Granular materials consist of macroscopic grains, interacting via contact forces, and unaffected by thermal fluctuations. They are one of a class systems that undergo jamming, i.e. a transition between fluid-like and disordered solid-like states. Roughly twenty years ago, proposals by Cates et al for the shear response of colloidal systems and by Liu and Nagel, for a universal jamming diagram in a parameter space of packing fraction, ϕ, shear stress, τ, and temperature, T raised key questions. Contemporaneously, experiments by Howell et al and numerical simulations by Radjai et al and by Luding et al helped provide a starting point to explore key insights into jamming for dry, cohesionless, granular materials. A recent experimental observation by Bi et al is that frictional granular materials have a a re-entrant region in their jamming diagram. In a range of ϕ, applying shear strain, γ, from an initially force/stress free state leads to fragile (in the sense of Cates et al), then anisotropic shear jammed states. Shear jamming at fixed ϕ is presumably conjugate to Reynolds dilatancy, involving dilation under shear against deformable boundaries. Numerical studies by Radjai and Roux showed that Reynolds dilatancy does not occur for frictionless systems. Recent numerical studies by several groups show that shear jamming occurs for finite, but not infinite, systems of frictionless grains. Shear jamming does not lead to known ordering in position space, but Sarkar et al showed that ordering occurs in a space of force tiles. Experimental studies seeking to understand random loose and random close packings (rlp and rcp) and dating back to Bernal have probed granular packings and their response to shear and intruder motion. These studies suggest that rlp's are anisotropic and shear-jammed-like, whereas rcp's are likely isotropically jammed states. Jammed states are inherently static, but the jamming diagram may provide a context for understanding rheology, i.e. dynamic shear in a variety of systems that include granular materials and suspensions.

中文翻译：

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颗粒材料的干扰物理学：综述

颗粒材料由宏观颗粒组成，通过接触力相互作用，不受热波动的影响。它们是受到干扰的一类系统之一，即类流体状态和类无序固体状态之间的过渡。大约 20 年前，Cates 等人关于胶体系统剪切响应的建议以及 Liu 和 Nagel 提出的关于填充率参数空间 ϕ、剪切应力、τ 和温度 T 中的通用干扰图的建议提出了关键问题. 与此同时，Howell 等人的实验以及 Radjai 等人和 Luding 等人的数值模拟帮助提供了一个起点，以探索对干燥、无内聚力、颗粒材料的干扰的关键见解。Bi 等人最近的一项实验观察是摩擦颗粒材料在其干扰图中具有一个凹进区域。在 ϕ 范围内，从最初的无力/无应力状态施加剪切应变 γ 会导致脆弱（在 Cates 等人的意义上），然后是各向异性剪切堵塞状态。固定 ϕ 处的剪切干扰可能与雷诺膨胀共轭，涉及在剪切下对可变形边界的膨胀。Radjai 和 Roux 的数值研究表明，无摩擦系统不会发生雷诺剪胀。几个小组最近的数值研究表明，剪切干扰发生在有限但不是无限的无摩擦颗粒系统中。剪切干扰不会导致位置空间中的已知排序，但 Sarkar 等人表明排序发生在力瓦片空间中。旨在了解随机松散和随机密堆积（rlp 和 rcp）并追溯到 Bernal 的实验研究已经探讨了颗粒堆积及其对剪切和入侵者运动的响应。这些研究表明 rlp 是各向异性的和类似剪切堵塞的，而 rcp 可能是各向同性的堵塞状态。堵塞状态本质上是静态的，但堵塞图可以提供理解流变学的背景，即包括颗粒材料和悬浮液的各种系统中的动态剪切。