Numerical Analysis of Angled IRJs

Abstract

For railway travel the Insulated Rail Joint (IRJ) is a critical part in most railway safety systems but at the same time also considered a weak link. The IRJ creates a discontinuity in stiffness and geometry that leads to wheel-rail impact forces. The angled IRJ is a proposal to reduce these impact forces. Despite the real-world experiences with angled IRJs the research on the topic is marginal. In this thesis a study is presented into the dynamic behaviour of the wheel-rail impact occurring at IRJs. Numerical models are established to simulate a wheel rolling over IRJs with angles of 0, 15, 30 and 45 degrees, using the implicit-explicit sequential finite element method with the software ANSYS/LS-DYNA. The impact forces are the main output and analysed. Three variations of the IRJ models were used for simulations. The basic version IRJ model is built up with a fully constrained rail foot to simulate an infinite support stiffness condition. The second version is supported by spring and damper elements to simulate supports such as ballast and rail pads. Height differences between the rail ends are generated when a wheel passes the joint, which corresponds to a real-world scenario. Different degrees of support degradation are simulated by varying the support stiffness, using the spring and damper element parameters. The third version also incorporates the spring and damper elements as support but couples some nodes between the fish plate and rail web in vertical displacement to reduce the rail height difference caused by wheel pass-by, aiming to simulate a ‘factory-new’ condition joint. The established models were validated in terms of wheel-rail contact solution and contact force amplitude. In comparison with existing FE wheel-rail impact models the proposed models in this thesis are less time consuming and more flexible for joint angle adjustments. The second version simulating degraded joint conditions provided the most interesting findings and was used in a sensitivity analysis by varying the velocity and wheel load. The simulation results show that angled IRJs are advantageous when degradation is present, whereas in ‘new joint’ conditions the gap width plays a significant role and angled IRJs with larger gaps produce higher impact forces. Based on the results the recommendation is given to consider angled IRJs on tracks with a low maintenance scheme and further research is suggested.