Note: Descriptions are shown in the official language in which they were submitted.
~og566~
Background of the Invention
This invention relates to composite blades for use in fluid flow
machilles and, more particularly, to improving the shear strength
characteristics thereof.
In ~ecent years, significant advances have been made in
developing composite blades for fluid flow machines, such as KaS turbine
compressors and fans, by making use of structural composite reinforcements
having high strength characteristics. Generally, the major portion, or
primary structure, of the blade comprises substantially parallel laminates of
small diameter reinforcing filaments, having high strength and high modulus
of elasticity, embedded in a lightweight matrix which is generally extremely
weak compared to the longitudinal strength of the filaments (tyl)ically only
one to five percent as strong). These laminates, possessing e~sentially
unidireclional strengrth characteristics, are laid up at specified predeterminedangles to each other, and to the blade longitudinal axis, and the matrix cured
to create a rigid structure. For example, the blade can be made strong in
tension longitudinally and chord-wise by suitably orienting the fibers in each
laminate. In embodiments involving predominantly nonmetallic materials,
the blades comprise graphite filament laminates in an epoxy resin, though
any fiber embedded in any binder, such as an organic resin, may be employed.
Further, the structures may also comprise any metallic system including
boron filaments in an aluminum matrix.
One factor which has discouraged the introduction of composite
blades into operational service in aircraft gas turbine engines is their
vulnerability to what is commonly referred to as foreign object damage.
Many types of foreign objçcts may be entrained in the inlet of a gas turbine
~095664
engine, ranging t`rom large birds such as eagles, to hailstones, sand and
rain While the smaller ob~jects can erode the blade materials and degrade
the performance of the fan or compressor, impact by the larger objects may
cause more severe damage. Under large impact loads, composite blades
5 severely distort, twist and bend developing high localized multidirectional
stresses. These may result in portions of the blade being torn loose or in
extensive delamination of the filament laminates~ A contributing factor is
that the laminated composite blade is very weak in tension perpendicular to
the plane of the blade (i. e., across the airfoil portion from pressure to
10 suction surface), and weak in resisting shear loads between the laminates.
In these types of loadings, the loads are carried entirely by the matrix which,
as noted above, is extremely weak compared to the filaments.
Several approaches have been considered in an effort to
improve the transverse and interlaminar shear strength of composite blade
15 airfoils and, thus, improve their impact tolerance. These approaches have
primarily involved selecting the proper filament/matrix system and processing
the material in a rnanner so as to optimize their load-carrying potential.
While moderate progress has been made, it is apparent that the foreseeable
structural materials may not afford adequate transverse shear capability
20 without a change in the structural configuration. Thus, it becomes desirable
to develop a composite blade for turbomachinery application which does not
rely entirely on the matrix properties for resisting transverse shear loads.
Summary of th_ Invention
Accordingly, it is the primary object of the present invention
25 to provide an arrangement of the filaments whereby t~nsile loading perpendi-
cular to the blade surface and shear loading (which tends to~move the blade
-- 2 --
lO9S664
pressure surface longitudinally or chord-wise relative to the suction surface)
are carried by the filaments.
It is another object of the present invention to provide shear
webs within the composite blade to permit the blade to carry bending loads,
5 as in a beam.
It is yet another object of the present invention to provide an
improved method of fabricating a filament composite blade which will increase
its transverse ~hear strength and improve its impact load tolerance.
These and other objects and advantages will be more clearly
10 understood from the following detailed description, the drawings and specific
examr)]es, all of which are intended to be typical of rather than in any way
limiting to the .scope of the present invention.
Briefly stated, the above objects are accom~lishe~l in a
turbomachinery blade by a unique choice of filament layup patterns wherein
15 high strength reinforcing filaments pass through the blade from one aerody-
namic surface to the other to carry the transverse (across the chord) shear
and tension loads. In one embodiment, bundles of longitudinal filaments are
formed, each having a rectangular or triangular cross section, and which
may be laid up adjacent to each other (chord-wise) essentially parallel to the
20 ~ blade longitudinal axis to form the hlade contour and to carry the majority ol
,;~ t he blade longitudinal loading. Around one or more of these fi~ament bundles
are wound sheets or plies of other reinforcing filaments embedded in a matrix,
the filaments in the sheets forming a predetermined angle with respect to the
filaments in the bundles, typically ~ 45. In this manner, the sheet filaments
i ~ :
25 run through the blade from one aerodynamic surface to the other to structurally
tie the blade together in the transverse direction. Preferably, each filament
-- 3 --
lOgS66~
h1ln(1]c i.~i 1ied 1O l~e s~dj.l( ent hl1nd]e ~y mean~; Or the li1arncnl ~ihee1 ~o .1~ to
rcasc the tr.msverse ~;hearing ~trength between adja(~ent b~1n~11e.~;.
