Corrosion quantification of plate-type structures using Lamb wavefield and monogenic signal processing.

Corrosion is one of the most common damage types which seriously affects structural safety. In this paper, a Lamb wavefield-based monogenic signal processing algorithm is proposed to quantify the corrosion parameters, including location, area, shape and depth, in plate-type structures. The monogenic signal processing based on Riesz transform will cause a serious problem, that is, phase wrapping. To solve this problem, a robust fast phase unwrapping algorithm is developed. Then, the phase spatial distribution of the extracted Lamb wavefield can be extracted, which can be used to calculate the wavenumber distribution. The wavenumber distribution is related to the structure thickness or corrosion depth, which can be further used for corrosion imaging. Simulated Lamb wavefield signals calculated by finite element simulation are employed to evaluate the parameters of circular corrosion and complex umbrella corrosion. The results show that the proposed algorithm has a great advantage in corrosion identification accuracy and calculation time compared with the existing algorithms. A completely non-contact laser ultrasonic system is established for acquiring Lamb wavefield containing square corrosion, and it is proved that the proposed algorithm is able to quantify the corrosion location, area, shape and depth with good accuracy in the experiment.