Abstract:
A method uses a three-dimensional, woven preform to assemble two components, the preform having at least a pair of legs extending from a base. The woven preform is infused with a resin, and at least one surface of one of the components is bonded to the legs of the preform using the resin within the preform. The other of the components is then attached to the preform by adhering the component with the resin in the preform. The preform is squeegeed into place, ensuring that air pockets are eliminated and a continuous bond line is created. Resin systems providing for oven or room-temperature curing may be used.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention generally relates to assembly of components using woven preforms and particularly relates to low-cost assembly of components using resin-infused preforms.  
           [0003]    2. Description of the Prior Art  
           [0004]    [0004]FIGS. 1 through 3 show typical structures formed with methods known in the art for connecting two components and using layers of composite fabric. FIG. 1 shows a T-shaped structure  11  formed by attaching planar, metal component  13  to planar, composite component  15 , with components  13 ,  15  being oriented to be perpendicular to each other and component  13  being located within the length of component  15 . Several layers  17  of woven fabric are laid at the intersection of components  13 ,  15 , a portion of a base layer  17  being applied to each of surfaces  19 ,  21  of component  13 , the remaining portion of each base layer  17  being applied to surface  23  of component  15 . Layers  17  may be pre-impregnated with resin, or resin may be applied onto layers  17  after laying them. Additional layers  17  are then applied over the base layers  17 , layers  17  forming L-shaped supports. Layers  17  are cured to form structure  11 , layers  17  typically being cured with heat and under vacuum. Though shown as connecting a metal component  13  to a composite component  15 , layers  17  can be used to connect components  13 ,  15  formed from various materials. Also, one or both of components  13 ,  15  may be formed to have a curved shape.  
           [0005]    In FIG. 2, components  13 ,  15  are attached to be perpendicular to each other, but component  13  is attached at one end of component  15 . Several layers  17  are laid on the inside of the intersection of components  13 ,  15 , with a portion of the base layer  17  being attached to surface  19  of component  13  and the remaining portion being attached to surface  23  of component  15 . Likewise, a base layer  17  is laid on the outside of the intersection, with a portion of the base layer  17  being attached to surface  21  of component  13  and the remaining portion being attached to surface  25  of component  15 . Additional layers  17  are applied over each base layer  17 , and layers  17  are cured to form structure  27 .  
           [0006]    Structure  29 , shown in FIG. 3, is formed by connecting components  13 ,  15  to lie in the same plane. Base layers  17  connect surface  19  of component  13  to surface  23  of component  15  and connect surface  21  of component  13  to surface  25  of component  15 . Additional layers  17  are then laid over base layers  17 , and layers  17  are cured.  
           [0007]    The joints created using the prior art methods have difficulty withstanding out-of-plane loading. Typical remedies for this are thick laminate stack-ups using many layers of-composite fabric and having large flange radii. While this reduces the tensions forces between the layers of the flanged section, the result is a heavy joint, reducing the weight savings realized when using composites. Also, to obtain the greatest performance, these joints are cured using vacuum and heat, increasing the cost of the structures. Therefore, there is a need for a low-cost, simple method for creating high-strength joints which does not require vacuum or heat.  
         SUMMARY OF THE INVENTION  
         [0008]    A method uses a three-dimensional, woven preform to assemble two components, the preform having at least a pair of legs extending from a base. The woven preform is infused with a resin, and at least one surface of one of the components is bonded to the legs of the preform using the resin within the preform. The other of the components is then attached to the preform by adhering the component with the resin in the preform. The preform is squeegeed into place, ensuring that air pockets are eliminated and a continuous bond line is created. Resin systems providing for oven or room-temperature curing may be used.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    The novel features believed to be characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:  
         [0010]    [0010]FIG. 1 is a profile view of a structure formed by connecting two components with composite layers using a prior-art method.  
         [0011]    [0011]FIG. 2 is a profile view of a second structure formed by connecting two components with composite layers using a prior-art method.  
