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PARAMETRIC STUDY OF SANDWICH PANEL BUCKLING IN COMPOSITE WIND TURBINE BLADES
Shicong Miao, Steven Donaldson, and Elias Toubia
Figure 6. Critical buckling strain versus core thickness for all five facing layers and all four core materials. Flat-section. 1m width sandwich panel.
Note that the strain is dependent on N cr /2t (assuming half of the load is
carried by top and bottom skin, t is the thickness of each the skin, N cr is
N/m per linear width b). For a low modulus core, core shear instability
(shear crimping) governs the buckling load. The shear modulus is not
stiff enough to engage the top and bottom skin. So if we look at the
formula: cr =G*h/(2t) ( core shear instability formula for isotropic
core), and = (str ain, )*E, and = (Ncr/2(b t))= (strain, )*E, then
N cr /2t decreases as strain decreases. Since N cr increases as the skin
thickness increases, N cr is divided by the number of plies, this number
decreases for the low modulus core. As for the stiffer core, the shear
modulus is high enough that the core is coupling and engaging the skins
to effectively carry the buckling load, therefore global buckling occurs.
The more the number of plies is increased, the more the structure is
straining, until an asymptotic line is reached that the buckling cannot go
beyond, until the shear modulus is increased.Figure 7 separates the
results by core type (M1-M4).
Figure 7. Critical buckling strain versus core thickness for core material M1, M2, M3, M4. Flat-section. 1m width sandwich panel
0.8
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20 25 30 35 40 45
0.9
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20 25 30 35 40 45
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