Fatigue Behavior of Resistance Spot-Welded Unequal Sheet Thickness Austenitic Stainless Steel.

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Fatigue Behavior of Resistance Spot-Welded Unequal Sheet

Thickness Austenitic Stainless Steel

Triyono1, Jamasri2, M. N. Ilman2 & R. Soekrisno2

Mechanical Engineering Department, Sebelas Maret University, Indonesia

Mechanical and Industrial Engineering Department, Gadjah Mada University, Indonesia

Correspondence: Triyono, Mechanical Engineering Department, Sebelas Maret University, Jl. Ir. Sutami 36A Surakarta, Indonesia. Tel: 62-27-163-2163. E-mail: tyon_bila@yahoo.co.id

Received: December 5, 2011 Accepted: April 7, 2012 Online Published: May 1, 2012 doi:10.5539/mas.v6n5p34 URL: http://dx.doi.org/10.5539/mas.v6n5p34

The research is financed by the Ministry of Research and Technology of Indonesia and Indonesian Railway Industry

Abstract

This paper presents a comparative study on the fatigue strength of resistance spot-welded unequal and equal sheet thickness austenitic stainless steel. Lap joints of 3.0-1.0 mm and 1.0-1.0 mm thick austenitic stainless steel were made using the same resistance spot welding schedule with current, weld time and electrode force of 4.7 kA, 20 cycles and 6 kN respectively. The sinusoidal wave form with a constant stress amplitude was selected in the fatigue tests whereas the stress ratio and frequency used were 0.1 and 8 Hz respectively. Fatigue strength and tensile-shear load bearing capacity of 3.0-1.0 mm joint were higher than that of 1.0-1.0 mm joint, although its nugget diameter was smaller. The joint stiffness was the controlling factor of the fatigue strength of resistance spot-welded unequal sheet thickness austenitic stainless steel.

Keywords: resistance spot welding, unequal sheet thickness, fatigue, austenitic stainless steel

1. Introduction

Austenitic stainless steels are used for a very broad range of applications especially in automotive, railway vehicle, ship body, and airplane structures when an excellent combination of strength and corrosion resistance in aqueous solutions at ambient temperature is required. Stiffened thin plate construction where the thinner plate is reinforced by thicker plate called a frame, is generally applied to the structures. Gean et al. (1999) have claimed that it is a cost-effective way of achieving a high-performance vehicle structure because it remains suited to low-volume manufacture. This structure is typically joined by the resistance spot welding (RSW) process. The advantages of using RSW are that it is a quicker joining technique, suitable for automation, no filler material is required, and that the low heat input implies less risk for altered dimensions during welding.

Many standards and recommendations are developed by individual companies, such as Ford Motor Company and General Motors. Professional organizations such as the American Welding Society (AWS), Society of Automotive Engineering (SAE), the American National Standards Institute (ANSI), and International Organization for Standardization (ISO) also contribute to a significant portion of the standards. Because of the drastic differences in design, understanding and perception of weld quality, automobile manufacturers and others tend to have very different requirements on weld quality. Zhang and Hongyan (2006) have concluded that in general, spot weld size is enveloped between 3√ and 6√ (t is the thickness of the sheets in millimeters). This recommendation is very useful in finding good weld schedules for equal sheet thickness welding. However, in automotive body application, the majority of welds are between two dissimilar thicknesses. In this case, schedules for welding unequal sheet thickness are generally developed by and practiced within individual manufacturers. Some researchers also have proposed the spot welding unequal sheet thickness researches to evaluate these recommendations. The joint of unequal thickness of the same metal may produce a strength problem due to the heat unbalance (Hasanbasoglu & Kacar, 2007) and have the unique failure mechanism (Pouranvari & Marashi, 2010).

