Finished version 2016

Investigation into How Brake Disk Design Affects Cooling

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This report is submitted in part fulfilment of the requirement

for the award of Bachelor of Engineering (Honours) in Mechanical Engineering

25ft May 2016

By

Sean Lydon


Institute of Technology, Sligo


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ABSTRACT

This thesis reports on an investigation of a novel approach to the cooling of brake disks, based

on the three different designs. The design features on a brake disk have the capacity of cooling

down the disks more efficiently without affecting the disk properties. The disk brake is a device

for slowing or stopping the rotation of the wheel, repetitive braking of the vehicle leads to heat

generation during each braking event. The author also set out to do some tests on a road at

emergency braking to see what heat was generated in a 0.2 km strip of road at 1470 psi of

pressure.

The law of conservation of energy states that energy cannot be created or destroyed but only

changed from one form into another. When two objects are sliding on a surface, friction is

created that energy is transferred onto the surface that the moving body is sliding upon. This

transferred energy turns kinetic energy into heat energy

The testing carried out on the three disks hoped to show that the additional design features on

that specific disk would cool down faster than other disk, later the author found that this did

not always happen as expected in spite of the added design features.

Using a purpose built test jig along with a brake line and additional brake hoses equipped with

a pressure gauge the author set out to apply the brakes at a set pressure and a set time to see

what heat was generated during that time and then applied the same principles to each set of

disks and finally compared all three to see which one was most effective at cooling the disk.


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ACKNOWLEDGEMENTS

I would like to thank all the people that took part in this research and helped me to complete

this thesis.

I would first like to thank my supervisor Dr David Mulligan for his continued support

throughout the year, His knowledge of materials and lab testing apparatus and his guidance on

my approach to testing have helped me overcome problems that arose throughout the course

of the thesis

I would also like to thank my local mechanic Billy Reilly for his extensive knowledge on cars

and also the use of his car for my testing. He has also helped me through some issues we had

that arose during the testing.

Finally, I would like to thank my brother David and my Dad for their assistance during the

testing, and the work that was put into to make the brake rig.


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Declaration of authorship

I hereby certify that the content of this project is entirely my own work and is submitted in part

fulfilment of the B.Eng (Honours) Degree in Mechanical Engineering at the Institute of

Technology, Sligo.

Any material adopted from other sources is dully cited and referenced and acknowledged as

such.

Signed: _______________________

Sean Lydon

Date: 25ft May 2016


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Table of Contents

Declaration of authorship ............................................................................................ 4

1.0 Introduction .................................................................................................... 7

1.1 Objectives ..................................................................................................... 8 1.2 Methodology.................................................................................................. 9

Chapter 2. 2.0 Literature review ........................................................................ 10

2.1 Structural and contact analysis of disk brake assembly during single stop braking event. .................................................................................................................... 11 2.2 Analysis of heat conduction in a disk brake system ........................................ 12 2.1 Design and optimization of ventilation disk brake for heat dissipation ......... 12

2.2 Analysis of ventilation disk brake using CFD to improve its thermal performance .......................................................................................................... 13

2.3 Structural and thermal analysis of rotor disk of disk brake .......................... 14

Chapter 3. How does cooling a brake system work? ..................................... 15

Chapter 4. Cooling in brake disk’s ................................................................... 16

4.1 Types of disks and ventilation features ....................................................... 17 4.2 Grooved and vented brake disk .................................................................. 18

4.3 Cross drilled and grooved brake disk .......................................................... 19 4.4 Benefits and drawbacks of different brake disks. ........................................ 20

4.5 Cross Drilled Brake Disk ............................................................................. 21 4.6 Advantages of ventilation in disks. .............................................................. 22

Chapter 5. Drum vs Disk brake braking systems ............................................ 23

5.1 Disk and Drum brake comparison ............................................................... 24

5.2 Drum Housing ............................................................................................. 25

5.3 Reliability .................................................................................................... 25 5.4 Reliability of braking systems ...................................................................... 26 5.5 Deterioration of a Disk brake ....................................................................... 27

5.6 Deterioration of brake Disk vs New Disk ..................................................... 28

Chapter 6. Installation ....................................................................................... 29

6.1 Warped disks .............................................................................................. 30

6.2 Brake corrosion ........................................................................................... 31 6.3 Methods for suppression ............................................................................. 31

Chapter 7. Material selection ............................................................................ 32

7.1 General material performance requirements ............................................... 33 7.2 Initial screening of candidate material ......................................................... 34 7.3 Material selection using digital logic method ............................................... 35

7.4 Optimum Material selection ......................................................................... 36 7.5 Conclusion .................................................................................................. 36 7.6 Ashby’s chart ............................................................................................... 36 7.7 Physical Insights ......................................................................................... 37

7.8 Microstructure of cast iron ........................................................................... 38 7.9 Lab setup .................................................................................................... 39 7.10 Viewing the specimen .............................................................................. 41


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7.11 Physical Micro-structure of cast iron untouched ...................................... 43

7.12 Applications and other uses ..................................................................... 44

Chapter 8. Testing and analysis ....................................................................... 45

8.1 My approach ............................................................................................... 46 8.2 Testing apparatus ....................................................................................... 47 8.3 Brake pedal rig ............................................................................................ 48 8.4 Planning ...................................................................................................... 50

8.5 Vehicle and Brake data: .............................................................................. 51 8.6 Static Testing .............................................................................................. 52 8.7 Equipment being tested: ............................................................................. 53 8.8 Test 1 (Standard vented brake disk – worn 151200km) .............................. 54 8.9 Thermal Imaging readings .......................................................................... 55

8.10 Test 2 (New standard brake disk) ............................................................ 56 8.11 Thermal imaging readings ....................................................................... 57

8.12 Test 3 (Grooved brake disk) .................................................................... 58

8.13 Test 4 (Cross drilled) ................................................................................ 60 8.14 SolidWorks sketches of brake disks ......................................................... 64 8.15 Vehicle braking calculations ..................................................................... 69 8.16 Vehicle configurations .............................................................................. 70

8.17 Calculations ............................................................................................. 72

Chapter 9. Practice braking tests ..................................................................... 74

9.1 Conclusions................................................................................................. 75

9.2 ......................................................................................................................... 76 9.3 Brake disk material: ..................................................................................... 76 9.4 Brake disk design: ....................................................................................... 77

9.5 Brake disk materials: ................................................................................... 77 9.6 Recommendations Thermal Analysis (SolidWorks) .................................. 78

9.7 ......................................................................................................................... 79 9.8 Thermal Analysis Overview ......................................................................... 79

9.9 Thermal Analysis Overview (2.0) ................................................................ 80 9.10 Finite element analysis ............................................................................ 81

9.11 ....................................................................................................................... 81 9.12 ....................................................................................................................... 82 9.13 ....................................................................................................................... 83

Chapter 10. References ....................................................................................... 84


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1.0 Introduction

Vehicles today whether big or small or how fast they go will need a good braking

system to slow down or stop the rotation of the wheel. Cars and trucks need brakes

for safety. A disk can be made out of different materials, most common ones are cast

iron/steel or ceramic composites. Brake pads are made up of frictional material which

is then forced mechanically by a hydraulic ram against the disk. This friction causes

the disk and attached wheel to slow down or come to a halt. Newton’s first law also

referred to the law of inertia states that “An object at rest will remain at rest unless

acted on by an unbalanced force, an object in motion continues in motion unless acted

upon by an unbalanced force”. In terms of our braking system, the disk will keep in its

state of motion unless acted upon an unbalanced force which will, in this case, slow it

down.


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1.1 Objectives

The objective of this thesis is to:

Investigate the different braking systems in a vehicle and their performances

Analyse the results of one practical braking distance test

Complete bench tests on all 3 disks and compare results to road tests

Investigate the various designs of brake disks and their cooling properties

Analyse the data and state which disk has the best rate of cooling

Use the TM3000 electro microscope to investigate the ware on the worn brake

disk

Compare all 3 results and show which disk is most efficient


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1.2 Methodology

Research was carried out using the vehicle provided to test the effectiveness of three

different vented brake disks to show the heat dissipation of each type and then draw

conclusions based on the evidence. The approach taken to accomplish this involved

the following steps:

Research journal papers that have already conducted this type of

work

Separate the brake hose from the calliper and connect to tee piece and appropriate gauges

Install brake rig to brake pedal as to have a consistence pressure when doing testing

Take heat readings using thermal camera to show heat output from brake disks

Analyse all date and determine which disk had best rate of cooling


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Chapter 2. 2.0 Literature review

This section of the thesis outlines the research that was carried out in order to

understand the heat dissipation of brake disks and how they cope under intensive

braking at high pressures.

