Feature-guided waves (FGW) in plate structures with 90° transverse bends

Ultrasonic guided waves are attractive for rapid remote screening of large structures and today they are widely used in several practical applications including the inspection of pipe and plate installations. More recently, guided wave modal solutions confined in extended local features have attracted much research interest, offering the possibility of inspecting complex geometric or topographical features. Such feature-guided wave (FGW) modes have been reported in plate waveguides with local cross-section variation or curvature, and in annular circular cylinders with cross-sectional anomalies. This paper focuses on FGW phenomena in 90 degree structural bends in plate structures, which commonly occur in various industrial structures. Modal studies are carried out using the Semi-Analytical Finite Element (SAFE) method, while 3D finite element (FE) simulations are used to gain visualization of results and also obtain cross-validation. Our studies reveal, perhaps for the first time, the possibility of bend-guided modes of the shear-horizontal (SH) family, in addition those of the Rayleigh-Lamb family reported earlier in the literature. This mode has attractive properties including low attenuation and limited dispersion. We investigate effects of plate thickness and bend radius on the physics of FGW in bends, arguing the strong role of geometry and curvature effects in causing mode confinement. Preliminary experiments have also been carried out to validate the existence of such bend-guided mode.