Carbon Fiber Fuselage Research Report

Carbon fiber reinforced
polymer as a Material for
Airliner Fuselages:
A Research Study and Cost-
Benefit Analysis
Kristopher Kerames
12/10/18

Kerames Carbon Fiber Reinforced Polymer ENGR-A210-26848
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Table of Contents
1 Abstract...............................................................................................................3
2 Introduction.......................................................................................................4
3 Properties............................................................................................................5
3.1 Types and Properties of CRP….........................................................................5
3.2 Mechanical, and Other, Physical Properties......................................................6
4 Structure..............................................................................................................8
4.1 Composition.......................................................................................................8
4.2 Atomic Structure................................................................................................8
4.3 Microstructure..................................................................................................10
4.4 Development of Microstructure.......................................................................11
4.5 Alteration of Physical Properties In Development of Material.......................11
4.6 Phase Transformations.....................................................................................12
5 Manufacturing................................................................................................13
5.1 Fabrication Process..........................................................................................13
5.2 Alteration of Mechanical Properties................................................................14
5.3 Cost..................................................................................................................14
6 Conclusion.......................................................................................................16
7 References........................................................................................................17

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1 Abstract
There are a variety of materials to choose from when manufacturing the fuselage of an
airliner. Optimal materials should be used that best suit their characteristic flight patterns.
Namely, materials, which will minimize cost and maximize benefits such as safety, and
reducing overall flight times. The objective of this research project is to identify those
materials, and explore the reasons why they are the best choice when manufacturing an
airliner’s fuselage. All suggestions in this study regarding the manufacturing of a
fuselage will be in reference to airliners only. Airliners fly at subsonic speeds, meaning
that heating due to friction is not as significant as it is for high-speed airplanes. This
means materials can be used that have moderate heat resistance properties. The fuselage
accounts for a large percentage of the plane’s total weight, so using lightweight materials
will increase the plane’s carrying capacity, increase its top speed, and lower its fuel
requirements. These materials must also have a high strength in order to improve the
plane’s structural integrity. Choosing materials with a high specific strength will take
both weight, and strength requirements into account. The material that is best suited for
the fuselage in most cases is a carbon fiber reinforced epoxy composite. With the help of
automated machinery, manufacturing with carbon fiber is a fairly simple process when
compared to manufacturing with other materials. Automated machinery weaves the
carbon fiber so it is aligned in the direction of longitudinal and transverse stresses. Then
it can be wrapped around a mold, covered with an epoxy coating, and heated until cured.
Carbon fiber composites have a mid-range cost when compared to other popular
materials for fuselages, but they increase the plane’s fuel efficiency, and have a lower
rate of failure after repeated flights lowering costs of fuel and repairs over time. These

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advantages to carbon fiber composites, and relatively low costs, make it the best material
for constructing a fuselage in the long-run.
2 Introduction
The fuselage is the main body of an aircraft. The optimal material for constructing
the fuselage is one that is the most appropriate for that aircraft’s function. In the case of
an airliner, the plane flies at subsonic speeds, and so heat from friction is not significant.
So expensive, heat-resistant, materials like titanium are unnecessary in the construction
of the fuselage. To minimize risk and lower maintenance costs, the fuselage must have a
high strength. Because airliners travel long distances, they also benefit from lightweight
materials because they increase range, and decrease fuel costs. Carbon fiber composites,
or carbon-reinforced polymers (CRP), exhibit all of these beneficial characteristics, and
are the optimal material for a fuselage. The manufacturing of CRP also requires the
implementation of equipment to align or weave the fibers, and to wrap them around a
large mold. For these steps, the use of automated machinery is imperative. The
implementation of which can be costly for airplane manufacturers who already have other
manufacturing equipment in place. The cost of the carbon fiber itself is about $20/kg.
This costs more than aluminum, but less than titanium, which are the other most common
materials used in the construction of aircraft. However, the operating cost of using CRP is
significantly lower than aluminum due to the lower weight and resulting fuel usage. So
the long-term benefit is worth the investment in equipment used to produce the CRP
fuselage. Due to the many benefits of using CRP, companies like Boeing are
implementing CRP’s into the construction of their planes’ fuselages like in the 787
Dreamliner. Airbus also recently produced the A350 XWB, an airliner with a CRP

