Improved composite material damping using high damping graphite fibers

Increased damping has been demonstrated for graphite/epoxy composite material made using bromine-intercalatefd graphite fiber. A resonant forced-vibration test method was used to measure the damping of unidirectional graphite/epoxy flexural specimens, at frequencies of about 100 hz, and at temperatures ranging from -120 to +30 degrees C. Specimens made from pristine P-100 as well as treated P-100 graphite fibers were characterized. The peak damping ratio observed for the pristine fiber composites was 8 × 10^-4 (damping capacity of 1%), while that exhibited by the brominated fiber composites was 16 × 10^-4 (damping capacity of 2%). These results are consistent with previous studies of the damping properties of single graphite fibers. Additional theoretical results indicate that, contrary to state-of-the-art composite design principles, the damping of quasi-isotropic composite materials made using these treated graphite fibers could be dominated by fiber damping instead of matrix shear damping.