Title of the invention
A 3D woven fiber structure, a fiber preform obtained
from such a fiber structure, and a composite material
part including such a preform
5
Backqround of the invention
The invention relates to making a fiber structure
woven as a single piece by three-dimensional (3D)
weaving, in particular for fabricating a composite
10 material part. One particular, but non-exclusive, field
of application of the invention lies in making fiber
structures for preforms of composite material parts for
aircraft or turbomachines, in particular for aviation
turbine engines.
15 In well-known manner, a composite material part may
be obtained by making a fiber preform and by densifying
the preform with a matrix. Depending on the intended
application, the preform may be made of glass, carbon, or
ceramic fibers, and the matrix may be made of an organic
20 material (polymer) of car-bon, or of ceramic.
For parts that are relatively complex in shape, it
is known to make a fiber structure or blank as a single
piece by 3D (or multiple-layer) weaving, and to shape the
blank so as to obtain a fiber preform that presents a
25 shape that is close to the shape of the part that is to
be fabricated. Shaping often includes a folding
operation in order to form an angle between two portions
of the 3D woven structure.
This can result in the yarns of the fiber structure
30 being excessively stressed mechanically in a fold zone,
in particular on the inside of the corner that is formed
when said corner is sharp.
Object and summary of the invention
35 An object of the invention is to remedy such a
drawback.
In a first aspect of the invention, this object is
achieved by a fiber structure woven by three-dimensional
weaving with a plurality of layers of warp yarns
interlinked by weft yarns of a plurality of layers of
weft yarns, the fiber structure having a first portion
5 and a second portion situated extending each other in the
weft direction and foldable relative to each other at a
fold zone;
- in which structure, in the fold zone and in each
weft plane of the fiber structure, the yarns of two
10 layers of weft yarns situated in a region adjacent to an
outside face of the fiber structure have paths that
cross.
As explained below, such an arrangement serves to
limit the curvature that is imposed on the yarns in the
15 fold zone while folding.
~ccording to another*aspect of the invention, the
invention provides a fiber preform formed by a fiber
structure woven by three-dimensional weaving with a
plurality of layers of warp yarns interlinked by weft
20 yarns of a plurality of layers of weft yarns, the fiber
structure having a first portion and a second portion
situated extending each other in the weft direction and
forming between them an angle by folding at a fold zone;
in which preform, in the fold zone and in each weft
25 plane of the fiber structure, the yarns of two layers of
weft yarns situated in a region adjacent to an outside
face of the fiber structure situated on the inside of the
corner have paths that cross.
Advantageously, one of the two weft yarns is the
30 yarn that, in the first or the second portion, is the
closest to the outside face.
In an embodiment of the fiber structure or of the
fiber preform, in the fold zone, the yarns of the two
layers of weft yarns closest to the outside face of the
35 fiber structure have paths that cross.
In another embodiment of the fiber structure or of
the fiber preform, in, the fold zone, the yarns of the
first and third layers of weft yarns from the outside
face,of the fiber structure have paths that cross, and
likewise the yarns of the second and fourth layers of
weft yarns.
In yet other aspects of the invention, the invention
grovides a fiber structure or a fiber preform-as defined
above in which the terms "weft" and "warpu are
interchanged.
In yetpanother aspect of the invention, the
invention provides a composite material part comprising a
fiber preform as defined above that is densified by a
matrix. a-
Brief description of the drawings
The invention can be better understood on reading
the following description given by way of non-limiting
indication with reference to the accompanying drawings,
in which :
Figure 1 is a highly diagrammatic view of a plane
of a 3D woven fiber structure in an embodiment of the
invention;
- Figure 2 is a highly diagrammatic view of a plane
of a fiber preform obtained after shaping the Figure 1
fiber structure;
- Figure 3 is a diagrammatic view in perspective of
a part fabricated from a preform of the Figure 2 type;
- Figure 4 is a diagrammatic view in perspectivk of
another part that can be fabricated from a fiber preform
of the invention;
Figure 5 is a highly diagrammatic view of a plane
of a 3D woven fiber structure in a variant of the
Figure 1 embodiment;
- Figure 6 is a highly diagrammatic view of a plane
of a fiber preform obtained after shaping the Figure 5
fiber structure;
- Figure 7 is a diagrammatic view in perspective of
a part fabricated from a preform of the Figure 6 type;
- Figure 8 is a highly diagrammatic view of a plane
of a 3D woven structure in another embodiment-of the
invention; and
Figure 9 is a highly diagrammatic view of a plane .
