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 ob jective of studying the constitutive behavior of these materials under high-temperature irradiation. The data analysis includes the empirica l 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 th e physical mechanisms of radiation effects on crystalline solids. Inel astic constitutive equations are then developed for SCS-6 SiC fibers, Nicalon fibers, and chemical vapor deposition SiC. The effects of appl ied stress, temperature, and irradiation fields on the deformation beh avior of this class of materials are simultaneously represented. Numer ical 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 mi cromechanical analysis that is relevant to slow crack growth and fiber pullout under fusion conditions.