Abstract:
A reinforced panel, made of a composite material, includes a single base layer. A first plurality of mutually parallel ridges is affixed to the surface of the base layer. A second plurality of mutually parallel ridges is also affixed to the surface of the base layer, but oriented transverse to the first plurality. Structurally, the ridges and the base layer are co-cured to create an integral, continuous structure that provides stiffness and rigidity to the panel.

Description:
FIELD OF THE INVENTION 
     The present invention pertains generally to structures that are made of composite materials. More particularly, the present invention pertains to rigid panels, and similar type structures, that are made with reinforced composite materials. The present invention is particularly, but not exclusively, useful as a one-piece reinforced composite material that is suitable for use as the external surface structure for a high-speed vehicle, such as an aircraft. 
     BACKGROUND OF THE INVENTION 
     A composite material is a structural material that is made of two or more different materials. Cermet for example, is a composite material made of ceramic articles that are bonded with metal. Another type of widely used composite material is made of carbon fibers that are reinforced with an epoxy resin. It is this last type of composite material (i.e. carbon fiber/epoxy) that is of interest for the present invention. 
     Carbon fiber composite materials are unique in several aspects when they are used as a structural material. For one, unlike many other types of construction materials, they can be accurately pre-formed to assume complex shapes. For another, after they have been cured, they exhibit very good strength in both tension and compression. Carbon fiber composite materials, however, are typically made as relatively thin layers and, as such, they can be somewhat floppy. In many applications, this may be undesirable. The solution for such applications is to then somehow reinforce the layer of composite material in a manner that will stiffen and make the material rigid for its use as a support structure. 
     By structural analysis, it can be shown that a bending moment results wherever a force couple is applied to a structure. This bending moment can be resisted, however, when portions of the structure are distanced from each other and are located in the same bending plane, with a same center of bending. Indeed, the more material that is in the respective portions, and the greater the distance between them, the greater will be the structure&#39;s ability to resist bending. The well-known I-beam is a good basic example of such a structure. 
     Insofar as composite materials are concerned, and as noted above, although they may be formed as thin layers, and are therefore susceptible to being floppy, they typically have good strength characteristics in both tension and compression. Again, by way of example, an I-beam requires these strength characteristics. Heretofore, when a stiff, rigid structure has been required, and it has been desirable to use composite materials for its construction, it has been common to use two different layers of the composite material. The layers of composite material are then distanced from each other and interconnected by another structure, such as honeycomb. Unfortunately, even though composite materials and honeycomb are both relatively light-weight when compared with other structural materials, they still add weight. In the two-layer example considered above, the additional layer of composite material and the honeycomb may add substantial weight. For some applications (e.g. the manufacture of aircraft) weight limitation is of the utmost importance. 
     In light of the above, it is an object of the present invention to provide a reinforced panel, made of a composite material, that is sufficiently stiff and rigid to resist operational bending forces. Another object of the present invention is to provide a reinforced panel, made of a composite material, that is extremely light weight. Yet another object of the present invention is to provide a reinforced panel that is suitable for use as the external surface of a high performance aircraft. Another object of the present invention is to provide a reinforced panel that is relatively simple to manufacture, is easy to use and is comparatively cost effective. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, a reinforced panel includes a single base layer of a composite material that has continuations extending from a surface thereof. It is these continuations that provide the reinforcing structure for the panel. In detail, as intended for the present invention, the continuations are formed as ridges that rise a predetermined distance from the surface of the layer. Further, there is a first plurality of mutually parallel ridges. There is also a second plurality of mutually parallel ridges that is transverse to the first plurality of ridges. Together, these pluralities of ridges can be arranged as either an ortho-grid, or as an iso-grid. 
     Structurally, the continuations (ridges) are each formed with a substantially U-shaped cross section. As so formed they have a base portion and a pair of substantially parallel and opposite legs that extend from the base portion to a respective edge. With this structure, there are effectively three embodiments for the reinforced panel of the present invention. These embodiments primarily differ from each other by the manner in which the edges of the ridges are affixed to the base layer of composite material. And, in one embodiment, a unidirectional ply is added to provide additional structure for reaction to forces borne by the base portion of the ridge. 
