INDENTATION STUDY OF HONEYCOMB SANDWICH COMPOSITE
MATERIALS
AMIR FOROUTAN
A thesis submitted in fulfilment of the
requirements for the award of the degree of
Master of Engineering (Mechanical)
Faculty of Mechanical Engineering
Universiti Teknologi Malaysia
JUNE 2013
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To my beloved father, mother and my entire family member.
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ACKNOWLEDGMENTS
First of all, I would like to thank to ALLAH Subhanahuwataala for his bless
and his permission to giving me strength, spirit and time to complete this project and
this report. In particular, I wish to grab this opportunity to express my sincere
appreciation to my supervisor, DR. Yob Saied Bin Esmail for their advice, guidance
and encouragement that have led to the success of this project. In the process of
carrying out this project, commencing from the title deciding until the completion of
project, I was in contact with many people such as academicians, postgraduate
researchers and lab assistants. They have rendered their assistant in various aspects
and contributed towards my understanding and thoughts.
I am also indebted to Universiti Teknologi Malaysia for providing me the
facilities to carry out my project. Librarians at UTM also deserve special thanks for
their assistance in the process of my project information obtaining. My fellow friends
should also be recognized for their continual support and encouragement. My sincere
appreciation also extends to my entire course mate and others who have provided
assistance at various occasions. Their views and tips are useful indeed.
Unfortunately, it is not possible to list all of them in this limited space. Gratefully, I
have my family to support and encourage me especially, my father, my mother and
all of my family members. Thanks a lot to you all.
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ABSTRACT
This study was conducted to quasi-static indentation study of composite
sandwich panels made of glass/vinylester facesheets and polypropylene honeycomb
core. Composite sandwich panel with different material types including chopped strand
mat and plain woven glass/vinylester were analyzed numerically and experimentally.
The effects of different parameters such as types of material, number of layers of
facesheets and consequently the thickness of facesheets and the loading rate on
indentation behavior were studied numerically and experimentally and the obtained
results were compared together. The results of the research study showed that the
maximum applied load on composite sandwich panel made of plain woven
glass/vinylester and energy absorption properties is higher than chopped strand mat
glass/vinylester. Also, the results of experimental tests showed that loading rate have big
effect on load-deflection and energy absorption properties of composite sandwich panel
and by increasing the loading rate, the maximum applied load and energy absorption
properties of sandwich panel with honeycomb core is increased and there is direct
relation between the loading rate and the indentation properties of sandwich panel. The
results of finite element analysis and experimental tests were compared together and it
has found that there is difference between the obtained results.
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ABSTRAK
Kajian ini melibatkan ujikaji kuasi statik lekukan bagi plat sandwich diperbuat
dari gentian kaca/poliester kulit permukaan dan teras polipropina. Panel komposit
sandwich yang di perbuat dari bahan yang berlainan terdiri dari jenis gentian kaca
bersulam dan rawak dianalisa secara ujikaji dan kajian berangka. Kesan dari beberapa
angkubah seperti jenis bahan, ketebalan, kulit permukaan dn kadar kelajuan beban bagi
kelakuan lekukan di analisa secara ujikaji dan berangka dan keputusan yang di perolehi
di buat perbandingan. Daripada keputusan yang diperolehi dari ujian, di dadapati beban
maksimum dan tenaga serapan yang maksimum di perolehi dari permukaan kulit yang
di perbuat dari gentian kaca jenis sulam. Dari keputusan ujikaji di dapati kadar kelajuan
beban juga mempengaruhi kadar serapan tenaga, dimana apabila kadar kelajuan beban
bertambah akan meningkatkan kadar serapan tenaga sebelum panel tersebut gagal.
Keputusan yang diperolehi menunjukkan ada pertalian yang rapat diantara kadar
kelajuan beban dan sifat bahan sandwich dari segi ujian lekukan. Keputusan dari ujikaji
juga dibuat perbandingan dengan kaedah berangka.
