nr. 1 of 22 > vacuum infused thermoplastic composites …

June 3, 2008

DESIGN AND PRODUCTION OF COMPOSITE STRUCTURES

OF 22NR. 1 >

Julie Teuwen, Kjelt van Rijswijk, Simon Joncasand H.E.N. Bersee

VACUUM INFUSED THERMOPLASTIC COMPOSITES FOR WIND TURBINE BLADES

2008 Wind Turbine Blade WorkshopSandia National Laboratories12-14 May 2008

OF 22NR. 2< >


ContentsIntroduction: Large Thermoplastic Composite Wind Turbine Blades

Materials, Design and Manufacturing

Vacuum Infusion of Thermoplastic Composites:Anionic Polyamide-6 ResinInfusion Process and Equipment

Composite Properties:Static mechanical propertiesDynamic mechanical properties

Conclusions

OF 22NR. 3< >


Large Wind Turbine Blades

Dedicated offshore wind power systems:

Stronger and more constant wind.Increasingly large blades to increase power output per turbine and reducecosts per kWh.No noise-pollution regulations and less aesthetical issues to deal with.

Larger blades require:

Materials with higher specific properties (E/ρ, σ/ρ): Carbon fiber composites or hybrid carbon/glass composites.More efficient structural designs

mblade ∼ (Rblade) 3mblade ∼ (Rblade) 32.35

OF 22NR. 4< >


Alternative Structural DesignRe-introduction of ribs:

Higher structural efficiency (E/ρ).Reduces local buckling of skin and webs.Provides attachment points and load paths for smart actuators/control surfaces and sensors.Not entirely new.

OF 22NR. 5< >


Thermoplastic Composites

Current blade manufacturing technology:Thermoset composites2 skins and 1 spar assembled by structural bondingVacuum infusion or pre-pregging of individual parts

OF 22NR. 6< >



Alternative blade manufacturing technology:Thermoplastic composites2 skins, 1 spar and many ribs assembled by weldingRubber forming and diaphragm forming of individual parts

Pre-cut laminate sheet material

Infra red heating panels

Rubber die

Metal die

Rubber press

Final thermoplastic composite part

Heating element

Clamp connection

Welded parts

Voltmeter

Ampmeter

OF 22NR. 7< >



Additional advantages:Better impact properties.Do not turn brittle at low temperatures.Unlimited shelf life of the raw materials.Fully recyclable (environmental and economic benefits).

Drawbacks:Poor fatigue performance due to weak fiber-to-matrix bond.Requires introduction of new technologies and expensive equipment.High material costs due to need for intermediates.High processing temperatures (>200°C): high costs, thermal stresses.Melt pressing technology limits achievable part size and thickness

OF 22NR. 8< >


Vacuum Infusion of Thermoplastic CompositesReactive processing of thermoplastic composites:

Manufacturing of larger, thicker and more integrated thermoplasticcomposite parts.

Improved chemical bonding due to in situ polymerization of the matrix around the fibers.

Does not require expensiveintermediate materials but allowsmanufacturing of parts directlyfrom the monomer.

Commonly used technology forblade manufacturing.

OF 22NR. 9< >


Vacuum Infusion of Thermoplastic CompositesReactive processing of thermoplastic composites:

Anionic Polyamide-6:

AP-Nylon®,Brüggemann Chemical, Germany.Availability of resin, additives and knowledge.Price/performance ratio (2-3 €/kg).Viscosity of the monomer (10 mPa⋅s).Processing temperatures (150-180°C).

0,001

0,01

0,1

1

10

100

1000

10000

100000

0 50 100 150 200 250 300 350 400 450

Processing temperature [ºC]

Mel

t vis

cosi

ty [P

a·s]

epoxyvinylester

polyester

PMMA

PA-6

PBT

PA-12

PEK

ETPUPC

PMMAPA-12

PA-6

PBTPPS

PES

PEI

PEEK

PEKK

Reactive processing of thermoset resins

Reactive processing of thermoplastic resins

Melt processing of thermoplastic polymers

0,001

0,01

0,1

1

10

100

1000

10000

100000

0 50 100 150 200 250 300 350 400 450

Processing temperature [ºC]

Mel

t vis

cosi

ty [P

a·s]

epoxyvinylester

polyester

PMMA

PA-6

PBT

PA-12

PEK

ETPUPC

PMMAPA-12

PA-6

PBTPPS

PES

PEI

PEEK

PEKK

Reactive processing of thermoset resins

Reactive processing of thermoplastic resins

Melt processing of thermoplastic polymers

OF 22NR. 10< >


Control of reaction rate

Anionic Polyamide-6

0

20

40

60

80

100

0 5 10 15 20 25 30 35 40

time [min]

Deg

ree

of c

onve

rsio

n [%

] .

