chap3_yield criteria.ppt

3Yieldcriteria3.1Generalconsideration3.2Yieldsurfaceandyieldlocus3.3Coordinateonplane3.4Trescayieldcriterion3.5Misesyieldcriterion3.6Comparisonofthetwoyieldingcriteria3.7Experimentalverificationofyieldcriteria3.8Plasticwork3.9Effectivestressandeffectivestrain3.1GeneralconsiderationsYieldcriteriaMaterialyieldsplasticdeformationstartstooccurwhenaparticularstresslevelhasbeenreached.Anyyieldcriterionisapostulatedmathematicalexpressionofthestressstatesthatwillinduceyieldingortheonsetofplasticdeformation.Ononehand,itisrelatedtostressstate,ontheotherhand,itisrelatedtomaterialproperties.YieldstressElasticdeformation0ddWorkhardeningreloadingunloadingSubsequentyieldstressTotaldeformationo3.1GeneralconsiderationsYieldcriteriacfijwhereciseitheramaterialconstantinthecaseofinitialyieldingorafunctionoftheamountofdeformationforworkhardeningmaterial.Anypointsalongaworkhardeningstressstraincurvemayberegardedassubsequentyieldpoints.Thestressesattainavaluewhichexceedsthatrequiredforelasticdeformationandthematerialissaidtohaveyielded.Assumptionsthematerialishomogeneousandisotropic.3.1GeneralconsiderationsAyieldcriterionisapostulatedmathematicalexpressionofthestressstatethatwillinduceyieldingortheonsetofplasticdeformation.Anyproposedyieldcriterionshouldbeverifiedexperimentally.Bymeansofayieldcriterionitisthenpossibletodecidewhetherplasticdeformationtakesplace.Thegeneralformofyieldcriterionis,,,,,0xyzxyyzzxf41Yieldcriteria0ijfor0ijfelasticstate0ijfnotexist