Low Velocity Impact Behaviour Of Advanced Composite Materials.
LOW VELOCITY IMPACT BEHAVIOUR OF ADVANCED COMPOSITE
MATERIALS
RASIDIN BIN SENAWI
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
LOW VELOCITY IMPACT BEHAVIOUR OF ADVANCED COMPOSITE
MATERIALS
RASIDIN BIN SENAWI
This report is proposed to fulfilled some of the requirement to be honor with
Bachelor of Mechanical Engineering (Structure & Material)
Fakulti Kejuruteraan Mekanikal
Universiti Teknikal Kebangsaan Malaysia
Oktober 2008
‘I admint that have read this work and to me this work was adequate form the aspect
scope and quality to be honor with Bachelor of Mechanical Engineering (Structural and
Material)’
Signature
st
:…………………………
Name 1 supervisor
: …………........................
Date
:………………………….
i
“I verify that this report is my own work except for the citation and quotation that the
source has been clarify for each one of them”
Signature: ……………………………….
Name of writer: …………………………
Date: …………………………………….
ii
To my beloved family and friends
iii
ACKNOWLEDGEMENT
Firstly, thanks to Allah for giving a good health and mind which enable to me to
faced the entire problem and complete this research.
I would like to express my deepest appreciation to my supervisor, Puan Siti
Hajar Binti Sheikh Md. Fadzullah who gave me the opportunity to do this research and
for supervising me all the way and offered for many suggestions and helps in conducting
the research to fulfill my Projek Sarjana Muda II course.
I also would like to thank all the lecturers, technician and laboratory assistant for
assisting me in this project from the start. I would like to tell that their help are very
much appreciated especially En Azhar from FKP(UTeM), En. Rashdan from
FKM(UTeM) and En Hamdan from FKM(UITM)
My thanks also go to my family for their love and support. Not forgetting, to all
my friends who have been very helpful and give me encouragement to finish the
research.
iv
ABSTRACT
The focus of this research is to study the effect of low velocity impact on
composite sandwich panel that is commonly used in aerospace industries. This research
investigates the effect of damage on the sandwich panel at low velocity. The specimen
used in this project is carbon fiber sandwich panel and three type of testing will be carry
out including Quasi-static compression test, Drop weight impact test and surface
analysis using SEM. In this study, Quasi-static compression test are carried out at
different velocity ranging from 2mm/min to 5mm/min. Drop weight impact test are
carried out at velocity 2, 2.4,2. 97 and 3.5m/s.From the result the velocity at 3mm/min
for compression test had the biggest load that is 1.95 KN. The biggest load for drop
weight test at 3.5m/s is 1.26 KN. The biggest energy also at velocity 3mm/min for
compression test and the value is 3.506 J. The biggest energy for drop weight test at
3.5m/s is 19 KN. From the result load and energy are directly proportional. The load
increase and the energy become more increase. Several type of damages were observed
under both impact test and this include upper skin failure,skin core debonding and core
crushing.
v
ABSTRAK
Fokus penyelidikan ini adalah untuk mengkaji kesan halaju rendah kesan ke atas
komposit “sandwich panel” iaitu biasanya digunakan dalam industri aeroangkasa.
Penyelidikan ini akan menyiasat kesan kerosakan di “sandwich panel” pada halaju
rendah. Spesimen yang akan digunakan dalam projek ini adalah gentian karbon
“sandwich panel” dan tiga jenis ujian akan dijalankan termasuk ujian mampatan Quasistatic, ujian hentaman dan permukaan analisis menggunakan SEM. Dalam kajian ini,
ujian mampatan Quasi-static akan dijalankan pada halaju berbeza meliputi 2mm / min
hingga 5mm / min. Untuk ujian hentaman dijalankan pada halaju 2, 2.4,2. 97 dan 3.5m /
s.Daripada hasil halaju pada 3mm / min untuk ujian mampatan, mempunyai nilai daya
terbesar iaitu 1.95 KN. Nilai daya terbesar untuk ujian hentaman pada 3.5m / s adalah
1.26 KN. Tenaga terbesar juga pada halaju 3mm / min untuk ujian mampatan dan
nilainya adalah 3.506 J Tenaga terbesar untuk ujian hentaman pada 3.5m / s adalah 19
KN. Daripada keputusan itu,daya berkadar langsung dengan tenaga.Lebih banyak daya
maka tenaga juga bertambah.Beberapa jenis kerosakan diperhatikan dibawah ujian
mampatan termasuk kerosakan “skin’ atas,teras bercantum dan kerosakan teras.
