Kevlar fabric styles and weaves were studied, as well as methods of application for advanced gas turbine engines. The Kevlar material was subjected to high speed impacts by simple projectiles fired from a rifle, as well as more complex shapes such as fan blades released from gas turbine rotors in a spin pit. Just contained data was developed for a variety of weave and/or application techniques, and a comparative containment weight efficiency was established for Kevlar containment applications. The data generated during these tests is being incorporated into an analytical design system so that blade containment trade-off studies between Kevlar and metal case engine structures can be made. Laboratory tests and engine environment tests were performed to determine the survivability of Kevlar in a gas turbine environment

Weaver, A. T.

English

NASA Technical Reports Server

• °
LIGHTWEIGHT ENGINE CONTAINMENT
A. T. Weaver
Pratt & Whitney Aircraft
United Technologies Corporation
SUMMARY
This presentation covers preliminary evaluation and development of Kevlar
fabric as a lightweight containment material for use to contain blades
released from gas turbine rotors. The evaluation and development included
review and selection of fabric styles and weaves as well as methods of
application for advanced gas turbine engines.
During this investigation effort, the Kevlar material was subjected to high
speed impacts by simple projectiles fired from a rifle, as well as more
complex sIIapes such as fan blades released from gas turbine rotors in a spin
pit. Just contained data is developed for a variety of weave and/or applica-
tion techniques and a comparative containment weight efficiency has been
established for Kevlar containment applications. The data generated during
these tests is being incorporated into an analytical design system that will
allow a designer of future engines to make blade containment trade-off studies
between Kevlar and metal case engine structures.
In addition to the evaluation of the containment efficiency of Kevlar, certain
laboratory tests and engine environment tests were performed to determine the
survivability of Kevlar in a gas tubine environment.
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1978002125-236
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A_rent recu!lations require that blade co,utair_,ent be provided on _ii gas turbine
e:_gines certified for commercial flight. Since the structures that provide this
",_regenerally parasitic, engine technoloL_y dictates that they be as light as pos-
sible, in order to meet this requirement, new materials _:d new contair_enf con-
cepts are being explored, initial data generated using fabrics as energy eJDsorbi.ni
devices under high speed impact indicate that a significant weight improvement
can be achieved. _.is presentation deals with the evaluation _md development of
fabric structures for blade containment applications for gas turbine engines.
7SCUSS!O_:
A cross section of a t_pical gas turbine engine is shown in figure i. The red out-
line represents a t_pical rotor stage for which a contairav.ent structure must be
provided. The rotor is enclosed in a metal case which provides support for the
engine weight, and imposed thrust loads. Additionally, the case must pravide the
necessary containment in the event of a blade failure. This contairLzent is pro-
vided by the energy absorbing capability of the impacted case structure which
normally bulges or deforms when struck by a released blade. Sufficient material
__ thic:_mess must be employed in the containment structure to prevent the blade from
eYiting the case.
Zn current gas turbine engines, the metal case structure is fabricated with adequate
thickness to provide the necessary containment, in future gas turbine engines,
fabric wrapped thin metal cases ma_ be used to provide the necessary level of con-
tainment capability with a minimum weight. (See yellow outline in Figure 2.)
The thickness of the engine cases, in the plane of the blades_ can then be reduced
to a value limited by normal engine loads -_ch as thrust and rotor support.
DEVELOPMZNT PROGRAM:
The following development program was performed at P&WA East Hartford to provide
a data base for future applications of fabric containment structures for gas
turbine engines:
/ • Ballistic impact Evaluations/
• Laboratory Tests#
• Spin Pit Tests
• Engine Tests
The ballistic impact tests consisted of subjecting various fabric structures to
impacts by projectiles fired from a gun. "Just-contained" data were developed for
a wide sp¢ .+rum of fabric weight densities and projectile velocities. (See Figure
3).
In this testing we were able to determine the degree of participation of Kevlar R DuPont
