Important assumptions & simplifications:• The materials of the shell and girder are identical• The blade is considered as a box beam model• The edgewise and flapwise bending are dominating~~~~~~~~~~~~~~~~~

Function: Wind turbine blade• Provide aerodynamic shape and performance• Withstand wind loads and harsh environment~~~~~~~~~~~~~~~~~

Conflicting objectives:• Minimize mass (Critical Objective 𝑚𝑚 = 2𝜌𝜌 ℎ + 𝑏𝑏 𝑡𝑡)• Minimize cost• Minimize embodied energy and 𝐶𝐶𝐶𝐶2 footprint~~~~~~~~~~~~~~~~~

Free variables• Thickness t and choice of material~~~~~~~~~~~~~~~~~

Multiple constraints:• length L, width b and height h specified• Strength: not fail under wind load

Material Index 𝑀𝑀1 = 𝜌𝜌𝜎𝜎𝑦𝑦

from 𝑚𝑚1 = 6 ℎ+𝑏𝑏 𝑀𝑀𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒

𝑏𝑏(𝑏𝑏+3ℎ)𝜌𝜌𝜎𝜎𝑦𝑦

• Stiffness: not deflect too much under wind load

Material Index 𝑀𝑀2 = 𝜌𝜌𝐸𝐸

from 𝑚𝑚2 = 3 ℎ+𝑏𝑏 𝑀𝑀𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝐿𝐿2

2b2(𝑏𝑏+3ℎ)𝛿𝛿𝜌𝜌𝐸𝐸

• Fatigue strength greater than 90𝑀𝑀𝑀𝑀𝑀𝑀• Fracture toughness greater than 10 𝑀𝑀𝑀𝑀𝑀𝑀 � 𝑀𝑀1/2

• Minimum service temperature: −100℃• Industrial Environment: Acceptable, Excellent• Marine Environment: Acceptable, Excellent• Fresh water and salty water: Acceptable, Excellent• Acid: Limited use, Acceptable, Excellent• UV radiation: Fair, Good, Excellent• Shaping: Composite forming, Molding, Casting• Surface Treatment: Surface Coating

The blade is the most critical component of the windturbine, this project aims to minimize its weight andenhance its sustainability for a offshore wind turbinefrom the material selection perspective. Desiredmaterials needs to exhibit high strength/stiffness todensity ratios and low environment impacts to make theblade structural effective and eco-friendly.

Most offshore wind turbines are larger than those on landand installation is difficult and expensive. In addition, the heavierthe blade, the heavier the tower so that the more costly it is toproduce, transport, and install. Thus minimizing mass is thecritical objective for offshore wind turbine blades.

CFRP, cast Al-alloys and stainless steel are the three bestmaterials for offshore wind turbine blades, among which CFRPoffers highest strength/stiffness-to-density ratio. Conversely, it isharder to achieve sufficient stiffness for steel and aluminum on along blade without adding excessive weight.

Although the price of CFRP is higher than other twomaterials, CFRP will exhibit its advantage when it comes toreducing the overall cost of building a complete wind turbine.

CFRP and stainless steel make blades maintain lowerembodied energy but compared to other two metal materials,CFRP is normally unrecyclable at present.

In conclusion, CFRP is the best material for a lightweight andsustainable offshore wind turbine blade. With development ofthe material technology, CFRP will be more competitive in thefuture. Also, it is very promising to combine CFRP with aluminumto create more innovative materials which has a lower price.

CEE 574 / ARCH 595 · Material Selection for Sustainable Design · Term Project · 2014 FallRui Hou · Master of Science in Infrastructure Systems

[1] Materials Selection in Mechanical Design, 4th edition, M.Ashby, published by Butterworth-Heinemann, 2011[2] Materials and the Environment, M. Ashby, 2nd edition,published by Butterworth-Heinemann, 2013[3] Ahmad, Samir. "Wind Blade Material Optimization." AppliedMechanics and Materials 66 (2011): 1199-1206.[4] Burton, Tony, et al. Wind energy handbook. John Wiley & Sons, 2011.

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Introduction Methods & Results

Design Scenario

References

Material Selection for a Lightweight and Sustainable Off-shore Wind Turbine Blade

Conclusions

shell

girder

Edge-wise

Flap-wise

Figure 1. Components of the blade and its analysis model

the

coup

ling

line

appr

oach

Minimize mass (materials with X on its label are eliminated)

Minimize cost (materials with X on its label are eliminated)

Minimize embodied energy (materials with X on its label are eliminated)

Under Strength & Stiffness Constraints

the

trade

-off

surf

ace

appr

oach

Trade-off between mass and cost

Trade-off between mass and embodied energy

Trade-off between cost and embodied energy

Under Strength Constraint

10 of 100 materials are left aftersetting constraints through the limit tool;

5 materials with poor performanceare ruled out through coupling lines;

CFRP, Cast Al-alloys and stainlesssteel are non-dominated solution inmost of the trade-off strategies.

Hybrid Synthesizer

Further StudyAmong all 29 kinds ofCFRP in level 3 energydatabase, the one withepoxy as its matrix andhigh strength carbonfiber as its filler is thebest material choice.More specifically, usingthe hybrid synthesizertool to combine thesetwo source materials bydifferent ratios, a newCFRP with a 70% reinforcement volume fraction that offersbetter compromise between mass and cost is obtained.

𝑚𝑚1 = 𝑚𝑚2 => 𝑀𝑀1 = 𝐿𝐿2

4𝑏𝑏𝛿𝛿𝑀𝑀2 = 𝐶𝐶𝑀𝑀2.

Coupling lines log 𝑀𝑀1 = log𝑀𝑀2 + log 𝐶𝐶Assume 𝐶𝐶 = 𝐿𝐿2

4ℎ𝛿𝛿are from 100 to 1000.

Exchange constants for penalty function

Cost Mass Embodied energy

𝛼𝛼1= 1 𝛼𝛼2 = 10 𝛼𝛼3 = 2 × 10−6

Among these three materials,CFRP is the optimal one based on theexchange constants set in thisproject, which indicates minimizingmass is the critical objective.