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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON. D.C. 20546
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L o t: i (CATEOORYI Materials f o r t h e Mach 3 Supersonic Transport
t R t R G C 1 George C . Deutsch
Chief, Materials Research Program
LI - - 1 2 I
rn Office of Advaxed Research and Technology M i Z i 5 ;
2 0
0 ; F Presented at the bhterials Division = E Q P
: .Iz American O ~ h m c e Association
o r n I T a + ( 3 0 Dayton, Chici, St.;?tember 23-25, 1964 The program t h a t I w i l l present has b e w - j o i n t e f f o r t of t h e NASA, t h e Air Force, axla the FAA. It i s a l i t t l e ak-bcrdtto diswss t h e Mach 3 supersonic transport at this time b e ~ a ~ r c it seems t o m e t h a t everytime I pick-up a t e z h i c a l magazine they are having a special issue devoted t o t h i s airplane. &en slach p?ablicatior;,s a t Time, Newsweek, t h e Washington Post, and t h e N e w York Times have %&%?ly carried lengthy a r t i c l e s I abmt t h i s airplan,?. This, of C S O ~ S S , mema t h a t what I a m about t o say I s hardly novel. Ho~?vcr, I hope t o EL? some new ideas o r perhaps some I grs&er detail t o what may have beer- said before.
% It may be well to dwell f o r a mimte OE the reasons why t h i s airplane has received so much publlcity. The !These a x dmwn i n my first figure.
first itam is t h a t t h e &ch 3 S.xp?r~mic Warsport represents a major Tx oae step t h i s airplane w i l l more than afivaxe i n a i r c r a f t technology.
t r i p l e the speed of' o'ctr p s e s e ~ thighly developed commercial transports.
This is, I believe, an excitizg pessibflity to contemplate. The second r e t t ~ o i i s that the airplane i s t h e o33ect of much international competition.
W h e z I read abwt t h e i n t e r x k i s c a l competition i n t h e W a l l Street Journal, they p o h t out t h a t t h e sales of t h i s airplane can make as much as nine billion iio33ars difference i n t h e gal? f l o v to o r from t h e United States.
Ircidentally, t o date the foreign m d domestic a i r l i n e s have placed Other publications stress $100,000 deposites f o r 91 of these a i r c r a f t s .
the Imprtm-ce of this a i r p a ? as a psastige item t o c l e a r l y establish The f i n a l item i s the tlle Vr-itsd States as pre-emir,e,r;t ir! techfiology.
hign cost of t h i s airplane. Ekch a i r c r a f t i s estimated t o cost w e l l i n C X ~ C O E H of 20 million dollars--and t o achieve the first one requires a development program that costs betw?eg five hundred miliion and one b i l l i o n dollars. It is, therefore, m t x m 1 t h . t ; t h i s airplane would arouse much comment. I w i l l discuss each of these items i n somewhat greater d e t a i l as ., However, before doing so, I would l i k e t o refresh your memory I gc along.
about what t h e airplane looks l i k e .
Figure 2 is an artist's conception of w h a t t h i s aillplaae might look l i k e .
Many versions have appeared i n print, and t h i s picture i s an a r b i t r a r i l y selected one. It i s introduced t o indicate not w h a t w e believe i s t h e preferred configuration but t o serve as a useful guide on which t o base t h e discussion. The temperatures t h a t w i l l exist i n the various p a r t s of the fuselage when t h e airplane is flying a t a speed three times t h e velocity of sound, about 2,000 miles per hour, a r e shown. It can be seen t h a t t h e nose of t h e airplane and t h e leading edges of the wings and t a i l operate a t temperatures as high as 6 0 0 0 ~ , and the r e s t of t h e fuselage i s 4500F o r higher. The hottest parts of the airplane a r e near the engine exhausts and nacelles where temperatures Yange as high as 1 2 0 0 ' F .
Figure 3 lists t h e goals f o r the performatlce fo7 t h i s airplane. It i s hoped that by about 1970 a preliminary version w i l l be available t h a t w i l l perfcrm s a t i s f a c t o r i l y at a speed of Mach 2.3. It should carry about 150 passengers, and it w i l l be propelled by four turbojet engines of types t h a t e x i s t today. A short time Later t h i s same airplane fuselage i s t o be upgraded t o a speed of Mach 3 by i n s t a l l i n g four engines of types that a r e currently under development. By 1975 w e would l i k e t o make another change i n t h e same fuselage and upgrade its speed t o about 3.5 by i n s t a l l - ing s i x turbojet engines that a r e currently i n t h e i r i n i t i a l phases of development. I have t r i e d t o s t r e s s t h a t t h e aircraft structure t h a t w e w m t t o bulld originally should peyfom s a t i s f a c t o r i l y over the e n t i r e $ range of conditions shown i n the figure. I n additio3 t o t h e specifications In t h e chart, the s i r l i n e s hvve stated tha% f o r t h i s plage t o be com- nerclal3.y a t t r a c t i v e it should have a l i f e of at l e a s t 10 years of tThich 30 t o 50,000 hours a r e t o be a t rated. speed. It i s t h i s last feature _I_ t h a t of having a long iifetime that dif'fezeiitiates t h i s airplane from t h e A - 1 1 and t h e XRB-70. If you stop t o think about the numbers i n the chart you come c p wLth t h e v e r j exciting concepi; of an airplane t'mt w i l l make day, &y a f t e r day.
