wind power application.docx

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Application of Fiber-Reinforced Composites in

Wind Turbine Blades

Jin Xu

College of Textiles and Clothing, Yancheng Institute of

Technology, Yancheng, Jiangsu, China

[email protected]

Zhenqian Lu

College of Textiles and Clothing, Yancheng Institute of

Technology, Yancheng, Jiangsu, China

Abstract — Wind turbine blades are the key components

in the wind power generation system. Fiber-reinforced

composites in wind turbine blades are widely used in the

development of large-scale wind turbines. The advantages

of fiber-reinforced composites and the characteristic of

reinforced fibers are introduced. The structure of fiber

aggregation is enumerated and their advantages and

disadvantages are analyzed. The development of wind

turbine blades is presented.

Keywords — blade; composite; reinforced fibers; fiber

aggregation

I. INTRODUCTION

With the global energy crisis becoming more and

more serious, and the public’s increasing demand for

improving the ecological environment, wind energy is

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a type of renewable energy. It is also a kind of green

energy that receives more attention from governments.

To encourage wind power, about fifty countries have

promulgated relevant laws and regulations to support

the development of renewable energy. China also

announced a policy to support wind power.

The wind turbine blade (fan blade) technology is the

core technology of the wind turbine, and costs about

15%-20% of the total cost. The airfoil design and the

structure of the blade directly affect the performance

and power of the wind power equipment, which is the

core part of wind generator. Because of the large size

and complex shape of the fan blades, there are higher

demands for strength and stiffness, designation

precision, surface roughness and uniformity in terms of

quality. The fiber-reinforced composites can meet these

requirements. These blades have been widely used in

large wind turbines.

II. ADVANTAGES OF FIBER-REINFORCED COMPOSITE

The shape and load of the blade is rather complex

and there are higher requirements in dimensional

accuracy, surface finish and quality distribution.

Therefore, there are many problems in making and

using metal blades, including complex processing

using many types of technical equipment, a long



production cycle, higher labor intensity and lower

finished production. Modern fan blades are textile

reinforced composite with a large-scale composite

structure. Compared with the metal blade, the

composite blade has the following advantages [1].

A. Light weight, high strength, and stiffness

According to the mechanical characteristics of the

wind turbine blade, they are design with strength and

stiffness. The fibers are light because they are arranged

in the main direction of force.

B. Simple molding process

To gain maximum pneumatic power, the blade needs

to possess a complex shape. It’s very difficult to make

medium or large leaves in a metal blade. The molding

process of a reinforced composite blade can be simple,

as long as there is a mold and the surface of blade is

smooth with the precious blade shape.

C. Good anti-vibration, and natural frequency can be

designed

Even though the damping of the reinforced

composite is big, it has good anti-vibration. The natural

frequency can be designed in a wide range to avoid the

resonance area.

D. Imperfection sensitivity of reinforced materials with

high fatigue



Gap extension restricted by the intact fibers can

improve the security of blade.

E. Good corrosion resistances and weather resistance

The composite blade can have a good acid and

alkali resistance, water resistance, climate resistance

and other properties by selecting suitable raw

materials.

F. Simple and easy to maintain and repair

The composite blade generally does not need repair

except for proper maintenance each year such as

uniformly painting the outer surface.

III.SELECTION OF REINFORCED FIBER MATERIAL

978-1-4244-8921-3/10/$26.00 ©2010 IEEE A. E-type glass fiber

The molecules of a glass fiber arrange in

three-dimensional network, so the glass fiber is

isotropic [2]. E-glass fiber is a kind of glass fiber with

low alkali and excellent strength, stiffness, ductility,

insulation, heat resistance and moisture resistance. It is

the primary reinforced material of wind turbine blades,

having low cost and good applicability. It is a better

match with many resins, and the molding process.

However, as the density of the E-type fiber is large, it

is generally used in smaller blades (about 22 meters).

More suitable materials will be applied in large-scale

blades.



B. S-type glass fiber

When there is a high requirement for the strength

and stiffness of blades, the high-strength S-type glass

fiber with a higher price can be used. The S-type glass

fiber is a glass fiber with higher strength, modulus, acid

resistance and heat resistance than the E-type. It also

has good performance for impact. Its modulus can

reach 85.5Gpa, which is 18% higher than the E-type

glass fiber, and 33% higher in strength [3]. From a

technical point of view, people will show interest in the

wind turbine blade with high strength and fracture

strain applied, but its price has been high (much higher

than E-type) so it did not become the mainstream of

leaf reinforcement. Currently, some producers see the

potential of the S-type glass fiber in the wind energy

market, so they are developing the S-type to cut down

its prices.

