Hexagonal Honeycomb Structure Research Articles

In-plane compression of graded hierarchical honeycombs

Hierarchical and graded honeycomb structures are extensively applied in many fields due to their excellent compression properties and energy absorption capacity. In the present study, the segmented graded hierarchical honeycomb structures with triangle substructures (GHT) are constructed to numerically investigate the in-plane crushing performance by the nonlinear finite element analysis code ABAQUS/Explicit. GHT exhibits the best energy absorption capacity compared to graded regular hexagonal honeycomb structures (GRH), graded hierarchical structures with Kagome substructures (GHK) and graded hierarchical structures with hexagonal substructures (GHH). The comprehensive effect of inertia and yield strength at each layer is illustrated by investigating the deformation modes under different loading speeds. The plateau stress is discussed in two ways: the overall average plateau stress corresponding to the whole structure and the segmental plateau stress corresponding to the specific layer. The relationship between overall average plateau stress, relative density and loading speed for the graded structure is established based on one-dimensional shock wave theory and compared with the uniform structure. The segmental properties of plateau stress at both impact and fixed ends are investigated in detail by combining theoretical analysis and deformation characteristics, and the results show good consistency with the simulation results at low, medium, and high loading speed conditions. Finally, the concept of cyclic graded structure is introduced, which can further optimize the energy absorption capacity and provide guidance for the design of new multifunctional structures.

Hydrothermal functionalization of graphene quantum dots extracted from cellulose

Functionalization is a promising approach to modify the physical and chemical properties of graphene quantum dots (GQDs). However, the synthesis of functionalized GQDs (F-GQDs) is usually conducted with strong acids. Thus, the sustainable synthesis route of F-GQDs remains a challenge. This is important for suitable optimization of GQDs to be applied in sustainable photovoltaic applications, especially dye-sensitized solar cells owing to the strong attachment of functional group elements. This study presents a detailed study of optical, structural, and chemical changes that occurred in GQDs during the functionalization process by adding an ionic liquid, 1-ethyl-1-methylpyrrolidium bis(trifluoromethylsulfonyl)imide via hydrothermal synthesis approach using an eco-friendly route comprising only cellulose and deionized (DI) water. The presence of ionic liquid provides fundamental elements (nitrogen (N), fluorine (F), and sulfur (S)), which are added to GQDs producing F-GQDs. The optimum result shows that the 20 wt% N, F, S functionalized GQDs have the largest UV–vis absorption and photoluminescence emission. The F-GQDs also revealed a single crystalline hexagonal graphene-like honeycomb structure in transmission electron microscopy and increased roughness relatively from atomic force microscopy. Moreover, the Fourier transform infrared and x-ray photoelectron spectroscopy have also confirmed the presence of C-N, C=S, C-F, and N-H functional groups in the F-GQDs produced.

Broadband Low-Frequency Sound Absorption via a Hexagonal Acoustic Metamaterial in the Honeycomb Structure

We proposed a low-frequency absorber comprised of a hexagonal honeycomb structure is presented and demonstrated. The acoustic metamaterial of the hexagonal honeycomb structure with different folding numbers n is investigated via finite element simulations to solve COMSOL multi-physics commercial software. This technique is design to expose the influence of thickness and eccentric hexagonal designs to improve acoustic performance. A hexagonal honeycomb structure made of a soft polymer is constructed. The effect of the folding number on the absorption peak is studied, and the results indicate that a more significant folding number can dramatically increase the absorption peak frequency with the absorber decreasing thickness. The impact of structural parameters for honeycomb structure designs is demonstrated to produce a low-frequency sound absorber. To achieve unitary sound absorption at low frequencies results via adjusting the inner and outer thicknesses with the folding number n. we show influenced the hexagonal folding number and adjusting the internal parameters of the acoustic metamaterial to paving the path for creating an ideal sound absorber

Sound Transmission Loss of a Honeycomb Sandwich Cylindrical Shell with Functionally Graded Porous Layers

