Determination of tribological history and wear through visualisation in lubricated contacts using a carbon-based composite
Résumé
Friction and wear of a carbon-based composite used for lubricated clutch applications in continuous slipping were studied. Representative simulations with high-resolution visualisations were carried out to identify velocity accommodation mechanisms in this parallel face contact. A new lubricated regime leading to specific changes of the carbon composite during friction was pointed out, In the contact, the load was carried by islands of composite over which the measured film thickness was lower than 0.5 mu m. A limited number of islands (called the activated islands) seemed to carry the load at one time. This new lubricated regime, called fractionated lubrication, was characterised by high shear rates (higher than 10(5) s(-1)), unusual local pressures (higher than 500 MPa) over reduced areas of contact, the islands, (about 100 x 100 mu m) independent in terms of geometry and of lubricant Bow. Various degrees in the morphological changes of the surface of these islands were pointed out, involving a process called tribological history. In this paper, further investigation into the tribological history of the islands is made. The influence of the lubricants and of changing steel counterfaces to glass counterfaces, both under different running conditions, were studied. A morphological examination oi the surfaces of the islands was performed after testing from a mechanical point of view and the activated wear phenomena were pointed out. Then the mechanisms involved in the tribological history both in clutch experiments and in simulations were identified as well as the main parameters which governed morphological changes. These results provided a better understanding of the tribological behaviour of the carbon-based composite, allowing one to control and optimise wear in the industrial application.