Visual Inspection of Irregular Cracks in Steel Structure by Double Gradient Fusion Algorithm Using Alternating Current Field Measurement Technique

The alternating current field measurement (ACFM) is an excellent nondestructive testing method for the inspection of cracks in the steel structure. Generally, the research of the ACFM focus on the inspection of one crack with specific direction. However, the crack may extend to an irregular crack with multi-direction due to the complex stress and the special structural shape. In this paper, the irregular crack was inspected visually without cleaning the coating using the ACFM technique. The distorted electromagnetic field was analyzed around the irregular crack by the finite element method (FEM). The double gradient fusion algorithm (DGFA) was presented to reconstruct the surface morphology of the irregular crack. The ACFM system was developed to inspect the irregular crack under the coating. The results show that the current disturbance effect and the magnetic leakage effect both present at different parts of the irregular crack. The surface morphology of the irregular crack can be inspected visually by the DGFA using the ACFM technique. The visual inspection results give more visible morphology information for the structural health monitoring of the steel structure.