vi
TABLE OF CONTENT
TOPIC
CHAPTER I
CHAPTER II
PAGE
CONFESSION
i
DEDICATION
ii
ACKNOWLEDGEMENT
iii
ABSTRACT
iv
ABSTRAK
v
TABLE OF CONTENT
vi
LIST OF TABLE
ix
LIST OF FIGURE
xi
LIST OF APPENDICES
xii
INTRODUCTION
1.1
General
1
1.2
Problem Statement
1
1.3
Scope of Research
2
1.4
Significant of research
2
1.5
Research Scopes
2
1.6
Planning and Execution for PSM 1 and 2
3
LITERATURE RIVIEW
2.1
Composite material
5
vii
2.1.1
processing of composites
5
2.1.2
Mechanical Properties of Composite 5
Materials
2.1.3
Categories of fiber reinforced
9
composite materials
2.2
Sandwich panel
9
2.2.1
Composite sandwich panel
10
2.2.2
Advantages of sandwich panel
10
2.2.3
Composite sandwich structure
11
2.2.4
Simple analysis of composite
sandwich
panel
2.2.5
Core
13
2.2.6
Skin
15
2.2.7
Mechanical properties of sandwich
panel
2.3
2.4
12
Impact Damage
Result and Discussion from the journal
2.4.1
16
18
18
Previous study on low velocity
impact
23
viii
CHAPTER III
METHODOLOGY
3.1
Process Flow of Research
27
3.2
sample
28
3.3
Quasi-static compression test
28
3.4
Drop weight impact test
30
3.5
Surface analysis via Scanning Electron
Microscope (SEM)
CHAPTER IV
CHAPTER V
CHAPTER VI
31
RESULT AND DISCUSSION
4.1
Result of compression test
33
4.2
Drop weight impact test
35
4.3
Discussion of compression test
36
4.4
Discussion of drop weight impact test
41
4.5
Comparison between compression test and drop
weight impact test
45
4.6
Impact characteristics of compression test
48
CONCLUSION
RECOMMENDATION FOR FUTURE WORK
51
52
ix
LIST OF TABLES
NO.
TITLE
PAGE
2.1
Mechanical properties of composite materials
06
2.2
Mechanic characteristics of fiber
07
2.3
Advantages of sandwich panel.
10
2.4
In-plane properties of carbon fabric/epoxy composite used for
16
2.5
Mechanical properties of sandwich core material: Divinycell H250
17
2.6
Basic material and geometrical properties of HSSA
18
4.1
Max. load and Max energy
33
4.2
Drop weight energy
35
4.3
Maximum energy at different velocity
36
4.4
Minimum energy at different velocity
37
x
NO.
TITLE
PAGE
4.5
Maximum load at different velocity
38
4.6
Minimum load at different velocity
39
4.7
Mean load different velocity
40
4.8
Mean load at different velocity
41
4.9
Maximum energy at different velocity
42
4.10
Result of velocity at 2.0 m/s
43
4.11
Result of velocity at 2.42 m/s
43
4.12
Result of velocity at 2.97 m/s
44
4.13
Result of velocity at 3.5 m/s
44
4.14
Mean load for compression test and drop weight test
46
4.15
Mean energy for compression test and drop weight test
47
4.16
Specimens observation for compression test
48
4.17
Specimens observation for drop weight impact test
50
xi
LIST OF FIGURES
NO.
TITLE
PAGE
2.0
Composite sandwich structure [12]
11
2.1
(Sandwich panel)I-beam structure [12]
12
2.2
Illustration of compression sandwich panel. [12]
14
2.3
Illustration of layer slide without resistance. [12]
14
2.4
Illustration of core weak in shear. [12]
15
2.5
Illustration of core strong in shear. [12]
15
2.6
Bending illustration [13]
16
2.7
Schematic outline of the sandwich beam test with clamped condition [1]
19
2.8
Schematic representations of the drop-weight test rig
20
xii
NO.
