Tapered hygo-thermally curvature-stable laminates with non-standard ply orientations

Stacking sequence configurations for hygro-thermally curvature-stable (HTCS) laminates have recently been identified in nine unique classes of coupled laminate with standard ply angle orientations +45, −45, 0 and 90°. All arise from the judicious re-alignment of the principal material axis of laminate classes with Bending-Twisting and/or Bending-Extension and Twisting-Shearing coupling; where off-axis material alignment of these parent classes gives rise to distinctly different mechanical coupling behaviour. However, for standard ply angle orientations, HTCS solutions were found in only 8-, 12-, 16- and 20-ply laminates. This article considers non-standard ply angle orientations +60, −60, 0 and 90°, which lead to solutions in all ply number groupings for 10 plies and above, thus offering a possibility for ply terminations and hence tapered HTCS laminate designs

Extension-twist coupled laminates for aero-elastic compliant blade design

A definite list of laminate configurations with extension-twisting (and shearing-bending) coupling is derived for up to 21 plies of identical thickness. The list comprises individual stacking sequences, containing standard angle-ply and cross-ply sub-sequences; combinations which are contrary to the previously assumed form for this class of laminate. The list also contains dimensionless parameters from which the extensional, coupling and bending stiffness terms are readily calculated for any fiber/matrix system. Lamination parameters are shown graphically to illustrate the extent of the design space with up to 21 plies. A special sub-group from this class of coupled laminate is identified that can be manufactured flat under a standard elevated temperature curing process; this sub-group possesses hygro-thermally curvature-stable behavior. Finally, bounds on the compression buckling strength are assessed using a closed form solution for all the laminate groups presented

Natural frequency prediction for laminated rectangular plates with extension-bending or extension-twisting and shearing-bending coupling

This article presents closed form natural frequency solutions for two classes of mechanically coupled laminate with: extension-bending or; extension-twisting and shearingbending. Details on the derivation of these two laminate classes are given; all of which contain combinations of standard ply angles, e.g. +45, -45, 0 and 90°. Upper and lower bounds on the non-dimensional natural frequencies are shown graphically for each class of laminate over a range of aspect ratios. Finally, differences are highlighted between these bounds and others obtained by the simplifying assumption that the two laminate classes contain only cross plies or angle plies, respectively

The Flexible Wing Project: Advanced Tailoring Strategies for Laminated Composite Materials Final Report

Manufacturers are beginning to consider the possibilities of moving away from traditional composite material designs but need further evidence that aero-elastically tailored composite materials can: produce weight savings; introduce aerodynamic efficiency and reduce manufacturing time without incurring cost penalties. This research has developed advanced composite tailoring strategies using novel fibre reinforced architectures, with mechanical coupling properties that can be either maintained or tailored through a novel ply termination scheme to change the laminate thickness. Most importantly however, all designs possess immunity to thermal warping distortions; hence they can be manufactured to the desired shape using a high temperature curing system. The research results have been exploited by a leading Brazilian airframe manufacturer for preliminary design of a new aero-elastically tailored wing

On bending-twisting coupled laminates

The definitive list of stacking sequences is presented for Bending-Twisting coupled (ASB0DF) laminates, with up to 21 plies. This class of laminate arises from the ubiquitous balanced and symmetric design rule, but symmetry is shown to be a sufficient rather than a necessary constraint. Each stacking sequence configuration is derived in symbolic form together with dimensionless parameters from which the extensional and bending stiffness terms are readily calculated for any fibre/matrix system and angle-ply orientation. Expressions for ply orientation dependent lamination parameters are also given, together with graphical representations, which demonstrate the extent of the design space. Pseudo Quasi-Homogeneous (ASB0DF) laminates are introduced as an important laminate sub-set, since such laminates have concomitant orthotropic properties, i.e. matching orthotropic or isotropic stiffnesses in extension and bending, from which the isolated effects of Bending-Twisting coupling can be studied. These coupling effects are quantified for compression buckling of Angle-ply and Quasi-Isotropic laminated plates with simply supported and clamped edges

