reduced variation in design and analysis of lightweight...

IN DEGREE PROJECT TECHNOLOGY AND LEARNING,SECOND CYCLE, 30 CREDITS

, STOCKHOLM SWEDEN 2017

Reduced variation in design and analysis of lightweight welded structureIn collaboration with Bromma and Volvo CE

CHUNYING LI

KTH ROYAL INSTITUTE OF TECHNOLOGYSCHOOL OF INDUSTRIAL ENGINEERING AND MANAGEMENT

Acknowledge

Firstofall,IamgratefulformysupervisorZuheirBarsoumwhohasameetingwithourproject

groupeverysecondweek.Zuheirisaveryniceprofessorwhoalwayscarefullyandpatiently

explainedeveryquestionthat Iraisedup.Meanwhile, Igotfamiliarwithvariousdetailsof

welding and designing requirements from SD2420 Advanced design of welded structures

coursetaughtbyZuheirBarsoum.

Secondly, my co-supervisor Joakim Hedegård and Mansoor Khurshid also gave me large

amount of beneficial suggestions. Joakim Hedegård is familiar with different welding

technologyandheprovidedmesomepractical information.MansoorKhurshidworked in

Brommaandtookpartinthesameprojectwithus.HewasaPhDstudentofZuheirBarsoum

beforeandhealwayshelpedmesolveproblemsactively.

Thirdly, Iwould like togive sincere thanks tomyexaminerArneMelanderwhohas close

collaborationwithmysupervisorZuheirBarsoum.

Fourthly, IalsohadgoodcommunicationandcooperationwithmypartnerPeterHaglund

whoisaPhDstudent.Sincemymasterthesisisapartoftwo-yearproject,Peterwilldomore

analysisonspecimensandImostlyfocusontheoryresearch.Hewillalsodofatiguetestsin

thefuture.

GreatthankswillbealsosenttomyfriendJinchaoZhuandCarlLjungwhoareinthesame

officewithmeandwehelpedeachotheralot.

Last but not least, Iwould like to givemy appreciation tomy family for their continuous

supportandencouragementofmylife.

ChunyingLi

KTH,August2017

Abstract

The subject of this master thesis is about reduced variation in design and analysis of

lightweightweldedstructures.TheprojectisacollaborationwithVolvo,BrommaandKTH.

Withtechnologydevelopment,lightweightstructuresarebecomemoreandmorepopular.

In manufacturing factories, improving fatigue life in lightweight welded structures is

necessary and essential. This thesis is about reduced variation in design and analysis of

lightweightweldedstructures.Differentmethodthatarelinearelasticfracturemechanics,

effectivenotchstressandnominalstressareimplementedtoanalysisofloadcarryingand

non-loadcarryingcases.Meanwhile,variouscodesIIW,Eurocode3andCranestandardare

compared.ForIIW,allthreemethodsareincluded.However,onlynominalstressmethodis

usedforEurocode3andCranestandard.Insimpleloadingandnon-loadcarryinggeometrical

models,changingplatethicknessandpenetrationwillresultindifferenteffectonfatiguelife.

ThelatterpartofthesisisfocusedintheevaluationofVolvostandards.Effectivenotchstress

method is applied toobtain stress values and then calculate fatigue life. Several typesof

imperfectioncasesareanalyzedforbothloadcarryingandnon-loadcarryingcases.Allfatigue

lifevaluesarecomparedtothereferencefatiguelifevaluewhichis2millioncyclessothatall

statisticsarepresentedinclearpercentages.

Thestudyshowsthatvariedplatethicknessandpenetrationwillinfluencefatiguelife.Various

methodsandcodeswill affect fatigue lifediversely in loadcarryingandnon-loadcarrying

cases.ThevariationofwelddefectsinVolvostandardcasesalsohavedifferentimpacton

loadcarryingandnon-loadcarryingcases.

Keywords:Fatigue,weldquality,FEM,nominalstress,effectivenotchmethod, lightweight

structures,linearelasticfracturemethod

AbstraktDetta examensarbete handlar omminskad variation i design och analys av lätta svetsadestrukturer.ExamensarbetetharutförtsinomettsamarbetemellanVolvo,BrommaochKTH.Medteknologiskutvecklingblirlättastruktureralltmerpopulära.Vidtillverkningavfabrikerärdetnödvändigtochviktigtatt förbättrautmattningslivslängd i lättasvetsadestrukturer.Detta examensarbete handlar omminskad variation i design och analys av lätta svetsadestrukturer. Tre olika metoder, linjär elastisk brottmekanik, effektivanvisningsspänningsmetod och nominell spänningsmetod implementeras för analys avlastbärande och icke-lastbärande fall. Samtidigt jämförs olika koder IIW, Euro code 3 ochLyftkransstandard. För IIW ingår alla tre metoder. Emellertid används endast nominellspänningsmetod för Euro Code 3 och Lyftkransstandard. För enkla lastbärande och icke-lastbärandegeometriskamodellerkommerändradplåttjocklekochpenetrationattresulteraiolikaeffekterpåutmattningslivslängden.Den senare delen av examensarbetet är inriktad på utvärderingen av Volvos standarder.Effektivanvisningsspänningsmetodtillämpasföratterhållastressvärdenochsedanberäknautmattningslivslängd. Flera typer av diskontinuiteter analyseras för både lastbärande ochicke-lastbärande fall. Alla värden för utmattningslivslängd jämförs medreferensutmattningsvärdetsomär2miljonercyklersåattallstatistikpresenterassomtydligaprocentandelar.Studien visar att varierad plåttjocklek och penetration kommer att påverkautmattningslivslängden.Olikametoderochstandarderpåverkarutmattningslivslängdenolikailastbärandeochicke-lastbärandefall.VariationenavsvetsdefekteriVolvosstandardfallharocksåolikainverkanpålastbärandeochicke-lastbärandefall.

