Damping of a laminated carbon/epoxy beam with carbon nanotube interlayers

Traditional lag dampers used in rotorcraft are ineffective in providing adequate damping for high speed coaxial compound rotorcraft which have rigid, hingeless blades. Carbon nanotubes (CNTs) have shown the potential to offer an intrinsic passive damping solution for such applications. The current paper evaluates the effectiveness of using CNTs to provide structural damping in a laminated fiber reinforced composite beam. Baseline composite and hybrid nanocomposite beams with [±45/0]_s stacking sequence were fabricated. CNT interlayers were placed between the continuous carbon-fiber/ resin plies within the hybrid composite. The volume fraction of CNTs added to the composite was 1%. The fabricated beams were subjected to free and forced vibration tests. Damping from CNTs was observed to be strain dependent. CNTs are believed to slip once a critical value of strain is reached and the slippage contributes to the composite damping. The damping ratio contribution from CNT interlayers was up to ∼2.2% for free vibration tests and up to ∼3.7% for forced vibration tests. The damping augmentation is significant as the baseline composite damping ratio is ∼0.2%. An in-house structural micromechanical model, incorporating the CNT parameters such as aspect ratio and critical shear stress, is able to reproduce the damping trends seen in the experiments.