The mechanism and application of stress testing for steel structure based on the magnetic memory effect

Magnetic memory testing (MMT) is a nondestructive testing (NDT) technique based on the magnetic memory effect of metal materials. MMT method is the only practicable NDT method, which can be used to carry out early diagnoses. In this paper, at first the magnetomechanical effect and the magnetic memory effect are explained. Then according to the feature of the magnetic memory effect for steel materials, the stress testing mechanism of magnetic memory is analyzed,the magnetic memory testing basis and evaluation of weld seams in steel structure pointed out,the parameters of the leakage magnetic field can be used to make a quantitative and comprehensive evaluation for the weld seam quality,the gradient of the leakage magnetic field and the intensity coefficient of stress concentration be used to find out weld defects. Furthermore, through the real testing for weld seams of three different steel components, it is shown that not only for macrodefects the results of MMT method are in a good agreement with the results of the ultrasonic (UT) method,but also for those latent discontinuities which haven't taken shape,such as the plastic deformation regions and the stress concentration regions, magnetic memory method is feasible. Compared to traditional NDT methods, MMT method still has several advantages,that is,it requires no specialized magnetization devices,no predisposition of test pieces to be tested,and through this MMT method a real time testing can be conducted conveniently.