Viscoelastic and elastic–plastic behaviors of amorphous polymeric surfaces during scratch

In this study, we propose an analysis of the residual groove after contact between a spherical indenter and an amorphous polymeric surface (polymethylmethacrylate, PMMA) in scratch experiments. The geometrical shape of the residual groove was mathematically described using an exponential decay law. Finite element modeling (FEM) of scratch tests was compared to the corresponding experimental results. Assuming a two-segment simplified constitutive law with linear elastic behavior followed by linear strain hardening, the friction at the interface between the indenter and the material was modeled with a Coulomb's friction coefficient varying from 0 to 0.4, for computed ratios a/R between 0.1 and 0.4. The FEM results for elastic–plastic contact indicate that the shape of the residual groove is directly related to the plastic strain field in the deformation beneath the indenter during scratching. It is shown that the dimensions of the plastically deformed volume and the plastic strain gradient both depend on the ratio a/R and also on the friction coefficient.