoulder problem. However, information about the basic epidemiological features of this condition is scarce. The aim of this study is to analyze the epidemiology of isolated AC dislocation in an urban population. Materials and Methods. A retrospective database search was performed to identify all patients with an AC dislocation over a 5-year period. Gender, age, affected side and traumatic mechanism were taken into account. X-rays were reviewed by two of the authors and dislocations were classified according to the Rockwood’s criteria. Results. A total of 108 patients, with a mean age of 37.5 years were diagnosed with AC dislocation. 105 (97.2% had an isolated AC dislocation, and 3 (2.8% were associated with a clavicle fracture. The estimated incidence was 1.8 per 10000 inhabitants per year and the male-female ratio was 8.5 : 1. 50.5% of all dislocations occurred in individuals between the ages of 20 and 39 years. The most common traumatic mechanism was sport injury and the most common type of dislocation was Rockwood type III. Conclusions. Age between 20 and 39 years and male sex represent significant demographic risk factors for AC dislocation.

  8. Mechanical formalism for tissue dynamics

    CERN Document Server

    Tlili, Sham; Graner, Francois; Marcq, Philippe; MOLINO, François; Saramito, Pierre

    2013-01-01

    The understanding of morphogenesis in living organisms has been renewed by tremendous progress in experimental techniques that provide access to cell-scale, quantitative information both on the shapes of cells within tissues and on the genes being expressed. This information suggests that our understanding of the respective contributions of gene expression and mechanics, and of their crucial entanglement, will soon leap forward. Biomechanics increasingly benefits from models, which assist the design and interpretation of experiments, point out the main ingredients and assumptions, and can ultimately lead to predictions. The newly accessible local information thus urges for a reflection on how to select suitable classes of mechanical models. We review both mechanical ingredients suggested by the current knowledge of tissue behaviour, and modelling methods that can help generate a constitutive equation. We also recall the mathematical framework developped for continuum materials and how to transform a constitut...

  9. Nucleation mechanism of a nickel-base superalloy during dynamic recrystallization

    Institute of Scientific and Technical Information of China (English)

    Shuai WANG; Lei WANG; Yang LIU; Guohua XU; Beijiang ZHANG; Guangpu ZHAO

    2011-01-01

    Hot compression test was carried out at 1000 ℃ to investigate the dynamic recrystallization nucleation mechanism of a nickel-base superalloy.It was found that the bulging of original grain boundaries was inhibited by carbides and deformation twins at the boundaries.Recrystallized nuclei evolved from the subgrains of dislocation reconfiguration along original grain boundaries,and the growth of the potential nuclei was carried out by the coalescence of subgrains.The necklace structure of recrystallized grains along original grain boundaries was attributed to the strain gradient from grain boundary to grain interior.

  10. Hydrogen-vacancy-dislocation interactions in α-Fe

    Science.gov (United States)

    Tehranchi, A.; Zhang, X.; Lu, G.; Curtin, W. A.

    2017-02-01

    Atomistic simulations of the interactions between dislocations, hydrogen atoms, and vacancies are studied to assess the viability of a recently proposed mechanism for the formation of nanoscale voids in Fe-based steels in the presence of hydrogen. Quantum-mechanics/molecular-mechanics method calculations confirm molecular statics simulations based on embedded atom method (EAM) potential showing that individual vacancies on the compressive side of an edge dislocation can be transported with the dislocation as it glides. Molecular dynamics simulations based on EAM potential then show, however, that vacancy clusters in the glide plane of an approaching dislocation are annihilated or reduced in size by the creation of a double-jog/climb process that is driven by the huge reduction in energy accompanying vacancy annihilation. The effectiveness of annihilation/reduction processes is not reduced by the presence of hydrogen in the vacancy clusters because typical V-H cluster binding energies are much lower than the vacancy formation energy, except at very high hydrogen content in the cluster. Analysis of a range of configurations indicates that hydrogen plays no special role in stabilizing nanovoids against jog formation processes that shrink voids. Experimental observations of nanovoids on the fracture surfaces of steels must be due to as-yet undetermined processes.

  11. Accumulation of dislocation loops in the α phase of Zr Excel alloy under heavy ion irradiation

    Science.gov (United States)

    Yu, Hongbing; Yao, Zhongwen; Idrees, Yasir; Zhang, He K.; Kirk, Mark A.; Daymond, Mark R.

    2017-08-01

    In-situ heavy ion irradiations were performed on the high Sn content Zr alloy 'Excel', measuring type dislocation loop accumulation up to irradiation damage doses of 10 dpa at a range of temperatures. The high content of Sn, which diffuses slowly, and the thin foil geometry of the sample provide a unique opportunity to study an extreme case where displacement cascades dominate the loop formation and evolution. The dynamic observation of dislocation loop evolution under irradiation at 200 °C reveals that type dislocation loops can form at very low dose (0.0025 dpa). The size of the dislocation loops increases slightly with irradiation damage dose. The mechanism controlling loop growth in this study is different from that in neutron irradiation; in this study, larger dislocation loops can condense directly from the interaction of displacement cascades and the high concentration of point defects in the matrix. The size of the dislocation loop is dependent on the point defect concentration in the matrix. A negative correlation between the irradiation temperature and the dislocation loop size was observed. A comparison between cascade dominated loop evolution (this study), diffusion dominated loop evolution (electron irradiation) and neutron irradiation suggests that heavy ion irradiation alone may not be enough to accurately reproduce neutron irradiation induced loop structures. An alternative method is proposed in this paper. The effects of Sn on the displacement cascades, defect yield, and the diffusion behavior of point defects are established.

  12. Multiscale Theory of Dislocation Climb.

    Science.gov (United States)

    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.

  13. Mechanisms of pit formation at strained crystalline Si(111)/Si3N4(0001) interfaces: Molecular-dynamics simulations

    Science.gov (United States)

    Bachlechner, Martina E.; Srivastava, Deepak; Owens, Eli T.; Schiffbauer, Jarrod; Anderson, Jonas T.; Burky, Melissa R.; Ducatman, Samuel C.; Gripper, Adam M.; Guffey, Eric J.; Ramos, Fernando Serrano

    2006-08-01

    Molecular-dynamics simulations of the crystalline silicon-silicon nitride interfaces are performed to investigate the mechanical failure mechanisms at the interfaces under external strain. At 8% applied tensile strain, parallel to the interface, regular crack initiation and propagation in silicon nitride and dislocation emission and propagation in silicon are observed. At larger 16% strain, however, the formation of a pit similar to that in experiments with lattice-mismatched systems is observed. The simulation results suggest the primary mechanism of pit formation is interaction of a local compressional pinch of the film at the interface with the close proximity to the arrival of a dislocation at the interface in the highly strained silicon.

  14. Non-singular dislocation fields

    Energy Technology Data Exchange (ETDEWEB)

    Aifantis, Elias C, E-mail: mom@mom.gen.auth.gr [Laboratory of Mechanics and Materials, Faculty of Engineering, Aristotle University of Thessaloniki, GR-54124, Thessaloniki (Greece); Center for Mechanics of Materials, Michigan Technological University, Houghton MI 49931 (United States)

    2009-07-15

    Non-singular solutions for dislocation and disclination fields have recently been obtained by the author and his co-workers by using a robust model of gradient elasticity theory. These solutions, whose form is simple and easy to implement, are obtained by reducing the gradient elasticity problem to a corresponding linear elasticity boundary value problem through the solutions of an inhomogeneous Helmholtz equation where the source term is the classical singular solution. The Laplacian in the Helmholtz equation, involving the extra gradient coefficient, produces a new term in the gradient solution which asymptotically approaches the negative of the classical elasticity solution on the dislocation line. Thus, the singularity is eliminated and an arbitrary estimate of the dislocation core size introduced in classical theory, is not required. These predictions are tested against atomistic calculations and their implications to various dislocation related configurations are discussed. Due to the simple and elegant form of these solutions, it is hoped that they will be useful in discrete dislocation dynamics simulations.

  15. Predicting High Temperature Dislocation Physics in HCP Crystal Structures

    Energy Technology Data Exchange (ETDEWEB)

    Hunter, Abigail [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Carpenter, John S. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Martinez Saez, Enrique [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-05-09

    This report applies models and experiments to answer key questions about the way materials deform; specifics regarding phase field dislocations dynamics; as well as high temperature rolling experiments.

  16. Dynamics of crank-piston mechanisms

    CERN Document Server

    Davitashvili, Nodar

    2016-01-01

    This monograph focuses on the dynamical research work on crank-piston mechanisms considering basic and additional motions. In order to have full dynamical analyses of piston machines and their mechanisms, the book studies the crank-piston mechanisms with clearances in kinematic pairs. The tasks are carried out by focusing on friction, wear and impacts in mechanisms, as well as cracks formation in links and elasticity of details, with distributed and concentrated masses. Then, the reliability and durability of the mechanisms of piston machines is applied on oil and gas transportation. The monograph is meant for design specialists. It is also useful for specialists-manufacturers and designers of piston machines, scientists and lecturers, doctoral students.

  17. Dynamical time versus system time inquantum mechanics

    Institute of Scientific and Technical Information of China (English)

    Du(s)an Arsenovi(c); Nikola Buri(c); Dragomir Davidovi(c); Slobodan Prvanovi(c)

    2012-01-01

    Properties of an operator representing the dynamical time in the extended parameterization invariant formulation of quantum mechanics are studied.It is shown that this time operator is given by a positive operator measure analogously to the quantities that are known to represent various measurable time operators.The relation between the dynamical time of the extended formulation and the best known example of the system time operator,i.e.,for the free one-dimensional particle,is obtained.

  18. Dislocation-mediated growth of bacterial cell walls

    CERN Document Server

    Amir, Ariel

    2012-01-01

    Recent experiments have illuminated a remarkable growth mechanism of rod-shaped bacteria: proteins associated with cell wall extension move at constant velocity in circles oriented approximately along the cell circumference (Garner et al., Science (2011), Dominguez-Escobar et al. Science (2011), van Teeffelen et al. PNAS (2011). We view these as dislocations in the partially ordered peptidoglycan structure, activated by glycan strand extension machinery, and study theoretically the dynamics of these interacting defects on the surface of a cylinder. Generation and motion of these interacting defects lead to surprising effects arising from the cylindrical geometry, with important implications for growth. We also discuss how long range elastic interactions and turgor pressure affect the dynamics of the fraction of actively moving dislocations in the bacterial cell wall.

  19. 'Inverse' temporomandibular joint dislocation.

    Science.gov (United States)

    Alemán Navas, R M; Martínez Mendoza, M G

    2011-08-01

    Temporomandibular joint (TMJ) dislocation can be classified into four groups (anterior, posterior, lateral, and superior) depending on the direction of displacement and the location of the condylar head. All the groups are rare except for anterior dislocation. 'Inverse' TMJ dislocation is a bilateral anterior and superior dislocation with impaction of the mandible over the maxilla; to the authors' knowledge only two cases have previously been reported in the literature. Inverse TMJ dislocation has unique clinical and radiographic findings, which are described for this case. Copyright © 2011 International Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.

  20. A template-dependent dislocation mechanism potentiates K65R reverse transcriptase mutation development in subtype C variants of HIV-1.

    Directory of Open Access Journals (Sweden)

    Dimitrios Coutsinos

    Full Text Available Numerous studies have suggested that the K65R reverse transcriptase (RT mutation develops more readily in subtype C than subtype B HIV-1. We recently showed that this discrepancy lies partly in the subtype C template coding sequence that predisposes RT to pause at the site of K65R mutagenesis. However, the mechanism underlying this observation and the elevated rates of K65R development remained unknown. Here, we report that DNA synthesis performed with subtype C templates consistently produced more K65R-containing transcripts than subtype B templates, regardless of the subtype-origin of the RT enzymes employed. These findings confirm that the mechanism involved is template-specific and RT-independent. In addition, a pattern of DNA synthesis characteristic of site-specific primer/template slippage and dislocation was only observed with the subtype C sequence. Analysis of RNA secondary structure suggested that the latter was unlikely to impact on K65R development between subtypes and that Streisinger strand slippage during DNA synthesis at the homopolymeric nucleotide stretch of the subtype C K65 region might occur, resulting in misalignment of the primer and template. Consequently, slippage would lead to a deletion of the middle adenine of codon K65 and the production of a -1 frameshift mutation, which upon dislocation and realignment of the primer and template, would lead to development of the K65R mutation. These findings provide additional mechanistic evidence for the facilitated development of the K65R mutation in subtype C HIV-1.

  1. Novel routes to nanocrystalline mechanical characterization

    Science.gov (United States)

    Cordill, M. J.; Mook, W. M.; Nair, A. K.; Farkas, D.; Gerberich, W. W.

    2007-09-01

    The use of nanoindentation techniques to measure nanoscale mechanical behavior is a new path of interest to researchers today. Load drops and displacement excursions can be utilized to measure activation volumes for dislocation events in single crystals, thin films, and nanoposts. Through the introduction of a new length-scale parameter, the dislocation wall spacing, a mechanism describing staircase yielding, is presented. The dislocation wall spacing can also be used to estimate activation volumes. Molecular dynamics simulations of nickel film indentation have been used to validate the origin of staircase yielding and also show consistent dislocation wall spacings. Additionally, stress relaxation experiments have been used to estimate activation volumes.

  2. Mechanics and dynamics of reconstituted cytoskeletal systems.

    Science.gov (United States)

    Jensen, Mikkel H; Morris, Eliza J; Weitz, David A

    2015-11-01

    The intracellular cytoskeleton is an active dynamic network of filaments and associated binding proteins that control key cellular properties, such as cell shape and mechanics. Due to the inherent complexity of the cell, reconstituted model systems have been successfully employed to gain an understanding of the fundamental physics governing cytoskeletal processes. Here, we review recent advances and key aspects of these reconstituted systems. We focus on the importance of assembly kinetics and dynamic arrest in determining network mechanics, and highlight novel emergent behavior occurring through interactions between cytoskeletal components in more complex networks incorporating multiple biopolymers and molecular motors.

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

    Science.gov (United States)

    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. Dislocation Nucleation and Pileup under a Wedge Contact at Nanoscale

    Directory of Open Access Journals (Sweden)

    Y. F. Gao

    2008-01-01

    Full Text Available Indentation responses of crystalline materials have been found to be radically different at micrometer and nanometer scales. The latter is usually thought to be controlled by the nucleation of dislocations. To explore this physical process, a dislocation mechanics study is performed to determine the conditions for the nucleation of a finite number of dislocations under a two-dimensional wedge indenter, using the Rice-Thomson nucleation criterion. The configurational force on the dislocation consists of the applied force, the image force, and the interaction force between dislocations. Dislocations reach equilibrium positions when the total driving force equals the effective Peierls stress, giving a set of nonlinear equations that can be solved using the Newton-Raphson method. When the apex angle of the wedge indenter increases, the critical contact size for dislocation nucleation increases rapidly, indicating that dislocation multiplication near a blunt wedge tip is extremely difficult. This geometric dependence agrees well with experimental findings.

  5. Mechanical Cushion Design Influence on Cylinder Dynamics

    DEFF Research Database (Denmark)

    Borghi, Massimo; Milani, Massimo; Conrad, Finn

    2005-01-01

    The paper deals with the simulation and the experimental verification of the dynamic behaviour of a linear actuator equipped with different configurations of mechanical cushion. A numerical model, developed and tailored to describe the influence of different modulation of the discharged flow-rate...

  6. Statistics of dislocation pinning at localized obstacles

    Energy Technology Data Exchange (ETDEWEB)

    Dutta, A. [S. N. Bose National Centre for Basic Sciences, Salt Lake, Kolkata 700098 (India); Bhattacharya, M., E-mail: mishreyee@vecc.gov.in; Barat, P. [Variable Energy Cyclotron Centre, 1/AF Bidhannagar, Kolkata 700064 (India)

    2014-10-14

    Pinning of dislocations at nanosized obstacles like precipitates, voids, and bubbles is a crucial mechanism in the context of phenomena like hardening and creep. The interaction between such an obstacle and a dislocation is often studied at fundamental level by means of analytical tools, atomistic simulations, and finite element methods. Nevertheless, the information extracted from such studies cannot be utilized to its maximum extent on account of insufficient information about the underlying statistics of this process comprising a large number of dislocations and obstacles in a system. Here, we propose a new statistical approach, where the statistics of pinning of dislocations by idealized spherical obstacles is explored by taking into account the generalized size-distribution of the obstacles along with the dislocation density within a three-dimensional framework. Starting with a minimal set of material parameters, the framework employs the method of geometrical statistics with a few simple assumptions compatible with the real physical scenario. The application of this approach, in combination with the knowledge of fundamental dislocation-obstacle interactions, has successfully been demonstrated for dislocation pinning at nanovoids in neutron irradiated type 316-stainless steel in regard to the non-conservative motion of dislocations. An interesting phenomenon of transition from rare pinning to multiple pinning regimes with increasing irradiation temperature is revealed.

  7. Extended Dislocations in Plastically Deformed Metallic Nanoparticles

    Directory of Open Access Journals (Sweden)

    Bin Zheng

    2016-05-01

    Full Text Available In the present study, the sawtooth nature of compressive loading of metallic nanoparticles is observed using a molecular dynamics simulation. The atomic structure evolution confirmed that extended dislocations are the main defects split into two asynchronous partial disloca‐ tions, along with stored and released fault energy. This is considered the essence of sawtooth loading. The size of the nanoparticles relative to the equilibrium width of the extended dislocation is discussed to explain the simulation results.

  8. Dislocation creation and void nucleation in FCC ductile metals under tensile loading: a general microscopic picture.

    Science.gov (United States)

    Pang, Wei-Wei; Zhang, Ping; Zhang, Guang-Cai; Xu, Ai-Guo; Zhao, Xian-Geng

    2014-11-10

    Numerous theoretical and experimental efforts have been paid to describe and understand the dislocation and void nucleation processes that are fundamental for dynamic fracture modeling of strained metals. To date an essential physical picture on the self-organized atomic collective motions during dislocation creation, as well as the essential mechanisms for the void nucleation obscured by the extreme diversity in structural configurations around the void nucleation core, is still severely lacking in literature. Here, we depict the origin of dislocation creation and void nucleation during uniaxial high strain rate tensile processes in face-centered-cubic (FCC) ductile metals. We find that the dislocations are created through three distinguished stages: (i) Flattened octahedral structures (FOSs) are randomly activated by thermal fluctuations; (ii) The double-layer defect clusters are formed by self-organized stacking of FOSs on the close-packed plane; (iii) The stacking faults are formed and the Shockley partial dislocations are created from the double-layer defect clusters. Whereas, the void nucleation is shown to follow a two-stage description. We demonstrate that our findings on the origin of dislocation creation and void nucleation are universal for a variety of FCC ductile metals with low stacking fault energies.

  9. APPLICATION OF MECHANIZED MATHEMATICS TO ROTOR DYNAMICS

    Institute of Scientific and Technical Information of China (English)

    胡超; 王岩; 王立国; 黄文虎

    2002-01-01

    Based on the mechanized mathematics and WU Wen-tsun elimination method,using oil film forces of short-bearing model and Muszynska's dynamic model, the dynamical behavior of rotor-bearing system and its stability of motion are investigated. As example,the concept of Wu characteristic set and Maple software, whirl parameters of short- bearing model, which is usually solved by the numerical method, are analyzed. At the same time,stability of zero solution of Jeffcott rotor whirl equation and stability of self-excited vibration are studied. The conditions of stable motion are obtained by using theory of nonlinear vibration.

  10. EBSD observations of dynamic recrystallization mechanisms in ice.

    Science.gov (United States)

    Montagnat, Maurine; Chauve, Thomas; Barou, Fabrice; Beausir, Benoît; Fressengeas, Claude; Tommasi, Andrea

    2014-05-01

    Dynamic recrystallization (DRX) strongly affects the evolution of microstructure (grain size and shape) and texture (crystal preferred orientation) in materials during deformation at high temperature. Since texturing leads to anisotropic physical properties, predicting the effect of DRX in metals is essential for industrial applications, in rocks for interpreting geophysical data and modeling geodynamic flows, or in ice for predicting ice sheet flow and climate evolution. Owing to its high viscoplastic anisotropy, ice has long been considered as a "model material". This happens to be particularly true in the case of the understanding of the fundamental of DRX mechanisms as they occur under a relatively easily controlled environment. Creep compression experiments were performed on polycrystalline ice samples in the laboratory in order to observe the evolution of the fabrics and microstructures during DRX. During the tests, performed at temperatures of -5°C and -7°C, under 0.8 MPa compressive stress, dynamic recrystallization was initiated after 1% macroscopic strain and could be followed up to 18% strain on separated samples. Fabrics and microstructures were analysed post-mortem using an Automatic Ice Texture Analyser (AITA, Russell-Head and Wilson 2001) and EBSD measurements with the Crystal Probe of Géosciences Montpellier. Both techniques enable high resolution observations, both in space and orientation (5 to 50 microns, EBSD: 0.7° - AITA: 3°), which is new for DRX observations in ice. While AITA provides only the c-axis orientations, EBSD provides full orientations (c- and a-axes). In particular, we could access to an estimate of a relative dislocation density (from the Nye tensor obtained with EBSD) and its evolution with strain. Fabric evolution with strain is very similar to what was measured by Jacka and Maccagnan (1984) with a strong strengthening toward a few maxima for c- and a-axes. The c-axes maxima are oriented about 30° from the compression

  11. THE INFLUENCE OF GRAIN SIZE AND TEMPERATURE ON THE MECHANICAL DEFORMATION OF NANOCRYSTALLINE MATERIALS:MOLECULAR DYNAMICS SIMULATION

    Institute of Scientific and Technical Information of China (English)

    WEN YU-HUA; ZHOU FU-XIN; LIU YUE-WU

    2001-01-01

    Nanocrystalline (nc) materials are characterized by a typical grain size of 1-100nm. The uniaxial tensile deformation of computer-generated nc samples, with several average grain sizes ranging from 5.38 to 1.79nm, is simulated by using molecular dynamics with the Finnis-Sinclair potential. The influence of grain size and temperature on the mechanical deformation is studied in this paper. The simulated nc samples show a reverse Hall-Petch effect. Grain boundary sliding and motion, as well as grain rotation are mainly responsible for the plastic deformation. At low temperatures, partial dislocation activities play a minor role during the deformation. This role begins to occur at the strain of 5%, and is progressively remarkable with increasing average grain size. However, at elevated temperatures no dislocation activity is detected, and the diffusion of grain boundaries may come into play.

  12. Introduction to Dynamical Systems and Geometric Mechanics

    Science.gov (United States)

    Maruskin, Jared M.

    2012-01-01

    Introduction to Dynamical Systems and Geometric Mechanics provides a comprehensive tour of two fields that are intimately entwined: dynamical systems is the study of the behavior of physical systems that may be described by a set of nonlinear first-order ordinary differential equations in Euclidean space, whereas geometric mechanics explores similar systems that instead evolve on differentiable manifolds. In the study of geometric mechanics, however, additional geometric structures are often present, since such systems arise from the laws of nature that govern the motions of particles, bodies, and even galaxies. In the first part of the text, we discuss linearization and stability of trajectories and fixed points, invariant manifold theory, periodic orbits, Poincaré maps, Floquet theory, the Poincaré-Bendixson theorem, bifurcations, and chaos. The second part of the text begins with a self-contained chapter on differential geometry that introduces notions of manifolds, mappings, vector fields, the Jacobi-Lie bracket, and differential forms. The final chapters cover Lagrangian and Hamiltonian mechanics from a modern geometric perspective, mechanics on Lie groups, and nonholonomic mechanics via both moving frames and fiber bundle decompositions. The text can be reasonably digested in a single-semester introductory graduate-level course. Each chapter concludes with an application that can serve as a springboard project for further investigation or in-class discussion.

  13. Primary traumatic patellar dislocation

    Directory of Open Access Journals (Sweden)

    Tsai Chun-Hao

    2012-06-01

    Full Text Available Abstract Acute traumatic patellar dislocation is a common injury in the active and young adult populations. MRI of the knee is recommended in all patients who present with acute patellar dislocation. Numerous operative and non-operative methods have been described to treat the injuries; however, the ideal management of the acute traumatic patellar dislocation in young adults is still in debate. This article is intended to review the studies to the subjects of epidemiology, initial examination and management.

  14. Electron energy can oscillate near a crystal dislocation

    Science.gov (United States)

    Li, Mingda; Cui, Wenping; Dresselhaus, Mildred S.; Chen, Gang

    2017-01-01

    Crystal dislocations govern the plastic mechanical properties of materials but also affect the electrical and optical properties. However, a fundamental and quantitative quantum field theory of a dislocation has remained undiscovered for decades. Here we present an exactly-solvable one-dimensional quantum field theory of a dislocation, for both edge and screw dislocations in an isotropic medium, by introducing a new quasiparticle which we have called the ‘dislon’. The electron-dislocation relaxation time can then be studied directly from the electron self-energy calculation, which is reducible to classical results. In addition, we predict that the electron energy will experience an oscillation pattern near a dislocation. Compared with the electron density’s Friedel oscillation, such an oscillation is intrinsically different since it exists even with only single electron is present. With our approach, the effect of dislocations on materials’ non-mechanical properties can be studied at a full quantum field theoretical level.

  15. Scattering of phonons by dislocations

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, A. C.

    1979-01-01

    By 1950, an explicit effort had been launched to use lattice thermal conductivity measurements in the investigation of defect structures in solids. This technique has been highly successful, especially when combined with the measurements of other properties such as optical absorption. One exception has been the study of dislocations. Although dislocations have a profound effect on the phonon thermal conductivity, the mechanisms of the phonon-dislocation interaction are poorly understood. The most basic questions are still debated in the literature. It therefore is pointless to attempt a quantitative comparison between an extensive accumulation of experimental data on the one hand, and the numerous theoretical models on the other. Instead, this chapter will attempt to glean a few qualitative conclusions from the existing experimental data. These results will then be compared with two general models which incorporate, in a qualitative manner, most of the proposed theories of the phonon-dislocation interaction. Until very recently, measurement of thermal conductivity was the only means available to probe the interaction between phonons and defects at phonon frequencies above the standard ultrasonic range of approx. = 10/sup 9/ Hz. The introductory paragraphs provide a brief review of the thermal-conductivity technique and the problems which are encountered in practice. There is also a brief presentation of the theoretical models and the complications that may occur in more realistic situations.

  16. Interfacial dislocation motion and interactions in single-crystal superalloys

    Energy Technology Data Exchange (ETDEWEB)

    Liu, B. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Raabe, D. [Max Planck Inst. fur Eisenforshung. Dusseldorf (Germany); Roters, F. [Max Planck Inst. fur Eisenforshung. Dusseldorf (Germany); Arsenlis, A. [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    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.

  17. Dynamics-dependent symmetries in Newtonian mechanics

    CERN Document Server

    Holland, Peter

    2014-01-01

    We exhibit two symmetries of one-dimensional Newtonian mechanics whereby a solution is built from the history of another solution via a generally nonlinear and complex potential-dependent transformation of the time. One symmetry intertwines the square roots of the kinetic and potential energies and connects solutions of the same dynamical problem (the potential is an invariant function). The other symmetry connects solutions of different dynamical problems (the potential is a scalar function). The existence of corresponding conserved quantities is examined using Noethers theorem and it is shown that the invariant-potential symmetry is correlated with energy conservation. In the Hamilton-Jacobi picture the invariant-potential transformation provides an example of a field-dependent symmetry in point mechanics. It is shown that this transformation is not a symmetry of the Schroedinger equation.

  18. Hybrid Dislocated Control and General Hybrid Projective Dislocated Synchronization for Memristor Chaotic Oscillator System

    Directory of Open Access Journals (Sweden)

    Junwei Sun

    2014-01-01

    Full Text Available Some important dynamical properties of the memristor chaotic oscillator system have been studied in the paper. A novel hybrid dislocated control method and a general hybrid projective dislocated synchronization scheme have been realized for memristor chaotic oscillator system. The paper firstly presents hybrid dislocated control method for stabilizing chaos to the unstable equilibrium point. Based on the Lyapunov stability theorem, general hybrid projective dislocated synchronization has been studied for the drive memristor chaotic oscillator system and the same response memristor chaotic oscillator system. For the different dimensions, the memristor chaotic oscillator system and the other chaotic system have realized general hybrid projective dislocated synchronization. Numerical simulations are given to show the effectiveness of these methods.

  19. Atomic-scale Modeling of the Structure and Dynamics of Dislocations in Complex Alloys at High Temperatures

    Science.gov (United States)

    Daw, Murray S.; Mills, Michael J.

    2003-01-01

    We report on the progress made during the first year of the project. Most of the progress at this point has been on the theoretical and computational side. Here are the highlights: (1) A new code, tailored for high-end desktop computing, now combines modern Accelerated Dynamics (AD) with the well-tested Embedded Atom Method (EAM); (2) The new Accelerated Dynamics allows the study of relatively slow, thermally-activated processes, such as diffusion, which are much too slow for traditional Molecular Dynamics; (3) We have benchmarked the new AD code on a rather simple and well-known process: vacancy diffusion in copper; and (4) We have begun application of the AD code to the diffusion of vacancies in ordered intermetallics.

  20. Traumatic vertical atlantoaxial dislocation.

    Science.gov (United States)

    Payer, M; Wetzel, S; Kelekis, A; Jenny, B

    2005-08-01

    We present a case of traumatic vertical atlantoaxial dislocation of 16 millimetres with a fatal outcome. We hypothesize that this extremely rare traumatic vertical atlantoaxial dislocation results from insufficiency of the C1/C2 facet capsules after rupture of the tectorial membrane and the alar ligaments.

  1. Dynamic aspects of the tubuloglomerular feedback mechanism

    DEFF Research Database (Denmark)

    Holstein-Rathlou, N H

    1992-01-01

    unlikely, it cannot be excluded that a vascular pacemaker is involved in the underlying oscillatory mechanism. To test the hypothesis that the oscillations are caused by the TGF system, a series of dynamic mathematical models of the TGF system have been developed.(ABSTRACT TRUNCATED AT 400 WORDS)......Tubuloglomerular feedback (TGF) is an important intrarenal regulatory mechanism, which acts to stabilize renal blood flow, GFR, and the tubular flow rate. The anatomical basis for this negative feedback system is the Juxtaglomerular Apparatus (JGA). This is located at the point of contact between...... the thick ascending limb of the loop of Henle (TAL) and the vascular pole of the glomerulus. The JGA includes the macula densa, a specialized plaque of cells in the TAL thought to be responsible for the sensing step in the feedback mechanism; the mesangial cells, a cushion of cells separating the macula...

  2. Nonsmooth mechanics models, dynamics and control

    CERN Document Server

    Brogliato, Bernard

    2016-01-01

    Now in its third edition, this standard reference is a comprehensive treatment of nonsmooth mechanical systems refocused to give more prominence to control and modelling. It covers Lagrangian and Newton–Euler systems, detailing mathematical tools such as convex analysis and complementarity theory. The ways in which nonsmooth mechanics influence and are influenced by well-posedness analysis, numerical analysis and simulation, modelling and control are explained. Contact/impact laws, stability theory and trajectory-tracking control are given in-depth exposition connected by a framework formed from complementarity systems and measure-differential inclusions. Links are established with electrical circuits with set-valued nonsmooth elements and with other nonsmooth dynamical systems like impulsive and piecewise linear systems. Nonsmooth Mechanics (third edition) has been substantially rewritten, edited and updated to account for the significant body of results that have emerged in the twenty-first century—incl...

  3. Traumatic Dislocation of the Elbow Joint

    OpenAIRE

    de Haan, Jeroen

    2011-01-01

    textabstractThis thesis addresses the major issues encountered in the diagnosis and treatment of adult elbow dislocation. Firstly, a literary review (Chapters Five and Eight) makes it clear that there is much uncertainty regarding trauma mechanism, biomechanics, and even anatomy (Chapter Two). Furthermore, an overview of the treatment options indicates that there is no uniformity in the treatment modalities applicable to elbow dislocation (Chapter Six). And last but not least, there is no Dut...

  4. Calculated electronic and magnetic structure of screw dislocations in alpha iron

    Energy Technology Data Exchange (ETDEWEB)

    Odbadrakh, Khorgolkhuu [ORNL; Rusanu, Aurelian [ORNL; Stocks, George Malcolm [ORNL; Samolyuk, German D [ORNL; Eisenbach, Markus [ORNL; Wang, Yang Nmn [ORNL; Nicholson, Don M [ORNL

    2011-01-01

    Local atomic magnetic moments in crystalline Fe are perturbed by the presence of dislocations. The effects are most pronounced near the dislocation core and decay slowly as the strain field of the dislocation decreases with distance. We have calculated local moments using the locally self-consistent multiple scattering (LSMS) method for a supercell containing a screw-dislocation quadrupole. Finite size effects are found to be significant indicating that dislocation cores affect the electronic structure and magnetic moments of neighboring dislocations. The influence of neighboring dislocations points to a need to study individual dislocations from first principles just as they appear amid surrounding atoms in large-scale classical force field simulations. An approach for the use of the LSMS to calculate local moments in subvolumes of large atomic configurations generated in the course of classical molecular dynamics simulation of dislocation dynamics is discussed. VC2011 American Institute of Physics. [doi:10.1063/1.3562217

  5. Three-dimensional imaging of dislocation propagation during crystal growth and dissolution

    Science.gov (United States)

    Schenk, Anna S.; Kim, Yi-Yeoun; Kulak, Alexander N.; Campbell, James M.; Nisbet, Gareth; Meldrum, Fiona C.; Robinson, Ian K.

    2015-01-01

    Atomic level defects such as dislocations play key roles in determining the macroscopic properties of crystalline materials 1,2. Their effects range from increased chemical reactivity 3,4 to enhanced mechanical properties 5,6. Dislocations have been widely studied using traditional techniques such as X-ray diffraction and optical imaging. Recent advances have enabled atomic force microscopy to study single dislocations 7 in two-dimensions (2D), while transmission electron microscopy (TEM) can now visualise strain fields in three-dimensions (3D) with near atomic resolution 8–10. However, these techniques cannot offer 3D imaging of the formation or movement of dislocations during dynamic processes. Here, we describe how Bragg Coherent Diffraction Imaging (BCDI) 11,12 can be used to visualize in 3D, the entire network of dislocations present within an individual calcite crystal during repeated growth and dissolution cycles. These investigations demonstrate the potential of BCDI for studying the mechanisms underlying the response of crystalline materials to external stimuli. PMID:26030304

  6. Dynamical Mechanical Properties for AD90 Alumina

    Institute of Scientific and Technical Information of China (English)

    REN Hui-lan; NING Jian-guo; LI Ping

    2007-01-01

    The dynamic response of polycrystalline alumina was investigated in the pressure range of 0 -13 GPa by planar impact experiments.Velocity interferometer system for any reflector(VISAR) was used to obtain free surface velocity profile and determine the Hugoniot elastic limit,and manganin gauges were employed to obtain the stress-time histories and determine Hugoniot curve.Both the free surface particle velocity profiles and Hugoniot curves indicate the dispersion of the "plastic" wave for alumina.With the measured stress histories,the complete histories of strain,particle velocity,specific volume and specific internal energy are gained by using path line principle of Lagrange analysis.The dynamic mechanical behaviors for alumina under impact loading are analyzed,such as nonlinear characteristic,strain rate dependence,dispersion and declination of shock wave in the material.

  7. Multiphase Flow Dynamics 2 Mechanical Interactions

    CERN Document Server

    Kolev, Nikolay Ivanov

    2012-01-01

    Multi-phase flows are part of our natural environment such as tornadoes, typhoons, air and water pollution and volcanic activities as well as part of industrial technology such as power plants, combustion engines, propulsion systems, or chemical and biological industry. The industrial use of multi-phase systems requires analytical and numerical strategies for predicting their behavior. .In its fourth extended edition the successful monograph package “Multiphase Flow Daynmics” contains theory, methods and practical experience for describing complex transient multi-phase processes in arbitrary geometrical configurations, providing a systematic presentation of the theory and practice of numerical multi-phase fluid dynamics. In the present second volume the methods for describing the mechanical interactions in multiphase dynamics are provided. This fourth edition includes various updates, extensions, improvements and corrections.   "The literature in the field of multiphase flows is numerous. Therefore, it i...

  8. The Design and Implementation of 3D Visualization System for Crystal Dislocations in Molecular Dynamics%分子动力学中晶体位错的三维可视化系统设计与实现

    Institute of Scientific and Technical Information of China (English)

    宁媛; 张鹏; 介军

    2014-01-01

    在材料科学中,位错线是晶体或晶格内滑移面上已滑动区的边界,位错线的识别对于鉴定晶体的性能有着重要的影响。该文将三维可视化技术应用到分子动力学领域,改进了原有的只能通过计算结果分析数据、通过二维图像简单观察数据的方法,设计了晶体位错可视化系统,使得晶体中各原子之间形成的三维结构易于观察,便于研究晶体位错等重要的材质特性,提高位错线的识别效率。%In the material science, the dislocation lines are the boundary sliding of a crystal or a lattice slip plane,the identification of dislocation lines have a important impact for the property of crystals. The essay using the application of 3D visualization tech-nology to the field of molecular dynamics and improving the conventional research ways, such as analyzing data by calculating re-sults and observing the data by 2D images inconveniently, designing a visualization system for crystal dislocations. This way can make the 3D structure among atoms be observed easily, which is convenient to research the crystal dislocations and other impor-tant material properties, and improve the efficiency of the identification of dislocation lines.

  9. Dynamic tensile behaviour and deformational mechanism of C5191 phosphor bronze under high strain rates deformation

    Energy Technology Data Exchange (ETDEWEB)

    Hu, Dao-chun [College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); College of Mechanical and Electrical Engineering, Taizhou Vocational & Technical College, Taizhou 318000 (China); Chen, Ming-he, E-mail: meemhchen@nuaa.edu.cn [College of Mechanical and Electrical Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016 (China); Wang, Lei; Cheng, Hu [College of Mechanical Engineering, Taizhou University, Taizhou 318000 (China)

    2016-01-01

    High speed stamping process is used to high strength and high electrical conductivity phosphor bronze with extremely high strain rates more than 10{sup 3} s{sup −1}. This study on the dynamic tensile behaviour and deformational mechanism is to optimise the high speed stamping processes and improve geometrical precision in finished products. Thus, the tensile properties and deformation behaviour of C5191 phosphor bronze under quasi-static tensile condition at a strain rate of 0.001 s{sup −1} by electronic universal testing machine, and dynamic tensile condition at strain rate of 500, 1000 and 1500 s{sup −1} by split Hopkinson tensile bar (SHTB) apparatus were studied. The effects of strain rate and the deformation mechanism were investigated by means of SEM and TEM. The results showed that the yield strength and tensile strength of C5191 phosphor bronze under high strain rates deformation increased by 32.77% and 11.07% respectively compared with quasi-static condition, the strain hardening index increases from 0.075 to 0.251, and the strength of the material strain rates sensitivity index change from 0.005 to 0.022, which presented a clear sensitive to strain rates. Therefore, it is claimed that the dominant deformation mechanism was changed by the dislocation motion under different strain rates, and the ability of plastic deformation of C5191 phosphor bronze increased due to the number of movable dislocations increased significantly, started multi-line slip, and the soft effect of adiabatic temperature rise at the strain rate ranging from 500 to 1500 s{sup −1}.

  10. DYNAMIC MECHANICAL RESPONSE OF CRAZES IN POLYSTYRENE

    Institute of Scientific and Technical Information of China (English)

    DING Jianfu; XUE Gi; CHENG Rongshi

    1994-01-01

    Dynamic mechanical analysis was used to study the mechanical properties and microstructure of crazes in polystyrene produced in air or in methanol at different temperatures. A new loss peak was found at about 82℃ ,which is assigned to glass transition peak of craze fibrils. The decrease of glass transition temperature of polymer in craze fibrils is due to the high values of surface to volume ratio. The glass transition temperature ratio of craze fibrils to bulk material(Tg'/Tg) has been expressed as a function of the fibrils diameter(d). From Tg'of craze fibrils ,the value of fibril diameter can be calculated. Annealing the crazed specimen at room temperature makes the fibrils plastically deform and cause the fibrils to thin slightly, whereas annealing the crazed specimen at the temperature near Tg of the craze fibrils makes the fibrils bundle together.

