Experimental investigation of the effect of grain morphology on packing density of granular assemblies

The physical and mechanical properties of granular media at the macro scale are greatly influenced by the morphology of its grains at the micro-scale. The morphology of grains is a multi-level property, with the morphological features at each level being independent. Thus, while understanding the effect of the granular morphology on the macro scale behaviour of granular media like sands, it becomes imperative to understand the influence of individual morphological features. The current study investigates the effects of macro and meso-scale morphological properties of grains on the packing density of granular media. Virtual granular assemblies with controlled shape parameters are generated using the spherical harmonics algorithm. The shapes of the grains in the virtual granular assemblies are varied to understand the effects of individual morphological properties at different levels. Polyjet 3D printing is employed to generate synthetic grains from virtual grain assemblies. Further, experimental investigations are performed using these synthetic grains with controlled shapes to estimate their minimum and maximum packing density. The effects of particle form and roundness on the packing density are analysed. The results highlight that the particle shape significantly affects the packing density of granular media at loose and dense states with packing density values decreasing with a decrease in roundness and regularity.