Fall 2016 Senior Design Report - Bob's Composites Shop

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BOB’S
COMPOSITES
SHOP
Design in motion
Cullen Billhartz, Ted Burns, Will Sixel, Brad Sternig,
Dylan Vassar

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Executive Summary
High performance vehicles always need an edge in performance over the competition.
One major edge is a lower unsprung and rotational mass of the vehicle. The easiest way to
lower mass is by improving the design and materials of pieces on the vehicle. A carbon
composite rim can be manufactured to be 50% lighter than traditional alloy wheel rims, while
increasing the overall strength. Performance can also be increased by the addition of an
airfoiled spoke design to help cool the braking system. Switching to manufacturing carbon fiber
material results in rims that now weigh 1.5 lbs, totaling an 8.4 lbs weight reduction in the
vehicle. While it may not seem like much, this is a weight reduction of 2% the weight of the
target 400 lbs vehicle and can make a large difference in the performance of the vehicle.
Braking performance is also a significant factor in performance vehicles. Our new wheel design
will include a wheel center with airfoiled spokes to increase cooling of the brake rotors and
therefore allow for smaller and lighter rotors to be used on the vehicle.
There is a large and growing market for this product in high performance sports cars,
weekend autocross cars, and factory team racecars. Despite a market for these high
performance wheel rims, there is a small list of companies currently pursuing this market, and
fewer companies pursuing designs that produce wheel rims as a single piece. Should a company
be able to design and manufacture a high performance carbon fiber rim, they could find
themselves in a position to dominate this market. Utilizing 2x2 twill carbon fiber in a 0⁰, 45⁰,
90⁰, -45⁰ layup pattern for 8 layers, Bob’s Composites Shop can market an individual carbon
fiber wheel rim with an airfoiled wheel center for $1750. This is $250 lower than competitors
who manufacture carbon fiber rims, as well as including a state of the art airfoiled wheel
center.
In addition to designing a sufficient wheel rim, the extensive manufacturing tools and
processes are also designed. A state of the art mold can be created in order to allow for the
manufacture of either 7” or 8” wheels depending on the request from the customer. Once
manufactured, the designed wheel rim must undergo static and dynamic testing to ensure
proper strength and the ability to carry the loads encountered from a high performance vehicle.
Should a design not withstand the proper loads, and fail to complete any of the designed tests,
it can be considered unfit for distribution and the design must be reiterated to fix the failures
found. With the use of high end materials and manufacturing processes, the traditional wheel
will be left in the dust, giving customers the edge desired in high performance vehicles.
A prototype aluminum mold and carbon fiber wheel shell was manufactured. The final
wheel shell design weighed 1.5 lb, significantly lower than the target weight of 2 lb. In addition,
modal testing was performed and the stiffness in the first mode was found to be almost
equivalent for the aluminum shell and the carbon shell, indicating that the carbon shell should
behave very similar to the aluminum shell structurally.

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Table of Contents
Introduction .................................................................................................................................... 1
Figure 1: Components of Wheel Rim .......................................................................................... 2
Problem Statement......................................................................................................................... 2
Product Space ................................................................................................................................. 2
Possible Solutions ........................................................................................................................... 3
Table 1: Decision Matrix.............................................................................................................. 4
Proposed Solution........................................................................................................................... 4
Edition CF Materials .................................................................................................................... 4
Shell Design ................................................................................................................................. 4
Figure 2: Single Piece Shell.......................................................................................................... 5
Figure 3: Shell Profile................................................................................................................... 5
Figure 4: 2x2 Twill in 0° Orientation............................................................................................ 6
Figure 5: : 2x2 Twill in 45° Orientation........................................................................................ 6
Wheel Center Design................................................................................................................... 6
Figure 6: Wheel center option 1 ................................................................................................. 8
Figure 7: Wheel center option 2 ................................................................................................. 8
Mold Design ................................................................................................................................ 9
Figure 8: Mold Design ............................................................................................................... 10
Product Design Specification ........................................................................................................ 10
Technical Feasibility...................................................................................................................... 11
Resources Required ...................................................................................................................... 11
Figure 9: Stiffness to Weight Ratio (Source: ESE Carbon)......................................................... 11
Cost Analysis ................................................................................................................................. 12
Table 2: Cost analysis ................................................................................................................ 12
Analysis ......................................................................................................................................... 13
Table 3: Target vehicle loads parameters for wheel................................................................. 13
Figure 10: Free body diagram of wheel shell analysis. ............................................................. 13
Figure 11: Carbon fiber orthotropic material coordinate system............................................. 14
Figure 12: Maximum principal stress in carbon fiber wheel shell and airfoil center ............... 15
Table 4: Finite element analysis results.................................................................................... 15

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Testing........................................................................................................................................... 16
Figure 13: Brake rotor temperatures with and without augmented airflow from airfoil center
................................................................................................................................................... 16
Figure 14: Reference coordinate system .................................................................................. 16
Vertical Testing.......................................................................................................................... 17
Figure 15: Assembly of vertical test fixture with rim................................................................ 17
Figure 16: Assembly of Vertical Test Fixture Without Rim ....................................................... 17
Figure 17: Vertical test fixture finite element analysis ............................................................. 18
Lateral Testing........................................................................................................................... 19
Figure 18: Lateral Test Fixture................................................................................................... 19
Torsional Testing ....................................................................................................................... 19
Figure 19: Torsion test fixture exploded view .......................................................................... 20
Figure 20: Torsional Test Fixture - Cross Section ...................................................................... 20
Vibration and Modal Testing..................................................................................................... 20
Figure 21: Shaker table test fixture........................................................................................... 21
Table 5: Natural frequencies of aluminum wheel shell compared to carbon fiber shell ......... 21
Figure 22: Modal excitation test setup for carbon fiber shell .................................................. 22
Product Lifespan ........................................................................................................................... 22
Conclusion..................................................................................................................................... 23
Appendix A.................................................................................................................................... 25
Appendix B.................................................................................................................................... 35
Appendix C.................................................................................................................................... 36
Appendix D: Key Design Decisions................................................................................................ 38
Appendix E: Referenced Material Properties............................................................................... 40
Table 6: Twill Mechanical Properties........................................................................................ 40
Table 7: Twill Mechanical Strength........................................................................................... 40

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Introduction
In high performance motorsports, mass reduction is an essential part of the continuous
improvement of increased vehicle performance. A vehicle’s suspension system consists of
springs to keep the tires in contact with the ground, increasing the traction and handling
capabilities of the vehicle. Mass that is part of the suspension system between the spring and
the ground is known as unsprung mass. As the unsprung mass of the vehicle decreases, its
ability to absorb vibration from bumps in the road increases. Therefore, there is a clear benefit,
especially in high performance vehicles, to reduce the unsprung mass of a vehicle in order to
improve handling and control.
The aluminum alloy wheel rim has been in standard production and used by high
performance cars since the 1980s. Although changes have been made to overall size, spoke
design and manufacturing process, the wheel rim has largely remained unchanged. The design
intent is to create lightweight wheels that feature airfoiled spokes. To achieve this, carbon fiber
will be used as the primary structural material. New molding processes and testing methods
will be designed to make fabrication possible.
The carbon fiber and airfoiled design will achieve reduced rotational inertia, increased
stiffness, increased ultimate strength, and will also create airflow through heat sensitive
components. The two primary design constraints for the wheel rim are the bolt pattern that it
will use to attach to the hub, as well as the offset of the spokes to allow for proper packaging of
braking components and tire patch contact area with the ground. These areas can be seen in
Figure 1. The design must consider the constraints of carbon fiber molding techniques and
contain geometry that is conducive to material selection. Although unassuming in appearance,
wheel rims have many different critical surfaces and design aspects that allow them to function.
Many of these surfaces are controlled by automotive design standards and the design of the
molding tools will have to take great consideration to create compliance with these standards.
A few of these standards that apply specifically to high performance vehicles include SAE J1986
which standardizes the configuration of balance weights and minimum performance
requirements, SAE J1102 which standardizes the material and heat treatment of wheel bolts,
and SAE J1095 which standardizes the process of fatigue testing.