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TABLE OF CONTENT
CHAPTER TITLE PAGE
DECLARATION ii
DEDICATION iii
ACKNOWLEDGEMENTS iv
ABSTRACT v
ABSTRAK vi
TABLE OF CONTENTS vii
LIST OF TABLES x
LIST OF FIGURES xi
LIST OF SYMBOLS xvii
1 INTRODUCTION 1
1.1 Background 1
1.2 Introduction 4
1.3 Scope of study 4
1.4 Statement of problems 5
1.5 Layout of thesis 6
2 LITERATURE REVIEWS 7
2.1 Introduction 7
2.2 History of the composite materials 7
2.2.1 Fibres in composite material 8
2.2.2 Matrixes in composite material 10
2.3 Sandwich panels and core materials 12
2.3.1 Sandwich Panels 13
2.3.2 Core materials 13
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2.4 Manufacturing process 16
2.4.1 Hand layup 16
2.4.2 Vacuum bagging process 16
2.4.3 Autoclave 18
2.4.4 Filament winding process 18
2.5 Composite sandwich panel subject to different
types of loading 19
2.6 Conclusion 23
3 Methodology 24
3.1 Introduction 24
3.2 Experimental procedure 24
3.2.1 Sample preparing 25
3.2.2 Indentation test 36
3.2.3 Failure analysis after indentation test 38
3.3 Finite Element Analysis 39
3.3.1 Structural finite element analysis 42
3.3.2 Engineering data 44
3.3.3 Modeling 46
3.3.4 Meshing 47
3.3.5 Applying boundary conditions and loads 48
3.3.6 Solving 49
4 RESULTS AND DISCUSSION 51
4.1 Introduction 51
4.2 Finite Element Modeling 51
4.2.1 Source of errors 52
4.2.2 Model verification and analysis parameters 53
4.3 Deformation behaviour of sandwich panel subject
to indentation loading 56
4.4 Effect of type of materials of facesheets on
Deformation behaviour of sandwich panel subject
to indentation loading 61
4.5 Total energy absorption behaviour of sandwich
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panel subject to indentation loading 67
4.6 Finite element stress and deformation behaviour of
sandwich panel subject to indentation loading 71
5 CONCLUSIONS 84
5.1 Overall Conclusions 84
5.2 Recommendation 86
5.3 Determination of laminate properties 80
5.4 Failure test of general composite dome Ends
Subject to internal pressure 84
5.5 Conclusion 89
REFERENCES 87
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LIST OF TABLES
TABLE NO. TITLE PAGE
1.1 A comparison of representative material properties 2
3.1 The configuration of specimens for indentation tests 35
3.2 Material properties of plain woven glass/vinylester 45
3.3 Material properties of chopped strand mat glass/vinylester 45
3.4 Material properties of polypropylene honeycomb core 45
4.1 The experimental results of composite sandwich panel subject
to indentation loading with loading rate of 4mm/min 60
4.2 The value of maximum applied load on sandwich panel in
finite element modeling 72
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LIST OF FIGURES
FIGURE NO. TITLE PAGE
1.1 The schematic of composite sandwich panel. 3
1.2 Three types of honeycomb core materials 3
2.1 Typical Honeycomb Sections 14
2.2 Schematic of hand layup process 17
2.3 The schematic of vacuum bagging process. 17
2.4 Filament winding process. 19
3.1 Cleaning the prepared mold (glass) by using acetone liquid 25
3.2 Two types of mold release agent 26
3.3 Applying mold release agent on the surface of glass. 26
3.4 Preparing resin and glass fibre for fabrication 27
3.5 Saturating the fibres with resin by using brush and roller 27
3.6 Applying a layer of core over the laminate 28
3.7 Fabrication of second facesheet of sandwich panel 28
3.8 Fabrication of second facesheet of sandwich panel 29
3.9 Applying a layer of perforated film 29
3.10 Applying a layer of absorber 30
3.11 Tubing system in vacuum bagging process 30
3.12 Applying a layer of bagging film over the laminate 31
3.13 Covering the system with bagging film and sealant tape 31
3.14 Connecting the system to resin collector 32
3.15 Absorbing the excess resin by absorber under
vacuum pressure 32
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3.16 Curing process of laminate under vacuum pressure 33
3.17 Vacuum bagging process of composite sandwich panel 34
3.18 Band saw machine for cutting the samples for
indentation tests 34
3.19 The prepared sample for indentation test 35
3.20 The test rig for indentation tests of composite
sandwich panel 36
3.21 Load-Deflection curve of sandwich panel subject to
indentation loading 37
3.22 Failure analysis of composite sandwich panel subject
to indentation loading 38
3.23 Three types of finite elements 40
3.24 Modeling of composite sandwich panel subject to
indentation loading by using ANSYS Software (Front view) 46
3.25 Modeling of composite sandwich panel subject to
indentation loading by using ANSYS Software (Side view) 46
3.26 The meshing of composite sandwich panel subject to
indentation loading 47
3.27 The applied load over the indentor in finite element analysis 48
3.28 The boundary condition in finite element analysis of
