Mechanics of Internal Stress and Microcrack Toughening Mechanisms in Ceramics

摘要

A simple constitive law is proposed for the description of a certain ceramic composite which undergoes stress induced martensitic transformation. This law is used in finite element calculations to investigate the shear effect on the transformation zone near a crack tip. A formula describing the stress intensity factor change due to the shear contribution of the transformation given. Significant loss of toughness is observed in the case of a stationary crack and is attributed entirely to the shear component of the transformation. On the contrary, the dilatant part brings about no change. As the crack grows, the wake of the transformed material left behind the crack constitutes a source of toughening. This toughening is due to both dilatancy and shear in the phase change and rises to a maximum level just after a propagation comparable with the zone height. Finally, it is shown that the shear component can be important when prediction of the fracture toughness of the transformation toughened ceramics are made.