**2.3 Weave structures and properties**

In 3D woven fabrics, generally multilayer, angle interlock and orthogonal weave architectures are the most widely used weave structures. While multilayer and angle interlock weave structures can be produced with conventional 2D weaving machines especially with shuttle looms, orthogonal weave architecture needs a special designed 3D weaving machine to be produced. Orthogonal weave structures consist of three sets of yarns that are perpendicular to each other (X, Y and Z coordinates). In this particular 3D woven fabric formation process, Z yarns interconnect all individual warp- and fill-directional yarns and thus solidify the fabric (Bogdanovich, 2007). Mechanical and structural properties of the composites having orthogonal weave architectures with various binding weaves and different numbers of layers were investigated (Chen&Zanini, 1997 as cited in Behera&Mishra, 2008). The results of the investigation are as follows:

 Since straight yarns exist in the orthogonal structures, tensile stiffness and strength properties of these structures are well regardless of type of binding weave. However, tensile stiffness and strength values of these weave structures are directly proportional with the number of layers.

The structural stability of multilayer structures increases when more layers are

For multilayer structures, the effect of weave combination is little on strength properties

 The increase in stitch density in multi-layer structures will generally reduce the strength of the structures, but its effect on the structural stability is not clear. The latter may be

The number of layers of weft threads in angle-interlock structures mainly increases the

Angle-interlock structures permit more elongation in the warp direction than in the

 The increase in the number of layers in angle-interlock structures makes the structures more difficult to bend; this is more significantly so in the weft direction than in the warp direction. However, the increase in the number of layers showed little influence

Weaving is an ancient tradition which dates back over seven millenniums. In traditional weaving, there are two sets of yarns, perpendicular to each other, interlace to form a woven fabric. While one set of the yarns that run lengthwise along the weaving machine direction are called warp, the other set of the yarns that run transversely from one side to the other

There are three basic motions in order to produce a fabric by ensuring the interlacing between warp and weft yarns. These three essential motions are; shedding, weft insertion and beat-up. For the continuation of weaving process, warp yarns have to be let-off and the produced fabric has to be taken-up. These necessary two motions are auxiliary movements

In order to get different weave structures in traditional weaving, the movement of the warp yarns have to be controlled and changed before each weft insertion. To perform warp yarns movement on a loom, warps that follow the same interlacing pattern have to be grouped with the same frame called harness. In each harness, there are heddles that have an eye in the middle in which the warp yarns pass through. By lifting the harness up or down, the

related to the distribution of the stitches and also to the weaving conditions.

tensile strength in the weft direction because of the construction.

whereas it plays a significant role on structural stability.

involved.

weft.

**3. Weaving** 

on the shear rigidity.

side of the machine are called weft (a.k.a. filling).

Fig. 2. Basic motions on weaving machine (Lord&Mohamed, 1982).

that are warp let-off and fabric take-up.


Multilayer weave structures consist of multiple layers each of which have its own sets of warp and weft yarns. The connection of the layers is done by self-stitching (existing yarns) or central stitching (external sets of yarns). In angle interlock weave structures; there are at least two sets of yarns such as warp and weft. In some cases, in order to increase fibre volume fraction and in-plane strength, stuffer yarns can be added. Angle interlock weaves are divided into two groups; through thickness angle interlock and layer to layer angle interlock weaves. In through thickness angle interlock weaves, warp yarn travels from one surface of the 3D fabric to the other holding all the layers together, whereas in layer to layer angle interlock weaves warp yarn travels from one layer to the adjacent layer and back. A set of warp weaves together hold all the layers of the weave structure. Mechanical properties of 3D angle interlock woven composites are not as good as the mechanical properties of corresponding laminated composites. However, composites having angle interlock woven structure have advantages of enhanced delamination resistance, impact/fracture resistance, damage tolerance and dimensional stability (Naik et al., 2002). Higher through-the-thickness elastic and strength properties can be achieved by using 3D orthogonal interlock woven composites (Naik et al., 2001).

Fig. 1. Weave structures (Stig, 2009; Badawi, 2007;Chen, 2011).

Composites having different weave architectures will have different mechanical properties as well as structural stability. Chen et al investigated the mechanical and structural properties of the composites produced from 3D woven preforms having warp self-stitched multilayer weave and angle interlock weave (Chen et al., 1999). The results of the investigation are as follows:

 Increasing number of layers in multilayer weave structures results in a stronger structure. As the multilayer fabrics are warp self-stitched, the strength increase in weft direction is more significant than in the warp direction.

 Number of layers and binding weaves do not affect the breaking elongation of the orthogonal structures. This property is mostly dependent on the elongation properties

Multilayer weave structures consist of multiple layers each of which have its own sets of warp and weft yarns. The connection of the layers is done by self-stitching (existing yarns) or central stitching (external sets of yarns). In angle interlock weave structures; there are at least two sets of yarns such as warp and weft. In some cases, in order to increase fibre volume fraction and in-plane strength, stuffer yarns can be added. Angle interlock weaves are divided into two groups; through thickness angle interlock and layer to layer angle interlock weaves. In through thickness angle interlock weaves, warp yarn travels from one surface of the 3D fabric to the other holding all the layers together, whereas in layer to layer angle interlock weaves warp yarn travels from one layer to the adjacent layer and back. A set of warp weaves together hold all the layers of the weave structure. Mechanical properties of 3D angle interlock woven composites are not as good as the mechanical properties of corresponding laminated composites. However, composites having angle interlock woven structure have advantages of enhanced delamination resistance, impact/fracture resistance, damage tolerance and dimensional stability (Naik et al., 2002). Higher through-the-thickness elastic and strength properties can be achieved by using 3D

 The shear rigidity and shearing hysteresis increases when more layers are involved. Tighter binding weaves and more layers of the orthogonal structure will produce

higher bending stiffness and bending hysteresis.

orthogonal interlock woven composites (Naik et al., 2001).

Fig. 1. Weave structures (Stig, 2009; Badawi, 2007;Chen, 2011).

direction is more significant than in the warp direction.

investigation are as follows:

Composites having different weave architectures will have different mechanical properties as well as structural stability. Chen et al investigated the mechanical and structural properties of the composites produced from 3D woven preforms having warp self-stitched multilayer weave and angle interlock weave (Chen et al., 1999). The results of the

 Increasing number of layers in multilayer weave structures results in a stronger structure. As the multilayer fabrics are warp self-stitched, the strength increase in weft

of the yarns used.