It outlines summaries of previous journal papers that were carried out on

brake disk heat dissipation, be it physical testing or simulated data or

both

Research into the comparison between physical testing and/or static

testing on brake disk design via heat dissipation.

Investigation into finite element analysis papers to show the simulated

data based on heat dissipation of brakes

Investigation into structural and thermal analysis of brake disks the use

of CFD to improve thermal performance.


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2.1 Structural and contact analysis of disk brake assembly during single

stop braking event.

(Ali Belhocine Abd Ramhim, 2013; Ali Belhocine, 2014)

The aim of this was project was to examine stress concentration, structural

deformation and contact pressure of the brake disks during the braking phase, other

factors which were taken into account was different coefficients and also different

speeds throughout the testing. The results than would provide better explanation of

contact pressure in a brake disk, (Figure 1 & 2) shows the designer using CFD which

provides an effective solution for multiple designs and engineering uses for brake disks

and brake pads. Where there is contact in any situation there is frictional heat

generated, this causes high temperatures which may in some cases exceed the critical

value of the given material, such problems which exist because of bad ventilation lead

to undesirable effects. Combined factors leading to failure in brake disks are stopping

at high speeds which generate high temperatures over time, poor thermal physical

and durable properties. Ventilation is very important in a braking system and poor

distribution of heat at the surface of the disk leads to thermal distortion such as coning.

The next step in improving the overall structural properties in a brake disk was to model

a 3D brake disk and run simulations on it, varying the numerical data so as to get the

best possible results one could generate.

Figure 1 Shows the thermal deformation

Figure 2 shows the thermal elastic

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2.2 Analysis of heat conduction in a disk brake system

(Faramarz Talati, Salman Jalalifar, 2009)

In this project, research was done using heat equations for the brake disk and the

brake pad to calculate the heat generated which are variables to time and space. Such

areas to be covered are duration of braking, vehicle velocity, geometrics and the

overall sizes of the disk, other factors such as disk material, contact pressure have

been taken into account. The main objective here is to eliminate the high rising

temperatures and brake fluid vaporization. Repetitive braking such as descending

down a hill will lead to temperature rise which in turn will reduce its thermal

performance. Results revealed that maximum rose more with uniform pressure than

that of uniform wear, the reason this happened is that with uniform pressure the high

friction and work done tends to rise more rapidly as the radius increase while with

uniform wear it does not vary with the radius.

Design and optimization of ventilation disk brake for heat dissipation

This involves research and analysis behind why

brake disks heat up. Braking is the process of

converting kinetic energy of a moving body into

heat energy. During this process friction is

generated and used to slow down or stop the

moving body. In (Figure 3) the heat generated

from this friction produced is stored in the disk

and later released into the air, repetitive hard

braking cause’s thermal stress in the disk multiple

failures such as premature wear, elastic instability, brake vibrations, in order to

address these issues ventilation has come into consideration. Various designs on a

brake disk are used to remove this heat along with ventilation along the rim of the disk.

The 3D model can be done by SolidWorks and the analysis was done by a software

known as ANSYS, which is a special programme used for determining the temperature

distribution and deformation of the disk. The best result will be based on magnitude

of von misses stresses, temperature distribution and deformation.

Figure 3 shows thermal stress


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2.2 Analysis of ventilation disk brake using CFD to improve its thermal

performance

(Ali Belhocine, Mostefa Bouchetra, 2013)

This journal took an approach to investigate

the thermal performance of brake disks and

study of fluid flow characteristics. This will

be done by calculations alongside the use

of test data available for existing designs

and heat transfer and air flow rate of the

disk. (Figure 4 shows how air flow is

passed over/through the brake system

while the brake disk was in motion, the heat

that was generated escapes through the

vents in the disk and is replaced by the

cold air that enters through the vents.

Rate of heat dissipation for the disk surfaces

Mass flow rate through the disk passage

Temperature uniformity on all the disks surfaces

Detailed aerodynamics of the air flow through the passage

The project was then divided into three steps, the model creation, and mesh

generation and CFD simulation.

Figure 4 Air flow analysis

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Methodology included modelling the part and its 20 degree sector, next a mesh is

created so that FEA can be simulated. Boundary conditions is next set and divided

into three domains, 1): Fluid stator, 2): fluid disk outer, 3): fluid disk inner, next some

values have to be set these are ambient temperature, ambient pressure, temperature,

and RPM. The final step is validation, this is bringing all previous together and

obtaining results. From obtaining the results, heat dissipation was calculated using

values such as speed, mass flow rate, heat transfer coefficient.

2.3 Structural and thermal analysis of rotor disk of disk brake

(Suresh, 2013)

This journal looked at repetitive braking and its effects on the brake disk. Repetitive braking

leads to high heat generation during each braking event. Software such as thermal analysis

helps to diskover these types of problems and how it can affect the disk properties under these

hoot temperatures. Transient thermal and structural analysis of the brake disk is aimed at the

performance of the disk of a car under repetitive braking conditions, and from there it will

assist in disk design and analysis. The main body of this research is to analyse the

thermomechanical behaviour of the dry contact of the brake disk during repetitive braking. If

study was done on a wet contact surface area it would give inaccurate results or rather different

results to what we are looking at, since as the water or air would cool the disk and the designer

would not see how effective the disk is at handling high temperatures.


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Chapter 3. How does cooling a brake system work?

First off we must understand what the actual brakes do in a car, and then we will talk

about how they work and what differs from other ways of cooling.

Any vehicle moving at high speeds will need a braking system, some methods require

different approaches, it really depends on what vehicle you are trying to slow down or

stop for example, your car or bike will use the latest disk brakes while older models

had drum brake, these do the same thing but one more efficient than the other.

There are many reasons why cooling is important in brakes. Improper cooling results

in faster wear and can/will lead to thermal stress/failure in brake disks.

Brake fluid is the other important component in the brake system. Repeated braking

will incur high temperatures and if this is not dissipated it will cause the temperature

of brake fluid to rise. Brake fluid absorbs water from the atmosphere and as it does

the boiling point drops. Brake fluid has been known to boil a serious effect – total loss

of braking power, the gas from boiling fluid is compressible. When fluid cools brake

performance returns to normal. In the light of that it is important to dissipate heat as

efficiently as possible, it is also important to always have the appropriate brake fluid to

suit your car’s performance and to change brake fluid at least every 2 years.


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Chapter 4. Cooling in brake disk’s

In a braking situation a few things are happening, first off the kinetic energy that is

generated from the pads that bite the disk is converted into heat energy. Some of the

heat is absorbed by the disk itself which is why we see in some cases the disk glowing

red, this would be seen more in high performance cars where high speeds are

happening in short periods of time, but also in trucks because of the weight involved

and the weight transfer to the front, the brakes need to withstand these massive loads

at any given time.

As a rule “the rate of heat loss via convection is directly proportional to the surface

area”, any features in the brake disk such as grooves or drilled holes increase the

surface area and also increase the rate of heat loss. For vented disks such as the

types that the author worked on had both vents, grooves, and drilled features, while

these additional features also make the disk look better atheistically they also provide

better cooling while wear rates are reduced in the long run. In these types of brake

disk’s the air that enters the disk through the vents by rotary motion cools the disk and

disperses the heat and gases which otherwise could cause trouble or cause an

accident to the driver unknowingly.


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4.1 Types of disks and ventilation features

This was the first type of brake rotor that the author used during testing and to compare

its cooling properties to the others, was a standard vented brake rotor and was vented

only, the author later will show the other 2 types that he used. This type is commonly

used for the everyday road car, properties of this disk will help keep the disk cool as

no major temperatures will be involved for the type of car on which it is used. The

brake rotor is also more efficient at removing dirt and water than the solid disk which

has no vents but just a solid mesh all around the disk.

Figure 5 shows a standard brake disk Figure 6 Straight vanes ventilation


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4.2 Grooved and vented brake disk

This was another design that the author choose to demonstrate his analysis in brake

disks that had additional features to improve cooling or heat loss rates. This brake

disk will offer more improved performance in cooling the disk when high temperatures

are acting on the disk, other advantages of this type include cleaning the surface pad

faster than normal due to the additional design features, the disk also offers more bite

so this means that it has better stopping power than your normal brake disks, this is

important for heavier vehicles and high performance cars when sudden braking may

apply, for example if the more powerful car is on track and suddenly needs to brake

when approaching a sharp corner, the car will need to slow down quickly and efficiently

otherwise it will crash, but the main reason is to slow down the car quickly while

dispersing the heat generated in the disk.

Below shows (Figure 7 & Figure 8) the outside surface of a grooved brake disk and

how alternative internal vents may look like apart from the usual straight vane.

