Abstract: By means of magnetic memory technology, a fatigue crack propagation test is carried out at room temperature for the standard SE(B) specimen of 40Cr steel. The magnetic field distributions of the specimen are investigated with the same load and different cycle numbers N. A new characteristic parameter for magnetic memory testing is defined, and the phase characteristics of the characteristic parameter in the process of fatigue crack growth are analyzed and discussed. The results show that the characteristic parameter changes more markedly than the traditional parameters. By analyzing the relations between the magnetic memory signals, the crack growth life and the cumulative fatigue damage, a new damage parameter model is established by using magnetic memory signals. According to this model, the residual life of ferromagnetic components can be evaluated excellently. This research provides a reference value for the application of magnetic memory testing technology in aspects of early damage and residual life assessment of ferromagnetic materials.

Key words: magnetic memory testing, nondestructive evaluation, crack propagation, residual life assessment, damage parameter model