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MODELLING DAMPING ELEMENT TO REDUCE DISC BRAKE SQUEAL NORAIDE BIN MD YUSOP UNIVERSITI TEKNOLOGI MALAYSIA

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Page 1: MODELLING DAMPING ELEMENT TO REDUCE DISC BRAKE SQUEALeprints.utm.my/id/eprint/39759/5/NoraideMdYusopMFKM2013.pdfMODELLING DAMPING ELEMENT TO REDUCE DISC BRAKE SQUEAL . NORAIDE BIN

MODELLING DAMPING ELEMENT TO REDUCE

DISC BRAKE SQUEAL

NORAIDE BIN MD YUSOP

UNIVERSITI TEKNOLOGI MALAYSIA

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MODELLING DAMPING ELEMENT TO REDUCE DISC BRAKE SQUEAL

NORAIDE BIN MD YUSOP

A thesis submitted in fulfillment of the

requirements for the award of the degree of

Master of Engineering (Mechanical)

Faculty of Mechanical Engineering

Universiti Teknologi Malaysia

FEBRUARY 2013

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Dedicate to my beloved mother, father, wife and brothers.

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ACKNOWLEDGEMENT

Alhamdulillah, all praise is due to Allah S.W.T, the Most Beneficent and the

Most Merciful, who has taught me what I knew not.

I would like to express my deepest appreciation to my project supervisor, Dr.

Abd. Rahim Abu Bakar for all the advices, guidance and motivation given

throughout this thesis. I also like to give my sincere thanks for giving me the

opportunity to do this research. This research work has given me valuable experience

especially in learning modeling and simulation. Special thanks also to my co-

supervisor Dr. Mohd. Zarhamdy Md. Zain for his inspiration, teaching and advices.

I would like to further extend my gratitude to all lecturers, researchers, my

friends in FKM and FKE, all suppliers and technicians who has assisted me directly

and indirectly throughout the progress in completion of my project. I will not forget

all opinions and supports given

Last but not least, I want to whole heartedly give my appreciations to my

beloved mother, father, wife and brothers for giving me the unlimited supports and

motivation when I faced the difficulties in carrying out this project.

Thank You.

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ABSTRACT A disc or drum brake system is very often generating undesirable and

annoying squeal noise that can disturb both driver and passengers. In order to prevent

or reduce brake squeal noise, structural modifications of brake components, damping

layers and active squeal control methods are commonly proposed and evaluated by

car manufacturers using analytical, numerical and experimental approach. Thus, this

thesis attempts to investigate the effectiveness of damping layers such as pad

insulator and clip to reduce disc brake squeal noise. In doing so, existing two (pad

model) and four (pad-disc model) degrees-of-freedom (DOF) brake models without

damping layers are adopted. The mass, stiffness and damping values of these brake

models are obtained from the experiments. These two brake models are then

validated against a real brake assembly test data and good correlation on the natural

and squeal frequency is achieved. Upon obtaining validated brake models, damping

layers i.e. the clip and insulator are modelled based on its mass, stiffness and

damping. The layers later are embedded into the validated pad and pad-disc models.

The parameter properties (stiffness and damping) of these damping layers are

measured from modal testing. Complex eigenvalue (CE) and dynamic transient (DT)

analyses are performed using MATLAB software package to predict squeal

occurrences. The squeal trigger mechanism used in this work is based on mode

coupling effect. The brake models with damping layers are simulated at a certain

brake parameter range such as friction coefficient, pad-disc contact stiffness and pad

wear. From the analysis, it is found that both CE and DT predict squeal frequency

close to the measured data with difference less than 4%. It is also found that the pad-

disc model is successfully predicting squeal or non-squeal occurrences close to the

squeal test results for both with clip and clip-insulator models. However, the pad

model is seen not capable to completely replicate the squeal test results particularly

with the clip model. This shows that the pad-disc model should be used to predict

squeal occurrences. From the parametric studies, it is shown that squeal noise can be

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completely eliminated for a wide range of friction coefficient, pad-disc contact

stiffness and pad wear. This can be suggested that the clip-insulator combination is

indeed effective in preventing squeal noise.

