t as 0

~

by Gf1 Avlt y ~ ea-s becaus~ tte~ re~-t proml

~xr1~srial thstand tl~

n t of the- middots1l~r a110ls ~et-ro -usi-on

d i2proved ria l s a~ still ~-ired to i~~rovebut

ce tin ogteraticm at hi$~rrfo

the rurboj et as ~xplained d sr

reali h1~b~r thrust and the turbopro~ll~r sectlins J fici~nc7 and pow~r

_ratJres a~ inc~ased 1ven i f these b~tVr

_ ter1ampls are not he pOll~rplan t t Jra~ at hizher

peratures these t-ria1s Will 1nc~ase s~rvce Efe and r~liaoi1i ty

arrr c t the present t the alloys in the j~t-~r ~ncine bull

can apr oxi tel y 15000 7a~nhei t 1 r r~seamprch

in this field th~ operatin or UleS~ ~~ra13 can roa~1middot1 be exshy

any of these allo-Js 1fe~ ~eve10~C b-j indus trJtlnded a f~ hLld~d

~ria1s bullp 0 t~~ on H~t- e3i

y of the 1erials now in use -ere d~7~10~d dlil t1 2 war by

cookbook metbo1s and a Ert of the researcn on lCltl1aiS

is d1~cted towartls an understadin of hOW tM3~ 2tcrials licr so that

ents basd on Lndallenta1 factcrs aff~ctr tr~ o-o- ra tion of

~r1als can b lJilde Uos t of the suo~r alloys ~ l arPe lalti ti~s of

scarce ~ria1s such as cobalt and co1UJ~lWl In tile case of a f utx-e

these less a lundant ca~r--a1s 11 lose

ampa

rected reOlcL use o these sca~A~ terials

~J

- 2 shybull

tho~ 57 rtich b~ r~sista~ce to te3 ra-~ ext~Ies can

An ~~ple of thipaSQ is bv the lSe of ma~rials tbat (an ~ cooea

+_ nAv7 ri bull rTlctaticn i~ Iis sh

ampis ar~al w~c fahLcated to

s you can see tbe oxy-ac etl~n~ fla=Je has h~atedIgt nave 0 ~rcen t porosit7

~ now ~ir~ct ~~ ai~ str~a~ ~~t~ a n~a1er or holethe block to a ~d ~ L

A

38 of an nch in dia1~~r thit has ooen 1illed into ti1c blocl bull

orcsi ty in tr~ bloc~ will liSr3 and conllct t~ air streaa in suct a

~r as efecti~ ccolin

c~ral3l ~ s can e readi faorcated Wit1 al~cs t atr des

e of )or os a~-als i s tia t of

s trerth is

ro~le ~ is also ~d~r in~st~~ticn bull

oOtai~i-1( hi~h ~orosi vj hil~ retainl hi

c )1 ~on ~l tshy

i t is natural to turn t rials lavi1

f r )sitr

a1ts aes i ners

in

~ Vt -rj hir~st ltelting oil ts bull hese aaterials ar~ hih-meltL1~-fOIf

tal such a s tlmgsten and ao17odem and the oT1ies nitri~s carbi des

ani bO~ce3 0 ll~ tdl ~is latter grOU ar~ c~l1~d c~ra ~c~ bull

teJ~ra tre scale along the top 0 this oa~l has on i t sClll~ 0 r UlII

i th 1rhic ~ 1 ir

res~ctive red

or t~ ~ry

of tn ra tutlS t

stress calliti

crart we can see in

~

~

~

~

bull

- J shy

aJPraxiJlaUily 24000 F These c~raric terials bein cClls -je r~d run fr

this paint uprar d to carbide at 7JX)deg

In o r to illustrate raphi~ally soe fa~ tors 12t nt-r in the J

perfOlllaIlce of materials I have hre a Sii1Jla~d mt~el se~~nt on whch

thre~ turbine blades bull fi r s t on~ 5 abrica ted r (]]l a typi cal

hi~h-teaperatilre al loy the s econd one is a pure c~ralic terial and t~

third one is a tal-bon~ed cera~c t eria l which p- have te~d a cer best c inatl oos ot pure ceraric Jrials for high- tezperature use in

turbines ve be~ 1evelo~d by the at i cnal eau ~ ~ ds middotmder

ccntract to the bull e now pass the wheel se=l~ t h=ough the oxy- ace t yl ene torches which are set to operate at apprCixila tltly 27X)deg - As 0 1 can s~e

~rature allCTJ olade has gt~en ~l~i ~ilc the ~eaic and cerara l

blamp are un ged ceraal blade however gtoss es s es -_~a thr lec-anical

shock parti cularl y at ele7ated teIper atues e _et a c onten t

er~ls -J ccns ide to oe sui tabl e for sanr hih- teJgte rature

aDDlicati provided that the craic and ~tal ccnstit~nts aT be

ded s~ccess fally tensive bvesti~tions are IDc iTa here to 1ete ri1e

the Cas ie factors affectinz the bonding a=d s~t-e s t1~ we t tng of the laquo

cerazric and th tal Toois such as elctrCfl- ifra~ticn irs tr-nn~s Le

1CTftd to de the na t ure of the la eS eYistin on the siTface of the

rticles cit e up the cera=al otoicro-ra-hs a I cbtaind

at opt ical gnificatims up to 15)) diaeters to stu7 the rti cles and

the er in which they oond ieraD4ls are relatively nw terlals but

~middot lr-a thev have shOllD eJcellen t Iva ted te shy pera tUIs d we shall c Jill to inv~sti~ate he as rapmiddotdly as possille

