Abstract:
A method for producing a one-piece preform for a composite structure includes the following steps: positioning a plurality of bundles of warp threads over two pairs of harnesses; making movements of low amplitude of each of the pairs of harnesses so as to make at least two adjacent and separate layers; and making movements of higher amplitude of the pairs of harnesses so as to at least partially link the at least two adjacent layers to an least one portion of the preform.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/FR2013/050609, filed on Mar. 21, 2013, which claims the benefit of FR 12/52563, filed on Mar. 22, 2012. The disclosures of the above applications are incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to a method for manufacturing a one-piece preform for a composite structure, and to a weaving loom for implementing such a method of producing. 
       BACKGROUND 
       [0003]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
         [0004]    The producing of a composite structure comprises the assembling of a reinforcement usually forming fibers providing the mechanical resistance of the structure, and a matrix providing the cohesion of the structure. 
         [0005]    In a known manner, the reinforcement may be formed by a fabric in two dimensions (2D) constituted by weft yarns woven with warp yarns, this yarn for example achieved in carbon, Kevlar, or even glass. 
         [0006]    The matrix is in a manner also known constituted by an organic or mineral resin. In the case of a matrix in resin for example, the method for manufacturing the composite piece will consist in a molding of the reinforcement layers, by Resin Transfer Molding (RTM), by Liquid resin Infusion (LRI), by Resin Film Infusion (RFI) or by any other method of impregnation or infiltration of resin, in dry fibrous elements. 
         [0007]    A recurrent issue is linked to the mechanical resistance of this type of structure, frequently being subject to a delamination between the layers. 
         [0008]    A known solution consists in achieving a composite structure based on a three-dimensional reinforcement (2.5D or 3D) having a better mechanical hold between the layers of fabric, with respect to an assembling of 2D fabrics. 
         [0009]    Typically, such a structure may have different types of weave (interlacing mode of the yarns) according to the selected weaving method. It is known for example as 3D weaving the weaving called “interlock” according to which several layers of warp yarns are woven with several layers of weft yarns, the whole able to be linked or not by at least one warp yarn called “reinforcing” which is added in the thickness of the fabric in order to link the different layers together. The mechanical resistance in particular, to delamination is higher with respect to an assembling of 2D fabrics. 
         [0010]    When the reinforcement is obtained, the operation aiming to give it the sought cohesion is achieved. It is necessary, before introducing the reinforcement in the mold for the resin injection, to give to the reinforcement a shape as close as possible to that which one wants to attain after achieving the cohesion operation. This operation of preparing the preform is accomplished for example thanks to cut-outs, foldings, etc. of certain parts of the preform. In order to achieve this phase of preparing the preform, it is hence essential that the preform be easily adjustable. 
         [0011]    According to the methods of 3D weaving known from the prior art, the layers of fabric are linked together in the direction of the thickness. 
         [0012]    Hence, it is understood that the step of preparing the preform prior to injection is in this case complex, since the folding is made impossible because of the linking of the layers together, and that the cutting out of warp yarns highly affects the mechanical resistance of the final composite structure. 
         [0013]    A solution to these issues consists in achieving several three-dimensional preforms that are linked together for example by sewing, of “tufting” type, in particular, in order to give several thicknesses to the final piece. This solution is not acceptable either for the aforementioned reasons with reference to the 2D structures, the mechanical hold between two preforms not being sufficient. 
       SUMMARY 
       [0014]    The present disclosure relates to a method for producing a one-piece preform for composite structure comprising said preform forming the reinforcement of the structure and a matrix, said preform being achieved by a three-dimensional weaving method thanks to a weaving loom comprising at least one reed and at least two pairs of harnesses, each of the harnesses comprising a plurality of heddles, each of the heddles being equipped with a plurality of eyelets of which each one is intended for the passage of a warp yarn, the at least two pairs of harnesses being distributed at distinct altitudes from the weaving loom in such a manner as to form a plurality of levels, said method of producing being characterized in that it comprises the following steps according to which:
       a plurality of bundles of warp yarns are positioned distributed on the at least two pairs of harnesses;   we carry out alternatively and as desired:   movements of low amplitude of each of the at least two pairs of harnesses for a predetermined warp yarn length, in such a manner that, during the introduction of the weft yarns, at least two adjacent layers are achieved, independent on at least one portion of the preform;   movements of increased amplitude, with respect to said movements of low amplitude, of the at least two pairs of harnesses, for a predetermined warp yarn length, in such a manner that, during the introduction of weft yarns the at least two adjacent layers are at least partly linked on at least one portion of the preform.       