In another embodiment, the inherent weakness is overcome
primarily by binding the filaments in a thin layer held together by an uncured
5 binder or matrix. These layers are then laminated to form a sheet, but with
the filaments of each layer in a predetermined orientation with respect to the
other layers, all layers being more or less parallel to each other. Thereafter,
the sheet is repeatedly folded in accordian-like fashion so that at least some
of the filaments are disposed in planes essentially perpendicular to the
10 original planar surface of the sheet. This provides a thicker sheet having
some generally longitudinal filaments but also having filaments which
criss-cross transversely from the top surface to the bottom surface of the
thicker sheet to hold the layers together, prevent delamination and to carry
shear loads across the thickness of the sheet. Facing sheets are provided
15 on the top and bottom surfaces of the thicker sheets and having reinforcing
filaments suitably oriented to provide reinforcement against the forces
tending to unfold the folded filament sheets. The final configuration is then
cured or bonded to rigidize the str ucture.
In yet a further extension of the preHent invention, the 1'ilamen~
20 orien1ation may be chosen as to prevcnt or minimi~,e hlade untwist unt1er
! ~
centrifugal loading, and to put the resulting stresses in a desirable portion of
the blade from a strength standpoint, such as at the thicker sections.
i ~ Consistent with the above structural improvements, a method
is provided for fabricating a blade to improve its transverse shear
25 characteristicJ,
.
, : , . , . . ~ ~,
.. , , . .. -.
. .. . . , - -, . : .. .. .... . : . .. .
~095664
Brief Description of the Drawings
While the specification concludes with claims particularly
pointing out and distinctly claiming the subject matter which is regarded as
part of the present invention, it is believed that the invention will be more
fully understood from the following description of the preferred embodiments
which is given by way of example with the accompanying drawings in which:
Figure 1 is a perspective view of a gas turbine engine composite
fan blade which may be constructed in accordance with the present invention;
Figure 2 illustrates, in perspective, the manner of assembling
composite filament laminates in the manufacture of prior art rotor blades;
Figure 3 is a simplified schematic showing the general
arrangement of one embodiment Or the preHent invention;
Fiuure 4 depi(ts the lorminK proces~ ror a composite rl:lament
core element for use with the subject invention;
lS Figure 5 illustrates schematically an alternative embodiment
i~ similar to Figure 3, of a composite article fabricated in accordance with the
: present invention;
Flgure 6 illustrates in an exploded view the constituent parts
of the article of Figure 5;
~; Figure 7 illustrates an alternative embodiment of the invention
o f Figure 3 wherein fi~ament laminate sheets are folded to enhance transver~e
shear characteristics;
Figure 8 depicts a partial blade section formed in accordance
with:the embodiment of Figure 7,
j:
~ 25 ~ Figure 9 illustrates a method of forming a tapered blade
, ~
section utilizing the teachings of Figures 7 and 8;
~ .
- 5 -
'' , ' . : ' ' ' ' ~ '
l~g5664
Figure 10 schematically depicts the filament orientation of
the ernbodiment of Figure 9;
Figure 11 schematically depicts a tapered blade section formed
in accordance with the pre~ent invention; and
s Figure 12 schematically depicts an alternative filament
orientation of the embodiment of Figure 7.
Descri tion of the Preferred Embodiment
P _ _
Referring to the drawings wherein like numerals correspond to
like elements throughout, attention is first directed to Figure 1 wherein a
composite blade 10 for use in a fluid flow machine and which may be
constructed in accordance with the present invention is illustrated. While not
so limiting, the blade 10 is adapted for use in axial flow ga~ turbine engine
fans. It will become apparent to those skilled in the art th~t the prefient
invention offers an improvement for many load-bearing composite articles
lS and that fan blade 10 is merely meant to be illustrative of one such application.
