Table Of ContentVolkerSchulze
ModernMechanicalSurface
Treatment
ModernMechanicalSurfaceTreatment.VolkerSchulze
Copyright(cid:1)2006WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
ISBN:3-527-31371-0
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Volker Schulze
Modern Mechanical Surface
Treatment
States, Stability, Effects
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(cid:1)2006WILEY-VCHVerlagGmbH&Co.KGaA,
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ISBN-13: 978-3-527-31371-6
ISBN-10: 3-527-31371-0
V
Contents
1 Introduction 1
2 ProceduresofMechanicalSurfaceTreatments 9
2.1 ShotPeening 9
2.1.1 DefinitionandDelimitationofProcedure 9
2.1.2 ApplicationExamples 9
2.1.3 Devices,ToolsandImportantParameters 11
2.2 StressPeening 14
2.2.1 DefinitionandDelimitationofProcedure 14
2.2.2 ApplicationExamples 14
2.2.3 Devices,ToolsandImportantParameters 15
2.3 WarmPeening 15
2.3.1 DefinitionandDelimitationofProcedure 15
2.3.2 ApplicationExamples 15
2.3.3 Devices,ToolsandImportantParameters 16
2.4 StressPeeningatElevatedTemperature 16
2.5 DeepRolling 16
2.5.1 DefinitionandDelimitationofProcedure 16
2.5.2 ApplicationExamples 17
2.5.3 Devices,ToolsandImportantParameters 18
2.6 LaserPeening 19
2.6.1 DefinitionandDelimitationofProcedure 19
2.6.2 ApplicationExamples 20
2.6.3 Devices,ToolsandImportantParameters 20
3 SurfaceLayerStatesafterMechanicalSurfaceTreatments 25
3.1 ShotPeening 25
3.1.1 ProcessModels 25
3.1.2 ChangesintheSurfaceState 44
3.2 StressPeening 72
3.2.1 ProcessModels 72
3.2.2 ChangesintheSurfaceState 74
3.3 WarmPeening 81
ModernMechanicalSurfaceTreatment.VolkerSchulze
Copyright(cid:1)2006WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
ISBN:3-527-31371-0
VI Contents
3.3.1 ProcessModels 81
3.3.2 ChangesintheSurfaceState 84
3.4 StressPeeningatelevatedTemperature 87
3.5 DeepRolling 89
3.5.1 ProcessModels 89
3.5.2 ChangesintheSurfaceState 92
3.6 LaserPeening 101
3.6.1 ProcessModels 101
3.6.2 ChangesintheSurfaceState 108
4 ChangesofSurfaceStatesduetoThermalLoading 135
4.1 ProcessModels 135
4.1.1 ElementaryProcesses 135
4.1.2 QuantitativeDescriptionofProcesses 137
4.2 ExperimentalResultsandtheirDescriptions 140
4.2.1 InfluencesonShapeandTopography 140
4.2.2 InfluencesonResidualStressState 142
4.2.3 InfluencesonWorkhardeningState 157
4.2.4 InfluencesonMicrostructure 170
5 ChangesofSurfaceLayerStatesduetoQuasi-staticLoading 179
5.1 ProcessModels 179
5.1.1 ElementaryProcesses 179
5.1.2 QuantitativeDescriptionofProcesses 180
5.2 ExperimentalResultsandtheirDescriptions 184
5.2.1 InfluencesonShapeandDeformationBehavior 184
5.2.2 InfluencesonResidualStressState 186
5.2.3 InfluencesonWorkhardeningState 227
5.2.4 InfluencesonMicrostructure 243
6 ChangesofSurfaceStatesduringCyclicLoading 247
6.1 ProcessModels 247
6.1.1 ElementaryProcesses 247
6.1.2 QuantitativeDescriptionofProcesses 250
6.2 ExperimentalResultsandtheirDescriptions 260
6.2.1 InfluencesonResidualStressState 260
6.2.2 InfluencesonWorhardeningState 291
6.2.3 InfluencesonMicrostructure 298
6.3 EffectsofSurfaceLayerStabilityonBehaviorduringCyclic
Loading 303
6.3.1 BasicResults 303
6.3.2 EffectsonCyclicDeformationBehavior 304
6.3.3 EffectsonCrackInitiationBehavior 310
6.3.4 EffectsonCrackPropagationBehavior 313
6.3.5 EffectsonFatigueBehavior 319
Contents VII
7 Summary 355
Acknowledgments 365
Index 367
1
1
Introduction
Technologicalpracticetoday,particularlyinthespring-manufacturing,automotive
and aerospace industries, is hardly imaginable without mechanical surface treat-
ments.Theoriginsoftheseprocessesdatebacktoancienthistory.[1.1]statesthat
inthecityofUr,goldhelmetswerehammeredandthusmechanicallyenhanced,
asearlyas2700BC.TheknightsoftheCrusadesusedthesamemethodtorein-
forcetheirswordswhenshapingthem.Thefirstmodern-dayapplications,again,
aretobefoundinmilitarytechnology,butalsoinrailroadtechnology.[1.1]reports
thatin1789,theoutersurfacesofartillerygunbarrelswerehammeredinorderto
improvetheirstrength,andby1848,trainaxlesandbearingboltswereevenedout
by rolling. Until that point, the methods had been intrinsically connected to the
skillandexperienceofthecraftspeople,whousedstrictconfidentialityinpassing
ontheirknowledgeinordertokeeptheircompetitiveadvantage.
