Study On Fracture Toughness In Low Carbon Steel Using Compact Specimens With And Without Carburizing.
‘Saya akui bahawa telah membaca
karya ini dan pada pandangan saya / kami karya ini
adalah memadai dari segi skop dan kualiti untuk tujuan penganugerahan
Ijazah Sarjana Muda Kejuruteraan Mekanikal (Rekabentuk dan Innovasi)’
Tandatangan
:…………………………
Nama Penyelia
: En. Omar bin Bapokutty
Tarikh
:………………………...
“Saya akui laporan ini adalah hasil kerja saya sendiri kecuali ringkasan dan petikan
yang tiap-tiap satunya saya telah jelaskan sumbernya”
Tandatangan
: …………………………..
Nama Penulis
: Khairul Idzham Bin Hasni
Tarikh
: 27th March 2008
To my beloved family,
thank you for your support and encouragement that you have given in my life.
ACKNOWLEDGEMENT
I would like to express an immense gratitude to the God Al-Mighty Allah s.w.t
and the true idol of ours, Rasulullah s.a.w. who gave me the will to pursue this report
until it finished, the courage to hold on to my thoughts, and the astuteness to think
wisely whenever I need it the most. I also want to dedicate a special appreciation to my
parents whose always stand by my side and keep encouraging me until the end of
whatever I am doing.
Special thanks to my respected lecturers Mr. Omar bin Bapokutty for his ideas
and agreeable of making this report as something can be touched and observed
physically, not just being expressed by speeches. His guidance, experiences and method
of teaching were really useful for me in the future and I definitely think that it will
somehow affect my opinion in a very positive way, indeed.
I also want to say thanks to all my friends for their helps and opinions because
all of it was functional to me in many kind of way. Hopefully this report is a piece of
written work that meets the criterion and worth to be observed by others because
somehow, the endeavor to finish this task was something I wish it to be worth my effort.
ABSTRAK
Kajian mengenai keliatan patah dalam keluli berkarbon rendah ini bertujuan untuk
menganalisis
keliatan
patah
dalam
dua keadaan;
keadaan
asal
dan
tanpa
penyusukkarbonan. Selain itu, kajian ini juga bertujuan untuk membuat perbandingan
mengenai kesan keliatan patah dalam dua keadaan ini. Keluli karbon jenis AISI 1020
digunakan dalam kajian ini. Spesimen jenis Compact Tension (CT) spesimen akan
digunakan dengan mengikut piawaian ASTM E399. Sepuluh spesimen akan disediakan
melalui proses pembuatan tertentu dan lima daripadanya akan melalui proses
penyusukkarbonan. Ujian-ujian yang akan dilakukan terdiri daripada tiga jenis bermula
dengan Ujian Ketegangan untuk mendapatkan daya maksimum dan juga kekuatan alah.
Ujian Pra-Retakan Lesu akan dilakukan selepas Ujian Ketegangan untuk menyediakan
spesimen dengan mulaan retak antara 2mm ke 2.5mm. Ujian Keliatan Patah adalah
ujian terakhir untuk melengkapkan kajian ini. Universal testing Machine; Instron 8802
akan digunakan untuk menjalankan ketiga-tiga kajian. Keputusan antara kedua-dua
keadaan ini akan dibandingkan melalui kaedah analitikal untuk mencapai objektif kaian
ini.
ABSTRACT
Study on Fracture Toughness in Low Carbon Steel carries the objectives to analyze the
effect on fracture toughness on Low Carbon Steel in two conditions; with and without
carburizing. Other than that is to compare the effect on fracture toughness between
carburizing and without carburizing. Carbon Steel type AISI 1020 is the selected
material for this study. Compact Tension (CT) specimen is the type of specimen used
for this study with standard constraint followed by ASTM E399. Ten specimens will be
prepared through manufacturing processes and five of will be carburized using pack
carburizing process. There are three types of testing methods will be conducted starts
with Tensile Test to get the maximum load and yield strength for both conditions.
Fatigue Pre-Cracking Test will be conducted after Tensile Test to prepare the specimens
with pre-crack in the range of 2mm to 2.5mm. Next, Fracture Toughness Test is the last
method to carry out to complete the finding of the study. Universal Testing Machine;
Instron 8802 will be used to conduct all testing methods. The results between both
conditions will be compared in analitical method in order to achieve the desired target
of this study.
