VELOCITY ACCOMMODATION IN POLYMER FRETTING

Polymers are often used as palliatives against fretting damage, particularly in quasi-static assemblies subjected to vibration. Velocity accommodation mechanisms and surface damage vary with the material chosen and the application. Transparent materials (polycarbonate and polymethylmethacrylate) were chosen and rubbed against steel counterfaces. Videos were taken through the back of the polymers. Cracks and particle detachment were observed. Cracks propagated until the fretting amplitude was taken up by the elastic deformation of the cracked substrate, at which time wear stopped since surface slip was zero. Particle detachment led to third-body formation which protected the substrate. Oxides were sometimes formed and the rate of progress of the oxide coating was determined. The conditions which led to the formation or not of oxides with the same material combination and under identical running conditions were not identified. However, in all cases oxide patches were initiated at the contact periphery and gradually spread over the entire contact. Results obtained elsewhere on the behaviour of polymers lubricated with solvents of close solubility were confirmed.