Delamination Detection in Laminated Composites Using Lamb Waves

This investigation examines the application of low frequency Lamb waves for the detection of delaminations in thick composite laminates. Surface mounted piezoelectric devices were excited with a tone burst of few cycles generating a stress wave that propagates along the structure. Experiments were carried out on composite beam specimens where wave propagation distances over 2 m were achieved and artificially induced delaminations as small as 1 cm2 were successfully identified. The resonance spectrum method, which is based on the study of spectra obtained by forced mechanical resonance of samples using sine-sweep excitation, was used for measuring the A_o Lamb mode phase velocity. Finite element analyses of wave generation and propagation in wide laminated plates are also presented. The feasibility of employing piezoelectric devices for the development of smart structures, where a small and lightweight transducer system design is required, has been demonstrated.