Energy Absorption Capacity of Bio-Inspired Honeycomb Integrated Beetle Elytron Plates ^†

Abstract

Growth in the advancement of 3D printing technology has made it easy to fabricate complicated bio-inspired structures (BISs). In this paper, the sandwich structure of the beetle elytron structure (BES) hollow cylinder, influencing every corner of the honeycomb structure, is designed by considering parameters like the thickness, length, and diameter of the hollow cylinder, with the different ranges taken giving minimum and maximum values in the response surface methodology (RSM). Sandwich structures are fabricated using VAT polymerization technology. A Universal Testing Machine (UTM) tests the fabricated structures for compression, and results are recorded from the tests of each specimen. All specimens’ compressive strength (CS) and energy absorptions (EA) values are calculated. Design parameters at which the energy absorbed and the compression strength are high are evaluated and considered optimal parameters for a specific range of values.

1. Introduction

High-performance materials and structures are now being designed quickly due to the intense need for components and devices with specialized qualities [1]. High-performance structures may be created for various applications by drawing inspiration from these geometrical shapes. It is well realized that the accessibility of lightweight designs with brilliant energy ingestion limits is fundamental for various design applications. BISs have been proven to significantly improve conventional designs regarding energy intake limit. They are motivated by several organic patterns seen in nature. As a result, the use of the biomimetic method for designing areas has been growing for revolutionary lightweight designs with excellent energy intake limitations [2].

Beetle Elytra Structure (BES) and Honeycomb Structure (HCS)

Zhang et al. [3] investigated bionic multi-cell tubes (BMCTs) modeled after beetle forewings’ structure. The crashworthiness of various MCTs and BMCTs concerning impact axial loads were compared to FE models of quadrilateral, hexagonal, and octagonal sections. The mechanical components of the EBEP crash box may be modified by varying the amplitude of the deformation lines, according to CS tests and simulation reports, to satisfy the design requirements for diverse engineering applications [4]. In addition to this work, Xiang et al. [5] fabricated a bi-tubular thin-walled structure (BBTS) by modeling hollow cylindrical structures with colorful cross-sectional polygons motivated by the internal architecture of lady beetle wings. The study articles [2,6,7] thoroughly review the aforementioned literature while comparing beetle forewing structures with other biomimetic structures. Zhang x et al. [8] generated the lightweight and high-strength material in the bio-inspired material, a honeycomb (HP) structure. It has the high compression strength required to increase the compression strength in that structure, adding the beetle elytra structure to HP at every corner of the hexagonal shape. There was an increment in the compression strength above 50%, and the energy absorbing capacity also increased in the BEP. Wang et al. [9] also investigated the mechanical performance of the honeycomb structures under low and medium strain rates. Both yield and plateau stress were estimated under dynamic compression tests. The prediction of the output results are also good for this type of bio-inspired structure, using an artificial intelligence technique in the latest research [10,11].

2. Materials and Methods

The design methodology followed in this study is shown in the flow chart in Figure 1. The experimental sandwich structure of the BES design included the below parameters. From the literature survey, the range of the design parameters was selected, as described below.

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Length of the wall [L] = $\left[\begin{array}{c}8 \mathrm{m}\mathrm{m}\\ 12 \mathrm{m}\mathrm{m}\end{array}\right]\begin{array}{c}min\\ max\end{array}$

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Diameter of hollow cylinder[D] = $\left[\begin{array}{c}4 \mathrm{m}\mathrm{m}\\ 6 \mathrm{m}\mathrm{m}\end{array}\right]\begin{array}{c}min\\ max\end{array}$

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Thickness of both wall cylinders [T] = $\left[\begin{array}{c}0.5 \mathrm{m}\mathrm{m}\\ 0.75 \mathrm{m}\mathrm{m}\end{array}\right]\begin{array}{c}min\\ max\end{array}$

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Height[H] = 10 mm

After finalizing the range of the design parameters, the module design of experiments (DOEs) in MINITAB 19 software was used to create the set of specimens. Once the set of design parameters was known, Fusion 360 2.0.15775 CAD software calculated specimens and converted the CAD file into an STL file. The slicing, fabrication, and testing processes of all specimens were carried out as mentioned in the research study [10]. The total procedure carried during the current research is visualized in Figure 2.

3. Results and Discussion

After testing all specimens, the compression strength values were recorded for each specimen, and the variations in all specimens are shown in Figure 3a. The area calculated for the energy absorption values of each specimen under the stress–strain curves was recorded through Blue Hill V 4.42 software connected to UTM. The formula used to calculate the EA values is given by Equation (1)

$$E_c={\sum }_0^n\frac{F_n+F_{n+1}}{2}\ast (d_{n+1}-d_n)$$

(1)

where $E_c$ is the specimen absorbing the energy, $\frac{F_n+F_{n+1}}{2}$ is the average crushing load, and $(d_{n+1}-d_n)$ is the difference between the final and initial crushing distance, respectively.

The variations in the EA values of all tested specimens are graphically represented, as shown in Figure 3b. Specimens 1, 3, and 5 are the structures that show good CSs as per the material used for the fabrication. The design sets of parameters of specimens 1 and 3 were the best performers among all 20 specimens. It was quite interesting that specimen 5 is in third place in terms of CS, but it was shown to have a highly reliable performance in terms of energy absorption. It was clear that specimen 1 showed a better CS but did not absorb that much energy after a failure. This is due to the internal failure of the honeycomb structures, which could not take the further load. By observing the graphs, it was noted that the EA capacity of the specimens was good even after the initial failure points are recorded. The main reason for these results was a perfect set of the diameter of the circle arranged at six corners like a hexagon pattern and the distance between them. The best performed specimens in terms of energy absorption values are shown in

Table 1. The best specimens with parameters.

Specimen/Run Order	Thickness (mm)	Length (mm)	Diameter (mm)
1	0.75	8	6
2	0.625	10	5
5	0.5	8	6

. The results seen in EA values of all specimens are interesting in terms of studying the bio-inspired BES and HCS, which may give new drive to the development of the lightweight high-strength components, a crucial need in the engineering sector.

4. Conclusions and Future Scope

This paper investigates the effects of design parameters, namely the thickness, length, and diameter of the hollow cylinder of the BES structures. It was observed that specimens 1 and 3 showed good compressive behavior among all specimens, and specimen 5 had the best value of EA due to its internal honeycomb integrated sandwich structure. Designs need to be developed with other geometries replacing the circular shapes, and we need to conduct different mechanical tests on specimens in the future.