Research On High-speed Switch Rail Fracture Detection Based On Elastic Wave Prepagation

With the gradual formation of China’s high-speed railway network,turnouts are the weak link of high-speed railway and the key point of maintenance.The detection of damage and fracture of switch rails has become a technical problem to be solved urgently.As a method of non-destructive detection,Elastic wave detection can judge the structure integrity by analyzing its signal.The research and its application have practical significance on the fracture detection of high-speed railway turnouts based on elastic wave propagation.The purpose of this paper is to detect the damage of the switch rail of the actual highspeed railway.Through the combination of finite element simulation and field test,the basic properties of the elastic wave and the feasibility of its application in the detection of the switch rail fracture are studied.The elastic wave signal feature extraction and recognition method proposed in this paper analyzes the recognition accuracy and recognition efficiency of elastic wave detection.The specific research conclusions are as follows:(1)Based on the semi-analytical finite element method to draw the dispersion curve of the 60D40 rail section,it can be concluded that there is a certain difference between the dispersion curve of the symmetrical section and the asymmetrical section.There are four initial modes of 60D40 rail.As the frequency increases,the number of modes of the rail gradually increases,and the dispersion curve appears to be coupled,which is likely to cause mode conversion.(2)Combining the actual cutting and pressing process of the switch rail,establish the switch rail model by defining the shape and path of the milling cutter,and consider the boundary conditions of the switch rail bolt hole,spacer iron,curved basic rail and under the rail foundation,and establish the No.18 high-speed turnout switch Model of tracker area.When the tip rail is completely broken,applying displacement excitation to the heel end of the tip rail can still extract effective signals at the tip of the tip rail,indicating that the elastic wave can be transmitted through the tip rail close-fitting area,the spacer rail and the foundation under the rail.When conducting elastic wave fracture detection,the boundary conditions of the switch rail should be considered.(3)Through finite element simulation and experimental verification,study three different excitation frequencies of low frequency 30 k Hz,intermediate frequency 60 k Hz,high frequency 90 k Hz,four different excitation modes of rail bottom vertical,horizontal,rail head vertical,and horizontal in the tip rail The propagation characteristics.As the excitation frequency increases,the dispersion and attenuation of the elastic wave gradually increase,and it is difficult to distinguish the excitation wave from the damage echo.Vertical excitation at the bottom of the rail can excite a single-mode,energy-concentrated elastic wave,and the rail head is vertical.Directional excitation can excite elastic waves whose energy is concentrated at the head of the rail and propagate.The 30 k Hz rail bottom vertical excitation is the effective excitation method for rail bottom fracture detection,and the 30 k Hz rail head vertical excitation is the effective excitation method for rail head fracture detection.(4)A signal feature extraction and identification method based on signal time domain,frequency domain,and frequency domain is proposed.The simulation results of the finite element model of switch show that the method can effectively identify the broken switch rail which occupies 2.43% of the rail bottom area and more than 4.90% of the rail head area,and as the degree of fracture deepens,the signal feature quantity changes regularly.The fracture level and the level of the point rail can be determined based on the identification of the signal feature quantity.The location of the fracture is analyzed.