Influence of polydispersity on the microstructure of frictionless disc packings under simple shear

¹ Departamento de Ingeniería Civil y Ambiental, Universidad de los Andes, Bogotá, Colombia
² Departamento de Ingeniería Industrial, Universidad de la Sabana, Chía, Colombia

^* e-mail: n.estrada22@uniandes.edu.co
^** e-mail: william.oquendo@unisabana.edu.co

Published online: 30 June 2017

Abstract

By means of 2D Contact Dynamics simulations, we explored the effects of the shape and size span of the grain size distribution (GSD) on the microstructure of a sheared granular packing, in terms of its packing fraction and the connectivity of its contact network. We focused on GSDs that can be represented by a power law, which are widely used in several engineering and industrial contexts. The interest in power law GSDs originates in the works of Fuller and Thompson in 1907 and 1919, in which it was found that a maximum density is obtained for a power law GSD with an exponent of 0.5. This disagrees with recent DEM results where the densest packing is obtained for linear cumulative volume distributions. In order to explore this discrepancy, we performed systematic simulations in which we varied both the size span (the ratio between the largest and the smallest diameter) and the exponent (shape) of the distribution. We find that the exponent equal to 0.5 produces the highest density for all size spans. Furthermore, the proportion of rattlers and coordination were also analyzed, showing that the system’s connectivity is strongly affected by both the size span and the shape of the distribution.