Detachment fronts and the onset of a dynamic friction

Full Text:Though studied for hundreds of years by names as distinct as Leonardo da Vinci, Coulomb, and Hertz many aspects in the study of solid friction remain as fresh today as they were was five hundred years ago. One such aspect is the onset of slip. First described by Coulomb and Amontons as the transition from static to dynamic friction, the onset of frictional slip is central to fields as diverse as physics tribology, mechanics of earthquakes and fracture. We perform real-time measurements of the net contact area between two blocks of like material at the onset of frictional slip. We show that the process of interface detachment, which immediately precedes the inception of frictional sliding, is governed by three different types of detachment fronts. These crack-like detachment fronts differ by both their propagation velocities and by the amount of net contact surface reduction caused by their passage. Two of these which propagate at Sub-Rayleigh and intersonic velocities, have beau tile subject of intensive recent interest. The most rapid fronts, propagating at intersonic velocities, generate a negligible reduction in contact area across the interface. Sub-Rayleigh fronts are crack-like modes which propagate at velocities up to the Rayleigh wave speed, VR, and give rise to an approximate 10% reduction in net contact area. We show that a new third type of front, which propagates au order of magnitude more slowly and give rise to an approximate 20% reduction in net contact area is the dominant mechanism for interface detachment. No over all sliding occurs until either of the slower two fronts traverses the entire interface