CONTENTS
CHAPTER
CHAPTER I
CHAPTER II
TITLE
PAGE
CONFESSION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRAK
v
ABSTRACT
vi
CONTENTS
vii
LIST OF TABLES
x
LIST OF FIGURES
xii
LIST OF SYMBOLS
xvi
LIST OF APPENDIXES
xviii
INTRODUCTION
1
1.1
An Overview on Analysis
1
1.2
Objective and Approach
2
1.3
Scope of Analysis
3
LITERATURE REVIEW
4
2.1
Overview on Fracture Toughness
4
2.2
Carburization
11
2.3
Carbon Steel
17
2.4
Research Done For the Effect of
19
Fracture Toughness
CHAPTER III
METHODOLOGY
21
3.1
Introduction
21
3.2
Specimen preparation
23
3.3
Notch Tips Cutting Process
28
3.4
Carburizing
29
3.5
Testing Method for Compact
30
Tension
CHAPTER IV
CHAPTER V
RESULTS
34
4.1
Tensile Test
34
4.2
Fatigue Pre-Cracking Test
38
4.3
Fracture Toughness Test
40
DISCUSSION
50
5.1
Introduction
50
5.2
Fracture Toughness
50
5.3
Factor Affecting The Results of
53
Tensile Test, Fatigue Pre-Cracking
Test and Fracture Test
5.4
Key factors In Performing fracture
54
Toughness Test
CHAPTER VI
CONCLUSION
55
REFERENCES
41
BIBLIOGRAPHY
42
APPENDIX
43
LIST OF TABLES
NO.
TITLE
2.1
Typical Fracture-Toughness Values for Selected
PAGE
5
Engineering Alloys
(Source: R.W. Herzberg, 1989)
2.2
Types of Carbon Steel
18
(Sources : www.wikipedia.com)
3.1
Specific value for a/W of Compact Specimens
33
(Source: ASTM E399,1997)
4.1
Results for loads of tensile test (Un-carburized
35
specimens)
4.2
Results for loads of tensile test (Un-carburized
36
specimens)
4.3
Comparisons of Tensile Test results between
38
carburized and un-carburized specimens
4.4
Comparisons of Fatigue pre-cracking test results
between carburized and un-carburized specimens
40
4.5
Table of fracture toughness for un-carburized Low
48
Carbon Steel
4.6
Table of fracture toughness for carburized Low Carbon
Steel
49
LIST OF FIGURES
NO.
TITLE
2.1
Load types for Modes of Fracture
PAGE
5
(Source: R.J Sanford, 2003)
2.2
Stress-strain behavior of Carbon Steel
7
(Source: NDT Resource Center, 2001)
2.3
Types of Fracture Toughness Specimen
9
(Source: P. Henryk, 2004)
2.4
Criteria of plain-stress and plain-strain
10
(Source: N.E. Dowling, 1993)
2.5
Orientation of crack plane in fracture toughness
11
(Source: ASTM E399, 1997)
2.6
Common method of carburizing
13
2.7
Case depth vs. carburizing time
14
(Source: S.Z. Elgun, 1999)
2.8
Pack Carburizing Process
17
(Source: Serdar Z. Elgun, 1999)
2.9
Illustration of Charpy and Izod Impact Tests.
20
(Source: Callister W.D. Jr, 1994.)
3.1
Methodology of Analysis
22
3.2
Compact Specimen C (T) Standard Proportions
23
(Source: ASTM E399, 1997)
3.3 (a)
Scantool 254vsh Model Bandsaw Machine
24
3.3 (b) Cutting process using Bendsaw Machine
24
3.4
Haas CNC Milling Machine
25
3.5
Facing cut process using CNC Milling Machine
25
3.6
Specimen surface after squaring process
25
3.7 (a)
Facing Cut
26
3.7 (b)
Holes grinding
26
3.7 (c)
Specimen after facing cut and grinding process
27
3.7 (d)
Constraint measured to make sure specimen dimension
27
follow the standard dimension.
3.7 (e)
All 12 specimens after finish cutting process
27
3.8:
Dimension for Notch Tips
28
3.9
EDM Wirecut Machine
28
3.10
Pack carburizing process flow
29
3.11
Tension Testing Clevis
31
3.12
Universal Tensile Machine
31
4.1
Graph of Tensile Test for Compact Specimen (Un-
34
Carburized)
4.2
Un-carburized specimen condition after tensile test
35
4.3
Graph of Tensile Test for Compact Specimen
36
(Carburized)
4.4
Carburized specimen condition after tensile test
37
4.5
Un-carburized specimens after fatigue pre-cracking test
39
and ready for fracture toughness test.
