Abstract:
A three-dimensional (3D) woven preform with channels in the through thickness direction developed for applications such as forming light weight preforms with an increased thickness.

Description:
[0001]    This application relates to a three-dimensional (3D) preform with channels through the thickness of the preform that may be used in applications such as forming light weight preforms with an increased thickness. 
       DESCRIPTION OF RELATED ART 
       [0002]    A leno weave is a weave in which two warp yarns are twisted around the weft yarns to provide a strong yet sheer/open fabric. The traditional leno, a single layer weave structure, is made by wrapping the warp yarns around each other between weft yarns. A variety of mechanical means are used, such as horizontally translating one warp to the other side of its neighbor with a mechanical actuator; using a propeller device that spins one direction for a long time, then spins the other direction, etc. A traditional leno weave acts to keep the two yarns locked very close to each other to either make an open fabric (like gauze), or to lock nearby yarn ends in place. 
         [0003]    The leno weave (also called Gauze Weave or Cross Weave) is a weave in which two warp yarns are twisted around the weft yarns to provide a strong yet sheer/open fabric. The standard warp yarn is paired with a skeleton or ‘doup’ yarn; these twisted warp yarns grip tightly to the weft yarn which improves the durability of the fabric. A leno weave produces an open fabric with almost no yarn slippage or misplacement of yarns. 
         [0004]    A leno weave fabric allows light and air to pass through freely so are used in any area where a sheer, open weave fabric is required that will not bruise or shove (where the yarns shift away from their woven uniformity disturbing the uniformity of the weave). If a simple in-and-out flat weave were woven very loosely to achieve the same effect, the yarns would have a tendency to this bruising/shoving/misplacement. 
         [0005]    Mock lenos, also known as imitation lenos, are a variety of weaves of ordinary construction which produce effects that are similar in appearance to the gauze or leno styles obtained without the aid of a doup mounting, These weaves are generally produced in combination with plain, twill, satin or other simple single layer weaves or even with brocade configuring, to produce striped fabrics, which bear a very close resemblance to true leno fabrics. This weave is also referred to as imitation gauze weave. 
         [0006]    The weave is a single layer weave arranging yarns in groups of equal or unequal sizes. Yarns working in a plain weave alternate with yarns floating on the face or back of the fabric. The yarn ends from each individual yarn group can be drawn into the same dent; this bunches the floating yarn ends together and causes a slight gap or opening between yarn groups in the fabric giving an appearance similar to a gauze or leno weave, hence the name “mock leno”. 
         [0007]    Mock leno woven fabrics may be generally defined as fabrics wherein groups of three or more warp or weft yarns are interlaced in such a way that the yarns of each group can come together easily in one group, while they are separated from the adjacent groups by reason of the last yarn of one group and the first yarn of the next group being interlaced in directly opposite order. Such an intersection prevents the two adjacent yarns from coming together and causes an opening at this point. These single layer woven fabrics may, be made from fibers or yarns of any well-known weavable materials such as glass or cotton, and are well known articles of commerce. 
         [0008]      FIG. 1A  illustrates an example of a related art single-layer mock leno fabric structure  1000  wherein both the warp and the weft yarns are grouped in groups of three yarns each. As shown in  FIG. 1A , the fabric comprises two kinds of mock leno patterns, i.e., 3×3 mock leno pattern I, and 3×3 mock leno pattern II. The 3×3 mock leno pattern I is formed by a group of three weft yarns a 1 -a 3  and a group of three warp yarns b 1 -b 3 , and the 3×3 mock lend pattern II is formed by a group of three weft yarns a 1 -a 3  and a group of three warp yarns b 4 -b 6 . The group of weft yarns a 1 -a 3  includes a first edge yarn a 1 , a central yarn a 2 , and a second edge yarn a 3 . The group of warp yarns b 1 -b 3  includes a first edge yarn b 1 , a central yarn b 2 , and a second edge yarn b 3 . Similarly, the group of warp yarns b 4 -b 6  includes a first edge yarn b 4 , a central yarn b 5 , and a second edge yarn b 6 . 
