CA2012032C

CA2012032C - Process for joining elements in the manufacture of thermostructural composite material parts

Info

Publication number: CA2012032C
Application number: CA 2012032
Authority: CA
Inventors: Yvon Sourdoulaud; Michel Vives
Original assignee: Societe Nationale dEtude et de Construction de Moteurs dAviation SNECMA
Current assignee: Safran Aircraft Engines SAS
Priority date: 1989-03-30
Filing date: 1990-03-13
Publication date: 1999-09-14
Anticipated expiration: 2010-03-13
Also published as: ES2033163T3; JPH02289472A; NO173257B; NO901338D0; EP0390685A1; NO173257C; FR2645223B1; US5310434A; DE69000125T2; DE69000125D1; NO901338L; FR2645223A1; EP0390685B1; CA2012032A1; JP2823646B2

Abstract

A structural connection is obtained between elements (21) 22) of the reinforcement texture to be assembled by using at least one blocking means (23). The latter is made of a fibrous texture that is compacted prior to being inserted in a corresponding lodging formed in at least one of the elements of the reinforcement texture in order to conform with the shape of the lodging. The blacking means (23) then locks itself into the lodging by relaxation of its fibrous texture, as a result of a removal of the prior compacting. The blocking means can be in the form of a dowel (23) inserted inside aligned lodgings formed in the elements (21, 22) of the reinforcement texture to be assembled, or may alternatively be part of one of the elements of reinforcement texture to be assembled.

Description

PROCESS FOR JOINING ELEMENTS IN THE MANUFACTURE OF THERMOSTRUCTURAL
COMPOSITE MATERIAL PARTS
BACKGROUND OF THE INVENTION
1. Field of the invention.
O5 The present invention relates to a process for joining elements in the manufacture of thermostructural composite material parts.
Thermostructural composite materials essentially comprise a fibrous reinforcement texture densified at its core by a matrix, the fibers of the reinforcement texture and the matrix material being selected to satisfy applications requiring excellent mechanical characteristics at high temperatures.
Typical examples of thermostructural composite materials include carbon-carbon materials (carbon fiber reinforcement texture and carbon matrix), carbon-ceramic (carbon fiber reinforcement structure and ceramic matrix) e.g. silicon carbide)) and ceramic-ceramic (ceramic fiber reinforcement structure and ceramic matrix).
In some applications, especially in the space and aviation field, there is an ever-increasing need for large-size parts made of thermostructural composite materials. This is e.g.
the case with stiffening web assemblies forming structural parts of a space vehicle.

