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STRENGTH INVESTIGATION ON RESISTANCE SPOT WELDING OF LOW
CARBON STEEL AND STAINLESS STEEL
MOHD NUR SYAFFIQ BIN MAHMOOD
A report submitted in partial fulfillment of the requirements
for the award of the degree of
Bachelor of Mechanical Engineering
Faculty of Mechanical Engineering
UNIVERSITI MALAYSIA PAHANG
JUNE 2013
vii
ABSTRACT
Resistance spot welding (RSW) had been widely used in automotive industry; because
of their advantages easily to process and low cost, high speed and high production,
suitability for automation. About 2000-7000 spot welds were used in joining modern
vehicles. This project deals with the investigation of failure mode and mechanical
properties of weld joint of low galvanized steel and stainless Steel. The main objective
of this project is strength investigation using RSW of low carbon steel and stainless
steel. For design of experiment, Taguchi method was employed by using Minitab
software, and total nine sets experiment with 3 type of parameter (current, squeeze time,
pressure) were conducted. The studies of mechanical properties, are consists of various
tests; Tensile test, Coach Peel test, Hardness test, microstructure to analyze and
investigate the weldability of galvanized Steel and stainless Steel sheet. Visual
inspection was done to determine the failure mode of the spot welding. As a result,
tensile test have larger strength variation than the coach-peel test. Wider width and
depth of weld nugget affect the weldability of the welding. Different parameters were
obtained for optimum parameter for tensile test and coach peel test by using Taguchi
method. Almost pullout failure mode occurs where failure at heat affected zone (HAZ)
around the nugget circumference.
viii
ABSTRAK
Kimpalan rintangan spot telah digunakan secara meluas dalam industri automotif kerana
kelebihan mereka mudah untuk di proses dan kos yang rendah, kelajuan yang tinggi dan
pengeluaran yang banyak, kesesuaian untuk automasi. Lebih kurang 2000-7000
kimpalan spot telah digunakan untuk pencantuman kenderaan moden. Projek ini
meliputi penyiasatan mod kegagalan dan sifat-sifat mekanik sambungan kimpalan keluli
tergalvani rendah dan keluli tahan karat. Objektif utama projek ini adalah siasatan
kekuatan menggunakan kimpalan rintangan spot kepada keluli karbon rendah dan keluli
tahan karat. Bagi procedure eksperimen, kaedah Taguchi telah bekerja dengan
menggunakan perisian Minitab, dan jumlah eksperimen sebanyak sembilan set dengan 3
jenis parameter (arus, masa tekanan, tekanan) telah dijalankan. Kajian sifat-sifat
mekanik, yang terdiri daripada pelbagai ujian iaitu ujian tegangan, ujian pengupasan
coach, ujian kekerasan, mikrostruktur untuk menganalisis dan menyiasat kebolehan
kimpalan kepingan keluli tergalvani dan keluli tahan karat. Pemeriksaan visual telah
dijalankan untuk menentukan mod kegagalan kimpalan. Hasilnya, ujian tegangan
mempunyai kekuatan lebih besar daripada ujian pengupasan ‘Coach’. Keluasan lebar
dan ke dalam spot kimpalan menjejaskan kebolehan kimpalan. Parameter yang berbeza
diperolehi untuk mendapatkan parameter optimum untuk ujian tegangan dan ujian
pengupasan coach dengan menggunakan kaedah Taguchi. Kebanyakan mod kegagalan
berlaku ialah penarikan di mana kegagalan di zon terjejas haba di lilitan spot kimpalan.
ix
TABLE OF CONTENT
Page
EXAMINER'S DECLARATION Error! Bookmark not defined.
