Experimental Investigations of Sheared Granular Materials

颗粒材料是宏观的、单独的固体颗粒或“颗粒”的大集合体。了解和控制它们的性质对于从农业到民用、化学工程到材料科学等广泛领域的工业过程具有极其重要的意义。颗粒物质最显著的行为之一是在外加剪应力的作用下从受阻状态转变为非受阻状态。在这一转变过程中，颗粒材料的性质由固体转变为流体，并表现出剪切带形成等特性。这也是一个在实验和理论上具有挑战性的制度，目前的理解水平远远落后于其他相变，如发生在普通流体或固体中的相变。智力上的功绩。除了与适当控制颗粒物相关的工业和经济价值外，颗粒材料的研究还提供了对基本科学问题的见解。在颗粒介质中设计了一系列实验来研究从静态堆积到流动区域的转变的本质。重点是研究剪切带的形成和技术，使测量一些以前无法进行实验的最重要的物理量成为可能。特别是，将使用新开发的光学力可视化设备直接测量剪切带内随时间演变的力和应力。介绍了一种新型的线形平行板剪切池，它可以测量剪切带内结构和粘度从最初的暂态行为到最终的稳态特性的开始和演化。最后，我们将使用一个具有宽可调剪切带的改进型裂底Couet型剪切室来检验当前关于有效温度适用性的一些最重要的理论，并确定波动对这些系统的重要性。这些研究将有助于为到目前为止只在理论或模拟中得到测试的一些关键想法提供实验基础。更广泛的影响：关于剪切颗粒材料的实验研究将与一系列多方面的教育和外联活动密切结合。它包括让不同的高中实习生和本科生积极参与研究，与两个科学博物馆密切合作，开展动手活动，以及开发一门关于颗粒材料的新课程。此外，我们还计划举办一次关于颗粒物质和干扰转变的跨学科研讨会。

ABSTRACT - 0405619Granular materials are large aggregates of macroscopic, individually solid particles, or "grains". Understanding and controlling their properties is of tremendous importance for industrial processes across a wide range of fields from agriculture to civil and chemical engineering to materials science. One of the most remarkable behaviors of granular matter is the transition from a jammed to an unjammed state under an applied shear stress. At this transition granular materials change character from solid- to fluid-like and exhibit characteristic properties such as the formation of shear bands. This also is an experimentally and theoretically challenging regime for which the current level of understanding is far less developed than for other phase transitions such as those occurring in ordinary fluids or solids. Intellectual Merit. In addition to the industrial, economic value associated with proper control of particulate matter, the study of granular materials provides insights into fundamental scientific issues. A series of experiments in granular media has been designed to investigate the nature of the transition from static packing to a flowing regime. Emphasis is placed on studying the formation of shear bands and techniques that make it possible to measure some of the most important physical quantities that were previously inaccessible to experiment. In particular, direct measurements of the time-evolving forces and stresses within shear bands will be made using a newly developed optical force-visualization apparatus. A new type of linear, parallel plate shear cell is introduced that can measure the onset and evolution of structure and viscosity within a shear band from its initial transient behavior to it final steady-state character. Finally, a modified split-bottom Couette-type shear cell with wide and tunable shear band will be used to test some of the most important current theories concerning the applicability of effective temperatures and determine the importance of fluctuations generic to these systems. These studies will help provide an experimental underpinning for some of the key ideas that have so far only been tested in theory or simulation. Broader Impact: The experimental research on sheared granular materials will be closely integrated with a multi-faceted set of education and outreach activities. It includes the active participation of a diverse group of high-school interns and undergraduates in the research, a close collaboration with two science museums to develop hands-on activities, and the development of a new course on granular materials. In addition, we plan an interdisciplinary workshop on granular matter and the jamming transition.