The Influence of Frictional Heating on the Sliding Friction of Elastomers and Polymers

Abstract

Abstract The friction of polymers and elastomers has been widely researched, both in practical applications and in fundamental experiments. Although some of the basic mechanisms of elastomer friction have been well explored, the effect of frictional heating has not received much attention. This is surprising since the low thermal conductivity of elastomers can result in quite high temperatures being generated at the interface. This paper is concerned specifically with the influence of heat generation on the level of friction at the interface. Some present theories of elastomer friction are well established. The important factors that govern friction are considered to be the strength of interface bonds and the loss tangent, tan δ, where δ is the phase lag between harmonically applied strain and the stress response. On a rough surface, friction is considered to occur from hysteretic losses. On a smooth surface, friction is considered to occur from the formation of bonds across the interface, the extension of the bonds and their eventual fracture. In several quantitative models of elastomer friction summarized by Moore and Geyer, the result for friction is directly proportional to tan δ, thus for a perfectly elastic material, the friction (according to these models) tends to approach zero. Factors affecting the interface bond strength are somewhat better understood, Schallamach proposed that the bonds were molecular. This allowed an Eyring-type rate process theory to be applied, as illustrated with great clarity by Grosch. Grosch showed that the Williams-Landel-Ferry transformation could be applied to condense the friction-speed characteristics measured at various temperatures to a single “master curve.” These experiments gave convincing evidence that rubber friction is a thermally activated, molecular kinetic, stick-slip process. Grosch's experiments were later confirmed by Ludema and Tabor.