Using static atomistic simulations, a study was made of the details of the mechanism by which dislocations homogeneously nucleated below the surface of an initially defect-free crystal during indentation. The mechanism involved the collective motion of a finite disk of atoms over two adjacent slip planes, the diameter of which depended upon the indenter size. The nucleation mechanism highlighted the need for using non-local considerations in the development of a nucleation criterion. Three published nucleation criteria were reviewed; each of which was based upon purely local measures of the state of stress. It was shown that none were sufficiently general to be able to predict nucleation in realistic atomic systems. A criterion based upon an eigenmode analysis of the atomic-scale acoustic tensor was then proposed. The accuracy of the criterion, which also worked in the presence of existing topological defects such as free surfaces or dislocation cores was demonstrated. The dependence of the size of the nucleated disk upon the indenter radius led to a self-similar nucleation process and almost no indentation size effect.

On the Nonlocal Nature of Dislocation Nucleation during Nanoindentation. R.E.Miller, D.Rodney: Journal of the Mechanics and Physics of Solids, 2008, 56[4], 1203-23