A Study On Rail Thermal Stress Online Monitoring Based On Ultrasonic Body Wave

ABSTRACT:With the development of high-speed, heavy haul railway, 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 when temperature changes. So the rail internally generates thermal stress. Usually change of10℃will make a fixed rail24.3MPa accumulation of stress. High temperature may lead to the expansion of rail, track buckling and low temperature may lead to 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.The paper is mainly focused on the rail thermal stress detection method based on ultrasonic. A rail longitudinal thermal stress detection system is proposed and completed based on acoustoelasticity principle, which is composed of ultrasonic sensor and multifunction board.The paper introduces the propagation characteristics of ultrasound in the rail, the theoretical basis of the rail thermal stress detection method based on ultrasonic: acoustoelasticity principle, and designs the C8051F410-based ultrasonic emission and receiving circuit. The circuit can launch ultrasonic signal and receive two-way ultrasonic signal. By the relevant program, the system can get get accurate calculation of the two ultrasonic signals and show the results on the digital screen. Finally, the stress detection system based on ultrasonic and rail thermal stress testing platform is proposed and completed. After the calibration and testing test, the results are contrasted and analyzed.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 wave and the stress in the rail, the correctness of acoustoelasticity principle and the feasibility of the measurement method, and lays a good foundation for the further study of the subject.