Approved:

--x This annual report documents the results of a basic research program aimed at (1) studying the high temperatfe failure mechanisms in ceramics, (2) establishing relationships between cavitation mechanisms and creep crack growth characteristics, and (3) developing a damage mechanism-based life prediction model. During the reporting period, the growth rate, near-bp creep responses, and damage processes of creep cracks in a pyroceram glass-ceramic were studied under tensile loading at elevated temperatures. The results of these studies indicated that creep crack growth in the pyroceram glass-ceramic occurred both in continuous and discontinuous manners, with the damage processes manifested as the nucleation, growth, and coalescence of inhomogeneously distributed cavities and microcracks. Sintering of cavities led to the existence of a growth threshold below which the creep crac