*3.1.4. Triaxial braided fabric*

developed to replace the unidirectional cross-ply laminate [42]. This fabric has warp (0˚ direction) and filling yarns (90˚ direction) as separate layers so that there is no interlacement between them, unlike traditional woven fabrics. Warp and weft layers are linked at intersection points by two sets of stitching yarns, one in 0˚ direction and another in 90˚ direction, as shown in Figure 1. Biaxial noncrimped fabrics largely eliminate the crimp and delamination problems

**Figure 1.** Two dimensional various woven fabrics (a) uniform plain (b) twill (2/2) (c) satin (4/1) (d) leno (1/1), and (e)

non-interlace woven fabric with stitching (f) non-interlace woven fabric without stitching yarn [41-43].

Triaxial weave structure consists of three yarn sets such as +bias (+warp), -bias (-warp), and filling [44]. These yarn sets make interlacements as in traditional biaxial fabric (Figure 2). The fabric generally has large hexagonal openings between interlacements. Open-reed process used in the fabrication of this type of fabric does not allow making fabrics as dense as a traditional woven fabric. Triaxial fabrics have two variants, namely, loose-weave and tight-weave. It was shown that loose-weave fabric has certain stability and higher shear

isotropic structure. Quart-axial fabric has four sets of yarns such as +bias, -bias, warp and filling as shown in Figure 2. All yarns are interlaced to each other to form the fabric structure [45]. Warp yarns are inserted to the fabric at selected places to increase directional strength and stiffness properties. Therefore the fabric structure can be tailored to fulfill various end-

**Figure 2.** Triaxial woven fabrics (a) loose fabric (b) tight fabric (c) one variant of triaxial woven fabric, and (d) quart-

Two-dimensional braided fabrics are extensively used in industrial textiles and composites. It has one yarn set, braiders oriented in +θ and –θ directions. In order to produce the fabric

directions when compared to the biaxial fabrics as well as having a more

of 2D woven composites.

88 Non-woven Fabrics

*3.1.2. Triaxial woven fabric*

stiffness in ±45˚

use requirements.

axial woven fabric [44, 45].

*3.1.3. Braided fabric*

Triaxial braided fabric has basically three sets of yarns: +braid (+bias), -braid (-bias), and warp (axial). Axial yarns lie across the fabric whereas braided yarns intertwine with each other around the axial yarns making about 45˚ angle (Figure 3). The intertwining is similar to that of a traditional braided fabric. –Braided yarns cross under and over the +braided yarns according to a pattern and this process is repeated throughout the fabric structure. Triaxial braided fabric generally has large openings between the axial yarns, intertwining regions. Although dense fabrics can be produced, the process is not suitable for the fabrication of fabrics as dense as a traditional biaxial braided fabric. It was shown that the mechanical properties of triaxial fabric are significantly higher than biaxial braided fabrics, especially in the direction of axial yarns [47]. This shows that the incorporation of axial yarns strongly enhances the directional properties of the fabric.

#### *3.1.5. Knitted fabric*

Knitted fabric is composed of yarn loops connected to each other and to the neighboring rows and columns by various techniques. This process is also called "interloping." The basic knitting types are weft knitting and warp knitting. In weft knitting, a continuous yarn forms one horizontal row of loops called a "course" connecting it to the previously formed courses in the process (Figure 4). The vertical columns of loops are called "wale." In warp knitting, yarn loops are connected vertically to form the fabric structure. Knitted fabrics are characterized by their 'wale density' and 'course density.' The wale density is defined as the number of wales per unit length in the course direction. The course density is defined as the number of courses per unit length in the wale direction. Stitch density is the product of course density and wale density [36, 48].

**Figure 4.** (a) Two-dimensional weft knitted fabric (b) warp knitted fabric, and (c) spiral knitted fabric [36].
