Hexagonal Honeycomb Research Articles

Evidence of Formation of Monolayer Hydrated Salts in Nanopores.

Despite much effort being devoted to the study of ionic aqueous solutions at the nanoscale, our fundamental understanding of the microscopic kinetic and thermodynamic behaviors in these systems remains largely incomplete. Herein, we reported the first 10 μs molecular dynamics simulation, providing evidence of the spontaneous formation of monolayer hexagonal honeycomb hydrated salts of XCl2·6H2O (X = Ba, Sr, Ca, and Mg) from electrolyte aqueous solutions confined in an angstrom-scale slit under ambient conditions. By using both the classical molecular dynamics simulations and the first-principles Born-Oppenheimer molecular dynamics simulations, we further demonstrated that the hydrated salts were stable not only at ambient temperature but also at elevated temperatures. This phenomenon of formation of hydrated salt in water is contrary to the conventional view. The free energy calculations and dehydration analyses indicated that the spontaneous formation of hydrated salts can be attributed to the interplay between ion hydration and Coulombic attractions in the highly confined water. In addition to providing molecular-level insights into the novel behavior of ionic aqueous solutions at the nanoscale, our findings may have implications for the future exploration of potential existence of water molecules in the saline deposits on hot planets.

Anti-blast performance of 3D-printed sandwich panels with auxetic hexagonal and regular hexagonal honeycomb cores

3D-printed auxetic honeycomb sandwich panels (HSPs) have considerable potential for blast resistance enhancement. This study aims to bridge the gap with regard to the experimental data on the effect of 3D-printed auxetic hexagonal honeycomb cores on the blast response of HSPs. To this end, the blast resistance of HSPs developed using auxetic re-entrant and regular hexagonal honeycomb cores is investigated experimentally and numerically. First, six HSPs are tested under close-in blast loadings. The HSPs comprise Q345 steel top and bottom sheets as well as a honeycomb aluminum alloy core with two configurations (regular hexagonal and auxetic re-entrant). According to the results, the former configuration enhances the HSP blast resistance by not only decreasing the deformation of the HSPs but also improving their damage tolerance. In addition, the responses of the HSPs are numerically studied via finite element analysis. The numerical method using the finite element program LS-DYNA achieves reasonable accuracy. Finally, a parametric study is conducted to investigate the effects of the honeycomb type, cell angle, debonding effects, and core material on the blast resistance of the HSPs. The results demonstrate that employing auxetic hexagonal honeycomb core, smaller cell angle, and ductile core material can improve the blast resistance of HSPs.

Design and optimisation of a passive Atmosphere-Breathing Electric Propulsion (ABEP) intake

In order to extend the orbital lifetime of spacecraft operating in Very-Low Earth Orbit (VLEO), Atmosphere-Breathing Electric Propulsion (ABEP) can be employed for atmospheric drag compensation. The concept is based on the ingestion of rarefied atmospheric particles to be used as propellant for an electric thruster, thereby removing the need for onboard propellant. The present paper aims to design and analyse a passive ABEP intake optimised for the RF Helicon-based Plasma Thruster (IPT), which is selected as the most promising system due to its electrodeless design, as it removes the issue of thruster corrosion, and reduced susceptibility to atmospheric variations. This is achieved by implementing the analytical model, referred to as the Balancing Model (BM), along with its main performance parameters. The Direct Simulation Monte Carlo (DSMC) solver dsmcFoam+ is thus employed to simulate the transmission probability of cylinders and hexagonal prisms with non-zero entrance velocity, yielding a mean percentage error of 2% when compared to independent DSMC results. In addition, a novel DSMC transmittance investigation of square prisms is performed. Various design configurations are optimised for circular and hexagonal intakes based on the functional requirements of the thruster, leading to a maximum collection efficiency of 45% for a cylindrical intake with a hexagonal honeycomb. The optimal intake is hence simulated via DSMC, showing a good accuracy with the BM with or without intermolecular collisions, yielding a percentage error of 0.22% in the former case and 5.53% in the latter one. The variation of incidence flow angle, accommodation coefficient and thruster transmission probability is finally investigated, and the results are validated by the agreement shown with values retrieved from the literature.

