Evaluating material degradation by the inspection of minor loop magnetic behavior using the moving Preisach formalism

The application of two magnetic nondestructive evaluation techniques is investigated to monitor material degradation caused by metal fatigue. First, a set of experimentally obtained major and minor quasistatic magnetization loops is analyzed within the framework of the moving Preisach formalism: the mean-field parameter k is found to increase with the number of stress cycles n and, moreover, the ratio d k ∕ d n is higher during the last 10% of the fatigue lifetime. Second, during the fatigue test a constant magnetic field is applied to the sample and the magnetization variation during each stress cycle due to the magnetomechanical effect is monitored: the peak-to-peak magnetization first increases, then stabilizes, and finally starts to decrease at 95% of the fatigue lifetime.