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Auxetic woven fabrics made with special geometrical structures have gained the interest of textile scientists in recent years. This paper reports a study on auxetic woven fabric based on a double-directional parallel in-phase zig-zag foldable geometrical structure. Such a fabric has been already produced and investigated for its negative Poisson's ratio effect in two principal directions (weft and warp directions). However, its negative Poisson's ratio effect in biased tensile directions as well as under repeated tensile loading conditions has not been studied yet. Therefore, in this paper, these two limitations are addressed. The auxetic woven fabric was firstly fabricated, and then subjected not only to tensile tests in different tensile directions, including two principle directions and three biased directions, but also to repeated tensile loading. It was found that both the negative Poisson's ratio effect and the resistance to tensile deformation are dependent upon the tensile direction, and the highest negative Poisson's ratio effect and higher resistance to tensile deformation are obtained in two principal directions.

This paper presents a study of using weft-knitting technology to fabricate negative Poisson’s ratio (NPR) knitted fabrics, which exhibit the unusual property of becoming wider when stretched. Based on a geometrical analysis of a three-dimensional NPR structure constructed with parallelogram planes of the same shape and size, a new kind of NPR weft-knitted fabric was firstly designed and fabricated on a computerized flat-knitting machine. Then the NPR values of these fabrics were evaluated and compared with those from the theoretical calculations. The results show that all knitted fabrics have the NPR effect, which decreases with increased strain in the course direction. This variation trend is consistent with the theoretical prediction. The results also show that the main structure parameter affecting the NPR effect of a fabric is the opening angle at its initial state. Fabric with a smaller opening angle will have higher NPR values. This paper demonstrates the feasibility of fabricating NPR-knitted fabrics by using weft-knitting technology if a suitable structure and parameters are selected.

The metamaterials with negative Poisson’s ratio are called auxetic materials, which as a branch of metamaterials has drawn a lot of attention in many areas. Existing auxetic knitting textiles combine flexibility and auxeticity, however the loose structure has been a main disadvantage for its application. In this study, we fabricated Miura origami structure fabrics by weaving technology in order to acquire more stable auxetic textiles. The results show that using the combination of fabric structure type and elastic yarns, an origami structure can be realized in a jacquard loom. In the Miura origami structure, the crease pattern can be separated into three parts, unfolding areas, convex areas, and concave areas. One warp system and two weft systems are compounded together, in which a weft backed weave is used to get elastic floats in the convex and concave areas, and to make the fabrics bend to the concave side. The physical map showed that the fabrics had a clear Miura origami structure and the unfolding areas were flat and even. On the basis of the designed geometric pattern, weft backed weaves can be used to construct different folded areas, spandex wrapped PET (Polyester) and inelastic PET are selected as two weft systems for weaving. Meanwhile, the Miura origami fabrics exhibit distinct in-plane negative Poisson’s ratio and out-of-plane positive Poisson’s ratio. Apart from the Miura origami structure, other origami and paper-cut structures can be realized using this method, and these special auxetic textiles have potential in protective cloths, ornamented textiles, wearable devices, and flexible sensors.

This paper reports a geometrical analysis of auxetic woven fabrics based on foldable geometry. Two fabrics having different geometrical parameters were first designed and fabricated and then subjected to tensile tests in two principal directions. Based on the experimental observations of the geometry of one fabric structural unit cell at different tensile strains, a geometrical model was first proposed and a relationship between the Poisson’s ratio and tensile strain was then established for each principal direction. Two semi-empirical equations are subsequently obtained for both principal directions by fitting the established relationships with experimental results. After validation by the experimental results of the other fabric, the obtained semi-empirical equations were finally used to predict the auxetic behavior of the fabric with a given geometrical parameter. The calculated and experimental results are found to be in excellent agreement with each other. Therefore, the semi-empirical equations obtained in this study could be useful in the design and prediction of the auxetic behavior of auxetic woven fabrics made with the same type of materials and foldable geometry but with different values of geometrical parameters.

