Plastic Behavior of Single Crystals with Multiple Slip Systems: Insights from Discrete Dislocation Dynamics

The collective motion of discrete dislocations governs the material plasticity. In this study, the plastic behavior of single crystals with multiple slip systems is investigated using a two-dimensional discrete dislocation dynamics approach. The elastic interactions are accurately captured in a local cycle with the time interval further discretized. When dislocations are capable of escaping from the free surfaces, a dislocation starvation state is observed, and the dislocation density reaches a steady state at a lower applied stress than the threshold for dislocation nucleation. The interaction of dislocations in multiple slip systems restricts their motion, which provides a possible explanation for the reduced size dependence of stress response in relatively larger specimens. When escaped dislocations are pinned at the passivation layers, dislocation motion patterns during loading-unloading are further investigated. The initiation of dislocation reverse motion during unloading is somehow related to the back stress generated from dislocation pile-up during loading. Simulations of single crystals subjected to tensile loading with constrained thermal expansion indicate that thermal-stress-induced strain-state changes affect dislocation nucleation and glide. The findings are expected to provide valuable insights into the dislocation mechanisms involved in the plastic deformation of crystalline materials.