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The excellent shape stability of thermally expanded metamaterials and the good bandgap properties of acoustic metamaterials have a wide range of promising applications in aerospace and sensors. Here, a bi-material-directional honeycomb metamaterial (BHM) with tunable coefficient of thermal expansion (CTE) and bandgap properties is proposed. The theoretical analysis and numerical simulations are employed to reveal the thermal deformation mechanism of the BHM. In addition, the analytical expression of the effective Young's modulus is established by considering both tensile and bending deformation. Based on the Bloch theorem, the band structures of the BHM are calculated by the finite element method. Parameter analysis confirms that the CTE and bandgap of the BHM can be simultaneously regulated and drastically adjusted by changing the geometric parameters and material combinations. Meanwhile, the coupling relationship of the effective CTE, Young's modulus, and total effective bandgap width are investigated. The results show that the BHM can have tunable CTE function and large total effective bandgap width by selecting suitable parameters while satisfying stiffness requirements. This study achieves a dual objective of specific CTE properties and bandgap design through rational material selection and shape design, which makes the metamaterials have better tunability and multifunctionality. [ABSTRACT FROM AUTHOR]

In the field of lightweight structures, foldcore sandwich structure is regarded as a promising replacement for conventional honeycomb sandwich structure. In this study, a new M-type glass fiber foldcore structure was fabricated by hot-pressing molding technology, and the effects of various factors on the low-velocity impact characteristics were investigated. In addition, a 3 D progressive damage numerical model matching the experimental results was established. The results showed that the impact energy exerted a certain influence on the response characteristics of the sandwich structure, but did not change the development trend of the load curve. The sandwich panel was able to achieve the overall load-carrying potential for the impactor whose size was longer than the foldcore span (25 mm). In addition, as the sharpness of the impactor increased, the damage range of the sandwich panel became concentrated and the load-bearing capacity gradually decreased. As revealed by the findings, the maximum load and specific energy absorption of laminated sandwich panels were improved by 150 and 40% respectively compared to single sandwich panel at base position. Therefore, it is beneficial to appropriately reduce the core span and increase the number of laminations to improve impact resistance of foldcore sandwich in practical applications. [ABSTRACT FROM AUTHOR]

A fatal weakness in flexible electrodes is mechanical fracture of conductive layer that occurs during repetitive stretching and bending deformation. Thereby, suppression of cracks development is crucially important for maintaining the properties of flexible electronics. Herein, topology optimization and structure design methods are utilized to greatly enhance mechanical properties of the existing island-bridge (I-B) structure. The flexible electrodes, with inner-concave honeycomb negative Poisson's ratio (I-CHNPR) structure and I-B structure, are designed and fabricated via screen-printed process, and conductivity is thoroughly investigated. The research demonstrates that the maximum stretching and bending stress of flexible electrodes with I-CHNPR structure-C are decreased by 30% and 28%, respectively, relative to the I-B structure. Fatigue life is enhanced by 18-fold. In addition, flexible electrode has advantages of better self-recovery and excellent conductivity. The flexible electrode proposed in this article is further applicated to realize the collection of ECG signals which has the advantages of wide application, reusable and high accuracy. The as-obtained flexible electrode with the above advantages is expected to greatly contribute to the emerging research field of flexible electronics. [ABSTRACT FROM AUTHOR]

Previous studies used to take the regular configuration as the element of the cellular structures, then carry out geometric optimization on the initial structures. Nowadays, more and more bionic metamaterial have been studied for their unique properties, such as bionic honeycomb tubular nested structure, bionic sinusoidal honeycomb, butterfly honeycomb, bamboo and beetle forewing thin-walled structures. Here, we report a novel gardenia-shaped honeycomb (GSH) by observing the gardenia from nature. Two valuable mechanical properties within GSH were explored in this study, which can simultaneously provide good deformability and zero Poisson's ratio effect. To understand the mechanical properties of GSH, we show by theoretical, numerical, and experimental methods where is a good agreement. The developed theoretical models for calculating the in-plane elastic modulus are based on Euler-Bernoulli beam theorem and energy principle. The numerical and experimental tensile process at coincident strain were captured to strongly show the deformability of GSH. The findings of this study provide essential guidance for the design of GSH structures with the desired mechanical properties. [ABSTRACT FROM AUTHOR]

In this study, a three-rib intersecting composite diamond honeycomb structure is fabricated by interlocking technology. The mechanical properties of the composite interlocked diamond honeycomb (CIDH) and corresponding sandwich structure (CIDHSS) are experimentally tested. The stiffness, strength, and failure characteristics of CIDH and CIDHSS are analyzed. The results show that CIDH has better mechanical properties than the interlocked Kagome and square honeycombs. The edge effect limits the edge compressive strength and stiffness of CIDH. Debonding is the main failure mode that limits both bending and compressive strength of CIDHSS. The reinforced plate added to the edge effectively improves the anti-debonding ability. [ABSTRACT FROM AUTHOR]

