Reliability Evaluation of Structural Ceramics Under Multiaxial Stress State

Strength and fatigue lifetime of structural ceramics under multiaxial stress state have been estimated and compared with experimental data. Biaxial strength tests were done by an anticlastic bending test method at room temperature. Biaxial fatigue tests were done by anticlastic bending and also ring-on-ring test method at 1200°C in air. Fracture probability and lifetime were predicted on the basis of a Weibull multiaxial distribution function and subcritical crack growth, using the results of stress analyses by the finite element method. Modified maximum hoop stress theory including an empirical parameter, T, was applied to the equivalent normal stress in the multiaxial distribution function. The empirical parameter T represents a shear stress sensitivity to mixed-mode fracture due to a grain interlocking effect. It has been confirmed that the predicted fracture probability and the fatigue lifetime agrees well with the experimental data if grain interlocking effects are taking into account.