Final Report FYP2014

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Nathan Dodd @00287566 - Final Year Project Report
1 Carbon Fibre Go-Kart Torsion Bar
Title page

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1. Abstract

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2. Acknowledgements
My thanks to Mr. P Walker, whose expertise, knowledge and patience has been invaluable and
very much appreciated. My thanks to Dr. P Hampson, for his guidance and positivity. My thanks
to Mr. M Clegg, for his services in manufacturing the ‘plugs’. My thanks to the University of
Salford, for providing the facilities and opportunity to undertake these works.

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3. Contents
1. Abstract...................................................................................................................................2
2. Acknowledgements.................................................................................................................3
3. Contents ..................................................................................................................................4
4. Introduction.............................................................................................................................6
5. Aims and objectives................................................................................................................7
6. Literature review.....................................................................................................................8
i. What is a composite? ..........................................................................................................8
ii. Composite types..................................................................................................................9
iii. Composites in industry..................................................................................................10
iv. Manufacturing of composites........................................................................................12
vi. The future of composites...............................................................................................14
vii. Finite element analysis..................................................................................................15
viii. Previous work on composites in torsion .......................................................................18
7. Theory...................................................................................................................................19
i. Karting ..............................................................................................................................19
ii. Composites........................................................................................................................20
iii. Strain gauges .................................................................................................................24
iv. Initial calculations .........................................................................................................26
8. Material selection..................................................................................................................28
i. Carbon fibre laminate MULTIPREG E720 - T300................................................................28

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10. Manufacturing the part......................................................................................................30
11. Strain gauging the part ......................................................................................................37
12. Modelling the part in ansys...............................................................................................39
13. Results...............................................................................................................................41
i. Initial calculations.............................................................................................................41
ii. Using finite element analysis ............................................................................................42
14. Discussion.........................................................................................................................44
i. Manufacturing...................................................................................................................44
ii. Calculations & Finite element analysis.............................................................................45
15. Conclusions.......................................................................................................................47
16. Further work......................................................................................................................48
17. References.........................................................................................................................50
18. Bibliography......................................................................................................................52
19. Tables................................................................................................................................53
20. Appendices........................................................................................................................54

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4. Introduction
The motorsports industry is one of the most competitive industries in the world. Large sums of
money are spent each year engineering modifications and new designs in the hope of providing
a sporting advantage.
The world of Karting is not dissimilar in this regard. Budgets may be a fraction of those seen in
the likes of formula one, but the will to win and the dedication of teams and drivers means that
the race for greater performance is still very much at the forefront of the sport.
In Karting, engineers can choose to use a torsion bar to change the characteristics of the vehicle
when cornering. Today, these bars are made from steel. Steel whilst strong, is also relatively
heavy. Because of this, the Karts ability to accelerate is compromised.
Composites have become almost synonymous with high end motorsports such as formula one
due to their high strength and low mass. Carbon Fibre is the most widely known composite today,
and is used extensively in the creation of formula one vehicles.
It is hoped that by conducting research in carbon fibre that a new carbon fibre torsion bar can be
manufactured as a replacement to the existing steel torsion bar.

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5. Aims and objectives
To understand the value of composites and how they are used in industry today. To discover the
different composite manufacturing methods and to decide an ideal method of manufacture for
this project.
To manufacture a carbon fibre torsion bar with dimensions closely matching those of the original
steel torsion bar.
To manufacture a carbon fibre torsion bar which is stronger and lighter than the steel torsion bar.
To create a finite element analysis model for the part to be able to make predictions of results and
add the reliably of results gained

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6. Literature review
i. What is a composite?
The word composite in its simplest sense means made up of several parts or elements. To
this end, composites have been being used for millennia. Fibre glass is widely considered as the
first modern composite material. It was discovered in 1930, almost by accident, “when an
engineer became intrigued by a fibre that was formed during the process of applying lettering to
a glass milk bottle” (Bent Strong 2008 p5) Carbon fibre began to be used in the 1960’s.
A composite material is made from two elements, the matrix and the reinforcement. The matrix
element of the composite provides the shape and protects the reinforcement element from the
environment. The reinforcement element of the composite provides nearly all of the strength to
the material. (Bent Strong 2008 p5)

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ii. Composite types
Srinivasan, K (2009) outlines the three main types of composites. Ceramic Matrix Composites
offer high strength and hardness, excellent high temperature properties, chemical inertness, wears
resistance and low density. There are issues however, they have poor ductility and plasticity and
cannot withstand tensile and impact loading.
Metal Matrix Composites offer Great conductivity, good temperature resistance, high ductility
and strength as well as high dimensional stability. They are limited however by the fact they have
a High density of metallic matrix, are complex manufacture and a result costly to produce.
Polymer Matrix Composites are more widely used than MMCs and CMCs due to their ease of
manufacture and lightness.

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iii. Composites in industry
Carbon fibre is the most widely known composite, and is used extensively in the motorsport
industry. In fact, DeAgostini (2012) suggests that a formula 1 car is made from 75% carbon fibre.
Lis, A (2012) tell us that it was “McLaren International technical director, John Barnard, who
pioneered the use of laminated sheets of carbon fibre in the manufacture of the monocoque of the
1981 McLaren MP4 Formula 1 car”
Carbon fibre wasn’t universally accepted at first. Lis, A (2012) states that “it had been predicted
by Sceptics that a carbon fibre chassis would crumble into a pile of black dust in a heavy impact.
John Watson ultimately proved the concept. At the 1981 Italian Grand Prix, his MP4 hit a barrier
hard enough to cause the engine and rear axle assembly to break off, yet the monocoque remained
intact. There was no fire, no pile of dust as predicted and Watson stepped out unharmed.”
Ultimately the benefits of carbon fibre (figure 9) became too obvious for anyone formula 1 team
to turn down. This is why we see today every formula 1 vehicle is made predominately of
composite materials.
In order for a formula 1 team to produce carbon fibre parts, a specialised process is used. The
first step is to cut the material into the correct shape. This is similar to what might happen in a
textile or clothes factories. In formula one A computer-controlled ultrasonic cutting machine
slices the precisely measured sheets of resin-impregnated carbon fibre cloth (DeAgostini 2012)
however some cutting work is still done by hand.
Interestingly, the carbon fibre has to be stored at -18 *C as it would be begin to harden at room
temperature. The next stage in the process is placing the cut sheets of carbon fibre into moulds,