On extension-shearing coupled laminates

The definitive list of Extension-Shearing coupled composite laminates with up to 21 plies is derived. The listings comprise of individual stacking sequences of entirely non-symmetric laminates, are characterized in terms of angle- and cross-ply sub-sequence relationships as well as the blend-ratio of unbalanced angle-plies. Dimensionless parameters, including lamination parameters, are provided, from which the extensional and bending stiffness terms are readily calculated. Because this new class of coupled non-symmetric laminate possesses in-plane coupling behaviour only it can also be manufactured flat under a standard elevated temperature curing process. Such laminates can be configured to produce bending-twisting coupling in wing-box type structures, which can be exploited to great effect in the design for passive load alleviation in wind-turbine blades, or for aero-elastic compliance in fixed wing aircraft or helicopter rotor-blades. It should be recognised that similar behaviour can also be achieved using less sophisticated designs, such as applying off-axis material alignment to otherwise balanced and symmetric laminates or by using un-balanced and symmetric designs, but additional forms of coupling behaviour arise in these cases, leading to detrimental effects on both stiffness and strength, which are demonstrated though comparisons of the structural response of competing laminate designs

Experimental validation of the mechanical coupling response for hygro-thermally curvature-stable laminated composite materials

Stacking sequence configurations for hygro-thermally curvature-stable (HTCS) laminates have recently been identified in 9 classes of coupled laminate with standard ply angle orientations +45, "1245, 0 and 9

Mechanically coupled laminates with balanced plain weave

Definitive listings of laminate stacking sequences are derived for balanced plain weave laminated materials, assuming each layer is composed of the same material with constant thickness throughout and that standard ply angle orientations 0, 90, and ±45° are adopted; consistent with industrial design practice. A single layer of balanced plain weave material is shown to be immune to thermal distortion following a standard high temperature manufacturing process, which implies that all laminates constructed of this material possess what is commonly referred to as the hygro-thermally curvature-stable or warp-free condition, irrespective of the individual ply orientations used or the laminate stacking sequence definition. A single uncoupled parent laminate class is shown to contain sub-groups with extensionally isotropic and fully isotropic properties that are invariant with off-axis orientation of the principal material axes with respect to the system or structural axes. By contrast a single mechanically coupled parent laminate class is shown to give rise to seven unique forms of coupled laminate through judicious off-axis orientation. Invariant off-axis properties are also identified in coupled laminate designs. Finally, example calculations, abridged stacking sequence listings and design data are presented

Experimental validation of design concepts for laminated composite materials with thermal and/or mechanical coupling response

New and important experimental observations are presented, revealing that cylindrical room-temperature shapes are present in a broader range of coupled laminate classes than previously observed, and that contrary to current understanding, at least one class of coupled laminate developed into a saddle shape at a relatively high side-length-to-thickness ratio. Bistable and Pseudo-Bistable Snap-through behaviour are also observed in a large proportion of the 24 classes of coupled laminate. Pseudo-Bistable behaviour implies that a snap-though may be invoked, but that a force must be continuously applied to prevent snap-back; this behaviour has not been characterised previously in the literature. Hygro-thermally curvature-stable laminates, identified in 13 of the 24 classes of coupled laminate with standard ply angle orientations, have also been validated experimentally. Such laminates are immune to thermal warping distortions, which has previously made the exploitation of these unique mechanical coupling properties impractical

On Extension–Shearing coupled laminates

The definitive list of Extension-Shearing coupled composite laminates with up to 21 plies is derived. The listings comprise of individual stacking sequences of entirely non-symmetric laminates, are characterized in terms of angle- and cross-ply sub-sequence relationships as well as the blend-ratio of unbalanced angle-plies. Dimensionless parameters, including lamination parameters, are provided, from which the extensional and bending stiffness terms are readily calculated. Because this new class of coupled non-symmetric laminate possesses in-plane coupling behaviour only it can also be manufactured flat under a standard elevated temperature curing process. Such laminates can be configured to produce bending-twisting coupling in wing-box type structures, which can be exploited to great effect in the design for passive load alleviation in wind-turbine blades, or for aero-elastic compliance in fixed wing aircraft or helicopter rotor-blades. It should be recognised that similar behaviour can also be achieved using less sophisticated designs, such as applying off-axis material alignment to otherwise balanced and symmetric laminates or by using un-balanced and symmetric designs, but additional forms of coupling behaviour arise in these cases, leading to detrimental effects on both stiffness and strength, which are demonstrated though comparisons of the structural response of competing laminate designs