Patent Publication Number: US-2017369148-A1

Title: Method of making pad-ups for composite structures and composite structures including pad-ups

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     The present application claims priority to U.S. provisional patent application No. 62/090,976 filed on Dec. 12, 2014, the entire contents of which are hereby incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention concerns a method for constructing one or more pad-ups for composite structures and composite structures including one or more pad-ups. In particular, the present invention concerns a method for constructing pad-ups for composite structures that incorporate prepreg composite materials. More specifically, the present invention is contemplated to be employed by an automated fiber placement (“AFP”) system for laying prepreg materials to provide composite structures including one or more pad-ups. 
     DESCRIPTION OF THE BACKGROUND AND RELATED ART 
     Pre-impregnated composite fabric materials (i.e., prepreg materials) are often used in the manufacturing of composite components, such as aircraft components, among other possibilities. Prior to being cured into a final composite component, the prepreg material comprises a fabric layer onto which has been applied resin, such that the resin at least partially impregnates the fabric layer. 
     To form a composite structure, it is customary to stack multiple layers, or plies, of composite fabric materials on top of one another. Typically, this is done by hand (i.e., hand lay-up), which is time consuming and, therefore, expensive. 
     With respect to certain aircraft components, it is customary to include thickened areas (referred to as “pad-ups”) at locations on the aircraft component where structural elements are to be attached. Conventionally, these pad-ups also are created using hand lay-up techniques. 
     In view of the foregoing, a need has developed whereby aircraft components, including those incorporating pad-ups, may be manufactured via automated or semi-automated techniques including, but not limited to AFP and/or automated tape laying (“ATL”) machines. 
     SUMMARY OF THE INVENTION 
     The present invention addresses one or more of the deficiencies noted with respect to the prior art. 
     The present invention provides a composite component for a vehicle. The composite component includes a laminate made from a composite material, a first pad-up area applied to the laminate, where the first pad-up area includes a plurality of first tows laid next to one another in a side-by-side arrangement and where the first pad-up area defines a first fiber orientation, and a second pad-up area, where the second pad-up area includes a plurality of second tows laid next to one another in a side-by-side arrangement and where the second pad-up area defines a second fiber orientation that differs by a predetermined angle from the first fiber orientation. The first pad-up area and the second pad-up area intersect at an intersecting area and together form a first pad-up ply on the laminate. 
     In one contemplated embodiment, the first fiber orientation is along a first load path of the composite component. 
     In another contemplated embodiment, the second fiber orientation is along a second load path of the composite component. 
     It is contemplated that the composite component may be constructed such that at least a portion of the first pad-up area and the second pad-up area lie in the same layer. 
     Still further, the composite component may be constructed so that at least one interleaf layer is positioned between the first pad-up area and the second pad-up area. 
     In another contemplated embodiment, the first pad-up area and the second pad-up area may overlap at the intersecting area. 
     It is also contemplated that the first pad-up area may abut the second pad-up area at the intersecting area. 
     In one contemplated embodiment, the predetermined angle is less than or equal to about 90°. 
     It is contemplated that the first pad-up ply may be applied to the laminate via an automated fiber placement machine. 
     Other embodiments contemplate that the first pad-up area may be applied to the laminate via an automated fiber placement machine by steering the plurality of first tows. 
     Still further, the second pad-up area may be applied to the laminate via an automated fiber placement machine by steering the plurality of second tows. 
     Where used, automated fiber placement machine may lay a plurality of first pad-up areas on the component prior to changing direction for laying a plurality of second pad-up areas on the component. 
     For one or more embodiments of the present invention, a plurality of first pad-up areas and a plurality of second pad-up areas on the component provide a lattice of pad-up areas. 
     With respect to one or more contemplated embodiments, the laminate, the first pad-up area, and the second pad-up area are made from carbon fiber materials preimpregnated with resin. 
     The present invention also provides a composite component for a vehicle that includes a lattice pattern of pad-up areas and interstitial areas positioned between the pad-up areas. The lattice pattern of pad-up areas includes at least a first pad-up area and at least a second pad-up area that intersects with the first pad-up area. The first pad-up area has a first fiber direction that extends along a first length of the first pad-up area and the second pad-up area has a second fiber direction that extends along a second length of the second pad-up area. The first pad-up area and the second pad-up area intersect at a predetermined angle. 
     In connection with this embodiment, it is contemplated that the pad-up area and the second pad-up area overlap at an intersecting area. 
     It is also contemplated for the composite component that the first pad-up area abuts the second pad-up area at an intersecting area. 
     The composite component may include at least one interleaf layer positioned between the first pad-up area and the second pad-up area. 
     With respect to the composite component, at least a portion of the first pad-up area and the second pad-up area may lie in the same layer. 