         [0012]    [0012]FIG. 3 is a profile view of a third structure formed by connecting two components with composite layers using a prior-art method.  
         [0013]    [0013]FIG. 4 is a perspective view of a Pi-shaped woven preform for use in the method of the present invention.  
         [0014]    [0014]FIG. 5 is a profile view of a structure formed by connecting two components with a woven preform using the method of the present invention.  
         [0015]    [0015]FIG. 6 is a perspective view of an H-shaped woven preform for use in the method of the present invention.  
         [0016]    [0016]FIG. 7 is a profile view of a second structure formed by connecting two components using the preform of FIG. 6 and the method of the present invention.  
         [0017]    [0017]FIG. 8 is a profile view of a third structure formed by connecting two components using the preform of FIG. 6 and the method of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]    The present invention is directed toward a low-cost, simple method of using multi-layered, three-dimensional (3-D), woven preforms to connect components in a structure. These structures will typically be used in applications in which high strength is required but weight is not as critical, for example, in tooling or in boats. FIGS. 4 and 6 show examples of 3-D preforms, whereas FIGS. 5, 7, and  8  show the application of these preforms.  
         [0019]    Referring to the figures, FIG. 4 shows api-shaped, 3-D, multi-layered, woven preform  31  used to connect two components, which may be formed to be planar or curved and of various materials, such as metal or composites. Preform  31  has a base  33  on its lower portion that has a continuous, flat lower surface  35 . A pair of spaced-apart planar legs  37  extend vertically upward from base  33 , forming a slot  39 . Each leg  37  is at a position that is offset from, but near to, the center of base  33 . Legs  37  are shown as parallel to each other and perpendicular to base  33 , though legs  37  could be at angles to each other and to base  33 . Legs  37  maybe oriented to be farther apart at the tops of legs  37 , forming a “V” shape. Likewise, legs  37  may be oriented so that the bottoms of legs  37  are farther apart than the tops, forming a trapezoidal shape. In the position shown, inner surfaces  41  of legs  37  face each other for receiving a component. Though it is preferable for the outer surface of legs  37  and the upper surface of base  33  to be tapered at their outer ends, the ends may also be squared, as shown.  
         [0020]    Preform  31  may be pre-impregnated with resin prior to assembly or may be dry. In the preferred method, preform  31  is prepregged with a heat-cured resin available from Cytec Industries, Inc., of West Paterson, N.J., under the trademark ONS. This resin system has a high viscosity and provides for a high-tack surface, allowing surfaces  35 ,  41  to stick to surfaces of components during assembly.  
         [0021]    Referring to FIG. 5, structure  43  comprises components  13 , 15  connected in the same orientation as structure  11  (FIG. 1). Surfaces  19 ,  21  of component  13  are bonded to inner surfaces  41  of legs  37 , and lower surface  35  of preform  31  is bonded to upper surface  23  of component  15 . As shown, component  13  is perpendicular to component  15 , though this is not required.  
         [0022]    To form structure  43  using a prepreg preform  31 , component  13  is placed between legs  37 , surfaces  19 ,  21  adhering to surfaces  41 , and surface  35  of base  33  is adhered to upper surface  23  of component  15 . Legs  37  and base  33  are then squeegeed or otherwise pressed against components  13 ,  15  to eliminate air pockets and to form continuous bondlines. The resin is then cured in an oven, bonding components  13 ,  15  to preform  31 .  
         [0023]    During curing of the resin in preform  31 , no vacuum bagging is necessary. Without vacuum bagging, the excess resin in preform  31  is not removed, yet structure  43  has a higher strength per weight than a joint made using the prior-art methods. Also, preform  31  has rough outer surfaces. When used in tooling or similar applications, the weight of the extra resin and the rough exterior do not significantly affect the use of structure  43 . However, the fabrication time and costs are greatly reduced when compared to the prior-art methods.  
