High-resolution damage imaging in flat and bent plate-like structures through warped-basis pursuit

Critical challenges related to Guided Wave (GW) inspection for Structural Health Monitoring (SHM) include the size and proximity of damages that can be individually resolved as well as accessibility of the areas to be monitored. Effective damage imaging has been recently demonstrated through a Warped-Basis Pursuit (W-BP) approach that provides dispersion removal and high localization accuracy. Theoretical limits to the distance range resolution of this technique are discussed in this paper, and practical resolution capabilities of the W-BP are assessed in challenging situations. This is done by processing the wavefield recorded by a Scanning Laser Doppler Vibrometer outside of the damaged area of an aluminum plate. Considered scatterer configurations include a couple of masses whose mutual distance is progressively reduced and a series of holes of various dimensions and spacing. Potentials and limitations of W-BP are analyzed, along with its application for the inspection of remote/inaccessible areas in complex waveguides. Specifically, the case of an L-bent plate is considered. Mode conversion associated to the structural feature is studied and the ability of W-BP to handle multimodal propagation is exploited to separate relevant damage-induced scattering from reflections due to the bend.