Itwasonlyinthe1920sand-30sthatsurfacetreatmentevolvedintotechnical
processingmethods.F(cid:1)ppl’sseminaltreatisesof1929[1.2,1.3]establishthecor-
relation between mechanical surface treatment and increased fatigue strength,
indicating significantly higher fatigue strength in surface-rolled samples than in
polishedsamples.Consequently,F(cid:1)ppl’sgroup[1.4]extendedtheirexaminations
toincludenotchedcomponentsandfoundthatthefatiguestrengthincreasedby
20–56%inthecaseofdeep-rolledthreadrods.Thesefindingswereconfirmedby
Thum [1.5] in his systematic examination of the relation of rolling and fatigue
strength,publishedin1932.Thumalsofoundthatresistancetocorrosionfatigue
[1.6,1.7]andfrettingfatigue[1.8]increased.
Analternativetodeeprollingemergedintheformofshotpeening.Itsprecur-
sor was developed in 1927 by Herbert [1.9], a process he termed “cloudburst”, in
whichlargequantitiesofsteelsballsare“rained”ontocomponentsurfacesfroma
height of 2–4 meters. Herbert observed increases of hardness, but did not give
any indications regarding contingent increases of fatigue strength. In his afore-
mentioned[1.2,1.3]paperof1929,F(cid:1)pplshowedthatsamplestreatedwithaball-
shaped hammer also exhibit significantly higher fatigue life under cyclic stress
thanpolishedsamplesdo.In1935,Weibel[1.10]independentlyprovedthatsand-
blastingincreasesthefatiguestrengthofwires.Thisadditionalprecursorofpres-
ent-dayshotpeeningmethodsbuildsontheBritishpatenttakenoutbytheAmer-
ican, Tilgham [1.11], in 1870, which was originally geared at drilling, engraving
ModernMechanicalSurfaceTreatment.VolkerSchulze
Copyright(cid:2)2006WILEY-VCHVerlagGmbH&Co.KGaA,Weinheim
ISBN:3-527-31371-0
2 1 Introduction
andmattingofironandothermetalsanddealswithsurfacetreatmentusingsand
acceleratedbypressurizedair,steam,waterorcentrifugalforce.In1938,Fryeand
Kehl [1.12] proved the positive effect of blast cleaning treatments on fatigue
strength,andin1939v.Manteuffel[1.13]foundhigherdegreesoffatiguestrength
insandblastedspringsthaninuntreatedsprings.Crucialsystematicexaminations
werepublishedintheUSintheearly1940s.WorkingatAssociatedSpringsCo.,
Zimmerli[1.14]usedshotpeeningtoincreasethefatiguestrengthofspringsand
analyzed the influence of peening parameters. At General Motors, Almen [1.15,
1.16] demonstrated fatigue strength improvements in engine components and
achieved increased reproducibility of the peening process by introducing the
Almen strips named after him. In 1948, fatigue strength improvements were
provenalsoforshotpeenedcomponentsunderconditionsofcorrosion[1.17].
The development of special methods brought an additional impetus for the
technicalapplicationofmechanicalsurfacetreatmentprocesses.StraubandMay
[1.18]werethefirsttoreportincreasesoffatiguestrengthinspringswhichwere
shotpeenedunderpre-stress.Whiletheypresentedmodelsinwhichthestateof
residual stress was to be shifted toward higher compressive residual stress by
meansoftensileprestressing,thiswasnotprovenuntil1959,whenMattsonand
Roberts[1.19]analyzedresidualstressstatesafter(cid:3)strainpeening’combinedwith
tensileorcompressiveprestrains.Today,thismethodiscalledstresspeeningand
ispredominantlyusedonsprings[1.20–1.25],butalsoonpistonrods[1.26,1.27].
