Influence of interface geometry on rubber friction

While the mechanics of rubber friction are still debated, it is widely accepted that there are two principal factors, adhesion and hysteresis, commonly considered to give rise to a frictional force during the sliding of a rigid surface on a flexible elastomer. The experiments described here, validated by finite element analysis (FEA), confirm an additional (third) geometric factor, which had been observed previously by Schallamach (1969) [14] and by Liang et al. (2009) [12], but which has not been fully investigated. Under certain conditions, it can increase the frictional force significantly above that expected from a consideration of the interfacial coefficient of friction alone. This contribution increases with the depth of penetration of the rigid surface into the elastomer and is therefore perhaps comparable to the frictional behaviour found when wrapping a rope around a capstan (Shames, 1980 [23]). This term is thought likely to make a significant contribution to most frictional sliding applications such as tyres on a road surface.