Hybrid effects on tensile properties of hybrid short-glass-fiber-and short-carbon-fiber-reinforced polypropylene composites

Hybrid composites of polypropylene reinforced with short glass fibers and s hort carbon fibers were prepared using extrusion compounding and injection molding techniques. The tensile properties of these composites were investi gated taking into account the effect of the hybridization by these two type s of short fibers. It was noted that the tensile strength and modulus of th e hybrid composites increase while the failure strain of the hybrid composi tes decreases with increasing the relative carbon fiber volume fraction in the mixture. The hybrid effects for the tensile strength and modulus were s tudied by the rule of hybrid mixtures (RoHM) using the tensile strength and modulus of single-fiber composites, respectively. It was observed that the strength shows a positive deviation from that predicted by the RoHM and he nce exhibits a positive hybrid effect. However, the values of the tensile m odulus are close to those predicted by the RoHM and thus the modulus shows no existence of a hybrid effect. Moreover, the failure strains of the hybri d composites were found to be higher than the failure strain of the single carbon fiber-reinforced composite, indicating that a positive hybrid effect exists. Explanations for the hybrid effects on the tensile strength and fa ilure strain were finally presented. (C) 2001 Kluwer Academic Publishers.