resulting

外文翻译--残余应力-精品

ResidualStress

Aresidualstressisonethatexistswithoutexternalloadingor

internal

uallya

mesitis

calledinitialstress,andtheoperations,e

structureormachineisputintorvice,therviceloadssuperimpo

esidualstressaddtothervice-loadstress,they

aredetrimental;iftheysubtractfromthervice-loadstressthey

arebeneficial.

Intheplasticdeformationtheexternalforcedoesthemeritturns

intooutsidetheheatexceptthemajorityofextensions,butalsosome

smallpartbythedistortioncantheformstoresupinthedeformation

ragecan

theconcretemanifestationwayis:Macroscopicresidualstress,

ingtothe

residualstressbalancescopedifference,usuallymaydivideintoit

threekinds:(1)Firstkindofinternalstress,alsocalledthemacroscopic

residualstress,itiscausbytheworkpiecedifferentpart

macroscopicdistortionnonuniformity,thereforeitsstressbalance

mple,rveswithJin

Shubangthecurvingload,thenaboveispulledelongates,under

receivesthecompression;Thedistortionsurpasswhenthelimitof

elasticityhashadtheplasticdeformation,afterthentheexternalforce

eliminationbyelongatedonesideontheexistencecompresdstress,

ndofresidualstress

correspondsthedistortioncannotbebig,onlyaccountsforalways

storesupcanabout0.1%.

(2)Secondkindofinternalstress,alsocalledthemicroscopic

residualstress,itisproducesbybetweenthecrystalgrainorthe

ereofactionandthecrystal

grainsize

quite,namelymaintainthebalancebetweenthecrystalgrainor

mesthiskindofinternalstressmayachievethe

verygreatvalue,evenpossiblycreatesthemicrocrackandcausthe

workpiecedestruction.

(3)Thirdkindofinternalstress,

sphereofactionisveraldozenstoveralhundrednanometers,it

isbecautheworkpieceformsintheplasticdeformationthemassive

latticeflaw(forexamplevacancy,interstitialatom,dislocationandso

on)istortionmetalthestoragecanthemajorpart

(80%~90%)rtofenergy

enhancedthedistortioncrystalenergy,causittobeatthe

thermodynamicsnon-steadystate,thereforeithasonekindtomake

thedistortionmetaltorestoretothefreeenthalpyloweststable

structureconditionspontaneoustendency,andcaustheplastic

deformationmetalinheatingtimereplyandtherecrystallization

process.

Onlyafewexamplesofdetrimentalresidualstresswillbegiven

,intheasmblyofmachinery,occurswhentwoshaftsare

notinlineorareafewthousandthsofaninchoutofparallel,andthey

ultingstressin

correction,whenperfectalignmentcannotbeeconomicallyattained,

asisfrequentlytheca,istouflexiblecouplingsofatypenecessary

forthedegreeofmisalignment.

Theprecedingcaoccurswithelasticstressonly,andthe

ications

esremainwhen

mple,theforgingofshaftsand

crankshaftsandthecoolingafterforgingmayinduceresidualstress,

theequilibriumofwhichidchangedinmachining,causingsome

encommonpracticetostraightenthe

htening

requiresabending

momentlargeenoughtocaupermanenttoryielding.

Detrimentalresidualstresscommonlyresultfromdifferential

sacommonexample,Theweldmetaland

theareasimmediatelyadjacentare,aftersolidification,atamuch

ural

contractionofthemetalalongthelengthoftheweldispartially

esidual

tensilestressaretupalongtheweld.

Ingeneral,localorshallowheatingwhichwouldexpandthe

regionorsurface,ifitwerefree,adistancewellbeyondthatwhichthe

adjacentlargervolumewillallowcausyieldingandupttingofthe

heatedmaterial,Thisreadilyoccursbecauofthereducedyield

ecoolervolumeprevents

theupt,heatedregionfromfullycontractingduringitscooling,and

tensilegeneralruleisthatthe“lasttocoolisintension,”although

thereisanexceptionifcertaintransformationsofmicrostructureoccur.

Methodsforminimizingorreversingthestressincludeannealing

forstressreliefandhammerorshotpeeningoftheweakenedsurface.

Annealingrequiresheatingmildsteelto1100~1200F,followedby

slowcooling,Somepreheatingofthepartstobejoinedmayminimize

thetensilestressinwelds.

Athinbuthighlyeffectivesurfacelayerofcompressivestressmay

beinducedbycold-rolling,coining,en

thattheprocesswork-hardenanouterlayer,thuscausing

compressivestresstoremain,togetherwithminortensilestressin

hecompressivelayerisreadilyobtained

allaround,theprocessaresuitableforreversingloadsand

rotatingcomponentswherethestressvariesbetweentensionand

cessmustbecarefullycontrolledinrespectto

rollerpressuresandfeeds,shotsizeandspeed,etc.,forwhich

extensiveinformationisavailableinengineeringbooksandperiodicals.

Cold-rollingisappliedprimarilytocylindricalandothershapes

that

canberotated,pe,size,

andpressureoftherollerandtheyieldstrengthoftheshaftdetermine

thedepthofpenetration,alfixture

maybeattachedtothecarriagesofalatheandmadetoslowly

traverthedesiredrollingofboltsandscrewshaslongbeenpartof

aformingprocessthatnotonlyformsbutstrengthensthethreadsby

deformationandgrainflowaroundtherootsandbyinducing

compressiveresidualstress.

Coiningofholes,alsocalledballdrifting,isamanufacturing

processofforcingahard,tungstencarbideorAIDI*****steel,slightly

oversizeballthroughaholeinaplate,bushing,ortubingtogivethe

gthoftheholemaybefrom

1/hineisoftentupforahigh

dentalresultis

thattheprocessincreashardness,hencewearresistance,and

inducesaroundtheholeacompressiveresidualstressthatisusually

advantageous,ksatehighlystresdin

pulsatingtensionwithaconcentrationofthestressatandnearthe

ecompressivestressfromballdrifting,thenet

tensilestressinrviceisdecread,andfailureisminimized.

Peeningisthemostwidelyudmethodforprestressingby

mpactofroundedstriking

objects,thesurfaceisdeformedinamultitudeofshallowdimples,

peening,usuallybyair-driventoolwitharoundedend,isufulon

limitedareas,suchasaweldinshaftoronareasfoundweakenedby

corrosion,decarburization,ard

sphericalendtothetool,thedepthofthecompresdlayer,which

occursbelowthesurface,isabouthalfthestrain-hardenedregion.

Shotpeeningisdoneonsteelsbythehigh-velocityimpingement

ofsmall,round,steelorchilledcast-ironshotwithdiametersfrom

0.007to

0.175in..Thecompresdlayerhasadepthfromafew

thousandthstoafewhundredthsofaninch,lessthanwithhammer

peening,butroughlyproportionedtotheshotsizeudandits

heresidualstressproducedisabouthalfofthestrain-

eningixtensivelyudbecauit

maybeappliedwithminimumcosttomostmetalsandshapes,except

metals,l

springsarecommonlyshotpeened,withuptoa60%increain

theimprovementmay

beduetotheremovaloftheweakeninglongitudinalscratchesleft

rly,coar-machinedand

coar-groundsurfacesaresmoothedandimprovedbyshotpeening,

whichmaybeamoreeconomicalmethodthanproducingafinalfinish

gisnotudonbearingandother

grindingforaccuracyafterpeeningwouldremovepartorallofthe

esareavailablefortheautomaticand

continuouspeeningofsmall-andmedium-sizepartsmovingona

conveyororturntablethroughtheblast.