INVESTIGATION ON MECHANICAL PROPERTIES AND FINITE ELEMENT ANALYSIS OF HDPE/EPR FILLED WITH CNT IRRADIATED NANOCOMPOSITES
MUHAMMAD ILHAM BIN KHALIT
A thesis submitted in fulfilment of the requirement for the degree of Doctor of Philosophy (Engineering)
Kulliyyah of Engineering
International Islamic University Malaysia
Shoe outsoles experience the most fatigue flexing effect during movement, thus initiating cracks with time. This crack will lead to changes in the mechanical property of the shoe outsole, where the effect of loading is dependent on the mechanical properties of the shoe outsole. Currently, ethylene vinyl acetate (EVA) is used to fabricate shoe outsoles. Due to a decaying problem, radiated high-density polyethylene (HDPE)/ethylene propylene rubber (EPR) filled with carbon nanotube (CNT) are now chosen to replace the current material (EVA) for outsole shoes. EPR possesses superior properties such as higher flexural strength as compared to EVA.
Furthermore, when CNT is added as nanofiller to a material, it can increase the lifetime of the material. Electron beam (EB) irradiation can also improve the mechanical property of the outsole. The aim of this study is to fabricate an irradiated HDPE/EPR filled with CNT nanocomposite outsole. The materials were prepared through a blending process involving HDPE, EPR and CNT materials, which are then compression moulded to a size 5 female outsole. The outsole was exposed to EB irradiation for the cross-linking process and its mechanical property characterised via a tensile and flexing test. The tensile fracture specimen was observed morphologically under SEM. Initially, the outsole was modelled in ABAQUS software with the exact design as the fabricated ones. Then, it was compared experimentally for model validation. After that, the outsole was modelled at thicknesses of 4.05 mm, 4.55 mm, 5.05 mm, 5.50 mm, 5.55 mm and 6.05 mm for size 4, 5 and 6. It was found that EB irradiation indeed improved the flexibility of the outsole, but the outsole became stiff with the addition of CNT. The most suitable material to fabricate the outsole was found to be the irradiated HDPE/EPR blend. The obtained numerical results were close to the experimental ones, which are 95% similar to each other. The numerical result simulations enable the prediction of experimental data. The results of finite element analysis (FEA) show that the outsole should be fabricated at a size 6 with a base thickness of 3.05 mm and a tread pattern thickness of 1 mm. This combination of thicknesses gives the best results such as the longest fatigue lifetime, minimum stress applied, and the lightest weight, at 51 g. This project has yielded highly significant results, which future researchers and fabricators can use for predicting the best material to replace the current material for shoe outsoles. The method to determine the fatigue lifetime and the flexibility of the outsole using different materials can also be replicated, and subsequently, will save cost and time required in the fabrication of the outsole.
يدؤي امم ,ةكرحلا ءانثأ تاداهجﻹا ةجيتن تاهوشتلا دشﻷ ءاذحلا لعن ضرعتي ءوشنل
٬ دمتعي ثيح ءاذحلا لعنل ةيكيناكيملا صاوخلا يف تاريغت ىلإ يدؤت قوقشلا
لعنلا صاوخ ىلع لمحلا ريثأت
٬ لعن عينصت يف تاتسإ لينيف نيليثﻹا ةدام مدختست ايلاح
ءاذحلا ) EVA (٬
يلاع نيليثإ يلوبلا ددعتم بكرمب ةضاعتسﻹا مت لكآتلا ةلكشم ببسب
ةفاثكلا ) HDPE (/
نيليثﻹا طاطم )
EPR ( ةيونانلا نوبركلا بيبانأب ءولمملا )
(٬ ٬ يكﻼهتسﻹا ةداملا رمع ليطي ( CNT ) ةيونانلا نوبركلا بيبانأ ةفاضإ عاعشﻹا ةيلمع
EB ( ةساردلا هذه نم فدهلا .ءاذحلا لعنل ةيكيناكيملا صاوخلا نسحت اضيا
بكرم نم ءاذح لعن عينصت وه EPR/HDPE
كلذ دعب مت يتلا
ساقم يئاسن ءاذح لكشب اهعينصت ٥
. حلا لعن ريرمت مت عاعشﻹا ةيلمعل ءاذ
EB ( وخلا طبض و طبارتلا نيسحتل ا
ط نع ةيكيناكيملا ص تارابتخا قير
٬ ينورتكلﻹا حسملا رهجمب ةنيعلا يف دشلا قوقش صحف مت )
SEM ( مت ءدبلا يف .
