13—A STUDY OF TORSIONAL STABILITY IN PLIED YARNS

In this paper, a study is made of the self-plying mechanism, by which torsional stability is spontaneously achieved in plied yarns. It is proposed that the state of twist balance, or zero torque, is reached when the torsional energy released by the effective untwisting of the yarn during plying is equal to the yarn-bending energy used in the plying process. This hypothesis is supported by extensive experimental evidence reported in the paper. Calibration curves are presented that give the ply twist of a balanced two-, four-, or seven-ply yarn as a function of the single-yarn twist factor. These curves are characterized by the basic yarn structure (i.e., multifilament or staple-fibre), the degree of relaxation of the torsional stresses in the single yarn before plying, and the constituent fibre type (specifically, the ratio of fibre torsional to bending rigidity.)     

Studies of the hybrid effect in mechanical properties of tencel blended ring-, rotor- and air-jet spun yarns

This paper presents a study of hybrid effect on mechanical properties of tencel blended ring-, rotor- and Murata jet spinning yarns. The tensile strength, breaking elongation, flexural rigidity and abrasion resistance of tencel-polyester and tencel-cotton blended yarns are examined and compared with the value predicted using linear and quadratic rule of mixture (ROM). It is observed that there is no significant hybrid effect on abrasion resistance of tencel-polyester mix yarns and tenacity and breaking extension of tencel-cotton mix yarns; hence, a linear ROM is found better in predicting the yarn properties. Further, for all yarn types, there is a significant hybrid effect on tenacity, breaking extension and flexural rigidity of tencel-polyester mixes and flexural rigidity and abrasion resistance of tencel-cotton mixes. A quadratic ROM model suits well for these yarns. Overall, it is found that there is a negative hybrid effect on tenacity and breaking extension whereas there is a positive hybrid effect on flexural rigidity for all the yarn samples irrespective of fibre and yarn type. The abrasion resistance has a mixed trend. Further, tencel-polyester yarns yield more satisfactory results than the tencel-cotton yarns in terms of strength and breaking extension but behave poorly during abrasion test for 200 cycles. Increasing tencel content both in tencel-polyester and tencel-cotton fibre-mix produces a rigid yarn with reduced abrasion resistance.     

29—YARN-BENDING AND THE WEIGHTED-RING STIFFNESS TEST

The standard ring-loop test for yarn flexural rigidity is in error unless the yarn bends linearly. The deformation and recovery behaviour of a ring of yarn is therefore recalculated on the basis of non-linear bending behaviour, in which a coercive or frictional couple must be overcome before the yarn bends linearly. Good agreement between theory and experiment is demonstrated.     

Analysis of bending properties of worsted wool yarns and fabrics based on quasi-three-point bending

Abstract

The bending behavior of worsted wool yarns and fabrics plays a crucial role in handling and performance of end-use textiles. Hence, the fabric/yarn bending properties were studied based on a quasi-three-point bending model by means of the theoretical modeling and the corresponding measuring method. By means of the formula and the measured curves, the curve of bending rigidity and the curvature of a fabric or a yarn can be calculated so as to characterize the bending behavior more precisely than in the previous work. All the experiments on the fabric/yarn bending rigidity have been conducted for both the worsted wool fabrics and the corresponding yarns procured from the fabrics, with the same apparatus bending evaluation system of fabric and yarn, which was developed independently. The measured results of bending rigidity and curvature curve show good correlation with the bending moment and the curvature relationship of the theoretical modeling, and the comparisons of bending rigidity among KES-FB2 (Kawabata Evaluation System for Fabrics-2 pure bending tester), FAST-2 (Fabric Assurance by Simple Testing-2 bending meter), and the independently developed apparatus show that the three systems exhibist reasonably high correlations. It is confirmed that the new apparatus and the theoretical model are both viable and precious. Meanwhile, the theoretical relationship between the yarns and the fabrics has also been discussed, and the theoretical analysis of the bending behavior between the yarns and the fabrics is helpful in selecting a better theoretical model of the fabric-to-yarn bending rigidity ratio.     

Modelling crease recovery behaviour of woven fabrics

Crease recovery behaviour is an important property of fabrics for apparel applications. A theoretical model is developed in which the fabric is represented by an elastic element and a frictional element. The frictional restraint is assumed to be proportional to the square root of the curvature of the fabric during deformation. An energy method is applied to the study of crease recovery behaviour of the fabric. Equations of crease recovery work and crease recovery force as a function of curvature are derived. Two basic parameters are needed to characterise the fabric in the crease recovery model: the bending rigidity and bending hysteresis of the fabric; both are readily measured in a pure bending test. Good agreement is observed between experimental data and theoretical predictions for wool/polyester blended and worsted fabrics.     