Geometry design and in-plane compression performance of novel origami honeycomb material

Origami is widely used for honeycombs to improve mechanical behavior. This research presents an origami-honeycomb material based on the assembly of Miura patterns. Firstly, the geometry stacking scheme and rigid folding mechanism are discussed. Secondly, the in-plane compression behavior of the proposed origami-honeycomb is experimentally and numerically investigated. Its performance is then compared with a hexagonal honeycomb. Both results show that the origami-honeycomb outperforms the conventional honeycomb in terms of in-plane compression strength and energy absorption behavior. Subsequently, deformation mode and energy efficiency ratio are obtained to illustrate the mechanical behavior. A parametric analysis is also conducted by employing finite element simulations. Finally, the analytical model of the proposed origami honeycomb is built to estimate the gather strain and plateau stress.

Bionic inspired honeycomb structures and multi-objective optimization for variable graded layers

Bionic and gradient designs offer promising applications in honeycomb structures. The intersection unit of the beetle elytra is extracted as to enhance regular hexagonal honeycomb (RHH), and several bionic honeycombs are proposed. Finite element (FE) modeling approach is verified through formulae and experiments. Curves of force and displacement of bionic honeycombs present two prominent stages under medium- and low-speed impacts in plateau stage, and several bionic honeycombs exhibit a zero or negative Poisson’s ratio. The specific energy absorption (SEA) of INT_6, whose crashworthiness is best in bionic honeycombs. A gradient design of INT_6 is implemented to further increase its crashworthiness. Multi-objective optimization design (MOD), which aims to simultaneously increase the SEA and reduce the peak crushing force, is adopted to determine the optimal parameters of each layer of graded INT_6. The SEA of the optimized graded INT_6 increase 142%, and its peak crushing force decrease by 25.4% compared with those of the INT_6.

High-precision direct ink writing of Li6.4La3Zr1.4Ta0.6O12

Due to its high ionic conductivity and stability to lithium metal, Li6.4La3Zr1.4Ta0.6O12 (LLZTO), as an element-doped garnet-type LLZTO material, has become one of the most promising solid electrolyte materials. However, traditional processing technologies of LLZTO materials lack of structural diversity and complexity, and the processing cost is high, making it difficult to be widely used in industrial production. Here, three LLZTO ink formulations are presented which allow for direct ink writing to print complex, cellular 3D structures with an accuracy of 150 µm, including hexagonal honeycombs, triangles and log pile square structures. Based on their tailored rheological properties, such as high modulus G' > 105 Pa, high yield stress σ ≈ 1000 Pa and distinct shear thinning, the inks have excellent printing properties. Based on these inks, LLZTO materials can be printed with three-dimensional freely designable electrolyte structures using common DIW 3D printers.

An FFT-based method for uncertainty quantification of Nomex honeycomb’s in-plane elastic properties

The honeycomb manufacturing process involves complex and inter-related procedures spanning multiple physics domains and scales. The geometry heterogeneity in honeycomb cells inevitably exists and propagates to the uncertainty of the honeycomb’s mechanical performance. Quantitatively characterizing the effect of cell geometry variability on the effective mechanical properties of honeycomb hence becomes critically important. In this study, a Fast Fourier Transform (FFT) based method was developed to predict the effective in-plane elastic properties of irregular hexagonal honeycomb. The honeycomb geometry heterogeneity was identified with a digital image technology by examining a large number of cells. Correlation analysis on the resulting statistical data enables determining the interdependence of cell wall lengths and angles. Using a Representative Unit Cell (RUC) with varying cell wall lengths and angles, an analytical function for the effective in-plane elastic parameters was established by incorporating the dependencies. The statistical quantification of cell geometry and the propagation of RUC’s elastic characteristics were further integrated into the FFT-based multiscale framework for predicting the in-plane elastic moduli of irregular honeycomb. The tensile and shear tests on the irregular honeycombs, together with the corresponding finite element analysis, were used to verify the proposed method. Both experimental and numerical results confirmed that the uncertainty of elastic moduli achieved by the FFT-based method provides a reasonable estimation.

