Rail Web Buried Defect Location and Quantification Methods in Hybrid High-Order Guided Wave Detection

The development of electromagnetic ultrasonic guided wave testing technology has provided effective solutions for highly accurate positioning and quantification of rail defects and online real-time monitoring of rail health status. However, the principal limitation of the guided wave testing method is the difficulty in accurately obtaining a defect's depth and normal shift at the rail web. Therefore, we investigate the normal energy distribution characteristics of hybrid high-order SH-guided waves and propose a highly sensitive baseline-free depth quantification and normal location method for buried defects based on the guided wave relative energy coefficient Grec and guided wave relative order coefficient Groc. These methods can rapidly and accurately locate and quantify buried defects by obtaining reflected and transmitted wave energies of different guided wave orders. Furthermore, the simulation and experimental results and the proposed quantification theory are mutually verified. The results indicated that the proposed damage index Grec without time-domain reconstruction can improve the accuracy of depth quantification by at least 15%, and the performance of Groc-based defect normal shift quantification surpassed commercial scanning ultrasonic body wave detectors and eddy current detectors. In general, this work has the potential to promote high-sensitivity holographic real-time monitoring of rail defects in the future.