Honeycomb structures have attracted wide attention due to outstanding mechanical properties as promising light material structures. Inspired by nature and artistic design, various honeycombs with different microstructural configurations have been designed for the sake of better mechanical performances and functions. Here, the Miura-origami reentrant honeycomb (MRH) structure integrating reentrant honeycombs (RH) and Miura-origami structures is investigated systematically. Dynamic impact behaviors of the present MRH structure are investigated numerically. The deformation modes and energy absorption capacity of RH and MRH are compared under different impact velocities, including low-velocity, medium-velocity and high-velocity. The results show that the plateau stress and the specific energy absorption(SEA) of MRH is much higher than RH. Moreover, the parametric study indicates that raising the inclined angle will decrease the plateau stress and the absolute value of Poisson'ratio for MRH structures. The specific energy absorption curves increase as the inclined angle of MRH grows up. In addition, the MRH with smaller dihedral angle can absorb much more impact energy and the variation of absorbed energy is proportional to the cell wall thickness of the MRH structure. This work is expected to provide a new thought for designing advanced energy absorption metastructures and achieving superior mechanical performances. [ABSTRACT FROM AUTHOR]

As a promising energy absorbing structure, reentrant honeycomb (RH) structures have been focus of interest in recent years. By reasonably adjusting the geometric configuration of the honeycomb cell, advanced structures with unique mechanical properties and deformation behaviors can be designed flexibly and novely. In this work, inspired by the composite laminates, a novel laminated reentrant honeycomb (LRH) structure is developed by controlling the orientations of RH layers for achieving excellent energy absorption capacity. Mechanical and deformation characteristics of the proposed structures under static and dynamic loadings are investigated experimentally and numerically. By comparing with single-layer RH structure with the same thickness, the results demonstrate that LRH structures have better energy absorption capacity. The deformation modes of RH and LRH structures are also discussed and it is noted that the LRH structure with ±30° honeycomb sublayers shows zero Poisson's ratio effect. It is worth emphasizing that LRH with 0° and 90° sublayers presents similar negative Poisson's ratio effect with RH by analyzing the equivalent Poisson's ratio-strain curves. In addition, it is found that the latter structure has the best energy absorption capacity when the thickness of single-layer 0° RH structure equals to 5 mm. This work provides a new and reliable thought to design the advanced protective structures under compression and impact loadings. [ABSTRACT FROM AUTHOR]

Based on a novel multi-arc concave cell, four types of thickness gradient honeycomb structures with positive gradient, negative gradient, symmetric positive gradient, and symmetric negative gradient are constructed by changing cell wall thickness, and the relative density of the structure is deduced. The in-plane impact dynamics of gradient structure are revealed by numerical method. The deformation collapse mode, the dynamic response curve, the energy absorption effect, and the platform stress of different gradient arrangement and impact velocity are analyzed. It is found that gradient arrangement and impact velocity have significant effects on the impact properties of the thickness gradient honeycomb structures. When the impact velocity is low, the structure shows laminar shrinkage deformation, but this phenomenon will gradually disappear with the increase of impact velocity. The results show that the energy absorption capacity of the negative gradient structure is the best under different impact velocities. The platform stress is greatly affected by the impact velocity and less affected by the gradient arrangement. [ABSTRACT FROM AUTHOR]

As a kind of synthetic aromatic polyamide, aramid fiber has many outstanding properties, such as high strength, high modulus, etc. The composited paper reinforced by aramid fiber is widely used in honeycombs and its strength is of great concerns. In this paper, a three-dimensional progressive failure phase field model is employed to investigate the failure mechanism of aramid honeycomb paper under microscopic length scale. A mesh mapping technique is used to handle the complex geometry of the material, and an explicit solving scheme is used to improve the solving efficiency. The theory is implemented into ABAQUS through the users' subroutine VUEL. The interfacial debounding and matrix cracking in the short fiber reinforced composite are captured successfully, and the complicated failure mechanism is explored from the modeling results. The present phase field modeling technique has provided a useful numerical tool for the strength prediction of aramid short fiber reinforced composites. [ABSTRACT FROM AUTHOR]

Additive manufacturing technology offers a high degree of design freedom that promises a high structural lightweight potential where, among others, cellular mesostructures such as honeycomb or lattice structures find a growing resonance. In order to exploit the inherent lightweight potential to its greatest extent, a reliable and reproducible assessment of the mechanical properties of lattice structures for different loading scenarios is essential. The test specimens used for material characterization have to be designed so that the required mechanical properties are not falsified by the test specimen geometry or the experiment itself. The current state of the art and the corresponding norms, which are based on conventional solid material specimens, provide only vague design concepts toward appropriate lattice test specimens and are therefore not applicable. This contribution highlights the challenges met by the actual standards of the characterization of mechanical properties of lattice structures by proposing a normalized sample design for tensile specimens and a corresponding design methodology for cubic truss lattices structures. Specimen design measures based on numerically verified analytical formulations are proposed in order to systematically assess mechanical properties of lattice structures in a reliable and reproducible way and are thus recommended for future use in engineering practice. [ABSTRACT FROM AUTHOR]

