Atomistic modelling of crack propagation in a randomly rough nano-scale metallic surface

Molecular dynamics simulations, based on many-body interatomic potentials, are performed to investigate the propagation of a Mode-I (edge) crack in a roughened two-dimensional (2D) (111) plane of a generic lattice for which we adopt the potential parameters pertinent to the elemental Ag. The randomly rough surface is generated with the help of a fractal-based technique referred to as fractional Brownian motion method. We show that fluctuations in the crack velocity, which lead to the phenomenon of crack branching, are also present for crack propagation in rough surfaces. However, as the roughness increases, this phenomenon becomes less pronounced, and another type of velocity fluctuation associated with the roughness of the surface emerges. Furthermore, it is found that as the roughness of the surface increases, the critical stress for the initiation of crack propagation is increased, and the fluctuations in the crack velocity make their appearance sooner.