Study On Real-time Detection Method For Broken Rail Based On Ultrasonic Guided Waves

As China's railway development heads toward high-speed railway and heavy-load freight, stricter requirements are enforced on the integrity of rail track structure, and the safety of rail transportation is become more and more important. As an essential component of track structure, the function of rail is to withstand the enormous pressure of the wheel, and pass it to the sleepers. It also guided train wheels move forward. Rail must provide continuous, smooth, least resistance of rolling surfaces and good adhesion of traction to the train wheels. Rail fractures may cause train derailment, rollover, and other disasters. Therefore, rail fractures must be detected in time in order to ensure the safety of rail transportation.To overcome the difficulties that non-track circuit section do not have the function of rail fracture detection and the current rail flaw detection devices can not monitor track problems in real-time, this dissertation proposed a fracture detection method suitable for long seamless tracks without track circuits.Firstly, this dissertation research the main causes and the distribution of broken tracks by analyzing the current data available in China. Variety of rail defects and long-term of external force will cause the phenomenon of rail fracture. There are two common reasons which will causes rail break. On the one hand, the repeated impact from the wheel when there is a train traveling on the rail will cause rail fracture. Another situation is tracks missing from man-made or natural disasters when the track is free. Rail broken must be find in time or it will bring great threat to the security of railway transport. It will cause a train late or turnover casualties. Therefore, detection of broken rails has important significance.Then after comparing the current domestic and international methods used to detect broken rail, this dissertation designed a new method for broken rail detection based on the detection of ultrasonic guided waves transmitted and attenuated in the rail, also motivated by the ideas in ultrasonic guided wave NDT.This method used two guided ultrasonic wave emitted from both ends and a receiver at the center and was not affected by the electrical properties of rails and tracks. The proposed system can replace the broken rail detection circuits where the track impedance is too low. The location and size of rail fractures can be determined utilizing the echo time and amplitude measured of sound waves. It can also detect track occupation via feature extraction of acoustic spectrum.To illustrate the detection mechanism of this method, this dissertation thoroughly studied the propagation characteristics of guided ultrasonic waves in the rails and the features of the excited waves in the railway environment. With the LabVIEW programming software, we build a simulation program for broken rail detection via ultrasonic waves, including user interface, signal generation, acquisition, alarm, and wave-shape retention. At last, this platform simulates the states of normal, train-on, broken rails state and determines the location and size of fractures based on theoretical analysis. This dissertation provided both theory and simulation tools for the real world application of broken rail detection with guided ultrasonic waves.