METHOD FOR MANUFACTURING A TURBINE ENGINE BLADE ROOT OF A
COMPOSITE MATERIAL AND BLADE ROOT OBTAINED BY SUCH A
METHOD1
5 Background of the invention
The present invention relates to the general field
of making a blade out of composite material for a rotor
wheel of a turbine engine. The invention relates more
particularly to fabricating the root of such a blade.
10 The intended field is that of gas turbine rotor
blades for aeroengines or for industrial turbines.
Proposals have already been made to make blades for
turbine engines out of composite material, and in
particular out of ceramic matrix composite (CMC)
15 material. Reference may be made in particular to
Document FR 2 939 129, which describes fabricating a
turbine engine blade out of composite material comprising
fiber reinforcement that is densified by a matrix. With
such a method, the resulting blade presents in particular
20 a root that is formed from a fiber strip extending in a
direction that corresponds to the longitudinal direction
of the blade.
Furthermore, in order to mount such a blade on a
rotor disk, it is known to give the blade root the shape
25 of a bulb. The blade root with its bulb shape cooperates
with a slot of complementary shape formed in the
periphery of the rotor disk in order to retain the blade
radially on the disk by means of a dovetail-type
connection.
30 When a blade is made out of composite material, the
bulb shape of the blade root is generally obtained during
the weaving of the fiber blank that is to constitute the
blade by forming extra thickness in the blade root, this
extra thickness subsequently being machined to the final
35 shapes of the bulb. In practice, the extra thickness is
' Translation of the title as established ex officio.
2
usually obtained by adding an insert while weaving the
fiber blank.
Nevertheless, such a method of fabricating a blade
out of composite material with a bulb-shaped root
5 presents numerous drawbacks. Making the insert and
putting it into position during weaving of the fiber
blank of the blade are operations that are very
difficult. In addition, the attachment of the blade
presents mechanical strength difficulties and it becomes
10 degraded in fatigue by oxidation.
Also known, from Document FR 2 941 487, is a
solution for mounting a composite material blade on a
rotor disk in which the blade root is clamped between
metal plates that are fastened together by means of a
15 welded peg. With that solution, the main force retaining
the blade on the rotor disk is taken up by shear in the
peg and by compression against the hole in the composite
material. Nevertheless, expansion differences between
the metal of the plate and the composite material of the
20 root give rise either to thermal shear stresses if the
fastening is rigid, or to uncertainty about the
positioning of the bearing plates if the fastening is
provided with slack.
25 Obj ect and summary of the invention
A main object of the present invention is thus to
mitigate such drawbacks by proposing a blade root made of
composite material in which the attachment with a rotor
disk by a dovetail-type connection does not present the
30 above-mentioned drawbacks.
This object is achieved by a method of fabricating a
turbine engine blade root out of composite material
comprising fiber reinforcement densified by a matrix, the
method comprising making a central fiber strip and two
35 outer fiber strips from three sets of yarn layers
interlinked by three-dimensional weaving, the fiber
strips extending in a common direction corresponding to
3
the longitudinal direction of the blade root to be
fabricated and the yarns of the yarn layer sets not being
interlinked between the various fiber strips, passing the
two outer strips through the central strip with the two
5 outer strips crossing each other inside the central
strip, eliminating the portions of the two outer strips
lying outside the central strip by cutting them off in
order to form a blade-root fiber blank, shaping the fiber
blank in order to obtain a fiber preform having a main
10 portion forming a blade-root preform integral with two
secondary portions forming bearing-plate preforms, and
densifying the fiber preform with a matrix in order to
obtain a blade root made of composite material having
fiber reinforcement constituted by the preform and
15 densified by the matrix.
Such a fabrication method enables a blade root to be
obtained having bearing plates that can withstand heavy
loads with less deformation. The forces of the rotor
disk on these bearing plates act in the direction of the
20 yarns of the fiber strip portions constituting the
bearing plate. In particular, these forces do not lead
to yarn layers being flattened. The lifetime of the
blade root is increased for a given size.
Furthermore, this fabrication method avoids having
25 recourse to using an insert while weaving the fiber blank
for the purpose of giving the root its bulb shape. That
simplifies the method, achieves greater robustness, makes
it possible to density the preform without significantly
exceeding the thickness of the central strip, and
30 achieves savings in terms of fabrication cycles and
costs.
Advantageously, the two outer strips pass through
the central strip in directions forming an angle lying in
the range 15° to 75°, and preferably equal to 45°,
35 relative to the direction of the central strip.
The central strip may also be used for making a
fiber preform for a blade airfoil. Likewise, at least
4
one of the outer strips may also be used for making a
fiber preform for an inner and/or outer blade platform.
The fiber strips may be woven with their
longitudinal directions that correspond to the direction
5 of the blade root that is to be fabricated extending in
the warp direction. Alternatively, the fiber strips may
be woven with their longitudinal directions that
correspond to the direction of the blade root that is to
be fabricated extending in the weft direction.
