全息干涉与散斑干涉综述

全息干涉与散斑干涉技术综述报告全息干涉无损检测技术是无损检测技术中的一个新分支，它是20世纪60年代末期发展起来的，是全息干涉计量技术的重要应用。我们知道结构在外力的作用下，将产生表面变形。若结构存在缺陷，则对应缺陷表面部位的表面变形与结构无缺陷部位的表面变形是不同的。这是因为缺陷的存在，使得缺陷部位的结构的刚度、强度、热传导系数等物理量均发生变化的结果。因而缺陷部位的局部变形与结构的整体变形就不一样。应用全息干涉计量技术就可以把这种不同表面的变形转换为光强表示的干涉条纹由感光介质记录下来。而激光散斑技术是在激光全息实验中，我们观察被激光所照射的试件表面，就可以看到上面有无数的小斑点，因而观察不到条纹，因此在前期，散斑是被看作是噪声来对待的，直到随着人们对全息干涉技术的进一步了解，才发现虽然这些斑点的大小位置都是随机分布的，但所有的斑点综合是符合统计规律的，在同样的照射和记录条件下，一个漫反射表面对应着一个确定的散斑场，即散斑与形成散斑的物体表面是一一对应的。在一定范围内，散斑场的运动是和物体表面上各点的运动一一对应的，这就启发人们根据散斑运动检测,来获得物体表面运动的信息，从而计算位移、应变和应力等一些力学量。因此全息和激光散斑方法由于其固有的高灵敏度，在非破坏性测试领域发现了越来越多的应用。可探测到表面及地下的裂缝、空洞、脱层和分层等缺陷。由于这些方法测量了在外部加载或其他条件的影响下，在这三个维度下研究对象的变形，它们也可以用于质量控制，也可以用于设计阶段。激光散斑的方法，还利用了电子检测和处理的发展（称为电视全息术），并可用于实时定量评价。本综述报告主要介绍利用光纤光刻技术，对全息和激光散斑测量方法进行了全面的研究，这两种方法都适用于焊接、复合材料的检验。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全息无损检测主要还是采用全息干涉计量技术的三种方法进行，即实时全息干涉法，两次曝光全息法和时间平均全息干涉法。