Effects of microstructure on the internal friction of carbon-carbon composites

Internal friction directly depends on the microstructure of material. For carbon-carbon composites made up of fibers, matrix and interface, internal friction mechanisms involved are more complex. In present work, the effects of microstructure on the internal friction in carbon-carbon composites are studied. During the Chemical Vapor Infiltration (CVI) process, the internal friction in carbon-carbon composites decreases with the increasing of density. The experimental result does not accord with the equation for conventional composites. Considering the porous structure and non-full ideal interfacial adhesion in carbon-carbon composites, we develop a modified equation for the quantitative description of internal friction, which shows good agreement with the experimental results. Furthermore, internal friction related to pyrolytic carbon matrix, fibers and interface are discussed, respectively, which gives us a fundamental understanding on the internal friction in carbon-carbon composites. Among these internal friction mechanisms, interfacial internal friction is of special interest, as it causes some abnormal internal friction phenomena in carbon-carbon composites. (C) 2000 Elsevier Science S.A. All rights reserved.