Case Study 2: Bearing Race
Examination of Figure 2 will show a similar damage scenario. However, there are more cracks visible where the flakes have not yet broken away. There appear to be more layers of smeared material. It is likely that the bearing race is much harder than the plate from case study 1.
A common wear “mechanism” in bearings involves subsurface cracks working their way out to the surface. Clearly this is not the whole story here. There must be some sliding friction that is smearing the material. The arrows show dark and light areas that are image artifacts due to grease remaining on the surface. The grease is not conductive and renders the specimen less photogenic. The electron buildup at the nonconductive areas interfere with clear details nearby as well.
Case Study 3: Fretting Damage and Associated Fatigue
Figures 3A-C are increasing-magnification views of details of a tapered cylindrical part that had a poorly matching tapered cylindrical part fitted over it. Instead of having a uniform contact surface, there were some areas that were not touching at all. Furthermore, an out-of-round condition on the mating part meant that it rocked back and forth relative to the stable position of the component shown. The parts shown were cracking in durability testing.
Note the magnification settings shown. The surface clearly has some rough areas between smoother areas, as depicted in Figure 3A. Figure 3B now renders visible some small particles. Again, we have evidence of charging interfering with the image quality. Cleaning the part would have also removed the particles that were clinging to the component and providing data about the wear scenario. Note that the cracks are only visible when the magnification is over 2,000x. These were not the cracks that caused the component fragmentation. They were nearby. These “secondary cracks” allow us to see the sequence of damage that leads to the eventual fragmentation of the component.