Progress and key problems in the research on metal magnetic memory testing technology

The nondestructive technique for testing ferromagnetic materials known as the metal magnetic memory method is formally proposed in 1997 by the Russian scholar Dubov at the 50th International Conference on Welding. The main advantage of this metal magnetic memory technology is that no external excitation magnetic field source is required. That is, by the excitation of the natural geomagnetic field, when a ferromagnetic member is subjected to external stress, a free magnetic leakage field is generated around the stress concentration or defect position of the ferromagnetic member due to the magnetic-force coupling effect. By measuring and analyzing the magnetic leakage signal on the surface of the material, the stress concentration, early damage, and degree of damage in the ferromagnetic member can be readily detected and evaluated to effectively prevent sudden brittle failure of the structure or member. This technique is the only effective nondestructive testing method for diagnosing early damage in ferromagnetic components. Because this metal magnetic memory testing technology can be used to assess the stress concentration, early damage position, and the degree of damage of ferromagnetic materials, it has great potential for use in predicting structural or component life and warning of damage. Its advantages include no manual magnetization or attached sensor, no surface treatment of components, and simple, convenient, and quick operation. As such, it has attracted wide interest from scholars around the world since its formal introduction. In this paper, based on the research on metal magnetic memory testing technology over the past 10 years, a theoretical model of the technology was established and the progress made in the theoretical research, experimental research, and engineering applications of this technology were summarized. The damage assessment criteria for magnetic memory testing technology were discussed and the factors that affect the magnetic memory detection signal were analyzed. Based on this review, the current problems were identified and future research directions of magnetic memory testing technology were proposed.