Contact stress and deformation are the stresses and deformations adjacent to the contact area when two curved objects are pressed against each other. The distribution of contact stress is related to many factors such as the shape and size of the contact surface, surface roughness, and hydrodynamic lubrication conditions. Hertz was the first to study the contact problem of two elastic bodies, and under some simplified assumptions, the stress distribution on the contact surface can be calculated. Under load, the contact line of two objects in line contact will expand into a rectangular contact surface, and the contact stress in the contact area will be distributed as a semi elliptical cylinder.

It is generally believed that rolling friction torque is related to contact surface roughness, elastic hysteresis, adhesion effects, and differential sliding. Matsuhara pointed out that when the roughness of the contact surface between two objects is at 1 μ Below m, there is almost no effect on the friction torque, so the effect of surface roughness can be ignored. It is believed that the rolling friction torque in overrunning clutches mainly comes from elastic hysteresis and adhesion effects, while the effects of micro sliding and plastic hysteresis are relatively small and can be ignored. Holling also has the same view, so only the power consumption caused by elastic hysteresis and adhesion effects is analyzed and studied, regardless of the impact of factors such as contact surface roughness and differential sliding.