“%copy ~:eRM E51H23
I
-1
.
. - * +. .—. , -—
-P
-L.”,.+ACA “’”-Li -__=>=~.:; __:—-
“q ---- -& --—-
E.. -
RESEARCHMEMORANDUM ‘–T
WIRE CLOTH AS POROUS MATERIAL FOR
TRANSPIRATION-C OOLED WALLS
By E.R.G. Eckert,MartinR.KinslerandReevesP.Cochran
LewisFlightPropulsionLaboratory(lPS:I ftc!,kd(or&lwff4aqgT:i@[email protected]}
By,i.j[li:-.!i. ~+&i&?#HO~~E6 ~fH~& $dfUbA,.imd!c.em!lt
By...... ,...........................................................[,1. ,
..............&
....................,...........................................GRADEOfOflICERMAKINGCtl GE)
~ b ?@L!.ld .. ................. .......
cl#srQlmUXUKEE
NATIONALADVISORY COMMITTEEFOR AERONAUTICS
WASHINGTON.
--November13,1951
TECHLIBRARYK.AFB,NM
I!llllllllllllllllllllllillu~“-1 NACARM
a
4.
E51H23
NATIONAL
NNcoCD
.
.
.
ADVISORYKMaTTEE FORAERONAUTICS
RESEARCHMEMORANDUM
WIRECLOTHAS POROUSMATERIALFORTRANSPIRATION-COOLEDWAILS
ByE. R. G.Eckert,MartinR.Kinsler,andReevesP. Cochran
su4MmAn investigationwasmadeto determinethepropertiesofwirecloth
asa porousmaterialfortranspiration-cooledwallswherea coolantisforcedthroughtheporousmaterialtoforman insulatinglayeroffluidontheheatedsurfaceofthewall.Materialspresentlyavailablefortranspirationcmling,suchas sinteredporousmetals,donothavesuf-ficientstrengthforapplicationsinwhichtheoperatingstressesarehigh. Forapplicationswherethestressesactprkril.yin onedirec-tion,a porousmaterialwithhighstrengthinthatdirectionisdesirable.An exampleof suchan applicatimisinturbine-rotorbladeswherethecentrifugalstresspredominates.Thesuitabilityofa corduroy-typewireclothmanufacturedfromAISItype304stainlesssteelwasinvestigatedforthispurpose.
Theclothwaswovenwithconsiderablymorewiresin onedirectionthanintheother.Aswoven,theclothwastoopermeableformosttranspiration-cedingappli&tions,butby cold-rollinga porousmaterialmaybe obtainedwitha widerangeofpermeabilities,whichshouldcovermostrequirementsfortrsaspiration-cooledwalls.Thestiffnessofthewireclothcouldbe increasedby a brazingprocessthatbondedthewirestogether.b ordertoprotideanadequatebasisforcomparisonofvariousporousmaterials,a reducedtensilestrengthwasintroducedforaircraftapplicationswherestrength-densityratiois important.Thereducedtensilestrengthoftheclothafterbrazingandrollingwasashighas 130,000poundspersqure inch,whichis.2 to 3 timestheulti-matecomparablestrengthof compactedsinteredmetals.Spot-weldingwasfoundtobe a satisfactorymethodofattachingwireclothto solidstruc-turesmd seambrazingaffordeda meansofattachinglayersof clothtoeachother.
INTRODUCTION
Transpirationcoolinghasbeenshowntobe an effectivemeansforcoolingstructuresinhigh-te~eraturehigh-velocitygasstreams(refer-ence1). Inthetranspiration-coolingprocess,thewallsofthestruc-turearemadeofa porousmaterialanda coolantisforcedthroughtheporouswalltoforman insulatinglayeroffluidbetweenthewalland
2 NACARM E51H23&
thehotgasstresm.Thismethodholdsparticularpremiseforair-cooledgap-turhtierotor..b~adeswhereconventionalconvection-coolingmethods %becomeinadequateat highgastemperatures.Thetranspiration-coolingmethodalsooffersattractivepossibilitiesforthecoolingof otherstructuralelementsin theaircraftpropulsionsystem,suchas com-bustionchsmbers,transitionducts,turbinestatorsandcasings,andjet-nozzlecomponents.Thismethodmayalsobe usedtoprotecttheskinofmissilesfromaerodyn~icheatingeffects.Additionalapplicationsforporouswallsmaybe foundindeicingwherewarmair Is forcedthroughthewalls,andinboundary-layercontroldeviceswheresuctionisapplied
m~..
to improveflowcharacteristics. N
A porousmaterialfortranspirationcoolingandtheotherapplica-tionsmentionedmustfu~illcertainbasicrequirements.Theserequire-mentsare: —
(a)Controllablepe?nneabilitywhichislocallyuniformor changeslocallyina prescribedmannertomeeta requiredcoolant-flawdistri-buteon
(b)Sufficientlywidevariationsincoolantflow
(c)Adequatestrength
.
rangeofpermeabilitiestoaccommodatelargerequirements .
fora proposedapplication
(d)Availabilityinquantityinpiecesofsufficientsizeandthick-nesstomeeta specificapplication
(e)Adaptabilityto conventionalfabricationmethods
Usuallya porousmateriqlproducedbysinteringofpowderedmetalsis consideredfortranspiration-coolingapplications.However,sinteredmetalsdonotasyetsatisfactorilyfulfillallthepreviously-mentionedrequirements.Theapplicabilityofothermaterialsforthetranspiration-coolingprocesswasthereforestudied.
.-Inmany
transpiration-coollngapplications,theprimarystressesarein onedirectionintheplaneoftheporouswall,as,forexample,ingas-turbinerotorbladeswheretheprimarystressesarecausedby centri- ‘fugalforcesandactinthedirectionofthoseforces.In sucha case,itisadvantageoustohavea porousmaterialthatiscomposedoffibersorwireswhichrun~aralleltothedirectionoftheseprimarystresses.Intheprocessofinvestigatingmaterialswhichmeetthisidea,a typeofwireclothhavingthegreaterportionofthetireswovenin onedirec-tionwasselectedforconsideration.Aswoven,thewireclothhasapermeabilitywhichistoohrge formosttranspiration-coolingapplica- *tions;however,itspermeabilitycanbe reducedtoanydesireddegreebycold-rolling.Thestiffnesswasincreasedbya brazingprocesswhichbondedthewirestogether. ~
NACARME!ZUi23 3.
