NSF-DFG: Hierarchical Design and Additive Manufacturing of Metallic Programmable Metamaterials

可编程机械超材料(PMM)通过特定的几何设计，在不改变材料组成的情况下，具有独特的力学性能和功能。目前的PMM主要由聚合物制成，不能承受高应力和高温。金属PMM可以在这些极端条件下使用，在航空航天、汽车和生物医学等行业具有潜在的应用前景。然而，现有的一个科学挑战是，将经过验证的聚合物PMM设计简单地转换为金属是不成功的，因为大多数金属的弹性应变极限比聚合物低很多，从而导致在循环载荷下的低寿命。如果没有完全的结构重新设计，在金属PMM中实现所需的机械性能将是极具挑战性的。虽然添加制造(AM)提供了制造复杂几何形状的可能性，但在金属PMM中实现功能所需的小尺寸和复杂几何形状已经达到了其分辨率极限。因此，迫切需要探索基本的AM加工机制，以获得所需的小特征和可接受的缺陷密度和残余应力。该项目利用普渡制造团队和弗莱堡设计团队的独特专业知识来应对这一挑战。这项国际合作将使两所大学的学生通过视频会议和年度学生交流，在实验和模拟方面奠定坚实的基础。本项目的目标是将激光粉末熔化技术应用于金属粉末冶金材料的制备，从根本上了解分层设计和AM工艺对金属粉末冶金材料的组织结构、缺陷密度、弹性应变极限和疲劳抗力的影响。项目组计划开发一个集成的实验和建模平台，该平台可以显著提高对制造具有优异机械性能(大全球应变和抗疲劳)的金属PMM的基本理解。这项研究将集成人工智能辅助计算机设计、AM建模和处理、表征和力学测试，以确定能够以最小的局部弹性应变承受大的全球应变的架构。普渡在扫描电子显微镜下进行现场小规模机械测试的能力和弗莱堡在小型结构疲劳测试方面的能力将被整合在一起，以了解潜在的变形和疲劳机制。如果成功，该项目将产生关于AM加工条件对内部缺陷和残余应力的产生的影响，以及由此对金属PMM疲劳性能的影响的新知识。该项目还有望导致金属材料的PMM和AM的新结构重新设计，提供聚合物PMM无法实现的大弹性变形、高应力和抗疲劳性的承诺。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。

Programmable mechanical metamaterials (PMMs) have unique mechanical properties and functionalities through specific geometric designs without changing the material composition. Current PMMs are primarily made of polymer, which cannot sustain high stress and temperature. Metallic PMMs can be used under these extreme conditions, and have potential applications for aerospace, automobile and biomedical industries. However, an existing scientific challenge is that a simple translation of the proven polymer PMM design into metals is unsuccessful because most metals have magnitudes lower elastic strain limit than polymers leading to a low lifetime under cyclic loading. Without a complete structural redesign, the required mechanical properties would be extremely challenging to achieve in metallic PMMs. Although additive manufacturing (AM) offers the potential to fabricate complex geometry, the small dimension and complex geometry required to achieve functionality in metallic PMMs have reached its resolution limit. Hence, there is an urgent need to explore the fundamental AM processing mechanism that can achieve desirable small features with acceptable defect density and residual stresses. This project leverages the unique expertise of the Purdue team on manufacturing and Freiburg team on design to tackle this challenge. The international collaboration will enable students from both institutes to develop a solid foundation in both experiments and simulations through videoconferences and annual student exchanges. The objective of this project is to apply laser powder bed fusion to fabricate metallic PMMs and understand fundamentally the influence of hierarchical design and AM processing on microstructures, defect density, elastic strain limit and fatigue resistance. The project team plans to develop an integrated experimental and modeling platform that can significantly improve fundamental understandings on the manufacturing of metallic PMMs with superior mechanical performance (large global strain and fatigue resistance). This research will integrate AI-assisted computer design, AM modeling and processing, characterization and mechanical testing to identify architectures that can sustain large global strain with minimal local elastic strain. Purdue’s capability on in-situ small scale mechanical testing in SEM and Freiburg’s capability on fatigue testing of small structures will be integrated to understand the underlying deformation and fatigue mechanisms. If successful, this project will generate new knowledge about the influence of AM processing conditions on generation of internal defects and residual stress, as well as the consequent impact on fatigue properties of metallic PMMs. This project is also expected to lead to new structural redesign of PMM coupled with AM for metallic materials that offers the promise to sustain large elastic deformation, high stress and fatigue resistance, not attainable in polymeric PMMs.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.