CA2046354A1

CA2046354A1 - Method for producing fibrous preforms formed of superposed layers and having small radii of curvature, for the manufacture of composite material components

Info

Publication number: CA2046354A1
Application number: CA002046354A
Authority: CA
Inventors: Jean-Pierre Ciais; Claude Grondin; Jacques Adan
Original assignee: Societe Europeenne de Propulsion SEP SA
Current assignee: Societe Europeenne de Propulsion SEP SA
Priority date: 1990-07-17
Filing date: 1991-07-05
Publication date: 1992-01-18
Also published as: GB2246320B; JPH04226749A; GB9114153D0; GB2246320A; FR2664852B1; DE4123547A1; FR2664852A1

Abstract

IN THE C A N A D I A N PATENT AND TRADEMARK OFFICE PATENT

APPLICATION

Entitled : Method for producing fibrous preforms formed of superposed layers and having small radii of curvature, for the manufacture of composite material components in the names of : Jean-Pierre CIAIS
Claude GRONDIN
Jacques ADAN
Assignee : SOCIETE EUROPEENNE DE PROPULSION

ABSTRACT OF THE DISCLOSURE

In a curved portion of the preform having a radius of curvature that is smaller than the thickness of the superposed layers (12), an insert (14) is introduced between two of the layers. The insert comprises a first curved surface (14a) having a first radius of curvature substantially equal to that of a surface of the layer adjacent an outer side of the preform, and a second curved surface (14b) having a second radius of curvature greater than the first radius of curvature and substantially equal to that of a layer adjacent an inner side of the preform.

Figure 2.

Description

~&3~1~

Method for prodilcing fAIbrous pre~orms ~rmed o~ superposed layers aDd having small radii of cur~ature, ~or the manufac~re of composite material components Background of the invention 1. Field oî the inventio~
The present invention relates to the manufacture of composite material components, and more particularly to the production of ~Ibrous reinforcement preforms that yield the composite material components after being densified.
o 2. Priorart Thc usual method for making ~Ibrous preforms involves superposing7 or draping, two-dimensional fibrous layers, such as layers o cloth, fabric, or laps of threads or cables, while imposing a shape to the superposed layers that corresponds - or approximately resembles - that of the composite material S workpiece to be made.
A difficulty appears when the preform has curved portions with small radii of curvature, especially when the radius of curvature is smaller than the total thickness of the superposcd layers.
Indeed, as shown in ~1gures lA and lB, there then inevitably occurs one or several gaps 3 between the layers nE superposed fibrous reinforcement 2, at the level of the curved portions of the preform 1.
These gaps 2 constitute discontinuities in the rcinforcemcnt that camlot b~
c~mpletely filled in during densiication, especially when the latter is achieved by chcmical vapor ~filtration. 'Ihe gaps that rema~n within the finished ~s composite workpiece constitute weak points and cause defects to appear~ or adeterioration of the workpiece, notably by delamination, i.e. separation of the layers.
Summary ol~ the ill~ention with objects It is an object of the present invention to overcome the aforementioned drawba~s by enabling fibrous reinforcemellt preforms to be produced exempt from gaps, even in portions that have small radii of curYature.
According to the present invention, this object is achieved by the provision of at least on& inse~ in the or each curved portion, the insert being placed between two layers and comprising a first cllrved surface having a first 3s radius of curvature substantially equal to that of a sur~ce of the layer adjacent an outer side of the preform, and a second curved surface having a second 2 ~ ~; 6 ~

radius of cunrature greater than the first radius of curvature and substantiallyequal to that of a layer adjacent an inncr side of the prcform.
Advantageously, the insert consists of ~1brous preform or structure that is kept in the required shape by means of a predensification, or consolidation 5 phase, or by molding using a ~ugitive resin.
Here9 the term consolidation refers to a partial densification that is just sufficient to bind togcther the ~Ibcrs of the insert so that the lattcr can be handled without losing its shape. The consolidation may e.g. be achieved by a chemical vapor infiltration that infiltrates into thc heart of the insert's fibrous o texture as the latter is kept in a holding tool that impresses the required shape.
The term fugitive resin refers to a resin that is susceptible of being eliminated without leaving behind a solid residue. The resin can be eliminatcd by heat, for instance during the raising in temperature required for the densification of the preform complete with its inserts. The fugitive resin can be 5 chosen to have a zero coke content, as in the case of a PVA (polyvinyl alcohol) type of resin.
The densification of the insert is achieved - or terminated if the preform has been previously consolidated - during the densification of the preform.
This densi~acation Gan be carried out by a gaseous method (chemical vapor 20 infiltration~ or a liquid method (a suceession of cycles comprising an impregnation of a matrix precursor followed by transformation trcatment on thc matrix of the precursor, such as a heat treatment).
The fibrous structure of the inscrt is preferably composed of the sarme fibers as the ones cornposing thc pre~orm of the componcnt being 2s manufactured.
Preferably, the insert's fibrous structure is prs)duced by first forming a superposition of layers, these layers being analogous to the layers used for tbepreform of the component to manufacture, then linking the superposed layers by consolidation, or by molding using a fugitive rcsin, and finally cutting or 30 machining the insert out of the superposed layers. Advantageously, the machining operation is carried out such as to keep the fibers within the insert's fibrous texturc oriented in roughly tbe same way as the fibers in the layers of the preform islto which the insert is to be placed, thereby avoiding discontinuities in the ~1ber orientataon when the insert is placed.

