CAREER: Plasticity and Jamming

职业：可塑性和干扰

• 批准号: 1056564
• 负责人: Craig Maloney
• 金额: $ 45万
• 依托单位: Carnegie-Mellon University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-08-15 至 2018-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1056564&HistoricalAwards=false
• 关键词: CAREER; Plasticity; Jamming

TECHNICAL SUMMARYThis CAREER award supports theoretical and computational research aimed at understanding the relationships between plasticity of amorphous solids and the jamming transition. It is generally accepted that the mechanical properties of crystals are controlled by their defects; however for amorphous solids, no such consensus has been reached. There is now mounting evidence for two different kinds of critical behavior in athermal, repulsive systems such as suspensions of soft particles or granular materials. On one hand, amorphous solids exhibit a kind of dynamical critical behavior similar to other depinning systems as they are driven at vanishing shear rate. On the other hand, confined random packings of repulsive particles exhibit critical behavior in their elastic response as the confining pressure vanishes. The key issue of the interplay between these behaviors during slow shear at low confinement pressure remains relatively unexplored.The PI will perform massively parallel computer simulations of suspensions of soft and hard particle systems under shear to identify the mechanisms for stress buildup and relaxation in various regimes of particle stiffness, packing density, and shearing rate. The spatio-temporal structure of these processes will be studied using emerging tools developed for supercooled liquids and glasses. The PI will address whether the dynamically critical behavior observed in systems above jamming persists at the jamming transition and, more generally, how proximity to the jamming transition affects spatio-temporal structures that allow shear.The educational activities lie along three main thrusts:1) The undergraduate curriculum development will involve the infusion of numerical modeling into core upper division coursework.2) The graduate curriculum development will involve the design and implementation of an introduction to statistical physics for engineering and theoretical mechanics students. 3) The secondary education outreach will be done in conjunction with the Pittsburgh Supercomputing Center in the context of a program which involves high school teachers from the Pittsburgh public schools. NON-TECHNICAL SUMMARYThis CAREER award supports theoretical and computational research aimed at a fundamental understanding of how amorphous materials behave when subjected to external forces. Many amorphous materials behave like ordinary solids without external forces. Even though they lack any underlying crystalline order, they hold their shape. A few of the many examples from everyday experience include windows (made of glass or plexiglass), mayonnaise, and sand on the beach. When the external forces become sufficiently large, the particles which make up these solids start to flow as if the material were a liquid and the material is said to undergo "plastic yield". In crystalline materials, plastic yielding has been understood for many decades to be governed by extended defects in the crystal structure known as "dislocations". In the amorphous solids, a microscopic understanding of plastic yielding is only beginning to emerge.In a certain subclass of these amorphous solids, e.g. the grains of sand, the constituent particles interact through purely repulsive forces. In this repulsive case, the materials can only behave like a solid when external forces confine the particles and force them to interact with each other. In such a confined state, the particles are said to be "jammed". At the transition point when the confinement is just about to be released, the elastic properties of the material are known to be completely anomalous, unlike anything observed in ordinary solids. Therefore, it is important to ask whether the system will yield via the same mechanism near jamming. The PI will perform very large-scale computer simulations and theoretical analysis to address this question.The educational activities lie along three main thrusts:1) The undergraduate curriculum development will involve the infusion of numerical modeling into core upper division coursework.2) The graduate curriculum development will involve the design and implementation of an introduction to statistical physics for engineering and theoretical mechanics students. 3) The secondary education outreach will be done in conjunction with the Pittsburgh Supercomputing Center in the context of a program which involves high school teachers from the Pittsburgh public schools.

该职业奖支持旨在理解无定形固体的塑性和堵塞转变之间的关系的理论和计算研究。人们普遍认为晶体的机械性能是由它们的缺陷控制的;然而对于无定形固体，还没有达成这样的共识。 现在有越来越多的证据表明，在无热的、排斥的系统中，如软颗粒或颗粒状材料的悬浮液中，存在两种不同的临界行为。一方面，无定形固体在剪切速率为零时，表现出类似于其他脱钉系统的动力学临界行为。另一方面，排斥性颗粒的受限随机填充在围压为零时在其弹性响应中表现出临界行为。这些行为之间的相互作用的关键问题，在缓慢的剪切在低约束压力仍然相对unexplored.The PI将进行大规模并行计算机模拟剪切下的软，硬颗粒系统的悬浮液，以确定在各种制度的颗粒刚度，堆积密度和剪切速率的应力积累和松弛的机制。这些过程的时空结构将使用新兴的工具开发的过冷液体和玻璃进行研究。PI将解决在干扰以上的系统中观察到的动态临界行为是否在干扰过渡时持续存在，以及更一般地，接近干扰过渡如何影响允许剪切的时空结构。教育活动沿着三个主要方向进行：1）本科课程开发将涉及到数值建模到核心上师课程的注入。研究生课程开发将涉及工程和理论力学学生的统计物理学入门的设计和实施。3)中学教育推广将与匹兹堡超级计算中心一起在一个涉及匹兹堡公立学校高中教师的方案中进行。 非技术性总结该职业奖支持理论和计算研究，旨在从根本上了解非晶材料在受到外力时的行为。 许多无定形材料在没有外力的情况下表现得像普通固体。即使它们缺乏任何潜在的水晶秩序，它们也保持着它们的形状。 日常经验中的许多例子包括窗户（由玻璃或有机玻璃制成），蛋黄酱和海滩上的沙子。 当外力变得足够大时，构成这些固体的颗粒开始流动，就好像材料是液体一样，并且材料被称为经历“塑性屈服”。 在晶体材料中，几十年来塑性屈服一直被理解为由晶体结构中被称为“位错”的扩展缺陷控制。 在无定形固体中，对塑性屈服的微观理解才刚刚开始出现。在这些无定形固体的某个子类中，例如沙粒，组成颗粒通过纯粹的排斥力相互作用。 在这种排斥的情况下，只有当外力限制粒子并迫使它们相互作用时，材料才能表现得像固体一样。 在这种受限状态下，颗粒被称为“堵塞”。 在转变点，当约束即将被释放时，材料的弹性性质是完全反常的，不像在普通固体中观察到的任何东西。 因此，重要的是要问系统是否会通过相同的机制接近堵塞。 PI将进行非常大规模的计算机模拟和理论分析来解决这个问题。教育活动沿着三个主要方面：1）本科课程开发将涉及到数值建模注入到核心的高年级课程。2）研究生课程开发将涉及到工程和理论力学学生的统计物理学入门的设计和实施。3)中学教育推广将与匹兹堡超级计算中心一起在一个涉及匹兹堡公立学校高中教师的方案中进行。