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 appears at the maximum alternating shear stress below the contact surface, and then expands to the surface to form different spalling shapes, such as pits or pitting spalling. Peeling into small flakes is called shallow peeling. Due to the gradual expansion of the spalling surface, and often expand to the deep layer, to form deep spalling. Deep spalling is the fatigue source of contact fatigue failure.

2. Wear failure

Wear failure refers to the failure caused by continuous wear of the metal on the working surface caused by the relative sliding friction between the surfaces. Continued wear and tear will cause gradual damage to bearing parts, and eventually lead to the loss of bearing dimensional accuracy and other related problems. Wear may affect change of the shape, the increase of the fit gap and the change of the working surface topography may affect the lubricant or make it contaminate to a certain degree, causing the lubrication function to be completely lost, thus causing the bearing to lose rotation accuracy and even fail to operate normally. Wear failure is one of the common failure modes of various types of bearings. According to the form of wear, it can usually be divided into the common abrasive wear and adhesive wear.

Abrasive wear refers to the wear caused by foreign hard particles squeezed between the working surfaces of the bearing, or hard foreign matter or wear debris on the metal surface relative to the contact surface. It often causes furrow-like scratches on the working surface of the bearing. Hard particles or foreign matter may come from the inside of the host or from other adjacent parts of the host system, and are brought into the bearing by the lubricating medium. Adhesive wear refers to the uneven force on the friction surface due to microscopic protrusions or foreign objects on the friction surface. When the lubrication conditions are severely deteriorated, local friction generates heat, which can easily cause local deformation of the friction surface and friction microscopic welding. At this time, the surface metal may be partially melted, and the force on the contact surface tears the local friction welded joints from the substrate, which increases the plastic deformation. This adhesion-tear-adhesion cycle process constitutes adhesive wear. Generally speaking, slight adhesive wear is called scratch and severe adhesive wear is called bite.

3. Fracture failure

The main reason for bearing fracture failure is the existence of defects and the bearing of overload. When the applied load exceeds the strength limit of the material, the part fracture is called overload fracture. The main cause of the overload is the sudden failure of the main engine or improper installation of the bearing. Defects such as microcracks, shrinkage cavities, bubbles, large foreign objects, overheated tissues, and local burns of bearing parts can also cause fracture at the defect when impact overload or severe vibration, which is called defect fracture. It should be pointed out that in the bearing manufacturing process, the re-inspection of raw materials, the quality control of forging and heat treatment, and the process control of processing can be correctly analyzed by the instrument for the existence of the above-mentioned defects. Generally speaking, most common bearing fracture failures are overload failures.

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