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Silicon oxycarbide (SiOC) ceramics have been used to fabricate microwave-absorbing metastructures, demonstrating impressive absorption capabilities. However, SiOC ceramic metastructures with excellent performance require simple fabrication processes and appropriate mechanical and electromagnetic properties. In this study, a solvent-free photosensitive polysiloxane preceramic was developed by blending methoxy/hydroxy polysiloxanes with acrylates, with a ceramic yield of over 60% after curing using a novel two-step ultraviolet (UV)/thermal method. The composition and microstructure of SiOC ceramics can be designed by controlling the preceramic composition. Dense, crack-free gyroid-shellular shaped triple periodic minimal surface (GS-TPMS) electromagnetic metastructures were fabricated using digital light processing (DLP) 3D printing technology. By designing the porosity of the GS-TPMS structure to 51%, an effective absorption bandwidth that covers the X-band can be achieved at a thickness of 3.1 mm. The honeycomb structure, with a geometric density of 0.69 g/cm3, exhibited a high compressive strength of 107.05 MPa. This paper presents an efficient approach for the prompt and customized fabrication of lightweight ceramic metastructures with outstanding microwave absorption properties. • A solvent-free polysiloxane/acrylate hybrid preceramics is developed for 3D printing. • The UV/thermal two-stage treatment achieved cross-linking curing of the preceramics. • Multiscale design of SiOC ceramics for enhanced microwave absorption properties. • SiOC ceramic metastructures with effective absorption in the X-band are prepared. [ABSTRACT FROM AUTHOR]

The novelty of this research lies in the successful fabrication of a 3D-printed honeycomb structure filled with nanofillers for acoustic properties, utilizing an impedance tube setup in accordance with ASTM standard E 1050-12. The Creality Ender-3, a 3D printer, was used for printing the honeycomb structures, and polylactic acid (PLA) material was employed for their construction. The organic, inorganic, and polymeric compounds within the composites were identified using fourier transformation infrared (FTIR) spectroscopy. The structure and homogeneity of the samples were examined using a field emission scanning electron microscope (FESEM). To determine the sound absorption coefficient of the 3D printed honeycomb structure, numerous samples were systematically developed using central composite design (CCD) and analysed using response surface methodology (RSM). The RSM mathematical model was established to predict the optimum values of each factor and noise reduction coefficient (NRC). The optimum values for an NRC of 0.377 were found to be 1.116 wt% carbon black, 1.025 wt% aluminium powder, and 3.151 mm distance between parallel edges. Overall, the results demonstrate that a 3Dprinted honeycomb structure filled with nanofillers is an excellent material that can be utilized in various fields, including defence and aviation, where lightweight and acoustic properties are of great importance. [ABSTRACT FROM AUTHOR]

A non-pneumatic tire (NPT) overcomes the shortcomings of a traditional pneumatic tire such as wear, punctures and blowouts. In this respect, it shows great potential in improving driving safety, and has received great attention in recent years. In this paper, a carbon fiber-reinforced polyethylene terephthalate (PET/CF) honeycomb is proposed as a support structure for NPTs, which can be easily prepared using 3D printing technology. The experimental results showed that the PET/CF has high strength and modulus and provides excellent mechanical properties. Then, a finite element (FE) model was established to predict the compression performance of auxetic honeycombs. Good agreement was achieved between the experimental data and FE analysis. The influence of the cell parameters on the compressive performance of the support structure were further analyzed. Both the wall thickness and the vertically inclined angle could modulate the mechanical performance of the NPT. Finally, the application of vertical force is used to analyze the static load of the structure. The PET/CF honeycomb as the support structure of the NPT showed outstanding bearing capacity and stiffness in contrast with elastomer counterparts. Consequently, this study broadens the material selection for NPTs and proposes a strategy for manufacturing a prototype, which provides a reference for the design and development of non-pneumatic tires. [ABSTRACT FROM AUTHOR]

In light of the rapid advancements within the electronic industry, the urgent need for the development and implementation of advanced electromagnetic interference (EMI) shielding materials has become paramount. Herein a novel approach is presented for developing of lightweight honeycomb structures using 3D printing technology, combined with subsequent conductive spray coating, containing Silver Nanowires (AgNWs), to achieve effective EMI shielding as well as air vent functionality for thermal cooling.Using polyol method, AgNWs were synthesized having high aspect ratio and crystallinity for to be used as conductive coating on 3D printed structures. The EMI shielding results in X-band demonstrated that the developed structures exhibit promising EMI shielding properties, up to 35 dB attenuation with 2 mm honeycomb cell size, making them suitable for applications requiring EMI protection along with air venting. More importantly in all samples major contribution of the shielding efficiency comes from the absorption of the EM waves (up to 75 %) inside the structures which is helpful to reduce reflected EM noise.Effort was to effectively addresses the inherent limitations of conventional processing technology, by using additive manufacturing and material science to create structures for EMI shielding applications, bridging the gap between existing materials and desired components.

In this study, Al 2 O 3 honeycomb sandwich structures with different core geometries (square, triangular, circular) have been fabricated through an additive manufacturing system based on the stereolithography (SLA) method. The debinding procedure was performed under both nitrogen and air atmospheres. The impacts of the debinding atmosphere and core geometry on the densification and mechanical properties were investigated. The stiffness and flexural strength of the ceramics were examined experimentally using an impulse excitation of vibration technique and a three-point bending test, respectively. The specific stiffness and specific strength of the ceramics were also evaluated, with the core geometries taken into consideration. The outcomes showed that higher densification was achieved when the ceramics were exposed to debinding in nitrogen. The stiffness values were found to be similar for the same debinding condition within the honeycomb sandwich structures, irrespective of the core geometry. Notably, the highest specific stiffness (98 MNm/kg) was achieved for the samples subjected to debinding in nitrogen with a square core geometry. Furthermore, ceramics with square cores for debinding in a nitrogen atmosphere also demonstrated the highest performance in terms of specific strength (110 kNm/kg) within the honeycomb structures. This study demonstrated that Al 2 O 3 honeycomb sandwich structures with square cores may be suitable candidates for lightweight-structure demanding applications. [ABSTRACT FROM AUTHOR]

Despite the wide growth of additive manufacturing, it is still very expensive to mass produce 3D-printed parts. The costs can be minimized if the quantity of material required to produce a part can be substantially reduced by introducing hollow cavities into the structure, without compromising its properties. This study investigates the effect of the degree of hollowness and different internal cavity structures on the mechanical properties of 3D-printed materials. Test specimens were prepared with four polymeric materials (i.e., acrylonitrile butadiene styrene (ABS), polylactic acid (PLA), carbon fiber-reinforced (CFR) ABS, and CFR PLA) using the fused deposition modeling 3D printing technique. Internal hollow cavities were introduced to the specimens during printing and the specimens were prepared with three different cavity structures (i.e., hexagonal honeycomb, circular drills, and squares), and the degree of hollowness was varied from 0% to 30% in 10% increments. Tensile and flexural properties of the 3D-printed specimens were evaluated and analyzed. The mechanical properties of all specimens were found to decrease with increasing hollowness levels, regardless of the type of material or the internal cavity structure. The hexagonal honeycomb structure showed the best tensile properties out of the three internal cavity structures, while the flexural properties were not significantly affected by the internal cavity structure. The material type had a significant impact on the mechanical properties with PLA exhibiting better tensile and flexural properties than ABS, while their carbon fire reinforced counterparts showed enhanced mechanical properties than pure ABS and PLA. [ABSTRACT FROM AUTHOR]

