FIBROUS REINFORCEMENT STRUCTURE FOR COMPOSITE MATERIAL
PART HAVING A REDUCED THICKNESS PORTION
Background of th'e invention
5 The present invention relates to making parts out of
composite material, and more particularly to making '
reinforcing fiber structures for such parts.
A particular field of application of the invention
lies in making parts of strucfural composite material,
10 i.e. parts having a fiber reinforcing structure that is
densified by a matrix. Composite materials make it
possible to fabricate parts that present overall weight .
that is less than that of the same parts' when made of
metal.
15 .In the context of making fiber structures by
multilayer weaving so as to produce the fiber
reinforcement for a composite.materia1 part, such as a
. blade for an aeroengine, it is necessary during weaving
. .
of the structure to withdraw yarns both in the warp
20 direction and in the weft direction in order to match
reductions in the thickness of-the part, e.g. in the
fastening or in the trailing edge of the blade, so as to
obtaiG a fiber preform that presents the quasi-final
shape and dimensions of the blade (i.e.' that presents its
~ ~ p ~ - . . ~~ ~ 25 . ~~ ~ ~~ "net -- shape"). ~~ ~ ~~~
~~~p-- Withdrawing ~p~yar-ns i~n-- -t his way during- --
weaving gives rise to non-woven yarns being present
~ ~ ~~ ~ 'locaJly af the surface of the fiberstructures-(i.e.-tb 1~~
. .
yarns that are floated), which yarns are subsequently cut . ~-
during a second operation.
~ -~ ~
30 Cutting these fibers at the surface of the'structure
gives rise 1ocally.to fiber misalignments and '
~~~ .
consequently, once the matrix has been deposited,
zones in the part that are rich in matrix material
zones are potential sources of microcracking in the
. .
35 material of the part.
In addition, because of the weave present at the
surface of the fabric, e.g. a satin weave, all of the
floated yarns present after the last interlinking point
of the yarn that has been extracted from the fiber need
to be cut, thereby giving rise locally to a significant
variation in the density of fibers.
5
Object anti summary of the invention
It is therefore desirable to be able to have fiber
structures available with the cpasi-finai shape and '
dimensions of the .composite material part that is to be
10 made, in particular in portions thereof that are of
decreasing thickness, and it is desirable for this to be
possible with,a surface state that is regular and with
. fiber densityvarying minimally in such portions.
To this end, the invention proSides a fiber
15 structure for reinforcing a composite material part, said
structure being woven as a single piece by multilayer
weaving between a first plurality of layers of yarns and
, a second plurality of layers of yarns, . . the fiber
. structure including at least one portion of decreasing
20 thickness,
the structure beisg characterized in that, in the
portion of decreasing thickness, the fiber structure
'includes at its surface:
. c . . one or more yarn withdrawal parts in surface
- 25 continuity -- in ~ each ~ of ~ wh. i_ c.-h yarns are interrupted ~ - ~ -~ - ~~ ~ that ~ - ~~ ~
* belong to a layer of yarns of the first plurality of
layers~oi-yarnsu nderlying the layer ~f yarns o. f. the
first plurality of layers of yarns situated at the
~
surface of the structure; and
3 0 : one or more yarn withdrawal parts in .surfgce
discontinuity in each of which yarns are. interrupted in
~ ~~.
the layer of yarns of the first plurality of layers of
yarns situated in the surface of the'structure, each
interrupted yarn being replaced in the surface of.the
. .
35 structure by a yarn of a layer of yarns underlying the
first plurality of layers- of yarns; and $
in that the yarns of the layers of the second
plurality of layers of yarns situated at the surface of
the fiher structure are continuous over at least the
entlre portion of decreasing thickness.
The presence of yarn withdrawa1,parts both in
surface continuity and in surface discontinuity in the
fiber structure makes it possible to optimize the yarn
continuity zones in the surface and consequently to limit
misalignments and'density variations of surface fibers in
the structure, while also making such a structure easier
to weave. If the yarns, e.g. the warp yarns, that are
situated at the surface in the portion of decreasing
thickness are conserved continuously over the entire
length of that portion, then the yarns need to cross a
large number of weft layers as a result of successive
withdrawals of weft,yarn layers all along the portion of
decreasing thickness. These crossovers give ~ i s eto high
levels of friction that can fray the continuous warp
- .
yarns at the surface and make .the structure more
difficult to weave. By interleaving yarn withdrar.~al
parts in surface discontinuity between the withdrawal
parts in surface continuity, such drawbacks are avoided,
since surface continuity is taken up using new yarns as
from the withdrawal part in surface discontinuity. . .