Construction of soft polyurethane cushioning composites based on integral fabric air layer: Reaching new levels in compression and cushioning behaviors

AbstractIn order to prepare a cushioning composite with good resilience and compressibility, the 3D fabric was perforated into a hexagonal honeycomb, high elasticity porous polyurethane foam was used as substrate, and the air layer structure was encapsulated with the packaging film. By changing the hexagonal side length and wall thickness of the honeycomb structure, the integral fabric air layer polyurethane buffer composite was prepared. The properties of the structure were studied, and its compressive capacity under different compressive strains was analyzed. The results show that the mechanical properties of polyurethane foam were improved after adding the integral fabric air layer structure. When the composite HPU‐R1L2 (polyurethane cushioning composites with 1 cm side length and 2 cm wall thickness of hexagonal honeycomb) was compressed to 75%, its compressive capacity was 8.24 times that of PU (Polyurethane foam with 2.5% bentonite). The prepared composite HPU‐R1L1 (Polyurethane cushioning composites with 1 cm side length and 1 cm wall thickness of hexagonal honeycomb) absorbed 96.7% of the energy in the dynamic impact test, indicating that the composite cushioning performance was stronger than that of polyurethane foam. The HPU composites based on the synergistic reinforcement strategy of polyurethane foam and monolithic fabric air‐layer structures are an excellent candidate in the field of commodity packaging and personal protection.

Nonlinear forced vibration of hybrid fiber/graphene nanoplatelets/polymer composite sandwich cylindrical shells with hexagon honeycomb core

Nonlinear forced vibration of hybrid fiber/graphene nanoplatelets/polymer composite sandwich cylindrical shells with hexagon honeycomb core

Dynamic Crushing Behaviors of Second-Order Hexagonal Honeycombs

Hexagonal honeycombs form the common core of composite sandwich structures. In this study, on the basis of the hexagonal honeycomb model, a second-order hexagonal honeycomb is established by cutting pores on the cell wall to realize secondary lightweight design. Furthermore, the in-plane and out-of-plane dynamic crushing behaviors of the second-order hexagonal honeycombs are investigated by combining theoretical analysis with numerical simulation. The effect of the variation in the pore sizes on the cell wall on the in-plane and out-of-plane deformation modes, the mechanical properties, and the energy absorption capacities of second-order hexagonal honeycombs under different impact velocities is discussed. Semi-empirical theoretical formulas for the in-plane and out-of-plane bearing strength of second-order hexagonal honeycombs are proposed. The results show that cutting pores on the cell wall reduces the weights of hexagonal honeycombs and improves their energy absorption capacities. This also provides a new method to realize hexagonal honeycombs that display pore characteristics along both in-plane and out-of-plane directions.

Ultra-thin corrugated metamaterial film as large-area transmission dynode

Large-area transmission dynodes were fabricated by depositing an ultra-thin continuous film on a silicon wafer with a 3-dimensional pattern. After removing the silicon, a corrugated membrane with enhanced mechanical properties was formed. Mechanical metamaterials, such as this corrugated membrane, are engineered to improve its strength and robustness, which allows it to span a larger surface in comparison to flat membranes while the film thickness remains constant. The ultra-thin film consists of three layers (Al2O3/TiN/Al2O3) and is deposited by atomic layer deposition (ALD). The encapsulated TiN layer provides in-plane conductivity, which is needed to sustain secondary electron emission. Two types of corrugated membranes were fabricated: a hexagonal honeycomb and an octagonal pattern. The latter was designed to match the square pitch of a CMOS pixel chip. The transmission secondary electron yield was determined with a collector-based method using a scanning electron microscope. The highest transmission electron yield was measured on a membrane with an octagonal pattern. A yield of 2.15 was achieved for 3.15 keV incident electrons for an Al2O3/TiN/Al2O3 tri-layer film with layer thicknesses of 10/5/15 nm. The variation in yield across the surface of the corrugated membrane was determined by constructing a yield map. The active surface for transmission secondary electron emission is near 100%, i.e. a primary electron generates transmission secondary electrons regardless of the point of impact on the corrugated membrane.

Selective growth of graphene films on gallium-focused ion beam irradiated domains

Graphene, a single layer of carbon atoms tightly bound in a hexagonal honeycomb lattice to form a two-dimensional lattice, is a very interesting material with promising electronic, optical, chemical, and mechanical applicative potential [Geim and Novoselov, Nat. Mater. 6, 183 (2007)]. The properties of graphene make it suitable for a wide range of applications; however, its applicative future still depends on large scale technologies capable to robustly and reproducibly transfer its outstanding intrinsic properties into devices or complex structures. It must be recognized that a crucial technological problem, that still inhibits the applicability of high quality graphene material properties, is related to the patterning of this material using traditional top down instruments and lithographical methods. In this work, we will detail our investigations on applying a precise 30 keV Ga+ ion irradiation to selectively shape and modify a copper precursor surface for promoting the local growth of graphene surface domains. The morphology of these domains is investigated using scanning tunneling microscopy and spectroscopy to probe simultaneously the structural and the electronic properties at the atomic scale of the graphene films.

