Cartesian 3D braiding

Cartesian 3D braiding K. Bilisik Erciyes University, Talas-Kayseri, Turkey 4.1 4 Introduction Textile structural composites are widely used in var...

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Cartesian 3D braiding K. Bilisik Erciyes University, Talas-Kayseri, Turkey

4.1

4

Introduction

Textile structural composites are widely used in various industrial sectors, such as civil and defense, as they possess some improved speciﬁc properties compared to basic materials like metals and ceramics (Dow and Dexter, 1997; Kamiya et al., 2000; Ko and Chou, 1989; Chou, 1992; Hearle, 1994; Mouritz et al., 1999). Research conducted on textile structural composites has shown that they can be considered as alternative materials because they are delamination-free and damage tolerant (Ko and Chou, 1989). Two-dimensional (2D) biaxial, triaxial and three-dimensional (3D) braided fabric structures are used as structural elements in the medical sector (Ambrosio et al., 2009), space and rocket propulsion and the transportation industries (Beyer et al., 2006). Examples of these elements are plate, stiffened panels, beams and spars, shell or skin structures, hip and medical devices and prostheses (Yamamoto and Hirokawa, 1990; Donnet and Bansal, 1990; Bilisik, 2009). From a textile-processing viewpoint, 3D braiding is a preform technique used in the multidirectional near-net-shape manufacturing of highly damage-tolerant structural composites (Uozumi et al., 2001; Furrow, 1996; Ko, 1987; Bogdanovich and Mungalov, 2002). 3D braiding is highly automated and readily available. The fabrication of small sectional 3D braided preforms is low cost, and not labor intensive (Dow and Dexter, 1997). However, the fabrication of large sections of 3D braided preform may not be feasible due to position displacement of the yarn carriers. Simple 3D braided preform consists of 2D biaxial fabrics and is stitched depending on stack sequence. Generally, 3D braided preforms are fabricated by traditional maypole braiding (slotted horngear matrix) or innovative Cartesian braiding called “4-step and 2-step braiding method,” which are alternatively called “track and column; row and column,” or more recently by 3D rotary braiding and multistep braiding (Ko, 1987; Bluck, 1969; Maistre, 1974; Florentine, 1983; Weller, 1985; Popper and McConnell, 1987; Kyosev, 2015). Multistep braiding is a relatively new concept, and with this technique it is possible to make multidirectional 3D braided preform by orienting the yarn in various directions in the preform (Kostar and Chou, 1994a, 2002). The aim of this study is to review Cartesian 3D braided fabrics, their production methods and equipment, properties and applications.

4.1.1

Patterning in three-dimensional braiding

In Cartesian 3D braiding, 3D braided preform structure was formed in four distinctive steps. The 3D fully braided and axially braided structures, both rectangular and Advances in Braiding Technology. http://dx.doi.org/10.1016/B978-0-08-100407-4.00004-1 Copyright © 2016 Elsevier Ltd. All rights reserved.

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concentric shapes, are patterned during formation as 1 1, 2 1, 3 1 and 4 1. The ﬁrst number represents row directional movement for making 3D braided rectangular shape and circumferential rotation to make a 3D braided concentric shape, whereas the second number represents column directional movement for making 3D braided rectangular shape and radial row directional movement to make a 3D braided concentric shape. The 1 1 braid pattern in 3D braided rectangular shape means the braider carrier moves just one braider carrier distance in the row and column directions, whereas the 2 1 braid pattern means the braider carrier moves two and one braider carrier distance in the row and column directions, respectively. The 3 1 braid pattern means the braider carrier moves three and one braider carrier distance in the row and column directions, respectively. In addition, the 4 1 braid pattern means the braider carrier moves four and one braider carrier distance in the row and column directions, respectively. The 1 1 braid pattern in a 3D braided concentric shape means the braider carrier rotates just one braider carrier distance in the circumferential direction and moves just one in the radial row direction, whereas the 2 1 braid pattern means the braider carrier rotates two and moves one braider carrier distance in the circumferential and radial row directions, respectively. The 3 1 braid pattern means the braider carrier rotates three and moves one braider carrier distance in the circumferential and radial row directions, respectively. In addition, the 4 1 braid pattern means the braider carrier rotates four and moves one braider carrier distance in the circumferential and radial row directions, respectively.

4.1.2

Classiﬁcations of three-dimensional braided fabrics

3D braided preforms are classiﬁed based on the yarn type and formation, the number of yarn sets, yarn orientation and interlacements, microemeso unit cells and macro geometry. One of the general classiﬁcation schemes was proposed by Ko (1987). Another classiﬁcation scheme was proposed depending upon microemeso unit cells and macro geometry. In this scheme, 3D braided preform is divided into thin- and thick-walled tubes, which include a contoured shape and connectors, and special and mobile structures, which include structural holes and bifurcations (Lee, 1990). Kamiya et al. (2000) classed 3D braided structure based on manufacturing techniques as solid, two-step, four-step, and multistep. Bilisik (2013) proposed a more speciﬁc classiﬁcation scheme of 3D braided preforms based on type of interlacement patterns, yarn orientation and the number of yarn sets. In the proposed classiﬁcation scheme, as shown in Table 4.1, 3D braiding is divided into three categories as 3D braid, 3D axial braid and multiaxis 3D braid, which are noninterlaced inside but only interlaced at the outside preform surface. They are further subdivided based on reinforcement directions ranging from two to six with Cartesian or polar forms. This classiﬁcation scheme may be useful for further research on the development of multiaxis 3D braided fabric and 3D braiding techniques (Bilisik, 2013).

Table 4.1

The classiﬁcation of 3D braiding based on interlacement and yarn axis Three-dimensional braiding

Number of yarn sets

Cartesian

Polar

1 or 2

Square

Tubular • Through-thethickness (out-ofplane at an angle) • 1 1 pattern 3 1 pattern

3D braid

3D axial braid Cartesian

Polar

Multiaxis 3D braid Cartesian

Polar

Rectangular • Through-the-thickness (out-of-plane at an angle)

Tubular • Through-the-thickness (out-of-plane at an angle)

Rectangular • Through-the-thickness (out-of-plane at an angle)

Tubular • Through-the-thickness (out-of-plane at an angle)

4

Rectangular • Through-the-thickness (out-of-plane at an angle)

Tubular • Through-the-thickness (out-of-plane at an angle)

5 or 6

Rectangular • Through-the-thickness (out-of-plane at an angle)

Tubular • Through-the-thickness (out-of-plane at an angle)

Rectangular • Through-thethickness (out-ofplane at an angle) • 1 1 pattern 3 1 pattern 3

Rectangular • Through-thethickness (out-ofplane at an angle) • 1 1 pattern 3 1 pattern

Bilisik, K., 2013. Three dimensional braiding for composites: a review. Text. Res. J. 83(13), 1414e1436.

Tubular • Through-thethickness (out-ofplane at an angle) • 1 1 pattern 3 1 pattern

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4.1.3 4.1.3.1

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Structure of Cartesian three-dimensional braids Three-dimensional fully braided fabric structure

Rectangular In 3D fully braided fabric structure, there is one set of longitudinal yarns arranged in column and row directions in the cross section. The braider yarns are intertwined simultaneously in predetermined paths relative to each other within the matrix to form the braided preform. Florentine (1982) developed a 3D fully braided preform and a method. The preform is layered and yarns are intertwined with each other depending upon a predetermined path. In this way, yarn passes thickness (through-the-thickness) of the fabric and is biased such that the width of the fabric is at an angle between 10 and 80 . Fig. 4.1 shows the unit cell of 3D fully braided preform (Li, 1990). Bilisik and Sahbaz (2012) have studied the multilayered (thick) Cartesian 3D braided structures. Yarns in the 3D braided unit cell at 1 1 braid pattern were intertwined with each other, and all yarns were interlocked in each braid layer in the in-plane directions and in each adjacent layer in the out-of-plane directions. Therefore, the 3D braided unit cell structures were fully interlocked as shown in Fig. 4.2(a) and (b). The braider yarn path on the edge and inside of the 3D representative braided unit cell structures is depicted with a few layers (three or four layers) and many layers (nine and ten layers) as shown in Fig. 4.2 (c, left) and (c, right), respectively. As seen in the Fig. 4.2 (c, left), the braid (þ) yarn on the edge changed its path from braid (þ) to braid () at one step, and later braid () follows the out-of-plane direction of the structure based on the predetermined path. As seen in Fig. 4.2 (c, right), braid (þ) yarn on the edge changed its path from braid (þ) to braid () in two steps. After the multilayer yarn path occurred due to the increasing number of layers in the 3D braided unit cell structure, braid () follows the out-of-plane direction of the structure based on the predetermined

Figure 4.1 Unit cell of Cartesian 3D fully braided preform (Li, 1990).

