OutlineThe Function(s) of SpringsSome ReviewTypes of SpringsMore SpringsHelical Compression SpringsLength TerminologyEnd ConditionsStresses in Helical SpringsCurvature StressSpring DeflectionSpring RateHelical SpringsStatic Spring DesignMaterial PropertiesSpring/Material TreatmentsWhat are You Designing?Static Spring Flow ChartStatic Design: Wire DiameterBucklingSlide 21Slide 22Modified Goodman for SpringsFatigue Safety FactorWhat are you Designing?Fatigue Spring Design StrategyFatigue Design:Wire DiameterNatural Frequency: SurgeReview of Design StrategyStrategy Review ContinuedConsider the Following:Slide 32Extension SpringsDifference 1: Initial ForceDifference 1a: DeflectionDifference 2: Initial StressDifference 3: Ends!: BendingDifference 3a: Ends: TorsionMaterialsStrategySlide 41Torsion SpringsStressesSlide 44Slide 45Slide 46OutlineSpring Functions & TypesHelical SpringsCompressionExtensionTorsionalThe Function(s) of SpringsMost fundamentally: to STORE ENERGYMany springs can also: pushpulltwistSome ReviewFyklinear springs: k=F/ynonlinear springs:dydFk Parallelktotal=k1+k2+k3Series3211111kkkktotalTypes of SpringsHelical:CompressionExtensionTorsionMore SpringsWasher Springs:Beams:Power springs:Helical Compression Springsd diameter of wireD mean coil diameterLffree lengthp pitchNtTotal coilsmay also need:Do and DiLength TerminologyFree LengthAssembledLengthMax WorkingLoadBottomed Outminimum of 10-15%clash allowanceLfLaLmLsEnd ConditionsPlainSquarePlain GroundSquare GroundNa=Active CoilsFFFFStresses in Helical SpringsSpring Index C=D/dCCKwheredFDKss212,83m axFFTTCurvature Stressunder static loading, local yielding eliminates stress concentration, so use Ksunder dynamic loading, failure happens below Sy: use Ks for mean, Kw for alternatingInner part of spring is a stress concentration(see Chapter 4)Kw includes both the direct shear factor and the stress concentration factorCCCKwheredFDKww615.04414,83maxSpring DeflectionGdNFDya438Spring RateGdNFDya438aNDGdk348k=F/yHelical SpringsCompressionNomenclatureStressDeflection and Spring ConstantStatic DesignFatigue DesignExtensionTorsionStatic Spring DesignInherently iterativeSome values must be set to calculate stresses, deflections, etc.Truly Designthere is not one “correct” answermust synthesize (a little bit) in addition to analyzeMaterial PropertiesSutultimate tensile strengthFigure 13-3Table 13-4 with Sut=AdbSystorsional yield strengthTable 13-6 – a function of Sut and setSpring/Material TreatmentsSettingoverstress material in same direction as applied load»increase static load capacity 45-65%»increase energy storage by 100%use Ks, not Kw (stress concentration relieved)Load Reversal with SpringsShot PeeningWhat type of failure would this be most effective against?What are You Designing?GivenF, yk, yFindkFSuch that:Safety factor is > 1Spring will not buckleSpring will fit in hole, over pin, within vertical spaced, C, D*, Lf*, Na*, clash allowance ()**, material**design variables+* - often can calculate from given** - often given/definedStatic Spring Flow ChartSTRESSESNs=Sys/for shut spring if possibleif not, for max working loadif GIVEN F,y, then find k; If GIVEN k, y, then find FD, Ks, Kwmaterial strengthsDEFLECTIONLf, yshut, FshutThree things to know:•effect of d•shortcut to finding d•how to check bucklingITERATE?d, CmaterialNa, CHECKbuckling, Nshut, Di, DoNshut=Sys/shutStatic Design: Wire DiameterThree things to know:•effect of d•shortcut to finding d•how to check buckling3max8dFDKsGdNFDya438**see Example 13-3A on MathCad CD*maintain units (in. or mm) for A, buse Table 13-2 to select standard d near calculated d )2(115.08bminitialworksAKFFCNdBased on Ns=Ssy/ and above equation for :Km=Sys/SutBucklingfworkinginitfLyyyDLRS..Three things to know:•effect of d•shortcut to finding d•how to check bucklingHelical SpringsCompressionNomenclatureStressDeflection and Spring ConstantStatic DesignFatigue DesignExtensionTorsionMaterial PropertiesSusultimate shear strengthSus0.67 SutSfw´torsional fatigue strengthTable 13-7 -- function of Sut, # of cyclesrepeated, room temp, 50% reliability, no corrosionSew´torsional endurance limitfor steel, d < 10mmsee page 816 (=45 ksi if unpeened, =67.5 ksi if peened)repeated, room temp., 50% reliability, no corrosionModified Goodman for SpringsSfw, Sew are for torsional strengths, so von Mises not used0.5 Sfw0.5 SfwamRepeatedSfsCBSusA fwususfwfsSSSSS5.05.0Fatigue Safety Factor0.5 Sfw0.5 SfwamSfsSusload lineSaaimmloadmgoodaafsSNa,load = a,good at intersection ausimfsiusfsfsSSSSN…on page 828Fi=FminFa=(Fmax-Fmin)/2Fm=(Fmax+Fmin)/2What are you Designing?GivenFmax,Fmin, yk, yFindkFSuch that:Fatigue Safety Factor is > 1Shut Static Safety Factor is > 1Spring will not buckleSpring is well below natural frequencySpring will fit in hole, over pin, within vertical spaced, C, D*, Lf*, Na*, clash allowance ()**, material**design variables+* - often can calculate from Given** - often given/definedFatigue Spring Design Strategyd, Cif GIVEN F,y, then find k; If GIVEN k, y, then find FNshut=Sys/shutCHECKbuckling, frequency,Nshut, Di, DoD, Ks, Kwmaterial strengthsDEFLECTIONLf, yshut, FshutTwo things to know:•shortcut to finding d•how to check frequencyITERATE?materialNa, STRESSES ausimfsiusfsfsSSSSNFatigue Design:Wire Diameteras before, you can iterate to find d, or you can use an equation derived from relationships that we already know:)2(1min134.1167.08bawfwbsfsfsmsfsFKSAdFKNNFKACNduse Table 13-2 to select standard d near calculated dTwo things to know:•shortcut to finding d•how to check frequency**see Example 13-4A on MathCad CD*maintain units (in. or mm) for A, bNatural Frequency: SurgeTwo things to know:•shortcut to finding d•how to check frequencySurge == longitudinal resonancefor fixed/fixed end conditions:anWkgf21(Hz)…see pages 814-815 for moreideally, fn will be at least 13x more than fforcing… it should definitely be
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