4.6
Graph of fracture toughness for un-carburized
41
specimen #1
4.7
Graph of fracture toughness for un-carburized
specimen #2
41
4.8
Un-carburized specimens after fracture toughness test
42
4.9
Compact Specimen (CT) Standard Proportions
42
(Source: ASTM E399, 1997)
4.10
Graph of fracture toughness for carburized specimen 1
45
4.11
Graph of fracture toughness for carburized specimen 2
45
4.12
Carburized specimens after fracture toughness test
46
5.1
Specimens after fracture toughness
51
5.2
Comparison of curves for ductile and brittle materials:
52
(a) ductile material; (b) brittle material
(Source: J.W. Fisher, 1984)
5.3
Result of tensile test: (a) un-carburized specimen;
52
(b) carburized specimens
5.4
Specimen holder
54
LIST OF SYMBOLS
a
=
Crack Length, mm
B
=
Specimen Thickness, mm
E’
=
Effective Young’s Modulus, Pa (psi)
KI
=
Stress Intensity Factor, MPa.m1/2
KIC
=
Plane-Strain Fracture Toughness, MPa.m1/2
KIC (t)
=
Rapid Load Plane-Strain Fracture Toughness, MPa.m1/2
KQ
=
Fracture Toughness, MPa.m1/2
P
=
Specific Load, klbf (kN)
Pmax
=
Maximum load that specimen able to sustain, klbf (kN)
RSC
=
Specimen Strength Ratio
Tx
=
Temperature of Rapid Load Toughness Test, K
t
=
Loading Time, ms
=
Crack Mouth Opening Displacement, mm
=
Poisson Ratio
F
=
Fracture Stress, MPa
YD
=
Dynamic Yield Strength, MPa
YS
=
Yield Strength, MPa
Vm
LIST OF APPENDICES
NO.
TITLE
PAGE
A
ASTM Standard Related to Fracture Mechanics
59
B
Standardized codes for specimen configurations and
60
applied load
C
Principal Types of Load-Displacement Records
D
Fractograph
of
ductile
cast
iron
showing
61
a
62
transgranular fracture surface
E
F
Fractograph of an intergranular fracture surface
K Calibrations for Typical Test Specimen Geometries
63
64
1
CHAPTER I
INTRODUCTION
1.1
An Overview on Analysis
This thesis systematically investigates the effect on fracture toughness of
Low Carbon Steel with and without carburizing. In order to run the analysis and
from the previous research done, Carbon Steel; type AISI 1020) is the most suitable
material that can be used for the testing to get the result. By using compact specimen
followed with ASTM standard, testing will be conducted in two conditions; with and
without carburization. Using ASTM E399 as a guide, Plane Strain Fracture
Toughness experiment using compact specimen will be carried out in order to obtain
the necessary information for the analysis.
In materials science, fracture toughness is a property which describes the
ability of a material containing a crack to resist fracture, and is one of the most
important properties of any material for virtually all design applications. It is
denoted as K1c.The subscript '1c' denotes mode 1 (crack opening; ordinary strain),
since the material can be made thick enough to resist shear (mode 2) or tear (mode
3). Fracture toughness is a quantitative way of expressing a material's resistance to
brittle fracture when a crack is present. If a material has a large value of fracture
toughness it will probably undergo ductile fracture. Brittle fracture is very
characteristic of materials with a low fracture toughness value.
2
Fracture occurs when the metal experiences stress that exceeds its yield
strength. Fractures occur as two different types, ductile fracture and brittle fracture.
Brittle fracture occurs when the metal doesn’t yield before it breaks. Instead of the
sheets of atoms in the metal sliding over each other as occurs in deformation, when
stressed, the sheets of atoms pull completely apart. This type of fracture most often
occurs in metals that are extremely hard. Brittle fracture almost always occurs at low
temperatures. Ductile fracture is the most common type of fracture in metal. Unlike
what occurs in a brittle fracture, the metal yields before it breaks in a ductile
fracture. The peak stress a metal can withstand before it breaks is called tensile
strength. Ductile fracture is caused by the stress exerted on the metal actually work
hardening the metal as it yields, cracks from fatigue develop, and then these cracks
propagate very rapidly through the metal until complete failure occurs
1.2
Objective and Approach
The main objectives of this analysis are:
I.
To analyze the effect on fracture toughness on Low Carbon Steel in two
condition; (1) with carburizing and (2) without carburizing.
II.
To compare the effect on fracture toughness between carburizing and
without carburizing.
The fracture toughness testing procedures specified in ASTM Standard No.
