EFFECTS OF NEUTRON-IRRADIATION ON MICROSTRUCTURE AND MECHANICAL-PROPERTIES OF CARBON CARBON COMPOSITES/

As an important part of the national R&D program to high performance a nd low cost C/C composite materials, a new manufacturing method of C/C composite with densified matrix without conventional densification pr ocess has been successfully developed. In this study, neutron irradiat ion effects on mechanical properties of the innovative C/C composites were examined. Materials used were one- and two-directionally reinforc ed composites with mesophase-pitch based carbon fibers as reinforcemen t 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 increas ing neutron fluence. On the contrary, fracture strain showed quite a l ittle dependence on neutron fluence. Flexural modulus at near O strain was increased with increasing fluence. Stress stiffening at near O st rain was suppressed with irradiation, while modulus drop was observed at high strain region and decreased with increasing neutron fluence. T hese results were interpreted in terms of microstructural change.