CAREER: Fundamentals of Modeling Deformation Twinning in Polycrystalline Materials Driven by Diffraction-Based Micromechanical Data

该奖项的全部或部分资金来自《2021年美国救援计划法案》(公法117-2)。现代汽车和飞机中的非技术部件的任务是在日益苛刻的条件下执行任务，以减轻重量和提高效率。这就需要更高的信心来理解材料的强度，工程师直接使用材料强度来设计安全、持久的部件。在金属中，原子是以周期性的结构排列的。由于外力的作用，这些原子排列的变化会影响金属的强度。原子间的这些分裂区域被称为缺陷。这项研究旨在更好地理解这些现象发生的原因和方式，以便更好地预测金属部件将如何以及何时发生故障。该项目将实验观测与高保真模拟相结合，以形成一个预测模型。这一模型构成了最先进的模拟软件的基础，以增加对金属微观水平的基本了解，更好地预测其强度，并最终设计出更安全的机器和新材料。在这项研究中开发的软件是免费和开源的，有一个互动网站，专门教其他人如何使用它，并纳入本科生和研究生水平的课程。其他外联活动包括每年举办一次教学讲习班，指导用户了解模拟的理论和操作，以鼓励更广泛、更多样化的用户群体。这些研讨会专门招收本科生，以培养在校研究经验，并为学生提供进入研究生院的渠道。技术概述现代工程部件的性能要求越来越苛刻，包括在接近其故障极限的条件下工作。这就需要对金属合金的各种微机械响应有一个基本的了解。虽然在许多高强度结构合金中观察到了形变孪晶，但与晶体滑移相比，控制其行为的机制还没有被很好地理解。通常的模型通过使孪生和晶体滑移的局部形变响应均一化来掩盖它们之间的差异，忽略了孪生的离散性质；因此，没有一个普遍接受的模型来描述形变孪生。本研究旨在建立一个控制晶界离散变形孪生行为的唯象模型，通过相关的实验-理论方法为多晶材料的变形提供更好的预测模型。利用高能X射线衍射仪对变形加载过程中的塑性演化(特别是形变孪晶的形核和演化)进行了原位跟踪。通过对实验数据的分析，可以建立一个控制晶界孪生行为的唯象模型，并将该模型应用到考虑离散变形孪晶区的精细晶体塑性有限元框架中。在这项研究中开发的软件是免费和开源的，有一个致力于操作教学的互动网站，并包括在本科生和研究生水平的课程中。其他外展活动包括每年一次的教学讲习班，指导用户了解模拟背后的理论和操作，以鼓励更广泛、更多样化的用户社区。这些研讨会专门招收本科生，以培养在校研究经验，并为研究生提供学习渠道。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2). NON-TECHNICAL SUMMARYStructural components in modern automobiles and aircraft are tasked with performing under increasingly strenuous conditions to reduce weight and increase efficiency. This requires a higher confidence in understanding the strength of materials, which is used directly by engineers to design safe, long-lasting components. In metals, atoms are arranged in a structured, periodic way. Changes in the arrangement of these atoms due to an applied force influences the strength of metals. These regions of disruption among atoms are known as defects. This study aims to develop a better understanding of why and how these phenomena occur in order to better predict how and when metal components will fail. This project pairs experimental observations with high-fidelity simulations to formulate a predictive model. This model forms the basis of a state-of-the-art simulation software to increase fundamental understanding of metals at their microscopic levels, to better predict their strength and ultimately design safer machines and new materials. The software developed in this study is disseminated free and open-source, with an interactive website devoted to teaching others how to use it and incorporated into undergraduate and graduate-level coursework. Additional outreach activities include yearly instructional workshops to guide users through the theory and operation of the simulations to encourage a wider, more diverse community of users. The workshops specifically recruit undergraduate students to foster on-campus research experiences and provide a pipeline of students to graduate school. TECHNICAL SUMMARY Modern engineering components are increasingly tasked with more strenuous performance demands, including operating under conditions closer to their failure limits. This necessitates a fundamental understanding of the various types of micromechanical responses of metallic alloys. While deformation twinning has been observed in many high-strength structural alloys, the mechanisms which govern their behavior are not well understood compared to crystallographic slip. Common models obscure the differences between twinning and crystallographic slip by homogenizing their local deformation response, ignoring the discrete nature of twinning; consequently, there is no universally accepted model describing deformation twinning. This study aims to formulate a phenomenological model governing the behavior of discrete deformation twinning at the grain scale to provide for better predictive models for the deformation of polycrystalline materials through a correlated experimental-theoretical approach. High energy X-ray diffraction experiments are performed in situ to track the evolution of plasticity (specifically the nucleation and evolution of deformation twins) at the grain scale during deformation loading. The analysis of this experimental data allows for formulating a phenomenological model governing the behavior of twinning at the grain scale and implementing this model into a refined crystal plasticity finite element framework that considers discrete deformation twin regions. The software developed in this study is disseminated free and open-source, with an interactive website devoted to operational instruction, and is included in undergraduate and graduate-level coursework. Additional outreach activities include yearly instructional workshops to guide users through the theory and operation behind the simulations to encourage a broader, more diverse community of users. The workshops specifically recruit undergraduate students to foster on-campus research experiences and provide a pipeline of students to graduate studies.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.