Mechanisms of third body formation with polymers Role of mechanical and adhesive interactions in the friction and transfer of polyethylene

This work is part of a systematic investigation concerning the mechanisms of transfer film formation in dry friction and their influence on frictional forces. This paper deals mainly with discontinuous films and is characterised by an experimental approach using image analysis to quantify the discrete particles formed on smooth surfaces, combined with the analysis of the parameters controlling transfer particle stability. This work aims to complete the previous investigations in the case of polymers, and check to what extent adhesion (measured by peel test) affects transfer particle density. It is based on the use of four well characterised films of polyethylene, differing mainly by the amount of grafted acrylic acid (respectively 0.0, 0.5, 1.0, and 2.0%). The variations of particle density with normal load, displaying either positive or negative slopes are of great interest. In agreement with previous hypotheses, these variations may be interpreted in terms of shear stresses τ, provided that they include the well known pressure dependence of τ.