1. 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 =
𝜌𝜌
𝜎𝜎𝑦𝑦
from 𝑚𝑚1 =
6 ℎ+𝑏𝑏 𝑀𝑀𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒
𝑏𝑏(𝑏𝑏+3ℎ)
𝜌𝜌
𝜎𝜎𝑦𝑦
• Stiffness: not deflect too much under wind load
Material Index 𝑀𝑀2 =
𝜌𝜌
𝐸𝐸
from 𝑚𝑚2 =
3 ℎ+𝑏𝑏 𝑀𝑀𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 𝐿𝐿2
2b2(𝑏𝑏+3ℎ)𝛿𝛿
𝜌𝜌
𝐸𝐸
• 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 wind
turbine, this project aims to minimize its weight and
enhance its sustainability for a offshore wind turbine
from the material selection perspective. Desired
materials needs to exhibit high strength/stiffness to
density ratios and low environment impacts to make the
blade structural effective and eco-friendly.
Most offshore wind turbines are larger than those on land
and installation is difficult and expensive. In addition, the heavier
the blade, the heavier the tower so that the more costly it is to
produce, transport, and install. Thus minimizing mass is the
critical objective for offshore wind turbine blades.
CFRP, cast Al-alloys and stainless steel are the three best
materials for offshore wind turbine blades, among which CFRP
offers highest strength/stiffness-to-density ratio. Conversely, it is
harder to achieve sufficient stiffness for steel and aluminum on a
long blade without adding excessive weight.
Although the price of CFRP is higher than other two
materials, CFRP will exhibit its advantage when it comes to
reducing the overall cost of building a complete wind turbine.
CFRP and stainless steel make blades maintain lower
embodied energy but compared to other two metal materials,
CFRP is normally unrecyclable at present.
In conclusion, CFRP is the best material for a lightweight and
sustainable offshore wind turbine blade. With development of
the material technology, CFRP will be more competitive in the
future. Also, it is very promising to combine CFRP with aluminum
to create more innovative materials which has a lower price.
CEE 574 / ARCH 595 · Material Selection for Sustainable Design · Term Project · 2014 Fall
Rui 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." Applied
Mechanics and Materials 66 (2011): 1199-1206.
[4] Burton, Tony, et al. Wind energy handbook.
John Wiley & Sons, 2011.
.
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
thecouplinglineapproach
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
thetrade-offsurfaceapproach
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 after
setting constraints through the limit tool;
5 materials with poor performance
are ruled out through coupling lines;
CFRP, Cast Al-alloys and stainless
steel are non-dominated solution in
most of the trade-off strategies.
Hybrid Synthesizer
Further Study
Among all 29 kinds of
CFRP in level 3 energy
database, the one with
epoxy as its matrix and
high strength carbon
fiber as its filler is the
best material choice.
More specifically, using
the hybrid synthesizer
tool to combine these
two source materials by
different ratios, a new
CFRP with a 70% reinforcement volume fraction that offers
better compromise between mass and cost is obtained.
𝑚𝑚1 = 𝑚𝑚2 => 𝑀𝑀1 =
𝐿𝐿2
4𝑏𝑏𝑏𝑏
𝑀𝑀2 = 𝐶𝐶𝑀𝑀2.
Coupling lines log 𝑀𝑀1 = log 𝑀𝑀2 + log 𝐶𝐶
Assume 𝐶𝐶 =
𝐿𝐿2
4ℎ𝛿𝛿
are 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 the
exchange constants set in this
project, which indicates minimizing
mass is the critical objective.