ميمصت ) جمانرب ىلع ءاذحلا لعن
ABAQUS عنصُملا ءاذحلا ميمصت سفنب يبوساحلا (
خا هتنراقم تمت و ققحتلل ميمصتلا عم ايرابت
٬ كمسب ءاذحلا لعن ميمصت مت كلذ دعب
٬ ٤٫٥٥ مم
٬ ٥٫٠٥ م م٬
٬ و ٦٫٠٥ مم
٬ تاساقملل ٤
و ٥ و ةيلمع نأ دج ُو . ٦
ينورتكلﻹا عاعاشﻹا )
EB ( بيبانأ ةفاضإب نكل ءاذحلا لعن ةنورم لعفلاب تنسح
ةيونانلا نوبركلا )
CNT ( هتواسق تدادزإ طيلخ يه لعنلا عينصتل داوملا بسنأ نأ دج ُو.
ةبيرق تءاج ةيبوساحلا ةاكاحملا جئاتن
ةبسنب ةيرابتخﻹا جئاتنلل ٩٥
٬ ةيرابتخﻹا جئاتنلا عقوتب تحمس ةاكاحملا جئاتن جئاتن .
يئاهنلا ميمصتلا ليلحت )
FEA ( ساقمب عنصي نأ بجي لعنلا نأ ترهظأ ٦
قمعب ليكشت طمن عم مم ١
٬ لثم جئاتنلا لضفأ ققحي ميمصتلا اذه لوطأ
نزو لقأ و يكﻼهتسإ رمع ٥١
و نيثحابلا نكمُت ةرهاب جئاتن عورشملا اذه ققح .مارج
لادبتسإ اهب نكمي يتلا داوملا لضفأ عقوت نم لبقتسملا يف نيعنصُملا عينصتلا داوم
٬ داوم ىلع اهقيبطت نكمي ةنورملا و ءاذحلا رمعل يكﻼهتسﻹا رمعلا عقوت ةقيرط
ي كلذب و ةفلتخم .ءاذحلا لعن عينصتل ةبولطملا ةفلكتلا و تقولا ليلقت مت
The thesis of Muhammad Ilham Bin Khalit has been approved by the following:
Hazleen Anuar Supervisor
Norhashimah Mohd Shaffiar Co-Supervisor 1
Ma’an Fahmi R. Al-Khatib Internal Examiner
Mat Uzir Bin Wahit External Examiner
Mohd Sapuan Salit External Examiner
Badruddin Bin Hj. Ibrahim Chairperson
I hereby declare that this thesis is the result of my own investigations, except where otherwise stated. I also declare that it has not been previously or concurrently submitted for any other degrees at IIUM or other institutions.
Muhammad Ilham Bin Khalit
Signature ……… Date ………
INTERNATIONAL ISLAMIC UNIVERSITY MALAYSIA DECLARATION OF COPYRIGHT AND AFFIRMATION OF
FAIR USE OF UNPUBLISHED RESEARCH
INVESTIGATION OF MECHANICAL PROPERTIES AND FINITE ELEMENT ANALYSIS OF HDPE/EPR FILLED CNT
I declare that the copyright holders of this thesis are jointly owned by the student and IIUM.
Copyright © 2018 Muhammad Ilham Bin Khalit and International Islamic University Malaysia. All rights reserved.
No part of this unpublished research may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without prior written permission of the copyright holder except as provided below
1. Any material contained in or derived from this unpublished research may only be used by others in their writing with due acknowledgement.
2. IIUM or its library will have the right to make and transmit copies (print or electronic) for institutional and academic purpose.
3. The IIUM library will have the right to make, store in a retrieval system and supply copies of this unpublished research if requested by other universities and research libraries.
