The Measurement of Residual Stress in Railway Rails by Diffraction and other Methods

Abstract

Residual stresses have been measured in a new roller-straightened railway rail and a worn ex-service rail. Synchrotron {211} lattice strain measurements at ID11 (ESRF) were used to map in-plane components of the stress tensor acting in cross-sectional rail slices. Stress maps made using laboratory X-rays and the magnetic measurement system MAPS, although coarser in detail, show similar trends. The validity of the measured data was examined using a stress balance requirement. Whilst generally true (to ± 15 MPa), stress balancing was worst (±50 MPa) in regions with significant plastic deformation, suggesting that the measured {211} lattice strain had become uncharacteristic of the bulk elastic strain. Attributable to plastic anisotropy, this is a well-established issue with diffraction-based stress determination. To complement the in-plane stress measurements, the contour method was used to map the longitudinal stress component in a similar new rail sample, this component being relieved in the slices. On the basis of this result, we show that the remaining unrelieved in-plane stresses in the rail slices are a suitable approximation of those in the original rail.