chap3 yield criteria.ppt
3Yieldcriteria3.1Generalconsideration3.2Yieldsurfaceandyieldlocus3.3Coordinateon-plane3.4Trescayieldcriterion3.5Misesyieldcriterion3.6Comparisonofthetwoyieldingcriteria3.7Experimentalverificationofyieldcriteria3.8Plasticwork3.9Effectivestressandeffectivestrain3.1GeneralconsiderationsYieldcriteriaMaterialyields(plasticdeformationstartstooccur)whenaparticularstresslevelhasbeenreached.Anyyieldcriterionisapostulatedmathematicalexpressionofthestressstatesthatwillinduceyieldingortheonsetofplasticdeformation.Ononehand,itisrelatedtostressstate,ontheotherhand,itisrelatedtomaterialproperties.YieldstressElasticdeformation0ddWorkhardeningreloadingunloadingSubsequentyieldstressTotaldeformationo3.1GeneralconsiderationsYieldcriteriacfij)(whereciseitheramaterialconstantinthecaseofinitialyieldingorafunctionoftheamountofdeformationforworkhardeningmaterial.Anypointsalongaworkhardeningstress-straincurvemayberegardedassubsequentyieldpoints.Thestressesattainavaluewhichexceedsthatrequiredforelasticdeformationandthematerialissaidtohaveyielded.Assumptions:thematerialishomogeneousandisotropic.3.1GeneralconsiderationsAyieldcriterionisapostulatedmathematicalexpressionofthestressstatethatwillinduceyieldingortheonsetofplasticdeformation.Anyproposedyieldcriterionshouldbeverifiedexperimentally.Bymeansofayieldcriterionitisthenpossibletodecidewhetherplasticdeformationtakesplace.Thegeneralformofyieldcriterionis(,)0xyzxyyzzxf(4-1)Yieldcriteria0)(ijfor0)(ijfelasticstate0)(ijfnotexist