Modeling contact size effect on fretting wear: a combined contact oxygenation - third body approach

This study investigates the effect of the contact size and the gross-slip sliding amplitude on the fretting wear rate of a steel flat-on-flat interface. Results confirm an asymptotic decrease of the wear rate with the contact size. This evolution is induced by an easier oxygen access to the interface favoring abrasive wear according to the Contact Oxygenation Concept (COC) and by a faster ejection of the protective debris particles from the interface according to the Third Body Theory (TBT). To decouple these COC and TBT contributions, the effect of the sliding amplitude and the contact orientation with respect to the sliding direction is assessed using an original macro-texturation test strategy. Wear rate evolutions as well as SEM-EDX fretting scar analyses suggested that COC is mainly driven by the minimum distance between the contact center and the open air contact edges (L-COC), whereas TBT wear process is chiefly controlled by the ratio of the collinear contact length to the sliding amplitude (L-TBT/delta(g)). Assuming a weighted influence of the contact oxygenation process on the TBT wear process, a simple power-law formulation is introduced to quantify the contact size effect on the energy wear rate fluctuation. A very good correlation with the experiments confirms the stability of the proposal.