Determination of the true projected contact area by in situ indentation testing

A major limitation in nanoindentation analysis techniques is the inability to accurately quantify pile-up/sink-in around indentations. In this work, the contact area during indentation is determined simultaneously using both contact mechanical models and direct in situ observation in the scanning electron microscope. The pile-up around indentations in materials with lowH/Eratios (nanocrystalline nickel and ultrafine-grained aluminum) and the sink-in around a material with a highH/Eratio (fused silica) were quantified and compared to existing indentation analyses. The in situ projected contact area measured by Scanning Electron Microscopy using a cube-corner tip differs significantly from the classical models for materials with lowH/Emodulus ratio. Using a Berkovich tip, the in situ contact area is in good agreement with the contact model suggested by Loubet et al. for materials with lowH/Eratio and in good agreement with the Oliver and Pharr model for materials with highH/Eratio.