8: Ceramic Matrix Composites
The principal advantages of ceramic materials over other materials is their resilience to oxidation and deterioration at eleveated temperatures, their high melting points, and high compressive strengths. Unfortunately, ceramics suffer from a susceptibility to brittle fracture and therefore have relatively low values of fracture toughness. One method of increasing the fracture toughness of a ceramic is to reinforce it with fibres, whiskers, or particles. Crack propagation is severely hindered by the presence of the reinforcing phase.
Fracture toughness values for ceramics are usually around 1-5 MPa.m1/2. With the addition of a reinforcing material to make a CMC these values have been shown to increase to 6-20 MPa.m1/2.
Other advantages of CMCs is improved high-temperature creep behaviour and resistance to thermal shock.