Abstract:
A doubler assembly repairs at least one damaged aperture of a composite flange. The doubler assembly includes an insert, an adhesive, and a support. The insert is positioned in the damaged aperture to provide compressive load transfer through the composite flange. The adhesive is positioned directly on at least a portion of the composite flange proximate the damaged aperture. The support is positioned over the adhesive.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention generally relates to the field of repairing composite structures. In particular, the invention relates to doubler repair assemblies for composite arcuate flanges.  
         [0002]     Composite structures that are formed of a thermoplastic material such as polyamideimide or polyetherimide are resistant to high temperatures and engine fluids. Thus, these composite structures can be exposed to extreme environments, such as hot engine oils in aircraft engines, which typically cause degradation of mechanical properties of most other elastomeric materials. However, while the composite structure may be temperature resistant, the composite structure and its parts are subjected to thermal stresses when rigidly attached to metal structures with significantly different coefficients of thermal expansion, causing cracks in the weaker composite structure. For example, arcuate flanges formed of composite materials can easily form cracks radiating from apertures in the flanges where the bolts are positioned. If left unattended, the thermal stresses of the environment may cause the crack to continue to extend to the edge of the flange and cause the entire flange to break.  
         [0003]     Traditional repair techniques are limited to flange reconstruction techniques using fiberglass/epoxy laminates or either solvent or thermal welded replacement sections. Most of these current repair techniques result in a repair assembly that has inferior mechanical properties when compared to the original structure and also do not account for thermal disparity between parts. One method of repairing the damaged composite structure is to replace the entire structure. However, this can be a costly process, particularly if only a single aperture or only a small percentage of the composite structure is damaged. Another option is to restore only a piece or segment of the flange to a workable condition using a splint or doubler assembly that is applied to the damaged portion of the structure. Additional methods of repairing a damaged composite structure are described in U.S. Pat. No. 5,876,651 and U.S. Pat. No. 5,965,240, issued to Blackburn et al.  
       BRIEF SUMMARY OF THE INVENTION  
       [0004]     A doubler assembly repairs at least one damaged aperture of a composite flange. The doubler assembly includes an insert, an adhesive, and a support. The insert is positioned in the damaged aperture to provide compressive load transfer through the composite flange. The adhesive is positioned directly on at least a portion of the composite flange proximate the damaged aperture. The support is positioned over the adhesive. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0005]      FIG. 1  is a perspective view of an arcuate flange having apertures.  
         [0006]      FIG. 2  is a top view of the arcuate flange having damaged ends.  
         [0007]      FIG. 3  is a top view of the arcuate flange having a three-hole doubler in two different locations.  
         [0008]      FIG. 4  is a top view of the arcuate flange having a four-hole doubler in three different locations.  
         [0009]      FIG. 5A  is a partial side view of a damaged arcuate flange.  
         [0010]      FIG. 5B  is a partial top view of the damaged arcuate flange of  FIG. 5A .  
         [0011]      FIG. 6A  is a partial side view of a repaired arcuate flange having a doubler.  
         [0012]      FIG. 6B  is a partial top view of the repaired arcuate flange of  FIG. 6A  having a doubler assembly.  
         [0013]      FIG. 7  is a block diagram of a method of installing the doubler to the arcuate flange. 
     
    
     DETAILED DESCRIPTION  
       [0014]      FIG. 1  shows a perspective view of composite seal  10  with arcuate flange  12 . Composite seal  10  is formed of a thermoplastic material and is typically exposed to extreme environments such as high-temperature jet engine oils. Arcuate flange  12  extends from composite seal  10  and has a plurality of apertures  14  along its perimeter. Bushings  16  and bolts  18  (shown in  FIG. 5A ) are positioned within apertures  14  of arcuate flange  12  and are used to connect composite seal  10  to a structure, such as a gearbox housing. Due to the extreme environment in which composite seal  10  is typically located, thermal stress resulting from coefficient of thermal expansion mismatches is constantly exerted on composite seal  10 , and particularly on apertures  14  of arcuate flange  12 . Thus, the area proximate apertures  14  can crack, with the crack typically radiating outward on arcuate flange  12  to the perimeter of composite seal  10 .  
         [0015]      FIG. 2  shows a top view of arcuate flange  12  having a damaged aperture  14   a  with crack  15  at wing end  20  and a damaged aperture  14   a  with crack  15  at non-wing end  22 . Arcuate flange  12  could be repaired by conventional methods by trimming the cantilevered area, or the area proximate the damaged apertures  14   a  to remove damaged wing end  20  and damaged non-wing end  22  from arcuate flange  12 , leaving only the undamaged apertures  14  on arcuate flange  12 . Alternatively, the systems and methods of this invention can be used to repair such damage.  
