Modelling the adhesion enhancement induced by sand particle breakage at the wheel-rail interface

The adhesion at the wheel-rail contact is critical in train operation. Low adhesion leads to a longer distance for a train to accelerate and brake, and this may cause serious accidents. Sand particles are applied onboard trains at the wheel-rail contact to enhance the adhesion level. In this study, a finite element model is developed to investigate the mechanical behaviour of sand particles in a wheel-rail contact and how they affect the adhesion level. The acceleration and braking events using rolling/slipping and sliding contacts are simulated. Morphological properties of sand particles such as size and aspect ratio are considered. The adhesion enhancement is quantified from each simulation for comparison. The results indicate that the adhesion enhancement during the first contact between the wheel and sand particles is negligible and starts to increase when the wheel is rolling on the fragments. Its magnitude is controlled by the new third-body layers generated during the particle breakage under both rolling and sliding contacts. However, under sliding contact, when a similar amount of fragments is considered, the coarser particles with a larger aspect ratio tend to produce a higher adhesion enhancement.