SUPERVISOR’S DECLARATION ii
STUDENT’S DECLARATION iv
ACKNOWLEDGEMENT vi
ABSTRACT vii
ABSTRAK viii
TABLE OF CONTENT ix
LIST OF FIGURES xii
LIST OF TABLES xiv
LIST OF EQUATIONS xv
LIST OF ABBREVIATIONS xvi
CHAPTER 1 INTRODUCTION
1.1 Research Background 1
1.2 Problem Statement 2
1.3 Objective 2
1.4 Scope Of Research 2
CHAPTER 2 LITERATUREREVIEW
2.1 Introduction 3
2.2 Dissimilar Welding 3
2.3 Resistance Welding 4
x
2.4 Principles Of Resistance Spot Welding 5
2.5 Spot Welds Parameters 6
2.5.1 The Parameters In Resistance Spot Welding 6
2.5.1.1 Welding Current 8
2.5.1.2 Weld Time 10
2.5.1.3 Squeeze Time 10
2.5.1.4 Hold Time 10
2.6 Material Selection 11
2.6.1 Galvanized Steel 11
2.6.2 Stainless Steel 12
2.7 Mechanical Test 12
2.7.1 Failure Mode 13
CHAPTER 3 METHODOLOGY
3.1 Introduction 15
3.2 Justification 15
3.3 Methodology 15
3.4 Work Piece And Materials 17
3.4.1 Preparing Material By Using Shearing Machine 17
3.4.2 Preparing Material For Coach Peel Test 18
3.5 Spot Welding Machine 20
3.6 Preliminary Testing 24
3.7 Tensile-Shear Test 26
3.8 Coach Peel Test 26
3.8.1 The Tensile Testing 26
3.8 Microhardness Test 29
3.9 Designing Parameter Of Experiment 31
xi
CHAPTER 4 RESULTS AND DISCUSSION
4.1 Introduction 33
4.2 Tensile Shear Test 33
4.2.1 The Tensile Shear Strength Graphs 34
4.2.2 Analysis Of Taguchi Method 35
4.3 Coach Peel Test 41
4.3.1 The Coach Peel Strength Graphs 41
4.3.2 Analysis Of Taguchi Method 43
4.4 Confirmation Experiment 48
4.4.1 Tensile Shear Test 48
4.4.2 Coach Peel Test 50
4.5 Microstructure View 51
4.5 Failure Mode 53
4.5.1 Failure Mode In Tensile Shear Test 54
4.5.2 Failure Mode In Coach Peel Test 55
4.6 Hardness Test 56
CHAPTER 5 CONCLUSION AND RECOMMENDATIONS
5.1 Conclusion 58
5.2 Recommendations 58
REFERENCES 60
APPENDICES 65
A Gantt Chart 66
B Gantt Chart FYP 2 67
C Repairing RSW Tongs Tip 68
xii
LIST OF FIGURES
Figure No. Tittle Page
2.1 Macrostructure of dissimilar RSW between stainless steel and
galvanized steel 4
2.2 Resistance Spot Welding Machine with workpiece 5
2.3 Schematic of the Resistance Spot Welding process 6
2.4 Procedure of RSW 7
2.5 Effect of welding current on the weld nugget growth: a) 8kA
b) 9 kA c) 10 kA d) 11 kA e) 11 kA 9
2.6 Effect of welding current on the FZS of GS and SS side 9
2.7 Welding Time Cycle 11
2.8 Load direction and failure mechanism of interfacial mode;
(a) pulling force direction, (b) material failure 13
2.9 Load direction and failure mechanism of pullout mode;
(a) force direction, (b) material failure at nugget circumference 14
3.1 Methodology Flow Chart 16
3.2 LVD shearing machine 17
3.3 Bending Process by using Bending Machine 18
3.4 Dimension of specimen for Tensile Test 19
3.5 Dimension for Coach Peel Test 19
3.6 Miller Spot Welder 20
3.7 Control Panel 21
3.8 Pressure Gauge 22
3.9 Lap Joint Welding 23
3.10 Coach Peel Joint Welding 23
3.11 Welded sample spot 1-5; (a) Galvanized Steel view (b) Stainless
Steel view 24
3.12 Welded sample spot 6-13; (a) Galvanized Steel view (b) Stainless
Steel view 25
3.13 Shimadzu Tensile Test Machine 27
3.14 Coach Peel Test 28
xiii
3.15 Load–displacement curve of spot welds during tensile shear test 28
3.16 Schematic of Vickers hardness test 30
3.17 Hardness level along the horizontal distance from nugget of
galvanized steel and stainless steel 31
4.1 Tensile Shear Test Stress vs Strain 34
4.2 Bar Graph (Force) N 35
4.3 Main Effects Plot for Means 39
4.4 Main Effects Plot for S/N Ratios 40
4.5 Coach Peel Test Stress vs Strain 42
4.6 Bar Graph (Force) N 42
4.7 Main Effects Plot for Means 46
4.8 Main Effects Plot for S/N Ratios 47
4.9 Stress vs Strain Graph Optimization Test in terms of Tensile
Shear Test 49
4.10 Stress vs Strain Graph Optimization Test in terms of Coach
Peel Test 51
