Studies on test technique of stress concentration for ferromagnetic component based on permeability

The stress concentration detection technology based on the permeability is an evaluating method on the stress concentration which is according to the induction voltage signal of the closed magnetic circuit composed of the probe and the specimen. The permeability is related to the detection signal, but also to the degree of stress concentration. Through the permeability parameter, the relation between the detection signal and the degree of stress concentration can be established. The permeability measurement technique can be used to detect various micro-structural changes of component related to permeability, such as stress concentration, fatigue damage, aging and transformation. The basic principle of permeability measurement technology is analyzed, and the optimum setting method of detection parameters is discussed. Taking steel 20 as an example, the relationships between the detected signal and the tensile stress, tensile residual stresses have been studied experimentally which is based on the measured signals data. It is found that the change of detection signal caused by tensile stress can reach 33.3%, and the change of detection signal caused by residual stress after unloading can reach 35.8%. It is also found that the detection signal is particularly sensitive to the yield strength, and the signal will decrease sharply when the stress exceeds the yield strength. According to the characteristics of the detected signal, it can effectively detect the stress state in a certain area of the specimen, and has a broad application prospect. (paper)