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Honeycomb structures made of carbon-fiber-reinforced plastic (CFRP) are increasingly used in the aerospace field due to their excellent energy absorption capability. Attention has been paid to CFRP structures in order to accurately simulate their progressive failure behavior and discuss their ply designability. In this study, the preparation process of a CFRP corrugated sheet (half of the honeycomb structure) and a CFRP honeycomb structure was illustrated. The developed finite element method was verified by a quasi-static test, which was then used to predict the low-velocity impact (LVI) behavior of the CFRP honeycomb, and ultimately, the influence of the ply angle and number on energy absorption was discussed. The results show that the developed finite element method (including the user-defined material subroutine VUMAT) can reproduce the progressive failure behavior of the CFRP corrugated sheet under quasi-static compression and also estimate the LVI behavior. The angle and number of plies of the honeycomb structure have an obvious influence on their energy absorption under LVI. Among them, energy absorption increases with the ply number, but the specific energy absorption is basically constant. The velocity drop ratios for the five different ply angles are 79.12%, 68.49%, 66.88%, 66.86%, and 60.02%, respectively. Therefore, the honeycomb structure with [0/90]s ply angle had the best energy absorption effect. The model proposed in this paper has the potential to significantly reduce experimental expenses, while the research findings can provide valuable technical support for design optimization in aerospace vehicle structures. [ABSTRACT FROM AUTHOR]

A honeycomb structure is a sandwich structure widely used in fuselage, among which the hexagonal honeycomb core is the most widely used. The energy absorption characteristics and impedance ability of the structure are the main reasons that directly affect the energy absorption characteristics of the honeycomb sandwich structure. Therefore, it is necessary to study the out-of-plane mechanical properties of the composite honeycomb sandwich structure. Based on the numerical simulation results, the energy absorption characteristics of several composite honeycomb sandwich structures are verified by drop hammer impact experiments. The research shows that the transient energy absorption characteristics of the composite honeycomb sandwich structure are mainly related to the cell size of the honeycomb structure. The smaller the size of the front cell, the stronger the overall impact resistance; the strength of the composite honeycomb sandwich structure exceeds that of 7075 aluminum alloy-NOMEX and carbon fiber-NOMEX honeycomb sandwich structures. In this paper, the energy absorption characteristics of composite honeycomb sandwich structures under different impact energy are compared and studied. The displacement, force and energy curves of energy absorption characteristics related to time variables are analyzed. The difference in protective performance between the composite honeycomb sandwich structure and existing airframe structure is compared and studied. The optimal structural design parameters of composite honeycomb sandwich under low-speed impact of drop hammer are obtained. The maximum energy absorption per unit volume of the designed honeycomb sandwich structure is 171.7% and 229.8% higher than that of the NOMEX-AL and NOMEX-C structures. The 6.4 mm and 3 mm cell sizes show good characteristics in high-speed buffering and crashworthiness. The composite honeycomb sandwich airframe structure can improve the anti-damage performance of the UAV airframe structure, ensure the same thickness and lightweight conditions as the existing honeycomb sandwich airframe structure, and improve the single-core bearing mode of the existing airframe structure. [ABSTRACT FROM AUTHOR]

Sandwich structures are often used as protective structures on ships. To further improve the energy-absorbing characteristics of traditional honeycomb sandwich structures, an energy-absorbing mechanism is proposed based on the gradient folding deformation of lotus root nodes and a leafy stem vein homogenizing load mechanism. A honeycomb sandwich structure is then designed that combines lotus root nodes and leafy stem veins. Four types of peak-nest structures, traditional cellular structure (TCS), lotus root honeycomb structure (LRHS), leaf vein honeycomb structure (LVHS), and lotus root vein combined honeycomb structure (LRVHS), were prepared using 3D printing technology. The deformation modes and energy absorption characteristics of the four honeycomb structures under quasistatic action were investigated using a combination of experimental and simulation methods. It was found that the coupling design improved the energy absorption in the structural platform region of the LRHS by 51.4% compared to that of the TCS due to its mechanical mechanism of helical twisting and deformation. The leaf vein design was found to enhance the peak stress of the structure, resulting in a 4.84% increase in the peak stress of the LVHS compared to that of the TCS. The effects of the number, thickness, and position of the leaf vein plates on the honeycomb structure were further explored. The greatest structural SEA effect of 1.28 J/g was observed when the number of leaf vein plates was four. The highest SEA of 1.36 J/g was achieved with a leaf vein plate thickness of 0.6 mm, representing a 7.3% improvement compared to that of the 0.2 mm thickness. These findings may provide valuable insights into the design of lightweight honeycomb sandwich structures with high specific energy absorption. [ABSTRACT FROM AUTHOR]

