Honeycomb Cell Research Articles

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

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

Dynamic Response and Energy Absorption Characteristics of a Three-Dimensional Re-Entrant Honeycomb

In this paper, we design a new three-dimensional honeycomb with a negative Poisson’s ratio. A honeycomb cell was first designed by out-of-plane stretching a re-entrant honeycomb and the honeycomb is built by spatially combining the cells. The in-plane response and energy absorption characteristics of the honeycomb are studied through the finite element method (FEM). Some important characteristics are studied and listed as follows: (1) The effects of cell angle and impact velocity on the dynamic response are tested. The results show that the honeycomb exhibits an obvious negative Poisson’s ratio and unique platform stress enhancement effect under the conditions of low and medium velocity. An obvious necking phenomenon appears when the cell angle parameter is 75°. (2) Based on the one-dimensional shock wave theory, the empirical formula of the platform stress is proposed to predict the dynamic bearing capacity of the honeycomb. (3) The energy absorption in different conditions are investigated. Results show that as the impact velocity increases, the energy absorption efficiency gradually decreases. In addition, with the increase of cell angle, the energy absorption efficiency is gradually improved. The above study shows that the honeycomb has good potential in using in vehicle industry as an energy absorption material. It also provides a new strategy for multi-objective optimization of mechanical structure design.

Free vibration analysis of an auxetic honeycomb sandwich plate placed at the wall of a fluid tank

This paper presents a parametric investigation of the free vibration characteristics of an auxetic honeycomb sandwich plate mounted at the wall of a liquid tank. Frostig's second model is utilized in the core, while first-order shear deformation theory (FSDT) is applied to the face sheets. The honeycomb core is homogenized using one of the newest revised models (Tornabene's model), and the fluid is assumed to be ideal. The governing equations of motion are derived using Hamilton's principle and solved using the Galerkin method. Present solution method, honeycomb core homogenization formula, and mathematical framework for the fluid-sandwich plate interaction are verified using 3D Finite Element Analysis (FEA). Finally, the wet fundamental frequency is investigated with geometric parameters such as the ratio of tank dimensions to the plate length, fluid height from the plate's bottom edge, plate location at the tank wall, and honeycomb cell geometry. According to the results of this study, the thickness of the face sheet and the cell wall enhance the wet fundamental frequency, while the cell aspect ratio decreases it.

Numerical study on the thermal energy storage employing phase change material with honeycomb structure: The effect of heat transfer fluid configuration and honeycomb cell angles

AbstractConsiderable literature has studied different techniques to improve the thermal performance of latent heat thermal energy systems (LHTES) that utilize phase change materials (PCMs). This study aims to contribute to this growing area of research by using honeycomb structure and exploring the effect of heat transfer fluid (HTF) configuration and honeycomb cell angle on the thermal performance of the LHTES during melting and solidification processes. In this work, five cases were designed: case (a) was regarded as reference case; cases (b) and (c) were related to HTF configuration; cases (d) and (e) were used to study the effect of honeycomb cell angle. A numerical study was conducted using ANSYS FLUENT R19.3, followed by experimental validation. In this study, a good agreement is obtained from the validation process. Computational fluid dynamics (CFD) model results show symmetrical melting and solidification behavior when using a honeycomb structure. The results of the HTF configuration show a significant effect. For case (c) with a multiple water block, significant melting and solidification enhancements are obtained with 56% and 50%, respectively. Thus, the HTF configuration can improve the thermal performance of the storage. However, considering different honeycomb cell angles show an insignificant effect on the melting and solidification rates.