-t
N)mmw
Theresultsarepresentedhereinof an investigationconductedat -.theNACALewislaboratoryoftheperm=bilityandstrengthofwireclothbothin itsnormalstateandasmodifiedby thepreviously-mentionedbrazingandrollingprocessesfortranspirationcooling.
SamplesofwireclothfortheseinvestigationswereobtainedfrcmTheW.S. TylerCompanyofCleveland.Theassistanceofthiscompanyandpartic&rlyMr=H&h Browninmaterialfortranspirationcooling
PREPARATION
A wireclothsuitableforthe
thedevelopmentofwireclothasais gratefullyacknowledged.
OFWIRECLOTH ‘
otitiedpurposeshouldbe suchthatthegreaterportionofthewiresruninthedirectionoftheprimarystresses.A specialweavecalledcorduroyclothfulfillsthisrequire-ment.-Themeshofwireclothisdesignatedbythenumberof openfngsperinchbetweenwiresinthewarpandshed,respectively.(Seefig.1.} Inthisreportthewiresintheshoatoftheclotharereferredtoas lengthwisewires,andthewiresinthewarpas crosswisewires.Dataforthethreedifferentmeshesofthewirecloth,whichwereinves-tigatedinthisreport,arecontainedintableI. Thenumberofwiresinthesecondandfourthcolumnswasdeterminedlyactualcountonthesamplesused. Forthe20X350wirecloth,thisnumberdeviatedconsider-ablyfromthenominalnumber.
ThematerialintheclothtestedinthisinvestigationisAISItype304stainlesssteel.However,thewireclothcanbe manufactured.franothermaterialsaswelL Thewiresfromwhichtheclothiswovenareinanannealedstate.Theweavingprocessitselfcausesscmeworkhardening.Frontmd sideviewsof sucha wireclothareshowninfig-ure2. Thisfiguredepictsthespecialtypeofweavewhichisusedinthemanufacturingprocess.
Aswoventhewireclothhasa permeabilitythatistoohighformostoftheapplicationsconsidered.However,thepermeabil.itiesmaybedecreasedto snydesireddegreeby a cold-rollingprocess.Thestrengthofthewiresisincreasedbythisrollingprocessas longasthereduc-tioninthicknessstaysbelowa certainlimit,approximatelyhalftheoriginalthickness.Frontandsidetiewsofthewireclothafteritwasrolledtohalfitsoriginalthiclmessarepresentedinfigure3. Thisphotographmaybe scmewhatmisleadingas itgivesthehpressionthatthespacesbetweenthewiresareclosedupexceptfortherawsofdarkholes.Inreality,theslotsthatrunobliquelyto thesurfaceoftheclotharestillpresentbetweenthewires.Inadditionto decreasingthepermeability,therollingprocesshasanotherbeneficialeffect.Formanyapplications,thesurfaceofthetranspiration-cooledwallh&tobe smooth.It c=be seenfrcma comparisonof figures2 and3 thatthesurfaceroughnessisdecreasedconsiderablyby therollingprocess.
4 NACARME51H23
In”ordertobe effective,therollinghastobe appliedinthe ‘lengthwisedirect-ion)whichistheaxialdirectionofthelargernumberofwires.In somecases,porous.materialpreparedinthiswayisundesirablebecauseitis considerablylessrigidagainstbendingforcesthan a pieceofsolidsheetmetal.Therigiditycanbe increasedbyinterconnectingthewiresatallplaceswheretheytoucheachother.Suchinterconnectionwasobtainedinthefollowingway:Thew&e clothwassprayedwitha low-temperaturesilverbrazingalloyby theuseofa metalspraygun;thebrazingmaterialappliedthiswaydidnotcloseup theporesbutcovered..thewiresonlyon thesurfacefacingthespraygun. Aviewofthesurfac.~ofthesprayedclothisshowninfigure4(a).A sil-verbrazingalloywitha meltingpetitof12”60°F wasusedinthisinves-tigation.Thesprayedclothwasdippedintoa saltbathat about1400°Ftemperature“untilthesprayedalloywasbraZedto thesurfaceofthewires(figs.4(b)and4(c)).It canbe seenthatthebrazingmaterialgavea verygoodinterconnectionofthewireswithoutclosingup thespacesneededfortheflowofthecoohnt.
Thematerialcontainingnobrazingmaterialisreferredtohereinas %nbrazedwirecloth”,andthesprayedandheatedmaterialas “brazed
--
tirecloth”.Thespecificapplicationdetermineswhetherpreferenceshouldbe giventothebrazedor theunlmazedwirecloth.An advantage .ofthebrazedclothisitsgreaterstiffness)but).it3.s to be expectedthattibrazedclothhasgoodvibrationdsmipingcharacteristics,whicharedesirableinmanycases.Also,thepermissibletemperaturewillbehigher.fortheunbrazedcloth.Forthesereasons,theinvestigationswereconductedonbothtypesofcloth.Air-flowtestsshowedthatthepermeabilitywasnotdecreasedseriouslyby thebrazingprocess.Thepermeabilityofthebrazedmaterialwasreducedto thedesireddegreebyrollingafterthebrazingprocesswasfinished.Photographsofthismaterialafteritsthicknesshasbeenreduced15and37percentoftheoriginalvaluearepresentedin figures5(a)and5(b),respectively.Thematerialpreparedinthiswayhasa smoothsurfaceanda stiffnesscomparableto solidsheetmetalofthesamethickness.
Methodsweredevelopedby TheW. S.TylerCompanyforjoiningpiecesofwire”clothby a brazingprocessandalsoforinterco~ec.ting.severallayersofwireclothby localapplicationofheatina mannercorrespond-ingto spotweldingor seamwelding.Of.thedifferentprocedurestestedatthe.Lewislaboratory”for”co?xiectingwire.clothtoa solidmetalstruc-ture,spotweldingwasfoundtobe mostsatisfactory.