~ ~ According to' a particular aspect of,the invention, ~ ~~~ . . - ~ ~ ----
in each'part in surface discontinuity, each interrupted
y.a r. n of the layer of the first plurality df layers of
yarns is interlaced with at least one yarn of a layer of
the second plurality of layers of yarns immediately
befb-re exiting the structure.
By interlacing in this way the yarn extracted from
, ~.
the fiber structure, non-woven yarns due to extracting
the yarn and that subsequently need to be cut at the end
of weaving are eliminated. This reduces variation in the
volume density of fibers in the fiber withdrawal parts in
surface$ discontinuity.
According to another aspect of the invention, the
fiber structure presents first and second outside faces
extending in a longitudinal direction, the yarn
withdrawal parts present in.the first' face being
5 longitudinally offset relative to the yarn withdrawal
' parts present in the second face.
According to yet another aspect of the invention,
the portion of decreasing thickness presents, in the
direction of the yarns of the first plurality of layers
10 of yarns, a decreasing number of layers of yarns.of the
second plurality of layers of yarns, the fiber structure
including yarn withdrawal parts in surface discontinuity
that are distributed as a function of a determined
decrease in the number bf layers of yarns of the second
15 plurality of layers of yarns.
The invention also provides a composite material,
part comprising a fiber structure of the invention.
densified by a matrix. In particular, the part may
. .
constitute an aeroengine blade.
2 0 The invention also provides a turboprop fitted.with
a pluralit9 of blades of the invention.
The invention also provides an aircraft fitted with
at least'one turboprop of e 3 is a warp section view on a 1arger.scale'
15 of a portion of decreasing thickness of the Figure 1
fiber structure;
Figure 4 is a diagrammatic perspective view of a
blade .fiber preform obtained from the Figure 1 fiber
. .
structure; and
2 0 Figure 5 is a diagrammatic perspective view of a
composite material blade obtained by densifying the
Figure 4 preform with a matrix.
Detailed description of embodiments . s
.P~ 25 p p ~ ~ p ~ ~ ~- - - The invention applies ~ . ~ ' . in ge-n -e-r al t-o making fiber i
~~~p - ~ ~ structure suitable for constituting fiber reinforcement,
~ ~~ - -~ referred to qs pre£orms, for use in fabridating.composite ~ --
. .
material parts, in particular aeroengine blades; ~~ the
parts being obtained by densifying fiber structures with
30 a matrix. Typically, thk matrix is made OF a resin, for'
.~~ composite materials that ar.e used up to temperatures th'at
-~ . .
are relatively. low, typically up to 300°C, or by a
refractory material such as carbon or ceramic for
thermostructural composite materials.
3 5 Figure 1 is a highly diagrammatic view of a fiber
structure 200 for forming the fiber reinforcement of an
aeroengine blade.
The fiber structure200 is obtained by multilayer
weaving performed in known manner using a jacquard type
loom having a bundle of warp yarns or strands 201
organized as a plurality of layers, the warp yarns being '
5 inter1inked.b~w eft yarns 202 likewise arranged as a
plurality of layets. An example of making a fiber
preform for forming the fiber reinforcement of an
aeroengine blade is described in particular in detail in
the following documents: US 7 101 154, US 7 241 112, and
10 WO 2010/061140, the contents of which is incorporated
herein by reference.
