Abstract
The effects of fiber/matrix interface on the inplane notched strength, the interlaminar shear strength, and the mode I and II interlaminar fracture toughness were investigated for 5H satin woven C/C composite materials by coating bismaleimide-triazine co-polymer (BT-resin). Carbonized C/C composites were used in this study with the heat-treatment temperature of 1600℃. While the notched strength of C/C composites without BT-resin coating indicated clear notch sensitivity, that with BT resin coating (weakened interface) was well estimated by the net section stress criterion. The initial fracture toughness under mode I loading, G_<Ic>, was insensitive to BT-resin coating. Moreover, the propagation values of the fracture toughness, G_<IR>, increased by coating BT-resin. On the other hand, the mode II interlaminar fracture toughness, G_<Ilc>, decreased by coating BT-resin. The change of the fracture mechanism in microscopic scale was well correlated to the change of the inplane and interlaminar fracture behavior. Comparison between inplane notched strength and interlaminar fracture toughness suggested the possibility to cope with both inplane and interlaminar properties by optimizing the interface control.
