EFFECT OF SIZE OF BOLT ON THE RELATIVE CRITICAL...
Transcript of EFFECT OF SIZE OF BOLT ON THE RELATIVE CRITICAL...
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EFFECT OF SIZE OF BOLT ON THE RELATIVE CRITICAL SLIPPAGE OF
BOLT-NUT JOINT UNDER TRANSVERSE LOADING
AHMAD SHAHRIL BIN RAZALI
This Report Is Submitted In Partial Fulfillment of Requirements For the
Bachelor of Mechanical Engineering (Structure & Materials) with Honor
Faculty of Mechanical Engineering
Universiti Teknikal Malaysia Melaka
MEI 2011
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SUPERVISOR DECLARATION
“I hereby declare that I have read this thesis and in my opinion this report is sufficient in
terms of scope and quality for the award of the degree of Bachelor of Mechanical
Engineering (Stricture Materials)”
Signature: ...................................
Supervisor 1 :HAIRUL BIN BAKRI
Date: ...................................
Signature: ...................................
Supervisor 1 :NADLENE BINTI RAZALI
Date: ...................................
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DECLARATION
“I hereby declare that the work in this report is my own except for summaries and
quotations which have been duly acknowledged.”
Signature :...................................
Author : AHMAD SHAHRIL BIN RAZALI
Date : ...................................
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Special for
My lovely Mom and Dad
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ACKNOWLEGEMENT
Assalammualaikum and Salam Satu Malaysia
Thanks to Allah, for giving me permission to complete this project. In here I
would like to record my graceful thank to all the support, encouragement and
inspirations that I have received during completing this project.
I would like to express greatest thankful and appreciation to my supervisor, Mr.
Hairul Bin Bakri of which we had a good working relationship, and who had offered me
a wonderful help and encouragement. He also gives me full of support and advice.
I also would like to express my gratitude to technician for Faculty of Mechanical
Engineering for giving me his cooperation and help in order to complete this project.
Last but not least to my family and all my fellow friends, for their concern,
encouragement and understanding.
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ABSTRACT
The thread joint has been frequently used for the efficient productivity and
maintainability as a machine element. However, many troubles such as loosening of
bolted joints or fatigue failure of bolt were often experienced. Many attentions must be
paid on the improvement of the strength and the reliability of the thread joints. It is
generally said that the fastening axial force rapidly decreases by the rotation loosening
of nuts if the relative slippage on the interfaces between nuts and fastened body goes
beyond a certain critical limit. This critical relative slippage (Scr) that prescribes the
upper limit for preventing the loosening behavior has been estimated according to the
theoretically obtained equation considering the bending deformation of bolt and the
geometrical constraint condition. In this paper, firstly is to provide the database for
Finite Element Analysis (FEA). Then, the experimental method is to determine the Scr.
After that, the behavior effect of the size bolt was determined and analyzes the result.
From the result, it can be confirmed with good agreement with calculation coincided
well with the experimental result.
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ABSTRAK
Sendi bebenang telah sering digunakan untuk produktiviti cekap dan kestabilan
sebagai unsur mesin. Namun, banyak masalah seperti melonggarnya sendi baut atau
kegagalan kelelahan baut sering dialami. Banyak perhatian perlu dibayar pada
peningkatan kekuatan dan kebolehpercayaan dari sendi benang. Hal ini umumnya
mengatakan bahawa gaya paksi pengikatan cepat berkurang oleh melonggarkan putaran
kacang jika selip relatif pada antara muka antara kacang dan tubuh diikat melampaui
batas kritis tertentu. Selip ini relatif kritis (Scr) yang mengatur batas atas untuk
mencegah perilaku melonggarkan telah dijangka berdasarkan persamaan teori diperolehi
mengingati deformasi lentur dari baut dan keadaan sekatan geometri. Dalam makalah
ini, pertama adalah untuk menyediakan database untuk Analisis Elemen Hingga (FEA).
Kemudian, kaedah eksperimental untuk menentukan Scr. Setelah itu, kesan perilaku dari
baut saiz ditentukan dan analisis hasilnya. Dari hasil tersebut, dapat disahkan dengan
perjanjian baik dengan perhitungan bertepatan dengan baik dengan keputusan
eksperimen.
