Collaborative Research: Discontinuous Shear Thickening and Shear Jamming in Dense Suspensions: Statistical Mechanics and the Microscopic Basis for Extreme Transitions of Properties

CBET-1605283/1605428PI：Morris，Jeffrey F./Chakraborty，BulBul这个合作项目包括对固体颗粒在液体中的悬浮流动的计算和理论研究。该项目专注于浓缩悬浮液，其中颗粒占据了混合物体积的一半以上。它们通常被称为致密悬浮液，可用作水泥、混凝土和矿浆。当流动条件改变时，稠密悬浮液的性质会突然改变。在某些情况下，随着流动强度或剪切速率的增加，混合物的流动阻力会突然出现极大的增加，这种现象被称为“不连续剪切增稠”(DST)。这种流动甚至可以停止，这就是所谓的“剪切堵塞”。DST可能会对涉及混合物的工业过程产生重大负面影响。虽然DST已经被知道很多年了，但它还没有被解释。这个项目的目标是确定这种现象发生的原因，这可以为如何设计悬浮和处理操作以减少DST的负面影响提供指导。这项研究的结果将被用在模块中，使高中生能够可视化多个颗粒系统导致大规模行为，例如玉米淀粉悬浮液中的DST，其中小颗粒的淀粉会导致流动特性的巨大变化。该项目将探索最近的观察结果，即DST可以通过颗粒接触和摩擦来解释。这项工作将探索颗粒之间的力网络结构，以及当流速增加到导致性质突然变化的水平时，这种结构如何变化。特别是，该团队将通过模拟不同流动中的离散粒子和应用统计物理的理论概念来探索流动性质转变是否具有相变的特征。液体的作用将通过将结果与干燥颗粒系统的行为进行比较来考虑，在干燥颗粒系统中，力网络的概念及其与干扰的关系已被他人检验。这项工作将探索流动诱导的性质变化与热力学相变的关系，并将建立不同颗粒流之间的异同。由于固液混合物在工业中广泛使用，并在泥石流等地球物理环境中发现，该项目将极大地扩展我们在重要应用中了解和最终预测这些复杂系统的动力学的能力。

CBET - 1605283/1605428PI: Morris, Jeffrey F./Chakraborty, BulbulThis collaborative project comprises computational and theoretical studies of the flow of suspensions consisting of solid particles in liquids. The project focuses on concentrated suspensions, where particles occupy more than half of the mixture volume. These are often called dense suspensions, and they are found in application as cement, concrete, and mineral ore slurries. Dense suspensions can change properties suddenly when flow conditions change. In some cases, as the strength of the flow, or shear rate, increases, the mixture can suddenly exhibit an extremely large increase in flow resistance, a phenomenon known as "discontinuous shear thickening" (DST). The flow can even stop, which is known as "shear jamming." DST can have major negative effects on industrial processes involving the mixtures. While DST has been known for many years, it has not been explained. The goal of this project is to determine why this phenomenon happens, which could provide guidance how to design suspensions and processing operations to diminish negative effects of DST. Results of the research will be used in modules that will enable high school students to visualize how many-particle systems result in large-scale behavior, such as DST in cornstarch suspensions, where small grains of starch cause enormous changes in flow properties.The project will explore recent observations that DST can be explained by particle contacts and friction. The work will explore the structure of networks of forces between the particles and how this structure changes as the flow rate is increased to a level causing abrupt changes in properties. In particular, the team will explore whether the flow property transition has the characteristics of a phase transition through simulations of discrete particles in different flows and applications of theoretical concepts from statistical physics. The role of the liquid will be considered by comparing results with the behavior of dry granular systems in which the force network concept and its relation to jamming have been examined by others. This work will probe the relationship of flow-induced property changes to thermodynamic phase transitions and will establish the similarities and differences between different particulate flows. Because solid-liquid mixtures are commonly used in industry and are found in geophysical settings such as mud flows, the project will significantly expand our ability to understand and ultimately predict the dynamics of these complicated systems in important applications.