Patent Publication Number: US-2015078891-A1

Title: Hoop Tow Modification for a Fabric Preform for a Composite Component

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 13/333,645 filed Dec. 21, 2011, the disclosure of which is hereby incorporated by reference in its entirety. 
    
    
     STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not applicable. 
     FIELD OF THE INVENTION 
     This disclosure relates to the formation of fabric preforms for composite components. In particular, this application relates to manipulation of a fabric to improve fabric preform quality. 
     BACKGROUND OF THE INVENTION 
     Composite components are often used in applications in which having a high strength-to-weight ratio is important such as, for example, aircraft components. Many structural composite components can be made by wrapping a high-strength fabric around a form to create what is known as a fabric preform, applying a resin to the fabric preform, and then curing the resin to form the final composite component. 
     Certain features, however, are problematic to form. For example, in a fan containment case with one or more end flanges, the end flanges typically must be separately formed from the remainder of the cylindrical body. Because fan containment cases are often made with a tri-axial fabric (hoop tows in a first direction and bias tows in two other directions) to increase strength, it is not trivial to form the end flanges with the same piece of fabric used to form the cylindrical or near-cylindrical body. 
     Traditional methods of forming an end flange are (1) including recurring linear darts in each ply, (2) eliminating hoop tows and allowing the bias tows to shear, and (3) adding a separate flange detail. However, all of these approaches add cost and weight since they generally require more material to reinforce the flange. 
     Hence, a need exists for improved ways to form fabric preforms with features that require high amounts of fabric shear without significantly compromising the structural integrity of the resultant component. 
     SUMMARY OF THE INVENTION 
     An improved fabric preform is disclosed that enables enhanced deformation of fabric without total elimination of hoop tows. In order to do this, at least some of the axial tows or hoop tows in the fabric are modified to have segments that are separable from one another within the fabric sheet. Upon the application of deformation to the fabric, the segments of the hoop tows can separate from one another to accommodate this change. However, the segments can still be substantially retained in the deformed portions of the fabric and can structurally reinforce these regions. 
     A fabric preform for a composite component is formed from a fabric having a plurality of hoop tows and a plurality of bi-axial tows. One end of the fabric is received on the form such that the hoop tows of the fabric extend in a direction generally perpendicular to a central axis of the form. The fabric is wrapped around the form by rotating the fabric and the form relative to one another about the central axis of the form. At least some of the hoop tows are separated into hoop tow segments while the fabric is under a tension during wrapping to enable a space to develop between ends of adjacent hoop tow segments along the length of the hoop tow. By separating at least some of the hoop tows into hoop tow segments to enable spaces to develop between adjacent hoop tow segments, increased deformation of the fabric is accommodated during formation of the fabric preform. This occurs while still maintaining a presence of hoop tow segments in at least portions of the fabric. 
     The separation of the hoop tows can facilitate deformation of the fabric. In some forms, this improved fabric deformation can be exploited to create a feature that extends at least in part in a radial direction away from the central axis of the form such as, for example, a flange. Accordingly, this method can be particularly beneficial for the formation of components such as fan containment cases, which have features, curvatures, and flanges that can demand increased amounts of fabric deformation. 
     The fabric could be prepared for the separation of the hoop tows into hoop tow segments in a number of ways. At least some of the hoop tows could be stretch broken at periodic intervals to define the hoop tow segments. In some forms, the method could further include the step of cutting the hoop tows at periodic intervals to define the hoop tow segments. This cutting may be performed by a device that separates the bias fibers surrounding a hoop tow at a point to be cut and then cutting at the point to be cut. A tool may be used to cut the hoop tows at periodic intervals and this tool may include a rolling drum and/or a punching tool. Other means or multiple different means of preparing the hoop tows for separation could also be employed. Moreover, in some instances, some of the hoop tows may not be separated or even be prepared to be separated. 
     In some embodiments, adjacent hoop tows may be arranged so that points of separation in the adjacent hoop tows are out of phase from adjacent hoop tows along the direction of hoop tow extension. In this way, a separation gap between two hoop tow segments in one hoop tow may be supported by the presence of a hoop tow segment in an adjacent hoop tow. To insure the segments do not become too small to be retained in the fabric, the length of the hoop tow segments may be configured to not be less than 10 times the width of a hoop tow. 
     A method of forming the fabric preform for a composite component and a composite component are also disclosed. The fabric preform and the composite component include a body formed from the fabric in which the body has a central axis extending there through. They also include at least one feature formed in the body in which at least some of the hoop tows in the feature are separated into hoop tow segments that are spaced from one another along the length of the hoop tow. In the instance of the composite component, the fabric of the fabric preform receives a resin to retain the tows of the fabric in place. 
     The feature formed in the body with the separated hoop tows may extend, at least in part, in a radial direction away from the central axis. This feature may be, for example, a flange; however, the feature could be something other than a flange. It is contemplated that the separation of the hoop tows is of particular benefit in forming features in which relatively high amounts of fabric deformation are imparted to the fabric in the formation of the feature. As noted above, it is contemplated that not all of the hoop tows need to be separable into hoop tow segments. In some instances, some of the hoop tows may not be prepared for separation and, even if they are, they need not all be separated. 
     This technology may be used in the formation of a wide array of fabric preforms and composite components. One particular application would be in the formation of a composite component for a fan containment case (or in making a fabric preform which is a precursor to the composite component for the fan containment case). 
