Rayleigh to Lamb wave conversion at a delamination-like crack

Composite structures require careful monitoring to detect and characterize hidden defects at an early stage of their development so that preventive measures can be taken before the structure loses its load carrying capacity and suffers from catastrophic failure. Ultrasonic guided waves offer an attractive tool for inspecting relatively large plate-like structural components due to the waves' large propagation range and sensitivity to defects in their propagation path. Since such waves are affected by geometrical structural features (e.g. stringers) as well as defects (e.g. delaminations), the application of guided waves in real structures requires a good understanding of their interaction with the aforementioned discontinuities. In this paper, a detailed study of the interaction of Rayleigh surface waves with defects in a thick aluminum plate is carried out using numerical simulations and laboratory experiments. The simple aluminum plate is used to demonstrate and analyze the basic characteristics of the interaction phenomena, which are shown to partially result in Lamb wave conversion. Furthermore, the agreement between simulated waveforms and those obtained from experiments are shown, indicating the possibility of applying the techniques to more realistic structures and their use in damage detection systems. (C) 2015 Elsevier Ltd. All rights reserved.