Figure 7 Alternative vented disk Figure 8 Surface of a grooved disk

https://www.google.ie/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwjuhIWgsaXLAhWF_A4KHZ65DtIQjRwIBw&url=https://www.quora.com/Why-are-there-holes-in-the-disc-of-my-bikes-brakes&bvm=bv.115339255,d.ZWU&psig=AFQjCNFT6xPcuTtHy1k1424B_X7CcPQFGg&ust=1457124322136616


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4.3 Cross drilled and grooved brake disk

This was the author’s 3rd and final choice in his research, the brake disk below shows

a disk with both grooved and drilled where the above had only grooved features. The

holes and grooves allow more surface contact with air that will be passing through to

cool the disk faster, the reasons why disks need to stay cool is because under these

stress conditions the disk could warp over time and cause vibrations in the foot pedal,

which is an sure indicator that your disk is warped. More seriously, under sever

heating the disk could disintegrate. Another important note to state is although roughly

20% is removed from the disk making it lighter, it also reduces the amount of friction

by 20% too because there is no surface contact where the pad meets the drilled holes

no friction can occur. While the disk does look pleasing to the eye it does serve an

important role none the less. With the directional vanes the disk acts as a propeller or

pump, sucking in the air and maintaining good flow rates keeping the disk cool.

Below shows my final testing brake disk which features grooves and drilled surface

features.

Figure 9 showing the surface of cross drilled disk


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4.4 Benefits and drawbacks of different brake disks.

For my testing I am investigating the cooling properties of each brake disk and

examining how each one performs under applied braking force over a period of

time. Brakes of course have one main function, to slow you down and stop you

running into the car in front of you, the factory brakes on your car provide ample

performance and while they may be good on the everyday commuter vehicle

other drivers such as the performance enthusiast needs an upgrade, either from

drilled or drilled and slotted.

Smooth Brake Disks

99% of new cars come with a set of factory brake disks from the factory and

provide the most surface area vs drilled or slotted disks and because of that, they

are very effective at acting as a heat sink. Another design feature would be that

they are less prone to cracking under the extreme heat conditions that they might

go under, and also have a high boiling point for brake fluid but this can depend

on your type of brake oil and as well as other factors such as your type of pads.

Slotted/Grooved Brake Disks

These got their name simply because of their design features, they have grooves

cut along the face of the disk. Under repetitive heavy the temperature will

increase dramatically on road conditions, and a layer of gas and dust will form

between the pad and disk which comes from the brake pads that rubs off when in

contact with the disk. The slots allow for escape route from this built up which

in turn offers more pad bite and lower temperatures. They also have higher

coefficient of friction because of more contact area which is good because you

are using less energy to slow the vehicle down.


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4.5 Cross Drilled Brake Disk

The cross drilled disks offer more or less the same principles as the grooved disks,

outgassing and less dust build more is less of an issue as technology progresses.

The drilled holes act as more of an aesthetic choice more than offering improved

performance, none the less they still provide dust build up from pad and disk

contact. The temperatures that the everyday family car will come nowhere close

to the performance enthusiast that he will incur on a track, so the ventilation

properties of the cross drilled offer these added benefits at keeping temperatures

down and have longer pad life and also improved wet-weather performance by

allowing water to escape the rotors surface.

Figure 10 Slotted Disk, Autoanything.com

Figure 11 Smooth Disk, Autoanything.com

Figure 12 Cross drilled Disk, AutoAnything.com

http://www.autoanything.com/brakes/20A50533A1.aspx?N=4294956350




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4.6 Advantages of ventilation in disks.

Ventilation in brake disks is very important as I have already stated above, under all

conditions wet or dry your braking system needs to be at its best, so what is the

purpose of ventilation?

1) The disk absorbs some of the generated heat and can cause it to

expand, ventilation acts against this.

2) It provides routes for water to disperse more quickly

3) It provides space for your brake dust to disperse

While all these additional features on a disk are designed to do a specific job they can

also lead to problems that you wouldn’t suspect. They are designed to remove heat

but the cross drilled holes can cause cracks and lower its yield stress. For these

reasons the cross drilled disks are mainly used for heavier vehicles and some high

performance cars

Figure 13 Ventilation in Disks,. Au/kangaroo-paw-ventilation


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Chapter 5. Drum vs Disk brake braking systems

In a drum brake braking system the surface area covers roughly 50% of the walls of

the drum assembly. How the drum brake works is by pushing the brake shoes against

the wall to slow down the rotation of the wheel. This, like the disk brake is done by

hydraulically actuated pistons and shoes are guided by a return spring assembly. The

disk brake on the other hand is also hydraulically operated but only covers about 10%

of the surface area but can offer more bite due to the pressure generated by the

hydraulic fluid pushing larger pistons against the pads on both sides of the disk. This

system is based on Pascal’s law which states “Pressure exerted anywhere in a

contained incompressible fluid is distributed in all directions throughout the fluid”. To

put in simple terms the brake calliper assembly uses the hydraulic force from the brake

pedal to pump a piston which squeezes the brake pads to the disk surfaces, creating

friction and decelerating the wheel. The calliper frame has a banjo fitting through

which the fluid will push the piston and force the pads in an outwards direction. The

pressurized fluid from the pedal is capable of pushing the piston with great force.

When you apply the brake, the calliper will receive the high pressure hydraulic fluid

from the brake master cylinder, the fluid then will push the piston which makes the

inner brake pad squeeze against the disk surface, as a result the pressure backward

force will push the calliper frame along the side pin which makes the outer brake pad

to squeeze the other side of the disk. This system is known as sliding calliper system,

on higher performance cars there can be pistons on both sides of the calliper instead

of a sliding system.

Figure 14 Disk Brake Assembly, Mr Engineer.com

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5.1 Disk and Drum brake comparison

When drum brakes were first used, they were used on all four wheels of car before the

disk came into existence. It got its name from its design, the system is housed in a

drum that rotates along with the wheel. When a car is accelerating and wants to slow

down there is a set of shoe’s that are pressed against the wall of the drum, when the

foot pedal is pressed the shoe’s would be forced against the drum thus slowing it down.

In most modern cars disks are used in the front while drums are used in the rear.

Probably two reasons for this, less expensive and easier to accommodate parking

brake. There are advantages and disadvantages of each type but the braking system

which shows the most promise is the disk brakes all around because it can produce

more braking power and greater force to slow down the rotation of the wheel. The

harder you press the brake pedal the harder the calliper will squeeze the brake pads

against the spinning disk with less danger of locking the wheels than with drum system.

Locked wheels lessen braking efficiency and lead to loss of control.

Figure 15 Disk and Drum Design, Arrc.ebscohost.com


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5.2 Drum Housing

Pictured below is a drum brake disk encased in its shell, the author has chosen this

image to show ease of use vs the disk and its parts. As you can see the drum brake

is more awkward to work with for a number of reasons.

1. To view the moving parts you have to remove the shell which is time

consuming and something which is not just loosen with a bolts or clips

especially if it has rust taken a beaten over the years.

2. Case can become seized over time making it harder to come off

3. Slower in response time compared to disk braking system

4. Not as efficient at dissipating heat as disk disk’s

5. Need more braking distance compared to a disk

5.3 Reliability

Figure 16 Drum Housing, Edmunds.com

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5.4 Reliability of braking systems

Next I would like to talk about the reliability of both braking systems, disk brakes have

the advantage of better stopping power. While drum brakes, like disk brakes, have a

hydraulic system they are not as powerful as the setup in disk brakes because drum

brakes tend to lock and make the vehicle unstable, therefore pressure to drums has

often to be limited. The main reason why disks are used at the front in today’s modern

cars is because of the weight transfer to the front so therefore you need more stopping

power at the front than you do at the rear. For drum brakes the moving parts may be

smaller and more compact but still don’t offer that stopping power that disks do. They

are also more susceptible to warping and brake fade due to the high temperatures.

The high temperatures that would be generated have nowhere to go and so are

absorbed by the material itself thus warping the disk or damaging it in some way over

a shorter period of time. Maintenance is also done at shorter intervals and needs a

lot cleaning because of the dust residue build up from the shoes that are kept inside

the casing. Disk brakes need more hardware and more hydraulic pressure to get the

full potential of the brake but are in many more ways more efficient at slowing down

your car than the drum brake

Disk brakes needs more hardware and more hydraulic pressure to get the full potential

of the brake but are in many more ways more efficient at slowing down your car than

the drum brake.

