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1、93FTM9 _U Gear Tooth BendingFatigue Crack Detectionby AcousticEmissionsand Tooth Compliance Measurements by: Jeffrey Wheitner,Donald Houser and Craig Blazakis Ohio State University AmericanGearManufacturersAssociation II TECHNICALPAPER Copyright American Gear Manufacturers Association Provided by IH
2、S under license with AGMA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/18/2007 10:50:19 MDTNo reproduction or networking permitted without license from IHS -,-,- Gear Tooth Bending Fatigue Crack Detection by Acoustic Emissions and ToothComplianceMeasurements Jeffrey Wheitn
3、er, Donald Houser and Craig Blazakis, Ohio State University Thestatementsandopinionscontainedhereinarcthoseoftheauthorandshouldnotbeconstrued asanofficial actionor opinionof theAmericanGearManufacancrs Association. ABSTRACT: Early detectionofcracksingearteeth subjectedto standardbending fatiguetests
4、haslongbeenadiffic_ _LThe purpose of this paperis to presentthe results ofgear toothbending fatigue tests inwhich the combinationof acoustic emissions measurements andtooth compliancemeasurementsare exploredas toolsfor early crackdetection. Single tooth bending fatigue tests for severaI different ge
5、ar materialswere performedon an eleclrohydraulic fatigue testing machine using a standardSAE fatigue test fixture andgeargeometry. Throughouttesting,acoustic emissions were monitored t/siflgan acoustic emissions lransduceraffixed to thesurfaceof the gear. Toothcompliancewas measured using an acceler
6、ometer affixed to the lower platform of the fatiguetest fixture. The combination of these two crack detectionmethods servesto describesuchfatiguetestcharacteristicsastheprobabletimeofcrackir6_a_on,rate ofcrack propagation, and percent of totalfatigue life spentin crackpropagationphase. Theeffects of
7、 materials, metallurgical processes suchas carbmSzationandshot peening,and theresultant surfacefinish on thefatigueprocess as revealed by thesecrack detection methods axealsopresented. Copyright 1993 American Gear ManufacturersAssociation 1500 King Street, Suite201 Alexandria, Virginia, 22314:_ Octo
8、ber, 1993 ISBN: 1-55589-621-9 Copyright American Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/18/2007 10:50:19 MDTNo reproduction or networking permitted without license from IHS -,-,- GearTooth Bend:ra
9、g Fatigue CrackDetectionBy AcousticEmissionsand Tooth ComplianceMeasurements C.A. Blazakis, Product Design Center, Newark, Ohio D. tL Houser, The Ohio State University,Dept. of MechanicalEngineering J.A.Wheitner, CumminsEngine Company,Inc., Columbus, Indiana Introductionmethodsinclude dye penetranti
10、nspection,magnetic particle inspection,eddycurrentinspection,ultrasonicinspection,and Because geartooth bending fatiguefailurestend toberadiography. moreseriousthan anyother gear failuremode Alban,1985, anTwo methods for detectingandmonitoringthe growth extensiveeffortisunderwayamong researchersto d
11、evelopof fatigue cracks, however, havebeenfoundto be very accuratemodels for thepredictionof gear tooth bendingfatiguecompatible with single tooth bending fatigue test conditions: life as well as to generate experimental data for comparisonacousticemissions measurementsandtooth compliance with such
12、models,measurements.Furthermore, the combination of these two As described by Collins Collin.%1981, “Fatiguemay bemethods applied in parallel during testing has produced reliable characterized asaprogressivefailure phenomenonthatcharacterization ofthe fatigueprocessforvarious gear proceeds by the in
13、itiation and propagationof cracks to anmaterials, surfacefinishes, etc. unstable size.“ This implies that fatigue life prediction modelsThe remainder of this paperpresents the results of must be designed to address both the crack initiation and theresearch aimed at exploring the use of these crack d
14、etection crack propagation regimesof the total fatigue processsuch thatmethods on gears of various materials, surface finishes, and metallurgical processes. N-Ni+Np Test Fixture and Gear Geometry where N is the total fatigue life, Ni is the number of cycles to initiation,and Np is the number of cycl
15、es ofpropagation.In order to facilitate consistent andreproducible This entire fatigue process, including both the crackfatigue test results, the Society of Automotive Engineers (SAE) initiation and crack propagation phases, can be simulatedin thehas developed a standard fatiguetestfixture,testgear
16、laboratory using an electrohydraulic testing machinefitted withgeometry, and testing procedure to be used throughout the a fixture which allows a cyclic bending load to be appliedgearing industry Buenneke, et al, 1982. The standard SAE directly to a single gear tooth.Such testing, known as singletes