Continuous fiber reinforced polymer composites are widely used in load-bearing components and energy absorbers owing to their high specific strength and high specific modulus. The path planning of continuous fiber is closely related to its structural defects and mechanical properties. In this work, continuous fiber reinforced polymer honeycomb structures (CFRPHSs) with different printing paths were designed and fabricated via the fused deposition modeling (FDM) technique. The investigation of fiber dislocation at path corners was utilized to analyze the structural defects of nodes caused by printing paths. The lower stiffness nodes filled with pure polymer due to fiber dislocation result in uneven stiffness distribution. The bending performance and deformation modes of CFRPHSs with different printing paths and corresponding pure polymer honeycomb structures were investigated by three-point bending tests. The results showed that the enhancement effect of continuous fibers on the bending performance of honeycomb structures was significantly affected by the printing paths. The CFRPHSs with a staggered trapezoidal path exhibited the highest specific load capacity (68.33 ± 2.25 N/g) and flexural stiffness (627.70 ± 38.78 N/mm). In addition, the fiber distributions and structural defects caused by the printing paths determine the stiffness distribution of the loading region, thereby affecting the stress distribution and failure modes of CFRPHSs. [ABSTRACT FROM AUTHOR]

Magnesium (Mg)/Polylactic acid (PLA) composites are promising materials for bone regeneration and tissue engineering applications. PLA is a biodegradable and biocompatible polymer that can be easily processed into various shapes and structures, such as scaffolds, films, and fibers, but has low biodegradability. Mg is a biocompatible metal that has been proven to have good biodegradability and osteoconductivity, which makes it suitable for bone tissue engineering. In this study, we prepared and characterized a Mg/PLA composite as a potential material for direct ink writing (DIW) in 3D printing. The results showed that the addition of Mg has a significant impact on PLA's thermal and structural properties and has also significantly increased the degradation of PLA. XRD was used to determine the degree of crystallinity in the PLA/Mg composite, which provides insight into its thermal stability and degradation behavior. The crystallization temperature of PLA increased from 168 to 172 °C for a 15 wt% Mg incorporation, and the melting temperature reduced from 333 °C to 285 °C. The surface morphology and composition of these films were analyzed with SEM. The films with 5 wt% of Mg particles displayed the best-ordered honeycomb structure in their film form. Such structures are considered to affect the mechanical, biological and heat/mass transfer properties of the Mg/PLA composites and products. Finally, the composite ink was used as a feed for direct ink writing in 3D printing, and the preliminary 3D printing experiments were successful in resulting in dimensionally and structurally integral scaffold samples. The shape fidelity was not very good, and some research is needed to improve the rheological properties of the ink for DIW 3D printing. [ABSTRACT FROM AUTHOR]

Inspired by the double-helix structure of biological DNA, low-volume fraction and high-strength Al 2 O 3 twisted honeycomb structures with characteristics similar to those of helical structures in the z -axis were prepared by digital light processing 3D printing technology. As the twist angle increased, the compressive strength of the fabricated Al 2 O 3 structure decreased, and the deformation mechanism of the Al 2 O 3 structures gradually changed from stretching-dominated to bending-dominated, which can be predicted by the Gibson–Ashby model. The relationship between the effective elastic modulus and the volume fraction that can be modified by varying the wall thickness was described by the Pabst–Gregorova exponential relationship. The compressive strength of the Al 2 O 3 structure with a twist angle of 0° can reach 62.4 MPa at a volume fraction of 13.3%, providing guidance to optimize lightweight structures of ceramics. [ABSTRACT FROM AUTHOR]

Three-dimensional printing by fused deposition modeling (FDM) coupled with hot-melt extrusion (HME) is a point of convergence of research efforts directed toward the development of personalized dosage forms. In addition to the customization in terms of shapes, sizes, or delivered drug doses, the modulation of drug release profiles is crucial to ensure the superior efficacy and safety of modern 3D-printed medications compared to those of conventional ones. Our work aims to solidify the groundwork for the preparation of 3D-printed tablets that ensure the sustained release of diclofenac sodium. Specifically, we achieved the fast release of a diclofenac sodium dose to allow for the prompt onset of its pharmacological effect, further sustaining by the slow release of another dose to maintain the effect over a prolonged timeframe. In this regard, proper formulation and design strategies (a honeycomb structure for the immediate-release layer and a completely filled structure for the sustained-release layer) were applied. Secondarily, the potential of polyvinyl alcohol to function as a multifaceted polymeric matrix for both the immediate and slow-release layers was explored, with the objective of promoting the real-life applicability of the technique by downsizing the number of materials required to obtain versatile pharmaceutical products. The present study is a step forward in the translation of HME-FDM-3DP into a pharmaceutical manufacturing methodology. [ABSTRACT FROM AUTHOR]

A non-pneumatic tire (NPT) overcomes the shortcomings of a traditional pneumatic tire such as wear, punctures and blowouts. In this respect, it shows great potential in improving driving safety, and has received great attention in recent years. In this paper, a carbon fiber-reinforced polyethylene terephthalate (PET/CF) honeycomb is proposed as a support structure for NPTs, which can be easily prepared using 3D printing technology. The experimental results showed that the PET/CF has high strength and modulus and provides excellent mechanical properties. Then, a finite element (FE) model was established to predict the compression performance of auxetic honeycombs. Good agreement was achieved between the experimental data and FE analysis. The influence of the cell parameters on the compressive performance of the support structure were further analyzed. Both the wall thickness and the vertically inclined angle could modulate the mechanical performance of the NPT. Finally, the application of vertical force is used to analyze the static load of the structure. The PET/CF honeycomb as the support structure of the NPT showed outstanding bearing capacity and stiffness in contrast with elastomer counterparts. Consequently, this study broadens the material selection for NPTs and proposes a strategy for manufacturing a prototype, which provides a reference for the design and development of non-pneumatic tires.

