New composite structure and method and matrix for the making thereof

The structure comprises a matrix formed by juxtaposing solid prefabricated matrix elements each provided with at least one cavity extending from one face to another face of the element, the matrix elements being arranged so that the cavities form continuous longitudinal housings, and reinforcing elements are inserted in the housings to form at least four bundles each constituted of spaced-apart reinforcing elements parallel to a same respective direction with the directions of the bundles being different fom each other and being such that, considering any plane of the space, at least two directions are not parallel to the plane, whereby a coherent composite structure is obtained without the need of binding material.

The present invention relates to the construction of a composite structure 
of the type comprising: rectilinear reinforcing elements forming at least 
four different bundles, each bundle consisting of a plurality of 
reinforcing elements parallel to a particular direction and distributed in 
the whole volume of the structure, the direction of the different bundles 
not being parallel to each other and to a same plane, and a matrix filling 
at least part of the volume of the structure between the reinforcing 
elements. 
Composite structures of this type are already known. They are especially 
used to produce parts which are required to withstand strong mechanical 
and thermal stresses, such as for example parts for rocket motor nozzles, 
the material constituting the reinforcing elements and the matrix being in 
this case mainly carbon. 
Such known structures are described in French patent applications Nos. 2 
276 916, 2 424 888 and 2 444 012. All three applications relate to 
reinforcing elements arranged in four or more bundles of different 
directions, to form a reinforcing structure which is then densified by 
introducing the material constituting the matrix in order to obtain the 
composite structure. It is therefore necessary for the reinforcing 
elements to be assembled together in space to obtain a reinforcement 
structure with enough cohesion to remain whole during subsequent phases of 
densification whilst sufficient access to all the voids between the 
reinforcing elements is preserved for the matrix. The formation of the 
matrix, or densification, is carried out by processes such as the chemical 
vapor deposition of the material of the matrix, or impregnation by a 
liquid or paste-like product which subsequently hardsets to form the 
matrix material. Hardsetting can, depending on the case, be obtained 
without particular treatment (such as for example with cement binding, or 
with room-temperature setting resins, or by solidification of a material 
introduced in the molten state) or it can be obtained by an appropriate 
thermal or physical treatment (such as hot-polymerization of hot-setting 
resins or cokefaction of resin or pitch by pyrolysis). 
Before filling the voids between the reinforcing elements with a material 
introduced in the fluid state (gaseous, liquid, or paste), said voids can 
be partly filled with a solid material introduced in powder form. 
These processes which are known to produce composite structures with 
multi-directional reinforcement, and consist in producing the matrix in 
situ from raw materials introduced in the fluid or powder state into the 
pre-assembled reinforcement structure, impose limitations in the choice of 
materials which can be used as the matrix and in the quality of the 
materials produced this way. 
Also, in certain cases, and in particular in the case of carbon-carbon 
composites, the densification necessitates repeated performances of these 
processes during successive cycles and under special conditions of 
temperature and pressure. This makes the densification an expensive and 
lengthy process. 
In order to facilitate the densification process, it has been proposed to 
realize a reinforcing texture by means of a method including the following 
steps: stacking sheets of unidirectional or bi-directional fibers, each 
sheet consisting of fibers bond together by a binding agent and being 
perforated; placing the sheets in the stack so that the perforations are 
aligned and that the fibers extend in the whole stack in at least two 
different directions; and placing rods or cores into the parallely 
extending channels formed by the aligned perforations. The reinforcing 
structure is then densified eventually after elimination of the binding 
agent. Such a method of making reinforcing textures is disclosed in French 
patent applications Nos. 2,398,705 and 2,433,003. This known method makes 
it possible to reduce the porosity of the reinforcing texture before 
starting the densification process and also to simplify and possibly to 
automatize the construction of this reinforcing structure. However, the 
whole matrix or nearly the whole matrix must still be deposited by means 
of usual densification processes. In addition, the bundle of parallel rods 
or cores placed into the aligned perforations cannot perform a locking of 
the stacked sheets, and appropriate means should then be used to maintain 
the stack during the densification process in order to prevent any 
de-cohesion of the stack. 
It is the object of the present invention to overcome the limitations 
imposed by the already known processes and to propose a simple and instant 
method for manufacturing composite structures of the type defined 
hereinabove, which are advantageous, costwise and qualitywise. 
