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

It is widely recognized that the accuracy of explicit finite element simulations is sensitive to the choice of interface parameters (i.e. contact stiffness/damping, mesh generation, etc.) and time step sizes. Yet, the effect of these interface parameters on the explicit finite element based solutions of wheel–rail interaction has not been discussed sufficiently in literature. In this paper, the relation between interface parameters and the accuracy of contact solutions is studied. It shows that the wrong choice of these parameters, such as too high/low contact stiffness, coarse mesh, or wrong combination of them, can negatively affect the solution of wheel–rail interactions which manifest in the amplification of contact forces and/or inaccurate contact responses (here called “contact instability”). The phenomena of “contact (in)stabilities” are studied using an explicit finite element model of a wheel rolling over a rail. The accuracy of contact solutions is assessed by analyzing the area of contact patches and the distribution of normal pressure. Also, the guidelines for selections of optimum interface parameters, which guarantee the contact stability and therefore provide an accurate solution, are proposed. The effectiveness of the selected interface parameters is demonstrated through a series of simulations. The results of these simulations are presented and discussed.Railway Engineerin

Improving the performance of finite element simulations on the wheel–rail interaction by using a coupling strategy

Over the past few years, a number of implicit/explicit finite element models have been introduced for the purpose of tackling the problems of wheel–rail interaction. Yet, most of those finite element models encounter common numerical difficulties. For instance, initial gaps/penetrations between two contact bodies, which easily occur when realistic wheel–rail profiles are accounted for, would trigger the problems of divergence in implicit finite element simulations. Also, redundant, insufficient or mismatched mesh refinements in the vicinity of areas in contact can lead to either prohibitive calculation expenses or inaccurate implicit/explicit finite element solutions. To address the abovementioned problems and to improve the performance of finite element simulations, a novel modelling strategy has been proposed. In this strategy, the three-dimensional explicit finite element analysis is seamlessly coupled with the two-dimensional geometrical contact analysis. The contact properties in the three-dimensional finite element analyses, such as the initial “Just-in-contact” point, the exact wheel local rolling radius, etc., which are usually a priori unknown, are determined using the two-dimensional geometrical contact model. As part of the coupling strategy, a technique has been developed for adaptive mesh refinement. The mesh and mesh density of wheel–rail finite element models change adaptively depending on the exact location of the contact areas and the local geometry of contact bodies. By this means, a good balance between the calculation efficiency and accuracy can be achieved. Last, but not least, the advantage of the coupling strategy has been demonstrated in studies on the relationship between the initial slips and the steady frictional rolling state. Finally, the results of the simulations are presented and discussed.Railway Engineerin