外文翻譯班級(jí)：學(xué)號(hào)：姓名:指導(dǎo)教師：PittingfailureoftruckspiralbevelgearAbstractSpiralbevelgearsaresomeofthemostimportantelementsusedintruckdifferential.Inthisstudy,thefractureofspiralbevelgearfortruckdifferentialproducedfromcasehardeningsteelisinvestigated.Inordertostudythecausesofthefailure,specimenspreparedfromthedamagedspiralbevelgearsweresubjectedtoexperiments,suchasvisualinspection,hardness,chemicalanalysisandmetallurgicaltests.Pittingoccurrenceongearsurfaceswasobserved.Theeffectofmicrostructureonthefracturewasconsidered.Lowsurfacehardnessvalueswerefound.Thecalculatedcontactstresswashigherthantheallowablecontactstresswhichisemphasizedinliterature.1.IntroductionDifferentialdrivesarepackagedunitsusedforawiderangeofpower-transmissionapplications.Thespiralbevelgearsarebeginningtosupersedestraight-bevelgearsindifferentialdrives.Theyhavecurvedobliqueteeththatcontacteachothergraduallyandsmoothlyfromoneendofthetoothtotheother,meshingwitharollingcontactsimilartohelicalgears(Fig.1).Theyhavetheadvantageofensuringevenlydistributedtoothloadsandcarrymoreloadswithoutsurfacefatigue.Thrustloadingdependsonthedirectionofrotationandwhetherthespiralangleoftheteethispositiveornegative1,2.Theinvestigatedspiralbevelgearsaremadeoftwodifferentcasehardeningsteel.Thecasehardeningsteel(20MnCr5,EN10084)hasalowcarbonchromiumandtheothersteel(17NiCrMo6-4,EN10084)hasalownickelchromiummolybdenumwithmediumhardenability,generallysuppliedintheasrolledconditionwithamaximumbrinellhardnessof280(30HRC).Itischaracterizedbygoodcorestrengthandtoughnessinsmalltomediumsectionswithcasehardnessupto62HRCwhencarburized,hardenedandtempered.Thesesteelscanalsobeused(uncarburized)ashightensilesteel,whichwhensuitablyhardenedandtemperedcanbeutilizedforvariousapplicationsrequiringgoodtensilestrengthandreasonabletoughness.Almostthreegearsaredamagedeverymonthintruckservice.Therefore,thedamagedspiralbevelgearsoftruckwereevaluated,andthecausesoffractureofagearmanufacturedfromcasehardeningsteelwerecarriedout.SomepropertiesoftruckdifferentialaregiveninTable1.Also,themaindimensionsofthegearsareshowninFig.2.Anumberofmechanicalandmicrostructureanalysesarecarriedouttodeterminethecausesoffracture.2.TechniquesusedinfractureanalysisFromonepointofview,causesofgearfailuremayincludeadesignerror,anapplicationerror,oramanufacturingerror.Designerrorsincludesuchfactorsasimpropergeargeometryaswellasthewrongmaterials,qualitylevels,lubricationsystems,orotherspecifications.Applicationerrorscanbecausedbyanumberofproblems,includingmountingandinstallation,vibration,cooling,lubrication,andmaintenance.Manufacturingerrorsmayshowupinthefieldaserrorsinmachiningorheattreating3.Inthisanalysis,thefourdamagedspiralbevelgearspecimensweresubjectedtovarioustests.Thefollowingexperimentalworksandstresscalculationsweredone:visualinspectionandfractography；hardnesstests；chemicalanalysis；metal