~

laquo

~

lt

~

-

~Cials rct have 2sirable_higt- te_ Ie c~s

10 4 used ~caU8~ hav~ Cor - c_ onatioo properti~s

In cr~r to v~r -hs isa

a ti1s d~veb~d wi fu plusmn~ inac al a5ss tance ani Imd~rrotec~ive c~ra=ic

t~~ s~nsors~i 0 tee IvS~ ~I ati 7Ial ~~au ~

f the orote~ti thus aifcrd is Ll the nezt de=O-tsta~on ~~ we

to ~~ has cen ivn ilave two cars f

rot-=~tiV~ c ir n tho a JPlca ton 0 --a~e ~i~zng

~ a~ lIi L

1~ 1P- notic~ ta t th~ bc~ ~a t has not ~~n s

r sLlts the caials rOlf il ~ ~ccain~ porJS ard ~S~~ its str~nmiddot-

The oth~r bar as lOll will see la~r has r~taine s shdpe and has su~ red

no apparent loss in str~n~th

_rtlJ~lr L h~~~rtt a~va ~e in ce=-aic and c~ra-a -verials s J-er

1 s ~-r tie s ~rial9 or hi7h- te3prature applcatioos haV

s~ci~ic 6a7it s r~pounding to 8 er alicJ he o ~r hand have

spe~i~i~ Era~ite s ralging ro~ 2 to 5 and are in~ ~~=iate with

speci ic =-ra~~izs tl n ce rr- to 7 TIris r ~T 7S in two VJI7

desiraSl e e~e~t3 First th~ e of cer ltllCS or era-als wcJlc r edu=e

~th~ r - all f e aircraft propulsi31 S7Sve ~cor ~ or

appli cati ons wtore he s ss is d~ t~ned i C~- tr -al o~e or

Axalpl tllbin~ ~lad~s th~ stss Will ~ lm~ ~~or t~ l~ --n-rr r t~rials

middot t is thlS not n~c~ssar- or t -tra l to Je ~1~ as hi~

stresss be ~rial can siad oJ cccause its s~ _i ~ht r tio is

hih

ro

~

~

- gt shy

~ ~arlr a rtP-pts to lSe c~ral cs lI~ ~ari9~ ~ ~ Oor t~Ilal

s~ ~~~~~r i e s 0 ~~~s~ ~tera~s l thol~ ES e c~~ot elual th~

~

ad __ S10c prc~~rt~s o ~ I s las i r07~Il-JS ~a1 dd d ve ~~nt~~Ci~

in the ~~ ~21 s~ ~i ~~~~~ tie 9 ~ c~ rcLics or exa b the ~1l-1n nm

a se nver5OS ~ zi~c ~ ~ ~ u~ S lp~eSS~ ~ ~7 D r r a i1itions of

-J ~~ 3 a~s =J-ov~~ ~~~r7z1 soc~ C ~t~ s -c ci- strate J

in e-is l_r rae c~ a~ 55 at ) )~p ~ ~~ ar lsn~hin~ W~ notic~

t ~ac s~~ter illus at~ t~~t ~~v~ ~~~~~l

shy r -)~r -= s can re Ecmiddoted in cara- i c a ~als ac -a arial ~

~~~~ c ~s -~7al sX I r~3 isa1ce ar =- 5 t~e ~3e c t t ha t 1ie

r~ _r~st ~a ~ ~~~

~ ~ f_ ~iatv__ 0 -_ s ~ En ii ~i lt hshy ~-r sap s 7~ ~

- - ___ r r- _J _ _ C1 ~ oJ c J ~ ~ is a ~- ~lj O~ 2middot1a w t- the n~1J

~~iU~3 r~ ~~3~ -lt J ~ a ~w -a~rial _n-3 a~ _ isola- a

~ L~~3-~l- s-t~ ~d ~1~n~ - r ts w~c ~~l~ _ ~n a ~~~a~d ro

~~~~~c =a~~~als -es~ rs 3~ ot ngc~ssail- d~v~ 10~i to t~ Oint

-middot~h~re -~~ 1till ~_ sta~ 1gt1 ~ ~1 2 L1 ~ ~ra~O middotJJt th~r 10 indicat~

lt h~ f~~s i lt middot ~ ~~~~~in- ~~rts fro c ~ a ~~ ~ ~ -~ 15 - LlJ ~n~ral

i- -_ - shyOv~ __ -L_ fa ~ ~~ ~a~~ tr= _ _ ~ t~s - cc s~s -~ C3stin 7

s~-ri -j C ~3 _= ~1- 3~ ~s 1~1 ~ _ e lasi - la-e

~~~-lt 3O ~ r~~ ~2 pl i _ - ~s a~ =-1 this -- ~-~ ~ 2~e _~tho shy ziss o~ ~~ ~ 1 -~~ -a t rJ 2r O O~ a~j s l~r-alte r

~ l_5 S1OW1 ~~ rJ tis th lL _- o~ aMcatin~e

__ J t a - i3 a ~ )ir -- )l bull -~ - -rs~ C~ ~~iallj7 ~ir~ ~te-

lr i~i - ~n- f=~ ish ~~~in~ ~-s rl middot -Lpl icates tal

- a l cO3~~~~tlJ ~aciliti~5 c~ ~aailr a7~labl~

~ I

~

~

- gt shy

~ ~arlr a rtP-pts to lSe c~ral cs lI~ ~ari9~ ~ ~ Oor t~Ilal

s~ ~~~~~r i e s 0 ~~~s~ ~tera~s l thol~ ES e c~~ot elual th~

~

ad __ S10c prc~~rt~s o ~ I s las i r07~Il-JS ~a1 dd d ve ~~nt~~Ci~

in the ~~ ~21 s~ ~i ~~~~~ tie 9 ~ c~ rcLics or exa b the ~1l-1n nm

a se nver5OS ~ zi~c ~ ~ ~ u~ S lp~eSS~ ~ ~7 D r r a i1itions of

-J ~~ 3 a~s =J-ov~~ ~~~r7z1 soc~ C ~t~ s -c ci- strate J

in e-is l_r rae c~ a~ 55 at ) )~p ~ ~~ ar lsn~hin~ W~ notic~

t ~ac s~~ter illus at~ t~~t ~~v~ ~~~~~l

shy r -)~r -= s can re Ecmiddoted in cara- i c a ~als ac -a arial ~