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which in turn are placed into vacuum bags. They are then moved into the autoclave. An autoclave
(see figure 13) is a sealed vessel capable of applying pressures up to 6 times that of atmospheric
pressure. The pressure pushes the fabric into the mould ensuring an exact fit. The heat, around
130 *C, hardens the resin.
Normally at this point parts would be sent to the assembly team for finishing. However it is not
uncommon for some parts, usually those with honeycomb cores made of another material such
as Kevlar, to be sent back to repeat the whole process.
In formula 1, there are four torsion bars, one near each of the wheels (see figure 14). Over the
course of a race season, a number of varying torsion bars will be used (Caterham video). By
changing the torsion bar, you change the softness/stiffness of the car and ultimately change the
vehicles responsiveness during cornering.

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iv. Manufacturing of composites
There is a tendency for shaping processes to be time consuming as regards composite
manufacture. As well as this, processes tend be very labour intensive. As a result of these two
factors, it is relatively expensive to manufacture composite parts. Davis, S (2014) notes that “in
general, the methods used for shaping composites are less efficient than for other materials”
There are a range of manufacturing methods available to use in composites processing. The
oldest form of processing is considered to be open mould processing. This method is relatively
common but requires a skilled operator. Open mould processing benefits from a low cost
moulding process. Unfortunately however, only the side of the part in contact with the mould
will have a smooth surface finish, with the opposite side having a fairly rough surface.
There are various open mould manufacturing methods which exist. The simplest of which is
hand lay-up. In hand lay-up, successive layers of resin and reinforcement are applied by hand to
the open mould. This method is considered to be very labour intensive and as such, slow and
costly. Products produced by these means are often quite large and produced in low quantities.
A more advanced version of hand lay-up is the automated tape laying machine method. This is
similar in principle to the hand lay-up technique however in this method, a pre-preg composite
tape is applied to the mould by a machine. The machine is capable of laying material faster than
a human.
There are also a number of closed mould processes which exist. Moulds are made from two
sections and are opened and closed each time a product is made. These methods are vastly more

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expensive than open mould methods in terms of tooling, not only because of the more complex
mould, but more specialised equipment is needed as well.
Compression moulding is an ideal example of closed mould production. The material is placed
in the lower mould and the upper mould is then pressed into the lower mould. Both halves are
then heated causing the composite to cure.

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vi. The future of composites
Deaton J,P (2013) discusses why carbon fibre has yet to truly breakthrough in the automotive
industry, citing costs as one of the main issues. There are only a select few cars available to buy
which use carbon fibre. The BMW M6, Ford GT and Audi R8 are examples of cars which have
used carbon fibre. These cars are all, high end, and very expensive. “Ten years ago, carbon fibre
cost $150 a pound. Now, the price is around $10 a pound. Steel, on the other hand, costs less than
a dollar per pound.”
This isn’t the only problem however. Consider what happens when a typical car breaks down. Its
steel can be melted and used to construct another car. In contrast, Carbon fibre cannot be melted
down, and is not easy to recycle. Recycled carbon fibre isn't as strong as new carbon fibre.
Zoltek.com (2013) considers the future of carbon fibre to be positive (figure 11); suggesting that
carbon fibres use will increase in a number of industries, such as the alternative energy market
where carbon fibre could be used in wind turbines or alternatively the oil exploration industry
could pursue carbon fibre when designing deep sea drilling platforms.
Interestingly however, motorsports may in fact be an industry where the use of carbon fibre
shrinks. The Managing director of ForMetch Composites, who supplied the carbon fibre
monocoques for the Marussia team in 2012, explains that the “cost-cutting measures introduced
in recent years have also had an impact on motorsport supplier infrastructure: ‘When in-season
testing went away, the requirement of car components was reduced by around 50 per cent. Before
that, teams would complete around 80,000kms” (Preston, M 2012)

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vii. Finite element analysis
Introduced in the 1950’s, Finite element analysis was developed for in aerospace and nuclear
engineering environments. By the 1970’s FEA had become more generally used in a wider range
of industries, such as the automotive industry, however its use was still limited due to the
requirements of the expensive computing power required and the scope of the analysis that where
capable. Today however, with the advances in computer technology, FEA packages are capable
on running on most home computers. The biggest area of advancement currently is in the
integration of FEA and CAD packages
A wide range of FEA packages are available today, and ANSYS is one of the more established
packages available. ANSYS, put simply, is an industry standard piece of software used to solve
structural engineering problems.
There are a variety of analysis options available to use in the ANSYS software.
o Linear static stress analysis
o Non- Linear stress analysis
o Modal analysis
o Transient analysis
o Buckling analysis
This report will concentrate on linear static stress analysis. The most common application of FEA
analysis is for the solution of stress related problems. These problems are solved by the medium
of stiffness matrices. It is these matrices that the ANSYS software solves. It is possible to solve
fairly simple stiffness matrices by hand.

