基于多稳态张拉整体结构的力学超材料设计和性能研究

Mechanical metamaterials are man-made structural materials with counterintuitive mechanical properties that originate in the geometry of their unit microstructure instead of the properties of each component. Tensegrities are grid structures consisting of axially compressive bars and axially tensile strings, holding a diversity of technologically significant applications in, for instance, aerospace engineering and smart robotics, and can be utilized as microstructure candidate for the design of metamaterials. The configuration of a tensegrity structure can be transformed from one stable state to another by applying certain external loads, in which process some novel mechanical properties could be found. This proposal is aimed to reveal the mechanical mechanisms of the existence and transformation of the multistable tensegrity configurations and further design the multistable tensegrity structure-based mechanical metamaterials. Specifically, based on the property difference among the multistable configurations, we will construct the multistable metamaterials whose geometric size, potential energy, efficient stiffness, and strength can be switched. Based on the mechanical response of the multistable tensegrity, we will also construct metamaterials whose Poisson's ratio, material stiffness, bulk modulus, and other efficient mechanical properties can be negative or zero values. For these purposes, a design scheme will be proposed for multistable tensegrity configurations, and some representative examples will be constructed as well as their physical samples. Theoretical models, numerical procedures, and experiment systems will be established to investigate the finite-deformation responses of multistable tensegrities. Finally, the multistable tensegrity structures will be assembled to form mechanical metamaterials and the mechanical properties of the metamaterials will be studies on the basis of the interactive relations among the microstructures. This work not only deepens the knowledge related to the self-equilibrium stability, deformation response, and other mechanical properties of tensegrity structures, but also supplies a new theoretical scheme for the construction and application of mechanical metamaterials.

力学超材料是经人工设计的、具有超常力学性质的结构型材料。张拉整体是由轴向承载构件组成的网状结构形式，在航天航空、智能机器人等领域有着重要应用，可用作超材料的微结构原型。多稳态张拉整体结构可在不同构型之间实现转变，表现出优异力学性质。本项目拟揭示张拉整体结构多稳态构型存在与转变的力学机理，并基于结构多稳态构型之间的性能差异，设计几何、能量、软硬和强弱可切换的多稳态力学超材料，以及基于构型转变时的结构力学特性，设计泊松比、材料刚度、体积模量等力学属性为负或零值的力学超材料。为此，将提出多稳态张拉整体结构的设计方法，构造典型实例和实物模型；建立结构发生多稳态构型转变时的有限变形理论模型、数值模拟方法和实验测试系统，研究结构的力学性能；使用多稳态结构组装力学超材料，基于结构间相互作用关系研究超材料的力学性能。本工作有助于加深对张拉整体结构力学特性的认识，并为力学超材料的设计和应用提供新的理论方法。

超材料是人工合成的具有超常物理性质的结构型材料，其特性由微结构而非化学成分来决定。通过对超材料的微结构进行精心设计，其可以表现出自然界材料难以具有的力学性能而称为力学超材料。张拉整体结构是一类轻质、网格状的空间结构体系，由预拉伸的绳和预压缩的杆通过球铰连接而成，在航天航空、土木建筑、仿生机械、生物力学、智能机器人等领域具有重要应用，可用作超材料的微结构原型。多稳态张拉整体结构可在不同构型之间实现转变，表现出优异的力学性质。本项目对基于多稳态张拉整体结构的力学超材料的设计方法和性能表征进行了系统性研究，开展了理论建模、模拟仿真和实验测试三方面结合的研究内容，涉及结构胞元及其超材料的构型设计、响应分析、性能调控等研究环节。主要研究内容包括：（1）提出了二维和三维多稳态张拉整体结构的设计方法，阐明了多稳态构型存在的力学机理，构造了二维X状、三维截角八面体状和柱状张拉整体结构实例；（2）建立了结构在外部载荷/内部驱动条件下发生多稳态构型转变时的有限变形理论模型、实物仿真模型和静力学测试系统，揭示了张拉整体结构多稳态构型转变条件与结构参数之间的关系，研究了结构等效刚度、等效泊松比等力学性能的变化规律；（3）以所构造的张拉整体结构为基础胞元，组装了几何、能量、软硬和强弱可切换的力学超材料，开展了超材料力学特性的理论预报、模拟仿真和实验验证，探究了结构几何、构件刚度、构件预应力、外加载荷、局部缺陷等调控手段对超材料性能的影响规律。本项目的研究工作加深了对张拉整体结构力学特性的认识，并为力学超材料的设计和应用提供了新的理论方法和测试方案。