BUCKLING OF ELLIPTICALLY DELAMINATED COMPOSITE PLATES

The buckling of laminated plates with elliptic delamination under compressive loading was studied experimentally and analytically. In the experiment, a tensile-test machine was used to determine the load-displacement behavior of the delaminated plates under uniaxial loading and the buckling strength was extracted therefrom. In analysis, a nonlinear finite element program based on the updated Lagrangian formulation was developed to analyze the response of the laminated plates. The formulation includes large displacements and large rotations. The plates were divided into finite elements and the degenerated shell elements were used. The Newton-Raphson method was used to solve the resulting equation for the nonlinear system and a displacement-controlled scheme was used in the solution procedure near the buckling load. This process was repeated until a desired accuracy was achieved. The buckling behavior of mixed and global types of the delaminated composite plates were examined. Four parameters, including the size of the delaminated region, the orientation of the fiber direction, the position of the delaminated region in the thickness direction and the orientation of the major axis of the elliptic region with the loading axis, were varied to assess their influence on the buckling behavior of the plates. Good agreement was obtained between the analytical and experimental results.