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Figure 1 Example of a stiffness matrix (Wikipedia)
However, as the complexity of the problem increases, it becomes much more difficult and time
consuming to solve the problem by hand. It is at this point that an FEA package such as ANSYS
would be sought. This is especially true for considering composite materials.
The ANSYS software works on the basis of Nodes and Elements. The area or volume of a
component is broken down into elements, with each element consisting of a number of nodes. It
is similar to saying that an image on a computer screen is made up of a number of pixels.
Elements can be either 2 dimensional or 3 dimensional, as seen in the figure below. For this
project it is necessary to use 3 dimensional elements. Nodes are not fixed in position and can be
displaced under loading.
Figure 2 Element Types (studioseed.net)

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It is important to mention that the ANSYS software is unit less. Meaning it is down to the user to
discern and ascertain the units being inputted and outputted from the software.
Moaveni, S (2003) tells us that “the 4 node tetrahedral element is the simplest three dimensional
element available in finite element analysis. The 8 node brick element is the next simplest element
available. The 10 node tetrahedral and 20 node brick elements are higher order versions of their
respective counterparts. They both offer more accuracy when modelling problems with curved
boundaries.”
The shell, layered 99 element type has been selected for this project, as it allows for layers of
material to be modelled, I.E each layer of carbon fibre. For consistency, this element type was
also used to model the steel plate.
It appears that a similar experiment has been performed by Çivgin, F (2005) whom investigated
torsional deflections and stress analysis of composite bars in torsion. In Çivgin ‘s study, finite
element analysis software (ANSYS 5.4) was used to provide computer generated results. This
version of ANSYS has now been superseded by ANSYS 15.0. Çivgin results show definite
differences between the experimental data and ANSYS.

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viii. Previous work on composites in torsion
In 2011, the BBC ran a TV series called engineering connections. In one episode, experiments
were conducted to understand the engineering behind a formula one car. One such experiment
was to consider the failure loads of a carbon fibre driveshaft and a steel driveshaft under torsion.
These experiments were conducted at the lotus f1 headquarters by Chris Jones, a test engineer.
The driveshaft’s had similar dimensions. The carbon fibre shaft was produced by filament
winding, as opposed to the hand lay-up technique used in this project.
The carbon fibre driveshaft was reported to be much lighter by presenter Richard Hammond, and
the experiment found that the carbon fibre shaft was also much stronger. This evidence supports
the theory previously that carbon fibre is generally considered to be both much lighter and much
stronger than steel.
Figure 3 Property comparisons of metals and composites (Bent Strong, A 2008)
0
1000
2000
3000
4000
5000
steel Carbon Fibre
NewtonMeters
Material
BBC EngineeringConnectionstorsionexperiment: Failure Loads

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7. Theory
i. Karting
Torsion bars are used as a tool to alter the stiffness of the chassis. Go karts vary between having
front and rear torsion bars and just having a rear torsion bar. Wright Karts (2011) say that “as a
rule of thumb, a stiffer chassis will induce less chassis flex”
The front torsion bar can be altered to provide 2 different levels of stiffness, standard and soft.
The rear torsion bar has 4 possible stiffness levels. Without the torison bar, the chassis is at its
most flexible and allows the go kart deal with quick changes of direction more easily.
The chassis can be set to ‘soft’ by setting the torsion bar with the plate section horizontal. A
standard stiffness can be achieved by either using a circular torsion as shown in the image, or by
setting the flattened torsion bar to 45 degrees. Finally the bar can be set to 90 degrees to provide
the stiffest possible set up, which allows greater stability during fast corners.
By creating the torsion bar using carbon fibre, it should be possible to attain the added chassis
stability advantages whilst also reducing the mass of the go-kart adding to the possible
performance benefits.

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ii. Composites
Composites are not particularly anisotropic, which is to say the properties of the material change
when measured in different directions, i.e. a material could be strong along its width but weak
along its length. “The strength of any sample of a glass or ceramic is predicted by Griffith’s
equation of fracture”
Equation 1 Griffith’s equation of fracture (Harris 1999 P4)
The equation describes why materials are not as strong as they should theoretically be when
considering their chemical structure of strong covalent and ionic bonds. Instead materials strength
is determined by the microscopic flaws within the material. The size of the biggest flaw (α)
directly affects the strength of the material (σ). Thin fibres can be made which due to their size
and manufacturing process, contain only the smallest of flaws. This gives the fibre much, much
more strength. “The finer the filament that can be made from a given solid, the stronger the
composite will be.” (Harris 1999 P5)
“many reinforcing fibres are marketed as wide, semi-continuous sheets of ‘prepreg’ consisting of
single layers of fibre tows impregnated with the required matrix resin and flattened between paper
carrier sheets” from here you can stack layers of prepreg on top of each other, with orientation
dependant on specific material properties. Once the required amount of layers have been placed,
they can then be “hot pressed to consolidate the laminate” (Harris 1999 P10)
Harris B (1999 P45) discusses how it is possible to interoperate the elastic properties of fibre
composites. Harris suggests that “the simplest way to estimate the stiffness of a unidirectional
composite is to assume that the structure is a simple beam.” If we assume that the two parts, the

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matrix and fibre, are perfectly bonded together, then we can assume that they deform together.
The strain in both elements is the same (iso-strain condition)
Figure 4 Simplified model of a unidirectional composite
Equation 2 Strain relationship Equation 3 Stress relationship
Equation 4 eq1 and eq2 combined Equation 5 Voigt estimate
The Voigt estimate makes the assumption that the Poisson ratios of the two components are equal.
There are more sophisticated models however which accounts for such effects. Harris B (1999
P45) suggests that the most familiar of these is from Hill (1964). Hills model shows that the true
stiffness of a unidirectional composite would be greater than that predicted by the Voigt estimate.
However Harris advises that this difference is so small as to be negligible.
Figure 5 Series model of a composite
As with the previous example, we continue to consider the matrix and fibre to be perfectly bonded
together and to have similar Poisson ratios. In this instance we consider the composite to be an
iso-stress model.
Equation 6 iso stress model
Clearly in this case, the total extension of the composite is the sum of the two components

