分析材料疲劳强度计算方法历史及分类

材料疲劳强度计算方法的历史及Alloftheseapproachesareempirical材料疲劳强度计算方法的历史及Alloftheseapproachesareempiricalinnatureandcontainlittleinformationonthephysicalprocessesoccurringinthematerial.1.Stress-Life••Oldestofthe3methods(>100Worksbestin“high-cycle”(long-life)applications--->10^3cycles(If<10^3cycles,thereistoomuchplasticaldeformationofspecimen)Assumesmaterialbehaveselastically;stressandstrainareproportional.Estimateslifetofracture(“TotalLife”).BasedonS-NorWöhlerDatageneratedfromsmall,polishedCurvesrelatealternatingstress（交变应力）tofatigue•••2.Strain-Life••About40yearsExtendsstress-lifeconceptbyPlasticNon-linearstress-strainWorksinbothhigh-cycleandlow-cycleapplications.EstimatesLifeto“Initiation”(typicallya1-3mmcrack).Basedonε-N•••–Generatedfromlow-cycle(strain-controlled)fatiguetestsonsmallpolishedspecimens.Numberofcyclestofailureofpolishedspecimenissameasnumberofcyclestoinitiationatacriticallocationonaspecimen.Criticallocationsareusuallynotchesorotherdiscontinuitiesthatconcentratestrain.––•Mostcommontechniqueingroundvehicle3.LinearElasticFractureMechanicsMethod---基于线弹性的断裂力学方法，研•••About30yearsEstimateslifetopropagateacrackfromsomeinitialsizetofracture.Lifeestimateishighlydependentontheinitialcracksize:Neednondestructiveinspectiontechniquestomeasureinitialcracksize,ormakeassumptions.Usedinconjunctionwithnondestructiveinspectiontopredict“SafeLife”ofdamagetolerantstructures.MostcommonusesareinaerospaceandnuclearConsequencesoffailuresareHavetheabilitytodothenecessaryVerylimiteduseingroundvehicleindustry.Notcoveredinthiscourse.••••1.WholeProcessofStress-LifefatiguedamageGenericStressLife(GSL)approachis1.WholeProcessofStress-LifefatiguedamageGenericStressLife(GSL)approachisanextensionoftheS-N(StressLifeCurve)method.Log(AlternatingLogBasquin’s=s2N CurveifCreorLifeEstimateD=Lad-TheGSLapproachallowsyoutoreplacestressmeasurementswithotherdamagemeasurements,suchascomponentloadortorque.2.WholeProcessofStrain-Lifefatiguedamage1.Levelcrossing 1sMassing’se=+ Ramberg-OsgoodConstructionofHysteresiss=Dsa 2Basquin’ssf=N+NeDaEfff2.WholeProcessofStrain-Lifefatiguedamage1.Levelcrossing