     Further aspects of the present invention will be made apparent from the paragraphs that follow. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
       The present invention will now be described in connection with the drawings appended hereto, in which: 
         FIG. 1  is a perspective illustration of an aircraft showing a portion of the tail section of the aircraft&#39;s fuselage of the type that may be constructed from one or more of the components manufactured according to the present invention; 
         FIG. 2  is a perspective illustration of the portion of the tail section of the aircraft illustrated in  FIG. 1 , providing enhanced details to facilitate the discussion of selected elements of the present invention; 
         FIG. 3  is a perspective illustration of a component, contemplated as a part of a fuselage, showing pad-up areas that support stringers and structural elements attached to or incorporated into the aircraft component; 
         FIG. 4  is a perspective illustration of the aircraft component shown in  FIG. 3  with the stringers and structural elements removed, thereby highlighting the location, size and shapes of the various pad-up areas; 
         FIG. 5  is a perspective illustration of an aircraft component, showing an exemplary, non-limiting application of a stack of plies for a pad-up area, such as may be applied by hand (i.e., a manual construction); 
         FIG. 6  is a perspective illustration of a first embodiment of the creation of one ply for a pad-up for an aircraft structure according to the present invention; 
         FIG. 7  is a graphical, top plan view of a second embodiment of one ply for a pad-up for an aircraft structure according to the present invention; 
         FIG. 8  is a graphical, top plan view of a third embodiment of one ply for a pad-up for an aircraft structure according to the present invention; 
         FIG. 9  is an exploded, perspective illustration of multiple plies layered on top of one another to form a pad-up for an aircraft structure according to the present invention; 
         FIG. 10  is a graphical, top plan view of a first ply of composite material employed in several of the layers illustrated in  FIG. 9 ; 
         FIG. 11  is a graphical, top plan view of a second ply of composite material employed in several of the layers illustrated in  FIG. 9 ; 
         FIG. 12  is a graphical, top plan view of a third ply of composite material employed in one of the layers illustrated in  FIG. 9 ; 
         FIG. 13  is a graphical, top plan view of a fourth ply of composite material employed in one of the layers illustrated in  FIG. 9 ; 
         FIG. 14  is a perspective illustration of a portion of an aircraft fuselage of the type that may be employed on the tail section of the aircraft illustrated in  FIG. 1 , showing the locations of selected pad-up areas to highlight aspects of the present invention; 
         FIG. 15  is a view of the interior surface of the portion of the aircraft fuselage illustrated in  FIG. 14 , showing the same, selected pad-up areas for illustration; 
         FIG. 16  is an enlarged illustration showing a portion of the pad-up areas for the portion of the fuselage element illustrated in  FIGS. 14 and 15 ; 
         FIG. 17  is a perspective illustration of the interior surface of the fuselage portion illustrated in  FIG. 14 , showing the curvature of the interior surface; 
         FIG. 18  is a top view of another embodiment of an aircraft structure according to the present invention; and 
         FIG. 19  is a perspective view of the embodiment illustrated in  FIG. 18 . 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENT(S) OF THE INVENTION 
     The present invention will now be described in connection with one or more embodiments thereof. The discussion of the embodiments is not intended to be limiting of the present invention. To the contrary, any discussion of embodiments is intended to exemplify the breadth and scope of the present invention. As should be apparent to those skilled in the art, variations and equivalents of the embodiment(s) described herein may be employed without departing from the scope of the present invention. Those variations and equivalents are intended to be encompassed by the scope of the present patent application. 
     The present invention will now be discussed in the context of a composite prepreg material for manufacture of components of a vehicle, such as a jet aircraft for example. A composite prepreg material is defined, generally, as a material which may be woven, non-woven, provided in sheets, and/or provided in tapes or tows. The material typically includes carbon fiber, but other materials (including, but not limited to, aramid fibers, nylon, glass, and fiberglass) may be employed. Additionally, while described in connection with the use of prepreg materials, the present invention may be employed with non-prepreg materials (or other substitutable materials). 
     Without limiting the scope of the present invention, it is contemplated that the construction of a composite fiber structure will include, at least in part, the assistance of an AFP machine or an ATL machine. In the context of the discussion that follows, the terminology of an AFP machine is used, as this encompasses the contemplated embodiment of the present invention. As noted, however, reference to an AFP machine is not intended to be limiting of the present invention. 
     In one embodiment, an AFP machine may create a composite structure for an aircraft by laying a plurality of carbon fiber tows in a side-by-side manner along a mold. The plurality of narrow tows may be laid simultaneously in order to provide a band having a total width greater than that of the individual tows. In a non-limiting embodiment, a band may be formed of sixteen (16) tows that are laid in a side-by-side manner to create the band having a width that is the sum of the sixteen (16) tows. The tows within the band may all be laid together, or alternatively, the AFP machine may lay one or more of the tows within the band individually. As few as one (1) tow may be laid at any given time and as many as sixteen (16) tows may be laid simultaneously, as required or as desired. The AFP machine is contemplated to have the capacity to stop laying the tows, to change its directional orientation, and begin laying the tows again. The operation and construction of an AFP machine should be apparent to those skilled in the art. Therefore, further details about the AFP machine are omitted, unless needed to discuss one or more of the details of the present invention that follow. 
     Individual tows are contemplated to be made from a non-woven carbon fiber material that is pre-impregnated with a suitable resin. As such, the tows may be prepregs as defined herein. In the contemplated embodiment, the tows are contemplated to include a plurality of carbon fibers that are oriented in the same direction or substantially the same direction. Specifically, the tows are contemplated to define a fiber direction that extends along the direction of the application of the tows to the laminate. As such, the fiber directions or orientations extend along the lengths of the pad-up areas, as defined herein. It is to be understood that as the tows are steered along the deposition surface, the fiber orientation may vary in relation to the laminate, but will still extend in a direction along the length of the pad-up area. 
     With reference to  FIG. 1 , the present invention is contemplated to be employed in the construction of aircraft  10 , such as jet aircraft  10 . While the invention is discussed in this context, the present invention is not intended to be limited solely to jet aircraft  10 . The present invention also is applicable to any other type of aircraft, as should be apparent to those skilled in the art. In addition, while discussed in the context of jet aircraft  10 , the present invention may apply to vehicles other than aircraft, such as cars, buses, and trains, as well as to non-transportation components, such as wind turbines. 
     In the following description, the same numerical references are intended to refer to similar elements. The re-use of reference numerals for different embodiments of the present invention is intended to simplify the discussion of the present invention. It should not be inferred, therefore, that the re-use of reference numbers is intended to convey that the associated structure or element is identical to any other described embodiment. 
     Although the preferred embodiments of the present invention as illustrated in the accompanying drawings comprise various components, and although the preferred embodiments of the system and corresponding parts of the present invention as shown consist of certain geometrical configurations as explained and illustrated herein, not all of these components and geometries are essential to the invention and, thus, should not be taken in their restrictive sense, i.e., should not be taken as to limit the scope of the present invention. 