Despite various applications of spot welded unequal thickness in automotive body, reports in the literature dealing with its mechanical behaviors, especially the fatigue behaviors are limited. In fact, Gean et al. (1999)

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have fo and thu the pre weldin 2. Exp 2.1 Ma Two ty 3.0-1.0 resistan in Tabl Table 1 Mater SUS3 Table 2 Mat SUS3 A mob used w recomm called w current determ force w the actu 2.2 Me The tra proced hydroc The Vi the met 2.3 Ten The te servo-h specim

ound that the s us fatigue crac esent work is ng austenitic sta

erimental Pro

aterials and We

ypes of austeni 0 mm joint and

nce spot weldi le 1 and 2 resp

1. The chemica

rial C

304 0,0

2. The mechan terial Yield

304

bile spot weldin with the elec mendations, th welding sched t possible with mined welding

were 4.7 kA, 2 ual conditions

etallography an

ansverse secti dure. The micr

chloric acid and ickers microha

tallographic sp

nsile-Shear Tes

ensile test of hydraulic SHI men are illustrat

spot welded joi cks are easily i to investigate ainless steel.

ocedure

Welding Process

tic stainless st d the other is ing (RSW). Th

ectively.

al composition

076 8,183

nical properties d Strength (MP

305

ng machine W trode diamete he spot-weld nu dule required to hout causing e schedule used 20 cycles and in the Indones

nd Microhardn

ons of weld p rostructure of d 30 ml water. ardness measur pecimens with

sts

base metal a IMADZU uni

ted in Figure 1

Figure 1

int provides a initiated at thi and analyze f

ses

eel joints, one 1.0 mm and 1 he chemical co

n of test materi

18,107

s of test materi Pa) Tensile

(M 6

WT-300SB equ er of 25 mm

ugget diameter o produce a we expulsion both d for making th

6 kN respectiv sian Railway I

ness Measurem

passing throug f austenitic sta Microstructur rements across h a load of 500

and tensile-sh versal testing 1.

. Dimension o

localized conn s location und fatigue behavi

is the joint be 1.0 mm thick omposition and ials, Wt-% Mn 0,252 0 ials e Strength MPa) 670 uipment produc m and a curv

r was selected eld nugget size h in the 3.0-1.

he test sample vely. Fortunate Industry.

ments

gh the weld n ainless steel w

re investigation s the weld nug

hear tests of machine. Th

of tensile-shear

nection which der fluctuating ior of the une

etween 3.0 mm joint called 1. d mechanical p

P Si

0,031 0,38

Elongation (%

ced by Mitsub ved surface r d between 3 an e was determin 0 mm joints a es including w

ely, this weldin

nugget were pr was revealed b ns were carried gget, HAZ, and

the spot-weld he geometry a

r test specimen

it is a source o loading. Ther qual sheet thi

m and 1.0 mm t .0-1.0 mm join properties of t

89 0,209

%) Electr

bishi Electric C adius of 100 nd 10.4 mm. Th

ned. This was and 1.0-1.0 mm

eld current, w ng schedule w

repared by sta by using 10 m d out using an d the base met

ded joint wer and dimension

ns (in mm)

of stress conce refore, the obje

ckness resista

thick hereinaft nt, were lap jo est materials a

0,486

rical Resistivit (μΩ cm)

Corporation Ja 0 mm. Based

he welding par done using the m joints samp eld time and e was in accordan

andard metallo ml nitric acids

optical micros tal were carrie

re performed ns of a typic

entration, ective of ance spot ter called oined by are given V 0,22 ty apan was on the rameters e highest ples. The electrode nce with ographic s, 20 ml scopy. ed out on

using a cal RSW

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These samples region at the c order to provid

2.4 Fatigue Te

The fatigue te SHIMADZU spot-welded te

These sample to provide sym ends of the sp ratio and frequ until fracture Applied force

3. Results and

The weld prof

Figure 3. W

It can be seen Because of th generated in t

s were similar center of the as de a tensile-sh

ests

ests were perfo testing machin est samples we

s were similar mmetry and to pecimen. A sin

uency used we occurred or to

range and num

d Discussion

file of 3.0-1.0 m

Weld profile of

n from Figure he unbalanced the thicker pla

to the sample ssembly repres hear loading co

formed at room ne with a softw ere made accor

Figure 2. Dim

r to the sample o prevent a mo nusoidal wave ere 0.1 and 8 H o a maximum 2

mber of cycles

mm joint is sh

f 3.0-1.0 mm th

3(a) that the heat resulting ate (Hasanbaso

s used in a wo sents the nugge ondition, 38 mm

m temperature ware package s

rding to the Fr

mension of fat

es used in a wo oment being ap e input with a

Hz respectivel 2x106 cycles. S s to failure wer

hown in Figure

hick joints (a)

nugget is asym g from unequal

oglu & Kacar,

ork which was et. The overlap m long shims w

in laboratory specifically des rench standard

tigue test speci

ork which was pplied at the w

constant load ly. Specimens Specimens tha re recorded and

e 3.