This paper aims to introduce the hierarchy design into sandwich beams and bumper systems to improve their mechanical performance. Two kinds of reentrant hierarchical sandwich beams are proposed and their energy absorption characteristics have been systematically investigated. Based on its excellent energy absorption ability, the reentrant hierarchical honeycombs with equilateral triangle substructures (RHT) core are introduced to the design of the bumper system, and the hierarchical bumper system exhibits better mechanical properties than the traditional bumper and the aluminum foam-filled bumper under different loading conditions. Then, the multi-objective optimization model of the hierarchical bumper system is established by combining the optimal Latin hypercube design method (OLHD) and the response surface model (RSM). The non-dominated sorting genetic algorithm-II (NSGA-II) algorithm is adopted to optimize the design parameters. The optimization results show that the objectives are optimized efficiently, and it performs remarkable performances in bumper system design. [ABSTRACT FROM AUTHOR]

The advantage of mechanical metamaterials is that the properties can be improved at the macro level through reasonable artificial design at the micro level. Mechanical metamaterials are applied to solve the problems of vibration and noise in engineering applications. In this paper, a creative chiral star-shaped compositive mechanical metamaterial (CSCMM) is proposed by combining the chiral lattice structure and star-shaped honeycomb. The generation mechanism of the bandgap and the impaction of structural parameters are studied to obtain the low-frequency bandgap by single-phase materials. On this basis, the influence of star angle on bandgap generation and the variation of structure vibration mode during bandgap generation are studied. In addition, the phase and group velocities of elastic waves in chiral star-shaped compositive mechanical metamaterial are studied. Finally, the frequency response function (FRF) of the elastic wave propagating in the structure is calculated, and the result is consistent with the band diagram. Therefore, the design method of compositive mechanical metamaterial can effectively realize the improvement of property and reduce the attenuation of elastic waves, and it provides a new design idea for the vibration and noise reduction design of metamaterial. [ABSTRACT FROM AUTHOR]

This paper reports a new annular honeycomb that shows tunable Poisson's ratio. The presented honeycombs can provide both the in-plane negative Poisson's ratio (NPR) and in-plane zero Poisson's ratio (ZPR) while the shapes of the honeycomb core change. The developed honeycomb core is constructed by an annulus with four ligaments distributed bi-axial symmetrically, which shows great diversity of mechanical properties. The developed theoretical models of the in-plane elasticity are based on Castigliano's Second Theorem and energy principle. Two parameters were used to describe the deformation mechanisms of the unit cell concisely. The effect of two parameters on the Poisson's ratio and Young's modulus was investigated. The Young's modulus derived from the Finite Element (FE) analysis all have an good agreement with that derived from theoretical results, and the experiments were carried out to confirm the validity of them convincingly. [ABSTRACT FROM AUTHOR]

Acoustic metamaterials (AMMs), especially based on hierarchical honeycomb structure and topology-optimized design with suitable mechanical properties and low-frequency band gaps (BGs), have been studied recently. The present work reports a series of anisotropy hierarchical honeycomb structure lattices composed of the cell walls and vertices of regular hexagonal lattice replacement honeycombs of various sizes, as well as improved BG evaluation indicators. The band structures of three different types of unfilled hierarchical honeycomb lattices are calculated and the mechanism of BGs generation is analyzed. To obtain multi-broad BGs in the low-frequency range, the scatterers filling schemes are optimized by using a genetic algorithm (GA). Additionally, the effects of structural/material parameters on the BG characteristics of the optimized structures are discussed. Finally, the transmission loss (TL) experiment verified the optimization of the structures. This paper aims to promote the application of hierarchical honeycomb metamaterials with low-frequency vibration isolation in the industrial field. [ABSTRACT FROM AUTHOR]

Sandwich structure is one of the blasts protecting and energy absorbing materials with different types of light weight cores. This article aimed at investigating blast response of hexagonal honeycomb sandwich structure having perforations along the cell height of core over conventional honeycomb cores. The study discussed the mechanics of deformation behavior of perforated sandwich structure to improve the energy absorption characteristics of the bare honeycomb core sandwich structure. Detailed numerical analysis is conducted to accurately produce the deformation process with finite element analysis using explicit software LS-DYNA®. Blast load resulting from 1 kg TNT on the sandwich structure is applied using Conventional Weapons Effects Program (ConWep) function available in LS-DYNA. Several different parameters consisting of varying sizes of perforation by changing d/l ratio, shape, number of perforations and different facesheet and backsheet thicknesses, and different scaled distances are investigated in detail. The results indicated that both size and shape and number of perforations have significant influence on reduction of blast impulse. The variation of facesheet and backsheet thicknesses without changing the overall thickness of the structure also has evident effect in blast resistance capability of perforated honeycomb sandwich structure. The blast mitigation and energy absorption capacity of honeycomb core sandwich structure can be improved with the provision of perforations and optimizing the arrangement of holes. The perforated honeycomb core is further investigated based on analytical formulation developed using single degree of freedom (SDOF) system analysis approach. Optimization study is done further to get the best configuration based on different design variable limits. [ABSTRACT FROM AUTHOR]

Sandwich structure with honeycomb core and CFRP facesheets is increasingly used in the high-performance fields due to the high specific stiffness and strength. However, it is susceptible to localized low-velocity impacts such as tool drop during maintenance, and thus, understanding the damage behavior is important for a safety design and optimization. The objective of this article is to investigate the influence of the structural parameters and impact energy on the damage behaviors of the composite honeycomb sandwich panels subjected to localized low-velocity impact. An effective computational framework considering complicate damage mechanisms is proposed to predict the failure patterns, load history, and energy absorption. Comparisons with the experimental data show that the error of predictions is within 4% and thus the framework is validated. Then, a comprehensive parametric study is conducted to explore the effects of wall thickness and height of honeycomb, impact energy, and stacking sequences of the laminated facesheets on the impact resistance, damage behaviors, and energy absorption of the sandwich structure. The reported results may be useful in practice. [ABSTRACT FROM AUTHOR]