Cartesian 3D braiding

(a)

111

(b)

(c) Edge path

Edge path Inside path Inside path Edge path

Surface path

Surface layer

Figure 4.2 (a) Surface of nine-layer representative Cartesian 3D fully braided preform structures in 1 1 braid pattern, (b) unit cell, (c) braider yarn path on the edge and inside of the Cartesian 3D representative braided preform with four layers (left) and six layers (Bilisik and Sahbaz, 2012) (right).

path. A one-step edge path was observed to have occurred on both surfaces of the 3D braided structure in the three- and four-layer unit cell structures, whereas on the inside layers of the 3D braided structure, a two-step edge path occurred in ﬁve- and 10-layer structures as shown in Fig. 4.2(c, left) for two- to three-layer structures and Fig. 4.2(c, right) for ﬁve- to 10-layer structures. This two-step edge path is called the “multilayer yarn path.” In the 2 1 braid pattern, yarns in the 3D braided unit cell were intertwined with each other, and all yarns were interlocked in each braid layer in the in-plane direction, whereas there was no interlocking in each adjacent layer in the out-of-plane direction. The exception occurs at the edge of the braid structure, at which the ﬁrst layer was locked to the second layer and the third layer was locked to the fourth layer on both edges of the braid structure. Therefore, there was an empty pocket between braid layers in the structure, as clearly shown in Fig. 4.3(a) for representative nine-layer Cartesian 3D fully braided structures (Bilisik and Sahbaz, 2012). The 3 1 and 4 1 braid pattern braided structures were similar to those of the 1 1 and 2 1 braid pattern braided structures, respectively. However, 3D braided structures in 3 1 and 4 1

(a)

(b)

(c)

(d)

(e)

(f)

Figure 4.3 (a) Side view of nine-layer representative Cartesian 3D fully braided preform structures in 2 1 braid pattern, (b) unit cell, (c) surface of three-layer representative Cartesian 3D fully braided preform structures in 3 1 braid pattern, (d) unit cell, (e) surface of three-layer representative Cartesian 3D fully braided preform structures in 3 1 braid pattern, (f) unit cell (Bilisik and Sahbaz, 2012).

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braid patterns become coarse compared to those of 1 1 and 2 1 braid patterns due to long ﬂoating in the crossing regions in the 3D braided structure. These structures are shown in Fig. 4.3(a)e(f), respectively.

Concentric In 3D circular fully braided fabric structure, there is one set of longitudinal yarns arranged in circumferential ring and radial row directions in the cross section. The braider yarns are intertwined circumferentially and simultaneously in predetermined paths relative to each other within the circular matrix to form the circular braided preform. Florentine (1982) developed a 3D fully braided preform and method. The preform is layered and yarns are intertwined with each other depending upon a predetermined path. In this way, yarn passes the wall thickness (through-the-thickness) of the circular braided fabric and is biased such that the diameter of the fabric is at an angle. Brown (1988, 1985) developed a 3D circular braided fabric. The fabric has one yarn set. These yarns are intertwined with each other to make a circular fully braided structure. The fabric has bias yarn orientation thickness of the cylinder wall and cylinder surface at the helical path, as shown in Fig. 4.4. Sahbaz (2013) has studied the multilayered (thick) 3D circular braided structures under the direction of Bilisik. Yarns in the 3D braided unit cell at 1 1 braid pattern were intertwined with each other and all yarns were interlocked between braid layers in the in-plane directions and in each adjacent layer in the out-of-plane directions. Therefore, the 3D braided unit cell structures were fully interlocked as shown in Fig. 4.5(a)e(c). The braider yarn path on the edge and inside of the 3D representative braided unit cell structures with many layers (10 layers) is shown in Fig. 4.5(d). As seen in Fig. 4.5(d), the braid (þ) yarn on the outside diameter changed its path from

(a)

(b)

1 mm ×8

30kv

Figure 4.4 (a) 3D circular representative fully braided structure (Bilisik, 1998), and (b) cross-sectional view of actual ﬁber-based 3D circular fully braided preform (Brown, 1985).

Cartesian 3D braiding

(a)

113

(b)

(c)

(d)

Figure 4.5 (a) Surface of 10-layer representative 3D circular fully braided preform structures in 1 1 braid pattern, (b) unit cell, (c) perspective view of unit cell, (d) braider yarn path from outside of the diameter to the inside of the diameter and vice versa in the 3D circular preform (Sahbaz, 2013).

braid (þ) to braid () at one step and its position shifts to the inside diameter of the structure, and later braid () follows the out-of-plane direction of the structure based on the predetermined path, and its position shifts to the outside diameter. Therefore, braider yarn path spirally biased the wall thickness of the 3D circular structure from the outside diameter to the inside diameter and vice versa. This is continued depending upon structure length. In the 2 1 braid pattern, yarns in the 3D circular braided unit cell were intertwined with each other and all yarns were interlocked in each braid layer in the in-plane direction, whereas there was no interlocking in adjacent layers in the out-of-plane direction as shown in Fig. 4.6. Therefore, there was an empty pocket between each braid layer in the structure, which looks like concentric rings, as shown in Fig. 4.6(d). Fig. 4.6(a)e(d) shows the (a) 3D circular braided representative preform, (b) unit cell, (c) perspective view of unit cell and (d) cross-sectional view of the structure. The 3 1 and 4 1 braid pattern braided structures were similar to those of the 1 1 and 2 1 braid pattern braided structures, respectively. However, 3D circular braided structures in 3 1 and 4 1 braid patterns become coarse compared to those

(a)

(b)

(c)

(d)

Figure 4.6 (a) Surface of 10-layer representative 3D circular fully braided preform structure in 2 1 braid pattern, (b) unit cell, (c) perspective view of unit cell, (d) cross-sectional view of braider layers in the radialecircumferential plane (Sahbaz, 2013).

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(a)

(b)

(c)

(d)

Figure 4.7 (a) Surface of four-layer representative 3D circular fully braided preform structures in 3 1 braid pattern, (b) unit cell, (c) perspective view of unit cell, (d) cross-sectional view of braider layers in the radialecircumferential plane (Sahbaz, 2013).

of 1 1 and 2 1 braid patterns due to long ﬂoating in the crossing regions in the 3D braided structure. These structures are shown in Fig. 4.7(a)e(d) and Fig. 4.8(a)e(d), respectively.

4.1.3.2

Three-dimensional axially braided fabric structure

Rectangular The 3D axially braided structure consisted of two yarn sets as axial and braider yarns. Braider yarns are intertwined with the axial yarns, which locate between the braiding yarns in each row and column, to form the structure depending upon predetermined path (Li, 1990). Fig. 4.9 shows the unit cell of 3D axially braided preform. The preform has layered and axial yarns extended to the preform fabrication direction, whereas braider yarns are biased such that the width of the fabric is at an angle. Another study on the multilayered (thick) Cartesian 3D axially braided structures (Bilisik, 2011) demonstrated that to make the representative 3D braided preform in a 1 1 braid pattern, the braider carrier and axial must be arranged in a matrix of rows and columns. Braider yarns were intertwined with the axial yarns and all

(a)

(b)

(c)

(d)

Figure 4.8 (a) Surface of four-layer representative 3D circular fully braided preform structures in 4 1 braid pattern, (b) unit cell, (c) perspective view of unit cell, (d) cross-sectional view of braider layers in the radialecircumferential plane (Sahbaz, 2013).

Cartesian 3D braiding

115

Figure 4.9 Unit cell of the Cartesian 3D axial braided preform (Li, 1990).

yarns were interlocked in each braid layer in the in-plane directions and in adjacent layers in the out-of-plane directions. Therefore, the 3D axially braided unit cell structures were interlocked and axial yarns were laid in the structure as shown in Fig. 4.10(a) and (b). In the 2 1 braid pattern, yarns in the 3D axially braided unit cell were intertwined around the axial with each other and all braider and axial yarns were interlocked in each axially braid layer in the in-plane directions, whereas there was no interlocking in adjacent layers in the out-of-plane direction except at the edge of the axial braid structure. In the latter, the ﬁrst layer was locked to the second layer, and the third layer was locked to the fourth layer on both edges of the axially braided structure (Bilisik, 2011). Therefore, there was an empty pocket between axially braided layers in the structure as clearly shown in Fig. 4.10(c) and (d). The 3 1 and 4 1 braid pattern axially braided structures were similar to those of the 1 1 and 2 1 braid pattern axially braided structures, respectively. However, 3D braided structures in the 3 1 and 4 1 braid patterns become coarse

(a)

(b)

(c)

(d)

Figure 4.10 (a) Surface of layered representative Cartesian 3D axially braided preform structures in 1 1 braid pattern; (b) unit cell; (c) surface and sectional views of layered representative Cartesian 3D axially braided preform structures in 2 1 braid pattern, respectively; (d) unit cell of 2 1 braid pattern (Bilisik, 2011).

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(a)

Advances in Braiding Technology

(b)

(c)

(d)

Figure 4.11 (a) Surface of layered representative Cartesian 3D axially braided preform structures in 3 1 braid pattern (Bilisik, 2011), (b) unit cell, (c) surface and sectional views of layered representative Cartesian 3D axial braided preform structures in 4 1 braid pattern, (d) unit cell of 4 1 braid pattern.

compared to those of 1 1 and 2 1 braid patterns due to long ﬂoating in the crossing regions. These structures are shown in Fig. 4.11(a)e(d).