This paper focuses on systematically analyzing the influence of macro fabric structure and yarn architecture on the mechanical and auxetic performance of parametric auxetic fabrics. Re-entrant hexagonal (REH) and helical auxetic yarn (HAY) were adopted as a macro fabric structure and weft yarn to produce three kinds of auxetic fabrics: REH fabric with HAY as weft yarn (REH-HAY); REH fabric with elastic yarn as weft yarn (REH-1, REH-2, REH-3); and plain fabric with HAY as weft yarn (NREH-HAY). By controlling the existence of the HAY and REH structure, the influence of the REH structure and HAY on the mechanical and auxetic properties was thoroughly analyzed. It is demonstrated that both the REH macrostructure and HAY micro configuration can contribute to the performance of the auxetic fabric. Specifically, in the presence of the REH structure and HAY, the auxeticity was found to a 77% increase compared with NREH-HAY and the breaking strain and load rises by about 37.50% and 90.42%, respectively. Notably, the variation of the polyurethane (PU) weft yarn per unit length influenced the tensile and auxetic performance to a lesser extent, while by changing PU to HAY, a significant increase of negative Poisson’s ratio value from –1.155 to –1.492 was noticed without greatly jeopardizing the stretchability. Furthermore, the cyclic tensile results demonstrate the stability and elasticity of the fabric. The comparative analysis can give guidance to optimize fabric design and inspire the innovative design of the auxetic textiles, all of which will pave the way for a quantitative and optimizing design for auxetic textiles.

In our previous study, a novel class of auxetic warp knitted fabrics were developed and their auxetic behaviors were studied under a single tensile test. However, during daily use, the fabrics are usually subjected to repeating tension rather than single tension. Therefore, the durability of the fabrics’ auxetic performance is of great importance. So far, the auxetic behavior of fabrics under repeating tension has not systematically been investigated. In this paper, we report a study on the auxetic behavior of warp knitted fabrics under repeating tension. All the fabric samples were subjected to a repeating tensile test within a tensile strain of 25% until 100 tensile cycles. The results show that the fabrics can keep their auxetic effect in both course and wale testing directions after 100 tensile cycles, and the auxetic effect in the wale direction is retained longer under higher tensile strains than that under lower tensile strains with the increase of tensile cycles. The results also indicate that auxetic stability in the course direction is much better than that in the wale direction. We hope that this study can offer useful information to improve the auxetic stability of auxetic fabrics for practical use.

Auxetic woven fabrics made of non-auxetic yarns have gained the interest of textile scientists in recent times. Such fabrics have already been produced and investigated for their negative Poisson's ratio (NPR) effect in two principle directions. However, the NPR effect of these fabrics in different biased tensile directions has not been studied. In particular, the influence of repeated tensile loading on the NPR effect retention ability of fabric has not been explored yet. Therefore, this paper aims to report the NPR effect of auxetic woven fabric in different tensile directions and the influence of repeating tensile cycle tests on its NPR effect retention ability. The auxetic woven fabric is firstly fabricated based on a re-entrant hexagonal geometrical structure by using elastic and non-elastic yarns, and then subjected to single and repeating tensile tests in five different tensile directions, which include two principle directions and three biased directions. It is found that the NPR effect is largely dependent upon the tensile direction and the number of repeating tensile cycles.

Auxetic warp-knitted spacer fabrics have gained increasing interest due to their excellent properties, such as shear resistance, indentation resistance, synclastic curvature and so on. Soft composites made from auxetic warp-knitted spacer fabrics and A/B two-component silicone rubbers were studied in this paper. The stabbing resistance of composites made by different auxetic fabrics (Fabrics 1–4#) and at different filling rates (0%, 20%, 40%, 70%, 100%), respectively, were tested using a universal Material Testing System. The results show that the peak load, energy absorption and deformation displacement of the composites increase with an increase of auxetic performance and filling rate. In addition, a better auxetic effect and larger filling rate can result in less damage. The composites with a higher filling rate are more like an elastomer. The auxetic effect also has an important role in stabbing resistance, which is due to fabrics with a larger negative Poisson's ratio value having a denser face layer structure and more deformable units, which can lead to better stabbing resistance for the composites.

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.

