**2. Classification of fabrics**

tional materials. The most important application area of 3D textiles, by far, is composite industry, where they are used as reinforcement materials in combination with several matrices to make textile structural composites. These composites are used extensively in various fields such as civil engineering and military industry [1, 2], thanks to their exceptional mechanical properties and lower density in comparison with common engineering materials like metals and ceramics [3, 4]. Textile structural composites are also superior to conventional unidirec‐ tional composites when the delamination resistance and damage tolerance are taken into account [5]. Textile preforms are readily available, low-cost, and not labor intensive [1]. They can be manufactured by weaving, braiding, knitting, stitching, and by using nonwoven techniques. Each manufacturing technique has its own advantages and disadvantages in terms of specific composite properties and the selection can be made based on the end-use. The simplest form of 3D woven preforms is made up of two dimensional (2D) woven fabrics that are stacked one on top of another and stitched together in the thickness direction to impart through-the-thickness reinforcement. Three-dimensional weaving is another preform produc‐ tion technique that can be employed to manufacture 3D woven preforms by using specially designed automated looms. Near-net shape parts can be produced with this technique which substantially reduces the amount of scrap [6, 7]. In-plane properties of 3D woven composites are generally low due to through-the-thickness fiber reinforcement, despite of its positive effect on out-of-plane properties [8]. Simple 3D braided preform consists of 2D biaxial fabrics that are stitched together in the thickness direction depending on a chosen stacking sequence. Three-dimensional braiding is a preform technique used in the multidirectional near-net shape manufacturing of high damage tolerant structural composites [9, 10]. Three-dimensional braiding is highly automated and readily available. Three-dimensional braided preforms are fabricated by various techniques such as traditional maypole braiding (slotted horn gear matrix), novel 4-step and 2-step braiding (track and column) or more recently 3D rotary braiding and multi-step braiding [11, 12]. The fabrication of small sectional 3D braided preforms is low-cost, and not labor intensive [1]. However, the fabrication of large 3D braided preforms may not be feasible due to position displacement of the yarn carriers. Threedimensional knitted preforms are fabricated by the 3D spatial formation of 2D warp or weft knitted fabrics in order to make near-net shape structures like spheres, cones, ellipsoids and T-pipe junctions. Three-dimensional knitted composites generally have low mechanical properties as a result of their characteristic looped architecture and low fiber volume fraction. A 3D nonwoven preform is a web or felt structure consisting of randomly positioned short fibers. There is no particular textile-type interlacing or intertwining between the fibers other than random entanglements. Through-the-thickness stitching of layered nonwoven webs is also possible. The most common methods for nonwoven production are needle-punching, stitch-bonding, high-frequency welding, chemical bonding, ultrasound and laminating. Recently, electrospinning method is utilized to make nonwoven nano web structure [13]. The entanglement type defines the fabric properties such as strength and modulus, flexibility, porosity and density [14]. Nonwoven fabrics and their composites display low mechanical properties due to fiber discontinuity. Multiaxis knitted preform comprises four fiber sets such as +bias, -bias, warp (0˚) and weft (90˚) along with stitching fibers which enhance in-plane properties [15]. Multiaxis knitted preform suffer from limitation in fiber architecture, through-

82 Non-woven Fabrics

Three-dimensional woven preforms are classified based on various parameters such as fiber type and formation, fiber orientation and interlacements and micro- and macro-unit cells. One of the general classification schemes has been proposed by Ko and Chou [3]. Another classi‐ fication scheme regarding yarn interlacement and process type was proposed (Table 1) [18]. In this scheme, 3D woven preforms are subdivided into orthogonal and multiaxis fabrics, and their processes have been categorized as traditional or new weaving, and specially designed looms. Chen [19] categorized 3D woven preforms made by traditional weaving techniques based on their macro-geometry. According to this classification, 3D woven preforms are grouped as solid, hollow, shell, and nodal structures with varying architectures and shapes (Table 2). Bilisik [20] suggested a more precise classification of 3D woven preforms according to their interlacement types (fully interlaced woven/non-interlaced orthogonal), macro geometry (cartesian/polar) and reinforcement direction (2-15) (Table 3).


**Table 1.** Three-dimensional woven fabric classification based on non-interlace structuring [18].


**Table 2.** Three-dimensional woven fabric classification based on macro-structure [19].


**Table 3.** The classification of three-dimensional weaving based on interlacement and fiber axis [20].

Three-dimensional braided preforms are classified based on various parameters, including manufacturing technique, fiber type and orientation, interlacement patterns, micro-meso unit cells and macro-geometry [10, 33]. Kamiya et al. [2] considered manufacturing techniques i.e., solid, 2-step, 4-step and multistep to classify 3D braided preforms. Grishanovi et al. [34] used a topological approach based on knot theory to describe and group braided structures whereby the braided fabric is considered as a multiknot structure. Bilisik [35] classified 3D braided structures as 3D braid, 3D axial braid, and multiaxis 3D braid, as shown in Table 4. These three categories were further divided according to their fiber directions (2-6) and geometry (carte‐ sian/polar).

**Structure Architecture Shape**

interlock Compound structure with regular or tapered geometry

levels in multi-directions

**Three dimensional weaving**

Tubular nodes and solid nodes

**Woven Orthogonal nonwoven**

Tubular Weft-insertion Weft-winding and

Open-lattice Solid

Corner across Face across

sewing

**Hollow** Multilayer Uneven surfaces, even surfaces, and tunnels on different

**Cartesian Polar Cartesian Polar**

Twill and Twill laid-in Tubular

Twill and Twill laid-in Tubular

Twill and Twill laid-in Solid Tubular

Hexagonal array Hexagonal array Hexagonal array Hexagonal array

6 to 15 Rectangular array Rectangular array Rectangular array Rectangular array

Three-dimensional braided preforms are classified based on various parameters, including manufacturing technique, fiber type and orientation, interlacement patterns, micro-meso unit

**Shell** Single layer; Multilayer Spherical shells and open box shells

Plain and Plain laid-in

Twill and Twill laid-in

Satin and Satin laid-in

Plain and Plain laid-in

Twill and Twill laid-in

Satin and Satin laid-in

Plain and Plain laid-in

Twill and Twill laid-in

Satin and Satin laid-in

**Table 3.** The classification of three-dimensional weaving based on interlacement and fiber axis [20].

**Table 2.** Three-dimensional woven fabric classification based on macro-structure [19].

**Solid** Multilayer; Orthogonal; Angle

**Nodal** Multilayer; Orthogonal; Angle interlock

> Angle interlock; Layer-to-layer; Through the thickness

Core structure

Plain and Plain laid-in

Satin and Satin laid-in

Plain and Plain laid-in

Satin and Satin laid-in

Plain and Plain laid-in

Satin and Satin laid-in

**Direction**

84 Non-woven Fabrics

2 or 3

3

4

5


**Table 4.** The classification of 3D braiding based on interlacement and fiber axis [35].

Hamada et al. [36] classified 3D knitted structures based on engineering applications, as shown in Table 5. Type I fabrics are simple 2-D flat knitted fabrics. These fabrics can be cut to the required dimensions and laminated just as woven fabric composites. Two dimensional knitted fabrics with 3D shapes are categorized as Type II fabrics. Type III fabrics are multiaxial warp knitted fabrics. Type IV fabrics are called sandwich fabrics or 3D hollow fabrics. Type IV fabrics are sometimes called "2.5 D fabrics" and are very effective for the production of high damagetolerant composites [37].


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

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



**Table 6.** Classification of nonwoven fabrics [38].
