Welded Joint Fatigue Cumulative Damage MMM Characteristic

Metal magnetic memory (MMM) technology, based on magnetic-mechanical effect, is a new nondestructive testing. In order to study MMM signal characteristics of welded joint fatigue cumulative damage, Steel 20 welded plate specimens were tested under multi-cyclic fatigue loading. The average value of fatigue loading is 35kN and the stress ratio is 1/6. The MMM behavior of the welded joint fatigue cumulative damage is given. It has been found that non-uniform welding residual stress influences MMM signal distribution at the initial stage of the experiment. With the increasing of fatigue cycles, welded joint fatigue damage is cumulated and the stress is redistributed again. MMM signal begins to be stable regular and shows a fluctuation-arising trend along with the increase of damage degree. By establishing the relationship between the damage degree and the MMM characteristic signals, the welded joint cumulative fatigue damage can be evaluated by MMM method.