PERMEABILITYCl?WIRECLOTH.
Theamountof c’cmlant”t~tcanbe forcedthrougha porousmaterialwitha givenpressuyedroprnus>be knownforthedesignerto selectthematerialandoperatingpressure”’fora specificapplicationoftranspira-tioncooling.
“
--l
.
NACARM E51H23
In orderto determinetheamountofairthatwillflowthroughrolledwireclothofvariouspermeabilitiesinboththebrazedandtheunbrazedstate,testsflowandthepressure
wereperformedduringwhichtheweightrateofdropacrosstheclothweremeasured.
ApparatusandProcedure
5
A “schematic”diagramofthetestequipmentusedfordeterminingthe*permeabilityofwire-clothisshowni?-fi-~e6. Airatrocmtem&ra-tureandata gagepressureof120poundspersquareinchis filteredandpassedthrougha pressureregulator.Theairflowis controll.edbya handvalveandmeasuredby a rotameter.Itthenpassesthroughaspecimenofwireclothheldbetweentwocoppergasketsina pipe-to-tubeconnectorcoupling.Thisarrangementisshownindetailinfigure6.Thetemperatureandthepressureoftheairpassingttioughtherotameterarealsomeasured.
Piecesofunbrazedwireclothselectedfromsheetssup~liedbythemanufacturerwererolledvarioussmountstomaximumreductionof50per-centoftheiroriginalthickness.Disks,l? inchesindiameter,were -
cutfromtheselectedpiecessndtheiraver=gethicknessesweredeter-mined.Thesediskswerethenclsmpedtightlybetweenthecoppergasketsin theconnectorcoupling.Airwaspermittedto flowthro@ thetestapparatus.Thepressu&sonbothsidesofthewire-clothspecimenaswelJastheweightflowthroughitweredetermined.Forthemostpart,measurementsweremadeonthreelayersoftheclothstackedoneontopoftheother.However,in orderto determinewhetherornotthereisadifferenceinpermeabilitywhendifferentnunibersof layersareused,testswerealsoperformedononeandfivelayersofthecloth.Similarpermeabilitytestsweremadeonbrazed-androlled-wirecloth.
ResultsofPermeabilityTests
Theweightrateofflowofgasesthrougha planewallofporousmaterialatlargepressuredifferencesandunderisothermalconditionsdependson thepressure-squaredifference(reference2). Therefore,theresultsofthepermeabilitytestsareplottedinfigures7 and8 as thedifferenceinthesqwes ofthepressuresonbothsidesoftheclothperunitofthiclmessof clothagainsttheweightrateof flowofgasesthroughthecloth.Twomeshsizesoftheunbrazedcloth(fig.7),andthreemeshsizesofbrazedcloth(fig.8)wereinvestigated.
. Eachofthefigurescontainsresultswithdifferentnumbersoflayersat thessmepercentageofthicknessreductionbyrolling.An
Yex&inationofthe~orrespondingpointsrevealsdifferenceperunitthicknessoftheclothdoes
thatthepress&e-squarenotdependsystematically
6 NACAEME51H23*-:,,m......----.
onthenumberof layers.Differencesthatoccurin somecasesareattributedto inaccuraciesinthepreparationoftheporousclothorthethicbessmeasurements.Especiallyat largevaluesofthicknessreduc-tion,thethicknessmeasurementhastobe extremelyaccurateInordertoobtainreproducibleresults.Thispointisdiscussedinthefollowingsection.Thefactthatthepressure-squaredifferenceperunitthick-nessdoesnotdependonthenumberof layersinticatesthatthepressuredropthrougha specifiednuniberoflayersisthesameregardlessof~ther thelayers areplacedsomedistanceapartorstackedcloselytogether.Thetwounconnectedpointsinfigure8(b)arefordataobtainedinanattemptto investigatea 20X350specimenofverylowper-meability.Therewasinsufficientpressuredropavailabletotestathigherweight-flowrates.
A comparisonofunbrazedandbrazedclothofa specificmesh(figs.7(a)and8(a)orfigs.7(b)and8(c),respectively)indicatesthatthepressure-squaredifferenceofthebrazedclothisabout20-percentlargerthanthepressure-squaredifferenceofunbrazedclothwiththessmethickness.Thebrazedclothmustbe rolledinorderto obtaincon-siderablereductioninthepermeability.However,thedifferenceinthepressure-squaredifferencevaluesof@razed andbrazedclothbeccmegreaterat largevaluesofthicknessreduction(figs.7 and8). Athighvalues,itisthereforeunnecessarytorollbrazedclothasmuchasunbrazedclothinordertoobtainthessmepermeability.Thisfactbecomestiportantwhenembrittlementisa considerationin clothsrolled’toverylowpermeability;itisdiscussedinthesectionentitled“TENSILESTRENGTHOFWIRECLOTH.”
No consistentdifferencescanbe found-betweenthevaluesofthepressure-squaredifferenceperunitthicknessforclothofdifferentmeshesineitherthebrazedortheunbrazedcondition.
ComparisonWithCompactedSintered’PorousMetals
A comparisonoftherelationbetweenporosityandpermeabilityofrolledwireclothwiththatofscmecompactedsinteredporousmetalsisof interestbecausesucha comparisonshouldgivesaneindicationofthenatureoftheflowas influencedby thegecanetryofthechannelsinbothmaterials.
Forthispurpose,theporosityofthewireclothwillbe calculated.TheporosityistheratioofthevolumeofvoidsVv tothetotalvolumeVt (allsymbolsaredefinedintheappendix):
Vvf ‘q (1)
.
.
*-”” -- ~ -’ ..-, .“.
.
-,
.
.