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fuselage. The CRP used by Boeing, incorporates a prepreg T800S carbon fiber. T800S
fibers are some of the highest tensile strength fibers in production. A prepreg carbon fiber
is one that has been presoaked in an epoxy so that the epoxy is evenly distributed
throughout the fiber. In this case, the epoxy makes up about 35% of the composite. It also
contains a curing agent, so all that is necessary to cure the CRP is heat and pressure. Due
to the long-term benefits of using CRP, Boeing and Airbus have plans to roll out more
airliner models constructed with CRP in the future. [1]
3 Properties
The most popular materials in the airliner industry are aluminum, titanium, and
CRP. Because CRP provides the most benefits per cost, this analysis will focus on the
properties of that material, and compare them to the other two materials.
3.1 Types and Properties of CRP
CRP can vary by choosing between various carbon fiber types with different
tensile strengths and density of fibers. The fibers themselves can be aligned in the epoxy
at either 0º or 90º.
Different Fiber Types and Their Strengths
Fiber Tensile Strength (ksi)
T800H 796
T800S 853
T1000G 924
T1100G 1017
T1100S 1017
Figure 3.1.1 [2]

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Figure 3.1.1 shows different carbon fiber types provided by the Japanese
company, Toray. They do not share costs online, but prices of their carbon fiber increase
from the top of the table to the bottom.
The types of polymers that can be used in the matrix of these composites are
epoxy, phenolic, polyester, and vinyl ester. They are typically used in different ratios
with epoxy making up the majority of the matrix. [2]
3.2 Mechanical, and Other, Physical Properties
T800S CRP is among the most widely used in commercial airliners, and will be
the composite considered in this analysis.
Properties of T800S CRP
Property Metric Unit
Tensile Strength 3,290 MPa
Compressive Strength 1,490 MPa
Flexural Strength 1,700 MPa
ILSS 87.9 MPa
In Plain Shear Strength 135 MPa
90° Tensile Strength 79 MPa
Specific Heat 0.740 J/g ·°C
Thermal Conductivity 0.113 J/cm ·s·°C
Figure 3.2.1 [2]
CRP has a particularly high Tensile strength, low specific heat, and a large
flexural strength all while being low-weight. This translates to having high rigidity, and a
high specific strength. Other properties of CRP include corrosion resistance, fatigue
resistance, fire resistance, and a low coefficient of thermal expansion. These properties

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make it a safe material up in the air, and one that is less likely to fail over time. The
fatigue resistance and a low coefficient of thermal expansion make CRP less likely to fail
after repeated cycles of temperature and pressure changes. [4]
Strength v. Density of Various Materials Used in Aerospace
figure 3.2.2: In this figure, “CFRP” refers to carbon fiber reinforced polymer, which is
the same as CRP [3]
From figure 3.2.2 above, we can see that the specific strength of aluminum is
about 100MPa/3,000kg•m3
= 3.0E-2 MPa/kg•m3
. Titanium alloys have a specific
strength of about 1000MPa/5,000 kg•m3
= 2.0E-1MPa/kg•m3
. CRP has a specific
strength of about 1000MPa/2,000 kg•m3 = 5.0E-1MPa/kg•m3 . Compared to titanium and
aluminum, CRP clearly has a higher strength to density ratio. This makes it one of the

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lightest materials that can be used in the production of a fuselage without sacrificing
structural integrity. In fact, CRP improves structural integrity of the fuselage because of
its relatively higher tensile strength. [3]
4 Structure
The structure of CRP is very different from the metal alloys that are typically used
in the construction of fuselages. Knowledge of this structure can help in the
manufacturing of a stronger fuselage. By aligning this structure in the proper direction,
the strength properties of the material are maximized.
4.1 Composition
CRP is made up of carbon fibers inside of a polymer resin matrix. The fibers form
multiple strips called, “tow”,
which are either aligned at 0º
or woven at 90º. The polymer
matrix is composed of epoxy,
and a small percentage of
phenolic, polyester, and vinyl
ester.
figure 4.1.1: A picture of CRP with fibers aligned at 0º [6]

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4.2 Atomic Structure
The carbon fibers are made up of chains of carbon atoms that are bonded together.
The polymer matrix surrounding the atom is made up of mostly epoxy resin, and a curing
agent, which is usually polymercaptan. Figure 4.2.1 below shows these chains. [6]
figure 4.2.1: carbonized polyacrylonitrile fibers [5]
An image of the epoxy resin, before and after being cured, is shown below.
Curing the epoxy involves the reaction of diamene with the epoxy group, then the
crosslinking of molecules. [7]