  11. Nambu mechanics for stochastic magnetization dynamics

    CERN Document Server

    Thibaudeau, Pascal; Nicolis, Stam

    2016-01-01

    The Landau-Lifshitz-Gilbert (LLG) equation describes the dynamics of a damped magnetization vector that can be understood as a generalization of Larmor spin precession. The LLG equation cannot be deduced from the Hamiltonian framework, by introducing a coupling to a usual bath, but requires the introduction of additional constraints. It is shown that these constraints can be formulated elegantly and consistently in the framework of dissipative Nambu mechanics. This has many consequences for both the variational principle and for topological aspects of hidden symmetries that control conserved quantities. We particularly study how the damping terms of dissipative Nambu mechanics affect the consistent interaction of magnetic systems with stochastic reservoirs and derive a master equation for the magnetization. The proposals are supported by numerical studies using symplectic integrators that preserve the topological structure of Nambu equations. These results are compared to computations performed by direct samp...

  12. Atomistic simulation of He bubble in Fe as obstacle to dislocation

    Science.gov (United States)

    Hafez Haghighat, S. M.; Lucas, G.; Schäublin, R.

    2009-07-01

    Degradation of mechanical properties due to nanometric irradiation induced defects is one of the challenging issues in designing materials for future fusion reactors. Various types of defects such as voids and He bubbles may be produced due to high dose of neutron irradiation due to fusion reaction. We study the influence of He bubble on the mobility of an edge dislocation in pure bcc-Fe using molecular dynamics simulation as a function of bubble size, He density and temperature. It appears that low contents He bubbles are penetrable defects, which size and temperature rise make them harder and softer, respectively. At high He contents a size dependent loop punching is observed, which at larger bubble sizes leads to a multistep dislocation-defect interaction. It also appears that the bubble surface curvature and temperature are the main parameters in the screw segments annihilation needed for the release of the dislocation from the bubble.

  13. Creep Deformation by Dislocation Movement in Waspaloy

    Directory of Open Access Journals (Sweden)

    Mark Whittaker

    2017-01-01

    Full Text Available Creep tests of the polycrystalline nickel alloy Waspaloy have been conducted at Swansea University, for varying stress conditions at 700 °C. Investigation through use of Transmission Electron Microscopy at Cambridge University has examined the dislocation networks formed under these conditions, with particular attention paid to comparing tests performed above and below the yield stress. This paper highlights how the dislocation structures vary throughout creep and proposes a dislocation mechanism theory for creep in Waspaloy. Activation energies are calculated through approaches developed in the use of the recently formulated Wilshire Equations, and are found to differ above and below the yield stress. Low activation energies are found to be related to dislocation interaction with γ′ precipitates below the yield stress. However, significantly increased dislocation densities at stresses above yield cause an increase in the activation energy values as forest hardening becomes the primary mechanism controlling dislocation movement. It is proposed that the activation energy change is related to the stress increment provided by work hardening, as can be observed from Ti, Ni and steel results.

  14. Dynamic congestion control mechanisms for MPLS networks

    Science.gov (United States)

    Holness, Felicia; Phillips, Chris I.

    2001-02-01

    Considerable interest has arisen in congestion control through traffic engineering from the knowledge that although sensible provisioning of the network infrastructure is needed, together with sufficient underlying capacity, these are not sufficient to deliver the Quality of Service required for new applications. This is due to dynamic variations in load. In operational Internet Protocol (IP) networks, it has been difficult to incorporate effective traffic engineering due to the limited capabilities of the IP technology. In principle, Multiprotocol Label Switching (MPLS), which is a connection-oriented label swapping technology, offers new possibilities in addressing the limitations by allowing the operator to use sophisticated traffic control mechanisms. This paper presents a novel scheme to dynamically manage traffic flows through the network by re-balancing streams during periods of congestion. It proposes management-based algorithms that will allow label switched routers within the network to utilize mechanisms within MPLS to indicate when flows are starting to experience frame/packet loss and then to react accordingly. Based upon knowledge of the customer's Service Level Agreement, together with instantaneous flow information, the label edge routers can then instigate changes to the LSP route and circumvent congestion that would hitherto violate the customer contacts.

  15. Molecular dynamics simulations of the mechanical strength of Si/ Si3 N4 interfaces

    Science.gov (United States)

    Bachlechner, Martina E.; Zhang, Jennifer; Wang, Ye; Schiffbauer, Jarrod; Knudsen, Steven R.; Korakakis, Dimitris

    2005-09-01

    Molecular dynamics simulations are performed on parallel computers to investigate the crystalline Si(111)/Si3N4(0001) interface that is modeled as an eight-component system. The average total energy per particle and the average kinetic energy per particle of the subsystems are monitored during the preparation of the system. The Young’s modulus of the interface is compared with that of the silicon part alone and that of the silicon-nitride film, respectively. The results for one extended simulation feature a crack in the silicon-nitride film and dislocated atoms in silicon below the crack. Simulations at rates of strain ranging from 0.00125to0.05ps-1 show that for lower strain rates, the systems stretched faster reach their ultimate strength at a higher strain value than those that were stretched more slowly. At the highest strain rates, however, the failure mechanisms change qualitatively indicative of a more ductile behavior.

  16. Galeazzi fracture-dislocations.

    Science.gov (United States)

    Mikić, Z D

    1975-12-01

    Among 125 patients with the Galeazzi-type fracture-dislocation of the forearm, there were fourteen children and eighty-six adults with the classic Galeazzi lesion, and twenty-five patients with a special type -- fracture of both bones and dislocation of the distal radio-ulnar joint. Conservative management was successful only in children. In adults this method resulted in failure in 80 per cent of cases. The results of operative treatment were much better. The fracture fragments of the radius and the dislocation of the radio-ulnar joint in this complex injury are very unstable, especially in the lesion with fractures of the radius and ulna, and it appears that rigid internal fixation is necessary for the dislocation as well as the fracture. With combined fixation over half of the results were excellent.

  17. An analysis of dislocation nucleation near a free surface

    NARCIS (Netherlands)

    Liu, Yufu; Van der Giessen, Erik; Needleman, Alan

    2007-01-01

    Molecular dynamics analyses of defect-free aluminum single crystals subject to bending are carried out to investigate dislocation nucleation from free surfaces. A principal aim of the analyses is to provide background for the development of dislocation nucleation criteria for use in discrete

  18. Non-basal dislocations should be accounted for in simulating ice mass flow

    Science.gov (United States)

    Chauve, T.; Montagnat, M.; Piazolo, S.; Journaux, B.; Wheeler, J.; Barou, F.; Mainprice, D.; Tommasi, A.

    2017-09-01

    Prediction of ice mass flow and associated dynamics is pivotal at a time of climate change. Ice flow is dominantly accommodated by the motion of crystal defects - the dislocations. In the specific case of ice, their observation is not always accessible by means of the classical tools such as X-ray diffraction or transmission electron microscopy (TEM). Part of the dislocation population, the geometrically necessary dislocations (GNDs) can nevertheless be constrained using crystal orientation measurements via electron backscattering diffraction (EBSD) associated with appropriate analyses based on the Nye (1950) approach. The present study uses the Weighted Burgers Vectors, a reduced formulation of the Nye theory that enables the characterization of GNDs. Applied to ice, this method documents, for the first time, the presence of dislocations with non-basal [ c ] or Burgers vectors. These [ c ] or dislocations represent up to 35% of the GNDs observed in laboratory-deformed ice samples. Our findings offer a more complex and comprehensive picture of the key plasticity processes responsible for polycrystalline ice creep and provide better constraints on the constitutive mechanical laws implemented in ice sheet flow models used to predict the response of Earth ice masses to climate change.

  19. Dislocations and elementary processes of plasticity in FCC metals: atomic scale simulations; Dislocations et processus elementaires de la plasticite dans les metaux CFC: apports des simulations a l'echelle atomique

    Energy Technology Data Exchange (ETDEWEB)

    Rodney, D

    2000-07-01

    We present atomic-scale simulations of two elementary processes of FCC crystal plasticity. The first study consists in the simulation by molecular dynamics, in a nickel crystal, of the interactions between an edge dislocation and glissile interstitial loops of the type that form under irradiation in displacement cascades. The simulations show various atomic-scale interaction processes leading to the absorption and drag of the loops by the dislocation. These reactions certainly contribute to the formation of the 'clear bands' observed in deformed irradiated materials. The simulations also allow to study quantitatively the role of the glissile loops in irradiation hardening. In particular, dislocation unpinning stresses for certain pinning mechanisms are evaluated from the simulations. The second study consists first in the generalization in three dimensions of the quasi-continuum method (QCM), a multi-scale simulation method which couples atomistic techniques and the finite element method. In the QCM, regions close to dislocation cores are simulated at the atomic-scale while the rest of the crystal is simulated with a lower resolution by means of a discretization of the displacement fields using the finite element method. The QCM is then tested on the simulation of the formation and breaking of dislocation junctions in an aluminum crystal. Comparison of the simulations with an elastic model of dislocation junctions shows that the structure and strength of the junctions are dominated by elastic line tension effects, as is assumed in classical theories. (author)

  20. Dynamic mechanical properties of an inlay composite.

    Science.gov (United States)

    Dionysopoulos, P; Watts, D C

    1989-06-01

    A visible light-cured composite resin (Brilliant DI) has been studied over a wide range of temperature and frequency by a dynamic mechanical flexural method. The derived data of logarithmic modulus and loss tangent (tan delta) show considerable changes following a secondary-cure process applied to the material. This involved the application of heat and intense light with temperatures rising to 120 degrees C in 7 min. Following this oven-cure the resin phase exhibited enhanced stiffness with the activation-energy barrier for molecular motion at the glass-transition rising from 220 to 291 kJ/mol. This study clarifies the nature and extent of the internal molecular changes which may be produced in the fabrication of a composite inlay.

  1. Pharmaceutical applications of dynamic mechanical thermal analysis.

    Science.gov (United States)

    Jones, David S; Tian, Yiwei; Abu-Diak, Osama; Andrews, Gavin P

    2012-04-01

    The successful development of polymeric drug delivery and biomedical devices requires a comprehensive understanding of the viscoleastic properties of polymers as these have been shown to directly affect clinical efficacy. Dynamic mechanical thermal analysis (DMTA) is an accessible and versatile analytical technique in which an oscillating stress or strain is applied to a sample as a function of oscillatory frequency and temperature. Through cyclic application of a non-destructive stress or strain, a comprehensive understanding of the viscoelastic properties of polymers may be obtained. In this review, we provide a concise overview of the theory of DMTA and the basic instrumental/operating principles. Moreover, the application of DMTA for the characterization of solid pharmaceutical and biomedical systems has been discussed in detail. In particular we have described the potential of DMTA to measure and understand relaxation transitions and miscibility in binary and higher-order systems and describe the more recent applications of the technique for this purpose.

  2. Dynamical phase transitions in quantum mechanics

    Directory of Open Access Journals (Sweden)

    Rotter Ingrid

    2012-02-01

    Full Text Available The nucleus is described as an open many-body quantum system with a non-Hermitian Hamilton operator the eigenvalues of which are complex, in general. The eigenvalues may cross in the complex plane (exceptional points, the phases of the eigenfunctions are not rigid in approaching the crossing points and the widths bifurcate. By varying only one parameter, the eigenvalue trajectories usually avoid crossing and width bifurcation occurs at the critical value of avoided crossing. An analog spectroscopic redistribution takes place for discrete states below the particle decay threshold. By this means, a dynamical phase transition occurs in the many-level system starting at a critical value of the level density. Hence the properties of the low-lying nuclear states (described well by the shell model and those of highly excited nuclear states (described by random ensembles differ fundamentally from one another. The statement of Niels Bohr on the collective features of compound nucleus states at high level density is therefore not in contradiction to the shell-model description of nuclear (and atomic states at low level density. Dynamical phase transitions are observed experimentally in different quantum mechanical systems by varying one or two parameters.

  3. New methods for quantum mechanical reaction dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Thompson, Ward Hugh [Univ. of California, Berkeley, CA (United States). Dept. of Chemistry

    1996-12-01

    Quantum mechanical methods are developed to describe the dynamics of bimolecular chemical reactions. We focus on developing approaches for directly calculating the desired quantity of interest. Methods for the calculation of single matrix elements of the scattering matrix (S-matrix) and initial state-selected reaction probabilities are presented. This is accomplished by the use of absorbing boundary conditions (ABC) to obtain a localized (L2) representation of the outgoing wave scattering Green`s function. This approach enables the efficient calculation of only a single column of the S-matrix with a proportionate savings in effort over the calculation of the entire S-matrix. Applying this method to the calculation of the initial (or final) state-selected reaction probability, a more averaged quantity, requires even less effort than the state-to-state S-matrix elements. It is shown how the same representation of the Green`s function can be effectively applied to the calculation of negative ion photodetachment intensities. Photodetachment spectroscopy of the anion ABC- can be a very useful method for obtaining detailed information about the neutral ABC potential energy surface, particularly if the ABC- geometry is similar to the transition state of the neutral ABC. Total and arrangement-selected photodetachment spectra are calculated for the H3O- system, providing information about the potential energy surface for the OH + H2 reaction when compared with experimental results. Finally, we present methods for the direct calculation of the thermal rate constant from the flux-position and flux-flux correlation functions. The spirit of transition state theory is invoked by concentrating on the short time dynamics in the area around the transition state that determine reactivity. These methods are made efficient by evaluating the required quantum mechanical trace in the basis of eigenstates of the

  4. Dislocation-enhanced experimental-scale vacancy loop formation in hcp Zirconium in one single collision cascade.

    Science.gov (United States)

    Zhou, Wei; Tian, Jiting; Zheng, Jian; Xue, Jianming; Peng, Shuming

    2016-02-12

    Large defects are the main factor leading to the degradation of material properties under irradiation environments. It is commonly assumed that the large defects are mainly formed through cluster growth under continuous irradiations. Besides this mechanism, recent experiments and simulations show that sometimes an individual ion can also directly create a large defect. Here we report a novel mechanism for the formation of the large defects, as discovered by our Molecular Dynamics (MD) simulations of the collision cascades in hcp Zirconium (Zr): a pre-existing edge dislocation (ED) can significantly promote the nucleation of the vacancy clusters, and even facilitate the direct formation of an experimental-scale large vacancy loop (about 3 nm) in only one single displacement cascade. This dislocation-related mechanism may be the key for understanding the experimental results in the low-dose irradiated Zr where the high-density large dislocation loops are observed but difficult to be explained by the two mechanisms mentioned above. Considering that intrinsic dislocations exist in nearly all crystalline materials, our results provide a significant concept: pre-existing dislocations have a strong influence on the primary damage production, and taking them into account is indispensable for assessing and improving the material's irradiation-resistance.

  5. Total carpometacarpal joint dislocation combined with trapezium fracture, trapezoid dislocation and hamate fracture

    DEFF Research Database (Denmark)

    Gvozdenovic, R; Vadstrup, Lars Soelberg

    2015-01-01

    Multiple metacarpal dislocations combined with carpal fracture - dislocations are rare injuries. We report a new combination of these injuries where fracture-dislocation of the base of the 1st metacarpal bone occurred simultaneously with a comminuted fracture of the trapezium, dislocation...... of the trapezoid and metacarpal joints (2nd to 5th) and an avulsion fracture of the hamate. This specific carpal injury has not been previously described and our description will contribute to understanding the mechanism of these complex injuries. The injury pattern in the case featured here was multifaceted...... and resulted from rupture of both transverse and longitudinal carpal columns. According to the Garcia-Elias classification of axial carpal disruptions, this particular injury mechanism was a combined axial-radial-ulnar type injury. These injuries are extremely rare and are only sporadically described...

  6. Intermittent dislocation density fluctuations in crystal plasticity from a phase-field crystal model

    DEFF Research Database (Denmark)

    Tarp, Jens M.; Angheluta, Luiza; Mathiesen, Joachim;

    2014-01-01

    Plastic deformation mediated by collective dislocation dynamics is investigated in the two-dimensional phase-field crystal model of sheared single crystals. We find that intermittent fluctuations in the dislocation population number accompany bursts in the plastic strain-rate fluctuations. Disloc...

  7. Cooperative dissociations of misfit dislocations at bimetal interfaces

    Directory of Open Access Journals (Sweden)

    K. Liu

    2016-11-01

    Full Text Available Using atomistic simulations, several semi-coherent cube-on-cube bimetal interfaces are comparatively investigated to unravel the combined effect of the character of misfit dislocations, the stacking fault energy difference between bimetal pairs, and their lattice mismatch on the dissociation of interfacial misfit dislocations. Different dissociation paths and features under loadings provide several unique deformation mechanisms that are critical for understanding interface strengthening. In particular, applied strains can cause either the formation of global interface coherency by the migration of misfit dislocations from an interface to an adjoining crystal interior or to an alternate packing of stacking faults connected by stair-rod dislocations.

  8. Cooperative dissociations of misfit dislocations at bimetal interfaces

    Science.gov (United States)

    Liu, K.; Zhang, R. F.; Beyerlein, I. J.; Chen, X. Y.; Yang, H.; Germann, T. C.

    2016-11-01

    Using atomistic simulations, several semi-coherent cube-on-cube bimetal interfaces are comparatively investigated to unravel the combined effect of the character of misfit dislocations, the stacking fault energy difference between bimetal pairs, and their lattice mismatch on the dissociation of interfacial misfit dislocations. Different dissociation paths and features under loadings provide several unique deformation mechanisms that are critical for understanding interface strengthening. In particular, applied strains can cause either the formation of global interface coherency by the migration of misfit dislocations from an interface to an adjoining crystal interior or to an alternate packing of stacking faults connected by stair-rod dislocations.

  9. Dislocation Model and Morphology Simulation of bcc fcc Martensitic Transformation

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    By using molecular dynamics computer simulation at atomic level, the effects of single dislocation and dipole dislocations on nucleation and growth of martensitic transformation have been studied. It was found that only the location of tension or compression stress fields of the dislocations are favorable for martensite nucleation in NiAl alloy and the dislocations can move to accommodate partly the transformation strain during the nucleation and growth of martensite. Combined with the molecular dynamics simulation, a two dimensional simulation for martensite morphology based on a dislocation model bas been performed. Many factors related to martensitic transformation were considered, such as supercooling, interface energy, shear strain, normal strain and hydrostatic pressure. Different morphologies of martensites, similar to lath, lenticular, thin plate, couple-plate and lenticular couple-plate martensites observed in Fe-C and Fe-Ni-C alloys, were obtained.

  10. Dynamic Matching Markets and the Deferred Acceptance Mechanism

    DEFF Research Database (Denmark)

    Kennes, John; Monte, Daniel; Tumennasan, Norovsambuu

    In many dynamic matching markets, priorities depend on previous allocations. In such environments, agents on the proposing side can manipulate the period-by-period deferred acceptance (DA) mechanism. We show that the fraction of agents with incentives to manipulate the DA mechanism approaches zero...... together justify the implementation of the period-by-period DA mechanism in dynamic markets....

  11. Growth and instability of charged dislocation loops under irradiation in ceramic materials

    CERN Document Server

    Ryazanov, A I; Kinoshita, C; Klaptsov, A V

    2002-01-01

    We have investigated the physical mechanisms of the growth and stability of charged dislocation loops in ceramic materials with very strong different mass of atoms (stabilized cubic zirconia) under different energies and types of irradiation conditions: 100-1000 keV electrons, 100 keV He sup + and 300 keV O sup + ions. The anomalous formation of extended defect clusters (charged dislocation loops) has been observed by TEM under electron irradiation subsequent to ion irradiation. It is demonstrated that very strong strain field (contrast) near charged dislocation loops is formed. The dislocation loops grow up to a critical size and after then become unstable. The instability of the charged dislocation loop leads to the multiplication of dislocation loops and the formation of dislocation network near the charged dislocation loops. A theoretical model is suggested for the explanation of the growth and stability of the charged dislocation loop, taking the charge state of point defects. The calculated distribution...

  12. Isolated dorsal dislocation of the tarsal naviculum

    Directory of Open Access Journals (Sweden)

    Kaziz Hamdi

    2015-01-01

    Full Text Available Isolated dislocation of the tarsal naviculum is an unusual injury, scarcely reported in the literature. The naviculum is surrounded by the rigid bony and ligamentous support hence fracture dislocation is more common than isolated dislocation. The mechanism and treatment options remain unclear. In this case report, we describe a 31 year old man who sustained an isolated dorsal dislocation of the left tarsal naviculum, without fracture, when he was involved in a motor vehicle collision. The reported mechanism of the dislocation is a hyper plantar flexion force applied to the midfoot, resulting in a transient disruption of the ligamentous support of the naviculum bone, with dorsal displacement of the bone. The patient was treated with open reduction and Krischner-wire fixation of the navicular after the failure of closed reduction. The wires were removed after 6 weeks postoperatively. Physiotherapy for stiffness and midfoot pain was recommended for 2 months. At 6 months postoperatively, limping, midfoot pain and weakness were reported, no X-ray abnormalities were found. The patient returned to his obvious activities with a normal range of motion.

  13. A computational method for dislocation-precipitate interaction

    Science.gov (United States)

    Takahashi, Akiyuki; Ghoniem, Nasr M.

    A new computational method for the elastic interaction between dislocations and precipitates is developed and applied to the solution of problems involving dislocation cutting and looping around precipitates. Based on the superposition principle, the solution to the dislocation-precipitate interaction problem is obtained as the sum of two solutions: (1) a dislocation problem with image stresses from interfaces between the dislocation and the precipitate, and (2) a correction solution for the elastic problem of a precipitate with an initial strain distribution. The current development is based on a combination of the parametric dislocation dynamics (PDD) and the boundary element method (BEM) with volume integrals.The method allows us to calculate the stress field both inside and outside precipitates of elastic moduli different from the matrix, and that may have initial coherency strain fields. The numerical results of the present method show good convergence and high accuracy when compared to a known analytical solution, and they are also in good agreement with molecular dynamics (MD) simulations. Sheared copper precipitates (2.5 nm in diameter) are shown to lose some of their resistance to dislocation motion after they are cut by leading dislocations in a pileup. Successive cutting of precipitates by the passage of a dislocation pileup reduces the resistance to about half its original value, when the number of dislocations in the pileup exceeds about 10. The transition from the shearable precipitate regime to the Orowan looping regime occurs for precipitate-to-matrix elastic modulus ratios above approximately 3-4, with some dependence on the precipitate size. The effects of precipitate size, spacing, and elastic modulus mismatch with the host matrix on the critical shear stress (CSS) to dislocation motion are presented.

  14. Dislocation morphology in deformed and irradiated niobium. [Neutron irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Chang, C. P.

    1977-06-01

    Niobium foils of moderate purity were examined for the morphology of dislocations or defect clusters in the deformed or neutron-irradiated state by transmission electron microscopy. New evidence has been found for the dissociation of screw dislocations into partials on the (211) slip plane according to the Crussard mechanism: (a/2) (111) ..-->.. (a/3) (111) + (a/6) (111).

  15. Dynamics and Mechanics of Zebrafish Embryonic Tissues.

    Science.gov (United States)

    Schoetz, Eva-Maria; Burdine, R. D.; Steinberg, M. S.; Heisenberg, C.-P.; Foty, R. A.; Julicher, F.

    2008-03-01

    In early zebrafish embryonic development, complex flows of cell populations occur, which ultimately lead to the spatial organization of the three germ layers: Ectoderm, mesoderm and endoderm. Here, we study the material properties of these germ layer tissues which are important for their dynamics and spatial organization in the embryo. In general, tissues can be classified as inherently active complex fluids. However, here we present examples of observed tissue behavior, which can be described satisfactorily in terms of passive visco-elastic fluids. We determined the material properties of the germ layer tissues quantitatively and found that differences in their properties influence tissue interaction. Specifically, quantitative differences in tissue surface tension result in tissue immiscibility and cell sorting behavior analogous to that of ordinary immiscible liquids. Surface tensions were measured with a tissue surface tensiometer. Furthermore, by tracking individual cells in the developing zebrafish embryo, we found differences in the migratory behavior of the different tissue types, which are, to some extent, governed by their mechanical properties. Finally, we generated a 3D velocity flow profile describing the tissue movements during zebrafish embryonic organizer development.

  16. A molecular dynamics investigation on the crizotinib resistance mechanism of C1156Y mutation in ALK

    Energy Technology Data Exchange (ETDEWEB)

    Sun, Hui-Yong [Shandong University of Technology, Zibo 255049 (China); Ji, Feng-Qin, E-mail: fengqinji@mail.hzau.edu.cn [National Key Laboratory of Crop Genetic Improvement, College of Life Science and Technology, Huazhong Agricultural University, Wuhan 430070 (China); Center for Bioinformatics, Huazhong Agricultural University, Wuhan 430070 (China)

    2012-06-29

    Highlights: Black-Right-Pointing-Pointer The study revealed the detailed resistance mechanism of the non-active mutation C1156Y in ALK. Black-Right-Pointing-Pointer C1156Y leads to crizotinib displacement and conformational changes in the binding cavity. Black-Right-Pointing-Pointer The conformations cause a decline in the vdW and electrostatic energy between crizotinib and ALK. -- Abstract: Crizotinib is an anaplastic lymphoma kinase (ALK) inhibitor that has recently been approved in the US for the treatment of non-small cell lung carcinoma (NSCLC). Despite its outstanding safety and efficacy, several resistant mutations against crizotinib have been detected in the treatment of NSCLC. However, in contrast to the widely accepted mechanism of steric hindrance by mutations at the active site, the mechanism by which the C1156Y non-active site mutation confers resistance against crizotinib remains unclear. In the present study, the resistance mechanism of C1156Y in ALK was investigated using molecular dynamics simulations. The results suggest that despite the non-active site mutation, C1156Y causes the dislocation of crizotinib as well as the indirect conformational changes in the binding cavity, which results in a marked decrease in the van der Waals and electrostatic interactions between crizotinib and ALK. The obtained results provide a detailed explanation of the resistance caused by C1156Y and may give a vital clue for the design of drugs to combat crizotinib resistance.

  17. Effective dislocation lines in continuously dislocated crystals. III. Kinematics

    CERN Document Server

    Trzesowski, Andrzej

    2007-01-01

    A class of congruences of principal Volterra-type effective dislocation lines associated with a dislocation density tensor is distinguished in order to investigate the kinematics of continuized defective crystals in terms of their dislocation densities (tensorial as well as scalar). Moreover, it shown, basing oneself on a formula defining the mean curvature of glide surfaces for principal edge effective dislocation lines, that the considered kinematics of continuized defective crystals is consistent with some relations appearing in the physical theory of plasticity (e.g. with the Orowan-type kinematic relations and with the treatment of shear stresses as driving stresses of moving dislocations).

  18. Dislocation evolution with rheological forming of metal

    Institute of Scientific and Technical Information of China (English)

    1999-01-01

    It is known that some internal defects exist in metal materials. Preliminary attempt to relate dislo cation evolution with metal rheological forming was done. By the attempt, it is learned that the evolution of dislocation density p( x, y, t ) is essentially the change of n independent internal variables qα (α = 1, 2, …n ) with material. The preliminary research in theory and experiments showed that dislocations piling-up could be avoided. One can improve the internal microstructure and mechanical properties of products by rheological forming method.

  19. Calculated electronic and magnetic structure of screw dislocations in alpha iron

    Energy Technology Data Exchange (ETDEWEB)

    Odbadrakh, K.; Rusanu, A.; Stocks, G. Malcolm; Samolyuk, G. D.; Eisenbach, M.; Wang, Yang; Nicholson, D. M.

    2011-01-01

    Local atomic magnetic moments in crystalline Fe are perturbed by the presence of dislocations. The effects are most pronounced near the dislocation core and decay slowly as the strain field of the dislocation decreases with distance. We have calculated local moments using the locally self-consistent multiple scattering (LSMS) method for a supercell containing a screw-dislocation quadrupole. Finite size effects are found to be significant indicating that dislocation cores affect the electronic structure and magnetic moments of neighboring dislocations. The influence of neighboring dislocations points to a need to study individual dislocations from first principles just as they appear amid surrounding atoms in large-scale classical force field simulations. An approach for the use of the LSMS to calculate local moments in subvolumes of large atomic configurations generated in the course of classical molecular dynamics simulation of dislocationdynamics is discussed.

  20. The effect of structural defects in SiC particles on the static & dynamic mechanical response of a 15 volume percent SiC/6061-Al matrix composite

    Energy Technology Data Exchange (ETDEWEB)

    Vaidya, R.U.; Song, S.G.; Zurek, A.K.; Gray, G.T. III

    1995-09-01

    Static and Dynamic mechanical tests, and microstructural examinations performed on a SiC particle reinforced 6061-Al matrix composite indicated that particle cracking significantly affected the strength, strain hardening, and failure mechanism of the composite. Cracks were observed to nucleate and propagate on stacking faults and interfaces between the various phases within the reinforcing SiC particles. Planar defects were the predominant artifacts seen in the SiC particles. Partial dislocations were also observed bounding the stacking faults within the reinforcement phase.

  1. Traumatic Dislocation of the Elbow Joint

    NARCIS (Netherlands)

    J. de Haan (Jeroen)

    2011-01-01

    textabstractThis thesis addresses the major issues encountered in the diagnosis and treatment of adult elbow dislocation. Firstly, a literary review (Chapters Five and Eight) makes it clear that there is much uncertainty regarding trauma mechanism, biomechanics, and even anatomy (Chapter Two). Furth

  2. Self-force on dislocation segments in anisotropic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Fitzgerald, S P [EURATOM/CCFE Fusion Association, Culham Science Centre, Abingdon, Oxon OX14 3DB (United Kingdom); Aubry, S, E-mail: steve.fitzgerald@ccfe.ac.u [Department of Mechanical Engineering, Stanford University, Stanford, CA (United States)

    2010-07-28

    A dislocation segment in a crystal experiences a 'self-force', by virtue of the orientation dependence of its elastic energy. If the crystal is elastically isotropic, this force is manifested as a couple acting to rotate the segment toward the lower energy of the pure screw orientation (i.e. acting to align the dislocation line with its Burgers vector). If the crystal is anisotropic, there are additional contributions to the couple, arising from the more complex energy landscape of the lattice itself. These effects can strongly influence the dynamic evolution of dislocation networks, and via their governing role in dislocation multiplication phenomena, control plastic flow in metals. In this paper we develop a model for dislocation self-forces in a general anisotropic crystal, and briefly consider the technologically important example of {alpha}-iron, which becomes increasingly anisotropic as the temperature approaches that of the {alpha}-{gamma} phase transition at 912 {sup 0}C.

  3. First Carpometacarpal Joint Dislocation and Review of Literatures

    Directory of Open Access Journals (Sweden)

    Farivar Lahiji

    2015-09-01

    Full Text Available Dislocation of the first carpometacarpal (CMC is a rare occurrence. Treatment of this dislocation varies from closed reduction and casting to ligament repair. Neglected dislocation or incomplete reduction of the 1st CMC cause chronic instability and painful arthritis, muscle imbalance and decreased grip force. In our study 6 patients is evaluated that were visited in less than 24 hours from their injury. All were primarily reduced and except one patient later injured ligament were repaired. All patient after 6 months had normal range of motion without pain and they had not any complaint. Stability at the 1st CMC joint is dependent on static and dynamic forces. However, dislocation of the 1st CMC occur rare, but important function of the thumb specially in gripping and grasping makes it a significant problem. Injured ligament should repair for increased stability of 1st CMC joint, because neglected dislocation or incomplete reduction cause chronic instability and painful arthritis.

  4. Arthroscopic findings after shoulder dislocation

    Directory of Open Access Journals (Sweden)

    Medenica Ivica

    2009-01-01

    Full Text Available Background/Aim. Recurrent instability of the shoulder joint is frequently difficult to differentiate from diseased or injured rotator cuff or tendon of the forearm flexor (m. biceps brachii. Shoulder joint arthroscopy has been only recently introduced into instable shoulder joint lesion examination. The aim of this study was to present and analyze an arthroscopic finding on instable shoulder joint in order to determine causes and mechanisms of instability, as well as principles of surgical treatment. Methods. Arthroscopy of the shoulder joint was performed in 158 patients with at least one documented shoulder joint dislocation. These patients were divided into two groups. The group I included the patients with one to three dislocations, while the group II those with more than three dislocations. Preoperative diagnosis was based on anamnestic data and clinical examination using specific tests, and on the diagnosis of shoulder joint using radiography or computed tomography. Results. Out of the total number of the patients 138 (87.34% had injury of the anterior patellar brim, 119 (75.32% had failure of the anterior capsule, 126 (79.75% had compressive cartilage injury of the posterior part of the head of the upper arm bone (Hill-Sachs lesion, 102 (64.56% had insufficiency of glenohumeral tendon, 11 (6.96 had complete cut of the rotator cuff, 23 (14.56% had injury of the posterior patellar brim, 12 (7.59% had injury of the upper anterior-posterior patellar brim (SLAP. Conclusion. According to the obtained results it could be concluded that there is no a unique injury that leads to shoulder joint instability. It is necessary to point out to the significance of anamnesis and clinical examination in making diagnosis. Arthroscopic diagnostics is indicated in clinically unreliable findings as an additional method for determining operative treatment.

  5. A thermal-mechanical constitutive model for b-HMX single crystal and cohesive interface under dynamic high pressure loading

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    Due to the significant thermal-mechanical effects during hot spot formation in PBX explosives,a thermodynamic constitutive model has been constructed for HMX anisotropic single crystal subjected to dynamic impact loading. The crystal plasticity model based on dislocation dynamics theory was employed to describe the anisotropic plastic behavior along the preferential slip systems. A modified equation of state (EOS) was introduced into the constitutive equations through the decomposing stress tensor and the nonlinear elasticity for materials was taken into account. The one-dimensional strain impact simulations for HMX single crystal and quasi-bicrystal were performed respectively,in which the cohesive elements were inserted over the interface areas for the latter. The predicted particle velocities for the single crystal sample agreed well with the experimental results in the literature. Furthermore,the effects of crystal orientations,interface,misorientations on localized strain,stress and temperature distributions were predicted and discussed.

  6. Kinetic Interaction of Uranium Vacancies and Dislocations in UO2

    Energy Technology Data Exchange (ETDEWEB)

    Uberuaga, Blas P. [Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Goyal, Anuj [Univ. of Florida, Gainesville, FL (United States); Subramanian, Gopinath [Univ. of South Mississippi, Hattiesburg, MS (United States); Andersson, Anders David [Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

    2016-10-25

    Understanding how point defects and defect clusters interact with dislocations in urania is important for a number of phenomena. For example, dislocations are one (of many) trap sites in the fuel where fission gases may accumulate and ultimately nucleate fission gas bubbles. Further, some creep mechanisms are governed by the flow of point defects to dislocations. Thus, for a variety of reasons, it is important to examine how dislocations attract and accelerate the kinetics of point defects.

  7. Thermal activation of dislocations in large scale obstacle bypass

    Science.gov (United States)

    Sobie, Cameron; Capolungo, Laurent; McDowell, David L.; Martinez, Enrique

    2017-08-01

    Dislocation dynamics simulations have been used extensively to predict hardening caused by dislocation-obstacle interactions, including irradiation defect hardening in the athermal case. Incorporating the role of thermal energy on these interactions is possible with a framework provided by harmonic transition state theory (HTST) enabling direct access to thermally activated reaction rates using the Arrhenius equation, including rates of dislocation-obstacle bypass processes. Moving beyond unit dislocation-defect reactions to a representative environment containing a large number of defects requires coarse-graining the activation energy barriers of a population of obstacles into an effective energy barrier that accurately represents the large scale collective process. The work presented here investigates the relationship between unit dislocation-defect bypass processes and the distribution of activation energy barriers calculated for ensemble bypass processes. A significant difference between these cases is observed, which is attributed to the inherent cooperative nature of dislocation bypass processes. In addition to the dislocation-defect interaction, the morphology of the dislocation segments pinned to the defects play an important role on the activation energies for bypass. A phenomenological model for activation energy stress dependence is shown to describe well the effect of a distribution of activation energies, and a probabilistic activation energy model incorporating the stress distribution in a material is presented.

  8. System dynamics an introduction for mechanical engineers

    CERN Document Server

    Seeler, Karl A

    2014-01-01

    This essential textbook takes the student from the initial steps in modeling a dynamic system through development of the mathematical models needed for feedback control.  The generously-illustrated, student-friendly text focuses on fundamental theoretical development rather than the application of commercial software.  Practical details of machine design are included to motivate the non-mathematically inclined student. This book also: Emphasizes the linear graph method for modeling dynamic systems Offers a systematic approach for creating an engineering model, extracting information, and formulating mathematical analyses Adopts a unifying theme of power flow as the dynamic agent that eases analysis of hybrid systems, such as machinery Presents differential equations as dynamic operators and stresses input/output relationships Introduces Mathcad and programming in MATLAB Allows for use of Open Source Computational Software (R or C) Features over 1000 illustrations

  9. Effect of dislocation blocking on fracture behavior of Al and {alpha}-Fe: a multiscale study

    Energy Technology Data Exchange (ETDEWEB)

    Noronha, S.J.; Farkas, D

    2004-01-25

    We use a multiscale approach in which results from atomistic simulations are combined with discrete dislocation (DD) dynamics simulations of crack-tip plasticity. The method is used to study the effects of dislocation blocking on the fracture behavior of {alpha}-iron and aluminum. We studied the effects of blocking for distances ranging from 5 nm to 1 mm and find that the fracture resistance is increased with increasing blocking distance. The atomistic and dislocation dynamics simulations show that the blocking of dislocations causes a net decrease in the shear stress projected on the slip plane, preventing further dislocation emission. Semi-brittle cleavage occurs after a certain number of dislocations are emitted, explicitly demonstrating the embrittling effects of dislocation blocking. This effect can contribute to the brittle behavior observed in some nanocrystalline metals.

  10. Dynamics modeling and simulation of mechanism with joint clearance

    Institute of Scientific and Technical Information of China (English)

    BAI Zheng-feng; TIAN Hao; ZHAO Yang

    2010-01-01

    The existence of clearance in the joints of mechanisms system is inevitable.The movements of the real mechanism are deftection from the ideal mechanism due to the clearances and the motion accuracv is decreased.The effects of the hinge clearance on the crank and rocker mechanism system are studied.The svstem dynamics equation with clearance is presented.The contact dynamics model is established using the nonlinear equivalent spring-damp model and the friction effect is considered by using Coulomb friction model.Then the models are incorporated into ADAMS,and based on the model,large numbers numeric simulations are made.The regularity of contact forces in clearance are studied in detail.And the effects of clearance size.clearance friction on the mechanism dynamics characteristic are analyzed.The simulation resuhs Can predict the effects of clearance on the mechanism dynamics characteristic preferably.

  11. Multibody dynamic simulation of knee contact mechanics.

    Science.gov (United States)

    Bei, Yanhong; Fregly, Benjamin J

    2004-11-01

    Multibody dynamic musculoskeletal models capable of predicting muscle forces and joint contact pressures simultaneously would be valuable for studying clinical issues related to knee joint degeneration and restoration. Current three-dimensional multibody knee models are either quasi-static with deformable contact or dynamic with rigid contact. This study proposes a computationally efficient methodology for combining multibody dynamic simulation methods with a deformable contact knee model. The methodology requires preparation of the articular surface geometry, development of efficient methods to calculate distances between contact surfaces, implementation of an efficient contact solver that accounts for the unique characteristics of human joints, and specification of an application programming interface for integration with any multibody dynamic simulation environment. The current implementation accommodates natural or artificial tibiofemoral joint models, small or large strain contact models, and linear or nonlinear material models. Applications are presented for static analysis (via dynamic simulation) of a natural knee model created from MRI and CT data and dynamic simulation of an artificial knee model produced from manufacturer's CAD data. Small and large strain natural knee static analyses required 1 min of CPU time and predicted similar contact conditions except for peak pressure, which was higher for the large strain model. Linear and nonlinear artificial knee dynamic simulations required 10 min of CPU time and predicted similar contact force and torque but different contact pressures, which were lower for the nonlinear model due to increased contact area. This methodology provides an important step toward the realization of dynamic musculoskeletal models that can predict in vivo knee joint motion and loading simultaneously.

