[en] A statistical mechanics framework for the evolution of the distribution of dislocations in a single crystal is established. Dislocations on various slip systems are represented by a set of phase-space distributions each of which depends on an angular phase space coordinate that represents the line sense of dislocations. The invariance of the integral of the dislocation density tensor over the crystal volume is proved. From the invariance of this integral, a set of Liouville-type kinetic equations for the phase-space distributions is developed. The classically known continuity equation for the dislocation density tensor is established as a macroscopic transport equation, showing that the geometric and crystallographic notions of dislocations are unified. A detailed account for the short-range reactions and cross slip of dislocations is presented. In addition to the nonlinear coupling arising from the long-range interaction between dislocations, the kinetic equations are quadratically coupled via the short-range reactions and linearly coupled via cross slip. The framework developed here can be used to derive macroscopic transport-reaction models, which is shown for a special case of single-slip configuration. The boundary value problem of dislocation dynamics is summarized, and the prospects of development of physical plasticity models for single crystals are discussed. (c) 2000 The American Physical Society

[en] The effect of dislocations in a silicon single crystal on the zeroth-order Laue-zone (ZOLZ) pattern in large-angle convergent-beam electron diffraction (LACBED) has been studied experimentally. It is found that edge disloctions cause the ZOLZ pattern to be compressed or elongated and screw dislocations cause it to be dislocated. This phenomenon is the consequence of opposite shifts of the two halves of the Tanaka pattern, separated by the shadow image of the dislocation line along directions b and -b of the Burgers vector. The shift direction of each half of the pattern depends on the dislocation characteristics and the position of the incident-beam crossover. The pattern on the side, pointed to by the vector uxc (or -uxc) from the shadow image of the dislocation line is shifted along b (or -b), where u is the direction of the dislocation-line vector and c is a vector pointing to the beam crossover from the dislocation line. This phenomenon can be used to determine the Burgers vector (both its direction and sense) of a dislocation. (orig.)

[en] Dislocation generation is studied in a generalized two-dimensional Frenkel-Kontorova model which allows consideration of dislocations of arbitrary Burgers vector and line shape. Two new mechanisms for dislocation generation at high stresses have been found: (1) heterogeneous nucleation of dislocations on preexisting dislocations and (2) generation of dislocation loops in the wake of a moving dislocation. These new mechanisms provide an understanding of how materials generate the density of dislocations required to accomodate arbitrary strains at high strain rates

[en] Experimental measurement has been performed to determine α, β and screw dislocation charges in the base plane (0001) and edge dislocation charges in the prismatic slip plane (1100) in cadmium sulphide. The measurements make it possible to draw some tentative conclusions as to the nature of dislocation charges in CdS

[en] Internal friction measurements were performed on Fe samples cold worked at 300K or irradiated at 77K and cold worked

[en] Effects of Zn atoms on basal dislocation in Mg solution have been studied by means of the improved 2D Peierls–Nabarro model in combination with misfit approximation under the Fermi–Dirac distribution function of solute atoms. With increasing Zn concentration, the separation distance for edge dislocation is decreased, while the separation distance is increased for screw dislocation. From function of the total dislocation line energy surfaces as shift displacement of dislocation center and separation distance between the partials, it is found that with the increase of solute concentration of Zn atoms, the Peierls energies, Peierls stresses and yield stresses for edge dislocation increase more quickly than ones for screw dislocation, and the increase of edge dislocation is stronger

No abstract available

[en] The objective of this work is to derive the parameters of macroscopic constitutive equations for the plasticity of fcc single crystals with the help of simulations performed at a dislocation level. The macroscopic model is based on the leading physical mechanisms which are involved in the plastic deformation. The three involved constitutive laws use the total dislocation densities on each glide system as fundamental variables. Those three expressions are derived from physical processes governing the behaviour of a single dislocation and adapted to be used at the macroscopic scale. Literature results could be widely used for the identification of the material parameters for different fcc materials but some of the parameters are mean values and must be seen as phenomenological parameters so that a good way to determine such values consists to use a numerical tool where each dislocation is individually simulated in a three dimensional network. Such a tool works at a mesoscopic scale (typically several microns) and deals with dislocations discretized into pure screw and edge segments. It includes all the well-known elementary events governing the dislocation motion such as the line tension effect, the Frank-Read multiplication mechanisms, the cross-slip events and the junction formations. The cross-analysis of several specific mesoscopic simulations allows to determinate the values of some macroscopic parameters and also to check the validity of both models. (orig.)

[en] The interaction forces between the partial dislocations forming an extended dislocation node are calculated using elasticity theory for anisotropic media.s are carried out for nodes of screw, edge and mixed character in Ag, which has an anisotropy ratio A equal to 3, and in a hypothetic material with A = 1 and the same shear modulus as Ag. The results are compared with three previous theories using isotropic elasticity theory. As expected, in Ag the influence of anisotropy is of the same order as the uncertainty due to the dislocation core energy

[en] In this paper, we mainly discuss the dechanneling effect caused by a lattice defect. From the general equation of motion we suggest that a dechanneling effect caused by a dislocation can be described by bent crystal. A sine-squared potential is introduced to describe the dechanneling behaviour of an edge dislocation. (author)