Santa Clara University Department of Mechanical Engineering

The Koinsegg Aircore Carbon Fiber Wheel

Authors:

Chris Clark W1024411 Marcus Grassi W0978852

Michael D’Arrigo W0985012

Mech 11: Materials and Manufacturing 16082

Winter 2015 P. Sepehrband

Due: Thursday, March 12, 2015

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Table of Contents Section Page Number

• Introduction……………………………………………………………………………5

• What is Carbon Fiber?...................……………………………………………………6

• Description of Material……………………………………………………………..…6

o General Production Processes…………………………………………..…6

o Types of Carbon Fiber and Mechanical Properties……………………..…8

• Justification for Use of Carbon Fiber in Automobiles……………………….……..…9

o Elevated Handling Capabilities……………………………………………9

o Appearance………………………………………………………………10

o Corrosion Resistance………………………………………….…………10

o Fatigue and Safety………………………………………………………..10

o Cost Versus Reward………………………………………..…………….11

o Cons of Carbon Fiber……………………………………………….……11

• Koenigsegg Aircore Carbon Fiber Wheels……………………..……………………12

o Production Processes…………………………………………………….12

§ First Stage…………………………………………………......…12

§ Second Stage……………………………………………..………12

o Balancing…………..………………………………………………….…13

o Safety Aspects of the Wheel……………………………………………..13

o Final Surface Quality………………………………………………….....13

• Working Conditions of the Koenigsegg Agera R……………………………....……14

• Conclusions and Summary……………………..……………………………………15

• References……………………………………………………………………………16

o Informational Sources……………………………………………………16

o Image Sources……………………………………………………………16

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List of Figures Figure Page Number Figure 1 5 Figure 2 6 Figure 3 7 Figure 4 8 Figure 5 9 Figure 6 12 Figure 7 13

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List of Tables Section Page Number Table 1: Material Properties Comparison 9 Table 2: Koenigsegg Agera R Specifications

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Introduction

Knowledge of a material’s mechanical, metallurgical and surface properties is

paramount when selecting a material for different applications. The push for

development and manipulation of new materials is fueled by the ever-changing

imaginations of today’s engineers. Engineers work to select appropriate materials based

on the working conditions that the part will face during use.

The world of supercars and auto racing is one particular sector that has always

been at the forefront of developing new materials. This exciting domain is often so

groundbreaking because dangerously high speeds are always the ultimate goal, and price

is rarely a limiting factor. One particular firm of interest is the award-winning Swedish

company, Koenigsegg. Founded in 1994 by Christian Von Koenigsegg at the age of 22,

Koenigsegg Car Company continues to push the boundaries of supercar production.

These vehicles are renowned for their blistering speed and beautiful aesthetics both on

and off the racetrack. One particularly model, the Koenigsegg Agera R, is particular

interesting from an engineering perspective because it is the first production car that

utilizes all carbon fiber wheels. [1] Figure 1: [f.1]

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What is Carbon Fiber? Description of Material

Carbon fiber is a composite material, meaning it is made up of two or more

chemically or physically different materials in order to create one new material that

possesses more preferable material properties than each original constituent material.

Carbon fiber can be more specifically classified as a type of reinforced plastic. Other

names for reinforced plastics include polymer-matrix composites (PMC) and fiber

reinforced plastics (FRP). Reinforced plastics comprise fibers laid in a polymer matrix.

Some of the characteristics of these materials that make them so useful include very high

strength to weight ratios, high stiffness to weight ratios, high toughness, good fatigue

limits, and good creep resistance. [2]

The matrix materials in reinforced plastics

add transverse stiffness, as the fibers themselves

are only longitudinally stiff. Therefore, the

direction of the fibers is very important. Matrix

materials also keep the fibers in place and transfer

the majority of the load in the composite material

onto the fibers. Matrix materials protect the fibers

against the elements and physical damage, as well

as slow the propagation and spreading of cracks in

composite materials. In the case of carbon fiber

composites, the matrix provides ductility while

the fiber contributes strength. The most commonly used polymer matrix material for

carbon fiber is a thermoset epoxy. [2] The epoxy is usually comprised of two parts, a

resin and a hardener, that form a strong adhesive when mixed together. The high

corrosion resistance of carbon fiber is due largely to the extreme corrosion resistance of

epoxy.