Figure 17 Disk and Drum reliability

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwil78WipbTLAhXC-g4KHUVwARoQjRwIBw&url=http://www.ridetillidie.com/how-are-disc-brakes-different-from-drum-brakes-&psig=AFQjCNH4H6NtOwXRxDRZZ7uYyLtD5F9F8w&ust=1457636496700253


27

5.5 Deterioration of a Disk brake

In today’s society a lot of people expect parts to last forever but that is not the case,

parts in the manufacturing industry are designed to fail after so long but are still

manufactured to reasonably safe specifications, below the author has shown what

happened after the brake pads had being used long after its life expectancy. The pad

below has been worn down to the bare metal which is not a good idea, given you will

have little to none braking power in the front and a possibility of welded brake disk,

again a dangerous situation if it were to happen driving along at 60 kph. There will

also be greater heat generated and much higher chance of Disk disintegration.

Figure 18 Brake Pad deterioration, MBworld.org


28

5.6 Deterioration of brake Disk vs New Disk

On the left you can see that the Disk has rusted away and looks pretty seized up vs a

new furbished one on the right. The left Disk could have brake dust built up and other

dirt particles built up inside, which will need cleaning to be able to perform at its best

efficiency. Another reason why disk (A) looks rusty could be from lack of use, when

it’s in use again it should start to look little like disk (B). Another indicator as to when

you should change your brake pads is when you hear a squealing noise, this is not to

be confused with noise often heard when they are first installed as they will make some

squealing noise due to the film on the brake pads and disk, you should not always rely

on this and should inspect them every 10,000 miles or so. Often some people just

replace the parts that have broken or worn away but when doing the brakes it is also

recommended to change the brake fluid at least every two years.

Figure 19 Disk pad deterioration Figure 20 Disk Pad refurbished


29

Chapter 6. Installation

Here I would like to talk a little about installation and what issues might arise if they

weren’t install in the correct manner.

Fitting, bedding in and tips to avoid warped Disks

The following below is quoted from an instruction manual that came with a set of brake

disks that we bought to use for testing, on how to avoid warped disks Give the

reference to this,,,,

“When using disks always make sure the mounting surfaces of the disks and the hubs are

spotlessly clean, failure to do so can result in run-out which lead to warped or juddering of

disks”.

“Run-out should be a maximum of 0.005 or 0.15mm when measured on outer edge”.

“The way disks are manufactured means new disks are very unlikely to be warped, but if you

do find run-out when fitting then simply reposition the disks on the hubs, rotate to the next

whole location”.

“It is crucially important that run-out is minimised at the fitting stage, as if there is run-out now

it can lead to variation in thickness at a later date that will cause juddering”.

“You should make sure all callipers and sliding pistons are free to move. Any binding can lead

to overheated disks and pads and even bearings”

“Bedding in will take around 200 miles, this will allow the pads to establish a good footprint

on the disks with even coverage. For the 1st 200 or so miles avoid emergency or heavy

braking”.


30

6.1 Warped disks

It is nearly impossible to warp disks from normal/slow road use. Vibration through the

steering wheel is mostly caused by brake deposits sticking onto the disk. This can

occur after some braking and particularly if stopped when the disks and pads are hot.

If at all possible avoid sitting for prolonged periods with the brake pedal applied, or

even the handbrake. If you think you have pad deposits on the disks then you can

remove them by doing serval hard braking procedures in a row and again avoid sitting

at the end with the brakes applied. Drive for 1 or 2 miles to allow the disks and pads

to cool in a constant manner. Different pads have different temperature ratings. When

this operating range is exceeded you can get vibration and juddering. This is simply

the pads getting pushed back off the disks when the pedal is applied. Allow the brakes

to cool down and all should be ok.

Figure 21 Warping caused by uneven wear, bimmerfest.com

http://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwi9pv7_hsHLAhUBPg8KHdcjA78QjRwIBw&url=http://www.bimmerfest.com/forums/showthread.php?t=762497&psig=AFQjCNEmZ9AfHOQ0H0aTVdj5g6qwhythyg&ust=1458074992725807


31

6.2 Brake corrosion

Dust and rust can cause serious issues down the road if left untreated. Both can occur

at any stage and only worsen if it isn’t looked after. Dust formed from the abrasion

that happens between the disks and brake pads due to the braking occurring. That

does not necessarily mean that there’s a problem straight away, after all you will

expect to see some brake dust coming from your pads from the contact that happens

between the two surfaces, although do not take this lightly as it will and has caused

issues such as alloy corrosion. Other problems such as vibration, squealing can

happen also and can sometimes but not always be an indicator that something is

wrong with your braking system.

6.3 Methods for suppression

Brake Pads: While some brake pads produce more dust than others for the obvious

reasons such as disk diameter, weight of vehicle, and type of braking system, but more

than not most cars will generally produce the same amount of brake particles and dust.

As I have states in a previous section like on the smooth disk dust particles will build

up and offer less bite and lose some braking performance.


32

Chapter 7. Material selection

Material selection has become an important factor when choosing a material to suit

the environment and the conditions that it will be put under for the obvious reasons

such as, reduced life expectancy or brake fade occurring as the cars speeds down the

road and may need to do an emergency stop or if repetitive braking is occurring the

disk will incur high temperatures. There are also other factors included such as

reduced weight of the car and fuel efficiency, such lightweight material would be

aluminium used in lighter cars or perhaps motorcycles. These materials have a lower

density but a higher thermal conductivity. The most important factor when considering

material selection would be safety and its ability to withstand high friction and wear

properties, other areas to consider is velocity temperature, environment and high

durability.

There are 4 stages of considering when selecting a material, I will discuss these below.

1. General material performance requirements

2. Initial screening of selected material

3. Material selection using digital logic method

4. Optimum material selection

Upon research I have seen that this is one type of application for material selection, I

have seen other methods which have done more work for selecting the material or

done fewer steps but also achieved the same result.


33

7.1 General material performance requirements

This involves research done about the actual braking system in a car, the stopping

system used to stop the rotation of the wheel. The brake system generates a high

braking force either through mechanically or hydraulically clamping pads onto the disk

and slowing it down, friction is than generated upon braking power. Different materials

have different frictional properties, the higher the coefficient of friction the more braking

power will be induced. For all disk brakes, they need the pads to push against them

to slow the car down

Figure 22 Vehicle Braking system, google images


34

7.2 Initial screening of candidate material

Most cars on the road today that have disk brakes installed have a cast iron type of

material. Cast iron weights in around 6800-7800 kg/m3 while Aluminium is 2712 kg/m3,

but because it of more practical properties cast iron is the most suitable material for

disk brakes. Cast iron does cost more but it is easier to manufacture than other

materials, most importantly it has higher thermal stability thus making it a suitable

candidate for it’s this purpose.

Aluminium was also shown as a promising type of material for disk brakes but further

research ruled this out. Aluminium is a lighter material with low density and saving

weight reduction on the car up to 50-60% but testing proved that repeated braking

lowered the coefficient and cause significant wear of the brake pads thus lower its life

expectancy. Following other tests which involved adding/mixing more particles to the

aluminium composite only resulted in more cost and more time to achieve the level of

results got with the cast iron disk.


35

7.3 Material selection using digital logic method

This method involves research done for what is the optimum material for its intended

purpose using a specified ranking. A list of 5 tables was drawn up and marked

accordingly for its values giving the result either a 1 or a 0 for a desired number of

tests, (1) Compressive strength, (2) Friction coefficient, (3) Wear resistance, (4)

Thermal capacity, (5) Specific gravity

Table (2) Weighting factors for brake disk

Further test scores for the chosen material.

Property

Positive decisions

Weighting factors

Compressive strength 1 0.1

Friction coefficient 3 0.3

Wear resistance 3 0.3

Thermal capacity 2 0.2

Specific gravity 1 0.1

http://www.google.ie/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwj3i_Sprv_JAhUDeg8KHZ5kBekQjRwIBw&url=http://www.google.com/patents/WO2000036169A1?cl=en&bvm=bv.110151844,d.ZWU&psig=AFQjCNHncmnkqKAMG3IlksGsOenk56VsJw&ust=1451419791526630


36

7.4 Optimum Material selection

Here the researcher is trying to improve the overall performance of the best suited

material, meaning that all other candidates must perform at a higher level than the

currently used material if it were to be accepted.

7.5 Conclusion

The selected material is then used for the design and application of automotive brake

disk. All results were taken into account and then used for future references. They

then could use these results if current standards were not up to use at a later date due

to the continual change in design and technologies.

7.6 Ashby’s chart

Ashby’s materials selection chart is a novel graphical way of presenting material property data.

Figure 23 shows Ashbys Chart


37

7.7 Physical Insights

Stiffness measures how much something stretches elastically when a load is applied.

Young modulus measures stiffness and is a material constant.

Young modulus and density both depend on the atomic packing within the material,

and Young modulus depends on the type of bonding between the atoms.

The metal and polymer bubbles are small – this is because the material composition

and processing do not have a significant effect on density or Young modulus.