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Equation 7 Extension of model
Dividiving through by stress and considering that Vf + Vm=1
Equation 8 Reuss estimate or inverse rule of mixtures
Equation 9Transverse modulus
There is an issue with the Reuss estimate, which is that the series modal of a composite (figure
7) doesn’t actually resemble a fibre composite perpendicular to the fibres. As a result of this, the
values predicted rarely agree with the experimental measurements. Thus the idea of a square
packed with fibres
Figure 6 Square packed with fibres
Because of this new geometry, the longitudinal stiffness is now referred to as E1 and the
transverse stiffness becomes E2. Knowing that typically Ef is much greater Em, the Reuss and
Voigt estimatese can be approximated to become
Equation 10 Longitudinal stiffness Equation 11 Transverse stiffness
It can clearly be seen that longitudinal stiffness is effected most by the fibre modulus, where as
the transverse stiffness is effected most by the matrix modulus.

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Figure 7 Shear stress in Cartesian axes
Two Poisson ratios exist in this instance. There is a major Poisson ratio and a minor Poisson
ratio.
Equation 12Major Poisson ratio
The major and the minor Poisson ratio are related
Equation 13Minor Major Relationship
The in-plane shear modulus is given by
Equation 14 in-plane shear modulus

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iii. Strain gauges
The most common way of measuring strain in an element is through the use of an electrical
resistance strain gauge. Not much bigger than a 1 pence piece, strain gauges are only small in
size. They are made from an electrically conductive wire (copper) and a sticky backing. The wire
is folded up and down a number of times (as in the below figure). Because of the formation of
the wire, it is only capable of reading strain in one direction (the sensitive direction).
The resistance of a wire is calculated by the below equation. Clearly as the cross section (A)
reduces, the resistance of the wire increases. The resistivity of a wire is a property of the material.
As the gauge is stretched, the wires elongate. As a result of Poisson’s ratio the cross sectional
area of the wire reduces. The wire is folded along the gauge a number of times. If only one section
of wire were to have its resistance change, it would be difficult to pick up.
Figure 8 How a Strain Gauge Works
(purdueMET 2011) Historically, strain gauges where used by doctors who wrapped latex tubes
around patient’s chests. Inside the latex tubes would be liquid mercury. Liquid mercury is
incompressible, and as such Poisson’s ration could be neglected. Because of this, it can be more
easily shown how the gauge factor is calculated
𝑅 =
𝜌𝐿
𝐴
×
𝐿
𝐿
=
𝜌𝐿2
𝑉
𝜌 = 𝑅𝑒𝑠𝑖𝑠𝑡𝑖𝑣𝑖𝑡𝑦, 𝐿 = 𝐿𝑒𝑛𝑔𝑡ℎ, 𝐴 = 𝑐𝑟𝑜𝑠𝑠 𝑠𝑒𝑐𝑡𝑖𝑜𝑛𝑎𝑙 𝑎𝑟𝑒𝑎
Starting with the original resistance equation, the right hand side is multiplied by length over
length, which is equivelant to one. The resulting equation has volume on the bottom. This is a
constant forliquid mercury.
𝑑𝑅
𝑑𝐿
=
2𝜌𝐿
𝑉
2𝜌𝐿
𝑉
×
𝐿
𝐿
=
2𝜌𝐿2
𝑉𝐿
Note, 𝑅 =
𝜌𝐿2
𝑉
Differentiating both sides gives the above. In order to remove volume from the equation, the
formula is again multiplied by length over length. It can be seen how the formula now has the
constituent parts of the resistance equation.

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Substituting R in,
𝑑𝑅
𝑑𝐿
=
2𝑅
𝐿
𝑑𝑅
𝑅
𝑑𝐿
𝐿
= 2 𝐾 =
𝑑𝑅
𝑅
𝜀
= 2
Substituting R in simplifies the equation. Dividing through by R and L gives the middle equation.
dL/L is equal to strain. The gauge factor (k) for liquid mercury is 2. For metals where Poisson’s
ratio must be considered, gauge factors tend to be not much greater than 2.
𝑑𝑅 = 𝐾𝑅𝜀 𝐾 = 2, 𝑅 = 120 𝑜ℎ𝑚𝑠, 𝜀 = 250𝑥10−6
For typical values, dR is very small. From the above, dR is calculated to be 0.06 ohms, which is
a very small percentage of the size of our resistor. Another problem is that the data acquisition
system used to register the changes is only capable of registering changes in volts. A Wheatstone
bridge is used in order to solve this problem.
R1 in the Wheatstone circuit would be the strain gauge. The wheatstone circuit works in the same
way a voltage divider works. Consider the voltage divider, if 1 volt (U1) was input, and the
voltage is discipated across both resistors, then if both resistors are the same value, say R1=R2=1
ohm, then U2 (the voltage out) would be half the voltage in. In the wheatstone circuit, this
equationis expanded slightly to compensate for the extra resistors.
Where R1xR3 = R2R4, this is considered to be balanced bridge. From the previous example,
consider R2=R3=R4 to be 120 ohms and R1= 120 ohms + 0.06 ohms, say that a voltage of 12
volts Vin, them the resulting voltage would be Vout= 1.5mV. whilst this may not be a high figure,
it is easy enough to measure and can also be amplified simply enough.

