Yielding, rigidity, and tensile stress in sheared columns of hexapod granules
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Granular packings of non-convex or elongated particles can form free-standing structures like walls or arches. For some particle shapes, such as staples, the rigidity arises from interlocking of pairs of particles, but the origins of rigidity for non-interlocking particles remains unclear. We report on experiments and numerical simulations of sheared columns of ``hexapods,'' particles consisting of three mutually orthogonal sphero-cylinders whose centers coincide. We vary the length-to-diameter aspect ratio, $\alpha$, of the sphero-cylinders and subject the packings to quasistatic direct shear. For small $\alpha$, we observe a finite yield stress. For large $\alpha$, however, the column becomes rigid when sheared, supporting stresses that increase sharply with increasing strain. Analysis of X-ray micro-computed tomography (Micro-CT) data collected during the shear reveals that the stiffening is associated with a tilted, oblate cluster of hexapods near the nominal shear plane in which particle deformation and average contact number both increase. Simulation results show that the particles are collectively under tension along one direction even though they do not interlock pairwise. These tensions comes from contact forces carrying large torques, and they are perpendicular to the compressive stresses in the packing. They counteract the tendency to dilate, thus stabilize the particle cluster.
Published Version (Please cite this version)10.1103/physreve.101.062903
Publication InfoZhao, Yuchen; Barés, Jonathan; & Socolar, Joshua ES (n.d.). Yielding, rigidity, and tensile stress in sheared columns of hexapod granules. Physical Review E, 101(6). pp. 062903. 10.1103/physreve.101.062903. Retrieved from https://hdl.handle.net/10161/21148.
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Professor of Physics
Prof. Socolar is interested in collective behavior in condensed matter and dynamical systems. His current research interests include: Limit-periodic structures, quasicrystals, packing problems, and tiling theory; Self-assembly and phases of designed colloidal particles; Organization and dynamics of complex networks; Topological elasticity of mechanical lattices.
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