High Specification Offshore Blades Work Package: 1D: Blade Manufacturing

Blades are regarded as the only component unique to wind turbine blades. They represent only 10 – 15% of the total system cost so the perception is that a reduction in the cost of energy through blade cost improvements is constrained. However, the use of advanced manufacturing technologies is expected to directly reduce cost savings. The aim of this report is therefore to identify manufacturing technologies offering potential for facilitate the construction of very large offshore blades and their potential for (patentable) intellectual property exploitation. This report should be read in conjunction with Package 1C

High Specification Offshore Blades. Work Package: 1C – Blade Materials.

Blades are regarded as the only component unique to wind turbine blades. They represent only 10 – 15% of the total system cost so the perception is that a reduction in the cost of energy through blade cost improvements is constrained. However, the use of novel materials technologies is predicted to reduce design loading by 10 – 20%, which may indirectly lead to substantial cost savings. The aim of this report is therefore to identify materials technologies offering potential for improved blade performance and their potential for (patentable) intellectual property exploitation

A Two-Ply Termination Strategy For Mechanically Coupled Tapered Laminates

Tapered designs are currently certified only for balanced and symmetric laminate construction, despite the severe design constraint that 1 angle-ply termination requires a further 3 angle-ply terminations: two terminations to maintain balanced construction and a further two terminations to maintain symmetry. This constraint is often violated in practice, leading to localised thermal warping; the effects of which have yet to be quantified.<p></p> An obvious, but somewhat controversial strategy for ‘thin laminate’ designs, with traditional uni-directional (UD) material, is to adopt unbalanced and/or nonsymmetric stacking sequence configurations to fully exploit the available design space, particularly where tapered designs are a requirement. This extended design space has previously been shown to contain warp-free laminates with either fully uncoupled mechanical properties or with Extension-Shearing and/or BendingTwisting coupling behaviour.<p></p> Extension-Shearing coupling, which arises in unbalanced construction, can be exploited to produce bending-twisting deformation in aircraft wing-box structures when top and bottom skins have identical bias fibre alignment, but equally, this can be eliminated with opposing bias fibre alignment. Bending-Twisting coupling, which is generally present in symmetric laminate construction, results in weaker compression buckling strength compared to the equivalent fully uncoupled laminate (with matching stiffness properties), but with potentially stronger shear buckling strength.<p></p> Recent studies on Extension-Shearing and Bending-Twisting coupled laminates have provided useful insight into the available design space for tapered laminates with single angle-ply or cross-ply terminations. Similar tailoring strategies are now applied to unconventional tapered laminate designs (i.e. those free from the ubiquitous symmetric and balanced, or un-balanced, design constraint) with two-ply terminations, to investigate the extent to which angleply layers can be terminated without introducing Extension-Shearing coupling, or the extent to which angle- and cross-ply combinations can be terminated to tailor or maintain Extension-Shearing throughout the tapered laminate. Consideration is also given to the potential effectiveness of introducing tailored mechanical coupling through ply terminations, e.g. to induce bending-twisting coupling in a wing-tip or winglet, using Extension-Shearing coupling at the laminate level, whilst maintaining fully uncoupled laminate behaviour in the tapered skins elsewhere in the wing-box

Influence of bending–twisting coupling on compression and shear buckling strength [Keynote]

No abstract available

On Mechanically Coupled Tapered Laminates with Balanced Plain Weave and Non-Crimp Fabrics

