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[Display omitted] • S-shaped reinforced cores are designed by flattening hexagonal honeycomb cores. • S-shaped reinforced structures can effectively change the deformation mode of cores. • The peak load of S-shaped reinforced core can be 86.12% greater than plain core. • Theoretical prediction model of S-shaped reinforced honeycomb cores is proposed. • The design capabilities of cores are expanded because of S-shaped structure. Honeycomb structures serve as the core of sandwich structures in various industries, such as aerospace and rail transit. In this study, a novel design was introduced where hexagonal honeycomb cores were flattened in specific areas to form S-shaped reinforced cores. Compression tests were conducted on S-shaped reinforced honeycomb cores with different rotational structures – left-hand, right-hand, and mixed rotation. The deformation process of these cores was thoroughly investigated. Additionally, a theoretical prediction model was proposed to determine the Young's modulus and peak load of S-shaped reinforced honeycomb cores. The experimental data was compared with the theoretical model to validate its accuracy. Moreover, the study examined the effects of changing the relative density and cell wall angle of S-shaped reinforced honeycomb cores on the peak and specific peak loads. The results demonstrated that the use of S-shaped reinforced structures successfully altered the deformation mode of the honeycomb cores. In particular, the peak loads of S-LL and S-LR specimens were 29.14% and 86.12% higher than that of plain honeycomb, respectively. In summary, increasing the relative density of S-shaped reinforced honeycomb cores proved to enhance the peak load and specific peak load, thereby augmenting the design capabilities of these cores. [ABSTRACT FROM AUTHOR]

• The effects of GDGQD reinforcement on GFRP honeycomb sandwich shells are investigated. • The mechanical characteristics of the GDGQD-reinforced GFRP composites were evaluated using experimental tests. • The GDGQD-GFRP composite surfaces were observed using SEM analysis. • HSDT is employed to model the GDGQD-reinforced GFRP sandwich shells. • The influences of various parameters on the bending and dynamic behavior of the GFRP sandwich shells are studied. The present study employs a finite element (FE) formulation to examine the free vibration and bending analyses of sandwich shells made of a glass fiber reinforced polymer (GFRP) composite honeycomb core and graphene decorated with graphene quantum dots (GDGQD) reinforced by GFRP composite face layers. The mechanical characteristics of the GFRP composites with GDGQD reinforcement were evaluated using experimental tests. The FE formulation was developed to compute the vibration and bending responses of the sandwich shells via MATLAB software. The Lagrange method is used for dynamic analysis, whereas the principle of potential energy is used for static analysis. The FE model's validity is compared to numerical data reported in the literature in terms of frequencies and deflection, and the results demonstrate excellent agreement. The impacts of the end conditions, core-to-facesheet thickness ratio, curvature ratios, and weight percent of GDGQD are studied further in relation to the bending and dynamic properties of GFRP sandwich shells. [ABSTRACT FROM AUTHOR]

Continuous-carbon-fibre-reinforced (CCFR) honeycomb structures with self-sensing abilities were fabricated by three-dimensional (3D) printing. Pure polylactic acid (PLA) honeycombs of the same size were also fabricated for comparison. Low-velocity impact (LVI) tests and compression after impact (CAI) tests were conducted. Cone beam computed tomography (CBCT) and scanning electron microscope (SEM) were employed to investigate the corresponding damage mechanisms. The LVI test results showed that the presence of continuous carbon fibre effectively inhibited the generation and propagation of the damage in the matrix during impact, which allowed the CCFR honeycomb structure to have better low-velocity impact resistance, especially for repeated impacts with small energies. In contrast to the PLA honeycomb, the CAI test results showed that the CCFR honeycomb still retained good specific compression strength and specific energy absorption properties even after experiencing impacts. Furthermore, the continuous carbon fibre integrated into the CCFR honeycomb could be used as a sensor element to realize the in-situ structural health monitoring during impact and compression. The 3D-printed CCFR honeycomb structure, investigated in this research, demonstrates remarkable mechanical performance and self-sensing capabilities both during LVI and CAI tests, which highlights the vast potential of 3D-printed CCFR honeycomb for diverse applications. [Display omitted] • Continuous carbon fiber (CCF) inhibits the damage generation in the matrix. • 3D-printed CCFR honeycomb has better impact resistance compared to PLA honeycomb. • CCFR honeycomb after low-velocity impact still has high compression performance. • CCF can be a sensing element for structural health monitoring of CCFR honeycomb. [ABSTRACT FROM AUTHOR]

Aluminum honeycombs are widely applied in weight sensitive applications, increasing their specific strength and energy absorption capacity are rather important. Thin-walled metallic tube was used to enhance the mechanical properties of aluminum honeycomb and formed a novel tube-reinforced honeycomb structure. Its compressive and three-point bending performances were studied experimentally and numerically. Due to tube filling, the specific compressive strength, elastic modulus and energy absorption have been increased by 16%, 26% and 73%, and the specific bending load and stiffness increased by 42% and 62% respectively. The strengthen mechanism study indicated that the sum of tube and honeycomb caused the increase of compressive properties, and aluminum tube filling changed the stress distribution and expanded the stress concentration region which led to a transformation of bending failure mode. The present reinforcement method will make honeycomb more competitive in light-weight structure applications. [ABSTRACT FROM AUTHOR]

Abstract In this study, comprehensive investigations of an innovative composited cellular structure—Honeycomb cells filled with circular aluminum tubes (HFCT) are conducted by means of numerical simulation and theoretical analyses. A conventional honeycomb was modeled to calibrate the numerical model and a good agreement between numerical and experimental results was achieved. With the calibrated numerical model, extensive comparisons between mechanical performances considering the deformation modes, nominal stress and energy absorption property were carried out in terms of HFCT, conventional honeycomb, and multi-tubes. The interaction effects between internal filler and outside container of HFTC were discussed through the comparison considering representative volume elements (RVE) of three structures. In addition, obvious matching effects in terms of cell thickness were observed between the filler and container of HFCT. Afterward, a theoretical model based on the minimum energy principle which considering the basic fold element of HFCT was constructed to determine the key compression characteristics (half-wave length and nominal plateau stress). Agreement between them was found in plateau stress and geometrical description of post-deformation mode. [ABSTRACT FROM AUTHOR]

