In this chapter, we discussed ceramic materials, materials that by and large do not deform plastically when subjected to high stresses. Consequently, ceramics have a low toughness and are very flaw sensitive. Methods of toughening ceramics involve grain or fiber pullout behind the crack front, phase transformations or microcracking on the flank of the crack, or deflection of the crack tip from the maximum stress path. With these procedures, the maximum toughness achievable for these materials is about 12 MPa m1/2. Hence, despite the efforts of the past 30 years, ceramics are still very brittle materials that require special care when they are required to carry structural loads. Except where proof testing can be used to eliminate weak components, failure statistics must always be considered when designing ceramics to carry structural loads. Although not heavily covered in this chapter, thermal stresses are important to ceramics, whether they arise due to a thermal mismatch between the ceramic and other components of the structure or because of thermal quenching. Finally, crack growth has to be considered in designing ceramics, whether it is due to cyclic loading or a stress enhanced chemical reaction at the crack tip. Because of the complexity of many structural components, three-dimensional analyses are often needed to assure reliability. Fortunately, these problems have been seriously considered over the past few decades and computer codes have been developed to factor these considerations into the design of ceramic components.
Encyclopedia of Comprehensive Structural Integrity