         [0016]      FIG. 3  shows a top view of arcuate flange  12  having doubler  24 , and specifically, two different three-hole doublers  24   a  and  24   b.  The following general discussion involving doubler  24  refers to all doublers subsequently disclosed. Doubler  24  is preferably fabricated having holes  26  with a diameter similar to apertures  14  of arcuate flange  12  to overlap damaged aperture  14   a  as well as undamaged apertures  14  proximate damaged apertures  14   a.  Doubler  24  is preferably formed of a material that is stronger than the material of composite arcuate flange  12  and that has a coefficient of thermal expansion similar to the coefficient of thermal expansion of the material that arcuate flange  12  is rigidly attached to. That allows the damaged area of arcuate flange  12  to be strengthened by doubler  24 , which is designed to act as a repair of an existing part. Cracks  15  radiating from damaged aperture  14   a  can be bridged using doubler  24 , which is operatively connected (i.e. bonded) to arcuate flange  12 . While those skilled in the art will understand that doubler  24  can be made of any suitable material, in one embodiment, doubler  24  is made of stainless steel.  
         [0017]     First and second three-hole doublers  24   a  and  24   b  as shown in  FIG. 3 , represent two exemplary uses of three-hole doubler  24 . In these particular embodiments, only one aperture  14   a  covered by each three-hole doubler  24   a  or  24   b  is damaged, while the remaining two apertures  14  covered by each three-hole doubler  24   a  or  24   b  are undamaged. In first doubler  24   a,  damaged aperture  14   a  is at non-wing end  22  of arcuate flange  12 . First doubler  24   a  is thus positioned on arcuate flange  12  such that an end hole  26   a  of first doubler  24   a  is positioned over damaged aperture  14   a,  while the remaining two holes  26   b  and  26   c  of three-hole doubler  24   a  are positioned over undamaged apertures  14 .  
         [0018]     Second doubler  24   b  is positioned on arcuate flange  12  such that center hole  26   b  of second doubler  24   b  is positioned over damaged aperture  14   a,  while the remaining two holes  26   a  and  26   c  of three-hole doubler  24   b  are positioned over undamaged holes  14 . In some embodiments, it may be desirable to have no more than six of the fifteen apertures  14  of arcuate flange  12  covered by doublers  24 , with no more than two damaged apertures  14   a  having cracks  15  radiating therefrom. As shown in  FIG. 3 , three-hole doublers  24   a  and  24   b  may be most effective if only one of the three apertures that three-hole doublers  24   a  and  24   b  cover is damaged, but other embodiments are also possible.  
         [0019]     Three different exemplary uses of four-hole doublers are shown in  FIG. 4 . Four-hole doublers  24   c - 24   e  function in the same manner as three-hole doublers  24   a  and  24   b,  except that four-hole doublers  24   c - 24   e  are designed with four-holes, rather than just three. In four-hole doubler  24   c,  damaged aperture  14   a  is on non-wing end  22  of arcuate flange  12 . Four-hole doubler  24   c  is thus positioned on arcuate flange  12  such that an end hole  26   a  of third doubler  24   c  is positioned over damaged aperture  14   a,  while the remaining three holes  26   b - 26   d  of four-hole doubler  24   c  are positioned over undamaged apertures  14 . In some embodiments, the last hole  26   d  of four-hole doubler  24   c  will cover an undamaged aperture  14 , and at least one of the middle holes  26   b  and  26   c  will also cover an undamaged aperture  14 .  
         [0020]     Four-hole doubler  24   d  is shown being used to repair two adjacent damaged apertures  14   a.  To repair arcuate flange  12 , four-hole doubler  24   d  may be positioned on arcuate flange  12  such that center holes  26   b  and  26   c  of four-hole doubler  24   d  are positioned over damaged apertures  14   a,  while end holes  26   a  and  26   d  are positioned over undamaged apertures  14  on either side of damaged apertures  14   a.    
         [0021]     Four-hole doubler  24   e  is shown being used to repair two other adjacent damaged apertures  14   a  on wing end  20  of arcuate flange  12 . Four-hole doubler  24   e  is positioned on arcuate flange  12  such that end hole  26   d  and center hole  26   c  of four-hole doubler  24   e  are positioned over damaged apertures  14   a,  while end hole  26   a  and center hole  26   b  are positioned over undamaged apertures  14 . In some embodiments, it may be desirable to have no more than eight out of fifteen apertures  14  covered by doublers  24  with no more than four damaged apertures  14   a  having cracks  15  radiating therefrom. As shown in  FIG. 4 , four-hole doublers  24   c - 24   e  may be most effective if only two of the four apertures that four-hole doublers  24   c - 24   e  cover are damaged, but other embodiments are also possible.  
         [0022]      FIGS. 5A and 5B  show a partial side view and a partial top view, respectively, of arcuate flange  12  with two undamaged apertures  14  and a damaged aperture  14   a.  In operation, a bushing  16  and a bolt  18  are positioned in each aperture  14  of arcuate flange  12 . Bushing  16  provides a compressive load path for bolt  18  through arcuate flange  12 . When exposed to high thermal stress, apertures  14  may exhibit damage in the form of cracking. Damaged aperture  14   a  can be distinguished by crack  15  radiating from damaged aperture  14   a  to the perimeter of arcuate flange  12 . When arcuate flange  12  has a damaged aperture  14   a,  doubler  24  (shown in  FIGS. 6A and 6B ) may be used to repair arcuate flange  12 .  