Abstract Recently, more and more attentions have been paid to structural defect suppression. In this study, branch point algorithm was first constructed for structural irregularity determination of honeycomb structure, so as to identify the geometric defect of similar cellular structures. Detailed principle and process were presented with key steps as image binarization, smoothing & noise suppression , skeletonization , vertex identification and cell reconstruction. A representative illustration was given. Afterwards, the routine difference has been discussed between the present method and classic Harris algorithm. Some examples in different cases were presented. As the findings turned out that, the branch point algorithm efficiently identifies the vertices of each cell with high precision, even in cases of poor images with low resolution. All these achievements pave a way for high standard honeycomb structure in consistency, reliability and homogeneity. [ABSTRACT FROM AUTHOR]

Graphene — the first discovered ideal two-dimensional material combines a wealth of exhibited novel physical phenomena with an overwhelming potential for practical applications. It is a one atom thick material where the carbon atoms sit on a honeycomb lattice. The honeycomb lattice is the cause for the many fascinating properties that graphene turns up with. Conventionally a material scientist would first like to know the symmetry that any newly discovered material possesses, as this can help determine the physical properties of the material. In this article, we discuss the space and point symmetry groups that the hallmark honeycomb structure of graphene possesses. [ABSTRACT FROM AUTHOR]

Abstract Damage severity of sandwich panels to underwater explosion load depend not only on the shock factors, but also on the fluid behind the structure. Underwater explosion tests were performed on water-backed sandwich panels to examine the deformation and failure of such composite structure. The dynamic blast response of water-backed sandwich panel was investigated using the LS-DYNA software. An analytical three-stage model was developed for the deformation history of water-backed sandwich panel subjected to shock loading in water. Blast resistance of water-backed sandwich panel was compared with monolithic plate of equivalent areal mass and air-backed sandwich panel with the same configurations. Water-backed sandwich panel exhibited the best deformation/damage resistant capability. Compared with air-backed sandwich panel, core material exhibited greater volumetric strain when the sandwich structure wetted on both sides. Overpressure in the water behind structure was reduced to about 7% by using sandwich structure over monolithic plate of equivalent thickness. Present study led to the apprehension of dynamic response of water-backed sandwich structure to underwater blast load, thereby developed useful guidelines for the design of blast-resistant structural systems. [ABSTRACT FROM AUTHOR]

Abstract In this study, sandwich panels with carbon/epoxy composite skins and an magnetorheological elastomer (MRE) honeycomb core in different proportions of magneto/elastomer (w/w%) are manufactured and studied numerically and experimentally. Test specimens in the beam form are subjected to free and forced vibrations and evaluated with and without the presence of an external (until 120 kA/m) magnetic field, positioned on the free end and on the center of the beam. The experimental results showed good performance in the attenuation of vibration level, especially on the fundamental vibration mode of the structures in question. The applied magnetic field on the free end of the test panel was capable of reducing until 37.45% their first natural frequency value. It can be noted from numerical and experimental results that sandwich panel with MRE honeycomb shifted the natural frequencies due to the increase of an induced magnetic field, especially for the first mode shape. [ABSTRACT FROM AUTHOR]

Abstract Predicting the honeycomb sandwich's response to impact loading is a major challenge in the aeronautical industry. Several papers demonstrated the possible use of non-linear springs to model Nomex's impact behavior. On the other hand, the authors show that the lack of transverse shear consideration constitutes a real limitation. The aim of this study is to overcome this limitation by introducing a compression/shear coupling to take into account the transverse shear. In this approach, the modelling of a low velocity impact test is performed on a sandwich composite with CFRP skins and Nomex® honeycomb. Composite skins are modeled as an elasto-plastic-damage material using a user field surbroutine (Abaqus©). The Nomex core is modeled with non-linear springs integrating a compression/shear coupling behavior. Then, the sandwich response under low speed impact is realized and compared with experimental data leading to a good correlation. [ABSTRACT FROM AUTHOR]

Abstract The paper investigated the dynamic impact response and characteristics of aluminum honeycomb filled with EPP foam (Expanded polypropylene) experimentally and numerically. It was found that the initial peak strength and mean strength of the filled honeycomb were improved significantly attributable to the interaction effect between the aluminum honeycomb and the foam, but the specific energy absorption (SEA) decreased. For the filled specimens with the same foam density, the initial peak strength, mean strength and SEA increased with the increase in impact velocity. Compared with the characteristics in the static compression test, the initial peak strength in the dynamic impact test increased, whereas the mean strength and SEA decreased. The study showed that EPP foam filling was effective to improve the impact characteristics of the bare aluminum honeycomb. Numerical simulation for the dynamic impact of filled honeycombs was also explored. It accurately reproduced the deformation process and addressed the interaction between the wall and EPP foam. By comparison of the properties in different filling types, it showed the single-cell filling was a good choice to improve the load resistance while using the least filling material. [ABSTRACT FROM AUTHOR]

This paper investigates the differences in structural response of lightweight internal structures using finite element (FE) simulation to provide quantitative comparison of the advantages of each type of structure. Various configurations, corresponding to different amounts of weight savings, were studied under distributed pressure loading and bending moment loading conditions. It was found that for configurations with less weight savings, the kagome possesses better performance than the honeycomb structure. However, as the amount of weight savings increases, the trend was observed to be reversed, with the honeycomb structure providing much better performance than the kagome structure. In general, it was shown that the honeycomb structure possesses better performance than the kagome structure under cantilever loading conditions. [ABSTRACT FROM AUTHOR]

