Experimental verification of Lamb waves dispersion curves in sandwich-like structures for damage detection in single lap joints

The scientific community is looking for novel strategies to move toward sustainable and climate-neutral aviation. For fuel savings and thus for reducing the carbon footprint of an aircraft, weight reduction is recognized as one of the most effective solutions. Substituting mechanical fasteners/rivets with purely adhesive bonded joints can significantly reduce the aircraft's weight. However, ensuring the adequate reliability of purely adhesive-bonded joints requires a sound understanding of the adhesive mechanical properties and the implementation of Structural Health Monitoring (SHM) techniques. Ultrasonic Guided Waves (UGWs) are employed to investigate the structure without altering its integrity as an SHM methodology. In this framework, the description of Lamb Waves (LWs) dispersion curves allows the understanding of the material properties through the analysis of the behavior of the wave propagating in the medium. In this study experimental verification of Lamb Waves dispersion curves is conducted to evaluate the materials’ properties and the adhesively bonded joint integrity. An experimental campaign was conducted on the adherent and adhesive layers separately. The investigation narrows down the experimental methodology carried out to obtain information about the materials. The developed methodology shall compare the experimentally obtained values of the LWs group velocities at different excitation frequencies with the outcomes of the analytical model elaborated by Dr. Pant. Moreover, the signal post-processing analysis was performed to read and correctly interpret the collected data. The aim of the thesis work consisted of the development of a methodology that could fully describe the LWs dispersion curves to determine the behavior of the waves propagating in sandwich layouts. This verification process can be considered a middle step for future research in the understanding of how the wave parameters vary across the overlapping area of an adhesive joint.