     It is to be understood, as should be apparent to a person skilled in the art, that other suitable components and cooperations therebetween, as well as other suitable geometrical configurations, may be used for the present invention, as will be briefly explained herein and as may be easily inferred therefrom by a person skilled in the art, without departing from the scope of the invention. 
     Additionally, it should be appreciated that positional descriptions such as “right,” “left,” “top,” “bottom,” and the like are, unless otherwise indicated, to be taken in the context of the figures and should not be considered to be limiting of the present invention. 
     It will be appreciated that the present invention may be practiced without all of the specific details which are set forth herein below in order to provide a thorough understanding of the invention. 
       FIG. 1  is perspective illustration of a jet aircraft  10 . The jet aircraft  10  is contemplated to be constructed at least partially from composite materials, such as carbon fiber composite materials. In the illustration provided in  FIG. 1 , the tail section  12  of the jet aircraft  10  is shown in a skeletonized manner. The skeletonized tail section  12  is contemplated to indicate that at least this section of the jet aircraft  10  may be made from carbon fiber composite materials. As should be apparent, any other portion of the jet aircraft  10 , in addition to the tail section  12 , may be constructed from a composite material without departing from the scope of the present invention. 
       FIG. 2  provides an enlarged, perspective view of the tail section  12  of the jet aircraft  10  illustrated in  FIG. 1 . The illustration of the tail section  12  provides details about selected structural elements  14  necessary for the construction of the jet aircraft  10 . 
       FIG. 3  is a perspective illustration of an aircraft component  16 . The aircraft component  16  shown in  FIG. 3  may form an exterior surface of the fuselage for the jet aircraft  10 . Alternatively, the aircraft component  16  may be part of a fairing or other component forming at least a part of the external structure of the jet aircraft  10 . Still further, the aircraft component  16  may be part of an internal structure within the jet aircraft  10 . While the present invention will be discussed in connection with the manufacture primarily of external, structural components (e.g., skin elements) of a jet aircraft  10 , the present invention should not be understood to be limited solely thereto. 
     As illustrated in  FIG. 3 , the aircraft component  16  includes a laminate, such as curved element  18 , which may form a portion of the fuselage of the jet aircraft  10 . While the curved element  18  is shown with a curved structure, it is noted that the curved element  18  may be planar in an alternative contemplated embodiment. Still further, it is contemplated that the curved element  18  may have any contour suitable for the construction of the aircraft in which the curved element  18  is incorporated. For example, the curved element  18  may be a single curvature element or a double curvature element. 
     The curved element  18 , also referred to herein as “the laminate,” may be any material onto which the pad-up areas  20  are formed. In one embodiment, it is contemplated that the laminate or curved element  18  may be as thin as a single ply of carbon fiber material. In other embodiments, the laminate or curved element may comprise a plurality of plies arranged to form a stack of plies. Still further constructions for the laminate or curved element  18  may be used without departing from the scope of the present invention. 
     In the illustrated embodiment, the laminate or curved element  18  includes a lattice pattern of pad-up areas  20  that are collectively formed on an interior surface thereof, with interstitial areas  30  positioned therebetween. In the non-limiting embodiment shown in  FIG. 3 , the lattice pattern of the pad-up areas  20  takes the appearance, at least in part, of perpendicularly intersecting lines on a piece of graph paper. In the illustrated embodiment, the lattice pattern of pad-up areas  20  includes first pad-up areas  22  that extend longitudinally along a length of the laminate or curved element  18  and second pad-up areas  24  that extend laterally across a width of the laminate or curved element  18  and intersect the first pad-up areas  22 . 
     As will be made apparent in the discussion that follows, the longitudinal axis of the laminate or curved element  18  is defined in relation to the length of the laminate or curved element  18 . Similarly, the lateral axis of the laminate or curved element  18 , while being described in terms of the width of the laminate or curved element  18 , is intended to refer to an orientation that is orthogonal to the longitudinal axis. It is further noted that the longitudinal and lateral orientations are merely provided to clarify spatial relationships between the elements described. The terms “longitudinal” and “lateral,” therefore, should not be understood as having any relation or correspondence to the longitudinal and lateral axes of the jet aircraft  10  illustrated in  FIG. 1 . 
     Two sets of structural elements  26 ,  28  are attached to the pad-up areas  22 ,  24 , respectively. Since the structural elements  26 ,  28  are disposed on the pad-up areas  22 ,  24 , the structural elements  26 ,  28  are arranged in the same lattice pattern established by the pad-up areas  22 ,  24 . First structural elements  26 , sometimes referred to as stringers, extend longitudinally along a length of the laminate or curved element  18  (i.e., along a first direction). Second structural elements  28 , sometimes referred to as C-frames, extend laterally across a width of the laminate or curved element  18 , in a direction cross-wise to the first structural elements  26  (i.e., in a second direction). As should be apparent from the illustrated embodiment, in this non-limiting embodiment, the first structural elements  26  are arranged orthogonally (or substantially orthogonally) to the second structural elements  28 . 
     Concerning the first and second structural elements  26 ,  28 , it is contemplated that the two structural elements  26 ,  28  may have any construction that is required or desired to provide additional strength to the location on the laminate or curved element  18  where the structural element  26 ,  28  are placed. The structural elements  26 ,  28  may be constructed as stringers, including, but not limited to, I-beams, C-beams, T-beams, L-beams, Z-beams, delta-beams, and/or omega beams and/or any other type of structural element  26 ,  28  that might be employed in the construction of the structure of a jet aircraft  10  and its associated components. Without limitation, the structural elements  26 ,  28  may extend longitudinally, laterally, orbitally, or at a predetermined angle with respect to one or more other structural elements  26 ,  28 . In other words, the present invention is not contemplated to be limited to any particular construction or orientation of the structural elements  26 ,  28 . 
