Marina Popova

Atomistic simulation of dislocation interactions in a model crystal subjected to shear

The interaction of edge dislocations in a two-dimensional (2D) model crystal subjected to “simple shear” is studied using molecular statics simulations. An initial point defect is introduced in the model to trigger the dislocation activities in a controlled manner. We consider dislocations gliding towards one another on parallel slip planes separated by various distances. The overall load-displacement response of the crystal is obtained from the simulations, which can be correlated with the nano-scale atomistic mechanisms. Although the crystal is inherently anisotropic, the incipient dislocation plasticity is such that slip is parallel to the primary shear direction as clearly demonstrated in this work. It is also illustrated that dislocation annihilation, as well as dislocation encounter which leaves behind a point defect, can be unambiguously modeled. Throughout the deformation history, more dislocations capable of gliding in the crystal tend to generate a weaker mechanical response and more pronounced plasticity. The present study also offers mechanistic insight into experimentally observed small-scale crystal plasticity.

Estimation of elastic compliances of planar interfacial cracks from homogeneous solutions

Formation of cracks in a material as a result of the damage accumulation may change (weaken) material effective properties. The present letter suggests an approach to estimate such changes when cracks form at interfaces of dissimilar materials (for example, at matrix/inclusion boundaries or film/substrate interfaces). Generally, solution of an interface problem is required to predict compliances of interfacial cracks, with the exception of planar cracks. We show that planar cracks possess a special property in the sense that their normal compliances may be approximated from solutions in a homogeneous medium. The method is then applied to analyze elastic compliances of the rectilinear, penny-shaped, elliptical, and annular interfacial cracks.

Note on the shape of a slip zone in planar frictional sliding

Effect of Poisson’s ratio on the evolution of planar sliding in the vicinity of a local drop in frictional resistance under remotely applied uniform shear load is discussed. The local reduction of frictional resistance may be caused by various factors (for example, variability of the friction coefficient). We demonstrate that under these mixed mode conditions the shape of the slip zone may be circular for the frictional resistance with non-axisymmetric distribution and non-circular for the frictional resistance with an axisymmetric distribution. Distortion of the shape is found to be related to Poisson’s ratio. Sliding propagation in the vicinity of the parabolic drop of the frictional resistance is studied in detail.