Stiff Yarns Research Articles

Study on a theoretical model of braided auxetic yarns made from a high-speed braiding machine

The main content of this article theoretically analyzes the yarn diameter and Poisson's ratio variation of braided auxetic yarns under axial strain. Braided auxetic yarns are composed of three components: wrap yarns, the core yarn, and the stiff yarn. The core yarn has a larger diameter and smaller elastic modulus than the other two kinds of yarns, but its rigidity is lower. There is a lack of theoretical basis for predicting the Poisson's ratio of braided auxetic yarn. Based on the geometric model, the curve of the Poisson's ratio has been determined and the Poisson's ratio trend of braided auxetic yarns is deduced, aiming to predict the Poisson's ratio of braided auxetic yarns under axial strain with accurate yarn parameters. The experimental results show that the minimum Poisson's ratio of theoretical value and actual value appears under the same axial strain, and the variation trend of Poisson's ratio of both values is consistent. The Poisson's ratio curve of braided auxetic yarns is predicted, which lays a theoretical foundation for the development of auxetic materials and also provides more possibilities for subsequent research.

Emergent behaviour as a forming strategy in craft: The workmanship of risk applied to industrial-loom weaving

Digital tools such as computer-aided design and computer-aided manufacturing (CAD/CAM) have expanded the nature of craft practice, offering new means of design and making. However, in weaving, handmaking continues to be privileged, despite the acceptance of digital design and computer-controlled lifting mechanisms. Through experimental design research methods, self-forming three-dimensional textiles were designed in CAD software and woven on a computer-controlled jacquard power loom (a CAM tool). The textiles’ three dimensionality arises from the combination of materials (contrasting shrinking and stiff yarns), structure and finishing. They are contextualized as craft objects through Pye’s concept of ‘the workmanship of risk’. As outcomes of a craft process, they illustrate the potential of industrial looms as tools for producing complex textile systems and expressions. The results include a method for crafting at the intersection of the workmanship of risk and CAD/CAM, providing a framework for this hybrid practice. The concept of emergent behaviour is discussed as a craft strategy when the workmanship of risk is focused on material forming rather than the tool or technique. This concept is contextualized beyond weaving, suggesting its applicability to other craft fields and practices, whether produced by hand or with the use of digital tools.

Effect of Different Yarn Combinations on Auxetic Properties of Plied Yarns

Abstract This study presents the effects of a novel plied yarn structure consisting of different yarn components and yarn twist levels on the Poisson's ratio and auxetic behavior of yarns. The plied yarn structures are formed with bulky and soft yarn components (helical plied yarn [HPY], braided yarn, and monofilament latex yarn) and stiff yarn components (such as high tenacity [HT] and polyvinyl chloride [PVC]-coated polyester yarns) to achieve auxetic behavior. Experimental results showed that as the level of yarn twist increased, the Poisson's ratios and the tensile modulus values of the plied yarns decreased, but the elongation values increased. A negative Poisson's ratio (NPR) was obtained in HT–latex and PVC–latex plied yarns with a low twist level. The plied yarns formed with braid–HPY and braid–braid components gave partial NPR under tension. A similar result was achieved for yarns with HT–latex and PVC–latex components. Since partial NPR was seen in novel plied yarns with braided and HPY components, it is concluded that yarns formed with bulky–bulky yarn components could give an auxetic performance under tension.

Maximum Negative Poisson’s Ratio of Double-Core Helical Auxetic Yarns Under Uniaxial Loading: A Study on the Effect of Structural Parameters via Full Factorial Experimental Design Method

Auxetic textiles have been attracted the attention of many researchers due to their enhanced mechanical behavior during loading condition. The developed Double-core helical auxetic yarn (DC-HAY) is a structural material with negative Poisson’s ratio (NPR) behavior. It consists of two similar soft yarns with a higher diameter and a stiff yarn with a lower diameter. The stiff yarn has been twisted around the soft yarns, alternatively. In this paper, the effect of structural parameters including, the initial helical angle of wrap component with five levels, diameter ratio of components with three levels, and modulus ratio of components with two levels, on Poisson’s ratio of DC-HAY, has been investigated through the full factorial experimental design method. SPSS software has been used for analyzing the results. The results showed that the highest maximum NPR belongs to the sample with the lowest initial helical angle, highest diameter ratio of components, and highest modulus ratio of components. Also, it has been found that all the main factors have a statistically significant effect on Poisson’s ratio of DC-HAY at a 95% of confidence level.

Double-core helical auxetic yarn: a Novel structure, geometrical modeling and experimental verification

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.

