Postbuckling of long laminated composite plates with unsymmetric laminate configurations under compression

The approximate solution for the postbuckling of infinitely long and unsymmetrically laminated composite plates is obtained by using a simple functional representation for the buckling mode in conjunction with the Calerkin method. Nondimensional parameters are used to express the approximate solution in a very simple and clear formulation. The results given by this solution are compared for axial compression in the longitudinal direction with the results given by the nonlinear finite element method for finite length rectangular long plates. The influence of the boundary conditions on postbuckling response is also studied. For the FEM analysis, two different simply supported boundary conditions on the long edges of the plate are considered. It is found that these two sets of boundary conditions give different results for the buckling and postbuckling finite element analysis. In most cases the FEM analysis overestimate and, respectively, underestimate the approximate closed form solution, depending on the type of simply supported boundary condition considered. Thus, the approximate solution appears useful for design purposes as an averaged quantity between the two FEM analyses. Also, it is found that the Reduced Bending Stiffness method can be successfully used for determining the approximate solution.