Adhesive bonded structures are used in safety critical applications because of high strength-to-weight ratio.However, they are prone to many defects. Interface weakness or weak bond type defects severely affects the integrity of the bonded structure and they are very difficult to detect using conventional non-destructive evaluation (NDE) techniques.


In this work, a method to quantify the adhesive thickness and adhesion parameter using higher-order SH-like modes is presented. A numerical model that employs spring stiffness boundary conditions at the adherend–adhesive interface is developed to generate the dispersion curves. Based on the dispersion curves, the SH2 -like mode was found to be sensitive to change in epoxy thickness alone while the SH1-like and SH3 -like modes were sensitive to adhesive thickness, adhesive shear modulus, and interfacial adhesion parameters. From experimental data, the cut-off frequency of SH2 -like mode was measured using a time-frequency spectrogram, and thickness is quantified. The interface stiffness and shear modulus of adhesive were then subsequently estimated using the other modes. The procedure is experimentally demonstrated on (1) aluminum-epoxy-aluminum and (2)composite-epoxy-composite. Finally, the estimated parameters are validated using spatio-temporal Fourier transform. Further, a method for optimizing the imaginary value of shear modulus is presented. The proposed method aids in estimating multiple adhesion parameters using SH wave modes.