Characterisation on rolling contact fatigue cracks in high-speed railway rails using ACFM By signals

Rolling contact fatigue (RCF) cracks are a critical factor affecting the operational safety of high-speed railway rails. As a non-contact electromagnetic non-destructive testing method, Alternating Current Field Measurement (ACFM) has been widely applied in the detection and quantitative evaluation of surface cracks. Existing techniques primarily rely on the Bx and the Bz signal components to assess crack length and depth. However, the potential of the By signal for characterising the spatial morphology of cracks has not been fully explored. In this study, a finite element model was developed to simulate the ACFM response of typical RCF cracks. The effects of crack length, pocket depth and inclination angle on the By signal were systematically investigated. A novel crack morphology estimation method based on the extraction of peak-valley features from the By signal is proposed. The results demonstrate that the By signal exhibits higher sensitivity to variations in surface crack length, pocket depth and inclination angle, providing a more efficient and accurate reflection of crack geometry. This approach offers both theoretical support and methodological innovation for the rapid identification and intelligent assessment of RCF cracks in high-speed railway systems.