Abstract:
A three-dimensional weave architecture for weaving preforms has fill fibers woven to provide layer-to-layer interlocking of layers of warp fiber as well as interlocking of fibers within each layer. The woven preform transfers out-of-plane loading through directed fibers to minimize inter-laminar tension. The preform has a base and at least one leg extending from the base, the base and leg each having at least two layers of warp fibers. The fill fibers follow a weave sequence which carries them through part of the base, then into the legs, then through the other portion of the base, and back through the base to return to the starting point of the fill tow. The leg may be connected at a single- or distributed-column intersection, and the intersection may be radiussed. The outer ends of the base and legs may have tapers formed from terminating layers of warp fibers in a stepped pattern.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to weaving of preforms and particularly relates to weaving of preforms used in bonding of components at structural joints. 
     2. Description of the Prior Art 
     When joining components in a structural joint, layers of fabric infused with a polymer resin can be used to join the components. For example, two components are brought to the desired positions and orientation, and layers of composites are adhered to the outer surfaces of the components: one portion of the fabric adhering to one component, another portion adhering to the other component. Multiple layers of fabric are stacked to increase the strength of the joint and to form a radiussed intersection. While this method works well, the joint can be improved by having fibers that extend through the intersection of the components, connecting the composite layers on both sides of the joint. A 3-D, woven, textile preform provides for fibers that extend through the intersection of a joint. The preform is infused with a resin that is cured to form a rigid polymer matrix surrounding the fibers of the preform. 
     Weave patterns for woven composite textiles have been used in the past which can provide for various shapes of three-dimensional preforms. However, these weave patterns were typically single-layer connectors, for example, U.S. Pat. No. 4,671,470 to Jonas, in which is disclosed an H-shaped connector for connecting a wing spar to a sandwich skin structure. Also, three-dimensional preforms have been woven to fill gaps formed during layup of composite layers into tight radius intersections. A gap-filling preform is disclosed in U.S. Pat. No. 5,026,595 to Crawford, Jr., et al. 
     However, these prior-art preforms have been limited in their ability to withstand high out-of-plane loads, to be woven in an automated loom proces, and to provide for varying thickness of portions of the preform. Weave construction and automation of preform weaving was in its infancy and provided only a small advantage over conventional laminated, fiber-wound, or braided composites, limiting the versatility of the preforms. 
     SUMMARY OF THE INVENTION 
     A three-dimensional weave architecture for weaving preforms has fill fibers woven to provide layer-to-layer interlocking of layers of warp fiber as well as interlocking of fibers within each layer. The woven preform transfers out-of-plane loading through directed fibers to minimize inter-laminar tension. The preform has a base and at least one leg extending from the base, the base and leg each having at least two layers of warp fibers. The fill fibers follow a weave sequence which carries them through part of the base, then into the legs, then through the other portion of the base, and back through the base to return to the starting point of the fill tow. The leg may be connected at a single- or distributed-column intersection, and the intersection may be radiussed. The outer ends of the base and legs may have tapers formed from terminating layers of warp fibers in a stepped pattern. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed to be characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings. 
     FIG. 1 depicts a global fill-tow weave pattern used to weave a T- or Pi-shaped preform in accordance with the invention, 
     FIG. 2 depicts an alternative embodiment of the fill-tow weave pattern of FIG. 1 in accordance with the invention. 
     FIG. 3 depicts an alternative embodiment of the fill-tow weave pattern of FIG. 1 that is used to weave a cross-shaped preform in accordance with the invention. 
     FIG. 4 depicts an alternative embodiment of the fill-tow weave pattern of FIG. 3 in accordance with the invention. 
     FIG. 5 depicts an alternative embodiment of the fill-tow weave pattern of FIG. 1 used to weave a Pi-shaped preform in accordance with the invention. 
     FIG. 6 is an enlarged view that depicts a substantially-single-column fill-tow weave pattern using the global pattern of FIG. 1 that is woven into layers of warp fibers and used to weave a T- or Pi-shaped preform in accordance with the invention. 
     FIG. 7 depicts a distributed-column weave pattern using the global pattern of FIG. 1 that is woven into layers of warp fibers and used to weave a T- or Pi-shaped preform in accordance with the invention. 
