Estimation of hardness by nanoindentation of rough surfaces

The roughness of a surface influences the surface mechanical properties, estimated using nanoindentation data. Assuming a relation between the penetration depth normalized with respect to a roughness scale parameter, and the effective radius encountered by the indenter, a first order model of roughness dependency of hardness is proposed. The practical usefulness of this model is verified by the numerical simulation of nanoindentation on a fractal surface. As the roughness of a surface is increased, the hardness measured at depths comparable with the roughness scale deviates increasingly from the actual hardness. Given the constants related to indenter geometry, the present work provides a rationale and a method for deconvoluting the effect of roughness in arriving at real hardness characteristics of the near surface region of a material