     As discussed more fully herein, it is contemplated that the structural elements  26 ,  28  will be affixed to the pad-up areas  22 ,  24 . Affixation is intended to encompass any number of different fasteners to connect the structural elements  26 ,  28  to the pad-up areas  22 ,  24 . In one contemplated embodiment, the structural elements  26 ,  28  are co-cured and/or co-bonded together with the pad-up areas  22 ,  24  and are, therefore, an integral part of the laminate or curved element  18 . In a second contemplated embodiment, the structural elements  26 ,  28  are cured before being attached to the pad-up areas  22 ,  24  via a suitable adhesive. In a third contemplated embodiment, the structural elements  26 ,  28  are cured before being attached to the pad-up areas  22 ,  24  via a suitable fastener, such as a rivet. In addition, one or more of the structural elements  26 ,  28  may be affixed to the pad-up areas  22 ,  24  via a suitable fastener, such as a rivet, in addition to being co-cured and/or co-bonded therewith. Finally, it is contemplated that one or more of the structural elements  26 ,  28  may be made from a metal alloy such as an alloy of aluminum, iron, titanium, magnesium, beryllium, or the like, and affixed to the pad-up areas  22 ,  24  via a suitable fastener, such as a rivet. As noted, the manner in which the structural elements  26 ,  28  are affixed to the pad-up areas  22 ,  24  is not considered to be limiting of the present invention. 
     In the embodiment of the aircraft component  16  illustrated in  FIG. 3 , the pad-up areas  22 ,  24  and the structural elements  26 ,  28  are contemplated to be in register with one another. Specifically, the structural elements  26 ,  28  are centered on and attached to respective ones of the pad-up areas  22 ,  24 . The structural elements  26 ,  28 , however, do not need to be centered exactly on the pad-up areas  22 ,  24  to practice the present invention. Instead, the structural elements  26 ,  28  may be offset from the centerlines of respective ones of the pad-up areas  22 ,  24 . 
     The pad-up areas  22 ,  24  establish areas on the laminate or curved element  18  that are thicker than the interstitial areas  30  therebetween. As a result, the pad-up areas  22 ,  24  provide locations with a greater structural strength than the interstitial areas  30 . With this construction, the pad-up areas  22 ,  24  provide areas with heightened strength to support the fasteners (mechanical, adhesive, or otherwise) that attach the structural elements  26 ,  28  thereon. In particular, the pad-up areas  22 ,  24  are made thick enough so that the structural elements  26 ,  28  may be fastened to the laminate or curved element  18  via suitable fasteners. As noted above, fasteners include, but are not limited to rivets, nuts and bolts, screws, adhesives, welds, etc. With the interstitial areas  30  being less thick than the pad-up areas  22 ,  24 , the aircraft component  16  may be lightened in weight to contribute to weight savings within the jet aircraft  10  as a whole, while maintaining a required thickness at the regions where fasteners are required and/or desired. 
     Furthermore, it is noted that the pad-up areas  22 ,  24  and the structural elements  26 ,  28  need not be arranged perpendicularly to one another. To the contrary, the pad-up areas  22 ,  24 , and the structural elements  26 ,  28  may be disposed at any predetermined angle with respect to one another without departing from the scope of the present invention, as will be described in more detail below. 
       FIG. 4  is a perspective illustration of the laminate or curved element  18  shown in  FIG. 3 . In this illustration, to facilitate an understanding of the locations of the pad-up areas  22 ,  24 , the structural elements  26 ,  28  are omitted. 
     In the embodiment illustrated in  FIGS. 3 and 4 , the pad-up areas  22 ,  24  are separated equidistantly from one another. Accordingly, the structural elements  26 ,  28  also are separated from one another equidistantly. The present invention, however, does not require equidistant spacing between adjacent pad-up areas  22 ,  24  or between adjacent structural elements  26 ,  28 . To the contrary, the spacing between adjacent pad-up areas  22 ,  24  and adjacent structural elements  26 ,  28  may vary without departing from the scope of the present invention. 
     In another contemplated embodiment, a greater number of pad-up areas  20  may be disposed on the laminate or curved element  18 . If so, the additional pad-up areas  20  may be angled with respect to the illustrated pad-up areas  22 ,  24 . For example, the additional pad-up areas  20  may be angled at 45° with respect to the first and second pad-up areas  22 ,  24 . If additional pad-up areas  20  are disposed on the laminate or curved element  18 , it is contemplated that additional structural elements  26 ,  28  will be disposed on the additional pad-up areas  20 , consistent with the placement of the structural elements  26 ,  28  on the pad-up areas  22 ,  24 . 
     With continued reference to  FIG. 3 , it is noted that the second structural elements  28  may include joggles  32  and cut outs  34  so that the structural elements  26 ,  28  may be placed onto the laminate or curved element  18  without interfering with one another. In addition, the joggles  32  and cut outs  34  permit the placement of the structural elements  26 ,  28  onto the laminate or curved element  18  so that the elements are within prescribed engineering tolerances. 
       FIG. 5  is a perspective illustration of a laminate or a curved element  32 , providing one example of the application of a stack  34  of composite plies thereto. While not illustrated, it is noted that the stack  34  of plies may include interleafed plies, as discussed further herein. A pad-up area  20  is created after the stack  34  of plies of composite material are affixed, with or without interleafed layers, to the interior surface  36  of the laminate or curved element  32 , where the stack  34  is applied by hand (or manually) to the laminate or curved element  32 . In this embodiment, the stack  34  of composite fiber plies takes the form of a “+.” The stack  34 , therefore, establishes a pad-up area  20  in both the longitudinal and the lateral directions of the laminate or curved element  32 . 
