Deformation and Fracture of Disordered Solids: Mechanisms Underlying Macroscopic Behavior

该奖项支持关于无序固体变形和断裂的理论和计算研究和教育，以确定宏观力学响应背后的微观机制。一个焦点将是非晶聚合物的失效模式。在这里，链连通性导致了不寻常的变形模式，包括裂纹形成、颈缩和明显的应变硬化。第二个重点将是在稳定、准静态剪切或压缩无序固体时的一般结垢行为。传统的工程塑性变形和断裂模型是基于具有现象学本构关系的宏观连续介质方程来计算空间平均响应的。关于这种反应的微观起源，实验提供了有限的信息。PI将进行模拟，为宏观力学与分子尺度相互作用和变形机制之间的联系提供新的见解。聚合物分子的连通性导致拓扑纠缠。大多数非晶聚合物的力学特性模型都假定这些缠结的作用类似于化学交联。在变形过程中跟踪缠结的运动将为这些模型提供详细的测试和新的信息，作为改进它们的基础。将研究聚合物结构和分子摩擦对缠结、应力-应变关系和失效模式的影响。聚合物界面缠结的研究将提供聚合物焊接和聚合物之间摩擦力的微观理解。剪切系统的研究在发展对非平衡行为的新认识方面发挥了重要作用。模拟将探索准静态剪切或压缩无序系统的标度行为。系统通过一系列类似地震的事件演变，其大小呈幂律分布。将研究单个事件的尺度和时空动态，形成它们的条件，以及它们在长时间和距离上的相关性。具体问题将是惯性和不可逆损伤如何影响非平衡临界现象。该项目将通过培养学生广泛的跨学科建模和计算方法，为21世纪的劳动力做出贡献。这一培训将扩展到受资助的学生之外，扩展到与当地的“复杂系统建模”相关的IGERT的学生。将与IGERT协调开发一门关于多尺度建模的新课程。该课程将针对来自不同学科的理工科学生，课程材料将在网络上共享。外展工作将与约翰霍普金斯大学为K-12学生提供的外展项目合作，将研究成果带给更广泛的受众，包括物理博览会、天文与工程青年和青年才俊中心。将开发动画和基于网络的模块来演示与赠款有关的概念。招收新学生将与上述IGERT合作进行，后者正在与妇女学院和其他大学合作，这些大学的学生中有很高比例来自代表性不足的群体。该奖项支持理论和计算研究和教育，以更好地理解材料在响应施加应力时如何变形。这项研究将集中在由相互纠缠的长链状分子制成的材料上。PI的目标是对这些非晶聚合物材料进行计算机模拟，以了解它们在分子水平上对机械应力的反应。研究应该在精确的数学意义上阐明这些链是如何纠缠在一起的，以及纠缠是如何变化的。本研究涉及影响许多技术的基本过程。一个推力将检查变形和断裂的一般方面，这可能与实验室和构造尺度上的工程和天然材料的强度和破坏有关。另一门课程将探讨影响非晶聚合物作为粘合剂、结构材料和固体润滑剂功能的特殊行为。对上述系统的更好理解将有助于结构部件的设计和建模，以及具有改进性能的定制材料的开发。这些研究项目也将作为新的计算建模技术的试验场，这些技术可以结合非常不同的材料描述。这些方法有潜力改善大范围复杂材料行为的建模，超出了本项目所涉及的具体项目。该项目将通过培养学生广泛的跨学科建模和计算方法，为21世纪的劳动力做出贡献。这一培训将扩展到受资助的学生之外，扩展到与当地的“复杂系统建模”相关的IGERT的学生。将与IGERT协调开发一门关于多尺度建模的新课程。该课程将针对来自不同学科的理工科学生，课程材料将在网络上共享。外展工作将与约翰霍普金斯大学为K-12学生提供的外展项目合作，将研究成果带给更广泛的受众，包括物理博览会、天文与工程青年和青年才俊中心。将开发动画和基于网络的模块来演示与赠款有关的概念。招收新学生将与上述IGERT合作进行，后者正在与妇女学院和其他大学合作，这些大学的学生中有很高比例来自代表性不足的群体。

TECHNICAL SUMMARYThis award supports theoretical and computational research and education on the deformation and fracture of disordered solids to determine the microscopic mechanisms underlying macroscopic mechanical response. One focus will be the failure modes of amorphous polymers. Here chain connectivity leads to unusual modes of deformation, including craze formation, necking and pronounced strain hardening. A second focus will be general scaling behavior during steady, quasistatic shear or compression of disordered solids.Traditional engineering models of plastic deformation and fracture are based on macroscopic continuum equations with phenomenological constitutive relations for the spatially averaged response. Experiments provide limited information about the microscopic origins of this response. The PI will perform simulations to provide new insight into the connection between macroscopic mechanics and molecular scale interactions and deformation mechanisms. The connectivity of polymer molecules leads to topological entanglements. Most models of the mechanical properties of amorphous polymers assume that these entanglements act like chemical crosslinks. Tracking the motion of entanglements during deformation will provide a detailed test of these models and new information to serve as a foundation for improving them. The effect of polymer structure and molecular friction on entanglements, stress-strain relations and mode of failure will be studied. Studies of entanglements at polymer interfaces will provide microscopic understanding of polymer welds and friction forces between polymers. Studies of sheared systems have played an important role in developing new understanding of non-equilibrium behavior. Simulations will explore scaling behavior in quasistatic shear or compression of disordered systems. Systems evolve through a series of earthquake like events with a power law distribution of sizes. The scaling and spatio-temporal dynamics of individual events, the conditions that nucleate them, and their correlations over long times and distances will be studied. Specific