The static friction peak in reciprocating sliding

This paper investigates why the static friction peak is mostly absent in reciprocating sliding and gross-slip fretting literature. Here, reciprocating sliding tests were conducted on ultra-smooth silicon surfaces. A prominent static friction peak was present in the initial cycles. However, a rapid wear-induced decay in the static friction peak occurred after the first cycle with the peak being mostly absent by about 30 cycles. Two possible explanations are proposed for the wear-induced decay: (1) that increasing surface roughness (with cycles) reduces the fully stuck contact area and (2) that wear reduces the bonding strength of the stuck interface by removing third body contaminant molecules. Predictions from a multi-asperity friction model are used to support these arguments.