To examine the acousto-structural behavior of a sandwich cylindrical shell benefiting from hexagonal honeycomb structures in its core and functionally graded porous (FGP) layers on its outer and inner surfaces, a comprehensive study based on an analytical model which also considers the effect of an external flow is conducted. A homogenous orthotropic model is used for the honeycomb core while its corresponding material features are found from the modified Gibson’s equation. The distribution pattern of FGP parts is either even or logarithmic-uneven, and a special rule-of-mixture relation governs their properties. Based on the first-order shear deformation theory (FSDT), Hamilton’s principle is exploited to derive the final coupled vibro-acoustic equations, which are then solved analytically to allow us to calculate the amount of sound transmission loss (STL) through the whole structure. This acoustic property is further investigated in the frequency domain by changing a set of parameters, i.e., Mach number, wave approach angle, structure’s radius, volume fraction, index of functionally graded material (FGM), and different honeycomb properties. Overall, good agreement is observed between the result of the present study and previous findings.

Investigation on mechanical characteristics of non-pneumatic tire with rhombus structure under complex pavement conditions

Non-pneumatic tires (NPTs) have gained more and more attention in recent years due to the advantages of no run-flat, maintenance-free and excellent load-bearing capacity. In this paper, a mechanical model of rhombic porous structure was derived based on the theory of the hexagonal honeycomb structure, and the difference of mechanical characteristics for rhombic NPT tread on horizontal pavement as well as complex pavement was studied. The results show that the average contact pressure of NPT with rhombic structure on horizontal road is much lower than that of pneumatic tire, the shape of its spoke bearing area is inverted trapezoid, and the stress concentration phenomenon is formed in the contact part corresponding to the connection between spokes and tread at different contact positions. Furthermore, the vertical displacement and contact pressure of NPT are decoupled on complex pavement. The maximum stress concentration point is shifted from the tire surface to the spoke-tread connection and then to the spokes of the rhombic bearing structure as the contact area between the tire and the ground increases. This study provides guidance for structural optimization of NPT applied to complex working conditions.

Compression Behavior of 3D Printed Polymer TPU Cubic Lattice Structure

Based on the face-centered cubic structure, several different types of cubic lattice structures are designed in this paper, the quasi-static compression behavior of the lattice structure is thoroughly investigated by finite element simulation and experimental testing, in which mechanical properties and energy absorption capacities are summarized. The experimental specimens made from thermoplastic polyurethane TPU are additively manufactured using the fused deposition technology. Effects of strut style, strut distance, arrangement form, curvature, and several honeycomb lattice structures are considered. The results show that: under the condition of the same relative density, the selection of sinusoidal struts with larger curvature, the arrangement of 45°/135°, and the inward gradient of the strut distance can all improve the energy absorption characteristics of the structure. Compared with the traditional face-centered cubic structure (specimen L-1), the SEA of the structure with the strut curvature of 0.25, the 45°/135° arrangement of the sinusoidal struts, and the inward gradient of the strut distance is improved by 64% , 190%, and 107%; the introduction of a honeycomb structure with a high relative density can effectively resist the buckling deformation of the structure, and the SEA of the triangular, re-entrant and hexagonal honeycomb structures are 354%, 603% and 548% higher than that of the basic structure, respectively. In addition, reducing the lattice height also resists destabilization.

First-principles study on the structural properties of 2D MXene SnSiGeN4 and its electronic properties under the effects of strain and an external electric field.

The MXene SnSiGeN4 monolayer as a new member of the MoSi2N4 family was proposed for the first time, and its structural and electronic properties were explored by applying first-principles calculations with both PBE and hybrid HSE06 approaches. The layered hexagonal honeycomb structure of SnSiGeN4 was determined to be stable under dynamical effects or at room temperature of 300 K, with a rather high cohesive energy of 7.0 eV. The layered SnSiGeN4 has a Young's modulus of 365.699 N m-1 and a Poisson's ratio of 0.295. The HSE06 approach predicted an indirect band gap of around 2.4 eV for the layered SnSiGeN4. While the major donation from the N-p orbitals to the band structure makes SnSiGeN4's band gap close to those of similar 2D MXenes, the smaller distributions from the other orbitals of Sn, Si, and Ge slightly vary this band gap. The work functions of the GeN and SiN surfaces are 6.367 eV and 5.903 eV, respectively. The band gap of the layered SnSiGeN4 can be easily tuned by strain and an external electric field. A semiconductor-metal transition can occur at certain values of strain, and with an electric field higher than 5 V nm-1. The electron mobility of the layered SnSiGeN4 can reach up to 677.4 cm2 V-1 s-1, which is much higher than the hole mobility of about 52 cm2 V-1 s-1. The mentioned characteristics make the layered SnSiGeN4 a very promising material for use in electronic and photoelectronic devices, and for solar energy conversion.

