Spatiotemporal dynamics of frictional systems: The interplay of interfacial friction and bulk elasticity

The Effects of Humidity on the Velocity-Dependence and Frictional Ageing of Nanoscale Silica Contacts

“…A basic prediction of this law is that during steady-state sliding, 𝜇 varies linearly with the logarithm of velocity with a slope of 𝑎 − 𝑏. Additionally, the frictional response is invariably mediated via the elastic coupling between the far-field application of a lateral stress and the sliding interface (e.g., torsion of the atomic force microscope (AFM) cantilever in this study) which can give rise to complex overall behaviors such as stick-slip motion [3][4][5]; note that this type of stickslip is not due to the position-dependent potential energy corrugation that leads to atomic lattice stick-slip motion [6], but rather, is due to an increase in static friction with time in stationary contact (static ageing) [4], and/or a decrease in kinetic friction with slip speed (evolution effect). [3] A hallmark of RSF is the history dependence of friction, which is described analytically with a state variable. The evolution of state with time is typically described by either of two equations, the slowness law and the slip law.…”

“…This effect has been observed in other studies [68,69] but is inconsistent with the most common forms of the RSF laws. [3,70,71] Such a transition velocity could have important effects in earthquake mechanics, such as promoting stable slip and limiting the magnitude of slip events. [3,68,72,73] As the humidity level rises, this transition velocity shifts to higher and higher values, as highlighted by the black dashed arrow.…”

“…[3,70,71] Such a transition velocity could have important effects in earthquake mechanics, such as promoting stable slip and limiting the magnitude of slip events. [3,68,72,73] As the humidity level rises, this transition velocity shifts to higher and higher values, as highlighted by the black dashed arrow. The velocity-dependence testing protocol (see SI for more details) involved traversing the entire velocity range during each sliding cycle, with eight cycles performed sequentially in a reciprocating fashion on the same, initially unworn wear track.…”

“…To date, however, such simulations have not been able to reproduce velocity-weakening friction, which is commonly observed in rock friction experiments and considered to be a necessary condition for earthquake nucleation. [3,5] The evolution of state may also be due to increases in the frictional strength (i.e., in the shear strength) of the contacts, instead of increases in contact area as described above. In particular, silica-silica interfaces are known to form bonds, including covalent siloxane (Si-O-Si) bonds [18,19].…”