Investigation and modelling of rubber friction

Abstract

The friction between a rubber surface in contact with a rigid surface is still not fully understood. Unlike other materials, friction behaviour in rubber is significantly dependent upon a variety of parameters due to its viscoelastic nature. The aim of this work is to understand frictional phenomena occurring on different length scales of intrest. In the first part of this work the influence of an entirely geometric factor on friction is confirmed by FEA and is validated by experiments for the first time. Under certain conditions, it can increase the frictional force significantly above that expected from a consideration of the interfacial coefficient of friction alone. This term is thought likely to make a considerable contribution to frictional sliding applications such as a tyre on a road surface. In the second part of this work an instability, observed at the rubber surface during sliding, is investigated. Despite experimental research in the past, virtually no information has been published on the modelling of the so-called Schallamach waves using FEA techniques. This work models successive Schallamach waves, giving the opportunity to investigate the transition of individual waves throughout the area of contact, for the first time. The use of FEA allows for a detailed stress and strain analysis at the interface and thus gives new insights into the onset of buckling instabilities. So far, Schallamach waves have only been observed experimentally for optically smooth rubber surfaces, however, during this work, surface waves have been also noticed for rough rubber surfaces. Furthermore, the examination of the frequency dependence of Schallamach waves allows for the consideration of a relationship to stick-slip behaviour. The third part of this work investigates the influence of the rubber surface topography as well as the rigid slider geometry on rubber friction under a wide range of experimental conditions. It was noted that subtle changes of surface finish significantly change the resulting frictional force. The knowledge gained from this can help in the design and understanding of more complex frictional interfaces.