PNNL

Abstract

A continuous fiber composite was simulated by four concentric cylinders (consisting of fiber, fiber/matrix interphase coating, matrix, and surrounding composite) to explore composite stresses when irradiation swelling of the various components is included as a function of neutron dose. SiC Type-S and Hi-Nicalon fibers and three types of transversely isotropic carbons for the fiber coating were considered. Radiation swelling terms were added by using parametric fits to strain (swelling) as a function of dose for the various materials. The swelling of beta-SiC and Type-S fibers for different temperatures [1, 2] was fit using linear swelling versus time and the swelling is assumed to be linearly dependent on dose up to a critical dose, which then saturates at constant swelling; the saturation dose being temperature dependent. For Hi-Nicalon fibers, fiber density as a function of neutron dose was converted to fiber strain. The data of Kaae [3] were used for the swelling of three pyrolytic carbons, denoted as high-density isotropic carbon (HDIC), low-density isotropic carbon, and high-density slightly anisotropic carbon.