Behavior Of Yarns Research Articles

Comments on "Tensile Fatigue Behavior of Staple Yarns"

Comments on "Tensile Fatigue Behavior of Staple Yarns"

Development of a Constitutive Theory for Short Fiber Yams

This article deals with the effects of fiber orientation and bending deformation on staple yarn behavior. First, the effect of fiber orientation is shown by comparing yarn properties determined using three different fiber orientation cases. Then, for a given fiber orientation distribution, radial distributions of both tensile stress and lateral pressure along the yarn cross section are predicted. The fiber obliquity effect at high yarn twist levels is attributed more to fiber bending deformation. Finally a modified yarn model is proposed that produces predictions in close agreement with existing experimental results.

Development of a Constitutive Theory for Short Fiber Yarns Part II: Mechanics of Staple Yarn With Slippage Effect

A general constitutive theory governing the mechanical behavior of staple yarns and including the effect of fiber slippage during yarn extension is presented in this paper. A differential equation describing the stress transfer mechanism as well as the slippage influence in a staple yarn is applied by which both the distributions of fiber tension and lateral pressure along a fiber length are derived. A so-called fiber slippage ratio λ is defined in terms of fiber and yarn properties to specify the length along both ends of a fiber that is slipping during yarn extension. Factors such as fiber dimensions and properties, the effect of the discontinuity of fiber length within the structure, and fiber orientations in the yarn are all included in the theory. The slippage effect is incorporated into the results obtained in Part I of this study, so that the tensile and shear moduli as well as Poisson's ratios of the yarn with slippage effect are theoretically determined. Comparisons of these properties in both cases with and without the slippage mechanism are provided in this paper.

Flexible thermomechanical analysis of polymeric fibers

A new microcomputer-controlled instrument has been developed for making measurements of thermomechanical behavior of polymeric fibers and yarns under conditions relevant to high-speed industrial fiber processing. The instrument can apply extension and/or twist, and rapid heating or cooling in the temperature range 20–300 °C, while tension and torque are measured. Particular novel features are: a temperature control device providing heating or cooling at rates up to 103 K/s; a new form of high-sensitivity torque transducer with resolution of 10−9 Nm; and computer integration of extension, twist, and temperature. The instrument provides an unprecedented degree of flexibility in the design of thermomechanical tests. It is suitable not only as a versatile research tool for material property measurements relevant to processes such as spinning, heat setting, and thermobonding of fibers, but also as a convenient tester for use in quality control on fibers and yarns.

Tensile Fatigue Behavior of Staple Yarns

The failure of warp yarns on a loom is often caused by repeated cyclical elongation at small stresses well below the breaking point applied under static load. The phenom enon, commonly known as fatigue, is caused by the gradually diminishing resistance of the material, attributable to cumulative damage. Generally, there is no prior indi cation of impending failure due to fatigue. In this work, we have studied the fatigue behavior of warp yarn under cyclical elongation accompanied by abrasion action as measured on a Sulzer-Ruti Webtester on the basis of three criteria—failure, damage rate, and visual appearance. Fatigue behavior expressed in terms of cycles at failure exhibits a wide scatter, displaying a pattern that deviates from normal distribution. A three-parameter Weibull distribution fitted to experimental results consistently displays a unimodal pattern. The rate of fatigue damage expressed in terms of loss in tensile property indicators has proven useful in assessing the fatigue-sustaining capacity of yarn and thereby predicting impending failure. SEM photographs display the abrasion fatigue damage inflicted on the fine structure of yarns and fibers. We have systematically studied, the effect of fatigue parameters that characterize the intensity of fatigue action, such as base tension, speed of fatiguing, abrasion pin position, and strain amplitude. Increasing intensity of fatigue action results in rapid yarn deterioration. Base tension and abrasion pin deflection have profound effects on fatigue. Fatiguing speed and strain amplitude tend to accelerate yarn deterioration, though the experimental results show a slower rate but greater variability. Representing fatigue data based on failure criterion in terms only of characteristic lifetime, which is one of the three parameters of the Weibull distribution, is not enough. A representation in terms of complete distribution yields more useful information about the extent of dispersion and the extreme value in the experimental results.

Compressional Behaviour of Double-rove Yarns

Little information is available in the literature about double-rove spun yarn's low-stress mechanical properties. An experimental investigation has been made in a short-staple spinning system to study the effect of strand spacing, twist, and spindle speed on a double-rove yarn's compressive resilience, and compressibility at low-stress levels. The response-surface equations developed from the experimental results, have been used to explain the compressional behaviour of the yarn studied.