Experimental Analysis on 3d Printed Onyx Specimens with Honeycomb Infill Structure

There is a demand for the development of products in a shorter time that resulted in the introduction of 3D printing which is also termed as “Additive Manufacturing” (AM). This technology has many advantages such as costeffectiveness, less manufacturing time and elimination of post-processing costs. Intensive research is being carried out on cellular structures manufactured using additive manufacturing technologies. Cellular structures have many applications in various areas. When compared to solid structures, these cellular structures possess high strength to weight ratio, good energy absorption characteristics, good thermal and acoustic insulation properties. They are used for aerospace, medical and engineering products. There are many additive manufacturing technologies whereas fused deposition modelling (FDM) is the most versatile one. This research consists of the analysis of hexagonal honeycomb structure by creating honeycomb structures of different dimensions in SolidWorks and manufacturing of those structures by using the FDM additive manufacturing process. These structures were designed by varying the internal hexagon’s wall thickness and side length. After printing these structures were subjected to Mechanical testings like tensile, compression, three-point bending, impact and thermal testing like heat deflection temperature tests. The three-point bending test was simulated numerically and compared with the experimental results. This study is finally validated by comparing experimental and simulation results, which were in agreement with each other. Experimental results show that the low-weight specimen exhibited good mechanical and thermal properties with a lesser printing time compared to the remaining specimens. The specimens with different hexagonal cell dimensions were introduced and discussed.

The Influence of Interface Design and External Frame on the Energy Absorption Performance of the Semi-Auxetic Structure.

In this article, four new semi-auxetic structures are designed by changing the way of interface connection and adding external frames. These structures were fabricated by fused deposition modeling, which is an additive manufacturing technology. The effects of interface design and external frame on deformation mode and energy absorption performance of semi-auxetic structure under quasi-static compression are studied. It was found that the deformation modes of framed and frameless structures are different. The specific energy absorption of the semi-auxetic structure is increased by ∼52% compared with the frameless hexagonal honeycomb structure. In addition, Abaqus was used to establish finite element models of the four new semi-auxetic structures and the frameless hexagonal honeycomb structure. It can be found that the simulation results were consistent with the experimental results.

Effect of F Functional Modification on the Stability and Electronic Structure of Borene

Since the discovery of graphene, two-dimensional materials have quickly won widespread attention in the academic community. Borene is a two-dimensional isomer of boron and the lightest element Dirac material. It becomes the latest and promising two-dimensional material due to its unique structure and electronic properties. In the periodic table, B is a close neighbor of C and has a certain similarity with C. It can also form a hexagonal honeycomb structure. An additional B atom is added to the center of the ring to form a triangular lattice borene. The triangular borene has surplus electrons and belongs to a multi-electron state, which is equivalent to a metastable structure. In this paper, the first principles are used to study the F functionalized modification of the triangular borene. The aim is to transfer the surplus electrons in the system, and probe its structural stability and electronic structure characteristics. The study found that functional modification significantly improved the stability of borene. This can provide feasible ideas and practical guidance for the experimental synthesis of stable boronene.

