Large deflection behavior of circular quasi-isotropic laminates under point loading

Eight-ply quasi-isotropic circular composite plates of Thornel 300 graphite in Narmco 5208 epoxy resin (T300/5208) were analyzed to obtain the large deformation behavior under low-velocity impact-type point loads. A simple plate-membrane coupling model was developed. The impact-type point loads were replaced by equivalent quasistatic point loads. The plate-membrane coupling model was used to obtain the large deformation shapes for the thin circular composite laminates. The analyses indicated that the large deformation shapes of the composite plates under point loads vary with the center point displacements, and hence are different for different load levels. Quasi-isotropic plates were analyzed by replacing anisotropic bending stiffness components with the equivalent flexural stiffness for the isotropic plates. The plate-membrane coupling model was verified by conducting a series of tests on clamped, circular quasi-isotropic laminates. Deflected shapes and loaddisplacement curves for the thin composite plates were experimentally obtained. These deflected shapes and load-displacement curves agreed well with the analytical results obtained using the plate-membrane coupling model.