Multiphysics model of chemical aging in frictional contacts

Abstract: An increase of static friction during stationary contacts of two solids due to interfacial chemical bonding has been reported in multiple experiments. However, the physics underlying such frictional aging is still not fully understood because it involves multiple physical and chemical effects coupled with each other, making direct interpretation of experimental results difficult. Here, we develop a multiphysics chemical aging model that combines contact mechanics, mechanochemistry, and interfacial chemical reaction kinetics. Our model predicts that aging is proportional to normal loads in a low-load regime and becomes nonlinear at higher loads. We also discovered a nonmonotonic temperature dependence of aging with a peak near room temperature. In addition, our simulations provide insights into contributions from specific physical/chemical effects on the overall aging. Our model shows quantitative agreement with available single-asperity experiments on silica-silica interfaces, and it provides a framework for building a chemical aging model for other material systems with arbitrary types of physical and chemical effects involved.