Defects evaluation near edges of structural elements using the fundamental mode of edge waves

Abstract

Structural elements with edges are widely used across many industries and applications; examples include tapered flange beams and the footing of rail tracks. The distant defect inspection of these structures using the conventional guided wave techniques can be challenging because of multiple wave reflections, dispersion, and wave modes coupling. In this article, the quasi-fundamental antisymmetric mode of edge wave (QEA0) is proposed for evaluation of defects emanating from curved edges. In the beginning, the dispersion properties and the modal displacement profiles of QEA0 are studied using the Semi-Analytical Finite Element (SAFE) method; and then the results are validated against outcomes of direct numerical simulations and an experimental study. The SAFE method demonstrated the feasibility of calculating the dispersion properties and the modal displacement profiles for the fundamental modes of edge waves propagating along ideal or non-ideal (rounded) edges. The proposed QEA0 mode has several advantages compared with the conventional guided waves as well as its symmetric counterpart, i.e., the quasifundamental symmetric mode of edge wave (QES0). The latter was found to have a limited range of propagation distances along curved edges. In contrast, the QEA0 mode propagates for much longer distances without significant decay. In addition, this guided wave mode is sensitive to small defects with the characteristic depth of more than 0.1 wavelength, and the defect reflection ratio is found to have a good correlation with the defect size. The reflected waves also allow to distinguish multiple defects as well as to determine their locations. Overall, the QEA0 mode shows a great potential for the purpose of non-destructive evaluation (NDE) and structural health monitoring (SHM) of structural edges with complex cross-sectional areas.