macrograph (b

mmetric where l thickness of

2007). Heat l

carried out by p is equal to th were attached

conditions us signed for runn d A03-405 as sh

imens (in mm)

s carried out by weld, 60mm lo amplitude wa were exposed at survived 2x1 d S-N curves f

b) nugget corn

e its centre lea the joined ma loss in thicker

y Gean et al. (1 he width of the at both ends o

sing a 40 kN s ning fatigue te hown in Figure

)

y Gean et al. ( ong shims wer as selected wh d to a constant

106 cycles are for the joints w

ner (c) nugget (

ans to the thic aterials, more t r plate is smal

1999). The dar e metal sheet. I of the specimen

servo-hydrauli ests. The doubl

e 2.

(1999). In orde re glued at bot hereas the stres load amplitud called run out were obtained.

(d) interface

cker workpiece thermal will b ller than that i rk In n.

ic le

er th ss de s.

e. be in

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thinner plate. F surface thickne (Wang be elon non-un 3(d) sh affecte Differe spot w separat interfac Figu In addi mm joi were a primari materia thickne The ha Figu

r plate. This co Further evalua e indentation w ess causes the

et al., 2010). T ngated paralle niform manner hows interface d zone (HAZ) ent from the m

elded equal sh tion, nugget m ce of nugget an

ure 4. Weld pro

ition, accordin ints were spot lso the same, h ily attributed t als were found ess (Zhang & H ardness profiles

ure 5. Microhar

ondition causes ation of Figure was very sligh e edge of shee

The microstru el to irregular r from all the s e microstructu

microstructure heet thickness microstructure

nd base metal

ofile of 1.0-1.0

ng to the macro t welded using however that a to the asymmet d to be much h Hongyan, 2006 s of weld nugg

rdness distribu

s penetration i e 3(a) shows t ht. The asymm ets warp to the

cture of weld n r direction as ides of the sur ure where the

of spot welde austenitic stai has regular dir

as seen in Figu

0 mm thick joi

oscopic examin g the same we

at the joint int try nugget of 3 higher than a m 6). Therefore, get, HAZ (heat

ution of the spo

s almost 100% that separation metry of temp

e thinner shee nugget has a c shown in Fig rrounding solid base metal an

d unequal she inless steel sho

rection and w ure 4.

ints: (a) macro

nation (Figure elding schedule

erface were 8. 3.0-1.0 mm joi minimum nugg

the weld nugg t affected zone

ot welded equa

% on the thicke n of the sheets perature field d et and makes t columnar struc gure 3(c). It d, in both the e nd the nugget

eet thicknesses ows that the nu

ide heat affect

ograph (b) nugg

e 3 and Figure e, the nugget .3 mm and 8.9 int. The measu get diameter o get sizes of all e), and the base

al and unequal

er plate and ver s is about 20 distribution in the sheet sepa ture in which t shows that so electrode and s

are separated

, the microstru ugget is symm ted zone (HAZ

get corner (c) n

4) when the 3 diameter at ce 9 mm respectiv ured weld nugg of the 3-6 time welded materi e metal are sho

thickness aust

ry slight on the mm (Figure 3 n spot welded aration is high

the grains are olidification o sheet directions d by very narr

ucture investig metry, there is

Z) band appea

nugget (d) inte

.0-1.0 mm and enter of total th vely. This diffe get sizes for al es the root of t ials were accep own in Figure

tenitic stainles e thinner 3(b)) and unequal h enough found to occurs in s. Figure row heat gation of no sheet ars at the

erface d 1.0-1.0 hickness erence is l welded the sheet ptable. 5. ss steel

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The hardness The highest h However, hard joint because o carbon, manga the carbon con been used in hardness of th microstructure Interesting ph hardness com hardness. This Hardness prof In order to de study, the ten stainless steel

