A fretting crack initiation prediction taking into account the surface roughness and the crack nucleation process volume

TL;DR

This study investigates how surface roughness influences fretting crack initiation in aluminium alloys, introducing an effective contact area concept and analytical predictions using the SWT parameter, relevant for aerospace applications.

Contribution

It introduces a new approach to predict fretting crack initiation considering surface roughness and effective contact area, enhancing understanding of crack nucleation in aerospace materials.

Findings

Surface roughness significantly affects crack nucleation thresholds.

Effective contact area allows for roughness-independent boundary prediction.

Analytical models using SWT parameter successfully predict crack initiation.

Abstract

This paper presents an experimental study of the fretting crack nucleation threshold, expressed in terms of loading conditions, with a cylinder/plane contact. The studied material is a damage tolerant aluminium alloy widely used in the aerospace application. Since in industrial problems, the surface quality is often variable, the impact of a unidirectional roughness is investigated via varying the roughness of the counter body in the fretting experiments. As expected, experimental results show a large effect of the contact roughness on the crack nucleation conditions. Rationalisation of the crack nucleation boundary independently of the studied roughnesses was successfully obtained by introducing the concept of effective contact area. This does show that the fretting crack nucleation of the studied material can be efficiently described by the local effective loadings inside the contact. Analytical prediction of the crack nucleation is presented with the Smith-Watson-Topper (SWT) parameter and size effect is also studied and discussed.