Dynamic Strength - Hybrid Anisotropic Materials for Wind Power Turbine Blades - page 138

5.7.2 History of Investigating Mechanical Properties

The. wind. turbine. blades. are. designed. in. relation. to. stiffness. and. fatigue..
Ratio. of. high. stiffness. and. high. strength. to. weight. are. two. characteristics.
that.depend.on.selection.of.the.carbon/glass.relationship..Usually,.the.rela-
tion. of. glass/carbon. with. matrix. resin. is:. 70. percent. reinforced. carbon,. 30.
percent. resin.. This. relationship. has. a. large. inluence. on. fatigue. strength..
Basic. properties. of. individual. constituencies. include. the. stiffness. predic-
tions.of.fabric.and.matrix.use..The.calculations.are.experimentally.veriied.
by.static.testing.that.measures.tension,.compression,.and.shear.stiffness.and.
stress..All.values.are.used.in.strength.criteria.for.estimated.lifespan.predic-
tions.. Stiffness,. static. strength,. and. fatigue. performance. are. measured. by.
testing.test.coupons.or.components.
Uniform.static.tests.are.carried.out.under.quasi-static.loading,.and.fatigue.
tests.done.under.varying.loading.conditions..Properties.are.measured.under.
tensile.loads,.compression.loads,.shear.loads,.or.combinations.of.this.in.bi-.
and.multiaxial.loading.modes..During.the.1980s.and.1990s,.three.European.
projects,.from.1986.to.1996, 18-20 .focused.on.research.on.the.mechanical.behav-
ior.of.the.wind.turbine.blades.and.the.materials..In.this.program,.they.mea-
sured. the. static. and. fatigue. properties. of. glass-polyester. and. glass-epoxy.
materials..Techniques.were.developed.with.design.curves.based.on.constant.
load. amplitude. tests. and. on. variable. amplitude. tests. using. stochastic. load.
histories. being. established.. The. results. from. these. projects. were. collected.
in.two.topics.edited.by.C..W..Kensche 21 .and.S..R..M..Mayer. 22 .E..C..Smet.and.
P.. W.. Bach. collected. the. data. into. a. database. FACT. 23 . Supported. by. Sandia.
National. Laboratories,. Montana. State. University. (MSU). has. worked. inten-
sively.since.1989.on.characteristics.of.composite.materials.for.wind.turbines..
The.result.from.this.nationally.supported.program.was.collected.in.a.large.
DOE.(Department.of.Energy)/MSU.database.that.was.irst.presented.in.1997.
by.J..F..Mandrell.and.D..D..Samborsky. 24 .Since.2001,.the.database.has.been.
updated.annually. 25
The.European.activities.have.continued.in.a.currently.running.European.
project. (2001-2006).. OPTIMAT, 26-28 . under. the. Fifth. European. Union. (EU).
framework. program,. provide. accurate. design. recommendations. for. the.
optimized.use.of.materials.within.wind.turbine.rotorblades.and.to.achieve.
improved. reliability.. The. project.is. investigating. the. structural.behavior. of.
the.composite.material.(glass-epoxy).under.the.unique.combinations.expe-
rienced.by.rotorblades,.such.as.variable.amplitude.loading,.complex.multiax-
ial.stress.states, 30-31 .extreme.environmental.conditions,.and.thick.laminates.
and. their. possible. interactions.. Techniques. will. be. developed. for. damage.
mechanisms, 29 .life.extension,.condition.assessments.and.repair.