Granular packings of elongated faceted particles deposited under gravity

Abstract

Abstract. We report experimental and theoretical results of the effect that particle shape has on the packing properties of granular materials. We have systematically measured the particle angular distribution, the cluster size distribution and the stress profiles of ensembles of faceted elongated particles deposited in a bidimensional box. Stress transmission through this granular system has been numerically simulated using a two-dimensional model of irregular particles. For grains of maximum symmetry (squares), the stress propagation localizes and forms chain-like forces analogous to those observed for granular materials composed of spheres. For thick layers of grains, a pressure saturation is observed for deposit depths beyond a characteristic length. This scenario correlates with packing morphology and can be understood in terms of stochastic models of aggregation and random multiplicative processes. As grains elongate and lose their symmetry, stress propagation is strongly affected. Lateral force transmission becomes less favored than vertical transfer, and hence, an increase in the pressure develops with depth, hindering force saturation.

Hard rectangles near curved hard walls: Tuning the sign of the Tolman length

“…Our results are in principle verifiable in experiments with sterically stabilized colloidal [43,46,[75][76][77][78][79] or granular [44,80] particles on a two-dimensional substrate. However, it should be noted that the particle number density field near the wall is more direct to obtain than the interfacial tension itself, which requires a thermodynamic integration.…”

Stress distribution of faceted particles in a silo after its partial discharge

“…Hence, the aspect ratio of the rods is d =2 .4a n dd =5 .4. It is important to note that the borders of the rods are truncated cones as explained in [23]. The square particles, d =1,are DIN 557 nuts 3.16 mm wide and 6.9 mm side.…”

“…In previous works we have clarified the remarkable role that flat faces play in the stress propagation of granular deposits [22,23]. Elongation favors rods' alignment transverse to gravity, hindering stress transmission to the lateral walls of the container.…”

“…These include effects in the packing fraction of granular piles [9,10], the pressure in the lateral walls of a silo during its discharge [11], the mean coordination number [12], the jamming [13] and the stress propagation in granular piles [14,15]. Moreover, there is currently increasing interest on the effect that faceted particles have in the global behavior of granular materials [16][17][18][19][20][21][22][23][24]. Those systems are common in geomaterials and with high relevance in civil engineering applications [25,26].…”

Granular materials composed of shape-anisotropic grains

“…For noncohesive particles, the packing topology is dominated by the formation of ordered structures consisting of aligned rods. Elongated grains tend to align horizontally and the stress is transmitted mainly from top to bottom, revealing an asymmetric distribution of local stress [74,75]. Kanzaki et al analyzed how this stress distribution changes if the two-dimensional container (silo) is partially discharged [76] through an orifice at the bottom.…”