Effect of geometric characteristics of a specimen on the mechanical properties of polyaramide fibres

-- The features of the deformation behavior of complex yarns from polyaramide fibres with different geometrical characteristics have been examined.

Effect of yarn geometry and fiber properties on tensile behavior of cotton yarns swollen and stretched in aqueous zinc chloride

AbstractSingle‐ and two‐ply yarns of different counts were swollen slack under optimum conditions in aqueous zinc chloride and stretched back to original length. While two‐ply yarns showed an improvement in tenacity that was less pronounced in finer counts, single yarns always showed a fall in tenacity. Various properties of the treated yarns like packing fraction, fiber and yarn orientation, cross‐sectional morphology, etc. were evaluated to ascertain the likely factors responsible for the differential behavior of the chemically treated single‐ and two‐ply yarns.

The Bending Behaviour of Plain-woven Fabrics Part I: A Critical Review

The mechanics of the bending of yarns and woven fabrics have received considerable attention in the literature. Efforts have been made to obtain analytical relations between yarn-bending behaviour and constituent-fibre properties. In the case of fabrics, the objectives have been to obtain analytical relations between fabric-bending behaviour and constituent-fibre behaviour or yarn behaviour, on the assumption of a given geometrical disposition of fibres or yarns in the fabric. In this paper, a review of these efforts is made. Comparisons of the theoretical models with available experimental observations are discussed.

Studies on the Abrasion-resistance of Weaving Yarns

An investigation is reported in which use was made of a simple test instrument designed to study the behaviour of yarns when they fail under abrasive forces. Yarn abrasion-resistance was found to depend primarily upon ply twist in two-fold yarns, with singles twist having only a small degree of influence. The abrasively weak places in two-fold yarns were found to be those of lower-than average twist, which are the thick places. The mechanism of yarn failure was observed to be a slow, incremental drafting of the yarn in the abraded zone, the rate of drafting increasing as the ply twist was reduced. Some estimate of weavability can be made by a method of interpreting the abrasion-test results that predicts the probability of occurrence of abrasively weak places in the yarn.

The Bending Behaviour of Plain-woven Fabrics Part II: The Case of Linear Thread-bending Behaviour

In the preceding paper, a critical review of the state of knowledge of the bending behaviour of yarns and woven fabrics was reported. In the present one, an elastica-based computational model of plain-woven fabrics in pure bending is developed. The thread moment/curvature relation is considered to be linear. Various contact conditions at the thread-crossover points are also considered. The threads are further considered to be unset, i.e., if released from the fabric, they would be completely uncrimped. The computational scheme developed requires the minimum interference from the user to solve the associated boundary-value problems.

EFFECT OF THE PHYSICAL PROPERTIES OF THE ORIGINAL YARN ON THE TENSION GENERATED IN A TWISTED YARN RUNNING ON A HEATER

The tension of running yarn during twist setting with a heating plate was studied in terms of the original yarn's physical properties.The results obtained are as follows:(1) The heat shrinkage of the original yarn caused by heating in the static state is influenced by the thermal hysteresis during spinning process, and this phenomenon depends on the characteristics of the original yarn. However, in the case of the hard twist yarn, the shrinkage did not occur, because the effects of twisting torque and elasticity caused by its spiral shape are large.(2) When the circumferential velocity of a feed roller equals a delivery roller's velocity, the tension during heat-setting can be estimated by the distance of the rollers, heater length and stress-strain behaviour of twist-setted yarn.(3) When the yarn tension during re-heating is too large, the twisting torque does not appear, because molecular chains begin to flow. Accordingly in order to obtain the high-quality crepe fabric, it is necessary to determine the scouring condition considering the twist-set temperature and the thermal hysteresis of the original yarn.

Damage to Continuous-filament Yarns during Weaving

A study of continuous-filament yarns and the damage caused to them during weaving is reported. In spite of experiencing greater stress and strain during weaving filaments used as warp show lower strength losses then similar filaments used as weft. This unexpected behaviour of continuous-filament yarn is explained on the basis of the different kinds of stress imposed separately on the warp and weft during weaving and of the structural sensitivity of the continuous-filament yarn to these forces. Several techniques were employed to examine and suitably explain the weakening brought about by mechanical stresses during weaving.

THE EFFECT OF HEAT TRANSFER OF YARN PACKAGE DURING HEAT SET ON PROPERTIES OF HARD-TWIST YARN

As a factor affecting the hard-twist yarn's physical properties during heat set, the heat transfer of a yarn package was studied with a simple model.The simple model used regards the yarn package as the complex of yarn and air without radiation and convection, and implies the effect of barrel to the heat transfer coefficient of inner side.The results obtained are as follows:(1) Heat transfer of the yarn package in dry air is able to analyze with the simple model. On the other hand, heat transfer in humid air is difficult to analyze only with the simple model because of humid air's diffusion in the yarn package. But, this method is useful to predict the behavior of yarn that forms the yarn package.(2) Irregularity of hard-twist yarn's physical properties that appears during heat set is caused by obstruction of shrinking by barrel, difference in temperature rise and irregularity of relaxation of winding tension.

