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HighlightsMIL-88C (Fe) with varying aspect ratios as a precursor was synthesized by regulating oil bath conditions, followed by one-step thermal decomposition to obtain carbon-coated iron-based composites.High-efficiency microwave absorption properties were achieved with RLmin value of -67.4 dB (2.13 mm) and wide effective absorption bandwidth (EAB) of 5.52 GHz (1.90 mm) under the low filler loading.A symmetric gradient honeycomb structure was constructed utilizing the high-frequency structure simulator, achieving an EAB of 14.6 GHz and a RLmin of -59.0 dB.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 (MD2)/polyvinylidene Difluoride (PVDF), MD3/PVDF, and MD4/PVDF absorbers all exhibited excellent MA properties with optimal filler loadings below 20 wt% and as low as 5 wt%. The MD2/PVDF (5 wt%) achieved a maximum effective absorption bandwidth (EAB) of 5.52 GHz (1.90 mm). The MD3/PVDF (10 wt%) possessed a minimum reflection loss (RLmin) 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 RLmin of − 59.0 dB. This research offers a viable inspiration to creating structures or materials with high-efficiency MA properties.

The bandgap properties of elastic metamaterials can be efficiently utilized to tailor the propagation characteristics of elastic and acoustic waves, which have promising applications in noise and vibration reduction and isolation. In this paper, an elastic metamaterial with a multilayered honeycomb structure (EMHS) is proposed to enlarge the bandgaps in the low-frequency range and its bandgap properties are analyzed. To meet the requirement of the lightweight design, an optimization model for maximizing the total relative bandgap width with a mass constraint is established. A novel optimization approach combining the Kriging surrogate model with the genetic algorithm (GA) is proposed to reduce the huge computational cost of the corresponding optimization problem. In the Kriging-GA approach, a high-precision Kriging-based surrogate model with addition of supplementary points is constructed to predict the bandgap objective function value, and the GA is employed to search for the optimal parameters. The performance of the proposed Kriging-GA approach is investigated by numerical examples, and the results are compared with those obtained by the commonly used FEM-GA method. The results show that the proposed Kriging-GA approach is highly efficient for the design optimization of the EMHS and can remarkably reduce the computational cost of the considered optimization problem, which has promising prospects in a wide range of engineering applications.

This study investigates the mechanical performance of additively manufactured hybrid honeycomb structures, incorporating hexagonal and re-entrant geometries, fabricated from acrylonitrile butadiene styrene (ABS), widely employed thermoplastic material, under bending conditions. Through three-point bending experiments and finite element analysis (FEA), the energy absorption capacity and flexural modulus of these cellular architectures are evaluated. A comparative assessment is conducted between hollow hybrid structures and those reinforced with polyurethane (PU) foam to elucidate the effects of its integration on mechanical properties. The findings indicate that re-entrant hybrid honeycombs exhibit superior reinforcement characteristics compared to hexagonal honeycombs, attributable to their variable cell ratios and dimensions, which allow control over mechanical properties without altering cell geometry. This adaptability facilitates the manufacturing process by enabling the selection of the most straightforward geometry while varying only cell ratios. Additionally, parametric FEA studies explore the influence of structural parameters and bending load configurations on honeycomb performance, revealing that hybrid structures exhibit improved stiffness and energy absorption under three-point bending. Notably, the experimental results closely align with the FEA results, thereby enhancing the reliability of the computational models employed. This research underscores the potential of hybrid designs in the development of advanced lightweight, high-performance materials for diverse engineering applications.

