Fibrous textiles and structures are obtained by different fibre forming techniques. The main techniques are knitting, weaving, braiding, placement of fibres, batting and filament winding. The technique, production parameters and the type of fibres used depend on the required characteristics (geometric, mechanical, electric, surface appearance, formability or impregnability, injectability) for the partly finished product or the finished product to be manufactured. The nature of the fibres to be used is very varied: natural fibres, organic fibres, mineral or ceramic fibres (glass, carbon, silicon carbide, basalt, etc.). Fibrous structures are usually used as reinforcement for composite materials (shells, panels and structures, reservoirs, etc.) but they also have some direct applications (filter or heating fabrics, braided cables, insulating knits, etc.).
There are several techniques for making fibrous structures. Braiding has the advantages that geometric design of structure thread paths (generic term) is very flexible, the structures obtained have good dimensional stability and good mechanical properties (stiffness, behaviour in torsion, resistance to damage), and complex shapes can be made directly (braiding on mandrel) with a high fibre content. However, this technique is not used quite as frequently as weaving or knitting because it is relatively slow and the mechanical properties of composites in compression are not as good. There are many similarities between braiding and filament winding. Maximum fibre contents are lower but it can be used to obtain more complex parts and give better shock resistance. The two techniques can sometimes be used in a complementary manner to make objects.
Textile braids are fibrous architectures obtained by interlacing of threads (threads, roving, ribbons or bundles of threads). Fibre arrangements relative to each other are defined by the shape and characteristics of the object to be obtained. The simplest braid that can be made, also called a mat, is composed of only three threads, in which one of the two external threads is alternately placed in the centre by crossing over, so that each thread periodically passes into the centre from one side and then from the other side of the braid. Braids composed of a larger number of threads are made using the same interlacing principle but more generally, with threads that follow the same direction over a longer distance.
“2-D” braids are composed of biaxial and triaxial braids. Biaxial braids are composed of two groups of threads that cross over each other at an angle of ±θ, where θ is defined as the braiding angle.
The triaxial braids are composed of the presence of an additional group of threads in line along the braiding direction (θ=0°).
“3-D” braids are an extension of “2D” braids obtained with simultaneous braiding of several layers of “2D” braids with a periodic connection from layer to layer. This type of texture is also known as “interlock braid”. This can give greater thicknesses, connections between layers (leading to better mechanical properties such as a better resistance to delamination) and more complex and more precise forms.
Braiding is a very old traditional textile technique (1748, weaving loom made by Thomas Wadford), originally used to make ropes, laces and reinforcement for tubes.
A 2D braiding machine that can be either vertical or horizontal is composed of a set of spindles 11 (thread bobbin supports) that move inside a guide path defined on a table and according to a braiding plane 12. For a simple circular braiding machine for making tubes, the spindles follow undulating paths around the periphery of the circular table, half in one direction around the circle and the other half in the other direction, the two paths being interlaced as shown in
The ratio of the spindle displacement speed to the mandrel displacement speed defines the braiding angle. The ratio of the number of bobbins relative to the number of intersections defines the type of the braiding pattern made. The addition of fixed bobbins can give triaxial braids. If the spindles turn back after some distance instead of making complete turns, then flat braids are obtained. Spindles comprise uniform tension systems, for tensioning or for compensating of threads (the distance from a spindle to the convergence zone on the braid not being constant) to obtain braids with uniform patterns and required compactness. As mentioned above, the thickness of a layer (biaxial braid) is equal to twice the thickness of a thread. Conventionally, a thick tubular part can be obtained by stopping displacement of the mandrel when the required length has been braided, the threads can be cut and a second pass can be made, and then the operation can be repeated until the required thickness is obtained.
There are two types of 3D braiding machines. The first is said to be rectangular, with an alternating movement along two directions in order to obtain “Cartesian” braids. The second type is circular with an alternating movement in the radial and circular directions, resulting in “polar” braids. Sections with different shaped cross-sections can be obtained by predetermined positioning of the spindles on the machine in the initial state. Hollow sections are obtained by polar braiding, solid sections are obtained by Cartesian braiding. Further information on this subject can be found in article N 2511 in Techniques de l'Ingenieur, mentioned above and in “Handbook of Composites” by G. Lubin et al., Springer, 1998.
