Yarn Cross-section Research Articles

Geometric and algebraic algorithms for modelling yarn in woven fabrics

This paper presents geometric and algebraic algorithms and relevant optimizing operators for 3D computer modelling of yarns in fabric. New algorithms and approaches are successfully employed to create more realistic and flexible geometry models with consideration of the differential and topological structure of yarns. By using asymptotic iterative approximation, we have developed a new algorithm for creating B-spline curves using periodic interpolation, where the actual curve shape passes through the control points of B-spline. The generator for irregular cross-sections of yarn in complex fabric structures is created with variability in both shape and size along the yarn path represented by combined spline curves, which allows the complicated shapes of yarn cross-sections in fabrics as the yarns are flattened by the compression at the crossovers. An algorithm of differential geometry is employed to track the vector of tangent orientation of the yarn path in 3D space to get the normal plane of yarn for creating the correct cross-section of yarn. The method described is demonstrated by the visualization of woven fabrics. The approach established can then be further generalized for more different and complicated fabrics (including braided fabrics and knitted fabrics) and 3D fabric.

Fiber Recognition of PET/Rayon Composite Yarn Cross-sections Using Voting Techniques

In this paper, we propose a new image processing method to recognize the fiber patterns in the image of PET/Rayon composite yarn cross-section. Our method consists of two voting techniques: the connected component voting (for obtaining single fiber locations) and the circle parameter voting (circle detection, for recognizing the fiber patterns). When compared with the previous approach, the new method needs fewer parameters and is more flexible. Several real images are used to show the performance of the proposed method.

Determining the Cross-Sectional Packing Density of Rotor Spun Yarns

Packing density, the fiber distribution in a yarn cross section, can to a great extent influence the properties and quality of the yarn. Thus, the need for precise and concise information about packing density becomes a must for an in-depth understanding of yarn structure and hence yarn mechanics. This paper describes a detailed method for determining packing density. We begin by acquiring yarn cross-sectional images to provide input data for calculating yarn cross-sectional packing density. These data include the coordinates of each fiber center and fiber radius. A program whose general writing algorithm is also elaborated in detail is compiled to calculate the packing ratio zone by zone. With these discrete packing ratios, a curve-fitting technique yields a continuous packing density function. In addition, a study of the relationship between packing density and yarn parameters such as yarn count and twist factor is included.

Measurement of eccentricity and twist in spun and plied yarns

The shape of yarn cross-sections can best be approximated as ellipses. This approximation requires the estimation of the major and minor axes and the orientation of the major axes. The diameters of several yarns were measured both circumferentially as well as along the length of the yarn, and the eccentricity was found to be normally distributed. In addition, the direction of the major axes rotated periodically with the twist of the yarn. This allows one to estimate the twist of the yarn indirectly from optical diameter measurements.

3D Modeling of Plain Weft Knitted Structures of Compressible Yarn

In this paper two methods for 3Dimensional modeling of the plain weft knitted structures are presented. The aim is models to be more realistic concerning yarn cross section properties. The first model is based on the assumption that yarn cross section changes to ellipse-like form in the areas with high curvature. The second one is a discrete particle model of the loops, which takes into account the local changes of the yarn following from the contact forces. It calculates actual yarn geometry on the contact places iteratively, as general nonlinear compression behavior of the yarn is assumed.

Structure and Elasticity of Fine Elastomeric Yarns

In this study, spandexes of three degrees of fineness are used as the core material with cotton fibers as the sheath to spin fine elastomeric yarns. We observe the cross sections of the core yarns and the migration of the spandex inside the core yarn concluding that producing a finer elastomeric yarn with a uniform structure is feasible. The results show that choosing the optimum spinning conditions gives a better cover effect to fine elastomeric yarn. In terms of elasticity, a 10 tex elastomeric yarn produced with a 2.2 tex/2f spandex core at a draw ratio of 4.0 and with a twist factor of 40 exhibits the best dynamic elastic recovery percentage.

