Wind Turbine Blade Modeling
Abstract
The part was made using thermosetting polymer of epoxy. It uses dispersed 20 nano meter diameter carbon nanotubes. The weight percentage is 10%. The matrix of carbon nano tubes are used in such a way that they are well dispersed, meaning the orientations are at random. If was observed that if we add silica Nano tubes, the fatigue life gets increased. The properties achieved are tested using tensile testing machines. It was observed that on most of the samples made using silica, higher fatigue life was observed. This happens due to reduction in crack propagation.
Introduction of FRP .of FRP
Plastic with Fiber are called F. R. P. composites. They are highly used in hull of ship; the airplane parts mainly the fuselage, wings, and tail planes. They have large strength to weight ration so are a preferred choice in aero plane structures, or in ship structures. They have high specific stiffness and strength.
The components used in ships or aero planes are subjected to oscillatory loading conditions, as fluid moving over the surfaces creates fatigue. The composite material have various cross linked fibers, hence there is redundancy and cracks cannot propagate.
The advantage is due to cross linking of the micro structure creates properties useful for the structure and help in creating high modulus failure due to fatigue or creep.etc.
Even so, thus it contributes to an unacceptable properties that the polypropylene is extremely brittle and has a low tolerance to crack formation and propagation. The general stress and crack efficiency of Composite materials with that same matrix would be influenced by this. Improving the properties of the epoxy matrix by adding a second phase of particles into the resin is one of the ways to enhance the material properties for FRPs. Polymeric.nanocomposites,.where.at.least.one.of.the.dimensions.of.the.particulate.material.is.less.than.100.nm,.have.shown.significant.improvements.in.mechanical.properties,.e.g.Various.types.of.particulate,.fibrous.and.layered.nanoparticles.have.been.employed.for.both.bulk.polymers.and.fibre.composites.
Fatigue Testing
The fatigue testing of specimens is performed as shown in the Figure. The test specimen was preparing dosing GFRP composite laminate. There should not be sharp edges; hence in the test specimen the edges are slightly rounded. This reduces the stress concentration. The fatigue tests are done using standard .ASTM.D3479M. The testing procedure uses loads up to 25,000 N. The loadings are controlled by the use of computer based programming. The loading along with the displacement information’s are captured during the testing.About.50 cycles offloading/displacement data are used for the regression analysis. The comparisons are performed by normalizing the stiffness as got in the first cycle, to the final stiffness at many fatigue cycles. The analysis using Annoys Software is presented in the figures.
What.are.composite.materials?.
Composite material is formed when two dissimilar materials are mixed together, which do not have a chemical reaction, thus maintained respective properties. These two materials have different physical chemical properties.
The reason for their use over traditional materials is because they improve the properties of their base materials and are applicable in many situations.
What.is.Finite element analysis?
Engineering often goes unappreciated until there’s a mistake.Then.everyone.knows.about.it.Engineering.mistakes.can.lead.to.high profile disasters.and.even.litigation.That’s.why.engineers.need.to.optimize.and.stress.test.their.designs.Doing.so.can.also.save.millions.on.iterative.prototyping.with.physical.materials. The FEM method is now a well proven method to arrive at the stresses level in a given material with defined loading conditions. Let us explore some examples of FEA use.
Finite element analysis method provides a well-established mathematical formulation for modeling the structure, defining the boundary conditions, and applying the required loadings. Thus engineers can use FEA for any physical problem which is amenable to a mathematical modeling. The FEA method is aloes used in fluid flow based problems. It helps us in complex design needs. The FEA provides engineers a technique which gives them scope for structural testing in a virtual environment. Thus before a structure is realized it gets tested in a computer based model.
The Finite element method
When we need to use the Finite element based methods, first we need to create the solid model of the desired part. Next step is constructing a mesh…Thus the designed part is mathematically broken down to much smaller parts, we can call them as mesh elements. Thus we get the name of Finite element as these elements though very small but are still finite in size. Further the loading data is also superimposed on the elements.
The governing equations are partial differential equations. By using FEM, these equations get simplified to set of algebraic equations.
Why is FEA useful?