E399 will be used. Ten compact specimens of nominal thickness 25mm will be
tested. Each sample contains a notch, or 'machined crack'. At the tip of the notch a
true crack has been produced by repeatedly loading (fatiguing) the specimen.
3
1.3
Scope of Analysis
In this analysis, there are three major scopes needs to be considered in order
to achieve the objectives of analysis.
Specimen preparation is the first step of analysis. There will be 10 specimen
needs to be prepared for this analysis. Dimensions and tolerances of the specimen
will be followed by ASTM Standard for compact specimen dimension. Material that
will be used for this analysis is AISI 1020 carbon steel that is the most suitable
specification of low carbon steel.
Carburizing process of the specimen will be conducted before the testing.
Only five (5) specimens will be carburized for testing while another five (5)
specimens will be used without carburizing. The method of carburizing will be
conducted using pack carburization method.
Testing method will be conducted using ASTM Standard Test Method for
Plain-Strain Fracture Toughness. Testing will be conducted in two different
conditions; (1) without carburizing, and (2) with carburizing. Then the result on both
conditions is to be analyzed to compare between both conditions.
4
CHAPTER II
LITERATURE REVIEW
2.1
Overview on Fracture Toughness
Fracture toughness is an indication of the amount of stress required to
propagate a preexisting flaw. It is a very important material property since the
occurrence of flaws is not completely avoidable in the processing, fabrication, or
service of a material/component. Flaws may appear as cracks, voids, metallurgical
inclusions, weld defects, design discontinuities, or some combination thereof. Since
engineers can never be totally sure that a material is flaw free, it is common practice
to assume that a flaw of some chosen size will be present in some number of
components and use the linear elastic fracture mechanics (LEFM) approach to
design critical components. This approach uses the flaw size and features,
component geometry, loading conditions and the material property called fracture
toughness to evaluate the ability of a component containing a flaw to resist fracture.
(from NDT Resource Center, 2001)
A parameter called the stress-intensity factor (K) is used to determine the
fracture toughness of most materials. A Roman numeral subscript indicates the
mode of fracture and the three modes of fracture are illustrated in Figure 2.1. Mode I
fracture is the condition in which the crack plane is normal to the direction of largest
tensile loading that is indicates testing in which a tensile stress causes the crack to
open. This is the most commonly encountered mode and, therefore, for the
remainder
of
the
material
Figure 2.1). (from R.J Sanford, 2003)
will
be
consider
as
KI
(refer
5
Stress intensity factor, KIc is the most often used engineering
design parameter.
Opening or tensile mode where the crack surfaces move directly
apart.
Tearing and anti-plane shear mode where the crack surfaces
move relative to one another and parallel to the leading edge of
the crack.
Mode-I
Mode-II
Mode-III
Figure 2.1: Load types for Modes of Fracture
(Source: R.J Sanford, 2003)
Table 2.1: Typical Fracture-Toughness Values for Selected Engineering Alloys
(Source: R.W. Herzberg, 1989)
Material
KIC
yield strength
Aluminium alloys;
2024-T851
26.4
24
455
66
7075-T651
24.2
22
495
72
7178-T651
23.1
21
570
83
55
50
1035
150
4340 (low alloy steel)
60.4
55
1515
220
17-7pH(precipitation hardening)
76.9
70
1435
208
55
50
1550
225
Titanium alloy;
Ti-6A1-4V
Alloy steels;
350 maraging steel
6
Fracture toughness values of material are most useful in mechanical design
when working with materials of limited toughness or ductility such as high-strength
aluminum, steel and titanium alloys. Table 2.1 lists KIC values for some of these
alloys. Material that show little plastic deformation before fracture have relatively
low fracture toughness, KIC values and tend to be more brittle, whereas those with
higher KIC values are more ductile. Fracture toughness values can be used in
mechanical design to predict the allowable flaw size in alloys with limited ductility
acted upon by specific stresses. (from R.W. Herzberg, 1989)
2.1.1
Toughness
The ability of a metal to deform plastically and to absorb energy in the
process before fracture is termed toughness. The emphasis of this definition should
be placed on the ability to absorb energy before fracture. Recall that ductility is a
measure of how much something deforms plastically before fracture, but just
because a material is ductile does not make it tough. The key to toughness is a good
combination of strength and ductility. A material with high strength and high
ductility will have more toughness than a material with low strength and high
ductility. Therefore, one way to measure toughness is by calculating the area under
the stress strain curve from a tensile test. This value is simply called “material
toughness” and it has units of energy per volume. Material toughness equates to a
slow absorption of energy by the material.
karya ini dan pada pandangan saya / kami karya ini
adalah memadai dari segi skop dan kualiti untuk tujuan penganugerahan
Ijazah Sarjana Muda Kejuruteraan Mekanikal (Rekabentuk dan Innovasi)’
Tandatangan
:…………………………
Nama Penyelia
: En. Omar bin Bapokutty
Tarikh
:………………………...