38

7.8 Microstructure of cast iron

During my research and before any testing had commenced I had done a lab

investigating on the microstructure of a worn Grey Cast iron disk. The brake disk

below is a standard disk that had covered 150,000 km and that was tested with the

original brake pads. Further testing that I had completed with other disk sets will be

discussed later. A section was cut from the test sample and put under the electronic

microscope which we used to view the microstructure at a magnification of 30,000.

Figure 24 Rusted Disk Surface Figure 25 Side View


39

7.9 Lab setup

Procedure:

(1) start up the microscope, (2) Prepare a sample, (3) Place a specimen on the

stage, (4) observe an image, (5) Save an image, (6) Finish the observation,

(7) Shut down the microscope

Items to prepare:

(1) Sample, (2) Conductive double sided tape, (3) tweezers,

(4) Specimen stub, (5) Specimen holder, (6) Height gauge

(1) Starting up the microscope:

Turn on the earth leakage breaker in the back of the main unit

Turn on the power switch on the right side of the main unit to start the device

The evacuation will start automatically when the EVAC LED (blue) on the display

panel blinks. When the AIR LED (yellow) lights, press the EVAC AIR switch to start

the evacuate EVAC LED (blue) lights when the evacuation ends

Figure 26 Sample cut for viewing Figure 27 Sample viewed on electro Microscope


40

(2) Prepare a specimen

Bulk sample (Conductive/Non-conductive)

(In this case, our sample is cast iron and is conductive)

(1) Stick the conductive tape on the specimen stub and attach the specimen

(2) Set the specimen stub in the specimen holder and adjust the interval

between the specimen surface and the height gauge to about 1mm

(3) Place a specimen on the stage

(1) Push the EVAC/AIR switch in introducing the air into the specimen chamber. After

introducing the air in the specimen chamber, the status the status of AIR/LED (yellow)

changes from blinking to stationary (for 1 minute)

(2) Draw out the specimen stage slowly, and set the specimen holder. Turn the XY

knob of the specimen stage, and adjust the specimen stage to the centre.

(3) When observing at high magnification or a heavy specimen, use the provided ball

wrench to fix the specimen holder.

(4)Tighten the hexagon socket head screw with the ball wrench to fix the specimen

holder.

(5)Close the specimen stage was drawn out. Press the EVAC/AIR switch to evacuate

the specimen chamber with the specimen stage when the EVAC LED blinks (blue).

You are now ready to view your specimen.


41

7.10 Viewing the specimen

I have put together a few images after viewing the worn brake disk at a magnification of

30,000. Here I will show what the disk looks like after it had 150,000 km done.

Normally your typical brake disks will need replacing anywhere from 15,000-70,000

(about 113,000 km) but this also depends on your driving style and type of pads, some

disks can last longer whereas other’s will need changing sooner. For our brake disks

and brake pads, it was time to change them as you may have seen how worn or

damaged the disk had become. As a rough guide if the lip on the outside edges is

less than one sixteenth of an inch or 1 mm there is still life in your disk. Fitting new

brake pads along with a new disk will require about 1000 miles to bed them in, do not

fret about them being noisy at this time as this is completely normal if fitted correctly.

If you wish to avoid some of this problem you could skim the disk about 0.0005 inches

on a lathe to address this issue although it is not a requirement and should be avoided.

Fig (1) Fig (2)

The above photos were taken from the electronic microscope TM3000 at a

magnification of 30,000. (Figure 1) shows little surface cracks and scratches that the

disk had incurred over the course of it life span. Although we expected to see a lot

more damage done than this we were surprised that at the mileage completed the

damage was only starting to show from that point onwards. The conclusion the author

could gather from this, is that the car was not under severe braking forces while this

disk was in use.


42

In (Figure 2) it shows a more close up inspection, at this level of magnification we were

able to measure the width and length of any crack the disk had.

Below I have shown a 3D image with dimensions measuring the various cracks and

dents that this surface had endured. Although we weren’t able to measure the depth

of the crack, we were able to measure other dimensions such as length and width. For

clarity reasons we had to clean the surface of the test sample (Figure 2) as there had

been residue left over such as dirt and dust from the brake pads. The author had to

be careful as not to leave any new scratch marks when cleaning the surface with sand

paper as it may be mistaken as a flaw when viewing it under such high magnification.

Figure 1 Figure 2

To the left is a specimen that

the author has cleaned and

polished to a better standard

so that he could see the

defects much clearer.

This specimen is almost

indistinguishable from the

atomic structure of cast iron

which is shown on the next

page.


43

7.11 Physical Micro-structure of cast iron untouched

Below is an image of the microstructure of cast iron. It is very similar to the

microstructure that I had viewed above using the microscope, almost indistinguishable

from a damaged-free cast iron sample. It has a flake like form with nodular nodes in

its appearance. It also has a worm like or vermicular compacted-graphite shape.

To the left is an image

of the atomic structure

of cast iron, just like

the clean sample

above it is hard to see

what is what,

Because the old worn

hadn’t taken much

damage the grain

structure hadn’t

changed, leaving the

viewer unsure if it was

a worn sample or not.

http://www.google.ie/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiZ0f62l4fKAhUGcw8KHUkwCZsQjRwIBw&url=http://www.asmet.com/news/2011/05/technical-introduction-to-metallurgical-process-control-for-compacted-graphite-irons-cgi&bvm=bv.110151844,d.d24&psig=AFQjCNHKNj8-lnemSxC_iT3ol6pkORwKZg&ust=1451687662896022


44

7.12 Applications and other uses

Cast iron is widely used in structural and decorative applications, it is cheap, durable,

and easily manufactured and also casting it into varieties of shapes. Other uses

include hardware, buildings, tools, piping.

It is extremely strong and durable when used appropriately and if protected from harsh

environments. Its properties allow it to be stronger in compression than tension for

example the brake pads squeezing against the brake disk receives compression

forces.

As strong as cast iron is, if exposed to moisture and oxygen it can develop problems

such as rusting which is unavoidable if precautions are not taken.


45

Chapter 8. Testing and analysis

To put the author’s thesis into perspective he set out to investigate how brake disk

design affects cooling, to do this the author bought 3 new brake disks each with their

own distinct design for improved cooling. The author then set out to start his testing

on a car because he felt that this would be the best way to mimic his braking situation’s,

rather than setup the brake disk’s on a lathe and apply a brake. Unfortunaly when I

went out to see an airport strip to my testing I was declined because of safety and

insurance reasons, I then went and did half my testing both on a closed road and in

my garage with the front of the car supported as to let the wheels freewheel. By using

a car my results would be very similar to those induced out in the open road but

because I had no airflow coming in at the wheels while testing in the garage the results

will be slightly different.

Figure 1, 2 & 3 show 3 brake disks that will be tested on


46

8.1 My approach

The aim of my thesis was to investigate the heat dissipation between different brake

disks’s, to do this I had to purchase special equipment to take heat readings. Speaking

to the specialist’s in the college they had told me to purchase a thermal imaging

camera. What this does is take heat readings at a close range displaying in degrees’

and also displaying how hot or cold an object is in colours from red (hot) and blue

(cold). This piece of equipment proved to be very useful in my experiments as the

main objective in my thesis was to analysis the heat dissipation in brake disks.

Figure 29 Flir Imaging camera Figure 27 Thermal imaging camera


47

8.2 Testing apparatus

During my testing I had been asked to investigate the total braking force in a car, this

came simple enough to test, I had expected that the full braking force in the braking

system would be quite high so I purchased a pressure gauge up to 1500 psi, lucky

enough the car’s braking pressure maxed out at 1470 psi. For my static testing I

bought smaller pressure gauges so that I knew what pressure I was applying and that

it remained constant at all times, I will explain more in detail about this later in the

process.

Another important factor to note about these gauges is there is a nip at the head of

the gauge that has to be cut to allow air in and out so there wouldn’t be a build-up of

pressure inside the unit. We split the brake line at the flexible hose so we could insert

the pipe with the pressure gauge.

Figure 29 1500 Pressure gauge


48

8.3 Brake pedal rig

Figure 30 & 31 shows the brake Rig used during testing


49

In the beginning we hadn’t initially on intended to use a rig but we quickly realised this

was needed to help provide a constant pressure it would provide a constant pressure

for us while we provided the acceleration ourselves. Through SolidWorks it saved us

some time physically making other rigs that may not be as suitable as the rig above,

with SolidWorks we could change it to whatever size or shape we needed with a click

of a button.

This was a purpose built rig that had to be fitted to the car as shown. Its purpose was

simple, it would act as a piston or lever that was adjustable in and out via a screw.