+'ov.r txa?satlantic crossSngs per To a t t s i n an airplane that will do t h i s job, one can hypothesize with assurance tkt a l l t h e materials for the supersonic transport will present problems. Such items as t i r e s , glazing materials, radomes, and hydraulic fluids and systems a l l have t o be improved before they w i l l perform satis- t h e bulk of t h e effort t o date has gone i n t o t h e study f e c t o r i l y . However, of t h e skin and fuselage materials an6 it i s i n t h i s area that I w i l l principally comment.
of t h e air-
Figure 4 shows t h e effect of a i r c r a f t speed on the temperatu-
c r a f t structure. W e can see t h a t a t the point a t which present a i r l i n e s operate today--just below Mach 1 --there i s very l i t t l e change i n temperature; however, above t h i s speed the temperature r i s e s veAy rapidly so a t Mach 3 Also shown i n t h e figure i s t h e strength it, i s s l i g h t l y i n excess of 500°.
of various mater-tals as a percentage of t h e i r room temperature strengths.
!The lowest cxme i s 2219, a s t r u c t u r a l aluminum alloy. W e can see t h a t i n t h e v i c i n i t y i n which we a r e interested, between Mach 2 and 3 the strength .
of t h i s a loy falls off very rap Ily. The t tanium alloy, 6-4, a l s o decreases i n strength as does the preciptation hardening s t e e l , AM 355, but not so precipitously as does t h e aluminum alloy. The best a l l o y i s the nickel alloy, INCO 718 which i s degraded only s l i g h t l y by t h e tem- perature. On the basis of t h i s figure one can eliminate t h e aluminum alloy. The remaining alloys must then be considered i n greater d e t a i l .
Figure 5 lists the properties that are required t o make f u r t h e r selections.
These properties include the conventional strength, forming, and joining parameters that are considered f o r every airplane. However, because of t h e high operating temperature we a r e also forced t o consider t h e metal- l u r g i c a l s t a b i l i t y of the alloy.
The metallurgical s t a b i l i t y i s t h e a b i l i t y of the a l l o y t o r e s i s t such processes as relaxation and aging, and t o r e t a i n i t s strength and toughness f o r the desired l i f e time.
O n t h e basis of such a list it would appear that t h e selection might be quite easy and it i s only necessary t o turn t o standard handbooks. This is not at a l l t h e case. The use temperatures are outside t h e range f o r which these alloys are normally considered and t h e l i f e times are beyond those used i n design.
Therefore, most of the work accomplished t o date has been t o accumulate the data required f o r selection purposes.
Figure 6 lists the alloys t h a t were considered. Our i n i t i a l job w a s t o survey these alloys t o obtain t h e properties I showed on t h e previous figure. The l i s t contains titaniums, superalloys, and both preciptation hardening and austenitic s t a i n l e s s steels. The titaniums included alpha and t h e alpha-beta alloys with particular emphasis on t h e alpha. A representative selection of iron, nickel, and cobalt-base superalloys were a l s o included. The list of alloys contained 24 candidate materials and when one considers t h e fact that several were considered i n more than one of' heat treatment it becomes apparent that the selection t a s k i s condition indeed formidable.
The data i s presented on a strength- Figure 7 shows some of the results.
to-weight r a t i o basis t o simplify comparisons. A most interesting feature of t h e figure i s that the titanium has proved t o be t h e most promising material. The reason is, of course, the low density of titanium. The two v e r t i c l e shaded bars indicate where t h e British-French Concorde and the United States airplane f a l l . W e can see t h a t the Concorde has been selected t o operate a t a range j u s t below that a t which t h e properties of aluminum This figure also i l l u s t r a t e s the f a c t that t h e Concorde doesn't decreases.
have t h e growth potential that we hope t o incorporate i n our airplane. For exatrple, t h e United States' airplane was set t o operate on t h e flat part of the curves, at temperatures reasonably below t h a t at which t h e s t e e l and titanium lose t h e i r strength.
Many newspaper accounts of t h i s airplane suggest that we a r e a l s o competing with t h e Russians; although, I have seen no definitive material on Russia's airplane, a good guess is t h a t one of the materials t h a t t h e Russians a r e looking at i s dispersion hardened aluminum a l l o y f o r t h e structure of the a i r c r a f t . This w i l l put them i n a temperature range with the United States rather than the Concorde.
Earlier I talked about t h e large volume of data t h a t i s being obtained.
Some of t h i s i s i l l u s t r a t e d i n t h e Figure 8. This data was obtained w i t h specimens t h a t have been suspended i n a furnace f o r very long periods of t i m e . The chage of strength t h a t may have taken place i s measured. W e can see t h a t now data f o r as long as 22,000 hours a r e available and that t h e data iooks very good. N o significant chaxges I n strength can be detected w i t h titanium o r the preciptation hardened s t a i n l e s s s t e e l s . O n t h e other hand, the austenitic s t e e l s that were strengthened by severe cold working have deteriorated badly. It i s only since significant quantities of such data and p a r a l l e l data obtained from loaded specimens a r e available that we f e e l confident i n our a b i l i t y t o build a plane having t h e desired l i f e .
