Abstract:
A fastener is configured to assemble parts of composite materials. The fastener includes a head; a sleeve including a first section including a first inner diameter, and a second section including a second inner diameter, the second inner diameter being less than the first inner diameter, the second section being between the first section and the head. The fastener also includes an insert inside the sleeve.

Description:
FIELD OF APPLICATION OF THE INVENTION 
       [0001]    The present invention relates to the field of rivets and in particular to adaptations enabling use thereof for fixing composite materials. 
       DESCRIPTION OF THE PRIOR ART 
       [0002]    Fixing composite materials by means of rivets has various constraints, including:
       good fatigue strength of the assemblies must be guaranteed,   damage to the composite material when the rivet is fitted must be avoided,   the phenomenon of delamination must be avoided,   shear strength must be optimised,   tear resistance under traction must be optimised,   fitting must not require countersinking at the head,   fitting corresponding to that of current solid rivets (by crushing) must be able to be carried out in order to use conventional riveting machines,   the cost must be improved.       
 
         [0011]    Solid rivets, although inexpensive, are not suitable for fixing parts made from composite materials. This is because, when it is crushed, the material of the rivet bears on the corner or rim of the hole in order to form the bulb (also referred to as the head). This abutment is particularly high in terms of force and the consequence thereof is that the phenomenon of delamination occurs because of the high level of radial stresses located in the rim of the hole. 
         [0012]    Semi-tubular rivets offer a bulb creation requiring less force to form the head than for a solid rivet but do not offer a fatigue strength equivalent to that of a solid rivet. 
         [0013]    Finally, blind structure fixing rivets providing crimping make it possible to achieve the majority of the objectives sought but at a particularly high cost both in terms of manufacture and installation tooling. 
       DESCRIPTION OF THE INVENTION 
       [0014]    Starting from the specification pre-established by the constraints defined for fixing in composite materials, the applicant carried out research that led to the design of an assembly method for composite materials and a particularly advantageous riveting member for implementation thereof. 
         [0015]    According to the invention, the method of assembling parts made from composite materials uses a riveting member of the type comprising firstly an insert and secondly a sleeve adapted to at least partially contain the insert and having an end provided with a head and a tubular end able to be deformed with a view to constituting a bulb on one side of the materials to be assembled,
       a hole passing through the materials to be assembled being produced,   the sleeve being introduced and held in the hole with its head in abutment on the rims of the end of the hole and so that its tubular end projects therefrom on the other side. The method is remarkable in that it consists of:   using a sleeve the hollow core of which has two different sections, a first section starting from the tubular end to be deformed having a first diameter and a second section starting at the end of the first section and with a lesser diameter,   using a insert not having a functional axial bearing surface for purposes of radial swelling of the sleeve in a hole but the diameter of which is able to allow housing thereof without deformation in the first section of the hollow core and able to allow forcible housing thereof in the second section,   axially introducing the insert in the sleeve so that the latter swells radially inside the hole at its small section and the recess defined by this small section is occupied by said insert,   providing, by means of a riveting die, a pressure at the end of the sleeve to be deformed on its first section in order to ensure folding thereof by centrifugal radial extension.       
 
         [0022]    This feature is particularly advantageous in that it combines the advantages of solid rivets with semi-tubular rivets without increasing the cost thereof. 
         [0023]    Thus the swelling of the sleeve within the hole and filling thereof by the insert will guarantee fatigue strength as well as good shear strength. In addition, the folding of the tubular end of the sleeve in order to form the bulb will enable said bulb to be created without great force. In addition, given that the folding will start along the length of the inserts simultaneously, just before or just after the swelling has commenced, that is to say when a part of the sleeve comes to be locked in the hole, the axial force imparted will necessarily tend to fold the material of the sleeve part situated outside, that is to say not gripped inside the hole. Thus the edge on the rivet head side of the hole passing through the materials to be assembled is protected from any damage. Thus one of the features of the assembly method of the invention is that it consists of producing a hole without countersinking in the composite material on the rivet head side. The time taken and the tooling required for such an operation are thus no longer necessary. 
