**3. Types of fabrics**

## **3.1. Two-dimensional fabrics**

## *3.1.1. Woven fabric*

**Type Fabric classification Weft knitted fabric Warp knitted fabric**

fabrics

Two- and three-dimensional nonwoven preforms are classified depending upon web bonding techniques, web structure, and fiber orientation (Table 6). The nonwoven structure is com‐ posed of short fibers that are held together by employing various techniques. The extent of fiber-fiber bonding is dependent upon fiber geometry, fiber tenacity and flexural rigidity, fiber location within the web, the areal mass of the web, etc. Mechanical, chemical or thermal methods can be utilized to achieve fiber-fiber bonding and thus create a continuous nonwoven web. Mechanical methods aim to commingle the fibers by an applied force (i.e., needling or water-jet) so that fiber-fiber entanglements occur in the web holding the structure together. In the chemical method, fiber surfaces are bonded together by using suitable binding agents, or the bonding is achieved by dissolving the fiber surfaces with a solvent followed by merging and solidification. Thermal bonding is generally used for thermoplastic fibers and powders. Fibers are melted by heat exposure, merged together, and solidified again by cooling [38]. Twoand three-dimensional nonwoven nano-web fabricated via electrospinning is a new develop‐

**fabric Web formation Formation techniques Web structure Fiber orientation in web**

Mechanical Looping Loops

Chemical Impregnation; Spraying; Printing;

Thermal Hot air; Calendaring; Welding - -

Foaming - -

Needling Plugs In plane and out-of-plane

Entangling Balls In plane fiber placement

fiber orientation

and entanglement

Short fiber in plane and continuous fiber in the outof-plane orientation

inlay fiber yarns

Dembigh, Atlas

fabrics

structure

Multiaxial warp knitted

Plain, rib Dembigh, Atlas

Single jersey face structure Single Dembigh face

I 2D fabric Plain, Milano rib, inlaid

III 3D solid fabric Plain and rib fabrics with

II 2D fabric base 3D

86 Non-woven Fabrics

shape

**Table 5.** Classification of typical warp and weft knitted fabrics [36].

ment to make nanofiber-based nonwoven fabrics [39].

**Nonwoven**

2D fabric 3D fabric

IV 3D hollow fabric/sandwiched fabric

> The 2D woven fabric is the most widely used material in the composite industry. It contains two yarn sets i.e., warp (0˚) and weft (90˚), that lie perpendicular to each other in the fabric plane. Warp and weft yarns make a series of interlacements with one another according to a weave type and pattern to make the woven fabric. Basic weave types produced by traditional weaving are plain, twill and satin. Different fabric structures can be constructed from a weave type by changing the weave pattern. There are also derivative weave types that are created to obtain desired combinations of fabric properties. Some of the weave types are shown in Figure 1 [40]. In plain weave, each warp yarn passes alternately under and over each weft yarn. Hence, it is symmetrical and has a good dimensional stability. However, plain woven fabric has high crimp and is difficult to form during molding due to high number of interlacements for a given area. In twill weave, a warp yarn passes over and under two or more weft yarns based on a diagonal pattern. The twill woven fabric has a smoother surface in comparison with plain weave, simply because of multiple jumps between interlacements. It has also lower crimp. In addition, it has a good wettability and drapability. However, it shows less dimensional stability compared to the plain weave. In satin weave, warp yarns alternately weave over and under two or more weft yarns to make fewer intersections. Therefore, it has a smooth surface, good wettability and a high degree of drapability. It has also low crimp. However, it has low stability and an asymmetrical structure. Another 2D woven architecture is leno weave in which adjacent warp yarn is twisted around consecutive weft yarn. One of the derivatives of the leno weave is mock leno in which occasional warp deviate from the alternate under-over interlacing and interlaces every two or more weft. This results in a thick and rough surface with high porosity [41-43].

> Two dimensional woven fabric composites show poor impact resistance as a consequence of fabric crimp. They also have low in-plane shear properties due to absence of off-axis fiber orientation other than material principle directions [4]. Another major problem of these composites is that they experience delamination under load due to lack of through-thethickness binder yarns (z-yarns). Through-the-thickness reinforcement eliminates the delami‐ nation problem, but it reduces the in-plane properties [1, 2]. Biaxial noncrimped fabric was

**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].

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 of 2D woven composites.
