CAREER: A Micromechanics-Based Approach to Ductile Fracture Simulation in Additively Manufactured Steels for Seismic Structural Fuse Design

该学院早期职业发展计划(CALEAR)奖将通过开发基于微观力学的附加制造(AM)钢的延性断裂预测框架，促进知识和创新，以提高国家民用基础设施的抗震性能。新兴的AM技术，如3-D金属打印，有望用于地震钢系统的基于性能的优化，因为它们可以通过高度受控的无焊接几何形状来适应高度不规则的部件设计。为了使AM钢部件在地震结构体系中过渡到功能部件，需要能够预测损伤极限状态，例如延性断裂和低周疲劳。由于在制造过程中形成了复杂的微观特征，现有的延性断裂模型缺乏准确捕捉AM钢合金断裂过程的能力。这项研究将开发一个创新的框架，用于扩大AM钢合金的微观材料测量，以预测地震结构引信部件的宏观尺度行为。这些微尺度测量和放大框架可以导致创建混合分析-AM框架，允许在制造之前通过概率断裂预测来迭代和优化地震结构引信性能。通过AM结构保险丝设计优化钢结构建筑抗震性能的能力将通过更安全、更具弹性和可持续的建筑建造来促进国家福利和繁荣，以更好地保护地震期间的生命和财产，并在响应和恢复期间保持基本服务和业务连续性。与这项研究相结合的是一个创新的中学推广计划和与瑞士联邦理工学院的研究生级别的国际研究合作。中学的推广活动以工程作曲工作坊的形式，将音乐教育与科学、技术、工程和数学(STEM)课程结合起来。这项名为STEMusic的推广计划旨在通过参与替代认知过程来促进创造力、对工程原理的理解和保留。国际研究合作将包括交换研究生。这一职业奖的目的是检验这样一个假设，即测量的微观机械材料行为可以被刻度，以准确预测通过选择性激光熔化等常见AM工艺产生的钢合金的宏观延性断裂。在这项研究中，扫描电子显微镜(SEM)、透射电子显微镜(TEM)和改进的纳米压痕等现代技术将被用来测量驱动AM钢延性断裂的基本局部化过程，并创建一个新的模拟框架，以允许未来创建更具普遍性的断裂模型。直径约0.002毫米的钢样将用聚焦离子束球磨制造，并使用改进的扫描电子显微镜纳米压痕装置进行机械测试。测量的微观力学行为，结合断口表面微结构的电子显微镜空间特征，将被用来提供统计体积元模拟，以扩大到更大的材料体积。这种基于微观力学的框架将被用来研究自由形式结构保险丝几何形状(使用AM工艺创建的几何形状)的延性断裂性能。除了所描述的抗震设计应用之外，该奖项的潜在影响包括材料工程和AM制造方面的进步。微观力学实验有可能为基础材料形态和化学成分对宏观机械AM钢合金响应的影响提供基本见解，从而允许将材料响应(例如断裂、屈服和变形)设计到AM几何创建过程中。将其与非线性拓扑优化领域相结合，将开发的框架对于获得满足涉及高塑性应变的复杂性能标准的最佳设计解决方案至关重要，高塑性应变会导致在各种复杂载荷下断裂或疲劳。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 Faculty Early Career Development Program (CAREER) award will advance knowledge and innovation to improve the seismic performance of the nation's civil infrastructure through the development of a micro-mechanics based framework for ductile fracture prediction in additively manufactured (AM) steels. Emerging AM technologies, such as 3-D metal printing, are promising for performance-based optimization of seismic steel systems, as they can accommodate highly irregular component designs through highly controlled weld-free geometry formation. In order for AM steel parts to transition to functioning components in seismic structural systems, the ability to predict damage limit states, such as ductile fracture and low-cycle fatigue, is needed. Existing ductile fracture models lack the ability to accurately capture fracture processes in AM steel alloys due to the complex micro features formed during fabrication. This research will develop an innovative framework for upscaling micro-scale material measurements in AM steel alloys to predict macro-scale behavior in seismic structural fuse components. These micro-scale measurements and up-scaling framework can lead to the creation of a hybrid analysis-AM framework, allowing iteration and optimization of seismic structural fuse performance through probabilistic fracture predictions prior to fabrication. The capability to optimize the seismic performance of steel buildings through AM structural fuse design will promote national welfare and prosperity through safer and more resilient and sustainable building construction to better protect life and property during earthquakes and to maintain essential services and business continuities during response and recovery. Integral with this research are an innovative middle school outreach program and a graduate-level international research collaboration with the Swiss Federal Institute of Technology. The middle school outreach, in the form of engineering songwriting workshops, will couple music education with science, technology, engineering, and math (STEM) curricula. Termed STEMusic, the outreach plan aims to promote creativity, understanding, and retention of engineering principles through the engagement of alternative cognitive processes. The international research collaboration will include the exchange of graduate students. The objective of this CAREER award is to test the hypothesis that measured micromechanical material behavior can be scaled to accurately predict macroscale ductile fracture in steel alloys created through common AM processes such as selective laser melting. In the research, modern technologies such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), and modified nano-indentation will be used to measure the fundamental localization processes driving ductile fracture in AM steels and create a new simulation framework to allow the future creation of more generalizable fracture models. Steel specimens approximately 0.002 millimeters in diameter will be fabricated using focused ion beam milling and mechanically tested using a modified in-SEM nano-indentation device. The measured micromechanical behavior, coupled with TEM spatial characterizations of the fracture surface microstructure, will be used to inform statistical volume element simulations for upscaling to larger material volumes. This micro-mechanics based framework will be used to investigate the ductile fracture performance of free-form structural fuse geometries (geometries created using AM processes). Potential impacts of this award outside the described application to seismic design include advances in materials engineering and AM fabrication. The micromechanical experiments have the potential to provide fundamental insights into the effects of underlying material morphology and chemistry on macro-mechanical AM steel alloy response, allowing material response (e.g., fracture, yielding, and deformation) to be designed into the AM geometry creation process. Coupling this within the field of nonlinear topology optimization, the framework to be developed will be essential for deriving optimum design solutions that satisfy complex performance criteria involving high plastic strains that lead to fracture or fatigue under various complex loadings.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.