“Saya akui laporan ini adalah hasil kerja saya sendiri kecuali ringkasan dan petikan
yang tiap-tiap satunya saya telah jelaskan sumbernya”
Tandatangan
: …………………………..
Nama Penulis
: Khairul Idzham Bin Hasni
Tarikh
: 27th March 2008
To my beloved family,
thank you for your support and encouragement that you have given in my life.
ACKNOWLEDGEMENT
I would like to express an immense gratitude to the God Al-Mighty Allah s.w.t
and the true idol of ours, Rasulullah s.a.w. who gave me the will to pursue this report
until it finished, the courage to hold on to my thoughts, and the astuteness to think
wisely whenever I need it the most. I also want to dedicate a special appreciation to my
parents whose always stand by my side and keep encouraging me until the end of
whatever I am doing.
Special thanks to my respected lecturers Mr. Omar bin Bapokutty for his ideas
and agreeable of making this report as something can be touched and observed
physically, not just being expressed by speeches. His guidance, experiences and method
of teaching were really useful for me in the future and I definitely think that it will
somehow affect my opinion in a very positive way, indeed.
I also want to say thanks to all my friends for their helps and opinions because
all of it was functional to me in many kind of way. Hopefully this report is a piece of
written work that meets the criterion and worth to be observed by others because
somehow, the endeavor to finish this task was something I wish it to be worth my effort.
ABSTRAK
Kajian mengenai keliatan patah dalam keluli berkarbon rendah ini bertujuan untuk
menganalisis
keliatan
patah
dalam
dua keadaan;
keadaan
asal
dan
tanpa
penyusukkarbonan. Selain itu, kajian ini juga bertujuan untuk membuat perbandingan
mengenai kesan keliatan patah dalam dua keadaan ini. Keluli karbon jenis AISI 1020
digunakan dalam kajian ini. Spesimen jenis Compact Tension (CT) spesimen akan
digunakan dengan mengikut piawaian ASTM E399. Sepuluh spesimen akan disediakan
melalui proses pembuatan tertentu dan lima daripadanya akan melalui proses
penyusukkarbonan. Ujian-ujian yang akan dilakukan terdiri daripada tiga jenis bermula
dengan Ujian Ketegangan untuk mendapatkan daya maksimum dan juga kekuatan alah.
Ujian Pra-Retakan Lesu akan dilakukan selepas Ujian Ketegangan untuk menyediakan
spesimen dengan mulaan retak antara 2mm ke 2.5mm. Ujian Keliatan Patah adalah
ujian terakhir untuk melengkapkan kajian ini. Universal testing Machine; Instron 8802
akan digunakan untuk menjalankan ketiga-tiga kajian. Keputusan antara kedua-dua
keadaan ini akan dibandingkan melalui kaedah analitikal untuk mencapai objektif kaian
ini.
ABSTRACT
Study on Fracture Toughness in Low Carbon Steel carries the objectives to analyze the
effect on fracture toughness on Low Carbon Steel in two conditions; with and without
carburizing. Other than that is to compare the effect on fracture toughness between
carburizing and without carburizing. Carbon Steel type AISI 1020 is the selected
material for this study. Compact Tension (CT) specimen is the type of specimen used
for this study with standard constraint followed by ASTM E399. Ten specimens will be
prepared through manufacturing processes and five of will be carburized using pack
carburizing process. There are three types of testing methods will be conducted starts
with Tensile Test to get the maximum load and yield strength for both conditions.
Fatigue Pre-Cracking Test will be conducted after Tensile Test to prepare the specimens
with pre-crack in the range of 2mm to 2.5mm. Next, Fracture Toughness Test is the last
method to carry out to complete the finding of the study. Universal Testing Machine;
Instron 8802 will be used to conduct all testing methods. The results between both
conditions will be compared in analitical method in order to achieve the desired target
of this study.
