Search

Three-dimensional reinforcements can improve overall mechanical and wear properties of matrix material. However, the structure of traditional three-dimensional reinforcement is difficult to control. In this work, the 316L honeycomb structure were fabricated by selective laser melting, and ZA8 alloy were added to prepared 316L/ZA8 alloy composites using squeeze casting. The tribological behavior of ZA8 alloy and composites at different temperatures was studied through pin-on-disc wear tests. The results show that the addition of honeycomb reinforcements can reduce the friction coefficient and improve the stability of ZA8 alloy after running-in stage at room temperature. At high temperatures, the reinforcements can restrain the plastic deformation of ZA8 alloy. The wear rate of the composite decreases with the increase of honeycomb apertures at both room temperature and 120 °C. The reinforcements have effect on the wear mechanisms of ZA8 alloy at different temperatures. The wear mechanism of ZA8 at different temperatures is mainly adhesive wear, while the plastic deformation on the surface of ZA8 is more severe at 120 °C. The composites with small honeycomb aperture exhibit adhesive wear and severe abrasive wear at both room temperature and 120 °C, accompanying with significant oxidative wear at 120 °C. The wear mechanism of composites with larger honeycomb aperture at different temperatures is mainly adhesive wear. [ABSTRACT FROM AUTHOR]

Carbon aerogels have attracted increasing interest as electrode material and conductive template for supercapacitors due to their unique porous structure and strong electrical conductivity. However, the satisfactory strategy for fabricating carbon aerogels with excellent electrochemical performance remains to be explored. Herein, polyimide aerogels with porous fibrous networks were successfully synthesized by ambient pressure drying, and nitrogen-doped carbon aerogel were obtained after high-temperature processing by using the polyimide aerogel as the precursor. The pore structure of carbon aerogel was controlled by adjusting the repeat unit of polyimide molecular chain. When the repeat unit was 60 and carbonization temperature was 800 °C, PA-60-800 exhibits a typical honeycomb porous structure, which contains numerous meso-micro-porosity and provides a large specific surface area > 1000 m2 g−1. In addition, PA-60-800 showed excellent electrochemical behavior with the specific capacitance of 314.1 F g−1 at 0.5 A g−1. After 10,000 cycles of galvanostatic cycling, the electrode still maintains a capacity retention of 98.8%. Moreover, PA-60-800-assembled symmetric supercapacitor display a high energy density of 23 Wh kg−1 at a power density of 535.8 W kg−1. This work proposes an alternative path for the preparation of high-performance nitrogen-doped carbon aerogel electrode materials. [ABSTRACT FROM AUTHOR]

As nanotechnology floods application areas like medicine, electronics, water remediation, space and textiles, just to name a few, some nanomaterials remain in the spotlight due to their fantastic properties and their incredible potential. Such is the case of the 2D, transparent, flexible, strong, carbon-based nanomaterial called graphene. Graphene consists of sp2 hybridized carbon arranged in a flat network packed in a honey-comb pattern, having thus mono-atomic thickness. Its isolation in 2004 opened the door to numerous investigations and its research is funded each year by governments, industries and academia worldwide. Due to its non-hydrophilic nature, some applications represent a challenge (particularly biological and medical applications), thus an oxygen/hydrogen-functionalized hydrophilic version of it has lately gained popularity, its name is graphene oxide. This document aims to review the synthesis methods of graphene, graphene oxide and reduced graphene oxide. A revision of the most important top-down and bottom-up methods is presented, focusing on chemical vapor deposition for the growth of graphene and the wet-chemical methods for the synthesis of graphene oxide and the reduction techniques available for reduced graphene oxide. We conclude by analyzing the current situation of graphene and graphene oxide production and the challenges that need to be tackled in order to meet the short-term demand of these nanomaterials for the promised applications. [ABSTRACT FROM AUTHOR]