         [0009]    As shown in  FIG. 1A , during the weaving of the 3×3 mock leno pattern I, both of the first edge warp yarn b 1  and the second edge warp yarn b 3  are woven under the first edge weft yarn a 1 , then over the central weft yarn a 2 , and finally under the second weft edge yarn a 3 . The central warp yarn b 2  is woven over all of the three weft yarns a 1 -a 3 . During the weaving of the 3X3 mock leno pattern II, both of the first edge warp yarn b 4  and the second edge warp yarn b 6  are woven over the first edge weft yarn a 1 , then under the central weft yarn a 2 , and finally over the second weft edge yarn a 3 . The central warp yarn b 5  is woven under all of the three weft yarns a 1 -a 3 . 
         [0010]      FIG. 1B  illustrates the interlacing of the yarns of another example of a single-layer mock leno weave fabric structure wherein both the warp and the weft yarns are also grouped in groups of three yarns each. As shown in  FIG. 1B , there are sections where all of the weft yarns cross between two warp yarns as indicated by the circle. Within the groupings of three warp yarns, weft yarns do cross between a pair of warp yarns, but not all weft yarns cross at the same time. 
         [0011]      FIG. 1C  illustrates another example of a single-layer mock leno weave fabric structure. This mock leno is another version of a plain weave in which occasional warp yarns, at regular intervals but usually several yarns apart, deviate from the alternate under-over interlacing and instead interlace every two or more yarns. This happens with similar frequency in the weft direction, and the overall effect is a fabric with increased thickness and a rougher surface. 
         [0012]      FIG. 2  illustrates another example of a single-layer mock leno weave fabric structure  2000  wherein both the warp and the weft yarns are grouped in groups of four yarns each. As shown in  FIG. 2 , the fabric comprises two kinds of mock leno patterns, i.e., 4×4 mock lend pattern I, and 4×4 mock leno pattern II. The 4×4 mock leno pattern I is formed by a group of four weft yarns c 1 -c 4  and a group of four warp yarns d 1 -d 4 , and the 4×4 mock leno pattern II is disrupted by a group of four weft yarns c 1 -c 4  and a group of four warp yarns d 5 -d 8 . Similarly, a group of four weft yarns c 5 -c 6  and a group of four warp yarns d 1 -d 4  form the 4×4 mock leno pattern II, and a group of four weft yarns c 5 -c 8  and a group of four warp yarns d 5 -d 8  form the 4×4 mock leno pattern I. 
         [0013]    The group of weft yarns c 1 -c 4  includes a first edge yarn c 1 , two central yarns c 2  and c 3 , and a second edge yarn c 4 . Similarly, the group of weft yarns c 5 -c 8  includes a first edge yarn c 5 , two central yarns c 6  and c 7 , and a second edge yarn c 8 . The group of warp yarns d 1 -d 4  includes a first edge yarn d 1 , two central yarns d 2  and d 3 , and a second edge yarn d 4 , Similarly, the group of warp yarns d 5 -d 8  includes a first edge yarn d 5 , two central yarns d 6  and d 7 , and a second edge yarn d 8 . 
         [0014]      FIGS. 3A-3H  illustrate sections along the warp yarns d 1 -d 8 , respectively, in the single-layer mock leno weave fabric structure  2000  shown in  FIG. 2 . As shown in  FIGS. 3A-3D , during the weaving of the 4×4 mock leno pattern I, both of the first edge warp yarn d 1  and the second edge warp yarn d 4  are woven under the first edge weft yarn c 1 , then over all the central weft yarns c 2  and c 3 , and finally under the second weft edge yarn c 4 , The two central warp yarns d 2  and d 3  are woven over all of the four weft yarns c 1 -c 4 . During the weaving of the 4×4 mock leno pattern II on the right side of the 4×4 mock leno pattern I, both of the first edge warp yarn d 1  and the second edge warp yarn d 4  are woven over the first edge weft yarn c 5 , then under the central weft yarns c 6  and c 7 , and finally over the second weft edge yarn c 8 . The two central warp yarns d 2  and d 3  are woven under all of the four weft yarns c 5 -c 8 . 
