Toughening by phase boundary propagation

Transformation toughening has enhanced the fracture toughness of certain Zi rconia-Toughened Ceramics (ZTC) by factors of 2-4. The primary explanation of toughening, by McMeeking and Evans [1] and Budiansky et al. [2], suggest s that the main source of toughening is the energy stored by the transforme d inclusions in the wake of a propagating crack. In the case of supercritic al ZTC where the boundary of the transformed zone is a phase boundary (surf ace of strain discontinuity), this paper suggests an additional source of t oughening - that due to propagation of the phase boundary. By extending the J-integral to cracked bodies containing surfaces of strain discontinuity, the transformation toughening for a steady Mode I crack is evaluated.