     FIG. 8 depicts an alternate embodiment of a fill-tow weave pattern that is woven into layers of warp fibers and used to weave a tapered outer edge of the base portion of a preform in accordance with the invention. 
     FIG. 9 depicts a complete, T-shaped, three-dimensional preform having tapered ends and in accordance with the invention. 
     FIG. 10 depicts a fill-tow weave pattern used to weave a hybrid preform with glass fill fibers woven into layers of carbon warp fibers and being in accordance with the invention. 
     FIG. 11 depicts a fill-tow weave pattern and used to weave a hybrid preform with carbon fill fibers woven into layers of glass warp fibers and being in accordance with the invention. 
     FIG. 12 depicts a fill-tow weave pattern used to weave a hybrid preform with carbon and glass fill fibers woven into layers of carbon and glass warp fibers and being in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A three-dimensional preform is created by weaving a tow pattern through several warp fibers that extend perpendicularly to the plane of the tow pattern. The warp fibers may comprise several layers, and all warp fibers in a preform are parallel to each other. The preform is usually woven from materials used for typical composites structures, for example, fiberglass and carbon fibers, and may have one of a variety of shapes, including T-, Pi-, X-, and L-shaped profiles, or may be flat. The shapes may have single, double, or triple legs, though the present invention is not limited to these variations. FIGS. 1 through 5 show tow patterns used to create woven preforms for structural joints. In the figures, the fill fibers are shown in the viewing plane, whereas the warp fibers are shown as perpendicular to the viewing plane. 
     FIG. 1 shows a fill-fiber tow pattern  11  for forming a T-shaped preform. The pattern begins at position A, and portion  13  is formed as the thread moves laterally toward the center of pattern  11  to position B. The thread is directed upward to position C, forming portion  15 , then returns downward to position B, forming portion  17 . The thread is directed toward position D, which is laterally opposed to A, and then returns to position A, forming portions  19  and  21  respectively. Portions  13 ,  19 , and  21  form a base of pattern  11 , whereas portions  15  and  17  form a leg. By forming a second loop (not shown) like that formed by portions  15  and  17 , a Pi-shaped preform can be manufactured. The tow patterns are repeated on each layer of warp fibers when weaving a preform. 
     FIG. 2 is a tow pattern  23  like that in FIG. 1, but a base is formed from more portions than that in pattern  11 . Pattern  23  begins at position E, and portion  25  is formed as the thread moves laterally toward the center of pattern  23  to position F. The thread is directed upward to position G, forming portion  27 , then returns downward to position F, forming portion  29 . The thread is directed toward position H, which is laterally opposed to E, and then returns to position E, forming portions  31  and  33 , respectively. The thread is then directed back to position H, forming portion  35 , and back to position E, forming portion  37 . Portions  25 ,  31 ,  33 ,  35 , and  37  form a base of pattern  23 , whereas portions  27  and  29  form a leg. This back-and-forth base pattern provides for improved performance in response to out-of-plane loading by increasing the number of fibers which run across the base without being directed upward to form a leg. A second loop (not shown) like that formed by portions  27  and  29  can be added to form a pattern from which a Pi-shaped preform can be manufactured. This type of pattern is shown in FIG.  5  and described below. 
     To form a cross-shaped preform, the patterns shown in FIGS. 3 and 4 are used. In FIG. 3, tow pattern  38  has a horizontal section formed by leg portions extending to positions I, J, and M, with I and M being laterally opposed and J being located between I and M. A vertical section passes through position J and extends from positions K and L, which are at opposite ends of the vertical section. Pattern  38  is created by using one thread to form the pattern. Starting at position I and moving laterally toward position J, the center of pattern  38 , forms portion  39 . The thread is directed upward to position K, forming portion  41 , then portion  43  runs downward from position K to position L. The thread turns upward from position L and extends to position J, forming portion  45 , then turns laterally, extending to position M. The thread then turns and returns laterally to position I. In pattern  38 , only half of the portions in each leg extend between opposite ends through center position J, the other half connecting adjacent legs. For example, the leg extending from position J to position K has one portion  41  that is connected to the leg extending from I to J, whereas portion  43  extends to position L through position J. 