Honeycomb sandwich structures have excellent energy absorption capabilities, combined with good mechanical properties and low density. These characteristics make them ideal for the transportation industry, which has a growing interest in reaching higher safety standards. The purpose of the present paper is the introduction of lightweight and more efficient crashworthy structures. Double-layer honeycomb sandwich structures were analysed and their energy absorption capabilities were evaluated by means of low-velocity impact tests. The specific energy absorption of double-layer panels was compared to single-layer honeycomb and other lightweight panels, in order to assess the effectiveness and the convenience of the introduced solution for lightweight and crashworthy devices. The impact absorption mechanism was evaluated through Computed Tomography images and visual inspection. A theoretical evaluation was applied to investigate the mono-layer impact response. The results were compared to those obtained with different boundary conditions and with a full-scale test. Contact parameters were influenced by boundary conditions since they depend on the specimens stiffness. Double-layer panels displayed a progressive collapse sequence, depending on the core arrangement and on the cell size. Honeycomb with larger cell size showed a better distribution of the impact loading which generated an almost uniform compression of the core. Such observations suggested the possibility to obtain energy absorber devices with a controlled deformation. Preliminary considerations on the existence of a size effect were drawn, since it was observed a relation among the contact parameters and the geometrical characteristics of the honeycomb and the indenter. [ABSTRACT FROM AUTHOR]

Nickel-based superalloy honeycomb core (NBSHC) is extensively used in aerospace field due to the light weight, high specific strength and high temperature resistance. The burrs of NBSHC are extremely prone to be formed during machining and the insufficient welding strength or false welding between NBSHC and skin is generated because of the large or unreasonable burr morphology, resulting in premature failure of the parts. In this work, a novel method of ice freezing combining with minimum quantity lubrication (MQL) was proposed to grind NBSHC to improve the burr morphology and size. The burr formation mechanisms of NBSHC under ice freezing and MQL conditions were revealed by single abrasive particle grinding cell wall and verified by grinding experiments. The grinding force, burr morphology transformation mechanisms and size were investigated in-detail by experiments combining with FEM results. The results indicated that MQL and ice freezing decreased the plastic flow property of material by reducing the temperature and friction of NBSHC, thereby promoting the transformation of burr size from large into micro, and the burr shape from long strip into block. Decreasing grinding depth can also improve the burr morphology by decreasing the volume of plastic flow material. The improving effects of full of ice freezing were better than MQL for NBSHC grinding. The machining efficiency under full of ice combining with MQL was 3 times of that under quasi-dry grinding. These findings are significant for improving the machining quality and exploring the burr morphology transformation of NBSHC. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A new auxetic honeycomb was designed by hybriding rhombic and star configurations. • A theoretical model was developed to predict the elastic modulus and Poisson's ratio. • The proposed honeycomb possesses higher auxetic effect and larger specific modulus than the star honeycomb. • The proposed honeycomb exhibits enhanced plateau stress and specific energy absorption compared with conventional auxetic honeycombs. Auxetic structures with negative Poisson's ratio exhibit excellent performance in cushioning, shear resistance and energy absorption, but their load-bearing capacity is usually poor. To address this drawback of the conventional Auxetic structure, a star-rhombic honeycomb (SRH) design is proposed in this paper to improve its load-bearing capacity. Analytical models of the elastic modulus and Poisson's ratio of this structure for different loading directions are developed. Quasi-static compression experiments were conducted on SRH specimens fabricated by selective laser melting (SLM) technique. Good agreement was achieved between the simulated and experimental stress response curves and deformation patterns. It was found that the SRH structure possessed better elastic modulus and energy absorption capacity than the SH structure without sacrificing the auxetic properties. The elastic modulus and Poisson's ratio of SRH under the x loading direction are more sensitive to the changes of structural parameters. An optimum energy absorption performance is achieved for an appropriate ratio of the inner rhombic strut thickness to outer reentrant strut thickness (k = 0.5). The specific energy absorption of SRH is improved by 136% and 75% compared to that of the conventional reentrant honeycomb (RH) and star honeycomb (SH), respectively. It has advantages for application scenarios with requirements for both auxetic and load bearing properties. [ABSTRACT FROM AUTHOR]

Aim of presented study was to compare plateau stress in honeycomb structures under out-of-plane load calculated using Wierzbicki formula with numerical simulations validated using experimental trials. ALUBOND® Alucore honeycomb structure was examined. The results of theoretical, experimental and numerical investigation are reported. Two methods of modeling core behavior were evaluated using simulations. Full core geometry and simplified Y-shaped element were analyzed. Both approaches were compared with experimental out-of-plane compression tests. Aim of the study was to determine the influence of core geometrical parameters on obtained plateau stress value. Various foil thicknesses and cell sizes were studied numerically. The results showed, that initial and final deformation mode strongly depends on the geometry of the honeycomb structure. Force required to crush the core grew with increase of wall thickness, and decreased with increase of cell size. Calculations were performed using an implicit integration scheme implemented in the LS-DYNA software. Research showed the presence of plateau relationship between stress and geometric dimensions and structure response. Good agreement between results obtained by all methods was achieved. Basing on the results, conclusions concerning modeling honeycomb materials were drawn. [ABSTRACT FROM AUTHOR]

Periodic honeycombs have been used for their high strength, low weight and multifunctionality. The quasi-static and dynamic compressive responses of three types of additively manufactured AlSi10Mg honeycomb structures, specifically a single-scale honeycomb and two hierarchical honeycombs with two and three levels of hierarchy, respectively, have been investigated using experimental measurement and finite element (FE) simulations. The validated FE simulation has been employed to investigate the effects of relative density of the honeycombs and the key experimental parameters. The following failure modes of the three types of honeycombs have been observed both under quasi-static and dynamic compression: (1) the single-scale honeycomb experienced a transition of failure mechanism from local plastic buckling of walls to local damage of the parent material without buckling with the increase of the relative density of the honeycomb; (2) the hierarchical honeycombs all failed with parent material damage without buckling at different relative densities. For both quasi-static and dynamic compression, the hierarchical honeycombs offer higher peak nominal wall stresses compared to the single-scale honeycomb at low relative density of ρ ¯ = 0.19 ; the difference is diminished as relative density increases, i.e. the three types of honeycombs can achieve similar peak wall stresses when ρ ¯ ⩾ 0.26 . Numerical results have suggested the hierarchical honeycombs can offer better energy absorption capacity than the single-scale honeycomb. The two-scale and three-scale hierarchical honeycombs achieved similar peak nominal wall stresses for both quasi-static and dynamic compression, which may suggest that the structural performance under out-of-plane compression is not sensitive to the hierarchical architecture. This work indicates that the structural advantage of hierarchical honeycombs can be utilised to develop high performance lightweight structural components. [ABSTRACT FROM AUTHOR]

