HyBlade

The layup sequences and thickness of each part (e.g. shear web, spar cap, etc) need to be designed once the loads are determined from the HyWind. HyBlade is a tool for structural designers. Calculating the deflection and the interal load distribution of the blade with an arbitrary layups of glass, carbon and bybrid NCF.

The bi-axial BX [±θ]s and tri-axial TX [θ2/±θ]s NCF laminates are homogenized for the structural analysis. Figure 1 shows the variation of the stiffness E₁, E₂ and G₆ of the TX NCF along with the ply angles. These variations show that the fiber angle can be optimized depending on the loading conditions, especially in the composite structures like wind turbine blades subjected to both bending and torsion.

Figure 1. The variation of stiffness of the TX NCF with the fiber angle.

The failure envelopes of the TX NCF laminate are obtained for q=45 and 25 degrees as in Figure 2. Obviously, the longitudinal tensile strength of the TX with 25 deg is higher than the TX with 45 deg while shear strength behaves on the contrary. Similar behavior is observed in the failure strain space. Note in the case of the shear failure strain that the TX with 25 deg has higher failure strain than 45 deg. It can be concluded that the TX with 25 is superior to the TX with 45. Again, considering bending and torsional behavior of the blade, the ply angle should be carefully chosen. Figure 9 was generated using Tsai-Wu failure criterion, and will be compared with the result by the PUCK theory.

Figure 2. The effective failure envelopes of the TX NCF laminates in longitudinal and shear stress (or strain) domain. The unit of the stress is MPa.

It was clearly shown in Figures 9 that the strengths of the TX laminate depend on the fiber angle. Now we examine effects of the ratio of shear/normal stresses on the overall strengths and deformations along the fiber angles. The 25 degree always decreases the failure index (stress), and also decreases the longitudinal deformation (e_1). Interestingly, the shear deformation gets larger, resulting in favorable higher attacking angle during rotation of blades.

It is well known in the design of wind turbine blades that higher attacking angle is desired to reduce aerodynamic loads, thus reducing the fatigue loads. The bend-twisting coupling of bidirectional NCF laminates can be very effective and economic among several passive and active control methods. Figure 3 shows the effects of the ply angle on the bend/twist coupling. The longitudinal stiffness needs to be compromised to accommodate the coupling effects. Designers should select design tools which can handle this effect.

Figure 3. A bidirectional NCF generating twist/bend coupling calculated from 3D-Beam.