  12. Dislocation of primary total hip arthroplasty and the risk of redislocation.

    LENUS (Irish Health Repository)

    Brennan, Stephen A

    2012-09-01

    6554 primary total hip arthroplasties were reviewed. Risk factors for dislocation were analysed to assess which were important in terms of predicting recurrent instability. The patients risk of having a second dislocation was independently associated with the surgical approach adopted (p = 0.03) and the time to first dislocation from the primary hip replacement (p = 0.002). Early dislocators whose surgery was performed through an anterolateral approach had less recurrence than late dislocators through a posterior or transtrochanteric approach. None of the other risk factors including head size (p = 0.59), modularity (p = 0.54), mechanism of dislocation (p = 0.23), leg length discrepancy (p = 0.69) and acetabular inclination (p = 0.31) were influential. The use of an abduction brace was not useful in preventing a further dislocation with 69.2% of those braced re-dislocating compared to 68.5% who were not braced (p = 0.96).

  13. High purity ultrafine-grained nickel processed by dynamic plastic deformation: microstructure and mechanical properties

    Energy Technology Data Exchange (ETDEWEB)

    Farbaniec, Lukasz; Dirras, Guy [Universite Paris 13, Sorbonne Paris Cite LSPM-CNRS, 99, Avenue J. B. Clement, 93430 Villetaneuse (France); Abdul-Latif, Akrum [Laboratoire d' Ingenierie des Systemes Mecaniques et des Materiaux 3, Rue Fernand Hainaut, 93407 St. Ouen Cedex (France); Gubicza, Jeno [Department of Materials Physics, Eoetvoes Lorand University Budapest, P.O. Box 32, H-1518 (Hungary)

    2012-11-15

    Bulk ultrafine-grained samples are processed by dynamic plastic deformation at an average strain rate of 3.3 x 10{sup 2} s{sup -1} from bulk coarse-grained nickel with purity higher than 98.4 wt.%. The obtained microstructure is investigated by electron backscattering diffraction, transmission electron microscopy and X-ray line profile analysis. After dynamic deformation the microstructure evolves into submicron-size lamellar and subgrain structures. Evaluation of average grain size shows a heterogeneous microstructure along both the diameter and the thickness of the sample. X-ray line profile analysis reveals high dislocation density of about 13 {+-} 2 x 10{sup 14} m{sup -2} in the impacted material. The mechanical properties are investigated by means of uniaxial quasi-static compression tests conducted at room temperature. The stress-strain behavior of the impacted Ni depends on the location in the impacted disk and on the orientation of the compression axis relative to the impact direction. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  14. Mechanical sensitivity reveals evolutionary dynamics of mechanical systems.

    Science.gov (United States)

    Anderson, P S L; Patek, S N

    2015-04-07

    A classic question in evolutionary biology is how form-function relationships promote or limit diversification. Mechanical metrics, such as kinematic transmission (KT) in linkage systems, are useful tools for examining the evolution of form and function in a comparative context. The convergence of disparate systems on equivalent metric values (mechanical equivalence) has been highlighted as a source of potential morphological diversity under the assumption that morphology can evolve with minimal impact on function. However, this assumption does not account for mechanical sensitivity-the sensitivity of the metric to morphological changes in individual components of a structure. We examined the diversification of a four-bar linkage system in mantis shrimp (Stomatopoda), and found evidence for both mechanical equivalence and differential mechanical sensitivity. KT exhibited variable correlations with individual linkage components, highlighting the components that influence KT evolution, and the components that are free to evolve independently from KT and thereby contribute to the observed pattern of mechanical equivalence. Determining the mechanical sensitivity in a system leads to a deeper understanding of both functional convergence and morphological diversification. This study illustrates the importance of multi-level analyses in delineating the factors that limit and promote diversification in form-function systems. © 2015 The Author(s) Published by the Royal Society. All rights reserved.

  15. Modeling of dislocation generation and interaction during high-speed deformation of metals

    DEFF Research Database (Denmark)

    Schiøtz, J.; Leffers, T.; Singh, B.N.

    2002-01-01

    at very high strain rates. We have used molecular-dynamics simulations to investigate high-speed deformation of copper crystals. Even though no pre-existing dislocation sources are present in the initial system, dislocations are quickly nucleated and a very high dislocation density is reached during...... the deformation. Due to the high density of dislocations, many inelastic interactions occur between dislocations, resulting in the generation of vacancies. After the deformation, a very high density of vacancies is observed, in agreement with the experimental observations. The processes responsible...

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

    Science.gov (United States)

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

    1992-01-01

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

  17. Fast, vacancy-free climb of prismatic dislocation loops in bcc metals

    Science.gov (United States)

    Swinburne, Thomas D.; Arakawa, Kazuto; Mori, Hirotaro; Yasuda, Hidehiro; Isshiki, Minoru; Mimura, Kouji; Uchikoshi, Masahito; Dudarev, Sergei L.

    2016-08-01

    Vacancy-mediated climb models cannot account for the fast, direct coalescence of dislocation loops seen experimentally. An alternative mechanism, self climb, allows prismatic dislocation loops to move away from their glide surface via pipe diffusion around the loop perimeter, independent of any vacancy atmosphere. Despite the known importance of self climb, theoretical models require a typically unknown activation energy, hindering implementation in materials modeling. Here, extensive molecular statics calculations of pipe diffusion processes around irregular prismatic loops are used to map the energy landscape for self climb in iron and tungsten, finding a simple, material independent energy model after normalizing by the vacancy migration barrier. Kinetic Monte Carlo simulations yield a self climb activation energy of 2 (2.5) times the vacancy migration barrier for 1/2 () dislocation loops. Dislocation dynamics simulations allowing self climb and glide show quantitative agreement with transmission electron microscopy observations of climbing prismatic loops in iron and tungsten, confirming that this novel form of vacancy-free climb is many orders of magnitude faster than what is predicted by traditional climb models. Self climb significantly influences the coarsening rate of defect networks, with important implications for post-irradiation annealing.

  18. Fast, vacancy-free climb of prismatic dislocation loops in bcc metals.

    Science.gov (United States)

    Swinburne, Thomas D; Arakawa, Kazuto; Mori, Hirotaro; Yasuda, Hidehiro; Isshiki, Minoru; Mimura, Kouji; Uchikoshi, Masahito; Dudarev, Sergei L

    2016-08-23

    Vacancy-mediated climb models cannot account for the fast, direct coalescence of dislocation loops seen experimentally. An alternative mechanism, self climb, allows prismatic dislocation loops to move away from their glide surface via pipe diffusion around the loop perimeter, independent of any vacancy atmosphere. Despite the known importance of self climb, theoretical models require a typically unknown activation energy, hindering implementation in materials modeling. Here, extensive molecular statics calculations of pipe diffusion processes around irregular prismatic loops are used to map the energy landscape for self climb in iron and tungsten, finding a simple, material independent energy model after normalizing by the vacancy migration barrier. Kinetic Monte Carlo simulations yield a self climb activation energy of 2 (2.5) times the vacancy migration barrier for 1/2〈111〉 (〈100〉) dislocation loops. Dislocation dynamics simulations allowing self climb and glide show quantitative agreement with transmission electron microscopy observations of climbing prismatic loops in iron and tungsten, confirming that this novel form of vacancy-free climb is many orders of magnitude faster than what is predicted by traditional climb models. Self climb significantly influences the coarsening rate of defect networks, with important implications for post-irradiation annealing.

  19. Effect of segregated elements on the interactions between twin boundaries and screw dislocations in Mg

    Science.gov (United States)

    Yoshida, Takashi; Yuasa, Motohiro; Mabuchi, Mamoru; Chino, Yasumasa

    2015-07-01

    Interactions of { 10 1 ¯ 2 } and { 10 1 ¯ 1 } twin boundaries (TBs), segregated by X (X = Sc, Y, or Nd), with screw partial dislocations were simulated using molecular dynamics (MD). In addition, mechanical tests were carried out on pure Mg and Mg-Y alloy. The MD simulation results suggested that the dislocations passed through the { 10 1 ¯ 2 } TB in all the models and that the shear strains for transmission in the Mg-X models were larger than that in the pure Mg model; in particular, the shear strain in the Mg-Y model was the largest. This corresponded to the experimental result that strain hardening was enhanced by Y addition. For interactions of a { 10 1 ¯ 1 } TB, some segregated atoms induced the emission of dislocations from the TB, whereas other segregated atoms locked the dislocation absorbed in the TB. As a result, the interaction behaviors of the { 10 1 ¯ 1 } TB were divided into five patterns. The interactions of this TB could be explained by the criterion of energy variations, as well as the interactions, of the { 10 1 ¯ 2 } TB, although segregation complicated the interactions of the { 10 1 ¯ 1 } TB.

  20. Damping mechanisms and models in structural dynamics

    DEFF Research Database (Denmark)

    Krenk, Steen

    2002-01-01

    Several aspects of damping models for dynamic analysis of structures are investigated. First the causality condition for structural response is used to identify rules for the use of complex-valued frequency dependent material models, illustrated by the shortcomings of the elastic hysteretic model...

  1. Bridging Atomistic/Continuum Scales in Solids with Moving Dislocations

    Institute of Scientific and Technical Information of China (English)

    TANG Shao-Qiang; LIU Wing K.; KARPOV Eduard G.; HOU Thomas Y.

    2007-01-01

    @@ We propose a multiscale method for simulating solids with moving dislocations. Away from atomistic subdomains where the atomistic dynamics are fully resolved, a dislocation is represented by a localized jump profile, superposed on a defect-free field. We assign a thin relay zone around an atomistic subdomain to detect the dislocation profile and its propagation speed at a selected relay time. The detection technique utilizes a lattice time history integral treatment. After the relay, an atomistic computation is performed only for the defect-free field. The method allows one to effectively absorb the fine scale fluctuations and the dynamic dislocations at the interface between the atomistic and continuum domains. In the surrounding region, a coarse grid computation is adequate.

  2. Dynamic Evolution Equations for Isolated Smoke Vortexes in Rational Mechanics

    CERN Document Server

    Jianhua, Xiao

    2011-01-01

    Smoke circle vortexes are a typical dynamic phenomenon in nature. The similar circle vortexes phenomenon appears in hurricane, turbulence, and many others. A semi-empirical method is constructed to get some intrinsic understanding about such circle vortex structures. Firstly, the geometrical motion equations for smoke circle is formulated based on empirical observations. Based on them, the mechanic dynamic motion equations are established. Finally, the general dynamic evolution equations for smoke vortex are formulated. They are dynamic evolution equations for exact stress field and dynamic evolution equations for average stress field. For industrial application and experimental data processing, their corresponding approximation equations for viscous fluid are given. Some simple discussions are made.

  3. Biomechanical and dynamic mechanism of locust take-off

    Science.gov (United States)

    Chen, Dian-Sheng; Yin, Jun-Mao; Chen, Ke-Wei; Li, Zhen

    2014-10-01

    The biomimetic locust robot hopping vehicle has promising applications in planet exploration and reconnaissance. This paper explores the bionic dynamics model of locust jumping by using high-speed video and force analysis. This paper applies hybrid rigid-flexible mechanisms to bionic locust hopping and studies its dynamics with emphasis laid on the relationship between force and jumping performance. The hybrid rigid-flexible model is introduced in the analysis of locust mechanism to address the principles of dynamics that govern locust joints and mechanisms during energy storage and take-off. The dynamic response of the biomimetic mechanism is studied by considering the flexibility according to the locust jumping dynamics mechanism. A multi-rigid-body dynamics model of locust jumping is established and analyzed based on Lagrange method; elastic knee and tarsus mechanisms that were proposed in previous works are analyzed alongside the original bionic joint configurations and their machinery principles. This work offers primary theories for take-off dynamics and establishes a theoretical basis for future studies and engineering applications.

  4. Dynamical seesaw mechanism for Dirac neutrinos

    Directory of Open Access Journals (Sweden)

    José W.F. Valle

    2016-04-01

    Full Text Available So far we have not been able to establish that, as theoretically expected, neutrinos are their own anti-particles. Here we propose a dynamical way to account for the Dirac nature of neutrinos and the smallness of their mass in terms of a new variant of the seesaw paradigm in which the energy scale of neutrino mass generation could be accessible to the current LHC experiments.

  5. The framework for simulation of dynamics of mechanical aggregates

    OpenAIRE

    Ivankov, Petr R.; Ivankov, Nikolay P.

    2007-01-01

    A framework for simulation of dynamics of mechanical aggregates has been developed. This framework enables us to build model of aggregate from models of its parts. Framework is a part of universal framework for science and engineering.

  6. Dynamic Evolution Equations for Isolated Smoke Vortexes in Rational Mechanics

    OpenAIRE

    2011-01-01

    Smoke circle vortexes are a typical dynamic phenomenon in nature. The similar circle vortexes phenomenon appears in hurricane, turbulence, and many others. A semi-empirical method is constructed to get some intrinsic understanding about such circle vortex structures. Firstly, the geometrical motion equations for smoke circle is formulated based on empirical observations. Based on them, the mechanic dynamic motion equations are established. Finally, the general dynamic evolution equations for ...

  7. Infinite-dimensional dynamical systems in mechanics and physics

    CERN Document Server

    Temam, Roger

    1997-01-01

    In this book the author presents the dynamical systems in infinite dimension, especially those generated by dissipative partial differential equations This book attempts a systematic study of infinite dimensional dynamical systems generated by dissipative evolution partial differential equations arising in mechanics and physics and in other areas of sciences and technology This second edition has been updated and extended

  8. Dynamics and Control of a Class of Underactuated Mechanical Systems

    OpenAIRE

    Reyhanoglu, Mahmut; van der Schaft, Arjan; McClamroch, N. Harris; Kolmanovsky, Ilya

    1999-01-01

    This paper presents a theoretical framework for the dynamics and control of underactuated mechanical systems, defined as systems with fewer inputs than degrees of freedom. Control system formulation of underactuated mechanical systems is addressed and a class of underactuated systems characterized by nonintegrable dynamics relations is identified. Controllability and stabilizability results are derived for this class of underactuated systems. Examples are included to illustrate the results; t...

  9. Introduction: Collective dynamics of mechanical oscillators and beyond

    Science.gov (United States)

    Belykh, Igor V.; Porfiri, Maurizio

    2016-11-01

    This focus issue presents a collection of research papers from a broad spectrum of topics related to the modeling, analysis, and control of mechanical oscillators and beyond. Examples covered in this focus issue range from bridges and mechanical pendula to self-organizing networks of dynamic agents, with application to robotics and animal grouping. This focus issue brings together applied mathematicians, physicists, and engineers to address open questions on various theoretical and experimental aspects of collective dynamics phenomena and their control.

  10. Dynamical Ensembles in Nonequilibrium Statistical Mechanics

    Energy Technology Data Exchange (ETDEWEB)

    Gallavotti, G.; Cohen, E.G.D. [Dipartimento di Fisica, Universita di Roma, La Sapienza, 00185 Roma (Italy)]|[The Rockefeller University, New York, New York 10021 (United States)

    1995-04-03

    Ruelle`s principle for turbulence leading to what is usually called the Sinai-Ruelle-Bowen (SRB) distribution is applied to the statistical mechanics of many particle systems in nonequilibrium stationary states. A specific prediction, obtained without the need to construct explicitly the SRB itself, is shown to be in agreement with a recent computer experiment on a strongly sheared fluid. This presents the first test of the principle on a many particle system far from equilibrium. A possible application to fluid mechanics is also discussed.

  11. Dislocation nucleation and vacancy formation during high-speed deformation of fcc metals

    DEFF Research Database (Denmark)

    Schiøtz, J.; Leffers, T.; Singh, B.N.

    2001-01-01

    dislocation densities in the foils after deformation. This was interpreted as evidence for a new dislocation-free deformation mechanism, resulting in a very high vacancy production rate. In this paper we investigate this proposition using large-scale computer simulations of bulk and thin films of copper......Recently, a dislocation-free deformation mechanism was proposed by Kiritani et al. on the basis of a series of experiments where thin foils of fee metals were deformed at very high strain rates. In the experimental study, they observed a large density of stacking fault tetrahedra but very low....... The dislocations are nucleated as single Shockley partials. The large stresses required before dislocations are nucleated result in a very high dislocation density, and therefore in many inelastic interactions between the dislocations. These interactions create vacancies and a very large vacancy concentration...

  12. Dynamics formulas and problems : engineering mechanics 3

    CERN Document Server

    Gross, Dietmar; Wriggers, Peter; Schröder, Jörg; Müller, Ralf

    2017-01-01

    This book contains the most important formulas and more than 190 completely solved problems from Kinetics and Hydrodynamics. It provides engineering students material to improve their skills and helps to gain experience in solving engineering problems. Particular emphasis is placed on finding the solution path and formulating the basic equations. Topics include: - Kinematics of a Point - Kinetics of a Point Mass- Dynamics of a System of Point Masses - Kinematics of Rigid Bodies - Kinetics of Rigid Bodies - Impact - Vibrations - Non-Inertial Reference Frames - Hydrodynamics .

  13. Mechanisms and dynamic of domestic violence

    Directory of Open Access Journals (Sweden)

    Abidovic Amela

    2013-12-01

    Full Text Available The most common synonyms for term family are: love, support, understanding, warmness, etc. The family should present the place of the most protected living where each its member gets everything what he/she needs for undisturbed psychological and physical growth. However, sometimes it isn't like that and the family present the place of violence, harassment and neglecting. Unfortunately, domestic violence is as old as the human being. Special mechanisms and tactics of harassment are built through history. They succeeded to make the domestic violence hidden and away from detailed socio-psyhological researches and practical interventions for so long. The aim of this work is to inspire experts' attention to more often phenomenon of domestic violence, and the need for more detailed analysis of mechanisms which determine appearance and maintenance of violence, and all this with intention to find out the most adequate solution in prevention of this social problem.

  14. Hygrothermal effect of bamboo by dynamic mechanical analysis

    Institute of Scientific and Technical Information of China (English)

    GUAN Mingjie; ZHANG Qisheng

    2006-01-01

    Dynamic properties of bamboo,Phyllostachys pubescens,with moisture content (MC) ranging from -130 to 130℃,were studied by dynamic mechanical analysis (DMA).The results showed that the hygrothermal effect on dynamic mechanical properties was negative.The storage modulus decreases with increasing temperature and MC,and glass transition temperature decreases with increasing MC.The glass transition temperature and tan delta of bamboo were 30.5℃,0.02 and 10.61℃,0.04,when MC was 10% and 34%,respectively.

  15. MECHANICAL CHARACTERISTICS OF DYNAMIC CLIMBING ROPES

    Directory of Open Access Journals (Sweden)

    Stojan Burnik

    2011-08-01

    Full Text Available Climbing rope is certainly one of the most important pieces of climbing equipment. On market there are many manufacturers of dynamic climbing ropes and even more of their products. All the ropes meet the requirements of the standards, which ensure that the ropes are safe enough for use in climbing. However the requirements are set only under certain conditions. In reality climbing ropes are exposed to various conditions that are many times different to those set by the standards. Consequently there are many different falls, which lead to very different loads of impact. By using appropriate method of testing rope samples made by three different manufacturers we discovered that there are differences between all three manufacturers. This leads us to a suggestion that standards should be improved.

  16. A New Dynamical Evolutionary Algorithm Based on Statistical Mechanics

    Institute of Scientific and Technical Information of China (English)

    LI YuanXiang(李元香); ZOU XiuFen(邹秀芬); KANG LiShan(康立山); Zbigniew Michalewicz

    2003-01-01

    In this paper, a new dynamical evolutionary algorithm (DEA) is presented basedon the theory of statistical mechanics. The novelty of this kind of dynamical evolutionary algorithmis that all individuals in a population (called particles in a dynamical system) are running andsearching with their population evolving driven by a nev selecting mechanism. This mechanismsimulates the principle of molecular dynamics, which is easy to design and implement. A basictheoretical analysis for the dynamical evolutionary algorithm is given and as a consequence twostopping criteria of the algorithm are derived from the principle of energy minimization and the lawof entropy increasing. In order to verify the effectiveness of the scheme, DEA is applied to solvingsome typical numerical function minimization problems which are poorly solved by traditionalevolutionary algorithms. The experimental results show that DEA is fast and reliable.

  17. Visualization in Mechanics: The Dynamics of an Unbalanced Roller

    Science.gov (United States)

    Cumber, Peter S.

    2017-01-01

    It is well known that mechanical engineering students often find mechanics a difficult area to grasp. This article describes a system of equations describing the motion of a balanced and an unbalanced roller constrained by a pivot arm. A wide range of dynamics can be simulated with the model. The equations of motion are embedded in a graphical…

  18. Dynamics and control of a class of underactuated mechanical systems

    NARCIS (Netherlands)

    Reyhanoglu, Mahmut; Schaft, van der Arjan; McClamroch, N. Harris; Kolmanovsky, Ilya

    1999-01-01

    This paper presents a theoretical framework for the dynamics and control of underactuated mechanical systems, defined as systems with fewer inputs than degrees of freedom. Control system formulation of underactuated mechanical systems is addressed and a class of underactuated systems characterized b

  19. Dynamics and Control of a Class of Underactuated Mechanical Systems

    NARCIS (Netherlands)

    Reyhanoglu, Mahmut; Schaft, Arjan van der; McClamroch, N. Harris; Kolmanovsky, Ilya

    1999-01-01

    This paper presents a theoretical framework for the dynamics and control of underactuated mechanical systems, defined as systems with fewer inputs than degrees of freedom. Control system formulation of underactuated mechanical systems is addressed and a class of underactuated systems characterized b

  20. Dynamic compressive mechanical response of a soft polymer material

    NARCIS (Netherlands)

    Fan, J.T.; Weerheijm, J.; Sluys, L.J.

    2015-01-01

    The dynamic mechanical behaviour of a soft polymer material (Clear Flex 75) was studied using a split Hopkinson pressure bar (SHPB) apparatus. Mechanical properties have been determined at moderate to high strain rates. Real time deformation and fracture were recorded using a high-speed camera. Frac

  1. Visualization in Mechanics: The Dynamics of an Unbalanced Roller

    Science.gov (United States)

    Cumber, Peter S.

    2017-01-01

    It is well known that mechanical engineering students often find mechanics a difficult area to grasp. This article describes a system of equations describing the motion of a balanced and an unbalanced roller constrained by a pivot arm. A wide range of dynamics can be simulated with the model. The equations of motion are embedded in a graphical…

  2. Dislocation-Governed Plastic Deformation and Fracture Toughness of Nanotwinned Magnesium

    Directory of Open Access Journals (Sweden)

    Lei Zhou

    2015-08-01

    Full Text Available In this work, the plastic deformation mechanisms responsible for mechanical properties and fracture toughness in  nanotwinned (NT magnesium is studied by molecular dynamics (MD simulation. The influence of twin boundary (TBs spacing and crack position on deformation behaviors are investigated. The microstructure evolution at the crack tip are not exactly the same for the left edge crack (LEC and the right edge crack (REC models according to calculations of the energy release rate for dislocation nucleation at the crack tip. The LEC growth initiates in a ductile pattern and then turns into a brittle cleavage. In the REC model, the atomic decohesion occurs at the crack tip to create a new free surface which directly induces a brittle cleavage. A ductile to brittle transition is observed which mainly depends on the competition between dislocation motion and crack growth. This competition mechanism is found to be correlated with the TB spacing. The critical values are 10 nm and 13.5 nm for this transition in LEC and REC models, respectively. Essentially, the dislocation densities affected by the TB spacing play a crucial role in the ductile to brittle transition.

  3. Electronic structure of edge dislocation of core-doped Ti in Fe

    Institute of Scientific and Technical Information of China (English)

    DANG Hongli; WANG Chongyu; SHU Xiaolin

    2004-01-01

    The electronic structure of an edge dislocation doped Ti lying in the (001) plane with Burgers Vector along [100] direction in body-centered cubic iron is investigated using the first principles discrete variational method (DVM) based on the density-functional theory. The binding energy, impurity formation energy, interatomic energy, Mulliken orbital populations and charge density difference are presented in this paper. By calculating the binding energy of the clean dislocation system and the Ti-doped system, it is found that the binding energy of Ti-doped dislocation system is lower than that of the clean dislocation system, which implies that the Ti-doped dislocation system is more stable than the clean dislocation system. The calculated result of the impurity formation energy predicts the trapping effect of dislocation core for Ti, which shows that Ti atom prefers to occupy the place at the dislocation core. The calculated results of the interatomic energy and the difference charge density of dislocation doped Ti system indicate that the stronger bonding formed between the Ti impurity and its neighbor Fe atoms will affect the mechanical property of edge dislocation. Considering the influence of Ti on the electronic structure and the energies, we can predict that the trace Ti in transition metal Fe with dislocation defect can give a significant contribution to the solid solution hardening effects and will influence the mechanical property of materials.

  4. Structure, stability, and motion of dislocations in double-wall carbon nanotubes

    Institute of Scientific and Technical Information of China (English)

    Zhang Kai-Wang; Li Zhong-Qiu; Wu Jian; Peng Xiang-Yang; Tan Xin-Jun; Sun Li-Zhong; Zhong Jian-Xin

    2012-01-01

    In this paper,a novel double-wall carbon nanotube (DWCNT) with both edge and screw dislocations is studied by using the molecular dynamics (MD) method. The differences between two adjacent tubule indexes of armchair and zigzag nanotubes are determined to be 5 and 9,respectively,by taking into account the symmetry,integrality,and thermal stability of the composite structures. It is found that melting first occurs near the dislocations,and the melting temperatures of the dislocated armchair and zigzag DWCNTs are around 2600 K-2700 K.At the premelting temperatures,the shrink of the dislocation loop,which is comprised of edge and screw dislocations,implies that the composite dislocation in DWCNTs has self-healing ability.The dislocated DWCNTs first fracture at the edge dislocations,which induces the entire break in axial tensile test. The dislocated DWCNTs have a smaller fracture strength compared to the perfect DWCNTs.Our results not only match with the dislocation glide of carbon nanotubes (CNTs) in experiments,but also can free from the electron beam radiation under experimental conditions observed by the high resolution transmission electron microscope (HRTEM),which is deemed to cause the motion of dislocation loop.

  5. Structure, stability, and motion of dislocations in double-wall carbon nanotubes

    Science.gov (United States)

    Zhang, Kai-Wang; Li, Zhong-Qiu; Wu, Jian; Peng, Xiang-Yang; Tan, Xin-Jun; Sun, Li-Zhong; Zhong, Jian-Xin

    2012-10-01

    In this paper, a novel double-wall carbon nanotube (DWCNT) with both edge and screw dislocations is studied by using the molecular dynamics (MD) method. The differences between two adjacent tubule indexes of armchair and zigzag nanotubes are determined to be 5 and 9, respectively, by taking into account the symmetry, integrality, and thermal stability of the composite structures. It is found that melting first occurs near the dislocations, and the melting temperatures of the dislocated armchair and zigzag DWCNTs are around 2600 K—2700 K. At the pre-melting temperatures, the shrink of the dislocation loop, which is comprised of edge and screw dislocations, implies that the composite dislocation in DWCNTs has self-healing ability. The dislocated DWCNTs first fracture at the edge dislocations, which induces the entire break in axial tensile test. The dislocated DWCNTs have a smaller fracture strength compared to the perfect DWCNTs. Our results not only match with the dislocation glide of carbon nanotubes (CNTs) in experiments, but also can free from the electron beam radiation under experimental conditions observed by the high resolution transmission electron microscope (HRTEM), which is deemed to cause the motion of dislocation loop.

  6. Photochemical Reactions of Cyclohexanone: Mechanisms and Dynamics.

    Science.gov (United States)

    Shemesh, Dorit; Nizkorodov, Sergey A; Gerber, R Benny

    2016-09-15

    Photochemistry of carbonyl compounds is of major importance in atmospheric and organic chemistry. The photochemistry of cyclohexanone is studied here using on-the-fly molecular dynamics simulations on a semiempirical multireference configuration interaction potential-energy surface to predict the distribution of photoproducts and time scales for their formation. Rich photochemistry is predicted to occur on a picosecond time scale following the photoexcitation of cyclohexanone to the first singlet excited state. The main findings include: (1) Reaction channels found experimentally are confirmed by the theoretical simulations, and a new reaction channel is predicted. (2) The majority (87%) of the reactive trajectories start with a ring opening via C-Cα bond cleavage, supporting observations of previous studies. (3) Mechanistic details, time scales, and yields are predicted for all reaction channels. These benchmark results shed light on the photochemistry of isolated carbonyl compounds in the atmosphere and can be extended in the future to photochemistry of more complex atmospherically relevant carbonyl compounds in both gaseous and condensed-phase environments.

  7. Composite modeling method in dynamics of planar mechanical system

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    This paper presents a composite modeling method of the forward dynamics in general planar mechanical system. In the modeling process, the system dynamic model is generated by assembling the model units which are kinematical determinate in planar mechanisms rather than the body/joint units in multi-body system. A state space formulation is employed to model both the unit and system models. The validation and feasibility of the method are illustrated by a case study of a four-bar mechanism. The advantage of this method is that the models are easier to reuse and the system is easier to reconfigure. The formulation reveals the relationship between the topology and dynamics of the planar mechanism to some extent.

  8. Composite modeling method in dynamics of planar mechanical system

    Institute of Scientific and Technical Information of China (English)

    WANG Hao; LIN ZhongQin; LAI XinMin

    2008-01-01

    This paper presents a composite modeling method of the forward dynamics in general planar mechanical system.In the modeling process,the system dynamic model is generated by assembling the model units which are kinematical determi-nate in planar mechanisms rather than the body/joint units in multi-body system.A state space formulation is employed to model both the unit and system models.The validation and feasibility of the method are illustrated by a case study of a four-bar mechanism.The advantage of this method is that the models are easier to reuse and the system is easier to reconfigure.The formulation reveals the rela-tionship between the topology and dynamics of the planar mechanism to some extent.

  9. Nature of Dislocations in Silicon

    DEFF Research Database (Denmark)

    Hansen, Lars Bruno; Stokbro, Kurt; Lundqvist, Bengt

    1995-01-01

    -binding Hamiltonian that scales linearly with the number of atoms. The partial edge dislocation is found to be very accurately described by the Peierls-Nabarro dislocation model, with generalized stacking-fault restoring forces, as reflected both in the interaction energy and in the displacement field. An asymmetric...... core reconstruction provides fourfold coordination, making Si behave elastically down to atomic distances....

  10. Dynamic wormholes with particle creation mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Pan, Supriya; Chakraborty, Subenoy [Jadavpur University, Department of Mathematics, Kolkata (India)

    2015-01-01

    The present work deals with a spherically symmetric space-time which is asymptotically (at spatial infinity) FRW space-time and represents wormhole configuration: The matter component is divided into two parts - (a) dissipative but homogeneous and isotropic fluid, and (b) an inhomogeneous and anisotropic barotropic fluid. Evolving wormhole solutions are obtained when isotropic fluid is phantom in nature and there is a big rip singularity at the end. Here the dissipative phenomena is due to the particle creation mechanism in non-equilibrium thermodynamics. Using the process to be adiabatic, the dissipative pressure is expressed linearly to the particle creation rate. For two choices of the particle creation rate as a function of the Hubble parameter, the equation of state parameter of the isotropic fluid is constrained to be in the phantom domain, except in one choice, it is possible to have wormhole configuration with normal isotropic fluid. (orig.)

  11. On the nature of transverse coronal waves revealed by wavefront dislocations

    CERN Document Server

    Ariste, A López; Arregui, I; Khomenko, E; Collados, M

    2015-01-01

    Coronal waves are an important aspect of the dynamics of the plasma in the corona. Wavefront dislocations are topological features of most waves in nature and also of magnetohydrodynamic waves. Are there dislocations in coronal waves? The finding and explanation of dislocations may shed light on the nature and characteristics of the propagating waves, their interaction in the corona and in general on the plasma dynamics. We positively identify dislocations in coronal waves observed by the Coronal Multi-channel Polarimeter (CoMP) as singularities in the Doppler shifts of emission coronal lines. We study the possible singularities that can be expected in coronal waves and try to reproduce the observed dislocations in terms of localization and frequency of appearance. The observed dislocations can only be explained by the interference of a kink and a sausage wave modes propagating with different frequencies along the coronal magnetic field. In the plane transverse to the propagation, the cross-section of the osc...

  12. Insights into dynamic strain aging under cyclic creep with reference to strain burst: Some new observations and mechanisms part-II: Microstructural aspects

    Energy Technology Data Exchange (ETDEWEB)

    Sarkar, Aritra, E-mail: aritra@igcar.gov.in [Mechanical Metallurgy Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102 Tamil Nadu (India); Nagesha, A. [Mechanical Metallurgy Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102 Tamil Nadu (India); Parameswaran, P.; Murugesan, S. [Materials Synthesis and Structural Characterization Division, Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, Tamil Nadu (India); Sandhya, R.; Laha, K. [Mechanical Metallurgy Division, Indira Gandhi Centre for Atomic Research, Kalpakkam, 603102 Tamil Nadu (India)

    2016-04-13

    Cyclic creep behavior of 316LN austenitic stainless steel (SS) was investigated at 823 K at different combinations of mean stress (σ{sub m}), stress amplitude (σ{sub a}) and stress rate. Characteristic strain bursts were observed being attributed to a pronounced influence of dynamic strain aging (DSA). Detailed microstructural investigation carried out through transmission electron microscope (TEM) revealed that dislocation substructure evolving under a process of strain burst during cyclic creep mainly consists of planar deformation bands. The number density of bands was found to be strongly sensitive to σ{sub m}- σ{sub a}-stress rate combination employed. An important substructural feature found in this study was the formation of microtwins. Either planar slip or twinning was found to dominate the substructure depending on the loading combination, which was demonstrated through a dislocation distribution map. Dislocation substructure was further correlated with evolution of surface relief studied through atomic force microscopy (AFM) and field emission gun-scanning electron microscopy (FEG-SEM), which depicts the formation of slip markings and nucleation of cracks from persistent slip markings during the course of a strain burst. Finally, well-known theoretical models explaining the mechanism of DSA during tensile deformation were suitably modified for load-controlled scenario and the origin of strain burst as a function of σ{sub m} or stress rate was explained based on the same. Dislocation density measurements were carried out for specimens undergoing strain burst during cyclic creep, which was utilized for reconstituting the models.

  13. Transmission electron microscopy in situ investigation of dislocation mobility in semiconductors

    CERN Document Server

    Vanderschaeve, G; Insa, P D T; Caillard, D

    2000-01-01

    TEM in situ straining experiments provide a unique way to investigate in real time the behaviour of individual dislocations under applied stress. The results obtained on a variety of semiconductors are presented: numerous dislocation sources are observed which makes it possible to measure the dislocation velocity as a function of different physical parameters (local shear stress, temperature, dislocation character, length of the moving dislocation, ...). The experimental results are consistent with a dislocation glide governed by the Peierls mechanism, even for II-VI compounds which have a significant degree of ionic character. For compounds, a linear dependence of the dislocation velocity on the length of the moving segment is noticed, whereas for elemental semiconductors a transition between a length-dependent and a length-independent velocity regime is observed. Analysed in the framework of the kink diffusion model (Hirth and Lothe theory), these results allow an estimation of the kink formation and migrat...

  14. Compression Stress Effect on Dislocations Movement and Crack propagation in Cubic Crystal

    OpenAIRE

    Suprijadi; Ely, Aprilia; Meiqorry, Yusfi

    2011-01-01

    Fracture material is seriously problem in daily life, and it has connection with mechanical properties itself. The mechanical properties is belief depend on dislocation movement and crack propagation in the crystal. Information about this is very important to characterize the material. In FCC crystal structure the competition between crack propagation and dislocation wake is very interesting, in a ductile material like copper (Cu) dislocation can be seen in room temperature, but in a brittle ...

  15. Dynamic Multiscale Quantum Mechanics/Electromagnetics Simulation Method.

    Science.gov (United States)

    Meng, Lingyi; Yam, ChiYung; Koo, SiuKong; Chen, Quan; Wong, Ngai; Chen, GuanHua

    2012-04-10

    A newly developed hybrid quantum mechanics and electromagnetics (QM/EM) method [Yam et al. Phys. Chem. Chem. Phys.2011, 13, 14365] is generalized to simulate the real time dynamics. Instead of the electric and magnetic fields, the scalar and vector potentials are used to integrate Maxwell's equations in the time domain. The TDDFT-NEGF-EOM method [Zheng et al. Phys. Rev. B2007, 75, 195127] is employed to simulate the electronic dynamics in the quantum mechanical region. By allowing the penetration of a classical electromagnetic wave into the quantum mechanical region, the electromagnetic wave for the entire simulating region can be determined consistently by solving Maxwell's equations. The transient potential distributions and current density at the interface between quantum mechanical and classical regions are employed as the boundary conditions for the quantum mechanical and electromagnetic simulations, respectively. Charge distribution, current density, and potentials at different temporal steps and spatial scales are integrated seamlessly within a unified computational framework.

  16. Dynamic mechanical behavior magnetorheological nanocomposites containing CNTs: A review

    Science.gov (United States)

    Ismail, Rozaina; Ibrahim, Azmi; Hamid, Hanizah Ab.; Mahmood, Mohamad Rusop; Adnan, Azlan

    2016-07-01

    Carbon nanotubes (CNTs) based polymer composites have variety of engineering applications due to their excellent mechanical, electrical, chemical, magnetic, etc. properties. This paper is an attempt to present a coherent yet concise review of as many of these publications as possible on the mechanical aspect of the Magnetorheological Elastomer (MRE) composites with the addition of multi-walled carbon nanotubes (CNTs). The dynamic mechanical response of the MR nanocomposites to applied magnetic fields has been investigated through dynamic mechanical analysis. It is found that a small amount of carbon nanotubes can effectively improve the mechanical performance of conventional MR elastomers. In summary, multi-walled carbon nanotubes reinforced magnetorheological composite has been developed to take advantage of both the smart MR technology and outstanding properties of carbon nanotubes. Furthermore review is also carried out on the capability of carbon nanotubes to impart the stiffness and damping performance encountered with the properties of CNT based Natural Rubber.

  17. Stochastically forced dislocation density distribution in plastic deformation

    CERN Document Server

    Chattopadhyay, Amit K

    2016-01-01

    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 type 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 sh...

  18. Dislocation following total knee arthroplasty: A report of six cases

    Directory of Open Access Journals (Sweden)

    Villanueva Manuel

    2010-01-01

    Full Text Available Background: Dislocation following total knee arthroplasty (TKA is the worst form of instability. The incidence is from 0.15 to 0.5%. We report six cases of TKA dislocation and analyze the patterns of dislocation and the factors related to each of them. Materials and Methods: Six patients with dislocation of knee following TKA are reported. The causes for the dislocations were an imbalance of the flexion gap (n=4, an inadequate selection of implants (n=1, malrotation of components (n=1 leading to incompetence of the extensor mechanism, or rupture of the medial collateral ligament (MCC. The patients presented complained of pain, giving way episodes, joint effusion and difficulty in climbing stairs. Five patients suffered posterior dislocation while one anterior dislocation. An urgent closed reduction of dislocation was performed under general anaesthesia in all patients. All patients were operated for residual instability by revision arthroplasty after a period of conservative treatment. Results: One patient had deep infection and knee was arthrodesed. Two patients have a minimal residual lag for active extension, including a patient with a previous patellectomy. Result was considered excellent or good in four cases and fair in one, without residual instability. Five out of six patients in our series had a cruciate retaining (CR TKA designs: four were revised to a posterior stabilized (PS TKA and one to a rotating hinge design because of the presence of a ruptured MCL. Conclusion: Further episodes of dislocation or instability will be prevented by identifying and treating major causes of instability. The increase in the level of constraint and correction of previous technical mistakes is mandatory.

  19. Galeazzi fractures and dislocations.

    Science.gov (United States)

    Giannoulis, Filippos S; Sotereanos, Dean G

    2007-05-01

    In 1934, fractures of the middle and distal third of the radius associated with instability of the distal radial ulnar joint (DRUJ) were described by Galeazzi. This type of lesion is characterized by its unstable nature and the need for open reduction and internal fixation to achieve a satisfactory functional outcome. A high index of suspicion should be maintained by the surgeon, and a thorough examination for instability of the DRUJ must be conducted. The marked instability of this fracture-dislocation complex is further enhanced by the disruption of the triangular fibrocartilage complex, either with or without ulna styloid fracture. Treatment in adults is surgical, and both bone and soft tissue injuries should be addressed.

