Fatigue of Wind Blade Laminates: Fatigue of Wind Blade Laminates: - - PowerPoint PPT Presentation

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Fatigue of Wind Blade Laminates: Fatigue of Wind Blade Laminates: Effects of Resin and Fabric Structure Details Details

David Miller, Daniel D. Samborsky and John F. Mandell M t St t U i it Montana State University

MCARE 2012

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Outline

• Overview of MSU Fatigue Program on

Wind Blade Materials Wind Blade Materials

• Recent Findings, Resin and Fabric

Structure Interactions for Infused Structure Interactions for Infused Laminates

• Comparison of Fatigue Trends for Various
• Comparison of Fatigue Trends for Various

Wind Blade Component Materials

Acknowledgements: Sandia National Laboratories/DOE (Joshua Paquette, Program Monitor). Thanks to our many industry collaborators Thanks to our many industry collaborators

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• DOE/MSU Fatigue Database for Wind Blade

Materials (Public, Sandia Website) – Over 250 Materials 12 000+ test results – 12,000+ test results – Updates each March Updates each March – Excel based – Trends analyzed in contractor reports ( t d / it / ) (www.coe.montana.edu/composites/ )

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• 1. Blade Laminate Performance
• Purpose: Explore critical issues for basic

blade laminates blade laminates

– Characterize the static and fatigue resistance of blade composite laminates

C d i l fib f b i i fib i i

• Current and potential fibers, fabrics, resins, fiber sizings,

processes, processing aids, laminate lay-ups, fiber contents, loading conditions, spectrum loading and design data

Identify failure modes and mechanisms – Identify failure modes and mechanisms

• Ex: Cracking at fabric backing strands deleterious to lower

cost polyester and vinyl ester resin laminates

Id tif t ti l t i l ith i d – Identify potential materials with improved performance, lower cost, processing advantages, etc.

• Ex: pDCPD resin (tough, low viscosity); aligned strand

l i t lik N t R dP k laminates like Neptco RodPack

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Glass Fabrics

Standard Laminate Fatigue

Glass Fabrics

S-N Curves, MD Laminates Effect of R-Value Carbon vs Glass Carbon vs Glass

Carbon Prepreg p g

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• 2. Complex Coupons with Material

T iti lik F b i J i t d Pl D Transitions like Fabric Joints and Ply Drops Thickness Tapering

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Purpose: Explore ply delamination issues related to structural details

Mixed Mode Delamination Testing, Different Resins and Fabrics

related to structural details

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Complex Structured Coupons with Ply Drops Resin Infusion Drops, Resin Infusion

Purpose: Mini-substructure

• test. Simplified, less costly

p , y approach to substructure

• testing. Efficient comparisons
• f resins, fabrics, geometric

details in structural context.

.

coupons represent more realistic internal (infused) blade structural detail areas than structural detail areas than standard laminate tests

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Damage Growth Curves

Static Fatigue, R = 0.1

Damage Growth with Different Resins Correlates with Interlaminar GIc, GIIc

Simulation

Ic, IIc

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• 3. Blade adhesives
• Bulk adhesive strength, fatigue,

g , g , fracture toughness, environmental effects

• Strength Based: standard joint geometry

g j g y like lap shear; test includes crack initiation and propagation to failure. May include ff f f effects of typical flaws like porosity and poor surface prep. F M h i B d k

• Fracture Mechanics Based: crack

propagation resistance for relatively large cracks cracks.

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Fatigue at R = 0.1 and -1 Adhesive Thickness Effects

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Adhesive Flexural Mixed Mode Fracture Tests

Mixed Mode Bending Apparatus Typical load-deflection graph from an MMB test

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Mixed Mode Fracture for ADH-1

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Typical Crack Path Transitions from Path B to C in MMB Specimens for ADH-1 Path B to C in MMB Specimens for ADH 1

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• 4. Core Materials

Purpose: To explore test methods for core materials which reflect critical core performance attributes for a wide range of emerging core materials and structures.

