title: Optimizing packing fraction in granular media composed of overlapping spheres.
abstract: What particle shape will generate the highest packing fraction when randomly poured into a container? In order to explore and navigate the enormous search space efficiently, we pair molecular dynamics simulations with artificial evolution. Arbitrary particle shape is represented by a set of overlapping spheres of varying diameter, enabling us to approximate smooth surfaces with a resolution proportional to the number of spheres included. We discover a family of planar triangular particles, whose packing fraction of ϕ ∼ 0.73 is among the highest experimental results for disordered packings of frictionless particles. We investigate how ϕ depends on the arrangement of spheres comprising an individual particle and on the smoothness of the surface. We validate the simulations with experiments using 3D-printed copies of the simplest member of the family, a planar particle consisting of three overlapping spheres with identical radius. Direct experimental comparison with 3D-printed aspherical ellipsoids demonstrates that the triangular particles pack exceedingly well not only in the limit of large system size but also when confined to small containers.
authors.affiliation: James Franck Institute and Department of Physics, The University of Chicago, Chicago, IL 60637, USA. rothl@uchicago.edu.
authors.forename: Leah K
authors.initials: LK
authors.lastname: Roth
authors.affiliation: James Franck Institute and Department of Physics, The University of Chicago, Chicago, IL 60637, USA. rothl@uchicago.edu.
authors.forename: Heinrich M
authors.initials: HM
authors.lastname: Jaeger