Onset of Microplasticity in Copper Crystal during Nanoindentation

Abstract

The nanoindentation test in the dislocation free crystal of copper is simulated by finite element calculations coupled with ab initio calculation of ideal shear strength. The onset of microplasticity, associated with the pop-in effect identified in experimental nanoindentation tests (creation of first dislocations), is assumed to be related to the moment of achieving the value of the ideal shear strength for the copper crystal. This value also depends on the normal stress in the critical shear system in an approximately linear way, as follows from recently published first principle calculations. The calculated values of the critical shear stress (related to the ideal shear strength) lie exactly at the lower limit of the range of experimentally observed pop-ins in the copper crystal.