Jamming Transition: Heptagons, Pentagons, and Discs

¹ Taishan College, Shandong University, Jinan, Shandong 250100, China
² Department of Physics and Center for Nonlinear and Complex Systems, Duke University, Durham, North Carolina 27708, USA

^* e-mail: xuyy95@outlook.com
^** e-mail: jb427@phy.duke.edu
^*** e-mail: yiqiu.zhao@duke.edu
^**** e-mail: bob@phy.duke.edu

Published online: 30 June 2017

Abstract

The jamming behavior of a system composed of discs has been well documented. However, it remains unclear how a granular system consisting of non-spherical particles transitions between unjammed and jammed states. Here, we present compression experiments to study the jamming transition of 2D granular materials composed of photoelastic heptagonal particles and compare these results to data for discs and pentagons. We determine the critical packing fraction of heptagons and make a comparison to discs and pentagons. In the experiment, we subject 618 heptagonal particles to cyclic compression. We track the motion (inlcuding rotations) of the particles, and we measure forces on particles by photoelasticity. We observe a power law relationship between the average contact number (Z) and the pressure (P). Furthermore, we classify the type of contacts by the relative orientation of pairs of contacting particles (creating point-to-face and face-to-face contacts), and we explore the evolution of the contacts during jamming.