Simulation of Nanoindentation into Hard Thin Film on Soft Substrate

摘要

Mechanical response of hard thin films on soft substrates subjected to indentation was investigated using finite element method (FEM), The load-displacement curves for different indentation depth were computed to calculate film hardness based on the Oliver-Pharr method. It was found that the indentation depth should be smaller than 6% of film thickness in order to neglect the influence of substrate. FEM results showed that the calibration of the coefficient of elastic displacement of the film surface at the contact was essential to improve the accuracy of the deduced value of film hardness at such a small indentation depth. Energy studies implied that the unloading process was not purely elastic. The yielding of the substrate resulted in not only an augmented value of the maximum displacement but also an overestimated value of contact stiffness in the Oliver-Pharr method. Both resulted in underestimation of film hardness.