On the low cycle fatigue failure of insulated rail joints (IRJs)

Insulated rail joints (IRJs) are safety critical components in the signalling system of railway corridors which provide a break in the continuity of the rail steel to locate trains. IRJs connect the two rail ends at the discontinuity to achieve geometric and mechanical requirements of rail. The bending stiffness of an IRJ is about one third that of continuous rail. As a result, the IRJs, especially those in heavy haul tracks, exhibit early failure predominantly due to ratchetting or alternating plasticity of railhead metal in the vicinity of the endpost insulators.A three-dimensional (3D) finite element numerical simulation is carried out to examine failures of railhead material in the vicinity of the endpost of an insulated rail joint considering high frequency dynamic wheel loading. A dynamic wheel load of 182kN is applied through a contact patch; the distribution of contact pressure is considered using a non-Hertzian formulation. A 12m long global IRJ model and a sub-model for localised analysis are employed. The shakedown theorem is employed in this study. Nonlinear isotropic/kinematic elastic-plastic material modelling is employed in the simulation. A peak pressure load lower than the shakedown limit is considered as the input load.The equivalent plastic strain plot for this load case lower than the shakedown limit demonstrates the railhead damage captured through a localised stress analysis in the vicinity of the endpost using the sub-modelling technique. The sub-surface plastic deformation of railhead material extends down to 8mm from the railhead top surface. The critical crack initiating stress components are at 2mm-4mm sub-surface depth. As such, the railhead material fails due to alternating plasticity through low cycle fatigue. Laboratory tests were performed to verify the simulation results and found that test and simulation results correlated well.