Nanoindentation and incipient plasticity

This paper presents a large-scale atomic resolution simulation of nanoinden tation into a thin aluminum film using the recently introduced quasicontinu um method. The purpose of the simulation is to study the initial stages of plastic deformation under the action of an indenter. Two different crystall ographic orientations of the film and two different indenter geometries (a rectangular prism and a cylinder) are studied. We obtain both macroscopic l oad versus indentation depth curves, as well as microscopic quantities, suc h as the Peierls stress and density of geometrically necessary dislocations beneath the indenter. In addition, we obtain detailed information regardin g the atomistic mechanisms responsible for the macroscopic curves, A strong dependence on geometry and orientation is observed. Two different microsco pic mechanisms are observed to accommodate the applied loading: (i) nucleat ion and subsequent propagation into the bulk of edge dislocation dipoles an d (ii) deformation twinning.