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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]

Highlights • Graphene composite was used to prepared multilayer structure for microwave absorbing. • The multilayer absorber possesses a gradient index of characteristic impedance. • Characteristic impedance was tailored by graphene content and rod width of unit cell. • The seven-layer absorber achieved an absorption above 90% in 4.5–40 GHz. • 3D printing process was used to fabricate the complex structure. Abstract An ultra-broadband electromagnetic (EM) absorber composed of composite metamaterials was designed, fabricated and characterized. Polylactic-acid/reduced graphene oxide (PLA/RGO) composites with different amounts of RGO were prepared as a primary material collection. To provide good impedance matching and efficient wave attenuation, the multilayer absorbers were designed with a gradient index (GRIN) of characteristic impedance by manipulating the RGO content and the geometric parameters of the unit cell. The absorbers with different numbers of layers were fabricated by a material extrusion process, and then the reflection loss (RL) of the prepared samples was measured. Results showed that the methodology for designing a metamaterial absorber with gradient impedance and fabricating through a 3D printing process was effective in producing ultra-broadband absorbers. The seven-layer absorber achieved an absorption above 90% in a broad bandwidth of 4.5–40 GHz. This work could provide inspiration for upgrading the performance of some conventional absorbing composites through a rational design of the composite proportion and structure. [ABSTRACT FROM AUTHOR]

A novel integrated manufacturing process based on continuous fibre reinforced thermoplastic composites 3D printing of continuous fibre reinforced composite lightweight structures (CFRCLSs) was proposed. Cross lap and panel-core lap design strategies were proposed to fabricate the CFRCLSs with a complex shape. The fracture modes during compression loading were analysed. Correlations between the process parameters, structure parameters, density, fibre content, and final performance of the printed specimens were discussed. The fibre content of the printed CFRCLSs were controlled by changing the process parameters. With a fibre content of 11.5% vol, a compression strength of 17.17 MPa was obtained for the 3D printed CFRCLSs. A heterogeneous lightweight sandwich structure specimen was fabricated to demonstrate process feasibility. This new and improved process has great potential for fabricating CFRCLSs with complex shapes, high mechanical properties, and multifunctional benefits. [ABSTRACT FROM AUTHOR]

Poly-ether-ether-ketone (PEEK) is a high-performance, temperature-resistant semicrystalline polymer which is frequently used as a replacement for metals in a wide variety of high-performance end-use application. Thermal processing conditions during manufacturing process for PEEK can implement a significant impact on its crystallinity and mechanical properties directly and indirectly. In this paper, we have used a temperature-control 3D printing system to prepare all the PEEK samples for calculating crystallinity and performing tension tests, in order to investigate the relationship between various thermal processing conditions (the ambient temperature, the nozzle temperature and heat treatment methods) in FDM process and crystallinity and mechanical properties (tensile strength, elastic modulus and breaking elongation) of pure PEEK material. All experiment results show temperature-control 3D printing method has tremendous potential to design, control and realize different degrees of crystallinity and mechanical properties for different PEEK parts, even in different regions of the same PEEK part. [ABSTRACT FROM AUTHOR]

In this paper, a multidisciplinary framework to design and produce a topological structure with inhomogeneous distributions of fiber orientation and content for 3D printed continuous fiber reinforced polymer composites (CFRPCs) was proposed to maximize load and fiber utilization efficiency. The combination of optimization design and 3D printing for composites with curvilinear fiber was achieved that the fiber orientation and content were progressively designed in the two-stage procedure. The fiber orientation and topological structure were concurrently optimized firstly. Then, the fiber content was designed through finite element analysis (FEA) and realized by changing continuous fiber path with a hierarchical structure design method. Based on this, the topological beam has been additively manufactured and experimentally investigated, showing 38.55% and 25.40% in stiffness and peak load enhancement compared with the original CFRPCs design, while 264.39% and 165.84% increments compared with pure polymer design. The proposed approach has widened design freedom of CFRPCs 3D printing, possessing potential application to solve engineering problem in aerospace, automotive and other fields. [ABSTRACT FROM AUTHOR]