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Figure 1: Components of Wheel Rim
Problem Statement
High performance wheel rims have remained stagnant since the transition from
magnesium to aluminum alloy in the 1960’s. As a part of the unsprung mass of a car, there is
always an effort to reduce weight and rotational inertia. The wheel rim has the potential to be
lighter and stronger if it transitions from aluminum to carbon fiber, providing enhanced
performance to racing vehicles.
Bob’s Composite Shop introduces the design and fabrication of carbon fiber wheel rims
to reduce the unsprung mass of a high performance vehicle. Along with the material transition
to carbon fiber, Bob’s Composite Shop also proposes air foiled spokes to induce air flow
towards the car. This will cool heat sensitive components such as the brakes creating better,
more consistent performance. The name of the product shall be Edition CF.
Product Space
Carbon fiber rims have only recently entered the high performance automobile market.
However, the design could be scaled to smaller vehicles such as autocross karts and smaller
Formula series cars. The Sports Car Club of America (SCCA) is a national level sanctioning body
for various racing disciplines including autocross, rally, road racing, and track day events. From
their website, in 2016, over 1300 individuals competed at the SCCA Solo Autocross National
Championships, with the SCCA containing over 65,000 currently registered members. There is a
significant opportunity to produce high performance rims and compete on a cost and reliability
standpoint within this existing market. In addition to the very small market competition for
Inner Rim
Outer Rim
Wheel Center
12”
Offset Area
Hub Bolt
Pattern

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carbon fiber rims, there are currently no known companies pursuing a design that incorporates
an airfoiled spoke design.
The two premier companies producing commercially available carbon-fiber reinforced
polymer (CFRP) rims are Carbon Revolution (Waurn Ponds, Australia) and ESE Carbon (Miami,
Florida). Carbon Revolution is primarily an OEM supplier for Ford, but also supplies aftermarket
components for other vehicles such as Porsche and BMW. ESE Carbon supplies only
aftermarket components that can be purchased for a variety of vehicles. Currently, US patents
are held on a chopped pre-impregnated spoke section (US20150130261 A1) as well as pending
patents from Carbon Revolution on single-piece infusion process rims. No patents are currently
held regarding the introduction of airfoil designed spokes in either of the currently available
options on the market.
Possible Solutions
Edition CF will be made of Carbon Fiber Reinforced Polymer (CFRP) and will consist of an
inner shell, outer shell, and wheel center. In order to create safe and consistent products,
sufficient testing and molding routines must be designed in accordance with various high
performance vehicle standards including the ones mentioned previously.
Edition CF could be designed to be either single, two, or three piece. A single-piece rim
would be one continuous CFRP layup of the inner, outer shell and wheel center. A two-piece
will split the lay-up of the shells and wheel center as shown in Figure 2. Finally, a three-piece
layup would have split the inner, outer shell and wheel center into individual components. All
piece combinations are discussed in Table 1. In both the two-piece and three-piece design, the
wheel center material could remain aluminum due to the fact that it is a separate piece than
the shell. Edition CF could be molded in or out of an autoclave as well as with either pre-
impregnated CFRP or vacuum infused resin. Each combination of number of pieces and molding
process will affect the rims geometry and strength in unique ways. For instance, any
honeycomb structures placed in an autoclave typically may not exceed 22.5° of inclination from
the horizontal because It would begin to collapse under autoclave pressures. Also, each piece
and process combination will drive testing goals. For example, multi-piece components will
have high failure potential at piece joints and thus testing should focus on ensuring the integrity
in these areas. In addition to design changes as a function of the molding process, the size,
thickness, shape, and number of spokes will be a major design consideration.
To decide which rim design and mold process, a decision matrix was created as shown in
Table 1. Categories and scoring are described in greater detail in Appendix D. It was decided
that the best solution will be a 2-piece rim with aluminum wheel center. This will allow for
more adaptability to a larger range of vehicles using the same molding process for the shell. A
separate spoke assembly will allow for more bolt pattern options, as well as vehicle specific
spoke tuning. Maintaining a single-piece shell provides greater static and dynamic strength and
stability over the two-piece shell.

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Table 1: Decision Matrix
DECISION MATRIX Weight Single Piece Shell and
Center
Single Shell - Alloy
Center
Two Piece Shell -
Alloy Center
Mold Design Complexity 2 3 5 5
Manufacturing
Complexity
3 3 5 7
Design Flexibility 1 3 5 5
Scalability 2 3 5 5
Weight Reduction 3 7 5 5
Structural Performance 3 7 5 1
Totals 66 70 64
Proposed Solution
Edition CF Materials
The shell will specifically be constructed of Tencate HTS40 3K 2x2 Twill and Tencate
TR50S 15K Unidirectional pre-impregnated fabrics with a 42% TC275 resin content. The majority
of the layup will be the 3K fiber and areas with needed increased stiffness in a single direction
will be strengthened with the 15K unidirectional fiber. To determine the material properties of
prospective layups, coupon testing was conducted. Tensile, shear, and density properties were
recorded and are listed in Appendix E. The wheel center will be manufactured from 7075
Aluminum. This alloy was chosen because of its high strength compared to 6061-T6.
Shell Design
The shell of the wheel rim is the key structural component, supporting the weight of the
vehicle. The shell experiences large compressive forces, particularly during sharp turns and
braking. Vibrational loading is also experienced at a frequency related to its rotation per
minute.

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Figure 2: Single Piece Shell
In addition to strength, the shell also must maintain a seal on tire to keep it pressurized.
The shell profile was first determined as shown in Figure 3. Edition CF’s shell will come in 7” and
8” widths for two different tire designs with a 10” diameter. The 7” and 8” lengths help to
widen Edition CF’s market space as teams typically switch between the two tire sizes depending
on track conditions. As the shell width increases, it is crucial to maintain where the force
transferred through the hub is located relative to the edges of shell. Constant orientation of the
shell offset relative to the vehicle maintains the ideal location of the tire contact area relative to
the suspension, maintaining the intent of the suspension design.
Figure 3: Shell Profile
11
”

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Edition CF will be fabricated with a 2x2 Twill alternating between orientations 0°, 45°,
90° -45°. Figure 4 below shows the alternating fibers of a 2x2 twill in the 0° orientation. Because
fibers only have unidirectional stiffness in tension, 2x2 Twills are only stiff in the directions
which the fibers run. The stiffness of Figure 4 will be greatest in the 0° direction, 2nd in the 90°
direction and significantly less in-between. The same is true of Figure 5 but in the 45° and -45°
directions. Alternating the twill orientations is a common composite practice because it creates
a part that will be approximately isotropic in the plane of the carbon. 12-ply and 8-ply layups
were considered for the design and it was determined by the finite element model that 8 plys
gave more than sufficient strength and stiffness for the load cases being considered, the results
of which will be summarized in the Analysis section.
Wheel Center Design
One of the major purposes of designing carbon fiber rims with air foiled wheel centers is
in order to create air flow towards the internal components of the wheel. If a wheel center can
be successfully designed in order to increase the air flow to components such as the braking
system, the chance for overheating and failure is greatly reduced. In order to design air foiled
wheel centers, there are a few design restrictions that must be met. The first being the need for
the outer bolt pattern to match the bolt pattern on the designed wheel rims and the inner bolt
pattern to match the bolt pattern on the bearing hub. Without meeting these constraints, the
wheel center will not be able to create the connection between the rim and the bearing hub.
The second major design constraint is the load in which it can withstand. Because the wheel
center connects the weight of the vehicle to the wheel itself, the center must be designed in
such a way that it can withstand the loads being applied to it during use; Therefore, the design
must create airflow, but also be structurally safe to use on the vehicle. In order to make sure
the wheel center has a load capacity that meets or exceeds the gross vehicle weight rating
(GVWR) the tests outlined later will be performed.
Figure 4: 2x2 Twill in 0°
Orientation
Figure 5: : 2x2 Twill in 45°
Orientation

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Brakes used on vehicles are able to slow and eventually stop a vehicle by converting
kinetic energy to thermal energy; Therefore, on high performance vehicles that are moving at
high velocities, brakes produce a large amount of thermal energy when braking. Conventionally,
the brake system will have the opportunity to cool off substantially during periods in which the
brakes are not being applied. This is can be problematic to the brakes as they will undergo large
temperature changes from periods of high heat during braking to low heat when not in use.
This large temperature change can lead to thermal shock and eventual disk failure. In an
attempt to decrease the maximum temperature being reached by the brake system, and in turn
decrease the overall temperature change the disks undergo, various methods of forcing air to
the braking system can be applied to a high performance vehicle. One of these such methods is
using airfoils to force additional air in from the wheel towards the braking system. By creating
airfoils on the spokes of the wheel center, the desired additional airflow can decrease the
maximum temperature brakes reach and increase their performance.
Multiple designs for air foiled wheel centers were created in order to get a variety of
centers that are structurally stable as well as create air flow. The multiple designs will then be
discussed among the group and analyzed for structural capacity and creation of air flow into the
braking system. In order to determine the amount of extra airflow that is generated by the
designed wheel center, a series of computational fluid dynamics analyses will be performed. As
a basis for desired air flow, the 7.25-inch diameter wheel center can be compared to a typical
fan.
In order to calculate the approximate desired air flow through the airfoiled wheel
center, a relation must be made to first compare the area of the airflow, and then to compare
the rpm in which the fan or airfoils are spinning. These calculations are based off of a 20”
diameter fan moving at 1507 rpm. This fan has been tested and found to move 4650 cfm of air.
41.28 𝑖𝑖𝑖𝑖2
314.15 𝑖𝑖𝑖𝑖2
=
𝑋𝑋 𝐶𝐶𝐶𝐶𝐶𝐶
4650 𝐶𝐶𝐶𝐶𝐶𝐶
Based on relating the two areas, for a wheel center with the same rpm as the fan, the induced
air flow should be 611.02 cfm. Now using this airflow in the wheel center with the initial
relation of areas, we can scale this figure down to an estimated airflow for the revolutions per
minute that are commonly found on a high performance car.
653 𝑅𝑅𝑅𝑅𝑅𝑅
1507 𝑅𝑅𝑅𝑅𝑅𝑅
=
𝑋𝑋 𝐶𝐶𝐶𝐶𝐶𝐶
611.02 𝐶𝐶𝐶𝐶𝐶𝐶
Property Fan Wheel Center
Area (in2) 314.15 41.28
Spin Rate (RPM) 1507 653
Air Flow (CFM) 4650 264.76

