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Quantitative Characterization of Stress Concentration of Low-carbon Steel by Metal Magnetic Memory Testing

In this research, the relationship between the degree of stress concentration and the sponta-neous magnetic signals of metal magnetic memory (MMM) was investigated by tensile tests. Sheet specimens of Q235 steel were machined into standard bars with rectangular holes to obtain various stress concentration factors. The variations of the MMM signal and its gradient with the applied loads were studied. It was found that both the tangential component, Hp(x), and the normal component, Hp(y), are sensitive to the local stress concentration caused by the discontinuity. The maximum magnetic gradient in the discontinuity area, kmax, was found to increase as the tension or the stress concentration factor increases. The kmax of the Hp(y) signal is effective in characterizing the degree of stress concentration. The magnetic stress concentration factor, αmHp(y), can be used as an indicator of the stress concentration degree. This research is useful for promoting the metal magnetic memory testing (MMMT) to a quantita-tive nondestructive technique for assessing the degree of stress concentration.


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