Abstract:
Amethod for constructing a composite structure is disclosed. The method comprises four steps. Step one calls for coupling a flexible layer to a base, where the flexible layer has a working surface and an underside surface. Step two requires coupling at least one support element to the underside surface of the flexible layer. The next step calls for coupling at least one adjustable element to the support element for adjusting the position of the flexible layer. The last step requires configuring the flexible layer to a configuration suitable for constructing the composite structure. More specifically, the flexible layer may have internal reinforcing elements for added strength and durability.

Description:
RELATED APPLICATIONS 
     This is a divisional application of U.S. Ser. No. 09/537,577, filed Mar. 28, 2000 now U.S. Pat. No. 6,298,896 and entitled “Apparatus for Constructing a Composite Structure” by David E. Sherrill and Kendall G. Young. 
    
    
     TECHNICAL FIELD OF THE INVENTION 
     This invention relates generally to the field of materials construction and, more specifically, to an apparatus and method for constructing a composite structure. 
     BACKGROUND OF THE INVENTION 
     Composite structures are desirable in many industries for many applications. For example, aircraft, space, and land/sea vehicles employ a variety of curved and multiple-contoured surface structures in their fabrication. Composite materials such as fiberglass/resin are commonly used for these structures because, among other desirable attributes, composite materials have high strength-to-weight ratios. Because of the ever-increasing use of composite structures throughout industry, manufacturers are continually searching for better and more economical ways of forming composite structures. 
     In the forming of composite structures many manufacturing steps are performed. One such step that is usually required is a curing step. During the cure process, composites must be formed over tooling that restrains them. These tools are generally monolithic dies that are machined or cast from a solid block to conform to a specific surface shape and, therefore, cannot have their shape modified once created. Subsequent structures having different surface shapes, though similar, must have a new tool fabricated. This is a source of manufacturing time and expense. In addition, such monolithic dies are bulky, require much setup time at the form press prior to commencement of manufacturing, and utilize large amounts of storage space when not in a production mode. Present solutions attempting to resolve this problem have relied on metallic tooling surfaces that can be reconfigured. They utilize articulating sections, sliding pins, and other methods to change the shape of the tooling surface. These methods can leave dimples on the surface of the finished structure due to the nature of the reconfigurable elements. To alleviate the problem of dimpling, manufacturers employ many reconfigurable elements spaced very close to one another. However, the more hardware, the greater the expense and maintenance. Furthermore, structure size can be limited by these methods since scale-up can be cumbersome and expensive. And when large quantities of various contoured surface structures are required, each structure would require a separate rigid surface tool and would have to be durable enough for a production run. Lower cost tooling material options such as foam, which can be easily machined to create a family of tools, do not have the desired durability and each would require its own support base adding to the tool&#39;s cost. 
     The challenges in the field of materials construction have continued to increase with demands for more and better techniques having greater flexibility and adaptability. Therefore, a need has arisen for a new apparatus and method for constructing a composite structure. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an apparatus and method for constructing a composite structure is provided that substantially eliminates or reduces disadvantages and problems associated with previously developed apparatuses and methods. 
     An apparatus for constructing a composite structure is disclosed. The apparatus comprises a flexible layer, which has a working surface and an underside surface, coupled to a base. At least one support element is coupled to the underside surface of the flexible layer, and at least one adjustable element is coupled to the support element for adjusting the position of the flexible layer. More specifically, the flexible layer may have internal reinforcing elements for added strength and durability. 
     A method for constructing a composite structure is disclosed. The method comprises four steps. Step one calls for coupling a flexible layer to a base, where the flexible layer has a working surface and an underside surface. Step two requires coupling at least one support element to the underside surface of the flexible layer. The next step calls for coupling at least one adjustable element to the support element for adjusting the position of the flexible layer. The last step requires configuring the flexible layer to a configuration suitable for constructing the composite structure. More specifically, the flexible layer may have internal reinforcing elements for added strength and durability. 
     A technical advantage of the present invention is to provide a durable tool surface that can be quickly reconfigured to produce a myriad of contoured surface structures, including prototypes for demonstration programs. 
