Research On Guided Wave Propagation Characteristics And Damage Identification Of High Speed Railway Turnout Rail

Under the action of the train load,the crack of the turnout rail will accelerate its expansion,and in severe cases,it will cause a rail breakage accident.At present,ultrasonic body waves are mainly used to detect cracks.Due to the complex structure of high-speed turnouts and the existence of special-shaped and variable-section rails,there is a blind spot for flaw detection in turnout rails,and full-section detection and real-time online monitoring cannot be realized.Ultrasonic guided waves are sensitive to cracks and can overcome the above shortcomings,and are the most promising crack detection technology.However,at present,the complex phenomenon of guided wave propagation caused by the special-shaped and variable cross-section of the turnout rail has not been deeply studied,which leads to great difficulties in the analysis of the interaction mechanism between the guided wave and the crack in the turnout rail.Aiming at the above problems,this paper proposes a method for identifying cracks in turnout rails based on ultrasonic guided waves.This paper studies key issues such as the propagation characteristics of guided waves,target wave mode excitation and crack detection in turnout rails,which lays a theoretical foundation for the realization of turnout rail crack detection and monitoring.The main research contents are as follows:1.Research on the propagation characteristics of the guided wave on the turnout railBased on the semi-analytical finite element method,the waveguide characteristics of the stock rail and the variable-section straight switch rail were respectively revealed,and the wavenumber dispersion curve and phase velocity dispersion curve of different waveguides were calculated and analyzed.The concept of three-dimensional dispersion surface containing wavenumber-frequency-position information is proposed,draws the modal displacement and deformation diagram of the guided wave at different frequencies,and reveals the difference between the dispersion characteristics of constant cross-section and variable cross-section.The results show that,different from the constant-section rail,when the modal displacement deformation is located in the variable-section region of the switch rail,the dispersion characteristics of the guided-wave mode and the guided-wave mode change with the change of position/section.Based on this,a "dispersion surface" is proposed to describe the dispersion characteristics of variable cross-section rails.The correctness of the analysis method is verified by finite element simulation and field test.2.Research on the excitation method of the guided wave mode of the switch railAiming at the problem of target wave mode excitation,the paper proposes a rail guided wave mode excitation method based on semi-analytical finite element method excitation response analysis and normal mode expansion method.This method can determine the optimal excitation position and signal receiving position of the target wave mode on the outer contour of the rail.When the frequency of the excitation signal is low,there are few guided wave modes,and the optimal excitation position can be found through the wave structure for single-point excitation;when the frequency of the excitation signal is high,there are many guided wave modes,and it is necessary to combine the array excitation method to excite the desired wave at the same time.The specific guided wave modes in the stock rail and the straight switch rail are excited by finite element simulation,which proves the effectiveness of the guided wave mode excitation method and lays a foundation for subsequent crack detection.3.Research on linear ultrasonic testing of switch rail cracksThe finite element method is used to study the influence of different degrees of damage on the propagation characteristics of guided waves in turnout rails.On the basis of selecting the best detection mode and excitation mode of guided wave,the quantitative relationship between the echo characteristic parameters of each defect and the geometric size of the defect section was established by setting different defect section sizes,and the interaction law of guided wave with different frequencies and the reflection characteristics of guided wave at different defects were analyzed.A single mode extraction algorithm based on the excitation response inverse transform is studied,and the number of wave modes is simplified through the two-dimensional Fourier transform.Through this algorithm,the reflected echo time domain signal of each wave mode can be separated,and the rail crack identification can be realized.4.Research on nonlinear ultrasonic testing of switch rail cracksThe nonlinear phenomenon of contact acoustic in turnout rails is studied by using nonlinear ultrasonic mixing technology.The finite element model of the turnout rail with close-fitting cracks is established.By selecting the mixing mode pairs suitable for damage detection at different positions,the influence of different mixing mode pairs and the size of the crack on the mixing signal are studied.The results show that the interaction between the guide wave of the switch rail and the crack can generate a mixing signal,and the mixing signal increases significantly with the increase of the crack size.Through the two-dimensional Fourier transform,it is found that a variety of guided wave modes are generated at the frequency mixing and frequency doubling under the interaction between the guided wave and the crack,and the guided wave mode with the largest mixing amplitude is related to the type of the fundamental frequency guided wave mode.At the same time,field tests are carried out to verify the damage detection capability of nonlinear ultrasonic mixing,which can provide a basis for the characterization and evaluation of turnout rail damage.