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Although honeycomb is a kind of lightweight structural material with great potential, its specific strength is not always able to meet the requirements, especially in the weight-sensitive field. Inspired by the bionic idea of cuttlebone, the curved-wall configuration design is proposed to strengthen the buckling impedance of honeycomb, which can effectively prevent the premature occurrence of buckling failure mode induced by thin walls. Compared with the straight-wall honeycomb materials of the same geometric size, the probability of buckling failure in curved-wall honeycomb materials proposed in this paper is reduced by more than 22 %. Moreover, to achieve the preparation of curved-wall configuration, a processing strategy that uses stretching process to prepare ultralight carbon fiber honeycomb (Carbcomb) material is firstly introduced. Compared to the Hexcel Corporation's aluminum honeycomb with a density of 21 kg/m3, for the Carbcomb, the specific compressive strength and specific shear strength along both the L and W directions respectively improved by 57 %, 61 % and 77 %. In addition, the minimum density of fabricated Carbcomb (14.6 kg/m3) is less than that of the Hexcel's products (16 kg/m3), and the research findings fill the gap of the carbon fiber honeycomb material in low density areas (10 ∼ 30 kg/m3). More importantly, this process which does not require much manual operation can effectively avoid the problems of unstable mechanical properties, difficult mass production and high preparation cost of the existing carbon fiber structural parts. This curved-wall configuration design and fabricated approach widens the potential of carbon fiber honeycomb as a structural material, and makes it possible for lower cost and higher efficiency in aerospace and transportation applications. [ABSTRACT FROM AUTHOR]

Real-time thermal deformation monitoring plays a crucial role in calibrating phase signals and maintaining satellite performance for large spaceborne antennas. The inverse finite element method (iFEM) represents a promising shape-sensing methodology applicable to monitor the three-dimensional displacement of structures through surface-measured strain. However, the high-accuracy reconstruction of large-scale structures involves a large number of inverse elements, which leads to the low level of computational efficiency. To address this issue, a displacement-gradient-based variable-size iFEM is proposed in this paper. According to the characteristics of deformation, this method optimizes the size of each inverse element to reduce the number of inverse elements required, which improves real-time performance and maintains the high accuracy of reconstruction. The real-time performance of the proposed method is verified by conducting a simulation test on a large-scale honeycomb antenna. According to the simulation results, the variable-size iFEM is applicable to achieve the same accuracy of reconstruction using fewer inverse elements than conventional iFEM. An experimental test is performed and the optimal variable-size discretization that balances accuracy and efficiency is determined. The results show that the maximum error of reconstructed displacement is less than 7.3 % and the reconstruction time is in no excess of 0.1 s. [ABSTRACT FROM AUTHOR]

Honeycomb structures are commonly adopted due to their superior energy absorption capacity. In this study, a new bionic glass sponge–type honeycomb structure (BSH) with a quadrilateral octagonal mesh microstructure inspired by the sea sponge structure was proposed. The in-plane crushing performance of the BSH with different geometrical parameters under different crushing speeds was investigated by ABAQUS/Explicit. The numerical findings suggested that the BSH displayed stronger energy absorption in contrast to the square, hexagonal and hierarchical honeycombs at both quasi-static and dynamic crushing conditions. More plastic hinges and more unit walls involved in deformation resulted in a high energy absorption capacity. In addition, three typical deformation modes of the BSH under different loading speeds were discussed, and the empirical model to predict the plateau stress of the BSH was established based on the shock wave theory. Finally, the effect of boundary segmentation parameter m on crushing performance was also illustrated. The energy absorption capacity reaches a maximum at m = 3 for quasi–static loading, whereas at m = 5 for dynamic loading. These findings provide valuable insights into the optimization of bionic honeycombs. [ABSTRACT FROM AUTHOR]

Thin-walled edge cutting angle (TWECA) refers to a unique trait of honeycomb core materials in the course of cutting, which is also a main influencing factor for the surface quality of machining. To validly overcome machining defects, making accurate TWECA prediction during the cutting process is necessary. In this study, a TWECA model for various kinds of thin-walled edges was proposed. Firstly, the thin-walled edges composing honeycomb cores were classified and unified based on the structural features of the cores, which lays the foundation for the modeling of honeycomb core architecture as well as the TWECA prediction. Then, the geometric relationships between tool and various types of thin-walled edges during contact were analyzed, and the differences in TWECAs of thin-walled edges in different tool feed directions were explored. Finally, the TWECA model accuracy was validated by using the tool mark characteristics on the machined surface as the research target. As demonstrated by findings of this research, our model achieves accurate TWECA forecasting during cutting process, thus providing a theoretical foundation for the requirements of low-damage and high-quality machining. [ABSTRACT FROM AUTHOR]

The main objective of this paper is to evaluate the dynamic behaviour of sandwich toroidal shells composed of a core with negative Poisson ratio (auxetic honeycomb material) and nanocomposite enriched coating layers under impulsive/periodic pressures considering the geometrical nonlinearity. The set of nonlinear equilibrium equations based on the first-order shear deformation theory are and the resultant nonlinear differential motion equations are approximately solved by the Galerkin method and 4th-order Runge–Kutta solution, respectively. The achieved responses show that the amplitude of outward deformations is intensively increased when the proposed sandwich shells are subjected to rectangular periodic and impulsive loadings which shows the destructive effects of this type dynamic loading. The performed parametric studies shows that these destructive effects can be controlled by changing the geometrical properties of the honeycomb cells and the volume fractions of the nanocomposites in the coating layers. It is notable that in the previous studies the nonlinear dynamic response of toroidal shells subjected to various periodic and impulsive pressures was not investigated. However, in the present work, the mentioned dynamic responses were achieved and investigated without spending time-consuming computational. In fact, the novelty of this work is to develop such a robust and efficient tool. [ABSTRACT FROM AUTHOR]

Sandwich panels with a hierarchical core facilitate the optimal utilization of limited materials to enhance bearing capacity in strategic locations. Nevertheless, the complex sub-structural cells have hindered extensive investigation into their static and modal characteristics. The objective of this study is to obtain the effective plate properties by homogenizing the representative unit cell and subsequently applying them to a two-dimensional equivalent single layer model (2D-ESL) based on the variational asymptotic method (VAM). Furthermore, three-point bending test of 3D-printed specimen and 3D detailed finite element results are employed to confirm the predictions of 2D-ESL under various load and boundary conditions. The effects of material factors (such as fiber volume fraction and layup configuration) and structural parameters (including aspect ratio, hierarchy ratio, and slenderness ratios of ribs and ligaments) on the equivalent stiffness and modal characteristics are also examined. Moreover, sandwich panels with different hierarchical configurations (including 2, 3 and infinite segments within the inclined ribs) are investigated to provide valuable insights for selecting appropriate hierarchies based on specific conditions. Notably, the transition from polyline to arc-shaped segments has been proven to effectively mitigate local stress concentration, leading to a more uniform distribution of local displacement. • Hierarchical core optimizes material utilization or enhanced bearing capacity. • The unit cell is homogenized to determine the equivalent plate properties. • 2D-ESL can improve computational efficiency while ensuring sufficient accuracy. • SP-HDH can achieve optimal bending stiffness at the slenderness ratio of 0.26. • HDH with different segment configuration offer insights for hierarchy selection. [ABSTRACT FROM AUTHOR]

