Elasticity tailoring of a composite D-Spar: Progress report for calendar year 1998

There are many potential benefits to be gained from the aeroelastic behavior of a wind-turbine blade with bend-twist coupling. However, the ability to manufacture blades with sufficient coupling to provide the desired benefits has yet to be established. This report investigates the feasible (or practical) range of the coupling coefficient that can be obtained on a uniform cross-section composite D-spar, which could be the backbone of a wind-turbine-blade. The most critical parameters are identified and studied across a range of possible values. Various features, such as the geometry, skin thickness, ply distribution, ply materials, and ply orientations, are evaluated for their effect on twist-bend coupling of a D-spar. It is found that sufficient coupling can be built into the D-spar shape, but that carbon-fiber composite plies angled between 15 and 30 degrees to the longitudinal axis may be required