     Another technical advantage of the present invention is that the flexible layer has internal reinforcing rods that have the ability to slide within the flexible layer&#39;s volume, thus permitting the flexible layer to be stretched in the plane of the material while resisting flexure in the direction perpendicular to the material. The rods support the flexible layer as it is being manipulated perpendicular to the plane of the material. This insures that a uniform surface curvature can be generated in the flexible material. In addition, the internal reinforcing rods, combined with the support elements underneath the flexible layer, help to avoid any “pillowing effect” of the flexible layer between the support elements. The reinforcing rods also increase the strength and durability of the forming tool. 
     A further technical advantage is that the present invention can be used for the construction of room temperature cured composites having large length and width dimensions. This is because there are no constraints such as the tool being able to fit inside of an autoclave. 
     Other technical advantages are readily apparent to one skilled in the art from the following figures, descriptions, and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the invention, and for further features and advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: 
     FIG. 1 is a perspective view illustrating one embodiment of an apparatus useful in the practice of the present invention; 
     FIG. 2 is a cross-sectional view of the apparatus in FIG. 1 showing one clamping arrangement for the flexible layer, and one arrangement of adjustable elements useful in the practice of the present invention; 
     FIG. 3 is a cross-sectional fragmented view showing, in greater detail, the reinforcing elements, support elements, and adjustable elements of the apparatus in FIG. 1; and 
     FIG. 4 is a flowchart demonstrating one method of constructing a composite structure in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The preferred embodiments of the present invention and its advantages are best understood by referring now in more detail to FIGS. 1-4 of the drawings, in which like numerals refer to like parts. 
     FIG. 1 is a perspective view illustrating one embodiment of an apparatus  100  useful for constructing a composite structure  112 . Apparatus  100  comprises a flexible layer  104  coupled to a base  102 . Flexible layer  104  has a working surface  106  and an underside surface  108 . As best shown in FIG. 3, apparatus  100  also comprises support elements  302  that are coupled to underside surface  108 , and adjustable elements  304  that are coupled to support elements  302 . 
     Flexible layer  104  is an elastomeric material such as polyurethane. However, other types of elastomeric materials may be used as long as they are resilient enough to be shaped into a myriad of contoured surfaces. As examples, two such types of material are neoprene and rubber. The shape and thickness of flexible layer  104  is dependent upon the size, shape, and material type of composite structure  112 . Since apparatus  100  may be used for an infinite number of composite structures  112 , then flexible layer  104  may also be an infinite number of shapes and thicknesses. 
     Referring to FIGS. 1 and 2, one embodiment of the present invention shows flexible layer  104  being clamped to the periphery of base  102  with bolts  200 , nuts  202 , and clamping bar  204 . Clamping bar  204  may cover the full periphery of base  102  (as best shown in FIG.  1 ). If clamping bar  204  is not included, there may be individual washers for each bolt  200  and nut  202 . Other ways of coupling flexible layer  104  to base  102  are contemplated by the present invention. For example, flexible layer  104  may be screwed or bonded to base  102 . As long as flexible layer  104  is restrained on its periphery, any type of coupling suffices. 
     Base  102  is generally a steel frame structure. However, other types of materials may be used for base  102 , such as other metals, composite materials, or plastics. Base  102  needs to be of a size and shape that will allow support elements  302  and adjustable elements  304  to function underneath flexible layer  104 . 
     FIG. 3 illustrates one technical advantage of the present invention. Reinforcing elements  300  are coupled to flexible layer  104 . Reinforcing elements  300  have the ability to slide within the volume of flexible layer  104 , thus permitting flexible layer  104  to be stretched in the plane of flexible layer  104  while resisting flexure in the direction perpendicular to flexible layer  104 . Reinforcing elements  300  may be coated with a release agent to aid in the slidability of reinforcing elements  300  within flexible layer  104 . Reinforcing elements  300  are generally made of structural steel or other types of metal such as aluminum. However, the present invention contemplates other types of materials as long as the required strength and durability of flexible layer  104  and apparatus  100  is obtained. Reinforcing elements  300  are coupled to flexible layer  104  by arranging them in a desired pattern depending on the type of strength and durability desired, and then pouring the matrix that makes up flexible layer  104  over the arrangement of reinforcing elements  300 . This process is similar to the pouring of concrete over re-bar when constructing concrete structures. Reinforcing elements  300  may be coupled to flexible layer  104  in other ways, such as manufacturing flexible layer  104  with conduits in its volume, and subsequently sliding reinforcing elements  200  into the conduit. In another embodiment, reinforcing elements  300  are not coupled to flexible layer  104 . This would be the case where little strength is needed when constructing composite structure  112 . 