 
         [0019]    Thus, by providing a partial unlinking of the adjacent layers, the achieved preform may be adjusted manually prior to proceeding with the step aiming to give cohesion to the preform. 
         [0020]    According to other features, the method of producing according to the present disclosure, comprises an additional step to position on the weaving loom means for separating adjacent layers of the preform. 
         [0021]    Thus, the forming of linkage between two adjacent layers is avoided. 
         [0022]    More particularly, the means for separating the layers comprise at least a stem that is positioned, as desired during the weaving, on the one hand between the reed and the pairs of harnesses, and on the other between the adjacent layers. 
         [0023]    According to a feature of the method of producing, at least one part of a bundle of warp yarns is positioned on at least one level of pairs of harnesses, in such a manner as to achieve during the introduction of weft yarns a current section of the preform, and at least one bundle of warp yarns is positioned at a distinct altitude from a same harness in such a manner as to achieve, during the introduction of weft yarns, at least an extra thickness of the layer. 
         [0024]    Thus, the thickness of the piece is varied punctually in such a manner as to create a hump in the direction of the warp yarn. 
         [0025]    According to another feature of the method of producing according to the present disclosure, several warp yarns are disposed between two levels of weft yarns. 
         [0026]    This advantageously allows easily creating a groove in one of the layers of the preform. 
         [0027]    Furthermore, the method of producing comprises a step of leaving at least one weft yarn free in such a manner as to define a machining area without impact. 
         [0028]    The method of producing according to the present disclosure also comprises an additional step to cut out and/or fold the preform in such a manner as to give it a shape close to that sought to be given to the composite structure. 
         [0029]    According to the present disclosure, the warp yarns and the weft yarns are woven according to an interlock type weaving method. 
         [0030]    The present disclosure also relates to a weaving loom for implementing the method of producing according to the present disclosure, characterized in that it comprises a plurality of pairs of harnesses disposed side by side in the weft direction, in such a manner as to allow an independent control of each of said harnesses. 
         [0031]    Thus, by disposing several independent harnesses in the direction of the width of the preform, the different needs of the preform in terms of thickness may be managed. The width of each of the harnesses corresponds to a width of extra thickness to be given to the preform. 
         [0032]    The present disclosure still relates to a composite beam intended to support the sliding of at least one cowl of thrust reverser of a turbojet engine nacelle, said beam comprising at least one three-dimensional preform and a cohesion matrix, and being characterized in that said preform is the result of the method of producing according to the present disclosure. 
         [0033]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       DRAWINGS 
         [0034]    In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which: 
           [0035]      FIG. 1  illustrates in isometric view the composite beam sought to be achieved; 
           [0036]      FIG. 2  represents the preform in flat view sought to be obtained by three-dimensional weaving; 
           [0037]      FIG. 3  schematically represents the weave of the weaving, that is to say the interlacing mode of the warp yarns and the weft yarns; 
           [0038]      FIG. 4  represents a second interlacing mode of the warp yarns and the weft yarns; 
           [0039]      FIG. 5  illustrates the preform represented in  FIG. 2 , one of the tabs being folded; 
           [0040]      FIG. 6  illustrates the linkage between two layers of the preform; 
           [0041]      FIG. 7  is similar to  FIG. 6 , according to another mode of linking layers of the preform; 
           [0042]      FIG. 8  represents the shape obtained by the mode of linking the layers represented on  FIG. 7 ; 
           [0043]      FIG. 9  represents two layers of the preform, between which are set layer separating means; 
           [0044]      FIG. 10  illustrates the achieving of a hump in the warp direction C of the preform; 
           [0045]      FIG. 11  represents the preform sought to be manufactured, of which the view is centered on the rails; 
           [0046]      FIG. 12  illustrates the achieving of a groove during the weaving of the preform; 
           [0047]      FIGS. 13 to 15  show the steps of folding and cutting out of the preform resulting from the weaving method; 
           [0048]      FIG. 16  illustrates a step of the method of producing according to the present disclosure, by which a non-perpendicular and unlinking of the warp yarns is achieved; 
           [0049]      FIG. 17  represents the preform of beam type, according to which the reinforcements are not perpendicular to the wall of the beam; 
           [0050]      FIG. 18  details the machining area without impact of the preform. 
       
    
    
       [0051]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
       DETAILED DESCRIPTION 
       [0052]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. 
         [0053]    An aircraft is moved by several turbojet engines each housed in a nacelle also accommodating a set of annex actuating devices linked to the operating thereof and providing various functions when the turbojet engine is in operation or stopped. These annex actuating devices comprise in particular, a mechanical system for actuating a thrust reverser, of which the role is to help with the braking of the aircraft during landing. 
