DynamicsandgenerationofstresswavesincrackedgraphitemoderatorbricksOriginalResearchArticle

Inthepresentstudy,staticanddynamicanalyseshavebeenperformedforgraphitemoderatorbrickswithandwithoutkeygroovesunderthedifferentinitialloadingconditionsofpurebendingandslotrotationbyusingthefiniteelementmethod.Thepossibilitiesoftheoccurrenceofmultiplecrackingduetointernalstresseshavebeeninvestigatedintermsofthe(1)initialloadingcondition;(2)vibrationmodeshapes;and(3)dampingofthebricks.Firstly,modaldynamicanalysishasbeencarriedout,andtheeffectoftheinitialloadingconditions,suchaspurebendingandslotrotation,onthedynamicstressresponseswasinvestigated.Itwasfoundthatstressenhancementwasmoresignificantundertheconditionofpurebendingthanthatofslotrotation.Forpurebending,thekeygroovewhichwasoppositetotheprimarycrackingsitehadthemaximumdynamiccircumferentialstress.Thisimpliedthatsecondarycrackingmightoccuratthispositionunderpurebending.Secondly,inordertoinvestigatethedominantmodeshapeforthestressenhancement,naturalfrequencyanalysishasbeenconducted.FastFourierTransformation(FFT)hasalsobeenperformedtoconverttime–domainstressresponsesintofrequency–domainstressresponses.Theinitialloadingconditionsdeterminedwhichmodeshapewasdominantforthestressenhancement.Itwasalsosuggestedthatafundamentalmodeshapeprincipallycontributedtotheoccurrenceofthemultiplecracking.Thirdly,modaldampinganalysishasbeenperformed,andtheeffectofdampingonthestressenhancementwasstudied.Itwasfoundthatdampinghadlittleeffectontheinitialpeakofthedynamicstressresponse.Thissuggestedthatsecondarycrackingmightstilloccuratthekeygrooveoppositetheprimarycrackingsite,evenifdampingwaspresent.Theresultsoftheanalysisgiveafundamentalinsightintothemechanismthatmayleadtomultiplecrackingingraphitecomponentssubjecttointernalstresses.However,theeffectsof3-D,crackpropagationspeedandexternalrestrainthavenotbeentakenintoconsiderationinthepresentstudy.Theseeffectsmaymitigatethepossibilityofsecondarycracking,andarepartsoffurtherinvestigation.