Corrosion Detection Based on Frequency Spectrum Difference Coefficient of Higher-Order Lamb Modes

In view of the corrosion detection of large thin-walled structural parts in industrial equipment, a corrosion detection method based on spectral coherence analysis using high-order Lamb waves was proposed. Firstly, the A1 mode Lamb wave with a frequency slightly higher than the cutoff frequency was adopted and transmitted at different positions on the corroded thin-walled structure, and the response signal of each propagation path was collected; then, the dispersion compensation technique was used to eliminate the dispersion effect in the signal, so the direct wave packet of A1 mode could be separated and extracted from the signal using a suitable window function. On this basis, the frequency spectrum difference coefficient (FSDC) of the extracted wave packet and the excitation signal was established as an index, which was subsequently discussed in terms of its sensitivity to corrosion defects of different widths and depths with the help of finite element simulation; finally, an experimental validation was conducted on a corroded aluminum plate, where the FSDC index of each path was combined with the probability imaging algorithm to locate and visualize the corrosion defect in the detection area. Results show that the FSDC value keeps zero for an intact path and stays between 0 and 1 for corrosions of different widths and depths. Compared with the traditional tomography method, the proposed method has better detection sensitivity and anti-interference ability.