Measuring Wear in a Fretting Test with a Confocal Microscope

Wear has been analyzed in several fretting fatigue tests with spherical contact performed on Al 7075 T651. The contact zone leaves a circular scar on the surface, which is easily detected because of the damage. Inside the contact zone, and almost concentric, another circular region called the stick zone can be distinguished. The annulus around it is called the sliding zone. The latter appears clearly damaged by wear and oxidation. The objective of this paper is to measure the size of these zones and their position, measure the wear in the sliding zone and establish a relation with the stresses at the contact. This has been done using a confocal microscope which gives a map of the surface: depth at each position. Given that the scar does not appear as an ideal circumference, the images have gone through a process of digital processing in order to obtain the geometric characteristics. Finally, the experimental data is combined with the analytical calculations through Archard wear model where a material parameter is calculated at each point in the sliding zone. It can be observed that despite the very different pressures and sliding distances in this zone, the material wear parameter is almost constant and similar to the ones in standard tests.