A cleaner production pattern for high-performance continuous carbon fiber reinforced thermoplastic composites (CFRTPCs) has been proposed on the base of recycling and remanufacturing of 3D printed continuous carbon fiber reinforced (CFR) PLA composites. Continuous carbon fiber and PLA matrix was recycled in the form of PLA impregnated carbon fiber filament from 3D printed composite components and reused as the raw material for further 3D printing process. The original printing trajectory is reversely applied, allowing for a 100% recycling of the continuous fiber without any effect on the mechanical properties. Tensile performance of recycled carbon fiber filaments was evaluated, which was higher than that of originally printed composites. Remanufactured CFRTPCs specimens also exhibited a 25% higher bending strength than that of original ones, which experimentally demonstrated the first non-downgrade recycling process for CFRTPCs. A material recovery rate of 100% for continuous carbon fiber and 73% for PLA matrix were achieved for a better environmental impact. Energy consumption of 67.7 and 66 MJ/kg respectively for recycling and remanufacturing processes was detected and compared with conventional methods. The proposed cleaner production pattern offered a potential strategy for the low-cost industrial application of fully recyclable composites. [ABSTRACT FROM AUTHOR]

Particle size gradation is regarded as an effective method for overcoming the contradicting requirements in three-dimensional printing (3DP). In present work, particle size gradation was optimized to obtain both acceptable flowability of the powder material and high-strength 3D-printed glass-ceramic products. The effect of gradation on the printing process, sintering process and performance of the 3D-printed glass-ceramic products was investigated comprehensively. The glass-ceramic powders with three size ranges were mixed in certain proportions and applied to print parts. The result showed parts printed with powder mixed by 60 wt% 45–100 µm and 40 wt% 0–25 µm particles had satisfactory density of 1.60 g/cm 3 and bending strength of 13.8 MPa. The flowability decreased with an increasing proportion of fine particles. Part density was determined by the powder bulk density in the powder bed as well as the shrinkage during sintering while strength of part was found to be dependent on the sintering degree. [ABSTRACT FROM AUTHOR]

[Display omitted] • 3D printing of monolithic TS-1 catalyst with hierarchical scaffolds was realized. • Combining CFD and reactor structure to design channel structures of TS-1 monolith. • The 3D@550 °C-0° TS-1 exhibits extraordinary efficiency in one-pot synthesis of EG. • 3D printed TS-1 catalysts showed outstanding separability and reusability. Structured monolithic catalysts have attracted increasing attention in the petrochemical industry due to their advantages of high heat and mass transfer rate, easy scale-up, and reusability. Herein, we put forward a strategy for one-step preparation of SiO 2 -based monolithic TS-1 catalysts with optimal hierarchical scaffolds by combining the flow field simulation of the reactor and 3D printing technology. Tunable hierarchical porosity from nano to micro scales, suitable pore characteristics, and numerous active sites have been obtained by innovatively combining the spherical porous structure of TS-1/SiO 2 material, direct ink writing (DIW) and post-sintering processes. Combined with computational fluid dynamics (CFD) analysis, the effects of different channel offset angles, axial and radial channel sizes on the 3D printed monolithic TS-1 in the catalytic reaction of one-step oxidation of ethylene to ethylene glycol (EG) were verified. 3D-printed monolithic TS-1 catalysts exhibited superior crush strengths (135.11 N/cm) and extraordinary catalytic efficiency, in which the yield of EG reached 82.7%, and the utilization of hydrogen peroxide reached 85.3%. Moreover, the 3D printed TS-1 monolith maintained high catalytic performance over 5 reusable cycles, which solved the problem that traditional catalysts are difficult to be manufactured, separated, and recycled, and presented considerable prospects in reactions requiring fluid agitation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Modeling and 3D printing of variable stiffness composites with curved fibers. • Limitations of 3D printing are taken into account in the modeling. • 3D printing of the variable stiffness composites without gaps and overlaps. • 3D printing by the control of positioning a nozzle and the adaptive feed of plastic. • Comparison of numerical and experimental strain fields of the VSCs via FEM and DIC. In this paper, biomimetic continuous fiber reinforced composite structures were modeled and printed on the basis of variable distributions of fiber orientation and the fiber volume fraction, which are similar to the wood structure in the vicinity of a knot. The variable distributions of curved fibers in the variable stiffness composites (VSCs) without gaps and overlaps were realized during the 3D printing process by the control of positioning a nozzle and the adaptive feed of plastic. To demonstrate efficiency of the modeling method and the 3D printing process, a VSC plate with a hole under tensile loading was designed, printed and tested. The results of tensile tests showed that the main failure of the composite plates occurs far from the hole. Furthermore, numerical and experimental strain fields obtained by the finite element method and digital image correlation, respectively, are similar. The efficiency in fiber savings for the composite plates was improved by the change in reinforcement from unidirectional fibers to curved fibers adapted to heterogeneous stress fields. [ABSTRACT FROM AUTHOR]