In this paper, a honeycomb Si3N4 ceramic was fabricated by 3D printing with a well‐preserved structure. The effects of Si3N4 content on the rheological properties of Si3N4/sol–silica ink and the printing resolution of products were investigated. The microstructure, phase composition, liner shrinkage rate, and fracture behavior of printed samples before and after sintering were systematically characterized in detail. The results showed that the modified inks had the optimized rheological properties, and the stress–shear rate curves corresponding to each slurry could be well described by Bingham and Herschel–Bulkley fluid models. The corresponding slump rates of the printed samples with different Si3N4 to sol–silica mass ratios were all lower than 4%, and the linear shrinkage rate of all of the samples after sintering was below 20%. The fracture behavior under compressive loading of the honeycomb Si3N4 ceramics tended to be non‐catastrophic fractures both before and after sintering. The compressive strengths of all of the printed samples decreased with the increase of the Si3N4 content, and the highest compressive strength of the honeycomb ceramics could reach 131.2 MPa after sintering at 1600°C, which was about 366.9% higher than that of the samples in green state prior to the sintering. [ABSTRACT FROM AUTHOR]

This research aims at enhancing the performance of scale-model scooter decks by investigating various architected cellular metamaterial and bio-inspired core structure designs, such as honeycomb, tetrachiral, re-entrant, arrowhead, and star-shaped arrangements. An initial effort is made toward the design and rapid prototyping of small-scale deck with a uniform honeycomb core structure. More specifically, polylactic acid is utilized to fabricate complex structures via fused filament fabrication technique. Investigation is then focused on its mechanical performance, such as its bending properties obtained through a three-point bending test. Simulations are also conducted with different core configurations using a geometrically non-linear finite element method which is implemented. Experiments are carried out to verify the numerical results. After validation, various patterns are modeled, and eventually, it is observed that the functionally graded arrowhead structure has the best bending resistance, compared to other bio-inspired and mechanical metamaterial structures. At a constant force of 845 N, the functionally graded arrowhead design lowers the deflection in the middle of the scale model of scooter deck by up to 14.7%, compared to the uniform arrowhead structure. Furthermore, comparing the tetrachiral and functionally graded arrowhead configurations at a constant force, a 30% reduction in central deflection was observed. Due to the lack of similar results and designs in the specialized literature, this work could potentially advance the state-of-the-art scooter core designs and provide designers with architectures that could enhance the performance and safety of scooters. [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]

Over the years, the building envelope has evolved from a protective barrier element to a complex filter system capable of optimizing the interactions between the external and internal environments. An efficient envelope reacts flexibly to variable external conditions, minimizing heat losses in the winter season. Therefore, insulating materials play a fundamental role in building's thermal performance. In this scenario, Additive Manufacturing represents an emerging and promising solution for the construction sector. Three-dimensional printing allows the creation of custom geometries, reduces material waste, and automates the construction process. This work aims to compare the thermal performance of a PLA (polylactic acid) 3D-printed block with an internal honeycomb structure whose air cavities are filled with natural and recyclable waste-insulating materials. The selected air cavity filling materials are (i) wood sawdust, (ii) sheep's wool, and (iii) hemp. The thermal behavior of the block with the different filling materials was experimentally tested via Heat Flow Meter (HFM) method in a controlled environment (Hot Box). The results showed that the introduction of waste material significantly improved the thermal performance of the 3D-printed block compared to the case of air cavities. A thermal transmittance (U-value) reduction of up to 57% was obtained. Moreover, the sheep's wool showed the best performance, with a U-value equal to 0.53 ± 0.02 W/m2K, i.e., 18.5% less than the wood sawdust and 19.7% less than hemp. [ABSTRACT FROM AUTHOR]

Continuous fiber reinforced polymer composites are widely used in load-bearing components and energy absorbers owing to their high specific strength and high specific modulus. The path planning of continuous fiber is closely related to its structural defects and mechanical properties. In this work, continuous fiber reinforced polymer honeycomb structures (CFRPHSs) with different printing paths were designed and fabricated via the fused deposition modeling (FDM) technique. The investigation of fiber dislocation at path corners was utilized to analyze the structural defects of nodes caused by printing paths. The lower stiffness nodes filled with pure polymer due to fiber dislocation result in uneven stiffness distribution. The bending performance and deformation modes of CFRPHSs with different printing paths and corresponding pure polymer honeycomb structures were investigated by three-point bending tests. The results showed that the enhancement effect of continuous fibers on the bending performance of honeycomb structures was significantly affected by the printing paths. The CFRPHSs with a staggered trapezoidal path exhibited the highest specific load capacity (68.33 ± 2.25 N/g) and flexural stiffness (627.70 ± 38.78 N/mm). In addition, the fiber distributions and structural defects caused by the printing paths determine the stiffness distribution of the loading region, thereby affecting the stress distribution and failure modes of CFRPHSs.

3D printing technology is the new frontier in building construction. It is especially useful for making small structures within a short period. Full construction, including interior partitions and exterior façades, can be achieved with this technology. This paper proposes a parametric Voronoi tessellations model for quickly generating and fabricating 3D-printed hexagonal honeycomb partitions for interior design. Comprehensive experimental testing was conducted to characterize the mechanical properties and investigate the energy absorption characteristics of the proposed 3D-printed hexagonal honeycomb while comparing it to alternative hexagonal honeycomb structures. The tests included tensile testing (ASTM-D638) of the printed Polylactic Acid (PLA) material, especially with the almost total absence of conducted research that reported mechanical properties for 3D printed material with low infill percentages such as 10%. In addition, an in-plane quasi-static axial compression testing of the lightweight honeycomb structures was also conducted on the printed structure with the same low infill percentage. Compared to non-Voronoi honeycomb structures, the Voronoi honeycomb resulted in superior mechanical and energy absorption properties with energy absorption values ranging from 350 to 435 J and crash force efficiency being 1.42 to 1.65.

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 time-dependent understanding of swelling characteristics and external stimuli behavior is crucial for the development and understanding of functional hydrogels. Magnetic resonance imaging (MRI) offers the opportunity to study three-dimensional (3D) soft materials nondestructively. This technique is already widely used as an image-based medical diagnostic tool and is applied here to evaluate complex structures of a hydrogel—a double network of chemically crosslinked casein enhanced with alginate—fabricated by 3D printing. When hydrogel disks immersed in four different liquid systems were analyzed, the material exhibited distinct system-dependent behavior characterized by rheological and mechanical measurements. Further material functionalization was achieved by macroscopic structuring of the hydrogel as an auxetic material based on a re-entrant honeycomb structure. MRI offers the advantage of monitoring overall changes in the area of the analyzed specimen and internal structural changes simultaneously. To assess the behavior of this complex structure, a series of short MRI measurements, each lasting 1.7 min, captured liquid diffusion and thus structural swelling behavior. A clear dependence of external and internal structural changes as a function of liquid properties causing these changes was observed. In conclusion, this approach might pave the way for prospective applications to monitor liquid diffusion into (e.g., vascularization) and swelling behavior of functional hydrogels. [ABSTRACT FROM AUTHOR]

To develop a composite filament with an electromagnetic-wave-absorbing function suitable for 3D printing, we combined thermoplastic polyurethane (TPU) as the matrix material and carbonyl iron powder (CIP) as the absorbing agent to prepare TPU/CIP composites by melt blending. The composites passed through a single-screw extruder to obtain a filament with 2.85 mm in diameter. Different absorber structures were printed using fused deposition modeling, and their absorption properties were tested using the bow method. The results showed that by increasing CIP content, the electromagnetic-wave absorption performance gradually improved, while the mechanical properties substantially decreased. When the mass fraction of the CIP was 60%, the TPU/CIP composite showed good absorption properties and could be prepared into a filament that met the requirements for fused deposition modeling. Simulation results of plate-wave-absorption performance showed that, when the plate thickness was 3 mm, the minimum reflection loss was −21.98 dB, and the effective absorption bandwidth (for reflection loss below −10 dB) was 3.1 GHz (4.55–7.65 GHz). After the TPU/CIP composite was printed into honeycomb, pyramid, and other absorber structures, the absorption performance was further improved. For a structure printed with a gradient-wall honeycomb structure at 3 mm thickness, the effective absorption bandwidth was 4.64 GHz (8.48–13.12 GHz), and the minimum reflection loss was −36.69 dB. The effective absorption bandwidth of the pyramid structure reached 15.88 GHz (2.12–18 GHz), and the minimum reflection loss was −49.75 dB. [ABSTRACT FROM AUTHOR]

