The beetle elytron plate: a lightweight, high-strength and buffering functional-structural bionic material

Foldable insect wings: from folding and unfolding mechanisms to inspired applications

The unfolding and folding mechanisms of insect wings have always been a research field of concern for scientists. Recently, many engineers have combined these mechanisms with origami to develop innovative foldable structures. This Review discusses the mechanisms of insect hindwing unfolding and folding, particularly in the Coleoptera and Dermaptera, revealing the inherent relationship between folding models and insect wing folding mechanisms, including the construction of bistable systems, the generation of internal elastic forces and the reasons for dual stiffness. In addition, this Review also discusses the effects of hydraulic pressure, thoracic muscles, abdominal movements, wing flapping and other mechanisms on the wings. Finally, we introduce the current applications in aircraft and grippers inspired by these mechanisms. Learning the mechanism of insect wing folding and utilizing mechanical structures and artificial materials to reproduce the delicate folding of insect wings can provide a wide range of inspirations for foldable structure design.

Out-of-Plane Mechanical Behavior of 3D-Printed Polymeric Circular-Vertex-Based Hierarchical Hexagonal Honeycombs

Many studies show that hierarchical honeycombs have a superior performance compared to regular honeycombs. However, relevant experimental studies are limited due to the fabrication challenges of hierarchical honeycombs featuring complex geometries. In this study, circular-vertex-based hierarchical hexagonal honeycombs (CHHHs) with different hierarchical parameters were fabricated using a polymeric 3D-printing technique, and their quasi-static out-of-plane mechanical behavior was investigated. The CHHHs were constructed by replacing each solid vertex of a regular hexagonal honeycomb (RHH) with a circular vertex. Quasi-static compression tests were conducted on CHHHs, and the effect of the hierarchical parameter on the deformation modes, mechanical properties, and energy absorption characteristics was investigated. The results revealed that both the CHHH and RHH specimens experienced cell wall fractures during compression, while the CHHH exhibited enhanced damage resistance, compressive strength, and specific energy absorption (SEA) compared to RHH. This study contributes to understanding the effect of circular-vertex-based hierarchy on the out-of-plane mechanical behavior of regular honeycombs.

Vibrational Characteristics of a Foam-Filled Short Basalt Fiber Reinforced Epoxy Resin Composite Beetle Elytron Plate

The vibrational properties and mechanism of a foam-filling short basalt fiber reinforced epoxy resin composite beetle elytron plate (EBEP_fc) were studied by experiments and the finite element (FE) method in this paper. The experimental results showed that the natural frequencies of the first two modes of the EBEP_fc were very close to those of a foam-filling short basalt fiber reinforced epoxy resin composite honeycomb plate (HP_fc), while the vibrational response of the EBEP_fc was weaker than that of the HP_fc, and the damping ratio was improved; the improvement of the second mode was significant. Therefore, the EBEP_fc had a better vibration reduction performance and could directly replace the HP_fc in engineering applications. The FE results showed that foam filling enhanced the shear stiffness of the whole core structure, and had a more obvious effect on the shear stiffness of the HP_fc. Meanwhile, it particularly reduced the shear force proportions and contributed to the protection of the skin and core skeleton. The mechanisms of the vibrational characteristics of these two types of sandwich plates were explored from the perspective of the equivalent cross-sectional area, shear stiffness, shear strain energy per unit volume and friction. These results provide a valuable reference for the promotion and application of EBEP_fc in the fields of vibration reduction and seismic resistance.

Research Progress on Curved Plates in China: Applications in Architecture

Curved surfaces can give plates a unique aesthetic effect and physical advantages in acoustics and optics. Assembling such curved plates can greatly improve the image of buildings and enrich their functions. It is thus not surprising to notice that their wide applications in designed or completed buildings in China have become a trend. Thus, this study offers a comprehensive summary of the application progress of curved plates in the architectural field from three aspects: image expression, acoustic characteristics, and optical characteristics. On this basis, future directions are proposed. The main findings or suggestions are as follows: (1) climate harshness has increased recently, and the safety of structures and materials and the coupling effect of the two must be fully considered when designing the shapes of curved surface buildings; (2) research on the mechanism and numerical calculation of curved diffuser systems with different sizes and curvatures needs to be further developed; and (3) experimental studies of various and complex curved plates and different conditions to explore their optimal reflectivity, transmittance, absorptivity, and other optical properties will be an important development direction.

Wing shape optimization design inspired by beetle hindwings in wind tunnel experiments

Flighted beetles have deployable hindwings, which enable them to directly reduce their body size, and thus are excellent bioinspired prototypes for microair vehicles (MAVs). The wing shape of MAVs has an important influence on their aerodynamics. In this paper, wing shapes, inspired from three beetle species' hindwings and designed in terms of the wing camber angle, geometry (including wing length, aspect ratio (AR), and taper ratio (TR)) and wing area, were selected and varied to optimize lift together with the efficiency of wing. All the wings were fabricated by a Tyvek membrane and tested in a wind tunnel. The camber angle and AR were found to have a critical role in force production. The best performance was obtained by a wing with a camber angle of 10°, wing length of 125 mm, AR of 7.06, TR of 0.40 and wing area of 4115 mm².

