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The motion of dislocations with Burgers' vector lying on the basal, prismatic and pyramidal slip planes in pure magnesium was investigated numerically under static and dynamic loading conditions. The analysis of the dislocation core structures revealed that the basal slip system was the most favorable energetically, and therefore a dislocation loop cannot extend on the pyramidal slip plane, because screw dislocations were not stable in this slip plane. In agreement with experimental data, a strong anisotropy between slip systems was observed. In both the basal and the prismatic slip planes, the dislocation velocity is consistent with phonon drag theory. In addition, the edge dislocation velocity was always larger than the screw dislocation velocity independent of the slip system, while the dislocation velocity on the prismatic slip plane was always lower than the dislocation velocity on the basal plane regardless of the dislocation character.

Knowledge of the deformation mechanisms of (Mg,Fe)2SiO4 olivine is important for the understanding of flow and seismic anisotropy in the Earth’s upper mantle. We report here a numerical modelling at the atomic scale of dislocation structures and slip system properties in Mg2SiO4 forsterite. Our study focuses on screw dislocations of [100] and [001] Burgers vectors. Computations are performed using the so-called THB1 empirical potential set for Mg2SiO4. Results of dislocation core structures highlight the primary importance of the (010) plane for [100] slip dislocations. For [001] dislocations, we confirm the occurrence of a stable narrow core that evolves into transient planar configurations to glide in (100) and (010). Such configurations suggest a locking–unlocking mechanism.

Discrete dislocation dynamics is a numerical tool developed to model the plasticity of crystalline materials at an intermediate length scale, between the atomistic modeling and the crystal plasticity theory. In this review we show, using examples from the literature, how a discrete dislocation model can be used either in a hierarchical or a concurrent multiscale framework. In the last section of this review, we show through the uniaxial compression of microcrystal application, how a concurrent multiscale model involving a discrete dislocation framework can be used for predictive purposes.

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Fatigue crack growth from a cracked elastic particle into a ductile matrix Groh, S.; Olarnrithinun, S.; Curtin, W. A.; Needleman, A.; Deshpande, V. S.; Van der Giessen, E. The monotonic and cyclic crack growth rate of cracks is strongly influenced by the microstructure. Here, the growth of cracks emanating from pre-cracked micron-scale elastic particles and growing into single crystals is investigated, with a focus on the effects of (i) plastic confinement due to the elastic particle and (ii) elastic modulus mismatch between the reinforcement and matrix phases. Due to the small sizes of the particles and cracks, plasticity in the ductile crystal is modelled using a 2D discrete dislocation plasticity framework wherein dislocations are modelled as line singularities in an isotropic elastic isotropic material. Crack growth is modelled using a cohesive surface. Calculations reveal a threshold for fatigue crack growth and a transition to Paris power-law behavior, both depending on the existence of the elastic particle and the modulus mismatch. For a matched-modulus particle, the threshold is reduced by 25% and is attributed to slip blockage by the particle. For a high-modulus particle, the threshold is reduced by 50% due to the enhanced stress intensity factor caused by elastic mismatch and due to some slip blockage. However, crack growth halts after some amount of crack advance due to the decreasing effect of elastic mismatch and slip blocking as the crack moves away from the particle. The broad results here are compared with experimental observations in the literature, and are consistent in a number of respects. These results show that fatigue crack growth from micron-scale particles is strongly influenced by plasticity size effects, elastic mismatch, and particle constraints on plastic flow, all of which are captured within a discrete dislocation plasticity framework.