~~~~ c ~s -~7al sX I r~3 isa1ce ar =- 5 t~e ~3e c t t ha t 1ie

r~ _r~st ~a ~ ~~~

~ ~ f_ ~iatv__ 0 -_ s ~ En ii ~i lt hshy ~-r sap s 7~ ~

- - ___ r r- _J _ _ C1 ~ oJ c J ~ ~ is a ~- ~lj O~ 2middot1a w t- the n~1J

~~iU~3 r~ ~~3~ -lt J ~ a ~w -a~rial _n-3 a~ _ isola- a

~ L~~3-~l- s-t~ ~d ~1~n~ - r ts w~c ~~l~ _ ~n a ~~~a~d ro

~~~~~c =a~~~als -es~ rs 3~ ot ngc~ssail- d~v~ 10~i to t~ Oint

-middot~h~re -~~ 1till ~_ sta~ 1gt1 ~ ~1 2 L1 ~ ~ra~O middotJJt th~r 10 indicat~

lt h~ f~~s i lt middot ~ ~~~~~in- ~~rts fro c ~ a ~~ ~ ~ -~ 15 - LlJ ~n~ral

i- -_ - shyOv~ __ -L_ fa ~ ~~ ~a~~ tr= _ _ ~ t~s - cc s~s -~ C3stin 7

s~-ri -j C ~3 _= ~1- 3~ ~s 1~1 ~ _ e lasi - la-e

~~~-lt 3O ~ r~~ ~2 pl i _ - ~s a~ =-1 this -- ~-~ ~ 2~e _~tho shy ziss o~ ~~ ~ 1 -~~ -a t rJ 2r O O~ a~j s l~r-alte r

~ l_5 S1OW1 ~~ rJ tis th lL _- o~ aMcatin~e

__ J t a - i3 a ~ )ir -- )l bull -~ - -rs~ C~ ~~iallj7 ~ir~ ~te-

lr i~i - ~n- f=~ ish ~~~in~ ~-s rl middot -Lpl icates tal

- a l cO3~~~~tlJ ~aciliti~5 c~ ~aailr a7~labl~

~ I

- 6 shy

sla Yaae8 turbotrupsrcbarger buck-ta an I-ul tshOllll ell ~

1 er __ in th1a

III ccmclaiCD we are iJlTe8t1gating the oasic soects of ratP-rials or

in aircraft iDclul alloys cellbics an1 + terial a comiddot

biDatiCD of _tal8 and ceramics called ceraaals

t

bull

~

1

1~

I

8S VIBRAlIOH EIFIElT PCR FIRS ~mUAL nSPPpoundTIO

October 8 9 and 10 1947 by S S Manson

DnROWCTICN

In an aircraft engine ~ 19bt st be combined with abeomte inshy

euranee against structural failure _ An iaportant phase of the research at

e IMA is therefore the determination of the criteria for structural

failure and a search for the _tllOds tomiddot increase the life of an engine while

the S8IIe tille reducing its weight and increasing its eftic1enC7 and power

output This phase of the research is known as stress and Vibration I

all l1A1t r ks to those aspects of the research relating to turbine

disks and turbine and coaresBor blades

TtRBIIE DIS

In turbine disks we are ccncerned with t major stress problelll8 The

irst of these 18 ria cracking which ico~n in disks in which the blades

are welded to the wheel It has been found that in such disks cracks occur

at the bases between the blades after periods ot operation Dch shorter than

bulluld ordinarily be c)osidered the reasonable Ute o t~ wheel Analytical

research has linked these cracks with high thelllal stresses due to hot -

operation plastic low that results froJ the high therDa1 stresses and a

tr~ss concentration inherent at the ba~e of tmiddothe blades Here is the apshy

p-ox1ate length of the cracks present of the blades of the disk

n the disk was removed froa service It was considered that this was a

dapgeroll8 length he Gna1rtical research indicated that it wuld be possible

to ~opagate the cracks bJ the ap l1cation ot successive heating and cooling I

cycles and here are BOI8 of the rcpagated cracks obtained by such crcles

ot tbeJlOtent1a1 eolutlol18 indicated by t~e analysis is the raval ot

Cf3

-- - --- shy

- 2 shy

bull

the stress concentration ~ drilling II holes at the bases ot the blades (

Pere are some cf the holes that were drilled prior to the aplicat ion of tne

heating cyc les and it will be seen that very few cracks propagated beyond

the holes The Derit of this type of solution has yet to be further tested

and we are building large spin ~its mere disks such as these will be able

to be tested under conditions of full speed and temperature gradient These

ts will also be used to middottest the cerit of a number of other indicated

lutions

The second problem associ ated with disks is that of disk burstingbull

Di9k bursting has occurred in practice but one of the cajor r easons f or

studying it is the desire to reduce the weight of the lIheel a step that

increase the number of this type of failure The results ot a pre1ia1nary

investigation of disk bursting are shown on this panel Here we were studying ~

he ef fect of ductility or the amount of stretch that the _ terial is capble

of withstanding without ruptm-e Here is a disk with a VI high ductility

Characteristic of its fracture are ~he low nucber of failed pieces and the

o fact that the lane of fracture is inclined at an angle of 45 to t he thickshy

ness of the disk As we decrease the ductility the nuber of fractured

pieces increases and t he plane I)f fr acture is perpendicular to thickness

of the disk The problem requ ires consider able additional- investigation and th~ pit s t hat will be used for t he r im cracking investigations will also

be used for testineuro ge disks such as shown on the other panel in disk bursting investigationsbull