Concentric The 3D circular axially braided structure consisted of two yarn sets as axial and braider yarns. Braider yarns are intertwined with the axial yarns, which locate between the braiding yarn in each circular ring and radial row, to form the structure depending upon predetermined path (Bilisik, 2013; Wall, 2002). Bilisik and Sahbaz (2013) have studied the multilayered 3D circular axially braided structures. It was claimed that to make the representative 3D circular axially braided preform in a 1 1 braid pattern, the braider carrier and axial must be arranged in a matrix of circular rings and radial rows. Braider yarns were circumferentially and simultaneously intertwined with the axial yarns and all yarns were interlocked in each braid layer in the in-plane directions and in each adjacent layer in the out-of-plane directions. Therefore, braider yarn path spirally biased the wall thickness of the 3D circular structure from the outside diameter to the inside diameter and vice versa, whereas the axial yarns were laid in the structure as shown in Fig. 4.12(a)e(d). In the 2 1 braid pattern, yarns in the 3D circular axially braided unit cell were intertwined with each other and all yarns were interlocked in each braid layer in the in-plane directions, whereas there was no interlocking in adjacent layers in the out-of-plane directions. Therefore, there was an empty pocket between each braid layers in the structure, which looked like concentric rings as shown in Fig. 4.13(d). Fig. 4.13(a)e(d) shows (a) the 3D circular axially braided representative preform, (b) unit cell and (c) perspective views of unit cell and (d) cross-sectional views of the structure. The 3 1 and 4 1 braid pattern braided structures were similar to those of the 1 1 and 2 1 braid pattern braided structures, respectively. However, 3D circular axially braided structures in 3 1 and 4 1 braid patterns become coarse compared to those of 1 1 and 2 1 braid patterns due to long ﬂoating in the crossing regions in the 3D braided structure. These structures are shown in Fig. 4.14(a)e(d) and Fig. 4.15(a)e(d), respectively.

Cartesian 3D braiding

(a)

117

(b)

(c)

(d)

Figure 4.12 (a) Surface of four-layer representative 3D circular axially braided preform structures in 1 1 braid pattern, (b) unit cell, (c) perspective view of unit cell, (d) cross section of the 3D circular axially braided structure.

(a)

(b)

(c)

(d)

Figure 4.13 (a) Surface of 10-layer representative 3D circular axially braided preform structures in 2 1 braid pattern, (b) unit cell, (c) perspective view of unit cell, (d) cross section of the 3D circular axially braided structure (Sahbaz, 2013).

(a)

(b)

(c)

(d)

Figure 4.14 (a) Surface of 10-layer representative 3D circular axially braided preform structures in 3 1 braid pattern, (b) unit cell, (c) perspective view of unit cell, (d) cross section of the 3D circular axially braided structure (Sahbaz, 2013).

Another 3D axially braided preform was developed by McConnell and Popper (1988). Axial yarns are arranged in a matrix array based on the sectional geometry of the braided structure. The braider yarns move along alternating diagonals of the axial array and interlock the axial yarns and hold them in the desired shape.

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(a)

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(b)

(c)

(d)

Figure 4.15 (a) Surface of four-layer representative 3D circular axially braided preform structures in 4 1 braid pattern, (b) unit cell, (c) perspective view of unit cell, (d) cross section of the 3D circular axially braided structure.

Figure 4.16 Schematic views of 3D various sectional axially braided preforms. Mcconnell, R.F., Popper, P., 1988. Complex Shaped Braided Structures. US Patent No 4719837, January 19.

The arrangement of yarns provides directional reinforcement and structural shape with a relatively small number of braider yarns (Popper and McConnell, 1987). It was also shown that a variety of braided preforms including T, H, TT and a braided bifurcation preform can be fabricated (Popper and McConnell, 1987). Fig. 4.16 shows the various structurally shaped 3D axially braided structures schematically.

4.1.3.3

Multiaxis three-dimensional braided fabric structure

Multiaxial 3D braided structure has braider yarns, warp (axial), ﬁlling and Z-yarns. The braider yarns are intertwined with the orthogonal yarn sets to form the multiaxis 3D braided preform (Chen and El-Shiekh, 1994), as shown schematically in Fig. 4.17(a). Another multiaxial 3D braided structure has bias yarns placed in the in-plane direction of the structure, and warp (axial), radial (Z-yarns) and braider yarns placed in the out-of-plane direction of the structure (Bilisik, 1998). The braider yarns are intertwined with the axial yarns whereas bias yarns are oriented at the surface of the structure and locked by the radial yarns to the other yarn sets. Fig. 4.17(b)e(d) shows the multiaxial cylindrical and conical para-aramid 3D braided structures. Table 4.2 presents the speciﬁcations of multiaxial 3D braided Kevlar® preforms.

Cartesian 3D braiding

(a)

(b)

119

(c)

(d)

Figure 4.17 (a) The unit cell of multiaxis 3D braided preform (Chen and El-Shiekh, 1994), (b) the multiaxis 3D cylindrical braided para-aramid preform, (c) tightly braided neck part of the conical Kevlar® preform, (d) conical part of the Kevlar® preform (Bilisik, 1998).

Kostar and Chou (1994b) developed a multistep braiding process which was based on a computer algorithm. In this way, the yarns make a large interlacement angle at the thickness of the fabric which results in a large-sized unit cell. In addition, the yarns may change to more positions in the unit cell compared to the unit cell in the four-step and two-step processes. On the other hand, the algorithm can also calculate the steps needed for the production of unusual braids which include surrogate material such as fasteners, additional yarn or voids (Kostar and Chou, 1994a).

4.1.4 4.1.4.1

Braiding techniques Four-step full braiding method

Rectangular Cartesian 3D fully braided preform was made by the four-step braiding method. This method involves four distinctive steps to form the 3D braided preform structure. Fig. 4.18 shows the 1 1 braid pattern (a1ee1), 2 1 braid pattern (a2ee2), 3 1 braid pattern (a3ee3), and 4 1 braid pattern (a4ee4). The 1 1 braid pattern means the braider carrier moves just one braider carrier distance in the row and column directions, whereas the 2 1 braid pattern means the braider carrier moves two and one braider carrier distance in the row and column directions, respectively. The same analogy can be applied to 3 1 and 4 1 braid patterns (Bilisik and Sahbaz, 2012). To make the Cartesian 3D fully braided preform in a 1 1 braid pattern, the braider carrier must be arranged in a matrix of rows and columns as presented in Fig. 4.18(a1). The ﬁrst step is sequential, and the reversal movement of the braider carriers is in the column direction (b1). The second step is sequential, and the reversal movement of the braider carriers is placed on the rapier in the row direction (c1). The third step is again sequential, and the reversal movement of the braider carriers is in the column direction (d1). The fourth step is again sequential, and the reversal movement of the braider carriers is placed on the rapier in the row direction (e1). After that, the 3D braided preform is removed from the braiding zone by takeup. These steps were repeated depending on preform length requirements. Braid patterns other than 1 1 are also shown in Fig. 4.18 in steps a2ee2 for the 2 1 pattern, a3ee3 for the 3 1 pattern,

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Multiaxis 3D braided para-aramid preform by six-step method (Bilisik, 2013)

Table 4.2

Fiber

Kevlar® 29(K29), Kevlar® 129(K129)

Axial yarn

1100 dtex (3 ply), K29

Bias yarn

1100 dtex (4 ply), K29

Radial yarn

1100 dtex (1 ply), K129

Braider yarn

1100 dtex (4 ply), K29

Structure

Multiaxis six-step 3D braided preform

Axial yarn

2 (Circumferential layers 18 radial rows)

þBias yarn

1 layer 18 radial rows

eBias yarn

1 layer 18 radial rows

Radial

18 ends (one radial for every axial row)

Cross-section

Cylinder

Dimensions

100 (Outside diameter) 5 (wall thickness) 250 (length) mm

Preform tightness

Very high

Fiber

Kevlar® 49

Axial yarn

3400 dtex (3 ply)

Bias yarn

3400 dtex (2 ply)

Radial yarn

3400 dtex (3 ply)

Braider yarn

3400 dtex (2 ply)

Structure

Multiaxis eight- step 3D braided preform

Axial yarn

2 (Circumferential layers 18 radial rows)

þBias yarn

1 layer 18 radial rows

Bias yarn

1 layer 18 radial rows

Radial

18 ends (one radial for every axial row)

Cross-section

Conical

Dimensions

140 (Large-diameter) 55 (small diameter) 5 (wall thickness) 210 (length) mm

Preform tightness

Medium

and a4ee4 for the 4 1 patterns, in which the braider carriers on the rapier move two, three, and four braider carrier distances in the row direction, respectively. The number of braider carriers can be expanded in row and column directions depending upon preform dimensions.

