title: Stress Relaxation for Granular Materials near Jamming under Cyclic Compression.
abstract: We have explored isotropically jammed states of semi-2D granular materials through cyclic compression. In each compression cycle, systems of either identical ellipses or bidisperse disks transition between jammed and unjammed states. We determine the evolution of the average pressure P and structure through consecutive jammed states. We observe a transition point ϕ_{m} above which P persists over many cycles; below ϕ_{m}, P relaxes slowly. The relaxation time scale associated with P increases with packing fraction, while the relaxation time scale for collective particle motion remains constant. The collective motion of the ellipses is hindered compared to disks because of the rotational constraints on elliptical particles.
authors.affiliation: Department of Physics and Center for Nonlinear and Complex Systems, Box 90305, Duke University, Durham, North Carolina 27708, USA.
authors.forename: Somayeh
authors.initials: S
authors.lastname: Farhadi
authors.affiliation: Department of Physics and Center for Nonlinear and Complex Systems, Box 90305, Duke University, Durham, North Carolina 27708, USA.
authors.forename: Alex Z
authors.initials: AZ
authors.lastname: Zhu
authors.affiliation: Department of Physics and Center for Nonlinear and Complex Systems, Box 90305, Duke University, Durham, North Carolina 27708, USA.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Behringer