A LOCK-FREE MATERIAL FINITE ELEMENT FOR NON-LINEAR OSCILLATIONS OF LAMINATED PLATES

The objective of the present paper is to propose an efficient, accurate and robust four-node shear flexible composite plate element with six degrees of freedom per node to investigate the non-linear oscillatory behavior of unsymmetrical laminated plates. The degrees of freedom considered are three displacement (u, v, w) along x-, y- and z -axis, two rotations (θx, θy) abouty - and x -axis and twist θxy. The elementc employs coupled displacement field, which is derived using moment-shear equilibrium and in-plane equilibrium of composite strips along the x - andy -axis. The displacement field so derived not only depend on the element co-ordinates but are a function of extensional, bending–extensional, bending and transverse shear stiffness coefficients as well. A bi-cubic polynomial distribution with 16 generalized undetermined coefficients for the transverse displacement is assumed. The element stiffness and mass matrices are computed numerically by employing 3×3 Gauss Legendre product rules. The element is found to be free of shear locking and does not exhibit any spurious modes. The element is found to be free of shear locking and does not exhibit any spurious modes. In order to compute the non-linear frequencies, linear mode shape corresponding to fundamental frequency is assumed as the spatial distribution and non-linear finite element equations are reduced to a single non-linear second order ordinary differential equation. This equation is solved by employing direct numerical integration method. A series of numerical examples is solved to demonstrate the efficacy of the proposed material finite element.