     In a preferred embodiment of the present invention, the legs of the ridges are continuations of the surface, and are thus affixed directly to the surface of the base layer. For this embodiment, a unidirectional ply is added to span the distance between opposite legs of each ridge, and to thereby provide additional structure for reaction to forces borne by the cross section of the ridge (continuation). In another embodiment, the edges of each ridge are formed as feet and the panel includes overlap layers that cover each foot and extend therefrom to contact the surface of the base layer and the leg. The overlap layer is then bonded to the base layer, and to the leg to affix the ridge to the base layer. In a third embodiment, the base layer is formed with a plurality of flaps. Specifically, each flap extends from an edge of a ridge and into the channel that is formed between the legs of the ridge. The flap is then bonded to the leg inside the channel. For the embodiment wherein an overlap layer is used, the flap is bonded to the side of the leg that is opposite the overlap layer. In all embodiments, the ridges are integrally bonded to the surface of the base layer to become continuations of the base layer. Also, they are arranged in a grid as mentioned above, to create the reinforced panel. 
     It is an important aspect of the present invention that the ridges be a continuation of the base layer, and that a portion of the ridge be distanced from the surface of the base layer by a predetermined distance “h”. Also, as implied above, it is an important aspect of the present invention that the panel is pre-formed with all of the components integrally associated with each other before they are all co-cured. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of this invention, as well as the invention itself, both as to its structure and its operation, will be best understood from the accompanying drawings, taken in conjunction with the accompanying description, in which similar reference characters refer to similar parts, and in which: 
         FIG. 1  is a perspective view of a reinforced panel in accordance with the present invention; 
         FIG. 2  is a cross-sectional view of a preferred embodiment of a stiffening member (ridge) for use with the present invention, as seen along the line  2 - 2  in  FIG. 1 ; 
         FIG. 3  is a perspective view of a unidirectional ply, as used for the preferred embodiment of the present invention, with portions broken away for clarity; 
         FIG. 4  is a cross-sectional view of an alternate embodiment of a stiffening member (ridge) for use with the present invention, as would be seen along the line  2 - 2  in  FIG. 1 ; 
         FIG. 5  is a cross-sectional view of a modified alternate embodiment of a stiffening member (ridge) for use with the present invention, as would be seen along the line  2 - 2  in  FIG. 1 ; and 
         FIG. 6  is a cross-sectional view of another preferred embodiment of a stiffening member (ridge) for use with the present invention, as would be seen along the line  2 - 2  in  FIG. 1 . 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring initially to  FIG. 1 , a reinforced panel in accordance with the present invention is shown and is generally designated  10 . As shown, the panel  10  includes a plurality of mutually parallel ridges  12 , and a plurality of mutually parallel ridges  14 . Further, the ridges  14  are transverse to the ridges  12  and intersect them at an angle “α”.  FIG. 1  also shows that the ridges  12  and  14  are mounted on the surface  16  of a common base layer  18 . 
     For purposes of disclosure, the ridges  12   a  and  12   b  are shown as only being exemplary of additional such ridges  12 . Likewise, the ridges  14   a  and  14   b  are also only exemplary. Further, although the term “ridge” is most frequently used herein to describe the structure shown and indicated by the numerical designators “ 12 ” or “ 14 ”, it is to be appreciated that the ridges  12 / 14  are, functionally, “stiffening members” for the panel  10  and are, structurally, “continuations” of the base layer  18 . Consequently, the terms “ridge”, “stiffening member” and “continuation” may be used interchangeably herein. Also, as will be appreciated by the skilled artisan, the ridges  12 / 14  will form an ortho-grid when the angle “α” is a right angle. Otherwise, the ridges  12 / 14  will form an iso-grid. 
     Turning now to  FIG. 2 , the structural construction of a preferred embodiment for a ridge  12 / 14  is shown in detail. In  FIG. 2  it will be seen that the ridge  12  has a substantially U-shaped, cross-sectional configuration (shown inverted in  FIG. 2 ). This configuration includes a base portion  20 . Also, extending substantially parallel from the base portion  20  are legs  22   a  and  22   b  that, together with the base portion  20 , define a channel  24 . As shown, the legs  22   a  and  22   b  are distanced from each other by a distance “w”, and the base portion  20  is distanced from the base layer  18  by a distance “h”. For purposes of the present invention, the respective distances “w” and “h” can be varied as desired for the particular application. 
