*3.2.2. Multistitched fabric structures*

A multistitched fabric preform is produced by stitching 2D fabric layers in thickness direction. Stitching can be applied (i) only in 0° direction, (ii) 0° and 90° directions, and (iii) 0° , 90° and ±bias directions as shown in Figure 9. Lockstitch is commonly used for pre‐ form production. Stitching can be done manually or with the aid of a stitching machine. Stitching can be applied to all fabric types such as woven fabrics, braided fabrics, knitted fabrics, or nonwoven fabrics [59].

**Figure 9.** Schematic views of multistitched 2D woven fabric. Stitching directions (a) one direction (b) two direction (c) four direction; cross-sectional view of four directionally machine and hand stitched structures on (d) 0° , (e) 90° , (f) +45° , and -45° [59].

#### *3.2.3. Fully interlaced woven fabric structure*

The 3D flat fully interlaced woven fabric structure consists of three yarn sets such as warp, weft and z-yarn. The weaving process takes place in in-plane and out-of-plane directions according to respective weave patterns. Warp yarns are interlaced with weft yarns at each layer according to the weave pattern in in-plane principal directions, whereas z-yarns are interlaced with warp yarns at each layer according to the weave pattern in out-of-plane principal directions. Three dimensional fully plain, 3D fully twill and 3D fully satin preform structures are shown in Figure 10. If the warp and weft yarn sets are interlaced based on any weave pattern but the z-yarns are not interlaced and only laid-in orthogonally between each warp layers, these 3D woven structures are called semi-interlaced woven structures.

The 3D circular fully interlaced woven fabric structure is composed of three yarn sets such as axial (warp), circumferential (weft) and radial (z-yarn) yarns. Here, radial yarns are similar to z-yarns in flat woven fabrics. Circumferential yarns are interlaced with axial yarns at each circular layer according to the weave pattern in circumferential direction, whereas radial yarns are interlaced with axial yarns at each layer according to the weave pattern in radial directions. Figure 11 shows the 3D fully plain, 3D fully twill and 3D fully satin circular woven preform structures [60, 61].

**Figure 10.** Three-dimensional fully-interlaced woven preform structures. General view of the five-layer computer-aid‐ ed drawing of (a) 3D plain (b) 3D twill, and (c) 3D satin woven preform structures [60].

**Figure 11.** Three-dimensional fully-interlaced circular woven preform structures. General view of the five-layer com‐ puter-aided drawing of (a) 3D plain (b) 3D twill, and (c) 3D satin circular woven preform structures [61].

#### *3.2.4. Orthogonal woven fabric*

**3.2. Three-dimensional fabrics**

92 Non-woven Fabrics

*3.2.1. Non-interlaced fabric structures*

oriented in 0/90/±45˚ directions (Figure 8) [43].

fabric, and (c) multiaxis non-interlaced fabric schematic and fabric [43].

direction. Stitching can be applied (i) only in 0° direction, (ii) 0°

*3.2.2. Multistitched fabric structures*

fabrics, or nonwoven fabrics [59].

*3.2.3. Fully interlaced woven fabric structure*

0°

and -45°

[59].

Non-interlaced fabrics consist of multiple fiber layers that are stacked one on top of another. There is no interlacement between these layers so the fibers lie across the structure without crimping. This is an obvious advantage for in-plane properties since the fibers are well oriented in in-plane directions. Out-of-plane properties, however, are poor due to lack of through-thethickness fibers (z-fibers). If the fabric has one set of yarn oriented in 0˚ direction it is referred to as uniaxial non-interlaced fabric preform. Biaxial non-interlaced fabric preform consists of two fiber sets oriented at 0/90˚. A multiaxis non-interlaced fabric preform has four fiber sets

**Figure 8.** (a) Unidirectional non-interlaced fabric schematic and fabric (b) biaxial non-interlaced fabric schematic and

A multistitched fabric preform is produced by stitching 2D fabric layers in thickness

, 90° and ±bias directions as shown in Figure 9. Lockstitch is commonly used for pre‐ form production. Stitching can be done manually or with the aid of a stitching machine. Stitching can be applied to all fabric types such as woven fabrics, braided fabrics, knitted

**Figure 9.** Schematic views of multistitched 2D woven fabric. Stitching directions (a) one direction (b) two direction (c)

The 3D flat fully interlaced woven fabric structure consists of three yarn sets such as warp, weft and z-yarn. The weaving process takes place in in-plane and out-of-plane directions according to respective weave patterns. Warp yarns are interlaced with weft yarns at each

four direction; cross-sectional view of four directionally machine and hand stitched structures on (d) 0°

and 90°

directions, and (iii)

, (e) 90°

, (f) +45° ,

> In orthogonal woven fabric, warp, filling, and z-yarn sets constitute the fabric. They are interlaced to one another and oriented in three orthogonal directions to form the fabric [60]. The schematic and real views of fabric unit cell are shown in Figure 12 [60, 62]. Warp yarns are placed in the fabric length direction whereas filling yarns are inserted between the warp

layers to form double picks. Z-yarns lock the other two yarn sets and provide structural integrity.

**Figure 12.** (a) Schematic view of 3D orthogonal woven unit cell (b) 3D woven carbon fabric preform [60, 62].

The 3D angle interlock is another type of 3D woven fabric that is produced by 3D weaving loom [63]. The fabric has a total of four yarn sets namely filling yarns, +bias yarns, -bias yarn, and stuffer (warp) yarns. Bias yarns are oriented in the thickness direction. There are two types of this fabric structure such as layer-to-layer and through-the-thickness as shown in Figure 13. In layer-to-layer fabric, bias yarns travel between two successive fabric layers making interlacements with several filling yarns according to the weave pattern. In through-thethickness fabric, on the other hand, bias yarns take a straight path along the fabric thickness until reaching to the top or bottom surface and then reverse its movement to make the same travel until reaching the other surface (Figure 13). This zig-zag movement continues across the fabric length. Bias yarns are locked by several filling yarns in the process depending upon the number of layers [60].

**Figure 13.** General view of the five-layer computer aided drawing of traditional (a) 3D angle interlock (b) 3D throughthe-thickness, and (c) 3D circular orthogonal woven preform structures [60, 61].

Three-dimensional circular weaving (i.e., 3D polar weaving) and fabric was developed [64]. The preform has mainly three sets of yarns such as axial, radial and circumferential as shown in Figure 13. In addition, central yarns are inserted to form the rod. Circumferential yarns are laid between adjacent axial yarn layers, whereas radial yarns are inserted between adjacent axial yarn layers in radial direction.
