PROPAGATION OF ULTRASONIC LAMB WAVES IN ALUMINIUM ADHESIVELY BONDED LAP JOINTS AND IN SINGLE PLATES

摘要

The analysis of the propagation of Lamb waves in multi- and single-layer systems is presented in this work. The study of this propagation problem is developed from matrix formulations, which describe elastic waves in layered media. The behavior of the different modes that propagate in the overlapped region is characterized. It is found that their relative amplitudes can be estimated based on the properties of the incident wave mode. It was verified that the excitation of these modes is ruled by the degree in which the shapes of both modes match each other. Other result of this method refers to the evaluation of the attenuation of both longitudinal and transversal waves in plates, which is usually difficult, especially in thin plates by using the conventional pulse-echo technique. By using the immersion pitch and catch setup, the total attenuation, the sum of the losses due to the leaking in the fluid and to the material damping can easily be obtained through two measurements at different distances. The leaking losses are calculated by the bulk properties of both the fluid and the plate, and, consequently, the attenuation of the longitudinal and the transversal waves (material damping).