     These and still other advantages of the invention will be apparent from the detailed description and drawings. What follows is merely a description of some preferred embodiments of the present invention. To assess the full scope of the invention the claims should be looked to as these preferred embodiments are not intended to be the only embodiments within the scope of the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a partial cross-sectional side view of a turbofan engine including a fan containment case and a fan case; 
         FIG. 2  is one embodiment of a fabric preform for a fan containment case or fan case; 
         FIG. 3  is a fan containment case or fan case similar to  FIG. 2 , but after flanges have been formed at the axial ends of the generally tubular body; 
         FIG. 4  is a partial view of the fabric preform of  FIG. 2  with a cross section taken there through; 
         FIG. 5  is a partial view of the fan containment case or fan case of  FIG. 3  with a cross section taken there through; 
         FIG. 6  illustrates a tri-axial fabric material that can be used to fabricate fabric preforms and composite components; 
         FIG. 7  is a detailed view of a segment of tri-axial fabric in which the axial or hoop tows extend from the end of the fabric; 
         FIG. 8  is a cross-sectional side view of the tri-axial fabric; 
         FIG. 9  is an illustration of a schematic for an apparatus used to form a fabric preform while separately tensioning each of the axial tows; 
         FIG. 10  is one embodiment of an intermediate connector that may be used to connect an axial tow to a tensioning mechanism; 
         FIG. 11  illustrates the fabric with edge strips for directing the bias tows in the fabric; 
         FIG. 12  is a detailed view of the edge strips attached to the fabric as in  FIG. 11  that provides further detail about the attachment of the edge strips to the bi-axial tows; 
         FIG. 13  is an apparatus for periodically cutting or severing the axial tows; 
         FIG. 14  is a side view of a portion of a flange that illustrates the placement and spacing of some of the hoop tow segments; 
         FIG. 15  is a side view of an apparatus that enables the continuous application of pressure during wrapping of the fabric preform by drawing a film against the preform using a vacuum; 
         FIG. 16  is a partial perspective view of the apparatus of  FIG. 15  in which the various elements of the apparatus in the form are illustrated in greater detail; and 
         FIG. 17  is a cross-sectional view of the apparatus of  FIG. 15  in which there is a sliding seal between a rotating portion of the form and a fixed portion connected to a vacuum. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     This disclosure is directed at improved methods of producing fabric preforms that can be further processed to make composite components or parts. Typically, once the fabric preform is wrapped, resin can be introduced into the fabric preform to form a composite component. This resin could be provided in any of a number of ways including, but not limited to, injection molding and transfer molding such as resin transfer molding (RTM) and vacuum-assisted resin transfer molding (VARTM). After curing the resin, the high-strength fibers of the fabric are held in place within the resin matrix to provide the composite material. 
     In this detailed description, some specific embodiments of fabric preforms and composite components are provided in which composite components for aircraft are described. However, the illustrated preforms and components should not be construed as the only preforms and components to which the recited methods are applicable. The methods described herein might also be used to make non-aircraft composite components, as well as any other process in which fabric is wrapped around a form to create a fabric preform. 
     Referring first to  FIG. 1 , a portion of a turbofan engine  10  for an aircraft is illustrated. This turbofan engine  10  includes a fan assembly  12  that is rotatable about a central axis A-A of the turbofan engine  10  to intake air and, ultimately, produce propulsion. The fan assembly  12  has a central rotor  14  that extends along the central axis A-A and includes a plurality of blades  16  that extend generally radially outward from the central rotor  14 . 
     This fan assembly  12  is surrounded, at least in part, by a fan containment case  18 . This fan containment case  18  is made of a high-strength composite material such as a fabric encased in a resin. For aircraft components, the fabric may be made of a carbon fiber material and the resin may be an epoxy or a high-temperature resin such as bismaleimide or polyamide to make an extremely strong and rigid component that is stable at high temperatures. However, other fabrics and resin material might be used depending on the demands of the application. Some of the materials that may be used to construct composite materials will be discussed in further detail below. 
     The fan containment case  18  helps to prevent any projectiles from radially exiting the turbofan engine  10  in a direction that could damage the engine  10  or the aircraft. For example, if one of the blades  16  of the fan assembly  12  fails in a “blade out” event in which some or all of a blade  16  breaks from the central rotor  14 , then the fan containment case  18  helps to contain the fractured portion of the blade  16 . Likewise, if an outside object is sucked into the turbo engine  10  during gas intake, then the fan containment case  18  can prevent a potentially catastrophic event from occurring if this item is shot radially outward after it contacts the blade  16 . 
       FIG. 1  also shows a fan case  19  attached behind the fan containment case  18 . This fan case  19  can be made of similar materials to the fan containment case  18  and continues the duct within which the engine bypass air flows. 
     Turning now to  FIGS. 2 through 5 , a fabric preform  20  for a fan containment case  18  having an axis B-B is illustrated before and after flanges  22  are formed on the axial ends  24  and  26 . The fabric preform  20  has a generally tubular body  28  extending between the two axial ends  24  and  26 . The body  28  includes a radially-inward facing surface  30  that contacts a form or mandrel during formation and a radially-outward facing surface  32 . In the particular embodiment shown, the body  28  includes a joggle or a portion of curvature  34  that separates the body  28  of the fan containment case  18  into two sections  36  and  38  of different diameter or radius. These sections  36  and  38  of differing diameters can help to accommodate a particular position of the blades  16  (as seen, for example, in  FIG. 1 ) and may also serve to direct the air flow through the turbofan engine  10 . This joggle or portion of curvature  34  conceptually is a feature of the body  28  that extends, at least in part, in the radial direction. 
     As best seen in  FIGS. 2 and 4 , the fabric preform  20  for the fan containment case  18  may be formed such that the axial ends  24  and  26  are thinner than the remainder of the generally tubular body  28  to define precursor flange regions  40  on the axial ends  24  and  26 . Before the introduction of the resin, these precursor flange regions  40  might be bent upward at the line  41  on  FIG. 4  to form the flanges  22  that are used to attach the fan containment case  18  to adjacent components in the final assembly. It is likewise possible that these precursor flange regions  40  might be bent downward at the line  41  on  FIG. 4  to form the flanges  22 . However, it is also contemplated that by employing the fabric manipulation techniques below, that the flanges  22  might be formed concurrently with the wrapping of the fabric. It is likewise possible to conceive of a design that has only one flange at either end  24  or  26 , or no flanges at all. 
     The fabric preform  20  for the fan containment case  18  includes multiple wrapped layers of fabric. The thickness of the fan containment case  18  is dictated in part by the number of layers of fabric and the thickness of the fabric. However, the quality of the wrapping and bulkiness of the fabric will also affect the thickness of the fabric preform  20  and the resultant composite component. For example, a fabric preform that is thoroughly debulked will typically have an average thickness that is less than a fabric preform that is not thoroughly debulked because imperfections in the wrapping of the fabric can create irregular regions. 
     To provide some understanding of the fiber structure of the fabric preform  20  in the fan containment case  18 , a description of one preferred fabric for forming the fabric preform  20  is now described in greater detail with additional reference to  FIGS. 6 through 8 . In  FIGS. 6 through 8 , a tri-axial fabric  42  is shown as including various tows of the fabric material which are braided together to form a fabric sheet  44 . The tri-axial fabric  42  includes a plurality of hoop or axial tows  46  and a plurality of bi-axial tows  48  and  50 . 