2 O 9,: 6 ~ L~;

Brief description of the drawings Thc prcscnt in~cntion invcntion shall bc more clcarly undcrstood upon reading thc following dcscription, given purely by way of a non-limiting example, with reference to the appended drawings in which:
s - figures lA and IB, described ultra, illustrate the formation of gaps in portions of small radius of curvature in a fibrous preform made of superposed layers, - ~lgure 2 illustrates the positioning of an insert in a portion of small radius of curvature in a superposition of layers according to an embodiment of 0 the present invention, - ~igure 3 illustrates the positioning of several inserts ~n a common portion of small radius of curvature, - ~Igure 4 illustrates the positioning of an insert extending over several portions of small radius of curvature, and - figures 5 and 6 illustrate a method for producing inserts according to the present invention.
Detailed description of the prefelTed embodiments Figure 2 shows an embodiment of a fibrous preforrn 10 made ~orn a superposition of layers 12 and comprising at least one curved portion with cylindrically curved faces, whose radius of curvature r at the level of the convex face is smaller than the total thickness e o~ the preform.
The layers consist of two-dimensional ~Ibrous layers such as layers of c1oth. The material forming the layers is chosen amon~st the fibcrs normally used in reinforcement tcxtures ~or compoxite material components, such as ~s glass fibers, ararnide ~lbers, carbon fibers or ceramic fibers, depending on the intended application of the component to be manufactured.
In figure 2, a number of first layers 12 are shown to be superposed on the outer side of the preformlO, i.e. on the side of the convex face 10a of the curved portion. The number of these first layers is chosen to be such that the total thickness of the tatter is less than the radius s)f curvature r of the curved portion of the preform at its convex face 10a. Consequently, the first laycrs 12 can be superposed without creating a gap at the level of the curved portion. At least one first layer 12 is necessary to proYide a con~inuous surface at the convex face of the preform.
3s An insert 14 is positioned in the curved portion of the preform, the insert having a crescent-shaped cross-section with one convex external face 14a, adjacent convex face 10a, that has a radius of curvature substantially equal to 2 0 ~

that of the surface of the adjacent layer 12. The external side vf insert 14 is shaped to correspond to the shapc of the inner side of the superposed first layexs 12, such that there is no gap betweerl this first superposition and the insert 14.
The concave internal face 14b of the insert 14 has a radius of curvature s greater than that of the extemal face 14a, the radius of curvature being at least as great as the thickness of the remaining part of the preform 10 from its innerside. This remaining part is formed by a superposition of second layers 12 to the total thickness e of the prcform. At the level of the curved portion of the preform, the layer among the sec ond layers 12 that is in contact with the inner0 face 14b of the insert matches the shape of that inner face, by adopting the same radius as the latter, so that there is no gap between the second superposition and the insert 14.
Beyond the edges 14c and 14d of the insert 14 where the two faces 14a and 14b join, the two superpositions of layers 12 are in rnutual contact without5 any intermediatc gap.
~ccordingly, the insert 14 makes it possible to match the radius of curvature at the level of the curved portion of the preform to avoid the appearance of gaps behveen the superposed layers in that part of the curve.
Alternatively, the aforementioned matching of the radius of curvature can be achieved progressively by means of several inserts, such as inserts 141, 142,and 143 shown in ~Igure 3. Each insert has a shape analogous to that of in6ert 14 shown in ~lgure 2 and, like the latter, have curved outcr and inner faces with radii of curvature c~esigned to prevent gaps -from being ~ormed in thc superposed layers 12 ot the pre~orm 10.
When thc preform has a number of closely grouped curved por~ions, each having a small radius of cuxvature, it is possible to use an insert extending continuously ~om one curved portion to the other, or several inserts each extending continuously form one cuNcd portion to another.
For instance, ~lgure 4 shows a ~1brous pre~orm 20 of which a part has a U-shaped section, each one o the two curved poltions 201 and 22 having a convex face with a radius of curvaturc smaller than the thickness of the prefi)rm 20.
The example shown uses only one insert 24, which is placed be~ween a first and second superposition of layers 22.
The inse~t 24 comprises a filrst portion 241 that serves to adapt the radius of curvature between the fi~t and second superposition of layers at thc level ofcurved portion 201, and a second portion 242 which similarly serves to adapt ~ o ~

