FINITE ELEMENTS ON BOND STRENGTH OF ADHESIVE / POLYMERIC COMPOSITES SYSTEM
NORAINI BINTI ASAKIL
This project is submitted in partial fulfillment of
The requirements for the degree of Bachelor of Engineering with Honours (Mechanical Engineering and Manufacturing Systems)
Faculty of Engineering
UNIVERSITI MALAYSIA SARAWAK
2006
Dedicated to my beloved Mom and 'Big Boss'
ACKNOWLEDGEMENT
First and foremost, I would like to express my grateful to Allah S. W. T, as I had managed to complete my final year project successfully. I would like to express my high gratitude to my supervisor Mdm Marini bt Hj Sawawi for her guidance and
support. Without her encouragement and priceless advice, this project would be an extremely hard task for me.
A special thanks goes to Dr Mohd Shahril Osman and Mdm Mashuri Yusof, for
their helpful feedback on the midreport and their useful advices in the progress meetings. I would like to thank to all technicians especially Sabariman, and Mr Masri
for their cooperation. They have always been exceptionally helpful whenever I faced any problem in developing the experimental set up.
Thanks must go to my friends, especially Harry Mamat, who always gave me a great hand during preparation of specimen. Many thanks to my lovely friend izah and
Ad for their support and advice. Also to my roommate, Poquepoque for all the kindness helps and laughers that we shared together.
Thanks finally go to my mom, Big Boss and my family for their constant love, support and understanding.
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ABSTRAK
Kaedah pencantuman dua bahan dengan menggunakan bahan pelekat mempunyai pelbagai kelebihan antaranya ialah tidak mudah berkarat dan lebih ringan. Kaedah ini telah mendapat sambutan yang meluas dalam pelbagai jenis industri, ekoran itu pelbagai persoalan telah timbul mengenai sifat bahan pelekat terutamanya mengenai kekuatan ikatan bahan pelekat tersebut. Justeru itu, objektif kajian ini dijalankan adalah untuk mengkaji tentang kekuatan tiga bahan pelekat iaitu `Polyester', 'Glass fiber polyester composite' dan `Bemban fiber polyester composite'. Model analitikal untuk menganalisis penyebaran tegasan ricih bahan pelekat tersebut direka berpandukan kepada piawaian ASTM 5868 dan perisian computer, ANSYS turnt digunakan.
Keputusan simulasi menunjukkan tegasan ricih bagi kesemua sampel tertumpu di kedua-dua hujung pelekatan. Selain itu, bahan pelekat jenis `Glass fiber polyester composite' merupakan bahan pelekat yang mempunyai daya ikatan yang paling kuat
berbanding dengan sampel yang lain. Kesan modulus kekenyalan pukal ke atas ikatan ikatan bahan pelekat turnt dikaji. Oleh itu, eksperiment telah dijalankan untuk mencari nilai modulus kekenyalan pukal ketiga-tiga sampel. Geometri sampel eksperiment tersebut adalah berpandukan kepada piawaian BS 2782; part 3: method 320 E, EN 61 dan ASTM 638. Keputusan simulasi menunjukkan modulus kekenyalan pukal bahan pelekat turnt mempengaruhi tegasan ricih. Secara kesimpulan, sifat bahan pelekat
memainkan peranan yang penting dalam menentukan kekuatan pencantuman dua bahan.
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ABSTRACT
Adhesive joint has been widely used due to the advantages offered such as light weight and high corrosion resistance. Many qualification-related issues e. g. bond strength issues become more important as the application of adhesive-bonded joint gains in popularity in many industries. Hence, objective of this project is to investigate the bond
strength of three type of adhesive namely polyester, glass-fiber polyester composite and bemban fiber polyester composites. An analytical model for determining adhesive stress distributions within the adhesive-bonded bonded single lap composites joints was developed. ASTM D5868 standard test specimen geometry was followed in the model
deviation. The analysis of model was perform using Window based FE analysis package called ANSYS. FE simulation results on the GFRP bonded system shows that the bond stress was highest at the end of adhesive boded. It also was found that, the
GFRP samples have the highest bond strength than polyester and Bemban fiber- polyester composite sample. This project also investigates the effect of tensile properties e. g. elastic modulus of adhesive on stress distribution. Hence, the tensile properties of adhesives were determined by using tensile test method. The composites
were fabricated using random continuous reinforcing fibres properties. The specimens were conditioned according to BS 2782; part 3: method 320 E, EN 61 and ASTM 638.
The FE simulation suggests that the adhesive properties have significant effect on the bond stress distribution. This indicates that, the adhesive properties play an important role in determining the bond strength of GFRP bonded system.
