Chemical aging of large-scale randomly rough frictional contacts

TL;DR

This study combines a kinetic Monte Carlo model with contact mechanics to analyze how chemical aging influences friction in rough silica contacts, revealing a logarithmic time dependence and load-dependent behavior.

Contribution

It introduces a multi-scale model that links chemical aging effects from single asperities to macroscopic rough contacts, accounting for surface roughness and contact mechanics.

Findings

Chemical aging shows a logarithmic dependence on time.

Friction aging transitions from linear to nonlinear with increasing load.

Surface roughness influences aging mainly through contact area and pressure.

Abstract

It has been shown that contact aging due to chemical reactions in single asperity contacts can have a significant effect on friction. However, it is currently unknown how chemically-induced contact aging of friction depends on roughness that is typically encountered in macroscopic rough contacts. Here, we develop an approach that brings together a kinetic Monte Carlo model of chemical aging with a contact mechanics model of rough surfaces based on the boundary element method to determine the magnitude of chemical aging in silica/silica contacts with random roughness. Our multi-scale model predicts that chemical aging for randomly rough contacts has a logarithmic dependence on time. It also shows that friction aging switches from a linear to a non-linear dependence on the applied load as the load increase. We discover that surface roughness affects the aging behavior primarily by modifying the real contact area and the local contact pressure, whereas the effect of contact morphology is relatively small. Our results demonstrate how understanding of chemical aging can be translated from studies of single asperity contacts to macroscopic rough contacts.