In-plane crushing behavior and energy absorption design of composite honeycombs

Theoretical analysis and numerical simulation methods were used to study the in-plane crushing behavior of single-cell structures and regular and composite honeycombs.Square,hexagonal,and circular honeycombs were selected as honeycomb layers to establish composite honeycomb models in the form of composite structures and realize the complementary advantages of honeycombs with type Ⅰ and type Ⅱ structures.The effects of honeycomb layer arrangement,plastic collapse strength,relative density,and crushing velocity on the deformation mode,plateau stress,load uniformity,and energy absorption performance of the composite honeycombs were mainly considered.A semi-empirical formula for plateau stress and energy absorption rate per unit mass for the composite honeycombs was developed.The results showed that the arrangement mode of honeycomb layers is an important factor that affects their mechanical properties.Appropriately selecting the arrangement of honeycomb layers and the proportion of honeycomb layers with different structures in a composite honeycomb can effectively improve its load uniformity and control the magnitude of plateau stress and energy absorption capacity.

OUT-OF-PLANE COMPRESSIVE PROPERTIES OF HEXAGONAL PAPER HONEYCOMBS

The compressive behaviour of paper honeycombs is studied by means of an experimental analysis. Experiment results show how geometry aspects of hexagonal paper honeycombs, e.g. the height of paper honeycomb, the thickness and length of honeycomb cell-wall, the drawing ratio of hexagonal honeycomb, affect the compressive properties of the paper honeycombs. It is in good agreement with the theory model. The constraint factor K of the critical buckling stress is mainly determined by the length of honeycomb cell-wail. It can be described as K=1.54 for B type paper honeycombs and K=3.32 for D type paper honeycombs. The plateau stress is the power exponent function of the thickness to length ratio of honeycomb cell-wall, and the experiment results show that the constant is 13.2 and the power exponent is 1.77. The research results can be used to characterize and improve efficiently the compressive properties of paper honeycombs.

Dynamic crushing behaviors and enhanced energy absorption of bio-inspired hierarchical honeycombs with different topologies

In order to pursue good crushing load uniformity and enchance energy absorption efficiency of conventional honeycombs, a kind of bio-inspired hierarchical honeycomb model is proposed by mimicking the arched crab shell structures. Three bio-inspired hierarchical honeycombs(BHHs) with different topologies are designed by replacing each vertex of square honeycombs with smaller arc-shaped structures. The effects of hierarchical topologies and multi-material layout on in-plane dynamic crushings and absorbed-energy capacities of the BHHs are explored based on the explicit finite element(FE) analysis.Different deformation modes can be observed from the BHHs, which mainly depend upon hierarchical topologies and impact velocities. According to energy efficiency method and one-dimensional(1D) shock theory, calculation formulas of densification strains and plateau stresses for the BHHs are derived to characterize the dynamic bearing capacity, which is consistent well with FE results. Compared with conventional honeycombs, the crushing load efficiency and energy absorption capacity of the BHHs can be improved by changing the proper hierarchical topology and multi-material layout. These researches will provide theoretical guidance for innovative design and dynamic response performance controllability of honeycombs.

Elastic properties of chiral,anti-chiral,and hierarchical honeycombs:A simple energy-based approach

The effects of two geometric refinement strategies widespread in natural structures, chirality and self-similar hierarchy, on the in-plane elastic response of two-dimensional honeycombs were studied systematically. Simple closed-form expressions were derived for the elastic moduli of several chiral, anti- chiral, and hierarchical honeycombs with hexagon and square based networks. Finite element analysis was employed to validate the analytical estimates of the elastic moduli. The results were also compared with the numerical and experimental data available in the literature. We found that introducing a hier- archical refinement increases the Young＇s modulus of hexagon based honeycombs while decreases their shear modulus. For square based honeycombs, hierarchy increases the shear modulus while decreasing their Young＇s modulus. Introducing chirality was shown to always decrease the Young＇s modulus and Poisson＇s ratio of the structure. However, chirality remains the only route to auxeticity. In particular, we found that anti-tetra-chiral structures were capable of simultaneously exhibiting anisotropy, auxeticity, and remarkably low shear modulus as the magnitude of the chirality of the unit cell increases.

