Design Of Rail Crack Detection System Based On Ultrasonic Guided Wave

Rail is an important part of the track structure,which directly bears the load of the locomotive and the vehicle.During using,the cracks will inevitably appear on rails due to the long-term exposure to harsh environments,combined with various factors such as internal stress and impact load.If the cracks are not treated in time,any expansion of them will inevitably lead to the breakage of the rails,thus significantly increasing the probability of occurrence of accidents such as train derailment.At present,rail-defect detection vehicles based on ultrasonic testing technology are widely used on railways.It has the problems such as long hold-up time and inability to monitor in real time,which needs to be improved.In order to improve the detection efficiency of cracks on rail and realize the real-time detection,a set of online detection system for rail cracks is designed in this thesis.The thesis firstly analyzes the causes of the cracks on rails and the common forms of cracks on the rails.Based on the positions of cracks,the rail cracks are divided into head cracks,waist cracks and bottom cracks.After comprehensively compared the detection methods of rail cracks at home and abroad,the ultrasonic guided wave detection technology is selected as the basic research method.Based on the basic theory of ultrasonic guided waves,the corresponding excitation positions are selected according to the cracks at different positions,and the sine wave modulated by Hanning-window is determined as the excitation signal and 35kHz is determined as the optimal excitation frequency.Through the simulation experiments on the 3D finite element model of cracks on the rail head,rail waist and rail bottom,the correctness of the selected excitation signal is verified.In addition,three kinds of guided wave modes that suitable for detecting the cracks on the rail head,rail waist and rail bottom are selected.Using the detection device that consisting of general-purpose equipment to carry out crack detection experiments on the rails in the laboratory,an effective detection of cracks at various positions of the rail is realized,and the error rate is less than 2%.On this basis,the design scheme of the rail crack detection system based on ultrasonic guided wave is developed.In this way,a set of detection devices that can realize real-time monitoring of rail cracks,including the hardware system and the software system.Targeting on the functions of guided wave signal excitation,echo signal reception and data storage etc.,the design scheme of crack detection system that based on STM32 and FPGA is adopted.Of this,ultrasonic guided wave transmitting circuit realizes the functions of guided wave signal generation,D/A conversion,differential amplification,low-pass filtering and power amplification etc.And ultrasonic guided wave receiving circuit realizes the functions of amplification filtering of echo signal,A/D conversion,and data buffering.FPGA uses the Verilog HDL hardware description language and IP core mixed programming method to construct a DDS module for generating guided signals,a FIFO module for data buffering,and a PLL module for clock management.By transplanting the ?C/OS-? operating system into the STM32 processor,the driver of LCD touch screen,SD card storage program and STM32 communication program were designed to realize the functions such as human-computer interaction,signal display and data storage.At last,the test of signal transmission and signal receiving functions of the rail crack detection device was carried out,and the transmission and reception functions were verified.Crack testing was performed on rails with head cracks,waist cracks,and bottom cracks.The final result shows that the rail crack detection system can identify the crack and determine its position,and the detection error rate is within 5%.