TITLE
PAGE
2.9
Results of quasi-static sandwich beam tests with the 8mm
core thickness
21
2.10
Results of quasi-static sandwich beam tests with the 10 mm
22
core thickness [1]
3.1
Process flow of research
27
3.2
The specimen of sandwich panel
28
3.3
The mark of “X”.
29
3.4
The Compression Machine
29
3.5
Drop weight impact test
30
3.6
weight set
31
3.7
The specimen in the base plate and the figure of cross heads
31
3.8
SEM Instrument
32
4.1
Representative curve
34
4.2
Graph maximum energy
36
4. 3
Graph minimum energy
37
xiii
NO.
TITLE
PAGE
4.4
Graph minimum energy
38
4.5
Graph minimum load
39
4.6
Graph mean load
40
4.7
Graph mean load
41
4.8
Graph mean energy
42
4.9
Comparison mean load for compression test and drop weight test
46
4.10
Comparison mean energy for compression test and drop weight test
47
xiv
LIST OF APPENDIX
NO.
TITLE
A
Results for compression and drop weight test
PAGE
55
1
CHAPTER I
INTRODUCTION
1.1
General
Sandwich panels are widely used in lightweight construction especially in
aerospace industries because of their high specific strengths and stiffnesses. In the
service life of a sandwich panel, impacts are expected to arise from a variety of causes.
Debris may be propelled at high velocities from the runway during aircraft takeoffs and
landings. Other examples include tools dropping on the structure during maintenance or
even collisions by birds. Visual inspection may reveal little damage on the sandwich
panel, but significant damage may occur between the impacted face sheet and the core.
Reduction of structural stiffness and strength can occur, and consequently, propagate
under further loading. Thus, their behaviour under impact had received increasing
attention.
1.2
Problem statement
There are many types of impact damage such as face/core bonding, hyper
velocity, drop weight, and etc. These sandwich panels may encounter low-velocity
impacts, such as tool-drop, runway stones, and tire blow out debris. Even though a
visual examination of the impacted surface may reveal very little damage, significant
damage might exist between the face sheet and the core. This type of damage leads to
substantial reduction of the compressive and bending strengths of the sandwich
construction. Will have to analyze the impact damage because to know the factors of
safety especially for the aerospace industries which have widely used the sandwich
panels. That is the first and important reason to study and analyze about the damage.
2
1.3
Objectives of Research
In this research, experimental investigation will be carried out to gain a better
understanding of the effects of low-velocity impact on composite sandwich
constructions.The objective of this study are:
i.
To study the effect of low velocity impact on composite sandwich panel.
ii.
To study the behaviour of composite sandwich panel under Quasi-static
Compression Testing.
iii.
To study the effect on composite sandwich panel after impact under Drop
Weight Testing Machine.
iv.
To study the type of impact damage on the surface of composite sandwich panel
using scanning Electron Microscope(SEM).
1.4
Significant of research
From this research, the result of the low velocity of impact via quasi-static
compression test, the effect on composite sandwich panel after impact under drop weight
testing machine, and the type of impact damage on the surface are investigated.
1.5
Research scopes
The research activities include the following:
i.
Sample preparation on composite sandwich panel.
ii.
Low velocity impact testing via Quasi-static Compression Test.
iii.
Drop weight impact testing.
iv.