Experimental investigation of chimney-enhanced natural convection in hexagonal honeycombs

The natural convective heat transfer performance of an aluminum hexagonal honeycomb acting as a novel heat sink for LED cooling is experi- mentally investigated. The concept of adding an adiabatic square chimney ex- tension for heat transfer enhancement is proposed, and the effects of chimney shape, height, and diameter are quantified. The average Nuav of a heated hon- eycomb with straight chimney is significantly higher than that without chimney, and the enhancement increases with increasing chimney height. At a given chim- ney height, honeycombs with divergent chimneys perform better than those with convergent ones. For a fixed divergent angle, the Nuav number increases mono- tonically with increasing chimney height. In contrast, with the convergent angle fixed, there exists an optimal chimney height to achieve maximum heat transfer.

Dual-level stress plateaus in honeycombs subjected to impact loading:perspectives from bucklewaves, buckling and cell-wall progressive folding

Dual-level stress plateaus (i.e., relatively short peak stress plateaus, followed by prolonged crushing stress plateaus) in metallic hexagonal honeycombs subjected to out-of-plane impact loading are characterized using a combined numerical and analytical study, with the influence of the strain-rate sensitivity of the honeycomb pare nt material accounted for. The predicti ons are validated against existing experimental measurements, and good agreement is achieved. It is demonstrated that honeycombs exhibit dual-level stress plateaus when bucklewaves are initiated and propagate in cell walls, followed by buckling and progressive folding of the cell walls. The abrupt stress drop from peak to crushing plateau in the compressive stress versus strain curve can be explained in a way similar to the quasi-static buckling of a clamped plate. The duration of the peak stress plateau is more evident for strain-rate insensitive honeycombs.

Finite Element Analysis for In-Plane Crushing Behaviour of Aluminium Honeycombs

A number of finite element simulations were performed to analyze the in-plane crushing behaviour of aluminium honeycombs and the results are presented and discussed. The simulations include both X1 and X2 cases. All the analyses are quasi-static, and can be divided into three groups, which are designed to investigate the effects of cell size, foil thickness and yield stress of the foil material, respectively, on the structural response of honeycombs. The result indicates that these factors can significantly affect the plateau stresses of honeycomb cellular structures in both directions, and the plateau stresses in X2 direction are slightly smaller than those in X1 direction. The simulation results were further compared with published theoretical predictions and show higher values. The difference was then analyzed and a new expression for the plateau stress of honeycombs was suggested.

Optimization design of chiral hexagonal honeycombs with prescribed elastic properties under large deformation

Flexible chiral honeycomb cores generally exhibit nonlinear elastic properties due to large geometric deformation.The effective elastic moduli and Poisson's ratio typically vary with an increase in deformation.Here,the size and shape optimization of the chiral hexagonal honeycombs was performed to keep the Young's moduli and Poisson's ratio unchanged under large deformations.The size of the honeycomb unit cell and the position coordinates of the key points were defined simultaneously as design variables.The equivalent Young's modulus and Poisson's ratio of chiral honeycombs were calculated through geometric nonlinear analysis.The objective was to minimize the allowable tolerance between the prescribed and actual properties within the range of the target strain.A genetic algorithm was then adopted.The optimal results demonstrate that the chiral honeycombs can maintain effective elastic properties that do not vary under large deformation.These results are meaningful to morphing aircraft designs.

Energy Absorption Performance of Bio-inspired Honeycombs:Numerical and Theoretical Analysis

Energy absorption performance has been a long-pursued research topic in designing desired materials and structures subject to external dynamic loading.Inspired by natural bio-structures,herein,we develop both numerical and theoretical models to analyze the energy absorption behaviors of Weaire,Floret,and Kagome-shaped thin-walled structures.We demonstrate that these bio-inspired structures possess superior energy absorption capabilities compared to the traditional thin-walled structures,with the specific energy absorption about 44%higher than the traditional honeycomb.The developed mechanical model captures the fundamental characteristics of the bio-inspired honeycomb,and the mean crushing force in all three structures is accurately predicted.Results indicate that although the basic energy absorption and deformation mode remain the same,varied geometry design and the corresponding material distribution can further boost the energy absorption of the structure,providing a much broader design space for the next-generation impact energy absorption structures and systems.

