A method using beam search to design the lay-ups of composite laminates with many plies

Due to high specific strength and stiffness ratios, composite materials are widely used in industries where minimising structural mass is of paramount importance, such as the aerospace sector. However, designing lightweight composite laminates is challenging due to the large number of discrete design variables involved, e.g. ply numbers and fibre orientations which are usually restricted to a set of predefined values. The number of possible laminate solutions grows exponentially with increasing ply count, quickly rendering complete enumeration impossible. Current mixed-integer programming techniques for designing composite laminates with many plies either exhibit insufficient design space exploration, or demand inconceivable computational effort. As a result, laminates often have sub-optimal properties, e.g. excessive weight. We propose a novel deterministic optimiser for finding the lay-up of composite laminates with many plies. Lay-ups must match desired stiffness properties called Lamination Parameters (LPs). The design-space is explored by a procedure that uses beam search to promote fast convergence towards optimal or near-optimal solutions. Additionally, the optimality of the design solutions is improved by local searches which are performed after a first guess of the stacking sequences. The proposed optimiser is shown to retrieve symmetric laminate lay-ups with as many as 300 plies within a few minutes.