Surface defect analysis using Scanning Electron Microscope(SEM)
3
1.6
Planning and execution
PLANNING AND EXECUTION FOR PSM I
RESEARCH ACTIVITY/TIME
Literature review
Research Methodology
-Design of experiment
- Design of test specimen
Report writing for PSM I
Preparation for PSM Seminar I
Submission of report & log book
JANUARY
W1
W2
W3
FEBRUARY
W4
W5
W6
W7
MARCH
W8
W9
W10
APR
W11
W12
W13
W14
4
200
8
PLANNING AND EXECUTION FOR PSM II
JULY
RESEARCH ACTIVITY/TIME
Literature review
Experimental activities:- Sample preparation
- Mechanical Testing
Quasi-Static Compression Test
Surface Analysis using SEM
Data collection
Results and analysis
Report writing for PSM II
Preparation for PSM Seminar II
Submission of report & log book
W
1
W2
W3
AUGUST
W4
W5
W6
W7
W8
SEPTEMBER
W1
W1
1
W9 0
W1
2
OCT
W1
W1
3
4
5
CHAPTER II
LITERATURE REVIEW
2.1
Composite materials
Composite materials (or composites for short) are engineered materials made
from two or more constituent materials with significantly different physical or chemical
properties and which remain separate and distinct on a macroscopic level within the
finished structure. Composite materials have gained popularity (despite their generally
high cost) in high-performance products that need to be lightweight, yet strong enough
to take harsh loading conditions such as aerospace components (tails, wings, fuselages,
propellers), boat and scull hulls, bicycle frames and racing car bodies. Other uses
include fishing rods and storage tanks. The new Boeing 787 Dreamliner structure
including the wings and fuselage is composed of over 50 percent composites.Carbon
composite is a key material in today's launch vehicles and spacecrafts. It is widely used
in solar panel substrates, antenna reflectors and yokes of spacecrafts. It is also used in
payload adapters, inter-stage structures and heat shields of launch vehicles.
2.1.1
Processing of composites
In general, the reinforcing and matrix materials are combined, compacted and
processed to undergo a melding event. After the molding event, the part shape is
essentially set, although it can deform under certain process conditions. For a thermoset
polymeric matrix material, the melding event is a curing reaction that is initiated by the
application of additional heat or chemical reactivity such as organic peroxide. For a
6
thermoplastic polymeric matrix material, the melding event is solidification from
the melted state. For a metal matrix material such as titanium foil, the melding event is a
fusing at high pressure and a temperature near the melt point. [9]
For many molding methods, it is convenient to refer to one mold piece as a
“lower” mold and another mold piece as an “upper” mold. Lower and upper refer to the
different faces of the molded panel, not the mold’s configuration in space. In this
convention, there is always a lower mold, and sometimes an upper mold. Part
construction begins by applying materials to the lower mold. Lower mold and upper
mold are more generalized descriptors than more common and specific terms such as
male side, female side, a-side, b-side, tool side, bowl, hat, mandrel, etc. Continuous
manufacturing processes use a different nomenclature. The molded product is often
referred to as a panel. For certain geometries and material combinations, it can be
referred to as a casting. For certain continuous processes, it can be referred to as a
profile. [9]
Autoclave method process using a two-sided mold set that forms both surfaces of
the panel. One the lower side is a rigid mold and on the upper side is a flexible
membrane made from silicone or an extruded polymer film such as nylon.
Reinforcement materials can be placed manually or robotically. They include continuous
fiber forms fashioned into textile constructions. Most often, they are pre-impregnated
with the resin in the form of prepreg fabrics or unidirectional tapes. In some instances, a
resin film is placed upon the lower mold and dry reinforcement is placed above. The
upper mold is installed and vacuum is applied to the mold cavity. The assembly is
placed into an autoclave pressure vessel.This process is generally performed at both
elevated pressure and elevated temperature. The use of elevated pressure facilitates a
high fiber volume fraction and low void content for maximum structural efficiency. [9]
2.1.2
Mechanical properties of composite materials
Composite materials have gained popularity (despite their generally high cost) in
high-performance products such as aerospace components (tails, wings, fuselages,
7
propellers), boat and scull hulls, bicycle frames and racing car bodies. More mundane
uses include fishing rods and storage tanks. [10]
Carbon composite is a key material in today’s launch vehicles and spacecrafts. It
is widely used in solar panel substrates, antenna reflectors and yokes of spacecrafts. It is
also used in payload adapters, inter-stage structures and heat shields of launch vehicles.
[10]
Table 2.1: Mechanical properties of composite materials [10]
I. Glass Fibers
Glass fibers have been used for many years to produce fabrics and reinforcement
materials for composites. They are gotten through warm spinning method of glasses
made in a suitable way (usually, alumino- borate –silicate) according to the use and the
environment where it will be used. The kinds of glass commonly used for fibers are kind
E and kind S, with a density of about 2,6 g/cm3, with elastic modules of about 80 and 90
GPa and break resistance of respectively 3,5 and 4,5 GPa. [9].
