Friction effect on contact pressure during indentation and scratch into amorphous polymers

Abstract

Using finite element analysis (FEA), for monotonic loadings, variations of the true contact geometry and of the mean contact pressure p m, defined by the ratio of the applied normal load to the true projected contact area, are described as a function of the testing conditions, the geometrical strain a/ R and the local friction coefficient μ loc, during indentation and scratch experiments with spherical indenter. The estimation of an equivalent plastic strain is also proposed and shown to be a complex function of a/ R and μ loc, especially during scratch experiments. The normalized contact pressure p m/ σ y, with σ y, the initial yield stress of the tested material, determined during indentation and scratch tests is compared to an expanding cavity model, recently developed for indentation of elastic-strain hardening plastic materials.