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.

非技术总结该奖项支持计算和理论研究，以及材料变形方面的教育。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态固体的材料的变形和失效，特别是关注结构金属玻璃。非晶态固体中的原子排列成高度无序的结构，不像晶体中的原子排列成规则的重复结构。目前的研究试图超越直接使用分子动力学模拟等技术来模拟原子尺度的行为。虽然分子动力学模拟一直是开创性的，但这种技术计算密集，不能在典型的实际工程兴趣的规模上扩大到模型结构。这项研究将专注于将分子动力学模拟中的信息转化为更大规模的计算高效模型。在这样做的时候，将在原子尺度表示法和大尺度理论之间进行比较，以确保大尺度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捉到支配材料行为的机制以及无序原子配置所导致的内在可变性。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设计非晶态材料，其中材料的结构被选择以满足特定的性能目标，并允许评估工程材料的可靠性。在这项研究中获得的见解和采用的方法有可能改变材料力学研究中跨越长度尺度的方式，超越那些具有非晶态结构的材料。该奖项还支持约翰霍普金斯大学和哈佛大学的教育倡议。通过NSF资助的巴尔的摩小学STEM成就项目，这些课程将解决将计算方法整合到核心材料科学和工程课程中的迫切需要，同时也将通过NSF资助的巴尔的摩小学STEM成就项目吸引小学生进入高需求的城市学校。该奖项支持计算和理论研究，以及关注变形的材料非平衡性质教育。原子论机制既控制着材料的动力学，也控制着材料在变形和破坏的内在非平衡过程中结构演变的方式。在物理学和力学的交叉点上，需要建立数值上易于处理的粘塑性连续统描述，其中以保留其基本方面的方式结合原子机制，这是一个巨大的挑战。在这项研究中采用的减少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。在剪切相变区理论的背景下，位形熵将被用来对非晶态固体的变形和破坏过程进行定量预测。这项研究将利用分子动力学模拟将剪切变化区理论的高度优化的完全欧拉实现参数化，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。剪切转变带本构关系不同于现有的关系，因为它引用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的数值实现的预测。严格的统计比较将通过一个新的随机框架进行，该框架建立了原子势能的随机场表示，该随机场表示被转化为连续的有效温度。这项工作将验证金属玻璃这一新兴结构材料在玻璃温度附近的均匀流动期间以及在较低温度下塑性局部化和断裂发展过程中的机械响应预测，其方式解释了与材料的非晶态结构相关的内在波动和关联。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，以及适用于大应变的预测性数值方案，这些大应变可以被严格分析并部署在工程环境中。该奖项还支持约翰·霍普金斯大学和哈佛大学的教育倡议。这些将解决将计算方法整合到核心材料科学和工程课程中的迫切需要，同时还将通过NSF资助的巴尔的摩小学STEM成就项目，让小学生进入高需求的城市学校。

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.