NASA NACA-TN-1174-1947 The application of high-temperature strain gages to the measurements of vibratory stresses in gas-turbine buckets《高温应变计对气体涡轮机叶片中振动性应力测量的应用》.pdf

1、I I.r. ., .,.-a: -1 ., ,i * r: a71. I ,1,. ,III.Iz!” J c)d1,Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.-” ,.- a*.THEAPPLICATIONOFHIGE-TEMPERATURESTRAINGAGESTOTHEByR.H.NT OFRATORY STR33S5ES .INGAS-TURBINEBUCKRTSKemp,W.C.Mcn?gan,andS.S.Ma.nmnL5UM

2、MARY -Thefeasibilityofmeasuringthevibrationinthebucketsofatheturbineswereoperatedatfullloadoverspeedsrangingfrom5000to20,000rpmandallvibrationphenomenawereobservedandrecorded,RESULTSMD DISCUSSIONThetestonthestandardturbinewheelwasintendedasachecktoverifythepremisethata.strain-gawhereae,duringtheperi

3、odwhenthebucketispassingthecoverednozzles,thepressurereducestonearlyzero.Ifthefrequencyofpressurefluctuationoranyharmonicthereofcoincideswiththenaturalfrequencyofthebucket,thebucketwould%eexcitedintoresonantvibration.A Fourierand.ysisofthepres-surediagramindicatesthatatanyresonancethenaturalfrequenc

4、yofthebucketwouldbeanintegralmultipleoftheturbinerotationalfrequency.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-m TNNO.1174 .Theresultspresentedwereohtalnedwithstraingaqescementedw?.thSav.ere”lsenNo.78cemsnt. wThe testEtherupturewaslocatedimmedi

5、atelyabovethegageposition.Inallcasesthevibratorystrainsignalwasclearandfreeofforeigninterferencesuchasslip-ringeffects.SUMMARYOFRESUZTSThesatisfactorydetectionenddeterminationofvibratorystressesona testsetupatactualspecimentemperaturesupto1500Fhasbeenaccomplishedbymeansofahigh-temperaturewiretrainga

6、ge.Thestraingagewasalsoappliedsatisfactorilyongas-turbinebucketsoperatingatspeedsencounteredinactualserviceandata nozzh:bxinlettemperatureof1505F.Thestrainsignalsfromthestraingagescementedto.thebucketsweretransmittedfreeofanyinter-ferencetothemeasuringinstrumentsthrougltisliprings.AircraftEngineRese

7、archLaboratory,NationalAdvisoryCommitteeforAeronauticsjCleveland,Ohio,February14,3947.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.8NACATNNO.1174M?PENDIXA .CONEH!RUCJUIONANDCALIBI#IONOFHIGEZEWERATUREmm GAGEConstructionMaterials.-Theobjectivefnthe

8、developnentiofthehlgh-.temperaturestraingagewastodeterminea suitablewire,wireform,andcementthatwouldpermitthemeasurentofvibratorystressesingas-turbinebucketssubjectedtogastemperaturesintheneh-borhoodof1500F, A largenumberofcomhlnationsafwireeandcementswastested;ofthese,Nichro?neV tirewoundonawovengl

9、ass-tapeformandcementedwitheitixrSaueieenNo.1orSauereisenNo.78cementiprovedtob%themosteatiefactorycombina- Vtionstodate.Methodofconstruction.-Thestrain-sensitivefilamentispre-paredbyreatstancdlead wirestotheendsofa 120-ohmlengthofO.001-inch-diameterNichrmeV wire.Bpendinguponthespoclftcrequlremmts,ei

10、therO.010-inch-diameterNichromeV wireorO.OIO-lnch-diameternickelwireieusedfortheloadwires.TheNlchrm!mV leadwireispreferablebecauseofItssuperiorhigh-temperaturecharac-teristicsbutwhenlongleadsarerequiredthelowerresistancenlclwireisused.Whengagelengthsofone-fouhowever,combinationsazztipssible.itisreco

11、mmendedthatthefor15minutesforreasonsA dynemiccalibrationthecyclesarenotcriticalandotherForapplicationwiththeNo.1 cementmountedstraingagebebakedatZ400Fthataresubsequentlydiscussed.Calibrationwasmadetodeterminetheeffectoftemmor-atureugmnthestrainsensitivityofthehigh-temperaturestraintherefore,equation

