The influence of plastic hardening on surface deformation modes around Vickers and spherical indents Original Research Article

Measurements of piling-up and sinking-in of material around Vickers and spherical indentations are conducted in metals and ceramics. The surface displacement at the contact boundary under applied load and in the unloaded state is correlated with the uniaxial strain hardening exponent, n. It is found that sinking-in predominates in materials where n>0.2. A state of non-uniform deformation is detected around Vickers indents in contrast to the case of spherical indentation, where the deformation state is more uniform as a result of the axisymmetry of the contact conditions. The average (mean) surface deformation state around the contact perimeter in Vickers indents follows a similar correlation with n as that found for spherical indentation. The present study of contact profiles enables an accurate assessment of contact area from measurements of depth of penetration which is central to the analysis of instrumented indentation experiments.