Abstract:
A method for fabricating a repair laminate for a composite part having an exposed surface includes applying a bonding material to the exposed surface and forming an uncured ply stack assembly on the bonding material. The uncured ply stack assembly is formed by forming and compacting a series of uncured ply stacks. The ply stack assembly and bonding material are then cured.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to methods of fabricating laminates made from polymeric-matrix composite materials. 
         [0003]    2. Description of Related Art 
         [0004]    Parts made from polymeric-matrix composite materials form many components in modern automotive, aeronautical, and marine vehicles, as well as components in many other types of equipment and structures. Such parts may, from time to time, become damaged, thus requiring repair or replacement. It is often required or at least more cost effective to repair a damaged part than to replace the part. Conventional methods of repairing polymeric-matrix composite parts require the use of specialized tooling and double vacuum tool/processes, which require multiple staging operations and cure cycles, or specialized layup tools and autoclave processing, which is expensive and often impractical when used to facilitate a repair. 
         [0005]    There are many ways to repair damaged polymeric-matrix composite parts that are well known in the art; however, considerable shortcomings remain. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0006]    The novel features believed characteristic of the invention are set forth in the description. However, the invention itself, as well as, a preferred mode of use, and further objectives and advantages thereof, will best be understood by reference to the following detailed description when read in conjunction with the accompanying drawings, in which the leftmost significant digit(s) in the reference numerals denote(s) the first figure in which the respective reference numerals appear, wherein: 
           [0007]      FIG. 1  is an elevated side view of uncured plies applied to an in-situ composite part according to the method of the present application. 
           [0008]      FIG. 2  is an elevated side view of a sealing bag enclosing a ply stack on the in-situ composite part according to the method of the present application. 
           [0009]      FIG. 3  is an elevated side view of multiple ply stacks on the in-situ composite part according to the method of the present application. 
           [0010]      FIG. 4  is an elevated side view of a sealing bag enclosing multiple ply stacks on the in-situ composite part according to the method of the present application. 
           [0011]      FIG. 5  is an elevated side view of a cured composite layer on the in-situ composite part according to the method of the present application. 
           [0012]      FIG. 6  is an elevated side view of an alternative embodiment of the in-situ composite part according to the method of the present application. 
       
    
    
       [0013]    While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as described herein. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0014]    Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developer&#39;s specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. 
         [0015]    The present invention represents a method for in-situ, multi-stage debulking, compaction, and single stage curing of thick composite repair laminates made from one or more polymeric-matrix composite materials. In one embodiment, the method is applied to the repair of an existing composite part. The method provides a composite part meeting the same laminate quality requirements as a thick laminate made using highly-pressurized autoclave processing. For the purposes of this disclosure, the term “thick laminate” means a laminate made from more than about 10 plies of polymeric-matrix composite material. 
         [0016]    Referring to  FIG. 1  in the drawings, a pre-existing composite part  101  is shown. It should be noted that composite part  101  may be planar or non-planar in form. An adhesive layer  103  is applied to composite part  101  and a first plurality of plies  105  (only one labeled in  FIG. 1  for clarity) of uncured, polymeric-matrix composite material is applied to adhesive layer  103 . Adhesive layer  103  is preferably a film adhesive. In a preferred embodiment, the number of plies  105  making up the first plurality of plies  105  is no more than about ten plies. The first plurality of plies  105  makes up a first ply stack  107 . Plies  105  may comprise “wet layup” plies or pre-impregnated, i.e., “pre-preg” plies. 
