Micromechanics of material detachment during adhesive wear: A numerical assessment of Archard's wear model

Adhesive wear is a direct result of material removal from surface asperities in contact due to adhesive forces. While macroscopic experiments confirmed the existence of a linear wear relation, referred to as Archard's wear relation (i.e. wear volume varies linearly with the normal load and sliding distance), recent small-scale wear experiments and simulations have questioned the validity of Archard's wear relation at the asperity level. We perform systematic long-timescale asperity-level wear simulations using two recently developed coarse-grained model potentials with extremely brittle and ductile behavior. A linear wear relation can be recovered from our simulations only when the material removal progresses by plastic deformation at the asperity tip, confirming the long-standing theoretical hypothesis made by Archard. However, this linearity breaks down when cleavage cracking dominates the material removal. As a result, we hypothesize that the breakdown of Archard's wear relation observed in previous numerical simulations and AFM experiments can be associated with the activation of other removal mechanisms than plastic deformation (e.g. asperity cracking or atomic attrition) and/or an inaccurate measurement of the normal load carried by the junction and the effective sliding distance (i.e. contact time). Supporting basic theoretical assumptions made by Archard, future studies should focus on up-scaling the mechanics of single-asperity to a multi-asperity contact to calculate the wear coefficient as the probability of material removal from asperity encounters.