Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session Z2: Invited Session: Jamming and Rheology of Disordered Systems |
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Sponsoring Units: DCMP GSNP Chair: Bulbul Chakraborty, Brandeis University Room: Ballroom II |
Friday, March 22, 2013 11:15AM - 11:51AM |
Z2.00001: Impact-activated solidification of dense suspensions Invited Speaker: Scott Waitukaitis Shear-thickening, non-Newtonian fluids have typically been investigated under steady-state conditions. This approach has produced two pictures for suspension response to imposed forcing. In the weak shear-thickening picture, the response is typically attributed to the hydrodynamic interactions giving rise to hydroclusters, small groups of particles interacting through lubrication forces. At the other end of the spectrum, in the discontinuous shear-thickening regime, the response can be seen as a system-wide jamming that is ultimately limited in strength by the system boundaries. While these steady-state pictures have proven extremely useful, some of the most interesting phenomena associated with dense suspensions is transient and local in character. A prototypical example is the extraordinarily large impact resistance of dense suspensions such as cornstarch and water. When poked lightly these materials respond like a fluid, but when punched or kicked they seem to temporarily ``solidify'' and provide enormous resistance to the motion of the impacting object. Using an array of experimental techniques, including high-speed video, embedded force and acceleration sensing, and x-ray imaging, we are able to investigate the dynamic details this process as it unfolds. We find that an impacting object drives the rapid growth of a jammed, solid-like region directly below the impact site. Being coupled to the surrounding fluid by grain-mediated lubrication forces, this creates substantial peripheral flow and ultimately leads to the sudden extraction of the impactor's momentum. With a simple jamming picture to describe the solidification and an added mass model to explain the force on the rod, we are able to predict the forces on the impactor quantitatively. These findings highlight the importance of the non-equilibrium character of dense suspensions near jamming and might serve as a bridge between the weak and discontinuous shear-thickening pictures. [Preview Abstract] |
Friday, March 22, 2013 11:51AM - 12:27PM |
Z2.00002: Dilatancy and shear thickening of particle suspensions Invited Speaker: Daniel Bonn Shear thickening is a fascinating subject, as 99.9{\%} of complex fluids are thinning; thickening systems thus are the ``exception to the rule'' that needs to be understood. Moreover, such tunable systems show very promising applications, e.g. to block large underground pores in oil recovery to maintain a constant oil flow by plugging water filled pores (an approach used in oil recovery by e.g. Shell), or to manufacture bulletproof vests that are comfortable to wear, but stop bullets nonetheless. We study the rheology of non-Brownian particle suspensions (notably, cornstarch) that exhibit shear thickening. Using magnetic resonance imaging (MRI), the local properties of the flow are obtained by the determination of local velocity profiles and concentrations in a Couette cell. We also perform macroscopic rheology experiments in different geometries. The results suggest that the shear thickening is a consequence of dilatancy: the system under flow attempts to dilate but instead undergoes a jamming transition, because it is confined. This proposition is confirmed by an independent measurement of the dilation of the suspension as a function of the shear rate. [Preview Abstract] |
Friday, March 22, 2013 12:27PM - 1:03PM |
Z2.00003: Simulations of shear-induced jamming in athermal particulate systems Invited Speaker: Corey O'Hern We perform simulations of athermal particulate systems that are prepared in unjammed states with zero static shear modulus and then subjected to successive pure or simple quasistatic shear strains at either fixed packing fraction or fixed pressure. In response to applied shear, these systems jam, forming anisotropic networks of interparticle contacts. We determine the onset of shear-induced jamming as a function of the amplitude of the shear strain, packing fraction, pressure, and system size. We find that the parameter space for shear-induced jamming expands for particles with frictional interactions and nonspherical shapes. [Preview Abstract] |
Friday, March 22, 2013 1:03PM - 1:39PM |
Z2.00004: Dilatancy and Diffusion in Sheared Granular Materials Invited Speaker: Joshua Dijksman Disordered materials such as sand, foams and emulsions display a wide variety of different forms of mechanical behavior. Currently the origin of this rich dynamics is the subject of intense study. Experimentally it has proved difficult to probe the microscopic dynamics in these systems. We present an overview of experimental investigations that have been successful in giving more insight into the microstructural dynamics of disordered systems. We focus on shear induced dilatancy and diffusion in quasi statically deformed granular materials and suspensions and contrast the behavior of low and high friction particulate materials. We shall discuss the consequences of our observations in the context of shear banding and jamming phenomena. [Preview Abstract] |
Friday, March 22, 2013 1:39PM - 2:15PM |
Z2.00005: Rigidity of Dry Granular Solids Invited Speaker: Dapeng Bi Solids are distinguished from fluids by their ability to resist shear. In traditional solids, the resistance to shear come as an energy cost of straining, which works to distort density modulations that exists in both crystalline or amorphous structures. In our recent work,we focus on the emergence of shear-rigidity in a special class of solids: dry (non-cohesive) granular materials which have no energetically preferred density modulations. In contrast to traditional solids, the emergence of mechanical rigidity in these marginal granular solids is a collective process, which is controlled solely by boundary forces, the constraints of force and torque balance, and the positivity of the contact forces. We develop a theoretical framework based on these constraints, and show that these solids can be characterized by topological invariants and that, in two dimensions, they have internal patterns that are most naturally represented in the space of gauge field of the stress. Broken translational invariance in this gauge space is a necessary condition for rigidity in granular solids. We apply our theory to experimentally shear-jammed states as well as numerically generated jammed force networks to show that the statistics of stress fluctuations, and the ability of jammed configurations to resist deformations can be understood within this theoretical framework. [Preview Abstract] |
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