Performance of Tensile Tested Resistance Spot and Laser Welded Joints at Various Angles

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PERFORMANCE OF TENSILE TESTEDRESISTANCE SPOT AND LASER WELDEDJOINTS AT VARIOUS ANGLES

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The introduction of modern materials has offered engineers tools to develop to satisfy the

demands of consumers and regulators. Advanced high strength steels combine high strength wiih good

formability and weldability. The increased strength levels allow manufacturers to reduce sheet gauges (thus

lowering weight) whilst retaining performance in safety critical areas of the construction. However issues have

been reported in literature concerning ihe failure behaviour of advanced high strength steels.

The performance of welded joints is usually evaluated using coupon tests under either normal or shear tensile

loading. The actual loading of these joints in an automotive structure may be quite different, especially con-

cerning the angle in which the load is applied.ln this reporl an overview is given of published results on the performance of welded joìnts in automotive

applications. Next the results from a series of resistance spot and laser welded joints in different steel sheet

materials (HSLA and DP of varying thickness) subjected to tensile tests under varying loading angles are

presented, The focus is on resistance spot welded joints, but the results are compared to similar tests per-

formed with laser welded joints, The performance of the welded joints in terms of failure mode and strength

are analysed, and the possible implications for automotive applications are discussed,

Fìnally some work using finite element simulations is presented. Here the characteristics of the base material

and welded joints of different grades of materials are evaluated to investigate the differences in performance

in tensile testing.It is concluded that the thickness of the materials is the main parameter determining the failure characteristics

of materials. The grade (HSLA or DP) is less of a factor determining failure mode. The fact that joints in DP

steel perform as well as HSLA steels allows designers and engineers to use the advanced high strength steel

without having to worry about unpredictable failure behaviour leading lo decreased pedormance for safety

critical applications,

llW-Thesaurus keywords: Resistance welding; lensile tests; Low alloyed steels; High-sirength sieels.

areas of the structure. Other parts remain relatively intacl,

transmitting loads around the passenger compartment, or

safety cage, to other areas of the structure [2]'

l+3

The demands on the performance of resistance spotwelded joints are related to their application, Several cat-egories can be distinguished [1]:

- Joints that can endanger human life as well as thesafety function, in the event of their failure.

- Joints whose failure make the product unusable for itsintended purpose or result in a loss of property

- Joints whose failure has only negativè impact on theproduct in terms of its intended use,

- Joints that have no quality requirements; they just need

to join parts,

The strictest requirements are set for the applications thataffect safety. The most important of these is the defor-mation of a construction in a crash, During a crash, spe-cific parts deform to absorb energy, while others resistdeformation to limit intrusion and transmit loads to other

Steel has been used for these applications because ofits properties thai allow engineers to optimise safety in

crash [2]:

- Ductility; steel exhibits a consistent, well documented,

ability to deform before fracture.

- Work hardening; steel increases in strength as it

deforms, and it does so consistent and predictably'

- Strain rate sensitivity; steel shows positive strain rate

sensitivity, i,e. the ability to gain strength is enhanced buy

the speed at which it deforms,

- Additionally steel is relatively cheap and available in

great quantities. lt is produced globally enabling automo-

tive manufacturers to use local suppliers without having

to change their design specifications for varying manu-

facturing sites.

N. den Uill, F. Azakane, S, Krlic and V, Docter

Dac lill-232'1, ¡et:tntne¡jeti íc¡ pt¡blt¡si¡t¡ i¡y 5(.',-,!,,ula'S'elcti ()ttv¡tllte Aulc'nrii¡e ¿nd f?aal f,zr,s;;oii"

'k) )t IN THE WORLD

141+

The introduction of advanced high strength steel (AHSS)

has enabled the automotive industry to increase the crashperformance of cars, without having to increase weight.Thus contributing to increased safety on the roads anddecreased emission of green house gasses. Howeverissues have been reported on the failure mode of resist-ance spot welded joints in AHSS [3-6].

