High-speed non-contact passive-only ultrasonic inspection of rails from deconvolutions of wheel-generated noise

Rail internal defects have been one of the major causes of train derailments in the U.S. While the conventional ultrasound wheel probe has been widely implemented for rail track inspection, it suffers from the drawback of limited testing speed (25 mph at most). This paper presents a radically new approach for ultrasonic rail inspection that utilizes non-contact receivers and no active transmitters. The transfer function between two points of the rail is reconstructed by deconvolutions of multiple pairs of receivers that sense the acoustics naturally excited in the rail by the running wheels. The deconvolution process eliminates the random effect of the excitation to reconstruct a stable acoustic transfer function of the rail. This approach lends itself to extremely high testing speeds (as fast as the running train, e.g. 100 mph and above), that would enable the implementation of "smart" technology on trains running at normal operational speeds. A prototype based on this passive-only inspection idea has been constructed and tested with the DOTX216 testing vehicle of the Federal Railroad Administration at the Transportation Technology Center (TTC) in Pueblo, CO in September 2016. Test runs were made at various speeds from 25 mph to 80 mph (the maximum speed allowed on the test track). The results show the feasibility of stable reconstruction of the transfer function from the random wheel excitation, as well as the detection of joints and welds present in the track. Some tests were also conducted on TTC Defect Farm showing the potential for defect defection.