title: Polydirectional stability of granular matter.
abstract: We investigate jammed granular matter in a slowly rotating drum partially filled with granular material and find a state of polydirectional stability. In this state, the material responds elastically to small stresses in a wide angular interval while it responds by plastic deformation when subjected to small stresses outside this interval of directions. We describe the evolution of the granulate by means of a rate equation and find quantitative agreement with the experiment. The state of polydirectional stability complements the fragile state, where the material responds elastically to small applied stresses only in a certain direction but even very small stresses in any other direction would lead to plastic deformations. Similar to fragile matter, polydirectionally stable matter is created in a dynamic process by self-organization.
authors.affiliation: Institute for Multiscale Simulation of Particulate Systems, Friedrich-Alexander-Universität Erlangen-Nürnberg, Naegelsbachstrasse 49b, 91052 Bavaria, Germany.
authors.forename: Fabian
authors.initials: F
authors.lastname: Zimber
authors.forename: Jonathan E
authors.initials: JE
authors.lastname: Kollmer
authors.forename: Thorsten
authors.initials: T
authors.lastname: Pöschel