Why is the contact stress cycle characteristic of rolling bearings pulsating?

Why is the contact stress cycle characteristic of rolling bearings pulsating?

The fatigue resistance of mechanical component materials is determined through testing, which involves adding a certain stress ratio of equal amplitude 

variable stress to a standard specimen of the material. This is usually achieved by adding a symmetric cyclic stress with a stress ratio of r=-1 or a pulsating 

cyclic stress with a stress ratio of r=0, which is obtained through experimentation. Your question is that the contact stress cycle characteristic is a pulsating 

cycle, which is not precise, but only a characteristic test of the contact stress cycle test.

The main reason why the contact stress cycle characteristics of rolling bearings are pulsating cycles is due to their working principle and stress variation 

characteristics. ‌

During the operation of rolling bearings, the surface contact stress between the rolling elements and the rotating rings undergoes a process of changing 

from maximum to zero, and then from zero to maximum. This stress change forms pulsating cyclic stress. Specifically, when two objects come into rolling 

contact, the shear stress changes from its maximum value to zero, and then from zero to its maximum value. This change causes the objects to experience 

contact fatigue failure, with the crack direction forming a 45 ° angle with the contact surface.

In addition, the definition of pulsating cyclic stress is that when the minimum stress σ min is zero, it is called pulsating cyclic stress. In rolling bearings, 

this stress variation characteristic results in a pulsating cyclic contact stress.

In summary, the pulsating cyclic characteristics of contact stress in rolling bearings are caused by the periodic changes in stress from maximum to zero 

during their operation.