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TABLE OF CONTENT
CONTENT
ACKNOWLEDGEMENT ABSTRAK
ABSTRACT
TABLE OF CONTENT LIST OF TABLES
LIST OF FIGURES LIST OF SYMBOLS LIST OF APPENDIX
CHAPTER I INTRODUCTION
1.1 Introduction
1.2 Problem Statement 1.3 Objectives
CHAPTER 2 LITERATURE REVIEW
2.0 Introduction
2.1 Material Description
PAGE
V vi vii viii
X11
xiv
xvii
XV 111
I
4 4
5
6
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2.1.1 Glass Fiber
2.1.2 Natural Fiber
2.1.3 Polyester Resin 2.2 Bond Stress Analysis
2.3 Finite Element Analysis 2.4 Single Lap Joint Analysis 2.5 Adhesive Bonding
2.6 Factor that Affect of Bond Strength
CHAPTER 3 METHODOLOGY
6 8
10 11 28 21 22 26
3.0 Introduction 30
3.1 Standard Testing
31
3.2.1 BS 2782; PART 3: METHOD 320E, EN 61 31
3.2.2 ASTM D 638 34
3.2 Determination of Tensile Modulus 36
3.3 Finite Elements Analysis 37
3.3.1 Lab Joint Shear test 37 3.3.2 2D model of single lab joint 38
3.3.3 Material Properties 38
3.3.4 Meshing 39
3.3.5 Boundary Conditions and Loading 41
3.4 Analysis Type 42
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CHAPTER 4 RESULTS AND DISCUSSION 4.0 Introduction
4.1 Theoretical Calculation Results 4.2 Experiment Result
43 44 44
4.2.1 Observation of Specimen after Tensile Test 45 4.2.2 Tensile Test Result of GFRP Specimen 46 4.2.3 Tensile Test Result of Polyester Specimen 49 4.2.4 Tensile Test Result Bemban Specimen 51 4.3 Comparison Result
4.4 Finite Element Simulation 4.5 Control Plot Results
4.5.1 Polyester Adhesive
53 54 55 55 4.5.2 Glass Fiber Reinforced Polyester Adhesive 57
4.5.3 Bemban Fiber reinforced Polyester Adhesive 59 4.6 Comparison Various Adhesive
4.7 Comparison Result
4.8 Effect of the Tensile Modulus
4.8.1 Effect of Adherend Modulus 4.8.2 Effect of Adhesive Modulus 4.9 Discussion
4.9.1 Tensile Test 4.9.2 FE Simulation 4.10 Summary
62
63
66 67 68 70 70 78 75
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CHAPTER 5 CONCLUSIONS AND RECOMMENDATION 5.0 Introduction
5.1 Conclusion
5.2 Recommendation
LIST OF REFERENCES
76 76 78
80
APPENDICES 83
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LIST OF TABLE
Tables
2.1 Properties of some glass fiber
2.2 Mechanical properties of GFRP, CFRP and AFRP
2.3 Relative properties of some of the
common natural fibre.
2.4 Typical properties of adhesive
Page 7
7
9
10
2.5 Several design of single lap joint 22
3.1 Tensile test specimen geometry 31
3.2 ASTM 638 recommended dimension 34
3.3 Polyester specimen geometry 35
3.4 Poison ratio of material 39
4.1 Data experiment of tensile test for GFRP 46 specimen
4.2 Mechanical properties of GFRP specimen 48
4.3 Result of tensile test for polyester 49
4.4 Tensile properties of polyester specimens 50
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4.5 Tensile properties of Bemban fiber specimens
