UNIVERSITI PUTRA MALAYSIA

MARYAM HOSSEINI

FK 2010 12

EXPERIMENTAL DETERMINATION OF FATIGUE LIFE FOR INTERNATIONAL RUBBER HARDNESS

DEGREE 60 ENGINE MOUNT RUBBER

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EXPERIMENTAL DETERMINATION OF FATIGUE LIFE FOR INTERNATIONAL RUBBER HARDNESS

DEGREE 60 ENGINE MOUNT RUBBER

By

MARYAM HOSSEINI

Thesis Submitted to the School of Graduate Studies, Universiti Putra Malaysia, in Fulfilment of the Requirements for the Degree of Master of Science

January 2010

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DEDICATION

To my beloved family for their love, support and encouragement

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Abstract of thesis presented to the Senate of Universiti Putra Malaysia in fulfilment of the requirement for the degree of Master of Science

EXPERIMENTAL DETERMINATION OF FATIGUE LIFE FOR INTERNATIONAL RUBBER HARDNESS

DEGREE 60 ENGINE MOUNT RUBBER

By

MARYAM HOSSEINI

January 2010

Chairman : Aidy Ali, PhD Faculty : Engineering

In the new millennium era, rubber materials are vigorously used in many industries

including automotive that cover a wide range of applications such as tires, seals, belts,

bushes and engine mounts. Rubber is an ideal material for many applications because it

can withstand very large strain with no permanent deformation or fracture.

The behavior of material under repeated loads differs from static loads. Elastomers fail

at cyclic stress or strain amplitude much lower than static stress or strain. It is based on

growth of cracks through the material. The fatigue analysis and its lifetime evaluation

are very important in design procedure to assure the safety and reliability of the rubber

components. Design of rubber against fatigue failure is one of the important topics to be

focussed for checking the failures during its operation life.

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Many mechanical and environmental factors could prolong the rubber fatigue life. The

fatigue failure process of materials is explained by two approaches including crack

initiation and crack propagation.

The present work deals with investigation of the fatigue behavior using rubber dumb-

bell test specimens under uniaxial loading. The material used in this study is a

vulcanized natural rubber with a typical engine mount formulation and the hardness of

International Rubber Hardness Degree 60. Test specimens were designed based on type

2 of MS ISO 37 standard and used for tensile and fatigue tests, both in ambient

temperature. Fatigue tests were conducted under the displacement controlled condition

with a sine waveform of 0.1 Hz and the ratio of the minimum displacement to the

maximum displacement was equal to zero. The experimental results were presented

under strain controlled condition.

For investigation of the fatigue damage behavior, a theoretical equation was developed

based on the continuum damage mechanics theory. The Ogden strain energy potential of

first order was used for defining a constitutive relation of the natural rubber. The

proposed theoretical formula was based on function of the strain range under cyclic

loading to determine the fatigue life of elastomeric material. The ability of predicted

fatigue life shows a reasonable agreement of 98% with experimental values. The

experimental results and theoretical equation were validated with the previous

experimental data which show a good agreement of 97% and 93% respectively.

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Abstrak tesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai memenuhi keperluan untuk ijazah Master Sains

PENENTUAN JANGKA HAYAT LESU BAGI KEKERASAN GETAH

DARJAH 60 PADA PENDAKAP ENJIN

Oleh

MARYAM HOSSEINI

Januari 2010

Pengerusi : Aidy Ali, PhD Fakulti : Kejuruteraan

Dalam era alaf baru zaman kini, bahan seperti getah banyak digunakan di dalam

industri, termasuklah di dalam industri automotif yang meliputi pelbagai aplikasi seperti

tayar, kedap, talisawat, sesendal dan peredam enjin. Getah adalah bahan yang sesuai

digunakan kerana ia boleh menahan terikan yang sangat tinggi tanpa perubahan bentuk

yang kekal atau patah.

Perilaku sesuatu bahan dalam beban berulang adalah berbeza jika dibandingkan dengan

beban statik. Elastomer akan mengalami kegagalan pada nilai tegasan atau terikan

berkitar yang kurang berbanding nilai tegasan atau terikan dikenakan secara statik. Ini

berlaku disebabkan oleh tumbesaran keretakan pada sesuatu bahan. Analisis kelesuan

dan penentuan jangka hayat adalah amat penting semasa rekabentuk untuk memastikan

keselamatan bagi komponen getah. Rekabentuk komponen getah dan kegagalan

komponen disebabkan oleh kelesuan telah menjadi salah satu tajuk yang penting untuk

difokuskan bagi mengenal pasti tahap kegagalan semasa dalam operasi.

