高速列车铝合金熔焊接头疲劳开裂同步辐射成像与表征-(6278)

《高速列车铝合金熔焊接头疲劳开裂同步辐射成像与表征-(6278)》由会员上传分享，免费在线阅读，更多相关内容在行业资料-天天文库。

1、万方数据西南交通大学硕士研究生学位论文第1I页AbstractToinvestigatetheinitiationandpropagationoffatiguecrackingrelatedwithmicro—poresinsidehybridlaserarcwelded7020-T651alloys，bothhighresolutioninsitusynchrotronX—raycomputedmicrotomographyandtraditionalfiniteelementbasednumericalmodelinghavebeenundertaken．

2、Theeffectivediameter,sphericityanddistancefrombarycentreofporestofreesurfaceofsamplesweremeasured，statisticallysummarizedandfitted．Accordingtothe3Dcharacterization，microporesinsidehybridweldedAIalloysaremainlymetallurgicalpores，whicharesymmetricallydistributedabouttheseamcenterline，

3、havingasphericitylargerthan0．65．Moreover,poresinsideupperweldsappeartobelargerineffectivediameter,butdenserinheataffectedzoneandlowerwelds．Besides，poreswithdiameterlessthan209mareexistedextensively,withafrequencyof65％and85％intheupperandlowerweld，respectively．Furthermore，itisfoundtha

4、ttheconnectionsofpore—poreandpore。hot。cracktogetherwiththehotcracksresultinthesmallersphericityofgasporesinthelowerwelds．Finallyitcanbeconfirmedthatthehigherweldingspeedgivesrisetothesmallerporevolumefraction，buthaslittleinfluenceonthedistributionofporepositionandsphericity．Multicra

5、cksareinitiatedfromporesatthesurfaceorsubsurfacebutonlyveryfewofthemcanpropagateintoaregularshape，withtypicallowcyclefatiguecharacteristics．Crackfrontsarelocallycomplexandnonlinearduetotheinfluenceofmicrostructures．Howevertheykeepregularonthewholeduringthestablegrowthstage，whichacco

6、untsatleast30％ofthetotalfatiguelifetimeofeachsample．Forthefusionweld，thestudiedcomerfatiguecrackcanbedescribed，despiteitssmalldimension，inthedomainoflinearelasticfracturemechanics．Basedonthefatiguecrackgeometryandmorphology,afiniteelementmodelhasbeenestablishedtoevaluatethecrackgrow

7、thrateparameters，theclosureeffectandfracturetoughnessviadeterminationofthecrackfrontevery500loadingcycles．Aquantitativeagreementbetweenexperimentandpredictionofcrackshapeunderexecutedloadingcyclesisobservedwhenacubicsplineisadoptedtosimulatethespatialevolutionofthecrackfront．Byusing

8、thecriticalstressin