     Pattern  50  is shown in FIG.  4  and also has horizontal and vertical sections forming a cross-shaped pattern  50 . However, unlike pattern  38  (FIG.  3 ), the pattern is formed from two threads and all of the portions extend between opposite ends through the center of pattern  50 . The horizontal section is formed by starting one of the threads at position N and extending it to position O, forming portion  51 . The thread then turns and returns to position N, forming portion  53 . The same type of sequence is used for the vertical section, with a separate thread extending from position P to position Q to form portion  55  and from Q to P to form portion  57 . The additional portions passing through the center of pattern  50  provide for greater strength in the woven preform. 
     FIG. 5 is a tow pattern  58  used to form a Pi-shaped preform having a multiple-portion base like pattern  23  in FIG.  2 . Pattern  58  begins at position R, and portion  59  is formed as the thread moves laterally toward the center of pattern  58  to position S. The thread is directed upward to position T, forming portion  61 , then returns downward to position S, forming portion  63 . This forms the first leg of the pattern. The thread is directed toward position U, forming portion  65 , then upward to position V to form portion  67 . The thread returns to position U, forming portion  69  and completing the second leg. The thread then travels to position W, which is laterally opposed to R, and returns to position R, forming portions  71  and  73 , respectively. The thread is then directed back to position W, forming portion  75 , and back to position R, forming portion  77 . Portions  59 ,  65 ,  71 ,  73 ,  75 , and  77  form a base of pattern  58 , whereas portions  61 ,  63  and  67 ,  69  form legs. 
     FIGS. 6 through 8 show methods for weaving the tow patterns into warp fibers to produce three-dimensional preforms. FIGS. 6 and 7 show weave patterns used for weaving legs in T-shaped preforms or Pi-shaped preforms, each preform having a four-layer thickness in the base and four-layer width in each leg of a preform, though the patterns will work with more or less layers of warp fibers. Fill fibers are shown in the viewing plane of FIGS. 6 through 8. Each warp fiber is parallel to the others and is shown as perpendicular to the viewing plane. 
     FIG. 6 depicts a weave pattern  79  that provides for interlocking between layers of warp fibers and provides for a central, substantially-single-column intersection of leg  81  with base  83 . For ease of description, the weave pattern will be described using the matrix formed by warp-fiber layers  1  through  8  and columns a through h. For example, the top, left-hand warp fiber in base  83  is designated a 5 , whereas the lower, right-hand fiber is h 8 . Leg  81  is woven in a laid-over, horizontal position, as shown, while the pattern is woven. Leg  81  is moved to a vertical, standing position after being woven, the width of leg  81  when standing upright comprising layers  1 ,  2 ,  3 , and  4 , the height comprising columns e, f, g, and h. The base comprises four layers  5 ,  6 ,  7 ,  8  and columns a, b, c, d, e, f, g, h. For the single-column intersection, substantially all of the threads that connect leg  81  to base  83  emerge from base  83  between columns d and e. Weave pattern  79  provides for interlocking between layers  1 ,  2 ,  3 ,  4  in leg  81  and between layers  5 ,  6 ,  7 ,  8  of base  83 . Each group of layers are interlocked by running a portion of pattern  79  over a warp fiber in a first layer in a first column and below a warp fiber in an adjacent, second layer in an adjacent, second column, the second layer being below the first layer. 
     FIG. 6 illustrates the completed weave in a vertical section of a preform  79  using the global fill-tow pattern in FIG. 1. A single thread  85  is shown for the weave, though the weave may also be created using multiple threads. The section in FIG. 6 is approximately 0.2 inches thick. Arrows are used to indicate the direction a particular portion of the thread  85  is traveling in the description of the figure, though the weave can also be done in the reverse order. Thread  85  begins by interlocking columns a, b, c, and d only in layer  5  by alternately wrapping over and under the fibers of layer  5 . Initially, thread  85  passes under warp fiber a 5 , then over fiber b 5 , then repeats the sequence, passing under fiber c 5  and over fiber d 5 . Thread  85  then exits base  83  from between column d and e and travels into layers  1 ,  2 ,  3 , and  4  at the inner end of leg  81 , beginning the weave for leg  81  by passing under fiber e 1 , over fiber f 1  under fiber g 1 , and over fiber h 1  at the outer end of leg  81 . Thread  85  then loops around to pass below fiber h 2  and begins traveling back toward the inner end of leg  81 . The return sequence interlocks layers  1  and  2  by then passing over fiber g 1 , under fiber f 1 , and over fiber e 1 . 