In this study, dynamically loaded sandwich panels with two different core materials and face sheets made of aluminum alloys (6061-T6) were investigated experimentally and numerically under low-velocity impact. Polypropylene, PP (C3H6)n honeycomb and extruded polystyrene foam, XPS (C8H8)n were preferred as core material. By using the contact force and kinetic energy changes, which were the impact test results of the sandwich panels, the contact and impact resistance was examined. As a result of the tests, damaged regions and permanent central displacement were determined and energy absorption capabilities were demonstrated for two different structures. The results obtained were compared with the results obtained by the open finite element method. In this study, it was shown that the face-sheet thickness of sandwich panels was an important parameter affecting the impact behavior. The behavior of the core material when the face-sheet loses its rigidity was investigated and it was found that polystyrene foam was more effective in preventing impact damage. However, it was found that using the PP honeycomb or XPS was affected the impact behavior in different points. [ABSTRACT FROM AUTHOR]

With the increase of demands for anti-collision performance in many fields, the negative Poisson's ratio structure has attracted the attention of researchers due to its light weight and high shear stiffness. Therefore, a new negative Poisson's ratio (NPR) structure named three-beam star honeycomb (TBSH) is proposed based on the classical star honeycomb (CSH). The stress equation of TBSH is derived by energy method, and its deformation characteristics and mechanical properties are studied. The results show that the structural deformation modes are different under different impact velocities, and TBSH has more obvious NPR effect. In addition, the influence of geometrical parameters on energy absorption of structures is also investigated. Finally, the thickness gradient is introduced into this structure, and the thickness gradient is optimized by multi-island genetic algorithm (MIGA). After optimization, the specific energy absorption (SEA) of the structure is significantly improved, while the initial peak stress (IPS) is decreased. The new structure proposed in this paper is expected to provide a novel design thinking and optimization idea for superstructure design. [ABSTRACT FROM AUTHOR]

In this paper, the energy absorption capacity of continuous fiber-reinforced thermoplastic auxetic structures is examined experimentally and the results compared with both numerical and analytical methods. To this extent, a 3 D printing technology of Fused Deposition Modeling (FDM) is implemented for fabricating the auxetic honeycombs and quasi-static compression test is conducted to extract the load-displacement behavior of the structure. Both hollow and foam filled lattice structures are tested, and the results revealed that the absorbed energy increased by 20% for PLA and 70% for PA specimens, when using foam. Finite element analysis is also performed using the explicit solver. The onset of failure is determined using the maximum stress criterion and VUSDFLD subroutine and the damage growth is modeled by decreasing the mechanical properties of the elements. The obtained results are in relatively good agreement with the experimental analysis. In addition, a theoretical formulation is developed and the probabilistic analysis is performed to draw the honeycomb failure design envelope, which is a practical tool for designing of various honeycomb configurations. The failure envelope shows that decreasing the strut angle increases the honeycomb failure load, however, the auxetic property of the structure decreases. [ABSTRACT FROM AUTHOR]

A two-scale computational continua (C2) model is proposed for the multiscale analysis of honeycomb sandwich plates. In this model, the macroscopic problem is simulated by the third-order shear deformation theory (TSDT), while a single computational unit cell (CUC) with facesheets and honeycomb core is regarded as the microscopic problem and it is discretized by the 3D solid elements, so the proposed model is called as two-scale C2-TSDT. In the numerical examples, the results of proposed C2 model are compared with these of the direct numerical simulation (DNS) model and the homogenization model, and a good agreement is achieved. [ABSTRACT FROM AUTHOR]

To improve the load carrying capacity, structural stiffness, and impact resistance of honeycomb sandwich structure, a novel tube-reinforced double-layer honeycomb sandwich structure was proposed by filling metallic tubes on the honeycomb holes. The low-velocity impact test was carried out on the tube-reinforced structure experimentally and numerically to evaluate its low-velocity impact response. It indicated that the stiffness, first linear stage slopes, and impact resistance of the honeycomb sandwich structure were increased by tube filling. Besides, the stress and deformation distribution of front and back panels were changed into more scattered and uniform, resulting in the reduction of maximum deflection. The maximum deflection of the front panel could be effectively reduced by filling the upper honeycomb core with aluminum tubes. Filling the lower honeycomb core with aluminum tubes could greatly reduce the maximum deflection of the middle and rear panels. The tube-reinforced honeycomb sandwich structure was a promising structure for weight sensitive applications owing to its improved load carrying capacity and impact resistance. [ABSTRACT FROM AUTHOR]