When traditional resistance spot welding parameters areapplied to advanced high strength steels, interfacial fail-ures and (partial) plug failures can occur, lnterfacial fail-ures of spot welds are considered to be brittle and less

energy absorbing than plug failures [7], Load carrying

capacity and energy absorption capability for those weldsthat fail under interfacial mode, are much less than thosewhich fail under plug failure mode [8], The pullout failuremode indicates that the welds have been able to transmita hìgh level of force, cause severe plastic deformation in

its adjacent components, and increased strain energy dis-sipaiion in crash conditions [9].

The safety parts of the cars depend principally upon theirassembled properties and, as a result, welds have to meetthe expected design specifications in respect of the appli-cation considered. The well-known practice in the shopfloor spot welding quality checking is to refer to the failuretype as a quality criterion: plug failure is accepted, interfa-cial failure is rejected [10],

lnitially it was thought that the issue was primarily related

to the relatively high carbon equivalent of advanced high

strength steels compared to traditional low alloyed steels,

coupled with the fast weld cooling rates observed in

resistance spot welding [11-12]. This can create a hard

and brittle martensite in the weld and parts of the heataffected zone [13-14]. Although marlensite formation will

enhance the tensile strength of the material it deterioratesits toughness, Empirical studies have shown that hard-ness levels exceeding 450HV correlate with an increased

tendency towards brittle failure through the nugget [15].This is generally associated with a large degree of mar-

tensite in the microstructure [13, 16-17],

Steel sheet thickness has also been identified as an

important factor determining the failure mode, with inter-facial failure becoming the dominant failure mode withincreasing thickness [16, 1B]. Combined with the factthat the load required to cause (interfacial) failure in very

high strength materials (e.g, Boron alloyed steels) [19-20], this has lead to the suggestion that load to failureshould be considered more important in judging weldquality [10, 19, 2 l].

The strength of the joint is dependent on the size of theweld nugget [18]. Larger welds fail through plug fail-ure, whereas smaller welds generally fail interfacially [7],Therefore automotive manufacturers use a minimum weldsize, Normally 4./t, where t is the sheet thickness in mm,

is used [8, ] l, 2Ol, but 3,5{t or 5!t are also used [22].It is also possible that a minimum weld size is defined

for ranges in thickness and variations can be allowed fordifferent applications [1, 23].

Steel manufacturers perform series of static tensile teston resistance spot welded joints before they are sub-jected to full size crash tests, These static tensile tests are

also used to gather information on the expected perfor-

mance of welded joints, during the development stage of

materials (when material availability is an issue), There are

several tensile test configurations in use, such as tensile

shear tests, peel iype tensile tests and cross tension tests,

Modern automotive design and engineering is heavily

based on the finite element modelling [24], For crash sim-

ulations predictable failure behaviour (strength and failure

mode) is important to enable assessment of the perfor-

mance of resistance spot welded joints [25-30],

r2æuAlthough standardised coupon tests do provide a lot of

information on the failure behaviour of welded joints, they

are limited to set loading conditions; either pure tensile

or pure shear loading. Welded joints in constructions are

however subjected to loads that vary from pure tensile

to pure shear loading, Therefore a series of experiments

was set up to compare the failure behaviour of resistance

welded advanced high strength sieels with the failure

behaviour of low alloyed high strength steels, An addi-

tional comparison was done between laser welded AHSS

and HSLA steel sheet, HSLA steels are known to show

good weldability with high failure strength and good fail-

ure modes,

The object is to investigate how the dual phase steel

would behave in various loading conditions compared

to the well known behaviour of HSLA materials. Next to

experimental results, finite elements simulations were

used to analyse failure of the joints.

