In the present study, the free and forced vibration responses of the composite sandwich plate with carbon nanotube reinforced honeycomb as the core material and laminated composite plates as the top and bottom face sheets are investigated. The governing equations of motion of hybrid composite honeycomb sandwich plates are derived using higher order shear deformation theory and solved numerically using a four-noded rectangular finite element with nine degrees of freedom at each node. Further, various elastic properties of honeycomb core materials with and without reinforcement of carbon nanotube and face materials are evaluated experimentally using the alternative dynamic approach. The effectiveness of the finite element formulation is demonstrated by performing the results evaluated experimentally on a prototype composite sandwich plate with and without carbon nanotube reinforcement in core material. Various parametric studies are performed numerically to study the effects of carbon nanotube wt% in core material, core thickness, ply orientations, and various boundary conditions on the dynamic properties of composite honeycomb sandwich plate. Further, the transverse vibration responses of hybrid composite sandwich plates under harmonic force excitation are analyzed at various wt% of carbon nanotubes and the results are compared with those obtained without addition of carbon nanotubes to demonstrate the effectiveness of carbon nanotube reinforcement in enhancing the stiffness and damping characteristics of the structures. The study provides the guidelines for the designer on enhancing both the stiffness and damping properties of sandwich structures through carbon nanotube reinforcement in core materials.

In the present study, the shear properties of a functionally graded (FG) honeycomb core (HCC) material without and with CNT reinforcement are investigated. The multi walled carbon nanotubes (MWCNTs) functionalized with carboxylic acid (COOH) were randomly added in an organic solvent to disintegrate and disperse homogenously into the viscous less epoxy resin matrix (LY556) using the ultrasonic liquid processor. The FG-HCC composite test materials were made-up without and with CNT reinforcement using high carbon-high chromium honeycomb die using the vacuum assisted hand-layup method. The dynamic analysis of HCC composite materials reinforced with CNT in the ribbon located along the transverse direction was carried out experimentally to identify the shear modulus along the corrugated (G_xz) and joined (G_yz) direction using the alternative dynamic approach method. The materials were functionally tailored in such a way that CNTs were reinforced in ribbon located in between the two honeycomb patters viz, continuously and alternatively, It was shown that the reinforcement of CNT continuous ribbon in the FG honeycomb core materials would increase the shear modulus considerably without any changes in the mass of the composite structure. The strong bonding and random dispersion of CNTs in the FG-HCC composite enhances the shear properties significantly than that of odd and even ribbon sheets reinforced composite structures. This study gives the guidelines for the designer on improving the shear properties of FG-HCC composite structures through CNT reinforcement in the ribbon reinforced core materials.