Vibration analysis of anisotropic plates with eccentric stiffeners

The analysis of vibration characteristics of anisotropic plates with eccentric stiffeners has been performed using the finite element method based on the shear deformable plate theory. The stiffeners are modeled as a beam element based on Timoshenko beam theory. The present analysis presents the effects of fiber orientation, dimension and location of the stiffener on the vibration characteristics of anisotropic stiffened plates. The stiffened plates are composed of graphite-epoxy(AS1/3501-6) composite laminate with a symmetric stacking sequence. The present finite element model uses nine-node quadrilateral elements for the skin plate and three-node quadratic elements for the stiffener. The solution of the eigenvalue problems has been obtained by the subspace iteration method. The results obtained by the present finite element model are compared with previous results for the stiffened isotropic plates. Also, the result of the present beam model for the stiffener made of composite material is compared with that of the shell model. This result shows that the present model for the stiffened plate gives quite accurate results. The size, fibre orientation angle and location of the stiffener affect the natural frequencies and mode shapes of the stiffened anisotropic plate.