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`

`Chapter 4
`
`3D Fabrics for Technical Textile Applications
`
`Kadir Bilisik, Nesrin Sahbaz Karaduman and Nedim Erman Bilisik
`
`Additional information is available at the end of the chapter
`
`http://dx.doi.org/10.5772/61224
`
`Abstract
`
`Two dimensional (2D) woven, braided, knitted and nonwoven fabrics have been used
`for the fabrication of soft and rigid structural composite parts in various industrial
`areas. However, composite structure from biaxial layered fabrics is subject to delami‐
`nation between layers due to the lack of through-the-thickness fibers. It also suffers
`from crimp which reduces the mechanical properties. Triaxial fabrics have an open
`structure and low fiber volume fraction. However, in-plane properties of triaxial fab‐
`rics are more homogeneous due to bias yarns. A 3D woven fabric has multiple layers
`and is free of delamination due to the z-fibers. However, 3D woven fabric has low in-
`plane properties. Three dimensional braided fabrics have multiple layers and they are
`without delamination due to intertwine type out-of-plane interlacement. However,
`they have low transverse properties. A 3D knitted fabric has low fiber volume fraction
`due to its looped structure. A 3D nonwoven fabric is composed of short fibers and is
`reinforced by stitching. However, it shows low mechanical properties due to lack of
`fiber continuity. Various unit cell based models on 3D woven, braided, knitted and
`nonwoven structures were developed to define the geometrical and mechanical prop‐
`erties of these structures. Most of the unit cell based models include micromechanics
`and numerical techniques.
`
`Keywords: Fabric architecture, woven fabric, braided fabric, knitted fabric, 3D non‐
`woven fabric
`
`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‐
`
`© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons
`Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution,
`and reproduction in any medium, provided the original work is properly cited.
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`82
`
`Non-woven 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. Three-
`dimensional 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-
`
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`
`83
`
`thickness 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.
`
`2. Classification of 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).
`
`Non-interlacing
`Orthogonally
`Orientating and
`Binding
`
`Type Uniaxial
`
`Type
`Multiaxial
`
`Direct
`Binding
`
`Indirect
`Binding
`
`Direct
`Binding
`
`Indirect
`Binding
`
`Modified 2D Weaving Machine
`
`Thick Panel [21]
`
`Specially Designed Machine
`
`Profiled Bar/Beam [22]
`
`Modified 2D Weaving Machine
`
`Profiled Bar/Beam [23]
`
`Specially Designed Machines
`
`Profiled Bar/Beam [24-26]
`
`Thick Tubular [27]
`
`Specially Designed Machine
`
`Thick-Walled Tubular [28]
`
`Modified Warp Knitting Machine
`
`Thin Panel [29]
`
`Specially Designed Machines
`
`Thick Panel [30, 31]
`
`Thin Panel [32]
`
`Table 1. Three-dimensional woven fabric classification based on non-interlace structuring [18].
`
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`

`84
`
`Non-woven Fabrics
`
`Structure
`
`Solid
`
`Hollow
`
`Shell
`
`Nodal
`
`Architecture
`Multilayer; Orthogonal; Angle
`interlock
`
`Multilayer
`
`Single layer; Multilayer
`Multilayer; Orthogonal; Angle
`interlock
`
`Shape
`
`Compound structure with regular or tapered geometry
`
`Uneven surfaces, even surfaces, and tunnels on different
`levels in multi-directions
`Spherical shells and open box shells
`
`Tubular nodes and solid nodes
`
`Table 2. Three-dimensional woven fabric classification based on macro-structure [19].
`
`Direction
`
`2 or 3
`
`3
`
`4
`
`5
`
`6 to 15
`
`Cartesian
`Angle interlock;
`Layer-to-layer;
`Through the thickness
`Core structure
`
`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
`
`Rectangular array
`Hexagonal array
`
`Woven
`Polar
`
`Tubular
`
`Three dimensional weaving
`
`Cartesian
`
`Orthogonal nonwoven
`Polar
`
`Weft-insertion
`
`Weft-winding and
`sewing
`
`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
`Rectangular array
`Hexagonal array
`
`Open-lattice
`Solid
`
`Tubular
`
`Corner across
`Face across
`
`Tubular
`
`Solid
`
`Tubular
`
`Rectangular array
`Hexagonal array
`
`Rectangular array
`Hexagonal array
`
`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
`
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`
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`
`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).
