Frictional weakening of slip interfaces

Science, 2010

The way in which a frictional interface fails is critical to our fundamental understanding of failure processes in fields ranging from engineering to the study of earthquakes. Frictional motion is initiated by rupture fronts that propagate within the thin interface that separates two sheared bodies. By measuring the shear and normal stresses along the interface, together with the subsequent rapid real-contact-area dynamics, we find that the ratio of shear stress to normal stress can locally far exceed the static-friction coefficient without precipitating slip. Moreover, different modes of rupture selected by the system correspond to distinct regimes of the local stress ratio. These results indicate the key role of nonuniformity to frictional stability and dynamics with implications for the prediction, selection, and arrest of different modes of earthquakes.

International Journal of Fracture, 2006

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 cracklike detachment fronts differ by both their propagation velocities and by the amount of net contact surface reduction caused by their passage. The most rapid fronts propagate at intersonic velocities but 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, V , and give rise to an approximate 10% reduction in net contact area. The most efficient contact area reduction (~20%) is precipitated by the passage of "slow detachment fronts". These fronts propagate at "anomalously" slow velocities, which are over an order of magnitude lower than V yet orders of magnitude higher than other characteristic velocity scales such as either slip or loading velocities. Slow fronts are generated, in conjunction with intersonic fronts, by the sudden arrest of sub-Rayleigh fronts. No overall sliding of the interface occurs until either of the slower two fronts traverses the entire interface, and motion at the leading edge of the interface is initiated. Slip at the trailing edge of the interface accompanies the motion of both the slow and sub-Rayleigh fronts. We might expect these modes to be important in both fault nucleation and earthquake dynamics. R R

Understanding the dynamics of frictional sliding is important for various fields,ranging from engineering to geophysics. We focus on the local dynamics of slip events that arrest before traversing an entire frictional interface. Our experiments measure slip and contact area evolution, at timescales spanning µsec to hundreds of seconds. We recognize three distinct phases of local slip dynamics. The first phase consists of a rapid drop in the contact area, accompanied by the onset of local slip at velocities of ~10-25cm/sec that occurs immediately upon passage of a rapid detachment front. The second phase consists of steady-sliding at constant lower velocities (0.3-1cm/sec). The final phase comprises logarithmic aging of the contact area, which starts immediately upon slip arrest, within 400µsec of the front arrival.

2021

The transition from static to dynamic friction is often described as a fracture-like instantaneous slip. However, studies on slow sliding processes aimed at understanding frictional instabilities and earthquakes report slow friction transients that are usually explained by empirical rate-and-state formulations. We perform very slow (∼ nm/s) macroscopic-scale sliding experiments and show that the onset of frictional slip is governed by continuous non-monotonic dynamics originating from a competition between contact aging and shear-induced rejuvenation. This allows to describe both our non-monotonic dynamics and the simpler rate-and-state transients with a single evolution equation.

Frontiers in Earth Science, 2020

Earthquakes have long been recognized as resulting from a stick–slip frictional instability. The development of a full constitutive law for rock friction now shows that the gamut of earthquake phenomena—seismogenesis and seismic coupling, pre-and post-seismic phenomena, and the insensitivity of earthquakes to stress transients—all appear as manifestations of the richness of this friction law.

Geophysical Research Letters, 2011

Since their discovery nearly a decade ago, the origin of seismic tremor remains unclear. Recent studies indicate that various driving phenomena such as Earth and ocean tides, regional and teleseismic earthquakes enhance tremor activity. Observations of the coincidence with slow-slip events and of fast migrations of tremors have led frictional slip to be considered as the possible source of tremors. Indeed, laboratory friction experiments succeeded in generating and recording tremor like signals (TLS). Here we show a systematic correlation between the onset of slip acceleration and the emission of TLS in a laboratory friction experiment. TLS are generated when the shear stress reaches the peak static resistance and the dilatancy meets its maximum that is when the mature interface is close to failure. This robust result provides a comprehensive image of how natural seismic tremors might be generated and/or triggered by passing seismic waves, tides or even slow slip events.

