universiti putra malaysia1. introduction 1.1 background 1.2 problem statement 1.3 objectives and...
TRANSCRIPT
UNIVERSITI PUTRA MALAYSIA
NOR HASNI BINTI ZAHARI
FK 2009 116
DEVELOPMENT OF CARBON FIBER-REINFORCED POLYPROPYLENE COMPOSITE FOR CAR BUMPERS
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DEVELOPMENT OF CARBON FIBER-REINFORCED POLYPROPYLENE
COMPOSITE FOR CAR BUMPERS
By
NOR HASNI BINTI ZAHARI
Thesis Submitted to
the School of Graduate Studies, Universiti Putra Malaysia
in Partial Fulfilment of the Requirements for the Degree of Master of Science
May 2009
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Thanks to my beloved husband, mom, auntie, sisters and brother for their support during the long preparation of this thesis.
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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 in Chemical Engineering.
DEVELOPMENT OF CARBON FIBER-REINFORCED
POLYPROPYLENE COMPOSITE FOR CAR BUMPERS
By
NOR HASNI BINTI ZAHARI
May 2009
Chairman : Professor Madya Robiah Bt. Yunus, PhD
Faculty : Engineering
Carbon fiber reinforced composites (CFRC) are very strong and extremely lighter
than steel. Their toughness provides excellent abrasion and tear resistance. The usage
of the CFRC in automotive industries is widely explored due to the new requirements
related to energy conservation, safety and antipollution. In this study, discontinuous
carbon fiber reinforced polypropylene composite was selected due its characteristics
such as light-weight, corrosion resistance, low to moderate cost, thermal stability and
ease of fabrication.
Polypropylene (PP) was chosen as the matrix because it is available in large
quantities and not very sensitive to chemical stress cracking. PP also has a
combination of high elongation and tensile strength. Carbon fibers are widely used in
polymer–matrix composites owing to their good mechanical, thermal and electrical
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properties. Cheap discontinuous carbon fiber or short fiber is the low quality carbon
fiber which cannot be used in aircraft and aerospace industry which requires high
quality continuous-fiber laminates as primary structures. The composite was
developed to fill the mechanical property gap between the discontinuous-fiber
composites and the un-reinforced polymers used in non-load-bearing applications.
The objectives of this work are to develop carbon fiber polypropylene composite
under various process conditions, and to investigate the mechanical and thermal
properties of carbon fiber polypropylene composite. In this study, two different
types of polypropylene composites were produced by mixing and compressing the
mixtures using hot press. In the first stage, the mixture was prepared by mixing
polypropylene with chopped carbon fiber and carbon fiber percentage (wt%) was
varied. The composites were evaluated for mechanical properties. Mixing time,
mixing temperature and rotor speed were varied to determine the best conditions.
Among the mechanical testing and analysis investigated were tensile test, impact test,
bending test and density test. Whilst the, the Scanning Electron Microscopy (SEM)
was employed to study the morphology of the composites and Dynamic mechanical
analysis (DMA) and Thermal gravimetric analysis (TGA) were used to determine the
thermal properties
The highest tensile strength was obtained for polypropylene with melt flow index 60
(MFI 60) composites reinforced with 10 wt% carbon fiber. The composite also
showed the best tensile and flexural properties. TGA analysis of composite with 10
wt% carbon fiber content revealed excellent thermal stability compared to the plain
polypropylene. The performance of the selected composite was comparable to a local
commercial car bumper.
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Abstrak thesis yang dikemukakan kepada Senat Universiti Putra Malaysia sebagai
memenuhi sebahagian keperluan untuk Ijazah Master Sains dalam Kejuruteraan
Kimia.
