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The performance of a multi-layer honeycomb skeleton can be significantly enhanced through tandem connection, while the structure's properties can be tailored by altering the layer stacking method of the honeycomb skeleton. To investigate the impact of layer stacking methods on the mechanical properties of multilayer honeycomb skeletons, 3D printing technology was used to prepare double-layer honeycomb skeleton tandem structures with different dislocation modes in compression testing. A finite element simulation model was established to conduct quasi-static simulation research. Compared to that of a single-layer honeycomb skeleton, the energy absorption of the honeycomb skeleton tandem structure increased. The optimal bearing capacity of the honeycomb skeleton was achieved when the upper and lower layers were precisely aligned. Once dislocation occurred, both the value of average platform stress and energy absorption decreased. Then, the bearing capacity of the honeycomb skeleton tandem structures increased with an enlargement of the dislocation, reaching its maximum at the half-dislocation period. An increase in the partition thickness and stiffness led to a reduction in the dislocation-induced effects on the mechanical properties. The research results can provide theoretical and data support for the engineering application of honeycomb skeleton tandem structures. [ABSTRACT FROM AUTHOR]

• Inspired by self-similar evolution, a novel concave-convex hierarchical honeycomb (NCHH) is proposed. • The NCHH show the characteristics of concave and convex, and the energy absorption characteristics of concave honeycomb is better than that of convex honeycomb. • Reasonable configuration of self-similarity coefficient, angle and wall thickness can effectively improve the crashworthiness of the structure under axial impact. A novel bi-directional hierarchical honeycomb is proposed. A finite element numerical model was constructed using Abaqus/Explicit, the model's accuracy was verified, and a series of in-plane impact studies were carried out. Firstly, the mechanical properties of axial impact were analyzed for different bi-directional hierarchical honeycombs. The results show that the mechanical properties of NBHH- h 1 h 2 2 h 3 -III and NBHH- h 1 h 2 h 3 h 4 -IV are the best and almost identical. Subsequently, the mechanical properties of NBHH-X h x Y h y -IIs with different layers were analyzed. Research results show that NBHH- h 3 3 h 4 -II has a 77.96 % increase in specific energy absorption (SEA) compared to NBHH- h 1 3 h 2 -II, and NBHH- h 1 3 h 2 -II has a 116.02 % increase in SEA compared to NBHH-3 h 1 h 2 -II. A parametric study of NBHHs was conducted. The mechanical properties of NBHHs with different layer ratio coefficients were analyzed, and it was found that the mechanical properties of NBHHs with l 2 = 12 and k = 0.2 are the best. Finally, the effects of wall thickness and velocity on NBHHs were analyzed. Increasing the wall thickness appropriately can effectively improve the impact resistance of the structure. Bi-directional hierarchical design provides a practical reference for enhancing the in-plane mechanical properties of honeycombs. [ABSTRACT FROM AUTHOR]

