Ultrasonic detection of surface-breaking railhead defects

On the UK rail network, changing usage patterns have led to rolling contact fatigue (RCF) on the railhead being an increasing problem and frequent testing for such defects is essential. Existing systems for detecting defects are limited in speed (< 30 mph) and accuracy (> 5 mm). We are currently working on novel ultrasonic methods of detecting RCF, designed to lift many of the speed limitations and/or significantly improve accuracy and resolution. A non-contact pitch-catch pulsed ultrasonic system comprising two electromagnetic acoustic transducers (EMATs) generating and detecting Rayleigh-like waves has the potential to operate at high speed, thus improving network inspection coverage. Phased array ultrasonic techniques are being designed to improve imaging and characterisation of the defects. A set of simulated defects on sections of rail have been machined, including half-face slots machined normal to the railhead surface, clusters of angled slots, and pocket defects more typical of real defects. The techniques have been tested on these rails and their potential for use on the rail network is discussed.