1、A Referencenumbe r ISO12714:1999(E) INTERNATIONAL STANDARD ISO 12714 Firstedition 19990715 NondestructivetestingAcoustic emissioninspectionSecondary calibrationofacousticemissionsensors EssaisnondestructifsContrleparmissionacoustiquetalonnage secondairedescapteursdmissionacoustiqueISO12714:1999(E) I
2、SO1999 Allrightsreserved.Unlessotherwisespecified,nopartofthispublicationmaybereproducedorutilizedinanyformorbyan ymeans,electronic ormechanical,includingphotocopyingandmicrofilm,withoutpermissioninwritingfromthepublisher. InternationalOrganizationforStandardization Casepostale56 CH1211Genve20 Switz
3、erland Internet isoiso.ch PrintedinSwitzerland ii Contents Page 1Scope 1 2Normativereferences . .1 3Termsanddefinitions .1 4Abbreviations .2 5GeneralRequirements. 2 6Requirementsofthesecondarycalibrationapparatus 3 7Calibrationdataprocessing .5 8Expecteduncertainty. 6 9Prooftestingofasecondarycalibr
4、ationsystem 8 10TypicalCalibrationResults. 8 Bibliography16ISO ISO12714:1999(E) iii Foreword ISO(theInternationalOrganizationforStandardization)isaworldwidefederationofnationalstandardsbodies(ISO memberbodies).TheworkofpreparingInternationalStandardsisnormallycarriedoutthroughISOtechnical committees
5、.Eachmemberbodyinterestedinasubjectforwhichatechnicalcommitteehasbeenestablishedhas therighttoberepresentedonthatcommittee.Internationalorganizations,governmentalandnongovernmental,in liaisonwithISO,alsotakepartinthework.ISOcollaboratescloselywiththeInternationalElectrotechnical Commission(IEC)onall
6、mattersofelectrotechnicalstandardization. InternationalStandardsaredraftedinaccordancewiththerulesgivenintheISO/IECDirectives,Part3. DraftInternationalStandardsadoptedbythetechnicalcommitteesarecirculatedtothememberbodiesforvoting. PublicationasanInternationalStandardrequiresapprovalbyatleast75%ofth
7、ememberbodiescastingavote. InternationalStandardISO12714waspreparedbyTechnicalCommitteeISO/TC135,Nondestructivetesting , SubcommitteeSC3, Acousticalmethods .ISO12714:1999(E) iv Introduction TheacousticemissionmethodofnondestructivetestingisaddressedbySC3onacousticalmethodsofTC135on nondestructivetes
8、ting.Standardsforgeneralproceduresandrequirementsarerequiredinordertoinsure quantitativeresultsandwideapplicability.ThisInternationalStandardaddressesthetransferofcalibration,or secondarycalibration,ofacousticemissionsensors.Inthismethod,thedeviceundertestiscalibratedby comparisonwithasensorthathasp
9、reviouslyundergoneprimarycalibration.Thesensorusedforcomparisonis calledthereferenceorsecondarystandardsensor.TheaimofthisInternationalStandardistoestablishuniformity ofacousticemissiontestingbystandardizingthemethodsusedtotransfercalibrationsofsensors.INTERNATIONALSTANDARD ISO ISO12714:1999(E) 1 No
10、ndestructivetestingAcousticemissioninspection Secondarycalibrationofacousticemissionsensors 1Scope ThisInternationalStandardspecifiesamethodforthesecondarycalibrationofacousticemissionsensorsas receiversofelasticwavesatthesurfaceofasolidmedium.TheInternationalStandardisapplicabletolaboratory tertiar
11、ystandardsensorsandacousticemissionapplicationssensors. Thesecondarycalibrationyieldsthefrequencyresponseofasensortowavesofatypenormallyencounteredin acousticemissionwork,namelyRayleighwaves.Thesourceproducingthesignalusedforthecalibrationis mountedonthesamesurfaceofatestblockasthesensorundertest(SU
