Core-Skin Disbond Detection in a Composite Sandwich Panel Using Guided Ultrasonic Waves

Advanced composite materials are being increasingly used in state-of-the-art aircraft and aerospace structures due to their many desirable properties. However, such composite materials are highly susceptible to developing internal damage. Thus, safe operation of such structures requires a comprehensive program of effective nondestructive inspection and maintenance of their critical load bearing components before the defects grow and become unstable, resulting in failure of the entire structure. Ultrasonic guided wave-based methods have the potential to significantly improve current inspection techniques for large plate-like structural components due to the waves' large propagation range and sensitivity to defects in their propagation path. The application of guided waves for nondestructive evaluation (NDE) of real structures, however, requires a thorough understanding of the characteristics of guided waves in composite structures in the presence and absence of any defects. In this paper, the interaction of guided waves with a core–skin disbond in a composite sandwich panel is studied using a semi-analytical method, numerical simulations, and laboratory experiments. It is shown that the disbond causes complex mode conversion at its leading and trailing edges. The theoretical findings are verified with laboratory experiments, and the applicability of the proposed pitch–catch setup for NDE of complex composite structures for damage detection is discussed.