         [0024]    Another feature participating in the protection of the rivet head stems from the fact that the insert has no axial surface with a function of deforming the sleeve which, in its axial movement inside the sleeve, makes it possible to have only radial deformations appear. The insert will not pack the material of the sleeve in the rim of the rivet head. On the contrary, the presence of the insert will serve as a guide to the deformation of the external part of the sleeve so that folding thereof takes place uniformly. The production of a bulb under satisfactory conditions makes it possible to obtain a fixing having good tear strength. In addition, the configuration of such a riveting member makes it possible to use the tooling conventionally used for fitting a solid rivet. 
         [0025]    According to another particularly advantageous feature, the method consists of pre-engaging the insert in the first section of the tubular end of the sleeve prior to the engagement of the riveting member in the hole. This feature avoids managing the handling of two parts and makes it possible to use the riveting member of the invention as a solid rivet. 
         [0026]    The partial or total swelling of the sleeve part placed inside the hole provides a first gripping of the sleeve body inside the hole. Nevertheless, in order to optimise fixing, another feature of the method consists of continuing the folding until the folded end is crimped on the insert, which helps to create a structural fixing with optimised tear strength. 
         [0027]    According to another particularly advantageous feature, the assembly method of the invention consists of using a sleeve the recess of which passes axially right through and inserting the insert through the end of the emerging recess of the head. 
         [0028]    According to another particularly advantageous feature of the invention making it possible to optimise the locking of the fixing, the assembly method of the invention consists of using a sleeve the recess of which passes right through it and inserting the insert through the tubular end of the sleeve, the insert comprising dimensions such that its two ends are respectively crimped in the head of the sleeve on the one hand and in the bulb formed by the tubular end of the sleeve on the other hand. 
         [0029]    The invention also concerns the riveting member for implementing the assembly method described above. 
         [0030]    This riveting member is remarkable in particular in that the recess formed in the tubular part of the sleeve is extended below the head. In this configuration, the sleeve has two ends: a closed end equipped with a head and the other end being tubular and emerging, the insertion then taking place through said distal end. 
         [0031]    This feature makes it possible to have available the greatest possible length of a sleeve part able to swell in the hole so as to produce a swelling and stressing of the walls of the hole that is as even as possible. According to another feature, the length of the small section corresponds to the minimum thickness of the elements made from composite materials to be fixed. 
         [0032]    According to another feature, the recess provided in the hole is extended in the head so that the end of the insert can be crimped in said head in order to optimise locking. According to a preferred embodiment, the cross section of the recess formed in the head is less than the cross section with the smallest diameter of the recess formed in the sleeve. 
         [0033]    According to another feature, the end of the insert on which the end of the folded sleeve is crimped is preformed with a recess that will facilitate its deformation while requiring less force and allowing deformation of the material without packing thereof on the edges of the hole. This recess may also be produced on the other end of the insert, which may then have a symmetrical configuration. 
         [0034]    Likewise, the crimping can be improved by the external arrangement of grooves or flutes on the body of the insert. 
         [0035]    Likewise, where one of the ends of the insert is crimped in the head, said end has the form of a cylindrical projection coaxial with the rest of the insert and the free end of which is itself provided with a recess facilitating deformation thereof. 
         [0036]    The fundamental concepts of the invention having been disclosed above in their most elementary form, other details and features will emerge more clearly from a reading of the following description and with regard to the accompanying drawings, giving, by way non-limitative example, several embodiments of an assembly method and a riveting member according to the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0037]      FIG. 1  is a schematic drawing of a view in cross section of the separate sleeve and insert making up a first embodiment of a riveting member according to the invention, 
           [0038]      FIG. 2  is a schematic drawing with an external view of the sleeve and insert assembled with the concealed edges visible, 
           [0039]      FIG. 3  is a schematic drawing of an external view of another embodiment of the riveting member, 
           [0040]      FIG. 4  is a schematic drawing of an external view of another embodiment of the riveting member, 
           [0041]      FIGS. 5 ,  6 ,  7 ,  8  and  9  are views in section of an assembly illustrating the fitting of the riveting member, 
           [0042]      FIGS. 10 ,  11 ,  12 ,  13  and  14  illustrate various embodiments of the insert for the aforementioned embodiments of the riveting member. 
           [0043]      FIGS. 15 and 16  illustrate, in a configuration ready to be fitted and in a configuration once fitted, another embodiment of a riveting member according to the invention. 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0044]    As illustrated in the drawing in  FIG. 1 , the riveting member referenced R overall comprises two parts:
       an insert  100 ,   and a sleeve  200  adapted to at least partially contain the insert and having an end provided with a head  210  and a tubular end  220  able to be deformed with a view to constituting a bulb on one side of the materials to be assembled.       
