german wind energy research - stahlbau.uni-hannover.de

© ForWind

Rasmus Eichstädt

Prof. Peter Schaumann

Lyngby, 26.06.2017

Wind Energy Science Conference

WESC 2017

Fatigue of very large high-strength bolting

assemblies in wind turbines

Rasmus Eichstädt -

Fatigue of very large high-strength bolting assemblies in wind turbines

Outline

© DOTI/alpha ventus

High-strength bolts in wind turbines

Experimental fatigue assessment

Test results on HV-bolt sets M36 and M64

Validation of normative S-N curves

Analytical fatigue assessment

Conclusions

Rasmus Eichstädt -








Conclusions

Outline

Rasmus Eichstädt -


M36 M48 M64 M72

Bolted ring-flange connections in wind turbines


Up to 200 high-strength bolt assemblies (System HV) per connection

High loads with large number of load cycles

© SENVION

Rasmus Eichstädt -


Preloading and hot-dip galvanizing

Nominal preload Fp,C* = 0.7 ∙ Rp0.2 ∙ Asp

High mean stress affects the fatigue

strength of bolts

Limited validation of fatigue

characteristics and normative S-N

curves for large bolt diameters

Preloading for limitation of fatigue loadss [N/mm²]

e [%]

Rupture

0.2

Rp,0.2

Rm

A

Rolled notch

N = 300.000

Hot-dip galvanizing for corrosion protection

Lower fatigue strength as uncoated

structural components

Fatigue cracks initiated at shrinkage

cracks in the zinc layer

Source: Simonsen (2015)

Rasmus Eichstädt -








Conclusions

Outline

Rasmus Eichstädt -


Test series for 3 boundary layer conditions:

Black bolts (B)

Normal temperature hot-dip galvanized (NT)

High temperature hot-dip galvanized (HT)

only M36

M36 and M64 HV-bolt sets (10.9), rolled before

head treatment

Fatigue tests with constant stress amplitudes

and high mean stress

Assessment of the “size effect”

M64

NT HT

NT B

B

Fatigue tests on large-size HV-bolt sets

Influence of hot-dip galvanizing

M36

Sa

S

t

1 load cycle

SmSm = 0.7 ∙ Rp0.2 = 630 N/mm2

Rasmus Eichstädt -


Photo

: A

lexander

Raba

1.1 m

Photo

: M

att

hia

s D

örin

g

2.1 m

M36 - tests M64 - tests

Mean load 515 kN

Testing frequency ca. 50 Hz

Over 100 specimens

Mean load 1680 kN

Testing frequency 2-4 Hz

18 specimens

High frequency pulsator Servo-hydraulic testing machine

Max:

1 MN

Max:

10 MN


Rasmus Eichstädt -


40

60

80

100

150

20

1.0E+04 1.0E+05 1.0E+06 1.0E+07

No

min

al str

ess a

mp

litu

de

Sa

[N/m

m²]

Load cycles N [-]

50% Survival probability

Rupture

Run-out

Mean stress Sm = 0.7 ∙ Rp0.2 = 630 N/mm²

NTB HT

Black

NT-galvanized

HT-galvanized

Decrease of fatigue strength in accordance with guideline VDI 2230

Fatigue tests on HV-bolt sets M36

approx.

- 20 %

Rasmus Eichstädt -


10

20

40

60

100

200

1.0E+04 1.0E+05 1.0E+06 1.0E+07

No

min

al str

ess a

mplit

ud

eS

a[N

/mm

²]

Load cycles N [-]

Ps = 50 %

Ps = 10 %

Ps = 90 %


Black bolts

M36

M64

Run-outs

Survival probabilities:

Results in comparison to M36 bolts

Transition region

to endurance limitHCF - Range

5∙105

M36 M64

BB


Rasmus Eichstädt -


10

20

40

60

100

200

1.0E+04 1.0E+05 1.0E+06 1.0E+07

No

min

al str

ess a

mp

litu

de

Sa

[N/m

m²]

Load cycles N [-]

Ps = 50 %

Ps = 10 %

Ps = 90 %

HCF - RangeTransition region

to endurance limit


M36

M64

Run-outs

Survival probabilities:

NT-galvanized bolts

5∙105

M36 M64

NTNT


Results in comparison to M36 bolts

Rasmus Eichstädt -


10

20

40

60

100

200

1,0E+04 1,0E+05 1,0E+06 1,0E+07

No

min

al str

ess a

mp

litu

de

Sa

[N/m

m²]

Load cycles N [-]

Rupture M36

Rupture M64

Rupture M48 (Marten)EC3

FAT 50

M36M48M64

Run-outs

c

c

c

M36 : 0,96 S

M48 : 0,89 S

M64 : 0,83 S

Size reduction:

Hot-dip galvanized bolts


Comparison to S-N curves from Eurocode 3

M36 M64

NTNT HT

M48

(Marten)

NT

0,25

c,red c

30S S

Rasmus Eichstädt -


20

40

60

100

200

ΔS (N = 2∙106) = 51,9 N/mm²

ΔSc (FAT 50, M36) = 47,8 N/mm²

1,0E+04 1,0E+05 1,0E+06 1,0E+07

No

min

al str

ess r

an

ge

ΔS

[N

/mm

²]

Load cycles N [-]

Rupture

Run-out

Ps,50%

Ps,95%

EC3 – FAT 50

(w/o reduction)