To obtain composites with good characteristics under stress, the break stretching
of the fiber (3 and 6% in many composites) must be less and the rigidity must be more
MATERIALS
RASIDIN BIN SENAWI
UNIVERSITI TEKNIKAL MALAYSIA MELAKA
LOW VELOCITY IMPACT BEHAVIOUR OF ADVANCED COMPOSITE
MATERIALS
RASIDIN BIN SENAWI
This report is proposed to fulfilled some of the requirement to be honor with
Bachelor of Mechanical Engineering (Structure & Material)
Fakulti Kejuruteraan Mekanikal
Universiti Teknikal Kebangsaan Malaysia
Oktober 2008
‘I admint that have read this work and to me this work was adequate form the aspect
scope and quality to be honor with Bachelor of Mechanical Engineering (Structural and
Material)’
Signature
st
:…………………………
Name 1 supervisor
: …………........................
Date
:………………………….
i
“I verify that this report is my own work except for the citation and quotation that the
source has been clarify for each one of them”
Signature: ……………………………….
Name of writer: …………………………
Date: …………………………………….
ii
To my beloved family and friends
iii
ACKNOWLEDGEMENT
Firstly, thanks to Allah for giving a good health and mind which enable to me to
faced the entire problem and complete this research.
I would like to express my deepest appreciation to my supervisor, Puan Siti
Hajar Binti Sheikh Md. Fadzullah who gave me the opportunity to do this research and
for supervising me all the way and offered for many suggestions and helps in conducting
the research to fulfill my Projek Sarjana Muda II course.
I also would like to thank all the lecturers, technician and laboratory assistant for
assisting me in this project from the start. I would like to tell that their help are very
much appreciated especially En Azhar from FKP(UTeM), En. Rashdan from
FKM(UTeM) and En Hamdan from FKM(UITM)
My thanks also go to my family for their love and support. Not forgetting, to all
my friends who have been very helpful and give me encouragement to finish the
research.
iv
ABSTRACT
The focus of this research is to study the effect of low velocity impact on
composite sandwich panel that is commonly used in aerospace industries. This research
investigates the effect of damage on the sandwich panel at low velocity. The specimen
used in this project is carbon fiber sandwich panel and three type of testing will be carry
out including Quasi-static compression test, Drop weight impact test and surface
analysis using SEM. In this study, Quasi-static compression test are carried out at
different velocity ranging from 2mm/min to 5mm/min. Drop weight impact test are
carried out at velocity 2, 2.4,2. 97 and 3.5m/s.From the result the velocity at 3mm/min
for compression test had the biggest load that is 1.95 KN. The biggest load for drop
weight test at 3.5m/s is 1.26 KN. The biggest energy also at velocity 3mm/min for
compression test and the value is 3.506 J. The biggest energy for drop weight test at
3.5m/s is 19 KN. From the result load and energy are directly proportional. The load
increase and the energy become more increase. Several type of damages were observed
under both impact test and this include upper skin failure,skin core debonding and core
crushing.
v
ABSTRAK
Fokus penyelidikan ini adalah untuk mengkaji kesan halaju rendah kesan ke atas
komposit “sandwich panel” iaitu biasanya digunakan dalam industri aeroangkasa.
Penyelidikan ini akan menyiasat kesan kerosakan di “sandwich panel” pada halaju
rendah. Spesimen yang akan digunakan dalam projek ini adalah gentian karbon
“sandwich panel” dan tiga jenis ujian akan dijalankan termasuk ujian mampatan Quasistatic, ujian hentaman dan permukaan analisis menggunakan SEM. Dalam kajian ini,
ujian mampatan Quasi-static akan dijalankan pada halaju berbeza meliputi 2mm / min
hingga 5mm / min. Untuk ujian hentaman dijalankan pada halaju 2, 2.4,2. 97 dan 3.5m /
s.Daripada hasil halaju pada 3mm / min untuk ujian mampatan, mempunyai nilai daya
terbesar iaitu 1.95 KN. Nilai daya terbesar untuk ujian hentaman pada 3.5m / s adalah
1.26 KN. Tenaga terbesar juga pada halaju 3mm / min untuk ujian mampatan dan
nilainya adalah 3.506 J Tenaga terbesar untuk ujian hentaman pada 3.5m / s adalah 19
KN. Daripada keputusan itu,daya berkadar langsung dengan tenaga.Lebih banyak daya
maka tenaga juga bertambah.Beberapa jenis kerosakan diperhatikan dibawah ujian
mampatan termasuk kerosakan “skin’ atas,teras bercantum dan kerosakan teras.
