Mixed finite element formulation and optimal design of thin composite laminates

A Hellinger-Reissner variational principle is introduced to derive the weak form equation of thin generally orthotropic laminates. It leads naturally to a mixed finite-element approximation that has the out-of-plane deflection and the bending and twisting moments as independent unknowns. A triangular element is derived that is used for both analysis and optimization purposes. Numerical simulations on example laminates of irregular geometry are presented to validate the theoretical framework.