The special energy-absorbing structure of beak protects the head of woodpecker from being hurt when pecking tree. Inspired by the micro wavy structure of the woodpecker beak, a novel bionic sinusoidal honeycomb is proposed and its crashworthiness performance is analyzed. Results show that the bionic sinusoidal honeycomb produces more folds than the conventional honeycomb under the same mass conditions, which greatly improves the energy absorption effect. Compared with the conventional honeycomb, although the initial peak crushing force of bionic sinusoidal honeycomb is generally higher (the change ranges from −1.64% to 11.84%), the specific energy absorption of all bionic sinusoidal honeycombs is much better (the increase ranges from 30.12% to 80.99%). Moreover, the bionic sinusoidal honeycomb has a better crush force efficiency when the amplitude is small. A comprehensive comparison of the impact resistance of the bionic sinusoidal honeycomb and conventional honeycomb shows that the proposed bionic sinusoidal honeycomb has better energy absorption and application scalability than the conventional honeycomb. A novel bionic sinusoidal honeycomb (BSH) is proposed based on woodpecker beaks The impact resistance of BSH is systematically studied using finite element analysis. Its specific energy absorption (SEA) can increase by 80.99% compared to conventional honeycomb. The SEA of BSH increases as the wall thickness increases, but it is weakly related to the amplitude and the wavenumber. [ABSTRACT FROM AUTHOR]

In this paper, the honeycomb sandwich panel (HSP) reinforced with bi-layer Ceramic (B4C)/Aluminum (Al7075-T6) facesheets is proposed to be used as a shield for spacecraft against meteoroid orbital debris. A modeling strategy based on Lagrange Finite Element-Smoothed Particle Hydrodynamics (FEM-SPH) coupled method to predict the damage characteristics and the hole morphology is presented for the proposed shielding subjected to hypervelocity impact. The results show good agreement with the experimental data. Based on this investigation, significant improvement in resistance capacities is obtained using the bi-layer B4C/Al7075-T6 facesheets compared to monolayer concepts for HSP. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

It is of great essence to unveil relationship between structure, mechanical properties, and application of bionic design. Targeting at alleviating the debonding failure issue in the internal structures of the wind turbine blade, the reversed-semi-reentrant (RSRE) honeycomb and the angular gradient (AG) honeycomb with zero Poisson's ratio are considered in the design of the spar/shear web structure. Through finite element methods, the mechanical behaviors of these two types of honeycombs were compared to that of the hexagonal honeycomb. The ability of the RSRE honeycomb to reduce the shear stress on the skin–core interface is proved. The AG honeycomb also proves to have advantages in improving the shear stress distribution inside the honeycomb. Then, the RSRE honeycomb and the AG honeycomb are assembled together to build a complete model of spar/shear web structure. The results of simulations of the whole model under different loading conditions show that these two honeycombs have effectively promoted the mechanical behaviors of the whole model. [ABSTRACT FROM AUTHOR]

Quasi-static indentation tests were conducted to characterize the mechanical behavior of honeycombs. The local failure mechanisms of honeycombs with different relative density were discussed in detail. Results showed that the spread area of tearing deformations increases with increasing relative density and that difference in the neatness of tearing edges are obvious under different indenter shapes and sizes. The effects of indenter geometry on the plateau force and energy absorption of the honeycombs were analyzed. The tear energy of the specimens was determined, and an empirical formula was proposed to describe the relationship of energy absorption with indenter geometry. [ABSTRACT FROM AUTHOR]

An analytical method is proposed to determine the displacements of a composite cylindrical shell with auxetic honeycomb core layer and variable thickness under combined axial, internal, and external pressures. The thickness and pressure profiles can be arbitrary continuous functions. The displacements are defined in the framework of the first-order shear deformation theory. The composite shell consists of three layers, in which the inner and outer layers are isotropic and the core layer is made of an auxetic honeycomb material. The constitutive equations obey the Hooke law. The equilibrium equations which are a system of coupled differential equations with variable coefficients are extracted by employing the virtual work principle, and they are solved using the matched asymptotic expansion method of the perturbation technique. The effects of different parameters such as the geometry, honeycomb structure parameters, different load profiles, and the thicknesses on the results are studied. The results are compared with the finite element method and some other references. [ABSTRACT FROM AUTHOR]

Honeycomb structure containing curved reentrant sides with negative Poisson's ratio (NPR) was designed and the impact dynamics behaviors were studied by finite element method. The Poisson's ratio and the energy absorption capacity of the honeycomb structure with different arc angle were studied under different compression velocities. The results show that the Poisson's ratio of the honeycomb structure can reach −0.373 with arc angle of 180°. The energy absorption capacity of the honeycomb structure increased with an increasing compression velocity, and the deformation mode changed from X type to V type and I type. When the compression velocity is low, the dynamic response curve of the honeycomb structure with arc angle of 180° has the characteristics of two-stage plateau region. When the compression velocity is high, the energy absorption capacity of the honeycomb structure increased with an increasing arc angle. When the arc angle is higher than 120°, the honeycomb structure has NPR effect, and the energy absorption capacity of the honeycomb structure is better than the honeycomb structure with other arc angles. [ABSTRACT FROM AUTHOR]

An appropriate finite element model is developed to simulate the high velocity impact of projectiles on polyurethane foam filled aluminum honeycomb. First, the numerical model of the high velocity impact of the projectiles on the empty aluminum honeycomb is developed using a strain rate dependent material model. A VUMAT subroutine including two different fracture criteria proposed by researchers is developed. The fracture criterion that shows similar behavior to experimental observations, is selected. The numerical model of the projectiles impact on the foam-filled honeycomb is compared with available experimental results, and the ballistic limit velocities are predicted with good accuracy. [ABSTRACT FROM AUTHOR]