4.6 Average properties for GFRP and Polyester specimen
4.7 Comparison result between theoretical and experiment
4.8 Material properties of model
4.9 The data for bonding failure of specimen with 25.4mm overlap length
4.10 Bond stress at loading edge for various adherend Elastic modulus
4.11 Bond stress at loading edge for various adhesive modulus
51
52
53
54 63
68
69
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LIST OF FIGURE
Figure Page
2.1 Strain-Stress Behavior GFRP, CFRP and Mild Steel 8
2.2 Modulus Values of Different Natural Fibre 9
2.3 Stress distribution along joint 12
2.4 Stress distribution along adhesive to composites 12 interface
2.5 Stress distribution through adhesive 12
2.6 Stress distribution 13
2.7 Von Mises stress 13
2.8 Comparison Nonlinear and linear shear distribution 14
2.9 Joint configuration and coordinate system 15
2.10 Adhesive stress distribution from FEA (ABASQUS) 15 2.11 (a) Adhesive von Mises distribution (b) Adhesive shear 16
stress distribution
2.12 Adhesive peel stress distribution 16
2.13 The (a) maximum axial (b) peel stress and (c) 17-18 interfacial stress for various adhesives.
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2.14 Effect of thickness of adhesive layer 28
2.15 Effect of moisture on Epoxy 29
3.1 Specimen dimension recommended by BS 2782; PART 31 3: METHOD 320 E, EN 61
3.2 Specimen ASTM D 638 (dimension in mm) 34
3.3 Polyester specimen 35
3.4 Specimen arrangement 37
3.5 Dimensional model 38
3.6 Coarse mesh of model 39
3.7 Model of fine mesh 40
3.8 Boundary condition and loading on the 2D model. 41
4.1 Brittle failure of Polyester specimen 45
4.2 Brittle failure of GFRP specimen 45
4.3 Force vs. Displacement for GFRP 46
4.4 Force vs. Displacement for Polyester 49
4.5 Force vs. Displacement for Bemban fiber reinforced 51 polyester
4.6 Force vs. Displacement for GFRP and Polyester 52 4.7 Shear stress distribution along gauge length of 55
Polyester
4.8 Bond stress distribution near the loading edge under 56 1 kN
4.9 Bond stress distribution free edge under I kN 56
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4.10 Shear distribution joint interface of GFRP-Polyester 57 4.11 Shear stress distribution along gauge length of GFRP 57
adhesive
4.12 Bond stress distribution nears loading edge given lkN 58 load
4.13 Bond stress distribution near free edge under lkN load 58 4.14 Shear stress distribution at joint interfaces of GFRP 59
adhesives
4.15 Bond stress distribution along gauge length of Bemban 60 adhesive
4.16 Bond stress distribution at free edge under 1 kN 60 4.17 Bond stress distribution near loading edge under 1 kN 61
4.18 Shear stress distribution 61
4.19 Comparison bond stress of various adhesive 62
4.20 Comparison between FE and theoretical calculation 66 4.21 Effect of adherend modulus on the bond stress 67
distribution
4.22 Effect of adhesive modulus on stress distribution 69
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LIST OF APPENDIX
APPENDIX NO TITLE
PAGE
Al Tensile test results for GFRP specimens 83
A2 Tensile test results for Polyester specimens 84
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LIST OF SYMBOLS
P, F - applied load a- normal stress T- shear stress
a, 0- radius
rl - adhesive thickness
u- poison ratio
G- shear modulus
c- center of bonded length E- Elastic modulus
t- thickness
I- length
h- gauge length
w- width
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CHAPTER 1
INTRODUCTION
1.1 Introduction
Now day, application of fiber reinforced plastic composite has shown rapidly growth in many fields during the last decades. Composites are intensively used in various branches of industry and technology including aircraft, automotive and rocket engineering also in ship-building. The attractive benefit of using composites material
are the high strength and stiffness to weight ratio, ability to controlling anisotropy and resistance to corrosion. Thus, composites have been used more and frequently in various combinations and situations over the last 20 to 30 years [1]
Many applications especially in construction industries required a composites component joining with different material e. g. steel. These joint can be constructed in
numbers ways such as bolted, welding or bonded joint. Adhesive joint have an
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advantages over traditional mechanically fastener. By using adhesive joint, drilled holes can be avoided consequently broken fibers and stress concentrations. Moreover,
adhesive bonding is becoming one of an interactive method to joining materials in construction industries since it offers different options over other techniques such as welding and diffusion bonding. Adhesively bonded joints have therefore been adopted when joining metal parts such as aluminum in a number of high performance
constructions.
The application of adhesive bonding is not only limited in construction industries but also used automotive industry. In German and Austrian has been used natural fibre bonded with adhesive in automotive industry which offered low cost and renew ability of fibre resource. Now day, applications of adhesive bonded with FRP material found
increasing specially in marine, aerospace and dentistry field due to strength and
capability of adhesive to joining dissimilar material. In comparison with other joining methods, adhesive bonded is essentially fast consequently increased production speed.
Besides that, adhesive joint also offered several advantages such as better fatigue behavior, greater construction stiffness and lower weight.
When design the adhesive joining, the important obsession must be consider is shear properties, this is due to the load transfer from adhesive layer to fibre reinforcement composites in shear manners. Besides that, performances of adhesive joint depend on preparation of joining. Thus, it crucial to give an attention in the
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adhesive selection and preparation also application procedure to avoided unnecessary failure.
Furthermore, joints can be symmetrical (e. g. double lap joint) and unsymmetrical (e. g. single lap joint). The single lap joint is least capable of these two
because the eccentricity of this type geometry generates significant bending of the adherends. However, the single lap joint is simple and convenient test geometry for evaluating adhesive bonding. Moreover, single lap joint easy to construct which only consists two sheets of the substrates joined by a simple overlay.
Several experimental and numerical investigations of adhesive bonding strengths were done to measured and estimate the bond strength which subjected to shear stress. Usually, Polyester, Wedon 100 and epoxy are prefer to use as an adhesive
and bonded together with FRP composite material. For example Li et al (2) used FRP composite bonded with epoxy adhesive to investigate stress distribution within idealized
single lap joints. For this project, three type of adhesive will be used to investigate distribution of shear stress within single lap joint. These types of adhesives are polyester, Glass fiber-polyester composite and Bemban fiber-polyester composite.