versus the associated metal structure. The res.ults of this testing showed:
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1978002125-237
i. :levl:___ i_o.pacresisl'_'_.ceby itself"is ) more weid._%twf'i'ici_.:itt :ahA!SI h!0
hardened steel.
2. Levlar structures lose efficiency if the fabric is not allowed to deflect.
3. Kevlar fabric can absorb multiple hits closely spaced without apparent loss
of containment strength.
The laborator%_ investigation included wicking and flammability tests to assess fire
risk associated with Kevlar fabric around the outside of an aircraft gas turbine.
__.neresults of this testing showed:
Wicking
Kevlar 29, style 71 fabric, wicked engine oil and
hydraulic fluid in an applicable bench test.
Flammability
Kevlar 29 was non burning by itself.
The spin pit testing consisted of wrapping Kevlar cloth around a Ôxengine
case and subjecting this contair.mentstructure to an impact by a released blade
from a spinning rotor. (See Figures 4 and 5). A thin aluminum witness case was
mounted outboard of the Kevlar wrapped blade containment structure to determine if
blades/pieces exited the Kevlar. "Just-contained" data were obtained for typical
: gas turbine speeds and several configurations of Kevlar fabric.
The fabric configurations evaluated were:
L
Kevlar 29 I:i plain weave
Kevlar "" 3:i weave
• Kevlar '" 6:1 weave
Kevlar " 3D weave |
The results of this testing showed that the blades would penetrate the thin engine
metal cases; however, the blades were contained by fabric wrap. The containment
weight efficiencies for the above Kevlar weave configurations were determined to
be basically identical.
/
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1978002125-238
\:)38 OR_INAI_ PA_E
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1978002125-239
_ FIGURE Z
• GAS TURBINE ENGINE SHOWING LOCATION OF FABRIC
CONTAINMENT WRAP (YET,LOW BAND). ??.441-004Z'B
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1978002125-241
_. FIGURE 4
SPIN PIT CONTAINMENT TEST RIG SHOWING KEVLAR WRAPPEDCASE.
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DISCUSSION
J.C. Wallin, BAC
AI, as one who spends much time worrying about fires, I think you
tossed off the absorbability of Kevlar pretty lightly. If the casing were
wrapped around with asbestos, I'd be pretty unhappy. But as you described
> the wicking, I would not be any happier with Kevlar. I think that before
you can have a practical system on the engine you've got to have some way of
avoiding that soak-up (fire hazard) problem. Is there a suitable coating
that can be used to prevent its soaking up fluids?
A. Weaver, P&W
I share your concern about the fires; an engine can experience some
leakage of oil or fuel at some time. This leakage could be characterized as
so many gallons of this flammable fluid; all the Kevlar played a part in was
simply in wicking it. I'm not too certain if that's any more of a threat
than allowing the fluid to collect in the bottom of the nacelle, although
this can be drained off or trapped.
However, this is not going to take care of all of the leakage. Some of /
. the engine parts are going to be covered with this liquid because of its natural
adherence.
A I'm not yet convinced about the Kevlar increasing the fire hazard. We
do agree that it wicks, and probably is going to hold more of the fluid than
a metal part would hold just because it sticks to it. But it still may be a
small quantity and not an increased threat.
J.H. Gerstle, Boeing
A1, wouldn't it be possible to put a very lightweight nonabsorbent sheet
around the Kevlar?
A. Weaver, P&W
• That is a possibility that is being considered. One could also put in
a certain amount of impregnation. This might result in some loss in contain-
' ability, but with a 65% weight saving as it is, I can afford to give up some
' ,_ of that and still have it very attractive.
/_'_ Some of these questions are long-range consideratior_ that we'd llke to ;
pursue and get answers on. That's why we're quite a ways away from putting
; this out in the field.
H. Garten_ GE-L_nn
How muchweight saving do you think that you get as compared with a
tltanlumshield?
D
A..Weaverf P&W
The data indicated a 65% weight saving compared with using 410 steel.
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1978002125-244
So, I think, the proper question would be: how does titanium compare with
410 steel? Then, obviously, how does it compare to Kevlar?
H. Garten, GE-Lynn
I thought you said that the actual engine test (the spinpit test) was
surprisingly good. I thought that it inferred that it was better than the
initial assessment of your ballistic test.
A. Weaver, P&W
Yes, there was some inference of that. We don't completely understand
it whether it's because the ballistic test does not completely model whac
