Comparative study of the effect of fiber surface treatments on the flexural and interlaminar shear strength of carbon fiber-reinforced composites

The aim of this study was to achieve enhanced flexure and interlaminar shear strength of carbon fiber-reinforced composites by grafting MWCNTs and depositing PyC layer on the fiber using CVD technique. The surface morphology of fiber prior and after treatment was examined by FESEM and TEM and the composites fabricated with surface modified fiber were tested by three-point bend test for comparative flexure and interlaminar shear behavior. A remarkable improvement of 32 % and 54 % was observed in the flexure strength of composites made of CNTs grafted and PyC-coated fiber respectively as compared to reference composites whereas significant augmentation of 35 % and 53 % respectively was found in the ILSS of composites. In-depth fractographic investigation was conducted to investigate the mechanisms responsible for this enhancement in flexure strength and ILSS of composites. The mechanical test results were supported and validated by the fractographic analysis. Individual CNT pullout, CNTs bundle pullout and crack bridging by CNTs were evidently observed as dominant mechanisms of fracture in these composites in addition to conventional interface debonding and fiber pullout.