     In  FIG. 5 , orthogonal arrows  38  are provided with reference to the stack  34  and the laminate or curved element  32  to facilitate understanding of the orientation of the stack  34  onto the laminate or curved element  32 . In addition, an arrow  40  is provided in the illustration to show the direction of application of the stack  34  of composite plies to the laminate or curved element  32  (i.e., the application direction  40 ). It is noted that orthogonal arrows  38  are provided in several of the figures to permit orientation of the various figures with respect to one another and, thereby, to facilitate an understanding of the scope and breadth of the present invention. 
     As may be apparent to those skilled in the art of constructing composite structures, it is common to apply multiple single plies, either individually or in a stack  34 , to create a pad-up area  20 . As also should be understood by those skilled in the art, individual plies each have a particular fiber orientation and the strength of the resulting composite material depends upon the fiber orientations within the single plies. To create a composite structure with good strength in multiple directions, therefore, single plies are often deposited onto the laminate or curved element  32  such that the fiber directions/orientations change between successive single plies. 
     As will be explained in more detail with respect to  FIGS. 6 through 8 , in accordance with the present invention, the pad-up areas of a composite component are formed from a plurality of first pad-up areas that intersect a plurality of second pad-up areas at intersecting areas. As used herein, the term “intersect” may mean that the first pad-up areas abut the second pad-up areas at the intersecting areas or that the first pad-up areas overlap the second pad-up areas at the intersecting areas, partially or wholly. Each of the first pad-up areas and second pad-up areas may be laid by the AFP machine such that the fiber orientation of the given pad-up area extends along the length of that pad-up area. In this manner, a single ply of a pad-up area is formed from a first pad-up area and a second pad-up area that have fiber orientations that extend in different directions. As will be explained in more detail below, the first pad-up area and the second pad-up area that form a single ply of a pad-up area may have interleaf layers of the composite component positioned therebetween. 
     Interleaf layers include composite materials in one contemplated embodiment. However, in other contemplated embodiments, the interleaf layers may include one or more layers of carbon fibers, strength materials, metal layers, metal mesh materials, copper mesh materials, galvanic corrosion protection layers, lighting strike protection layers, etc. In other words, the interleaf layers may be made from a wide variety of materials without departing from the scope of the present invention. Interleaf layers may be coextensive, partially or wholly, with the laminate or curved element  32 . In other words, the interleaf layers may cover only a part of the laminate or curved surface  32 . Alternatively, some interleaf layers may cover the entire surface of the laminate or curved surface  32 . 
       FIG. 6  is a perspective illustration of a first embodiment of an aircraft component  42  according to the present invention, showing a pad-up area  48  that comprises the deposition of a plurality of first tows  44  and a plurality of second tows  46  onto the laminate or curved element  50 . The plurality of first tows  44  are oriented in a first direction (which in the embodiment shown is in the longitudinal direction of the laminate or curved element  50  and the plurality of second tows  46  are oriented along a second direction (which in the embodiment shown is in the lateral direction) of the laminate or curved element  50 . In this first embodiment, it is contemplated that the pad-up area  48  is deposited using an AFP machine as discussed above. For reference, a pair of orthogonal arrows  52  are included in  FIG. 6 . 
     As also illustrated in  FIG. 6 , the plurality of first tows  44  are laid, side-by side, to form a first pad-up area  54  and the plurality of second tows  46  are laid, side-by-side, onto the laminate or curved element  50  to form the second pad-up area  56 . When both the first plurality of tows  44  and the second plurality of tows  46  are laid onto the laminate or curved surface  50 , they establish a single ply of the pad-up area  48 . However, as described above, it is to be understood that there may be interleaf layers positioned between the first pad-up area  54  and the second pad-up area  56 , such that the two areas of the single pad-up ply do not lie in the same layer. 
     For the pad-up area  48  illustrated in  FIG. 6 , it is noted that the first pad-up area  54  intersects with the second pad-up area  56  in an intersecting area  55 . As a result, the first pad-up area  54  is divisible into a first region  58  and a second region  60 . The first region  58  lies on one side of the second pad-up area  56 . The second region  60  lies on the other side of the second pad-up area  56  opposite to the first region  58 . Therefore, although the first region  58  and the second region  60  intersect the second pad-up area  56 , neither the first region  58  nor the second region  60  overlaps the second pad-up area  56 . As a result, the pad-up area  48  has a consistent thickness throughout, such that both the first plurality of tows  44  of the first pad-up area  54  and the second plurality of tows  46  of the second pad-up area  56  form parts the same pad-up ply. Alternatively, and as indicated above, there could be interleaf layers between the first pad-up area  54  and the second pad-up area  56 . The interleaf layers may cover a portion of the laminate or curved surface  50  or may cover the entirety of the laminate or curved surface  50 . 
       FIG. 7  is a graphical representation of a second embodiment of the present invention. This second embodiment is a variation of the first embodiment illustrated in  FIG. 6 . In this second embodiment, the first pad-up area  54  and the second pad-up area  56  are placed onto the laminate or curved element  50  such that the two pad-up areas  54 ,  56  overlap one another. In this contemplated embodiment, a thicker pad-up section is created at an intersecting area  62  where the first pad-up area  56  overlaps the second pad-up area  54 . As in the embodiment illustrated in  FIG. 6 , in the non-intersecting area, both the tows  44  of the first pad-up area  54  and the tows  46  of the second pad-up area  56  have a fiber direction that extends along the direction of the pad-up area  54 ,  56  respectively. 
       FIG. 8  is a graphical, top view of a fourth embodiment of an aircraft component  82  according to the present invention. The aircraft component  82  includes a pad-up area  84  that is disposed onto a laminate, such as a curved element  86 . The pad-up area  84  includes a first plurality of tows  88  laid along a first direction of the laminate or curved element  86 . The pad-up area  84  also includes a second plurality of tows  90  that are disposed along a second direction of the laminate or curved element  86 . Consistent with the nomenclature provided above, the first plurality of tows  88  form a first pad-up area and the second plurality of tows  90  form a second pad-up area. Together the tows  88 ,  90  form a single pad-up ply. 