2009

The frictional behavior of a single crystal salt slider is investigated under constant conditions of normal load, driving velocity, and temperature. We observe a progressive change from stick-slip to stable sliding with accumulative displacement. During the experiment, all frictional parameters are evolving: a and b are decreasing while dc is increasing. These changes are contemporary to the morphological evolution of the contact interface, i.e. the development of a striated pattern driven by the coupling of pressure solution creep and slip. The increase in dc and the decrease in (b-a) both lead to the progressive vanishing of Kc, the critical stiffness for stick-slip. The salt slider is therefore forced to a mode of stable sliding, with no more rate and state dependence. Contemporary to the evolution of slip patterns, the recorded Acoustic Emission evolves with cumulative displacement and interface ageing, following a trend from strong impulsive events similar to earthquake seismic signals, to a collection of smaller amplitude and longer duration signals similar to Non Volcanic Tremor. Allowing deformation of the contact interface to interfere with friction reveals a continuum of slip patterns. Earthquakes, slow events, silent quakes and continuous sliding appear as different aspects of a holistic process. The ageing of the contact interface with cumulated displacement provides a global framework to capture the occurrence of the different slip patterns and seismic signals along subduction zones. Considering the cumulative displacement as a sine qua non condition for the occurrence of SSE and NVT reproduces the absence of these latter above the locked zone. The experimental results are consistent with and rationalize a posteriori: (i) the modeling of aseismic slip transients by a decrease in b-a [Liu and Rice, 2005] and an increase in dc [Shibazaki and Iio, 2003]; (ii) the hypothesis that silent slip and NVT pertain to one and unique phenomenon of friction; (iii) the hypothesis that NVT are local reminiscence of frictional instabilities in these aseismic slip transients [Shelly et al., 2007].

Tribology Letters, 2010

We present an experimental study of the onset of local frictional motion along a long, spatially extended interface that separates two PMMA blocks in dry frictional contact. At applied shear forces significantly below the static friction threshold, rapid precursory detachment fronts are excited, which propagate at near sound speeds along the interface. These fronts initiate from the interface edge and arrest prior to traversing the entire sample length. Along the fronts’ path, we perform real-time measurements of the real contact area at every spatial point within the interface. In addition, the motion (slip) of the material adjacent to the interface is simultaneously measured at chosen locations. Upon their arrival at each spatial point along their path, these fronts instantaneously (within 4 μs) reduce the net contact area. Net slip is only initiated after this contact area reduction occurs. Slip is initially rapid and progresses at its initial velocity for a constant (60 μs) duration. Slip dynamics then undergo a sharp transition to velocities an order of magnitude slower, which remain nearly constant until slip arrest. We demonstrate that this scenario can be quantitatively explained by a model of interface weakening caused by instantaneous fracture-induced heating. Sustained rapid slip occurs in this weakened phase. Once the interface cools beneath its glass temperature the sharp transition to slow slip takes place. A similar fracture-induced weakening scenario might be expected in additional classes of materials.

Lubricants, 2015

Description of the transitional process from a static to a dynamic frictional regime is a fundamental problem of modern physics. Previously we developed a model based on the well-known Frenkel-Kontorova model to describe dry macroscopic friction. Here this model has been modified to include the effect of dissipation in derived relations between the kinematic and dynamic parameters of a transition process. The main (somewhat counterintuitive) result is a demonstration that the rupture (i.e. detachment front) velocity of the slip pulse which arises during the transition does not depend on friction. The only parameter (besides the elastic and plastic properties of the medium) controlling the rupture velocity is the spatial distribution of the shear to normal stress ratio. In contrast to the rupture velocity, the slip velocity does depend on friction. The model we have developed describes these processes over a wide range of rupture and slip velocities (up to 7 orders of magnitude) allowing, in particular, the consideration of seismic events ranging from regular earthquakes, with rupture velocities on the order of a few km/s, to slow slip events, with rupture velocities of a few km/day.