An analysis of fatigue crack path in welded rails

Some typical fatigue failures of butt-welded rails consist in fractures of the web. In the early stage, crack propagates parallel to rail surface but, after a while, it tends to propagate with a slant surface. The aim of the present work is to analyse the mechanisms involved in crack propagation in rail’s web in order to be able to predict the crack path and, in a second step, the rail inspection intervals. From this point of view, FEM analyses of an observed fracture were carried out in order to determinate KI and KII history at different positions of crack tip during the passages of the typical loads induced by trains. The results have shown that the initial flaw tends to follow a path where KII is close to maximum values and a small superimposed KI traction is present. Fractographic analyses have confirmed that propagation is mainly controlled by mode II and that mode I is prevalent only after the final bifurcation of the cracks.