The purpose of this research project is to contribute to the development of life and reliability methodology for ceramics whose failure at high temperatures is controlled by the material's microstructure. The specific microstructural influence of interest is the high-temperature "wake-effect" which results from traction imposed on a crack behind the crack tip by viscous ligaments, whiskers or acicular grains, and other similar microstructural elements. It is proposed that this wake-effect will be studied for three different types of ceramic materials, namely, two-phase ceramics such as liquid sintered alumina and siliconized silicon carbide, whisker-reinforced ceramic composites and ceramics with acicular grain structure such as certain silicon nitrides. The study will involve tests on macroscopic cracks using compact tension specimens, as well as, tests on microscopic cracks using indented and creep-cracked flexural and tensile specimens. Details of the crack growth and the inelastic deformation in the vicinity of the crack tip will be studied using the Digital Image Correlation technique. The study is expected to result in the characterization of crack growth with respect to applied stress, temperature, and time. These results then will be used to construct models for crack growth and failure.
