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, which are characterised 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.