Abstract: Metal magnetic memory testing technology is an effective way of the non-destructive testing techniques for early damage diagnosis of ferromagnetic materials. To further explore the mechanism of metal magnetic memory testing, the magnetic domain structure of Q235 tablet samples are observed by bitter pattern, the characteristics changes of magnetic domain structure under the different stress states in earth magnetic are researched, and the high-precision weak magnetic detection devices are used to obtain the magnetic flux leakage signal of the specimen surface. The results show that the magnetic domain types and domain wall morphology change significantly with the change of external loads; and different regions have different change speed of magnetic domain, but they have a similar trend; the same time, the magnetic flux leakage signal of specimen surface increases with the external loads increases. The magnetic domain of ferromagnetic materials move by stress and preserve such changes after the withdrawal of the stress in earth magnetic are verified. Thus it provides reliable and effective experimental basis for further study of the microscopic mechanism of ferromagnetic materials magnetic memory testing.

Key words: Bitter pattern, Different stress states, Magnetic domain structure, Magnetic flux leakage signal, Magnetic memory testing