DYNAMIC RESPONSE OF A GRID-STIFFENED COMPOSITE CYLINDRICAL SHELL REINFORCED WITH CARBON NANOTUBES TO A RADIAL IMPULSE LOAD

Equilibrium equations of a rib grid-stiffened composite cylindrical shell reinforced with carbon nanotubes (CNTs) are derived based on the first-order shear deformation theory considering the effect of shear deformation and moment of inertia. The distribution of CNTs across the shell thickness is assumed uniform, and the elastic modulus of the CNT-reinforced polymer is calculated using the rule of mixtures. In order to determine the equivalent stiffness of the grid-stiffened composite cylindrical shell, the smeared stiffness method is used. Equilibrium equations for free and forced vibration of the rib grid-stiffened composite cylindrical shell are solved using the Galerkin method, and the effects of grid ribs on the dynamic response of the shell are investigated. The results found indicate that the use of circumferential ribs in the structure can increase the frequency, change the fundamental mode shape, and reduce the radial displacement by similar to 12% (especially in higher modes). In addition, the results demonstrate that a 5-degree increase in the angle of helical ribs can decrease the radial displacement linearly by 5%. Eventually, the corresponding outcomes reveal that the rib thickness and presence of CNTs may significantly increase the natural frequencies and decrease the radial displacement of such shells.