Finite element analysis of the mechanical behaviour of insulated rail joints due to impact loadings

Abstract

Insulated rail joints (IRJs) are safety-critical components in the signalling system of rail corridors. They are subjected to dynamic loads generated by heavy rolling-stock/track- system interactions and degrade faster than the other components of the rail track. Degraded IRJs diminish the reliability of the signalling system, thus posing a serious threat to the safety of rail operations. Therefore, there is a pressing need to closely examine the failure mechanisms of the end posts made of insulated material and inserted into the discontinuity in the rail at IRJs with a view to improving their service life, reliability and efficiency. Only a limited literature is available that examines different materials for IRJ end posts, and these primarily focus on contact pressure and contact stress distributions in the vicinity of the end post, disregarding the damage to the rail ends and end post materials. In this paper, a detailed three-dimensional finite element analysis procedure is carried out to quantify plastic deformation and material damage to the end post and railhead materials of IRJs due to a wheel load above that of the shakedown limit of rail steel. A modified Hertzian contact pressure distribution is considered in this simulation. A 5 mm thickness of an end post is considered at the discontinuity in the rail, which is required to form the six-bolt IRJ. Three popular IRJ end post materials are considered in this study: fibreglass, polyhexamethylene adipamide, and polytetrafluoroethylene. A total of 2000 cycles of a 174 kN dynamic wheel load (in pressure format over the wheel/rail contact patch) are applied on the top of the rail’s surface in the vicinity of the IRJ. Equivalent plastic deformations along with vertical and longitudinal plastic strains for unloaded conditions are presented. The strain plots depict damage of end post materials and ratchetting failure of rail ends. The ratchetting failure modes follow the established trend of decay in ratchetting rate in successive wheel load cycles. Comparisons of strain and stress on the railhead surface and in the railhead sub-surface considering all three different end post materials are put forward. Out of the three end post materials, fibreglass is the optimal material considering the ratchetting mode for the damage of the railhead material.

Numerical study of wheel-rail impact contact solutions at an insulated rail joint

“…Sandstrom and Ekberg [8] employed a 3D elastoplastic FEM model to predict the plastic deformation and fatigue resulting from wheel-IRJ impacts by capturing the accumulation of plastic strain. Mandal and Dhanasekar [9] proposed a sub-modeling FE strategy to examine the ratcheting failure of IRJs, and the same strategy was adopted by Mandal [10] to study the influences of end-post materials on railhead deterioration at IRJs. Zong et al [11] applied an implicit-explicit FE model to simulate rail/wheel dynamic contact impact and railhead damage in the vicinity of IRJ.…”

“…Although many researchers believe that dynamic effects play certain roles during wheel-rail impacts [4,6-8, 10,15,16] , quasi-static wheelrail contact is still generally assumed in the FE models [2,4,[8][9][10] . Transient solutions that can reflect dynamic effects in the wheel-rail impact contact have rarely been studied, which may be because well-accepted methods [3,5,[17][18][19] capable of resolving common wheel-rail contact problems are generally based on the quasi-static contact assumption, and the dynamic effects during contact are therefore not necessarily considered in many situations.…”

Ratchetting damage of railhead material of gapped rail joints with reference to free rail end effects

“…This type of element was considered because it is widely used in elastic-plastic material deformation. 24,25 Finally, in the job module, the simulation was completed to obtain the displacement DOFs at the nodes of the global model and the displacement DOFs were then used to run a separate sub-model of rail ( Figure 6) which is discussed in the following section. The positive global coordinate directions are shown in Figure 6 such that the '3' direction is for longitudinal, '2' is for vertical and '1' is for lateral.…”

Effect of wheel–rail interface parameters on contact stability in explicit finite element analysis

“…5–7 These approaches have been verified and/or validated to be effective and efficient enough for addressing the problems of wheel–rail (W/R) contact in elasticity as well as in the cases of quasi-static and/or low-frequency dynamics. 2,8–12 Regarding the complex problems with both realistic contact geometries and material plasticity considered, finite element (FE) method, as opposed to the aforementioned approaches, appears to be much preferable and powerful for ensuring the desired solutions.…”

“…It was found that the contact pressure and the micro-slip were critical variables responsible for the surface damage of crossing rail. More recent modeling advances of W/R interaction, including the development of implicit FE models 11,12,23 (i.e. not referenced but of equal importance as those explicit FE models), can be found in Meymand et al.…”