GB2393972A

GB2393972A - Preventing a concentration of defects from forming during the manufacture of a textile preform

Info

Publication number: GB2393972A
Application number: GB0319462A
Authority: GB
Inventors: Olivier Kern; Jerome Bertrand; Louc Rousseau; Francis Haucaguerre
Original assignee: EADS Space Transportation SA
Current assignee: EADS Space Transportation SA
Priority date: 2002-08-22
Filing date: 2003-08-19
Publication date: 2004-04-14
Anticipated expiration: 2023-08-19
Also published as: US20040244859A1; FR2843758A1; GB2393972B; FR2843758B1; JP2004084157A; GB0319462D0

Abstract

A method of producing a textile fibre preform in which filaments 12 are laid, e.g. by winding, on to a support [16, Figure 2] and held in place by spikes 18 located on or about the surface of the support, comprises the step of relocating the pins 18 during the laying of the filaments so as to prevent a concentration of defects being formed. The preform may be used in the manufacture of a carbon, resin, ceramic or metallic composite for the aeronautical or space fields. The preform may take a circular, cylindrical or frustoconical shape.

Description

TEXTILE PREFORM AND METHOD OF PRODUCING THE SAME

The present invention relates to a method of producing a textile preform, preferably a multidirectional textile preform, more particularly intended for a piece of composite material used in particular in the aeronautical and space fields.

Such a type of preform, produced from interlaced fibres (or threads) in particular 5 mineral, is embedded in a resin, ceramic, carbon, metallic or other matrix.

Methods and machines for producing such a preform are described in the documents FR-2,718,757, FR-2,718,758 and EP-0,284,497.

According to these techniques, the preform is obtained by the superimposition, on a mould, support or tube, of sheets of threads crossed in at least two directions, these sheets 10 then being connected together by means of threads which pass through them in another direction substantially perpendicular to the sheets.

The sheets are obtained by the deposition of rectilinear portions of thread forming part of a continuous thread, tensioning each portion of thread between two fixing spikes.

According to a first method of realization, the fixing spikes are obtained by stitching the 15 thread at each end of the portion in the support. According to another method, spikes (or needles) are implanted on the support at the ends of the portions, the thread passing between the spikes so as to obtain rectilinear portions of thread between them. The use of spikes becomes necessary, in particular for producing sheets on a cone with a large angle at the vertex, in order to keep the threads wound and to prevent the latter sliding towards the 20 end of the cone.

The present invention seeks to provide an improved method of producing a textile preform and an improved textile preform per se. The present invention preferably relates more particularly to methods using spikes.

The pieces containing this type of preform are in particular used as heat shields for 25 space rockets subjected to very high thermal and mechanical stresses.

The mechanical, thermal and electrical properties of these pieces are related to the homogeneous character of the fibre content at any spike on the preform. Thus, if the amount of fibres in the preform varies, the mechanical, thermal or electrical properties are altered. Moreover, the variation in the amount of fibres is liable to interfere with the 30 densification and any machining and thus to give rise to defects helping to degrade the characteristics of the piece.

The present invention aims to improve the techniques of the prior art by proposing

a method of producing a multidirectional textile preform making it possible to obtain a more homogeneous fibre content, which helps to improve the characteristics, in particular mechanical and thermal, of the piece obtained from said preform.

5 To this end, an aspect of the present invention provides a method of producing a textile preform from interlaced threads or portions of thread using a support with shapes appropriate to the preform to which there are applied superimposed layers of threads or portions of thread crossing in at least two directions, said layers being connected together by means of thread or portions of thread which pass through them, the threads or portions 10 being tensioned or held on said support by spikes, wherein the method includes the step of relocating the spikes by shifting them, in a manner as to prevent the concentration of defects inherent in the use of spikes.

The spikes are preferably shifted approximately in the direction of threads in order to limit the concentration of defects caused by the inclination of the spikes, and/or shifted 1 S approximately in a direction perpendicular to the threads in order to reduce the concentration of defects appearing between the spikes between which the threads or thread portions are tensioned.

