Blade materials, testing methods and structural design - Wind Power Generation and Wind Turbine Design - page 419

L

Wing scale L ~ 10-60 m

Face (laminate) Core

H ~ 50-100 mm

Sandwich scale

H

Laminate scale h ~ 1-50 mm

h

t t ~ 100-500 m μ

Lamina scale

Matrix

d

Microscale d ~ 5-150 m μ

Fiber

R a

R 10-50 nm

a ~

Roughness scale

~ 0,5-10 nm

Molecular scale

Figure 1: Modern blade design requires an understanding of how materials and
structures behave at various length scales, ranging from the molecular
scale (e.g. interfacial adhesion in adhesive joints) to the blade scale (e.g.
the dynamic coupling of the blade and tower). Changes made at any
length scale will affect the blade reliability. For instance, an increase in
the bond strength of the fi ber/matrix interface will increase the materi-
als strength at the lamina scale, potentially leading to an increase in the
overall blade strength.

in bending fl apwise. The second load source is the gravity varying edgewise from
tension/compression in leading edge and compression/tension in trailing edge. This
is the main reason for the edgewise fatigue bending of the blade. Finally, the blades
are exposed to centrifugal forces during the rotation. However, these longitudinal
loads are relatively low and often not taken into account in the design. Furthermore,
the design loads are divided into static loads and cyclic loads. International design
recommendations (e.g. IEC 61400-1 [1]) specify both types of loads. Moreover, the
blades will be subjected to a wide range of environmental conditions.

2.2 Blade construction

Modern wind turbine blades are structurally advanced constructions utilizing
composite laminates, sandwich core materials, gelcoat fi lms and adhesive joints.