Moreover, the tensile properties of these materials also determined through tensile test. Consequently, using the data obtained from experiment, finite element
analysis was carried out to predict strength of bond strength. Data that obtained from the experimental was used to estimate the bond strength along the joint interfaces of
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polymeric composite materials. FE analysis allowed predicting the start point of debonding / failure due to stress concentration on the lap joint. FE analysis also illustrated effect of elastic modulus polymeric composites (epoxy, GFRP/ epoxy,
Bemban/ epoxy) on the bond stress distribution.
1.2 Problem Statement
It is well known that bond stress is strongly depending on material properties e. g. elastic modulus of adhesive. For this reason, this project aims at the tensile properties determination for three types of adhesive namely, polyester, Glass fiber-
polyester composite and Bemban fiber-polyester composite by pull-out test method.
This project also concern about the shear stress distribution on the single lap joint.
Consequently, FE simulation was carried out to evaluate the shear stress distribution at the joint interfaces of GFRP bonded system.
1.3 Scope and Objective
The main objectives of this project as listed below: -
1. To determine experimentally the tensile properties of Polyester and Glass Fibre Polyester Composite.
2. To predict the stress distribution of composite bonded system
3. To investigate effect of Elastic modulus on stress distribution of GFRP bonded through FEA application.
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CHAPTER 2
LITERATURE REVIEW
2.0 Introduction
In this chapter, properties of each material for this project is discussed where it heavily focuses on brittle material namely polyester and Glass Fibre Reinforcement Plastic (GFRP). Apart from that, numbers of previous researches on bond strength of adhesive either under pull out or flexural test are review. The specimen geometry of interest is a single lap joint. This type of specimen has been proven most simples design to determine bonding strength. Besides that, analysis on the bond stress also presented.
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2.1 Material Description
As mention before, the chosen material for this project is brittle materials namely polyester, Glass fiber Reinforcement Polymers and Bemban Fiber
Reinforcement Polymers. For some material, the difference between elastic limit stress and the stress at which failure is very small with very little plastic deformation occurring. Thus, the length of a piece of material after breaking is not much different
from the initial length, for such materials known as brittle materials [3]. Brittle fracture takes place without any appreciable deformation and by rapid crack propagation. The direction of crack motion is very nearly perpendicular to the direction of the applied tensile stress and yields a relatively flat fracture surface [3]. The general description of
each material can be found in the following sections of this chapter.
2.1.1 Glass Fiber
Matthews and Rawlings [ 14] stated that glass fibre is a noncrystalline material with are short-range network structure. There are many groups of glasses for example
silica, oxynitride, phosphate and halide glasses. Glass composites have been used for strengthening RC structures in both practical application and research.
Usually the glass fibre has high strength and stiffness especially s-glass fibre (lower than carbon fiber). The C-glass, E-CR glass and AR-glass have been develop to reduce the degradation in environments and increased the corrosion resistance. Table
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2.1 below illustrates typical properties of glass fibres and Table 2.2 show mechanical properties of some FRP composite.
Table 2.1: - Properties of some glass fiber
E-glass S-glass AR- glass
Modulus (GPa) 70 80 75
Strength (MPa) 2200 2600 1700
Density(Mg/m3) 2.54 2.49 2.7
Table 2.2: - Mechanical properties of GFRP, CFRP and AFRP
Unidirectional Fibre content
advanced composites (% by weight) Density (kg/m3)
Longitudinal
tensile modulus (GPa)
Tensile Strength (MPa)
Glass fibre/
polyester GFRP 50-80 1600-2000 20-55 400-1800
laminate
Carbon/ epoxy 65-75 1600-1900 120-250 1200-2250
CFRP laminate
Aramid/epoxy AFRP 60-70 1050-1250 40-125 1000-1800 laminate
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Figure 2.1 showed the stress-strain behavior of three fiber reinforcement composites; CFRP, GFRP and mild steel which linear elastic up to final brittle rupture
when subject to tension. In this study, the random and long fibre are selected due to superior in term of performance i. e. strength.
Ä
Strain (%)
Figure2.1: - Strain-Stress Behavior GFRP, CFRP and Mild Steel
2.1.2 Natural Fiber
Human being liked centuries ago used natural fibres such as cotton, silk, wool, jute, hemp and sisal as there are widely used for textiles, twine and rope throughout the
world. Centre of Lightweight Structure TUD-TNO [5] stated that natural fibre as a substitute for glass fibres in composites components have gained renewed interest the
last decade especially in automobile industries. In essence, natural fiber are of course animal or plant products which consisting of cellulose fibres in an amorphous matrix of lignin and hemicelluloses. The strength and stiffness of these fibres are low compared
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