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 regular finite elements, and utilizes the efficient Semi-Analytical Finite Element (SAFE) method in the global region. Kinematic and mechanical constraints ensure the displacements and stresses continuity at the global-local interface. The evaluation of the energy of reflected and transmitted waves is used to check the before-after scattering energy balance. Numerical results are shown with regard to the specific cases of a composite skin-to-stringer assembly used in modern aircraft construction and a railroad track with a common section. The effects of different damage configurations are analyzed in both cases studying the reproduced scattered spectra related to specific incident waves. The results can be useful to select the best incident mode-frequency range in order to best identify specific defects in these structures.