**1. Introduction**

The objective of this chapter is to provide up-to-date information on the development of 2D and 3D fabric formation and formation techniques particularly on 2D and 3D nonwoven fabrics, methods, and properties of nonwoven web, including possible emerging application areas. Three-dimensional (3D) fiber structures produced by textile processes are used in various industrial applications since they have distinct properties when compared to conven‐

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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, throughthickness reinforcement due to the thermoplastic stitching thread and three dimensional shaping during molding [3]. Multiaxis 3D woven preforms and their composites exhibit improved in-plane properties due to off-axis fiber positioning [16, 17].

In this chapter, 3D fabrics including 3D nonwoven for technical textile applications are reviewed in the light of the existing literature. First, the classification of textile fabric structures was introduced based on various classification schemes suggested by experts in the field. Types of textile fabric structures were explained under two main groups such as 2D and 3D fabrics. Various formation techniques including 2D and 3D nonwoven techniques were reviewed with regard to manufacturing processes and resulting fabric and composite prop‐ erties. Applications of technical textiles in various industrial areas were covered with an emphasis on the future trends and technologies.
