The role of the fiber/matrix interface in the first matrix cracking of fiber-reinforced brittle-matrix composites

Abstract

Details of the microfracture mechanics and mechanisms of first matrix cracking are addressed for unidirectionally reinforced brittle-matrix composites. The fracture toughness of first matrix cracking is experimentally determined by the controlled surface flaw method. Toughening is achieved by the composite approach through the crack-tip stress shielding processes of the fiber/matrix interface debonding in the frontal process zone as well as the internal elastic stress partition between the fiber and the matrix due to the difference in their elastic moduli. The toughness improvement by the elastic stress partition combined with the interface debonding process is studied using a carbon-fiber/carbon-matrix composite and three different types of carbon-fiber/Si 3N 4-matrix composites.