A wear particle-based model of friction in a polymer-metal high pressure contact
Résumé
Sliding contact under high pressure between a more or less rough metal surface and a polymer occurs in diverse manufacturing processes. Transfer of the softer material on the harder counterpart is a common phenomenon under such conditions (high pressure) due to high level of polymer wear. The transfer of worn polymer particles on the metal surface generally has a large influence on friction. A model of wear, transfer and their consequences on friction is described. Based on the third body concept, it shares the created wear particles between the transfer film and particles escaping the contact. The model includes unknown parameters describing particles creation and movement on the one hand, and the friction-transfer relationship on the other hand. The parameters are determined experimentally on a linear reciprocating sliding tribometer, where a polymer-coated bar slides on a rough metallic cylinder in a point contact configuration, under conditions of large sliding length (10 mm) and high pressure. Abrasive wear and transfer occur, the initial friction coefficient is shown to follow Coulomb's model (no variation with the applied average pressure); it increases with sliding length (or cycle number) due to increasing coverage of the metal surface by wear particles (or transfer film average thickness). It is shown finally that the model describes quite well the evolution of friction along several cycles.