Search

Due to the high energy absorption capability and excellent bending strength of the sandwich panels, they are mostly preferred as protective structures against explosive blast attacks. The evaluation of their blast-mitigation characteristics through experiments is highly dangerous, costly, time-consuming, and polluting for the environment. Therefore, in this presented work, a series of numerical analyses were performed to evaluate the blast mitigation of the outstanding sandwich panels with honeycomb, corrugated, auxetic, and foam cores. The masses of sandwich panels were kept constant, and their areal densities were maintained constant throughout the study to effectively compare their performance under identical air blast loading conditions. To apply the air blast loads to the designed sandwiches, 1–3kg of spherical-shaped trinitrotoluene charges were used for a 100mm stand-off distance. The sandwiches are made of high-strength AL-6XN steel and crushable aluminum foam. The rate-dependent Johnson–Cook constitutive model of plasticity and the crushable foam model with volumetric hardening were used for the evaluation of sandwich panels’ plastic deformations. The findings of the work depicted that the honeycomb core is more efficient than the other core structures of the same masses because the sandwich panels with honeycomb core provide smaller back skin deflections, globalized core crushing, and higher core energy absorption than the other sandwich panels for extreme conditions of air blast loading. [ABSTRACT FROM AUTHOR]

Energy-absorbing materials have extensive applications in aerospace and automotive applications. Research has shown buckling initiators, or triggers, in energy-absorbing tubular structures increase the energy absorbed by encouraging the side panels to fold when loaded out of plane in compression conditions. Additively manufactured TPE honeycombs were designed in this study to include these buckling initiators, which introduced a slight decrease in initial weight, as well as initial stress concentrations, while improving crashworthiness characteristics. The samples with buckling initiators (1BI) showed an increase in crush efficiency when directly compared to their no buckling initiator (0BI) counterparts. The 1BI samples maintained an increased crush efficiency regardless of the strain rate used. The samples with 1BI were able to better equilibrate the peak stress with the plateau stress. These honeycomb samples were found to maintain their crush efficiency, even after multiple rounds of compression testing. The quasi-static 0BI samples experienced a 23.4% decrease in the peak stress after multiple rounds of compression testing, while the 1BI samples saw approximately a 23.0% decrease. The 1BI samples averaged a decrease in crush efficiency of 0.5%, while the 0BI samples saw a decrease in crush efficiency of 5%. As the strain rate increased, the crush efficiency for the 1BI samples showed an increase in performance, with a smaller degradation in crush efficiency over multiple uses. Visco-elastic honeycomb with buckling initiators has a higher energy absorption than samples with no buckling initiators when exposed to multiple impact cycles. [ABSTRACT FROM AUTHOR]

Honeycomb cores are widely used in the aerospace and automotive fields as a part of protective structures. Unfortunately, standard prismatic honeycomb cores offer a limited amount of energy absorption under lateral loads and suffer from degradation of their impact-deadening properties when their dimensional scale is increased. In this work, a multiscale study on energy absorption under quasi-static load is carried out on 3D-printed honeycomb core samples constituted by a variable section and compared to the cases of standard hexagonal honeycomb samples having the same mass and external dimensions. When doubling the dimensional scale in the case of lateral loads, the novel core geometry showed a substantial absence of specific energy absorption degradation, whereas the hexagonal core suffered from a 12.2%-degradation. Furthermore, by increasing the dimensional scale, the novel core geometry shows a delay in the densification onset. The variable-core geometry showed an average increase, in terms of energy absorption under lateral loads, of 46.8% for the regular scale and 71.4% for the double scale. Under axial loads, a 12.4%-decrease in energy absorption was observed for the samples with novel geometry, which, nevertheless, showed a relatively constant profile of reaction force under compression: this property could potentially allow it to avoid pre-crushing. [ABSTRACT FROM AUTHOR]