PEMBANGUNAN KOMPOSIT GENTIAN KARBON-
MEMPERKUAT POLIPROPILENA UNTUK BAMPER KERETA
Oleh
NOR HASNI BINTI ZAHARI
Mei 2009
Pengerusi : Profesor Madya Robiah Bt. Yunus, PhD
Fakulti : Kejuruteraan
Komposit diperkuat gentian karbon (CFRC) adalah sangat kuat dan jauh lebih ringan
berbanding aloi. Sifatnya yang tahan lasak menjadikan ia tahan hakisan dan
mempunyai rintangan carikkan. Penggunaan CFRC di dalam industri automotif telah
dipraktikkan secara meluas berdasarkan kepada kehendak terkini yang
mengutamakan penjimatan tenaga, keselamatan dan antipencemaran. Dalam kajian
ini, komposit gentian karbon tidak bersambung perkuat polipropilena telah dipilih
berdasarkan ciri-ciri seperti ringan, tahan karat, kos yang rendah ke sederhana,
kestabilan terma dan mudah dibentuk.
Polipropilena (PP) telah dipilih sebagai matrik kerana ia boleh diperolehi dalam
kuantiti yang banyak dan tidak terlalu sensitif terhadap retakan tekanan kimia. PP
juga mempunyai kombinasi sifat yang tinggi rintangan dan kekuatan tegangan.
Gentian karbon telah digunakan secara meluas dalam komposit polimer-matrik
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kerana sifat-sifat mekanikal, terma dan elektriknya. Gentian karbon tidak
bersambung atau gentian pendek yang murah adalah gentian karbon yang berkualiti
rendah di mana ia tidak boleh digunakan dalam industri pesawat udara dan angkasa
yang memerlukan penggunaan lapisan gentian bersambung berkualiti tinggi sebagai
struktur asas. Komposit ini dibangunkan untuk memenuhi jurang sifat mekanikal di
antara gentian karbon tidak bersambung dan polimer yang tidak bertetulang yang
digunakan untuk aplikasi galas tidak berbeban.
Objektif bagi kajian ini adalah untuk membina komposit gentian karbon
polipropilena di bawah pelbagai kondisi proses, dan untuk mengkaji sifat mekanikal
dan terma bagi komposit gentian karbon prolipropilena. Dalam kajian ini, dua jenis
polipropilena yang berbeza dihasilkan melalui pencampuran dan himpitan bahan
campuran itu dengan menggunakan penekan panas. Campuran dihasilkan dengan
mencampurkan polipropilena bersama gentian karbon yang telah dipotong dan
peratusan (wt%) gentian karbon ini dipelbagaikan. Komposit ini dinilai melalui sifat-
sifat mekanikalnya. Masa pencampuran, kelajuan rotor, suhu dan masa pengacuan
dipelbagaikan untuk mendapatkan kondisi terbaik.
Antara ujian dan analisa secara mekanikal diperoleh melalui ujian kekuatan
tegangan, kekuatan hentaman, kekuatan lenturan dan ujian ketumpatan. Analisis
dinamik mekanik (DMA) dan analisis gravitian terma (TGA) dijalankan untuk
mengenalpasti sifat-sifat terma. Scanning Electron Microscopy (SEM) digunakan
untuk mengkaji kesan morfologi.
Kekuatan tegangan yang tertinggi bagi komposit gentian karbon perkuat
polipropilena diperoleh adalah pada 10 wt% gentian karbon perkuat polipropilena
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dengan MFI 60. Komposit tersebut menunjukkan keputusan sifat-sifat kekuatan
tegangan dan lenturan yang lebih baik. Analisis TGA bagi 10 wt% gentian karbon
memberi menunjukkan kestabilan terma yang lebih baik berbanding polipropilena
asli. Prestasi komposit terpilih telah dibandingkan dengan sebuah bamper komersial
tempatan.
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ACKNOWLEDGEMENTS
First and foremost, I would like to thank my Advisor and Chairman of the
Supervisory Committee, Assoc. Prof. Dr. Robiah Yunus for her support and
encouragement throughout this study. My appreciation also goes to my supervisory
committee Dr. Mohamad Amran Mohd Salleh and Dr. Nor Azowa Ibrahim, for their
constant guidance and encouragement. Thank you for providing me with professional
training, advice and suggestion.
I am grateful to the staff, technicians and my colleagues in the Material Science and
Engineering Laboratory, Department of Chemical and Environmental Engineering,
Faculty of Engineering and Polymer Laboratory, Chemical Department, Faculty of
Science, Universiti Putra Malaysia. And last, but not least I would like to express my
gratitude to my dear husband, my beloved mother, my auntie, sisters and brother for
their continuous support during the completion of this thesis.
