Test research on low-cycle fatigue damage of parts by metal magnetic memory methods

Low-cycle fatigue tests of notched 18CrNi4A steel specimens were carried out under three different fatigue stresses, and metal magnetic memory (MMM) signals were detected. The effects of stress concentration, fatigue damage and fatigue stress on the MMM signals were investigated. The results show that fatigue-damaged locations can be predicated effectively according to the mutational characters of the MMM signal Hp(y) curve and K curve. It is found that the zero-crossing points of the MMM signal H'p(y) curve (H'p(y) = Hp(y)N-Hp(y)0) have the same positions as the fracture points, so it can be concluded that fatigue-damaged locations can be predicated more effectively by zero-crossing points. The absolute value of the MMM signal feature parameter Kmax increases with the aggravation of the fatigue damage. The fatigue damage can be assessed effectively by the value of Kmax. In addition, there is an inherent relationship between the fatigue stress and the MMM signal feature parameters Hp(y)max, Hp(y)min and Hp(y)sub; the larger the fatigue stress is, the larger the absolute values of the feature parameters are.