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TherecentdevelopmentsofshotpeeninginChinaKeweiXu1,ChuanhaiJiang2,RenzhiWang31SchoolofMaterialscienceandengineering,Xi'anJiaotongUniversity,Xi'an,7100492SchoolofMaterialscienceandengineering,ShanghaiJiaotongUniversity,Shanghai,2002403InstituteofAeronauticalMaterials,Beijing,100095Abstract:WiththedevelopmentofChineseindustry,shotpeeningtechnologyiswidelyusedinmachinerymanufacturingindustryinChinainrecentdecade.
ThispapergivesabriefintroductionofdevelopmentofshotpeeningindustryinChina,whichincludesshotpeeningequipmentandpeeningmediamanufacturing,processplanningaboutshotpeeningandapplicationfieldsofdifferenttypesofshotpeening.
Intermsofbasicresearchofshotpeening,thispapersummarizessomenotableresearchresultsaboutstressstrengtheningandmicrostructurestrengtheningofshotpeening,influenceofshotpeeningonfatiguelifeofspecificmaterial,resistancetosomeformsofstresscorrosionandsoon.
Furthermore,applicationofconventionalshotpeeningtreatmentonadvancedmaterials,newshotpeeningtechniqueandcomputermodelingtechniqueaboutshotpeeningprocessalsodevelopveryrapidlyinChina.
Keywords:Shotpeening,Development,ChinaIntroductionPeeningmachine(PM),peeningshot(PS)andpeeningtechnologies(PT)arethreeveryimportantfactorsofshotpeening(SP)treatmenttechnologiesforworkpieces.
TherelationshipbetweenthesethreefactorshasbeenshowninFig.
1.
Fig.
1.
ThreefactorsofSPtreatmenttechnologiesforworkpiecesandtherelationshipwitheachother.
PS/PTPM/PS/PTPMPSPM/PSPM/PTPTSPtreatmenttechnologiesworkjustlikeamedicine,whichcantreatandimprovethefatiguefractureresistance(FFR)andstresscorrosioncrackingresistance(SCCR)ofmechanicalworkpieces.
Inordertoobtaintheoptimumstrengtheningeffect,thePMandPSmustfulfillalltherequirementsofPTdecidedbyworkpieces,suchaslocationsofSP,SPintensities,coverageofsurface,roughnessofSPandsoon.
AfterSP,thestructuresofsurfacelayersofworkpiecesarechangedasfollows:circulatingstrainhardeningofsurfacestructureandintroducedcompressiveresidualstress,whichcanimproveFFRandSCCRofmaterials/workpiece(M/W)accordingtostructurehardeningmechanismandresidualstresshardeningmechanismrespectively,besides,circulatingstrainrelaxationofsurfacestructureandincrementofsurfaceroughnesscanreduceFFRandSCCRofM/Wtoacertainextent.
ThevariationshavebeenshowninFig.
2.
TheSPtreatmentsofM/WshoulddependonfinePMandPStoobtaincompositestrengtheningeffectsofthevariationsmentionedinFig.
2tothemostdegree.
Fig.
2.
ThechangesofworkpiecesinsurfacelayersafterSPAccordingtothethreefactorsmentionedinFig.
1,combinethedevelopmentofSPinChinaandeachfactorwillbepresentedasfollows.
1.
ThedevelopmentofPMmanufacturePMismainlyusedtomodifyandimproveFFRandSCCRofM/W.
AndmanufacturecompaniesdesignandfabricatePMaccordingtofollowbasicprinciples.
(1)Basedonthematerials,shape,size,peeninglocation,etaltodesignthePM.
(2)Basedontherisklocationstendedtofatiguefracture,andspecialSPparameters(SPintensities,surfacecoverage,shottype,sizeandhardness)todesignthePM.
(3)InordertoimprovethestabilityandrepeatofSPparameters,theshotdiameterfilter,thecrackedshotsegregator,themonitorofshotvelocityandflux,andotheraccessoriesshouldbefixedinPM.