Analytical modeling and vibration analysis of fiber reinforced composite hexagon honeycomb sandwich cylindrical-spherical combined shells

Analytical modeling and vibration analysis of fiber reinforced composite hexagon honeycomb sandwich cylindrical-spherical combined shells

Nanoarchitectonics effect of few-layer graphene on the properties of cement mortar

• The number of layers is an important indicator to measure the properties of graphene. • Few-layer graphene can improve the mechanical properties of cement mortar. • Within the scope of test, the optimal dosage of Few-layer graphene is 0.04% ∼ 0.06%. To further study graphene/mortar composites, the effects of few-layer graphene (FLG) on the fluidity, mechanical properties (compressive strength and flexural strength) and electrical properties of cement mortar were systematically studied in this paper, through SEM, XRD and EDS to analyze the mechanism. Meanwhile, AFM, Raman and SEM were used to characterize the layer number and structure of FLG. The results show that the layer number of FLG is between 3 and 6 layers, which shows a hexagonal honeycomb structure and interlayer stacking phenomenon. The addition of FLG can reduce the fluidity of mortar, while improve the conductivity of mortar, and FLG/mortar composites present NTC effect. 28 d compressive strength and flexural strength of mortar increased by 38.1% and 58.03% respectively with the addition of FLG. FLG has the effect of nano filling and overlapping hydration products, which can promote the better connection between cement paste and aggregate, thus the structure of mortar more dense.

The in-plane, elastic-plastic response of a filled hexagonal honeycomb at finite strain

Finite strain numerical solutions are derived for the in-plane, elastic-plastic response of a filled hexagonal honeycomb in uniaxial compression and in uniaxial tension. The cell walls and core are treated as elastic, ideally plastic von Mises solids, but the uniaxial strength of the core material is much less than that of the cell walls. The honeycomb has sides of equal length, and its inclined (but non-vertical) cell walls subtend an angle with respect to the transverse direction that can deviate from the usual value of +/-30° which is characteristic of a regular honeycomb. Two responses of the core are assumed: the fully bonded, ‘non-cavitating core’ (in the presence of a sufficiently high macroscopic pressure) and a ‘cavitating core’ that can cavitate or debond freely from the cell walls. When the honeycomb has cell walls that are inclined at 30° or less, the unit-cell response in uniaxial compression is stable and displays macroscopic hardening, regardless of whether the core can cavitate or not. In contrast, when the inclination of the cell walls exceeds 30°, the honeycomb with a cavitating core displays mild softening in uniaxial compression while the honeycomb with a non-cavitating core has a high initial yield strength, followed immediately by a strongly softening response. The strongly softening, isochoric mode occurs in an inclined shear band by the rotation of inextensional plastic hinges in the cell walls over a wavelength of two cells. A Maxwell construction is adequate for prediction of the propagation stress of the shear band in a finite specimen from a starter defect. Additional insight into the collapse mechanisms of the filled honeycomb (with a cavitating or non-cavitating core) is obtained via analytical solutions for a rigid, ideally plastic honeycomb, whereby the cell walls are treated as slender beams and the core has vanishing deviatoric strength. The full numerical solutions reveal that the filled honeycomb exhibits strong tension-compression asymmetry for both a cavitating core and a non-cavitating core.

Low-velocity impact behavior of sandwich composite structure with 3D printed hexagonal honeycomb core: varying core materials

Additive manufacturing technology is extensively used in aeronautical applications, especially in designing the sandwich composite structures for repair tasks. However, the composite structures are vulnerable to impact loadings because of their exposure to, for instance, loading field carriages, flying debris, and bird strikes. This may lead to crack propagation and ultimately the structural failure. Therefore, it is important to investigate the mechanical behavior of sandwich composite structures under low-velocity impact. In this research, carbon fiber fabric reinforced 3D-printed thermoplastic composite of hexagonal honeycomb cores structures were fabricated with different unit cells (6, 8, and 10 mm) and varying materials (polylactic acid (PLA), PLA-Wood and PLA-Carbon). A drop weight impact test was performed under impact energies (5, 8, and 11 J) to determine the energy absorption performance of the structures whereas the surface morphology was analyzed using a high-intensity optical microscope. Comparing unit cells of materials used, it is observed that the unit cell of 8 mm is the best configuration for lightweight materials with impressive energy absorption capabilities. Under an impact energy of 11 J, the PLA-Wood of unit cell 8 mm shows 9.22 J higher in energy absorption than unit cell 10 mm which is 7.44 J due to intermediate stiffness that resists further deformation. While the filled PLA shows the PLA-Wood material offers better performance in energy absorption capability compared to PLA-Carbon. The PLA-Wood demonstrates 9.22 J more energy absorption for an unit cell 8 mm under an impact energy of 11 J than the PLA-Carbon, which is 8.49 J. This is due to the good compatibility between the hydroxyl groups of the polymer matrix and lignocellulose filler, which translates to better stiffness.

