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而不改变材料成分，具有独特的机械性能和功能。目前的永磁材料主要由聚合物制成，不能承受高应力和温度。金属永磁材料可以在这些极端条件下使用，并且在航空航天、汽车和生物医学工业中具有潜在的应用。然而，现有的科学挑战是，将经验证的聚合物PMM设计简单地转化为金属是不成功的，因为大多数金属具有比聚合物低的弹性应变极限，导致在循环载荷下的低寿命。如果没有完整的结构重新设计，金属永磁电机所需的机械性能将极具挑战性。虽然增材制造（AM）提供了制造复杂几何形状的潜力，但在金属PMM中实现功能所需的小尺寸和复杂几何形状已达到其分辨率极限。因此，有一个迫切需要探索的基本AM处理机制，可以实现理想的小功能与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赖堡设计团队的独特专业知识来应对这一挑战。国际合作将使两个研究所的学生通过视频会议和年度学生交流在实验和模拟方面打下坚实的基础。本研究的目的是将激光粉末床熔凝技术应用于金属粉末冶金材料的制备，并从根本上了解分层设计和增材制造工艺对材料的微观组织、缺陷密度、弹性应变极限和抗疲劳性能的影响。该项目团队计划开发一个集成的实验和建模平台，可以显着提高对制造具有上级机械性能（大的全局应变和抗疲劳性）的金属PMMs的基本理解。这项研究将整合人工智能辅助的计算机设计、AM建模和处理、表征和机械测试，以确定能够以最小的局部弹性应变维持大的全局应变的架构。Purdue的SEM原位小规模机械测试能力和弗赖堡的小型结构疲劳测试能力将被整合，以了解潜在的变形和疲劳机制。如果成功，该项目将产生新的知识AM加工条件对产生的内部缺陷和残余应力的影响，以及随之而来的对金属PMM的疲劳性能的影响。该项目还有望导致PMM与AM的金属材料的新结构重新设计，提供了承诺，以维持大的弹性变形，高应力和抗疲劳性，在聚合物PMM中无法实现。该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

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.