NACARME51H23
or ifthevolume
... . . ... . . ... .
ofmetal Vm isused
Vmr l-—=
~t
However,thevolumeofthemetalincludesthevolumeofthesteelVfiandthevolumeofthebrazingalloyVb, therefore.
vm=v~+vb
Whenthis
thecorrespondingweighteqwa.tionmaybewritten
W andspecificweighty areused,
Ws Wbvm=~+—
s rb
Then
()Ws Wbf l-~—+—=
Vt rs Yb
andbecauseVt = AT where A isthesurfacethicknessofthecloth
[ 1llWS1%f l--—~+———=~ Ys rb A
.
areaand T is the
7
(2)
By thisformulatheporositycanbe calculatedbecausethespecificweightofthesteelandofthebrazingmaterialisknown.Theweightperunitareaoftheunbrazedmaterialis Wfi/Aandthedifferenceinwetghtofthebrazedandtheunbrazedmaterialis ~/A.
In figure9,theporosityofrolled-wirecloth,as determinedlyequation(2),isplottedagainstthepercentagereductioninoriginalthickness.Thevalueoftheporosityofunbrazedwireclothata givenvalueofthicknessreductimincreaseswithan increaseintheratioofthetismeterofthecrosswisewirestothediameterofthelengthwise
● wires(seetableI). A largediameterratiocausesmorebending02thewiresinweavingandconsequentlymorevoidspace.Theamountofbrazematerialaddedtotheclothwaslargestforthe28X500meshsize.This
*-, factexplainswhythereductioninporosityby thebrazingprocesswaslargestforthistypeof cloth.
8 M4CARME51H23
ThepermeabilitycoefficientK isdefinedby Darcy’slaw(refer-ence3) as follows:
(3)
where ZT iSthetotalthicknessofa nunibefioflayersof clothinseries.A lin&arrelationbetweenthepressure-squaredifferenceandtheweightrateofflowisassumedinthislaw. Actually,therelationisnotquitelinea~(figs.7 ad 8). Thisrelationwasexpressedinreference2 by theequation
I@’- P22Z!T
= a[2RTp)G+ ~ ~G2 ‘ (4)
By eqmtingequations(3)and(4)andsolvingfor K, itis foundthat
K1 1=-!3ai+—W$G
(5)
Thisequationshowsthatthepermeabilitycoefficientactuallyvariessomewhatwiththeweightrateofflowandthetemperature(viscosity)ofthefluidpassingthroughtheporousmaterialaswellas theconfigura-tionofthepassagesin thematerial.A permeabilitycoefficientbasedonDarcy!slawisusedhereinin orderto comparethewireclothwithcompactedsinteredmetalswhichwereevaluatedonthissamebasisinreference4. Forsmallvalues’ofweightflow,thismethodgivesa goodapproximationofthepermeabi~tycoefficientK inequation(5)
becausethesecondterm --&G inthedenominatorbeccwnessmallas ccm-
paredwiththefirstterm.“‘Forlargevaluesofweightflow,theeffectsofthissecondtermbecomeappreciableandcannotbe neglected.
Thepermeabi~tycoefficientK or l/cLisplottedagainstthepercentagereductionin originalthickness@ figure10. Thetestpointsappeartobe groupedaroundtwocurves,one.forbrazedclothandoneforunbrazedcloth.
Finally,theporositywasplottedagainstthepermeabilitycoeffic-ient infigureXlalongwithtestresultsonsinteredlnetalcompactsobtainedfromreference4. FrcmfigureU itis seenthatalthoughthesamerangeofporositiesisconsideredtherangeofpermeabilitycoeffi-cientsforthewireclothismuchgreaterthan
. r..—-..—
thatofthestitered
.
.—
.
.
● ✎
.
e,.
2 NACARM E51H23 9.
N&’CD
compacts.Fora smallchangeinporosityofthewirecloth,it ispos-. sibleto obtaina largechangein thepermeability.On theotherhand,
becausetheporosityismainlycontrolledbytherollingprocess,asmallerrorinobtaininga requiredthicknessoftheclothmeansa rel.a-tivel.ylargeerrorinthepermeability.As an example,itisfoundfromfigures9 and11thatforbrazed20X250meshclothhavinga porosityintheregionof14percentan [email protected] =3 percentvariationinthepermeabilitycoefficient.Therollingprocessmustthereforebe controlledwithextremecareto obtainreproducibleresults.ws factalsoexplainsthescatterin”figures9 andlQ,.Foreqwl per-meabilityvalue6,therequiredporosityof sinteredmaterialisgenerallygreaterthanthatofthewireclothprobablybecauseofthesmaller
.
.
crosssectionandthemoretortuouscourseof
T!ENsmSTRENGTHOFWIRE
ExpertientalProcedpreand
thepassages.
cIlOI!H
Results
Sufficientstrengthissn importantconsiderationinmanyapplica-tionsofporousmaterialsto trszmpirationcoolingaswasmentionedintheINTRODUCTION.ThethreemeshesofwireclothtestedwerewovenfromA.ISItype304stainlesssteel,whichhasa tensilestrengthintheannealedstateof 87,000poundspersquareinch.Thismaterialwillelongateabout65percentina 2-inchgagelengthbeforerupturing(reference5). Themanufactureroftheclothestimatesthata 20-percentelongaticmoccursduringtheweavingprocess,andthatthiscold-working.ofthematerialraisesthetensilestrengthoftheclothto about100,000poundspersquareinch.Theeffectof coldworkon thetensilestren@handpercentelongationofAISItype302stainlesssteel(refer-ence5) isshowninfigure12. ThebehaviorofAISItype304stainlesssteelis similarexceptfora slightlyhigherrateofworkhardeningbecauseofthelowercarboncontent.Itcanreadilybe seenfromthesecurvesthatinadditiontobringingthepermeabilityofthewireclothintoa desirablerange,therollingwillincreasethetensilestrengthandreducethepercentageelongation.
