The influence of friction on elasto-plastic material in nanoindentation

A comprehensive computational study is undertaken to identify the influence of friction in
nanoindentation of elasto-plastic materials, the impacts of friction on calculation results with conical and spherical indenters are shown in this paper. The results clearly demonstrate that, for some elasto-plastic materials, the P  h curves obtained either by spherical or conical indenters with different friction coefficients cannot be distinguished. However, if utilizing the parameter  (see text for details), to quantify the deformation of piling-up or sinking-in, it is easy to find that the influence of friction on piling-up or sinking-in in nanoindentation is significant. Therefore, the material parameters derived from the projected area will have a large error caused by the influence of friction. In this paper, the maximum error on hardness can reach 14% for some elastic materials. These results do not agree with those from researchers who stated that instrumented indentation experiments are not significantly affected by friction. Moreover, in conical indentation, friction can effectively restrain the slip on the interface between indenter and specimen, which leads to a decrease in the amount of piling-up or increase in the amount of sinking-in. However, when the half apex angle is large enough, the influence of friction becomes a minor factor in indentation. In spherical indentation, the amount of piling-up decreases or of sinking-in increases with an increasing friction coefficient. But the friction is independent of the radius of spherical indenter, the piling-up or sinking-in obtained by two different spherical indenters with varying friction coefficients are nearly identical.