5 of a fiber preform obtained after shaping the Figure 8
fiber structure.
Detailed description of embodiments
In order to avoid overcrowding the drawings, in
10 Figures 1, 2, 5, 6, 8, and 9 , which show weft planes, the
paths of the weft yarns are represented by straight line
segments, while the warp yarns are represented by dots.
The term "weft planet1 is used to mean a plane
perpendicular to the warp direction and containing a
15 column of weft yarns. Since 3D weaving is involved, it
will be understood that the yarns of one of the weft and
warp directions follow sinuous paths in order to
interlink the yarns of the other direction belonging to
different layers of yarns, with the exception of any non-
20 interlinked zones and of any weft yarns that may be added
at the surface in order to perform two-dimensional (2D)
weaving therein. Various 3D weaves may be used, such as
interlock, multiple-satin, or multiple-plain weaves, for
example as described in particular in Document
25 WO 2006/136755. It is possible in particular to make use
of a 3D interlock weave where this definition includes a
satin type surface weave.
Figure 1 is a highly diagrammatic view of a weft
plane of a fiber structure 10 that is 3D woven as a
30 single piece having opposite outside faces 10a and lob.
The fiber structure 10 is made up of a plurality of
layers of warp yarns - c, the warp yarns of the different
layers being interlinked by weft yarns in a plurality of
layers of weft yarns t, to t, that provide the 3D weaving.
35 In Figure 1, reference t designates the weft direction. . -
The fiber structure 10 comprises two portions 12 and
14 extending each other and that are foldable relative to
each other in a fold zone 16 in order to form a fiber
preform 20 as shown in Figure 2, with the portions 12 and
14 then forming between them a non-zero angle a. The
fiber preform 20 in the example shown presents a section
that is substantially L-shaped.
The paths of the weft yarns t, and t, that are
closest to the face 10a cross in the fold zone 16, the
face 10a being the face that, after folding, is situated
on the inside of the angle formed by the portions 12 and
14. As a result, the arrangements of the weft yarns t,
and t, in each plane of the fiber structure in the portion
12 and in the portion 14 are inverted on opposite sides
of the fold zone 16.
As can be seen more particularly in the detail on a
larger scale in Figure 2, the radius of curvature imposed
on the weft yarns t, and t, is thus greater than the
radius of curvature (shown as a dashed line) that would
be imposed on the yarn t, if it did not cross the yarn t,.
The risk of weft yarns being damaged or buckling in the
vicinity of the face 10a is thus reduced by this
reduction in the amount of curvature that is imposed,
which risk is particularly high when the angle a is
small.
Figure 3 shows a composite material part 30 of the
kind. that can be obtained by densifying the preform 20
with a matrix, the part having two portions 32 and 34
that form a non-zero angle between each other.
In Figures 2 and 3, the folding is performed about
an axis that is substantially parallel to the-warp
direction.
In a variant, the folding may be performed about an .
axis e that is parallel to a plane formed by the weft and
warp directions but that is not parallel to either of
them so that, after densification of the fiber preform,
the part 40 as shown in Figure 4 presents two portions 42
and 44 that form a non-zero angle between each other.
Under such circumstances, in order to comply with the
orientation of the fold zone, arrangements are made so
that the locations of the crossovers between the weft
yarns in the vicinity of the face 10a are not all
situated on the same warp column over the entire width of
5 the preform, but vary from one weft plane to another. In
a variant, it is possible to use a preform similar to
that used for the part shown in Figure 3, but with the
preform being shaped by being placed on the bias in a
mold that has the desired shape, so as to put the
10 locations of the crossovers between the weft yarns in
alignment with the axis !.
Figure 5 is a highly diagrammatic view of a weft
plane of a fiber structure 50 that is 3D woven as a
single part having opposite outside faces 50a and 50b.
15 The fiber structure 50 is made up of a plurality of
layers of warp yarns - c.
The fiber structure 50 includes a portion 52 in
which the warp yarns in all of the layers of warp yarns
are interlinked by 3D weaving by means of the weft yarns
20 of a plurality of layers of weft yarns t, to t, that
.provide 3D weaving. The fiber structure 50 also has two
portions 54a and 54b that are situated so as to extend
the portion 52 on either side of a non-interlinked zone
58 that extends from one edge 50c of the fiber structure
25 50 over a fraction of its dimension in the weft
direction. In each of the portions 54a and 54b, the warp
yarns in all of the warp yarn layers are interlinked by .
