It is well known that fretting fatigue is affected by various factors such as contact pressure, relative slip, contact length, specimen size, loading type and so on. The reason why these factors affect fretting fatigue was investigated. The stress distribution near the contact edge was measured using a small stress concentration gage. It was shown that the stress concentration varied significantly depending on these factors. It was found that the S-N curve was expressed uniquely on the basis of the local stress at the contact edge. The meaning of the local stress in fretting fatigue was also studied based on the fracture mechanics. The crack analysis showed that the fatigue limit condition could be evaluated based on the threshold condition for short fatigue crack and the ΔK behavior of small fretting fatigue crack was uniquely determined by the local stress.
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