M36 HV-bolts

(tZn NT)

Regression w/

fixed slope m = 3

12 M36 M48 M64 7235

40

45

50

55

Ch

ar.

fa

tig

ue

str

en

gth

ΔS

C(N

= 2

∙10

6)

[N/m

m²]

Bolt diameter [mm]

EC 3 FAT 50

Test result

Size reduction of EC3 FAT 50


Evaluation of FAT-class and size-reduction acc. to Eurocode 3

Rasmus Eichstädt -


20

40

60

100

200

ΔS (N = 2∙106) = 48,4 N/mm²

ΔSc (FAT 50, M36) = 44,5 N/mm²

1,0E+04 1,0E+05 1,0E+06 1,0E+07

No

min

al str

ess r

an

ge

ΔS

[N

/mm

²]

Load cycles N [-]

Rupture

Run-out

Ps,50%

Ps,95%

EC3 – FAT 50

(w/o reduction)

M48 HV-bolts

(tZn NT)

Regression w/

fixed slope m = 3

12 M36 M48 M64 72

w/o upper HCF test level

35

40

45

50

55

Ch

ar.

fa

tig

ue

str

en

gth

ΔS

C(N

= 2

∙10

6)

[N/m

m²]

Bolt diameter [mm]

EC 3 FAT 50

Test result




( )

Rasmus Eichstädt -


20

40

60

100

200

ΔS (N = 2∙106) = 48,0 N/mm²

ΔSc (FAT 50, M36) = 41,4 N/mm²

1,0E+04 1,0E+05 1,0E+06 1,0E+07

No

min

al str

ess r

an

ge

ΔS

[N

/mm

²]

Load cycles N [-]

Rupture

Ps,50%

Ps,95%

EC3 – FAT 50

(w/o reduction)

M64 HV-bolts

(tZn NT)

Regression w/

fixed slope m = 3

12 M36 M48 M64 72

w/o upper HCF test level

35

40

45

50

55

Ch

ar.

fa

tig

ue

str

en

gth

ΔS

C(N

= 2

∙10

6)

[N/m

m²]

Bolt diameter [mm]

EC 3 FAT 50

Test result




( )

Rasmus Eichstädt -


M36 M64

Black bolts


Comparison to S-N curves from Eurocode 3

10

20

40

60

100

200

1,0E+04 1,0E+05 1,0E+06 1,0E+07

No

min

al str

ess a

mp

litu

de

Sa

[N/m

m²]

Load cycles N [-]

Rupture M36

Rupture M64

EC3

FAT 71

EC3

FAT 50

M36M64

M36M64

Run-outs

c

c

M36 : 0,96 S

M64 : 0,83 S

Size reduction:

0,25

c,red c

30S S

BB

Rasmus Eichstädt -








Conclusions

Outline

Rasmus Eichstädt -


e1,max

Fatigue calculation with local concept (strain-life)

-500

0

500

1000

1500

0,00 0,01 0,02 0,03

Loca

l str

ess σ

[N

/mm

²]

Local strain ε [-]

Local hysteresis

100

1.000

10.000

100.000

1,0E+00 1,0E+02 1,0E+04 1,0E+06 1,0E+08P

SW

T[N

/mm

²]

Load cycle number until initial crack Ni [-]

Damage parameter S-N curve (PSWT)

N(PSWT) / N(Sa, Sm)

s s e ( )SWT a m aP E

FE -Model

Nominal loading

32CrB4

Non-linear material implementation

Preloading:

monotonic material law

Cyclic loading:

cyclic stabilized material law

Base material fatigue

strain-life curve

Rasmus Eichstädt -


20

40

60

80

100

200

1,0E+03 1,0E+04 1,0E+05 1,0E+06 1,0E+07

No

min

al str

ess a

mp

litu

de

Sₐ

[N

/mm

²]

Load cycles N [-]

Initial crack (w/o relax.)

Initial crack (with relax.)

Rupture (with relax.)

Analytical:

Test

M36

(Ps,50%)

Fatigue calculation with local concept

Sm = 0.7 ∙ Rp0.2 B

Initial crack

Initial crack

with cyclic

relaxation

Crack

propagation

until rupture

(additional)

Local str

ess σ

Local strain ε

Rasmus Eichstädt -


20

40

60

80

100

200

1,0E+03 1,0E+04 1,0E+05 1,0E+06 1,0E+07

No

min

al str

ess a

mp

litu

de

Sₐ

[N

/mm

²]

Load cycles N [-]

Initial crack (w/o relax.)

Initial crack (with relax.)

Rupture (with relax.)

Analytical:

Test

M36

(Ps,50%)

Sm = 0.7 ∙ Rp0.2

Fatigue calculation with local concept

Effect of hot-dip

galvanizing is not

covered in analytical

approach!

NT

Rasmus Eichstädt -








Conclusions

Outline

Rasmus Eichstädt -


Fatigue capacity of high-strength, large-size bolts significantly

affected by hot-dip galvanizing

EC 3 fatigue class FAT50 confirmed for bolts up to diameter M64

Size reduction necessary, better fatigue classification of uncoated

bolts must be seen critically

Analytical calculations with local concept show good approximation

to experimental results for bolts w/o boundary layer influence

Conclusions

Rasmus Eichstädt -


Thank you!

Funding:

Research partner:

german wind energy research - stahlbau.uni-hannover.de

Documents