Cartesian 3D braiding

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a1

b1

c1

d1

e1

a2

b2

c2

d2

e2

a3

b3

c3

d3

e3

a4

b4

c4

d4

e4

Figure 4.18 Four-step braiding method to make representative Cartesian 3D fully braided preforms (Bilisik and Sahbaz, 2012); braid pattern 1 1 (a1ee1), braid pattern 2 1 (a2ee2), braid pattern 3 1 (a3ee3) and braid pattern 4 1 (a4ee4).

Concentric 3D circular braided preform was also made by the four-step braiding method. This method involves four distinctive steps to form the 3D circular braided preform structure. Fig. 4.19 shows the 1 1 braid pattern (a1ee1), 2 1 braid pattern (a2ee2), 3 1 braid pattern (a3ee3), and 4 1 braid pattern (a4ee4). The 1 1 braid pattern means the braider carrier moves just one braider carrier distance in the radial row and circumferential ring directions, whereas the 2 1 braid pattern means the braider carrier moves two and one braider carrier distance in the radial row and circumferential ring directions, respectively. The same analogy can be applied to 3 1 and 4 1 braid patterns (Bilisik and Sahbaz, 2013). To make the 3D circular braided preform in a 1 1 braid pattern, the braider carrier must be arranged in a matrix of circumferential rings and radial rows as presented in Fig. 4.19(a1). The ﬁrst step is sequential, and the reversal movement of the braider carriers is in the inner and outer radial row directions (b1). The second step is circumferential sequential, and the reversal movement of the braider carriers placed on the circular inner rings is in the circumferential direction (c1). The third step is again sequential, and the reversal movement of the braider carriers is in the inner and outer radial row directions (d1). The fourth step is again circumferential sequential, and the reversal movement of the braider carriers placed on the circular inner rings is in the circumferential direction (e1). After that, the 3D circular braided preform is removed from the braiding zone by takeup. These steps were repeated depending on preform length requirements. Braid patterns other than 1 1 are also shown in Fig. 4.19 in steps a2ee2 for the 2 1 pattern, a3ee3 for the 3 1 pattern, and a4ee4 for the 4 1 patterns, in which the braider carriers on the circular ring move two, three, and four braider carrier distances in the radial row direction (Bilisik and Sahbaz, 2013), respectively. The number of braider carriers can be expanded in circumferential ring and radial row directions depending upon preform dimensions.

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Figure 4.19 Four-step braiding method to make 3D circular braided preforms (Sahbaz, 2013); braid pattern 1 1 (a1ee1), braid pattern 2 1 (a2ee2), braid pattern 3 1 (a3ee3) and braid pattern 4 1 (a4ee4).

4.1.4.2

Four-step axial braiding method

Rectangular Cartesian 3D axially braided preform was made by the four-step braiding method. This method involves four distinctive steps to form the 3D braided preform structure. Fig. 4.20 shows the 1 1 braid pattern (a1ee1), 2 1 braid pattern (a2ee2), 3 1 braid pattern (a3ee3), and 4 1 braid pattern (a4ee4). The 1 1 braid pattern means the braider carrier moves just one braider carrier distance in the row and column directions, whereas the 2 1 braid pattern means the braider carrier moves two and one braider carrier distance in the row and column directions, respectively. The same analogy can be applied to 3 1 and 4 1 braid patterns (Bilisik, 2011). To make the Cartesian 3D axially braided preform in a 1 1 braid pattern, the braider carrier and axial must be arranged in a matrix of rows and columns as presented in Fig. 4.20(a1). The ﬁrst step is sequential, and the reversal movement of the braider carriers is in the column direction (b1). The second step is sequential,

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Figure 4.20 Four-step axial braiding method to make 3D axially braided preforms (Bilisik, 2011); axial braid pattern 1 1 (a1ee1), axial braid pattern 2 1 (a2ee2), axial braid pattern 3 1 (a3ee3) and axial braid pattern 4 1 (a4ee4).

and the reversal movement of the braider carriers placed on the rapier is in the row direction (c1). The third step is again sequential, and the reversal movement of the braider carriers is in the column direction (d1). The fourth step is again sequential, and the reversal movement of the braider carriers placed on the rapier is in the row direction (e1). After that, the 3D axially braided preform is removed from the braiding zone by takeup. These steps were repeated depending on preform length requirements. Braid patterns other than 1 1 are also shown in Fig. 4.20 in steps a2ee2 for the 2 1 pattern, a3ee3 for the 3 1 pattern, and a4ee4 for the 4 1 patterns, in which the braider carriers on the rapier move two, three, and four braider carrier distances in the row direction (Bilisik, 2011), respectively. The number of braider carriers and axes can be expanded in row and column directions depending upon preform dimensions.

Concentric 3D circular axially braided preform was also made by the four-step braiding method. This method involves four distinctive steps to form the 3D circular braided preform structure. Fig. 4.21 shows the 1 1 braid pattern (a1ee1), 2 1 braid pattern (a2ee2), 3 1 braid pattern (a3ee3), and 4 1 braid pattern (a4ee4). The 1 1 braid pattern means the braider carrier moves just one braider carrier distance in the radial row and circumferential ring directions, whereas the 2 1 braid pattern means the braider carrier moves two and one braider carrier distance in the radial row and circumferential ring directions, respectively. The same analogy can be applied to 3 1 and 4 1 braid patterns (Sahbaz, 2013). To make the 3D circular axially braided preform in a 1 1 braid pattern, the braider carrier and axial must be arranged in a matrix of circumferential rings and radial rows as presented in Fig. 4.21(a1). The ﬁrst step is sequential, and the reversal movement of the braider carriers, which is between adjacent axials, is in the inner and outer radial

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b1

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e1

a2

b2

c2

d2

e2

a3

b3

c3

d3

e3

a4

b4

c4

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Figure 4.21 Four-step braiding method to make 3D circular axially braided preforms (Sahbaz, 2013); braid pattern 1 1 (a1ee1), braid pattern 2 1 (a2ee2), braid pattern 3 1 (a3ee3) and braid pattern 4 1 (a4ee4).

row directions (b1). The second step is circumferential sequential, and the reversal movement of the braider carriers placed on the circular inner rings is in the circumferential direction (c1). The third step is again sequential, and the reversal movement of the braider carriers is in the inner and outer radial row directions (d1). The fourth step is again circumferential sequential, and the reversal movement of the braider carriers placed on the circular inner rings is in the circumferential direction (e1). After that, the 3D circular axially braided preform is removed from the braiding zone by takeup. These steps were repeated depending on preform length requirements. Braid patterns other than 1 1 are also shown in Fig. 4.21 in steps a2ee2 for the 2 1 pattern, a3ee3 for the 3 1 pattern, and a4ee4 for the 4 1 patterns, in which the braider carriers on the circular ring move two, three, and four braider carrier distances in the radial row direction, respectively. The number of braider carriers and axes can be expanded in circumferential ring and radial row directions depending upon preform dimensions.

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4.1.4.3

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Two-step braiding method

Cartesian 3D braided axial preform structure can be made by two-step braiding method which was developed by McConnell and Popper (1988). In this process, axial yarns are arranged in a matrix array based on the sectional geometry of the braided structure. The braider yarns move along alternating diagonals of the axial array and interlock the axial yarns and hold them in the desired shape (Popper and McConnell, 1987; Spain, 1990). The arrangement of yarns requires a relatively small number of braider yarns. Thus, the number of the braiding carriers in the process is reduced and eventually makes the process automation simple. The two-step braiding process involves two distinct motions by each of the braider carriers as shown in Fig. 4.22(a) and (b). It was also shown that a variety of braided preforms including T, H, TT and a braided bifurcation preform can be fabricated (Popper and McConnell, 1987).

4.1.4.4

Six-step braiding method

Multiaxial 3D braided structure produced by the six-step method has braider yarns, warp (axial), ﬁlling and Z-yarns. The braider yarns are intertwined with the orthogonal yarn sets to form the multiaxis 3D braided preform. In this process, there are six distinct steps in each cycle. In steps 1 and 2, braider yarns are intertwined around the axial yarns as in the four-step method. Step 3 inserts ﬁlling yarns in the transverse direction. In steps 4 and 5, the braider yarns are intertwined around the axial yarns as in the four-step method, and step 6 inserts Z-yarns in the thickness direction (Chen and El-Shiekh, 1994). Another multiaxial 3D braided structure produced by the six-step method has bias yarns placed in the in-plane direction of the structure, and warp (axial), radial (Z-yarns) and braider yarns placed in the out-of-plane direction of the structure (Bilisik, 1998). The braider yarns are intertwined with the axial yarns whereas bias yarns are oriented at the surface of the structure and locked by the radial yarns to the other yarn sets. In this process, there are six distinct steps in each cycle. In steps 1 and 2, braider yarns are intertwined around the axial yarns as in the four-step braiding method. In step 3, bias yarns are laid down on the surface of the structure. In step 4, the radial yarns move in the thickness direction of the structure and lock the bias yarns to the

(a)

(b)

Figure 4.22 Two-step axial braiding method to make Cartesian 3D axially braided performs (McConnell and Popper, 1988); (a) ﬁrst step of braider carrier path, (b) second step of braider carrier path.

