A Novel Probe of DC Electromagnetic NDT Based on Drag Effect: Design and Application in Crack Characterization of High-Speed Moving Ferromagnetic Material

Electromagnetic nondestructive testing (NDT) of high-speed moving ferromagnetic material is a challenging topic; due to the relative motion between ferromagnetic material and detection devices, motion-induced eddy current (MIEC) will be generated and the drag effect will show up, which result in a more complex magnetic field distribution in the ferromagnetic material than static or quasi-static testing. Therefore, an electromagnetic NDT probe, which is suitable for multiple crack detection in high-speed moving ferromagnetic materials, is urgently required. In this article, a novel probe of dc electromagnetic NDT based on drag effect is designed considering the strength and sensitivity of the detection signal by experiment, and then it is applied to crack characterization of high-speed moving ferromagnetic material. After that, the measurement uncertainty of the detection signal based on a multiconvolutional approach is investigated and estimated. The investigation indicated that the proposed probe can quantitatively characterize the multiple cracks at 20 m/s within the relative error and standard deviation of 10% when the crack depth is deeper than 1.0 mm; furthermore, the deeper the crack, the higher the experimental repeatability. Accordingly, the proposed probe can be expected to detect the multiple cracks in high-speed moving ferromagnetic materials, such as rotating bearings, pipelines, and high-speed railway.