Experimental measurement and numerical simulation of the plastic strain during indentation and scratch tests on polymeric surfaces

Abstract

For elastic–plastic contacts, we propose a complete description of the plastic strain field beneath the indenter during indentation and scratch with a spherical indenter (with R, the tip radius), as a function of the testing conditions, defined by the geometrical strain, noted a/R (with a, the contact radius), and the local friction coefficient μ_loc. The main parameter of the description is the level of the plastic deformation imposed during test into amorphous polymeric surfaces, related in first approximation to the ratio a/R. An equivalent average plastic strain, noted (ε^p)_av, is calculated over a representative plastically deformed volume, both for indentation and scratch tests. The equivalent average plastic strain (ε^p)_av, is observed to increase with the ratio a/R, as predicted by the empirical Tabor’s rule, but also with the local friction coefficient μ_loc for a given ratio a/R, especially during scratching. The plastic zone dimensions and the plastic strain gradient developed beneath the moving tip are shown to depend both on the geometrical strain a/R and also on the friction coefficient μ_loc.