When the author was doing the testing we had to have a constant pressure applied to

the brakes when we were taking heat readings, just as we did in our emergency

braking situations otherwise we our results would be meaningless, our investigation

was to apply the same pressure across all brake disks and then compare all the results

and write our conclusions to say which one had the most best rate of cooling. The

only job in this situation was to press the accelerator for the given time which we had

in mind, our speed was measured via the car’s speedometer according to our set

speeds during the testing.

This was our pressure gauge

set up along with our brake

pedal rig. Through this we

could set our brake pressure

and see what pressure was

applied via our gauge.

We had to have it setup on the

passengers door so that the

driver could see what pressure

he was setting, once set to 50

psi, it was set for the whole of

the testing, the only thing to do

was control acceleration.

Figure 32 Pressure gauge setup


50

8.4 Planning

When we first started testing, the car which would be tested on had already one of our

test disks so we decided to begin road testing on that and then compare these results

without static testing and see do they match or show any differences. For our 1st

experiment we used the new grooved and drilled brake disk’s, at this stage it didn’t

matter which ones were on because we had decided to compare road tests on all new

disks with our static testing which I will explain later. The idea here was to do

emergency stops at different speeds and see what heat was generated and later then

to compare which disk had the best rate of cooling. While doing research on my thesis

throughout the year I had expected that the disks with the additional features to

dissipate the heat quicker but after some analysis and testing I found that this was not

the case.

An important factor to note is that all disk disks will incur some heat in them without

the driver touching the brakes, this is because of the slightest surface contact area

between the brake pads and the disk’s.

Below I have a table showing emergency stops at different speeds, I have recorded

several factors during testing that could affect the experiment in some ways such as

weight, speed, distance. All starting temperatures are recorded both at beginning of

the testing and exactly after the car has stopped, this is to get a heat reading as precise

as we can. As you can see below the faster the car went, the more heat was generated

in the disks

Figure 33 First Testing analysis


51

8.5 Vehicle and Brake data:

Vehicle Characteristics

mVehicle Mass 1266kg

Brake force Distribution 60:30

Brake Application Characteristics

Initial vehicle speed 80 km/h (22.22 m/s)

Duration of brake application 30 s

Initial Brake temperature 15 degrees Celsius

Front Brake Disks (Solid)

Disk outer diameter 280 mm

Disk ring inner diameter 15.5 cm

Disk Thickness 20 mm

Number of Vanes 28

Figure 34 Car which was tested on


52

8.6 Static Testing

Now that we done some road testing, we are now going to do static testing but with

same principles involved. Below I have listed out all the apparatus that will be used

throughout the testing.

Test equipment:

1. Jig for keeping constant pressure on brake pedal/accelerator pedal

2. 2 flexible brake pipes, standard fitment

3. 4ft length of copper brake pipe

4. Tee piece, standard brass as used in motor vehicle brake circuits

5. Male to male connector, again standard in brake circuits, to connect female to female

pipe endings

6. Number of fittings to enable connection of flexible brake pipe to gauges, supplied by

Pirtek, experts in supply and manufacture of hydraulic and brake pipes

7. Gauges covering range from 0 to 1500 psi


53

8.7 Equipment being tested:

Brake disks as follows:

$ Standard brake disk having covered 150,000 kms, tested with existing brake pads

$ New set of standard brake disks, made by Mintex

$ New set of high performance grooved disks made by high performance disk

manufacturers Mtec.

$ New set of high performance grooved and bored disks made by high performance disk

manufacturers Mtec.

$ New disks tested with new high performance eco-friendly pads made by EBC. New

pads were bedded in for approx. 600kms as recommended by manufacturer.


54

8.8 Test 1 (Standard vented brake disk – worn 151200km)

For our first static testing as shown the old worn vented brake disk was tested before

the new standard one, the reason this was done was to compare its rate of cooling at

this stage with a new disk that had no wear on it. Also the worn brake pads were used

for this test and to be compared with the new brake pads.

The table above shows that heat readings were taken at the start and at the end while

keeping the same pressure across the board and the time so that the results could be

as accurate as possible for all disks. If I applied different brake pressure to the disks

than my experiment would have no meaning, again like I have said before, the same

pressure was applied for the testing to get as accurate results as can be. Because we

had done emergency stops on our road test we want to mimic the idea here on our

static testing.

Figure 35 Worn Disk Figure 36 Worn Brake Pad

Figure 37 First Bench test results


55

8.9 Thermal Imaging readings

Below is a graph of the first test we did, the top row indicates the speed while the blue

line indicate the starting temperature and the orange line indicates the end

temperature.

20

Start Temp 14.2 15.6 24 30.5

End Temp 15.6 24 30.5 48.7

0102030405060

Test 1

Start Temp End Temp

40 60 80

Here I have displayed all the

thermal imaging of the results

that the author obtained during

testing.

Do you know notice the hot air

escaping through the vents of

the brake disk?

Figure 38 Test 1 results

Image 1-5, Thermal imaging heat readings


56

8.10 Test 2 (New standard brake disk)

Below the author is testing the standard brake disks and new brake pads, the previous

test had the same disk and pads but were worn and had 151200 km on them. As I

stated back in my lab testing where I viewed the specimen under a microscope I also

compared the worn material vs the new material to show the subtle differences.

As shown above there is considerable difference between the new standard disks and

the worn one’s, this could be for different reasons such as worn brake pads not making

full contact at all times with the disk, either way the author was surprised to see that

the old disks did not heat up as much as the new ones.

Figure 39 Bench test No.2

Figure 40 Standard Brake disk Figure 41 Graph for bench test


57

8.11 Thermal imaging readings

Above are the results that were obtained using the thermal imaging camera from the

new standard brake disks. Surprisingly the new disks heated up quicker than the worn

disks. The time period between each result was 30 seconds. What’s important to

note here us that the heat is escaping through the vents as shown in the last 3 images.

The last image shows the whole disk heating up to 138 degree’s, this might happen

because on this disk here doesn’t feature additional ventilation features like the other

2 test disks that we will be explaining later on, such as the grooves and cross drilled

disks

Image 1-5 shows heat readings for Standard Disk


58

8.12 Test 3 (Grooved brake disk)

As you can see I keep the same brake pressure applied across so that my results will

be as accurate as can be and also that they mimic the road testing as close as

possible.

Our heat readings were more or less the same as in our previous testing, this has

surprised the author because with the additional grooves on the face of the disk they

should theoretically dissipate the heat better than the standard disks but our results

prove otherwise.

Grooved brake

disk

Figure 42 Grooved Disk Figure 43 Heat readings for grooved disk

Figure 44 Results from grooved disks


59

Thermal imaging readings

Here is the heat readings as taken from the thermal imaging camera, before any

braking is applied we took a cold reading (image 1) just to take as a bench mark, if we

did a run and then took a reading our results would be inaccurate. As I have previous

stated there is a slight surface contact area between the disk and the pads when

driving along the road so some heat will be generated but nothing high as you might

expect

Images 1-5 showing thermal readings for Grooved disk


60

8.13 Test 4 (Cross drilled)

Above is my final test results for the cross drilled disks, these disks out of all 3 types

had heated up the most, theoretically this should not have happened, this type of disk

is the one I was expecting to have the best rate of cooling but again my results prove

otherwise. I will talk about why this might happen at a later stage in my investigation.

Image 1 and graph 1 showing readings for cross drilled rotors

Graph 1 for cross drilled thermal readings


61

Thermal imaging readings

As shown for my final testing the cross drilled disk starts off with a cold reading at 18

degrees and peaks at 214.9 degrees Celsius. You may notice why there is a particular

section on the disk that heats up quicker than the rest of the surface such as the

middle?, this is because that where the brake pads touch the disks first at any point

when braking.

Images 1-5 showing final heat readings for cross drilled disks


62

Comparing results

In this section I would like to compare all 3 brake disks to see which one had the best

rate of cooling, given that each experiment had the same pressure applied and also

had set speeds and time allowed it will be an interesting result, theoretically the disk

with the cross drilled should have had the best rate of cooling but our results proved

that this one heated up more than the others.

(Standard disk) (Grooved disk) (Cross-drilled)

Image 1 reached a temperature of 106.8, image 2 reached a temperature of 138.6,

and our final test reached a temperature of 214.9 degrees Celsius, all taken at 50 psi

for 30 seconds and at a speed of 80 kmh.

Can you see the middle section in the image to left, it

appears to be hotter than any other surface on the

disk, as I have explain above it is because that is

where the brake pads make contact with disk and the

friction between them will cause heat, more than any

other surface area on the disk, later the excess heat

will be absorbed by the disk and spread outwards

towards the vents where the suction is pulling it away.

Figure 45 shows for contact surface area


63

Therefore from my analysis the author can conclude that the standard brake disk with

no additional features such as grooves or drilled holes proved to have the best rate of

cooling given that all the parameters were the same.

