Metal fatigue : what it is, why it matters

277 Pages·2007·2.496 MB·English

by  L P Pook

METALFATIGUE
SOLID MECHANICS AND ITS APPLICATIONS
Volume 145
Series Editor: G.M.L. GLADWELL
Department of Civil Engineering
University of Waterloo
Waterloo, Ontario, Canada N2L3GI
Aims and Scope of the Series
The fundamental questions arising in mechanics are: Why?, How?, andHow much?
The aim of this series is to provide lucid accounts written by authoritative researchers
giving vision and insight in answering these questions on the subject of mechanics as it
relates to solids.
The scope of the series covers the entire spectrum of solid mechanics. Thus it includes
the foundation of mechanics; variational formulations; computational mechanics;
statics, kinematics and dynamics of rigid and elastic bodies: vibrations of solids and
structures; dynamical systems and chaos; the theories of elasticity, plasticity and
viscoelasticity; composite materials; rods, beams, shells and membranes; structural
control and stability; soils, rocks and geomechanics; fracture; tribology; experimental
mechanics; biomechanics and machine design.
The median level of presentation is the first year graduate student. Some texts are
monographs defining the current state of the field; others are accessible to final year
undergraduates; but essentially the emphasis is on readability and clarity.
For a list of related mechanics titles, see final pages.
Metal Fatigue
What It Is, Why It Matters
by
LESPOOK
UniversityCollegeLondon,UK
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ISBN978-1-4020-5596-6(HB)
ISBN978-1-4020-5597-3(e-book)
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©2007Springer
Nopartofthisworkmaybereproduced,storedinaretrievalsystem,ortransmitted
inanyformorbyanymeans,electronic,mechanical,photocopying,microfilming,recording
orotherwise,withoutwrittenpermissionfromthePublisher,withtheexception
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andexecutedonacomputersystem,forexclusiveusebythepurchaserofthework.
Theauthor’sfirstcar,a1932Riley9Falcon.Itsmanyailmentsincludedmetal
fatiguefailuresinagearboxselectorfork,timinggearteeth,ahalfshaft,anda
suspension spring. Moderncarsaremuchbetterinthatmetalfatigue failures
areveryunusual.
Leslie Philip (Les) Pook was born in Middlesex, England in 1935. He ob-
tainedaBScinmetallurgyfromtheUniversityofLondonin1956.Hestarted
his career at Hawker Siddeley Aviation Ltd, Coventry in 1956. In 1963 he
moved to the National Engineering Laboratory, East Kilbride, Glasgow. In
1969, while at the National Engineering Laboratory, he obtained a PhD in
mechanical engineering from the University of Strathclyde. Dr Pook moved
to University College London in 1998. He retired formally in 1998 but re-
mained affiliated to University College London as avisiting professor. Heis
a Fellow of the Institution of Mechanical Engineers and a Fellow of the In-
stituteofMaterials,MineralsandMining.LesmarriedhiswifeAnnin1960.
Theyhaveadaughter, Stephanie, andason,Adrian.
Contents
Preface...................................................... xiii
Notation..................................................... xv
1 Introduction ............................................. 1
2 Historical Background .................................... 7
2.1 Introduction. ......................................... 7
2.2 ExperimentalWork.................................... 8
2.2.1 FatigueTestingofComponentsandStructures ....... 8
2.2.2 FatigueTestingofLaboratorySpecimens ........... 9
2.2.3 Investigation oftheMechanisms ofMetalFatigue .... 10
2.2.4 Investigation ofFatigueCrackPaths................ 10
2.2.5 FatigueCrackPropagation RateTesting............. 11
2.3 TheModernEra ...................................... 12
2.3.1 FractureMechanics.............................. 12
2.3.2 Servohydraulic TestingEquipment ................. 12
2.3.3 InfluenceofComputers .......................... 13
2.3.4 Standardisation ................................. 13
3 ConstantAmplitudeFatigue ............................... 15
3.1 Notation ............................................. 15
3.2 S/N (Wöhler)Curves ................................. 15
3.3 ScatterinFatigueData................................. 20
3.4 MechanismsofMetalFatigue ........................... 24
3.4.1 FatigueCrackInitiation .......................... 25
3.4.2 FatigueCrackPropagation........................ 26
3.4.3 Ratchetting..................................... 30