ChangesofsurfaceroughnessIncreaseofsurfacestressconcentratecoefficientKtDecreaseofsurfacestressconcentratecoefficientKtIntroduceresidualstressinsurfacelayersTensileresidualstressindeepsurfaceCompressiveresidualstressintopsurfaceDynamiccirculatingstrainhardeningofstructureDynamiccirculatingstrainintenerateofstructureVariationsofsurfacelayerofM/WafterSP(4)Accordingtotheoutput,geometricshape,size,andeconomicbenefitofworkpieces,considerwhichtypePMwillbechose,airblasttypePMormechanicaltypePM.
Basedonaboveprinciples,manytypesofPMhavebeenmanufacturedinlatest20years.
Somerepresentativetypeshavebeendisplayedasfollows.
(1)SpecialairblasttypePMdesignedforSPonaircraftengines,turbinediscandturbineblade.
(2)SpecialairblasttypePMdesignedforSPonlandinggearworkpieces.
(3)SpecialPMdesignedforSPoninner-hollow(Φ120mm)longaxes(1700mm).
(4)SpecialmechanicaltypePMdesignedforSPonlongsuckers(8m)usedinoilwell.
(5)SpecialPMdesignedforSPonsuspensionspring,valvespringandtunnelworkpieces.
(6)Specialcomputerizednumericalcontrol(CNC)airblasttypePMdesignedforSPongasturbinebigblade.
(7)AirblasttypeandmechanicaltypePMdesignedforSPonsomekindsofgears.
Recently,thecombiningresearchesbyShanghaiCarthingMachinaryCo.
,Ltd(Shanghai,China)andShanghaiJiaoTongUniversity(Shanghai,China)makefive-shaftdiveCNCairblasttypePMmanufactured,andwhichmakesthehighaccurateCNCPMhomebredfirstly.
Afterthat,ShanghaiCarthingMachinaryCo.
,LtdhasmanufacturedtherobotcontrolledCNCPM,usingtherobotsonPMsuccessfully.
Andnow,SomeCNCPMsmadeinChinahavebeenexportedtoIndia,Turkeyandothercountries.
Certainly,itisjusttheinitialdevelopmentofCNCPMinChina,andthereisabiggapbetweendevelopedcountries.
Wewillhavealongwaytogocomparedwithforeigndevelopments.
2.
ThedevelopmentofPSmanufactureIn1950's,afewdepartmentsofindustry(eg.
aerialindustry)hadstartedusingPT.
Early,thematerialofPSwascaststeel,thentheglassbeadswereintroducedasshotmediaforaircraftenginesworkpieces.
ThepeeningcaststeelshotsaccordedwithSAEJ444astylehadbeenmanufacturedin1970'sinChina.
ShandongKaiTaiIndustrialTechnologiesCo.
,LtdisthebiggestcompanyinChina,andthefourthbiggestcompanyintheword.
Intherecentdecade,withthefastdevelopmentofautomobileindustry,thedemandsofcuttingsteelshotsbecomemoreandmorein-country.
SomecompanieslikeJiangsuDaQiGroupCo.
,Ltd.
astheheadcanmanufacturethousandstonsofcuttingsteelshotseachyearwhichareconsistentwiththestandardofSAEJ441,AMS2431,MIL-S-13165C,VDFI8001andDIN8201.
Thesecuttingsteelshotscanbefulfillednotonlythedemandofin-countrycompanies,butalsoexportedtothemarketofEurope.
3.
ThedevelopmentofPTmanufactureIn1960's,theinfluenceofSPonthefatigueandfracturepropertiesatelevatedtemperatureofNi-basedhightemperaturealloyshavebeeninvestigatinginsystem,andthePThadbeenusedonturbinebladeandaircraftenginessuccessfullyaccordingtoaboveinvestigations.
Theinvestigationscanreducetroublesofturbinebladeandprolongtheuselifeindouble.
Theindustrystandardof"TheIllustrationofShotPeeningTechnologiesofAircraftWorkpieces"(HB/Z26-92)designedbyaircraftmanufactureisthefirstaeronauticalandspaceflightindustrystandardofP.
R.
China.
Inrecent40years,theexperimentalstudyofappliedfundamentaltheoryofPThasbeenshowninfollowthreefacets.
