Detection and depth gauging of transverse cracks in the rail head

Abstract

A 'pitch–catch' low frequency ultrasonic technique has been developed that can be used for detection and depth gauging of transverse cracks in the rail head, such as the gauge corner cracking identified as a contributory factor in recent UK rail failures. The electromagnetic acoustic transducers (EMATs) used in this technique employ a guided wave mode with very similar characteristics to classical Rayleigh surface waves. These waves propagate along the surface of the rail, penetrating to a depth of approximately 2–15 mm. The surface wave generated is wideband, containing a range of frequencies in one single pulse. Crack depth can be estimated by comparing the surface wave at a particular frequency that has passed underneath the crack with a wave propagated through a defect-free region. Preliminary measurements indicate that the ultrasonic system has the potential to assess the microstructure–stress state around the rail head, thus identifying precursors to crack formation.