TableofContents

Acknowledge..........................................................................................................................................2

Abstract..................................................................................................................................................3

Listoffigures.................................................................................................................................6

Listoftables..................................................................................................................................7

1Introduction...............................................................................................................................81.1Background......................................................................................................................................8

1.2Problemdescription.........................................................................................................................8

1.3Objective..........................................................................................................................................8

1.4Layoutofthereport.........................................................................................................................8

1.5Overviewofmethodandcodes.......................................................................................................8

1.5.1Linearelasticfacturemechanics(LEFM)...................................................................................9

1.5.2Effectivenotchstress(ENS).......................................................................................................9

1.5.3Nominalstress(NS).................................................................................................................10

1.5.4Eurocode3.............................................................................................................................10

1.5.5Cranestandard........................................................................................................................10

2Loadcarryingcruciformcase..................................................................................................112.1TheInternationalInstituteofWelding(IIW)...................................................................................11

2.1.1Applicationoflinearelasticfracturemechanics(LEFM).........................................................11

2.1.2Applicationofeffectivenotchstressmethod(ENS)................................................................13

2.1.3Applicationofnominalstress(NS)..........................................................................................14

2.2Eurocode3application..................................................................................................................15

2.3Cranestandardapplication............................................................................................................15

3Non-loadcarryingcruciformcase...........................................................................................163.1TheInternationalInstituteofWelding(IIW)....................................................................................16

3.1.1Applicationoflinearelasticfracturemechanics(LEFM).........................................................16

3.1.2Applicationofeffectivenotchstressmethod(ENS)................................................................17

3.1.3Applicationofnominalstress(NS)..........................................................................................18

3.2Eurocode3application..................................................................................................................19

3.3Cranestandardapplication............................................................................................................19

4Comparisonbetweenmethodsandcodes.............................................................................20

5SpecificcasesofVolvostandards............................................................................................215.1VolvostandardcaseNo.106...........................................................................................................21

5.2VolvostandardcaseNo.108...........................................................................................................22





6SummaryofwelddefectsinVolvostandardcases.................................................................29

7Demonstrator..........................................................................................................................30

8Conclusions..............................................................................................................................31

9Futurework.............................................................................................................................32

10References.............................................................................................................................33

AppendixA-Effectivenotchfatigueresistanceforsteel...........................................................34

AppendixB-LoadcarryingweldedjointsofEurocode3..........................................................34

AppendixC-VolvostandardNo.203..........................................................................................35

AppendixD-VolvostandardNo.204..........................................................................................36

AppendixE-VolvostandardNo.211..........................................................................................37

Listoffigures

Figure1.Fractureinmodes I, II, and III..................................................................................9Figure2.Recommendedroundingofweldtoesandfilletweldroots[2]..............................10

Figure3.Loadcarryingcruciformstructure...........................................................................11

Figure4.Loadcarryingwithpenetrationof2mminFRANC2D.............................................12

Figure5.FatiguelifeofdifferentplatethicknessinloadcarryingcaseforLEFMmethod....13

Figure6.FatiguelifeofdifferentpenetrationinloadcarryingcaseforLEFMmethod.........13

Figure7.Loadcarryingcase,penetrationof2mm.................................................................13

Figure8.FatiguelifeofdifferentplatethicknessinloadcarryingcaseforENSmethod.......14

Figure9.FatiguelifeofdifferentpenetrationinloadcarryingcaseforENSmethod............14

Figure10.Non-loadcarryingcruciformstructure..................................................................16

Figure11.Non-loadcarryingwithpenetrationof2mminFRANC2D...................................16

Figure12.Fatiguelifeofdifferentplatethicknessinnon-loadcarryingforLEFMmethod...17

Figure13.Fatiguelifeofdifferentpenetrationinnon-loadcarryingforLEFMmethod........17

Figure14.Non-loadcarryingcase,penetrationof2mm.......................................................18

Figure15.Fatiguelifeofdifferentplatethicknessinnon-loadcarryingforENSmethod.....18

Figure16.FatiguelifeofdifferentpenetrationinloadcarryingforENSmethod..................18

Figure17.ComparisonofIIWmethods..................................................................................21

Figure18.ComparisonbetweenIIW,EurocodeandCranestandard...................................21

Figure19.Legdeviationanalysis............................................................................................22

Figure20.Fatiguelifeforthelegdeviationcase...................................................................22

Figure21.Badfit-uploadcarrying,gapheighth=3mm.........................................................23

Figure22.Badfit-upnon-loadcarrying,gapheighth=3.......................................................23

Figure23.Fatiguelifeofdifferentgapheightsinnon-loadcarrying.....................................24

Figure24.Loadcarryingcase,weldqualityC,r=2mm...........................................................25

Figure25.Non-loadcarryingcase,weldqualityC,r=2mm....................................................25

Figure26.Fatiguelifeofdifferenttransitionradiusinnon-loadcarrying.............................26

Figure27.Loadcarryingcase,undercutA=1.5mm................................................................26

Figure28.Non-loadcarryingcase,undercutA=1.5mm.........................................................27

Figure29.Fatiguelifeofdifferentundercutinnon-loadcarrying.........................................27

Figure30.Fatiguelifeofdifferentthroatthicknessinnon-loadcarrying..............................28

Figure31.Loadcarryingα=105°.............................................................................................28Figure32.Non-loadcarryingα=105°.....................................................................................29Figure33.Fatiguelifeofdifferentanglesinnon-loadcarrying.............................................29

Figure34.Simplifiedstructureofthedemonstrator.............................................................30

Listoftables

Table1.Materialproperties...................................................................................................12

Table2.Fatigueresistancesvaluesforcruciformjointsand/orT-joints...............................14

Table3.Fatiguestrengthofconstructionaldetailsforcranestandard.................................15

