Blade materials, testing methods and structural design - Wind Power Generation and Wind Turbine Design - page 421

(a)
(b)
Figure 3: Two common design concepts of wind turbine blades manufactured as
two half-shells joined by adhesive bonds: (a) integrating the load-carrying
laminates in the aeroshell, which is supported by shear webs, and (b)
use of a box girder which is glued to the inside of the aeroshells.
2.3 Materials
Materials used for wind turbine blades must be low density and possess high
strength, fatigue resistance and damage tolerance. Large parts of the blades are
made of composite materials, i.e. materials that consist of more constituents, e.g.
long aligned fi bers embedded in a continuous phase called the matrix material.
The shells that defi ne the aerodynamic blade profi le are typically constructed
using polymer matrix composites (PMCs) (e.g. glass fi ber reinforced polyester)
and sandwich structures consisting of PMC face sheets and lightweight closed-cell
polymer foam or end-grain balsa wood cores. The box girder is constructed using
glass fi ber composites or carbon fi ber composites.
Concerning fi bers , the majority of large turbine blades use E-glass laminates for
the aeroshells. Because blade mass is a critical design consideration, more expen-
sive carbon fi ber composites are also being increasingly utilized. In addition to
much lower density (a factor of 2/3 lower than glass fi bers), carbon fi bers offer
several advantages for blade applications, including a much higher elastic modu-
lus, strength and fatigue life. Carbon fi ber laminates and hybrid carbon/glass fi ber
laminates are currently being utilized by some blade manufacturers. For the aeroshell,
carbon fi bers can be used for selective reinforcement but offer great potential for
innovative blade designs. Although carbon fi bers have attractive modulus, density