As can be see 1.0-1.0 mm jo This result dif Ozyurek (200 welded joint. It seems that stiffness. As k rotation of the

Figure 7. Defo

When there w

of nugget for b hardness value dness of the nu of the chemica anese that affe ntent exceeds this study had he thinner shee

henomenon occ mpared to base s could be attr file of thin she etermine the lo nsile shear loa are compared

Figure

en from Figure oint even thou ffers from the 08). They foun

the enhancem known when t e joint. Figure

ormation mech

was certain amo

both 3.0-1.0 m of weld nugg ugget of 3.0-1 al composition ects the harden about 0.08% ( d less than th et of the 3.0-1.

curs in a thin s e metal unless

ributed to the et was more in oad range on th

ad bearing ca and results ar

e 6. Tensile she

e 6, the tensile ugh its nugget

results obtaine nd that increas

ment in tensile tensile load wa

7 shows the de

hanism of lap j

ount of rotation

mm and 1.0-1.0 gets was over 2

.0 mm joint di n of base metal nability. Spot w

(AWS, 1982; O hat of percent

0 mm joint co

sheet of the 3. s the nugget e asymmetric nu nfluenced by st

he fatigue test apacity of spo e given graphi

ear load bearin

e shear load be diameter at th ed from a wor ing of the nug

shearing load as applied in a eformation me

joint during lo load distributi

n, the tensile s

0 mm joint was 250 HV 0.5 w id not show m ls in which the welds in thin sh Ozyurek, 2008 carbon. In ad ompared to bas

0-1.0 mm join edge in which

ugget that occ train hardening ts, the strength ot welded equ

ically in Figure

ng capacity of

earing capacity he joint interfa rk which was c gget diameter

bearing capac a lap joint, the echanism of lap

ading, (a) low on in a lap join

stress called pe

s found to be h which was obs many difference ere is not so mu heet can have r 8). As seen in ddition, there w

se metal becau

nt where there h its hardness curred on the u

g due to electr h of weldment ual and unequ

e 6.

spot welded m

y of 3.0-1.0 m face is smaller

carried out by increased tens

city of 3.0-1.0 e eccentricity o

p joint during

load level, (b) nt

eeling stress (i

higher than tha erved on the e es compared to uch alloying el relatively high Table 1, base was no signifi use there was n

was no signif value was sim unequal sheet rode indentatio t was also dete ual sheet thick

materials

mm joint is high and it fail on Vural and Ak sile-shear stren

0 mm joint is a of the load pa loading.

) plastic hinges

.e. the normal

at of base meta edge of nugge o that of 1.0-1. lements such a h hardness whe metals that ha icant change i no change in it

ficant change i milar to nugge

thickness join on.

ermined. In thi kness austeniti

her than that o n the thin shee kkus (2004) an ngth of the spo

attributed to it ath resulted in

s, (c) schemati

stress acting i al. et. .0 as en ad in ts in et nt. is ic of et. nd ot ts a ic in

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the thro deform at the peeling

Since l test (N bearing The S-N

All dat fatigue than 1. was 0.7 Nordbe have b calcula

where range-c higher

ough-thicknes mation in sheet

nugget circum g stress of

3.0-Figure 8. The

load bearing c Nordberg, 2006

g capacity than

N curves, the r

Figure 9. Comp

ta points belon e life of the spe

0-1.0 mm join 7 kN.

erg (2006) has been analyzed. ated as follows

t1 > t2. The S

cycle relation and increasing

ss direction of thickness dire mference (Nor 1.0 mm joint w

(a) fracture mode

capacity of spo 6) this mecha n 1.0-1.0 mm j results of fatig

parison of fatig

nged to a mean ecimens increa nts. The endur

s proposed a l Line load is s:

S-N curve in as seen in Fig g to much high

the joint, exp ection. Increas rdberg, 2006). was smaller th

e of tensile she

ot welds under nism can exp oint.