General Production Processes

Carbon fibers are produced during a heating process known as pyrolysis.

Pyrolysis is the thermochemical decomposition of organic material at elevated

temperatures in the absence of any oxygen and all halogens. [3] This is an irreversible

Figure  2:  [f.2]  

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process, and involves the simultaneous change of chemical composition and physical

phase. The organic material used in construction of carbon fibers is commonly

polyacrylonitrile (PAN) because this material produces carbon fiber with very high

tensile strength. Rayon and Pitch, which are based on coal tar and petroleum products,

can also be used as organic material for the construction of carbon fibers. However, PAN

carbon fiber is more highly favored in engineering applications, but also more expensive

than Rayon and Pitch carbon fiber. The carbon fiber mainly discussed in this project, the

fiber used in the Koenigsegg Agera R’s Aircore carbon fiber wheels, is PAN based.

The construction of PAN based carbon fibers begins when Acrylonitrile is mixed

with another plastic, either methyl acrylate or methyl methacrylate. After the addition of

a catalyst, this mixture becomes polyacrylonitrile plastic, which is spun by extruding the

mixture into a quenching chamber that solidifies the plastic into fibers. Then, the fibers

can be stretched until they have the desired diameter. Before carbonization, the fibers are

drawn through heating chambers in order to stabilize their atomic bonds into a more

thermally stable pattern. This heating process takes place between 200 to 400 degrees

Celsius for a duration of 30 to 120 minutes. The only limiting factor is overheating the

fibers. The fibers are then pyrolyzed (or carbonized) at temperatures ranging from 1500

to 3000 Celsius. When PAN fibers are pyrolyzed, the elevated temperatures expel

hydrogen and nitrogen,

leaving tightly bonded

carbon crystals. The

resulting fibers are

surface treated either

electrolytically or

through oxidation to

ensure that the surface

will bond well with the

epoxy matrix material.

Lastly, the treated fibers

are coated in epoxy to

Figure 3: [f.3]

 

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prevent damage during weaving before being wound onto bobbins. These bobbins are

then shipped to weavers or prepreggers who form the carbon fibers into the desired final

structure. [4]

Types of Carbon Fiber and Mechanical Properties

A general comparison of a material typically involves analyzing the material

properties in terms of strength to weight ratio and stiffness to weight ratio. Considering

these ratios is especially crucial in racing applications when attempting to design a car

that can withstand constant forces due to bumps, centripetal force, friction, and heat.

Carbon fiber is a material that is incredibly strong, stiff, and extraordinarily lightweight

in comparison with other materials such as aluminum and steel. A material’s strength is

typically determined by its ultimate tensile strength and the material’s stiffness is

determined by its modulus of elasticity.

The carbon fiber composite materials are known for having low density, high

strength, and high stiffness. The composition is also known as carbon fiber reinforced

plastic (CFRP). Carbon fibers are at least 90% carbon by composition and consist of

amorphous (non-crystalline) carbon. Carbon fiber is generally grouped into two

categories, high strength and high modulus. For these two different types, the density

remains constant while other material properties change.

Figure 4: [f.4]

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Table 1: Material Properties Comparison

Material Tensile Strength

(MPa)

Elastic Modulus

(GPa)

Density

(kg/m^3)

High Strength

Carbon Fiber

3000 275 1900

High Modulus

Carbon Fiber

2000 415 1900

4130 Steel 670 205 7850

2023-T3

Aluminum

483 73.1 2780

[1], [5]

Justification for Use of Carbon Fiber in Automobiles

Elevated Handling Capabilities

The use of carbon fiber is justified

in performance vehicle applications for

several reasons. Often, much of a supercar

is made of carbon fiber. Specifically,

wheels are one of the most important areas

to reduce weight, because a car’s wheels

are “rotational unsprung mass.” [1] This

means that the wheel is not only bumping

up and down with the vehicle’s suspension

components, but also has angular momentum from rotating at great speeds. Additionally,

this angular momentum changes direction as the car is steered by driver input.

