Sinking' in a bed of grains activated by shearing

• Published in: arXiv.org
• Main Authors: Hu, Zheng, Wang, Dong, Barés, Jonathan, Behringer, Robert P
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 11.12.2017
• Subjects: Cylinders; Drag; Excitation; Fluid dynamics; Fluid flow; Granular materials; Physics - Soft Condensed Matter; Physics - Statistical Mechanics; Polytetrafluoroethylene; Shearing; Stiffening
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1712.03908

We show how a weak force, \(f\), enables intruder motion through dense granular materials subject to external mechanical excitations, in the present case stepwise shearing. A force acts on a Teflon disc in a two dimensional system of photoelastic discs. This force is much smaller than the smallest force needed to move the disc without any external excitation. In a cycle, material + intruder are sheared quasi-statically from \(\gamma = 0\) to \(\gamma_{max}\), and then backwards to \(\gamma = 0\). During various cycle phases, fragile and jammed states form. Net intruder motion, \(\delta\), occurs during fragile periods generated by shear reversals. \(\delta\) per cycle, e.g. the quasistatic rate \(c\), is constant, linearly dependent on \(\gamma_{max}\) and \(f\). It vanishes as, \(c \propto (\phi_c - \phi)^a\), with \(a \simeq 3\) and \(\phi_c \simeq \phi_J\), reflecting the stiffening of granular systems under shear as \(\phi \rightarrow \phi_J\). The intruder motion induces large scale grain circulation. In the intruder frame, this motion is a granular analogue to fluid flow past a cylinder, where \(f\) is the drag force exerted by the flow.