• The metamaterials have asymmetric Poisson's ratios under tension and compression. • The metamaterials break Maxwell-Betti's reciprocity. • The Poisson's ratios of the metamaterials surpass the thermodynamic limits. • The Poisson's ratios can be tailored by designing the self-contacting stop. Although metamaterials with unconventional Poisson's ratios have been extensively explored for their counterintuitive and desirable properties, most exhibit only a single behavior. Here, we design novel metamaterials capable of both positive and negative Poisson's ratios, which simultaneously demonstrate outstanding performances: asymmetric, non-reciprocal, and even exceeding thermodynamic limits. These abnormal properties are achieved by combining honeycomb and re-entrant structures with self-contacting stops set at different positions. The unique topology allows for mode switching, where the unit cell can transition between "honeycomb" and "re-entrant" configurations under different load conditions. This mode convertibility endows the metamaterials not only different signs of Poisson's ratios under various load conditions in a single direction but also anisotropy in orthogonal directions. Through theoretical analysis, the deformation modes and the corresponding Poisson's ratios are predicted. Experiments and simulations then validate the intriguing Poisson's ratios and the model predictions. Notably, these Poisson's ratios can be further tailored by adjusting the initial states of the self-contacting stops, offering a powerful tool for manipulating Poisson's ratios and unlocking new functionalities of metamaterials. [ABSTRACT FROM AUTHOR]

This study provides an experimental and numerical evaluation of the energy absorption performance of a 3D-printed star hourglass honeycomb structure with a novel design made from pure and reinforced PLA by chopped carbon fibers and continuous glass fiber. The study further investigates the energy absorption response of this structure after the shape recovery due to thermal stimuli under the quasi-static compressive loading. As an additive manufacturing process, Fused Deposition Modeling is used to produce the specimens with pure and reinforced PLA filament. The difference in the nonlinear response of PLA due to plasticity and damage in tension and compression loading directions, as a feature that helps the shape recovery, is considered in mechanical response analysis using the Finite Element approach. Then, in the obtained results distinguish constitutive laws in tension and compression mechanical properties are employed leading to a failure model using the appropriate algorithm consistent with the experiments. According to the obtained results which reveal good agreement regarding the experimental results, by designing appropriate auxetic configuration selecting suitable geometry parameters, and employing the proper material with diverse properties in tension and compression directions, it is possible to fabricate a lattice structure inherits the shape recovery after the compression deformation which exhibits acceptable energy absorption performance even the second shape recovery. [ABSTRACT FROM AUTHOR]

Honeycomb structures offer the benefits of being lightweight and having high out-of-face compressive stiffness, making them a popular choice for aerostructures. The present study delineates the design and active vibration control effect for fiber-reinforced cruciform honeycomb laminates (CHLs) characterized by variable parameters. Employing a continuous fiber 3D printer, carbon fiber filament and shape memory polymers (SMPs) were utilized in the fabrication of the specimens. Differential equations of motion for CHLs were deduced from Kirchhoff plate theory. To ascertain their frequency response, these laminates were subjected to a sinusoidal swept frequency excitation. Subsequently, the classical proportional integral derivative (PID) program was employed to scrutinize the efficacy of closed-loop active vibration control on CHLs. The investigation extended to analyzing the impact of active vibration control across laminates with disparate parameters, including an examination of the convergence speed during vibration control procedures. A comparative analysis of simulated versus experimental data revealed a substantial consonance between the two, thereby corroborating the accuracy of the experimental findings. This study offers crucial insights and reference value for the utilization of CHLs in the aerospace industry. [ABSTRACT FROM AUTHOR]

Ultralight all-CFRP honeycomb sandwich cylinders were fabricated using a stretching process. Subsequently, critical failure loads corresponding to five typical failure modes of the sandwich cylinders under axial compression were obtained through theoretical derivation. Three-dimensional failure mechanism maps were generated, which intuitively revealed the influence of the dimensionless parameters on structural failure. The panel thickness was selected as a variable, and quasi-static axial compressive tests were performed on the sandwich cylinders. Two failure modes, intracellular buckling and face crushing, were observed, which is consistent with theory. The experimental results were analysed and discussed systematically. The ultralight all-CFRP honeycomb sandwich cylinders were compared with existing cylinders to reveal their bearing advantages. The established failure mechanism maps provide guidance for the preparation and optimisation of honeycomb sandwich cylinders. Compared with the traditional fabrication processes of honeycomb cores, the novel stretching process is expected to achieve mass production, which is helpful to provide technical support for the lightweight manufacturing of aerospace structural components. [ABSTRACT FROM AUTHOR]

This paper examines the impact of polyurethane foam (PUF) filling on the dynamic response of honeycomb sandwich beams (HSBs) through the blast testing. The HSBs are composed of steel face sheets and an aluminium alloy honeycomb core filled with PUF. A comparative analysis of damage modes is conducted between conventional hexagonal and auxetic HSBs, considering both foam-filled and unfilled configurations. The results reveal that the HSBs with foam filling demonstrate significantly enhanced blast performance compared to their counterparts without foam filling. This superiority is evident in both global deformation and local damage characteristics. Furthermore, a well-validated numerical model is developed to examine the damage mechanisms of PUF-filled HSBs under blast loading. The investigation reveals that appropriate PUF filling methods can effectively enhance bending resistance while minimizing the decline in the energy absorption efficiency. Finally, a multiobjective optimization was conducted using the back-propagation (BP) neural network and the SPEA2 algorithm to identify the optimal position for PUF. By utilizing a reduced foam filling approach as opposed to completely filling the structure, the two optimized configurations show a decrease in deformation of 5.38 % with an equivalent specific energy absorption (SEA) or an increase in the SEA by 5.26 % with an equivalent deformation. [ABSTRACT FROM AUTHOR]

A sandwich shell with an ultra-low-density honeycomb core was designed and manufactured from a carbon-fibre prepreg via a stretching process. Subsequently, the bending bearing limits of the sandwich shell corresponding to five possible failure modes (shear buckling, shear fracture, intracellular dimpling, face fracture, and core debonding) were obtained through theoretical predictions. Failure mechanism maps were generated to reflect the possibility of each failure mode intuitively. In addition, three-point bending tests were performed on specimens with different shell thicknesses to acquire as many of these typical failure modes as possible. Moreover, the competition mechanism between different failure modes was revealed. The research results provide theoretical guidance for parameter optimisation and applications in advanced engineering fields for ultra-low-density carbon-fibre honeycomb sandwich shells. [ABSTRACT FROM AUTHOR]