In this study, impact behavior and deformation mechanism of triply periodic minimal surface (TPMS) sheet (Schwarz' P, Schoen's I-WP, and Neovius) were numerically investigated. The convergence study of mesh size, sensitivity of cell number, and parametric investigation of shell thickness were performed. Three different collapse modes " ⋁ + ⋀ = X , " " / + \ = X , " and "Whole-X" were experienced corresponding to Schwarz' P, Schoen's I-WP, and Neovius sheets, respectively. Comparison between the anisotropic 2D circular honeycomb and isotropic 3D TPMS were conducted. The results show that TPMS sheets perform excellent mechanical properties due to their isotropic smooth surface transitions and open-cell connectivity. Cell number sensitivity of TPMS structures is investigated and Mesh size convergence study of TPMS structure is performed. Systematic regular TPMS patterns are obtained and collapse mechanisms related to deformation mode are revealed. Comparison between TPMS structure and the representative 2D cellular circular honeycomb structure is conducted, better performance in withstanding uniaxial compression is confirmed. [ABSTRACT FROM AUTHOR]

The current impact attenuator used by the Formula Student team of University of Lisbon is an out-of-shelf solution consisting in an aluminum honeycomb. The competition regulations defined for the impact attenuator's design allow room for innovation, which can be used to build more efficient structures and explore new materials. The main objective of this work is to design and optimize a composite impact attenuator lighter than the solution currently used by the team. Experimental results and numerical models presented in previous works are considered in the development of a new approach. Several design parameters are studied and their influence on the behavior of the impact attenuators are taken into account. Direct Multisearch (DMS) algorithm directly coupled to Abaqus software is used to perform the optimizations. The lighter solutions' mass is compared to the baseline aluminum structure's and detailed descriptions are presented for chosen optimal designs, which constitute an improvement regarding the baseline's mass. [ABSTRACT FROM AUTHOR]

To provide sufficient data and theoretical support for the practical application of Nomex honeycomb sandwich panels, the bending behavior and energy absorption characteristics of the Nomex honeycomb sandwich panels have been analyzed. Based on experiment, theory, and simulation, the relationship between bending performance and specification parameters was clarified, and the failure map of the Nomex honeycomb sandwich panels was plotted, which can provide strong data and theoretical support for the performance prediction and parameter selection of Nomex honeycomb sandwich panels. [ABSTRACT FROM AUTHOR]

Enlightened by face-centered cubic crystal structure, an ultra-lightweight composite sandwich panel with face-centered cubic core (CSPFCC) is proposed, which demonstrates excellent broadband sound insulation as well as great mechanical property. Sound insulation of the new structure was studied experimentally and numerically. Simulation models are established with considerations of acoustic–structure interactions. The experimental results are consistent with the simulation results of CSPFCC. Furthermore, the effects of boundary conditions, material parameters and so forth on the acoustic properties of CSPFCC are studied by numerical model. In addition, the CSPFCC is compared with the composite quadrilateral honeycomb sandwich structure, and its property is better than that of the latter. Sound insulation property of the CSPFCC exhibits good quasi-isotropy, which provides guidance for the research of structural-functional integration design and engineering application. [ABSTRACT FROM AUTHOR]

The present study develops a new type of epoxy resin–aluminum honeycomb composite sandwich panel. Failure modes and typical force–displacement curves are measured through quasi-static localized indentation tests. The effects of different parameters on the elastic ultimate load and energy absorption are analyzed. The results indicate that the newly developed composite sandwich panel has good integrality, stability, and energy absorption capacity. The typical force–displacement curve exhibits three types and all of them consist of six phases, namely: elastic phase, local damage phase, strengthening phase, global damage phase, compaction phase, and bottom destruction phase. The strength and the energy absorption capacity of the composite sandwich panel are affected by composite layer thickness, additional layer thickness, boundary condition, and indenter type. Compared to those of traditional sandwich panel, the mechanical properties of the integrated composite sandwich panel are significantly improved, as the specimen maintains good stability under indentation without undergoing detachment or cracking between the composite layer and the core. [ABSTRACT FROM AUTHOR]

The present work investigates the mechanical properties of honeycombs made up of cell walls with different tension and compression modulus. In particular, the stiffness under both compressive and tensile loads is determined as a function of the ratio of compression and tension modulus of constituting cell walls. Furthermore, the onset of failure in bi-modulus hexagonal/diamond lattices is studied. It is found that the overall stiffness significantly reduces with decreasing the ratio of compression and tension modulus of cell walls. Numerical relations for the dependence of the stiffness of bi-modulus honeycombs on their relative density are given. [ABSTRACT FROM AUTHOR]

In this article, the quasistatic penetration tests were investigated on unfilled and polyurethane foam filled honeycomb sandwich panels. Failure mechanisms, specific energy absorption, interaction mechanisms, and some structural responses were studied. Comparing the three types of the foam filled sandwich panels with unfilled type, indicates that the absorbed energy of the first, second, and third type of the panels are 23%, 33%, and 58% more than unfilled ones, respectively. In addition, the results showed the enhancement in the dynamic strength and remarkably decrease in the damage area of the sandwich structure when its honeycomb core was filled with polymer foam. [ABSTRACT FROM AUTHOR]