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Flexural Testing of Nextel Core Infused Laminate Core Infused Laminate Static Failure

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• 5. Property Data for Analysis
• 3-D static properties of

100 mm thick glass/epoxy

Laminate Elastic Constants1

Tensile Modulus EL (GPa) 44.6

g p y laminate

L (

) Tensile Modulus ET (GPa) 17.0 Tensile Modulus EZ (GPa) 16.7 Compressive Modulus EL (GPa) 42.8 C i M d l E (GP ) 16 0 Compressive Modulus ET (GPa) 16.0 Compressive Modulus EZ (GPa) 14.2 Poisson Ratio νLT 0.262 Poisson Ratio νLZ 0.264 Poisson Ratio νTL 0.079 Poisson Ratio νTZ 0.350 Poisson Ratio νZL 0.090 Poisson Ratio ν 0 353 Poisson Ratio νZT 0.353 Shear Modulus GLT (GPa) 3.49 Shear Modulus GLZ (GPa) 3.77 Shear Modulus GTL (GPa) 3.04 Shear Modulus GTZ (GPa) 3.46 Shear Modulus GZL (GPa) 3.22 Shear Modulus GZT (GPa) 3.50

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LAMINATE STRENGTH STRESS DIRECTION STRENGTH (MPa) ULTIMATE STRAIN

Static Strength Properties in Three-Directions

STRENGTH PROPERTIES DIRECTION (MPa) STRAIN (%) Tension L 1240 3.00 T i

1

T 43 9 0 28 Tension1 T 43.9 0.28 Tension Z 31.3 0.21 Compression L 774 1.83 Compression T 179 1.16 Compression Z 185 1.44 Shear2 LT 55.8 5.00 Shear LT 55.8 5.00 Shear2 LZ 54.4 5.00 Shear TL 52.0 4.60

2

Shear2 TZ 45.6 5.00 Shear ZL 33.9 1.10 Shear ZT 28.4 0.81

1Transverse tension properties given for first cracking (knee) stress 2Shear values given for 5% strain following ASTM D5379

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( ) Sh B t Fit St St i C

Shear coupons and best fit stress-strain curves

(c) Shear Best Fit Stress-Strain Curves

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Recent Findings Effects of Fabric Construction and Effects of Fabric Construction and Resin Type on Fatigue Performance

• Poor tensile fatigue performance has been

found for some lighter weight fabrics with all resins; and for most fabrics with vinyl esters and resins; and for most fabrics with vinyl esters and polyesters

• Consistent fatigue performance is found with

g p some epoxies for a broad range of stitched unidirectional (UD) Fabrics F ti f d i ifi tl

• Fatigue performance can decrease significantly

as fiber volume fraction (Vf) increases for many fabrics and resins fabrics and resins

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Data Representation

Polyester (UP) vs Epoxy (EP) Million Cycle Million Cycle Strain Parameter; Power Law Fits: S = A NB; Exponent B = 1/n S: Stress or Strain Linear-Log Plots,

Multidirectional Laminates;TT: Database Laminate Designation; [±45/0/±45/0/±45]

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PPG-Devold L1200/G50-E07 (MSU Fabric H, 1261 gsm) B k Front Back Aligned Strand

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Unidirectional (0)2 fabric H laminates; effect of removing 90o backing strands. No effect with epoxy significant No effect with epoxy, significant improvement with polyester; failure along backing strands with UP, VE resins. resins.

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Poorly-performing fabric/resin combinations Resin cracks along transverse fabric backing strand take out primary uni-strands in current infusion fabric (polyester resin) Resin cracks along stitch line take out uni-strands in early hand lay-up triax fabric (tight stitching, polyester resin)

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Aligned Strand (AS) vs UD Fabric H (02) Fatigue data, Three Resins (AS laminates fabricated by PPG/Reichhold by dry strand winding/infusion; same strands and resins as in the fabrics Aligned strand laminates higher same strands and resins as in the fabrics. Aligned strand laminates higher Vf, stronger, significantly more fatigue resistant compared to UD fabrics)

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Fabric Efficiency: Fabric vs Aligned

Resin EP1/EP5 VE4 UP5 Fiber Volume Fraction, Vf

g Strands (AS)

AS Laminates 0.64 0.66 0.68 Fabric Laminates 0.58 0.55 0.58 0o Vf , Fabric L i t 0.53 0.50 0.53