  20. Mechanical, Thermal and Dynamic Mechanical Properties of PP/GF/xGnP Nanocomposites

    Science.gov (United States)

    Ashenai Ghasemi, F.; Ghorbani, A.; Ghasemi, I.

    2017-03-01

    The mechanical, thermal, and dynamic mechanical properties of ternary nanocomposites based on polypropylene, short glass fibers, and exfoliated graphene nanoplatelets were studied. To investigate the mechanical properties, uniaxial tensile and Charpy impact tests were carried out. To study the crystallinity of the compositions, a DSC test was performed. A dynamic mechanical analysis was used to characterize the storage modulus and loss factor (tan δ). The morphology of the composites was studied by a scanning electron microscope (SEM). The results obtained are presented in tables and graphics.

  1. A Dynamic Adaptive Layered Multicast Congestion Control Mechanism

    Institute of Scientific and Technical Information of China (English)

    REN Liyong; LU Xianliang; WEI Qingsong; ZHOU Xu

    2003-01-01

    To solve the problem that most of existing layered multicast protocols cannot adapt to dynamic network conditions because their layers are coarsely granulated and static, a new congestion control mechanism for dynamic adaptive layered multicast(DALM) is presented. In this mechanism, a novel feedback aggregating algorithm is put forward, which can dynamically determine the number of layers and the rate of each layer, and can efficiently improve network bandwidth utilization ratio.Additionally, because all layers is transmitted in only one group, the intricate and time-consuming internet group management protocol(IGMP) operations, caused by receiver joining a new layer or leaving the topmost subscribed layer, are thoroughly eliminated. And this mechanism also avoids other problems resulted from multiple groups. Simulation results show that DALM is adaptive and TCP friendly.

  2. Characterisation of Dynamic Mechanical Properties of Resistance Welding Machines

    DEFF Research Database (Denmark)

    Wu, Pei; Zhang, Wenqi; Bay, Niels

    2005-01-01

    The dynamic mechanical properties of a resistance welding machine have significant influence on weld quality, which must be considered when simulating the welding process numerically. However, due to the complexity of the machine structure and the mutual coupling of components of the machine system...... characterizing the dynamic mechanical characteristics of resistance welding machines is suggested, and a test set-up is designed determining the basic, independent machine parameters required in the model. The model is verified by performing a series of mechanical tests as well as real projection welds......., it is very difficult to measure or calculate the basic, independent machine parameters required in a mathematical model of the machine dynamics, and no test method has so far been presented in literature, which can be applied directly in an industrial environment. In this paper, a mathematical model...

  3. Characterisation of Dynamic Mechanical Properties of Resistance Welding Machines

    DEFF Research Database (Denmark)

    Wu, Pei; Zhang, Wenqi; Bay, Niels

    2005-01-01

    The dynamic mechanical properties of a resistance welding machine have significant influence on weld quality, which must be considered when simulating the welding process numerically. However, due to the complexity of the machine structure and the mutual coupling of components of the machine system......, it is very difficult to measure or calculate the basic, independent machine parameters required in a mathematical model of the machine dynamics, and no test method has so far been presented in literature, which can be applied directly in an industrial environment. In this paper, a mathematical model...... characterizing the dynamic mechanical characteristics of resistance welding machines is suggested, and a test set-up is designed determining the basic, independent machine parameters required in the model. The model is verified by performing a series of mechanical tests as well as real projection welds....

  4. An Analytical Dynamics Approach to the Control of Mechanical Systems

    Science.gov (United States)

    Mylapilli, Harshavardhan

    A new and novel approach to the control of nonlinear mechanical systems is presented in this study. The approach is inspired by recent results in analytical dynamics that deal with the theory of constrained motion. The control requirements on the dynamical system are viewed from an analytical dynamics perspective and the theory of constrained motion is used to recast these control requirements as constraints on the dynamical system. Explicit closed form expressions for the generalized nonlinear control forces are obtained by using the fundamental equation of mechanics. The control so obtained is optimal at each instant of time and causes the constraints to be exactly satisfied. No linearizations and/or approximations of the nonlinear dynamical system are made, and no a priori structure is imposed on the nature of nonlinear controller. Three examples dealing with highly nonlinear complex dynamical systems that are chosen from diverse areas of discrete and continuum mechanics are presented to demonstrate the control approach. The first example deals with the energy control of underactuated inhomogeneous nonlinear lattices (or chains), the second example deals with the synchronization of the motion of multiple coupled slave gyros with that of a master gyro, and the final example deals with the control of incompressible hyperelastic rubber-like thin cantilever beams. Numerical simulations accompanying these examples show the ease, simplicity and the efficacy with which the control methodology can be applied and the accuracy with which the desired control objectives can be met.

  5. The Clean Development Mechanism and Dynamic Capabilities of Implementing Firms

    DEFF Research Database (Denmark)

    Aggarwal, Aradhna

    This study assesses the impact of the Clean Development Mechanism (CDM) on the dynamic capabilities of implementing firms in India. While doing so, it uses three indicators of firms' dynamic capabilities: R&D expenditures to sales ratio, fuel consumption to sales ratio and total factor productivi...... the PROWESS database. Our results reveal that the CDM implementation does not have significant outcome effects on the dynamic capabilities of firms. Much depends on the type and size of the project, and size of the firm....

  6. Analytical generation of the dynamical equations for mechanical manipulators

    Directory of Open Access Journals (Sweden)

    Geir Horn

    1995-07-01

    Full Text Available A package to generate the symbolic dynamic equations describing the relation between forces and movements for serial mechanical linkages with rigid constituents is presented. The relative movement between the rigid parts is assumed to be either a rotation about an axis or a translation along an axis. Two algorithms are implemented, a Lagrange-Euler method and a Newton-Euler method. The former can be used to solve both the inverse and the forward dynamics problems, while the latter requires fewer arithmetical operations but only allows solution of the inverse dynamics problem. Two test examples are presented, the double pendulum and the modified Stanford manipulator.

  7. Operational dynamic modeling transcending quantum and classical mechanics.

    Science.gov (United States)

    Bondar, Denys I; Cabrera, Renan; Lompay, Robert R; Ivanov, Misha Yu; Rabitz, Herschel A

    2012-11-09

    We introduce a general and systematic theoretical framework for operational dynamic modeling (ODM) by combining a kinematic description of a model with the evolution of the dynamical average values. The kinematics includes the algebra of the observables and their defined averages. The evolution of the average values is drawn in the form of Ehrenfest-like theorems. We show that ODM is capable of encompassing wide-ranging dynamics from classical non-relativistic mechanics to quantum field theory. The generality of ODM should provide a basis for formulating novel theories.

  8. Microstructure–mechanical property correlation of cryo rolled Zircaloy-4

    Energy Technology Data Exchange (ETDEWEB)

    Sarkar, Apu, E-mail: asarkar5@ncsu.edu; Murty, Korukonda L.

    2015-01-15

    The evolution of microstructure and the mechanical properties of cryo-rolled Zircaloy-4 were both investigated to understand the origin of the alloy’s strength processed at a cryogenic temperature. The correlation of dislocation density, grain size and yield stress of the rolled product indicated that an increase in dislocation density due to the suppression of dynamic recovery is the primary source of strengthening.

  9. Quantum mechanics emerging from stochastic dynamics of virtual particles

    CERN Document Server

    Tsekov, R

    2015-01-01

    It is demonstrated how quantum mechanics emerges from the stochastic dynamics of force-carriers. It is shown that the quantum Moyal equation corresponds to some dynamic correlations between the momentum of a real particle and the position of a virtual particle, which are not present in classical mechanics. The new concept throws light on the physical meaning of quantum theory, showing that the Planck constant square is a second-second cross-cumulant. The novel approach to quantum systems is extended to the relativistic case and an expression is derived for the relativistic mass in the Wigner quantum phase-space.

  10. Bubble interaction dynamics in Lagrangian and Hamiltonian mechanics.

    Science.gov (United States)

    Ilinskii, Yurii A; Hamilton, Mark F; Zabolotskaya, Evgenia A

    2007-02-01

    Two models of interacting bubble dynamics are presented, a coupled system of second-order differential equations based on Lagrangian mechanics, and a first-order system based on Hamiltonian mechanics. Both account for pulsation and translation of an arbitrary number of spherical bubbles. For large numbers of interacting bubbles, numerical solution of the Hamiltonian equations provides greater stability. The presence of external acoustic sources is taken into account explicitly in the derivation of both sets of equations. In addition to the acoustic pressure and its gradient, it is found that the particle velocity associated with external sources appears in the dynamical equations.

  11. VERIFICATION OF TORSIONAL OSCILLATING MECHANICAL SYSTEM DYNAMIC CALCULATION RESULTS

    Directory of Open Access Journals (Sweden)

    Peter KAŠŠAY

    2014-09-01

    Full Text Available On our department we deal with optimization and tuning of torsional oscillating mechanical systems. When solving these problems we often use results of dynamic calculation. The goal of this article is to compare values obtained by computation and experimentally. For this purpose, a mechanical system built in our laboratory was used. At first, classical HARDY type flexible coupling has been applied into the system, then we used a pneumatic flexible shaft coupling developed by us. The main difference of these couplings over conventional flexible couplings is that they can change their dynamic properties during operation, by changing the pressure of the gaseous medium in their flexible elements.

  12. Irreducible, incarcerated vertical dislocation of patella into a Hoffa fracture

    Directory of Open Access Journals (Sweden)

    Prasad C Soraganvi

    2014-01-01

    Full Text Available Rotational dislocations of patella, which involve rotation of the patella around a horizontal or vertical axis are rare. These rotational dislocations of patella are difficult to reduce by close methods. These dislocations can have associated osteochondral and retinacular injury. We report a case of a 20-year-old male who presented with swelling and pain in the right knee following a motor cycle accident. Radiological evaluation using the computed tomography revealed a patellar dislocation with a concomitant Hoffa fracture. Patella was rotated around the vertical axis and was incarcerated into the Hoffa fracture. This is a very rare injury and first of its kind to be reported. The difficulties in diagnosis, mechanism of injury and management have been discussed. We feel closed reduction of such an injury is likely to fail and open reduction is recommended.

  13. Femoral head fracture without hip dislocation

    Institute of Scientific and Technical Information of China (English)

    Aditya K Aggarwal; Ashwani Soni; Daljeet Singh

    2013-01-01

    Femoral head fractures without dislocation or subluxation are extremely rare injuries.We report a neglected case of isolated comminuted fracture of femoral head without hip dislocation or subluxation of one year duration in a 36-year-old patient who sustained a high energy trauma due to road traffic accident.He presented with painful right hip and inability to bear full weight on right lower limb with Harris hip score of 39.He received cementless total hip replacement.At latest follow-up of 2.3 years,functional outcome was excellent with Harris hip score of 95.Such isolated injuries have been described only once in the literature and have not been classified till now.The purpose of this report is to highlight the extreme rarity,possible mechanism involved and a novel classification system to classify such injuries.

  14. Open Galeazzi fracture with ipsilateral elbow dislocation.

    Science.gov (United States)

    Adanır, Oktay; Yüksel, Serdar; Beytemur, Ozan; Güleç, M Akif

    2016-08-01

    Combination of the Galeazzi fracture and dislocation of the elbow joint in same extremity is very rare. In this article, we report a 26-year-old male patient with a posterolateral dislocation of the elbow and ipsilateral volar type Galeazzi fracture. We performed closed reduction for the elbow dislocation during admission to the emergency department. Patient was taken to the operating room in the sixth hour of his application to emergency department and open wound on the ulnovolar region of the wrist was closed primarily after irrigation and debridement. We performed open reduction and internal fixation of the radial fracture with a dynamic compression plate. After fixation, we evaluated the stability of the elbow joint and distal radioulnar joint. Distal radioulnar joint was unstable under fluoroscopic examination and fixed with one 1.8 mm Kirschner wire in a pronated position. Then, elbow joint was stable. One year after surgery, patient had no pain or sings of instability. At the last follow-up, range of motion of the elbow was 10°-135° and forearm pronation and supination were 70°.

  15. Dislocation Starvation and Exhaustion Hardening in Mo-alloy Nanofibers

    Energy Technology Data Exchange (ETDEWEB)

    Chisholm, Claire [University of California, Berkeley & LBNL; Bei, Hongbin [ORNL; Lowry, M. B. [University of California, Berkeley; Oh, Jason [Hysitron, Inc., MN; Asif, S.A. Syed [Hysitron, Inc., MN; Warren, O. [Hysitron, Inc., MN; Shan, Zhiwei [Xi' an Jiaotong University, China & Hysitron, Inc., MN; George, Easo P [ORNL; Minor, Andrew [University of California, Berkeley & LBNL

    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.

  16. Buckling of dislocation in graphene

    Science.gov (United States)

    Yao, Yin; Wang, Shaofeng; Bai, Jianhui; Wang, Rui

    2016-10-01

    The buckling of dislocation in graphene is discussed through the lattice theory of dislocation and elastic theory. The approximate solution of the buckling is obtained based on the inner stress distribution caused by different structure of dislocations and is proved to be suitable by the simulation. The position of the highest buckling is predicted to be at the vertex of the pentagon far away from the heptagon. The buckling is strongly influenced by the internal stress and the distance between the extrusive area and stretching area, as well as the critical stress σc. The SW defect is proved to be unbuckled due to its strong interaction between extrusion and stretching.

  17. Patellar Dislocations and Reduction Procedure.

    Science.gov (United States)

    Ramponi, Denise

    2016-01-01

    Acute patellar dislocations are a common injury occurring in adolescents involved in sports and dancing activities. This injury usually occurs when the knee is in full extension and sustains a valgus stress on the knee. The medial patellofemoral ligament is the medial restraint that assists in stabilizing the patella from lateral dislocations. The patella usually dislocates laterally and is usually not difficult to reduce after patient evaluation and prereduction radiographs. After postreduction radiographs confirm proper position of the patella postreduction and the absence of fractures, the patient is usually treated conservatively with initial immobilization, orthopedic referral, and physical therapy.

  18. MATHEMATICAL MODEL FOR ESTIMATION OF MECHANICAL SYSTEM CONDITION IN DYNAMICS

    Directory of Open Access Journals (Sweden)

    D. N. Mironov

    2011-01-01

    Full Text Available The paper considers an estimation of a complicated mechanical system condition in dynamics with due account of material degradation and accumulation of micro-damages. An element of continuous medium has been simulated and described with the help of a discrete element. The paper contains description of a model for determination of mechanical system longevity in accordance with number of cycles and operational period.

  19. VERIFICATION OF TORSIONAL OSCILLATING MECHANICAL SYSTEM DYNAMIC CALCULATION RESULTS

    OpenAIRE

    2014-01-01

    On our department we deal with optimization and tuning of torsional oscillating mechanical systems. When solving these problems we often use results of dynamic calculation. The goal of this article is to compare values obtained by computation and experimentally. For this purpose, a mechanical system built in our laboratory was used. At first, classical HARDY type flexible coupling has been applied into the system, then we used a pneumatic flexible shaft coupling developed by us...

  20. Molecular dynamics study of void effect on nanoimprint of single crystal aluminum

    Energy Technology Data Exchange (ETDEWEB)

    Yuan Ying [Center for Precision Engineering, Harbin Institute of Technology, Harbin (China); Sun Tao, E-mail: spm@hit.edu.cn [Center for Precision Engineering, Harbin Institute of Technology, Harbin (China); Zhang Junjie; Yan Yongda [Center for Precision Engineering, Harbin Institute of Technology, Harbin (China)

    2011-06-01

    Pre-existing defects can alter mechanical behavior of materials significantly under applied load. In current study molecular dynamics (MD) simulations are performed to reveal pre-existing void effect on nanoimprint of single crystal Al thin films, such as deformation mechanism and spring back phenomenon. Current simulation results show void acts as strong barrier to dislocation motion, although plastic deformation is dominantly controlled by dislocation activities. It indicates the void volume fraction has strong influence on nanoimprint: the larger the void volume fraction, the smaller the maximum force required for initial dislocation nucleation, and the stronger the interaction between extended dislocation and void. It also demonstrates that there is a critical void volume fraction for minimum spring back, which is resulted from competition between two roles affecting dislocation annihilation.

  1. Dislocation-density based description of the deformation of a composite material

    Science.gov (United States)

    Schulz, K.; Sudmanns, M.; Gumbsch, P.

    2017-09-01

    Composite materials consisting of hard particles in a ductile metallic matrix are of major interest since their strength and deformability can be dramatically changed by varying volume fraction, size and shape of the particles. Understanding dislocation motion in composite materials as the cause of plastic deformation therefore is an important task. Recently, advanced dislocation-based continuum theories of plasticity have been developed for performing meaningful averages over systems of straight and curved dislocation lines in a continuum approach. In this paper, we focus on a single slip heterogeneous microstructure and investigate how the dislocation interactions can be represented in an averaged dislocation density based continuum description. The representation of strong dislocation density gradients is discussed in the context of a formulation, which aims at a coarse-grained resolution. We introduce a set of dislocation density evolution equations which account for the formation and dissolution of dislocation dipoles. By applying the model to a composite structure, we demonstrate that the dislocation density based description can well describe the physical processes in the microstructure and a comparison to discrete dislocation dynamics simulations shows good agreement for the relaxation behavior of the considered composites.

  2. Classical mechanics systems of particles and Hamiltonian dynamics

    CERN Document Server

    Greiner, Walter

    2010-01-01

    This textbook Classical Mechanics provides a complete survey on all aspects of classical mechanics in theoretical physics. An enormous number of worked examples and problems show students how to apply the abstract principles to realistic problems. The textbook covers Newtonian mechanics in rotating coordinate systems, mechanics of systems of point particles, vibrating systems and mechanics of rigid bodies. It thoroughly introduces and explains the Lagrange and Hamilton equations and the Hamilton-Jacobi theory. A large section on nonlinear dynamics and chaotic behavior of systems takes Classical Mechanics to newest development in physics. The new edition is completely revised and updated. New exercises and new sections in canonical transformation and Hamiltonian theory have been added.

  3. Crystal-Orientation Dependent Evolution of Edge Dislocations from a Void in Single Crystal Gu

    Institute of Scientific and Technical Information of China (English)

    SONG Zhen-Fei; ZHU Wen-Jun; DENG Xiao-Liang; HE Hong-Liang

    2006-01-01

    @@ The micro-void growth by dislocation emission under tensile loading is explored with focus on the influence of crystal orientations. Based on the elastic theory, a dislocation emission criterion is formulated. It is predicted that the preferential location of dislocation nucleation and its threshold stress are dependent on the crystal orientation.Large-scale molecular dynamics (MD) simulations are also performed for single crystal copper to illustrate the dislocation evolution pattern associated with a nano-void growth. The results are in line with those given by the theoretical prediction. As revealed by MD simulations, the characteristics of void growth at micro-scale depend greatly on the crystal-orientation.

  4. Research of dynamic mechanical performance of cement rock

    Institute of Scientific and Technical Information of China (English)

    WANG Qiang; WANG Tong; WANG Xiang-lin

    2007-01-01

    As Daqing Oilfield is developing oil layer with a big potential, the requirement for the quality of well cementation is higher than ever before. Cement rock is a brittle material containing a great number of microcracks and defects. In order to reduce the damage to cement ring and improve sealed cementing property at the interface, it is necessary to conduct research on the modification of the cement rock available. According to the principle of super mixed composite materials, various fillers are added to the ingredients of cement rock. Dynamic fracture toughness of cement rock will be changed under the influence of filler. In order to study the damage mechanism of the cement circle during perforation and carry out comprehensive experiments on preventing and resisting connection, a kind of comprehensive experiment equipment used to simulate perforation and multifunctional equipment for testing the dynamic properties of the material are designed. Experimental study of the dynamical mechanical performance of original and some improved cement rock and experiment used to simulate the well cementation and perforation are carried out. Standard for dynamical mechanical performance of the cement rock with fine impact resistance and mechanical properties of some improved cement rock are also given.

  5. Dynamics of five-bar COBOT using differential mechanism

    Institute of Scientific and Technical Information of China (English)

    ZHANG Li-xun; LU Dun-min; WANG Lan; SHEN Jin-hua; BERNHARD R.

    2003-01-01

    COBOT is a new kind of collaborative robot , which can work with people in a shared space. In this paper a new kind of CVT using differential mechanism is introduced, which is major parts of five-bar COBOT and based the feature of nonhlonnmic constraint. The dynamic model of differential mechanism and five-bar architecture COBOT is founded. There are two kinds of coupled mode of two CVT:serial and parallel. In this paper, we present the dynamic model of serial and parallel COBOT take five-bar COBOT as research object. From the dynamic analysis foregoing, both serial and parallel COBOT model are have the feature of nonholonomic constraint. The ending track and moving state are controlled by the force of control motor and operator. The control motor can not control the movement and ending track of COBOT without the cooperation of operator.

  6. [Traumatic elbow dislocations in bouldering].

    Science.gov (United States)

    Sandmann, G H; Siebenlist, S; Lenich, A; Neumaier, M; Ahrens, P; Kirchhoff, C; Braun, K F; Lucke, M; Biberthaler, P

    2014-03-01

    Bouldering is a new trend sport which has become popular in recent years. From April 2011 to June 2012 a total of 5 patients with elbow dislocations from bouldering were admitted to our level 1 trauma center. The injuries varied from simple elbow dislocations to complex fracture dislocations. Elbow dislocations occurred during falling backwards when patients tried to protect themselves by retroversion of both arms. In all cases the falling height was less than 4 meters. The bouldering injury pattern, the diagnostic and therapeutic management as well as the rehabilitation program are described in detail in this article. To the best of our knowledge this is the first report on the special danger of bouldering for complex elbow injuries.

  7. Estimation of dislocation density from precession electron diffraction data using the Nye tensor.

    Science.gov (United States)

    Leff, A C; Weinberger, C R; Taheri, M L

    2015-06-01

    The Nye tensor offers a means to estimate the geometrically necessary dislocation density of a crystalline sample based on measurements of the orientation changes within individual crystal grains. In this paper, the Nye tensor theory is applied to precession electron diffraction automated crystallographic orientation mapping (PED-ACOM) data acquired using a transmission electron microscope (TEM). The resulting dislocation density values are mapped in order to visualize the dislocation structures present in a quantitative manner. These density maps are compared with other related methods of approximating local strain dependencies in dislocation-based microstructural transitions from orientation data. The effect of acquisition parameters on density measurements is examined. By decreasing the step size and spot size during data acquisition, an increasing fraction of the dislocation content becomes accessible. Finally, the method described herein is applied to the measurement of dislocation emission during in situ annealing of Cu in TEM in order to demonstrate the utility of the technique for characterizing microstructural dynamics.

  8. Habitual dislocation of patella: A review

    Science.gov (United States)

    Batra, Sumit; Arora, Sumit

    2014-01-01

    Habitual dislocation of patella is a condition where the patella dislocates whenever the knee is flexed and spontaneously relocates with extension of the knee. It is also termed as obligatory dislocation as the patella dislocates completely with each flexion and extension cycle of the knee and the patient has no control over the patella dislocating as he or she moves the knee1. It usually presents after the child starts to walk, and is often well tolerated in children, if it is not painful. However it may present in childhood with dysfunction and instability. Very little literature is available on habitual dislocation of patella as most of the studies have combined cases of recurrent dislocation with habitual dislocation. Many different surgical techniques have been described in the literature for the treatment of habitual dislocation of patella. No single procedure is fully effective in the surgical treatment of habitual dislocation of patella and a combination of procedures is recommended. PMID:25983506

  9. Vibrational mechanics nonlinear dynamic effects, general approach, applications

    CERN Document Server

    Blekhman, Iliya I

    2000-01-01

    This important book deals with vibrational mechanics - the new, intensively developing section of nonlinear dynamics and the theory of nonlinear oscillations. It offers a general approach to the study of the effect of vibration on nonlinear mechanical systems.The book presents the mathematical apparatus of vibrational mechanics which is used to describe such nonlinear effects as the disappearance and appearance under vibration of stable positions of equilibrium and motions (i.e. attractors), the change of the rheological properties of the media, self-synchronization, self-balancing, the vibrat

  10. Investigation of deformation mechanisms of staggered nanocomposites using molecular dynamics

    Science.gov (United States)

    Mathiazhagan, S.; Anup, S.

    2016-08-01

    Biological materials with nanostructure of regularly or stair-wise staggered arrangements of hard platelets reinforced in a soft protein matrix have superior mechanical properties. Applications of these nanostructures to ceramic matrix composites could enhance their toughness. Using molecular dynamics simulations, mechanical behaviour of the bio-inspired nanocomposites is studied. Regularly staggered model shows better flow behaviour compared to stair-wise staggered model due to the symmetrical crack propagation along the interface. Though higher stiffness and strength are obtained for stair-wise staggered models, rapid crack propagation reduces the toughness. Arresting this crack propagation could lead to superior mechanical properties in stair-wise staggered models.

  11. A Dynamic Market Mechanism for Markets with Shiftable Demand Response

    DEFF Research Database (Denmark)

    Hansen, Jacob; Knudsen, Jesper Viese; Kiani, Arman

    2014-01-01

    renewables, this mechanism accommodates both consumers with a shiftable Demand Response and an adjustable Demand Response. The overall market mechanism is evaluated in a Day Ahead Market and is shown in a numerical example to result in a reduction of the cost of electricity for the consumer, as well......In this paper, we propose a dynamic market mechanism that converges to the desired market equilibrium. Both locational marginal prices and the schedules for generation and consumption are determined through a negotiation process between the key market players. In addition to incorporating...

  12. A fatigue crack initiation model incorporating discrete dislocation plasticity and surface roughness

    NARCIS (Netherlands)

    Brinckmann, Steffen; Van der Giessen, Erik

    2007-01-01

    Although a thorough understanding of fatigue crack initiation is lacking, experiments have shown that the evolution of distinct dislocation distributions and surface roughness are key ingredients. In the present study we introduce a computational framework that ties together dislocation dynamics, th

  13. Solution Hardening in Al-Zn Alloys. Mean Jump Distance and Activation Length of Moving Dislocations

    NARCIS (Netherlands)

    Hosson, J.Th.M. De; Boom, G.; Schlagowski, U.; Kanert, O.

    Pulsed nuclear magnetic resonance proved to be a complementary new technique for the study of moving dislocations in Al-Zn alloys. The NMR technique, in combination with strain-rate change experiments and transmission electron microscopy have been applied to study dislocation dynamics in Al-Zn

  14. Mechanic: a new numerical MPI framework for the dynamical astronomy

    CERN Document Server

    Slonina, Mariusz; Migaszewski, Cezary

    2012-01-01

    We develop the Mechanic package, which is a new numerical framework for dynamical astronomy. The aim of our software is to help in massive numerical simulations by efficient task management and unified data storage. The code is built on top of the Message Passing Interface (MPI) and Hierarchical Data Format (HDF5) standards and uses the Task Farm approach to manage numerical tasks. It relies on the core-module approach. The numerical problem implemented in the user-supplied module is separated from the host code (core). The core is designed to handle basic setup, data storage and communication between nodes in a computing pool. It has been tested on large CPU-clusters, as well as desktop computers. The Mechanic may be used in computing dynamical maps, data optimization or numerical integration. The code and sample modules are freely available at http://git.astri.umk.pl/projects/mechanic.

  15. Complex Dynamics of Nano-Mechanical Membrane in Cavity Optomechanics

    CERN Document Server

    Akram, Muhammad Javed

    2016-01-01

    Theoretical analysis of a suspended nano-mechanical membrane subject to an optical driving field in cavity optomechanics is presented, which is confirmed through numerical simulations. In the presence of an optical field between its mirrors a high finesse nano-mechanical resonator acts as an oscillator driven by radiation pressure force. The periodic nature of the radiation pressure force makes the nano-mechanical membrane in the optomechanical system as kicked harmonic oscillator. Mathematically the physical system displays a stochastic web map that helps to understand several properties of the kicked membrane in classical phase space. We find that our web map is area preserving, and displays quasi-periodic symmetrical structures in phase space which we express as q-fold symmetry. It is shown that under appropriate control of certain parameters, namely the frequency ratio (q) and the kicking strength (K), the dynamics of kicked membrane exhibits chaotic dynamics. We provide the stability analysis by means of...

  16. The dynamical complexity of work-hardening: a large-scale molecular dynamics simulation

    Institute of Scientific and Technical Information of China (English)

    Markus J. Buehler; Alexander Hartmaier; Mark A. Duchaineau; Farid F. Abraham; Huajian Gao

    2005-01-01

    We analyze a large-scale molecular dynamics simulation of work hardening in a model system of a ductile solid.With tensile loading, we observe emission of thousands of dislocations from two sharp cracks. The dislocations interact in a complex way, revealing three fundamental mechanisms of work-hardening in this ductile material. These are (1) dislocation cutting processes, jog formation and generation of trails of point defects; (2) activation of secondary slip systems by Frank-Read and cross-slip mechanisms; and (3) formation of sessile dislocations such as Lomer-Cottrell locks.We report the discovery of a new class of point defects referred to as trail of partial point defects, which could play an important role in situations when partial dislocations dominate plasticity. Another important result of the present work is the rediscovery of the Fleischer-mechanism of cross-slip of partial dislocations that was theoretically proposed more than 50 years ago, and is now, for the first time, confirmed by atomistic simulation. On the typical time scale of molecular dynamics simulations, the dislocations self-organize into a complex sessile defect topology. Our analysis illustrates numerous mechanisms formerly only conjectured in textbooks and observed indirectly in experiments. It is the first time that such a rich set of fundamental phenomena have been revealed in a single computer simulation, and its dynamical evolution has been studied. The present study exemplifies the simulation and analysis of the complex nonlinear dynamics of a many-particle system during failure using ultra-large scale computing.

  17. Chemical theory of dislocation mobility

    Energy Technology Data Exchange (ETDEWEB)

    Gilman, J.J. [Materials Science and Engineering, University of California at Los Angeles, Los Angeles, CA 90095 (United States)]. E-mail: gilman@seas.ucla.edu

    2005-11-15

    Crystal dislocations were invented (circa. 1930) to explain why pure metal crystals are soft compared with homogeneous shear strengths calculated from atomic theory. They do this very well. However, later (circa. 1945) it was found that pure semiconductor crystals (e.g., Ge and Si) have hardnesses at room temperature comparable with calculated homogeneous shear strengths. Furthermore, it was known that pure metal-metalloid crystals (e.g., TiC and WC) are very hard, although they conduct electricity like metals. How can these differences be explained? The differences just outlined cannot be explained by means of a classical mechanical model. However, they can be explained by considering the chemical bonding in differing solid crystals. In particular, hardness depends on the degree of localization of the valence (bonding) electrons. Qualitatively, this is a very old idea. What is new is that it is possible to provide quantitative theories by using the results of quantum chemistry, and relatively simple analysis. Selected sets of crystal types must be treated, of course, just as selected sets of molecules are treated in theoretical chemistry. Otherwise the rationalization becomes unmanageable.

  18. Embedded atom study of dislocation core structure in Fe

    Energy Technology Data Exchange (ETDEWEB)

    Farkas, D.; Rodriguez, P.L. (Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Materials Science and Engineering Centro Atomico Bariloche (Argentina))

    1994-04-01

    The relaxed atomistic structure of dislocation cores in body centered cubic metals was investigated many years ago, using pair potentials. These studies are now classic and have been the basis for understanding mechanical behavior of these materials. They constitute the classic example of the importance of non-elastic core effect for the dislocations responsible for deformation, as described in several reviews written on the subject. Volume-dependent interatomic potentials were introduced in 1984. Despite the importance of the results obtained with pair potentials, no calculation of dislocation cores in pure bcc metals using volume-dependent interatomic potentials has yet been performed. The purpose of the present investigation is to compute the structures of 1/2[111] screw dislocation cores Fe. The objective is to compare these results with the structures obtained with pair potentials. The computation of Peierls stresses with pair potentials usually gives an overestimate of the actual Peierls stress. In the present work, they also use an improved boundary condition technique for the simulation of the dislocation cores can give more accurate Peierls stresses using manageable atomic block sizes. They also use a more recent graphical method for the representation of the core structures to obtain the information on the core structures and their relationship to the various crystallographic planes in the material and to analyze the shape of core in relation with the possible glide planes of the dislocation.

  19. Autoinhibitory mechanisms of ERG studied by molecular dynamics simulations

    Science.gov (United States)

    Lu, Yan; Salsbury, Freddie R.

    2015-01-01

    ERG, an ETS-family transcription factor, acts as a regulator of differentiation of early hematopoietic cells. It contains an autoinhibitory domain, which negatively regulates DNA-binding. The mechanism of autoinhibitory is still illusive. To understand the mechanism, we study the dynamical properties of ERG protein by molecular dynamics simulations. These simulations suggest that DNA binding autoinhibition associates with the internal dynamics of ERG. Specifically, we find that (1), The N-C terminal correlation in the inhibited ERG is larger than that in uninhibited ERG that contributes to the autoinhibition of DNA-binding. (2), DNA-binding changes the property of the N-C terminal correlation from being anti-correlated to correlated, that is, changing the relative direction of the correlated motions and (3), For the Ets-domain specifically, the inhibited and uninhibited forms exhibit essentially the same dynamics, but the binding of the DNA decreases the fluctuation of the Ets-domain. We also find from PCA analysis that the three systems, even with quite different dynamics, do have highly similar free energy surfaces, indicating that they share similar conformations.

  20. Dynamic mechanical analysis of double base rocket propellants

    Directory of Open Access Journals (Sweden)

    Marcin Cegła

    2016-03-01

    Full Text Available The article presents dynamic mechanical analysis (DMA for solid rocket propellants testing. Principles of operation and measured values are briefly described. The authors refer to the previous research of PTFE material and literature data providing information about proper experimental conditions and influence of measurement frequency, load amplitude, and heating rate on the results of DMA tests. The experimental results of solid double-base rocket propellant testing obtained on the N Netzsch DMA 242 device are presented. Mechanical properties such as the dynamic storage modulus E´, the dynamic loss modulus E˝ and tan(δ were measured within temperature range from (–120°C to (+90°C at the heating rate of 1 K/min. The test sample was subjected to a dual cantilever multi-frequency test. Special attention was paid to determination of the glass transition temperature of the tested propellant in reference to the NATO standardization agreement 4540 as well as influence of the measurement frequency on the glass transition.[b]Keywords[/b]: Dynamic mechanical analysis, solid rocket propellants, glass transition temperature

  1. New Mechanism of Flavor Symmetry Breaking from Supersymmetric Strong Dynamics

    CERN Document Server

    Carone, C D; Moroi, T; Carone, Christopher D.; Hall, Lawrence J.; Moroi, Takeo

    1997-01-01

    We present a class of supersymmetric models in which flavor symmetries are broken dynamically, by a set of composite flavon fields. The strong dynamics that is responsible for confinement in the flavor sector also drives flavor symmetry breaking vacuum expectation values, as a consequence of a quantum-deformed moduli space. Yukawa couplings result as a power series in the ratio of the confinement to Planck scale, and the fermion mass hierarchy depends on the differing number of preons in different flavor symmetry-breaking operators. We present viable non-Abelian and Abelian flavor models that incorporate this mechanism.

  2. The Clean Development Mechanism and Dynamic Capabilities of Implementing Firms

    DEFF Research Database (Denmark)

    Aggarwal, Aradhna

    This study assesses the impact of the Clean Development Mechanism (CDM) on the dynamic capabilities of implementing firms in India. While doing so, it uses three indicators of firms' dynamic capabilities: R&D expenditures to sales ratio, fuel consumption to sales ratio and total factor productivity...... and non-CDM firms as the control group for the pre- and post-CDM implementation periods. We control for unobserved fixed effects of firms and time periods and observed characteristics of firms and CDM projects. The analysis draws on the balance sheet data of 612 firms from India between 2001 and 2012 from...

  3. Dynamic balancing of mechanisms and synthesizing of parallel robots

    CERN Document Server

    Wei, Bin

    2016-01-01

    This book covers the state-of-the-art technologies in dynamic balancing of mechanisms with minimum increase of mass and inertia. The synthesis of parallel robots based on the Decomposition and Integration concept is also covered in detail. The latest advances are described, including different balancing principles, design of reactionless mechanisms with minimum increase of mass and inertia, and synthesizing parallel robots. This is an ideal book for mechanical engineering students and researchers who are interested in the dynamic balancing of mechanisms and synthesizing of parallel robots. This book also: ·       Broadens reader understanding of the synthesis of parallel robots based on the Decomposition and Integration concept ·       Reinforces basic principles with detailed coverage of different balancing principles, including input torque balancing mechanisms ·       Reviews exhaustively the key recent research into the design of reactionless mechanisms with minimum increase of mass a...

  4. DECREASING OF MECHANISMS DYNAMIC LOADING AT THE TRANSIENT STATE

    Directory of Open Access Journals (Sweden)

    V. S. Loveikin

    2015-11-01

    Full Text Available Purpose. It is necessary to select modes of motion to reduce the dynamic loads in the mechanisms. This choice should be made on optimization basis. The purpose of research is to study methods of synthesis regimes of mechanisms and machines motion that provide optimal modes of movement for terminal and integral criteria. Methodology. For research the one-mass dynamic model of the mechanism has been used. As optimization criteria the terminal and comprehensive integral criteria were used. The stated optimization problem has been solved using dynamic programming and variational calculation. The direct variation method, which allowed finding only approximate solution of the original problem of optimal control, has been used as well. Findings. The ways of ensuring the absolute minimum of terminal criterion have been set for each method of problem solving. The stated characteristics show softness changes of kinematic functions during braking of mechanism. They point to the absolute minimum of adopted terminal criterion in the calculation. Originality. It is necessary to introduce new variables in the system equations during the solving of optimal control problems using dynamic programming to achieve an absolute minimum of terminal criteria. In general, to achieve a minimum of n-order terminal criterion an optimization problem should find relatively (n+1-th order function. When optimization problems is solving by variational calculation in order to ensure a minimization of n-th order terminal criterion by selecting the appropriate boundary conditions, it is necessary to solve the Euler-Poisson 2(n+1-th order equation (subject to symmetric setting boundary conditions. It is a necessary condition for an extremum of the functional with the (n+1-th order integrant. Practical value. Minimizing of adopted terminal criterion in the calculation allows eliminate the brunt in kinematic gearing of mechanisms, which increases their operational life. In addition

  5. Atomic-scale investigation of point defects and hydrogen-solute atmospheres on the edge dislocation mobility in alpha iron

    Energy Technology Data Exchange (ETDEWEB)

    Bhatia, M. A.; Solanki, K. N., E-mail: kiran.solanki@asu.edu [School for Engineering of Matter, Transport, and Energy, Arizona State University, Tempe, Arizona 85287 (United States); Groh, S. [Institute of Mechanics and Fluid Dynamics, TU Bergakademie Freiberg, Freiberg 09556 (Germany)

    2014-08-14

    In this study, we present atomistic mechanisms of 1/2 [111](11{sup ¯}0) edge dislocation interactions with point defects (hydrogen and vacancies) and hydrogen solute atmospheres in body centered cubic (bcc) iron. In metals such as iron, increases in hydrogen concentration can increase dislocation mobility and/or cleavage-type decohesion. Here, we first investigate the dislocation mobility in the presence of various point defects, i.e., change in the frictional stress as the edge dislocation interacts with (a) vacancy, (b) substitutional hydrogen, (c) one substitutional and one interstitial hydrogen, (d) interstitial hydrogen, (e) vacancy and interstitial hydrogen, and (f) two interstitial hydrogen. Second, we examine the role of a hydrogen-solute atmosphere on the rate of local dislocation velocity. The edge dislocation simulation with a vacancy in the compression side of the dislocation and an interstitial hydrogen atom at the tension side exhibit the strongest mechanical response, suggesting a higher potential barrier and hence, the higher frictional stress (i.e., ∼83% higher than the pure iron Peierls stress). In the case of a dislocation interacting with a vacancy on the compressive side, the vacancy binds with the edge dislocation, resulting in an increase in the friction stress of about 28% when compared with the Peierls stress of an edge dislocation in pure iron. Furthermore, as the applied strain increases, the vacancy migrates through a dislocation transportation mechanism by attaining a velocity of the same order as the dislocation velocity. For the case of the edge dislocation interacting with interstitial hydrogen on the tension side, the hydrogen atom jumps through one layer perpendicular to the glide plane during the pinning-unpinning process. Finally, our simulation of dislocation interactions with hydrogen show first an increase in the local dislocation velocity followed by a pinning of the dislocation core in the atmosphere, resulting in

  6. [The mechanism of the development of residual deformation and complications after the reduction of congenital hip dislocation in children and their conservative treatment].