The high variability of shock in terrorist attacks poses a threat to people's lives and properties, necessitating the development of more effective protective structures. This study focuses on the angle gradient and proposes four different configurations of concave hexagonal honeycomb structures. The structures' macroscopic deformation behavior, stress-strain relationship, and energy dissipation characteristics are evaluated through quasi-static compression and Hopkinson pressure bar impact experiments. The study reveals that, under varying strain rates, the structures deform starting from the weak layer and exhibit significant interlayer separation. Additionally, interlayer shear slip becomes more pronounced with increasing strain rate. In terms of quasi-static compression, symmetric gradient structures demonstrate superior energy absorption, particularly the symmetric negative gradient structure (SNG-SMS) with a specific energy absorption of 13.77 J/cm³. For dynamic impact, unidirectional gradient structures exhibit exceptional energy absorption, particularly the unidirectional positive gradient honeycomb structure (UPG-SML) with outstanding mechanical properties. The angle gradient design plays a crucial role in determining the structure's stability and deformation mode during impact. Fewer interlayer separations result in a more pronounced negative Poisson's ratio effect and enhance the structure's energy absorption capacity. These findings provide a foundation for the rational design and selection of seismic protection structures in different strain rate impact environments.

The use of Nomex honeycomb structures is essential for the aerospace and aeronautics industry because of their high out-of-plane strength and their advantageous weight/rigidity ratio. Nevertheless, milling these structures presents technical and scientific challenges, including premature wear of cutting tools and the quality of the machined surface. In general, the machining process relies on carrying out experimental tests. However, the high rotation speed of the cutting tool makes it difficult to monitor the cutting process correctly. Thus, it has become imperative to adopt reliable numerical models to collect instantaneous and accurate physical data. For this purpose, a 3D finite element numerical model was developed using the Abaqus/Explicit software, taking into account the real conditions of the experiment. An experimental validation was carried out by analyzing the premature wear of the cutting tool. After having validated the numerical model, an in-depth analysis was carried out to evaluate the influence of the number of teeth of the cutting tool on the optimization of the machining of the Nomex honeycomb structure. This analysis specifically focused on the cutting forces, the quality of the machined surface, and the accumulation of chips in front of the cutting tool. The obtained results clearly underline that low feed rates improve the integrity of the cutting tool, while a limited number of cutting tool teeth significantly improves cutting forces and the quality of the machined surface.

The honeycomb sandwich structure is widely used in energy-absorbing facilities because it is lightweight, has a high specific stiffness and high specific strength, and is easy to process. It also has dynamic mechanical characteristics such as a high impact resistance and high energy absorption. To explore the influence of the Poisson’s ratio on the local impact resistance, this paper compares and analyzes the local impact resistance of a series of honeycomb cores with different Poisson’s ratios under the impact of a spherical projectile at different speeds. Three typical honeycombs with negative/zero/positive Poisson ratios (re-entrant hexagon, semi-re-entrant hexagon, and hexagon) are selected to change the geometric parameters in order to have the same relative density and different Poisson ratios (−2.76–3.63). The relative magnitude of the rear face sheet displacement is in the order of negative Poisson’s ratio > zero Poisson’s ratio > positive Poisson’s ratio, which reveals that the honeycomb structure with the positive Poisson’s ratio has better protection ability than the others. Finally, a dual-wall hexagonal honeycomb is proposed. The rear face sheet displacement of the dual-wall hexagonal honeycomb sandwich structure is reduced by 34.4% at 25 m/s compared with the hexagonal honeycomb, which has a better local impact resistance.

Negative Poisson's ratio materials show great potential in aerospace, automotive engineering, and military protection owing to their unique deformation behavior and superior mechanical properties. Nevertheless, current negative Poisson's ratio honeycomb structures suffer from an inherent conflict between stiffness and energy absorption, along with poorly understood mechanical regulation mechanisms in complex three-dimensional nested configurations. To address these issues, this paper proposes a novel Cross Re-entrant Hexagon Nested Star-shaped Cell (CRNSC). Through theoretical derivation, finite element simulation, and quasi-static compression experiments, the mechanical properties and energy absorption characteristics of the structure are systematically investigated. A geometric characterization system based on length, angle, and thickness parameters is established. The results show that the cell wall thickness significantly increases the relative density, while the angle between the inner inclined strut and the horizontal line induces polarity reversal of the Poisson's ratio. The outer inclined strut angle and the inner angle exhibit monotonic or nonlinear regulatory effects on the equivalent Poisson's ratio and the effective Young's modulus, respectively. The optimal load-bearing configuration ( = 65°, = 35°) achieves a peak stress of 1.01 MPa, and the optimal deformation configuration ( = 55°, = 25°) reaches an ultimate strain of 4%. Theoretical, simulated, and experimental results are in good agreement with errors below 7%, validating the model's effectiveness.