12、(2)maybeconsideredsufficientlyacurateforpracticalpurposes.thedroppingresistor this$XQdysShasbeenconsideredequaltothestrainG=whenthecircuitsoffigure9(c)weretested,thestraingagesfailedatapproximately1200F. Inspectionofthecircuitsshowsthatthefailuresoccurredwhentheaveragepotentfalofthestrain-sensitivef

13、flamentwasnegativewithresecttothetestspeclneh(ground)I didnotoccurwhentheaveragepotentfalwas&asitivewithrespecttothetestscimen.Operationthoutcircuitgrounding(fig.9(b)wassuccessfulrege,rdiessofthebatterypolarity.Thecorrosionmaybeexplainedbycomparingittoanelectro-lyticeffectinwhichthestrain-sensitivef

14、ilamentandthetestspecimenactaetheelectrodewhereastheSauereisencementactsastheelectrolyteattheelevatedtcmporatures.Theequivalentcircuitisillustratedinfigure10,whichshowsboththecorrectmethodofconnectingthecirouit(fig.10(a)andtheincorrectmethod(fig.10(b).Wheatstone-bridgacircuits,commoninstrain-gagecir

15、cuitsinvolvingtheuse ofsliprings,mustlilm-wisebesoarrangedthattheaveragepotentialofthestraingageispositivewithrespecttothetestsurface.Thevariationoftheresistancewithtemperatureofthehigh-temp&atureutraingagesfabricatedwithNichromeV wireisshowninfigure11. Itisnotedthatduringthefirsthalfofcycle1 anProv

16、ided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-12 l?ACATNNO.1174-increaseintheresistanceofaproximately17percentIsobtained_Ulwncompletionofcyole1 (returntoroomtemperature)theresic3t-ancewasfoundtoreturntoa valueapproxmately12percenthigherthantheoriginal.

17、Insubsequentheat3.ngandcoollngcyolesthetrendo?thesecondhalfofcycle1 1retainedalnwninfig-urellbycycle2.Thestrainsensitivitiesofthestraingagesatelevated.tem-peratureswereplottedastheratioofthesensitivityfac”torattheelevatedtemperaturetothesensitivityfactoratroomtemperature.Thismthodprovidesameansofcom

18、paringthestrainsensitivitiesatelevatedtemeraturesofmr3.ousstrain&agesthathavedifferentroom-temperaturestraineenflitivitiee.Thestrain-sensitivityfactorsatroomtemperatureoftheform-w&ndstraingagestestedwere1.75*1Opercent.Ifthegagefactorina specificapplicationcannotbemeasured,a valueof1.75isreccvmmmdedf

19、ora form-woundgage.Theeffectoftemratureuponthestrain-sensitivityfactorofatypicalNichrozueV filament-typestraingage(withoutwfndingform)cementedwithSauereisenNo.1 iEIshowninfigure12. A relativelyconstantsensitivityfactorwasobtainedupto15000F andsubsequenttempera-turecyclinghadnoeffectupontheuniforrgit

20、yofthemsnsittvityfactor.Atroomtemperature,theaveragesensitivityfactorwas2.05wtthavariationfromgagetogageofapproximately45pefomt.Gagescement-edwlthSauemlsenNo.78jxmentgavequantitativelysimilarresults.Thevariationoftheratioofstrati-sensitivityfactors 51%withtemperatureforstraingagescementedwithSauerel

21、senNo.78cementIsshownfnfigure13. Twocompletaheat+fngandcoollngcyclesareshownwitha temperaturerangefromroohtemperatureto15000F,Thefmnsitvityfactorissensiblystabieandreproduciblethroughouttheheatingendcoolingcycles.Thewaveformofthestratn-agesignalduringtestingwasequallyasgoodat1500F asItwasatroomtempe

22、ra-ture.Thevariationof / withtemperatureforforq-womdstraingagesCementedwithSauereisenNo.1 isshowninfigure14. Aeharpriseoccursduringthefirstincreaseintemperatureatapproximately130 F butwhencooledthisrisedisappears.ForthisreasonjItisrecommendedthatthespecimensuponwhichstraingagesarecenentedwith$auerei

23、senNo.1bepreheatedtoappnxi?mtely14000F fora shorttmebeforeactualtesting.TheVariattinol?thestrainsensitivitiesduringsubsequentheatfngandcoolingcycleswillbesubstantiallythesame.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-,8.9NACATNNo. Z74 . 13There