the radius of curvature between the first and second superposition of layers at the level of curved portion 202.
The, or each insert used in the implementation of the present invention is comprised of a fibrous texture, preferably made of the same fibers as used for s the superposed layers making up the preform of the component being manufactured~
The fibrous texture of an insert can be produced in different ways.
A first process consists of preparing an body of short, non-oriented fibers molded into shape by means of a fugitive resin. The fibers are arranged in a 0 mold having the sarne shape as the insert to be made, and the fugitive resin is injected into the mold.
The quantity of fugitive resin used is just sufficient to link the fibers together so that the ~lbrous texture retains its shape af~er unmolding. It is not necessary that the fugitive resin should provide a high degree of densification.Another process consists in preparing a body of fibrous layers of the same nature as the layers used for the preform. The insert is then cut out from that body, e.g. by rnachining.
Preferably, the layers are superposed while being curved> so as to present an inner side having a radius of curvature corresponding to that of the concave face of the insert.
Fi~ure 5 shows such an body of ~lbrous layers 32 destined to yield thc insert 14 of figure 2.
The superposed layers 32 are held in shape by molding with a fugitive resin thc insert is then cut out as shoYYn by the broken line of figure 5.
The use of a curved superposition of layers 32 makes it possible to obtain a fibrous texture in which the fibers have orientations similar to those of the fibers making up the layers of the preform into which this fibrous texture is tobe placed. Consequently, the placing of the insert 14 does not give rise to any discontinuity in the orientation of the fibers.
Similarly, figure 6 shows a body of layers havLrlg two cunred portions and produced for cutting ~ut a ~lbrous texture that is apt to form the insert 24 of ure 4.
After placing of the insert(s), the ~lbrous prc~rm undergoes a densi~lcation by a ma~rix material to yield the desired composite workpiece.
The matrL~ material is chosen as a function of the intended use of the component. For instance, carbon or ceramic may be employed for making thermostru tural composite components. In this case, the ~lbers of the preform 3 t~

and the insert(s) are also made of carbon or ceramic. Here, a thermostNctural composite material desi~,nates a material which has mechanical properties enabling the material to be used for making structural parts and which retains such rmechanical properties up to high temperatures.
The preform is densified by a liquid or gaseous process using techniques known in the art.
Liquid phase densification consists in impregating the preform with a liquid precursor that will yield the required matrix material after a given treatment, such as a heat treatment, and then carrying out that treatment. The lo above operations are repeated over successive cycles until the desired degree of densi~1cation is attained. In the case of a carbon matrix, the impregnating liquid is typically a resin having a high coke content.
Gas, or vapor phase densi~1cation, consists in effecting a chemical vapor in~lltration on the preform while it is held in shaping tool, at lcast until theconsolidation phase, that is until its constituent ~1bers become linked together.
The fugitive resin that gives its cohesion to the fibrous texture of the insert is automatically eliminated when the preform is raised in temperature for the densification.
In a variant of the invention, the constituent fibers of the fibrous texture forming an insert can be interlinked by consolidation (partial densification) in a chemical vapor infiltration process. During this consolidation, the body of ~Ibers forming the insert, or the layers from which the insert is to be Cllt out, are kept in shape in a tool.
The densification o the fibrous texture of the insert is then completed concomitantly with the densification of the preform.
When the fibers of the insert are interlinked by a pre-densi~lcation, the material used for this pre~densification is, of course, compatible with or identical $o the matrix material of the of the cornposite component being made.

Claims

1. A process for producing a fibrous preform to be used in the manufacture of a composite material component, said preform being formed by a superposition of layers and comprising at least one curved portion having a radius of curvature smaller than a thickness of said superposed layers, wherein at least one insert is introduced in said or each curved portion, said at least one insert being placed between two layers and comprising a first curved surface having a first radius of curvature substantially equal to that of a surface of the layer adjacent an outer side of the preform, and a second curved surface having a second radius of curvature greater than the first radius of curvature and substantially equal to that of a layer adjacent an inner side of the preform.

2. The process of claim 1, wherein a plurality of inserts are placed in the said or each curved portion of said preform.

3. The process of claim 1as applied to produce a fibrous preform having a pluralilty of curved portions, wherein at least one insert is placed in said preform, said insert consisting of a single piece with parts lodged in said curved portion(s) and connected together

4. The process of claim 1, wherein said insert is comprised of a fibrous texture whose fibers are interlinked.

5. The process of claim 1, wherein said insert is comprised of a fibrous texture whose fibers are interlinked, said linking of fibers being obtained by means. of a fugitive resin.

6. The process of claim 1, wherein said insert is comprised of a fibrous texture whose fibers are interlinked, said linking being obtained by means of a pre-densification.

7. The process of claim 1, wherein said or each insert is comprised of a fibrous texture produced by forming a superposition of layers that are substantially similar to the layers used for making said preform of said component being made, linking said superposed layers, and cutting out said insert from said superposition of layers.