Design Of Magnetic Flux Leakage Signal Detection System For Top Surface Crack Of Rail

With the rapid development of high-speed rail and subway,the mileage and operation scale of Chinese rail transit has increased in recent years.The safety of rails is the basis of rail transit safety.Due to the repeated extrusion,friction and impact of train wheels,rails may be damaged.Initial rail cracks are usually small and concentrate on the top of a rail.This paper focuses on the non-destructive testing technology of crack on the top surface of rails,and develops a non-contact magnetic flux leakage(MFL)detection system.The system software and hardware are designed and the effectiveness of the system is verified by experiments.It provides an effective technical means for the detection of cracks on the top surface of steel rails.In this paper,the formation mechanism,the magnetic circuit and the distribution of the leakage magnetic field(LMF)are studied.According to the characteristic of the LMF in z-direction,a differential sensor probe structure is designed.On this basis,the appropriate sampling speed is determined according to the size of the defect,the inspection speed and other factors.The reasonable spacing of two differential sensors is derived.The relationship between the LMF strength and the magnetic reluctance is analyzed,and a leakage magnetic field enhancement method based on ferrite magnetism gatherer(FMG)is proposed.The influence of the section shape of the FMG on the LMF is studied by simulation.The FMG with square cross section has strong magnetizing effect and can enhance the signal better.Furthermore,the influence of square side length on the magnetic focusing ability is studied.It is found by simulation that the larger the side length,the better the magnetic focusing ability of the FMG,but the larger the interference of vibration and other factors during the inspection.On the basis of both enhancing signal and suppressing interference,the appropriate side length is determined.Based on these research and simulation,a non-contact MFL detection system is designed.The system uses FMG to enhance the signal and use differential probe to suppress interference.Experiment results on artificial defects and natural defect samples show that the designed system can increase the amplitude of the defect signal and effectively suppress the vibration interference.