Global-Local Modeling of Guided-wave Scattering for Quantitative NDE

Among the several NDE and SHM techniques, ultrasonic guided waves are very suitable for the inspection of wide structures and complex geometries. Their behavior and interaction with geometrical or potential defective discontinuities needs to be understood to assist the experimental set-up of NDE tests and to interpret the collected data for quantitative damage detection and structural characterization. The Global- Local method is utilized here to investigate the guided-wave scattering in presence of very complex geometries, involving multi-layered materials and various types of defects. The standard Finite Element (FE) approach discretizes the region with discontinuities, while the Semi-Analytical Finite Element (SAFE) method discretizes the cross-section only of the waveguide geometry and propagates the solution along the wave propagation direction, analytically through eigenvector decomposition. The two problems are coupled at the interacting boundaries in terms of tractions and displacements, to guarantee energy conservation. The scattering coefficients due to an incident wave mode are calculated by least square method and will be used in terms of reflected and transmitted energy and cross-sectional Poynting vectors to understand frequencymode sensitivity to defects. Results will be shown for the skin-to-stringer assembly of composite aircraft structures that are affected by various types of impact damage that are relevant to aircraft safety.