Three-point bending tests were performed on two types of SiC/SiC composites with different fibre-matrix interfaces, after ageing up to 1400°C and 1000 h in air and in an inert atmosphere. Strength measurement, acoustic emission monitoring, and fracture energy evaluation revealed important changes in the materials. Damage to the materials is confirmed by the fractographic observations of broken specimens. Evaluation of the average length of the fibres pulled-out during fracture in each case of ageing confirms the major rôle played by the change in the strength of the interfaces in modification of the mechanical behaviour of the composites. Microprobe analysis on polished sections and Auger spectroscopy on fibres pulled-out during fracture gave indications about the origin of the development of bonding between fibre and matrix in relation to the mode of oxidation of the interface. © 1989.