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iv. Initial calculations
Before beginning computational analysis, it was deemed useful to find results analytically in
order to validate future work. In order to simplify the problem, the plate section of the torsion bar
was considered as a single entity. The plate was fixed at one end and forces applied on the
opposing end to create a torque, as seen in the below figure. A range of forces where used to
calculate torsion angles and stresses.
Roark (2014) tells us that when a torque is applied to a bar, “The bar twists with each section
rotating about its torsional centre. These sections do not remain plane to one another, but in fact
warp. The distribution of shear stress on the section is not necessarily linear, and the direction of
the shear stress is not necessarily normal to the radius.”
In this instance, the cross section of the plate is not circular and thus the problem is not a standard
torsion problem. Normally the value of J (the polar moment of inertia) for a material could be
used, and the standard equations for torsion could then be simply applied.
In order to be able to solve this problem, the above equation is used to start, where T = twisting
moment, L = length of the member, r = outer radius of the section, θ = angle of twist (radians),
G= modulus of rigidity of the material. K is a factor dependent on the form and dimensions of
the cross section. The maximum stress is a function of the twisting moment and of the form and
dimensions of the cross section.

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The steel plate section of the torsion bar contains a small hollow section. Findings will be
calculated for both a hollow plate and whole plate in order to discern how much of an error is
incurred by making this simplification.
It is expected that the hollow cross sectional version will be weaker than the solid plate, however
it is not known by how much. Should the difference be negligible, then it is advisable to continue
with the solid plate cross section as this is clearly the simpler piece to model. In terms of shear
stress, it is expected that the hollow plate should have greater shear stresses, due to there being
less material to effectively spread the load across.

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8. Material selection
i. Carbon fibre laminate MULTIPREG E720 - T300
The carbon fibre torsion bar to be manufactured from carbon fibre will be made using prepreg
sheets. The process of manufacturing with composite fibres is not a flawless one, and there is
the potential for a number of defects to appear such as those in figure 7. It is hoped that by
using prepreg sheets that these defects are less likely to occur.
Figure 9 Composite laminate defects (Harris B 1999)
Amber composites (now officially named tencate advanced composites) provides a prepreg
carbon fibre sheet – MULTIPREG E720 – which has the required characteristics for use in this
project.
MULTIPREG E720 is an ideal material because it can be easily laminated onto mold surfaces,
provides a good surface finish and doesn’t require the use of solvents during processing. Amber
composites (2014) suggest that MULTIPREG E720 is used in “structural components in motor
racing, marine, aircraft fittings and sports equipment.” Which again provides confidence is its
use in this project.

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There are two different types of MULTIPREG E720 available, T300 and T800. T300, the more
commonly used of the two, has been chosen for this project. T300 is a woven carbon fibre
sheet, such that 50% of the fibres run horizontally and 50% vertically

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10.Manufacturing the part
Figure 10 Go-Kart Torsion Bar
After considering all of the possible manufacturing methods, the hand lay-up method appears to
be the most suitable. Whilst the process may be time consuming, there should be sufficient time
available to complete the production of the part. The method is often used for products produced
in low quantities, and considering that only on part is expected to be produced, the manufacturing
method would seem the best fit for this project. In addition to this, the university is able to supply
skilled expertise in this manufacturing method such that there is a good chance of a product being
produced successfully. Whilst filament winding would be an interesting alternative, the resources
are not currently available for this method of manufacturing to be used.
Figure 11 box production

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In order to produce a carbon fibre torsion bar, a mould must first be made. The first step is to
create a wooden box which will ultimately contain the resin. A quick design was produced
(figure 18) and dimensions where marked out on a sheet of wood for the 2 sides, 2 ends and
base. The box dimensions are such that there should be approximately and inch clearance
between the box and the torsion bar. The sheet was then cut on the jigsaw (figure 19)
Marking’s where made on the 2 ends and sides at 3cm intervals to denote where pilot holes
would be drilled. These were drilled using a pneumatic drill. (Aside – the drill bit is fragile and
broke on one occasion)
1 ¼ inch long nails were then located into all of the pilot holes (figure 20). Wood adhesive was
used to glue the sides to the base, and the nails where then hammered in. extra wood adhesive
was used to fill in cracks in the base (figure 21).
Figure 12 Plug design and initial manufacture
Plugs were required to plug the two open ends of the steel torsion bar. They have been designed
to fit tightly within the bar and are of a length to ensure stability. Upon fitting the completed
plugs into torsion bar, it was identified that the flanges where too large and were further
manufactured so that the plugs were ‘flush’ with the torsion.

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Figure 13 box lined with plastic sheet
The box was lined with a plastic sheet so that the mould could be more easily removed from the
box once set. The mould is produced by mixing three ingredients. Four parts a white ‘flour’
substance, two parts resin and one part hardener. The hardener is only added to the resin after
the resin is mixed with the flour. This is because when the resin and hardener mix, it can give
off carcinogenic gases. In addition to this, the mixture will solidify too quickly without the
addition of the flour. The mould should normally solidify in three to four days. 562g Flour,
281g Resin and 140.5g Hardener were initially used. However the resulting mixture proved too
thin, and further flour was added until the viscosity and consistency of the liquid was treacle
like (figure 24). Once sufficient mould mixture had been poured into the box, the steel torsion
bar was pressed into the top of the mould mixture to create an impression of one half of the bar.
The bar was left in place for the mould to set around.
Figure 14 steel bar removed leaving mould cavity
Once the mould had solidified it was necessary to remove the steel torsion bar. Unfortunately,
mould had set a few millimetres too high. This meant removing the bar was going to require

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extra time and effort. Had the bar simply been removed using blunt force, the mould would
have broken and as such been rendered useless. The excess mould material was sanded down
and WD40 was applied in order help release the bar from the mould. Once the bar had been
released, there appeared to be some minor damage around the rim of the mould, however
because the mould had set slightly too high, it meant that this was not a problem, as the area
below the minor cracks was fine. It is useful to note at this point that the completed mould is re-
usable, allowing for any number of parts to be produced which can be made from, but not
limited to, carbon fibre.
Figure 15 minor damage to the mould along edges
The process of hand laying the carbon fibre had begun at this point. As previously decided, the
bar is going to be produced so that it is 6 layers thick, however because there are two halves
being produced, 12 sheets of carbon fibre were required to be cut. Each sheet was cut to be
approx. 60mm wide by 120mm long. The first layer was applied to mould by peeling the white
covered side and pressing the carbon fibre into the mould. Once fitted to the mould, the green
side of the carbon fibre was removed and the process was repeated. As each layer is added,
check were made to ensure that the carbon fibre sheets were conforming correctly to mould
shape. In some instances, due to the sticky nature of the carbon fibre prepreg sheets, the layers
were sat with crease in. where this occurred, the layers were carefully split reattached properly.
The process was repeated in the exact same manner to produce both halves.