C. Carbon fiber

The longitudinal strength of high strength carbon

fiber is 2.2 - 4.0Gpa and the longitudinal modulus of

high modulus carbon fiber is 350 - 700Gpa. The

following are recently developed carbon fibers. The

strength and modulus of T1000 made by Japan is

respectively 9Gpa and 300-350Gpa. The strength and

modulus of N60J carbon fiber is respectively 5Gpa and



700Gpa. As the density of carbon fiber is only 1.76～

1.81g/cm3

, the specific strength and stiffness is high. It

has good heat resistance, corrosion resistance, damping

and X-ray and other characteristics. It also provides the

resin matrix composite materials with electrical

conductivity and thermal stability [4-5]. In addition, the

diameter of a carbon fiber is only 8μm; the matrix is

more rigid, and its surface can be treated by different

methods (oxidation, coating, electrolysis, and

plasma, etc.) to integrate with the substrate, which can

be better reinforced material, so it is suitable for a wind

new leaf material, but its price is higher.

D. Other high performance fibers

Some new fibers can be used as candidates, such as

aramid fiber, ultra-high molecular polyethylene fiber,

basalt fiber and so on. Aramid fiber belongs to organic

fibers. Its degree of axial orientation is very high and

the longitudinal tensile strength and modulus is high,

while its weight is light with higher strength and

stiffness than other organic fibers. What’s more, it

tolerates temperatures well. Basalt fiber is a new type

of organic fiber, which is drawn from a melted state at

high temperature. It has the same mechanical properties

as S2 glass fiber, but with better acid and temperature



resistance. The main properties of all fibers are shown

in Table 1. In addition, to reduce costs, we can mix

several fibers, such as carbon/glass fiber, carbon

fiber/light wood/ E glass fiber hybrid and so on. Hybrid

materials are seen as a means to access high strength

and stiffness with low cost.

TABLE 1PROPERTIES OF REINFORCED FIBERS

Type

Tensile

strength

/GPa

Tensile

modulus

/GPa

Density

g/cm3

Elongation

%

E-type glass

fiber 3.1 74 2.54 2.5-3

S-type glass

fiber 4.6 90 2.5 4.0

Carbon fiber 5.5 294 1.76 1.9

Aramid fiber 2.8 124 1.44 2.8

Polyethylene



fiber 3.0 172 0.97 2.7

Basalt fiber 3.0～4.8 79.3～

93.1 2.80 3.1

IV.SELECTION OF FIBER ASSEMBLY

Requirements applicable for composite fabrics

include a linear, planar and three-dimensional structure.

The processing methods are organic woven, knitted,

woven and non-woven, those used in the wind turbine

blade are organic fabrics or knitted fabrics. The

following describes their structures and characteristics.

A. Woven fabric

This is a common fabric made of two or more

groups of yarn that interweave, as shown in Fig. 1. The

structure can be designed with good nature, its warp

and weft show good stability and large surface

coverage factor. Currently plain weave fabric, side flat

organizations, twill weave and stain weave are used in

composite materials. The disadvantage of this fabric is

anisotropy, finite deformation that limits its

applicability, poor sheer resistance performance in

surface causing difficulty in weaving the opening

component, and the yarn crossing curls as reduced

shrinkage yarn tension on the delivery of efficiency.

In order to overcome the shortcoming of anisotropy

this ordinary fabric has, a three axial plane fabric has been developed, using three yarn systems with

cutting



angle of 60° as shown in Fig. 2. In the oblique direction,

the fabric stiffness and strength is the same as that of

other parts. Therefore, the three axial plane fabric is

isotropic. At same time, the fabric’s plane sheer

stiffness is high and its uniformity can create an open

structure.

In order to overcome the loss of strength caused by

the blending of yarns and the disadvantage of low

intensity in a two-dimensional layer, three-dimensional

woven fabric can be used as shown in Fig. 3. The

structures of the fiber in warp and broad wise can be

designed for a non-curled shape, which means high

strength and high stiffness are retained. Z-fiber

improves the fracture toughness and the poor damage

of composite materials. Considering the costs of

manufacturing, because the structure allows resin

infusion faster, it shortens the working hours; the shape

is thicker, reducing the number of levels, saving labor,

and therefore lower manufacturing costs.

