To improve the understanding of dynamic impact in 1:9 crossing panel, which is suffering from rapid surface degradation, detailed modelling and experimental studies are performed. A three-dimensional explicit finite element (FE) model of a wheel rolling over a crossing rail, that has an adaptive mesh refinement procedure coupled with twodimensional geometrical contact analyses, is developed. It is demonstrated that this modelling strategy performs much better than the 'conventional' FE modelling approach. Also, the experimental validations show that the FE results agree reasonably well with the field measurements. Using the validated FE model, the tribological behaviour of contact surfaces is studied. The results indicate that the proposed modelling strategy is a promising tool for addressing the problems of wheel-crossing dynamic impact.

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 through a series of simulations. It can be concluded that the results obtained from most of the explicit FE simulations agree reasonably well with the ones from CONTACT. Also, the increase of the friction and traction can bring the stress concentrations from the subsurface upwards to the surface.

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.

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.

A crossover is a pair of crossings that connects two parallel rail tracks. The utility of a crossover is to provide skylight time for each line in busy track. This speciality involves wheel/crossing interaction mainly in straight direction. On the other hand, extra interruptions are brought into straight lines. The presented study is a part of the ongoing project Structural Health Monitoring System (SHMS) for railway turnouts (TU Delft). The objective is to evaluate the performance of these crossings, then further assess the structural degradation procedure and give advice on maintenance. MEASUREMENT OVERVIEW Field conditionThe crossings are casted manganese steel frogs (1:9) in a double crossover in the railway network in the Netherlands. These frogs are located on the same track line. Trains pass through one frog (Frog 1) in the facing direction and another (Frog 2) in the trailing direction. Therefore, the wheel/rail impact position on Frog 1 is on the wing rail, while on Frog 2 is on the crossing nose. Regarding to the frog number, the train operating velocity on this line is relatively high -140 km/h. The problems observed on these frogs mostly related to rail damage and geometry deterioration. By the start of monitoring, Frog 1 was in normal operation condition, Frog 2 was brand new. ABSTRACT: This paper presented the performance study of two frogs in a double crossover in the railway network in the Netherlands. These frogs are located on the same track line. Each train passes through Frog 1 in the facing direction and Frog 2 in the trailing direction. Both frogs are monitored with ESAH-M crossing dynamic behaviour measurement tool and remote displacement measurement system Video Gauge.Results indicate that Frog 1 experiences high wheel/rail contact force (acceleration) and wear in Frog 2 develops fast. Frog 2 suffers from lack support of ballast, while the potential damage in Frog 1 is mainly related to the rail part.