Collaborative Research: Connecting Atomistic and Continuum Amorphous Solid Mechanics via Non-equilibrium Thermodynamics

合作研究：通过非平衡热力学连接原子和连续非晶固体力学

• 批准号: 1408685
• 负责人: Michael Falk
• 金额: $ 30万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-15 至 2018-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1408685&HistoricalAwards=false
• 关键词: Collaborative; Research; Connecting; Atomistic; Continuum

NONTECHNICAL SUMMARYThis award supports computational and theoretical research, and education on materials deformation. The objective of this collaborative research project is to develop computational models to predict the deformation and failure of a class of materials known as amorphous solids, particularly focusing on structural metallic glasses. The atoms in amorphous solids are arranged in a highly disordered structure unlike crystals in which atoms are arranged into a regular repeating structure. The current research seeks to go beyond directly simulating the atomic scale behavior using techniques like molecular dynamics simulations. While molecular dynamics simulation has been groundbreaking, this technique is computationally intensive and cannot be scaled up to model structures on scales of typical practical engineering interest. This research will focus on translating information from molecular dynamics simulations to computationally efficient models at larger scales. In doing so, comparisons will be made between atomic scale representations and larger scale theories to ensure that the larger scale theories are statistically consistent and adequately verified. Particular attention will be paid to testing whether they capture the mechanisms governing material behavior and the inherent variability that results from the disordered atomic configurations. This verification will permit the use of these models for testing theories of large-scale material behavior, particularly failure and fracture; successful theories will help to enable the design of amorphous materials wherein the structure of a material is chosen to meet certain performance objectives, and permitting the assessment of the reliability of engineering materials. The insights gained and methods employed in this research have the potential to transform the way in which length-scales are spanned in the study of the mechanics of materials beyond those with amorphous structure. This award also supports educational initiatives at both Johns Hopkins University and Harvard University. These will address the critical need to integrate computational methods into the core Materials Science and Engineering curriculum while also engaging elementary school students in high-need urban schools through the NSF funded STEM Achievement in Baltimore Elementary Schools project.TECHNICAL SUMMARYThis award supports computational and theoretical research, and education on nonequilibrium properties of materials with a focus on deformation. Atomistic mechanisms govern both a material's kinetics and the manner in which its structure evolves during the inherently nonequilibrium process of deformation and failure. The need to establish numerically tractable continuum descriptions of viscoplasticity that incorporate atomistic mechanisms in ways that retain their essential aspects presents a grand challenge at the intersection of physics and mechanics. The strategy employed in this research for reducing the operative degrees of freedom is to extend thermodynamic concepts beyond their common equilibrium application. The configurational entropy will be deployed in the context of the shear transformation zone theory to make quantitative predictions of deformation and failure processes in amorphous solids. This study will utilize molecular dynamics simulation to parameterize a highly optimized fully Eulerian implementation of the shear transformation zone theory that permits investigation of very large strains such as those that arise in failure processes like strain localization and fracture. This will require development and analysis of new numerical projection methods for viscoplasticity. The shear transformation zone constitutive law differs from existing relations insofar as it makes reference to a configurational effective temperature that quantifies the structure. These structural parameters can be independently measured in molecular dynamics to cross-validate the predictions of the numerical implementations of the constitutive theory. Rigorous statistical comparisons will be made through a novel stochastic framework that establishes a random field representation of the atomic potential energy that is translated to a continuum effective temperature. This work will validate predictions of the mechanical response of metallic glasses, emerging structural materials, both during homogeneous flow near the glass temperature and during the development of plastic localization and fracture at lower temperatures in a manner that accounts for inherent fluctuations and correlations associated with the material's amorphous structure. This will lead to a greatly increased understanding of deformation and failure in materials with varying degrees of disorder and predictive numerical schemes suitable for large strains that can be rigorously analyzed and deployed in engineering contexts.This award also supports educational initiatives at both Johns Hopkins University and Harvard University. These will address the critical need to integrate computational methods into the core Materials Science and Engineering curriculum while also engaging elementary school students in high-need urban schools through the NSF funded STEM Achievement in Baltimore Elementary Schools project.