~ ~
The fiber structure 200 is woven in the form of a
strip extending generally in a direction X corresponding
to th.e longitudinal direction of the blade that is to be
15 made. The fiber structure presents thickness that varies
in a manner that is hetermined as a function of the
longitudinal thickness of the airfoil profile of the
blade . t. hat is to be made. In its portion that is to form
a ro0.t preform, the fiber structure 200 presents extra
20 thickness 203 determined as a function of the thickness
of the root of the blade that i's to be made and that may
be implemented, for example, by using yarns of greater
weight or by using an insert.' The fiber structgre 200 is
extended by a portion of decreasing thickness 204 that is
~~ - - 25 to form the tang ~ of the blade ~ followed ~ - by ~ a portion ~~ ~ 205 .. . ~~. that is.to form the airfoil of the blade. In a direction
perpendicular to -the 'direction-X , the portion ,205 , . .
presents a profile of thickness'that varies between its
~ -
edge 205a that is to form the leading edge of the.blade .
30 and its edge 205b-that is to form the trailing edge bf '.
the blade' that' is to be made. ..
~ . ~ , ~- ~.
The. fiber structure 200 is woven as a single piece
and, after cutting non-woven yarns, it ".needs 'to present
the quasi-final shape and dimensions of the blade (i.e. .
. . - .
35 its "net shape"). To this end, in the portions of
varying thickness in the fiber structure, and in the
portion of decreasing thickness 204, the thickness of the
preform is reduced by progressivelywithdrawing layers of
warp yarns and of weft yarns during weaving.
Figure 2 is a weft section view showing the weaving
of a part of'the portion of decreasing thickness 204 of
5 the fiber structure 200, the structure 200 comprising at
the beginning of this part of the portion of decredsing
thickness 204, ten layers C, to C,, of warp yarns (here
shown as occupying a single column) extending in the
direction X and ten layers' T, to TI, of weft yarns. In
10 the example described here, the outside faces or skins
206a and 206b of the fiber structure 200 are made using a
satin type weave, here a satin-4 weave (floating over ,
three )left yarns before an interlink' point), while the .
internal part of the structure 200 is made using an
15 interlock type weave. The term "interlock" is used
herein to mean a weave in which each layer of warp yarns
interlocks a plurality of-layers of weft yarns with a13
of the yarns in a given warp column having the same
. .
movement in the weave plane.
20 Other known types of multilayer weaving may be used,
in particular such as those described in document
WO 2006/136755, the content of which is incorporated
he>ein by reference.
The fiber structure of the invention may in
. . 25 particular, but not exclusively, be woven using fibers ~~~ ---- ~ -~ ~ - - ~ - - ~ ~ ~- ~-~ ~~ . . ~ ~ . .
made of carbon or of ceramic such as silicon carbide.
* .
~ ~ As weaving prbgresses in'the direction -X of the ~ -~~~
portion 204' of decreasing thickness; yarns of the warp
yarn layers and also of the weft yarn layers are
30 withdrawn fcom the structure 200. In the example
described here, one layer of weft yarns is'withdrawn for
~ ~ ~~ ~ .- ~~ .
every ten warp columns.
Concerning the warp yarns, these are extracted or
removed from the structure at.a determined location
35 referred to as the "harp yarn withdrawal part" and they
are no longer woven with the weft yarns situated after
the warp yarn withdrawal part. In the present invention,
two types of warp yarn withdrawal part are to be
distinguished, namely withdrawal parts referred to as
being "in surface continuity" and withdrawal
referred to as being "in surface discontinuity".
5 . In withdrawal parts in surface continuity, there are
removed from the texture warp yarns that belong to a
layer of warp yarns underlying the layer of warp yarns
situated at the surface of the structure, as applies for
example to the withdrawal parts 210, 211, and 212 in
10 surface continuity shown in Figure 2. More precisely, at
the part 210, there is withdrawn from the structure the
warp yarn,F,, that forms part of the warp yarn layer C,
situated at this location of the fiber structure beneath
the warp yarn layer C, that is sTtuated at the surface of
15 the structure. The same applies to the parts 211 and 212
from which there are withdrawn from the texture
respectively the warp yarns F,, and F,, belonging to the
warp yarn layers C8 and C, situated . . respectively beneath
the surface layers C, and C, of warp yarns.
