Equivalent plate formulation of Double–Double laminates for the gradient-based design optimization of composite structures

The Double–Double concept of composite laminates suggests huge simplifications in aerospace structural design and manufacturing. This work presents a homogenized composite formulation introducing an analytical DD equivalent plate. Additionally, an optimization strategy is proposed using the DD parameterization as design variables to derive an optimized thickness and stiffness distribution on the basis of gradient-based numerical sensitivities. The method is applied to a simple wing box benchmark model for composite design applications. Based on this model, the usage of gradients is verified for the newly implemented DD formulation with a global optimum and a robust convergence. Furthermore, the DD design is compared to a lamination parameter-based optimization of conventional Quad laminates. The DD optimized wing box shows small weight gains, due to the fact that one building block is distributed to an assembly of panels, whereas the Quad design provides individual optimality for each design region. At the same time, the proposed DD optimization process shows lower computational efforts, due to a lower amount of variables and constraints, while all laminate manufacturing constraints are implicitly fulfilled. Thus, the introduced DD formulation provides an efficient option to obtain a feasible structural design and therefore improve the maturity level for early aircraft design phases. • Continuous Double–Double laminate formulation for gradient-based optimization • Simplified composite design rules and recovered manufacturability • Reduced number of design variables to adjust the wing stiffness • Increased computational efficiency for aircraft design optimization • Comparison of Double–Double and Quad laminate design on benchmark use case