         [0054]    A thrust reverser comprises one or several mobile cowls between, on the one hand, a deployed position in which they open in the nacelle a passage intended for the diverted flow, and on the other hand, a retractable position in which they close this passage. 
         [0055]    The mobile cowl or mobile cowls slide along one or several beams comprising rails in such a manner that when reversing during the opening phase, they uncover grids of jet vanes disposed in the thickness of the nacelle, the cold air flow crossing the nacelle thus discharged upstream of the nacelle. 
         [0056]    Certain passages of the description refer directly to such a beam for describing the method of producing according to the present disclosure, but in no case would this method be limited to this beam, but allows on the contrary to achieve any type of woven preform for composite structure, the hypothesis according to which the structure to manufacture is a beam being simply adopted in order to make the understanding of the present disclosure easier. 
         [0057]      FIG. 1  illustrates the beam in composite materials that are sought to be achieved. 
         [0058]    As described before, a composite structure comprises a piece called “reinforcement”, which gives the final structure mechanical hold, and a matrix, usually resin-based, which provides the cohesion of the structure. 
         [0059]    The reinforcement structure is achieved according to the method according to the present disclosure, according to which a one-piece 3D preform is manufactured woven by the weaving loom according to the present disclosure. 
         [0060]      FIG. 2  illustrates the preform, flat, that is sought to be obtained as a result of the 3D weaving. 
         [0061]    The preform  1  comprises a tab  3  in its lower part, surmounted by an intermediate wall  5 , then a current section  7 . 
         [0062]    The current section  7  comprises in its upper face  9  two tabs  11 , of parallelepiped shape, forming an extra thickness of the current section  7 . The tab  3 , the intermediate wall  5 , the current section  7  and the tabs  11  form sub-assemblies of the preform, which need to be achieved in a unitary manner, that is to say without having to add a sub-assembly with respect to another sub-assembly. The achieving of such a one-piece preform allows, as mentioned earlier, giving the final composite structure a mechanical resistance higher than that obtained by a reinforcement composed of multiple preforms. 
         [0063]    The preform  1  is achieved by three-dimensional weaving, and comprises in the direction of the length thereof warp yarns (according to direction C), and in the direction of the width thereof weft yarns (according to direction T). 
         [0064]    The weaving weave, that is to say the interlacing mode of the warp yarns and the weft yarns, is illustrated in  FIG. 3 . 
         [0065]      FIG. 3  represents in longitudinal section (in the warp direction) an area of the preform that has been achieved by 3D weaving. 
         [0066]    The warp yarns  13  adopt a sawtooth shape over the entire length of the represented area of the preform. Weft yarns  15  are set perpendicularly to the warp yarns, in such a manner as to link the warp yarn together. 
         [0067]    This type of interlacing of the warp  13  and weft  15  yarns of the preform  1  is called interlock weaving. 
         [0068]    The interlock armature is retained as an example in the description, but it goes without saying that the preform may be achieved by any other type of armature, for example of “plain”, “twill”, “satin” type, etc. 
         [0069]    According to another type of interlock weave, represented on  FIG. 4 , the warp  13  and weft  15  yarns are not interlaced together, but warp yarns called reinforcement  16  yarns are introduced, crossing the preform in its thickness in order to maintain the weft yarns and the warp yarns together. The density of the reinforcement warp yarn  16  is variable according to the type of armature retained. 
         [0070]    The sub-assemblies of the preform  1  may indifferently be achieved by any type of armature of 3D fabrics, each of the sub-assemblies possibly able to be achieved based on a different armature if the one skilled in the art finds it particularly useful. 
         [0071]    Reference is made to  FIGS. 2 and 5 , respectively illustrating the preform such as obtained as a result of the weaving method, and the same preform in progress partly adjusted prior to resin injection. 
         [0072]    It is required to fold over the tab  3  so that it is substantially perpendicular to the intermediate wall  5 , as represented on  FIG. 5 . 
         [0073]    It is understood that given that it is sought to achieve the preform in one single piece, the tab  3  and the wall  5  must only partly be linked together, in order to be able to handle each of these sub-assemblies independently from each other on the non-linked part. 
         [0074]      FIG. 6  illustrates in longitudinal section the manner in which the lower adjacent layers  17 , forming the tab  3 , and upper  19 , forming the wall  5 , have been woven thanks to the method according to the present disclosure. 
         [0075]    The layers  17  and  19  comprise a plurality of warp  13  and weft  15  yarns. The layers  17  and  19  are independent on the portions  21   a  and  21   b  and are linked together on the portion  23 . 