2 0 By withdrawing warp yarns from a layer underlying
the layer of warp yarns situated at the surface of the
fiber structure, surface continuity is ensured for the
layers of warp yarns at the surface'of the preform,
. . thereby making it possible in particular to avoid yarns
25 becoming misaligned, as occurs when it is always the ~ ~ ~ - - p-ppp--p- ~ ~-~ ' . . ~ ~~ -~ ~~~ ~ ~ ~~
yarns on the surface that are cut, thereby giving'rise
~ ~ ~ ~~ ~ ~~ - ~ after densification to zones 'that,are r.ich in resinand 4 -
that constitute sources of microcracks in the composite
material. ~urthermdre, the warp yarn withdzawal parts
30 ' that are in surface continuity make it possib'le to reduce
the variation in the concentration gf fibers at .this
location of the structure.
Nevertheless, if the yarns of the same layer of warp
yarns are conserved at the surface of the fiber structure
35 over the entire length of the portion of decreasing
thickness, then the yarns in said layer are conserained
to cross a large number of layers of weft yarns because
of the way they are withdrawn progressively as weaving
continues. These crossovers can give rise to high levels
of'friction that may fray the warp yarns and make the
'structure more difficult to weave.
5 To this end, and in accordance with the invention,
the fiber structure also includes warp'yarn withdrawal
parts in surface discontinuity in which warp yarns are
withdrawn from the fiber structure, which warp yarns
belong to the'warp yarn layer situated at the surface of
10 the fiber structure, as applies for example in the parts
220 and 221 shown in Figure 2. More precisely, in the
part 220, there is withdrawn the yarn F,, forming part of
the layer C, of warp yarns situated at the .surface in this
location of the fiber structure-immediately after the
15 column C,,,, of weft yarns. Once extracted from the fiber
structure, the yarn F,, is replaced at the surface by the
yarn F,, of the underlying layer C, of warp yarns that is
woven beyond the part 220 qith the same satin weave as
was used f6r yarn F,, prior 'to the part 220. Similarly,
20 from the part 221, there is withdrawn the yarn F,,, that
forms part of the layer C,, of warp yarns situated at the
surface in this location of the fiber structure
immediately after the column.C,,,, of weft yarns. Once
'extracted from the fiber structure, the yarn FClb5s
-~--- ~ ~ 25 replaced ~ at the surface ~ ~- by the yarn F cg of the underlying ~
. ?
. ~ ~
layer Cg of warp yarns that is woven beyond the part 221
with the same sayin weave as isused £orthe yarn~Fcg
. '
before the part 221. . .
The positioning of warp yarn withdrawal parts in
' 30 ':surface discontinuity may be determined as a function of
- ~~
the number of weft layers that' are withdrawn in .- order to
limit friction and improve weaveability. By way of
example, the fiber structure may include' in each of its
.faces a warp yarn.withdrawa1 part in surface
35 discont&uity whenever five weft layers have been
withdrawn and then another one after five more weft
layers have been withdrawn, and so on. The fiber
structure of the invention preferably has a majority of
yarn withdrawal parts that are in surface continuity
compared with the yarn withdrawal p&rts that are, in
surface discontinuity.
5 The yarn withdrawal parts, whether in surface
continuity or discontinuity, that are present on a face
of the fiber structure are preferably offset in the
longitudinal direction of the structur6 relative to the
withdrawal parts presented on the other face of said
10 structure, as shown in Figure 2 in order to balance the
fiber structure.
The yarn withdrawal parts, whether in surface
continuity or discontinuity, may also be present on only
one of the faces of'the fiber structure in order to
15 optimize the surface skate of one of the faces relative
to the other.
Furthermore, according to an aspect of the
invention, when a warp yarn is to be extracted from the
fiber structure, said yarn is always interlaced with at
20 least one yarn of the column of weft yarns that.is
situated immediately before the withdrawal part.from
which the warp yarn is extracted, with this being
independent of the pattern of the weave at this location .
ofthe fiber structure. For example, in Figure 2, the . '
25 warp yarn F,, that is extracted from the . -~ ~ - ~ - ~ fiber structure ~ - ~-~ ~ . - ~~ . _ 7 ~- ~ ~ ~ ~p~~-
at the withdrawal part 221 is interlaced. with two .
~ ~-~ consecutive weftyarn3 of the weft yarn-layer Tg even^- . ~ ~ ----
. .