Table4.Fatigueresistancevaluesfornon-loadcarryingattachmentsNo.511[2]................18

Table5.Detailcategoriesofconstructionaldetailsinnon-loadcarryingforEurocode3.....19

Table6.Fatiguestrengthofconstructionaldetailsinnon-loadcarryingforcranestandard20

Table7.VolvostandardNo.106requirementdetails[8].......................................................22



1Introduction

1.1BackgroundLightweight structures reduce the environmental impact by decreased fuel consumption,

materialusage,andproductionresourcesused.Aknownandpossiblyreducedvariationin

theentirevaluestreamwillincreasethecontrolofsafetymarginshenceenablingreduced

leadtimeandincreasedflexibility.Theintroductionoflightweightstructuresisconnectedto

thepossibilitytousehighstrengthsteel(HSS).Highqualityrequirementsonweldedjoints

areseldomusedwhichlimittheintroductionofmoreHSSmaterialinindustrialmanufacturing

process.Theweightofstructurescanbereduced20%byimprovedtechnologies,meanwhile

theproductioncostisreduced.Withareducedscatterinproduction,loadestimation,and

structuralstrengthabetterutilizationofHSSispossiblewiththegreatpotentialoflightweight

structures.

In this master thesis, different of variation will be studied and mapped. High quality

requirementsonwelded jointsareseldomusedwhich limit the introductionofmoreHSS

heavierthanwhat ispossible.Thereferencefatiguelifevaluesare2millioncycles.Allthe

fatiguelifevaluesarecomparedwiththereferencefatiguelifesoalltheresultsareshown

veryclearly.

1.2ProblemdescriptionAlargecontributoroftheslowintroductionofHSSisduetothelargescatterintheproduction

processwhichresultsinvariationinthefactorsthataffectthefatigueproperties,forexample,

weldqualityandresidualstresses.

1.3ObjectiveThegoalofthethesisworkistomapandstudyvariationinthedesignandFEanalysisprocess

oftheproductdevelopmentinfabricationofweldedstructures.

1.4LayoutofthereportInthebeginningofthereport,thegeneralideasofthismasterthesisaredescribed.Different

concepts of methods and codes are introduced. Then, two basic cases of load carrying

cruciformandnon-load carrying cruciformare specified. The correspondingmethods and

codesareimplementedintothetwocasesandarecompared.Chapter5isaboutanalysisof

failureandimperfectionofVolvostandardcases.Chapter6isthesummaryinapedagogical

waythemagnitudeofeffectofdifferentwelddefects.Intheend,conclusionandfuturework

areclarified.

1.5OverviewofmethodandcodesLinearelasticfracturemechanics(LEFM),Effectivenotchstress(ENS)andnominalstress(NS)

are three fatigue assessmentmethods to analysis. Different codes and standards such as

InternationalInstituteofWelding(IIW),Eurocode3(EC3)andCranestandard(CrandSTD)will

beusedtostudythevariationinlifeassessment.

1.5.1Linearelasticfacturemechanics(LEFM)Linearelasticfracturemechanicsmethodisusedtopredictthebehaviorofcracksinsolids

subjectedtofatigueloading.TherearethreebasictypesofloadcasethatisshowninFigure

1.ModeIisanopenmode.ModeIIisaslidingorshearingmode.ModeIIIisatearingmode.

In order to predict fatigue crack propagation, numerous empirical or semi-empirical

equationshavebeenproposedtorelatefatiguecrackgrowthratedatatotheparameterΔ#[1].NumericalintegrationofParislawisusedinfatiguelifeassessment,thatis

$%

$&= ( ∙ Δ#*

.

Where+, / +. is the crack growth rate per cycle, C and m are material specific input

parameters. Cmeans fatigue crack growth coefficient andmmeans fatigue crack growth

exponent.

Figure1.Fractureinmodes I, II, and III.

Inthisthesis,FRANC2Dsoftwareisusedtoanalysisthecrackpropagationprocess.Thestress

intensityfactorscanbeobtainedautomaticallyinFRANC2D.Then, exporttheSIFhistorytocomputecyclesinExcelwhichistheExcelsheetshownonCornellFractureGroupwebsite[3].

1.5.2Effectivenotchstress(ENS)Thetotalstressacquiredassuminglinear-elasticmaterialbehavioriseffectivenotchstress.

Forstructuralsteelsandaluminumalloysaneffectivenotchrootradiusofr=1mmhasbeen

verified to give consistent results if plate thickness is equal or bigger than 5mm [4]. This

methodassessesweldedjointsrestrictedlywithrespecttopotentialfatiguefailuresfromthe

weldrootorweldtoe.Thefatigueassessmentisassociatedfatigueclass(FAT)forthebase

material. In thispaper, thematerial is steel and the correspondingFATvalue is225 from

AppendixA.RecommendedroundingofweldtoesandfilletweldrootsisshowninFigure2.

Figure2.Recommendedroundingofweldtoesandfilletweldroots[2]

1.5.3Nominalstress(NS)Nominal stress is the stress that is calculated in the sectional area under consideration,

containingthestressraisingeffectsofthemacro-geometricshapeofthecomponentnearthe

joint,ignoringthelocalstressraisingeffectsoftheweldedjoint.

Inmost simple cases, the nominal stress can be calculated using elementary theories of

structuralmechanicswhichisbasedonlinear-elasticbehavior.Nominalstressistheaverage

stressintheweldthroatorintheplateattheweldtoeasindicatedinthetablesofstructural

details[4].ThecalculationofnominalstressiscomparedwithaFAT-value.Selectedfroma

catalogue of details, the geometry most closely resembling the actual welded detail.

Meanwhile, small misalignments are covered in the FAT values, also residual stresses.

NominalstressmethodcouldbeusedifFAT-valueandloadingareconsistentwiththefatigue

class.Usually,forcomplexstructuresisnoteasytodefinenominalstress.

