桥式起重机毕业设计外文翻译.docx

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,thedetachmentofaloadfromthebaseoccur