The effects of hole shape and orientation on the mechanical properties of micro-scale 2D honeycomb structures, fabricated using a focused ion beam equipment, have been investigated using an in situ micro-mechanical testing machine inside the scanning electron microscope. The material used was single-crystal Ni oriented in the < 100 > direction, with the plane of the 2D micro-lattice having a {001} normal direction. The hole shapes explored were hexagonal and circular, while two different orientations of the hexagonal holes were also compared. One of these orientations had a horizontal arm (designated 0° orientation), while the other had a vertical arm (30° orientation) in each hexagon. The results indicate that there is substantial change in strength and ductility depending on the orientation and shape of the holes with respect to the tensile axis. The samples with 30° oriented hexagonal holes had the lowest strength and highest ductility, while the samples with circular holes showed the greatest yield and tensile strength. The samples with the 0° orientated hexagonal holes had much higher strength and lower ductility than the 30° orientated ones. Moreover, the samples with 0° orientated hexagonal holes, which had a similar hole pattern arrangement to the ones with circular holes, had a similar strength to those of the latter type. Thus, it is apparent from this study that the orientation or arrangement of the holes is more important in determining the properties of the 2D microlattice than the shape of the holes. Finite element simulation of the lattice structures utilised the GTN (Gurson, Tvergaard and Needleman) model to evaluate the failure modes under uniaxial tension. The lattice structure has been shown, in a previous paper by the authors, to exhibit composite like behaviour with strength differences in various parts arising from size effects. These size effect variations were incorporated into the model, and a generalised formulation for the GTN parameters was proposed on the basis of one of the experimental configurations and subsequently applied to the other geometries. The models were in good quantitative agreement with the experimental results with accurate representation of the flows stress and failure modes. [ABSTRACT FROM AUTHOR]

Honeycomb is considered an excellent structural material because of its high strength and shear rigidity, excellent energy absorbing property, high impact strength, lower weight, high crushing stress, and almost constant crushing force. Honeycomb being a cellular solid is a well-known core used to build a sandwich structure while making structural composites. Because of this excellent mechanical performance, honeycombs are frequently used in the aircraft industry as a core of sandwich panels and in the automotive industry as efficient impact attenuators. The hollow spaces in the honeycomb structure reduce weight but also ensure required strength, provided they are designed correctly. 3D woven honeycomb composite has a promising future in the lightweight application areas and can be the real substitutes for aluminum and other metal alloys as these structures provide structural integrity. In this review, the basic concept of textile-based 3D woven honeycomb composites, engineering design, manufacturing process, structure-properties relationship, and applications of 3D woven honeycomb fabrics and their composites are discussed in detail. Geometrical modeling of 3D woven honeycomb fabric and theoretical analysis of impact, flexural, and compression behavior of their composites are summarized to appreciate the potential advantages of textile-based honeycomb structural composites. [ABSTRACT FROM AUTHOR]

Based on the butterfly pattern structure and the star-shaped honeycomb structure, a novel auxetic butterfly-shaped honeycomb structure (BSH) was constructed, which realized the coupling improvement of negative Poisson's ratio and in-plane stiffness. Under uniaxial tension, the equivalent elastic modulus and Poisson's ratio of the BSH structure were derived by the energy method. The relationship between Poisson's ratio and structural parameters of the BSH structure was discussed to optimize the structural parameters by numerical analysis. Poisson's ratio and relative elastic modulus were taken as the objective function groups. The Pareto solution set was obtained by the Gamultiobj multi-objective genetic algorithm method. The Pareto solution set was sorted based on the entropy-weight TOPSIS method, and the optimal solution was selected as the solution of the novel structure optimization design. The correctness of the theoretical results was verified by the finite element analysis and experiment results. Furthermore, compared with the traditional re-entrant hexagonal honeycomb structure and the star-shaped honeycomb structure, the relative elastic modulus and auxetic effect of the BSH structure were greatly improved, and the stiffness of the novel structure was improved while maintaining a high auxetic effect. [ABSTRACT FROM AUTHOR]