Accordingly, fan blade 10 is shown to comprise an airfoil portion 12, generally
; of radialk variant camber and stagger, and a root portion 14 which enables
~ the blade to be mounted on and retained by a rotatable disc or hub in a
; ~ conventional manner. A leading edge protective device 16 provides a
20 protective sheath bonded to the leading edge of the blade to increase its
tolerance to foreign object impact. Additionally, a typical flow path defining
platform, not shown, could be mounted between the airfoil and root portions
of the blade.
Heretofore, composite blades (or at least the major portion
thereof) have comprised laminates of small diameter reinforcing filaments
having high strength and high modulus of elaRticity embedded in a lightweight
" :' ' ' ' , : .
.
~095664
matrix. As best depicted in Figure 2, an individual blade is formed from a
plurality of laminates 18 cut from larger sheets, and of varying contour to
provide the tapering blade cross section typical of fan blades. The assembly
of laminates 18 is placed in a mold and, with the application of heat and
5 pressure, is bonded to form a composite blade having a profile as in Figure 1.
In a nonmetallic composite blade, the airfoil portion 12 would typically
comprise laminates of graphite filaments in an epoxy resin, though the present
invention anticipates the use of any fiber embedded in any binder, such as an
organic resin, for its ~tructure. Further, it i~ well known that laminate 18
10 could comprise any metallic system, such as boron filaments in an aluminum
matrix. It is recognized that the present invention soon to be described is
adapted to take advantage of all known or anticipated materials, but which
utiliæes them in a unique structural relationship distinct from that of Figure 2.
Continuing with Figure 2, it may be recognized that the blade
15 may be made strong in tension longitudinally (along the Y axis direction) and
axlally (along the Z, axis direction) by ~uitably orienting the filaments 20 in
each laminate sheet 18 (typically + 45 to the Y axis, wherein Y is generally
the radiai direction of an assembled bladed rotor). In general, the matrix
material is extremely weak compared to the filaments 20, typically only 1 to
20 5 percent as strong. Hence, the laminated blade possesses an inherent
weakness in tension in the X direction (the substantially circumferential
dlrection of an assembled rotor), and in the direction generally perpendicular
;I to the surfaces of airfoil portion 12. In other words, the blade is entirely
dependent upon the matrix strength and intermatrix bonding to prevent relative
25 separation of the laminates 18. Additionally, there is a similar weakness in
resisting shearing loads which tend to move adjacent laminates longitudinally
-- 7 ~
:~095664
or axially with respect to each other, since these loads are also resisted
entirely by the matrix material. All of the foregoing tend to occur when an
assernbled blade is impacted upon one side by a foreign object which causes
the blade to bend and/or twist, and delamination is prevented only if the
strength of the matrix material is not exceeded.
In accordance with one of the objects of the present invention,
a filament orientation is provided which permits the foregoing three types of
loading to be carried directly by the filaments, thereby sub~tantially freeing
the blade strength in these three directions from its other dependence upon
matrix strength, Accordingly, Figure 3 depicts in schematic form a
simplified embodiment of the subject matter of the present invention. Therein,
a plurality of elements 22 of generally triangular cross section are laid up in
alternating inverted relationship to form the primary structure of an airfoil,
herein depicted as a plate 23 for simplicity. Each element comprises a
central core 24, also of generally triangular cross section, and a plurality of
substantially parallel, high strength, reinforcing filaments, Referring briefly
to Figures 4a through 4d for a preferred method of forming core 24, a plurality
of such unidirectional, small-diameter filaments embedded in a partially
cured polymeric resin, for example, and generally designated 17 is initially
formed in a sheet 19 which is sub~equently tightly rolled into a cylindrical
shape 21 (Figures 4a and 4b). While not necessary to the practice of the
present inventionj the resulting cylinder can be twisted for reasons to be
, discussed hereinafter. The cylinder is placed between representative
-` cooperating dies 26, 28 (Figure 4c) and, with the addition of sufficient heat
25 and pressure, IS formed and cured into triangular core 24 (Figure 4d).
Continuing with the embodiment of Figure 3, each such core 24
--8--
.
