Assessment of Research Needs for Wind Turbine Rotor Materials Technology (1991) / Chapter Skim
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3 MATERIALS PROPERTIES AND LIFE PREDICTION
3 MATERIALS PROPERTIES AND LIFE PREDICTION
Pages 35-66
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From page 35... ...
The commercially available fibers and their typical properties are listed in Table 3-1. While E-glass fiber is most widely used in wind turbine rotor blades mainly because of its low cost, carbon fibers are the fibers of choice in many aerospace applications.
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From page 36... ...
36 TABLE 3-1 Typical Properties of Fibers Tensile Failure Diameter, Specific Modulus, Strength, Strain, CTE Fiber ~m Gravity GPa* GPa % 10-6j°C E-glas" 3-20 2.4 72.4 3.45 S2-glass 10-20 2.4 86.9 4.59 poron 142 2.5 400 2.80 0.7 Carbon, PAN based High strength 1.8 230 2.5 1.1 -0.4 High modulus 1.9 370 1.0 0.5 -0.5 Ultra-high modulu ~2.0 520 1.0 0.2 -1.1 High strain 1.8 230-260 3.0-4.8 1.6-2.0 Intermediate modulu ~1.8 290 5.2 1.8 Carbon, pitch based P25 10 1.8 140 1.4 1.0 -0.9 P55 10 2.02 380 1.4 0.4 -1.3 P75 10 2.00 520 1.4 0.3 -1.6 P100 10 2.15 700 1.4 0.2 -1.6 P120 820 1.4 0.2 -1.6 P140 960 1.4 0.2 -1.8 Silicon carbide SCS 140 3.0 430 3.4 0.8 Nicalon 15 2.6 180-210 2.5-3.3 1.5 3.1 AVCO 6-10 300 2.8 MPDZ 10-15 2.3 180-210 1.8-2.1 HPZ 10 2.35 140-175 2.1-2.5 MPS 10-15 2.6-2.7 175-210 1.1-1.4 Alumina PP 20 3.9 345-380 1.4 0.36-0.4 Sumitomo 9-17 3.2 210-260 1.8-2.6 0.96 Saffil 3 3.3 300 2.0 0.67 PRD-166 4.2 385 2.1-2.5 Alumina-nilica Fiberfrax 2.7 100 1.0 Fibermax 3.0 150 0.8 0.5 Alumina-boria-silica Nextel 312 11 2.7 150 1.4-1.7 Mextel 440 10-12 3.1 200-240 1.4-2.0 0.9 Nextel 480 10-12 3.1 224 2.3 0.9 Si, Ti, C, O Tyranno 8-10 2.3-2.5 200 3.0 1.5 Aramid Kevlar 49 12 1.44 124-131 3.6 2.8 -2.0 Kevlar 29 12 1.44 83 3.6 4.0 Kevlar 149 12 1.47 186 3.4 2.0 HM-50 12 1.3 81 3.1 4.4 Polyethylene Spectra 900 38 0.97 117 2.6 3.5 Spectra 1000 27 0.97 172 3.1 0.7 Tung~ten 13 19.4 410 4.0 *
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From page 37... ...
E-glas" fiber cost" around S2/lb; a high-strength carbon fiber cost" about S30/lb. Thus, an all-carbon fiber composite costs 3.S times more than an all-glass fiber composite to provide the weight savings of 76 percent.
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From page 38... ...
Beyond 10 million cycles, however, the carbon fiber is expected to outlast the glass fiber. The cost ratio to obtain the same long-term fatigue strength is then at least the same as that needed to obtain the same stiffness.
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From page 39... ...
39 PARTIC LES t,'~ ',rn -~ fills ~ '''to item CONTINUOUS FIBERS it: SHORT FIBERS ,-\~-111 -- -- 'l] ~BIAXIAL WEAVE MULTIAXIAL MULTILAYER WARP KNIT ANGLE-INTERLOCK CONSTRUCTION \\~,llI, \\~/i \\\,l//i '.\\~ TRIAXIAL WEAVE ~4 ~ KNIT THREE - DIMENSIONAL ORTHOGONAL FABRIC , ~ -, -, _ THREE-DIMENSIONAL CYLINDRIC CONSTRUCTION THREE-DIMENSIONAL BRAIDING FIGURE 3-2 Schematics of various f iber preforms .
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From page 40... ...
Despite the long cure tome required and higher cost, epoxy resins are gaining greater acceptance due to their superior chemical resistance, good adhesion, low cure shrinkage, good electrical properties, and high mechanical strength. A reasonably good compromise between cost, cure time, and the above-mentioned physical properties is achieved in epoxy-based vinyl ester resins, which have especially shown very rapid growth over the past few years by filling the gap between polyesters and epoxies.
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From page 41... ...
However, vinyl eaters and polyester" are similar in that they both utilize a coreactant or crosslinking agent, such as styrene, and free radical-producing initiator=, much as peroxide-, to effect cure. An a result, vinyl ester resins can be cured in a very short time like polyesters, but their static strength and modulus properties are similar or comparable to those of epoxy resins.
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From page 42... ...
As a result, the effectiveness of elastomer toughening of polyester resins i" much lower than that of DGEBFA epoxy resins. For instance, by adding 8 wt% of vinylterminated polyepichlorhydrin elastomer, the fracture toughness GIC of isophthalic polyester resin is increased from 60 to 110 J/m2 with a 23 percent reduction of tensile modulus.
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From page 43... ...
