“%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@~kitl@.......--}

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 errorof@.0001inchcausesa =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 thelen@h-wisewires.However,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

.