Double-double laminates
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. The concept is employed in structural engineering applications involving composite materials.