In this paper, sorghum and reed, which possess light stem structures in nature, were selected as biomimetic prototypes. Based on their mechanical stability characteristics—the porous structure at the node feature and the porous feature in the outer skin— biomimetic optimization design, simulation, and experimental research on both the traditional hexagonal structure and a hexagonal honeycomb structure were carried out. According to the two types of straw microcell and chamber structure characteristics, as well as the cellular energy absorption structure for the bionic optimization design, 22 honeycomb structures in 6 categories were considered, including a corrugated cell wall bionic design, a modular cell design, a reinforcement plate structure, and a self-similar structure, as well as a porous cell wall structure and gradient structures of variable wall thickness. Among them, HTPC-3 (a combined honeycomb structure), HSHT (a self-similar honeycomb structure), and HBCT-257 (a radial gradient variable wall thickness honeycomb structure) had the best performance: their energy absorption was 41.06%, 17.84%, and 83.59% higher than that of HHT (the traditional hexagonal honeycomb decoupling unit), respectively. Compared with HHT (a traditional hexagon honeycomb decoupling unit), the specific energy absorption was increased by 39.98%, 17.24%, and 26.61%, respectively. Verification test analysis revealed that the combined honeycomb structure performed the best and that its specific energy absorption was 22.82% higher than that of the traditional hexagonal structure. [ABSTRACT FROM AUTHOR]

The shape memory alloy (SMA) can deform pseudo-plastically under external load, based on which a reusable impact energy absorption structure was designed. According to the classical SMA constitutive model, the finite element model for thin-wall structures was established, and the dynamic characteristics such as deformation modes and energy absorption of different forms of honeycomb structures under different impacting velocities, were analyzed, and the optimal energy absorption performance of the SMA structures was obtained. In addition, through comparison of the energy absorption performance of the SMA honeycomb with that of the aluminum honeycomb, the energy absorption of the SMA honeycomb with different structure configurations was different from that of the aluminum honeycomb under different-velocity impacts, with the optimal structure changes. The work provides a reference for the selection and design of the SMA honeycomb structures. [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]

Metastructures are extensively used in aerospace engineering. In the present work, a high-strength structure was designed based on a reentrant hexagonal honeycomb (RHH) by topology optimization. To generate a negative Poisson's ratio (NPR) effect, topologically optimized cells were alternately arranged with RHH cells to obtain a hybrid hexagonal honeycomb (HHH). In comparison with other NPR structures, this structure had superior energy absorption characteristics. In addition, the mechanical properties and deformation behavior of this structure were analyzed. Finally, single, double, and triple functional gradients were introduced into the HHH. It was found that the introduction of functional gradients improved the energy absorption capacity of the structure, and that the energy absorption capacity increased with the increase in the number of functional gradients. [ABSTRACT FROM AUTHOR]

Novel designs of paper-based bandstop frequency-selective surfaces (FSSs) are presented in this article. The characteristics of the paper-based honeycomb structure are investigated first. One folded dipole resonator with first-order bandstop response is analyzed and further printed on the sidewalls of the honeycomb structure accordingly. A second-order response with two cascade FSSs is proposed with controllable bandwidth by the coupling coefficient of the resonators with the aid of the equivalent circuit model. Two paper-based FSS samples were fabricated and measured to demonstrate the validity of the proposed design strategies. Benefiting from the merits of lightweight and strong mechanical properties, the proposed paper-based FSS is a potential candidate for application in radar systems and aircraft. [ABSTRACT FROM AUTHOR]

The mechanical performance of honeycomb sandwich structures fabricated with thermoplastic elastomer nylon core and 0D/2D hybrid polymer nanocomposite skin was investigated. The cell sizes were varied from 10 to 36 mm, and mechanical performance was evaluated along out-plane and in-plane orientations. Different tests like sandwich compression, bare core flexural, beam deflection and drop over impact test were carried out. The energy absorption ability of sandwich panels was evaluated by compression and drop weight impact test, and it was effectuated by cell size variation. A close agreement between the test results of the drop weight impact tester and FEM simulation was noted. The analysis of test results confirms that nylon honeycomb core with the variation of cell size possesses both compliance and stiffness besides good energy absorption abilities. The possible area of application includes backing layer in the body armor that can provide protection against blunt trauma and scar. [ABSTRACT FROM AUTHOR]

