Three-dimensional study of a fretting crack using synchrotron X-ray micro-tomography

High resolution synchrotron X-ray tomography has been used to obtain three-dimensional images of a crack initiated under fretting wear loading in a 2024 Al alloy. Quantitative information about the 3D crack shape is extracted from the images. It is found that the local microstructure may play a key role in the fretting crack initiation stage. In addition, the crack extension process seems to be quite independent of the microstructure encountered by the crack front, at least in the first 300 μm for the investigated experimental conditions. This depth is likely to correspond to the zone where the propagation is completely dominated by the mechanical loadings imposed by the contact conditions. Further growth beyond this length seems again more influenced by the local microstructure. This last point can account for the scatter observed in classical fretting experiments where fretting crack length is measured.