     Also shown in FIG. 3, support elements  302  are shown to be coupled to underside surface  108  of flexible layer  104 . This coupling is preferably an adhesive bonding. However, support elements  302  may be coupled using other methods, such as mechanical methods. Support elements  302  are typically made of structural steel. However, other types of materials are contemplated by the present invention, such as other metals, composite materials, or plastics. Support elements  302  will generally have a substantially square shape in the area where it couples to flexible layer  104 . However, support elements  302  may be any shape desirable. Support elements  302  are closely spaced in a pattern that permits uniform stretching of flexible layer  104 . The lesser the space there is between support elements  302 , the lesser chance of a “pillowing effect” resulting between support elements  302 . Spacing of support elements  302  is a function of the thickness of flexible layer  104 , its inherent stiffness, the size of reinforcing elements  300  and amount of displacement required to create the desired apparatus  100  surface shape. The substantially square shape of support elements  302  is the best way to reduce the gaps between support elements  302 . In addition, support elements  302  have a larger surface area than adjustable elements  304 , which will reduce cost by reducing the number of adjustable elements  304  required. 
     Still referring to FIG. 3, support elements  302  are shown to be coupled to adjustable elements  304 . Coupling of support elements  302  to adjustable elements  304  may be accomplished by a clevis  306 . However, other coupling arrangements may be employed, such as hinging, bolting, welding, or adhesive bonding. Adjustable elements  304  are preferably screw jacks that allow for the adjustment of the position of flexible layer  104 . There can be other ways of adjusting the position of flexible layer  104  instead of using screw jacks, such as electric motors, hydraulic mechanisms, or a pneumatic mechanisms. Adjustable elements  304  may or may not be coupled to base  102 , depending on what type of arrangement is used for adjustable elements  304 . Adjustable elements  304  provide a technical advantage for the present invention in that a durable surface of apparatus  100  can be quickly reconfigured to produce a myriad of contoured surface structures. This will also allow prototypes for demonstration programs to be quickly manufactured. 
     FIG. 4 is a flowchart demonstrating one method of constructing composite structure  112  in accordance with the present invention. In one embodiment, flexible layer  104  is coupled to a base  102  at step  400 . Flexible layer  104  may have at least one reinforcing element  300  coupled thereto. At least one support element  302  is coupled to flexible layer  104  at step  402 , and at least one adjustable element  304  is coupled to support element  302  at step  404 . Adjustable element  304  may be a screw jack. Adjustable elements  304  are used to configure flexible layer  104  to a desired shape and contour at step  406 . This shape or contour depends upon what type of composite structure  112  is being formed. Composite structure  112  is then layed-up on flexible layer  104  at step  408 , and composite structure  112  is formed at step  410 . 
     In one embodiment of the present invention, apparatus  100  is used for room temperature forming of composite structure  112 . The present invention also contemplates elevated temperature forming of composite materials. In elevated temperature forming, the maximum temperature of apparatus  100  will depend upon the material used for flexible layer  104 . The present invention is especially suited for the VARTM (Vacuum Assisted Resin Transfer Molding) process that is proprietary to Northrop Grumman Corporation. 
     Composite structure  112  may be layed-up on flexible layer  104  as a solid laminate or as a sandwich-type composite material assembly. If a sandwich-type structure is layed-up, then the core material will be prepared so that it can be easily draped over the surface of flexible layer  104 . This is a technical advantage of the present invention in that it has the ability to fabricate a compound curvature sandwich shape. An example of a core material is balsa wood. The balsa wood, or other core material, needs to be “diced” so that it can conform to the surface of flexible layer  104  when layed-up. This type of “diced” core that permits a draping of the core material is readily available through commercial vendors. After laying-up the materials that comprise composite structure  112 , a vacuum bag forming process, that is well known in the art of forming composite materials, may be performed. 
     Although an embodiment of the invention and its advantages are described in detail, a person skilled in the art could make various alternations, additions, and omissions without departing from the spirit and scope of the present invention as defined by the appended claims.