This paper reports a study on the geometrical analysis of bi-stretch auxetic woven fabric based on a re-entrant hexagonal geometry. The fabric was first designed and fabricated. Then, the fabric was subjected to tensile tests, and changes in the geometry of the fabric structural unit cell at different tensile strains were observed when stretched either in the warp or weft direction. Based on the observations, a geometrical model was proposed for each stretch direction and used to establish the relationship between Poisson’s ratio and tensile strain. The semi-empirical equations for both stretch directions were finally obtained by fitting geometrical parameters with experimental results. It is expected that the semi-empirical equations obtained in this study could be used in the design and prediction of the auxetic behavior of bi-stretch auxetic woven fabrics made with the same type of materials and geometry, but with different values of geometrical parameters.

Currently, auxetic yarns consisting of a core filament and a wrap filament are generally utilized as complex materials, which are attributed to residual torque. Thus, the main content dealt with in this paper was to analyze the structure formation and effect of heat treatment of helical auxetic complex yarn spun by a modified ring-spinning system. Firstly, an orthogonal experiment with three factors and three levels was carried out to study the effects of diameter ratio, yarn twists and initial helical angle on the structure and Poisson’s ratio of complex yarn. Secondly, a heat treatment process with polyamide filament with low melting point (80℃) was conducted to improve the structural stability of auxetic complex yarn. It was found that the heat treatment process can not only improve the structural stability of complex yarn, but also promote the expansion effect. By comparing experimental and theoretical results, it was found that the variation of Poisson’s ratio with axial strain had good consistency. Therefore, the heat treatment method can effectively solve the slippage problem of helical auxetic complex yarn.

This paper presents five different auxetic warp-knitted spacer fabrics and discusses their energy absorption under uniaxial tension through integrals of stress on strain. Structures of auxetic fabrics are designed based on rotating hexagonal models and knitted for experimental tests, including Poisson's ratio tests and tensile tests. Results show that energy absorption of auxetic warp-knitted spacer fabric is mainly determined by its structural deformation capacity and yarn loading capacity, between which the yarn loading capacity of fabrics plays the dominant part in energy absorption, while the structural deformation capacity, which is affected by Poisson's ratio, has relatively little influence. With equivalent yarn loading capacity, the energy absorption of fabrics with negative Poisson's ratios are relatively better.

Textile structures with negative Poisson’s ratio (PR) behavior are called auxetic textile structures. They have received increasing attention in recent years and have been designed and fabricated through spinning, knitting, weaving and non-woven methods. However, auxetic textile structures fabricated using braiding method have not been reported so far. This paper reported a novel type of auxetic braided structure based on a helical structural arrangement. The geometry of the structure and its deformation mechanism were first introduced and described. Then a special manufacturing process was developed by the modification of commonly used tubular braiding technology. Various auxetic braids were fabricated with different structural parameters and yarns and tested under uniaxial extension conditions. The results showed that all manufactured braids exhibited high negative PR behavior and maintained this behavior until the fracture of the component wrap yarn. Among three structural parameters discussed, namely wrap angle, braiding angle and braiding yarn diameter, the wrap angle had more effects on the tensile properties of auxetic braided structure than the other two parameters. The success of fabricating auxetic braids with commercially available yarns in this study provides an alternative way to manufacture auxetics from positive PR materials.

This paper introduces a novel extrusion process for manufacturing helical auxetic yarn (HAY). A range of semi-coextruded HAYs have been manufactured in a cost-effective, consistent and readily usable form. The semi-coextruded HAYs were compared to the conventional spun yarns in terms of tensile properties and auxetic behavior. The results show the presence of the auxetic effect in newly fabricated semi-coextruded HAYs. Similar to the traditional spun HAYs, the new HAYs are sensitive to parameters such as the initial wrap angle, the core/wrap diameter ratio and component moduli. Importantly, a few new manufacturing parameters have been identified for tailoring the auxetic behavior of the semi-coextruded HAYs. The semi-coextruded HAYs are auxetic when an instantaneous true Poisson’s ratio analysis method is applied. The semi-coextruded HAYs give a larger maximum negative Poisson’s ratio than the conventional HAYs due to the advantages of the pre-formed helical wrap structure.