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Once 6 layers had been fitted into the mould, the mould was put into a vacuum bag. The
vacuum bag was created by placing the mould centrally on a glass surface and fixing a plastic
sheet over the mould. The plastic sheet was attached around the circumference of the glass
using strips of black sticky stuff. Three pump attachments were placed inside the vacuum bag,
sat loosely on the glass. Two pumps where then attached and a pressure gauge attached to the
third remaining attachment in order to check the quality of the vacuum which was created. The
pressure within the vacuum was indicated to be 20 psi, which is the pressure amber composites
(2014) recommends.
Figure 16 Vacuum bag
The mould, still in the vacuum bag, was moved into the oven to cure. The vacuums were
reattached, and the heat cycle set. The curing process approx. 30-40 minutes from room temp to
120*C and then 2 hours at a constant 120*C. During the heat raising period, the carbon fibre
was manually prodded at intervals of 10*C, starting at 80*C. this was because the carbon fibre
was beginning to soften during this period, and it provided one last opportunity to ensure that
the carbon fibre was conforming to the mould.

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The pressure readings for the vacuum whilst in the oven were less than had been seen initially,
ranging between 15 psi to 20 psi. A third pump was added in order to compensate for this. This
process was repeated to create both sections of the part.
Figure 17 cured carbon fibre
Once the parts had cured, the excess material was cut. In order to get to carbon fibre version of
the bar match the steel bar as closely as possible in terms of dimensions, the edges were sanded
down until the diameter of the two sections joined was to within +/- 1mm, 30mm. unfortunately
during this process, one edge was sanded 2mm to deep, creating a gap when joining the two
sections. This was resolved by carefully sanding the other edges to close the gap as much as
possible. It is interesting to note this section is still somewhat noticeable now, with the key give
away being the amount of glue which is visible between the sections at this point.

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]
Figure 18 gluing the middle section
Glue was initially applied to the flat sections of the bars, and the bars where quickly then
clamped into place. Glue was then applied internally along the joining edges. Once the glue had
hardened, the ends of the bar needed to be removed. As a result of the production method, each
end was very rough, and had neither cured properly nor conformed entirely to the mould. This
was not a problem however as the bar was built slightly too long with this in mind. About half
an inch was removed from each side.
The surface of the bar was then sanded and cleaned to provide a better surface finish. This
would help with the strain gauging.
Figure 19 visual comparison [carbon fibre top, steel bottom]

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11.Strain gauging the part
Begin by marking out on the part where the strain gauge will be intended to go. Then on a
separate, chemically clean, clear surface, position the copper solder terminal(s) close to the strain
gauges, leaving a gap between the two of not much more than 5mm. cut a length of tape and stick
the gauge and terminal onto the tape by pressing the tape down onto them. Make sure the gauge
is central. Carefully lift the tape, making sure not to bend the gauge. Line the gauge up with the
marking on the part. Loosely stick the tape to the surface, and peel back slightly. Thinly apply
the M-Bond200 catalyst along the gauge and apply M-Bond200 adhesive at the part where the
gauge will sit. Lower the tape and wipe excess adhesive. The glue will cure at room temperature,
allowing for the tape to be removed almost instantaneously. Again be careful when removing the
tape.
Figure 20 Strain gauged torsion bar
Wires on the gauge can then be soldered to the copper solder terminals by carefully peeling the
wires from the glue using tweezers. Use a small amount of masking tape over one half of the
terminal to ensure that room is kept clear to attach the electrical wires later.
Once all of the gauges have been soldered to the terminal, the wires will require preparing for
solder. To do this, separate the wires on one end slightly such that the green black and white wires
are free from each other. The remove 5mm worth of the wire insulation to expose the metal
wiring. A similar process is required at the other end, only this time ensure that the black and

38
]
green wires are kept together and only the white is separated. Once this is completed, number the
wires using some masking tape and a pen, from 0 to 7.
The end with which only the white was separated is soldered to the terminals, the white wire
always being on the left relative to the strain gauge. When soldering at the terminal, ensure that
the left and right wire connections are kept separated, as this could cause the circuit to fail. Do
this in numerical order, such that for the strain gauge rosettes, the numbers run chronologically
clockwise.
Once all wires have been soldered to the part, tape them together along every inch to form a cable.
The other ends of the wires are soldered into the plug, again in numerical order, in the order of
white green black. Be sure not to solder between the plug terminals, as this could result in a circuit
failure.

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]
12.Modelling the part in ansys
The plate shape was created in ansys by in putting the position of the 4 corners as Key points in
active CS. the Area was then added to the model
At this point the element type was selected. Shell: linear layer 99. Real constants were added,
which is to say that the number of layers and the thickness of each layer was selected.
The material properties (young’s modulus / Poisson’s ratio) were added. For steel these were
isotropic and for carbon fibre, orthotropic. This relates to the properties of the material in different
directions. As previously discussed, carbon fibre can be made to have very different properties
from one axis to another.

40
]
The modal was then meshed using meshed, with element size 3mm x 3mm and the using the quad
element type.
The left side of the modal was fixed by setting the degrees of freedom for the displacement to 0.
Forces where added, acting at a normal to the area. Using the Rotation vector sum option for
nodal solutions, the maximum rotation was noted with the result in radians.

