Detection of defects in rail bolt holes based on ultrasonic guided waves

Minor defects are easy to appear at the rail web bolt holes, which seriously affect the safety of trains when passing through, and accurately identifying the bolt hole defects is crucial. Leveraging the symmetry of the rails, this study proposes an innovative guided wave signal processing workflow. This enables the orientation determination and relative size identification of millimetre-scale defects in rail bolt holes. In this paper, a comb excitation method based on the group velocity principle is employed to obtain a single guided wave mode for the detection of bolt holes in the rail web. Then, millimetre-scale defects were fabricated by a hybrid division of hexahedral and tetrahedral elements. The model utilises a circular dot matrix on both sides of the rail web as the signal receiving points. The symmetry of rails is used to superimpose the signals and apply a band-pass filtering process. This allows for the successful localisation of defects in eight positions of bolt holes using cumulative amplitude intensity and normalised dynamic time warping. The model also investigates the relative size recognition of bolt hole defects in terms of length and depth. Furthermore, the feasibility of detecting bolt hole defects was experimentally validated.