Effect of sample tilt on nanoindentation behaviour of materials

Analysis of nanoindentation is based on the elastic solution of a rigid indenter perpendicularly penetrating a flat contact surface. In reality, nanoindentation is often performed on a tilt sample surface due to sample tilt mounting or the existing roughness of a polished or raw surface. In this study, finite element simulations as well as nanoindentation experiments on a fused-quartz sample with different tilt angles were carried out to investigate the influence of sample tilt on nanoindentation behaviour of materials. It was found that sample tilt results in increases in the indentation load, contact area and contact stiffness at the same penetration depth. The contact area increase caused by sample tilt cannot be accounted for by Sneddon's equation, commonly used in nanoindentation analysis. This results in a significant underestimation of indentation projected contact area, which in turn leads to an overestimation of the mechanical properties measured by nanoindentation.