Research On Health Monitoring Techniques Of Rail Bottom Based On Ultrasonic Guided Waves

With the rapid development of railway construction, railway safety issues are increasingly concerned about. A large number of rail tracks have been working under dynamic load, which are prone to corrosions, deformations, wears, cracks and even fractures, causing increasingly serious threats to railway transport safety. Nondestructive testing technology of rails mainly based on Ultrasonic inspection has the detection blind spots in the rail bottom edge. Health monitoring techniques of rail bottom based on ultrasonic guided wave, combining the advantages of ultrasonic guided wave and structural health monitoring, can detect the structural integrity of entire rail base without affecting the normal operation of trains by permanently installing ultrasonic guided wave transducers on the rail base, which doesn’t need extra manpower and time, greatly improves the detection efficiency. In this dissertation, the magnetostrictive ultrasonic guided wave transducer was firstly analyzed and designed. A monitoring algorithm for rail bottom, which can overcome various monitoring influence factors, track signal change, capture and extract defects, was also proposed. Finally, a scheme of rail bottom monitoring system based on ultrasonic guided wave was proposed, and the corresponding multichannel rail bottom structural health monitoring system was developed. The details of this dissertation were presented as follows:Chapter 1, the importance of rail bottom structural health monitoring was analyzed. The research status and development trends of this technique were summarized to clarify the main issues waiting to be addressed in this dissertation.Chapter 2, the basic concept and characteristics of ultrasonic guided wave firstly introduced. Then the appropriate mode and frequency of ultrasonic guided waves for the detection of rail bottom were analyzed. Subsequently, the design and layout scheme of magnetostrictive guided wave transducer were presented. And finally the feasibility and sensitivity of magnetostrictive ultrasonic guided wave to defects were studied.Chapter 3, the influence factors of rail bottom structurral health monitoring, such as temperature, the stability of system power, the performance of guided wave transducer, rail structure, were studied by experiments.Chapter 4, on the one hand, an algorithm overcoming the monitoring influence factors based on reference signal subtraction and temperature compensation was proposed. On the other hand, an algorithm which can automatically track and extract defects based on attenuation compensation, power operation and SVD was proposed. Finally, the reliability of the monitoring algorithm combing the above two algorithms was verified by experiments.Chapter 5, according to the system function goals, the multichannel rail bottom structural health monitoring system based on ultrasonic guided wave was developed, and the feasibility of the system was tested in the practical application.Chapter 6, the main work and conclusions were summarized and the prospect for further research was put forward.