The combined effect of particle angularity and inter-particle friction on micro- and macroscopic properties of granular assemblies

Both inter-particle friction and particle shape are known to influence the micro- and macroscopic properties of granular assemblies individually. However their combined influence is still poorly understood. In this work we perform a series of Discrete Element Simulations to systematically study the combined effect of particle angularity and friction on the shear resistance of granular aggregates. We find that for angular particles the residual shear resistance as a function of inter-particle friction shows a local maximum, while for round particles it increases monotonically until it saturates. In contrast, no such effect is observed in the packing structure of the aggregates. The non-monotonic behaviour of angular particles is mirrored by the critical state directional and normal force fabric anisotropies, while the tangential normal force anisotropy shows more similarity to the bulk porosity and the mobilization of friction at the individual particle contacts. Our results now provide a much clearer picture on the origin of the non-monotonic behaviour of the critical state shear resistance on the inter-particle friction, as a competition between sliding and rolling in two different rolling regimes.