Abstract:Verification of the explicit finite element (FE) model with realistic wheel-rail profiles against the CONTACT model, which has not been sufficiently discussed, is performed by comparing the resulting shear stress, slip-adhesion area, etc., obtained from the two models. The followup studies using the verified FE model on the influence of the varying operational patterns (such as different friction, traction, etc.) on the surface and subsurface tribological responses of wheel-rail interaction are accomplished th… Show more
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 wheelrail 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-incontact'' 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.
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 wheelrail 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-incontact'' 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.
“…18 To improve the performance of FE simulations on W/R interaction, 24 a novel adaptive mesh refinement procedure based on the 2D geometrical contact analysis is introduced. Also, the accuracy of that model has been successfully verified 31 against CONTACT, which is a rigorous and well-established computational program developed by Professor Kalker 5 and powered by VORtech Computing. 3 The modeling strategy proposed 24 has been further extended to study the dynamic impact between wheel and crossing.…”
Section: Introductionmentioning
confidence: 91%
“…In this way, the comparability of FE results to those of CONTACT, which focuses on the cases of steady-state contact, 5,33 can be enhanced for the purpose of verification. 19,31 The results of the verification of FE model with realistic W/R profiles considered have already been presented in Ma et al. 31 Figure 1.FE model of W/R dynamic contact: (a) schematic graph; (b) FE model – side view; (c) refined mesh at the rail potential contact area; (d) refined mesh at the wheel potential contact area; (e) FE model – cross-sectional view; (f) close-up view in refined regions.…”
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.
“…The coefficient of friction ( ) is dependent on slip (creepage) velocity between wheel and rail, which was observed by several researchers and described in [26,33]. The slip dependent coefficient of friction can be expressed as (8) where A0 stands for the ratio of friction coefficient ( / 0 ), B0 is the coefficient of exponential friction decrease (in s/m) and s is the total slip or slip velocity (in m/s). For a dry wheel-rail contact scenario, 0 = 0.55, A0 = 0.4 and B0 = 0.6 [34].…”
Section: ( )mentioning
confidence: 99%
“…Ertz and Knothe [7] have calculated the temperature distribution on the wheel due to rolling along with sliding friction and concluded that the temperature rise due to braking is confined within a very thin layer near the contact surface. Among other notable works, Ma et al [8] studied the tribological…”
The increased temperature of the rail wheels due to tread braking causes changes in the wheel material properties. This article considers the dynamic wheel material properties in a wheel wear evolution model by synergistically combining a multi-body dynamics vehicle model with a finite element heat transfer model. The brake power is estimated from the rail-wheel contact parameters obtained from vehicle model and used in a finite element model to estimate the average wheel temperature. The wheel temperature is then used for wheel wear computation and the worn wheel profile is fed to the vehicle model, thereby forming a recursive simulation chain. It is found that at a higher temperature, the softening of the rail-wheel material increases the rate of wheel wear. The most affected dynamic performance parameter of the vehicle is found to be the critical speed, which reduces sharply as the wheel wear exceeds a critical limit.
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