Strain dependent energy dissipation in multi-scale carbon fiber composites containing carbon nanofibers

This study investigates strain dependent energy dissipation characteristics in carbon nanofiber (CNF) reinforced carbon fiber epoxy composites (multi-scale composites) by characterizing their viscoelastic properties and vibrational damping response. The air damping effect on the energy dissipation characteristics is also examined. The viscoelastic properties of epoxy containing two weight fractions (3 and 5 wt%) of added CNFs were characterized using dynamic mechanical analysis. Carbon fiber layers were then infiltrated with the two epoxy resins containing the CNFs to form multi-scale composites. A strain dependent loss factor behavior of the multi-scale composites was observed in the dynamic cyclic testing due to CNF's stick-slip friction, showing a 53% increase in loss factor for the composites containing 5 wt% CNFs. The beam vibration test results also indicated an improvement in loss factor for the multi-scale composite beams relative to those without the CNF addition in the first two resonant frequencies. The multi-scale composite beams exhibit an increase in loss factor, up to 43%, at high amplitude excitation, while a reduction in loss factor was seen at low amplitude. These observed strain dependent damping characteristics seem to result from both the stick-slip friction and the air damping effect. (C) 2012 Elsevier Ltd. All rights reserved.