Structural composite materials are composed of fibrous reinforcement such as braids and a matrix that is the material between the fibres (and gives cohesion to the material). They are characterised by different types of matrices:
There are no braided tubular structures closed at one or both ends. Due to the inherent principle of 2D and 3D braiding (see
U.S. Pat. No. 7,204,903 very briefly discloses an innovative solution. Braiding is done on a liner that is cylindrical shaped at the centre and hemispherical (domes) at the ends. At least one of the domes has an insert at its end (pole). Braiding is conventionally done on the cylindrical part and on the hemispherical part as far as the insert. The innovation lies in the fact that at this moment, a second layer is made by stopping braiding and turning the bobbins (by about 180°), instead of starting in the opposite direction; half of the bobbins turn in one direction and the other half turn in the other direction which puts the bobbins opposite their initial position. Braiding is then resumed (next layer) along the inverse direction to the previous direction. The advantage mentioned compared with conventional braiding is that there is no need to cut the threads or to bend them and fold them over if they are sufficiently flexible, when changing from one braiding layer to the next. The result of the fabrication method used is that during the 180° rotation, one layer out of two in the hemispherical part corresponds to thread placements without any connection between each other (equivalent to filament winding) and a large thickness at the insert (the threads overlap each other in contact with the insert). Note that no value or information is given about braiding itself or the diameters of the cylinder or the insert, neither in the description of the invention nor the examples (the only numerical value is the rotation angle between two braids). The information in this patent does not solve the problem of closing one end, simply the integration of an insert. Furthermore, the invention does not offer a solution for the small diameters problem.
Document US 2008/0264551 discloses the fabrication of composite vessels (cylinder and hemispherical bottoms) based on dry threads (not impregnated with resin) for the storage of low or high pressure gas. The invention lies in the fact that the internal liner acts as a mould during injection of the resin and also as a heating or cooling system during polymerisation. Braiding is done by a combination of biaxial or triaxial braiding on the faces of the domes, by turning over and deforming the biaxial braid and sealing the ends of the threads by a means such as gluing. According to the authors, this method gives good control over the thickness and the contour. This system uses conventional braids and it does not result in continuity of the threads on the domes because their ends are glued, nor closing based on threads.
Document WO-A-89/05724 discloses the fabrication of a bottle made of a composite material at a moderate price for the storage of high pressure gas. The ends of the bottles comprise two end pieces connected to each other through a central rod, one of the two being used for adding or drawing off of gas. The body of the bottle is composed of coaxial braids with a resin matrix. The ends may be truncated or hemispherical, made of metal or plastic. This document does not describe the braiding technique, apparently the braids used are standard. Nor does this patent describe how to make closed braids because the ends are composed of inserts at the ends.
Document EP-A-0 487 374 presents a high pressure gas storage vessel composed of threads placed by filament winding and/or a braid. The vessel is cylindrical in shape with bottoms. It gives no information about the braid used other than that it is used as a longitudinal reinforcement and therefore a priori on the cylindrical part. There is no description of a closure by a continuous thread.
U.S. Pat. No. 3,765,557 presents a means of making a high pressure vessel made by filament winding in which the standard thread is replaced by a braided thread. Therefore, this patent does not apply to the braiding technique and gives very different structures. It is also conventional to be able to obtain a closed end, but with an overthickness by filament winding.
U.S. Pat. No. 5,070,914 discloses a new woven architecture and its fabrication means. The technique is based on weaving, with threads starting radially and circumferentially woven threads following a spiral. These structures are based on a path of threads following the line of a spiral without any cylindrical or axial symmetry, unlike the invention which will be described in appended claims.
