ABSTRACT
This chapter discusses the mechanics that are required to understand the mechanisms and predicts the amount of toughening in a material that undergoes a stress-induced transformation. The fracture of ceramics can usually be described by the linear elastic fracture mechanics parameters G, K, and R, and there may be a need to introduce more sophisticated fracture mechanics formalism. The overall trends in the fracture toughness increment due to microcracking are very similar to those of transformation toughening. Crack tip shielding involves the reduction of the stresses in the crack tip region below those expected from the applied stress intensity factor. An important aspect of R-curve behavior in a material is that small cracks can grow more easily than large ones and thus, such materials become insensitive to the presence of large, preexisting flaws. The thermodynamics of crack advance can be examined by applying a conventional Griffith free-energy approach or by adopting energy-balance integrals.
