Hardness testing provides a simple method for measuring the properties of a metal. Recently, it has been used to evaluate the properties of engineered surfaces such as coatings and ion-implanted surfaces. The advantages of hardness testing for these applications are its simplicity and, more importantly, its ability to sample the surface properties with minimal substrate interference. The interpretation of such tests, though, is complicated by fact that the properties of surface-modified materials vary with depth from the surface.
Because indentation causes large-strain plastic deformation, there is little one can do analytically to study this problem. Hence, finite element methods are the most common technique used to simulate hardness testing (see, for instance, Blanchard [1] and Blanchard et al. [2]). This work presents the results of finite element simulations that help to elucidate some of the features of hardness tests for surface-modified materials, in which the properties vary either abruptly or smoothly as a function of depth.