Accelerated aging tests for Marine Energy applications...Static and cyclic properties evolve with...

Accelerated aging tests for Marine Energy applications

Ifremer-ONR Workshop

Nantes

August 2012

IFREMER

Materials & Structures group

Presentation

� Introduction� Materials for marine energy structures� Particular loading conditions, tidal turbines


Nantes

August 2012

� Particular loading conditions, tidal turbines� Environment: Acceleration factors� Examples of test results� Some conclusions, future work

WindWaves

Tides

Marine biomass

Wave energy

Tidal energy

What are the renewable

Offshore wind

Tidal current

Introduction


Nantes

August 2012

Currents

Salinity Temperature

Biomass

Salinity gradients Thermal energy

What are the renewableMarine Energyresources ?

IFREMERThe French Ocean Research Institute

1400 staffFrench Oceanographic fleet

Extensive test facilities

Introduction


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August 2012

Marine Renewable Energy

• Resource evaluation• Hydrodynamics• Materials & Structures• Marine engineering• Environmental impact

Polymeric Materials in Marine Energy Conversion structures

Floatingwind

OTEC


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August 2012

wind

Wave energy

Materials for Tidal Current Turbines

Many designs but all use a lot of composites

MCT/Siemens Andritz Hydro


Nantes

August 2012e.g. MCT blades weigh > 2 tons

MCT/Siemens Andritz Hydro

NautricityOpenHydro

TGL/RR

Atlantis

Tidal Current Turbine Blade Example

Blade construction:

Glass or Carbon fibre reinforced resinAdhesively bonded


Nantes

August 2012

Adhesively bondedWith or without foam core

Must gurantee the durability of these three components

Particular loading conditionsLoads

Permanent immersion in sea water


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August 2012

- Tidal currents , which induce the rotation which generates energy

- Rotation , pressure variation due to depth changes of up to 20 m

- Waves , which affect underwater structures in shallow depths.

Permanent immersion in sea water PLUS:

Influence of waveson submerged structures

Loads


Nantes

August 2012

Flume tank tests on instrumented bladesStrain gages + measurement of Fx, Fy, Fz and Mx, My, Mz

Measured strains on 2 PU blades, 100 rpm

1000

1500

2000

mic

rost

rain

Loads


Nantes

August 2012

0

500

0,5 0,6 0,7 0,8 0,9 1

Flow speed, m/s

Data generated:a) to compare with numerical models

b) to compare with prototype response

Std.Dev/Mean

Loads


Nantes

August 2012

Large variations in strain when waves added to a constant velocity flow

Importance of design Loads

e.g. Horizontal versus Vertical axis tidal turbines


Nantes

August 2012

HARVEST (Grenoble INP)

Fatigue must be considered in design

Fatigue of composites : extensive published data

•

Several large wind blade fatigue projects : DNV, Sandia, MSU, OPTIMAT, UPWIND…

Loads


Nantes

August 2012

DOE/MSU composite material fatigue database

OPTIMAT OPTIDAT database

Some data from composite propeller studies

Very few studies of fatigue of composites in seawater

Weitsman, Chateauminois, Kotsokis, Liao …

Loads


Nantes

August 2012

Published data suggest coupling can occur

Environment: Acceleration factors

temperature

Require information on long term immersion behaviour (5 to 20 years) ….. in a few months


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August 2012

Raising temperature is widely used to accelerate water diffusion

Mechanical loads, alternative fluids may also be used

Examples of accelerated water diffusionAcceleration

Mean weight gains, composite panels, 8 year immersion

0

0,5

1

1,5

2

2,5

0 50 100

M%

root time (h)

Epoxy resin

3°C

20°C

40°C

60°C


Nantes

August 2012

0

0.5

1

1.5

2

0 20 40 60 80 100 120

root(time in hours en h)/thickness (mm)

M%

wei

ght

gain

20°C

60°C

40°C

Presentation

IntroductionMaterials for marine energy structuresParticular loading conditions, tidal turbines


Nantes

August 2012

Particular loading conditions, tidal turbinesEnvironment: Acceleration factorsExamples of test resultsSome conclusions, future work

Accelerated testing of Fatigue behaviourof composites in seawater

4-year study, PhD Amélie Boisseau, co-financed by:Ifremer, 3B, OCV, Hexion/Momentive


Nantes

August 2012

Different glass fibre typesE-glass, Advantex™, HiPertex™

Different resinsDifferent fibre sizings

Starting point: Composites used today for wind turbine blades(infused glass/epoxy 90% UD)

Experimental studies

e.g. tests in natural sea water (T constant)

Hydraulic grips

Specimen

SeawaterIn

Hydraulic grips

Specimen

SeawaterIn

4 pt flexfixture

Station 1Station 2

PC,Controller,Data recording

4 pt flexfixture

Station 1Station 2

PC,Controller,Data recording

Examples


Nantes

August 2012

1. Fatigue in seawater2. Influence of seawater aging3. Fatigue after aging

Specimen

SeawaterOut

Specimen

SeawaterOut

Tension fatigue

SeawaterBath

SeawaterBath

4-pt flex fatigue

Fatigue in air and seawater, new (unaged) specimens

600

800

1000

1200M

ax. S

tress

app

lied,

MP

a

Examples


Nantes

August 2012

0

200

400

3 4 5 6 7

Log cycles to failure

Max

. Stre

ss a

pplie

d, M

Pa

AirSeawater

Influence of sea water agingExamples

0

0,5

1

1,5

2

2,5

0 20 40 60 80

M%

root time (h)

