Design Of Thermal Stress Detection System For Continuous Welded Rails Based On Ultrasonic Guided Waves

With the development of high-speed, continuous welded rail (CWR), due to eliminate the rail joints, greatly improve the track structure and reduce vibration, is widely used. But because of the disappearance of rail joints, rail cannot expand freely when temperature changes. So the rail internally generates thermal stress which may lead to track buckling and break rail, seriously affecting road safety. Therefore, a fast and accurate rail thermal stress detection method to prevent the track buckling, break rail and accident occurring is of great significance to ensure the safety of railway.This paper focuses on the rail temperature stress detection method based on ultrasonic guided waves, and completed the rail temperature stress detection systems based on elasticity theory, the ultrasonic guided wave transducers, high voltage driver circuit boards, high-speed multi-function receiver circuit boards.The paper introduces the propagation characteristics of ultrasonic guided wave in the rail, the theoretical basis of the rail thermal stress detection method based on ultrasonic:acoustic-elasticity principle, and designed the ultrasonic guided wave exciting circuit based on PIC and FPGA and receiving circuit based on ARM and FPGA. The system achieved the excitation for ultrasonic guided waves. And also achieved guided wave signal reception, storage and processing of two-way ultrasonic guided wave signal. By writing procedures to achieve a precise reading two ultrasonic guided signal’s time delay. Finally, we established a rail-based ultrasonic guided wave temperature stress detection system and stress testing platform, complete system calibration and testing, and measurement error is less than3.5MPa.The measurement system is tested in our laboratory; it can detect the rail longitudinal thermal stress based on ultrasonic with3.5MPa measurement error. The result shows that the approximate linear correspondence between the propagation velocity of ultrasonic guided wave and the stress in the rail, the correctness of acoustic-elasticity principle and the feasibility of the measurement method, and lays a good foundation for the further study of the subject.