In this paper, we briefly reviewed the development of cranial windows and their functions in brain sciences. We demonstrated that a 3D-printed titanium frame coated with a polydimethylsiloxane (PDMS) film could serve as an excellent transparent cranial window for long-period, in vivo optical experiments in mice and rats, and the devices also allowed multiple injections through the elastic PDMS window, without leaking. Our large-area honeycomb structured Ti-PDMS samples had a relative transparent area ratio of over 90% but a mechanical strength close to that of a human skull, showing a promising potential for applications in large animals as multifunctional cranial windows. We also suggested that more functional modules could be integrated in the large-area Ti-PDMS cranial device, thus turning it into a novel wearable smart platform for wireless data communication, electro-probing and brain stimulation, optical imaging, transcranial injection, and so on, for both fundamental research on neuroscience and clinical practices dealing with brain damage and disease. [ABSTRACT FROM AUTHOR]

The advancement of 3D-printing technology has ushered in a new era in the production of machine components, building materials, prototypes, and so on. In 3D-printing techniques, the infill reduces the amount of material used, thereby reducing the printing time and sustaining the aesthetics of the products. Infill patterns play a significant role in the property of the material. In this research, the mechanical properties of specimens are investigated for gyroid, rhombile, circular, truncated octahedron, and honeycomb infill structures (hexagonal). Additionally, the tensile properties of PLA 3D-printed objects concerning their infill pattern are demonstrated. The specimens were prepared with various infill patterns to determine the tensile properties. The fracture of the specimen was simulated and the maximum yield strengths for different infill structures and infill densities were determined. The results show the hexagonal pattern of infill holds remarkable mechanical properties compared with the other infill structures. Through the variation of infill density, the desired tensile strength of PLA can be obtained based on the applications and the optimal weight of the printed parts. [ABSTRACT FROM AUTHOR]

• A central self-similar strategy is proposed to develop bio-inspired honeycombs. • Central self-similar degradable polymer honeycombs are additively manufactured. • The interaction effect of different connections between the two walls can promote EA. • Theoretical models of the proposed central self-similar honeycombs are built. At present, improving the energy absorption capacity of lightweight degradable polymer honeycombs is crucial for one of the future engineering applications and bio-inspired strategy based on hierarchy is considered an efficient method for designing honeycomb structures. To improve the energy absorption performance and stability of polymer honeycombs, this study develops three central self-similar bio-inspired honeycombs combining the microstructure of horsetails and designs different connections between the two walls and connecting structures for the central self-similar honeycombs. Bio-inspired honeycombs are fabricated using toughened polylactic acid (PolyMax™ PLA) through fused deposition modelling and subjected to axial compression tests. The finite element (FE) models of the bio-inspired honeycombs are developed to simulate the axial compression process and verified with experimental results. Results show that the connecting structures distributed on the outer wall of the central self-similar honeycombs considerably improve the energy absorption performance of the bio-inspired honeycombs. In the double-cell honeycombs, connecting structures interact with the cell walls, leading to the formation of more folding lobes on the cell walls and increased cell wall utilisation. Furthermore, the effects of geometrical parameters on the energy absorption performance of the bio-inspired honeycombs are investigated. Suitable connecting structure size and cell wall thickness can improve the energy absorption performance and stability of the honeycombs. In addition, the theoretical calculation models of the three bio-inspired honeycombs are established, and the errors with the FE calculation results are within 6 %, which verifies the accuracy of the theoretical models. [Display omitted] [ABSTRACT FROM AUTHOR]

3D printing of continuous carbon fiber-reinforced composites relieves molds in composite manufacturing and gives flexibility to the design of lightweight and robust circular honeycomb structures. Nevertheless, how process defects affect the failure mechanisms of 3D-printed continuous carbon fiber-reinforced honeycomb structures remains undisclosed. To advance this research area, it requires a comprehensive investigation of the failure mechanisms and process defects of 3D-printed continuous carbon fiber-reinforced composite circular honeycomb structures (CCFRCCHSs), with particular attention to the influence of stacking orientations. In this study, 3D printing has been introduced to fabricate CCFRCCHSs using the identical composite material and geometry but different stacking orientations. Both in-plane and out-of-plane quasi-static compression experiments were carried out on these CCFRCCHSs. The mechanical properties and failure mechanisms were investigated through experimental analysis and cross-section observation, from which the microscopic voids and weak interfaces were identified as the dominating factors influencing the failure modes of CCFRCCHSs. This study provides insights into the association between process defects and failure mechanisms of 3D-printed CCFRCCHSs with different stacking directions, which offers guidance for the design of lightweight and robust composite circular honeycomb structures. [Display omitted] [ABSTRACT FROM AUTHOR]

The development of microwave absorbing technology raises the demands for all-band absorption. The topological structures expand the frequency range of electromagnetic wave absorption and eliminate the differences caused by scattering in different incident directions. The multi-wall carbon nanotube and carbonyl iron particles were mixed with polylactic polymer to fabricate filaments for fused deposition. The distribution characteristics of the structures using carbonyl iron/carbon nanotube hybrid material for the key absorption frequency band are obtained. The reflectivity of the honeycomb structure in X and Ku bands is verified experimentally through the preparation method of fused deposition modeling 3D printing. With the decrease of the fractal dimension number, the electromagnetic loss performance basically increases. Preliminary research results showed that the topological structure could significantly expand the absorbing frequency range, and the effective frequency band less than −10 dB is 2–40 GHz, which has a clear application potential for radar absorption. [ABSTRACT FROM AUTHOR]

The necessity for more efficient manufacturing approaches of high-performance complex fiber reinforced composites parts is increasing. This study develops a framework to design and produce topologically optimized continuous carbon fiber reinforced composites (CCFRCs) with both high manufacturing efficiency and manufacturability, and experimentally validates via material extrusion (MEX) 3D printing technique in a more than 1-m wing spar for the unmanned aerial vehicle (UAV). The load-carrying structure can be topologically optimized by a solid orthotropic material with penalization method and further designed into a continuous fiber trajectory under the consideration of optimal material density, optimal fiber orientation and 3D printing process limitation. Based on this method, the complex topological CCFRCs can be realized by a single-stroke printing path with intact fiber. The feasibility and effectiveness of the proposed framework have been evaluated on the Messerschmitt-Bölkow-Blohm (MBB) beam which reveals obvious higher performance in specific stiffness and peak load compared with commonly used honeycomb structure. As a case study, a topologically optimized UAV wing spar was designed and validated experimentally. Mechanical testing shows that the designed wing spar can survive in operating loads. Furthermore, a proof-of-concept internal wing structure was presented where conventional wing spar and ribs are replaced by CCFRCs 3D printed structures. It exhibits high load-carrying characteristics, is lightweight and simple to fabricate. [ABSTRACT FROM AUTHOR]