This paper proposes a novel flexible pressure sensor based on carbon black (CB), carboxy-methyl cellulose (CMC), and gelatin. CMC and gelatin are both food-grade materials that are degradable, non-toxic, and environmentally friendly. Freeze drying is performed to obtain a sensor porous honeycomb structure that achieves not only a wide monitoring range from 0 to 140% strain, but also high sensitivity (maximum gauge factor of 12.5, which is higher than ordinary conductive CB composite systems). After 3000 repeated presses, the sensor remains unchanged and retains its high sensitivity. This stable sensor response is promising for long-term practical applications. The proposed sensor is applied to a speech recognition system and can distinguish the different components of a sentence, thereby achieving accurate speech recognition. It is also capable of monitoring human body movements, including joint flexion and finger movement. Finally, a sensor integrated network is constructed for application to a human–machine interface. The proposed CB sponge pressure sensor has important applications for medical wearable devices and smart wear. [ABSTRACT FROM AUTHOR]

Honeycomb woven fabric is a single-layer fabric with three-dimensional effect. The effect is attributed to the increased length of warp and weft floats from the center to the sides of a weave unit, resulting in an inverted pyramid space on surface and an internal closed space in fabric. In order to study the practical application of such fabrics, 12 honeycomb woven fabrics were fabricated by considering the type of weft yarns (PET FDYs/PET DTYs/carbon fibers) and weft density (60/80/100 yarns per inch). Physical properties, including air permeability, warmth retention, water absorption, vapor transfer and flexible rigidity, compressibility and tensile properties, were all investigated. In addition, the characteristics of as-made fabrics were explored as a flexible normal pressure sensor with the capacitive structure of carbon fiber bundles, including the sensitivity, hysteresis and repeatability. The results showed that the weft density and elastic yarns have a regular influence on the physical properties, and the carbon fibers increase the initial modulus remarkably. Besides, an excellent sensing performance of as-made fabric was noted to be a flexible pressure sensor. Demonstrations of such fabric sensor in detecting finger pressing and object placing were performed, and corresponding actions were noted for the output clear and effective capacitive signals. [ABSTRACT FROM AUTHOR]

Graphene oxide (GO) belongs to carbon family with honeycomb structure having hydroxide, carbonyl, and carboxylic moieties at its basal plane. These functionalities are decreased in reduced graphene oxide (rGO), and this boosts the intrinsic properties of GO. Herein, in this work, the effect on physical and chemical properties of GO and rGO in combination with copper-doped zinc oxide (Cu-ZnO) thin films, prepared via DC/RF sputtering, was investigated for the very first time. The deposition of Cu-ZnO over rGO (Cu-ZnO@rGO) showed remarkably superior properties and presented an extension in d-spacing without preferred plane orientation of Cu-ZnO plane, and this was found to be due to its hydrophobic nature. The decrease in band gap of composite thin films was due to the surface electric charge conducted by GO or rGO. The enhanced dielectric constant is attributed due to increase in electron-hole pairs owing to the increase in sp2 hybridization. However, sp2 network was also found to be responsible to provide the conductivity path way which increases the dielectric loss in Cu-ZnO@rGO thin films as compared to that in Cu-ZnO@GO; this might be due to aggregation of Cu-ZnO nanoparticles over the rGO films in comparison with GO as evident from the morphological analysis by AFM. The change in surface chemistry was ascribed with the ratio of COOH, C=O, C-OH and C-C bonding in the Cu-ZnO@GO and Cu-ZnO@rGO thin films as unveiled in their XPS analysis. The developed thin films exhibited enhanced antimicrobial activity against E. coli and E. faecalis which might be due to the synergistic effects of Cu-ZnO with GO or rGO. [ABSTRACT FROM AUTHOR]

In this study, a novel bio-inspired honeycomb sandwich panel (BHSP) based on the microstructure of a woodpecker's beak is proposed. Unlike a conventional honeycomb, the walls of the bio-inspired honeycomb (BH), which is used as the core of a sandwich panel, are made wavy. Finite element simulation shows that under dynamic crushing the proposed BHSPs exhibit superior energy absorption capability compared with the conventional honeycomb sandwich panel (CHSP). In particular, the specific energy absorption (SEA) of the BHSP increases by 125% and 63.7%, respectively, compared with that of the honeycomb sandwich panel with the same thickness core or the same volume core. In addition, a parametric study of the BHSPs is carried out to investigate the influences of the wave amplitude, wave number and core thickness on the energy absorption performance of the BHSPs. It is found that the BH core with a larger wave number and amplitude shows higher SEA. Furthermore, an increase in core thickness can improve the SEA. These results provide guidelines in the design of a lightweight sandwich panel for high-energy absorption capability. [ABSTRACT FROM AUTHOR]