• An attractive structure with superior dynamic crushing performance was proposed. • Reliable numerical models were established to avoid severe element distortion. • Dynamic crushing response was illuminated in the full range of deformation process. • The effects of strain-rate sensitivity and impact velocity were evaluated in depth. To achieve excellent dynamic crushing performance, an attractive foam-filled periodic hybrid cellular (F-PHC) structure containing both hexagonal and re-entrant cells was designed and fabricated. Dynamic crushing experiments for foam-filled PHC structures were carried out using a direct impact Kolsky bar testing system. Reliable numerical simulations using both finite element method and smoothed particle hydrodynamics method were developed to analyze the dynamic crushing responses of F-PHC structures in the full range of deformation processes. Effects of inertia, strain-rate sensitivity, cell number, and impact velocity were evaluated. The results show that the dynamic plateau stresses of periodic hybrid cellular structures can be substantially enhanced by filling foams. The dynamic crushing response of F-PHC structure is very susceptible to impact velocity due to inertia effect. Compared with foam-filled hexagonal honeycomb and foam-filled re-entrant honeycomb structures, F-PHC structures exhibited superior dynamic crushing performances, including smoother and longer dynamic plateau stresses, more uniform deformation distributions, and much more stable deformation processes. Moreover, F-PHC structures exhibited much lower dynamic initial peak stresses at the rear face. This study provides a fascinating design idea and shines light on attractive F-PHC structures with a promising application prospect in the field of impact protection. [ABSTRACT FROM AUTHOR]

Cellular honeycomb beams are widely encountered in nature and engineering applications. The mechanical responses of them under various loads are critical to their applications. However, theoretical analyses and predictions of these mechanical responses are quite challenging. In this paper, theoretical studies are carried out to predict their large deformation bending responses. Theoretical expressions are derived for bending moment responses of honeycomb beams under both pure bending and three-point bending by considering the bending theory of solid beams and incorporating the relative density ρ* of the cellular honeycomb beams. Numerical simulations are performed to demonstrate the effectiveness and accuracy of the proposed theories by using the numerical model validated by experiment. Rectangular honeycomb beams with the relative density 0 < ρ * ≤ 1 are selected by Latin hypercube sampling. The theoretical bending moment curves of these beams predicted by the proposed theories agree well with the numerical results for both pure bending and three-point bending. In addition, the proposed theories are also validated to be effective in predicting the bending responses of honeycomb beams with different sectional cell shapes. [ABSTRACT FROM AUTHOR]

Honeycomb structure as a thin-walled structure has excellent mechanical properties. In this work, three types of novel embedded chiral honeycomb (ECH) structures are proposed based on a hybrid strategy and manufactured by using the additive manufacturing (AM) technique. Quasi-static uniaxial compression tests in lateral and diagonal loading are carried out. The loading-displacement curves and deformation modes of ECHs are recorded and analyzed. The numerical models are established and its simulation results are in good agreement with the experiments. The results show chiral units have a significant enhancement on macro mechanical properties. It is found that ECH4 has the best energy absorption characteristics (EA of 49.52 J, SEA of 1.55 J/g) in lateral loading and ECH3 has the best (EA of 62.25 J, SEA of 2.14 J/g) in diagonal loading. The deformation patterns of structures are also discussed. Moreover, the effects of geometric parameters on the mechanical responses of ECHs are analyzed, including the effects of the circular node radii and the wall thickness. The optimal interval of parameter design is finally determined. The findings from this study are helpful for a new topology optimization design for hexagonal honeycomb structures with enhanced mechanical properties. [ABSTRACT FROM AUTHOR]

• A novel meta -honeycomb was obtained and fabricated, which reversed the energy absorption method of traditional materials. • The enhanced bandgap property was established by multi-resonator. • The dynamic response of the meta -honeycombs was measured under the impact and blast loads. • The optimization of the meta -honeycomb was verified by coupling different resonators. Conventional honeycomb materials are difficult to resist multiple blast because the enormous energy generated by the explosion would cause plastic deformation of the material, which weakens the strength of the structure. In this paper, a novel meta -honeycomb is designed by adding local resonance system to hierarchical cells, which is based on the multi-resonator-enhanced bandgap property, to withstand multiple blast. This meta -honeycomb reverses the energy absorption mode of traditional honeycomb materials; that is, the energy absorption by plastic deformation of the material becomes the reflection of the stress wave through the equivalent negative mass property generated by the local resonance system, which significantly reduces the deformation of the material and the reaction force at the support under impact loads. In particular, for the secondary explosion loading, the maximum deformation of the meta -honeycomb is reduced by 74% compared with the traditional hierarchical honeycomb. Furthermore, it is demonstrated that the design of meta -honeycomb can be optimized by coupling the bandgap generated by the negative mass property, thereby improving the energy absorption efficiency. This research result provides a new concept for the design of blast-proof materials, which has a high potential for a wide range of engineering applications. [ABSTRACT FROM AUTHOR]

Auxetic lattice structures are known for their superior stiffness-to-density and strength-to-density ratios. Re-entrant hourglass exhibits an acceptable equivalent elastic modulus and remarkable energy absorption capacity among various auxetic configurations due to their flexibility and hinge deflecting during crushing loads. This study introduces a curved hourglass honeycomb which can be produced using 3D printing with pure or reinforced filaments incorporating continuous fibers. New closed-form formulations are analytically derived using an energy method by considering an extracted unit cell to predict the equivalent in-plane mechanical properties for the first time. The plateau stress of the proposed honeycomb is evaluated at the densification state of a unit cell using the energy conservation theory, equating external work with plastic energy dissipation. The accuracy of these extended relations is validated against experimental outcomes, demonstrating good agreement between analytical and experimental results. Additionally, robust linear and nonlinear finite element analyses are conducted to assess the accuracy of the obtained relations, including the equivalent stiffness and plateau stress for structures produced with reinforced filaments. The nonlinear finite element code employs appropriate subroutines to model plasticity/damage events. Based on the established analytical relations for stiffness and plateau stress, multi-objective optimization using Genetic Algorithm is applied to define optimum values for the Pareto front chart's objective functions of stiffness and plateau stress. The optimization process involves exploring the design space and defining the values of geometrical parameters to achieve the desired objectives. In conclusion, this study presents a novel approach to developing curved re-entrant honeycomb structures, with analytical formulations validated against experimental and numerical results. Optimization helps to identify optimal configurations concerning stiffness and plateau stress, offering potential applications in lightweight and high-strength materials design. According to the obtained results, for selection of the best value for curved strut angle which results in the optimum value of stiffness and plateau stress, a range between 10°-34° can be considered depending on the volume fraction of fibers. [ABSTRACT FROM AUTHOR]