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ABSTRAK

Sistem brek cakera atau gelendong seringkali menghasilkan bunyi decitan

yang tidak diingini dan akan mengganggu para pemandu dan penumpang. Dalam

usaha untuk mencegah atau mengurangkan bunyi decitan brek, pengubahsuaian

struktur komponen brek, lapisan redaman dan kaedah kawalan bunyi decitan aktif

biasanya dicadang dan dinilai oleh pengeluar kereta secara kaedah analitik, berangka

dan eksperimen. Oleh itu, tesis ini cuba mengkaji keberkesanan lapisan redaman

seperti klip dan penebat dalam usaha untuk mengurangkan bunyi decitan daripada

sistem brek cakera. Dalam menjalankan kajian ini, model sedia ada iaitu dua-(model

pad) dan empat-(model pad-cakera) darjah kebebasan (DOF) digunakan. Nilai jisim,

kekakuan dan redaman untuk kedua-dua model brek ini diperolehi melalui

eksperimen. Kedua-dua model ini disahkan melalui data ujian brek sebenar di mana

pertalian yang baik untuk frekuensi nyata dan frekuenci bunyi decitan diperolehi.

Setelah mendapatkan kesahihan model brek, lapisan redaman iaitu klip dan penebat

dimodelkan mengikut nilai jisim, kekakuan dan peredam. Lapisan ini kemudiannya

dimasukkan ke dalam model pad dan pad-cakera. Nilai parameter (kekakuan dan

redaman) lapisan redaman diukur dari data ujian modal. Nilai Eigen (CE) dan

analisis dinamik fana (DT) dilakukan menggunakan pakej perisian MATLAB untuk

meramalkan berlakunya bunyi decitan. Mekanisma bunyi decitan terhasil dalam

kerja ini hanya mengambil kira kesan gandingan mod. Model brek dengan lapisan

redaman disimulasikan pada pelbagai parameter brek tertentu seperti pekali geseran,

kekakuan antara pad cakera dan kehausan pad. Daripada analisis, didapati bahawa

CE dan DT meramal frekuensi decitan hampir sama dengan frekuensi melalui

eksperimen dengan perbezaan kurang daripada 4%. Didapati juga bahawa model

pad-cakera berjaya meramal bunyi decitan dan keadaaan tanpa bunyi decitan hampir

sama dengan keputusan bunyi decitan eksperimen untuk model klip dan klip-

penebat. Namun, model pad dilihat tidak berupaya untuk menyamai keputusan

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eksperimen terutama pada model klip. Ini menunjukkan bahawa model pad-cakera

perlu digunakan untuk meramal berlakunya bunyi decitan. Daripada kajian

parameter, ia menunjukkan bahawa bunyi decitan boleh dihindari bagi julat pekali

geseran, kekakuan sentuhan pad-cakera dan kehausan pad yang besar. Ini

merumuskan bahawa gabungan klip dan penebat sangat berkesan untuk menghalang

bunyi decitan.

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TABLES OF CONTENTS CHAPTER TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vii