~~ ~ though; in the satin-4 pattern implemented up to 'that . . ~ ~
point on the surface of the strbcture, the warp yarn F;,
~ -~
30 ought to leave the structure at the column preceding the
~ ~
part 221 without interlgicing the weft yarn of-the weft
. . . ~~ - .- ~ ~
yarn column C,,,, situaGed at the surface of the structure.
At the part 22'0, the?e is no need in this example to
force any interlacing of the warp. yarn F,,, since it is
35 extracted from the fiber structure 200 immediately after
its point where it interlinks with the weft yarn situated
at the surface of the column C,,,, of weft yarns.
By ensuring that the warp yarn is always interlaced
with at least the last weft yarn situated immediately
before its exit from the fiber structure, the number of
weft yarns that are unwoven as a result of a warp yarn
belng extracted and that must subsequently be cut after
weaving is thus reduced. This reduces variation in the
density of fibers per unit volume in the warp yarn
withdrawal parts that are in surface discontinuity.
In the example described herein, it is the warp
yarns that are situated at the surface of the fiber
structure that are extracted from the withdrawal parts in
surface discontinuity. Under puch circumstances,
continuity is maintained of the weft yarns situated at
the surface of the fiber structure, as shown in ~iguie 3,
which shows the weaving in a warp section view in a part
of the profile of varying thickness of the portion 205 of
the structure that is to form.the airfoil of the blade
and in which the weft yarns F,,, and F,,, situated . . in the
surface on both sides of the fiber structure 200 are
continuous over the entire structure, whereas the weft
yarns F,, to F,,, belonging to the weft ygrn layers
underlying the surface weft yarn layers to which the
yarns Fk5, and F Tb~el ong~respectively' are extracted
progressively from the textlre. It .should be observed
that the weave ~ shown in Figure 3 ~~~ is different ~ f-ro m the . . ~-~
weave shown in Figure 2.
!In a variant of the-present invention,. the fiber , . ,
texture includes yarn withdrawal parts in surface
~ ~ ~ ~
discontinuity and/or continuity in the weft yarn layers
, . ~ ~
that 'are situated at the:surface of the texture. Under
such circumstances, continuity is maintained.of the warp..
. , .
yarns situated at the surface of the fiber structure. .
Once weaving of the fiber structure 200 has been'
completed, the non-woven yarns are cut, in particular
those that have been extracted from the texture at the
withdrawal parts whether in surface continuity or in
surface discontinuity. This produces the fiber preform
100 as shown in Figure 4, which preform is woven as a
single piece.
Thereafter the fiber preform 100 is densified in
order to farm a blade 10 of composite material as shown
5 in Figure 4. The fiber preform that is to constitute,the
fiber reinforcement of the part that is to be fabricated '
is densified by filling in the pores of the preform,
throughout 211 or part of its volume, with the material
that constitutes the matrix. This'densification may be
10 performed in known manner using a liquid technique or a
~ ~
gaseous technique (chemical vapor infiltration (CVI)), or
~ ~~
i indeed by using both of these techniques one after the
other.
The liquid technique consists in impregnating the
15 preform with a liquid composition containing a precursor
for the material of the matrix. The,precursor is
generally in the form of a polymer, such as a high
performance epoxy resin, possibly diluted in a .s .o lvent.
The preform is placed in a mold-suitable for being closed
20 in leaktight manner with a recess that has the shape of
the final molded blade. Thereafter., the mold is closed
and the liquid precursor of the matrix (e.g. a resin) is
injected into the entire recess so as toimpregnate all--
of the fiber structure of the preform. . +
~ ~p~~ -~~ 2 5 ~ ~~~~ ~ ~ . . The precursor ~ is transformed ~~ .into ~~~ the ma~t-r~-i-x~~, i.e. -- A - - - .-
it is polymerized, by applying heat treatment, generally
~~ - ~ ~~ - - ~ by iieatiqg the,mold after eliminating~any solvent and ~~ ~ ~- --
. +
curing the polymer, with the preform continuing to be
held in the mold that has a shape corresponding to th
30 shape of the paYt th'at-is to be made.
