Blending constraints for composite laminates in polar parameters space

This work proposes a new formulation of blending constraints, in the framework of the multi-scale two-level (MS2L) optimisation strategy for composites. This approach aims to optimise simultaneously both geometrical and mechanical parameters of the laminate at each characteristic scale (macroscopic and mesoscopic ones). In particular, this study deals with the first level of the MS2L optimisation strategy which focuses on the laminate macroscopic scale. At this scale, the behaviour of the laminate is described in terms of the polar parameters of each constitutive stiffness matrix in the framework of the First-order Shear Deformation Theory (FSDT). Therefore, blending constraints are formulated as equivalent mechanical requirements to be imposed to both polar and geometric parameters of the laminate within the first-level problem. The effectiveness of the proposed approach is tested on a meaningful benchmark: the least-weight design of a composite wing-box subject to constraints of different nature. The optimised solutions provided by the MS2L design strategy are characterised by a weight saving of about 12% (when compared to the reference solution taken from the literature) by meeting the full set of feasibility, manufacturing and mechanical requirements.