         [0076]    The weaving loom allowing this type of partial linkage comprises a plurality of pairs of harnesses, disposed at different altitudes of the weaving loom, forming a plurality of levels. 
         [0077]    More particularly, a harness typically comprises two frames linked and separated by heddles. Each heddle comprises a plurality of eyelets in which the warp yarns are introduced. 
         [0078]    It is considered that the weaving loom comprises two levels of harnesses, that is to say a pair of lower harnesses and a pair of upper harnesses. 
         [0079]    The warp yarns  13  are inserted at the beginning of the method of weaving in the eyelets the pair of lower and upper harnesses. 
         [0080]    The lower and upper harnesses are put in movement in such a manner as to create, during the introduction of the weft yarn  15 , the lower  17  and upper  19  adjacent layers, independently from each other, obtained by a limited amplitude of the harness movement. 
         [0081]    It is managed to punctually link these two adjacent layers by temporarily increasing the amplitude of the harnesses with respect to the amplitude retained for achieving the distinct layers. Weft yarn is also set over the entire thickness of the preform at the portion  23 . 
         [0082]    Thus, the adjacent layers  17  and  19  are made independent on the portions  21   a  and  21   b  and linked together on the portion  23 , thus allowing to achieve a folding, for example manual or using a specific external machine, of the tab  3  with respect to the wall  5 . 
         [0083]    The amplitude of the movements of the harnesses may be variable during weaving, in such a manner as to allow the achieving of hollow shapes of different thicknesses. 
         [0084]    For example, according to one form represented on  FIG. 7 , the amplitude of the movement of the harnesses is reduced on a portion  25 , on which the weft yarns are no longer set, in such a manner as to form a hollow area  27 . The skilled person completes by symmetry in such a manner as to obtain the piece represented on  FIG. 8 . 
         [0085]    The adjacent layers are of identical and constant thicknesses such as represented on  FIG. 8 . However, it is possible to achieve adjacent layers of distinct and progressing thickness thanks to the method of producing according to the present disclosure. 
         [0086]    This disposition is advantageous as the preform may be equipped in this hollow area with a tool-piece allowing to achieve an opening in the final composite structure. This hollow area may also be of interest when it is sought to integrate within the final composite structure a foam or a honeycomb type core, for example, advantageously allowing to improve the mechanical resistance of the final piece, in particular in compression. 
         [0087]    According to another form of the method according to the present disclosure, represented on  FIG. 9 , means for separating layers  17  and  19  are set. 
         [0088]    The separating means comprise, as represented on  FIG. 9 , a stem  28  that is disposed between the reed of the weaving loom (not represented) and the harnesses (not represented), and between two independent adjacent layers  17  and  19 . Thus, it is provided that the warp yarns of one of the layers  17  or  19  are not linked inadvertently with the weft yarns of the other of the layers  17  or  19 . 
         [0089]    It is now referred to  FIG. 10 , illustrating the achieving of a hump in the warp direction C of the preform. 
         [0090]    It is initially provided the harnesses of warp yarns  13  that are disposed in such a manner as to define, during the introduction of weft yarns  15 , the layer  17  corresponding to the current section of the preform. 
         [0091]    It is also disposed the harnesses of warp yarns  29 , disposed at distinct altitude of the warp yarns  13 . 
         [0092]    It is achieved such a hump in the warp direction C by temporarily setting during the weaving weft yarns  30  on a thickness  31  distinct from the layer  17  which defines the current section. 
         [0093]    The weaving loom comprises a plurality of pairs of harnesses disposed side by side in the weft direction, in such a manner as to allow an independent control of each of said harnesses. 
         [0094]    This prevents that the introduction of weft yarns causes to define an extra thickness of the current section over the entire width of the preform. 
         [0095]    Thus, the width of a pair of harnesses corresponds to widths of the extra thicknesses that are sought to be given to the preform. Thus, it is made possible to introduce weft yarn which will be linked to the structure only on the predetermined widths of the preform in such a manner as to achieve an extra thickness on a predetermined width. 
         [0096]    By way of example, and by referring again to  FIG. 2 , to each of the extra thicknesses  11  corresponds a pair of harnesses, of which the width of a pair of harnesses is substantially equal to a width L of an extra thickness. 
         [0097]    For a considered level, the weaving loom comprises as many pairs of harnesses as required, each of the pairs corresponding to a layer width. 
         [0098]    Thus, it is achieved as desired extra thicknesses of the current section, of which the width is variable as desired. 
         [0099]    In the considered example, the extra thicknesses  11  of the current section  7  are intended to provide the function of rails  32  of the beam, visible on  FIG. 11 , along which the thrust reverser cowl will slide. 