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figure 4.2.2: An image of epoxy curing at the molecular level [7]
4.3 Microstructure
The carbon fibers have a rough coating after being formed. This coating can be
left on, or stripped off to create denser carbon fiber tow. Each fiber is between 5-10µm in
diameter. These fibers can be aligned at 0º in the polymer matrix, or woven at 90º.
Figure 4.3.1: Fractured carbon fiber strand. [8]

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4.4 Development of Microstructure
Carbon fiber is made from polyacrylonitrile fibers. These fibers are heated to
about 5,000ºF without oxygen (as to avoid a combustion reaction) until they are
carbonized. This means that the fibers are stripped of all elements other than carbon,
which is left behind in chains. The fibers are then slightly oxidized to promote bonding
with epoxies. The fibers are pre-impregnated with thermoset, usually an epoxy resin
mixed with small percentages of phenolic, polyester, and vinyl ester. This must be kept
away from heat/radiation so the epoxy resin does not cure early. [5]
figure 4.4.1: polyacrylonitrile fibers before they are carbonized [5]
4.5 Alteration of Properties in Development of Material
The two major ways in which the CRP is altered during production are, changing
the alignment of the fibers, and curing the epoxy.
The prepreg CRP is delivered to manufactures before it has been cured. In this
state, it is a liquid. The epoxy is only cured after is has been set in place on a mold. Once

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the thermoset has been cured, it becomes a solid that cannot be melted back into a liquid.
This solid epoxy resin is much more rigid than in the liquid form.
Before the carbon fibers are dipped in epoxy, they can be aligned, or woven at a
90º angle. This changes the direction in which the CRP has the most tensile strength. It
will have the highest tensile strength in the direction of the fibers. [9]
4.6 Phase Transformations
The carbon fiber does not undergo any phase transformation as it remains a solid.
However, the epoxy resin transforms from a liquid to a solid during the curing process
With the help of a curing
agent, the epoxy can be
heated to just above 100ºC
for about two hours to
transform it from a liquid,
to a solid.
figure 4.6.1: phase diagram for typical thermoset [8]

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5 Manufacturing
This section will cover the manufacturing process from when the pre-made CRP
is purchased, to completing the fuselage.
5.1 Fabrication Process
Once a manufacturer obtains the pre-made CRP, they use automated machinery to
weave the fibers, which are pre-impregnated with epoxy, at 90º. This woven carbon fiber
cloth is then wrapped around a fuselage mold. There are three molds; one for the front,
middle, and rear of the fuselage. Once the molds are wrapped with the CRP, they are
vacuum packed and moved into an oven at 120ºC for about two hours to cure. The molds
are then removed, and covered with an electrostatic discharge cloth. This cloth is meant
to discharge electricity in case of a lightning strike. It also creates a smooth, non-porous,
surface to reduce drag. This surface also allows airlines to paint emblems onto the surface
of the fuselage. Cutouts are made in the surface of the CRP such as window cutouts and
holes for fasteners. Then the interior of the fuselage is installed, which contains things
like seating and overhead carrying compartments. The three fuselage modules are then
bolted together with additional sheets of CRP and titanium alloy fasteners. This process is
proprietary so information on the type of titanium alloy is limited. [1]

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figure 5.1.1: rear third of fuselage on Boeing 787-9 after curing epoxy resin [10]
5.2 Alteration of Mechanical Properties
The biggest alteration of mechanical properties comes from lying the CRP at
different angles along the mold depending on which direction the major stresses will be
applied to the fuselage. The majority of stresses will occur in the longitudinal and
transverse directions. These angles will be different in some places, including around the
center segment of the fuselage where the wings will connect. [1]
5.3 Cost
CRP is a relatively costly material in the aerospace industry. However, its long-
term benefits outweigh the cost of the material and production.
The common materials used in the construction of fuselages cost anywhere
between $2/kg-$80/kg. Aluminum costs about $2/kg, Titanium cost about $25/kg-$40/kg.
CRP cost $15/kg-$80/kg depending on the grade of CRP. In the case of Boeing’s 787,
they use a grade of CRP which costs about $20/kg [4]. Because carbon fiber is less than

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half as dense as these metal alloys, its cost per volume is between the cost of aluminum
and titanium.
In order to produce fuselages with CRP, the use of automated machinery is
imperative. The type of machinery and, therefore, their costs are propriety information.
However, even though this equipment is expensive, the lower operational costs of the
lightweight airliners will allow airline companies to make greater profits than with other
materials after they break even. The Boeing 787-9 is estimated to save about 20% of the
fuel that other airliners in its class use. Additionally, the more fatigue-resistant CRP will
require less maintenance costs over time. [4]
Cost of Materials Typically Used in The Production of Airplanes
figure 5.3.1 [11]