Far-field thermal radiation properties of graphene under uniaxial strain

Electronic band structure and optical conductivity of single-layer graphene could be altered by applied uniaxial strain. Valley and space inversion symmetries are broken. Dirac cones are deformed. We investigate the effect of uniaxial strain on the radiative properties of graphene from the perspective of direction and modulus. Optical conductivity exhibits wealthy phenomenon due to the degeneracy of the energy band broken by strain. The total energy radiation exhibits a novel behavior of periodicity in , in accordance with the symmetry of the hexagonal honeycomb lattice.

Additively manufactured novel Ti6Al7Nb circular honeycomb cellular solid for energy absorbing applications

This investigation addresses a novel additively manufactured circular honeycomb sample of the titanium alloy Ti6Al7Nb which exhibits superior mechanical properties compared to hexagonal honeycomb samples. Compared to other lattice structures/cellular solids of Ti-based alloys, the circular honeycomb sample provides an optimum combination of strength and fracture strain. During compression testing, the circular honeycomb exhibits a wide stress-strain curve with higher tensile stress and elongation compared to hexagonal honeycomb samples. The failure of the circular honeycomb sample occurs layer-by-layer, so the whole sample fails not before the fracture of all single layers of the cells in the circular honeycomb leading to higher elongations. In this regard, the hexagonal honeycomb sample fails by shear of struts oriented at 45° to the loading axis. The area near the fracture region shows a fine acicular αʹ microstructure. Electron Backscattered Diffraction (EBSD) data analysis reveals coarse prior β grains in the surrounding microstructure. So, the circular honeycomb sample is superior to the hexagonal honeycomb sample concerning impact and energy absorption applications.

Dynamic Performance and Crashworthiness Assessment of Honeycomb Reinforced Tubular Pipe in the Jacket Platform under Ship Collision

The collision between the pipe legs of jacket platforms and bypassing ships is of great concern for the safety assessment of platforms. Honeycomb structures have been widely used owing to their unique deformation and mechanical properties under dynamic impact loads. In this paper, two typical honeycomb structures, namely hexagonal honeycomb and arrow honeycomb, were constructed for the impact protection of inclined pipe legs in jacket platforms, and the present study aimed to assess the dynamical performance and crushing resistance of the designed honeycomb reinforced structure under ship collision by using the numerical simulation software ANSYS/LS-DYNA. The dynamical performance of the honeycomb reinforced pipe leg was investigated considering various influential parameters, including the impact velocity and impact direction. The crashworthiness of the two types of honeycomb was evaluated and compared by different criteria, namely the maximum impact depth (δmax), specific energy absorption (SEA) and the proposed index offset sliding (OS). The results demonstrated that both the hexagonal honeycomb structure and the arrow honeycomb structure can reduce the damage of inclined pipe legs caused by ship collision, while the hexagonal honeycomb can provide the better anti-collision capacity, which can well reduce the offset sliding and better protect the pipe leg from ship collision.

Numerical modeling of flatwise energy absorption behavior of 3D woven honeycomb composites with different cell structures

Numerical simulation along with experimental validation are used to investigate the flatwise compression behavior in the out-of-plane direction of several 3D woven honeycomb composites with varied cell geometry such as hexagonal (HX), triangular, and rectangular structures. For all the structures, the perimeter of the unit cell was kept constant. Edgewise compression and three-point bending behavior were compared experimentally for all three configurations. The flatwise compression behavior of honeycomb structures has been predicted using FEM on the LS-DYNA platform, and the results have been validated using experimental data. The predicted values are found to be in good agreement with the experimental results. Hexagonal honeycomb shows better results as compared to other cell structures as revealed by both experimental and numerical analysis.