This object is reached with a method including, according to the invention, 
the steps which comprise: 
(a) providing solid, prefabricated matrix elements having a prismatic or 
parellelepipedic form and each provided with at least one cavity extending 
from one face to another face of the matrix element; 
(b) juxtaposing said matrix elements in such a way that the cavities 
thereof extend one from the other and form rectilinear housings, the 
cavities being oriented so as to define at least four groups of 
rectilinear housings, each group consisting in a plurality of housings 
parallel to a same respective direction and distributed in the whole 
volume occupied by the juxtaposed matrix elements and the directions of 
said groups of housings being different from each other and such that, 
considering any plane of the space, at least two directions are not 
parallel to each other and to said plane; and 
(c) inserting thereafter said reinforcing elements in at least a part of 
the housings of each group, whereby a coherent composite structure is 
obtained with said reinforcing elements performing a locking of the 
assembled matrix elements. 
Thus, according to one feature of the invention, the matrix is produced 
first, with prefabricated elements, before inserting the rectilinear 
reinforcing elements. It is therefore easier to obtain a homogeneous 
matrix without any of the long and expensive operations which are often 
necessary when building a composite structure by densifying a 
prefabricated multidirectional reinforcement structure. 
The reinforcing elements act as pins or bolts which simultaneously ensure 
the positioning and assembly of the pre-juxtaposed matrix elements, which 
contributes to simplifying and speeding up the production of composite 
structures. Considering any plane of the structure, at least two bundles 
of reinforcing elements can be found which are not parallel to each other 
and to this plane. Therefore, the reinforcing elements perform a complete 
locking of the matrix elements, eliminating any risk of de-cohesion. 
The composite structure made in accordance with the invention can in itself 
constitute a finished product, which can be used as is, in particular to 
produce objects or buildings which are coherent without bond and can, if 
need arises, be dismountable. By contrast with known building processes 
using stacked prefabricated blocks provided with grooves for vertical and 
horizontal metal rods forming a bidimensional reinforcement, the method 
according to the invention provides a tridimensional and at least 
quadri-directional reinforcement, which implies that the matrix elements 
are not only stacked but juxtaposed on all their faces (if they are 
pararellepipedic) or on all their lateral faces (if they are prismatic), 
and a coherent locked structure is obtained without the need of binding 
agent. 
As a variant, and according to another feature of the method according to 
the invention, the composite structure can, once constructed, be subjected 
to a mechanical and/or thermal treatment designed to modify the 
compactness of the assembly or the properties of its constituents or their 
bondage, depending on the intended application. This subsequent treatment 
or compaction operation can take, for example, the form of a forging 
operation. 
Yet another feature of the method according to the invention is that the 
composite structure can, if necessary, be completed, once constructed, by 
the addition of one or more constituents filling all or part of each void 
between the reinforcing elements and the matrix elements, and thus bonding 
them together. The composite material then obtained is more particularly 
suitable for applications where high mechanical and thermal stresses are 
expected (for example refractory composite materials used for making 
rocket motor nozzles) because they show high cohesion due to the presence 
of a multidirectional reinforcement structure closely bonded to a matrix. 
Said latter is then composed mainly by the matrix elements which are 
introduced, in the solid state, during the construction of the composite 
structure, and for the rest, by the material introduced after the said 
construction. Said material can only be introduced in the fluid or powder 
state, and by one of the known methods indicated hereinabove, i.e. the 
chemical vapor deposition process, or the impregnation with a liquid or 
pasty substance followed by a hard-setting treatment. It is to be noted 
that said known methods are then only used as a complement to a matrix 
constituted of juxtaposed solid materials, and are not necessary to 
achieve the cohesion of the structure according to the invention. 
Advantageously, the matrix elements are all identical. They can for example 
be composed of parallelepipedal blocks or prismatic bars. Matrix elements 
can be densely assembled, leaving in this case no free space between them, 
except for the voids formed by the cavities of the elements. But it is 
possible, depending on the application required, to juxtapose the matrix 
elements so as to leave voids in the assembly such as for example 
non-occupied spaces of matrix elements. 
By cavity formed in a matrix element is meant here for example a hole, a 
groove or a slot extending from one side of the element to the other. Each 
matrix element advantageously comprises cavities oriented in at least four 
different directions for receiving at least one reinforcing element of 
each bundle. 
