Liangang Zheng

Thermoplastic composites have a high application demand in aerospace, marine military and other cutting‐edge industry. However, it poses a considerable obstacle in achieving three‐dimensional (3D) thermoplastic composites because of the inadequate infiltration of highly viscous thermoplastic resins. In this paper, high‐toughness Polyetheretherketone (PEEK) resin‐based 3D orthogonal carbon fiber thermoplastic composites were designed and obtained. Low‐velocity impact test was conducted on 3D orthogonal woven composite (3DOWC) under the energy levels of 5 and 10 J, and its performance was compared with that of the 2D unidirectional layup composite (2DULC) and the 2D plain layup composite (2DPLC). The results showed that 3DOWC possessed superior elastic energy absorption capacity and less damage morphology compared to 2D composites. 3DOWC had the highest contact force value of 2420.25 N at 10 J, which is 36.83% higher than that of 2DPLC. Furthermore, a finite element model in multi‐scale was established to investigate the damage evolution and failure mechanism of the 3D orthogonal woven CF/PEEK composites. The damage morphology observed in both experimental and numerical findings demonstrated that the matrix shedding, while the yarn fractured on the nonimpact side beneath the impact point. Additionally, enhancing the tensile strength of the yarn in the bottom layer can lead to further improvement in impact resistance. This work provides an innovative method for manufacturing 3D thermoplastic composites and lays the foundation for the impact simulation analysis of such composites.Highlights: A novel approach was introduced for fabricating 3D carbon fiber/PEEK composites, which exhibits remarkable resistance to impact. A comprehensive investigation was conducted to evaluate the impact properties of 3D thermoplastic composite compared to 2D composite. A finite element model in multi‐scale including failure criteria was established to simulate the damage evolution.

Polymer composites with lightweight, ultralow dielectric constant, excellent thermal insulation and mechanical properties are in high demand in aerospace, transport, wireless communications and other fields. In this work, the three‐dimensional woven Kevlar/glass hybrid composites (3DKGC) with lightweight, high strength, excellent dielectric and thermal insulation properties were obtained with the Kevlar fiber and glass fiber as the raw materials. The results showed that the volume content of air in 3DKGC is over 82% and the volume density is as low as 0.29 g·cm⁻³, while the compression strength is as high as 7.68 MPa. 3DKGC exhibits an ultra‐low dielectric constant of 1.21. The wave transmission performance of 3DKGC was simulated using the CST software. The simulation results showed that 3DKGC has a return loss of 0.036 and a gain of 0.9982. Moreover, the 3DKGC provides superior thermal insulation than three‐dimensional woven Kevlar composites (3DKC) and conventional polystyrene foams. In summary, this work offers an attractive material that holds significant potential for application in aerospace, wireless communications and other fields where lightweight multi‐purpose composites are required.Highlights: 3D woven Kevlar/glass hybrid composites (3DKGC) were proposed and fabricated. 3DKGC exhibits low density of 0.29 g·cm⁻³ but high compression stress (7.68 MPa). 3DKGC possesses outstanding dielectric and thermal insulation properties. 3DKGC leverages the benefits of cost‐effectiveness and holistic functionality.

In this study, to further improve the anti‐impact property of 3D woven spacer composites (3DWSC), three kinds of integrated 3DWSC with double‐layer cores assembled at different height combinations of 4 + 8 mm, 6 + 6 mm, and 8 + 4 mm, were designed and prepared. And the impact performances and the post‐impact lateral compressive properties of the resulting composites were investigated and compared to the single‐layer 3DWSC of the same height. The results show that among the three combinations, 3DWSC‐4 + 8 has the highest contact force value of 2454.33 N at 10 J, which is 90.60% higher than that of single‐layer 3DWSC. And the residual compressive strength of 3DWSC‐4 + 8 maintains 91.30% after 10 J energy impact, while the retention value of single‐layer 3DWSC is only 68.43%. The above results can be attributed to the fact that the addition of the middle panel in double‐layer 3DWSC is benefical to improve the capacity of the material to withstand transverse load or bending moment and to absorb more energy through its damage compared to the single‐layer 3DWSC. In addition, the SEM images showed that only resin cracks in the double‐layer 3DWSC and no fiber breakage and delamination, indicating exceptional mechanical stability of the as‐prepared double‐layer 3DWSC. This work can serve as a reference for the design and fabrication to multi‐layer 3DWSC, a promising material in the field of high‐performance composites.

Polymer matrix composites with lightweight, low dielectric constant (ε) and dielectric loss tangent (tan δ), high‐temperature resistance, and excellent mechanical properties are urgently needed in the fields of aviation, aerospace, transportation, and wireless communication services. In this work, 3D woven spacer Kevlar/polyimide composites (3DKPC) with excellent dielectric properties and robust mechanical properties were designed and obtained by combining 3D weaving technology and thermal imidization process. Results show that the volume density of the prepared composites is as low as 0.24 g·cm ⁻³ , but its compressive strength can be up to 6.24 MPa. The dielectric constant and loss tangent of 3DKPC at room temperature are extremely low, with the value of ~1.32 and 6.9 × 10 ⁻³ , respectively. Moreover, the compressive strength retention rate is more than 96% and the dielectric constant can be consistently lower than 1.36 when the temperature increases from 25 to 300°C, demonstrating the outstanding mechanical and dielectric stability of 3DKPC. In addition, as an application example of resulting composites, a microstrip antenna with 3DKPC as the substrate material was designed, followed by the simulation of its electromagnetic properties via High Frequency Structural Simulator. The results display that the gain of the microstrip antenna is 6.2 dB, which is superior to those of many other reported microstrip antennas, indicating that the 3DKPC proposed here has great application potential in aerospace, wireless communication, and other fields.

In this work, three‐dimensional woven spacer glass fiber/epoxy composites (3DWSC) and epoxy foam‐filled three‐dimensional woven spacer composites (FF‐3DWSC) were prepared, and the behavior of the two composites under bending load was investigated experimentally and numerically. The results show that compared with 3DWSC, FF‐3DWSC displayed a higher bending strength of 134.30 MPa and superior bending stiffness of 9.48 × 10⁶ N·mm², which was attributed to the synergistic effect of the foam and the skeleton. And unlike the serious damage caused by the significant stress concentration in 3DWSC under bending load, less damage appeared in FF‐3DWSC because the stress was dispersed by the efficient transmission of the load between foam and column yarns. Besides, there was no delamination between the foam and the skeleton after the bending test, indicating the excellent integrated structure of FF‐3DWSC. In addition, the bending behavior of 3DWSC and FF‐3DWSC was simulated on the macro‐scale model by HyperMesh and HyperView. As a result, the finite element analysis results were in close agreement with the experimental results, demonstrating the finite element simulation method proposed here is capable of being used in replacing time‐consuming experiments to study the bending properties of such 3D composites.