24、producibilityof / fromstraingagetostraingageoftheform-woundtypeissuchthataccuratequantitativedatacanbeobtaineduptc1200F. From1200to150CF variationsoccurandvibratorystressdataobtainedwithsuchgagesshouldbetreatedqualitativel.y,Inherentphysicalcharacteristicsofthewbven-glassformonwhichtheresatancewirei

25、swoundcausesthedecreaseofsensitivityfactorwithincreaseoftemperatureabove1200F. Themeasuzwmentof thefrequencyof thevibrationisaccurateup to1500F. Itisrecommendedthatwheneverpossible,a straingagewithoutwindingformbeusedbecauseaccuratequantitativedatac=.beobtatnedwiththistypeupto1500F.-.Thechoicebetwee

26、nSauereieenNo.1andSauereisenNo.78cementdependsupontheparticularapplication.SauereisenNo.78cementhabbettercement-to-metaladhesivequalitiesthanNo,1,buttheNo.1hasbettercement-to-ceentadhesionthantheNo.78. TheNo.78isalsomre hydroscopicand,fthereisanymoisturenearthetestinstallation,itsuseshouldbeavoided,

27、TheadditionofSauereisenNo.15thinnertotheNo,78cementhasa detrimentaleffectuponthestr&in-gagesenQitfvityfactoratelevatedtempera-,tures.TheNo.78cehentisthereforemeredifficulttoapplyandgoodreproduciblestrain-gagemountsarelikewisemcmedif:iculttoobtain.InmostapplicationstheuseofNo.1 cementisrecommended.In

28、thetestswhereNo.78cementwasused,itwasfounddesirabletodirectthehatofaninfraredlamponthestrain-gageinstallationdurhgthenonrunningperiods,SatisfactoryadhesionoftheSauereisenNo.1andNo.78cementshasbeenobtanedonsuohhigh-tempmaturealloysas17W,Timken,Vitallium,andInconel.-. #- .Provided by IHSNot for Resale

29、No reproduction or networking permitted without license from IHS-,-,-14fwmn BliACATNNo. 1174SLIP-RINGEFFECTSBecauseoftheneed.forconductingcurrentsandvoltage8betweenthestatioyequipmentandthetatingstraingage,slipringarenecessanllya pa.ofstrain-gagecircuits,!l?heinterferenceeffectsofslipringsonstrain-g

30、ageelgnahathighspeedsofrota-tioncanbeminimizedbyreducfngtheresistancefluctuationsbetweentheslipringsandbrushesthemselvesandbyarrangingtheelectricalcircuittobeasinsensitiveas”esibletotheresistance :fluctuatlmsthatdooccur.rienceindicatedtkt thecom-binationofmonel-metalslipringsandsilver-graphitebrushe

31、swould.-*servesatisfactorilyforthepresentproblem.Onemethodnowincomunuseforminimizingtheeffectofsllp-ringresistemcevariationisthemountingaftheentirestraln- :2 .8,2:m a71Gj2mc-lo .4:*2.20 mo 400 am 800 1000 lmo 1400 lmTemperature,FFigure 1.- Average variation with temperatureof ratio of strain-gage se

32、nsitivity faotorat elevated temperaturesto strain-gage factor atroom temperature for form-woundstraingages cemented with Sauereisen No. 78cement.1zzo,.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Fig. 2 NACA TN NO. 1174.rR+120 v18v 2-120vt* *I Rot

33、ating system 6 Vacuum-tubevoltmeter2 Powersupp17i Oscilloscope1?Controlcircuit SignalgeneratorAmplifier RsHigh-temperaturestraingage5 Osclllograph RCCalibratorstraingage(a) Instrumentation.BRl4c NATIONAL ADVISORYCCMM17TEE FOR AERONAUTICSR D Ev*,R BallastresistorRI StraingageFixedresistors %J%UPPIYv(

34、b) Equivalentcircuitforanalyticalpurposes.FQure2.-Instrumentatlonandclrcultsusedin theinvestigationof vibratorystressesinturbinebuckets. .-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.NACA TN NO. 1174 Fig. 3StandardModifiedbucket bucket Locationo

35、f straingage.(a)Modificationof (b)9ectionof turbinewheelshowingtestbucket. modified,stub,andstandardbuckets.Weldednozzle-boxcoverIONAL ADVISORYEE FOR AERONAUTICS(c) Modifiedbox.Figure3. - Modificationsmadenozzlebox.turbine nozzleto turbine bucket, wheel, andProvided by IHSNot for ResaleNo reproducti