The battery-pack system of electric vehicles is prone to collide with low obstacles on the road, causing battery short circuits and even explosions. It poses a great safety threat to passengers and drivers. The honeycomb structure's high energy absorption and lightweight properties have made it a popular choice in the automotive industry. This paper designs different bio-inspired honeycomb structures to a battery-pack system of electric vehicles to improve the crashworthiness performance. The effects of different bio-inspired honeycomb structures on the crashworthiness of a battery-pack system during frontal impact are analyzed based on a nonlinear finite element model. First, the geometric parameters of seven different bio-inspired honeycomb individual units are described. The overall structure of the honeycomb is applied to a battery-pack system. Second, the nonlinear finite element model of a battery-pack system and honeycomb structures are established and verified. Then, collision simulations are conducted. The deformation and the maximum stress of a battery-pack's bottom shell are computed. The energy absorbed by the honeycomb structures during frontal impact are investigated. The results indicate that the proposed bio-inspired honeycomb structure mimicking grass stems improves the safety performance of battery-pack systems most. Finally, a parametric design is carried out on the bio-inspired honeycomb structure. The effects of wall thicknesses and the number of replacement hexagons on the crashworthiness performance are analyzed. The honeycomb structure preforms best when thickness is 1 mm and the number of replacement hexagons is 2 and 4. The optimized bio-inspired honeycomb structure reduces the deformation of the battery-pack' bottom shell by up to 30%, and maximum stress by 10%. • The deformation, maximum stress, and energy absorption are investigated. • The effects of seven bio-inspired honeycomb structures are analyzed. • Parametric design is carried out to further improve the crashworthiness performance. • The deformation of the bottom shell can be reduced by up to 30%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel viscoelastic cell arrays are incorporated in a bicycle helmet liner. • Shear and compressive response of the cells are controlled via changing their curvature. • Significant improvements with the novel cell arrays over conventional EPS foam. • Shear-compliant cells can significantly reduce rotational kinematics and brain strain. • Placement of cells with varying amounts of shear stiffness should be optimised. Rotational head motion is one of the major contributors to brain tissue strain during head impacts, which damages axons and vessels and leads to traumatic brain injury. Helmet technologies have come to market promising enhanced protection against such rotational head motion. We recently introduced novel air-filled viscoelastic cell arrays and showed that their shear response under oblique impacts can be tailored through altering the cell wall curvature. We found that concave cells provide shear stiffness that is a few folds larger than that of convex cells. Here we test whether altering the cell curvature can reduce head rotational kinematics and brain strain and whether the viscoelastic cell arrays outperform the reference EPS foam-based liner. To test these hypotheses, we incorporate the viscoelastic cell arrays in a bicycle helmet liner. We use validated finite element models of the helmet and replace the liner with validated finite element models of the cellular cell arrays. We simulate oblique impacts at different locations to represent a wide range of real-world bicycle head impacts. In all cases, the head kinematics and brain deformation metrics indicate significant improvements with the novel cell arrays over the conventional EPS liner. We show that the shear-compliant cell arrays can reduce head rotational acceleration by as much as 64 % and brain strain by 69 %, but not in all impact locations. Cell arrays with similar axial stiffness yet lower shear stiffness often bottomed out, indicating that a considerable amount of energy is dissipated via cell shearing around the impact zone. Our results show that placement of cells with varying amounts of shear stiffness should be optimised, with the most shear-compliant cells near the crown and the least near the temples. This study shows the promising performance of viscoelastic cell arrays in protecting the head and brain under oblique impacts and provides avenues for optimising the distribution of their compressive-shear properties. [ABSTRACT FROM AUTHOR]

Recently, auxetic metamaterials have turned into an area of growing interest, because of their deformation uniqueness, design flexibility, and functional diversity. To achieve their programmable design of densification and energy absorption, the variable stiffness factor method (VSF) emerged. However, the energy absorption capacity of the metamaterials designed by this method has a significant reduction. In this work, to remedy this defect, several different lightweight specimens are proposed and fabricated to extend the stage of energy absorption and retain the tunability. Then quasi-static compression tests and finite element methods are carried out to analyze the mechanical properties of the designed boundary-constrained structure (BCS) and X-shape constrained structure (XCS). The accuracy of the densification points and energy absorption capacity of the two structures at different VSF values are also studied. The results show that the densification points of the designed structures can be adjusted quantitatively, and their deformation modes are more stable than conventional structures during compression. Furthermore, their specific energy absorption is four and five times higher than that of non-lightweight structures with VSF = 40%, respectively. These findings contribute to advancing the implementation of auxetics in applications of multistage protective structures. • A lightweight metamaterial based on the variable stiffness factor (VSF) method is proposed. • The proposed structures realize multi-level energy absorption and stable deformation. • The SEA of proposed structures was 4 and 5 times higher than that of VSF = 40% structure. [ABSTRACT FROM AUTHOR]