Fast systemSlow system

infusion

cureCAPROLACTAM

ACTIVATOR C20 INITIATOR C1

OF 22NR. 11< >


CN

-

O

CN

OC

NH

O

CN

OC

NH

ON

-

CNH

O+

CN

OC

NH

ON

-

CNH

O

CNH

O

+C

N

OC

NH

O

NHC

NH

O

CN

-

O

+

CN

-

O

CN

OC

NH

O

CN

OC

NH

ON

-

CNH

O+

Initiator Activator

Monomer

PA-6

Anionic Polyamide-61. Ring-opening polymerization of caprolactam into PA-6

2. Crystallization of PA-6 chains

O

NH O

HN O HN

HN

NHO

O

H

O HN

NH O

O

Hydrogen bonding between amide groups

Grouping of polymer chains into Switchboards

Stacks of switchboards forming spherical conglomerates calledspherulites

O

NH O

HN O HN

HN

NHO

O

H

O HN

NH O

O




O

NH O

HN O HN

HN

NHO

O

H

O HN

NH O

O

O

NH O

HN O HN

HN

NHO

O

H

O HN

NH O

O




n

CN

OC

ONH

CNH

O

*

Tpol < Tc ⇒Polymerization

and crystallizationoccur

simultaneously.

Tpol < Tc ⇒Polymerization

and crystallizationoccur

simultaneously.

OF 22NR. 12< >


Selecting the optimum polymerization temperature:

Temperature too low: polymerization stops

Temperature too high:Crystallization difficult

Temperature much too high:Crystallization stopped

Anionic Polyamide-6

Crystal

MonomerCrystal

Long polymer chain

Branched polymer chain

Bricking-inBricking-inBricking-inBricking-in

OF 22NR. 13< >


Selecting the optimum polymerization temperature:

Temperature too low: polymerization stops

Optimum temperature:Continuous polymerization& crystallization

Temperature too high:Crystallization difficult

Temperature much too high:Crystallization stopped

Anionic Polyamide-6

Short polymer chain

OF 22NR. 14< >


Polymer tensile properties

Compared to injection molded PA-6

Condition Young’s modulus [GPa]

Maximum strength [MPa]

Strain at failure [%]

23ºC, dry 4.2 (+ 41%) 96 (+ 14%) 9 (-) 23ºC, 50% RH 2.1 (+ 59%) 61 (+ 4%) 28 (-)

80ºC, dry 1.6 (+ 65%) 51 (+ 32%) 29 (-)

Anionic Polyamide-6

σ2

σ1

0.1

σ

ε0.2 εf

σm

OF 22NR. 15< >


Vacuum Infusion of Polyamide-6 Composites

110°C

110°C

160-180°C

60 minutes

250 mbar

OF 22NR. 16< >


100

120

140

160

180

200

0 5 10 15 20 25 30

Time [min]

Tem

pera

ture

[ºC

]

APA-6 140ºCAPA-6 150ºCAPA-6 160ºCAPA-6 170ºCAPA-6/GF 180ºCAPA-6/GF 170ºCAPA-6/GF 160ºC

Processing temperatures:

Neat APA-6: 150-170°C

APA-6 Composites: 160-180°C

Processing temperatures:

Neat APA-6: 150-170°C

APA-6 Composites: 160-180°C

Exothermic nature

Vacuum Infusion of Polyamide-6 Composites

OF 22NR. 17< >


Anionic Polyamide-6 Composites

Static mechanicalproperties

Physical properties

OF 22NR. 18< >



0

50

100

150

200

250

1.0E+04

1.0E+05

1.0E+06

n

S [M

Pa]

APA-6 (160ºC)APA-6 (170ºC)APA-6 (180ºC)

( ( ))

Higher ILSSHigher toughnessLower void content

OF 22NR. 19< >



050

100150200250300350400

1.0E+02

1.0E+03

1.0E+04

1.0E+05

1.0E+06

1.0E+07

n

S [M

Pa]

APA-6 (180ºC)PA-6Epoxy

APA-6 composite manufactured at 180C has better fatigue properties than the melt processed PA-6 composite:

• Same toughness

• Higher interfacial bond strength

The epoxy composite outperforms both thermoplastic composites.

OF 22NR. 20< >


For increasing blade lengths, switching to more efficient structural designs is inevitable: the re-introduction of ribs is suggested.

For rib/spar/skin-structures, thermoplastic composites are favoured over thermoset composites. Parts can be rapidly melt processed and assembledthrough welding. Blades will be fully recyclable.

Vacuum infusion of thermoplastic composites is introduced to overcomethe classical drawbacks of these materials: limited size and thickness of parts, poor fatigue resistance, expensive materials.

The cure of a semi-crystalline thermoplastic resin is more complicated thanof a thermoset resin.

Conclusions

OF 22NR. 21< >


AP Nylon® has a low viscosity (10 mPa⋅s), good availability, a low price (2-3 €/kg), and a relatively low processing temperature (150-180°C).

Reactively processed PA-6 outperforms melt processed PA-6 in all temperatures and humidities tested.

Static properties of APA-6 composites are better than of their HPA-6 and epoxy counterparts in dry conditions. When moisture conditioned, the performance of APA-6 composites drop rapidly, which is caused by the low conversions and high void contents.

Reactive processing of thermoplastic composites results in a stronginterfacial bond strength and leads consequently to better fatigue

performance compared to melt processing.

Conclusions

June 3, 2008


OF 22NR. 22 >

Julie Teuwen, Kjelt van Rijswijk, Simon Joncasand H.E.N. Bersee

VACUUM INFUSED THERMOPLASTIC COMPOSITES FOR WIND TURBINE BLADES

Questions?

nr. 1 of 22 > vacuum infused thermoplastic composites …

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