     As used herein, tows refer to a bundle of fibers or filaments so arranged as to form a continuous length of material. Typically, for aircraft composite structures, such tows are made of carbon fibers or graphite, which have excellent strength for their weight. 
     The hoop or axial tows  46  are arranged to be generally parallel with one another. For the sake of clarity, these tows  46  extend in a direction that is generally parallel with the direction of travel of the fabric sheet  44  as the fabric sheet  44  is wrapped around a form or mandrel. Therefore, in the context of the fabric feeding or wrapping, these tows may be said to be axial. Because these tows  46  are then wrapped about a central axis of the form or mandrel, these tows  46  may also be referred to as “hoop tows” because they extend around the form in the hoop direction once the fabric  44  is laid onto the form. 
     The plurality of bi-axial tows  48  and  50  include two sets of tows that are oriented at a positive angle from the axial tows  46  and at a negative angle from the axial tows  46 , respectively. The bi-axial tows  48  and  50  are alternatively passed over and under axial tows  46  to form the fabric sheet  44  as is best illustrated in  FIG. 8  so as to form a braid in the fabric sheet. This means that the axial tows  46  extend roughly linearly through the fabric sheet  44 . When the fabric sheet  44  is laid flat, each of the sets of bi-axial tows  48  and  50  are generally parallel with one another (i.e., the various tows in the first set of bi-axial tows  48  are parallel with one another and the various tows in the second set of bi-axial tows  50  are parallel with one another). 
     Although a tri-axial fabric has been described and provides the base material for the production of the fabric preform  20  illustrated in the example composite component of a fan containment case  18 , it is contemplated that other types of fabric might be used with some of the methods described herein. Accordingly, it should be understood that other types of fabric might be used, although some techniques may be inherently limited by the characteristics of the fabric. For example, the separate and independent tensioning of hoop tows might not be readily practiced if the fabric does not contain axial tows. 
     Returning now to  FIGS. 2 through 5  and more specifically with reference to  FIGS. 4 and 5 , multiple layers of the tri-axial fabric  42  are wrapped upon one another to create the fabric preform  20 . The tri-axial fabric  42  is disposed in the fabric preform  20  such that the axial tows  46  extend along the hoop direction of the fabric preform  20  and are generally perpendicular to the axis B-B, while the bi-axial tows  48  and  58  are generally helically disposed around the generally tubular body  28 . 
     Generally, to form the fabric preform  20 , one end of the fabric  44  is received on the form such that the axial tows of the fabric extend in a direction generally perpendicular to the central axis of the form. The fabric  44  is then wrapped about the form, normally by the rotation of the form pulling the fabric  44  onto the form, to lay down the layers of the fabric  44  (although it is possible that the free end of the fabric may be orbited around the form either while the form is held stationary or while the form also rotates). During this wrapping, the fabric  44  might be periodically debulked or could be continuously debulked using the apparatus and process described below. 
     To form the comparably thinner sections of the precursor flange regions  40 , the fabric  42  might be cut prior to being laid on the form. In this way, fewer layers of the tri-axial fabric  42  are laid down on the axial ends of the form. 
     Now, various improvements to the wrapping process will be described that can help to provide a fabric preform with a fiber architecture that promotes the formation of a strong composite component. The described methods provide for better control of the fabric during the wrapping process and for improved continuous debulking of the preform as it is wrapped. This means that the resultant fabric preform is more tightly wrapped, has less bulk than preforms made using conventional wrapping, and has fewer wrinkles and waviness in the as-wrapped fabric preform. When the composite component is formed by application of resin to the preform, the final composite component has a higher fabric-to-resin volume ratio (also known as fiber volume ratio or fiber fraction) which improves the strength to weight ratio of the composite and provides a more consistent fiber structure within the composite component. 
     Turning to  FIG. 9 , an apparatus  52  is shown that can be used to wrap the fabric  44  around a form  54  while simultaneously tensioning each of the axial or hoop tows  46  separately and independently from each other. The apparatus  52  includes the form  54  having a central or rotational axis C-C and a table  56  spaced from the form  54  that supports a plurality of separate tensioning mechanisms  58 . 
     In the embodiment illustrated, the form  54  is a rotatable mandrel that receives one end of the fabric  44  there on. The reception of the end of fabric  44  could be made in any of a number of ways including, for example, attachment of one end of the fabric  44  to the form  54  by taping, adhesive, fasteners, clamping, or so forth. The fabric  44  could also be received on the form  54  by wrapping the fabric  44  around the form  54  at least one full rotation and then holding the fabric  44  taut such that the tension of the fabric  44  wrapped over itself holds the fabric  44  on the form  54 . 
     As shown, the form  54  has a cylindrical shape (i.e., having a constant radius over the axial length of the form  54  onto which the fabric is wrapped thereby defining an outwardly-facing cylindrical surface  60  centered about the axis C-C). However, in other embodiments, the form  54  could have a different shape. For example, the form could have a square or rectangular cross section which would result in a tubular rectangular shape for the fabric preform. In another example, the form could have a radius that varies over at least a portion of the axial length of the form. This variable radius could be used to form a joggle or a like, such as is found on the fan containment case  18  depicted in  FIG. 1 . 
     Looking at the other half of the apparatus  52 , the tensioning mechanisms  58  are fanned out or spread out across the table  56 . Each of the tensioning mechanisms  58  have a line  62  that feeds out there from. These lines  62  are each coupled to one of the axial tows  46  on a free end  64  of the fabric  44  (that is, the end of the fabric  44  opposite to the end of the fabric  44  that is initially wrapped around or received on the form  54  such that the axial tows  46  extend from one end to the other). The lines  62  from the tensioning mechanisms  58  are fed through a guide or comb  66  such that the each of the lines  62  are generally collinear with a corresponding axial tow  46  to which a line  62  is coupled. In this way, each of the tensioning mechanisms  58 , which are considerably larger than the size of the axial tows  46 , can be spaced apart from one another on the table  56  and provide ample clearance for the running of the lines  62 . 
