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[en] In this paper we consider the dynamics of dislocations with the same Burgers vector, contained in the same glide plane, and moving in a material with periodic obstacles. We study two cases: i) the particular case of parallel straight dislocations and ii) the general case of curved dislocations. In each case, we perform rigorously the homogenization of the dynamics and predict the corresponding effective macroscopic elasto-visco-plastic flow rule.
[en] Highlights: • The interfacial dislocations by GMS and O-lattice are calculated. • Interpretation of interfacial dislocations in Ni–TiN system is given. • Secondary Burgers vectors of interfacial dislocations is obtained. • Occurrence frequency of precipitates is interpreted by O-line model. The preferred state in an interface is the key to evaluating misfit strain, especially for the interphase interfaces in secondary preferred state. The structure of good matching site (GMS) in a GMS clusters offers a guidance for the preferred state, especially for identifying the coincidence site lattice in two dimension for secondary preferred state and the Burgers vectors in a large misfit system. Here, we combine the GMS with O-lattice theory to calculate the secondary dislocation structure in the habit planes of the type II and III TiN precipitates in a Ni–TiN system. We find that under a slight elastic strain, the type III habit plane contains a single set of secondary dislocations, consistent with the experimental observation. The type II habit plane contains three sets of secondary dislocations, two of which can be relaxed to be nearly parallel and another of which may be invisible in diffraction contrast due to its short Burgers vector. The present study provides a reasonable interpretation to the observed interfacial dislocations, and also suggests Burgers vectors for the dislocations that are not determined experimentally.
[en] We describe a novel analysis method to quantify the Burgers vectors of dislocations in atomistic ensembles and to calculate densities of geometrically necessary and statistically stored dislocations. This is accomplished by combining geometrical methods to determine dislocation cores and the slip vector analysis, which yields the relative slip of the atoms in dislocation cores and indicates the Burgers vectors of the dislocations. To demonstrate its prospects, the method is applied to investigate the density of geometrically necessary dislocations under a spherical nanoindentation. It is seen that this local information about dislocation densities provides useful information to bridge the gap between atomistic methods and continuum descriptions of plasticity, in particular for non-local plasticity
[en] A total variation diminishing (TVD) limiter is proposed that attempts to maximize performance given that the inherent limitation of TVD formulations is peak loss. For the scalar advection and Burger's equation, the present results are qualitatively superior to those using the harmonic and superbee limiters, balancing well the competing effects of skewing, smearing, and squaring. In the case of the Euler equations, the current results appear to significantly improve upon previous TVD results and are quite comparable with more elaborate algorithms. 23 refs., 13 figs
[en] Formulae are derived for calculating the displacement field of a prismatic hexagonal vacancy-type dislocation loop with the Burgers vector b vector=a/3 (111) with a radius of a circumference r0. In the case of an arbitrary dislocation structure (fracture, dislocation bend, nonplane polygon, dislocation grid) the field of such a structure is derived from summing up the contribution of its segments taking the orientation and the Burgers vector value b vector sub(i) for every segment into account
[en] Irradiation growth and creep are crucially dependent on the movement of dislocations under irradiation. However, despite being amongst the most commonly existing prior defects in polycrystals, the evolution of pre-existing dislocations and their impact on the formation of dislocation loops during irradiation have been relatively rarely investigated. In this study, the evolution of pre-existing dislocations and their impact on the formation of dislocation loops were investigated in magnesium by electron irradiation at different temperatures. The pre-existing dislocations have a profound influence on the loop size, density and Burgers vector of irradiation loops, and this influence is dependent on both the density of the pre-existing dislocations and irradiation temperature. Dislocation climb and glide were observed, but a significant change in pre-existing dislocation density was not seen.
[en] The elastic theory calculations are conducted to clarify the interaction between a large dislocation loop and a small glissile loop in face-centered-cubic systems. In the parallel Burgers vector case, the interaction force changes from repulsive to attractive when the small loop moves along its glide cylinder. In the perpendicular Burgers vector cases, the interaction strongly depends on the spatial position of the glide cylinder of the small loop from the center of the large loop. There are attractive regions in any combinations of the Burgers vectors and spatial positions calculated in this study, which may induce the loop decoration.