An experimental investigation into dynamic fracture I Crack initiation and arrest

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1、InternationalJournalofFracture25(1984)247-262©1984MartinusNijhoffPublishers,TheHague.PrintedinTheNetherlandsAnexperimentalinvestigationintodynamicfracture:I.CrackinitiationandarrestK.RAVI-CHANDARandW.G.KNAUSSGraduateAeronauticalLaboratories,CaliforniaInstituteofTechnology,Pasadena,CA911

2、25,USA(ReceivedApril1,1984;inrevisedformMay2,1984)AbstractProblemsofdynamiccrackpropagationareexaminedexperimentallyinaseriesoffourpapers.Inthispaper,thefirstofthisseries,crackinitiationandarrestareinvestigatedinthinsheetsofHomalite-100.Itisfoundthatastherateofloadingincreasestoashighas

3、105MPa/sec,thestressintensityfactorrequiredtoinitiatecrackgrowthincreasesmarkedly.Crackarrestresultingfromasimulatedpressurizedsemi-infinitecrackinanunboundedmediumwasfoundtooccurabruptly.Therewasnocontinuousdecelerationandthecrackalwaysstoppedataconstantvalueofthestressintensityfactor,

4、whichvaluewaslowerthanthestressintensityfactorrequiredforquasi-staticcrackgrowthinitiation.Thesecondpaperinthisseriesdealswiththeoccurrenceofmicrocracksatthefrontoftherunningmaincrackwhichcontroltherateofcrackgrowth.Themicrocracksarerecordedbyrealtimephotography.Bythesamemeansitisshownt

5、hatthesemicrocracksgrowandturnawaysmoothlyfromthedirectionofthemaincrackintheprocessofbranching.Thethirdcontributionestablishesthehithertounreportedoccurrencethatcrackscanpropagaterapidlywithconstantvelocityeventhoughthestressintensityfactorvariesconsiderablyduringthispropagation.Thisve

6、locityisdeterminedbytheinitialstresswaveloadingonthecracktip,andischanged,withinlimits,onlybystresspulsesofsufficientmagnitudeandbrevityofrisetime.Thefinalpaperintheseriesdealswiththeeffectofstresswavesonthebehaviorofrunningcracks,inparticularwiththeinfluenceofstresswavesonthebranchingp

7、henomenon.Also,crackcurvingundertransientstresswavesisexamined.TheseresultsarebelievedtoapplytomaterialsotherthanHomalite100andthereasonsforthisbeliefarediscussedinthisfirstcontribution.1.IntroductionQuasi-staticfracturehasreceivedagreatdealofattentionsincetheworkofGriffith[1,2