基于激光多普勒频移的钢轨缺陷监测

针对现阶段我国铁路上应用的探伤设备只能在天窗时间进行人工巡检,无法在线监测的问题,提出一种基于超声导波的激光多普勒频移法钢轨内部缺陷监测方法。首先,引入环境温度作为变量改进了半解析有限元方法,并应用该方法获得了我国无缝线路CHN60钢轨在特定温度下的频散曲线。通过分析振型并结合激励响应算法确定了适于检测缺陷的模态及其激励方式,从而激励该超声导波模态使其在钢轨中传播。然后,应用半反半透玻璃镜将激光分为参考光和测量光,测量光通过Bragg Cell进行频偏照射钢轨表面,通过反射光产生的多普勒频移与参考光干涉得到光强度变化曲线,经过信号处理及标定测得钢轨内部缺陷的回波速度信号,再经过数字化处理和计算得到缺陷的位置。最后,在北京环形铁路试验基地进行了现场实验,以钢轨接地孔模拟钢轨内部核伤,得到缺陷定位误差均小于0. 5 m,验证了该方法的可行性。使用激光多普勒频移方法检测导波信号从而定位缺陷的方法可以有效避免由于换能器接触性测量而产生的误差。该方法在不影响列车的正常运营的同时,实现了全天候无间断的在线监测,提高了检测效率。

Rail defect monitoring based on laser Doppler frequency shift theory

The flaw detection equipment applied on railway in China can only be inspected at the time of maintenance-skylight and cannot be on-line monitored at the present stage. A detection method of rail internal defects based on ultrasonic guided waves and laser Doppler frequency shift theory is proposed.First, the semi-analytical finite element method is improved by adding the environment temperature as a variable. The method is used to obtain the dispersion curve of the CHN60 rail in China at a specific temperature. Then, the modes which are suitable for the detection of defects and incentive methods have been selected through combining the analysis of mode shape with stimulation and response algorithm. Then, the laser is divided into reference light and measuring light by semi-transparent mirror. The measurement light is irradiated on the rail surface through Bragg Cell, and the change curve of the light intensity is obtained by the Doppler shift of reflected light and the interference of the reference light. The echo velocity signal of the internal defect of the rail is measured by signal processing and calibration. While this mode is stimulated and propagating in the railroad, the position of the defect can be detected after digital signal processing. Finally, the research group has conducted field experiments on the Beijing Ring Railway Experimental Base and verified the feasibility of the method. It shows that the error in defect location is less than 0.5 m. Using laser Doppler frequency shift method for guided wave signals to locate defects can effectively avoid the error caused by transducer contact measurement. It not only guarantees the normal operation of the train, but also realizes the all-weather on-line monitoring without interruption, which improves the detection efficiency.