CAREER: Reduced-scale Additively Manufactured Models for Quantifying the Behavior of Large Structural Steel Castings

这项学院早期职业发展(Career)补助金将支持扩展缩尺物理模型的适用性的研究，以量化全尺寸结构钢铸件在地震荷载下的失效行为。钢结构采用铸件模块化结构，减轻了结构重量，缩短了施工时间，降低了安装成本。钢铸件还提供了非凡的建筑自由度以及高抗震和抗爆能力。然而，它们往往很大，几何形状复杂，因此传统的力学试验并不普遍可行，这阻碍了结构工程师充分挖掘它们的潜力。该项目的成果将使工程师能够使用能力有限的测试实验室对规模模型进行多次测试，而不是在拥有昂贵设备的庞大设施中对全尺寸原型进行更少的测试，从而以相对较低的成本更好地了解系统级行为。这项研究还将促进结构钢铸件设计指南的制定，增加其市场份额，在美国制造业创造新的就业机会，并减少碳足迹。作为赠款的一部分，还将寻求一系列广泛的教育和推广活动，以增加美洲原住民对STEM学科的参与，并提高他们的留校率和毕业率，包括本科生实习、为期数天的研讨会以及比赛和辩论。满足几何和材料强度相似要求以及推导比例关系是精确的缩小比例物理模型需要克服的两个挑战。这项研究旨在量化地震载荷作用下附加制造、缩尺物理模型和足尺铸钢的强度、超低周疲劳断裂(ULCF)起始应变和寿命之间的基本比例关系。该方法以小比例模型的加法制造为中心，采用数据驱动的方法，建立参数和后处理，以满足几何和材料强度的相似性。它还包括开发一个深度神经网络框架，用来自真实微观结构的大量断口数据进行训练，以了解损伤比例关系，该关系将把添加剂制造的模型的疲劳断裂行为与全尺寸铸钢联系起来。实验验证计划包括使用X射线层析成像对微观疲劳损伤进行表征，以及对两个全尺寸部件进行结构测试。总体而言，基于力学、附加制造的物理模型和机器学习的比例关系的相似理论将推动缩减尺度物理模型的使用超越大变形进入疲劳断裂领域。该项目由土木、机械和制造创新部门(CMMI)和既定的激励竞争研究计划(EPSCoR)联合资助。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 (CAREER) grant will support research to extend the applicability of reduced-scale physical models to quantify the failure behavior of full-scale structural steel castings under seismic loads. The modular construction of steel structures using castings reduces the structural weight, construction time, and erection costs. Steel castings also offer exceptional architectural freedom and high seismic and blast resistance. However, they are often large and geometrically complex, hence traditional mechanical testing is not commonly feasible, which prevents structural engineers from exploring their full potential. The outcome of this project will enable engineers to perform multiple tests on scaled-models using testing laboratories with limited capabilities instead of fewer tests on full-scale prototypes in sprawling facilities with expensive equipment, providing a better understanding of system-level behavior at a relatively meager cost. The research will also facilitate the development of design guidelines for structural steel castings, increase their market share, create new jobs in the US manufacturing sector, and reduce the carbon footprint. As part of the grant, an extensive set of education and outreach activities will also be pursed to increase the participation of Native Americans in STEM disciplines and improve their retention and graduation rates, including undergraduate internships, multi-day workshops, and competitions and debates.Satisfying the geometrical and material strength similitude requirements and deriving scaling relationships are the two challenges that accurate reduced-scale physical models are required to overcome. This research aims to quantify the fundamental scaling relationships between strength, ultra-low cycle fatigue fracture (ULCF) initiation strain, and life of additively manufactured, reduced-scale physical models and full-scale steel castings subject to seismic loads. The approach is centered on the additive manufacturing of reduced-scale models with the help of data-driven process and build parameters and post-heat treatments to satisfy geometric and material strength similitudes. It also comprises development of a deep neural network framework to be trained with large quantities of fracture data, numerically generated from realistic microstructures, to learn the damage scaling relationship that will relate the fatigue fracture behavior of additive manufactured models to full-scale steel castings. The experimental validation plan includes characterization of the microscopic fatigue damage using x-ray tomography and structural testing of two full-scale components. Overall, the similitude theory based on mechanics, additively manufactured physical models, and machine-learned scaling relationships will advance the use of reduced-scale physical modeling beyond large deformations into the realm of fatigue fracture.This project is jointly funded by the Division of Civil, Mechanical and Manufacturing Innovation (CMMI) and the Established Program to Stimulate Competitive Research (EPSCoR).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.