The natural beesʼ honeycombs maintain long-term structural stability in harsh environments, employing a highly material-efficient approach. However, the reasons remain somewhat ambiguous. To clarify the stabilization mechanism and investigate quasi-static compression responses of double-layer ordered cellular structures, honeycomb, Tóth and single-layer cellular structures with a relative density (ρ r) of 25.84 % were fabricated using 3D printing technology. Then, quasi-static compression experiments in three directions were conducted. Further, a numerical study was conducted to uncover the stabilization mechanism and effect of ρ r on compressive behaviors. Results revealed that the stabilization mechanism was mainly attributed to bearing load priority of intermediate layer and its inhibition on formation of plastic hinges. A relative density of 5.17 % served as a transition point for deformation mode, beyond which honeycomb and Tóth structures exhibited stronger in-plane compressive strength at expense of less sacrificed out-of-plane compressive strength, below which they both exhibited more stable compressive curves compared to single-layer cellular structures, which were favorable for energy absorption. This study clarifies the stability mechanism of beesʼ honeycombs and addresses the lack on compression behaviors of double-layer ordered cellular structures. Moreover, it introduces two available bionic structures with controllable deformation modes to expand the application of single-layer cellular structures. [ABSTRACT FROM AUTHOR]

Existing auxetic honeycomb meta-structures are generally integrated structures with complicated microstructural geometry which hence should be fabricated by costly additive manufacturing (AM) technology. The high cost and low production efficiency of AM technology is still the main bottleneck restricting the engineering applications of such kind of structures. In this work, a prefabricated auxetic honeycomb meta-structure with modularized components was proposed based on mortise and tenon (M&R) principle originated in ancient China. The modularized components of the prefabricated auxetic honeycomb are all tubular structures which can be easily fabricated by traditional manufacturing with low cost and high technical maturity. The mechanical properties of the proposed meta-structure were then detailed investigated numerically under quasi-static and dynamic loading conditions. The referenced integrated auxetic honeycomb meta-structure was also considered as a benchmark for comparison. Results show that the proposed prefabricated design exhibits lower strength and stiffness compared with its integrated counterpart, owing to the introduction of more flexibility. Consequently, the proposed design processes a much more stable stress plateau stage with a larger deformation range and effectively reduces the reactive force of the protected structure. The present work paves a novel avenue to design protective meta-structures with low-cost and high performance. [ABSTRACT FROM AUTHOR]

The composite honeycomb sandwich with auxetic reentrant honeycomb (CSP-ARH) is a typical negative Poisson's ratio structure, which has better mechanical properties than composite structure with positive Poisson's ratio. In this study, a 2D asymptotic equivalent model (AEM) based on the variational asymptotic method (VAM) is proposed and used to analyze the vibration and buckling problems of CSP-ARH incorporating CFRP facesheets and an aluminum honeycomb core. After validation with 3D finite element results, a particle swarm optimization (PSO) algorithm is applied to optimize the mesoscopic size of composite facesheets and honeycomb core. The primary objectives of the optimization process involve maximizing the buckling load and natural frequency, minimizing the mass while satisfying specific mechanical properties requirements. Moreover, a few additional optimization iterations are performed to find the optimal shape coefficients of the curved fibers in the CFRP facesheets for variable stiffness composite sandwich panels. The shape of the curved fiber is defined using a cubic polynomial function f (x , y) and is described by a 20 × 20 grid of discrete elements. The results indicate that CSP-ARH with optimal curved fibers shapes exhibit superior performance compared to those with straight fibers, with buckling load and natural frequency increased by 8.18% and 7.09%, respectively. • VAM is extended to establish 2D-AEM of CSP-ARH, and verified by the 3D-FEM. • 2D-AEM reduces the DOFs of the CSP-ARH and improves calculation efficiency. • The PSO algorithm is applied to optimize the structural parameters of CSP-ARH. • The buckling and free vibration behaviors of CSP-ARH and CSP-ARH-CLF are studied. • Optimizing curved fiber direction improves the mechanical properties of CSP-ARH-CLF. [ABSTRACT FROM AUTHOR]

Multi-layered design is an effective method to improve the damping performance of structures. The existing research focuses more on the multi-layered design of the structure from the macro-perspective, but lacks attention to the material itself from the micro-perspective. Thus, whether microscale multi-layered (MML) viscoelastic polymers have advantages in damping performance is not clear. Moreover, damping materials preparation and structural noise control is an interdisciplinary study. The noise and vibration control effect of MML viscoelastic polymers in actual composite structures needs to be further investigated. This paper conducts such a study on these issues. First, two different types of MML viscoelastic polymers, i.e., free damping (FD) and micro-constrained damping (MCD) composites, were prepared, and their material properties were characterized. Second, the frequency-dependent damping loss factors and elastic modulus of the different damping composites were identified. The influences of damping composite types and MML designs on material damping loss factor and elastic modulus were compared. Third, a prediction model of vibroacoustic behaviours of the honeycomb sandwich structure was established and validated to investigate the noise and vibration control effects of the MML damping composites on composite structures. The influences of the types, numbers of layers and application positions of the MML damping composites on the honeycomb sandwich structure were studied. The results indicated that MML design is helpful to improve the damping performance of viscoelastic polymers, but its influence on different damping composites is quite different. For noise control, MML-FD is more suitable for controlling airborne sound propagation, while MML-MCD is more suitable for controlling structural sound propagation. [ABSTRACT FROM AUTHOR]

In the end milling of aluminum honeycomb core, the bottom edge of the cutter and the feed direction of the cutter will have a significant impact on the surface machining quality. If the above two factors are neglected in mechanistic modeling, the surface machining quality will be difficult to improve. In this paper, a mechanistic model considering the bottom edge cutting effect and the anisotropic characteristics of the material is firstly proposed to accurately predict cutting forces. Based on the contact relationship between the bottom edge and the honeycomb wall, a cutting force model of the bottom edge is developed, which includes the geometric characteristics of the bottom edge and the thin-walled edge cutting angle. For anisotropic characteristics of the material, a dynamic variation model of the entry and exit angles in any cutting direction is established on the basis of the structural model of the honeycomb core and cutting edge trajectory. The proposed mechanistic model was validated through a series of milling experiments. The results indicate that this model can be used to predict the cutting force of various parts of the cutter (including bottom and flank edges) and any feed direction. [ABSTRACT FROM AUTHOR]