)UMiDUSCOPIC VTIIUlIO

I should like to leaTe now the subject ot turbine disks and go on to

-

if

- 3 shy

r and turbine blades In this case we are concerned with blade

V1bration Vibration is a DOYeDent back and torth or the blade which re-

Its in aGme c in critical stress and fracture of the blade I t is

treacherous type of stress condition f irst because at any one time the

rese may DOt ~ great enough to campuae fracture but over a period of time

the ac lated e cause fracture wit hout nrning It is a l so

treacberou because so little is Imom about the causes for blade vitI-ation

~ ~ It fIl17 be present in engines but not in others and in any one engine r

be Jresent under SOlIe conditions but not under others It has taken

a good deal of research to gain eYen an e ntar understanding or blade

vibration

UJt _ dsonstrate a blade in a condition or vibration - Here is a

J

blade which has vibrational characteristics quite similar to t ho se of t urshy

l bine COIltressor blades except that i t is constructed to a JlUch larger

scale tban orcl1nary blades Connected to the end of the blade is an

electronic exc iter br which can vary the excttation llIIpulses until t he

natural frequency of the blade is r eached The blade will t hen go irto a

bullcondition of vitration The vibration i s too r apid to view with t he naked

and _ therefore uae stroboscopic light to stuctr it This light flickers

on and off at apJrOx1ateq the s frequency as t he blade vi

~ therefore JUkes the blAde appear to be standing still or to vi brate slowl y-

while in reality- i t is 1brati~ verf rap~

ltI

vibration 1Ou have seen is a verf simple t~ of vibr ation At any-

point along the length of the blade the entire section r e l y moving up

and down re are other IlUcb more complicated types of vibration and 0

IS

- h shy

of the first pob lens in the science is to categorize these yitrations This

is done h7 the use of mat we call sand patterns I ehall srinkle sand oyer

the entire blade and then vary the excitation trequenq on the blade Wltil

i t begins to vibrate in one ot its IIOre complex odes The sand particles

boWlce aroWld and naturally tend to pile up at the locations ot ainbIua vibrashy

t io Here is one jat tern I now increase the excitation trequeIlC7 until

I reach another vibr ational requenq ot the blade the sand bounces around

~ in another t)attern and again in another pattern In this way we can class itr

the vibrational characteristics of a~ blade according to t he frequen~ of

vibration and the stress condition in the bladB at anyone fr equellC7

HIGH TEJ~E STRAr~ I

The next p-obl en is to learn which types ot vibration actually do exist

in an engine For this FWpose _ e use of wire strain g~es The strain

gage consists nerely of a strand 01 resistance wire 1Ihich is cemented onto

he blade As this blade vibrates it changes minutely the elect rical reshy

sistance ot t he wire By measuring the change in electrical resistance the

amount and type ot vibration can be determined We had had a great deal ot

experience with wire-resistar1 ~

strain gages as applied to r eciprocati

ng

enpoundines When we started to study turbines we learned that the strain gages

t~at had tormerly been used were suitable tor the terlperatures of hCXLsocP F

revicusly encountered but were certainly not suitable tor the temperat ures

in the range ot 1500 o

- 180(0

F which were now ot interest After considerable

~

laquo

r esearch we learned however that by using th suitable I18terials and lOst

imjOr tant by using proper electronic c ircuits it was possible to find strain 0

gages capable ot withstanding 1500 -180( F I shoulc1 like to demonstrate

to you the operation of Slch a strain Z8gs Here 118 have a strain ~age ounted

I

8S VIBRAlIOH EIFIElT PCR FIRS ~mUAL nSPPpoundTIO

October 8 9 and 10 1947 by S S Manson

DnROWCTICN

In an aircraft engine ~ 19bt st be combined with abeomte inshy

euranee against structural failure _ An iaportant phase of the research at

e IMA is therefore the determination of the criteria for structural

failure and a search for the _tllOds tomiddot increase the life of an engine while

the S8IIe tille reducing its weight and increasing its eftic1enC7 and power

output This phase of the research is known as stress and Vibration I

all l1A1t r ks to those aspects of the research relating to turbine

disks and turbine and coaresBor blades

TtRBIIE DIS

In turbine disks we are ccncerned with t major stress problelll8 The

irst of these 18 ria cracking which ico~n in disks in which the blades

are welded to the wheel It has been found that in such disks cracks occur

at the bases between the blades after periods ot operation Dch shorter than

bulluld ordinarily be c)osidered the reasonable Ute o t~ wheel Analytical

research has linked these cracks with high thelllal stresses due to hot -

operation plastic low that results froJ the high therDa1 stresses and a

tr~ss concentration inherent at the ba~e of tmiddothe blades Here is the apshy

p-ox1ate length of the cracks present of the blades of the disk

n the disk was removed froa service It was considered that this was a

dapgeroll8 length he Gna1rtical research indicated that it wuld be possible

to ~opagate the cracks bJ the ap l1cation ot successive heating and cooling I

cycles and here are BOI8 of the rcpagated cracks obtained by such crcles

ot tbeJlOtent1a1 eolutlol18 indicated by t~e analysis is the raval ot

Cf3

-- - --- shy

- 2 shy

bull

the stress concentration ~ drilling II holes at the bases ot the blades (

Pere are some cf the holes that were drilled prior to the aplicat ion of tne

heating cyc les and it will be seen that very few cracks propagated beyond

the holes The Derit of this type of solution has yet to be further tested

and we are building large spin ~its mere disks such as these will be able

to be tested under conditions of full speed and temperature gradient These

ts will also be used to middottest the cerit of a number of other indicated

lutions

The second problem associ ated with disks is that of disk burstingbull

Di9k bursting has occurred in practice but one of the cajor r easons f or

studying it is the desire to reduce the weight of the lIheel a step that

increase the number of this type of failure The results ot a pre1ia1nary

investigation of disk bursting are shown on this panel Here we were studying ~

he ef fect of ductility or the amount of stretch that the _ terial is capble

of withstanding without ruptm-e Here is a disk with a VI high ductility

Characteristic of its fracture are ~he low nucber of failed pieces and the

o fact that the lane of fracture is inclined at an angle of 45 to t he thickshy

ness of the disk As we decrease the ductility the nuber of fractured

pieces increases and t he plane I)f fr acture is perpendicular to thickness

of the disk The problem requ ires consider able additional- investigation and th~ pit s t hat will be used for t he r im cracking investigations will also

be used for testineuro ge disks such as shown on the other panel in disk bursting investigationsbull

