Research On Rail Crack Detection Technology Based On Alternating Current Field Measurement (ACFM) Principle

The long-term rolling contact of the service rails with the wheels will cause fatigue cracks on the rail surface.The initiation and expansion of rail fatigue cracks not only increase the operating cost of the railway,but also directly endanger the driving safety in severe cases.Studying the detection of rail cracks and carrying out the detection and evaluation of rail surface cracks are beneficial to guide on-site rail maintenance operations(such as rail grinding,etc.),so as to eliminate cracks or slow down the propagation process of cracks,which is of great significance to ensure the safe operation of railway systems.Alternating Current Field Measurement(ACFM)technology has the advantages of fast detection speed,non-contact measurement,quantitative detection,etc.,and has obvious advantages in rail crack detection.Therefore,in this paper,the method of combining finite element simulation and experimental verification is used to study the problem of rail crack detection based on ACFM.Aiming at the detection of rail cracks,the simulation model of rail crack detection based on ACFM was established.According to the simulation analysis results,the ACFM-based rail crack detection device was designed and built;Considering that the signal is easily affected by many factors in the actual detection process,the influence of different system parameters and crack size on the ACFM signal was analyzed by using eigenvalue analysis method.Different types of complex cracks and rail cracks were detected by the ACFM-based rail crack detection device,and the effectiveness of the rail crack detection method based on ACFM was verified.The main conclusions of the research are as follows:(1)Based on the principle of ACFM technology,using ANSYS Maxwell software,the simulation model of rail crack detection based on ACFM was established,and the electromagnetic field distribution law around the rail crack and the distortion law of ACFM signal were analyzed.The influence of the sensor spacing of the array probe on the ACFM signal was simulated and studied,and the reasonable design range of the sensor spacing was obtained.(2)Based on the simulation analysis results,the ACFM-based rail crack detection device was designed and built.On the basis of the traditional single probe,an array probe was designed,and a signal conditioning circuit was designed according to the characteristics of the application circuit.The host computer software based on Lab VIEW was developed,and the visual detection methods based on the time-base scanning graph,butterfly graph and contour color graph were realized respectively.(3)Using the ACFM-based rail crack detection device,combined with the amplitude variation and the sensitivity eigenvalues,the influence of various factors on the ACFM signal in the actual detection process,such as the frequency and amplitude of the excitation signal,the depth and length of the crack,the scanning method of the probe,the fluctuation of the probe,etc.,are studied.The influence of various factors on the ACFM signal provided a reference for parameter optimization of the rail crack detection device and quantitative detection of cracks.(4)Different types of cracks(rectangular cracks,clustered cracks,Y-shaped cracks and W-shaped cracks)were detected by array probes,and the change rule of magnetic field signals caused by different types of cracks was analyzed combined with the contour color map.The rail crack detection experiment was carried out with single probe and array probe,and the validity of the rail crack detection method based on ACFM was verified.