Theory and Simulation of the Transition from Amorphous to Nanocrystalline Mechanical Response

技术总结该奖项支持关于塑性变形的理论和计算研究，塑性变形是一种内在的非平衡过程。PI的目的是促进对非晶态固体中的塑性变形的理解，以提高对结构有序度越来越高的材料的理解。非晶态固体作为金属、陶瓷、半导体和聚合物等在工业上得到了应用，但它们的无序性阻碍了对它们变形的充分理论的发展。最近，大规模的原子模拟在分析这些固体中的结构无序以及将它们的力学性质与其结构演化相关联方面取得了巨大的进展。在这个过程中，发展出了本构定律，它使用非平衡统计物理的概念将宏观尺度行为与原子尺度结构联系起来。这些本构定律不同于现有的关系，因为它们引用了某些类似温度的密集变量，这些变量量化了结构。这些结构参数可以在仿真中独立测量，以验证关系。金属玻璃是一种新兴的结构材料，无论是在玻璃温度附近的均匀流动过程中，还是在低温下塑性局部化的发展过程中，对金属玻璃的机械响应的预测都证明了这些方法的成功。这项研究项目将把这些研究扩展到包括部分晶体和纳米晶体固体。研究这个范围内的结构连续体将检验这些变形理论在预测偏序固体中的塑性行为方面的普适性。这将大大提高对具有不同程度无序的材料中的变形和破坏的了解。这一计算和理论研究计划将与约翰·霍普金斯大学(JHU)的一个教育计划相结合，该计划旨在满足将计算方法整合到材料科学和工程核心课程中的迫切需要。这将在动力学、相变、材料力学和材料物理性质课程的背景下进行。该研究所正在继续开发一门研究生水平的课程，涵盖用于分子模拟的计算材料科学方法。此外，PI有让本科生参与研究的历史。这个项目将包括JHU的本科生和通过JHU的NSF MRSEC和PREM项目招募的本科生，这些项目吸引了来自美国各地和少数族裔院校的学生。非技术性总结该奖项支持将模拟和理论统计物理相结合的研究，以调查材料在压力下如何变形，并开发一个预测塑性行为的框架。当对材料施加小力时，材料将弯曲或变形，当力被移除时，材料将弹回其原始大小和形状。随着力的增加，当力被移除时，材料将变形并不再弹回原始大小和形状的点。PI旨在了解这种塑性变形是如何在一系列材料中发生的，从由几个纳米大小的微小晶体镶嵌而成的金属，到原子没有明显排列的非晶态金属。PI旨在直接解决对开发具有潜在应用的新兴新材料至关重要的问题，因为它们具有高强度和硬度。通过在材料的结构和由此产生的机械性能之间建立强有力的联系，这些研究将提供预测性理论，可以用来分析工艺、结构和性能之间的联系，以及材料失效的先兆。这些研究将增加对从主体金属到其他材料的了解，包括玻璃聚合物、颗粒介质、胶体和伴随摩擦的过程。这一计算和理论研究计划将与约翰霍普金斯大学(JHU)的一个教育计划相结合，该计划旨在满足将计算方法整合到材料科学和工程核心课程中的迫切需求。这将在更传统的材料课程的背景下进行。该研究所正在继续开发一门研究生水平的课程，涵盖用于分子模拟的计算材料科学方法。此外，PI有让本科生参与研究的历史。该项目将涉及JHU的本科生和通过JHU的NSF MRSEC和PREM项目招收的本科生，这些项目从美国各地和少数族裔占多数的院校招收学生。

TECHNICAL SUMMARYThis award supports theoretical and computational research on plastic deformation, an inherently non-equilibrium process. The PI intends to advance understanding of plastic deformation in non-crystalline solids to materials with increasing degrees of structural order. Non-crystalline solids find industrial application as metals, ceramics, semiconductors and polymers, but the fact of their disorder has discouraged the development of adequate theories for their deformation. Recently large-scale atomistic simulation has allowed dramatic progress in analyzing the structural disorder in these solids and in relating their mechanical properties to their structural evolution. In the process constitutive laws have been developed that use concepts from non-equilibrium statistical physics to connect macroscale behavior to atomic scale structure. These constitutive laws differ from existing relations insofar as they make reference to certain temperature-like intensive variables that quantify the structure. These structural parameters can be independently measured in simulation to validate the relations. Evidence of the success of these methods has been established by predictions of the mechanical response of metallic glass, an emerging structural material, both during homogeneous flow near the glass temperature and during the development of plastic localization at low temperatures. This research project will extend these investigations to include partially crystalline and nanocrystalline solids. Examining a continuum of structures over this range will test the generality of these theories of deformation for predicting plastic behavior in partially ordered solids. This will lead to a greatly increased understanding of deformation and failure in materials with varying degrees of disorder.This computational and theoretical research program will be integrated with an educational program at Johns Hopkins University (JHU) that addresses a critical need to integrate computational methods into the Materials Science and Engineering core curriculum. This will be done in the context of courses on kinetics, phase transformations, mechanics of materials and physical properties of materials. The PI is continuing to develop a course on the graduate level covering computational materials science methods for molecular simulation. In addition the PI has a history of involving undergraduates in research. This project will involve both JHU undergrads and undergraduates recruited through the NSF MRSEC and PREM programs at JHU that bring in students from around the U.S. and majority-minority institutions.NON-TECHNICAL SUMMARYThis award supports research that combines simulation and theoretical statistical physics to investigate how materials deform when stressed and to develop a framework to predict plastic behavior. When a small force is applied to a material, a material will bend or deform in such a way that the material will spring back to its original size and shape when the force is removed. As the force is increased, a point is reached where the material deforms and no longer springs back to original size and shape when the force is removed. The PI aims to understand how this plastic deformation occurs in a range of materials from metals that are a mosaic of tiny crystals the size of a few nanometers to amorphous metals where the atoms are not arranged in any apparent pattern. The PI aims to directly address issues critical to the development of emerging new materials with potential applications due to their high strength and hardness. By making a strong connection between the structure of the material and the resulting mechanical properties, these investigations will provide predictive theories that can be used to analyze the connection between processing, structure and properties and the onset of precursors to materials failure. These investigations will increase understanding beyond subject metals to other materials including glassy polymers, granular media, colloids and the processes that accompany friction.This computational and theoretical research program will be integrated with an educational program at Johns Hopkins University (JHU) that addresses a critical need to integrate computational methods into the Materials Science and Engineering core curriculum. This will be done in the context of more traditional courses on materials. The PI is continuing to develop a course on the graduate level covering computational materials science methods for molecular simulation. In addition the PI has a history of involving undergraduates in research. This project will involve both JHU undergrads and undergraduates recruited through the NSF MRSEC and PREM programs at JHU that bring in students from around the U.S. and majority-minority institutions.