sandwich panel 48
3.29 The deformation behaviour of sandwich panel subject to
indentation loading 49
3.30 The deformation behaviour of sandwich panel subject to
indentation loading with hidden top facesheet 49
3.31 The stress behaviour of sandwich panel subject to
indentation loading 50
4.1 The effects of number of elements on total deformation of
composite sandwich panel subject to indentation loading 54
4.2 Finite element model of sandwich panel with optimum
number of elements 54
4.3 The comparison between the results of experimental tests
and finite element analysis 55
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4.4 Load –deflection behaviour of sandwich panel made of two
layers of chopped strand mat glass/vinylester facesheets 57
4.5 Load –deflection behaviour of sandwich panel made of three
layers of chopped strand mat glass/vinylester facesheets 57
4.6 Load –deflection behaviour of sandwich panel made of four
layers of chopped strand mat glass/vinylester facesheets 58
4.7 Load –deflection behaviour of sandwich panel made of
two layers of woven glass/vinylester facesheets 58
4.8 Load – deflection behaviour of sandwich panel made of
three layers of woven glass/vinylester facesheets 59
4.9 Load – deflection behaviour of sandwich panel made of
four layers of woven glass/vinylester facesheets 59
4.10 Load – deflection behaviour of sandwich panel made of two
layers of plain woven and chopped strand mat glass/vinylester
facesheets subject to indentation loading with loading
rate 4mm/min 61
4.11 Load – deflection behaviour of sandwich panel made of three
layers of plain woven and chopped strand mat glass/vinylester
facesheets subject to indentation loading with loading
rate 4mm/min 62
4.12 Load – deflection behaviour of sandwich panel made of four
layers of plain woven and chopped strand mat glass/vinylester
facesheets subject to indentation loading with loading
rate 4mm/min 62
4.13 Load – deflection behaviour of sandwich panel made of two
layers of plain woven and chopped strand mat glass/vinylester
facesheets subject to indentation loading with loading
rate 6mm/min 63
4.14 Load – deflection behaviour of sandwich panel made of three
layers of plain woven and chopped strand mat glass/vinylester
facesheets subject to indentation loading with loading
rate 6mm/min 63
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4.15 Load – deflection behaviour of sandwich panel made of four
layers of plain woven and chopped strand mat glass/vinylester
facesheets subject to indentation loading with loading
rate 6mm/min 64
4.16 Load – deflection behaviour of sandwich panel made of two
layers of plain woven and chopped strand mat glass/vinylester
facesheets subject to indentation loading with loading
rate 8mm/min 65
4.17 Load – deflection behaviour of sandwich panel made of three
layers of plain woven and chopped strand mat glass/vinylester
facesheets subject to indentation loading with loading
rate 8mm/min 65
4.18 Load – deflection behaviour of sandwich panel made of four
layers of plain woven and chopped strand mat glass/vinylester
facesheets subject to indentation loading with loading
rate 8mm/min 66
4.19 Energy absorption of sandwich panel made of two layers of
chopped strand mat glass/vinylester subject to indentation
loading with different loading rate 68
4.20 Energy absorption of sandwich panel made of three layers of
chopped strand mat glass/vinylester subject to indentation
loading with different loading rate 68
4.21 Energy absorption of sandwich panel made of four layers of
chopped strand mat glass/vinylester subject to indentation
loading with different loading rate 69
4.22 Energy absorption of sandwich panel made of two layers
of plain woven glass/vinylester subject to indentation loading
with different loading rate 69
4.23 Energy absorption of sandwich panel made of three layers
of plain woven glass/vinylester subject to indentation loading
with different loading rate 70
4.24 Energy absorption of sandwich panel made of four layers
of plain woven glass/vinylester subject to indentation loading
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with different loading rate 70
4.25 finite element stress analysis of sandwich panel made of two
layers of plain woven glass/vinylester subject to 1556N
indentation loading 73
4.26 Finite element deformation analysis of sandwich panel made
of two layers of plain woven glass/vinylester subject to 1556N
indentation loading 73
4.27 Finite element stress analysis of sandwich panel made of three
layers of plain woven glass/vinylester subject to 1928N
indentation loading 74
4.28 finite element deformation analysis of sandwich panel made
of three layers of plain woven glass/vinylester subject to
1928N indentation loading 74
4.29 Finite element stress analysis of sandwich panel made of four
