uscar-7v001

DEEMBRITTLEMENTVERIFICATIONTESTTheresearchdata,analysis,conclusion,opinionsandothercontentsofthisdocumentaresolelytheproductoftheauthors.NeithertheSocietyofAutomotiveEngineers,Inc.(SAE)northeUnitedStatesCouncilforAutomotiveResearch(USCAR)certifiesthecomplianceofanyproductswiththerequirementsofnormakesanyrepresentationsastotheaccuracyofthecontentsofthisdocumentnortoitsapplicabilityforpurpose.Itisthesoleresponsibilityoftheuserofthisdocumenttodeterminewhetherornotitisapplicablefortheirpurposes.Copyright1998,USCARAllrightsreserved.PrintedinU.S.A.IssuedDecember1998SAE/USCAR-7QUESTIONSREGARDINGTHISDOCUMENT:(724)772-8545FAX(724)776-0243TOPLACEADOCUMENTORDER:(724)776-4970FAX(724)776-07901.SCOPE:Thisstandardoutlinestestmethodsandpracticeswhichcandetectembrittlementofsteelparts.Itisaprocesscontrolorrefereeverificationtest.Theriskofembrittlementofsteelisminimizedbyusingbestpracticesinthefinishing/coatingprocess.OnesuchpracticeisdescribedinSAE/USCAR-5,AvoidanceofHydrogenEmbrittlementofSteel.2.REFERENCES:2.1SAEPublications:AvailablefromSAE,400CommonwealthDrive,Warrendale,PA15096-0001.SAE/USCAR-5,AvoidanceofHydrogenEmbrittlementofSteel3.DEEMBRITTLEMENTTESTAtorque/tensiontestisusedforthreadedpartsandatensiletestisusedfornon-threadedparts.Thetestconsistsofthreesteps:1)Determinetheultimatetorqueortensilestresstofailureforthreadedandnon-threadedpartsrespectively;2)Loadthepartstosomepercentageoftheultimatetorqueortensilestress;3)Maintainthetorqueortensilestressforsomedeterminedlengthoftime.Wheneverpossible,thetestfixtureshouldsimulatetheintendedapplication.Section3.5discussesalternativestotestfixtures.SAE/USCAR-7December1998DEEMBRITTLEMENTVERIFICATIONTEST-2-3.1TestLoadDetermination3.1.1ThreadedPartsa.Randomlyselectaminimumof5partsfromthelotbeingevaluatedtoestablishthetesttorqueforthestresstest.Notethatthefivepartsampleisonlytoestablishthetesttorqueusedforthedeembrittlementtests.Thedeembrittlementtestsamplesizeisdiscussedinsection3.2.b.Applytorquetothetestpart,orthematingpartofthetextfixtureuntilultimatefailureofthetestpartoccurs.SomeideasoffixturingmethodsarediscussedinSection3.5.Handorpowertooltighteningisacceptable,however,theselectedtighteningmethodmustalsobeusedinperformingthedeembrittlementtest(section3.3).Recordthemaximumtorqueforeachofthefivefasteners.Theaveragemaximumtorqueforallfivetestpartsistheultimatefailuretorquewhichcompletesstep1referredtoinsection3.c.Thetesttorquetobeusedinstep2,referredtoinsection3.,is80%oftheultimatefailuretorque.Thistesttorquevaluedoesnotnecessarilycorrespondtotheactualapplicationinstallationtorqueforthepart.3.1.2Non-ThreadedPartsa.Randomlyselectaminimumof5partsfromthelotbeingevaluated.(Notethatthefivepartsampleisonlytoestablishthetestloadusedfordeembrittlementtests.)Thedeembrittlementtestsamplesizeisdiscussedinsection3.2.b.Determineanacceptabletensiletestmethodforthegeometryandconfigurationofthepart.Thetestfixtureandtestproceduremustbeagreeduponbythesupplierandthepurchaser.Someideasonfixturingmethodsarediscussedinsection3.5.Applyatensileloadtothepartuntilfailureofthetestpartoccurs.Recordthemaximumtensileloadforeachofthefiveparts.Theaveragemaximumloadforallfivetestpartsistheultimateloadwhichcompletesstep1.Thefixtureandtestmethodusedforstep1mustbeduplicatedforsteps2and3.Steps1,2,and3aredescribedinsection3.c.Thetensileloadusedinstep2,referredtoinsection3.,istobesomepercentageoftheultimateload.Typicaltestloadsarebetween70to80percentoftheultimateload.Thesuppliermustdetermineatestloadsufficienttodetectembrittlementsusceptibility.Ataminimum,thetestloadshouldexceedthetensileloadappliedduringassemblyofthepartintoit’sactualapplication.SAE/USCAR-7December1998DEEMBRITTLEMENTVERIFICATIONTEST-3-3.2SampleSizeDeterminationAlotforthepurposeofthedeembrittlementtestisdefinedasfollows.Forabatchoven,alotisaloadofbakedpartswiththesamepartnumber.Foracontinuousbakingfurnace,alot(foraparticularpartnumber)istobedefinedbythesupplierasisagreeablewiththeirprocess;keepinginmindthatifafailureshouldoccurduringthesubsequentdeembrittlementtest,thelotshallbescrapped.Thelotshallbedefinedsuchthatallprocessingtraceabilityismaintainedforeachpartnumber/lotidentification.Thenumberofpartstobesubjectedtothedeembrittlementtestmustbedeterminedbyagreementbetweenthesupplierandpurchaser.Thecontrolplanwillspecifythetestsamplesize.3.3PerformingDeembrittlementTest3.3.1Thetotalnumberofpartsdeterminedinsection3.2aretosubjectedtothedeembrittlementtest.3.3.2Thesepartsaretobeloadedusingthesamefixture,thesameloadingmethodsandthesametestloaddeterminedinparagraph3.1.1forthreadedpartsorparagraph3.1.2fornon-threadedparts.Partswhichfailwhileattemptingtobeassembledtothetestload(torque)shouldbediscardedandcannotbecountedaspartofthetestlot.3.3.3Thesepartsaretobeheldatloadinthefixtureasdescribedbelow.a.Forthreadedparts:Reapplytesttorqueafterthepartshavebeenheldfor24hours.Ifanyfailuresoccuratthis24hourcheck,thetestistobeterminatedandtheentirelotshallberejectedasdescribedinparagraph3.4.Ifnofailuresoccur,continuetoholdthepartsatloadforanadditionalminimumof24hours,reapplytesttorquethenremovefromthefixtureandexamineperparagraph3.4.b.Fornon-threadedparts:Holdthepartsatloadinthefixtureforaminimumperiodof48hours.Removefromthefixtureandexamineperparagraph3.4.3.4Pass/FailDeterminationVisuallyinspectthepartswhichhaveundergonethe48hourtest.Thepartsshouldbefreeofcracksormulti-piecefractures.Ifcrackingorfracturinghasoccurredononeormoreofthesamples,theentirelotshallberejectedandscrapped(noreworkofthesepartsisallowed).Ifnoneofthesamplepartshavecrackedorfractured,theprocessisconsideredtobeincontrolforthatlotandthereforecanbeshipped.3.5FixturingMethodsThefollowingsuggestionsareprovidedtoassistinestablishingthetestloadandmethodoftesttoinducehightensilestressforperformingthedeembrittlementtest.SAE/USCAR-7December1998DEEMBRITTLEMENTVERIFICATIONTEST-4-3.5.1Screwsmaybeseatedagainsta4degreewedgetorepresentaworstcaseassemblycondition.3.5.2Aflatwashermaybeinsertedbetweenthescrewandthewedgetestplatetoeliminatetheeffectsoftorquerobbingserrations,rings,etc.whichmaypreventtorquingthefastenertofailureduetosocketcamofforrecessbitcamout.(NotethatthewasherI.D.shouldnotbelargerthat0.04in(1.0mm)overthemajordiameterofthescrew.)TheO.D.ofthewashershouldbeequaltoorgreaterthanthemaximumflangediameterofthescrewbeingtested.3.5.3Largediameterthreadedfastenersmaybelubricatedtoreducethetorquerequiredtofailthefastenerandestablishthetesttorque.Iflubeisused,thesamelubemustbeusedandappliedfortheentiretest.3.5.4Screwswithinternaldriveswhichcannotbetorquedtofailureduetobitcamoutorfailure,maybetestedtoatorqueequalto80%oftheaveragetorqueachievedatcamoutorbitfailure.Thiswillbeconsideredthefailuretorqueforthedeembrittlementtestforthisfastener.3.5.5Tappingscrewsmaybetestedusingpre-threadedholesintestplatestoachievescrewfailuresinsteadofthreadstrippage.3.5.6Screwsmaybetestedbyapplyingtorquetoheadofthescrewortoanutifanutisusedaspartofthetestsetup.3.5.7Flatandconedwashers,pre-assembledorloose,canbetestedonafixturehavinganoversizeclearanceholesothatthewasherinvertsandthereforeinduceshightensilestresstotheconvexsurface.Washersaretobeloadedoveraholediameterequalto80%oftheminimumoutsidediameterofthewasher.Theloadingdeviceorbolthexsizebeingusedtoloadthewashershouldnotbegreaterthan1.5timestheinsidediameterofthewasher.Fivewashersmustbeloadedtotheyieldstrengthofthematerial.Eighty(80%)percentofthisaverageloadisthetestloadforthedeembrittlementtest.4.KEYWORDS:Fastener,Hydrogen,DelayedFailurePREPAREDBYTHEUSCARFASTENERTECHNICALCOMMITTEE