BUCKLING OF ELLIPTICALLY DELAMINATED COMPOSITE PLATES

The buckling of laminated plates with elliptic delamination under comp ressive loading was studied experimentally and analytically. In the ex periment, a tensile-test machine was used to determine the load-displa cement behavior of the delaminated plates under uniaxial loading and t he buckling strength was extracted therefrom. In analysis, a nonlinear finite element program based on the updated Lagrangian formulation wa s developed to analyze the response of the laminated plates. The formu lation includes large displacements and large rotations. The plates we re divided into finite elements and the degenerated shell elements wer e used. The Newton-Raphson method was used to solve the resulting equa tion for the nonlinear system and a displacement-controlled scheme was used in the solution procedure near the buckling load. This process w as repeated until a desired accuracy was achieved. The buckling behavi or of mixed and global types of the delaminated composite plates were examined. Four parameters, including the size of the delaminated regio n, the orientation of the fiber direction, the position of the delamin ated region in the thickness direction and the orientation of the majo r axis of the elliptic region with the loading axis, were varied to as sess their influence on the buckling behavior of the plates. Good agre ement was obtained between the analytical and experimental results.