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Textile auxetic materials with negative Poisson's ratio (NPR) have potential applications in protective textile, filtration, and energy absorbance. However, cotton core-spun based auxetic textile is rarely investigated. In this study, cotton core-spun (Lycra)-based helical auxetic yarn (HAY) was developed, and the effects of core filament linear density on the auxetic behavior were studied. Core-spun cotton yarns of 8/1 Nec containing core filament (180, 260, and 420 D) were developed. Then, these core-spun yarns were wrapped with 50 D Dyneema filament at 393 twist/m to make the HAY. The diameter, NPR, and tensile strength of HAY were increased with increasing linear density of Lycra filament. Image analysis of HAY containing 420 D Lycra showed 57% diameter increase with the change in axial strain from 0 to 15 mm. The maximum auxetic behavior with NPR of -3.97 and tensile strength of 26.71 cN/tex was observed in 420 D Lycra-based HAY. This study proved that the cotton core spun-based HAY can be produced with significant auxetic properties for practically potential use in wearable protective textiles. [ABSTRACT FROM AUTHOR]

In this work, a new structure for designing auxetic yarn and its geometrical analysis is presented. The proposed structure is referred to as a double-core helical auxetic yarn (DC-HAY). It consists of two core components of soft yarn with a larger diameter and one wrap component of stiff yarn with a smaller diameter. A primary geometrical model for predicting the Poisson's ratio of the structure was presented through the deformation analysis of the DC-HAY during the tensile loading. Also, the primary proposed model was modified by considering the non-linear behavior of Poisson's ratio of the core components. For the verification of the proposed models, some experiments were conducted based on the initial wrapping angle, as well as the diameter ratio and modulus ratio of components. The results showed that the proposed yarn structure exhibits an apparent auxetic outcome. Moreover, the modified model is capable of predicting the maximum negative Poisson's ratio of the DC-HAY with a desirable error. Furthermore, it was found that the higher modulus ratio of components, higher diameter ratio of components and the lower initial wrapping angle will result in a higher maximum NPR, which were −8.23, −8.16 through the main lateral directions of samples. [ABSTRACT FROM AUTHOR]

Auxetic textiles are defined as textiles with negative Poisson's ratio. These textiles possess unique properties that render them suitable for special applications. This work aims to investigate the effect of fabric structural parameters such as thread densities, weave design and warp yarn count. Thus, 30 fabric samples were woven at 3 weft and 2 warp densities, respectively. Two warp counts and three weave designs of plain, basket 3/3 and weft-backed satin 6 were used. The samples were uniaxially loaded in weft direction and dimensional changes at various strains levels were evaluated. The evaluation was carried out using the image processing technique based on MATLAB software. The weft yarns used were found to exhibit auxetic behavior at the whole spectrum of the strain level used. The least weft yarn Poisson's ratio was found to be −0.9. It was established that in general the fabric samples exhibit auxetic effect within the stated range of strain. Additionally, it was concluded that while fabric thread densities together with warp count influence the minimum fabric Poisson's ratio, auxetic behavior of the samples is not dependent on weave design alone. Rather, it was illustrated that the combined effect of weave design in association with stated structural parameters on auxetic feature cannot be ignored. [ABSTRACT FROM AUTHOR]

This paper reports a new type of auxetic yarn made with circular braiding technology to overcome the yarn slippage problem in the conventional helical auxetic yarn structure. Various auxetic yarn structures are firstly produced on a vertical circular braiding machine with 16 yarn carries by changing the number and arrangement of stiff yarn as well as diameter of elastic yarn and core yarn, and then tested under single and repeating tensile conditions. The results show that not only yarn slippage problem could be overcome in the newly developed auxetic yarn structure, but also an early activation and a higher magnitude of negative Poisson's ratio could be achieved. The results also show that all structural parameters including stiff yarn number and arrangement, core yarn, and elastic yarn diameter have an influence on the auxetic effect of the novel yarn structure. Since the new auxetic yarn is produced by using standard braiding manufacturing technique and conventional non-auxetic yarns, there are few technological barriers for its largescale manufacture for practical application. [ABSTRACT FROM AUTHOR]

Auxetic yarn was successfully produced by a wrap filament and a core filament based on a ring-spinning system, which showed an auxetic effect when stretched, that is, expanding transversely under tension. Yarns were spun by different structural parameters of the core filament and the wrap filament, including diameter ratio, helical angle and tensile modulus of the wrap filament. Corresponding tensile tests were utilized to analyze the effects of structural parameters and performance on outer contour deformation of auxetic yarn. Experimental results showed that the outer contour of auxetic yarn expanded transversely under tension and there existed significant negative Poisson's ratio values in the Poisson's ratio-strain curve, and it was found that the auxetic effect became more observable with a higher diameter ratio of the core filament to the wrap filament, and lower helical angle and larger tensile modulus of the wrap filament. Moreover, compared with theoretical results by theoretical modeling in Part I, good relations of Poisson's ratio-strain curves were obtained between experimental and theoretical results. This proves the effectiveness of spinning auxetic yarn by selecting reasonable components of yarn and it is feasible to design yarn with a negative Poisson's ratio effect. [ABSTRACT FROM PUBLISHER]