    Science.gov (United States)

    Rogova, A A

    1991-01-01

    There is described the mechanism of development of hip joint instability of different types and associated secondary complications. Conservative biomechanical approach of treatment of residual instability and its complications: enchondral growth and ossification, delay, pathologic restructuring and coxarthrosis, is proposed.

  7. Chemisorption-facilitated dislocation emission and motion, and induced nucleation of brittle nanocrack

    Institute of Scientific and Technical Information of China (English)

    宿彦京; 王燕斌; 褚武扬

    1997-01-01

    Using a special TEM constant deflection device, the change in dislocation configuration ahead of a loaded crack tip before and after adsorption of Hg atoms and the initiation of liquid metal-induced nanocracks (LMIC) have been observed. The results show that chemisorption of Hg atoms can facilitate dislocation emission, multiplication and motion. Nanocracks will be initiated in the dislocation-free zone (DFZ) or at the crack tip when chemisorption-facilitated dislocation emission, multiplication and motion reach a critical condition. On the basis of the available experimental evidence concerning liquid metal embnttlement (LME), a new mechanism for this phenomenon is considered. This involves the fact that the decrease in surface energy induced by chemisorption of Hg atoms results in a reduction in the critical stress intensity factors for dislocation emission and the resistance for dislocation motion. On the other hand, the plastic work and KIC will decrease with the decrease in the surface energy.

  8. Determination of the of rate cross slip of screw dislocations

    DEFF Research Database (Denmark)

    Vegge, Tejs; Rasmussen, Torben; Leffers, Torben;

    2000-01-01

    The rate for cross slip of screw dislocations during annihilation of screw dipoles in copper is determined by molecular dynamics simulations. The temperature dependence of the rate is seen to obey an Arrhenius behavior in the investigated temperature range: 225-375 K. The activation energy...

  9. New Concept of Dynamic Complexity in Quantum Mechanics and Beyond

    CERN Document Server

    Kirilyuk, A P

    1996-01-01

    The qualitatively new concept of dynamic complexity in quantum mechanics is based on a new paradigm appearing within a nonperturbational analysis of the Schroedinger equation for a generic Hamiltonian system. The unreduced analysis explicitly provides the complete, consistent solution as a set of many incompatible components ('realisations') which should permanently and probabilistically replace one another, since each of them is 'complete' in the ordinary sense. This discovery leads to the universally applicable concept of dynamic complexity and self-consistent, realistic resolution of the stagnating problems of quantum chaos, quantum measurement, indeterminacy and wave reduction. The peculiar, 'mysterious' character of quantum behaviour itself is seen now as a result of a dynamically complex, intrinsically multivalued behaviour of interacting fields at the corresponding lowest levels of the (now completely causal) structure of reality. Incorporating the results of the canonical theories as an over-simplifie...

  10. Thermal, dynamic mechanical, and dielectric analyses of some polyurethane biocomposites.

    Science.gov (United States)

    Macocinschi, Doina; Filip, Daniela; Vlad, Stelian; Cristea, Mariana; Musteata, Valentina; Ibanescu, Sorin

    2012-08-01

    Polymer biocomposites based on segmented poly(ester urethane) and extracellular matrix components have been prepared for the development of tissue engineering applications with improved biological characteristics of the materials in contact with blood and tissues for long periods. Thermal, dynamical, and dielectrical analyses were employed to study the molecular dynamics of these materials and the influence of changing the physical network morphology and hydrogen bond interactions accompanied by phase transitions, interfacial effects, and polarization or conductivity. All phenomena that concur in the tested materials are evaluated by cross-examination of the dynamic mechanical characteristic properties (storage modulus, loss modulus, and loss factor) and dielectric properties (relative permittivity, relative loss factor, and loss tangent) as a function of temperature. Comparative aspects were elucidated by calculating the apparent activation energies of multiplex experiments.

  11. Systematic development of reduced reaction mechanisms for dynamic modeling

    Science.gov (United States)

    Frenklach, M.; Kailasanath, K.; Oran, E. S.

    1986-01-01

    A method for systematically developing a reduced chemical reaction mechanism for dynamic modeling of chemically reactive flows is presented. The method is based on the postulate that if a reduced reaction mechanism faithfully describes the time evolution of both thermal and chain reaction processes characteristic of a more complete mechanism, then the reduced mechanism will describe the chemical processes in a chemically reacting flow with approximately the same degree of accuracy. Here this postulate is tested by producing a series of mechanisms of reduced accuracy, which are derived from a full detailed mechanism for methane-oxygen combustion. These mechanisms were then tested in a series of reactive flow calculations in which a large-amplitude sinusoidal perturbation is applied to a system that is initially quiescent and whose temperature is high enough to start ignition processes. Comparison of the results for systems with and without convective flow show that this approach produces reduced mechanisms that are useful for calculations of explosions and detonations. Extensions and applicability to flames are discussed.

  12. An evolution model of dislocation patterns in plastic deformation and its applications

    Institute of Scientific and Technical Information of China (English)

    高维林; 白光润; 周志敏

    1995-01-01

    By combining the classic dislocation theory with the principle of dissipative structure and synergetics, an evolution model of dislocation patterns has been developed. Using this model, the evolution of dislocation patterns and the corresponding mechanical behavior have been analyzed, discussed and simulated under different deformation conditions of constant strain rate, creep and static recovery. As one of the most essential problems in the plastic deformation, the evolution of dislocation patterns has been dealt with by using non-linear methods. Results show that various problems in plastic deformation may be solved in a unified theoretical framework.

  13. Flavor Cosmology: Dynamical Yukawas in the Froggatt-Nielsen Mechanism

    CERN Document Server

    Baldes, Iason; Servant, Geraldine

    2016-01-01

    Can the cosmological dynamics responsible for settling down the present values of the Cabibbo-Kobayashi-Maskawa matrix be related to electroweak symmetry breaking? If the Standard Model Yukawa couplings varied in the early universe and started with order one values before electroweak symmetry breaking, the CP violation associated with the CKM matrix could be the origin of the matter-antimatter asymmetry. The large effective Yukawa couplings which lead to the enhanced CP violation can also help in achieving a strong first-order electroweak phase transition. We study in detail the feasibility of this idea by implementing dynamical Yukawa couplings in the context of the Froggatt--Nielsen mechanism. We discuss two main realizations of such a mechanism, related phenomenology, cosmological and collider bounds, and provide an estimate of the baryonic yield. A generic prediction is that this scenario always features a new scalar field below the electroweak scale.

  14. Dynamic Mechanical Behaviors of 6082-T6 Aluminum Alloy

    Directory of Open Access Journals (Sweden)

    Peng Yibo

    2013-01-01

    Full Text Available The structural components of high speed trains are usually made of aluminum alloys, for example, 6082. The dynamic mechanical behavior of the material is one of key factors considered in structural design and safety assessment. In this paper, dynamic mechanical experiments were conducted with strain rate ranging from 0.001 s−1 to 100 s−1 using Instron tensile testing machine. The true stress-strain curves were fitted based on experimental data. Johnson-Cook model of 6082-T6 aluminum alloy was built to investigate the effect of strain and strain rate on flow stress. It has shown that the flow stress was sensitive to the strain rate. Yield strength and tensile strength increased with a high strain rate, which showed strain rate effect to some extent. Fracture analysis was carried out by using Backscattered Electron imaging (BSE. As strain rate increased, more precipitates were generated in fracture.

  15. Borghini's Mechanism for Dynamic Polarization in Polarized Targets

    CERN Document Server

    de Boer, Wim

    2015-01-01

    This paper is a contribution to the memorial session for Michel Borghini at the Spin 2014 conference in Bejing, honoring his pivotal role for the development of polarized targets in high energy physics. Borghini proposed for the first time the correct mechanism for dynamic polarization in polarized targets using organic materials doped with free radicals. In these amorphous materials the spin levels are broadened by spin-spin interactions and g-factor anisotropy, which allows a high dynamic polarization of nuclei by cooling of the spin-spin interaction reservoir. In this contribution I summarize the experimental evidence for this mechanism. These pertinent experiments were done at CERN in the years 1971 - 1974, when I was a graduate student under the guidance of Michel Borghini. I finish by shortly describing how Borghini's spin temperature theory is now applied in cancer therapy.

  16. Flavor cosmology: dynamical yukawas in the Froggatt-Nielsen mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Baldes, Iason; Konstandin, Thomas [DESY,Notkestraße 85, Hamburg, D-22607 (Germany); Servant, Géraldine [DESY,Notkestraße 85, Hamburg, D-22607 (Germany); II. Institute for Theoretical Physics, University of Hamburg,Luruper Chaussee 149, Hamburg, D-22761 (Germany)

    2016-12-15

    Can the cosmological dynamics responsible for settling down the present values of the Cabibbo-Kobayashi-Maskawa matrix be related to electroweak symmetry breaking? If the Standard Model Yukawa couplings varied in the early universe and started with order one values before electroweak symmetry breaking, the CP violation associated with the CKM matrix could be the origin of the matter-antimatter asymmetry. The large effective Yukawa couplings which lead to the enhanced CP violation can also help in achieving a strong first-order electroweak phase transition. We study in detail the feasibility of this idea by implementing dynamical Yukawa couplings in the context of the Froggatt-Nielsen mechanism. We discuss two main realizations of such a mechanism, related phenomenology, cosmological and collider bounds, and provide an estimate of the baryonic yield. A generic prediction is that this scenario always features a new scalar field below the electroweak scale. We point out ways to get around this conclusion.

  17. Dynamic mechanism and its modelling of micromachined electrostatic ultrasonic transducers

    Institute of Scientific and Technical Information of China (English)

    葛立峰

    1999-01-01

    A tensile-plate-on-air-spring model (or called TDK model for short) for micromachined electrostatic ultrasonic transducers has been developed based on a thorough investigation of their dynamic mechanism. The mechanical stiffness effects caused by the compressibility of air gaps, bending stiffness of the diaphragm and in-plane tension applied to the diaphragm, together with an electrostatic negative stiffness effect are included completely in the model. Desired particular fundamental frequency and bandwidth can be obtained by only properly tailoring the geometry, dimensions and materials of transducers according to the model, which provides thereby a reliable theoretical basis for the understanding and optimised design of such transducers.

  18. Dynamic Mechanism for Development of Urban and Rural Spatial Integration

    Institute of Scientific and Technical Information of China (English)

    Lufeng; DUAN

    2014-01-01

    The space is a place where human beings conduct social and economic activities,and also the carrier of any public living form and right action. Urban area and rural area are two integral parts of regional economic system. Without joint and coordinated development of urban and rural areas,it is impossible to realize global optimization of economy and maximization of social welfare. Through study of dynamic mechanism for development of urban and rural spatial integration,it is expected to understand laws,mechanism and means of urban and rural spatial structure evolution,so as to better promote sustainable development of urban and rural population,resources and environment.

  19. Acoustic Simulation with Dynamic Mechanisms in Virtual Reality

    Institute of Scientific and Technical Information of China (English)

    张琼; 石教英

    1998-01-01

    Although most investigators have realized the importance of acoustic simulation in sophisticated VR systems,large computational load involved in this process often contradicts the requirements of real-time interaction,which in return bring on applying the expensive hardware or VR-specific workstations to this area.In order to reduce the computational cost and try to realize the real-time acoustic simulation in software with (or even without)some low-cost hardware,this paper proposes some dynamic mechanisms which can be used as possible strategies embedded into acoustic simulation in VR.Preliminary implementation of those mechanisms has proved to be fairly effective.

  20. Entropic fluctuations in statistical mechanics: I. Classical dynamical systems

    Science.gov (United States)

    Jakšić, V.; Pillet, C.-A.; Rey-Bellet, L.

    2011-03-01

    Within the abstract framework of dynamical system theory we describe a general approach to the transient (or Evans-Searles) and steady state (or Gallavotti-Cohen) fluctuation theorems of non-equilibrium statistical mechanics. Our main objective is to display the minimal, model independent mathematical structure at work behind fluctuation theorems. In addition to its conceptual simplicity, another advantage of our approach is its natural extension to quantum statistical mechanics which will be presented in a companion paper. We shall discuss several examples including thermostated systems, open Hamiltonian systems, chaotic homeomorphisms of compact metric spaces and Anosov diffeomorphisms.

  1. Entropic Fluctuations in Statistical Mechanics I. Classical Dynamical Systems

    CERN Document Server

    Jakšić, Vojkan; Rey-Bellet, Luc

    2010-01-01

    Within the abstract framework of dynamical system theory we describe a general approach to the Transient (or Evans-Searles) and Steady State (or Gallavotti-Cohen) Fluctuation Theorems of non-equilibrium statistical mechanics. Our main objective is to display the minimal, model independent mathematical structure at work behind fluctuation theorems. Besides its conceptual simplicity, another advantage of our approach is its natural extension to quantum statistical mechanics which will be presented in a companion paper. We shall discuss several examples including thermostated systems, open Hamiltonian systems, chaotic homeomorphisms of compact metric spaces and Anosov diffeomorphisms.

  2. A dynamic, mitotic-like mechanism for bacterial chromosome segregation.

    Science.gov (United States)

    Fogel, Michael A; Waldor, Matthew K

    2006-12-01

    The mechanisms that mediate chromosome segregation in bacteria are poorly understood. Despite evidence of dynamic movement of chromosome regions, to date, mitotic-like mechanisms that act on the bacterial chromosome have not been demonstrated. Here we provide evidence that the Vibrio cholerae ParAI and ParBI proteins are components of an apparatus that pulls the origin region of the large V. cholerae chromosome to the cell pole and anchors it there. ParBI interacts with a conserved origin-proximal, centromere-like site (parSI) that, following chromosome replication, segregates asymmetrically from one pole to the other. While segregating, parSI stretches far away from neighboring chromosomal loci. ParAI forms a dynamic band that extends from the pole to the segregating ParBI/parSI complex. Movement of ParBI/parSI across the cell occurs in concert with ParAI retraction. Deletion of parAI disrupts proper origin localization and segregation dynamics, and parSI no longer separates from nearby regions. These data suggest that ParAI forms a dynamic structure that pulls the ParBI-bound chromosome to the pole in a process analogous to anaphase of eukaryotic mitosis.

  3. Mechanical characterization of nanoindented graphene via molecular dynamics simulations

    Directory of Open Access Journals (Sweden)

    Wang Tong

    2011-01-01

    Full Text Available Abstract The mechanical behavior of graphene under various indentation depths, velocities, and temperatures is studied using molecular dynamics analysis. The results show that the load, elastic and plastic energies, and relaxation force increased with increasing indentation depth and velocity. Nanoindentation induced pile ups and corrugations of the graphene. Resistance to deformation decreased at higher temperature. Strong adhesion caused topological defects and vacancies during the unloading process.

  4. Molecular dynamics simulation of nanocrystalline nickel: structure and mechanical properties

    Energy Technology Data Exchange (ETDEWEB)

    Swygenhoven, H. van [Paul Scherrer Inst. (PSI), Villigen (Switzerland); Caro, A. [Comision Nacional de Energia Atomica, San Carlos de Bariloche (Argentina). Centro Atomico Bariloche

    1997-09-01

    Molecular dynamics computer simulations of low temperature elastic and plastic deformation of Ni nanophase samples (3-7 nm) are performed. The samples are polycrystals nucleated from different seeds, with random locations and orientations. Bulk and Young`s modulus, onset of plastic deformation and mechanism responsible for the plastic behaviour are studied and compared with the behaviour of coarse grained samples. (author) 1 fig., 3 refs.

  5. Threading and misfit-dislocation motion in molecular-beam epitaxy-grown HgCdTe epilayers

    Science.gov (United States)

    Carmody, M.; Lee, D.; Zandian, M.; Phillips, J.; Arias, J.

    2003-07-01

    Lattice mismatch between the substrate and the absorber layer in single-color HgCdTe infrared (IR) detectors and between band 1 and band 2 in two-color detectors results in the formation of crosshatch lines on the surface and an array of misfit dislocations at the epi-interfaces. Threading dislocations originating in the substrate can also bend into the interface plane and result in misfit dislocations because of the lattice mismatch. The existence of dislocations threading through the junction region of HgCdTe IR-photovoltaic detectors can greatly affect device performance. High-quality CdZnTe substrates and controlled molecular-beam epitaxy (MBE) growth of HgCdTe can result in very low threading-dislocation densities as measured by the etch-pit density (EPD ˜ 104cm-2). However, dislocation gettering to regions of high stress (such as etched holes, voids, and implanted-junction regions) at elevated-processing temperatures can result in a high density of dislocations in the junction region that can greatly reduce detector performance. We have performed experiments to determine if the dislocations that getter to these regions of high stress are misfit dislocations at the substrate/absorber interface that have a threading component extending to the upper surface of the epilayer, or if the dislocations originate at the cap/absorber interface as misfit dislocations. The preceding mechanisms for dislocation motion are discussed in detail, and the possible diode-performance consequences are explored.

  6. Singular orientations and faceted motion of dislocations in body-centered cubic crystals.

    Science.gov (United States)

    Kang, Keonwook; Bulatov, Vasily V; Cai, Wei

    2012-09-18

    Dislocation mobility is a fundamental material property that controls strength and ductility of crystals. An important measure of dislocation mobility is its Peierls stress, i.e., the minimal stress required to move a dislocation at zero temperature. Here we report that, in the body-centered cubic metal tantalum, the Peierls stress as a function of dislocation orientation exhibits fine structure with several singular orientations of high Peierls stress-stress spikes-surrounded by vicinal plateau regions. While the classical Peierls-Nabarro model captures the high Peierls stress of singular orientations, an extension that allows dislocations to bend is necessary to account for the plateau regions. Our results clarify the notion of dislocation kinks as meaningful only for orientations within the plateau regions vicinal to the Peierls stress spikes. These observations lead us to propose a Read-Shockley type classification of dislocation orientations into three distinct classes-special, vicinal, and general-with respect to their Peierls stress and motion mechanisms. We predict that dislocation loops expanding under stress at sufficiently low temperatures, should develop well defined facets corresponding to two special orientations of highest Peierls stress, the screw and the M111 orientations, both moving by kink mechanism. We propose that both the screw and the M111 dislocations are jointly responsible for the yield behavior of BCC metals at low temperatures.

  7. Node reserve mechanism (over dynamic load-balancing)

    Energy Technology Data Exchange (ETDEWEB)

    Muniz, Francisco Junqueira; Azevedo, Carlos Vicente Goulart de; Dalle, Hugo Moura, E-mail: muniz@cdtn.br, E-mail: cvga@cdtn.br, E-mail: dallehm@cdtn.br [Centro de Desenvolvimento da Tecnologia Nuclear (CDTN/CNEN-MG), Belo Horizonte, MG (Brazil)

    2011-07-01

    Multiple-Instruction Multi-Data (MIMD) distributed-memory processing systems (such as an IBM like set of PCs, connected by a communication device) are since long time commercially available and in use. But many Research Institutions still use them as a mono-user facility: they are much more cost effective if used as a (multi-user) shared resource. However, the use of MIMD machines as a shared resource is often limited due to lack of an efficient, easy-to-use and on hand dynamic load-balancing technique. This work describes the arrangements that were made to establish the interface between a mechanism of processing power availability (resource determined from a shared computer facility) and simultaneous users, demand for resources. The key point is to allow the application designer to ask for (at once) as many nodes as he needs (a multi-reserve mechanism). The system runs over Linux/X86 computing nodes (a cluster). In order to show the interface functionality, the startup module of a MCNP package was modified in such a way that the multi-reserve node mechanism together with a multi-user dynamic load-balancing approach could be used. Nodes set demand is an intrinsic feature of MCNP package. Such modified MCNP package was successfully run over a dynamic load-balancing system. (author)

  8. Dislocations and other topological oddities

    Science.gov (United States)

    Pieranski, Pawel

    2016-03-01

    We will show that the book Dislocations by Jacques Friedel, published half a century ago, can still be recommended, in agreement with the author's intention, as a textbook "for research students at University and for students at engineering schools as well as for research engineers". Indeed, today dislocations are known to occur not only in solid crystals but also in many other systems discovered more recently such as colloidal crystals or liquid crystals having periodic structures. Moreover, the concept of dislocations is an excellent starting point for lectures on topological defects occurring in systems equipped with order parameters resulting from broken symmetries: disclinations in nematic or hexatic liquid crystals, dispirations in chiral smectics or disorientations in lyotropic liquid crystals. The discussion of dislocations in Blue Phases will give us an opportunity to call on mind Sir Charles Frank, friend of Jacques Friedel since his Bristol years, who called these ephemeral mesophases "topological oddities". Being made of networks of disclinations, Blue Phases are similar to Twist Grain Boundary (TGB) smectic phases, which are made of networks of screw dislocations and whose existence was predicted by de Gennes in 1972 on the basis of the analogy between smectics and superconductors. We will stress that the book by Jacques Friedel contains seeds of this analogy.

  9. Calculated Electronic and Magnetic Structure of Screw Dislocations in Alpha Iron

    Energy Technology Data Exchange (ETDEWEB)

    Odbadrakh, Khorgolkhuu [ORNL; Rusanu, Aurelian [ORNL; Stocks, George Malcolm [ORNL; Samolyuk, German D [ORNL; Eisenbach, Markus [ORNL; Wang, Yang [Pittsburgh Supercomputing Center; Nicholson, Don M [ORNL

    2011-01-01

    Local atomic magnetic moments in crystalline Fe are perturbed by the presence of dislocations. The effects are most pronounced near the dislocation core and decay slowly as the strain field of the dislocation decreases with distance. We have calculated the local moments using the Locally Self-consistent Multiple Scattering (LSMS) method for an 1848 atom supercell containing a screw- dislocation quadrupole. The atomic positions were determined by relaxation with an embedded atom force field. Finite size effects are found to be significant for this small cell size indicating that dislocation cores affect the electronic structure and magnetic moments of neighboring dislocations. The influence of neighboring dislocations point to a need to study individual dislocations from first principles just as they appear amidst surrounding atoms in large scale classical force field simulations. An approach for the use of the LSMS to calculate local moments in sub-volumes of large atomic configurations generated in the course of classical MD simulation of dislocation dynamics is discussed.

  10. Mobility of dissociated mixed dislocations under an Escaig stress

    Science.gov (United States)

    Burbery, Nathaniel; Das, Raj; Ferguson, George

    2017-06-01

    In FCC metals, the structure of a mixed dislocation core consists of two Shockley Partials which have different screw and edge character. The interactions between the partial dislocations can influence the stacking fault width (SFW). The SFW can also be manipulated by controlling the non-glide component of the total shear stress within the glide plane, commonly referred to as the ‘Escaig stress’, or τ e . Molecular dynamics simulations were used to reproduce the dynamic behaviour of the atomistic core and stacking fault of a moving mixed 30° dislocation in copper and with several magnitudes of τ e stress. Results showed that the {τ }e must be relatively large to cause a significant effect on the SFW and that once the SFW is changed it also has a corresponding effect on the drag coefficient for a dislocation moving at steady-state. The reduction of the SFW, to the extent that the partial dislocations come within close proximity (i.e., partially merge into an imperfect full dislocation), changed the linear curve-fit of the stress-velocity curve and could be associated with a ‘quasi-Peierls barrier’ effect. The SFW was also shown to change under a pure glide stress without the addition of a τ e stress when the velocity approached the supersonic limit, and caused an increase of the SFW in one direction and a reduction of the SFW in the other direction. This result demonstrates a unique characteristic of mixed dislocations which cannot be observed in the traditionally representative core structures of pure screw and pure edge dislocations because of their perfect symmetry. Surprisingly, the effects of the glide stress on the SFW were similar in magnitude to the effects of {τ }e, and also were found to have a corresponding effect on the drag coefficient. The unique characteristics observed are summarised in terms of a unified equation for the force equilibrium at steady-state, which considers the drag coefficient of the two partials as independent functions

  11. Subdiffusive dynamics of bump attractors: mechanisms and functional roles.

    Science.gov (United States)

    Qi, Yang; Breakspear, Michael; Gong, Pulin

    2015-02-01

    Bump attractors are localized activity patterns that can self-sustain after stimulus presentation, and they are regarded as the neural substrate for a host of perceptual and cognitive processes. One of the characteristic features of bump attractors is that they are neutrally stable, so that noisy inputs cause them to drift away from their initial locations, severely impairing the accuracy of bump location-dependent neural coding. Previous modeling studies of such noise-induced drifting activity of bump attractors have focused on normal diffusive dynamics, often with an assumption that noisy inputs are uncorrelated. Here we show that long-range temporal correlations and spatial correlations in neural inputs generated by multiple interacting bumps cause them to drift in an anomalous subdiffusive way. This mechanism for generating subdiffusive dynamics of bump attractors is further analyzed based on a generalized Langevin equation. We demonstrate that subdiffusive dynamics can significantly improve the coding accuracy of bump attractors, since the variance of the bump displacement increases sublinearly over time and is much smaller than that of normal diffusion. Furthermore, we reanalyze existing psychophysical data concerning the spread of recalled cue position in spatial working memory tasks and show that its variance increases sublinearly with time, consistent with subdiffusive dynamics of bump attractors. Based on the probability density function of bump position, we also show that the subdiffusive dynamics result in a long-tailed decay of firing rate, greatly extending the duration of persistent activity.

  12. Dislocation following revision total hip arthroplasty.

    Science.gov (United States)

    Gioe, Terence J

    2002-04-01

    Dislocation is a relatively common complication following revision total hip arthroplasty. Risk factors include surgical approach, gender, underlying diagnosis, comorbidities, surgical experience, and previous surgery; for later dislocations, risk factors include wear/deformation of polyethylene, trauma, and decreased muscle strength. Prevention and precaution are the watchwords for dislocations following revision total hip arthroplasty. For dislocations that do occur, treatment rests first on identifying the source of instability. Most dislocations can be managed by closed reduction. Constrained components may increase success rates, but only for appropriate indications. Prevention and treatment of dislocations following revision total hip arthroplasty are discussed in this article.

  13. A general numerical method to solve for dislocation configurations

    Science.gov (United States)

    Xin, X. J.; Wagoner, R. H.; Daehn, G. S.

    1999-08-01

    The shape of a mechanically equilibrated dislocation line is of considerable interest in the study of plastic deformation of metals and alloys. A general numerical method for finding such configurations in arbitrary stress fields has been developed. Analogous to the finite-element method (FEM), a general dislocation line is approximated by a series of straight segments (elements) bounded by nodes. The equilibrium configuration is found by minimizing the system energy with respect to nodal positions using a Newton-Raphson procedure. This approach, termed the finite-segment method (FSM), confers several advantages relative to segment-based, explicit formulations. The utility, generality, and robustness of the FSM is demonstrated by analyzing the Orowan bypass mechanism and a model of dislocation generation and equilibration at misfitting particles. Energy differences from previous analytical methods based on simple loop shapes are significant, up to 80 pct. Explicit expressions for the coordinate transformations, energies, and forces required for numerical implementation are presented.

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

    Science.gov (United States)

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

    2015-07-16

    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.

  15. Dynamic thermo-mechanical properties of various flowable resin composites

    Science.gov (United States)

    Balthazard, Rémy; Vincent, Marin; Dahoun, Abdessellam; Mortier, Eric

    2016-01-01

    Background This study compared the storage modulus (E’), the loss modulus (E’’) and the loss tangent (tan δ) of various flowable resin composites. Material and Methods Grandio Flow (GRF), GrandioSo Heavy Flow (GHF), Filtek Supreme XTE (XTE) and Filtek Bulk Fill (BUL) flowable resins and Clinpro Sealant (CLI) ultra-flowable pit and fissure sealant resin were used. 25 samples were tested using a dynamical mechanical thermal analysis system in bending mode. Measurements were taken within a temperature range of 10 to 55°C. The results were statistically analyzed using mixed-effect and repeated-measure analysis of variance followed by paired multiple comparisons. Results For all the materials, the E’ values decrease with temperature, whereas the tan δ values increase. Irrespective of the temperature, GHF and GRF present E’ and E’’ values significantly higher than all the other materials and CLI presents values significantly lower than all the other materials. Observation of the values for all the materials reveals a linear progression of the tan δ values with temperature. Conclusions A variation in temperature within a physiological range generates modifications in mechanical properties without damaging the material, however. Filler content in volume terms appears to be the crucial parameter in the mechanical behavior of tested materials. Key words:Dynamic mechanical thermal analysis, elastic modulus, filler content, flowable resin composites, loss modulus, loss tangent. PMID:27957266

  16. Mechanics of post-cam engagement during simulated dynamic activity.

    Science.gov (United States)

    Fitzpatrick, Clare K; Clary, Chadd W; Cyr, Adam J; Maletsky, Lorin P; Rullkoetter, Paul J

    2013-09-01

    Posterior-stabilized (PS) total knee arthroplasty (TKA) components employ a tibial post and femoral cam mechanism to guide anteroposterior knee motion in lieu of the posterior cruciate ligament. Some PS TKA patients report a clicking sensation when the post and cam engage, while severe wear and fracture of the post; we hypothesize that these complications are associated with excessive impact velocity at engagement. We evaluated the effect of implant design on engagement dynamics of the post-cam mechanism and resulting polyethylene stresses during dynamic activity. In vitro simulation of a knee bend activity was performed for four cadaveric specimens implanted with PS TKA components. Post-cam engagement velocity and flexion angle at initial contact were determined. The experimental data were used to validate computational predictions of PS mechanics using the same loading conditions. A lower limb model was subsequently utilized to compare engagement mechanics of eight TKA designs, relating differences between implants to geometric design features. Flexion angle and post-cam velocity at engagement demonstrated considerable ranges among designs (23°-89°, and 0.05-0.22 mm/°, respectively). Post-cam velocity was correlated (r = 0.89) with tibiofemoral condylar design features. Condylar geometry, in addition to post-cam geometry, played a significant role in minimizing engagement velocity and forces and stresses in the post. This analysis guides selection and design of PS implants that facilitate smooth post-cam engagement and reduce edge loading of the post.

  17. Interpretation of structure of dislocation on ground of the TFD model

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Mechanism underlying the formation of dislocation is expounded based on Thomas-Fermi-Dirac (TFD) electron theory. The criterion condition on the limit size of dislocations is raised, and the calculated results of the limit sizes of a set of elements are given.

  18. A Galeazzi-variant type fracture-dislocation in adults.

    Science.gov (United States)

    Vaishya, Raju; Shrestha, Sundar Kumar; Vaish, Abhishek

    2013-01-01

    Fracture of either radius or ulna with a dislocation either at the proximal or distal radioulnar joint (DRUJ) is not a common injury and is inherently unstable. Here we report a case series, with both-bone forearm fractures associated with dislocation of DRUJ, as a Galeazzi-variant type fracture-dislocation, and try to analyze this injury pattern. The study was based on 6 patients having Galeazzi-variant type fracture-dislocation of different age (20 to 45 years). All fractures were closed type. Two fractures involved the same level and three fractures were at different levels of radius and ulna shaft. After thorough examination and investigations they were treated with limited contact dynamic compression plate without additional fixation for DRUJ. All cases were followed up for 24 weeks. The maximum incidence occurred in age group between 31 and 40 years. All the fractures of both radius and ulna were united in average time of 12 weeks. Range of motion of wrist and elbow, supination and pronation at final follow-up were normal. There was no subsequent re-subluxation or dislocation of the DRUJ in any of the cases. Galeazzi variant in adult is a new undescribed pattern of forearm with wrist injury. Stable open reduction and internal fixation of both-bone forearm fractures is mandatory, followed by 3 to 4 weeks of immobilization in a cast for the healing of disrupted DRUJ.

  19. LDA Calculations of Dislocation Mobility in Fe & Mo

    Energy Technology Data Exchange (ETDEWEB)

    Murray S. Daw; Daryl Chrzan

    2007-07-13

    This Project was a collaborative effort between Murray Daw (Clemson) and Daryl Chrzan (LBNL/UCB). The main goal of this project was to accomplish the first-ever first principles calculations of the structure of the screw dislocation in Fe and to study the effects of stress and magnetization. The calculations were completed and reported at conferences. During the work on this project, the collaboration also tackled an important related question - the effect of periodic boundary conditions in dislocation dalculations on the stress-state. The solution to the problem for this particular case has had much broader impact than the specific results of the calculation in iron. This technique was published in Computational Materials Science, and has been applied recently to the study of dislocations on nanotubes (submitted). Finally, the collaboration considered the application of scaling formalism to a simple problem of dislocation emission from a single, stress-actived source. The result is a very elegant, compact solution to a simple textbook problem, which was published in Phil Mag. This result lays the foundation for continuing work on applying scaling formalism to dynamics of more complex dislocation problems.

  20. Atomistic deformation mechanisms in twinned copper nanospheres.

    Science.gov (United States)

    Bian, Jianjun; Niu, Xinrui; Zhang, Hao; Wang, Gangfeng

    2014-01-01

    In the present study, we perform molecular dynamic simulations to investigate the compression response and atomistic deformation mechanisms of twinned nanospheres. The relationship between load and compression depth is calculated for various twin spacing and loading directions. Then, the overall elastic properties and the underlying plastic deformation mechanisms are illuminated. Twin boundaries (TBs) act as obstacles to dislocation motion and lead to strengthening. As the loading direction varies, the plastic deformation transfers from dislocations intersecting with TBs, slipping parallel to TBs, and then to being restrained by TBs. The strengthening of TBs depends strongly on the twin spacing.

  1. Investigation of deformation mechanisms of staggered nanocomposites using molecular dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Mathiazhagan, S., E-mail: smathi.research@gmail.com; Anup, S., E-mail: anupiist@gmail.com

    2016-08-19

    Biological materials with nanostructure of regularly or stair-wise staggered arrangements of hard platelets reinforced in a soft protein matrix have superior mechanical properties. Applications of these nanostructures to ceramic matrix composites could enhance their toughness. Using molecular dynamics simulations, mechanical behaviour of the bio-inspired nanocomposites is studied. Regularly staggered model shows better flow behaviour compared to stair-wise staggered model due to the symmetrical crack propagation along the interface. Though higher stiffness and strength are obtained for stair-wise staggered models, rapid crack propagation reduces the toughness. Arresting this crack propagation could lead to superior mechanical properties in stair-wise staggered models. - Highlights: • The deformation behaviour of staggered nanocomposites is studied. • Stair-wise staggered model has high stiffness and strength, but low toughness. • Rapid crack growth in overlap region causes this low toughness. • Toughness could be enhanced by arresting interfacial crack in the overlap.

  2. A Dynamic Load Balancing Mechanism for Distributed Systems

    Institute of Scientific and Technical Information of China (English)

    蓝有然

    1996-01-01

    It is desirable in a distributed system to have the system load balanced evenly among the nodes so that the mean job response time is minimized.In this paper,we present a dynamic load balancing mechanism(DLB).It adopts a cntralized approach and is network topology independent.The DLB mechanism employs a set of threscholds which are automatically adjusted as the system load changes.It also provides a simple mechanism for the system to switch between periodic and instantaneous load balancing policies with ease.The performance of the proposed algorithm is evaluated by intensive simulations for various parameters.Te simulation results show that the mean job response time in a system implementing DLB algorithm is significantly lower than the same system without load balancings.Furthermore,compared with a previously proposed algorithm,DLB algorithm demonstrates improved performance,especially when the system is heavily loaded and the load is unevenly distributed.

  3. Geometry, mechanics, and dynamics the legacy of Jerry Marsden

    CERN Document Server

    Holm, Darryl; Patrick, George; Ratiu, Tudor

    2015-01-01

    This book illustrates the broad range of Jerry Marsden’s mathematical legacy in areas of geometry, mechanics, and dynamics, from very pure mathematics to very applied, but always with a geometric perspective. Each contribution develops its material from the viewpoint of geometric mechanics beginning at the very foundations, introducing readers to modern issues via illustrations in a wide range of topics. The twenty refereed papers contained in this volume are based on lectures and research performed during the month of July 2012 at the Fields Institute for Research in Mathematical Sciences, in a program in honor of Marsden's legacy. The unified treatment of the wide breadth of topics treated in this book will be of interest to both experts and novices in geometric mechanics. Experts will recognize applications of their own familiar concepts and methods in a wide variety of fields, some of which they may never have approached from a geometric viewpoint. Novices may choose topics that interest them among the ...

  4. Spatial localization of nonlinear waves spreading in materials in the presence of dislocations and point defects

    Science.gov (United States)

    Erofeev, V. I.; Leontieva, A. V.; Malkhanov, A. O.

    2017-06-01

    Within the framework of self consistent dynamic problems, the impact of dislocations and point defects on the spatial localization of nonlinear acoustic waves propagating in materials has been studied.

  5. The dynamic mechanism of presenilin-function: Sensitive gate dynamics and loop unplugging control protein access

    DEFF Research Database (Denmark)

    Somavarapu, Arun Kumar; Kepp, Kasper Planeta

    2016-01-01

    molecular dynamics in an explicit membrane with particular account of the as yet unexplored loop dynamics. We find that mature PSEN1 contains multiple distinct conformational states whereas non-mature PSEN1 is a typical one-state protein. We confirm a previously suggested gating mechanism, and find......There is no molecular explanation for the many presenilin 1 (PSEN1) mutations causing Alzheimer's disease, but both gain of function relating to amyloid production and loss of isolated PSEN1 function have been implied. We report here the first detailed dynamic all-atom model of mature PSEN1 from...... that the 106-131 loop acts as a "hinge" for the TM2 and TM6 "doors". More importantly, we identify an unplugging mechanism of the Exon 9 loop associated only with mature PSEN1. Proper opening of both the "gate" and "plug" in the membrane produces channel-like morphologies and access to the catalytic aspartates...

  6. Trapping of hydrogen and helium at an {110} edge dislocation in tungsten

    Science.gov (United States)

    Xie, Hongxian; Xu, Ke; Lu, Guang-Hong; Yu, Tao; Yin, Fuxing

    2017-02-01

    We have performed an atomistic simulation to investigate energetics and dynamic behaviour of hydrogen (H) and helium (He) at an {110} edge dislocation in tungsten (W). The edge dislocation is shown to attract H/He at the tensile stress region according to the negative interaction energy of H/He at the tensile stress region, which implies that the dislocation is energetically beneficial to accommodate both H and He. Dynamically both H and He are easy to diffuse into the dislocation core, indicating the 'down-hill' diffusion due to the presence of the dislocation serving as a trapping center for both H and He. Further, He exhibits much lower interaction energy and much faster diffusion into the dislocation core region as compared with H owing to the close shell electronic structure of He. The results suggest the edge dislocation as a trapping center facilitates the H/He accumulation, contributing to the understanding the role of the dislocation on the H/He accumulation and bubble formation in W.

  7. Continuum representation of systems of dislocation lines: A general method for deriving closed-form evolution equations

    Science.gov (United States)

    Monavari, Mehran; Sandfeld, Stefan; Zaiser, Michael

    2016-10-01

    Plasticity is governed by the evolution of, in general anisotropic, systems of dislocations. We seek to faithfully represent this evolution in terms of density-like variables which average over the discrete dislocation microstructure. Starting from T. Hochrainer's continuum theory of dislocations (CDD) (Hochrainer, 2015), we introduce a methodology based on the 'Maximum Information Entropy Principle' (MIEP) for deriving closed-form evolution equations for dislocation density measures of different order. These equations provide an optimum representation of the kinematic properties of systems of curved and connected dislocation lines with the information contained in a given set of density measures. The performance of the derived equations is benchmarked against other models proposed in the literature, using discrete dislocation dynamics simulations as a reference. As a benchmark problem we study dislocations moving in a highly heterogeneous, persistent-slip-band like geometry. We demonstrate that excellent agreement with discrete simulations can be obtained in terms of a very small number of averaged dislocation fields containing information about the edge and screw components of the total and excess (geometrically necessary) dislocation densities. From these the full dislocation orientation distribution which emerges as dislocations move through a channel-wall structure can be faithfully reconstructed.

  8. Bipolar dislocation of the clavicle

    Directory of Open Access Journals (Sweden)

    Wei Jiang

    2012-01-01

    Full Text Available 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.

