It was recalled that the indentation responses of crystalline materials were radically different at the μm and nm scales. The latter was usually assumed to be controlled by the nucleation of dislocations. To explore this process, a dislocation mechanics study was used to determine the conditions for the nucleation of a finite number of dislocations, under a two-dimensional wedge indenter, using the Rice-Thomson nucleation criterion. The configurational force on the dislocation consisted of the applied force, the image force and the interaction force between dislocations. The dislocations reached equilibrium positions when the total driving force equalled the effective Peierls stress; giving a set of non-linear equations that could be solved using the Newton-Raphson method. When the apex angle of the wedge indenter was increased, the critical contact size for dislocation nucleation increased rapidly, indicating that dislocation multiplication near to a blunt wedge tip was extremely difficult. This geometrical dependence agreed well with experimental findings.

Dislocation Nucleation and Pileup Under a Wedge Contact at Nanoscale. Y.F.Gao, J.Lou: Journal of Nanomaterials, 2008, 1