GOALI/Collaborative Research: Strain Gadient Plasticity Modeling to Link Microstructural Non-Local Effects of Dislocation/Interface Interactions with Ductility and Springback

在减少有害排放的轻量化车辆战略中，一个关键组成部分是在各种车辆部件中引入先进的轻合金。然而，高级合金的延展性通常低于其较重的前辈，并且在成形和成形操作中容易断裂。另一方面，各种经验观察表明，在成形过程中仔细选择应变(变形)路径可以显著延迟构件的破坏。目前的模拟框架没有考虑到微观结构一级的关键现象，这些现象需要分析和设计更好的成形工艺，并指导合金的选择和开发，以优化利用现有和即将到来的轻质材料。通过结合显微镜和建模方面的新发展，这项授予与工业学术联系机会(GOALI)研究项目要探索的关键问题涉及促进成分形状变化的原子移动平面(位错)之间的相互作用，以及微观结构界面，如沉淀物和晶界。位错滑移势垒会导致原子堆积和相关的背应力效应，这在传统模型中没有考虑到，但可以通过仔细设计成形过程中发生的应变路径来潜在地提高整体延展性。工业合作伙伴Aleris将把这项研究整合到工业实践中，以在车辆轻量化努力中提供潜在的转型能力。作为这种合作的结果，参与其中的学生还将了解行业挑战和驱动因素。从研究中获得的知识将被整合到研究生和本科生的课程中，而托管所开发模型的基于云的应用程序将通过材料资源有限责任公司向更广泛的研究社区提供。这个跨学科的项目涉及两所大学和一个工业合作伙伴的互补专业知识，其驱动假设是在成形过程中准确计算应变梯度以及相关的背应力和局部化领域，可以用于设计应变路径，以优化材料的延展性，有效地延缓高强铝合金板材的局部化/破坏。该团队将构思和实施一种新的应变梯度晶体塑性有限元模型来封装科学见解。该模型将由两种尖端微结构技术的组合指导，将在相关的长度尺度上提供前所未有的变形行为细节。高分辨率电子背散射衍射(HREBSD)将被用于绘制每个应变路径的几何必要的位错、伴随的应变梯度和相关的背应力，而高分辨率数字图像相关(HRDIC)将提取塑性应变张量以获得完整的变形图像。这些科学进展将应用于两种不同微观结构的高强度合金的温成型，即AA6022-T4和AA7050-T6。该奖项反映了NSF的法定使命，并已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。

A key component in the strategy to lightweight vehicles for reducing harmful emissions involves the introduction of advanced light alloys across a wide spectrum of vehicle components. However, advanced alloys are typically less ductile than their heavier predecessors and are liable to fracture during the shaping and forming operations. On the other hand, various empirical observations have demonstrated that careful selection of strain (deformation) path during the forming process can significantly delay component failure. Current simulation frameworks do not account for key phenomena at the microstructural level needed to analyze and design better forming processes and to guide alloy selection and development for optimal exploitation of current and forthcoming lightweight materials. By combining novel developments in microscopy and modeling, the critical issue to be explored in this Grant Opportunities for Academic Liaison with Industry (GOALI) research project involves interactions between mobile planes of atoms (dislocations) that facilitate shape change of the component, and microstructural interfaces, such as precipitates and grain boundaries. Barriers to dislocation glide cause atomic pileups, and related backstress effects, that are not considered in traditional models, but can potentially be manipulated to improve overall ductility via careful design of strain paths that occur during forming. The research will be integrated into industrial practice by the industrial partner, Aleris, to deliver potentially transformational capabilities in vehicle lightweighting efforts. As a result of this collaboration, the students involved will also gain an understanding of industrial challenges and drivers. Knowledge derived from the research will be integrated into course curricula for graduate and undergraduate students, while a cloud-based App hosting the developed model will be made available to the broader research community via Materials Resources, LLC. This interdisciplinary project, involving the complementary expertise of two universities and an industrial partner, is driven by the hypothesis that accurate calculation of strain gradients, and related backstress and localization fields, during forming can be used to design strain paths that optimize material ductility, effectively delaying localization/failure in high-strength aluminum (Al) alloy sheets. The team will conceive and implement a novel strain-gradient crystal plasticity finite element model to encapsulate the scientific insights. The model will be guided by a combination of two cutting-edge microstructural techniques that will provide unprecedented detail of the deformation behavior at the relevant length-scale. High-resolution electron backscatter diffraction (HREBSD) will be employed for mapping both geometrically necessary dislocations, accompanying strain gradients, and related backstress for each strain path, while high-resolution digital image correlation (HRDIC) will extract the plastic strain tensor for a complete picture of the deformation. The scientific advances will be applied to warm forming of two high strength alloys with different microstructures, namely AA6022-T4 and AA7050-T6.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.