         [0015]    As shown in  FIGS. 3E-3H , during the weaving of the 4×4 mock leno pattern II, both of the first edge warp yarn d 5  and the second edge warp yarn d 8  are woven over the first edge weft yarn c 1 , then under all the central weft yarns c 2  and c 3 , and finally over the second weft edge yarn c 4 , The two central warp yarns d 6  and d 7  are woven under all of the four weft yarns c 1 -c 4 . During the weaving of the 4×4 mock leno pattern I on the right side of the 4×4 mock leno pattern II, both of the first edge warp yarn d 5  and the second edge warp yarn d 8  are woven under the first edge weft yarn c 5 , then over the central weft yarns c 6  and c 7 , and finally under the second weft edge yarn c 8 , The two central warp yarns d 6  and d 7  are woven over all of the four weft yarns c 5 -c 8 . 
       SUMMARY OF THE DISCLOSURE 
       [0016]    A three dimensional (3D) woven preform with large channels in the warp and weft directions can be used itself or as part of a composite structure requiring light weight at an increased thickness versus other 3D or laminated preform structures. For 3D woven preforms that will be densified by Chemical Vapor Infiltration (CVI), larger channels within a preform can also provide multiple, large pathways for the chemical vapor to pass through the preform. In addition, the 3D weave that creates the channels can also create a preform with high thickness and a low fiber volume that might or might not be densified. Such an architecture might be useful in the preform state as a lightweight thermal or electrical insulator between two surfaces. The present invention discloses a 3D woven preform with channels. In the 3D woven version, warp yarns cluster together and weft yarns cluster together in groups. This creates channels in the through-thickness direction. These channels are created by locking the warp and weft yarns into place through a unique series of 3D weave patterns using a concept similar to the single layer mock leno weave. This differs from the traditional single layer leno pattern that is achieved through the use of a mechanical device that twists a warp yarn around another warp yarn as they cross a weft yarn to look them all into place. The traditional style leno mechanical devices are typically used in single layer preform weaves for composites for selvedges of the single layer woven preforms, where a tight weave is required to prevent-yarns from sliding out of place. 
         [0017]    In one aspect of the disclosure, a three-dimensional (3D) woven preform can include a plurality of groups of warp yarns and a plurality of groups of weft yarns, the warp yarns woven with the weft yarns to form a mock leno structure having a plurality of layers of the 3D woven preform. A first group of warp yarns in a particular layer can include a first set of at least one warp central yarn that binds weft yarns in the particular layer to weft yarns in a subsequent layer and at least two first warp edge yarns, one on each side of the first set of the at least one warp central yarn. A second group of warp yarns in the particular layer can include a second set of at least one warp central yarn that binds weft yarns in the particular layer to weft yarns in a preceding layer and at least two second warp edge yarns, one on each side of the second set of the at least one warp central yarn, such that through thickness channels are formed in the multilayer preform. 
         [0018]    This 3D woven preform of can include in a first group of weft yarns in the particular layer can include a first set of at least one weft central yarn that binds warp yarns in the particular layer to warp yarns in the subsequent layer and at least two first weft edge yarns, one on each side of the first set of the at least one weft central yarn. Also included can be a second group of weft yarns in the particular layer that can include a second set of at least one weft central yarn that binds warp yarns in the particular layer to warp yarns in the preceding layer and at least two second weft edge yarns, one on each side of the second set of the at least one weft central yarn. The first and second warp edge yarns can be woven over the first set of at least one weft central yarn and under the second set of at least one weft central yarn in the particular layer. The first and second weft edge yarns can be woven over the first set of at least one warp central yarn and under the second set of at least one warp central yarn in the particular layer. 
         [0019]    Another aspect of the disclosure is a three-dimensional (3D) woven preform including a plurality of groups of warp yarns and a plurality of groups of weft yarns, the warp yarns woven with the weft yarns to form a mock leno structure having a plurality of layers of the 3D woven preform. A first group of weft yarns in a particular layer can include a first set of at least one weft central yarn that binds warp yarns in the particular layer to warp yarns in a subsequent layer and at least two first weft edge yarns, one on each side of the first set of the at least one weft central yarn. A second group of weft yarns in the particular layer can include a second set of at least one weft central yarn that binds warp yarns in the particular layer to warp yarns in a preceding layer and at least two second weft edge yarns, one on each side of the second set of the at least one weft central yarn, such that through thickness channels are formed in the multilayer preform. 
