The Global-Local approach for damage detection in composite structures and rails

Structural components with waveguide geometry can be probed using guided elastic waves. Analytical solutions are prohibitive in complex geometries, especially in presence of structural discontinuities or defects. The Global-Local (GL) approach provides the solution by splitting the waveguide in “local” and “global” regions. The “local” region contains the part of the structure responsible for the complex scattering of an incident wave. What happens in this region cannot be reproduced analytically. The “global” region is regular and sufficiently far from the scatterer, in order to exploit known analytical wave propagation solutions. The proposed GL approach discretizes the local region by finite elements, and utilizes the efficient SAFE method in the global region. Kinematic and mechanical constraints ensure the displacements and stresses continuity at the global-local interfaces. The sum of reflected and transmitted waves energy is used to check the before-after scattering energy balance. Numerical results regard the specific cases of a composite skin-to-stringer assembly used in modern aircraft construction and a rail-road track with a common section. The effects of different damage configurations are analyzed in both cases. The results can be useful to select the incident mode-frequency range in order to best identify specific defects in these structures.