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UD MEEG 304 - Fatigue Loading

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Update What is fatigue?  Types of Fatigue Loading Empirical Data Estimating Endurance/Fatigue Strength Strategies for Analysis¾Uniaxial Fully Reversed¾Uniaxial Fluctuating¾Multiaxial0=mσ0≠mσUniaxialMultiaxialDoes Mean Stress Matter?Fluctuating Stress Failure PlotσaσmSySeor SfSutSyFailureSafetyconstructed for a given number of cycles NGerberSoderbergYieldmodified-GoodmanThe Data“Augmented” Modified-Goodman Plotvon Mises calculated for σaand for σmseparatelyσaσmSeor SfSutSySySyc1=′+′yaymSSσσ1=′+′fautmSSσσ1=′+′−ycaycmSSσσfaS=′σStress Concentration Factorsσa– same as for fully reversedσmBrittleuse static KtDuctile0 so ,02 if if ifminmaxmaxmaxnomnomnom==>−−=>=<fmmyfmafyfmyfffmyfKSKKSKSKKKSKnomnomnomσσσσσσσFactors of Safety  Four cases1) σaconstant, σmvaries2) σavaries, σmconstant3) σa and σmincrease at constant ratio4) σa and σmincrease independently If you know how the stress can vary, only use one of four cases If stress can vary in any manner, Case 4 should be used (the most conservative)Factors of Safety – Case 1σaconstant, σmvaries1=′+′yaymSSσσ1=′+′fautmSSσσZmQmfN@@σσ′′=if Q is on segment DE:′−′=yamyfSSNσσ1Factor of Safety- Case 21=′+′yaymSSσσ1=′+′fautmSSσσZaPafN@@σσ′′=if P is on segment CD:′−′=utmaffSSNσσ1σavaries, σmconstantFactor of Safety – Case 31=′+′yaymSSσσ1=′+′fautmSSσσfmutautfZmRmfSSSSNσσσσ′+′=′′=@@If R is on CD, then through a similar procedure:σa and σmincrease at constant ratioFactor of Safety – Case 4BIGequations for this… see your book!σa and σmincrease independentlyUniaxial Fluctuating StrategyStress & LoadingN (umber of cycles) Fluctuating Load (Fa)Tentative DesignTentative MaterialKfKtKfmσ1a, σ2a, σ3a; σ1m, σ2m, σ3m(principal)σ´a, σ´m(von Mises)σaσm(nom)σa(nom)σmUniaxial Fluctuating Strategy Fatigue AspectsSe´or Sf´Seor SfCloadCsurfCsizeCtempCreliabModified-Goodman DiagramUniaxial Fluctuating StrategyN (umber of cycles) Fluctuating Load (Fa)Tentative DesignTentative Material Tentative DesignTentative Materialσ1a, σ2a, σ3a; σ1m, σ2m, σ3m(principal)σ´a, σ´m(von Mises)KfσaKtσm(nom)σa(nom)KfmσmSe´or Sf´Seor SfSeor SfCloadCsurfCsizeCtempCreliabCloadCsurfCsizeCtempCreliabModified-Goodman DiagramModified-Goodman DiagramNfUniaxial, Fluctuating Example3032 353875 100250 1251030Fm=1 kNFa= 2 kN10ABCDABCDMBMcMmax(mm)3mm filletsSut=690 MPaSy=580 Mpa*NOT a rotating shaft*Strategy Find σ´aand σ´mwith appropriate stress concentration factors Find Se Plot modified-Goodman diagram Find factor of safetyModified-GoodmanσmSe=197Sy=580Sy=580 Sut= 69051.4102.5ODEFCZPSRQCase ICase IICase IIICase


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UD MEEG 304 - Fatigue Loading

Documents in this Course
Agenda

Agenda

9 pages

Bearings

Bearings

12 pages

Bearings

Bearings

12 pages

Fatigue

Fatigue

8 pages

Concept

Concept

3 pages

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