Formation and development of surface fold defects in heavy-duty rails

This study explored the formation and propagation of longitudinal cracks in the webs of in-service rails. Based on the mechanical property testing, hardness measurements, and microstructural analyses, the cracks were identified as originating from a rolling-induced defect known as“folding”. The formation mechanism of the folding defect and its contribution crack propagation were further analyzed through corrosion resistance experiments and stress analysis simulations. The results indicated that microcracks and shrinkage porosity within the metal oxide film at the folding site exposed the underlying metal to the external environment. Under cyclic fatigue loading during rail operation, this exposure accelerated the crack growth from the folding defect. The associated safety risk is closely linked to the rail stress state: fold defects located on the outer surface (non-load-bearing) side of the web are less critical than those on the inner surface (load-bearing) side. As rail wear progressed, the stress concentrations increased by a factor of 1in straight sections and more than threefold in curved sections, which substantially posed the risk of failure under repeated loading and a significant threat to railway operational safety.