Kadir Bilisik

Three-dimensional braiding for composites: A review

The aim of this study is to review three-dimensional (3D) braided fabrics and, in particular, to provide a critical review of the development of 3D braided preform structures and techniques. 3D braided preforms are classified based on various parameters depending on the yarn sets, yarn orientation and intertwining, micro-meso unit cells and macro geometry. Biaxial and triaxial two-dimensional (2D) braided fabrics have been widely used as simple- and complex-shaped structural composite parts in various technical areas. However, 2D braided fabric has size and thickness limitations. 3D braided fabrics have multiple layers and no delamination due to intertwine-type out-of-plane interlacement. However, the 3D braided fabrics have low transverse properties and they also have size and thickness limitations. On the other hand, various unit cell base models on 3D braiding were developed to analyze the 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. The in-plane properties of multiaxis 3D braided fabrics may be enhanced due to the ±bias yarn layers. However, the multiaxis 3D braiding technique is at an early stage of development and needs to be fully automated.

Multiaxis three-dimensional weaving for composites: A review

The aim of this study is to review three-dimensional (3D) fabrics and a critical review is especially provided on the development of multiaxis 3D woven preform structures and techniques. 3D preforms are classified based on various parameters depending on the fiber sets, fiber orientation and interlacements, and micro–meso unit cells and macro geometry. Biaxial and triaxial two-dimensional (2D) fabrics have been widely used as structural composite parts in various technical areas. However, they suffer delamination between their layers due to the lack of fibers. 3D woven fabrics have multiple layers and no delamination due to the presence of Z-fibers. However, the 3D woven fabrics have low in-plane properties. Multiaxis 3D knitted fabrics have no delamination and their in-plane properties are enhanced due to the ±bias yarn layers. However, they have limitations regarding multiple layering and layer sequences. Multiaxis 3D woven fabrics have multiple layers and no delamination due to Z-fibers and in-plane properties enhanced due to the ±bias yarn layers. Also, the layer sequence can be arranged based on end-use requirements. However, the multiaxis 3D weaving 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 weaving.

Single and multiple yarn pull-outs on aramid woven fabric structures:

The aim of this study was to understand the pull-out properties of para-aramid woven fabrics. Para-aramid Twaron CT714 and CT716 woven fabrics were used to conduct the pull-out tests. Twaron CT714 and CT716 woven fabrics have low and high fabric densities, respectively. A previously developed yarn pull-out fixture was improved to test various fabric sample dimensions. Data generated from the single and multiple yarn pull-out tests using various dimensions of CT714 and CT716 woven fabrics included fabric pull-out forces, yarn crimp extensions in the fabrics and fabric displacements. Yarn pull-out forces depend on fabric density, fabric sample dimensions and number of pulled ends in the fabric. Results showed that the multiple yarn pull-out force was higher than that of the single yarn pull-out test. Single and multiple yarn pull-out forces in Twaron CT716 (tight fabric) were higher than those of Twaron CT714 (loose fabric). Yarn crimp extension in Twaron CT714 and CT716 fabrics depends on crimp ratios in the warp and weft directions in the fabrics and on fabric density. High crimp ratio fabrics showed high yarn crimp extension in the fabric compared to that of low crimp ratio fabrics. Wide and long fabric samples also showed high yarn crimp extension compared to that of the narrow and short fabric samples. Fabric displacement in Twaron CT714 and CT718 fabrics depends on fabric sample dimensions and the number of pulled yarns. Wide and long fabric samples showed high fabric displacement compared to that of the narrow and short fabric samples. Fabric displacement resulting from the multiple yarn pull-out test was also higher than that of the single yarn pull-out test. Future research will concentrate on the development of the analytical relations between pull-out and yarn-fabric structural parameters which could result in a ballistically better fabric structure for use in soft ballistic applications.

