Leaky Lamb waves for the detection and sizing of defects in bonded aluminium lap joints

The possibility of using ultrasonic leaky Lamb waves in a pitch and catch configuration for detecting and sizing defects in bonded aluminium lap joints is presented in this paper. Based in Transfer Matrix method the dispersion curves and the propagation modes behaviour are obtained. First the experimental scattering effects of circular holes with different dimensions on the fundamental symmetric mode S0 are analysed and compared with the results obtained by analytical model. Very good agreement with the analytical model used is found. After, using the same methodology, scattering effects produced by artificial defects located in the bond line of lap joints are measured and the results show that the previous model could be used when an estimation of defect dimensions is needed. Finally an empirical relation between an experimental parameter and the defect dimensions is established revealing a high linear correlation meaning. So, this parameter could be used for more accurate defect dimensions evaluation.