The response and energy absorption of novel sandwich beams with combined re-entrant double-arrow auxetic honeycomb (RDAH) cores subjected to three-point bending were studied experimentally and numerically. Two typical sandwich beams loaded at different loading positions were considered. Quasi-static three-point bending experiments were conducted to obtain the failure modes and force–displacement curves. The reliable numerical simulation models were further established based on experimental validations. The results indicate that when the loading roller is located directly above the re-entrant cell, the RDAH core sandwich beam has better load-carrying and energy absorption capacity. Subsequently, the influence of face sheet distribution, cell-wall thickness, impact velocity and cell configuration on the structural response were explored. For the sandwich beams with same total mass, the arrangement where the thickness of the front face sheet is larger than that of the back face sheet is beneficial for improving the load-carrying and energy absorption capacity. In addition, the cell-wall thickness has an influence on the local deformation mode of the sandwich beam, and increasing its value can produce more stable deformation and improve the load-carrying capacity. Increasing impact velocity has a significant influence on the initial deformation but little influence on the final deformation of the sandwich beams. As the impact velocity increases, the total energy absorption of the sandwich beam gradually increases, and the negative Poisson's ratio characteristic of the core still exists. Compared to the traditional re-entrant honeycomb (RH) core sandwich beams, RDAH core sandwich beams have better energy absorption capacity and bending resistance. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new assembly design method for structural components is proposed. • Small deformation loads of complex structures are accurately predicted based on Euler theory. • The bionic structure assembly method effectively improves the bearing capacity and heat conduction characteristics. • Battery pack impact resistance and thermal conductivity models are taken as examples to verify the value of structural assembly method. A new assembly design method for structural components is proposed. Inspired by the feathers of the grey crane, which have an energy dissipation effect, novel re-entrant scapus component and novel re-entrant double-crank component are proposed. Novel re-entrant structures are formed by assembling honeycomb structure (HS), poisson structure (PS), and chiral structure (CS). Laser powder bed fusion technology (LPBF) is utilized for the manufacturing of bio-inspired structures. And the impact of structural assembly on mechanical performance is comprehensively analyzed through experimental, numerical, and theoretical approaches. Euler theory is employed to predict the influence of bionic components on structural load trends, while explaining the relationship between compression load and deformation. Specifically, the average load capacity of bio-inspired scapus re-entrant structures and double-crank re-entrant structures exceeds that of their original designs by at least 55% and 13.2%, respectively. Moreover, specific energy absorption increases by a minimum of 8.6% and 3.4%, accompanied by improved heat dissipation performance in these structures. Finally, battery pack impact resistance models as well as thermal conductivity models for electric-powered vehicles are presented as examples to validate the potential application prospects of this novel bio-inspired re-entrant structure in engineering. [ABSTRACT FROM AUTHOR]

CFRP circular cell honeycomb has promising applications in the aerospace field due to its excellent mechanical properties. However, a large number of periodically distributed tearing damages severely restrict the high-quality machining of CFRP circular cell honeycomb. This paper investigates the formation mechanism of tearing damages during end-face grinding of CFRP circular cell honeycomb and proposes suppression strategies. In this paper, a maximum undeformed chip thickness model considering tearing damage distribution is developed, and the evolution behavior of tearing damage is studied by combining the material removal process and grinding force. The grinding force and maximum tearing damage depth in different grinding conditions are analyzed. The results show that the formation of tearing damage in the cut-in stage is related to the weak stiffness of thin walls and the radial grinding force. The radial grinding force and maximum tearing depth can be altered by changing the maximum undeformed chip thickness which can be adjusted for different grinding speeds, feed rates, and offset ratios. The low-damage machining of CFRP circular cell honeycomb can be achieved by using a large offset ratio and variable feed rate. [ABSTRACT FROM AUTHOR]

Arched structures have increased in importance over the last few years due to their high efficiency in bearing loads. This paper introduces arched ribs to the classical re-entrant honeycomb (RH) as reinforced structures, and then its energy absorption is improved by simultaneously utilizing the reinforced structures and the auxetic deformation of RHs. Herein, the in-plane crashing response of reinforced RHs (RRH) under different impact velocities is investigated with finite element methods verified against the quasi-static compression experiment of 3D-printed RRH specimens. By introducing arched structures, the deformation of RHs becomes more stable and regular, and two plateau stresses are produced in the stress-strain curves of RRHs. Benefiting from the stacking deformation of RRHs and pure compression characteristic of catenary arches, the second plateau stress of all-reinforced RHs (ARH) is 3.8 times higher than the first one. Two plateau stresses of ARHs are derivated theoretically with a relative error of less than 7 %. Furthermore, a parametric study is performed to explore the effect of impact velocities, thicknesses, and the height of arched ribs on the crashing response of RRHs. The present investigation paves a new way toward strengthening the energy absorption of conventional honeycombs. [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]

3D printable multi-material honeycombs have attracted increasing interest recently due to the improved elastic moduli, buckling and energy absorption properties. This paper proposes an analytical homogenization for the equivalent in-plane elastic moduli (EIEM) of multi-material honeycombs. First, the axial and bending stiffness of a cantilever beam consist of three sections made of different materials is formulated. Then based on unit cell method and cantilever beam model, the closed-form expressions of EIEM are proposed by fully considering the deformations of both joints and cell walls with arbitrary stiffness, which are sufficiently general to be applied to hexagonal, auxetic and rectangular multi-material honeycombs and validated very well by numerical simulations and experiments. Furthermore, the effects of geometric and material distribution ratios on EIEM are discussed. The results show that the geometric and material distribution ratios of inclined cell wall have a significant effect on all five EIEM while that of vertical cell wall shows a significant effect on shear modulus but only a slight effect on y- direction elastic moduli. Compared with single-material honeycombs, changing joint stiffness has a significant effect on the equivalent Young's moduli and shear modulus but a slight effect on Poisson's ratios. • Closed-form expressions of equivalent elastic moduli for multi-material honeycombs. • Axial and bending stiffness formulated for a dual-material cantilever beam. • Analytical expressions of moduli match well with numerical and experimental results. • Dependency of material and geometric distributions on moduli investigated. • Proposed method applied to multi-material hexagonal and auxetic honeycombs. [ABSTRACT FROM AUTHOR]

Wave-absorbing honeycomb sandwich structure (HSS) is widely used in aviation equipment, playing an important role in the integration of load-bearing and stealth shielding. The high-intensity service of aviation equipment beyond design condition accelerates damage and complicates failure triggers. In this work, a decentralized construction strategy with multiple resonant absorption peaks is proposed to enhance the electrical performance damage tolerance (EDT) of wave-absorbing HSS in 4–18 GHz frequency band. The designed multi resonant absorption peaks for 30 mm thick wave-absorbing honeycomb with 1 mm thick SiO 2 fiber reinforced epoxy resin (SiO 2f /ER) composites as top and bottom panels occur in the vicinity of 5 GHz, 9 GHz, 13 GHz, and 17 GHz, respectively. When the panel damage area accounts for 72 % or the penetrating damage area accounts for 18 %, the effective absorption bandwidth (EAB) of proposed HSS covers 4–18 GHz, indicating excellent EDT. By analyzing the normalized impedance, Smith chart, as well as power loss density, the excellent EDT is attributed to the pinning effect at each resonant frequency point, which benefits both impedance matching and electromagnetic wave (EMW) attenuation. [ABSTRACT FROM AUTHOR]

Negative Poisson's ratio honeycombs have been widely studied in recent years due to their unique mechanical properties. A tetrachiral honeycomb (TCH) exhibits a bulging effect when subjected to in-plane impact, reducing its Poisson's ratio effect. To improve the performance of TCH, this study proposes two types of axisymmetric tetrachiral honeycombs (ATCH-1 and ATCH-2). First, the in-plane impact performances of TCH, ATCH-1, and ATCH-2 are compared via experiments, and the accuracy of the finite element model is validated. Then, the effects of the different parameters on the deformation modes, energy absorption characteristics, and negative Poisson's ratio effects of the three types of honeycombs are analyzed via finite element models. ATCH-1 and ATCH-2 have higher specific energy absorption (SEA) and a more significant negative Poisson's ratio effect than TCH at an impact velocity of 10 m/s. However, the axisymmetric honeycombs do not have advantages at impact velocities of 50 m/s and 100 m/s. The cylindrical radius r significantly affects the deformation mode of the three types of honeycombs. The axisymmetric design provides a new concept for the novel negative Poisson's ratio honeycomb design. [ABSTRACT FROM AUTHOR]

