The effect of material properties on the stick–slip behavior of polymers: A case study with PMMA, PC, PTFE, and PVC

The stick–slip behavior of polymers sliding on a cast-iron counter surface was investigated using four different polymers: polymethylmethacrylate (PMMA), polycarbonate (PC), polyvinyl chloride (PVC), and polytetrafluoroethylene (PTFE). Particular attention was given to the correlation between the stick–slip pattern and the material properties such as the tensile strength, modulus, and surface energy of the polymers. Results show that the modulus of the polymer determines the slope of the stick episode of a stick–slip profile, while the stick–slip frequency and amplitude are more dependent on the polar contribution of the surface energy rather than the cohesive strength of the polymers. Assuming no influence from the system dynamics of the tribotester, these material properties at the sliding interface, therefore, determine the friction instability of the friction material, which can trigger the vibration of a sliding system. The critical velocity for the transition from stick–slip to smooth sliding is also affected by the polar component of the surface energy and modulus. The results from this study suggest that the friction instability of polymers sliding on cast iron can be reduced by selecting a polymer with a high modulus and a small polar contribution of the surface energy.