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I certify that the Examination Committee meet on 21st May 2009 to conduct the final
examination of Nor Hasni Binti Zahari on her Master of Science in Chemical
Engineering thesis entitled “Development of Carbon Fiber Reinforced
Polypropylene Composite for Car Bumper Application” in accordance with
Universiti Pertanian Malaysia (Higher Degree) Act 1980 and Universiti Pertanian
Malaysia (Higher Degree) Regulations 1981. The Committee recommends that the
candidate be awarded a relevant degree. Members of the Examination Committee are
as follows:
Fakhru’l-Razi Ahmadun, PhD
Professor
Faculty of Graduate Studies
Universiti Putra Malaysia
(Chairman)
Luqman Chuah Abdullah, PhD
Associate Professor
Faculty of Graduate Studies
Universiti Putra Malaysia
(Internal Examiner)
Suraya Abdul Rashid, PhD
Lecturer
Faculty of Graduate Studies
Universiti Putra Malaysia
(Internal Examiner)
Ahmad Fauzi Ismail, PhD
Professor
Faculty of Graduate Studies
Universiti Putra Malaysia
(External Examiner)
________________________
BUJANG KIM HUAT, PhD
Professor and Deputy Dean
School of Graduate Studies
Universiti Putra Malaysia
Date: 24 December 2009
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This thesis submitted to the Senate of Universiti Putra Malaysia and was accepted as
fulfilment of the requirement for the degree of Master of Science in Chemical
Engineering. The members of the supervisory committee were as follow:
Robiah Yunus, PhD
Associate Professor
Faculty of Engineering
Universiti Putra Malaysia
(Chairman)
Nor Azowa Ibrahim, PhD
Lecturer
Faculty of Science
Universiti Putra Malaysia
(Member)
Mohamad Amran Mohd Salleh, PhD
Lecturer
Faculty of Engineering
Universiti Putra Malaysia
(Member)
________________________________
HASANAH MOHD GHAZALI, PhD
Professor and Dean
School of Graduate Studies
Universiti Putra Malaysia
Date: 14 January 2010
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DECLARATION
I hereby declare that the thesis is based on my original work except for quotations
and citations which have been duly acknowledged. I also declare that it has not been
previously or co currently submitted for any other degrees at UPM or other
institutions.
__________________________
NOR HASNI BINTI ZAHARI
Date:
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TABLE OF CONTENTS
DEDICATION ii
ABSTRACT iii
ABSTRAK v
ACKNOWLEDGEMENTS viii
APPROVAL ix
DECLARATION xi
LIST OF TABLES xiv
LIST OF FIGURES xv
LIST OF ABBREVIATIONS xviii
CHAPTER
1. INTRODUCTION
1.1 Background
1.2 Problem Statement
1.3 Objectives and Scope of Research Work
1.4 Thesis Layout
1
1
2
5
6
2. LITERATURE REVIEW
2.1 Carbon Fiber
2.1.1 PAN Carbon Fiber
2.1.2 Pitch Carbon Fiber
2.2 Glass Fiber
2.3 Composites
2.3.1 Polymer Composites
2.3.2 Composite Manufacturing
2.4 Resin System
2.4.1 Thermoset Polymer
2.4.2 Thermoplastic Polymer
2.5 Polyurethane
2.6 Polypropylene
2.7 Thermoplastic Composites
2.7.1 Long Fiber Reinforced Thermoplastic (LFT) Composites
2.7.2 Short Fiber Reinforced Polymer (SFRP) Composites
2.7.3 Carbon Fiber Reinforced Polypropylene Composite
(CFPP)
2.8 Polymer Properties: Molecular Weight and Flow Rate
2.8.1 Dynamic Mechanical Properties of Polymer
2.9 Bumper System and Components
2.10 Comparison between Metal and Composites
2.11 Summary
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3. METHODOLOGY
3.1 Carbon Fiber Reinforced Polyurethane (CFPU)
3.1.1 Material Preparation
3.1.2 Preparation of CFPU composites by internal mixer
3.1.3 Results and Discussions of CFPU composites (by
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Internal Mixer)
3.1.4 Preparation of CFPU Composites by Open Cast
3.2 Carbon Fiber Reinforced Polypropylene (CFPP)
