Chapter 7 - High temperature crack growth in unreinforced and whisker-reinforced ceramics under cyclic loads

Abstract

This chapter provides an overview of recent advances in the understanding of the mechanics and micromechanisms of creep-fatigue crack growth in discontinuously reinforced ceramics. The chapter begins with a description of the micromechanisms of damage and fracture at elevated temperatures in monolithic and reinforced ceramics. Characterization of creep-crack growth on the basis of fracture mechanics is addressed in the chapter. Under this topic, emphasis is placed on the identification of conditions under which different crack tip parameters provide descriptions of creep-crack growth under cyclic loading conditions. The chapter also addresses the mechanics, mechanisms, and subcritical fracture characteristics of unreinforced ceramics and ceramic composites at elevated temperatures. Wherever feasible, results of detailed transmission electron microscopy (TEM) of damage, including TEM of crack tip damage, are presented to illustrate the connection between microstructure and damage evolution in the chapter. The effects of various mechanical, microstructural, and environmental factors on high-temperature fatigue fracture are also reviewed. The chapter seeks to provide a state-of-the-art review of the mechanics and micromechanisms of high-temperature crack growth in ceramics and discontinuously reinforced ceramic composites. Particular attention has been devoted in the chapter to identifying the differences between static and cyclic load-failure processes in discontinuously reinforced ceramic materials at high temperatures.