CONTENTS
CHAPTER
CHAPTER I
CHAPTER II
TITLE
PAGE
CONFESSION
ii
DEDICATION
iii
ACKNOWLEDGEMENT
iv
ABSTRAK
v
ABSTRACT
vi
CONTENTS
vii
LIST OF TABLES
x
LIST OF FIGURES
xii
LIST OF SYMBOLS
xvi
LIST OF APPENDIXES
xviii
INTRODUCTION
1
1.1
An Overview on Analysis
1
1.2
Objective and Approach
2
1.3
Scope of Analysis
3
LITERATURE REVIEW
4
2.1
Overview on Fracture Toughness
4
2.2
Carburization
11
2.3
Carbon Steel
17
2.4
Research Done For the Effect of
19
Fracture Toughness
CHAPTER III
METHODOLOGY
21
3.1
Introduction
21
3.2
Specimen preparation
23
3.3
Notch Tips Cutting Process
28
3.4
Carburizing
29
3.5
Testing Method for Compact
30
Tension
CHAPTER IV
CHAPTER V
RESULTS
34
4.1
Tensile Test
34
4.2
Fatigue Pre-Cracking Test
38
4.3
Fracture Toughness Test
40
DISCUSSION
50
5.1
Introduction
50
5.2
Fracture Toughness
50
5.3
Factor Affecting The Results of
53
Tensile Test, Fatigue Pre-Cracking
Test and Fracture Test
5.4
Key factors In Performing fracture
54
Toughness Test
CHAPTER VI
CONCLUSION
55
REFERENCES
41
BIBLIOGRAPHY
42
APPENDIX
43
LIST OF TABLES
NO.
TITLE
2.1
Typical Fracture-Toughness Values for Selected
PAGE
5
Engineering Alloys
(Source: R.W. Herzberg, 1989)
2.2
Types of Carbon Steel
18
(Sources : www.wikipedia.com)
3.1
Specific value for a/W of Compact Specimens
33
(Source: ASTM E399,1997)
4.1
Results for loads of tensile test (Un-carburized
35
specimens)
4.2
Results for loads of tensile test (Un-carburized
36
specimens)
4.3
Comparisons of Tensile Test results between
38
carburized and un-carburized specimens
4.4
Comparisons of Fatigue pre-cracking test results
between carburized and un-carburized specimens
40
4.5
Table of fracture toughness for un-carburized Low
48
Carbon Steel
4.6
Table of fracture toughness for carburized Low Carbon
Steel
49
LIST OF FIGURES
NO.
TITLE
2.1
Load types for Modes of Fracture
PAGE
5
(Source: R.J Sanford, 2003)
2.2
Stress-strain behavior of Carbon Steel
7
(Source: NDT Resource Center, 2001)
2.3
Types of Fracture Toughness Specimen
9
(Source: P. Henryk, 2004)
2.4
Criteria of plain-stress and plain-strain
10
(Source: N.E. Dowling, 1993)
2.5
Orientation of crack plane in fracture toughness
11
(Source: ASTM E399, 1997)
2.6
Common method of carburizing
13
2.7
Case depth vs. carburizing time
14
(Source: S.Z. Elgun, 1999)
2.8
Pack Carburizing Process
17
(Source: Serdar Z. Elgun, 1999)
2.9
Illustration of Charpy and Izod Impact Tests.
20
(Source: Callister W.D. Jr, 1994.)
3.1
Methodology of Analysis
22
3.2
Compact Specimen C (T) Standard Proportions
23
(Source: ASTM E399, 1997)
3.3 (a)
Scantool 254vsh Model Bandsaw Machine
24
3.3 (b) Cutting process using Bendsaw Machine
24
3.4
Haas CNC Milling Machine
25
3.5
Facing cut process using CNC Milling Machine
25
3.6
Specimen surface after squaring process
25
3.7 (a)
Facing Cut
26
3.7 (b)
Holes grinding
26
3.7 (c)
Specimen after facing cut and grinding process
27
3.7 (d)
Constraint measured to make sure specimen dimension
27
follow the standard dimension.
3.7 (e)
All 12 specimens after finish cutting process
27
3.8:
Dimension for Notch Tips
28
3.9
EDM Wirecut Machine
28
3.10
Pack carburizing process flow
29
3.11
Tension Testing Clevis
31
3.12
Universal Tensile Machine
31
4.1
Graph of Tensile Test for Compact Specimen (Un-
34
Carburized)
4.2
Un-carburized specimen condition after tensile test
35
4.3
Graph of Tensile Test for Compact Specimen
36
(Carburized)
4.4
Carburized specimen condition after tensile test
37
4.5
Un-carburized specimens after fatigue pre-cracking test
39
and ready for fracture toughness test.
