陶瓷材料机械性能yan liu.pptx

Fatiguecrackpropagation

--origin,basisandtechniqueYanLiu2012.10.28

Content1.Historicalorigin2.Basischaracterization,significance,propertyandmechanism3.TechniqueStandard,Unloadingelasticcompliancemeasurementofcracklength.

HistoricaloriginThephysicalphenomenonoffatigue:midnineteenthcenturywhenwidespreadfailuresofrailwayaxles.Fatiguelimit:Firstsystematicinvestigations----W?hler,1860Fatiguecrackpropagation:linearelasticfracturemechanicsandso-called‘defect-tolerantdesign’---Paris,1961;JohnsonandParis,1967;Defect-tolerantdesign:Lifetimeisthenassessedonthebasisofthetimeornumberofloadingcyclesforthelargestundetectedcracktogrowtofailure.Linearelasticfracturemechanics:subcriticalcrackgrowthcanbecharacterizedintermsofsomegoverningparameter(cracksize,geometry,stress)

BasisCharacterizationcompactspecimen,loadedintensile,C(T)Middlecrackspecimen,loadedintension,M(T)Sideedgenotchedplate,loadedinBending,SE(B)

BasisSignificanceAerospaceAirspaceAutomobileHighspeedtrainNatureMaterials10,817–822(2011)TheconflictsbetweenstrengthandtoughnessRobertO.Ritchie---2011naturematerials

PropertyandmechanismPropertyNatureMaterials10,817–822(2011)Int.J.Fracture100:55–83,1999.

PropertyandmechanismMechanismExtensionofacrack:crackdrivingforce----------describesthedominantstressanddeformationfieldsinthevicinityofthecracktip.resistanceofthemicrostructure-----crackadvanceisthusrestrainedbyloweringtheappliedloadorbytoughening“thematerial

PropertyandmechanismCrackpropagationmechanicsIntrinsicmechanisms；Extrinsicmechanisms；NatureMaterials10,817–822(2011)Int.J.Fracture100:55–83,1999.

PropertyandmechanismIntrinsicmechanismsFailurebycleavage;Repetitivebluntingandresharpeningofthecracktip;Microviodcoalesc