2材料科学基础英文版课件_(9)

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1、ImpactFractureTestingImpactFractureTesting(1)Impacttestingistomeasuretheenergyabsorbedbyamaterialduringitsimpactfracture(thefracturewithahighstrainrate)Whenamaterialissubjectedtoasudden,intenseloading(e.g.impact),itoftenbehavesinamorebrittlemannerthanobservedinthetensi

2、letest.Tensiletesting:theloadisappliedslowlyImpacttesting:thefullloadisappliedveryrapidlySpecimenforCharpyandIzodtestsTwotypesoftest:CharpytestandIzodtestImpactFractureTesting(2)ImpactTestingTechniquesSize:10mm10mm55mmImpactFractureTesting(3)Loadingmanners:Charpytest

3、IzodtestInengineeringpractice,usuallyusingCharpytestingtodeterminetheimpactenergyImpactFractureTesting(4)RepresentationoftheCharpyimpacttestStartingpositionEndingpositionh0mghfmg(m–mass;g-gravityacceleration)Impactenergy=h0mg-hfmgImpactFractureTesting(5)Ductile-To-Brit

4、tleTransitionOneofthemajorfunctionsofimpacttestsistodeterminewhetherornotamaterialexperiencesductile-to-brittletransitionHighimpactenergyatalltemperatures,noductile-to-brittletransitionLowerimpactenergy,ductile-to-brittletransitionImpactFractureTesting(6)FCCmaterials(e

5、.g.austeniticstainlesssteels,Cu,Ni,andAlalloys):thereisnoductile-to-brittletransitionBCCmaterials(e.g.ferriticsteels,CrandMoalloys)andHCPmaterials(Mgalloys):thereisductile-to-brittletransitionDuctile-to-brittletransitiontemperature(DBTT):thetemperatureatwhichamaterialc

6、hangesfromductiletobrittlestateDefinition1:definedbytheaverageenergybetweentheductileandbrittleregionsDefinition2:definedby50%ductilefracture(fractureappearancetransitiontemperature,FATT)Forengineeringapplications,thelowertheDBTT,thebetteristhematerialImpactFractureTes

7、ting(7)~50oCImpactFractureTesting(8)Ductile-to-brittletransitionmaycausedisasterse.g.DuringWorldWarII,someshipssuddenlysplitinhalfbecausetheenvironmentaltemperaturewasapproachingtheDBTToftheconstructingmaterial(e.g.astructuralsteel)orbelow,butatthattime,peopledidnotkno

8、wwhy.Strengthening:solid-solutionstrengthening,precipitationstrengthening,andstrainhardening(yieldstrengthincrease)D