• A novel EARE is designed by introducing an elliptical annular into RE cell. • EARE produces extra vertical support without hindering lateral deformation. • EARE concurrently enhances auxetic performance, stiffness, and SEA. • Adjusting geometric parameters rationalizes designing mechanical properties. Auxetic structures have sparked a lot of interest due to their excellent mechanical characteristics and unusual negative Poisson's ratio influence. However, the large porosity property results in low stiffness, which limits their application scope. Current approaches to augment stiffness often result in diminished auxetic performance. Therefore, it is challenging to simultaneously enhance the auxetic, stiffness and energy absorption capacity of auxetic structures. To address this issue, this paper proposes a novel elliptical annular re-entrant honeycomb (EARE) by introducing an elliptical annular structure into a conventional re-entrant honeycomb (RE) cell, which can provide extra longitudinal support without hindering lateral deformation. The plateau stress, Poisson's ratio and energy absorption properties of the EARE are investigated by quasi-static compressive tests and finite element modeling. The results show that the EARE honeycomb has two plateau stages due to the supporting effect of the elliptical annular structure. Compared with the conventional RE honeycomb with the same wall thickness, the EARE honeycomb not only exhibits a stronger auxetic effect embodied in the Poisson's ratio reduced by 5.19%, but also has a higher average plateau stress and a higher specific energy absorption of 171.63% and 28.03%, respectively, which significantly improves the stiffness and energy absorption performance. The parameterized analysis reveals that by appropriately adjusting the geometric parameters, the stiffness, energy absorption, and auxetic effect of the EARE honeycomb can be enhanced. The research findings address the conflict between auxetic performance and honeycomb stiffness, providing new insights into the optimization of honeycomb structure design. [Display omitted] [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]

Novel honeycombs with buckling-induced features and tailorable properties have been designed and fabricated using the fused deposition modeling (FDM) method. Quasi-static out-of-plane compression tests were carried out to investigate the topological dependence of the crushing behavior of the buckling-induced honeycombs (BIHs). The results demonstrated that the crushing performance of BIHs can be artificially controlled by altering their shape parameters. In particular, the initial peak force (IPF) and the undulation of the mechanical response of BIH can be effectively reduced by increasing the layer number or arranging the asymmetric layers. A finite element model validated against experimental results was also utilized to reveal the underlying deformation mechanism and study the corresponding displacement-crushing force responses for BIHs with different topological parameters. It was uncovered that the buckling-induced mechanism is beneficial for tuning the stiffness and mitigating local buckling resistance through the pre-determined collapse behavior of cell walls. Further, a multi-objective optimization process of BIH was performed to seek the optimal design solution for energy-absorbing structures in specific scenarios. The findings of this study provide a theoretical basis for the development of new ideas and optimization solutions for the design of lightweight and performance-tailored energy-absorbing structures. [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]

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 A novel triangular tube reinforced corrugated honeycomb, which is professionally termed as ripplecomb, is proposed by integrating triangular tubes with sine-wave corrugated plates to construct a quasi-hexagon honeycomb structure. The mechanical performance of ripplecomb under quasi-static out-of-plane uniform compression is investigated based on three-dimensional finite element method. Combining the eccentricity factor, amplitude factor with the basic folding mechanism, an analytical approach based on rigid perfectly plastic model is applied to predict the mean impact force of the ripplecomb under quasi-static axial crushing loading theoretically. The mean crushing force obtained from analytical model is well consistent with those of the simulation. Besides, parametric investigations are carried out to explore the influence of the wave amplitude, wave number and cell-wall thickness on the out-of-plane crashworthiness performance of the ripplecomb structure. The numerical results demonstrate that the ripplecomb structure can improve the specific energy absorption as well as lowering the initial peak force compared with the traditional hexagonal honeycomb structure. This work indicates that the proposed hybrid ripplecomb structure exhibits superiority in energy absorption as crushing protection structures in comparison with conventional lightweight constructions with identical mass. [ABSTRACT FROM AUTHOR]