     As shown in  FIG. 8 , the plurality of second tows  90  do not extend, unbroken, across the width of the laminate or curved element  86 . Instead, the first plurality of tows  88  and the second plurality of tows  90  are laid in a stepped, abutting pattern with respect to one another. In this third embodiment, none of the first plurality of tows  88  or the second plurality of tows  90  overlap one another, thereby avoiding any buildup of composite materials within the intersecting area  92 . As before, the plurality of first tows  88  and the plurality of second tows  90  may overlap one another in a variation of the illustrated embodiment. Once again, orthogonal arrows  94  are provided to provide an orientation with the other embodiments described herein. 
     In the embodiments shown in  FIGS. 6 through 8 , the tows or the first pad-up areas and the second pad-up areas are laid such that their fiber directions extend along the lengths of the two pad-up areas. In this manner, within a single pad-up ply (that includes both a first pad-up area and a second pad-up area) there are tows that extend in different directions in relation to each other, angled with respect to one another by a predetermined angle, i.e., 30°, 45°, 60°, and/or 90°. Among others, this provides the benefit, within the same pad-up ply, of two directions of fiber strength. In addition, by laying the tows such that they extend along the lengths of the of the pad-up areas, it becomes possible to lay longer strips of tows than if the entire pad-up ply had tows laid in the same direction. The lengths of the fiber tows also adds to the strength of the pad-up areas. 
     In addition, the directions of the first and second pad-up areas may be selected such that at least one of the first pad-up area and the second pad-up area extends along a load-path of the component. In this manner, the fiber directions of the pad-up area extend along the load paths, thereby aligning the directions of the fibers (and therefore the fiber strength) with the load paths. In a non-limiting embodiment, both the first pad-up area and the second pad-up area extend along load paths of the component, thereby taking advantage of fiber strength in both directions within the same pad-up ply. 
       FIG. 9  is an exploded, perspective illustration of an aircraft component  96 , showing one contemplated arrangement of multiple plies of prepreg materials layered on top of one another to form a pad-up area  98 . In between the plies that form the pad-up area  98  are interleafed layers of composite material that also form the aircraft component  96 . 
     In  FIG. 9 , ten pad-up areas  100 ,  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 ,  118  are layered on top of the interleafed layers of the aircraft component  96  and on top of one another to form a stack. Fiber orientations for the pad-up areas  100 ,  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 ,  118  are discussed in accordance with the legend provided on  FIG. 9 . The 0° orientation is parallel to the width of the curved surface  120  (i.e., the lateral direction or first fiber orientation). The 90° orientation is parallel to the longitudinal dimension of the curved surface  20  (i.e., the longitudinal direction or second fiber orientation). Several of the pad-up areas  100 ,  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 ,  118  have different shapes and fiber orientations, the details of which are provided below. 
     As illustrated in  FIG. 10 , the first pad-up area  100  is contemplated to include tows  122  that extend along a length of the pad-up area  100 , which is along a longitudinal dimension of the laminate or curved surface  120 . The tows  122 , therefore, have a fiber orientation  124  of 90°. As discussed above, it is contemplated that the tows  122  forming the first pad-up area  100  will be laid side-by side by an AFP machine. The fourth pad-up area  106 , the seventh pad-up area  112 , and the tenth pad-up area  118  are contemplated to share the same construction and fiber orientation as the first pad-up area  100 . It is noted that the pad-up areas  100 ,  106 ,  112 ,  118  may have different fiber orientations  124  without departing from the scope of the present invention. 
     As illustrated in  FIG. 11 , the second pad-up area  102  is contemplated to include tows  126  that extend along the length of the pad-up area  102 , which in the embodiment shown is along a lateral dimension of the laminate or curved surface  120 . The tows  126 , therefore, have a fiber orientation  128  of 0°. As discussed above, it is contemplated that the tows  126  forming the second pad-up area  102  will be laid side-by side by an AFP machine. The fifth pad-up area  108 , the sixth pad-up area  110 , and the ninth pad-up area  116  are contemplated to share the same construction and fiber orientation as the second pad-up area  102 . 
     As illustrated in  FIG. 12 , the third pad-up area  104  is a “plus”-shaped pad-up area  104  that includes tows  130  at a −45° angle. The third pad-up area  104  defines arms  132 ,  134 ,  136 ,  138  that extend in both the longitudinal and the lateral directions. The tows  130  of the third pad-up area  104  are contemplated to have fiber orientations  140  that are parallel to the directions of the tows  130  and are, therefore, at a −45° angle with respect to the axes of the curved element  120  illustrated in  FIG. 9 . 
     As illustrated in  FIG. 13 , the eighth pad-up area  114  also is a “plus”-shaped pad-up area  114  that includes tows  142  at a 45° angle. This eighth pad-up area  114  is similar to the third pad-up area  104 , except that the orientation is rotated 90° with respect to the third pad-up area  104 . The arms  144 ,  146 ,  148 ,  150  of the eighth pad-up area  114 , therefore, extend in both the longitudinal and the lateral directions. The tows  142  of the eighth pad-up area  114  are contemplated to have fiber orientations  152  that are parallel to the directions of the tows  142  and are, therefore, at a 45° angle with respect to the axes of the curved element  120  illustrated in  FIG. 9 . 
     In connection with the fiber orientations  124 ,  128 ,  140 ,  152  discussed with respect to  FIGS. 9-13 , it is noted that the fiber orientations  124 ,  128 ,  140 ,  152  change in increments of 45° for the different pad-up areas  100 ,  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 ,  118  in the stack. The present invention, however, is not contemplated to be limited to constructions where the fiber orientations  124 ,  128 ,  140 ,  152  change in increments of 45° for the different pad-up areas  100 ,  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 ,  118  in the stack. 
