Abstract:
The invention relates to an L-shaped fitting obtained after molding a composite material, including two portions defining an angle therebetween and having holes formed therein for connecting the two portions using an attachment device, and having side reinforcements in the form of brackets. At least one portion has a concave curved profile on the inner side of the fitting, and the hole(s), formed in the portion having a concave curved profile on the inner side are each formed along an axis radial to the curvature.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     The object of the present invention is an L-shaped fitting obtained after molding a composite material, as well as the method for the production thereof and the mold for implementing said method. 
     (2) Description of the Prior Art 
       FIG. 1  of the attached drawing represents an L-shaped fitting  1  made out of composite material presently used, namely in the field of aeronautics, for assembling parts. This fitting  1  is obtained after molding a composite material, it essentially includes two portions  10  and  11  forming between them an angle, in this case a right angle, having holes  12  and  13 , respectively, formed therein in order to allow making them integral, and at right angles by means of side reinforcements  14 . 
     Such a fitting  1  is aimed, as shown in  FIG. 2 , at being used pairwise for assembling and fixing two parts A and B, one of which is perpendicular to the other one, one of both parts, A, being enclosed by two fittings  1 , the whole being made integral through fixing means, not shown, such as studs. 
     These fittings  1  are subjected to tensile and compression forces, and they must therefore meet strict specifications; however, because they are made out of composite material, these fittings are subjected, during their stress, to bending deformations, which generate a delamination of the fibers. 
     Such fittings are described in GB 2 444 645, one made out of metal and the other one made out of composite material. These two fittings essentially differ in that the one made out of composite material has walls provided with extra thicknesses aimed at reinforcing the structure, so as to try to cope with the drawbacks related to the selection of material. 
     The solution consisting in making the walls thicker permits to increase only slightly the strength of the structure, while exhibiting other drawbacks such as an increase in size and weight of the fitting. 
     SUMMARY OF THE INVENTION 
     The present invention is aimed at providing an L-shaped fitting obtained after molding of a composite material the new design of which permits not only to meet the above-mentioned specifications, but also to cope with the drawbacks of deterioration when it is stressed in traction or compression, and without exhibiting the drawbacks related to the addition of material. 
     The L-shaped fitting obtained after molding a composite material, according to the invention, comprises two portions forming between them an angle, having holes formed therein for permitting to make two parts integral through fixing means, and at right angles by means of side reinforcements, and it is essentially characterized in that at least one of said two portions has, on the inner side of the fitting, a concave curved profile, and in that the hole or holes, provided for in the portion or portions having on the inner side a concave curved profile, are each made according to an axis radial to the curvature. 
     According to an additional feature of the inventive L-shaped fitting, the area for connecting the two portions has, on the inner side, a concave curved profile. 
     According to another additional feature of the inventive L-shaped fitting, the side reinforcements have a concave bent profile on the inner side. 
     According to another additional feature of the inventive L-shaped fitting, at least one of the portions has a flat coupling outer face. 
     This feature namely permits to increase the compression strength, in particular, but not restrictively, when the direction of the compression force is substantially constant and perpendicular to the flat coupling face. 
     According to another additional feature of the inventive L-shaped fitting, the flat coupling outer face of one of the portions consists of the outer face of an element molded on said externally convex portion. 
     The wall of the fitting at the level of the area with curved profile permits to transmit the forces into the composite material, while avoiding inter-laminar shearing and traction. 
     It should be noted that the interfaces at the level of the hole or holes provided for in an area with a spherical or cylindrical profile, namely when the coupling faces are not flat, are made through spherical or cylindrical bearing elements, such as washers with an adapted shape. 
     The method for producing the inventive L-shaped fitting obtained after molding of a composite material consists in performing the following successive steps:
         arranging on the inner walls of the hollow cavity of a mold reproducing the outer shape to be conferred to said L-shaped fitting pre-impregnated fibers in the form of fabrics or mats,   inserting into said cavity a varying-geometry core,   developing said core until it adopts externally the inner shape of said L-shaped fitting,   applying special pressure and/or temperature conditions, so as to bring about the polymerization of said composite material.       