Tensiletestshavebeenmadeat roomtemperatureonrolledandunrolledwirecloth,bothbrazedandunbrazed.Thesetestsweremadeonstripsofmeshapproximately0.8inchwideand10 incheslong. In orderto obtainbettergrippingintheJawsofthetestingmachine,theendsoftheteststripswerecoatedwithsoftsolder.Particularlywiththeunbrazedcloththiscoatinginsuredthatallwireswouldbe stressedequally.Duringthetests,theloadwasincreasedprogressivelyin
. incrementsof100poundsandtheelongatimofthetestspecimenwasmeasuredat eachloadingup toandincludingthebreakingload. Theelongationofrolledspecimensofbrazedandunbrazedclothis shownin
t figures13and14aspercentageelongationin4 inches.Thepercentage
10 NACARME51E23
0)mN‘N
.
elongationdueto tensilestressdecreaseswithincreasedmount ofroll-ingperformedonthecloth.Thisdecreaseispartlydueto compacting .ofthewovenstructure,andpartlytotheincreaseinthehardnessofthematerial.Themarkedeffectofcold-workingontheelongationofAISItype302stainlesssteelisapparentinfigure12. Cold-workingofAISItype304stainlesssteelwill.producesimilareffects.Iftheallowablestressesina structurearedeterminedby theelongation,thenthestressesmustbe keptbelow0.5to 0.7ofthetensilestrengthdependingontheamountofrolling(figs.13and14).
Theeffects@ rollingonthetensilestrengthofthewireclothareshowninfigures15and16. Inthisreport,thetermtensilestrengthreferstotheultimatetensilestrengthunlessotherwiseindi-cated.Theleftsidesof_bothfigureswerecomputedbydividingthebreakingloadby thesumofthecross-sectionalareasofthelengthwisewiresas determinedfromthediametersbeforeroH.ingandtheactualnumberofwiresperinchgivenin tableI. Forstructuralelementsllketurbinebladeswhichhaveto carrytheirownweightina centrifugalfield,theratioofthetensilestrengtha tothespecificweightyisa valuemoresuitableforccmparingdifferentmaterialsthanthe@n- ●
silestrengthu alone.Also,fornonrotatingpartssuchas combustion-chamberliners,thewei@t isthemainfactorlimitingthethiclmessof
—
thematerial.Ingeneral,theratio u/y Isthereforethebestbasis.-
fora comparisonofdifferentmaterialsforaircraftstructuralcompon-ents. ml theporousmterialswhichwillbe comparedhereinaremanu-facturedfrom18-8stainlesssteel.A reducedtensilestrengthO’ wasthereforedeterminedby multiplyingthestrength- specific-weightratioby thespecificweightys
Thisvaluecanbe ccmparedstainlesssteelforwhich
ofthestainlesssteel:
a’=~~ys (6)
withthefamiliarstrengthvaluesof solidr = l-s”
Forthewirecloth,thereducedtensilestrengthwasdeterminedinthefollowingway: Thetensilestrengtha isdefinedby theequation
CJF=-a
Thespecificweightofa specimenoftheclothoflengthL, cross-sectionalarea a,andwei&htW is
(7)
T’-J&
NACARM E51H23
Thereducedtensilestrengthfortheclothistherefore
Thisstrengthcanbeforceandweightper
u’= Fw~ Ts
IL
(8)
calculatedfromthemeasuredvaluesofthebreakingunitlengthofthespecimenusedfortherupture
test.Therightsidesoffi&s 15andi6 showthesereducedt&silestrengths.ThevalueofthereducedtensilestrengthU’ isalwayslowerthanthevalueofthetensilestrengthu becausein computingtheredncedstrengththelengthwisewiresareconsideredto carryinadditionto theirownweighttheweightofthecrosswisewires.Thevaluesofthereducedstrengthal increaseat a fasterratewithreductionofthicknessby rollingthanthevaluesofthetensilestrengtha. Thismorerapidincreaseisexplainedbythefactthatthelengthofthewiresincreasedandthecorrespondingcross-sectionalareadecreasedintherollingprocess;a factwhichisaccounted-forinthedeterminationofthereducedstrengtha’,whereasthestrengtha isbasedonthenominalcross-sectionalareabeforerolling.Thediffer-encebetweentheoriginalandthereducedstrengthis largerforthebrazed28X500meshcloththanforthetwoothertypesbecausetheweightofthe28X500meshclothwasincreased30percentby thebrazingprocessas cmparedwith16percentforthe20x250typeand17percentforthe20x350type. Itisprobablypossibletoreducetheamountofweightadditionfromthebrazingofthe28x500meshclothby maintainingaclosercontrolonthesprayingprocess.
As showninfigure15,thetensilestrengthoftheunbrazedcloth ‘reachesa maximumwhentheclothhasbeenreduced40percentinoriginalthicknessby rolling.Althoughthetensilestrengthofthebrazedclothincreasesevenaftera 45-percentreductionin originalthicknesswiththeexceptionofthe20x350type.(fig.16),a practicalldmitisreachedatabout40 or45percentbecausethematerialbecomestoobrittletobendbeyondthispoint.
Twospectiensof 20X250brazedwireclothreduced40percentinoriginalthiclmessweretestedfortensilestrengthinthedirectionofthecrosswisewireswithan averageresultof150,000poundspersquareinch.Thistensilestrengthisbasedonthenominalcross-sectionalareasofthecrosswiresas listedintableI. Thisvalueishigherthanthatforthetenstlestrengthu ofthelengthwisewires,as thecross-wisewiresarelessdeformedbytherollingprocessthan are [email protected],becausethenumberof crosswisewiresperinchismuchlessthanthenumberoflengthwisewires,thestrengthofthecloth. inthecrosswisedirectionwillbe onlya fractionofthestrengthinthelengthwisedirection.
#
12 NACARME51E23
ComparisonWithCompactedSinteredPorousMetals
Usuallysinteredporousmetalsareconsideredasmaterialfortranspiration-cooledwalls.Thestrengthof compactedsinteredporousmetalsas describedinreference4 willthereforebe comparedwiththestrengthofwirecloth.Twooftheporousmetals(designatedinfigs.11,17,and18astheUnexcelledPowderandtheHardycompacts)wereproducedfromAISItype302stainless-steelpowder.Thethirdtypeofporousmetalcompact(designatedinfigs.17and18asVA com-pacts)wasmadefromatomize@owderofAISItype301stainlesssteel.Theccmmarisonwillbe madeforthereducedtensilestrengthcr~.Fromtheval~esoftensilestrengthusilestrengthU’ wasdeterminedweightoftheporousmetaltothebe expressedintermsofporosity
.
giveninreference4,a reducedten-..
asfollm”s:Theratioofthespecificspecificweightof stainlesssteelcanf oftheporousmetals.
