Investigation of the Lamb Wave Modes Sensitivity in the Inspection of Bonding between Aluminum and Composite Patch

Nowadays, composite patches are widely used to repair damaged metal structures in different industries. In order to assure the perfect performance of these structures, the bonding between composite patches and metal structures should be inspected. Ultrasonic Lamb waves are among the common methods for assessment of the bonding between the composite patches and metal plates. The main goal of this research is to evaluate the sensitivity of the ultrasonic Lamb wave modes in bonding inspection. For this purpose, dispersion curves of an aluminum plate bonded to a composite patch were obtained and using the through thickness stress distribution, the sensitivity of existing modes to the bonding was evaluated. An experimental examination was also performed to generate the possible modes obtained from the theory and to show the effect of disbond on the output signals. Based on the experimental results, the mode which had been predicted to be more sensitive to the bonding was more affected by the disbond. Three Lamb wave modes were excited for inspecting the disbond between aluminum and composite with the angle wedge transducer. As it was theoretically predicted, the Lamb wave mode with higher values of shear stress in the adhesive layer was more affected by the disbond. On the other hand, disbond detection using the mode with poor values of shear stress at the adhesive layer was difficult. These results were concluded from the amplitude change percentage due to disbond in the experiments.