Process Zone Modeling of Elevated Temperature Structural Ceramics.

Post fracture tensile PFT experiments on two microstructures elucidated the crystallographic and microstructural contributions to the pullout resistance. In alumina, the average residual stresses arising from TEA diminish with increasing temperature, causing two effects evidenced by a general downward shift of the characteristic wake stress-displacement curves. Similar tests conducted on the cubic spinel exhibited no change in bridging efficiency. Similar experiments at the higher temperatures identify topographic changes of the fracture surface as the critical influence on the observed increased toughening behavior. Also, using the post fracture tensile PFT technique, the isolated wake region was tested in direct tension to determine the wake stiffness, offering further insight to those featured of the microstructure that control the bridging efficiency. From these studies, we found that alternate, more compliant micro-mechanisms must be included in the modeling effort to faithfully represent the relatively low measured wake stiffnesses.