Design and analysis using aluminium 6061 for lengthwise gradient honeycomb structure to obtain graded beam properties

Honeycomb structures are natural or artificial structures that offer more strength and are low weight structures relatively. In this study, different types (different cell orientations) of hexagonal honeycomb structures are designed, and geometrical dependent properties are derived to analyze the trend when dimensions of cells in honeycomb structures are increased gradually. The diagonal length of cells in honeycomb was varied from 12 mm to 21 mm and mechanical properties like total deformation were evaluated when the honeycomb structure was made to act like a cantilever beam with a point load at its free end. Similarly, a gradient honeycomb structure was designed and mechanical properties like total deformation was evaluated when subjected to point load at its free end by fixing one the other end of the structure(cantilever). On average, gradient honeycomb structure deforms 15.43% less than the regular honeycomb structure. Drop over impact tests were simulated in the Ansys workbench by dropping a stainless steel sphere onto aluminum gradient honeycomb structure to evaluate energy absorbed at different times during the impact. The analysis of simulated results confirms that lengthwise gradient (variation of cell size along the length) honeycomb structures (both vertical and horizontal oriented) possess both bending resistance and good energy absorption abilities.

Effect of loading rates on the in-plane compressive properties of additively manufactured ABS and PLA-based hexagonal honeycomb structures

Honeycomb structures find numerous applications in automotive, aerospace, sports, and other similar engineering fields. Such incorporation is made possible by the excellent crushing resistance and specific energy absorption capabilities. However, manufacturing such structures through conventional processes is highly laborious and expensive. Such a drawback can be largely mitigated by the adoption of additive manufacturing (AM) processes. Consequently, in this study, hexagonal honeycomb structures are subjected to experimental tests to determine their compressive strength under different loading rates. In addition to this, attempts have also been made to evaluate the effect of different materials and the unit cell dimensions on the compressive properties. The test specimens of different wall thicknesses are manufactured by fused deposition modelling (FDM) using PLA and ABS as the base materials. The samples are then subjected to compressive tests using a standard UTM to quantify the effect of the cell geometrical parameters and the loading rate on the overall compressive nature of the structures. The results show that the compression properties are primarily affected by the loading rate, material properties and the cell-wall thickness of the structures. The initial compressive yield stress and plateau stress generally increase up to a given value of loading rate, after which the strength decline. The cell-wall thickness of the structure influences the threshold loading rate. Therefore, this study provides a preliminary understanding of the compressive properties of AM hexagonal honeycomb structures to analyse the prospects for application in real-world engineering applications. It is proposed that such structures find profound applications in structural components of aerospace equipment, automotive parts, sports gear, and other similar areas of interest where high strength and energy absorption are of predominant importance.

Analytical buckling temperature prediction of FG piezoelectric sandwich plates with lightweight core

Buckling temperature prediction of a functionally graded piezoelectric (FGP) sandwich plate with lightweight core is studied in the present work. The composite plate is made of three layers. The upper and lower layers are made of two different piezoelectric materials so that the electrical and mechanical properties are smoothly varied through the thickness based on a power law distribution. Whereas, the lightweight core is considered as hexagonal honeycomb structure or functionally graded porous structure. The porous core contains internal pores with different porosity distributions. According to a modified four-unknown shear deformation plate theory, the displacement field is described. The smart advanced plate is subjected to thermal and humid loadings as well as external electric voltage. The thermal and humid loadings may be uniform, linear or non-linear through the thickness. The stability equations are constructed from the principle of virtual work based on the proposed shear deformation plate theory. The obtained results will be validated by introducing some comparison examples. Finally, the influences of different parameters like the side-to-thickness ratio, aspect ratio, core type, core thickness, power law index, moisture concentration, external applied voltage and boundary conditions on the buckling temperature change of the sandwich plates with honeycomb core or with porous core are discussed. It is found that the buckling temperature of the sandwich plate with honeycomb core is greater than that of the sandwich plate with porous core. Moreover, with increasing the lightweight core thickness, the sandwich plate stiffness decreases leading to a reduction of the buckling temperature.