By signing this form, I acknowledged that I have read and understand the IIUM Intellectual Property Right and Commercialization policy.
Affirmed by Muhammad Ilham Bin Khalit
To my beloved parents and family
Alhamdulillah, all praises to Allah for His blessings and guidance given through the people that have contributed towards the completion of my study. First and foremost, I would like to thank my supervisor, Associate Prof. Dr. Hazleen Anuar, for her guidance, patience, motivation, and encouragement that have enabled me to complete my study efficiently. Special thanks go to my co-supervisor, Norhashimah Mohd Shaffiar, for all her guidance and cooperation through the entire period of this study.
This thesis would not be possible without the assistance of staff from the Department of Manufacturing and Materials, as a whole, especially Brother Hairi, who has directly and indirectly assisted me in completing my research.
In addition, utmost thanks go to my family, especially my mother and father, my wife, Zarina and daughters, Batrisya and Audadi, for their unconditional love and support towards me. My heartfelt appreciation also goes to my siblings, relatives, and all my friends inside and outside of my university, who have always supported me and prayed for the successful completion of my study. Without them, I have no doubt that success in any capacity would be unachievable for me. My utmost gratitude and thanks to everyone who was involved in completing my thesis. May Allah bless all of you.
TABLE OF CONTENT
Abstract ... ii
Abstract in Arabic………..iii
Approval Page ...iv
Declaration ... v
Acknowlegements ... viii
Table of Content ...ix
List of Tables ...xi
List of Figures ... xii
List of Abbreviations………...xvi
List of Symbols………...xvii
CHAPTER ONE: INTRODUCTION ... 1
1.1 Background ... 1
1.2 Problem Statement and Significance of Study ... 3
1.3 Research Philosophy ... 6
1.4 Objectives ... 7
1.5 Scope of Research ... 9
1.6 Thesis Organisation ... 9
CHAPTER TWO: LITERATURE REVIEW ... 11
2.1 Shoe Sole ... 11
2.2 Important Properties of Shoe Sole ... 13
2.2.1 Tensile Properties ... 14
2.2.2 Flexibility / Flexing Property ... 15
2.3 Materials For Shoe Sole ... 16
2.3.1 EVA ... 17
2.3.2 HDPE ... 18
2.3.3 EPR ... 21
2.3.4 HDPE / EPR ... 23
2.3.5 HDPE / EPR FILLED WITH CNT ... 25
2.4 Electron Beam Radiation Process for Polymer ... 28
2.5 Foot Motion in Walking ... 32
2.6 Flexing Test and Flexing Loading ... 34
2.7 Finite Element Analysis (FEA) ... 37
CHAPTER THREE: MATERIALS AND METHODS ... 47
3.1 Introduction ... 47
3.2 Materials ... 47
3.3 Methods ... 47
3.3.1 Material Preparation ... 48
3.3.2 Mixing Materials ... 49
3.3.3 Compression Moulding Process ... 50
3.4 Electron Beam Irradiation ... 51
3.5 Mechanical Test ... 52
3.5.1 Tensile Test ... 53
3.5.2 Flexing Test ... 54
3.5.3 Flexing Test Using Own Machine ... 56
184.108.40.206 Fabrication of Flexing Tester ... 56
220.127.116.11 Pulley ... 58
18.104.22.168 Flexing Test ... 61
3.6 Scanning Electron Microscopy (SEM)... 63
3.7 Simulation of Flexing Test Using Abaqus ... 64
CHAPTER FOUR: RESULT AND DISCUSSION ... 71
4.1 The Effect of CNT Incorporation on the HDPE/EPR Blend ... 71
4.1.1 Tensile Properties ... 71
4.1.2 Lifetime and Flexing Behaviour ... 74
4.2 Comparison Between Irradiated and Non-Irradiated of HDPE/EPR and HDPE/EPR Filled with CNT ... 78
4.2.1 Tensile Properties ... 78
4.2.2 Lifetime and Flexing Behaviour ... 82
4.2.3 Lifetime and Flexing Behaviour of Self-Fabricated Fexing Machine ... 85
4.3 The Effect of CNT Incorporation and Irradiation on the Morphology of Tensile Fracture Specimen of HDPE/EPR Blend and HDPE/EPR Filled with 3 wt% CNT Nanocomposite ... 96
4.4 Finite Element Analysis ... 101
