High temperature fatigue crack growth in ceramics and ceramic composites. (Annual report, August 1991--July 1992)

摘要

This three-year program (8/1990--7/1993) is aimed at developing a detailed quantitative understanding of the elevated temperature fracture properties of ceramics and ceramic-matrix composites. In the second year (8/1991--7/1992), considerable progress had been made in our experimental studies and numerical modelling of deformation and fracture in ceramics composites at ambient and elevated temperatures. As part of this effort, new experimental techniques have already been developed for the study of elevated temperature fracture in brittle materials in direct tension loading. The newly set-up facility is now in operation. Furthermore, new experimental results based on quantitative transmission electron microscopy are obtained on high-temperature phase transformations in SiC-whisker-reinforced alumina which have important implications for high-temperature fracture properties. The initially proposed work on the role of glass phase on the high-temperature fracture and fatigue response has been completed. Finite element analyses of cyclic damage zones ahead of tensile and compressive fatigue cracks in ceramic materials have been completed using several different constitutive models for matrix materials.