02 TRACK SYSTEMSSUPPLEMENT Steve Yianni


Director of Engineering at Network Rail and European Railway Review Editorial Board Member


OPTIMISING THE WHEEL/RAIL INTERFACE:


Reducing forces for the benefit of all!


The contact patch between the wheel and rail is a fundamental, but often misunderstood, interface in the railway. The vehicle/track interaction team within Network Rail are engaged in a variety of projects with the objective to improve their understanding of, and manage initiatives to reduce, the forces in the contact patch. These initiatives bring benefits to both the infrastructure manager and the train operator through reducing wheel and rail damage and wear, therefore improving reliability of the rail network, reducing maintenance costs and increasing wheelset life.


Computer simulation is an established and important tool in the battle to improve the working of the wheel/rail interface, and also for understanding the impact of changes to the system on damage and maintenance requirements – be they the introduction of new vehicles, increased traffic levels, or the use of new rail materials. Over the last 10 years Network Rail has led


the world in research into the causes of wheel and rail damage, particularly rolling contact fatigue (RCF). Our understanding of the relationship between forces and damage is a lot better now than at the time of the Hatfield derailment in October 2000, when there wasn’t much ‘science’ involved in managing the railway. The situation is very different now, with Network Rail developing tools to help track engineers understand the causes of track damage, to better predict rail life, and to select the most appropriate grade of rail material, grinding regime and management plan. This has only been possible following the application


European Railway Review Volume 18, Issue 2, 2012


of detailed computer simulation of vehicle dynamics behaviour to predict the forces generated in the contact patch as each wheelset negotiates the curves, variations in track alignment and switches and crossings. Such analysis is able to show the forces associated with locations where particular forms of rail surface damage are experienced, such as RCF and wear. With the benefits of computer simulation this can be used to produce ‘maps’ of the rail head at different sites, highlighting the positions where damage is likely to occur. The strength of numerical simulation is that


it allows us to understand the effects that any changes to the vehicles or track will have on the level of damage. This helps us determine the most appropriate mitigation measures to minimise impact at different sites based on the characteristics of each site and any local restrictions which may limit the applicability of some possible solutions. Through computer simulation it has become clear that there is no one solution which can be applied to solve


problems at all locations: solutions will vary from site to site, and the challenge for the track engineer is to select the most appropriate solution. Through this research we have now developed a simplified tool, Track-Ex, which can be used by engineers without a detailed knowledge of vehicle dynamics and the physics of the forces in the contact patch. The tool informs them of locations at risk of developing different forms of damage and which particular remediation measure will be of best overall benefit to wheel/rail system. Track-Ex is a spreadsheet-based software


tool which combines the complex outputs from vehicle dynamics simulations with asset and track geometry data and information about the type and quantity of vehicles on each segment of a route in a form which can be used by track engineers to predict and manage rail damage. Development of the software has been entirely within Network Rail, allowing the format of its outputs to be tailored to the requirements of the track engineers and since the software is embedded within a spreadsheet it can be easily distributed and shared amongst users. Regular training sessions and user forums are employed to bring users together to share experiences, updates to the software and to spread understanding of the basics of wheel/rail interaction and dynamics. These sessions are well appreciated by users, with an enthusiastic network of users developing and helping track


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