Early Damage Stress State MMM Testing

The stress state testing and evaluation is the major concern in early damage testing. The metal magnetic memory (MMM) testing, based on ferromagnetic theory, is a new NDE technology that can find the most serious stress concentration zones, microscopic defect, etc. However, there is no quantitative analysis standard in engineering practice. This paper is to find out MMM critical signal characteristics of early damage to offer a foundation data for MMM quantitative testing. The relation between stress distribution and magnetic memory signal has been studied by experiments. Two different states of stress, including one-direction tensile stress state and two-direction bend stress state, were created. The critical magnetic characteristics are given in zones of stress concentration, which can serve as a rule for testing early damage. The result of metallographic examination proves the validity of MMM early damage testing.