l8nçmçnFour materials were used in this investigation: 1,0 mm

thick galvanised HSLA340 and DP800 and 1.5 mm

thick galvanised HSLA340 and DPB00. Table 1 gives

the mechanical characteristics of the different materi-

als and Table 2 shows the chemical composition of the

materials used in this report. The chemical composition ofthe grades differs for various thicknesses as the materi-

als were made from different charges of liquid steel. The

materials used for these tests have been taken form com-

mercially supplied batches, so that they reflect materials in

actual use for automotive applications, Table 2 also gives

the llW Carbon Equivalence (CE) number [29] which

gives an indication of the weldability of the material. A low

CE value indicates low hardenability, which is associated

with good weldability.

tr TtrSTtrN RFSISTANCF SPOT ANI) \ /trl nFn.totNTs aTvARloÌlsPFRFORMANCF OF

Table'l - Mechanical charactelistics of the materials used in this report

Table 2 - Chemical composition and llW CE number of the materials used in this report

28.8456HSLA34O 1.0 40931.7338 438HSLA34O 1.518.08521.0 491DPSOO12j848DPSOO 1.5 562

thickness[mm]

Rpo,r

lMPal

Auo

Io/o]

Rgrade

lMPal

0.0650.0140.035 0.0161.0 0.050 0.247 0.004HSLAS4O0.0650.010 0.0080.072 0.030HSLAS4O 1,5 0.065 0.498

0.001 0.2730.019 0.0102.548 o.746DPSOO 1.0 0.0920.2660.0020.037 0.009o.124 1.987 0.268DPSOO 1.5

thicknesslmml [wto/o] [wto/o] [wto/o] [wto/o] [wto/ol

S

lwto/olCE

PS¡ AIc Mngrade

Tensile tests were done on U-shaped tension test speci-

men joined together by either resistance spot welding or

laser beam welding (see Figure 1), Resistance spot weld-

ing was done using a 50 Hz AC spot welding machine,

Parameters were set to produce welds with a diameter

of 4r/t, with t the sheet thickness. Resistance spot welds

were made at the centre of the adjoining surfaces. Table

3 gives the process settings use for resistance welding'

Laser welding was done using a 4,5 kW Nd:YAg laser'

with a 0.6 mm spot size, Welds of 25 mm length welds

were made diagonally over the specimen according to

VDEh standards [33], The diagonal direction was chosen

that the results of tensile testing would not be affected by

the orientation of the weld beád, eliminating the influence

of beginning and end of welding.

Tensile test specimen were mounted in a specially

designed clamping tool that allowed loading of the welded

joints under an angle in standard tensile testing machine

(see Figure 2 a, b, c). The clamp allows testing at seven

145

Figure 1 - Tensile test specimen used in this report(left with spot welded ioint, right with laser welded ioint)

c)b)a)

Figure 2 - Clamping tool used in this report, with (a) clamp mounted in

with an un-welded U-shaped sample, and (c) tensile tests at antensile tester,

angle of 75"(b) clamp

Table 3 - Resistance spot weld process parameters

15 cycles 4.5 kN17 cycles25 cycles1.0 F16x5.5HSLA34O4.0 kN15 cvcles'1 7 cyclesF16x5.5 25 cycles1.5HSLAS4O4.5 kN15 cycles17 cyclesF16x5.5 25 cyclesDPSOO 1,04.5 kN19 cycles 15 cycles25 cycles1.5 F16x5.5DPSOO

thicknesslmml

Electrode type Squeeze timeWeld

timeHoldtime

Electrodeforcegrade

PFRFORMANCF OF-TFNSII F ÍFSIFI) qÞnr ^Nrn

r ÀqtrFl \^/Ê ntrn tôtNtTs aT \/ÀRlol ls aNGl Fs

146

different angles (0o, 15o, 30o, 45o, 60o, 75o, and 90"). The

test specimens were fixed by two plates bolted with a

moment of 100 Nm. Tensile tests were performed with a

uniform displacement of 10 mm/min.

lSr,armrThe tensile test results are listed in Tables 4 to 9. The

tables give the average tensile strength and the stand-ard deviation. For each material (grade and thickness)21 samples were tested per welding process; 3 for each

angle. No standard deviation is given for the tensile testresults of resistance spot welded 1.0 mm thick DP800under 0o (Table 5), because all but one results had to be

discarded.

