Detection and Characterization of Local Defect Resonances Arising from Delaminations and Flat Bottom Holes

The concept of local defect resonance (LDR) can be used to diagnose the presence of defects, such as delaminations and cracks, and enable their localisation. This paper describes an automated detection methodology of LDR frequencies using signals measured by laser Doppler vibrometry. The performance of the detection algorithm is validated, both numerically and experimentally, on an aluminum sample containing a flat bottom hole. Subsequently, the algorithm has been applied on a sample made of glass-fiber-reinforced polymer that contains a single circular delamination and a composite sandwich structure with a disbond. In all cases, the lowest order LDR frequencies were successfully identified.