Analysis of electric field efficacy and remediation performance of triclosan contaminated soil by Co–Fe/al oxidation electrodes coupled with peroxymonosulfate (PMS) in an ECGO system with diversified electrode configurations

Triclosan (TCS) is commonly used as a biocide against bacterial and fungal infections. The overuse of TCS has resulted in its abundance in the natural environment. Sulfate radicals have been used for in-situ groundwater remediation because of their superior performance. In this study, Co–Fe/Al oxidation electrodes were prepared to investigate the effect of electrode configurations on TCS remediation using electrokinetic geooxidation (ECGO) technology coupled with peroxymonosulfate (PMS) in a soil system. The Co–Fe/Al electrodes catalyzed the activity of PMS by solid-phase Co2+ to produce sulfate radicals. Four electrode configurations, named G1–G4, applying a potential gradient of 2 V/cm, were conducted for ten days in all experiments. Results showed that 14.2–66.2% of TCS remediation efficiency was observed. TCS was mainly degraded by the Co–Fe/Al electrode and sulfate radicals rather than being removed by the electroosmotic flow. The degradation efficiencies of the G4 system (66.0%) and the G2 or G3 system (36.6% or 64.4%, respectively) were much higher than that of the G1 system. (13.5%). Three regions (effective, ineffective, and enhanced) were classified to explore the effect of the electric field on TCS remediation. The arrangement of the honeycomb cells was related to the area of enhanced region in the system, in which the superior remediation performance of the TCS was found. Therefore, TCS remediation performance is highly related to the electrode configuration and honeycomb arrangement in the system. The seven-unit honeycomb system (G4) demonstrated a linear and centralized arrangement, resulting in fast migration and excellent degradation of the TCS.

In-plane dynamic crashing behavior and energy absorption of novel bionic honeycomb structures

A series of novel bionic honeycombs (bio-honeycombs) are proposed by incorporating the microstructure of the beetle elytra intersection unit into the regular hexagonal honeycomb (Hex) cell. To explore the in-plane mechanical properties and energy absorption performance of bio-honeycombs under different impact speeds, finite element (FE) models are established and verified by empirical formulas and current experiments. The results indicate that the bio-honeycombs outperform the Hex in terms of energy absorption capacity, and the nominal stress–strain curves of the bio-honeycombs show two prominent stages (stage Ⅰ and stage Ⅱ) under quasi-static and mid-impact. Bionic units also undergo two evident deformation stages: preliminary collapse and further crushing. The bending and traction of bionic units make more adjacent cells added to the collapse earlier, forming a global crushed trend, leading to an interesting phenomenon that the localized band of bio-honeycombs are always wider than that of Hex. Also, negative Poisson’s ratio is observed in stage Ⅱ from several bio-honeycombs under quasi-static and mid-speed due to bionic units' bending and traction in the further crushing stage. Besides, the number and distribution of ribs have a considerable impact on the crashworthiness of bio-honeycombs. Compared with the Hex, the incorporated bionic units reduce the peak crushing force (PCF) while improving the crashworthiness of bio-honeycomb in the case of the same relative density, which provides a promising potential solution to strengthen the energy absorption performance of honeycomb structures.

Modeling of hexagonal honeycomb hybrids for variation of Poisson’s ratio

Abstract In this research, the compressive behavior of structures consisting of two types of cells were studied (honeycombs and re-entrant), in order to know the effect of the ratios of these cells on the mechanical properties of the structures. In addition, by controlling the Poisson’s ratio with a constant Young’s modulus, three types of structures (traditional honeycomb, auxetic and zero Poisson’s ratio (ZPR)) were obtained together with the ability to control their mechanical properties without changing the geometric properties of the cell. Numerical models were created and compared with the results obtained from the structures manufactured by the 3D printer experimentally, and where the Young’s modulus, Poisson factor and compressive deformation were close to the experimental results. In this current research, new structures have been proposed by incorporating traditional honeycomb cells with auxiliary honeycomb cells into a single structure without changing the cell geometry. The aim was to control the Poisson’s ratio in order to obtain all types of structures mentioned above without changing the geometric properties of the cell.