Prediction of the uniaxial tensile curve of 4-step 3-dimensional braided preform

Prediction of the uniaxial tensile curve and tensile strength of 3-dimensioanl braided preforms is the first step in predicting the uniaxial tensile strength of 3-dimensional braided composite. This paper presents an analytical model to predict the uniaxial tensile strength and uniaxial tensile curve within the whole tensile strain range. First, the equations of spatial configuration of trace yarn in each yarn group were obtained from the coordinates of center point of the trace yarn cross-section in preform and the microstructure of 3-dimensional braided preform was described in mathematical way. Based on the mathematical description of trace yarn and microstructure of preforms, the uniaxial tensile strain relations between 3-dimensional braided preform and braiding yarn at small and large strain were established. Then, from the energy conservation law that the sum of strain energy of all braiding yarns equals to the work of external force applied to the preform, the uniaxial tensile load at every uniaxial tensile strain points of braiding yarn can be calculated and then the whole uniaxial tensile curve of 3-dimensional braided preform can be obtained (also for uniaxial tensile strength). The maximum strain failure criterion is used in calculations. From experimental verification, the method proposed in this paper predicting the uniaxial tensile load and tensile strain simultaneously from the uniaxial tensile curve of braiding yarn is valid and simple in application.

Multi-chain digital element analysis in textile mechanics

The concept of multi-chain digital element analysis is established. This new approach is a general numerical tool for textile mechanics. It can be used for textile process design and for fabric deformation, strength and failure analyses. In multi-chain digital analysis, fabric is considered as an assembly of yarns; furthermore, a yarn is considered as an assembly of fibers. Each fiber is modeled as a frictionless pin-connected rod element chain, defined as “digital chain”. Once the length of these rod elements approaches zero, the digital chain becomes a fully flexible one-dimensional entity with a circular cross section. It imitates the physicality of the fiber. Since a yarn is composed of many fibers, it is modeled as an assembly of digital chains. Contact between digital chains is modeled by contact elements. A procedure, similar to finite element analysis, is adopted. Displacement of fiber inside a fabric is derived based upon the global stiffness matrix and the boundary conditions. As a result, both detailed yarn paths and cross-section shape can be traced during the textile forming process or fabric deformation. In order to describe the new concept, two numerical examples are presented. The multi-chain digital element approach is used for the simulation of the two-dimensional weaving and three-dimensional braiding processes. One can observe, section-by-section, the yarn cross-section shape inside the woven and braided fabric.

Microstructure Analysis of 4-Step Three-Dimensional Braided Composite

The yarn architecture of 3-D braided composites products by the four-step 1 × 1 braiding technique has been studied by means of a control volume method in conjunction with experimental investigation and a numerical method, respectively. An ellipse assumption for the cross-section of yarn was proposed in this analysis method with considering the yarn size and yarn-packing factor. Two types of local unit cell structures were identified for 4-step braided composites by considering the nature of the braiding processes and by observing the sample cross-sections. The relations hip between the braiding procedure and the properties for 3-D braided structural shapes was established. This method provides the basis for analyzing stiffness and strength of 3-D braided composites.

Geometrical modelling and control of a triaxial braiding machine for producing 3D preforms

Abstract Braiding is a relatively less explored textile process for producing composite preforms. Biaxial braids can be produced as hoses and subsequently be draped over different three-dimensional surfaces. However, triaxial braids are relatively stable structures and should be produced to the desired shape during the braiding process. This is achieved by over-braiding on mandrels that either form part of the finished composite or removed before the moulding process. Triaxial braided composites have superior mechanical properties due to fibre orientations along three directions. Geometry of a braided structure depends on the number of yarn carriers, rotational speed of the carriers, take-up speed and the effective perimeter of the cross-section of a mandrel. In the present work, a VRML based geometrical visualisation tool has been developed to simulate a braid structure on any predefined mandrel geometry, and using a predefined yarn cross-section. Braid angles, cover factors and yarn volume fractions can be computed from these simulations. A triaxial braiding machine has been developed with an independent servo control of the carrier movement and the take-up mechanism; geometrical simulation is used as an input to the control system to continuously vary the braid structure along the length of a mandrel. Flexible tooling is important for rapid product development. A flexible mandrel has been developed that can be mechanically adjusted to change the cross-section and the taper. This system enables rapid development of braided preforms.

