负泊松比经编间隔织物的准静态拉伸性能

为探究织物受单向拉伸时的能量吸收性能与负泊松比之间的关系,测算和表征了基于旋转六边形结构设计和制备的4 种经编间隔织物的负泊松比,并分别对其进行经向和纬向的单向拉伸,通过应力与应变曲线积分换算得到各织物受单向拉伸时吸收的能量。结果发现：织物单向拉伸时的能量吸收性能由结构变形容量和纱线承载容量决定,其中纱线承载容量起主要作用,结构变形容量的影响较小,负泊松比的影响则包括在结构变形容量内;在纱线承载容量相同的情况下,织物受某一单向拉伸时的负泊松比越好,该方向上的能量吸收性能越好。     

Analysis of warp-knitted fabric structure. Part II: theoretical study on initial modulus of warp-knitted fabrics (tricot,locknit, and satin)

In the first part of this series, a 3D straight line model was presented for the geometry of two-guide-bar warp-knitted fabrics. In this part, first, the variation of unit cell geometry under uniaxial tension in the range of elastic deformation is investigated. In the present study, the energy method and Castiglianos's theorem were used to derive the fabric's initial modulus. Energy terms which are considered in this study are extension, bending, and compression energies. Also, the friction phenomenon is taken into account by using frictional energy term. For this purpose, the loop of each bar is divided into eight elements. Free-body diagrams of elements are drawn to show the relative magnitude and direction of all forces acting upon an object in a given situation. After obtaining the force details, strain energy of each element is calculated. Finally, the initial modulus of warp-knitted fabrics is obtained. To verify the model, samples of tricot fabrics were produced and tested. Results showed that the generated model can predict precisely the initial modulus of aforementioned warp-knitted structures.     

Analysis of warp-knitted fabric structure part IV: modeling the initial Poisson’s ratio in elastic deformation region

The effect of Poisson’s ratio on the mechanical properties of fabrics is undeniable. In the present study, a geometrical model for the Poisson’s ratio of two-guide-bar warp-knitted fabrics is developed, based on the presented models in the previous parts of this series. For this purpose, warp-knitted fabrics are categorized into two groups, according to their structures. Thereafter, a geometrical model is presented to predict the Poisson’s ratio of each group. To verify the generated models, theoretical results are compared with the available experimental data. The results show that the generated models are a suitable guidance to consider the Poisson’s ratio of warp-knitted fabrics.     

Model modification and prediction of mechanical behaviour of fabrics in uniaxial tension

The objective of this study is to predict the mechanical behaviour of fabrics in uniaxial tensile using only their technical parameters. To achieve this objective, it was necessary, in first stage, to develop a model which can simulate this fabric mechanical behaviour. A modified form of a rheological model is used to describe the mechanical behaviour of fabrics in uniaxial tension. The proposed analytical model can fairly well replicate the behaviour of fabrics during relaxation and simple traction. In order to characterise the coefficients of this model, simple uniaxial tension and relaxation tests were performed for 29 fabrics in the warp and the weft directions. A retro‐propagation algorithm is applied in training the artificial neuronal network, which performs a functional mapping between these mechanical coefficients and the technical parameters of fabric. This allowed us to predict the mechanical behaviour in tension and relaxation of fabrics starting only from their technical parameters.     

A relationship between dry-relaxed warp-knitted fabric structure and curling distance

This study provides us information about relationship between curling and knitted structure and density of two-guide bar warp-knitted fabrics. Five standard warp-knitted fabrics are produced with three densities (Tricot, Locknit, three-needle Satin, Reveres Locknit and three-needle Sharkskin). Certain cut lengths of sample fabrics in both wale and course direction are analyzed through image processing to define curling value. A mechanical model, a function of fabric structure and yarn parameters, is also suggested to predict the curling force. The results of experimental and theoretical results show a greater curling value for course-wise cut in comparison to that of wale-wise in all warp-knitted structures and densities. The lowest curling value is found for three-needle Sharkskin structure in both directions and all densities.     