Minimizing the weight of such a part diminishes the forces that the wheel imparts on the

car as a whole, and enables better handling capabilities. This makes the supercar easier

to control by giving it better traction, allowing the driver to capitalize on increased

precision in a racing environment.

Figure  5:  [f.5]  

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Because less weight in the wheels leads to less force on the car, carbon fiber

wheels also decreases overall stopping distance and increases acceleration abilities.

These qualities are important for instances such as needing to reduce speed before

entering a tight corner on a racetrack, or gaining an advantage when accelerating at the

starting line.

Appearance

Carbon fiber wheels are also a good choice for high-end car applications because

of their desirable appearance. Carbon fiber is inherently aesthetically pleasing because it

has a nice checkerboard pattern by nature, and is shiny with only minimal amounts of

polishing. In addition, it looks futuristic and sporty, adding to the overall list of benefits

that carbon fiber has to offer. Corrosion Resistance

The increased corrosion resistance of carbon fiber helps to justify its application

in motorsport greatly. The racing environment inherently involves many corrosive

chemicals including fuels and cleaning agents used to remove brake dust and other

debris. Even moisture accumulation due to condensation is common in the motorsport

industry, especially on parts that reach high temperatures, including wheels because of

their proximity to braking system components.

Fatigue and Safety

Because carbon fiber has a virtually nonexistent fatigue limit for cyclical loading,

it is well suited for high-speed applications where the safety of the driver is a primary

concern. Failure due to fatigue, can thus be minimized, allowing the operator of the

vehicle and his or her race team to trust in their equipment. This is also important

because the high performance driving and racing environments are inherently more

stressful on a vehicle than everyday commuter driving. Furthermore, wheels made of

carbon fiber will not need to be “overbuilt” to compensate for fatigue over time by

making them stronger than they need to be, as is the case with some materials that tend to

fail from cyclical loading. [1] Overbuilding leads to weight increase, but this issue can be

eliminated altogether with the use of carbon fiber.

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Cost Versus Reward

It is important to recognize the market for any product that is to be considered for

manufacturing. Carbon fiber wheels clearly have a limited eligible consumer base.

Increased cost and the need for elevated performance are only justified for in two cases

for automobiles: first, in high-end performance vehicles that cater to upper class

individuals, and second, in racecars. Expensive consumer vehicles common among

wealthy individuals may include carbon fiber wheels for several reasons. These can

include, but are not limited to: desire for actual performance characteristics and speed,

status related or vanity motives, i.e. simply the desire to possess a top-of-the-line sports

car, or aesthetically driven motives i.e. having nice, beautiful things. In the racing world,

on the other hand, carbon fiber wheels are justified because shaving a few seconds off of

lap times on the track sometimes means million dollar paydays. Anything and everything

that can be done to reduce weight and increase speed is often accomplished by racing

teams that seem to have endless budgets. There are also teams that desire to push

motorsport and its existing boundaries as far as possible for the sake of achievement

itself. However, in everyday driving and normal automobile use, outside factors like

stoplights and traffic make the need for carbon fiber wheels irrelevant.

Cons of Carbon Fiber

Despite the overwhelming amount of benefits that arise from using carbon fiber as

an alternative to other materials, there are also some negative aspects and tradeoffs to

consider. The main concern with carbon fiber is that solid carbon fiber bends under load

but does not plastically deform. [6] As a result, if the ultimate tensile strength is exceeded

then carbon fiber will fail suddenly without warning. This means that although it is

incredibly unlikely for a carbon fiber wheel to fracture from fatigue, if it does there will

be virtually no warning, and catastrophic damages are likely to ensue. Additionally, as

mentioned before, carbon fiber is significantly more expensive than other materials and

more difficult to work with. Creating products made of carbon fiber requires a high level

of expertise, specialized tools, and difficult manufacturing processes. Working with this

material is incredibly expensive and difficult, but if one can master the art and fund the

design process then revolutionary projects can be accomplished.