     In the illustrated embodiment of  FIG. 9 , each of the tensioning mechanisms  58  is a magnetic clutch. Each of the magnetic clutches have a spool that feeds the line  62  out there from. During this feed out of the line  62 , the magnetic clutch provides controlled resistance against the rotation of the spool as the line  62  is pulled or unwound from the spool. Because each line  62  is attached to an axial tow  46 , as will be described in greater detail below, each of the axial tows  46  are separately and independently tensioned and paid out. 
     As used herein, for an axial tow to be “separately tensioned” means that the axial tow is tensioned apart from at least some of the other axial tows in the fabric. In one preferred embodiment, each and every one of the axial tows of the fabric are separately tensioned from one another. This separate tensioning can result in one or more of the axial tows  46  slipping within the bi-axial tows  48  and  50  of the fabric  44 . However, in other forms the separate tensioning of the axial tows may be performed in groups. For example, two or more axial tows might be tensioned apart from the other tows. This may be beneficial to minimize the size and/or cost of the apparatus. Individually paid out means that the tows can be paid out in different lengths. One tow may be fed at a different rate than another tow, at least for a period of time. 
     Returning now to the illustrated embodiment of the apparatus  52  in  FIG. 9 , although the individual axial tows  46  are separately tensioned, this does not necessarily mean that each of the axial tows  46  receives a different tension. In fact, the tensioning mechanisms  58  may be set to provide the same tension or substantially the same tension to each of the axial tows  46 . Due to either differences in the fabric  44  itself, or in the shape of the form  54  over its axial length, separately maintaining a constant axial tension over the various axial tows  46  can result in a differential pay out of the axial tows  46  in the fabric  44 . In contrast, if the fabric  44  was clamped across its entire width, then the clamping force would inhibit the movement or individual pay out of the axial tows  46  of the fabric  46  relative to one another. 
     The ability for the axial tows  46  to pay out differentially can be used to improve the quality and consistency of the fabric preform  20 . Whereas a singularly tensioned fabric needs to be very carefully aligned with respect to the form to prevent uneven wrapping of the fabric, the disclosed apparatus  52  is more forgiving and greater misalignment can be accommodated. Additionally, because the axial tows  46  can slip relative to one another, a form having different cross sections over its width might be better accommodated because the axial tows  46  being wrapped around a portion of the form having a shorter periphery can pay out more than the axial tows  46  being wrapped around a portion of the form having a longer periphery. This might be the case for a form that is used to produce the fabric preform  20  for the fan containment case  18  that is illustrated in  FIGS. 1 through 5 . 
     It is contemplated that the lines  62  from the tensioning mechanisms  58  might be directly connected to the axial tows  46  or that the axial tows  46  might be connected to the lines  62  via an intermediate connector. When an intermediate connector is used, the intermediate connector may attach to both the line  62  and to the axial tow  46 . By using some kind of linkage, the connection of the intermediate connector to the corresponding line  62  can be made in such a manner as to preserve the integrity of the line  62 . While a direct connection might involve knotting or adherence of the line to the axial tow and can be difficult to reverse without sacrificing some length of the line, an intermediate connector could be used to reversibly connect an axial tow  46  to a line  62 . 
     One type of intermediate connector  68  is partially illustrated in  FIG. 10 . This intermediate connector  68  includes a pair of pads  70  with apertures  72 . The pads  70  can be disposed on either side of an end  74  of an axial tow  46  and then put together to sandwich the end  74  of the axial tow  46  there between. In some forms, the pads  70  could be used in conjunction with adhesive to attach to the axial tow  46 . In other forms, one or more of the pads  70  might be magnetically attracted toward one another. In still other forms, a mechanical pressure might be applied to the pads  70  such that they pinch the end  74  of the axial tow  46 . A hook  76  tied to the end of the line  62  can then be directed through the aperture  72  in the pads  70  to temporarily link the pads  70  to the lines  62  of the tensioning mechanisms  58 . 
     Because the fabric is more densely wrapped than in a fabric preform not formed by separately tensioning at least some of the plurality of axial tows, a higher fabric-to-resin volumetric ratio can be realized in the composite component formed after resin is applied to the fabric preform. 
     Referring now to  FIGS. 11 and 12 , edge strips  78   a ,  78   b ,  78   c , and  78   d  are shown which can be attached to ends of the bi-axial tows  48  and  50  of the fabric  44 . When attached to the ends of the bi-axial tows  48  and  50 , these edge strips  78   a ,  78   b ,  78   c , and  78   d  can be moved to better control shear angles within the fabric and to steer the various tows. This represents yet another mode of manipulating the fabric  44  before and during wrapping of the fabric preform  20  to control the fiber structure. 
     Each of the edge strips  78   a ,  78   b ,  78   c , and  78   d  are attached to ends of one of the sets of bi-axial tows  48  or  50  on one of the lateral edges  80  and  82  of the fabric  44 . The lateral edges  80  and  82  are “lateral” relative to the feed direction (depicted by arrow D in  FIG. 11 ) of the fabric  44  onto the form  54 , which is generally perpendicular to its rotation axis C-C. In the form illustrated, edge strip  78   a  is attached to the ends of the first set of bi-axial tows  48  and edge strip  78   b  is attached to the ends of the second set of bi-axial tows  50  on the lateral edge  80  of the fabric  44  as can be seen in  FIG. 12 . On the other lateral edge  82  of the fabric  44  (which is opposite the first lateral edge  80 ), the edge strip  76   c  is attached to the other ends of the first set of bi-axial tows  48  and the edge strip  76   d  is attached to the other ends of the second set of bi-axial tows  50 . 
     Edge strips  78   a ,  78   b ,  78   c , and  78   d  could be attached to the ends of the respective set of tows in any of a number of ways. For example, the edge strips  78   a ,  78   b ,  78   c , and  78   d  may be adhered to the tows. In another example, the edge strips  78   a ,  78   b ,  78   c , and  78   d  may each include multiple components that clamp together under an applied force to grasp the ends of the tows. 
