Guided Lamb waves have been successfully used for some years as a monitoring technique for damage in plates and pipes. Multimodal Lamb waves are typically observed in thick structures, e.g. steel canisters in dry cask storage systems. Different modes have different sensitivity for certain types of cracks, and it is usually desired to excite specific symmetric or antisymmetric Lamb wave modes. To quantify the participation of different modes, it is important to know the power that each mode shares when exciting multiple modes. This study presents an analytical development and numerical simulations of wave power distribution between different ultrasonic Lamb wave modes using normal mode expansion (NME) technique. Piezoelectric wafer active sensor (PWAS) transducers were used to excite ultrasonic Lamb waves in the structure. The interaction between the PWAS and the structure was studied. Numerical simulations were performed for (1) thin aluminum plate (1-mm) in which one symmetric and one antisymmetric modes exist, (2) thick steel plate (1/2)′ in which three symmetric and three antisymmetric modes exist. In the later case study, power partition between the 6 modes was presented, and a parametric study was performed for different transducer sizes and excitation frequencies.
展开▼