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Banyak faktor mekanikal dan persekitaran boleh mempengaruhi jangka hayat lesu bagi

getah. Kegagalan komponen getah disebabkan oleh kelesuan dapat diterangkan melalui

dua pendekatan, iaitu permulaan retak dan rambatan retak.

Kerja terkini melibatkan siasatan penentuan kelesuan menggunakan spesimen dumbel

yang dikenakan beban pada satu arah. Getah yang digunakan ialah getah asli yang telah

divulkankan dengan kekerasan International Rubber Hardness Degree 60, formulasi

yang biasa digunakan di dalam komponen peredam enjin. Spesimen direka mengikut

spefikasi berdasarkan MS ISO 37 jenis 2, dan digunakan dalam ujikaji regangan dan

kelesuan dengan keadaan suhu persekitaran. Ujian kelesuan dijalankan dengan

kawalan terikan menggunakan bentuk gelombang sin berfrekuensi 0.1 Hz dan nisbah

terikan minimum dan terikan maksimum bersamaan dengan sifar. Keputusan ujikaji

ditunjukkan dalam keadaan kawalan terikan.

Di dalam siasatan kerosakan disebabkan oleh kelesuan, satu persamaan teori telah

dihasilkan berdasarkan teori kontinum mekanik kerosakan. Potensi tenaga terikan

Ogden peringkat pertama digunakan untuk menentukan hubungan konstitutif bagi getah

asli. Formula teori yang dicadangkan ialah berdasarkan fungsi antara julat terikan

dengan bebanan berkitar untuk menentukan jangka hayat elastomer. Perbandingan

keputusan eksperimen dan jangka hayat yang diramalkan mencapai persetujuan

sebanyak 98%. Keputusan eksperimen dan teori disahkan oleh keputusan eksperimen

yang telah dijalankan dahulu dan menunjukkan kesepakatan yang baik, iaitu masing-

masing 97% dan 93%.

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ACKNOWLEDGEMENTS

I would like to express my sincere appreciation to all those who encouraged me and

made it possible for me to complete this thesis.

First and foremost, I would like to express my deep gratefulness to my supervisor Dr.

Aidy Ali for his guidance, constructive comments, invaluable advices and suggestions to

complete my research successfully. My sincere appreciation is also extended to the

committee member, Prof. Dr. Ir. Barkawi Sahari for his guidance and suggestions

throughout my research.

My sincere thanks also go to the Malaysian Rubber Board (MRB) for providing rubber

materials, dumb-bell test specimens and some experiments for this study. All of these

supports are highly appreciated.

I wish to express my profound gratitude to Prof. Dr. Waqar Asrar, Head of Department

of Mechanical Engineering and Dr. Kassim Abdulrahman Abdullah, Assistant

Professor, at International Islamic University Malaysia (IIUM) for supporting through

permission to use the fatigue test machine of their laboratory.

Finally, I would like to express my heartiest gratitude and appreciation to my beloved

family for support, encouragement and understanding throughout my studies, without

their love, it would not be possible for me. I am very thankful to my husband, Mansour,

and my son, Amir hossein, for their lasting love, support and patience.

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I certify that a Thesis Examination Committee has met on 7 January 2010 to conduct the final examination of Maryam Hosseini on her thesis entitled “Experimental Determination of Fatigue Life for International Rubber Hardness Degree 60 Engine Mount Rubber” in accordance with the Universities and University Colleges Act 1971 and the Constitution of the Universiti Putra Malaysia [P.U.(A) 106] 15 March 1998. The Committee recommends that the student be awarded the Master of Science.

Members of the Thesis Examination Committee were as follows:

Mohd Sapuan bin Salit, PhD Professor Faculty of Engineering Universiti Putra Malaysia (Chairman)

Nor Mariah binti Adam, PhD Associate Professor Faculty of Engineering Universiti Putra Malaysia (Internal Examiner)

Nawal Aswan bin Abdul Jalil, PhD Lecturer Faculty of Engineering Universiti Putra Malaysia (Internal Examiner)

Shahrum Abdullah, PhD Associate Professor Faculty of Engineering Universiti Kebangsaan Malaysia (External Examiner)

BUJANG KIM HUAT, PhD

Professor and Deputy Dean School of Graduate Studies Universiti Putra Malaysia Date: 11 March 2010

