Wheel/Rail Interface Friction Assessment: High Pressure Torsion Testing; Creep Force Modelling and Field Validation

The wheel/rail interface has to be carefully managed to achieve friction levels needed for efficient and safe train operation. Sometimes friction needs to be at an intermediate level to reduce energy consumption and wear; at other times, if there are leaf layers present, friction needs to be increased and at the rail gauge corner in curves it might need reducing to very low levels, to deal with wear and crack formation.

Different types of products can be applied to the wheel/rail interface using wayside applicators, or from onboard trains to achieve the varying friction levels required. These are usually tested in small scale laboratory tests to evaluate their performance. One of the challenges then is scaling from the friction level recorded in these to the full-scale operation contacts.

This work was aimed at assessing product performance using a High Pressure Torsion (HPT) method. The outputs were then 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 work presented is based on case studies of top-of-rail friction modifiers designed to give intermediate friction and sand used to increase friction from low levels.