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CONTENTS
CHAPTER TITLE PAGE
SUPER VISOR DECLARATION ii
DECLARATION iii
DEDICATION iv
ACKNOWLEDGEMENT v
ABSTRACT vi
ABSTRAK vii
CONTENTS viii
LIST OF TABLES xi
LIST OF FIGURES xii
LIST OF SYMBOLS xiv
CHAPTER I INTRODUCTION 1
1.1 Background 1
1.2 Problem Statement 2
1.3 Objective 2
1.4 Scopes 3
1.5 Project Outline 3
CHAPTER II LITERATURE REVIEW 5
2.1 Introduction 5
2.2 Theory of Bolt-Nut Joint 5
2.3 Bolts under Flange Separation 6
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CHAPTER TITLE PAGE
2.4 Bolt under Flange Compression 7
2.5 Transverse Direction 8
2.6 Loosening Behavior of Bolt-Nut Joint 8
2.7 Critical Relative Slippage 10
2.8 Mechanics of Bolt-Nut Joints 10
2.9 Derivations and Equation 12
2.10 Standard of Bolt 14
2.11 Drill Press 14
2.11.1 Using a Center Finder 16
2.11.2 Drilling a Hole 16
2.11.3 Deburring a Hole 17
2.11.4 Reaming a Hole 17
2.11.5 Tapping a Hole 17
CHAPTER III METHODOLOGY 19
3.1 Introduction 19
3.2 Preparation of Specimen 19
3.2.1 Preparation for Bolt 21
3.3 Calibration 22
3.3.1 Calibration data 26
3.3.2 Discussion on Calibration 28
3.4 Experimental Method 29
3.4.1 Material and Equipment 30
CHAPTER IV ANALYSIS GRAPH AND RESULT 31
4.1 Introduction 31
4.2 Static Test 31
4.2.1 Static Test for Bolt Size M10 32
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CHAPTER TITLE PAGE
4.2.2 static test for bolt size M16 34
4.3 fatigue test 35
4.3.1 fatigue test for bolt size M10 35
4.3.2 fatigue test for bolt size M16 41
CHAPTER V DISCUSSION 48
5.1 introduction 48
5.2 discussion on static test 48
5.3 discussion on fatigue test 50
CHAPTER VI RECOMMENDATION AND CONCLUSION 53
6.1 conclusion 53
6.2 recommendation 54
REFERENCE 55
APPENDIX 59
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LIST OF TABLE
NO TITLE PAGE
2.1 Standard of Bolt 14
3.1 Table of Plate and Bolt Size 20
3.2 Table of Dimension Plate 21
4.1 Table Of Point ∆Scr For Bolt M10 in Static Test 33
4.2 Table Of Point ∆Scr For Bolt M16 in Static Test 35
4.3 Table of loosing rate for axial force 4kN for bolt size M10 38
4.4 Table of loosing rate for axial force 6kN for bolt size M10 39
4.5 Table of loosing rate for axial force 8kN for bolt size M10 39
4.6 Table of loosing rate for axial force 10kN for bolt size M10 39
4.7 Table of loosing rate for axial force 12kN for bolt size M10 40
4.8 Table of Point ∆Scr for bolt M10 in fatigue test 41
4.9 Table of loosing rate for axial force 15kN for bolt size M16 44
4.10 Table of loosing rate for axial force 20kN for bolt size M16 45
4.11 Table of loosing rate for axial force 25kN for bolt size M16 45
4.12 Table of loosing rate for axial force 30kN for bolt size M16 45
4.13 Table of loosing rate for axial force 35kN for bolt size M16 46
4.14 Table of Point ∆Scr for bolt M16 in fatigue test 47
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LIST OF FIGURES
NO TITLE PAGE
2.1 Bolt-Nut Joint 6
2.2 Flange Separation 6
2.3 Flange Compression 7
2.4 Transverse Coupled at Flange Joint 8
2.5 Critical Relative Slippage 10
2.6 Behavior of the bolt-nut joint in different load condition 11
2.7 Deflection of Bolt from Transverse Loading 12
2.8 Drill Press 15
2.9 Type of Tapper 18
3.1 Example of Plate 20
3.2 Bolts with a Hole 22
3.3. Bolts with Strain Gauge 23
3.4 Calibration of Displacement 24
3.5 Example of graph Strain Vs Load 24
3.6 Example of Graph Displacement Vs Strain 25
3.7 Apparatus Set Up 26
4.14 Table of Point ∆Scr for bolt M16 in fatigue test 29
4.2 graph load versus strain for bolt M16 30
4.3 graph load versus strain for bolt M20 31
4.4 Graph of load (N) versus Relative slippage (mm)
for M10 in Static Test 32
4.5 Graph of load (N) versus Relative slippage (mm)
for M16 in Static Test 34
4.6 Graph of axial force versus number of cycle for M10 (4kN) 36
NO TITLE PAGE
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4.7 Graph of axial force versus number
of cycle for M10 (6kN) 36
4.8 Graph of axial force versus number
of cycle for M10 (8kN) 37