For cylindrical, conical or frustoconical shaped preforms, the number of spikes is increased during the relocation phase so as to increase the number of threads or portions 20 disposed in the longitudinal direction.

For producing a preform which includes a frustoconical or conical part, the threads are deposited at the conical or frustoconical part, by angular sector, in a manner as to form chevrons, the latter being discontinued gradually as the radius decreases so as to obtain a constant thread content. To prevent the concentration of the defects inherent in the use of 25 spikes, the latter used for the production of the chevrons are relocated at least once, by shifting them longitudinally and angularly.

Advantageously, the number of chevrons per angular sector is increased during the relocation. Another aspect of the present invention provides a piece of composite material 30 comprising a textile preform produced according to the invention, embedded in a resin, ceramic, carbon, metallic or other matrix.

Embodiments of the present invention are described below, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a view in section of an example of a textile preform comprising a cylindrical part extended by a conical part, S Figure 2 is a view in section of the support or tube used for obtaining the preform of Figure I, Figure 3A is a view in perspective illustrating the weft insertion step, Figure 3B is a view in perspective illustrating the winding step, Figure 3C is a view in transverse section illustrating the stitching step, and 10 Figure 4 is a detail view illustrating the production of chevrons during the step of weft insertion of the conical part.

Figure l depicts an example of a multidirectional textile preform 10 obtained according to a preferred embodiment of production method.

This type of preform, produced from interlaced threads (or fibres) 12, in particular 15 mineral, is embedded in a resin, ceramic, carbon, metallic or other matrix, in order to obtain a piece of composite material used in particular in the aeronautical and space fields.

According to the embodiment chosen, the preform 10 has a cylindrical part 14 extended by a conical part 1 S. Naturally the invention is not limited to this shape and comprises any volume shape.

20 For making the preform, a support or stitching device 16 is used, on the surface of which spikes 18 can be implanted.

This support 16 has a profile adapted to the shape of the preform 10. According to the example chosen, a support 16 called a tube is used, illustrated in Figure 2, whose external shape corresponds to the internal shape of the preform.

25 This support is made from an appropriate material enabling the spikes 18 to be implanted and held.

According to the example, the textile preform 10 is obtained from interlaced fibres or threads, disposed in at least two directions, preferably three directions which are advantageously orthogonal.

30 Figures 3A to 3C illustrate the various steps of the depositing of the threads, Figure 3A illustrating the weft insertion phase corresponding to the depositing of the threads in the longitudinal direction, Figure 3B illustrating the winding phase corresponding to the

depositing of threads in the circumferential direction and Figure 3C illustrating the stitching phase, the threads being disposed in the radial direction.

For the remainder of the description, the terms "thread" or "fibre" and the terms

"sheet" or "layer" will be used for designating the assembly obtained by a weft insertion 5 and winding operation.

The spikes 18 are necessary as fixing points between which the portions of thread are tensioned during the weft insertion phase in order to ensure that the threads are held during the winding operation, in particular when the angle of the cone is very open, and finally to produce the conical part, as is explained below.

10 In order to obtain optimum mechanical, thermal and electrical characteristics, it is important to reach a degree of thread volume, corresponding to the ratio between the intrinsic volume of the threads and the volume occupied by the threads, which is homogenous. However, the use of the spikes 18 routinely causes defects.

15 On the one hand, as a result of the inclination of the spikes, during winding, there remains an area without circumferential threads situated on the side where the pin is inclined. On another hand, the use of spikes generates during the weft insertion an area with a low thread content at the generatrices carrying the spikes.

20 Finally, the production of a circular, conical or frustoconical shape by the superimposition of successive layers produces, at the external radii, a relatively small amount of weft threads.

To mitigate the concentration of these defects, the preferred method of producing a multidirectional textile preform includes the step of relocating the spikes by shifting them.

25 In this way the defects are distributed over the entire volume, which makes it possible to obtain an item or piece with a more homogeneous amount of threads and a lesser variation.

For a better distribution, during the reimplantation, the spikes are shifted in the longitudinal direction so as to reduce defects caused by the inclination of the spikes and/or 30 in the circumferential direction so as to reduce the defects caused at the generatrices.