PF: Property for Fabric Laminates

Fabric efficiency: Translation of aligned strand (AS) structure

Laminates 0o Direction Fabric Efficiency, PF/PAS 0o Vf 0.83 0.76 0.78 M d l E 0 88 0 85 0 81

PAS: Property for AS Laminates

g ( ) properties into UD fabric H (PPG- Devold L1200/G50-E07) laminate properties for different resins (PPG 2400 Tex rovings with

Modulus, E 0.88 0.85 0.81 UTS 0.73 0.68 0.62 106 cycle stress 0.64 0.37 0.40

6

(PPG 2400 Tex rovings with Hybon 2026 sizing). E and UTS translate efficiently

106 cycle strain 0.73 0.43 0.49 PF/PAS Adjusted to AS Vf [(PF/PAS) (AS Vf /Fabric 0o Vf)] Modulus E 1 06 1 12 1 04

for all resins; 106 Cycle Fatigue properties translate well for epoxy resin (EP1/EP5), but poorly for vinyl ester (VE) and

Modulus, E 1.06 1.12 1.04 UTS 0.88 0.89 0.79 106 cycle stress 0.77 0.49 0.51 106 l t i 0 88 0 49 0 63

poorly for vinyl ester (VE) and polyester (UP)

106 cycle strain 0.88 0.49 0.63

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Typical Infused Laminate Property Ratios Polyester (UP) to Epoxy (EP)*

Property Ratio UP/EP Axial Tensile Modulus (UD) 1.0 Axial Tensile Modulus (MD) 1 0

AS Ali d St d

Axial Tensile Modulus (MD) 1.0 Axial (UD) Static Tensile Strength 0.90-1.0 Axial (MD) Static Tensile Strength 0.90-1.0 T (UD) T il C ki St i 0 42

AS: Aligned Strand UD: Unidirectional Fabric (0)2 MD: Multidirectional

Transverse (UD) Tensile Cracking Strain 0.42 Axial (AS) 106 Cycle Strain (R = 0.1) 0.66 Axial (UD) 106 Cycle Strain (R = 0.1) 0.51

MD: Multidirectional Fabric (0/±45..) Biax: ±45 Fabric

Axial (MD) 106 Cycle Strain (R = 0.1) 0.65 Axial (Biax) 106 Cycle strain (R = 0.1) 0.91 Interlaminar GI (0-0 interface) 0 55 Interlaminar GIc (0 0 interface) 0.55 Interlaminar GIIc (0-0 interface) 0.48 Complex Coupon Ply Drop Delamination, Threshold Fatigue Strain (R = -1) 0.74 Threshold Fatigue Strain (R = -1) *Vf = 0.5 to 0.6, UD Fabrics D and H, Biax Fabrics M and P

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Summary, Fabric/Resin Effects

• AS laminates give baseline for potential performance for

particular resins and strands.

• Fabric efficiency relates the translation of AS properties into

y p p typical UD fabric laminates, considering the reduced fiber content in the axial direction.

• Fabric efficiency is good for static strength and modulus
• Fabric efficiency is good for static strength and modulus.

Fabric efficiency is good for high cycle fatigue for epoxy resin, but poor for polyester; vinyl esters range from poor to good. The cause of low fabric efficiency for some resins is cracking

• The cause of low fabric efficiency for some resins is cracking

associated with transverse strands, and varies with fabric details.

• Multidirectional laminate efficiency may be similar to that of

the UD fabric, but may be reduced in some cases by premature failure induced by biax fabric cracking.

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Comparison of Fatigue Trends for Various L i t T d ith Oth Bl d Laminate Types and with Other Blade Materials and Structural Details

Which laminates, materials, and material transitions will develop damage first as a function of service life and environment? How will the damage propagate? Consequences to structural performance? Compare fatigue exponents and strain capability in the context of detailed blade FEA and critical loading detailed blade FEA and critical loading. Future work: defined failure mode substructure studies.

