Fabrication and braiding angle effect on the improved interlaminar shear performances of 3D braided sandwich hybrid composites

While the interlaminar hybrid composites have been used widely and still remain in great demands, interlayer delamination, undesirable in most cases, keeps a common defect, due to the lack of interlaminar fiber-connection. Here, on the basis of the yarn interlacing rule in three-dimensional (3D) four-step braiding technology, 3D braided carbon fibers/Kevlar fibers sandwich (S_) hybrid composites with different braiding angles (S_20°, S_30° and S_40°) have been designed and fabricated with interlaminar fiber-connection. Short-beam shear tests were applied to evaluate the interlaminar shear performances of specimens. The in-situ strain maps during tests were characterized by digital image correlation (DIC) technique and specimen damages were observed via scanning electron microscope (SEM) and computed tomography (CT). Results showed that, comparing to the conventional co-cured laminated hybrid composites, 3D braided sandwich hybrid composites resisted the delamination effectively by the fiber-connection hybrid region. Braiding angle effect of 3D braided sandwich hybrid composites revealed that S_20° showed better deformability and higher structural toughness than their counterparts in S_30° and S_40°. The results presented in the current work would be helpful for the design and manufacturing of well structured hybrid preforms and composites with dramatically improved interlaminar shear properties.