Peculiar surface deformation of sapphire: Numerical simulation of nanoindentation

This report addresses the origin of peculiar anisotropic deformation of sapphire. The three-dimensional finite element simulation of the contact between spherical indenter and elastically anisotropic solid allowed us to analyze stress under the tip that penetrates in the (10 (1) over bar0) and (0001) planes, and consequently, to localize those regions in which particular deformation mechanisms are likely to be activated. This approach contrasts the available models of hardness anisotropy, which routinely apply a modified uniaxial-stress approach to this essentially three-dimensional, nonisotropic contact problem. The calculated results are in agreement with the microscopic inspection of impressions; that is, the surface features reflect the distribution of stress. The computations made it also possible to evaluate the actual radius of the tip (nominally 5 mum ball). (C) 2003 American Institute of Physics.