Fretting fatigue properties and detection of crack initiation of inconel alloy

Plain and freeting fatigue tests of inconel alloy NCF690 were carried out under tension-compression axial loading. In the fretting fatigue test, the contact pad of stainless steel SUS405 was clamped and the pressure of the contact pads was changed from 60 to 200MPa. The fatigue strength in fretting fatigue substantially reduced comparing with that of the plain fatigue and fundamentally decreased with the increase of the contact pressure, but did not change in the region that the contact pressure was higher than 150MPa. The friction force amplitude and the relative slip amplitude increased with the increase of the stress amplitude. However, the friction force amplitude became almost constant in the region that the stress amplitude was high, when the contact pressure was equal to 60MPa. After that, measuring the strain information in the neighborhood of the contact surface of specimen and pad, the applicability of the strain interference method to the detection of the crack initiation in fretting fatigue w as investigated. It was shown that the crack initiation life at which the crack length reached about 0.5mm could be detected by the strain interference method.