1.5.4Eurocode3Eurocodes,EN1993-1-9isusedforfatiguestrengthinstructuralsteels. Thefatiguestrengthfornominalstressrangesisrepresentedbyaseriesof(log∆01)-(logN)curvesand(log∆21)- (log N) curves (S-N-curves), which correspond to typical detail categories. Each detail

categoryisdesignatedbyanumberwhichrepresents, inN/334,thereferencevalue∆01 and∆21 forthefatiguestrengthat2millioncycles[5].

Thefatigue lifeassessmentshouldbecarriedoutwiththeuseofnominalstressrangefor

detailsshown inthetables.Thevalueof thestressrange∆05 correspondingtoavalueof.5=2millioncycleswerecalculatedfora75%confidencelevelof95%probabilityofsurvival

forlogN,meanwhile,thestandarddeviationandthesamplesizeandresidualstresseffects

aretakenintoconsideration.

1.5.5CranestandardCrane standard deals only with the nominal stress method. The stresses are calculatedaccordingwiththenominalstressconcept.Anominalstressisastressinthebasematerial

adjacenttoapotentialcracklocation,calculatedinaccordancewithsimpleelasticstrength

ofmaterialstheory,excludinglocalstressconcentrationeffects[6].Thecharacteristicfatigue

strengthvaluescontaintheeffectsoflocalstressconcentrationduetotheshapeofthejoint

andtheweldgeometry,thestressdirection,residualstresses,theweldingprocess,etc.

Thelimitdesignstressofaconstructionaldetailischaracterizedbythecharacteristicfatigue

strength, that is the value of∆05 . The representation of∆05 is the fatigue strength at

2×10:cyclesunderconstantstressrange loadingandwithaprobabilityofsurvival97.7%.Thevaluesof∆05dependontheweldqualitylevels.

2LoadcarryingcruciformcaseFirstbasicmodelisloadcarryingcruciformcaseinwhichtheupperpartisnotfullpenetration

andlowerpartisfullpenetrationsothatthismodelcanbeconsideredasT-joint.Theplate

thicknessinthisstudyis6mm,12mmand21mm.Andthepenetrationinthisstudyis1mm,

2mm,3mmand4mm.Thestressrangeisaconstant,thatis100Mpa.Thegeometrymodelis

showninFigure3.

Figure3.Loadcarryingcruciformstructure

2.1TheInternationalInstituteofWelding(IIW)The International Institute ofWelding was found in 1948 by the welding institute of 13

countrieswhofeltimportanttomakemorerapidscientificandtechnicalprogress.

ThetechnicalareaofIIWencompassesthejoining,cuttingandsurfacetreatmentofmetallic

andnon-metallicmaterialsbysuchprocessesaswelding,bracing,soldering,thermalcutting,

thermalspraying,adhesivebondingandmicrojoining.IIWworkalsoembracesalliedfields

includingqualityassurance,non-destructivetesting,standardization,inspection,healthand

safety,education,training,qualification,designandfabrication[4].

2.1.1Applicationoflinearelasticfracturemechanics(LEFM)HerearesomebasicstepswhicharedoneinFranc2D.Inthebeginning,somepreliminary

work shouldbedone.UseAnsysAPDL to createabasicT-jointmodel,makemeshesand

archivethefilein*.cdbfile.Thentranslate*.cdbfileto*.inpfilebytranslator.

Inputthe*.infileandruntheFRAND2Dprogram.First,inPRE-PROCESS,choosePlanstress

inPROBLEMTYPE.Then,selecttheMATERIALoption,thismodelismadeofsteel.SelectE

andwritetheYong’smodulusof210000MPa.

t[mm] Platethickness 10

H[mm] Leglength 9.9

2a[mm] Weldrootgap 8

S[MPa] Nominalstressrange 100

Materialdata:

-Basic:Steel:DOMEX550MC

Yieldstrength=550Mpa

Ultimatestrength=700Mpa

E-modulus=210GPa,n=0.3-FractureandFatigue:��m=3�C=5.0E-12(unitsinMPaandmeter)

R=0(stressratio)�K<==120MPa√m(fracturetoughness)

∆K>?=2MPa√m(thresholdvalue)

Table1.Materialproperties

Inloadcarryingcase,thecrackspropagatefromtherootsides.Extractstressintensityfactors

computedwithinFRANC2Dtogetfatiguelife.

Figure4.Loadcarryingwithpenetrationof2mminFRANC2D

When three different plate thicknessmodels are compared, the penetration is kept as a

constant1mm.Allthroatthicknessis0.7timesplatethickness.Adeclinetrendthatasthe

platethicknessincreases,thefatiguelifewilldecreaseisshownclearly.

0.00%

40.00%

80.00%

120.00%

160.00%

200.00%

240.00%

6 12 21

Percentageofreferencelife

Platethickness[mm]

!"/(2E+6)

Figure5.FatiguelifeofdifferentplatethicknessinloadcarryingcaseforLEFMmethod

Whentheplatethickness issetasaconstantthat is12mm,weldpenetrationwillmakea

differenceonfatiguelife.Thecorrespondingfatiguelifewillincreasewiththeincreaseofthe

penetration.

Figure6.FatiguelifeofdifferentpenetrationinloadcarryingcaseforLEFMmethod

2.1.2Applicationofeffectivenotchstressmethod(ENS)

Figure7.Loadcarryingcase,penetrationof2mm

Herethreeplatethicknesseswhichare6mm,12mmand21mmarechoseninthestudy.All

throatthicknessis0.7timesplatethickness.Whenthepenetrationiskeptasaconstantwhich

is1mm,thefatiguelifevalueswilldecreaseastheplatethicknessincrease.

