GB2246320A

GB2246320A - Preform insert

Info

Publication number: GB2246320A
Application number: GB9114153A
Authority: GB
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: 1991-07-01
Publication date: 1992-01-29
Anticipated expiration: 2011-07-01
Also published as: JPH04226749A; DE4123547A1; GB9114153D0; CA2046354A1; FR2664852B1; FR2664852A1; GB2246320B

Abstract

In a curved portion of a fibrous 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. <IMAGE>

Description

1 0 ::;-, A CS: -7-,---RC! - 1 Method for producing fibrous preforms

formed of superposed layers and having small radii of curvature, for the manufacture of composite material components lle: present invention relates to the manufacture of composite material components, and more particularly to the production of fibrous reinforcement preforms that yield the composite material components after being densified.

The usual method for making fibrous preforms involves superposing, or draping, two-dimensional fibrous layers, such as layers of 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 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 superposed layers.

Indeed, as shown in figures 1A and 1B, there then inevitably occurs one or several gaps 3 between the layers of superposed fibrous reinforcement 2, at the level of the curved portions of the preform 1.

These gaps 2 constitute discontinuities in the reinforcement that cannot be completely filled in during densification, especially when the latter is achieved by chemical vapor infiltration. The gaps that remain within the finished composite workpiece constitute weak points and cause defects to appear, or a deterioration of the workpiece, notably by delamination, i.e. separation of the layers.

It is an object of the present invention to overcome the aforementioned drawbacks by enabling fibrous reinforcement preforms to be produced exempt from gaps, even in portions that have small radii of curvature.

According to the present invention, this object is achieved by the provision of at least one insert in the or each curved portion, the 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 1 2 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.

Advantageously, the insert consists of fibrous preform or structure that is kept in the required shape by means of a predensification, or consolidation phase, or by molding using a fugitive resin.

Here, the term consolidation refers to a partial densification that is just sufficient to bind together the fibers of the insert so that the latter can be handled without losing its shape. The consolidation may e.g. be achieved by a chemical vapor infiltration that infiltrates into the heart of the insert's fibrous 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 eliminated 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 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 densification can be carried out by a gaseous method (chemical vapor infiltration) or a liquid method (a succession of cycles comprising an impregnation of a matrix precursor followed by transformation treatment on the matrix of the precursor, such as a heat treatment).

The fibrous structure of the insert is preferably composed of the same fibers as the ones composing the preform of the component being manufactured.

Preferably, the insert's fibrous structure is produced by first forming a superposition of layers, these layers being analogous to the layers used for the preform of the component to manufacture, then linking the superposed layers by consolidation, or by molding using a fugitive resin, and finally cutting or machining the insert out of the superposed layers. Advantageously, the machining operation is carried out such as to keep the fibers within the inserVs fibrous texture oriented in roughly the same way as the fibers in the layers of the preform into which the insert is to be placed, thereby avoiding discontinuities in the fiber orientation when the insert is placed.

1 i i 1 i 1 i 1 1 i i i i i i k 3 The present invention invention shall be more clearly understood upon reading the following description, given purely by way of a non-fimiting example, with reference to the appended drawings in which:

- figures IA and IB, described ultra, illustrate the formation of gaps in portions of small radius of curvature in a fibrous preform made of superposed layers, - figure 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 the present invention, - figure 3 illustrates the positioning of several inserts in a common portion of small radius of curvature, - figure 4 illustrates the positioning of an insert extending over several portions of small radius of curvature, and is - figures 5 and 6 illustrate a method for producing inserts according to the present invention.

v Figure 2 shows an embodiment of a fibrous Preform 10 made from 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 of the preform.

The layers consist of two-dimensional fibrous layers such as layers of cloth. The material forming the layers is chosen amongst the fibers normally used in reinforcement textures for composite material components, such as 2S glass fibers, aramide fibers, 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 preforml.0, 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 latter is less than the radius of curvature r of the curved portion of the preform at its convex face 10a. Consequently, the first layers 12 can be superposed without creating a gap at the level of the curved portion. At least one first layer 12 is necessary to provide a continuous surface at the convex face of the preform.

