Micromechanical Origins of Adhesive Wear Mechanisms: From Asperity Smoothing to Debris Creation

The adhesive wear process consists of several physical phenomena including plasticity and fracture which occur at different length and time scales. Despite the critical importance of the adhesive wear process in all engineering applications, it is still described via classical, yet fully empirical, models [1,2] since the microscopic principles have not been yet understood. Using novel coarse-grained atomistic simulations , we for the first time capture the debris formation during the adhesive collision between surface asperities [3]. A systematic set of atomistic simulations reveals a characteristic length scale that controls the adhesive wear mechanisms (i.e. asperity smoothing versus debris formation) at the asperity level. This length scale provides a critical adhesive junction size where bigger junctions produce wear debris by fracture while smaller ones smooth out plastically. This finding explains why wear debris has not been observed in previous atomistic simulations of adhesive wear, where the junction is too small and/or weak to form debris by fracture. Based on this observation, we formulate a simple analytical model that predicts the transition in the asperity-level adhesive wear mechanisms in both the simulation results and atomic force microscope (AFM) wear experiments. We show that the proposed framework opens up a new research path to implicitly model and explore the wear process and revisit classical models. References: [1] J. F. Archard (1953) Journal of Applied Physics [2] E. Rabinowicz (1961) Journal of Applied Physics [3] R. Aghababaei, D.H. Warner and J.F. Molinari (2016) Nature Communications