Department of Physics & Center for Nonlinear and Complex Systems, Duke University, Durham, North Carolina 27708, USA.
Laboratoire de Mécanique et Génie Civil, Université de Montpellier, CNRS, Montpellier, 34090, France.
Phys Rev Lett. 2019 Oct 11;123(15):158001. doi: 10.1103/PhysRevLett.123.158001.
We study the jamming phase diagram of sheared granular material using a novel Couette shear setup with a multiring bottom. The setup uses small basal friction forces to apply a volume-conserving linear shear with no shear band to a granular system composed of frictional photoelastic discs. The setup can generate arbitrarily large shear strain due to its circular geometry, and the shear direction can be reversed, allowing us to measure a feature that distinguishes shear-jammed from fragile states. We report systematic measurements of the stress, strain, and contact network structure at phase boundaries that have been difficult to access by traditional experimental techniques, including the yield stress curve and the jamming curve close to ϕ_{SJ}≈0.75, the smallest packing fraction supporting a shear-jammed state. We observe fragile states created under large shear strain over a range of ϕ<ϕ_{SJ}. We also find a transition in the character of the quasistatic steady flow centered around ϕ_{SJ} on the yield curve as a function of packing fraction. Near ϕ_{SJ}, the average contact number, fabric anisotropy, and nonrattler fraction all show a change of slope. Above ϕ_{F}≈0.7 the steady flow shows measurable deviations from the basal linear shear profile, and above ϕ_{b}≈0.78 the flow is localized in a shear band.
我们使用一种新颖的带有多环底部的 Couette 剪切装置研究了剪切颗粒物质的阻塞相图。该装置使用小的基底摩擦力对由摩擦光弹性盘组成的颗粒系统施加具有体积守恒的线性剪切，没有剪切带。由于其圆形几何形状，该装置可以产生任意大的剪切应变，并且剪切方向可以反转，使我们能够测量到区分剪切阻塞与易碎状态的特征。我们报告了在传统实验技术难以达到的相界处的应力、应变和接触网络结构的系统测量，包括屈服应力曲线和接近ϕ_{SJ}≈0.75 的阻塞曲线，这是支持剪切阻塞状态的最小堆积分数。我们观察到在ϕ<ϕ_{SJ}范围内的大剪切应变下产生的易碎状态。我们还发现，在屈服曲线作为填充分数的函数的中心，在ϕ_{SJ}附近准静态稳定流动的特征发生了转变。在ϕ_{SJ}附近，平均接触数、织物各向异性和非跳动器分数都显示出斜率的变化。在ϕ_{F}≈0.7 以上，稳定流动表现出与基底线性剪切轮廓的可测量偏差，在ϕ_{b}≈0.78 以上，流动在剪切带中局部化。