         [0023]      FIGS. 6A and 6B  show a partial side view and a partial top view, respectively, of arcuate flange  12  with doubler  24  installed. Doubler  24  is used to transfer the load across the damaged area of arcuate flange  12  and to provide compressive load distribution at apertures  14 . A thin sheet, or thick film adhesive  28  may be positioned on top of the surface of arcuate flange  12  to act as an expansion joint between arcuate flange  12  and doubler  24 . Before adhesive  28  is positioned on arcuate flange  12 , holes  30  may be cut from adhesive  28  to allow inserts  32  to be positioned within apertures  14  and overlap apertures  14 . Adhesive  28  may comprise any suitable material. In some embodiments, adhesive  28  may be a fluoroelastomer film that is stable in high temperature environments, for example, DuPont&#39;s Viton® fluoroelastomer, available from Eagle Elastomer, Cuyahoga Falls, Ohio. In some embodiments, it may be desirable to use a fluoroelastomer for adhesive  28  because of its rubbery and ductile properties, which allow for thermal expansion differences when heated to high temperatures. Additionally, fluoroelastomers may be employed for their fluid resistance, which is necessary in extreme environments, such as near hot aircraft engine oil. Doubler  24  may then be positioned over adhesive  28  and thereby become attached to arcuate flange  12 , bridging the damaged area of arcuate flange  12 .  
         [0024]      FIG. 7  shows an exemplary non-limiting method of installing doubler  24  to an arcuate flange  12  having one or more damaged apertures  14   a.  First, the surface of arcuate flange  12  may be cleaned and the cracked material may be trimmed away, if desired, as represented by Step  100 . Any adhesive in damaged aperture  14   a  around bushing  16  may also be removed. Additionally, any remaining bushings  16  in apertures  14  on either side of damaged aperture  14   a  may also be removed.  
         [0025]     In some embodiments, repair inserts  32  may then be attached to arcuate flange  12  in any suitable manner, such as by being tack welded to doubler  24  or bonded to arcuate flange  12 , as represented by Step  102 . Inserts  32  may comprise any suitable material, such as for example, a metallic material. In some embodiments, inserts  32  can be bonded with a high temperature epoxy to damaged apertures  14   a,  replacing the original bushings  16 . Inserts  32  provide a load transfer path through arcuate flange  12  by extending beyond both faces of arcuate flange  12 . The rigid bond created by inserts  32  may help restore damaged apertures  14   a.  In another embodiment, inserts  32  may be tack welded to metallic doubler  24  for certain locations, such as on wing end  20  or non-wing end  22  where arcuate flange  12  is trimmed away to remove damage, where doubler  24  may be cantilevered over the area that wing end  20  or non-wing end  22  previously occupied to prevent misalignment of arcuate flange  12  during assembly.  
         [0026]     In some embodiments, holes  30  may then be cut from adhesive  28  to match up with apertures  14  of arcuate flange  12 . Doubler  24  is preferably machine-holed with any appropriate number of holes, depending on the needs of the particular arcuate flange  12  (represented by Step  104 ). After lining up holes  30  in adhesive  28  with inserts  32  positioned in apertures  14  and damaged aperture  14   a  of arcuate flange  12 , adhesive  28  may be applied to the surface of arcuate flange  12 , Step  106 . Holes  26  of doubler  24  may then be aligned with apertures  14  and  14   a  and inserts  32 , Step  108 . In some embodiments, it may be preferable to prevent bonding between inserts  32  and doubler  24 . In some embodiments, doubler  24  may be mechanically clamped to arcuate flange  12  while adhesive  28  is curing.  
         [0027]     When adhesive  28  is initially positioned on arcuate flange  12 , adhesive  28  is preferably in a semi-cured state. Adhesive  28  may then be heated to a temperature sufficient to cure adhesive  28  to arcuate flange  12  and doubler  24 , as represented by Step  110 . Adhesive  28  may also be cured at a sufficient pressure to bring adhesive  28  into contact with both arcuate flange  12  and doubler  24 . In some embodiments, adhesive  28  may be heated to a temperature of approximately 320° F. to 360° F. for approximately fifteen minutes to thirty minutes under vacuum or at a pressure of approximately 10 pounds per square inch (psi) to 100 psi. Doubler  24  may then be allowed to cool to approximately 150° F. before removing the clamp. After doubler  24  has cooled down, adhesive  28  may then be post cured, Step  112 . In some embodiments, adhesive  28  may be post cured by being heated to a temperature of approximately 340° F. to 360° F. for approximately two to four hours.  
         [0028]     Any excess adhesive  28  may then be removed from apertures  14  and  14   a  while maintaining adhesive  28  around the perimeter of doubler  24 , as represented by Step  114 . Adhesive is preferably excluded between the contact surfaces of inserts  32  and doubler  24  so that adhesive  29  does not prevent load transfer between doubler  24  and inserts  32 .  
         [0029]     The doubler assembly of the present invention can be used to repair damaged apertures of various composite structures, such as those that are exposed to harsh environments.  
         [0030]     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. For example, while only three or four aperture doublers were described, the doublers of this invention could have any number of apertures therein.