• Comparative impact tests of novel FHCB were performed. • Foam filling enhances impact resistance. • Gradient design can optimize foam energy absorption. Auxetic structures have attracted a lot of attention as they can meet the requirements of impact resistance and lightweight performance of protective structures in aerospace and defense industries. To enhance the impact resistance and improve the capacity of energy absorption of auxetic structures, foam-filled hybrid-chiral honeycomb beams (FHCB) were designed and fabricated through SLM (Selective laser melting) printing method and foaming method. The localized impulse loading was generated through the impact from foam projectile, accelerated by light gas gun. The dynamic responses of EHCB (empty hybrid-chiral honeycomb beam) and FHCB were compared. In the experimental results, FHCB showed enhanced impact resistance and higher SEA (specific energy absorption) value than EHCB. A validate finite element model was used to study the influence of cell-wall thickness on the impact resistance of EHCB and FHCB. Results indicated that by changing the cell-wall thickness, the potential energy absorption capacity of the filled foam can be fully utilized. Furthermore, the impact resistance of FHCB can be effectively improved by using a gradient cell-wall thickness arrangement. This study can provide reference for the optimal design of blast mitigation and impact resistant structures. [ABSTRACT FROM AUTHOR]

The mechanical behavior of honeycomb sandwich structures under low-velocity impact is of great significance. An experimental and numerical investigation on surface deformation and energy absorption subjected to low-velocity impact is undertaken. A high-speed camera system is employed to record the acceleration attenuation process of the impactor, a projection profile system is introduced to measure the surface profiles of the panel and the depth of the ultimate indentation is obtained. A three-dimensional finite element model is constructed and validated by the experimental results. Indentation characteristics and energy absorption are analyzed and in good agreement with experimental data. Effect of adhesive layers on energy absorption is discussed and the contribution of the facesheets and the honeycomb core to the energy absorption process is analyzed separately. Results shown that the effect of adhesive layers on energy absorption is non-ignorable and the honeycomb core plays a dominant role in energy absorption. Most of the energy absorbed by the honeycomb sandwich panel is expended as plastic dissipation, and the rest is transformed into strain energy. [ABSTRACT FROM AUTHOR]

• Novel layered aux-hex honeycomb (LAHH) filled tube (LAHHFT) structures are designed and investigated. • Aux-hex interaction and LAHH-tube interaction lead to superior energy absorption performance. • Theoretical models are carried out to describe the double interaction effect. • Deformation modes of the LAHHFT structures are recognized and theoretically interpreted. In this work, a novel layered aux-hex honeycomb (LAHH) filled tube (LAHHFT) structure is proposed and investigated. A series of LAHH and LAHHFT structures with different number of aux-hex interfaces is designed and analyzed via extensive finite element analyses (FEAs). The results indicate that the designed LAHH and LAHHFT structures possess significantly higher effective Young's modulus, mean crushing stress (MCS) and specific energy absorption (SEA) than the single honeycombs and single honeycomb filled tubes under the same relative density. Double interaction effect, i.e. aux-hex interaction and LAHH-tube interaction, contributes to the superior improvement. Quantification of the interaction effect shows that the relative improvement of the MCS and SEA due to the double interaction effect could reach up to 617% and 557% for the LAHHFT structures. Theoretical models are carried out to predict the mechanical and crushing stress properties of the proposed hybrid structures considering interaction effect, which agree well with the FEA results. Besides, the interaction also affects the deformation modes of the LAHH and LAHHFT structures, which in turn influences the energy absorption performance. Three different crushing deformation modes including global bending mode, straight folding mode and mixed deformation mode occur to the LAHHFT structures. A theoretical model is also established and provides a good explanation to the change of deformation modes. This study offers a new route and a useful guideline for the design of future high-performance light-weight materials and structures. [Display omitted] [ABSTRACT FROM AUTHOR]

