Slip-stick and the evolution of frictional strength

Abstract

The evolution of frictional strength has great fundamental and practical importance. Applications range from earthquake dynamics to hard-drive read/write cycles. Frictional strength is governed by the resistance to shear of the large ensemble of discrete contacts that forms the interface that separates two sliding bodies. An interface's overall strength is determined by both the real contact area and the contacts' shear strength. Whereas the average motion of large, slowly sliding bodies is well-described by empirical friction laws, interface strength is a dynamic entity that is inherently related to both fast processes such as detachment/re-attachment and the slow process of contact area rejuvenation. Here we show how frictional strength evolves from extremely short to long timescales, by continuous measurements of the concurrent local evolution of the real contact area and the corresponding interface motion (slip) from the first microseconds when contact detachment occurs to large (100-second) timescales. We identify four distinct and inter-related phases of evolution. First, all of the local contact area reduction occurs within a few microseconds, on the passage of a crack-like front. This is followed by the onset of rapid slip over a characteristic time, the value of which suggests a fracture-induced reduction of contact strength before any slip occurs. This rapid slip phase culminates with a sharp transition to slip at velocities an order of magnitude slower. At slip arrest, 'ageing' immediately commences as contact area increases on a characteristic timescale determined by the system's local memory of its effective contact time before slip arrest. We show how the singular logarithmic behaviour generally associated with ageing is cut off at short times. These results provide a comprehensive picture of how frictional strength evolves from the short times and rapid slip velocities at the onset of motion to ageing at the long times following slip arrest.

Strength and permeability recovery of tuffisite-bearing andesite

“…Regardless of which process is dominant, we find that tuffisites can recover their original rock properties. The proposed recovery mechanisms can act on relatively short timescales (Ben-David et al, 2010;Olgaard and Fitz Gerald, 1993;Russell and Quane, 2005;Venkatachari and Raj, 1986) and we therefore speculate that tuffisites spend most of the time in the edifice in this recovered state.…”

Electrostatic precursors to granular slip events

“…Several research groups have studied granular stick-slip (32,35,36), however an electrical precursor to slip does not appear to have been reported before. The mechanism underlying these precursors remains to be definitively determined: The materials studied are not piezoelectric, the effects persist in the presence of active static elimination as well as at relative humidities up to 70%, and stresses are several orders of magnitude too small to produce chemical changes reported elsewhere (37)(38)(39) to lead to measurable voltages.…”

On relaxations and aging of various glasses

“…However, the relaxation of many systems in nature is far from exponential, as was noticed already in the 19th century by Weber (1). In many cases, the relaxation is logarithmic: Such relaxations have been experimentally observed in the decay of current in superconductors (2), current relaxation in metal-oxidesemiconductor field-effect transistor devices (3), mechanical relaxation of plant roots (4), volume relaxation of crumpling paper (5), and frictional strength (6), to name but a few. Fig.…”