Microscopic reversibility and emergent elasticity in ultrastable granular systems
Microscopic reversibility and emergent elasticity in ultrastable granular systems
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DOI：
10.3389/fphy.2022.1048683
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发表时间：
2022-09
期刊：
影响因子：
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通讯作者：
Yiqiu Zhao;Yuchen Zhao;Dong Wang;Hu Zheng;B. Chakraborty;J. Socolar
中科院分区：
文献类型：
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作者：
Yiqiu Zhao;Yuchen Zhao;Dong Wang;Hu Zheng;B. Chakraborty;J. Socolar
在最近的一篇论文中（Zhao等人，Phys Rev X，2022，12：031，021），我们报道了在受到小振幅循环剪切的剪切堵塞颗粒系统中的"超稳定"状态的实验观察。在这样的状态下，所有的颗粒位置和接触力在每个剪切循环之后被再现，使得应力和颗粒位置的选通图像看起来是静态的。在目前的工作中，我们报告进一步分析这些实验的数据，以表征全球和本地的超稳态响应在一个剪切周期内，而不仅仅是频闪的动态。我们发现，超稳定状态遵循指数β = 0.5的剪切模量和压力之间的幂律关系，让人联想到临界堵塞附近的标度律。我们还研究了使用光弹性测量法测量的接触力的演变。我们发现，有两种类型的接触：非持久性接触，可逆地打开和关闭;和持久性接触，从来没有打开，并显示没有可测量的滑动。我们表明，非持久接触的紧急剪切模量作出不可忽略的贡献。我们还分析了应力张量的空间相关性，并将其与最近的颗粒固体涌现弹性理论的预测进行比较，颗粒力学和动力学的矢量电荷理论（VCTG）（Nampoothiri等人，Phys Rev Lett，2020，125：118，002）。我们表明，我们的实验结果可以很好地拟合VCTG，假设单轴对称的接触网络。拟合结果表明，超稳态对外加应力的响应比原始剪切堵塞状态的响应更具有各向同性。我们的研究结果提供了重要的洞察力的机械性能的摩擦颗粒状固体剪切。
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.