)UMiDUSCOPIC VTIIUlIO

I should like to leaTe now the subject ot turbine disks and go on to

-

if

- 3 shy

r and turbine blades In this case we are concerned with blade

V1bration Vibration is a DOYeDent back and torth or the blade which re-

Its in aGme c in critical stress and fracture of the blade I t is

treacherous type of stress condition f irst because at any one time the

rese may DOt ~ great enough to campuae fracture but over a period of time

the ac lated e cause fracture wit hout nrning It is a l so

treacberou because so little is Imom about the causes for blade vitI-ation

~ ~ It fIl17 be present in engines but not in others and in any one engine r

be Jresent under SOlIe conditions but not under others It has taken

a good deal of research to gain eYen an e ntar understanding or blade

vibration

UJt _ dsonstrate a blade in a condition or vibration - Here is a

J

blade which has vibrational characteristics quite similar to t ho se of t urshy

l bine COIltressor blades except that i t is constructed to a JlUch larger

scale tban orcl1nary blades Connected to the end of the blade is an

electronic exc iter br which can vary the excttation llIIpulses until t he

natural frequency of the blade is r eached The blade will t hen go irto a

bullcondition of vitration The vibration i s too r apid to view with t he naked

and _ therefore uae stroboscopic light to stuctr it This light flickers

on and off at apJrOx1ateq the s frequency as t he blade vi

~ therefore JUkes the blAde appear to be standing still or to vi brate slowl y-

while in reality- i t is 1brati~ verf rap~

ltI

vibration 1Ou have seen is a verf simple t~ of vibr ation At any-

point along the length of the blade the entire section r e l y moving up

and down re are other IlUcb more complicated types of vibration and 0

IS

- h shy

of the first pob lens in the science is to categorize these yitrations This

is done h7 the use of mat we call sand patterns I ehall srinkle sand oyer

the entire blade and then vary the excitation trequenq on the blade Wltil

i t begins to vibrate in one ot its IIOre complex odes The sand particles

boWlce aroWld and naturally tend to pile up at the locations ot ainbIua vibrashy

t io Here is one jat tern I now increase the excitation trequeIlC7 until

I reach another vibr ational requenq ot the blade the sand bounces around

~ in another t)attern and again in another pattern In this way we can class itr

the vibrational characteristics of a~ blade according to t he frequen~ of

vibration and the stress condition in the bladB at anyone fr equellC7

HIGH TEJ~E STRAr~ I

The next p-obl en is to learn which types ot vibration actually do exist

in an engine For this FWpose _ e use of wire strain g~es The strain

gage consists nerely of a strand 01 resistance wire 1Ihich is cemented onto

he blade As this blade vibrates it changes minutely the elect rical reshy

sistance ot t he wire By measuring the change in electrical resistance the

amount and type ot vibration can be determined We had had a great deal ot

experience with wire-resistar1 ~

strain gages as applied to r eciprocati

ng

enpoundines When we started to study turbines we learned that the strain gages

t~at had tormerly been used were suitable tor the terlperatures of hCXLsocP F

revicusly encountered but were certainly not suitable tor the temperat ures

in the range ot 1500 o

- 180(0

F which were now ot interest After considerable

~

laquo

r esearch we learned however that by using th suitable I18terials and lOst

imjOr tant by using proper electronic c ircuits it was possible to find strain 0

gages capable ot withstanding 1500 -180( F I shoulc1 like to demonstrate

to you the operation of Slch a strain Z8gs Here 118 have a strain ~age ounted

8S VIBRAlIOH EIFIElT PCR FIRS ~mUAL nSPPpoundTIO

October 8 9 and 10 1947 by S S Manson

DnROWCTICN

In an aircraft engine ~ 19bt st be combined with abeomte inshy

euranee against structural failure _ An iaportant phase of the research at

e IMA is therefore the determination of the criteria for structural

failure and a search for the _tllOds tomiddot increase the life of an engine while

the S8IIe tille reducing its weight and increasing its eftic1enC7 and power

output This phase of the research is known as stress and Vibration I

all l1A1t r ks to those aspects of the research relating to turbine

disks and turbine and coaresBor blades

TtRBIIE DIS

In turbine disks we are ccncerned with t major stress problelll8 The

irst of these 18 ria cracking which ico~n in disks in which the blades

are welded to the wheel It has been found that in such disks cracks occur

at the bases between the blades after periods ot operation Dch shorter than

bulluld ordinarily be c)osidered the reasonable Ute o t~ wheel Analytical

research has linked these cracks with high thelllal stresses due to hot -

operation plastic low that results froJ the high therDa1 stresses and a

tr~ss concentration inherent at the ba~e of tmiddothe blades Here is the apshy

p-ox1ate length of the cracks present of the blades of the disk

n the disk was removed froa service It was considered that this was a

dapgeroll8 length he Gna1rtical research indicated that it wuld be possible

to ~opagate the cracks bJ the ap l1cation ot successive heating and cooling I

cycles and here are BOI8 of the rcpagated cracks obtained by such crcles

ot tbeJlOtent1a1 eolutlol18 indicated by t~e analysis is the raval ot

Cf3

-- - --- shy

- 2 shy

bull

the stress concentration ~ drilling II holes at the bases ot the blades (

Pere are some cf the holes that were drilled prior to the aplicat ion of tne

heating cyc les and it will be seen that very few cracks propagated beyond

the holes The Derit of this type of solution has yet to be further tested

and we are building large spin ~its mere disks such as these will be able

to be tested under conditions of full speed and temperature gradient These

ts will also be used to middottest the cerit of a number of other indicated

lutions

The second problem associ ated with disks is that of disk burstingbull

Di9k bursting has occurred in practice but one of the cajor r easons f or

studying it is the desire to reduce the weight of the lIheel a step that

increase the number of this type of failure The results ot a pre1ia1nary

investigation of disk bursting are shown on this panel Here we were studying ~

he ef fect of ductility or the amount of stretch that the _ terial is capble

of withstanding without ruptm-e Here is a disk with a VI high ductility

Characteristic of its fracture are ~he low nucber of failed pieces and the

o fact that the lane of fracture is inclined at an angle of 45 to t he thickshy

ness of the disk As we decrease the ductility the nuber of fractured

pieces increases and t he plane I)f fr acture is perpendicular to thickness

of the disk The problem requ ires consider able additional- investigation and th~ pit s t hat will be used for t he r im cracking investigations will also

be used for testineuro ge disks such as shown on the other panel in disk bursting investigationsbull