A form error evaluation method of honeycomb core surface

Form error evaluation of the machined honeycomb surfaces has the power to deliver tremendous benefits to improve the machining accuracy and guide the assembly process. The line laser measurement can meet the high-resolution requirement for thin-walled honeycomb cell walls, but faces a high proportion of noise data consisting of burrs and outliers. In this paper, dimensionality reduction combined with random sample consensus or regression analysis is adopted to distinguish the irregular noise from the measurement data. A directional extraction of honeycomb core surface form based on locally weighted regression is proposed. A highly realistic honeycomb surface simulation method is established to solve the lack of honeycomb benchmarks. The simulation experiment shows that the accuracy of the proposed method is ±7 μm. The comparison experiment with coordinate measuring machine demonstrates the surface form RMS error differences for the polygonal and curved honeycomb by the two method are 7 μm and 19 μm, respectively.

Cell wall fracture mechanism in ultrasonic-assisted cutting of honeycomb materials

Revealing the ultrasonic cutting mechanism of honeycomb composite is important for determining the acoustic parameters of the ultrasonic system and selecting the parameters of the cutting process. Understanding more details of the stress on the cell wall from ultrasonic vibrating tool and the conditions for cell wall breakage is essential to study the machining mechanism. According to the evolution of contact state between the straight edge cutter and the honeycomb cell wall in a cycle, the cutting force acting on the cell wall is divided into three stages: transverse cutting load action, longitudinal cutting load action, and no cutting load action. The cell wall deflection and stress equations under transverse cutting load were established by applying elastic thin plate small deflection theory. The deformation and fracture characteristics of the honeycomb cell wall were analyzed by combining the analytical and the finite element model. The results showed that the ultrasonic vibration of the cutter greatly improved the stiffening effect of the cell wall and its fracture was caused by the deflection under the transverse cutting load, which exceeded the maximum allowable deformation after local stiffening. In addition, with only longitudinal cutting load, it was difficult to break the critical buckling state that leads to cell wall fracture.

Dynamic compressive behaviour of shear thickening fluid-filled honeycomb

Shear thickness fluid (STF) is considered an ideal filler to enhance the mechanical behaviour of in-plane honeycomb due to its special rheological properties. In order to investigate the dynamic compressive behaviour of STF-filled honeycomb, a comparative study between a STF-filled honeycomb and an empty honeycomb is numerically carried out after the fluid-structure coupled model has been validated against experimental testings. It is shown that the addition of STF in the honeycomb cells results in significant improvement in the energy absorption of the STF-filled honeycomb, which in turn, effectively prevents the premature collapse of the honeycomb cell walls. Furthermore, a parametric study of STF-filled honeycomb is conducted to investigate the contributions of each component to the total energy. It is found that the honeycomb plastic deformation is the predominant mechanism of energy absorption during impact, whilst the proportion of viscous energy contribution to the total energy is significantly reduced when the honeycomb wall thickness is increased. Additionally, the mean crushing force of STF-filled honeycomb has a power law relation to the honeycomb wall thickness for each specific loading velocity. Moreover, the mean crushing force contributed by STF is proportional to loading velocity and the increase in velocity significantly improves the percentage of viscous energy to the total energy. Meanwhile, optimal honeycomb thickness and weight fraction of STF are crucial to avoid earlier plastic densification of the honeycomb during the loading process. The results of this paper provide useful insights for future design and optimization of STF-filled structures.

Multi-objective structural optimization of honeycomb cells

This paper develops an optimum cell structure design method considering the in-plane tensile/compression and shear properties to improve the stiffness and strength of the honeycomb core. The equivalent elastic modulus in the X or Y direction and shear modulus in the XY plane are derived using Energy Method for hexagonal, quadrilateral and concave hexagonal cells, and are compared with the results in the related literatures. The multi-objective optimization model in which the vertical wall length, wall thickness and inner angle of the cell are taken as design variables is solved by Genetic Algorithm to maximize the equivalent elastic moduli. The static and dynamic characteristics of the honeycomb cores with original and optimized cells are studied using Finite Element Method. The results show that after the cell optimization, the maximum displacement, stress and strain obviously decrease, thus improving the structural performance of the honeycomb core. The research provides significant guidance for the design of the cell structure.

