Frustrated Metamaterials as Shape-Morphing Structures

该基金将支持受挫机械超材料的力学研究，并将探索其在大型结构中的适用性。超材料是由梁和板等简单结构元素组合而成的，它们协同作用，产生极端的形状变化和其他非常规的反应。周期性超材料具有称为机制的低能变形模式。在非周期性存在的情况下，相邻单元变形之间的不相容阻碍了机制的发展。这些通常被视为令人讨厌的东西；在这个项目中，它们被用来实现功能。事实上，在二维系统中，由不相容引起的几何“挫折”导致面外屈曲，并且最初的平面系统变形（字面上，弹出）为三维壳状物体。本研究将创造关于二维超材料受挫的起源和表现的知识，并将探索它们作为具有以下独特属性的大规模可展开结构的适用性：(i)它们由于拉伸（而不是压缩）力而弹出；（ii）可在无须地面锚固的情况下进行预应力；（iii）由于在所述平面前驱体内编码了所需的形状，因此可以精确地部署它们。这个项目中的想法有可能彻底改变工程师对设计可展开系统和建造轻型自由形状结构（如网格壳、大圆顶和弹出式避难所）的看法。教育活动以形状变形为主题，以课程开发和本科生授权为基础，将激发结构工程专业学生的创造力，并重新审视他们对结构作为不变的静态实体的先入为主的想法。该项目的主要目标是提供对各种非周期性超材料系统中的几何挫折的系统理解，并利用这些知识来实现创新的形状变形结构。第一步将是通过理论、实验和数值手段阐明平面内挫折的先决条件。我们将关注驱动的位置和大小、超材料的结构以及容易屈曲的压缩区域的位置之间的相互作用。将利用降阶数值模型来预测面外形状的转变。还将采取步骤制定机械逆设计，即找到平面内结构以及获得目标三维形状所需的作动力的位置和程度。最后，最初通过桌面尺度原型研究的挫折原理将被转化为大尺度。本文将通过实验和数值模拟研究受超材料启发的受挫结构的可展开性和承载能力。计划开设一门关于变形的新课程。本科生和研究生都将被培养成新一代的“结构思考者”。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

This grant will support research on the mechanics of frustrated mechanical metamaterials and will explore their applicability as large-scale structures. Metamaterials are assemblies of simple structural elements like beams and plates that, in concert, yield extreme shape transformations and other unconventional responses. Periodic metamaterials feature low-energy modes of deformation called mechanisms. In the presence of non-periodicity, mechanisms are impeded by incompatibilities between the deformations of neighboring units. These are usually seen as a nuisance; in this project, they are instead embraced to achieve functionality. Indeed, in two-dimensional systems, the geometric “frustration” stemming from incompatibilities results in out-of-plane buckling, and the initially flat system morphs (literally, pops-up) into a three-dimensional shell-like object. This research will create knowledge on the origin and manifestation of frustration in two-dimensional metamaterials and will explore their applicability as large-scale deployable structures with the following unique attributes: (i) they pop-up due to tensile (rather than compressive) forces; (ii) they can be prestressed without ground anchoring; (iii) they can be accurately deployed since the desired shape is encoded within the flat precursor. The ideas within this project have the potential to revolutionize how engineers think about designing deployable systems and erecting lightweight freeform structures like gridshells, large domes, and pop-up shelters. The educational activities, centered around the theme of shape morphing and based on both curriculum development and undergraduate student empowerment, will stimulate structural engineering students to embrace creativity and to revisit their preconceived idea of structures as non-changing, static entities. The primary objective of this project is to provide a systematic understanding of geometric frustration in various non-periodic metamaterial systems, and to exploit this knowledge to realize innovative shape-morphing structures. The first step will be to elucidate the in-plane prerequisites to frustration via theoretical, experimental, and numerical means. Attention will be devoted to the interplay between the location and magnitude of the actuation, the metamaterial’s architecture, and the location of the compressive regions prone to buckling. Reduced-order numerical models will be leveraged to predict out-of-plane shape transitions. Steps will also be taken to formulate a mechanistic inverse design, i.e., to find the in-plane architecture and the location and extent of the actuating forces necessary to obtain a target three-dimensional shape. Finally, the principles of frustration, initially studied via tabletop-scale prototypes, will be translated to large scales. The deployability and load bearing capacity of metamaterial-inspired frustrated structures will be investigated via experiments and numerical simulations. A new course on shape-shifting is planned. Both undergraduate and graduate students will be trained as the new generation of "structures thinkers."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.