FEA.allows.engineers.to.prototype.a.design.in.action.without.the.need.to.create.a.physical.working.model.The.nature.of.FEA.offers.a.few.more.advantages.The.use.of.finite.elements.allows.themodelingof.multiple.material.types,.testing.of.complex.geometry,.and.the.ability.to.capture.localeffects.acting.on.a.small.area.of.the.design.
In practice, engineers.can.use.finite.element.modeling.software.on.a.huge.variety.of.tasks.The.deformation.of.a.car.on.impact,.stresses.on.human.joints,.and.fluid.dynamics.over.turbines.are.justa.few.of.its.varied.applications.
Finite element analysis is only a predictive model. It doesn’t confirm that a design will survive the modeled stresses.But.it.gives.engineers.a.clearer.picture.of.how.the.design.will.react.to.stresses.and.reduces.the.need.for.extensive.prototyping.
Effective use of Finite element analysis
Finite.element.analysis.is.a.powerful.tool.in.the.belt.of.an.engineer, and.effective.use.of.FEA.cansave.companies.time.and.money.through.mathematical.prototyping.FEA is just one of the digital technologies transforming the future of engineering.
Why is fatigue analysis important?
Train Cycles
Includes the effect of mean residual stresses, hysteresis loop capture and rain flow cycle counting
Factors that Affect Fatigue Life
Includes.Component.Size,.Loading.Type,.Surface.Finish,.Surface.Treatment.(that.is,.MechanicalTreatments,.Plating,.and.Thermal.Treatments),.and.Effect.of.Surface.Treatments.on.Endurance.Limit.The.solver.technology.integrated.with.Creo.Simulate.fatigue.analysis.is.provided.by.nCode.International..Fatigue analysis requires a Fatigue Advisor license from PTC.
History of Fatigue
The.majority.of.component.designs.involve.parts.subjected.to.fluctuating.or.cyclic.loads.Such.loading.induces.fluctuating.or.cyclic.stresses.that.often.result.in.failure.by.fatigue.About.95%.of.all.structural.failures.occur.through.a.fatigue.mechanism.The.damage.done.during.the.fatigue.process.is.cumulative.and.generally.unrecoverable,.due.to.the.following:
- .It.is.nearly.impossible.to.detect.any.progressive.changes.in.material.behavior.during.the.fatigue.process, so failures often occur without
- Periods of rest, with the fatigue stress removed, do not lead to any measurable healing or
It.was.wellknown.that.wood.or.metal.could.be.made.to.break.by.repeatedly.bending.it.back.and.forth.with.a.large.amplitude.But,.it.was.then.discovered.that.repeated.stressing.can.produce.fracture.even.when.the.stress.amplitude.is.apparently.well.within.the.elastic.range.of.the.material..When.fatigue.failures.of.railway.axles.became.a.widespread.problem.in.the.middle.of.the.nineteenth.century, this drew attention. to cyclic loading effects.This.was.the.first.time.that.many.similar.components.had.been.subjected.to.millions.of.cycles.at.stress.levels.well.below.the.monotonic.tensile.yield.stress.Between.1852.and.1870.the.German.railway.engineer.August.Wöhler.set.up.and.conducted.the.first.systematic.fatigue.investigation.
Some of Wohler’s data are for Krupp axle steel and are plotted, in terms of nominal stress (S).vs. number of cycles to failure (N), on.what.has.become.known.as.the.SN.diagram.Each.curve.on.such.a.diagram.is.still.referred.to.as.a.Wöhler.line.
Figure 1 S-N CURVE DIAGRAM
At about the same time, other.engineers.began.to.concern.themselves.with.problems.of.failures.associated.with.fluctuating.loads.in.bridges, marine equipment, and.power.generation.machines.During.the.first.part.of.the.twentieth.century, more.effort.was.placed.on.understanding.the.mechanisms.of.the.fatigue.process.rather.than.just.observing.its.results.This.activity.finally.led,.in.the.late.fifties.and.early.sixties,.to.the.development.of.the.two.approaches,.one.based.on.linear.elastic.fracture.mechanics,.LEFM,.to.explain.how.cracks.propagate,.and.the.socalled.CoffinManson.local.strain.methodology.to.explain.crack.initiation..Through.this.understanding, modern.designers.and.engineers.have.been.able.to.create.more.fatigue-resistant.components.without.relying.solely.on.experimentation.From.a.practical.point.of.view,.this.has.been.a.much.more.profitable.approach.
