Observation of the adhesive- and deformation- contribution to the friction and wear behaviour of thermoplastic polyurethanes

In this study unfilled and graphite filled thermoplastic polyurethanes (TPU) were investigated in tribological pin-on-disc tests. The two main frictional mechanisms, namely adhesion and deformation, were characterised by tribological tests. Measurements were performed at ambient air and under vacuum by varying the relative humidity, surface roughness of the counterparts (honed and polished) and ambient temperature (23 °C and −30 °C). Combined with qualitative microscopic analysis more knowledge was obtained about the differences and influencing factors related to the ratio between the two main components of friction of TPU. Furthermore, to support the development of a phenomenological model, the bulk material properties in terms of viscoelastic material parameters were determined both under cyclic loading in dynamic mechanical measurements in creep tests. Finally, the usage of a graphite filler influences the wear mechanisms under vacuum condition significantly. The results indicate that the ratio between the two frictional mechanisms is strongly influenced by the load, surface roughness, viscoelastic material behaviour and ambient conditions. The findings lead to a better understanding of the fundamental friction and wear mechanisms of injection moulded TPUs.