Simulation and Experiments for Magneto-Optical Imaging Detection of Complex Welding Cracks

The feasibility and imaging process of magneto-optical imaging (MOI) in detecting complicated welding cracks are studied. Magnetic field distribution of welding cracks is simulated by Maxwell 3D, and the obtained magnetic field is converted into light intensity to simulate the process of welding crack detection. Research results show that the simulated magneto-optical images of welding cracks are basically consistent with the actual magneto-optical images of welding cracks. The transverse and lengthwise differences in extremums of magnetic flux density affect the clarity and consistency of magneto-optical images. Also, there are special magnetic fields at the intersection and endpoint of the complex-shaped welding cracks. The welding crack intersection does not affect the transverse difference in extremums of magnetic flux density, but the variation range of the lengthwise difference in extremums increases because of the intersection. The reduction of magnetic field around the welding crack endpoints needs a transition process, which leads to the blurring of welding crack endpoint boundary in magneto-optical images. With the increase of lift-off value, the correlation between transverse difference of extreme points and welding crack width weakens. The crack images obtained by proposed simulation method can be used as the theoretical basis of practical applications, which can shorten the development cycle of MOI sensor for detecting welding cracks.