| Author: | Hasan, Kamrul |
| Title: | Study of bi-stretch woven fabrics with negative poisson's ratio |
| Advisors: | Hu, Hong (ITC) |
| Degree: | Ph.D. |
| Year: | 2021 |
| Subject: | Textile fabrics Elasticity Hong Kong Polytechnic University -- Dissertations |
| Department: | Institute of Textiles and Clothing |
| Pages: | xxiv, 209 pages : color illustrations |
| Language: | English |
| Abstract: | Auxetic textile materials have a negative Poison's ratio (NPR) that makes them laterally expand when stretched or laterally shrink when compressed. Over the past few years, many studies have been conducted to investigate different auxetic textile materials including auxetic yarns, auxetic woven fabrics, auxetic weft knitted fabrics, auxetic warp knitted fabrics, 3D auxetic textile reinforcements, auxetic braided structures, auxetic non-woven, and auxetic textile composites. Among them, auxetic fabrics have gained the attention of textile researchers because of their exceptional properties. These properties include synclastic behavior under the bending condition, better shape fitting ability, and reduced garment pressure exerted by the fabric on joints of the human body during movement or exercise. Another important property is the pore opening behavior under tension, which leads to increased air permeability of fabrics and controlled drug delivery for wound healing. In addition, other properties including sound absorption, energy absorption ability, and vibration damping could be improved. These counterintuitive properties make auxetic fabrics a very attractive choice for many applications, such as protective sportswear, children's wear for size adaptability, functional underwear, medical applications, blast curtains, maternity clothes, and aerospace, and military applications. However, comparing to other auxetic textile materials, development of auxetic woven fabrics is still limited. Until today, two methods have been implemented to produce auxetic woven fabrics. The first method is based on auxetic yarns where yarns can be used in the weft or warp direction of the fabrics. However, the production of auxetic woven fabrics using auxetic yarns has not widely been used due to the inadequate availability of auxetic yarns in the current market. Besides, the NPR effect of auxetic yarns cannot be transferred completely to fabrics due to the obstructions rendered by the interlacement pattern in the woven fabric structure. Another approach to fabricate auxetic woven fabrics is based on the realization of auxetic geometry into the fabric structure by using non-auxetic yarns. This method has attracted many researchers since there is no limitation for fiber materials and fabric structures. Using this technique, the developed auxetic fabrics show a smaller NPR effect when stretched in either principle direction (warp and weft directions). There are certain limitations of current research associated with these developed auxetic woven fabrics. Firstly, the NPR effect in different tensile directions of the auxetic woven fabrics is still unaddressed. Secondly, the retention ability of the NPR effect under repeating tensile cycles (RTCs) has not been explored yet. Thirdly, the mechanical and physical properties of the developed auxetic woven fabrics are not studied yet. Lastly, geometrical analyses of these auxetic woven fabrics are limited. To address these issues, it is essential to study the NPR effect in different tensile directions since the fabrics are not only stretched in the warp or weft directions but also undergo stretching in other tensile directions during real-life usage. Therefore, such a study can provide more comprehensive information about the NPR effect of the auxetic woven fabrics in different tensile directions. Besides, the developed auxetic woven fabrics are suggested for tight garments which required to undergo repeated tensile loading during real usage. Therefore, it essential to study the NPR effect under repeated tensile loading conditions. The developed bi-stretch auxetic woven fabrics are suggested to be used as sportswear, tight-garments, maternity wear, and children's wear to improve the shape fitting ability at joint parts of the body and increase comfort during real-life use. Hence, it is important to examine the mechanical and physical properties of the developed auxetic fabrics. The geometrical analysis is conducted to understand the relationship between Poisson's ratio and the tensile strain of the developed fabric. This thesis is aimed to design and develop bi-stretch auxetic woven fabrics based on foldable geometrical structure (FDGS), and reentrant hexagonal geometrical structure (REHG) by using conventional non-auxetic yarns and weaving machinery. A series of experiments was carried out by using an Instron 5566 machine to investigate the NPR effect under tensile strain, tensile properties until the breaking strength and the NPR effect under RTCs with the fixed tensile extension of the developed fabrics. The tensile test was subjected to the developed fabrics in five different tensile directions including two principal directions and three biased directions. The mechanical and physical properties of the fabrics were then measured and analyzed following different testing standards. Finally, two geometrical models were developed to predict the relationship between Poisson's ratio and tensile strain of the bi-stretch auxetic woven fabric based on FDGS in the warp and weft directions. According to the theoretical and experimental results, the main conclusions of this thesis can be drawn as follows: 1. The bi-stretch auxetic woven fabrics were designed based on the FDGS and REGH and developed by using conventional yarns and the weaving machine. The NPR effect can be induced into the woven fabric structure by adopting special interlacement patterns. 2. The geometrical structures could be realized into woven fabric by creating a differential shrinkage effect or the phenomenon of non-uniform contraction profile within the unit cell of the woven fabric structure. This effect could be created using elastic and non-elastic yarns by a combination of loose and tight weaves with different contraction properties. 3. The developed bi-stretch auxetic woven fabrics have the NPR effect in principal as well as in biased directions. Higher NPR effect and tensile deformation resistance ability were obtained when the fabric is stretched in the principal directions as compared to those obtained in biased directions. 4. The NPR effect under RTCs is higher along principle directions than biased directions. This is because the unit cell is more stable along principle directions so that it can keep its unit cell shape even after the completion of many repeating tensile cycles. 5. The developed fabrics have excellent physical properties such as stretch and recovery properties under a specified tensile loading, and elastic recovery property under repeating tensile cycles. Also, the developed fabrics have shown excellent air-permeability properties, moisture management properties, bending properties, and fabric thickness properties under different percentages of the tensile strain. 6. The semi-empirical equations obtained in this study could be used to design and predict the auxetic behavior of the auxetic woven fabrics made with the same type of materials but with different geometrical parameters. |
| Rights: | All rights reserved |
| Access: | open access |
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