Guided Wave Tomography of Surface Defects Based on the Method of Moments

The detection and evaluation of corrosion, cracks, flaws, and other imperfections in aged structures are critical for enhancing safety and evaluating residual service life in structural health monitoring (SHM) and nondestructive testing (NDT). A guided wave tomography based on the method of moments (MOM) for exact detection of the surface defects in plates, including their profile, size, and position is proposed in this paper. The mathematical relationship between the plate thickness and the objective function is derived theoretically for the A0 mode. Based on the obtained relationship, a plate thickness imaging technique is proposed. The efficiency of the proposed technique is confirmed by the results of numerical simulation and experimental data. Center and off-center surface defects are considered. 64 probes are evenly distributed in a circle outside the defect to capture omnidirectional wave signals. Both numerical and experimental results demonstrate that the guided wave tomography proposed can effectively reconstruct the spatial plate thickness distribution, enabling the precise identification of the defect's shape, depth, and position. The qualitative analysis and quantitative data provide effective guidance for NDT or SHM technologies in engineering.