Tribological effects in granular materials and their impact on the macroscopic material behaviour

Abstract

In the discrete element simulation of granular materials, the modelling of contacts is crucial for the macroscopic material behaviour. From the tribological point of view, friction at contacts needs to be modelled carefully, as it depends on several factors, e.g. contact normal load or temperature to name only two. In discrete element method (DEM) simulations the usage of Coulomb’s law of friction is state of the art. It reduces all tribological effects to only one constant coefficient of friction. Motivated by research on wheel-rail contacts, a pressure dependency of the interparticle coefficient of friction is introduced in a new DEM model. Direct shear tests are conducted on steel spheres of a certain size distribution. The strong influence of interparticle friction on the bulk friction is shown via a variation of the constant interparticle friction coefficient. Simulations with constant and pressure dependent interparticle friction are compared. For the pressure dependent interparticle friction a pressure dependency of the bulk friction is seen which matches qualitatively the behaviour known from testing reported in literature.