Effect of Reinforcement Orientation on the Impact Fracture of Carbon Fiber Reinforced 7075-T6 Aluminum Matrix Composite

The impact response and fracture characteristics of 7075-T6 aluminum alloy reinforced with 10% Vf laminated carbon fiber are studied experimentally with regard to the relations between mechanical properties, reinforcement orientation, strain rate and temperature. Cylindrical specimens prepared with two different fiber layer orientations, transverse and longitudinal, are deformed over a strain rate range of 10−2 to 5×103 s−1 at temperatures from 25 to 300°C using a Saginomia 100 metal forming machine for low strain rates and a compressive split-Hopkinson bar for high strain rates. The resulting data indicate that the strength of the composite is strongly strain rate and temperature sensitive, and that the strength is considerably improved if the fiber layers are aligned in the transverse orientation. In the high strain rate region, the transverse composite displays a stronger rate sensitivity than the longitudinal composite. The activation volume of the composite changes significantly with variation of temperature and work hardening stress, but changes only slightly with fiber layer orientation. Fracture feature observations reveal that the transverse specimens failed mainly by shear along a plane of maximum shear stress, while the longitudinal specimens failed by longitudinal interfacial splitting due to relatively weak fiber/matrix bonding and lower matrix constraints. Under high temperature conditions, all specimens showed extensive plastic matrix flow and exhibited a pronounced tendency for the adhesion of matrix to the fiber surface.