4.11 Specimen F (6 kA, 4.0 cycle, 35 Psi) under 5X magnification 52
4.12 Specimen B (5 kA, 3.5 cycle, 40 Psi) under 5X magnification 52
4.13 Interfacial Failure Mode: Sheet is pulled and fracture initiate
from the centre of the nugget 53
4.14 Pullout Failure Mode: parent metal where one sheet is punctured
and other sheet with extended metal 54
4.15 Sample of specimens of different current input; (a): 5 kA,
(b): 6 kA, (c): 7 kA 54
4.16 4 specimens of different parameter; Specimen C, Specimen E,
Specimen H, Specimen I 55
4.17 Point of Hardness Measurement 56
4.18 Hardness Profile of SS and GS of Specimen E 56
xiv
LIST OF TABLES
Table No. Tittle Page
3.1 Setting Table 18
3.2 Chemical composition of Stainless Steel (SS) and Galvanized Steel
(GS)(wt.%) 19
3.3 Sample Spot Numbering and Parameter 24
3.4 Sample Spot Numbering and Parameter 25
3.5 DOE (L9 Orthogonal Array) 32
3.6 Table Design of Experiment 32
4.1 Result obtain from Shimadzu tensile Test Machine 34
4.2 Parameter and Result 36
4.3 S/N Ratio for Tensile Shear Test 37
4.4 Estimated Model Coefficients for Means 38
4.5 Analysis of Variance for Means 38
4.6 Response Table for S/N Ratios 39
4.7 Prediction of Optimize parameter 40
4.8 Result obtain from Shimadzu tensile Test Machine 41
4.9 Parameter and Result 43
4.10 S/N Ratio for Coach Peel Test 44
4.11 Estimated Model Coefficients for Means 45
4.12 Analysis of Variance for Means 45
4.13 Response Table for S/N Ratios 46
4.14 Prediction of Optimize parameter 47
4.15 Comparison between experimental (A~I) and Optimize specimen
(OP) in terms of Tensile Shear Test 48
4.16 Comparison between experimental (A~I) and optimize specimen
(OP) in terms of Coach Peel Test 50
xv
LIST OF EQUATIONS
Equation No.
Title Page
2.1 Heat Generated 6
3.1 Vickers Hardness 28
4.1 S/N Ratio equation 35
4.2 S/N Ratio equation 42
xvi
LIST OF ABBREVIATIONS
RSW Resistance Spot Welding
GS Galvanized Steel
SS Stainless Steel
RSEW Resistance Seam Welding
PW Resistance Projection Welding
DOE Design of Experiment
OA Orthogonal Array
AC Alternating Current
DC Direct Current
LED Light Emitting Diode
S/N Signal-to-Noise
ANOVA Analysis of Variance
FZS Fusion Zone Size
HAZ Heat Affected Zone
BM Base Metal
1
CHAPTER 1
INTRODUCTION
1.1 RESEARCH BACKGROUND
Nowadays, economic and environmental considerations are resulted in research
in the automotive industry to form better designs and material combinations for
reducing vehicle mass, low fuel consumption and the most important is structural
integrity which increases the crashworthiness of vehicles. Typically, there are about an
average of 2000–7000 spot welds in a modern vehicle. In seeking production
optimization, resistance spot welding (RSW) is a key technology because a technique
most widely used for bonding during automotive assembly. Simplicity, fast (low
process time), low cost and automation possibility are among the advantages of this
process. In addition, resistance spot welding does not alter the weight of materials very
much as compared to traditional arc welding (Chao, 2003; Bayraktar et al., 2004; D. J.
Radakovic et al., 2008; Khan et al., 2008; Goodarzi et al., 2009; Pereira et al., 2010;
Mehdi, 2010; Badheka et al., 2010; Charde and Arumugam, 2011; Pouranvari, 2011;
Jung, 2011; Hayat, 2011,2012; Xu, Chen et al., 2012; Hamidinejad et al., 2012).
The project title is “Strength Investigation on Resistance Spot Welding of Low
Carbon Steel and Stainless Steel”. From literature low carbon steel and stainless steel
possess a good combination of mechanical properties, weldability, formability and resist
to corrosion (Kola et al., 2012). Type of low carbon steel in this research is Galvanized
2
Steel. The project research is to obtain the optimize parameter in RSW with good
weldability of the dissimilar welding.
