BIDIRECTIONAL BENDING OF LAMINATED COMPOSITE PLATES USING AN IMPROVEDZIGZAG MODEL

The behaviour of simply supported rectangular symmetric cross-ply lami nated composite Plates subjected to bidirectional bending is determine d using an improved zig-zag displacement model. The zig-zag model is b ased upon a layerwise cubic variation of the in-plane displacements an d a parabolic variation of the transverse shear stresses with zero val ues at the free surfaces. By satisfying the continuity conditions of t he in-plane displacements and the transverse shear stresses at the int erfaces, the number of variables is shown to be the same as that in th e first-order shear deformation theory of Mindlin, independent of the number of layers in the laminate. The accuracy of the model and its su itability for use in engineering design is examined by applying it to four established bidirectional bending problems which have been solved by Pagano using exact elasticity theory. The numerical results indica te that the present model predicts very accurate results for displacem ents and stresses for symmetric cross-ply laminates, even for small le ngth-to-thickness ratios.