This scientific research presents a modal analysis of the impact of honeycomb structures on rotors’ dynamic characteristics. The natural frequencies and mode shapes of free vibration were determined employing the modal analysis. The impact hammer and the laser vibrometer were used for experimental modal analysis to provide valuable data using OptoGUI data acquisition software. The numerical modal analysis was performed by the finite element method using ANSYS software to validate the experimental results. The main objective of this study was to evaluate the influence of honeycomb structures on natural frequencies and critical speeds by comparing the dynamic behaviour of the rotors with the simple hollow shafts and the hollow shaft with honeycomb structures. The results indicated that the integration of honeycomb structures injected important stiffness and damping properties, leading to significant variations in the natural frequencies and critical speeds of the rotors. The agreement between the experimental and numerical results validated the accuracy of the numerical model and predicted the dynamic behaviour of the rotors. This validation is crucial for the dynamics of rotor design and future applications. The results offer new perspectives on rotor behaviour with honeycomb structures that develop and optimize future design. 

HighlightsCreate a hierarchical honeycomb-inspired triboelectric nanogenerator (TENG) with excellent transparency, compactness, lightweight and deformability.Amplify capacitance variation by dividing large hollow space into numerous energy generation units with porous honeycomb architecture.Demonstrate self-powered insole plantar pressure mapping applications by the self-sustained elastic nature of the h-TENG device.Integrate the h-TENG into the morphing wing of small-unmanned aerial vehicles for converting flapping motions into electricity for the first time.Flexible, compact, lightweight and sustainable power sources are indispensable for modern wearable and personal electronics and small-unmanned aerial vehicles (UAVs). Hierarchical honeycomb has the unique merits of compact mesostructures, excellent energy absorption properties and considerable weight to strength ratios. Herein, a honeycomb-inspired triboelectric nanogenerator (h-TENG) is proposed for biomechanical and UAV morphing wing energy harvesting based on contact triboelectrification wavy surface of cellular honeycomb structure. The wavy surface comprises a multilayered thin film structure (combining polyethylene terephthalate, silver nanowires and fluorinated ethylene propylene) fabricated through high-temperature thermoplastic molding and wafer-level bonding process. With superior synchronization of large amounts of energy generation units with honeycomb cells, the manufactured h-TENG prototype produces the maximum instantaneous open-circuit voltage, short-circuit current and output power of 1207 V, 68.5 μA and 12.4 mW, respectively, corresponding to a remarkable peak power density of 0.275 mW cm−3 (or 2.48 mW g−1) under hand pressing excitations. Attributed to the excellent elastic property of self-rebounding honeycomb structure, the flexible and transparent h-TENG can be easily pressed, bent and integrated into shoes for real-time insole plantar pressure mapping. The lightweight and compact h-TENG is further installed into a morphing wing of small UAVs for efficiently converting the flapping energy of ailerons into electricity for the first time. This research demonstrates this new conceptualizing single h-TENG device's versatility and viability for broad-range real-world application scenarios.

A new thin-walled honeycomb structure for Li-ion battery packaging is designed and optimized in this study. Compared with other battery packaging structures, the designed honeycomb structure described here uses a grid to reinforce its strength. At the same time, the weight is reduced to improve the energy density of the entire package. Moreover, the new thin-walled structure can better protect the internal battery and improve the safety of an electric vehicle (EV). A space mapping (SM) algorithm is used to efficiently optimize the thin-walled honeycomb structure due to the expensive computational cost of each evaluation of a fine FE model. Compared with other SM algorithms, the coarse model of SM is based on a pseudo-plane-strain model. The result shows that the magnitude of stress and the distribution of stress are significantly improved compared with the initial structure. Moreover, the computational cost of optimization for the problem is also decreased significantly due to importing the coarse model.