Realistic rendering and animation of knitwear

We present a framework for knitwear modeling and rendering that accounts for characteristics that are particular to knitted fabrics. We first describe a model for animation that considers knitwear features and their effects on knitwear shape and interaction. With the computed free-form knitwear configurations, we present an efficient procedure for realistic synthesis based on the observation that a single cross section of yarn can serve as the basic primitive for modeling entire articles of knitwear. This primitive, called the lumislice, describes radiance from a yarn cross section that accounts for fine-level interactions among yarn fibers. By representing yarn as a sequence of identical but rotated cross sections, the lumislice can effectively propagate local microstructure over arbitrary stitch patterns and knitwear shapes. The lumislice accommodates varying levels of detail, allows for soft shadow generation, and capitalizes on hardware-assisted transparency blending. These modeling and rendering techniques together form a complete approach for generating realistic knitwear.

Analysis of Blend Irregularities and Fiber Migration Index of Wool/Acrylic Blended Worsted Yarns by Using an Image-analysis Technique

Fiber-blending irregularities and fiber distribution in blended-yarn cross-sections are particularly important in determining the mechanical, functional, and aesthetic properties of textile products. In the work reported in this paper, wool/acrylic blended worsted yams with a linear density of 32 tex (31 Nm), twist level of 414 tpm and with different blend ratios (75/25, 50/50 and 25/75) were produced. The digital images of yarn cross-sections with pre-dyed fibers were prepared using an optical microscope and a digital image capturing system. By applying a mathematical technique on bitmap data, the Index of Blend Irregularities, sizes of fiber clusters and preferential fiber migration were measured. The experimental results indicated a good correlation between the proposed image processing technique and that of the visual method. The index of blend irregularities and sizes of fiber clusters for wool/acrylic blended yarns were shown to range from 1.97 to 2.2 and from 3.87 to 4.88, respectively. In addition, the acrylic fibers in blended yarns were preferentially positioned in outer layers of the yarn cross-section.

Failure Mechanism in Staple Yarns

The failure mechanism in staple yarns is strongly influenced by yarn structure. Manufacturing methods impose certain constraints on the disposition and distribution of fibers in the yarn cross section. This paper investigates the failure mechanism in ring, rotor, air-jet, and vortex yarns. The yarns are subjected to uniaxial loading on a tensile tester, and images of the yarns before and after breaking are recorded. Image analysis of the failure regions yields some interesting features and reveals typical mechanisms occurring in different yarn structures. The failure mechanism in each yarn type is discussed in terms of some basic parameters characteristic of the structure.

A finite element model of mechanical properties of plain weave

The arrangement, properties and structure of the fibers within the yarn and the yarns within the fabric, generate a complex mechanism of deformation. Therefore the present work intends to develop a theoretical model of the mechanical behavior of the plain weave. The modeling of textile structures by the finite element method is a new approach based on the combination of geometric and mechanical models. The finite element method permits a construction and representation of fabrics by taking into consideration the yarn undulation, the existence or not of symmetries in the basic cell and the type of contact between warp and weft yarns. These different parameters allow the mesh of weaves to be obtained, the closest to the reality, without any restriction and any simplifying assumption. In every model defined by its partial derivative equation of the fabric mechanical behavior, and whatever the method of homogenization employed to obtain a homogeneous model, we will be brought to solve a cellular problem. The three-dimensional structure of the basic cell of the various fabrics is very complex. Therefore, the mathematical study starts by meshing the different fabrics, which will enable us to take the geometry as well as the mechanical characteristics of the yarn into account, as well as the stresses applied. The application of this method first requires a mathematical formulation of the problem and then a mesh of the basic cell. The next step is the simulation of shearing and tensile tests. The analysis of the results has proved to be very hard and, thus, has demanded a study of the stress field in the basic cell. From the analysis of the plain weave behavior under those different tests we can assess that the yarn cross-section is one of the crucial factors that influences the mechanical behavior of fabrics, and the phenomenon of stress concentration appears to be located at the level of contact surfaces between warp and weft yarns. For all models that deal with the mechanical behavior of textile structures and regardless of the method of homogenization, the problem has to be solved at the basic cell level before moving on to the global model. The geometry of the textile structures is very complex due to the nonsymmetrical aspect of the majority of weaves. After having defined the geometrical form and completed the meshes of the basic cells of the plain weave, we have carried on the treatment of the problem from the mechanical point of view by the finite element method.

