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Rail Crack Monitoring using Fiber Optic Based Ultrasonic Guided Wave Detection Technology



Rail health conditions are among the top concerns in the area of train safety. In this study, a fiber optic monitoring system is developed to achieve ultrasonic guided wave based rail crack detection. Although fiber Bragg grating (FBG) sensor is a wellknown suitable candidate for long-distance monitoring of rail, the sampling speed of commercially available optic spectrum analyzers limits their application to ultrasonic wave detection. A high-speed FBG interferometric interrogation module is developed, which constitutes the rail monitoring system in conjunction with an active wave generation module and a sensing network. To find appropriate excitation frequency and FBG dimension for ultrasonic guided wave generation and reception, dispersion analysis of rail, a waveguide with complex cross-section, is conducted to guide subsequent design of damage detection experiment. The system and the crack detection technique are then implemented on a long full-scale rail segment, by deploying PZT (lead zirconate titanate) actuator and FBG sensor in pitch-catch and pulse-echo configurations. Artificial cracks in different lengths are introduced to the rail. Frequency-domain analysis of the rail responses is used to identify the damageinduced discrimination after direct observation of time-domain signals. Power spectral density analysis of the purified signals, assisted by discrete wavelet filtering, leads to the graphic presentation of rail integrity.


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