TABLE OF CONTENTS ix

LIST OF TABLES xii

LIST OF FIGURES xiii

LIST OF ABBREVIATIONS xviii

LIST OF SYMBOLS xix

LIST OF APPENDICES xx

1 INTRODUCTION 1

1.1 General Introduction 1

1.2 Problem Statement 2

1.3 Objective of the study 4

1.4 Scope of the Study 4

1.5 Significance of Study 5

1.6 Organization of the Thesis 6

2 LITERATURE REVIEW 7

2.1 Introduction 7

2.2 Theories of Brake Squeal Mechanisms 8

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2.2.1 Negative mu-v Slope 8

2.2.2 Sprag Slip 10

2.2.3 Stick Slip 12

2.2.4 Mode Coupling 13

2.2.5 Hammering 15

2.3 Approaches to Study Brake Squeal 16

2.3.1 Experimental Approach 17

2.3.2 Numerical Approach 19

2.3.3 Analytical Approach 22

2.4 Squeal Prevention 32

2.4.1 Damping 32

2.4.2 Structural Modifications 34

2.4.3 Control Methods 35

2.5 Reviews of Brake Squeal 36

2.6 Summary 37

3 METHODOLOGY 40

3.1 Introduction 40

3.2 A Brake Model 42

3.2.1 A Pad Model 42

3.2.2 A Pad Model with Clip 44

3.2.3 A Pad Model with Clip and Insulator 45

3.2.4 A Pad-Disc Model 46

3.2.5 A Pad-Disc Model with Clip 47

3.2.6 A Pad-Disc Model with Clip and Insulator 49

3.3 Experimental Modal Analysis (EMA) 50

3.3.1 Free-Free Condition 51

3.3.2 Contact Condition 53

3.4 Determination of Spring Stiffness 55

3.5 Determination of Damping Coefficient 57

3.6 Determination of Diagonal Spring Stiffness 60

3.7 FRF for Validation 62

3.8 Complex Eigenvalue Analysis 63

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3.9 Dynamic Transient Analysis 64

3.10 Summary 67

4 RESULT AND DISCUSSION 68

4.1 Introduction 68

4.2 Modal Testing 69

4.2.1 Diagonal spring 73

4.3 Brake Squeal Test 74

4.4 A Pad Model 75

4.5 A Pad Model with Clip 81

4.6 A Pad Model with Clip and Insulator 83

4.7 A Pad-Disc Model 85

4.8 A Pad-Disc Model with Clip 93

4.9 A Pad-Disc Model with Clip and Insulator 101

4.10 Overall Discussion 104

4.11 Summary 107

5 CONCLUSION AND RECOMMENDATIONS 108

5.1 Conclusion 108

5.2 Recommendations for Future Works 110

REFERENCES 111

PUBLICATIONS 120

Appendices A - D 121 - 1

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LIST OF TABLES

TABLE NO. TITLE PAGE

3.1 Brake disc components properties 51

4.1 Modal testing result for all components under free-free

condition 69

4.2 Modal testing result for joined components under contact

condition 70

4.3 Parameters for pad model 71

4.4 Parameters for pad-disc model 72

4.5 Comparison between all models 106

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LIST OF FIGURES

FIGURE NO. TITLE PAGE

2.1 A single degree of freedom featuring a block sliding on the

running conveyor 9

2.2 Negative slope µ-v characteristic 10

2.3 Schematic diagram of sprag-slip theory 11

2.4 Displacement (mm) and velocity (mm/sec) versus time [67] 11

2.5 Mode lock in plot for complex eigenvalue result of two DOFs

model by Hoffman et al. [12] 14

2.6 Cantilever-disc model by Jarvis and Mills [20] 23

2.7 Pin-disc mode by Earles and Soar [13] 24

2.8 Binary flutter model by North [18] 25

2.9 Four-degree-of-freedom pin/disc model by Earles and Lee [17] 26

2.10 Two-degree-of-freedom analysed by Hoffmann et al. [9] 26

2.11 Minimal model by Popp et al. [14] 27

2.12 Minimal model by Popp and Rudolph [18] 28

2.13 Shin model of friction induced vibration 29

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3.1 The flow chart of overall approach of this research 41

3.2 Disc brake assembly [80] 42

3.3 A pad model 43

3.4 A pad model with the clip 44

3.5 A pad model with the clip and insulator 45

3.6 A pad-disc model 46

3.7 A pad-disc model with clip 48

3.8 A pad-disc model with the clip and insulator 49

3.9 Modal experiment setup for free-free condition 51

3.10 Modal experiment setup for pad, disc, clip and insulator 52

3.11 Method to determine stiffness [31] 54

3.12 Example of FRF to measure clip/insulator properties 54

3.13 Modal testing for pad with disc, pad with clip and pad with

insulator 55

3.14 Bandwidth method of damping measurement in a single-degree-

of-freedom system. [81] 59

3.15 Horizontal and vertical force for 1-DOF 60

3.16 FRF measurement for assembled brake 62

3.17 Simulink diagram for the pad model 66

3.18 Simulink diagram for the pad-disc model 66

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4.1 In-plane and out-plane displacement for model without diagonal