Physics of Fatigue
Since past 170 years it is observed that when repetitive loads are applied the material fails at much lower level of stress. This phenomenon was given the name fatigue failure. Thus in failure with oscillatory loading the failure occurs at much lower level of loading compared to what it will occur with just one single loading. In the diagram given below a specimen subjected to uniform loading with crack is shown. If crack starts near the circular cut portion, the crack will propagate at faster rate compared. Further if the loading is repetitive crack propagation continues as show in diagram in exploded view in right side of this figure.
Figure 2 STAGES OF FATIGUE
The.physical.development.of.a.crack.is.generally.divided.into.2.separate.stages.These.relate.to.the.crack.initiation.phase (Stage I).and the crack growth phase (Stage.II).Fatigue.cracks.initiate.through.the.release.of.shear.strain.energy.The.following.diagram.shows.how.the.shear.stresses.result.in.local.plastic.deformation.along.slip.planes.As.the.loading.is.cycled.sinusoidally,.the.slip.planes.move.back.and.forth.like.a.pack.of.cards,.resulting.in.small.extrusions.and.intrusions.on.the.crystal.surface..These surface disturbances are approximately 1 to 10 microns in height and. constitute embryonic cracks.
Figure 3 CRACK INITIATION
A.crack.initiates.in.this.way.until.it.reaches.the.grain.boundary.At.this.point.the.mechanism.is.gradually.transferred.to.the.adjacent.grain
When.the.crack.has.grown.through.approximately.3.grains, it is seen to change its direction of propagation.Stage.I.growth.follows.the.direction.of.the.maximum.shear.plane, or.45°.to.the.direction.of.loading.During.Stage.II.the.physical.mechanism.for.fatigue.changes.The.crack.is.now.sufficiently.large.to.form.a.geometrical.stress.concentration.A.tensile.plastic.zone.is.created.at.the.crack.tip.as.shown.in.the.following.diagram..After.this.stage, the crack propagates perpendicular to the direction of the applied load.
Results and Discussion
Analysis of Wind Turbine Blade
To analysis wind turbine blade on Annoys Software and get results
First Step
Preparing the suitable geometry on the Ansys workbench
Second Step
Applying required loading conditions
Graph Analysis
Manual Solution of the Problem
The figure shows the loading case of pure tension, here the fixed end and the loading side is marked as hash and it is the left hand side of the structure.
The right hand side loading is pure tensile load of 10,000 N is applied 2 mm below the center line. The next loading case is a pure bending type of loading as shown in next figure.
The bending moment applied is M = 20 Nm. The direction of bending moment is counter clock wise.
Due to tensile loading the stress developed = 10,000/ (0.01*0.01) = 100,000,000Pa = 100 MPa, where 0.01m * 0.01 m is the cross section area. Now due to bending moment we get a compressive loading at X and additional tensile loading at Z. At center point Y no extra loading occurs due to bending.
The value of stress at X is
The maximum value will occur at bottom point Z = 100+ 120 = 220 M Pa and
The minimum value will occur at bottom point Z = 100- 120 = – 20 M Pa
As we know that for 1020 Steel, the yield strength is 350 MPa, we can estimate the factor of safety.
Factor of safety = = 1.5
Since factor of safety is >1, the material will not fail.
Conclusion
Their.first.announcement.was.an.excess.of.events.recorded.after.56.days, who presented the results to a conference at the University of California, was quoted. If it’s real, they looking at a very beautiful dark matter signal. This signal contrasts with several other studies that also have struggled to locate any data, including such Helium & Lux but seems to support findings from DAMA. They found an annual modulation in the event intensity that may suggest lighter dark energy. In 3 years of evidence, annual modulation has continued to be seen. More recent work, however, has shown that the abundance of events assigned to a preliminary compact objects signal was simply due to an exaggerated surface event history. There is no support for a signal in data from the CoGeNT experiment after allowing for this context and no conflict to zero effects from other studies.
References
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