10 Correspondingly, the invention provides a turbine
engine blade root made of composite material comprising
fiber reinforcement densified by a matrix, the blade root
being characterized in that it includes a blade-root
constituting portion integrally formed with two bearing-
15 plate constituting portions, the two bearing-plate
constituting portions passing through the blade-root
constituting portion with the bearing-plate constituting
portions crossing within the blade-root constituting
portion.
20 The blade root may be made of ceramic matrix
composite material.
The invention also provides a turbine engine blade
having a blade root as defined above or fabricated using
the method as defined above. The invention also provides
25 a turbine engine fitted with at least one such blade.
Brief description of the drawing
Other characteristics and advantages of the present
invention appear from the following description made with
30 reference to the accompanying drawing, which show an
implementation having no limiting character. In the
figures:
• Figure 1 is a view of a blade root of the
invention mounted on a rotor disk;
35 • Figure 2 is a highly diagrammatic view showing the
arrangement of three fiber strips for making a fiber
blank in order to fabricate the Figure 1 blade root; and
5
• Figure 3 is a diagrammatic view of the fiber blank
obtained by the arrangement of Figure 2.
Detailed description of the invention
5 The invention is applicable to various blades made
of composite material for a turbine engine, and in
particular to the compressor and turbine blades of
various spools of a gas turbine engine, for example to
the blades of a low pressure turbine, such as the blades
10 shown in part in Figure 1.
In known manner, the blade 10 shown in this figure
comprises an airfoil 12, a root 14, and a platform 16
situated between the root 14 and the airfoil 12. The
blade could also have an outer platform (not shown) in
15 the vicinity of its free end (or tip).
The airfoil 12 of the blade has a curved aerodynamic
profile that extends (in the longitudinal direction) from
the platform 16 to its tip. This profile is of varying
thickness and is formed with a pressure side surface and
20 a suction side surface that join together transversely
via a leading edge and via a trailing edge (not shown).
In this example, the root 14 of the blade is in the
shape of a bulb and it is for mounting in a slot 18
formed in the periphery of a rotor disk 20 via a
25 connection of the dovetail type.
The blade 10 and its root 14 are made of composite
material, and preferably of ceramic matrix composite
(CMC) material. By way of example, reference may be made
to international patent application WO 2010/061140, which
30 describes an example of fabricating a turbine engine
blade by making a airfoil preform by three-dimensional
weaving and by densifying the preform with a matrix.
More particularly, that method provides for using
three-dimensional weaving to make a single-piece fiber
35 blank, shaping the fiber blank in order to obtain a
single-piece fiber preform having a first portion forming
a blade airfoil and root preform, and at least one second
6
portion forming a preform for an inner or outer platform
of the blade, and then densifying the preform with a
matrix. That method thus enables a blade to be obtained
that is made out of composite material having fiber
5 reinforcement constituted by the preform and densified by
the matrix, and forming a single piece with at least one
platform incorporated therein.
Figures 2 and 3 are highly diagrammatic and show how
to make a fiber blank from which a fiber preform 100 for
10 a blade root can be shaped so that, after being densified
and possibly also machined, a root is obtained for a
blade of the kind shown in Figure 1.
The blank is made from three fiber strips, each
obtained by three-dimensional weaving or multilayer
15 weaving, namely a central strip 102 surrounded by two
outer strips 104 and 106. These three fiber strips
extend generally in a direction X corresponding to the
longitudinal direction of the root to be fabricated.
In this example, it is assumed that the weaving of
20 the fiber strips 102, 104, and 106 is performed with warp
yarns extending in the longitudinal direction X of the
root to be fabricated, it being observed that weaving
with weft yarns extending in this direction is also
possible.
25 Furthermore, in the example of Figure 2, the central
strip 102 comprises a set of warp yarn layers, with the
number of these layers in this example being equal to
nine {layers c1 to c9). As for the outer strips 104 and
106, each of them comprises a set of warp yarn layers
30 equal to five (layers c10 to c14 for the outer strip 104
and layers c15 to c19 for the outer layer 106) .
The warp yarns of the sets of yarn layers forming
the central strip 102 and the two outer strips 104 and
106 are interlinked by three-dimensional weaving using
35 respective weft yarns given respective references tL, t2,
and t3. It is possible to use various types of threedimensional
weaving. In particular, reference may be
7
made to Document WO 2006/136755, which gives various
examples.
When fabricating a blade using the method described
in Document WO 2010/061140, the central strip 102 is
5 advantageously used for making the portion that, after
shaping, is to constitute a blade preform portion
corresponding to the airfoil preform. Likewise, one of
the two outer strips may advantageously be used for
making the portion that, after shaping, is to constitute
10 a blade preform portion corresponding to the platform
preform.
Beyond the portion of the central strip 102 that,
after shaping, is to constitute the blade preform portion
corresponding to the airfoil preform, each of the outer
15 strips 104 and 106 passes through the central strip 102
so as to emerge from the side of the central strip
opposite from the side of their insertion. In addition,
in this movement of passing through the central strip,
these outer strips cross each other inside the central
20 strip.
