Determination of constants for cowper-symonds constitutive equation using response surface method in sharp indentation

Instrumented indentation is widely used to investigate the elastic and plastic properties of mechanical materials. During an indentation experiment, a rigid indenter penetrates normally into a homogeneous solid, where the indentation load and the displacement are continuously recorded during loading and unloading. It was known that the micro-indentation test was strongly affected by the strain rate in the materials with strain rate dependence of strength. In the second report, the new approach for the evaluation of the strain rate dependence of materials was developed using the loading curvature-displacement relation obtained from the sharp indentation. Therefore, we attempted to use the response surface method in order to determine the constants for Cowper-Symonds constitutive equation (dynamic constants). First, the relationship between the dynamic constants and the loading curvature was constructed by the response surface, and then those were determined using the inverse analysis. It was confirmed that the dynamic constants could be obtained by substituting the result of the micro-indentation for the unknown materials into the response surface up to the strain rate of 102s-1. By using this method, it is possible to evaluate the strain rate dependence of materials in such a strain rate range. © 2015 The Society of Materials Science, Japan.