Development of severity parameter for wear study of thermoplastics

The effect of normal load, sliding velocity, roughness and counter-body material, on the wear behavior of POM and UHMWPE was studied. The pin-on-disc tests, with the polymeric pins and alumina and duplex stainless steel discs, were performed with three different levels of load, velocity and surface finishing of counter-face. For each one of the 36 test conditions 3 assays had been carried out. The near contact temperature, friction force and the vertical displacement of the pin, which was used to evaluate the wear rate of polymers, were recorded. The covered distance was of 3500 m and the tests were carried through in an environment with controlled air relative humidity in 50 ± 5%. The wear behavior was analysed and a severity parameter (PVR/DpDd) was proposed. This parameter considered mechanical factors (P—contact pressure and V—velocity values), a topographical factor (roughness of counter-face, R) and a thermal factor (thermal diffusivity of the materials in contact, DpDd). It was observed that the vertical pin displacement occured not only due to the wear, but also due to the polymer creep and melting in extreme test conditions. The wear results were organized in the form of wear maps that considered three phenomena: creep, wear and melting. It was suggested that the more important factor controlling the wear rate is the capacity of heat dissipation at the contact region.