A designer of metallic energy absorption structures using additively manufactured cellular materials must address the question of which of a multitude of cell shapes to select from, the majority of which are classified as either honeycomb, beam-lattice, or Triply Periodic Minimal Surface (TPMS) structures. Furthermore, there is more than one criterion that needs to be assessed to make this selection. In this work, six cellular structures (hexagonal honeycomb, auxetic and Voronoi lattice, and diamond, gyroid, and Schwarz-P TPMS) spanning all three types were studied under quasistatic compression and compared to each other in the context of the energy absorption metrics of most relevance to a designer. These shapes were also separately studied with tubes enclosing them. All of the structures were fabricated out of AlSi10Mg with the laser powder bed fusion (PBF-LB. or LPBF) process. Experimental results were assessed in the context of four criteria: the relationship between the specific energy absorption (SEA) and maximum transmitted stress, the undulation of the stress plateau, the densification efficiency, and the design tunability of the shapes tested—the latter two are proposed here for the first time. Failure mechanisms were studied in depth to relate them to the observed mechanical response. The results reveal that auxetic and Voronoi lattice structures have low SEA relative to maximum transmitted stresses, and low densification efficiencies, but are highly tunable. TPMS structures on the other hand, in particular the diamond and gyroid shapes, had the best overall performance, with the honeycomb structures between the two groups. Enclosing cellular structures in tubes increased peak stress while also increasing plateau stress undulations. [ABSTRACT FROM AUTHOR]

• Face-centered hierarchical strategy is proposed to develop a novel honeycomb. • Face-centered hierarchical network provides strong lateral support to resist the multi-crushing loads. • Effect of hierarchy order and thickness gradient is significant on the multi-crushing properties. • Face-centered hierarchical honeycomb possesses the more stable and efficient multi-crushing properties. The undesirable resistance to multi-crushing loads limits the development of regular honeycomb structures in advanced engineering fields. Therefore, a novel hierarchical strategy, namely face-centered hierarchical strategy, is proposed to improve the multi-crushing properties of honeycombs. The honeycombs with the face-centered hierarchical network are manufactured by selective laser melting to test their energy absorption mechanism against the oblique crushing load. The multi-crushing properties of face-centered hierarchical honeycomb (FCHH) are explored by a numerical investigation. The carrying capacity and energy absorption of the FCHH decrease with the increasing crushing angle. The parameter configuration design indicates that the hierarchy order has a positive effect on the multi-crushing resistance of the FCHH. The face-centered hierarchical network not only provides the strong lateral support, improving the collapse of the honeycomb, but also reduces the folding wavelength, improving its material utilization. Specifically, the specific energy absorption and crushing force efficiency of the FCHH improve by 27.65 % and 30.83 % respectively as the hierarchy order increases from 1 to 3 at the crushing angle of 30°. Furthermore, when the thickness gradient factor is close to 1, the FCHH obtains a more reasonable material distribution to resist the oblique crushing load. Compared with other hierarchical honeycombs for the oblique crushing resistance, the FCHH demonstrates a more stable carrying process and more efficient energy absorption. This research expects to propose a promising reinforcement strategy to guide the design of multi-crushing properties for honeycombs. [Display omitted] [ABSTRACT FROM AUTHOR]