CHAPTER FIVE: CONCLUSION AND RECOMMENDATION ... 121
REFERENCES ... 123
APPENDIX A: DETAILS PART OF THE SELF-FABRICATED FLEXING MACHINE...……… 134
APPENDIX B: LIST OF PUBLICATION………. 158
LIST OF TABLES
Table 3.1 Preparation of HDPE/EPR blend via melt blending method 49 Table 3.2 Preparation of HDPE/EPR and HDPE/EPR filled with CNT via melt
blending method 49
Table 3.3 Pulley speed result 60
Table 3.4 Thickness of the outsoles 65
Table 3.5 Size and partition 66
Table 3.6 Young’s Modulus and Poisson’s Ratio 67
Table 4.1 Mechanical properties of the materials 72
Table 4.2 Result of the outsole flexing test for non-irradiated HDPE/EPR blend and non-irradiated HDPE/EPR filled with 3 wt% CNT nanocomposite 76 Table 4.3: Mechanical properties of the irradiated and non-irradiated HDPE/EPR 79 Table 4.4: Mechanical properties of the irradiated and non-irradiated HDPE/EPR
filled with 3 wt% CNT nanocomposite 81
Table 4.5 Result of the outsole flexing test for irradiated and non-irradiated
HDPE/EPR blend 83
Table 4.6 Result of the outsole flexing test for non-irradiated HDPE/EPR filled with 3 wt% CNT nanocomposite irradiated HDPE/EPR filled with 3 wt% CNT
Table 4.7 Flex count using the self-fabricated flexing machine 86
Table 4.8 Summary for flexing test 91
Table 4.9 Summary of the weight for outsoles size 4, 5 and 6 120
LIST OF FIGURES
Figure 2.1 Chemical structure of: a) HDPE, b) LDPE ... 19
Figure 2.2 Schematic diagram of electron beam irradiation facility (Wang et al., 2018) ... 29
Figure 2.3 Various phases of forefoot running: (a) touchdown, (b) forefoot eversion and torsion, (c) rearfoot pronation, (d) takeoff (Stacoff et al.,1991) ... 33
Figure 2.4 MTS Q-Test machine (Ballun, Williams, Goehler, & Sevener, 2011) ... 35
Figure 2.5 Testing device setup for football shoes (Hillstrom et al., 2005) ... 35
Figure 2.6 Zoning of the foot in several masks for the left foot (Speksnijder et al., 2005) ... 36
Figure 2.7 Colour contour to simplify results interpretation (Esther et al., 2016) ... 39
Figure 2.8 Location of maximum stress during vertical landing (Jalil & Alex, 2013) 40 Figure 2.9 FEA of EVA outsole material a) outsole exposed to 588 N force; b) maximum stress occurred at the heel breast; c) maximum displacement at the forepart (Mondal et al., 2016) ... 41
Figure 2.10 FEA of EVA insole material (Pastina et al., 2012) ... 41
Figure 2.11 The outer sole of the five tread patterns (Sun et al., 2005) ... 42
Figure 2.12 Outsole structure and subdomain (Shimoyama et al., 2011)... 43
Figure 2.13 Stress distribution of bending movement (Tan & Alexander Chee, 2013) ... 44
Figure 2.14 Finite element model for a random unit cell (Sun et al., 2007) ... 45
Figure 2.15 Finite element models for periodic unit cells. (a) Single-particle unit cell and (b) two-particle unit cell (Sun et al., 2007) ... 45
Figure 3.1 An overview of the study ... 48
Figure 3.2 The mould for the outsole ... 50
Figure 3.3 The mould for the dumbbell shape ... 50
Figure 3.4 a) HDPE/EPR blend sole, b) HDPE/EPR filled CNT sole ... 51
Figure 3.5 Electron beam irradiation on the outsole ... 52
Figure 3.6 a) Strain gauge for measuring transverse strain, b) Strain gauge for measuring axial strain ... 54
Figure 3.7 Flexed line ... 55
Figure 3.8 Gotech Testing Machine ... 55
Figure 3.9 a) Flexing machine b) Isometric View ... 57
Figure 3.10 Bill of Materials (BOM)... 58
Figure 3.11 Free body diagram of the pulley system ... 59
Figure 3.12 Speed test using a tachometer a) Pulley 1 RPM, b) Pulley 2 and 3 RPM, c) Pulley 4 RPM ... 60
Figure 3.13 Sample mounted on clamp ... 61
Figure 3.14 90 o angles setup ... 62
Figure 3.15 Position of the strain gauge ... 63
Figure 3.16 Base and Tread pattern ... 65
Figure 3.17 Partition of the part ... 66