The reason for this could be that given it was static testing and also housed in a

garage, there was no air flow coming in like there would be out on the road testing, if

all the disks were road tested the author believes that he would have seen the opposite

of what was found in his results, the cross drilled would have proved to be the best

while the standard would have proven to be the least efficient


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8.14 SolidWorks sketches of brake disks

Here is a just a SolidWorks image of the grooved disk that the author did some testing

on. Using this types of software the user can do many scenarios at little cost before

being sent off to the manufacture for production, such adjustments might include

smaller or bigger disks, more or less vents, or the important features such the grooves

and cross drilled that could be drawn up by the user and do thermal analysis to show

the limits of the disk in terms in stress and distortion over time, of course the software

is only as true as the values that are inputted by the user and has to be as the exact

figures that you obtained from your research otherwise the design will have a shorter

life expectancy than previous though.

To the left is hottest temperature achieved at 80 kph which

was our top speed throughout the testing. It’s also important

to note that the disk material had a co-efficient of 0.7-0.8, as

this will have differences in heat readings, be sure to have

your thermal camera set at the correct settings also.


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SolidWorks of cross drilled disk

Here is another SolidWorks image of one of my disks, this is the type I had expected

to prove the most capable of dissipating the heat but our results proved otherwise, the

author suspects that if he had done road testing on all the disks he would have

achieved the results he was expecting.

Here is the highest temperature recorded for the cross

drilled disk at 80 KPH, this disk displayed the highest out

of all disks, theoretically it should have not but I have

explained this earlier why this might be.


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SolidWorks of standard disk

Lastly here is our standard disk in a SolidWorks image, while the author would like to

point out that it’s not just important to design a disk with additional surface features it

would also be wise to adjust your air vents as not to allow excessive heat built up. On

our standard brake disk they are just straight through vents, others might feature

directional vanes which act as a propeller when the disk is rotating at high speeds

sucking in the cold air keeping the disk cool.

As shown above the disks feature their own distinct vane pattern, all do the same job

which is to remove the heat made from the friction of the pads but one can be efficient

more than the other at dissipating the heat which is the main concern overall.

Figure 45, Concepts for ventilation,

Superstreetonline.com

http://www.google.ie/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiu9veNhp7MAhWBD8AKHR3jAG8QjRwIBw&url=http://www.superstreetonline.com/how-to/wheels-tires/modp-0908-project-nissan-350z-stoptech-brakes/&bvm=bv.119745492,d.ZGg&psig=AFQjCNEIEhxYqyNPl5DAINbvdIe7gf1pYg&ust=1461269938980239


67

Advantages of cross drilling or slotted disks

Drilled disks Advantages

The drilled disks will have more grip than other 2 types

The holes feature better ventilation and dissipate heat,

(While this is commonly accepted it was not proven in my testing)

They will run cooler and cool down much faster

Slots increase brake pad bite

Holes and slots reduce wear

Holes and slots eject water and prevent hydroplaning

They are lighter

Duly noted that these have advantages. But there are also disadvantages of the cross

drilled disk and it’s up to the owner to discern which one is fit for the purpose or his

driving style

Drilled disks Disadvantages

Drilled disk are more prone to crack

Drilled disks are more expensive


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Comparing road with static testing.

Earlier, the author explain that the cross drilled rotors would have proven to be more

efficient at dissipating the heat along with our other disks had they been all tested on

the road. Our results prove that without the airflow entering the wheel when driving

along the road, the disk simply lacks the power to dissipate the heat better than the

grooved, and the standard brake disk.

Another factor that surprised the author is that during the static testing, the weight of

the car was taken out of the equation and still the disk heated up more than it did on

the road, even with the weight of the car along with a driver and a passenger.

Our road test above shows that at 80 km/h at an emergency stop the maximum heat

came to 82 degrees Celsius. Our static testing shows the disks heated up about 62%

more than it did on the road, an additional 132 degree’s more on the static testing that

in itself shows how important airflow is in a brake system.


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8.15 Vehicle braking calculations

Here the author is going to talk about some calculations regarding the braking

distances in regards to the speed that was disk was rotating at.

The formula used to calculate braking distance is as follows:

Co-efficient of friction can be different for all materials, for brake disks we are looking

at a co-efficient of 0.7.

This value represents the surface contact on a dry road via the grip or bite.


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8.16 Vehicle configurations

Mass of vehicle 1266

Initial velocity 22.22 (80 km/h)

Vehicle speed at end of braking 0 m/s

Brake disc diameter 0.280 m

Axle weight distribution 30% on each side y = 0.3

% of kinetic energy that disc absorbs K=0.9

Acceleration due to gravity 9.81

Coefficient of friction for dry 0.7 μ = 0.7

Kinetic energy equations

The equations below found in this journal paper can be applied to my values so that

we can calculate the heat flux in the brake disc

Energy generated during braking

K.E=k(0.5)y𝑚(𝑢−𝑣)^2

2 = (0.9)

𝟏

𝟐(𝟎. 𝟑)

𝟏𝟐𝟔𝟔(𝟐𝟐.𝟐−𝟎)^𝟐

𝟐 = 42115.6422J

To calculate stopping distance

𝑑 =𝑢^2

2𝑢𝑔= 𝟑𝟓. 𝟗𝟒 𝐦

To calculate deceleration time

V = u + at Deceleration time = braking time = 1s on bench test but 4s on road

Braking power

Pb = K.E/t = 𝟒𝟐𝟏𝟏𝟓.𝟔𝟒𝟐𝟐

𝟒 = 10528.91 W


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Calculate heat flux (Q)

(Heat flux is defined as the amount of heat transferred per unit area unit time, from or

to a surface)

Q = Pb/A = 𝟏𝟎𝟓𝟐𝟖.𝟗𝟏

.𝟐𝟖𝟎= 𝟑𝟕𝟔𝟎𝟑. 𝟐𝟓 𝑾/𝒎𝟐

Analytical temperature rise calculations (Adopted from same journal paper)

Heat forms in the braking system due to the contact area between the pads and disc of its

components. On the basis of law of conservation of energy which states that the kinetic energy

of the vehicle during motion is equal to the dissipated heat after vehicle stop.

Material properties Cast Iron

Thermal conductivity 50

Density, p(kg/m3) 6600

Specific Heat, C (J/kg C) 380

Thermal expansion, α(10-6/k) .15

Elastic modulus E (Gpa) 110

Coefficient of friction, u 0.5

Heat transfer coefficient h(w/km2) 120

Hydraulic pressure, P (M pa) 50


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8.17 Calculations

RPM x 2π

60

Rads/s = M/s

Diameter of disk: 280mm = 0.28m

Radius of disk: 140mm = 0.14m

M/s = MPH

1m/s = 2.236 MPH

Brakes applied @ 20 kph = 12.43 mph = 5.55m/s

(5.55)^2

2(0.7)(9.81)= 2.242 Metres


(11.11)^2

2(0.7)(9.81)= 8.99 Metres


(16.66)^2

2(0.7)(9.81)= 20.21 Metres


(22.22)^2

2(0.7)(9.81)= 35.95 Metres


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Thermal calculations

In this section I am going to research calculations that are used to determine thermal

flow in brake disks.

For the rotor “𝐀𝐬𝐫” √“𝐊𝐫𝐏𝐫𝐂𝐩𝐫”

“𝐀𝐬𝐫” √(“𝐊𝐫𝐏𝐫𝐂𝐩𝐫” )”+𝐀𝐬𝐫” √(“𝐊𝐬𝐏𝐬𝐂𝐩𝐬” )

For the Stator

“𝐀𝐬𝐬” √“𝐊𝐬𝐏𝐬𝐂𝐩𝐬”

“𝐀𝐬𝐬” √(“𝐊𝐬𝐏𝐬𝐂𝐩𝐬” )” + 𝐀𝐬𝐫” √(“𝐊𝐫𝐏𝐫𝐂𝐩𝐫” )

Asr, Ass = Friction surface area of the rotor and stator respectively

K: = Thermal conductivity

P: = Mass density (kg/m3), Cp: = Specific heat at constant volume (J/kg K.)n


74

Chapter 9. Practice braking tests

Testing was carried out to determine the heat output generated in the disks at different

speeds for an x amount of time, the same principles were applied to the 3 disks and

then compared at the end to determine which one had the best rate of cooling.

Two tests were carried out, a road test which the author did emergency braking at the

different speeds and then applied the same principles during the static testing.

Because the car will be up on a hydraulic ramp the front wheels will be free to move,

with the car motionless, and also without the weight of the car when the brakes are

applied to the spinning disks they will stop almost instantly.

