Towards understanding the adhesion increasing effect of sand in wheel-rail contacts

Abstract. Sand in wheel-rail contacts is successfully used for a long time to increase adhesion. However, the physical effects responsible for this adhesion increase remain unclear. To improve the understanding of these effects an approach combining experiments with Discrete Element Method (DEM) modeling is followed. Results from initial breakage and high loading experiments on single sand grains under purely normal loading conditions show that the spreading behavior and the forming of clusters of solidified sand fragments depend on the type of sand and the contact conditions, namely dry and wet. The experimental data were used to develop, calibrate and validate DEM models including particle breakage. These DEM models can describe the observed effects. Finally, a systematic classification is presented where tangential relative motion due to slip can occur in a sanded wheel-rail contact. This is seen as an important basis for future experimental and modelling work.