采用激光声磁技术检测钢轨踏面缺陷

Testing the defect of rail with laser-EMA ultrasonic method

钢轨踏面与车轮之间的滚动接触疲劳形成的大量表面缺陷严重危害着铁路行车安全,传统的无损检测(NDT)方法已不能适应铁路快速发展的需要。根据激光声磁技术的基本原理和钢轨踏面缺陷检测的特点,研究了钢轨踏面缺陷检测的激光声磁检测技术。通过对比激光声磁技术与压电超声检测钢轨踏面横向裂纹缺陷的实验,表明本文方法能准确的检测和定位踏面横向裂纹。通过小波阈值去噪技术对激光声磁信号进行处理,在保留了原始信号的各种特征的同时大大提高了信噪比(SNR),更有利于缺陷的识别和特征的提取。分析了提离效应对激光声磁信号的影响,获得了提离距离与接收信号幅值变化曲线图。实验结果表明,本文方法无需耦合剂、对钢轨表面状况要求低,可实现钢轨踏面缺陷的非接触、快速和准确的检测。

Rolling contact fatigue between the rail tread and the wheel can cause a large amount of surface flaws, and therefore can cause serious damage to the rail operation safety.The traditi onal nondestructive testing （NDT） is not suitable for the rail developing needs and we need to develop a new met hod.The laser-electro magnetic acoustic （EMA） testing system of rail tread is designed based on the pr inciples of the laser-EMA ultrasonic technology and the characteristics of the rail tread flaws.The comparison experiment is conducted by using the piezoelectric transition （PZT） and laser-EMA technology to test t he transverse crack in the rail tread.The results show that the method can preci sely test and locate the crack.From the laser-EMA signal proce ssed based on wavelet threshold denoising,it could be seen that the signal-to-noise ratio （SNR） is greatl y improved and all characteristics of the original signal are remained,which wi ll be convenient for the damage identification and feature extraction. We analyze the influence of left-off effect on the laser-EMA signal,and obtain the relation between the lift-off reffect of EMAT and signal amplitude.Experimenta l results show that this method is feasible and doens′t need coupling medium or good surface condit ions, and could realize non-contact,rapid scanning and precise testing to the rail t read.