spring. 73

4.2 Squeal frequencies measured in the tests [65] 74

4.3 Squeal frequencies against friction coefficient [63] 75

4.4 Natural frequency for assembled disc brake for pad in the y-axis 76

4.5 Squeal prediction for μ = 0.1 to 0.6 using CEA 77

4.6 Mode-coupling phenomenon for μ = 0.1 to 0.6 using CEA 77

4.7 Vibration response for μ = 0.20 (stable) using DTA 78

4.8 Vibration response for μ = 0.27 (unstable) using DTA 78

4.9 Stability region for contact stiffness (kc) 79

4.10 Real part for various contact stiffness (kc) 80

4.11 Stability region for mass of pad (m1) 80

4.12 Natural frequency for assembled disc brake with clip for pad in

the y-axis 81

4.13 Stability region for contact stiffness (kc) 82

4.14 Stability region for mass of pad (m1) 82

4.15 Natural frequency for assembled disc brake with clip and

insulator for pad in the y-axis 83

4.16 Stability region for contact stiffness (kc) 84

4.17 Stability region for mass of pad (m1) 84

4.18 Vibration response for μ = 0.6 using DTA 85

4.19 Natural frequency for assembled disc brake 86

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4.20 Squeal prediction for μ = 0.1 to 0.6 using CEA 87

4.21 Mode-coupling phenomenon for μ = 0.1 to 0.6 using CEA 87

4.22 Vibration response for μ= 0.25 (unstable) using DTA 88

4.23 Vibration response for μ= 0.27 (unstable) using DTA 89

4.24 Stability region for contact stiffness (kc) 90

4.25 Real part for various contact stiffness (kc) 91

4.26 Stability region for mass of pad (m1) 91

4.27 Mode coupling phenomenon for various μ and kc 92

4.28 Mode coupling phenomenon for various μ and m1 93

4.29 Natural frequency for assembled disc brake with clip 94

4.30 Squeal prediction for μ= 0.1 to μ= 0.6 using CEA 95

4.31 Vibration response for μ = 0.3 (stable) using DTA 96

4.32 Vibration response for μ = 0.4 (unstable) using DTA 97

4.33 Stability region for contact stiffness (kc) 98

4.34 Real part for various contact stiffness (kc) 98

4.35 Stability region for mass of pad (m1) 99

4.36 Mode coupling phenomenon for various μ and kc 100

4.37 Mode coupling phenomenon for various μ and m1 100

4.38 Natural frequency for assembled disc brake with clip and

insulator 101

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4.39 Vibration response for μ = 0.6 using DTA 102

4.40 Stability region for friction coefficient (kc) 103

4.41 Real part for various contact stiffness (kc) 103

4.42 Stability region for mass of pad (m) 104

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LIST OF ABBREVIATIONS FE - Finite Element

FIV - Friction Induce Vibration

CEA - Complex Eigenvalue Analysis

DTA - Data Transient Analysis

NVH - Noise, Vibration and Harshness

DOF - Degree of Freedoms

EMA - Experimental Modal Analysis

DPHI - Double-Pulsed Laser Holography Interferometry

ESPI - Electronic Speckle Pattern Interferometry

FEM - Finite Element Method

DOE - Design of Experiments

ACSL - Advanced Continuous Simulation Language

DPT - Derjaguin-Push-Tolstoi

AFC - Active Force Control

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LIST OF SYMBOLS Hz - Frequency unit

dB - Decibel

mu-v - Negative slope

m - Mass

c - Damper

k - Spring

x - Displacement in-plane

y - Displacement out-plane

µ - Friction coefficient

v - velocity

g - gravity

θ - angle

Ff - Fricion force

N - Normal force

R - Reaction force

kg - Kilogram

N/m - Newton per meter

Ns/m - Newton second per meter

N - Newton

m - meter

m/s - meter per second

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LIST OF APPENDICES APPENDIX TITLE PAGE A Matlab codes to identify brake squeal using eigenvalue analysis 121