55—SOME FACTORS AFFECTING THE HAIRINESS OF WORSTED-SPUN YARNS

Further experiments are reported on the hairiness of worsted-spun yarns, chiefly of mohair. The effect of some fibre physical properties on the hairiness of man-made-fibre blended-fibre yarns was also studied. Leading hairs are predominant among the singles yarns spun by different drafting systems, although their proportions may vary. The hairiness of yarns spun by different drafting systems is compared. The Ambler Superdraft Uniflex spinning machine produced the least hairy Courtelle acrylic-fibre yarns from the different drafting systems studied. An increase in the drafting angle and an increase in traveller weight reduced the yarn hairiness, and there appeared to be a critical value of flume-setting, above and below which yarn hairiness increased. The Uniflex spinner appeared to produce at least equally lean, if not leaner mohair yarns, both singles and two-fold, than did the flyer system.     

丽赛纤维喷气纺纱性能研究探讨

文章采用丽赛、天丝、粘胶、棉、涤棉为原料分别进行喷气纺纱，并将喷气纱线性能进行比较，研究丽赛喷气纺的纱线强力、条干、毛羽、弯曲刚度等性能。     

常用高性能纱线弯曲刚度的测量和表征

由于轴向织物增强薄壳体复合材料越来越成为研究的热点课题。衬纱是轴向织物的重要组成部分,弯曲变形是织物变形的主要形式,因此,衬纱的弯曲刚度对织物的三维成型性能有着重要影响。本文借助KES织物风格仪,通过测量最大弯矩值M_max和拟合斜率值s,表征四种常用高性能纱线的弯曲刚度。实验结果表明：在相同线密度下,高性能纱线的弯曲刚度大于传统纱线的弯曲刚度,四种高性能纱线的弯曲刚度由大到小依次是碳纱线、玻璃纱线、高强聚乙烯纱线、芳纶纱线;高性能纱线的弯曲刚度受纱线中单丝的排列、聚集状态影响,并且随着进入角度的增加而减小。     

Study of Fundamental Factors Affecting Fabric Surface Protrusion Part II: The Effect of Yarn Bending Rigidity on the Fabric Surface Protrusion

Abstract

This paper reports the results of an investigation on the effects of yarn bending rigidity on fabric surface protrusion. The bending rigidity is regarded as the multiple of the elastic modulus E, and the moment of inertia of the cross-section of the yarn (EI). The study was based on an analytical model adopted from the elastic theory. The experimental results are found to be in reasonable agreement with the theoretical values.     

Some studies on hairiness reduction of polyester ring spun yarns by using air-nozzles during winding

This paper reports on the hairiness reduction of polyester yarns at winding using air-nozzles. Three yarns of the same count were spun each from fibres of 1.0, 1.2 and 1.4 deniers respectively. Using a CFD (computational fluid dynamics) model, airflow inside the nozzles is simulated to explain the role of nozzle parameters viz., axial angle of air inlets and yarn channel diameter on yarn hairiness reduction during winding. Air drag forces acting on hairs are calculated. Transverse drag forces acting on hairs play a major role in bending the hairs. Vortex nature of air and air velocity profile inside the nozzle are the important phenomena in reducing yarn hairiness. Box and Behnken factorial design of experiments is used to optimize nozzles parameters, fibre denier, and air pressure to maximize the hairiness reduction. Axial angle of 45° for air inlets, 2.2 mm yarn channel diameter, 1.4 denier fibre, and 0.9 bar (gauge) air pressure are the combinations to get maximum reduction in S3 hairiness values of nozzle wound yarns. Fibre denier is a major influencing factor in reducing yarn hairiness.     

Studies on cotton–acrylic bulked yarns and fabrics. Part I: Yarn characteristics

The effect of variables, namely yarn fineness, shrinkable acrylic proportion and twist level, on various properties of cotton–acrylic blended bulked yarns has been studied by relaxing shrinkable component of the yarns using boiling water treatment. A three-variable factorial design technique proposed by Box and Behnken was used to investigate the combined interaction effect of the above variables on the properties of these yarns. The design variables were optimized for all the yarn properties by using the response surface equations. The shrinkage percentage of yarn was found to be higher in the case of coarser yarn, yarn with higher proportion of acrylic fibre and higher twist level. During bulking treatment as the yarns shrink, the effective number of twist per unit length also increases significantly. It is observed that the specific volume of the yarn increases with an increase in the acrylic proportion and decreases with an increase in the twist factor. The breaking extension increases significantly after bulking with a slight increase in tenacity. The flexural rigidity and initial modulus of yarn considerably decrease on bulking. The vertical wicking heights for all the bulked yarns were found to be higher than comparable 100% cotton yarn.     