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Koenigsegg Aircore Carbon Fiber Wheels Production Processes

First stage

In the first stage of the design process, sheets of woven carbon fiber are placed

into a negative tool. Koenigsegg uses the highest quality of commercially available

carbon fiber in their wheels, which is Prepreg. Prepreg is commonly used in formula one

cars, aviation, and aerospace applications. The material is pre-impregnated with a resin

system involving an epoxy and a curing agent. Since the material is already infused with

a resin system it is immediately ready to be placed

in a mold without additional resin or processing.

It is important to note that a releasing agent must

be added to the tool in order to prevent the fabric

sticking. Prepreg is incredibly flexible and is

formatted in a weave pattern that is applied

differently layer by layer depending on the part

that is needed. [1]

Second Stage

In the second stage of the design process, the wheel must be prepared to undergo

heat treatment and curing. The outer part of the tool is covered in different types of

layers, weaves, and overlapping carbon fibers. It is critical that these carbon fibers are

stiff and “locked” into their pattern for handling so that the outer part of the wheel does

not bend. The spokes and center of the wheel are hollow and undergo a specific process

in order to attain this. Unfortunately, this process is one of the company’s many secrets

and was thus not revealed. Once the outer part is covered in multiple layers of carbon

fiber, it is prepped to be placed in the autoclave. First, the wheel is compressed in a

vacuum bag. Next, a breathable felt is placed over the wheel in order to disperse pressure

evenly and minimize the voids between the carbon fiber layers. Finally, the material is

baked under pressure in an autoclave, which enables the compression, adhesion, and

hardening of the material. [1]

Figure 6: [f.6]

 

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Balancing

Balancing an object that is incredibly lightweight can prove to be a difficult task,

especially in a wheel made of carbon fiber. The only part of the wheel that is not made of

carbon fiber is the metal air valve. In order to avoid an imbalance caused by this metal

part, extra layers of carbon fiber are placed on the spoke opposite to the air valve. This

procedure allows for a pre-balancing of the wheels in the design process even before a

tire is put on. The tires also have natural imbalances that must be accounted for. [1]

Safety Aspects of the Wheel

Wheels undergo constant external forces due to bumps, potholes, flat spots, and

curves. Thus, the design of the wheel must be capable of withstanding these impacts

without negative effects to the wheel and tire pressure. Due to the high strength of

carbon fiber, these wheels survive much harder impacts than wheels made of aluminum

before losing air pressure. Another quality of these wheels is that you can’t “flat spot”

them; it is either in excellent working conditions or broken, there is no in-between.

Although, it takes much more force to damage and break a carbon fiber wheel than an

aluminum wheel. [1]

Final Surface Quality

Typically, after wheels have

undergone pressure-cooking they

must undergo other processes in

order to enhance the finish of the

wheel. However, the final surface

quality of Koenigsegg Aircore

carbon fiber wheels is so high that it

only needs to be polished and does

not need a layer of clear coat applied.

The carbon fiber surface of the wheel

is a harder surface than acrylic paint

and thus it is more difficult to scratch

as well. The wheel is polished and

waxed with a UV protective layer.

Figure 7: [f.7]

 

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Working Conditions for the Koenigsegg Agera R Table 2: Koenigsegg Agera R Specifications

Specification Value

Vehicle Length 169 inches

Vehicle Width 79 inches

Vehicle Height 44 inches

Dry Weight 2,932 pounds

Weight Distribution 44% Front, 56% Rear

Horsepower 1,100 hp

Torque 885 lb-ft

Top Speed 280 mph

0-200 mph Time 17.86 seconds

200-0 mph Time 7.28 seconds

Lateral G-Force 1.6 G

Price $1,611,000

Number of Models Produced 18

Price of Aircore Wheels $42,500

Weight per Wheel ~13 lbs

[7],[8],[9]

The Koenigsegg Agera R is the amazing vehicle onto which the Aircore Wheels

are mounted. By examining the values within the above table, one can see the massive

amount of force that Koenigsegg wheels must withstand when accelerating, decelerating,

and turning at speeds up to almost 300 mph. The carbon fiber wheels helps in part to

achieve such astounding statistics.

