Magneto-Optical Imaging Analysis of Welding Defects Under Vertical Combined Magnetic Field

Previous research on magneto-optical imaging of welding defects primarily focused on detecting artificially simulated known defects, and its industrial applicability remains uncertain. To optimize existing magneto-optical imaging technology, this study investigates non-destructive testing using magneto-optical imaging under vertical combined magnetic field(VCMF) excitation. First, A simulation model was established to analyze how alternating magnetic field(AMF) variations within a VCMF affect leakage magnetic flux from cross-shaped grooves, employing the controlled variable method. Subsequently, magneto-optical imaging experiments were conducted to capture images of radial cracks in spot welds under constant, alternating, and VCMFs. The study focuses on radial cracks from spot welding, which better represent industrial product requirements. By comparing VCMF magneto-optical imaging characteristics across different AMF strengths, analysis showed that alternating field intensity affects imaging in vertical composite fields. Results demonstrate that contrast variations in magneto-optical images are more pronounced under VCMFs than under single alternating fields. Furthermore, the relationship between AMF intensity and image contrast enhancement is nonlinear.