Effect of Impact Damage on Lamb Wave Propagation in Laminated Composites

An investigation was performed to study the effect of impact damage in laminated composites on propagation of Lamb waves generated by piezoelectric materials that were built into the composites. Piezoceramics were selected in the study as either actuators for generating Lamb waves or as sensors for monitoring the propagating waves. Only surface-mounted piezoceramics were used in the study. By precisely controlling the dynamic response of piezoceramics by means of electric inputs, various types of propagating waves could be generated by the piezoceramic actuators. The first symmetric and asymmetric modes of Lamb waves with narrow-banded frequencies were selected for the study. The selected Lamb waves were nearly non-dispersive and preserved well the wave form while propagating in composites. Experiments were conducted to generate the selected Lamb waves on composite plates before and after the plates had been subjected to a foreign-object impact. By comparing the measured wave forms before and after impact, the results showed that impact damage could significantly alter both the wave form and the magnitude of the transmitted Lamb wave. The change due to impact damage in the transmitted Lamb waves could be differentiated from the change resulting from interference with reflected waves and from modifications in boundary conditions.