Structural rearrangements and transport properties of cyclically sheared granular packings

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。本课题提出应用最先进的荧光指数匹配技术来测量颗粒在体中的三维位置，以研究密集颗粒体系在循环剪切作用下的弹塑性响应。所提出的研究将是变革性的，因为它允许人们系统地检查颗粒的堆积结构和输运系数，其体积分数范围从随机松散堆积到六边形紧密堆积，这在工业应用中是最常见的。有必要进行这样的研究，因为非热颗粒物质缺乏一个健全的流体动力学描述，尽管它们在工业过程中占主导地位，导致特设的解决方案。所提出的工作建立在初步实验的基础上，在初步实验中，发现剪切致密颗粒介质的速度自相关函数显示出快速衰减，这增加了水动力计算可以扩展到比平衡状态下弹性硬球液体更大的体积分数范围的可能性。研制了一种循环剪切室装置，在土体中得到了较宽的剪切带。三维粒子跟踪允许人们测量最近邻分布，二十面体有序参数，除了Voronoi体积分布作为体积分数和应变的函数，这在胶体玻璃共聚焦显微镜中完成的方式很多，但在这里是100倍大的尺度。这些信息可以揭示颗粒系统的基本假设，并了解它们与其他颗粒物质（如胶体玻璃和悬浮液）的性质，此外还有助于建立计算模型。剪切应用的循环和准静态性质将使我们能够确定在有限刚性多接触颗粒系统中可以体验弹性响应的参数。此外，一旦塑性变形发生，检测非均质性，识别不可见的剪切转变区并确定其拓扑结构。然后，PI将研究多分散性对颗粒堆积和输运性能的影响。众所周知，即使微粒之间存在微小的差别，它们也会分离。特别是，我们将检查一个入侵者粒子的运动在一个循环剪切系统和研究大小，粗糙度，密度和重力之间的竞争。将测试波动耗散原理在其运动中的应用。与理论计算的比较将与班加罗尔印度科学院化学工程系的V. Kumaran教授合作进行。此外，PI建议建立一个可从网上下载的数据库，其中包含所有粒子的轨迹，作为剪切循环的函数，该领域的其他成员可以使用它来进行自己的分析。建议的工作除了促进国际合作外，还将对本科生、研究生和博士后的培养产生重大影响。代表性不足的成员参与STEM职业将受到积极影响，因为从事该项目的研究生是女性，而博士后有部分非洲血统。这项资助将增加本科生的暑期研究经验，并帮助他们在实验室完成荣誉论文项目。该研究的各个方面也将被改编成目前由PI正在开发的力学课程。

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).0853943KudrolliIntellectual Merit The PI proposes to apply a state of the art fluorescent index matching technique to measure the three dimensional positions of particles in the bulk to investigate the elastic and plastic response of a dense granular system undergoing cyclic shear. The proposed research will be transformative because it allows one to systematically examine the packing structure and transport coefficients of the particles over a volume fraction ranging from random loose packing to hexagonal close packings in a regime which is most common to industrial applications. There is a need for such a study because athermal granular matter lacks a sound hydrodynamic description in spite of their preponderance in industrial processes leading to ad hoc solutions. The proposed work builds on preliminary experiments where it is found that velocity auto correlation function for sheared dense granular media show a fast decay, which raises the possibility that hydrodynamic calculations can be extended to significantly greater range of volume fractions compared with elastic hard sphere liquids at equilibrium. A cyclic shear cell apparatus is developed, and a broad shear zone is obtained in the bulk. Three dimensional particle tracking allows one to measure nearest neighbor distribution, the icosahedral order parameter, besides the Voronoi volume distribution as a function of volume fraction and strain, much in the way this is being accomplished in colloidal glasses with confocal microscopy, but here at a 100 times larger scale. Such information can reveal fundamental assumptions about granular systems and understanding of their properties in relation to other particulate matter such as colloidal glasses and suspensions, besides help develop a computational model. The cyclic and quasi static nature of the shear application, will allow us to identify parameters over which one can experience an elastic response in finite, rigid multi contact particulate systems. Furthermore, once plastic deformation has occured, detect heterogenities, identify irrevisible shear transformation zones and determine their topology. Then, the PI will investigate the effect of polydispersity on granular packing and transport properties. It is well know that particulates segregate even if minor differences between them exist. In particular, we will examine the motion of an intruder particle in a cyclically sheared system and study the competition between size, roughness, density and gravity. The application of the fluctuation-dissipation principle to their motion will be tested. The comparison with theoretical calculations will be conducted in collaboration with Professor V. Kumaran of the Department of Chemical Engineering at the Indian Institute of Sciences, Bangalore. Further, the PI proposes to build a database downloadable from the web, containing the trajectories of all the particles as a function of shear cycle that other members in the field can use to carry out their own analysis.Broader Impact The proposed work will have significant impact on undergraduate, graduate and post doctoral student training, besides fostering international collaborations. The involvement of underrepresented members in STEM careers will be positively impacted because the graduate student working on the project is female, and the post doctoral student has partial African heritage. The grant will enhance summer research experience of undergraduate students and help accomplish their honor thesis projects in the laboratory. Aspects of the research will be also adapted into a course on mechanics currently being developed by the PI.