3.
1Theexperimentalstudyoffatigueandfractureofmetalengineeringmaterials(1)Accordingtotheinvestigationonfatiguecrackinitiationofengineeringmaterials,microprocesstheoryoffatiguecrackinitiationhasbeenproposed[1].
(2)Accordingtotheinvestigationonfatigueexperimentandobservedresults,therearetwokindsoffatiguelimitexistonM/Wwithinfatiguefracturelife(Nf=106~107cycles),oneisfatiguecracksinitializingonthetopsurfaceofM/Wcalledsurfacefatiguelimit(wsσ)andanotherisfatiguecracksinitializingonthesub-surfaceofM/Wcalledinternalfatiguelimit(wiσ)[1].
(3)Basedonthedislocationtheory,therelationshipbetweenwsσandwiσcanbeobtainedinthesamekindengineeringmaterialafterheattreatment[1].
40.
1~35.
1=wswiσσ(1)Eq.
(1)illustratesthatifhighcompressiveresidualstressesareintroducedinthetopsurface,thefatigueheadstreamcanbesuppressedinsub-surface,andthefatiguelimitofhighfatiguelife(Nf=106~107cycles)canbeimproved35%~40%.
3.
2ThecalculationofoptimizedcompressiveresidualstressfieldinM/WsurfaceintroducedbySP[2]Basedon"microprocesstheoryoffatiguecrackinitiation"and"internalfatiguelimittheory",inordertoimprovethefatiguelimitofhighfatiguelife(Nf=106~107cycles)fromwsσ(Surfacefatiguelimit)towiσ(Internalfatiguelimit),twocriterionsaboutobtainingoptimizedcompressiveresidualstressfieldhavebeenproposed.
CriterionA:Therelationshipbetweenwiσandintroducedcompressiveresidualstressesofsurfacersσhasbeenshowninformula(2).
wiσ-rsσtσ/wiσ>0.
96Fromformula(3),itrevealsthatonlytσincreasesandreachesthevalueofwiσatZs,thefatigueheadstreamisabletogerminateandcausefatiguefractureunderhigherstresses(wiσ).
Basedonabovediscussionabouttwocriterions,itcanbefoundthatonlyfulfillabovetwocriterions,theintroducedresidualstressfieldbySPwillbeoptimizedstressfieldandtheeffectofpeeningwillreachesthebest.
Thiseffectofresidualstressstrengtheningisnamedindirectstrengtheningmechanismofresidualstress.
3.
3EstablishthecompositestrengtheningtheoriesofSP(1)Residualstressindirectstrengtheningmechanismhasbeendiscussedin3.
2.
(2)ResidualstressdirectstrengtheningmechanismAsthefatiguelimitofmiddlefatiguelife(Nf=105~106cycles),thePTandintroducedcompressiveresidualstressesshouldfulfiltherequirementsasfollows.
(a)AvoidtheincreaseofstressconcentrationfactorKtresultedfromtheincreaseofsurfaceroughnessRa.
(b)ImprovetheresidualstressofsurfacersσofM/WbychoosinganappropriatePT,suchasMulti-SP,prestressingSP,warmSPetal.
(c)Improvetheresidualstressofsurfaceinordertoimprovefatiguecrackgerminationlife(Ni)andreducetheexpandingvelocity(da/dN)offatiguecrackinresidualstressfield.
(3)MicrostructuralstrengtheningmechanismTherearethreekindsoffracturemodels(FM)ofM/Wwhenenduringalternatingtwistloading,normaltensilefracturemodel(NTFM),longitudinalshearfracturemodel(LSFM),andtransverseshearfracturemodel(TSFM).
Thefatiguefracturelife(Nf)iscontrolledbyFM.
Theexperimentsoftwistfatigue[3]revealthatwiththeincreaseoftensileyieldstrength(0.
2σ)andtwistyieldstrength(0.
3τ),thesequenceofthelengthofNfwithdifferentFMisshownasNTFMLSFM>TSFM.
Consequently,thevariationofstructureresultsinthechangeofFMandtheimprovementofNf,whichisthemicrostructuralstrengtheningmechanism.