         [0020]    In this second aspect of the 3D woven preform, a first group of warp yarns in the particular layer can include a first set of at least one warp central yarn that binds weft yarns in the particular layer to weft yarns in the subsequent layer and at least two first warp edge yarns, one on each side of the first set of the at least one warp central yarn. A second group of warp yarns in the particular layer can include a second set of at least one warp central yarn that binds weft yarns in the particular layer to weft yarns in the preceding layer and at least two second warp edge yarns, one on each side of the second set of the at least one warp central yarn. The first and second weft edge yarns can be woven over the first set of at least one warp central yarn and under the second set of at least one warp central yarn in the particular layer. The first and second warp edge yarns can be woven over the first set of at least one weft central yarn and under the second set of at least one weft central yarn in the particular layer. 
         [0021]    It is noted that in this disclosure and particularly in the claims and/or paragraphs, terms such as “comprises”, “comprised”, “comprising” and the like can have the meaning attributed to it in U.S. Patent law; e.g., they can mean “includes”, “included”, “including”, and the like. 
         [0022]    The terms “threads”, “fibers”, “tows” and “yarns” are used interchangeably in the following description. “Threads”, “fibers”, “tows” and “yarns” as used herein can refer to monofilaments, multifilament yarns, twisted yarns, multifilament tows, textured yarns, braided tows, coated yarns, bicomponent yarns, as well as yarns made from stretch broken fibers of any materials known to those skilled in the art. 
         [0023]    The above and other objects, features, and advantages of various embodiments as set forth in the present disclosure will be more apparent from the following detailed description of embodiments taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]      FIG. 1A  illustrates an example of a related art single-layer mock leno weave fabric structure wherein both the warp and the weft yarns are grouped in threes. 
           [0025]      FIG. 1B  illustrates another example of a related art single-layer mock leno weave fabric structure wherein both the warp and the weft yarns are grouped in threes. 
           [0026]      FIG. 1C  illustrates another example of a related art single-layer mock lend weave fabric structure. 
           [0027]      FIG. 2  illustrates another example of a related art single-layer mock leno weave fabric structure wherein both the warp and the weft yarns are grouped in fours. 
           [0028]      FIGS. 3A-3H  illustrate sections along the warp yarns in the single-layer mock leno weave fabric structure shown in  FIG. 2 . 
           [0029]      FIG. 4A  illustrates a top view of an example of a 3D woven preform with channels of the present disclosure. 
           [0030]      FIG. 4B  illustrates an oblique view of the 3D woven preform with channels. 
           [0031]      FIGS. 5A-5H  illustrate sections along the warp yarns in the 3D woven preform of the present disclosure. 
           [0032]      FIG. 6  illustrates the plans used to generate the top of a 3D woven preform with channels 
           [0000]    of the present disclosure. 
           [0033]      FIG. 7  illustrates other examples of 3D woven preforms of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0034]      FIG. 4A  illustrates a top view of an example of 3D woven preform with channels of the present disclosure.  FIG. 4B  illustrates an oblique view of the 3D woven preform with channels. As shown in  FIGS. 4A-4B , the 3D woven preform with channels of the present disclosure includes a multi-layer mock leno weave fabric structure wherein both the warp and the weft-yarns are grouped in fours. 
         [0035]    The 3D woven preform may comprise two kinds of 3D mock leno weave patterns, i.e., 3D mock leno weave pattern I, and 3D mock leno weave pattern II.  FIGS. 5A-5D  show an example of 3D mock leno weave pattern I, and  FIGS. 5E-5H  show an example of 3D mock leno weave pattern II. Both of the 3D mock leno weave patterns I and II are formed by a group of four warp yarns and a group of four weft yarns in a plurality of layers. Each group of four warp yarns includes a first edge warp yarn, two central warp yarns, and a second edge warp-yarn, the edge yarns on opposite sides of the central yarns. Similarly, each group of four weft yarns includes a first edge weft yarn, two central weft yarns, and a second edge weft yarn, the edge yarns on opposites of the central yarns. 