Enhancing the stiffness of high-porosity honeycomb sandwich panels is a critical research field. To address this issue, a novel improved star-shaped honeycomb sandwich panel (SP-ISH) is designed by replacing the sharp corners with cubic struts and elongating the inclined ribs of the traditional star honeycomb. To fill the gap between global behaviors and local field distribution, an asymptotic analysis of the energy functional stored in periodic unit cells is performed. Based on the obtained effective plate properties, a two-dimensional equivalent downscaling model (2D-EDM) is developed and validated through comprehensive comparisons with results from 3D-printed experiments and 3D FE models, including assessments of static displacement, global buckling, and local field distribution. Furthermore, the effects of material and structural parameters on the effective plate properties and static performance are systematically investigated. The results reveal that the slenderness ratio of the rib and the core height-width ratio have the strongest influence on the equivalent tensile stiffness and bending stiffness, respectively. Notably, the SP-ISH outperforms other star-shaped honeycomb panels in specific stiffness, deformation resistance, and buckling load capacity due to the extended ribs and added struts. The study's findings provide valuable insights for future designs and applications of this honeycomb structure. • A novel improved SSH is designed by adding the cubic struts and elongating the inclined ribs. • The VAM-based 2D-EDM of SP-ISHs is developed and verified by comparing with 3D-FEM results. • The influence of material and structural parameters on static performance is systematically studied. • The increasing core height-width ratio can significantly enhance the deformation resistance of SP-ISP. • The cross-ply SP-ISH has high equivalent stiffness to achieve more balanced performance. [ABSTRACT FROM AUTHOR]

Negative Poisson's ratio honeycombs have been extensively studied due to their unique mechanical properties. In this paper, a novel negative Poisson's ratio honeycomb (NPH) is proposed by introducing a reinforced strut into the negative Poisson's ratio honeycomb (NPR). A finite element numerical model was constructed using Abaqus/Explicit, and the accuracy of the model was verified, and a series of researches were carried out. First, the mechanical properties of NPH at different angles were analyzed under different loading conditions, and the results showed that under the loading conditions of y-direction and x-direction, NPH-120 and NPH-105 had the best mechanical properties respectively. Subsequently, the mechanical properties of NPH at different velocities were studied. The research showed that the NPR effect of NPH was the most obvious under low-velocity impact, and as the velocity increased, the inertia effect increased, and NPH's deformation mode has changed. And the dynamic Poisson's ratio of NPH at medium-velocity is analyzed, and its energy absorption mechanism is analyzed through the deformation of subunits. Finally, the mechanical properties of NPH under different wall thicknesses were studied, and the mechanical properties of several typical reinforced supports and NPH-120 were compared. [ABSTRACT FROM AUTHOR]

To enhance the mechanical properties of Nomex honeycomb, the honeycomb was foamed in-situ using rigid polyurethane (PU) foam and flexible polyurethane foam (NHRPU, NHFPU, collectively NHPU). Mechanical properties were studied based on tests, theoretical and finite element (FE) methods, respectively. The results showed that NHRPU and NHFPU improve the energy absorption by 85.25% and 47.27% compared to the sum of PU and honeycomb alone. The specific energy absorption (SEA) of NHRPU is improved by 21.76%, while the SEA of NHFPU decreases, NHRPU significantly improves in terms of the honeycomb energy absorption performance, while NHFPU enhances the resilience of the honeycomb. The mesoscale FE model and equivalent FE model were constructed to achieve better prediction of NHPU. 75.6% energy absorption and 19.8% SEA can be improved by NHPU as a core-filled thin-walled tube compared with empty tube, and the passive safety protection capability is significantly improved by applying NHPU-filled structures in railway vehicles. [ABSTRACT FROM AUTHOR]

• The negative mass meta-honeycomb is designed and fabricated, whose impact wave resistance is verified by experiments and simulations. • The negative mass property and the directional bandgap property of the local resonance plate are investigated to form wider bandgaps to enhance the impact resistance of the honeycombs. • The energy absorption performance of the meta-honeycombs is strengthened by coupling different resonators. Impact and blast waves are difficult to isolate entirely because of their tremendous energy and wide-band characteristics. In this study, the meta-honeycombs are designed by adding the local resonance plates (LRP) to the honeycombs to improve the impact resistance. The negative mass property and the directional bandgap property of the LRP are investigated to form wider bandgaps to predict the impact resistance of the meta-honeycombs. For one thing, in the corresponding frequency range of the equivalent negative mass, the LRP and the impact wave vibrate towards each other, which can resist wave propagation. For another, when the frequency of impact energy is concentrated in the directional bandgap, the energy is trapped in the vibrations of the LRP plate, accelerating the attenuation of the impact wave. It is verified that the three meta-honeycombs, whose cores are re-entrant, hexagonal, and semi-re-entrant honeycombs, can effectively protect the stability of the structure against impact and blast waves through experiments and simulations. Further, the mechanical properties of the meta-honeycombs are optimized by coupling the bandgap generated by the LRP containing different resonators. The universality of the design method lays the foundation for engineering application. [ABSTRACT FROM AUTHOR]

The fundamental challenge for microwave-absorbing honeycomb composites with grading coating thickness is the unsatisfactory absorption bandwidth. In this work, an effective equivalent permittivity prediction model was established based on the homogenization method, also both the result of calculations and simulation exhibit good consistency which indicates the validity of the model. Furthermore, in-depth analysis was done on the impact of structural factors like honeycomb height and coating thickness on single layer microwave absorption. Finally, both the microwave absorption properties and the electromagnetic response of grading honeycomb microwave absorbing composites were investigated which show a bright future in reducing electromagnetic wave irradiation and interference. The present work could provide a powerful theoretical basis for designing advanced grading honeycomb microwave absorbing composites. [ABSTRACT FROM AUTHOR]

Honeycomb sandwich structures, especially those with carbon-fiber panels and Nomex-honeycomb cores, are widely employed in automobiles and aircraft due to their excellent mechanical properties. Here, in-plane compression and 4-point bending experiments, as well as FEM simulations, are performed for a composite honeycomb sandwich structure with face-core de-bonding defects or impact damage to evaluate the damage sensitivity. It is found that the structure exhibits a higher sensitivity to impact damage than to de-bonding defects. Impact damage caused by an energy of 3 J–5.5 J can alter the failure mode under both in-plane compression and 4-point bending loads, and reduce in-plane compression strength by more than 50 % and 4-point bending strength by 15 %. In comparison, de-bonding defects of the same size can change the failure mode and decrease the strength by only 10 % under in-plane compression. The developed FEM model predicts all failure modes and residual strengths obtained from experiments. The simulation results show that the structural characteristics of producing concaves in the facesheet and core are the dominant contributors to structural failure. Our model, covering all geometric and structural details of the honeycomb core, provides a useful tool for studying the mechanical behaviors of such structures. [ABSTRACT FROM AUTHOR]

