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 can vary in magnitude and biaxiality, and the resultant error in the measured hardness is difficult to estimate. A prediction of the effect in the contact pressure with and without residual stresses is carried out by a new 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 an 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.