Abstract: Metal magnetic memory testing technology is a new kind of testing method in the field of nondestructive testing. With special testing concept, it is expected to accomplish veracious nondestructive testing job for ferromagnetic metal work pieces in the early damage phase. Owing to the immature development of metal magnetic memory testing technology, a lot of basic researches about theory and application range of this new technology need to be carried out. The change of magnetic memory signals for medium carbon 45 steel is studied by a variety of fatigue experiments. The research shows that magnetic memory signals varies regularly in the special fatigue mode. The magnetic memory testing technology can test the high-load fatigue damage better than it can do for the low-load one. It has better ability of testing defect specimens than that of testing the smooth ones. Furthermore, the cause of formation of magnetic memory phenomenon is analyzed. It is deduced that it is the fatigue action that results in the formation and development of dislocation stress fields in the weak region of loaded specimens and arises obviously different distribution of magnetic domains between these weak regions and normal regions, and these special regions can be found by special magnetic signals. Experiments reveal that, magnetic memory testing technology is useful to judge damage state of metal materials, but the judge veracity may be influenced by a variety of factors, such as the condition of loading and specimen shape.

Key words: Fatigue, Magnetic field strength curve, Magnetic memory, Stress concentration, Debris, Tenmat bearing, Thermal EHL, Water lubrication