Membrane Boundary Condition Effects on Unsymmetric Laminates

This paper examines the influence of membrane boundary conditions on the stiffness of unsymmetrically laminated plates. Three different types of inplane restraints were considered for transversely loaded simply supported rectangular plates. Plate deflections according to linear theory were calculated by the Ritz method for antisymmetric angle-plys and 0°/90° cross-plys. Results show that by changing only the membrane boundary condition, lateral deflections can vary by more than 200%. In contrast to previous studies, this much greater sensitivity to in-plane boundary conditions affects a broader range of laminates and shows that bending-stretching coupling can have a much smaller effect on laminate stiffness. Since the reduced bending stiffness approximation does not account for the type of inplane restraint, it can lead to errors of over 200%. Results also indicate that bending-induced stress resultants may be large enough to produce nonlinear response in unsymmetric laminates for small deflections. Previous studies are discussed and some limitations of the reduced bending stiffness approximation are identified.