 
         [0047]    In accordance with the invention, the hollow core  230  has two different sections  231  and  232 , that is to say volumes of the cylindrical recessing having different diameters, a first section  231  starting from the tubular end  220  to be deformed having a first diameter D 1  and a second section  232  starting at the end of the first section  231  and with a lesser diameter D 2 . 
         [0048]    These recesses with different diameters match the insert  100  which, not having a functional axial bearing surface, has a diameter D 3  enabling it to be housed without deformation in the first section  231  of the hollow core  230  and to enable it to be housed forcibly in the second section  232  for purposes of radial swelling of the sleeve  100 . 
         [0049]    Thus the largest diameter D 3  of the insert  100  is less than or slightly greater than the diameter D 1  of the first section in order to enable it to be received without force and without deformation and is larger than the diameter D 2  of the second section in order to cause the deformation of this sleeve part  200 , which will be situated inside the hole passing through the parts to be assembled. As illustrated, the second hollowed out section with smaller diameter extends to below the head of the sleeve. 
         [0050]    The riveting member is as illustrated by  FIGS. 2 ,  3  and  4 , with the insert  100  pre-engaged in the first part of the tubular core so that it can be managed as a solid rivet. This pre-engagement is maintained by a light tight mounting between the insert  100  and the first section  231 , as illustrated in  FIGS. 2 and 3 , or by a deformation of the sleeve at three points  240  disposed at  120  degrees for purposes of clamping of the insert  100 . As illustrated, the insert  100  projects out of the sleeve  200  in the pre-engaged position. 
         [0051]      FIG. 3  illustrates more specifically a riveting member R′ where the thickness of the sleeve part to be folded  220  is reduced also externally so that the force necessary for deformation thereof is reduced and the external shoulder defined by the separation between the two external cylinders facilitates and delimits the folding necessary for creating the bulb. 
         [0052]    The materials used for producing the insert and/or the sleeve can be chosen from those known by the following designations:
       titanium T40,   niobium-titanium,   stainless steel A286,   stainless steel 304L,   aluminium and alloys thereof,   etc.       
 
         [0059]    According to an embodiment preferred for reasons of saving weight, low cost and simplicity of implementation, the insert is made from plastics material. This plastic insert can cooperate with a sleeve made from titanium T40. 
         [0060]    According to another embodiment preferred for reasons of improved shear strength and capacity for elongation, the insert is made from grade 9 titanium. 
         [0061]    The various steps of the assembly implemented by such a riveting member R will now be described with regard to the drawings in  FIGS. 5 to 9 . 
         [0062]    As illustrated on the drawing in  FIG. 5 , the riveting member R is disposed inside a hole T passing through two parts made from composite materials P 1  and P 2  to be assembled. The head  210  of the sleeve  200  comes into abutment on the external surface of P 1  around the hole T. The diameter of the hole T is such that the body of the sleeve enters inside with clearance. In addition, the “foldable” portion of the sleeve projects out of the hole T on the same side as the part P 2 . 
         [0063]    The sleeve head  210  is held in position by means of a fixed riveting die  300  and another movable riveting die  400  is disposed on the rivet head side and comes into abutment against the end of the insert  100  projecting out of the sleeve  200 . In a movement represented by the arrow F 1 , the movable riveting die  400  exerts an axial pressure against the riveting member R for the purpose of inserting the insert  100 , expanding the sleeve body  200  disposed in the hole, folding the sleeve body  200  disposed outside the hole T and crimping the sleeve body  200  on the body of the insert  100 . In accordance with the invention, the length of the small section  232  corresponds substantially to the minimum thickness of the parts P 1  and P 2 . 
         [0064]    As illustrated in  FIG. 6 , under the effect of the movement of the movable riveting die  400 , the insert  100  starts its forcible insertion in the sleeve body part situated in the hole T. In accordance with the invention, the effect of this insertion is a radial swelling of the sleeve, in the direction of the arrows F 2 , which tends to press the sleeve on the walls of the hole T and ensure the filling in of the clearance existing initially between the external periphery of the sleeve  200  and the internal surface of the hole T. 
