Blade materials, testing methods and structural design - Wind Power Generation and Wind Turbine Design - page 456

90 deg Strain Gauges on shear web towards leading edge

900

FEM NL-Outer surface
FEM NL-Inner surface
Exp.-Outer surface
Exp.-Inner surface
FEM Lin.-Outer surface
FEM Lin.-Inner surface

800

700

600

500

400

300

200

100

0

0% 20% 40% 60% 80% 100%

% of ultimate load of the blade including skin

Figure 27: Comparison of FE results and measurements for back to back strain
gauges on upper web part. The positions for the strain gauges are indi-
cated in the sketch (top) [76].

effect. The transverse strains are positive (tension) in the shear webs of the upper
half part of the box girder where the bending cause compression and the transverse
strains are negative (compression) in the lower half part.
Initially, the transverse strain increased linearly with load, see Fig. 27. However,
as the load increases, the strains become non-linear with respect to applied load
and it is noted that the graphs defl ect towards compressive strains.