Search

In order to obtain a lightweight, high-strength, and customizable cellular structure to meet the needs of modern production and life, the mechanical properties of four thickness gradient honeycomb structures were studied. In this paper, four types of honeycomb structure specimens with the same porosity and different Poisson's ratios were designed and manufactured by using SLA 3D-printing technology, including the honeycomb, square honeycomb, quasi-square honeycomb, and re-entrant honeycomb structures. Based on the plane compression mechanical properties and failure mode analysis of these specimens, the thickness gradient is applied to the honeycomb structure, and four structural forms of the thickness gradient honeycomb structure are formed. The experimental results show that the thickness gradient honeycomb structure exhibits better mechanical properties than the honeycomb structure with a uniform cellular wall thickness. In the studied thickness gradient honeycomb structure, the mechanical properties of the whole structure can be significantly improved by increasing the thickness of cell walls at the upper and lower ends of the structure. The wall thickness, arrangement order, shape, and Poisson's ratio of the cell all have a significant impact on the mechanical properties of the specimens. These results provide an effective basis for the design and application of cellular structures in the future. [ABSTRACT FROM AUTHOR]

Cellular infill structures such as honeycomb have been widely used in the field of light weighting. In recent years, the emergence of additive manufacturing technologies has provided a new solution to fabricate complicated cellular infill structures. This paper presents a continuous printing path planning method for gradient honeycomb structures. Given a 2D filling region represented by a polygon, a honeycomb graph that covers the filling area is trimmed to generate an infill pattern. Then an algorithm is proposed to transform the honeycomb filling pattern into an Eulerian graph, which can be traversed by a single-stroke printing path. For each honeycomb, double-spiral paths are used to generate gradient honeycomb structures with varying wall thicknesses. Later, the 2D honeycomb infills are generalized to 3D cases that are suitable for multi-axis printing. First, three mutually orthogonal vector fields that are embedded on the tetrahedral mesh of the printed part are generated by considering the support-free condition. Then the three vector fields are used to calculate three monotonically increasing scalar distance fields, which span a non-Euclidean space. Finally, the 2D honeycomb infills are generated in the non-Euclidean space with parallel sliced layers, which are then mapped back to the Euclidean space to obtain the real self-supporting 3D honeycomb infills. The proposed 2D/3D honeycomb infill structures generation algorithms have been verified by both simulation and experimental tests. [ABSTRACT FROM AUTHOR]

An ongoing growth of the available materials dedicated to additive manufacturing (AM) significantly extends the possibilities of their usage in many applications. A very good example is 20MnCr5 steel which is very popular in conventional manufacturing technologies and shows good processability in AM processes. This research takes into account the process parameter selection and torsional strength analysis of AM cellular structures. The conducted research revealed a significant tendency for between-layer cracking which is strictly dependent on the layered structure of the material. Additionally, the highest torsional strength was registered for specimens with a honeycomb structure. To determine the best-obtained properties, in the case of the samples with cellular structures, a torque-to-mass coefficient was introduced. It indicated the best properties of honeycomb structures, which have about 10% smaller torque-to-mass coefficient values than monolithic structures (PM samples). [ABSTRACT FROM AUTHOR]

In this paper, the vibroacoustic performance of the star-shaped honeycomb-core annular cellular structures is investigated. The results imply the superiority of these structures over the hexagonal honeycomb-core annular cellular structures, with constant mass and overall structure size, in terms of sound insulation relative to static bending compliance. The spectral element method (SEM) is employed to accurately evaluate natural frequencies and dynamic responses with a reduced number of elements within a wide frequency range. The sound transmission loss (STL) is used as a metric to define vibroacoustic performance. The in-plane effective shear modulus of star-shaped honeycombs is derived analytically to analyze the mechanical and vibroacoustic characteristics of the structures. A structural–acoustic optimization study of star-shaped honeycombs for the maximum sound transmission loss under constant mass and high static bending stiffness constraints is evaluated and presented for a specified target range. An increase of sound transmission loss by 490.23% for the considered target range in the optimized star-shaped honeycombs shows significant vibroacoustic performance. [ABSTRACT FROM AUTHOR]