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Based on the above calculations, in order for the wheel center to be comparable to the
box fan, around 265 cfm must be pushed through the wheel center. This is a tall task to ask
from a component with little room for geometry change, so a more realistic goal of about half
the flow is set at 130 cfm. This is a reasonable number and can make a true contribution to the
performance of a vehicle. While cooling systems can be used on brakes in vehicles, cooling
systems that require no input (mechanical, electrical, otherwise) in order to get the desired
cooling effects are not common practice in wheel designs. These airfoils could prove to be low
cost, high performance piece that has undeniable benefits.
The first proposed wheel center design is shown in Figure 6. This design features nine
spokes in the wheel center that are created with air foil cross sections. The cross sections are
similar to many NACA airfoil shapes in order to create a pressure difference above and below
Figure 7: Wheel center option 1
Figure 6: Wheel center option 2

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the profile and create increased down force and airflow into the braking system. Because of the
complexity of the design, this air foiled wheel center will most likely need to be cast as opposed
to being machined.
A second option for the airfoil wheel center is shown in Figure 7. Option 2 uses a slightly
modified NACA 0012 airfoil cross section of the 9 spokes. These spokes are then oriented at a
16° angle-of-attack relative to the axis of rotation of the wheel. One difference in this design is
that the spoke profile is not symmetric, and a different design is required for the left-hand side
wheels and the right-hand side wheels. Figure 6 shows a right-hand design that pulls air
towards the outside of the wheel.
After analyzing the above designs using computational fluid dynamics, it was shown that
the second option shown in Figure 7 can push around 56.97 cfm of flow making it the best
design option, and one that will be implemented into the wheel rim. This does not meet the
desired goal, but it was the best option that was designed. Further design iterations may be
needed. Option 1 as designed weighs 0.85 lb and Option 2 weighs 0.54 lb compared to 0.72 lb
for the currently existing 9-spoke wheel center. Because of the weight difference, Option 2 was
pursued for prototyping.
Mold Design
To manufacture Edition CF, a suitable mold was designed and fabricated. The main
material candidates for the mold were 4130 steel and 6061-T6 aluminum. Steel includes
benefits of longer tooling life and a heat expansion coefficient closer to the carbon fiber over
the aluminum. The steel round stock however is more expensive, harder to machine and
heavier than aluminum. The aluminum has the benefit of having a large coefficient of
expansion. The larger coefficient is a benefit because when the mold is cooled, it will be easier
to remove the part and reduce chances of delamination upon release. 6061-T6 aluminum was
chosen as the mold material primarily for the reduced delamination as well as cost and
machinability.
Since Edition CF is designed for two offset configurations, the mold has to accompany
this. The design of the mold features two removable leafs as shown in Figure 8: Mold Design.
When in place, the mold will construct an 8” shell with a 2” offset, and when removed the mold
will construct a 7” shell with a 1.5” offset. Each piece of the mold also features a bolt hole
pattern that mates with the handle shown in Figure 8. Once the part is set in the molding
process, the handle assists in removing each mold piece. For locating, mold piece also has
locating pins. Although the part is axisymmetric, the alignment holes and pins will constrain the
mold concentrically and radially.

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Figure 8: Mold design
Product Design Specification
The main goal of the carbon fiber rim is to reduce mass, increase strength, and create
airflow through the wheel. Specifically, the CFPR rim will be 50% the weight of its alloy
counterpart. The CFPR rim will sufficiently pass stress tests in the vertical, lateral and rotational
directional as well as vibrational (directions and passing values defined in figure four). Airflow
through the rim will be 150 cubic feet per minute at 35 miles per hour. The carbon fiber rim
must follow all relevant aspects of SAE standard J1986-201603 which defines standards for
steel and aluminum wheel rims. The rim must be no more difficult to install than an alloy
counterpart. Each rim manufactured will go through non-destructive inspection to ensure bond
and layup integrity throughout the thickness of carbon fiber. Initial rims will undergo multiple
loading tests, as well as fatigue and vibration tests to ensure safe extended use. The rim needs
to withstand temperature gradients from -20 to 120 °F. This specification will be critical in
regards to thermal expansion of metallic inserts and their compatibility with the carbon. The
rim must also not cause galvanic corrosion on any metallic components the assembly will come
in contact with. To build a product that best fits these specifications, the design proposals were
down-selected with a decision matrix highlighting key performance parameters. This decision
matrix is included in Appendix D.
Removable Leaves
12”

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Technical Feasibility
Carbon fiber is a material that is increasing in usage within many industries ranging from
automotive, aerospace, and even sporting goods. New applications are constantly being added
and wheel rims are another area of application that have not been sufficiently explored. Carbon
fiber offers ultimate strength, stiffness and density that are roughly 450% larger, 75% larger and
160% lighter than that of aluminum respectively. These properties allow for carbon fiber to rise
above most materials when considering its stiffness to weight ratio as shown in figure three.
This higher performance in material properties will allow for stiffer, lighter, and stronger
rims, greatly increasing the performance of any vehicle utilizing the technology. This makes it a
desired product in the high performance vehicle market.
Resources Required
In order to create a successful product design, some materials will be required. The
primary material is pre-impregnated carbon fiber. This material will be coming from the FSAE
teams supply of pre- impregnated that was donated by Cirrus Aircraft. The mold material will
be 6061-T6 aluminum for cost and weight reduction. Aluminum’s higher coefficient of thermal
expansion (compared to steel) also assists in removing the CFPR rim from the mold post-cure.
This material will be purchased using the FSAE teams budget, potential sponsors, and the class
provided funds. The last material needed is aluminum alloy for the wheel center. This material
will be provided by the Formula SAE team.
0
20
40
60
80
StiffnesstoDensityRatio
106m2/s2
Material
Stiffness to Density
Ratio
Figure 9: Carbon material properties comparison (Source: ESE Carbon)
0
250
500
750
1000
1250
1500
StrengthtoDensityRatio
kN-m/kg
Material
Strength to Density Ratio

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Cost Analysis
In the current market, wheel rims made of carbon fiber have a ticket price of around
$2000. It was the goal of Bob’s Composites Shop to manufacture and sell a single carbon fiber
wheel rim with a unique airfoiled wheel center for around $1300. Based on the estimated costs
of labor and materials as shown in Table 2, it is estimated that it will cost around that price to
manufacture each rim. Due to the desire to make a profit on the venture, the price per rim is
expected to increase to $1750. Found in the product design specifications, it is the goal to
produce thirty sets of wheels a year netting a profit of over $50,000 for Bob’s Composites Shop.
While the largest cost of creating carbon fiber wheel rims comes from the carbon fiber
material, the labor costs are more difficult to estimate and need to be given great thought.
The labor costs will come from the initial machining of the molds in order to lay up each
rim as well as the cost of each layup. Using a CNC lathe, the machining labor costs of the mold
should be around 20 hours; and using a 5 axis mill the wheel centers should be machined in
roughly two hours. Luckily, by utilizing these aluminum molds, multiple rims can be laid up and
cured before the mold needs to be recreated. It is believed that these molds can be used for
around 5 years when being used to pull 30 sets off a year. The majority of the rim’s labor cost
comes in the layup process. Utilizing a CNC ultrasonic cutting machine, the pieces for layup can
be quickly cut, and due to the mold having two large pieces that fit together, they can be laid
up by two different people at the same time. After the layup and curing process a few hours
will need to be dedicated to sanding and demolding. Because of the size and shape of the rims,
they can be fit into FedEx XL Flat Rate shipping boxes and shipped for $25.50 per rim. The
estimated selling price is a great deal for customers when compared to other companies in the
market, and no other company is including airfoiled wheel rims with their rims. This puts Bob’s
Composites Shop above competitors and will provide good business for the company.
Table 2: Cost analysis
Reason for
Cost
Time of Labor or Amount of
Materials
Estimated Cost of Labor
Cost Per Rim
Materials
5400 in2
$300/1800in2
(for carbon) $900.00
1” THK x 7.25” OD $57 (for wheel center stock) $57
Labor
20 machines hrs (for mold)/600
pulls off
$18/hr $0.60
2 machines hrs (for wheel center) $50/hr $100
6 hrs layup x 2 people $30/hr $180.00
2 hrs post cure $25/hr $50.00
Cost of
Mold
100 lbs 10” OD Aluminum
Stock/600 pulls off mold
$500/600 pulls off mold $0.84
Shipping Flat Rate shipping $25/rim and center $25
Desired
Profit
$1750/ set of rims and centers x $437.5
Total Cost Per Rim = $1750.94

