# Dragonfly-Inspired 3D Bionic Folding Grid Structure Design
## 1 Introduction  
Natural biomaterials are both structural and functional components. The study of the relationship between the structure and properties of natural biomaterials is the basis for the development of biomimetic structures [1]. Flight animals have evolved various strategies to adjust flight performance, including the strategy of controlling wing movement and the strategy of adjusting wing shape. Although the movement of the wings is always actively controlled by the flight muscles, the shape of the wings can be regulated through one of the active and passive mechanisms. The adjustment of wing shape in birds is mainly achieved by using muscles to actively control wing shape [2]. However, insect wings have no muscles, except for those located on the chest. Thus, unlike birds, aerodynamic production in flying insects relies primarily on passive changes in wing shape, and possibly some secondary shape control by chest muscles [3, 4]. Insect wings are intricate marvels of evolution and bioengineering, complex mechanical structures. The growth of wing biomechanics research has shown that it is becoming clear how the design and material properties of insect wings influence their deformation under flight forces [5, 6, 7, 8]. They are light, strong, durable, and flexible, thanks to a \"veined\" thickened columnar structure embedded in the wing surface. The fractal structure produced by these veins divides the wings of insects into multiple units, and the density and spatial arrangement of the veins vary greatly among insects, possessing many functions: increasing wing strength, preventing crack propagation, forming ripplevertices, conducting fluids, supporting structures, and maintaining structural characteristics when deformation occurs under aerodynamic action [9; 10; 11; 12]. Therefore, the study of insect wing structure is more conducive to the study of the design method of biomimetic material structures. Simulating the formation process of insect wing structure can guide the design process of imitating insect wing structure [13; 14]. Compared with other insect wings, dragonfly wings are characterized by a distinct grid structure. Dragonfly wings consist of a thin membrane supported by a hollow tubular system composed of wing veins, which are cross-connected to form closed \"cells\". This gives rise to the characteristics of the entire structure [15; 16]. The load is distributed between the veins and the wing membrane of the dragonfly, which is made up of a large number of irregular grid structures, accounting for only 1-2% of the total weight. This highly optimized structure is shown in Figure 1, where the wings of a dragonfly exhibit stability and high load-carrying capacity in various flight actions such as flapping, gliding, and hovering [17; 18]. It is found that wing veins play an important role in the stability of ultralight wing structure. This structure can handle bending forces in different areas and the mechanical wear that the wings experience during flapping. Flexible cross-vein connections and variations in vein size and fold structure are all important features [19; 20; 21; 22]. The fold structure shown in Figure 2 consists of symmetrical waves at regular intervals along the chord, enhancing the wings' carrying capacity significantly. The grid structure of the dragonfly wing is a rigid-flexible coupling structure, which makes the wings with a large aspect ratio not only resistant to bending and torsion deformation, but also able to ensure the stability of the structure under the condition of high-frequency vibration, which is very close to the required characteristics of aviation materials. Therefore, this paper takes the dragonfly wing as the research object to study the design method of bionic structural materials. [PERSON] et al. summarize the recent work on modeling insect wing structure and show how these studies have evolved from simple conceptual models of wing structure to analytical and numerical methods [23]. Researchers used finite element models to build insect wing models.