Disbond contours evaluation in aluminum/CFRP adhesive joint based on excitation recovery of Lamb waves

Adhesively bonded joints between metallic plates and composite laminates are frequently used in various fields including aviation, automobile industry, and marine manufacturing. The edge of adhesive layer is exposed to pollutants in the air, which implies that the joints are inclined to suffer debonding defects along the adhesive bond line. To evaluate the contours of the edge disbond, a method based on propagation characteristic analysis and Lamb wave excitation recovery is proposed. Firstly, the dispersion curves of Lamb waves in bonded area and single-layer plate are obtained via the Semi-Analytical Finite Element (SAFE). Subsequently, the effect of disbond on propagation characteristics of Lamb waves is analyzed and discussed numerically. On this basis, the excitation recovery method is proposed and applied to the received waves. The value of envelope at the initial position is extracted as the index during backward propagation for quantitative evaluation of disband size for every transmitter-receiver propagation path. Finally, the disbond contours are sketched by synthesizing the information of all paths with a hypothesis that disbond exists at the edge of the adhesive layer. The proposed method is applied to a lap joint specimen composed of a quasi-isotropic CFRP laminate and an aluminum plate experimentally, and the result demonstrates the effectiveness of proposed method for the accurate evaluation of disbond contours.