41
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13.Results
i. Initial calculations
Figure 21 There is a 19.6% difference in the torsion angle produced for all torques.
Table 1 Values for K for different cross sections
Figure 22 the solid plate shears by 44% consistently as torque is increased.
Table 2 2nd method comparison for shear stress (Freestudy.co.uk 2014)
K- Hollow 771.2975543 mm4
K- Plate 906.2402797 mm4
Roarks 2nd method
shear stress (N/mm2
) shear stress (N/mm2
)
0 0
40 38
79 75
119 113
159 150
199 188
Solid Plate
Roarks 2nd method
shear stress (N/mm
2
) shear stress (N/mm
2
)
0 0
28 26
55 52
83 78
110 103
138 129
Hollow Plate

42
]
ii. Using finite element analysis
The theoretical result seems to match quite well with the computational results. The solid plate
torsion angle is consistently 7.8% greater than the ansys prediction. This is a relatively small
discrepancy; however it is not inconsequential in size. It can be considered that the ansys software
is providing reliable results for this simulation.
Straight away, there is clearly a huge difference in the two materials ability to cope with torsion.
The carbon fibre plate appears almost incapable of resisting any torque, whereas the steel plate
twists by only a small amount. This result appears contradictory to the previous evidence.
0
20
40
60
80
100
120
140
0 9000 18000 27000 36000 45000
Torsionangle(degrees)
Torque (Nmm)
Carbon Fibre Versus Steel
steel
Carbon
Fibre Orth

43
]
The steel also appears to suffer less shear stress than the carbon fibre; however this is by much
closer margins than the torsion angles. Again the results indicate that the steel torsion bar will
perform better.
0
50
100
150
200
250
300
350
400
0 9000 18000 27000 36000 45000
ShearStress(Newtons/mm2)
Torque (Nmm)
Max shear stress
Carbon Fibre
Steel

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]
14.Discussion
i. Manufacturing
There were a number of issues which arose during the manufacturing process. It is possible that
these issues could have compromised the potential strength of the carbon fibre torsion bar.
One key issue came during the vacuum bagging process. Initially the required pressure was
achieved within the bag, however this pressure proved difficult to attain once the part had been
moved into the oven. In the future a number of things could be done to combat this. The simplest
is perhaps to use extra vacuum pumps as was done in this project. However another solution
should finance and circumstances allow, would be to use an autoclave instead.
By improving the pressure during the curing process, it is more likely that the carbon fibre laminas
will be pressed tightly together, thus increasing the fibre density across the cross section of the
part.
During the joining process of the halves, a section of the part was sanded 1mm too deep. This in
turn meant that more glue was required to join the part at this section. It can be considered that
the strength characteristics of the bar are not uniform across the length of the bar as a result,
however it is unknown the scale of this effect.

45
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ii. Calculations & Finite element analysis
The initial calculations proved to show expected results, with the hollow cross section twisting
by more than the solid plate. Whilst 19.6% may seem a large error, this nominally small for low
values, even at its most extreme no more than 1* degree.
What is more unexpected is that there appears to be a greater shear stress in the solid plate. The
results appear to show that the solid plate experiences 44% more shear. The reliability of these
results is questionable, given that in this scenario, the solid plate (which has twisted less) would
be first to fail. One hypothesis for this difference is that the Roark’s equations are for shear max
on the solid plate and shear average on the hollow plate. This is why further investigation was
conducted using a 2nd methodology from a separate source (freestudy.co.uk 2014). The results
are similar between to the two different methods, meaning that they are either correct, or the
fundamental understanding of what the equations mean is flawed. In my opinion it is the
understanding which maybe flawed, in terms of what the average shear stress means for the
hollow plate.
It was with this reasoning that the solid plate was used as the basis for further analysis as it appears
to represent adequately the real world situation. There is also much more confidence in the solid
plate results.
The solid plate theoretical results where compared with those gained using finite element
analysis. The results match fairly closely, with only a 7.8% error. It can be considered that the
ansys software is providing reliable results for this simulation.

46
]
The ansys software appears to show that the steel torsion bar would be the much stronger of the
two. Whilst this result is not what was expected, it does not mean that the carbon fibre torsion bar
is without use in the application of motorsport. It is still possible that because of the mass
advantage over the steel torsion bar, that if the carbon fibre bar provides enough extra chassis
stiffness relative to its mass, it could still provide a performance advantage over the steel bar.
Both the shear and torsion angle results support a hypothesis that steel is stronger than carbon
fibre. However from the research conducted within this project, this would appear to not be the
case.
In the case of the BBC engineering connections experiment, one possible and likely key,
difference between the computational results in this project and their results is the method of
manufacture. It is perhaps that case that for torsion of composites, filament wound products are
much stronger than those created via hand lay-up. Alternatively, the manufacturing method may
be useable but require the use of more layers of carbon fibre in order to work. However is this
were to be the case, the cross section of the part would cease to match as closely with the steel
counterpart, which was one of the aims of the part.
There may be issues with how the problem was modelled within ansys. This may be the case
despite evidence that ansys is providing reliable results. Modelling of composites is much more
complex than modelling of standard materials such as metals. As a result of this, it is possible
that errors in the programming of the problem may have occurred. In order to truly know how
accurate the ansys results are, they must be compared to experimental data.

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]
15.Conclusions
Without experimental data to prove otherwise, the ansys results are deemed to be reliable as there
is more evidence to support this hypothesis than there is to object to it.
The results therefore indicate that the steel torsion bar is the more likely to provide a greater
chassis stiffness, at a higher mass.
In order to manufacture the best possible carbon fibre torsion bar, another manufacturing method
may be required. Filament winding appears to show the most promise.

