Generation of low-attenuation lamb wave modes in three-layer adhesive joints

Abstract

In this paper, the attenuation of lamb waves in three-layer adhesive joints, including two elastic plates bonded together by a viscoelastic adhesive layer, is investigated using the global matrix method and then a suitable incidence angle is calculated to generate a low-attenuation lamb wave using an angle beam transducer. The theoretical boundary value problem in adhesive joints with a perfect bond and traction-free boundary conditions on their outer surfaces is solved to find a combination of frequencies and modes with lowest attenuation. A characteristic equation is derived by applying continuity and boundary conditions in adhesive joints using the global matrix method. Phase velocity and attenuation dispersion curves are obtained with numerical solution of this equation by a computer code for a three-layer joint, including an aluminum repair patch bonded to the aircraft aluminum skin by a layer of viscoelastic epoxy adhesive. To validate the numerical solution results, wave structure curves are plotted for a special mode in two different frequencies in the adhesive joint. Also, the transducer incidence angle is calculated in terms of frequency to generate lamb wave modes with low attenuation level using the theoretical method.