     In one alternative embodiment, it is contemplated that the fiber orientations  124 ,  128 ,  140 ,  152  may be changed in increments of 30° and/or 60°. As such, it is contemplated that the fiber orientations  124 ,  128 ,  140 ,  152  may be set at 0°, 30°, −30°, 60°, −60°, and 90°, etc., respectively. 
     In a further contemplated embodiment, the fiber orientations  124 ,  128 ,  140 ,  152  may be altered in 15° increments without departing from the scope of the present invention. 
     As should be apparent from the foregoing, the angle of change for the fiber orientations  124 ,  128 ,  140 ,  152  between pad-up areas  100 ,  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 ,  118  in the stack may be selected to be any particular value without departing from the scope of the present invention. It is noted, however, that increments of 30° are preferred to enhance the strength of the resulting composite structure. 
     In other contemplated embodiments, such as the embodiments illustrated in  FIGS. 10-13 , the change in fiber orientations may vary from pad-up area to pad-up area. In other words, the present invention contemplates, but does not require that the changes in fiber orientations follow any particular pattern. 
       FIG. 14  is a perspective illustration of an aircraft component  154  manufactured according to the present invention. The aircraft component  154  may be a portion of the fuselage of the jet aircraft  10 . In particular, the aircraft component  154  may be a part of the tail section  12  of the jet aircraft  10 . 
     The aircraft component  154  is contemplated to include a plurality of pad-up areas  156 . For simplicity, the pad-up areas  156  include first pad-up areas  158  and second pad-up areas  160 . The first pad-up areas  158  are contemplated to extend along the longitudinal direction  162  (i.e., a first fiber orientation). The second pad-up areas are contemplated to extend along the lateral direction  164  of the aircraft component  154  (i.e., a second fiber orientation). The pad-up areas  158 ,  160  are contemplated to comprise a plurality of tows that are laid onto the laminate or curved surface  166  in one or more of the manners described hereinabove. 
       FIG. 15  is a view of the aircraft component  154  illustrated in  FIG. 14 . In this view, the longitudinal axis  168  of the aircraft component  154  is included as a reference tool. It is noted that the first pad-up area  158  is illustrated as being substantially parallel to the longitudinal axis  168 . Accordingly, the second pad-up areas  160  are shown as being orthogonal to the first pad-up areas  158 . It is noted that the illustration of the first pad-up areas  158  as being disposed along the longitudinal axis and the orientation of the second pad-up areas as being orthogonal to the first pad-up areas  158  is merely illustrative. The pad-up areas  158 ,  160  may have any orientation with respect to the longitudinal axis  168  without departing from the scope of the present invention. 
       FIG. 16  provides an enlarged detail of a portion of the aircraft component  154  that is illustrated in  FIGS. 14 and 15 . The first pad-up areas  158  are laid as a plurality of first tows  170  by an AFP machine. The second pad-up areas  160  also are laid as a plurality of second tows  172  by an AFP machine. The tows  170 ,  172  cross each other at intersecting areas  174 , which may or may not include overlapping tows  170 ,  172 . The first plurality of tows  170  are disposed at an angle  176  from the longitudinal axis  168 . 
     With continued reference to  FIG. 16 , it is noted that the first plurality of tows  170  are disposed at the angle  176  because the aircraft component  154  has a curved shaped in three dimensions. This deviation angle  176  should be understood by those skilled in the art as being a direction in which the tows  170  are “steered” to form the first pad-up area  158 . 
     For purposes of the present invention, “steering” refers to the ability of the AFP machine to direct the tows  170  in a direction that deviates, by the deviation angle  176 , from the reference axis, in this case the longitudinal axis  168 . Steering permits the AFP machine to establish changes in the direction of the first pad-up area  158  to accommodate changes in the curvature of the surface of the aircraft component  154 . 
       FIG. 17  is a perspective illustration of the interior surface  178  of the aircraft component  154  illustrated in  FIGS. 14-16 . The first plurality of tows  170  are illustrated as being steered across the interior surface  178 , in the manner discussed above. 
       FIG. 18  is a top view of another embodiment of an aircraft structure  180  according to the present invention.  FIG. 19  is a perspective view of the aircraft structure  180  illustrated in  FIG. 18 . As made apparent from the illustrations in  FIGS. 18 and 19 , the aircraft structure  180  has a curved structure and appears somewhat like a turtle shell. The aircraft structure  180  is referred to as a “pressure shell,” because it assists with maintaining suitable cabin pressure when the jet aircraft  10  is in a flight mode of operation. The aircraft structure  180  is contemplated to include pad-ups  182 , interstitial areas  184 , and openings  186  therethrough. 
     To construct the aircraft structure  180 , it is contemplated that the lattice pattern of pad-up areas comprise first pad-up areas  188  (a portion of which are delineated in  FIG. 18 ) and second pad-up areas  190  (a portion of which are delineated in  FIG. 18 ) that may be applied to a component in a tortoise shell manner, such that the first pad-up areas  188  are provided as substantially concentric wheels and the second pad-up areas  190  are provided as spokes that intersect the wheels. After a sufficient number of tows are layered on top of one another, the final structure of the aircraft structure  180  is produced. 
     Consistent with other embodiments, constructing the aircraft structure  180  with first pad-up areas  188  and second pad-up areas  190  that intersect at intersecting areas  192  results in an aircraft component  180  with suitable strength in the load bearing directions of the structure. It is noted that the aircraft component includes interstitial areas  184  that are between the pad-up areas  188 ,  190 , as illustrated in other embodiments. As a pressure shell, the aircraft component  180  is provided with beneficial strength properties in the directions of the pad-up areas  188 ,  190 . 
