Effect of fiber volume fraction on hybrid effects of tensile properties of unidirectional aramid/carbon fiber hybrid composites

Aramid/carbon fiber hybrid reinforced polymer (A/CHFRP) composites were prepared via compression molding to obtain carbon-fiber-reinforced polymer (CFRP) composites with better toughness. Based on the existing theoretical model, the effects of the carbon fiber volume fraction on the properties of the A/CHFRP were studied using thermal gravimetric analysis (TGA), tensile tests, and scanning electron microscopy (SEM) analysis. According to the TGA results, the hybrid fiber improved the thermal stability of the CFRP. With increasing carbon fiber content, the thermal stability of the A/CHFRP composites also increased. The tensile results showed that the A/CHFRP composite with a carbon fiber volume fraction of 22.7% exhibited "pseudo-ductility," with the failure strain 54.09% higher than that of the CFRP composite. With increasing carbon fiber content, the ductility of the A/CHFRP composites decreased. The elastic modulus of the A/CHFRP composites conformed to the prediction model of the rule of mixtures (ROM). The strength was found to fall in the triangular area surrounded by the ROM and the bilinear ROM and exhibited a positive hybrid effect. The SEM results showed that the tensile failure modes of the A/CHFRP composites were mainly fiber and resin matrix debonding and fiber fracture. Brittle fracture of the carbon fibers was observed in the A/CHFRP composites, while aramid fibers appeared to peel off and silk crimp for ductile failure. Thus, this study provides a theoretical basis for toughening CFRPs.