     In the embodiment illustrated, the edge strips  78   a ,  78   b ,  78   c , and  78   d  each have a row of openings  84  formed therein that can be, for example, engaged by a line of hooks to selectively and independently move the edge strips  78   a ,  78   b ,  78   c , and  78   d . Such hooks might be used to move the edge strips  78   a ,  78   b ,  78   c , and  78   d  forward or backward relative to the fabric  44  (i.e., parallel or anti-parallel to the direction of arrow D, respectively) and/or laterally outward with respect to the fabric  44  (i.e., perpendicular to the direction of arrow D in the plane of the fabric  44 ). Other or alternative means of engagement of the edge strips  78   a ,  78   b ,  78   c , and  78   d  might also be used, such as, but not limited to, sprockets. 
     These edge strips  78   a ,  78   b ,  78   c , and  78   d  can be controlled independently of one another. Because they are attached to two sets of bias tows (which are, in the form illustrated, the first and second sets of bi-axial tows  48  and  50 ), the first set of bias tows can be controlled independently of the second set of bias tows by the four edge strips  78   a ,  78   b ,  78   c , and  78   d . By moving one or more of the edge strips  78   a ,  78   b ,  78   c , and  78   d , the attached set of bi-axial tows  48  and  50  can be directed before and/or during wrapping of the fabric  44  around the form  54  to create the fabric preform  20 . This directing of the bi-axial tows  48  and  50  might be used to steer tows for performance purposes or to otherwise induce shear or stress in the fabric  44  in a manner that is beneficial during the formation of the fabric preform  20  and the resultant composite component. 
     It should be appreciated that in order to fully steer a bi-axial tow as it is wrapped onto a form, it may be desirable to maintain the force on the edge strips until the entire tow is placed on the form. Accordingly, it may be the case that the end of a bi-axial tow that is first received on the form may be held until the second end is also received on the form. Because the bi-axial or bias tows are at an angle relative to the feed direction of the fabric, this may mean that the tows need to be held for some distance after they are received on the form. 
     A number of examples of movements of the edge strips  78   a ,  78   b ,  78   c , and  78   d  are now described to highlight potential ways in which the fabric  44  might be manipulated. The examples are intended to be illustrative, but not the only examples of how the edge strips  78   a ,  78   b ,  78   c , and  78   d  might be employed. 
     To induce stress or shear in the fabric  44 , one or more of the edge strips  78   a ,  78   b ,  78   c , and  78   d  might be advanced or retarded relative to the fabric  44  to control the orientation of the respectively attached set of tows and to change the angle between the first set of bias tows and the second set of bias tows. For example, the edge strip  78   a  could be advanced relative to the feed direction D of the fabric  44  along a direction indicated by arrow A and the edge strip  78   c  retarded relative to the feed direction D of the fabric  44  along a direction indicated by arrow R to sharpen the angle between the axial tows  46  and the first set of bi-axial tows  48 . This might result in shift in this set of bi-axial tows  48  from −60 degrees to −50 degrees, for example. Simultaneously, the edge strip  78   b  might be retarded relative to the feed direction D of the fabric  44  and the edge strip  78   d  might be advanced relative to the feed direction D of the fabric  44  to sharpen the angle between the axial tows  46  and the second set of bi-axial tows  50 . Again, this might be a change from +60 degrees to +50 degrees. This has the effect of narrowing the fabric  44  and scissoring the bi-axial tows  48  and  50  to reduce the lateral spacing between the axial tows  46 . This may result in differential spacing of the axial tows  46  depending on the shape of the form  54  and the amount of localized shear induced in the fabric  44 . 
     Alternatively, each of the edge strips  78   a ,  78   b ,  78   c , and  78   d  could be moved in the opposite direction (i.e., advanced rather than retarded and vise-versa), to cause the bi-axial tows  48  and  50  to have angles that become larger with respect to the axial tows  46 . This results in the fabric  44  effectively becoming wider under the applied movement of the edge strips  78   a ,  78   b ,  78   c , and  78   d.    
     In another example, the edge strips  78   a ,  78   b ,  78   c , and  78   d  may be pulled laterally outwardly along a direction indicated by arrows L to maintain tautness over the width of the fabric  44 . This could be done with or separately from advancing or retarding the edge strips  78   a ,  78   b ,  78   c , and  78   d.    
     It is contemplated that each of the edge strips  78   a ,  78   b ,  78   c , and  78   d  could have a force applied thereto with a direction of applied force anywhere along an arc of 180 degrees in the plane of the fabric  44  from a pure advance direction A to a pure reverse direction R and that passes through the laterally outward direction L. Essentially, this means that a force having a combination of the (A or R) and/or L directions could be applied to each of the edge strips  78   a ,  78   b ,  78   c , and  78   d . This force or these forces could be applied as separately discrete vectors in the (A or R) and/or L directions or as a single combined vector depending on the apparatus that applies the force to the edge strips  78   a ,  78   b ,  78   c , and  78   d.    
     Ultimately, this means each of the edges strips  78   a ,  78   b ,  78   c , and  78   d  can be independently moved or held stationary relative to the direction and rate of fabric feed D to provide many modes of fabric manipulation. As noted above, each of the four edge strips  78   a ,  78   b ,  78   c , and  78   d  could be advanced, retarded, held stationary and/or moved laterally outward relative to fabric feed direction D. Moreover, the fore/aft movement for each of the edge strips  78   a ,  78   b ,  78   c , and  78   d  could be combined with a laterally outward force such as that each of the edge strips  78   a ,  78   b ,  78   c , and  78   d  could be pulled in any direction within 180 degrees in the plane of fabric. As all four edge strips  78   a ,  78   b ,  78   c , and  78   d  can be separately controlled this results in many combinations of potentially applied forces. 
     Although four edge strips  78   a ,  78   b ,  78   c , and  78   d  are illustrated, it is contemplated that fewer than four edge strips  78   a ,  78   b ,  78   c , and  78   d  might be used to steer or guide the tows. For example, a single edge strip might be used to guide or steer one end of a single set of tows. In another example, a pair of edge strips might be attached to only a single lateral edge of the fabric such that each of the edge strips are attached to one of the set of edges of each of the sets of the bias fibers. Then by advancing one and retarding the other of the edge strips, a localized shear can be induced in that side of the fabric. 
     This localized deformation of fabric can be exploited during wrapping of complex shapes. For example, if a joggle or some other feature is present on the form  54 , then the bias fibers can be controlled or directed to be better contoured to the surface (e.g., have fewer wrinkles, lay flatter on the form, etc.). This may be done, by example, by the selective inducement of shear to facilitate formation of a feature on the fabric preform  20 . 