12、T).Thesensitivityofthesensoris determinedforexcitationwithintherangeof100kHzto1MHz.Sensitivityvaluesareusuallydeterminedat frequenciesapproximately10 kHzapart.Theunitsofthecalibrationarevoltsperunitofmechanicalinput (displacement,velocityoracceleration). 2Normative references Thefollowingnormativedo
13、cumentscontainprovisionswhich,throughreferenceinthistext,constituteprovisionsof thisInternationalStandard.Fordatedreferences,subsequentamendmentsto,orrevisionsof,anyofthese publicationsdonotapply.However,partiestoagreementsbasedonthisInternationalStandardareencouragedto investigatethepossibilityofap
14、plyingthemostrecenteditionsofthenormativedocumentsindicatedbelow.For undatedreferences,thelatesteditionofthenormativedocumentreferredtoapplies.MembersofISOandIEC maintainregistersofcurrentlyvalidInternationalStandards. ISO12713:1998, NondestructivetestingAcousticemissioninspectionPrimarycalibrationo
15、ftransducers. ISO12716: 1) , NondestructivetestingAcousticemissioninspectionVocabulary. ASTME11495, StandardPracticeforUltrasonicPulseEchoStraightBeamTestingbytheContactMethod. ASTME110686(1992)e1, StandardMethodforPrimaryCalibrationofAcousticEmissionSensors. ASTME131697b, StandardterminologyforNond
16、estructiveExaminations. 3 Termsanddefinitions ForthepurposesofthisInternationalStandardthetermsanddefinitionsinISO12716andinASTME1316aswell asthefollowingapply. 3.1referencesensor(RS) sensorwhichhashaditsresponseestablishedbyprimarycalibrationseeASTME1106orISO12713 NOTE Alsocalledsecondarystandardse
17、nsor. 1) Tobepublished.ISO12714:1999(E) ISO 2 3.2secondarycalibration procedureformeasuringthefrequencyortransientresponseofanacousticemissionsensorbycomparisonwithan RS 3.3testblock blockofhomogeneous,isotropicelasticmaterialonwhichasource,anRSandaSUTareplacedforcarryingout secondarycalibration 4Ab
18、breviations AE: acousticemission ASTM: AmericanSocietyforTestingandMaterials FFT: fastFouriertransform ISO: InternationalOrganizationforStandardization RS: referencesensor SUT: sensorundertest 5General requirements 5.1 SensorUnderTest Thismethodisapplicabletotheabsolutecalibrationofnormalmotionsenso
19、rsforuseastertiarystandardsandto thecalibrationofacousticemissionsensorsforuseinAEsensing.Fortertiarystandardspurposes,thesensor beingcalibratedshouldbeofasmallaperture,highfidelitytype(suchastheNBSConicalTransducer).Ingeneral, resultsfromanysensorwillbedegradedbylargeapertureandlackofflatnessoffreq
20、uencyresponse. Thestatedaccuracyappliesonlyifthesensorbeingcalibratedishighlydamped.Thesignalfromthesensor followingtheshockexcitationofthecalibrationsignalshouldbedampedtoaninsignificantlevel(20%ofpeak signal)withinthetime(30 msfortheprototypesecondarycalibrationsystem)oftheallowedcapturewindow,lim
21、ited byechoesfromboundariesofthecalibrationblock.Ifthisconditionisviolated,calibrationaccuracywillsuffer. (See8.1.) 5.2 UnitsfortheCalibration Secondarycalibrationproducesthesametypeofinformationaboutasensorasdoesprimarycalibration.AnAE sensorrespondstomotionatitsfrontface.Theactualstressandstrainat
