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

• Published in: Europhysics letters Vol. 115; no. 6; p. 64003
• Main Authors: Cox, Meredith, Wang, Dong, Barés, Jonathan, Behringer, Robert P.
• Format: Journal Article
• Language: English
• Published: Les Ulis EDP Sciences, IOP Publishing and Società Italiana di Fisica 01.09.2016; IOP Publishing; European Physical Society / EDP Sciences / Società Italiana di Fisica / IOP Publishing
• Subjects: 47.57.Gc; 78.20.Fm; 81.05.Rm; Compressive strength; Condensed Matter; Coordination numbers; Disordered Systems and Neural Networks; Elastic anisotropy; Engineering Sciences; Granular materials; Granular media; Jamming; Magnetic properties; Magnets; Materials; Materials Science; Mechanical properties; Mechanics; Mechanics of materials; Physics; Shear strain; Statistical Mechanics; Tuning
• ISSN: 0295-5075; 1286-4854
• DOI: 10.1209/0295-5075/115/64003

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.