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》(Public Law 111-5)获得资助的。0853943 Kudroli智力优势PI建议应用最先进的荧光指数匹配技术来测量颗粒在散体中的三维位置，以研究经历循环剪切的致密颗粒系统的弹性和塑性响应。这项拟议的研究将是变革性的，因为它允许人们系统地检查颗粒在从随机松散堆积到六角形紧密堆积的体积分数范围内的堆积结构和传输系数，这在工业应用中是最常见的。有必要进行这样的研究，因为尽管非热颗粒物质在工业过程中具有优势，但缺乏合理的流体动力学描述，从而导致了特别的解决方案。这项工作建立在初步实验的基础上，发现剪切致密颗粒介质的速度自相关函数表现出快速衰减，这增加了流体动力学计算可以扩展到比平衡时弹性硬球液体的体积分数更大的范围的可能性。研制了循环剪切室装置，获得了较宽的块体剪切带。三维粒子跟踪使人们能够测量最近的邻居分布，二十面体有序参数，除了作为体积分数和应变的函数的Voronoi体积分布，这很像用共焦显微镜在胶体玻璃中实现的方法，但这里的尺度要大100倍。这些信息可以揭示关于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)相关的性质，此外还有助于开发计算模型。剪切作用的循环和准静态性质，将使我们能够识别在有限的、刚性的多接触颗粒系统中可以体验弹性响应的参数。此外，一旦发生塑性变形，检测异质性，识别不可见的剪切相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传输特性的影响。众所周知，即使微粒之间存在微小的差异，它们也是相互隔离的。特别是，我们将研究入侵者粒子在周期性剪切系统中的运动，并研究大小、粗糙度、密度和重力之间的竞争。将检验涨落耗散原理在它们运动中的应用。与理论计算的比较将与班加罗尔印度科学研究所化学工程系的V.Kumaran教授合作进行。此外，PI建议建立一个可从网络下载的数据库，其中包含作为剪切循环函数的所有粒子的轨迹，该领域的其他成员可以使用该数据库进行自己的分析。代表人数不足的成员参与STEM职业生涯将受到积极影响，因为参与该项目的研究生是女性，博士后学生有部分非洲血统。这笔助学金将增强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。这项研究的各个方面也将被改编成国际和平研究所目前正在开发的一门力学课程。

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.