Performance Assessment of Friction Management Products in the Wheel-Rail Interface

The wheel-rail contact is a crucial aspect of all railway systems. Within the wheel-rail contact, an important factor is the frictional behaviour between the wheel and rail materials. Frictional behaviour can dictate how effectively a railway vehicle accelerates/ decelerates, its steering behaviour, as well as influencing how much damage occurs to wheel and rail materials as the vehicles negotiates a railway system. An inherent property of the wheel-rail contact is that it is an open system, vulnerable to outside influences such as the weather conditions and third body materials entering the contact; this results in variable and difficult to predict frictional behaviours affecting the operation of the railway system as a whole. Improving understanding of friction in the wheel-rail interface and how it affects damage mechanisms allows for better predictive models to estimate the prevalence of damage, and allow us to predict the effect of altering friction. This is turn allows us to estimate the cost benefit of altering frictional behaviour in the wheel-rail interface. This aim of this project has been to develop laboratory testing of friction behaviour in the wheel-rail interface (WRI), considering how the results of laboratory tests can be related to behaviour in the full scale interface. There was a particular focus on the behaviour of Friction Management products in the interface. Twin-disc testing was performed to investigate the suitability of twin-disc testing for assessing the performance of friction management products and other third bodies materials. This concluded that twin-discs are suitable for the testing of some third body materials, however, limitations were found when investigating third body layers that might be consumed as a test progresses. High Pressure Torsion (HPT) testing, in conjunction with the Extended Creep Force (ECF) model, was suggested as an alternative addressing the limitations of twin-disc experimentation. The most significant section of this project details the development of the HPT methodology on a servo-hydraulic test machine at the University of Sheffield; from the design of specimens and initial trials, to the final procedure and trials. The results of the HPT trials were used as inputs to the ECF model, allowing comparison against both a full-scale test and scaled twin-disc test results. The ECF model successfully predicted the results of both full-scale and scaled-down experiments. Issues with the input parameters which determine the influence of temperature were found; the issue can be solved and recommendations for further work to improve and validate the HPT/ECF methodology have been made.