happens in the spinpit or not.
We have not pinned down in the spinpit the exact weight savings with the
Kevlar. On the surface, it appears to me that the spinpit test results were
going to be better than ballistic-test results. This may be due to the way we
bookkeep the results. We have not completely understood the bookkeeping of the
Kevlar versus the inner _teel wrap that we have.
i
D. McCarthy, Rolls-Royce
We tested some Kevlar and found that when it was wetted with oil, its
containment capability was seriously diminished; you suggested that the effect /
of oil wetting depended upon the shape of the missile. Have you done tests,
firing blades at the Kevlar shield while it is oil-impregnated?
A. Weaver, P&W
No, we haven't; we certainly intend to do that. We would have done it
some time ago had we not re¢ _ived the advice we did from Watertown saying,
"you really don't have to worry about it -- your initial ballistic tests
kidded you". We put that down to the lower part of our priority list, but it
- still remains to be done. We will not consider Kevlar to be fully developed 4
unless we run tests in a spinpit _ith the blades impacting into the oil-soaked _Kevlar.
?
R. Bristow, Boein_
I think you may very well find out that when you soak the Kevlar shield
in oil that you're getting a similar effect to having a matrix, that is, the
/ mass of the oil and the mass of the matrix is causing the problem.
j
E.A. Witmer, MIT-ASRL
Could you clarify the nature of the discussed test in the spin chamber:
the way the failure was initiated and the sequence of events?
A. Weaver, P&W
! We take a fully-bladed rotor, and purposely weaken a blade in the rotor
so that when you operate it at red-line speed, that blade is running very near
its ultimate tensile strength. The chamber is evacuated so the blade doesn't
have a significant vibration imposed on its P/A stress, and it continues to
remain intact. We then impose on the whole rotor a vibratory stress which
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1978002125-245
forces the one weakened blade to failure, usually in a second. That's the
simple way we conduct most of those tests. We normally fail the blade in
a root attachment or in the root airfoil. This would be a significant mass
of blade.
I think in the particular photograph you looked at on the viewgraph,
there was probably a root airfoil. Though, on the same rotor we've also
run with the full root attachments released into the case.
J. Meaney, Rohr
I have two questions. First, had you spliced the Kevlar and in what
direction? Second, you say that the Kevlar must deflect to work, but in
the pictures of the engine you show a lot of pnetulatic lines that run very
close to the shield. Do the deflections exceed that distance?
A. Weaver, P&W
Concerning the first question, the Kevlar application that you were
looking at is a very simplified application that I would think of as analogous
to an ace bandage. When you put an ace bandage on your wrist, you take the
one piece and you hold it and you wrap the other piece around, and you depend
on the friction of the layers to keep it there; the last little end of the
ace bandage you take a couple little hooks and you hook. That's all we've
really done here. I propose to let the designer make it very simple; don't _'
require him to add weight.
As to your second question, the particular engine case you saw was
: simply a vehicle for subjecting the Kevlar to the environment of an engine.
This was not designed to be a mock-up of a final design. One must provide
for adequate clearance because Kevlar must deflect appreciably to do its work.
We had put some structure outboard of the Kevlar (not against _he Kevlar)
and the Kevlar has deflecteu into these structures. At the present time in the
number of tests we've run, we've seen no effect on the containability of the
Kevlar if it was deflected into a structure. If you back the Kevlar up in
intimate contact with the structure, yes, you would probably lose containability.
But, if you don't back it up and you give the Kevlar a gap and allow it to deflect
through that gap, then if you hit the structure it didn't really appear to affect
the Kevlar. The Kevlar still did its job.
J. Salvino, NAPTC
In your spin pit containment test on Kevlar, where did you find the blade
_ fragment? Was it between the Kevlar and the outer case?
A. Weaver, P&W
Typically, the Kevlar is ripped and torn, and many layers of it are
penetrated; the blade is trapped in the layers. The blade is generally in one
piece not including the root; it does not always break up.
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Lightweight engine containment

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