17、t gear geometryhas 34 teeth, a 20pressure angle, a tooth bending fatigue testing, allows the exploration of thediametralpitch of six, and an outer diameterof six inches. A effects of materials, metallurgical processes,surface finish,detailed descriptionofthistest gearand fixturegeometry can be geome
18、try, etc. on the fatigue process,found in the above reference.Throughout this research, the Due to the nature of this type of testing, however, thestandard SAE geometry and testing procedure were used. abilityto detect fatigue crack formation duringeachtest can beFigures 1 and 2 illustrate the test
19、fixture and the test gear difficult. Safety concerns prohibit the close-up visual inspectiongeometry. of the tooth fillet during the test.Also, the geometricGearMaterials constraintsimposed by the test fixture make conventional crack detection methodsdifficult to apply during testing.SuchSeveralmate
20、rialswereusedforfatiguetesting, 1 Copyright American Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/18/2007 10:50:19 MDTNo reproduction or networking permitted without license from IHS -,-,- J Table 2. 41
21、18 Root SurfaceFinishes #4118ARa = 32 lain Group Cnoup#4118BRa =42 lain qF Group #4118CRa = 64 lain allof the gears except the 9310 had lead crowning. Fatimae Testin_ Procedure All fatigue testing was performed on an MTS Systems Corporation Model 810 fatigue testing machine using a 55 kip hydraulic
22、actuator which was fined with the SAE fixture.All Figure 1. SAE Standard Test Geartesting was performed using a sinusoidal applied load with a frequency of 10Hz. A load ratio, R, where lLo_d _1al_ Cell _of 0.1 Was maintained for all tests.Each test was allowed to run continuously until finalfracture
23、 occurred, at which time the machine automatically shut down, or until the established run- - -out life was reached. Due to time constraints, a run-out life of 106 cycles wasusually observed. V-II II “II-“I, ,I itAco.stio mi sionsM rements L-_Pi_o,_Acoustic emissions are small amplitude transient el
24、astic Actuator nIstress waves resulting from the suddenrelease of energy duringt_- Figure 2. SAE Standard Fatigue Test Fixturedeformation and failure processes in stressed materials.The V, primary sources of acoustic emissions are crack growth and including: carburized 4118 alloy steel carburized 86
25、20 alloyplastic deformation.Sudden movement at the source produces steel, carburized 9310 alloy steel, carburized and shot peeneda stress wave which radiates to the surface of the structure and excites a piezoelectric transducer. 9310 alloy steel,and carburized 4320 alloy steel. The carburized 9310
26、gears were all manufactured andIn order to monitor acoustic emissionswithin the heattreatedtogether,withfourofthesegearsbeinggear during each fatigue test,a Physical Acoustics model subsequently shot peened to the specifications listed in Table 1.#NAN030 acoustic emissions sensor which is resonant a
27、t 300 These gears are referred to as groups #9310 and #9310P,kHz is used.Prior to each fatigue test, the transducer is attached to the gearjust below the root of the tooth to be tested respectively. using ordinary super glue.Emissions are amplified using a Physical Acoustics model #1220 preamplifier
28、 set at 40 dB gain, Table 1. 9310 Shot Peening Speesand are then monitored using a Physical Acoustics mode/ #1200A crack detector.The crack detector is able to record a-_ z cumulative total of the emission counts from the growing crack, Specification:MIL-S-13165 which is output to a dual channel str
29、ip chart recorder.Each Shot Size:MI-330-H count represents a single incidence of the acoustic emissions-_ Intensity:12-16Asignal crossing a pre-defined threshold.A detailed description Coverage:200%of acoustic emissions can be found in Metals Handbook Pollock,1989. Nine of the 4118 gears were manufa
30、ctured by one company using three different cutting speeds, feeds, and tools,Gear Tooth StiffnessMeasurements to give three different root surface finishes, listed in Table 2. These gears are referred to as groups #4118A, #4118B, andTooth stiffness is a measure of the force developedin #4118C. Ra is
31、 the measured peak to valleysurface roughness,the tooth per unit displacement.Because the introduction of a The 4320 gears are referred to as group #4320, andthefatigue crackinto the tooth fillet reduces tooth stit_ess, 8620 gears as group #8620.Most of the gears tested wereobservations of changes i
32、n tooth stiffness taken duringa fatigue donated by companies so gear finishing was characteristic oftest serve as reliable indicators of the presence and sizeof such each particular companies manufacturing process.Therefore,acrack. 2f Copyright American Gear Manufacturers Association Provided by IHS
33、 under license with AGMA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/18/2007 10:50:19 MDTNo reproduction or networking permitted without license from IHS -,-,- In ordertomonitorchangesin thestiffnessof the system due to the propagationof a crack in the test tooth,an _acce