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braider and axial yarns. In steps 5 and 6, the braider yarns are intertwined around the axial yarns as in the four-step braiding method (Bilisik, 1998, 2013).

4.1.4.5

Multistep braiding method

Kostar and Chou (1994a,b) developed a multistep braiding method which was based on a computer algorithm. The four-step or two-step braiding process was employed to fabricate the multistep Cartesian 3D braided preforms (Kostar and Chou, 1994b; Bilisik, 2013). In this way, the yarns make a large interlacement angle at the thickness of the fabric which results in a large-sized unit cell. In addition, the yarns may change to more positions in the unit cell compared to the unit cells in the four-step and two-step processes. On the other hand, the algorithm can also calculate the steps needed for the production of unusual braids which include surrogate materials such as fasteners, additional yarn or voids (Kostar and Chou, 1994a).

4.1.5 4.1.5.1

Braiding equipment Four-step braiding

The four-step braiding process was developed by Florentine (1982). The process has a rectangular array of individual row and column arrangements in the machine bed. Each individual row has a braider carrier to make four distinct Cartesian motions, as shown in Fig. 4.23(a). The braider carriers move simultaneously in predetermined paths relative to each other within the rectangular machine bed as shown in Fig. 4.23(b). Braider carriers (bobbins) are arranged in each row and column. Later, they are shifted by electromagnetic actuators based on braid pattern such as 1 1 which is explained in the braiding method section. The 1 1 based predetermined yarn path is shown in Fig. 4.23(b). After the braider yarns are intertwined to form braided fabric, it is removed from the formation zone for each braiding cycle by a takeup mechanism in which a stepping motor is generally employed.

(a) (b)

Figure 4.23 (a) Schematic views of four-step braiding process (Florentine, 1982), (b) predetermined braider carrier yarn. Florentine, R.A., 1982. Apparatus for Weaving a Three Dimensional Article. US Patent No 4312261, January 26.

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(c)

Figure 4.24 (a) Schematic views of small portion of the braiding machine bed by four-step braiding process (Brown and Ratliff, 1986; Brown, 1985), (b) schematic view of scale-up Isectional braiding machine bed, (c) actual rectangular braiding machine. Brown, R.T., Ratliff, E.D., 1986. Method of Sequenced Braider Motion for Multi Ply Braiding Apparatus. US Patent No 4621560, November 11.

Brown and Ratliff (1986) made further improvements on Florentine’s apparatus to make 3D braided structures with varying cross section (Brown and Ratliff, 1986; Brown, 1985). They eliminated jamming of yarn carriers due to machined inaccuracies in components. Pneumatic actuators replaced electromagnetic ones. This modiﬁcation also permitted expanding the machine size easily in both row and column directions as shown in Fig. 4.24(a)e(c). Brown (1988, 1985) also developed a 3D circular braiding machine in which 3D circular braided preform could be fabricated. The process has concentric rings connected to a common axis. Braid carriers are circumferentially mounted to the inside diameter of the ring. The rings are arranged side by side according to preform thickness. Rings rotate according to a predetermined path at only one braid carrier distance. Then, the braid carriers are shifted in the axial direction. After that, the cycles are repeated in the above sequence. The fabric has bias yarn orientation thickness of the cylinder wall and cylinder surface at the helical path, as shown in Fig. 4.25(a) and (b). Wall, 2002 designed a 3D circular braiding machine. The process has concentric rings of differing diameters which ﬁt properly together in the machine bed. Braid carriers are circumferentially mounted on each concentric ring. Rings rotate according to a predetermined path at only one braid carrier distance. Then, the braid carriers are shifted in the radial row direction. After that, the cycles are repeated in the above sequence as shown in Fig. 4.26(a)e(c).

4.1.5.2

Two-step braiding

McConnell and Popper (1988) developed a 3D axial braiding process. The process has a machine bed, axial unit, braid carrier, compaction and takeup unit. The braid carrier moves around the axial unit according to the predetermined path to make two distinct Cartesian motions for creating braider-type interlacements. The braid carrier is either motorized or a computer-controlled belt-driven movement mechanism. The axial unit

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(a)

(b)

Figure 4.25 (a) Schematic views of 3D circular braiding machine (Brown, 1988), (b) actual 3D circular braiding machine (Lee, S.M., 1990. International Encyclopedia of Composites. VHC Publisher Inc, New York.)

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Figure 4.26 (a) Horizontal 3D circular axial braiding machine (Wall, 2002), (b) vertical 3D circular full braiding machine (Mamel, 2015), (c) yarn carrier path (Florentine,1982). Wall, J.W., 2002. An investigation of the ballistic impact resistance of modiﬁed 2x1, four-step, three-dimensionally braided composites with axial reinforcement, MSc thesis, NCSU, Raleigh, NC, USA. Mamel Web Site, Mechanical Analysis of Hybrid 3D Fiber Braided Reinforced Composites (Online). Available from: http://mamel.snu.ac.kr/index.html?Pagenum1/4 83. (accessed 20.01.15.). Florentine, R.A. 1982. Apparatus for Weaving a Three Dimensional Article. US Patent No 4312261, January 26.

feeds the axial (0 ) yarns in the machine direction. The compaction unit forms the preform and takeup unit feeds the braided fabric from the braiding zone as shown in Fig. 4.27.

4.1.5.3

Six-step braiding

Chen and El-Shiekh (1994) designed multiaxial 3D braiding apparatus at North Carolina State University. The process has a rectangular array of individual row and column arrangements in the machine bed in which there is a warp (axial) yarn between

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Figure 4.27 Schematic view of 3D axial braiding apparatus based on two-step braiding (McConnell and Popper, 1988). Mcconnell, R.F., Popper, P., 1988. Complex Shaped Braided Structures. US Patent No 4719837, January 19.

adjacent rows. Each individual row has a braider carrier to make four distinct Cartesian motions. The braider carriers move simultaneously in predetermined paths relative to each other within the rectangular machine bed (not shown). They are shifted by pneumatic actuators based on braid pattern such as 1 1. After the braider yarns are intertwined with axial to form braided fabric, ﬁlling and Z-yarns are inserted in the cross section of the braided preform by manually driven carriers. Then, the braided structure is removed from the formation zone for each braiding cycle by the takeup mechanism in which a stepping motor is generally employed. Another multiaxis 3D braiding apparatus was designed by Bilisik (1998). The process has concentric rings of differing diameters which ﬁt together in the machine bed. The outer two rings were used for bias carriers which are circumferentially and reversely rotated from each other for one braider carrier. These carriers do not make any intertwined type interlacement. On the other hand, braid carriers are circumferentially mounted on each inner concentric ring. Braid rings rotate according to a predetermined path at only one braid carrier distance. Then, the braid carriers are shifted in the radial row direction and intertwine the braider yarn and lock the axials in their place. After that, radial carriers move the adjacent radial lines to lock the bias yarns to the surface of the braided structure. The cycles are repeated, and takeup removes the multiaxis 3D structure from the braiding zone.

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Multistep braiding

Kostar and Chou (1994b) developed a computer algorithm for the four-step and two-step braiding machine to make multiaxis 3D braided preform. The braided yarns in the unit cell of the preform are changed to more positions. In addition, the algorithm can also calculate the steps needed for the production of various sectional braids including surrogate material such as fasteners, additional yarn or voids (Kostar and Chou, 1994a).

4.1.5.5

Braiding carrier

The yarn carrier is an essential element in braiding. It carries braider bobbins and maintains constant tension on the yarn. It feeds the required yarn during braiding. It also compensates for excessive yarn length. Fig. 4.28(a) and (b) shows traditional braider carrier (Freitas et al., 1999; Steeger GmbH, 2011). A new carrier was developed to prevent tension variations on the yarn during braiding and was especially suitable for horizontal braiding. This carrier has a spool which acts as reservoir of the braider yarn; a spiral spring provides constant tension on the yarn during displacement of the braider carrier in the machine plate; a magnetic clutch releases the spool during feeding of the yarn and locks the spool during retraction of excessive yarn length from the braiding zone to prevent slackness of yarn. The carrier also has gearing assembly to connect the spiral spring and magnetic clutch to the spool (El-Shiekh et al., 1992; Wall, 2002), as shown in Fig. 4.28(c)e(e). The main advantage of this carrier is that there is no compensation limit as in the case of a traditional carrier. However, the new carrier has limited length of yarn due to spool size.

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Figure 4.28 (a) Traditional large-size braider carrier (Steeger GmbH, 2011), (b) schematic front view of spool carrier (El-Shiekh et al., 1992), (c) detail view of carrier mechanism (El-Shiekh et al., 1992), (d) actual view of spool carrier (Wall, J. W., 2002). El-Shiekh, A., Li, W., Hammad, M., 1992. Yarn Carrier Apparatus for Braiding Machines and the Like. US Patent No 5156079, October 20.