         [0036]    A 4×4 (4 warp yarns in each group and 4 weft yarns in each group) mock leno weave pattern is illustrated and described, However, it should be appreciated that there do not necessarily have to be an equal number of yarns in the warp and weft yarn groups. Moreover, it is not necessary to have 4 yarns in a group as long as there is at least one central yarn and at least one edge yarn on either side of the central yarn in each warp and weft group. 
         [0037]    In the 4×4 3D mock leno weave patterns I shown in  FIGS. 5A-5D , there are two central warp yarns in the warp yarn group in a particular layer, e.g. layer n, that alternate between being woven over all of the four yarns in the weft yarn group in the same layer n, and then woven under all of the four yarns in the weft yarn group in the next layer n+1, which is under this particular layer n in the through-thickness direction. 
         [0038]    In the 3D mock leno weave patterns II shown in  FIGS. 5E-5H , there are two central warp yarns in the warp yarn group in a particular layer, e.g. layer n, that alternate between being woven under all of the four yarns in the warp yarn group in the same layer n, and then woven over all of the four yarns in the warp yarn group in the upper layer n−1, which is over this particular layer n in the through-thickness layers of the fabric. 
         [0039]    In more detail,  FIGS. 5A-5H  illustrate sections along two groups of warp yarns in the 3D woven preform which structure has, for example, 12 layers. As shown in  FIGS. 5A-5H , the two groups of warp yarns include warp yarns  11 - 14  of a first warp group and warp yarns  15 - 18  of a second warp group in the first layer of the 3D preform. Also illustrated are warp yarns  21 - 24  and  25 - 28  of first and second warp groups of the second layer. This pattern continues to warp yarns  111 - 114 ;  115 - 118  of first and second warp groups of the eleventh layer, and warp yarns  121 - 124  and  125 - 128  of first and second warp groups of the twelfth layer. 
         [0040]      FIGS. 5A-5H  also show two groups of 4 weft yarns each that includes weft yarns  54 ,  69 ,  78 , and  93  in a first weft yarn group and weft yarns  49 ,  63 ,  73 , and  87  in a second weft yarn group on the first layer of the 3D woven preform, and two groups of 4 weft yarns that includes weft yarns  56 ,  67 ,  80 , and  91  in a first weft yarn group and weft yarns  52 ,  71 ,  76 , and  95  in a second weft yarn group on the second layer. The weft groupings continue in a similar manner to two groups of weft yarns  58 ,  65 ,  82 , and  89  in a first weft yarn group  59 ,  64 ,  83 , and  88  in a second weft yarn group in the tenth layer, weft yarns  60 ,  62 ,  84 , and  86  in a first weft yarn group and weft yarns  51 ,  61 ,  75 , and  85  in a second weft yarn group in the eleventh layer. 
         [0041]    In the following discussion the term “subsequent layer” is used for convenience of discussion only. However, “subsequent layer” as used herein means “another layer” not necessarily a layer lower or deeper in the 3D preform than a particular layer. Indeed, a “subsequent layer” could be above or higher in the 3D preform than the particular layer, The term “preceding layer” is only used to describe a layer in a direction opposite to that of the “subsequent layer.” 
         [0042]    As shown in  FIGS. 5A and 5D  there are 4 yarns in a first group of warp yarns: warp yarns  11 ,  14 , one on either side of central yarns  12 ,  13 . During the weaving of the 3D mock leno weave pattern I, the first edge warp yarn  11  and the second edge warp yarn  14  are woven under the first edge weft yarn  54  of the first weft yarn group of the first layer, then over all the central weft yarns  69  and  78 , and finally under the second weft edge yarn  93  in the weft yarn group. Edge warp yarns  11 ,  14  are then woven over the first edge weft yarn  49  of the first layer, then under all the central weft yarns  63  and  73 , and finally over the second weft edge yarn  87 . Edge warp yarns  11 ,  14  alternate the over/under in this manner for subsequent columns of weft yarns. 
