Dalibor Barta

The purpose of the investigations was to assess the influence of repeated sleeve assembly on the wear of forced-in joint elements. The test methodology assumed operating a forced-in joint in rotational bending conditions, dismantling the joint after every thousand fatigue cycles, and then joint reassembling. The total number of fatigue cycles was 106, or as many as needed for fatigue cracking. The macroscopic observations of the shaft surface demonstrated the traces of fretting wear in the form of randomly spaced grey and dark brown stains at the axle seat circumference close to the joint edge. The size and number of the wear traces would increase with the number of fatigue cycles. The top layer wear also depended on the number of sleeve/shaft assembly processes. The microscopic observations confirmed fretting wear, which developed on the shaft surface. Numerous instances of surface microabrasion as well as micropullouts and surface scratches were observed. Material build-ups were also observed, which would crack and migrate. The chemical analysis of the composition of wear products demonstrated the presence of iron and oxygen atoms, which confirms the oxidation of wear products. The measurement of the maximum force needed to remove the sleeve from the shaft after the next fatigue cycle showed the need to use a greater force each time; however, a smaller force was needed to press the sleeve onto the shaft. As a result of the development of fretting wear, shafts would become fatigue-worn after 3.6 × 106 fatigue cycles.