R Curves and Crack-Stability Map: Application to Ce-TZP/Al2O3

The concept of a crack‐stability map is developed by considering the interaction between the crack‐driving force and the rising crack‐growth resistance of a toughened ceramic. The map plots normalized transition crack length as function of the ratio of the crack‐initiation fracture toughness and the plateau toughness to delineate regimes of stable and unstable crack growth. The plot is used to analyze R curves and fracture stresses of a transformation‐toughened Ce‐TZP/Al2O3. It is shown that the fracture stress and the small scatter measured for this ceramic are consistent with its R‐curve behavior, which enables stable growth of surface cracks from flaws (pores and second‐phase particles), leading to a flaw‐insensitive ceramic.