Tapered laminate designs for new non-crimp fabric architectures

Abstract

Non-Crimp Fabric (NCF) materials are now available in a range of areal weights and layer architectures, including 0/45, 0/-45, 45/-45 and 0/90, which correspond to the standard ply orientations employed in traditional UD material lay-ups.The benefit of NCF material is generally associated with increased deposition rate, but this advantage may be offset by reduced design freedoms when a specific form of mechanical coupling behaviour is required, layer terminations must be introduced and/or thermal warping distortion eliminated.This article investigates the extent to which new NCF architectures can be tailored to achieve warp free tapered laminates with mechanical Extension-Shearing Bending-Twisting couplings, by single axis (longitudinal) deposition of all ply angles; thus avoiding ply discontinuities that may be introduce in large component manufacture.Lamination parameter design spaces are used to demonstrate the extent of the feasible solutions both before and after applying a laminate tapering scheme. 2 IntroductionDesign issues associated with tapered composite laminates have been comprehensively reviewed in a number of articles [1,2]. These reviews reveal an extensive literature, focussing primarily on delamination initiation and propagation in the region of ply terminations, but also reveal that little attention has been given to the extent to which plies may be dropped without introducing thermal warping distortion and associated changes in mechanical coupling characteristics. Indeed, current tapering schemes tend to consider only short ramps or pad-ups, and few [3] consider thermal warping and the associated locked in stresses. By contrast, tapering schemes for continuous wing or fuselage panel construction, in which only single ply terminations may be necessary between adjacent ribs or ring stiffeners, to satisfy strength and/or buckling constraints, are currently restricted to balanced and symmetric laminate designs. Hence, with few exceptions [4], such designs generally require a minimum of 4 ply terminations to avoid introducing thermal warping distortions; their inherent mechanical Bending-Twisting coupling characteristics can also lead to significant reductions in the compression buckling strength [5]. New joint requirements for aero-elastic tailoring and more efficient manufacturing of composite wing or winglet construction requires a more considered tapering scheme, which has resulted in the recent development of bi-angle non-crimp fabrics (NCF) architectures, consisting of two plies of UD material, one at 0° and the other at either a shallow angle,   20°, or the standard 45° angle, stitched together. The repeating biangle [/0]rT NCF concept [6] has the potential to reduce wet lay-up times by half, in comparison to traditional UD tape. In what follows, a layer (of NCF material) contains 2 plies (of UD material). Ply terminations can also be applied to any layer without 3 changing the Extension-Shearing and Bending-Twisting dominant mechanical coupling, necessary for aero-elastic tailoring of wi...

Design of Multi-Coupled Laminates with Extension-Twisting Coupling for Application in Adaptive Structures

“…Subsequently, York successively studied the hygro-thermally warpage stable laminates of standard laminates [6] and other special angle laminates [12], and then designed extension-shearing and bending-twisting coupled laminated plates [13] to maximize the shear buckling strength of the adaptive flexible wing box structure. On this basis, a large number of researches on laminate layup design have been carried out [14,15]. Furthermore, the buckling load and coupling of hygro-thermally stable laminates were simultaneously considered by Li in the process of optimization design, including extension-shearing coupled laminates [16] and extension-twisting coupled laminates [17].…”