22、thefrontfaceofamountedsensor dependsontheinteractionbetweenthemechanicalimpedanceofthesensor(load)andthatofthemountingblock (driver);neitherthestressnorthestrainisamenabletodirectmeasurementatthislocation.However,thefree displacementthatwouldoccuratthesurfaceoftheblockintheabsenceofthesensorcanbeinf
23、erredfrom measurementsmadeelsewhereonthesurface.SinceAEsensorsareusedtomonitormotionatafreesurfaceofa structureandinteractiveeffectsbetweensensorandstructurearegenerallyofnointerest,thefreemotionisthe appropriateinputvariable.Itisrequiredtherefore,thattheunitsofcalibrationbevoltsperunitoffreedisplac
24、ement orfreevelocity,i.e.voltspermeterorvoltsecondspermeter. Thecalibrationresultsmaybeexpressedinthefrequencydomainasthesteadystatemagnitudeandphase responseofthesensortosteadystatesinusoidalexcitation,orinthetimedomainasthetransientresponseofthe sensortoadeltafunctionofdisplacement. 5.3 Importance
25、ofthetestblockmaterial Thespecificacousticalimpedance( Z ac )ofthetestblockisanimportantparameterwhichaffectsthecalibration results.Calibrationsperformedonblocksofdifferentmaterialsyieldsensorsensitivitiesthatareverydifferent,e.g., asensorthathasbeencalibratedonasteelblock,ifcalibratedonaglassoralum
26、inumblock,mayhaveanaverageISO ISO12714:1999(E) 3 sensitivitythatis50%ofthevalueobtainedonsteel,and,ifcalibratedonapolymethylmethacrylateblock,may haveanaveragesensitivitythatis3%ofthevalueobtainedonsteel 2 . Forasensorhavingacircularaperture(mountingface)withuniformsensitivityovertheface,therearefre
27、quencies atwhichnullsinthefrequencyresponseoccur.ThesenullsoccuratthezeroesofthefirstorderBesselfunction, J 1 (ka),where k=2 pf/c, fisfrequency, cistheRayleighspeedinthetestblockand aistheradiusofthesensor face 2 .Therefore,calibrationresultsdependupontheRayleighwavespeedinthematerialofthetestblock.
28、 Forthereasonsoutlinedintheprevioustwoparagraphs,allsecondarycalibrationresultsarespecifictoaparticular material;asecondarycalibrationproceduremustspecifythematerialoftheblock.AlthoughthisInternational Standardaddressessecondarycalibrationsontestblocksofdifferentmaterials,theonlyexistingprimary cali
29、brationsareperformedonsteeltestblocks.Toestablishasecondarycalibrationonanothermaterialwouldalso requiretheestablishingofaprimarycalibrationforthesamematerial. 6 Requirementsofthesecondarycalibrationapparatus 6.1Basic Scheme AprototypeapparatusforsecondarycalibrationisshowninFigure1.Aglasscapillaryb
30、reakdeviceorother suitablesourcedevice(A)isdeployedontheupperfaceofthesteeltestblock(B).TheRS(C)andtheSUT(D)are placedequallydistantfromthesourceandinoppositedirectionsfromit.Becauseofthesymmetryofthesensor placement,thefreesurfacedisplacementsatthelocationsoftheRSandtheSUTarethesame.Voltagetransien
31、ts fromthetwosensorsarerecordedsimultaneouslybydigitalwaveformrecorders(E)andprocessedbyacomputer. ActualdynamicdisplacementsofthesurfaceofthetestblockatthelocationsoftheRSandtheSUTmaybe differentbecausetheRSandtheSUTmaypresentdifferentloadimpedancestothetestblock.However,consistent withdefinitionsu
32、sedforprimaryandsecondarycalibration,theloadingeffectsofbothsensorsareconsideredtobe characteristicsofthesensorsthemselves,andcalibrationresultsarestatedintermsoffreedisplacementofthe blocksurface. 6.2 Qualificationofthetestblock Theprototypesecondarycalibrationapparatuswasdesignedforsensorsintended
