试验 应力 疲劳分析

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1、试验应力疲劳分析本文由yangxj0713贡献ppt文档可能在WAP端浏览体验不佳。建议您优先选择TXT，或下载源文件到本机查看。mFatigueAnalysisConceptsforGroundVehicleDurabilityTestingPage1mFatigue?WhatisFatigue??TheFatigueProcessinStructuralMetals.?AnalyticalLifePrediction:––––Stress-Life.Strain-Life.Notches.VariableAmplitudeLoading.Page2mF

2、atigue–AStandardDefinition“Theprocessofprogressivelocalizedpermanentstructuralchangeinamaterialsubjectedtoconditionsthatproducefluctuatingstressesandstrainsatsomepointorpointsandthatmayculminateincracksorcompletefractureafterasufficientnumberoffluctuations.”–ASTME-1823,StandardTer

3、minologyRelatingtoFatigueandFractureTesting.Page3mFatigue–KeyConcepts?Acyclicloadisrequired.?Fatigueisaprocessthatstartsonthefirstloadingcycle.?Fatiguedamageislocalized.?Fatiguedamageispermanentandirreversible.?Crackformationmayoccur.?Cracksmaygrowandcausefracture.Page4mFatiguePro

4、cessSlipoccursinareasofconcentratedstress/strain.?Intrusions/extrusionsmaybeformedwhereslipbandsintersectsurface.?Slipbandsintensifyandcracksdevelopalongthem.?Dominantcrack(s)propagatethroughmultiplegrains.?Crackgrowthproceedsapproximatelyperpendiculartoappliedload.?Fractureoccurs

5、whenremainingligamentcannotsupportload.Page5mFatigueProcessSlipBands:–Extrusionsandintrusionsmaydevelopatsurface.–Highlyconcentratedshearstrain.–Fatiguecracksforminslipbands.Page6mFatigueProcess?Slipbandsincoppersinglecrystal.(Hoeppner)CrackPage7mFatigueProcessSlipbandprofiles,alu

6、minumsinglecrystal.(Mughrabi)StageI(shear)fatiguecrackinaslipband(coppersinglecrystal).(Mughrabi)Page8mFatigueProcess(Hoeppner)Page9mInitiationandPropagationInitiationPropagationWhatisInitiation?––––FractureTimeLifespentdevelopingan“engineeringsize”crack.Lifetofirstdetectablecrack

7、.Crackformation.Initiationisnotpreciselydefined;thereisnostandarddefinition(e.g.ASTM).WhatisPropagation?–Portionoflifespentgrowinganexistingcracktofinalfracture.Theboundarybetweeninitiationandpropagationisarbitrary,notphysical.Page10mFatigueProcessFractureCrackSizeStressdominatedc

8、rackgrowthLifeCrackformationphase