The main essentials of a braking system are as follows

Friction pair surface temperatures & temperature distributions

Thermal and thermomechanical stresses

Thermal deformations and deflections

Cooling characteristics

Brake fluid temperature

Temperatures of seals, bearings & associated brake components


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9.1 Conclusions

To begin with, before the author had in mind to do static testing, he had intended on

doing all road testing on an airport runway on which he had done research and found

2 airports nearby, the reason he wanted to do this was because it would have been

closed off to traffic and also because we would be doing excessive speeds throughout

the remaining of the testing, it was unsafe to do so on public roads, unfortunaly the

author was denied access to both locations because of insurance reasons and also

because there was interruptions of flights.

The aim of this thesis was to analyse the heat dissipation of 3 different brake disks, 1)

standard disk, 2) grooved disk, 3) cross drilled disk. We set out to do a road test on

one brake disk and then compare that with our static testing, the author also set out to

do static testing on all 3 new brake disk’s and again compare those with each other to

see which one had the best rate of cooling. Along with doing physical testing the

author did some research on the analysis side of brake disk to show what forces might

be generated on a disk brake.

There are several advantages of disk brakes over drum brakes, 1) have more stopping

power, 2) can disperse the heat better than drum’s, 3)have less moving parts than

drums, 4) easier to work. They also have their disadvantages: 1) more expensive, 2)

prone to crack more easily because of nature of the design, 3) more difficult to install

parking brake.


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9.2

A cars stopping distance depends on multiple things, 1) Tire to road friction, 2), vehicle

balance, 3), skill of driver, 4), system reaction time, what it doesn’t depend on is the

type of brakes, and the size even though this might seem the case. Most if not all of

today’s cars are fitted with front brake disks and rear drum brakes, this is because as

a car applies the brakes in any situation all of the weight is transferred to the front so

you have disk brakes at the front and not at the back, you need good stopping power

at the front. Weight distribution is 40%-60% at no braking while hard braking is 20%-

80%

Our practical braking tests went as expected but when the author applied the same

principles when doing the static testing, the results did not turn out as quite as he had

expected. The best of the 3 disks which was the cross drilled turned out to be the

worst at dissipating the heat while the other 2 proved to be better

9.3 Brake disk material:

All of brake disks are made from cast iron for 4 reasons,

It is hard and durable

It resists wear

It is less costly than steel or aluminium

It has better properties for dissipating heat to cool the brakes


77

9.4 Brake disk design:

Brake disks can differ in terms of their surface design and also in terms of their vane

design, both will have impacts on the disk and from there will show which is better at

dissipating the heat from the disk. From research the author has found that currently

there are 70 different cooling rib configurations in the disk themselves, examples

include straight vaned, curved vaned, and even segmented, and others are evenly

spaced while others are not. There are vanes which are zigzagged like a maze so on

so forth, the main idea manufactures are getting at is that different cooling rib

configurations included are will be used to optimise brake cooling.

9.5 Brake disk materials:

The material which the disk is made from is also important, a material with a good

thermal property would be a suitable candidate for the job, materials differ in all

aspects such as strength, noise, wear, and braking characteristics. Disks are carefully

manufactured so that the material cools in a way that won’t affect the overall structure

that could lead to failure when high temperatures are applied. Other factors that are

carefully monitored are the tensile strength, hardness and the microstructure.


78

9.6 Recommendations Thermal Analysis (SolidWorks)

From doing this thesis the author learn a lot and could have done further research and

improvements if he had more time.

The author’s final recommendations was to do some SolidWorks simulation on the

brake disks if he were to do it again using an analysis called the thermal analysis.

Both the author and his supervisor had a keen interest in doing this over the course of

his thesis but due to time constraints, he was unable to put any more time into his work

as he was leading into the last few days of the deadline.

The author’s head of year Mr Sean Dalton had introduced him to thermal analysis on

SolidWorks but had little to none experience in that area which left too much pressure

on the author to learn the software in such a short space of time.

Thermal analysis definition:

“Thermal analysis is a branch of materials science where the properties of materials

are studied as they change with temperature. Several methods are commonly used –

these are distinguished from one another by the property which is measured: Dielectric

thermal analysis (DEA): dielectric permittivity and loss factor”


79

9.7

Using this software the designer is enabled to carry out thermal analysis at any point

in the process of his design to ensure that all components and assembly performs in

the correct manner and most importantly within the temperature range, in this manner

the designer can spot safety issues before they arise, this saves time and costs in the

process.

The software allows you to calculate the temperature and heat transfer within the

structure of your design, every material has its own independent properties which is

important for the user to know so that the correct material will fit the purpose. Safety

also is integrated into everything these days, brake disks also need a safety design to

prevent failure over time, perhaps extra ventilation or guards.

9.8 Thermal Analysis Overview

The following below is quoted from the SolidWorks website under thermal analysis

section.

“The heat flow through the components can be in a steady state (where the heat flow

does not change over time) or transient in nature. The thermal analogy of a linear

static analysis is a steady-state thermal analysis, while a dynamic structural analysis

is analogous to a transient thermal analysis”.

Heat transfer problems can be solved using structural and fluid flow analysis methods:

In a thermal structural analysis, the effect of the moving air or a moving liquid is approximated by a series of boundary conditions or loads. In a thermal fluid analysis, the effect of the air or a liquid is calculated, increasing the run time but also increasing to overall solution accuracy.

http://www.solidworks.com/sw/products/simulation/thermal-structural-analysis.htm

http://www.solidworks.com/sw/products/simulation/thermal-fluid-analysis.htm


80

9.9 Thermal Analysis Overview (2.0)

Heat can adversely affect the performance of a design, whether it is exceeding the

permissible temperature of the device or by thermal expansion or contraction of its

components. This allows us to simulate steady state thermal performance and heat

analysis over time. Looking at the current temperature and see how quickly the design

cools down after a heat source is removed.

We are testing the heat distribution due to a fast braking action. The goal was to see

how quickly the disk cools afterwards, this can insure that heat dissipation meets

performance requirements to prevent brake fade

SolidWorks makes it very easy to interrogate the model and view temperatures over

the disk and then plot them over time

Animating the temperatures show the transfer of heat through the structure based on

the material characteristics

Heat transfer properties vary over surfaces due to shape or fluid flow SolidWorks

simulation. From the thermal analysis you can quickly obtain the structural

performance of your design

For the disk the focus is on insuring that thermal expansion does not cause problems

with the internal stress or shape of the disk

With SolidWorks simulation testing the thermal performance of your deign is highly

efficient and always up to date which helps develop the best design faster.


81

9.10 Finite element analysis

This is used for numerical solutions of a wide range of engineering problems, here it is used

for calculating the thermal performances of a brake disc which will show us heat values under

repetitive braking or if an emergency stop was generated what the maximum heat was

generated.

Examples of thermal analysis software

9.11

Above is the thermal stress of a brake disk, the designer here is trying to determine

how much thermal stress the disk can incur before failure, using this software allows

the user to interchange any details at the click of a button to achieve the best possible

results.

Figure 45 showing thermal stress


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9.12

This is thermal deflection on the same disk after a period of time, after the analysis the

user was allowed to see any deformation that occurred over a period of time, upon

looking at the results it was clear that the disk deformed quite considerably given the

stress that was applied. With these results the user can decide which material

performs better over the other, which in turn saves cost and time in the manufacturing

process, being able to simulate data before any designs are put into production and

see the results is very impressive in today’s software

Figure 46 shows thermal deflection Figure 47 showing side view deflection


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Thermal Distribution

9.13

This is also an area that could have been analysed using thermal analysis, the user is

researching thermal distribution on the disk after a braking situation was simulated. A

static study was approached and upon doing the analysis the user saw that the disk

warped under the specified conditions that were inputted from the beginning. A probe

tool can also be selected to pin point any location on the disk to see any desired result

that the user might want to view.

Figure 48 shows thermal heat distributed over the surface


84

Chapter 10. References

Ali Belhocine Abd Ramhim. (2013). Structural and contact analysis of disc brake

assembly during single stop braking event. India: The indian institute of metals.

Ali Belhocine, A. R. (2014). Structural and Contact Analysis of Disc Brake Assembly

During Single Stop Braking Event. Metallurgy Materials Engineering.

Ali Belhocine, Mostefa Bouchetra. (2013). Analysis of ventilation disc brake using CFD

to improve its thermal performance. Ain Shams Engineering journal, 4, 475-

483.

Faramarz Talati, Salman Jalalifar. (2009). Analysis of heat conduction in a disc brake

system. Heat Mass transfer.

Suresh, D. (2013). Structural and thermal analysis of rotor disc of disc brake.

International Journal of innovative research in science, engineering and

technology, 2(12). Retrieved from

http://www.ijirset.com/upload/2013/december/51A_Structural.pdf

Documents

Finished version 2016