Three-dimensional (3D) printing of ceramics has attracted increasing attention in various fields. However, the pyrolysis of organic components used for binding or polymerization in 3D printing commonly causes a large shrinkage (up to 30 %–40 %), high porosity, and cracking or deformation, severely limiting practical applications. In this study, 3D printing of Al 2 O 3 ceramic architectures with ultra-low shrinkage is realized by introducing inorganic binder aluminum dihydrogen phosphate (Al(H 2 PO 4) 3 , AP) as a ceramic precursor. Compared to organic binders, the inorganic AP binder can undergo crystallization conversion, which reduces mass loss during sintering at high temperatures, resulting in low shrinkage. Moreover, AP can be used as a rheological modifier to regulate the printability of the ceramic ink for direct ink writing of Al 2 O 3 ceramic architectures, such as wood-piled scaffolds, honeycomb structures, and tubes with high fidelity. The resultant Al 2 O 3 structural ceramics sintered at 1250 °C exhibit good mechanical performance and structural integrity. Most importantly, the linear shrinkage of the printed ceramics is less than 5 %, which is several times lower than that of ceramics with organic binders. This study provides a viable strategy for fabricating high-performance ceramic architectures with good dimensional fidelity for practical applications. ∙ Al 2 O 3 ceramics with aluminum phosphate binder were printed by using direct ink writing. ∙The resultant Al 2 O 3 ceramic exhibited ultra-low dimensional shrinkage owing to the inorganic binder. ∙Al 2 O 3 ceramics are programmable in size and shape, with good stability, reusability, and fidelity. [ABSTRACT FROM AUTHOR]

The mechanical properties of Fused Filament Fabrication (FFF) 3D printed specimens of acrylonitrile butadiene styrene (ABS), ABS reinforced with carbon fibers (ABS/CFs) and ABS reinforced with carbon nanotubes (ABS/CNTs) are investigated in this paper using various experimental tests. In particular, the mechanical performance of the fabricated specimens was determined by conducting compression and cyclic compression testing, as well as nanoindentation tests. In addition, the design and the manufacturing of hierarchical honeycomb structures are presented using the materials under study. The 3D printed honeycomb structures were examined by uniaxial compressive tests to review the mechanical behavior of such cellular structures. The compressive performance of the hierarchical honeycomb structures was also evaluated with finite element analysis (FEA) in order to extract the stress-strain response of these structures. The results revealed that the 2nd order hierarchy displayed increased stiffness and strength as compared with the 0th and the 1st hierarchies. Furthermore, the addition of carbon fibers in the ABS matrix improved the stiffness, the strength and the hardness of the FFF printed specimens as well as the compression performance of the honeycomb structures. [ABSTRACT FROM AUTHOR]

Continuous-carbon-fibre-reinforced (CCFR) honeycomb structures with self-sensing abilities were fabricated by three-dimensional (3D) printing. Pure polylactic acid (PLA) honeycombs of the same size were also fabricated for comparison. Low-velocity impact (LVI) tests and compression after impact (CAI) tests were conducted. Cone beam computed tomography (CBCT) and scanning electron microscope (SEM) were employed to investigate the corresponding damage mechanisms. The LVI test results showed that the presence of continuous carbon fibre effectively inhibited the generation and propagation of the damage in the matrix during impact, which allowed the CCFR honeycomb structure to have better low-velocity impact resistance, especially for repeated impacts with small energies. In contrast to the PLA honeycomb, the CAI test results showed that the CCFR honeycomb still retained good specific compression strength and specific energy absorption properties even after experiencing impacts. Furthermore, the continuous carbon fibre integrated into the CCFR honeycomb could be used as a sensor element to realize the in-situ structural health monitoring during impact and compression. The 3D-printed CCFR honeycomb structure, investigated in this research, demonstrates remarkable mechanical performance and self-sensing capabilities both during LVI and CAI tests, which highlights the vast potential of 3D-printed CCFR honeycomb for diverse applications. [Display omitted] • Continuous carbon fiber (CCF) inhibits the damage generation in the matrix. • 3D-printed CCFR honeycomb has better impact resistance compared to PLA honeycomb. • CCFR honeycomb after low-velocity impact still has high compression performance. • CCF can be a sensing element for structural health monitoring of CCFR honeycomb. [ABSTRACT FROM AUTHOR]

The aim of this study is to establish the dependence of the mechanical strength of products with the geometry of the Schwarz P-surface on the number and size of unit cells. The products are manufactured using selective laser sintering on an EOS Formiga P110 3D printer made of polyamide-12. A Grasshopper script is developed to simulate the samples. Grasshopper is the visual programming language integrated into the Rhinoceros 3D CAD program. The manufactured samples have the same dimensions (inscribed in cubes with dimension of 60 × 60 × 60 mm) and the same degree of space filling. The nature of the fracture and the areas in which the maximum stresses accumulate in the samples are established using the finite element method in the Comsol Multiphysics program. A hypothesis is put forward, according to which, with an increase in the number of unit cells, the specific strength of the samples increases, and a mathematical model is proposed that describes this phenomenon. The mechanical tests confirm this hypothesis. [ABSTRACT FROM AUTHOR]

Ceramic honeycombs exhibit unique mechanical properties based on engineered formulations and geometry of cells. Extrusion of formable paste through a complex honeycomb die is the commonly practiced technique for the manufacturing of honeycombs globally. Extrusion die fabrication is a complex process which necessitates sophisticated infrastructure facilities that provide high geometrical accuracy and finish to produce defect free honeycombs. Furthermore, every configuration of honeycomb requires a specific tool. Additive manufacturing (AM)/ 3D printing is a rapid prototyping technique which offers flexibility in fabrication of honeycombs with desired geometries from a virtual model directly. Further, this does not require complicated dies. In this study, viscoplastic printable cordierite raw mix paste with a shear rate exponent of 0.87 was printed into honeycombs with hexagonal, square, and triangular cells using a ram type 3D printer. The printed honeycomb samples are found to possess good integrity and near net shape after drying. Sintered 3D‐printed honeycomb samples of all configurations have exhibited cordierite as a major phase along with minor phases of magnesium aluminate (MgAl2O4) spinel, clinoenstatite (MgSiO3), and corundum (Al2O3) with sintered density of 2.41‐2.48 g/cc. The samples are also subjected to compression testing under quasi‐static condition. The study demonstrates 3D printing as a viable and flexible technique for rapid prototyping of honeycombs with desired configurations and engineered properties. [ABSTRACT FROM AUTHOR]

