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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]

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]

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]

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]

Continuous fiber reinforced thermoplastic composite (CFRTPC) auxetic honeycomb structures were fabricated using the 3D printing technology with a specific printing path planning. For comparison, auxetic honeycombs were also fabricated with pure polylactic acid (PLA). In-plane compression tests were conducted, with corresponding damage types explored using Scanning Electron Microscopy (SEM) images. A printing path-based finite element (FE) method was developed to mimic both small and large deformations of CFRTPC auxetic honeycombs, while analytical model was proposed to predict their effective stiffness and Poisson ratio. Good agreement was achieved among analytical predictions, FE simulation results and experimental measurements. A systematic parametric study was subsequently carried out to quantify the dependence of in-plane mechanical properties on geometrical parameters. Compared with pure PLA structures, the presence of continuous fibers efficiently prohibited crack propagation in the matrix for each ligament of CFRTPC auxetic honeycombs. Adding continuous fibers increased the mass only by 6%, but led to dramatic increase in compressive stiffness and energy absorption by 86.3% and 100% respectively and smaller Poisson ratios. The proposed 3D printing technology has great potential in integrated fabrication of continuous fiber reinforced composite lightweight structures having complex shapes, attractive mechanical properties, and multifunctional attributes. • The continuous fiber reinforced composite auxetic honeycomb was fabricated by 3D printing technology. • A combined experimental, analytical and numerical approach was employed to investigate the in-plane behaviors. • Adding continuous fibers lead to dramatic increase in mechanical properties and smaller Poisson ratios. [ABSTRACT FROM AUTHOR]