Contact fatigue failure refers to the failure of the bearing working surface under the action of alternating stress. Contact fatigue spalling occurs on the working surface of the bearing, and is often accompanied by fatigue cracks. It first occurs from the maximum alternating shear stress below the contact surface, and then expands to the surface to form different spalling shapes, such as pitting or pitting spalling. The peeling off into small flakes is called shallow peeling. Due to the gradual expansion of the peeling surface, it often expands to the deep layer, forming deep peeling. Deep spalling is a fatigue source for contact fatigue failure.

Wear failure refers to the failure caused by the relative sliding friction between the surfaces that leads to the continuous wear of the metal on the working surface. Continued wear will cause gradual damage to the bearing parts and eventually lead to loss of bearing dimensional accuracy and other related problems. Wear may affect shape changes and increase the fit clearance