Minimum mass laminate design for uncertain in-plane loading

Requirements for lower emissions and operating costs make mass reduction of composite structures a significant issue for future aircraft. Here, minimisation of normalised elastic energy under an uncertain, general in-plane loading is used to indicate laminate efficiency and by equivalence minimum mass. Results are the first to investigate the comparative robustness of standard and non-standard angles to uncertain loading. They indicate that weight reductions of up to 8% can be achieved if optimum design, using standard angle (θ = 0°, ±45° or 90°) and industrial design rules, is replaced by optimising non-standard angles (0° ≤ θ ≤ 180°) directly for uncertain loading. However, greater reductions of up to 20% are possible through alignment of laminate balancing axes with principal loading axes. As such, a non-standard angle design strategy is only shown to be warranted if the demonstrated non-uniqueness of optimum designs can be exploited to improve other performance drivers.