         [0043]    As shown in  FIGS. 5B and 5C , the two central warp yarns  12  and  13  of the warp yarn group  11 - 14  in the first layer are woven over all of the four weft yarns  54 ,  69 ,  78 , and  93  of the first layer and under the four weft yarns  52 ,  71 ,  76 , and  95  of the second layer. Therefore, the first layer and the second layer are tied to each other. 
         [0044]    In a similar manner, the first edge warp yarn  21  and second edge warp yarn  24  of the warp yarn group  21 - 24  in the second layer are woven under the first edge weft yarn  56  of the first weft yarn group of the second layer, then over the central weft yarns  67  and  80 , and under the second weft edge yarn  91 . And the first edge warp yarn  21  and the second edge warp yarn  24  are woven over the first edge weft yarn  52  of the second weft yarn group of the second layer, then under the central weft yarns  71  and  76 , and finally over the second weft edge yarn  95 . 
         [0045]    The two central warp yarns  22  and  23  of the warp yarn group  2124  in the second layer are woven over all of the four weft yarns  56 ,  67 ,  80 , and  91  of the second layer and under all four weft yarns  53 ,  70 ,  77 , and  94  in the third layer. Therefore, the second layer and the third layer are tied to each other. 
         [0046]    As shown in  FIGS. 5E and 5H  there are 4 yarns in a second group of warp yarns: edge warp yarns  15 ,  18 , one on either side of central yarns  16 ,  17 . During the weaving of the 3D mock leno weave pattern II, the first edge warp yarn  15  and the second edge warp yarn  18  are woven over the first edge weft yarn  54  of the first weft yarn group of the first layer, then under all the central weft yarns  69  and  78 , and finally over the second weft edge yarn  93  in the weft yarn group. And edge warp yarns  15 ,  18  are then woven under the first edge weft yarn  49  of the first layer, then over all the central weft yarns  63  and  73 , and finally under the second weft edge yarn  87 , Edge warp yarns  15 ,  18  alternate the over/under in this manner for subsequent columns of weft yarns. 
         [0047]    As shown in  FIGS. 5F and 5G , the two central warp yarns  16  and  17  of the warp yarn group  15 - 18  in the first layer are woven under all of the four weft yarns  54 ,  69 ,  78 , and  93  of the first layer and over the four weft yarns  50 ,  72 ,  74 , and  76  of the layer above the first layer. Therefore, the first layer and the layer above the first layer are tied to each other. 
         [0048]    In a similar manner, the first edge warp yarn  25  and second edge warp yarn  28  of the warp yarn group  25 - 28  in the second layer are woven over the first edge weft yarn  56  of the first weft yarn group of the second layer, then under the central weft yarns  67  and  80 , and over the second weft edge yarn  91 . And the first edge warp yarn  25  and the second edge warp yarn  28  are woven under the first edge weft yarn  52  of the second weft yarn group of the second layer, then over the central weft yarns  71  and  76 , and finally under the second weft edge yarn  95 . 
         [0049]    The two central warp yarns  26  and  27  of the warp yarn group  25 - 28  in the second layer are woven under all of the four weft yarns  56 ,  67 ,  80 , and  91  of the second layer and over all four weft yarns  49 ,  63 ,  73 , and  87  in the first layer. Therefore, the second layer and the first layer are tied to each other. 
         [0050]    Therefore, as shown in  FIGS. 5A   5 H, warp yarn  11  and warp yarn  21  may come in contact with each other, but weft yarn  93  and weft yarn  49  are inhibited from contacting each other, In fact, all the weft yarns in the columns containing yarns  45  and  54  are inhibited from contacting each other. As a result channels are formed through the thickness of the fabric layers. 
         [0051]    In a similar manner, of the 4 weft yarns in groups of a particular layer, n, the two central weft yarns are woven with the warp yarns in the particular layer alternating between being woven under all of the four yarns in the warp yarn group in the same layer, n, and then woven over all of the four yarns in the warp yarn group in the upper layer n−1, which is over this particular layer n in the through-thickness direction. 
         [0052]    For example, as shown in  FIGS. 5A-5H , in a first group of four weft yarns  54 ,  69 ,  78 , and  93 , edge weft yarns  54 ,  93  are woven over first warp edge yarn  11 , under all central warp yarns  12 ,  13  and then over second warp edge yarn  14  in the first warp group of the first layer, and then edge weft yarns  54 ,  93  are woven under first warp edge yarn  15 , over all central warp yarns  16 ,  17  and then under second warp edge yarn  18  in the second warp group of the first layer. 