B Simulink block diagram for brake model 124

C Vibration Response for modal testing under free-free condition 127

D Vibration Response for modal testing under contact condition 130

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CHAPTER 1

INTRODUCTION

1.1 General Introduction

Brake system is an important safety system in the passenger car to slow down

or for complete stop and to hold to hold the vehicle stationary while parking. During

braking process the brake pads come into contact with a rotating disc which

generated friction which slows down the car and finally make it stop. During

braking, this friction force may also induce dynamic instability to the system and

leads to unwanted vibration and unpleasant noise. This undesired brake noise may

cause discomfort to drivers and passengers. There are a number of terminologies to

describe this noise and vibration phenomena such as squeal, groan, chatter, judder,

moan and hum [1]. Among of these categories, squeal is the most annoying and

disturbing. According to Lang and Smales [2] brake squeal is usually generated at

frequency above 1 kHz and Eriksson [3] stated that a sound pressure level for the

squeal is set at 78 dBA and above. Hence, brake squeal is a major concern not only

to the customers due to the uncomfortable and irritating sound but also to the car

makers, brake and friction suppliers where every year they have to bear a high cost

payment for warranty claims by customers [4-6].

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1.2 Problem Statement

Brake squeal is an unpleasant sound that might reduce both driver and

passenger comfort feeling. However, until now brake squeal issue remains

completely unresolved despite large efforts have been done to understand, to predict

and to eliminate squeal using various methods from a lower order disc brake model

(theoretical) to a high complexity model (finite element) and the use of sophisticated

squeal experimental work.

Amongst those mentioned methods, theoretical method is cheap and fairly

fast in providing solution [7]. However in practice the theoretical model is said to be

inadequate to resemble a real disc brake assembly. Nevertheless, theoretical method

can at least be used in the early brake design stage in order to predict squeal

occurrence and to provide countermeasure against squeal. Unlike theoretical method,

finite element (FE) method can predict squeal with a better accuracy. An FE model

can be developed accurately to replicate a real brake assembly. However, the main

disadvantage of this technique is the requirement of computer intense and it demands

a long simulation time especially when performed on the high complexity FE model

[8]. Although experimental work can provide result based on a real condition of disc

brake system, the hardware and software development are expensive and required a

significant time to complete the designing process. In addition, discoveries made on

a particular type of brake are not always transferable to other types of brake and quite

often product developments are based on trial-and-error basis [9].

It is well accepted that brake squeal is a result of a friction induced vibration

(FIV) [1]. To date, numerous FIV models [10-27] have been proposed and some of

them were said to represent brake squeal model [12-27]. These models were typically

incorporated with acceptable squeal trigger mechanisms such as mode coupling [11-

15] and negative gradient of friction coefficient over sliding speed (mu-v) [16-21].

However, Chen and Zhou [28] suggested that negative mu-v behavior is not a

necessary condition for squealing brake whilst Wagner et al. [29] believed that mode

coupling is more realistic cause of brake squeal.

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In predicting squeal propensity there are in general, two major techniques

available: complex eigenvalue analysis in the frequency domain and dynamic

transient analysis in time domain. Both analyses have their pros and cons. The

complex eigenvalue analysis can reveal which system modes of vibration are

unstable but a shortcoming of this technique is that they do not allow time-dependant

material properties and could not take into account full effect of nonlinearity away

from steady sliding [8]. Meanwhile, divergence of a transient solution indicates that

instability is present in the system and this technique could overcome the

shortcomings in complex eigenvalue analysis with the drawback long computing

time and slow turnaround time for design iterations.

There are a number of techniques have been introduced in order to reduce

squeal and they are damping layer [30-34] structural modification, structural

modifications [7, 35-41] and active noise control [43-45]. These three techniques are

commonly incorporated in the finite element model [46-56] and experimental works

[57-66] but very rare in the lower order model except for active noise control [43-

45]. It is seen that damping layer is mostly preferred by car makers and brake

suppliers due to its capability to suppress squeal and cost effective compared to the

other techniques. However most of the previous researches for damping layer are on

the finite element and experimental approach. The existing analytical models almost

did not consider the damping element rather previous researchers were only used a

range of parameters for damping layer [30-34] to predict stability of the brake

system.

