A large number of application practices and life tests have shown that bearing failure is mostly caused by contact surface fatigue. GB/T 24611—2020/ISO15243:2017 lists fatigue as the first of the six common failure modes of bearings. The fracture listed sixth is also called fatigue fracture due to fatigue during the formation process. Typical fatigue failures are divided into subsurface origin types and surface origin types.

1. Subsurface origin fatigue

The maximum contact stress in rolling contact occurs somewhere under the surface at a certain depth. Under the repeated action of alternating stress, fatigue sources (microcracks) are formed there.The crack source gradually expands to the surface under cyclic stress, forming open flaky cracks, which are then torn into flaky particles that peel off from the surface, causing pitting and pits. If there are some weak points or defects in the bearing steel (common ones such as non-metallic inclusions, air gaps, and grain interfaces of coarse carbides), the formation of fatigue sources and the expansion of fatigue cracks will be accelerated, greatly reducing the fatigue life.

2. Surface origin fatigue

There is damage on the contact surface. These damages may be original, that is, scratches and bump marks formed during the manufacturing process, or they may be caused by use, such as hard particles in the lubricant and tiny scratches caused by the relative movement of bearing parts. There may be poor lubrication in the damaged area, such as lack of lubricant and lubricant failure; poor lubrication conditions aggravate the relative sliding between the rolling elements and the raceway, resulting in microscopic cracks at the roots of the asperities at the surface damage area. Crack propagation causes micro-protrusions to fall off or form flaky peeling areas.

3. Fatigue fracture

The origin of fatigue fracture is fatigue yielding caused by assembly stress and cyclic alternating stress caused by excessive tight fit. Once the balance between assembly stress, alternating stress and yield limit is lost, fracture will occur along the axis of the ferrule, forming a through-hole cracks.

In practice, the damage of bearings that fail under normal use is mostly as mentioned above, that is, contact surface fatigue. Among the three types of fatigue failure, subsurface origin fatigue is the most common. The bearing life calculation method recommended by ASO281 and ISO281/amd.2 is Based on fatigue of subsurface origin.