ULTRASONIC DETECTION OF SURFACE-BREAKING RAILHEAD DEFECTS

Abstract

We recently presented measurements of defects on the railhead, using a novel pitch‐catch ultrasonic system comprising of two electro‐magnetic acoustic transducers (EMATs) generating and detecting Rayleigh waves. Current systems used on the UK rail network for detecting surface breaking defects are limited in speed (<30 mph) and accuracy (depths >5 mm). The non‐contact EMAT system has the potential to operate at higher line speed, improving network inspection coverage. The current system detects signals and performs an FFT in less than 1 ms, and changes in the detected signal amplitude and frequency content are used to characterise defects. A new set of simulated defects on sections of rail have been produced, including half‐face slots machined normal to the railhead surface, clusters of angled slots, and pocket defects more typical of real defects. The smallest pocket defects are difficult to detect, with changes in signal amplitude and cut‐off falling close to the noise level. However, at chosen higher frequencies a drop in FFT magnitude indicates the presence of a defect, and this indicator can be logically combined with amplitude and cut‐off measurements to provide a more reliable result. Preparation for testing on a rotating rail rig at high speeds is ongoing.