Moreover, in order to compensate for the reduction in the amount of weft threads at high radii, during reimplantation the number of spikes is increased so as to increase the

s number of threads tensioned during the weft insertion phase, in order to obtain a thread density which is more constant throughout the thickness of the preform.

Even though if it may be considered that many reimplantations would make it possible to obtain a better distribution of defects, it has been found in practice that one to 5 two reimplantations suffice with a total number of approximately 40 layers in order to obtain a satisfactory distribution of defects and a thread density which is substantially constant throughout the volume of the preform.

The reimplantation or each reimplantation is carried out after the production of a certain number of layers, which may be variable.

10 At the conical part 15, the threads 12 are deposited during the weft insertion step by angular sector so as to form chevrons 20, as illustrated in Figure 4. The chevrons 20 are discontinued as the radius decreases so as to obtain a constant thread density.

The position of discontinuation of the chevrons is determined according to the shape, which may be conical or not, the number of layers already produced, preferably by a 15 dichotomy method, so as to obtain a weft thread density which is as constant as possible.

In order to distribute the defects, as before, recourse is made to at least one reimplantation by longitudinally and angularly shifting the spikes necessary for producing the chevrons 20.

In addition, in order to compensate for the reduction in the thread density produced 20 by the increase in diameter, the number of chevrons per sector is increased during the reimplantation. For the implementation, the spikes can be disposed directly on the tube or support 16 or attached to guide rings disposed at one end of the tube or at both ends thereof. The reimplantation of the spikes takes place preferably on the tube, the spikes being 25 reimplanted in the preform already produced, which confers to them a better rigidity.

Naturally the invention is not limited to the embodiment depicted and described above but on the contrary covers all variants, particularly with regard to the shape of the textile preform to be produced and the nature of the threads and of the matrix.

The disclosures in French patent application no. 0210495, from which this

30 application claims priority, and in the abstract accompanying this application are incorporated herein by reference.

Claims

1. A method of producing a textile preform from interlaced threads or portions of thread using a support (16) with shapes appropriate to the preform to which there are 5 applied superimposed layers of threads or portions of thread crossing in at least two directions, said layers being connected together by means of thread or portions of thread which pass through them, said threads or portions being tensioned or held on said support (16) by spikes (18), the method including the step of relocating the spikes (18) by shifting them, in a manner as to prevent the concentration of defects.

2. A method of producing a preform according to claim 1, wherein the spikes (18) are shifted approximately in the direction of the threads in order to limit the concentration of defects caused by the inclination of the spikes (18).

15

3. A method of producing a preform according to claim 1 or 2, wherein the spikes (18) are shifted approximately in a direction perpendicular to the threads in order to reduce the concentration of defects appearing between the spikes between which the threads or thread portions are tensioned.

20

4. A method of producing a preform according to any one of claims 1 to 3, wherein for a surface which increases when the layers are superimposed, in particular a cylindrical, conical or frustoconical shape, the method includes the step of increasing the number of spikes ( 18) during the reimplantation phase so as to increase the number of threads or portions disposed in the direction of the generatrices.

5. A method of producing a preform according to any one of claims 1 to 4, wherein for a frustoconical or conical item, the method includes the step of depositing the threads (12) at the conical or frustoconical part by angular sector so as to form chevrons (20), the latter being discontinued gradually as the radius decreases so as to obtain a constant thread 30 density.

6. A method of producing a preform according to claim 5, including at least one step of reimplantation by shifting longitudinally and angularly the spikes necessary for producing the chevrons (20).

57. A method of producing a preform according to claim 5 or 6, wherein the number of chevrons per angular sector is increased during reimplantation.

8. An item of composite material comprising a textile preform produced according to any one of claims l to 7, embedded in a resin, ceramic, carbon, metallic or other matrix.

9. A method of producing a preform substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

l O. An item of composite material comprising a textile preform substantially as 15hereinbefore described with reference to and as illustrated in the accompanying drawings.