0.00%

40.00%

80.00%

120.00%

160.00%

200.00%

240.00%

1 2 3 4


Penetration [mm]

!"/(2E+6)

Figure8.FatiguelifeofdifferentplatethicknessinloadcarryingcaseforENSmethod

Whentheplate thickness iskeptasaconstantwhich is12mm, the fatigue lifevalueswill

increaseaccordingtheincreaseofpenetration.

Figure9.FatiguelifeofdifferentpenetrationinloadcarryingcaseforENSmethod

2.1.3Applicationofnominalstress(NS)

Table2.Fatigueresistancesvaluesforcruciformjointsand/orT-joints

Innominalstress,theassociatedfatigueclassisrelativelylow(FAT36-FAT40),definingthe

characteristic fatigue strength of the design S-N curve at 2 million cycles for a survival

probability of 97.7%. The reasons for the low fatigue class are that a very sharp notch is

presentandthatthenominalstressinthewelddisregardsanylocalbendingeffects[7].

FAT:=36Mpa,∆0@ =A

4%∙ ∆0* +

A

:%∙ ∆0C=71.4Mpa,.D:=2∙ 10

: ∙ (FGH

∆IJ)L=2.56E+5cycles

0.00%

30.00%

60.00%

90.00%

120.00%

150.00%

180.00%

6 12 21


Plate thickness [mm]

!"/(2E+6)

0.00%

30.00%

60.00%

90.00%

120.00%

150.00%

1 2 3 4


Penetration [mm]

!"/(2E+6)

However, if plate thickness t is kept as a constant, throat thickness a is decreased, FAT:

=40Mpa,.D:=2∙ 10: ∙ (

FGH

∆IJ)L=3.52E+5cycles,fatiguelifewillincrease.

2.2Eurocode3applicationFromtheappendixB,detailcategoriesforconstructionaldetailsareshown.

Detailcategory:=36Mpa,∆σN =>

4O∙ ∆σP +

>

:O∙ ∆σQ=71.4Mpa,

NS:=2∙ 10: ∙ (

$UA%VWX%AUYZ[\

∆]^)L=2.56E+5cycles

Themisalignmentoftheload-carryingplatesshouldnotexceed15%oftheplatethicknessoftheintermediateplate[5].

Theminimumvalue:∆σN =}~.�ÄÅO

~~Ç%= 62.09Mpa, NS:=2∙ 10

: ∙ ($UA%VWX%AUYZ[\

∆]^)L=3.9E+5

cycles,fatiguelifewillincrease.

Themaximumvalue:∆σN =}~.�ÄÅO

àÇ%= 84Mpa, NS:=2∙ 10

: ∙ ($UA%VWX%AUYZ[\

∆]^)L=1.6E+5

cycles,fatiguelifewilldecrease.

2.3Cranestandardapplication

Table3.Fatiguestrengthofconstructionaldetailsforcranestandard

Here,∆0X,∆2Xarethecharacteristicfatiguestrengths.Stressinweldthroat,FAT:=45Mpa,∆σN=F/(2×,×ℓ)=F/(2×0.7×ç×ℓ)=71.4Mpa

NS:=2∙ 10: ∙ (

éèê

∆]^)L=5.01E+5cycles.

InTable3,itisshownthecharacteristicfatiguestrengthsforweldqualitylevelCandlevelB.

WeldqualitylevelC,FAT:=63Mpa,NS:=2∙ 10: ∙ (

éèê

∆]^)L=5.01E+5cycles.

WeldqualitylevelB,FAT:=71Mpa,NS:=2∙ 10: ∙ (

éèê

∆]^)L=7.16E+5cycles,.Dincrease

3Non-loadcarryingcruciformcaseAnotherbasicmodelisnon-loadcarryingcruciformcaseinwhichboththeupperpartandthe

lowerpartisnotfullpenetration.Theplatethicknessinthisstudyis6mm,12mmand21mm.

Andthepenetrationinthisstudyis1mm,2mm,3mmand4mm.Thestressrangeisaconstant,

thatis100Mpa.TheweldqualityforthiscaseismainlyVE,VDandVC.Thegeometrymodel

isshowninFigure10.

Figure10.Non-loadcarryingcruciformstructure

3.1TheInternationalInstituteofWelding(IIW)3.1.1Applicationoflinearelasticfracturemechanics(LEFM)

Figure11.Non-loadcarryingwithpenetrationof2mminFRANC2D

Innon-loadcarryingcase,thecrackspropagatefromtheedgeoftoe.IneverymodelofFRANC

2D,aninitialcrackof0.38mmwhichisacasualvaluebutissmallandgoodenoughisformed

inthebeginning.Theninthesimulation,thecrackpropagatesautomaticallyandthecrack

endswiththecracklengthof5.38mm.Thefinalcracklength5.38mmischosenarbitrarily.All

thestressintensityfactorvaluescanbeobtainedinstressintensityhistory.Inputallthese

valuesintotheExcelsheetshownonCornellFractureGroupwebsitetogetthefatiguelife.

Astheplatethicknessincrease,thefatiguelifewilldecrease.

Figure12.Fatiguelifeofdifferentplatethicknessinnon-loadcarryingforLEFMmethod

However,thechangeofpenetrationwillnotaffectfatigue life.Theaveragepercentageof

fatiguelifeisaround83%whichcanbeseeninfigure13.

Figure13.Fatiguelifeofdifferentpenetrationinnon-loadcarryingforLEFMmethod

3.1.2Applicationofeffectivenotchstressmethod(ENS)TheFEManalysiswhenthepenetrationis2mminnon-loadcarryingisshowninFigure14.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

6 12 21


Plate thickness [mm]

!"/(2E+6)

Figure14.Non-loadcarryingcase,penetrationof2mm

Ineffectivenotchmethod,ifpenetrationiskeptasaconstant1mm,fatiguelifedecreasewith

the increase of the plate thickness.When the plate thickness is 6mm, the percentage of

fatiguelifeis148.91%.However,whentheplatethicknessis21mm,thepercentageoffatigue

lifeisonly19.78%.ThestatisticsareshowninFigure15.

