MR imaging of Reynolds dilatancy in the bulk of smooth granular flowsK. Sakaie1, D. Fenistein2, T. J. Carroll3, M. van Hecke2 and P. Umbanhowar4
1 The Cleveland Clinic - 9500 Euclid Ave., Mailcode U-15, Cleveland, OH 44195, USA
2 Kamerlingh Onnes Lab, Universiteit Leiden - Postbus 9504, 2300 RA Leiden - The Netherlands
3 Departments of Biomedical Engineering and Radiology, Northwestern University 676 N. St. Clair, Suite 1400, Chicago, IL 60611, USA
4 Department of Mechanical Engineering, Northwestern University - Evanston, IL 60208, USA
received 28 July 2008; accepted in final form 15 September 2008; published November 2008
published online 14 October 2008
Dense granular matter has to expand in order to flow, a phenomenon known as dilatancy. Here we perform, by means of Magnetic Resonance Imaging (MRI), direct measurements of the evolution of the local packing density of a slow and smooth granular shear flow generated in a split-bottomed geometry. The degree of dilatancy is found to be surprisingly strong. For flows without appreciable transient, the dilated zone follows the region of large strain rate, while for flows with a strong transient, the dilated zone extends also into the region where transient flow took place. In all cases, the dilated zone slowly spreads as a function of time. These findings suggest that the local packing density is governed by the total amount of local strain experienced since the start of the experiment.
83.80.Fg - Granular solids.
47.57.Gc - Granular flow.
45.70.-n - Granular systems.
© EPLA 2008