Crashworthiness index of honeycomb sandwich structures under low-speed oblique impact

It is expected to quantitatively determine the crashworthiness of honeycomb sandwich structures in engineering. However, it is challenging due to diverse cell features, hybrid component materials, as well as varied types of impact load. In this study, two dimensionless indexes (i.e., horizontal dent offset displacement per unit depth ϕ and the ratio of horizontal to vertical energy absorption η) are proposed for sandwich structures based on the mechanical response characteristics (deformation and energy absorption) of sandwich structures under low-speed oblique impact. Unlike conventional crashworthiness indexes such as dent depth, specific energy absorption, damage area, etc., the proposed indexes take into account the influence of impact angle (θ) on the mechanical behavior of sandwich structures. Multiple sets of simulation of honeycomb sandwich structures, including conventional hexagonal honeycombs, honeycomb-filled structures and negative Poisson's ratio structures, obliquely impacted (θ varies from 15° ~ 75°) by a rigid body are performed by using the finite element method, whereby the crashworthiness index values of all the sandwich structures are obtained. The index values (ϕ and η) become smaller as the crashworthiness is enhanced (where the wall thickness of the sandwich structure is thickened from 0.02 ~ 0.1 mm). It manifests that the proposed indexes can capture the crashworthiness of sandwich structures under low-speed oblique impact reasonably well. In addition, the proposed indexes can more clearly distinguish the crashworthiness of sandwich structures of different configurations than conventional indexes. The index values (ϕ and η) show that the oblique crashworthiness of the negative Poisson's ratio structure, hexagonal honeycomb, and honeycomb-filled structure becomes stronger in order.

Design of Shape Reconfigurable, Highly Stretchable Honeycomb Lattice With Tunable Poisson’s Ratio

The mechanical behaviors of lattice structures can be tuned by arranging or adjusting their geometric parameters. Once fabricated, the lattice’s mechanical behavior is generally fixed and cannot adapt to environmental change. In this paper, we developed a shape reconfigurable, highly stretchable lattice structure with tunable Poisson’s ratio. The lattice is built based on a hexagonal honeycomb structure. By replacing the straight beam with curled microstructure, the stretchability of the lattice is significantly improved. The Poisson’s ratio is adjusted using a geometric angle. The lattice is 3D printed using a shape memory polymer. Using its shape memory effect, the lattice demonstrates tunable shape reconfigurability as the ambient temperature changes. To capture its high stretchability, tunable Poisson’s ratio and shape reconfigurability, a phase evolution model for lattice structure is used. In the theoretical model, the effects of temperature on the material’s nonlinearity and geometric nonlinearity due to the lattice structure are assumed to be decoupled. The theoretical shape change agrees well with the Finite element results, while the theoretical model significantly reduces the computational cost. Numerical results show that the geometrical parameters and the ambient temperature can be manipulated to transform the lattice into target shapes with varying Poisson’s ratios. This work provides a design method for the 3D printed lattice structures and has potential applications in flexible electronics, soft robotics, and biomedicine.

Computational modeling of electrolytic deposition of a single-layer silicon film on silver and graphite substrates

Electrodeposition of silicon from a KF-KCl-KI salt melt at 1000 K using silver and graphite substrates has been studied by the molecular dynamics method. Silicon films of monatomic thickness with a predominantly hexagonal honeycomb structure were obtained on each substrate. The adhesion energy between the obtained film and the silver substrate is 2.5 times higher than that between the film and the graphite substrate. A single cluster grows much faster on a graphite substrate than on a silver substrate, where several clusters are formed at once. As the substrates are filled with silicon, the diffusion coefficient of Si atoms decreases faster on a graphite substrate than on a silver one. The silver substrate is completely covered with silicon, while a three-dimensional Si cluster begins to grow on a graphite substrate incompletely filled with silicon. The obtained silicon films on both substrates do not have the characteristic buckling, which is found in silicene prepared by the chemical vapor deposition on a silver substrate. Films obtained on both substrates have low mechanical stress. The stress distribution in the case of a graphite substrate is more uniform.