This study proposes a type of trabecular-honeycomb biomimetic structures with high-efficiency energy-absorbing abilities inspired by beetle elytra. Because the trabecular structure is distributed at the ends of the honeycomb walls, the proposed structure is named an end-trabecular beetle elytron plate crash box, or EBEP crash box for simplification. A comparison between the EBEP crash box and conventional crash box (a buffering structure generally used in modern devices and vehicles) is conducted using compression experiments and finite element method. We present the following results. (1) In contrast to the fluctuation stage with a low force in a conventional crash box, the force-displacement curve of the EBEP crash box possesses a rising stage and an approximate plateau with a higher force; as a result, the absorbing energy ability and compression force efficiency are 5 and 2.6 times greater than those of a conventional crash box, respectively. (2) Experimental and numerical comparisons reveal that there is cracking failure in the conventional crash box; however, the coordinated and uniform S-typed laminated compression deformation is developed in the EBEP crash box. (3) The influences of the amplitude (A) of the sine wave deformation line on the peak force and the compression force efficiency of the EBEP crash box are investigated, thereby providing a feasible method for adjusting the peak force according to different engineering requirements. These results provide new inspiration for applying EBEP crash boxes and exploiting new buffering structures and materials in the energy-absorbing field. [ABSTRACT FROM AUTHOR]

This study presents the electrochemical studies of activated carbon prepared from palm kernel shell (ACPKS), with CaO impregnation. The CaO is obtained from chicken eggshell waste to produce CaO/ACPKS, which shows highly porous honeycomb structure with homogeneous distribution of CaO nanoparticles (30-50 nm in size). The prepared materials are evaluated as supercapacitor electrodes by testing their electrochemical characteristics. A high specific capacitance value of 222 F g−1 at 0.025 A g−1 is obtained for CaO/ACPKS, which is around three times higher than that for ACPKS (76 F g−1). In addition, electrochemical impedance data show lower impedance for CaO/ACPKS. Lastly, a practical symmetrical supercapacitor is fabricated by CaO/ACPKS and its performance is discussed. [ABSTRACT FROM AUTHOR]

An investigation of the mechanical behaviors on hierarchical re-entrant honeycomb structures was undertaken using finite element method. The hierarchical structure with a hierarchy order n (n ≥ 1) was constructed by replacing each vertex of a re-entrant hexagonal structure of hierarchy order n − 1 with a smaller re-entrant hexagon with identical geometry aspect ratio. The Poisson’s ratio and energy absorption capacity of re-entrant structures of different hierarchy orders were studied under various compression velocities. The minimum Poisson’s ratios of the first-order (n = 1) and second-order (n = 2) hierarchical re-entrant structures were − 1.581 and − 1.823, respectively; they were 32.9 and 53.2% lower than that of a zeroth-order hierarchical structure (i.e., conventional re-entrant hexagon). The second-order hierarchical structure exhibited the highest rate of increase in energy absorption capacity with an increasing compression velocity. The plateau stresses of the first- and second-order hierarchical structures were lower than that of the zeroth-order hierarchical structure; however, the second-order hierarchical structure exhibited the highest energy absorption capacity at high compression velocity rate (v > 40 m/s). The energy absorption capacities of the first- and second-order hierarchical structures proposed in the present study are 1.5 and 1.8 times, respectively, higher than those of the hierarchical re-entrant structures proposed in our previous work (Li et al. in Smart Mater Struct 26:025014, 2017). [ABSTRACT FROM AUTHOR]

