GOALI/Collaborative Research: Understanding Multiscale Mechanics of Cyclic Bending under Tension to Improve Elongation-to-Fracture of Hexagonal Metals

减少运输行业化石燃料消耗的各种战略的核心是减轻结构重量的目标，通常被称为“轻量化”。某些金属，如钛和镁，具有被称为六方密排(HCP)的晶体结构，这有助于实现优异的强度与重量比。然而，HCP金属通常不具备在室温下将其成形为所需形状所需的延展性。这个GOALI学术联络机会(GOALI)研究项目不再对材料进行加热，而是实施、描述和模拟一种名为“拉伸下连续弯曲”(CBT)的新型渐进式成形工艺。该项目的目标是将六氟化碳金属在室温下的成形性提高一倍。通过与Goali合作伙伴波音公司合作，该团队将解决对工业具有直接价值的成形问题，同时实现航空航天结构的轻量化。此外，建模和材料表征工具将封装在开放源码软件中，供整个科学界免费使用。参与研究的学生将通过实习机会获得对行业挑战的知识和理解。该项目的一个关键部分将是鼓动一个名为Capstone Connect的外展项目。将专门为高中生创建一个在线论坛，让他们在处理最后一年的Capstone项目时与学术和工业专家联系。学生不仅将对工程设计项目有更深入的了解，而且这些互动将启发他们对未来STEM职业生涯的看法。虽然已经证明了通过CBT提高钢的断裂伸长率(ETF)的能力，但在HCP金属上的应用一直受到限制。此外，需要更深入地了解改善塑性背后的机理，以优化CBT工艺条件，并将潜在的想法转化为实际的成形操作。该项目将利用高分辨率数字图像相关(HRDIC)和高分辨率电子背散射衍射(HREBSD)来观察局部滑移活动、应变梯度、位错重排、亚结构发展以及与之相关的背应力在CBT期间ETF显著增加中所起的作用。实验活动将在关键机构长度尺度上提供并验证新的非局域晶体塑性有限元(CPFE)模型，使人们能够理解CBT中的力学，以提高HCP金属的ETF。这一结合的实验和建模工作将为CBT提供前所未有的见解，该项目的实际成功将通过与波音公司一起形成尖端的钛部件来展示。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。

At the core of various strategies to reduce consumption of fossil fuels in the transportation industry is the goal to reduce structural weight, generally termed ‘lightweighting’. Certain metals, such as titanium and magnesium, have crystal structures known as hexagonal closed-packed (HCP), which contribute to superior strength-to-weight ratios. However, HCP metals often do not have the required ductility to form them into the desired shapes at room temperature. Instead of heating the material, with the accompanying expense, this Grant Opportunities for Academic Liaison with Industry (GOALI) research project will implement, characterize, and model a novel incremental forming process called ‘continuous bending under tension’ (CBT). The goal of the project is to double the formability of HCP metals at room temperature. By working with GOALI partner Boeing, the team will solve forming problems that are of immediate value to industry while enabling the lightweighting of aerospace structures. Furthermore, the modeling and materials characterization tools will be encapsulated in open-source software for free access to the entire scientific community. The students involved in the research will gain knowledge and understanding of industrial challenges through internship opportunities. An essential part of the project will be the instigation of an outreach program called Capstone Connect. An online forum will be created specifically for senior high-school students to connect with academic and industrial specialists as they tackle their final year Capstone projects. Not only will students gain deeper insights into engineering design projects, but the interactions will enlighten them concerning future STEM careers. While the ability to increase elongation-to-failure (ETF) in steels, for example, via CBT has been demonstrated, application to HCP metals has been limited. Furthermore, a deeper understanding of the mechanics behind the improved ductility is required to both optimize CBT process conditions and to transfer the underlying ideas into practical forming operations. This project will utilize high resolution digital image correlation (HRDIC) and high-resolution electron backscatter diffraction (HREBSD) to observe local slip activity, strain gradients, dislocation rearrangement, substructure development and associated back stresses that play a role in the remarkable increase in ETF during CBT. The experimental campaign will serve to inform and validate a novel non-local crystal plasticity finite element (CPFE) model at the critical mechanism length-scale, enabling understanding of mechanics in CBT to improve ETF of HCP metals. This combined experimental and modeling effort will provide unprecedented insights into CBT, and the practical success of the project will be demonstrated via the forming of a leading-edge titanium component with Boeing.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.