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, tflat has a radius of curvature substantially equal to 4 that of the surface of the adjacent layer 12. The external side of insert 14 is shaped to correspond to the shape of the inner side of the superposed first layers 12, such that there is no gap between this first superposition and the insert 14.

The concave internal face 14b of the insert 14 has a radius of curvature greater than that of the external face 14a, the radius of curvature being at least as great as the thickness of the remaining part of the preform 10 from its inner side. This remaining part is formed by a superposition of second layers 12 to the total thickness e of the preform. At the level of the curved portion of the preform, the layer among the second layers 12 that is in contact with the inner 10 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 mutual contact without any intermediate gap.

Accordingly, 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 between 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 figure 3. Each insert has a shape analogous to that of insert 14 shown in figure 2 and, like the latter, have curved outer and inner faces with radii of curvature designed to prevent gaps from being formed in the superposed layers 12 of the preform 10. When the preform has a number of closely grouped curved portions, each having a small radius of curvature, it is possible to use an insert extending continuously from one curved portion to the other, or several inserts each extending continuously form one curved portion to another. For instance, figure 4 shows a fibrous preform 20 of Which a part has a U-shaped section, each one of the two curved portions 201 and 202 having a convex face with a radius of curvature smaller than the thickness of the preform 20.

Me example shown uses only one insert 24, which is placed between a first and second superposition of layers 22.

The insert 24 comprises a first portion 241 that serves to adapt the radius of curvature between the first and second superposition of layers at the level of curved portion 201, and a second portion 242 which similarly serves to adapt i 1 1 J i I 1 1 i j i 1 1 j i 1 1 i 1 i the radius of curvature between the first and second superposition of layers at the level of curved portion 202.

Tbe, 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 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. Ile fibers are arranged in a mold having the same 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 fibrous texture retains its shape after 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 machining.

Preferably, the layers are superposed while being curved, so as to present an inner sid-- having a radius of curvature corresponding to that of the concave face of the insert.

Figure 5 shows such an body of fibrous layers 32 destined to yield the insert 14 of figure 2.

The superposed layers 32 are held in shape by molding with a fugitive resin. the insert is then cut out as shown 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 to be 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 having two curved portions and produced for cutting out a fibrous texture that is apt to form the insert 24 of figure 4.

After placing of the insert(s), the fibrous preform undergoes a densification by a matrix material to yield the desired composite workpiece.

The matrix material is chosen as a function of the intended use of the component. For instance, carbon or ceramic may be employed for making thermostructural composite components. In this case, the fibers of the preform 6 and the insert(s) are also made of carbon or ceramic. Here, a thermostructural composite material designates a material which has mechanical properties enabling the material to be used for making structural parts and which retains such mechanical 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 above operations are repeated over successive cycles until the desired degree of densification 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 densification, consists in effecting a chemical vapor infiltration on the preform while it is held in shaping tool, at least until the consolidation phase, that is until its constituent fibers become linked together.

Tle 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 fibers forming the insert, or the layers from which the insert is to be cut out, are kept in shape in a tool.

The densification of 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-densification, the material used for this pre-densification is, of course, compatible with or identical to the matrix material of the of the composite component being made.

1 i i 1 1 i 1 1 1 1 1 i i 1 i i 1. i 1 J1 1 7

Claims

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, characterized in that 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, characterized in that a plurality of inserts are placed in the said or each curved portion of said preform.

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

4. The process of any one of claims 1 to 3, characterized in that said insert is comprised of a fibrous texture whose fibers are interlinked.

5. The process of claim 4, characterized in that said linking of fibers is obtained by means of a fugitive resin.

6. The process of claim 4, characterized in that said linking of fibers is obtained by means of a pre-densification.

7. The process of any one of claims I to 6, characterized in that 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.

Published 1992 at The Patent Office. Concept House. Cardiff Road. Newport. Gwent NP9 1 RH. Further copies may be obtained froni Sales Branch. Unit 6. Nine Mile Point. Cwrnfelinfach. Crosh Keys. Newport. NP I 7HZ. Printed by Multiplex techniques ltd. Si Mary Cray. heni.