2. Prior art.
It could be envisaged to produce a large-size part from several separately produced parts that are finally assembled by mechanical means or gluing. However, known methods for assembling pre-fabricated elements made of thermostructural composite materials are difficult to put into practice, or do not give complete satisfaction.
One solution would then consist in producing the elements of reinforcement texture separately and then assembling them, possibly after a pre-densification step) prior to a simultaneous densification by the matrix material at the core of the assembled elements of reinforcement texture. The elements of reinforcement texture are assembled simply by bringing them into mutual contact and holding them in contact by means of a tool.
The linking between the elements of reinforcement texture results from the co-infiltration of the matrix material within the core of the porous structure of these elements. The co-infiltration can e.g. be obtained by means of a well-known method of chemical vapor deposition.
This type of linking by co-infiltration requires large contact surfaces to obtain an effective link by the matrix material, and presents a permanent risk of cohesion loss, both during manufacture and in use.
SUMMARY OF THE INVENTION
The aim of the present invention is therefore to provide a process that makes it possible to produce large-size thermostructural composite material parts without the drawbacks of the prior art processes.
More specifically, the aim of the invention is to provide a process for the manufacture of thermostructural composite material parts by co-densification of pre-assembled elements of reinforcement texture, such that the resulting parts present no risk of cohesion loss, even when the area of mutual contact between the elements of reinforcement texture is small.
An aspect of this invention is as follows:
A process for the manufacture of thermostructural composite material parts by co-densification of pre-assembled elements of reinforcement texture wherein a structural connection is obtained between said elements of reinforcement texture by at least one blocking means having a fibrous texture that is subjected to compacting prior to engagement inside a corresponding lodging formed in at least one of said elements of said reinforcement k 2a ~ ~ ~ ~ ~ ~ 2, texture in order to conform to the shape of said lodging and lock thereinto by relaxation of said fibrous texture upon elimination of said prior compacting, said elements of reinforcement texture and said blocking means being thereafter co-densified.
The locking of the blocking means into its corresponding lodging ensures an effective pre-assembly of the elements of the reinforcement texture prior to co-densification by the matrix and acts to prevent cohesion loss during the part's densification ~~~ 0'~w stage. Moreover, this locking effect combines with the bonding by the matrix material co-infiltrated into the core of the porous elements forming the reinforcement texture, including the blocking means. This guarantees an effective linking that virtually 05 eliminates the risk of cohesion loss when the part is used) while requiring but a small area of surface contact between the pre-assembled elements of reinforcement texture.
The blocking means can be in the form of a dowel of fibrous texture engaged inside registered lodgings formed within the elements of reinforcement texture to be assembled.
Alternatively) the blocking means can comprise a portion of one of the elements of reinforcement texture to be assembled.
The fibers that form elements of the reinforcement texture and the fibers forming the fibrous texture of the blocking means are made of the same substance) such as carbon or ceramic) or materials that are inter-compatible as regards thermal effects (e. g. expansion).
The compacting of the blocking means can be achieved by means of a tool in which the blocking means is held until the insertion thereof in the corresponding lodging.
Alternatively, the blocking means can be maintained in its compacted state by impregnation with a product binding together the fibers of the fibrous texture of the blocking means in order to maintain the blocking means in a compacted state) the impregnating product being capable of being eliminated or softened to allow a relaxation of the fibrous texture after insertion of the compacted and impregnated blocking means into the corresponding lodging.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention shall be more easily understood upon reading the following description given as a non-limiting example, with reference to the appended drawings in which:
- figures 1 to 5 illustrate the successive stages in the manufacture of a thermostructural composite material part by co-densification of the assembled elements of reinforcement texture according to a first embodiment of the process according to the invention;
- figures 6 and 7 illustrate an alternative method for assembling the elements of reinforcement texture;
- figures 8 to 10 illustrate an alternative method for 05 compacting the blocking means and maintaining the latter in a compacted state;
- figures 11 and 12 illustrate other alternative methods for assembling the elements of reinforcement texture;
- figures 13 and 14 illustrate the successive stages in the manufacture of a thermostructural material part according to a second embodiment of the present invention;
- figure 15 illustrates an alternative to the method of figures 13 and 14; and - figure 16 illustrates an application of the inventive process for the production of a thermostructural composite material part in the form of a web provided with stiffening elements.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Generally speaking, the present invention is applicable to the manufacture of a composite part whose reinforcement texture can be produced from several separate elements that are subsequently assembled prior to being simultaneously densified to obtain the final part.
In the example illustrated by figures 1 to 5, the composite part under manufacture is obtained by densification of a reinforcement texture formed by assembling two plate-shaped elements of reinforcement texture 11 and 12 (figure 1). Any known type of fibrous reinforcement texture can be used for the composite materials forming the elements 11 and 12, to endow the part with the properties required for its intended use.
Accordingly) elements 11 and 12 can be made of the same fibrous texture formed e.g. by a superposition of layers. The latter can be layers of material not linked together (two-dimensional, or 2D, textures) or inter-linked e.g. by implantation of threads running transversally with respect to the layers) or by needling (three-dimensional, or 3D, textures). Depending on the shape of the parts to be produced, elements 11 and 12 may have shapes of varying complexity, e.g. shapes with a profiled cross-section. The elements 11 and 12 can be maintained in the appropriate form by impregnation of the fibrous texture by a resin. The latter is e.g.
05 chosen for its capability of being eliminated before or during the infiltration of the matrix, or for leaving a residue compatible with the material of the matrix.
In some instances) the elements 11 and 12 can be consolidated) or weakly densified, by the selected matrix material deposited by chemical vapor deposition or liquid infiltration.
The structural assembling of elements 11 and 12 is performed by means of one, and preferably several dowels 13 that are inserted and locked into lodgings each formed by bores 14) 15 that are registered and formed in the parts of the plates 11, 12 that come into mutual contact to make up the complete reinforcement texture of the part being manufactured. In order to maintain an adequate hold at the level of the bores, the elements 11 and 12 are preferably made of an impregnated 2D texture) or a 3D texture, and preferably a needled 3D texture. For the sake of simplicity, only one dowel 13 and only one assembly corresponding to the bores 14) 15 are shown in the figures. As can be seen in figure 1) for instance, a chamfer 15a is formed at the end of the bore 15 on the side of the plate 12 opposite the side contacting plate 11.
As shown in figure 2, the dowel can e.g. be obtained by cutting out a cylinder in a plate 16 of 3D fibrous texture by means of a tool 17. The length L of the cylinder (i.e. the thickness of the plate 16) is slightly greater than the thicknesses of plates 11 and 12 (i.e. the length of the lodging formed by the bores 14 and 15 end-to-end)) while the diameter of the cylinder is greater than the diameter d of the bores 14 and 15 and is at least equal to the maximum diameter of bore 15 at the level of the chamfer 15a.