Figure15.Fatiguelifeofdifferentplatethicknessinnon-loadcarryingforENSmethod

Whentheplatethicknessiskeptasaconstantwhichis12mm,fatiguelifevalueswillnothave

largevariationwiththechangeofpenetration.

Figure16.FatiguelifeofdifferentpenetrationinloadcarryingforENSmethod

3.1.3Applicationofnominalstress(NS)

Table4.Fatigueresistancevaluesfornon-loadcarryingattachmentsNo.511[2]

0.00%

30.00%

60.00%

90.00%

120.00%

150.00%

180.00%

6 12 21


Platethickness[mm]

!"/(2E+6)

FAT:=80Mpa,∆0@=100Mpa.Thiscaseanangularmisalignmentcorrespondingto#*=1.2isconsideredsothatthelimitvalue∆0* =100/#*=83.33Mpa.

.D:=2∙ 10: ∙ (

FGH

∆Ië)L=1.77E+6cycles

However,ifthestructureischangedfromcruciformtotwosidesfilletsorweldtoeisground,

thesituationwillchange.ThenFAT:=100Mpa,∆0@=100Mpa,∆0*=100/#*=83.33Mpa,.D:

=2∙ 10: ∙ (FGH

∆IJ)L=3.46E+6cycles,fatiguelifewillincrease.Inproductionprocess,moreafter-

workshouldbedonesoproductioncostwillalsoincrease.

3.2Eurocode3application

Table5.Detailcategoriesofconstructionaldetailsinnon-loadcarryingforEurocode3

Inthiscase,theplatethicknessisalwayssmallerthan50mm.FromTable13shownabove,

detailcategoryis80withcorrespondingtotheplatethicknesslessthan50mm.

FAT:=80Mpa,∆0@ = 100Mpa,.D:=2∙ 10: ∙ (

FGH

∆IJ)L=1.02E+6cycles

Increaseplatethicknesslandkeeptherangefrom50mmto80mm,FAT:=71Mpa,

.D:=2∙ 10: ∙ (

FGH

∆IJ)L=7.16E+5cycles,.Dincrease.

3.3Cranestandardapplication

Table6.Fatiguestrengthofconstructionaldetailsinnon-loadcarryingforcranestandard

FatiguestrengthvaluesarevariedwithweldqualitylevelBandqualitylevelC[6].Meanwhile,

inthisthesis,thestudiedstructureisdoublefilletweld.FromTable6,

WeldqualitylevelC,FAT:=90Mpa,∆σN = 100Mpa,NS:=2∙ 10: ∙ (

éèê

∆]^)L=1.46E+6cycles

WeldqualitylevelB,FAT:=100Mpa,∆σN = 100Mpa,NS:=2∙ 10: ∙ (

éèê

∆]^)L=2E+6cycles

4ComparisonbetweenmethodsandcodesComparingthreedifferentmethodsofIIWcode,somevaluesaresetasconstant.Theplate

thicknessis12mm,thestressrangeis100Mpa,throatthicknessis0.7timesofplatethickness

andthepenetrationis3mm.

FromFigure17,wecanseethatforbothloadcarryingandnon-loadcarrying,themethodof

linear elastic fracturemechanicswould always reach thehighest percentageof reference

fatiguelife.

12.80%

81.38%

118.70%

51.20%

73.88% 84.63%

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

140.00%

NS ENS LEFM


ComparisonofIIWmethods

load-carrying nonload-carrying

Figure17.ComparisonofIIWmethods

When three codes IIW, Euro code 3 and Crane standard are in comparison, the control

conditions of plates are the same as above. In addition, some misalignment values are

considered in some specific codes. Thenon-load carrying caseof IIW is coveredwith the

maximumangularmisalignmentcorrespondingto#*=1.2whichmeansthatthelimitvalue

∆0* =100/#* =83.33Mpa. The load carrying case of Euro code 3 includes that themaximummisalignmentoftheload-carryingplatesis15%oftheplatethicknessoftheintermediateplate.

Figure18.ComparisonbetweenIIW,EurocodeandCranestandard

5SpecificcasesofVolvostandardsOverall,variationsthateffectsfatigue lifeofweldedstructureshavebeenclearlyclarified.

Thensomescattersareconsidered intoVolvostandard181-0004tostudyvariousspecific

cases.InVolvostandards,severalspecificcaseswhichcovermisalignmentandfailuresare

usedtoanalysisfatiguelifebyeffectivenotchstressmethodwhichshowsgeometrymodels

clearly.AllthemodelsarecreatedinAnsysbyinputtingcodesintoit,meshing,solving,etc.

Differentweldclassaredescribedtofulfillvariousproductionrequirement.VSisweldclass

for static strength. VE, VD, VC, VB are weld classes for fatigue strength from lowest

requirementtohighestrequirement.

5.1VolvostandardcaseNo.106ThecaseofVolvostandardNo.106isaboutlegdeviationshowninTable7.Sincetheplate

thicknessis10mm,themaximumdeviationdistanceis3.4mmforalltheweldrequirements

VE,VD,VCandVB.Meanwhile,thedeviationisalwaysinthesamedirectionalongwiththe

loading direction. In this study, the referencemodelswhich don’t have leg deviation are

comparedwithmodelswhichhave themaximum legdeviation.The stressanalysisof the

geometrymodelswithdeviation3.4mmareshowninFigure19.

12.80% 19.50%

25.05%

88.50%

51.20%

73.00%

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

IIW Eurocode3 Cranestandard


Comparisionofcodes

load-carrying nonload-carrying

Table7.VolvostandardNo.106requirementdetails[8]

Figure19.Legdeviationanalysis

Fromthestaticsshownbelow,bothforloadcarryingandnon-loadcarrying,percentageof

referencefatiguelifewillincreaseaslegdeviationoccurs.ThisisshowninFigure20.