Fabrics with zero or negative Poisson’s ratio are referred as auxetic fabrics, which have the unusual property of lateral expansion or zero expansion upon stretch. The use of conventional materials and machinery to produce auxetic fabrics has gained the interest of researchers in recent years. However, this approach is limited to knitted fabrics only. The development of auxetic fabric using conventional yarns and weaving technology is a research area that is still unaddressed. This paper reports a study on the development of a novel class of stretchable auxetic woven fabrics by using conventional yarns and weaving machinery. The phenomenon of differential shrinkage was successfully employed to realize auxetic geometries capable of inducing auxetic behavior in woven fabrics, and a series of auxetic woven fabrics were fabricated with elastic and non-elastic yarns and a dobby machine. The uni-axial tensile tests showed that auxetic woven fabrics developed exhibited zero or negative Poisson’s ratio over a wide range of longitudinal strain.

In this paper, the design, manufacturing and characterization of two-dimensional warp-knitted textiles with auxetic performance is reported. Four warp-knitted structures based on a rotational hexagonal structure are produced, and these structures can lead to a negative Poisson’s ratio mathematically. The testing results have confirmed that the knitting structure of the front bar, as well as let-off values of the front bar’s chain parts, has a great effect, and auxetic properties of the warp-knitted textiles have a complicated relationship with the rotation angle. These novel structures can expand the applied area of auxetic structures.

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.

This paper reports the tensile deformation behavior of an auxetic warp-knitted spacer fabric structure by using the finite element (FE) method. The precise geometry of the outer layer structure of the fabric was firstly obtained from a micro X-ray computerized tomography scan and then inputted to an ANSYS 13.0 software to generate geometrical models. The geometrical models were then meshed using the PLANE 183 element to build FE models. Based on the FE models built, deformation behaviors of the auxetic fabric in the course direction and wale direction were simulated and compared with experimental results. The FE analysis showed that the simulated fabric deformations at different tensile strains were very close to the real fabric deformations and the FE-generated Poisson’s ratio-strain curves agreed well with the experimental ones. Therefore, the FE models could be used for predicting the deformation behaviors of the auxetic warp-knitted spacer fabric stretched in different fabric plane directions.

Auxetic materials are a kind of non-conventional materials having negative Poisson’s ratio. They laterally expand when stretched or laterally shrink when compressed. Compared to conventional materials, auxetic materials have a number of enhanced properties that could be very interesting for some special applications. This paper reviews the latest achievements in auxetic materials, including their properties, structures and applications. A special discussion on their potential applications in textiles is also made. It is expected that this review could provide some useful information for the future development of auxetic textile materials.

Auxetic spacer fabrics are a novel kind of three-dimensional (3D) fabric structure with a negative Poisson’s ratio. They have found a number of applications in functional garments, protective pads and sportive shoes due to their unusual properties. In this paper, a study on deformation behaviors of 3D spacer fabrics that could be fabricated on a large scale is reported. Through experimental observations of deformation of a basic hexagonal unit at different tensile strains, two different geometrical models are proposed for the fabric structure when extended in the course direction and wale direction, respectively. Based on the geometrical models, two semi-empirical equations between the Poisson’s ratio and tensile strain are established for both tensile directions. The study shows that the established semi-empirical equations fit well with experimental results. Therefore, they could be used in the design and prediction of 3D auxetic spacer fabrics with different values of geometrical parameters.

An auxetic material is one which exhibits a negative Poisson's ratio; it expands laterally when stretched longitudinally and contracts laterally when compressed longitudinally. The helical auxetic yarn is a novel fibre structure with a diverse range of potential applications. The unusual mechanical properties of the yarn can be determined by particular combinations of geometry and component material properties. This paper reports on the development of low-stiffness auxetic yarns and fabrics which offer a range of applications such as medical devices, particularly bandages, compression hosiery and support garments and fashion apparel. The mechanical performance of the yarns and fabrics is elucidated, with emphasis on the ability to exploit significant changes through a prescribed strain range. A yarn Poisson's ratio as low as −1.5 is demonstrated, and fabrics with in-plane and out-of-plane negative Poisson's ratios are illustrated. Stiffness is shown to be highly dependent upon yarn geometry.

Auxetic materials are referred to as those having negative Poisson’s ratio (ν). Initial work at Bolton successfully fabricated auxetic polypropylene fiber using a novel thermal melt-spinning technique. This paper reports in detail both the methods and principles involved in screening polyester powder and also the manufacturing method for successful production of auxetic polyester fibers. Videoextensometry along with micro-tensile testing were used to measure the Poisson’s ratio of the fiber. The Poisson’s ratio of the polyester fiber was found to vary between -0.65 and -0.75.