         [0053]    As shown in  FIGS. 5A-5H , in the first group of four weft yarns  54 ,  69 ,  78 , and  93 , central weft yarns  69 ,  78  are woven under all the warp yarns  11 - 14  in the first warp yarn group, and then over all the warp yarns  15 - 18  in the second warp yarn group. 
         [0054]    In the second weft yarn group  49 ,  63 ,  73 , and  87 , weft edge yarns  49 ,  87  are woven under warp edge yarn  11 , over all central warp yarns  12 ,  13  and then under second warp edge yarn  14 , and then edge weft yarns  49 ,  87  are woven over first warp edge yarn  15 , under central warp yarns  26 ,  27  of the second warp yarn group in the second layer and then under second warp edge yarn  18  of the second warp group of the first layer. Subsequent, weft edge yarns in each group alternate in a similar manner. 
         [0055]    Central weft yarns  63 ,  73  of the second weft yarn group  49 ,  63 ,  73 , and  87  are woven under the first edge warp yarn  15  of the second warp yarn group in the first layer, and then under the warp yarn  26 ,  27  of the second warp group in the second layer, and then under the second edge warp yarn  18  of the second warp yarn group in the first layer. Therefore, the first layer and the second layer are tied to each other. 
         [0056]    Similarly, as shown in  FIGS. 5A-5H , in a first group of four weft yarns  56 ,  67 ,  80 , and  91  of the second layer, edge weft yarns  56 ,  91  are woven over first warp edge yarn  21 , under all central warp yarns  22 ,  23  and then over second warp edge yarn  24  in the first warp group of the second layer, and then edge weft yarns  56 ,  91  are woven under first warp edge yarn  25 , over all central warp yarns  26 ,  27  and then under second warp edge yarn  28  in the second warp group of the second layer. 
         [0057]    As shown in  FIGS. 5A-5H , in the first group of four weft yarns  56 ,  67 ,  80 , and  91 , central weft yarns  67 ,  80  are woven under all the warp yarns  21 - 24  in the first warp yarn group, and then over all the warp yarns  25 - 28  in the second warp yarn group. 
         [0058]    In the second weft yarn group  52 ,  71 ,  76 , and  95 , weft edge yarns  52 ,  95  are woven under warp edge yarn  21 , over all central warp yarns  22 ,  23  and then under second warp edge yarn  24 , and then edge weft yarns  52 ,  95  are woven over first warp edge yarn  25 , under central warp yarns  36 ,  37  of the second warp yarn group in the third layer and then under second warp edge yarn  28  of the second warp group of the second layer. Subsequent, weft edge yarns in each group alternate in a similar manner. 
         [0059]    Central weft yarns  71 ,  76  of the second weft yarn group  52 ,  71 ,  76 , and  95  are woven under the first edge warp yarn  25  of the second warp yarn group in the second layer, and then under the warp yarn  36 ,  37  of the second warp group in the third layer, and then under the second edge warp yarn  28  of the second warp yarn group in the second layer. Therefore, the second layer and the third layer are tied to each other. 
         [0060]      FIG. 6  illustrates the plans used to generate the top of a 3D woven preform with channels. The pattern, as shown in  FIG. 6 , works by allowing some columns of yarns (warp and weft) to repel each other ( 4  and  5 ;  8  and  1 ) while others enable compact nesting ( 1  and  4 ;  5  and  8 ). Plans  2 ,  3 ,  6 , &amp;  7  are used to tie one layer to the next. 
         [0061]    The stiffness of the fiber yarns, combined with a specific over and under weave path, lead to a natural repulsion of some yarns and attraction of other yarns. This leads to the grouping of yarns in each direction that is beneficial for some applications. Stiffer yarns result in larger spacings between yarns, thus resulting in larger channels. 