Supplyingthermalenergysimultaneousorconsecutivetotheactualpeeningpro-
cess constitutes an approach for increasing the effect of the mechanical surface
treatment even further. Warm peening, i.e. shot peening at high workpiece tem-
peratures,wasfirstsuggestedina1973Japanesepatent[1.28]toachieveincreased
fatiguestrengthinspringsbyusingthe“Cottrelleffect”.Inthemeantime,appli-
cationsinthespringmanufacturingindustryhavebeenexamined[1.29–1.35]and
fundamentalresearchbytheV(cid:1)hringerandSchulzegroup[1.36–1.38],inparticu-
lar,hasbeenpushingtowardadeeperunderstandingoftheprocessesandanopti-
mizationofwarmpeening.Conventionalshotpeeningandconsecutiveannealing
was examined more closely by the teams of Scholtes [1.39] as well as V(cid:1)hringer
andSchulze[1.41]asanalternativemethod.Theseexaminationsshowthatappro-
priately selected annealing temperatures and times are able to achieve effects
comparable to warm peening, while complexity is reduced. Wagner and Gregory
[1.42–1.46]increasedthedensityofnucleiforre-crystallizationorprecipitationin
the surface layers of titanium and aluminum alloy workpieces which is effective
duringannealingaftershotpeeningorrolling,andthusenablesfinegrainforma-
tionandselectiveorpreferredsurfacehardening.Theseprocedures,too,allowfor
considerableincreasesoffatiguestrengthatroomtemperatureorhighertempera-
tures.Acompletelynewmethodhasbeendevelopingsincethe1970sintheform
oflasershocktreatment.However,ithasattainedtechnicalrelevanceonlygradu-
ally. Its importance has started to increase since suitable laser technologies have
becomeavailableandtheenhancementprocesshasbeentransferredfromlabora-
tory lasers, which are irrelevant for technical applications, to industrially applic-
ablelasers[1.47–1.52].
1 Introduction 3
Inthecourseofmethoddevelopment,atfirstthequestionremainedwhichsur-
facechangesoftheworkpiecestheobservedincreasesinfatiguestrengthcouldbe
attributed to. Samples manufactured by machining were used to prove and to
quantitatively record the influence of surface topography on fatigue strength.
HoudremontandMail(cid:4)nder[1.53]demonstratedthatthedifferenceinroughness
between polished and coarsely cut surfaces leads to fatigue strength changes
which become more pronounced the greater the strength of a material is. Siebel
andGaier[1.54]in1956statedafactorforroughnessthatexpressestheeffecton
fatigue strengthand decreaseslinearly withthe logarithmof roughness.Atfirst,
an intense and controversial debate centered on whether the cause for fatigue
strengthincreaseswastobefoundintheeffectsofmechanicalworkhardening,as
postulatedbyF(cid:1)pplandhisteam[1.2,1.3],ortheeffectsoftheinducedcompres-
sive residual stress states, as Thum and his team [1.5, 1.55] assumed. Fig. 1.1
summarizestheessential approaches.Todayitiscommonly acceptedknowledge
that the inhomogeneous plastic deformations required for generating residual
stresses always involve local alterations of the material state, which may affect a
component’s fatigue strength. However, the residual stress stability within the
given operating conditions of a component determines whether the residual
stressesaretobetreatedasloadingstresses,inwhichcasetheyarepredominant
in comparison with the effect mentioned first. Both effects may be taken into
accountintheso-calledconceptofthelocalfatiguelimit[1.56,1.57]andbesuper-
without mechanical with mechanical causes of changes
surface treatment surface treatment in fatigue strength
hardness hardness
surface
distribution distribution mechanical workhardening
depth of due to cold work
cold work O. Foeppl (1929)
compressive
without residual
surface residual stresses stresses mechanical prestressing
depth of due to residual stresses
residual -
stresses A. Thum (1931)
+
surface depth of micro-notch effects
notch stress due to roughness
superelevation
E. Siebel & M. Gaier (1956)
Fig.1.1: Approachesfortheexplanationofchangesinfatigue
behaviourduetomechanicalsurfacetreatments