viii Contents
3.5 EffectofMechanismsonS/N Curves .................... 31
4 VariableAmplitudeandMultiaxialFatigue.................. 35
4.1 Introduction. ......................................... 35
4.2 Mathematical DescriptionofFatigueLoadings............. 37
4.2.1 ConstantAmplitudeFatigueLoadings .............. 39
4.2.2 GaussianRandomLoadings....................... 39
4.2.3 BlockFatigueLoadings .......................... 42
4.3 Miner’sRule ......................................... 44
4.3.1 WeightedAverageStressRange ................... 47
4.3.2 DamageDensityFunctions ....................... 49
4.3.3 CycleCounting ................................. 50
4.4 StandardLoadHistories................................ 53
4.4.1 Applications ofStandardLoadHistories ............ 54
4.4.2 DevelopmentofStandardLoadHistories............ 55
4.5 MultiaxialFatigueinMetals ............................ 59
4.5.1 Multiaxial FatigueTests .......................... 59
4.5.2 Multiaxial FailureCriteria ........................ 62
5 FatigueDesign ........................................... 67
5.1 Introduction. ......................................... 67
5.2 FailureAnalysis ...................................... 68
5.3 Situations, Philosophies andApproaches.................. 69
5.3.1 Situations ...................................... 69
5.3.2 Philosophies.................................... 70
5.3.3 Approaches .................................... 72
5.4 ProductLiability ...................................... 77
5.4.1 TheConsumerProtectionAct ..................... 78
5.4.2 EnforcementAuthorities ......................... 79
5.5 SafetyRegulations .................................... 79
5.5.1 TheGeneralProductSafetyRegulations ............ 80
6 TheUncrackedSituation .................................. 83
6.1 Introduction. ......................................... 83
6.2 EffectofSurfaceFinish ................................ 84
6.3 EffectofMeanStress .................................. 85
6.3.1 EffectofResidualStresses........................ 88
6.4 EffectofMultiaxialFatigueLoading ..................... 88
6.5 EffectofNotches ..................................... 89
6.6 BicycleCrankshaft Analysis ............................ 93
Contents ix
6.7 ScatterunderVariableAmplitudeFatigueLoading ......... 96
6.8 ImprovementofFatigueLife............................ 97
7 TheCrackedSituation .................................... 101
7.1 Introduction. ......................................... 101
7.2 InitialCrackSize ..................................... 102
7.3 FinalCrackSize ...................................... 103
7.4 ConstantAmplitudeFatigueCrackPropagation ............ 105
7.4.1 Determination ofFatigueCrackPropagation Rates ... 106
7.4.2 FactorsAffectingFatigueCrackPropagationRates ... 109
7.4.3 ThresholdforFatigueCrackPropagation............ 116
7.4.4 OverallFatigueCrackPropagation Behaviour........ 117
7.4.5 ShortCracks ................................... 118
7.4.6 FatigueLifeinthePresenceofaCrack ............. 122
7.5 VariableAmplitudeFatigueCrackPropagation ............ 124
7.5.1 WeightedAverageStressRange ................... 124
7.5.2 Interaction Effects............................... 127
7.6 Fractography ......................................... 129
7.6.1 FatigueCrackPropagation inaWeldedJoint ........ 130
8 FatigueCrackPaths ...................................... 135
8.1 Introduction. ......................................... 135
8.1.1 ClassesofFatigueCrackPropagation............... 137
8.2 CrackPathsinTwoDimensions ......................... 138
8.2.1 MixedModeThresholds ......................... 138
8.2.2 CrackPathStability ............................. 142
8.2.3 CrackPathPrediction............................ 148
8.3 PlanarCrackPaths .................................... 151
8.3.1 CrackPathDevelopment ......................... 151
8.3.2 LeakbeforeBreak............................... 154
8.4 CrackPathsinThreeDimensions........................ 155
8.4.1 LowerBoundMixedModeThresholds ............. 157
8.4.2 CrackPathDetermination ........................ 158
9 WhyMetalFatigueMatters ............................... 161
9.1 Introduction. ......................................... 161
9.2 Avoidance ofFatigueFailure............................ 162
9.3 ResearchandDevelopment ............................. 163
9.4 TheRoleofNonDestructiveTesting ..................... 164
9.5 CurrentTrends ....................................... 164