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

该奖项支持塑性变形的理论和计算研究，这是一个固有的非平衡过程。PI旨在提高对非结晶固体塑性变形的理解，以提高结构有序度的材料。非结晶固体在工业上有应用，如金属、陶瓷、半导体和聚合物，但它们无序的事实阻碍了对其变形的适当理论的发展。最近，大规模原子模拟在分析这些固体的结构紊乱以及将其力学性能与结构演变联系起来方面取得了巨大进展。在此过程中，本构定律被开发出来，利用非平衡统计物理的概念将宏观尺度的行为与原子尺度的结构联系起来。这些本构定律与现有关系的不同之处在于，它们参考了量化结构的某些类似温度的密集变量。这些结构参数可以在仿真中独立测量以验证关系。这些方法成功的证据已经通过预测金属玻璃（一种新兴的结构材料）在玻璃温度附近的均匀流动和在低温下塑性局部化的发展过程中的机械响应来建立。这个研究项目将扩展这些研究，包括部分结晶和纳米结晶固体。在这个范围内检查连续的结构将测试这些变形理论的通用性，以预测部分有序固体的塑性行为。这将导致极大地增加理解变形和破坏在不同程度的无序材料。这个计算和理论研究项目将与约翰霍普金斯大学（JHU）的一个教育项目相结合，该项目解决了将计算方法整合到材料科学与工程核心课程中的关键需求。这将在动力学、相变、材料力学和材料物理性质等课程的背景下完成。PI正在继续开发研究生水平的课程，涵盖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，这些项目将从美国各地和少数族裔院校招收学生。该奖项支持将模拟和理论统计物理相结合的研究，以调查材料在受力时如何变形，并开发一个框架来预测塑性行为。当一个小的力施加在材料上时，材料会弯曲或变形，当力被移除时，材料会弹回到原来的大小和形状。随着力的增加，达到一个点，在这个点上，当力被移除时，材料就会变形，不再弹回原来的尺寸和形状。PI的目标是了解这种塑性变形是如何在一系列材料中发生的，从几纳米大小的微小晶体马赛克金属到原子没有以任何明显模式排列的无定形金属。PI旨在直接解决新兴新材料开发的关键问题，由于其高强度和硬度，具有潜在的应用前景。通过在材料结构和由此产生的机械性能之间建立牢固的联系，这些研究将提供预测理论，可用于分析加工、结构和性能之间的联系以及材料失效前兆的开始。这些研究将增加对其他材料的理解，包括玻璃聚合物、颗粒介质、胶体和伴随摩擦的过程。这个计算和理论研究项目将与约翰霍普金斯大学（JHU）的一个教育项目相结合，该项目解决了将计算方法整合到材料科学与工程核心课程中的关键需求。这将在更传统的材料课程的背景下进行。PI正在继续开发研究生水平的课程，涵盖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，这些项目将从美国各地和少数族裔院校招收学生。

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.