Epoxy resin

3°C

20°C

40°C

60°C


Nantes

August 2012

0

0,2

0,4

0,6

0,8

1

0 2 4 6 8 10 12 14 16 18 20

Wei

ght g

ain

[%]

Immersion time [day^1/2]

HPExp. 4°C Opt. 4°C

Exp. 20°C Opt. 20°C



root time (h)

Static and cyclic properties evolve with aging time

4 pt flexural strength

800

1000

1200

1400

1600

Str

engt

h, M

Pa


Nantes

August 2012

0

200

400

600

0 20 40 60 80 100 120

Immersion time, days

Str

engt

h, M

Pa

Coupons immersed in seawater at 60°C for different periodsThen tested wet

Influence of aging, F max=1600N

5

6

7

Coupons immersed in seawater at 60°C for different periods

Then tested wet, F=60% Fr, R=0.1, 2Hz


Nantes

August 2012

0

1

2

3

4

5

Ref

Ref

Ref

Log

Nf

Influence of seawater aging on fatigue

Coupons saturated in seawater at 60°CThen tested wet

a) Glass/Epoxy, Quasi-UD, Wet fatigue, 2 Hz, R=0,1Dogbone specimens

800

1 000

1 200M

ax. a

pplie

d st

ress

(M

Pa)

.

NEW

Examples


Nantes

August 2012

0

200

400

600

1 2 3 4 5 6 7log (Cycles to failure)

Max

. app

lied

stre

ss (

MP

a).

AGED 3 months

NB Material used today for wind turbine blades

Influence of seawater aging on fatigue

Strong influence of matrix resin and fibre sizing

Influence of Matrix resin, same glass fibres

500

600

700

800

900

1 000

Str

ess

max

. [M

Pa]

RESIN 2RESIN 2RESIN 2RESIN 2Aged 3 monthsAged 3 monthsAged 3 monthsAged 3 months

Examples


Nantes

August 2012

200

300

400

500

1 2 3 4 5 6 7

log (Nf)

Str

ess

max

. [M

Pa]

RESIN 1Aged 3 months Influence of sizing, same fibres, same resin

400

500

600

700

800

900

1000

1100

1 2 3 4 5 6 7

Log (Cycles to failure)

Max

. Str

ess,

MP

a

What about carbon/epoxy composites ?Examples

b) Carbon/epoxy UD, Wet fatigue, 2Hz, R=0,1Parallel specimens

0

200

400

600

800

1000

1200

0 2 4 6 8

Max

. ap

plie

d st

ress

, M

Pa

.

NEW

AGED 9 months


Nantes

August 2012

0 2 4 6 8Log (Cycles to failure)

Failure by delamination after aging

UD L/h=40

These tests provide help with material selection and an indicationof composite sensitivity to sea water environment

Coupled approach : use relationshipsbetween changes in static and fatigue

Lifetime prediction models

Different levels of complexity

Traditional approach : Estimate stresses, apply safety factors for environmental effects,

S-N plots, constant life diagrams


Nantes

August 2012

between changes in static and fatigue strengths and water content

Ideally would like:Realistic load spectra,

evolution of 3-D static and cyclic properties in sea waterfor multi-directional composites,

Plus viscoelastic parameters…….

Example of coupled approach for Adhesive agingPhD Bordes 2009, collaboration IFPEN/INSA/ENSTA Bretagne

Weak coupling: Water affects mechanical properties, but assume stress doesn’t affect diffusion kinetics

4%

6%

8%

10%

mt-m

0/m

0 m

oyen

(%)


Nantes

August 2012

0%

2%

0 10 20 30 40t1/2.S/V (jours1/2.mm-1) moyen

mt-m

0/m

0 m

oyen

(%)

0

500

1000

1500

2000

2500

0% 2% 4% 6% 8% 10%mt simulation

Mod

ule

(MP

a)

20°C ED40°C ED

60°C ED20°C ES

60°C ES

Tens

ileM

odul

us, M

Pa

0

2

4

6

8

10

12

14

16

18

0 2 4 6 8 10mt simulation (%)

Con

trai

nte

(MP

a)

20°C - eau deionisee20°C eau de mer60°C - eau deionisee

Yie

ldst

ress

, MP

a

Application to a bonded Arcan specimen aged in sea water

Prediction of adhesiveyield stress


Nantes

August 2012

Prediction of water concentration

Overlap, mm

Overlap, mm

Factor α = σe/σvm

Material limit/applied stressσvm maximum

at centre

von

Mis

es s

tres

s, P

a


Nantes

August 2012

Damage Initiation

Overlap, mm

Overlap, mm

von

Prototype

Industrial structure

Prototype

Industrial structure

Qualification framework


Nantes

August 2012

Material characterization tests, aging

Small structures, assemblies

Flume tank, scale models

Material characterization tests, aging

Small structures, assemblies

Flume tank, scale models

At each level both testing and modelling.

Some conclusions

� Starting to gather data on fatigue behaviour in seawater

� Material selection is critical� Root regions need particular attention


Nantes

August 2012

� Need more information on real loads during service in order to limit test conditions

� Coupled models need test developments

� Core materials and adhesives

Accelerated aging tests for Marine Energy applications...Static and cyclic properties evolve with...

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