A systematic study on the predictability of different methods to predict the maximum Poisson’s ratio of helical auxetic yarn

Helical auxetic yarn is a structural material with negative Poisson’s ratio which contains a soft yarn with a higher diameter as a core component and a stiff yarn with a lower diameter as wrap component that has been wrapped around the core component. In the present study, a semi-empirical model based on the improvement of a theoretical model and an artificial neural network model was developed for predicting the maximum negative Poisson’s ratio of helical auxetic yarn. In order to verify the models, an experiment according to the initial helical angle of wrap component, the diameter ratio of components, and the modulus ratio of components has been designed. To measure the Poisson’s ratio of helical auxetic yarn, an algorithm based on the image processing technique has been proposed. Unlike the results of previous studies, the experimental results showed that increasing the diameter ratio of components so much, will decrease the maximum negative Poisson’s ratio of helical auxetic yarn due to higher bending stiffness of core component. The results of the comparison between the predicted and experimental values indicated that the artificial neural network model has a lower error than the semi-empirical model. It is expected that this work provides engineering tools to predict the auxetic behavior of helical auxetic yarn based on the required precision.

Development of auxetic warp knitted fabrics based on reentrant geometry

This paper reports a novel method to fabricate auxetic warp knitted fabrics on a tricot warp knitting machine based on a special structure design and knitting process. Three auxetic warp knitted structures were successfully developed and all of them were designed to form a reentrant hexagonal geometry to acquire an auxetic effect. To provide the fabrics with reentrant frames, elastomeric yarns and stiff yarns were used to form the elastic underlaps and stiff underlaps, respectively. While the elastic underlaps can keep the reentrant structures stable, the stiff underlaps can support the reentrant structures to keep their reentrant frames. To alleviate the transfer of yarns in the loops under tension, an additional front yarn guide bar was used to feed binding yarns to basic reentrant structures. After knitting, all the fabrics were subjected to a heat setting process to keep their shape and a tensile test to assess their auxetic behavior. The experimental results showed that all the fabrics exhibited an obvious auxetic behavior within a wide range of strain. In particular, the fabrics retained auxetic behavior until breaking when stretched in the wale direction, and the Poisson’s ratio of the fabrics could be as low as –0.5. On the other hand, the fabrics exhibited a large tensile elongation when stretched in the course direction and their Poisson’s ratios changed from negative to positive after the tensile strain exceeded a certain value.

Mechanical modeling of an auxetic tubular braided structure: Experimental and numerical analyses

An auxetic braided structure was developed in our previous work for overcoming the slippage problem encountered in the double-helix yarn. However, the influences of the micro-geometric parameters on the macroscopic behavior, which are significant for the structure's design and application, have not been addressed yet. By using a standard tubular braiding technology, several samples of the auxetic braided structure were fabricated in this work and the design concept and manufacture process were described in detail. Then, systematic parameters studies were completed through experimentally validated finite element models. The study showed that the braided structure could achieve a robust auxetic behavior and its Poisson's ratio and stiffness were strongly dependent on their initial micro-geometric parameters, especially initial braiding angle and diameter of component yarns. A maximum negative Poisson's ratio of -9.49 could be achieved by lowering the angle value to 15°. Higher negative Poisson's ratio effect could be obtained with grosser stiff yarn and finer elastic yarns. However, the existence of the elastic wraps would diminish the auxeticity of the braided structure, which should be taken into consideration in design and application.

Auxetic Yarn Made with Circular Braiding Technology

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 large‐scale manufacture for practical application.

Finite element simulation of an auxetic plied yarn structure

Auxetic plied yarn is a novel type of yarn structure formed with two types of component yarns with different moduli. Although the effect of structural parameters on its negative Poisson's ratio behavior has been investigated by both experimental and geometrical analyses, the influence of material properties, including yarn tensile modulus and friction, has not been studied yet. In this work, these two factors are further investigated via finite element simulation. The finite element model is first created by using the commercial software ANSYS 15.0. Then, the simulation results are compared with the experimental and analytical data. Finally, the effects of the tilt angle of stiff yarn, yarn friction and tensile modulus are discussed. It is expected that the outcomes of this work would be useful to guide the design and fabrication of this type of auxetic yarn structure.

A Novel Interlaced-helical Wrapping Yarn with Negative Poisson’s Ratio

The two-component complex yarn with helical wrapping structure has been reported with auxetic behavior and unique performance, however, the residual torque could lead to the slippage of the wrap component from the core in the natural state and poor stability and applicability. Therefore, this paper aims to introduce a novel interlaced-helical wrapping yarn with negative Poisson’s ratio, stable structure, practicability and continuous preparation. The differences in geometry and auxetic behavior between helical structure and interlaced-helical structure were presented and analyzed. Both the structure stability and auxetic effect of the interlaced-helical complex yarn have advantages over the helical wrap yarn with same materials and initial wrap angle. It can be shown that the interlaced-helical wrap yarns with lower initial wrap angle and bigger tensile modulus of the stiff yarns will produce better auxetic effect. Besides, the deformation mechanism and the manufacturing process were described in detail. Several kinds of yarns have been fabricated to discuss the effect of initial wrap angle and tensile modulus on the Poisson’s ratio of the structure. The maximum value of Poisson’s ratio for the yarns manufactured was -2.8. It is also expected that auxetic yarns with novel braided structure can prompt the applications of auxetic textiles.