• Impact response of AHS and AlHS sandwich structure was compared. • Ballistic limits and EA was obtained against conical and hemispherical projectile. • EA was enhanced by increasing cell and facesheet thickness, reverse for cell size. • A higher specific energy absorption was obtained in AHS as compared to AlHS. This study investigated the perforation phenomenon of aramid and aluminium honeycomb sandwich structures under high-velocity impacts and compared the impact responses experimentally and numerically. The dimension of the face sheets used was 1 mm in thickness and 220 mm in diameter, and for both the honeycomb cores, the cell thickness of 0.05 mm and the cell size of 3.2 mm was used. Ballistic impact tests were conducted by employing a pneumatic air gun to study damage behavior and failure modes under different impact velocities between 35 m/s and 150 m/s using conical shaped and hemispherical shaped projectiles. Three-dimensional finite element models were implemented in ABAQUS/Explicit to model sandwich panels. The numerical model was validated with experimental data and, subsequently, the numerical study was further extended to study the effects of different geometrical parameters affecting the impact response of sandwich structures. The results showed that for the ballistic limit, sandwich structure having an aluminium honeycomb core performed better than the aramid honeycomb core by 3.09% and 2.5% against conical and hemispherical projectiles, respectively. However, the aramid honeycomb structure was proven to be more efficient than the aluminum honeycomb structure in terms of energy absorption and specific energy absorption. [ABSTRACT FROM AUTHOR]

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

• The dynamic responses and energy absorption characteristics of aluminium honeycomb sandwich panels under ice wedge impact are investigated. • A three-dimensional nonlinear finite element model of AHSP under ice impact is established. • The ice wedge impact tests of AHSPs were conducted. • The plastic deformation energy absorption and ice facture energy dissipation mechanism is revealed. In this paper, the dynamic responses and energy absorption characteristics of aluminium honeycomb sandwich panels (AHSPs) under ice wedge impact are numerically and experimentally investigated. A three-dimensional nonlinear finite element model of AHSP under ice impact is established based on a concrete constitutive ice model in the commercial package ANSYS/LS-DYNA. The impact force-displacement curves and energy absorption properties as well as the crushing process of ice wedge are numerically achieved. In addition, the ice wedge impact tests of AHSPs were conducted by using a horizontal impact experimental apparatus. Furthermore, the effects of impact parameters and structural parameters on the dynamic responses and energy absorption are performed. Results show that the numerical results of ice wedge-AHSP impact dynamic responses are consistent well with the experimental results. The permanent deformation profiles of face sheets are approximately axisymmetric about the vertical and horizontal centerline. The ice impact energy is mainly converted into the plastic deformation energy of AHSP and rebound kinetic energy of ice wedge as well as the fracture energy of ice wedge. With the increase of the impact energy and thickness of face sheets, the energy dissipation ratio of ice broken increases dramatically and the energy dissipation by ice wedge makes an increasingly contribution to the impact energy absorption. [ABSTRACT FROM AUTHOR]

The National Aeronautics and Space Administration (NASA) has sponsored research to evaluate an externally deployable composite honeycomb designed to attenuate loads in the event of a helicopter crash. The concept, designated the deployable energy absorber (DEA), is an expandable Kevlar honeycomb. The DEA incorporates a flexible hinge that allows the honeycomb to be stowed collapsed until needed during an emergency. Evaluation of the DEA began with material characterization of the Kevlar-129 fabric/epoxy and ended with a full-scale crash test of a retrofitted MD-500 helicopter. During each evaluation phase, finite-element (FE) models of the test articles were developed, and simulations were performed using the dynamic FE code LS-DYNA. This paper focuses on simulations of two full-scale impact tests involving the DEA: a mass simulator and a DEA-retrofitted MD-500 helicopter. Isotropic (Mat 24) and composite (Mat 58) material models that were assigned to DEA shell elements were compared. Based on simulation results, the Mat 58 model showed better agreement with the test results. [ABSTRACT FROM AUTHOR]

