Mixed Mode Fracture Toughness and Fracture Mechanism in Short-Glass-Fiber-Reinforced Polycarbonate

This paper deals with mixed mode fracture toughness and fracture mechanism in short-glass-fiber-reinforced polycarbonate. The fiber volume fractions of four materials fabricated by injection moulding are 0%, 10%, 20% and 30%, and short fibers in these materials were aligned mostly in the mould-fill direction. Mode I fracture toughness for a crack perpendicular to the fibers is higher than that for a crack parallel to the fibers, and the difference between the two "namely anisotropy" increases with an increase in the fiber volume fraction. The direction of crack extension and fracture toughness under mixed mode loading are affected by the anisotropy of the materials. In order to predict the fracture behavior from a mixed mode crack in anisotropic materials, a new criterion is proposed. Microdamage such as debonding of the fiber-matrix interface, fiber fracture and matrix plasticity, develops around a crack tip and acts as the toughening mechanism, especially in the case of crack extension perpendicular to the fibers. However, such a toughening mechanism does not sufficiently apply to a material with a high content of fibers in which the matrix plasticity and the microdamage are restrained in the vicinity of the crack surfaces.