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This thesis was submitted to the Senate of Universiti Putra Malaysia and has been accepted as fulfilment of the requirement for the degree of Master of Science. The members of the Supervisory Committee were as follows: Aidy Ali, PhD Senior Lecturer Department of Mechanical and Manufacturing Engineering Faculty of Engineering Universiti Putra Malaysia (Chairman) Barkawi Sahari, PhD Professor Department of Mechanical and Manufacturing Engineering Faculty of Engineering Universiti Putra Malaysia (Member)

HASANAH MOHD GHAZALI, PhD

Professor and Dean School of Graduate Studies Universiti Putra Malaysia Date: 8 April 2010

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DECLARATION

I declare that the thesis is my original work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously, and is not concurrently, submitted for any other degree at Universiti Putra Malaysia or at any other institutions.

MARYAM HOSSEINI Date:

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TABLE OF CONTENTS

Page DEDICATION ii ABSTRACT iii ABSTRAK v ACKNOWLEDGEMENTS vii APPROVAL viii DECLARATION x LIST OF TABLES xiii LIST OF FIGURES xiv LIST OF ABBREVIATIONS xviii

CHAPTER

1 INTRODUCTION �

1.1 Introduction 1 1.2 Problem Statement 2 1.3 Hypothesis 4 1.4 Research Objectives 6 1.5 Scope of Study 6 �.6 Layout of the Thesis 6

2 LITERATURE REVIEW 7 2.1 Introduction to Elastomer 7 2.2 Elastomer Types 8 2.3 Compounding 9 2.4 Elastic Properties 10 2.4.1 Elastic Properties at Small Deformations 11 2.4.2 Elastic Properties at Large Deformations 14 2.5 Viscoelasticity 15 2.6 Tensile Stress-Strain 17 2.7 Hyperelastic Models 19 2.7.1 Polynomial Model 22 2.7.2 Reduced Polynomial Model 23 2.7.3 Ogden Model 24 2.7.4 Mooney-Rivlin Model 24 2.7.5 neo-Hookean Model 25 2.7.6 Yeoh Model 26 2.7.7 Arruda and Boyce Model 27 2.7.8 Van der Waals Model 28 2.8 Durability of Rubber 29 2.9 Life Prediction Methodology 30 2.10 Initiation and Propagation of Cracks 32 2.10.1 Fatigue Crack Nucleation 32 2.10.2 Fatigue Life and Crack Growth 34

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2.10.3 Fatigue Crack Growth 36 2.11 Existing Predictors for Fatigue Crack Nucleation 39 2.11.1 Classical Fatigue Life Predictors 40 2.11.2 Plane-Specific or Critical Plane Approach 47 2.12 Summary 50

3 METHODOLOGY 53 3.1 Introduction 53 3.2 Material Description 55 3.3 Form of Test Piece for Tensile Stress-Strain and Fatigue Tests 57 3.3.1 Static Test Specimen 58 3.3.2 Fatigue Test Specimen 60 3.3.3 Forming the Specimen 61 3.3.4 Measurement of Test Pieces 65 3.4 Mechanical Properties Test Description 66 3.4.1 Tensile Test Procedure 67 3.4.2 Fatigue Test Procedure 76 3.5 Analytical Solution 84 3.6 Summary 85

4 RESULTS AND DISCUSSION 87 4.1 Introduction 87 4.2 Tensile Test Results 88 4.2.1 Tensile Test with Extensometer 88 4.2.2 Tensile Test without Extensometer 91 4.3 The Hyperelastic Constitutive Model for Material Characterization 94 4.4 Fatigue Test Results 98 4.5 Analytical Solution for the Fatigue Life of Elastomeric

Materials 102

4.5.1 Continuum Damage Mechanics Theory 102 4.5.2 Assumptions for Damage and Fatigue of Elastomers 103 4.5.3 The Damage Model 104 4.6 Limitation and Range of Parameters in Fatigue Life Equation 109 4.7 Validation and Verification 112 4.8 Mechanism of Failure 114 4.9 Effect of Hardness on Stress-Strain Properties 116 4.10 Heat-Aging Effects on Hardness and Stress-Strain Properties 119 4.11 Summary 124

5 CONCLUSIONS AND RECOMMENDATIONS 126 5.1 Conclusions 126

5.2 Recommendations 127

REFERENCES 129 BIODATA OF STUDENT 137 PUBLICATION 138