Supershear Frictional Ruptures Along Bimaterial Interfaces

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.

Unstable cracks trigger asymptotic rupture modes in bimaterial friction

“…The present approach significantly extends the results of our analysis in the transonic and supersonic regimes [15,16] to the subsonic regime where all ruptures initiate. This work will allow for a more complete picture of the onset of frictional sliding between dissimilar materials and reveals a qualitatively new class of instabilities.…”

“…These studies revealed that interfacial crack tip speeds in bimaterials can exceed not only the c R of the softer material but also its shear wave speed. Such 'supershear' modes were also later observed [10,16,46] in frictional bimaterial experiments. While certainly related to bimaterial frictional ruptures, it is still unclear how the two systems map to one another.…”

“…• In the negative direction, subsonic ruptures can be observed. They are, however, less prevalent supershear ruptures which are the preferred propagation mode [10,16] with speeds concentrated in a narrow band that has been explained theoretically [16].…”

“…1. Recently, this configuration has been used to determine the asymptotic behavior of the stress field near the rupture front in subsonic, transonic and supershear propagation regimes [15,16]. These studies enabled successful theoretical characterization of various features observed in experiments.…”

“…Starting from the work of Da Vinci [1], Amontons and Coulomb [2] and later work by Dieterich [3] and Ruina [4], this view suggests that a characteristic "friction coefficient" is sufficient to describe the onset of frictional motion. Recent experiments have, however, highlighted the importance of considering the spatial degrees of freedom within the frictional interface that separates two contacting bodies [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20]. This work has demonstrated that the onset of frictional sliding is mediated by rupture fronts that propagate along the interface, while detaching the contacts that form it.…”