Abstract: High-cycle fatigue tests of notched 40Cr steel specimens are carried out under three different fatigue stresses and two-dimensional metal magnetic memory testing (2-D MMMT). Two-dimensional signals are detected and analyzed by the method of Lissajous figure. The effects of stress concentration, fatigue damage and fatigue stress on two-dimensional magnetic signals are investigated. The relationship of the area of Lissajous figure and the degree of fatigue damage is analyzed. The results show that zero-crossing of the magnetic memory normal component and peak values of the magnetic memory tangential component appear in areas of stress concentration, and that the position of these phenomena drifts gradually closer to the notch root with the increase of fatigue damage. Location of the specimen damage can be characterized by the mutation peak characteristic of K curve of the normal component gradient and the tangential component gradient of magnetic memory signals. The maximum values of the normal component gradient and tangential component gradient of the magnetic memory signals increase gradually with the augmentation of the degree of fatigue damage in the whole trend. Therefore the maximum value is regarded as a characteristic quantity that reflects the degree of specimen damage, and the area of Lissajous figure has a good correlation with the degree of fatigue damage.

Key words: metal magnetic memory, two-dimensional testing, fatigue damage, stress concentration, magnetic field measurement, nondestructive examination