Investigating fluid penetration of rolling contact fatigue cracks in rails using a newly developed full-scale test facility

Fluid penetration of surface breaking rolling contact fatigue cracks in rails is believed to be a key factor in their growth to dangerous lengths. Fluid entry has been proved for surface breaking cracks in laboratory twin disc contact simulations, but the authors are not aware of direct evidence for fluid penetration of cracks in full-scale rail-wheel contacts. There is, however, a widely held view that the behaviour observed in the laboratory will translate to full-scale cases. To investigate fluid penetration of cracks in full-scale rail-wheel contacts, cracked rails with a range of rolling contact fatigue severity were removed from mainline railway track and re-installed at a newly developed test facility. Investigation was undertaken using two different water-based marker fluids, and the rails subjected to over 1000 wheel passes with a locomotive. The rails were subsequently removed and selected crack faces broken open for observation by placing the rail in four-point bending. Ultra-violet and visible light were used to assess the degree to which the marker fluids had entered the surface breaking cracks. Good evidence of fluid penetration was found for one of the marker fluids, but the second fluid was not observed inside the cracks. The possible reasons behind this difference in behaviour are discussed.