  9. A Novel Method of Mechanical Oxidation of CNT for Polymer Nanocomposite Application: Evaluation of Mechanical, Dynamic Mechanical, and Rheological Properties

    Directory of Open Access Journals (Sweden)

    Priyanka Pandey

    2014-01-01

    Full Text Available A new approach of oxidation of carbon nanotubes has been used to oxidize the CNTs. A comparative aspect of the mechanical oxidation and acid oxidation process has been established. FTIR analysis and titration method have shown the higher feasibility of the mechanical oxidation method to oxidize the CNTs. Comparatively less damage to the CNTs has been observed in case of mechanically oxidized as compared to acid oxidized CNTs. The mechanical properties of the nanocomposites reinforced with the acid oxidized CNT (ACNT and mechanically oxidized CNTs (McCNT were analyzed and relatively higher properties in the nanocomposites reinforced with McCNT were noticed. The less degree of entanglement in the McCNTs was noticed as compared to ACNTs. The dynamic mechanical analysis of the nanocomposites revealed much improved load transfer capability in the McCNT reinforced composites. Further, the rheological properties of the nanocomposites revealed the higher performance of McCNT reinforced composites.

  10. Dynamics and control of mechanical systems in offshore engineering

    CERN Document Server

    He, Wei; How, Bernard Voon Ee; Choo, Yoo Sang

    2014-01-01

    Dynamics and Control of Mechanical Systems in Offshore Engineering is a comprehensive treatment of marine mechanical systems (MMS) involved in processes of great importance such as oil drilling and mineral recovery. Ranging from nonlinear dynamic modeling and stability analysis of flexible riser systems, through advanced control design for an installation system with a single rigid payload attached by thrusters, to robust adaptive control for mooring systems, it is an authoritative reference on the dynamics and control of MMS. Readers will gain not only a complete picture of MMS at the system level, but also a better understanding of the technical considerations involved and solutions to problems that commonly arise from dealing with them. The text provides:                                                                                                                                 ...

  11. A conciliation mechanism for self-organizing dynamic small groups.

    Science.gov (United States)

    Ren, Minglun; Hu, Zhongfeng; Jain, Hemant

    2016-01-01

    A group of individuals, organizations or things in internet of things (IoT) often dynamically self-organizes in small groups to accomplish certain tasks. This is common in virtual organization, social networks and the evolving field of IoT. These small groups have different behavioral characteristics than large groups. Members individually have some requirements and contribute some resources to the group. The organization and operation of such a group requires dynamic identification of group requirements that can be fulfilled by available resources and is approved by the group. We apply design science methods to develop an artifact that helps in conciliation of collective requirements and resources of small groups while maintaining each member's satisfaction. The mechanism also supports dynamic conciliation as members leave and new members join the group. Each member's requirement is specified as an explicit/implicit objective that is feasible/not feasible based on resources available to the group and whether the requirement is in alignment with other members' objectives. We validate the artifact by using it for a manufacturing service group and simulating the change in collective group requirements and resources as group membership changes dynamically.

  12. Dynamics of fluid and light intensity in mechanically stirred photobioreactor.

    Science.gov (United States)

    Zhang, T

    2013-10-10

    Turbulent flows in a single-stage and a two-stage impeller-stirred photobioreactor with a simple geometric configuration were analyzed using computational fluid dynamics. The trajectories of the microorganisms entrained in the flow field were traced by the particle tracking method. By projecting these trajectories onto a radial-axial (r-z) plane with a given azimuth angle, we were able to observe four different dynamics zones: circulation, pure rotation, trap, and slow-motion. Within the pure rotation zone, turbulence can be observed near the edges of the impeller. The light intensity and the light/dark cycles subjected by the microorganisms differ significantly in these zones. These differences can be further changed by providing different incident light illuminations on the reactor surface. The dynamics zones can be altered by modifying the geometric configuration of the reactor and the impeller stirring mechanism. In combination with the utilization of different incident light illuminations, the light intensity dynamics and the light/dark cycles subjected by the microorganisms can be controlled such that an optimal photobioreactor design with a high efficiency of light utilization and a high formation rate of the biochemical products can be realized.

  13. Bilateral Shoulder Dislocations Following a Motocross Accident

    National Research Council Canada - National Science Library

    H J Schroepfer; B M Martin; P J Millett

    2017-01-01

    .... A professional motocross racer experienced a high speed traumatic accident which resulted in bilateral shoulder dislocations with a rare associated complete anterosuperior RC tear due to a posterior dislocation...

  14. Three-dimensional imaging of dislocations in a nanoparticle at atomic resolution.

    Science.gov (United States)

    Chen, Chien-Chun; Zhu, Chun; White, Edward R; Chiu, Chin-Yi; Scott, M C; Regan, B C; Marks, Laurence D; Huang, Yu; Miao, Jianwei

    2013-04-04

    Dislocations and their interactions strongly influence many material properties, ranging from the strength of metals and alloys to the efficiency of light-emitting diodes and laser diodes. Several experimental methods can be used to visualize dislocations. Transmission electron microscopy (TEM) has long been used to image dislocations in materials, and high-resolution electron microscopy can reveal dislocation core structures in high detail, particularly in annular dark-field mode. A TEM image, however, represents a two-dimensional projection of a three-dimensional (3D) object (although stereo TEM provides limited information about 3D dislocations). X-ray topography can image dislocations in three dimensions, but with reduced resolution. Using weak-beam dark-field TEM and scanning TEM, electron tomography has been used to image 3D dislocations at a resolution of about five nanometres (refs 15, 16). Atom probe tomography can offer higher-resolution 3D characterization of dislocations, but requires needle-shaped samples and can detect only about 60 per cent of the atoms in a sample. Here we report 3D imaging of dislocations in materials at atomic resolution by electron tomography. By applying 3D Fourier filtering together with equal-slope tomographic reconstruction, we observe nearly all the atoms in a multiply twinned platinum nanoparticle. We observed atomic steps at 3D twin boundaries and imaged the 3D core structure of edge and screw dislocations at atomic resolution. These dislocations and the atomic steps at the twin boundaries, which appear to be stress-relief mechanisms, are not visible in conventional two-dimensional projections. The ability to image 3D disordered structures such as dislocations at atomic resolution is expected to find applications in materials science, nanoscience, solid-state physics and chemistry.

  15. Cortical dynamics as a therapeutic mechanism for touch healing.

    Science.gov (United States)

    Kerr, Catherine E; Wasserman, Rachel H; Moore, Christopher I

    2007-01-01

    Touch Healing (TH) therapies, defined here as treatments whose primary route of administration is tactile contact and/or active guiding of somatic attention, are ubiquitous across cultures. Despite increasing integration of TH into mainstream medicine through therapies such as Reiki, Therapeutic Touch,(TM) and somatically focused meditation practices such as Mindfulness-Based Stress Reduction, relatively little is known about potential underlying mechanisms. Here, we present a neuroscientific explanation for the prevalence and effectiveness of TH therapies for relieving chronic pain. We begin with a cross-cultural review of several different types of TH treatments and identify common characteristics, including: light tactile contact and/or a somatosensory attention directed toward the body, a behaviorally relevant context, a relaxed context and repeated treatment sessions. These cardinal features are also key elements of established mechanisms of neural plasticity in somatosensory cortical maps, suggesting that sensory reorganization is a mechanism for the healing observed. Consideration of the potential health benefits of meditation practice specifically suggests that these practices provide training in the regulation of neural and perceptual dynamics that provide ongoing resistance to the development of maladaptive somatic representations. This model provides several direct predictions for investigating ways that TH may induce cortical plasticity and dynamics in pain remediation.

  16. Measurement of dynamic surface tension by mechanically vibrated sessile droplets

    Science.gov (United States)

    Iwata, Shuichi; Yamauchi, Satoko; Yoshitake, Yumiko; Nagumo, Ryo; Mori, Hideki; Kajiya, Tadashi

    2016-04-01

    We developed a novel method for measuring the dynamic surface tension of liquids using mechanically vibrated sessile droplets. Under continuous mechanical vibration, the shape of the deformed droplet was fitted by numerical analysis, taking into account the force balance at the drop surface and the momentum equation. The surface tension was determined by optimizing four parameters: the surface tension, the droplet's height, the radius of the droplet-substrate contact area, and the horizontal symmetrical position of the droplet. The accuracy and repeatability of the proposed method were confirmed using drops of distilled water as well as viscous aqueous glycerol solutions. The vibration frequency had no influence on surface tension in the case of pure liquids. However, for water-soluble surfactant solutions, the dynamic surface tension gradually increased with vibration frequency, which was particularly notable for low surfactant concentrations slightly below the critical micelle concentration. This frequency dependence resulted from the competition of two mechanisms at the drop surface: local surface deformation and surfactant transport towards the newly generated surface.

  17. Relaxation mechanisms in glassy dynamics: the Arrhenius and fragile regimes.

    Science.gov (United States)

    Hentschel, H George E; Karmakar, Smarajit; Procaccia, Itamar; Zylberg, Jacques

    2012-06-01

    Generic glass formers exhibit at least two characteristic changes in their relaxation behavior, first to an Arrhenius-type relaxation at some characteristic temperature and then at a lower characteristic temperature to a super-Arrhenius (fragile) behavior. We address these transitions by studying the statistics of free energy barriers for different systems at different temperatures and space dimensions. We present a clear evidence for changes in the dynamical behavior at the transition to Arrhenius and then to a super-Arrhenius behavior. A simple model is presented, based on the idea of competition between single-particle and cooperative dynamics. We argue that Arrhenius behavior can take place as long as there is enough free volume for the completion of a simple T1 relaxation process. Once free volume is absent one needs a cooperative mechanism to "collect" enough free volume. We show that this model captures all the qualitative behavior observed in simulations throughout the considered temperature range.

  18. Simultaneous bilateral anterior shoulder dislocation: report of two cases and review of the literature

    Directory of Open Access Journals (Sweden)

    Tripathy Sujit Kumar

    2012-02-01

    Full Text Available 【Abstract】Bilateral shoulder dislocations are rare and almost always occur in the posterior direction. Simultaneous bilateral anterior shoulder dislocation is even rarer and only a few cases are stated in the literature. The most interesting part of a bilateral shoulder dislocation is about its injury mechanism as a synchronous and simultaneous force is needed to result in it. In cases of epilepsy or electrocution, the mechanism is different and the forceful contractions of the selective group of muscles result in the dislocation. This article reports two cases of bilateral simultaneous anterior shoulder joint dislocation that occurred after a road side accident and after an episode of convulsion in an epileptic patient. The dislocations were diagnosed early and reduced immediately with a proper postreduction rehabilitation. During their follow-up, both patients had sa-tisfactory functional outcome. This article emphasizes on the importance of shoulder examination in road side accident victims and epileptic patients. All orthopedic surgeons and emergency physicians should be aware of such unusual possibilities to have an early diagnosis and treatment. An early reduction and appropriate rehabilitation can provide satisfactory functional outcome. This article also briefly discusses the injury mechanisms, diagnoses and treatments of bilateral shoulder dislocation as reported in the literature. Key words: Shoulder dislocation; Epilepsy; Accidents, traffic

  19. Atomistic simulations of dislocation processes in copper

    DEFF Research Database (Denmark)

    Vegge, T.; Jacobsen, K.W.

    2002-01-01

    We discuss atomistic simulations of dislocation processes in copper based on effective medium theory interatomic potentials. Results on screw dislocation structures and processes are reviewed with particular focus on point defect mobilities and processes involving cross slip. For example, the sta......We discuss atomistic simulations of dislocation processes in copper based on effective medium theory interatomic potentials. Results on screw dislocation structures and processes are reviewed with particular focus on point defect mobilities and processes involving cross slip. For example...

  20. Financial Dislocations among Divorcing Families.

    Science.gov (United States)

    Little, Marilyn J.

    Extensive economic changes may be brought about by divorce. In an attempt to demonstrate that the degree of financial dislocation following divorce depends on three factors--custody arrangements, wife's employment, and social class--data on men's and women's employment, income, and support payments were gathered for 222 divorcing families. Total…

  1. Molecular dynamics simulations of diffusion mechanisms in NiAl

    Energy Technology Data Exchange (ETDEWEB)

    Soule De Bas, B.; Farkas, D

    2003-03-14

    Molecular dynamics simulations of the diffusion process in ordered B2 NiAl at high temperature were performed using an embedded atom interatomic potential. Diffusion occurs through a variety of cyclic mechanisms that accomplish the motion of the vacancy through nearest neighbor jumps restoring order to the alloy at the end of the cycle. The traditionally postulated six-jump cycle is only one of the various cycles observed and some of these are quite complex. A detailed sequential analysis of the observed six-jump cycles was performed and the results are analyzed in terms of the activation energies for individual jumps calculated using molecular statics simulations.

  2. Intermediate filaments: a dynamic network that controls cell mechanics.

    Science.gov (United States)

    Gruenbaum, Yosef; Aebi, Ueli

    2014-01-01

    In humans the superfamily of intermediate filament (IF) proteins is encoded by more than 70 different genes, which are expressed in a cell- and tissue-specific manner. IFs assemble into approximately 10 nm-wide filaments that account for the principal structural elements at the nuclear periphery, nucleoplasm, and cytoplasm. They are also required for organizing the microtubule and microfilament networks. In this review, we focus on the dynamics of IFs and how modifications regulate it. We also discuss the role of nuclear IF organization in determining nuclear mechanics as well as that of cytoplasmic IFs organization in maintaining cell stiffness, formation of lamellipodia, regulation of cell migration, and permitting cell adhesion.

  3. Posterior Dislocation of the Hinge-Post Extension in a Rotating Hinge Total Knee Prosthesis

    Directory of Open Access Journals (Sweden)

    Givenchy Manzano

    2013-01-01

    Full Text Available The rotating hinge knee prosthesis is a popular intervention in patients lacking stability with highly constrained total knee arthroplasty. Despite improvements in design, nonmechanical and mechanical complications continue to be a problem. Dislocation of the hinge has been widely described, mainly due to the component fracture. Few reports describe isolated dislocation of the rotating stem. We report a case of isolated disengagement of the rotating hinge mechanism, due to severe flexion gap imbalance, leading to subsequent posterior dislocation of the hinge and anterior knee dislocation, in a patient with a history of multiple total knee arthroplasty revisions. This case suggests the importance of the soft tissue balancing, the adequate patellar tracking, and use of a long cylindrical, minimally tapered rotating stem in hinge arthroplasty to minimize hinge dislocation.

  4. Dynamical weakening of pyroclastic flows by mechanical vibrations

    Science.gov (United States)

    Valverde, Jose Manuel; Soria-Hoyo, Carlos; Roche, Olivier

    2017-06-01

    Dynamical weakening of dense granular flows plays a critical role on diverse geological events such as seismic faulting and landslides. A common feature of these processes is the development of fluid-solid relative flows that could lead to fluidization by hydrodynamic viscous stresses. Volcanic ash landslides (pyroclastic flows) are characterized by their high mobility often attributed to fluidization of the usually fine and/or low-density particles by their interaction with the entrapped gas. However, the physical mechanism that might drive sustained fluidization of these dense granular flows over extraordinarily long runout distances is elusive. The behavior of volcanic ash in a slowly rotating drum subjected to mechanical vibrations shown in this work suggests that fluid-particle relative oscillations in dense granular flows present in volcanic eruption events can promote pore gas pressure at reduced shear rates as to sustain fluidization.

  5. Dynamic Mechanical Properties of Bio-Polymer Graphite Thin Films

    Science.gov (United States)

    Saddam Kamarudin, M.; Rus, Anika Zafiah M.; Munirah Abdullah, Nur; Abdullah, M. F. L.

    2017-08-01

    Waste cooking oil is used as the main substances in producing graphite biopolymer thin films. Biopolymer is produce from the reaction of bio-monomer and cross linker with the ratio of 2:1 and addition of graphite with an increment of 2% through a slip casting method. The morphological surface properties of the samples are observed by using Scanning Electron Microscope (SEM). It is shown that the graphite particle is well mixed and homogenously dispersed in biopolymer matrix. Meanwhile, the mechanical response of materials by monitoring the change in the material properties in terms of frequency and temperature of the samples were determined using Dynamic Mechanical Analysis (DMA). The calculated cross-linked density of biopolymer composites revealed the increment of graphite particle loading at 8% gives highest results with 260.012 x 103 M/m3.

  6. Characterizing short-range vs. long-range spatial correlations in dislocation distributions

    Energy Technology Data Exchange (ETDEWEB)

    Chevy, Juliette, E-mail: juliette.chevy@gmail.com [Laboratoire de Glaciologie et Geophysique de l' Environnement-CNRS, 54 rue Moliere, 38402 St. Martin d' Heres (France)] [Laboratoire Science et Ingenierie des Materiaux et Procedes, Grenoble INP-CNRS-UJF, BP 75, 38402 St. Martin d' Heres Cedex (France); Fressengeas, Claude; Lebyodkin, Mikhail; Taupin, Vincent [Laboratoire de Physique et Mecanique des Materiaux, Universite Paul Verlaine-Metz/CNRS, Ile du Saulcy, 57045 Metz Cedex (France); Bastie, Pierre [Laboratoire de Spectrometrie Physique, BP 87, 38402 St. Martin d' Heres Cedex (France)] [Institut Laue Langevin, BP 156, 38042 Grenoble Cedex 9 (France); Duval, Paul [Laboratoire de Glaciologie et Geophysique de l' Environnement-CNRS, 54 rue Moliere, 38402 St. Martin d' Heres (France)

    2010-03-15

    Hard X-ray diffraction experiments have provided evidence of a strongly heterogeneous distribution of dislocation densities along the axis of cylindrical ice single crystals oriented for basal slip in torsion creep. The dislocation arrangements showed a complex scale-invariant character, which was analyzed by means of statistical and multifractal techniques. A trend to decreasing autocorrelation of the dislocation distribution was observed as deformation proceeds. At low strain levels, long-range spatial correlations control the distribution, but short-range correlations in relation with cross-slip progressively prevail when strain increases. This trend was reproduced by a model based on field dislocation dynamics, a theory accounting for both long-range elastic interactions and short-range interactions through transport of dislocation densities.

  7. Towards further understanding of stacking fault tetrahedron absorption and defect-free channels – A molecular dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Fan, Haidong, E-mail: haidongfan8@foxmail.com [Department of Mechanics, Sichuan University, Chengdu 610065 (China); Key Laboratory of Energy Engineering Safety and Disaster Mechanics, Ministry of Education, Chengdu 610065 (China); Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218 (United States); El-Awady, Jaafar A. [Department of Mechanical Engineering, Johns Hopkins University, Baltimore, MD 21218 (United States); Wang, Qingyuan, E-mail: wangqy@scu.edu.cn [Department of Mechanics, Sichuan University, Chengdu 610065 (China); Key Laboratory of Energy Engineering Safety and Disaster Mechanics, Ministry of Education, Chengdu 610065 (China)

    2015-03-15

    Highlights: • Stacking fault tetrahedron (SFT) is fully absorbed by screw dislocation. • Absorbed SFT becomes moveable with the aid of Lomer dislocations. • Finally SFT is removed from the specimen or from defect-free channels. • Two scenarios responsible for the formation of defect-free channels were proposed. - Abstract: The mechanisms leading to stacking fault tetrahedron (SFT) absorption via interactions with dislocations, and subsequent formation of plastic flow localization in defect-free channels, which were frequently observed in irradiated materials in transmission electron microscopy experiments, are still unclear. To address this, screw dislocation interactions with SFTs in copper were investigated using molecular dynamics (MD) simulations. The interaction details reveal that a screw dislocation can fully absorb an SFT through the thermally activated transformation of Lomer–Cottrell lock into Lomer dislocations. After absorption, almost all the vacancies in the SFT are transferred into Lomer dislocations, which are able to move transversely under complex loading conditions. As a result, SFTs can be removed from the material (for SFTs near surface) or from defect-free channels (for SFTs in the bulk) with the aid of Lomer dislocations. In addition, it was shown that this absorption process is favorable only at high temperature, low applied shear stress and/or high SFT density. These results are in good agreement with in situ TEM observations. The current simulations and analyses provide useful insights into the formation mechanisms of defect-free channels in irradiated materials.

  8. Dynamic Response of Linear Mechanical Systems Modeling, Analysis and Simulation

    CERN Document Server

    Angeles, Jorge

    2012-01-01

    Dynamic Response of Linear Mechanical Systems: Modeling, Analysis and Simulation can be utilized for a variety of courses, including junior and senior-level vibration and linear mechanical analysis courses. The author connects, by means of a rigorous, yet intuitive approach, the theory of vibration with the more general theory of systems. The book features: A seven-step modeling technique that helps structure the rather unstructured process of mechanical-system modeling A system-theoretic approach to deriving the time response of the linear mathematical models of mechanical systems The modal analysis and the time response of two-degree-of-freedom systems—the first step on the long way to the more elaborate study of multi-degree-of-freedom systems—using the Mohr circle Simple, yet powerful simulation algorithms that exploit the linearity of the system for both single- and multi-degree-of-freedom systems Examples and exercises that rely on modern computational toolboxes for both numerical and symbolic compu...

  9. The superspreading mechanism unveiled via molecular dynamics simulations

    Science.gov (United States)

    Theodorakis, Panagiotis; Muller, Erich; Craster, Richard; Matar, Omar

    2014-11-01

    Superspreading, by which aqueous droplets laden with specific surfactants wet hydrophobic substrates, is an unusual and dramatic phenomenon. This is attributed to various factors, e.g., a particular surfactant geometry, Marangoni flow, unique solid-fluid interactions, however, direct evidence for a plausible mechanism for superspreading has not yet been provided. Here, we use molecular dynamics simulations of a coarse-grained model with force fields obtained from the SAFT- γ equation of state to capture the superspreading mechanism of water drops with surfactants on model surfaces. Our simulations highlight and monitor the main features of the molecular behavior that lead to the superspreading mechanism, and reproduce and explain the experimentally-observed characteristic maxima of the spreading rate of the droplet vs. surfactant concentration and wettability. We also present a comparison between superspreading and non-superspreading surfactants underlining the main morphological and energetic characteristics of superspreaders. We believe that this is the first time a plausible superspreading mechanism based on a microscopic description is proposed; this will enable the design of surfactants with enhanced spreading ability specifically tailored for applications. EPSRC Grant Number EP/J010502/1.

  10. Bilateral Traumatic Anterior Dislocation of Shoulder – a rare entity

    Directory of Open Access Journals (Sweden)

    Yashavantha Kumar C

    2013-01-01

    Full Text Available Introduction: Bilateral shoulder dislocation are most commonly posterior type. These are most commonly due to seizure disorder and electrocution. Anterior shoulder dislocations occurring bilaterally without any predisposing factors are very rare. These types of injuries are due to trauma with a unique mechanism of injury. To best of our knowledge there are only few cases of similar kind are reported in literature. We hereby report a interesting case of posttraumatic, bilateral anterior dislocation of shoulder without associated fracture in a 45 old women without any predisposing pathoanatomy.Case Report: A 45-year-old women presented to casualty with sudden onset of pain and restriction of movement in both shoulders fallowing trauma. Immediately post trauma she had severe pain and restriction of both shoulders. On examination arms were abducted and externally rotated. Bilateral shoulder movements were painful and restricted . There was loss of round contour of shoulder with increased vertical diameter of axilla anteriorly. Radiological examination revealed bilateral anterior dislocation of the shoulders without any associated fractures. Closed reduction done by Milch technique after intraraticular lignocaine injection. MRI of bilateral shoulder showed no pathological lesion. Both shoulders were immobilized with a shoulder immobilizer for three weeks.Conclusion: Most of the bilateral shoulder dislocations are posterior type seen in seizure disorders. Bilateral traumatic anterior shoulder dislocations are rare and are seen as a result of unique mechanism of injury. In our case patient had a fall on her elbows causing forced extension. If diagnosed and treated promptly completely normal function of the shoulders can be restored.

  11. Discrete dislocation plasticity

    NARCIS (Netherlands)

    van der Giessen, E.; Finel, A; Maziere, D; Veron, M

    2003-01-01

    Conventional continuum mechanics models of inelastic deformation processes axe size scale independent. In contrast, there is considerable experimental evidence that plastic flow in crystalline materials is size dependent over length scales of the order of tens of microns and smaller. At present ther

  12. Mechanical Models of the Dynamics of Vitreous Substitutes

    Science.gov (United States)

    Pralits, Jan O.; Repetto, Rodolfo; Romano, Mario R.

    2014-01-01

    We discuss some aspects of the fluid dynamics of vitreous substitutes in the vitreous chamber, focussing on the flow induced by rotations of the eye bulb. We use simple, yet not trivial, theoretical models to highlight mechanical concepts that are relevant to understand the dynamics of vitreous substitutes and also to identify ideal properties for vitreous replacement fluids. We first recall results by previous authors, showing that the maximum shear stress on the retina grows with increasing viscosity of the fluid up to a saturation value. We then investigate how the wall shear stress changes if a thin layer of aqueous humour is present in the vitreous chamber, separating the retina from the vitreous replacement fluid. The theoretical predictions show that the existence of a thin layer of aqueous is sufficient to substantially decrease the shear stress on the retina. We finally discuss a theoretical model that predicts the stability conditions of the interface between the aqueous and a vitreous substitute. We discuss the implications of this model to understand the mechanisms leading to the formation of emulsion in the vitreous chamber, showing that instability of the interface is possible in a range of parameters relevant for the human eye. PMID:25147810

  13. A concept of dynamic permission mechanism on android

    Science.gov (United States)

    Aron, Lukas; Hanacek, Petr

    2016-02-01

    This paper discuss the main security topic in mobile security area and this topic is protect user against the leakage of data. This work primarily contains the proposal of concept of dynamic permission mechanism for Android operating system. This mechanism deals with assignment or enforcement permissions to the application according to files that the application works with. Application has set of permissions that can use, but if the user opens confident files the application permissions should change its permission set and there should not be possible leakage of this secret data. The permissions set should be stricter according to opened confidential file or more open (without restriction) if the file is not secret file. The concept proposes the solution for protecting this data leakage. Idea covers rule that user should be avoided of change this permissions himself, but this behavior should be dynamic, automatic and independent. This proposal is mainly aimed to Android operating system, but the concept can be applied to other mobile platforms with some implementation changes.

  14. Experimental study on dynamic mechanical behaviors of polycarbonate

    Science.gov (United States)

    Zhang, Wei; Gao, Yubo; Ye, Nan; Huang, Wei; Li, Dacheng

    2017-01-01

    Polycarbonate (PC) is a widely used engineering material in aerospace field, since it has excellent mechanical and optical property. In present study, both compressive and tensile tests of PC were conducted at high strain rates by using a split Hopkinson pressure bar. The high-speed camera and 2D Digital Image Correlation method (DIC) were used to analyze the dynamic deformation behavior of PC. Meanwhile, the plate impact experiment was carried out to measure the equation of state of PC in a single-stage gas gun, which consists of asymmetric impact technology, manganin gauges, PVDF, electromagnetic particle velocity gauges. The results indicate that the yield stress of PC increased with the strain rates in both dynamic compression and tension tests. The same phenomenon was similar to elasticity modulus at different strain rate. A constitutive model was used to describe the mechanical behaviors of PC accurately in different strain rates by contrast with the results of 2D-DIC. At last, The D-u Hugoniot curve of polycarbonate in high pressure was fitted by the least square method.

  15. Mechanical Models of the Dynamics of Vitreous Substitutes

    Directory of Open Access Journals (Sweden)

    Krystyna Isakova

    2014-01-01

    Full Text Available We discuss some aspects of the fluid dynamics of vitreous substitutes in the vitreous chamber, focussing on the flow induced by rotations of the eye bulb. We use simple, yet not trivial, theoretical models to highlight mechanical concepts that are relevant to understand the dynamics of vitreous substitutes and also to identify ideal properties for vitreous replacement fluids. We first recall results by previous authors, showing that the maximum shear stress on the retina grows with increasing viscosity of the fluid up to a saturation value. We then investigate how the wall shear stress changes if a thin layer of aqueous humour is present in the vitreous chamber, separating the retina from the vitreous replacement fluid. The theoretical predictions show that the existence of a thin layer of aqueous is sufficient to substantially decrease the shear stress on the retina. We finally discuss a theoretical model that predicts the stability conditions of the interface between the aqueous and a vitreous substitute. We discuss the implications of this model to understand the mechanisms leading to the formation of emulsion in the vitreous chamber, showing that instability of the interface is possible in a range of parameters relevant for the human eye.

  16. Respiratory mechanics and fluid dynamics after lung resection surgery.

    Science.gov (United States)

    Miserocchi, Giuseppe; Beretta, Egidio; Rivolta, Ilaria

    2010-08-01

    Thoracic surgery that requires resection of a portion of lung or of a whole lung profoundly alters the mechanical and fluid dynamic setting of the lung-chest wall coupling, as well as the water balance in the pleural space and in the remaining lung. The most frequent postoperative complications are of a respiratory nature, and their incidence increases the more the preoperative respiratory condition seems compromised. There is an obvious need to identify risk factors concerning mainly the respiratory function, without neglecting the importance of other comorbidities, such as coronary disease. At present, however, a satisfactory predictor of postoperative cardiopulmonary complications is lacking; postoperative morbidity and mortality have remained unchanged in the last 10 years. The aim of this review is to provide a pathophysiologic interpretation of the main respiratory complications of a respiratory nature by relying on new concepts relating to lung fluid dynamics and mechanics. New parameters are proposed to improve evaluation of respiratory function from pre- to the early postoperative period when most of the complications occur.

  17. Dislocation structure in interfaces between Si wafers with hybrid crystal orientation

    Energy Technology Data Exchange (ETDEWEB)

    Vdovin, Vladimir [Institute for Chemical Problems of Microelectronics, Moscow (Russian Federation); Zakharov, Nikolai; Pippel, Eckhard; Werner, Peter [Max-Planck-Institut fuer Mikrostrukturphysik, Halle (Saale) (Germany); Milvidskii, Mikhail [Institute of Rare Metals ' Giredmet' , Moscow (Russian Federation); Ries, Mike; Seacrist, Mike [MEMC Inc., 501 Pearl Drive, St. Peters, MO (United States); Falster, Robert [MEMC Electronic Materials SpA, Novara (Italy)

    2009-08-15

    Dislocation structure in Si(110)/Si(001) wafer bonding (WB) structures have been studied by transmission electron microscopy (TEM). The behavior of intermediate native oxide layers during high temperature annealing, the nature of interfacial dislocations and dislocation generation mechanisms are the main issues of this work. Samples were fabricated by direct hydrophilic WB of 200 mm wafers with native oxide. The as-bonded structures containing 140-nm thick layers were thermally annealed in the temperature range 1150 to 1200 C. The dislocation structure composed of a pattern of unidirectional parallel but broken dislocation arrays is formed in the structures with partial or entire dissolution of the oxide layer. The contrast of broken dark lines usually observed in TEM bright field micrographs is supposed to be caused by integral effect of steps compensating twist misorientation and arrays of 60-degree dislocations. We suggest that nucleation of dislocation loops at the interface due to the agglomeration of intrinsic point defects is a plausible mechanism of dislocation generation. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  18. Estimation of dislocation density from precession electron diffraction data using the Nye tensor

    Energy Technology Data Exchange (ETDEWEB)

    Leff, A.C. [Department of Materials Science & Engineering, Drexel University, Philadelphia, PA (United States); Weinberger, C.R. [Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, PA (United States); Taheri, M.L., E-mail: mtaheri@coe.drexel.edu [Department of Materials Science & Engineering, Drexel University, Philadelphia, PA (United States)

    2015-06-15

    The Nye tensor offers a means to estimate the geometrically necessary dislocation density of a crystalline sample based on measurements of the orientation changes within individual crystal grains. In this paper, the Nye tensor theory is applied to precession electron diffraction automated crystallographic orientation mapping (PED-ACOM) data acquired using a transmission electron microscope (TEM). The resulting dislocation density values are mapped in order to visualize the dislocation structures present in a quantitative manner. These density maps are compared with other related methods of approximating local strain dependencies in dislocation-based microstructural transitions from orientation data. The effect of acquisition parameters on density measurements is examined. By decreasing the step size and spot size during data acquisition, an increasing fraction of the dislocation content becomes accessible. Finally, the method described herein is applied to the measurement of dislocation emission during in situ annealing of Cu in TEM in order to demonstrate the utility of the technique for characterizing microstructural dynamics. - Highlights: • Developed a method of mapping GND density using orientation mapping data from TEM. • As acquisition length-scale is decreased, all dislocations are considered GNDs. • Dislocation emission and corresponding grain rotation quantified.

  19. Spatio-temporal Dynamics and Mechanisms of Stress Granule Assembly.

    Directory of Open Access Journals (Sweden)

    Daisuke Ohshima

    2015-06-01

    Full Text Available Stress granules (SGs are non-membranous cytoplasmic aggregates of mRNAs and related proteins, assembled in response to environmental stresses such as heat shock, hypoxia, endoplasmic reticulum (ER stress, chemicals (e.g. arsenite, and viral infections. SGs are hypothesized as a loci of mRNA triage and/or maintenance of proper translation capacity ratio to the pool of mRNAs. In brain ischemia, hippocampal CA3 neurons, which are resilient to ischemia, assemble SGs. In contrast, CA1 neurons, which are vulnerable to ischemia, do not assemble SGs. These results suggest a critical role SG plays in regards to cell fate decisions. Thus SG assembly along with its dynamics should determine the cell fate. However, the process that exactly determines the SG assembly dynamics is largely unknown. In this paper, analyses of experimental data and computer simulations were used to approach this problem. SGs were assembled as a result of applying arsenite to HeLa cells. The number of SGs increased after a short latent period, reached a maximum, then decreased during the application of arsenite. At the same time, the size of SGs grew larger and became localized at the perinuclear region. A minimal mathematical model was constructed, and stochastic simulations were run to test the modeling. Since SGs are discrete entities as there are only several tens of them in a cell, commonly used deterministic simulations could not be employed. The stochastic simulations replicated observed dynamics of SG assembly. In addition, these stochastic simulations predicted a gamma distribution relative to the size of SGs. This same distribution was also found in our experimental data suggesting the existence of multiple fusion steps in the SG assembly. Furthermore, we found that the initial steps in the SG assembly process and microtubules were critical to the dynamics. Thus our experiments and stochastic simulations presented a possible mechanism regulating SG assembly.

  20. Resistive Switching of Individual Dislocations in Insulating Perovskites -- A Potential Route Towards Nanoscale Non-Volatile Memories.

    Science.gov (United States)

    Szot, Krzystof; Speier, Wolfgang; Bihlmayer, Gustav; Waser, Rainer

    2006-03-01

    Electrically controlled resistive switching effects have been reported for a broad variety of binary and multinary oxides in recent years. In particular, titanates, zirconates, and manganites have been in the focus of the studies. In many cases, the mechanism of the switching and the geometrical extension of the phenomenon (filaments vs. bulk) are still under discussion. In this work, we present evidence for a redox-based switching mechanism and we indicate a potential route towards highly scalable non-volatile memories based on this switching effect. The challenge our work is to utilize resistive switching mechanism with the aim to construct active electronic elements on a real nanoscale level, here by reversibly switching the electrical properties of individual dislocations by electrical stimuli. We demonstrate that standard undoped SrTiO3 single crystals, utilized as a model system, exhibit a switching behavior along filaments based on dislocations, mediated by oxygen transport. For this, we employed a three-step procedure: the crystals were, at first, annealed at elevated temperatures under reducing conditions, then exposed to 200mbar O2 pressure at room temperature, and finally subjected to an electric field under ultrahigh vacuum (electroformation). This treatment induced in a metal-insulator (SrTiO3)-metal (MIM) system a transition to metallic state. A hysteretic behavior appears after dynamical polarization of the MIM structure at the maximum electroforming currents. The shape of the I/V curve has the typical signature for bi-stable switching known for these types of perovskites. The positive temperature dependence of the resistance of the low- (LRS) and the high-resistance (HRS) state clearly identifies both states to be metallic in character. The inhomogeneity of the electrical transport becomes directly evident from a simple optical inspection and the conductivity maps as measured by LC-AFM of a planar structure. One can trace the formation of the

  1. Solute drag on perfect and extended dislocations

    Science.gov (United States)

    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.

  2. Limits of Dislocation-based Deformation of Ni

    Science.gov (United States)

    Follstaedt, David; Knapp, James; Hugo, Richard; Kung, Harriet

    2001-11-01

    How small can metallic grains be and still deform by dislocation glide? This question is critical to understanding the mechanical properties of nanocrystalline Ni and for enhancing yield strength and hardness while maintaining ductility. As grain size is reduced in the micrometer range, the hardness of Ni scales as H = Ho + kd-1/2 in accordance with the dislocation-based Hall-Petch relation; however, below 100-50 nm the observed hardness no longer increases. Theoretical treatments indicate that intergranular types of deformation will replace dislocation motion at a few 10's of nanometers. To probe this limit, we have prepared a nearly ideal Ni material with very fine, uniform grain size and uncontaminated grain boundaries by using pulsed laser deposition. In situ tensile straining in the TEM directly shows dislocation motion in grains as small as 20 nm. Moreover, the material exhibits excellent ductility, consistent with this mechanism. We also find high yield strengths (2.4 GPa) and hardnesses (10 GPa) that agree with extensions of the Hall-Petch mechanism down to 12 nm grain-size. Sandia is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy under Contract DE-AC04-94AL85000.

  3. Cell Mechanics From cytoskeletal dynamics to tissue-scale mechanical phenomena

    Science.gov (United States)

    Banerjee, Shiladitya

    This dissertation explores the mechanics of living cells, integrating the role of intracellular activity to capture the emergent mechanical behavior of cells. The topics covered in this dissertation fall into three broad categories : (a) intracellular mechanics, (b) interaction of cells with the extracellular matrix and (c) collective mechanics of multicellular colonies. In part (a) I propose theoretical models for motor-filament interactions in the cell cytoskeleton, which is the site for mechanical force generation in cells. The models predict in a unified manner how contractility, dynamic instabilities and mechanical waves arise in the cytoskeleton by tuning the activity of molecular motors. The results presented in (a) holds relevance to a variety of cellular systems that behave elastically at long time scales, such as muscle sarcomeres, actomyosin stress fibers, adherent cells. In part (b) I introduce a continuum mechanical model for cells adherent to two-dimensional extracellular matrix, and discuss how cells can sense mechanical and geometrical cues from its surrounding matrix. The model provides an important step towards a unified theoretical description of the dependence of traction forces on cell size, actomyosin activity, matrix depth and stiffness, strength of focal adhesions and makes experimentally testable predictions. In part (c) we combine experiment and theory to reveal how intercellular adhesions modulate forces transmitted to the extracellular matrix. We find that In the absence of cadherin-based adhesions, cells within a colony appear to act independently, whereas with strong cadherin-based adhesions, the cell colony behaves like a liquid droplet wetting the substrate underneath. This work defines the importance of intercellular adhesions in coordinating mechanical activity of cell monolayers and has implications for the mechanical regulation of tissues during development, homeostasis, and disease.

  4. A Practical Quantum Mechanics Molecular Mechanics Method for the Dynamical Study of Reactions in Biomolecules.

    Science.gov (United States)

    Mendieta-Moreno, Jesús I; Marcos-Alcalde, Iñigo; Trabada, Daniel G; Gómez-Puertas, Paulino; Ortega, José; Mendieta, Jesús

    2015-01-01

    Quantum mechanics/molecular mechanics (QM/MM) methods are excellent tools for the modeling of biomolecular reactions. Recently, we have implemented a new QM/MM method (Fireball/Amber), which combines an efficient density functional theory method (Fireball) and a well-recognized molecular dynamics package (Amber), offering an excellent balance between accuracy and sampling capabilities. Here, we present a detailed explanation of the Fireball method and Fireball/Amber implementation. We also discuss how this tool can be used to analyze reactions in biomolecules using steered molecular dynamics simulations. The potential of this approach is shown by the analysis of a reaction catalyzed by the enzyme triose-phosphate isomerase (TIM). The conformational space and energetic landscape for this reaction are analyzed without a priori assumptions about the protonation states of the different residues during the reaction. The results offer a detailed description of the reaction and reveal some new features of the catalytic mechanism. In particular, we find a new reaction mechanism that is characterized by the intramolecular proton transfer from O1 to O2 and the simultaneous proton transfer from Glu 165 to C2.