The main content dealt with in the paper is to make a theoretical analysis of the contour diameter of auxetic yarn under tension, which expands transversely under axial tension. The auxetic yarn is designed by two components, that is, a core filament and a wrap filament. Compared with the wrap filament, the core filament is thicker, softer and much more extensible. In the initial status, the core filament is straight in the center of the auxetic yarn and the wrap filament wraps the core filament helically in a certain helical angle. Based on theoretical analysis, the formula of negative Poisson’s ratio of stretched auxetic yarn is obtained. It is found that the value of Poisson’s ratio is related to axial strain, helical angle and the diameter ratio of the core filament to the wrap filament. An applied example is presented to verify the Poisson’s ratio value-strain curve of auxetic yarn. In order to better investigate effects on negative Poisson’s ratio, the effect of different parameters of yarn, including mesh size, diameter ratio, tensile modulus and helical angle of the wrap filament, is investigated using finite element analysis based on ABAQUS software to analyze the negative Poisson’s ratio of auxetic yarn when stretched. It verified that yarn spun by two different components produced a negative Poisson’s ratio effect under tension and structure parameters of auxetic yarn significantly affected negative Poisson's ratio values. It is expected that this study could help us understanding the deformation mechanism of auxetic yarn under axial tension load. [ABSTRACT FROM PUBLISHER]

The present work reports application of auxetic yarns in development of abrasion resistant socks which can be used for better serviceability without shoes even on rough surfaces. Socks used in the current research were produced by using helical auxetic yarns which consist of different combinations of high performance and conventional materials e.g. Kevlar P-AR (para-aramid), cotton, elastomeric yarn, polyamide (PA6) and polyester with same linear density of 74 Tex. Three different types of fabrics were produced e.g. flat knit, sandwich half terry short and sandwich half terry long. For investigating the auxeticity, all samples were subjected to tensile loading and the resulting change in their thickness was measured. Abrasion resistance and other comfort related properties e.g. air permeability, vertical wicking and absorbency were also evaluated. The influence of different yarn combinations, twist levels and fabric types on abrasion resistance and breathability of socks were investigated by using fractional (half) factorial design. Statistical analysis was performed for the obtained results by using analysis of variance. Conventional socks samples were also produced in all fabric types for comparison with the auxetic materials. From the results it was concluded that the overall abrasion resistance of auxetic yarn-based sock is higher than conventional cotton sock. Results also revealed that abrasion resistance was increased by 46% in flat knit socks sample, 50% in sandwich half terry short sample and 58% in sandwich half terry long sample as compared to conventional cotton sock. In addition to this all the socks samples exhibited good comfort/breathability properties. [ABSTRACT FROM AUTHOR]

Helical auxetic yarn (HAY) is a newly developed composite yarn with negative Poisson's ratio. HAYs offers advantageous merits as a reinforcing element in composite materials. In this paper high stiffness HAYs composed of Nylon filament core and fine steel wire wrap yarns were developed. The importance of the stiffness ratio of the wrap to the core components in the resultant auxetic yarn was examined. The differences between instantaneous and engineering Poisson's ratio analyses in the understanding of the strain-dependent behavior of HAY was investigated. Results revealed that the utilization of the fine steel multifilament in the developed HAY samples enormously improves the stiffness of HAY. It was possible to obtain an elastic modulus of 9 GPa and a maximum auxetic effect of –16.82 in the samples. It was concluded that such highly stiff auxetic yarn can successfully be used as reinforcement in various composite materials such as cementitious composites. [ABSTRACT FROM AUTHOR]

In this paper, we report a new multi-scale NPR composite based on auxetic fabric/elastomer matrix (AF/EM) composite structure. The multi-scale AF was obtained via using helical auxetic yarn (HAY) as weft yarns and constructing re-entrant hexagonal (REH) geometry structure on the macro scale, then the AF was combined with EM to fabricate the auxetic composite (AC). The AF and AC exhibit the NPR of −1.492 and −0.379. Simultaneously, high tensile strain over 108% (AF) and 82% (AC) can be subjected, indicating good mechanical performance. The superior performance of the AC is its ability to maintain NPR and resilience, with elastic recovery ratio over 94% and work recovery coefficient with a stable value over 80% after 10 cycles. Also, the damping properties results further evidence the good elasticity of our AC. The paper shows that our AF and AC are promising candidates in protective composites. [ABSTRACT FROM AUTHOR]