最新二 海洋平台疲劳强度设计分析ppt课件.ppt

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1、二海洋平台疲劳强度设计分析第二节结构疲劳轻度设计和分析StructuralFatigueStrengthDesignandAnalysisOutline4hourscourseworkBasicconceptoffatigueBasicknowledgeofstructuralfatiguedesignFatiguedamageandfatiguelifecalculationFactorsaffectingstructuralfatiguelifeFatiguestrengthdesignforoffshorestructuresExamples

2、BasicKnowledgeofFatigueDesignLifePredictionMethodsS-NApproach:thenominalstressapproach.Itemploystherelationshipsbetweennominalstressandlife,andisbasedprimarilyonlinear-elasticstressanalysis.LocalStrainApproach.Itconsidersthevariationsinthelocalstressandstrainatacriticallocatio

3、n,suchasastressraiser.ItissimilartothenominalstressapproachinthatitusesaformofanS-Ncurve,butdiffersinthatstrainisthevariablerelatedtolife,andalsointhatplasticdeformationeffectsarespecificallyconsidered.FractureMechanicsApproach.Where:a:cracklengthN:numberofcyclesDs:stressrange

4、DK:stressintensityfactor(应力强度因子，是表征裂纹尖端应力、应变状态控制失稳扩展的参量，是断裂力学/破坏力学中极其重要的一个参量。)DKth:thresholdstressintensityfactorC:coefficientofvariationofS-Ncurvem:inverseslopeconstantFatigueAnalysisMethodFrequencyDomainStressResponseSpectralFatigueAnalysisStressConcentrationFactor(SCF)Stres

5、sConcentrationStressconcentrationcanbecausedbyvariousfactors:GeometrychangesTerminationsEccentricity(偏心率)ofstructuralloadtransferNotch/dent(切口/凹痕)inplatestructureWeldingEffectofstressconcentrationCauselocalstructuraloverstressandfailureReducefatiguelifeStressConcentration(cont

6、.)EngineeringconsiderationsinreducingstressconcentrationGeometrytransitionsmoothlyAvoidthicknessabruptchangesStiffenersin-linewithbracketsUsecurvedbracketfortransitionsAvoiddamageonsurface/edgeofplatePlateedgeneedtoberound,nosharpedgeWeldingtransitionsmoothlyBasicS-NCurveAWS(美

7、国焊接标准）S-NCurvesUKHSES-NCurvesFatigueLifeCalculationThicknessEffectOnFatigueLifeFatigueAssessmentAndDesignFatigueDesignConsiderationFactorsFatiguesensitivityWeldeddetailMaterialselectionFabricationtolerancesInspectionFatigueCriticalityZoneClassificationPeakstresslevel(staticplu

8、sdynamic)CyclicstressrangeCriticality/redundancyFailureimplic