THE EARLY DETECTION OF ROLLING SLIDING CONTACT FATIGUE CRACKS

Many previous laboratory studies of the rolling-sliding contact fatigue behaviour of rail steels have been performed on twin-disc wear machines. Usually the discs have been run until spalling occurs due to extensive rolling contact fatigue (RCF) damage; hence metallurgical factors affecting crack initiation and propagation have been difficult to assess. A new wear machine is described, capable of testing large, standard cylindrical discs at high contact stresses with accurate control at low creepages. An eddy current method has been used for the detection of the initial propagation of cracks during an RCF test. The first significant crack or cracks are accurately located by a scanning, high resolution, differential eddy current probe. The method is being used to examine the relationship between rolling-sliding contact fatigue, contact stress, creepage, microstructure and surface events for a range of pearlitic rail steels.