Geometry and bluntness tip effects on elastic–plastic behaviour during nanoindentation of fused silica: experimental and FE simulation

Abstract

A procedure to develop a true geometric finite element (FE) model of a Berkovich indenter using fused silica as a reference material is proposed. 2D and 3D models of the indenter tip were evaluated based on the delimiting factors such as the indenter true geometry, elastic modulus, yield stress and hardening modulus, and compared with the experimental results. The true geometry of the Berkovich indenter paying special attention to the tip end was determined by a non-linear regression of the indentation data at small indentation depths using the equation of a sphere, and by image analysis of AFM micrographs. The tip bluntness was described with a so-called rounding radius and incorporated into the 3D FE model, which was in fact the most important parameter considered for a better representation of the load–displacement curves obtained experimentally. The advantages of using 3D models instead of 2D models are described and discussed here. Finally, different methods were used to determine the yield stress of fused silica, including the analysis of the load–penetration data transformed to 'stress–strain' indentation curve as well as by the analysis of the von Mises equivalent stress distribution obtained with the 3D FE models. The results show that the yield stress of fused silica is 4.5–4.6 GPa.