The housings formed by the cavities of the juxtaposed matrix elements are 
preferably continuous, i.e., each housing extends right through from one 
end of the matrix to the other. Reinforcing elements are inserted through 
the entire length of these housings or in only part thereof. In this last 
case, one or more housings contain no reinforcing elements throughout 
their entire length or through only part thereof. It will be further noted 
that at least some of these reinforcing elements may be discontinuous, a 
housing being then occupied by several portions of reinforcing elements 
placed end-to-end. Preferably, each reinforcing element fits exactly 
inside the perimeter of the cross-section of each cavity that it occupies. 
The present invention relates not only to a method for making a composite 
structure, but also to a matrix for use in the making of a composite 
structure and such as obtained by assembling matrix elements as described 
hereinabove, as well as to a composite structure such as that made 
according to the method defined hereinabove.

The following examples are given to illustrate several embodiments of the 
composite structure according to the invention. 
EXAMPLE 1 
A coherent construction of any size is produced without bond with matrix 
elements in the form of cube-shaped bricks 10 with sides of 10 cm, each 
brick comprising four slots such as shown in FIG. 1, said bricks being 
juxtaposed and bonded together by reinforcing elements shaped as 
cylindrical rods of 2 cm diameter circular cross-section, as shown in FIG. 
3. 
Each brick 10 is provided with four slots 21, 22, 23, 24 designed to 
receive four reinforcing elements which are respectively parallel to the 
four diagonals of two adjacent faces of the cube 10, as shown in FIG. 2. 
The slots are perpendicular to four edges of the cube, the edge facing an 
edge traversed by a slot not being traversed by a slot. 
Two slots, respectively 21-22, 23-24 issue on each of two opposite faces 
11, 12 of the cube 10, but only one slot respectively 23, 24, 21, 22 
issues on each respective one of the other faces 13, 14, 15, 16 of the 
cube. 
The slots of one cube are mutually set off so that the reinforcing elements 
placed inside them do not interfere one with the other. Thus, the slots 
21, 22 both of which issue on to face 11 and are parallel to the sides 
11a, 11b of said face, have different longitudinal planes of symmetry. The 
same applies to slots 23, 24 both of which issue onto face 12. 
It will be noted that faces 11, 12 of the cube are not identical seeing 
that if the cube is turned over, the face 12 is not superimposable on the 
face 11. In effect, the face 11 describes an S whereas the face 12 
describes a Z (or N). A cube 10 in the turned over position is shown in 
chain-dotted lines in FIG. 1. 
FIG. 2 shows how four cylindrical rods 31, 32, 33, 34 having different 
directions are respectively housed in the four slots 21, 22, 23, 24 of a 
cube 10. 
FIG. 3 shows a composite structure made up of stacked and juxtaposed cubes 
10 and of cylindrical rods forming four bundles of different directions, 
the rods of each bundle being parallel and regularly spaced in the whole 
structure. It will be noted that one rod of each bundle goes through each 
cube 10. 
The cubes 10 are so assembled that two adjacent cubes are in reversed 
position one with respect to the other. For example, referring to FIG. 1, 
the orientation of the cube shown in chain-dotted lines is obtained by 
simply turning over the cube shown in block lines above it, about an axis 
which is perpendicular either to faces 13 and 14 or to faces 15 and 16. 
The slots of the stacked cubes define passages for inserting cylindrical 
rods, each passage being made up by slots extending one from the other. 
To this effect, the width of each slot is at least and preferably equal to 
the diameter of a cylindrical rod. Moreover, the longitudinal median plane 
of a slot is situated at a distance d from the nearest parallel face of 
the cube, the value of which is the same for all the slots. Said distance 
d is preferably equal to half the distance D separating the longitudinal 
median planes of slots 21, 22 or 23, 24. The distance d is then equal to a 
quarter of the length of the edges of the cube. Thus, the cylindrical rods 
31, 32 form equidistant and alternated parallel layers, and so do the 
cylindrical rods 33, 34. Finally, the length 1 of the openings of the 
slots on the faces of the cube 10, measured from the edge which they 
traverse to the axis of their semi-cylindrical base is at least equal to 
half the length c of the edges of the cube. The slots of the juxtaposed 
cubes thus form adequate passages for the cylindrical rods. When choosing 
l=c/2, the exact passage necessary for the cylindrical rods is obtained. 