3D printing of continuous fiber reinforced thermoplastic composites (CFRTPCs) enables the fabrication of multiscale structures, whose features can simultaneously span the microscale fiber trajectory and macroscale topological structure. In this study, a multiscale design and manufacturing strategy integrating concurrent optimization of micro fiber orientation and macro structural topology was developed for CFRTPCs and realized by ingenious path planning for 3D printing process. Typical structures, such as Messerschmitt-Bölkow-Blohm (MBB) beam and cantilever beam, were verified experimentally in comparison with the monoscale structures. Structural stiffness and peak load could be improved by 36.27% and 64.43% respectively for MBB beam, 123.07% and 52.16% respectively for cantilever beam, showing the significant influence on concurrent material and structure design for CFRTPCs. Multiscale concurrent design and 3D printing could promote the potential of CFRTPCs, and even challenge traditional design and manufacturing mechanism relating material and structure scale. [ABSTRACT FROM AUTHOR]

Overall performance of curvilinear fiber reinforced composite structures (CFRCSs) can be designed by adjusting the local fiber orientation and content. In this paper, an optimized design method based on stress gradient distribution for CFRCSs was proposed to improve the efficiency in strength of continuous fiber reinforced composites. The mechanism of fiber content regulation in continuous fiber reinforced composites 3D printing was studied. The adaptive feed calculation method of resin was proposed, and the 3D printing of CFRCSs was realized. A 3D printed composite perforated plate with a hole under tensile loading was optimized and fabricated to verify the effectiveness of the proposed methods. After the optimized design, the maximum stress concentration factor was reduced by 36%, and the ultimate tensile strength was increased by 42%. Through the proposed optimization design method, the fiber content distribution corresponds to the stress distribution, and the fiber direction distribution corresponds to the maximum principal stress direction distribution. At the same time, the stress was redistributed to reduce the stress concentration. Therefore, the ultimate strength was improved. The optimized design method and 3D printing method of CFRCSs have potential application prospects in aerospace, automotive and other fields. Image 1 [ABSTRACT FROM AUTHOR]

The local properties of continuous fiber reinforced heterogeneous composites (CFRHCs) can be tailored through fiber arrangement design to maximize load and fiber utilization efficiency. Design method and integrated manufacturing process for CFRHCs have been investigated in the current research, based on 3D printing of continuous fiber reinforced composites (CFRCs). Based on the tensile and compressive properties of 3D printed CFRCs, the optimal design method of CFRHCs under process constraints and actual working conditions was studied. The mapping relationship between fiber volume content and process parameters was studied, and a digital transition from optimized design to 3D printing solutions was implemented. The flexural strength of the optimized CFRHCs is 207 MPa, and the maximum increase ratio is 115% compared with other heterogeneous designs with the same fiber volume content. The failure process of CFRHCs was analyzed by the simulation model, and the damage mechanism of CFRHCs under bending load was revealed. The optimization design and integrated manufacturing solution of the CFRHCs have potential applications in aerospace, automotive and other fields. [ABSTRACT FROM AUTHOR]

A shape-performance synergistic design and additive manufacturing strategy was developed for the transfemoral prosthetic sockets (TPS) to fulfill the demands of customized geometry and long-term load bearing. The 3D printing path of the continuous fiber reinforced polymer composites (CFRPC) was generated by reversing the milling path of subtractive manufacturing. The mechanical properties of the 3D printed CFRPC samples were investigated as a foundation, and the customized fiber trajectories were designed based on the analyzed stress pattern of the TPS in daily gait. The CFRPC TPS with weight of 28 % less than those made by pure resin had a safety factor larger than 3 and passed the fatigue testing of 3 million cycles. The design and additive manufacturing strategy developed in this study was also applicable for other parts with freeform surfaces. • Fiber trajectory was designed based on the stress analyses of prosthetic socket. • Multi-DOF system enabled 3D printing of thin-walled freeform surface with CFRPC. • Self-adjusting printing speed and feeding rate improved surface quality of CFRPC. • Shape-performance synergistic strategy can apply to other freeform surface parts. [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]