Understanding how slip at a frictional interface initiates is important for e.g. earthquake prediction and precision engineering. The force needed to start sliding a solid object over a flat surface is classically described by a “static friction coefficient”: a constant established by measurements. It was recently questioned if such constant exists, as it was shown to be poorly reproducible. Over the recent years I have proposed a novel theory for the onset of slip (formerly known as the “static friction coefficient”) that is based on:
An armouring mechanism that results in few “soft spots” after slip .
A competition between disorder and elasticity that results in spatial correlations in stress .
A phase-transition-like behaviour that results in a critical stress for slip (the “dynamic friction coefficient”) .