Theoretical approach to energy-dissipative mechanisms in zirconia and other ceramics

A theoretical model, for the fracture toughness of ceramics is developed which takes into account such energy-dissipative mechanisms as stress-induced microcracking or phase transformations. To establish the general fracture criterion, a Griffith-type energy balance is employed. This energy balance comprises the elastic energy release rate, the fracture surface work consumed in the process zone at the crack tip, the energy dissipated in the dissipation zone, and the energy stored by residual stresses. Within this model, the effect of stress-induced phase transformations and microcracking on the increase of fracture toughness can be calculated on the basis of micromechanical data. The influence of residual stress states is especially studied whereby other work is critically examined