A theoretical analysis of deformation behavior of auxetic plied yarn structure

This paper presents a theoretical analysis of the auxetic plied yarn (APY) structure formed with two types of single yarns having different diameter and modulus. A model which can be used to predict its deformation behavior under axial extension is developed based on the theoretical analysis. The developed model is first compared with the experimental data obtained in the previous study, and then used to predict the effects of different structural and material parameters on the auxetic behavior of the APY. The calculation results show that the developed model can correctly predict the variation trend of the auxetic behavior of the APY, which first increases and then decrease with the increase of the axial strain. The calculation results also indicate that the auxetic behavior of the APY simultaneously depends on the diameter ratio of the soft yarn and stiff yarn as well as the ratio between the pitch length and stiff yarn diameter. The study provides a way to design and fabricate APYs with the same auxetic behavior by using different soft and stiff yarns as long as these two ratios are kept unchanged.

Woven Fabrics Made of Auxetic Plied Yarns.

Auxetic plied yarns are specially constructed with two types of single yarns of different sizes and moduli. This paper investigates how to use these types of yarns to produce woven fabrics with auxetic effects. Four-ply auxetic yarns were first incorporated into a series of woven fabrics with different design parameters to study their auxetic behavior and percent open area during extension. Effects of auxetic plied yarn arrangement, single component yarn properties, weft yarn type, and weave structure were then evaluated. Additional double helical yarn (DHY) and 6-ply auxetic yarn woven fabrics were also made for comparison. The results show that the alternative arrangement of S- and Z-twisted 4-ply auxetic yarns in a woven fabric can generate a higher negative Poisson’s ratio (NPR) of the fabric. While the higher single stiff yarn modulus of auxetic yarn can result in greater NPR behavior, finer soft auxetic yarn does not necessarily generate such an effect. Weft yarns with low modulus and short float over the 4-ply auxetic yarns in fabric structure are favorable for producing high NPR behavior. The weft cover factor greatly affects the variation of the percent open area of the 4-ply auxetic yarn fabrics during extension. When different kinds of helical auxetic yarns (HAYs) are made into fabrics, the fabric made of DHY does not have the highest NPR effect but it has the highest percent open area, which increases with increasing tensile strain.

Auxetics and Other Systems of Anomalous Characteristics

Auxetics and Other Systems of Anomalous Characteristics

Tensile and Deformation Behavior of Auxetic Plied Yarns

This paper presents an experimental study of tensile and deformation behavior of an auxetic plied yarn structure. The basic configuration of the plied structure formed with two soft yarns and two stiff yarns was firstly introduced. Based on this 4‐ply helix structure, six kinds of yarn samples were made by different combinations of soft yarns, stiff yarns and twist levels. These yarn samples were first tested and the effects of different design parameters were analyzed. Apart from the tensile test, changes in the internal structure of two samples upon stretching were also studied through microscopic examination. Finally, double helix yarn and 6‐ply auxetic yarn were made for a comparative purpose to investigate the effect of helical structure. The study shows that all of the 4‐ply auxetic yarn samples exhibit negative Poisson's ratio (NPR) throughout the entire tensile process, and the magnitude of NPR gets larger with a smaller soft yarn diameter, a higher tensile modulus of stiff yarn and a lower twist level. The study also shows that auxetic behavior inside the 4‐ply structure is generated by the interplay between the soft yarns and stiff yarns and 4‐ply auxetic yarns have the advantages to produce immediate auxetic effect upon stretching.

A novel plied yarn structure with negative Poisson’s ratio

This article presents an experimental and geometrical study of a novel kind of plied yarn structure with negative Poisson’s ratio (NPR). The deformation mechanism of the yarn structure formed with two stiff yarns and two soft yarns to achieve NPR behavior was firstly introduced. Based on the proposed yarn structure, four kinds of yarn samples were then fabricated with two kinds of stiff yarns and two types of soft yarns and tested under the axial extension to verify their auxetic or NPR effect. A geometric analysis was finally conducted to theoretically calculate the Poisson’s ratio of the yarn structure and compared with the experimental results. The study shows that the proposed yarn structure has obvious NPR effect and the geometrical analysis can well predict its Poisson’s ratio in the higher axial strain range. It is expected that this study could promote further development of auxetic textiles with unusual behavior.

Auxetic Materials and Related Systems

to mechanical metamaterials and related systems with particular emphasis on auxetic systems. Such materials show counter-intuitive, negative behaviours. For example, auxetic materials exhibit negative Poisson’s ratios which mean that these systems get fatter rather than thinner when stretched. Due to the superior properties exhibited by these systems, their study and characterisation has experienced a signifi cant increase, particularly in the last decade, something which may be perceived from the always increasing number of publications and patents in these areas. In fact, this issue is the seventh in a series of special issues published in physica status solidi (b) dedicated to auxetic materials and related systems (see [1–6]).