NiS@polypyrrole/nickel foam (NiS@PPy/NF) composite was successfully synthesized by combining a facile hydrothermal synthesis and a simple electrochemical-deposited process. For comparative study, the honeycomb-shaped NiS had in situ been grown on NF without the addition of any nickel salt to obtain the NiS/NF composite. The electrochemical measurement results show that the area capacitance of the NiS@PPy/NF electrode is 1.13 F cm that is slightly lower than 1.26 F cm of the NiS/NF electrode at a high current density of 30 mA cm, yet its rate capability and cycling stability are far better than those of the NiS/NF electrode. Meanwhile, an asymmetric supercapacitor on the basis of the NiS@PPy/NF anode and the AC cathode exhibits a high energy density and power density of 17.54 Wh kg and 179.33 W kg at 2.5 mA cm, respectively; besides, the energy density is still 8.67 Wh kg at a power density of 3587.41 W kg even at 50 mA cm. Moreover, the capacitances of the device remain unchanged after 3000 galvanostatic charge/discharge cycles at a high current density of 30 mA cm. Furthermore, two such 1 cm devices connected in series can light five 40-mW LED indicators or power one of the same-power LED indicator for 20 min after being fully charged. The results demonstrate that our asymmetric supercapacitor has a promising potential in commercial applications. [ABSTRACT FROM AUTHOR]

Microstructural changes in porous cordierite caused by machining were characterized using microtensile testing, X-ray computed tomography, and scanning electron microscopy. Young's moduli and Poisson's ratios were determined on ~215- to 380-μm-thick machined samples by combining digital image correlation and microtensile loading. The results provide evidence for an increase in microcrack density and decrease of Young's modulus due to machining of the thin samples extracted from diesel particulate filter honeycombs. This result is in contrast to the known effect of machining on the strength distribution of bulk, monolithic ceramics. [ABSTRACT FROM AUTHOR]

The effect of internal architecture on the mechanical properties of stochastic honeycombs was investigated by using four polypropylenes with varying rheological properties. The polymers were first characterized in terms of their thermal and mechanical properties, and then used to fabricate a set of stochastic honeycombs over a range of densities. The internal architecture was characterized by X-ray tomography, and the out-of-plane compressive properties of the stochastic honeycombs were determined. Overall, the strengths varied from 1 to 4 MPa over a core density range of 7-14 %. A thin-plate buckling model was developed to build a predictive strength model. This model was split into a material properties portion (dependent on the polymer stiffness) and an architectural portion (dependent on the fraction of bound webs in the honeycomb). The model was found to serve as a good first step towards predicting the strength of irregular honeycombs. [ABSTRACT FROM AUTHOR]

In an effort to improve thermal stability and mechanical properties of porous polypropylene (PP) separators for lithium-ion battery, SiO/PP/SiO composite separators were prepared by introducing SiO layer on both sides of PP separator through a dip-coating process, with polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) as binder. SiO nanoparticles are evenly distributed and closely packed in the coated layer, which features a porous honeycomb structure. This unique porous structure was quantitatively analyzed by Gurley value, and it can retain liquid electrolyte, leading to higher electrolyte uptake and ionic conductivity of the composite separator. The introduction of SiO-coated layers can not only suppress thermal shrinkage but also improve mechanical properties of the composite separator. C-rate capability and cycle performance of composite separator were also investigated, and compared to those of pristine PP separator. [ABSTRACT FROM AUTHOR]

An optimization method to obtain the cell wall properties of Nomex honeycomb material is presented. There, the outcomes of physical experiments and micromechanical simulations are compared in an effort to identify the geometric or/and material parameters for the best match. Only the cell wall thickness and Young's modulus, called here as the hidden parameters, are used in the matching as the Young's modulus is difficult measure reliably. The mean values and standard deviations of the geometric parameters of the cell structure model are obtained through image analysis. In the micromechanical model used, the cell walls are considered as linearly elastic Bernoulli beams. The optimum hidden parameter values for the Nomex case turn out not to be unique but they appear in a combination known as the bending stiffness. [ABSTRACT FROM AUTHOR]

Interconnected submicron pores were created on the walls of a honeycomb monolith structure by the unidirectional freezing of a binary polymer solution. Agglomerated globules of polyethylene glycol (PEG) in a binary solution of polystyrene (PS) and PEG in 1,4-dioxane solvent were frozen unidirectionally in a liquid nitrogen bath. Removing the frozen solvent and the agglomerated globules of PEG by freeze-drying and leaching, respectively, enabled us to create interconnected pores in the PS walls. The combination of PS and PEG was effective in creating interconnected pores in the walls because PS and PEG are poorly soluble in one another. The higher freezing rate and lower PEG weight fraction of the binary solution effectively reduced the pore size in the microtube walls. [ABSTRACT FROM AUTHOR]

