Under the action of cyclic loading, fracture often occurs even when the stress is lower than the yield strength. This phenomenon is called fatigue fracture.The fatigue fracture of imported bearing, especially the fatigue fracture of high-strength imported bearing material, generally has no obvious plastic deformation before the fracture, so it is difficult to detect and prevent, so it is very dangerous.

Fatigue strength of imported bearing refers to the maximum stress of the material that does not break after countless stress cycles, which is used to characterize the ability of the material to resist fatigue fracture.The easiest way to measure the fatigue strength of a material is to do a rotational bending fatigue test.The cyclic stress of the material was measured experimentally.And its fracture stress cycles before Ⅳ called breaks curves, curves of relationship between as shown in figure 1-8.

As can be seen from the figure, the smaller the cyclic stress is, the more cycles the material bears before fracture.When the stress decreases to a certain value, the curve tends to be horizontal, which means that under the action of this stress, the material does not break after countless stress cycles.According to the engineering regulations, when the material reaches a certain cardinal N under the action of cyclic stress and does not break, its maximum stress will be regarded as the fatigue limit of the material.The circulating base of general steel material is 10.Times.When the material is subjected to symmetrical cyclic stress, the fatigue limit of the material is used.

The process of fatigue fracture of imported bearing is the formation, growth, connection and expansion of cracks on the surface and inside of the material.The anti-fatigue capability of the components can be improved by means of improved design (such as avoiding sharp Angle, reducing surface roughness and other measures to avoid stress concentration) and surface strengthening (such as surface quenching, chemical heat treatment, shot peening and rolling).