4.6
Graph of fracture toughness for un-carburized
41
specimen #1
4.7
Graph of fracture toughness for un-carburized
specimen #2
41
4.8
Un-carburized specimens after fracture toughness test
42
4.9
Compact Specimen (CT) Standard Proportions
42
(Source: ASTM E399, 1997)
4.10
Graph of fracture toughness for carburized specimen 1
45
4.11
Graph of fracture toughness for carburized specimen 2
45
4.12
Carburized specimens after fracture toughness test
46
5.1
Specimens after fracture toughness
51
5.2
Comparison of curves for ductile and brittle materials:
52
(a) ductile material; (b) brittle material
(Source: J.W. Fisher, 1984)
5.3
Result of tensile test: (a) un-carburized specimen;
52
(b) carburized specimens
5.4
Specimen holder
54
LIST OF SYMBOLS
a
=
Crack Length, mm
B
=
Specimen Thickness, mm
E’
=
Effective Young’s Modulus, Pa (psi)
KI
=
Stress Intensity Factor, MPa.m1/2
KIC
=
Plane-Strain Fracture Toughness, MPa.m1/2
KIC (t)
=
Rapid Load Plane-Strain Fracture Toughness, MPa.m1/2
KQ
=
Fracture Toughness, MPa.m1/2
P
=
Specific Load, klbf (kN)
Pmax
=
Maximum load that specimen able to sustain, klbf (kN)
RSC
=
Specimen Strength Ratio
Tx
=
Temperature of Rapid Load Toughness Test, K
t
=
Loading Time, ms
=
Crack Mouth Opening Displacement, mm
=
Poisson Ratio
F
=
Fracture Stress, MPa
YD
=
Dynamic Yield Strength, MPa
YS
=
Yield Strength, MPa
Vm
LIST OF APPENDICES
NO.
TITLE
PAGE
A
ASTM Standard Related to Fracture Mechanics
59
B
Standardized codes for specimen configurations and
60
applied load
C
Principal Types of Load-Displacement Records
D
Fractograph
of
ductile
cast
iron
showing
61
a
62
transgranular fracture surface
E
F
Fractograph of an intergranular fracture surface
K Calibrations for Typical Test Specimen Geometries
63
64
1
CHAPTER I
INTRODUCTION
1.1
An Overview on Analysis
This thesis systematically investigates the effect on fracture toughness of
Low Carbon Steel with and without carburizing. In order to run the analysis and
from the previous research done, Carbon Steel; type AISI 1020) is the most suitable
material that can be used for the testing to get the result. By using compact specimen
followed with ASTM standard, testing will be conducted in two conditions; with and
without carburization. Using ASTM E399 as a guide, Plane Strain Fracture
Toughness experiment using compact specimen will be carried out in order to obtain
the necessary information for the analysis.
In materials science, fracture toughness is a property which describes the
ability of a material containing a crack to resist fracture, and is one of the most
important properties of any material for virtually all design applications. It is
denoted as K1c.The subscript '1c' denotes mode 1 (crack opening; ordinary strain),
since the material can be made thick enough to resist shear (mode 2) or tear (mode
3). Fracture toughness is a quantitative way of expressing a material's resistance to
brittle fracture when a crack is present. If a material has a large value of fracture
toughness it will probably undergo ductile fracture. Brittle fracture is very
characteristic of materials with a low fracture toughness value.
2
Fracture occurs when the metal experiences stress that exceeds its yield
strength. Fractures occur as two different types, ductile fracture and brittle fracture.
Brittle fracture occurs when the metal doesn’t yield before it breaks. Instead of the
sheets of atoms in the metal sliding over each other as occurs in deformation, when
stressed, the sheets of atoms pull completely apart. This type of fracture most often
occurs in metals that are extremely hard. Brittle fracture almost always occurs at low
temperatures. Ductile fracture is the most common type of fracture in metal. Unlike
what occurs in a brittle fracture, the metal yields before it breaks in a ductile
fracture. The peak stress a metal can withstand before it breaks is called tensile
strength. Ductile fracture is caused by the stress exerted on the metal actually work
hardening the metal as it yields, cracks from fatigue develop, and then these cracks
propagate very rapidly through the metal until complete failure occurs
1.2
Objective and Approach
The main objectives of this analysis are:
I.
To analyze the effect on fracture toughness on Low Carbon Steel in two
condition; (1) with carburizing and (2) without carburizing.
II.
To compare the effect on fracture toughness between carburizing and
without carburizing.
The fracture toughness testing procedures specified in ASTM Standard No.
