Turbulent-like velocity fluctuations in two-dimensional granular materials subject to cyclic shear

Sun, Aile; Wang, Yinqiao; Chen, Yangrui; Shang, Jun; Zheng, Jie; Yu, Shuchang; Su, Siyuan; Sun, Xulai; Zhang, Jie

doi:10.1039/d1sm01516h

Cited by 5 publications

(3 citation statements)

References 45 publications

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“…Notably, the ultrastable states follow G ~pβ with β ≈ 0.5, consistent with a numerical simulation with particles having similar friction coefficient and contact force law [42]. To our knowledge, the range of boundary strain within which a frictional system behaves elastically is usually very small because boundary strain may induce sliding at contacts [60][61][62][63]. Thus the shear modulus has typically been determined from measurements of sound speeds [44] rather than from stress-strain curves.…”

Section: Concluding Discussionsupporting

confidence: 66%

Microscopic reversibility and emergent elasticity in ultrastable granular systems

Zhao

Wang

et al. 2022

Front. Phys.

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In a recent paper (Zhao et al., Phys Rev X, 2022, 12: 031,021), we reported experimental observations of “ultrastable” states in a shear-jammed granular system subjected to small-amplitude cyclic shear. In such states, all the particle positions and contact forces are reproduced after each shear cycle so that a strobed image of the stresses and particle positions appears static. In the present work, we report further analyses of data from those experiments to characterize both global and local responses of ultrastable states within a shear cycle, not just the strobed dynamics. We find that ultrastable states follow a power-law relation between shear modulus and pressure with an exponent β ≈ 0.5, reminiscent of critical scaling laws near jamming. We also examine the evolution of contact forces measured using photoelasticimetry. We find that there are two types of contacts: non-persistent contacts that reversibly open and close; and persistent contacts that never open and display no measurable sliding. We show that the non-persistent contacts make a non-negligible contribution to the emergent shear modulus. We also analyze the spatial correlations of the stress tensor and compare them to the predictions of a recent theory of the emergent elasticity of granular solids, the Vector Charge Theory of Granular mechanics and dynamics (VCTG) (Nampoothiri et al., Phys Rev Lett, 2020, 125: 118,002). We show that our experimental results can be fit well by VCTG, assuming uniaxial symmetry of the contact networks. The fits reveal that the response of the ultrastable states to additional applied stress is substantially more isotropic than that of the original shear-jammed states. Our results provide important insight into the mechanical properties of frictional granular solids created by shear.

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Section: Concluding Discussionsupporting

confidence: 66%

Microscopic reversibility and emergent elasticity in ultrastable granular systems

Zhao

Wang

et al. 2022

Front. Phys.

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“…Collective motion in granular materials is often associated with phenomena such as jamming, particle polarity, and particle shape. In densely packed granular systems subjected to quasi-static shear, the behavior of contacts and contact forces plays a crucial role in floppy modes 10 , 11 , plastic deformation 12 , 13 , and the formation of turbulent-like vortices 14 , 15 . When granular materials are subjected to vibration, inelastic collisions become prominent, and the polarity and shape of the particles become significant factors.…”

Section: Introductionmentioning

confidence: 99%

Anomalous flocking in nonpolar granular Brownian vibrators

Chen,

Zhang

2024

Nat Commun

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Using Brownian vibrators, we investigated the structures and dynamics of quasi-2d granular materials, with packing fractions (ϕ) ranging from 0.111 to 0.832. Our observations revealed a remarkable large-scale flocking behavior in hard granular disk systems, encompassing four distinct phases: granular fluid, flocking fluid, poly-crystal, and crystal. Anomalous flocking emerges at ϕ = 0.317, coinciding with a peak in local density fluctuations, and ceased at ϕ = 0.713 as the system transitioned into a poly-crystal state. The poly-crystal and crystal phases resembled equilibrium hard disks, while the granular and flocking fluids differed significantly from equilibrium systems and previous experiments involving uniformly driven spheres. This disparity suggests that collective motion arises from a competition controlled by volume fraction, involving an active force and an effective attractive interaction resulting from inelastic particle collisions. Remarkably, these findings align with recent theoretical research on the flocking motion of spherical active particles without alignment mechanisms.

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“…Collective motion in granular materials often relates to jamming or a particle's polarity and shape. In quasistatically sheared dense granular packings, contacts and contact forces are essential in floppy modes [10,11], plastic deformation [12,13], and turbulent-like vortices [14,15]. Under vibration, inelastic collisions are prominent, where the particle's polarity and shape are essential.…”

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confidence: 99%

Clusters and collective motions in Brownian vibrators

Chen¹,

Zhang²

2023

Preprint

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Using Brownian vibrators, where single particles can undergo Brownian motion under vibration, we experimentally investigated self-organized structures and dynamics of quasi-two-dimensional (quasi-2d) granular materials with volume fractions 0.111 ≤ φ ≤ 0.832. We show rich structures and dynamics in hard-disk systems of inelastic particle collisions, with four phases corresponding to cluster fluid, collective fluid, poly-crystal, and crystal. While poly-crystal and crystal are strikingly similar to the equilibrium hard disks, the first two phases differ substantially from the equilibrium ones and the previous quasi-2d experiments of uniformly driven spheres. Our investigation provides single-particle-scale evidence that granular materials subject to uniform random forcing are weakly cohesive with complex internal structures and dynamics. Moreover, our experiment shows that large-scale collective motion can arise in a purely repulsive hard-disk system. The collective motion emerges near φ = 0.317, where the most significant clusters span half of the system, and disappears near φ = 0.713, around which the system crystallizes and the melting transition occurs in the equilibrium hard disks.

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Turbulent-like velocity fluctuations in two-dimensional granular materials subject to cyclic shear

Abstract: We perform a systematic experimental study to investigate the velocity fluctuations in the two-dimensional granular matter of low and high friction coefficients subjected to cyclic shear of a range of...

Cited by 5 publications

References 45 publications

Microscopic reversibility and emergent elasticity in ultrastable granular systems

Microscopic reversibility and emergent elasticity in ultrastable granular systems

Anomalous flocking in nonpolar granular Brownian vibrators

Clusters and collective motions in Brownian vibrators

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