An oxygen generator using Y-doped Bi2O3 as electrolyte to transport oxygen ions has been developed, having honeycomb-type structure with dimensions of 40 mm × 35 mm × 30 mm and consisting of 13 × 12 channels. External wire circuitry for the channels arrayed using parallel, series, and hybrid connection was evaluated to achieve the best oxygen separation efficiency. It was observed that the oxygen generator with hybrid connection facilitated evolution of oxygen at maximum of 117 sccm and high purity > 99.9% at 550°C under current flow of 14 A. Addition of 5 wt.% silane and 3 wt.% glass-ceramic powder to the Ag slurry used at both electrodes not only increased the coverage of the metal electrode on the ceramic substrate during dip coating but also prevented cracking at the electrode layer of the module under stress from the electric field and temperature during high-temperature operation, thus reducing the decay rate of the oxygen generator in durability testing. [ABSTRACT FROM AUTHOR]

This work is a contribution to the understanding of the nonlinear shear behaviour caused by cell postbuckling in Nomex honeycomb cores. First, an experimental benchmark study was made of different designs for the shear testing of honeycomb cores. Then, several test specimens were fabricated and tested, a 3D DIC system being used to measure and record the displacements. An Artificial Neural Network (ANN) was also used to identify the onset of bucking and collapse of the cells. The influence of the overall boundary conditions of shear tests on the buckling of the cells is presented both experimentally and numerically. The reversibility and test procedure results suggest that it may be possible to allow the shear strength to be increased by up to 35% under certain conditions. [ABSTRACT FROM AUTHOR]

The yield surfaces of several honeycombs with tunable Poisson's ratio, i. e. hexagonal honeycomb, augmented hexagonal honeycomb, re-entrant honeycomb, and augmented re-entrant honeycomb, are investigated by both theoretical analysis and numerical simulations. A theoretical model is developed to predict the mechanical response of these honeycombs considering the coupling effect of the shear stress and axial stress. Explicit expressions of the yield strength are derived for the four types of honeycombs. Good consistency is obtained between the analytical solutions and the numerical simulations. The results of the study provide a new idea for designing new honeycomb materials with tunable Poisson's ratio for engineering applications in the future. [ABSTRACT FROM AUTHOR]

Biological tissues like bone, wood, and sponge possess hierarchical cellular topologies, which are lightweight and feature an excellent energy absorption capability. Here we present a system of bio-inspired hierarchical honeycomb structures based on hexagonal, Kagome, and triangular tessellations. The hierarchical designs and a reference regular honeycomb configuration are subjected to simulated in-plane impact using the nonlinear finite element code LS-DYNA. The numerical simulation results show that the triangular hierarchical honeycomb provides the best performance compared to the other two hierarchical honeycombs, and features more than twice the energy absorbed by the regular honeycomb under similar loading conditions. We also propose a parametric study correlating the microstructure parameters (hierarchical length ratio r and the number of sub cells N ) to the energy absorption capacity of these hierarchical honeycombs. The triangular hierarchical honeycomb with N  = 2 and r  = 1/8 shows the highest energy absorption capacity among all the investigated cases, and this configuration could be employed as a benchmark for the design of future safety protective systems. [ABSTRACT FROM AUTHOR]

The thin-walled honeycomb structures are one of the most common energy absorber types. These structures are of particular use in different industries due to their high energy absorption capability. In this article, the finite element simulation of honeycomb energy absorbers was accomplished in order to analyze their crushing behavior. 48 panels with different hexagonal edge length, thickness and branch angle were examined. In the following, the amounts of mean stresses versus the geometric variables using neurotic lattices were considered. Comparison between the finite element results and the obtained neural network model verified the high accuracy of the obtained model. Then the model was optimized by one of the efficient genetic algorithm methods called "Multi-objective Uniform-diversity Genetic algorithm". The obtained optimum results provide practical information for the design and application of these energy absorbers regards to designer requirement. It was observed that honeycomb energy absorbers with 11.07 mm hexagonal edge length, 0.078 mm wall thickness and 123-degree branch angle have the maximum energy absorption over the panel mass. [ABSTRACT FROM AUTHOR]

Recently, cellular-filled structure has gained popularity due to its evident promotion in energy absorption capacity of absorber. In this study, a new pattern of composited filling structure— honeycomb cells filled with circular tubes (HFCT) has been put forward. Comprehensive experimental investigations have been conducted in terms of ten types of HFCT structures with hollow and different fillers including circular carbon fiber reinforced polymer (CFRP) tubes as well as circular Al tubes in different filling patterns. Detailed mechanical performances on energy absorption, deformation mode and interaction between inside circular CFRP filler and outside hexagonal honeycomb container were determined. The analyses show that, when undergoing axial loading, the HFCT structure not only maintains the same excellent mechanical properties with conventional hollow honeycomb core, but also gains evident promotion in energy absorption when filled in appropriate filling pattern. Obvious filling effect and matching effect were extensively discussed around the kind patterns of filling structures, which have significant influence on HFCT structure's performance. All the achievements prove that the HFCT structure can be considered as a perfect choice in aid to design of energy absorption device. [ABSTRACT FROM AUTHOR]

The effective in-plane elastic moduli of different types of honeycomb cores with thick walls are studied using analytical and numerical approaches. Analytical equations derived in this paper take a proposed jointed rectangle into consideration. The analytical results under plane stress and plane strain conditions are also obtained. The effective in-plane elastic moduli are studied as a function of their own relative densities because of the different methods of describing the geometrical shapes of honeycomb cores. The results are quantitatively compared with the available experimental results in this paper. It indicates that the present model can better predict the elastic properties in x -direction but are less suitable in y -direction. The proposed jointed rectangle has significant effect at high relative density. Moreover, the effective in-plane modulus increases with the relative height of honeycomb cores because of the Poisson effect of the material, and the results under plane stress and plane strain conditions are the lower and upper bounds, respectively. [ABSTRACT FROM AUTHOR]

