Research On Rail Bottom Defect Detection Technology Based On Ultrasonic Guided Wave

High speed railways are one of China’s shining business cards,and the normal state of steel rail tracks is related to driving safety.Therefore,steel rail inspection has always been a focus of attention in the railway industry.At present,there is a blind spot in the detection of rail bottom by traditional detection methods.Based on the ultrasonic guided wave technology,this thesis uses numerical simulation method and experimental research method to complete the actual detection research of rail bottom defects,which promotes the application of time-domain finite difference method in the field of ultrasonic simulation,and provides technical support for the research of nondestructive detection of steel rail bottom.This article takes the actual project of the Key Laboratory of Electromagnetic Environmental Effects and Information Processing in Hebei Province as the background,and collaborates with relevant central enterprises to conduct research on rail bottom detection technology based on ultrasonic guided waves.The main work is as follows:(1)Simulation analysis of the propagation characteristics of ultrasonic guided waves at the bottom of the rail.A method combining analogy method and numerical simulation method was studied to address the blind spot issue in rail bottom detection.The guided wave in the rail bottom was compared with the Lamb wave in the plate,and the Lamb wave dispersion curve in the plate was plotted using analytical method.The similarity between the A0 mode in the plate and the vertical vibration mode of the rail bottom was analyzed.The finite element method is used to model and simulate the simplified model of the rail bottom and the three-dimensional model of the rail bottom.The group velocity verification method is used to obtain a single A0 mode guided wave.The characteristic frequency method is used to analyze the energy distribution of the low,medium,and high frequency guided waves propagating at the rail bottom.64 k Hz is determined as the optimal frequency for rail bottom detection,providing guidance for the design of subsequent rail bottom guided wave detection schemes.(2)Research on Ultrasonic Guided Wave Rail Bottom Defect Detection.The finite element method is used to simulate the propagation characteristics of ultrasonic guided waves in the case of cracks on the rail bottom,and the influence of the three detection positions of rail head,rail waist and rail bottom on the propagation of guided waves is analyzed.Based on the energy analysis method,the energy distribution in the process of guided wave propagation is analyzed by comparing the echo signal and the field displacement diagram,and the conclusion that the best excitation position for rail bottom detection is the upper surface of the rail bottom is reached.The spontaneous self harvesting excitation method was successfully studied to detect and locate cracks with different lengths and widths of 1mm at the bottom of the rail,with an error range of 2%.An experimental environment was established outdoors,and a guided wave detection system was established.Compared with theoretical values,group velocity verification and crack defect detection experiments of different lengths were achieved.(3)Research on ultrasonic guided wave detection based on finite difference time-domain method.In order to reduce the dependence on the traditional business simulation software,the wave equation of sound waves in steel materials was preliminarily calculated and simulated using the time-domain finite difference method.The self-developed software simulated the propagation process of guided waves in the simplified rail model,obtained the received signal data,and compared with the simulation results of commercial software to verify the correctness of the software.