Zero-Point Correction Method for Nanoindentation Tests to Accurately Quantify Hardness and Indentation Size Effect

摘要

An original treatment method is proposed to accurately determine by nanoindentation, the macrohardness and the indentation size effect (ISE). This method is applied to stainless steel specimens having different rough surfaces. It uses load versus indentation depth curves and is based on two main original features. The first one concerns the correction of the zero point (i.e. depth equals to 0) to minimise the scattering between experimental curves. The latter are all described by usual hardness equations and are shifted by minimising the distance from a leading curve chosen in a random way among the experimental curves. The second feature is the simultaneous treatment of all the nanoindentation curves to compute the macrohardness and evaluate the ISE. The standard deviation for the estimated macrohardness is small, which indicates the robustness of the approach. It is shown that using a single nanoindentation curve can alter macrohardness estimation because of a bad consideration of the ISE. To prevent this misinterpretation, the curves should be treated simultaneously instead of averaging results of separately treated curves. A correlation is identified between the standard deviations of both surface roughness and correction of zero point, which highlights the effect of surface roughness on the scattering of the indentation curves.