24—A STUDY OF THE STRENGTH OF WRAPPED YARNS PART I: THE THEORETICAL MODEL

The tensile behaviour of wrap-spun yarns is influenced by their structure and by the properties of both the parallel-fibre core and the filament binder yarn. A general model of wrap-spun yarns is proposed, which, with appropriate assumptions, can be used to predict the relationship between yarn strength and structural parameters.

Effect of drawing temperature on the behavior of polyester yarns in subsequent heat-treatment

An effect of drawing temperature on the change in structural-mechanical properties of 111 tex polyester yarns during subsequent heat-treatment has been demonstrated.

Fatigue behaviour of synthetic fibres, yarns, and ropes

S-N fatigue and creep-rupture data have been obtained for nylon 6,6 single fibres, interlaced yarns, and small ropes under a variety of loading conditions. The results show a similar degradation rate at each level of structure, with no apparent influence of inter-fibre effects. Cyclic lifetimes of single fibres of nylon 6,6 as well as polyester and aramid can be predicted from a creep rupture model. Consistent with this model, the time to failure is insensitive to frequency over a broad range. For each level of structure the strain at failure is the same whether tested in simple tension or under cyclic or creep loading. Failure modes were generally similar in creep rupture and cyclic fatigue tests; no effect of a slack load on each cycle was evident either in the failure mode or specimen lifetime.

2—THE MECHANICS OF STAPLE-FIBRE YARNS PART I: MODELLING ASSUMPTIONS

The development of a model for the long-gauge behaviour of staple-fibre yarns based on earlier work by Hearle incorporating fibre migration and slippage, is reported. The tensile strength of the model stems from frictional forces, which are calculated by using Grosberg's theory of fibre-withdrawal force from a sliver. A special method is derived to define the geometry of the path of a migrating fibre in such a yarn to enable the model to be extended to yarns of variable density.

The Low-Stress Mechanical Properties of Wool and Wool-Blend Woven Fabrics

The uniaxial-tensile and bending properties have been examined for a series of wool and wool/polyester woven apparel outerwear fabrics. The fabrics tested include a wide range of laboratory-produced woven materials (varying systematically in weave structure and the ratio of the two yarn curvilinear lengths) and also a range of commercially-produced woven fabrics. The fabric load-extension curves and yarn- decrimping curves are analyzed and discussed in terms of the following dimensionless parameters: the normalized tension per thread (the applied tension divided by the yarn-bending rigidity and multiplied by the square of curvilinear length in the extended direction); the relative yarn or fabric extension (the yarn or fabric extension divided by the yarn crimp); the initial fabric tensile modulus (i.e., initial slope of the normalized tension vs. relative extension curves); the yarn-decrimping modulus; the relative energy of stretching (i.e., area under the normalized load-extension curve); and the energy loss due to hysteresis (i.e., area of the hysteresis loop of the normalized load-extension curve during tensile-recovery measurements). Inelastic and elastic parameters are described for the fabric-bending hysteresis curves. Fabric tensile and bending properties are shown to depend largely on the yarn linear density, the crimp value of yarns, under deformation, and the ratio of the two yarn curvilinear lengths in the structural repeat unit of the fabric. It is shown that there are considerable constraints imposed on the yarn curvature within the fabric, resulting in increased resistance to fabric stretching and bending compared to the results measured on yarns removed from the fabric. A study is made of the effect of yarn extensibility on the decrimping behavior of yarns unravelled from fabric. The effect of weave construction is prominent on the tensile behavior of fabric; its effect on the decrimping behavior of yarn and bending properties of fabrics is only marginal. The effect of blend composi tion on these mechanical properties has been examined for a series of wool/polyester woven fabrics produced from yarns of the same linear density and was found not to be significant.

The Behavior of Twistless and Low-Twist Staple Yarns in a Plain-Weave Fabric

Bonded untwisted staple yam has been used experimentally in the production of fabrics. The present study, an extension of previous work, has shown that the tensile strength of fabric made from twistless filling was low. The addition of twist to the filling increases the strength of both the yarn and fabric. Waxed yarns provided the strongest fabrics and caused the tear strength in the warp direction to be markedly improved. Fabric made from bonded yams were less permeable than those made from ring filing.