Effect of plastic deformation on the evolution of wear and local stress fields in fretting

During fretting, the removal of material by wear leads to an increase of contact stress in the stick zone. If elastic behavior is assumed, the boundary between stick and slip zones does not move, wear eventually ceases, and a mode-I singularity of contact pressure is predicted after infinitely many cycles. For real materials, the development of singular stresses must be limited by plastic deformation. Here we investigate the effect of plasticity on fretting wear, using a finite-element model. We find that the principal effect of plasticity is to allow the wear scar to extend continuously into the contact region. Thus, wear continues indefinitely, and extensive damage or catastrophic failure is to be anticipated, given a sufficient number of fretting cycles. In the elastic regime, the results can be cast in dimensionless terms, permitting application to any material or loading condition. Plasticity introduces an additional dimensionless parameter into the analysis, but results of considerable generality can still be obtained. In particular, the contact pressure distribution exhibits a stable maximum related to the yield strength of the material, and the maximum accumulated plastic strain increases approximately linearly with the number of loading cycles and occurs close to the instantaneous slip-stick boundary. (C) 2016 Elsevier Ltd. All rights reserved.