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Analysis
Finite element models were built to analyze stress in the wheel center. The models were
used to inform the number of carbon fiber plys needed to provide adequate thickness to
support the loads in the shell. The load cases for the wheel were developed as follows. Using
the target vehicle design properties listed below, a conservative load case for the wheel
assembly was assumed. The center of gravity and aerodynamic center of pressure were
assumed to be at the midpoint between the front and rear axles.
Table 3: Target vehicle loads parameters for wheel
Weight 620 lb
Maximum longitudinal acceleration 1.5 g
Maximum lateral acceleration 2 g
Maximum aerodynamic downforce 210 lb
Maximum rotational speed 1500 RPM
Vertical load supported by wheel 415 lb
Lateral load supported by wheel 620 lb
The vehicle was assumed to be in a 2g steady-state corner with only the two outside
tires supporting the vertical and lateral inertial forces. This vehicle dynamics case represents
the highest load seen in the tires and thus the wheels. Therefore, a 1240 lb lateral force will be
distributed between the two tires and 830 lb of total vertical force will be distributed between
Lateral acceleration
of vehicle
Lateral force from
tire on bead
Vertical force from
tire on beads
Figure 10: Free body diagram of wheel shell analysis.
11”

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the two tires. These loads would be equally distributed between front and rear and the loads
on a single tire are shown in Figure 10. Therefore, these loads become 415 lb in the vertical
direction and 620 lb in the lateral direction.
In the stress analysis of the carbon fiber wheel shell, the lateral force was assumed to be
equally distributed around the inside bead. The vertical force was assumed to be equally
distributed about the bottom (towards the ground) half of both of the tire beads. A tire
pressure of 20 psi was also applied to all exterior surfaces of the wheel shell between the
beads. The wheel center and wheel shell were analyzed in Scan&Solve as a bonded assembly.
Fiber reinforced materials can be difficult to model because they do not behave as
isotropic materials. For the quasi-iso layup being used in the design of the wheel rim, carbon
fiber can be modeled as an orthotropic material with in-plane (IP) and out-of-plane (OOP)
material properties. The material coordinate system for the analysis is shown in Figure 11. Red
and green arrows indicate the in-plane direction (material properties assumed to be the same
IP). The blue arrows indicate the out-of-plane direction, which follows the shell surface normal
direction per the carbon fiber layup process.
The resulting stress distribution for this load case is shown in Figure 12. In this figure,
the maximum value of the 1st or 3rd principal stress is plotted and the sign value indicates
tension or compression. This maximum principal stress value was used because the von Mises
stress is only valid for ductile materials, and a comparison between the aluminum airfoil center
and the carbon shell was desired. The maximum stress in the airfoil center was found to be 23.7
ksi and was located at the bolted interface between the wheel shell and center.
Figure 11: Carbon fiber orthotropic material
coordinate system

15
The maximum stress in the wheel shell (the shell offset) was found to be -9.3 ksi and
located in the region where the two halves come together. The factor of safety according to in-
plane properties is reported in Table 4. As the offset region is largely in bending, the peak stress
here will be in the plane of the material.
Table 4: Finite element analysis results
Maximum
Stress
(ksi)
Yield
Strength
(ksi)
Yield
Factor of
Safety
Ultimate
Strength
(ksi)
Ultimate
Strength Factor
of Safety
Aluminum center 23.7 (von Mises) 73 3.1 83 3.5
CFRP Shell -9.3 (principal) 80 (IP) 8.6 110 (IP) 11.82
Our next analysis concerns the air flow induced by the airfoil wheel center. The 100
ft3/min (CFM) target at maximum speed is equivalent to increasing the airflow over the brake
rotors by approximately 15% at any vehicle speed. This airflow number will be validated with
testing. This effective increase in the brake rotor cooling can be modeled by increasing the free-
stream velocity of the flow past the rotor. A brake rotor thermal model was built in Thermal
Desktop and the results with and without the flow augmentation from the wheel center are
shown in Figure 13. The analysis indicated that the operating temperature was able to be
reduced by 25°C.
Figure 12: Maximum principal stress in carbon fiber wheel shell and airfoil center
Peak stress in center
Peak stress in shell

16
Testing
One of the largest challenges that will be faced during the design of a carbon fiber wheel
rim is creating a design that meets the required size restrictions and load capacities. In order to
make sure the design meets the requirements as outlined in the Product Design Specification
document and to validate the developed
finite element models, a series of both static
and dynamic tests will be completed. These
tests will include vertical (Y), lateral (X),
rotational (about X).
In place of the aluminum wheel
center, steel mounting plates will be used to
restrain the shell to the test fixture. The shell
will not be tested because the failure modes
(yield, fracture, and fatigue) are well known
and consistent for 7075-T6 aluminum. This is
in contrast to the carbon fiber shell, for
which material properties (especially failure
strengths) are extremely dependent on the
quality of the components and the
manufacturing process. As such, testing the
shell alone isolates it and allows us to obtain
the desired strength and elastic properties.
Figure 14: Reference coordinate system
X axis
Y Axis
Figure 13: Brake rotor temperatures with and without augmented airflow from airfoil center

17
Vertical Testing
One of the most basic scenarios in which a wheel rim receives an applied load is through
the wheel center in the vertical direction. This load is derived from the rim supporting the static
weight of the car and the dynamic weight transfer in acceleration and turns. In order to
simulate the vertical load on the shell and center, a force will be applied through the wheel
center via the top assembly while constraining the tire bead via the bottom part displayed in
Figures 13 and 14.
The vertical test fixture will thus have an assembly to apply the load and a fixture to
constrain the bead. This will effectively simulate the cases in which the vehicle is applying a
vertical load through the wheel center and the contact between the tire and ground restrict the
bead deformation. The test fixture will also interface with the Instron 1000 to apply a maximum
of 10,000 lb of compressive load and therefore need to be designed to be held by its hydraulic
grips. The fixture will be fabricated from AISI 1045 Cold Rolled Steel Tubing. The frame will be
joined by MIG welding. For a successful test, the rim must not fail under 1000 lbs. In order to
verify that the test stand can withstand these loads, FEA was completed for an applied load of
1000 lbs. Figure 17 shows the results of the finite element analysis, and that the maximum
stress in the test fixture is approximately 25 ksi. This is well below the 85 ksi yield strength of
AISI 1045 steel. The addition of the 45° support members was extremely effective in
triangulating the bending stresses and reducing the overall bending stress in the fixture.
Figure 16: Assembly of Vertical Test
Fixture Without Rim
Figure 15: Assembly of vertical test
fixture with rim
11”

18
Although the test will result in a success if the rim does not fail under 1000 lbs, a test to
failure in the vertical direction may be desired in order to confirm the rim’s factor of safety. Due
to this desire, the vertical test fixture has been designed to withstand loads much greater than
1000 lbs. Using 1045 Cold Rolled Steel Tubing because of its strong mechanical properties, and
further confirming with FEA, the designed test fixture can reasonably withstand applied loads
up to 2500 lbs. As can be seen in Figure 17, the maximum stresses occur near the connections
of the two angled sections along the left and right sides. The maximum stresses at these
locations were found to be roughly 28 ksi. Scaling the maximum stresses found to the yield
stress of 1045 Steel, it can be concluded that this test fixture can reasonably withstand a
vertical load of 2500 lbs.
Figure 17: Vertical test fixture finite element analysis
9”

19
Lateral Testing
Similar to the vertical test, the lateral load must be applied through the wheel center
while constraining the tire bead. The lateral load occurs in the wheel when the car is turning.
The test fixture will interface with the Instron 1000. A flat circular piece of mild steel will be
used in place of an actual wheel center. Welded to the stand-in wheel center will be mild steel
rod which will interface with the Instron 1000. On the underside, clamp downs designed to the
shape of the bead will constrain the rim. This is to prevent outward deflection of the rim and
maintain normal forces. The lateral test will test normal bond strength at the joining of the two
shell halves as well as compressive capability of the wheel rim. For a successful test, the rim
must not fail under 1200 lbs.
Torsional Testing
For the torsion test, the load will be applied through the wheel center bolt hole pattern
will be constrained by the inner shell. This will test the torsional capability of the designed
wheel center as well as the bond strength between the two halves of the wheel shell. Figure 20.
below shows a cross section of the test fixture. The axial rods must be constructed of steel to
ensure component failure before test fixture failure. For a successful test, the inner or outer
radius bolts of the wheel center must fail before the shell bond or wheel center.
Figure 18: Lateral Test Fixture
8”

20
Vibration and Modal Testing
Given the severe vibration environment due to road noise, bumps, and the vehicle’s
engine, vibration testing will also need to be performed on the wheel. Modal finite element
analysis will be used to determine the rim’s natural frequencies and this will be validated during
the dynamic testing. A key design constraint will be to ensure that the final design has no
significant modes in the operating range of the wheel. In addition, high-cycle testing may be
performed on the LDS shaker table to verify the reliability of the wheel under nominal loads.
A test fixture was designed to test the shell on a shake table. The shaker table plate was
modeled and a plate and clamp fixture was designed to fix the shell to the table. The maximum
speed of the target vehicle corresponds to 70 mph, and with the rolling radius of the tire a
maximum frequency that the wheel will operate at will be 25 Hz. However, due to imbalances
in the rotating wheel and uneven road surface, several multiples of this operating range will
need to be excited to properly simulate the driving environment. In addition, 10g excitation will
be desired to create sufficient inertial loads for fatigue testing on the shaker table.
Modal excitation testing may also be performed to validate the modulus of elasticity
used in the finite element stress calculations. The natural frequencies of the shell can be
compared and correlated to modal testing by varying the stiffness properties in the finite
element model. To perform modal excitation testing, the wheel shell will be supported in a
Figure 20: Torsional Test Fixture - Cross
Section
Figure 19: Torsion test fixture exploded view
11”

