Preliminary mechanical testing of continuous stretch broken carbon fiber cured laminates

Abstract

Application of carbon fiber prepregs in cost-sensitive, high-volume structural applications are limited due to the difficulty to form deep drawn parts. Stretch broken carbon fiber (SBCF), is an aligned discontinuous form of carbon fiber that is under development at Montana State University (MSU). The improved SBCF has the potential to increase the formability of these carbon fiber prepregs. However, any formability benefits of SBCF would be limited if the laminates have reduced mechanical properties when compared to conventional continuous carbon fiber composites. Two studies were performed to evaluate the mechanical potential of MSU SBCF. The first study compared the 0° unidirectional tensile mechanical properties of continuous carbon fiber and SBCF laminates both manufactured by MSU at ambient room temperature. Materials included Hexcel IM7-G continuous carbon fibers and SBCF using a Solvay Cytec 977-3 resin as the matrix. The results of the study show that the unidirectional tensile mechanical properties of stretch broken carbon fiber laminates did not significantly differ from the continuous laminates. Normalized for a fiber volume of 60%, the MSU continuous and stretch broken materials had nearly equivalent tensile properties, and their properties were within 15% of stated values for commercial material. Failure modes and strain to failure were nearly identical between the two types of laminates. The second study compared tensile, compression and shear mechanical properties of commercial continuous carbon fiber and MSU SBCF laminates at ambient room temperature. Materials included Hexcel IM7-G carbon fiber with Hexcel 8552 resin as the matrix. The preliminary results of the study showed that the fiber dominated mechanical properties of stretch broken carbon fiber laminates were slightly lower when compared to the commercial continuous laminates. Fiber dominated mechanical properties had at least a 17% loss of strength while matrix dominant mechanical properties were found to be equivalent and unchanged.