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 Montana State University t St t U i it MCARE 2012
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
• 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 ( (www.coe.montana.edu/composites/ ) t d / it / )
1. Blade Laminate Performance • Purpose: Explore critical issues for basic blade laminates blade laminates – Characterize the static and fatigue resistance of blade composite laminates • Current and potential fibers, fabrics, resins, fiber sizings, C d i l fib f b i i fib i i 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 – Identify potential materials with improved Id tif t ti l t i l ith i d performance, lower cost, processing advantages, etc. • Ex: pDCPD resin (tough, low viscosity); aligned strand l laminates like Neptco RodPack i t lik N t R dP k
Standard Laminate Fatigue Glass Fabrics Glass Fabrics S-N Curves, MD Laminates Effect of R-Value Carbon vs Glass Carbon vs Glass Carbon Prepreg p g
2. Complex Coupons with Material T Transitions like Fabric Joints and Ply Drops iti lik F b i J i t d Pl D Thickness Tapering
Purpose: Explore ply delamination issues related to structural details related to structural details Mixed Mode Delamination Testing, Different Resins and Fabrics
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 of 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
Damage Growth Curves Static Fatigue, R = 0.1 Damage Growth with Different Resins Correlates with Interlaminar G Ic , G IIc Ic , IIc Simulation
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 effects of typical flaws like porosity and ff f f poor surface prep. • Fracture Mechanics Based: crack F M h i B d k propagation resistance for relatively large cracks cracks.
Fatigue at R = 0.1 and -1 Adhesive Thickness Effects
Adhesive Flexural Mixed Mode Fracture Tests Typical load-deflection graph Mixed Mode Bending Apparatus from an MMB test
Mixed Mode Fracture for ADH-1
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
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.
Flexural Testing of Nextel Core Infused Laminate Core Infused Laminate Static Failure
5. Property Data for Analysis Laminate Elastic Constants 1 • 3-D static properties of 100 mm thick glass/epoxy g p y Tensile Modulus E L (GPa) L ( ) 44.6 laminate Tensile Modulus E T (GPa) 17.0 Tensile Modulus E Z (GPa) 16.7 Compressive Modulus E L (GPa) 42.8 C Compressive Modulus E T (GPa) i M d l E (GP ) 16 0 16.0 Compressive Modulus E Z (GPa) 14.2 Poisson Ratio ν LT 0.262 Poisson Ratio ν LZ 0.264 Poisson Ratio ν TL 0.079 Poisson Ratio ν TZ 0.350 Poisson Ratio ν ZL 0.090 Poisson Ratio ν ZT Poisson Ratio ν 0.353 0 353 Shear Modulus G LT (GPa) 3.49 Shear Modulus G LZ (GPa) 3.77 Shear Modulus G TL (GPa) 3.04 Shear Modulus G TZ (GPa) 3.46 Shear Modulus G ZL (GPa) 3.22 Shear Modulus G ZT (GPa) 3.50
Static Strength Properties in Three-Directions LAMINATE STRESS STRENGTH ULTIMATE STRENGTH STRENGTH DIRECTION DIRECTION (MPa) (MPa) STRAIN STRAIN PROPERTIES (%) Tension L 1240 3.00 Tension 1 1 T i T T 43 9 43.9 0 28 0.28 Tension Z 31.3 0.21 Compression L 774 1.83 Compression T 179 1.16 Compression Z 185 1.44 Shear 2 Shear LT LT 55.8 55.8 5.00 5.00 Shear 2 LZ 54.4 5.00 Shear TL 52.0 4.60 Shear 2 2 TZ 45.6 5.00 Shear ZL 33.9 1.10 Shear ZT 28.4 0.81 1 Transverse tension properties given for first cracking (knee) stress 2 Shear values given for 5% strain following ASTM D5379
Shear coupons and best fit stress-strain curves ( ) Sh (c) Shear Best Fit Stress-Strain Curves B t Fit St St i C
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 • Fatigue performance can decrease significantly F ti f d i ifi tl as fiber volume fraction (V f ) increases for many fabrics and resins fabrics and resins
Data Representation Polyester (UP) vs Epoxy (EP) Million Cycle Million Cycle Strain Parameter; Power Law Fits: S = A N B ; Exponent B = 1/n S: Stress or Strain Linear-Log Plots, Multidirectional Laminates;TT: Database Laminate Designation; [±45/0/±45/0/±45]
PPG-Devold L1200/G50-E07 (MSU Fabric H, 1261 gsm) k Back B Aligned Strand Front
Unidirectional (0) 2 fabric H laminates; effect of removing 90 o backing strands. No effect with epoxy significant No effect with epoxy, significant improvement with polyester; failure along backing strands with UP, VE resins. resins.
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)
Aligned Strand (AS) vs UD Fabric H (0 2 ) 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 V f , stronger, significantly more fatigue resistant compared to UD fabrics)
Fabric Efficiency: Resin EP1/EP5 VE4 UP5 Fiber Volume Fraction, V f Fabric vs Aligned g AS Laminates 0.64 0.66 0.68 Strands (AS) Fabric Laminates 0.58 0.55 0.58 0 o V f , Fabric 0.53 0.50 0.53 P F : Property for Fabric Laminates L Laminates i t P AS : Property for AS Laminates 0 o Direction Fabric Efficiency, P F /P AS Fabric efficiency: Translation of 0 o V f 0.83 0.76 0.78 aligned strand (AS) structure g ( ) M d l Modulus, E E 0 88 0.88 0 85 0.85 0 81 0.81 properties into UD fabric H (PPG- UTS 0.73 0.68 0.62 Devold L1200/G50-E07) laminate 10 6 cycle stress 0.64 0.37 0.40 properties for different resins (PPG 2400 Tex rovings with (PPG 2400 Tex rovings with 10 6 cycle strain 6 0.73 0.43 0.49 Hybon 2026 sizing). P F /P AS Adjusted to AS V f [(P F /P AS ) (AS V f /Fabric 0 o V f )] E and UTS translate efficiently Modulus, E Modulus E 1 06 1.06 1 12 1.12 1 04 1.04 for all resins; 10 6 Cycle Fatigue UTS 0.88 0.89 0.79 properties translate well for 10 6 cycle stress 0.77 0.49 0.51 epoxy resin (EP1/EP5), but poorly for vinyl ester (VE) and poorly for vinyl ester (VE) and 10 6 cycle strain 10 6 l t i 0 88 0.88 0 49 0.49 0 63 0.63 polyester (UP)
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