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

TL;DR

This paper introduces a novel method of tuning granular material properties by embedding weak magnetic particles, which self-organize into force networks, influencing the system's mechanical behavior during unjamming and re-jamming processes.

Contribution

The study demonstrates that magnetic interactions in granular systems can self-organize into force networks, providing a reversible way to control mechanical properties.

Findings

Magnetic particles form stable chains that overlap with force chains.

Magnetic interactions influence force network evolution during unjamming.

Magnetic self-organization can reversibly alter granular mechanics.

Abstract

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. Some of the particles have embedded cuboidal magnets. The strength of the magnetic interactions between particles are 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 states. In this case, a statistically stable network of magnetic chains self-organizes and overlaps with force chains, strengthening the granular medium. We believe this property can be used to reversibly control mechanical properties of granular materials.