Behaviors of Frictional Force in Fretting Fatigue

The relation between tangential force and relative slip displacement under fretting fatigue is analyzed by using a model of a spring system, and is compared with the experimental results. And the correspondence of the damaged layer of a carbon steel due to fretting fatigue with the stress conditions near the contact surface is studied. When slip amplitude Δy is small, it is proportional to tangential force T because of elastic adhesion which exists within contact surfaces partly. Both the wave forms of T and Δy are sinusoidal. When Δy becomes so large that macro-slip occurs, T shows a peak value and then decreases with progress of cycles. The wave form of T is trapezoidal and that of Δy is not sinusoidal, agreeing well with the analytical results. The frequency effect appears under Δy showing macro-slip, coefficient of friction being smaller under higher frequency due to the lubricating action of more oxidized debris. The depth of the damaged layer due to fretting fatigue is measured in several tens of microns. This depth is nearly equal to the depth where the combined maximum repeated shearing stress reaches the fatigue strength of materials.