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It should be noted that the prices in figure 5.3.1 are by weight, not volume. The
price of aerospace grade CPR by volume is lower than that of titanium.
6 Conclusion
There are many materials that can be used to build the fuselage of an airliner, but
CRP is the best in the long-run. It has the highest strength to weight ratio out of the other
materials, a relatively low cost per unit volume compared to titanium, and is relatively
easy to manufacture once the manufacturing infrastructure is in place. These properties
translate to an airliner with a longer range, lower maintenance costs, and lower emissions.
Ultimately, after breaking even on the cost of manufacturing equipment, using CRP
drives profits while enhancing the safety of airliners.
CRP does have its drawbacks. It is more difficult to repair when something does
go wrong. However, there are ways to avoid this drawback. The polymer matrix can be
toughened with the addition of thermoplastics to increase the fracture toughness and to
minimize damage. Better water-resistant coatings can also be incorporated in order to
prevent water molecules from reaching, and weakening, the CRP. With the addition of
these improvements, the use of CRP in the production of airliner fuselages would have
few drawbacks in the long-run when compared to alternative materials commonly used in
the industry.

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7 References
[1] Dale Brosius. “Boeing 787 Update”. Compositesworld.com. 2007. [online]
https://www.compositesworld.com/articles/boeing-787-update , [Accessed 10
Dec. 2018].
[2] Toray Composite Materials America Inc. “Types of Carbon Fiber”. 2018 [online]
https://www.toraycma.com/page.php?id=661 , [Accessed 10 Dec. 2018].
[3] Amna. “New Alloy is As Strong As Titanium but as light as Aluminum”,
gadgtecs.com. 2 Jan. 2016. [online] https://gadgtecs.com/2016/01/02/new-alloy-
strong-titanium-light-aluminum/ , [Acessed 10 Dec. 2018].
[4] James Mereditha
, Edward Bilsonb
, Richard Poweb
, Ed Collingsc
, Kerry Kirwan.
“A performance versus cost analysis of prepreg carbon fibre epoxy energy
absorption structures”, sciencedirect.com, June 2015, [online]
https://www.sciencedirect.com/science/article/pii/S0263822315000343 ,
[Accessed 9 Dec. 2018]
[5] “Materials Chemistry,” Maritime Theater. [online].
http://web.mit.edu/3.082/www/team2_f01/chemistry.html. [Accessed: 10-Dec-
2018].
[6] Element6composites. “What is Carbon Fiber?”, element6composites.com, 2018,
[online] https://element6composites.com/what-is-carbon-fiber/ , [Accessed 11
Dec. 2018]
[7] Jeffrey Gotro. “Thermoset Cure Chemistry Part 3: Epoxy Curing Agents”,
polymerinnovationblog.com, 17 March 2014, [online]
https://polymerinnovationblog.com/thermoset-cure-chemistry-part-3-epoxy-
curing-agents/ , [Accessed 8 Dec. 2018]
[8] Yan Jia, Kezhi Li, Li zhen, Xue Junjie, Ren Shouyang, Zhang Xinmeng.
“Microstructure and mechanical properties of carbon fiber reinforced multilayered
(PyC–SiC)n matrix composites”, Materials & Design, 5 Dec. 2015, [online]
https://www.sciencedirect.com/science/article/pii/S0264127515300927 ,
[Accessed 9 Dec. 2018]
[9] Professor Cogdell, Mohammad Ali. “Raw material life cycle in Boeing 787
Airframe”, designlife-cycle.com, 1 Dec. 2016, [online] http://www.designlife-
cycle.com/boeing-787/ , [Accessed 8 Dec. 2018]
[10] “Forward fuselage of the 787 on a mandrel. Credit: Boeing.,” TESLARATI.com,
2017, [Online]. Available: https://www.teslarati.com/spacex-bfr-tent-spy-shot-
mars-rocket-tooling-molds/forward-fuselage-of-the-787-on-a-mandrel-credit-
boeing/. [Accessed: 10-Dec-2018].

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[11] Rao, S., Rao, S. and Kumar, R. (2018). Carbon composites are becoming
competitive and cost effective. [online] Infosys.com. Available at:
https://www.infosys.com/engineering-services/white-papers/Documents/carbon-
composites-cost-effective.pdf [Accessed 9 Dec. 2018].

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