Crashworthiness Optimization Design of Thin-Walled Tube Filled with Re-entrant Triangles Honeycombs

A novel re-entrant triangles-filled tube(RTT)is proposed through decoupling structural stiffness and energy absorption.Inner re-entrant triangles are employed to satisfy energy absorption,and outer thin wall is used to acquire high stiffness.This paper starts from establishment of theoretical models between geometric parameters of re-entrant triangles and relative density,equivalent elastic modulus and energy absorption characteristics,which are validated by experiments.On this basis,the optimal geometric parameters of unit cell are sought to maximize unit volume energy absorption and minimize relative density by adopting NSGA-II method.Subsequently,the cross-section of tube with optimal stiffness is obtained with targets for maximizing axial stiffness and lateral stiffness by employing static topology optimization method.To verify the proposed optimization method,RTT is analyzed and compared with positive Poisson’s ratio foam-filled tube(PFT),non-filled traditionally optimized tube(NTT)and pre-optimized square tube(PST).The results show that the novel RTT can improve stiffness and energy absorption performance simultaneously.Compared with the positive Poisson’s ratio material,re-entrant triangles honeycomb shows superior advantages in energy absorption.In comparison with the PFT,energy absorption of the RTT increases by 17.23%,and the peak crush force reduces by 5.04%.Therefore,the proposed decoupling design method demonstrates superiority in satisfying various performance requirements simultaneously.

Dynamic Crushing Strength Analysis of Auxetic Honeycombs

The in-plane dynamic crushing behavior of re-entrant honeycomb is analyzed and compared with the conventional hexagon topology.Detailed deformation modes along two orthogonal directions are examined,where a parametric study of the effect of impact velocity and cell wall aspect ratio is performed.An analytical formula of the dynamic crushing strength is then deduced based on the periodic collapse mechanism of cell structures.Comparisons with the finite element results validate the effectiveness of the proposed analytical method.Numerical results also reveal higher plateau stress of re-entrant honeycomb over conventional hexagon topology,implying better energy absorption properties.The underlying physical understanding of the results is emphasized,where the auxetic effect（negative Poisson＇s ratio） induced in the re-entrant topology is believed to be responsible for this superior impact resistance.

The effects of ripple amplitude on heat transfer and fluid flow of X-lattice corrugated honeycombs

A previous study showed that the thermal performance of the X-lattice cored corrugated honeycomb(XCCH)is better than that of most other periodic cellular materials(PCMs).To further improve the thermal performance of the XCCH,the effects of different ripple amplitudes(i.e.,a=0.5,0.7 and 1.0)on the characteristics of the flow and heat transfer are numerically investigated by thorough comparisons.In terms of the flow characteristics,with the increase of ripple amplitude,the vortex interaction in the channel becomes stronger,which results in evident increase of kinetic energy of turbulence at the boundary of vortex and reduction in the turbulent kinetic energy dissipation.As far as the heat transfer is concerned,within the Reynolds number range of 3696–7436,the heat transfer increases with the increase of ripple amplitude.The overall Nusselt number of the XCCH with a=1.0 is 15.7%higher than that with a=0.5.Within the corresponding range of pumping power,the thermal performance of the XCCH with a=1.0 is up to 7%higher than that with a=0.5 at relatively higher Reynolds numbers.

Thermo-fluidic characteristics of natural convection in honeycombs:The role of chimney enhancement

The natural convective heat transfer performance and thermo-fluidic characteristics of honeycombs with/without chimney extensions are numerically investigated.The present numerical simulations are validated by the purposely-designed experimental measurements on honeycombs with/without chimney.Good agreement between numerical simulation and experimental measurement is obtained.The influences of inclination angle and geometric parameters such as cell shape,streamwise and spanwise length are also numerically quantified.With the increment in inclination angle,the overall heat transfer rate decreases for the honeycombs with/without chimney.For honeycombs with the same void volume fraction but different cell shapes,there is little difference on the overall heat transfer rate.To enhance the natural convective heat transfer of honeycombs,these techniques including increasing the length of honeycomb in the streamwise/spanwise direction,increasing the thermal conductivity of hon-eycomb structure or adding a chimney extension may be helpful.

