VIBRATIONS OF IMPERFECT LAMINATED PANELS UNDER COMPLEX PRELOADS

The objective of this paper is to analyze the effect of complex, arbitrary in-plane and out-of-plane loads on the transverse vibrations of thin arbitrarily laminated panels with or without geometric imperfections. The finite-element method is used. A 48 degree-of-freedom thin shell element previously formulated by the senior author is employed. The formulation is general with respect to the boundary conditions, types of imperfections, and number, orientation, and stacking sequence of the lamina. A large radius to thickness ratio is assumed so as to ignore the shear and rotary inertia effects. The results are presented for angle-ply rectangular plates and cross-ply cylindrical panels, with both of these having simply supported edge conditions along all the four edges, and isotropic square plates involving free edges under non-uniform combined loads. The panels are subjected to both axial and shear in-plane stresses. The effects of geometric parameters (aspect ratio, panel curvature, and geometric imperfections) and material properties (varying the number of layers but the same thickness) are examined. The results are presented in the form of frequency-load interaction curves for various geometric parameters. Whenever possible, the present results are compared with those available in the existing literature. A good agreement is observed.