Control of a Batch Dyeing Process with Three Acid Dyes

The process of dyeing of nylon with tertiary acid dye mixtures is controlled by automatic metering of dyes and chemicals. Closed-loop control is achieved by real-time data acquisition of the dyebath conditions coupled with a feedback control strategy. The objective of controlled dyeing is to obtain an on-tone build-up of shade using three monosulfonated acid dyes in mixture combinations. Computerized dosing pumps control the pH, the dyebath concentrations of the individual dyes, and the total sorption of each dye during the process. Photographs of yarn cross sections examined under the polarizing microscope reveal uniform penetration of dye in the individual fibers of the yarns. Color matching of samples dyed under identical dyeing conditions shows good shade reproducibility. It is also possible to re-use a dyebath of residual dyes and chemicals from a previous dyeing. Thus, good shade reproducibility and uniform shade build-up can be achieved in a laboratory dyeing machine by adopting real-time closed-loop control.

Three-Dimensional Analysis of Migration and Staple Yarn Structure

This study describes a visualization and data analysis method for quantitatively analyzing the migration behavior of staple fiber yarns. The fiber migration of ring spun yarns with different levels of twist is measured and analyzed, and the results confirm the usefulness of the proposed method. The analysis shows reproducibility and generates new information on yarn structure. Furthermore, the data analysis processes are also able to be efficiently automated. The major migration frequency of the fibers along the yarn axis is obtained by frequency analysis. At the same time, the distributions of fiber position and orientation angle of the constituent individual fiber segments, according to the radial position of the yarn cross section, are evaluated. Finally, a parameter, the migration factor, to assess the migration effect as a whole is suggested. The experimental results show that migration reaches a saturation point as yarn twist increases.

Effects of Fabric Parameters on Specular Reflection of Single-Jersey Knitted Fabrics

This paper is concerned with the prediction of goniophotometric curves (distribution curves of specularly reflected light) based on our mathematical model developed earlier for single-jersey knitted fabrics made from monofilament yarns. The theory is extended to include fabrics from multifilament yarns. Four physical and optical parameters related to the fabric and the light source are investigated: fiber refractive index, yarn cross section, incident light angle, and fiber ellipticity. Their effects on the goniophotometric curves and luster index of knitted fabrics are determined. In addition, the great difference is high lighted between light reflected from knitted fabrics and light received by the goniopho tometer.

Finite Element Modeling of Plain Weave Composites

Finite element models always include certain simplifications of the problem to be analyzed. Already Chapman and Whitcomb studied the influence of some simplifications on the elastic properties of a woven composite. This paper evaluates the influence of further assumptions on the predicted longitudinal Young's modulus and on the peak stresses. In particular, such assumptions are the refinement of the mesh, the size of pure matrix regions, the longitudinal shape function of the yarn, the constraints, and a linear versus a nonlinear analysis. Also a new approximation for the shape of the yarn's cross section is introduced and compared to the existing yarn architecture.

Fiber Recognition and Distribution Analysis of PET/Rayon Composite Yarn Cross Sections Using Image Processing Techniques

Traditionally, the blending composition of a composite yams has been analyzed by human visual inspection, but such a method is time-consuming and inaccurate. In this study, we apply image processing techniques to analyzing cross sections of a PET/ Rayon composite yam, obtaining single fiber positions in the image with mask pro cessing. Fibers are recognized with four features: area, perimeter, compactness, and shape factor, and fiber distributions of cross sections of composite yarns are analyzed using three predefined index categories: the radial distribution index, the lateral distri bution index, and the angular distribution index.

Image Analysis of Composite Yarn Cross Sections

This work discusses the application of computer image analysis to study cross sections of polyester filament/rayon staple fiber composite yarns. It attempts to quantify the distri bution of dispersed filaments in images of cross sections obtained with a scanning electron microscope and analyzed by computer algorithms. This work also defines parameters such as radial and lateral distribution indices and aggregation and normalized indices for quan tifying the composite yarn cross sections. The results reveal that computer image analysis and manual analysis systems provide nearly identical results.