Combined effects of particle geometry and applied vibrations on the mechanics and strength of entangled materials

Abstract

Entangled materials offer attractive structural features including tensile strength and large deformations, combined with infinite assembly and disassembly capabilities. How the geometry of individual particles governs entanglement, and, in turn, translates into macroscopic structural properties, provides a rich landscape in terms of mechanics, and offers intriguing possibilities in terms of structural design. However, there are major knowledge gaps on the entanglement mechanisms and how they can generate strength. In this report, we present tensile tests and discrete element method simulations on bundles of entangled staple-like particles that capture the combined effects of particle geometry and vibrations on local entanglement, tensile force chains, and strength. Standard steel staples with θ = 90° crown-leg angle initially entangle better than θ = 20° modified staples because of their more “open” geometry. However, as vibrations are applied, entanglement increases faster in θ = 20° bundles so that they develop strong and stable tensile force chains, producing bundles which are almost ten times stronger than θ = 90° bundles. Both tensile strength and entanglement density increase with vibrations and with deformations, up to a steady state value where the rate of entanglement balances the rate of disentanglement. Finally, we show that vibration and mechanical confinement can be used as a strategy to manipulate entanglement and disentanglement for disassembly and recycling. This work provides a fundamental understanding of how particle geometry and vibrations govern the properties of entangled materials, which can lead to better design guidelines for lightweight, reversible materials and structures and aggregate architectures.