The vibration characteristic of the sandwich plate with a honeycomb core was investigated by experimental measurements and numerical calculation based on radial basis function (RBF). RBF method was used not only in the meshless approach but also in the post-processing of the experimental data. During the experiment, amplitude-fluctuation electronic speckle pattern interferometry was applied to access the resonant frequencies and the corresponding vibration mode shapes simultaneously. Then RBF method was used to improve the quality of patterns and reconstruct the out-of-plane vibration amplitude after fringe analysis. As for numerical calculation, the modal parameters were numerically predicted using the first-order shear deformation theory. The computation approach was based on collocation with multi-quadric radial basis function. To understand the influence of the thickness of face sheet on dynamic behaviors, three types of specimens with different thickness were tested and analyzed. Of particular interest was that the vibration modes show veering due to the thickness increment. Furthermore, the numerical predicted results were compared with the experimental measurements for the first five modes. They are in good agreement with each other for resonant frequencies, mode shapes and relative out-of-plane amplitudes. [ABSTRACT FROM AUTHOR]

This paper presents a finite-element analysis of honeycomb and re-entrant honeycomb structures made of a two-phase composite material which is optimized with respect to selected parameters. It is shown that some distributions of each phase in the composite material result in the counter-intuitive mechanical behaviour of the structures. In particular, negative values of effective Poisson's ratio, i.e., effective auxeticity, can be obtained for a hexagonal honeycomb, whereas re-entrant geometry can be characterized by positive values. Topology optimization by means of the method of moving asymptotes (MMA) and solid isotropic material with penalization (SIMP) was used to determine the material's distributions. [ABSTRACT FROM AUTHOR]

This paper aimed to experimentally understand the effects of Expanded Polypropylene (EPP) foam filling on the mechanical properties of aluminum (Al) honeycomb panels. The process of lightweight EPP foam with different densities filling in Al honeycomb composites was first studied, then a series of axial (out-of-plane) and lateral (in-plane) compression tests were carried out on the bare and filled honeycombs. It is showed that the peak strength, mean crushing strength and total energy absorption (EA) in the axial tests increased with foam filler (increased by approximately 2.310–43.069%, 34.791–120.219% and 46.765–179.474% with respect to bare honeycomb, respectively); and the higher foam density, the greater filling effect, whereas the specific energy absorption (SEA) remained unchanged with increase in the foam density. Interestingly, more significant improvement in total energy absorption and SEA were found under lateral crushing. All the foam filled panels were of even greater energy absorption than the sum of bare honeycomb and EPP foam separately under both axial and lateral crushing. The foam filler had no significant effect on its deformation pattern under axial crushing, whereas it helped decrease local densification in honeycomb, leading the filled panels to deform in uniform rhombus shapes under lateral crushing. [ABSTRACT FROM AUTHOR]

Honeycomb structures are essentially constituted of a repetition of regularly-arranged and loaded sub-structures. The present study carries out a parametrically investigation of the behavior of a multi re-entrant honeycomb structure with variable stiffness and Poisson’s ratio effects. A refined analytical model is specifically developed and compared to full-scale numerical simulations. The analytical model developed is based on energy theorems and takes into full consideration bending, shearing and membrane effects. The influence of the cell walls thickness on the elastic homogenized constants is investigated. The results obtained show a good agreement between the refined analytical approach developed and the numerical computations carried out. [ABSTRACT FROM AUTHOR]

This paper deals with hypervelocity impacts of submillimer-sized debris on honeycomb sandwich panels. These debris, which are mostly present within the low Earth orbit, indeed represent a real threat for spacecrafts and satellites. In fact, for debris large enough to be tracked, pre-determined debris avoidance manoeuvre is usually conducted to prevent any damage. Submillimer-sized debris, however, are too small to be identified and therefore spatial structures must be protected against such threat. Honeycomb structural panels and whipple shields have been used as primary shielding against orbital debris impact. The protection capability is usually estimated using Ballistic Limit Equations (BLE). These data have been built from experimental tests on whipple shield protection and transposed to honeycomb sandwich panels. In the case of Whipple shield, the debris cloud generated at the impact on the bumper sheet expands until reaching the rear wall. BLE for Whipple shields only depends on materials properties, protection geometry, angle of incidence and impact velocity. For honeycomb sandwich panels, the debris cloud is partially channelled within honeycomb cells, thus limiting its radial expansion. The channelling effect is thus a function of the honeycomb cell geometry. The honeycomb BLE presented by the Centre d’Etudes de Gramat (CEG) in 2008 has been introduced in order to take into consideration such effect. The present study proposes to extend the results of the CEG. The main approach is to consider the relative dimensions between the projectile diameter and the honeycomb geometry in order to evaluate the perforation risks of submillimer-sized hypervelocity impacts. The impact process on honeycomb sandwich panel has first been modelled using commercial hydrocode LS-Dyna using hybrid Lagrange and Smooth Particle Hydrodynamics (SPH) solvers. The numerical model has been validated through several hypervelocity impacts experiments carried out at Thiot Ingenierie Shock Physics Laboratory at velocities up to 9.3 km/s. This model has then been used to define a ballistic curve which defines the critical projectile diameter of a specific sandwich panel subjected to submillimer-sized debris impact. The results are finally compared to the ones obtained by the CEG leading to an updated estimation of the protection capability of honeycomb sandwich panels. [ABSTRACT FROM AUTHOR]

This work describes the out-of-plane bending performance, shape memory effect and variable stiffness of a zero Poisson’s ratio honeycomb structure made from the tessellation of re-entrant hexagons and thin plates. The re-entrant hexagons are fabricated with ABS plastics and the thin plates are made from thermosetting styrene-based shape memory polymers (SMPs). The hexagons and the SMP plates are bonded within the groove joints in the thickness direction of the re-entrant cell units. The re-entrant hexagons generate out-of-plane flatwise compressive stiffness and in-plane compliance, while the SMPs thin plates support out-of-plane flexibility, the shape memory effect and a variable bending stiffness. Because the ABS plastics possesses a significantly higher glass transition temperature than the SMPs, the ZPR honeycomb structure features a higher out-of-plane flexibility when the environmental temperature rises from room temperature to the glass transition temperature of the SMPs. On the contrary, the flatwise compressive stiffness of the ZPR honeycomb remains unchanged. Three-point bending tests have also been performed to determine the out-of-plane bending performance of the ZPR structures at varying temperatures. [ABSTRACT FROM AUTHOR]

