Interfacial strain energy dissipation of hybrid nanocomposite beams under axial strain fields

A micromechanics and structural modeling analysis of inherent structural damping ex- hibited by hybrid nanocomposite beams under axial strains is presented. The model is used to assess, for the first time, the potential aeroelastic/aeromechanical stability enhancement of representative helicopter rotor blade structures by utilizing matrix nano-inclusions. The matrix/nano-inclusion micromechanics before interfacial slip occurs are similar to the Cox model for short fiber reinforcement, and the frictional energy dissipation is assumed to be proportional to the interfacial shear force over the matrix/nano-inclusion interface where slip has occurred. The micromechanics model is compared with experimental measure- ments of storage and loss moduli for a polymer nanocomposite under interfacial slip condi- tions. It is shown that the relatively simple model captures the salient features of interfacial energy dissipation associated with nanocomposites once uncertainties in fiber orientation and dispersement are accounted for using an effective volume fraction. The validated model is then used to calculate damping of the first beam bending mode when the structure is subjected to axial strain fields that are representative of helicopter rotor blades, including contributions from centrifugal loads. Results indicate that hybrid nanocomposites based on carbon nanotube matrix inclusions show significant potential for augmenting the inherent structural damping and aeromechanical stability of hingeless/bearingless rotors, without the need for additional auxiliary mechanical dampers or significant additional blade weight.