Time-Frequency Analysis on Numerical and Experimental Ultrasonic Guided Wave Scattering for Quantitative Damage Characterization in Plates

Abstract

Ultrasonic guided waves (UGWs) have been proven to be an effective technique for structural health monitoring (SHM) due to their low attenuation and high sensitivity to defects across the entire structural cross-section, outperforming conventional inspection methods. However, the dispersive and multi-mode nature of UGWs presents significant challenges for structural inspection, limiting their effectiveness in damage detection and characterization. The interaction between different mode-frequency combinations and structural defects, such as delaminations and notches, affects UGW scattering according to complex mechanisms that challenge inspection techniques. Therefore, a deeper understanding of the distinct scattering phenomena with respect to defect types and sizes is essential for improving the diagnostics and prognostics of damage. In this study, numerical and experimental methods are employed to analyze UGW interactions with plate-like structures in both the time- and frequency- domains. First, the hybrid Global-Local method is used to simulate UGW propagation in isotropic and composite plates with defects of varying types and sizes. This enables a comprehensive investigation of the wave-damage interaction over a broad frequency range. Then, experimental testing is performed to observe and validate the numerical findings, using broadband guided wave testing. Signal processing is applied in the time and frequency domain to extract transfer and impulse response functions via the deconvolution method. The results from the numerical simulations reveal amplitude, time shifting and frequency content alterations that align with the experimental tests and that vary with defect type and severity, providing valuable insights for effective SHM applications. These studies demonstrate the effectiveness of the Global-Local approach in enabling quantitative SHM and prognostics by providing accurate and efficient predictions of UGW scattering responses. Furthermore, the distinct scattering behavior observed for different defect types and sizes highlight the potential of leveraging these features to solve the inverse problem of defect characterization.