Real-time monitoring of broken rails in heavy haul railways is crucial for ensuring the safe operation of railway lines. U78CrV steel is a common material used for heavy haul line rails in China. In this study, the semi-analytical finite element (SAFE) method is employed to calculate the dispersion curves and modal shapes of ultrasonic guided waves in U78CrV heavy steel rails. Guided wave modes that are suitable for detecting rail cracks across the entire cross-section are selected based on the total energy of each mode and the vibration energy in the rail head, web, and foot. The excitation method for the chosen mode is determined by analyzing the energy distribution of the mode shape on the rail surface. The ultrasonic guided wave (UGW) signal in the rail is analyzed using ANSYS three-dimensional finite element simulation. The group velocity of the primary mode in the guided wave signal is obtained through continuous wavelet transform to confirm the existence of the selected mode. It is validated that the selected mode can be excited by examining the similarity between the vibration shapes of a specific rail section and all modal vibration shapes obtained through SAFE. Through simulation and field verification, the guided wave mode selected and excited in this study demonstrates good sensitivity to cracks at the rail head, web, and foot, and it can propagate over distances exceeding 1 km in the rail. By detecting the reflected signal of the selected mode or the degree of attenuation of the transmitted wave, long-distance monitoring of broken rails in heavy-haul railway tracks can be achieved.
Heavy haul railway transportation offers substantial advantages such as large transportation capacity, high efficiency, and low transportation costs, greatly fostering the development of China's national economy1. China's heavy haul railway mainly uses seamless rail; the phenomenon of thermal expansion and cold contraction of seamless rail is pronounced, coupled with the wheel-rail force of heavy haul railway, it is easy to lead to rail fracture. In addition, rail top abrasion, rail core damage, rail splint clamp damage, rail welding quality, and other problems can also lead to rail fracture2.
Currently, rail fracture detection methods are primarily categorized into mobile detection and fixed detection. Mobile detection involves assessing rail conditions using hand-propelled rail detection trolleys or large rail inspection vehicles. The detection methods mainly consist of ultrasonic, eddy currents, and magnetic flux leakage. Within ultrasonic detection, there are piezoelectric and electromagnetic methods. China's rail detection vehicle is mainly developed based on piezoelectric ultrasonic technology. For instance, the GT-2 rail detection trolley utilizes seven ultrasonic transducers with varying angles to simultaneously emit and receive ultrasonic waves on the rail for internal crack detection3. Based on electromagnetic ultrasonic detection technology, Canada's Tektrend company developed the RailPro rail detection vehicle4, which can detect defects in the rail head and web...
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