Exploring the contact types within mixtures of different shapes at the steady state by DEM

A series of numerical tests on the quasi-static deformation of dense granular media by the discrete element method (DEM) are performed to investigate the behaviour of mixtures of shapes that are composed of round and non-convex (elongate) particles. Four representative contact types, which are classified into circle-circle contacts (CC), circle-elongate contacts (CE), simple elongate-elongate contacts (EE1) and multiple elongate-elongate contacts (EEm), are studied with respect to the macroscopic granular mechanical responses. It is found that the contact force ratio (K) of these four contacts can be considered to explain the variation of the steady friction angle. Another interesting finding is that the probability density function (PDF) of friction mobilisation (Im) for the CE contacts is insensitive at the mixture of 30%–60% elongated particles. However, the PDF curves of the normalised contact forces of EE1 and EEm show a nearly linear increasing relationship with the increased percentage of Elongated particles. It should be point out that the variation of the contact normal anisotropic coefficient is insensitive with the contact portions of EE1 and EEm in this study.