Contact aging, i.e., the strengthening of a tribological contact with time, is a phenomenon that is commonly attributed to an increase of the effective contact area between multiasperity surfaces based on contact mechanical processes. Only recently, atomic force microscopy experiments and simulations on single silica nanojunctions have also demonstrated logarithmic aging with contact time for single-Asperity contacts and the effects were attributed to a gradual formation of chemical bonds in the contact, thereby suggesting an atomistic mechanism of "contact aging."Generally, this atomic bond-formation process is considered as a shear-Assisted thermally activated process, where both temperature and loading conditions are expected to influence the aging behavior. A direct link between aging and temperature has recently been substantiated by temperature-dependent aging experiments and complementary molecular dynamics simulations, but the potential influence of shear stress on single-Asperity aging still remains largely elusive. To analyze the role of shear stress, we now apply a simple and semianalytical model for thermally activated bond formation, which explicitly considers the reduction of energy barriers by a shear-stress-related Eyring term. Based on this model, characteristic fingerprints of mechanical shear can be identified in our temperature-dependent contact aging experiments, including, for instance, the counterintuitive decrease of aging effects with increasing temperature. Our results thereby hint at a path to introduce this form of qualitative contact aging to the phenomenological rate and state friction, where the local aging effects might be closely linked to the shear-stress distribution within multiasperity contacts.
|Number of pages||10|
|Journal||Physical Review B|
|Publication status||Published - 2 May 2022|