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This article presents an experimental study of bending properties of multilayer‐connected biaxial weft knitted (MBWK) fabrics‐reinforced composites made with carbon fibers. Three types of composites are used in bending test, which are three‐layer‐connected biaxial weft knitted fabric‐reinforced composite, four‐layer‐connected biaxial weft knitted fabric‐reinforced composite and five‐layer‐connected biaxial weft knitted fabric‐reinforced composite. Two‐way ANOVA analyzing method was used to deal with whether the carbon fiber volume fraction and the cutting direction have significant effect on the bending strength of the MBWK fabrics‐reinforced composites. Failure analysis is also available by means of samples debris examination to identify the failure mode. POLYM. COMPOS., 36:2291–2302, 2015. © 2014 Society of Plastics Engineers

Based on the representative volume element (RVE) model of single layer in multilayer-connected biaxial weft-knitted (MBWK) fabric-reinforced composites, the elastic properties of multilayer-connected biaxial weft-knitted fabric-reinforced composites have been developed and presented hereafter. The average stiffness matrix of the multilayer-connected biaxial weft-knitted fabric-reinforced composites, taking into account the contribution the final geometrical of the knitting loops, can be obtained by the volume average stiffness of the unidirectional composites with different local coordinate system, and the engineering elastic constants of this kind of composites have been figured out. Numerical predictions have compared to the results of tensile tests performed on composite samples. The percentage error of the numerical prediction results and the experimental results is less than 10%.

In order to characterize the process-induced distortions of 3D thin shell composites with complex shape, the multilayered biaxial weft knitted (MBWK) fabric reinforced high-performance composite helmet was selected as the research object, and the 3D laser scanning machine was used to scan the helmet surface, then the 3D scanning data was compared with the CAD model to evaluate the deformation. The results and discussion indicated that the conventional method was workable, but the speed of convergence was slow and the calculation results were easy to drop into local optimization. According to detailed analysis, a measurement method focusing on the principle of “Feature Distance” was developed. The measurement results shown that this method can not only give accurate results, but also reduce working procedure and greatly save the computing resources, which is proved to be a feasible approach for the deformation measurement foundation of 3D thin shell textile composites.

3D fabric‐reinforced composites with electromagnetic interference (EMI) shielding performance are in urgent demand to deal with the electromagnetic (EM) pollution. In this work, carbon spacer fabrics/polyurethane foam (CSF/PUF) composites were prepared via in situ integration of PUF with fabrics. Their EMI shielding and frequency‐selective performances were realized via designing 3D fabric. CSF/PUF possesses two types of Fabry‐Pérot cavities that generated incident EM waves' resonances according to the quarter‐wavelength theory. The average total EMI shielding effectiveness (SET) of 3CSF/PUF was 69.6 dB in the X band. The maximum EMI SET of 3CSF/PUF was up to 83.2 dB in 9.7 GHz. The peaks of EMI SE move to the high‐frequency region with the increase of carbon spacer yarns' density. Moreover, CSF acted as a reinforcement role and significantly improved the mechanical properties of PUF. The peak stress under compression, three‐point bending and low‐velocity impact increased by 4.2‐, 5.6‐, and 4.9‐folds, respectively. CSF/PUF also exhibited good thermal insulation properties, maintaining a temperature difference of at least 19.5°C across its thickness at 60°C. The as‐prepared spacing yarn carbon fabric‐reinforced composite foams may raise an interest to explore multifunctional EMI materials via fabric structure design.