A global-local variational model has been introduced for the analysis of laminated composites. The whole region of laminates is divided into two types. A local variational model based on Reissner's functional is used for detailed stress analysis for regions of interest, while the remaining region is modeled by a global variational approach where some effective modulus concept is used for the specific group of layers.
The proposed model has been applied for the analysis of interlaminar stress in a finite width composite laminate under uniform axial strain. A set of governing differential equations has been derived and solution methods given. Numerical results for illustrative problems are compared with existing solutions by FEM. The method is shown to be powerful and efficient. Several different partitionings of local and global regions are also tried and discussed.
Failure stresses for delamination and first ply failure are predicted and compared with experiments for $[(±30)_n/90]_s$ (n=2,4,6) T300/5208 Graphite/Epoxy composite laminates. The Tsai-Wu quadratic failure criterion with the concept of average stress at a free edge zone is used. Various failure modes have been reasonably well explained and the applicability of the approach discussed.