该奖项支持材料变形的计算和理论研究以及教育。这个合作研究项目的目标是开发计算模型来预测一类被称为非晶固体的材料的变形和破坏，特别是关注结构金属玻璃。非晶固体中的原子排列在一个高度无序的结构中，不像晶体中的原子排列成一个规则的重复结构。目前的研究试图超越使用分子动力学模拟等技术直接模拟原子尺度的行为。虽然分子动力学模拟具有开创性，但该技术计算量大，不能按比例扩大到典型实际工程兴趣的模型结构。本研究的重点是将分子动力学模拟的信息转化为更大规模的计算效率模型。在此过程中，将比较原子尺度的表示和更大尺度的理论，以确保更大尺度的理论在统计上是一致的，并得到充分的验证。将特别注意测试它们是否捕获控制材料行为的机制和由无序原子构型引起的固有变异性。这种验证将允许使用这些模型来测试大规模材料行为的理论，特别是破坏和断裂；成功的理论将有助于实现非晶材料的设计，其中材料的结构被选择以满足某些性能目标，并允许评估工程材料的可靠性。本研究中获得的见解和采用的方法有可能改变在非晶结构材料力学研究中跨越长度尺度的方式。该奖项还支持约翰霍普金斯大学和哈佛大学的教育计划。这些将解决将计算方法整合到核心材料科学与工程课程中的关键需求，同时通过美国国家科学基金会资助的巴尔的摩小学STEM成就项目，吸引高需求城市学校的小学生。该奖项支持计算和理论研究，以及以变形为重点的材料非平衡特性的教育。原子机制控制着材料的动力学及其结构在变形和破坏的固有非平衡过程中演变的方式。需要建立黏塑性的数值可处理连续体描述，以保留其基本方面的方式纳入原子机制，这是物理和力学交叉的一个巨大挑战。在本研究中采用的降低操作自由度的策略是将热力学概念扩展到它们通常的平衡应用之外。构型熵将在剪切转变区理论的背景下进行部署，以定量预测非晶固体的变形和破坏过程。本研究将利用分子动力学模拟来参数化剪切转变区理论的高度优化的全欧拉实现，该理论允许研究非常大的应变，例如在应变局部化和断裂等失效过程中出现的应变。这将需要开发和分析新的粘塑性数值投影方法。剪切转变区本构律与现有关系的不同之处在于，它参考了量化结构的构型有效温度。这些结构参数可以在分子动力学中独立测量，以交叉验证本构理论数值实现的预测。严格的统计比较将通过一个新的随机框架，建立一个随机场表示的原子势能转化为连续有效温度。这项工作将验证金属玻璃（新兴结构材料）的机械响应预测，无论是在玻璃温度附近的均匀流动过程中，还是在较低温度下塑性局部化和断裂的发展过程中，以一种解释与材料非晶结构相关的固有波动和相关性的方式。这将大大增加对材料变形和破坏的理解，这些变形和破坏具有不同程度的无序性，并且适用于可以在工程环境中严格分析和部署的大应变的预测数值方案。该奖项还支持约翰霍普金斯大学和哈佛大学的教育计划。这些将解决将计算方法整合到核心材料科学与工程课程中的关键需求，同时通过美国国家科学基金会资助的巴尔的摩小学STEM成就项目，吸引高需求城市学校的小学生。

项目成果

Connecting Local Yield Stresses with Plastic Activity in Amorphous Solids

• DOI: 10.1103/physrevlett.117.045501
• 发表时间: 2016-07-20
• 期刊: PHYSICAL REVIEW LETTERS
• 影响因子: 8.6
• 作者: Patinet, Sylvain;Vandembroucq, Damien;Falk, Michael L.
• 通讯作者: Falk, Michael L.