InfluenceofflowstresschoiceontheplasticcollapseestimationofaxiallycrackedsteamgeneratortubesOriginalResearchArticle

Theinfluenceofthechoiceofflowstressontheplasticcollapseestimationofaxiallycrackedsteamgenerator(SG)tubesisconsidered.Theplasticlimitandcollapseloadsofthick-walledtubeswithexternalaxialsemi-ellipticalsurfacecracksareinvestigatedbythree-dimensionalnon-linearfiniteelement(FE)analyses.Thelimitpressuresolutionasafunctionofthecrackdepth,lengthandtubegeometryhasbeendevelopedonthebasisofextensiveFElimitloadanalysesemployingtheelastic–perfectlyplasticmaterialbehaviourandsmallstraintheory.Unliketheexistingsolutions,thenewlydevelopedanalyticalapproximationoftheplasticlimitpressureforthick-walledtubesisapplicabletoawiderangeofcrackdimensions.Further,theplasticcollapseanalysiswitharealstrain-hardeningmaterialmodelandalargedeformationtheoryisperformedandananalyticalapproximationfortheestimationoftheflowstressisproposed.Numericalresultsshowthattheflowstress,definedbysomefailureassessmentdiagram(FAD)methods,dependsnotonlyonthetubematerial,butalsoonthecrackgeometry.Itisshownthattheplasticcollapsepressureresults,inthecaseofdeepercracksobtainedbyusingtheflowstressastheaverageoftheyieldstressandtheultimatetensilestrength,canbecomeunsafe.