Research On Electromagnetic Testing Technology For Internal Hole Defects Of High Speed Train Hollow Axle

The defects in the hollow axle of high-speed train can not be ignored.Under the external impact and distortion,these defects will lead to fatigue fracture of the axle.Early detection of defects in axles can effectively reduce the possibility of accidents.Therefore,it is very important to detect defects of hollow axle by nondestructive testing.At present,there are some shortcomings in the near-surface defects detection methods of hollow axle inner hole wall at home and abroad.Based on the analysis of the research status of defect detection technology of hollow axle and planar array electromagnetic sensor,the electromagnetic detection technology of internal hole defects of high speed train hollow axle is explored and studied in this paper.The main research contents are as follows:The detection mechanism of the research topic is analyzed.The principle of eddy current testing and the working mechanism of planar array electromagnetic sensor are expounded.The planar array electromagnetic testing is analyzed theoretically.The formula of eddy current penetration depth of planar array sensor is derived from the differential form of Maxwell equations,and the relationship between the penetration depth and signal frequency,sensor wavelength and material properties is analyzed.A planar array electromagnetic sensor for detecting inner wall defects of hollow axle is designed.The wavelength of the sensor is determined by analyzing the penetration depth formula of the planar array eddy current sensor,and the structure of the excitation coil and the detection coil is analyzed by constructing the simulation model.Then the linewidth and the longitudinal length of the excitation coil are determined by the defect detection simulation model of the sensor unit.Finally,the structural parameters of the sensor are explained.A defect detection system is designed based on sensors.The hardware part generates the current signal loaded on the excitation coil of the sensor and collects the output signal of the sensor.LabVIEW programming software is used in the computer to further process the signal.Orthogonal vector lock-in amplification method is used to extract effective signals from multiple channels of the array sensor.A sensor calibration algorithm is proposed to complete sensor calibration combined with least square method.A hidden defect discrimination algorithm is proposed to complete defect judgment based on grabbs criterion.A hollow axle inner hole wall defect detection system testing platform is built,and test the hidden defects in different hidden depths,different lengths.verify the detection ability of the planar array eddy current sensor designed in this study.