         [0100]    The rails  32  are subjected to mechanical forces during the sliding of the cowl, and the method of producing according to the present disclosure, which allows achieving the preform in one single part, is particularly advantageous for providing the piece with the required mechanical hold. 
         [0101]    It must be understood that such levels of mechanical requirements cannot be reached by method of producing a preform according to the prior art, according to which the rails are inevitably constituted by preforms added to the main preform. 
         [0102]    Finally, according to another step of the method of producing according to the present disclosure, it is disposed several warp yarns  13  between two levels of weft yarns  15 , as illustrated in  FIG. 12 . 
         [0103]    The warp yarns  13  are packed by the weft yarns  15 , thus allowing to create a groove. 
         [0104]    It is possible, during the achieving of certain pieces, to combine several of the aforementioned weaving methods, on the one hand in order to limit the additional steps of fashioning the preform, and on the other hand in order to prevent the assembling of multiple preforms, which affect the mechanical features of the final composite structure. 
         [0105]    Reference is now made to  FIGS. 13 to 15 , illustrating the steps to be achieved in order to attain the required shape. 
         [0106]    It is attained the shape of the preform such as illustrated in  FIG. 14  thanks to a step of folding the current section  7  of the preform, along a line  33 . 
         [0107]    Then, in order to achieve the reinforcements  34 , it is first achieved an operation of cutting out the intermediate wall  5 , along lines  35   a,    35   b,    35   c,    35   d.  Then, each of the two parts resulting from the cutting out of lines  35   a,    35   b,    35   c,    35   d  is folded over. Thus, the reinforcements  34  are obtained. 
         [0108]    Advantageously, these reinforcements are achieved based on the preform  1 , without having to add an additional piece, thus allowing to obtain good mechanical features of the final composite structure. 
         [0109]    Then, the reinforcements  34  are cut out in order to give them their final shape, such as represented on  FIG. 15 . 
         [0110]    Then, it is attained, after these steps of cutting out and folding the portions of the preform  1  resulting from the method of producing according to the present disclosure, a one-piece three-dimensional preform close to the shape of the final composite structure. 
         [0111]    The warp yarns which are not assembled with weft yarns after the weaving method are cut out. 
         [0112]    It is now referred to  FIG. 16 , illustrating a step of the method of producing according to which it is achieved a non-perpendicular unlinking of the warp yarns. 
         [0113]    The stem  28  is mounted moveable in translation on the weaving loom in a direction parallel to that of the warp direction, and slides during weaving. This prevents the linkage of the  2  adjacent layers  17 ,  19  on the totality of the width of the fabric where the stem is found. 
         [0114]    According to an alternative (not represented on the figures), in order to obtain a linking or a parallel unlinking, it is provided two stems each positioned at an end of the linked part of the preform. The stems are mounted moveable in translation on the weaving loom, and move in a direction parallel with that of the warp direction, in the opposite direction. 
         [0115]    In the example of producing of the preform of beam type, represented on  FIG. 17 , the reinforcements  34  should not be perpendicular to the wall  5  of the beam. For this, the interlock links are stopped angled thanks to the stem. 
         [0116]    According to another aspect of the method of producing according to the present disclosure, the preform may also be subject to a machining in order to achieve piercings  36 , visible in particular, on  FIG. 15 . 
         [0117]    According to an aspect of the present disclosure, it is provided in the preform a portion only provided with weft yarns. 
         [0118]    In reference to  FIG. 18 , it is achieved by the method of producing according to the present disclosure a machining area without impact  37 , corresponding to a portion of the layer in which the weft yarns are left free, allowing to not affect the tops  39  of the warp yarns  13  during a piercing operation. 
         [0119]    Thanks to the method according to the present disclosure, it is possible to manufacture a one-piece three-dimensional woven preform, partly non-linked in the warp direction, which can be advantageously adjusted in order to form the reinforcement of a composite structure. 
         [0120]    Thus, it is no longer necessary to achieve multiple preforms, of which the links do not have a good mechanical hold. 
         [0121]    It is worth noting that the preform described in the present disclosure may be achieved indifferently by replacing the warp yarns by the weft yarns, and by replacing the weft yarns by the warp yarns. This substitution may allow saving time for the manufacture of the preform or a decrease in the loss of material. 
         [0122]    It may also be interesting to invert the weft yarns and the warp yarns according to the nature of the weaving loom, or according to the technical constraint linked to the geometry of the piece to manufacture. 
         [0123]    As it goes without saying, the method of producing is no way limited to the producing of a preform of a beam for thrust reverser, this example having been described solely for the purpose of illustrating the implementation of the method, but on the contrary applies to any three-dimensional weaving method.