The low stiffness resulting from substantial core porosity within the re-entrant honeycomb sandwich panel can be addressed by introducing rib-reinforcements. To investigate its static and vibration characteristics, an energy-based 2D equivalent-homogenization model (2D-EHM) was derived through asymptotic analysis of the leading terms in the governing equations considering the energy-related characteristics. The accuracy of the constructed model for predicting the elastic bending performance of the sandwich panel was verified by comparing the results of a three-point bending experiment with 3D-printed specimens. Comparative analysis with a 3D FE model demonstrates that the 2D-EHM exhibits maximum errors of only 4.65% and 6.46%, respectively, in analyzing static deformation and natural frequency while improving computational efficiencies by up to 59- and 173-folds. Parameter analysis reveals that the performance of SP-RRH is minimally affected by the reinforcement-to-honeycomb wall thickness ratio. However, its performance is compromised when the honeycomb walls align in an equilateral triangle with the reinforcing walls. Comparing specific stiffness as well as static and vibration characteristics of sandwich panels with different core configurations (including traditional and diamond reinforced re-entrant honeycombs) shows that inclusion of rib reinforcements enhances deformation resistance and natural frequencies through increased specific stiffness. These findings provide valuable insights for optimizing design of re-entrant honeycomb sandwich panels. [Display omitted] • VAM-based 2D model of SP-RRH accurately validated against 3D-FEM results. • Equivalent stiffness obtained via asymptotic analysis of unit cell's energy functional. • The tailorability of the unit cell facilitates the customization of its properties. • Rib-reinforcing walls enhance deformation resistance of sandwich panels. • The performance of SP-RRH is influenced by equilateral triangular cellular structure. [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]

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]

• A two-stage hybrid optimization for honeycomb structures is proposed. • The material properties and wall thickness are considered. • The Taguchi-based grey correlation discrete optimization is applied. • The proposed algorithm can be used to solve more complicated problems. Honeycomb structures with better balance between lightweight and crashworthiness have aroused growing attentions. However, structural parameters design by traditional optimization algorithm in small design space is not sufficient to significantly enhance the specific energy absorption (SEA) with the lower peak acceleration (a max). In this paper, a two-stage hybrid optimization for honeycomb-type cellular parameters is proposed to achieve rapid positioning of design space and significantly increase crashworthiness in a larger variable domain under out-of-plane dynamic impact. In stage I, a Taguchi-based grey correlation discrete optimization, combining Taguchi analysis, grey relational analysis, analysis of variance (ANOVA) with grey entropy measurement, is performed to determine the initial optimal value with a higher robustness and the significant influence variables. In stage II, a multi-objective design technique, namely non-nominated sorting genetic algorithm II based on surrogated model, is adopted to maximize the SEA and minimize the a max in a relatively small design domain. And it is found that the proposed two-stage hybrid method can broaden the optimal design space compared to that of traditional method attributable to its center point positioned by stage I. And the final optimization based on the proposed strategy is superior to the original structure, i.e., the SEA is increased by 47.55% and the a max is decreased by 80.8%. Therefore, the proposed algorithm can also be used to solve other more complicated engineering problems in a large design space with insightful design data. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrathin ZIF layers were fabricated on flexible hollow fibers. • Highly (2 2 2)-oriented ZIF-8 layer with honeycomb cellular structure was obtained. • Orientation originated from the difference in attachment energy of crystal planes. • Membrane with H 2 permeance of 75,711 GPU and H 2 /CO 2 selectivity of 21.2 at 150 °C. • Excellent membrane flexibility and thermal stability. Metal-organic framework (MOF) membranes demonstrate enormous potential for energy-efficient gas separations, while the construction of flexible and oriented MOF-based membranes remains a significant challenge. Herein, we prepared an ultrathin and highly (2 2 2)-oriented ZIF-8 layer with unique honeycomb cellular structures on porous aminated polyethersulfone (PES) hollow fibers (HF) via UV radiation-induced surface amino-grafting followed by a homogeneous fluidic processing method, and the reaction conditions including amino-grafting density, radiation power, flow rate, and reaction time et al. were systematically investigated and optimized. The orientation of reflection originated from the difference in attachment energy of crystal planes induced by the surface amino groups. The coherent (2 2 2)-oriented NH 2 -ZIF-8@HF membrane exhibited distinguished H 2 /CO 2 separation performance with a mixed-gas H 2 permeance of 75711 ± 610 GPU, among the highest values of previously reported hollow fiber supported ZIF membranes, and the H 2 /CO 2 selectivity of 21.2 ± 0.11 at 150 °C. Additionally, the NH 2 -ZIF-8@HF membrane displayed outstanding mechanical and thermal stability with negligible deterioration of gas separation performance after folding and unfolding at 180° for 20 times and several temperature-swing cycles. ZIF-7 and ZIF-67 composite membranes were also prepared with outstanding H 2 /CO 2 separation performance following the same strategy. The facile membrane fabrication method and exceptional separation performance make NH 2 -ZIF@HF membranes attractive for important industrial energy-efficient H 2 recovery from steam cracking and similar processes. [ABSTRACT FROM AUTHOR]