This produces an X-shaped cross of the two outer
strips 104 and 106 within the central strip 102, with the
outer strip being interchanged beyond the zone of the
fiber blank that corresponds to them passing through the
25 central strip.
It should be observed that the yarns of the various
sets of yarn layers making up the central strip 102 and
the two outer strips 104 and 106 are not interlinked
ahead of or beyond the zone of the fiber blank
30 corresponding to the two outer strips passing through the
central strip.
The two outer strips 104 and 106 pass through the
central strip 102 in directions forming an angle a lying
in the range 15° to 75° relative to the direction X of
35 the central strip. Preferably, this angle a is equal to
45°.
8
The fiber strips are then cut as follows. The
central strip 102 is cut a little beyond the zone
corresponding to the two outer strips crossing each other
therein. The outer strips 104 and 106 are cut firstly
5 level with the respective faces of the central strip
through which they emerge after crossing (the outer
portions of the central strip are cut), and secondly
ahead of the zone corresponding to passing through the
central strip in order to leave strip segments 104a and
10 106a remaining on either side of the central strip
(Figure 3).
A fiber preform 100 for the blade root that is to be
fabricated is then obtained by molding so as to form a
preform with a main portion forming a root preform
15 integrally with two secondary portions corresponding to
the strip segments 104a and 106a and forming bearingplate
preforms. After molding, the strip segments 104a
and 106a form an angle lying in the range 15° to 75°
relative to the longitudinal direction of the blade.
20 After machining, v/here necessary, the preform of the
blade root is densified with a matrix in order to obtain
a blade root made of composite material having fiber
reinforcement constituted by the preform and densified by
the matrix.
25 In the context of fabricating a blade using the
method described in Document WO 2010/061140, it should be
observed that the preform of the blade root 100 is
advantageously formed as a single piece with the portion
of the preform that corresponds to the airfoil preform.

CLAIMS
1. A method of fabricating a turbine engine blade root
out of composite material comprising fiber reinforcement
densified by a matrix, the method comprising:
5 • making a central fiber strip (102) and two outer
fiber strips (104, 106) from three sets of yarn layers
(Cj_ to cg, c10 to c14, c15 to c19) interlinked by threedimensional
weaving, the fiber strips extending in a
common direction corresponding to the longitudinal
10 direction of the blade root to be fabricated and the
yarns of the yarn layer sets not being interlinked
between the various fiber strips;
• passing the two outer strips through the central
strip with the two outer strips crossing each other
15 inside the central strip;
• eliminating the portions of the two outer strips
lying outside the central strip by cutting them off in
order to form a blade root fiber blank;
• shaping the fiber blank in order to obtain a fiber
20 preform having a main portion forming a blade-root
preform integral with two secondary portions (104a, 106a)
forming bearing-plate preforms; and
• densifying the fiber preform with a matrix in
order to obtain a blade-root made of composite material
25 having fiber reinforcement constituted by the preform and
densified by the matrix.
2. A method according to claim 1, wherein the two outer
strips pass through the central strip in directions
30 forming an angle (a) lying in the range 15° to 75°
relative to the direction of the central strip.
3. A method according to claim 2, wherein the two outer
strips pass through the central strip in directions
35 forming an angle (a) of 45° relative to the direction of
the central strip.
10
4. A method according to any one of claims 1 to 3,
wherein the central strip is also used for making a fiber
preform for a blade airfoil.
5 5. A method according to any one of claims 1 to 4,
wherein at least one of the outer strips is also used for
making a fiber preform for a blade platform.
6. A method according to any one of claims 1 to 5,
10 wherein the fiber strips are woven with their
longitudinal directions (X) that correspond to the
direction of the blade root that is to be fabricated
extending in the warp direction.
15 7. A method according to any one of claims 1 to 5,
wherein the fiber strips are woven with their
longitudinal directions (X) that correspond to the
direction of the blade root that is to be fabricated
extending in the weft direction.
20
8. A turbine engine blade root (14) made of composite
material comprising fiber reinforcement densified by a
matrix, the blade root being characterized in that it
includes a blade-root constituting portion integrally
25 formed with two bearing-plate constituting portions, the
two bearing-plate constituting portions passing through
the blade-root constituting portion with the bearingplate
constituting portions crossing within the bladeroot
constituting portion.
30
9. A blade root according to claim 8, wherein the two
bearing-plate constituting portions form an angle lying
in the range 15° to 75° with the blade-root constituting
portion.
11
10. A blade root according to claim 9, .wherein the two.
bearing-plate constituting portions form an angle of 45°
with the blade-root constituting portion.
11. A blade root according to any one of claims 8 to 10,
wherein the blade root is made of ceramic matrix
composite material.
12. A turbine engine blade (10) having a blade root (14)
according to any one of claims 8 to 11 or fabricated
using the method of any one of claims 1 to 7.
13. A turbine engine having at least one blade (10)
according to claim 12.