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Accelerated aging tests for Marine Energy applications...Static and cyclic properties evolve with...
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Accelerated aging tests for Marine Energy applications
Ifremer-ONR Workshop
Nantes
August 2012
IFREMER
Materials & Structures group
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Presentation
� Introduction� Materials for marine energy structures� Particular loading conditions, tidal turbines
Ifremer-ONR Workshop
Nantes
August 2012
� Particular loading conditions, tidal turbines� Environment: Acceleration factors� Examples of test results� Some conclusions, future work
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WindWaves
Tides
Marine biomass
Wave energy
Tidal energy
What are the renewable
Offshore wind
Tidal current
Introduction
Ifremer-ONR Workshop
Nantes
August 2012
Currents
Salinity Temperature
Biomass
Salinity gradients Thermal energy
What are the renewableMarine Energyresources ?
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IFREMERThe French Ocean Research Institute
1400 staffFrench Oceanographic fleet
Extensive test facilities
Introduction
Ifremer-ONR Workshop
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August 2012
Marine Renewable Energy
• Resource evaluation• Hydrodynamics• Materials & Structures• Marine engineering• Environmental impact
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Polymeric Materials in Marine Energy Conversion structures
Floatingwind
OTEC
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August 2012
wind
Wave energy
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Materials for Tidal Current Turbines
Many designs but all use a lot of composites
MCT/Siemens Andritz Hydro
Ifremer-ONR Workshop
Nantes
August 2012e.g. MCT blades weigh > 2 tons
MCT/Siemens Andritz Hydro
NautricityOpenHydro
TGL/RR
Atlantis
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Tidal Current Turbine Blade Example
Blade construction:
Glass or Carbon fibre reinforced resinAdhesively bonded
Ifremer-ONR Workshop
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August 2012
Adhesively bondedWith or without foam core
Must gurantee the durability of these three components
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Particular loading conditionsLoads
Permanent immersion in sea water
Ifremer-ONR Workshop
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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:
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Influence of waveson submerged structures
Loads
Ifremer-ONR Workshop
Nantes
August 2012
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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
Ifremer-ONR Workshop
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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
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Std.Dev/Mean
Loads
Ifremer-ONR Workshop
Nantes
August 2012
Large variations in strain when waves added to a constant velocity flow
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Importance of design Loads
e.g. Horizontal versus Vertical axis tidal turbines
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August 2012
HARVEST (Grenoble INP)
Fatigue must be considered in design
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Fatigue of composites : extensive published data
•
Several large wind blade fatigue projects : DNV, Sandia, MSU, OPTIMAT, UPWIND…
Loads
Ifremer-ONR Workshop
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August 2012
DOE/MSU composite material fatigue database
OPTIMAT OPTIDAT database
Some data from composite propeller studies
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Very few studies of fatigue of composites in seawater
Weitsman, Chateauminois, Kotsokis, Liao …
Loads
Ifremer-ONR Workshop
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August 2012
Published data suggest coupling can occur
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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
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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
Ifremer-ONR Workshop
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
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Presentation
IntroductionMaterials for marine energy structuresParticular loading conditions, tidal turbines
Ifremer-ONR Workshop
Nantes
August 2012
Particular loading conditions, tidal turbinesEnvironment: Acceleration factorsExamples of test resultsSome conclusions, future work
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Accelerated testing of Fatigue behaviourof composites in seawater
4-year study, PhD Amélie Boisseau, co-financed by:Ifremer, 3B, OCV, Hexion/Momentive
Ifremer-ONR Workshop
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)
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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
Ifremer-ONR Workshop
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
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Fatigue in air and seawater, new (unaged) specimens
600
800
1000
1200M
ax. S
tress
app
lied,
MP
a
Examples
Ifremer-ONR Workshop
Nantes
August 2012
0
200
400
3 4 5 6 7
Log cycles to failure
Max
. Stre
ss a
pplie
d, M
Pa
AirSeawater
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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
Ifremer-ONR Workshop
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
Exp. 40°C Opt. 40°C
Exp. 60°C Opt. 60°C
root time (h)
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Static and cyclic properties evolve with aging time
4 pt flexural strength
800
1000
1200
1400
1600
Str
engt
h, M
Pa
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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
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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
Ifremer-ONR Workshop
Nantes
August 2012
0
1
2
3
4
5
Ref
Ref
Ref
Log
Nf
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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
Ifremer-ONR Workshop
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
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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
Ifremer-ONR Workshop
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
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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
Ifremer-ONR Workshop
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
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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
Ifremer-ONR Workshop
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…….
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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
(%)
Ifremer-ONR Workshop
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
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Application to a bonded Arcan specimen aged in sea water
Prediction of adhesiveyield stress
Ifremer-ONR Workshop
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August 2012
Prediction of water concentration
Overlap, mm
Overlap, mm
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Factor α = σe/σvm
Material limit/applied stressσvm maximum
at centre
von
Mis
es s
tres
s, P
a
Ifremer-ONR Workshop
Nantes
August 2012
Damage Initiation
Overlap, mm
Overlap, mm
von
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Prototype
Industrial structure
Prototype
Industrial structure
Qualification framework
Ifremer-ONR Workshop
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.
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Some conclusions
� Starting to gather data on fatigue behaviour in seawater
� Material selection is critical� Root regions need particular attention
Ifremer-ONR Workshop
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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