Gaye Yolacan

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.

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.

Abrasion Properties of Upholstery Flocked Fabrics

Flocked fabrics are particularly used in outwear and home upholstery since they are comfortable and soft. In this study, Martindale abrasion and token rubbing properties of the flocked fabrics were investigated and characterized. It was observed that the surface abrasion properties of the flocked fabrics varied depending on the flock fiber density and flock fiber length. The abrasion resistance of flocked fabrics was increased by increasing flock fiber length and decreasing flock fiber density. The surface rubbing properties of flocked fabrics showed similar tendencies with the abrasion properties. However, the flocked fabrics showed more resistance to rubbing in dry form than wet form. These results were in agreement with the optical microscope images.

Warp and weft directional tensile properties of multistitched biaxial woven E-glass/polyester composites

The objective of this research work was to understand the warp and weft directional tensile properties of the two-dimensional multistitched multilayer E-glass/polyester woven composites. The warp and weft directional specific tensile strength and modulus of unstitched structure were higher than those of multistitched structures as stitching caused minor warp and weft yarn filament breakages. Contrarily, the specific tensile strains of unstitched structure were slightly lower than those of all multistitched structures. The stitching yarn type, the number of stitching directions, and the stitching density generally influenced the warp and weft directional tensile properties of multistitched E-glass/polyester woven composites. The failure of warp and weft directional multistitched woven E-glass/polyester composite structures was matrix breakages, and partial and complete yarn breakages in their surfaces. They had a local delamination in their cross-sections and the delamination did not propagate to the large areas due to multidirectional stitching. Also, the failure was confined at a narrow area and resulted in the catastrophic fiber breakages. The warp and weft directional specific damaged areas of multistitched structures, in particular four-directional stitching, were significantly lower than those of the unstitched structures. This indicated that the multistitching made the structures better damage-tolerance materials.

Experimental off-axis tensile characterization of multistitched woven nano composites

The aim of this study was to understand the off-axis tensile properties of the developed two dimensional multistitched multilayer E-glass/polyester woven nano composites. It was found that the specific off-axis tensile strength of unstitched structure was higher than that of the machine stitched structure due to stitching caused filament breakages. But it was slightly lower than that of the machine stitched/nano structure. In addition, the specific off-axis tensile strength of machine stitched/nano composite structure was slightly higher than that of the machine stitched structure. When the nano silica material in the unstitched E-glass/polyester composite structure increased, the off-axis specific tensile strength and the modulus of the unstitched/nano structures increased whereas, the off-axis specific tensile strain of the unstitched/nano structures decreased. The damaged areas of the unstitched/nano structures increased, when the nano silica material in the unstitched E-glass/polyester woven composite structures increased. The failures under the off-axis tensile load of the stitched or stitched/nano structures were confined at narrow area due to the multistitching. On the other hand, it was observed that the off-axis failure of unstitched/nano or stitched/nano woven E-glass/polyester composite structures showed more brittle behavior.

Single and multiple yarn pull-out on E-glass woven fabric structures

The aim of this study was to understand the pull-out properties of E-glass woven fabrics. For this purpose, low yarn linear density E-Glass-F1 and high yarn linear density E-Glass-F2 woven fabrics were used to conduct the pull-out tests. A developed yarn pull-out fixture was used to test short and long fabric sample dimensions. Data generated from the single and multiple yarn pull-out tests using E-Glass-F1 and E-Glass-F2 woven fabrics included fabric pull-out forces, yarn crimp extensions in the fabrics and fabric displacements. Yarn pull-out forces depend on yarn linear density, fabric density, fabric sample dimensions and the number of pulled ends in the fabric. Results showed that multiple yarn pull-out force was higher than single yarn pull-out force. Single and multiple yarn pull-out forces in high yarn linear density E-Glass-F2 were higher than those of low yarn linear density E-Glass-F1 fabric. It was found that the crimp ratio in the fabric and fabric lengths is an important structural parameter for yarn crimp extension. Fabric displacement resulting from the multiple yarn pull-out test was higher than that of the single yarn pull-out test. Fabric displacement generated from single and multiple pull-out tests depended on fabric sample dimensions and the number of pulled yarn ends. Future research will concentrate on the development of the analytical relationship between pull-out and yarn fabric structural parameters which could result in a better fabric structure for use in composite applications.

