Analytical insight into local defect resonance induced by disbond in multilayered structures

Despite the demonstrated effectiveness of methods based on local defect resonance (LDR) in defect identification and sizing, the precision of LDR prediction is limited owing to the inconsistency between the fundamental assumption of existing methods and the reality. To tackle this deficiency, an analytical framework to interpret the formation of LDR induced by defects in multilayered structures is proposed. In this framework, reflections of Lamb waves at defect boundaries are investigated analytically, whereby the phase shift of reflected waves at defect boundaries is obtained. On this basis, the resonance formation is analyzed from a perspective of wave propagation and superposition, and the relation between the LDR frequency components and the defect size is ascertained. Experimental validations are performed in which LDR generated by defects in adhesively bonded multilayer structure are measured. This investigation provides an analytical insight into the defect-induced LDR and improves the precision of quantitative characterization of defects using LDR.