An analysis of the bending rigidity of warp-knitted fabrics: a comparison of experimental results to a mechanical model

This study focuses on the bending rigidity of warp-knitted fabrics as a function of knit structure (underlaps length), density (wale and course spacing) and yarn bending properties. Seven standard warp-knitted fabrics are produced with three different densities (Tricot, Locknit, three and four needles Satin, Reveres Locknit, three and four needles Sharkskin). The bending rigidity of the fabrics is measured using a Kawabata evaluation system and an automatic cyclic bending tester. Results show that the bending rigidity increases for the fabrics with a higher density and underlaps length of the front and back guide bars. In addition, a new mechanical model for the bending behaviour of warp-knitted fabrics using an energy method is presented. In this model, the knitted loop structure is assumed to consist of a series of straight and skew yarns simulating legs and underlaps while considering a rigid region lying in the direction of bending. Experimental results show that there is a reasonable agreement between the calculated and measured values for both wale and course directions.     

Role of filament cross-section in properties of PET multifilament yarn and fabric. Part II: effect of fibre cross-sectional shapes on fabric hand

To investigate the effect of fibre cross-sectional shape on hand of polyethylene terephthalate continuous multifilament fabrics, different fabric samples are developed with similar fabric areal density, weave, yarn and fibre linear density. The effect of fibre cross-sectional shape on various structure–property relationship of fabric is precisely characterized. Different cross-sectional shapes have different stiffness as well as different packing index with ideal geometry of filament yarns. The low-stress mechanical properties and hand behaviour of fabric are also altered by change in cross-sectional shape of filaments. The experimental results indicate that the alteration in cross-sectional shape can be a powerful tool for fabric engineering.     

27—THE NORMAL FORCE BETWEEN TWISTED FILAMENTS: PART II: EXPERIMENTAL VERIFICATION

In a previous paper, the importance of lateral pressure in the tension and bending behaviour of yarns was discussed; a theoretical model, which included the effects of bending and torsional rigidities as well as the tensile, shear, and frictional forces, was proposed, and expressions for the lateral pressures were derived. In this sequel, the experimental verification of the previously derived expressions has been carried out on a very simple twisted structure, consisting of two rubber strands. The results obtained support the theoretical predictions of the lateral pressure for the experimental model and lead to the conclusion that, for filaments with significant torsional and bending rigidities, lateral pressures are obtained in the yarn even when there is no significant tension on the individual filaments. An approximate scheme for estimating the lateral pressures in an idealized, close-packed, multilayered continuous-filament yarn is proposed as an extension of the above results.     

Effect of Yarn Type and Twist Factor on Air Permeability,Absorbency, and Hand Properties of Open-end and Ring-spun Yarn Fabrics

The paper investigates the effects of yarn type, i.e. open-end yarn (OE) and ring-spun yarn (RS) and the twist factors of the warp (W) and filling (F) of the OE yarns on the permeability to air and moisture and the hand properties of various test fabrics woven from both OE and RS yarns. A comparison is made of the effect of yarn types and various twist levels of warp and filling of the OE yarns on the air permeability, absorbency, coefficient of friction and flexural rigidity of fabrics woven from such yarns.

It is intended that future studies will explore a wider range of twist levels and different yarn types than those investigated on this initial exercise.     

Effect of elastane draft on the rheological modelling of elastane core spun yarn

The main purpose of modelling the yarn structure is to find relations that are more reliable giving the behaviour of the yarn starting from its components. In this paper, the identification of the mechanical behaviour of the elastic core spun yarns by a rheological modelling on the basis of pre-existent phenomenological models is presented. In this model, the elastic core spun yarn is considered as a viscoelastic material. The model is verified experimentally with two types of elastic core spun yarns 50/78 and 59/156 and a range of draft of five values for two types of yarn and two values of elastane count in dtex (78 and 156). Comparative analysis of the theoretical and experimental tensile curves indicates a high level of correlation between both data-sets. The effect of the elastane draw ratios on the parameters of this model is established in the second part of this paper. Our test results revealed that the elastane draft is one of the important factors influencing the elasticity and the viscosity of elastic core spun yarns.     