Experimental determination of yarn pull-out properties of para-aramid (Kevlar®) woven fabric

The aim of this study was to determine the pull-out properties of the para-aramid woven fabrics. Para-aramid Kevlar 29® (K29) and Kevlar 129® (K129) woven fabrics were used to conduct the pull-out tests. K29 and K129 woven fabrics had high and low fabric densities, respectively. For this reason, yarn pull-out fixture was developed to test various K29 and K129 fabric sample dimensions. Data generated from single and multiple yarn pull-out tests in various dimensions of K29 and K129 woven fabrics included fabric pull-out forces, yarn crimp extensions in the fabrics, and fabric displacements. Yarn pull-out forces depended on fabric density, fabric sample dimensions, and the number of pulled ends in the fabric. Multiple yarn pull-out force was higher than single yarn pull-out force. Single- and multiple-yarn pull-out forces in K29 (tight fabric) were higher than those of K129 (loose fabric). Yarn crimp extension in K29 and K129 fabrics depended on crimp ratio in the fabrics and fabric density. High crimp ratio fabrics showed high yarn crimp extension compared to that of the low crimp ratio fabrics. Long fabric samples also showed high yarn crimp extension compared to that of the short fabrics. Fabric displacement in K29 and K129 fabrics depended on fabric sample dimensions and the number of pulled yarns. Long fabric samples showed high fabric displacement compared to that of short fabric samples. Fabric displacement from multiple yarn pull-out test was also higher than that of the single yarn pull-out test. It was considered that fabric pull-out properties can play important roles for absorption of impact load due to the yarn frictions in the fabric structures.

Structure-unit cell-based approach on three-dimensional representative braided preforms from four-step braiding: Experimental determination of effects of structure-process parameters on predetermined yarn path

The aim of this study was to understand the effects of braid pattern and the number of layers on three-dimensional (3D) braided unit cell structures. Various unit cell-based representative 3D braided preforms were developed. Data generated from these structures included unit cell dimensions, yarn angle, and yarn length in the unit cell structures. It was shown that braid patterns affected the 3D braided unit cell structures. The 1 × 1 braid pattern made fully interconnected integral 3D braided unit cell structures, whereas the 2 × 1 braid pattern created disconnected braid layers that were connected to the structures edges. When the number of layers increased, 3D braided unit cell thickness also increased. Braid pattern slightly affected the braider yarn angle, whereas the number of layers did not influence it. It was observed that the number of layers considerably affected the yarn length in the unit cell structure. Increasing the layer number from five to 10 layers created a yarn path in the unit cell edge regions called the ‘multilayer yarn length’. This yarn path was not observed below five-layer 3D braided unit cell structures. In jamming conditions, minimum jamming decreased the width of the unit cell structure, but maximum jamming increased its width. On the other hand, minimum jamming decreased the surface angle of the unit cell structure, whereas maximum jamming increased the surface angle. In addition, it was realized that jamming conditions influenced the density of the unit cell but did not affect the yarn length in the unit cell structures.

Experimental determination of fabric shear by yarn pull-out method

The aim of this study was to determine fabric shear by the yarn pull-out method. For this purpose three fabric types were tested. The fabric width/length ratio and the number of pull-out ends were identified as important test parameters. After the yarn in the fabric was pulled from the top ravel region before the start of the crimp extension stage, it was found that fabric shear strength increased as the number of pulled ends increased. On the other hand, when the fabric width/length ratio decreased the fabric shear strength increased. Fabric shear rigidity was also identified for each fabric type and it was found that the number of pulled ends and the fabric width/length ratio influenced fabric shear rigidity. Finally, shear jamming angles were found to be a function of the number of pulled ends. Local fabric shear properties could be identified by pulling the yarn ends in various regions of the fabric. This could be important for the handling of a fabric during its formation. The pull-out method is considered to be a simple way of defining overall and local fabric shear properties for various end-uses.

Experimental characterization of multistitched two-dimensional (2D) woven E-glass/polyester composites under low-velocity impact load

The aim of this study was to understand the low-velocity impact energy absorption mechanism of the developed two-dimensional multistitched multilayer E-glass/polyester-woven composites. It was found that the specific front and back face damaged areas of the two-dimensional multistitched E-glass/polyester-woven composites were smaller than those of the two-dimensional unstitched structures. When the stitching density increases, the front and back face damaged areas generally decrease. In addition, when the number of stitching directions increased, the front and back face damaged areas decreased. Therefore, stitching density, stitching directions, stitching yarn, and stitching type on the composite structures were considered as important parameters. Impact load caused a small indentation in the center of front face and resulted in fiber splitting and fiber breakages in the center of the back face of the structure. On the surrounding area of the front and back face damaged zones of the structures, fiber-matrix debonding and matrix breakages were observed. These results indicated that multistitching suppressed the impact energy to a small area of the composite structure. Thus, the two-dimensional Kevlar®129 or E-glass-multistitched E-glass/polyester-woven composite structures showed better damage tolerance performance compared to the unstitched composite structures.