issues will be how inertia and irreversible damage affect non-equilibrium critical phenomena.This project will contribute to the twenty first century workforce by training students in a wide range of interdisciplinary modeling and computational methods. This training will extend beyond the students supported by the grant to students associated with a local IGERT on "Modeling Complex Systems." A new course on multiscale modeling will be developed in coordination with the IGERT. The course will be aimed at science and engineering students from a range of disciplines and course materials will be shared on the web. Outreach efforts will bring research results to a wider audience in partnership with Johns Hopkins based outreach programs for K-12 students, including the Physics Fair, Youth for Astronomy and Engineering, and the Center for Talented Youth. Animations and web-based modules for demonstrating concepts related to the grant will be developed. Recruitment of new students will be done in collaboration with the above IGERT, which is partnering with women's colleges and other universities with a high percentage of students from underrepresented groups.NONTECHNICAL SUMMARYThis award supports theoretical and computational research and education to better understand how materials deform in response to applied stress. The research will focus on materials made from long chain-like molecules that are entangled with each other. The PI aims to perform computer simulations of these amorphous polymer materials to understand how they respond to mechanical stress at a molecular level. The research should elucidate how the chains are tangled and the way that the entanglement changes in a precise mathematical sense.This research addresses fundamental processes that impact many technologies. One thrust will examine general aspects of deformation and fracture that may be relevant to the strength and failure of engineered and natural materials on laboratory and tectonic scales. Another will explore specialized behavior in amorphous polymers that affects their function as adhesives, structural materials, and solid lubricants. An improved understanding of the above systems will aid the design and modeling of structural components and the development of tailored materials with improved properties. The research projects will also serve as a testing ground for new computational modeling techniques that couple very different descriptions of materials. These approaches have the potential to improve modeling of a broad range of complex materials behavior beyond the specific projects addressed in this project. This project will contribute to the twenty first century workforce by training students in a wide range of interdisciplinary modeling and computational methods. This training will extend beyond the students supported by the grant to students associated with a local IGERT on "Modeling Complex Systems." A new course on multiscale modeling will be developed in coordination with the IGERT. The course will be aimed at science and engineering students from a range of disciplines and course materials will be shared on the web. Outreach efforts will bring research results to a wider audience in partnership with Johns Hopkins based outreach programs for K-12 students, including the Physics Fair, Youth for Astronomy and Engineering, and the Center for Talented Youth. Animations and web-based modules for demonstrating concepts related to the grant will be developed. Recruitment of new students will be done in collaboration with the above IGERT, which is partnering with women's colleges and other universities with a high percentage of students from underrepresented groups.