Investigating the influence of mm-scale contact processes on dynamic weakening in high-speed rock friction experiments

Monica R. Barbery, Frederick M. Chester, & Judith S. Chester

Submitted August 16, 2021, SCEC Contribution #11614, 2021 SCEC Annual Meeting Poster #171

Dynamic weakening due to flash heating arises from asperity-scale processes during seismic slip, however processes at the mm-scale and larger may contribute to the total weakening and help resolve transient and hysteretic friction observed in laboratory experiments. In previous SCEC work, we documented inhomogeneous mm-scale contact temperatures in experiments using a high speed-biaxial apparatus equipped with a high-speed infrared (IR) camera. Through thermal modelling, we characterized the distribution of local normal stress (sl) at the mm-scale and its evolution with slip. Here, we advance this work by conducting additional high-speed experiments with IR imaging on Westley granite, combined with surface profilometry to characterize roughness and photographic imaging to determine the surface mineralogy before and after high-speed sliding. We performed velocity-step (VS) experiments from quasi-static rates (1 mm/s) to target rates (300-900 mm/s) with up to 37 mm of displacement at a normal stress (sn) of 9 MPa, using both constant- and decreasing-velocity paths after the VS. To document the influence of mm-scale contact life-times (LT) and rest-times (RT) on friction, two sliding surface geometries with constant LT but different RT (RT=LT, RT=LT/2) were used. Both shorter contact rest-times and higher sliding velocity lead to greater frictional weakening. Observed macroscopic surface temperature (Ts) distributions are similar to previous results in that Ts is inhomogeneous but increases with slip and V, and decreases with RT. We document that the initial morphology of the ground sliding surfaces correlates with the distribution of the dominant phases of the granite (feldspar, quartz, biotite). The surface morphology also correlates with the IR-imaged distribution of local Ts during high-speed-slip. These data suggest that the distributions of local Ts and sl at the mm-scale reflect the initial distribution of mineral phases at the sliding surface. Currently we are documenting roughness, wear, and mineralogy of the surfaces following high-speed sliding to understand the processes responsible for the evolution of Ts and sl distributions during sliding.

Key Words
dynamic weakening, surface temperature, surface roughness

Citation
Barbery, M. R., Chester, F. M., & Chester, J. S. (2021, 08). Investigating the influence of mm-scale contact processes on dynamic weakening in high-speed rock friction experiments. Poster Presentation at 2021 SCEC Annual Meeting.


Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)