• Inspired by pomelo peel and bamboo structure, corrugated and layered honeycombs are designed and fabrication by metal 3D printing. • The deformation modes and energy absorption capacity of the bionic inspired honeycombs are experimentally investigated with quasi-static and dynamic drop-weight tests. • The influence of impact speed on the crashworthiness performance of the honeycombs is investigated. To improve the energy absorption of traditional structures, impact resistant natural materials are usually mimicked to develop novel structures with desirable energy absorption. In this work, inspired by the unique 3D corrugated microstructure of vascular bundles in pomelo peel, a new design of honeycomb structure with corrugated characteristics is proposed. Further, motivated by special nodal bulkhead architecture of bamboo, layered honeycombs with diaphragms are designed and fabrication by metal 3D printing technology. The quasi-static and dynamic crushing responses and energy absorption characteristics of six types of bio-inspirational honeycombs (ISWH, LSWH, ISCH, LSCH, IPCH and LPCH) are studied using quasi-static testing machine and dynamic drop-weight impact experimental systems. To investigate the effect of impact speed on the crashworthiness performance of the honeycombs, the tests of the honeycombs impacted by the drop-weight with two different mass (106.07 and 59.60 Kg) and three impact velocity (V 1 =6.23, V 2 =8.82 and V 3 =11.77 m/s), respectively, are performed. The experimental results indicate that the crush failure mode of the layered honeycombs is more regular than that of the integrated honeycombs. Failure of all layered honeycombs occurs first at the junction of the honeycomb and diaphragms. Under impact loading, the layered corrugated wall honeycombs exhibit a greater final crushing distance than their corresponding integrated honeycombs. The design of corrugated wall can effectively reduce the initial peak force of the integrated honeycombs, while the layered honeycomb design also facilitates the reduction of the initial peak force, thus avoiding damage to personnel or equipment from excessive peak collision forces. The layered design will reduce the specific energy absorption of the integrated honeycombs in most cases, but a reasonable combination of layered and corrugated wall design can also effectively increase the specific energy absorption of the honeycombs under a specific loading speed. And, the layered design can also effectively improve the crush force efficiency of the corresponding integrated honeycombs. [ABSTRACT FROM AUTHOR]

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

Abstract In this study, a novel grid skeleton (i.e., the 3D printed healing-agent based honeycomb structure) was embedded in a syntactic foam matrix to enable the composites to own crack closing and healing capabilities. There is always a trade-off between crack healing efficiency and overall structural properties. The new type grid skeleton was proposed here to make syntactic foam composites owning excellent crack healing ability without sacrificing overall mechanical properties. The volume fraction of glass microballoons within syntactic foam matrix remained constant at 30%. The reinforcing honeycomb cell sizes varied with a ratio from 3.8, to 5.4 and 7.3, which resulted in various physical and mechanical properties, such as different density and compressive strength. The thermal properties of the syntactic foam composites were tested through Differential Scanning Calorimetry (DSC). The interfaces between the syntactic foam matrix and PCL grid skeleton (i.e., printout) was investigated by the Fourier Transform Infrared (FTIR) spectrum. It displayed that the interaction between those phases were completely in a physical manner. Nano-indentation tests were conducted to study the composite component mechanical properties. Three-point bending tests were conducted to initiate structural level cracks to examine the crack healing capability. Healing efficiency was obtained according to the comparison between specific flexural strength before and after the crack healing event. Under free constraint condition, the 3D printed PCL honeycomb reinforced syntactic foam exhibited promising crack healing performance with healing efficiencies above 80%. This study provided an understanding on the interface property and crack healing mechanisms in the 3D printed honeycomb reinforced syntactic foam system. Graphical abstract Image 1 Highlights • A syntactic foam matrix was reinforced by a 3D printed polycaprolactone (PCL) honeycomb as a new type of grid skeleton. • The interfaces between foam matrix and PCL printout was investigated by the FT-IR and nano-indentation. • Compressive behavior of the syntactic foam composites was investigated under in-plane and out-of-plane loading conditions. • Flexural behavior of the syntactic foam composite was investigated under in-plane and out-of-plane loading conditions. • Under free constraint condition, the composites exhibited promising self-healing performance with efficiencies above 80%. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multifunctional fixed-bed reactor and 3D-CeO 2 /ATP are constructed by 3D printing. • 3D-CeO 2 /ATP possess superior adsorption desulfurization effect at room temperature. • Adsorption-elution process realizes sulfur removal and high-value sulfide recovery. The construction of monolithic adsorbents can promote the potential industrial application for adsorption desulfurization of fuel. Herein, the 3D-CeO 2 /ATP monolithic adsorbents were successfully constructed through a 3D printing strategy, possessing superior adsorption desulfurization performance of more than 85 % sulfur removal under optimized adsorption reaction conditions at room temperature. Combined with the 3D-printed multifunctional fixed-bed reactor, the reaction process capable of adsorption-elution was designed for continuously realizing the deep adsorption of sulfide in fuel and the resource recovery of high-value sulfide products. The structure and physicochemical property of 3D-CeO 2 /ATP monolithic adsorbents were analyzed by series of characterizations, and the adsorption and elution mechanism were investigated in detail. The results reveal that the monolithic adsorbent with the internal staggered honeycomb structure was compared with that of the traditional in-line structure in terms of adsorption performance and computational fluid dynamics (CFD) fluid simulations, reflecting the advantages of 3D printing in structural forming to enhance mass transfer for promoting the adsorption process. Moreover, the 3D-printed monolithic adsorbents exhibit exceptional mechanical stability and good circulation performance, reaching the requirements for potential industrial application. [ABSTRACT FROM AUTHOR]

Based on previous research, we proposed changes in the classic honeycomb structure. We have changed the approach to modeling. In a classic structure, cells are modeled using the walls that form them. In the modified structure, the main modeled element is the hexagon-shaped void. The distribution of cells was proposed as in a truss. In full places the spaces were smaller and in empty places the cells were larger. We changed the size of cells and the transition between cells in different layers. In comparison to previous research, it was necessary to enlarge the models. This was due to the limitations of incremental technology, which was used to fabricate samples - FDM. This technology introduced limitations of changes that the structure underwent. We selected several types of models as a result of the numerical simulation and produced. Then, experimental tests were carried out on them - the same as in numerical simulation. In the final stage, we compared the obtained results. [ABSTRACT FROM AUTHOR]

With advances in 3D printing technology, now honeycomb structures can be made with virtually unlimited unit cell geometries and cell arrangements giving a wide range of possible mechanical properties. However, studies on such structures have been mainly limited to the hexagonal honeycombs with little work done on other cell geometries. This paper investigates the effect of unit cell geometry on the in-plane compressive response and energy absorption behaviour of honeycombs using full-scale non-linear numerical simulations. Nine types of honeycombs are designed from different unit cell shapes, but having the same relative density. Finite element analysis is used to simulate the honeycombs' behaviour under uniaxial compression loading. The results showed that unit cell geometry and cell arrangement affect the honeycombs' compressive response significantly and provide different energy absorption characteristics. This comparison study shows that the honeycombs in which the deformation mode is dominated by bending of cell edges present a lower stiffness (effective modulus) and compressive strength, but a smoother plateau stress. The honeycombs having their deformation mode dominated by plastic buckling present a higher stiffness with less stable and undulated plateau stress. The results of this study provide more understanding in predicting the global behaviour of honeycomb structures and their energy absorption characteristic through their micro-topology. The effect of cell shape and its arrangement on the selection of honeycombs for energy absorption application is discussed and a methodology is proposed to balance the energy absorption with maximum transmitted stress, which is crucial for energy-absorbing design of structures. [ABSTRACT FROM AUTHOR]