Figure 3.18 Initial Position of the outsole ... 67
Figure 3.19 Half cycle Position of the outsole ... 68
Figure 3.20 Position of Boundary Conditions ... 69
Figure 3.21 Tetra shape for meshing ... 69
Figure 3.22 Visualization section ... 70
Figure 4.1 Stride for the outsole ... 75
Figure 4.2 a) The initial crack for a non-irradiated HDPE/EPR blend outsole; b) The
final crack for a non-irradiated HDPE/EPR blend outsole ... 77
Figure 4.3 The lifetime of the outsole ... 77
Figure 4.4 The lifetime of the outsole ... 83
Figure 4.5 The lifetime of the outsole ... 84
Figure 4.6 Non-irradiated HDPE/EPR blend outsole during first cycle ... 88
Figure 4.7 Non-irradiated HDPE/EPR blend outsole during last cycle ... 88
Figure 4.8 Non-irradiated HDPE/EPR filled–3 wt% CNT nanocomposites outsole during first cycle ... 90
Figure 4.9 Non-irradiated HDPE/EPR filled–3 wt% CNT nanocomposites outsole during last cycle ... 90
Figure 4.10 Irradiated HDPE/EPR-3 wt% CNT nanocomposite outsole during first cycle ... 92
Figure 4.11 Irradiated HDPE/EPR 3 wt% CNT nanocomposite outsole during last cycle ... 93
Figure 4.12 Irradiated HDPE/EPR blend outsole during first cycle ... 94
Figure 4.13 Irradiated HDPE/EPR blend outsole during last cycle ... 95
Figure 4.14 Scanning electron micrographs of (a) Non-irradiated HDPE/EPR blend (b) Non-irradiated HDPE/EPR filled with 3 wt% CNT nanocomposite ... 97
Figure 4.15 Scanning electron micrograph of (a) Non-irradiated HDPE/EPR blend (b) Irradiated HDPE/EPR blend ... 99
Figure 4.16 Scanning electron micrographs of (a) Non-irradiated HDPE/EPR filled with 3 wt% CNT nanocomposite (b) Irradiated HDPE/EPR filled with 3 wt% CNT nanocomposite ... 99
Figure 4.17 Scanning electron micrographs of (a) Irradiated HPE/EPR filled with 3 wt% CNT under tensile loading (b) Irradiated HDPE/EPR filled with 3 wt% CNT
under flexing loading ... 100
Figure 4.18 Stress comparison between FEA and self-fabricated flexing machine for outsole size 5 ... 103
Figure 4.19 FEA for outsole Size 4 with different tread pattern thickness ... 105
Figure 4.20 FEA for outsole Size 4 with different base thickness ... 106
Figure 4.21 Summary of FEA for outsole Size 4 ... 107
Figure 4.22 : Estimated weight for outsole size 4, tread pattern and base thickness 1 mm and 3.05 mm ... 109
Figure 4.23 FEA for outsole Size 5 with different tread pattern thickness ... 110
Figure 4.24 FEA for outsole Size 5 with different base thickness ... 111
Figure 4.25 Summary of FEA for outsole Size 5 ... 112
Figure 4.26 Estimated weight for outsole size 5, tread pattern and base thickness 1mm and 3.05mm ... 114
Figure 4.27 FEA for outsole Size 6 with different tread pattern thickness ... 115
Figure 4.28 FEA for outsole Size 6 with different base thickness ... 117
Figure 4.29 Summary of FEA for outsole Size 6 ... 118
Figure 4.30 Estimated weight for outsole size 6, tread pattern and base thickness 1 mm and 3.05 mm ... 119
LIST OF ABBREVIATIONS
11MP 11th Malaysia Plan
ASTM American Standard Testing Material
BISGMA/TEGMA Bisphenylglycidyl Dimethacrylate/Triethylene Glycol Dimethacrylate
BS British Standard
CNT Carbon Nanotubes
EB Electron Beam
EPR Ethylene Propylene Rubber FEA Finite Element Analysis GNP Graphene Nanoplatelet HDPE High Density Polyethylene
HEER High Energy Electromagnetic Radiation HEPE High Energy Particles Beams
ISO International Organization for Standardization LDPE Low Density Polyethylene
NR/R Natural Rubber/Recycle
P565 Pebax at 99.8% and Irganox 565 at 0.2%
PVC Polyvinyl Chloride
SBR Stryene/butadiene copolymer SEM Scanning Electron Microscope SMR Standard Malaysia Rubber
STRIDE Science and Technology Research Institute and Defence Malaysia
TPR Thermoplastic Rubber
