Dynamic Mechanical Properties of Graphite-Epoxy and Carbon-Epoxy Composites

Dynamic elastic moduli and damping of carbon- and graphite-filled epoxy composites have been measured over the temperature range of 85 to 300° K. The epoxy resin matrix was cured with diethylenetriamine. Dynamic elastic moduli increase with filler content in both cases; however, graphite powder is more effective than carbon powder in increasing the modulus. For the graphite composite, experimental data agree with Wu’s equation for disk-shaped filler particles with a modulus of 56 × 10 dyne/cm2.For the carbon composite, experimental data cannot be effec-tively compared to any theoretical model, probably because the carbon powder is composed of agglomerated particles. The effect of voids on the dynamic modulus of a particulate composite is also discussed. The β damping peak (∼ 250° K) does not change in its intensity with filler con-tent, while the intensity of the γ peak (∼ 150°K) is decreased as the amount of filler is increased. The relation between the filler content and the intensity of the β peak suggests that damping in the composites in-cludes a component due to friction at the interface between the filler and matrix. The decrease in the y peak with filler content may be explained by interaction between the filler surface and unreacted epoxides I