Noncontact Ultrasonic Guided Wave Detection of Rail Defects

Recent train accidents, increasing tonnage, and aging rail transportation infrastructure have reaffirmed the need to improve current rail inspection technologies, consisting primarily of ultrasonic wheel testing. A recent development in rail inspection is the use of ultrasonic guided waves in the 20 kHz to 1 MHz range and noncontact probing techniques. This paper first reports on theoretical studies of ultrasonic guided wave propagation in rails based on a semianalytical finite element approach. The paper then describes the latest version of the University of California, San Diego, and FRA rail defect detection prototype, which is based on noncontact guided wave testing and real-time statistical pattern recognition for defect detection and classification. The system specifically targets transverse head cracks such as transverse fissures and detail fractures. It is also expected to be sensitive to longitudinal head cracks such as vertical split heads and mixed-mode cracks such as compound fractures. The system was field tested in March 2008 at speeds of up to 10 mph with excellent results under changing environmental conditions. Plans are in place for further improvements, including higher test speeds of up to 40 mph and installation of the system in an FRA research car for technology demonstration.