Numerical simulations of honeycomb behaviour under mixed shear-compression loading are performed to overcome a limitation of the experimental measurements and to investigate the normal and the shear honeycomb behaviours separately. A detailed FE model allowing to simulate the mixed shear-compression honeycomb behaviour is presented. A validation between numerical and experimental results in terms of crushing responses and collapse mechanisms allows to dissociate the normal and shear forces components. They are used to identify the parameters of a macroscopic yield criterion expressed as a function of the impact velocity, the loading angle and the in-plane orientation angle. A well known dynamic enhancement phenomenon is confirmed by this macroscopic yield criterion. However, as a new result, this dynamic enhancement is reversed when the loading angle reaches a critical value. An analysis of the collapse mechanisms is carried out under both quasi-static and dynamic loading conditions in order to explain this inversion. [ABSTRACT FROM AUTHOR]

Sandwich structure composite is one of the most potential and effective materials to comprehensively realize microwave absorption in wide frequency range and structural lightweight function. Here, honeycomb (HC) composites were fabricated by immersion method, consisting of a carbon nanotubes/carbon black/polyurethane (CNTs/CB/PU) absorbing layer and an aramid HC core. The using CNTs and CB were both modified by improved Hummers method with a heterogeneous structural surface to enhance the dielectric properties of the carbon materials. The sandwich honeycomb (SHC) absorber showed excellent broadband absorption performance with an effective absorption bandwidth (RL<−10 dB) of 15.5 GHz. Furthermore, the compressive stress of the absorber reached 3.69 MPa. With the integrated high microwave absorption and load-bearing performance, the as-prepared SHC absorber demonstrated promising future for applications in avionics. [Display omitted] • The SHC absorber exhibited excellent absorption and comprehensive properties. • Maxwell-Garnett formula was modified by a coefficient to fit honeycomb structure. • Multilayer impedance matching was realized using Jaumamn structure design method. • The EAB of 15.5 GHz was due to heterogenous CNTs/CB and impedance matching. [ABSTRACT FROM AUTHOR]

• A class of multistable shape-reconfigurable origami honeycombs are proposed. • The honeycomb has scalability in 3D space by tilling or tessellating. • The honeycomb is lightweight and owns flexible and easy designability. • A simplified rod-hinge model can easily predict the behavior of the bistable unit. Increasing energy and space utilization efficiency is crucial for lightweight shape-reconfigurable materials/structures that require tunable functions and multiple applications. Mechanical multistable origami/kirigami structures can improve the controlling stability and energy utilization efficiency of shape-reconfiguration. However, their scalability in 3-dimensinal (3D) space by tilling or tessellating remains largely unexplored. Inspired by origami, we propose a class of novel multistable shape-reconfigurable honeycombs that are lightweight, scalable in 3D space and have flexible and easy designability. It is architected by periodically arranged truncated diamond-shaped units composed of crease-connected panels. Each unit has two stable states, i.e., the deployed state and collapsed state, which can switch from each other reversely and repeatedly. Firstly, the bistability and mechanical tunability of the unit are verified by experiments. Then a simplified rod-hinge model for investigating the mechanical behavior of the unit is established and validated numerically. Based on this simplified rod-hinge model, the effects of edge number and geometric parameters of the unit on its mechanical behaviors are studied. This novel design and its mechanical model may pave a new way for the design and analysis of lightweight shape-reconfigurable materials/structures. [Display omitted] [ABSTRACT FROM AUTHOR]

This work describes the development, manufacturing and testing of a zero Poisson’s ratio PEEK cellular structure (AuxHex) made using Kirigami-inspired techniques. The AuxHex hybrid cell pattern is a combination of cells with different shapes that interlock with each other. This principle can lead to graded honeycombs possessing, in different areas, synclastic as well as anticlastic behavior. The AuxHex samples produced have been tested for flatwise compression according to ASTM standards and the results are compared with a unit-cell-based analytical model. Hexagonal-cell shaped honeycombs were also produced with the same technique and used for direct comparison. The mechanical flatwise properties have been benchmarked against the ones of other experimental PEEK-based cores and commercially available honeycombs. AuxHex samples are found to have higher stiffness compared to other experimental PEEK honeycombs, but lower compared with the commercially available honeycombs. The strength thought, while it is still higher compared to the other experimental PEEK cores, it is comparable with other honeycomb configurations. [ABSTRACT FROM AUTHOR]

Introducing gradient into cellular materials has been envisioned as an effective way to improve their performance. In this study, a novel in-plane graded honeycomb is proposed and its dynamic behavior under out-of-plane compression is investigated using numerical simulation and theoretical analysis. The in-plane gradient is introduced by changing the thickness of each cell wall of honeycomb unit cell along its side length. Numerical results show that the crushing strength and energy absorption capacity of honeycombs with positive gradient are substantially enhanced compared to those of honeycombs without gradient. To explore the enhancement, theoretical and numerical analyses on the energy absorption mechanism of honeycombs are performed. It is found that severe plastic deformation is mainly concentrated near the intersecting edge of cell walls, and the energy absorption can be further improved by distributing more material near the intersecting edge when the total mass remains constant. In addition, analytical formulas for the crushing strength and energy absorption of graded honeycombs are developed, and good agreement is obtained with numerical results. [ABSTRACT FROM AUTHOR]

Changes in air relative humidity and temperature exert a negative influence on hygroscopic wood based composites from which honeycomb sandwich panels are manufactured. Ready market globalisation causes that furniture from honeycomb sandwich panels manufactured in conditions of a dry climate are utilised in a tropical climate or are transported for several weeks through a tropical climate zone and then used in a dry climate. Water sorption and desorption processes by wood composites affect their loss of stiffness and strength. This study determined the impact of changes in ambient climatic conditions on the stiffness and strength of joints manufactured from honeycomb panels. A new method of numerical stiffness and strength modelling of joints subjected to changes in air relative humidity and temperature was developed. [ABSTRACT FROM AUTHOR]