     As for the prepreg composite material from which the tows are made, as noted above, it is contemplated that the individual tows have a width of about 0.25 inches (or 0.64 cm). While this dimension is contemplated to be applied to all of the embodiments described herein, the present invention should not be understood to be limited to tows with this width. For the present invention, the tows may have widths of 0.5 in. (1.27 cm), 0.75 in. (1.91 cm), 1 in. (2.54 cm), 2 in. (5.08 cm), for example. The present invention is not contemplated to be limited to tows with any particular width or other physical characteristics. 
     As noted above, the present invention is contemplated to employ carbon fiber materials that are pre-impregnated with resin. However, the present invention should not be understood to be limited to this material. To the contrary, the present invention is contemplated to find applicability to any number of different composite materials. 
     In addition, while the present invention contemplated that an AFP machine will be employed to create the pad-up areas  100 ,  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 ,  118  discussed in connection with  FIGS. 9-13 , the present invention is not intended to be limited thereto. Other types of machines may be employed to build-up the pad-up areas  100 ,  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 ,  118  without departing from the scope of the present invention. 
     Concerning the fiber orientations  124 ,  128 ,  140 ,  152 , it is contemplated that they will be oriented with respect to a 0° direction established by the laminate. In other words, the fiber orientations  124 ,  128 ,  140 ,  152  of the pad-up areas  100 ,  102 ,  104 ,  106 ,  108 ,  110 ,  112 ,  114 ,  116 ,  118  will be set according to the primary orientation established by the laminate. While not critical to operation of the present invention, it is contemplated that the 0° orientation will be consistent with the longitudinal axis of the aircraft. 
     As noted above, and as should be apparent from the discussion of steered tows in connection with  FIGS. 16-17 , any discussion of the “longitudinal” or “lateral” direction should not be understood as limiting the present invention to orientations that are parallel to the longitudinal axis of the jet aircraft  10  or any other axes orthogonal thereto. The terms “longitudinal” and “lateral” have been used herein to facilitate, but not limit, the description of the present invention. 
     With respect to the present invention, as noted above, the fiber orientations are contemplated to extend in directions that are parallel (or substantially parallel) to the lengths of the associated tows. With this fiber orientation, the tows are laid, for the most part, in directions that are parallel to the travel directions of the pad-up areas created therewith, and as such, extending along the lengths of the respective pad-up areas. As a result, it is contemplated that the pad-ups will provide sufficient strength to perform as required or as desired. 
     As should be apparent from the foregoing, by employing tows to create the pad-up areas, it becomes possible to control strictly the final weight of the aircraft component created thereby. As may be apparent, each tow adds a very small amount of weight to the aircraft component but greatly strengthens that same aircraft component. By laying the tows in a layer by layer fashion, it becomes possible to create an aircraft component with considerable strength properties but also with reduced weight by comparison with an equivalent aircraft component made from aluminum or an aluminum alloy. This weight savings contributes to an overall weight savings for the jet aircraft  10  as a whole. 
     In addition, given that each pad-up ply includes first pad-up areas and second pad-up areas that have respective different fiber directions, less plies can be used to build the pad-ups than in the case where a single pad-up ply includes fibers in only a single fiber direction. It is contemplated that fewer plies includes, but is not limited to, embodiments where there is less material used, less fiber material used, and/or fewer tows, among others More specifically, the pad-up plies according to the present invention provide similar fiber strength properties to what previously required two separate pad-up plies. Therefore, less plies can be used, thereby saving weight. 
     In addition, by laying the tows along the directions of their respective pad-up areas, it is contemplated that the AFP machine itself will benefit from enhanced efficiencies. As may be apparent to those skilled in the art, AFP machines are well-suited to lay tows in a line, whether steered or not. As such, there is an increased efficiency in instances where the tows may be laid in long strips rather than in short segments. The greater the distance traversed by the AFP machine in a single direction, the greater the operational efficiency of the AFP machine. 
     In connection with the positioning of the first and second pad-up areas described above, it is noted that the second pad-up areas are described as being orthogonally disposed, or substantially orthogonally disposed with respect to the first pad-up areas. The orthogonal orientation of the first and second pad-up areas is contemplated to establish a lattice pattern that enhances the strength properties of the aircraft component on which the first and second pad-up areas are disposed. As should be apparent to those skilled in the art, the overall strength properties of the aircraft component are further enhanced by the attachment of the structural elements to the pad-up areas. 
     It is noted that the first and second pad-up areas are contemplated to be disposed along a load path of the aircraft component. More specifically, first load paths of the aircraft component are contemplated to lie along a longitudinal axis of the aircraft component, which may or may not align with the longitudinal axis of the jet aircraft  10 . Second load paths of the aircraft component are contemplated to extend orthogonally to the first load paths. In the preceding discussion, this may be consistent with a lateral axis or a circumferential direction associated with the aircraft component. 
     It is noted that the first and second load paths are not intended to be limiting of the present invention. There are instances, particularly in the construction of the wings and control elements of the jet aircraft  10  where first and second load paths merge and/or are indistinguishable from one another. The present invention is intended to encompass the greatest breadth and, therefore, is not limited to the exemplary orientations of the first and second load paths discussed herein. 
     As noted above, the first and second pad-up areas intersect with one another, either in an overlapping or a non-overlapping manner, to form a lattice structure, which enhances the strength properties of the aircraft component. As discussed above, the first and second pad-up areas may intersect one another at an intersection area. The first and second pad-up areas my overlap or may not overlap one another. Regardless of whether or not the first and second pad-up areas overlap one another, the first and second pad-up areas are contemplated to for a single pad-up ply, as discussed. Multiple pad-up plies are stacked on top of one another, as illustrated in  FIG. 9 . The difference plies are contemplated to include tows at varying angular displacements, as discussed in connection at least with  FIG. 9 . 
     As noted above, the embodiment(s) described herein are intended to be exemplary of the wide breadth of the present invention. Variations and equivalents of the described embodiment(s) are intended to be encompassed by the present invention, as if described herein.