Failure behavior of sandwich beams with glass fiber-reinforced epoxy/aluminum laminates face-sheets and aluminum honeycomb core under three-point bending

The failure behavior and energy absorption performance of aluminum honeycomb sandwich beams with glass fiber-reinforced epoxy/aluminum laminates (GLARE) face-sheets under three-point bending are experimentally and numerically studied. The experimental specimens consists of 2/1 (2 aluminum sheets and 1 glass fiber/epoxy laminates) GLARE and aluminum honeycomb core. The effects of core height (8 mm, 20 mm, 40 mm) and indenter shape (cylindrical indenter and flat indenter) on bending failure behavior are tested in quasi-static three-point bending. Six sandwich beam specimens (300 mm-long and 40 mm-wide) were prepared. The initial failure modes of GLARE sandwich beams are observed, i.e. core shear and indentation. The numerical model considering geometric nonlinearity is established by ABAQUS/Explicit software and its effectiveness is verified by the experimental results of specimens with the same size and loading conditions. The effects of geometric and material parameters on the load-carrying capacity and energy absorption of the GLARE sandwich beams are discussed in details. It is shown that increasing the face-sheet thickness, honeycomb wall-thickness, the ratio of the core height to span length and the elasticity effect of metal materials or reducing the side length of the honeycomb cell can improve the load-carrying capacity and energy absorption of GLARE sandwich beams. The work can provide the guidance for the design of the GLARE sandwich structure with honeycomb core.

Parametric optimization of corner radius in hexagonal honeycombs under in-plane compression

What is the optimum corner radius for a regular hexagonal honeycomb in the context of in-plane, quasistatic compression loading? Drawing inspiration from social insect hexagonal cell nests, where a non-zero corner radius appears to be a design feature, a 400-point design of experiments study is conducted using 2D plane strain Finite Element Analysis (FEA) to study the influence of cell size, beam thickness and corner radius on effective modulus and maximum corner stress in the honeycomb cells. An experimental study is conducted to examine these relationships beyond the bounds of the small deformation, linear elastic FEA analysis. The study finds that corner radii always increase the effective modulus of the honeycomb, even after accounting for the additional mass associated with the corner fillet. A key finding of this work is that while corner radii also reduces the maximum corner stress, there exists a clear optimum, beyond which stresses rise again as the corner radius increases in magnitude. This optimum corner radius is shown to be a function of the beam thickness (t) to beam length (l) ratio (t/l), with the optimum value increasing with increasing t/l. The experimental study shows that the presence of a corner radius shifts the failure mechanism from nodal fracture to plastic hinging for honeycombs with thick beams, and may have benefits for energy absorption applications. This work makes the case for the treatment of the corner radius as an independent design feature for optimization in the wider context of cellular materials, as well as has implications for the study of the geometry of insect nests.

Експериментальний і чисельний аналіз напруженого стану стільникових заповнювачів, виготовлених адитивними технологіями

This paper proposes an approach to the experiment-and-calculation analysis of the tension of honeycombs made by FDM additive technologies. The approach includes experimental tension analysis. Tension tests of honeycombs were conducted on a certified TiraTest 2300 universal tension testing machine. To do this, sets of honeycomb samples were prepared. The method of honeycomb manufacturing by FDM additive technologies is described. The vertices of a honeycomb cell row are fixed in the vise-type clamps of the tension testing machine. The experimental analysis is accompanied by a numerical finite-element simulation of tension tests. To simulate honeycomb tension, nine mechanical characteristics of the material in material axes must be known. These nine parameters are considered in the paper. A direct finite-element simulation of a honeycomb with account for the deformation of all its cells was performed. To provide the uniformity of sample deformation in a physical experiment, the sample is loaded by setting the displacement of one of its ends to a constant value. In doing so, the other end is clamped. As follows from the experimental analysis, before failure the honeycomb cell end displacements are comparable with the honeycomb cell thickness. Because of this, the geometrically nonlinear deformation of the honeycomb cells in tension is accounted for in the calculations, and a nonlinear problem is solved using ANSYS. The direct simulation of honeycombs and the analysis of their homogenized model give different results. In the direct simulation of honeycombs, they are considered as thin-walled beams working in bending. In this case, the geometrical nonlinearity contributes significantly to the structural deformation. For plate tension (homogenized model), the contribution of the geometrical nonlinearity is very small, Because of this, the stress-strain response is close to linear.