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Tensile Fatigue Trends, Effects of Reinforcement Type and Lay-up (S = A NB; exponent B = 1/n)

Material Form Res- in UTS, MPa A/ UTS B n 106 Cycle Strain, % UD Ali d St d (AS) L i t

(PPG 2400 T

H b 2026 Fi i h)

UD Aligned Strand (AS) Laminates (PPG 2400 Tex, Hybon 2026 Finish)

AS

EP5

1369 1.149

• 0.072

13.9

1.20

AS

VE4

1340 1.457

• 0.088

11.4

1.23

AS

UP5

1382 1 558 0 123 8 13

0 79

AS

UP5

1382 1.558

• 0.123

8.13

0.79 UD Fabric H Laminates (contain PPG 2400 Tex/Hybon 2026 Strands)

(0)2 Fabric H

EP1

995 1.265

• 0.088

11.4

0.88

(0)2 Fabric H

VE4

912 2.485

• 0.170

5.88

0.53

(0)2 Fabric H

UP5

884 1.940

• 0.173

5.78

0.39 MD Laminates, UD Fabric H and Biax Fabric T ,

[(±45)2/(0)2]s

EP1

704 1.957

• 0.130

7.69

0.79

[(±45)2/(0)2]s

VE4

628 1.955

• 0.146

6.85

0.53

[(±45)2/(0)2]s

UP5

663 1.736

• 0.151

6.62

0.42

[( )2 ( )2]

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Material Resin

UTS, A/UTS B n

106 Cycle

Fatigue Trends, Other Laminate Types and Directions

Material Form Resin

, MPa

10 Cycle Strain, % Transverse Direction Fabric H UD Laminates (90)6 Fabric H EP5

52.4a 1.857

• 0.114

8.77

0.124 Biax Fabric M (±45/mat) Laminates (±45/m)3 b i EP1

224 1.004

• 0.092

10.9

0.53 Fabric M (±45/m)3 Fabric M VE1

239 1.000

• 0.090

11.1

0.44 (±45/m) UP1

208 0 972

• 0 098

10 2

0 41 (±45/m)3 Fabric M UP1

208 0.972 0.098 10.2

0.41 Triax Fabric W (±45/0)s EP1

585 2.20

• 0.143

6.99

0.70 ( 45/0)s Fabric W EP1 0.70

aFirst cracking stress

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Material Resin Stre- A/ B n 106 Cycle

Fatigue Trends, Other Blade Details

Form ngth UTS Strain, % Delamination at thick ply drops 1 l d F b i D EP1

189b

0 55 1 ply drop, Fabric D EP1

189b

0.55 2 ply drop, Fabric D EP1

135b

• 0.120

8.3 0.39 4 ply drop, Fabric D EP1

106b

• 0.099

10.1 0.35 1 ply drop, Fabric D UP1

N/A

0.39 Thick Adhesive Lap Shear Joints

Hexion Adhesive EP135G3/EKH1376G N/A 13.90c 1.63

• 0.109

9.17

N/A EP135G3/EKH1376G 3M W1100 N/A 13.80c 2.11

• 0.135

7.41

N/A

Triax Skin/Core Sandwich Flexural Fatigue

In Progress In Progress

bForce (kN) at 30-mm delamination length cApparent lap shear strength for 3.25 mm thick adhesive, 25 mm

• verlap length 5 mm thick UD Fabric D/EP-1 adherends
• verlap length, 5 mm thick UD Fabric D/EP 1 adherends.

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Summary: Comparison of Blade Materials for High Cycle Fatigue Performance g y g

• Epoxy Resin EP1:

– Transverse and biax damage before UD laminate g failure (damage progression) – Ply drop delamination at similar strain to biax cracking Adh i (ADH 1) f i i il h – Adhesive (ADH-1) fatigue exponent similar to other materials

• UP and VE Resins:
• UP and VE Resins:

– Similar failure strains for UD and biax components and single ply drop; very low transverse strain for UP g y y – Adhesive (ADH-1) fatigue exponent similar to biax laminate exponent, lower than UD exponent

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Future Research

• Shift toward substructure oriented studies

while maintaining database testing while maintaining database testing

• Major uncertainties lie

in the performance of in the performance of complex structure with realistic multi axial realistic, multi-axial loading