3D weaving by means of weft yarns respectively t, to t,
and t, to t,, with no interlinking taking place across the
30 .non-interlinked zone 58 between the portions 54a and 54b.
In the example shown, the*numbers of layers of warp yarns
in the portions 54a and 54b are equal to four.
Naturally, these numbers need not necessarily be four,
and they could even be different from each other,
35 providing that each of them is not less than two.
The portions 54a and 54b can be folded outwards
relative to the portion 52 in respective fold zones 56a
and 56b in order to form a fiber preform 60 as shown in
Figure 6 and presenting a section that is substantially
T-shaped.
The paths of the weft yarns t, and t, that are
5 closest to the face 10a cross in the fold zone 56a so
that the arrangements of the weft yarns t, and t, in each
plane of the fiber structure 50 in the portion 52 and in
the portion 54a are interchanged. Similarly, the paths
of the weft yarns t, and t, that are closest to the face
10 50b cross in the fold zone 56b so that the arrangements
of the weft yarns t, and t, in each plane of the fiber
structure in the portion 52 and in the portion 54b are
interchanged.
As in the embodiment of Figures 1 and 2, reduced
15 curvature is thus imposed on the weft yarns adjacent to
the faces 50a and 50b in comparison with an arrangement
. in which the weft yarns t, & t, and t, & t, do not present
any mutual crossings.
Figure 7 shows a part 70 made of composite material
20 that presents a substantially T-shaped section and that
can be obtained by densifying the preform 60 with a
matrix, the part presenting a portion 72 that is extended
at one end by flanges 74a and 74b.
Figure 8 is a highly diagrammatic view of a weft
25 plane of a fiber structure 80 that is 3D woven as a
single piece, having opposite outside faces 80a and 80b.
The fiber structure 80 isAmade up of a plurality of
layers of warp yarns c, with warp yarns - of different
layers being interlinked by weft yarns in a plurality of
30 layers of weft yarns t, to t, that provide 3D weaving.
The fiber structure 80 comprises two portions 82 and
84 that extend each other and that are foldable relative
to each other in a fold zone 86 so as to form a fiber
preform 90 as shown in Figure 9, in which the portions 82
35 and 84 form a non-zero angle P between each other. The
fiber preform 90 in the example shown presents a section
that is substantially L-shaped.
The paths of the weft yarns t, and t, forming part of
the first and third layer of weft yarns t, to t, starting
from the face 80a cross one another in the fold zone 86,
with the face 80a being the face that, after folding, is
situated on the inside of the corner formed by the
portions 82 and 84. In addition, the paths of the weft
yarns t, and t, forming part of the second and fourth
layers of weft yarns t, to t, starting from the face 80a
likewise cross one another in the fold zone 86.
By means of this arrangement, and as shown in the
detail on a large scale in Figure 9, the radii of
curvature imposed in particular on the yarns t, and t, are
further increased in comparison with the embodiment of
Figures 1 and 2.
Densifying the fiber preform 90 with a matrix makes
it possible to obtain a composite material part of the
type shown in Figure 3.
After a fiber preform has been shaped, it is
densified by forming a matrix of a nature that is
selected as a function of the intended application, e.g.
an organic matrix that may be obtained in particular from
a resin that is precursor of a polymer matrix such as an
epoxy, bismaleimide, or pblyimide resin, or a carbon
matrix, or a ceramic matrix. With a carbon matrix or a
ceramic matrix, densification may be performed by
chemical vapor infiltration (CVI) or by impregnation with
a liquid composition containing a resin that is a carbon
or ceramic precursor followed by heat treatment for
pyrolyzing or ceramizing the precursor, which methods are
themselves well known. The fibers of the fiber preform
are likewise of a material that is selected as a function
of the intended application, being made for example of
glass, of carbon, or of ceramic.
Finally, it should be observed that in the described
embodiments of structures and of fiber preforms, the
terms "weftH and "warp" could be interchanged.
CLAIMS
1. A fiber structure woven by three-dimensional weaving
with a plurality of layers of warp yarns interlinked by
weft yarns of a plurality of layers of weft yarns, the
5 fiber structure having a first portion (12; 52; 82) and a
second portion (14; 54a, 54b; 84) situated extending each
other in the weft direction and foldable relative to each
other at a fold zone (16; 56a; 56b; 86);
.the structure being characterized in that in the
10 fold zone and in each weft plane of the fiber structure,
the yarns of two layers of weft yarns situated in a
region adjacent to an outside face (10a, 50a; 50b; 80a)
of the fiber structure have paths that cross.
