Effect of Void on Yielding Behaviors in a Bicrystalline Copper

Nanovoids make a big contribution to the plasticity and failure of nanocrystalline metallic materials. To develop a further understanding of the role played by spherical voids in governing the plasticity of nanocrystalline metals, molecular dynamics simulations are performed on bicrystalline copper models with a spherical void at room temperature under 1 × 10⁸ s⁻¹ strain rate. The simulation results indicate that the introduction of void lead to the reduction in yield stress with increasing void diameter. The spherical void acts as either a barrier or a source for dislocations. For intergranular spherical void, the dislocations are emitted from the intersections between the void and grain boundary (GB). However, the initial dislocation nucleation site transits from GBs to spherical void surface at a critical diameter of 9.5 nm in the models with intragranular void. According to the Lubarda model, the dislocation emission critical stress at intermediate void diameters is effectively predicted, but it is not applicable for the model with extremely large and small void since the factors of GB and grain orientation are not considered. Some more suitable models need to be developed.