3.2.1 Preparation of CF Reinforced PP Composites (CFPP)
3.3 Mechanical Testing
3.3.1 Tensile Test
3.3.2 Flexural Test
3.3.3 Izod Impact Test
3.3.4 Hardness Measurement
3.4 Characterization of CFPP Composites
3.4.1 Density Measurement
3.4.2 Scanning Electron Microscope (SEM) Analysis
3.4.3 Thermal Gravimetric Analysis (TGA)
3.4.4 Dynamic Mechanical Analysis (DMA)
3.5 Bumper Analysis
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4. RESULTS AND DISCUSSIONS
4.1 Introduction
4.2 Carbon Fiber Reinforced Polypropylene (CFPP)
4.2.1 Effect of Mixing Temperature for CFPP MFI 60
4.2.2 Effect of Rotor Speed for CFPP MFI 7
4.3 Density Test
4.4 Tensile Test
4.4.1 Tensile Strength
4.4.2 Tensile Modulus
4.5 Flexural Properties
4.5.1 Flexural Strength
4.5.2 Flexural Modulus
4.6 Impact Properties
4.7 Hardness Measurement
4.8 Thermal Gravimetric Analysis (TGA)
4.9 Dynamic Mechanical Analysis (DMA)
4.9.1 Storage Modulus (E’)
4.9.2 Loss Modulus (E”)
4.9.3 Tan Delta (Tan δ)
4.10 Scanning Electron Microscope (SEM)
4.11 Comparison of CFPP Composite and Commercial Plastic
Bumper Fascia
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5. CONCLUSIONS AND RECOMMENDATIONS
5.1 Introduction
5.2 Conclusions
5.3 Recommendations
109
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110
REFERENCES 111
APPENDIX 118
BIODATA OF STUDENT 120
LISTS OF PUBLICATION 121
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LIST OF TABLES
Table Page
2.1 Summary of the Diverse Method of Processing Composite Product 18
2.2 Advantages and Disadvantages of Polymer and Steel Systems 45
2.3
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
3.10
Distribution of Materials in a Typical Vehicle
Mechanical and Physical Properties of CF, PU and hardener
Parameters and setting on CFPU study
Parameters and Setting for CFPU Mixing Process
Parameters and setting for CFPU Molding Process
Mechanical Properties of Polypropylene with melt flow rate (MFI)
60 and 7
Mechanical and Physical Properties of CF and PP
Carbon Fibers and Polypropylene Percentage and Weight
Parameters and Conditions for Compounding CFPP MFI 60
Parameters and Conditions for Compounding CFPP MFI 7
Parameters and Setting for Compression Molding of CFPP MFI 60
and CFPP MFI 7
46
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50
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59
60
60
61
4.1 Storage Modulus and % Improvement at 60oC for CFPP MFI 60 92
4.2 Storage Modulus and % Improvement at 60oC for CFPP MFI 92
4.3 Comparison of Composites and Commercial Plastic Fascia
107
4.4 Percentage of Improvement of CFPP MFI 60 at 10 wt% CF
Compared to Commercial Plastic Bumper Fascia
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LIST OF FIGURES
Figure Page
2.1 Carbon Fiber Reel 8
2.2 Flow Diagram for Manufacturing Process of Carbon Fiber
(PAN type)
9
2.3 Alignment of Mesophase Pitch into a Pitch Filament 10
2.4 Glass Fiber (a) Glass Strand (b) Glass Fiber Perform for a Boat
Deck
11
2.5 Mechanical Properties of Different Material 13
2.6 Polymer Structure (a) Themoset Polymer (b) Thermoplastic
Polymer
19
2.7 Morphology of Elastomer Polymer 21
2.8 General Reaction in the Production of Polyurethane 24
2.9 Molecular structure of MOCA 25
2.10 Polypropylene Molecule Chain (a) Isotactic; (b) Sydiotactic
where R is CH3
26
2.11 Build-up of Stress on a Fiber in a Matrix 33
2.12 Bumper Systems in Common Use 40
2.13
3.1
GMT Bumper Beam for BMW
Tensile Strength of CFPU Composites
43
51
3.2
3.3
3.4
3.5
3.6
Tensile Modulus of CFPU Composites
Method of Producing Polyurethane
Design of Equipment for CFPU Production
Carbon Fiber Yarn
Chopped Carbon Fiber
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3.7
3.8
