Blade materials, testing methods and structural design - Wind Power Generation and Wind Turbine Design - page 455

Figure 26: Comparison of experimental and FE predicted failure loads for
specimens containing a delamination in the C position and one of
the positions from A to G [ 75 ].
strength for two delaminations occurred when the delaminations split the laminate
into sub-laminates of similar thickness.
7.3.4 Modeling of a full main spar to determine the webs infl uence
on ultimate strength
The deformation and strength of a box girder used as a spar in a 34 m wind turbine
blade was examined by Branner et al . [76]. The study also examined the effect
of sandwich core properties on ultimate strength of the box girder. In Fig. 27, the
transverse (vertical or 90°) strains for both faces of the sandwich web are com-
pared with both linear and non-linear FE analysis. The strains presented in Fig. 27
are measured on the upper part of the web towards the leading edge at the position
where the failure was observed (also indicated in the fi gure). The longitudinal
normal strains (in the z -direction) caused by bending of the box girder lead to
associated strains in the transverse direction (the y -direction) due to the Poisson's