Insummary,theexperimentalinvestigationsonPTandthefieldofappliedfoundationinChinacanbeconcludedinFig.
3.
TheaimofSPisthatonthebaseofconsideringthecompositepropertiesofM/Wtotreateachworkpiece.
Ofcourse,nometterinthedegreeofdepthandinthescope,itisnotasgoodasthedevelopedcountriesontheapplicationofshotpeeningtechnologiesinthefieldofmanufacturesinChina.
WewillworkhardtodevelopthepracticalapplicationofPTinthedifferentfieldsofmanufacturesinChina.
Fig.
3CompositestrengthenmechanismofSPReferences[1]WangRenzhi,YaoMei,etal.
AMicro-meso-ProcessTheroyofFatigueCrackInitiationandTheroyofInternalFatigueLimit,Trans.
ofMetalHeatTreatm.
,Vol.
16(4)(1995)pp26-33.
[2]WangRenzhi,YaoMei.
TheEngineeringCalculationMethodoftheOptimumResidualStressFieldIntroducedbyShotPeeningintotheSurfaceLayerofSpring,Trans.
ofMeterialsandHeatTreatm.
,Vol.
24(4)(2003)pp3-7.
[3]Z.
Hu,L.
MaandS.
Gao.
AStudyofShearFatigueCrackMechanisms.
FatigueFract.
Engng.
Mater.
Struct.
,Vol.
15(6)(1992),pp563-572.
[4]WangRenzhi,JiangChuanhai.
NormalandShearFatigueFractureModelofCircularCoilSpringandtheWayforImprovementofItsFatigueFractureResistance.
Proceedingsof11thInternationalConferenceonShotPeening,(2011)ImproveshearstressfatiguestrengthM/WResidualstressdirectstrengtheningmechanismResidualstressindirectstrengtheningmechanismImproveσ0.
2andτ0.
3ofsurfaceImproveHv,σ0.
2andτ0.
3ofsurfaceCycleplasticstrainhardeningandstructuralstrengtheningmechanismCompressiveresidualstressstrengtheningmechanismReduceStressconcentrationfactorKtaccordingtoreducetheroughnessofsurfaceDeformationstrengtheningmechanismofSPonsurfaceImprovecompressivestressfatiguestrengthofM/W
ThispapergivesabriefintroductionofdevelopmentofshotpeeningindustryinChina,whichincludesshotpeeningequipmentandpeeningmediamanufacturing,processplanningaboutshotpeeningandapplicationfieldsofdifferenttypesofshotpeening.
Intermsofbasicresearchofshotpeening,thispapersummarizessomenotableresearchresultsaboutstressstrengtheningandmicrostructurestrengtheningofshotpeening,influenceofshotpeeningonfatiguelifeofspecificmaterial,resistancetosomeformsofstresscorrosionandsoon.
Furthermore,applicationofconventionalshotpeeningtreatmentonadvancedmaterials,newshotpeeningtechniqueandcomputermodelingtechniqueaboutshotpeeningprocessalsodevelopveryrapidlyinChina.
Keywords:Shotpeening,Development,ChinaIntroductionPeeningmachine(PM),peeningshot(PS)andpeeningtechnologies(PT)arethreeveryimportantfactorsofshotpeening(SP)treatmenttechnologiesforworkpieces.
TherelationshipbetweenthesethreefactorshasbeenshowninFig.
1.
Fig.
1.
ThreefactorsofSPtreatmenttechnologiesforworkpiecesandtherelationshipwitheachother.
PS/PTPM/PS/PTPMPSPM/PSPM/PTPTSPtreatmenttechnologiesworkjustlikeamedicine,whichcantreatandimprovethefatiguefractureresistance(FFR)andstresscorrosioncrackingresistance(SCCR)ofmechanicalworkpieces.
Inordertoobtaintheoptimumstrengtheningeffect,thePMandPSmustfulfillalltherequirementsofPTdecidedbyworkpieces,suchaslocationsofSP,SPintensities,coverageofsurface,roughnessofSPandsoon.