[Display omitted] • Spinal interbody cages adapted for an auxetic, and honeycomb using standard CAD software operations and manufactured with SLM. • Auxetic-based cages exhibit higher strength properties than honeycomb-based cages. • The stiffness of the auxetic cages is comparable to stiffness of human cortical bone. • The honeycomb cages exhibit lower value of Young's modulus closer to that for vertebrae. This paper presents a method for modeling a biomedical device by adaptation a commercially available interbody cage for an auxetic metamaterial and honeycomb structure using standard operations in Computer-Aided design software. The mechanical properties of experimental prototypes of Ti-6Al-4 V cages made by selective laser melting using computer modeling (finite element analysis), static and low-cycle fatigue compression tests (up to 3500 cycles) are characterized. 3D printed cells with structures with an angle of inclination between cell edges of less than 90˚ (auxetic metamaterial) are shown to exhibit higher static compressive strength and fatigue resistance than cells based on structures with an angle of inclination greater than 90˚ (honeycomb structure). The changes in the inclination angle differently affect to the porosity and consequently to mechanical behavior of auxetic metamaterial and honeycomb structure. The Young modulus of the auxetic-based interbody cage is 6.68 ± 0.28 GPa and comparable to the elastic modulus of human cortical bone. The honeycomb-based cage exhibits lower values of Young modulus (1.19 ± 0.03 GPa) close to that of trabecular bone and vertebrae. Importantly, the auxetic-based cage is not destroyed after 3500 cycles under 14 kN load with residual deformations ≤ 1 % (0.21 ± 0.10 mm displacements). [ABSTRACT FROM AUTHOR]

• DLP technology was successfully used to manufacture lattice-based substrates. • 3D-printed lattices showed a superior light-off behaviour for all studied species. • Hydrogen presence further decreased light-off temperatures in ED and D45. This study proposes 3D-printed diamond-based lattice substrates as catalytic converters in the automotive aftertreatment system to improve vehicle cold-start emissions. The study aimed to compare the influence of 3D-printed diamond-based catalyst structures on the light-off behaviour compared to the conventional 400 Cell Per Square Inch (CPSI) honeycomb catalyst design in a real exhaust gas environment. Moreover, the benefits of H 2 addition on the performance of advanced lattice structures are examined for the first time to further increase the low-temperature catalytic efficiency. Digital Light Processing (DLP) technology was effectively utilised to manufacture lattice structures with high cell density to allow a comparison between conventional and advanced geometry designs. Further, the 3D-printed substrates were catalyst coated, and their light-off behaviour was studied in a diesel exhaust environment. The results of the light-off showed a significant improvement in the light-off temperatures for CO, THC and NO in the 3D-printed lattice structures. Furthermore, H 2 presence additionally enhanced the low-temperature activity of the AM lattice structures. [ABSTRACT FROM AUTHOR]

Integrated lightweight metastructures with microwave absorption and mechanical properties are of great significance in practical applications, but so far relevant study is still lacking. In this paper, an integrated lightweight gradient honeycomb metastructure (GHM) was proposed using 3D printing and screen printing technologies. Using the equivalent circuit method (ECM), we provided an in-depth analysis of how to broaden the absorption bandwidth and derived the mathematical formula of the equivalent resistance of the hexagon loop. The simulation results reveal that the proposed metastructure has the characteristics of broadband absorption, polarization insensitivity, oblique incidence stability, and radar cross section (RCS) suppression in the operating frequency range. The measured results are in good agreement with the simulation ones. In addition, the compression test results show that the metastructure has good compression strength. This work provides a route to achieve integrated metastructures with thin, lightweight, excellent absorption and mechanical properties. [ABSTRACT FROM AUTHOR]

• A kind of two-layer oblique honeycomb sandwich structure of flaky carbonyl iron powder/photosensitive resin composites with high precision was prepared by liquid crystal display (LCD) 3D printing method. • The structure is beneficial to improve the microwave absorption strength, and has the characteristics of light weight and low material consumption. • LCD 3D printing technology has the advantages of high precision, free forming and less time consumption. Carbonyl iron powder (CIP) is one of the most widely used magnetic loss absorbents due to its high saturation magnetization, strong wave absorption performance and low cost. However, CIP has a very high density (7.86 g/cm2) and requires a high addition amount (more than 50 wt%) when used as a microwave absorbing filler, which leads to high weight and low mechanical properties of the composite. Taking the diverse attenuation mechanisms during the electromagnetic energy conversion process into considerations, this paper designs a two-layer oblique honeycomb sandwich structure, which was prepared by liquid crystal display (LCD) 3D printing. This structure combines porous structure with strong absorbing materials to achieve strong electromagnetic wave (EMW) absorption performance at low concentrations and improve mechanical properties. When the inclined honeycomb core angle is 15° with only 15 wt% FCIP addition, the EMW absorption and mechanical properties of the composite are significantly improved compared with the full-filled structure. [ABSTRACT FROM AUTHOR]

Lattice truss reinforced honeycombs (LTRHs), termed honeytubes, were developed based on a hybrid design of micro-lattice truss and square honeycomb topologies. Carbon fiber reinforced composite and polymer LTRHs were fabricated using different manufacturing approaches. Out-of-plane compression tests were performed on the LTRHs, and the properties were compared with the conventional square honeycombs. The stiffness and strength values of composite LTRHs didn’t surpass those of composite square honeycombs due to the manually induced defects. On the other hand, polymeric LTRHs with perfect geometries were stiffer and stronger than the corresponding polymeric square honeycombs. A parametric study of the buckling resistance was carried out via finite element analysis, and the results indicated that hollow lattice stiffens honeycombs and increases the resistance to buckling, while the specific properties of honeytubes depend on their geometrical parameters. Moreover, the crush force efficiency and specific energy absorption were greater than those of square honeycombs and hollow lattice. This work demonstrates that hybrid designs that capitalize on micro-topologies can populate vacant regions in mechanical property charts, and provide increased energy absorption as crushing protection structures. [ABSTRACT FROM AUTHOR]

Plant hydro-actuated systems provide a rich source of inspiration for designing autonomously morphing devices. One such example, the pentagonal ice plant seed capsule, achieves complex mechanical actuation which is critically dependent on its hierarchical organization. The functional core of this actuation system involves the controlled expansion of a highly swellable cellulosic layer, which is surrounded by a non-swellable honeycomb framework. In this work, we extract the design principles behind the unfolding of the ice plant seed capsules, and use two different approaches to develop autonomously deforming honeycomb devices as a proof of concept. By combining swelling experiments with analytical and finite element modelling, we elucidate the role of each design parameter on the actuation of the prototypes. Through these approaches, we demonstrate potential pathways to design/develop/construct autonomously morphing systems by tailoring and amplifying the initial material’s response to external stimuli through simple geometric design of the system at two different length scales. [ABSTRACT FROM AUTHOR]