21
free-free condition by elastic bands and excited at several points. The acceleration response of
the shell will be recorded and frequency response calculated to estimate natural frequencies.
A finite element model of an 8” aluminum wheel shell was compared to the modal
excitation testing performed on the carbon fiber shell. Due to time limitations, the aluminum
shell alone was not able to be tested and therefore a finite element model was used in its place.
However, the finite element model of the aluminum shell should predict the natural
frequencies quite well because the material properties are well known. The results of the
comparison are summarized in Table 5. Notably, the carbon fiber shell has significantly lower
natural frequencies, and this is because of the reduced mass of the carbon fiber shell. Despite
this decrease, the first natural frequency is still much higher than the operating range of the
wheel (approximately 25 Hz). The modal excitation test setup is shown in Figure 22. Three
accelerometers were used and the response of 10 excitation points was measured.
Table 5: Natural frequencies of aluminum wheel shell compared to carbon fiber shell
Mode 1 Mode 2 Mode 3 Mode 4 Mode 5 Mode 6
Aluminum Shell Finite Element Model 432 Hz 655 Hz 1180 Hz 1200 Hz 1420 Hz 1475 Hz
Carbon Fiber Shell Modal Excitation Test 258 Hz 521 Hz 673 Hz 795 Hz 900 Hz 1048 Hz
Figure 21: Shaker table test fixture
8”

22
One interesting result of the modal test is the comparison between the first mode of the
aluminum shell and the carbon fiber shell. The natural frequencies can be used to compute the
effective stiffness for a given mode from the equation for a natural frequency. The ratio
between the stiffnesses was calculated to be 1.0013 per Equation 1, using an aluminum shell
weight of 4.2 lb, a carbon fiber shell weight (measured) of 1.5 lb, and the natural frequencies
from Table 5.
𝑘𝑘𝑎𝑎𝑎𝑎
𝑘𝑘_𝑐𝑐𝑐𝑐
=
𝑚𝑚𝑐𝑐𝑐𝑐
𝑚𝑚𝑎𝑎𝑎𝑎
𝜔𝜔𝑛𝑛1,𝑎𝑎𝑎𝑎
2
𝜔𝜔𝑛𝑛1,𝑐𝑐𝑐𝑐
2 = 1.0013 (1)
Because the ratio is almost one, the equivalent stiffness in the first bending mode is
almost identical. This indicates that our design will have similar deflections in this bending
mode in comparison to the aluminum shell design. In addition, the almost equal stiffness
validates the selection of carbon fiber and shell design as the material for the new shell as the
difference in density and increase in stiffness results in an equally stiff design for a much lower
mass part.
Product Lifespan
One of the major concerns when developing a new and innovative design that provide
an edge in competition for a high performance vehicle, is the fact that in as little as a couple of
years the design may become obsolete and need to be redesigned in order to further improve
performance on the vehicle. Because of the general lack of carbon fiber wheel rims being
1-axis accelerometers
Figure 22: Modal excitation test setup for carbon fiber shell

23
created for high performance vehicles, a slightly longer product lifespan can be expected as
there is not a large push to out-design and out-perform a large number of companies. Due to
the necessity of constant improvement to design, but the lack of pressure from other
companies to outperform their design, it is expected that one design will be in production for as
long as up to five years. This is subject to change with a growing market and entrance of more
companies attempting to outperform. It is not expected that a need for a reiteration of any
single design be required with each year, or each racing season.
Prototyping
The aluminum shell mold was manufactured and a carbon fiber wheel shell was
produced. Several concerns become apparent during the manufacturing process that will have
to be resolved in the next design iteration. First, the offset area radius was too small and it is
possible that laminate bridging may occur during the bagging process. In addition, it was
difficult to get the vacuum bag inserted all the way into the offset region and this may impact
the quality of the laminate in that area.
After the part was removed from the oven, it proved difficult to remove the part from
the mold. Mold release compound was added during the layup process, however, we neglected
to add mold release in between the two mating halves of the shell. During the curing process,
epoxy had penetrated into this region and effectively bonded the two halves of the shell
together. In the future, a seal and filler material will need to be added into this area of the mold
to prevent epoxy penetration during curing.
The second airfoiled wheel center option was prototyped by 3-D printing. Although the
printed center cannot be used structurally, it can be mounted and the induced flowrate can be
used to validate the airflow and brake rotor temperature calculations.
Conclusion
The overall proof of concept was deemed a success after completion of porotype
manufacturing. The 2 lb mass target was met as the 8 ply prototype weighed 1.5 lb after
manufacturing. From modal excitation testing, the stiffness of the carbon rim was found to be
very similar to the stiffness of the existing aluminum shell, indicating that the structure will
perform to expectations under dynamic operation. Further structural testing will need to be
performed to ensure the shell can handle the rated loads and validate the stresses obtained
from the finite element model.
The airfoil wheel center was designed and found to decrease the brake rotor operating
temperature by 25°C. The calculated flow rate can be validated by flow rate testing of the 3-D
printed wheel center prototype. In addition, finite element analysis showed a factor of safety of
3 in the designed wheel center.

24
From manufacturing the prototype, the cost predictions of manufacturing the design
was refined. Initial cost predictions were expected to be $1300, and this was revised to $1750
after prototype manufacturing. This price is less than the current competition and includes the
airfoiled wheel center technology. Further price reductions could be obtained by refinements
to the manufacturing process.
By utilizing 21st century composites technology, it is possible to make significant
improvements to vehicle performance. The current design shows that it is possible to reduce
mass and rotational inertia by 50% in the wheel rim. In addition, the integrated airfoil in the
wheel spokes will allow for increased brake performance – a critical element in high
performance autocross vehicles.

25
Appendix A: Product Design Specifications
Overall Design Intent: A carbon fiber automotive wheel rim will provide increase
stiffness and reduce mass on high performance cars to increase acceleration ability.
The spokes of the rim will also be shaped as an airfoil to provide flow across the breaks,
allowing for increased cooling and more efficient performance.
Date: (9/26/2016)
Revision (1)
Group Members (Cullen Billhartz, Bradly Sternig, Will Sixel, Dylan Vassar, Ted
Burns)
Guidelines Specification Element Competition best This design intent
The performance demanded or likely to be
demanded should be fully defined; how fast,
how slow, how often — continuously or
discontinuously, loadings likely (maximum and
average) — electrical, hydraulic or pneumatic,
tolerance of speed, rate of working, Duty Cycle,
etc. Remember that the more complex the
product, the more likelihood there is of
ambiguities and conflict between the
performance figures specified — for example,
the specification of an electrical cable to carry 20
kVA to an underwater vehicle when the sum of
the vehicle power requirements amounted to 50
kVA?
Is the performance demanded attainable in an
economic manner? A common failing in
specifying performance is to ask for the ultimate,
rather than that which is obtainable. Research
evidence shows that successful design teams pay
great attention to establishing objectives that
can be attained.
It is extremely easy to tighten up a performance
specification to such an extent that if one
designed to meet that performance, the
customer would not be willing or able to afford
it, even if the company could possibly afford to
make it in the first place. Sales departments and
clients never cease to be amazed that the
product emerging from their specification costs
so much. It takes little effort or thought to
specify ± zero as a tolerance for any parameter,
which in reality means infinite cost.
While the practice of over-specifying (belt and
suspenders) sometimes occurs in mass
production industries, it is more likely to occur
with specialist equipment, particularly in the
large, one-of field where the client does not
really know the adequate level of performance
needed to suit his requirements. Beware
therefore of ‘over-specification’ of performance,
and also remember that performance is but one
component of the PDS.
Performance
-Stiffness
-Mass Optimization
-Ultimate strengths
-Airflow across brakes
-Downforce Generation
ESE Rims:
-Stiffness: 135 GPa
-Mass: 1.8g/cc
-Ultimate strengths:
2250 MPa
-Airflow across
breaks: N/A
-Downforce
improve: N/A
-Stiffness: 110 GPa
-Mass: 2.5g/cc
Ultimate strength:
1800 MPa
Airflow across
breaks: 100cfm over
typical rims
-Drag/downforce
improve: 5%
increase downforce,

