title: Shear-induced alignment and dynamics of elongated granular particles.
abstract: The alignment, ordering, and rotation of elongated granular particles was studied in shear flow. The time evolution of the orientation of a large number of particles was monitored in laboratory experiments by particle tracking using optical imaging and x-ray computed tomography. The experiments were complemented by discrete element simulations. The particles develop an orientational order. In the steady state the time- and ensemble-averaged direction of the main axis of the particles encloses a small angle with the streamlines. This shear alignment angle is independent of the applied shear rate, and it decreases with increasing grain aspect ratio. At the grain level the steady state is characterized by a net rotation of the particles, as dictated by the shear flow. The distribution of particle rotational velocities was measured both in the steady state and also during the initial transients. The average rotation speed of particles with their long axis perpendicular to the shear alignment angle is larger, while shear aligned particles rotate slower. The ratio of this fast/slow rotation increases with particle aspect ratio. During the initial transient starting from an unaligned initial condition, particles having an orientation just beyond the shear alignment angle rotate opposite to the direction dictated by the shear flow.
authors.affiliation: Institute for Solid State Physics and Optics, Wigner Research Center for Physics, Hungarian Academy of Sciences, PO Box 49, H-1525 Budapest, Hungary. borzsonyi.tamas@wigner.mta.hu
authors.forename: Tamás
authors.initials: T
authors.lastname: Börzsönyi
authors.forename: Balázs
authors.initials: B
authors.lastname: Szabó
authors.forename: Sandra
authors.initials: S
authors.lastname: Wegner
authors.forename: Kirsten
authors.initials: K
authors.lastname: Harth
authors.forename: János
authors.initials: J
authors.lastname: Török
authors.forename: Ellák
authors.initials: E
authors.lastname: Somfai
authors.forename: Tomasz
authors.initials: T
authors.lastname: Bien
authors.forename: Ralf
authors.initials: R
authors.lastname: Stannarius
mesh_terms: D003102:Colloids / Q000737:chemistry*; D003198:Computer Simulation; D055119:Elastic Modulus; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D033081:Shear Strength; D013314:Stress, Mechanical
chemical_list: D003102:Colloids