Cypacb Ameri c an Cyanamid Cypac 450 575-650 7000/ 7005 Cypac 545 650-700 7156 Polyarylether Amorphous Radel C Amoco 476 650 Polyethersulfone Amorphous HTA ICI 510 575 Polyamide-imide Amorphous Torlon Amoco 470 650 Polyimide Pseudo- A`rimid Du Pont 480 680 thermoplastic K-III LaRC-TPI Mitsui Toatsu, 482 660 Rogers Corp. 2080 Lenzing 536 660 9725 Ciba-Geigy 536 660 'Tg is the glass transition temperature, the temperature at which a polymer changes from a rigid glassy solid to a soft rubbery solid.
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From page 44... ...
Epoxy resins have good mechanical properties and dimensional stability. Their drawback i" longer cure time and higher cost; however, new epoxy resins are now available for pultrusion and resin transfer molding, which require fast curing.
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From page 45... ...
When fully saturated, the glass transition temperature of epoxy resins can be reduced by as much as 100°C Clinton, 19771. At room temperature, absorbed moisture has a rather minimal effect on mechanical properties.
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From page 46... ...
For E-giass/epoxy laminates, B is about 0.1 regardless of whether the laminate is unidirectional or multidirectional when the fatigue stress ratio R - 0.1 (Mandell, 1990~. Since very little fatigue data exist beyond ~ million cycles, fatigue strength at 100 million cycle-, which is a minimum requirement for wind turbine blade design, is estimated to be 20 percent of the ultimate strength.
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From page 47... ...
Once the fatigue cycles are defined, the lifetime is predicted by using a combination of Miner's rule and constant-amplitude fatigue data or a crack growth law (Sutherland, 1989~. It in difficult, however, to predict lifetimes of composite wind turbine blades because their failure modes are complex and no sufficient database exists.
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From page 48... ...
At the same time, realistic Impact energy levels should be established, and their effect on fatigue lifetime should be investigated. An mentioned earlier, carbon fibers, unlike glass fibers, are almost insensitive to fatigue degradation.
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From page 49... ...
Glass fibers are more resistant to impact damage than carbon fibers. Thus, any scheme of composite toughening is expected to work better with glass fibers than with carbon fiber=.
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From page 50... ...
Theme data were valuable in assessing which species would likely be best suited to wind turbine use and in estimating the weight, stiffness, and static strength of a candidate design. However, only minimal guidance concerning the effects of fatigue, load duration, and component size on long-term allowable strength was given.
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From page 51... ...
A tiny specimen of fir may show static tensile strength nearly twice its static compression strength, but for laminated members the size of large wind turbine blades, the static tension and compression strength will be about equal. This is due to a much more rapid loos of strength with size for tension than for compression.
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From page 52... ...
52 At\' ~ ~ ~ i= ~8utt Joint . .~ , Scart Joint Along Grain Shear Rolling Shear tong Grain Shear xz z0~0: 1 ~r 1 6~~ 5~ Pew 1 Pay 1 Get ~ 2, [D,4D L ~[ ~ 1 G~A/~ 5~ ~d 1 P`v 11 G~~ Logo It PLY L G ~ /~ 50~ ^~ Ace: PLY G~A'~ Along Grain Shear Along Grain Shear Rolling Sexy ~ LOGO 11 PLY 1 1 OR 5~ A~, s 1 ALV 11 GO NOTES: XZ Logo I' PAY I I GO 5~ Van: t1 ~v f' G - /~ 1.
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From page 53... ...
Larger structures are characterized by lower mechanical properties. Adjustments in properties due to size effects and other conditions are considered by Gougeon Brothers in engineering each application.
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From page 54... ...
All of the above effect" continue to play a role in determining the safe fatigue strength of wood/epoxy laminate, but their description, interaction, and quantification become more complicated for fatigue compared to static strength. To provide a logical separation of tension from compression fatigue effects, Department of Energy (DOE)
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From page 55... ...
, 1 0 0 ° F ~ _ _ _ -_ ~ ~_ _ ___ 60 70 RELATIVE HUMIDITY (PERCENT) FIGURE 3-7 Wood moisture content versus atmospheric relative humidity.
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From page 56... ...
11~11 = ~ Illitl At Tact Specimen Uniformly Stressed Volume 32 cu in ~ ~I~1 ~ ~ i~lll I I 11 10 6 10 7 10 8 N - CYCLES FIGURE 3-9 Typical tensile fatigue strength of wood/epoxy laminate.
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From page 57... ...
1 Longitudinal DlrCctj~n Rnom l omnr~r~t~ 1n 10 5 10 6 10 7 10 8 N - CYCLES FIGURE 3-10 Typical compression fatigue strength of wood/epoxy laminate.
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From page 58... ...
While size effect for static tensile strength along the grain shows strength lose that can be a factor of 2 between laboratory samples and large blades, it becomes worse for tension fatigue where it can reach roughly a factor of 3. For fully reversed R = -1 fatigue, the size effect drops back about to the 2:1 level of static tension.
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From page 59... ...
Long-term fatigue data should be generated to at leant 100 million cycles for the most useful composite laminates and critical elements containing manufacturing defects, under appropriate environmental condition". Separate tension and compression fatigue data should be generated so that independent lifetime projections for upwind and downwind portions of blade "kin can be made.
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From page 60... ...
It should include mechanical properties on fibers, matrix resin-, and composites, including wood/epoxy. An extensive search of all fatigue data on both GRP and wood/epoxy should be conducted and the results included in the database.
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From page 61... ...
Fatigue Testing of Wood Composites for Aerogenerator Rotor Blades. School of Material" Science, Bath University, England.
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From page 62... ...
1979. Fatigue Behavior and Life Prediction of Composite Laminates.
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From page 63... ...
1981. Effects of Elastomeric Additive" on the Mechanical Properties of Epoxy Resins and Composite Systems.
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From page 64... ...
1981. Fitting Models to Composite Materials Fatigue Data.
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From page 65... ...
U.S. Forest Products An Exploratory Study into the Fatigue of Journal of Composite Materials, Vol.
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