The role of evanescent modes in global-local analysis of ultrasonic guided waves in plates with varying local zone-scatterer relations

In order to provide a reliable and robust SHM performance, Ultrasonic Guided Waves (UGWs) need to be analyzed and understood. Numerical modeling of UGW propagation and scattering by hybrid methods offers the possibility of simulating UGW interaction with waveguides of arbitrary cross-sections and discontinuities. Maximizing the accuracy of such methods is important to perform quantitative SHM, while maintaining minimum computational cost. This work investigates the role of evanescent modes in the numerical analysis of UGWs in aluminum and composite plates with defects, by the hybrid Global-Local method. The complex solutions to the UGW eigenvalue problem are found and the scattering spectra for A0 and S0 incident modes are calculated. The accuracy of the numerical solution is then studied by computing the error in terms of energy balance. Parametric studies with respect to the local zone size, defect dimensions and shape are conducted including and excluding evanescent modes in the analysis. Considerations are provided to obtain a solution with error no greater than 5%, in terms of varying local zone - scatterer relations within plate waveguides.