This article presents definitive stacking sequence listings for tapered, warp-free balanced plain weave and non-crimp fabric (NCF) laminate designs with and without Extension-Shearing and/or Bending-Twisting coupling behaviour.<p></p> With few exceptions, tapered designs for uni-directional (UD) material are currently certified only for balanced and symmetric laminate construction, despite the severe design constraint that 1 angle-ply termination therefore requires a further 3 angle-ply terminations. By contrast, an extensive design space has recently been discovered for tapered UD laminates with single ply terminations, including single angle-ply terminations, representing unconventional laminate designs with unbalanced and/or non-symmetric stacking sequences. Such designs give rise to Bending-Twisting and/or Extension-Shearing coupling:<p></p> Extension-Shearing coupling, which arises in unbalanced construction, can be exploited to produce bending-twisting deformation in aircraft wing-box structures when top and bottom skins have identical bias fibre alignment, but equally, this can be eliminated with opposing bias fibre alignment; Bending-Twisting coupling, which is generally present in symmetric laminate construction, results in weaker compression buckling strength compared to the equivalent fully uncoupled laminate (with matching stiffness properties), but with potentially stronger shear buckling strength.<p></p> Single ply terminations applied to NCF or balanced plain weave materials are equivalent to two adjacent ply terminations in traditional UD materials, and therefore introduce a constraint that may reduce the design space substantially, particularly in ‘thin laminate’ designs. However, this can be overcome by adopting ‘thin-ply’ or ‘spread-tow’ technology, which will allow an exponential increase in tailoring opportunities by bringing design flexibilities, found only in traditionally thick laminate construction, into the thin laminate domain.<p></p> Thin-ply technology will, for instance, offer the prospect of a repeating 8-ply NCF laminate, with a similar thickness to that of a single ply of traditional UD material. This design also follows the repeating bi-angle philosophy, possessing Extension-Shearing and Bending-Twisting coupling, but now with immunity to thermal warping distortions, which are eliminated in bi-angle laminates only when the number (r) of repeats becomes very large

Bounds on the natural frequencies of laminated rectangular plates with extension-twisting (and shearing-bending) coupling

Anti-symmetric angle-ply laminates are widely believed to uniquely possess Extension-Twisting (together with Shearing-Bending) coupling behaviour. The results in this article serve to dispel this misconception by presenting solutions for both standard laminates, containing combinations of angle plies (+45 and -45) and cross plies (90 and/or 0), and angle-ply laminates, containing only +45 and -45 ply orientations; chosen to reflect current industrial design practice, and also because they serve to produce hygro-thermally curvature-stable properties in some standard laminate configurations, i.e., with immunity to the thermal distortions that generally arise in this class of mechanically coupled laminate as a result of the high temperature curing process. Details of the algorithm used to develop the definitive list of laminate stacking sequences, with up to 21 plies, are given first. Closed form natural frequency solutions for each of these sub-groups are then presented, identifying significant differences in the frequency spectrum bounds across a range of aspect ratios, with respect to the ubiquitous anti-symmetric angle-ply designs

Buckling strength improvements for Fibre Metal Laminates using thin-ply tailoring

The buckling response and load carrying capacity of thin-walled open cross-section profiles made of Fibre Metal Laminates, subjected to static axial compression loading are considered. These include thin-walled Z-shape and channel cross-section profiles adopting a 3/2 FML lay-up design, made of 3 aluminium layers. The objective of the investigation is the comparison of standard thickness Fibre Reinforced Plastic layers versus thin-ply material technology. Whilst thin ply designs differ only by the layer thickness, they offer an exponential increase in stacking sequence design freedoms, allowing detrimental coupling effects to be eliminated. The benefit of different hybrid materials are also considered. The comparisons involve semi-analytical and finite element methods, which are validated against experimental investigations

On extension-shearing bending-twisting coupled laminates

This article presents details of the development of a special class of laminate, possessing Extension-Shearing Bending-Twisting coupling, necessary for optimised passive-adaptive flexible wing-box structures. The possibility of achieving a measurable drag reduction in cruise flight, without the cost or reliability issues associated with active control mechanisms, is of significant interest for achieving increased fuel burn efficiency, and meeting associated emissions targets. The introduction of passive Bending-Twisting coupling at the wing-box level has been previously demonstrated through laminate level tailoring with Extension-Shearing coupling only, but the limited design space and the possibility for ply terminations (to produce tapered thickness) effectively rule out this special class of laminate for practical construction. The study is now broadened to consider laminates with Extension-Shearing and Bending-Twisting coupling, beyond the less well-known un-balanced and symmetric design rule or indeed balanced and symmetric designs with off-axis alignment. Results reveal a vast laminate design space with Extension-Shearing coupling that can be maximised without the unfavourable strength characteristics associated with off-axis alignment. Results also reveal that shear buckling strength can be maximised through Bending-Twisting coupling when load reversal is not a design constraint

Tapered laminate designs for new non-crimp fabric architectures

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 coupling, 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