Figure20.Fatiguelifeforthelegdeviationcase

5.2VolvostandardcaseNo.108Thiscaseisaboutbadfit-upwhichmeansthattwoplateshaveagapdistance.Thisisshown

inTable8.Forallweldqualities,iftheplatethicknessis10mm,maximumgapheightis3mm.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

0 3.4


Leg deviation A [mm]

loadcarrying nonload carrying

!"/(2E+6)

Here, four conditions inwhichgapheight are0mm,1mm,2mmand3mmare taken into

consideration.


Figure21.Badfit-uploadcarrying,gapheighth=3mm

Inloadcarryingcases,gapheightswill influencethefatiguelife.Thegeometrymodelwith

gapheighth=3mminbadfit-uploadcarryingcaseisshowninFigure21.Whenthegapheight

is2mm,thefatiguelifevalueisthemostandwhenthegapheightis3mm,thefatiguelife

valueistheleast.ThisisshowninFigure23.

Figure22.Badfit-upnon-loadcarrying,gapheighth=3

Innon-loadcarryingcases,gapheightsdon’thaveimpactonthefatiguelife.Asthegapheight

changes from 0 to 3mm, the average fatigue life is around 3.13E+06 cycles. The average

percentageofreferencefatiguelifeis156.5%.

Figure23.Fatiguelifeofdifferentgapheightsinnon-loadcarrying

5.3VolvostandardcaseNo.202VolvostandardNo.202 isabout requirementsofouter transitionradiusshown inTable9.

Welding requirement VE doesn’t have requirements. The outer transition of weld

requirement VD should be equal to or bigger than 0.3mm. The outer transition ofweld

requirement VC should be equal to or bigger than 1 mm. The outer transition of weld

requirementVBshouldbeequaltoorbiggerthan4mm.Hence,thenotchradiusforCE,VD,

VCandVBareseparately1mm,1.3mm,2mmand5mm.


0.00% 20.00% 40.00% 60.00% 80.00%

100.00% 120.00% 140.00% 160.00% 180.00%

0 1 2 3


Gap height h [mm]


!"/(2E+6)

Figure24.Loadcarryingcase,weldqualityC,r=2mm

Forloadcarrying,fatiguelifevariesalittleasthetransitionradiuschange.Whentheweld

qualityisVB,thereferenceoffatiguelifeisthemost.However,whentheweldqualityisVC,

thereferenceoffatiguelifeisthe79%andistheleast.Thegeometrymodelwithtransition

radius2mmisshowninFigure24.

Figure25.Non-loadcarryingcase,weldqualityC,r=2mm

Fatiguelifewillincreasefastasthetransitionradiusincreasesfornon-loadcarrying.When

theweldqualityisVB,thepercentageofreferencefatiguelifecanreach197%.Thegeometry

modelwithtransitionradius2mminnon-carryingcaseisshowninFigure25.

Figure26.Fatiguelifeofdifferenttransitionradiusinnon-loadcarrying

5.4VolvostandardcaseNo.203VolvostandardNo.203isaboutundercutandtheanalysisofthisthesis isfocusedonfillet

welding.AppendixCshowsspecificrequirementsfordifferentweldqualities.Fortheweld

requirementVE,VDandVC,themaximumundercutis1.5mm.FortheweldrequirementVE

andVD,A≤0,1t,thatisA≤1mmsincetheplatethicknessforthiscaseis10mm.Andforthe

weldrequirementVC,A≤0,08t,thatisA≤0.8mm.

Figure27.Loadcarryingcase,undercutA=1.5mm

Figure27showsthegeometrymodelwithundercutA=1.5mminloadcarryingcase.Undercut

doesn’thaveabiginfluenceonfatiguelifeinloadcarryingcases.

0.00%

50.00%

100.00%

150.00%

200.00%

250.00%

300.00%

350.00%

1 1.3 2 5


Transition radius r [mm]


!"/(2E+6)

Figure28.Non-loadcarryingcase,undercutA=1.5mm

Figure28showsthegeometrymodelwithundercutA=1.5mminnon-loadcarryingcase.In

non-loadcarryingcases,theresultswillbeincontrastthatdeeperundercutwillcauselower

percentage of reference fatigue life. If there’s no undercut, the percentage of reference

fatigue life is 155.59%. However, if the undercut is 1.5mm, the percentage of reference

fatiguelifeisonly23%.ThiscanbeseeninFigure29.

Figure29.Fatiguelifeofdifferentundercutinnon-loadcarrying

5.5VolvostandardcaseNo.204Volvo standard No.204 is under passed throat dimension from Appendix D. If the plat

thickness is10mm,thepermission forminimumthroat is larger than0.9a, that is6.3mm.

Meanwhile,deviationnotexceed-2mm.Hence,threethroatthicknesseswhichare5mm,6.3

and7mmareconsidered.

Inloadcarryingcase,biggerthroatthicknesscausehigherfatiguelife.Innon-loadcarrying

case,throatthicknessdoesn’thavebiginfluenceonfatiguelife.Alittledeclinetrendisshown

withtheincreaseofthroatthickness.ThisisshowninFigure30.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

140.00%

160.00%

180.00%

0 0.8 1 1.5


A [mm]


!"/(2E+6)

Figure30.Fatiguelifeofdifferentthroatthicknessinnon-loadcarrying

5.6VolvostandardcaseNo.211ThefailureofVolvostandardNo.211 isabout incorrectweldtoe.Theanglesbetweenthe

weldingfaceandtheplatesformabnormalangles.ItshowsindetailsfromAppendixE.Here

theanalysisisthroughfourangleswhichare90°,105°,120°and135°.Whentheangleis105°,

themodelisshowninFigure31.