     Moreover, by application of some amount of tension or force to the bias or bi-axial tows as the fabric  44  is laid down on the form  54 , this fabric shaping or contouring can be preserved or locked into the fabric  44  in the fabric preform  20 . This means that the fabric  44  can be coaxed into shapes and contours that would be difficult, if not impossible, to obtain using conventional wrapping techniques and then frozen into that configuration by further wrapping, which initially holds the underlying fibers in the stressed condition and, ultimately, the application of resin. Unless this shaping of the fabric is captured on the form during wrapping, the fabric will tend to flex back toward its original relatively generally planar state as the stress is naturally worked out of the fabric. 
     It should be appreciated that some consideration needs to be made to balancing the strength of the various applied forces to the fabric. The forces applied to the bias or bi-axial tows must be sufficiently great to overcome the forces used to keep the fabric taut in the feed or machine direction. If the forces applied to the bias or bi-axial tows of the fabric are too small, then it is possible that the strength of the forces used to keep the fabric taut will overcome them and neutralize their effect. 
     Accordingly, using this method, fabric preforms and composite components can be formed having heretofore unseen tow architecture in the as-laid fabrics. 
     In some embodiments, the fabric preform includes a first volume in which the first and second set of bias or bi-axial tows are disposed at a first angle relative to one another and a second volume in which the first and second set of bias or bi-axial tows are disposed at a second angle relative to one another in which the first angle is different than the second angle. This means the fabric may be selectively stretched over certain regions of the form to meet a selected geometry. 
     In other embodiments, the bias or bi-axial tows are under an induced stress by alteration of their orientation in comparison to a relaxed fabric and the induced stress is locked into the fabric preform during wrapping to maintain the orientation of the bias or bi-axial tows. This may result in induced stress or shear in the fabric of the preform, although this induced stress or shear could be uniform throughout the preform. 
     In some embodiments, features can be formed on the fabric preform that extend, at least in part, in a radial direction relative to a central axis of the fabric preform such as a joggle or change in diameter. 
     As noted above, any of the as-laid tow architectures could be locked into place by applying a resin to the fabric preform and curing it to form the composite component. 
     It should be appreciated that this edge manipulation of fabric might be practiced with any type of fabric having at least two sets of bias fibers. For example, it might be practiced with bias woven fabrics, bi-axial fabrics, and tri-axial fabrics. If the fabric is a tri-axial fabric  42  as described herein, then one of the two sets of bi-axial tows  48  can constitute the first set of bias tows and the other of the two sets of bi-axial tows  50  can constitute the second set of bias tows. In one preferred embodiment, the tows comprise the carbon fibers, which are commonly used in aircraft composite components. 
     A third method of manipulating the fabric to facilitate the formation of fabric preforms and their resultant composite components is now described. According to this third method, the fabric  44  wrapped around the form  54  has hoop tows  46  and these hoop tows  46  are capable of being separated into segments to permit improved flexure of the fabric  44 . This improved flexure as a result of hoop tow segment separation assists in forming features which require particularly high amounts of deformation or elongation (e.g., flange formation). 
     According to the general method, one end of the fabric  44  is received on the form  54  such that the hoop tows  46  of the fabric  44  extend in a direction generally perpendicular to a central axis C-C of the form  54  such as was generally depicted in  FIG. 9 . The fabric  44  is then wrapped around the form  54  by rotating the fabric  44  and the form  54  relative to one another about the central axis C-C of the form  54 . Either during wrapping or after wrapping, at least some of the hoop tows  46  are separated into hoop tow segments while the fabric  44  is under tension, stress, or shear. This separation enables spaces to form between the ends of adjacent hoop tow segments along the length of the hoop tow  46 . 
     Advantageously, by separating at least some of the hoop tows into hoop tow segments to enable spaces to develop between adjacent hoop tow segments, increased deformation of the fabric is accommodated during formation of the fabric preform. Moreover, this accommodation occurs while still maintaining a presence of hoop tow segments in at least portions of the fabric for strength. 
     Historically, in order to form features that require high levels of fabric deformation such as, for example, flanges  22 , the hoop tows  46  would be eliminated from the sections of the fabric  44  that would be formed into that feature. This is because the hoop tows  46  would typically inhibit the formation of a radially-extending feature such as a flange  22  to be formed, as the act of bending the precursor flange regions  40  into flanges  22  would be greatly resisted by the hoop tows  46  in the initial fabric preform  20 . However, the elimination of the hoop tows  46  left certain regions of the fabric preform  20  with only bi-axial tows  48  and  50  and made these regions comparably weaker to the rest of the part. 
     It has been found desirable to modify the fabric  44  so as to permit the hoop tows  46  to selectively separate under tensions, stresses, or shear, so that hoop tows  46  can be maintained in regions of the composite component such as flanges without impairing the ability of the feature to be formed in the first instance. 
     The hoop tows  46  may be made separable by preparing the fabric  44  prior to wrapping. In some embodiments, at least some of the hoop tows  46  are stretch broken at periodic intervals to define the hoop tow segments. In other embodiments, the hoop tows  46  might be cut at periodic intervals to define the hoop tow segments. 
     Looking now at  FIG. 13 , an apparatus  86  is shown for cutting the hoop tows  46  at periodic intervals into hoop tow segments  87 . This apparatus  86  includes a pair of rolling drums  88  and  90  between which the fabric  44  can be fed. One of the pair of rolling drums  88  has radially-extending blades or punches  92  that can be used to selectively cut the hoop tows  46 . Although not shown, the rolling drum  90  may have corresponding slots into which the punches  92  of the rolling drum  88  are received (so as to ensure a complete cut) or the rolling drums  88  and  90  may be spaced sufficiently that there is inter-roller clearance between the rolling drums  88  and  90  through which the blades  92  can pass. Although not illustrated, it is contemplated the bias fibers or bi-axial tows  48  and  50  could be separated to provide access to the hoop tow  46  before the hoop tow  46  is cut so as to minimize the damage to the bi-axial tows  48  and  50 . 