ue test of the s

gue strength of

n value of three ases as expecte ance limit of 3

line load meth the load divid

e(

Figure 9 wil gure 10. At hi her at lower loa

ressed as P sin ing of the join . Due to the an that of

ear test sample

r coach-peel te plain why

3.0-spot welded jo

f 3.0-1.0 mm a

e tests. As show ed. The 3.0-1.0 3.0-1.0 mm joi

hod when fatig ded by the wi

3 2

14 t  3 )

ll has slightly igh loads fatig ads than that o

n θ) formed ar nt rotation incr

higher stiffne 1.0 mm joint a

s: (a) 3.0-1.0 m

est is much lo -1.0 mm joint

ints are presen

and 1.0-1.0 mm

wn in Figure 9 0 mm joints ex ints was 2.9 kN

gue data of dis idth of the joi

1 2

y different pat gue strength o of the 1.0-1.0 m

round the nug eased peeling ss, joint rotati as shown in Fi

(b)

mm joint (b) 1

ower than that t has a higher

nted in Figure 9

m joint based o

9, while the loa xhibited much h

N whereas tha

scontinuous jo int, and the w

ttern if it is d of the 3.0-1.0 m mm joint.

gget and cause stress that led ion and conse gure 8.

.0-1.0 mm join

of under tens r tensile shear

on the load ran

ad range decre higher fatigue at of 1.0-1.0 m

oints like spot width of the jo

displayed in l mm joint was

d plastic necking equently,

ile-shear ring load

nge

eases, the strength mm joints

welding int, e, is

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ine load s slightly

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Figure 10.

Similar to ten also attributed 3.0-1.0 mm jo occurred just Consequently, initiated on bo started in the b

After initiatio propagating th in Figure 12(a circumference behavior is si Khanna, 2007

Figu

Comparison o

nsile shearing l d to its stiffnes oint can be us on thin sheet , crack of 3.0-oth sheet side base metal adj

(a) Figure 1

on, the crack hrough the wid a). Different fr e due to high imilar to fractu 7).

ure 12. The frac

of fatigue stren

load bearing c ss. The explan sed to explain

t and it was s -1.0 mm joint as shown in F acent to the HA

1. Initial crack

propagation dth of the thin rom fracture of

peel stress an ure of coach p

(a) cture mode of

ngth of 3.0-1.0

capacity, the e nation of the e that in fatigu smaller than t initiated just igure 11. For b AZ area.

k location: (a)

of 3.0-1.0 mm sheet. Finally f 3.0-1.0 mm j nd led to the peel samples

fatigue test sam

mm and 1.0-1

enhancement in enhancement in ue strength. Du that of 1.0-1.0 on the thin sh both 3.0-1.0 m

(b) 3.0-1.0 mm jo

m joint occur y, this mechani oint, cracks of pull out fractu at high load t

mples: (a)

3.0-.0 mm joint ba

n fatigue stren n tensile shear ue to the high 0 mm joint w heet side wher mm and 1.0-1.0

oint (b) 1.0-1.0

rred through t ism led to the t f 1.0-1.0 mm j

ure mode as that reported i

(b) -1.0 mm joint

ased on the lin

ngth of 3.0-1.0 ring load bear her stiffness, r which rotated o

reas that of 1. 0 mm joint spe

mm joint

the thickness tearing fractur oint propagate shown in Figu in a previous

(b) 1.0-1.0 mm

ne load range

0 mm joint wa ring capacity o rotation of join on both sheet

0-1.0 mm join ecimens, crack

and continue re mode as see ed at the nugge

ure 12(b). Thi study (Long &

m joint

as of nt s. nt ks

ed en et is &

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Given SEM views in Figure 13 and Figure 14 are the comparison of the last fracture surfaces of the 3.0-1.0 mm and 1.0-1.0 mm joint specimens which were subjected to same load of 3.4 kN. As seen in Figure 13(a), crack of 3.0-1.0 mm joint initiated on the inside of thin sheet. On the more half of thickness, it propagated slowly due to low peel stress and induced ductile fracture characterized by intergranular cracking. Ductile fracture changed to brittle fracture characterized by transgranular cracking on the remaining thickness due to increased peel stress. The embrittlement of stainless steel was attributed to strain-induced martensite forming during the fatigue tests (Vural et al., 2006). Different view was given by fracture surface of 1.0-1.0 mm joint specimen as shown in Figure 13(b). It displayed brittle fracture characterized by transgranular cracking on the entire thickness due to high peel stress.