  5. Mechanical energy losses in plastically deformed and electron plus neutron irradiated high purity single crystalline molybdenum at elevated temperatures

    Energy Technology Data Exchange (ETDEWEB)

    Zelada, Griselda I. [Laboratorio de Materiales, Escuela de Ingenieria Electrica, Facultad de Ciencias Exactas, Ingenieria y Agrimensura, Universidad Nacional de Rosario, Avda. Pellegrini 250, 2000 Rosario (Argentina); Lambri, Osvaldo Agustin [Laboratorio de Materiales, Escuela de Ingenieria Electrica, Facultad de Ciencias Exactas, Ingenieria y Agrimensura, Universidad Nacional de Rosario, Avda. Pellegrini 250, 2000 Rosario (Argentina); Instituto de Fisica Rosario - CONICET, Member of the CONICET& #x27; s Research Staff, Avda. Pellegrini 250, 2000 Rosario (Argentina); Bozzano, Patricia B. [Laboratorio de Microscopia Electronica, Unidad de Actividad Materiales, Centro Atomico Constituyentes, Comision Nacional de Energia Atomica, Avda. Gral. Paz 1499, 1650 San Martin (Argentina); Garcia, Jose Angel [Departamento de Fisica Aplicada II, Facultad de Ciencias y Tecnologia, Universidad del Pais Vasco, Apdo. 644, 48080 Bilbao, Pais Vasco (Spain)

    2012-10-15

    Mechanical spectroscopy (MS) and transmission electron microscopy (TEM) studies have been performed in plastically deformed and electron plus neutron irradiated high purity single crystalline molybdenum, oriented for single slip, in order to study the dislocation dynamics in the temperature range within one third of the melting temperature. A damping peak related to the interaction of dislocation lines with both prismatic loops and tangles of dislocations was found. The peak temperature ranges between 900 and 1050 K, for an oscillating frequency of about 1 Hz. (Copyright copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  6. Dislocation Strengthening without Ductility Trade-off in Metastable Austenitic Steels

    Science.gov (United States)

    Liu, Jiabin; Jin, Yongbin; Fang, Xiaoyang; Chen, Chenxu; Feng, Qiong; Liu, Xiaowei; Chen, Yuzeng; Suo, Tao; Zhao, Feng; Huang, Tianlin; Wang, Hongtao; Wang, Xi; Fang, Youtong; Wei, Yujie; Meng, Liang; Lu, Jian; Yang, Wei

    2016-10-01

    Strength and ductility are mutually exclusive if they are manifested as consequence of the coupling between strengthening and toughening mechanisms. One notable example is dislocation strengthening in metals, which invariably leads to reduced ductility. However, this trend is averted in metastable austenitic steels. A one-step thermal mechanical treatment (TMT), i.e. hot rolling, can effectively enhance the yielding strength of the metastable austenitic steel from 322 ± 18 MPa to 675 ± 15 MPa, while retaining both the formability and hardenability. It is noted that no boundaries are introduced in the optimized TMT process and all strengthening effect originates from dislocations with inherited thermal stability. The success of this method relies on the decoupled strengthening and toughening mechanisms in metastable austenitic steels, in which yield strength is controlled by initial dislocation density while ductility is retained by the capability to nucleate new dislocations to carry plastic deformation. Especially, the simplicity in processing enables scaling and industrial applications to meet the challenging requirements of emissions reduction. On the other hand, the complexity in the underlying mechanism of dislocation strengthening in this case may shed light on a different route of material strengthening by stimulating dislocation activities, rather than impeding motion of dislocations.

  7. Molecular-dynamics study of detonation. II. The reaction mechanism

    Science.gov (United States)

    Rice, Betsy M.; Mattson, William; Grosh, John; Trevino, S. F.

    1996-01-01

    In this work, we investigate mechanisms of chemical reactions that sustain an unsupported detonation. The chemical model of an energetic crystal used in this study consists of heteronuclear diatomic molecules that, at ambient pressure, dissociate endothermically. Subsequent association of the products to form homonuclear diatomic molecules provides the energy release that sustains the detonation. A many-body interaction is used to simulate changes in the electronic bonding as a function of local atomic environment. The consequence of the many-body interaction in this model is that the intramolecular bond is weakened with increasing density. The mechanism of the reaction for this model was extracted by investigating the details of the molecular properties in the reaction zone with two-dimensional molecular dynamics. The mechanism for the initiation of the reaction in this model is pressure-induced atomization. There was no evidence of excitation of vibrational modes to dissociative states. This particular result is directly attributable to the functional form and choice of parameters for this model, but might also have more general applicability.

  8. Static and Dynamic Amplification Using Strong Mechanical Coupling

    KAUST Repository

    Ilyas, Saad

    2016-07-28

    Amplifying the signal-to-noise ratio of resonant sensors is vital toward the effort to miniaturize devices into the sub-micro and nano regimes. In this paper, we demonstrate theoretically and experimentally, amplification through mechanically coupled microbeams. The device is composed of two identical clamped-clamped beams, made of polyimide, connected at their middle through a third beam, which acts as a mechanical coupler. Each of the clamped-clamped microbeams and the coupler are designed to be actuated separately, hence providing various possibilities of actuation and sensing. The coupled resonator is driven into resonance near its first resonance mode and its dynamic behavior is explored via frequency sweeps. The results show significant amplification in the resonator amplitude when the signal is measured at the midpoint of the coupler compared with the response of the individual uncoupled beams. The static pull-in characteristics of the resonator are also studied. It is shown that the compliant mechanical coupler can serve as a low-power radio frequency switch actuated at low voltage loads. [2016-0100

  9. Femoral neuropathy due to patellar dislocation in a theatrical and jazz dancer: a case report.

    Science.gov (United States)

    Shin, Chris S; Davis, Brian A

    2005-06-01

    This case report describes a teenage female, high-level modern dancer who suffered multiple left patellar dislocations. Her history is atypical in that after her fifth dislocation, her recovery was hindered secondary to persistent weakness and atrophy of her quadriceps out of proportion to disuse alone. Electrodiagnostic studies and magnetic resonance imaging showed evidence of a subacute femoral neuropathy correlating chronologically with her most recent patellar dislocation. This case suggests that further diagnostic study may be warranted in patients with persistent quadriceps weakness or atrophy after a patellar dislocation, because this may suggest the presence of a femoral neuropathy. This is important because the strength training goals and precautions differ in disuse atrophy and a neuropathy. We believe this is the first reported case of a femoral neuropathy associated with the mechanism of a patellar dislocation.

  10. Nucleating and propagating of nanocrack in dislocation-free zone in brittle materials

    Institute of Scientific and Technical Information of China (English)

    褚武扬; 高克玮; 陈奇志; 王燕斌; 肖纪美

    1995-01-01

    Nudeating and propagating of nanocrack forming in dislocation-free zone (DFZ) for a brittle material, TiAl alloy, was studied through in situ tensile test in TEM and analyzed using micro-fracture mechanics. The results show that many of dislocations can be emitted from a crack tip when the applied stress intensity KIa is larger than the stress intensity for dislocation emission KIe = 1.4MPa·m1/2 and a DFZ is formed after reaching equilibrium. The stress in a certain site in the DFZ, which is an elastic zone and is thinned gradually through dislocation multiplication and motion in the plastic zone, may be equal to the cohesive strength, resulting in initiating of a nanocrack in the DFZ or sometimes at the notch tip. The nanocrack forming in the DFZ is stable and can propagate into a cleavage microcrack through multiplication and movement of dislocations in the plastic zone under constant displacement condition.

  11. New approach to the growth of low dislocation relaxed SiGe material

    Science.gov (United States)

    Powell, A. R.; Iyer, S. S.; LeGoues, F. K.

    1994-04-01

    In this growth process a new strain relief mechanism operates, whereby the SiGe epitaxial layer relaxes without the generation of threading dislocations within the SiGe layer. This is achieved by depositing SiGe on an ultrathin silicon on insulator (SOI) substrate with a superficial silicon thickness less than the SiGe layer thickness. Initially, the thin Si layer is put under tension due to an equalization of the strain between the Si and SiGe layers. Thereafter, the strain created in the thin Si layer relaxes by plastic deformation. Since the dislocations are formed and glide in the thin Si layer, no threading dislocation is ever introduced in to the upper SiGe material, which appeared dislocation free to the limit of the cross sectional transmission electron microscopy analysis. We thus have a method for producing very low dislocation, relaxes SiGe films with the additional benefit of an SOI substrate.

  12. Atomically informed nonlocal semi-discrete variational Peierls-Nabarro model for planar core dislocations.

    Science.gov (United States)

    Liu, Guisen; Cheng, Xi; Wang, Jian; Chen, Kaiguo; Shen, Yao

    2017-03-02

    Prediction of Peierls stress associated with dislocation glide is of fundamental concern in understanding and designing the plasticity and mechanical properties of crystalline materials. Here, we develop a nonlocal semi-discrete variational Peierls-Nabarro (SVPN) model by incorporating the nonlocal atomic interactions into the semi-discrete variational Peierls framework. The nonlocal kernel is simplified by limiting the nonlocal atomic interaction in the nearest neighbor region, and the nonlocal coefficient is directly computed from the dislocation core structure. Our model is capable of accurately predicting the displacement profile, and the Peierls stress, of planar-extended core dislocations in face-centered cubic structures. Our model could be extended to study more complicated planar-extended core dislocations, such as {111} dislocations in Al-based and Ti-based intermetallic compounds.

  13. Hydrogen-enhanced dislocation emission, motion and nucleation of hydrogen-induced cracking for steel

    Institute of Scientific and Technical Information of China (English)

    吕宏; 李密丹; 张天成; 褚武扬

    1997-01-01

    The change in dislocation configuration ahead of a loaded crack tip before and after charging with hydrogen was in situ investigated in TEM using a special constant deflection loading device The results showed that hydrogen could facilitate dislocation emission, multiplication and motion The change in displacement field ahead of a loaded notch tip for a bulk specimen before and after charging with hydrogen was in situ measured by the laser moire interferometer technique. The results showed that hydrogen could enlarge the plastic zone and increase the plastic strain The in situ observation in TEM showed that when hydrogen-enhanced dislocation emission and motion reached a critical condition, a nanocrack of hydrogen-induced cracking ( HIC) would nucleate in the dislocation-free zone (DFZ) or at the main crack tip. The reasons for hydrogen-enhanced dislocation emission, multiplication and motion, and the mechanisms of nucleation of HIC have been discussed

  14. Effects of residual stress and dislocation on tensile deformation behavior of SiCw/Al composites

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    By means of XRD, Instron electronic tensile machine and TEM, the dislocation states and strengthening mechanisms of SiC whisker reinforced pure aluminum matrix composites were studied with different annealing treatment processes and matrixes. The results showed that the strengthening mechanisms of SiCw/p-Al composite and SiCw/6061Al composites are different. For the SiCw/p-Al composite, the thermal residual stress plays more important role in strengthening than the high density dislocations in matrix; for the SiCw/6061Al composite, the dislocation strengthening and precipitation are main strengthening factors.

  15. Evolution of nanoscale interstitial dislocation loops under coupling effect of stress and temperature

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Ning; Shen, Tielong; Kurtz, Richard; Wang, Zhiguang; Gao, Fei

    2017-07-01

    The properties of nano-scale interstitial dislocation loops under the coupling effect of stress and temperature are studied using atomistic simulation methods and experiments. The decomposition of a loop by the emission of smaller loops is identified as one of the major mechanisms to release the localized stress induced by the coupling effect, which is validated by the TEM observations. The classical conservation law of Burgers vector cannot be applied during such decomposition process. The dislocation network is formed from the decomposed loops, which may initiate the irradiation creep much earlier than expected through the mechanism of climb-controlled glide of dislocations.

  16. Lattice dislocation in Si nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Omar, M.S., E-mail: dr_m_s_omar@yahoo.co [Department of Physics, College of Science, University of Salahaddin, Arbil, Iraqi Kurdistan (Iraq); Taha, H.T. [Department of Physics, College of Science, University of Salahaddin, Arbil, Iraqi Kurdistan (Iraq)

    2009-12-15

    Modified formulas were used to calculate lattice thermal expansion, specific heat and Bulk modulus for Si nanowires with diameters of 115, 56, 37 and 22 nm. From these values and Gruneisen parameter taken from reference, mean lattice volumes were found to be as 20.03 A{sup 3} for the bulk and 23.63, 29.91, 34.69 and 40.46 A{sup 3} for Si nanowire diameters mentioned above, respectively. Their mean bonding length was calculated to be as 0.235 nm for the bulk and 0.248, 0.269, 0.282 and 0.297 nm for the nanowires diameter mentioned above, respectively. By dividing the nanowires diameter on the mean bonding length, number of layers per each nanowire size was found to be as 230, 104, 65 and 37 for the diameters mentioned above, respectively. Lattice dislocations in 22 nm diameter wire were found to be from 0.00324 nm for the 1st central lattice to 0.2579 nm for the last surface lattice. Such dislocation was smaller for larger wire diameters. Dislocation concentration found to change in Si nanowires according to the proportionalities of surface thickness to nanowire radius ratios.

  17. Smooth dynamics and new theoretical ideas in nonequilibrium statistical mechanics

    CERN Document Server

    Ruelle, D

    1998-01-01

    This paper reviews various applications of the theory of smooth dynamical systems to conceptual problems of nonequilibrium statistical mechanics. We adopt a new point of view which has emerged progressively in recent years, and which takes seriously into account the chaotic character of the microscopic time evolution. The emphasis is on nonequilibrium steady states rather than the traditional approach to equilibrium point of view of Boltzmann. The nonequilibrium steady states, in presence of a Gaussian thermostat, are described by SRB measures. In terms of these one can prove the Gallavotti-Cohen fluctuation theorem. One can also prove a general linear response formula and study its consequences, which are not restricted to near equilibrium situations. Under suitable conditions the nonequilibrium steady states satisfy the pairing theorem of Dettmann and Morriss. The results just mentioned hold so far only for classical systems; they do not involve large size, i.e., they hold without a thermodynamic limit.

  18. Development of test methodology for dynamic mechanical analysis instrumentation

    Science.gov (United States)

    Allen, V. R.

    1982-08-01

    Dynamic mechanical analysis instrumentation was used for the development of specific test methodology in the determination of engineering parameters of selected materials, esp. plastics and elastomers, over a broad range of temperature with selected environment. The methodology for routine procedures was established with specific attention given to sample geometry, sample size, and mounting techniques. The basic software of the duPont 1090 thermal analyzer was used for data reduction which simplify the theoretical interpretation. Clamps were developed which allowed 'relative' damping during the cure cycle to be measured for the fiber-glass supported resin. The correlation of fracture energy 'toughness' (or impact strength) with the low temperature (glassy) relaxation responses for a 'rubber-modified' epoxy system was negative in result because the low-temperature dispersion mode (-80 C) of the modifier coincided with that of the epoxy matrix, making quantitative comparison unrealistic.

  19. Mechanical reaction-diffusion model for bacterial population dynamics

    CERN Document Server

    Ngamsaad, Waipot

    2015-01-01

    The effect of mechanical interaction between cells on the spreading of bacterial population was investigated in one-dimensional space. A nonlinear reaction-diffusion equation has been formulated as a model for this dynamics. In this model, the bacterial cells are treated as the rod-like particles that interact, when contacting each other, through the hard-core repulsion. The repulsion introduces the exclusion process that causes the fast diffusion in bacterial population at high density. The propagation of the bacterial density as the traveling wave front in long time behavior has been analyzed. The analytical result reveals that the front speed is enhanced by the exclusion process---and its value depends on the packing fraction of cell. The numerical solutions of the model have been solved to confirm this prediction.

  20. Exploring dynamic mechanisms of learning networks for resource conservation

    Directory of Open Access Journals (Sweden)

    Petr Matous

    2015-06-01

    Full Text Available The importance of networks for social-ecological processes has been recognized in the literature; however, existing studies have not sufficiently addressed the dynamic nature of networks. Using data on the social learning networks of 265 farmers in Ethiopia for 2011 and 2012 and stochastic actor-oriented modeling, we explain the mechanisms of network evolution and soil conservation. The farmers' preferences for information exchange within the same social groups support the creation of interactive, clustered, nonhierarchical structures within the evolving learning networks, which contributed to the diffusion of the practice of composting. The introduced methods can be applied to determine whether and how social networks can be used to facilitate environmental interventions in various contexts.

  1. Dynamic Discontinuous Control for Active Control of Mechanical Vibrations

    Directory of Open Access Journals (Sweden)

    Orestes Llanes Santiago

    2010-02-01

    Full Text Available This article shows the use of the discontinuous control using dynamic sliding modes for the active isolation of vibrations in mechanical systems. This type of control law constitutes a robust feedback control policy due to its insensitivity to external disturbance inputs, certain immunity to model parameter variations, within known bounds, and to the ever present modelling errors.  The whole theoretical analysis is applied to a lineal model of two degrees of freedom of the vehicle's suspension where the irregularities of the land represent of direct  way the external interferences to the system . To carry out the isolation an electro-hydraulic operator it is used. Simulations are performed which validate the proposed approach.

  2. Spindle mechanics and dynamics during mitosis in Drosophila.

    Science.gov (United States)

    Kwon, Mijung; Scholey, Jonathan M

    2004-04-01

    Drosophila melanogaster is an excellent model for studying mitosis. Syncytial embryos are amenable to time-lapse imaging of hundreds of synchronously dividing spindles, allowing the quantitation of spindle and chromosome dynamics with unprecedented fidelity. Other Drosophila cell types, including neuroblasts, cultured cells, spermatocytes and oocytes, contain spindles that differ in their design, providing cells amenable to different types of experiments and allowing identification of common core mechanisms. The function of mitotic proteins can be studied using mutants, inhibitor microinjection and RNA interference (RNAi) to identify the full inventory of mitotic proteins encoded by the genome. Here, we review recent advances in understanding how ensembles of mitotic proteins coordinate spindle assembly and chromosome motion in this system.

  3. Knee dislocation: descriptive study of injuries Luxação do joelho: estudo descritivo das lesões

    OpenAIRE

    2013-01-01

    OBJECTIVE: Describe the ligamentous and associated injuries that occur in the traumatic knee dislocation, relating them to the mechanisms of trauma and to identify patterns of injuries. METHODS: Twenty three knee dislocations were described in the period between March 2010 and March 2011. After the diagnosis of the lesions, the reduction and transarticular external fixation of the dislocated knees were done. At the second moment, the patients were evaluated with physical examination under...

  4. Influence of loading control on strain bursts and dislocation avalanches at the nanometer and micrometer scale

    Science.gov (United States)

    Cui, Yinan; Po, Giacomo; Ghoniem, Nasr

    2017-02-01

    Through three-dimensional discrete dislocation dynamics simulations, we show that by tuning the mode of external loading, the collective dynamics of dislocations undergo a transition from driven avalanches under stress control to quasiperiodic oscillations under strain control. We directly correlate measured intermittent plastic events with internal dislocation activities and collective dynamics. Under different loading modes, the roles of the weakest dislocation source and the defect population trend are significantly different. This finding raises new possibilities of controlling correlated dislocation activities and obtaining a low defect density in nanostructured devices by tuning external constraints. In addition, the effect of machine stiffness comes to light. The statistical analysis of the burst magnitude is revisited and carefully discussed. Self-organized criticality and scale-free statistics of strain bursts are obeyed under stress control. However, this behavior is shown to break down under strain control. Rapid stress drops under pure strain control force truncation of dislocation avalanches, leading to a dynamical transition to quasiperiodic oscillations.

  5. Dynamical mechanism of antifreeze proteins to prevent ice growth

    CERN Document Server

    Kutschan, B; Thoms, S

    2014-01-01

    The fascinating ability of algae, insects and fishes to survive at temperatures below normal freezing is realized by antifreeze proteins (AFPs). Antifreeze proteins (AFPs) are surface-active molecules and interact with the diffusive water/ice interface preventing a complete solidification. A new dynamical mechanism is proposed how these proteins inhibit the freezing of water. We apply a Ginzburg-Landau type approach to describe the phase separation in the two-component system (ice, AFP). The free energy density involves two fields: one for the ice phase with low AFP concentration, and one for the liquid water with high AFP concentration. The time evolution of the ice reveals microstructures as a result of phase separation in the presence of AFPs. We observe a faster clustering of pre-ice structure connected with a locking of grain size by the action of AFP which is an essentially dynamical process. The adsorption of additional water molecules are inhibited and the further growth of ice grains are stopped. The...

  6. Fracture mechanisms of glass particles under dynamic compression

    Energy Technology Data Exchange (ETDEWEB)

    Parab, Niranjan D.; Guo, Zherui; Hudspeth, M.; Claus, Benjamin; Fezzaa, Kamel; Sun, Tao; Chen, Weinong W.

    2017-08-01

    In this study, dynamic fracture mechanisms of single and contacting spherical glass particles were observed using high speed synchrotron X-ray phase contrast imaging. A modified Kolsky bar setup was used to apply controlled dynamic compressive loading on the soda-lime glass particles. Four different configurations of particle arrangements with one, two, three, and five particles were studied. In single particle experiments, cracking initiated near the contact area between the particle and the platen, subsequently fragmenting the particle in many small sub-particles. In multi-particle experiments, a crack was observed to initiate from the point just outside the contact area between two particles. The initiated crack propagated at an angle to the horizontal loading direction, resulting in separation of a fragment. However, this fragment separation did not affect the ability of the particle to withstand further contact loading. On further compression, large number of cracks initiated in the particle with the highest number of particle-particle contacts near one of the particle-particle contacts. The initiated cracks roughly followed the lines joining the contact points. Subsequently, the initiated cracks along with the newly developed sub-cracks bifurcated rapidly as they propagated through the particle and fractured the particle explosively into many small fragments, leaving the other particles nearly intact.

  7. Neural dynamics and circuit mechanisms of decision-making.

    Science.gov (United States)

    Wang, Xiao-Jing

    2012-12-01

    In this review, I briefly summarize current neurobiological studies of decision-making that bear on two general themes. The first focuses on the nature of neural representation and dynamics in a decision circuit. Experimental and computational results suggest that ramping-to-threshold in the temporal domain and trajectory of population activity in the state space represent a duality of perspectives on a decision process. Moreover, a decision circuit can display several different dynamical regimes, such as the ramping mode and the jumping mode with distinct defining properties. The second is concerned with the relationship between biologically-based mechanistic models and normative-type models. A fruitful interplay between experiments and these models at different levels of abstraction have enabled investigators to pose increasingly refined questions and gain new insights into the neural basis of decision-making. In particular, recent work on multi-alternative decisions suggests that deviations from rational models of choice behavior can be explained by established neural mechanisms.

  8. A molecular understanding of the dynamic mechanism of aquaporin osmosis

    CERN Document Server

    Shua, Liangsuo; Qian, Xin; Wanga, Xiyun; Lin, Yixin; Tan, Kai; Shu, Chaohui; Jin, Shiping

    2014-01-01

    AQPs (aquaporins), the rapid water channels of cells, play a key role in maintaining osmotic equilibrium of cells. In this paper, we reported the dynamic mechanism of AQP osmosis at the molecular level. A theoretical model based on molecular dynamics was carried out and verified by the published experimental data. The reflection coefficients ({\\sigma}) of neutral molecules are mainly decided by their relative size with AQPs, and increase with a third power up to a constant value 1. This model also indicated that the reflection coefficient of a complete impermeable solute can be smaller than 1. The H+ concentration of solution can influence the driving force of the AQPs by changing the equivalent diameters of vestibules surrounded by loops with abundant polar amino acids. In this way, pH of solution can regulate water permeability of AQPs. Therefore, an AQP may not only work as a switch to open or close, but as a rapid response molecular valve to control its water flow. The vestibules can prevent the channel b...

  9. Misfit dislocation gettering by substrate pit-patterning in SiGe films on Si(001)

    Energy Technology Data Exchange (ETDEWEB)

    Grydlik, Martyna; Groiss, Heiko; Brehm, Moritz; Schaeffler, Friedrich [Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz, Altenbergerstrasse 69, A-4040 Linz (Austria); Boioli, Francesca; Montalenti, Francesco; Miglio, Leo [L-NESS and Department of Material Science, University of Milano-Bicocca (Italy); Gatti, Riccardo; Devincre, Benoit [LEM, CNRS/ONERA, Chatillon Cedex (France)

    2012-07-02

    We show that suitable pit-patterning of a Si(001) substrate can strongly influence the nucleation and the propagation of dislocations during epitaxial deposition of Si-rich Si{sub 1-x}Ge{sub x} alloys, preferentially gettering misfit segments along pit rows. In particular, for a 250 nm layer deposited by molecular beam epitaxy at x{sub Ge} = 15%, extended film regions appear free of dislocations, by atomic force microscopy, as confirmed by transmission electron microscopy sampling. This result is quite general, as explained by dislocation dynamics simulations, which reveal the key role of the inhomogeneous distribution in stress produced by the pit-patterning.

  10. Mechanical compaction directly modulates the dynamics of bile canaliculi formation.

    Science.gov (United States)

    Wang, Yan; Toh, Yi-Chin; Li, Qiushi; Nugraha, Bramasta; Zheng, Baixue; Lu, Thong Beng; Gao, Yi; Ng, Mary Mah Lee; Yu, Hanry

    2013-02-01

    Homeostatic pressure-driven compaction is a ubiquitous mechanical force in multicellular organisms and is proposed to be important in the maintenance of multicellular tissue integrity and function. Previous cell-free biochemical models have demonstrated that there are cross-talks between compaction forces and tissue structural functions, such as cell-cell adhesion. However, its involvement in physiological tissue function has yet to be directly demonstrated. Here, we use the bile canaliculus (BC) as a physiological example of a multicellular functional structure in the liver, and employ a novel 3D microfluidic hepatocyte culture system to provide an unprecedented opportunity to experimentally modulate the compaction states of primary hepatocyte aggregates in a 3D physiological-mimicking environment. Mechanical compaction alters the physical attributes of the hepatocyte aggregates, including cell shape, cell packing density and cell-cell contact area, but does not impair the hepatocytes' remodeling and functional capabilities. Characterization of structural and functional polarity shows that BC formation in compact hepatocyte aggregates is accelerated to as early as 12 hours post-seeding; whereas non-compact control requires 48 hours for functional BC formation. Further dynamic immunofluorescence imaging and gene expression profiling reveal that compaction accelerated BC formation is accompanied by changes in actin cytoskeleton remodeling dynamics and transcriptional levels of hepatic nuclear factor 4α and Annexin A2. Our report not only provides a novel strategy of modeling BC formation for in vitro hepatology research, but also shows a first instance that homeostatic pressure-driven compaction force is directly coupled to the higher-order multicellular functions.

  11. In Situ Observation on Dislocation-Controlled Sublimation of Mg Nanoparticles.

    Science.gov (United States)

    Yu, Qian; Mao, Min-Min; Li, Qing-Jie; Fu, Xiao-Qian; Tian, He; Li, Ji-Xue; Mao, Scott X; Zhang, Ze

    2016-02-10

    Sublimation is an important endothermic phase transition in which the atoms break away from their neighbors in the crystal lattice and are removed into the gas phase. Such debonding process may be significantly influenced by dislocations, the crystal defect that changes the bonding environment of local atoms. By performing systematic defects characterization and in situ transmission electron microscopy (TEM) tests on a core--shell MgO-Mg system, which enables us to "modulate" the internal dislocation density, we investigated the role of dislocations on materials' sublimation with particular focus on the sublimation kinetics and mechanism. It was observed that the sublimation rate increases significantly with dislocation density. As the density of screw dislocations is high, the intersection of screw dislocation spirals creates a large number of monatomic ledges, resulting in a "liquid-like" motion of solid-gas interface, which significantly deviates from the theoretically predicted sublimation plane. Our calculation based on density functional theory demonstrated that the remarkable change of sublimation rate with dislocation density is due to the dramatic reduction in binding energy of the monatomic ledges. This study provides direct observation to improve our understanding on this fundamental phase transition as well as to shed light on tuning materials' sublimation by "engineering" dislocation density in applications.

  12. Plastic deformation of tubular crystals by dislocation glide

    Science.gov (United States)

    Beller, Daniel A.; Nelson, David R.

    2016-09-01

    Tubular crystals, two-dimensional lattices wrapped into cylindrical topologies, arise in many contexts, including botany and biofilaments, and in physical systems such as carbon nanotubes. The geometrical principles of botanical phyllotaxis, describing the spiral packings on cylinders commonly found in nature, have found application in all these systems. Several recent studies have examined defects in tubular crystals associated with crystalline packings that must accommodate a fixed tube radius. Here we study the mechanics of tubular crystals with variable tube radius, with dislocations interposed between regions of different phyllotactic packings. Unbinding and separation of dislocation pairs with equal and opposite Burgers vectors allow the growth of one phyllotactic domain at the expense of another. In particular, glide separation of dislocations offers a low-energy mode for plastic deformations of solid tubes in response to external stresses, reconfiguring the lattice step by step. Through theory and simulation, we examine how the tube's radius and helicity affects, and is in turn altered by, the mechanics of dislocation glide. We also discuss how a sufficiently strong bending rigidity can alter or arrest the deformations of tubes with small radii.

  13. Determination of dislocation densities in InN

    Energy Technology Data Exchange (ETDEWEB)

    Ardali, Sukru; Tiras, Engin [Department of Physics, Faculty of Science, Anadolu University, Yunus Emre Campus, Eskisehir 26470 (Turkey); Gunes, Mustafa; Balkan, Naci [School of Computer Science and Electronic Engineering, University of Essex, Wivenhoe Park, Colchester CO4 3SQ (United Kingdom); Ajagunna, Adebowale Olufunso; Iliopoulos, Eleftherios; Georgakilas, Alexandros [Microelectronics Research Group, IESL, FORTH and Physics Department, University of Crete, P.O. Box 1385, 71110 Heraklion-Crete (Greece)

    2012-03-15

    The magneto-transport measurements, carried out at magnetic fields up to 11 T and in the temperature range between 1.8 K and 300 K, are used to investigate the scattering mechanisms in GaN/InN/AlN double heterojunctions. Theoretical modeling is based on a variational approach to solving Boltzmann transport equation. It is found that dislocation scattering is the dominant scattering mechanisms at low temperatures because of the large lattice mismatch with the substrate and hence the high density of dislocations in these material systems. Nevertheless, InN epilayers are characterized by a high background carrier density, probably associated with unwanted impurities. Therefore, we also included in our calculations the ionized impurity scattering. However, the effect of ionized impurity scattering as well as the acoustic phonon scattering, remote- background-ionized impurity scattering, and interface roughness scattering on electron mobility are much smaller than that of dislocation scattering. The dislocation densities, in samples with InN thicknesses of 0.4, 0.6 and 0.8 {mu}m, are then determined from the best fit to the experimental data for the low-temperature transport mobility (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  14. Plastic deformation of tubular crystals by dislocation glide.

    Science.gov (United States)

    Beller, Daniel A; Nelson, David R

    2016-09-01

    Tubular crystals, two-dimensional lattices wrapped into cylindrical topologies, arise in many contexts, including botany and biofilaments, and in physical systems such as carbon nanotubes. The geometrical principles of botanical phyllotaxis, describing the spiral packings on cylinders commonly found in nature, have found application in all these systems. Several recent studies have examined defects in tubular crystals associated with crystalline packings that must accommodate a fixed tube radius. Here we study the mechanics of tubular crystals with variable tube radius, with dislocations interposed between regions of different phyllotactic packings. Unbinding and separation of dislocation pairs with equal and opposite Burgers vectors allow the growth of one phyllotactic domain at the expense of another. In particular, glide separation of dislocations offers a low-energy mode for plastic deformations of solid tubes in response to external stresses, reconfiguring the lattice step by step. Through theory and simulation, we examine how the tube's radius and helicity affects, and is in turn altered by, the mechanics of dislocation glide. We also discuss how a sufficiently strong bending rigidity can alter or arrest the deformations of tubes with small radii.

  15. Simultaneous bilateral anterior shoulder dislocation: report of two cases and review of the literature

    Institute of Scientific and Technical Information of China (English)

    Sujit Kumar Tripathy; Ramesh Kumar Sen; Sameer Aggarwal; Sarvdeep Singh Dhatt; Naveen Tahasildar

    2011-01-01

    Bilateral shoulder dislocations are rare and almost always occur in the posterior direction. Simultaneous bilateral anterior shoulder dislocation is even rarer and only a few cases are stated in the literature. The most interesting part of a bilateral shoulder dislocation is about its injury mechanism as a synchronous and simultaneous force is needed to result in it. In cases of epilepsy or electrocution, the mechanism is different and the forceful contractions of the selective group of muscles result in the dislocation. This article reports two cases of bilateral simultaneous anterior shoulder joint dislocation that occurred after a road side accident and after an episode of convulsion in an epileptic patient. The dislocations were diagnosed early and reduced immediately with a proper postreduction rehabilitation. During their follow-up, both patients had satisfactory functional outcome. This article emphasizes on the importance of shoulder examination in road side accident victims and epileptic patients. All orthopedic surgeons and emergency physicians should be aware of such unusual possibilities to have an early diagnosis and treatment.An early reduction and appropriate rehabilitation can provide satisfactory functional outcome. This article also briefly discusses the injury mechanisms, diagnoses and treatments of bilateral shoulder dislocation as reported in the literature.

  16. Comparison of the mechanical properties of NiTi/Cu bilayer by nanoindentation and tensile test: molecular dynamics simulation

    Science.gov (United States)

    Fazeli, Sara; Vahedpour, Morteza; Khatiboleslam Sadrnezhaad, Sayed

    2016-12-01

    Molecular dynamics simulation was used to study of mechanical properties of NiTi/Cu bilayer by nanoindentation and tensile testing. A comparison has been made among mechanical properties measured and plastic deformation process at different copper thickness during nanoindnetation and tensile test of the samples. Embedded atom method potentials for describing of inter-atomic interaction and Nose-Hoover thermostat and barostat are employed in the simulation at 400 K. The results showed that as the copper film thickness decreased, the maximum load and hardness values increased during nanoindetation. Saha and Nix model is used to describe reduced young’s modulus behaviour of the bilayer system through nanoindentation. A good agreement among calculated reduced elastic modulus by nanoindentation test and young’s modulus behaviour via tensile test have been obtained. The ‘incoherent interface’ in both of nanoindentation test and tensile testing is one of the governing factors for the dislocation propagation, which resulted in significant strengthening of the bilayer. It was observed that during tensile test, only copper layers were necked and fractured in all of samples. However, the present study seeks to examine the effect of film thickness on the free energy values that is obtained using Jarzynski’s equality during nanoindentation. As the copper film thickness was decreased, the free energy difference increased. According to both techniques, the thin film copper thickness provides lower number of nucleation locations resulting in the higher value of yield strength, hardness and free energy difference during nanoindenation. Mechanical properties of bilayer systems are improved with decreasing of copper film thickness. However, it specifies that strengths of all bilayer systems have prominent increase in young’s modulus in compared to the pure NiTi.

  17. Dynamics of mechanical waves in periodic graphene nanoribbon assemblies

    Directory of Open Access Journals (Sweden)

    Chowdhury Rajib

    2011-01-01

    Full Text Available Abstract We simulate the natural frequencies and the acoustic wave propagation characteristics of graphene nanoribbons (GNRs of the type (8,0 and (0,8 using an equivalent atomistic-continuum FE model previously developed by some of the authors, where the C-C bonds thickness and average equilibrium lengths during the dynamic loading are identified through the minimisation of the system Hamiltonian. A molecular mechanics model based on the UFF potential is used to benchmark the hybrid FE models developed. The acoustic wave dispersion characteristics of the GNRs are simulated using a Floquet-based wave technique used to predict the pass-stop bands of periodic mechanical structures. We show that the thickness and equilibrium lengths do depend on the specific vibration and dispersion mode considered, and that they are in general different from the classical constant values used in open literature (0.34 nm for thickness and 0.142 nm for equilibrium length. We also show the dependence of the wave dispersion characteristics versus the aspect ratio and edge configurations of the nanoribbons, with widening band-gaps that depend on the chirality of the configurations. The thickness, average equilibrium length and edge type have to be taken into account when nanoribbons are used to design nano-oscillators and novel types of mass sensors based on periodic arrangements of nanostructures. PACS 62.23.Kn · 62.25.Fg · 62.25.Jk

  18. Mechanical properties of Indonesian-made narrow dynamic compression plate.

    Science.gov (United States)

    Dewo, P; van der Houwen, E B; Sharma, P K; Magetsari, R; Bor, T C; Vargas-Llona, L D; van Horn, J R; Busscher, H J; Verkerke, G J

    2012-09-01

    Osteosynthesis plates are clinically used to fixate and position a fractured bone. They should have the ability to withstand cyclic loads produced by muscle contractions and total body weight. The very high demand for osteosynthesis plates in developing countries in general and in Indonesia in particular necessitates the utilisation of local products. In this paper, we investigated the mechanical properties, i.e. proportional limit and fatigue strength of Indonesian-made Narrow Dynamic Compression Plates (Narrow DCP) as one of the most frequently used osteosynthesis plates, in comparison to the European AO standard plate, and its relationship to geometry, micro structural features and surface defects of the plates. All Indonesian-made plates appeared to be weaker than the standard Narrow DCP because they consistently failed at lower stresses. Surface defects did not play a major role in this, although the polishing of the Indonesian Narrow DCP was found to be poor. The standard plate showed indications of cold deformation from the production process in contrast to the Indonesian plates, which might be the first reason for the differences in strength. This is confirmed by hardness measurements. A second reason could be the use of an inferior version of stainless steel. The Indonesian plates showed lower mechanical behaviour compared to the AO-plates. These findings could initiate the development of improved Indonesian manufactured DCP-plates with properties comparable to commonly used plates, such as the standard European AO-plates.

  19. Dynamic Self-Healing Mechanism for Transactional Business Process

    Directory of Open Access Journals (Sweden)

    Yuhai Zhao

    2015-01-01

    Full Text Available It is clear that transactional behavior consistency is a prerequisite and basis for construction of a reliable services-based business application. However, in previous works, maintaining transactional consistency during exception handling was ignored. Maintaining transactional consistency requires functionality for rolling back some operations and revoking uploaded data. Replacing only the failed service will eventually lead to overall business application failure. In this study, we take fully into account the behavioral consistency of transactional services and propose two effective self-healing mechanisms for service-based applications. If a service enters into potential failure condition, a rescheduling mechanism is triggered to maintain consistent transactional behavior and to ensure reliable execution; if a service fails during execution, the compensation operation is triggered and the system will take action to ensure transactional behavior consistency. Meanwhile, cost-benefit analysis with compensation support is proposed to minimize the dynamic reselection cost. Finally, the experimental analysis shows that the proposed strategies can effectively guarantee the reliability of Web-based applications system.

  20. Dynamic mechanical and swelling properties of maleated hyaluronic acid hydrogels.

    Science.gov (United States)

    Lin, Hai; Liu, Jun; Zhang, Kai; Fan, Yujiang; Zhang, Xingdong

    2015-06-05

    A series of maleated hyaluronan (MaHA) are developed by modification with maleic anhydride. The degrees of substitution (DS) of MaHA vary between 7% and 75%. The DS of MaHA is both higher and wider than methacrylated HA derivatives (MeHA) reported in the literature. MaHA hydrogels are then prepared by photopolymerization and their dynamic mechanical and swelling properties of the hydrogels are investigated. The results showed that MaHA hydrogels with moderate DS (25%, 50% and 65%) have higher storage modulus and lower equilibrium swelling ratios than those with either low or high DS (7%, 15% and 75%). Theoretical analyses also suggest a similar pattern among hydrogels with different DS. The results confirm that the increased cross-linking density enhances the strength of hydrogels. Meanwhile, the hydrophilicity of introduced groups during modification and the degree of incomplete crosslinking reaction might have negative impact on the mechanical and swelling properties of MaHA hydrogels.

  1. Dislocation substructure of mantle-derived olivine as revealed by selective chemical etching and transmission electron microscopy

    Science.gov (United States)

    Kirby, S.H.; Wegner, M.W.