     Thread  85  reenters base  83  between columns d and e and continues through the remaining portion of base  83 , interlocking the fibers in columns e through h of layer  5  in the same sequence as used for columns a through d. Thread  85  passes under fiber e 5 , over fiber f 5 , then under fiber g 5  and over fiber h 5  at the edge of base  83  opposite the edge where thread  85  begins. As happens at the outer end of leg  81 , thread  85  loops around to pass below fiber h 6  and begins traveling back toward the opposite edge of leg  81 , interlocking layers  5  and  6 . Thread  85  passes over fiber g 5 , under fiber f 6 , and over fiber e 5 , but thread  85  does not turn upward to go into leg  81 , instead continuing across base  83  to interlock layers  5  and  6 . Thread  85  passes under fiber d 6 , over fiber c 5 , under fiber b 6 , and over fiber a 5 , completing one complete fill-tow sequence. Thread  85  then loops around and under fiber a 6  to begin a second fill-tow sequence, passing over fiber b 6  and continuing the weave. During the weaving process, the loom indexes downward to accommodate the change in layers for as many times as there are layers. 
     When layers  1  through  8  have been woven in one vertical section, thread  85  may loop back up and under fiber a 5  to repeat the weave sequence in a vertical section adjacent to the section of FIG.  6 . Alternatively, thread  85  may begin the sequence in reverse by starting the weave sequence at layer  8  and moving up through the layers, ending on layer  5 . Though not shown in the figures, use of either of the tow patterns of FIGS. 2 and 5 to weave a preform necessitates additional layers in the base. For example, the base would have twice as many layers as the leg to accommodate the extra thread portions passing across the base without entering the leg(s). 
     FIG. 7 shows a preform weave pattern  93  having a distributed intersection. Like weave pattern  79 , pattern  93  forms a leg  95  and a base  97 , base  97  and leg  95  having a plurality of columns of warp fibers. Leg  95  is woven while in a horizontal position, leg  95  being moved to a vertical, standing orientation after being woven. The central columns of base  97  are labeled as i, j, k, and l. Unlike pattern  79 , though, threads  99 ,  101 ,  103 ,  105 ,  107 ,  108 ,  109 ,  111  connect leg  95  to base  97  at multiple positions, the positions being located between columns i and j, between columns j and k, and between columns k and l. For example, threads  107 ,  108 , and  109  connect leg  95  to base  97  between columns j and k. This provides for the load to be distributed between warp fibers in several columns, rather than a significant majority of the loading being between two columns, as is true in pattern  79 . 
     A tapered edge can be formed on an outer edge of a preform by terminating successive layers of warp fibers at lengths which are longer than prior layers. A preform having a tapered edge has a better resistance to peel loads than a preform in which the warp-fiber layers all terminate at the same length. FIG. 8 shows a weave pattern  113  for a six-layer preform section, only one outer end of the preform being shown in the figure, the weave producing a tapered edge. The same interlocking sequence as described for FIGS. 6 and 7 is continued outward to the start of the taper. Thread  115  begins by interlocking the fibers in only layer  1  by wrapping under fiber m 1 , then over fiber n 1  and under fiber o 1 . To start the taper, thread  115  wraps over fiber p 1 , then is directed downward, terminating layer  1 . Thread  115  then reverses direction to wrap under fiber p 2  and travels over fiber o 1 , under fiber n 2 , and over fiber m 1 . Layer  2  is terminated in the same manner, but layer  2  terminates at column r. Each subsequent layer also terminates at a length two columns longer than the layer immediately above, e.g., layer  3  ends at column t. The stepped edge creates a tapered profile which can be made more steep by shortening the extra length of each layer to only one column or can be made more shallow by lengthening the stepped ends of the layers. Rather than the interlocking weave pattern of layers  1  through  5 , thread  117  begins at column m and alternately wraps over and under only the fibers of layer  6 , then reverses direction at column z and wraps over and under the fibers on the opposite side of layer  6 . Layer  6  is interlocked with layer  5  by thread  119  at columns n, p, r, t, v, and x. Though not shown in the figures, when a tapered edge is added to the edge of a preform such as preform  79  in FIG. 6, various techniques are available for providing that thread  85  begins and ends at the same location as shown in FIG. 6 or at other desired locations. 
