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1、CommunicationsDirectObservationofSurfaceFatigueDamageintheSEMWOLFGANGKROMP,BRIGITTEWEISS,ANDROLANDSTICKLERTHEaccumulationoffatiguedamageandthenucleationandpropagationoffatiguecracksareofconsiderable/~Tran,l~nle~Hall-!ave/erlgt::::odscientificandtechnicalinterest.For
2、theidentificationTransducerandtheinvestigationofthevariousprocessesoccurringS~ecimenChamberduringfatigueexposuremethodsarerequiredwhichpermitdirectexaminationofthespecimenduringcyclicFig.1--Schematicdiagramofspecimenstageassemblyforhigh-frequencyfatiguetestinginasca
3、nningelectronmicro-straining.scope.Thescanningelectronmicroscope(SEM)appearstobethemostsuitableinstrumentforsuchinvestigationsbecauseofitslargedepthoffield,itshighresolution,Usingthisexperimentalstage,aresolutionofbetteranditseaseofmagnificationchange.'Amongthevari-
4、than700A(pointtopointresolutioninhighmagnifica-ousmethodsoffatiguetestinghigh-frequencytesttionmicrographs)wasobtainedwithaworkingdistancemethods(employingultrasonictestfrequencies)arebetween10and20mm.suitablebecauseoftherelativelysimpletestequipmentRod-shapedanddum
5、bbell-shapedspecimenswereandtheshorttesttimesrequiredtoachievelargenum-used,thedimensionsofwhichwerecalculatedtoachievebersofstraincycles.2-4Recentinvestigationshavealongitudinalresonancefrequencyof20kHz.Forcop-shownthatultrasonicfatigueprocessesaresimilartoperspeci
6、menstherod-shapedspecimenswere100mmthoseoccurringduringconventionallow-frequencylongatadiameterof3mm,thedumbbell-shapedspeci-push-pullfatiguetesting.3'~Quantitativerelationships,mensasshowninFig.1hadthefollowingdimensions:however,needstilltobedeterminedfllengthofend
7、sections7mm,lengthofgagesection31Inordertoinvestigatethedeformationprocessesoc-mm,diameterofendsections7mm,diameterofgagecurringduringultrasonicfatiguetestingwehaveadaptedsection3.5mm.Themaximumofthestressandstrainahigh-frequencytestequipment*toacommercialSEM.~ampli
8、tudeislocatedinthecenterofthecorrectlytunedspecimen.*Ultrasonicgeneratorandtransducer,1kw,operatingat20kHz,manufacturedThepresentstagewasd
