Critical stress state evaluation for early damage with metal magnetic memory method

To find out MMM critical signal characteristics of early damage, this paper offers a foundational data for MMM quantitative testing. The relation between the critical stress states and magnetic memory signals was studied by experiments. Different states of stress, including tensile stress state and three-point bending stress state, were created in experiments. Steel Q235B and X70 samples with different shapes were tested by MMM method. The critical magnetic characteristics of the critical yielding state for tension experiment and those of the ultimate bending moment for three-point bending test are presented, which can serve as a rule for testing early damage. The result of metallographic examination proves the validity of the early damage MMM characteristics.