Cellular structures exhibit attractive mechanical properties like lightweight, high specific stiffness, and excellent energy absorption. Materials and structures design offers valuable enhancement of nature honeycombs. This work proposed a variable cross-section unit cell to improve compressive and energy absorption properties of the cellular structure constituting these unit cells. In the developed variable cross-section unit cell, the inclined cell walls of the traditional accordion honeycomb were flipped at an angle in the out-of-plane direction or swept along a cousin wave path. The Fused Deposition Modeling (FDM) technique was employed to prepare honeycomb specimens from polylactic acid (PLA). In-plane quasi-static compressive tests were carried out to investigate mechanical behavior and energy absorption of the designed honeycomb structures. The results indicate that the design of the variable cross-section in the width direction enhanced compressive strength and improved energy absorption capability. Based on the variable stiffness characteristic of PLA, isothermal compression experiments were conducted to investigate the temperature dependence of the compressive behavior. This work provides a demonstration for improving the mechanical performance and energy absorption of lightweight cellular structures. [ABSTRACT FROM AUTHOR]

Rapid increase in the operating speeds of aerospace/automobile vehicles has demanded for the design of light weight structures resisting high velocity impact loads. Cellular structures have shown significant potential for mitigating the effects of extreme loading. Due to its geometry, honeycomb structure is observed to possess the highest load carrying capacity as compared to other regular shapes. In this study, three different hybrid cellular structures, namely: design 2, design 3 and design 4, are designed and developed for impact applications, through a systematic study considering the hexagonal basic unit cell, and combining order and levels by mimicking bamboo-spiderweb structures. Parametric studies are performed and the proposed unit cell in design 4 is observed to demonstrate the best performance in terms of specific energy absorption and crush force efficiency. Analytical models are developed to estimate the energy absorption of unit cells in designs 2–4 during the impact. Numerical studies are performed considering the proposed unit cells to estimate the energy absorption characteristics. Results from analytical and numerical investigations are compared to notice a close agreement, with a maximum error of 9.97%. The resistance to local impact is tested by developing sandwich structures with cores developed from the proposed unit cells. Bullet impact studies are performed on the sandwich structures at three different identified locations with an impact velocity of 115 m/s. Design modifications are carried out by combining the multi-staging and strategically offsetting the unit cells in each core of a two core sandwich structure, such that it can withstand the impacts at arbitrary locations for bullet speeds up to 115 m/s. The proposed novel fourth order and third level hybrid unit cell in design 4 is found to efficiently resist the impact loads. Hence, it is recommended for applications involving energy absorption under extreme loads. [ABSTRACT FROM AUTHOR]

Inspired by heterogeneous structures observed in nature (graphene, insects' eyes, and beehives), we demonstrate that topological defects in hexagonal honeycombs can enhance strength and energy absorption capacity. These defects consist of pentagon-heptagon pairs (known as 5–7 defects). Experimental studies of additive manufactured specimens and computational studies are performed on honeycomb panels that are perfectly periodic or that contain defects in one of two arrangements: (i) clustered to form inclusions or (ii) aligned to form 5–7 domain boundaries. The focus is on the compressive response in out-of-plane, in-plane, and inclined orientations. The results show a 25–30% strength improvement when the 5–7 defects are arranged into aligned domain boundaries. The boundaries induce asymmetric deformation and hydrostatically reinforce the neighbouring hexagonal cells. Such effects can be attributed to differences in topological network adjacency. The results suggest that there remains a largely untapped design space involving heterogeneous cellular structures. [Display omitted] [ABSTRACT FROM AUTHOR]

