ABSTRACT
Realization that the innate brittleness and attendant unreliability of ceramics may be mitigated by exploitation of microstructure-sensitive toughening mechanisms has led to global research efforts aimed at designing ceramic microstructures for specified structural performance [1-5]. The most potent toughening mechanisms discovered to date derive their efficacy from crackmicrostructure interactions that shield an otherwise brittle (Griffith) crack from remotely applied driving forces. Intrinsic dependencies on microstructural scale of such interactions generally result in toughening characteristics that vary with crack extension. The generic designations used to specify crack-scale dependent toughness characteristics are resistance-curve, Rcurve, behavior, or toughness curve, KR-or Γ-curve, behavior. Each of these are used interchangeably in the literature and differ simply by whether re sistance to fracture is specified in terms of energy release rates (R-curve) or stress intensity factors (KR-or Γ-curve).