经编组织的三维仿真与动态实现

为了对经编针织物的结构特征和外观效果进行预测,通过分析普通经编针织物的线圈结构,对O Goktepe的三维实体纱线模型进行了改进,得出线圈三维结构尺寸。利用非均匀有理B样条（NURBS）曲线和曲面原理,建立经编组织成圈线圈和衬纬线圈的三维实体模型;运用这些三维线圈模型,结合经编组织的垫纱数码,实现各种形态线圈的自由连接;最后运用Visual C++和Open GL开发工具,将织物的光照和材质因素引入织物三维结构模型中,成功实现对单梳和双梳经编组织的三维模拟。     

经编组织三维仿真中的线圈偏移

 为了采用计算机技术更真实地模拟经编组织中线圈的形态结构,通过观察各种经编针织物的线圈结构,分析由纱线张力所引起的线圈偏移规律,得出了线圈偏移理论和计算公式。该理论假设同一枚针上的线圈偏移量是该针上所有线圈偏移量的累加值。结合此偏移理论,在已建立的经编线圈三维模型的基础上,修正了定义线圈三维结构的部分控制点坐标。最后结合Visual C+ +. NET编程语言和OpenGL工具,成功实现了各类单针床经编针织物的计算机三维仿真。仿真图片与真实织物对比,在形态结构上具有较高的相似度。     

Application of warp-knitted spacer fabrics in car seats

Polyurethane foam is commonly used as padding in car seats despite some problems concerning comfort and recycling. Compared with polyurethane foam, textile seat padding is easier to recycle; so textile padding is a good candidate to substitute foam padding as regulations on recycling have become more stringent on car manufacturers. With the available textile option, warp-knitted spacer fabrics are likely a good substitute for polyurethane foam as padding in car seats. Warp-knitted spacer fabric structures can be designed to be quite flexible in a variety of thicknesses. Warp-knitted spacer fabrics can be very resilient and may display good breathing properties. The current work presents a study on the application of warp-knitted spacer fabrics as cushion in car seats. The results show that, relatively to polyurethane foam, warp-knitted spacer fabrics demonstrate better recovery to compression, thermal properties and breathability. Furthermore, warp-knitted spacer fabrics retain their original thickness for longer time and can be easily recycled.     

Experimental and computational analysis of acoustic characteristics of warp-knitted spacer fabrics

Abstract

As a kind of porous medium, textiles have recently received increased attention for acoustic applications due to their high profitability and low cost and environmental impact. 3D knitted spacer fabrics stand out as a unique class of textile materials. These materials simultaneously are soft, voluminous and highly porous and therefore are expected to be suitable for sound absorbing applications. This article aims to investigate the acoustic performance of 3D warp-knitted spacer fabrics. To this end, acoustic behavior of warp-knitted spacer fabrics was experimentally measured using the impedance tube method. In order to predict the sound absorption behavior of fabrics, a simple geometrical model was created. Flow resistivity was calculated by numerically solving incompressible laminar Newtonian flow through the 3D pore space of generated structure. The frequency-dependent sound absorption coefficient of the warp-knitted spacer fabric was predicted using the empirical models of Delany and Bazley, Garai and Pompoli and Dunn and Davern. The results showed that the Dunn and Davern model can predict sound absorption characteristics of warp-knitted spacer fabrics in the mid-to high-frequency ranges. At low frequency ranges; however, none of the empirical models can reasonably predict sound absorption behavior of the fabrics.     

经编导电织物弹性对传感性能的影响

为探讨经编导电织物弹性与传感性能的关系,将镀银基锦纶纱线作为导电纱线分别与氨纶包覆纱线和氨纶裸丝在特里科经编机上交织,制备了具有不同弹性的3种经编导电织物。测试了3种织物在一定拉伸范围内的应力大小与电阻变化,并根据实验数据计算出弹性性能和静态评价指标,得出弹性与传感性能的关系。结果表明:弹性导电织物的电阻随应变呈线性变化,原料越粗则电阻变化的速度越快;弹性模量随着织物弹力的增大而减小,弹性伸长与织物弹力的大小成正相关;在中小应变范围内,弹性模量越低、弹性伸长越大的导电织物传感性能越优。     

负泊松比经编间隔织物的抗低速冲击性能

为研发具有不同负泊松比效应的经编间隔织物,对5 种负泊松比经编间隔织物试样进行落锤冲击实验,通过冲击载荷与时间和位移的关系曲线分析5 种织物在低速冲击载荷下的形态变化和能量吸收性能,研究负泊松比织物在低速冲击下的能量吸收性能与负泊松比值及初始冲击能量的关系。结果表明：织物的能量吸收性能随织物负泊松比值的增大而提高,织物的能量吸收性能越好,耐冲击性能也越好;初始冲击能量的大小也会影响织物的能量吸收速率和耐冲击性能,初始冲击能量越高,织物的耐冲击持久性越差,但对织物总的能量吸收影响不大。     

