Analysis of the nanoindentation data measured with a Berkovich indenter for brittle materials: effect of the residual contact stress

Nanoindentation tests were conducted on three typical brittle materials with a Berkovich indenter and the experimental data were analyzed with the traditional Oliver–Pharr (OP) method. It was found that, even for a given material, the experimentally determined power-law exponent m varies significantly. A new analytical approach was then proposed for the description of the unloading data based on the conical indenter approximation and by introducing a term describing the residual contact stress effect into the classical solutions of elastic contact theory. Analysis showed that the elastic modulus and the hardness determined with this new approach are comparable to those obtained with the OP method but the new approach presents advantages compared to the OP method in understanding the nanoindentation unloading behavior. A reasonable explanation for the variation of the power-law exponent m was also presented.