A sandwich panel that autonomously repairs sudden large holes and defects for tankers and pipelines carrying hazardous matter

The self-healing of micro and macro cracks is vital for eliminating defects such as damage progression and loss of strength in structures. In this study, a polyurethane (PU) based geometrically self-healing sandwich structure was developed. The geometric healing agent, PU resin and activator, were filled into macrocapsules, and these capsules were filled into the Aluminum (Al) honeycomb cells. Self-healing of structural strength, large holes and cracks in developed sandwich structures were investigated by performing quasi-static compression and impact penetration tests. The sandwich structure with a self-healing capsules-filled core was damaged by subjecting it to quasi-static and penetration impact loads, and the healing agents in the broken capsules were mixed. The damage in the specimen was removed by geometric self-healing. Liquid and air permeability tests were applied to the PU foam used as a healing agent. No liquid permeability was observed in the structure. In addition, significant reductions in air permeability were obtained. Scanning electron microscope images were used to explore the characterization of the PU foam structure cells.

Natural convection characteristics of honeycomb fin with different hole cells for battery phase-change material cooling systems

As a nature production the lightweight honeycomb is used as a fin to increase the contact area with the PCM and improve its overall thermal conductivity. In this paper the effects of different honeycomb core shapes, sizes, and arrangements on melting under natural convection were investigated to determine the optimal honeycomb cell parameters. In this study, transient simulations based on VOF and enthalpy-porosity methods are developed, and the results show that compared with heat conduction, the melting time under natural convection conditions can be reduced. By analyzing different shapes, it is discovered that the melting effects of triangles, trapezoids, rectangles, and rhombuses are better than that of hexagons, the triangular melting time is reduced by 23.1%. The orthogonal experiments show that the ranking order of the effects on melting time and natural convection is Ra > Shape > LHR. Furthermore, the optimal honeycomb hole core parameters are obtained from the analysis of a single factor. Compared with the hexagonal honeycomb fin, a battery's PCM with an optimal triangular honeycomb fin under natural convection exhibits a 23.3% increase in terms of temperature decrease.

New viscoelastic circular cell honeycombs for controlling shear and compressive responses in oblique impacts

Cellular structures such as honeycombs are used to manage impact loads in many engineering applications, where often the impact load is oblique (non-axial). Although these structures have been extensively studied under axial impacts, a key question remains largely unaddressed: How may their axial and shear responses be independently tailored for oblique impacts? Here we test whether incorporating curvature in the form of axisymmetric shape changes in the cell walls of viscoelastic circular cell honeycombs enables independent control over their shear and compressive responses during oblique impacts. We developed detailed finite element models of the circular cell honeycombs made of the 3D printable viscoelastic material Agilus. Using a new rig, we validated the predictions of the finite element models under oblique impacts. We performed a full-factorial computational design-of-experiments, varying the cell shape from concave to convex with different amplitudes and impact velocities from 2.5 to 7.5 m/s in order to determine their effects on the shear and compressive responses of the honeycombs under oblique impacts. The finite element models demonstrate remarkable agreement with experimental oblique impacts for both concave and convex cells. Our full-factorial computational search shows that both convex and concave cells have similar compressive stresses. However, the post-buckling shear stress of the concave cells are up to 300% larger than the convex cells. In addition, increasing the impact velocity increases both compressive and shear stresses by 211% due to the viscoelastic nature of the material. Our results show that these new recoverable honeycombs provide a compelling control over their shear response under oblique impacts, which is nearly independent from their compressive response. These new honeycombs can be used to manage oblique impacts in a wide range of products, such as helmets, shoes and seats, where enabling an independent control over shear and compressive responses will open new design avenues. In addition, the proposed simple control mechanism, i.e. the curvature change, can be exploited in future to actively morph the honeycomb cells during use for real-time performance adjustment.