Deformation characteristics of flexible PU-coated multi-axial warp knitted fabrics under uniaxial tensile

Based on the characteristics of high tenacity, low density, flexible design, the coated fabric has emerged as a promising construct for tensile test. Here, it reports the deformation mechanism of a PU-coated multi-axial warp-knitted fabric under uniaxial tensile via a digital image correlation system. Specimens produced by us are chase in three fibre-reinforced directions namely 0°, 45° and 90°, respectively. The result shows that the crease does not have an effect on the deformations in the small deformation range (strain < 5%), and the deformation was evidently occurred near the fixed end lags because of the faster movement of specimen at the loading end, and the transverse shrinking at the edges is faster than that in the middle of the specimen. In the large deformation range, the strain fields are inconsistent at the same displacement revealing that the deformations of this kind of flexible coated fabric is in-homogeneous under tensile.     

Design and manufacturing of warp-knitted filterable fabric with PET/PVDF fiber

In this paper, the filtering effect on fine particle of warp-knitted mesh fabrics was investigated. Polyester yarn (PET) and polyvinylidene fluoride (PVDF) fiber were used as materials to knit the fabrics with five different structures on KS4 tricot warp-knitted machine. After knitting, the fabrics were treated with tourmaline liquid with five different concentrations of tourmaline. Then, the filtration efficiency of samples was tested by the comprehensive test machine. By comparing the filtration efficiency of samples with different concentrations of tourmaline and different structures, the optimal process parameters were obtained that the concentration of tourmaline liquid was 30% and the structure of fabric was one by two insertion. The experimental data of the comprehensive test also revealed that the application of the PVDF and tourmaline did have effects on the promotion of the filtration performance of the warp-knitted fabrics.     

经编间隔织物的应用及其发展

介绍经编间隔织物的特性,指出经编间隔织物在座椅包覆、鞋材、箱包和床垫等方面的常规应用及其优势,并根据当前经编间隔织物结构和原材料的发展,详述经编间隔织物在时装面料、成型鞋材、卫浴产品、建筑增强材料、农业无土栽培和包装材料等方面的新应用,得出经编间隔织物的三个未来发展方向——个性产品、功能产品和智能产品。     

基于均匀化理论的小变形纬编针织物线圈形态有限元分析

为解决针织物在平幅印染过程中线圈拉伸易变形的问题,以纯棉纬编针织物为研究对象,基于小参数渐近展开和多尺度均匀化方法,建立针织物宏观-细观位移变化率和应变变化率的计算模型,分析低应变状态下针织物拉伸时线圈形态变化的规律。结果表明:针织物受均匀载荷拉伸时,线圈变形具有不均匀性,变化规律与线圈的空间位置、幅宽以及导布辊间距相关,凸形导布辊可以改善线圈变形状况的差异;针织物受均匀、非均匀载荷拉伸时的线圈形态变化量计算值与实测值趋势一致,最大偏差为9.6%。均匀化理论与有限元技术结合可以用于进一步分析多成分、多规格针织物的宏观-细观变形规律,为针织物平幅印染设备的张力控制、导布辊布局设计、变直径(凹凸辊)导布辊辊形开发提供理论参考。     

基于数字图像相关法的针织物泊松比测定

为解决针织物因其各向异性,传统泊松比测定方法不适用的问题,结合数字图像相关法对针织物进行单轴拉伸测试,提出了一种以纬平针织物试样整体作为研究对象且在其较大形变下测试其泊松比的方法。实验选取3种纬平针织物,首先录制试样单轴拉伸的整个过程,导出每1帧图像,将图像转化为灰度图后,在MatLab软件中用数字图像相关法进行位移分析,用SPSS软件对载荷方向拉伸的计算值与实际拉伸值进行t检验,验证了可行性,计算所得泊松比在正常取值范围内,避免了织物颈缩问题,且每秒可提取30帧图片进行位移分析,提高了精度,为研究针织物的泊松比提供新思路。     

Theoretical and experimental investigation of tensile properties of net warp-knitted spacer fabrics