vi
TABLE OF CONTENT
TOPIC
CHAPTER I
CHAPTER II
PAGE
CONFESSION
i
DEDICATION
ii
ACKNOWLEDGEMENT
iii
ABSTRACT
iv
ABSTRAK
v
TABLE OF CONTENT
vi
LIST OF TABLE
ix
LIST OF FIGURE
xi
LIST OF APPENDICES
xii
INTRODUCTION
1.1
General
1
1.2
Problem Statement
1
1.3
Scope of Research
2
1.4
Significant of research
2
1.5
Research Scopes
2
1.6
Planning and Execution for PSM 1 and 2
3
LITERATURE RIVIEW
2.1
Composite material
5
vii
2.1.1
processing of composites
5
2.1.2
Mechanical Properties of Composite 5
Materials
2.1.3
Categories of fiber reinforced
9
composite materials
2.2
Sandwich panel
9
2.2.1
Composite sandwich panel
10
2.2.2
Advantages of sandwich panel
10
2.2.3
Composite sandwich structure
11
2.2.4
Simple analysis of composite
sandwich
panel
2.2.5
Core
13
2.2.6
Skin
15
2.2.7
Mechanical properties of sandwich
panel
2.3
2.4
12
Impact Damage
Result and Discussion from the journal
2.4.1
16
18
18
Previous study on low velocity
impact
23
viii
CHAPTER III
METHODOLOGY
3.1
Process Flow of Research
27
3.2
sample
28
3.3
Quasi-static compression test
28
3.4
Drop weight impact test
30
3.5
Surface analysis via Scanning Electron
Microscope (SEM)
CHAPTER IV
CHAPTER V
CHAPTER VI
31
RESULT AND DISCUSSION
4.1
Result of compression test
33
4.2
Drop weight impact test
35
4.3
Discussion of compression test
36
4.4
Discussion of drop weight impact test
41
4.5
Comparison between compression test and drop
weight impact test
45
4.6
Impact characteristics of compression test
48
CONCLUSION
RECOMMENDATION FOR FUTURE WORK
51
52
ix
LIST OF TABLES
NO.
TITLE
PAGE
2.1
Mechanical properties of composite materials
06
2.2
Mechanic characteristics of fiber
07
2.3
Advantages of sandwich panel.
10
2.4
In-plane properties of carbon fabric/epoxy composite used for
16
2.5
Mechanical properties of sandwich core material: Divinycell H250
17
2.6
Basic material and geometrical properties of HSSA
18
4.1
Max. load and Max energy
33
4.2
Drop weight energy
35
4.3
Maximum energy at different velocity
36
4.4
Minimum energy at different velocity
37
x
NO.
TITLE
PAGE
4.5
Maximum load at different velocity
38
4.6
Minimum load at different velocity
39
4.7
Mean load different velocity
40
4.8
Mean load at different velocity
41
4.9
Maximum energy at different velocity
42
4.10
Result of velocity at 2.0 m/s
43
4.11
Result of velocity at 2.42 m/s
43
4.12
Result of velocity at 2.97 m/s
44
4.13
Result of velocity at 3.5 m/s
44
4.14
Mean load for compression test and drop weight test
46
4.15
Mean energy for compression test and drop weight test
47
4.16
Specimens observation for compression test
48
4.17
Specimens observation for drop weight impact test
50
xi
LIST OF FIGURES
NO.
TITLE
PAGE
2.0
Composite sandwich structure [12]
11
2.1
(Sandwich panel)I-beam structure [12]
12
2.2
Illustration of compression sandwich panel. [12]
14
2.3
Illustration of layer slide without resistance. [12]
14
2.4
Illustration of core weak in shear. [12]
15
2.5
Illustration of core strong in shear. [12]
15
2.6
Bending illustration [13]
16
2.7
Schematic outline of the sandwich beam test with clamped condition [1]
19
2.8
Schematic representations of the drop-weight test rig
20
xii
NO.
