Homogenisation of Double-Double (DD) laminates: Warpage mitigation and new stacking sequence approaches

Homogenisation of Double-Double (DD) laminates is investigated herein. DD laminates are a new layup design approach composed of repeated sub-laminates or Building Blocks (BB), comprising two sets of bi-angled plies, ± Φ ° and ± Ψ ° . The DD laminate approach simplifies the design of composite structures, potentially reducing manufacturing complexity, and allows for rapid thickness tapering, presenting substantial prospects for reducing structural mass. Sufficient through-thickness homogenisation of the laminate eliminates undesirable out-of-plane distortions, commonly observed in asymmetric composite laminates. DD homogenisation criteria previously proposed in literature are evaluated through laminate manufacture using Carbon Fibre Reinforced Polymer (CFRP) prepreg material. Based on these evaluations, revised homogenisation criteria are proposed, which are found to effectively suppress warpage in DD laminates. Two new DD stacking sequence approaches, termed Symmetry-Enhanced Double-Double (SEDD) laminates, are introduced. These approaches are based on a foundation symmetric DD sub-laminate, [ B B ] s , and involve either the continuous addition of asymmetric BBs or the mirroring of the BB configuration at every alternate repeat. SEDD laminates are shown to have the capability to produce warpage-free panels using a reduced number of sub-laminate repeats, while maintaining the benefits of the traditional DD method.