(a) (b)

Figure 13. Initial crack of fatigue test samples: (a) 3.0-1.0 mm joint (b) 1.0-1.0 mm joint

(a) (b)

Figure 14. Crack propagation zone: (a) 3.0-1.0 mm joint (b) 1.0-1.0 mm joint

On the crack propagation zone, brittle fracture characterized by transgranular cracking was observed on both 3.0-1.0 mm and 1.0-1.0 mm joint specimens. They displayed wave of plastic deformation as shown in Figure 14. However, plastic deformation intensity of 1.0-1.0 mm joint was higher than that of 3.0-1.0 mm joint. It was indicated by the number of waves in the same observation area as seen in Figure 14.

4. Conclusions

Fatigue of resistance spot welded unequal sheet thickness austenitic stainless steel has been studied. Due to significant thickness difference, the asymmetric weld nugget, high microhardness on the edge of nugget and tearing fatigue fracture mode were observed. The fatigue strength of 3.0-1.0 mm joint was higher than that of 1.0-1.0 mm joint, although its nugget diameter was smaller. The endurance limit of 3.0-1.0 mm and 1.0-1.0 mm joint were 2.9 kN and 0.7 kN respectively. Ductile and brittle fractures were observed on 3.0-1.0 mm fatigue specimens whereas 1.0-1.0 mm fatigue specimens failed to fully brittle fracture mode. The joint stiffness was the controlling factor of the fatigue strength of resistance spot-welded unequal sheet thickness austenitic stainless

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steel.

5. Acknowledgments

The authors would like to express their sincere gratitude for the financial support of the Ministry of Research and Technology of Indonesia and Indonesian Railway Industry.

References

American Welding Society. (1982). Metals and their weldabilty, Welding handbook(7th ed.),4. United States of America.

Gean, A., Westgate, S. A., Kucza, J. C., & Ehrstrom, J. C. (1999). Static and Fatigue Behavior of Spot Welded 5182-0 Aluminium Alloy Sheet. Welding Journal, 78(3), 80s-86s.

Hasanbasoglu, A., & Kacar, R. (2007). Resistance Spot Weldability of Dissimilar Materials (AISI 316L-DIN EN 10130-99 Steels). Material and Design, 28, 1794-1800. http://dx.doi.org/10.1016/j.matdes.2006.05.013 Long, X., & Khanna, S. K. (2007). Fatigue properties and failure characterization of spot welded high strength

steel sheet. International Journal of Fatigue, 29, 879-886. http://dx.doi.org/10.1016/j.ijfatigue.2006.08.003 Nordberg, H. (2006). Fatigue Properties of Stainless Steel Lap Joints. SAE Transactions: Journal of Materials &

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As can be see 1.0-1.0 mm jo This result dif Ozyurek (200 welded joint. It seems that stiffness. As k rotation of the

Figure 7. Defo

When there w

rg/mas

of nugget for b hardness value dness of the nu of the chemica anese that affe ntent exceeds this study had he thinner shee

henomenon occ mpared to base s could be attr file of thin she etermine the lo nsile shear loa are compared

Figure en from Figure oint even thou ffers from the 08). They foun the enhancem known when t e joint. Figure

ormation mech

was certain amo

both 3.0-1.0 m of weld nugg ugget of 3.0-1 al composition ects the harden about 0.08% ( d less than th et of the 3.0-1. curs in a thin s e metal unless

ributed to the et was more in oad range on th

ad bearing ca and results ar

e 6. Tensile she e 6, the tensile ugh its nugget

results obtaine nd that increas ment in tensile tensile load wa

7 shows the de

hanism of lap j

ount of rotation

Modern Appli

mm and 1.0-1.0 gets was over 2

.0 mm joint di n of base metal nability. Spot w

(AWS, 1982; O hat of percent

0 mm joint co sheet of the 3. s the nugget e asymmetric nu nfluenced by st

he fatigue test apacity of spo e given graphi

ear load bearin e shear load be diameter at th ed from a wor ing of the nug shearing load as applied in a eformation me

joint during lo load distributi n, the tensile s

ied Science

0 mm joint was 250 HV 0.5 w id not show m ls in which the welds in thin sh Ozyurek, 2008 carbon. In ad ompared to bas

