TOUGHNESS ANISOTROPY IN TEXTURED CERAMIC COMPOSITES

In this investigation, a model predicting toughness anisotropy in text ured ceramics containing elongated grains and in composites reinforced with rod-shaped particles is presented. The model predictions are bas ed on the assumption that crack deflection is the only toughening mech anism. In the model, toughness anisotropy is calculated as a function of texture degree. For composite materials, the volume fraction of the reinforcement phase is also an input parameter. Correspondence betwee n model and experiment was established by comparing measured toughness anisotropies in beta-Si3N4 and Al2O3/SiC whisker composites to model predictions. In these model predictions, measured orientation distribu tions from hot-pressed and hot-forged specimens were employed. The pot ential for relating other toughening mechanisms in a similar format is also addressed, since the model and experimental measurements give di fferent results. The crack deflection model simultaneously (overpredic ts the toughening enhancement and underpredicts the toughening anisotr opy observed in the experiments.