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:
- 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.
- 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.
- 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.
- 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.
- 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.