The emergence of double-double in the form of [± Φ / ± Ψ] to replace traditional quad in the form of [ 0, ±45, 90] is based on a number of innovative steps in the modelling of composite laminates.
What is double-double ?
It is a laminate in the general form of [± Φ / ± Ψ]n
Φ and Ψ are laminate orientations from 0° to 90° and cover in a continuous way the whole possible spectrum of stiffness and strength.
The sub-laminate is very simple and always the same throughout the whole structure. Manufacturing is made so simple ! The variation from point to point will be only on the thickness that is the repeating n. This tapering solution is similar to what is done on metal parts. Homogenization is made possible with only 4- instead of normally 20-ply quad laminate building blocks. Homogenized Double-double laminates are naturally symmetric, and ply drop can be in singles, rather than symmetric pairs for quad.
The stacking sequence of Φ and Ψ has no or very little effect of the properties where for QUADS the number of permutations is so high by thousands that optimization is impossible.
One axis lay-up manufacturing
If DD is made from ply angle NCF (such as C ply from CHOMARAT) then the lay-up is just along 1 axis and can be up to 9 times faster than conventional QUAD lay-up. Ply drops can be located on the exterior surfaces. In the interior of laminates, it is with resin-pockets, fiber breaks, and ply movement that causes wrinkles commonly encountered with quad laminates. Thus faster, less error prone layup, and defects free interior make DD laminates lower cost and higher quality.
One DD can cover the entire domain of a component with taper strength and/or buckling based taper. There will be no blending issue common with quad laminate. Hard point and repair can use the same in-family DD so the patch will not cause discontinuity stresses.
Manufacturing of Double Double laminates
DD laminates can be lay-up like any composite material by hand lay-up or by Automatic Tape Laying Machine. A very effective way is to use pre-manufactured angle-ply NCF such as Chomarat C-ply. Then producing DD laminate becomes extremely faster and more efficient than any classical QUAD laminate. The présentation below explains the various possiblities of manufacturing high speed DD using NCF. Cnnsolidation with resin can be achieved like any other composite by infusion, prepreging, or thermoplastic enduction…etc.
A new standard for composite laminates
It is the difference between day and night. DD in time will be the standard and composites laminates and structures will be more competitive. It is really like an orthotropic aluminum. As easy to design and manufacture as aluminum except it weight less than 50 percent. While complete data on DD are forthcoming, there are no indications that they are weak in any aspect that would include damage to damage toleration, BVID, and fatigue. It is a new dawn and engineers should be pleased to be armed with a better approach to make composites more competitive.
For a few years special attention has been focused on Double-double as a revolutionary way of designing composite materials. Under patent of University of Stanford, this very simple concept of stacking sequence has indeed many properties which will fundamentally change the way engineers are designing composite structures.
Find below two PW presentations to download about the new Double double concept to start on the right lane !