On the effect of a general residual stress state on indentation and hardness testing

During indentation experiments, residual stresses are superimposed on the applied indentation stress field and influence the measurement of the volume of interest. The residual stress state call vary in magnitude and biaxiality, and the resultant error in the measured hardness is difficult to estimate. A prediction of the effect ill the contact pressure with and without residual stresses is carried out by a flew model that accounts for nonlinearities caused by the von Mises' flow rule. The model can also be used for the correction of the effect of a general residual stress state on any further analysis of mechanical properties and stress-strain behaviour from the Measured indentation data. The model provides ail estimation of the measurement uncertainty when the stress ratio or the strength of the material is unknown a situation that is a commonly encountered with hardness testing of thin films and welded materials. (C) 2008 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.