After cutting out, the dowel 13 is compacted circumferentially and lodged inside a tube 18 whose inner diameter is substantially equal to that of bores 14 and 15. The tube 18 is positioned coaxially with the bores 14) 15 of the assembled _~_ fd 5 J ~d parts 11, 12 (figure 3) so that the dowel 13 can be introduced into the latter by means of a piston 19 guided in the tube 18 and pressing against an end 13a of the dowel 13.
The insertion of the dowel 13 is carried out e.g. from 05 the side of plate 11 and continues until its end 13b opposites that acted upon by the piston 19 reaches the level of the outer face of plate 12. After withdrawal of the tube 18, the dowel 13 assumes the shape illustrated in figure 4. The compacting effect of the tube 18 having ceased) the fibrous texture of the dowel 13 is relaxed at its end 13b to occupy the chamfered part of the bore 15 at its end 13a, so forming a head at the side of the outer face of plate 11, the length L of the dowel being greater than the sum of the thicknesses of plates 11 and 12. The tapered end 13b of the dowel 13 and the head 13a of the latter have the effect of locking the dowel 13 in the bores 14, 15, so creating a structural connection by the presence of obstacles between the elements of the reinforcement texture 11 and 12. The dowel 13 remains compacted between its end portions 13a and 13b.
After the plates 11 and 12 have been assembled, they are densified together, along with the dowel 13. The densification is obtained e.g. by chemical vapor infiltration of the matrix material inside the accessible pores of the fibrous texture. With the elements of the fibrous reinforcement texture assembled by a structural connection) it is possible to maintain perfect cohesion of the assembly during densification. Once the matrix is deposited (figure 5), its constituent material serves to adhere the elements 11, 12 and the dowel 13 by virtue of the continuity of the interface between them. This adhesion, in combination with the mechanical locking produced by the,dowel 13, endows the finished part with a high degree of resistance to cohesion loss. After densification, the head 13a of the dowel 13 protruding towards the outside can be machined away.
Alternatively, a 'chamfer is also formed at the end of the bore 14 on the outside face of plate 11) the length of the dowel in that case being substantially equal to the sum of the thicknesses of plates 11 and 12. A structural linkage, with blocking between the elements 11 and 12) is obtained by expansion of the dowel at its two ends in the respective conical parts having a greater diameter than the bores 14 and 15.
05 In another embodiment, the bores 14 and 25 are made without a chamfer) and the dowel 13 is sufficiently long to form a head by expansion of the fibrous texture at each of its ends protruding outside the bores 14 and 15, the blocking effect being produced by the heads formed at the two ends of the dowel and pressing on the outer faces of plates 11 and 12.
In yet another embodiment, shown in figure 6, the bores 14) 15 formed in plates 11) 12 are conical) with the large diameter located on the outer face of the plates. After being introduced into the axially aligned bores 14 and 15, e.g, using the type of means shown in figure 3, the dowel 13 occupies all the volume of the bores 14 and 15 and mutually locks the plates 11) 12 together (figure 7).
Figures 8 to 10 show another method for keeping the dowel 13 made of fibrous texture compacted before it is locked inside the bores 14 and 15 of elements 11 and 12.
The dowel 13) which is obtained e.g. by cutting out a plate of 3D type fibrous texture as shown in figure 2, is circumferentially compacted while being introduced inside a cylindrical sleeve 28 that may be drilled (figure 8). The dowel 13 thus held in a compacted state is impregnated with a resin by immersion in a bath 29.
After resin impregnation, followed by a drying stage, the sleeve 28 can be removed and the dowel 13) held in its compacted state by the resin, is introduced into the bores 24 and 15 (figure 9).
The impregnating resin is selected according to its ability to be eliminated, or at least softened, prior to infiltration of the matrix. The elimination or softening of the resin has the effect of suppressing the compacting effect (figure 10), so that the dowel 13 locks itself into the bores 14 and 15 by ~:~.3~
relaxation of the fibrous texture in the manner described above with reference to figures 1 to 5.
The elimination or softening of the impregnating resin is achieved by a chemical treatment or by raising the temperature. In 05 the latter case, it would be advantageous to use the temperature rising phase preceding the infiltration as such of the matrix material.
Preferably, use is made of a fugitive resin that is eliminated by a thermal treatment, practically without trace of a residue, prior to co-densification of the elements 11 and 12. A
resin that leaves a residue after softening or pyrolysis can be used so long as the residue is compatible with the matrix material.
Alternatively, a dowel 13 compacted in sleeve 28 is impregnated by a liquid that is solidified by cooling so that the dowel retains its compacted state after removal of the sleeve 28.
The thawing out of the impregnating liquid causes the texture of the dowel 13 to relax once the dowel has been placed into position.
Figures 11 and 12 show the assembly of two parts of a reinforcement texture 21 and 22 by compacted and impregnated dowels 23 each introduced in two frusto-conical blind holes 24, 25 formed in respective parts 21, 22. The diameters of the holes 24, increase when going towards the blind end, so that the dowel 23 locks the parts 21, 22 together upon relaxing from its compacted state.
25 Figures 13 and 14 illustrate yet another embodiment of the invention according to which the blocking means between the elements of reinforcement texture are formed by portions of at least one of the elements to be assembled. Here, the composite part is obtained by densification of a fibrous reinforcement texture formed by assembling two elements 31, 32. Element 31 is e.g. in the form of a plate intended to be assembled perpendicularly to element 32 which is also in the form of a plate. Assembling is achieved by means of finger portions 33, formed on one edge of element 31) and intended to penetrate into holes 34 formed in element 32. The finger portions 33 and holes __ 34 are obtained by machining (in the figures, only one finger 33 and only one hole 34 are shown for the sake of simplicity).
As shown in figure 13) the finger portion 33 has a cylindrical shape and is machined in the texture of element 31 05 after the latter has been at least locally compacted and impregnated. The hole is a frusto-conical through hole or blind hole depending on the thickness of element 32. The finger 33 is introduced in a compacted state into the hole 34. The diameter of the finger 33 is chosen so that the finger, after loosening of the compacting) fills up all the volume of hole 34 (figure 14).
After assembly, the elements 31 and 32 are co-densified by chemical vapor infiltration of the matrix material. The latter creates an adhesion between the elements 31 and 32 that combines with the structural link provided by the fingers 33 to ensure that the finished part has the required cohesive strength.
Alternatively, as shown in figure 15) the holes 34 are bores having a cylindrical shape) with a chanfer 34a formed at one end of the bore to allow the finger 33 to lock in the bore by expansion of the finger's texture or the level of the chanfer. A
neck 33a can be formed at the base of the fingers 33 so as to avoid) after relaxation of the finger's fibrous texture, the formation of bulges at the interface between the elements 31 and 32.
As already explained) the invention has particular applications in the manufacture of thermostructural composite material parts forming stiffened web structures.
The fibrous reinforcement texture is then produced in the form of distinct elements 51) 51', 52 corresponding to the portions of the part constituting the stiffeners and the web. The elements of reinforcement texture are assembled structurally, using an obstacle defined by finger portions 53) 53' formed on the edges of elements 51) 51') to link bores 54 formed in element 52 to receive finger portions 51, 51', and bores 54' formed in element 51' to receive finger portions 53) as shown in figure 16.