All resistance spot welded joints in 1.0 mm HSLA340showed full plug failure; except for a single partial plug

failure in pure shear loading (90"). lnterfacial failure

occurred in predominant shear loading (75" and 90") of1.0 mm thick resistance spot welded DPB00, with fullplug failure dominating all other load angles (one par-

tial plug failure recorded for 0o & 309. lnterfacial fail-ure occurred in all 1.5 mm thick HSLA340 and DP800resistance spot welded joints loaded at angles of 75"and 90o, with full plug failure occurring in all other

specimens,

Table 4 - Tensile test results for resistancespot welded 1,0 mm thick HSLA340

Table 5 - Tensile test results for resistancespot welded 1,0 mm thick DP800

Table 6 - Tensile test results for resistancespot welded 1.5 mm thick HSLA340

Table 7 - Tensile test results for resistancespot welded 1.5 mm thick 0P800

Table I - Tensile test resultsfor laser beam welded',l.0 mm thick HSLA340

Table 9 - Tensile test resultsfor laser beam welded 1'0 mm thick DP800

6.1110.35 0,6304.7215 9.58 0.45

0.49 5.3330 9.14

9.40 o.42 4.42454,7010.42 0.4960

1.01 9.2575 10.88

1.10 8.8890 12.34

avefagetensile

strengthtkNl

standarddeviation

tkNl

standarddeviation

Ioio]

angle

r1

0.49 4.860 10.13

0.25 2.83'15 8.71

5.959,08 0.5430o.92 10,9345 8.460.53 4.8660 10.94

10.901.2475 1 1.38

4.2314,5ô 0.6290

averagetensile

strengthtkNl

standarddeviation

IKNI

standard

deviationIo/o]

angle["1

5.25 0.38 7.180

15 5.19 0.04 0.80

4.3730 5.34 0.23

0.18 3.4245 5.30

5.70 0.39 6.886075 6.58 0.41 6.29

4.6290 769 0.36

averagetensile

strengthtkNl

standarddeviation

tkNl

standarddeviation

to/oI

angle

rl

0.71 12.970 5.488.200.5815 7.09

7.707.49 0.58302.17 25.138.64452.57 29.5160 8.71

15,171.581^ 10.39

8.0712.09 0.9890

averagetensile

strengthtkNl

standarddeviation

tkNl

standarddeviation

Io/ol

angle

["]

5.31U

4.50 0,25 5.54tc7.6130 4.24 0.32

0.39 7.5245 5.17

5.36 0.23 4.38605.83 0.83 14.15aÉ

6.5290 7.12 0.46

averagetensile

strengthtkNl

standarddeviation

tkNl

standarddeviation

[o/o]

angle

H

7058.77 0.6201,06 1 1.4615 9.23o.72 76630 9.42

10.4710.12 1.06459.5410.21 0.9760

2.38 25.2375 9.45

o.97 7.6190 12.78

avera9etensile

strengthtkNl

standarddeviation

tkNI

standarddeviation

tolol

angle

t"1

ôtr TtrNIqII tr TtrCTtrN cpôT ^Nrn

I astrR wFl nFn^T

\/ÂFilall ls aNGl Fs

Brittle failure occurred in pure shear loading (90") of all

laser welded 1,0 mm thick HSLA 340, with base metal

failure in all other specimens. Brittle failure also occurred

in laser welded '1.0 mm thick DP800 loaded at 75" and

9Oo angles, Here failure in the heat affected zone occurred

in specimens loaded at 15o and 0o angles and base metal

failure in all other specimens,

The AWS specifies a minimum shear tension strength

and a minimum cross tension strength for resistance spot

welded joints in steel sheet for automotive applications.

