Multiscale modeling of ductile crystals at the nanoscale subjected to cyclic indentation

A multiscale method is applied to study the response of an aluminum single-crystal substrate to cyclic indentation at finite temperature. The evolution of contact-induced deformation on the nanoscale is controlled based on defect nucleation beneath the indenter. The method allows for visualization of atomistic deformation during loading and unloading. Although there are inherent limitations to our two-dimensional model, we have found qualitative similarities to the mechanisms of homogeneous defect nucleation and deformation in three-dimensional face-centered cubic crystals. It is shown that the atomistic surface roughening process mostly arises from homogeneous dislocation nucleation during successive loading/unloading processes. These sub-surface defects cause major permanent deformation of the substrate during indentation. The slip steps forming on the surface of the indented substrate contribute their own dislocation activity, sending dislocations directly from the surface into the crystal, but those activities mostly remain localized near the indented surface. Force-displacement curves and the hysteresis which occurs due to inelastic deformation and heating of the substrate are studied for each cycle, and correlated with sub-surface and surface nucleation of defects