Crack initiation in metallic structural members subject to cyclic loading is predicted by sensing metallurgical changes taking place as a result of the cyclic loading. Fatigue loading produces a cycle comprising a condition described as fatigue relaxation followed by fatigue intensification. By monitoring this cycle, measured strain for a known applied load will increase or decrease. By monitoring the change in strain load, crack initiation can be predicted as fatigue relaxation becomes fatigue intensification. In a preferred embodiment, the strain gauge is mounted beneath a patch excluding ambient atmosphere during monitoring of the structural members.
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