15 2. A fiber structure according to claim 1, characterized -
in that one of the two weft yarns (tl; t2; t7; t8) is the
yarn that, in the first portion or in the second portion,
is the closest to the outside face.
+
20 3. A fiber structAre according to claim 2, characterized
in that, in the fold zone, the yarns (tl; t2; t7; t8) of
the two layers of weft yarns closest to the outside face
of the fiber structure have paths that cross.
25 4. A fiber structure according to claim 2, characterized
in that, in the fold zone (86), the yarns (tl; t3) of the
first and third layers of weft yarns from the outside
face of the fiber structure have paths that cross, and
likewise the yarns (t2; t4) of the second and fourth
30 layers of weft yarns.
5. A fiber structure woven by three-dimensional weaving
with a plurality of layers of weft yarns interlinked by
warp yarns of a plurality of layers of warp yarns, the
35 fiber structure having a first portion and a second
portion situated extending each other in the warp
direction and foldable relative to each other at a fold
zone ;
the structure being characterized in that in the
fold zone and in each warp plane of the fiber structure,
the yarns of two layers of warp yarns situated in a
5 . region adjacent to an outside face of the fiber structure
have paths that cross.
6. A fiber structure according to claim 5, characterized
in that one of the two warp yarns is the yarn that, in
10 the first portion or in the second portion, is the
closest to the outside face. %
7. A fiber structure according to claim 6, characterized
in that, in the fold zone, the yarns of the two layers of
15 warp yarns closest to the-outside face of the fiber
structure have paths that cross.
8. A fiber structure according to claim 6, characterized
in that, in the fold zone, the yarns of the first and
20 third layers of warp yarns from the outside face of the
fiber structure have paths that cross, and likewise the
yarns of the second and fourth layers of warp yarns.
9. A fiber preform (20; 60; 90) formed by a fiber
25 structure woven by three-dimensional weaving with a
plurality of layers of warp yarns interlinked by weft
yarns of a plurality of layers of weft yarns, the fiber
structure having a first portion (12; 52; 82) and a
second portion (14; 54a, 54b; 84) situated extending each
30 other in the weft direction and forming between them an
angle by folding at a fold zone;
the structure being characterized in that in the
fold zone and in each weft plane of the fiber structure,
the yarns of two layers of weft yarns situated in a
35 region adjacent to an outside face (lOa, 50a; 50b; 80a)
. of the fiber structure situated on the inside of the
corner have paths that cross.
10. A fiber preform according to claim 9, characterized
in that one of the two weft yarns (tl; t2; t7; t8) is the
yarn that, in the first portion or in the second portion,
5 is the closest to the outside face.
11. A fiber preform according to claim 10, characterized *
in that, in the fold zone, the yarns (tl; t2; t7; t8) of
the two layers of weft yarns closest to the outside face
10 of the fiber structure have paths that cross.
%
12. A fiber preform according to claim 10, characterized
in that, in the fold zone (86) , the yarns (tl; t3) of the
first and third layers of weft yarns from the outside
15 face of the fiber structure have paths that cross, and
likewise the yarns (t2; t4) of the second and fourth
layers of weft yarns.
13. A fiber preform woven by three-dimensional weaving
20 with a plurality of layers of weft yarns interlinked by
warp yarns of a plurality of layers of warp yarns, the
fiber structure having a first portion and a second
portion situated extending each other in the warp
direction and forming between them an. angle by folding at
25 a fold zone;
the structure being characterized in that in the
fold zone and in each warp plane of the fiber structure,
the yarns of two layers of warp yarns situated in a
region adjacent to an outside face of the fiber structure
30 situated on the inside of the corner have paths that
cross.
14. A fiber preform according to claim 13, characterized
in that, in the fold zone, the yarns of the first and
35 third layers of warp yarns from the outside face of the
fiber structure have paths that cross, and likewise the
yarns of the second and fourth layers of warp yarns.
15. A fiber preform according to claim 14, characterized
in that, in the fold zone, the yarns of the two layers of '
warp yarns closest to the outside face of the fiber
5 structure ,have paths that cross.
16. A fiber preform accorkng to claim 14, in the fold
zone, the yarns of the first and third layers of warp
yarns from the outside face of the fiber structure have
10 paths that cross, and likewise the yarns of the second
and fourth layers of warp yarns.
17. A composite material part comprising a fiber preform
according to any one of claims 9 to 16 densified by a
15 matrix.