33、foruseonsteel.Thetestblockis therefore,madeofsteel(hotrolledsteelA36material).Forasteelblock,itisrecommendedthatspecificationtothe metalsupplierrequirethattheblockbestressrelievedat566Corgreaterandthatthestressreliefbecarriedout subsequenttoanyflamecutting. Forasteeltestblock,thereshallbetwoparallel
34、faceswithathickness,measuredbetweenthefaces,ofatleast 180mm.Thevolumeoftheblockshallcontainacylinderwhichis400mmindiameterby180mmlong,andthetwo facesshallbeflatandparalleltowithin0,12mmoverall( 0,06mm). Forasteeltestblock,thetopsurfaceoftheblock(theworkingface)shallhaveanRMSroughnessvaluenogreater t
35、han1 mm,asdeterminedbyatleastthreeprofilometertracestakeninthecentralregionoftheblock.Thebottom surfaceoftheblockmusthaveanRMSroughnessvaluenogreaterthan4 mm.Thereasonforhavinga specificationonthebottomsurfaceistoassurereasonableabilitytoperformtimeofflightmeasurementsofthe speedofsoundintheblock. F
36、orblocksofmaterialsotherthansteel,minimumdimensionalrequirements,dimensionalaccuraciesandthe roughnesslimitationshallbescaledinproportiontothelongitudinalsoundspeedintheblockmaterialrelativeto thatinsteel. Thetopfaceoftheblockshallbetheworkingfaceonwhicharelocatedthesource,RSandSUT.Theselocations sh
37、allbechosennearthecentresoastomaximizethedistancesofsourceandreceiverstothenearestedgeofthe face.Foratestblockofanymaterial,thedistancefromthesourcetotheRSandthedistancefromthesourceto theSUTshalleachbe100mm 2mm(thesameasthatspecifiedforprimarycalibration). Theblockshallundergolongitudinalultrasonic
38、inspectionforflawsatafrequencybetween2MHzand5MHz. ProcedureinaccordancewithASTME114shallbefollowed.Theblockshallcontainnoflawswhichgivea reflectiongreaterthan12%ofthefirstbackwallreflection.ISO12714:1999(E) ISO 4 Key 1Sensorundertest 2Capillarybreaksource 3Referencesensor 4Twochannelwaveformrecorder
39、system 541cm 341cm 319cmsteelblock Figure1Schematicrepresentationoftheprototypesecondarycalibrationapparatus Thematerialoftheblockshallbehighlyuniformasdeterminedbypulseechoandtimeofflightmeasurementsof bothlongitudinalandshearspeeds.Thesemeasurementsshallbemadethroughtheblockataminimumofseven locat
40、ionsregularlyspacedoverthesurface.Theuncertaintyofeachmeasurementoftimeofflightshallbeno greaterthan0,1%.Itisrecommendedthatthepulseechotransducerhaveitsmainresonanceintherange between2MHzand5MHz.Fortheseven(ormore)measurementsoflongitudinalwavevelocity,themaximum differencebetweentheindividualvalue
41、softhemeasurementsshallbenomorethan0,3%oftheaveragevalue. Themeasurementsofshearwavevelocityshallsatisfythesamecriterion. 6.3The source Thesourceemployedintheprototypesecondarycalibrationsystemisabreakingglasscapillary.Thecapillariesare preparedbydrawingdown6mmPyrextubingtoadiameterof0,1mmto0,25mm.S
42、ourceeventsaregeneratedby squeezingthecapillarytubingagainstthetestblockusingpressurefromthesideofa4mmdiameterglassrodheld inthehand. Ingeneral,asecondarycalibrationsourcemaybeanysmallaperturedevicewhichcanprovidesufficientenergyto convenientlymakethecalibrationmeasurementsatallfrequencieswithintherangefrom100kHzto1MHz. Dependingonthecalibrationtechniquethesourcecouldbeatransientdevicesuchastheglassbreakapparatus,a sparkapparatus,apulsedriventransducero
