A Magnetic Field Concentration Method for Magnetic Flux Leakage Detection of Rail-Top Surface Cracks

Magnetic Field Leakage (MFL) is one of the prominent methods used to detect rail top surface cracks. However, it has been shown that detecting narrow rail top cracks is a major challenge because of their weak magnetic leakage fields. This paper proposes a method to enhance MFL signals by using magnetic field concentration sheets. First, a simulation model of a cylindrical magnet is designed to analyze the stability of magnetic concentration effects in a uniform magnetic field environment with sheets of different sizes and types. Next, the simulation process is extended to investigate the effects of the magnetic concentration sheets on the leakage fields resulting from rail cracks. Meanwhile, a magnetic circuit model is built to analyze the magnetic field concentration mechanism. To validate the proposed method, a data acquisition system and an inspection trolley equipped with a magnetic field concentrating sheet are designed to detect artificially produced cracks on a rail top surface. Experimental results show that the proposed method can enhance the magnetic leakage field strength resulting from the cracks and improve the signal-to-noise ratio of the MFL signals. These results prove the benefits of the proposed method to rail top inspection efforts by reducing the probability of missing minor cracks when using the magnetic field concentration method.