桥式起重机毕业设计外文翻译.docx
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桥式起重机毕业设计外文翻译.docx
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桥式起重机毕业设计外文翻译
英文原文:
Fatiguelifepredictionofthemetalworkofatravellinggantry
crane
V.A.Kopnov
Abstract
Intrinsicfatiguecurvesareappliedtoafatiguelifepredictionproblemofthemetalworkofatravelinggantrycrane.Acrane,usedintheforestindustry,wasstudiedinworkingconditionsatalogyard,anstrainmeasurementsweremade.Forthecalculationsofthenumberofloadingcycles,therainflowcyclecountingtechniqueisused.Theoperationsofasampleofsuchcraneswereobservedforayearfortheaveragenumberofoperationcyclestobeobtained.Thefatiguefailureanalysishasshownthatfailuressomeelementsaresystematicinnatureandcannotbeexplainedbyrandomcauses.卯1999ElsevierScienceLtd.Allrightsreserved.
Keywords:
Cranes;Fatigueassessment;Straingauging
1.Introduction
FatiguefailuresofelementsofthemetalworkoftravelinggantrycranesLT62Bareobservedfrequentlyinoperation.Failuresasfatiguecracksinitiateandpropagateinweldedjointsofthecranebridgeandsupportsinthree-fouryears.Suchcranesareusedintheforestindustryatlogyardsfortransferringfull-lengthandsawnlogstoroadtrains,havingaload-fittingcapacityof32tons.Morethan1000cranesofthistypeworkattheenterprisesoftheRussianforestindustry.Theproblemwasstatedtofindtheweakestelementslimitingthecranes'fives,predicttheirfatiguebehavior,andgiverecommendationstothemanufacturersforenhancingthefivesofthecranes.
2.Analysisofthecraneoperation
Fortheanalysis,atravelinggantrycraneLT62BinstalledatlogyardintheYekaterinburgregionwaschosen.Thecraneservestwosawmills,createsalogstore,andtransferslogstooroutofroadtrains.Aroadpassesalongthelogstore.Thesawmillsareinstalledsothatthereceptionsitesareunderthecranespan.AschematicviewofthecraneisshowninFig.1.
1350-6307/99/$一seefrontmatter1999ElsevierScienceLtd.Allrightsreserved.
PII:
S1350一6307(98)00041一7
Aseriesofassumptionsmaybemadeafterexaminingtheworkofcranes:
·ifthemonthlyremovaloflogsfromtheforestexceedstheprocessingrate,i.e.thereisacreationofalogstore,thecraneexpectswork,beingabovethecentreofaformedpilewiththegrabloweredonthepilestack;
·whenprocessingexceedsthelogremovalfromtheforest,thecraneexpectsworkaboveanoperationalpileclosetothesawmillwiththegrabloweredonthepile;
·thestoreoflogsvaries;theheightofthepilesisconsideredtobeamaximum;
·thestorevariationtakesplacefromthesideoppositetothesawmill;
·thetotalvolumeofaprocessedloadisontheaveragek=1.4timesmorethanthetotalvolumeofremovalbecauseofadditionaltransfers.
2.1.Removalintensity
Itisknownthattheremovalintensityforoneyearisirregularandcannotbeconsideredasastationaryprocess.Thestudyofthecharacterofnon-stationaryflowofroadtrainsat23enterprisesSverdlespromforfiveyearshasshownthatthemonthlyremovalintensityevenforoneenterpriseessentiallyvariesfromyeartoyear.Thisisexplainedbythecomplexofvarioussystematicandrandomeffectswhichexertaninfluenceonremoval:
weatherconditions,conditionsofroadsandlorryfleet,etc.Allwoodbroughttothelogstoreshould,however,beprocessedwithinoneyear.
Therefore,thelesspossibilityofremovingwoodintheseasonbetweenspringandautumn,themoreintensivelythewoodremovalshouldbeperformedinwinter.Whileinwintertheremovalintensityexceedstheprocessingconsiderably,insummer,inmostcases,themorefull-lengthlogsareprocessedthanaretakenout.
Fromtheanalysisof118realizationsofremovalvaluesobservedforoneyear,itispossibletoevaluatetherelativeremovalintensityg(t)aspercentagesoftheannualloadturnover.TheremovaldatafistedinTable1isconsideredasexpectedvaluesforanycrane,whichcanbeappliedtotheestimationoffatiguelife,and,particularly,foraninspectedcranewithwhichstrainmeasurementwascarriedout(seelater).Itwouldbepossibleforeachcranetotakeadvantageofitsloadturnoverperonemonth,buttoestablishthesedatawithoutspecialstatisticalinvestigationisdifficult.Besides,tosolvetheproblemoflifepredictionaknowledgeoffutureloadsisrequired,whichwetakeasexpectedvaluesoncraneswithsimilaroperationconditions.
ThedistributionofremovalvalueQ(t)permonthperformedbytherelativeintensityq(t)iswrittenas
whereQistheannualloadturnoverofalogstore,AisthemaximaldesignedstoreoflogsinpercentofQ.SubstitutingthevalueQ,whichfortheinspectedcraneequals400,000m3peryear,andA=10%,thevolumesofloadstransferredbythecraneareobtained,whicharelistedinTable2,withthetotalvolumebeing560,000m3foroneyearusingK,.