1.2 PROBLEM STATEMENT
Common problems occur in dissimilar metal joining is the parameters setup to
obtain a high strength welded joint (Oba, 2006; Hamidinejad et al., 2012). This happens
because of different thermal conductivity and the different ways in which metals
respond to heat (Hasanbaşoğlu and Kaçar, 2007; Tewari, 2010; Miller, 2012; Xu et al.,
2012). In order to overcome the problem is by controlling RSW parameters, and by
using the DOE for predicting optimize parameter. Despite that RSW of galvanized steel
is difficult because of the zinc coating. The melting point of the zinc coating is lower
than the fusion temperature of the steel sheet This causes the zinc to vaporize and
tendency alloying with the electrode resulting in increased tool wear, and effecting the
weldability (Thakur et al., 2010; Miller, 2012).
1.3 OBJECTIVE
This research is focus on:
i. To control and identify the optimum parameters affecting the weldability.
ii. To investigate and characterize the failure mode of dissimilar resistance spot
welds between galvanized steel and stainless steel.
1.4 SCOPE OF RESEARCH
In order to achieve the objective, it should have proper arrangement of scopes
project.This research is focusing on the strength of resistance spot weld joints of
different parameters (Current, Squeeze Time and Pressure). The welded samples were
all equal size and underwent tensile test, coach peel test and metallurgical testing to
characterize the formation of weld nuggets.
3
CHAPTER 2
LITERATURE REVIEW
2.1 INTRODUCTION
A literature search was performed to study and analysis the resistance spot
welding and self-pierce riveting process. It also includes the investigation of what others
have done in this area.
2.2 DISSIMILAR WELDING
Dissimilar metal welding are common in found in construction where welding is
involve because of their excellent performance to the function of the whole structure.
Dissimilar metal welding involves two or more different metals or alloys joining
together (M. Alenius et al., 2006). In joining two dissimilar metals, several problems
arise, related to the different on physical and mechanical properties, microstructure,
chemical composition, melting point, electrical resistivity, thermal conductivity and
thermal coefficient (Saeed et al., 2010; Kola et al., 2012). Differences in the electrical
resistivity and thermal conductivity of two dissimilar steel in RSW will lead to an
asymmetrical weld nugget in joints (Mehdi, 2010). Figure 2.1 shows the asymmetrical
weld of galvanizes steel and stainless steel.
4
Another common problem in dissimilar welding is an intermetallic compound
(IMC) layer is form (Xu et al., 2012; Liu et al., 2013). It is believed that brittle
intermetallic layers are the main reason for poor dissimilar joint performance because
fatigue failure of dissimilar welds always occurred at the interface where intermetallic
compounds were formed. Which typically have a low critical stress intensity factor and
easily to crack (X. Sun et al., 2004; Tewari, 2010; Liu et al., 2010, 2013).
Figure 2.1: Macrostructure of dissimilar RSW between stainless steel and galvanized
steel
Source: Marashi et al., 2008
2.3 RESISTANCE WELDING
There are several types of resistance welding which are Resistance spot welding
(RSW), resistance seam welding (RSEW) and resistance projection welding (PW). This
process has been predominant mode in joining process in the manufacturing industries
and automotive production (Chao, 2003; Oba, 2006; Kahraman, 2007; D. J. Radakovic
And M. Tumuluru, 2008; Thakur et al., 2010; Tewari, 2010; Pouranvari, 2011).
As the name is resistance welding, it is refer to the material resistance to the
flow of electric current that causes a localized heating in the joint and weld is made
(Tewari, 2010; Miller, 2012). The process is completed within a specified cycle time.
Generally, melting occurs at the faying surface during welding. The Resistance Spot
5
Welding (RSW) is getting significant importance in manufacturing car, bus and railway
bodies etc. due to automatic and fast process (Thakur et al., 2010).
Figure 2.2: Resistance Spot Welding Machine with workpiece
Source: Jenis, 2009
2.4 PRINCIPLES OF RESISTANCE SPOT WELDING
Resistance spot welding(RSW) is one of the oldest of the electric welding
processes today and the technique applied for joining almost all known metals (Tewari,
2010; Hayat, 2011). It is a process of joining metal components through the fusion of
discrete spots at the interface of the work pieces (Pereira et al., 2010). RSW process
involves electric current and mechanical force of the electrode tips of a proper
magnitude for a length of time (Pouranvari, 2011).The flow of electric current via two
copper electrodes tips that also press the work sheets together to form weld (Charde and
Arumugam, 2011). The weld nugget is formed due to the fusion of the melted metal
localized heating in the joint due to the resistance of the joint surfaces of the base metal
to electrical current flow (Goodarzi et al., 2009).
