Abstract: Ultrasonic guided waves technology has attracted wide attention in defect detection and health monitoring in railway track because of the advantages of long-range capability and full cross-section coverage. However, due to the natures of dispersion and multiple modes, current researches on ultrasonic guided waves in rail focus on relatively low-frequency below than 90 kHz. Ultrasonics wave with low frequencies is not sensitive enough to small defects. However, the safety-critical region such as the switch rail is very short and its inspection present more request for high sensitivity to small defect. In order to improve the defect detection ability of ultrasonic guided wave in rail, a single mode ultrasonic guided wave excitation in high frequency range based on array sensing technology is proposed. Firstly, semi-analytical finite element method is applied to investigate the characteristics of ultrasonic guided wave propagation in rail. The dispersion curves and modal shape are calculated for CHN60 rail. Then, specific wave mode sensitive to the certain area is carefully chosen are selected based on the dispersion curves and mode shapes. By three-dimension finite element modelling, a single mode at 100 kHz is excited along rail foot, after optimizing the array parameters, including element spacing, excitation length, period number and window function. Also, the interaction between this selected mode and surface and internal defects was investigated. The results show that this single mode is capable to detect the defects as small as 3 mm. Finally, laboratory experiment proved that the single-mode ultrasonic guided wave is excited along rail. This technology to excite single-mode ultrasonic guided wave in high-frequency range along offer a potential technology for defect detection with high sensitivity for the safety-critical region of rail, such as switch rails.

Key words: rail track, ultrasonic guided wave, single mode, sensor array, defect detection