全息干涉與散斑干涉技術綜述報告全息干涉無損檢測技術是無損檢測技術中的一個新分支，它是20世紀60年代末期發展起來的，是全息干涉計量技術的重要應用。我們知道結構在外力的作用下，將產生表面變形。若結構存在缺陷，則對應缺陷表面部位的表面變形與結構無缺陷部位的表面變形是不同的。這是因為缺陷的存在，使得缺陷部位的結構的剛度、強度、熱傳導系數等物理量均發生變化的結果。因而缺陷部位的局部變形與結構的整體變形就不一樣。應用全息干涉計量技術就可以把這種不同表面的變形轉換為光強表示的干涉條紋由感光介質記錄下來。而激光散斑技術是在激光全息實驗中，我們觀察被激光所照射的試件表面，就可以看到上面有無數的小斑點，因而觀察不到條紋，因此在前期，散斑是被看作是噪聲來對待的，直到隨著人們對全息干涉技術的進一步了解，才發現雖然這些斑點的大小位置都是隨機分布的，但所有的斑點綜合是符合統計規律的，在同樣的照射和記錄條件下，一個漫反射表面對應著一個確定的散斑場，即散斑與形成散斑的物體表面是一一對應的。在一定范圍內，散斑場的運動是和物體表面上各點的運動一一對應的，這就啟發人們根據散斑運動檢測,來獲得物體表面運動的信息，從而計算位移、應變和應力等一些力學量。因此全息和激光散斑方法由于其固有的高靈敏度，在非破壞性測試領域發現了越來越多的應用。可探測到表面及地下的裂縫、空洞、脫層和分層等缺陷。由于這些方法測量了在外部加載或其他條件的影響下，在這三個維度下研究對象的變形，它們也可以用于質量控制，也可以用于設計階段。激光散斑的方法，還利用了電子檢測和處理的發展（稱為電視全息術），并可用于實時定量評價。本綜述報告主要介紹利用光纖光刻技術，對全息和激光散斑測量方法進行了全面的研究，這兩種方法都適用于焊接、復合材料的檢驗。IntroductionHolographyisatwostepprocessofrecordingawavefrontandthenreconstructingthewave.WhileHolographyisoftenusedtoobtaintherecreationsofbeautiful3-dimensionalscenes,thereareseveralengineeringapplications,themostcommonandimportantonebeingHolographicNon-DestructiveTesting.Thisisaccomplishedwithholographicinterferometry,whereininterferometryiscarriedoutwithholographicallygeneratedwavefronts.Aspecklepatternisgeneratedwhenanobjectwitharoughsurfaceisilluminatedwithahighlycoherentsourceoflightsuchaslaser.Initiallythisspecklenoisewasconsideredasthebaneofholographers,untilitwasrealizedthatthesespecklescarryinformationaboutthesurfacethatproducethem.Again,asinthecaseofholography,thecombinationofinterferometricconceptswithspecklepatterncorrelationgaverisetospeckleinterferometry.ThedevelopmentsinelectronicdetectionandprocessingfurtheraddedwingstolaserspecklemethodsgivingrisetoElectronicSpecklePatternInterferometry(ESPI),or“TVHolography”.ThispaperdescribesabriefoutlineofholographicandspecklemethodsforNon-DestructiveTestingapplications,whereinthedeformationsofanobjectunderloadaremeasuredinanoncontactway.MeasurementofsurfaceshapesusingcontouringandderivativesofdisplacementusingShearographyarealsopresented.1.HolographyTheschematicforrecordingahologramisshowninFig.1.Thelightfromalaserissplitintotwobeams.Onebeamilluminatestheobjectandtheotherbeamisusedasareference.Attherecordingplane,aninterferenceoftheFig.1 :Experimentalarrangementforrecordingahologram.wavefrontscatteredbytheobjectwiththereferencewavefronttakesplace.Arecordingismadeonahighresolutionphotographicplate.Thedevelopedplate,nowcalleda“Hologram”，whenilluminatedbythereferencewave,reconstructstheobjectwave.Thereareseveralrecordinggeometriessuchasin-line,off-axis,imageplane,FourierTransform,reflectionandrainbowholograms.Thetheorybehindtherecordingandreconstructionofobjectwavefrontiswelldocumented.1.1HolographicInterferometry(HI)Whileholographyisusedtoobtainrecreationsofbeautiful3Dscenes,mostengineeringapplicationsofholographymakeuseofitsabilitytorecordslightlydifferentscenesanddisplaytheminutedifferencesbetweenthem.ThistechniqueiscalledHolographicInterferometry(HI).HerewedealwithInterferenceoftwowavesofwhichatleastoneofthewavesisgeneratedholographically.MethodsofHolographyInterferometryareclassifiedas(i)Real-timeHI,(ii)Double-ExposureHI,and(iii)TimeaverageHI.Inholographicinterferometry,werecordthehologramsofthetwostatesofanobjectundertest,onewithoutloadingandonewithloading.Whensuchadoublyexposedhologramisreconstructed,weseetheobjectsuperposedwithafringepatternwhichdepictsthedeformationundergonebytheobjectduetoloading.ThetheorybehindthefringeformationinHIisasfollows[3]:LettheO]andO?representtheundeformedanddeformedobjectwaves,whicharewrittenasOJx,y)=IO(x,y)lexp[-i①(x,y)] (1)°2(x，y)=IO(x,y)lexp[-i①(x,y)+8] (2)where8isthephasechangeduetodisplacementordeformationoftheobject.TheintensityduetosuperpositionofthesetwowavesisI(x，y)=lOJx,y)+O(x,y)|2=OO*+OO*+OO*+O*O11221212=I+I+2IICos8(3)1212whereI]and【2aretheintensitiesofO[&O?.ThePhaseDifference8isgivenby8=(K2-K1).L ⑷whereK?istheobservationvector,K]istheilluminationvectorandListhedisplacementvector.Thustheevaluationofthephase8isgivesthedisplacement.Thefringesformedrepresentcontoursofconstantdisplacement.1.2HolographicNon-DestructiveTesting(HNDT)ThispowerfultechniqueofHolographicinterferometry,isaninvaluableaidinEngineeringdesign,QualityControlandNon-DestructivetestingandInspection.InHNDT,theobjectunderstudyissubjectedaverysmallstressorexcitationanditsbehaviorisstudiedusingHI.Thedefectsintheobjectcanbespottedasananomalyintheotherwiseregularfringepattern.HNDTisahighlysensitive,whole-field,non-contacttechniqueandisapplicabletoobjectsofanyshapeandsize.ThetypesofexcitationusedforHNDTaremechanical,thermal,pneumaticorvibrational.Defectssuchascracks,voids,debonds,delaminations,residualstress,imperfectfits,interiorirregularities,inclusionscouldbeseen.HNDTisappliedtoinspectthedisbondsbetweenthepliesofanaircrafttyre,delaminationofthecompositematerialofahelicopterrotorblade,PCBinspection,rocketcastings,pressurevessels,andsoon.Useofdouble-pulsedlasermakesHImoreattractiveforstudyoftransientsandimpactloads.Fig.2showsthedoubleexposurehologramofaturbinebladesubjectedtoanimpactloading(recordedusingadouble-pulsedRubylaser).Fig.2:Double-pulsehologramofaturbinebladeimpactloadedwithasmallmetallicball.TimeaverageHI,whereinahologramofavibratingobjectisrecorded,providesinformationaboutthemodesandthevibrationamplitudesatvariouspointsontheobject.Figs.3(a)and(b)showthetimeaveragehologramsofarectangularplatevibratingat1826Hzand5478Hz,fromwhichtheresonantmodepatternscouldbeeasilystudied.InHNDT,thistechniqueisusedforstudyofvibrationsofmachinery,cardoors,enginesandgearboxesandtoidentifythepointswheretheyshouldbeboltedtoarrestthevibrationandnoise.Fig.3:(a)and(b)Timeaveragedhologramofacentrallyclampedplateat(0,0)and(1,0)modewhenvibratedat1826Hzand5478Hz respectively2.ElectronicSpecklePatternInterferometry(ESPI)Recentholographicapplicationsinengineeringuseavideocameraforimageacquisition,whichiscoupledtoacomputerimageprocessingsystem.ThisistermedasTVHolography,thoughtechnicallycalledElectronicSpecklePatternInterferometry(ESPI).Thetechniquemakesuseofthespecklepatternproducedwhenanobjectwitharoughsurfaceisilluminatedwithalaser[4-6].Thecorrelationbetweenthespecklepatterns,beforeandafteranobjectisdeformed,arecarriedoutusingimageprocessingtechniques.Figure4showstheschematicofanESPIsystem.TheobjectisilluminatedbythelightfromalaserandisimagedbyaCCDcamera.Anin-linereferencebeam,derivedfromthesamelaser,isaddedattheimageplane.Thespecklecorrelationiscarriedoutbystoringanimagewhiletheobjectisinitsinitialstate,andsubtractingthesubsequentframefromthisstoredframe,displayingthedifferenceonthemonitor.Whentheobjectissubjectedtosomeloadingorexcitation,thecorrelatedareasappearblackwhiletheuncorrelatedareaswouldbebright,resultinginafringepattern.AsinHI,thefringesrepresentcontoursofconstantdisplacementoftheobjectpoints.ThefringeformationinESPIiswelldocumented. TheintensitydistributionsI](x,y)and】2(x,y)recordedbeforeandaftertheobjectdisplacementrespectivelycanbewrittenasI(x,y)=a2+a2+2aacos(o) (5)【2(【2(x,y)=a2+aj+2a】a2cos(p+S) (6)Fig.4 :ExperimentalarrangementforESPIcomputerFig.6:(a)Delaminationinaplate(b)Longitudinalcrackinasteelweldmentwherea】anda?aretheamplitudesoftheobjectandreferencewaves,5isthephasedifferencebetweenthemand申istheadditionalphasechangeintroducedduetotheobjectmovement.Thesubtractedsignalasdisplayedonthemonitorisgivenby,I]-I2=4laia2Sing+(5/2)]Sin(d/2)l (7)Thuswefindthebrightnessismodulatedbyasinefactorofthephase.Thebrightnessonthemonitorismaximum

LaserDiodeDisplayMonitorCCDPCbased

fmageProcessorFHObjectFig.7:FiberOpticShearographysystemPZT- TransducerFS-FingerSpliceFH?FiberHolderBS-耳舉朋pljft』M-Mirrorwhen6=(2m+1)兀LaserDiodeDisplayMonitorCCDPCbased

fmageProcessorFHObjectFig.7:FiberOpticShearographysystemPZT- TransducerFS-FingerSpliceFH?FiberHolderBS-耳舉朋pljft』M-Mirrorratioofthematerialoftheplatecouldbecalculateddirectlyfromthesmalleranglebetweentheasymptotesofthehyperbolicfringes[8].Figure6(a)showsthedelaminationbetweentwoplatesbondedtogether,whileFig.6(b)showsalongitudinalcrackinaweldments[9].4.ShearographyFigure7showstheschematicofafiberopticShearographysystem.AdoubleimageofthelaserilluminatedobjectismadeontheCCDcamera.Asmallshearisintroducedbetweenthetwoimagesbytiltingoneofthemirrors.PoissIFigure7showstheschematicofafiberopticShearographysystem.AdoubleimageofthelaserilluminatedobjectismadeontheCCDcamera.Asmallshearisintroducedbetweenthetwoimagesbytiltingoneofthemirrors.PoissIonnc'orpsorationoffiberopticsmakesthesystemverycompactandthetechniqueapplicabletoobjectsatinaccessiblelocations.ShearographyisaveryusefultoolinexperimentalstressanalysisandNDTaswell.Withtheuseofphaseshiftingtechniques,thefringepatternscanalsobeautomaticallyprocessedbythecomputertoobtainquantitative3-dimensionalplots.Figure8showstheresultsofanNDTapplicationofShearographytodetectdelaminationinglassfiberreinforcedplastic(GFRP).TheGFRPspecimenswerepreparedwithunidirectionalglassfibermatandepoxyresinwithandwithoutprogrammeddefects.ThedefectswereintroducedbyplacingathinTeflonfilmof10mmdiameterandthickness0.23mmbetweenthelayersofglassfibermatduringthelamination.FourlayersofGlassfibermatwereusedtomakethelaminate.Thespecimensweremadeintheformofcirculardiaphragm.Thediaphragmwasclampedalongtheedgesan*Fig.8:SlopefringesobtainedonacircularGFRPspecimenwhichwas(a)Defectfree(b)HavingaprogrammeddelaminationDefectsiteloadedmechanicallyatthecenter.TheopticalconfigurationofFig.8wasused,whichissensitivetotheslopeoftheout-of-planedisplacement.Figure8(a)showsthefringesobtainedwithadefect-freespecimen,whileFig.8(b)showsthefringeswhenadelaminationwasintroducedbetweenthethirdandfourthlayers.Thedefectsitecouldbeeasilyseenasalocalizedfringe.*Fig.8:SlopefringesobtainedonacircularGFRPspecimenwhichwas(a)Defectfree(b)HavingaprogrammeddelaminationDefectsite全息無損檢測主要還是采用全息干涉計量技術的三種方法進行，即實時全息干涉法，兩次曝光全息法和時間平均全息干涉法。