焊点的疲劳寿命分析与优化改进研究

上海交通大学硕士学位论文轿车车身结构及焊点的疲劳寿命分析与优化改进研究姓名：杜中哲申请学位级别：硕士专业：车辆工程指导教师：朱平20060201I80SUVDII(1)Cbar(2)(3)IIIStudyonfatiguelifeanalysisandoptimizationofauto-bodystructureandspotweldABSTRACTWiththedevelopmentofmodernindustryrapidly,theproblemofmachinefatiguelifebecomesprominentineverydomain.Accordingtostatisticaldata,about80percentofstructuraldamageisinducedbyfatigueinvalidation.So,inordertoavoidtheincidentsoffatiguefracture,researchonfatiguelifeandfindingthewaystoimprovingthelifeofpartsisimportantfordevelopmentofnationaleconomyandtechnology.Inthepresentstiffnessandstrengthofauto-bodystructureisalwaysattachedimportancetoduringthecourseofautomobiledesign.Andthelevelcanreachanagreement.Fatiguestrengthofauto-bodystructureisignoredbycustomer,salesmanandproducer.Inthephaseofautomobiledesign,predictionoflifeofauto-bodywithFEMandimprovementoffeeblepartscandecreasethecostofdevelopmentandmanufactureandprolongtheapplicationlifeofauto-body.Soitisnecessaryforanalysisoffatiguelifeofauto-bodystructure.Thereisacaseofsomecarbodyinthispaper.Inthiscase,aFEmodelofbodyhadbeenbuilt.Thenonthebaseofresultofstressandstrainoffrequencyresponseofbodyunderunitexcitation,fatiguelifeofauto-bodyisanalyzedwithtimedomainfatiguemethod.AndLifeofauto-bodystructureandspotweldisestimatedatsomespeedontheroadofDlevel.Thenlifeofsomeparts,whichareprovedtodamageeasily,arecalculatedagainwithfrequencydomainfatiguemethod.Thecalculationcantestifythefeasibilityandrationalityoftheoptimizationscheme.Themethodcanbereferentialtoresearchonanalysisandimprovementoffatiguelifeofautomobiles.Therearethreepartsofthemaincontentinthepaper,asfollow:IV(1)Toconstructandtestifythefiniteelementmodelofauto-bodyTheFEmodelofauto-bodystructureisconstructedwithshelltypeelementsandspotweldwithCbartypeelements.Themodeliscalculatedofnormalmode,torsionalstiffnessandbendingstiffnessofauto-bodyafteritisundertheloadingandconstrainedconditions.Bycontrastofthetestresult,thevalidityoftheFEmodelistestified.(2)Tocalculateandanalyzethefatiguelifeofauto-bodystructureandspotweldThefatiguelifeofauto-bodystructureandspotweldiscalculatedwithtimedomainfatiguemethodrespectively.Throughthecalculationthedistributionoffatiguelifeonthewholeauto-bodyisattainedandthepartswithlowerfatiguelifearefound.Theconclusionofcalculationagreeswiththefact.Thenlifeofsomeparts,whichareprovedtodamageeasily,arecalculatedagainwithfrequencydomainfatiguemethod.Thenthevalidityofthetimedomainfatiguemethodistestified.(3)Tooptimizeandimprovetheauto-bodystructureandspotweldAuto-bodystructureandspotweldisoptimizedandimprovedonthebaseofanalysisoftheirfatiguelife.Toimprovementofauto-bodystructure,tailorweldedblanksareappliedtoenhancethelifeofpartsinhighstresszoneandprolongtheirlife.Tooptimizationofspotweld,thespotweldwithhighstressisfoundfirstly,andthenthelocationofsomespotweldisadjustedtoincreasethenumberofspotweldinhighstresszoneinordertoenhancetheirlife.Atthesametimethetotalnumberofspotwelddoesnotincrease.Bycontrastoftheoriginallife,thelifeoptimizedisenhancedobviously.Sothefeasibilityandrationalityoftheoptimizationschemeistestified.KEYWORDS:Auto-body,Structuralfatiguelife,Spotweldfatiguelife,Structuralimprovement,Spotweldoptimization20062152006215200621511.1[1]4.4%95%[2]680%[3][4]2302[5]8632004AA4110101.21.2.1[6]31945M.A.MinerJ.V.PalmgfenL1966Manson1977Duggancrackformationlifecrackpropagationlifelmm[9]195760J.taylorG.jacobyN.H.SandlinW.WeibullR.E.LittleCLiPsonA.M.FreudenthalF.B.StulenE.B.HaugenD.Kececioglu1985ICOSSAR8525030[7,8,9]702041.2.2,:,,,(1),,-,-,-(2),Neuber,,Neuber:ESKfεσ∆∆=∆221-1,:ELKLεσ∆∆=∆221-2fLcKK=(3),FMKL5,,,,,,,,LK:21][)(iiLLiK∆∆∆=εσ1-3i(4)(Man-TenROQ-100),,,KLKL,,,Neuber-,ELKL22∆=∆∆εσ1-4]2[221KEn′∆+∆=∆′σσε1-5K′n′,-,,KL(5),,,,(El),,,,,6]1[*MEEiiσ−=1-6*iEiEσM(6),NeuberELKLεσ∆∆=∆1-7LKE,(L),Neuberεσ∆∆=,,,(7)KL,,,,,ELKL∆(8),:,-(9),Miner,,Smith,(εσ∆max)dfafNDNA)2()2(max+=∆⋅εσ1-8,,1-8fN27.,,,,,nCodenSoft,,,nSoft(Ford)(Jaguar)(Volvo)(Chrysler)Rover(Mercedes)(Nissan)(Toyota)(Daewoo),:,,,,,,,,,(),,,,,,,,,,,,,,,8,,,,,,/,,,,,1.31.3.1ETAVIRTUALPROVINGGROUNDVPGFEM9NVH1994[10]1996[11]1997/[12]2001[13]2002FATIGUE[14]2003Goodman[15]2004,,[16],1.3.21995Rupp[5]Msc.FatigueRupp()10S—N1998Raji[17]Sheppard[18,19]2002SmithCooper—[20]1.41.4.1SUVHypermeshMsc.Fatigue(1)11HypermeshCbar(2)Msc.Fatigue(3)1.4.2CAEDSN12132.1N1nNnC=D∑==liiiNnD1liniiNifDfliiiDNnD==∑=1fD[21]2.1.1MinerMinerMinerMinerPalmgren1924Miner.M.A1945Palmgren-14MinerMinerMinerWNlnlWNnWWll=211σ2σlσl1N2NlN1n2nln11==∑=liiNnD22WMiner1MinerMinerα==∑=liiiNnD123αMinerfDMinerfliiDNnD==∑=124fDMiner1=D152.1.2MansonManson2018811iN12iN2)exp(1φfifiiZNNN=25−=25.02125.0212165.01ln35.0lnln1NNNNNNφ26φ125.02135.0lnNNNZ=27ifiiNNN12−=28fiNi1N2N2.1.3Corten-Dolan16fD1fD1fD1MarcoStarkey1954DCα∝NnD29α1αα1Corten-DolanCortenDolan1956mαmrnD=210αmrnD∑==lidiiNN111σσα211N1σMPa1N1σiαiσdld1722lglgN′−σSN2.22.2.1KKK)(2)(2)(2Θ+Θ+Θ=iiiifrKfrKfrKuπππ213)(2)(2)(2Θ+Θ+Θ=ijijijijgrKgrKgrKπππσ214rθ2121Fig.2-1Cracktipcoordinateifijg22GKG1822221