AfterSP,thestructuresofsurfacelayersofworkpiecesarechangedasfollows:circulatingstrainhardeningofsurfacestructureandintroducedcompressiveresidualstress,whichcanimproveFFRandSCCRofmaterials/workpiece(M/W)accordingtostructurehardeningmechanismandresidualstresshardeningmechanismrespectively,besides,circulatingstrainrelaxationofsurfacestructureandincrementofsurfaceroughnesscanreduceFFRandSCCRofM/Wtoacertainextent.
ThevariationshavebeenshowninFig.
2.
TheSPtreatmentsofM/WshoulddependonfinePMandPStoobtaincompositestrengtheningeffectsofthevariationsmentionedinFig.
2tothemostdegree.
Fig.
2.
ThechangesofworkpiecesinsurfacelayersafterSPAccordingtothethreefactorsmentionedinFig.
1,combinethedevelopmentofSPinChinaandeachfactorwillbepresentedasfollows.
1.
ThedevelopmentofPMmanufacturePMismainlyusedtomodifyandimproveFFRandSCCRofM/W.
AndmanufacturecompaniesdesignandfabricatePMaccordingtofollowbasicprinciples.
(1)Basedonthematerials,shape,size,peeninglocation,etaltodesignthePM.
(2)Basedontherisklocationstendedtofatiguefracture,andspecialSPparameters(SPintensities,surfacecoverage,shottype,sizeandhardness)todesignthePM.
(3)InordertoimprovethestabilityandrepeatofSPparameters,theshotdiameterfilter,thecrackedshotsegregator,themonitorofshotvelocityandflux,andotheraccessoriesshouldbefixedinPM.
ChangesofsurfaceroughnessIncreaseofsurfacestressconcentratecoefficientKtDecreaseofsurfacestressconcentratecoefficientKtIntroduceresidualstressinsurfacelayersTensileresidualstressindeepsurfaceCompressiveresidualstressintopsurfaceDynamiccirculatingstrainhardeningofstructureDynamiccirculatingstrainintenerateofstructureVariationsofsurfacelayerofM/WafterSP(4)Accordingtotheoutput,geometricshape,size,andeconomicbenefitofworkpieces,considerwhichtypePMwillbechose,airblasttypePMormechanicaltypePM.
Basedonaboveprinciples,manytypesofPMhavebeenmanufacturedinlatest20years.
Somerepresentativetypeshavebeendisplayedasfollows.
(1)SpecialairblasttypePMdesignedforSPonaircraftengines,turbinediscandturbineblade.
(2)SpecialairblasttypePMdesignedforSPonlandinggearworkpieces.
(3)SpecialPMdesignedforSPoninner-hollow(Φ120mm)longaxes(1700mm).
(4)SpecialmechanicaltypePMdesignedforSPonlongsuckers(8m)usedinoilwell.
(5)SpecialPMdesignedforSPonsuspensionspring,valvespringandtunnelworkpieces.
(6)Specialcomputerizednumericalcontrol(CNC)airblasttypePMdesignedforSPongasturbinebigblade.
(7)AirblasttypeandmechanicaltypePMdesignedforSPonsomekindsofgears.
Recently,thecombiningresearchesbyShanghaiCarthingMachinaryCo.
,Ltd(Shanghai,China)andShanghaiJiaoTongUniversity(Shanghai,China)makefive-shaftdiveCNCairblasttypePMmanufactured,andwhichmakesthehighaccurateCNCPMhomebredfirstly.
Afterthat,ShanghaiCarthingMachinaryCo.
,LtdhasmanufacturedtherobotcontrolledCNCPM,usingtherobotsonPMsuccessfully.
Andnow,SomeCNCPMsmadeinChinahavebeenexportedtoIndia,Turkeyandothercountries.
Certainly,itisjusttheinitialdevelopmentofCNCPMinChina,andthereisabiggapbetweendevelopedcountries.
Wewillhavealongwaytogocomparedwithforeigndevelopments.
2.
ThedevelopmentofPSmanufactureIn1950's,afewdepartmentsofindustry(eg.
aerialindustry)hadstartedusingPT.
