Mechanical Properties and Fracture Mechanism of CF Flat Braided Composites With Dispersed Carbon Nanofibers in the Matrix

In this research, laminated flat braided carbon fabrics were performed via flattening tubular braided fabrics with braiding angle of ±45° by applying carefully compressive loads laterally on the tubular fabrics. Then, carbon fiber reinforced epoxy matrix composites were fabricated from the above-mentioned biaxial fabrics with and without uniformly dispersed carbon nanofibers throughout the epoxy matrix. Three loading percentages of carbon nanofibers (specifically, 0.5, 1, and 2 wt%) were dispersed in the matrix of the composites to enhance the matrix and interlaminar/inter-ply properties. The influence of matrix and interlaminar properties improvements on the in-plane tensile and shear response of the laminated flat braided composites was clarified via conducting of ±45° laminates tensile tests. The experimental results of tensile tests revealed that the tensile and in-plane shear properties as well as the fracture behavior of the composites are substantially influenced by the incorporation of the dispersed carbon nanofibers in the matrix of the composites. A pulsed thermography technique was used to inspect the occurrence of the delamination after the fracture under tensile loadings. The thermal wave image and logarithmic temperature-time curves of the pulsed thermography inspection illustrated that the composites with dispersed carbon nanofibers rendered higher interlaminar properties than that of composites without nanofibers. The main conclusion of this research can be summarized that dispersion of carbon nanofibers through the epoxy matrix of laminated flat braided composites not only enhanced the matrix properties but also improved the interphase morphology between the composite plies that maximized the stress transfer of the composites.