Localized defect evaluation method based on beam-coupled vibration

This study develops and validates an innovative method for detecting localized structural defects using beam-coupled local modes, which confine vibration to targeted areas and remain sensitive to changes in structural properties while unaffected by external boundary conditions. The proposed method creates a beam-coupled local mode by attaching a small auxiliary beam to the host structure, allowing for precise defect identification through localized modal analysis. The coupled wavelength and resonance frequency of this mode are measured and used to determine local bending stiffness, which directly reflects the presence and severity of defects. Theoretical modeling leverages Euler-Bernoulli beam theory to predict vibrational characteristics, focusing on the emergence of local modes at specific frequencies when structural properties are altered. Numerical simulations conducted via the finite element method highlight robustness against changes in external boundary stiffness and its sensitivity to localized changes. Experimental validation using beam structures with systematically introduced defects further confirms the effectiveness of the method in accurately quantifying localized stiffness variations. Compared to existing modal-based methods, the proposed method eliminates the need for complex signal processing and expensive experimental setups, making it a practical and cost-effective alternative for structural health monitoring. The ability of the proposed method to remain unaffected by boundary condition variations and its capability to isolate localized defects enhance its applicability for reliable structural integrity assessments across diverse engineering applications.