Top-of-rail friction modifier performance assessment: High pressure torsion testing; creep force modelling and field validation

Top-of-Rail products that give intermediate friction offer many benefits when applied to the wheel/rail interface. Water-based top-of-rail friction modifiers (TOR FMs), have been shown to reduce energy consumption, wear, noise, corrugation and rolling contact fatigue. This work was aimed at developing a test approach, based on the High Pressure Torsion (HPT) method, that allowed an improved assessment of their performance over those that recycle constantly over the same test surface. The outputs would then be used to parameterise the Extended Creep Force (ECF) model to enable full-scale predictions to be made that could be compared with field measurements of wheel/rail interface friction. The HPT method developed used representative amounts of product based on assessment of wayside and on-board application rates. Friction levels achieved matched those expected for intermediate levels. The friction level was sensitive to the amount applied though. The parameterised ECF model was able to predict friction levels that matched those from the field very closely. A framework for using friction measured in small-scale tests has been developed that could now be applied to other third body materials for making valid predictions of full-scale performance.