UTS Ultimate Tensile Strength
LIST OF SYMBOLS
∆ Changes in length
∆ Elongation-initiated resistance change A Cross-sectional Area
℃ Degree celsius
e Output voltage
L Original length
MeV mA hp N D F1
Mega electron-volt Milliampere Horsepower Pulley Speed Pulley Diameter Belt tension Belt compression MFI Melt flow index
mm % Millimetre Percentage
MPa Mega pascal
N Force, newton
nb Number of Bending
P Internal force
R Original Resistance of Strain Gauge RPM Revolution per minute
V Poisson’s ratio
Strain Micro Micrometre Stress
CHAPTER 1 INTRODUCTION
Sports activity has increased in Malaysia and women participation are particularly showing a significant increase. It is directly proportional to the government's involvement in promoting sports to the people of Malaysia to produce healthy and balanced life. Construction of schools and sports institutions evidence that the government is committed in implementing this agenda. The government has targeted an increase in sports engagement for the Olympic Games for the coming year.
As renowned, Malaysia has a good track record for sports such as hockey, but sports such as runs are still lagging behind compared to other countries.
Malaysia can increase the chance of a win for the running sports events if the athlete's quality is well maintained. Apart from the athlete’s health aspect, high- quality running shoes are crucial to ensure that athlete wins the competition. It would be impossible for an athlete to perform in a competition without good shoes. Thus, it is important for researchers to investigate shoe design, as this will help athletes to perform well in competitions. The primary function of shoes or athletic apparel is to eliminate or at least reduce any potential injury that could occur under repetitive loading during running motions. The most exposed part of the shoes is the outsole; as it is crucial for it to have good material property, so that the foot is well protected.
Running shoes should be lighter than other types of shoes. To produce lightweight shoes, outsole should be made of advanced and lightweight materials. For
this purpose, the use of cross-linked nanocomposite materials is extremely timely and appropriate as it will enhance the performance of Malaysian athletes in related sports.
In addition to the lightweight property, outsole should have good flexing properties, which should be made by materials such as rubber and plastic. Husniyah et al. (2016) discovered a potential polymer blends material based on high-density polyethylene/ethylene-propylene-rubber (HDPE/EPR) and carbon nanotube (CNT) can be fabricated as a material for the shoe outsole. But in their finding, it only focused on the tensile property of the material, while for the outsole, it need further test such as flexing test for the application purposes. There are studies that have been made about the addition of nanofillers into polymer based materials such as the addition of CNT into the polyethylene material causing the mechanical property of polyethylene to increase and become better (Kanagaraj et al., 2007; Rama Sreekanth et al., 2012). This material is able to provide adequate stability for aggressive or violent movements of the athlete, resistant to high abrasion, and can prolong the life of the shoe outsole. In addition, the performance of the outsole can be enhanced with some changes made to its mechanical properties—by exposing it to electron beam (EB) irradiation (Szebényi et al., 2012). As a result, the fatigue stress of the cross- linked nanocomposite-based material is minimised and its lifetime cycle was increased (Kane et al., 2008; Loos et al., 2013; Manjunatha et al., 2013; Manjunatha et al., 2009; Yu, Zhang et al., 2008).