     The mold permitting the implementation of the method for producing the inventive L-shaped fitting is essentially characterized in that it comprises a portion comprising a hollow cavity reproducing the outer shape of said L-shaped fitting, a second portion or core formed of the association of several elements, designed capable of sliding against each other through oblique surfaces, at least one of said elements forming a wedge so as to permit, during its insertion, to deform said core so that it has externally the inner shape of said L-shaped fitting. 
     The advantages and features of the inventive fitting will become clear from the following description, which refers to the attached drawing, which represents a non-restrictive embodiment of same. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       In the attached drawing: 
         FIG. 1  represents a schematic and perspective view of an L-shaped fitting of the state of the art, 
         FIG. 2  represents a schematic, perspective and exploded view of a mounting using L-shaped fittings of the state of the art, 
         FIG. 3  represents a schematic and perspective view of an L-shaped fitting according to the invention, 
         FIG. 4  represents a schematic and perspective view according to another angle of the same fitting, 
         FIG. 5  represents a schematic and cross-sectional view according to the axis BB of  FIG. 6  of the same fitting, 
         FIG. 6  represents a schematic and cross-sectional view according to the axis AA of  FIG. 5  of the same fitting, 
         FIGS. 7 and 8  represent results of tensile tests on fittings, 
         FIGS. 9 and 10  represent results of compression tests on fittings, 
         FIG. 11  represents a schematic and perspective view of a variant of the L-shaped fitting according to the invention, 
         FIG. 12  represents the results of compression tests on the fitting shown in  FIG. 11 . 
         FIGS. 13 and 14  represent schematic plan views of a mold for producing an L-shaped fitting according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In  FIGS. 3. 4 .  5  and  6 , one can see an L-shaped fitting  2  according to the invention. This fitting  2  comprises two portions  20  and  21  forming between them an angle, in this case a right angle, having holes  22  and  23 , respectively, formed therein, and at right angles by means of side reinforcements  24 . 
     Though the portion  20  is flat, the portion  21  has, in turn, a curved profile, which creates two deformations  25  in the form of a spherical cap, which is concave on the inner side and convex on the outer side, and at the pole of each one of which is drilled a hole  23  with an axis radial to the deformations  25  permitting the passing-through of a fixing means, not shown, for example the screw of a bolt.  FIGS. 4 and 5  show the deformation  25  forming the second inner surface  25 a.  FIG. 5  shows the radius  25 b of the second inner surface  25 a in a dashed line. 
     It should be noted that the selection of the location of the holes  23  depends on the use of the fitting  2  and especially on the directions of the forces it has to withstand, since the location of a hole  23  is characterized by an axis. In this case, for the fitting  2  shown, the selection of the poles is a particular case. 
     It should be noted in addition that it is advantageously possible for the axes of the holes  23  not to be parallel. 
     Furthermore, the side reinforcing portions  24  also have an internally concave and externally convex curved profile. 
     It should be noted that the area or transition area  26  for connecting the two portions  20  and  21  to each other has an internally concave and externally convex curved profile through which occurs the transmission of the forces from one portion onto the other one.  FIG. 4  shows the transition area  26  between the portions  20  and  21 . The fibers, which in this area connect both portions  20   and  21 , follow a curvature and permit the pressure transfer. 
     In order to measure the advantages of the fitting  2  with respect to a fitting  1  made out of composite material and presently used, they have been subjected to comparison tests, which will now be described. 
     It should be noted first of all that the fittings  1  and  2  used during these tests have been molded with fabrics from one and the same badge and using the same number of plies for the same thickness and with the same method, polymerized according to the same thermal cycle. While increasing successive pressures are applied during the tests, in order to visualize the state of the fitting at each level of pressure. 
     The first tests consist in examining the behavior of the fittings  1  and  2  during tensile forces. 
     In  FIG. 7  has been shown the graphic reproducing the results of the tensile tests on a fitting  1 . 
     It should be noted that the offset of the starting point of each curve corresponds to the taking up of the backlash of the traction machine after each release, and that the curves of the first five rises in pressure are not reproduced. 
     The first cracks, referred to as first damages, are audible during the 6 th  rise in pressure, starting from about 5400 N, without visual degradation of the fitting. From that pressure on, the fitting will &lt;&lt;crunch&gt;&gt; nearly continuously, which corresponds to the breaking of the fibers. For the following tractions, the cracking always restarts only from the preceding level of pressure. One observes on the various curves a change in slope, which corresponds to a decrease in rigidity, resulting from the breaking of the fibers. Starting from about 9000 N, the cracks intensify, however without showing visual breaking, delamination or irreversible deformation. 
     At about 10500 N, the fitting largely deforms, but this deformation is however reversible. At 11500 N, one observes the same deformation, however this time it is irreversible, while at 11600 N breaking occurs. 
     In  FIG. 8  has been shown the graphic reproducing the results of the tensile tests on a fitting  2  according to the invention. 
     The first cracking occurs at about 15500 N, without showing any damage. Starting from this pressure, the fitting  2  behaves in the same way as the fitting  1 , restarting of the cracking from the preceding level of pressure, and reduction of the rigidity. 
     The first visible defect appears at about 19900N, this is a delamination, which is visible only under pressure, and visually disappears when the force is released, then, at 18500N the fitting breaks. 
     In  FIG. 9  has been shown the graphic reproducing the results of the compression tests on a fitting  1 . 
     On each fitting are applied increasing successive pressures, in order to visualize the state of the fitting at each level of pressure. The offset of the starting point of each curve corresponds to the taking up of the backlash of the traction machine after each release. 
     The first cracks appear at about 11400 N, they continue, without visible consequences, until 13500 N, then at 13700 N collapsing occurs. 
     In  FIG. 10  has been shown the graphic reproducing the results of the compression tests on a fitting  2  according to the invention. 
     The first cracks appear at about 12500 N, without showing any damage. Starting from this pressure, the cracks restart from the maximum pressure of the preceding test. No visible damage is observed until the fifth test, or at about 13800 N an important delamination occurs, the following test confirming that the fitting is destroyed. 
     The following table summarizes the results obtained: 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                 Fitting 1 
                 Fitting 2 
                 U 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 MASS 
                 22 
                 16 
                 g 
               