3.9
3.10
3.11
3.12
3.13
Experimental Steps for The Composite Preparation
Internal Mixer (Thermo Haake Rheomix)
HSINCHU Hot Press Machine
Instron Universal Testing Machine 4302
Izod Impact Tester
Notch Cutter
Local Bumper
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4.1 Tensile Strength for Various Carbon Fiber Loading at Different
Mixing Temperature
70
4.2 Tensile Strength for 5wt% CF Reinforced PP with MFI 7 at
Different Rotor Speeds
72
4.3 Tensile Modulus for 5wt% CF Reinforced PP with MFI 7 at
Different Rotor Speeds
72
4.4 Density Measurement for CFPP MFI 60 and CFPP MFI 7 at
Different Fiber Loading
73
4.5 Tensile Strength (MPa) for CFPP Carbon Fiber (wt%) 74
4.6 Tensile Modulus (MPa) for CFPP Carbon Fiber (wt%) 78
4.7 Flexural Strength (MPa) versus Carbon Fiber (wt%) 80
4.8 Flexural Modulus (MPa) versus Carbon Fiber (wt%) 81
4.9 Impact Strength for Various CF Loading 83
4.10 Hardness Property at Various CF Loading 84
4.11 TGA of PP and CFPP at 10wt% fiber 86
4.12 Storage Modulus for PP MFI 60 and CFPP MFI 60 Composites 89
4.13 Storage Modulus for PP MFI 7 and CFPP MFI 7 Composites 91
4.14 Loss Modulus for PP MFI 60 and CFPP MFI 60 Composites 94
4.15 Loss Modulus for PP MFI 7 and CFPP MFI 7 Composites 95
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4.16 Tan Delta for PP MFI 60 and CFPP MFI 60 Composites 97
4.17 Tan Delta for PP MFI 7 and CFPP MFI 7 Composites 98
4.18 SEM micrograph of tensile fracture surface of 5 wt% CF
reinforced PP MFI 60 composite
101
4.19 SEM micrograph of tensile fracture surface of 7 wt% CF
reinforced PP MFI 60 composite
101
4.20 SEM micrograph of tensile fracture surface of 10 wt% CF
reinforced PP MFI 60 composite
102
4.21 SEM micrograph of tensile fracture surface of 15 wt% CF
reinforced PP MFI 60 composite
102
4.22 SEM micrograph of tensile fracture surface of 20 wt% CF
reinforced PP MFI 60 composite
103
4.23 SEM micrograph of tensile fracture surface of 5 wt% CF
reinforced PP MFI 7 composite
104
4.24 SEM micrograph of tensile fracture surface of 7 wt% CF
reinforced PP MFI 7 composite
104
4.25 SEM micrograph of tensile fracture surface of 10 wt% CF
reinforced PP MFI 7 composite
105
4.26 SEM micrograph of tensile fracture surface of 15 wt% CF
reinforced PP MFI 7 composite
105
4.27 SEM micrograph of tensile fracture surface of 20 wt% CF
reinforced PP MFI 7 composite
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LIST OF SYMBOLS AND ABBREVIATIONS
ASTM American Society for Testing Materials
BIW Body-In-White
CF Carbon Fiber
CFPP Carbon Fiber Reinforced Polypropylene
CFPU Carbon Fiber Reinforced Polyurethane
CR Controlled Rheology
CTE Coefficients of Thermal Expansion
DMA Dynamic Mechanical Analysis
E’ Storage Modulus or Elastic Modulus
E” Loss Modulus or Viscous Modulus
FRP Fiber Reinforced Plastic
GFRP Glass Fiber Reinforced Plastic
GMT Glass Mat Thermoplastic
IC Isocyanates
Lc Critical Fiber Length
LFT Long Fiber Thermoplastic
MFI Melt Flow Index
Mn Number Average Molecular Weight
Mn/Mw Molecular Weight Distribution or Dispersity Index
MOCA 4,4'-methylene-bis(2-chloroaniline)
mph Miles Per Hour
MFR Melt Flow Rate
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Mw Weight Average Molecular Weight
NVH Noise, Vibration, and Harshness
OEM Original Engineering Manufacturing
PAN Polyacrylonitrile
PP Polypropylene
PU Polyurethane
r Fiber Radius
RH Rockwell Hardness
RIM Reaction Injection Molding
SEM Scanning Electron Microscope
SFRP Short Fiber Reinforced Polypropylene
SFRT Short Fiber Reinforced Thermoplastic
SMC Sheet Moulding Compound
t Interfacial Shear Strength
Tan δ Tangen delta
Tg Glass Transition
TGA Thermal Gravimetric Analysis
Tm Melting Point (oC)
UPM Universiti Putra Malaysia
wt Weight
