Multiscale simulation of onset plasticity during nanoindentation of Al (001) surface

The onset of plasticity in crystalline materials is important to the fundamental understanding of plastic deformation and the development of precision devices. Dislocation nucleation and interactions at the onset of plasticity are investigated here using a multiscale quasi-continuum (QC) method for the nanoindentation of the (001) surface of a single crystal aluminiurn (Al) of 200 x 100 nm(2) with infinite thickness. Deformation twinning was noted to Occur during the nanoindentation of Al. We used unrelaxed and relaxed QC simulations with three embedded atom potentials of Al to evaluate the generalized planar fault (GPF) energies. The energy barrier for initial dislocation nucleation is much higher than that for subsequent nucleation events adjacent to the pre-existing defect. This mechanism promotes deformation twinning when some of the available slip systems are constrained. Dislocation initiation causes a minor load drop in the load-displacement curve, whereas major displacement excursion from experimental observations is the result of collective dislocation activities. (Some figures in this article are in color only in the on-line version.) (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.