Self-organized magnetic particles to tune the mechanical behavior of a granular system

Meredith P Cox (1) , Dong P Wang (1) , Jonathan P Barés (1, 2, 3) , Robert P Behringer (1)

1 Department of Physics & Center for Nonlinear and Complex Systems
2 LMGC - Laboratoire de Mécanique et Génie Civil
3 PMMD - Physique et Mécanique des Milieux Divisés

Above a certain density a granular material jams. This property can be controlled by either tuning a global property, such as the packing fraction or by applying shear strain, or at the micro-scale by tuning grain shape, inter-particle friction or externally controlled organization. Here, we introduce a novel way to change a local granular property by adding a weak anisotropic magnetic interaction between particles. We measure the evolution of the pressure, P, and coordination number, Z, for a packing of 2D photo-elastic disks, subject to uniaxial compression. A fraction Rm of the particles have embedded cuboidal magnets. The strength of the magnetic interactions between particles is too weak to have a strong direct effect on P or Z when the system is jammed. However, the magnetic interactions play an important role in the evolution of latent force networks when systems containing a large enough fraction of the particles with magnets are driven through unjammed to jammed states. In this case, a statistically stable network of magnetic chains self-organizes before jamming and overlaps with force chains once jamming occurs, strengthening the granular medium. This property opens a novel way to control mechanical properties of granular materials.

Domaines: Mécanique statistique [cond-mat.stat-mech]; Systèmes désordonnés et réseaux de neurones [cond-mat.dis-nn]; Science des matériaux [cond-mat.mtrl-sci]; Matériaux; Mécanique des matériaux [physics.class-ph]

Meredith P Cox, Dong P Wang, Jonathan P Barés, Robert P Behringer. Self-organized magnetic particles to tune the mechanical behavior of a granular system. EPL - Europhysics Letters, 2016, 115 (6), pp.64003 - 64003. ⟨10.1209/0295-5075/115/64003⟩. ⟨hal-01394287⟩