Damping characteristics of CVI-densified carbon-carbon composites

The damping behavior of various carbon-carbon (C/C) composites fabricated by chemical vapor infiltration (CVI) techniques has been investigated in the low-frequency range by means of a pendulum method. Two groups of samples of C/C composites were employed in this study, one with constant fiber volume fractions but with various densities from 1.02 to 1.69 g cm^-3, and the other with the same densities but with volume fractions of carbon fibers varying from 45 to 61%. The internal friction of the C/C composites has been found to decrease with an increase in density and to increase with an increase in the volume fraction of the fibers. Meanwhile, the porosity of the C/C composites with different density was calculated, and the internal friction of the composites was found to increase with increasing porosity. According to the observed experimental results, the damping mechanisms associated with the C/C composites have been analyzed and the porosity damping and interface damping are used to explain the experimental results.