In this study, mechanical performance of octagonal structure subjected to out-of-plane compression was investigated theoretically and numerically. Theoretical derivation was carried out according to super folding element, formulas were constructed in terms of relative density, half-wave length, average force, mean stress as well as specific energy absorption (SEA). To validate, full scale numerical finite element (FE) models were created to analyze the mechanical behavior of the present structure computationally. Analytical solutions were in good agreement with computational results. Parametric study shows that different geometric configurations heavily influence the mechanical performances. Detailed comparisons between octagonal and conventional hexagonal honeycomb were performed. [ABSTRACT FROM AUTHOR]

This study presents numerical and theoretical investigation for the vertex-based hierarchical honeycomb structure subjected to axial compression. Mechanical behavior as well as predictable formulas were explored based on folded element and Minimal Energy Principle. Parametric studies were numerically conducted with different scale ratio, and the influence of wall thickness on mechanical performance was determined. Good agreement was observed between the numerical results and theoretical solutions, which validates the analytical model well. Furthermore, deformation mode comparisons were conducted between vertex-based hierarchical honeycomb and other filled-type honeycomb structures. Evident promotion on energy absorption was obtained for vertex-based hierarchical honeycomb. [ABSTRACT FROM AUTHOR]

Miura-ori core sandwich structures have aroused considerable research interests as a potential alternative to conventional honeycomb sandwich structures due to various superiorities, e.g., open channels and continuous manufacturing process. Although quasi-static or impact mechanical behaviors have been extensively studied, modal response of Miura-ori core sandwich structures has not been investigated yet. In this paper, carbon-fiber-reinforced Miura-ori core sandwich panels (MSPs) were fabricated with an autoclave processing method. Modal tests were carried out to investigate the structural vibration performances. A finite element analysis of MSPs was developed and validated with the tests results. Fiber orientation influences of both face sheets and core on the natural frequencies were investigated. Furthermore, a parametric study on the modal response of various MSPs models subjected to virtual free vibration was performed, through which the relationships between the fundamental frequencies and the geometric parameters were established. Compared with corrugated core sandwich panel under identical dimension and weight, MSP always possesses higher fundamental frequency, with an increase of 11.7% in the optimum case. It indicates that MSP is much stiffer and could be designed even lighter in aerospace applications. [ABSTRACT FROM AUTHOR]

In this work, a modelling strategy based on damage mechanics is presented for Nomex honeycomb core. The proposed approach is based on the experimental analysis presented by the authors in [1] and consists of the decoupled modelling of the buckling and collapse of cells for the HRH-78 Nomex honeycomb core with two damage parameters. The proposed approach shows good agreement with the experimental tests. The computational cost is low, proving the efficacy of this technique. This strategy may avoid using full 3D models that mimic the real shape and is a step toward a full compression/shear nonlinear model for honeycomb core. [ABSTRACT FROM AUTHOR]

Frequencies and energies of vibrations for a honeycomb sandwich plate with negative Possion's ratio are investigated. Based on Reddy's third-order shear deformation plate theory, von Karman type nonlinear theory and Hamilton theory, the equations of motion for the plate are obtained, free vibrations and vibrations with the damping and in-plane force of the plate are considered, respectively. The changes of real parts of the eigenvalues with the damping and in-plane forces of the plate are obtained. In order to obtain the analytic solutions of the frequencies and energies of the plate, lateral free vibrations are considered by using the Hamilton energy method, and we compare the results with that of the previous free vibrations. The potential energies and the total energies variation with parameters of the plate are given. The research results from the two methods show that the change trends of the frequencies and energy of the plate are exactly consistent, but the values of natural frequencies and potential energies are lager in lateral vibrations. [ABSTRACT FROM AUTHOR]

The truss and honeycomb sandwich plates with transverse crack and delamination in the facesheets are studied, and an Extended Layerwise/Solid-Element (XLW/SE) method is developed. The governing equations of laminated composite facesheets and cores (truss or honeycomb) are established based on the Extended Layerwise Method (XLWM) and 3D solid elements, respectively. The XLW/SE method can obtain the local stress and displacement fields accurately, considering complicated cores without any assumptions. In the numerical examples, the results obtained by the proposed method are compared with those obtained by the 3D elasticity models, and the good agreements are achieved. [ABSTRACT FROM AUTHOR]

The dynamic response of honeycomb sandwich panels under aluminum foam projectile impact was investigated. The different configurations of panels were tested, and deformation/failure modes were obtained. Corresponding numerical simulations were also presented to investigate the energy absorption and deformation mechanism of sandwich panels. Results showed that the deformation/failure modes of sandwich panels were sensitive to the impact velocity and density of aluminum foam. When the panel was impacted by the aluminum foam projectile with the back mass of nylon, the “accelerating impact” stage can be produced and may lead to further compression and damage of the sandwich structures. [ABSTRACT FROM AUTHOR]

