Viscoelastic analysis of mismatch stresses in ceramic matrix composites under high-temperature neutron irradiation

Abstract

Abstract Fiber-reinforced ceramic matrix composites, such as SiCSiC, are proposed for structural applications in future fusion energy systems. In a fusion nuclear reactor environment time-dependent inelastic effects are induced by irradiation and hence mismatch stresses are expected to change in time. The time evolution of the internal mismatch stresses in ceramic fiber composites under high-temperature neutron irradiation is presented, with application to SiCSiC composite structures. The effects of thermal creep, irradiation-induced creep and dimensional changes on the build-up and relaxation of the interface pressure and residual stresses in fibers and matrix are investigated. Residual stresses are determined as functions of temperature and neutron exposure time. It is shown that initial mismatch stresses are relaxed within hours because of irradiation creep. It is also demonstrated that fibers with low density, such as Nicalon, will debond from the matrix due to excessive irradiation-induced densification.