Optimization of composite aircraft structures in consideration of postbuckling behavior

An approach is presented to determine the design that minimizes the weight in consideration of the postbuckling behavior of stiffened composite panels. Since, due to computational expense, for optimization purposes a nonlinear finite element approach is not appropriate, a semianalytical approach is implemented in the EADS MAS software LAGRANGE. A gradient-based optimization scheme is employed to determine the ply thicknesses and fiber orientation of the composite skins and the cross-sectional areas of the stiffeners. Strength and stability constraints are used. Based on two examples of different complexity, weight savings are shown to be due to the fact, that skin buckling is allowed above a certain load level.