This paper describes the experimental and analytical evaluation of an externally deployable composite honeycomb structure that is designed to attenuate impact energy during helicopter crashes. The concept, designated the deployable energy absorber (DEA), uses an expandable Kevlar honeycomb to dissipate kinetic energy through crushing. The DEA incorporates a unique flexible-hinge design that enables the honeycomb to be packaged and stowed efficiently until needed for deployment. Experimental evaluation of the DEA included dynamic crush tests of multicell components and vertical drop tests of a composite fuselage section retrofitted with DEA blocks onto multiterrain. Finite-element models of the test articles were developed and simulations were performed using the transient dynamic code LS-DYNA. In each simulation, the DEA was represented using shell elements assigned two different material properties: Mat 24, an isotropic piecewise linear plasticity model, and Mat 58, a continuum damage mechanics model used to represent laminated composite fabrics. DEA model development and test analysis comparisons are presented. [ABSTRACT FROM AUTHOR]

Abstract: Compressive response and energy absorption of a composite honeycomb is studied. The base material is a circular cell hexagonally packed thin-wall polycarbonate honeycomb. Polydimethylsiloxane (PDMS) elastomer is used as the filler material. Filled honeycomb specimens are quasi-statically loaded under controlled displacement along an inplane direction. Synergistic energy absorption in the filled specimen is observed, as its load response is much greater than the sum of the individual load responses of unfilled honeycomb and the filler material, respectively. Analysis of the crush response is conducted using two methods: (a) Digital image correlation (DIC) to monitor strains and displacement fields in the sample during initial stages of loading and in the vicinity of first failure. (b) Finite element (FE) modeling of the filled honeycomb using the ABAQUS/Explicit finite element code, accounting for the hyperelastic compression response of the PDMS filler. The smeared crack approach (SCA) is implemented in the honeycomb to simulate the longitudinal tearing of the cell wall and to subsequently capture the localization failure in the model. Good agreement between experiment and analysis is reported. [Copyright &y& Elsevier]

Aiming at achieving excellent energy absorption capacity, a novel periodic auxetic reentrant honeycomb structure is proposed by defining an octagon honeycomb unit cell with various shape parameters and reentrant angles. Additive manufacturing is applied to fabricate three groups of resin samples with different design parameters. Quasi-static compression experimental test is conducted obtaining the effects of negative Poisson's ratio (NPR) on the compressive stress–strain relationship of the proposed structure. The results show the excellent lateral material shrinkage under axial compression and distinct hardening process with sharp stiffness increase when the structure experiences densification. The experiment results are then used to validate the corresponding 3D finite element models. Good agreements are found between the experiment and finite element simulation results. Furthermore, a geometry parameter study is used to analyze the effect of design parameters on energy absorption capacity of the structure and the results can be a good reference for future optimal design of similar meta -materials. To summarize, in addition to the good energy absorption capacity, thanks to the obvious NPR effects and lateral shrinkage behavior, the newly proposed honeycomb meta-material with specific auxetic reentrant design becomes a solid material with low porosity and high stiffness after full compression to provide further protection or support for its neighbor objectives. [ABSTRACT FROM AUTHOR]

Abstract: The out-of-plane crushing properties of rhombic and kagome honeycombs are studied in this paper by dividing the whole structure into basic angle elements: corner elements and X-shaped elements. Two theoretical models are presented to analyze the energy absorption mechanisms for inextensional mode of corner elements and one of collapse modes of X-shaped elements respectively. Expressions are derived to predict the mean crushing force of the angle elements. Numerical simulations are also carried out for angle elements under out-of-plane crushing by using nonlinear finite element code LS-DYNA. Crush resistance of angle elements with different geometric configurations including angle, width and thickness is analyzed. A comparison between theoretical predictions and numerical results shows that the theoretical models can effectively predict the mean crushing force of angle elements with a very good accuracy. [Copyright &y& Elsevier]

