Transformation, microcrack,and thermal residual stress as interactive processes in ZrO2-Toughened Al2O3, Simulated by the finite element method

Abstract

Some important aspects associated with the transformation, microcrack, and thermal residual stress in ZrO2-toughened A12O3 are analyzed by a computer simulation based on the finite element method. These aspects include (1) the behavior of the transformation toughening, (2) microcracking in a thermal residual stress field, and (3) the interaction between transformation and microcracking. The following findings are confirmed by the numerical study. (1) The transformation within 120 deg fan ahead of the crack tip (frontal zone) gives rise to an amplification of stress intensity, whereas that behind this fan (wake zone) shields the crack tip. The effect of shielding is dominant. These trends are consistent with the continuum model. (2) The thermal residual stress does not give rise to an additional volume expansion, and hence, the dilatation induced by the microcrack opening cannot be estimated from the relief of the residual tensile stress. (3) The transformation and microcracking in the frontal zone encourage each other, whereas in the wake zone, they suppress each other. As a result of this interaction, the combined toughening effect is lower than that estimated by simple superposition. Points (2) and (3) differ from the central hypothesis of the continuum model.