4.9 Graph of axial force versus number
of cycle for M10 (10kN) 37
4.10 Graph of axial force versus number
of cycle for M10 (12kN) 38
4.11 Graph of dFb/dN Vs relative displacement for M10 40
4.12 Graph of axial force versus number
of cycle for M16 (15kN) 42
4.13 Graph of axial force versus number
of cycle for M16 (20kN) 42
4.14 Graph of axial force versus number
of cycle for M16 (25kN) 43
4.15 Graph of axial force versus number
of cycle for M16 (30kN) 43
4.16 Graph of axial force versus number
of cycle for M16 (35kN) 44
4.17 Graph of dFb/dN Vs relative displacement for M60 46
5.1 Graph of initial load (kN) versus point
of ∆Scr (mm) for bolt M10in static test. 49
5.2 Graph of initial load (kN) versus point
of ∆Scr (mm) for bolt M16 in static test 50
5.3 Graph of initial load (kN) versus point
of ∆Scr (mm) for bolt M10 in fatigue test 51
5.4 Graph of initial load (kN) versus point
of ∆Scr (mm) for bolt M16 in fatigue test 51
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LIST OF SYMBOLS
NOTATION DESCRIPTION
Scr Critical Relative Slippage
E Young Modulus of bolt
Ig Second Moment of Area of Bolt’s Cylindrical Portion
Ip Second Moment of Area of Thread Portion
𝜇𝑏 Coefficient Friction of Bolt Bearing Surface
𝑘𝑤 Bolt Head’s Inclination Compliance
W Load
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CHAPTER I
INTRODUCTION
1.1 Background
Bolt-nut joint, one of the joint structures is widely used as it’s easiness to install
and remove, produces big fastening power with small force and low price in
production. Disadvantage of bolt-nut, when vibration and thermal load applied to the
thread joint, bolt will lose and fastening became unsustainable. In FE method,
substitute for a simplified and accurate numerical model to predict load share on
every joint. So, this method can investigated the results of the sliding and loosening
behaviour and bending moment at the bolt neck which are the critical relative
slippage Scr and bending moment of bolt.
There have 2 type of load acting which is tensile load and transverse load.
Tensile load is line of forces is parallel to axes of the bolt. Transverse load is line of
action forces is perpendicular to the axes of the bolt. From other research, transverse
load loosen to the bolt-nut joint more than tensile load.
The problem occurs is bolt-nut is model as unit and thread of bolt and nut do not
exist at the corresponding portion. This problem can simplify presume that relative
between fastened plates. In order to predict the sliding behaviour and relative critical
slippage, consideration of clearance between bolt and nut thread surface must be
made. The bending moment stress needs to be considered due to fatigue failure. The
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new model must be considered both critical relative slippage and bending moment
generated at the bolt neck.
The loosening behaviour of bolt-nut joint shows the same occurrence if the
transverse load applied in the opposite direction. The axial tension will decrease
when transverse cyclic load applied to the joint. At the worst stage, fatigue failure
also will occur.
In this project, firstly we present the equation for estimating the Scr based on the
fundamental cantilever deformation model. Then we present the investigated results
of the deformation behaviour of bolt-nut joint under transverse loading condition
considering the reaction moment by nut. Finally, we can confirm that these estimated
results of critical relative slippage coincided well with the experimental results.
1.2 Problem Statement
When vibration and thermal load applied to the thread joint, bolt loosening
occurs which lead to failure of the joint. There were analysis had been done by using a
CAE software which is low cost and can shorten analysis time. However many of the
joints were analyze with the CAE simulation recently but the method was insufficient.
This is because the mechanical property for database for bolted joint is not sufficient.