Early,thematerialofPSwascaststeel,thentheglassbeadswereintroducedasshotmediaforaircraftenginesworkpieces.
ThepeeningcaststeelshotsaccordedwithSAEJ444astylehadbeenmanufacturedin1970'sinChina.
ShandongKaiTaiIndustrialTechnologiesCo.
,LtdisthebiggestcompanyinChina,andthefourthbiggestcompanyintheword.
Intherecentdecade,withthefastdevelopmentofautomobileindustry,thedemandsofcuttingsteelshotsbecomemoreandmorein-country.
SomecompanieslikeJiangsuDaQiGroupCo.
,Ltd.
astheheadcanmanufacturethousandstonsofcuttingsteelshotseachyearwhichareconsistentwiththestandardofSAEJ441,AMS2431,MIL-S-13165C,VDFI8001andDIN8201.
Thesecuttingsteelshotscanbefulfillednotonlythedemandofin-countrycompanies,butalsoexportedtothemarketofEurope.
3.
ThedevelopmentofPTmanufactureIn1960's,theinfluenceofSPonthefatigueandfracturepropertiesatelevatedtemperatureofNi-basedhightemperaturealloyshavebeeninvestigatinginsystem,andthePThadbeenusedonturbinebladeandaircraftenginessuccessfullyaccordingtoaboveinvestigations.
Theinvestigationscanreducetroublesofturbinebladeandprolongtheuselifeindouble.
Theindustrystandardof"TheIllustrationofShotPeeningTechnologiesofAircraftWorkpieces"(HB/Z26-92)designedbyaircraftmanufactureisthefirstaeronauticalandspaceflightindustrystandardofP.
R.
China.
Inrecent40years,theexperimentalstudyofappliedfundamentaltheoryofPThasbeenshowninfollowthreefacets.
3.
1Theexperimentalstudyoffatigueandfractureofmetalengineeringmaterials(1)Accordingtotheinvestigationonfatiguecrackinitiationofengineeringmaterials,microprocesstheoryoffatiguecrackinitiationhasbeenproposed[1].
(2)Accordingtotheinvestigationonfatigueexperimentandobservedresults,therearetwokindsoffatiguelimitexistonM/Wwithinfatiguefracturelife(Nf=106~107cycles),oneisfatiguecracksinitializingonthetopsurfaceofM/Wcalledsurfacefatiguelimit(wsσ)andanotherisfatiguecracksinitializingonthesub-surfaceofM/Wcalledinternalfatiguelimit(wiσ)[1].
(3)Basedonthedislocationtheory,therelationshipbetweenwsσandwiσcanbeobtainedinthesamekindengineeringmaterialafterheattreatment[1].
40.
1~35.
1=wswiσσ(1)Eq.
(1)illustratesthatifhighcompressiveresidualstressesareintroducedinthetopsurface,thefatigueheadstreamcanbesuppressedinsub-surface,andthefatiguelimitofhighfatiguelife(Nf=106~107cycles)canbeimproved35%~40%.
3.
2ThecalculationofoptimizedcompressiveresidualstressfieldinM/WsurfaceintroducedbySP[2]Basedon"microprocesstheoryoffatiguecrackinitiation"and"internalfatiguelimittheory",inordertoimprovethefatiguelimitofhighfatiguelife(Nf=106~107cycles)fromwsσ(Surfacefatiguelimit)towiσ(Internalfatiguelimit),twocriterionsaboutobtainingoptimizedcompressiveresidualstressfieldhavebeenproposed.
CriterionA:Therelationshipbetweenwiσandintroducedcompressiveresidualstressesofsurfacersσhasbeenshowninformula(2).
wiσ-rsσtσ/wiσ>0.
96Fromformula(3),itrevealsthatonlytσincreasesandreachesthevalueofwiσatZs,thefatigueheadstreamisabletogerminateandcausefatiguefractureunderhigherstresses(wiσ).
Basedonabovediscussionabouttwocriterions,itcanbefoundthatonlyfulfillabovetwocriterions,theintroducedresidualstressfieldbySPwillbeoptimizedstressfieldandtheeffectofpeeningwillreachesthebest.
