DIMENSIONAL STABILITY AND TENSILE-STRENGTH OF IRRADIATED NICALON-CG AND HI-NICALON FIBERS

Nicalon-CG and Hi-Nicalon fibers were characterized by measuring their density and tensile strength in the unirradiated, thermal annealed, a nd irradiated conditions. The results indicate the fibers that perform best after irradiation to 43 dDa SiC at 1000 degrees C are those Chat approach stoichiometric and crystalline SiC. Hi-Nicalon fiber exhibit ed less than 1% densification, accompanied by a slight increase in ten sile strength after irradiation. Nicalon-CG, in contrast, was signific antly weakened in the annealed and irradiated conditions. In addition, Nicalon-CG exhibited substantial irradiation-induced shrinkage. Loss of fiber tensile strength after irradiation is shown to reduce the fle xural strength of irradiated composites while fiber shrinkage, and res ultant debonding from the matrix, are linked to a reduced composite el astic modulus. (C) 1998 Elsevier Science B.V.