Fatigue Life Design of Mechanical Structure智慧樹知到期末考試答案章節(jié)答案2024年北京理工大學(xué)

FatigueLifeDesignofMechanicalStructure智慧樹知到期末考試答案+章節(jié)答案2024年北京理工大學(xué)Cyclicstabilizationisusuallyreasonablycompletewithin10to40percentofthetotallife.（）

答案:對(duì)Stressrelaxationisthesameasthecyclicsoftening.（）

答案:錯(cuò)Fatiguelimitisassociatedwiththematerialdefect(inclusion).（）

答案:對(duì)Higherfrequenciestypicallyallowmoreenvironmentalinteractiontooccur.（）

答案:錯(cuò)Thefatigueprocessiselasticdeformationandfatiguecrackusuallyinitiatesfromelasticstraininginlocalizedregion.（）

答案:錯(cuò)Theda/dNmodelrequirestheuseoffracturemechanics.（）

答案:對(duì)Fine-grainmaterialstendtogivelowerfatigueresistance,whilecoarse-grainmaterialsgivehighercreepresistance.（）

答案:錯(cuò)Acrystalliteisasmallorevenmicroscopiccrystalwhichforms.（）

答案:對(duì)Veryshortlifeandverylonglifedataarenotincludedindatafits.（）

答案:對(duì)Mostoffatiguefailuresareunexpected.（）

答案:對(duì)Fatigueinducedmechanicalfailureisaveryimportantfactorintheengineeringdesign.（）

答案:對(duì)VHCFFailuremodesarerelatedtosurfaceconditions,environmentaleffects,materials,appliednumberofcycles,etc.（）

答案:對(duì)Crackgrowthratesareinitiallyhighbutdecrease,withthedecreasingcracklength.（）

答案:錯(cuò)Hydrogenembrittlementisoftenfoundinsomehighstrengthsteels.（）

答案:對(duì)ThemodifiedGoodmancurveortheGerbercurve,isconservativeforhightemperatureunnotchedmeanstresseffects.（）

答案:錯(cuò)Thecharacteristicsofductilefractureinclude（）

答案:Lowstrength/highductilemetals;Micro-voidcoalescence(dimpling);Highenergyabsorption;SubstantialplasticityTheS-Nbehaviorcanbeaffectedbymanyfactors（）

答案:Surfacecondition;Microstructure;Frequency;SizeeffectThreeprincipleparametersinHaighdiagram,asfollows（）

答案:Netregionalmeanstress;Notchfactor;NominalstressamplitudeTheunderstandingofoxidationiscorrectasfollows（）

答案:Oneoftheprimaryfactorsindegradationoffatigue/creepresistance;Protectiveoxidefilmscanbebrokendownbyreversedslip;High-temperaturefatiguecracksinavacuumaremorefrequentlytranscrystalline;CrackgrowthratesarealsoacceleratedSeveralempiricalequationsusedforevaluatingmeanstresseffectinclude（）

答案:Goodmanequation;GerberequationParametersinthenotcheffectshouldbeconsidered,asfollows（）

答案:Nucleationandgrowthofcracks;Meanstresseffectsandresidualstresses;Concentrationofstressandofstrain;FatiguelimitThefollowingmechanicalpropertiesareusuallyobtainedfrommonotonictensiontest（）

答案:Ultimatetensilestrength;Modulusofelasticity;PercentreductioninareaKeywordsinthedefinitionoffatigueinclude（）

答案:Permanent;Fluctuating;Localized;ProgressiveThecharacteristicsofGeneralS-Nbehaviorareasfollows（）

答案:S-Ncurvesareusuallydrawnthroughmedianlife;Adiscontinuityor“knee”;LessscatterinshorterliferegionFactorsofinfluencingstrain-lifebehaviorinclude（）

答案:Multiaxialstressstates;Stressconcentration;Residualstresseffects;EnvironmenteffectsIngeneral,fatigueresistanceforagivenmetalinanairenvironmenttendsto（）asthetemperatureincreases

答案:DecreaseThefeatureofexcessdeformationdoesnotinclude（）

答案:MaximumtensilestresscriterionThefeatureofsafe-lifedesigninclude（）

答案:FinitelifeAlargerfractionoflifeforcracknucleationoccurs（）

答案:AtlowerstresslevelsThehysteresisloopsathightemperaturesare（）

答案:DiscontinuousWhichisthefeatureofsmallcrack（）

答案:DiscontinuityThefeatureofcorrosiongenerallydoesnotinclude（）

答案:ElevatedtemperatureThecorrectstatementisasfollows（）

答案:LifecanbeignoredinunstablegrowthregionThenumberofbeachmarksisrelatedto（）

答案:EnvironmentAboutplanestrain,thecorrectstatementisasfollows（）

答案:OnedimensionisverylargeMetal’shardeningorsofteningduringcyclicdeformationcanoccur（）