Instead of being made integral with one of the elements of the reinforcement texture) the linking means 53, 53' can be made in the form of distinct slugs or dowels that are put into place in the registered holes of the elements to be assembled.

Claims

1. A process for the manufacture of thermostructural composite material parts by co-densification of pre-assembled elements of reinforcement texture wherein a structural connection is obtained between said elements of reinforcement texture by at least one blocking means having a fibrous texture that is subjected to compacting prior to engagement inside a corresponding lodging formed in at least one of said elements of said reinforcement texture in order to conform to the shape of said lodging and lock thereinto by relaxation of said fibrous texture upon elimination of said prior compacting, said elements of reinforcement texture and said blocking means being thereafter co-densified.

2. The process as claimed in claim 1, wherein said blocking means is in the form of a dowel of fibrous texture engaged inside registered lodgings formed within the elements of reinforcement texture to be assembled.

3. The process as claimed in claim 1, wherein the elements of reinforcement texture to be assembled are impregnated with a resin.

4. The process as claimed in claim 1, wherein the elements of reinforcement texture to be assembled are weakly densified by a material of a matrix chosen for the co-densification of the elements.

5. The process as claimed in claim 1, wherein the blocking means is comprised of a portion of one of the elements of reinforcement texture to be assembled.

6. The process as claimed in claim 1, wherein the compacting of the blocking means is obtained by means of a tool in which the blocking means is held until the insertion thereof in the corresponding lodging.

7. The process as claimed in claim 1, wherein the blocking means is compacted and then impregnated with a product binding together the fibers of the fibrous texture of the blocking means in order to maintain said blocking means in a compacted state, the impregnating product consisting of a product capable of being eliminated or softened to allow a relaxation of the fibrous texture after insertion of the compacted and impregnated blocking means into a corresponding lodging.