There are many mechanical properties of the outsole that can be examined such as tensile strength, surface roughness, shear strength, etc. However, the most important mechanical property of the outsole is its flexural strength (Chen et al., 2014). The outsole tends to be exposed to consistent flexing loading due to walking.
This can cause cracks and lead to a reduction in the functional characteristics of the
sole and the entire footwear. Flexing resistance of a shoe is a very important property to assess as the quality of a shoe depends on this property. Therefore, this study focuses more on this flexing condition.
Mechanical tests, such as tensile test can be used to determine mechanical property of materials. This test includes Young’s modulus, tensile strength, and Poisson’s ratio. Usually, this test is carried out on newly developed materials. There are various other types of mechanical tests; flexing test is to determine the flexural strength of a material. However, this test is a destructive test, which is costly and time consuming. To overcome this problem, Finite Element Analysis (FEA) is introduced to produce a much more detailed set of results than experimental investigations. FEA is also often quicker and less expensive. FEA is a numerical method for solving problems in engineering, mathematics, and physics. There are much more benefits from using FEA such as the safe simulation of potentially dangerous, destructive, or impractical load conditions and failure modes. In addition, several failure modes or physical events can be tested within a common model, thus consuming less time compared to experimental investigations. For this project, a simulation of real flexing conditions, which comply with the mechanical test, is adopted and discussed in Section 4.4.
1.2 PROBLEM STATEMENTAND SIGNIFICANCE OF STUDY
People wear shoes to protect their foot during movement, whether from any kind of dangerous objects or for comfort. There are two important parts of the shoe that give protection to the foot, which are the outsole and insole. These parts are exposed to fatigue stress during foot movement.
The outsole is the most affected area that is exposed to fatigue stress during movement, as it is the external part. Meanwhile, the insole is the internal part of the shoe, and is therefore less exposed to fatigue stress. Fatigue stress leads to the initiation of cracks on the outsole. Thus, to overcome the crack problem that arises due to fatigue stress during movement, a new material can be applied, which is predicted to have superior property and therefore can minimise or eliminate the problem. This study proposes a new material, which is CNT filled HDPE/EPR irradiated nanocomposite, to fabricate the outsole. The current outsole is fabricated using ethylene vinyl acetate (EVA).One study found that EVA has a decaying problem and is not suitable as a shoe outsole (Brückner et al.,2010). To overcome this problem, a study proves that it can be overcome by compressing EVA in a pressurized mould so then the outsole forms a thick skin. This way EVA outsoles are made to last longer (Davetimberwolf, 2016).As stated earlier, outsole is vulnerable to fatigue stress in particularly flexing loading during running and walking. Unfortunately, the durability of EVA materials to repeated impacts is not ideals which it could lead to the fracture of the outsole(Mills, 2007). A study of mixture of Polyformaldehyde (POM) / EVA / HDPE polymer blends has been conducted in order to overcome this problem, which the presence of HDPE into that mixture was able to improve the fracture toughness of the EVA material. However EVA is heavy, hard, and difficult to degrade, which usually translates to environmental issues (Hung, 2015). Study has been made by Husniyah et al. (2016), they have suggested that HDPE / EPR blends have the potential to replace EVA materials as a material for shoe outsole. Their study is supported by Ames (2004) where durability of the EPR materials is higher than EVA materials and possessed a good flexible property which is good for an outsole.
The durability can be seen through abrasion test and wear test. Therefore, EPR was
used in this study, where as much as 30% is employed to fabricate the shoe outsole.
EPR is a major and important material, as it possesses superior properties compared to EVA.
