Influence of endpost materials on sub-surface railhead material damage of insulated rail joints due to wheel/rail contact loadings

Insulated rail joints (IRJs) are very important for signalling systems in controlling trains on a railway track. They are also helpful to locate broken rails. The IRJs are considered as one of the weakest links of a railway track. The bending rigidity of an IRJ is only 2/3rd that of continuous rail. Consequently, larger stresses and deflections are experienced in the vicinity of IRJs. It is, therefore, necessary to give proper attention in designing the geometrical configuration of IRJs, focussing on composite endpost materials and other parameters to reduce plastic flow and stress states. This paper addresses the question of which stress state causes plastic deformation of IRJs? To answer that question, a 3D finite element analysis (FEA) is carried out using the Abaqus code to focus on damage and plastic deformation of sub-surface railhead material considering different composite endpost materials. At the wheel/rail contact patch on IRJs, vertical wheel impacts up to a total of 2000 cycles in the form of non-Hertzian pressure loadings are applied. A non-linear isotropic kinematic material hardening rule is applied. The subsequent analysis considers the sub-surface railhead damage to rank the commonly used endpost materials (fibre glass (fb), nylon 66 (ny) and polytetrafluoroethylene (ptfe)) based on the mechanical behaviour of the IRJs. The mechanical behaviour of ny and ptfe are benchmarked against that of fb for 50, 1000 and 2000 loading cycles. Significant sub-surface material damage occurs down to a depth of 8mm from the top of the railhead and, below 12mm depth, the material behaviour is elastic. Almost all damage parameters exhibit a similar damage level (flat type) for a depth up to 8mm initially and, as the cyclic loading increases, the flat pattern damage changes to a horizontal ‘Bell-Shape’ pattern indicating that the fb is a better endpost material to control sub-surface railhead material damage.