Studies on the Compressive Mechanical Properties of Antitetrachiral Honeycombs with Different Thickness Ratios of Ligament to Cylinder

This paper investigated the compressive mechanical properties of antitetrachiral honeycombs with different thickness ratios of ligament to cylinder.The deformation and energy absorption performance of the structures were characterized by the cooperation of experimental and numerical methods.First,two types(small and large thickness ratios)of antitetrachiral honeycombs were manufactured by 3D printing.Then,the deformation mode,negative Poisson’s ratio(NPR)and crushing stress of the honeycombs were obtained experimentally.After that,a finite element(FE)model was established by using ABAQUS/Explicit,and the numerical model and method were validated.Based on experimental and numerical results,the X mode,double-parallel line mode and cylinder mode were obtained in the compressive deformation of the honeycomb with a small thickness ratio.The Bi-V mode,“e”mode and Z mode were obtained in the compressive deformation of the honeycomb with a large thickness ratio.The influence of the thickness ratio of ligament to cylinder was studied,and a thickness ratio of 1.625 was the critical value for the transformation of the antitetrachiral honeycomb deformation modes.

Designing Symmetric Gradient Honeycomb Structures with Carbon‑Coated Iron‑Based Composites for High‑Efficiency Microwave Absorption

The impedance matching of absorbers is a vital factor affecting their microwave absorption(MA)properties.In this work,we controllably synthesized Material of Institute Lavoisier 88C(MIL-88C)with varying aspect ratios(AR)as a precursor by regulating oil bath conditions,followed by one-step thermal decomposition to obtain carbon-coated iron-based composites.Modifying the precursor MIL-88C(Fe)preparation conditions,such as the molar ratio between metal ions and organic ligands(M/O),oil bath temperature,and oil bath time,influenced the phases,graphitization degree,and AR of the derivatives,enabling low filler loading,achieving well-matched impedance,and ensuring outstanding MA properties.The MOF-derivatives 2(MD_(2))/polyvinylidene Difluoride(PVDF),MD_(3)/PVDF,and MD4/PVDF absorbers all exhibited excellent MA properties with optimal filler loadings below 20 wt%and as low as 5 wt%.The MD_(2)/PVDF(5 wt%)achieved a maximum effective absorption bandwidth(EAB)of 5.52 GHz(1.90 mm).The MD_(3)/PVDF(10 wt%)possessed a minimum reflection loss(RL_(min))value of−67.4 at 12.56 GHz(2.13 mm).A symmetric gradient honeycomb structure(SGHS)was constructed utilizing the high-frequency structure simulator(HFSS)to further extend the EAB,achieving an EAB of 14.6 GHz and a RL_(min) of−59.0 dB.This research offers a viable inspiration to creating structures or materials with high-efficiency MA properties.

Dynamic response of honeycomb-FGS shells subjected to the dynamic loading using non-polynomial higher-order IGA

The main goal of this study is to use higher-order isogeometric analysis(IGA)to study the dynamic response of sandwich shells with an auxetic honeycomb core and two different functionally graded materials(FGM)skin layers(namely honeycomb-FGS shells)subjected to dynamic loading.Touratier's non-polynomial higher-order shear deformation theory(HSDT)is used due to its simplicity and performance.The governing equation is derived from Hamilton's principle.After verifying the present approach,the effect of input parameters on the dynamic response of honeycomb-FGS shells is carried out in detail.

Experimental and numerical study of effecting core configurations on the static and dynamic behavior of honeycomb plate with aluminum material

The sandwich panel incorporated a honeycomb core,a widely utilized composite structure recognized as a fundamental classification of composite materials.Comprised a core resembling a honeycomb,possessing thickness and softness,and is flank by rigid face sheets that sandwich various shapes and materials.This paper presents an examination of the static and dynamic analysis of lightweight plates made of aluminum honeycomb sandwich composites.Honeycomb sandwich plate samples are 300 mm long,and 300 mm wide,the heights of the core have been varied at four values ranging from 10 to 25 mm.The honeycomb core is manufactured from Aluminum material by using a novel technique namely resistance spot welding(RSW)instead of using adhesive material,which is often used when an industrial flaw is detected.Numerical optimization based on response surface methodology(RSM)and design of experiment software(DOE)was used to verify the current work.A theoretical examination of the crashworthiness behavior(maximum bending load,maximum deflection)and vibration attributes(natural frequency,damping ratio,transient temporal response)of honeycomb sandwich panels with different design parameters was also carried out.In addition,the finite element method-based ANSYS software was used to confirm the theoretical conclusions.The findings of the present work showed that the relationship between the natural frequency,core height,and cell size is direct.In contrast,the relationship between the natural frequency and the thickness of the cell wall is inverse.Conversely,the damping ratio is inversely proportional to the core height and cell size but directly proportional to the thickness of the cell wall.The study indicates that altering the core height within 10-25 mm leads to a significant increase of 82%in the natural frequency and a notable decrease of 49%in the damping ratio.These findings are based on a specific cell size value of 0.01 m and a cell wall thickness of 0.001 m.Also,the results indicate that for a given set of cell wall thickness and size values,an increase in core height from(0.01-0.025)m,leads to a reduction of the percentage of maximum response approX imately 76%.Conversely,the increasing thickness of the wall of cell wall,ranging 0.3-0.7 mm with a constant core height equal to 0.015 m,resulted in a de crease of maximum transient response by 7.8%.

