Long Term Friction: from Stick-Slip to Stable Sliding

TL;DR

This study investigates how frictional behavior transitions from stick-slip to stable sliding in a salt slider, revealing changes in contact morphology and friction parameters over many deformation cycles, with implications for natural fault mechanics.

Contribution

It introduces a novel laboratory experiment using salt to observe the evolution of frictional regimes and parameters over extensive deformation cycles.

Findings

Stick-slip behavior diminishes and transitions to stable sliding.

Contact asperities grow and develop a striated morphology.

Friction parameters a and b decrease and vanish with cumulative slip.

Abstract

We have devised an original laboratory experiment where we investigate the frictional behaviour of a single crystal salt slider over a large number of deformation cycles. Because of its physical properties, salt, a surrogate for natural faults, allows for friction and plastic deformation and pressure solution creep to be efficient on the same timescale. During the same experiment, we observe a continuous change of the frictional behaviour of the slider under constant conditions of stiffness, temperature and loading velocity. The stick-slip regime is progressively vanishing, eventually reaching the stable sliding regime. Concomitantly, the contact interface, observed under the microscope, develops a striated morphology with contact asperities increase in length and width, arguing for an increase in the critical slip distance dc. Complementary experiments including velocity jumps show that the frictional parameters of the rate and state friction law, a and b, progressively vanish with the cumulative slip. In our experimental conditions, the ultimate stage of friction is therefore rate and state independent.