A SUBLAMINATE ANALYSIS METHOD FOR PREDICTING DISBOND AND DELAMINATION LOADS IN COMPOSITE STRUCTURES

A novel analysis method has been developed with the goal of providing accurate assessments of the forces that can delaminate composite laminates and bonded structures. The method uses interconnecting high-order plates to represent the cross section of a structural element. The plates can be both stacked and connected end-to-end. When stacked, the interfacial tractions generated between the plates can be calculated, providing a measure of the delaminating stresses. The plate equations are solved exactly, thus giving accurate numerical results even in cases where the stress gradients are steep. The plate theory used incorporates a linear distribution through the thickness for the u, v, and w displacements. This set of assumed displacements makes the plate shear deformable, and allows stretching in the thickness direction. Consequently, both shearing and normal tractions can be computed at the interfaces between stacked plates. The plate equations have been derived for completely general stacking sequences of composite plies; i.e. unsymmetric and unbalanced laminates are allowed. Both flat and cylindrically curved plates have been implemented. Beyond stress analysis, the method also provides strain-energy-release-rate (SERR) results for the growth of existing delaminations. The individual modes of the total SERR can be calculated for input to interactive crack growth laws.