PHENOMENOLOGICAL INELASTIC CONSTITUTIVE-EQUATIONS FOR SIC AND SIC FIBERS UNDER IRRADIATION

Experimental data on irradiation-induced dimensional changes and creep in beta-silicon carbide (SiC) and SiC fibers are analyzed with the objective of studying the constitutive behavior of these materials under high-temperature irradiation. The data analysis includes the empirical representation of irradiation-induced dimensional changes in an SiC matrix and SiC fibers as functions of time and irradiation temperature. The analysis also includes the formulation of simple scaling laws to extrapolate the existing data to fusion conditions on the basis of the physical mechanisms of radiation effects on crystalline solids. Inelastic constitutive equations are then developed for SCS-6 SiC fibers, Nicalon fibers, and chemical vapor deposition SiC. The effects of applied stress, temperature, and irradiation fields on the deformation behavior of this class of materials are simultaneously represented. Numerical results are presented for the relevant creep functions under the conditions of the fusion reactor (ARIES IV) first wall. The developed equations can be used in estimating the macromechanical properties of SiC-SiC composite systems as well as in performing a time-dependent micromechanical analysis that is relevant to slow crack growth and fiber pullout under fusion conditions.