Stick–slip behavior of para-aramid (Twaron®) fabric in yarn pull-out

The aim of this study was to understand the stick–slip properties of para-aramid woven fabrics. Para-aramid Twaron CT®716 (CT716) and Twaron CT®714 (CT714) woven fabrics were used to conduct the pull-out tests. CT716 and CT714 woven fabrics have low and high fabric densities, respectively. Data generated from the single and multiple yarn pull-out tests using various lengths of CT716 and CT714 woven fabrics included fabric stick–slip force and accumulative retraction force. Stick–slip force and accumulative retraction force depend on fabric density and the number of pulled ends in the fabric. Stick–slip force and accumulative retraction force in the multiple-yarn pull-out test were higher than those of the single-yarn pull-out test. Stick–slip force and accumulative retraction force in single- and multiple-yarn pull-out tests in the dense CT716 fabric were higher than those of the loose CT714 fabric. In addition, long fabric samples showed high stick–slip force compared with that of the short fabric samples.

Experimental determination of bending behavior of multilayered and multidirectionally-stitched E-Glass fabric structures for composites

The aim of this study was to experimentally determine the bending behavior of developed multilayered multistitched E-Glass preform structures. For this reason, a bending rigidity test instrument based on the cantilever test principle was used. A bending rigidity test was conducted on all developed multilayered multistitched E-Glass preform structures. Yarn linear density and fabric density influenced the bending rigidity of single layer E-Glass fabric. The single layer fabrics bending rigidity depended on the off-axis angle orientations in the fabric plane. On the other hand, the bending rigidity of the multilayered unstitched E-Glass fabric structure depended on the number of fabric layers. The bending rigidities of the multilayered four directional hand and machine stitched E-Glass preform structures were high compared with one and two directional hand and machine stitched E-Glass preform structures. The bending rigidities of all heavy (6 step/cm) machine stitched E-Glass preform structures were high compared with light (2 step/cm) machine and hand (1 step/cm) stitched E-Glass preform structures. In addition, the bending rigidities of all developed multilayered hand and machine stitched E-Glass preform structures were higher than those of unstitched preform structures due to stitching. In addition, the multilayered multistitched preform structures showed a low order of bending curvatures compared with the multilayered unstitched preform structures. The results indicated that the number of stitching directions and stitching steps substantially affected the bending rigidity of the developed preform structures. Stitching yarn type was also a parameter for the bending behaviorof the multistitched preform structures. It was considered that the unstitched fabric structure could be easily formed whereas the directional stitched E-Glass preform structure became stiff and could not be easily formed.

Three Dimensional Axial Braided Preforms: Experimental Determination of Effects of Structure-Process Parameters on Unit Cell

The aim of this study was to understand the effects of braid pattern and number of layers on 3D axial braided unit cell structures. Various unit cell based representative 3D axial braided preforms were developed. Data generated from these structures included unit cell dimensions, yarn angle and yarn length in the unit cell structures.It was shown that braid patterns affected the 3D axial braided unit cell structures. The 1 × 1 braid pattern made fully interconnected integral 3D axial braided unit cell structures, whereas the 2 × 1 braid pattern created disconnected braid layers which were connected to the structure edges. When the number of layers increased 3D axial braided unit cell thickness also increased. Braid pattern slightly affected the braided yarn angle. On the other hand, it was observed that the number of layers considerably affected the yarn length in the unit cell structure. Increasing the layer number from six to eight layers created a yarn path in the unit cell edge regions called the ‘multilayer yarn length’. This yarn path was not observed below eight layer 3D axial braided unit cell structures. In jamming conditions, minimum jamming decreased the width of the unit cell structure but maximum jamming increased its width. In addition, minimum jamming decreased the surface angle of the unit cell structure, conversely, however, the maximum jamming increased the surface angle. Also, it was realized that jamming conditions influenced the density of the unit cell but did not affect the yarn length in the unit cell structures.