Rolling contact fatigue cracking in rails subjected to in-service loading

摘要

Rolling contact fatigue (RCF) is one of the most important failure mechanisms in rails with significant cost- and safety-related implications on the operation of railway systems. In this work, a metallurgical analysis of RCF crack initiation and propagation, including geometrical characteristics of RCF cracks - length, depth from surface, angle of propagation and spacing between cracks, is presented. The role of proeutectoid ferrite in crack initiation has been studied. Analysis of the fracture surface of an RCF crack revealed a ductile initiation zone followed by a quasi-cleavage crack propagation. Iron oxide formed in the interior of all cracks in rails exposed to stagnant water with implications to crack propagation rate because of crack closure effects. Sequential sectioning parallel to the rolling surface revealed that RCF cracks possess convoluted surfaces. The crack trace expands with depth from the rolling surface. Subsurface crack initiation has also been documented.