Page 416 - Wind Energy Handbook

390 COMPONENT DESIGN

Figure 7.7 Blade Production. View of Veneer Lay-up in Mould to Make One Blade Skin.
The Blade is Completed by Glueing Face and Camber Skins Together. (Reproduced by
permission of NEG-Micon)
Table 7.2 Properties of Unjointed Wood/Epoxy Laminates

Species Specific Mean tensile Mean Young’s Shear
gravity strength compression Modulus strength
along the strength along the (MPa)
grain along the grain
(MPa) grain (MPa) (GPa)
Khaya ivorensis 0.55 82 50 10 9.5
Poplar 0.45 63 52 10 9
Baltic pine 0.55 105 40 16
Birch 0.67 117 81 15 16
Beech 0.72 103 69 10 16
Douglas fir 0.58 100 61 15 12

reduction in tensile strength to 50 MPa for butt jointed Khaya. Scarf jointed Khaya
specimens, with a 1:6 length to thickness ratio, performed much better, achieving a
tensile strength of 75 MPa. In all cases the joints in the different veneers making up
the laminate were staggered.
An important consideration for design is the variability of strength properties,
particularly as wood is an inherently variable material. Strength tends to increase
with density, and density varies according to the growing conditions of the tree and