Aluminum honeycombs are widely applied in weight sensitive applications, increasing their specific strength and energy absorption capacity are rather important. Thin-walled metallic tube was used to enhance the mechanical properties of aluminum honeycomb and formed a novel tube-reinforced honeycomb structure. Its compressive and three-point bending performances were studied experimentally and numerically. Due to tube filling, the specific compressive strength, elastic modulus and energy absorption have been increased by 16%, 26% and 73%, and the specific bending load and stiffness increased by 42% and 62% respectively. The strengthen mechanism study indicated that the sum of tube and honeycomb caused the increase of compressive properties, and aluminum tube filling changed the stress distribution and expanded the stress concentration region which led to a transformation of bending failure mode. The present reinforcement method will make honeycomb more competitive in light-weight structure applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new auxetic honeycomb was designed by hybriding rhombic and star configurations. • A theoretical model was developed to predict the elastic modulus and Poisson's ratio. • The proposed honeycomb possesses higher auxetic effect and larger specific modulus than the star honeycomb. • The proposed honeycomb exhibits enhanced plateau stress and specific energy absorption compared with conventional auxetic honeycombs. Auxetic structures with negative Poisson's ratio exhibit excellent performance in cushioning, shear resistance and energy absorption, but their load-bearing capacity is usually poor. To address this drawback of the conventional Auxetic structure, a star-rhombic honeycomb (SRH) design is proposed in this paper to improve its load-bearing capacity. Analytical models of the elastic modulus and Poisson's ratio of this structure for different loading directions are developed. Quasi-static compression experiments were conducted on SRH specimens fabricated by selective laser melting (SLM) technique. Good agreement was achieved between the simulated and experimental stress response curves and deformation patterns. It was found that the SRH structure possessed better elastic modulus and energy absorption capacity than the SH structure without sacrificing the auxetic properties. The elastic modulus and Poisson's ratio of SRH under the x loading direction are more sensitive to the changes of structural parameters. An optimum energy absorption performance is achieved for an appropriate ratio of the inner rhombic strut thickness to outer reentrant strut thickness (k = 0.5). The specific energy absorption of SRH is improved by 136% and 75% compared to that of the conventional reentrant honeycomb (RH) and star honeycomb (SH), respectively. It has advantages for application scenarios with requirements for both auxetic and load bearing properties. [ABSTRACT FROM AUTHOR]

Biological tissues like bone, wood, and sponge possess hierarchical cellular topologies, which are lightweight and feature an excellent energy absorption capability. Here we present a system of bio-inspired hierarchical honeycomb structures based on hexagonal, Kagome, and triangular tessellations. The hierarchical designs and a reference regular honeycomb configuration are subjected to simulated in-plane impact using the nonlinear finite element code LS-DYNA. The numerical simulation results show that the triangular hierarchical honeycomb provides the best performance compared to the other two hierarchical honeycombs, and features more than twice the energy absorbed by the regular honeycomb under similar loading conditions. We also propose a parametric study correlating the microstructure parameters (hierarchical length ratio r and the number of sub cells N ) to the energy absorption capacity of these hierarchical honeycombs. The triangular hierarchical honeycomb with N  = 2 and r  = 1/8 shows the highest energy absorption capacity among all the investigated cases, and this configuration could be employed as a benchmark for the design of future safety protective systems. [ABSTRACT FROM AUTHOR]

Introducing gradient into cellular materials has been envisioned as an effective way to improve their performance. In this study, a novel in-plane graded honeycomb is proposed and its dynamic behavior under out-of-plane compression is investigated using numerical simulation and theoretical analysis. The in-plane gradient is introduced by changing the thickness of each cell wall of honeycomb unit cell along its side length. Numerical results show that the crushing strength and energy absorption capacity of honeycombs with positive gradient are substantially enhanced compared to those of honeycombs without gradient. To explore the enhancement, theoretical and numerical analyses on the energy absorption mechanism of honeycombs are performed. It is found that severe plastic deformation is mainly concentrated near the intersecting edge of cell walls, and the energy absorption can be further improved by distributing more material near the intersecting edge when the total mass remains constant. In addition, analytical formulas for the crushing strength and energy absorption of graded honeycombs are developed, and good agreement is obtained with numerical results. [ABSTRACT FROM AUTHOR]

• Auxetic energy absorption structures with re-entrant configurations manufactured by 3D-printed superior elastic-plastic stainless steel. • High speed drop hammer impact tests conducted under varying input impact energies. • Comparison results with a convex honeycomb structure indicate excellent energy absorption performance of auxetic specimens. • Different crushing modes verified for the auxetic specimens with different impact energies and side length-to-thickness ratios. • The side length-to-thickness ratio was found to have a significant effect on the anti-impact performance of auxetic specimens. In order to fully comprehend dynamic responses of metallic auxetic honeycombs, drop hammer impact tests and corresponding finite element (FE) analyses were conducted. The three-dimensional (3D) printing technology was adopted to manufacture stainless steel specimens with varying cell side length-to-thickness ratios and cell configurations. The specimens were crushed under three distinct energy inputs, and the deforming process and relevant mechanical parameters, e.g., the Poisson's ratio, failure mode, plateau stress and energy absorption capacity were studied. The FE results can generally compare well with the experimental ones and facilitate clarifying the impact mechanisms of the experimental results. Improvements of the auxetic specimens in energy absorption were verified through comparison with that of the corresponding convex honeycomb. The results reveal that the specimen with an auxetic honeycomb has higher plateau stress and specific energy absorption with less deformation when the geometric size is the same. A small side length-to-thickness ratio and input impact energy can lead to greatly improved energy absorption efficiency. [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]

