A large number of application practices and life tests show that bearing failure is mostly due to contact surface fatigue.  

Iso25243-2004 fatigue is listed in the first of six common failure modes of bearings, is listed in the sixth fracture in the formation process also due to fatigue reasons, known as fatigue fracture.  Typical fatigue failures can be divided into sub-surface origin and surface origin.  

1.Subsurface origin fatigue  

The maximum contact stress of rolling contact occurs at a certain depth below the surface, where the fatigue source (microcrack) is formed under the repeated action of alternating stress.   

The crack source gradually expands to the surface under cyclic stress, forming open flaky cracks, which are then torn into flaky particles peeling off from the surface, resulting in pitting and pits.  If there is some weak point or defect (such as non-metallic inclusion, air gap, grain boundary of coarse carbide) in the bearing steel, it will accelerate the formation of fatigue source and the expansion of fatigue crack, and greatly reduce the fatigue life.  

2. Surface origin fatigue  

There is damage to the contact surface, which may be original, i.e. scratches and dents formed during manufacturing, or may be produced during use.  

Such as hard particles in lubricants, tiny scratches produced by the relative movement of bearing parts;  

Damage may exist poor lubrication, such as poor lubricant, lubricant failure;  

Poor lubrication aggravates the relative sliding between the rolling body and the raceway, resulting in microcracks at the root of the micro-convex body at the surface damage.  

Crack propagation results in the shedding of microconvexity or the formation of flake exfoliation zone.  This spalling depth is shallow and is sometimes confused with dark gray plaque.

3.  Fatigue fracture  

The origin of fatigue fracture is fatigue yield caused by over-tight fit assembly stress and cyclic alternating stress. Once the balance between assembly stress, alternating stress and yield limit is lost, it will fracture along the ring axis and form a through-through crack.