Nonlinear vibration characteristics of fibre reinforced composite cylindrical shells in thermal environment

Abstract

In this paper, an analytical model for fiber reinforced polymer composite cylindrical shells (FRPCCSs) accounting for material and geometric nonlinearities and thermal effect is proposed, which is capable of predicting natural frequencies, damping ratios, and resonant responses under different excitation amplitudes and temperatures. Firstly, the nonlinear Young's and shear moduli and loss factors of fiber reinforced polymer composites considering amplitude and temperature dependent properties are represented based on the Jones-Nelson nonlinear material theory, complex modulus principle, together with polynomial fitting technique. Then, the equations of motion for FRPCCSs are derived accounting for nonlinear strain–displacement relations of the von Kármán type. The procedure of determining fitting coefficients for nonlinear Young's and shear moduli and loss factors is also presented in details. Following theoretical studies, a series of thermal vibration experiments on two shell specimens made of CF120 carbon/epoxy composites are carried out to validate the proposed modeling approach as well as evaluating nonlinear vibrations of FRPCCSs experimentally. It has been found that the first three natural frequencies of composite shell specimens are initially decreased and then increased along with the increase of excitation amplitude. This variation trend becomes more significant at high temperature with the maximum variation degree of 8.2%. Meanwhile, the corresponding damping ratios and resonant responses of FRPCCSs show upward trends as the excitation amplitude and environmental temperature increase. Compared to excitation amplitude, environmental temperature has more significant effect on the damping performance of FRPCCSs, of which the relative variation degree is up to 300.5% as the temperature raises from 20 to 200 °C.