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Comparison of braided fabric structure and methods

The design of the 3D braided composite for structural components depends mainly on loading conditions in the end-uses. The basic parameter of the 3D braided composites is yarn which has continuous monoﬁlament or multiﬁlament and matrix properties, total and directional volume fraction, preform architecture, yarn orientation in the architecture and preform shape. These parameters together with end-use requirements determine the types of 3D braided preform techniques. This requires sophisticated calculation techniques integrated with computer-aided design and manufacturing (CAD/CAM)-controlled preform and a composite manufacturing machine (Kamiya et al., 2000; Ko and Chou, 1989; Chou, 1992). Many calculation techniques were developed with the aid of computer-supported numerical methods to predict stiffness and strength properties and to understand the complex failure mechanism of the 3D braided structural composites (Kamiya et al., 2000; Ko and Chou, 1989; Chou, 1992). The 3D braided preform has been shown to have high out-of-plane properties and it is possible to fabricate near-net-shape preform. The process is semi-automated. However, it is slow and has size limitations (Kamiya et al., 2000; Ko and Chou, 1989; Chou, 1992). Kamiya et al. (2000) compared 3D braided fabrics and methods based on the yarn placement, uniformity, the number of layers and through-the-thickness reinforcements. It was concluded that the 3D braided fabrics and methods are readily available. A more general comparison is carried out and presented in Table 4.3. As seen in Table 4.3, the 3D braided fabric parameters are yarn sets, intertwining method, yarn directions, preform shape and the number of layers, and ﬁber volume fraction. The 3D braiding process parameters are bed arrangement based on the predetermined yarn path, manufacturing type such as continuous or part, braider carrier type and yarn volume in the carrier, packing and the development stage. It can be seen that Cartesian 3D fully and axially braided fabrics in the form of ﬂat or circular shapes are well developed and are commercially available. However, multiaxis 3D braided fabrics with additional yarn sets are still in the early stages of development.

4.1.6 4.1.6.1

Properties of Cartesian three-dimensional braided fabric Pattern and jamming in three-dimensional braided fabric

Unit cell structure It was demonstrated that braid patterns inﬂuence the Cartesian 3D fully and axially braided unit cell structures produced by the four-step method. Patterns on oddnumbered rows resulted in fully interconnected integral unit cell structures, whereas patterns on even numbered rows resulted in layer-to-layer interconnection on the edge of the unit cell structure in which there was an empty pocket between each braided layer. The unit cell structure has a ﬁne intertwine in the 1 1 pattern, whereas it has a coarse intertwine for other braid patterns. On the other hand, the number of layers affects the Cartesian 3D fully and axially braided unit cell structures: when the number of layers increases, the thickness of the unit cell structure increases for

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Comparison of 3D braided fabrics and methods Yarn sets

Method

Yarn directions

Fabric shape

Development stage

Florentine (Florentine, 1982)

One

Four-step

Bias (out-of-plane at an angle)

Flat or complex shape (multilayer)

Low or medium

Commercial stage

Brown (Brown, 1988)

One

Four-step

Bias (out-of-plane at an angle)

Circular or complex shape (multilayer)

Low or medium

Commercial stage

McConnell and Popper (McConnell and Popper, 1988)

Two

Two-step

Bias/Axial (out-ofplane at an angle)

Flat or complex shape (multilayer)

Medium or high

Commercial stage

Chen and El-Shiekh (Chen and El-Shiekh, 1994)

Four

Six-step

Bias/Axial/Filling/ Z-yarn (out-of-plane at an angle and orthogonal)

Flat or complex shape (multilayer)

Medium or high

Early prototype stage

Bilisik (Bilisik, 1998)

Four

Six-step

Bias (in-plane) Bias/Axial/Radial (out-of-plane at an angle)

Circular or complex shape (multilayer)

Medium or high

Early prototype stage

Kostar and Chou (Kostar and Chou, 1994a)

One

Multistep

Bias (out-of-plane at angle)

Flat or complex shape (multilayer)

Medium or high

Commercial stage

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Fiber volume fraction

Fabric

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all braid patterns. In addition, for the same layer number, the thickness of the unit cell structure in the 1 1 pattern is less than that of other patterns. This indicated that all braid patterns except 1 1 resulted in a coarse form of unit cell structure (Brown and Ratliff, 1986). Jamming conditions considerably affect Cartesian 3D fully and axially braided unit cell structures for all braid patterns. Minimum jamming decreases the width of the unit cell structures, whereas maximum jamming increases their width. Width reduction of the unit cell structure in the 1 1 pattern was high compared to that of 2 1, 3 1 or 4 1 patterns. However, the width increment of the unit cell structure in the 1 1 pattern was slightly higher than that of other patterns. In addition, minimum jamming increased the densities of the Cartesian 3D fully and axially braided unit cell structures, whereas maximum jamming decreased their densities (Bilisik and Sahbaz, 2012; Bilisik, 2011). Cartesian 3D fully braided structure has a large directional Poisson ratio which leads to instabilities in the axial direction of the preform. However, adding the axial yarn layer to the 3D fully braided preform strengthens the axial direction of the 3D braided preform which also reduces the directional Poisson ratio. In addition, adding the ﬁlling and Z-yarn to the axial 3D braided preform could enhance the properties of the 3D braided preform in the transverse direction and the Poisson’s ratios of the structure could become identical.

Unit cell angle It was shown that braid pattern slightly inﬂuences the yarn angles in Cartesian 3D fully and axially braided unit cell structures produced by the four-step method. In 3D fully braided perform, the braider angle slightly decreased when the braid pattern changed from 1 1 to 3 1, whereas the surface angle increased when the braid pattern changed from 1 1 to 3 1. It was found that increasing the number of layers did not considerably affect the braider angle. In 3D axially braided perform, the braider angle slightly increased when the braid pattern changed from 1 1 to 3 1, whereas the surface angle slightly increased when the braid pattern changed from 1 1 to 3 1. It was found that increasing the number of layers affected the braider angle (Bilisik and Sahbaz, 2012; Bilisik, 2011). Jamming conditions affect the yarn angles in 3D fully braided and 3D axially braided unit cell structures. Minimum jamming decreased the surface angle of the 3D fully braided and 3D axially braided unit cell structures, whereas maximum jamming increased their surface angle.

Unit cell yarn length The number of layers affects yarn length in Cartesian 3D fully and axially braided unit cell structures. Increasing the layers caused increase in braider and surface yarn lengths and multilayer yarn length in the 3D fully and axially braided unit cell structures. However, increasing the number of layers also decreased the surface arc length and corner yarn length, as well as edge yarn lengths. It was found that jamming conditions did not affect yarn length in 3D fully and axially braided unit cell structures (Bilisik and Sahbaz, 2012; Bilisik, 2011).

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Unit cell yarn path The study showed that increasing the layer number created an additional yarn path, the “multilayer yarn path,” on the edge of the Cartesian 3D fully and axially braided unit cell structures, and this could affect the mechanical behavior of the 3D fully and axially braided composites. This was considered especially important for the manufacturing of near-net-shape thick Cartesian 3D fully and axially braided preforms and composites (Bilisik and Sahbaz, 2012; Bilisik, 2011, 2013).

4.1.7 4.1.7.1

Properties of Cartesian three-dimensional braided composite Three-dimensional fully braided composites

Modeling studies on 3D braided fabric composites generally include the geometric models of unit cells, identiﬁcation of key process parameters such as pattern and takeup rate, limiting geometries of braided fabric jamming, microstructural characteristics such as braid yarn orientation and ﬁber volume fraction, and the properties of the yarn and matrix (Byun and Chou, 1996). The mathematical models based on the unit cell approach predicted the structural features of 3D braided composites such as yarn orientation, ﬁber volume fraction, and interyarn voids from the key process variables of braiding pattern, takeup rate, and yarn geometry. The limiting geometry was computed by considering yarn jamming in the structure. Using the yarn jamming factor makes it possible to identify the complete range of allowable geometric arrangements for 3D braided perform (Du et al., 1991). On the other hand, the design of complex 3D braids was studied as that grouping of yarns that was carried out via an iterative simulation of the braiding process, which was called the universal method. Using this method, the fabrication of a complex sectional braid structure with surrogate material including transverse, fastener, and ﬁller insertion was accomplished (Kostar and Chou, 2002). A 3D braided 1 1 pattern preform with complex rectangular cross sections was studied by means of the control volume method. The paths of the braider carriers were traced, particularly in the joint region in which the control volume of the unit cell is a cube in the interior, a heptaprism on the corner, and a pentaprism at the surface (Zhang et al., 2008, 2007). The microstructure of 3D braided 1 1 pattern preforms was analyzed and the mathematical relationships among the structural parameters, such as the yarn packing factor, yarn orientation, ﬁber volume fraction and braiding pitch, were derived. It was noted that the unit cell size and shape changed during the consolidation of braided perform. Therefore, this affects the properties of the 3D braided performs (Chen et al., 1999). The fabric geometry model (FGM) was developed to characterize the 3D braided preform composite with regard to yarn and matrix, and processing parameters. 3D braided unit cell geometry in FGM requires two basic components: fabric geometry and the determination of the ﬁber volume fraction. Fabric geometry is a function of the takeup rate during fabric formation, whereas yarn displacement values, in terms of the number of yarns, depend on row and column motions. The orientation of the