Structural design and characteristics of a non-pneumatic tire with honeycomb structure

The structure of non-pneumatic tire is complex and various, but its performance is superior to ordinary tire, so it has broad prospects. In this paper, a design method of honeycomb structure was proposed based on tangent method, and the hexagonal and circular honeycomb structure were established. The rules of displacement, radial stiffness and ground pressure of honeycomb structure with different density were studied. Meanwhile, the most basic bearing performance of non-pneumatic tire was analyzed by finite element method under static conditions. The results show that the radial stiffness of honeycomb increases with the increase of density. When the density is small, the bearing capacity of circular structure is stronger than that of hexagonal structure, the ground pressure decreases with the increase of density and the maximum stress of the two is located on the honeycomb structure. When the density is high, the maximum stress is on the contact surface between the rim and the inner circumference. This study provides a reference for other types of non-pneumatic tire structure design and builds the foundation to study contact performance analysis of non-pneumatic tire under complex working conditions.

Equivalent theories and tension properties of semi-reentrant structures

Semi Reentrant structures, which exhibit zero Poisson’s ratio and monoclastic curvature, are combinations of hexagonal Honeycomb and auxetic Reentrant structures. Deflections and strain analysis based on the deformation of unit cells were conducted, and four different equivalent theories for predicting the elastic modulus and Poison’s ratio in two in-plane directions were developed by considering different mechanisms, including flexural, stretching, hinging and shearing deformations, as well as the influence of cell wall thickness. Single sidewall and double sidewall were considered for the cell wall thickness. The theoretical models of Semi Reentrant structures cell could be obtained by assuming that the deformation is a combination of deformation for a hexagonal honeycomb cell (with a positive angle) and a Reentrant cell (with a negative angle). The effectiveness and accuracy of the four theoretical models for Semi Reentrant structures were validated by comparing with the corresponding tensile test simulation results via the finite element method. It was indicated that the fourth theories (T4) were the most accurate, which include the consideration of flexural, stretching, hinging, shearing deformations and cell wall thickness. The influence of geometrical parameters (inclined arm length l, vertical arm length h, angle α, angle β, structure thickness d and cell wall thickness t) on the in-plane tensile properties (elastic modulus and stiffness) was also analysed in tensile test simulations via the finite element method. Comparison of tension results between Semi Reentrant, Reentrant and Honeycomb demonstrated that the mechanical properties of Semi Reentrant were combinations between the others.

Crashworthiness analysis and multi-objective optimization for honeycomb structures under oblique impact loading

Oblique impact loading conditions are unavoidable in practical applications, which strongly influence the performance response of energy-absorbing structures. In this paper, the finite element models of four typical cellular structures (hexagon honeycomb, re-entrant hexagon honeycomb, star-shape honeycomb, double arrow honeycomb) are established and experimentally validated. The dynamic responses of four structures under different impact angles (from 0 to 30°) and impact velocities (from 5 to 50 m/s) are investigated. On this basis, the influences of impact angle and impact velocity on the specific energy absorption (SEA) and peak crushing force (PCF) of four structures are discussed. The results reveal that the negative Poisson’s ratio structure has the advantage of energy absorption under axial impact due to the characteristics of compression and contraction at the low impact velocity. The hexagonal honeycomb structure has great advantages in terms of comprehensive energy absorption capacity and better stability at varying inclination angles. The Non-dominated Sorting Genetic Algorithm (NSGA-II) coupled with the ideal point method (IPM) is utilised to explore the optimal design of hexagon honeycomb structure, which is then verified by a detailed crashworthiness comparison with the original design. The optimal honeycomb structure shows excellent crashworthiness characteristics and demonstrates great potential for applications in impact engineering, especially the oblique impact loading situations.

An exergy analysis for overall hidden losses of energy in solar water heater

This study investigates the hidden thermal losses of glass plate, collector plate, water pipe and storage tank of solar water heater in the process of energy conversion. The present non-conventional energy methods are insufficient, whereas the exergy analysis provides a remarkable solution. Thus, employing the exergy analysis, entropy generation, exergy destruction, and exergy efficiency of each subsystem of solar water heater are computed. The obtained results showed that the entropy generation and exergy destruction are high during the heat transfer in each subsystem. Henceforth, the existing solar water heater design is modified placing hexagonal honeycomb structure between the glass plate and the collector plate and also water pipe is insulated to trap huge amount of solar energy. The proposed design exhibits improved exergy efficiency when compared with the existing model, which enhances the performance of the system.