NEUTRON-IRRADIATION EFFECTS ON CORRELATIONS BETWEEN MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF C/C COMPOSITES

Neutron irradiation effects on microstructure and mechanical properties of C/C composites were examined, and correlations between changes of mechanical properties and microstructure of composites were inspected. Materials used were one- and two-directionally reinforced composites with mesophase-pitch based carbon fibers as reinforcement and the mixture of green coke and phenolic resin as matrix precursor. Neutron irradiation was performed to 1.3 x 10(21) and 1.5 x 10(22) n/m(2) (E > 1 MeV) at about 350 K. Mechanical properties were measured by bend tests. Flexural and shear strength were increased with increasing neutron fluence. On the contrary, fracture strain showed quite a little dependence on neutron fluence. Flexural modulus at near 0 strain was increased with increasing fluence. Stress stiffening at near 0 strain was suppressed with irradiation. While, modulus drop was observed at high strain region and was decreased with increasing neutron fluence.