Influence of affected layer for micro-indentation tests

A micro-indentation test is useful for evaluating mechanical properties of a micro-structure. But because the measurement values are very small, there are some significant error factors. In this paper, the influences of a work-hardened surface which has been made by a mechanical polishing were investigated using experiments and finite element analyses. The indentation results on a ductile material, like an annealed copper, are very sensitive to a work-hardened surface. The indentation's shape varies, according to a penetration depth, from piling up to sinking in. It is important to improve the elastic modulus by changing the calculated contact area to a measured value by the proposed method. However the hardness of a material is not able to be improved by the measured contact area, so it would be misleading to assume that these results are applicable to a material which is entirely as hard as the work-hardened surface. In order to evaluate properties of a material accurately, an electrochemical polishing is needed after mechanical polishing to remove the work-hardened surface.