Koiter method and solid shell finite elements for postbuckling optimisation of variable angle tow composite structures

The optimisation of the structural behaviour of the wing is one of the key aspects in the design of future aircraft. Enhanced freedom to designers has been offered by the stiffness-tailoring capability of Variable Angle Tow (VAT) laminates. Efficient and robust optimisation strategies are, consequently, of great importance to fully explore such an increased design domain. Simultaneously, taking account of the initial postbuckling behaviour can provide hidden load-bearing capability, leading to reduction in weight and costs. In this work we propose an optimisation strategy of the postbuckling behaviour of a recently-proposed VAT wingbox. Being based on an efficient reduced order model for the evaluation of the equilibrium path and on robust stochastic algorithms for the solution of the optimisation problem, the approach shows its viability as a general design tool for buckling dominated structures. Manufacturing constraints are included and the influence of geometrical imperfections is efficiently handled during the optimisation. Different optimisation scenarios are investigated and results show a much improved solution with respect to the initial VAT design.