SAMPE Journal - May/June 2021 - 9

The two blade halves were then manufactured
separately within each mould. After 30 layers
had been placed, the two halves were placed
under vacuum and B-staged to ensure the plies
conformed to the shape of the mould. After the
layup was completed, each torsion box half was
B-staged again. Finally, both torsion box halves
were placed back into the moulds and fully cured
together in a process that ensured good bond
strength and surface finish.
TEST SETUP
Test Objectives
The torsion box demonstrator testing consisted
in subjecting the blade to the 4 load cases, which
were used as a basis for the design structural
optimisation. The main aims of this test were to:
	 -	Ensure that the blade did not fail under the 	
		 design loads
	 -	Verify that no damage detrimental to the blade 	
		 structure occurred during testing
	 -	Measure the strains at 4 quadrants around the 	
		 blade and at 5 different positions along 		
		 the length.
	 -	Measure the displacement at the loading point 	
		 as well as the middle of the blade.
	 -	Measure the natural frequency and blade 		
		damping.
Reaction Frame Design
C-channel steel beams were used for the
construction of the main reaction frame. As shown
in Figure 2, the beams were arranged to support
the torsion box root connection and transfer the
reaction forces and bending moments through a
concrete strong floor (approx. 9 m x 6 m). Similarly,
a frame was used to apply the test load to the
torsion box loading connector, with the reaction
forces also transferred to the strong floor.
Loading the Demonstrator
The 4 load cases to be applied to the blade are
summarized in Table 1. The orientation of the loads
is shown in Figure 3. The load cases were carried
out in increasing load order (4,3,2,1). At the end of
the test, the 4th load case will be repeated to verify
the structural integrity has not changed (i.e. change
in the load-strain response).
All load cases were applied at a point 5.5
m from the root. For each load case, a unique
loading connection was designed and machined
from medium-density fibreboard (MDF), then
fixed in place by rigid steel beams as shown
in Figure 2. Neoprene rubber inlays (1.5 mm

w w w. s a m p e . o r g

May June 2021 Journal.indd 9

Figure 2. Overview of reaction
frame design.

Torsion Box
LC

Angle [deg]

RBM [kNm]

Force at 5.5m [kN]

1

-20

111.29

20.23

2

-30

107.7

19.58

3

-165

70.04

12.73

4

55

44.26

8.05

Table 1. Combined loading vectors for each load
case (LC).

Figure 3. Load case vectors with respect to the
blade orientation. The blade is pointing out of the
Plane.

thick) were used to improve friction and reduce
contact stresses between the composite and MDF.
Loading was performed using a double- acting
hydraulic actuator. The actuator was hinged to
accommodate the out-of-plane deflection of the
blade during testing. A 25 kN S-beam load cell was
placed between the hydraulic actuator and the
loading connection to record the applied load. The
hydraulic actuator was attached to the reaction
frame via a slot, which allowed it to slide sideways.
This allowed loads to be applied up to an angle of
10° compared to the vertical direction.

M AY/J U N E 2 0 2 1

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SAMPE Journal - May/June 2021

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