Honeycomb structures exhibit outstanding mechanical properties with specific unit cell configurations. We introduce a novel honeycomb structure that can enhance the compression property and energy absorption capacity by utilizing four-dimensional (4D) printing technology with polylactic acid (PLA) materials. In the designed honeycomb structure, the walls of the adjacent unit cells are independent, and the shape of the unit cells can be transformed between a hexagon and triangle under external loading and temperature stimulus. 4D printing technology is employed to prepare the honeycomb specimens, and the deformation processes of the innovative honeycombs are implemented. Structure I (a novel hexagonal honeycomb structure) and Structure II (a semi-triangular honeycomb structure) can be transformed into each other. Uniaxial quasi-static compression and impact tests are conducted to investigate the compression property and energy absorption capacity of the designed honeycomb structures. The results indicate that the novel honeycomb had a high compression property with Structure II, and had high energy absorption capacity with Structure I; thus, the developed honeycomb structures have broad application prospects for the multifunctional applications of honeycomb structures in the future. [ABSTRACT FROM AUTHOR]

Phenolic syntactic foam sandwich composites are potential materials for aerospace and marine applications because of their good strength to weight ratio, stiffness to weight ratio, fire resistance and better energy absorption characteristics. In the present work, syntactic foam is prepared by uniform mixing of cenosphere and phenolic resin in equal proportions. The effect of stiffening the syntactic foam core by resin impregnated paper honeycomb (RIPH) structure on compression behavior and energy absorption capacity of sandwich composites is experimentally investigated under flatwise and edgewise loading configuration. Bare RIPH core and only syntactic foam core sandwich composites are also investigated for comparison purpose. The results show that RIPH incorporated syntactic foam has the highest compressive properties and energy absorption capacity compared to only syntactic foam core sandwich composites. Microscopic features of syntactic foam fragments tested under flatwise compression are also investigated to predict the failure mode. [ABSTRACT FROM PUBLISHER]

Abstract: The in-plane impact behavior of honeycomb structures randomly filled with rigid inclusions was studied by using the finite element method to clarify the effect of inclusions on the deformation process, mean stress, densification strain, and absorbed energy. The deformation processes of the models were disturbed by inclusions; shear bands were pinned, and the cell regions surrounded by inclusions were shielded. Mean stress, densification strain, and absorbed energy per unit volume normalized by the values of the model without inclusions were found to be only dependent on the fraction of inclusions. As the volume fraction of inclusions increased, the normalized mean stress linearly increased and the normalized densification strain linearly decreased. The normalized absorbed energy per unit volume could be approximated by an inverted parabolic equation. The energy absorption of models with inclusions having volume fractions from 0 to 0.25 was larger than that of the models without inclusions. In particular, honeycomb models with fractions of inclusion from 0.1 to 0.2 exhibited the maximum absorbed energy. The model with a volume fraction larger than 0.4 could not be compressed because the inclusions in the model had already percolated before deformation. The in-plane impact behavior of honeycomb structures as energy absorbing materials can be designed by using the approximate equation and selecting the volume fraction of inclusions. [Copyright &y& Elsevier]

• Co/Carbon (Co/C) composites were prepared by facile hydrothermal and calculation process. • Modulating permeability of Co/C is achieved by adjusting the amount of Co2+. • The obtained Co/C composite exhibits a bandwidth of 5.8 GHz at a low thickness of 1.8 mm. • The electromagnetic simulated honeycomb made by Co/C shows an ultrabroad bandwidth of 11.6 GHz. [Display omitted] Confronting with increasing electromagnetic pollution, traditional microwave absorbing materials have their limitations, such as low yield and long preparation periods. At the same time, it is well established that electromagnetic simulation is an effective technology to enhance work efficiency, which can quickly explore the impedance matching conditions and electromagnetic characteristics to improve absorbing performance. Honeycomb structure has been widely used in the field of microwave absorption due to its light weight, high strength and heat resistance. This structure also possesses the advantages of multiple scattering, which is beneficial to microwave attenuation. In this work, Co/carbon (Co/C) particles with effective absorption bandwidth (EAB) (the band corresponding to the reflection loss value less than −10 dB) of 5.8 GHz were synthesized by a simple hydrothermal method. Whereupon through the high-frequency structure simulator (HFSS) electromagnetic simulation, Co/C absorbers with honeycomb structure were macroscopically designed, achieving an ultra-broad effective absorption bandwidth of 11.6 GHz. Herein, the effective combination of electromagnetic simulation and honeycomb structure design greatly improves the absorption bandwidth of Co/C. This work paves the way for designing microwave absorption materials with broad effective absorption bandwidth. [ABSTRACT FROM AUTHOR]