Furthermore the reliability of the CAE analysis database cannot be used in order to study
the effect. The database for the CAE can be provide by using experimental method in
order to study the effect of length of bolt nut joint under critical slippage.
1.3 Objective
Objective of this study is to find the effect of size of bolt on the relative critical
slippage, ∆Scr of bolt-nut joint/fastener experimentally. Second, Provide database for
CAE analysis to make a comparison at the end of the study.
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1.4 Scopes
Scopes of this study are:
1. Literature review on deformation behavior of bolt-nut joint under transverse
loading.
2. Design and conduct experiment to obtain ∆Scr for various size of bolt.
3. Investigate and conclude the effect of size of bolt on ∆Scr when transverse
load applied to the joint.
1.5 Project Outline
Chapter 2 is the literature review for this project. This chapter will describe the
theory of bolt-nut loosening behavior and others. All materials that used in this project
will completely explain to give more understanding about this project.
Chapter 3 would describe the method and procedures that used for this project
experiment. This chapter includes the study of preparation for the specimen, calibration
the apparatus and lastly is study about the experimental method.
Chapter 4 is includes the analysis and result. This chapter will introduce the
result and study to find the effect of size of bolt on the relative critical slippage, ∆Scr.
The graph will shown the result about the ∆Scr.
Chapter 5 is the result and discussion. This chapter will discuss about the result
from the chapter 4 and provide this experimental data for data base for CAE analysis.
And then, compare the result between experimental and CAE analysis.
Chapter 6 is the conclusion and recommendation of this project. This chapter will
concludes all results discussion, decision and also recommendation for the future work
to further this study.
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CHAPTER II
LICTERATURE REVIEW
2.1 Introduction
In this chapter will describe the theory of bolt-nut joint and others. All materials
that used in this project will completely explain to give more understanding about this
project.
2.2 Theory of Bolt-Nut Joint
The bolt-nut joint is a very popular method of fastening components together.
The prime reason for selecting bolts as opposed to welding, or rivets are that the
connection can be easily released allowing disassembly, maintenance and/or inspection.
The bolts are generally used in groups to fasten plates together. A bolt is a screwed
fastener with a head, designed to be used with a nut. A screw is a fastener designed to
be used with a formed female thread in one of the components being attached. These
notes generally relate to bolts and nuts and hex headed screws
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Figure 2.1 Bolt-Nut Joint
(source: http://www.boltscience.com/pages/nutorbolttightening.htm)
2.3 Bolts under Flange Separation
By Jerome Montgomery(2010), when a load tries to separate a bolted flange
joint, the job of the bolt is to hold the flanges together. The pretension should be more
than the applied load. When the applied load exceeds the pretension, the part will
separate. From a simulation standpoint, the surfaces that are in contact must be able to
separate. This is where the contact elements are used. For bolt under flange separation,
the contact elements are not required for the contact surface between flange and head/nut
of the bolt. These surfaces can be glued together. That is, the head contact can share the
same surface as the top flange, and the nut contact can share the same surface as the
bottom flange. The contact elements are required at the horizontal joint between the top
and the bottom flange.
Figure 2.2 Flange Separation
(source: Jerome Montgomery(2010) )
Bolt
Nut
Flange
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2.4 Bolts under Flange Compression
By Jerome Montgomery(2010), when a flange is under compression, there is no
load on the bolt. In this case, the head and nut contact must be able to separate from the
flanges, whereas, the horizontal joint contact can share the same surface. The surfaces
where the top flange and bottom flange meet (horizontal joint contact surface) can be
glued together. Due to non-linear effects of contact elements, the above approach will
help in saving considerable computation time during the solution phase.
Figure 2.3 Flange Compression
(source: Jerome Montgomery (2010))
2.5 Transverse Direction
By Jerome Montgomery(2010), to incorporate the transverse effects of the bolt
when two mating surfaces slide, a node at the bolt near the horizontal joint, and a node at
the two mating surfaces are coupled to each other. Friction resists loads in the transverse
direction. If we assume that the direction from the head to the nut is the vertical direction
Z, then the transverse direction would be the direction X and direction Y. In solid
models, the transverse loads are transferred from the bolt head/nut to the bolt. In non-
solid head/nut simulations, other means are used to account for the transverse load as
described later. Figure 7 shows the case with a solid head/nut assuming friction is
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ignored. To account for the transverse load, a node from the line element of the stud is
coupled to a node from the top flange and the bottom flange.