26
It is not uncommon, say, with hydraulic pumps,
for manufacturers to specify performance
parameters that are not attainable
coincidentally, but independently with
reductions in the other parameters — for
example, pressure and flow for variable delivery
pumps. In other words, maxima do not always
occur together.
All aspects of the product’s likely environment
should be considered and investigated:
Temperature range
pressure range (altitude)
humidity
shock loading (gravity forces)
dirty or dusty — how dirty? — how clean?
Corrosion from fluids — type of fluid or chemical
noise levels
insects
vibration
training and background of those who will use
and maintain the equipment •— likely degree of
abuse?
Any unforeseen hazards to customer, user or the
environment —for example, inclusion of CFCs?
All manufactured items experience a number of
these environmental changes in any or all of the
areas before being called on to function for the
user. These may occur at the following stages:
During manufacture — exposure to cutting
fluids, solvents, fluxes (flow soldering), acids
(plating and cleaning), etc.
During storage — in the plant.
During assembly — assembly forces,
contamination from sweating hands?
During packaging.
During transportation.
During storage — at a wholesaler’s warehouse.
During display.
During use.
These environmental subsets must be
considered at the outset, otherwise the essential
performance required during usage may never
be achieved, or at best may be somewhat less
than the user expectation.
Environment
- temperature
- Noise/vibration
- pressure due to altitude
-weather conditions
-rotational G’s
-inertial G’s
-poor surfaces
-carbon exposure to
moisture
-anywhere people
want to drive cars
- (-20)-120(degrees
F)
-sea level-10k ft in
altitude
-rain/snow
-pot holes
- (-20)-120(degrees
F)
-sea level-10k ft in
altitude
-rain/snow
-pot holes
-need low humidity
during layup and
storage
Should service life be short or long and against
which criteria should this be applied? Against
which part of the PDS is (or should) the product
life be assessed? One year on full performance,
24 hours a day, seven days a week, or what?
Consider the Duty Cycle.
Life in service
(performance)
-mileage
50,000 mi 10,000 miles
Is regular maintenance available or desirable?
Will designing for maintenance-free operation
prejudice the design to such an extent that the
product will become too expensive to buy in the
first place? Does the company, or indeed the
market into which the product will ultimately go,
have a definitive maintenance policy? Is the
market used to maintaining equipment once it is
purchased? The following points are relevant:
•Specify ease of access to the parts that are
likely to require maintenance. It is no good
Maintenance
-rim itself should be
maintenance free for its
lifetime
- balancing
-may need
rotational balancing
-may need
rotational balancing
-re-apply

27
calling for regular maintenance if it takes 10 days
to reach the part.
• What is the maintenance and spares
philosophy of the company and market?
• What is the likely need and desirability of
special tools for maintenance?
Target production costs should be established
from the outset and checked against existing or
like products. Invariably, all target costs are on
the low side, and in many cases they are
unattainable within the constraints of the PDS.
Care should be taken at this stage to ascertain
whether the target cost is compatible with
competitors’ products and, most importantly,
with the manufacturing facility available to make
the product. Cost patterns should be established
and studied in detail before setting the target
cost.
If a life cycle cost model is the norm in the
company or market area into which you are
entering, then this should be properly analyzed,
with particular reference to maintenance trade-
off and down time.
Make sure you specify retail price, production
cost, or something else as you consider this item.
There are large differences dollar differences in
these numbers
Target product cost -$2,000 per rim
(ESE)
-$1,300 per rim
A thorough analysis of competition must be
carried out, including a comprehensive literature
search, patent search and product literature
search relating not only to the proposed product
area, but also to analogous product areas.
The nature and extent of existing and likely
competition is probably the most important
aspect of a PDS, at least from a comparative
viewpoint. If, for example, the evolving
specification shows serious mismatches or
deficiencies when compared with what already
exists, then the reasons for such departures
must be fully understood. Therefore, it is
essential that a proper analysis be carried out
(perhaps a parametric analysis). Typical
magnitudes of such searches are:
Useful papers: 300—600
Relevant patents: 10-100
Competing products: 2—80
Useful parametric graphs: 5—30 (from a
selection of perhaps 100).
In order to stay in business, more and more
companies are carrying out these sort of
searches very thoroughly indeed, and are looking
for world-class parameters.
Competition
-Existing aluminum rims
-Full-scale CFRP rims
-Magnesium rims
-Carbon Revolution
-ESE Carbon
-must not infringe
on existing US
patents
It is necessary to determine how the product is
to be delivered:
By land, sea or air — home or overseas; what
type and size of truck, pallet container (look to
ISO standards) or type of aircraft used for the
type of product under consideration. It is not
unknown for equipment not to be able to pass
through cargo hatches of aircraft or ships, or to
be expensive in terms of shipping volume. This
Shipping
- Flat Rate Shipping
- Box for each
individual rim
- FedEx XL flat rate
shipping
($25.50)(per rim)

28
can affect the subassembly breakdown of the
product.
A product may be competitive here, but by the
time it is shipped overseas it may have become
too expensive. For example, a pump designed
for land irrigation and sold mainly overseas
became non-competitive because it was made
portable (a good idea) by putting it on a trolley.
The consequent doubling of shipping volume
rendered it non-competitive even though the
increase in basic prime cost of the pump itself
was very small.
Lifting capability, provision of lifting points.
Depending on the type of product being
designed, some form of packaging may be
necessary for transport, storage, etc. The cost of
packing will add to the product cost and volume.
Should the packaging protect against the
environmental effects of shipping such as salt
water, corrosion, shock-loading, etc?
Packaging
- No packaging restrictions
- Cardboard box and
foam to prevent
damage from small
impact
- Cardboard box and
foam block to
prevent damage
from small impact
-2 box sizes, single
rim and set of 4
Likely numbers to be produced by run and by
year over the product life will affect all aspects
of a product’s design. A one-off may require very
little tooling, although there are exceptions, such
as the Channel Tunnel. Moderate numbers may
require cheap temporary tooling, while large
numbers may require permanent, expensive
tooling. Further, purchasing quantities,
purchasing discounts and inventory costs for raw
materials and finished goods have a considerable
effect on the supportive investment required.
Quantity
-units produced per year
-Approximately
100k per year on
high performance
vehicles for a given
design.
30 units per year
Are we designing to fill an existing plant or is the
plant and machinery involved a constraint to our
design? What are the plans for new plant and
machinery? It is no good designing for a one-
plant set-up to find a new one in existence by
the time the production phase arrives.
Make or buy policy: is the product constrained to
techniques with which the company is familiar?
Is our proposed flexible manufacturing system
the ultimate in inflexibility? More and more
companies are resorting to subcontract
manufacture which will make them less capital
intensive and reduce their fixed costs. It also
allows them the ultimate in flexibility in terms of
manufacturing processes and technologies.
Manufacturing facility
-Clean Room
-Laser cutter
-Oven/autoclave
-Machine shop(for mold),
5-axis
-clean room
-laser cutter
-autoclave
-machine shop for
post processing
-Conference rooms
-Scissors
-Oven
-Sponsors to
machine molds
Are there any restrictions on the size of the
product? Size constraints should be specified
initially. So many designs ‘grow’ like Topsy, with
the result that the equipment will not fit into the
space provided, and even though it may do so
ultimately, access for maintenance could be
difficult. Does the product size and shape make
it difficult to handle?
Size
-10” Outer Diameter
- 8” tire width
- Increase inner diameter
-Varying sizes
depending on
vehicles
-made to fit FSAE
tires
What is the desirable weight? (Remember that,
for a given technology, weight is frequently
related to cost.) Allied to size, weight is
important when it comes to handling the
product on the shop floor during manufacture, in
transit, during installation or in the user situation
Weight
-Less than 5 lbs
-varies by size -2.5 lbs

29
with the customer. Should the design be
modular to assist in the size/weight area? Should
lifting points be provided
The appearance of a product is a difficult thing to
specify and therefore, in many instances, it is left
to the designer: the complaints come
afterwards. Color, shape, form and texture of
finish should always be considered from the
outset. Advice and opinion should always be
sought either from within the company or
without. Sales, marketing, production and others
will always criticize a design once it exists.
Therefore, efforts should be made to obtain
these opinions before the design commences,
and certainly as it progresses. Every person is a
design critic, accomplished or otherwise. So
often the final appearance of a product ‘just
happens’ and then strenuous efforts are made to
make it look better, which usually prejudices the
design in all aspects.
Never forget, whatever the product, that the
customer sees it first, before he buys it — the
physical performance comes later. The visual
performance is always first.
Aesthetics, appearance
and finish
-Carbon shiny finish
-Doesn’t yellow from UV
-Carbon Finish
-Paint or coating for
durability
-Should be shiny on
outside surface
inside will be rough
-will yellow w/o
clear coat
The choice of materials for a particular product
design is invariably left to the design team.
Usually, this is not a bad thing. However, if
special materials are necessary, they should be
specified, preferably by quoting the appropriate
standard. The converse is also true. If it is known
that certain materials, such as lead-based paint
for consumer products, must not be used, they
should not be specified. Aluminum or its alloys
on exposed surfaces for underground coal-
mining equipment is forbidden in the UK but not
in the USA. For material selection assistance, see
ASM Vol 20, pg 288 & vicinity.
Materials
-Carbon Fiber
-Epoxy
-Steel molds
-Pre-impregnated
carbon
-3K 2x2 twill, 12K
2x2, or UNI fabric
available
-Pre-impregnated
carbon
Some indication of the life of a product as a
marketable entity should be sought. Is it likely to
remain in production for two years or 20 years?
The answer is crucial as it can affect the design
approach and interacts with the market and
competition, tooling policy, manufacturing
facility and the like. Product life spans are
reducing rapidly for example. Consider printers
and calculators.
Product life Span
years of relevant
production
-unknown -five years per
iteration before
obsolescence
The product must designed to current US,
international, and perhaps other standards. If so,
then these should be specified and copies
obtained. Cross-correlation of such standards
should be carried out prior to commencement of
the design. It is difficult, costly, time consuming,
and inefficient to attempt retrospective
matching of finalized designs to such standards.
Also, bear in mind that while standards are
extremely useful and essential, they generally
represent an industry or technology consensus
at a point in time. They must not be allowed to
freeze innovation However, reasons for not
following particular standards must be carefully
evaluated and documented for the inevitable
Standards and
Specifications
-ANSI
-
-unknown -ANSI Standards
-ISO 9001:2015
-OSHA
-ASME FY15
-SAE J 1986