     By spacing the punches  92  over the axial length of the rolling drum  88  and over the circumference of the rolling drum  88 , the spacing of the cuts  94  of the hoop tows  46  in the fabric  44  can be selected to be at periodic intervals. Based on the illustrated spacing of the punches  92  on the rolling drum  90 , points of separation in the hoop tows are out of phase from those in adjacent hoop tows along the direction of hoop tow extension. This periodic spacing of the cuts  94  can be beneficial because, once spaces or gaps develop during forming of the fabric  44 , a separation gap between two hoop tow segments in one hoop tow can be supported by a hoop tow segment in an adjacent hoop tow. 
     For example and with additional reference to  FIG. 14 , a side-on view of a flange  22  after it is bent up is provided in which the hoop tows  46  are schematically illustrated (although the bi-axial tows are absent for the sake of clarity). As can be seen, in portions of the flange  22  that are subjected to shear, some of the hoop tows  46  are separated into hoop tow segments  87  such that spaces develop between the ends of adjacent hoop tow segments along the length of the hoop tows  46 . Under locally applied tension or pulling, each of the hoop tows  46  can break and/or separate at the points of separation to relieve the tension. 
     The spacing between the hoop tow segments  87  can vary throughout the preform  20  (or resultant component  18 ). For example, near the inner circumference  96  of the flange  22 , the hoop tows  46  have cuts  94  but are minimally, if at all, separated. However, near the outer circumference  98 , the required deformation of the fabric  44  during forming demands that the hoop tows  46  expand into hoop tow segments  87  with gaps or spaces  100  between the hoop tow segments  87 . As can be seen, these spaces  100  between the hoop tow segments  87  are greater in areas of the flange  22  where the fabric  44  is exposed to increased diametrical dimension. Moreover, because the cuts  94  are out of phase with one another, lines of gaps or spaces are avoided, which prevents lines of weakness in the final composite component. 
     To ensure that the gaps  100  are sufficiently covered and that the hoop tow segments  87  are retained in the fabric  44 , the hoop tow segments  87  may be selected to be at least some minimal length based on the width or diameter of the tow. For example, in one embodiment, the length of the hoop tow segments  87  are not less than 10 times the width of a hoop tow. 
     The amount of separation or the space of the gaps  100  between the hoop tow segments  87  can be substantial and non-trivial. For example, the gaps  100  between the hoop tow segments  87  could be at least as long as the fabric tows are wide. In still another example, the overall length of a hoop tow, including the gaps  100  formed after the hoop tow segments  87  are separated, could exceed the maximum length of the same hoop tow under elastic deformation due to an applied tension without the provided points of separation in the hoop tow. 
     Moreover, it should be observed that in preparation of fabric  44 , only certain regions of the fabric  44  could be prepared to have separable hoop tows  46 . For example, in the example of fabric preform  20  for the fan containment case  18 , only the precursor flange regions  40  and/or the joggle  34  might be prepared to have separable hoop tows, because these are the only regions that will require heightened levels of fabric deformation and stretching to be formed. The generally cylindrical portions of the body may have standard non-separable hoop tows  46  to maximize the structural strength of these regions. 
     It is contemplated that in fabrics with separable hoop tows, certain features might be formable during wrapping that conventionally have been difficult to produce. For example, by guiding a fabric with selectively separable hoop tows (and perhaps by further moving the bi-axial tows  48  and  50  using the edge strip technique described above) that a flange  22  could be formed in the as-laid preform rather than requiring secondary bending of the preform to obtain this feature. 
     It is also contemplated that the fabric structure could be modified to limit the relative placement of the hoop tow segments  87  in adjacent hoop tows. For example, a lateral connecting thread could be separately linked to various adjacent hoop tow segments  87  to keep them together. If the connection of the thread to the hoop tow segments  87  is greater than the force required to separate the hoop tow segments  87  in a particular hoop tow from one another, this lateral connecting thread could generally limit the placement and spacing of the hoop tow segments  87  from one another. This could be used, for example, to inhibit the formation of a single large gap in a hoop tow rather than a plurality of smaller gaps. Additionally, where the points of separation are intentionally out of phase with one another, such a lateral connecting thread could be used to make sure that the gaps do not form lines of weakness. 
     Accordingly, a fabric preform or a composite component is provided that includes a body formed from the fabric and at least one feature formed in the body. At least some of the hoop tows in the feature (e.g., a flange in a fan containment case) are separated into hoop tow segments that are spaced from one another along the length of the hoop tow. To exploit the benefit of the expandable or separable hoop tows, the feature (which includes the hoop tows) may extend, at least in part in a radial direction away from the central axis of the body. Again, some of the hoop tows in the base fabric may be separable while others may not be to maximize the strength of the structure. 
     Finally, a method of continuously debulking the fabric preform could be employed, either separately from the fabric manipulation techniques described herein or in conjunction with one or more of the fabric manipulation techniques. 
     Referring now to  FIGS. 15 through 17 , an apparatus  102  for continuously debulking a fabric preform is illustrated. This apparatus applies a compaction pressure to a portion of the top layer of the fabric as it is being laid down. 
     Looking first at the simplified schematic of  FIG. 15 , the apparatus  102  includes a form  104  rotatable about a central axis D-D for receiving a fabric  44  for the fabric preform  20 . In some respects, this form  104  is similar to other forms in that the fabric  44  is pulled onto the form for wrapping the fabric preform  20 . 
     However, the apparatus  102  is different than a traditional wrapping apparatus in that it is also configured to concurrently run a film  106  around at least a part of the form  104 . The film  106  is fed off of a film supply spool  108  and has a film path that extends to the form  104 , around at least a portion of the form  104  (which as illustrated is approximately 300 degrees), around an intermediate roller  110 , and onto a film take-up spool  112  that is spaced from the form  104 . This film  106  is disposed radially outward of the form  104  such that the fabric  44  of the fabric preform  20  is captured between the film  106  and the form  104 . Because the film  106  extends around only a portion of the form  104  before the film  106  is routed onto the take-up spool  112 , the film  106  is not made part of the fabric preform  20 , but rather surrounds a portion of the fabric preform  20 . 
     The film  106  and the fabric  44  may be fed onto the form  104  together such that the film  106  is disposed outward of the fabric  44  relative to the form. In this way, it might be said that the film  106  serves as a backing sheet that carries the fabric  44  as it is initially wrapped onto the form  104 . 
     Now with additional reference to  FIGS. 16 and 17 , further details of the apparatus  102  are illustrated. Specifically, a structure is illustrated for drawing a vacuum between the form  104  and the film  106  such that the fabric  44  is compressed there between. 
