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Three‐dimensional (3D) braided composites have good integrity and high stability, but aramid fiber (AF) has an inert surface and poor interfacial bonding with resin, which affects the mechanical properties of aramid 3D braided composites and limits their development. This paper used catechol/pyrogallol polyamine (CA/PGPA) to modify the AF. The effects of different mass fraction ratios of CA/PGPA and different reaction temperatures on the surface properties of AF and the mechanical properties of 3D braided composites were investigated. The results showed that after the CA/PGPA modification, fiber surface oxygen‐containing groups increased, the roughness became more extensive, the fiber strength increased, and the interfacial shear strength increased. When AF‐CAPG‐II‐40°C, the mechanical properties of the 3D braided composites were improved most significantly. Compared with unmodified composites, the bending modulus was increased by 70%, the compression modulus by 124%, and the shear strength by 55.7%. The epoxy resin modification was carried out based on AF‐CAPG‐II‐40°C, and when the mass fraction of aramid nanofiber/graphene nanoparticle (ANF/G) was 0.7 wt%, 3D braided composites exhibited satisfactory mechanical properties. The bending modulus, compression modulus, and shear strength were increased by 15.3%, 23.3%, and 25.7%, respectively, compared with AF‐CAPG‐II‐40°C. [ABSTRACT FROM AUTHOR]

Aramid fibers and ultra‐high molecular weight polyethylene (UHMWPE) fibers lack active surface functional groups, and the surface is smooth, limiting their practical application in textile composite materials. In this study, zinc oxide nanorods were used to grow on aramid fibers surfaces, and oxygen plasma followed by treatment with a silane coupling agent was used to modify UHMWPE fibers. The effects of surface modification on the surface morphology and composition, and mechanical properties of fibers and composites were investigated. The mechanical response of interlayer hybrid textile composite materials based on modified aramid and UHMWPE fabrics was examined. The results reveal that surface roughness, active surface functional groups, and wettability that can be controlled by treatment conditions and parameters are important for improving interface adhesion. In addition, the interlayer hybridization pattern as a result of using dissimilar layer materials and altering stacking sequence has a great impact on the mechanical behavior of hybrid textile composite materials. [ABSTRACT FROM AUTHOR]

Abstract\nThe inherent brittleness of unidirectional fiber-reinforced composites represents a major complication in their broad practical applications. However, exploiting different reinforcement architectures can offer an opportunity for highly desirable ductile fracture nature. This article is aimed at investigating experimentally the tensile behavior of an epoxy laminate reinforced by different layers of plain weft-knitted fabrics. The fabricated laminates were subjected to uniaxial tension in different loading directions, and the corresponding tensile responses were recorded. Basic mechanical properties were characterized and digital image correlation (DIC) was employed to capture surface deformations. Tensile test results demonstrated strong nonlinearity and pseudo-ductility as well as loading-direction dependence in this type of composite laminates. Fracture tests were conducted showing high fracture toughness ranging from 10 to 20 MPa·m1/2. Typical damage modes were characterized using microscopy, which were coupled to a few distinct tensile deformation stages. This work demonstrates that weft-knitted composites are promising in permitting great amounts of pseudo-ductility with clear warning before complete failure. It is also expected to contribute to the understanding of the specific role of weft knit fabrics in composite laminates.Analysis of the deformation process of plain weft-knitted composites and various failure modes by DIC and microscopy.Observation and explanation of pseudo-ductility in the knitted composites subjected to off-axis tension.Translaminar fracture toughness measured by over-height compact tension (OCT) specimens. Flaw insensitive length scale estimated on the order of 10 mm.Yarn loop reorientation permitted by matrix plasticity contributing to identified stiffening in off-axis specimens. [ABSTRACT FROM AUTHOR]