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yarns in a 3D braided preform depends on fabric construction, fabric shape, and the dimensions of the braiding loom (Ko, 1985). The yarn orientation angle tends to decrease as the number of yarns in the fabric increases. For the same number of yarns in the fabric, the yarn orientation angle decreases as the linear density of the fabric decreases. It was reported that the maximum attainable Vf (ﬁber volume fraction) in a uniaxially aligned ﬁber structure was 90.6%, whereas the maximum ﬁber volume fraction of a 3D fully braided preform was 68% (Ko, 1985; Ko and Pastore, 1985). The effective Young’s modulus and Poisson’s ratios of 3D braided composites with internal crack were characterized by using the homogenization theory and the modiﬁed ﬁnite-element method (FEM) (Byun and Chou, 1989; Zeng et al., 2005a,b; Sun et al., 2003; Zeng and Jiang, 2010). Nonlinear progressive damage under tensile loading was investigated in 3D braided composite based on the method of Asymptotic Expansion Homogenization combined with ﬁnite-element analysis (FEA). Tensile strength decreases with increase in braiding angle, but the fracture strain has different failure modes. It was veriﬁed that 3D braided composites with a small braiding angle have better strength but poorer ductility than composites with a large braiding angle (Dong and Feng, 2010). The digital element approach on 3D braided tubular preform was studied to deﬁne it geometrically. The size of unit cells and the yarn inclination in the preform varied with its radial position throughout the perform shape which inﬂuenced braiding angle, ﬁber volume fraction and yarn inclination angle (Sun, 2004; Wang and Sun, 2001). The two-scale method was applied for the prediction of the structure property of 3D braided composites. The braiding angle and the ﬁber volume fraction were found as important structural parameters which inﬂuence the tensile, bending and torsion strengths (Yu and Cui, 2007). Computer-aided geometric modeling in conjunction with the FEM was developed to predict the mechanical behavior of 3D braided composites. The model includes the interior and boundary elements of the entire cross section and bending moment of the yarns. The model predicts a lower value of elastic modulus than that of experimental results (Lei et al., 1991). Research revealed that the strength of 3D braided preforms, for a given yarn, tends to increase as the number of yarns in the fabric increase (Ko, 1986). The rate of increase is more rapid for fabrics with yarns of lower linear density. For the same number of yarns in the fabric, the axial strength of the fabric tends to increase as the linear density of the fabric decreases. On the other hand, fabric linear density is directly related to yarn orientation angle (Ko, 1986). The effects of cut edges, ﬁlament bundle size and braid pattern were examined through tensile, compressive, ﬂexural and shear tests. It was found that the specimens were sensitive to cut edges in which the tensile strength of the cut and shaped graphiteeepoxy preform composite was reduced (Macander et al., 1984). In general, it was found that the tensile strength and modulus of 3D braided composites tend to increase as ﬁlament bundle size increases. Although the strength and modulus of braided composites were signiﬁcantly higher than those of the 0 /90 woven laminates, the Poisson’s ratios of the braided composites were very large, leading to instability in the transverse direction (Macander et al., 1984). The elastic strain energy method was used to correctly predict the axial direction elastic modulus of the

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braided structure as functions of the yarn orientation and ﬁber volume fraction. The elastic modulus was determined to be sensitive to the braid geometry, increased as the yarn orientation angle decreased, namely, as the yarns become more aligned with the tensile axis (Ma et al., 1986). Another model was developed to characterize the yarn structures in 3D braided preform produced by four-step braiding. The method involved the general topology of the yarn structure based on the braiding processing parameters. It was shown that the topological characteristics in both rectangular and tubular braided preforms were the same (Wang and Wang, 1994). On the other hand, modeling of the preform’s unit cell was carried out by using micromechanics which included the braiding parameters. It was demonstrated that the unit cells in the preform interior were different from those on the boundaries (Wang and Wang, 1995). The ballistic performance of 3D braided para-aramideepoxy composites was investigated. A ﬁber-inclination model for 3D textile composites was adapted to decompose the 3D braided composite at quasimicrostructure level for geometrical modeling in FEM software. The ﬁnite-element code LS-DYNA was used to simulate the impact interaction between projectile and inclined lamina (Gu and Xu, 2004). Another study was carried out on the uniaxial tensile properties of 3D braided E-Glasseepoxy composites which were tested with a split Hopkinson tension bar. From the stressestrain curves of the composites at various strain rates, it was shown that 3D braided composite is a rate-sensitive material. Uniaxial tensile stiffness and failure stress increased with the increase in strain rate, whereas the failure strain decreased. It was shown that 3D braided composites failed in a more brittle mode in tension at high strain rates (Sun et al., 2005).

4.1.7.2

Three-dimensional axially braided composites

Braid topology on 3D axially braided preform produced by the two-step method can be used to analyze the effects of yarn size and spacing, and pitch length on the resulting braided fabric geometry (Kuo, 1997). The axial yarns carried most of the load in the axial direction of the structure, and the braider yarns were the main load carriers in the transverse direction of the structure. Therefore, it was desirable for the orientation angle of the braiders to be large (Li, 1990). 3D ﬂat axially braided composites were analyzed by a 3D ﬁnite-element model based on a representative volume element under periodic displacement boundary conditions, which simulates the spatial conﬁguration of the braider yarns and the axial yarns. The software ABAQUS was adapted to study the mechanical properties and the mesoscale mechanical response of 3D axially braided composites (Xu and Xu, 2008). A ﬁber-inclination model was developed to predict the strength of 3D axial braided 1 1 pattern perform composite produced by the four-step method. The analysis was based upon the transverse isotropy of unidirectional laminate and the Tsai-Wu polynomial failure criterion. The results showed that braider angle has a signiﬁcant inﬂuence on tensile modulus and strength. The transverse angle has an obvious inﬂuence upon Poisson’s ratio, and axial yarns can improve the tensile properties of 3D braided ﬂat composites (Sun and Qiao, 1997; Yang et al., 1986).

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It was found that the energy absorption capabilities and crushing failure modes of a 3D braided square tube were signiﬁcantly dependent upon the braiding parameters. The crush failure modes were splaying, folding, spiky folding and curling. The speciﬁc energy absorption capability increased with decreasing braiding pitch length. The larger number of braiding layers led to higher energy absorption capability. Based on the crush failure mechanism, the axial yarns were the main sources of energy absorption and the braiding yarns were the controllers for crush failure modes. Axial carbon yarns displayed higher energy absorption capability, whereas the braider Kevlar® yarns exhibited better postcrush integrity (Chiu and Cheng, 2000).

4.1.8 4.1.8.1

Applications of Cartesian three-dimensional braided composites Composite component design

Fiber orientation (q) and volume fraction (Vf) are key engineering parameters for a braided textile composite from formability, permeability, and performance standpoints. The manufacturing of composites often requires transformation of the ﬁber reinforcements into various structural shapes through net-shape fabrication. Accordingly, in fabric formability modeling, ﬁber volume fraction distribution, ﬁber orientation and ﬁber interlacing intensity as well as the limit of geometric deformation must be considered. The ﬂuid ﬂow permeability of textiles is an indication of how easily and uniformly a matrix can be inﬁltrated into the ﬁbrous assembly. The permeability of textile preforms is affected by the dynamic interaction of ﬁber architecture and ﬁber volume fraction. It was found that the introduction of through-the-thickness ﬁbers significantly increases the permeability of the preforms, especially for preforms with high ﬁber volume fraction (Ko, 2008). The mechanical behavior of a composite depends upon ﬁber orientation, ﬁber properties, ﬁber volume fraction, and matrix properties. The ﬁber volume fraction is related to the machine in terms of the number of yarns and the orientation of those yarns. The ﬁber geometry is also strongly related to the machine which determines the orientation of the ﬁbers and the ﬁnal shape. For 3D circular braided preform, the shape is formed using a mandrel, and the ﬁber volume fraction can readily be determined by the orientation and amount of ﬁbers used as shown schematically in Fig. 4.29(a)e(c). The total material area of yarns in a given cross section of a composite preform can be determined as follows (Ko, 2008): Am ¼ Ay Ny =cos q

[4.1]

in which, Am is the area of material in the cross section (mm2); Ay is the cross-sectional area of the yarn (mm2); Ny is the number of yarns on the machine (M number of plies, in which M is the number of carriers on machine), and q is the orientation of the braider yarns with respect to the mandrel axis (degree). Thus, once the composite dimensions are known, the ﬁber volume fraction can be expressed as follows: Vf ¼ Am=A

c

[4.2]

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(a)

(b)

z

(c)