σmax Tensile Stress Acting on the Fiber
µm Micro Meter
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CHAPTER ONE
INTRODUCTION
1.1 Background
Glass fibers are the most common reinforcing fibers for polymeric (plastic) matrix
composites. The advantages of this fiber are low cost, high tensile strength, high
chemical resistance and excellent insulating properties. Thus it has always been chosen
as a filler in a composite production. However, this type of fibers has a low tensile
modulus, relatively high specific gravity (among commercial fibers), sensitive to
abrasion and low fatigue resistance (Mallick, 1993).
In the early 1960s, carbon fiber was invented at the Royal Aircraft Establishment,
Farnborough, Hampshire (England) (Wikipedia, 2006). Carbon fibers are fibrous
material with carbon content of more than 90%. They are transformed from organic
matter by 1000-1500oC heat treatment, which is the substance with imperfect graphite
crystalline structure arranged along the fiber axis (Donnet et al. 1998). They are
characterized by very high stiffness and low density. Some carbon fibers have a
stiffness that are ten times higher and densities that are one half that of glass fibers.
According to Adam (1997), the application of carbon fiber is due to the high energy
absorption ability. Thus the material can contribute to an improved crash management
and therefore to an improved passive safety of a passenger car.
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Carbon fiber composite can be designed as a component of energy absorbers to absorb a
portion of the kinetic energy from a vehicle collision. Energy absorbers are very
effective in a low speed impact, where the bumper springs back to its original position.
Energy absorber types include foam, honeycomb and mechanical devices. All foam and
honeycomb absorbers are made from polypropylene, polyurethane or low-density
polyethylene. Mechanical absorbers are metallic and resemble shock absorbers.
However, mechanical absorbers have several times the weight of foam or honeycomb
absorber and receive very limited usage. In some bumper systems, the reinforcing beam
itself is designed to absorb energy and separate energy absorbers are not required.
1.2 Problem Statement
A bumper is a shield made of steel, aluminum, rubber or plastic that is mounted on the
front and rear of a passenger car. Traditionally, metal alloys were used in manufacturing
automobile exteriors. Nowadays, the car bumper generally consists of a plastic cover
and, underneath, reinforcement is made of steel, aluminum, fiberglass composite or
plastic and includes mechanisms that compress to absorb crash energy. Usually, bumper
system consists of built-in fascia, beam and energy absorbers.
There are several factors that an engineer must consider when selecting a bumper
system. The most important factor is the ability of the bumper system to absorb enough
energy to meet the Original Engineering Manufacturing (OEM) internal bumper
standard. Another important factor is the bumper’s ability to absorb energy and stay
intact at high-speed impacts (AISI, 2003). Five miles per hour (5 mph) is a benchmark
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that engineers must comply when designing the bumper system. It is an impact speed at
which bumpers could prevent damage in barrier test (Cheon, et al. 1995). The 5 mph
crash test can be used to assess bumper performance, including front-into-flat-barrier
test, rear-into-flat-barrier test, front-into-angle-barrier test and rear-into-pole test. The
least demanding impacts are front and rear-into-flat-barrier because the energy of the
crash is spread across the whole width of the vehicle.
