Tensile failure of unidirectional carbon/epoxy laminate, Toray T300/#2500, was studied using the center-notched specimens having various notch sizes and fiber orientations relative to the loading axis. The failure features of the notched unidirectional laminates can be classified into two types. For the case of the 0° specimens (the fiber orientation was parallel to the loading axis), gitudinal split grew along fibers in a stable manner. The fracture surface of these specimens was characterized by many hackles and fiber/matrix interfacial debonding. On the other hand, the specimens with fiber orientations between 30° and 90° fractured catastrophically at the maximum load. The fracture surface was covered with epoxy resin.
A predictive method for the macrocrack initiation from notches was proposed from the modified average stress model combined with the maximum stress criterion. The average of the transverse normal stress (perpendicular to the fiber direction) over a characteristic length was critical for tensile failure, and that of the shear stress for shear failure. The predicted strength of the notched unidirectional laminates showed good agreement with the experimental results.