         [0024]    To form structure  43  using a dry preform  31 , a two-part resin system that cures at room temperature is preferably used. Resin is applied to the lower, bonding portions of surfaces  19 ,  21  of component  13  and to the bonding portion of upper surface  23  of component  15 . Component  13  is then placed between inner surfaces  41  of legs  37 , and lower surface  35  of preform  31  is placed against upper surface  23  of component  15  in the desired position. Alternatively, preform  31  can be positioned on components  13 ,  15  prior to application of resin, then legs  31  and base  33  can be pulled back to apply resin to surfaces  19 ,  21 ,  23  of components  13 ,  15 . Additional resin is applied to the outer surfaces of preform  31 , wetting the fibers of preform  31  and ensuring a sufficient amount of resin to form a continuous bondline between surfaces  41  and surface  19 ,  21  and between surface  35  and surface  23 . A vacuum assist can optionally be used to ensure complete wet-out. Legs  37  and base  33  are squeegeed onto components  13 ,  15 , respectively, to remove air pockets, then the resin in preform  31  is allowed to cure at room temperature. Though the need for heating is eliminated, heat may optionally be used during curing.  
         [0025]    [0025]FIG. 6 shows an H-shaped, 3-D, woven preform  45  used to connect components as in structure  27  (FIG. 2) and structure  29  (FIG. 3). Preform  45  comprises two sets of spaced-apart legs  47 , legs  47  extending from a central base section  49  to form slots  51 ,  53 . Inner surfaces  55  of legs  47  face each other for receiving a component in slots  51 ,  53 . Legs  47  within each set are shown as parallel, though legs  47  may also be at angles to each other. Also, the sets of legs  47  are shown to be parallel, though preform  45  may be formed or positioned so that the sets of legs  47  are at an angle relative to each other. Preform  45  may be pre-impregnated with resin, or may be used dry using the same method of assembly as described above.  
         [0026]    [0026]FIGS. 7 and 8 show preform  45  being used to connect components  13 ,  15  in structures  55 ,  57 , respectively. Component  13  is adhered to surfaces  55  in slot  51 , and component  15  is adhered to surfaces  55  within slot  53 . In structure  57 , components  13 ,  15  are oriented to be perpendicular to each other, whereas components  13 ,  15  are parallel in structure  59 .  
         [0027]    To assemble structures  57 ,  59 , a prepreg preform  45  is preferably used. Component  13  is placed between legs  47  of slot  51 , and surfaces  55  are placed against surfaces  19 ,  21 . Component  1  is placed within slot  53 , and surfaces  55  are placed against surfaces  23 ,  25 . Legs  47  are then oriented at the desired angle relative to each other to form structure  57  or  59 , and legs  47  are squeegeed onto components  13 ,  15  to form consistent bondlines before curing in an oven.  
         [0028]    When using a dry preform  45 , a two-part resin is applied to an end portion of surfaces  19 , 21  of component  13 , and component  13  is placed within slot  51 , surfaces  55  being placed against component  13 . Resin is also applied to an end portion of surfaces  23 ,  25  of component  15 , which is then placed within slot  53 . As described above, preform  45  may be assembled with components  13 ,  15  before application of resin, wherein legs  47  are pulled back to allow for resin to be applied to surfaces  19 ,  21 ,  23 ,  25 . Additional resin is applied to the outer surfaces of preform  45 , and legs  47  are squeegeed onto components  13 ,  15 . Components  13 ,  15  are positioned in their desired angular orientation, and the resin is allowed to cure at room temperature.  
         [0029]    The advantages of the present invention include the increased strength from using an a 3-D woven preform to connect components, while providing a low-cost, simple method of use. The present method avoids the thick, heavy stack of layers used in the prior art methods, and heat during curing is not required when using a resin system that cures at room temperature. Thus, fabrication time and costs are reduced.  
         [0030]    While the invention has been shown in only some of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit thereof. For example, a cross-shaped preform may be used, or the preform may have more than two legs extending from the base.