Study of High Temperature Failure Mechanisms in Ceramics.
Annual rept. 1 Apr 85-31 Mar 86,
SOUTHWEST RESEARCH INST SAN ANTONIO TEX DEPT OF MATERIALS SCIENCES
Pagination or Media Count:
This report summarizes the results of a fundamental study involving experimental characterization and analytical modeling of grain boundary cavitation and creep crack growth in structural ceramics exposed to pure tensile loading. The major experimental techniques employed in the program are the use of small-angle neutron scattering to characterize cavity nucleation and growth and stereoimaging analysis to characterize the stress and strain fields associated with growing creep cracks. In the first section of the report, the experimental progress is summarized. The design of the pure tensile creep apparatus, which is being used for the creation of bulk damage and for creep crack growth, is discussed. The progress made in the determination of surface preparation conditions that are adequate for the stereoimaging analysis is also discussed. The second section of the report describes the results of a critical review of recent experimental and theoretical studies of creep cavitation in ceramics. The results of this critical study have identified a number of stochastic aspects of cavitation. The stochastic nature of cavitation arises primarily due to the dependence of both cavity nucleation and cavity growth on grain boundary sliding. A degree of randomness is also imposed by the nonuniform distribution of nucleation sites. These results sugggest that the measurement of grain boundary sliding rates and the development of a statistical model of cavitation will be crucial to the understanding and modeling of tensile creep failure.
- Ceramics, Refractories and Glass