The main functions of nanofillers are to enhance the mechanical properties of the polymer blends if added to the blends. There are various studies conducted primarily on the use of CNT as nonofiller into polymer blends. One of it is a complete review by Rahmat & Hubert (2011) on CNT use as nanofiller into polymer blends. It has been shown to increase the mechanical capacity of the polymer blends. Not much research has been done for the use of CNT as nanofiller into HDPE/EPR blends.
However, the use of HDPE material in the use of CNT as nanofiller is proved to improve the lifetime of the polymer materials. As an example of a study made by Sadeqhipour et al. (2013), they use CNT as a nanofiller into HDPE material where it was proved that the lifetime of the polymer is improved. For this project, CNT was added as nanofiller into the HDPE/EPR blends. As referred to Wypych (2016), CNT is suitable nanofiller to blend with EPR polymer and it might binds between the HDPE and EPR and strengthens the bonding between them. Therefore, it can also reduce the crack problems that decrease the lifetime of the outsole.
Besides the addition of CNT as additive to strengthen outsole and to overcome decaying problems, application of radiation to polymer blends has proven to enhance the mechanical property of the polymer blends. This can be verified by a study conducted by Husniyah & Hazleen (2014) where Electron Beam Irradiation strengthens the cross-linking between HDPE/EPR blends. The use of EB irradiation to HDPE/EPR blends is significant to overcome cracking problems on the outsole lifetime as it is proven that strength and modulus of elasticity have also increased.
Flexing test is the most significant to determine the HDPE/EPR blends are the best materials to replace current material as an outsole. In Malaysia, this test can be run at STRIDE (Science & Technology Research Institute for Defence) by using GT- 70711-ES Gotech testing machine. However, this machine has limitation as it can only measure the flexes count (flex resistance of the outsole). Flex resistance alone is not enough to determine whether the outsole is in the best possible condition. It needs additional data such as deflexion of the outsole, strain and stress that are present when the flexing test is carried out. Therefore, the own flexing machine will be built to obtain the data such as deflexion, stress and strain. With the presence of this data, it can be concluded whether the outsole made by HDPE/EPR blends can solve the problem of cracking that existing on EVA materials as an outsole.
1.3 RESEARCH PHILOSOPHY
The blend of HDPE with ethylene propylene rubber (EPR) will improve the outsole’s overall impact strength, tensile strength, and provide better gripping ability (Liu et al., 2008). Moreover, it also provides necessary characteristics such as high resistance to heat, ozone, and environmental degradation factors such as cold temperatures and high humidity (Li et al., 2003). Due to the component’s mutual chemical compatibility, blending of HDPE with EPR is seen to be attractive (Ali et al.,
& Radusch, 2010; Basak et al., 2011).
CNT is one of the stiffest materials. In addition, CNT has excellent mechanical properties. Adding it to rubbery matrices will result in a significant increase in the overall strength of the material (Ma et al., 2010). Therefore, CNT will also increase the lifetime of the material.
To enhance the mechanical properties of the developed materials, electron beam (EB) irradiation is proposed as an alternative technique to facilitate cross- linking of the polymer blend. EB irradiation can significantly alter the molecular structure of these compositions. Furthermore, better dispersion of CNT is expected when the surface of the developed materials is exposed to electron beam irradiation (Shin & Lee, 2015). The use of EB irradiation will provide unique properties that may not otherwise be achieved using standard chemical cross-linking methods. The process of EB irradiation also does not require any material preconditioning and requires shorter exposure time (typically less than 10 min) (Sabu & Laly A., 2009).
The technique, in contrast, is environmentally friendly in that it does not need chemicals nor produce any chemical residues (Vallat et al., & Mendoza Patlan, 2005;
Żenkiewicz & Dzwonkowski, 2007).
Therefore, the development of nanocomposites from EB irradiated HDPE/EPR filled with CNT for the outsole is projected to be reasonable due to a simple and efficient manufacturing process as well as resulting in good material features.
The main objective of this research is to develop a cross-linked nanocomposite outsole through the blending of HDPE and EPR in the presence of CNT as filler. To achieve this objective, the following sub-objectives are identified:
1. To investigate the effect of CNT incorporation into HDPE/EPR blend on tensile properties, flexing behaviour and lifetime of the HDPE/EPR filled with CNT shoe outsole.