*5.2.4. Orthogonal woven fabric structure*

Gowayed and Pastore [136] reviewed computational methods for 3D woven fabric. The developed analytical methods were stiffness averaging, fabric geometry and inclination models. They were based on classical lamination theory, and a micromechanical approach was considered. Gu [137] reported that the directional/total fiber volume fraction in 3D woven preforms is influenced by the take-up rate during weaving process. It is possible to obtain higher packing densities by applying double beat-up. Cox et al. [5] stated that 3D woven preform with a low volume fraction may perform well under the impact load compared to 3D woven preform with a high volume fraction. Dickinson [138] studied 3D carbon/epoxy composites. It is realized that the amount and placement of z-yarn in 3D woven preform influence the in-plane properties of the 3D woven structure. When the volume ratio of z-yarns was increased, in-plane properties of the 3D woven fabric decreased. On the other hand, local delamination was monitored when the ratio of z-yarns was decreased. Bobcock and Rose [139] found that when 3D woven or 2D woven/stitched composites were subjected to an impact loading, the impact energy was confined to a limited area owing to the z-yarns.

## *5.2.5. Multiaxis woven fabric structure*

Uchida et al. [17] examined five-axis 3D woven fabric composites. They reported that multiaxis woven fabric and stitched 2D laminate composites showed similar results in terms of tensile and compression properties whereas multiaxis fabric composite yielded better open hole tensile and compression values. Impact tests revealed that the damaged area is smaller in 3D woven composites when compared to that of the stitched laminate. Furthermore, 5-axis 3D woven composite gave better results in Compression After Impact (CAI) tests in comparison with stitched fabric composite. Bilisik [67] stated that the most important process parameters for multiaxis 3D flat woven preform production are bias angle, width ratio, packing, tension and fiber waviness. The bias angle can be manipulated by tube-block movement.

Bilisik and Mohamed [140] investigated the mechanical properties of 3D carbon/epoxy composites by applying the stiffness averaging method. The directional tensile and shear constants obtained are shown in Table 7. The shear properties were influenced by the orien‐ tation of yarns within the preform.

The process parameters for multiaxis 3D circular weaving are the following: bias orientation, radial and circumferential yarn insertion, beat-up and take-up. Bias yarns on the outer and inner surfaces of the structure create helical paths and there is a slight angle difference between them particularly in the case of thick-walled fabrics. It was shown that there is a correlation between preform density (fiber volume fraction), bias yarn orientation and take-up rate. The excessive yarn length during circumferential yarn insertion is because diameter ratio (preform outer diameter/outermost ring diameter) is not equal to 1. The diameter ratio depends on the number of the rings. When the excessive circumferential yarn is not retracted, it causes


waviness in the structure. However, there must be an adequate tension on the circumferential yarns to get proper packing during beat-up [68].

is the structures outside surface length (cm), *Cr* is the radial crimp (%), *lrt* is the uncrimped

Gowayed and Pastore [136] reviewed computational methods for 3D woven fabric. The developed analytical methods were stiffness averaging, fabric geometry and inclination models. They were based on classical lamination theory, and a micromechanical approach was considered. Gu [137] reported that the directional/total fiber volume fraction in 3D woven preforms is influenced by the take-up rate during weaving process. It is possible to obtain higher packing densities by applying double beat-up. Cox et al. [5] stated that 3D woven preform with a low volume fraction may perform well under the impact load compared to 3D woven preform with a high volume fraction. Dickinson [138] studied 3D carbon/epoxy composites. It is realized that the amount and placement of z-yarn in 3D woven preform influence the in-plane properties of the 3D woven structure. When the volume ratio of z-yarns was increased, in-plane properties of the 3D woven fabric decreased. On the other hand, local delamination was monitored when the ratio of z-yarns was decreased. Bobcock and Rose [139] found that when 3D woven or 2D woven/stitched composites were subjected to an impact

loading, the impact energy was confined to a limited area owing to the z-yarns.

and fiber waviness. The bias angle can be manipulated by tube-block movement.

Uchida et al. [17] examined five-axis 3D woven fabric composites. They reported that multiaxis woven fabric and stitched 2D laminate composites showed similar results in terms of tensile and compression properties whereas multiaxis fabric composite yielded better open hole tensile and compression values. Impact tests revealed that the damaged area is smaller in 3D woven composites when compared to that of the stitched laminate. Furthermore, 5-axis 3D woven composite gave better results in Compression After Impact (CAI) tests in comparison with stitched fabric composite. Bilisik [67] stated that the most important process parameters for multiaxis 3D flat woven preform production are bias angle, width ratio, packing, tension

Bilisik and Mohamed [140] investigated the mechanical properties of 3D carbon/epoxy composites by applying the stiffness averaging method. The directional tensile and shear constants obtained are shown in Table 7. The shear properties were influenced by the orien‐

The process parameters for multiaxis 3D circular weaving are the following: bias orientation, radial and circumferential yarn insertion, beat-up and take-up. Bias yarns on the outer and inner surfaces of the structure create helical paths and there is a slight angle difference between them particularly in the case of thick-walled fabrics. It was shown that there is a correlation between preform density (fiber volume fraction), bias yarn orientation and take-up rate. The excessive yarn length during circumferential yarn insertion is because diameter ratio (preform outer diameter/outermost ring diameter) is not equal to 1. The diameter ratio depends on the number of the rings. When the excessive circumferential yarn is not retracted, it causes

total radial length (cm) and *St* is the structures wall thickness.

*5.2.4. Orthogonal woven fabric structure*

122 Non-woven Fabrics

*5.2.5. Multiaxis woven fabric structure*

tation of yarns within the preform.

**Table 7.** Multiaxis 3D woven preform elastic constants from multiaxis 3D weaving [140].
