STRUCTURE AND METHOD OF FABRICATING A METAL COMPOSITE DRIVE SHAFT

METHODE DE FABRICATION D'UN ARBRE DE TRANSMISSION COMPOSITE EN METAL

English Abstract

-6-
ABSTRACT OF THE DISCLOSURE
A high specific modulus shaft for a gas turbine
engine is constructed having a metal outer tube to trans-
mit the torque and a metal and high modulus filament com-
posite sleeve bonded to the tube's inner diameter. The
composite sleeve is fabricated and bonded to the inner
diameter of the tube by winding the composite composition
tape on a mandrel with the filaments axially aligned. The
mandrel is then inserted into a metal outer tube. The as-
sembly is encapsulated, evacuated and sealed and the man-
drel pressurized at a sufficient temperature to achieve
consolidation and diffusion bonding of the wound composite
to itself and the shaft inner diameter.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
-4-
1. A composite shaft for a gas turbine engine having
a high specific modulus comprising:
an outer tubular sheath constructed of machinable
high torsion resistant material and having an interior
axially extending passage; and
an interior shell constructed of a metal matrix
containing axially aligned filaments of a high modu-
lus material, said shell being completely consolidated
and bonded on the inner diameter of the tubular sheath
2. A composite shaft for a gas turbine engine having
a high specific modulus as described in claim 1 wherein the
tubular sheath is constructed of steel.
3. A composite shaft for a gas turbine engine having
a high specific modulus as described in claim 1 wherein the
tubular sheath is constructed of titanium.
4. A composite shaft for a gas turbine engine having
a high specific modulus as described in claim 1 wherein the
metal matrix is aluminum.
5. A composite shaft for a gas turbine engine having
a high specific modulus as described in claim 1 wherein the
metal matrix is titanium.
6. A composite shaft for a gas turbine engine having
a high specific modulus as described in claim 1 wherein the
high modulus material is boron.
7. A method of fabricating a composite shaft for a
gas turbine engine having a high specific modulus compris-
ing the steps of:
constructing an outer tubular sheath of machinable
high torsion resistant material and having an interior
axially extending passage;
constructing a metal matrix tape having longitud-
inally extending high modulus material filaments im-
bedded therein;
rolling the matrix tape on a mandrel with the high
modulus filaments oriented in an axial direction;
inserting the tape and mandrel into the axially
extending passage in close contact with the inner di-
ameter of the tubular sheath; and

-5-
subjecting said assembly to sufficient temperature
and pressure to achieve consolidation and diffusion
bonding of the filament reinforced metal tape into the
outer tubular sheath.
8. A method of fabricating a composite shaft for a
gas turbine engine as described in claim 7 wherein consoli-
dation is achieved by:
placing said assembly in an autoclave;
raising the pressure in said autoclave to an in-
termediate level;
increasing the temperature in said autoclave to a
temperature which increases the ductility of the man-
drel and film and promotes bonding; and
further raising the pressure in the autoclave to
promote bonding and consolidation and holding said
pressure until said processes are complete.
9. A method of fabricating a composite shaft for a
gas turbine engine having a high specific modulus as de-
scribed in claim 7 wherein the outer tubular sheath is
constructed of steel.
10. A method of fabricating a composite shaft for a
gas turbine engine having a high specific modulus as de-
scribed in claim 7 wherein the outer tubular sheath is con-
structed of titanium.
11. A method of fabricating a composite shaft for a
gas-turbine engine having a high specific modulus as de-
scribed in claim 7 wherein the metal matrix tape is formed
by sandwiching the longitudinally aligned filaments between
two thin films of metal.
12. A method of fabricating a composite shaft for a
gas turbine engine as described in claim 8 wherein the
metal matrix is constructed of aluminum.
13. A method of fabricating a composite shaft for a
gas turbine engine as described in claim 12 wherein the
high modulus filaments are constructed of boron.