30
day of the product liability law suit. Further,
some standards are mandated by Law—EPA,
OSHA, state and local building codes, etc. These
MUST be followed in the design.
All products have, to some degree, a person—
machine interface, certainly during manufacture,
and if not directly during usage, again at the time
when maintenance is required. It is therefore
necessary to elucidate the likely nature of the
interaction of the product with humans. What
height, reach, forces and operating torque are
acceptable to the user. Postures and lighting
should be considered; the devices must be a
delight to use—potential users must be
consulted
Ergonomics/Human
Factors
-Able to be installed easily
and tires mounted by
machine
-Same ease of
installation as
current market
rims. Time to install
on car: 5 minutes
It is essential to obtain first-hand information on
customer likes, dislikes, preferences and
prejudices. Eyeball-to-eyeball discussion,
question and answer, and examination of
competitors’ trends and specifications are all
useful inputs to the specification.
To a great extent, such input will depend on
whether there are product line precedents
already on the market or whether it is a product
breaking new ground. Customer input is,
nevertheless, essential to success. The degree of
difficulty with which this input is obtained varies
enormously from the large one-of turnkey type
of project where the designer will interface
directly with the customer, to the mass-
produced product where s/he will not.
Customer
Performance oriented
aftermarket customers
Go karting
OEMs
-OEM’s
-Aftermarket
Customers
-
Performance/Racing
Cars
-OEM’s
-Aftermarket
Customers
-
Performance/Racing
Cars
-Performance
karting
-Car Mod
Enthusiasts
The laying down of levels of quality and
reliability necessary to ensure product success
and acceptability in a particular market is a cause
for increasing concern. They are the most
difficult aspects to quantify in absolute terms,
although statistical data from company product
precedents are helpful here. In electronics, mean
time before failure (MTBF) and mean time to
repair (MTTR) are familiar expressions, although
it must be remembered that by comparison with
mechanical, hydraulic, pneumatic and even
electrical components, electronic components
experience a relatively controlled, sheltered life.
Nonetheless, some quantitative expression must
be made in respect of quality and reliability at
the specification stage.
A company must ensure adequate feedback of
any failure analysis to the design team and the
safety team.
Quality and Reliability
MTBF 2 years
NDT to ensure
UV Protective coating for
resin decomposition
-5 year structural
warranty
-Corrosion
resistance (vs
aluminum)
-Fatigue life
improvement (vs
aluminum)
-MTBF 2 years
-NDT to ensure
-UV Protective
coating for resin
decomposition
A factor often overlooked in specifications is that
of ‘shelf life’ (applied to units) or storage on site
(as applied to a complete plant). With respect to
units, shelf life must be specified at the outset
and the means to combat decay considered,
otherwise rusty gearboxes, hardened rubber
components, seized bearings, defective linings,
corrosion and general decay will occur.
The designers of a complex plant should also be
aware of these problems, since equipment
designed on the assumption of immediate
Shelf Life (storage)
-Post-cure life
-Pre-cure life
-pre-preg 1 year
-post cure life
-uncured life
- immeasurable
shelf life after
curing
-un-cured a year if
frozen, week open
depending on resin
system

31
installation and commissioning may lie around
on site for months on end without adequate
protection and storage.
In-house process specifications, as opposed to
manufacturing techniques, are vitally important.
If special processes are to be used during
manufacture, they should be defined — for
example, plating specifications wiring
specifications. Alternatively, the relevant
standards —US, international, foreign, in-house,
etc. — should be called upon.
Processes
-Carbon layup and cure in
oven
-Autoclave -Out of Autoclave
Layup
-Foam insert in
spokes
What is the time-scale for the project as a whole,
in parts or phases? Is there a need to fit in with
the time-scales of others concerned with the
project? Lead times allowed for design activity
are frequently inadequate, but they determine
the time-scale for the whole project up to
manufacture and product launch. Design time
must be adequate to ensure that the product is
designed effectively and efficiently — in other
words, professionally. Lack of adequate time
spent at the beginning of a design project will be
made up for later and to other people’s time-
scales due to defective products, market
mismatches, overwhelming competition and the
like. There is no alternative to adequate design
time. Use Microsoft Project to monitor your own
design progress.
Time-scales
-Design
-Mold manufacturing
-Manufacturing
-unknown -Design-100hours
(one time)
-Mold
manufacturing-
50hours (one time
for mold life)
-Manufacturing-8
hours (per rim)
Most products require some form of testing
after manufacture, either in the factory, on site
or both. Products for the consumer or
engineering markets usually require a factory
test to verify the quality of the product and its
compliance with the PDS. Curiously, this usually
relates to the performance aspects which,
although essential, represent a narrow view of
the whole question of product evolution.
Do we sample test one in ten, one in a hundred,
or what? Do we need a new test facility? How
can we be sure that the product is designed to
have rapid engagement with and detachment
from the test rig? Data collection and product
history are needed to answer these questions.
An initial test specification should be written at
this stage. It is too late after the design has been
completed! Process plants and projects of this
nature usually have acceptance and witness
tests, in addition to factory tests. As with all
testing, these require careful planning and
execution, not only to ensure compliance with
the PDS, but also to limit the cost. Do not forget
to include testing relating to product safety and
the potential of product liability legislation.
Testing
-NDI Testing
-Destructive testing
-Continuous life testing
during use
-Non-destructive
testing (ultrasound
or x-ray) to verify
adhesion
-coupon
tensile/compression
testing until failure
w/ each layup
-full assembly
destructive test
1:100
-NDI on all full
assembly units (x-
ray for bond
integrity)
The safety aspects of the proposed design and its
place in the market must be considered. Indeed,
there is a substantial body of law and standards
covering this aspect of design. Companies pay
large sums on a daily basis because they failed to
adequately consider this element of design. First,
one must identify each and every hazard. Then,
one must in decreasing order of desirability:
Safety
-Maintenance checks
-Manufacturing
techniques
Extensive -Structural integrity
tests to ensure
product is safe to
use.
-Appropriate check
schedules to ensure

32
Design out the hazard
Guard the Hazard
Warn of the Hazard
Labeling should give adequate warning. Likely
degree of abuse, whether obvious or not, should
also be considered; also likely misrepresentation
of function of equipment. Definitive operating
and maintenance instructions must be prepared.
fractures do not
form
The constraints of current company practice
should be highlighted and discussed. Is the
company constrained by its previous products? If
so, it is as well to know about it at the
specification stage. Possible manufacturing
facility constraints, financial and investment
constraints, and attitudes are very relevant. Are
there adequate in-house facilities for research,
design, development, testing, etc., including
quality of personnel.
Company Constraints -limited market
-limited material
suppliers
-limited market
-limited material
suppliers
Feedback from the market place should be
considered. It is poor design to incorporate
certain firm’s engines in equipment for some
Middle East countries, as they will not accept
them. The first rough terrain telescopic handler
was designed to utilize a range of Ford engines.
At that point in time, and for the foreseeable
future, Ford products were unacceptable in the
Middle East. Therefore, the design was changed
to accommodate Perkins engines, as well as Ford
engines. Knowledge of local conditions,
particularly overseas, combined with a full
knowledge of the market must be incorporated
in the PDS at the beginning of the project and as
the design evolves. Otherwise, if during the
course of the project the market disappears, the
whole activity may have proved to be a waste of
time.
Market Constraints
-Cost and demand
-Demand for high
performance
vehicles
-Porsche 911 and
Ford GT350R
-
All areas of likely useful information should be
investigated and researched, and in particular
possible patent clashing should be known about
as soon as possible. It is pointless designing
something for sale in ignorance of someone
else’s patent. For patent information, see the
course web site. Also, see the prior section on
Competition.
Patents, literature and
product data
-Fusion patent
owned by Carbon
Revolution
The likely effect of the product on the political
and social structure of the market or country for
which it is to be designed and manufactured
should be considered. Typical factors include the
effect of consumer movements, the stability of
the market, and the avoidance of product
features that can create social unrest and upset.
Political and social
implications
-No major impacts
-n/a -n/a
Product liability legislation, intellectual property
legislation, and other relevant legislation make it
essential to consider the legal aspects of a design
at the PDS stage. Product liability legislation
considers ‘product defect’ as its primary basis.
Many defects are designed into a product
through lack of adequate consideration of all the
constraints at the outset. You must consider ALL
aspects of use and ALL aspects of forseeable
Legal -No legal conflicts -Potential patent
conflicts with
Carbon Revolution

