Full-scale testing of low adhesion effects with small amounts of water in the wheel/rail interface

Low adhesion in the wheel/rail contact can be caused by small amounts of water combining with iron oxides. This happens in light rain or at dew point. In small-scale tests, ultra-low adhesion (≤0.05) has not been maintained. The aim here was to see if the mechanism could be realized at a larger scale. Sustained ultra-low adhesion was achieved when water was applied constantly to the wheel/rail contact at a rate of 25μL/s. In these conditions wear debris and oxide was clearly visible in the contact band. Creep force data has been generated that can now be used to inform wheel/rail contact models and multi-body dynamics simulations of train behaviour with a view to developing mitigation

Assessing the impact of small amounts of water and iron oxides on adhesion in the wheel/rail interface using High Pressure Torsion testing

A new High Pressure Torsion (HPT) set-up has been developed for assessing the effect of third body materials in the wheel/rail interface in a representative and controlled manner. In this study the technique has been used to investigate the effect of small amounts of water and iron oxides mixtures when subjected to different contact pressures. HPT tests showed reduction in adhesion relative to a dry contact when testing with small amounts of water and/or oxides, however sustained low adhesion (μ<0.05) was not produced. To aid interpretation of the results a model has been developed to explore the behavior encountered when testing with water and iron oxide mixtures. The model relates the shear properties of water and oxide mixtures (with increasing solid content) to a predicted adhesion. The model shows a narrow window of water to oxide fraction is required for reduced adhesion, particularly on rough surfaces, and this correlates with the behavior observed

Wheel-rail creep force model for predicting water induced low adhesion phenomena

A computationally efficient engineering model to predict adhesion in rolling contact in the presence of water is presented which may be implemented in multibody dynamics software or in braking models to study train performance and braking strategies. This model has been developed in a project funded by the Rail Safety and Standards Board (RSSB) and Network Rail. It is referred to as the water-induced low adhesion creep force (WILAC) model. The model covers a wide range of conditions from dry over damp to wet. Special emphasis is put on little amounts of water which can cause low adhesion without any oil or grease. Such conditions may be encountered in humid weather or at the onset of rain. The model is parameterised based on experimental results from a tram wheel test rig. Adhesion values as low as 0.06 are observed at high creep with only wear debris and little water present in the contact. The model results also agree with experimental data from locomotive tests in dry and wet conditions