Jamming by compressing a system of granular crosses

Hu Zheng,Robert Behringer,Dong Wang,Jonathan Barés,F. Radjai,J.Y. Delenne,S. Luding,S. Nezamabadi

doi:10.1051/epjconf/201714006014

Abstract

A disordered stress-free granular packing can be jammed, transformed into a mechanically rigid structure, by increasing the density of particles or by applying shear deformation. The jamming behavior of systems made of 2D circular discs has been investigated in detail, but very little is known about jamming for non-spherical particles, and particularly, non-convex particles. Here, we perform an experimental study on jamming by compression of a system of quasi-2D granular crosses made of photo-elastic crosses. We measure the pressure evolution during cyclic compression and decompression. The Jamming packing fraction of these quasi-2D granular crosses is ϕJ ≃ 0.475, which is much smaller than the value ϕJ ≃ 0.84 for-2D granular disks. The packing fraction shifts systematically to higher values under compressive cycling, corresponding to systematic shifts in the stress-strain response curves. Associated with these shifts are rotations of the crosses, with minimal changes in their centers of mass.

Highlights

Granular materials can be found in nature and in industrial applications
The jamming point is not a unique function of packing fraction, and it depends on the compression protocol
We have experimentally investigated the jamming transition of a packing formed from 2D photoelastic crosses subject to multiple cycles of compression that is either uniaxial or biaxial

Summary

Introduction

Granular materials can be found in nature and in industrial applications They have gas-like, liquid-like or solid-like properties depending on their density or shear stress [1,2,3,4]. Several authors have shown that 3D systems of rods [18] or of non-convex particles, such as staples, or star-shaped particles have interlocking or entangled states that are mechanically stable [19,20,21]. Star-shaped non-convex particles, i.e. hexapods are interesting to both granular science and architecture design. These particles form stable granular aggregates by pouring [22]. We apply strain with a bi-axial apparatus [2, 27] which allows controlled strains in two directions, as in Fig. 1(c) and (d)

Experimental techniques

Experimental apparatus

Protocol

Results and discussion

Conclusion