The Basic Research On On-Line Monitoring Of Stress In Continuously Welded Rails Based On Ultrasonic Guided Waves

A large number of continuous welded rails (CWR) this new type of track structure are used on high-speed railway and the main line in China. Stress in CWR is tremendous when the rail temperature variation is very large, this will directly affect the safety of rail traffic. On-line monitoring stress of high-speed CWR in real time and warning when stress exceeds the limit are of great theoretical and practical significance for the safe of high-speed rail and enhancing the infrastructure detecting level of existing line.Monitoring internal temperature stress in CWR is a worldwide hard problem. For existing problems, a new method based on ultrasonic guided waves is proposed. Compared to ultrasonic bulk waves, guided waves provide larger monitoring ranges and the complete coverage of the waveguide cross-section. The principle of detection welded rails’ internal temperature stress is based on acousto-elasticity. It is very simple. But there are still a lot of problems need to study because of the complexities of guided wave. These complexities include the existence of multiple modes and the frequency dependent velocities. First and foremost, guided wave dispersion curves in our country’s CWR are needed to be acquired, it is the premise to study guided waves’ vibration characteristics. Second, we need to select the optimal mode used to detect stress in CWR. Finally, we need to find the method to excite the optimal mode in CWR.To solve above problems, the characteristics of different modes of ultrasonic guided waves in CHN60CWR are studied in-depth through theoretical analysis and simulation.The main innovations include:1. A semi-analytical finite element method is developed and the ultrasonic guided wave dispersion curves in CHN60rail are acquiredBy traditional finite element modal analysis method, complete dispersion curves of ultrasonic guided wave can’t be obtained. Semi-analytical finite element method is an effective method which is used internationally, to solve frequency dispersion curves of any cross section of the waveguide medium. However, Chinese related research can only be conducted through the purchase of semi-analytical finite element software abroad. After reading a lot of related papers, the semi-analytical finite element method has been designed by Matlab software in this paper.This dissertation first obtains the dispersion curves of CHN60continuous welded rail by semi-analytical finite element method. Combined with mode analysis, exciting and response analysis, stress sensitivity analysis and other methods, the vibration and propagation characteristics of each guided wave mode in CWR have been obtained, which provides a theoretical reference basis for the detection service of Chinese CWR broken rail infrastructure and rail stress.2. An indicator model to select the optimal guided wave mode is proposedBased on frequency, stress sensitivity, mode of vibration, exciting position and the mode identification those five factors, the dissertation first proposed the indicator model to select the optimal guided-wave mode. With this model, the most suitable ultrasonic guided-wave mode can be quickly selected for CWR stress testing system, which achieves a transfer from theoretical analysis to engineering application.3. A location algorithm of the optimal exciting position is designedAccording to vibration characteristics of each ultrasonic guided-wave mode, combined with the analysis results of stimulation and response, the dissertation designs the location algorithm of the optimal exciting position. Through drawing three degrees of displacement curve of guided wave mode, filtering out smaller extreme point based on statistical regularities, the algorithm gets the exciting position of the feature points of each guided wave mode. It does not require repeating experiments and promotes the efficiency in engineering application.The field experiment has been performed in Xi’an-Baoji high-speed railway, using selected ultrasonic guided wave mode and exciting position in the dissertation. Experimental results show that the location algorithm can give the exciting position and direction fast and correctly. The selected mode by indicator model is easy to excite and used in field line. This mode is sensitive to stress and has long propagation distance, it is very suitable for stress monitoring in continuous welded rails.