Honeycombs resemble the structure of a number of natural and biological materials such as cancellous bone, wood, and cork. Thick honeycomb could be also used for energy absorption applications. Moreover, studying the mechanical behavior of honeycombs under in-plane loading could help understanding the mechanical behavior of more complex 3D tessellated structures such as porous biomaterials. In this paper, we study the mechanical behavior of thick honeycombs made using additive manufacturing techniques that allow for fabrication of honeycombs with arbitrary and precisely controlled thickness. Thick honeycombs with different wall thicknesses were produced from polylactic acid (PLA) using fused deposition modelling, i.e., an additive manufacturing technique. The samples were mechanically tested in-plane under compression to determine their mechanical properties. We also obtained exact analytical solutions for the stiffness matrix of thick hexagonal honeycombs using both Euler-Bernoulli and Timoshenko beam theories. The stiffness matrix was then used to derive analytical relationships that describe the elastic modulus, yield stress, and Poisson's ratio of thick honeycombs. Finite element models were also built for computational analysis of the mechanical behavior of thick honeycombs under compression. The mechanical properties obtained using our analytical relationships were compared with experimental observations and computational results as well as with analytical solutions available in the literature. It was found that the analytical solutions presented here are in good agreement with experimental and computational results even for very thick honeycombs, whereas the analytical solutions available in the literature show a large deviation from experimental observation, computational results, and our analytical solutions. [ABSTRACT FROM AUTHOR]

Re-entrant honeycombs are one type of lightweight cellular materials with superior energy absorption and impact resistance. Yet, the mechanical properties of re-entrant honeycombs need to be further improved due to its bending-dominated deformation mechanism. In this study, we designed a novel stretching-dominated re-entrant honeycomb by combining the structural hierarchy and auxetic cellular configurations. Such hierarchical re-entrant honeycomb (H-ReH) is manufactured through fine-resolution 3D printing technique. The mechanical behavior and deformation mechanism of the designed H-ReH has been investigated through combined digital image correlation and finite element simulation. The 3D-printed H-ReHs exhibit enhanced specific stiffness, specific initial-buckling strength, structural stability and specific energy absorption capacity due to the uniquely combined deformation mechanisms. A competition between the 1st order and the 2nd order hierarchy has been revealed, which governs the mechanical properties of the H-ReHs. These findings provide thorough understandings and facilitate future design of lightweight but robust cellular materials. [ABSTRACT FROM AUTHOR]

The authors comment on the fabrication and the geometric designs of the cellular actuating structures. The topics discussed include the methods of actuating the honeycombs, the prediction of honeycombs' actuation capacity, and its cellular structures. Moreover, it cites the honeycomb's volume expansion.

As the operation reliability for gas sensors under complex environments is in increasing demand, the stability and safety performance are significant besides qualified gas sensing properties. In this work, structural-strengthened and self-protective ammonia sensing micro-tunnels were constructed by 3D printing. Modified methyl-silsesquioxane (MK) resin was employed as the feedstock to build the SiOC honeycomb structures. Polypyrrole (PPy) nanoparticle decorated TiO 2 arrays sensitized the structures to form inner gas-sensitive tunnels. The sensing structure exhibited high selectivity toward ammonia at room temperature. Response to 50 ppm NH 3 was 18.67%, while the response and recovery times were 119 and 86 s, respectively. The excellent long-term stability also ensured reliable operation in complex environments. More importantly, the enhanced honeycomb had an outstanding mechanical performance with the compressive strength, Young's modulus, and energy absorption of 33.72 MPa, 2.40 GPa, and 28.22 kJ/m3, respectively. It can serve as a load-bearing part of the fundamental component to avoid catastrophic collapse while maintaining a regular sensing capability under pressure loading as the excellent deformation resistance ensured the integrity and connection of the sensing layer. Moreover, the inner through-holes facilitated the exposure of the sensing tunnels to the atmosphere, which can detect target gas simultaneously without the embedding of extra sensors. Thus, the construction of self-protective gas sensing structures was promising to be an efficient strategy for reliable gas detection in extreme environments. • PPy/TiO 2 arrayed SiOC honeycombs constructed by 3D printing. • The structures served as load-bearing parts and gas detectors simultaneously without the embedding of extra sensors. • Avoiding catastrophic rupture and ensuring reliable operation under pressure. [ABSTRACT FROM AUTHOR]

With booming development of 5G communications and electronic devices, electromagnetic waves (EMWs) radiation pollution has aroused much concern on public, and great efforts are being made to develop the high-performance electromagnetic interference shielding (EMI SE) materials. However, inherent deficiencies of traditionally processing technology restrain the current materials to fabricate desirable architectures for SE applications. Herein, taking full advantages of 3D printing in free-construction, architected honeycombs featuring lightweight and high-efficient EMI SE are designed with polylactic acid (PLA) as matrix, and graphene nanosheets and carbon nanotubes hybrids (GNs/CNTs) as functional fillers. The optimal printed material shows a high electrical conductivity up to 110.8 S/m and outstanding EMI SE property of 53.5 dB, far exceeding the standard of commercially shielding materials (20 dB). More encouragingly, this work makes a deep insight into the intrinsic connection of porous structure of 3D-printed components on shielding mechanism, which reveals that as the pore size is far less than a certain proportion of incident wavelength (λ/5), the components exhibit a good reconcilability on the lightweight (0.4–1.0 g/cm3) and high-performance EMI SE (35–45 dB). From fundamental materials to desirable components, this breakthrough lays a solid foundation for the free-construction of diversified architectures in EMI SE applications. [Display omitted] • The strong conductive networks are constructed by the hybridization of graphene nanosheets and carbon nanotubes. • The hybrid networks endow the 3D-printed components with superior electromagnetic interference shielding (∼53.5 dB). • The diameter of porous structures should be less than the 1/5 of incident wavelength (λ) to shield electromagnetic waves. • The 3D-printed honeycombs exhibit a good reconcilability on lightweight and electromagnetic interference shielding. [ABSTRACT FROM AUTHOR]

Abstract: W–Ni alloy parts were produced with selective laser melting (SLM) and the influence of the Ni content on the microstructure evolution and microhardness was investigated methodically. The resultant microstructure of the SLM specimens with a Ni content of 10wt.%, 20wt.% and 40wt.% exhibited bar-shaped structures, dendrites and honeycomb structures respectively. It was found that a higher Ni content decreased the melt viscosity and increased the densities of W–Ni parts. The microhardness decreased on the other hand with increasing Ni content. The microstructure formed in the SLM process was characterized by a mixture of typical liquid phase sintering (LPS) microstructure and W dendritic structure. This revealed that the forming mechanism of the SLM process on W–Ni particles was a combination of LPS and partial melting of W particles. The microstructure showed that SLM process improved the bonding ability of the powder particles and therefore enhancing the mechanical properties. [Copyright &y& Elsevier]