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$: Introduction to scaling issues of damage and fracture in ... · PDF fileIntroduction to scaling issues of damage and fracture in wind turbine blades ... Case 3. Cracks in bondlines$
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


Main blade structures- manufacturing of wind turbine rotor blades

Main laminate

Shear webs


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]


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


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



from a ply-drop


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



from a ply-drop


Model application: Find maximum ply-

thickness, h1 for c = 0.3%


J0(=45)= 300 J/m2

E1= 40 GPa = 120 MPa

Say: h2 = 50 mm

h1 = 1.7 mm

Accounting for fibre bridging:


Jss 2000 J/m2

h1 20 mm


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



Gliding arc set-up

Case 3. Cracks in bondlines– plasma treatment of surface to be bonded



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


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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