Atomistic insights into the loading – Unloading of an adhesive contact: A rigid sphere indenting a copper substrate

Abstract

A molecular dynamics simulation model is developed to investigate the loading–unloading behavior during nanoindentation of a spherical contact considering material anisotropy and adhesion. A comparison with analytical Hertz solution, JKR and DMT models is performed to determine the differences between macroscale and nanoscale. The single-crystal copper (001) substrate has a sudden jump in contact with the indenter due to adhesion. The simulated critical interference for yielding inception is several orders of magnitude larger than the calculated value using Hertz theory. Plastic yielding caused by intensive dislocation is observed in the sudden load drop region. The JKR and DMT theories used in macro scale are not able to describe accurately the contact behavior in nanoscale. A nearly linear increase in the contact area with the indentation depth is observed in the elastic regime of deformation. The Tabor parameter can be used to evaluate the transition of jump-in or jump-out behavior for the load–displacement curve in an elastic–plastic adhesive contact in nanoscale.