Shear Driven Flow of Granular and Soft-Matter Materials

非技术总结该奖项支持颗粒材料和软物质材料的理论和计算研究及教育。颗粒和软物质材料在自然界和日常生活中无处不在。一类这样的材料是干燥的颗粒状材料，它包括粉末、种子、颗粒、沙子和砾石。另一类被归类为软物质材料，通常由悬浮在流体中的颗粒组成。它们包括：由一种液体的液滴悬浮在另一种液体中的乳状液，如蛋黄酱、醋酱和均质牛奶；由悬浮在液体中的气泡组成的泡沫，如剃须膏、肥皂泡和生奶油；以及由悬浮在液体中的固体颗粒组成的悬浮液，如番茄酱、芥末和油漆。这些材料对各种各样的技术和工业过程都很重要，从药品和食品的加工到种子和谷物的运输，再到材料的制造。在最简单的抽象层面上，人们可以认为这些材料是由大粒子组成的，对这些大粒子来说，热波动可以忽略不计，只有当它们相互接触时才会相互作用，在这种情况下，它们相互排斥。然而，尽管表面上看起来很简单，但可能会出现令人惊讶的复杂行为，特别是从流动的类液体状态转变为刚性但无序的固体状态，因为颗粒堆积密度或施加的应力是不同的。这就是所谓的“干扰过渡”。在这个项目中，计算机模拟将被用来研究这种堵塞转变的性质，以及在剪切驱动流下出现的这种材料的更一般的行为，其中相邻的颗粒层以不同的相对速度彼此平行移动。将研究不同的能量消散机制，以及不同颗粒形状的影响。该项目还将促进多个机构的广泛学生的教学、培训和参与科学研究。本科生将通过在地方和国家研究会议上发表工作来获得科学研究和科学交流方面的经验。研究生将接受现代理论和高性能计算方法的培训，以及理论和实验之间直接互动的经验研究。通过这种方式，他们为未来在学术界或工业界从事高科技职业做好了准备。通过与从事这一领域补充实验和计算研究的国内和国际同事建立合作网络，将加强研究和教育的基础设施。技术总结该奖项支持颗粒和软物质材料方面的理论和计算研究及教育。将进行计算机模拟，以研究颗粒和软物质材料在干扰转变附近的不同方面的行为，该转变标志着随着颗粒堆积的增加，从流动的类液体状态突然转变为刚性但无序的固体状态。感兴趣的材料包括干燥的颗粒物质、浆液中的致密颗粒颗粒、乳剂、泡沫、非布朗悬浮液和胶体。具体问题将被调查，目的是增加对这种材料的流动液体和无序固相，以及它们之间的转变的了解。这些包括：(I)均匀环境中剪切流动材料剪切条带背后的物理机制；(Ii)不连续剪切增厚、剪切应力在增加应变率时的快速跳跃和微观颗粒间弹性摩擦之间的关系；(Iii)摩擦颗粒系统中各向同性压缩干扰和剪切干扰的区别；(Iv)取向有序化和颗粒翻滚对由非球形颗粒组成的材料剪切流动的影响；(V)非球形颗粒剪切驱动阻塞转变的临界性；(Vi)颗粒表面凹陷对剪切流变学的影响。与在这些领域工作的实验小组的合作将有助于提供信息和指导理论进展。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NONTECHNICAL SUMMARYThis award supports theoretical and computational research and education in granular and soft-matter materials. Granular and soft-matter materials are ubiquitous in nature and every day life. One such class of materials is dry granular materials, which includes powders, seeds, grains, sand, and gravel. Another class are classified among soft-matter materials, and generally consist of particles suspended in fluids. These include: emulsions consisting of droplets of one fluid suspended in a second fluid, such as mayonnaise, vinaigrettes, and homogenized milk; foams consisting of bubbles of gas suspended in a fluid, such as shaving cream, soap bubbles, and whipped cream; and suspensions consisting of solid particles suspended in a fluid, such as ketchup, mustard, and paint. These materials are important for a wide variety of technologies and industrial processes, from the processing of pharmaceuticals and foods, to transportation of seeds and grains, to materials fabrication. At the simplest level of abstraction, one may think of these materials as consisting of large particles, for which thermal fluctuations are negligible, that interact only when they come into contact with each other, in which case they repel. Yet despite this seeming simplicity, surprisingly complex behavior may emerge, in particular a transition from a flowing liquid-like state to a rigid but disordered solid state, as either the particle packing density or applied stress is varied. This is known as the "jamming transition." In this project, computer simulations will be used to investigate the nature of this jamming transition, along with more general behavior of such materials that emerges under shear driven flow where adjacent granular layers move parallel to each other with different relative speed. Different mechanisms for energy dissipation, and the effects of different particle shapes will be investigated.This project will also promote the teaching, training, and engagement in science and research, of a wide range of students across multiple institutions. Undergraduate students will gain experience in both scientific research and scientific communication by presenting work at local and national research conferences. Graduate students will be trained in the methods of modern theory and high-performance computing and experience research with direct interaction between theory and experiment. In this way, they become prepared for future high-tech careers in academia or industry. The infrastructure for research and education will be enhanced by the formation of a network of collaborations with domestic and international colleagues engaged in complementary experimental and computational research in this area. TECHNICAL SUMMARYThis award supports theoretical and computational research and education in granular and soft-matter materials. Computer simulations will be carried out to study different aspects of the behavior of granular and soft-matter materials near the jamming transition that marks the abrupt change from a flowing liquid-like state to a rigid but disordered solid state, as the particle packing is increased. Materials of interest include dry granular matter, dense granular particles in a slurry, emulsions, foams, non-Brownian suspensions, and colloids. Specific problems will be investigated, with the objective of increasing understanding about the flowing liquid and disordered solid phases of such materials, and the transitions between them. These include: (i) the physical mechanisms behind shear banding of shear flowing materials in homogeneous environments; (ii) the relation between discontinuous shear thickening, the rapid jump in shear stress upon increasing the strain rate, and microscopic inter-particle elastic friction; (iii) the differences between isotropic compressional jamming and shear jamming, in systems of frictional particles; (iv) the effect of orientational ordering and particle tumbling on the shear flow of materials consisting of aspherical particles; (v) the criticality of the shear-driven jamming transition for aspherical particles; (vi) the effect of particle surface concavity on shearing rheology. Collaborations with experimental groups working in these areas will help inform and guide theoretical progress.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.