Author/Authors :
MikaKemppainen، نويسنده , , IikkaVirkkunen، نويسنده , , JormaPitk?nen، نويسنده , , RaimoPaussu، نويسنده , , HannuH?nninen، نويسنده ,
Abstract :
Oneofthekeyissuesinin-serviceinspectionqualificationistherepresentativenessofthedefectsusedinqualificationspecimens.Thebestrepresentativenessisachievedwithrealisticdefects.However,presentspecimenproductiontechniqueshavesomesignificantweaknesses,suchasunrealisticdefectsoradditionalalterationsinducedinthesurroundingmaterial.Specimensmanufactured,forexample,byweldimplantationorwithweldsolidificationdefectsalwaysresultinoneormoreextraweldinterfaces.TheseinterfacescanbedetectedbyNDT.Toovercomeproblemswiththecurrentspecimens,anewdefectmanufacturingtechniquewasdeveloped.Thenewtechniqueproducesnatural,representativedefectswithoutintroducingadditionalweldmetalorotherunwantedalterationstothespecimen.
Thenewmethodenablesartificialproductionofsingle,separatefatiguecracksbythermalloading.Themethodisbasedonanaturalthermalfatiguedamagemechanismandenablesproductionofrealcracksdirectlyintothesamples.Cracksareproducedwithoutweldingormachiningandwithoutanypreliminarysurfacetreatmentorartificialinitiatorsuchasanotchoraprecrack.Singlecrackoranetworkofcrackscanbeinducedintothebasematerial,weldedareas,HAZ,weldcladdings,threadedareas,T-joints,etc.Thelocation,orientationandsizeofproducedcrackscanbeaccuratelycontrolled.Producedcrackscanbeusedtosimulatedifferenttypesofservice-inducedcrackssuchasthermalfatigue,mechanicalfatigueandstresscorrosioncracks.Itisshownthatartificiallyproducedthermalfatiguecrackscorrespondwellwiththereal,service-inducedcracksandovercometheproblemsoftraditionalqualificationspecimenmanufacturingtechniques.