1(~9`5664
is wrapped with a similar filament/matrix sheet 30 wherein the filaments of
the wrapping are disposed at a predetermined angle with respect to the
longitudinal axis of the core 24, typically 45. In some applications, two
wrapping sheets may be wound successively or simultaneously around the
5 core so as to provide ~ 45 fiber orientation in each element, and it is
recognized that other fiber orientations may be chosen to solve unique
structural problems, Clearly, the filaments within the wrapping sheet 30
between adjacent cores run across the plate (up and down in Figure 3) to
structurally tie the blade together in the transverse direction without reliance
10 on weak matrix materials to carry shear loads. Elements 22 are then laid
side by side and sandwiched between thin facing sheets 32 of filament/matrix
material, the filaments of which are also deposited at an angle with respect to
the core longitudinal direction to aid in tieing the elements together. The
entire structure is then subjected to heat and pressure to cure or polymerize
15 the matrix material and to form a rigid, unitized blade. ~f course, the cores
24 may be tapered as required by the structure and may be square, r ectangu-
lar, hexogonal, circular or otherwise in cross section, as well as triangular.
However, the structure of Figure 3 is particularly well adapted for carrying
loads in the chordwise direction (A to B) because of the truss-like configura-
20 tion, the wrapping sheets 30 forming shear webs to permit the blade to carrybending loads, as in a beam.
Figures 5 and 6 depict a modification of the embodiment of
Figure 3 to further strengthen the cleavage planes between adj,acent triangular
elements 22. Therein, a slightly modified plate 23' ~also representative of a
25 blade portion, for example) is shown to comprise a repeating plurality of two
basic elements: core 24 as defined with respect to Figure 3 and three-sided
_g_
lOgS664
channel 34, the base 36 of which forms an acute angle with respect to one
side 3~ and an obtuse angle with respectto the a~er side 40 to thereby conform
to the cross-sectional profile of core 24. Preferably, channel 34 comprises
a sheet (or laminate of several sheets) of unidirectional, small diameter,
high strength, reinforcing filaments cornposited in a matrix in a manner now
well understood. Plate 23' is formed by nesting together elements 24 and 34
in alternating, inverted relationship as depicted in Figure 5. It becomes
readily apparent that each channel 34 receives at least one core 24 within its
closed end and at least partially overlaps the next core to the left thereof in
Figure 5. In fact, in Figure 5, each channel receives portions of at least
three adjacent cores.
The filament orientation within channel 34, with respect to the
longitudinal direction of core 24, may be chosen in the direction of overlap as
at 40 so as to resist across-the-chord loads across the plate (from D to C)
and to prevent lateral separation of adjacent cores when the plate is bonded
into a rigid article. Alternatively, the filament orientation could be as
represented at 42 or 44 to assist in carrying some of the longitudinal tension
loads in cooperation with cores 24. ~ften, both filament orientations will be
selected for use in the same plate, the channel compri~ing a laminate of two
or more sheets with the angle of the constituent filament~ chosen consistent
with anticipated shear loads. The configuration of Figures 5 and 6 is partic-
ularly well adapted to mass manufacturing processes since it comprises only
two separate element types which, when properly nested, form a plate
structure
Figures 7 and 8 illustrate an alternative embodiment wherein
inherent weaknesses in the blade nonlongitudinal direction have beenovercome.
~10-
~095664
In this embodiment, the weaknesses are overcome by arranging the filaments
in sheets of partially cured polymeric resin, for example, and laminating the
sheets such that the filament longitudinal axes are oriented in predetermined
directions. Preferably, the first sheet would be oriented essentially parallel
5 to the blade longitudinal axis while other sheets would be oriented t 45 to
the first sheet, This technique yields a lamination having strength in two or
more directions, alL more or less in a plane or continuous curved surface and
is, so far, completely conventional and representative of common practice.
In the present invention, however, such a laminated sheet (or even a single
sheet layer) is repeatedly folded in accordian-like fashion as in Figure 7 with
the fold lines 44 running in the substantially longitudinal direction so that some
of the filaments are in surfaces disposed at an angle to the original surface
plane. Thus, the resultin~ plate 46 is considerably thicker than the original
lamination and possesses filaments which criss-cross from the top surface
to the bottom surface of the thicker sheet. These criss-cross filaments
provide fibrous strength to hold the filament sheet together and prevent
delamination. The entire structure, with top and bottom facing sheets 48 and
50, respectively (F'igure 8), added and having filament orientation such as to
prevent unfolding, is then subjected to heat and pressure sufficient to cure or
20 polymerize the matrix material and form the unitized, rigid plate 4~.
