Residual stress mapping in railway rails

Residual stress has been mapped in the heads of ex-service railway rails. Three normal grade rails and one mill-heat-treated (MHT) rail were examined. Transverse, vertical and in-plane shear stresses were deduced using energy dispersive synchrotron X-ray, magnetic permeability and laboratory X-ray measurements. Differences were found between samples both in the distribution of compressive stress introduced at the running surface, and in the locations of the balancing tensile stress below this. The mill heat treated rail was found to have tensile stress closer to the gauge corner than the other rails. While the effect of residual stress in rails must be considered alongside the transient stresses present during wheel passage, tensile residual stresses close to the running surface are believed to be detrimental to rail integrity.