(?ne important consideration that the materials must have is t h e a b i l i t y t o withstand the presence of cracks. This a b i l i t y i s shown i n Figure 9 f o r the three temperatures of i n t e r e s t t r , the airplane. The low temperature (-109°F) i s the ambient temperature at the cruise a l t i t u d e , room temperature t h e temperature a t which t h e airplane w i l l take off, and 55OoF the normal ope;.ating temperature f o r the s t r x - l u r e . As i n t h e pmceeding figure, the strength has been divided by the density t o permit comparisons between alloys.
The sha?.!ed bars give the smooth specimen strength and t h e solid black bars t h e strength i n t h e presence of a one inch crack i n the eight inch wide specimen. Tne 8-1-1 titanium, i n t h e t r i p l i x annealed condition is superior on t h e basis of t e n s i l e and notch strength at every temperature except 55OoF, The design people where t h e same alloy i n the annealed condition excelled.
l i k e t h e type of numbeP"s shown i n this figurs. The titanium i s r e l a t i v e l y insensitive t o cracking and they point out t h a t t h i s amomt of decrease i s less weakening then i s present i n %he aluminum alloys i n some of our present subsonic commercial transports.
Figure 10 a l s o deals w i t h the abi1i';y o f ' a material t o keep operating i n the presence of cracks. O n "cis figure we have plotted t h e r a t e at which a crack w i l l grow under cyclic loading conditions. The figure contains an a1u.num, a s%air,less s t e e l , a i d a titmi- alloy. It can be seen that t h e
m t e s;t which the crack gram is lowest f o r t h e titanium a l l o y - but t o m e
t h e most surprising fea-hre or' the f i g J r e is that t h e r a t e i s considerably l m e r than f o r t h e 2024 alumincm--an alloy we cozlsider t o be of the "fail- s d e " variety.
Thus far we have considered what a r e cmdidate materials f o r the structure of supersonic transport an& how do they stack up with each other. One other factor t o be considered i s corrosion resistmce. The supersonic transport is expected t o operate primaTily from a?rpoi+x i n the v i c i n i t y of t h e oceans and spenl! rrmch of its flyiiig t i m e over these oceans. It appears very l i k e l y it w i l l f r e q u w t l y encounter sea salt. 1% i s of course e s s e n t i a l that it be Figure ll shows t h e able t o resist t h e corrosive effect of t h i s salt.
behavior of titanium i n t h e presence of sea salt as a f'unction of the s t r e s s This figure was prepared from a compilation of a l l and exposure time.
It can be seen that at a published data available t o date and i s at 65OoF.
Stress of about 20,000 p s i t h e titanium alloy i s r e s i s t a n t t o s t r e s s corrosion cracking f o r very long times. It can also be seen t h a t above a stress of about 100,000 p s i f r e c t u r e occurs i n a very short t i m e . A t intermediate n stresses the behavior i s intermediate. It should be recalled t h a t t h i s
figure i s f o r r e s u l t s at 650'~ - a temperatare i n excess of that which w i l l
be encountered by t h e airplane. Unfortunately, a+, t h e Mach 3 operating temperature t h e data i s not yet definitive. Many people, however, f e e l t h a t there i s a threshold f o r corrosion and it i s above t h e temperatures which t h e airframe w i l l see at a speed of Mach 3 . The temperature ( 6 5 0 0 ~ ) shown i n t h e figure w i l l , however, be encountered i n th compresser vanes and disk; and overhaul and inspection procedures w i l l have t o take t h i s i n t o account.
at 550' i s shown i n Figure 12, I n t h i s test, specimens that a r e Some data bowed t o induce s t r e s s a r e held a t 559' f o r up t o three thousand hours a f t e r being l i g h t l y coated with salt. After exposure these specimens a r e compressed and i f cracking has occurred the specimen w i l l f r a c t u r e rather than bend.
The upper curve shows then effect of compression f o r a blank exposed t o tem- perature without salt. The lower curves shows t h e very serious effect of salt. A t the present time the situation with regards t o s t r e s s corrosion is rather confused. Essentially t h e engineers f e e l that t h e s i t u a t i o n i s com- parable t o t h a t which has existed many times before during preliminary that, as i n the past, solutions w i l l planning of the a i r c r a f t and they f e e l be forthcoming. The metallurgist tends t o be more cautious.
To summarize, I have t r i e d t o present some of t h e metallurgical problems that have been encountered w i t h t h e structure of t h e Mach 3 supersonic transport and some of t h e progress that has been made towards solving these problem,. As was stated earlier, t o date most a t t e n t i o n has been placed on ' t h e a i r c r a f t skin, however, programs on materials f o r t h i c k sections com- ponents, t h e engines, and othe? parts are moving rapidly along.