0-1.0 mm join edge in which

ugget that occ train hardening ts, the strength ot welded equ

ically in Figure

ng capacity of earing capacity he joint interfa rk which was c gget diameter

bearing capac a lap joint, the echanism of lap

ading, (a) low on in a lap join stress called pe

ISS s found to be h which was obs many difference ere is not so mu heet can have r 8). As seen in ddition, there w

se metal becau nt where there h its hardness curred on the u

g due to electr h of weldment ual and unequ

e 6.

spot welded m y of 3.0-1.0 m face is smaller

carried out by increased tens city of 3.0-1.0 e eccentricity o

p joint during

load level, (b) nt

eeling stress (i

Vol. 6, No.

SSN 1913-1844 higher than tha erved on the e es compared to uch alloying el relatively high Table 1, base was no signifi use there was n was no signif value was sim unequal sheet rode indentatio t was also dete ual sheet thick

materials mm joint is high

and it fail on Vural and Ak sile-shear stren 0 mm joint is a

of the load pa loading.

) plastic hinges

.e. the normal

5; May 2012

E-ISSN 1913-185 at of base meta edge of nugge o that of 1.0-1. lements such a h hardness whe metals that ha icant change i no change in it ficant change i milar to nugge

thickness join on.

ermined. In thi kness austeniti

her than that o n the thin shee kkus (2004) an ngth of the spo

attributed to it ath resulted in

s, (c) schemati

stress acting i

52 al. et. .0 as en ad in ts in et nt. is ic of et. nd ot ts a ic in

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www.cc Publish the thro deform at the peeling Since l test (N bearing The S-N

F All dat fatigue than 1. was 0.7 Nordbe have b calcula

where range-c higher

csenet.org/mas

hed by Canadian

ough-thicknes mation in sheet

nugget circum g stress of

3.0-Figure 8. The load bearing c Nordberg, 2006

g capacity than N curves, the r

Figure 9. Comp ta points belon e life of the spe

0-1.0 mm join 7 kN.

erg (2006) has been analyzed. ated as follows

t1 > t2. The S

cycle relation and increasing

n Center of Scien

ss direction of thickness dire mference (Nor 1.0 mm joint w

(a) fracture mode capacity of spo 6) this mecha n 1.0-1.0 mm j results of fatig

parison of fatig nged to a mean

ecimens increa nts. The endur

s proposed a l Line load is s:

S-N curve in as seen in Fig g to much high

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the joint, exp ection. Increas rdberg, 2006). was smaller th

e of tensile she ot welds under nism can exp oint.

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the load divid e( Figure 9 wil gure 10. At hi her at lower loa

rn Applied Scien

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ressed as P sin ing of the join . Due to the an that of

ear test sample r coach-peel te plain why

3.0-spot welded jo

f 3.0-1.0 mm a e tests. As show ed. The 3.0-1.0 3.0-1.0 mm joi hod when fatig ded by the wi

3 2 14 t  3 ) ll has slightly igh loads fatig ads than that o

nce

n θ) formed ar nt rotation incr

higher stiffne 1.0 mm joint a

s: (a) 3.0-1.0 m est is much lo -1.0 mm joint ints are presen

and 1.0-1.0 mm wn in Figure 9 0 mm joints ex ints was 2.9 kN gue data of dis

idth of the joi 1

2 t

t y different pat gue strength o of the 1.0-1.0 m

Vol

round the nug eased peeling ss, joint rotati as shown in Fi

(b)

mm joint (b) 1 ower than that

t has a higher nted in Figure 9

m joint based o 9, while the loa xhibited much h

N whereas tha scontinuous jo int, and the w ttern if it is d of the 3.0-1.0 m mm joint.

l. 6, No. 5; May

gget and cause stress that led ion and conse gure 8.

