Fretting fatigue of 42CrMo4 steel at ultrasonic frequency

Fretting fatigue problem is commonly approached by testing the materials/components under contact in conventional fatigue machines. In this paper, a new fretting fatigue experiment faculty has been developed of which the principle is based on the resonant vibration of a system at a frequency of 20 kHz. This new test system permits variation of the slip amplitude and the fatigue stress individually without the change of the pad length and to dramatically reduce test time. Fatigue experiments of a high strength steel 42CrMo4 with and without fretting have been carried out. A factor of reduction of fatigue strength was introducing to estimate the degradation of fretting fatigue life. The results show that in ultrasonic fretting fatigue with a contact of cylinder on cylinder, crack initiation occurs at the edge region of the initial contact area, and takes a greater fraction of the whole fatigue life.