layers of plain woven glass/vinylester subject to 2290N
indentation loading 76
4.30 Finite element deformation analysis of sandwich panel made
of four layers of plain woven glass/vinylester subject to 2290N
indentation loading 76
4.31 Finite element stress analysis of sandwich panel made of two
layers of chopped strand mat glass/vinylester subject to 772N
indentation loading 78
4.32 Finite element deformation analysis of sandwich panel
made of two layers of chopped strand mat
glass/vinylester subject to 772N indentation loading 78
4.33 Finite element stress analysis of sandwich panel made of
three layers of chopped strand mat glass/vinylester
subject to 966N indentation loading 79
4.34 Finite element deformation analysis of sandwich panel made
of three layers of chopped strand mat glass/vinylester subject
to 966N indentation loading 79
4.35 Finite element stress analysis of sandwich panel made of
four layers of chopped strand mat glass/vinylester subject
to 1383N indentation loading 81
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4.36 Finite element deformation analysis of sandwich panel
made of four layers of chopped strand mat
glass/vinylester subject to 1383N indentation loading 81
4.37 The comparison between the results of finite element stress
analysis of sandwich panel made of different number of
chopped strand mat and woven facesheet 82
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LIST OF SYMBOLS
t - The thickness of facesheets
E - Energy absorption
F - Load
- Deflection of sandwich panel
E - Modulus elasticity
v - Poison ratio
G - Shear modulus
- Stress
CHAPTER 1
INTRODUCTION
1.1 Background
Composite materials are composed of reinforcements such as fibres,
particles, and flakes that surrounded in a matrix (resin) such as polyester, epoxy, and
vinylester. The resin holds the fibres together to create products with any shape and
transfer the applied load to the fibres and the fibres improve the physical and
mechanical properties of the resin and most of the applied loads are taken by the
fibres. Fibre reinforced polymer materials unlike common materials such as steel and
aluminum are not isotropic materials and they are anisotropic. The mechanical
properties of anisotropic materials are not same in any direction and the mechanical
properties are different in different directions while the mechanical properties are
same in any direction in isotropic materials. Therefore, fibre reinforced polymers are
directional materials or in other words, the optimum mechanical properties are in
direction of reinforcement. Therefore, the fibres are placed in the composite
materials according to the applied load. Also, the type and direction of
reinforcements are selected according to the application.
Fibre reinforced polymer materials have been used in a wide range of
applications, the primary focus of which involves either mass reduction or resistance
to corrosive environments. Consequently the aerospace, motor sport and boating
industries have dominated FRP usage. These would indicate that FRPs possess
2
substantial potential for the production of structures which are not only low in mass,
but are practical, cost competitive alternatives to more traditional materials.
A comparison of materials properties of common materials such as aluminum
and steel and composite materials such as carbon/epoxy and E-glass/epoxy were
listed in Table 1. It can be seen from Table 1.1 that the composite materials provide
several advantages such as high stiffness to weight ratio over the common materials.
Although the fibre reinforced polymer materials have several advantages, but the
cost of this materials are the disadvantages of composite materials.
Table 1.1: A comparison of representative material properties
Type of
materials
Density
(kg/m3)
Tensile
Strength
(MPa)
Tensile
Modulus
(GPa)
Max.
Elastic
(%)
Specific
Tensile
Strength (Ult.)
(MPa/kg/m³)
Specific
Tensile
Modulus
(Mpa/kg/m³)
Carbon/Epoxy 1750 1000(UTS) 100 1.0 0.57 57
E-glass/Epoxy 2540 700 (UTS) 40 1.75 0.28 16
Steel 7850 350 (Yield)
480 (UTS)
200 0.18 0.06 25
Aluminium 2800 110 (Yield)
151 (UTS)
69 016 0.05 25
Composite sandwich materials are special types of composite materials that
are manufactured by bonding two skins (Facesheet) to a core (Figure 1.1). The
facesheets are very thin and stiffness of them is very high and the core materials
usually are light and thick in comparison with the facesheets. Any type of materials
such as aluminum, steel, carbon/epoxy and glass/vinylester can be used as facesheets
the materials such as aluminum honeycomb, Polypropylene honeycomb, foam core
can be used as core materials in sandwich panels and this materials usually have low
strength and low weight materials, but higher thickness of these materials provide the
sandwich composite materials with high bending stiffness with low weight.
