Crack Path Prediction Under Fretting Fatigue—A Theoretical and Experimental Approach

Abstract

In this paper, the direction of crack growth under fretting fatigue loading is studied through an experimental and theoretical approach. The experimental work enabled the fretting conditions to be known and the site of initiation and crack trajectory to be viewed; theoretical work permitted a prediction of those processes. Fretting wear and fretting fatigue loadings induce non-proportional mixed mode loading at the tip of the cracks initiated within the contact zone. The classical criteria predicting the direction of crack growth cannot account for the non-proportional loading. Tests were carried out to study the cracking phenomena under cumulative effects of contact and external loadings, i.e., fretting fatigue loading. The fretting contact between the two contacting bodies is modeled to evaluate the operating contact loading conditions. The response of the cracked body is determined in terms of stress intensity factors using the continuous distribution of dislocations theory coupled with a unilateral contact analysis with friction. The angle of crack extension is then predicted, at different stages of crack life, according to a new approach. The correlation of the predicted angle of crack extension with the experimental observation enables the conclusion that, under fretting fatigue loading, cracks propagate by a mode I process.