An optimization based on sequential quadratic programming (SQP) algorithm to increase the thermal insulation and sound transmission loss of honeycomb panel in thermal environments is presented. First, heat transfer analysis is performed to reveal the steady-state thermal performance of hexagonal aluminum honeycomb sandwich panel, by using the semi-empirical Swann and Pittman formula. Next, the influences of temperature on acoustic performance of honeycomb panel based on statistical energy analysis method (SEA) is performed. Results show that increasing the thickness of the honeycomb core can improve the acoustic performance and heat insulation behavior. [ABSTRACT FROM AUTHOR]

One of the authors has investigated the stress concentration in honeycomb core subjected to an uniaxial loading due to defect, in which some vertical cell walls are missing consecutively along one row. The objective of this paper is to extend the previous study to the consideration of more general cases, in which the damaged cell walls may exist more than one row and the honeycomb may be subjected to not only the uniaxial loading but also a biaxial loading. Based on our numerical results, it is found that the previous technique by replacing the defect with a crack are not suitable for estimating the stress field. Instead, a new technique by replacing the defect with an elliptical hole is proposed, and approximation methods for evaluating the stress and moment concentrations in the front of the defect are developed. The validity of these values is checked by the results of FEM. [ABSTRACT FROM AUTHOR]

Nowadays, there has been an increasing interest in the study of cellular structures under non-ideal loading situation. In this study, comprehensive investigations of honeycomb structure embedded with the inclined cells were carried out to understand the mechanical behavior subjected to compression. Factorial analyses in several of inclined angles ranging from 0 to 90° were conducted both experimentally and numerically, from which excellent correlation has been observed. Three patterns of deformation modes of various inclined cell honeycomb structures with different tilt angle were categorized, some key spinodals of off-axis angle have been determined. In addition, theoretical relationship between inclined angle and strength of honeycomb has been successfully constructed, and validated with experiments as well as numerical simulation. Excellent agreement has been observed between them. According to this study, the mean plateau stress is not only related with the out-of-plane crush strength, but also related to in-plane crush strength. In general, it shows a cosine-like function with the tilt angle before 45°. These provide significant guidelines to characterize the mechanical properties of the honeycomb under non-ideal loading situation, so as to combine them in kinds of equivalent constitutive model in finite element simulation. [ABSTRACT FROM AUTHOR]

Flow around and/or through a honeycomb disk is a common problem encountered in aggregation, filtration and sedimentation processes. Mean flow, turbulent statistics and flow structures behind a solid and a honeycomb disk were experimentally studied by 2D PIV system. The results revealed that the mean flow structure behind a honeycomb disk was quite different from that of the solid disk wake. Due to the extra fluid through the small holes on the disk, the recirculation zone of honeycomb disk was much smaller both in length and in width. Meanwhile, the entrainment of the shear layer was significantly reduced and the length of the wake was increased. As the result, the honeycomb disk drastically decreased the velocity deficit, the rate of velocity recovery. The cross-stream distributions of Reynolds normal stresses exhibited symmetry while Reynolds shear stress showed asymmetry at x/d = 1, 3, 5, respectively. Using proper orthogonal decomposition (POD), it was found that, for both solid and honeycomb disk, the instantaneous wake configuration at reflectional-symmetry-breaking (RSB) mode with hairpin vortices periodically shedding could be detected by the first two POD modes. The POD mode 3 consisted of two pairs of contours, showed well plane-symmetric large-scale vortices shedding from the mixing layers region (y = ±0.5D). Due to different wake recovery rate and the interaction between the backflow and the shear layer, mode 4 structures in the both near wakes were obviously different. [ABSTRACT FROM AUTHOR]

Sandwich panels are used in many industries for the advantageous properties of high stiffness, good strength to weight ratio, and impact resistance. This paper investigates properties of thin-walled cores manufactured through Fused Deposition Modeling (FDM); a process which, through a wider design space, could improve the functionality of sandwich panels. The bond strength between the layers of thin walls manufactured through FDM was evaluated through tensile testing. To measure the effect of modified manufacturing speeds, wall thicknesses were varied through the flow rate and nozzle speed. Honeycomb cores using FDM were produced with different toolpaths, and compared with an example of an industry standard Nomex honeycomb core. During tensile testing, thick-walled FDM components exhibited a more ductile failure with a lower yield point when compared to thinner specimens. The ultimate tensile stress remained constant across samples within each of the tested ABS and PLA polymers used. Honeycomb cores produced using FDM were found to have a higher compressive failure force than Nomex honeycomb, and a lower specific strength. The force–displacement curves of compressive failure show a ductile response for thick specimens, consistent with the previous result. These results, combined with the increased flexibility of additive manufacture technologies, could provide a method of manufacturing high strength cores with complex geometry. [ABSTRACT FROM AUTHOR]

In the present work, a new design of honeycomb is proposed by embedding the rhombic configuration into the normal re-entrant hexagonal honeycomb (NRHH), in order to enhance the honeycomb’s in-plane mechanical properties. Both theoretical analysis and numerical simulations are employed to calculate the in-plane mechanical properties of the new honeycomb under uniaxial compression, including Young’s modulus, Poisson’s ratio and critical buckling strength. The results show that the new honeycomb can maintain auxetic performance, while both the in-plane Young’s modulus and the critical buckling strength are significantly improved compared to the NRHH. Comparisons between the present design and other exiting enhanced periodic topologies are also carried out. With respect to them, the present design features superior performances. For these outstanding properties, this layout may provide a new concept for the optimization and design of auxetic materials. [ABSTRACT FROM AUTHOR]

Nickel-cobalt layered double hydroxide (NiCo-LDH) is an attractive electrode material for supercapacitors (SCs) due to its high theoretical capacitance. However, the poor electrical conductivity greatly limits the charge transfer characteristic of NiCo-LDH, preventing its wide applications. Herein, the honeycomb NiCo-LDH nanosheet supported by carbonized polydopamine (PDA-C/NiCo-LDH) is constructed by polymerization, carbonization and electrodeposition. The active NiCo-LDH nanosheets are tightly embedded on the conductive framework of PDA-C, which can hinder the aggregation of NiCo-LDH nanosheets and accelerate the charge transfer and redox reactions. Benefiting from the honeycomb structure of NiCo-LDH and conductive framework of PDA-C, the optimal PDA-C/NiCo-LDH electrode exhibits a high capacitance of 2458.1 F g−1 at 1 A g−1, along with superior rate performance and cyclic stability. Furthermore, an asymmetric supercapacitor (ASC) is assembled with the PDA-C/NiCo-LDH as cathode and active carbon (AC) as anode. The ASC exhibits a high energy density of 62.7 Wh kg−1 at a power density of 714.3 W kg−1 and exceptional cyclic performance (92.5 % retention after 10,000 cycles), indicating a huge potential of the PDA-C/NiCo-LDH electrode in energy storage fields. • The carbonized polydopamine/honeycomb NiCo-LDH (PDA-C/NiCo-LDH) was constructed. • The charge transfer and redox reaction kinetics were greatly accelerated. • The PDA-C/NiCo-LDH exhibited excellent electrochemical performances. [ABSTRACT FROM AUTHOR]