.0-1.0 mm join of under tens r tensile shear

on the load ran ad range decre higher fatigue at of 1.0-1.0 m oints like spot width of the jo

displayed in l mm joint was

y 2012 39 d plastic necking equently, nt ile-shear ring load nge eases, the strength mm joints welding int, e, is (1) ine load s slightly

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www.ccsenet.or

Figure 10. Similar to ten also attributed 3.0-1.0 mm jo occurred just Consequently, initiated on bo started in the b

After initiatio propagating th in Figure 12(a circumference behavior is si Khanna, 2007

Figu

rg/mas

Comparison o nsile shearing l

d to its stiffnes oint can be us on thin sheet , crack of 3.0-oth sheet side base metal adj

(a) Figure 1 on, the crack hrough the wid a). Different fr e due to high imilar to fractu 7).

ure 12. The frac

of fatigue stren load bearing c ss. The explan sed to explain

t and it was s -1.0 mm joint as shown in F acent to the HA

1. Initial crack propagation dth of the thin rom fracture of

peel stress an ure of coach p

(a) cture mode of

Modern Appli

ngth of 3.0-1.0 capacity, the e nation of the e that in fatigu smaller than t initiated just igure 11. For b AZ area.

k location: (a)

of 3.0-1.0 mm sheet. Finally f 3.0-1.0 mm j nd led to the peel samples

fatigue test sam

ied Science

mm and 1.0-1 enhancement in

enhancement in ue strength. Du that of 1.0-1.0 on the thin sh both 3.0-1.0 m

(b) 3.0-1.0 mm jo m joint occur y, this mechani oint, cracks of pull out fractu at high load t

mples: (a)

ISS .0 mm joint ba n fatigue stren n tensile shear ue to the high 0 mm joint w heet side wher mm and 1.0-1.0

oint (b) 1.0-1.0 rred through t ism led to the t f 1.0-1.0 mm j

ure mode as that reported i

(b) -1.0 mm joint

Vol. 6, No.

SSN 1913-1844 ased on the lin ngth of 3.0-1.0 ring load bear her stiffness, r which rotated o

reas that of 1. 0 mm joint spe

mm joint the thickness tearing fractur oint propagate shown in Figu in a previous

(b) 1.0-1.0 mm

5; May 2012

E-ISSN 1913-185 ne load range

0 mm joint wa ring capacity o rotation of join on both sheet

0-1.0 mm join ecimens, crack

and continue re mode as see ed at the nugge

ure 12(b). Thi study (Long &

m joint

52 as of nt s. nt ks

ed en et is &

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www.ccsenet.org/mas Modern Applied Science Vol. 6, No. 5; May 2012

Published by Canadian Center of Science and Education 41

(a) (b)

Figure 13. Initial crack of fatigue test samples: (a) 3.0-1.0 mm joint (b) 1.0-1.0 mm joint

(a) (b)

Figure 14. Crack propagation zone: (a) 3.0-1.0 mm joint (b) 1.0-1.0 mm joint

4. Conclusions

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www.ccsenet.org/mas Modern Applied Science Vol. 6, No. 5; May 2012

ISSN 1913-1844 E-ISSN 1913-1852 42

steel.

5. Acknowledgments

The authors would like to express their sincere gratitude for the financial support of the Ministry of Research and Technology of Indonesia and Indonesian Railway Industry.

References

American Welding Society. (1982). Metals and their weldabilty, Welding handbook(7th ed.),4. United States of America.

Gean, A., Westgate, S. A., Kucza, J. C., & Ehrstrom, J. C. (1999). Static and Fatigue Behavior of Spot Welded 5182-0 Aluminium Alloy Sheet. Welding Journal, 78(3), 80s-86s.

Manufacturing, 114, 675s-690s.

Ozyurek, D. (2008). An effect of weld current and weld atmosphere on the resistance spot weldability of 304L

austenitic stainless steel. Materials and Design, 29, 597-603.

http://dx.doi.org/10.1016/j.matdes.2007.03.008

Pouranvari, M., & Marashi, P. (2010). Resistance Spot Welding of Unequal Thickness Low Carbon Steel Sheet.

Advanced Materials Research, 83, 1205-1211.

http://dx.doi.org/10.4028/www.scientific.net/AMR.83-86.1205

Zhang, H. Y., & Senkara, J. (2006). Resistance welding: fundamentals and applications. Boca Raton: Taylor & Francis Group.

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Fatigue Behavior of Resistance Spot-Welded Unequal Sheet Thickness Austenitic Stainless Steel.