Effect of boundary conditions on the MD simulation of nanoindentation

The present work investigates the effect of different boundary conditions on the simulation of nanoindentation using molecular dynamics (MD). The MD simulations of nanoindentation on Ni single crystal thin films are conducted using various boundary conditions and thicknesses. The coupling effects of indenter size and boundary conditions are studied using the spherical indenter with different radii. Silicon substrate is used as one of the boundary conditions. Three different atomic potentials including embedded-atom method (EAM), Tersoff, and Lennard–Jones (LJ) are incorporated to model the atomic interactions of Ni–Ni, Si–Si, and Ni–Si, respectively. The effect of boundary conditions on the elastic behavior of thin films with various thicknesses is investigated. The results show that the effect of boundary conditions on the elastic response is a function of the film thickness and indenter radius, such that as the thickness increases and the indenter radius decreases, the boundary conditions effects become less significant. Next, the nucleation and early evolution of dislocations in the simulated samples is addressed. Three different patterns of dislocation structures are observed which are governed by two mechanisms of indentation and bending. Finally, the incipient plasticity in thin films with different boundary conditions and thicknesses is investigated. The results show that the dislocation structure controls the mean contact pressure at the onset of plasticity.