Abstract: Fatigue tests of notched 18CrNi4A steel specimens are carried out and metal magnetic memory (MMM) signals are detected. The variation of the MMM signals in the process of fatigue testing is investigated. Based on continuum damage mechanics theory, two fatigue damage variables are established on the basis of the MMM signal feature parameters, and two new fatigue damage models are founded accordingly. The results show that the variation of the MMM signals is unobvious before the cracks initiate, but that the MMM signals increase obviously with the propagation of the cracks and vary abruptly after rupture. The MMM signal feature parameters demonstrate three stages, and their absolute values rise with the increase of the fatigue damage. In addition, there is an inherent relationship between fatigue stress and the feature parameters; the larger is the fatigue stress, the larger are the absolute values of the feature parameters. The MMM signal damage variable based on the MMM signal feature parameters is measured during the stresscontrolled fatigue experiments to verify the new MMM signal fatigue damage model, which is in good agreement with the results.

Key words: metal magnetic memory methods, stress concentration, fatigue, continuum damage mechanics, quantitative assessment