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Ratchetting of railhead material of insulated rail joints (IRJs) with reference to endpost thickness
journal contributionposted on 06.12.2017, 00:00 by Nirmal Mandal
Insulated rail joints (IRJs) are the most important structural link in a railway track for electrical signal purposes. Because of the presence of the discontinuity in the rail material at IRJs, problems with maintaining rail/track geometric requirements and much increased dynamic wheel load effects on IRJs result. Material degradation and damage to the rail ends at the discontinuity therefore occur. A few studies have been carried out to address this issue globally. A local stress and damage analysis is essential to study the material behaviour of the rail ends with an appropriate elasto-plastic material model. For cyclic loading, a kinematic hardening material model alone is not enough to predict ratchetting damage, plastic deformation and initiation of rolling contact fatigue (RCF) defects at the rail ends of IRJs.In this paper, a three-dimensional (3D) finite element analysis (FEA) is carried out to study the distribution of stresses and strains in the vicinity of the IRJs using modified Hertzian Contact Theory (HCT). A solid rail model with a 10mm thick fibreglass insulating endpost filling the rail discontinuity is considered and two beam elements are connected to the solid rail model by equation constraints. A 5mm fibreglass endpost is also considered for comparison purposes. A combination of nonlinear kinematic and isotropic hardening material models is considered in the simulation. A local stress analysis model, called sub-modelling, is incorporated to capture degradation of materials accurately and to obtain ratchetting damage of the endpost material of the IRJ. It also captures the decay of the ratchetting rate. The effects of cyclic wheel loads on the IRJ are also presented. The analysis indicates that material degradation occurs progressively due to the loading spectra. Simulation results also present the IRJs mechanical behaviour with response to endpost thicknesses for enhancing better geometric design of IRJs.