Fracture behaviour and toughness of a plane-woven SiC fibre-reinforced SiC matrix composite

This study investigates the fracture behaviour and fracture resistance of a bi-directional woven SiC fibre-reinforced SiC matrix composite fabricated by chemical vapour infiltration. The tensile stress-strain curve shows nonlinear behaviour above 70 MPa, and the effective Youngʹs modulus decreases above this tensile stress. The compositeʹs effective Youngʹs modulus at fracture was about 40% of the initial value, and all the applied load at fracture was supported by the longitudinal fibre bundle composites (FBCs). The gross fracture stress of a notched specimen showed reduced notch sensitivity in comparison with a monolithic SiC matrix, though it never completely vanished. The origin of the increase in the compositeʹs fracture toughness was explained using an FBC bridging model that employs the strength of an FBC obtained from separated tensile testing. Results demonstrate that the cracking of the transverse FBC, which occurs before longitudinal FBC fracture, plays an important role affecting the bridging condition, and that the tensile fracture strength and toughness of the composite can be modelled by the presented FBC bridging model.