The forms that can be obtained with braiding are solid forms (cables, strands), flat braids and tubular forms with varied sections and variable on the same part for example air conduits for aircraft). There is a technical limitation for tubular braids that makes it impossible to close braids at their ends, or to make a large reduction in their section. The purpose of this invention is to overcome this limitation, enabling continuity of the fibrous architecture, keeping the same reinforcement threads between the closed part or the bottom and the body or the tubular portion of the part. The purpose of the invention is firstly a new type of tubular fibrous architecture (or hollow form) closed at least one end, and its manufacturing process or method.
Therefore, the purpose of the invention is a method for making a tubular fibrous architecture closed at one of its ends, the method comprising the following steps:
a) make a pair of bobbins from threads, toying, ribbons or bundles of threads, hereinafter referred to under the generic term of threads, each pair of bobbins being made by winding a first part of a thread from a first end of the thread, onto a first bobbin in the pair and winding a second part of the thread from the second end of the thread, onto the second bobbin of the pair,
b) place pairs of bobbins on the spindles of a loom, arranging them as a function of a required Primary Structure,
c) make the Primary Structure on the loom in step b), this Primary Structure corresponding to the bottom of the fibrous architecture,
d) put a support conforming with the tubular part of the fibrous architecture into position on a loom to support, position and maintain said threads during their crossover in the next step,
e) use said threads and the loom in step d) to make the tubular part of the fibrous architecture on the support,
f) repeat the previous steps as many times as necessary, if any.
According to one embodiment, the pairs of bobbins are arranged in step a) such that the Primary Structure obtained is radiating.
According to another embodiment, the pairs of bobbins are arranged in step a) such that the Primary Structure obtained is of the biaxial type.
According to another embodiment, the pairs of bobbins are arranged in step a) on the spindles and in the creel of the loom, such that the Primary Structure obtained is triaxial.
The threads on the bobbins in step d) may be supported, positioned and held in place so as to obtain a biaxial tubular architecture. They may also be supported, positioned and held in place so as to obtain a triaxial tubular architecture.
The loom in step d) could be the loom in step b).
The Primary Structure may be made using a technique chosen from among weaving, braiding, batting and placement of threads. It may be a multi-layer, multi-dimensional or multi-directional texture, in which the threads derived from it are used to make the tubular part that is then multi-layer.
The tubular part of the fibrous architecture may be made on the support using a technique chosen from among weaving, braiding, batting and placement of threads. It may also be made on the support using multi-layer, multi-dimensional or multi-directional texture methods.
The loom in step d) may be a weaving loom, a braiding machine, a batting machine or a thread placement machine.
The process may include an additional step g) during which the tubular part of the fibrous architecture is prolonged on one end of the support to form a second bottom of the fibrous architecture. The additional step g) may be continued until a second closed bottom is obtained by braiding, weaving, batting or placement of threads.
In step c), the Primary Structure may possibly be made by incorporating at least one insert or at least one end piece into the Primary Structure.
During step e), the tubular part of the fibrous architecture may be made by incorporating at least one insert or at least one end piece into the tubular part.
Another purpose of the invention is a tubular fibrous architecture with a closed tubular part at least one of its ends or bottom, in which:
The bottom may be composed of a structure obtained by superposition of batting, a two-directional fabric, three-directional fabric, multi-layer or multi-directional fabric.
The tubular part may be formed by superposition of batting, three-dimensional fabric, multi-layer or multi-directional fabric.
At least one insert or end piece may be incorporated into at least one bottom.
At least one insert or end piece may be incorporated into at least the tubular part.
The threads may be composed of organic, metallic, mineral or ceramic fibres.
Another purpose of the invention is a composite material composed of the fibrous architecture described above, embedded in an organic, metallic or mineral matrix.
The invention will be better understood and other advantages and special features will become clear after reading the following description given as a non-limitative example accompanied by the appended drawings in which:
The principle of the invention for fabrication of a tubular fibrous architecture closed at one of its ends consists of performing the following operations:
The primary structure 30 forming the bottom of the tubular structure is arranged on one end of a mandrel with tubular braiding 34 mounted on a braiding tray 35. Braiding is continued to cover the mandrel 34. This is shown in
The design of the primary structure requires that the part made should have the number of threads (or pairs of bobbins) corresponding to the number required for the tubular form (that can be determined from the characteristics of the part that is to be made). The article by M. Munro et al. mentioned above provides further information about this subject.