)UMiDUSCOPIC VTIIUlIO

I should like to leaTe now the subject ot turbine disks and go on to

-

if

- 3 shy

r and turbine blades In this case we are concerned with blade

V1bration Vibration is a DOYeDent back and torth or the blade which re-

Its in aGme c in critical stress and fracture of the blade I t is

treacherous type of stress condition f irst because at any one time the

rese may DOt ~ great enough to campuae fracture but over a period of time

the ac lated e cause fracture wit hout nrning It is a l so

treacberou because so little is Imom about the causes for blade vitI-ation

~ ~ It fIl17 be present in engines but not in others and in any one engine r

be Jresent under SOlIe conditions but not under others It has taken

a good deal of research to gain eYen an e ntar understanding or blade

vibration

UJt _ dsonstrate a blade in a condition or vibration - Here is a

J

blade which has vibrational characteristics quite similar to t ho se of t urshy

l bine COIltressor blades except that i t is constructed to a JlUch larger

scale tban orcl1nary blades Connected to the end of the blade is an

electronic exc iter br which can vary the excttation llIIpulses until t he

natural frequency of the blade is r eached The blade will t hen go irto a

bullcondition of vitration The vibration i s too r apid to view with t he naked

and _ therefore uae stroboscopic light to stuctr it This light flickers

on and off at apJrOx1ateq the s frequency as t he blade vi

~ therefore JUkes the blAde appear to be standing still or to vi brate slowl y-

while in reality- i t is 1brati~ verf rap~

ltI

vibration 1Ou have seen is a verf simple t~ of vibr ation At any-

point along the length of the blade the entire section r e l y moving up

and down re are other IlUcb more complicated types of vibration and 0

IS

- h shy

of the first pob lens in the science is to categorize these yitrations This

is done h7 the use of mat we call sand patterns I ehall srinkle sand oyer

the entire blade and then vary the excitation trequenq on the blade Wltil

i t begins to vibrate in one ot its IIOre complex odes The sand particles

boWlce aroWld and naturally tend to pile up at the locations ot ainbIua vibrashy

t io Here is one jat tern I now increase the excitation trequeIlC7 until

I reach another vibr ational requenq ot the blade the sand bounces around

~ in another t)attern and again in another pattern In this way we can class itr

the vibrational characteristics of a~ blade according to t he frequen~ of

vibration and the stress condition in the bladB at anyone fr equellC7

HIGH TEJ~E STRAr~ I

The next p-obl en is to learn which types ot vibration actually do exist

in an engine For this FWpose _ e use of wire strain g~es The strain

gage consists nerely of a strand 01 resistance wire 1Ihich is cemented onto

he blade As this blade vibrates it changes minutely the elect rical reshy

sistance ot t he wire By measuring the change in electrical resistance the

amount and type ot vibration can be determined We had had a great deal ot

experience with wire-resistar1 ~

strain gages as applied to r eciprocati

ng

enpoundines When we started to study turbines we learned that the strain gages

t~at had tormerly been used were suitable tor the terlperatures of hCXLsocP F

revicusly encountered but were certainly not suitable tor the temperat ures

in the range ot 1500 o

- 180(0

F which were now ot interest After considerable

~

laquo

r esearch we learned however that by using th suitable I18terials and lOst

imjOr tant by using proper electronic c ircuits it was possible to find strain 0

gages capable ot withstanding 1500 -180( F I shoulc1 like to demonstrate

to you the operation of Slch a strain Z8gs Here 118 have a strain ~age ounted

-- - --- shy

- 2 shy

bull

the stress concentration ~ drilling II holes at the bases ot the blades (

Pere are some cf the holes that were drilled prior to the aplicat ion of tne

heating cyc les and it will be seen that very few cracks propagated beyond

the holes The Derit of this type of solution has yet to be further tested

and we are building large spin ~its mere disks such as these will be able

to be tested under conditions of full speed and temperature gradient These

ts will also be used to middottest the cerit of a number of other indicated

lutions

The second problem associ ated with disks is that of disk burstingbull

Di9k bursting has occurred in practice but one of the cajor r easons f or

studying it is the desire to reduce the weight of the lIheel a step that

increase the number of this type of failure The results ot a pre1ia1nary

investigation of disk bursting are shown on this panel Here we were studying ~

he ef fect of ductility or the amount of stretch that the _ terial is capble

of withstanding without ruptm-e Here is a disk with a VI high ductility

Characteristic of its fracture are ~he low nucber of failed pieces and the

o fact that the lane of fracture is inclined at an angle of 45 to t he thickshy

ness of the disk As we decrease the ductility the nuber of fractured

pieces increases and t he plane I)f fr acture is perpendicular to thickness

of the disk The problem requ ires consider able additional- investigation and th~ pit s t hat will be used for t he r im cracking investigations will also

be used for testineuro ge disks such as shown on the other panel in disk bursting investigationsbull