Alternatively, the folded sheet may be skewed as in Figure 12 such that the
filaments are in surfaces forming acute angles to the c:hordwise direction to
increase chordwise shearing strength,
Figures 9 through 11 teach a method of forming a tapered
25 composite blade utilizing the concept of Figures 7 and 8. As p~eviously
discussed, a lamination of several filament sheets may be formed, the
. ,
1095664
resulting laminatiorl 52 being generally planar. Deperlding on the width and
taper desired in the resulting plate, and the required strength, the lamination
52 may contain several changes of filament sheet orientations. For example,
in Figure 10 the filament orientation of layer 54 is su~)~tantially longitudinal
5 whereas the filaments of layers 56 and 58 are disposed at predetermined
angles to the longitudinal direction,
In Figure 9, lines 60 represent the longitudinal filament
direction of layer 54. Fold lines 62 are labeled T and B in an alternating
relationship depending upon final location of each fold line in the finished
10 tapered plate 64 of Figure 11. The surfaces between the fold lines represent
the final vertical sections through the completed plate 64. By comparison of
the filament direction with the fold lines in Figure 9, it will be apparent that
the final plate contain~ filaments running not only longitudinally, but also
generally from top to bottom. Though a plate tapered in one direction only
15 is shown, a plate having transverse taper or varying thickness for an airfoil
contour can readily be formed by varying the folding pattern. As with the
plate of Figures 8 and 12, it may be desirable to bond surface layers of
filaments to the plate with the filament orientation such as to prevent unfolding
or to provide torsional rigidity. It will al~o be de~irable at times to bond one
20 tapered plate to another to form nonlinear tapers a~, for instance, a dovetail
on an airfoil. Additionally, it may also be desirable to insert slivers of
metallic material between the folds to further optimize the material's
properties and enhance their load-carrying capability.
The teachings of the present invention may be utilized to
2S overcome yet another problem inherent in rotating turbomachinery, In
particular, fan blades as shown in Figure 1 can be considered to be twisted,
-12-
~C~95664
tapered, bent plates. Due to the twist of the blades, required for aerodynamic
reasons, the blade tends to untwist due to loads produced by the centrifugal
force ïield caused by blade rotation. This untwist has two adverse conse-
quences: first, it tends to modify the shape of the blade so that it is no longer
aerodynamically correct, and, secondly, it causes high stresses in the leading
and trailing edges of the blade. These are the regions where the blades are
thinnest and, hence, unable to strongly resist these stresses. The present
invention provides a means to minimize the untwist and for shifting the result-
ing stresses to a desirable portion of the blade, such as to the thicker sections.
Referring again to Figure 4b, it was earlier mentioned that the
roll or cylinder 2t of elongated filaments could be twisted prior to forming it
into tr iangular core member 24. If twisted into a gcllerally s~iral confi~Sura-tion, and ultimately fabricated into a plate (or blade) as taught in Figures 3 or
5, the spiraled filaments will tend to cause the triangular core section to
untwist under the influence of centrifugal loads. By the proper selection of
spiral angles and filament orientation within the core, the torque generated
by the core untwist can completely (or partially) balance the torque generated
by the untwist tendency of the overall blade geometry. Thus, blade distortion
and edge stresses will be minimized. On the other hand, it may be desirable
in some cases to spiral the fibers in the opposite direction so as to provide
for increased blade twist. This will, in some cases, be useful to modify the
aerodynamic configuration as a function of rotational speed.
It will be obvious to one skilled in the art that certain changes
can be made to the above-describèd invention without departing from the
broad inventive concepts thereof. For example, while the present discussion
has been directed primarily to a single type of high strength, reinforcing
1095664
filament bonded in a single type of matrix material, it is clear that different
materials may be used for the various layers and binders to further match the
material's properti~s to the requirements. And, while a rotating blade
structurc has been emphasized herein, it is obvious that the teachings of the
S present invention are equally applicable to stationary compcsite articles. It
is intended that the appended claims cover these and all other variations in
the present invention's broader inventive concepts.
-14-