2.2.Numberofloadingblocks
Thesetofoperationssuchasclamping,hoisting,transferring,lowering,andgettingridofaloadcanbeconsideredasoneoperationcycle(loadingblock)ofthecrane.Asaresulttoinvestigations,theoperationtimeofacyclecanbemodeledbythenormalvariablewithmeanequalto11.5minandstandarddeviationto1.5min.unfortunately,thischaracteristiccannotbesimplyusedforthedefinitionofthenumberofoperationcyclesforanyworkperiodasthelocalprocessingisextremelyirregular.Usingatotaloperationtimeofthecraneandevaluationsofcycledurations,itiseasytomakelargeerrorsandincreasethenumberofcyclescomparedwiththerealone.Therefore,itispreferredtoactasfollows.
Thevolumeofaunitloadcanbemodeledbyarandomvariablewithadistributionfunction(t)havingmean22m3andstandarddeviation6;一3m3,withthenominalvolumeofonepackbeing25m3.Then,knowingthetotalvolumeofaprocessedloadforamonthoryear,itispossibletodeterminedistributionparametersofthenumberofoperationcyclesfortheseperiodstotakeadvantageofthemethodsofrenewaltheory[1].
Accordingtothesemethods,arandomrenewalprocessasshowninFig.2isconsidered,wheretherandomvolumeofloadsformsaflowofrenewals:
Inrenewaltheory,realizationsofrandom:
,,,havingadistributionfunctionF(t),areunderstood
asmomentsofrecoveryoffailedunitsorrequestreceipts.Thevalueofaprocessedload:
,,after
}thoperationisadoptedhereastherenewalmoment.
LetF(t)=P﹛
<t﹜.ThefunctionF(t)isdefinedrecurrently,
Letv(t)bethenumberofoperationcyclesforatransferredvolumet.Inpractice,thetotalvolumeofatransferredloadtisessentiallygreaterthanaunitload,anditisusefulthereforetotakeadvantageofasymptoticpropertiesoftherenewalprocess.Asfollowsfromanappropriate
limitrenewaltheorem,therandomnumberofcyclesvrequiredtotransferthelargevolumethas
thenormaldistributionasymptoticallywithmeanandvariance.
withoutdependenceontheformofthedistributionfunction月t)ofaunitload(therestrictionis
imposedonlyonnonlatticeofthedistribution).
Equation(4)usingTable2foreachaveragedoperationmonth,functionofnumberofloadcycleswithparametersm,.and6,.,whichnormaldistributioninTable3.Figure3showstheaveragenumbersofcycleswith95%confidenceintervals.Thevaluesoftheseparameters
forayearareaccordingly12,719and420cycles.
3.Strainmeasurements
Inordertorevealthemostloadedelementsofthemetalworkandtodeterminearangeofstresses,staticstrainmeasurementswerecarriedoutbeforehand.Verticalloadingwasappliedbyhoistingmeasuredloads,andskewloadingwasformedwithatractorwinchequippedwithadynamometer.TheallocationschemesofthebondedstraingaugesareshowninFigs4and5.Aswasexpected,thelargesttensionstressesinthebridgetakeplaceinthebottomchordofthetruss(gauge11-45MPa).Thetopchordofthetrussissubjectedtothelargestcompressionstresses.Thelocalbendingstressescausedbythepressureofwheelsofthecranetrolleysareaddedtothestressesofthebridgeandtheloadweights.ThesestressesresultinthebottomchordoftheI一beam
beinglesscompressedthanthetopone(gauge17-75and10-20MPa).Theotherelementsofthebridgearelessloadedwithstressesnotexceedingtheabsolutevalue45MPa.Theelementsconnectingthesupportwiththebridgeofthecraneareloadedalsoirregularly.Thelargestcompressionstressestakeplaceinthecarryinganglesoftheinteriorpanel;themaximumstressesreachh0MPa(gauges8and9).Thelargesttensionstressesinthediaphragmsandanglesoftheexteriorpanelreach45MPa(causes1andhl.
Theelementsofthecranebridgearesubjected,ingeneramaximumstressesandrespondweaklytoskewloads.Thesuhand,aresubjectedmainlytoskewloads.1,toverticalloadspportsofthecranegmmgrisetoontheother
Theloadingofthemetalworkofsuchacrane,transferringfull-lengthlogs,differsfromthatof
acraneusedforgeneralpurposes.Atfirst,itinvolvestheloadcomplianceoflogpacksbecauseof
progressivedetachmentfromthebase.Therefore,theloadingincreasesratherslowlyandsmoothly.Thesecondcharacteristicpropertyisthelowprobabilityofhoistingwithpickingup.Thisisconditionedbythepresenceofthegrab,whichmeansthatthefalloftheropefromthespreaderblockisnotpermitted;theloadshouldalwaysbebalanced.Thepossibilityofslackbeingsufficienttoaccelerateanelectricdrivetonominalrevolutionsisthereforeminimal.Thus,theforesttravelinggantrycranesaresubjectedtosmallerdynamicstressesthaninanalogouscranesforgeneralpurposeswiththesamehoistingspeed.Usually,whenaccelerationissmooth,thedetachmentofaloadf
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