`
`Number of
`Yarn Sets
`
`3D Braid
`Cartesian
`
`Polar
`
`Three Dimensional Braiding
`3D Axial Braid
`Cartesian
`Polar
`
`Square
`
`Rectangular
`(Out-of-plane at
`an angle)
`1×1 pattern
`3×1 pattern
`
`Tubular
`(Out-of-plane at
`an angle)
`1×1 pattern
`3×1 pattern
`
`Triaxial fabric
`(In-plane)
`Rectangular
`(Out-of-plane at
`an angle)
`1×1pattern
`3×1 pattern
`
`Triaxial fabric
`(In-plane)
`Tubular
`(Out-of-plane at
`an angle)
`1×1 pattern
`3×1 pattern
`
`1 or 2
`
`3
`
`4
`
`5 or 6
`
`Multiaxis 3D Braid
`Cartesian
`Polar
`Rectangular
`Tubular
`(Out-of-plane at
`(Out-of-plane at
`an angle)
`an angle)
`
`Rectangular
`
`Tubular
`
`(Out-of-plane
`at an angle)
`
`(Out-of-plane at
`an angle)
`
`Rectangular
`(Out-of-plane
`at an angle)
`Rectangular
`(Out-of-plane
`at an angle)
`
`Tubular
`(Out-of-plane at
`an angle)
`Tubular
`(Out-of-plane at
`an angle)
`
`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 damage-
`tolerant composites [37].
`
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`86
`
`Non-woven Fabrics
`
`Type
`I
`
`II
`
`III
`
`IV
`
`Fabric classification
`2D fabric
`
`2D fabric base 3D
`shape
`3D solid fabric
`
`3D hollow fabric/sandwiched
`fabric
`
`Weft knitted fabric
`Plain, Milano rib, inlaid
`fabrics
`Plain, rib
`
`Warp knitted fabric
`Dembigh, Atlas
`
`Dembigh, Atlas
`
`Plain and rib fabrics with
`inlay fiber yarns
`Single jersey face structure
`
`Multiaxial warp knitted
`fabrics
`Single Dembigh face
`structure
`
`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]. Two-
`and three-dimensional nonwoven nano-web fabricated via electrospinning is a new develop‐
`ment to make nanofiber-based nonwoven fabrics [39].
`
`Nonwoven
`fabric
`
`2D fabric
`3D fabric
`
`Web formation
`
`Formation techniques
`
`Web structure Fiber orientation in web
`
`Needling
`
`Mechanical
`
`Looping
`
`Entangling
`
`Plugs
`
`Loops
`
`Balls
`
`In plane and out-of-plane
`fiber orientation
`
`Short fiber in plane and
`continuous fiber in the out-
`of-plane orientation
`
`In plane fiber placement
`and entanglement
`
`Thermal
`
`Chemical
`
`Hot air; Calendaring; Welding
`
`Impregnation; Spraying; Printing;
`Foaming
`
`-
`
`-
`
`-
`
`-
`
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`
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`
`Nonwoven
`fabric
`
`Web formation
`
`Formation techniques
`
`Web structure Fiber orientation in web
`
`Electric field
`
`Nanofiber entanglement under
`electric energy
`
`nanofiber
`
`In plane continuous nano
`fiber placement and
`entanglement
`
`Table 6. Classification of nonwoven fabrics [38].
`
`3. Types of fabrics
`
`3.1. Two-dimensional fabrics
`
`3.1.1. Woven 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-the-
`thickness 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
`
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`

`88
`
`Non-woven Fabrics
`
`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.
`
`3.1.2. Triaxial woven fabric
`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
`stiffness in ±45˚ directions when compared to the biaxial fabrics as well as having a more
`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-
`use requirements.
`
`Figure 2. Triaxial woven fabrics (a) loose fabric (b) tight fabric (c) one variant of triaxial woven fabric, and (d) quart-
`axial woven fabric [44, 45].
`
`3.1.3. Braided fabric
`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
`
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`surface shown in Figure 3, braiders are intertwined with each other. Basic braid patterns that
`can be produced by traditional methods are diamond, regular and hercules braid [46]. The 2D
`braided fabric reinforced composite fabrication is similar to that of 2D woven composites.