6
Figure 2.3: Schematic of the Resistance Spot Welding process
Source: Jenis, 2009
2.5 SPOT WELDS PARAMETERS
A quality desired product in resistance spot welding is need to either by control
the changing variables that affect during welding process or the parameters that affect
the process (Oba, 2006).
2.5.1 The Parameters in Resistance Spot Welding
The three main parameters in spot welding well known are electrode force,
welding current and welding time. These are the most important welding parameters in
resistance spot weld (Qiu, 2009). In order to produce good quality weld the above
parameters must be controlled properly. The amount of heat generated in this process is
governed by the formula,
Q = I2 R T ( 2.1)
7
Where
Q = heat generated, Joules
I = current, Amperes
R = resistance of the work piece, Ohms
T = time of current flow, second
Source: Thakur et al., 2010
Figure 2.4 below shows the procedure of the welding parameter on resistance spot weld.
Figure 2.4: Procedure of RSW
Source: Salem, 2011
8
2.5.1.1 Welding Current
Welding current is one of most the important parameter in the welding process.
In resistance spot welding, current is important for determining the heat generation from
the process. An optimum amount of welding current is generally required to produce
adequate heat energy for a weld nugget to form with minimum size diameter. However,
excess welding current causes void and crack formations (Qiu, 2009; Salem, 2011).
On the basis of macrostructure analysis, it can be stated that the higher the
welding current that is used, the larger the fusion zone (Mehdi, 2010; A. Aravinthan
And C. Nachimani, 2011; Pouranvari, 2011; Kola et al., 2012). Lower electrical
resistance of carbon steels, which is even lower for low carbon galvanized steel, but its
higher thermal conductivity compared to stainless steel which leads to smaller fusion
zone in the former. Heat affected zone (HAZ) in the galvanized steel side is wider than
that in the stainless steel side. This determine that galvanized related to higher thermal
conductivity as shows in Figure 2.5 (Pouranvari et al., 2008). Figure 2.6 Shows that the
fusion zone size (FZS) of both stainless steel and galvanized steel side increases with
the welding current with the exception of really high currents of more than 11 kA which
show a decrease in the FZS due to expulsion. Optimum welding current that produce
good weld quality has to be determined and selected in the resistance welding process
(Oba, 2006).
9
Figure 2.5: Effect of welding current on the weld nugget growth: a) 8kA b) 9kA c) 10
kA d) 11 kA e) <11 kA
Source: M. Pouranvari et al.,2008
Figure 2.6: Effect of welding current on the FZS of GS and SS side
Source: Marashi et al., 2008
10
2.5.1.2 Weld Time
Weld time is the time during which electric current is applied to the metal sheets
for welding. In the welding process, when the welding time increase the size of weld
nugget also increase. This is because the relation of the heat generation is directly
proportional to the welding time. From the process, the heat transfer from the electric
current to the workpiece, usually start from the weld zone then to the surrounding base
metals of workpiece. In AC systems, the weld time is expressed in cycles (one cycle is
1/60 of a second in a 60 Hz power system), while millisecond is used for DC systems.
During squeeze time, metal sheets are placed in position and clamped by electrodes
(Jung, 2011).
Weld time increased, the weld strength initially shows an increase due to
sufficient time given for the weld to develop. However at prolonged weld time, would
increase the softening effect, overheating causes the molten metal to expel from the
weld zone and hence the joint strength decrease (Salem, 2011; Charde and Arumugam,
2011).
2.5.1.3 Squeeze Time
Squeeze time as shown in Figure 2.4, is a time where pressure application and
weld to occur in between. During squeeze time, metal sheets are placed in position and
clamped by electrodes. When the electrode force has reached the desired level, welding
proceeds by the application of current. During this time, melting and joining occurs
(Jung, 2011). For the process, the squeeze time required level of the pressure is set for
the electrode pressing pressure to the workpiece before the electric current is flow and
weld is form (Oba, 2006).
2.5.1.4 Hold Time
Hold time is the period of time, after the welding time is complete and occurred
when the electrodes are still applied to the sheet with current switched off but pressure
continued. This time is to chill the welded part. The period of hold time must be set
optimum to give time for the molten metal to solidify but it must not be too long to
prevent the heat in the weld spot to spread to the electrode and heating it. The electrode
11
will then get more exposed to wear. In addition, the thicker the workpiece the longer the
hold time needed (Oba, 2006; Kahraman, 2007).