• The mechanical properties and deformation behavior of cellular MGs with different cellular structures are investigated. • The structure-mechanical properties relationship for cellular MGs is established. • MGs with stochastic cellular structures exhibit much higher energy absorption capacity than those with microlattice structures. • The mechanical properties of cellular MGs can be tuned by adjusting their cellular structures. The mechanical properties of cellular metallic glasses (MGs) are governed by the shape of their cellular structures. We employ finite element method analysis to characterize the mechanical behavior under quasi-static compression of cellular MGs with the same porosity but different shape, including stochastic (disordered) structures with uniform or gradient porosity and periodic (ordered) microlattice structures such as honeycomb, chiral, and body-centered cubic structures. The results show that stochastic structures with graded porosities degrade the yield strength and Young's modulus compared to uniform cellular MGs. MGs with microlattice structures display much lower Young's modulus and yield strength than stochastic cellular MGs with uniform porosity. However, the chiral structure presents the largest Young's modulus of all cellular MG models investigated. Furthermore, MGs with stochastic cellular structures exhibit much higher energy absorption capacity than those with microlattice structures. It is found that the deformation behaviors of cellular MGs can be tuned by adjusting their cellular structures. The obtained structure-mechanical properties relationship can provide useful guidance for designing cellular MG-based composites for advanced multifunctional applications. [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]

Cellular structures are light weight structures with high specific, impact, flexural strength and stiffness. Hierarchical structures offer higher load-bearing capacity compared to their conventional counter parts. In this study, performance of enhanced hierarchical honeycomb core cellular structures under compression and impact loads is investigated. The hierarchy is proposed by varying the order and the level of the cells. Hierarchical patterns are developed by replacing the vertex cells of regular hexagonal honeycomb with circular cells. The local arrangement of the proposed hierarchical cellular structures is improved to withstand higher loads. The out-of-plane performance of honeycomb structure is enhanced by a hierarchical scheme. As a result, a novel hierarchical second order second level hexagon based hybrid cell has been developed. Furthermore, the influence of sandwiching the cellular structures between face sheets against impact loads is also studied using numerical simulations. In order to transfer the loads efficiently from the top and bottom ends to the mid walls of the unit cell, the structural angle β is introduced as the angle between the normal of the face-sheet and the axis of the unit cell. Such an arrangement is observed to enhance the load distribution in the cellular structures. [ABSTRACT FROM AUTHOR]

The heat accumulator designed for the purposes of this study consists of two chambers with metal foam structures and honeycomb segments casted by the means of investment casting from an Al Si alloy. The cellular metal castings, characterized by a relatively large coefficient of thermal conductivity, provide rapid transport of heat energy from the source to the heat storage materials (paraffin or zeolite). In order to simulate the conditions of solar heating, two outdoor halogen reflectors were used for the heating stage. Multiple long-term cycles of charging and discharging of this heat accumulator, with and without porous metallic inserts to improve the thermal conductivity and increase the heat transfer area, were conducted and subsequently analysed. The metal foams are suitable for enhancing heat transfer in a zeolite bed, whereas the durable honeycomb casting is preferable for phase change material. Additionally, the porous foam improves the conditions for transporting vapour during dehydration/hydration. The application of cast inserts in the zeolite chamber helped to decrease the temperature gradient to below 50 °C. The overall amount of energy stored in the hybrid TES unit equaled 7676.4 kJ (2.14 kWh). [ABSTRACT FROM AUTHOR]

Periodic cellular structures are widely used in structural protection due to their lightweight and excellent energy absorption characteristics, but the corresponding crashworthy design is still limited. Based on the framework of hybrid cellular automata (HCA), the optimal design of periodic cellular structure for crashworthiness is carried out. To guarantee the periodicity of cellular structure, elemental internal energy (EIE) is redistributed averagely as a periodic constraint. Then, by iteratively modifying the local EIE target, the cellular structure is optimized until the maximum energy absorption (EA) is obtained under the specific volume fraction constraint. Through several 2D and 3D numerical examples, this design method is proved to be efficient for the crashworthiness design of periodic cellular structures. Specifically, EA of the optimized cellular structures in this study can be improved by design comparing with solid structures and classical honeycombs. Effects of cellular number and volume gradient on crashworthiness are also discussed. [ABSTRACT FROM AUTHOR]