Understanding the dynamic behavior of cellular foam is essential for designing anti-collision structures. In this work, the rate-sensitivity of cellular foam was analyzed on dynamic experiments of split Hopkinson pressure bar and finite element methods (FEM). A typical circular ring structure is introduced in the FEM analyses to estimate the effects of the post-buckling behavior of cell walls on the properties of stress enhancing as the strain rate increases. The quadrilateral/circular honeycomb foam structure is used to estimate the contribution of micro-structure and matrix effects. These results show that the post-buckling of a micro-structure is an important rate-sensitivity factor. [ABSTRACT FROM AUTHOR]

Honeycomb has turned out to be an outstanding buffered material. In regards to energy absorber design, how to accurately evaluate the energy-absorbing capacity of any piece of honeycomb core block becomes an urgent issue. This article presents a direct assessment methodology for axial compressed hexagonal honeycomb. Series theoretical formulas for TEA (total energy absorption) and SEA (specific energy absorption) against geometrical configuration and loading situation were constructed based on folded elements. Afterwards, corresponding experiments and numerical simulations were performed. Excellent correlation has been observed between them. This methodology provides an efficient way to aid in a honeycomb's design and selection. [ABSTRACT FROM AUTHOR]

A numerical model based on one-dimensional cell wall behavior is used to study the influence of changes in the cell wall properties on the global stiffness parameters of two-dimensional open-celled honeycombs. Following validation of results for intact microstructures, cases are considered, including regular and irregular cellular structures, structures with missing/broken cell walls, and structures with cell walls of non-uniform thickness. The influence of each of these flaws or changes in microstructure is quantified, with broken cell walls dominating changes in bulk behavior and varying cell wall thickness resulting in changes to bulk properties that can be considered negligible. [ABSTRACT FROM AUTHOR]

This paper studies the performance of novel honeycomb materials with the cell walls made of natural fiber reinforced thermoplastics. It focuses on developing a methodology for the maximization of the specific transverse shear strength of reinforced honeycombs and prediction of the corresponding cell geometry. The load carrying capacity of wood fiber reinforced polypropylene honeycomb shows a substantial improvement as compared to that of a polypropylene honeycomb of the same density. Theoretical predictions agree well with the experimental results. Excellent performance of the reinforced polypropylene honeycombs indicates a promising future for such materials. [ABSTRACT FROM AUTHOR]

Thermal deformation analysis was performed on a carbon fiber reinforced plastic (CFRP) mirror with sandwich structure. To obtain unexpected asymmetry of the surface sheet, we investigated the deformation of a quasi-isotropic laminate under hot and humid conditions. Despite the symmetric lay-up, quasi-isotropic laminate deforms into twisted saddle shape with time, and this deformation could be simulated by assuming ply angle misalignment. Then, the elastic moduli of honeycomb cores were calculated theoretically. A honeycomb sandwich mirror model was constructed by adopting a sheet model and using honeycomb elements. The thermal deformation analysis was performed considering the ply angle misalignment. The test results clarified that the deformation of the surface sheet was a critical factor in the dimensional stability of the CFRP mirror. [ABSTRACT FROM AUTHOR]

A micromechanics model is developed for hexagonal honeycomb structures by using a modified couple stress theory. The formulation is based on structural analysis of repeating units and a homogenization procedure. Both bending and axial deformations of cell walls are considered here, unlike earlier models. The closed-form expressions for five effective in-plane elastic constants (including two Young's moduli, one shear modulus and two Poisson's ratios) of a honeycomb structure are derived in terms of the Young's modulus of the cell wall material and the slenderness (length-to-thickness) ratio of the cell wall. The formulas for two length scale parameters are obtained in terms of the slenderness ratio and thickness of the cell wall, thereby providing a direct measure of the microstructure of the honeycomb. The constitutive relations for the two-dimensional couple stress continuum equivalently representing the discrete honeycomb structure are provided using the five effective elastic constants and two length scale parameters. The numerical results reveal that for honeycombs with small slenderness ratios the effective Young's moduli and shear modulus are strongly dependent on the slenderness ratio. For low-density honeycombs with large slenderness ratios, the effective elastic constants predicted by the current model agree well with those by an existing model that considers only bending deformations. [ABSTRACT FROM AUTHOR]

The purpose of this study is to develop tools dedicated to the design of sandwich panels involving Nomex® honeycomb cores. Special attention is paid to the ability to perform full three dimensional calculations up to failure of such structures. In the first part, the determination of effective elastic properties of Nomex® honeycomb cores is carried out thanks to strain based periodic homogenization technique. Using an equivalence in energy between a real honeycomb and a fictitious continuous medium, it becomes possible to evaluate the elastic behavior of Nomex® cores, starting from the knowledge of the behavior of the constitutive paper. Next, relying on experimental observations, the strengths of Nomex® honeycomb cores are evaluated with a linear Euler's buckling analysis. Results are compared with data coming from manufacturers, and give satisfaction. In order to carry out these two first studies, the NidaCore software has been developed using the finite element code Cast3M from CEA. The last part deals with the modeling of the nonlinear compressive response of Nomex® cores. A model based on the thermodynamics of irreversible process is proposed and the identification technique detailed. Good agreement between experimental data and computed values is obtained. [ABSTRACT FROM AUTHOR]