Modeling of Polymer/Carbon nanotube nanocomposite to estimate structural damping in a rotorcraft blade

The development of next-generation rotorcraft requires advancement in certain key areas such as cruise speed, payload, range, along with cost considerations. Coaxial and tiltrotors are two promising candidates for future of high speed vertical flight. Traditional lag dampers are unable to produce adequate levels of damping for the rigid fiber composite blades of coaxial rotorcraft. A promising approach for achieving lightweight damping in composite blades is to add carbon nanotubes (CNTs) to the matrix material. The current investigation aims to predict the damping behavior of a rotating beam that represents a simplified fiber reinforced polymer/CNT nanocomposite blade. The developed model takes in account different physical variables such as the critical shear stress (τ c) for slip onset of the CNTs and CNT aspect ratio (l/d), volume fraction (ν CNT), and orientation. The study first looks at a case where the nano-inclusions are aligned with the direction of loading for the rotor blade. The model predicts maximum damping for low τ c in combination with relatively low l/d. The damping trend increases with increase in ν CNT of the nano-inclusions. A damping ratio of 7.3% and 8% was observed with optimally configured parameters for aligned and randomly oriented CNTs respectively. Overall, the results suggest significant damping augmentation from the CNTs.