Effects of slip on fretting behavior: experiments and analyses

The role of relative slip on fretting behavior was investigated by conducting experiments and analyses. The first series of tests was conducted at different substrate applied stress amplitudes, and the second series at different applied fretting pad displacements with a constant substrate stress amplitude. A fretting map was developed using fretting fatigue life, relative slip range and normal force. This map provides useful information about the inter-relationships between these parameters and contact conditions (partial and gross slip) as well as about damages induced by these conditions. Partial and gross slip conditions were modeled using finite element analysis (FEA). FEA showed that gross slip simply shifted the stress distribution and the location of the trailing edge without any appreciable change in magnitude. Modified shear stress range (MSSR) parameter, a critical plane-based multi-axial fatigue model, was used to characterize fretting fatigue crack initiation behavior. With increasing applied relative slip, the MSSR parameter initially increased and the fatigue life decreased; thereafter the MSSR remained constant but the fatigue life increased. This increase in the fatigue life appears to be due to an increased wear rate. There was thus a competition between crack initiation and material removal during fretting as the contact condition changed from partial slip to gross slip.