Damage localization in metallic plates through lamb wave frequency variation: A numerical study

Abstract. Lamb wave is extensively used in the structural health monitoring (SHM) of various structures for defect detection. However, the Lamb wave is constrained by two interlinked complexities: inherent dispersion and multimode characteristics. The presence of many dispersive modes poses challenges in their application for structural damage localization. The aim of this work is to examine Lamb wave behavior and determine the location of the damage when its central frequency varies in the range specified by its dispersion curve for a particular structural thickness. The analysis methodology is illustrated by twenty numerically simulated cases of aluminium plates using a three-dimensional finite element method (FEM) in Abaqus/CAE. A hole as a defect is included in the plate that extends through its entire thickness. The fundamental symmetric Lamb mode (S0) with increasing central frequency in the chosen range is actuated in the first ten cases as it exhibits minimal dispersion. History output for the out-of-plane components of the signal is obtained, which is used for damage location imaging using Matlab. A similar approach is repeated for the next ten cases using the fundamental anti-symmetric mode (A0). The images obtained for the damage locations show a clear distinction among the accuracy of Lamb wave frequencies that are used. As the central frequency is increased for S0 mode, the size of the located damage area increases, resulting in a decrease in the optimization of damage localization. Whereas a reverse output is observed with the A0 mode, where the localized area decreases with increases in frequency. In all cases, the location is accurately localized. However, the estimated area of damage is shifted from its central location. Another significant outcome from this investigation showed that at a higher frequency range, the localized area of the damage is approximately the same. The investigation concludes that low-frequency Lamb modes are better suited for damage localization using imaging techniques. It is also confirmed by the investigation that the low-frequency Lamb wave gives better localization results when applied to identifying comparatively large defects (in mm).