There are two possible embodiments, direct mode and indirect mode.
With direct mode, the first step is to make pairs of bobbins with a single thread (for each pair). The bobbins thus made are placed on the spindles of the braiding machine with crossing of threads or without crossing in the case of simple batting, to make the primary structure. This latter case is shown in
With indirect mode, the first step is to make the primary structure with the threads each of which is wound onto a bobbin at each of its ends. The primary structure obtained, the mandrel and the bobbins on the spindles are put into place on the braiding machine. Braiding can then be done conventionally.
The primary structure from which the bottom is made can also be made directly on the form or liner to be coated, particularly if the form is not nearly flat and is strongly curved (for example hemispherical).
The primary structure may be made using different techniques. For example, the following three techniques can be mentioned.
According to a first technique, the threads are simply placed along three different directions (see
According to a second technique, the threads are placed in triaxial interlacing.
A third technique consists of classical weaving as shown in
These solutions have the advantage that the thickness and fibre content are similar to the thickness and fibre content of the tubular braid that is continuous with the primary structure or the bottom.
Several layers, possibly with different structures, can all be stacked at the same time to form the primary structure. Braiding done for the tubular part may be 2D (biaxial or triaxial) or 3D.
Thick. closed structures can be made by making a stack of layers (bottom and cylindrical part), adding a layer each time using the previously described technique, as is done conventionally for 2D type braids.
Instead of making a completely closed primary structure, a partial closure can be made, or the closure can be made with a large reduction in section. The partial closure may include an end piece or an insert. This is shown in
It is possible to make a total or partial closure at the other end, by stopping braiding of the cylindrical part when the required length has been made, and by inverting the position by a 180° rotation (along the braiding direction) of the part to be braided and moving the bobbins relative to the three axes of symmetry.
The entire principle of the invention may be applied to other techniques that use continuous threads such as placement of fibres, batting of fibres or weaving of fibres. In the same way as above, the following steps can be used:
This can be used to continuously make parts combining different types of structures.
The structures obtained either by braiding or by the previously described techniques, can be densified by different conventional means as indicated above.
One example embodiment is the production of SiC/SiC test pieces closed at one end for a high temperature composite tube application.
The first step is to make the primary structure of the bottom or the closure (first layer). This can be done by unwinding twelve bobbins of Tyranno SA3 1600 filament fibres (7 μm diameter) and rewinding on twelve other bobbins to have twelve pairs of bobbins with a thread length of about 1 m between the two bobbins. A triaxial structure is made with twelve pairs of bobbins distributed in a balanced manner (with orientations 0°, +120°, −120°).
The next step (second step) is to make the remainder of the braid (first layer). The bottom and the bobbins are brought onto the braiding machine. The bobbins are put into place on the spindles, each bobbin connected to another bobbin being placed respecting the initial geometry of the triaxial structure (see
The next step (third step) is to make the three other layers. A second primary structure, repeating the first step is made and is then placed on the fabricated braid as described in the second step. Braiding is done in the same way as in the second step. The two other layers are then made in the same way.
The purpose of the fourth step is to densify the braids by silicon carbide. Braids are densified in a relatively conventional manner. The part is placed in a CVI (Chemical Vapour Infiltration) furnace, in which carbon is deposited about 0.2 μm thick in interphase (deposition conditions: T=1000° C., P=5 kPa, precursor: propane, residence time=3 s, propane insertion time=5 minutes 30 s) followed by a deposit of SiC (T=950° C., P=2 kPa, precursor: 25% methyltrichlorosilane in hydrogen, residence time=1 s, infiltration time: 60 h). The graphite mandrel is then eliminated. The composite SiC/SiC density obtained is 2.5.
Number | Date | Country | Kind |
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09 58155 | Nov 2009 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/EP2010/067736 | 11/18/2010 | WO | 00 | 7/18/2012 |