Cyclic deformation and crack initiation in brittle solids

Abstract

In this chapter, we examine the mechanics and mechanisms of cyclic damage and crack nucleation in a wide range of brittle materials, including ceramics, glasses and ionic crystals. The fatigue behavior of brittle polymers is considered in the next chapter. Although the discussion of cyclic deformation and fatigue crack initiation for ductile materials was provided earlier in separate chapters, the corresponding descriptions for brittle materials warrant a single, unified presentation because of the nebulous demarkation between deformation mechanisms and flaw nucleation. For example, crack nucleation along grain boundaries can be regarded as the initial stage of the cyclic deformation process in some brittle materials. Fatigue crack growth in brittle ceramics and polymers are considered in Chapters 11 and 12, respectively. It is also pertinent at this juncture to clarify the terminology used in the description of cyclic failure of brittle solids. In the metallurgy, polymer science and mechanical engineering communities, the word fatigue is a well accepted term for describing the deformation and failure of materials under cyclic loading conditions. However, in the ceramics literature, the expression static fatigue refers to stable cracking under sustained loads in the presence of an embrittling environment (which is commonly known as stress corrosion cracking in the metallurgy and engineering literature). The expression cyclic fatigue is used in the ceramics community to describe cyclic deformation and fracture.