Figure31.Loadcarryingí=105°

Asthevaluesshownbelowaboutloadcarryingcases,comparingallothersangleswiththe

reference angle 135°, the fatigue life will decrease gradually and slowly when the angle

decreasesfrom90°to135°.ThisisshowninFigure33.

0.00%

20.00%

40.00%

60.00%

80.00%

100.00%

120.00%

5 6.3 7


Throat thickness a [mm]


!"/(2E+6)

Figure32.Non-loadcarryingí=105°

Whentheangleis105°innon-loadcarrying,themodelisshowninFigure32.Asthevalues

shownbelowaboutthenon-loadcarryingcases,anglesdon’thavegreateffectonfatiguelife.

Astheanglevariesfromthereferenceangle135°to120°,fatiguelifeincreasealittle.But

whentheanglevariedfrom120°to90°,fatiguelifedecreasealittle.Themodeledgeometry

thattheangleis105°isshowninFigure33.

Figure33.Fatiguelifeofdifferentanglesinnon-loadcarrying

6SummaryofwelddefectsinVolvostandardcasesInloadcarryingcases,ifthevariatesoflegdeviation,underpassedthroatandincorrectweld

toeincrease,thecorrespondingfatiguelifewillincrease.Thevariationofundercutdoesn’t

influencefatiguelife.Innon-loadcarryingcases,ifthevariatesoflegdeviationandtransition

radiusrise,thecorrespondingfatiguelifewillincrease.Ifthevariatesofundercutandunder

passedthroatreduce,thefatiguelifewilldecrease.Thevariationofbadfit-updoesn’thave

animpactonfatiguelife.

0.00% 20.00% 40.00% 60.00% 80.00%

100.00% 120.00% 140.00% 160.00% 180.00%

90° 105° 120° 135°


α


!"/(2E+6)

7Demonstrator

Acommonrepresentativecomponentwhichcoversmostaspectsofvariationinanalysisand

designwillbesuggestedbytheparticipatingcompanies,whichthestudents(andengineers

at the different companies) will carry out design and analysis on the demonstrator. The

simplifiedstructureofthedemonstratorisshowninFigure34.Thespecimensareprovided

fromBrommacompany.PeterHaglundwhoisaPhDstudentfrommysupervisorZuheirwill

continueallthespecimensresearch.

Figure34.Simplifiedstructureofthedemonstrator

8Conclusions

Reducingvariationindesignandanalysisofweldedstructureswillmakeconvenienceforthe

researchofimprovingfatiguelife.Thevariationofpenetrationandplatethicknessarestudied

inloadcarryingandnon-loadcarryingcases.Thecomparisonwithdifferentmethodsoflinear

elasticfracturemechanics,effectivenotchstressandnominalstressshowsthatlinearelastic

fracturemechanicsmethodwillobtainhighestfatiguelifeforbothloadcarryingandnon-load

carryingcases.VariouscodesofIIW,Eurocode3andCranestandardarecomparedtoshow

thediversity.Thestudyofdifferentmethodsandcodeswillprovidethereferencefor the

researchofspecimens.

TheanalysisofimperfectionweldmodelsinVolvostandardcasesprovethevariationofweld

analysis. Imperfectionsof legdeviation,gapheight, transition radius,underpassed throat

thickness,undercutandincorrectweldtoehavedifferenteffectonloadcarryingandnon-

load carrying cases. Fatigue life research of analyzing misalignment and failure in Volvo

standardswillencouragetheweldingdevelopmentinmanufacturingprocess.

9Futurework

In the future, there are still some further research to be done. For example, if different

misalignments and failure occur simultaneously on the models, fatigue life will change

differently. Meanwhile, that kind of cases would be much more complicated. For Volvo

standardcaseNo.203,theundercutheightisconsideredinthisstudy,butinfact,thebottom

radius of the hole is also a considerable factor. There are still someother cases in Volvo

standardwhichcanbeanalyzedbyothermethods.

Fatiguetestsofspecimenswouldbedonesothatrealvaluescouldbeobtainedtocompare

withresearchvalues.Thedifferenceofresearchvaluesandrealisticvalueswouldexit.

Volvowouldmodifysomestandardssubjectedtodifferentweldqualities.Theestimatedtime

tostartisthebeginningof2018.Improvingweldingqualitytoimprovefatiguelifeisagreat

objectiveformanyfactories.

10References

[1]T.Nykänen,G.Marquis, T.Björk, July2006, Fatigueanalysisofnon-load-carrying fillet

weldedcruciformjoints,EngineeringFractureMechanics74(2007)399-415

[2] John B. Wachtman,W. Roger Cannon and M. John Matthewson, September 2009, MechanicalPropertiesofCeramics,SecondEdition, DOI:10.1002/9780470451519.ch5,P71[3]Website:http://cfg.cornell.edu/software/

[4] A.F. Hobbacher, 2014, Recommendations for Fatigue Design of welded joints and

components,SecondEdition,IIW-2259-15

[5]Eurocode3:Designofsteelstructures-Part1-9:Fatigue,2005,Authority:TheEuropean

UnionPerRegulation305/2011,Directive98/34/EC,Directive2004/18/EC

[6] Cranes-GeneralDesign-Part3-1:LimitStatesandproofcompetenceofsteelstructure,

July2013,EuropeanCommitteeforStandardization

[7]Wolfgang Fricke, June 2012, IIW Guideline for the Assessment ofWeld Root Fatigue,

WeldingintheWorld,IIW-Doc.XII-2380r3-11/XV-1383r3-11,Revision3

[8]VolvoGroupStandard,April2013,STD181-004

AppendixA-Effectivenotchfatigueresistanceforsteel

AppendixB-LoadcarryingweldedjointsofEurocode3

AppendixC-VolvostandardNo.203

AppendixD-VolvostandardNo.204

AppendixE-VolvostandardNo.211

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