36、on or networking permitted without license from IHS-,-,-Figure 4. - Test installation showing modified turbine wheel and slip-ring assembly.lProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-. 91000 AAf800&0600.&2.$ 400200o0 2000 4000 6000 ao/ /K/ 0-Ec

37、/ / / / / / .0 Observed natural7” / frequencies excited/ at various turbine/ speeds/ .IIATIONAL ADVISORYCCWITTEE FOR AERoNM)TICS1 1 I IMeasured stresses ateach resonanceStressPoint(lln. )A 28,800B 18,000: i29,0021,00E 40,200-.10,000 12,000 14,000 16,000Turbine speea, rprnFigure5. - Resonancespectrum

38、formodifiedturbosuperchargerturbinebucket.+zzo.n10*ulProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Fig. 6NACA TN NO. 1174Clamp Lead wire Q: IIr I /- -0 .Strain-gageform-/-:reslstancewire(a) Strain-gageformclampedwith wires preparedforwlndiNATIONAL

39、ADVISORYCWITTEE FOR AERONAUTICSIlu61m(b) Completedstrain gage.,ng.Figure 6.- Constructionof high-temperaturestrain gage. .Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.a,+NACA TN NO. 1174 Fig. 7Cantileverbar/Furnacer- - -:11I /ILstraingage, RaLow-

40、temperaturestraingage,Rb(a) Essentialparts of calibrationsetup.NATICNAL ADvIsoRVCCMMITTEE FOR AERONAUTICSRa1Rb I- 1vEv dIi I(b) Equivalentcircuit.Figure7.- Calibratlonsetupandelectricalcircuitusedindeterminingthe sensitivityofthehigh-temperaturestrain “ gage.Provided by IHSNot for ResaleNo reproduct

41、ion or networking permitted without license from IHS-,-,-oNATIDNAL ADVISORYcCUdl TTEE FoR AERONAW ICS,.00.m.80 N % .70.m ro 200 400 m 6001000 1200 1400 1600Temperature, OFI4Figme 8.-Varlatlan of elastlotiulus of Inconel with temperature. (Taken fiwm reference 1. +* , &9 o “Provided by IHSNot for Res

42、aleNo reproduction or networking permitted without license from IHS-,-,-NACA TN No. 1174 Fig. 9(a)Batterypolarityingroundedcircuitsthatoperatedsatlsfaotorllyat1500F.m+-(b)Batterypolarityinungrounded.clreuitsthatoperatedsatisfactorilyat1500F.(a)Batterypolarityingroundedcircuitsthatfailedatapproximate

43、ly12000F.Figure9.- SchematIcdiagramscircuitstestedtodetermineNAT10N4LADVISORYCOhWITTEE FOR AERONAUTICSor e lt strain-gagepotentiometertheeffectofbatterypolarlty.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Fig. 10 NACA TN No. 1-174RaI + (a)Average

44、strain-gagepotentialabove ground.Ra(b)Averagestrain-gagepotentialbelowground.Rd,tNATIONAL ADVISORYCOMMITTEE FOR AERONAUTICSFigure10.-Polarityeffectofhigh-temperaturestraingage2Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-150-HAT IONAL ADVISORYCCM4

45、1 TTEE FOR AERONAIJT ICS4510.a!2 1355:a130125120fj 200 400 60tI UooTemperature, Figure IL. Vapiation of resistance of a Biohrome V tirestrain gage with temperature.zo.-1$.nal.Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-.-n1.9190.8d.4NATIWL AOV IS

46、CRYCOn!ITTEE F(M AER0?4Wr KSiIO Heatlmgo coolingI,0 200 m em W 1000 1200 14CKI lmoTemperature,%Figure12.- Varlatlonofratioof strain-gagesensitivityfaatorat elevatedtemperaturesto factor at room temperature with temrature for strtin gagI WI thout winding formsoemsnted WI th Sauerei scn No. I c.m!ent.

47、M. , . I. . . . .Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-u ?*Q-1oNAT I(WAL ADv ISIMYCCUUITTEE FOR AERIMAuTICS.2b g .Z3L y -u- +!s.h a71 L .0 a r-e- Rw “J%ck.8 0 Heating a75 cooling cycle 1 -c ,-.-cycle 2 .6 - :j.4.20 200 boo 600 800 1000 1200 1doo lbTemperature,FFigure 13.- Variationof ratio of strain-gagesensitivity factorat elevatedtemperaturesto -factor at room temperaturewith temperaturef