Said rods are then housed exactly at the base of the slots and are in 
contact over their entire length with bricks 10 placed alternately on 
either side of the same longitudinal plane of symmetry. The rods 31, 32, 
33, 34 thus lock the stacked bricks 10 together, in bolted manner. 
A coherent composite structure is thus obtained without having to use a 
bond, in which structure the matrix is constituted by the stacked bricks 
10, the reinforcement being of the 4D type, i.e. made up of reinforcing 
elements forming four bundles of different orientation (4D), the elements 
in each bundle being parallel and regularly spaced apart. In FIG. 3, the 
four bundles are formed respectively by the rods 31, the rods 32, the rods 
33 and the rods 34. 
The bricks 10 may be produced by direct molding. A typical application of 
this kind of construction is the production of furnaces, or of hot 
chambers in general, using fireproof bricks assembled together by likewise 
fireproof bars. 
EXAMPLE 2 
A metal/metal type of composite material is obtained by closely bonding a 
multi-directional reinforcement structure made from a metal showing high 
mechanical properties to a matrix in ductile metal. The matrix is made up 
of perforated bars in ductile metal and the reinforcement structure is 
made up of four bundles of cylindrical rods in a metal showing high 
mechanical properties. 
A bar 40 is shown in FIG. 4. It is constituted by a prism of 5 mm-square 
cross-section for example. The prism is provided with holes to receive 
without play four sets of cylindrical rods of 2 mm diameter for example. 
As can be seen in FIGS. 4 and 5, two sets of holes 51, 52 traverse through 
the bar 40 issuing on two opposite faces 41, 42 thereof. The axes of the 
holes 51 are in the same plane P1 parallel to the other faces 43, 44 of 
the bar and form with the face 41 the same angle .alpha. different from 
90.degree.. The axes of the holes 52 are in another plane P2 parallel to 
the faces 43, 44 and likewise form with the face 41 an angle .alpha., but 
the directions of the axes of the holes 51 and 52 are symmetrical together 
with respect to a line perpendicular to faces 41, 42. 
In the same way, two series of holes 53, 54 traverse through the bar 40, 
issuing on faces 43, 44. The axis of the holes 53 and 54 are contained in 
two planes P3, P4 parallel to faces 41, 42 forming with the face 43, 
angles .alpha. different from 90.degree., the axes of the holes 53 and 54 
being symmetrical together with respect to a line perpendicular to faces 
43, 44. The inclination of the axes of the different holes with respect to 
the faces on to which they issue is for example 55.degree., the axes of 
the holes in each set of holes being equidistant, with for example a pitch 
p of 7 mm in the longitudinal direction of the bar. 
FIG. 5 shows four sets of cylindrical rods 61, 62, 63, 64 inserted in the 
holes 51, 52, 53, 54. 
A composite structure is built by juxtaposing identical bars 40, two 
adjacent bars being set off lengthwise, by a distance equal to half the 
pitch p between holes of a same set of holes (FIG. 6). Thus, the holes 
issuing on the contacting faces of the juxtaposed bars are situated in 
extension one from the other and constitute housings for the four bundles 
of cylindrical rods which completely lock the building together. The 
cylindrical rods in each bundle are regularly spaced. 
Each one of planes P1, P2, P3, P4 of the axes of holes 51, 52, 53 54 is 
preferably at a distance from the nearest face of the bar parallel 
thereto, which is equal to a quarter of the width of the side of the bar. 
Thus, the bundles formed by the rods 61, 62 are constituted of equidistant 
and parallel alternate sets of rods, and so are the bundles formed by the 
rods 63, 64. 
The resulting composite structure has a matrix in ductile metal made from a 
juxtaposition of bars 40 and a reinforcing 4D structure in a metal showing 
high mechanical properties, formed by cylindrical rods 61, 62, 63, 64. 
The cohesion of this assembly can be improved by a compaction operation the 
effect of which is to finish off the contacts between matrix and 
reinforcement, on the one hand, and between the elements of matrix on the 
other hand. Depending on the nature of the materials used, on their 
responsiveness to heat treatments, on their respective coefficient of 
expansion, or their affinity, etc . . . compaction is possible using a 
press, or the isostatic method or any other known means in hot or cold 
conditions. 