• A novel auxetic honeycomb (NAH) combined with chiral and re-entrant was proposed. • The EA and SEA of NAH are improved under Quasi-static compression and impact. • Under high-velocity impact, the EA of NAH is better than hexagonal honeycomb. • NAH with thickness gradient shows obvious auxetic behavior under high-velocity impact. Auxetic metamaterials as a cutting-edge field have attracted extensive attention from researchers because of their peculiar deformation mode and excellent mechanical properties. However, the unstable deformation and low stiffness of auxetic structure limit their potential development. To address these limitations, a novel auxetic honeycomb (NAH) has been proposed by combining an original re-entrant hexagonal honeycomb (RH) with cross-chiral honeycomb (CH). The proposed structure has higher stiffness than RH, and more stability than CH. Additionally, the stiffness, densification point, and auxetic behavior can be adjusted by the angle of cell ribs (θ). In this study, the static mechanical properties and deformation behavior of NAH are investigated experimentally and numerically. Furthermore, the energy absorption and deformation behavior of NAH under different impact loadings (low-, medium- and high-velocity) are investigated numerically. Finally, a series of functionally graded NAHs with varying thicknesses are studied to improve the impact resistance of NAH. The results show that NAH has better specific energy absorption than RH and CH under static compression. Moreover, NAH with θ < 90 ° exhibits greater energy absorption capacity compared to NAH with " θ > 90°" at high-velocity impacts. [ABSTRACT FROM AUTHOR]

Lantern, also known as coloured-lantern making, is known for being an ancient traditional craft in China that can be dated back as early as West Han Dynasty. Inspired by the lantern, the lattice element is built by vertically rotating and duplicating the 2D units, then the 3D auxetic metamaterial is formed by connecting the 8 ligaments of the lattice element on two perpendicular planes. As the elastic behaviors associated with this metamaterial are still almost unknown to a large extent, in this study, an analysis has been conducted to investigate how the geometric parameters related to the lattice design influence its elasticity. For this reason, a novel 3D lantern-shaped honeycomb structure (LSH) has been proposed, the Castigliano's second theorem, energy principle, and Moore's theorem are utilized to solve its Young's modulus and Poisson's ratio in the three main directions. The theoretical results exhibit good agreement with the numerical and experimental results. The results showed that the elasticity of LSH structures can be programmed by adjusting a range of geometric parameters. In addition, LSH features a bidirectional zero Poisson effect and a good stress distribution during compression. It shows potential in terms of load-bearing to meet the requirement of lightweight and high stiffness. This structure shows good promise for applications in aerospace, construction and other fields. [ABSTRACT FROM AUTHOR]

Sandwich panel with Honeycomb Filled with Circular Tubes (HFCT) as core is numerically investigated by using ABAQUS/Explicit in this study. To calibrate the numerical model, the panels equipped with conventional hexagon honeycomb cores are modeled. Good agreement between numerical and experimental results is achieved. The sandwich panels with HFCT are compared with the sandwich panels with Honeycomb and Multi-tube cores of identical mass subjected to vertical and oblique impacts. The maximum displacement of face-sheets, plastic energy absorption, boundary reaction forces and impact load time history are calculated to assess the impact resistant capacity. The panel with HFCT core has smaller rear face-sheet displacement and higher energy absorption capacity as compared to the panels with the Multi-tube and Honeycomb core. Under oblique impact, both HFCT and Multi-tube panels have superior impact resistant capacity than the Honeycomb panel. In addition, the impact resistances of four types of multi-arc tube filled Honeycomb (HFMT) are also analysed. Their performances under vertical and oblique impacts are compared with those of HFCT. [ABSTRACT FROM AUTHOR]

Abstract Static and fatigue behaviors of Nomex honeycomb sandwich structures were characterized by compression and bending experiments. And the finite elemental numerical simulation research was carried out based on the test data. The load level for fatigue test was determined and the necessary stiffness information for the construction of finite element model was provided by the study of static load performance. The fatigue failure mode and damage mechanism of Nomex honeycomb sandwich structures were analyzed by comparing the fatigue life curves and experimental phenomena of bending fatigue and compression tests. This study presented a method to predict the fatigue life of honeycomb sandwich structures and its feasibility was verified by experiments. [ABSTRACT FROM AUTHOR]

Abstract In this article, an analytical model is derived to investigate the in-plane homogenized stress-strain relationship of an adhesively bonded commercial hexagonal honeycomb core under large deformation. The model incorporates some advanced features of the core cell such as cell wall curvatures, node bond adhesive layers, and adhesive fillets at the cell wall intersections in the analysis. Nonlinear homogenized results of the fiberglass/phenolic honeycomb core predicted by the analytical model are compared with test data as well as predictions from finite element models (FEMs) of both real and idealized (without modeling the node bond adhesive) core cells to investigate the effects of the node bond adhesive. Predictions of the analytical model are in good agreement with the test data and predictions of the FEM of the real core cell. Homogenized properties of the honeycomb core obtained from the analytical model at infinitesimal strains are compared with several analytical models from the literature. Adhesive peel stress is also calculated by the analytical model and compared with the FEM. [ABSTRACT FROM AUTHOR]

Abstract Disbond damage propagation in honeycomb core sandwich structures is investigated numerically and experimentally. A fully parametric two-dimensional finite element model of a disbonded honeycomb core sandwich specimen is presented. Energy release rate and mode-mixity were numerically determined using the Crack Surface Displacement Extrapolation (CSDE) method. An advanced method was adopted to obtain the homogenized mechanical properties of the honeycomb core based on the geometry of a single honeycomb cell and the material properties of the cell wall paper. The numerical model was benchmarked against CFRP/Nomex® Single Cantilever Beam (SCB) specimen tests and a closed-form semi-analytical model. The results show a close agreement between analytical, numerical and experimental energy release rate, as well as analytical and numerical mode-mixity. An extensive sensitivity analysis was also carried out and the effects of the geometry and the material properties of the SCB specimen on the energy release rate and mode-mixity have been investigated. [ABSTRACT FROM AUTHOR]

Abstract Damage severity of sandwich panels to underwater explosion load depend not only on the shock factors, but also on the fluid behind the structure. Underwater explosion tests were performed on water-backed sandwich panels to examine the deformation and failure of such composite structure. The dynamic blast response of water-backed sandwich panel was investigated using the LS-DYNA software. An analytical three-stage model was developed for the deformation history of water-backed sandwich panel subjected to shock loading in water. Blast resistance of water-backed sandwich panel was compared with monolithic plate of equivalent areal mass and air-backed sandwich panel with the same configurations. Water-backed sandwich panel exhibited the best deformation/damage resistant capability. Compared with air-backed sandwich panel, core material exhibited greater volumetric strain when the sandwich structure wetted on both sides. Overpressure in the water behind structure was reduced to about 7% by using sandwich structure over monolithic plate of equivalent thickness. Present study led to the apprehension of dynamic response of water-backed sandwich structure to underwater blast load, thereby developed useful guidelines for the design of blast-resistant structural systems. [ABSTRACT FROM AUTHOR]

