Beyond Double-Double theory: n-Directional stacking sequence optimisation in composite laminates

This paper presents a novel stacking sequence design framework for composite laminates, extending the recently established Double-Double (DD) laminate theory developed by Stephen Tsai. By introducing and evaluating n-Double (n-D) layouts, ranging from single-angle (D) sequences to multi-directional designs such as DD, DDD, and DDDD; this study expands the design space for laminated composite structures, enabling improved trade-offs between buckling resistance and failure strength. A genetic algorithm (GA) is used to optimise the stacking sequences of 48- and 64-layer graphite/epoxy laminates under biaxial and uniaxial compressive loading across a range of geometric aspect ratios. Results show that while GA-based free-angle designs yield the highest buckling loads, structured DDDD configurations achieve similar or superior failure performance and maintain a high level of robustness across geometric variations. The DDDD designs also approximate GA-level buckling performance, with significantly improved regularity and manufacturability. These findings highlight the benefit of generalising Tsai’s DD theory towards n-D layouts, providing a systematic, practical, and high-performing approach to laminate optimisation.