EXPERIMENTAL STUDY ON MECHANICAL PROPERTIES OF CARBON / Aramid Fiber Hybrid 3D Braided Composites

Three-dimensional(3D) braided composites are fiber-reinforced structural materials having overall space forming mesh, completely overcome the weakness of laminated composites, which have low resistance to delamination and poor interlaminar strength, thus significantly improving the mechanical properties of the composites. In addition, three-dimensional braided composites have an obvious advantage of making complex structural components, they can achieve integration design of Material-Structure-Performance. Hybrid composites can conquer some performance weaknesses of the traditional composites and satisfy the composites structure, performance design, because they are able to make full use of the properties of the reinforcements and matrix. Hybrid composites enjoy immense space for further development, are also becoming one of the important research directions of the future composites.By hybridization of the braided yarns and axial/transverse yarns, we can take full advantage of the flexible designability of three-dimensional braiding technology, while avoiding some issues such as the extra damage to the fibers during the manufacture and the difficulty in controlling the uniformity of hybridizations within the bundles. Based on 3D 5-dirictional(5d) and 6-directional(6d) braided architectures, four kinds of carbon/aramid fibers hybrid 3D braided composites with different hybrid structures were designed and prepared in this study. On the one hand, in order to optimize the braiding process and reduce material damages, the influences of 3D5d and 3D6d braiding process on the tension properties of carbon fibers and aramid fibers were analyzed. On the other hand, the axial tension and compression after impact(about 18 J impact energy) properties of 3D5d and 3D6d braided composites using carbon fibers as braided yarns, aramid fibers as axial yarns and transverse yarns and aramid fibers as braided yarns, carbon fibers as axial yarns and transverse yarns were investigated, hoping to master the hybrid effect of the basic mechanical properties of carbon/aramid fibers hybrid 3D braided composites preliminarily.The tensile tests of the fiber bundles around braiding molding showed that the braiding process damage to the braided yarn is larger, mainly because the whole network structure is formed by the constant motions of the braided yarns, but axis yarns and transverse yarns hardly participate in the movements, which have a relatively small impact on its performance. Besides, because the strength and modulus of carbon fibers are larger than aramid fibers, the damage to carbon fibers are larger than aramid fibers during braiding process, therefore carbon fibers occur brittle failure mode. While the elongation at break of aramid fibers is larger than carbon fibers apparently so that aramid fibers occur ductile fracture mode.Based on Digital Image Correlation (DIC) of the ADAMS system, the axial tensile properties of the carbon/aramid fibers hybrid 3D braided composites showed that hybrid style and braided structure are the important factors affecting the axial tensile properties. As the result of this chapter, the highest tension properties was achieved by 3D5d braided composites when using aramid fibers as braided yarns, carbon fibers as axial yarns (hybrid style 2).Instron and SHIMADZU material testing machine combined with DIC system were used to test compression after impact properties of the carbon/aramid fibers hybrid 3D braided composites, it was found that when braided composites using aramid fibers as braided yarns, carbon fibers as axial yarns, the compression after impact(about 18 J impact energy) properties of 3D5d braided composites(hybrid style 2) is the highest and most insensitive to the low-speed impact damage, exhibiting the higher impact damage tolerance. Toughness of aramid fibers added to change the compression failure mode of the non-hybrid carbon/epoxy composites.