Mandrel

Ay

l

θ

x y

Figure 4.29 (a) Schematic views of 3D circular fully braided preform with simple mandrel, (b) predetermined yarn path in the braided preform, (c) unit yarn segment in coordinated system.

in which Vf is the ﬁber volume fraction (%); Ac is the cross-sectional area of the composite (mm2) and Am is the cross-sectional area of material in the composite (mm2). If a composite of a given cross-sectional area and a particular yarn and ﬁber volume fraction are required, the fabric can be designed based on the number of plies and the orientation of the yarns. The analytic relation can be given as follows: cos q ¼ M Nply Ay =ðVf Ac Þ

[4.3]

in which, Nply is the number of plies per bobbin. Thus, the design is determined for a certain number of plies. In summary, the braiding parameters for braided composites can be presented in the following equations as follows: d0 ¼ M Nply Ay =ðptVf cos qÞ þ t

[4.4]

d1 ¼ M Nply Ay =ðptVf cos qÞ t

[4.5]

in which d0 is the outside braid diameter (mm); d1 is the inside braid diameter (mm); and t is the composite (fabric) thickness (mm). With this equation, the effect of braiding angle, ﬁber volume fraction, and the number of plies on the number of carriers required to produce a given braid diameter for a speciﬁc composite can be calculated. The take-up/rotation ratio (R) indicates the distance the mandrel traverses for one rotation of the carriers. Thus, for a given mandrel diameter (d), the relation between q and R is given as follows: d ¼ R tan q=p

[4.6]

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Thus, to maintain the proper ﬁber orientation (and thus the desired ﬁber volume fraction), the machine should be set for a take-up/rotation ratio of R. If the mandrel is of irregular shape, R can be monitored and modiﬁed accordingly along the length of the mandrel. Using these equations, one can easily determine the total number of yarns required to make a fabric with a given ﬁber volume fraction and cross-sectional area if the parameters of ﬁber density, yarn linear density, and yarn surface angle are known. The maximum volume fraction that is attainable with a given construction is dependent on the ﬁber architecture. The fabric geometry method (FGM) is a volume-averaging homogenization method, which takes into consideration the volumetric angular distribution associated with ﬁber architecture via wellestablished coordinate transformation methodology. The input information generated from FGM is incorporated into the Algor® package program FEA, along with standard composite engineering practices, to optimize the laminate schedule and to minimize weight in the vehicle (Ko, 2008). On the other hand, a feature of the braiding process which makes it particularly interesting in composite applications is the relative ease with which cut outs, pins, fasteners and ﬁttings can be incorporated into the work pieces. For example, if a transverse pin is positioned in a cylindrical mandrel, the braiding yarns can automatically accommodate the geometry of the pin, and, though they follow a locally distorted path, there are no yarn ends in the vicinity of the pin and the full strength of the yarn assembly is maintained. If the pin is subsequently removed, a fully reinforced, integrally incorporated hole remains. The failure load in a pin-loaded hole is approximately 1.8 times greater for a braided hole than for a machined hole, and the tensile failure load of cylinders with braided holes is approximately 1.23 times greater than that of cylinders with machined holes (Skelton, 1989).

4.1.8.2

Structural components

In ground transportation applications, 3D braided structures should meet some general requirements such as low cost, manufacturability, good mechanical performance, no corrosion, repairability and recyclability, as well as high damping, fuel economy and low noise level. The energy absorption and structural integrity of braided structures highly prevent the component from delamination. Typical structural components in transportation engineering are knot elements for space frame-like structures, beams, shells, seats and chassis. Because of the complex geometry and loading of these parts, cost-effective manufacturing techniques based on the 3D braiding processes are attractive. For instance, the use of braided composites in chassis, exhaust and structural applications allows a signiﬁcant reduction in component number and provides a substantial weight reduction compared with metal (Drechsler, 1999). Furthermore, braided preforms and rigid composite connectors were made by 3D circular braiding techniques enabling to braid the connector preform with multiple openings in which connections are required. This was achieved by directional intertwining in which the particular section of the modular braiding carriers was rotated based on the structural opening part of the braided preform. 2D and 3D triaxial braids are more developed and more widely applied than complex 3D braids. Coupled with the fully

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integrated nature and the unique capability for near-net-shape manufacturing, the current trend in braiding technology includes the following: to expand to large-diameter braiding; to develop more sophisticated techniques for braiding over complex-shaped mandrels, multidirectional braiding with near-net shapes; and to extend the use of CAD/CAM.

4.1.8.3

Space and aerospace applications

3D braided fabrics are used in aerospace applications as space shuttle components, aircraft seat cushions. 3D braided composites are currently employed in civil and military aircraft in critical structures such as the fuselage, wings and the skin of the aircraft. Other areas of use are in the top and side tail units, fuselage paneling, leading edges on side rudders, and engine paneling (Jinlian, 2008; Naveen et al., 2006).

4.1.8.4

Ballistic applications

3D braided fabric and rigid ballistic plate could be used to protect the human and goods under various threats as projectile, blast, fragment and high-energy explosives. In addition, they can be utilized as protective products for vehicular crash guards, composite helmet, interlinings, insulation and protective industrial work wear and ﬁre ﬁghter suits (Jinlian, 2008; Naveen et al., 2006). 3D braided structures for ballistic soft and rigid applications are made by using the high-modulus and high-strength ﬁbers as para-aramid and polyethylene ﬁbers.

4.1.8.5

Marine

3D braided composites can be used in minesweepers, sonar domes, cargo ships, patrol and pleasure boats. In addition, composites are being increasingly used for navigational aids such as buoys. Recently, a new generation hovercraft has been designed which makes use of aramid-braided composites in place of aluminum. Its advantages include lighter weight, corrosion resistance, less noise in operation, better shock absorbency and higher abrasion resistance to rocks and sand surfaces. In addition, all marine vessels use large amounts of braided material for vibration, thermal and noise insulation, especially in and around turbines and engine rooms (Summerscales, 1987).

4.1.8.6

Automotive

3D braided preform and composites have been used in racing car bodies, structural members such as beams which are made up of foam cores over braided with a carbon preform structure, aprons and spoilers, and connecting rods (Lee, 1990). Also, car noses, monocoques and bumpers are made from braided-carbon structures. They reduce weight and improve the crash behavior (Jinlian, 2008).

4.1.8.7

Medical applications

2D and 3D braid structures ﬁnd more functional applications as in vascular prostheses due to good mechanical properties and better ingrowths of tissue to seal the prosthesis

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walls, grafts for inborn vessel anomaly or arteriosclerotic damage, soft tissue as skin and cartilage, artiﬁcial tendons and ligaments, wound dressing, absorbable and non-absorbable sutures, stents, tissue engineering scaffolds as to repair or regenerate tissues through combinations of implanted cellsebiomaterial scaffoldsebiologically active molecules, blood ﬁlters, plasters, compression bandages, surgical hosiery and hospital bedding. It was also demonstrated that 2D and 3D braided fabrics are dimensionally stable, similar to the mechanical properties of human organs and biocompatible applications (Bilisik, 2009; Jinlian, 2008).

4.1.8.8

Sports applications

3D braided composite structures are employed in various sports, especially golf, baseball and tennis. The speciﬁc applications are roller blades, bike frames, golf clubs, tennis rackets, baseball bats, ski and surf equipment and footwear (Uozumi et al., 2001; Jinlian, 2008).

4.2

Future trends

Biaxial and triaxial 2D braided fabrics have been widely used as simple and complex-shaped structural composite parts in various technical areas. In addition, biaxial and triaxial braiding methods and techniques are well developed. 3D fully braided and axially braided fabrics have multiple layers and show no delamination. However, 3D braided fabrics have low transverse properties due to the absence of yarns being equivalent to the ﬁlling yarns in 3D woven fabric. They also have size and thickness limitations. Various methods and techniques have been developed for 3D braiding, and these 3D braiding techniques are commercially available. However, the multiaxis 3D braiding technique is at an early stage of development and needs to be fully automated. This will be a future technological challenge in the area of multiaxis 3D braiding (Bilisik, 2013).

4.3

Conclusion

In this chapter, 3D braided fabrics, methods and techniques were reviewed. 3D braided fabrics have multiple layers and no delamination due to intertwine-type out-of-plane interlacement. Various methods and techniques were developed for 3D braiding, and these 3D braiding techniques are commercially available. On the other hand, various unit cell base models on 3D braiding were developed to deﬁne the geometrical and mechanical properties of 3D braided structures. Most of the unit cell base models include micromechanics and numerical techniques. Multiaxis 3D braided fabrics have multiple layers and no delamination, and their in-plane properties are enhanced due to the bias yarn layers. However, the multiaxis 3D braiding technique is at an early stage of development.

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Sources of further information and advice Although numerous studies have been carried out on the characterization and modeling of 3D braided structures, there is limited information available on the development of 3D braiding technologies due to the grant received from defense-related funding agencies which imposed some restrictions on the research output.

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Cartesian 3D braiding

Cartesian 3D braiding

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