FRACTURE-BEHAVIOR AND FRACTURE-TOUGHNESS OF CEO2-STABILIZED ZRO2 UNDER MIXED-MODE LOADINGS

The fracture toughness of CeO2 stabilized ZrO2 (CeO2-ZrO2) has been measured under mode I, mode II and their mixed-mode conditions. The conventional single-edge-notched bending (SENB) test was carried out to obtain the mode I fracture toughness. The anti-symmetric four-point bending (AS4PB) test, which is the modified SENB test, was adopted for the mixed-mode and mode II fracture toughness tests. The obtained stress intensity factors at unstable fracture were discussed with the phase transformation behavior of ZrO2 and the phase-transformation toughening mechanism. The results showed the maximum principal stress criterion and the non-coplanar strain energy release rate criterion is applicable to the K(I)-K(II) fracture curve. Under the mode II loading condition, the K(IIC)/K(IC) value of CeO2-ZrO2 was 0.6, which was lower than those of non-transforming brittle materials. The low K(IC)/K(IIC) value is attributed to the shielding effect by the transformation which is effective only on the mode I stress intensity.