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]
16.Further work
In the future it might be possible to use an alternative method of manufacture. The most promising
alternative being the filament winding method.
Figure 23 filament winding process
Filament winding has been described as a relatively simple process (Akovali, G 2001). In
principle it is not so dissimilar to knitting. A series of parallel individual fibres are wrapped
around a mandrel. A mandrel is a rod or spindle which is used to aid the manufacture of a given
material
There are a number of advantages in choosing to filament wind the part. Filament winding is a
highly repeatable method of manufacture, which would be ideal should the product be brought to
market. Because continuous fibres are used in the loading direction, high strengths can be attained
by finding the best winding angles and pattern. High fibre volume percentages are used allowing
high strength products to be produced. Capitol cost and process costs are relatively low, for
example the filament winding process does not require the use of an autoclave. Material costs are
relatively low as well in comparison to prepreg materials. Whilst not applicable to this project, it
can be noted that it is possible to create very large parts using this process.
However, there are also a number of limitations. Complicated shapes require the use of very
complex mandrel designs which are costly. Reverse curvature parts are not able to be produced

49
]
via this method. A reverse curvature is a curve which follows an ‘S’ shape. The current design of
the torsion has reverse curves between the flat plate and tube sections. However it may be possible
to redesign the torsion bar as cylinder in order to allow the filament winding method to be used.
Figure 24 possible issue
Mandrels are expensive to purchase and/or create and are indispensable once attained. The
surface quality of filament wound products is not as good as those created by means of an
autoclave and surface machining is often required.
The resin system for filament winding differs somewhat from the hand lay-up system. Filament
winding, as with other composite production techniques, requires the use of a resin. The purpose
of the resin remains nearly identical to any other production method. In filament winding the
resin protects the fibres from abrasion during winding and once cured the resin protects the fibres
from abrasion and corrosion. As regards filament winding, the most widely used resins are epoxy,
polyester and vinyl thermosets, however phenolics, polyimides and silicones are also used in
winding applications.
For most high performance applications epoxy resins are most commonly used, especially within
the aerospace and military applications. Polyester and vinyl resins are much more cost effective
however and are used much more extensively for commercial applications.
When deciding which resin is most suitable, there are a number of factors to take into account.
Resin viscosity can have a profound effect on the filament winding process.

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]
17.References
Akovali, G (2001) Handbook of composite fabrication. Rapra technology limited, Shawbury,
Shrewsbury.
Bent Strong, A (2008) Fundamentals of Composites Manufacturing: Materials, Methods and
Applications 2nd edition, society of manufacturing engineers, Michigan.
ÇIVGIN, F (2005) ANALYSIS OF COMPOSITE BARS IN TORSION, DOKUZ EYLUL
UNIVERSITY GRADUATE SCHOOL OF NATURAL AND APPLIED SCIENCES.
Davis, S (2014) Composite processing lecture notes, the University of Salford, Salford.
DeAgostini (2012) what is a Formula 1 Car Made of?, DeAgostini Model Space
Retrieved 23/11/13 from http://www.model-space.com/nz/articles/what-is-a-formula-1-car-
made-of/
Deaton J,P (2013) Can carbon fibre solve the oil crisis?, How stuff works
Retrieved 25/11/13
http://auto.howstuffworks.com/fuel-efficiency/fuel-economy/carbon-fiber-oil-crisis2.htm
FreeStudy.co.uk (2014) Torsion of thin walled sections and thin strips
Retrieved 16/04/14 from http://www.freestudy.co.uk/statics/torsion/torsion2.pdf
Formula1.com (2005) Monaco set-up - dampers
Retrieved 23/11/13 from www.formula1.com/news/technical/2005/737/121.html

51
]
Harris B (1999) Engineering composite materials 2nd edition, IOM Communications ltd,
London
Srinivasan, K (2009) Composite materials- production, properties, testing and applications, Alpha
Science International Limited, Oxford
Tsai S W (1992) Theory of composites design. Think Composites, France
Lis, A (2012) Current trends in composite thinking, Racecar Engineering
Retrieved 07/02/14 from www.racecar-engineering.com/wp-
content/uploads/2012/08/compositesMAINOpti.pdf
Moaveni, S (2003) finite element analysis – theory and application with ansys, second edition.
Pearson education, upper saddle river, New Jersey
Pisanello, G (2012) What is a torsion bar?: Caterham F1 technical
Retrieved 23/11/13 from www.youtube.com/watch?v=MKt39DhgtX8
Preston, M (2012) Current trends in composite thinking, Racecar Engineering
Retrieved 07/02/14 from www.racecar-engineering.com/wp-
content/uploads/2012/08/compositesMAINOpti.pdf
vishaypg.com (2011) Strain Gage Installations with M-Bond 200 Adhesive, www.micro-
measurements.com

52
]
Wrights Karts (2011) Kart maintenance & general set-up manual
Retrieved 08/02/14 from
http://www.wrightkarts.com/FileLib/Manual%202011%20Chassis%20-
%20General%20User%20Guide.pdf
Zoltek.com (2013) The Future of Carbon fibre, Zoltek.com
Retrieved 07/01/2014 from http://www.zoltek.com/carbonfiber/the-future-of-carbon-fiber/
18.Bibliography
USA DEPARTMENT OF DEFENSE (2002) COMPOSITE MATERIALS HANDBOOK
Accessible: http://www.lib.ucdavis.edu/dept/pse/resources/fulltext/HDBK17-3F.pdf
Composites Leadership Forum (2013) UK COMPOSITES 2013: A Study into the Status,
Opportunities and Direction for the UK Composites Industry.
Phillips, N L (1989) Design with advanced composite materials 1st edition. The design council,
Haymarket, London.

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19.Tables

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20.Appendices

Final Report FYP2014

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