The minimum shear tension strength is computed using

equation I:

51:((6,36.1O-? x 52 + 6,58.10-4 x S + 1,674) xSx4xlrs)71OOO (1)

where:

ST: Shear tension strength [kN]

S: Base metal tensile strength [MPa]

t: Material thickness [mm]

li is stated that the cross tension strength has not been

conclusively found to be a function of base metal strength,

and therefore a lower bound of all material strength as a

function of material thickness is given:

CT: 1.25 x i22 (2)

where:

CT: Cross tension strength [kN]

t: Material thickness [mm]

The tensile test specimens used in these experiments do

not comply with the prescribed geometry of the shear ten-

sile and cross tensile test specimen of the standard, but

loads applied at a Oo and 90o can be compared with the

cross and shear tensile tests respectively. This is shown

in Figure 3. lt can be seen in this graph that all welds do

exceed minimum strength levels.

e collated results

The measured tenerror bars. From thmain factor influen

ance of resistance spot welded joints in tensile testing is

the sheetthickness, notthe grade, Also itcan be seen that

147

16

14zx 1.)

,E

ÞtooitBîtE6¡ttr!¿o'E

2

0

DPBOO

(1,5m)l-ß40(1.5m)

DP6OO

(1.0m)

ôF(0o) vs CT(min)

E F(90o) vs ST(min)H340(1.0rm)

H340 I CP800

(1,0m)

Minimum vs Measured strength

!

¡o

0 2 14 164681012Minimum strength tkNI

Figure 3 - Minimum required cross tensile (CT) and shear tensile (ST) strength according

compared to measured strength at 0" and 90" load anglesto AWS standard,

r H340 (1,5 mm)

I DP800 (1,5 mm)

tr H340 (1,0 mm)

tr DP800 (1,0 mm)

Tensile strength vs Load angle (RSW)

l50

0 75 9030 45 60

Test angle [l

16

zåã8Erl 4

Figure 4 - Sttength at various loading angles for resistance spot welded joints, with 950/o er¡or bars

^tr TtrNIQII tr TtrCTtrN RtrqIqTANICtr CP'IT ANIN I ASFR WFI rôrNffq

^T \/ÀFilalt lq aNlGl Fs

1 lrB

for similar sheet thickness the strength of the HSLA340and DP800 is equal. The error bars between differentloading angles overlap but trends can be observed. ln all

cases measured strengths in shear loading are highest.

Figure 5 shows the measured tensile strength with 95%error bars for laser welded joints. lt can be seen in thisgraph that no significant conclusion can be drawn about

the differences in performance of laser welded joints

between HSLA340 and DP800 except for pure tensile(0") loading, where DP800 outperforms HSLA340. Again

error bars between loading angles overlap but trends can

be observed, The measured strength levels in shear load-

ing are highest,

Comparing measured tensile strength of laser weldedjoints with resistance spot welded joints (see Figure 6)

it can be seen that generally laser welded joints perform

better than resistance spot welded joints' This can be

attributed to the fact that the laser welds were larger than

the spot welds, lt can also bee seen that ihe spread in

results with laser welded joints is generally larger than the

spread with resistance spot welding,

As mentioned the main differentiator in strength levels is

the sheet thickness. This is for a large part due to the fact

that the weld size is directly related to the sheet thickness'

lf the results are normalised for the sheet thickness, by

dividing the tensile strength with the weld nugget cross

section area, it can be seen that the differences are much

less pronounced (see Figure 7). The remaining difference

can be attributed to the tensile component of the joint

strenglh which works on the circumference of the weld

nugget, causing plug failure at lower loading angles.

Most resistance spot welded joints showed full plug fail-

ure under tensile loading and interfacial failure in shear

loading, The absence of partial plug failure (except for

two specimens) is a positive result, as this failure mode

is considered unpredictable and therefore undesirable,

lnterfacial failure in resistance spot welded joints relates

to brittle failure in the laser welded joints, whereas base

metal failure in laser welded joints corresponds to full plug

failure in the resistance spot welded joints, except for the

laser welded joinis in DP800 loaded in predomlnant ten-

sile mode. Here the laser welded joints failed in the heat

affected zone.