33
misuse, including maintenance, when designing
your product.
Many products must interface with other
products or be assembled into larger products
(or buildings). Installation therefore must be
considered in the PDS. This will include fixing
holes and lugs, access, the volume available for
the product, system compatibility, power
compatibility and the like.
Installation -install tire, valve
stem
-possibly press in
aluminum hub
-Once
manufactured,
installation of tire
and onto vehicle is
identical to metal
wheel rims.
-Bolt mounting
pattern and rim
offset must match
vehicle
Product documentation is always important in
terms of instructions to the user, the maintainer
or others. Even with consumer products, it is an
important and vital task that must not be shirked
(see ‘Safety’ and ‘Legal’. With large turnkey
projects, the associated documentation can
become a substantial part of the overall design
task, say for a power station.
In the light of previous comments re legal
requirements, it is imperative that full
documentation is prepared for all projects — this
should be done formally, not informally. It is not
unusual to refer to detailed documentation
many years after a product is in service.
Documentation -unknown -Safety and disposal
-Installation
-Warranty,
2yr/10,000 mi
-Material and
assembly properties
Disposal has been included as a primary element
as the effects of products and product design
impinge more and more on our environment.
With many products, it is not possible to ‘forget’
about the item after ownership has passed to
the customer. If the product contains hazardous
or toxic parts, or indeed parts worth reclaiming,
these should be considered at the PDS stage.
Should we, for instance, design for disassembly?
This is becoming an increasing problem with
many products, and is not necessarily confined
to time-expired nuclear reactors, chemical
process plants and the like.
Non-biodegradable plastic packaging and items
made from plastic present a problem of
increasing magnitude — in fact the whole
problem of waste disposal and recycling looms
large indeed.
While the preceding points discussed represent
the primary elements or ‘triggers’, thus enabling
the preparation of a PDS, never forget that a
specification will be, and should be, subject to
amendment and alteration with the passage of
time, it is evolutionary. When a design has been
completed, the evolved specification may be
suitably embellished with detail. Almost by
definition, it provides the basic material for
handbooks, sales and technical literature. The
PDS becomes the specification of the product
itself, rather than the specification for its design.
Therefore, it provides the basis for the user or
producer to make his decisions in a
Disposal
Product must be recycled
or incinerated.
In the EU, landfill disposal
is not acceptable
-Product must be
recycled or
incinerated.
-In the EU, landfill
disposal is not
acceptable

34
comprehensive manner. There are no
alternatives to a meticulous and thorough
approach o PDS preparation in a competitive
world. It is perhaps worthwhile reiterating that
the PDS is defined as that which sets. out in
detail the requirements to be met to achieve a
successful product or process. When the product
has been designed, it is itself specified by the
drawings, documentation, etc., which go to
describe the product in great depth. This is
known as the specification of the product — the
product specification. Try to avoid the use of
loose semantics where the one may be confused
with the other. There is a great deal of evidence
to the effect that a poor PDS is a very common
cause of unsuccessful designs.

35
Appendix B: Project Schedule

36
Appendix C: Related Patents
Edge Arrangement for a Composite Wheel, WO 2014082115 (A1) - 2014-06-05
A rim component (102) of a composite wheel (100) comprising a rim body (118) formed
around a central axis (X-X), the rim body (118) axially extending between two annular
edges (120), the rim body (118) comprising: a plurality of layers (126) of reinforcement
fibers, at least one of the layers (126) having an end (128) which extends to at least one
of the annular edges (129); and at least one substantially continuous capping layer (132)
comprised of reinforcement fibers wrapped over and around the respective ends of the
layers (126) of at least one of the annular edges (129) of the rim body (118).
Method of Designing and Producing Carbon Fiber Wheels, US 2015130261 (A1) - 2015-05-14
A method of designing and producing the spoke section of a vehicle wheel using chopped
carbon fiber pre-impregnated composite material is provided, wherein the method
allows wheel designers to machine several different wheel designs, wheel diameters, and
wheels with different offsets without using different material molds for each, as is
customary with traditional carbon fiber reinforced plastic wheels designed using a layup
procedure. The present method greatly reduces material waste, engineering design
effort for each wheel, and the cost of each wheel over existing methods by using a single
mold that can accommodate different wheel designs.
Rotary Structures, GB1425097 (A) ― 1976-02-18, IMP METAL IND KYNOCH LTD
A rotary structure comprises a hub 7, a continuous circular rim 5 of thermoplastic
material concentric with the hub and at least two equiangularly disposed spokes
attached to and extending radially between the hub and the rim, the spokes being of
filament-reinforced plastic material and having a common modulus such that upon
rotation of the structure the radial expansion of each spoke is approximately equal to the
radial expansion of the rim whereby there is negligible distortion of the circularity of the
rims. In other words the moduli of rim and spokes is such that even if there was no
connection between them the increase in length of each spoke, i.e. the point at which
the centrifugal force is balanced by the reduced stress, is equal to the increase in radius
of the rim determined by the balance between the centrifugal force and the stress
needed to stretch the rim to the increased circumferential length. In the preferred
embodiment a film may be placed on the inside of the rim of a camera drum of radius
180 mm. and capable of 25,000 r.p.m. comprises a rim of 60% by volume carbon fiber of
modulus 29 p.s.i. and spokes of 60% by volume E glass of modulus 6À8 Î 10 p.s.i. Each of
the five spokes comprised two half spokes 9, 10, each half spoke being integral with the
adjacent half spoke of the next spoke. The spokes are received in recesses in the hub and
are attached to the hub and the rim by bonding. Adjacent the rim each half spoke is

37
supplemented by a triangular cross section wedge 11 which is bonded to the rim and the
spoke. The wedges each of weight 0À005 lb increase the area of bonding between spoke
and rim and provide additional mass thereby increasing the stress on the spokes. The
correct ratio of rim modulus to spoke modulus may be obtained by varying the
proportion of filament reinforcement from 40 to 80% by volume for the spokes and 30 to
65% by volume for the rim.

38
Appendix D: Key Design Decisions
DECISION MATRIX Weight Single Piece Shell and
Center
Single Shell - Alloy
Center
Two Piece Shell -
Alloy Center
Mold Design Complexity 2 3 5 5
Manufacturing
Complexity
3 3 5 7
Design Flexibility 1 3 5 5
Scalability 2 3 5 5
Weight Reduction 3 7 5 5
Structural Performance 3 7 5 1
Totals 66 70 64
Mold Design Complexity –
Scoring: 3 is most complex and 7 is least complex.
Weight: 2 – A major part of 469 is design and it is important the project is designable in the
scope of the course. The time for design in accelerated and an easily designable project is of importance.
Reasoning for scores: Single and two-piece shells with aluminum center were ranked the same
at 5 because their mold complexity is identical, having two vertical halves with the complexity stemming
from machining and designing for the bead. A single piece shell and center was significantly more
complex. The geometry in a mold assembly designed to capture the appropriate contours of the spoke
design is beyond the scope of a semester project.
Manufacturing Complexity –
Scoring: 3 is most complex and 7 is least complex
Weight: 3 – If the part cannot be manufactured, it cannot exist in this course. Extremely
important the design can be fabricated by reasonable means.
Reasoning for scores: Similar to the mold design, the single piece shell and center would have
been out of the scope of the semester. It would require intensive 5 axis CNC capabilities to fabricate the
mold. The single shell and two-piece shell differed in manufacturing because of the interfacing required
in the single shell.
Design Flexibility –
Scoring: 3 is least flexible and not constrained by design type and 7 is most flexible
Weight: 1 - Flexibility was not of great importance because the design will greatly remain similar
between the three design types.
Reasoning for scores: The single piece shell and center is the least flexible. The geometry to
construct the mold assembly would limit the complexity of curves in the wheel center design. The single
shell and two piece with alloy center are of similar flexibility, both being restricted by mold assembly
geometry on the shell and primarily unrestricted in the wheel center
Scalability –
Scoring: 3 is least scalable and will service the smallest market space and 7 is most scalable

39
Weight: 2 – it is important the product cover the largest market space possible put being too
broad also has disadvantages in an already niche market. If the consumer wants something particular,
they will not want a serve-all product.
Reasoning for scores: For the single piece shell and center, a unique mold will have to be
designed and constructed for each unique part and center. This is extremely limiting for scalability. The
single shell and two-piece shell with alloy center both will have molds constructed with leaves that will
serve two different offsets and the alloy center can be more easily modified and manufactured.
Weight Reduction –
Scoring: 3 is least weight reduction and 7 is most weight reduction
Weight: 3 – Reducing weight while maintaining strength is the entire purpose of designing and
fabricating the carbon fiber wheel rim is to reduce weight. The single piece offers the most weight
reduction because the entire rim is carbon and has no fasteners. The single piece and two-piece shell
with alloy center provide the same weight reduction, but is still significant enough to warrant a 5 over a
3.
Structural Performance –
Scoring: 3 is the least strong and consistent and 7 is the best performance
Weight: 3 – if the rim cannot maintain structural integrity, it is a failed product.

40
Appendix E: Referenced Material Properties
The material properties used in the finite element analysis are summarized below. Only in-
plane properties were available for the carbon fiber twill used.
Table 6: Tencate HTS40 3K 2x2 Twill Mechanical Properties
E1 (psi) 7000000
E2 (psi) 7200000
G12 (psi) 548167
G1z (psi) 438533
G2z (psi) 438533
Poisson's
Ratio
0.042
Density
(lbm/in3)
0.052
Table 7: Tencate HTS40 3K 2x2 Twill Mechanical Strength
In-plane ultimate
tensile strength (psi)
110000
In-plane yield strength
(psi)
98000
In-plane bearing
stress yield strength
(psi)
80000
Interlaminate shear
strength (psi)
6100
Interlaminate tensile
strength (psi)
2200

Fall 2016 Senior Design Report - Bob's Composites Shop

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