Comparison of tensile fracture morphologies among various polyacrylonitrile-based carbon fibers

Tensile fracture morphologies of three kinds of polyacrylonitrile-based carbon fibers were investigated by scanning electron microscope and high resolution transmission electron microscope. Homogeneous and granular texture could be observed in cross sections of all these three carbon fibers. There is a void up to 1 mu m in diameter in fracture surface of T1, which limits its compactness and tensile strength. Apart from homogeneous texture, linear and fan-shaped morphology are found on surface of T300 and T700, respectively. No core-sheath structure was found in these specimens. Misoriented crystallites are also found from HRTEM images in the transverse sections of T1, T300 and T700, which initiate fiber tensile failure. The tensile fracture mechanism and the implication of the fiber structure under tensile force were also elucidated. T700 has the smallest interplanar spacing, the highest degree of graphitization and the highest crystallinity among three carbon fibers.