= 1 -f--
.
ThereducedtensilestrengthistherefOre
.Csa’=—l-f
(9)
Thisevaluationcreditstheporousmaterialwithitslighterweightwhichisadvantageousforaircraftapplications.Thereducedtensilestrengthsoftheporouscompactsandthewireclotharecomparedforvariousvaluesofporosityinfigure17,wherethecurvesforthewireclothwereobtainedby cross-plottingfigures9,15,and16. Thetensilestrengthsofthe20X250meshand20X350meshcloth,bothbrazedandunbrazed,arefrom2 to 3 timesthatofthesinteredcompactsfora rangeofporositiesbetween15and20percent.Thereducedtensilestrengthofthebrazed28X500meshclothisabout1$to 2 timesthatofthesinteredcompactsforthissamerangeofporosities.
A furtherstrengthcomparisonbetweenthewireclothandtheporousmetalswasmadeonthebasisofthepermeabilitycoefficientK definedintheprevioussection.Theresultsofthiscanparisonaregiveninfigure180 Permeabilitydatafortheporousmetalswereobtainedfromreference4, andthestrengthfiguresforthewireclotharedeterminedfromcrossplotsoffigures10,15,and16. Thestrengthsofthewireclothareasmuchas 4 timeshigherintherangeofpermeabilitiescon-sideredthanthestrengthsoftheccmpactedsinteredmaterials(fig.18).Thesecomparisonsareonthebasisoftheultimatestrengthsofthematerials,buteveniftheworkingstrengthsofthewirecloth,whichareshowninfigures13and14tobe from60,000to 80,000poundspersquareinch,arecomparedwiththeultimatestrengthsoftheporouscompacts,thewireclothisstillabouttwiceas strong.
.——.
.-
.
NACARME51H23 13
.
-.
INNmCD
StrengthofConnectionsBetweenWireClothandSo13dMetals
Variousmethodsofattachingthewireclothto a supportingstruc-turehavebeenconsidered.Testsweremadeontheuseof spot-weldingto determinethestrengthofsuchanattachmentandtheamountof sur-faceinterruptioncaused.Specimensofbrazed20X250meshclothreduced40percentinoriginalthicknesswerespot-weldedtotheedgeof0.040-inch-thickfinsusinga l/32-inch-diameterelectrode.Theshearstrengthperspotweldforsuchan attachmentwasfoundtobe upwardsof150pounds.Thisstrengthiscomparabletothatobtainedona 0.018-inch-thickstripofsheetmetalinthesametest.Nomeasurementoftensilestrengthof thespotweldswasmade,butfromteststo determinethedeflectionoftheclothunderdifferentialairpressure,itmaybe con-cludedthatanyspacingof spotweldswhichwillkeepthisdeflectionina rangecmnparableto castingtolerancesforturbinebladeprofiles(about0.005in.deviationin0.25in.lineardistance)willhavesuffi-cientstrengthtowithstandanydifferentialpressurelikelytobe usedintranspirationcooling.
SUMMARYOFRESULTS
An experimentalinvestigationwasconductedto determinetheper-meabilityandstrengthcharacteristicsofwireclQthforuseas theporousmaterialfortranspiration-cooledwallsandthefollowingresultswereobtained:
1.By cold-rollingofcorduroywirecloth,a porousmaterialmaybeobtainedwitha widerangeofpermeabilities,whichshouldcovermostrequirementsfortranspiration-cooledwalls.-
2. In’therangeoflowporosities,smallchangesinofthicknessbyrollingcausedverylargechangesintheTherollinghadtobe verycarefullycontrolledinofierducibleresults.
3.Thetensilestrengthatmoderateamountsofrollingbutmaterialwhenthethiclmesshadoftheoriginalvalue.
thereductionpermeability.to obtainrepro-
roomtemperaturesincreasedtithstarted~o decreasefortheunbrazedbeenreducedto approximately60percent
4.Thestiffnessoftheclothagainstbendingforceswasincreasedconsiderablyby a brazingprocessthatinterconnectedthewireswheretheytouchedeachotherwithoutclosingup thechannelsnecessaryforthecoolsmtflow..
5.Thetensilestrengthofthewireclothatroomtemperaturebased* onthesumofthewirecrosssectionsinthestressdirectionwas
increasedby thebrazingprocess.
-.
14 NACARME51H23.
6.Thetensilestrengthsofthewireclothwereintherangeofvaluesbetween100,OCX3and130,000poundspersquareinch.Thereducedtensilestrength,whichwasintroducedinorderto evaluatethematerial
0-
properl.yforaircraftapplication,comprisedvaluesbetween80,000and120,000poundspersqyareinchwiththeexceptionof’brazed28x500meshcloth,whichhadvaluesaround70,000poundspersquareinch.
7.As comparedwithsinteredporousmaterialmadefromstainless-steelpowder,thereducedtensilestrengthof20X250and20X350meshwireclothinthedirectionofthelargernumberof wires was2 to %3 timesas large,andthereducedtensilestrengthofbrazed28X500wire mlclothfrom1~to 2 timesas large.
ml2
8. Interconnectionbetweenlayersofwireclothwasacccmplishedbya seambrazingprocess,whereasfora connectionwithsolidmetalparts,spot-weldingprovedsatisfactory.
LewisFlightPropulsionLaboratoryNationalAdvisoryCommitteeforAeronautics
Cleveland,Ohio.
NACARME51H23 15.
-,
.
.
●
u
Thefollowingsymbols
eurfacearea,sq in.
cross-sectionalarea,
force,lb
APPENDIX- SYMBOLS
areusedinthisreport:
Sq in.
porosity,dimensionless
weightrateofflaw,lb/(sec)(sqin.)
gravitationalconstant,in./(sec)2
permeabilitycoefficient,sq in.
length,in.
staticpressure,lb/sqin.
gasconstant,in./oR
statictemperature,‘R
volwne,cu in.
weight,lb
constant,in.-2
constant,in.-1
specificweight,lb/cuin.
absoluteviscosity,(lb)(sec)/sqin.
summation,dimensionless
tensilestrength,lb/sqin.
reducedtensilestrength,lb/sqin.
thicknessofonelayerofporousmaterial,in.