Bioinspired energy absorbing material designs using additive manufacturing

Nature provides many biological materials and structures with exceptional energy absorption capabilities. Few, relatively simple molecular building blocks (e.g., calcium carbonate), which have unremarkable intrinsic mechanical properties individually, are used to produce biopolymer-bioceramic composites with unique hierarchical architectures, thus producing biomaterial-architectures with extraordinary mechanical properties. Several biomaterials have inspired the design and manufacture of novel material architectures to address various engineering problems requiring high energy absorption capabilities. For example, the microarchitecture of seashell nacre has inspired multi-material 3D printed architectures that outperform the energy absorption capabilities of monolithic materials. Using the hierarchical architectural features of biological materials, iterative design approaches using simulation and experimentation are advancing the field of bioinspired material design. However, bioinspired architectures are still challenging to manufacture because of the size scale and architectural hierarchical complexity. Notwithstanding, additive manufacturing technologies are advancing rapidly, continually providing researchers improved abilities to fabricate sophisticated bioinspired, hierarchical designs using multiple materials. This review describes the use of additive manufacturing for producing innovative synthetic materials specifically for energy absorption applications inspired by nacre, conch shell, shrimp shell, horns, hooves, and beetle wings. Potential applications include athletic prosthetics, protective head gear, and automobile crush zones.

Analysis of microstructure characteristics and mechanical properties of beetle forewings, Allomyrina dichotoma

In this study, the internal microstructure of the forewings of Allomyrina dichotoma is investigated by scanning electron microscopy (SEM) analysis. The results of SEM test show that the inner microstructure of the forewings possesses an integrated sandwich-like plate supported by trabeculae, which is composed of upper and lower skins of unequal thicknesses, and a honeycomb core with trabeculae. Beetle forewing is a natural composite material composed of chitin fibres and proteins. Also, based on the micro dimensions of the forewings observed by SEM, two groups of micro finite element (FE) models of the forewings (i.e., core with trabeculae and core without trabeculae) are established to compare and comprehensively understand the effect of trabeculae on the mechanical properties of the forewings. The FE simulation results demonstrate that the trabeculae could effectively (1) improve the stress state on the upper skin, lower skin, and core layer of the forewings, (2) improve the overall bending stiffness of the forewings, (3) enhance the peeling resistance between the skins and core layer, and (4) improve the buckling strength of the thin-walled core layer. The unique forewing structure of the Allomyrina dichotoma can provide an excellent bionic model for optimizing the traditional honeycomb panel structure.

Effects of changes in the structural parameters of bionic straw sandwich concrete beetle elytron plates on their mechanical and thermal insulation properties

To develop new, environmentally friendly prefabricated building materials, the effects of individual changes in structural parameters on the mechanical and thermal insulation properties of straw sandwich concrete beetle elytron plates (SCBEPs), i.e., sandwich plates with trabeculae constituting the core layer structure, were analyzed by ABAQUS. In addition, based on the analysis results, the structural parameters were preliminarily optimized. The results revealed the following. 1) The bearing capacity of a SCBEP is mainly controlled by deformation (i.e., the maximum deflection). The two most influencing factors on the deflection are the panel thickness T and the trabecular radius R. In contrast, although the panel area is very large, the influence of changing the panel thickness on the thermal insulation performance ranks only third. This demonstrates that the thermal bridge effect of the concrete trabeculae and edges is the primary limitation on further improvements to the thermal insulation performance of SCBEPs. 2) Based on the effects of individual changes in structural parameters on the performance of SCBEPs and their actual processing and application requirements, the structural parameters of a SCBEP with optimized mechanical properties and thermal insulation properties are determined. 3) Compared with aerated concrete wallboards, the optimized SCBEP has a higher rigidity, more compacted surface and better durability. Compared with straw concrete wallboards, the optimized SCBEP has a higher straw content and better thermal insulation performance. Thus, it provides a new avenue for the development of a new, lightweight wallboard.

Development and ultrastructure of the rigid dorsal and flexible ventral cuticles of the elytron of the red flour beetle, Tribolium castaneum

Insect exoskeletons are composed of the cuticle, a biomaterial primarily formed from the linear and relatively rigid polysaccharide, chitin, and structural proteins. This extracellular material serves both as a skin and skeleton, protecting insects from environmental stresses and mechanical damage. Despite its rather limited compositional palette, cuticles in different anatomical regions or developmental stages exhibit remarkably diverse physicochemical and mechanical properties because of differences in chemical composition, molecular interactions and morphological architecture of the various layers and sublayers throughout the cuticle including the envelope, epicuticle and procuticle (exocuticle and endocuticle). Even though the ultrastructure of the arthropod cuticle has been studied rather extensively, its temporal developmental pattern, in particular, the synchronous development of the functional layers in different cuticles during a molt, is not well understood. The beetle elytron, which is a highly modified and sclerotized forewing, offers excellent advantages for such a study because it can be easily isolated at precise time points during development. In this study, we describe the morphogenesis of the dorsal and ventral cuticles of the elytron of the red flour beetle, Tribolium castaneum, during the period from the 0 d-old pupa to the 9 d-old adult. The deposition of exocuticle and mesocuticle is substantially different in the two cuticles. The dorsal cuticle is four-fold thicker than the ventral. Unlike the ventral cuticle, the dorsal contains a thicker exocuticle consisting of a large number of horizontal laminae and vertical pore canals with pore canal fibers and rib-like veins and bristles as well as a mesocuticle, lying right above the enodcuticle. The degree of sclerotization appears to be much greater in the dorsal cuticle. All of these differences result in a relatively thick and tanned rigid dorsal cuticle and a much thinner and less pigmented membrane-like ventral cuticle.