[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]

Energy resulting from an impact is manifested through unwanted damage to objects or persons. New materials made of cellular structures have enhanced energy absorption (EA) capabilities. The hexagonal honeycomb is widely known for its space-filling capacity, structural stability, and high EA potential. Additive manufacturing (AM) technologies have been effectively useful in a vast range of applications. The evolution of these technologies has been studied continuously, with a focus on improving the mechanical and structural characteristics of three-dimensional (3D)-printed models to create complex quality parts that satisfy design and mechanical requirements. In this study, 3D honeycomb structures of novel material polyethylene terephthalate glycol (PET-G) were fabricated by the fused deposition modeling (FDM) method with different infill density values (30%, 70%, and 100%) and printing orientations (edge, flat, and upright). The effectiveness for EA of the design and the effect of the process parameters of infill density and layer printing orientation were investigated by performing in-plane compression tests, and the set of parameters that produced superior results for better EA was determined by analyzing the area under the curve and the welding between the filament layers in the printed object via FDM. The results showed that the printing parameters implemented in this study considerably affected the mechanical properties of the 3D-printed PET-G honeycomb structure. The structure with the upright printing direction and 100% infill density exhibited an extension to delamination and fragmentation, thus, a desirable performance with a long plateau region in the load–displacement curve and major absorption of energy. [ABSTRACT FROM AUTHOR]

• A general tensor formula was obtained for the effective thermal conductivity of metal frame structures. • A novel design strategy was established for controlling the anisotropy of the thermal conductivity. • Various structures such as deformed octet truss, deformed tetrakaidecahedron and honeycomb structures were proposed for possible anisotropic structure candidates. • Analytical expressions for the individual components of effective thermal conductivity obtained for these anisotropic structures agree well with those of fully numerical results. The summation law (k x x + k y y + k z z = (1 − ε) k s ) for those structures made of the same metal frames has been generalized in terms of the thermal conductivity tensor k i j = ∑ n = 1 N s n k s ( g → n · e → i) ( g → n · e → j) in order to identify the conditions for orthotropic thermal conductivity and the level of the anisotropy of thermal conductivity in metal frame structures. A novel design strategy was proposed for controlling the anisotropy of the effective thermal conductivity tensors in various metal frame structures. Both three-dimensional lattice frame structurers and two-dimensional prismatic cellular honeycomb structures were considered to achieve their desired levels of the anisotropy in the thermal conductivity tensors. The relationships between the level of the anisotropy and frame design parameters are found for rectangular frame structures, deformed octet-truss structures, deformed tetrakaidecahedron structures and various kinds of honeycomb structures. The relationships analytically obtained for these structures agree well with the full 3D numerical results, and thus can serve as a theoretical basis to design the anisotropy of the effective thermal conductivity in metal frame structures according to their particular thermal applications. [ABSTRACT FROM AUTHOR]

Graphene is one-atom thick nanocarbon displaying a unique honeycomb structure and extensive conjugation. In addition to high surface area to mass ratio, it displays unique optical, thermal, electronic and mechanical properties. Atomic scale tunability of graphene has attracted immense research interest with a prospective utility in electronics, desalination, energy sectors, and beyond. Its intrinsic opto-thermal properties are appealing from the standpoint of multimodal drug delivery, imaging and biosensing applications. Hydrophobic basal plane of sheets can be efficiently loaded with aromatic molecules via non-specific forces. With intense biomedical interest, methods are evolving to produce defect-free and dispersion stable sheets. This review summarizes advancements in synthetic approaches and strategies of stabilizing graphene derivatives in aqueous medium. We have described the interaction of colloidal graphene with cellular and sub-cellular components, and subsequent physiological signaling. Finally, a systematic discussion is provided covering toxicological challenges and possible solutions on utilizing graphene formulations for high-end biomedical applications. Unlabelled Image • Graphene is a one-atom thick nanocarbon displaying high surface area-to-mass ratio. • Dispersion stable graphene is of great biomedical interest. • Advancement in synthetic approaches and interaction of colloidal graphene with biointerfaces are discussed. • Toxicological challenges on utilizing graphene for high-end biomedical applications have been reviewed. [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]