TITLE
PAGE
2.9
Results of quasi-static sandwich beam tests with the 8mm
core thickness
21
2.10
Results of quasi-static sandwich beam tests with the 10 mm
22
core thickness [1]
3.1
Process flow of research
27
3.2
The specimen of sandwich panel
28
3.3
The mark of “X”.
29
3.4
The Compression Machine
29
3.5
Drop weight impact test
30
3.6
weight set
31
3.7
The specimen in the base plate and the figure of cross heads
31
3.8
SEM Instrument
32
4.1
Representative curve
34
4.2
Graph maximum energy
36
4. 3
Graph minimum energy
37
xiii
NO.
TITLE
PAGE
4.4
Graph minimum energy
38
4.5
Graph minimum load
39
4.6
Graph mean load
40
4.7
Graph mean load
41
4.8
Graph mean energy
42
4.9
Comparison mean load for compression test and drop weight test
46
4.10
Comparison mean energy for compression test and drop weight test
47
xiv
LIST OF APPENDIX
NO.
TITLE
A
Results for compression and drop weight test
PAGE
55
1
CHAPTER I
INTRODUCTION
1.1
General
Sandwich panels are widely used in lightweight construction especially in
aerospace industries because of their high specific strengths and stiffnesses. In the
service life of a sandwich panel, impacts are expected to arise from a variety of causes.
Debris may be propelled at high velocities from the runway during aircraft takeoffs and
landings. Other examples include tools dropping on the structure during maintenance or
even collisions by birds. Visual inspection may reveal little damage on the sandwich
panel, but significant damage may occur between the impacted face sheet and the core.
Reduction of structural stiffness and strength can occur, and consequently, propagate
under further loading. Thus, their behaviour under impact had received increasing
attention.
1.2
Problem statement
There are many types of impact damage such as face/core bonding, hyper
velocity, drop weight, and etc. These sandwich panels may encounter low-velocity
impacts, such as tool-drop, runway stones, and tire blow out debris. Even though a
visual examination of the impacted surface may reveal very little damage, significant
damage might exist between the face sheet and the core. This type of damage leads to
substantial reduction of the compressive and bending strengths of the sandwich
construction. Will have to analyze the impact damage because to know the factors of
safety especially for the aerospace industries which have widely used the sandwich
panels. That is the first and important reason to study and analyze about the damage.
2
1.3
Objectives of Research
In this research, experimental investigation will be carried out to gain a better
understanding of the effects of low-velocity impact on composite sandwich
constructions.The objective of this study are:
i.
To study the effect of low velocity impact on composite sandwich panel.
ii.
To study the behaviour of composite sandwich panel under Quasi-static
Compression Testing.
iii.
To study the effect on composite sandwich panel after impact under Drop
Weight Testing Machine.
iv.
To study the type of impact damage on the surface of composite sandwich panel
using scanning Electron Microscope(SEM).
1.4
Significant of research
From this research, the result of the low velocity of impact via quasi-static
compression test, the effect on composite sandwich panel after impact under drop weight
testing machine, and the type of impact damage on the surface are investigated.
1.5
Research scopes
The research activities include the following:
i.
Sample preparation on composite sandwich panel.
ii.
Low velocity impact testing via Quasi-static Compression Test.
iii.
Drop weight impact testing.
iv.
