Abstract

We experimentally and analytically explore supershear ruptures that are excited at the onset of frictional motion within "bimaterial interfaces," frictional interfaces formed by contacting bodies having different elastic (or geometric) properties. Our experiments on PMMA blocks sliding on polycarbonate show that the structure, transition sequence, and range of existence of such supershear ruptures are highly dependent on their propagation direction relative to the slip direction in the softer of the two materials. These properties are characterized for both the positive (parallel) and negative (antiparallel) propagation directions. An analytic, fracture-mechanics based description of supershear ruptures is derived. The theory quantitatively predicts both supershear structure and the allowed propagation range of supershear ruptures. The latter compares well with both the experimentally observed supershear ruptures in the negative direction as well as localized slip pulses in the positive direction, whose propagation speed lies between the shear velocities of both materials. Supershear ruptures in the positive direction, which are composed of trains of propagating slip pulses, evade this theoretical description.