Description

11463'~;~
STRUCTURE AND METHOD OF FABRICATING
A METAL COMPOSITE DRIVE SHAFT
Background of the Invention
One persistent trend in the gas turbine industry is
the development of smaller, more efficient engines with in-
creased specific power. These changes invariably result in
correspondingly higher speed and stress levels on the prin-
cipal engine components. An engine drive or power shaft is
a prime example of this condition since the combination of
increased rotor speed and smaller shaft diameter create
critical speed problems. One solution is to decrease the
effective shaft length by adding additional bearing sup-
ports. This creates added mechanical complexities to
achieving and assemblying a smaller engine. A simplier and
more practical ~olution to the problem is to construct
shafts with higher modulus to density ratio which will re-
sult in an increased specific stiffr.ess and critical speed.
Summary of the Invention
A combined metal and composite shaft i5 constructed to
withstand the torsional and bending ~tresses placed on a
small diameter drive shaft for a gas turbine engine.
First, an outer tubular steel shaft is constructed. Then
boron filaments are carefully positioned and spaced between
two thin film layers of aluminum to form an aluminum sheet
having interior longitudinally oriented boron filaments.
The boron/aluminum sheet is rolled onto a mild steel man-
drel and inserted into the tubular steel shaft with the
filaments aligned axially. The assembly is placed in an
autoclave which is first pressurized to 4 - 5 ksi, heated
to 960 F and then subjected to an increased pressure of
10 ks~ for a half hour. This process results in a fully
i~

1~6372
--2--
consolidated composite shaft having a steel outer shell
and an aluminum inner sleeve reinforced by axially aligned
boron filaments to enhance bending stiffness.
Description of the Drawing
This invention is described in more detail below with
reference to the drawing in which:
Figure 1 is a perspective view of one end of the fab-
ricated shaft; and
Figure 2 is a sectional view taken along a longitudi-
nal plane through the axis.
Detailed Descri~tion of_the Preferred Embodiment
A completed shaft 1 constructed according to this in-
vention is shown in Figures 1 and 2 and consists of a hard-
ened steel tubular outer shaft 2 including hardened spline
6 to which is bounded on its inner diameter a high speci-
fic modulus layer 3. The layer 3 as best seen in Figure 2
consists of a fully consolidated aluminum matrix in which
multiple boron filaments 4 are imbedded in general align-
ment with axis S.
The layer 3 consists of 7 mil thick aluminum matrix
tape with 5.6 mil boron filaments sandwiched inside. A
titanium tape could al~o be used, but in that instance
silicon carbide or boron carbide coated boron filaments
should be used to prevent interaction between the titanium
and boron.
The layer 3 i8 rolled onto a mild steel mandrel and i~
inserted into the tubular steel shaft 2. This assembly is
then placed into an autoclave in which the pressure is
then raised to an intermediate pre~ure of 4 to 5 ksi. By
raising the *emperature at this point to 960~ F the duct-
ility of the layer 3 and its mandrel are increased to fac-
ilitate the initial stages of bonding. As a final step,
the pressure is then elevated to 10 ksi and held for ap-
proximately a half hour to allow complete consolidation.
35 The mandrel is then removed through a chemical milling
process.
The turbine shaft 2 can be constructed of either steel
or titanium to insure torsional integrity of the composite
shaft. A typical shaft 1 could have a steel or titanium

i372
--3--
outer sheath having an outside diameter of 1 inch and
an interior diameter of .625 inch with a .070 inch thick
boron/aluminum layer 3 bonded at the interior diameter.
In this manner a composite shaft is constructed hav-
ing a high specific modulus which provides a greatercritical speed~ Since the outer surface is constructed
of steel, it may be machined or welded as required.
To avoid the use of an autoclave, the assembly of
the shaft and mandrel may be sealed and evacuated. The
assembly could then be pressurized through an internal
axial passage within the mandrel. By pressurizing under
high temperature consolidation and diffusion, bonding
of the tape and the tape to the shaft can be assured.