Abstract

This work aimed to investigate the tensile behavior of net warp-knitted spacer fabrics using the experimental and theoretical approaches. Tensile behavior of the warp-knitted spacer fabrics is one of the fundamental parameters which rarely considered in the literature. Therefore, the net spacer fabrics were made with three different variables (fabric thickness, size of meshes, and the position of meshes of the outer layer with respect to each other) in order to study the effects of structural parameters on the tensile behavior. A 2D net-fabric which used for the outer fabrics was made for in-depth considerations and also the comparison between the 2D fabrics and spacer fabrics. The initial linear elastic modulus of the 2D fabrics and the initial linear elastic modulus of the spacer fabrics were selected for the assessment of the tensile characteristics. First, a mechanical model was developed based on the geometrical structures and material properties of the 2D fabrics using energy method and Castigliano’s theorem. Then, the effects of spacer yarns on the tensile behavior of spacer fabrics were taken into account. The latter model was proposed using the bending theory of a curved bar. Experimental data were compared with the values obtained from the theoretical approaches and the end results showed that the developed models can predict the modulus reasonably. Moreover, the results indicated that the tensile behavior of the spacer fabrics are independent of the position of the holes in the outer layer whilst the fabric thickness and size of meshes affect the tensile modulus.     

短纤纱经编产品开发与应用

短纤纱经编产品的开发是经编产品创新研究的重点之一,近年来在我国发展较快。本文叙述了近年来我国短纤纱经编产品的开发现状;研究了经编用短纤纱成纱质量要求,包括纱线断裂强度、表面毛羽和延伸性能等,并进一步从原料、整经和织造3个方面分析了短纤纱经编产品生产技术中的问题和解决方法;重点以棉纱在经编产品开发中的应用为例,分析了短纤纱经编产品的应用现状;结合我国经编行业当前面临的形势及迫切需求,展望了短纤纱经编产品逐渐向多样化、高档化和功能化的发展趋势。     

Characterization of shear behavior of warp-knitted fabrics applied to composite reinforcement

Different types of textile fabrics are now widely used for reinforcing composite structural parts. In this work, three types of weft-inserted warp-knitted fabrics differing in stitch pattern and composed of glass roving were produced. The shear behavior of the developed fabrics was determined according to stitch type. Three basic stitch types were chosen: tricot, cord, and pillar. The shear behavior was examined by the picture frame test method. It was observed that the stitch type significantly affects the shear behavior of the fabrics. The deformation phases during the fabric shear test were analyzed. To estimate the changes in the shear stiffness of the fabrics, shear moduli were calculated as a function of the shear angle. In general, the fabric with the tricot stitch has the greatest shear resistance than that of fabrics with the cord and pillar stitches. The results of the characterization of shear behavior of the warp-knitted fabrics are presented and discussed.     

The influence of two bar warp-knitted structure on the fabric tensile stress relaxation Part I: (reverse locknit,sharkskin, queens’ cord)

Time-dependent mechanical behavior of textiles has particular importance. One of such behaviors is the stress relaxation. If a fabric is under tension over a period of time, some of the stresses in it will be relieved. During the manufacture and application of clothing and footwear, materials experience various long-lasting deformations, and relaxation process in materials arises. For example, if medical pressure garments such as compression stockings are under tension over a long period of time, some of their stresses will be relieved, with a consequent reduction in the skin and garment interfacial pressure. Thus, with theoretical and experimental study of the factors affecting stress relaxation, the ability to design and produce appropriate clothes will be increased. The aim of this study was to investigate the effect of fabric structure on the stress relaxation of two bar warp-knitted fabrics (reverse locknit, sharkskin, queens’ cord), as well as to find the effect of strain value and loading direction on the stress relaxation of the fabrics. The results reveal that the fabric structure, strain, and loading direction are important factors affecting the stress and stress relaxation percent of the fabrics. By increasing the strain and the length of underlap in the back guide bar, stress will be increased, but stress relaxation percent will be decreased. Also, stress relaxation percent in wale direction is more than course direction for reverse locknit and sharkskin3, but this is reversed for sharkskin4 and queens’ cord. Finally, among the mechanical models used to describe the stress relaxation behavior of the fabrics, three-component Maxwell’s model with parallel-connect nonlinear spring showed the best agreement with the experimental relaxation curve of the analyzed fabrics.