     It should be noted that in order to draw a vacuum, seals should be formed at the lateral or axial ends of the form  104  between the form  104  and the film. In the embodiment shown, because the form  104  is generally cylindrical, the seals extend over an arc. 
     The other spots that need to be “sealed” are the lines transverse to the fabric feed path at (1) the point at which the fed fabric initially contacts the form  104  (or the fabric  44  already wrapped around the form) and (2) the point at which the film  106  separates from the outer periphery of the form. By keeping the film  106  and the fabric  44  taut, these lines can form a pseudo-seal through which little gas can pass. 
     A vacuum source (depicted by arrows  114 ) is used to draw a vacuum between the film  106  and the form  104 . This vacuum causes the film  106  to be pulled toward the form  104 , thereby applying a compaction pressure to the outwardly facing surface of the fabric being wrapped into the fabric preform  20 . 
     In the particular embodiment of the apparatus  102  shown, the vacuum is drawn through a portion of the form  104 . As best seen in  FIGS. 16 and 17 , the form  104  includes a fixed portion  116  and a rotating or rotatable portion  118  which are both generally annular because of shape of the form  104 . As illustrated, the rotating portion  118  includes a central section  120  with lateral sections  122  fixedly connected at the ends thereof. The outwardly facing portions of the central section  120  and the lateral sections  122  generally define the surface of the form  104  that the fabric  44  is wrapped around. 
     In cross section, the lateral sections  122  are generally upside-down U-shaped channels. These lateral sections  122  include a plurality of openings  124  that extend from the outwardly-facing side of the section  112  (that defines a part of the form  104 ) to an inwardly-facing side on the inside of the “U”. 
     In cross section, the fixed portions  116  are a generally U-shaped channel that is roughly received in the upside-down shaped “U”. A pair of annular seals  126  is fixed to one of the fixed portion  116  and the rotating portion  118  for forming an annular shaped vacuum chamber  128  there between. In the particular form illustrated, the seals  126  are connected to the fixed portion  116  and are pressed against the inwardly-facing surface of the rotating portion  118 . 
     A series of vacuum lines  130  are connected to the fixed portion  116  and are in communication with the vacuum chamber  128 . Through these vacuum lines  130 , it is possible to draw a vacuum in the vacuum chamber  128  using the vacuum source  114 . Because the openings  124  are in communication with the vacuum chamber  128 , a vacuum drawn in the vacuum chamber  128  is communicated to the area between the film  106  and the form  104 . When sufficient seals are provided on the lateral edges of the form  104  and the lines transverse to the fabric feed path, this vacuum causes the film  106  to be drawn down such that the film applies a compaction pressure to the partially-wrapped fabric preform  20 . 
     In the form illustrated, the lateral seals are formed by placing a pair of raised gaskets  132  axially outward of the portion of the form  104  around which the fabric  44  is wrapped. Some openings  124  are placed between the gaskets  132  to place the space between the gaskets  132  in communication with the vacuum chamber  128 . When a vacuum is drawn, the film  106  is sucked down onto the gaskets  132  and a lateral seal is formed. 
     Accordingly, using an apparatus  102  of the type described above, a compaction pressure can be continuously applied to a fabric during formation of a fabric preform. Initially one end of the fabric  44  is applied to the form  104 . The form  104  with the fabric  44  applied thereto is at least partially surrounded by the film  106  in which the film  106  extends along a film path from the film supply spool  108  to the form  104  and around at least a portion of the form  104 . The fabric  44  and the film  106  is fed onto the form  104  such that the fabric  44  is wrapped around the form  104  to form the fabric preform  20  while the film  106  is fed around the form  104  (although not made part of the preform  20 ). During this feeding a vacuum is drawn to evacuate a gas from between the form  104  and the film  106 , thereby pressing the film  106  onto the fabric  44  and applying the compaction pressure to the fabric  44 . 
     This compaction pressure could be applied simultaneously with wrapping and may be constant. It is contemplated, however, that alternatively variable and/or periodic pressures could be applied using the apparatus  102 . The compaction pressure applied by the film  106  to the fabric  104  can be approximately 12 psi; however, different compact pressures might be applied based on the mechanical properties of the fabric  44 , the geometry of the form  104 , the forces applied to the fabric  44  during wrapping, and so forth. 
     Again, the film  106  can surround a substantial portion, but not all of the fabric  44  wrapped around the form  104 . This means that the compaction pressure is applied to the fabric over less than one full rotation of the form  104 . It is contemplated 75 percent or more of the surface area of the topmost fabric layer may be compressed against the form by the film  106 . Accordingly, in contrast to typical debulking methods, only a portion of the fabric preform is debulked at a given time, and that particular portion is constantly changing during the rotation of the form  104 . 
     In some forms of the method, the intermediate roller  110  routes and redirects the film  106  from around at least a portion of the form  104  to the take-up spool  112 . This intermediate roller  110  can have an axis that is parallel with, but spaced from, the central axis D-D of the form  104  and, moreover, can be biased into contact with the form  104  to assist in forming a good seal. 
     Using this method a fabric preform for a composite component, such as a fan containment case or fan case may be formed. The resultant fabric preform would be substantially free of bulk and wrinkles as the fabric is continuously debulked during wrapping. Accordingly, this technique provides a fiber architecture in the underlying fabric that is superior to conventional wrapping techniques. 
     This method might also be used to debulk prepreg or non-prepreg fabrics. Prepreg fabrics are those which contain some amount of resin in the fabric as supplied and can therefore be said to be pre-impregnated with the resin material. However, because prepreg fabrics are solid and not very permeable to gas in comparison to non-prepreg fabrics, it is contemplated that the film  106  could be textured to transfer the vacuum over the axial length of the form  104  between the bottom surface of film  106  and the upper surface of the topmost prepreg fabric layer. 
     It should again be stressed that this debulking technique might be combined with the other fabric manipulation techniques to synergistically result in fabric preforms for ultra-high strength composite components. For example, the debulking technique could be combined with the separate axial tensioning method to result in a preform having extremely high fiber volume ratio. 
     It should be appreciated that various other modifications and variations to the preferred embodiments can be made within the spirit and scope of the invention. Therefore, the invention should not be limited to the described embodiments. To ascertain the full scope of the invention, the following claims should be referenced.