Thiseffectofresidualstressstrengtheningisnamedindirectstrengtheningmechanismofresidualstress.
3.
3EstablishthecompositestrengtheningtheoriesofSP(1)Residualstressindirectstrengtheningmechanismhasbeendiscussedin3.
2.
(2)ResidualstressdirectstrengtheningmechanismAsthefatiguelimitofmiddlefatiguelife(Nf=105~106cycles),thePTandintroducedcompressiveresidualstressesshouldfulfiltherequirementsasfollows.
(a)AvoidtheincreaseofstressconcentrationfactorKtresultedfromtheincreaseofsurfaceroughnessRa.
(b)ImprovetheresidualstressofsurfacersσofM/WbychoosinganappropriatePT,suchasMulti-SP,prestressingSP,warmSPetal.
(c)Improvetheresidualstressofsurfaceinordertoimprovefatiguecrackgerminationlife(Ni)andreducetheexpandingvelocity(da/dN)offatiguecrackinresidualstressfield.
(3)MicrostructuralstrengtheningmechanismTherearethreekindsoffracturemodels(FM)ofM/Wwhenenduringalternatingtwistloading,normaltensilefracturemodel(NTFM),longitudinalshearfracturemodel(LSFM),andtransverseshearfracturemodel(TSFM).
Thefatiguefracturelife(Nf)iscontrolledbyFM.
Theexperimentsoftwistfatigue[3]revealthatwiththeincreaseoftensileyieldstrength(0.
2σ)andtwistyieldstrength(0.
3τ),thesequenceofthelengthofNfwithdifferentFMisshownasNTFMLSFM>TSFM.
Consequently,thevariationofstructureresultsinthechangeofFMandtheimprovementofNf,whichisthemicrostructuralstrengtheningmechanism.
Insummary,theexperimentalinvestigationsonPTandthefieldofappliedfoundationinChinacanbeconcludedinFig.
3.
TheaimofSPisthatonthebaseofconsideringthecompositepropertiesofM/Wtotreateachworkpiece.
Ofcourse,nometterinthedegreeofdepthandinthescope,itisnotasgoodasthedevelopedcountriesontheapplicationofshotpeeningtechnologiesinthefieldofmanufacturesinChina.
WewillworkhardtodevelopthepracticalapplicationofPTinthedifferentfieldsofmanufacturesinChina.
Fig.
3CompositestrengthenmechanismofSPReferences[1]WangRenzhi,YaoMei,etal.
AMicro-meso-ProcessTheroyofFatigueCrackInitiationandTheroyofInternalFatigueLimit,Trans.
ofMetalHeatTreatm.
,Vol.
16(4)(1995)pp26-33.
[2]WangRenzhi,YaoMei.
TheEngineeringCalculationMethodoftheOptimumResidualStressFieldIntroducedbyShotPeeningintotheSurfaceLayerofSpring,Trans.
ofMeterialsandHeatTreatm.
,Vol.
24(4)(2003)pp3-7.
[3]Z.
Hu,L.
MaandS.
Gao.
AStudyofShearFatigueCrackMechanisms.
FatigueFract.
Engng.
Mater.
Struct.
,Vol.
15(6)(1992),pp563-572.
[4]WangRenzhi,JiangChuanhai.
NormalandShearFatigueFractureModelofCircularCoilSpringandtheWayforImprovementofItsFatigueFractureResistance.
Proceedingsof11thInternationalConferenceonShotPeening,(2011)ImproveshearstressfatiguestrengthM/WResidualstressdirectstrengtheningmechanismResidualstressindirectstrengtheningmechanismImproveσ0.
2andτ0.
3ofsurfaceImproveHv,σ0.
2andτ0.
3ofsurfaceCycleplasticstrainhardeningandstructuralstrengtheningmechanismCompressiveresidualstressstrengtheningmechanismReduceStressconcentrationfactorKtaccordingtoreducetheroughnessofsurfaceDeformationstrengtheningmechanismofSPonsurfaceImprovecompressivestressfatiguestrengthofM/W
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