Investigation on optimal detection position of DC electromagnetic NDT in crack characterization for high-speed rail track

Due to the long-term harsh working environment and cyclic loadings, Rolling Contact Fatigue (RCF) crack will occur on the tread of the rail. Therefore, a fast quantitative detection of cracks periodically is essential to guarantee the operation safety of the high-speed rail track. Electromagnetic Nondestructive testing (NDT) technique is one of the effective methods for quantitative crack characterization in conduction metals. For high-speed Electromagnetic NDT, because of the relative motion between the rail and detection device, motion induced eddy current (MIEC) is generated in the surface of the rail, which causes the magnetic field distribution inside the rail more complicated due to the dragging effect, and the literatures focus on the investigation on the optimal detection position is rare. Hence, to obtain the optimal detection sensitivity and strength, it is essential to investigate the optimal detection position in electromagnetic NDT for crack characterization in high speed. This paper perform a deep investigation on the optimal detection position in direct current (DC) electromagnetic NDT by numerical simulation, and the influence of detecting position on the detecting signal at different speeds is investigated. The results show that the DC Electromagnetic NDT can be used for quantitative crack depth characterization, and the optimal detection position with strongest detection signal and high sensitivity for crack depth characterization is located near the inner edge of the excitation coil on the opposite side of the direction of the probe motion. According to the findings in this paper, the high-speed DC electromagnetic NDT method can be applied to other moving metal components crack characterization, such as rotating metal components and pipelines.