Non-destructive testing of weld defects based on finite element analysis of magneto-optical images

Magneto-optical imaging is based on the theory of leakage magnetic field and the Faraday magneto-optical effect. A magnetic dipole model of pit was established and verified by comparing with gray value of magneto-optical image of pit. The sag, pit, non-melting and non-defect of welded pieces made in the detection of magneto-optical were simulated by the two-dimensional finite element models. The magnetic induction intensity distributions of defects in the lift strength of 1mm were obtained in the simulations. Experiments on detecting the defects referred above by magneto-optical detection were carried out and magneto-optical images of the defects were acquired. The simulations were proved reliable when compared with magnetic field distribution of models and gray curves of magneto-optical images of the corresponding defects. Also, these models analyzed magnetic induction intensity distributions of different defects in different strengths of lift. Furthermore, it provided the theoretical and experimental basis for further study of the mechanism of magneto-optic imaging.