extending steinberg’s fatigue analysis of electronics

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1、ExtendingSteinberg’sFatigueAnalysisofElectronicsEquipmentMethodologytoaFullRelativeDisplacementvs.CyclesCurveRevisionBByTomIrvineEmail:tom@vibrationdata.comMarch12,2013Vibrationfatiguecalculationsare“ballpark”calculationsgivenuncertaintiesinS-Ncurves,stressconcentrationfactors,naturalfrequen

2、cy,dampingandothervariables.Furthermore,damageincreasesexponentiallywithanincreaseinstress,whichmagnifiestheeffectofanyerrorinthestresscalculationorinthereferenceS-Ncurve.Perhapsthebestthatcanbeexpectedistocalculatetheaccumulatedfatiguetothecorrect“order-of-magnitude.”IntroductionElectronicc

3、omponentsinvehiclesaresubjectedtoshockandvibrationenvironments.Thecomponentsmustbedesignedandtestedaccordingly.DaveS.Steinberg’sVibrationAnalysisforElectronicEquipmentisawidelyusedreferenceintheaerospaceandautomotiveindustries.Steinberg’stextgivespracticalempiricalformulasfordeterminingthefa

4、tiguelimitsforelectronicspiecepartsmountedoncircuitboards.Theconcernisthebendingstressexperiencedbysolderjointsandleadwires.Thefatiguelimitsaregivenintermsofthemaximumallowable3-sigmarelativedisplacementofthecircuitboardsforthecaseof20millionstressreversalcyclesatthecircuitboard’snaturalfreq

5、uency.Thevibrationisassumedtobesteady-statewithaGaussiandistribution.Notethatclassicalfatiguemethodsusestressastheresponsemetricofinterest.ButSteinberg’sapproachworksinanapproximate,empiricalsensebecausethebendingstressisproportionaltostrain,whichisinturnproportionaltorelativedisplacement.Th

6、euserthencalculatestheexpected3-sigmarelativedisplacementforthecomponentofinterestandthencomparesthisdisplacementtotheSteinberglimitvalue.ThereareseverallimitationstoSteinberg’sfatiguelimitmethod:1.Anelectroniccomponent’sservicelifemaybewellbeloworwellabove20millioncycles.271.Acomponentmayun

7、dergononstationaryornon-Gaussianrandomvibrationsuchthatitsexpected3-sigmarelativedisplacementdoesnotadequatelycharacterizeitsresponsetoitsserviceenvironments.2.Thecomponent’scircuitboardwilllikelybehaveasamulti-degree-of-freedomsystem,withhighermod