Fig. 1. Structure of general woven fabrics

Fig. 2. Structure of three-directional fabric

Fig. 3. Structure of three-dimensional fabric

B. 3.2 Knited fabric

Knitted fabric is formed by one or more root of

spun yarn. The area of the structure of the knitted



fabric can change greater than the woven fabric. The

structure of both warp and weft has rather large

extension in all directions, so it can well adapt to the

deep drawing formed composited material. Knitted

fabric can be divided into warp and weft. The biaxial

and multiaxial fabric can be formed by pad yarn, which

can give the best stability to structural materials.

1) Warp knitted fabric

Warp knitted fabric is formed by a group, or several

groups, of parallel yarns feeding through the warp

knitting machine needle simultaneously forming into a

circle. Figures 4 - 6 show the structures of uniaxial,

biaxial and multiaxial warp knitted fabrics.

Fig. 4. Structure of uniaxial warp knitted fabric

Fig. 5. Structure of biaxial warp knitted fabric

Fig. 6. Structure of multiaxial warp knitted fabric As the mechanical characteristics and the sizes of

the various parts of the wind turbine blades are

different, the biaxial, three-axial, and four-axial warp

knitted fabrics are applied to the wind turbine blades

[6]. Warp knitted fabric has the characteristic of good

dimensional stability, falls of easy, smaller extension

and so on. It can reasonably use the good performances

of each component in material. The warp knitted fabric

as the composite material with its structural diversity,

the integrated performance, the designable form, good



shape and the permeability to enhance the framework,

has gained wide attention in the wind turbine blade and

industrial areas.

2) Weft knitted fabric

In the weft knitting process, the yarns on the loom

are in order forming coil rows, which are woven in

weft into weft knitted fabric. The multi-layer biaxial

and multi-axial fabrics can be developed by adding

directional yarns. Figures 7 - 8 shows the structures of

multi-layer biaxial and multi-axial fabrics.

Fig. 7. Structure of biaxial weft knitted frabic

Fig. 8. Structure of multi-axial knitted fabric

In the multi-axial knitted fabric, the yarn in each

layer is very strict, therefore, we can take full use of the

performance of the yarn to create fabric with high

tensile strength, but it’s time to tear, the parallel

arrangement of the yarn layer will produce the

phenomenon of agglomeration, so the fabric has a high

tear strength.

Multi-layer biaxial and multiaxial wefts knitted

fabrics have better formability because of the

characteristics of the weft structure. Therefore, it has

excellent application prospects used in the structure of

blades.

V. CONCLUSION



Compared with other materials, fiber-reinforced

composites are used in the wind turbine blades, which

have the absolute advantages of flexible design, good

vibration in use, good fatigue resistance, corrosion

resistance, weather resistance, easy maintenance and so

on. Blades made of glass fiber-reinforced composite

are mostly used. As the leaves move forward to being

large, lightweight, environmental protected and with

the growing development of high-performance fiber

materials, the blades will go to the direction of carbon

composite, carbon/light wood/glass hybrid composite

and thermoplastic composite.

REFERENCES

[1] G. X. Qiu, L. S. Liu, and Y. M. Jiang, “Textile composites and

wind power,” Science of Textile, 2006(5): pp. 56-61.

[2] X. M. Tao, X. J. Xi, and G. X. Gao, Textile Structural

Composites, Science Press, 2001.

*3+ X. F. Xie, and Z. H. Bi, “New progress of abroad wind turbine

material,” FRP, 2006, (4): pp. 21-25.

*4+ Y. Pan, Z. P. Zhou, and J. Wang, “Overview of wind turbine

blade technology,” Hunan University of Technology, 2007, 21

(3): pp. 48-51.

*5+ S. J. Shao, S. H. Shen, and H. S. Xu, “Composite materials

and wind turbine blades,” Nameable Energy, 2008, 26 (2): pp.

90-92.



*6+ L. J. Li, G. M. Jiang, and X. H. Miao, ”Multi-axial warp

knitted fabric applied in the wind power,” Science of Textile,

2009 (5): pp. 68-72.

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