         [0065]    As illustrated in  FIG. 7 , the advancement of the insert  100  inside the sleeve  200  affords direct contact between the end  220  of the sleeve  200  and the movable riveting die  400 . Thus, as the internal part of the sleeve swells, the external part of the sleeve is subjected to the pressure of the riveting die  400 , which causes the start of the centrifugal folding by radial expansion in the direction of the arrows F 3  of the external sleeve part  200 . The prior swelling of the sleeve part  200  situated inside the hole T blocks any possibility of axial movement of the material of the sleeve  200  inside the hole T, which creates an abutment that will cause the folding of the external part and which prevents damage to the rim of the hole T. 
         [0066]    As illustrated on the drawing in  FIG. 8 , while effecting, through its adapted dimensions, the swelling of the part of the sleeve  200  situated inside in the hole T, the insert  100  bears at the tubular portion bottom and occupies the whole of the internal recess of this sleeve part  200 , thus changing the riveting member R to a configuration of the solid rivet type. By virtue of this configuration, almost all the external surface of the sleeve part situated inside the hole T has undergone a swelling, the elastic return of which will be negligible, which maintains radial stresses inside the hole T. In addition, the external end of the sleeve  200  that undergoes the folding is guided during this operation by the body of the insert, guaranteeing regularity in deformation. 
         [0067]    As illustrated on the drawing in  FIG. 9 , the continuation of the axial movement of the riveting die  400  in the direction of the arrow F 1  ends the folding of the sleeve  200  for the creation of a bulb bearing on the piece P 2  around the hole T. In addition, the insert  100  will deform and the end of the bulb will be crimped on the body of the insert  100  for the purpose of guaranteeing locking. 
         [0068]    In order to facilitate this final deformation as well as the crimping, several embodiments of insert  100  have been imagined. Thus, for example,  FIG. 10  shows an insert  100  generally cylindrical in shape, the two ends  110  and  120  of which are bevelled externally and the end  120  of which, corresponding to the end on which the sleeve  200  is crimped, comprises a recess  121  facilitating deformation thereof. 
         [0069]      FIG. 11  shows an embodiment of an insert  100 , the body of which is preformed with a groove  130  situated close to the end  120  and the two ends of which are provided with a recess. 
         [0070]      FIG. 12  shows an insert the body of which is provided over almost all its periphery with a narrowing of its diameter. 
         [0071]      FIG. 13  shows an insert  100  the body of which is provided with flutes that will facilitate crimping. 
         [0072]    The embodiments illustrated by the drawings in  FIGS. 1 ,  11 ,  12  and  13  show a recess provided at the two ends of the insert. 
         [0073]    Finally,  FIG. 14  illustrates a recess  121  allowing deformation of the end  120  of the insert with less force. 
         [0074]    As illustrated in the drawings in  FIGS. 15 and 16 , the riveting member R 3  is equipped with a sleeve  200 , the recess  230  of which passes right through it. The adapted insert  100  comprises dimensions such that its two ends are respectively crimped in the head of the sleeve  210  on the one hand and in a bulb formed by the tubular end  200  of the sleeve once folded on the other hand. 
         [0075]    As illustrated, the recess  230  provided in the sleeve  200  is extended in the head  210  so that the suitably shaped end  140  of the insert  100  can be crimped in said head  210  in order to optimise locking. Insertion is achieved by the emerging tubular end not equipped with the head. According to the embodiment illustrated, the cross section of the recess  211  formed in the head  210  is less than the cross section  232  of smaller diameter D 2  of the recess  230  formed in the sleeve. 
         [0076]    The end  140  of the insert that has just been crimped in the head by the translation movement represented by the arrow F 1  is in the form of a cylindrical projection coaxial with the rest of the insert, and the free end of which is itself provided with a recess facilitating deformation thereof. To accommodate it, the recess  211  formed in the head splays in the direction of the progression of the insert in the sleeve in order to accept the volume of the deformed material of the head  140  of the insert  100  and thus optimise locking. 
         [0077]    It will be understood that the riveting methods and members that have just been described and depicted above were so described and depicted with a view to a disclosure rather than a limitation. Naturally various arrangements, modifications and improvements could be made to the above example without for all that departing from the scope of the invention. 
         [0078]    Thus for example, although the embodiment presented illustrates a rivet provided with a protruding head, the riveting member may be of the type comprising a sleeve with a countersunk head.