         [0062]    Certain selections of warp yarn groupings in the reed can mute or accentuate the formed paths or channels. Similarly, certain patterns of take-up spacing can also mute or accentuate the formed paths or channels. The most accentuated results come from arranging the yarns as in Plans  1 - 4  in a dent, Plans  5 - 8  in a dent, and smaller take-ups between weft yarn columns  1 - 4  and again  5 - 8 . 
         [0063]    Therefore, in the 3D woven preform of the instant invention, an open weave is accomplished by using only the up and down yarn movement pattern available on the weaving system and without using additional mechanical actuators. 
         [0064]      FIG. 7  illustrates other examples of 3D woven preforms. A variety of thicknesses (layers) and spacings may be used for a warp/weft column. 
         [0065]    The 3D mock leno weave pattern has the following characteristics and features:
       make 3D woven preforms with higher thickness at a lower fiber weight at the same thickness as a conventional 3D pattern or laminated structure. For example, a 3D preform with a traditional fiber volume (FV) has a certain thickness and a certain weight, and a preform with open channels disclosed in the instant invention, which has the same thickness, has a weight less than that of the 3D preform with the traditional fiber volume;   create through thickness channels for fluid to flow either during processing of the preform into a composite; or as a “cooling channel” when the preform or composite is used as part of another assembly requiring heat dissipation;   vary the channel spacing by varying the number of warp yarns grouped together; vary the dimensions of the channels in the Z (through thickness) direction;   have less “bruising”, shoving or yarn displacement;   have at least 3 warp and weft yarns in a group;   stiffer warp and/or weft yarns will increase the repulsive force between yarn groups thus creating larger channels in the x or y planes (z being through thickness plane);   vary take-up between yarn groupings to vary the channel size in the warp direction;   groupings occur in both x-y plane directions, which results in “rectangular, other polygonal shaped channels”;   warp and/or weft yarns bind from one layer to the next layer below, or bind multiple layers with one yarn.       
 
         [0075]    After the desired 3D woven preform structure has been formed, the structure may be impregnated in a matrix material to form a composite. The structure becomes encased in the matrix material and matrix material fills some or all of the interstitial areas between the constituent elements of the structure. The matrix material may be any of a wide variety of materials, such as epoxy, polyester, vinyl-ester, ceramic, carbon and/or other materials, which also exhibit desired physical, thermal, chemical, and/or other properties. The materials chosen for use as the matrix may or may not be the same as that of the structure and may or may not have comparable physical, chemical, thermal or other properties. Typically, however, they will not be of the same materials or have comparable physical, chemical, thermal or other properties, because a common objective sought in using composites is to achieve a combination of characteristics in the finished product that is not attainable through the use of one constituent material alone. So combined, the structure and the matrix material may then be cured and stabilized in the same operation by thermosetting or other known methods, and then subjected to other operations toward producing the desired component. After being so cured, the then solidified masses of the matrix material are adhered to the structure. As a result, stress on the finished component, particularly via its matrix material acting as an adhesive between fibers, may be effectively transferred to and borne by the constituent material of structure. Further, if Chemical Vapor Infiltration (CVI) is utilized to add the matrix material to form the composite, some or all of the channels formed in the substrate might remain open and free of the resin material. 
         [0076]    It should be appreciated that the yarns in the warp and weft directions may be of same or different materials and/or sizes. For example, the warp yarns and weft yarns can be made of carbon, nylon, rayon, fiberglass, cotton, ceramic, aramid, polyester, metal, polyethylene, and/or other materials that exhibit desired physical, thermal, chemical or other properties. 
         [0077]    It should be appreciated that other 3D mock leno weaves can be used to create the polygonal shaped channels, and that the number of layers of warp yarns is at least two or more. It should also be appreciated that in some embodiments, all the channels extend through the entire preform thickness. In other embodiments, a plurality of channels extend through the entire thickness. That is, in a desired pattern, not all of the channels necessarily extend through the entire thickness of the preform. 
         [0078]    It should also be appreciated that on one or both outer surfaces of the 3D woven preform, or one or both outer surfaces of the composite, other structures may be attached as a separate “skin” by methods such as stitch bonding, pinning, T-Forming (see U.S. Pat. No. 6,103,337), mechanically bolting, use of appropriate adhesives, or other methods known to those skilled in the art.