Strength improvement by densification of C/C composites

The tensile strength of carbon/carbon composites (C/Cs) was examined as a f unction of the density in the range above rho = 1.6 g/cm(3). Three processi ng routes of preformed yarn, resin char, and HIP processes were adopted to densify the C/C composites. The density was increased to 1.95 g/cm(3) throu gh these routes. The interfacial strength between the fiber and matrix was significantly and unexpectedly varied by repeating the HIP process, though the detailed source mechanisms could not be identified. The tensile strengt h of the densified C/Cs was shown to be dependent on the processing routes. In particular, opposite tendencies were obtained as a function of rho, i.e . the monotonic strength increases for the C/Cs with the preformed yarn and resin char treatments. while a monotonic decrease was observed using the H IP process. However, after the tensile strength was re-examined, the ultima te tensile strain was found to be expressed by a monotonic decreasing funct ion of the interfacial strength. This implies that weakening fiber interfac es is a key factor for obtaining C/C composites with the higher tensile str ength. (C) 2000 Elsevier Science Ltd. All rights reserved.