The Research On Monitoring Methods Of Thermal Stress Of Cwr Based On Rail Guided Wave

With the rapid development of China’s railway,continuous welded rail is widely used in high-speed railway and urban rail transit.Although continuous welded rail improves the stability of train operation,due to the elimination of rail gap,the constrained rail can’t expand freely under the change of temperature,and there will be a huge thermal stress inside the rail,which can cause rail buckling and broken rails accidents in serious cases.These accidents would have a huge impact on the economy and operation safety.However,most of the existing detection methods need to be detected in the skylight time,which can’t meet the requirements of high-density railway transportation.Therefore,it is of great significance to realize online monitoring of rail temperature stress and timely alarm before exceeding the limit for the safe operation of CWR.In this thesis,the problem of thermal stress monitoring for continuous welded rail is discussed.Compared with the existing detection methods,the feasibility of using the ultrasonic guided wave as the monitoring method of the temperature stress of the rail is Studied.By studying the dispersion characteristics of the ultrasonic guided wave in the rail and improving the original index calculation method,the guide wave mode selection index is established.And it will provide a more objective reference for the formulation of the guide wave excitation scheme.The dispersion curves of CHN60 rail are objected in 5k Hz by semi analytical finite element method and finite element method in this thesis.And the correctness of semi analytical finite element method also is verified.Combined with simulation,the modal selection index based on frequency factor,stress sensitivity factor,mode factor,excitation deviation factor and modal identification factor is established from the practical point of view.According to the entropy weight method,the influence degree of each factor on the guide wave excitation scheme is evaluated objectively.Finally,the optimal excitation point is obtained in the x-direction of No.94 rail waist node at 40 k Hz.In addition,the influence of different receiving modes on the measurement of guided wave group velocity is studied,and the best receiving mode and receiving position in line with the actual situation also are determined.The influence of fastener on guided wave mode can be ignored at the high frequency above 1000 Hz by analyzing results.Finally,the influence degree of different rail wear on guided wave mode is analyzed and compared in this thesis.It is concluded that the rail wear mainly affects the high-order modes of guided waves,which is verified that the group velocity of the selected guided wave mode is only sensitive to temperature stress,and the rationality of the selected scheme is further confirmed.