Determination of yield stress from nano-indentation experiments

The aim of this paper is to investigate the possibilities of getting information on the initial yield stress Y from nano-indentation experiments with sharp indenters. Berkovich indenters have been used for the experiments and the data evaluation was performed by using two expanding cavity models (ECM) described in the literature, one for elastic-perfectly plastic, and one for power law work hardening materials. To characterize the ECMs, finite element simulations with extensive material parameter variations together with substantial experimental data are used. As a first result, the possibilities of determining Y using the introduced ECMs can be shown for the simulated materials (Fig. 3) and the presented selection of real specimens. Furthermore, the restriction of the ECMs to materials where the yield behavior obeys the von Mises yield criteria is discussed. In doing so it is shown that the indentation work, which can be determined directly from the indentation force-displacement curves, represents a useful quantity to assess the applicability of an ECM to a particular material.