Process and performance characterization of stretch broken carbon fiber materials

Interest in aligned discontinuous fiber composite materials has increased significantly in recent years. These material systems offer the potential for implementation of new and more cost effective processing technologies for aerospace composites as they allow greater flexibility in their deformation mechanics compared to continuous fiber systems. Kinematic inadmissibility associated with fiber axis inextensibility is reduced and resultant increased formability may benefit a wide range of established and emerging lower cost composite process technologies. Prior to appropriate application of such architectures, however, a thorough understanding of both material process physics and ultimate mechanical performance must be fully established. This paper presents results for key processing parameters and mechanical properties of the latest optimized Stretch Broken Carbon Fiber (SBCF) materials. Deformation results are related to anticipated process technologies, and a comprehensive comparison of current SBCF properties to both earlier SBCF forms and continuous fiber systems is provided. With reference to automated forming of prepreg the paper shows SBCF materials are capable of large deformations along the fiber axis without the occurrence of undesirable deformation modes. Mechanical test results of SBCF-based composites (tension, compression, short beam shear, OHT, OHC) are also presented which compare favorably to those of continuous fiber composites.