Compensating for elastic deformation of the indenter in hardness tests of very hard materials

The current method of analysis for hardness measurements by indentation is examined. Although the method is based on Sneddon's solution for an elastic stress field within a homogeneous half space indented by an elastically deformable indenter, it implicitly assumes a fixed indenter geometry. Therefore, if indentations are made on materials whose hardness or elastic modulus are close to those of the indenter, this method underestimates the contact area and, thus, overestimates the hardness and modulus values of the indented materials. A new method, based on the Hertz contact theory, is proposed that accounts for the elastic deformation of the indenter and provides a simple way to calculate the tip radius. The restrictions of this method are also indicated and discussed. Finally, the hardness and modulus for two recently developed films are measured by this method, and the results are compared with published finite element method (FEM) results.