Simulation Analysis Of Crack Identification Of High-Speed Railway Turnout With Movable Point Rail Based On Ultrasonic Guided Wave

Turnout is the weak link of high-speed railway line and the key point of maintenance.The damage and fracture detection of turnout point rail has become an urgent technical problem to be solved.Ultrasonic guided wave nondestructive testing technology has the advantages of long detection distance,full-section detection,and high detection efficiency.The technology has achieved good application in the damage detection of slender components such as rails with equal sections in section lines.It also shows application potential for damage detection of variable cross-section rails.This paper combines theoretical analysis,numerical simulation and experimental research to conduct a relatively complete study of the excitation,propagation and reception of ultrasonic guided waves in point rail.The specific research contents and conclusions are as follows:(1)The semi-analytical finite element model of each key section of the point rail is established,the dispersion characteristics of the point rail section are theoretically solved,and the guided wave excitation frequency and guided wave mode suitable for the point rail damage detection are selected at the theoretical level.It is found that in the process of the guided wave propagating from the heel end of the point rail to the tip,mode conversion is easy to occur due to the variable cross-section characteristics of the point rail,and it will be difficult to excite a single guided wave mode.(2)The semi-analytical finite element models of 60D40 rails with different wear degrees were established respectively to study the effect of wear on the dispersion characteristics of the point rail.The research shows that the insensitive wave mode with small change in group velocity mainly propagates through the rail web and the rail bottom,which is suitable for the damage detection of the rail web and rail bottom after wear.Sensitive wave modes with large changes in group velocity mainly propagate through the rail head and the full section.The wear factor of the rail head in the service rail should be considered when selecting the sensitive wave mode for damage identification,so as to improve the damage identification accuracy of ultrasonic guided wave inspection.(3)A finite element model of the movable point rail of a high-speed railway turnout is established,and the influence of the slide bed platen and the bolt holes of the rail waist is considered in the modeling.The close contact between the sliding bed platen and the bottom of the point rail produces a nonlinear effect,and a frequency-doubling signal appears on the platen and the point rail at the same cross-sectional position;the higher the excitation frequency,the greater the influence of the bolt hole on the guided wave propagation in the point rail.The excitation is applied to different parts of the finite element model with and without bolt holes.In terms of the time domain signal response difference,the response at the rail waist position is much larger than that at the rail head position and greater than the rail bottom position.The comparison between the experimental results and the simulation results shows that the established point rail finite element model can effectively describe the propagation process of guided waves.(4)By using different excitation methods to simulate the finite element model of the point rail,it is shown that 30 kHz is the appropriate excitation frequency for selecting the excitation mode for damage detection in the long point rail and the short point rail.The difference is that vertical excitation is applied to the heel end for the damage detection of the rail bottom and rail head of the long point rail,and vertical excitation is applied to the rail bottom at the bending point for the damage detection of the short point rail.The point rail head damage detection applies vertical excitation to the rail head at the heel end.The difference lies in the choice of the excitation position,the damage detection of the rail bottom and rail head of the long point rail chooses to apply vertical excitation at the heel end.For the damage detection of the rail bottom of the short point rail,vertical excitation is applied to the rail bottom at the bending point,and vertical excitation is applied to the rail head at the heel end for the damage detection of the rail head.(5)The influence of cracks at different positions along the longitudinal direction and cracks with different cracking degrees in the cross section on damage identification is studied by simulation.The cross-correlation coefficient in the time domain and the wavelet transform results in the frequency domain are used as indicators to effectively identify the damage of the point rail.