Abstract This study is focused on the influence of constraints on the extensional in-plane modulus of isolated honeycomb core (HC) and honeycomb core sandwich elements. Such constraints develop when the core is bonded to stiff face sheets. Finite element analysis (FEA) is conducted on unconstrained and constrained HC core under inplane loading. FEA results for the extensional in-plane modulus and Poisson ratios of isolated unconstrained HC core are in good agreement with estimates from the classical Gibson-Ashby analysis. Such analysis reveals that the isolated core has very low extensional modulus ( E x ) and large Poisson ratio ν x y . Constraints imposed on the lateral deformation of the core substantially increased the effective axial stiffness. In the limit of equal biaxial strains, the increase was close to a factor of 1000. The FEA results for the effective modulus of the HC core sandwich element are in good agreement with predictions from classical laminated plate theory. [ABSTRACT FROM AUTHOR]

Abstract In this study, sandwich panels with carbon/epoxy composite skins and an magnetorheological elastomer (MRE) honeycomb core in different proportions of magneto/elastomer (w/w%) are manufactured and studied numerically and experimentally. Test specimens in the beam form are subjected to free and forced vibrations and evaluated with and without the presence of an external (until 120 kA/m) magnetic field, positioned on the free end and on the center of the beam. The experimental results showed good performance in the attenuation of vibration level, especially on the fundamental vibration mode of the structures in question. The applied magnetic field on the free end of the test panel was capable of reducing until 37.45% their first natural frequency value. It can be noted from numerical and experimental results that sandwich panel with MRE honeycomb shifted the natural frequencies due to the increase of an induced magnetic field, especially for the first mode shape. [ABSTRACT FROM AUTHOR]

Abstract Recently, auxetic honeycombs have attracted considerable attention for their excellent mechanical properties, especially the potential applications for energy absorption. In this paper, a novel re-entrant auxetic honeycomb is proposed and named as re-entrant star-shaped honeycomb (RSH), with the in-plane impact responses explored theoretically and numerically. Three types of microstructural deformation modes are observed under different impact velocities, including low-velocity mode, medium-velocity mode and high-velocity mode. Moreover, a deformation map is summarized to illustrate the effects of the impact velocity and the relative density on the deformation modes. Two typical plateau stress regions are detected under low-velocity impact loading, and the second plateau stress is almost twice higher than the first one. The transverse contraction of the RSH mainly occurs at the first plateau region, which is different for the classical re-entrant honeycomb (RH). In addition, the absorbed energy of the RSH decreases slightly and then increases with the impact velocity. The results of the finite element simulations suggest that the RSH shows more excellent impact resistance, compared with the RH and SSH with same cell wall thickness. Furthermore, the effects of the cell wall thickness and the impact velocity on the crushing strength of the RSH are discussed, and the theoretical results are in good agreement with the finite element simulations. [ABSTRACT FROM AUTHOR]

Abstract This paper mainly concerns effects of the auxetic structure on the crash performances in terms of the axial crash force, specific energy absorption, and deceleration, which are evaluated with the conventional and honeycomb structures. Based on the systematic design procedure, the re-entrant units for the auxetic structure are regularly arranged in the tube wall, which are produced by the additive manufacturing with SUS316L metal powder. Under the low impact condition, the auxetic does not only exhibit higher specific energy absorption, but also demonstrate substantially low deceleration due to effect of the densification during the axial crash compared with the conventional tube. Furthermore, while the honeycomb tube demonstrates oscillating behavior in the deceleration, the auxetic tube tends to maintain steady deceleration after the first peak during the axial crash, which is able to guarantee enhanced damping performances under the low impact condition. [ABSTRACT FROM AUTHOR]

Abstract It is generally acknowledged that the indentation resistance or hardness of auxetic materials is higher than that of their conventional counterparts under elastic deformation. However, this property of the auxetic material may not always be superior to that of the non-auxetic materials when the deformation is relatively large with plasticity considered. In this study, we come up with an index to quantitatively depict the indentation resistance of the hexagonal honeycombs under large deformation. The indentation resistance of both the auxetic and non-auxetic hexagonal honeycombs is compared and discussed. Results show that in the premise of honeycombs possessing the same relative density, the indentation resistance of auxetic hexagonal honeycombs is not always higher than that of the non-auxetic honeycombs. This phenomenon is verified by the numerical simulations. Further analysis shows that there is a critical value of the absolute value of Poisson's ratio, which is determined by the cell-wall length ratio, to estimate the higher indentation resistance between the auxetic and non-auxetic hexagonal honeycombs. The influence of indentation velocity is also analyzed based on numerical simulations. This present work is supposed to shed light on the design and evaluation of the indentation resistance for both auxetic and conventional honeycombs. [ABSTRACT FROM AUTHOR]

Abstract The cell-wall thickness induced and cell-wall angle induced piecewise linear graded honeycombs (PLGHs) are presented and investigated under in-plane compression. Effects of cell-wall angle on the strength of honeycombs are discussed. Results reveal that the normalized crushing strength displays similar variety to that of the shape ratio within a given range. Based on this, traditional theoretical models of plateau stresses are improved. Comparative studies on different kinds of PLGHs are conducted. Quasi-static and dynamic deformation mode, strength and energy absorption capacity are intensively discussed. Both weak-to-strong and top-to-bottom layer-by-layer deformation mode are observed. Comparison of strain-stress curves shows that cell-wall angle induced PLGHs generally express lower level of stress than that of cell-wall thickness induced PLGHs under quasi-static compression, but the difference is insignificant as the crushing velocity increases. Theoretical prediction is also conducted to estimate the stress level under quasi-static and high crushing velocities. Both the constant velocity and initial velocity loadings are applied to studying the energy absorption capacity. It is interesting to note that cell-wall angle induced PLGHs shows a time saving characteristic as the normalized initial kinetic energy increases from 0.75 to 1, which has not been discovered in other types of honeycombs. [ABSTRACT FROM AUTHOR]

Abstract Predicting the honeycomb sandwich's response to impact loading is a major challenge in the aeronautical industry. Several papers demonstrated the possible use of non-linear springs to model Nomex's impact behavior. On the other hand, the authors show that the lack of transverse shear consideration constitutes a real limitation. The aim of this study is to overcome this limitation by introducing a compression/shear coupling to take into account the transverse shear. In this approach, the modelling of a low velocity impact test is performed on a sandwich composite with CFRP skins and Nomex® honeycomb. Composite skins are modeled as an elasto-plastic-damage material using a user field surbroutine (Abaqus©). The Nomex core is modeled with non-linear springs integrating a compression/shear coupling behavior. Then, the sandwich response under low speed impact is realized and compared with experimental data leading to a good correlation. [ABSTRACT FROM AUTHOR]