Search

Due to an increasing trend towards environmentally friendly public transport, rail networks face higher speeds and wheel loads affecting the material degradation of the railway components. Within this study, influencing parameters on the formation of stratified surface layers, forming on railway wheels during service due to thermal loadings in the wheel-rail contact, are studied. These layers consist of white etching layer and underlying brown etching layer and are susceptible to fatigue crack initiation. By using laser surface treatments, its formation based on two consecutive thermal loadings is systematically demonstrated on ER7 wheel steel. Further, a decrease in layer thickness with decreasing laser power, and an increase in brown etching layer thickness with increasing laser power difference is shown. Moreover, the effect of finer grain size leading to an increased layer thickness, and the influence of the chemical composition by comparing the standard ER7 wheel steel to a micro-alloyed wheel steel are demonstrated. [ABSTRACT FROM AUTHOR]

The railway industry uses top-of-rail products to control and manage the friction in the wheel/rail interface to help ensure efficient train operations and reduce wheel and rail damage. A product is typically applied from a wayside applicator that pumps a puddle onto the rail head where a passing wheel will pick it up and then transfer it down the track. The aim of this study was to study the transfer mechanisms of water-based top-of-rail friction modifiers (TOR-FMs) and how they are linked to the friction conditions in the wheel/rail interface. The transfer mechanisms were split into three parts: pick-up, carry-on and consumption. Pick-up looks at how the product transfers from the puddle on the rail to a wheel tread, whereas the carry-on mechanism relates to the product transfer back to the wheel. Consumption focuses on the removal rate of the product layer from the wheel or rail. A full-scale rig and twin disc machine were chosen to perform the tests because each rig could give different insights into understanding the product transfer mechanisms. Two products were tested of similar formulation. Results show that there are differences in the transfer and friction between the two products despite them being relatively similar. The test methods developed can clearly resolve differences between varying product types, which could be useful for product development studies or approvals work. The outcomes could also be used to develop a model of transfer/consumption. [ABSTRACT FROM AUTHOR]

For the development of rail materials with improved properties regarding rolling contact fatigue and wear, it is at first important to know and understand the loading conditions in railway operation. Based on the loading conditions, crack initiation can be predicted. This has been done by a local analysis of the wheel/rail contact conditions with the so-called wedge model. This model takes the plastic shear deformation condition in a layer near the rail surface into account. Results for a specific railway operation scenario and test rig experiments are analysed to demonstrate how such different scenarios can be compared. The work contributes to the understanding of the transferability of test rig results to the behaviour in the field. [ABSTRACT FROM AUTHOR]

Predicting the behaviour of trains when braking under low adhesion conditions presents considerable challenges. This paper describes an approach to the problem using a model of the full train braking system known as LABRADOR (Low Adhesion Braking Dynamic Optimization for Rolling Stock) and an improved method for representing the creep force–creepage behaviour when low adhesion is presently known as WILAC (Water Induced Low Adhesion Creep Force Model). The development of these models and their integration are summarized and a number of test cases are presented to demonstrate the improvements which can be gained from this approach. A number of suggestions are made for future enhancements with the aim of providing brake engineers and systems integrators with reliable simulation tools for optimizing train braking performance when low adhesion is present. [ABSTRACT FROM AUTHOR]

Train operators report low adhesion in autumn, which they suspect is caused by fallen leaves on a track surrounded by forest and farmland. To investigate and quantify this effect, vehicle tests have been performed in autumn on a track partially surrounded by forest. To also investigate the influence of different weather conditions, the tests were performed on a day with sunny weather and one with high humidity in the morning and drizzle at noon. The results were then compared to other tests and different creep force models from the literature. The results showed a significant influence of the surrounding forest on the traction especially in sunny weather. [ABSTRACT FROM AUTHOR]

In this work, the authors present a methodology for assessing running gear with respect to rolling contact fatigue of wheels and rails. This assessment is based on the wheel/rail contact data of different wheel profile wear states obtained from a wheel profile prediction methodology. The approach allows a cumulative assessment of the rolling contact fatigue of rails in different curve radii (e.g. the sum of damage over the lifetime of wheel profiles). Furthermore, the assessment of the rolling contact fatigue can be undertaken at different wear states of the wheel profiles to provide an insight on how the rolling contact fatigue of wheels and rails varies depending on the evolution of wheel wear. The presented methodology is exemplarily applied to two bogie types, the UIC-Y25 standard bogie and the so-called FR8RAIL bogie with a mechanical wheelset steering device. The presented methodology has been shown to be a useful tool for the optimisation of vehicles already in an early stage of the vehicle development process. [ABSTRACT FROM AUTHOR]

The coefficient of friction between a wheel tread and the top of the rail should be maintained at intermediate levels to limit frictional tangential contact forces. This can be achieved by applying top-of-rail products. Reducing the coefficient of friction to intermediate levels reduces energy consumption and fuel costs, as well as damage to the wheel and rail surfaces, such as, e.g., wear, rolling contact fatigue, and corrugation. This work describes a simulation model that predicts the evolution of the coefficient of friction as a function of the number of wheel passes and the distance from the application site for wayside application of top-of-rail products. The model considers the interplay of three mechanisms, namely the pick-up of product by the wheel at the application site, the repeated transfer of the product between the wheel and rail surfaces, and the product consumption. The model has been parameterized with data from small-scale twin disc rig experiments and full-scale wheel–rail rig experiments. Systematic investigations of the model behaviour for a railway operating scenario show that all three mechanisms may limit the achievable carry-on distance of the product. The developed simulation model assists in understanding the interplay of the mechanisms that govern the evolution of the coefficient of friction in the field. It may aid in finding optimal product application strategies with respect to application position, application amount, and application pattern depending on specific railway operating conditions. [ABSTRACT FROM AUTHOR]