Stick-Slip Fluctuations in Granular Drag.pdf

a r X i v : c o n d - m a t / 0 1 0 2 5 2 3 v 1 [ c o n d - m a t .d i s - n n ] 2 8 F e b 2 0 0 1 Stick-Slip Fluctuations in Granular Drag I. Albert1, P. Tegzes1,2, R. Albert1, J. G. Sample1, A.-L. Baraba?si1, T. Vicsek2, and P. Schiffer1,2,? 1 Department of Physics, University of Notre Dame, Notre Dame, IN 46556 2 Department of Biological Physics, Eo?tvo?s University, Budapest 1117, Hungary 3 Department of Physics, Pennsylvania State University, University Park, PA 16802 (February 1, 2008) Abstract We study fluctuations in the drag force experienced by an object moving through a granular medium. The successive formation and collapse of jammed states give a stick-slip nature to the fluctuations which are periodic at small depths but become ”stepped” at large depths, a transition which we interpret as a consequence of the long-range nature of the force chains and the finite size of our experiment. Another important finding is that the mean force and the fluctuations appear to be independent of the properties of the contact surface between the grains and the dragged object. These results imply that the drag force originates in the bulk properties of the granular sample. Typeset using REVTEX 1 I. INTRODUCTION. The propagation of stress in granular media presents a complex problem which has been the subject of extensive study. An applied external stress results in the development of an internal structure resisting the stress, a so-called ”jammed state” that is dependent on the direction and magnitude of the stress [1,2]. The origins of this jamming lie in the fact that the forces do not propagate uniformly through the granular sample but are localized along directional force chains [3–10], and the jammed state is ultimately characterized by the properties of the network of these chains. In this paper we investigate the jamming of spherical granular media by analyzing the drag force opposing the movement of a solid object through such media. The object’s motion