Optimising the ply dropping order in variabel stiffness, variable thickness laminates using stacking sequence tables

Modern composite structures o
er two avenues of optimising performance. One, optimising a single stacking sequence over the structure leading to constant sti
ness designs. Two, varying the sti
ness over the structure. This may be achieved by dropping plies, changing the thickness, or by steering the fibres, changing the fibre angles. Optimising ply drops involves two decisions: the selection of ply drop boundaries, and of the ply drop order. Previous work considered the problems of optimising the fibre angle distribution and ply drop boundaries but ply drop order was pre-specified. This paper extends the work to simultaneously optimise the fibre angle distribution, the ply drop boundaries, and order. The optimisation of fibre angle distribution lends itself to gradient-based methods. The ply drop boundary optimisation is formulated using topology optimisation techniques and is thus also solvable using gradient-based methods. The ply drop order optimisation requires discrete variables and is hence approached using an evolutionary algorithm based on stacking sequence tables. In this paper an e
cient multi-step algorithm is developed combining the optimisation of all aspects of variable sti
ness laminates. The results indicate that significant improvements may be obtained by including the ply drop order in the optimisation at a relatively modest computational cost.