This study proposed a new bio-inspired hierarchical circular honeycomb (BHCH), mimicking the hierarchical structures from wood. The mechanical properties and energy absorption characteristics of the proposed structures were investigated by means of quasi-static compression tests and finite element (FE) analysis. Subsequently, the influences of geometric parameters and material selections on the energy absorption capacity were investigated. The experimental results and parametric study indicated that the BHCH outperformed the conventional circular honeycomb (CH) in terms of energy absorption capacity. Specifically, the BHCH had a higher specific energy absorption (SEA) than the corresponding CH with the same wall thickness (i.e. 45.3%) and the same volume of honeycombs (i.e. 71.2%). Furthermore, the relative stiffness, relative strength, and relative energy absorption of the BHCH were significantly higher than other popular cellular structures. Finally, a theoretical model was developed to estimate the mean crushing stress (MCS) and interaction effect of the proposed structure, which further demonstrated its enhanced energy absorption mechanisms. A good correlation between the predicted values and the numerical results proved the reliability of the proposed analytical models. With its excellent performance, the proposed BHCH provided a promising solution for the enhanced energy absorption of the honeycomb structure used in a wide range of applications from structural components of defence structures to protection systems in vehicles. [ABSTRACT FROM AUTHOR]

• An innovative graded hierarchical honeycomb is proposed to improve its crashworthiness. • Two gradient distributions (negative & positive) and two sub-structural topologies (hexagonal & triangular) are considered. • Crushing mechanism of graded hierarchical honeycomb is investigated via numerical and theoretical analyses. • Specific energy absorption of graded hierarchical honeycombs is enhanced up to 32.2% as compared to uniform counterpart. • Three plateau stages can be observed for graded hierarchical honeycomb under dynamic crushing. Nature's bio-organisms are typically hybrid structures composed of hierarchical and functionally graded micro-architectures, which are lightweight and of high mechanical performances. Inspired by nature, an innovative graded hierarchical honeycomb is proposed in this study to enhance its crashworthiness behaviors. The structure is created by replacing cell walls of regular honeycombs with triangular and hexagonal sub-structures and varying the hierarchical length ratio in each layer. The in-plane crushing performances of the graded hierarchical honeycombs are comprehensively analyzed and compared with their uniform hierarchical counterpart. The former exhibits a progressive deformation model under different impact velocities and three plateau stages can be observed under in-plane crushing loads through theoretical predictions. The triangular sub-structure presents better energy absorption than the hexagonal sub-structure, and its specific energy absorption is enhanced by up to 32.2% as compared to the uniform hierarchical honeycomb. The present study suggests that the combination of hierarchy and gradient is an effective strategy to improve the dynamic crushing behaviors of honeycombs, which can be further explored in protective devices to enhance their impact resistance. [Display omitted] [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: Honeycomb cellular structures and multi-cell prismatic columns are highly efficient and effective energy dissipating components and are widely used in the crashworthiness design of vehicles. Due to the complex features during large plastic deformation, only few special sections have been theoretical modeled for their energy absorption capacity under axial compression. In this paper, based on a simplified FE model, the energy absorption characteristics of angle elements with three panels are investigated by using the non-linear finite element code LS-DYNA. Theoretical models are proposed to predict the crush resistance of three-panel angle elements with different angles. Numerical results show that the proposed theoretical model can predict the energy absorption of these angle elements with good accuracy. [Copyright &y& Elsevier]

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]