答案:LoadingonsetTwofracturemodesareindependenton（）

答案:FinalfractureThefeatureofbrittlefracturedoesnotinclude（）

答案:Dimpling.Fatiguebehaviorandlifepredictionsaremorecomplicatedathightemperaturesbecauseof（）

答案:ComplexinteractionbetweencreepandfatigueBothfrequencyandtemperaturewillaffectthefatigueresistanceofmaterials.（）

答案:對(duì)TheHigh-temperaturefatigueis（）

答案:Morethan40percentoftheabsolutemeltingtemperatureTemperatureinfluenceonfatiguestrengths（）

答案:Thefatiguestrengthcontinuouslydecreaseswithcyclestofailure;108cyclesmaybeareasonablevalueforobtainingalong-lifefatiguestrength;MetalsathightemperaturesdonotusuallyshowafatiguelimitThedescriptionofNeuber’sruleisasfollows（）

答案:Coarse-grainmaterialsgivehighercreepresistance;Fine-grainmaterialstendtogivehigherfatigueresistanceAstheholdtimeincreased,thelifedecreaseddrasticallyatbothteststrainranges.（）

答案:對(duì)Thenotchedfatiguestrengthmaybeagreaterfractionofthesmoothfatiguestrength.（）

答案:對(duì)ThreeprincipleparametersinHaighdiagramcontain（）

答案:Nominalstressamplitude;Notchfactor;NetregionalmeanstressTheincorrectstatementis（）

答案:NotchedfatiguestrengthonlydependsonthestressconcentrationfactorWhichisnotthecharacteristicoftypicalloadingmodeorcrackmode（）

答案:FatiguefractureTwostressconditioncontain（）

答案:Planestrain;PlanestressThelimitingconditionsforLEFMareasfollows（）

答案:Theplasticzonesizeatthecracktipmustbesmallerrelativetothecracklength;Theplasticzonesizeatthecracktipmustbesmallerrelativetothegeometricaldimensionsofspecimenorpart;ThenetnominalstressinthecrackplanemustbelessthantheyieldstrengthTheincreasingRratiohasatendencytoincreasethecrackgrowthrates.（）

答案:對(duì)Thecrackcanbeclosedduringunloadingwhilethespecimenisstillunderapositivetensilestress.（）

答案:對(duì)Thecharacteristicsofhysteresisloopareasfollows（）

答案:Progressivechangesinthestress-strainbehavior;"Lag"phenomenon;Areawithinhysteresisloopisenergyperunitvolumedissipatedduringacycle;Differentstrains,differenthysteresisloopsThecorrectconclusionsaboutdatafittingareasfollows（）

答案:Thestressandplasticstrainamplitudesshouldbetreatedasindependentvariables;Stressrelaxationisdifferentfromcyclicsoftening;Inaccuraciesinmeasuringsmallplasticstrainsatlowloadscaninfluencethetestresults;FatiguelifeasthedependentvariableTherateoramountofrelaxationdependsonthemagnitudeofplasticstrainamplitude.（）

答案:對(duì)Incremental-steptestmethod:Aseriesofspecimens,eachofwhichissubjectedtoaconstantstrainamplitude.（）

答案:錯(cuò)Whichisnotthecharacteristicofunloading（）

答案:PermanentdeformationThiscycliccreepdecreasesthedetrimentaleffectsoftensilemeanstressonfatiguelife.（）

答案:錯(cuò)Thecorrectconclusionsareasfollows（）

答案:Thecompressivemeanstressisbeneficial;ThetensionmeanstressisdetrimentalFatiguelimithasrangedfrom1to70percentofultimatetensilestrength.（）

答案:對(duì)WhichisnotthecharacteristicofrealfatigueLimit（）

答案:Testingfrequencyislargerthan100HzThecharacteristicsofbeachmarkareasfollows（）

答案:Wavybands;Crack’sstarting,stoppingandgrowingatdifferentrates;Patternofcrackgrowth;Twoadjacentcracksurfaceswithopen,close,andrubWhichisnotthecharacteristicofslip（）

答案:ThesamecharacteristicsundermonotonicloadingandcyclicloadingModesoffatiguecrackgrowthwithfractureareasfollows（）

答案:Inter-crystallinefracture;Trans-crystallinefractureCracknucleateatsurfaceandgrowacrossseveralgrains(stageI,microcrack),andthentogrowinazigzagmanner(stageII,macrocrack).（）

答案:對(duì)Themechanicalpropertyofeachgrainisthesame.（）

答案:錯(cuò)Analysisneedstobeconfirmedbytests.（）

答案:對(duì)Allowableservicelifeshouldbelesstha