Fig.13 Dimple patterns in the IFZ.
CONCLUSIONS
Based on the morphology observation and multiaxial fretting fatigue test on 35CrMoA steel, the following conclusions can be drawn:
  1. Under different loading paths, the strain response behavior of 35CrMoA steel is significantly different. However, contact stress has the same effect on the cyclic softening rate under different loading paths. The greater the contact stress, the greater the cyclic softening rate. Moreover, the axial strain and the rate of change in axial strain dominates in the whole strain. Therefore, the main damage form under the two paths is axial style.
  2. Under SP and DP, the fretting fatigue life of 35CrMoA steel shows a downward trend with increasing contact stress. In this process, large plastic deformation and abrasive wear wiping microcracks play a dominant role.
  3. With a contact stress of 150 MPa under DP, the damage in the fretting area is the most serious, a large amount of material tear appeared in the stick zone, and the crack in the slip area only initiates at the edge of the pit; Wear debris basically consists of sample material and its oxide, but the oxidation portions of the sample material in the slip zone are much higher than those in the stick zone.
  4. With the increase of contact stress, the area of CSZ and IFZ in the fretting fatigue fracture gradually decreased; At low contact stress, only one CSZ dominates in the two corresponding fretting regions; At high contact stress, cracks generated in both fretting regions are dominant, and the IFZ is symmetrical nearly circular shape.
  5. Within a certain number of cycles (including the crack initiation and propagation stage), the crack first propagates in its initiating cross section, where the crack propagation is mainly affected by contact stress; As the crack grows, when reached to a certain depth, a longitudinal component will be generated during the crack growth. At this situation, the cyclic stress has a significant effect on crack growth. As the crack depth becomes deeper, the longitudinal component becomes larger.