| Railway is an important transportation infrastructure in China,and rail is an important part of railway infrastructure.With the rapid development of high-speed and heavy haul railways in China,the train operation density is increasing,and the load borne by the rail is increasing.The long-term impact of the train on the rail will gradually form fatigue cracks,which has become a major hidden danger affecting the driving safety.The rail crack detection method based on ultrasonic guided wave has the advantages of long detection distance,high efficiency and no detection blind area of rail bottom corner.Therefore,based on the previous theoretical research in the laboratory,this thesis designs and develops a set of rail crack ultrasonic guided wave integrated detection system to realize the excitation,acquisition,storage,analysis and remote transmission of steel rail ultrasonic guided wave,According to different application scenarios,the guided wave signal anomaly monitoring algorithm and rail bottom crack detection algorithm are studied,and the accuracy of the system in detecting rail cracks is verified through laboratory experiments,which is of great significance to improve the efficiency of rail crack detection on the railway site and ensure the safety of train operation.According to the requirements of the ultrasonic crack detection system based on the ultrasonic guided wave technology,this thesis puts forward the ultrasonic crack detection system based on the heterogeneous proccessor.The time-frequency domain characteristics of rail ultrasonic guided wave excitation source and ultrasonic guided wave propagating in rail are studied.Based on their characteristics,the guided wave excitation and acquisition hardware circuit is designed to realize the excitation and acquisition of rail ultrasonic guided wave.A heterogeneous dual core processing hardware system based on FPGA and ARM is designed,which provides a hardware platform for the acquisition,cache,analysis and transmission of long-distance and highspeed ultrasonic guided wave signals.According to the system characteristics of online monitoring scene and portable detection scene of rail crack,based on the designed dual core ultrasonic guided wave excitation and acquisition system,the remote rail crack ultrasonic guided wave online monitoring system and portable rail crack ultrasonic guided wave detection system are integrated.Aiming at the problem that the high-speed acquisition of rail long-distance ultrasonic guided wave requires high sampling rate,memory capacity and data processing rate of the system,this thesis studies the high-speed acquisition and cache mechanism of ultrasonic guided wave based on FPGA.The ARM end can flexibly request different excitation pulses,different acquisition time and rate,cache and share ultrasonic guided wave signals of any address and length from FPGA with large memory,Thus,the highspeed and large-capacity acquisition and cache of long-distance rail ultrasonic guided wave are realized,which provides flexible data support for the rail crack ultrasonic guided wave detection software system.According to the field application characteristics of rail crack detection system,the ARM end software system is designed to realize the flexible acquisition,storage,lightweight analysis and Ethernet transmission of rail guided wave signal.Aiming at the problem of long change period of rail guided wave signal and repeated uploading of normal signal,the monitoring algorithm of light rail ultrasonic guided wave abnormal signal is studied to monitor the abnormal guided wave data,which saves the communication bandwidth and shortens the monitoring cycle.Aiming at the blind area of rail bottom detection of traditional rail flaw detection methods,based on the designed rail crack ultrasonic guided wave detection system,the rail bottom crack detection algorithm based on ultrasonic guided wave is studied,and the identification and location of rail bottom crack are realized.Finally,the system performance,rail crack ultrasonic guided wave signal monitoring algorithm and rail bottom crack detection algorithm are verified by design experiments.The system performance verification experiment has completed the function test of system excitation and acquisition,and the performance evaluation of excitation circuit and acquisition circuit.It is proved that the system can realize narrow-band guided wave excitation and long-distance guided wave signal acquisition,in which the excitation guided wave signal can propagate 1000 meters,and the acquisition and storage depth is up to 60 M,which can meet the needs of rail crack detection on the railway site.Through the actual switch rail crack monitoring,it is proved that the guided wave signal monitoring algorithm of the system can detect the simulated crack of the switch rail mass block.Through the rail bottom crack detection experiment,the accuracy of the rail bottom crack identification and location algorithm is verified.The relative error of location is less than5%,which meets the detection requirements. |
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