How rubber grips and slips Schallamach waves and the friction of elastomers

Abstract

Abstract In certain circumstances when an elastomer is slid over another surface no true sliding occurs at the interface. Instead, waves of detachment traverse the interface and it is only in those regions where contact is temporarily lost that relative displacement occurs. These waves are called Schallamach waves, they resemble macro-dislocations, and energy seems to be dissipated by peeling the contact apart as the wave propagates. There are three important aspects of this phenomenon: (i) how the waves form; (ii) the interfacial stress required to propagate them; (iii) their regime of existence. An equation is derived which expresses the frictional stress in terms of the mechanical properties of an elastomer and a constant which can be deduced tentatively from the mode of the formation of the waves. The interfacial stress is predicted to be proportional to the shear modulus, and this is in good agreement with published experimental values. The same expression also allows prediction, with more limited confirmation, of the circumstances required for wave formation and propagation.