Abstract: The in-plane dynamic crushing of two dimensional honeycombs with both regular hexagonal and irregular arrangements was investigated using detailed finite element models. The energy absorption of honeycombs made of a linear elastic-perfectly plastic material with constant and functionally graded density were estimated up to large crushing strains. Our numerical simulations showed three distinct crushing modes for honeycombs with a constant relative density: quasi-static, transition and dynamic. Moreover, irregular cellular structures showed to have energy absorption similar to their counterpart regular honeycombs of same relative density and mass. To study the dynamic crushing of functionally graded cellular structures, a density gradient in the direction of crushing was introduced in the computational models by a gradual change of the cell wall thickness. Decreasing the relative density in the direction of crushing was shown to enhance the energy absorption of honeycombs at early stages of crushing. The study provides new insight into the behavior of engineered and biological cellular materials, and could be used to develop novel energy absorbent structures. [ABSTRACT FROM AUTHOR]

Abstract: Energy absorption characteristics of regular polygonal columns and angle elements under dynamic axial compression are investigated by using non-linear explicit finite element code LS-DYNA. The influence of central angle on deformation mode and mean crushing force of angle elements is studied. Based on two types of deformation mechanisms known by experiments, two types of initial indentation triggers are introduced. By assuming appropriate boundary condition on the edges, a simplified finite element model is adopted in the analysis of angle elements and validated by comparing with full polygonal column model. Numerical investigations are also carried out to study the influence of angle on angle elements with three and four panels by using the simplified model. Several useful conclusions are drawn about the axial crushing of polygonal columns and angle elements and can be used to guide the design of crashworthiness structures. In addition, a comparison is conducted between the numerical results and theoretical predictions of the mean forces of some special angle elements. Good agreement is obtained. [Copyright &y& Elsevier]

In this paper a review of impact mechanics and high-energy absorbing materials is presented. We review different theoretical models (rigid-body dynamics, elastic, shock, and plastic wave propagation, and nonclassical or nonlocal models) and computational methods (finite-element, finite-difference, and mesh-free methods) used in impact mechanics. Some recent developments in numerical simulation of impact (e.g., peridynamics) and new design concepts proposed as high energy absorbing materials (lattice and truss structures, hybrid sandwich composites, metal foams, magnetorheological fluids, porous shape memory alloys) are discussed. Recent studies on experimental evaluation and constitutive modeling of strain rate-dependent polymer matrix composites are also presented. Impact damage on composite materials in aerospace engineering is discussed along with future research needs. A particular example for the design of a sandwich material as an impact mitigator is given in more detail. This brief review is intended to help the readers in identifying starting points for research in modeling and simulation of impact problems and in designing energy absorbing materials and structures. [ABSTRACT FROM AUTHOR]

To replace wood as the filler material for the impact limiter of the spent nuclear fuel transportation cask, a bi-directional corrugated honeycomb aluminum (BDCHA) was manufactured. First, five materials with different cell thickness/cell size ratios (t 0 /a) were designed, and compression tests were performed under quasi-static conditions. The results show that the initial peak stress and the plateau stress both increase with the increase of the t 0 /a ratio. The plateau zone determines the energy absorption performance; therefore, this study focuses on the analysis of the mechanical properties of the plateau stage. Furthermore, through the compression theory, the energy dissipation process of the unit cell was evaluated, and the mean stress equation was obtained; the theoretically obtained plateau stress was similar to the test plateau stress. Moreover, the ideal constitutive relationship of the material based on the t 0 /a ratio under static load was derived. Finite element analysis was used for simulation. The stress-strain results of the test and the simulation were close. Furthermore, the structural parameters were optimized via multiobjective optimization. Through the analysis of the mechanical properties of BDCHA, derived its rationality and feasibility as a shock-absorbing filling material. [ABSTRACT FROM AUTHOR]