Figure 2.4 Transverse Coupled at Flange Joint
(source: Jerome Montgomery (2010))
2.6 Loosening Behavior of Bolt-Nut Joint
A significant advantage of a bolted joint over other joint types, such as welded
and riveted joints, is that they are capable of being dismantled. This feature however,
can cause problems if it unintentionally occurs as a result of operational conditions.
Such unintentional loosening, frequently called vibration loosening in much of the
published literature, is an important phenomenon and is widely misunderstood by
engineers. It is important for the designer to be aware of the bolt loosening mechanisms
which can operate in order to design reliable joints.
Study of most engineering magazines will reveal the multitude of proprietary
locking mechanisms available for fasteners. For the designer without the theoretical
knowledge of why fasteners self loosen, this represents a bewildering choice. Presented
below is key information, for the designer, on why fasteners self loosen, and, how it can
be prevented. It is widely believed that vibration causes bolt loosening. By far the most
frequent cause of loosening is side sliding of the nut or bolt head relative to the joint,
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resulting in relative motion occurring in the threads. If this does not occur, then the bolts
will not loosen, even if the joint is subjected to severe vibration. By a detailed analysis
of the joint it is possible to determine the clamp force required to be provided by the
bolts to prevent joint slip.
Often fatigue failure is a result of the bolt self-loosening which reduces the
clamp force acting on the joint. Joint slip then occurs which leads the bolt being
subjected to bending loads and subsequently failing by fatigue.
Pre-loaded bolts (or nuts) rotate loose, as soon as relative motion between the
male and female threads takes place. This motion cancels the friction grip and originates
an off torque which is proportional to the thread pitch and to the preload. The off torque
rotates the screw loose, if the friction under the nut or bolt head bearing surface is
overcome, by this torque. There are three common causes of the relative motion
occurring in the threads:
1. Bending of parts which results in forces being induced at the friction surface. If slip
occurs, the head and threads will slip which can lead to loosening.
2. Differential thermal effects caused as a result of either differences in temperature or
differences in clamped materials.
3. Applied forces on the joint can lead to shifting of the joint surfaces leading to bolt
loosening.
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2.7 Critical Relative Slippage
The critical relative slippage (Scr) that prescribes the upper limit for preventing
the loosening behavior has been estimated according to the theoretically obtained
equation considering the bending deformation of bolt and the geometrical constraint
condition. Equation for estimating the (Scr) is based on the fundamental cantilever
deformation model. From the investigate results, the behavior of bolt-nut joint under
transverse loading by considering the reaction moment by nut (Mn). To confirm the
estimated result of critical slippage coincided well with the experimental result.
Figure 2.5 Critical Relative Slippage
(Source: Yamashita et al. 2010)
2.8 Mechanics of Bolt-Nut Joints
From Yamashita et al. 2010, the sliding behavior of bolt-nut joint and reverse
rotation of nut under transverse load is showed in Fig. 2.5. The deformation behavior of
bolt-nut joint is depends on the amount of transverse load level applied on the joint. In
figure 3 (a), the load, W is low, bolt and fastened components (fixed plate and movable
plate) are deformed. There is no slip occur at the bolt and nut bearing surface. The slip
occur only at the contact surface between fixed plate and movable plate when W
exceeded the frictional force (Where frictional force = number of bolts, n × friction
coefficient, µ × initial axial tension, Fb) is given to the joint. However, in Figure 3(b)
when relative displacement, S between upper and lower plate is still small, by the
bending deformation of the bolt, sliding at the bolt and nut bearing surface is not occur.
Then, load and relative displacement between plates increased and at one stage (relative
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displacement exceeded ΔS (Fig. 3(c)), slip is also occurs at the bolt and nut bearing
surface. This slip leads to the reverse rotation of the nut and decrease the axial tension.
The loosening behavior of bolt-nut joint shows the same occurrence if the transverse
load applied in the opposite direction. When transverse cyclic load applied to the joint,
bolt axial tension slowly decreases and at the worst stage, not only loosening occurs but
also the fatigue failure of the bolt. So, it is important to evaluate both loosening behavior
and fatigue failure of the bolt-nut joint.
Figure 2.6 Behavior of the bolt-nut joint in different load condition.
(Source: Yamashita et al. 2010)