Simulating nanoindentation and predicting dislocation nucleation using interatomic potential finite element method

Dislocation nucleation is central to our understanding of the onset of plasticity during nanoindentation. The shear stress in small volumes beneath the nanoindenter can achieve the theoretical limit of a perfect crystal. The ensuing nonlinear elastic instability can trigger homogenous dislocation nucleation inside the crystal. Here we employ the interatomic potential finite element method to simulate nanoindentation and predict dislocation nucleation. Simulations are performed for indentation on the (1 1 1), (1 1 0) and (1 0 0) surfaces of Al, Cu, Ni single crystals. We quantify the critical conditions of dislocation nucleation, including the indentation load of nucleation, location of nucleation site, nucleation stress and activated slip system. We find these conditions sensitively depend on indentation orientation, but are consistent for different crystals. The results highlight the critical role of hyperelasticity (the nonlinear elasticity caused by elastic softening at large strain) and crystallography in dislocation nucleation in small material volumes. Our study also reveals the deficiency of commonly used nucleation criterion such as the critical resolved shear stress.