         [0017]    Referring now to  FIG. 2 , bleeder material and a bag  201  is applied over first ply stack  107  and adhesive layer  103  in a conventional manner. Bag  201  is attached to a surface  203  of composite part  101  to create a substantially airtight seal between surface  203  and bag  201 . A vacuum port  205  extends through bag  201  to allow gases to be withdrawn from bag  201  within the substantially airtight seal between bag  201  and surface  203 . A vacuum source is attached to vacuum port  205 , which evacuates gases, as represented by arrow  207 , from within the sealed volume of bag  201 . In a preferred embodiment, vacuum at a level of two to three inches of mercury is applied to the sealed volume of bag  201 . In addition to applying vacuum, a heat source  209  heats at least first ply stack  107  to a desired debulking and compaction temperature. In a preferred embodiment, sufficient heat is applied to first ply stack  107  by heat source  209  to raise the temperature of first ply stack  107  to a temperature of about 125 degrees Fahrenheit. First ply stack  107  is maintained at the desired temperature, e.g., about 125 degrees Fahrenheit, under vacuum, e.g., about one to two inches of mercury, for a time period sufficient to debulk and partially compact first ply stack  107 . In a preferred embodiment, first ply stack  107  is maintained at the desired temperature and under vacuum for about one hour. Subsequently, first ply stack  107  is preferably maintained at the desired temperature under full vacuum, e.g., about 28 inches of mercury, for a period of time of about 30 minutes to further compact first ply stack  107 . After the desired period of debulking and compaction time, bag  201 , the breather material, and any other ancillary processing materials are removed from first ply stack  107  and composite part  101 . First ply stack  107  is now debulked and compacted. 
         [0018]    It should be noted that the debulking and compaction temperature is a temperature below a curing temperature of the polymer-matrix composite material and below a curing temperature of adhesive layer  103 . 
         [0019]    Referring now to  FIG. 3 , a plurality of ply stacks, such as first ply stack  107 , a second ply stack  301 , and a third ply stack  303 , are combined to form a ply stack assembly  305 . Ply stack assembly  305  may comprise any suitable, desired number of ply stacks, such as ply stacks  107 ,  301 , and  303 . In the illustrated embodiment, second ply stack  301  is formed by applying a plurality of plies, preferably no more than about ten plies, to first ply stack  107 . A bag, such as bag  201 , is then applied to first ply stack  107  and second ply stack  301 . Vacuum and heat are then applied to bagged first ply stack  107  and second ply stack  301  according to the method described herein concerning  FIG. 2 . Third ply stack  303 , as well as any desired ply stacks in addition to third ply stack  303 , are formed by the same method as second ply stack  301 . 
         [0020]    Once the total number of desired ply stacks have been debulked and compacted, e.g., third ply stack  301  in the illustrated embodiment, the bleeder material and a bag  401  remains covering ply stack assembly  305 , as depicted in  FIG. 4 , for curing of ply stack assembly  305 . A vacuum source is attached to vacuum port  403 , which evacuates gases, as represented by arrow  405 , from within the sealed volume of bag  401 . In a preferred embodiment, full vacuum, e.g., about 28 inches of mercury, is applied to the sealed volume of bag  401 . In addition to applying vacuum, a heat source  407  heats at least ply stack assembly  305  to a desired curing temperature, which is dependent upon the particular composite material being used. In one embodiment, sufficient heat is applied to ply stack assembly  305  by heat source  407  to raise the temperature of ply stack assembly  305  to a temperature of about 250 degrees Fahrenheit. Ply stack assembly  305  is maintained at the desired temperature under full vacuum for a time period sufficient to sufficiently cure ply stack assembly  305  and adhesive layer  103  to form composite laminate  501 , shown in  FIG. 5 . In a preferred embodiment, ply stack assembly  305  is maintained at the desired temperature and under vacuum for about two hours. After the desired curing time, bag  401 , the breather material, and any other ancillary processing materials are removed from composite laminate  501 , as depicted in  FIG. 5 . The cured ply stack assembly  305  and the previous composite part  101  now form parts of composite laminate  501 , as the cured ply stack assembly  305  is adhesively bonded to the pre-existing form of composite part  101 . 
         [0021]    It should also be noted that a damaged composite part  601 , shown in  FIG. 6 , may be machined or scarfed to define a recess  603  into which a ply stack assembly  605  is received, cured, and adhesively bonded to composite part  601  to form composite laminate  607 . 
         [0022]    The particular embodiments disclosed above are illustrative only, as the invention may be modified and practiced in different but equivalent manners apparent to those skilled in the art having the benefit of the teachings herein. It is therefore evident that the particular embodiments disclosed above may be altered or modified and all such variations are considered within the scope and spirit of the invention. Accordingly, the protection sought herein is as set forth in the description. It is apparent that an invention with significant advantages has been described and illustrated. Although the present invention is shown in a limited number of forms, it is not limited to just these forms, but is amenable to various changes and modifications without departing from the spirit thereof.