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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.

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.