     A completed, woven, T-shaped preform  121 , as shown in FIG. 9, has a base  123  and a leg  125 , base  123  having tapers  127  at its outer ends, leg  125  having a taper  129  on one side of the upper end of leg  125 . An untapered surface  131  of base  123  extends from each lateral side of the lower end of leg  125 , each surface  131  extending to the beginning of taper  127 . Likewise, an untapered surface  132  of leg  125  extends upward from the base  123  at a lower end of leg  125 , surface  132  extending to the beginning of taper  129 . Preform  121  is used to assemble components, the components being adhered to surface  133  of base  123  and surface  135  of leg  125 . Tapers  127  and  129  increase the resistance of the adhesive joints to a peeling load. An additional feature shown on preform  121  are radiussed areas  136  where leg  125  and base  123  intersect. The radius  136  is formed in a manner similar to that for a taper, but additional layers are added to the base of leg  125  while weaving preform  121 , the additional layers forming a stepped pattern. 
     Typically, preforms are woven using one type of fiber, for example, carbon (graphite) fibers, for both the warp and fill fibers. However, FIGS. 10 through 12 depict hybrid preform weave patterns which use fibers made form multiple materials, such as carbon and glass fibers. In the figures, glass fibers perpendicular to the viewing plane are indicated by an “o”, whereas carbon fibers perpendicular to the viewing plane are indicated by an “x.” These patterns can result in preforms having higher toughness, reduced cost, and optimized thermal-expansion characteristics. FIG. 10 shows four-layer preform weave pattern  137  in which the warp fibers  139  are carbon and the fill tows  141  are glass fibers. Conversely, FIG. 11 shows a four-layer weave pattern  143  in which all of the warp fibers  145  are glass fibers and the tow fibers  147  are carbon fibers. 
     In weave pattern  149  shown in FIG. 12, the types of fibers used for fill tows  151 ,  153 ,  155 ,  157 ,  159 ,  161 ,  163 ,  165  and warp fibers  167 ,  169  are alternated between glass fibers and carbon fibers. Fill tows  151 ,  153 ,  159 , and  161  are carbon fibers, whereas tows  155 ,  157 ,  163 ,  165  are glass fibers. Warp fiber  167  is a glass fiber; warp fiber  169  is a carbon fiber. The pattern shown has four layers, which are numbered  1  through  4 , and fibers  167 ,  169  are arranged in a “checkerboard” pattern throughout the layers. In layers  1  and  3 , the first and third fibers are carbon fibers  169 , and the second and fourth fibers are glass fibers  167 . In layers  2  and  4 , the first and third fibers are glass fibers  167 , and the second and fourth fibers are carbon fibers  169 . 
     An alternative method for creating preforms uses the warp fibers to interlock the layers of a preform. Again referring to FIGS. 10 through 12, the fibers in the viewing plane could be warp fibers, and the fibers perpendicular to the viewing plane could be fill fibers. The fill fibers would be used to simply interlock the warp fibers in a single layer without interlocking the layers, but the fill fibers would still be used to create legs extending from a preform. 
     The advantages of the present invention include the ability to weave a high strength and easy-to-use preform for assembling components into structures. A plurality of shapes can be created from using the weave sequences to weave fill fibers into a plurality of layers of warp fibers. The weave interlocks the warp fibers of each layer and interlocks the layers to each other. The weave can produce one or more legs that extend from a base to produce T- or Pi-shaped preform. By alternately using fibers made from carbon and glass, the strength, cost, and thermal expansion of a preform can be optimized. 
     While the invention has been shown in only some of its forms, it is not thus limited but is susceptible to various changes and modifications without departing from the spirit thereof.