The influence of plastic hardening on surface deformation modes around vickers and spherical indents

Measurements of piling-up and sinking-in of material around Vickers and sph erical indentations are conducted in metals and ceramics. The surface displ acement at the contact boundary under applied load and in the unloaded stat e 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-un iform deformation is detected around Vickers indents in contrast to the cas e of spherical indentation, where the deformation state is more uniform as a result of the axisymmetry of the contact conditions. The average (mean) s urface deformation state around the contact perimeter in Vickers indents fo llows a similar correlation with n as that found for spherical indentation. The present study of contact profiles enables an accurate assessment of co ntact area from measurements of depth of penetration which is central to th e analysis of instrumented indentation experiments. (C) 2000 Acta Metallurg ica Inc. Published by Elsevier Science Ltd. All rights reserved.