A 3D-Printed Honeycomb Cell Geometry Design with Enhanced Energy Absorption under Axial and Lateral Quasi-Static Compression Loads

This work presents an innovative honeycomb cell geometry design with enhanced in-plane energy absorption under quasi-static lateral loads. Numerical and experimental compression tests results under axial and lateral loads are analyzed. The proposed cell geometry was designed to overcome the limitations posed by standard hexagonal honeycombs, which show relatively low stiffness and energy absorption under loads that have a significant lateral component. To achieve this, the new cell geometry was designed with internal diagonal walls to support the external walls, increasing its stiffness and impact energy absorption in comparison with the hexagonal cell. 3D-printed unit-cell specimens made from ABS thermoplastic material were subjected to experimental quasi-static compression tests, in both lateral and axial directions. Energy absorption was compared to that of the standard hexagonal cell, with the same mass and height. Finite element models were developed and validated using experimental data. Results show that the innovative geometry absorbs approximately 15% more energy under lateral compression, while maintaining the same level of energy absorption of the standard hexagonal cell in the axial direction. The present study demonstrates that the proposed cell geometry has the potential to substitute the standard hexagonal honeycomb in applications where significant lateral loads are present.

Effect of fillers on compression loading performance of modified re-entrant honeycomb auxetic sandwich structures

The auxetic sandwich panels for structures have been designed to provide impact protection. The aim of this work is to modify an auxetic (re-entrant) honeycomb cell to reduce the stress concentrations within the cell structure, and further enhancement of this design. The auxetic structure was filled to achieve a greater energy absorbance and enhance safety applications. Analytical and elastic three-dimensional finite element approaches were used to investigate the structural strength performance. The basic model (i.e. modified re-entrant strut cell design) consisted of the honeycomb auxetic polypropylene (PP) structure sandwiched between two steel plates (known as safety panels) which were placed under static compression loading. The cell geometry and size were then modified to reduce the stress concentration zones. The structure cells were filled with silly putty and polyvinyl chloride (PVC) foam. The effect of the filling the cells on the stress concentration and energy absorbance were analysed using elastic stress and deformation analysis methods. During the stress path analysis, it was found that an increase in Young’s modulus of the filling was directly proportional to a decrease in internal stresses. It was concluded that while filling the basic model with soft materials reduced the stress concentration, but it led to a reduction in the energy absorbance capability. Further on, the lower stress produced by the enhanced could be useful to prevent significant penetration of the protective panel. Compared to similar structures of steel, auxetic foam panels have the advantage of having only a fraction of the weight and being corrosion resistant at the same time as keeping impact strength. Graphical abstract [Formula: see text]

Energy absorption in carbon fiber honeycomb structures manufactured using a liquid thermoplastic resin

In this study, carbon fiber/thermoplastic (Elium®) honeycombs were manufactured using the resin infusion process in a customized metallic mold. Honeycomb cores, based on different carbon fiber layers, were manufactured to achieve four different fiber weight fraction composites. Two different types of specimens, based on a single honeycomb cell and five honeycomb cells, were prepared and subjected to compression loading. The results of these tests were compared with data from similar honeycomb structures based on carbon fiber–reinforced epoxy composite. It has been shown that the compressive strength and the specific energy absorption capacity of the honeycombs increase rapidly with increasing fiber weight fraction. The specific energy absorption capability of the novel thermoplastic honeycomb structures has been shown to be as high as 50 kJ/kg which compares favorably with other energy-absorbing core materials. The thermoplastic honeycomb specimens exhibited a similar specific energy absorption capability and an improved compressive strength compared to their epoxy counterparts. Furthermore, the CF/thermoplastic honeycombs exhibited enhanced structural stability and displayed a more uniform and progressive core failure mode than the longitudinal splitting observed in the CF/epoxy honeycombs. The honeycomb core that exhibited the best performance was then used to manufacture thermoplastic sandwich specimens based on CF/thermoplastic face sheets. Three point bend tests were conducted to determine the flexural strength of the sandwich samples and to identify the failure modes. Optical micrographs revealed that the flexural damage was primarily due to the core crushing and adhesive failure between the core and the composite skins.