3
Figure 1.1 The schematic of composite sandwich panel.
The structures that naturally have the geometry of honeycomb shape are
known as honeycomb structures. The minimum amount of materials is used in
honeycomb materials. Therefore, the cost of raw materials in honeycomb materials is
very low but the manufacturing process has a high effect on the cost of these
materials. Different types of materials such as paper, aluminum, steel, composite
materials and plastic can be used in fabrication of honeycomb materials. Aluminum
honeycomb, polypropylene honeycomb and paper honeycomb are three examples of
honeycomb materials (Figure 1.2).
(a) Aluminum honeycomb (b) paper honeycomb (c) polypropylene honeycomb
Figure 1.2 Three types of honeycomb core materials.
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Polypropylene honeycomb material is one of the widely used honeycomb
materials that are used in composite sandwich panel. This material is made of
polypropylene materials. In this material, the ratio of strength to weight is high and
the resistance to chemical and corrosion and energy absorption property is very high
and thermoforming ability and recyclable is two other advantages of this material.
1.2 Introduction
This study deals with experimental and numerical investigations of composite
sandwich panel with polypropylene honeycomb core and different number of layers
of chopped strand mat and woven glass/vinylester including two, three and four
layers under quasi static indentation loading. Experimental tests were conducted on
composite sandwich panel subject to indentation loading with different loading rate
including 4mm/min, 6mm/min and 8mm/min by using Instron universal testing
machine. All of the specimens for experimental testing were fabricated by using
vacuum bagging process. For different types of sandwich panels with polypropylene
honeycomb core, the contact force-displacement curves and energy absorption-
displacement curves of composite sandwich panel were determined and analyzed and
the obtained results were compared together.
Also, the numerical investigation of composite sandwich panels was
studied by using ANSYS Workbench Software. In this section, static analysis of
composite sandwich panels with polypropylene honeycomb core subject to
indentation loading were modeled and studied and the deformation behaviour and
stress behaviour of sandwich panels were determined and compared with the
results of experimental tests.
1.3 Scope of study
The scopes of this research are listed below:
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Literature study on composite material and composite sandwich material
subject to different types of loading including indentation loading.
Preparation of different forms of composite sandwich materials with
polypropylene honeycomb core and different number of layers of
chopped strand mat and woven glass/vinylester facesheets by using
vacuum bagging process.
Perform experimental quasi-static indentation tests on composite
sandwich panel and data collecting.
Calculating the contact force-displacement curves and energy absorption-
displacement curves of composite sandwich panel at different loading
rate.
Finding the effect of different parameters such as the number of layers
and type of facesheets and the loading rate on indentation properties of
composite sandwich panel.
Finite element analysis of composite sandwich panel with polypropylene
honeycomb core subject to indentation loading.
Comparing the results of finite element analysis with the experimental
and validate.
Defining the stress and deformation behaviour of composite sandwich
panel subject to indentation loading numerically.
1.4 Statement of problems
Composite sandwich panels are made of two facesheets and core material.
The type of facesheets and core material and the geometry of sandwich panel are
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most important factors in designing of sandwich panel. Therefore, understanding the
effect of these parameters such as the thickness of facesheets and type of materials of
facesheets on mechanical behaviour of these structures is important in design and
analyze of these structures. Therefore, In this research, the effect of different
parameters such as the type of materials including chopped strand mat and woven
glass/vinylester and the loading rate on mechanical properties of sandwich panel with
polypropylene honeycomb core especially indentation properties were studied
experimentally and numerically and the force-displacement curve and energy
absorption-displacement curve were determined.
1.5 Layout of thesis
This thesis is consist of six chapters; Introduction, Literature review, finite
element analysis, Experimental procedure, Results and discussion and Conclusions
and recommendation. Chapter 1 defines composite materials and composite
sandwich panels, introduction, state of problems, objective and scope of the study. In
Chapter 2, history of composite materials and literature reviews on the subject of
composite sandwich panel and different types of loading on these types of materials.
In Chapter 3, finite element analysis of composite sandwich panels subject to
indentation loading was presented. In Chapter 4 the experimental procedure of
composite sandwich panels with polypropylene honeycomb core was defined. In
Chapter 5, the results of experimental tests and finite element analysis were
described and the effects of different parameter on indentation properties of
composite sandwich panel were studied and the experimental results and numerical
results were compared together. In Chapter 6, Conclusions were drawn from the
experimental and numerical results and then recommendation was presented.
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