26—THE ELASTIC RESISTANCE TO BENDING OF PLAIN-WOVEN FABRICS

The elastic resistance to bending of woven fabrics has previously been considered in terms of the existence in the yarns of rigid and elastic sections. The difficulties inherent in such a model and the noticeable differences between the predicted and experimental findings are examined in this paper. Two models of a plain-woven fabric in which the yarn cross-sections are incompressible are then analysed theoretically to obtain the predicted relationship between the applied couple and the curvature of the fabric.

In the first model, the yarns are considered to be unset, i.e., if released from the fabric, they would be uncrimped, and in the second model they are considered to be completely set, i.e., if released from the fabric, they would retain all their crimp. The predicted bending resistance does not agree with the behaviour of actual fabrics owing to the difficulty of defining the ‘radius’ of the yarn in the fabric, but many puzzling qualitative aspects of the bending behaviour of woven fabrics are, as a result of the analysis given, satisfactorily explained.     

39—AN ENERGY ANALYSIS OF WOVEN-FABRIC MECHANICS BY MEANS OF OPTIMAL-CONTROL THEORY PART I: TENSILE PROPERTIES

The general energy analysis of fabric mechanics by means of optimal control presented in a previous publication is applied to the woven-fabric structure for deformations whereby the yarns remain in the same plane. The three-dimensional equations of the general theory are reduced to two-dimensional form, the boundary conditions are evaluated for the plain-weave fabric in biaxial tension, and an important mechanism of woven-fabric extension, which was not included in the general analysis, namely, the possibility of yarn extension, is introduced into the theory. The fabric load–extension curves and yarn-decrimping curves for the plain-weave construction are computed for a realistic range of input parameters: the yarn extension rigidity, weave crimp, degree of set, lateral yarn compression, and ratio of the curvilinear length of yarn in the warp direction to that in the weft direction of the fabric. The computed results are discussed in terms of the following dimensionless parameters: the applied tension per thread and the interaction force on the crossing thread (divided by the yarn bending rigidity), the relative fabric extension (the fabric extension divided by the yarn crimp), the initial relative fabric tensile rigidity, the Poisson's ratio of the fabric, and the initial tensile rigidity of the crimped yarn unravelled from the fabric. The tensile properties of plain-weave fabrics in both the grey state and the finished state are illustrated by reference to the computed results, which are also employed to explain the behaviour of yarns during the extension of woven fabrics.     

Torsional properties of staple fibre plied yarns

A mathematical analysis of the mechanical governing equations applying to the torsional behaviour of multi-ply yarns under tension has been carried out. This analysis clearly shows that there are two components, a geometric component that determines the slope or gradient of the torque due to tension and a component that determines the yarn torque at zero applied tension (intrinsic torque) that depends on the fibre number, fibre moduli and diameter as well as the strand structural geometry. The effect of the ratio of the ply twist to the spinning twist on the two components of yarn torque has been numerically analysed for two-, three- and four-ply yarns prepared from singles 31 yarns spun with different spinning twists and for two different fibre diameters. Other comparisons are made for two-ply yarns prepared from 40 and 80 tex singles yarn. The model allows the effects of the various yarn and fibre parameters to be assessed and compared with experimental data. Experimental torque data for a range of two-ply yarns plied at different percentages of the singles spinning twist and also with different yarn histories and test environments are consistent with the trends identified by the model.     

Influence of fibre strength and yarn structural characteristics on tensile failure of blended spun yarns: a prediction model

The study reports on the static failure behaviour of P/V blended ring, rotor and air-jet spun yarns explained on the basis of fibre failure coefficient. Fibre failure coefficient is an index introduced to represent fibre break and slip in combination occurring during tensile failure. Fibre break/slip during tensile failure is found dependent on fibre strength, fibre cohesiveness and internal structural developments in yarns. Tensile failure behaviour of ring, rotor and air-jet yarns found to be different owing to their difference in fibre consolidation mechanism. The contribution of individual components towards fibre failure coefficient varies with the spinning technology. An attempt has been made to develop mathematical models to explain the spun yarn failure behaviour under static condition. The developed mathematical models have incorporated the fibre property (fibre strength) and few structural characteristics of yarns which are strategically selected to justify the essence of models to enhance the prediction capability. Individual models are developed for ring, rotor and air-jet yarns owing to their structural changes caused by their inherent fibre consolidation mechanism. The developed mathematical models are free from assumptions and based on pure applied mathematics and have very high potential for prediction of spun yarn failure behaviour.