Surface defect analysis using Scanning Electron Microscope(SEM)
3
1.6
Planning and execution
PLANNING AND EXECUTION FOR PSM I
RESEARCH ACTIVITY/TIME
Literature review
Research Methodology
-Design of experiment
- Design of test specimen
Report writing for PSM I
Preparation for PSM Seminar I
Submission of report & log book
JANUARY
W1
W2
W3
FEBRUARY
W4
W5
W6
W7
MARCH
W8
W9
W10
APR
W11
W12
W13
W14
4
200
8
PLANNING AND EXECUTION FOR PSM II
JULY
RESEARCH ACTIVITY/TIME
Literature review
Experimental activities:- Sample preparation
- Mechanical Testing
Quasi-Static Compression Test
Surface Analysis using SEM
Data collection
Results and analysis
Report writing for PSM II
Preparation for PSM Seminar II
Submission of report & log book
W
1
W2
W3
AUGUST
W4
W5
W6
W7
W8
SEPTEMBER
W1
W1
1
W9 0
W1
2
OCT
W1
W1
3
4
5
CHAPTER II
LITERATURE REVIEW
2.1
Composite materials
Composite materials (or composites for short) are engineered materials made
from two or more constituent materials with significantly different physical or chemical
properties and which remain separate and distinct on a macroscopic level within the
finished structure. Composite materials have gained popularity (despite their generally
high cost) in high-performance products that need to be lightweight, yet strong enough
to take harsh loading conditions such as aerospace components (tails, wings, fuselages,
propellers), boat and scull hulls, bicycle frames and racing car bodies. Other uses
include fishing rods and storage tanks. The new Boeing 787 Dreamliner structure
including the wings and fuselage is composed of over 50 percent composites.Carbon
composite is a key material in today's launch vehicles and spacecrafts. It is widely used
in solar panel substrates, antenna reflectors and yokes of spacecrafts. It is also used in
payload adapters, inter-stage structures and heat shields of launch vehicles.
2.1.1
Processing of composites
In general, the reinforcing and matrix materials are combined, compacted and
processed to undergo a melding event. After the molding event, the part shape is
essentially set, although it can deform under certain process conditions. For a thermoset
polymeric matrix material, the melding event is a curing reaction that is initiated by the
application of additional heat or chemical reactivity such as organic peroxide. For a
6
thermoplastic polymeric matrix material, the melding event is solidification from
the melted state. For a metal matrix material such as titanium foil, the melding event is a
fusing at high pressure and a temperature near the melt point. [9]
For many molding methods, it is convenient to refer to one mold piece as a
“lower” mold and another mold piece as an “upper” mold. Lower and upper refer to the
different faces of the molded panel, not the mold’s configuration in space. In this
convention, there is always a lower mold, and sometimes an upper mold. Part
construction begins by applying materials to the lower mold. Lower mold and upper
mold are more generalized descriptors than more common and specific terms such as
male side, female side, a-side, b-side, tool side, bowl, hat, mandrel, etc. Continuous
manufacturing processes use a different nomenclature. The molded product is often
referred to as a panel. For certain geometries and material combinations, it can be
referred to as a casting. For certain continuous processes, it can be referred to as a
profile. [9]
Autoclave method process using a two-sided mold set that forms both surfaces of
the panel. One the lower side is a rigid mold and on the upper side is a flexible
membrane made from silicone or an extruded polymer film such as nylon.
Reinforcement materials can be placed manually or robotically. They include continuous
fiber forms fashioned into textile constructions. Most often, they are pre-impregnated
with the resin in the form of prepreg fabrics or unidirectional tapes. In some instances, a
resin film is placed upon the lower mold and dry reinforcement is placed above. The
upper mold is installed and vacuum is applied to the mold cavity. The assembly is
placed into an autoclave pressure vessel.This process is generally performed at both
elevated pressure and elevated temperature. The use of elevated pressure facilitates a
high fiber volume fraction and low void content for maximum structural efficiency. [9]
2.1.2
Mechanical properties of composite materials
Composite materials have gained popularity (despite their generally high cost) in
high-performance products such as aerospace components (tails, wings, fuselages,
7
propellers), boat and scull hulls, bicycle frames and racing car bodies. More mundane
uses include fishing rods and storage tanks. [10]
Carbon composite is a key material in today’s launch vehicles and spacecrafts. It
is widely used in solar panel substrates, antenna reflectors and yokes of spacecrafts. It is
also used in payload adapters, inter-stage structures and heat shields of launch vehicles.
[10]
Table 2.1: Mechanical properties of composite materials [10]
I. Glass Fibers
Glass fibers have been used for many years to produce fabrics and reinforcement
materials for composites. They are gotten through warm spinning method of glasses
made in a suitable way (usually, alumino- borate –silicate) according to the use and the
environment where it will be used. The kinds of glass commonly used for fibers are kind
E and kind S, with a density of about 2,6 g/cm3, with elastic modules of about 80 and 90
GPa and break resistance of respectively 3,5 and 4,5 GPa. [9].
To obtain composites with good characteristics under stress, the break stretching
of the fiber (3 and 6% in many composites) must be less and the rigidity must be more