Yielding, Rigidity, and Tensile Stress in Sheared Columns of Hexapod Granules

Abstract

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.

arXiv comment12 pages, 23 figures

References in corpus (14)

• scikit-image: Image processing in Python
• Stress-strain behavior and geometrical properties of packings of elongated particles
• Particle Shape Effects on the Stress Response of Granular Packings
• Force transmission in a packing of pentagonal particles
• Granular materials composed of shape-anisotropic grains
• Jamming of 3D Prolate Granular Materials
• Column collapse of granular rods
• Strain-stiffening in random packings of entangled granular chains
• Jammed frictional tetrahedra are hyperstatic
• Transforming mesoscale granular plasticity through particle shape
• Perspective: Mechanics of randomly packed filaments -- the `bird nest' as meta-material
• Packings of 3D stars: Stability and structure
• Ideal isotropic auxetic networks from random networks
• Yielding and hardening of flexible fiber packings during triaxial compression

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