Control and vibration analyses of a sandwich doubly curved micro-composite shell with honeycomb,truss,and corrugated cores based on the fourth-order shear deformation theory

Curved shells are increasingly utilized in applied engineering due to their shared characteristics with other sandwich structures,flexibility,and attractive appearance.However,the inability of controlling and regulating vibrations and destroying them afterward is a challenge to scientists.In this paper,the curve shell equations and a linear quadratic regulator are adopted for the state feedback design to manage the structure vibrations in state space forms.A five-layer sandwich doubly curved micro-composite shell,comprising two piezoelectric layers for the sensor and actuator,is modeled by the fourth-order shear deformation theory.The core(honeycomb,truss,and corrugated)is analyzed for the bearing of transverse shear forces.The results show that the honeycomb core has a greater effect on the vibrations.When the parameters related to the core and the weight percentage of graphene increase,the frequency increases.The uniform distribution of graphene platelets results in the lowest natural frequency while the natural frequency increases.Furthermore,without taking into account the piezoelectric layers,the third-order shear deformation theory(TSDT)and fourth-order shear deformation theory(FOSDT)align closely.However,when the piezoelectric layers are incorporated,these two theories diverge significantly,with the frequencies in the FOSDT being lower than those in the TSDT.

Functional–Structural Integrated Aramid Nanofiber‑based Honeycomb Materials with Ultrahigh Strength and Multi‑Functionalities

Multifunctional microwave-absorbing(MA)honeycombs are in urgent demand both in civil and military fields,while they often suffer from great limitations due to the complicated preparation process,inferior strength,and the susceptible peeling off of the absorbent coatings.Herein,we develop a straightforward strategy of assembly of aramid nanofibers(ANFs)and MXene nanosheets to honeycombs,obtaining a functional–structural integrated microwave absorption aramid honeycomb(MAAH).Benefiting from the robust and integrated cell nodes and dense network structure,the compressive strength and toughness of ANF honeycomb can reach up to 18.6 MPa and 2.0 MJ m^(−3),respectively,which is 6 times and 25 times higher than that of commercial honeycomb.More importantly,the synergistic effect of the unique three-dimensional(3D)conductive network formed by uniformly distributed MXene and the hierarchical structure of the honeycomb endow it with superior wave-absorbing performance,which exhibits a minimum reflection loss(RL_(min))of−38.5 dB at a thickness of only 1.9 mm,and covering almost the entire X-band bandwidth.Additionally,MAAH presents exceptional infrared thermal stealth,sound absorption performance,and real-time monitoring of structural integrity.Therefore,these impressive multi-functionalities of MAAH with outstanding wave-absorbing performance,ultrahigh strength,along with the straightforward and easy-toscalable and recyclable manufacturing technique,demonstrating promising perspectives of the MAAH materials in aerospace and military fields.

Dynamics of a rotating ring-stiffened sandwich conical shell with an auxetic honeycomb core

The free vibration analysis of a rotating sandwich conical shell with a reentrant auxetic honeycomb core and homogenous isotropic face layers reinforced with a ring support is studied.The shell is modeled utilizing the first-order shear deformation theory(FSDT)incorporating the relative,centripetal,and Coriolis accelerations alongside the initial hoop tension created by the rotation.The governing equations,compatibility conditions,and boundary conditions are attained using Hamilton’s principle.Utilizing trigonometric functions,an analytical solution is derived in the circumferential direction,and a numerical one is presented in the meridional direction via the differential quadrature method(DQM).The effects of various factors on the critical rotational speeds and forward and backward frequencies of the shell are studied.The present work is the first theoretical work regarding the dynamic analysis of a rotating sandwich conical shell with an auxetic honeycomb core strengthened with a ring support.