Tensile behavior of irradiated SiC fibers

The strength and toughness of continuous fiber reinforced ceramic composites (CFCCs) are highly dependent on the fiber strength distribution. To first order, weaker fibers lead to low strength but higher toughness while stronger fibers lead to high strength composites of relatively low toughness. Toughness is associated with pullout of the fibers from the ceramic matrix. It has been shown previously that both strength and toughness of SiC/NicalonTM composites are drastically changed following irradiation. Tensile results are presented for low oxygen Nicalon fibers neutron irradiated at damage levels of 0.013 displacements per atom (dpa), 0.13 dpa and 0.32 dpa. Single fibers were tensile tested and analyzed, using Weibull statistics, for mean strength and distribution. Tensile modulus was also determined. Using a diffractometer, the fiber grain size and percent crystallinity were determined. The initial results of these low fluence neutron irradiations exhibit no substantial degradation of the properties investigated. Therefore, continued research at higher doses is recommended. ((orig.))