When forming a matrix of carbon or of ceramic,'the
~- ~- .
heat treatment consists in pyrolyzing the precursor in
order to transform the matrix into a carbon or ceramic
matrix depending on the precursor used and on pyrolysis
35 conditions. By way of example, liquid precursors for
ceramic, in particular for Sic, may be resins of the
polycarbosilane (PCS) type, or of the
polytitanocarbosilane (PTCS) type, or of the polysilazane
(PSZ) type, whereas liquid precursors of carbon may be
resins having a relatively high coke content, such as
phenolic resins. A plurality of consecutive. cycles, 6ach
5 running.from impregnation to heat treatment, may be
performed in 6rder to achieve a desired degree of
densif ication.
According to an aspect of the invention, in
particular when .forming an organic matrix, the fiber
10 preform may be densified by the well-known resin
transform molding (RTM) method. In the RTM method, the
~~~~ ~~~
fiber preform is laced in a mold presenting the outside
shape of the part.that is to be made. A thermosetting
resin is injected into the inside volume'of the mold that
15 contains the fiber preform. A pressure gradient is
generally established in said inside space between the
location where the resin is injected and orifices for
exhausting the resin in order to control . . and optimize the
w.ay the preform is impregnated by the resin.
20 In known manner, the fiber preform may also be
densified using a gaseous tkchnique of chemical vapor
infiltration (CVI) of the matrix. The fiber preform
corresponding to the fiber reinforcement of'the blade
. < that is to be made is placed in an oven into which a
25 reaction gas is admitted. The pressure and the ~ ~~. -~ ~ ' . ~ ~ ~~
temperature that exist inside the oven and the
. composition~~o'fthgea s are selected in such a manner as
- t o enable the gas to diffuse within the pores of the
~ ~~~ ~~~~ ~~
preform >. so as to form the matrix therein by depositibg a
30 solid mateiiiil in the core of the material in contact'.
with the fibers, which solid material is the..result of a.
-~~~~
~~
~~ ~ - .
component of the gas decomposing or of a reaction between
a plurality of components, in contrast to;the pressure
and temperature conditions that are specific to chemical
35 vapor deposition (CVD) methods that lead to deposition
taking place solely on the surface of the material.
An Sic matrix may be formed using
methyltrichlorosilane (MTS) that gives Sic by
decomposition of the MTS, whereas a carbon matrix may be
. obtained'using hydrocarbon gases such as methane and/or
5 propane that produce carbon by cracking. .
It is also possible to perform densificatfon by
combining the liquid technique and the gaseous technique
so as to facil'itate implementation, limit cost, and limit
the number of fabricatlon cycles while still obta-ining .
10 characteristics tha'c are satisfactory for the intended
utilization.
After densification, a composite material blade 10
is obtained, as shown in Figure 5, that includes a .root
103 in its bottom portion that is constituted by the
15. extra thickness 203 of the fiber structure 200, which is
extended by a tang 104 formed by the portion of
decreasing thickness 2.04 of the structure 200, and.by an
airfoil 105 formed by the portion 205 of . . the fiber
structure 200.
20
CLAIMS
1. A fiber structure for reinforcing a composite material
part, said structure being woven as a singl& piece by .
multilayer weaving between a ficst plurality of layers of
yarns and a second plurality of layers of yarns, the
fiber structure including at least one portion of
decreasing thickness,
the structure being characterized in that,'in the
portion of decreasing thickness, the fiber structure '
includes at its surface:
one or more yarn withdrawal parts in surface
continuity in each of which yarns are interrupted that
belong to a layer of yarns of the first plurality of
layers of yarns underlying fhe layer of yarns of the
first plurality of layers of yarns situated at the
surface of the structure; and
: one or more yarn withdrawal parts in surface
discontinuity in each of which yarns are interrupted in
the layer of yarns of the first plurality of layers of
yarns situated in the surface of the structure, each
interrupted yar'n being replaced in the surface of the
structure by a yarn of a layer of yarns underlying the
first plurality of layers of and
in that.the yarns of the layers of the second
,plurality of ~~ ~~~~ layers ~ ~~~~ ~ of yarns ~ -~ ~~ situated ~ - at the surface . . o£ -
the fiber structure are continuous over at least .the
entire portion-of~-.decreas.itnhgi ckness .~
~ ~- ~ ~~- ~
2. A fiber structure according to claim~2, characterized
30. :in that in each part in surface disc.ontinuity, each
+ . . .