Polymeric honeycomb microporous films were prepared from fluorinated diblock copolymers, poly(tert-butyl acrylate)- b-poly(2-[(perfluorononenyl)oxy]ethyl methacrylate) (PtBA- b-PFNEMAs), and four other commercial polymers, including polystyrene (PS), polycarbonate (PC), polylactic acid (PLA), and polymethylmethacrylate (PMMA) via breath figures method. The as-formed fluorinated diblock copolymer micelles in chloroform were not only utilized to stabilize the templated water droplets in bulk, but also introduced as the water droplets stabilizer in other polymeric materials. Our strategy was successfully achieved, as the micropores were decorated with the fluorinated diblock copolymer as directly shown in the SEM images and FT-IR/ATR-FTIR. Polymer concentration and the solution casting volume effects were checked to tune the sizes of the micropores in diblock copolymer films. The ratio of the added fluorinated diblock copolymer as a novel factor to tune the sizes of the micropores was also investigated. [ABSTRACT FROM AUTHOR]

Currently, there is incomplete knowledge of the damping level and its sources in satellite structures and a suitable method to model it constitutes a necessary step for reliable dynamic predictions. As a first step of a damping characterization, the damping of honeycomb structural panels, which is identified as a main contributor to global damping, has been considered by ALCATEL SPACE. In this work, the inherent vibration damping mechanism in sandwich panels, including those with both aluminium and carbon fibre-reinforced plastic (CFRP) skins, is considered. It is first shown how the theoretical modal properties of the sandwich panel can be predicted from the stiffness and damping properties of its constituent components using the basic laminate theory, a first-order shear deformation theory and a simple discretization method. Next, a finite-element transcription of this approach is presented. It is shown to what extent this method can be implemented using a finite-element software package to predict the overall damping value of a sandwich honeycomb panel for each specific mode. Few of the many theoretical models used to predict natural frequencies of plates are supported by experimental data and even fewer for damping values. Therefore, in a second, experimental part, the Rayleigh–Ritz method and NASTRAN (finite-element software used by ALCATEL SPACE) predicted modal characteristics (frequency and damping) are compared with the experimentally obtained values for two specimens of typical aluminium core honeycomb panels (aluminium and CFRP skins) used by ALCATEL SPACE as structural panels. It is shown through these results that the method (theoretical and finite element) is satisfactory and promising. [ABSTRACT FROM AUTHOR]

Reports the derivation of elastic properties of a Poisson-Shear material for infinitesimal deformation based on a combined hexagonal honeycomb and re-entrant microstructures. Computation of the elastic coefficients by taking the double derivative of the potential energy of hinge rotational stiffness with respect to the orthogonal strains.

Thirteen commerical wing panels were fabricated and flown on a commercial aircraft to investigate the mechanisms of water migration through various honeycomb cores. A 12.2 J impact damage was not observed to cause damage propagation in aluminum and Korex® honeycomb materials. This was attributed to the ability of the cores to localize the impact damage. In Nomex® and glass fiber cores a different damage propagation mechanism was observed. In these cores, the damage was not confined to the localized area around the impact. Instead, core damage was seen as far as 2.0 cm from the point of impact. This increased core damage allowed the core to retain water. The retained water helped propagate the impact damage through a freeze thaw mechanism. Speed-tape repairs were only found to be statistically significant when water migrated through the core. Filling the honeycomb core with foam was shown to be an effective method for minimizing the damaging effects of water ingression. Slotting and draining the core also offered some relief from water accumulation in the core, but foaming damaged core was established as the most effective technique. [ABSTRACT FROM AUTHOR]

Demonstrates the creation of a honeycomb-type material by using a technique microembossing. Machining of small grooves into an aluminum plate; Pressing of the aluminum plate into the polymeric sheet using heat and pressure to produce grooves in the polymer; Putting together of thin sheets with the orientation of the grooves being different on each sheet; High stiffness-to-weight ratio of the structure.