Abstract :
AtVTT,developmentworkhasbeeninprogressfor15yearstodevelopandvalidatetestingandanalysismethodsapplicableforfractureresistancedeterminationfromsmallmaterialsamples.TheVTTapproachisaholisticapproachbywhichtodeterminestatic,dynamicandcrackarrestfracturetoughnesspropertieseitherdirectlyorbycorrelationsfromsmallmaterialsamples.Thedevelopmentworkhasevolvedatestingstandardforfracturetoughnesstestinginthetransitionregion.Thestandard,knownastheMasterCurvestandardisinaway“firstofakind”,sinceitincludesguidelinesonhowtoproperlytreatthetestdataforuseinstructuralintegrityassessment.Nostandard,sofar,hasdonethis.ThestandardisbasedontheVTTapproach,butpresently,theVTTapproachgoesbeyondthestandard.Keycomponentsinthestandardarestatisticalexpressionsfordescribingthedatascatter,andforpredictingaspecimenssize(crackfrontlength)effectandanexpression(MasterCurve)forthefracturetoughnesstemperaturedependence.Thestandardandtheapproach,itisbasedupon,canbeconsideredtorepresentthestateoftheartofsmallspecimenfracturetoughnesscharacterization.Normally,theMasterCurveparametersaredeterminedusingtestspecimenswith“straight”crackfrontsandcomparativelyuniformstressstatealongthecrackfront.ThisenablestheuseofasingleKIvalueandsingleconstraintvaluetodescribethewholespecimen.Forarealcrackinastructure,thisisusuallynotthecase.Normally,bothKIandconstraintvaryalongthecrackfrontandinthecaseofathermalshock,eventhetemperaturewillvaryalongthecrackfront.ApropermeansofapplyingtheMasterCurvemethodologyforsuchcasesispresentedhere.
