ABSTRACT
This chapter addresses grain effects on crack propagation, fracture toughness, and related phenomena in nominally dense, single phase, i.e. monolithic, ceramics. Grain parameters include grain size, shape, and orientation (the latter reflecting effects of intrinsic property changes as a function of grain, crystal, orientation), as well as grain boundary phases. Grain size effects, though often neglected, have received a fair amount of investigation, and grain shape and orientation substantially less (mostly qualitative for shape). Studies, which have focused on tests designed to provide controlled crack propagation well prior to, and not necessarily culminating in, catastrophic propagation under uniaxial tensile stress, are addressed along with slow crack growth (SCG) due to environmental effects, microcracking, crack branching and bridging, and related formation of crack wake zones and R-curve effects. These lead up to, or are aspects of, the basic fracture mechanics parameters of fracture toughness (KIC) and related fracture energy (γ) via
(2.1)
where the~sign reflects the fact that for plane stress the term in the square root should be multiplied by 1-v2 (Poisson’s ratio)2 but is exact for plane strain conditions. Attention is also given to crack size effects and fracture mode, i.e. the extent of trans-versus intergranular fracture.