E399 will be used. Ten compact specimens of nominal thickness 25mm will be
tested. Each sample contains a notch, or 'machined crack'. At the tip of the notch a
true crack has been produced by repeatedly loading (fatiguing) the specimen.
3
1.3
Scope of Analysis
In this analysis, there are three major scopes needs to be considered in order
to achieve the objectives of analysis.
Specimen preparation is the first step of analysis. There will be 10 specimen
needs to be prepared for this analysis. Dimensions and tolerances of the specimen
will be followed by ASTM Standard for compact specimen dimension. Material that
will be used for this analysis is AISI 1020 carbon steel that is the most suitable
specification of low carbon steel.
Carburizing process of the specimen will be conducted before the testing.
Only five (5) specimens will be carburized for testing while another five (5)
specimens will be used without carburizing. The method of carburizing will be
conducted using pack carburization method.
Testing method will be conducted using ASTM Standard Test Method for
Plain-Strain Fracture Toughness. Testing will be conducted in two different
conditions; (1) without carburizing, and (2) with carburizing. Then the result on both
conditions is to be analyzed to compare between both conditions.
4
CHAPTER II
LITERATURE REVIEW
2.1
Overview on Fracture Toughness
Fracture toughness is an indication of the amount of stress required to
propagate a preexisting flaw. It is a very important material property since the
occurrence of flaws is not completely avoidable in the processing, fabrication, or
service of a material/component. Flaws may appear as cracks, voids, metallurgical
inclusions, weld defects, design discontinuities, or some combination thereof. Since
engineers can never be totally sure that a material is flaw free, it is common practice
to assume that a flaw of some chosen size will be present in some number of
components and use the linear elastic fracture mechanics (LEFM) approach to
design critical components. This approach uses the flaw size and features,
component geometry, loading conditions and the material property called fracture
toughness to evaluate the ability of a component containing a flaw to resist fracture.
(from NDT Resource Center, 2001)
A parameter called the stress-intensity factor (K) is used to determine the
fracture toughness of most materials. A Roman numeral subscript indicates the
mode of fracture and the three modes of fracture are illustrated in Figure 2.1. Mode I
fracture is the condition in which the crack plane is normal to the direction of largest
tensile loading that is indicates testing in which a tensile stress causes the crack to
open. This is the most commonly encountered mode and, therefore, for the
remainder
of
the
material
Figure 2.1). (from R.J Sanford, 2003)
will
be
consider
as
KI
(refer
5
Stress intensity factor, KIc is the most often used engineering
design parameter.
Opening or tensile mode where the crack surfaces move directly
apart.
Tearing and anti-plane shear mode where the crack surfaces
move relative to one another and parallel to the leading edge of
the crack.
Mode-I
Mode-II
Mode-III
Figure 2.1: Load types for Modes of Fracture
(Source: R.J Sanford, 2003)
Table 2.1: Typical Fracture-Toughness Values for Selected Engineering Alloys
(Source: R.W. Herzberg, 1989)
Material
KIC
yield strength
Aluminium alloys;
2024-T851
26.4
24
455
66
7075-T651
24.2
22
495
72
7178-T651
23.1
21
570
83
55
50
1035
150
4340 (low alloy steel)
60.4
55
1515
220
17-7pH(precipitation hardening)
76.9
70
1435
208
55
50
1550
225
Titanium alloy;
Ti-6A1-4V
Alloy steels;
350 maraging steel
6
Fracture toughness values of material are most useful in mechanical design
when working with materials of limited toughness or ductility such as high-strength
aluminum, steel and titanium alloys. Table 2.1 lists KIC values for some of these
alloys. Material that show little plastic deformation before fracture have relatively
low fracture toughness, KIC values and tend to be more brittle, whereas those with
higher KIC values are more ductile. Fracture toughness values can be used in
mechanical design to predict the allowable flaw size in alloys with limited ductility
acted upon by specific stresses. (from R.W. Herzberg, 1989)
2.1.1
Toughness
The ability of a metal to deform plastically and to absorb energy in the
process before fracture is termed toughness. The emphasis of this definition should
be placed on the ability to absorb energy before fracture. Recall that ductility is a
measure of how much something deforms plastically before fracture, but just
because a material is ductile does not make it tough. The key to toughness is a good
combination of strength and ductility. A material with high strength and high
ductility will have more toughness than a material with low strength and high
ductility. Therefore, one way to measure toughness is by calculating the area under
the stress strain curve from a tensile test. This value is simply called “material
toughness” and it has units of energy per volume. Material toughness equates to a
slow absorption of energy by the material.