Experimental validation of a fracture-mechanics model for evaluating fretting-fatigue strength by focusing on non-propagating cracks

• Fretting fatigue limits were explained well by the crack propagation model.
• Experimental crack propagation angles in stage II were expressed by this model.
• This model expressed the experimental results of non-propagating cracks.
• ΔKth for small cracks were experimentally obtained under various values of R.

Fretting-fatigue strengths of 12%-chromium steel with different static strengths were evaluated quantitatively by applying fracture mechanics considering the effects of small crack and mean stress on the threshold value of stress-intensity factor range, ΔKth. Crack-propagation behavior was investigated by obtaining non-propagating crack lengths of run-out specimens and ΔKth from fretting pre-cracks under several stress ratio, R values, including negative mean stress. It was confirmed that test results concerning fretting fatigue strength can be successfully explained by applying maximum-tangential-stress theory. Cracks were confirmed to propagate in stage II at an angle at which the maximum stress-intensity factor range occurred. This model also confirmed the experimental result that the depth of non-propagating cracks decreases as mean stress and material strength increase.