34、lerometeris screw mountedto the base of the fixture.A500/ PCBmodel#302B03piezoelectricaccelerometerwitha_ 46o, J scnitivitv of 299.9 mW_along with a I(i_lermodel_504E4t_ 400 ._-.350t dual mode amplifier is used.Accelerometeroutputduringa_300 fatigue testcan be used to calculatethe inenance,I, of the
35、_ 250i gear/fixture system using the equationtu 200 = 150i/“ _100i/: l=F_60 -0_i 5000060000700008000090000 whereF is the loadappliedto the fixture,x is thefixtureCycles displacement,and_c“istheaccelerationof thefixtureasFigure3. Acoustic Emission Count vs. Fatigue Life for an measuredby the accelero
36、meter.WheitnerWheitner,19928620 Gear Tooth demonstratedthat based upon a lumped parametermodel of the system, the dynamiceffectsof the fixturena_s have no effectbeen calibratedto show the correspondingnumber of cycles as on the fixturestiffness,andthusthe fixturestiffnesscan bedeterminedusingthe str
37、ipchart recorderspeed andthe test measuredstatically.The inertancecan thereforebe related tofrequency. the stiffmess of the gear tooth,k, by the equationInthiscase,crackinitiationappearstooccurat approximately61000 cycles.It should be noted, however,that becausea physicaldefinitionof crackinitiation
38、has yet to be k = Ice2 = Fee2defined,and becausethe acousticemi._sions detectionsystem has a finite sensitivity,the term “crackinitiation“ simply refers to the time at which the first detectableemissionsare recorded. where co= 20 7rrad/sec is the test frequency.This implies thatIt maybepossibletofur
39、therrefinetheacousticemissions detectionsysteminordertoincreasesensitivity.Such refinementmay includeadjustmentsto the natural frequencyof Fee:the transducer,the thresholdvalue, the amplifier gain, or the 5_= knumber and placementof transducers. Noticethatprior to the initiationpoint, the number of
40、Thus, for a constan.t applied load and a constantfrequency,therecordedacousticemissionscountsis non-zero.This is the measuredaccelerometeroutputis inversely proportionalto theresultof backgroundnoise whichis generatedby the testing sti_essof thegeartooth.Basedonthisanalysis,it wasmachine.Becauseit i
41、s difficult to separate the noise signal from determinedthat the accelerometeroutputcould be used as athe signal generatedby the growing crack, the sensitivity of the directmeasureof thechangein stiffnessof thegear toothdetectionsystemmust be maintainedat levels which minimize duringafatiguetestwith
42、outactuallyealcalatingthe tooththe amountof backgroundinterference. stiffness.In some cases the accelerometeroutput was recordedAs seen in the figure, the emissionsslowly increase until, using a PC data acquisitionsystem,while othertimes it wasat approximately87000 cycles, the rate of emissionsincre
43、ases recorded in parallel with the acoustic emissionsoutput on a dualdramatically,leadingto final fractureat 89000cycles.This channel strip chart recorder.This allows for easy comparisonacousticemissionsfootprintis typicalof the 4118and 4320 of the data from both crack detection methods,gears as wel
44、l. In both the peenedand unpeened9310 gears,however, the crackinitiationmode was verydifferent,as illustratedin Figure4.Asthegearreachedthecriticalpoint,it Resultsinstantaneouslycrackedalongthethickness.Whenthis happened,the gear let out an audible pop that sounded like the The remainderof this pape
45、rdescribesthe resultsthatsnappingof ones fingers.At the same time this pop was heard, wereobtainedusingthe previouslydescribedequipmentandthe acoustic emissionsrose very rapidly.After this abrupt jump procedures.Resultsare presentedfor arepresentativecross-in emissions,thecarveflattensoutduringpropa
46、gation,then section of the materialswhich were tested,in addition to casesonceagain increases very rapidly until failure. in which unusual behavior was observed.Itisproposedthatinthe9310gears,asmall discontinuityis growingbelowthe surface near the case-core transition.After this crackreaches a criti
47、cal length, it quickly AcousticEmissionsResuJt.propagatestothesurfaceresultingin thesuddenburstof acoustic _emissions.ThisWpe of failureis consistentwith A typicalacousticemissionsplotfor an 8620 gear isfailures that occur below the surface in earbufizedsteel in which illustratedin Figure3.Thegraphc
48、onsistsof stripcharttheendurancelimitofthecoreismuchlowerthatthe recorderoutputinwhichthey-axisrepresentsacousticendurancelimitof the case.The endurancelimit in directly emissionscounts,andthe x-axisrepresentstime, whichhasproportionalto thehardnessof the material in steels.This 3 Copyright American
49、 Gear Manufacturers Association Provided by IHS under license with AGMA Licensee=IHS Employees/1111111001, User=Wing, Bernie Not for Resale, 04/18/2007 10:50:19 MDTNo reproduction or networking permitted without license from IHS -,-,- 1400 _o120 o_“$ _- 1000_9z2 _o ,_ 800/_ _: 600:-“_“ 14.1,_86- u400,_“_,;,E 200=5 ,r_3 0i,l 14000142