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Fatigue failure forms and anti fatigue methods of rolling bearings

Release time:

2022-12-06

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

1、 Subsurface origin fatigue

Rolling contact stress occurs at a certain depth below the surface, where fatigue sources (microcracks) are formed under the repeated action of alternating stress. The crack source gradually expands towards the surface under cyclic stress, forming open sheet like cracks, which are then torn apart into sheet like particles peeling off the surface, resulting in pits and pits. If there are some weak points or defects in the bearing steel at this location (such as non-metallic inclusions, air gaps, and crystal interfaces of coarse carbides), it will accelerate the formation of fatigue sources and the propagation of fatigue cracks, greatly reducing fatigue life.

2、 Surface induced fatigue

There are damages at the contact surface, which may be original, such as scratches and scratches formed during the manufacturing process, or may be generated during use, such as hard particles in lubricants or minor scratches caused by relative motion of bearing parts; There may be poor lubrication at the damaged area, such as insufficient lubricant or lubricant failure; The poor lubrication condition exacerbates the relative sliding between the rolling element and the raceway, resulting in microcracks at the root of the micro convex body at the surface damage location; Crack propagation leads to the detachment of micro convex bodies or the formation of flaky peeling areas. This type of peeling has a shallow depth and is sometimes confused with dark gray corrosion spots.

3、 Fatigue fracture

The origin of fatigue fracture is the assembly stress generated by excessive tight fitting and the fatigue yield formed by cyclic alternating stress. Once the balance between assembly stress, alternating stress, and yield limit is lost, fracture will occur along the axis of the ring, forming penetrating cracks.

In practice, bearings that fail in normal use are mostly damaged as described above, namely contact surface fatigue, and the three types of fatigue failure are more common with subsurface fatigue. The recommended bearing life calculation methods for ASO281 and ISO281/amd. 2 are based on subsurface fatigue.

Common anti fatigue methods include:

A. Heat treatment technology

Heat treatment is a commonly used process to improve the mechanical properties of Strength of materials. In order to meet the different use requirements of different materials and parts, different heat treatment processes need to be selected. The pre heat treatment organization, quenching heating temperature, heating speed, cooling method (medium and speed), tempering temperature and time all have a significant impact on the mechanical properties. Many heat treatment parameters need to be optimized and combined, To achieve better performance that adapts to usage conditions, thereby extending the fatigue life of the parts. Build a virtual production platform for heat treatment and promote the transformation of heat treatment technology into high-tech knowledge intensive. The optimization of heat treatment process parameters and the development of digital heat treatment technology are important prerequisites for achieving anti fatigue manufacturing.

B. Surface chemical heat treatment

The modification effect of surface chemical heat treatment is mainly on the surface, and the chemical elements that can be infiltrated can be selected according to different usage requirements, such as infiltration