EXAMPLE 3 
This example relates to the making of a carbon-carbon composite structure 
by closely associating a multidirectional reinforcing structure containing 
carbon fibers to a matrix entirely made of carbon. 
The matrix elements are grooved bars 70 in graphite such as illustrated in 
FIG. 7. The reinforcing elements are cylindrical bars with circular 
cross-section made of carbon fibers solidly bonded together by a 
polymerized resin, carbonized either before or after the construction of 
the composition structure. 
Each bar 70 is prismatic, with a cross-section which is contained inside a 
15 mm-square, for example. Each face 71, 72, 73, 74 of the bar is provided 
with a set of grooves 81, 82, 83, 84 respectively. The grooves in each set 
of grooves are parallel together and form with the longitudinal direction 
of a bar an oblique angle .beta.. Said angle is the same for all four sets 
of grooves and equal to about 56.degree.19' (angle having a tangent equal 
to 3/2). The grooves in each set of grooves are placed at regular 
intervals along the bar with a pitch of 10 mm. As clearly shown in FIG. 7, 
and assuming that the bar is placed vertically, the grooves of two 
adjacent faces of the bar are all directed upwards or downwards from the 
edge separating said two faces. Each edge is cut alternately and at 
regular intervals (5 mm) by the groove of a face adjacent to said edge and 
by the groove of the other face adjacent to said edge. For the sake of 
clarity, the edges of the bar 70 which correspond to the edges of the 
prism with square cross-section described around the bar have not been 
shown in FIGS. 7 and 8. Each edge being cut into by the grooves of the two 
faces which it separates, some parts of it are thinner as a result, and if 
they become too delicate, they could break easily when the structure is 
built and thereafter interfere with the insertion of the reinforcing 
elements. Therefore, it will be advantageous to remove these thin parts 
after grooving (by fettling) or to groove a bar on which the edges have 
been removed, such as shown in FIG. 7. 
The grooves have 3 mm-square cross-sections and are obtained by milling. 
Said grooves are milled on the four faces of the bar in such a way that 
the reinforcing rods of 3 mm diameter inserted in said grooves, intersect 
without touching. 
FIG. 8 shows four families of rods 91, 92, 93, 94 respectively housed in 
four sets of grooves 81, 82, 83, 84. 
The composite structure is built by regularly juxtaposing the bars so that 
the grooves of the successive bars extend one from the other (FIG. 9). 
Passages are thus defined for the reinforcing rods which will ensure the 
complete locking of the building and form a multidirectional reinforcement 
structure of the 4D type. Each bundle is made up of regularly spaced 
parallel reinforcing elements. 
A good quality composite material is obtained by subjecting the composite 
structure so obtained to further treatments meant for example to carbonize 
the resin used to bond the fibers constituting the reinforcing elements, 
or meant to bond together all the matrix elements and reinforcing elements 
which are only assembled and to fill in the voids between same and in 
particular the voids between the square grooves and the cylindrical rods. 
These additional treatments consist for example in introducing a material 
in fluid or even powder form. This can be done by a known method of 
densification. 
EXAMPLE 4 
This example is concerned with the production of a carbon-carbon composite 
material which comprises, as in Example 3, a 4D multidirectional 
reinforcement structure made up of four bundles of reinforcing elements 
and of a carbon matrix. 
The matrix elements are grooved bars 100 in graphite such as shown in FIG. 
10. The reinforcing elements are circular rods of circular cross-section 
such as used in Example 3. 
Each bar 100 is prismatic, with a 15 mm-square cross-section. Each face 
101, 102, 103, 104 of the bar is provided with a set of grooves 111, 112, 
113, 114, respectively. The grooves in each set of grooves are parallel 
together and form with the longitudinal direction of the bar the same 
oblique angle .alpha. equal to about 56.degree.19'. The grooves in each 
set of grooves are regularly spaced with a pitch of 10 mm. 
Contrary to the case presented in Example 3, the bar 100 being vertical, 
the grooves of two adjacent faces are respectively directed upwards for 
one face and downwards for the other, from the edge common to said two 
faces. 