)UMiDUSCOPIC VTIIUlIO

I should like to leaTe now the subject ot turbine disks and go on to

-

if

- 3 shy

r and turbine blades In this case we are concerned with blade

V1bration Vibration is a DOYeDent back and torth or the blade which re-

Its in aGme c in critical stress and fracture of the blade I t is

treacherous type of stress condition f irst because at any one time the

rese may DOt ~ great enough to campuae fracture but over a period of time

the ac lated e cause fracture wit hout nrning It is a l so

treacberou because so little is Imom about the causes for blade vitI-ation

~ ~ It fIl17 be present in engines but not in others and in any one engine r

be Jresent under SOlIe conditions but not under others It has taken

a good deal of research to gain eYen an e ntar understanding or blade

vibration

UJt _ dsonstrate a blade in a condition or vibration - Here is a

J

blade which has vibrational characteristics quite similar to t ho se of t urshy

l bine COIltressor blades except that i t is constructed to a JlUch larger

scale tban orcl1nary blades Connected to the end of the blade is an

electronic exc iter br which can vary the excttation llIIpulses until t he

natural frequency of the blade is r eached The blade will t hen go irto a

bullcondition of vitration The vibration i s too r apid to view with t he naked

and _ therefore uae stroboscopic light to stuctr it This light flickers

on and off at apJrOx1ateq the s frequency as t he blade vi

~ therefore JUkes the blAde appear to be standing still or to vi brate slowl y-

while in reality- i t is 1brati~ verf rap~

ltI

vibration 1Ou have seen is a verf simple t~ of vibr ation At any-

point along the length of the blade the entire section r e l y moving up

and down re are other IlUcb more complicated types of vibration and 0

IS

- h shy

of the first pob lens in the science is to categorize these yitrations This

is done h7 the use of mat we call sand patterns I ehall srinkle sand oyer

the entire blade and then vary the excitation trequenq on the blade Wltil

i t begins to vibrate in one ot its IIOre complex odes The sand particles

boWlce aroWld and naturally tend to pile up at the locations ot ainbIua vibrashy

t io Here is one jat tern I now increase the excitation trequeIlC7 until

I reach another vibr ational requenq ot the blade the sand bounces around

~ in another t)attern and again in another pattern In this way we can class itr

the vibrational characteristics of a~ blade according to t he frequen~ of

vibration and the stress condition in the bladB at anyone fr equellC7

HIGH TEJ~E STRAr~ I

The next p-obl en is to learn which types ot vibration actually do exist

in an engine For this FWpose _ e use of wire strain g~es The strain

gage consists nerely of a strand 01 resistance wire 1Ihich is cemented onto

he blade As this blade vibrates it changes minutely the elect rical reshy

sistance ot t he wire By measuring the change in electrical resistance the

amount and type ot vibration can be determined We had had a great deal ot

experience with wire-resistar1 ~

strain gages as applied to r eciprocati

ng

enpoundines When we started to study turbines we learned that the strain gages

t~at had tormerly been used were suitable tor the terlperatures of hCXLsocP F

revicusly encountered but were certainly not suitable tor the temperat ures

in the range ot 1500 o

- 180(0

F which were now ot interest After considerable

~

laquo

r esearch we learned however that by using th suitable I18terials and lOst

imjOr tant by using proper electronic c ircuits it was possible to find strain 0

gages capable ot withstanding 1500 -180( F I shoulc1 like to demonstrate

to you the operation of Slch a strain Z8gs Here 118 have a strain ~age ounted

- 3 shy

r and turbine blades In this case we are concerned with blade

V1bration Vibration is a DOYeDent back and torth or the blade which re-

Its in aGme c in critical stress and fracture of the blade I t is

treacherous type of stress condition f irst because at any one time the

rese may DOt ~ great enough to campuae fracture but over a period of time

the ac lated e cause fracture wit hout nrning It is a l so

treacberou because so little is Imom about the causes for blade vitI-ation

~ ~ It fIl17 be present in engines but not in others and in any one engine r

be Jresent under SOlIe conditions but not under others It has taken

a good deal of research to gain eYen an e ntar understanding or blade

vibration

UJt _ dsonstrate a blade in a condition or vibration - Here is a

J

blade which has vibrational characteristics quite similar to t ho se of t urshy

l bine COIltressor blades except that i t is constructed to a JlUch larger

scale tban orcl1nary blades Connected to the end of the blade is an

electronic exc iter br which can vary the excttation llIIpulses until t he

natural frequency of the blade is r eached The blade will t hen go irto a

bullcondition of vitration The vibration i s too r apid to view with t he naked

and _ therefore uae stroboscopic light to stuctr it This light flickers

on and off at apJrOx1ateq the s frequency as t he blade vi

~ therefore JUkes the blAde appear to be standing still or to vi brate slowl y-

while in reality- i t is 1brati~ verf rap~

ltI

vibration 1Ou have seen is a verf simple t~ of vibr ation At any-

point along the length of the blade the entire section r e l y moving up

and down re are other IlUcb more complicated types of vibration and 0

IS

- h shy

of the first pob lens in the science is to categorize these yitrations This

is done h7 the use of mat we call sand patterns I ehall srinkle sand oyer

the entire blade and then vary the excitation trequenq on the blade Wltil

i t begins to vibrate in one ot its IIOre complex odes The sand particles

boWlce aroWld and naturally tend to pile up at the locations ot ainbIua vibrashy

t io Here is one jat tern I now increase the excitation trequeIlC7 until

I reach another vibr ational requenq ot the blade the sand bounces around

~ in another t)attern and again in another pattern In this way we can class itr

the vibrational characteristics of a~ blade according to t he frequen~ of

vibration and the stress condition in the bladB at anyone fr equellC7

HIGH TEJ~E STRAr~ I

The next p-obl en is to learn which types ot vibration actually do exist

in an engine For this FWpose _ e use of wire strain g~es The strain

gage consists nerely of a strand 01 resistance wire 1Ihich is cemented onto

he blade As this blade vibrates it changes minutely the elect rical reshy

sistance ot t he wire By measuring the change in electrical resistance the

amount and type ot vibration can be determined We had had a great deal ot

experience with wire-resistar1 ~

strain gages as applied to r eciprocati

ng

enpoundines When we started to study turbines we learned that the strain gages

t~at had tormerly been used were suitable tor the terlperatures of hCXLsocP F

revicusly encountered but were certainly not suitable tor the temperat ures

in the range ot 1500 o

- 180(0

F which were now ot interest After considerable

~

laquo

r esearch we learned however that by using th suitable I18terials and lOst

imjOr tant by using proper electronic c ircuits it was possible to find strain 0

gages capable ot withstanding 1500 -180( F I shoulc1 like to demonstrate

to you the operation of Slch a strain Z8gs Here 118 have a strain ~age ounted

- h shy

of the first pob lens in the science is to categorize these yitrations This

is done h7 the use of mat we call sand patterns I ehall srinkle sand oyer

the entire blade and then vary the excitation trequenq on the blade Wltil

i t begins to vibrate in one ot its IIOre complex odes The sand particles