It is thought that full plug failure in resistance spot welding

of advanced high strength steels is related to softening

of the heat affected zone, During welding the mariensitic

under tensile loading.

Hardness measurements were done to characterise'the

resistance spot welded joints in the I.5 mm thick sheet

16

12

I4

0

r H340 (1,0 mm)

tr DP800 0mm

Tensile strength vs Load angle (LBW

zJxaË

El!

15 9060 750 30 45

Test angle [lat various loading angles for laser welded ioints, with 950/o error barsFigure 5 - Strength

16,00

12,00

8,00

4,00

0,00

r H340 (LBW)

B DP800 (LBW)

tr H340 (RSW)

tr DPSoo (RSW)

z-fxa!EII

150 75 9030 45 60

Test angle [t

Tensile strength vs Load angle (1,0 mm)

,/

Figu¡e 6 - Strength at va¡ious loading angles for laser and resistance welded ioints, with 950/o e¡ror bars

qpaìT aNn I^etrP

\^/trr ntrn lôlNlTs aT \/^Ptôt tq ^Nlrìl

trqôtr TtrNIqII tr TtrSTFN

Normatised tensile strength vs Load angle (RSW

r ffi40 (1,5 mm)

u DP800 (1,5 mm)

tr H340 (1,0 mm)

tr DP800 (1,0 mm)

ÈtsE

.Y

x(ú

El!

2

I

0

300 15 45 60 75 90

Test angle [l

Figu¡e 7 - No¡malised strength at varioug loading angles for resistance spot welded ioints' with 95Vo error bars

material (see Table 10), li can be seen that although

the average hardness of DP800 is higher than that of

HSLA340 in both base metal and weld nugget. The

harder base metal corresponds with martensitic compo-

nent of the microstructure of the DP material, which gives

the material its increased strength. The harder weld metal

is due to the increased hardenability of the material (as

expressed in the carbon equivalence number) which leads

to the formation of martensite during the rapid forced

coolinging occleadingbase mthan base metal hardness,

To investigate the behaviour of the resistance spot welds

in tensile mode finite analysis was used. A model was

are taken into account:

[F*/FAX]" + [F"/F.J. + [F'lFrl' + lFtlFr]d>l (3)

The exponents a, b, c and d are set at 2. Failure occurs

when a single component or a combination of several

exceeds the maximum load, The load was applied as a

displacement, fixed at the centre line through the holes in

flanges of the specimen, where they are fixed in tensile

testing (see Figure 1).

Three zones were introduced to model the weld nug-

the base metal (see

e up of triangular rigid

beiween the sheetsd zone and the base

metal was made up of quad elements which are less

stiff compared to triangular elements and can thus be

used to better simulate displacement of the material dur-

ing deformation, The size of the heat affected zone was

derived from finite element simulations using Sopras, a

dedicated resistance welding simulation software pack-

age, The load was applied to the f langes of ihe U-shaped

parts in the form of a uniform displacement'

Each of the different zones was modelled using separate

stress strain curves, based on hardness measurements,

extrapolated using available literature data, Figure 10 a)

shows the stresJ strain curves for the HSLA340 and

Figure 1O b) shows the stress strain curves for DPB00'149

Table 10 - Average Vickers hardness in

Figure I - Set-up of FEA model with different zones

for weld nugget, heat affected zone and base metal

3402201501.5HSLA34O4202202501.5DPSOO

average hardness [HV]

heat affected zonethickness [mm] weld nuggetbase metalgrade

2O12 v<¡ '*:

Ôtr TFNISII F TtrSTFI-) qÞôT ÂNN I ASFR WFI NFN,IOINTS \/AFIIÔI IS ANGI FS

The results of simulations were compared with Aramis

measurements to evaluate the deformation. Figure 11

shows the Aramis measurement and results of FEA simu-

lations for HSLA340 and Figure 12 the same for DP800'It can be seen that the results of simulation compare rea-

sonably well with measured deformations.

ln both cases the measured maximum deformation is

higher than simulated, This is likely due to the fact that the

modelled weld nugget cannot deform, Maximum defor-

mation in the HSLA340 is larger compared to DPB00,

which is to be expected. From the results of simulations

it can be seen that maximum deformation in both cases

occurs at the edge of the heat affected zone with the base

metal, ln the HSLA340 the maximum values are reached

in the base metal, whereas maximum deformation in the

DPB00 occurs in the heat affected zone. This confirms

the assumption that failure occurs in DP800 due to sof-

tening of the heat affected zone,

150

Figure 9 - Set up of weld nugget of rigid body elements

with connections between the parts

f.

)/

:5 l¡Iì4lJ HÊl

4

)f

{-

!t' dptlLrUHÉL-

t0B0

24 h340_5P0fWELD

e00

630

o.14oos 0lôQ,04

ETTECTÍVE-SIRAINETfECTÍI/E-STRÁIN b)a)

Cwvo-h34023

24

Plot IPlot Is0o

810

720

0..1 0.0.o4 0.06tr2 024

23 i Currc-dp80t)

DPStìO-SPOTWELD

Figureyellow:

10 - Stress strain curves for ditferent zones, with green: base metal,

heat affected zone and blue: weld nuggeti a) HSLA340 and b) DP800

lb@lt4túltbul

I+ DJr l&Dl0Þß24e Õ¡

r¡0N,

IÈ

11 - Aramis measurements (left) and simulation results (right) for HSLA 340Figure

ôF TtrNIRII F TFSTFN qÞÔT ANID I AStrFì WFI DFD. IôINITq AT \/ARIOI IS ANGI FS

7t r_l

tt

í

5 Þ4015 r42¡?d:4 HO2. wp:3;Ê4)2

33d:2ßm22W::l€fi2I bm21 &¡)lt1#ì JèO33 ?Ér¡3

0 Ê+30

L

(!gr-

Figure 12 - Aramis measurements (left) and simulation results (right) for DP800

l?tlçaærlln this report the failure behaviour of resistance spot

welded DPB00 sheet material (1 .0 and 1.5 mm) was com-

pared with HSLA34O sheet material (1.0 and 1'5 mm) at

various loading angles for both resistance spot and laser

welded joints, lt was found that in general the behaviour of

the DP material per{ormed as well as the HSLA, Allwelds

achieved minimum required strength levels as prescribed

by the AWS,

Changes in performance with changing angle of load-

ing occurred gradually, Trends for resistance spot weld

joints were similar compared to laser welded joints, but

the behaviour of resistance spot welded joints was found

to be more consistent, lt was found that the main fac-

tor determining weld performance was sheet thickness(1,0 mm vs. 1.5 mm), The material grade (HSLA vs, DP)

appeared to be much less of an influencing factor.

Finite Element Simulations indicated that plug failure in

DP material in tensile loading can be attributed to soften-

ing in the heat affected zone, The fact that joints in DP

steel perform as well as HSLA steels allows designers

and engineers to use the advanced high strength steel

without having to worry about unpredictable failure behav-

iour leading to decreased performance for safety critical

applications.

FIII?:EIIIEã

[1] BMW Group Standard GS 96002-2: Widerstand-

spunktschweissen (RP) von Stählen' (Resistance Spot

Welding (RP) of Steels),

[2] American lron and Steel lnstitute:Anatomy of a Crash:

The most important 100 Milliseconds of Your Life, Poster'

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Nick den Utjl (ndenuijt@tudelftn/) ls w¡th HAN lJniversity of Applied Sciences'

Automolive Institute, Arnhem and Detf| LJniversily of Technology, FacullySamet

About the authors