Residual Stresses in Rail-Ends from the in-Service Insulated Rail Joints Using Neutron Diffraction

Abstract

Insulated rail joints (IRJs) are an integral part of the rail track signaling system and pose significant maintenance and replacement costs due to their low and fluctuating service lives. Failure occurs mainly in rail head region, bolt-holes of fishplates and web-holes of the rails. Propagation of cracks is influenced by the evolution of internal residual stresses in rails during rail manufacturing (hot-rolling, roller-straightening, and head-hardening process), and during service, particularly in heavy rail haul freight systems where loads are high. In this investigation, rail head accumulated residual stresses were analysed using neutron diffraction at the Australian Nuclear Science and Technology Organisation (ANSTO). Two ex-service two head-hardened rail joints damaged under different loading were examined and results were compared with those obtained from an unused rail joint reference sample in order to differentiate the stresses developed during rail manufacturing and stresses accumulated during rail service. Neutron diffraction analyses were carried out on the samples in longitudinal, transverse and vertical directions, and on 5mm thick sliceed samples cut by Electric Discharge Machining (EDM). Ex-service rail samples, irrespective of loading conditions and service times, were found to have similar depth profiles of stress distribution. Evolution of residual stress fields in rails due to service was also accompanied by evidence of larger material flow. Stress evolution in the vicinity of rail ends was characterised by a compressive layer, approximately 5 mm deep, and a tension zone located approximately 5-15mm below the surfaces. A significant variation of d0 with depth near the top surface was detected and was attributed to decarburisation in the top layer induced by cold work. Stress distributions observed in longitudinal slices of the two different deformed rail samples were found to be similar. For the undeformed rail, the stress distributions obtained could be attributed to variations associated with thermomechanical history of the rail. Residual stresses in rail-ends from the in-service insulated rail joints using neutron diffraction AbstractInsulated rail joints (IRJs) are an integral part of the rail track signaling system and pose significant maintenance and replacement costs due to their low and fluctuating service lives. Failure occurs mainly in rail head region, bolt-holes of fishplates and web-holes of the rails. Propagation of cracks is influenced by the evolution of internal residual stresses in rails during rail manufacturing (hot-rolling, roller-straightening, and head-hardening process), and during service, particularly in heavy rail haul freight systems where loads are high. In this investigation, rail head accumulated residual stresses were analysed using neutron diffraction at the Australian Nuclear Science and Technology Organisation (ANSTO). Two ex-service two head-hardened rail joints damaged under different loading were examined and results were compared with those obtai...

A Neutron Diffraction Investigation of Residual Stresses in Rail Ends after Severe Deformation of Rail Surfaces

“…Compared to destructive relaxation methods that involve cutting and drilling, neutrons are also the preferred non-destructive method to determine the whole strain. The first reported neutron diffraction investigation of residual strain in full rail sections [6] involved significant beam time, and this has been followed up by less time consuming neutron diffraction investigations of strain in rail slices [7], including a recent investigation of strain in rail ends of ex-service IRJs [8,9].…”