;interrupted yarn ofthe layer of. the first plurality of
- . ~,~ ~ ~ ~- ~~. ~~
layers of yarns is interlaced yith at least one yarn of a
layer of the second plurality of layers of yarns
immediately before exiting the structure..
. .
3 5
3. A structure according to claim 1 or claim'2,
characterized in that the fiber structure presents first
and second outside faces extending in a longitudinal
direction, and in that the yarn withdrawal parts present
'
in the first face are longitudinally offset relative to
the yarn withdrawal parts present in the second face.
5
4. A fiber structure according to any one of claims 1 to
3, characterized in that the portion of decreasing
thickness presents, in the direction of the yarns of the
first plufality of layers of yarns, a decreasing number
10 of layers of yarns of the second plurality of layers of
yarns, and in that the fiber structure includes yarn
withdrawal parts in surface discontinuity that are
distributed as a function of a determined decrease in the
number of layers of yarns oi the second plurality of
15 layers of yarns.
5. A composite material part comprising fiber
reinforcement densified by a matrix, wherein the fiber .
. .
reinforcement is formed by a fiber structure according to
20 any one of.claims 1 to 4.
6. A part according to claim 5, characterized in that it
constitutes an aeroengine blade.
3 7 : A turboprop turbo~pr~op --i-n cplu~din g ~p~~p a plurality ~p~~ of blades -p~- p according ~ ~ . .
to claim 6.
- - ~ ~ ~~p~ -- ~~ ~ - ----
. .
8. An aircraft fitted with at least one turboprop ~. ~~~
accordino to claim 7 2
30.
., . . 9. A method of fabricatiAg'a f,i ,b-~e>r structure for
reinforcing a composite material part, the method
comprising weaving as a single piece' by multilayer
weaving between a first plurality of layers of yarns and
35 a second plurality of layers of yarns, the fiber
3
*structure including at least one portion of decreasing
thickness;
the method being characterized in that during the
weaving of the portion of decreasing thickness, there are
defined :
yarn withdrawal parts in surface continuity in
5 each of which yarns of a layer of yarns of the first
plurality of layers of yarns underlying the layer of
yarns of the first plurality of layers of yarns situated
at the surface of the structure are no longer woven with
- the yarns of the layers of the second plura'lity of layers
10 of yarns; and
yarn withdrawal parts in surface discontinuity in
each of which yarns of the layer of yarns of the first
plurality of layers.of yarns situated in the surface bf .
the structure a?e no longer woven with the yarns of the,
15 layers of the second plurality of layers of yarns, yarns
from a layer of yarns underlying the first plurality of
layers of yarns being used to replace in the surface of
the texture the yarns that are no longer woven as from , . .
the surface discontinuity part; and
2 0 in that the yarns of the layers of the.second
plCcality of layers of yarns situated at the surface of
the -fiber texture are continuous, at least over the
entire portion of dkcreasing thickness. ~ ~
10. A method ~~ ~~ according ~ to claim 9, characterized ~ in th-at ~ ~
the yarns of the layer of the first plurality of.layers .
of--yarns that are, no lqnger woven from the surface .
discontinuity part are interlaced with at least one yarn ~~-
of a layer, of the second plurality of layers of yafns
immediately prior to exiting'the structure.
.' .
11. A method according to claim 9 or claim 10,
characterized in'that the fiber structure presents first
and second outside faces extqnding in a longitudinal
direction, and in that the yarn withdrawal parts present
in the first face are longitudinally offset relative to
the yarn withdrawal parts present in the second face.
12. A method according to any one of claims 9 to 11,
characterized in'that the portion of decreasing thickness
presents, in the..!direction of the yarns of the first-
5 plurality of la$,:rs of yarns, a decreasing number of
layers of yarns of the' second plurality of layers of
yarns, and in that the fiber structure includes yarn
withdrawal parts in surface discontinuity that are
distributed as a function of a .determined decrease in