With each wheel weighing in at around 13 pounds, a total weight of 2932 pounds,

and a weight distribution 44% front and 56% rear, it can be calculated that when at rest,

each front wheel must support around 633 pounds of downward force, and each rear

wheel must support 804 pounds, excluding the weight of the wheels themselves.

The volume and density of each wheel are impossible to calculate with the

information at hand because we do no know the volume of wheels or spokes, the density

of the weave used, the composition of the binding agent, or what percentage of the wheel

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is hollow. This makes it nearly impossible to estimate the centrifugal forces that the

wheel will experience during racing conditions, but it can be expected that they will be

many times the force experienced at rest.

Lastly, in light of the extremely high performance characteristics of this vehicle, it

is easy to see why the car itself is sold at such a high price of over a million dollars, and

so few models were produced. The market for such a car with advanced technologies is

quite exclusive, as the group of consumers who have the need for such a machine is

miniscule. The group of individuals with the means to pay for one is even smaller.

Conclusions and Summary

Carbon fiber is an excellent material for engineering applications, that consists of

carbon strands in a two part epoxy matrix. Its great strength to weight ratio, aesthetic

finish, and other properties make it highly favorable. Carbon fiber is thus great for use in

the world of racing and high performance vehicles.

The world of motorsport often calls for the implementation of groundbreaking

technologies in order to progress the sport. Koenigsegg Car Company is one

organization at the forefront of this charge, especially due to their advance carbon fiber

Aircore wheels. Carbon fiber composition makes these some of the strongest, most

lightweight wheels on the market today. This lightweight wheel enables the vehicle to

accelerate and decelerate more quickly, and improves overall performance on the

racetrack. However, it must be noted that these wheels and the types of vehicles that they

are suited for are quite expensive, and are typically only purchased by race teams and

very affluent individuals.

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References Informational Sources

[1] Drive. "Making 280mph Capable Carbon Fiber Wheels - /INSIDE KOENIGSEGG."

YouTube.com. Google.com, 22 Apr. 2014. Web. 12 Mar. 2015.

[2] Kalpakjian, Serope, and Steven R. Schmid. Manufacturing Engineering

and Technology. 7th ed. New Jersey: Pearson Education, Inc., 2014. Print.

[3] Hegde, Raghavendra R., Atul Dahiya, M.G. Kamath, Monika Kannadaguli, and

Haoming Rong. “Carbon Fibers.” engr.utk.edu. The University of Tennessee Knoxville.,

April 2004. Web. 8 Mar. 2015.

[4] [Cavette, Chris. “Carbon Fiber.” madehow.com. Advameg, Inc., 2015. Web. 9 Mar.

2015.

[5] Aerospace Specification Metals inc. N.p., n.d. Web. 9 Mar. 2015.

[6] Dragon Plate. Allred & Associates Inc., n.d. Web. 9 Mar. 2015.

[7] Joseph, Jacob. "Koenigsegg Finally Releases Agera US Price List." CarBuzz.

CarBuzz, n.d. Web. 12 Mar. 2015.

[8] "Specifications Koenigsegg Agera R." ZePerfs.com. N.p., n.d. Web. 9 Mar. 2015.

[9] "2015 Koenigsegg Agera R." LeftLane News. MNM Media, n.d. Web. 12 Mar. 2015.

Image Sources

[f.1] <http://koenigsegg.com/koenigsegg-the-company >

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[f.2] <http://www.aphotoaday2010.com/wp-content/uploads/2010/11/101104-carbon-

fibre.jpg>

[f.3] <http://www.madehow.com/Volume-4/Carbon-Fiber.html>

[f.4] http://www.engr.utk.edu/mse/Textiles/CARBON%20FIBERS.html

[f.5] <http://bridgetogantry.com/2/index.php/home/amusingamazing/618-spotted-at-the-

nuerburgring-koenigsegg-agera-r>

[f.6] <https://www.youtube.com/watch?v=PGGiuaQwcd8>

[f.7] <https://www.youtube.com/watch?v=PGGiuaQwcd8>