Control on the mesoporous nanostructures with uniform-sized and well-arranged mesopores can provide enhanced surface areas and mechanical properties, which are preferred for the development of energies, sensors, and electro-optical devices. Herein, Pt-containing ordered honeycomb (Pt/OHC) nanocomposites with regularly arranged mesopores were synthesized via self-assembly of polystyrene- block -poly(4-vinylpyridine) (PS- b -P4VP) block copolymers (BCPs), following mechanism study of morphological evolution, concept of structural control, potential in catalyst application, and exploration of various metals. Particularly, it was found that the self-assembly of BCP directed the ordered arrangement of the mesopores, whereas the P4VP blocks incorporated Pt and precisely positioned it on the pore walls and on the outer surface of the honeycomb matrix. Mono- to multi-layered Pt/OHCs could be generated by controlling the thicknesses of the self-assembled pristine templates, and the average diameters of the mesopores could be varied from 12 nm to 40 nm by tuning the PS:P4VP block mass ratios. The obtained Pt/OHC demonstrated promising application as electrocatalysts in hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR), for which an overpotential of 39 mV at current density of 10 mA/cm2 (η 10) and a high half wave potential (E 1/2) of 0.87 V (vs. RHE), respectively, were observed in acidic media. In addition, the strategy developed here could be expanded for other metals, such as Au and Ir, to be incorporated into the ordered honeycomb matrix, providing a robust method to synthesize metal-containing mesoporous nanomaterials. With this work, we aim to offer an insight of designing ordered mesoporous nanocomposites, a concept of control over the mesoporous nanostructures, and a potential for their application in electrocatalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

Most of the existing redox flow batteries adopt 1-dimensionally stacked cells in which electrodes, flow frames, gaskets, and membranes are repeatedly stacked in one direction. However, these stacked cells suffer from system complexity, high cost, and insufficient cell performance. Herein, we suggest an attractive cell configuration with a 3-dimensional ceramic framework by adopting an industrially available cordierite honeycomb structure. We successfully demonstrate a zinc bromine battery (ZBB) with this 3-dimensional framework. Because the porous ceramic structure shows multi-functional characteristics as membranes and electrolyte channels as well as the cell housing, it does not require expensive membranes or flow frames, thus significantly reducing the stack manufacturing cost by about 64.5%. Furthermore, it shows superior behavior in terms of cell performance such as rate characteristics (>97% coulombic and >63% energy efficiencies at 60 mA/cm2), practical energy density (52 Wh/L), and cyclability over 500 cycles, compared to previous studies on ZBBs. By connecting more channels in serial or parallel mode, flexible scale-up is feasibly demonstrated without any performance degradation. [Display omitted] • A successful demonstration of zinc bromine battery in 3-dimensional ceramic framework. • Partition walls inside honeycomb-shaped ceramic framework can function as a membrane. • HC-ZBB can reduce the stack manufacturing cost by more than 60%. • It shows superior behavior in rate characteristics, energy density, and cyclability. • In serial or parallel mode, flexible scale-up of HC-ZBB is feasibly demonstrated. [ABSTRACT FROM AUTHOR]

• Blast experiments were conducted to study the close-in blast effect and failure characteristics of honeycomb HSPs. • The blast performance of auxetic HSPs is compared with regular hexagonal HSPs. • Simulation is in good agreement with experiments and can describe the deformation and fracture damage. • The effect of the core type and unit-cell angle on the damage of HSPs is investigated. 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. [ABSTRACT FROM AUTHOR]

This work describes the bending performance of a zero Poisson’s ratio (ZPR) cellular structure made from the tessellation of hexagons and thin plates. This particular ZPR configuration allows achieving large out-of-plane deformations and tailored in-plane and out-of-plane mechanical properties. We present a series of analytical models, finite element simulations and experimental tests to evaluate the bending capability of these cellular structures. A comparison of the out-of-plane bending behavior of six different types of cellular topologies with the same relative density of the ZPR honeycomb has also been carried out by using three-point bending tests. Further parametric analyses have also been performed to determine the dependence of the equivalent bending modulus versus the geometric parameters that define the ZPR honeycomb. The novel ZPR lattices show the highest bending compliance at large strains, and highly tailorable mechanical properties for the design of composite structures for airframe morphing applications. [ABSTRACT FROM AUTHOR]

This paper presents the study of influence of core geometry on vibration and acoustic response characteristics of sandwich panels which are used as aerospace structures. Sandwich panels considered in this research work are: (a) Honeycomb core, (b) Truss and Z core, (c) Foam core. The present study has found that (i) For a honeycomb core sandwich panel in due consideration to space constraint, the better acoustic comfort can be achieved by reducing the core height and increasing the face sheet thickness. (ii) It is demonstrated that, for a honeycomb core sandwich panel, vibration and acoustic response is not sensitive to the cell size. (iii) It is observed that, triangular core gives better acoustic comfort for the truss core sandwich panel compared to other type of core. (iv) For foam core sandwich panels, it is observed that sandwich panel with carbon-epoxy (high stiffness) face sheet radiates less sound in the lower frequency range (0–100 Hz). While the sandwich panel with Titanium (high density) face sheet radiates less sound at the higher frequencies. In order to reduce the preprocessing time and computational effort throughout the analysis in the present study, equivalent 2D elastic properties are calculated and used to find out the vibration and acoustic response characteristics. [ABSTRACT FROM AUTHOR]