Thus, the present study aims to investigate squeal using lower order of disc

brake models where Butlin and Woodhouse [67] suggested that it is sufficient for the

lower order brake model, e.g. three-degree-of-freedom brake model to give a

reasonable approximation to the global prediction. The selected models are then

incorporated with mode coupling effect. In order to prevent squeal, damping layers

such as insulator and clip are considered and modeled. Complex eigenvalue and

dynamic transient analysis are performed to predict squeal occurrence.

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1.3 Objective of the Study

The main objectives of this research are to predict brake squeal by using a

lower degree of freedom brake model that initially considers pad/disc element, to

include damping layer model for pad shim and clip ,and finally to assess the

effectiveness of these damping layers against squeal.

1.4 Scope of Study The scope of study is as follows:

i. Existing two (pad only) and four (pad and disc) degrees of freedom models of

a disc brake system are used. All parameter values in the models are obtained

from the experiments. Validation of these models is made against test data at

assembly level. Complex eigenvalue and dynamic transient analysis are

performed to predict squeal between 4 to 5 kHz using MATLAB software

package.

ii. Insulator and clip are explicitly modelled as damping layers in order to

reduce squeal noise. Their damping and stiffness values are estimated from

modal testing.

iii. Mode coupling is the only mechanism considered to contribute for squealing

brake.

iv. Verifications of squeal and non-squeal noise are partly made against test data.

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1.5 Significance of study

It is essential that brake squeal issue addressed in the early design stage using

a proper way, quick turnaround with reasonable outcomes. This can be achieved

using theoretical method where to date numerous lower order of brake models are

available and some of them can predict brake squeal reasonably well against test

data. Furthermore, prevention approaches can also be modelled and incorporated

into the lower order of brake model.

Regarding to Dessouki et al. [45] disc brake squeal can be identified with

three different families:

i. Caliper Bracket induced squeal (2 - 6.5 kHz).

ii. Pad-induced, also defined as axial, or out-of plane squeal (4-11 kHz).

iii. Rotor induced, also defined as tangential, in-plane and longitudinal (7-16

kHz)

Therefore, an existing two [11] and four [45] degrees-of-freedom brake

model are selected and analysed. These two models are named as pad model and

pad-disc model. Both models consider a translational axis with coupling criteria for

out-planes and in plane axis. The model parameters are determined using

experimental modal analysis (EMA) to ensure its validity against actually disc brake

and squeal test data. Then, insulator and clip models are proposed by introducing

mass (m), damper (c) and spring (k) where all the parameter values can be estimated

by weight scale (m) and again with modal testing (k and c). The methodology used

in this work can be used as design guidelines for brake engineers to predict squeal

and later to estimate properties of damping layer that can prevent squeal occurrence

in the early design stage.

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1.6 Organization of the Thesis This thesis is organized into six chapters.

Chapter 1: Presents an overview of the research work, objective and scope of the

study and methodology of the research.

Chapter 2: Focuses on the literature review that has been carried out related to the

main subjects of interest to cover brake squeal and the mechanisms that cause it and

the relevant works that have been implemented to suppress it through a number of

techniques.

Chapter 3: Concentrates on the methodology of the disc brake squeal modeling

using FIV model and provides the overall framework of the complex eigenvalue and

dynamic transient analysis.

Chapter 4 Presents squeal prediction results using complex eigenvalue analysis for

the baseline model and model with damping layers. Correlation between the

predicted and experimental results is sought. Test results for stiffness and damping

coefficients of the insulator and clip are also given.

Chapter 5: Summaries the results and provides conclusions of the present work.

Recommendations for further work are also presented in this chapter.

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PUBLICATIONS

1. N. Md Yusop, A.R. Abu-Bakar , S. M. H. Dehkordi and M.Z. Md. Zain.,

“Stability Analysis of A simple Disc Brake System Disc Brake Model Using

Eigenvalue Approach” 3rd Regional Conference on Noise, Vibration and

Comfort (NVC ) 2010,. 28-30th June, 2010, Putrajaya, Malaysia.

2. N. Md Yusop, A.R. Abu Bakar, M.Z. Md. Zain., “Stability Analysis of A

Simple Disc Brake Model Using Analytical Approach”. World Engineering

Congress 2010, 2nd – 5th August 2010, Kuching, Sarawak, Malaysia.