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EvaluationofFractureToughnessofMaterialsUsingInstrumentedIndentationTechnique Ductile BrittleFractureModels 2013 08 30 WonJeJo Contents Introduction IndentationFractureToughnessModels BrittlefracturemodelDuctilefracturemodel VerificationoftheModels ComparisonbetweenfracturetestresultsandIITresultsApplicationsatlowtemperature Basicconceptofindentationfracturetoughness Fracturetest Crackpropagationandfracture Indenter IIT Nocrackandnofracture Issueofindentationfracturetoughness WhatisacorrelationbetweenfracturetestandIIT Inthecaseofmetals Constrainteffect aheadofacracktip Plasticregionconstrainedbyelasticregion beneathanindenter Similarconstrainteffect R 250 m Indenter Material APIX70 loading Constrainteffect 2 33 0 Triaxialityofcracktip Triaxialityofindentation Indentationfracturetoughness Analogoussituation Energyconcept Requiredenergyforcrackpropagation EquivalentfractureenergyinIndentation Analysisofindentationprocess Indentationprocess Formationofaplasticzonetothesurface Formationofafully developedplasticzone c aisconstant Expansionofplasticzone c aincrease c a c a Assumption Onsetofformationofafully developedplasticzone Maximumstrainenergybeneaththeindenter Formationofequivalentfractureenergy h c a h h FractureBehavior BrittleFractureModel DuctileFractureModel BrittleFractureModel Criterion rr Criticalstress pressure ath Criterion Assumption Onsetofformationtoafully developedplasticzone FormationofEquivalentfractureenergy Applicationofindentationtheories Step1Yieldingrightoutsidethecontactarea Formationofaplasticzonetothesurface Step2Expansionoftheplasticzone Formationoffully developedplasticzone c a h Hertzelasticcontacttheory Stressoutsidethecontactarea r a Whenaradialstressattheedgeofthecontactarea r a satisfiedyieldingcriterion ByVonMises yieldcriterion Expandingcavitymodel E Ptheory Stresswithinplasticzone a r c Changeofthecorepressure r a untilformingthefully developedplasticzone byK E Puttick 1977 core Criterionofequivalentfractureenergy Step1 Thetotalpressurerequiredforequivalentfractureenergy Step2 Fracturetoughnessforbrittlematerial Pm hcurve Indentationload depthcurve Meancontactpressureateachunloadingdepth 1 Indentationtesting 6 Indentationfracturetoughness KJC 2 Measuring ys DeterminingPmc ysfromanalyzingL hcurve 3 FittingPm hcurve 4 Determiningh InsertingdeterminedPmcintoPm hcurve 5 Equivalentfractureenergyuntilh DuctileFractureModel Criterion rr Criticalstrainath Criterion Criticalstrainath Criterion Absorbedstrainenergyuntilfracturestrain Toughness tensileenergy Assumption Elasticenergyreleasedduetothecrackgrowthisequaltotheamountofplasticworkaheadofthecracktip PeelandFrosyth 1973 Plasticworkdoneperunitarea r theradiusoftheplasticzoneUT plasticworkdoneperunitvolume Forsmallscaleyielding Elasticenergyreleasedperunitarea Plasticwork Mechanicalmetallurgy G E Dieter Plasticworkdone AreaUndertheStress StrainCurve sR flowstressef engineeringfracturestrain Mechanicalparameters Estimationfromindentationparameters Plasticzonesize Fracturestrain Measuredparameters Fracturetoughness rc ef Measuredbyindentationtest Plasticzonesize rc P Plasticflow Elasticconstraint Plasticzone Abalancebetweenplasticflowandelasticconstraint Dominantelasticconstraint Dominantplasticflow SmallPZS LargePZS Resilience Fracturestrain ef Experimentalrelationbetweentrueuniformstrainandengineeringfracturestrain Plasticzonesize Fracturestrain Measuredparameters Fracturetoughness Fracturetoughnessforductilematerial Contents Introduction IndentationFractureToughnessModels BrittlefracturemodelDuctilefracturemodel VerificationoftheModels ComparisonbetweenfracturetestresultsandIITresultsApplicationsatlowtemperature Basicconceptofindentationfracturetoughness Listofthetestedmaterials Comparingbetweenconventionalfracturetoughnessresultsandinstrumentedindentationtestingresultsfor31metals Testingconditions Indenter Indenterradius Controllingmethod WCsphericalindenter 250um Max depthcontrol Equipment AISSystem Max indentationdepth 150um Zeroindex 0 06kgf Surfaceroughness Sandpaper 2000 20 20 KJCResults KJCfromIIT MPa m KJCfromJc MPa m Brittlefracturemodel Ductilefracturemodel KJCResults Brittlematerials Ductilematerials LowTemperatureChamberSystem Evaluationoffracturetoughnesswithchangingtemperature MeasurementoffracturetoughnessatlowtemperatureAnalysisofsubzerotemperatureusingASTME1921 Application Specifications ChamberController AISSystem Chamber CharpyV notchsample RelationbetweenCVNresultsandIITtoughnessresults Material 2 25Cr1MoVsteel Weldments Testtemperature RTand 29oC Applicationsatlowtemperature Applicationsatlowtemperature MasterCurve KJCfromIIT KJCfromJ Test Specimeninformationandtestingconditions Chemicalcompositionofspecimen Applicationsatlowtemperature MasterCurve KJCfromIIT KJCfromJ Test Reference Bong SangLee Min ChulKim Maan WonKim Ji HyunYoon Jun HwaHong Mastercurvetechniquestoevaluateanirradiation