16 NACARME5SE23
Subscripts:
1 sideofporousmaterialathighpressure
2 sideofporousmaterialat lowpressure
b braze
m metal
s steel
t total
v voids
REFERENCES
1.Eckert,E. R.G.,andEsgar,JackB.: SurveyofAdvantagesandProblemsAssociatedwithTranspirationCoolingandFilmCoolingofGas-TurbineBlades.NAcARME50K15,1950.
2.Green,Leon,Jr.: FluidFlowThroughPorousMetals.Prog.Rep.No.4-ill,JetProp.Lab.,C.I.T.,Aug.19,19.49.(ContractNo.W-04-200-ORD-455,OrdnhnceDept.)
‘3.DuwezjPol,andMartens,HuwardE.: ThepowderMetallurgyofPorousMetalsandAlloysHavinga ControlledPorosity.Trans.A.I.M.M.E.,MetalsDiv.,VO1.175,”1948,pp.848-874.
4.Hill,M.,Reen,O.W.,Vermilyea,D.A.,andLenel,F.V.: Produc-tionofPorousMetalCompacts.Bi-MonthlyProg.Rep.No.3,Pow-derMetallurgyLab.,RensselaerPolytechnicInstitute,Oct.6,1950. (NavyRes.ContractNOa(s)11022.)
5.Thum,ErnestE.: TheBookofStainlessSteels.Am.Sot.Metals,2dcd.,1935,p. 371.
.
I 0) ‘“comaN.
—
—
.
.
—
.
v
.:-- -.. -.
.
3.
NACARME51H23
TABLEI - SPECIFICATIONSFORTHREEMESHESOFWIRJ2CLOI’E
.
.
Mesh Lengthwisewires Crosswisewires Originalthick-Number DiameterNumberDiameternessoftieper (h.) per (in.) clothaswovenin. in. (in.)
20X250 250 0.008 20 0.010 0.026920)(350 315 .0065 20 .010 . 023a28X500 496 .004 28 .008 .0169
.
.
17
.—
POJ
(a) Mad, 2WZ33. (b)
Figure1. .- msh aizead
. ,
Mmh, 20X350. = ‘ (c)Ned, 2@CO0.
I..
Etaimlem-eteelcorduroy vlre clothaS ~.~
.,,
CA
● ✎68ZZ
1 ,22& ,1 .
-=x@=’(a)hmt view C-28272 (b)Sldaview.
mglll’a2. - h mmn 20X25-Omwh mdnwy tirecloth. (Xlo) i-U3
I
-.
Flgm-e3. - 20%2.50MeshcOl?dWOYwirecloth@tar reduotkmof Xlyrcat ino*1
*. .
,:,,6W?
2289# ,
(a)Aftersp’ajlngwithsilver “x (b)Aftm @PiDSoti ealtbath (c)
braciw alloy, at 14C0 F.
Figure4. - Reaul’csd bmdw P?YJm6Sm 2W~ mm o~~~ ~~ olo~h. (no)
E@ vIev d & oldbdhownm figure4(b).
2
.-
,
(a) lsPercentreaucticmh Ori@lal (b)37-PerBgntI’eduotimh (migmlthickeaB. (C) m tiw UP WIIW cloth
thlckn33@. ShOwn h ffglm 5(b).
Fignro5. - Resultsofbrazingprocesson 2W.541mwh corduroyvim clothaftercold-ml-. (lJ-O) E
;
5E&
, ,I ,,
. ,
1,.:’ , 6W2
NACARM E51H23●
✎
Air,120lb/sqin.gage
mEml
.
.
IR
23
Wirecloth
Metalgaskets
Connectorcoupling
-Filter
1
rFressureregulator
1
\ IL w
\—
‘Flowcontrolvalve
7-Static-pressuretap
_7Thermocouple
‘Static-pressuretap
<Rotameter
. Figure6. - Schematicdiagramoftestequipmentformeasuringairflowthroughspecimensofwirecloth.
24
m(percent) I
6.321.921.429.733.742.551..-I
1111111 I
NACARM E51H23
.0036.001 .032 .(Weight-flowrate,G,lb/(see)(SQin.)
(a)Mssh,20X250.
Figure7. - Correlationofair-flowdatafor unbrazedandrolledcorduroywirecloth.
.
. ccl
!#
.
.
stainless-steel
.
4
.
NACARM E51H23
10:
.
104In
101
1 I I I I IReduction”in Ley=sthiClmeBs(percent)
o 0❑ 12..5A 25
37.5; 304 50
533331 m
A
A ~-w- a
/ - a> - w
/ -AA
a +>
100 =$sy.Q302 .OC64 .CxxK .CKKM.001 .002 .004 .0
Weight-f’h?rate,G, lb/(see)(sqin.)
(b)Mesh,28X500.
Flguce7. - concluded. Correlationofair-flowdateforunbrazedandrolledstainless-steelcorduroywirecloth.
5
26 NACARM E5JH23.
.
-.,
ReductionInthiclmeas(percent)
o 0❑ 8A X5v 26.5
372 0D 80 Eo 27
iayer”s
335331111
n 37 1I
/ 9w-
-
>
)2 .0004 .0006 .C
IEEE
.
f
-
—
—
—
—
—
I=uitJ78 .001 .002 .004 .1
Weight-flowrate,G,lb/(see)(sqin,)
(a)Mesh,20X250.
Flmre 8.- Correletlonofati-flowdataforbrazedandrolledstainless-stwlcorduroy
.
—6
wirecloth.
w
.
.
.
.
NAC.ARM E51H23a
Reductionin,thlckness
(percent)
o 0u 9A 18v 240 324 5s.5* 45
Layers
3333311
27
—
.0006.W1 .CQ2 .Q04 .0
—
6Weight-flowrate,G, lb/(see)(sqin.)
(b)Mesh,20X350.-
Figme 8. - Continued.Ckmrelat$onofair-flowdataforbrazedandrolledstainless-steelcorduroy wirecloth.
.
28 NACARM E5JH23
I I IReductionin Lay5rsthiclmeas(percent)
A 16.S 3v 27 30 40 34 39.5 1
lo5
/
K# a A < e& ~ H
m$
“k
N’~03
$S’I ;
~a.