               
                   
                 Tensile strength 
                 10500 
                 19900 
                 N 
               
               
                   
                 Crushing strength 
                 13500 
                 13800 
                 N 
               
               
                   
               
             
          
         
       
     
     One can thus observe that the fitting  2  according to the invention has much higher tensile strength characteristics than a fitting  1 , but that the crushing strength characteristics are identical. 
     It should be noted that in the studied cases the fitting  2  has a smaller mass than the fitting  1 , so that it can be considered that at the same weight, by making the wall thicker, the fitting  2  can exhibit an eventually proportional increase of its tensile strength characteristics, both the tensile and the compression strength. 
     When referring now to  FIG. 11 , one can see a variant of the L-shaped fitting  2 , which consists of a fitting  2  on the portion  21  of which has been molded a heel  27 , which has externally a flat coupling face  28 , in this case perpendicular to the flat outer face  29  of the portion  20 . The heel  27  is made integral with the second portion  21 , and the flat coupling face  28  has the second outer surface  28 a opposite the second inner surface  25 a. 
     The portion  21  maintains its concavity on the inner side, as well as the area  26  for connecting the two portions  20  and  21 . By contrast, the compression surface is flat, which avoids the use of elements with a spherical or cylindrical bearing face, such as washers with an adapted shape, for creating the interface on the outer side. 
     From the production point of view, the heel  27  is molded at high pressure onto the portion  21  of the fitting  2 , after the latter has been produced. Thus, the fitting  2  maintains the same architecture, the heel  27  forming an interface. 
     Such a fitting  2  provided with a heel  27  has been tested under the same conditions as the fittings  1  and  2  without a heel. The tensile tests provided the same results as those performed on a fitting  2  without a heel. The results of the crushing tests are given in the graphic of  FIG. 12 . 
     The first cracks are perceived at about 33000 N at the fifth test, while breaking occurs at 35000 N. The following table summarizes the results obtained: 
     
       
         
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
               
               
                   
                   
                   
                 Fitting 2  
                   
               
               
                   
                   
                 Fitting 1 
                 with heel 
                 U 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 MASS 
                 22 
                 21  
                 g 
               
               
                   
                 Tensile strength 
                 10500 
                 19900 
                 N 
               
               
                   
                 Crushing strength 
                 13500 
                 33500 
                 N 
               
               
                   
               
             
          
         
       
     
     One can thus observe the superiority of the performances of fitting  2  with a heel  27  according to the invention, though it has, in this case, a smaller mass than the tested fitting  1 . 
     When referring now to  FIGS. 13 and 14 , one can see a mold  3  permitting to produce by molding a part according to the method for producing an inventive fitting  2 . 
     The mold  3  includes, on the one hand, a portion  30  in which is provided for a hollow cavity  31  corresponding to the outer shape of the part to be molded and, on the other hand, a unit  32  of independent parts  33 , movable with respect to each other, designed capable of sliding against each other through oblique surfaces  34 , and which are assembled in a determined position permitting the unit  32  to reproduce the exact inner shape of the part to be molded, while some of these parts  33 , which have a wedge shape, can, through the oblique surfaces, be pushed towards the interior of the unit  32 , so as to permit a contraction of the unit  32 . 
     It is obvious that during its use, the hollow cavity  31  is provided with a layer of pre-impregnated fibers in the form of fabrics or mats, then the unit  32 , in contracted form, is inserted into the hollow cavity  31 , finally the wedge-shaped elements  33  are pushed back towards the outside by means of a cam  35  so that the unit  32  adopts its expanded shape and thus presses the layer  5  of composite material. 
     It should be noted that this molding method and the mold permitting its implementation are not exclusively aimed at producing a fitting  2 , but can perfectly be applied to the production of other objects.