Automotive bumper system plays a very important role not only in absorbing impact
energy (original purpose of safety) but also in a styling stand point. In recent years, a
great deal of attention within the automotive industry has been focused upon lightweight
and safety issues. The bumper system equipped with thermoplastic and energy absorbing
element is a new trend in the market. While experimental test is rather costly and time
consuming, finite element analysis helps engineers to study design concept at an early
design stage when prototypes are not available (Lee and Jang, 1993).
Automobile design engineers face many constrictions when designing with metal, such
as corrosion and dents. Low-cost, single-unit production of large automobile sections,
such as a front grille, is nearly impossible when using metal. Plastic offers auto
engineers a variety of practical, costs-effective alternatives, as well as tremendous
advantages over traditional automobile production materials. By using plastics,
manufacturers have the possibility of adopting modular assembly practices, lowering
production costs, improving energy management, achieving better dent resistance, and
using advanced styling techniques for sleeker, aerodynamic exteriors. However, plastic
outer cover does not promise good protection if it performs alone (Mallick, 1993).
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With current technology, many manufacturers are using composite instead of plastic
alone to fabricate the automotive parts including the bumper. Fuel efficiency and
emission gas regulations are the main causes for reducing the weight of passenger cars
by using composite structures (Hosseinzadeh et al. 2005). In the last few years, more
intense effort have been spent on the application of fiber reinforced plastics. While glass
fiber reinforced plastics (GFRP) are used in several vehicle components, the carbon
fibers as reinforcing material are of relative low significance for the lightweight
construction in motor vehicles (Adam, 1997).
Short fiber reinforced composites have enormous potential for automotive application
(Adam, 1997). To achieve these advantages, many researchers focus on the
discontinuous carbon fiber reinforced polypropylene composite where the material is
expected to have a better property and has a potential to reduce the weight of a car and
fuel consumption. The use of a short-carbon-fiber or discontinuous carbon fiber
reinforced polypropylene (SCF/PP) composite has been investigated by Rezaei et.al
(2007) for car bonnet application. They found that the SCF/PP composite is a good
option for replacing steel in car bonnet and can achieve the standards of car bonnet with
remarkable lower weight and higher mechanical properties. However, this study focuses
on the use of discontinuous carbon fiber reinforced polypropylene composite for the
application of car bumper which requires different specifications.
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1.3 Objectives and Scope of Research Work
The objectives of this research are:
(a) To develop carbon fiber polypropylene composites under various process
conditions.
(b) To investigate the mechanical and thermal properties of carbon fiber
polypropylene composites.
Based on the first objective, the scope of work stated with preliminary investigation on
the existing bumper system of a passenger car in order to understand the material
properties. This was undertaken so that improvement on the material designs can be
made. A local commercial car bumper was used as a reference to develop an alternative
material that is comparable with the existing material for the application of bumper. This
is an important step to ensure that the composite is viable and practical to be used as a
bumper fascia. The work continued with the manufacture of carbon fiber reinforced
polypropylene composite where the procedure were began with fiber preparation
followed by melt compounding process. Hot press was used to mold the composite into
a sheet so that the sample for analysis can be made. As to accomplish the second
objective, the research work was continued with sample analysis where the samples
were evaluated to investigate the mechanical and thermal properties. The analyses
consist of tensile, flexural, impact and hardness test, thermal gravimetric and dynamic
mechanical analysis. These results were finally compared with local commercial car
bumper properties.
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1.4 Thesis Layout
This thesis contains five chapters. Chapter One covers the introduction that includes the
background of carbon fiber and its application followed by the problem statement and
the objectives of the research. In Chapter Two, a survey is presented on carbon fiber
composite, matrix and the concept of bumper system. Subsequently, Chapter Three
describes the research materials and methodology used in the study. The results and
discussion are covered in Chapter Four where the analysis on experimental results is
included. The thesis ends with the Conclusion in Chapter Five. Here the results are
compared with the objectives and some recommendations for future works are also
presented.
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