Figure 2.7: Welding Time Cycle
2.6 MATERIAL SELECTION
Stainless steel and low carbon steel such as Galvanized steel formed a good
combination of formability, weldability, mechanical properties and resistance to
corrosion. This combination of steels is mostly used in the power generation industry
(Kola et al., 2012).
2.6.1 Galvanized Steel
Galvanized steel is chemically treated steel which prevent it from corroding. It is
because the steel was coated in layers of protective metal that is zinc oxide because
which does not get rust easily. The coating gives the steel a harder, durable and to hard
scratch finish. Galvanizes steel commonly used as infrastructure to ensure that the
structure will withstand corrosion for longer period. Galvanized steel frames are used in
essential industries such as power infrastructure where failure cannot be tolerated. Steel
frames used in commercial buildings and residential homes also use galvanized steel to
form structures that will last. Bridges are made with galvanized steel to withstand water
vapor from rivers or the sea. Structures made with galvanized steel typically need less
maintenance than those formed from other materials, which are prone to rusting.
Galvanizes steel is lower electrical resistance than low carbon steel but high
conductivity (Marashi et al., 2008; M. Pouranvari et al., 2008; Mehdi, 2010).
12
The common ways of making steel resist rust is by alloying (combining) it with
a metal that is not likely to corrode for example zinc. The steel was bonded to zinc
permanently by chemical reaction when submerged the steel in melted zinc. The outer
layer is all zinc, but successive layers are a mixture of iron and zinc, with an internal
layer of pure steel. The more demanding of galvanized steel sheet in weldability than of
ordinary steel sheets because of the existence of spatter generating and cause electrode
pollution during the spot welding. The application of galvanized steel sheets is limited
in extensive automatic fabrication of automotive products (Hamidinejad et al., 2012).
2.6.2 Stainless Steel
Stainless steel is made from several numbers of different steels and was used for
their anti-corrosive element to resist of corrosive environments. It ensures for longer
lasting and safety in in the used for example tools and infrastructure. Stainless steel is an
earth friendly material because it can be recycled by melted it down and made into
something else.
Stainless steel is usually made by chromium minimum 10.5% to make the steel
stainless. A layer of chromium oxide film on the steel improves the corrosion resistance.
Despite that, there are other elements used to make stainless steel. It’s including
nitrogen, molybdenum and nickel. The mixing of these elements together enables a
variety of properties in machining, forming and welding and also welding because of
different crystal structures form.
2.7 MECHANICAL TEST
Mechanical testing is an important aspect of weldability study. Such testing is
either for revealing important welds characteristics, such as weld nugget diameter or
weld button size, or for obtaining and evaluating the quantitative measures of weld’s
strength. Mechanical testing of a weldment can be static or dynamic test and among the
static test, tension shear or tensile shear testing is commonly used in determining weld
strength or the tensile strength of the welded joints because it is easy to conduct the test
and the specimens for the test is simple in fabrication.
13
2.7.1 Failure Mode
Failure mode is a qualitative measure of resistance spot weld (RSW) weldability
performance. The failure developed criterions of spot welds are performing the strength
test using interfacial and pullout mode.
Generally, failure mode in resistance spot weld (RSW) is the manner in which
spot weld fails which occurs in two modes interfacial and pullout mode (Chao, 2003). In
the interfacial mode, failure occurs via crack propagation through the fusion zone as
shown Figure 2.8. In the pullout mode, failure occurs via complete or partial nugget
withdrawal from one sheet as shown in Figure 2.9. Failure mode of RSW can
significantly affect their energy absorption capability and load carrying capacity. Spot
welds that fail in nugget pullout mode provide higher peak loads and energy absorption
levels than those spot welds which fail in interfacial failure mode. To ensure reliability
of the spot welds during automotive lifetime, optimized parameters should be determine
so that failure mode will be guaranteed (Chao, 2003; Goodarzi et al., 2009; M.
Pouranvari and P. Marashi, 2009).
(a) (b)
Figure 2.8: Load direction and failure mechanism of interfacial mode; (a) pulling force
direction, (b) material failure
Source: Badheka et al., 2010
Force
Force
Force Force
weld nugget weld nugget