[Display omitted] • Parametric design inspired by bamboo microstructure with improved EA, and CFE. • Bamboo Biomorphic Structure (BBS) showed significantly higher densification strain. • BBS design showed uniform stress distributed across the vertically angled beams. • Higher density distribution within biomorphic layers improved the collapse stress. • BBS-GS showed a stepwise deformation, and absorbed impact energy more efficiently. Bamboo cell wall exhibits a microscopically graded architecture, and micro-layer distributed cells around individual cell walls, which leads to the preferred mechanical properties of bamboo for impact loading. This work proposes a cellular structure, as called Bamboo Biomorphic Structure (BBS), which is a functionally graded honeycomb cellular structure inspired by the microstructure of bamboo and manufactured using fused filament fabrication (FFF). It is hypothesized that, by introducing bamboo biomorphic micro-unit cells, including a range of thickness step differences within an individual honeycomb unit cell, the successive stages of deformation of the honeycomb structure can be controlled, making the system absorb impact energy more efficiently. Characterization of the designed structures was conducted under in-plane quasi-static loading conditions, and then evaluated using a nonlinear finite element commercial code LS-DYNA. The proposed gradient BBS showed higher absorbed impact energies by four times compared with the conventional Honeycomb structure. The proposed parametric design would aid engineering design principles for the development of a novel biomorphic cellular structure, which has the potential for large-scale manufacturing of efficient energy-absorbing engineering structures. Such an energy-absorbing structure can help improve the lightweight structure design for various applications, including automobiles and aircrafts, while ensuring safety under impact load. [ABSTRACT FROM AUTHOR]

Honeycomb structures have attracted much attention in various engineering fields due to its superiorities in high specific strength, high specific stiffness and excellent energy-absorbing characteristics. The light-weight materials with exceptional mechanical behaviors can be achieved by incorporating the reinforced mesostructure into the regular honeycomb structures. In the present work, a novel circular-celled honeycomb was proposed by incorporating the petal-shaped mesostructures into the regular circular cell honeycomb. The 3D finite element models of the petal-shaped honeycombs (PSH) are established to investigate the in-plane crushing behavior and energy absorption capacity under different impact velocities through the nonlinear finite element code LS-DYNA. A comparison between the regular circular-cell honeycomb, the single petal nested circular honeycomb and the PSH was carried out, and the simulation results indicated that the PSH exhibited the best mechanical behavior and energy absorption characteristics compared with the other two types of honeycombs. Three representative deformation modes, namely quasi-static, transition and dynamic mode, were observed from the numerical simulations of the PSH with different geometric configurations and impact loadings, and the failure mode map was also summarized to furtherly clarify the localized deformation characteristics. In addition, the influences of impact velocity and the relative density on the plateau stress and the energy absorption behavior of the PSH were also investigated in this paper. The results showed that the specific energy absorption of PSH can be improved by up to nearly twice than the regular circular honeycomb under the same impact speed. [ABSTRACT FROM AUTHOR]

The paper presents a new approach for failure modeling of a cellular structure manufactured with a 3D printing technology. For this purpose, the honeycomb topology was designed and fabricated using fused deposition modeling of ABSplus material. The proposed method was based on the tiebreak contact for connecting plastic joints with cell walls. Additionally, two methods based on constitutive models were also analyzed. In the first case, an elasto-plastic material model was adopted, whereas in the second case an elasto-visco-plastic material model with damage was included. Firstly, the mechanical properties of ABSplus material were determined and numerically correlated with experimental outcomes. Subsequently, a contact parametric study was performed, and the optimal contact parameters were evaluated. The quasi-static experimental compression tests were simulated using LS-Dyna software. The results of actual tests and numerical analyses with three different methods for honeycomb structure modeling were compared in terms of deformation, force history, failure behavior and energy absorption capabilities. It was shown that the contact-based method resulted an in an increase of the results quality with better reproduction of force characteristic and progressive failure behavior during the deformation process, compared to other two methods. Unlabelled Image • A new approach for failure modeling based on tiebreak contact algorithm is proposed • The proposed approach is compared with two standard constitutive model based methods • Contact parametric study is performed to assess failure parameters of tiebreak based algorithm • Crashworthiness properties of the Honeycomb cellular structure are investigated in experimental and numerical tests [ABSTRACT FROM AUTHOR]