     Still referring to  FIG. 2 , a preferred embodiment of the present invention includes a unidirectional ply  26  that extends in the plane of the base layer  18  and interconnects the leg  22   a  with the leg  22   b . More specifically, each of the legs  22   a  and  22   b  terminate at a respective edge  28   a  and  28   b , and it is these edges  28   a  and  28   b  that engage with the unidirectional ply  26 . Turning to  FIG. 3 , it will be seen that the unidirectional ply  26  is characterized by having a plurality of tows  30  that are aligned substantially in parallel with each other during the manufacture of the ply  26 . Consequently, the maximum tension force that can be resisted by the unidirectional ply  26  will be a force that is applied in the direction of the aligned tows  30 . Thus, during the construction of a ridge  12  (e.g. ridge  12   a  in  FIG. 1 ) the unidirectional ply  26  is positioned at a distance “h” from the base portion  20  of the ridge  12  (see  FIG. 2 ), with the tows  30  of ply  26  aligned substantially parallel to the axis  32  of the channel  24 . 
     In an alternate embodiment for the panel  10  of the present invention, shown in  FIG. 4 , the ridge  12  includes legs  22   a  and  22   b  that are each formed with a foot  34   a  and  34   b  at the respective edges  28   a  and  28   b  of the legs  22   a  and  22   b . Further, an overlap layer  36   a  is positioned over the foot  34   a  and is secured to the leg  22   a , as well as the base layer  18 . Similarly, an overlap layer  36   b  is positioned over the foot  34   b  and is secured to the leg  22   b , as well as the base layer  18 . In another alternate embodiment for the panel  10  of the present invention, shown in  FIG. 5 , the embodiment shown in  FIG. 4  is modified by cutting the base layer  18  along the middle of the channel  24 . This creates a pair of opposed flaps  38   a  and  38   b . These flaps  38   a  and  38   b  are then folded into the channel  24  and into contact with the side of respective legs  22   a  and  22   b.    
     For yet another preferred embodiment of the present invention, refer to  FIG. 6 . There it will be seen that a second unidirectional ply  26 ′ is added onto the base portion  20  of a stiffening member (ridge)  12 . Specifically, as shown in  FIG. 6 , this additional ply  26 ′ is affixed to the base portion  20  and is positioned substantially at the distance “h” from the unidirectional ply  26  on base layer  18 . Consequently, the ply  26  and the ply  26 ′ will alternatively resist tension forces that are imposed during a bending of the panel  10 . With the exception of the additional unidirectional ply  26 ′, the ridge  12  that is shown in  FIG. 6  is similar in all other important respects to the ridge  12  shown in  FIG. 2 . 
     Although the disclosure above has been directed primarily to a single ridge  12 , it is to be appreciated that the disclosure applies equally to all ridges  12 / 14  of the reinforced panel  10 . Moreover, for all embodiments of the present invention (i.e. ridges  12  shown in  FIGS. 2 ,  4 ,  5  and  6 ), the construction material for the base panel  18  and for the ridges  12 / 14  is a composite material. Preferably, this composite material is a combination of carbon fibers and epoxy resin. Also, for all embodiments of the present invention, it is intended that after the composite material components have been assembled as disclosed above, the entire combination is co-cured. The consequence of this is a reinforced panel  10  that is essentially of a one-piece, unitary structure wherein the cooperative resistance of the base portion  20  and the base layer  18  (along with ply  26  and ply  26 ′ in the preferred embodiments (see  FIG. 2  and  FIG. 6 )) provide stiffness and rigidity for the panel  10 . 
     While the particular Reinforced Composite Panel as herein shown and disclosed in detail is fully capable of obtaining the objects and providing the advantages herein before stated, it is to be understood that it is merely illustrative of the presently preferred embodiments of the invention and that no limitations are intended to the details of construction or design herein shown other than as described in the appended claims.