    1978-01-01

    Cleaved and mechanically polished surfaces of olivine from peridotite xenoliths from San Carlos, Arizona, were chemically etched using the techniques of Wegner and Christie (1974). Dislocation etch pits are produced on all surface orientations and they tend to be preferentially aligned along the traces of subgrain boundaries, which are approximately parallel to (100), (010), and (001). Shallow channels were also produced on (010) surfaces and represent dislocations near the surface that are etched out along their lengths. The dislocation etch channel loops are often concentric, and emanate from (100) subgrain boundaries, which suggests that dislocation sources are in the boundaries. Data on subgrain misorientation and dislocation line orientation and arguments based on subgrain boundary energy minimization are used to characterize the dislocation structures of the subgrain boundaries. (010) subgrain boundaries are of the twist type, composed of networks of [100] and [001] screw dislocations. Both (100) and (001) subgrain boundaries are tilt walls composed of arrays of edge dislocation with Burgers vectors b=[100] and [001], respectively. The inferred slip systems are {001} ???100???, {100} ???001???, and {010} ???100??? in order of diminishing importance. Exploratory transmission electron microscopy is in accord with these identifications. The flow stresses associated with the development of the subgrain structure are estimated from the densities of free dislocations and from the subgrain dimensions. Inferred stresses range from 35 to 75 bars using the free dislocation densities and 20 to 100 bars using the subgrain sizes. ?? 1978 Springer-Verlag.

  2. Oxide particle–dislocation interaction in 9Cr-ODS steel

    OpenAIRE

    Yuta Ijiri; N. Oono; Ukai, S.; Ohtsuka, S; T. Kaito; Matsukawa, Y.

    2016-01-01

    Oxide Dispersion Strengthened (ODS) ferritic/martensitic steels have an excellent high temperature strength primarily due to a dislocation pinning effect of nanometric oxide particles. In the present work, the interaction between oxide particles and dislocations in 9CrODS ferritic steel was investigated by both static TEM observation and in-situ TEM observation under dynamic straining conditions. The primary concerns of those observations were the obstacle strength of oxide particles and the ...

  3. Trends in nanoscale mechanics mechanics of carbon nanotubes, graphene, nanocomposites and molecular dynamics

    CERN Document Server

    2014-01-01

    This book contains a collection of the state-of-the-art reviews written by the leading researchers in the areas of nanoscale mechanics, molecular dynamics, nanoscale modeling of nanocomposites and mechanics of carbon nanotubes. No other book has reviews of the recent discoveries such as a nanoscale analog of the Pauli’s principle, i.e., effect of the spatial exclusion of electrons or the SEE effect, a new Registry Matrix Analysis for the nanoscale interfacial sliding and new data on the effective viscosity of interfacial electrons in nanoscale stiction at the interfaces. This volume is also an exceptional resource on the well tested nanoscale modeling of carbon nanotubes and nanocomposites, new nanoscale effects, unique evaluations of the effective thickness of carbon nanotubes under different loads, new data on which size of carbon nanotubes is safer and many other topics. Extensive bibliography concerning all these topics is included along with the lucid short reviews. Numerous illustrations are provided...

  4. Vibrational spectrum at a water surface: a hybrid quantum mechanics/molecular mechanics molecular dynamics approach.

    Science.gov (United States)

    Ishiyama, Tatsuya; Takahashi, Hideaki; Morita, Akihiro

    2012-03-28

    A hybrid quantum mechanics/molecular mechanics (QM/MM) molecular dynamics (MD) simulation is applied to the calculation of surface orientational structure and vibrational spectrum (second-order nonlinear susceptibility) at the vapor/water interface for the first time. The surface orientational structure of the QM water molecules is consistent with the previous MD studies, and the calculated susceptibility reproduces the experimentally reported one, supporting the previous results using the classical force field MD simulation. The present QM/MM MD simulation also demonstrates that the positive sign of the imaginary part of the second-order nonlinear susceptibility at the lower hydrogen bonding OH frequency region originates not from individual molecular orientational structure, but from cooperative electronic structure through the hydrogen bonding network.

  5. Dislocation nucleation in heteroepitaxial semiconducting films

    Energy Technology Data Exchange (ETDEWEB)

    Pichaud, B.; Burle, N.; Texier, M.; Alfonso, C.; Gailhanou, M.; Thibault-Penisson, J. [IM2NP UMR6242 CNRS, Aix-Marseille University, Marseille (France); Fontaine, C. [LAAS CNRS, Toulouse (France); Vdovin, V.I. [Institute for Chemical Problems of Microelectronics, Moscow (Russian Federation)

    2009-08-15

    The nucleation of dislocation in semiconductors is still a matter of debate and especially in heteroepitaxial films. To understand this nucleation process the classical models of dislocation nucleation are presented and criticized. Two main points are then developed: emission of dislocations from surface steps and the role of point defects agglomeration on dislocation nucleation. Recent atomic simulation of half loops emission from surface steps and experimental evidences of anisotropic relaxation of GaInAs films deposited on vicinal (111)GaAs substrates strongly support surface steps as preferential sites for nucleation. In low temperature buffer layer structures (SiGe/Si) an original dislocation structure is observed which corresponds to the dislocation emission in different glide systems by a unique nucleation centre. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  6. Kink pair production and dislocation motion

    Science.gov (United States)

    Fitzgerald, S. P.

    2016-12-01

    The motion of extended defects called dislocations controls the mechanical properties of crystalline materials such as strength and ductility. Under moderate applied loads, this motion proceeds via the thermal nucleation of kink pairs. The nucleation rate is known to be a highly nonlinear function of the applied load, and its calculation has long been a theoretical challenge. In this article, a stochastic path integral approach is used to derive a simple, general, and exact formula for the rate. The predictions are in excellent agreement with experimental and computational investigations, and unambiguously explain the origin of the observed extreme nonlinearity. The results can also be applied to other systems modelled by an elastic string interacting with a periodic potential, such as Josephson junctions in superconductors.

  7. Compression Stress Effect on Dislocations Movement and Crack propagation in Cubic Crystal

    CERN Document Server

    Suprijadi,; Yusfi, Meiqorry

    2012-01-01

    Fracture material is seriously problem in daily life, and it has connection with mechanical properties itself. The mechanical properties is belief depend on dislocation movement and crack propagation in the crystal. Information about this is very important to characterize the material. In FCC crystal structure the competition between crack propagation and dislocation wake is very interesting, in a ductile material like copper (Cu) dislocation can be seen in room temperature, but in a brittle material like Si only cracks can be seen observed. Different techniques were applied to material to study the mechanical properties, in this study we did compression test in one direction. Combination of simulation and experimental on cubic material are reported in this paper. We found that the deflection of crack direction in Si caused by vacancy of lattice,while compression stress on Cu cause the atoms displacement in one direction. Some evidence of dislocation wake in Si crystal under compression stress at high tempera...

  8. Imaging findings of anterior hip dislocations

    Energy Technology Data Exchange (ETDEWEB)

    Pfeifer, Kyle [Mallinckrodt Institute of Radiology, Department of Radiology, St. Louis, MO (United States); Leslie, Michael [Yale School of Medicine, Department of Orthopedics and Rehabilitation, New Haven, CT (United States); Menn, Kirsten; Haims, Andrew [Yale University School of Medicine, Department of Radiology and Biomedical Imaging, New Haven, CT (United States)

    2017-06-15

    Anterior hip dislocations are rare orthopedic emergencies resulting from high-energy trauma and have unique imaging characteristics on radiography, computed tomography (CT), and magnetic resonance imaging (MRI). Imaging findings on CT and MRI allow for the prompt recognition and classification of anterior hip dislocations, which guides patient management and reduces complications. The purpose of this article is to review imaging findings of anterior hip dislocations, specifically focusing on CT and MRI. (orig.)

  9. Analogy betwen dislocation creep and relativistic cosmology

    OpenAIRE

    J.A. Montemayor-Aldrete; J.D. Muñoz-Andrade; Mendoza-Allende, A.; Montemayor-Varela, A.

    2005-01-01

    A formal, physical analogy between plastic deformation, mainly dislocation creep, and Relativistic Cosmology is presented. The physical analogy between eight expressions for dislocation creep and Relativistic Cosmology have been obtained. By comparing the mathematical expressions and by using a physical analysis, two new equations have been obtained for dislocation creep. Also, four new expressions have been obtained for Relativistic Cosmology. From these four new equations, one may determine...

  10. Mechanic: The MPI/HDF code framework for dynamical astronomy

    Science.gov (United States)

    Słonina, Mariusz; Goździewski, Krzysztof; Migaszewski, Cezary

    2015-01-01

    We introduce the Mechanic, a new open-source code framework. It is designed to reduce the development effort of scientific applications by providing unified API (Application Programming Interface) for configuration, data storage and task management. The communication layer is based on the well-established Message Passing Interface (MPI) standard, which is widely used on variety of parallel computers and CPU-clusters. The data storage is performed within the Hierarchical Data Format (HDF5). The design of the code follows core-module approach which allows to reduce the user’s codebase and makes it portable for single- and multi-CPU environments. The framework may be used in a local user’s environment, without administrative access to the cluster, under the PBS or Slurm job schedulers. It may become a helper tool for a wide range of astronomical applications, particularly focused on processing large data sets, such as dynamical studies of long-term orbital evolution of planetary systems with Monte Carlo methods, dynamical maps or evolutionary algorithms. It has been already applied in numerical experiments conducted for Kepler-11 (Migaszewski et al., 2012) and νOctantis planetary systems (Goździewski et al., 2013). In this paper we describe the basics of the framework, including code listings for the implementation of a sample user’s module. The code is illustrated on a model Hamiltonian introduced by (Froeschlé et al., 2000) presenting the Arnold diffusion. The Arnold web is shown with the help of the MEGNO (Mean Exponential Growth of Nearby Orbits) fast indicator (Goździewski et al., 2008a) applied onto symplectic SABAn integrators family (Laskar and Robutel, 2001).

  11. Luxación facetaria unilateral lumbosacra postraumática. [ Post-traumatic lumbosacral unilateral facet dislocation].

    Directory of Open Access Journals (Sweden)

    Manuel González Murillo

    2016-08-01

    Full Text Available In the literature have been reported around fifty cases of lumbosacral dislocations; treated most bilateral facet dislocations. We report the case of a female 42 year old with unilateral lumbosacral facet dislocation of one month duration after accident. Circumferential instrumented fusion L5-S1 with interbody cage and pedicle screws L5-S1 was performed.   The lumbosacral dislocation is a rare injury that occurs due to the combination of a high-energy mechanism predisposing anatomical factors. Recent publications advocate the surgical reduction and stabilization with instrumentation as standard treatment.

  12. Congenital dislocation of the patella - clinical case

    Directory of Open Access Journals (Sweden)

    Pedro Miguel Sá

    2016-02-01

    Full Text Available ABSTRACT Congenital patellar dislocation is a rare condition in which the patella is permanently dislocated and cannot be reduced manually. The patella develops normally as a sesamoid bone of the femur. This congenital dislocation results from failure of the internal rotation of the myotome that forms the femur, quadriceps muscle and extensor apparatus. It usually manifests immediately after birth, although in some rare cases, the diagnosis may be delayed until adolescence or adulthood. Early diagnosis is important, thereby allowing surgical correction and avoiding late sequelae, including early degenerative changes in the knee. A case of permanent dislocation of the patella is presented here, in a female child aged seven years.

  13. Structure of the Dislocation in Sapphire

    DEFF Research Database (Denmark)

    Bilde-Sørensen, Jørgen; Thölen, A. R.; Gooch, D. J.;

    1976-01-01

    of ⅓ 01 0 and are separated by two identical faults. The distance between two partials is in the range 75-135 Å, corresponding to a fault energy of 320±60 mJ/m2. Perfect 01 0 dislocations have also been observed. These dislocations exhibited either one or two peaks when imaged in the (03 0) reflection......Experimental evidence of the existence of 01 0 dislocations in the {2 0} prism planes in sapphire has been obtained by transmission electron microscopy. By the weak-beam technique it has been shown that the 01 0 dislocations may dissociate into three partials. The partials all have a Burgers vector...

  14. A study of conditions for dislocation nucleation in coarser-than-atomistic scale models

    Science.gov (United States)

    Garg, Akanksha; Acharya, Amit; Maloney, Craig E.

    2015-02-01

    We perform atomistic simulations of dislocation nucleation in defect free crystals in 2 and 3 dimensions during indentation with circular (2D) or spherical (3D) indenters. The kinematic structure of the theory of Field Dislocation Mechanics (FDM) is shown to allow the identification of a local feature of the atomistic velocity field in these simulations as indicative of dislocation nucleation. It predicts the precise location of the incipient spatially distributed dislocation field, as shown for the cases of the Embedded Atom Method potential for Al and the Lennard-Jones pair potential. We demonstrate the accuracy of this analysis for two crystallographic orientations in 2D and one in 3D. Apart from the accuracy in predicting the location of dislocation nucleation, the FDM based analysis also demonstrates superior performance than existing nucleation criteria in not persisting in time beyond the nucleation event, as well as differentiating between phase boundary/shear band and dislocation nucleation. Our analysis is meant to facilitate the modeling of dislocation nucleation in coarser-than-atomistic scale models of the mechanics of materials.

  15. Dislocations in single hemp fibres-investigations into the relationship of structural distortions and tensile properties at the cell wall level

    DEFF Research Database (Denmark)

    Thygesen, Lisbeth Garbrecht; Eder, M.; Burgert, I.

    2007-01-01

    The relationship between dislocations and mechanical properties of single hemp fibres (Cannabis sativa L. var. Felina) was studied using a microtensile testing setup in a 2-fold approach. In a first investigation the percentage of dislocations was quantified using polarized light microscopy (PLM......) prior to microtensile testing of the fibres. In a second approach PLM was used to monitor the dislocations while straining single fibres. The first part of the study comprised 53 hemp fibres with up to 20% of their cell wall consisting of dislocations. For this data set the percentage of dislocations...

  16. Patellar dislocation with genu valgum treated by DFO.

    Science.gov (United States)

    Kwon, Jae Ho; Kim, Jong In; Seo, Dong-Hyun; Kang, Kyung-Woon; Nam, Ji Ho; Nha, Kyung-Wook

    2013-06-01

    Congenital habitual patellar dislocation is a rare condition of the knee where the patella dislocates during flexion and relocates during extension. The congenital form is permanent, irreducible, and presents at birth. It is characterized by a short quadriceps and a major patellofemoral dysplasia and short height. This article presents a rare case of a 27-year-old woman with recurring bilateral habitual dislocation of the patella after a failed previous proximal and distal realignment procedure. Clinical examinations of both knees revealed genu valgus knees and lateral joint pain that recurred after several previous operations. Radiographs of both knees showed patellar dislocation and genu valgum associated with patellofemoral dysplasia and osteoarthritis of the lateral compartment. Long-leg standing radiographs showed an anatomic tibiofemoral angle of right 13° and left 6° valgus and a mechanical tibiofemoral angle of right 8° and left 2° valgus and weight-bearing line of 65% on the right and 48% on the left. The authors performed a distal femoral closing wedging osteotomy to correct the valgus deformity, and then percutaneous lateral release and medial reefing were performed to stabilize the patellas of both knees simultaneously. Copyright 2013, SLACK Incorporated.

  17. A Galeazzi-variant type fracture-dislocation in adults

    Institute of Scientific and Technical Information of China (English)

    Raju Vaishya; Sundar Kumar Shrestha; Abhishek Vaish

    2013-01-01

    Objective:Fracture of either radius or ulna with a dislocation either at the proximal or distal radioulnar joint (DRUJ) is not a common injury and is inherently unstable.Here we report a case series,with both-bone forearm fractures associated with dislocation of DRUJ,as a Galeazzi-variant type fracture-dislocation,and try to analyze this injury pattern.Methods:The study was based on 6 patients having Galeazzi-variant type fracture-dislocation of different age (20 to 45 years).All fractures were closed type.Two fractures involved the same level and three fractures were at different levels of radius and ulna shaft.After thorough examination and investigations they were treated with limited contact dynamic compression plate without additional fixation for DRUJ.Results:All cases were followed up for 24 weeks.The maximum incidence occurred in age group between 31 and 40 years.All the fractures of both radius and ulna were united in average time of 12 weeks.Range of motion of wrist and elbow,supination and pronation at final follow-up were normal.There was no subsequent re-subluxation or dislocation of the DRUJ in any of the cases.Conclusion:Galeazzi variant in adult is a new undescribed pattern of forearm with wrist injury.Stable open reduction and internal fixation of both-bone forearm fractures is mandatory,followed by 3 to 4 weeks of immobilization in a cast for the healing of disrupted DRUJ.

  18. Dislocations via incompatibilities in phase-field models of microstructure evolution

    Science.gov (United States)

    Gröger, R.; Marchand, B.; Lookman, T.

    2016-08-01

    We develop a phase-field model that describes the elastic distortion of a ferroelastic material with cubic anisotropy due to an arbitrary dislocation network and a uniform external load. The dislocation network is characterized using the Nye tensor and enters the formulation via a set of incompatibility constraints for the internal strain field. The long-range elastic response of the material is obtained by minimization of the free energy that accounts for higher-order terms of the order parameters and symmetry-adapted strain gradients. The influence of dislocations on the microstructure is studied using a static equilibrium analysis of a material without dislocations and with a random array of parallel edge dislocations. A minimal continuum dislocation dynamics is then used to investigate the simultaneous evolution of the network of geometrically necessary dislocations and the internal strain field. The model developed here is directly applicable to single-phase cubic crystals with an arbitrary degree of anisotropy as well as to ferroelastic materials undergoing temperature-driven cubic-to-tetragonal phase transitions.

  19. The injection of a screw dislocation into a crystal: Atomistics vs. continuum elastodynamics

    Science.gov (United States)

    Verschueren, J.; Gurrutxaga-Lerma, B.; Balint, D. S.; Dini, D.; Sutton, A. P.

    2017-01-01

    The injection (creation) process of a straight screw dislocation is compared atomistically with elastodynamic continuum theory. A method for injecting quiescent screw dislocations into a crystal of tungsten is simulated using non-equilibrium molecular dynamics. The resulting stress fields are compared to the those of elastodynamic solutions for the injection of a quiescent screw dislocation. A number of differences are found: a plane wave emission is observed to emanate from the whole surface of the cut used to create the dislocation, affecting the displacement field along the dislocation line (z), and introducing displacement field components perpendicular to the line (along x and y). It is argued that, in part, this emission is the result of the finite time required to inject the dislocation, whereby the atoms in the cut surface must temporarily be displaced to unstable positions in order to produce the required slip. By modelling this process in the continuum it is shown that the displacements components normal to the dislocation line arise from transient displacements of atoms in the cut surface parallel to x and y. It is shown that once these displacements are included in the elastodynamic continuum formulation the plane wave emission in uz is correctly captured. A detailed comparison between the atomistic and continuum models is then offered, showing that the main atomistic features can also be captured in the continuum.

  20. Dynamic Performance Evaluation of a 2-DoF Planar Parallel Mechanism

    Directory of Open Access Journals (Sweden)

    Hao Qi

    2012-12-01

    Full Text Available The acceleration performance function and dynamic performance evaluation combining the acceleration, velocity, gravity and external force of a 2‐DoF planar parallel mechanism are presented in this paper. By means of the principle of virtual work, the inverse dynamic model and acceleration performance function of the planar parallel mechanism are setup. Based on the factors in the acceleration performance function, the effect on the acceleration performance of parallel mechanisms is investigated. Then a new method considering the acceleration factor, velocity factor, gravity factor and external force factor for dynamic performance evaluation of the parallel mechanism is introduced, which can evaluate the dynamic performance of high‐speed parallel mechanisms more exactly. Based on this method, the evaluation indices used in dynamic optimization are introduced. These indices overcome the limitation of commonly used indices, and lay the foundation for dynamic optimization of parallel mechanisms.

  1. Novel neuronal and astrocytic mechanisms in thalamocortical loop dynamics.

    Science.gov (United States)

    Crunelli, Vincenzo; Blethyn, Kate L; Cope, David W; Hughes, Stuart W; Parri, H Rheinallt; Turner, Jonathan P; Tòth, Tibor I; Williams, Stephen R

    2002-12-29

    In this review, we summarize three sets of findings that have recently been observed in thalamic astrocytes and neurons, and discuss their significance for thalamocortical loop dynamics. (i) A physiologically relevant 'window' component of the low-voltage-activated, T-type Ca(2+) current (I(Twindow)) plays an essential part in the slow (less than 1 Hz) sleep oscillation in adult thalamocortical (TC) neurons, indicating that the expression of this fundamental sleep rhythm in these neurons is not a simple reflection of cortical network activity. It is also likely that I(Twindow) underlies one of the cellular mechanisms enabling TC neurons to produce burst firing in response to novel sensory stimuli. (ii) Both electrophysiological and dye-injection experiments support the existence of gap junction-mediated coupling among young and adult TC neurons. This finding indicates that electrical coupling-mediated synchronization might be implicated in the high and low frequency oscillatory activities expressed by this type of thalamic neuron. (iii) Spontaneous intracellular Ca(2+) ([Ca(2+)](i)) waves propagating among thalamic astrocytes are able to elicit large and long-lasting N-methyl-D-aspartate-mediated currents in TC neurons. The peculiar developmental profile within the first two postnatal weeks of these astrocytic [Ca(2+)](i) transients and the selective activation of these glutamate receptors point to a role for this astrocyte-to-neuron signalling mechanism in the topographic wiring of the thalamocortical loop. As some of these novel cellular and intracellular properties are not restricted to thalamic astrocytes and neurons, their significance may well apply to (patho)physiological functions of glial and neuronal elements in other brain areas.

  2. Mechanisms of intergranular fracture

    Energy Technology Data Exchange (ETDEWEB)

    Farkas, D. [Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States). Dept. of Materials Science and Engineering

    1999-08-01

    The authors present a study of the atomistic mechanisms of crack propagation along grain boundaries in metals and alloys. The failure behavior showing cleavage crack growth and/or crack-tip dislocation emission is demonstrated using atomistic simulations for an embedded-atom model. The simulations follow the quasi-equilibrium growth of a crack as the stress intensity applied increases. Dislocations emitted from crack tips normally blunt the crack and inhibit cleavage, inducing ductile behavior. When the emitted dislocations stay near the crack tip (sessile dislocations), they do blunt the crack but brittle cleavage can occur after the emission of a sufficient number of dislocations. The fracture process occurs as a combination of dislocation emission/micro-cleavage portions that are controlled by the local atomistic structure of the grain boundary. The grain boundary is shown to be a region where dislocation emission is easier, a mechanism that competes with the lower cohesive strength of the boundary region.

  3. Anterior fracture dislocation of sacroiliac joint: A rare type of crescent fracture

    Directory of Open Access Journals (Sweden)

    Vivek Trikha

    2015-01-01

    Full Text Available Crescent fractures of the pelvis are usually described as posterior sacro iliac fracture dislocations. Rarely anterior displacement of the fractured iliac fragment along with dislocation has been reported in crescent fractures. Four cases of anterior fracture dislocation of the sacro iliac joint managed in the last two years by a single surgeon are presented. The injury mechanism, radiological diagnosis, management protocol along with functional outcomes of all the four patients have been discussed. CT scan is essential in the diagnosis and preoperative planning of this injury pattern. Early fixation along with proper reduction leads to excellent functional outcome in this subset of lateral compression injuries of the pelvis.

  4. A review of dynamic mechanical characterization of high temperature PMR polyimides and composites

    Science.gov (United States)

    Pater, Ruth H.

    1988-01-01

    This paper reviews the applications of dynamic mechanical characterization for high-temperature PMR polyimides and their graphite-fiber-reinforced composites. This characterization technique provides insights into the processability, performance, and structure property relationships of the polyimides and composites. The dynamic mechanical properties of various molding powders, commercially obtained prepregs, neat resins, and as-fabricated as well as aged composites are presented. Some applied aspects of the dynamic mechanical data are discussed.

  5. Behavior of a self-interstitial-atom type dislocation loop in the periphery of an edge dislocation in BCC-Fe

    Directory of Open Access Journals (Sweden)

    Sho Hayakawa

    2016-12-01

    Full Text Available The behavior of the dislocation loop of a self-interstitial atom (SIA near an edge dislocation and its conservative climb process were modeled in body-centered cubic Fe by incorporating loop rotation. The stable position of the loop and its rotational angle due to the interaction with an edge dislocation were evaluated through molecular dynamics simulations and calculations of the isotropic elasticity. The results were used as input variables in kinetic Monte Carlo simulations to model the absorption of the loop by the dislocation via a conservative climb. Loop rotation was found to affect the velocity of the conservative climb only at short-distances because the gradient in the interaction energy between the dislocation and an atom at the edge of the loop, which is a driving force of the conservative climb, could not be precisely evaluated without loop rotation. Depending on the distance between the dislocation and the loop, allowing the loop rotation resulted in either an increase or decrease in the velocity of the conservative climb.

  6. Exploring the Dynamics of a Quantum-Mechanical Compton Generator

    Science.gov (United States)

    Kandes, Martin; Carretero, Ricardo

    2017-01-01

    In 1913, when American physicist Arthur Compton was an undergraduate, he invented a simple way to measure the rotation rate of the Earth with a tabletop-sized experiment. The experiment consisted of a large diameter circular ring of thin glass tubing filled with water and oil droplets. After placing the ring in a plane perpendicular to the surface of the Earth and allowing the fluid mixture of oil and water to come to rest, he then abruptly rotated the ring, flipping it 180 degrees about an axis passing through its own plane. The result of the experiment was that the water acquired a measurable drift velocity due to the Coriolis effect arising from the daily rotation of the Earth about its own axis. Compton measured this induced drift velocity by observing the motion of the oil droplets in the water with a microscope. This device, which is now named after him, is known as a Compton generator. The fundamental research objective of this project is to explore the dynamics of a quantum-mechanical analogue to the classical Compton generator experiment through the use of numerical simulations. We present our preliminary results on this system and the future direction of the project. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation Grant Number ACI-1053575.

  7. Viscoelastic behavior of maize kernel studied by dynamic mechanical analyzer.

    Science.gov (United States)

    Sheng, Shao-Yang; Wang, Li-Jun; Li, Dong; Mao, Zhi-Huai; Adhikari, Benu

    2014-11-04

    The creep recovery, stress relaxation, temperature-dependence and their frequency-dependence of maize kernel were determined within a moisture content range of 11.9% to 25.9% (w/w) by using a dynamic mechanical analyzer. The 4-element Burgers model was found to adequately represent the creep behavior of the maize seeds (R(2)>0.97). The 5-element Maxwell model was able to better predict the stress relaxation behavior of maize kernel than the 3-element Maxwell model. The Tg values for the maize kernels decreased with increased moisture content. For example, the Tg values were 114 °C and 65 °C at moisture content values of 11.9% (w/w) and 25.9% (w/w), respectively. The magnitude of the loss moduli and loss tangent and their rate of change with frequency were highest at 20.7% and lowest at 11.9% moisture contents. The maize kernel structure exhibited A-type crystalline pattern and the microstructure was found to expand with increase in moisture content.

  8. Effect of bracing on dynamic patellofemoral contact mechanics.

    Science.gov (United States)

    Wilson, Nicole A; Mazahery, B Tom; Koh, Jason L; Zhang, Li-Qun

    2010-01-01

    Decreases in patellofemoral pain have been demonstrated with bracing; however, the mechanisms of pain reduction remain unclear. Our purpose was to evaluate the hypothesis that patellofemoral bracing decreases peak pressure on the retropatellar surface through an increase in patellofemoral contact area. Nine cadaveric knees were tested during simulated free-speed walking with no brace, a knee sleeve, two different patellar stabilization sleeves, and a wrap-style patellar stabilization brace. Contact area and pressure were measured using a dynamic pressure sensor located in the patellofemoral joint. For the unbraced knee, contact area and peak pressure varied with knee flexion angle, ranging from 0.30 ± 0.3 cm(2) and 1.80 ± 1.7 MPa at full extension to 2.28 ± 0.5 cm(2) and 4.19 ± 1.7 MPa at peak knee flexion. All braces increased contact area, while the wrap-style brace decreased peak pressure (p < 0.001). Sleeve braces compress the quadriceps tendon causing the patella to engage the trochlear groove earlier during knee flexion. The wrap-style brace reduced peak pressure by shifting the location of highest pressure to a region with increased articular cartilage thickness. Sleeve braces may be useful for treatment of patellar subluxation disorders, while wrap-style braces may be effective for treatment of disorders associated with degenerative cartilage changes.

  9. Dynamic respiratory mechanics and exertional dyspnoea in pulmonary arterial hypertension.

    Science.gov (United States)

    Laveneziana, Pierantonio; Garcia, Gilles; Joureau, Barbara; Nicolas-Jilwan, Fadia; Brahimi, Toufik; Laviolette, Louis; Sitbon, Olivier; Simonneau, Gérald; Humbert, Marc; Similowski, Thomas

    2013-03-01

    Patients with pulmonary arterial hypertension (PAH) may exhibit reduced expiratory flows at low lung volumes, which could promote exercise-induced dynamic hyperinflation (DH). This study aimed to examine the impact of a potential exercise-related DH on the intensity of dyspnoea in patients with PAH undergoing symptom-limited incremental cardiopulmonary cycle exercise testing (CPET). 25 young (aged mean±sd 38±12 yrs) nonsmoking PAH patients with no evidence of spirometric obstruction and 10 age-matched nonsmoking healthy subjects performed CPET to the limit of tolerance. Ventilatory pattern, operating lung volumes (derived from inspiratory capacity (IC) measurements) and dyspnoea intensity (Borg scale) were assessed throughout CPET. IC decreased (i.e. DH) progressively throughout CPET in PAH patients (average 0.15 L), whereas it increased in all the healthy subjects (0.45 L). Among PAH patients, 15 (60%) exhibited a decrease in IC throughout exercise (average 0.50 L), whereas in the remaining 10 (40%) patients IC increased (average 0.36 L). Dyspnoea intensity and ventilation were greater in PAH patients than in controls at any stage of CPET, whereas inspiratory reserve volume was lower. We conclude that DH-induced mechanical constraints and excessive ventilatory demand occurred in these young nonsmoking PAH patients with no spirometric obstruction and was associated with exertional dyspnoea.

  10. Mechanic: the MPI/HDF code framework for dynamical astronomy

    CERN Document Server

    Słonina, Mariusz; Migaszewski, Cezary

    2014-01-01

    We introduce the Mechanic, a new open-source code framework. It is designed to reduce the development effort of scientific applications by providing unified API (Application Programming Interface) for configuration, data storage and task management. The communication layer is based on the well-established Message Passing Interface (MPI) standard, which is widely used on variety of parallel computers and CPU-clusters. The data storage is performed within the Hierarchical Data Format (HDF5). The design of the code follows em core-module approach which allows to reduce the user's codebase and makes it portable for single- and multi-CPU environments. The framework may be used in a local user's environment, without administrative access to the cluster, under the PBS or Slurm job schedulers. It may become a helper tool for a wide range of astronomical applications, particularly focused on processing large data sets, such as dynamical studies of long-term orbital evolution of planetary systems with Monte Carlo metho...

  11. Advances to Dynamic Mechanical Analysis: High Frequencies and Environmental Applications

    Science.gov (United States)

    Foreman, Jonathon

    2002-03-01

    In dynamic mechanical analysis (DMA) the sample is deformed and released sinusoidally providing information about the modulus and damping behaviors with respect to temperature, time, oscillation frequency and amplitude of motion. It offers exceptional sensitivity to glass transitions and secondary relaxations. Recent developments have increased the frequency range up to 1000 Hz, which allow properties measurements under actual end-use conditions. Furthermore high frequencies enhance the ability to determine the kinetics of viscoelastic relaxations. Another recent development allows DMA measurements while samples are immersed in fluids or enveloped in gases. Most significant is the ability to alter the furnace control parameters to account for the thermal properties of the environment used. This configuration allows temperature-controlled measurements (both heating and isothermal profiles) on a wide range of sample shapes and sizes. Environmental DMA is easier to interpret than standard DMA (in air or inert gas) on preconditioned samples because such samples often lose the conditioning solvent or gas during the measurement. easy.com/dma_apps.asp>Examples will show real-time property changes from the interaction of unconditioned materials with conditioning environments and experiments on pre-conditioned materials that are heated while immersed in conditioning environments. -------------------------------------------------------------

  12. Dynamics of Biased Domain Walls and the Devaluation Mechanism

    CERN Document Server

    Pina-Avelino, P; Sousa, L

    2008-01-01

    We study the evolution of biased domain walls in the early universe. We explicitly discuss the roles played by the surface tension and volume pressure in the evolution of the walls, and quantify their effects by looking at the collapse of spherical wall solutions. We then apply our results to a particular mechanism, known as the devaluation scenario, in which the dynamics of biased domain walls was suggested as a possible solution to the cosmological constant problem. Our results indicate that devaluation will in general lead to values of the cosmological constant that differ by several orders of magnitude from the observationally inferred value, $\\rho^{1/4}_{vac}\\sim10^{-3} \\rm eV$. We also argue that the reasons behind this are not specific to a particular realization, and are expected to persist in any scenario of this kind, except if a low energy cut-off on the spectra of vacuum energy densities, of the order of the critical density at the present time, is postulated. This implies that any such scenario w...

  13. Dynamics of biased domain walls and the devaluation mechanism

    Science.gov (United States)

    Avelino, P. P.; Martins, C. J. A. P.; Sousa, L.

    2008-08-01

    We study the evolution of biased domain walls in the early universe. We explicitly discuss the roles played by the surface tension and volume pressure in the evolution of the walls, and quantify their effects by looking at the collapse of spherical wall solutions. We then apply our results to a particular mechanism, known as the devaluation scenario, in which the dynamics of biased domain walls was suggested as a possible solution to the cosmological constant problem. Our results indicate that devaluation will, in general, lead to values of the cosmological constant that differ by several orders of magnitude from the observationally inferred value, ρvac1/4˜10-3eV. We also argue that the reasons behind this are not specific to a particular realization, and are expected to persist in any scenario of this kind, except if a low-energy cutoff on the spectra of vacuum energy densities, of the order of the critical density at the present time, is postulated. This implies that any such scenario will require a fine-tuning similar to the usual one.

  14. Dislocation

    Science.gov (United States)

    To help prevent injuries in children: Create a safe environment around your home. Help prevent falls by placing ... no substitute for close supervision, no matter how safe the environment or situation appears to be. Teach children how ...

  15. "Dislocation"

    Institute of Scientific and Technical Information of China (English)

    Li Wei

    2006-01-01

    @@ Over the past five years since September 11, the international community has been highly focused on the increasingly serious terrorist threat. In order to strike the international terrorist force, with al Qaeda as its core, the United Nations Security Council has established a special counter-terrorism committee, drawing up 12 related resolutions, agreements and conventions; multilateral and bilateral counter-terrorism cooperation has been expanding and deepening unceasingly. Many countries have brought counter-terrorism into their national security strategy, established or revised relevant laws, increased the input of manpower, material resources, and funds, actively researched and developed new technology and strengthened all kinds of counter-terrorist measures. Theoretically, international society has created an "inescapable net" for terrorism.

  16. Dislocations

    Science.gov (United States)

    ... sure kids wear the appropriate safety gear during sports activities. Supervise children when they're playing — a hard fall can happen anywhere, anytime. Avoid tugging hard on a young child's arm or shoulder, which can cause injury or ...

  17. Video Analysis of Primary Shoulder Dislocations in Rugby Tackles

    Science.gov (United States)

    Maki, Nobukazu; Kawasaki, Takayuki; Mochizuki, Tomoyuki; Ota, Chihiro; Yoneda, Takeshi; Urayama, Shingo; Kaneko, Kazuo

    2017-01-01

    Background: Characteristics of rugby tackles that lead to primary anterior shoulder dislocation remain unclear. Purpose: To clarify the characteristics of tackling that lead to shoulder dislocation and to assess the correlation between the mechanism of injury and morphological damage of the glenoid. Study Design: Case series; Level of evidence, 4. Methods: Eleven elite rugby players who sustained primary anterior shoulder dislocation due to one-on-one tackling between 2001 and 2014 were included. Using an assessment system, the tackler’s movement, posture, and shoulder and head position were evaluated in each phase of tackling. Based on 3-dimensional computed tomography, the glenoid of the affected shoulder was classified into 3 types: intact, erosion, and bone defect. Orientation of the glenoid defect and presence of Hill-Sachs lesion were also evaluated. Results: Eleven tackles that led to primary shoulder dislocation were divided into hand, arm, and shoulder tackle types based on the site at which the tackler contacted the ball carrier initially. In hand and arm tackles, the tackler’s shoulder joint was forcibly moved to horizontal abduction by the impact of his upper limb, which appeared to result from an inappropriate approach to the ball carrier. In shoulder tackles, the tackler’s head was lowered and was in front of the ball carrier at impact. There was no significant correlation between tackle types and the characteristics of bony lesions of the shoulder. Conclusion: Although the precise mechanism of primary anterior shoulder dislocation could not be estimated from this single-view analysis, failure of individual tackling leading to injury is not uniform and can be caused by 2 main factors: failure of approach followed by an extended arm position or inappropriate posture of the tackler at impact, such as a lowered head in front of the opponent. These findings indicate that injury mechanisms should be assessed for each type of tackle, as it is unknown

  18. Understanding mechanical properties of polymer nanocomposites with molecular dynamics simulations

    Science.gov (United States)

    Sen, Suchira

    Equilibrium Molecular Dynamics (MD) simulations are used extensively to study various aspects of polymer nanocomposite (PNC) behavior in the melt state---the key focus is on understanding mechanisms of mechanical reinforcement. Mechanical reinforcement of the nanocomposite is believed to be caused by the formation of a network-like structure---a result of polymer chains bridging particles to introduce network elasticity. In contrast, in traditional composites, where the particle size range is hundreds of microns and high loadings of particle are used, the dominant mechanism is the formation of a percolated filler structure. The difference in mechanism with varying particle sizes, at similar particle loading, arises from the polymer-particle interfacial area available, which increases dramatically as the particle size decreases. Our interest in this work is to find (a) the kind of polymer-particle interactions necessary to facilitate the formation of a polymer network in a nanocomposite, and (b) the reinforcing characteristics of such a polymer network. We find that very strong polymer-particle binding is necessary to create a reinforcing network. The strength of the binding has to be enough to immobilize polymer on the particle surface for timescales comparable and larger than the terminal relaxation time of the stress of the neat melt. The second finding, which is a direct outcome of very strong binding, is that the method of preparation plays a critical role in determining the reinforcement of the final product. The starting conformations of the polymer chains determine the quality of the network. The strong binding traps the polymer on the particle surface which gets rearranged to a limited extent, within stress relaxation times. Significant aging effects are seen in system relaxation; the inherent non-equilibrium consequences of such strong binding. The effect of the polymer immobilization slows down other relaxation processes. The diffusivity of all chains is

  19. Dislocated interests and climate change

    Science.gov (United States)

    Davis, Steven J.; Diffenbaugh, Noah

    2016-06-01

    The predicted effects of climate change on surface temperatures are now emergent and quantifiable. The recent letter by Hansen and Sato (2016 Environ. Res. Lett. 11 034009) adds to a growing number of studies showing that warming over the past four decades has shifted the distribution of temperatures higher almost everywhere, with the largest relative effects on summer temperatures in developing regions such as Africa, South America, southeast Asia, and the Middle East (e.g., Diffenbaugh and Scherer 2011 Clim. Change 107 615-24 Anderson 2011 Clim. Change 108 581; Mahlstein et al 2012 Geophys. Res. Lett. 39 L21711). Hansen and Sato emphasize that although these regions are warming disproportionately, their role in causing climate change—measured by cumulative historical CO2 emissions produced—is small compared to the US and Europe, where the relative change in temperatures has been less. This spatial and temporal mismatch of climate change impacts and the burning of fossil fuels is a critical dislocation of interests that, as the authors note, has ‘substantial implications for global energy and climate policies.’ Here, we place Hansen and Sato’s ‘national responsibilities’ into a broader conceptual framework of problematically dislocated interests, and briefly discuss the related challenges for global climate mitigation efforts.

  20. Evaluation of mobile dislocation density based on distribution function of dislocation segments

    Institute of Scientific and Technical Information of China (English)

    周志敏; 孙艳蕊; 周海涛

    2004-01-01

    A function is offered to represent the distribution of reduced length of dislocation segments. The segment distribution of materials, e. g. , MgO and Cu, can be well described by taking appropriate values of parametersm and n. Based on this function, a model for evaluating the mobile dislocation density is developed. Provided the total dislocation density and applied stress are known, the mobile dislocation density could be readily assessed by using this model. For pure copper the mobile dislocation density and strain rates at deferent strains are evaluated. The calculated results are consistent with the known experimental data.