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Introduction to scaling issues of damage
and fracture in wind turbine blades
Bent F. Sørensen
Composites and Materials Mechanics Section
Department of Wind Energy
Technical University of Denmark
Risø Campus, 4000 Roskilde
Denmark
Wind Energy Denmark, October 2-3 2017, Herning, Denmark
DTU Wind Energy, Technical University of Denmark
Note the turbine size
relative to the car...
Wind turbines- big structures... composite blades
DTU Wind Turbine Test Center, Østerlid, Denmark
[Be
nt F.
Sø
ren
se
n]
Blades are designed against deflection and fatigue
Composites are damage tolerant materials
DTU Wind Energy, Technical University of Denmark
Main blade structures- manufacturing of wind turbine rotor blades
Main laminate
Shear webs
DTU Wind Energy, Technical University of Denmark
Joining of blade structures- assemblage and joining
Bondlines
(webs)
Adhesive bond
(leading edge)
Adhesive bond
(trailing edge)
Blade design- common blade designs
Box type
Web type
Failure modes- failure of a wind turbine rotor
blade tested to failure
25 m wind turbine blade
(Vestas V52)
[Risø-R-1390(EN), 2004, "Improved design of
large wind turbine blade of fibre composites
based on studies of scale effects (Phase 1) -
Summary Report"]
Failure modes- a wind turbine blade
Progressive failure:
- multiple damage types
- most are weak interfaces
[Risø-R-1390(EN), 2004]
DTU Wind Energy, Technical University of Denmark
Case 1: Cracks in gel-coat
Channelling cracking in elastic layer:
[Beuth, J. L., Int. J. Solid Structures, 1992; 29, 1657–75]
1
1
2
),(E
hDDfch
I
G
DTU Wind Energy, Technical University of Denmark
Case 1: Cracks in gel-coat
Channelling cracking in elastic layer:
[Beuth, J. L., Int. J. Solid Structures, 1992; 29, 1657–75]
1
1
2
),(E
hDDfch
I
G
Model application: Find maximum
gel-coat thickness, h1 for c = 0.3%
GIc=100 J/m2
E1=4 GPa, E2= 40 GPa D = -0.80
f(D,D) 1.5
h1= 0.00185 m = 1.9 mm
2
2
2
2211
11
)2(2 E
h
hEhE
hEJext
Thick laminate
(root section)
Thin laminate
(tip section)
delamination
(crack parallel to fibres)
Case 2: Delamination
from a ply-drop
Siemens Wind Power A/S
2
2
2
2211
11
)2(2 E
h
hEhE
hEJext
Thick laminate
(root section)
Thin laminate
(tip section)
delamination
(crack parallel to fibres)
Case 2: Delamination
from a ply-drop
Siemens Wind Power A/S
Model application: Find maximum ply-
thickness, h1 for c = 0.3%
Data: [Sørensen and Jacobsen, 2009]
J0(=45)= 300 J/m2
E1= 40 GPa = 120 MPa
Say: h2 = 50 mm
h1 = 1.7 mm
2
2
2
2211
11
)2(2 E
h
hEhE
hEJext
Thick laminate
(root section)
Thin laminate
(tip section)
delamination
(crack parallel to fibres)
Case 2: Delamination
from a ply-drop
Siemens Wind Power A/S
Model application: Find maximum ply-
thickness, h1 for c = 0.3%
Data: [Sørensen and Jacobsen, 2009]
J0(=45)= 300 J/m2
E1= 40 GPa = 120 MPa
Say: h2 = 50 mm
h1 = 1.7 mm
Accounting for fibre bridging:
Data: [Sørensen and Jacobsen, 2009]
Jss 2000 J/m2
h1 20 mm
DTU Wind Energy, Technical University of Denmark
Case 3: Cracks in bondlines
Generic bondlines:
Untreated adhesive/glass fibre laminate interface
Case 3. Cracks in bondlines– surface treatments
0.000 0.001 0.002 0.003 0.004 0.0050
50
100
150
200
250
Cracking propagation
No crack growth
Frac
ture
Res
ista
nce,
JR (J
/m2 )
End-Opening, * (m)
BMA05-01
BMA05-02
BMA05-03
BMA05-04
BMA05-05
BMA05-06
BMA05_all.opj nom
= 0o
Onset of cracking
[Kusano, Sørensen, Andersen, Toftegaard, Leipold, Salewski, Sun, Zhu, Li & Alden, 2013, "Water-cooled non-thermal gliding
arc for adhesion improvement of glass-fibre-reinforced polyester", Journal of Physics D: Applied Physics, Vol. 46, 135203]
Gliding arc set-up
Case 3. Cracks in bondlines– plasma treatment of surface to be bonded
[Kusano, Sørensen, Andersen, Toftegaard, Leipold, Salewski, Sun, Zhu, Li & Alden, 2013, "Water-cooled non-thermal gliding
arc for adhesion improvement of glass-fibre-reinforced polyester", Journal of Physics D: Applied Physics, Vol. 46, 135203]
Gliding arc set-up
Case 3. Cracks in bondlines– plasma treatment of surface to be bonded
[Kusano, Sørensen, Andersen, Toftegaard, Leipold, Salewski, Sun, Zhu, Li & Alden, 2013, "Water-cooled non-thermal gliding
arc for adhesion improvement of glass-fibre-reinforced polyester", Journal of Physics D: Applied Physics, Vol. 46, 135203]
Resulting fracture mechancis properties:
A significant increasing fracture resistance due to crack
bridging in laminate
0.000 0.001 0.002 0.003 0.004 0.0050
100
200
300
400
500
Fra
ctur
e R
esis
tanc
e, J R
(J/
m2 )
End-Opening, * (m)
BMA02-01 BMA02-02 BMA02-03 BMA02-04 BMA02-05 BMA02-06
BMA02_all.opj nom
= 0o
DTU Wind Energy, Technical University of Denmark
Scaling issues...- consequences of manufacturing of large blades
Future design rules should incorporate design rules for
various damage modes and account for scaling issues
Materials research can provide improvements in material
properties (more damage tolerant materials)
Thanks for your attention!
Supported by the Danish Centre for Composite Structures and Materials for
Wind Turbines (DCCSM), grant no. 09-067212, the Danish Strategic
Research Council
Any questions?
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