boWlce aroWld and naturally tend to pile up at the locations ot ainbIua vibrashy

t io Here is one jat tern I now increase the excitation trequeIlC7 until

I reach another vibr ational requenq ot the blade the sand bounces around

~ in another t)attern and again in another pattern In this way we can class itr

the vibrational characteristics of a~ blade according to t he frequen~ of

vibration and the stress condition in the bladB at anyone fr equellC7

HIGH TEJ~E STRAr~ I

The next p-obl en is to learn which types ot vibration actually do exist

in an engine For this FWpose _ e use of wire strain g~es The strain

gage consists nerely of a strand 01 resistance wire 1Ihich is cemented onto

he blade As this blade vibrates it changes minutely the elect rical reshy

sistance ot t he wire By measuring the change in electrical resistance the

amount and type ot vibration can be determined We had had a great deal ot

experience with wire-resistar1 ~

strain gages as applied to r eciprocati

ng

enpoundines When we started to study turbines we learned that the strain gages

t~at had tormerly been used were suitable tor the terlperatures of hCXLsocP F

revicusly encountered but were certainly not suitable tor the temperat ures

in the range ot 1500 o

- 180(0

F which were now ot interest After considerable

~

laquo

r esearch we learned however that by using th suitable I18terials and lOst

imjOr tant by using proper electronic c ircuits it was possible to find strain 0

gages capable ot withstanding 1500 -180( F I shoulc1 like to demonstrate

to you the operation of Slch a strain Z8gs Here 118 have a strain ~age ounted

- Sshy at the base on a typical turbine blade SUrrourvljng the blade is an inshy

ductlon beating coil This coil rov1des a rapidly fiuctuating magnetic

field around the gage and in 80 do~ induces eddy currents in the blade

ncb beat up to a Yery high value At the present t the blade in the

ovicinity of the gage is fairly close to ISco F Attached to the block

in ~1ch the gage is _lted is a 11 air turbine It I increase the air

preeaure the peed or the turbine ~reases and provides a mechanical ~

J

excitation mich men it reaches the natural frequency of t he bl ade

cau it to vibrate The rl~at1on of the blade is lfxiicated by the apshy

anee of a waYe on the oscillograph screen above the blade

~~ DOOBIE REFRACTlm

Yen when _ know about the presence of vibration the trequency of the

vibration and the characteristics of the vibration at the Parti cular freshy

- qulllc YtJry often we do not kD01l the source of t he excitation and therefor e

it is 1ampposs1ble to find a remedy In some cases the excitation y be

lleCban1cal as it was in this dsonstration In 80_ cases however the

Gcitatlon aerodynaaic t hat is it is due to flnctuat ion of air forces

on the bladll Ie have recently introduced the streaa1ng double retract ion bull

~ thod of flDid no into our r esearch in order to gain a better undershy

~ standing of the no phe~na that My cause vibration The equi1ll1ent for

tfi type of research consist of a ~urce of polarized light and a channel

in which a blade ccntour is suspended in a tluid consisting of bentonite clay

_ter Th~ fluid has the pecuUar Jroperty of double retraction in that

a beD of light passing through it bave one or more of its color COl1shy

PODe~S retarded 80 Uat the portion of the light that leaves the channel has

o~ that color co2lpgtnent of the entering tdte light which is not r etarded

17

- 6 shy

The r esult is a color pattern which rep-esents the condition of fluid no t= middot77 ~~~L~

in a very colorful and graphical manner It we turn on the equiPlent atbull

first s lowlY so that the flow around t he blade contour is stream] 1ned we

see the close adhererce of the f luid to the b lade contour Even at this

slow speed t here i s present a small amount of wiggling in the wake of the

blade and this fluct uation or f luid flow maJ produce excitation forces I

both on this b1ade and on arr blade that succeeds this b l ade It we now

increase the rate of rIow the fluid creaks away from the model a1d t he ~

flow becomes turbulent 7he exc itation force under this condition are

r e vo1ent The colCr pat tern becomes somewhat more diffuse because the

flow is so r apid that the various colors are interacting with cne another

prcducing what appears to th~ eye to be white light It 118 had been able

to use stroboscopic light as we did in the case or the vibrating blade

we would be able to see the Jrecise luctuation of the fiuid flow Unshy

fortunately stroboscopi c l ight does not project very well but we have b7

~rect observation studied the pattern of flo If we now further increase

the rate of flow the flo pattern disappears a lmost entirelJ as far as the

naked eye is concer ned but the exc itation forces are 80 vio l ent as to ake

the b lade flutter vehecently

CCUCLUSION

Gentlemen I have demonstr ated several of the t echniques that we use in

the basic r esearch of stres s a~d vibration In the last analysis however

it is necessary act ually to get into the turbine or pre ssor in order to

stuctr the existing phenomena Here we have a compressor that was 1nstruenteci

with strain gages and ru under lull operating condi tione bave l earned

from this compressor the effeets of such pbenoaena as 8I1rging and tbe IreHDCe

f(

- 6 shy

The r esult is a color pattern which rep-esents the condition of fluid no t= middot77 ~~~L~

in a very colorful and graphical manner It we turn on the equiPlent atbull

first s lowlY so that the flow around t he blade contour is stream] 1ned we

see the close adhererce of the f luid to the b lade contour Even at this

slow speed t here i s present a small amount of wiggling in the wake of the

blade and this fluct uation or f luid flow maJ produce excitation forces I

both on this b1ade and on arr blade that succeeds this b l ade It we now

increase the rate of rIow the fluid creaks away from the model a1d t he ~

flow becomes turbulent 7he exc itation force under this condition are

r e vo1ent The colCr pat tern becomes somewhat more diffuse because the

flow is so r apid that the various colors are interacting with cne another

prcducing what appears to th~ eye to be white light It 118 had been able

to use stroboscopic light as we did in the case or the vibrating blade

we would be able to see the Jrecise luctuation of the fiuid flow Unshy

fortunately stroboscopi c l ight does not project very well but we have b7

~rect observation studied the pattern of flo If we now further increase

the rate of flow the flo pattern disappears a lmost entirelJ as far as the

naked eye is concer ned but the exc itation forces are 80 vio l ent as to ake

the b lade flutter vehecently

CCUCLUSION

Gentlemen I have demonstr ated several of the t echniques that we use in

the basic r esearch of stres s a~d vibration In the last analysis however

it is necessary act ually to get into the turbine or pre ssor in order to

stuctr the existing phenomena Here we have a compressor that was 1nstruenteci

with strain gages and ru under lull operating condi tione bave l earned

from this compressor the effeets of such pbenoaena as 8I1rging and tbe IreHDCe

f(

-7 shy of high pressure ratio Here is a turbine which was instrumented with highshy

rature strain gages and operated under hot gas cOnditions We have

fro it the effects on the rlbration of such factors as the l1UJIber

of collbastion ch-bers )(any of the results of these tests have already

been ~b1i8bed in lac reX)rts her r esults are in Ule process of JQbshy

lication Much research raains to be done It is hoped that tliis research

will Jrovicie the necessary data to aake possible the realization of the

re efficient and powerful engines of the future

T

bull

SSM

I

1

LL

bull

LL

bull