102
~ol
10°.OCKlz .0004 .0006.(X$38.Cx31 .002 .004 .0Weight-flowrate,G, lb/(see)(sq in. )
(C) IA?sh,28)6~.
Figure8. - Concluded.Correlationatair-flowdataforbraaedandrolledstainless-eteelcorduroywirecloth.
6
.
.
:-+. ...--- ..’-.-..... ~. ---., ----
?IACARM E53H23 2’3.
.
m8N
.
.
.
.
-.
48
40
32
Mesh\ o 20x2k0Brazed( ❑ 20x350Bzazed
\A 28x500Brazed
Y 20x250Unbrazed; 20x350Unbrazed
[1 \4 26X500Udlrazea\
[1I .
\
\ \\ *
\
\\
\\ w
o
c1 \ .
\
24
16
9\w \
8n\-
.-
0 10 20 30 40 50 60Reductioninoriginalthickness,percent
Figure9. -Effectofrollingonporosityofbrazedatiunbrazedwireclothinthreeme6hsizes.
30 NACARM E5JH23.
1O-*o 10
~. \
r
20
1 I I [
MeshLayers— Brazedclotho 20X250 3❑ 20X350 3A 28X500 3
20X250 1; 20X350 14 28X500 1---- Unbrazed cloth
20X250 320X350 326X500 320X250 128x500 1
\\
\ P
4
,7
<>4
.
—
30 ._ 40 50 60Reductioninoriginalthickness,percent
Figure10.-Effectofrollingonpermeabilitycoefficientofbrazedandunbrazedwireclothinthreemeshsizes.
.
.
r“l-
, 2289 ,
we 4
I
-w
Rmeabilitycoefficient,K, sq in.
I Ix
Flwre Il.- C-iaon of pmosityti psrmebffltycoefficientforbrazedam.1unbrezedrolJ.adstainless-steelCOrdurcgvim clothad soreEd.ntered-m’talCcqacts.
32 NACARM E51H23.
.
22OX1O3 {
Teneile6tre@h
200 /
Elca&rMon +atrupture
1s0 1 /
~ I
g> 160As’9$m 140
38$ / \
120
Im
“d
!!80--. 0 10 20 30 40 50 60
Reductioninmeaby cold-rolling, percent
Figure12.-Effectofcold-rollingonAISI302stainlesssteel(reference5).
,
.
Il!li
,
1 1 1I Reductionh originel
(a) Mach, 20X250.
.
40 20 0
/
o 10 m 50ElongationIn 4 Inches,percent
(1)) Mesh, 20)650.
2289
40
A A
20
;/
I10 20
r UI
(C) ?&h, 28)@39.
!FigureM. - Elongationof threemesh sizesaf unbrazedend rolledstainless-steelcoMu’oy
-e clothundertensilslmd.
FILlucti&In.&giIJLthlka
Mcxl&58 .(Wcent) o
437
4.5 24
4 / ? 34 x! h Q //u* o
39
!lzo
Y
.IIxl <3
Jt
@<
4
Is
m > IB
20 g I&o 10 20
e300 10 20 300 m 20
Elongatlmin 4 inm, pmmnt
(a)Ms*, 20X250. (b)Mesh, 20X50. (C) Mssh,~.
Figure14. - ElOm@ti of W E8h Bke6 C& brwmd ad MM ddnle%m-sted curdmcu tie cbth umler. .
t.emlle bad.U I
. .1,
,
I Ei8zz
II
, ,
14OX1O3
SjIJ
~ 1.20, u // h
--; -- --
A 0 ❑\
; ❑A ->. ~-” “\ \
L1A
E-Pul \\
MeshI
gm‘El 20x250 I
----- 20X36028X3CQ
A—.—
,;
,60 I I I ●
o 20 40 60
, Zim ,
Moxld I
120
\/-- -
I
.80 / ~ “-\ ,“
~ ““
\
60“o 20 40 60
Reductioninoriginalthickness,percent
Figure1.5.-Effectof rollhg on tensile drength of unbrazed statiless-steel corduroy
wire cloth.
—.
01m
140XL03
j
g
> Eo-.
-B.
iii& 100*m
3::60al
/; ●
L% / / ‘
. ./ -—
600 20 40
Reduction in orlglual thiclcnms, peroent
IHgore 16. - Effect of rolllmg on tensile strength of brazed stainless-steel corduroy
wire cloth.
60
2!
.
NACARM E5JH23 37.
..
m8N
.
.
.
.
WireCloth CcxnpactedSinteredMetals (reference4)Mesh
1 20x250brazed2 20X350brazed3 28X5Wbrazed4 20X250unbrazed5 20X350unbrazed6 2SX500unbrazed
120xlo3
100
80 /
60r
\
40 \
20.
0 10 2(
7 Unexcelledpowtkr,AISI type 3028 -200+325mesh, VA,AISItype3019 -200+325mesh,Hardy,AISItype30210 -100+200mesh,VA,AISItype30111 -100+200mesh,Hardy,AISItype3027
—
6
\
Y
-7‘11
=&=
30 40 50 &Porosity,f,percent
Figure 17.- Comparisonofreduced tensile strengthand unbrazed rolled stainless-steel corduroy wiresintered metals.
amd porosity for brazedcloth and some compacted
.
U.fre clnthI&al
1 20X250brawal2 20X352bre=a3 20S30 bmzed4 20X2KIunbrazed5 213x51Munbrazed
-Cmpectd SirkeredMetul.a(rdemnce4)6 Urmxcelledpowder,AIEItyps3027 -2C4H25msh, mrdy, AISItYW 3028 -10cbt2wmesh,VA,A121tme 3319 -1(xw2c0?mah,KardF,AISItYW 602
E FemsebiliWcoefficient,K, w in.~Yz Figure1.2-- ccqccdson d rednced tensile strength @ permabi13tycoefficimtforbrazedamlunhrazedrolledstelnleas-
steelmrduroyvim clothandmm cmpacttxlsint4redmtala.:
.I I 6SZZ
.
Top Related