`Multiple braided fabrics can be stacked one on top of another to produce reinforced compo‐
`sites. These composites suffer from yarn crimp and lack through-the-thickness reinforcement
`(z-yarns) and thus experience delamination leading to a poor impact behavior [4]. In order to
`overcome the delamination and related problems, 2D fabric layers can be stitched together in
`the thickness direction to impart out of plane fiber reinforcement. Stitching was shown to
`substantially decrease delamination but it can lead to a reduction in in-plane properties due
`to the holes created by stitching needle which act as stress concentration points.
`
`Figure 3. (a) Two-dimensional traditional biaxial braided fabric, and (b) triaxial braided fabric [47].
`
`3.1.4. Triaxial 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
`
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`

`90
`
`Non-woven Fabrics
`
`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].
`
`3.1.6. Uniaxial knitted fabric
`
`The special looped structure of knitted fabrics results in large gaps in the fabric structure. This
`reduces the overall fiber volume fraction of the composite leading to low mechanical proper‐
`ties. Furthermore, the fabric is loosely formed unlike a woven fabric, which leads to high
`elongation and low stiffness. These problems have led to structural modifications of knitted
`fabrics by using inlay yarns either in fabric length or width direction to increase the mechanical
`properties of the resulting composites. Figure 5 presents the schematic views of these modifi‐
`cations. The inlay yarns are trapped inside the knitted loops during the fabric formation. It
`was shown that the tensile strength of uniaxial knitted fabric composites can be improved
`significantly in the inlaid directions [49].
`
`Figure 5. (a) Two-dimensional warp in-laid weft knitted fabric (b) 2D weft in-laid weft knitted fabric (c) 2D warp in-
`laid warp knitted fabric (d) 2D weft in-laid warp knitted fabric, and (e) 2D weft in-laid spiral knitted fabric [49].
`
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`
`3.1.7. Biaxial knitted fabric
`
`Biaxial knitted structures were developed by the insertion of warp (0°), weft (90°) or diagonal
`(±45°) yarns to the weft or warp knitted fabrics, as shown in Figure 6. The in-laid yarns improve
`the directional mechanical properties of the resulting composites.
`
`Figure 6. (a) Two-dimensional weft in-laid 0°/90° knitted fabric and schematic view (b) warp in-laid 0°/90° knitted fab‐
`ric, and (c) warp in-laid ±45° knitted fabric [50-52].
`
`3.1.8. Nonwoven fabric
`
`Nonwoven fabric is a web structure made up of short fibers that are held together by various
`techniques. These techniques include needling, knitting, stitching, thermal bonding, chemical
`bonding, and electrospinning. Needling is a method where vertically positioned barbed
`needles or water jets strike into the fiber web so as to entangle the fibers and create a mechanical
`locking between them. Knitting aims to entrap the fibers and fix them in position with the aid
`of knitting loops. In stitching technique, the fiber web is stitched in through-the-thickness
`direction. Thermal bonding is generally applied to thermoplastic fibers and powders. Fiber
`web is subjected to heat treatment which softens and unifies the neighboring fiber surfaces.
`This process is followed by cooling that solidifies the fibers and gives the web its final form.
`In the chemical process, polymer dispersions are used as binders to consolidate the nonwoven
`fabric. In electrospinning method, polymer solution is drawn under high electric energy field
`by using needles. Various fibers can be used to make nonwoven nano fibers such as polyur‐
`ethane, polyvinyl alcohol and carbon. The nonwoven produced from these fibers can provide
`interesting physical and electrical properties with their high surface area. Nanofibers with
`diameters in the range of 40-2000 nm (0.04-2 μm) can be made. Fiber diameters can be varied
`and controlled [53-55]. Figure 7 shows the schematic and real views of 2D nonwoven fabrics
`manufactured by various methods [56, 57].
`
`Figure 7. Schematic view of 2D nonwoven fabric by (a) mechanical needling (b) hydroentanglement (c) schematic view
`of stitched nonwoven structure (d) knitting loop surface, and (e) knitting loop reverse surface [58].
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`3.2. Three-dimensional fabrics
`
`3.2.1. Non-interlaced fabric structures
`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-the-
`thickness 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
`oriented in 0/90/±45˚ directions (Figure 8) [43].
`
`Figure 8. (a) Unidirectional non-interlaced fabric schematic and fabric (b) biaxial non-interlaced fabric schematic and
`fabric, and (c) multiaxis non-interlaced fabric schematic and fabric [43].
`
`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
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`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
`
`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
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`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-the-
`thickness fabric, on the other hand, bias yarns take a straight path along the f