Fretting Fatigue and Contact Conditions: A Rational Explanation of Palliative Behaviour

Abstract

This paper considers what palliative effects can be achieved for fretting fatigue by modifying the contact conditions. A previous literature survey of palliatives by the authors is briefly reviewed to demonstrate the contrary nature of much of the evidence. Two simple geometries (sphere and cylinder on plane) are then considered, and the tensile stresses generated in the wake of the sliding contact derived. It is contended that fretting fatigue is the result of such tensile stresses contributing to the crack initiation process. The effect on these tensile stresses of modifying the contact conditions of the friction coefficient and clamping force is examined, so that successful palliatives can be identified. The analysis shows that conditions exist where increasing or decreasing either the friction coefficient or clamping force can be of benefit, and there is no panacea. The correct action depends on geometry, slip regime and the controlling factor for relative displacement. The analysis therefore provides an explanation of the apparent contradictions in the literature. Suggestions are made for the best approach to ameliorate a fretting fatigue problem, given this complicated situation.