Short beam strength properties of multistitched biaxial woven E-glass/polyester nano composites

The aim of this study was to understand the warp and weft directional short beam strength properties of the developed two-dimensional multistitched multilayer E-glass/polyester woven nano composites. The warp and weft directional specific short beam strengths of unstitched structures were lower than those of the multistitched/nano structures. When the amount of nano silica material in the unstitched E-glass/polyester composite structure increased, the warp and weft directional specific short beam strengths of the unstitched/nano structures increased. When the stitching direction increased from two to four directions, the warp and weft directional short beam strengths of all hand-stitched structures slightly increased. In addition, the warp and weft directional short beam strengths of high modulus (stitching yarn Kevlar® 129) lightly and densely machine-stitched structures were slightly higher than those of the low modulus (stitching yarn Nylon 6.6) lightly and densely machine-stitched structures. All composite structures had interlaminar shear failure between layers in their cross-sections, but the interlaminar shear failure in machine-stitched and machine-stitched/nano structures did not propagate to the large areas. The stitching direction, stitching density, stitching yarn, stitching type, and amount of nano materials in the composite structures were identified as important parameters.

Warp and weft directional tensile properties of multistitched woven fabric E-glass/polyester nano composites

The aim of this study was to understand the warp and weft directional tensile properties of the developed two dimensional (2D) multistitched multilayer E-glass/polyester woven nano composites. It was found that the warp and weft directional specific tensile strength and modulus of unstitched structure were higher than those of the machine stitched and machine stitched/nano structures due to stitching caused filament breakages. When the nano silica material in the unstitched E-glass/polyester composite structure increased, the warp and weft directional specific tensile strength and the modulus of the unstitched/nano structures increased. The failure of warp and weft directional 2D unstitched and unstitched/nano woven E-glass/polyester composite structures had a complete delamination in their cross-sections. But, the failure of warp and weft directional 2D stitched and stitched/nano woven E-glass/polyester composite structures had a local delamination in their cross-sections and the failure was confined at a narrow area. The warp and weft directional specific damaged areas of unstitched structure were higher than those of the stitched and stitched/nano structures. Also, the warp and weft directional specific damaged areas of machine stitched structure were slightly higher than those of the machine stitched/nano structure. It could be concluded that the addition of nano silica to the stitched structures improved to their damage resistance.

Multiaxis multilayered non-interlaced/ non-Z E-Glass/polyester preform composites and determination of flexural properties by statistical model

In this study, non-interlaced/non-Z single layer and multilayered uniaxial, biaxial and multiaxis preform structures were developed to produce E-Glass/polyester composite structures. The data generated from the flexural tests of the composite structures were analysed by using a regression model. The flexural strength of the E-Glass/polyester structures depended on yarn orientation and the number of layers. In addition, the flexural properties of the composite structures were proportional to their total fiber volume fractions. If all the E-Glass/polyester structures are produced with the same preform packing density, the structures made from coarse fiber show high flexural strength, compared to structures made from fine fiber, due to high fiber volume fraction. All structures showed mode-I type delamination failure which occurred in the out-of-plane direction as a form of interlayer splitting perpendicular to the applied bending load direction. Local interlayer failures were observed between warp/warp in uniaxial structures, warp/filling in biaxial structures and bias/bias and bias/filling in multiaxis structures due to the no-Z yarn reinforcement. The developed regression model was considered as a suitable and viable tool to predict the flexural properties of the composite structures.

Analyses and statistical modeling of crimp extension stage of single and multiple yarn ends pull-out in textured polyester woven fabric

The aim of this study was to understand the crimp extension stage of yarn, being pulled out of fabric. Polyester woven fabrics were used to conduct the pull-out tests. Yarn pull-out crimp extension depends on sample dimensions, fabric density, fabric weave, crimp ratio and the number of pulled ends in the fabric. Results showed that multiple and single yarn pull-out crimp extensions of long samples were higher than those of short samples, and the multiple yarn pull-out crimp extension was higher than that of the single-yarn pull-out force, and the crimp extensions in fabrics were proportional to their crimp ratios. Satin fabric weave showed high weft directional single and multiple pull-out crimp extension compared to plain and ribs fabric weaves. The developed regression model may be helpful for the design of multifunctional fabrics in technical textile applications.