Another difference between the grooves of the bar 100 and those of the bar 
70 is that the first ones have a U-shaped cross-section with a 
semi-circular base of 1.5 mm radius, the total depth of the grooves being 
3 mm. In the present case, the shape of the grooves is adapted to that of 
the reinforcing elements which they are designed to receive. 
FIG. 11 shows four families of rods 121, 122, 123, 124, respectively housed 
in the four sets of grooves 111, 112, 113, 114. It will be noted that 
here, as in all the other examples, the cross-sections of the reinforcing 
elements are entirely contained in the cavities formed in the matrix 
elements. 
A composite structure is built by regularly juxtaposing the bars in such a 
way that the grooves of successive bars extend one from the other. This 
composite structure can likewise be subjected to further treatments such 
as those indicated in Example 3. 
It is noted from FIG. 10 that the grooves of two adjacent faces are 
separated one from the other, along each edge, by thin "horn-shaped" 
portions 105. When these parts are fragile to the point of breaking up and 
of possibly interfering with the insertion of the reinforcing elements, it 
is advisable to remove them. A trimmed bar 100' is then obtained, such as 
that illustrated in FIG. 12. Said bar 100' can be used exactly like the 
bar 100. 
EXAMPLE 5 
This example differs from Example 3 in that, first, the grooves made in 
each prismatic bar 130 (FIG. 13) have a 2 mm-square cross-section and, 
second, the reinforcing elements are rods of 2 mm-square cross-section, 
and not of circular cross-section. Said rods 141, 142, 143, 144 are shown 
in FIG. 14. 
It will be noted that the composite structure built by juxtaposing the bars 
130 in such a way that the grooves of successive bars extend one from the 
other, and by inserting rods in all the cavities formed by said grooves, 
has no voids between the matrix elements and the reinforcing elements. 
EXAMPLE 6 
This example is concerned with a carbon-carbon composite material 
comprising a 6D multi-directional reinforcement structure made up of six 
bundles of reinforcing elements and of a carbon matrix. 
The matrix elements are bars 150 (FIG. 15) similar in dimensions to the 
bars 70 described in Example 3 and comprising on their faces 151, 152, 
153, 154, grooves 161, 162, 163, 164 of similar shape, dimensions and 
disposition as the grooves 81, 82, 83, 84. As a variant, the grooves 161, 
162, 163, 164, whilst retaining the same orientations on the different 
faces of the bar as the grooves 81, 82, 83, 84, could have a U-shaped 
cross-section, identical to the cross-section of the grooves of bar 100 of 
FIG. 10. 
The bar 150 differs from the bar 70 in that it comprises two sets of holes 
155, 156 (FIG. 15). The axes of the holes 155 are situated in the median 
plane of the bar which is parallel to the faces 153, 154 and they are 
perpendicular to the faces 151, 152; the holes 155 are regularly 
distributed along the bar, one between two consecutive grooves 161 or 162. 
In like manner, the axes of the holes 156 are situated in the median plane 
of the bar which is parallel to the faces 151, 152, and they are 
perpendicular to the faces 153, 154; the holes 156 are distributed 
regularly along the bar, one between two consecutive grooves 163 or 164. 
The holes 155, 156 have a diameter of 3 mm to receive respectively 
cylindrical rods 175, 176 of circular cross-section of 3 mm. Said rods are 
identical to rods 171, 172, 173, 174 fitted in the grooves 161, 162, 163, 
164 (FIG. 16) in the same way as the rods 91, 92, 93, 94 are fitted in the 
grooves 81, 82, 83, 84. 
The composite structure is built by juxtaposing the bars 150 in such a way 
that the holes 155 are aligned, as well as the holes 156 (FIG. 17). The 
rods 171 to 176 having then been fitted in, six bundles of reinforcing 
elements are obtained, two of which are oriented perpendicularly one to 
the other. In the bundles formed by the rods 155, 156, as in the other 
bundles, the reinforcing elements are regularly spaced. 
It will be noted on this point that in all the preceding examples, each 
bundle of reinforcing elements is constituted of parallel and regularly 
spaced elements. 
The composite structure obtained according to Example 6 can be densified by 
further treatments such as described in Example 3. 
The invention is in no way limited to the description and examples given 
hereinabove and on the contrary covers any modifications or additions that 
can be made thereto without departing from its scope.