Double–double (DD) laminates, or DD laminates, are a class of composite laminates composed of repeated four-ply sub-laminates arranged in the form [±Φ/±Ψ], where the ply orientations are defined by two continuous angle parameters, Φ and Ψ. Unlike conventional composite laminates that employ a limited set of discrete ply angles, DD laminates use continuous variation of ply orientation.123 The concept is employed in structural engineering applications involving composite materials.
Mechanical behavior
Studies have reported that, when DD laminates are manufactured using thin plies and a sufficiently large number of repeated sub-laminates, the laminate response can be approximated as homogenized.456 Under these conditions, the overall mechanical behavior has been described as similar to that of a symmetric laminate, even though the stacking sequence is not explicitly symmetric.456 A characteristic feature of this homogenization is the reduction of bending–stretching coupling effects, such that the corresponding terms in the ([B]) stiffness matrix become negligible.789
Applications and manufacturing considerations
DD laminates have been discussed in the literature in the context of lightweight structural applications, particularly where changes in laminate thickness are required.10 Under homogenized conditions, tapering has been reported to be implemented on a ply-by-ply basis using single-ply drops, without the requirement to maintain mid-plane symmetry.4 In addition, the use of continuous ply-angle parameters has been presented as allowing a broader range of stiffness tailoring compared with conventional quadriaxial laminates, which typically rely on standard ply orientations of 0°, ±45°, and 90°.1 DD laminates are typically described as being manufactured by stacking of repeated four-ply sub-laminates, following the prescribed angle parameters.1
References
References
- Tsai SW. Double–Double: New Family of Composite Laminates. AIAA Journal 2021; 59 (11): 4293-4305. DOI: 10.2514/1.J060659.
- Zhao K, Kennedy D, Miravete A, Tsai SW, Featherston CA, Liu X. Defining the Design Space for Double-Double Laminates by Considering Homogenization Criterion. AIAA Journal 2023; 61(7): 3190-3203. DOI: 10.2514/1.J062639.
- Ju R, Zhao K, Featherston CA, Liu X. Buckling Performance Evaluation of Double-Double Laminates with Cutouts Using Artificial Neural Network and Genetic Algorithm. Materials 2024; 17(19): 4677. DOI: 10.3390/ma17194677.
- Kappel E. Unique manufacturing opportunity. In: Double-Double: simplifying the design and manufacture of composite laminates. Stanford University Press, 2023.
- Kappel E. Double–double laminates for aerospace applications — finding best laminates for given load sets. Composer Part C Open Access 2022; 8: 100244. DOI: 10.1016/j.jcomc.2022.100244.
- Vermes B, Tsai SW, Massard T, Springer GS, Czigany T. Design of laminates by a novel "double–double" layup. Thin-Walled Struct 2021; 165: 107954. DOI: 10.1016/j.tws.2021.107954.
- Garofano A, Sellitto A, Di Caprio F, Riccio A. On the use of double-double design philosophy in the redesign of composite fuselage barrel frame components. Polymer Composites 2024; 45(5): 4250-4265. DOI: 10.1002/pc.28056.
- Hawkins A, Millen SLJ, Aravand A. Homogenisation of Double-Double (DD) laminates: warpage mitigation and new stacking sequence approaches. Journal of Composite Materials 2025. DOI: 10.1177/00219983251362358.
- Kappel E. On stacking-sequence independent bending properties of Double-Double laminates—A short communication. Composites and Advanced Materials 2024;33. DOI: 10.1177/26349833241237244.
- Shrivastava S, Sharma N, Tsai SW, Mohite P.M. D and DD-drop layup optimization of aircraft wing panels under multi-load case design environment. Composite Structures 2020, 248: 112518. DOI: 10.1016/j.compstruct.2020.112518.