Nonlinear vibrations of laminated composite stiffened skewed cylindrical panels

Abstract

The review of literature indicates that free vibration of skewed unstiffened cylindrical panels was solved by the researchers using geometrically linear finite element models. The vibration studies of skewed stiffened panels are absolutely missing in the literature, especially using the geometrically nonlinear strains. This paper fills that void and proposes an isoparametric C0 continuous nonlinear finite element code which formulates the skewed panels using eight noded elements and stiffeners by three noded elements. Both curved panels and stiffeners are formulated by the nonlinear approach. Lagrange's equation of motion, Hamilton's principle and first order shear deformation theory are combined to solve the free vibration of skewed stiffened panels for graphite/epoxy and glass/epoxy composites. Sensitivity of the proposed model to shear correction factors for stiffeners are tested. Correctness of the proposed model is confirmed by comparing present results with closed form, experimental and numerical findings available in the literature. The results are obtained for CFCF and FCFC boundary conditions, varying laminations and skew angles of centrally and multi-stiffened panels. The numbers, orientations, depth and eccentricities of stiffeners are varied. The findings indicate that the performances of stiffened panels are compromised when skewed and hence, such panels should be avoided. The multi-stiffened panels offer superior performances than centrally stiffened ones. Among the CFCF panels, the 450/-450/450/-450 laminate and nx = 3, ny = 7 stiffeners yield the best performance. The FCFC panels show the maximum frequencies for 00/900/00 laminate and nx = 4, ny = 7 stiffeners. The graphite/epoxy composites show better performances than glass/epoxy ones. The multi-stiffened panels must have the stiffeners below the mid-surfaces while maintaining dst/h = 2, Ryy/b = 0.75 and a/b = 0.5 for achieving the best performances. The CFCF panels must include the first four modes of vibration for a comprehensive performance study while for FCFC panels, the first mode estimates the vibration performances correctly. © 2025 Institution of Structural Engineers